Update: 27-Dec-2019

Title:
Single Crystal Growth of Relaxor Ferroelectric Ba2PrFeNb4O15 by the Optical Floating Zone Method
Authors:
Wang, BX, Zheng, H, Ren, Y, Krogstad, M, Mitchell, JF, Phelan, D
Source:
CRYST GROWTH DES 19 (12):7249 10.1021/acs.cgd.9b01147 DEC 2019
Abstract:
Uniaxial tungsten bronzes have received increasing interest because of their potential application as lead-free ferroelectrics as well as their flexibility-via chemical substitution. Here we demonstrate growth of single crystals of one such material, Ba2PrFeNb4O15, which possesses the tetragonal tungsten bronze structure, by the optical floating zone method. The challenge of this growth is to control the stability of the molten zone which allows the growth to persist for a long enough time to achieve large volume single crystals. Our work reveals that the use of a slight overpressure of air allows the molten zone to be maintained up to 7 h at a traveling speed of 4 mm/h. The obtained crystals were studied using high-resolution single crystal scattering, powder X-ray diffraction, and dielectric measurements. We find that Ba2PrFeNb4O15 possesses a rather complex average structure with a monoclinic symmetry in a P112/m space group and unit cell parameters of a = 12.49188(8) angstrom, b = 12.49232(8) angstrom, c = 3.92863(1) angstrom, and gamma = 90.056 degrees, with an additional incommensurate superstructural modulation superimposed. The temperature dependence of dielectric properties has been investigated by comparing as-grown, O-2-annealed, and Ar-annealed samples. A broad relaxation dielectric peak is observed around 150 K for the O-2-annealed sample, indicating a typical relaxor behavior below 150 K. A larger dielectric permittivity (epsilon' approximate to 1300) than those of corresponding ceramics (up to epsilon' approximate to 200) is found in the oxygen annealed crystals. We suggest that as-grown single crystals are oxygen deficient and that the oxygen vacancies can be eliminated by an oxygen annealing treatment.
Title:
Influence of weak frustration on quench dynamics of 1D spin-1/2 ANNNI model
Authors:
Cheraghi, H, Tafreshi, MJ, Mahdavifar, S
Source:
J MAGN MAGN MATER 497 10.1016/j.jmmm.2019.166078 MAR 1 2020
Abstract:
In this work we study the dynamical quantum phase transition in the 1D spin-1/2 transverse axial next-nearest-neighbor Ising (ANNNI) model by employing the mean field Jordan-Wigner approach. The NNN interaction breaks the integrability of the ANNNI model. We have focused on the induced dynamical effects of the frustration on quench dynamics of the system. The approach helps us to diagonalize the Hamiltonian in the region where the frustration is weak and the analytical method is reliable. First, the non-analyticity of the rate function is analyzed. It is found that only by quenching across the quantum critical point, regular nonanalyticitic behaviors at periodic instants are seen in the dynamics of the rate function. Here, our results confirm the existence of paramagnetic commensurate and paramagnetic incommensurate phases in the system. Second, the order parameter dynamics as a system's macroscopical property is investigated and the oscillatory behavior is reported. Third, the nonequilibrium dynamics of the quantum correlations as the entanglement and the quantum discord are studied. We have compared the efficiency of the quantum discord with respect to the entanglement in the detection of the occurrence of the dynamical quantum phase transition.
Title:
Quasicrystalline Chern insulators
Authors:
He, AL, Ding, LR, Zhou, Y, Wang, YF, Gong, CD
Source:
PHYS REV B 100 (21) 10.1103/PhysRevB.100.214109 DEC 11 2019
Abstract:
A Chern insulator or a quantum anomalous Hall state is a topological state with integer Hall conductivity but in absence of the Landau level. It had been well established on various two-dimensional lattices with periodic structure. Here, we report similar Chern insulators that can also be realized on a quasicrystal with fivefold rotational symmetry. Providing the staggered flux through plaquettes, we propose two types of quasicrystalline Chern insulators. Their topological characterizations are well identified by the robustness of edge states, nonzero real-space Chern number, and quantized conductance. We further find the failure of integer conductivity but with the quantized Chern number at some special energies. Our study, therefore, provides a new opportunity to searching topological materials in aperiodic systems.

Update: 12-Dec-2019

Title:
Single phase charge ordered stoichiometric CaFe3O5 with commensurate and incommensurate trimeron ordering
Authors:
Cassidy, SJ, Orlandi, F, Manuel, P, Clarke, SJ
Source:
NAT COMMUN 10 10.1038/s41467-019-13450-5 DEC 2 2019
Abstract:
Mixed-valent transition metal compounds display complex structural, electronic and magnetic properties which can often be exquisitely tuned. Here the charge-ordered state of stoichiometric CaFe3O5 is probed using neutron powder diffraction, Monte Carlo simulation and symmetry analysis. Magnetic ordering is dominated by the formation of ferromagnetic Fe3+-Fe2+-Fe3+ trimers which are evident above the magnetic ordering transition. Between T-N= 289 K and 281 K an incommensurate magnetically ordered phase develops due to magnetic frustration, but a spin Jahn-Teller distortion lifts the frustration and enables the magnetic ordering to lock in to a charge-ordered commensurate state at lower temperatures. Stoichiometric CaFe3O5 exhibits single phase behaviour throughout and avoids the phase separation into two distinct crystallographic phases with different magnetic structures and Fe valence distributions reported recently, which likely occurs due to partial Fe2+ for Ca2+ substitution. This underlines the sensitivity of the magnetism and chemistry of these mixed-valent systems to composition.
Title:
Antiferromagnetic order survives in the higher-order quasicrystal approximant
Authors:
Yoshida, S, Suzuki, S, Yamada, T, Fujii, T, Ishikawa, A, Tamura, R
Source:
PHYS REV B 100 (18) 10.1103/PhysRevB.100.180409 NOV 25 2019
Abstract:
We report the observation of antiferromagnetic (AFM) transitions in 1/1 and 2/1 quasicrystal approximants having slightly different electron-per-atom (e/a) ratios, in the same Au-Ga-Eu system, at Ned temperatures of 7.0 and 8.5 K, respectively. This clearly demonstrates that an antiferromagnetic order survives when the degree of approximation to the quasicrystals is raised provided that the e/a ratio is kept nearly the same. Since, unlike the 1/1 approximant, the 2/1 approximant has all the building blocks necessary for the construction of the quasicrystal, this finding can be a significant leap toward the long-sought realization of an AFM quasicrystal.
Title:
Emergent Quasicrystalline Symmetry in Light-Induced Quantum Phase Transitions
Authors:
Mivehvar, F, Ritsch, H, Piazza, F
Source:
PHYS REV LETT 123 (21) 10.1103/PhysRevLett.123.210604 NOV 22 2019
Abstract:
The discovery of quasicrystals with crystallographically forbidden rotational symmetries has changed the notion of the ordering in materials, yet little is known about the dynamical emergence of such exotic forms of order. Here we theoretically study a nonequilibrium cavity-QED setup realizing a zero-temperature quantum phase transition from a homogeneous Bose-Einstein condensate to a quasicrystalline phase via collective superradiant light scattering. Across the superradiant phase transition, collective light scattering creates a dynamical, quasicrystalline optical potential for the atoms. Remarkably, the quasicrystalline potential is " emergent" as its eightfold rotational symmetry is not present in the Hamiltonian of the system, rather appears solely in the low-energy states. For sufficiently strong two-body contact interactions between atoms, a quasicrystalline order is stabilized in the system, while for weakly interacting atoms the condensate is localized in one or few of the deepest minima of the quasicrystalline potential.
Title:
Twisted Graphene Bilayers and Quasicrystals: A Cut and Projection Approach
Authors:
Aragon, JL, Naumis, GG, Gomez-Rodriguez, A
Source:
CRYSTALS 9 (10) 10.3390/cryst9100519 OCT 2019
Abstract:
In this work, a modified version of the cut and projection approach is proposed to describe the structure of graphene bilayers with twist angles. With this method, the rotation between two graphene layers is viewed as a rotation of the projection space and the resulting projected structure is interpreted as the set of points of best fit between the two rotated structures. Additionally, focus is given to the pertinence of the many algebraic and geometric tools used in grain boundaries and in quasicrystals to graphene bilayer system (or any other bilayer system, for that matter) case.
Title:
Multiple Influences of Molybdenum on the Precipitation Process in a Martensitic PH Stainless Steel
Authors:
Thuvander, M, Andersson, M, Stiller, K
Source:
METALS-BASEL 9 (10) 10.3390/met9101118 OCT 2019
Abstract:
Molybdenum has been found to influence the complex precipitation process in a martensitic precipitation hardening stainless steel during aging at 475 degrees C in several different ways. Three steels with different Mo content (0, 1.2 and 2.3 at.%) were investigated. Studies of the microstructure were performed with atom probe tomography and energy filtered transmission electron microscopy. It is shown that, at the initial stage of aging, a faster nucleation of Cu-rich clusters takes place with increasing Mo content. The Cu-clusters act as precipitation sites for other solute elements and promote the nucleation of Ni-rich phases. During further aging, a higher Mo content in the material instead slows down the growth and coarsening of the Ni-rich phases, because Mo segregates to the interface between precipitate and matrix. Additionally, Mo promotes decomposition of the matrix into alpha and alpha' regions. After longer aging times (>40 h) quasicrystalline Mo-rich R' phase forms (to a greater extent in the material having the highest Mo content). The observations serve to understand the hardness evolution during aging.

Update: 5-Dec-2019

Title:
Magnetic structures
Authors:
Rodriguez-Carvajal, J, Villain, J
Source:
CR PHYS 20 (7-8):770 10.1016/j.crhy.2019.07.004 NOV-DEC 2019
Abstract:
While ferromagnetism has been known since many centuries, more complex magnetic structures have only been identified in the twentieth century: ferrimagnetism, antiferromagnetism, helimagnetism, modulated structures... Incommensurable or long-period structures have first been deduced as consequences of phenomenological models, e.g., the Heisenberg Hamiltonian. The more fundamental explanation of Rudermann, Kittel, Kasuya, and Yoshida relies on the general phenomenon of Friedel oscillations. The coexistence of crystallographic order and magnetic order is sometimes antagonistic and results in sequences of transitions that may be continuous or not. The most effective experimental technique to observe magnetic order is neutron diffraction, but the analysis is sometimes very complicated and requires sophisticated numerical methods involving group theory. In the case of incommensurable structures, it may be useful to consider the three-dimensional system as the section of a higher-dimensional crystal. The determination of magnetic structures from neutron scattering data is facilitated by computers and adequate programs. (C) 2019 Academie des sciences. Published by Elsevier Masson SAS.
Title:
Discovery of quasicrystals: The early days
Authors:
Gratias, D, Quiquandon, M
Source:
CR PHYS 20 (7-8):803 10.1016/j.crhy.2019.05.009 NOV-DEC 2019
Abstract:
This paper is a survey of the initial developments of the research on quasicrystals starting from their discovery by Daniel Shechtman (Nobel Prize in Chemistry in 2011) in 1982 at the National Bureau of Standards (now National Institute for Standard and Technology) in Gaithersburg (Maryland, USA) up to the beginning of the early 1990s, a time when the crystallographic methods were well developed and mastered enough to decipher the ultimate atomic structures of quasicrystals. These early works have enlarged our understanding of spatial order in solids through a strong multidisciplinary effort between mathematicians, physicists, chemists and material scientists. (C) 2019 Academie des sciences. Published by Elsevier Masson SAS.

Update: 28-Nov-2019

Title:
Verification of the de Wolff hypothesis concerning the symmetry of beta-MnO2
Authors:
Fabrykiewicz, P, Przenioslo, R, Sosnowska, I, Fauth, F, Oleszak, D
Source:
ACTA CRYSTALLOGR A 75:889 10.1107/S2053273319013408 NOV 2019
Abstract:
The symmetry lowering from tetragonal to orthorhombic is demonstrated using high-resolution diffraction and also justified by using the magnetic superspace groups formalism for the rutile-type compound beta-MnO2. The (lower) orthorhombic symmetry is observed at temperatures both below and above the Neel temperature. The magnetic ordering of beta-MnO2 is of spin density type and not screw-type helical. The results support the de Wolff [Acta Cryst. (1959), 12, 341-345] hypothesis about the orthorhombic symmetry of beta-MnO2.
Title:
C-60 adsorption on a dodecagonal oxide quasicrystal
Authors:
Zollner, EM, Schenk, S, Forster, S, Widdra, W
Source:
PHYS REV B 100 (20) 10.1103/PhysRevB.100.205414 NOV 14 2019
Abstract:
Quasicrystalline surfaces are potential templates for highly ordered but aperiodic molecular self-assemblies. Here, we report on the adsorption of C-60 molecules on a two-dimensional oxide quasicrystal (OQC) and its sigma-phase approximant at room temperature and 150 K. The molecular films have been characterized by means of scanning tunneling microscopy and low-energy electron diffraction. A weak interaction of the molecules with the dodecagonal oxide template is found, resulting in a low desorption temperature of 510 K. For low temperatures specific adsorption sites within the tiling of the OQC and the s-phase approximant have been identified as preferred nucleation sites. The narrow spacing between these sites introduces repulsive interaction between C60 molecules and restricts the epitaxial growth to small patches. At room temperature, C-60 nucleates in hcp islands of almost arbitrary rotational orientation on the OQC. A slight orientational preference for hexagonal islands with a 15 degrees rotation against the OQC tiling is discussed as a consequence of the preferential adsorption on the quadratic tiles.
Title:
A surface-stacking structural model for icosahedral quasicrystals
Authors:
Ajlouni, R
Source:
STRUCT CHEM 30 (6):2279 10.1007/s11224-019-01413-x DEC 2019
Abstract:
An original structural model for the description of icosahedral quasicrystals is proposed. This novel theoretical approach is based on a surface-stacking image of icosahedral quasicrystals and is in concert with the step-terrace morphology observed in many experimental investigations of real icosahedral surfaces. According to this model, the infinite icosahedral structure is constructed by stacking two arrangements of quasi-periodic surfaces along each of the 5-fold axis of the icosahedral symmetry. In this stacking order, the spacings between the layered surfaces are governed by Fibonacci sequence. The proposed model operates within the real physical (Euclidean) space and provides a direct three-dimensional visual representation of the icosahedral superstructure, which can be instrumental for conducting different modes of experimentations, analyses, and fabrication strategies; eliminating a major roadblock for researchers especially outside the fields of crystallography and material science. More importantly, understanding the long-range surface-stacking logic of the icosahedral structure will hopefully provide a deeper understanding of the structure of quasicrystals at an atomic scale and help achieve improved control over material compositions and structure.

Update: 21-Nov-2019

Title:
Antiferromagnetic Semiconductor BaFMn0.5Te with Unique Mn Ordering and Red Photoluminescence
Authors:
Chen, HJ, McClain, R, He, JG, Zhang, C, Olding, JN, dos Reis, R, Bao, JK, Hadar, I, Spanopoulos, I, Malliakas, CD, He, YH, Chung, DY, Kwok, WK, Weiss, EA, Dravid, VP, Wolverton, C, Kanatzidis, MG
Source:
J AM CHEM SOC 141 (43):17421 10.1021/jacs.9b09382 OCT 30 2019
Abstract:
Semiconductors possessing both magnetic and optoelectronic properties are rare and promise applications in opto-spintronics. Here we report the mixed-anion semiconductor BaFMn0.5Te with a band gap of 1.76 eV and a work function of 5.08 eV, harboring both antiferromagnetism (AFM) and strong red photoluminescence (PL). The synthesis of BaFMn0.5Te in quantitative yield was accomplished using the "panoramic synthesis" technique and synchrotron radiation to obtain the full reaction map, from which we determined that the compound forms upon heating at 850 degrees C via an intermediate unknown phase. The structure refinement required the use of a (3+1)-dimensional superspace group Cmme(alpha 01/2)0ss. The material crystallizes into a ZrCuSiAs-like structure with alternating [BaF](+) and [Mn0.5Te](-) layers and has a commensurately modulated structure with the q-vector of 1/6a* + 1/6b* + 1/2c* at room temperature arising from the unique ordering pattern of Mn2+ cations. Long-range AFM order emerges below 90 K, with two-dimensional short-range AFM correlations above the transition temperature. First-principles calculations indicate that BaFMn0.5Te is an indirect band gap semiconductor with the gap opening between Te 5p and Mn 3d orbitals, and the magnetic interactions between nearest-neighbor Mn2+ atoms are antiferromagnetic. Steady-state PL spectra show a broad strong emission centered at similar to 700 nm, which we believe originates from the energy manifolds of the modulated Mn2+ sublattice and its defects. Time-resolved PL measurements reveal an increase in excited-state lifetimes with longer probe wavelengths, from 93 ns (at 650 nm) to 345 ns (at 800 nm), and a delayed growth (6.5 +/- 0.3 ns) in the kinetics at 800 nm with a concomitant decay (4.1 +/- 0.1 ns) at 675 nm. Together, these observations suggest that there are multiple emissive states, with higher energy states populating lower energy states by energy transfer.
Title:
Ferromagnetic Ising chains in frustrated LnODCO(3): the influence of magnetic structure in magnetocaloric frameworks
Authors:
Dixey, RJC, Stenning, GBG, Manuel, P, Orlandi, F, Saines, PJ
Source:
J MATER CHEM C 7 (42):13111 10.1039/c9tc04980k NOV 14 2019
Abstract:
Probing the magnetic interactions in functional magnetic materials can reveal detailed insight into how to optimise the properties they possess while providing key understanding of the exotic phenomena they may host. This study probes the short and long range magnetic order in the LnODCO(3) (where Ln = Tb, Dy, Ho, and Er) framework magnetocalorics using variable-temperature neutron scattering measurements. Reverse Monte Carlo analysis of neutron scattering data shows that TbODCO3, DyODCO3 and HoODCO3 develop short range Ising-like magnetic order between 1.5 and 20 K, consistent with dominant ferromagnetic correlations within chains along the b-axis. Through magnetic susceptibility measurements we identify that long range magnetic order develops in TbODCO3 and HoODCO3 at similar to 1.2 and similar to 0.9 K, respectively. Neutron diffraction measurements were conducted on HoODCO3 revealing incommensurate magnetic order develops between 1.2 and 0.9 K, before a commensurate magnetic phases emerges at 0.8 K with long-range ferromagnetic order in the chains. The results suggest Ising-like ferromagnetic chains associated with frustration are responsible for the improved magnetocaloric properties, of some members in this family, at higher temperatures and low applied fields.

Update: 14-Nov-2019

Title:
New modulated structures of solid bromine at high pressure
Authors:
Li, PF, Du, XD, Gao, GY, Sun, RX, Zhang, LJ, Wang, WH
Source:
COMP MATER SCI 171 10.1016/j.commatsci.2019.109205 JAN 2020
Abstract:
Crystal structures of bromine under pressure have been studied through the advanced structure search method in combination with first-principles calculations. At 10 and 90 GPa, we successfully reproduced the experimentally observed molecular phase I and monatomic body-centred orthorhombic phase II, respectively. At 120 and 200 GPa, the lowest-enthalpy structures predicted are body centered tetragonal and face-centered cubic phase, respectively, which are also consistent with previously theoretical study. Interestingly, in the pressure range of 50-80 GPa, our structural searches predicted four structurally similar and modulated structures, oF20, oC24, oF28 and oC12, whose magnitude of the modulation vectors k are 2/5, 1/6, 2/7 and 1/3, respectively. Enthalpy calculations show that oF20, oC24, oF28 and oC12 are thermaldynamically stable in the pressure range of 52-53, 53-58, 58-65 and 65-79 GPa, respectively. Through comparison of the structural characterization and X-ray diffraction patterns of the predicted oF28, oC12 in bromine and the known incommensurate modulated phase V in iodine, we suggest that bromine might also adopt an incommensurate modulated structure. In addition, the prediction of two new phases (oF20 and oC24) between molecular phase I and incommensurate phases are consistent with Raman scattering and X-ray absorption spectroscopy (XAS) experimental results. For the first time, we presented the structure information between molecular phase I and monatomic phase II in bromine. The calculated elastic stiffness coefficients indicate that the four modulated phases are mechanically stable. The calculated electronic density of states for these four predicted phases show that they are all metallic.
Title:
Helical magnetic ordering in Sr(Co1-xNix)(2)As-2
Authors:
Wilde, JM, Kreyssig, A, Vaknin, D, Sangeetha, NS, Li, B, Tian, W, Orth, PP, Johnston, DC, Ueland, BG, McQueeney, RJ
Source:
PHYS REV B 100 (16) 10.1103/PhysRevB.100.161113 OCT 29 2019
Abstract:
SrCo2As2 is a peculiar itinerant magnetic system that does not order magnetically, but inelastic neutron-scattering experiments observe the same stripe-type antiferromagnetic (AF) fluctuations found in many of the Fe-based superconductors along with evidence of magnetic frustration. Here we present results from neutron diffraction measurements on single crystals of Sr(Co1-xNix)(2)As-2 that show the development of long-range AF order with Ni doping. However, the AF order is not stripe type. Rather, the magnetic structure consists of ferromagnetically aligned (FM) layers (with moments laying in the layer) that are AF arranged along c with an incommensurate propagation vector of (0 0 tau), i.e., a helix. Using high-energy x-ray diffraction, we find no evidence for a temperature-induced structural phase transition that would indicate a collinear AF order. This finding supports a picture of competing FM and AF interactions within the square transition-metal layers due to flat-band magnetic instabilities. However, the composition dependence of the propagation vector suggests that far more subtle Fermi surface and orbital effects control the interlayer magnetic correlations.
Title:
A commensurately modulated crystal structure and the physical properties of a novel polymorph of the caesium manganese phosphate CsMnPO4
Authors:
Bolotina, N, Yakubovich, O, Shvanskaya, L, Dimitrova, O, Volkov, A, Vasiliev, A
Source:
ACTA CRYSTALLOGR B 75:822 10.1107/S2052520619009296 OCT 2019
Abstract:
A novel modification of the CsMnPO4 beta-phase was achieved by hydrothermal synthesis at 553 K. The compound crystallizes in the monoclinic system with the basic unit-cell parameters a = 11.0699 (4), b = 11.0819 (6), c = 9.1106 (3) angstrom, gamma = 119.480 (5)degrees; the modulation vectors are q1 = 0.4a* and q2 = 0.4b*. The structure was determined based on single-crystal X-ray diffraction data obtained from a pseudo-merohedral twin using a superspace approach in the (3 + 2)D symmetry group P11a(a1,b1,0)0(a2,b2,0)0 and refined to R = 0.083 for 10 266 reflections with I > 3 sigma (I). It is considered as a low-temperature polymorph of CsMnPO4 with the same UUUDDD-type layer topology built by MnO4 and PO4 tetrahedra, and stacked in a framework in the same manner as beta-tridymite. Large open channels parallel to the [110] and [001] directions incorporate Cs atoms. All Cs atoms are distributed along the a(super) = 55.35 (1) and b(super) = 55.41 (1) axes of the large unit cell with pseudo periods of a(super)/5 and b(super)/5 which are broken mainly by the positions of oxygen atoms (orientation of Mn- and P-centered tetrahedra). The beta-phase is discussed as a member of the morphotropic series of manganese phosphates with large cations of AMnPO(4), where A = Cs, Rb, K and Ag. The title compound is an antiferromagnet with the Neel temperature T-N = 4.5K.

Update: 31-Oct-2019

Title:
Analysis of elastic-plastic fracture in two-dimensional decagonal quasicrystals using the displacement discontinuity method
Authors:
Dang, HY; Zhao, MH; Ren, JL; Fan, CY Author Full Names: Dang, HuaYang; Zhao, MingHao; Ren, JingLi; Fan, CuiYing
Source:
ENGINEERING ANALYSIS WITH BOUNDARY ELEMENTS, 108 366-371; 10.1016/j.enganabound.2019.07.021 NOV 2019
Abstract:
The generalized Dugdale model of cracks in two-dimensional decagonal quasicrystals is studied by developing the extended displacement discontinuity boundary element method. Expressions for the phonon and phason stress intensity factors and energy release rate are given in terms of the phonon and phason displacement discontinuities near the crack front. The extended displacement discontinuity boundary element method, with an iterative approach of determining the size of the yielding zone, is adopted to numerically simulate the nonlinear fracture problem. The effects of phonon and phason loadings, as well as the yield stress on the size of yielding zone and energy release rate, are discussed.
Title:
Structural Peculiarities of the Intermediate Phase in Zr-Rich Lead Zirconate Titanate
Authors:
Andronikova, DA; Bronwald, IA; Leontyev, NG; Leontyev, IN; Chernyshov, DY; Filimonov, AV; Vakhrushev, SB Author Full Names: Andronikova, D. A.; Bronwald, I. A.; Leontyev, N. G.; Leontyev, I. N.; Chernyshov, D. Yu; Filimonov, A., V; Vakhrushev, S. B.
Source:
PHYSICS OF THE SOLID STATE, 61 (10):1772-1778; 10.1134/S1063783419100056 OCT 2019
Abstract:
This paper presents the results of X-ray diffraction studies on a single crystal of lead zirconate titanate PbZr0.993Ti0.007O3 in the region of existence of an intermediate ferroelectric phase. In addition to the known superstructure reflections of the M type q(M) = {\frac{1}{2},\frac{1}{2},0} \right\}$$\end{document} and the first-order satellite reflections q(M) + {delta, delta, delta}, unknown second-order satellites have been observed near q(M) and near the Bragg reflections. Structural model of regular system of antiphase domains is used for diffraction calculation. The model is shown to describe the first- and second-orders satellite reflections in the vicinity of q(M), but it cannot explain the appearance of satellites around the main Bragg peaks. A possible origin of the system of the superstructures observed in the intermediate phase is discussed.
Title:
Crack Detection in High-Velocity Oxygen-Fuel-Sprayed Al59.2Cu25.5Fe12.3B3 Quasicrystalline Coatings Using Piezoelectric Active Sensors
Authors:
Gomes, R; Feitosa, FR; Souto, C; Lima, BA; Anselmo, J; Cunha, M; Sobrinho, JMB; Dubois, JM Author Full Names: Gomes, Rodinei; Feitosa, Francisco Riccelly; Souto, Cicero; Lima, Bruno Alessandro; Anselmo Junior, Jose; Cunha, Maxsuel; Basilio Sobrinho, Jose Marques; Dubois, Jean-Marie
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 28 (9):5649-5660; 10.1007/s11665-019-04298-3 SEP 2019
Abstract:
Quasicrystals have received some attention in recent years regarding their potential usefulness as low friction and wear resistant materials. When quasicrystalline (QC) coatings are exposed to different levels of external loading or are subjected to thermal stresses, crack nucleation, and propagation become life-limiting factors. In this investigation, Al59.2Cu25.5Fe12.3B3 QC coatings were deposited onto AISI-A36 steel substrates using the high-velocity oxygen-fuel (HVOF) technique. The coatings were deposited at different oxygen-to-fuel ratios. To characterize the integrity of the coatings, the active piezoceramic excitation technique was applied to detect the propagation of cracks during three-point bending tests. The piezoelectric transducer signal was processed using wavelet transformation analysis. The results revealed that the coated samples displayed different densities of cracks depending on the oxygen-to-fuel. The crack density was found higher for coatings formed using a slightly oxidizing flame. The opening of the pre-existing cracks in the coating was the main reason of signal attenuation during piezoelectric excitation. The HVOF-sprayed AlCuFeB quasicrystalline coating, with thickness between 150 and 180 mu m, withstands a flexural stress as high as 340 MPa. To the best of our knowledge, this study is the first that provides a quantitative assessment of the viability of QC coatings in mechanical applications in spite of their intrinsic brittleness.

Update: 24-Oct-2019

Title:
Lattice and magnetic dynamics in the polar, chiral, and incommensurate antiferromagnet Ni2InSbO6
Authors:
Prosnikov, MA; Smirnov, AN; Davydov, VY; Araki, Y; Arima, T; Pisarev, RV Author Full Names: Prosnikov, M. A.; Smirnov, A. N.; Davydov, V. Yu; Araki, Y.; Arima, T.; Pisarev, R., V
Source:
PHYSICAL REVIEW B, 100 (14):10.1103/PhysRevB.100.144417 OCT 10 2019
Abstract:
Complex systems with coexisting polarity, chirality, and incommensurate magnetism are of great interest because they open new degrees of freedom in the interaction between crystal and magnetic subsystems and therefore they host a plethora of intriguing physical properties. Here we report the optical properties and lattice and spin dynamics of Ni2InSbO6 single crystals. This material was studied with the use of polarized optical microscopy and micro-Raman spectroscopy in the temperature range 10-300 K. Ni2InSbO6 crystallizes in a polar structure described by the noncentrosymmetric space group R3 and the two types of structural domains were visualized due to the natural optical activity of opposite chirality. Raman tensor elements of most A and E phonons along with their symmetry were determined. The manifestation of LO-TO splitting was observed for the A modes. By tracking the temperature dependencies of phonon frequencies, the well pronounced spin-phonon interaction was observed for several modes below and above the Ned transition temperature T-N = 76 K. In the antiferromagnetic phase, a broad excitation centered at 247 cm(-1), was detected and assigned to the two-magnon mode and this value was used for estimating exchange parameters through linear spin-wave theory calculations.
Title:
Stability of three-dimensional icosahedral quasicrystals in multi-component systems
Authors:
Jiang, K; Si, W Author Full Names: Jiang, Kai; Si, Wei
Source:
PHILOSOPHICAL MAGAZINE, 10.1080/14786435.2019.1671997
Abstract:
The relative stability of three-dimensional icosahedral quasicrystals in multi-component systems has been investigated based on a phenomenological coupled-mode Swift-Hohenberg model with two-length scales. A recently developed projection method, which provides a unified numerical framework to study periodic crystals and quasicrystals, is used to compute free energy to high accuracy. Compared with traditional approaches, the advantage of the projection method has also been discussed in detail. A rigorous and systematic computation demonstrates that three-dimensional icosahedral quasicrystal and two-dimensional decagonal quasicrystal are both stable phases in such a simple multi-component coupled-mode Swift-Hohenberg model. The result extends the two-length scales interaction mechanism of stabilising quasicrystals from single-component to multi-component systems.
Title:
Equilibrium Configurations for Generalized Frenkel-Kontorova Models on Quasicrystals
Authors:
Trevino, R Author Full Names: Trevino, Rodrigo
Source:
COMMUNICATIONS IN MATHEMATICAL PHYSICS, 371 (1):1-17; 10.1007/s00220-019-03557-7 OCT 2019
Abstract:
I study classes of generalized Frenkel-Kontorova models whose potentials are given by almost-periodic functions which are closely related to aperiodic Delone sets of finite local complexity. Since such Delone sets serve as models for quasicrystals, this setup presents Frenkel-Kontorova models for the type of aperiodic crystals which have been discovered since Shechtman's discovery of quasicrystals. Here I consider models with configurations u:Zr -> Rd}, where d is the dimension of the quasicrystal, for any r and d. The almost-periodic functions used for potentials are called pattern-equivariant and I show that if the interactions of the model satisfies a mild end{document} requirement, and if the potential satisfies a mild non-degeneracy assumption, then there exist equilibrium configurations of any prescribed rotation rotation number/vector/plane. The assumptions are general enough to satisfy the classical Frenkel-Kontorova models and its multidimensional analoges. The proof uses the idea of the anti-integrable limit.

Update: 17-Oct-2019

Title:
Development of quasicrystal morphology in gas-atomized icosahedral-phase-strengthened aluminum alloy powders
Authors:
Leonard, HR; Rommel, S; Watson, TJ; Policandriotes, T; Aindow, M Author Full Names: Leonard, H. R.; Rommel, S.; Watson, T. J.; Policandriotes, T.; Aindow, M.
Source:
MATERIALS & DESIGN, 182 10.1016/j.matdes.2019.108094 NOV 15 2019
Abstract:
The microstructures in gas-atomized powders and in blind-die-compacted material from three AI-Cr-Mn-Co-Zr alloys have been studied using X-ray diffraction and electron microscopy. The materials consist of a mixture of FCC AI and icosahedral quasicrystalline phases, but three different phase distributions are observed which depend on the powder particle size, and hence on the cooling rate. The finest particles contain a nano-composite mixture of equiaxed Al grains and fine (<200 nm) quasicrystalline dispersoids. Coarser particles exhibit large cellular dendritic AI grains with thin films of Co- and Cr/Mn-rich phases at the cell boundaries and coarser (up to 2 mu m) quasicrystals at the particle surfaces. The largest particles contain coarse (up to 5 mu m) radial quasicrystalline growths within the particle. The same microstructures were observed for each alloy, but the volume fractions of the microstructural types varied with the alloy content. These effects are explained on the basis of competing nucleation and growth phenomena during solidification of the atomized droplets. Since these microstructures are retained in the bulk material following blind-die-compaction, they could have a profound influence on the mechanical and other properties of materials made from such powders. The importance of such effects for alloy and process design are discussed. (C) 2019 The Author(s). Published by Elsevier Ltd.
Title:
Topological Anderson insulator phase in a quasicrystal lattice
Authors:
Chen, R; Xu, DH; Zhou, B Author Full Names: Chen, Rui; Xu, Dong-Hui; Zhou, Bin
Source:
PHYSICAL REVIEW B, 100 (11):10.1103/PhysRevB.100.115311 SEP 27 2019
Abstract:
Motivated by the recent experimental realization of the topological Anderson insulator and research interest on the topological quasicrystal lattices, we investigate the effects of disorder on topological properties of a two-dimensional Penrose-type quasicrystal lattice that supports the quantum spin Hall insulator (QSHI) and normal insulator (NI) phases in the clean limit. It is shown that the helical edge state of the QSHI phase is robust against weak disorder. Most saliently, it is found that disorder can induce a phase transition from NI to QSHI phase in the quasicrystal system. The numerical results based on a two-terminal device show that a quantized conductance plateau can arise inside the energy gap of the NI phase for moderate Anderson disorder strength. Further, it is confirmed that the local current distributions of the disorder-induced quantized conductance plateau are located on the two edges of the sample. Finally, we identify this disorder-induced phase as topological Anderson insulator phase by computing the disorder-averaged spin Bott index.
Title:
Electronic band structure of a two-dimensional oxide quasicrystal
Authors:
Chiang, CT; Ellguth, M; Schumann, FO; Tusche, C; Kraska, R; Forster, S; Widdra, W Author Full Names: Chiang, Cheng-Tien; Ellguth, Martin; Schumann, Florian O.; Tusche, Christian; Kraska, Richard; Foerster, Stefan; Widdra, Wolf
Source:
PHYSICAL REVIEW B, 100 (12):10.1103/PhysRevB.100.125149 SEP 23 2019
Abstract:
The valence band electronic structure of a BaTiO3-derived oxide quasicrystal (OQC) is studied by photoemission using momentum microscopy. An upward-dispersive Q(2p) band is identified, and it can be assigned to a combination of in-plane orbitals according to the symmetry and the overlap of the wave functions. In addition, the signature of Ti-3d states near the Fermi level is observed, which results in a metallic character of the OQC with 3d(1) occupation. Our experiments reveal two-dimensional electronic states within the OQC based on a symmetry-adapted decomposition of photoelectron intensity distribution in the momentum space.
Title:
Fabrication and electrochemical hydrogen storage performance of Ti49Zr26Ni25 alloy covered with Cd/Pd core/shell particles
Authors:
Liu, H; Tan, LY; Guo, YL; Chen, P; Gao, S; Su, ZM; Liu, WQ; Zhao, JX Author Full Names: Liu, Heng; Tan, Liyuan; Guo, Yalan; Chen, Peng; Gao, Shang; Su, Zhongmin; Liu, Wanqiang; Zhao, Jianxun
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 44 (45):24800-24809; 10.1016/j.ijhydene.2019.07.094 SEP 20 2019
Abstract:
A facile two-step reduction method is employed to obtain the Cd/Pd core/shell particles. Mechanical alloying and subsequent annealing are used to fabricate the Ti49Zr26Ni25 quasicrystal. Composite materials of Ti49Zr26Ni25 mixed with different contents of Cd/Pd particles are obtained via ball-milling. The electrochemical performance and kinetics properties of the alloy electrodes for Ni/MH secondary batteries are studied. Ultimately, a maximum discharge capacity of 272.9 mA h/g is achieved for 7% additive content of Cd/Pd. Ti49Zr26Ni25 + Cd/Pd shows higher capacity than Ti49Zr26Ni25 + Pd (246.8 mA h/g) and original Ti49Zr26Ni25 (212.5 mA h/g). Moreover, the composites also exhibit improved cyclic stability and high-rate dischargeability. The Cd/Pd particles with special core/shell microstructure can enhance the electro-catalytic activity of Pd. The Cd/Pd material covered on the surface of alloy can further decrease the charge-transfer resistance and accelerate the hydrogen transmission, thus improving the electrochemical properties and reaction kinetics of the electrode. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Update: 10-Oct-2019

Title:
Elastic field for a blunt crack in a decagonal quasicrystalline material
Authors:
Wang, X; Schiavone, P Author Full Names: Wang, Xu; Schiavone, Peter
Source:
ENGINEERING FRACTURE MECHANICS, 220 10.1016/j.engfracmech.2019.106657 OCT 15 2019
Abstract:
We show that the full-field solution for the plane strain deformations of a decagonal quasicrystalline material with traction-free parabolic boundary can be used to directly obtain the elastic field describing phonon and phason stresses as well as displacements in the vicinity of a blunt crack tip in a decagonal quasicrystalline material. The aforementioned full-field solution is derived by applying complex variable methods to the boundary value problem in the physical plane without any recourse to conformal mapping and a corresponding image plane.
Title:
Fundamental solutions and analysis of the interface crack for two-dimensional decagonal quasicrystal bimaterial via the displacement discontinuity method
Authors:
Fan, CY; Lv, SY; Dang, HY; Yuan, YP; Zhao, MH Author Full Names: Fan, CuiYing; Lv, ShouYi; Dang, HuaYang; Yuan, YanPeng; Zhao, MingHao
Source:
ENGINEERING ANALYSIS WITH BOUNDARY ELEMENTS, 106 462-472; 10.1016/j.enganabound.2019.05.029 SEP 2019
Abstract:
The extended displacement discontinuity method is developed to analyze an interface line crack in a two-dimensional decagonal quasicrystal bimaterial. According to the general solutions and Fourier transform, fundamental solutions for phonon and phason displacement discontinuities and phonon and phason stresses are obtained. The delta function in the phonon and phason stresses is replaced by the Gaussian distribution function to eliminate the oscillatory singularity near the crack front. The expressions of phonon and phason stress intensity factors are given in terms of phonon and phason displacement discontinuities. The finite element analysis software COMSOL is used to validate the developed method.

Update: 3-Oct-2019

Title:
Magnetic ground state of the frustrated spin-1/2 chain compound beta-TeVO4 at high magnetic fields
Authors:
Pregelj, M; Zorko, A; Klanjsek, M; Zaharko, O; White, JS; Prokhnenko, O; Bartkowiak, M; Nojiri, H; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Zorko, A.; Klanjsek, M.; Zaharko, O.; White, J. S.; Prokhnenko, O.; Bartkowiak, M.; Nojiri, H.; Berger, H.; Arcon, D.
Source:
PHYSICAL REVIEW B, 100 (9):10.1103/PhysRevB.100.094433 SEP 19 2019
Abstract:
Frustrated spin-1/2 chains, despite the apparent simplicity, exhibit a remarkably rich phase diagram comprising vector-chiral (VC), spin-density-wave (SDW), and multipolar/spin-nematic phases as a function of the magnetic field. Here we report a study of beta-TeVO4, an archetype of such compounds, based on magnetization and neutron diffraction measurements up to 25 T. We find the transition from the helical VC ground state to the SDW state at similar to 3 T for the magnetic field along the a and c crystal axes, and at similar to 9 T for the field along the b axis. The high-field (HF) state, existing above similar to 18 T, i.e., above similar to 1/2 of the saturated magnetization, is an incommensurate magnetically ordered state and not the spin-nematic state, as theoretically predicted for the isotropic frustrated spin-1/2 chain. The HF state is likely driven by sizable interchain interactions and symmetric intrachain anisotropies uncovered in previous studies. Consequently, the potential existence of the spin-nematic phase in beta-TeVO4 is limited to a narrow field range, i.e., a few tenths of a tesla bellow the saturation of the magnetization, as also found in other frustrated spin-1/2 chain compounds.
Title:
Metallic-mean quasicrystals as aperiodic approximants of periodic crystals
Authors:
Nakakura, J; Ziherl, P; Matsuzawa, J; Dotera, T Author Full Names: Nakakura, Joichiro; Ziherl, Primoz; Matsuzawa, Junichi; Dotera, Tomonari
Source:
NATURE COMMUNICATIONS, 10 10.1038/s41467-019-12147-z SEP 17 2019
Abstract:
Ever since the discovery of quasicrystals, periodic approximants of these aperiodic structures constitute a very useful experimental and theoretical device. Characterized by packing motifs typical for quasicrystals arranged in large unit cells, these approximants bridge the gap between periodic and aperiodic positional order. Here we propose a class of sequences of 2-D quasicrystals that consist of increasingly larger periodic domains and are marked by an ever more pronounced periodicity, thereby representing aperiodic approximants of a periodic crystal. Consisting of small and large triangles and rectangles, these tilings are based on the metallic means of multiples of 3, have a 6-fold rotational symmetry, and can be viewed as a projection of a non-cubic 4-D superspace lattice. Together with the non-metallic-mean three-tile hexagonal tilings, they provide a comprehensive theoretical framework for the complex structures seen, e.g., in some binary nanoparticles, oxide films, and intermetallic alloys.
Title:
High strain rate behaviour of nano-quasicrystalline Al93Fe3Cr2Ti2 alloy and composites
Authors:
Pedrazzini, S; Galano, M; Audebert, F; Siegkas, P; Gerlach, R; Tagarielli, VL; Smith, GDW Author Full Names: Pedrazzini, S.; Galano, M.; Audebert, F.; Siegkas, P.; Gerlach, R.; Tagarielli, V. L.; Smith, G. D. W.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 764 10.1016/j.msea.2019.138201 SEP 9 2019
Abstract:
We demonstrate the outstanding dynamic strength of nano-quasicrystalline Al93Fe3Cr2Ti2 at.% alloy and composites. Unlike most crystalline Al alloys, this alloy exhibits substantial strain rate sensitivity and retains ductility at high strain rates. This opens new pathways for use in safety-critical materials requiring impact resistance.
Title:
How Accurate Do X-ray Data Need To Be To Obtain a Reliable Order of Stability for Polymorphs? The Case Study of p-Hydroxyacetophenone Polymorphs
Authors:
Sztylko, M; Malinska, M; Petricek, V; Gutmann, MJ; Hoser, AA Author Full Names: Sztylko, Marcin; Malinska, Maura; Petricek, Vaclav; Gutmann, Matthias J.; Hoser, Anna A.
Source:
CRYSTAL GROWTH & DESIGN, 19 (9):5132-5141; 10.1021/acs.cgd.9b00518 SEP 2019
Abstract:
Technical progress in crystallographic instruments allows contemporary crystallographers to more routinely conduct excellent quality low-temperature diffraction measurements. As a result, even crystal structures that have been extensively studied at ambient conditions start to reveal their more complex nature. The importance of low-temperature measurements is discussed based on the new, modulated structures found for polymorphs of 4'-hydroxyacetophenone (HAP). Diffraction data for this polymorphic system have been collected in the temperature range from 40 K to 330 K. At 123 K, form II of HAP appears to be a new, commensurately modulated structure with a modulation vector q = [0.4, 0.0, 0.0]. The structure can be solved and refined with 10 molecules in the asymmetric unit. A further decrease of temperature to 40 K resulted in the discovery of a new, incommensurately modulated phase with four independent molecules in the P2(1) monoclinic space group with the modulation vector q = [0.37, 0.17, 0.0]. Consequences of modulation for the relative stability of polymorphs will be discussed.

Update: 26-Sep-2019

Title:
Structural correlation of magneto-electric coupling in polycrystalline TbMnO3 at low temperature
Authors:
Agarwal, H; Yadav, P; Lalla, NP; Alonso, JA; Srivastava, ON; Shaz, MA Author Full Names: Agarwal, Harshit; Yadav, Poonam; Lalla, N. P.; Alonso, J. A.; Srivastava, O. N.; Shaz, M. A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 806 510-519; 10.1016/j.jallcom.2019.07.228 OCT 25 2019
Abstract:
The present study is focused on the structural correlation of magneto-electric coupling that exists in polycrystalline TbMnO3. The X-ray diffraction patterns are collected at various conditions, which are (1) at 300 K without a magnetic field, (2) at 2 K without magnetic field and (3) at 2 K with 7 Tesla magnetic fields. The structural transition in TbMnO3 has been observed at 2 K and some lattice modulation after applying the magnetic field at 2 K. The Rietveld refinement of TbMnO3 confirms the orthorhombic phase with centrosymmetric space group Pnma at 300 K. We have observed that the inversion symmetry breaks at 2 K and the polycrystalline TbMnO3 has been refined using a non-centrosymmetric orthorhombic space group which can be either Pn2(1)a or P2(1)ma. This structural transition confirms the presence of a ferroelectric phase at 2 K. After the application of 7 Tesla magnetic field, the signature of an incommensurate phase has been observed in polycrystalline TbMnO3 at 2 K. The DC magnetization behaviour with temperature M(T) and field M(H) reveals the antiferromagnetic behaviour of polycrystalline TbMnO3 below 42 K. We have also measured magneto-dielectric property of polycrystalline TbMnO3 at the low temperature, which confirms the strong magneto-electric coupling in polycrystalline TbMnO3 below the transition temperature. (C) 2019 Elsevier B.V. All rights reserved.
Title:
Highly dispersive magnons with spin-gap-like features in the frustrated ferromagnetic S=1/2 chain compound Ca2Y2Cu5O10 detected by inelastic neutron scattering
Authors:
Matsuda, M; Ma, J; Garlea, VO; Ito, T; Yamaguchi, H; Oka, K; Drechsler, SL; Yadav, R; Hozoi, L; Rosner, H; Schumann, R; Kuzian, RO; Nishimoto, S Author Full Names: Matsuda, M.; Ma, J.; Garlea, V. O.; Ito, T.; Yamaguchi, H.; Oka, K.; Drechsler, S-L; Yadav, R.; Hozoi, L.; Rosner, H.; Schumann, R.; Kuzian, R. O.; Nishimoto, S.
Source:
PHYSICAL REVIEW B, 100 (10):10.1103/PhysRevB.100.104415 SEP 12 2019
Abstract:
We report inelastic neutron scattering experiments in Ca2Y2Cu5O10 and map out the full one-magnon dispersion which extends up to a record value of 53 meV for frustrated ferromagnetic (FM) edge-sharing CuO2 chain (FFESC) cuprates. A homogeneous spin-1/2 chain model with a FM nearest-neighbor (NN), an antiferromagnetic (AFM) next-nearest-neighbor (NNN) inchain, and two diagonal AFM interchain couplings (ICs) analyzed within linear spin-wave theory (LSWT) reproduces well the observed strong dispersion along the chains and a weak one perpendicularly. The ratio alpha = vertical bar J(a2)/J(a1)vertical bar fall of the FM NN and the AFM NNN couplings is found as similar to 0.23, close to the critical point alpha(c) = 1/4 which separates ferromagnetically and antiferromagnetically correlated spiral magnetic ground states in single chains, whereas alpha(c) > 0.25 for coupled chains is considerably upshifted even for relatively weak IC. Although the measured dispersion can be described by homogeneous LSWT, the scattering intensity appears to be considerably reduced at similar to 11.5 and similar to 28 meV. The gaplike feature at 11.5 meV is attributed to magnon-phonon coupling whereas based on density matrix renormalization group simulations of the dynamical structure factor the gap at 28 meV is considered to stem partly from quantum effects due to the AFM IC. Another contribution to that gap is ascribed to the intrinsic superstructure from the distorting incommensurate pattern of CaY cationic chains adjacent to the CuO2 ones. It gives rise to nonequivalent CuO4 units and Cu-O-Cu bond angles Phi and a resulting distribution of all exchange integrals. The J's fitted by homogeneous LSWT are regarded as average values. The record value of the FM NN integral J(1) = 24 meV among FFESC cuprates can be explained by a nonuniversal Phi(not equal 90 degrees) and Cu-O bond length dependent anisotropic mean direct FM Cu-O exchange (K) over bar (pd) similar to 120 meV, similar to a value of 105 meV for Li2CuO2, in accord with larger values for La2CuO4 and CuGeO3 (similar to 110 meV) reported by Braden et al. [Phys. Rev. B 54, 1105 (1996)] phenomenologically. Enhanced K-pd values are also needed to compensate a significant AFM J(dd) >= 6 meV from the dd channel, generic for FFESC cuprates but ignored so far.
Title:
Growth interactions between icosahedral quasicrystals
Authors:
Senabulya, N; Shahani, AJ Author Full Names: Senabulya, Nancy; Shahani, Ashwin J.
Source:
PHYSICAL REVIEW MATERIALS, 3 (9):10.1103/PhysRevMaterials.3.093403 SEP 11 2019
Abstract:
We investigate the solidification pathways of a population of icosahedral quasicrystals in a liquid through in situ synchrotron x-ray tomography. The wealth of three-dimensional space- and time-resolved data enables us to test the predictions of various models and theories of crystallization on a quasi-crystal-forming alloy. Remarkably, we find the general evolution equation-that accounts for the competing effects of growth, coalescence, and coarsening-fits well our experimental data on surface area concentration. Furthermore, we quantify the orientation selection, screening length, and coarsening rate of the dodecahedra, and compare these results to that of periodic crystals. The latter is a full order of magnitude smaller than that of elemental metal dendrites in the limit of zero volume fraction, a reflection of the low solid-liquid interfacial energy of the icosahedral phase. Our paper provides the critical input data for microstructural models used for integrated computational materials engineering of complex intermetallics, including quasicrystals.
Title:
Multiple charge density waves compete in ternary rare-earth nickel carbides, RNiC2 (R: Y, Dy, Ho, and Er)
Authors:
Maeda, H; Kondo, R; Nogami, Y Author Full Names: Maeda, Hiroyuki; Kondo, Ryusuke; Nogami, Yoshio
Source:
PHYSICAL REVIEW B, 100 (10):10.1103/PhysRevB.100.104107 SEP 9 2019
Abstract:
Single-crystal x-ray-diffraction experiments and electrical resistivity measurements were performed on intermetallic compounds of formula RNiC2 [rare earth (R): Y, Dy, Ho, and Er]. In the series of diffraction studies, we found three kinds of satellite reflections that had different wave vectors [incommensurate q(1)(ic):(0.5, 0.5 + eta, 0) and commensurate q(1)(c):(0.5, 0.5, 0) and q(2c):(0.5, 0.5, 0.5)] at temperatures where their resistivities show anomalies, such as a hump, a sharp increase, or a dent. Satellite reflections with nearly identical wave vectors have also been reported in RNiC2 composed of earlier lanthanide atoms (GdNiC2 and TbNiC2). These results indicate the formation of a charge density wave (CDW) also in RNiC2 studied in this paper. We found strong competition between the q(1ic) and the q(2c) CDWs in DyNiC2 and YNiC2, and that only the q(2c) CDW existed in HoNiC2 and ErNiC2. Based on the results obtained in the present paper and those of SmNiC2, GdNiC2, and TbNiC2 reported before, we discuss the CDW transitions in the RNiC2 family.
Title:
Formation of Incommensurate Charge Density Waves in Cuprates
Authors:
Miao, H; Fumagalli, R; Rossi, M; Lorenzana, J; Seibold, G; Yakhou-Harris, F; Kummer, K; Brookes, NB; Gu, GD; Braicovich, L; Ghiringhelli, G; Dean, MPM Author Full Names: Miao, H.; Fumagalli, R.; Rossi, M.; Lorenzana, J.; Seibold, G.; Yakhou-Harris, F.; Kummer, K.; Brookes, N. B.; Gu, G. D.; Braicovich, L.; Ghiringhelli, G.; Dean, M. P. M.
Source:
PHYSICAL REVIEW X, 9 (3):10.1103/PhysRevX.9.031042 SEP 6 2019
Abstract:
Although charge density waves (CDWs) are omnipresent in cuprate high-temperature superconductors, they occur at significantly different wave vectors, confounding efforts to understand their formation mechanism. Here, we use resonant inelastic x-ray scattering to investigate the doping- and temperature-dependent CDW evolution in La2-xBaxCuO4 (x = 0.115-0.155). We discover that the CDW develops in two stages with decreasing temperature. A precursor CDW with a quasicommensurate wave vector emerges first at high temperature. This doping-independent precursor CDW correlation originates from the CDW phase mode coupled with a phonon and "seeds" the low-temperature CDW with a strongly doping-dependent wave vector. Our observation reveals the precursor CDW and its phase mode as the building blocks of the highly intertwined electronic ground state in the cuprates.
Title:
Reply to comment on Couzi et al. (2018): a phenomenological model for structural phase transitions in incommensurate alkane/urea inclusion compounds
Authors:
Christensen, K; Williams, PA; Patterson, R; Palmer, BA; Couzi, M; Guillaume, F; Harris, KDM Author Full Names: Christensen, Kirsten; Williams, P. Andrew; Patterson, Rhian; Palmer, Benjamin A.; Couzi, Michel; Guillaume, Francois; Harris, Kenneth D. M.
Source:
ROYAL SOCIETY OPEN SCIENCE, 6 (8):10.1098/rsos.190518 AUG 2019
Abstract:
In a recentpaper (Couzi et al. 2018 R. Soc. open sci. 5, 180058. (doi: 10.1098/rsos.180058)), we proposed a new phenomenological model to account for the I <-> II <->"III" phase sequence in incommensurate n-alkane/urea inclusion compounds, which represents an alternative interpretation to that proposed in work of Toudic et al. In a Comment (Toudic et al. 2019 R. Soc. open sci. 6, 182073. (doi: 10.1098/rsos. 182073)), Toudic et al. have questioned our assignment of the superspace group of phase II of n-nonadecane/urea, which they have previously assigned, based on a (3 + 2)-dimensional superspace, as C222(1)(00 gamma)(10 delta). In this Reply, we present new results from a comprehensive synchrotron single-crystal X-ray diffraction study of n-nonadecane/urea, involving measurements as a detailed function of temperature across the I <-> II <->"III" phase transition sequence. Our results demonstrate conclusively that "main reflections" (h, k, l, 0) with h+k odd are observed in phase II of n-nonadecane/urea (including temperatures in phase II that are just below the transition from phase I to phase II), in full support of our assignment of the (3+ 1)-dimensional superspace group P212121(00.) to phase II. As our phenomenological model is based on phase II and phase '' III '' of this incommensurate material having the same (3+ 1)-dimensional superspace group P2(1)2(1)2(1)(00 gamma), it follows that the new X-ray diffraction results are in full support of our phenomenological model.
Title:
Comment on Couzi et al. (2018): a phenomenological model for structural transitions in incommensurate alkane/urea inclusion compounds
Authors:
Toudic, B; Guerin, L; Mariette, C; Frantsuzov, I; Rabiller, P; Ecolivet, C; Hollingsworth, MD Author Full Names: Toudic, B.; Guerin, L.; Mariette, C.; Frantsuzov, I.; Rabiller, P.; Ecolivet, C.; Hollingsworth, Mark D.
Source:
ROYAL SOCIETY OPEN SCIENCE, 6 (8):10.1098/rsos.182073 AUG 2019
Title:
Compression behavior of selected laser melted Al/quasicrystal composite lattice structure
Authors:
Kang, N; Lin, X; Xu, J; Joguet, D; Li, Q; Liao, HL; Huang, WD; Coddet, C Author Full Names: Kang, N.; Lin, X.; Xu, J.; Joguet, D.; Li, Q.; Liao, H. L.; Huang, W. D.; Coddet, C.
Source:
JOURNAL OF LASER APPLICATIONS, 31 (2):10.2351/1.5096152 MAY 2019
Abstract:
In this work, Al/quasicrystal (QC) composite lattice samples with several cellular sizes ranging from 1.5 to 5 mm were manufactured using selective laser melting (SLM). The porosity of all the designed lattice structure samples is fixed as 50%. The morphology of QC reinforcement on the top surface changes from micro desquamated to nano in situ reacted, as the cellular size increases. The result indicates that cellular size has a significant influence on the compressive behavior of SLM processed lattice samples. As the cellular size increases from 1.5 to 5 mm, the fractural mechanism changes from three stages of linear elastic-plateau-densification to two stages of elastic collapse. Moreover, both the first peak compressive strength and the strain at failure decrease, when the cellular size increases. Furthermore, the SLM processed lattice 3 sample, which possesses a large cellular size, broke into small fragments after the compression test.

Update: 18-Sep-2019

Title:
Supercell refinement: a cautionary tale
Authors:
Lovelace, J; Petricek, V; Murshudov, G; Borgstahl, GEO Author Full Names: Lovelace, Jeffrey; Petricek, Vaclav; Murshudov, Garib; Borgstahl, Gloria E. O.
Source:
ACTA CRYSTALLOGRAPHICA SECTION D-STRUCTURAL BIOLOGY, 75 852-860; 10.1107/S2059798319011082 9 SEP 2019
Abstract:
Theoretically, crystals with supercells exist at a unique crossroads where they can be considered as either a large unit cell with closely spaced reflections in reciprocal space or a higher dimensional superspace with a modulation that is commensurate with the supercell. In the latter case, the structure would be defined as an average structure with functions representing a modulation to determine the atomic location in 3D space. Here, a model protein structure and simulated diffraction data were used to investigate the possibility of solving a real incommensurately modulated protein crystal using a supercell approximation. In this way, the answer was known and the refinement method could be tested. Firstly, an average structure was solved by using the 'main' reflections, which represent the subset of the reflections that belong to the subcell and in general are more intense than the 'satellite' reflections. The average structure was then expanded to create a supercell and refined using all of the reflections. Surprisingly, the refined solution did not match the expected solution, even though the statistics were excellent. Interestingly, the corresponding superspace group had multiple 3D daughter supercell space groups as possibilities, and it was one of the alternate daughter space groups that the refinement locked in on. The lessons learned here will be applied to a real incommensurately modulated profilin-actin crystal that has the same superspace group.
Title:
Coordination shells and coordination numbers of the vertex graph of the Ammann-Beenker tiling
Authors:
Shutov, A; Maleev, A Author Full Names: Shutov, Anton; Maleev, Andrey
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 746-757; 10.1107/S2053273319008179 5 SEP 2019
Abstract:
The vertex graph of the Ammann-Beenker tiling is a well-known quasiperiodic graph with an eightfold rotational symmetry. The coordination sequence and coordination shells of this graph are studied. It is proved that there exists a limit growth form for the vertex graph of the Ammann-Beenker tiling. This growth form is an explicitly calculated regular octagon. Moreover, an asymptotic formula for the coordination numbers of the vertex graph of the Ammann-Beenker tiling is also proved.
Title:
Robust minimal matching rules for quasicrystals
Authors:
Kalugin, P; Katz, A Author Full Names: Kalugin, Pavel; Katz, Andre
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 669-693; 10.1107/S2053273319008180 5 SEP 2019
Abstract:
A unified framework is proposed for dealing with matching rules of quasiperiodic patterns, relevant for both tiling models and real-world quasicrystals. The approach is intended for extraction and validation of a minimal set of matching rules, directly from the phased diffraction data. The construction yields precise values for the spatial density of distinct atomic positions and tolerates the presence of defects in a robust way.
Title:
Twinning and incommensurate modulation in baumoite, Ba-0.5[(UO2)(3)O8Mo2(OH)(3)](H2O)(similar to 3), the first natural Ba uranyl molybdate
Authors:
Elliott, P; Plasil, J; Petricek, V; Cejka, J; Bindi, L Author Full Names: Elliott, Peter; Plasil, Jakub; Petricek, Vaclav; Cejka, Jiri; Bindi, Luca
Source:
MINERALOGICAL MAGAZINE, 83 (4):507-514; 10.1180/mgm.2019.20 AUG 2019
Abstract:
Baumoite, Ba-0.5[(UO2)(3)O8Mo2(OH)(3)](H2O)(similar to 3), is a new mineral found near Radium Hill, South Australia, where it occurs in a granite matrix associated with baryte, metatorbernite, phurcalite and kaolinite. Baumoite forms thin crusts of yellow to orange-yellow tabular to prismatic crystals. The mineral is translucent with a vitreous lustre and pale yellow streak. Crystals are brittle, the fracture is uneven and show one excellent cleavage. The Mohs hardness is similar to 21/2 . The calculated density is 4.61 g/cm(3). Optically, baumoite crystals are biaxial (-), with alpha = 1.716(4), beta= 1.761(4), gamma = 1.767(4) (white light); and 2V(calc) = 42.2 degrees. Electron microprobe analyses gave the empirical formula Ba0.87Ca0.03Al0.04U2.97Mo2.02P0.03O22H11.99, based on 22 O atoms per formula unit. The eight strongest lines in the powder X-ray diffraction pattern are [d(obs )angstrom (I) (hkl)]: 9.175(39)(12 (1) over bar), 7.450(100)(020), 3.554(20)(221), 3.365(31)(004, 202), 1255(31)(123, 30 (2) over bar), 3.209(28)(12 (4) over bar), 3.067(33)(30 (3) over bar, 222, 32 (2) over bar) and 2.977(20)(142). Single-crystal X-ray studies (R-1 = 5.85% for 1892 main reflections) indicate that baumoite is monoclinic, superspace group X2/m(a0g)0s with X = (0,1/2,0,1/2), with unit-cell parameters: a = 9.8337(3), b = 15.0436(5), c = 14.2055(6) angstrom, beta = 108.978(3)degrees, V= 1987.25(13) angstrom(3) and Z = 4. The crystal structure is twinned and incommensurately modulated and is based upon sheets of U6+ and Mo6+ polyhedra of unique topology. Four independent cationic sites partially occupied by Ba atoms are located between the sheets, together with H2O molecules.
Title:
Debye temperature of single-crystal Cr with incommensurate and commensurate magnetic structure
Authors:
Dubiel, SM; Zukrowski, J Author Full Names: Dubiel, Stanislaw M.; Zukrowski, Jan
Source:
EPL, 127 (2):10.1209/0295-5075/127/26002 JUL 2019
Abstract:
Single crystals of Cr and Cr3%Mn doped with similar to 0.2 at.% Sn-119 were studied by means of Sn-119-site Mossbauer spectroscopy. Mossbauer spectra recorded in the temperature range of 78-300 K were analyzed using a hyperfine field distribution method. Additionally, the spectra recorded on the Cr3%Mn sample were analyzed in terms of three sextets. Derived therefrom values of a center shift, CS, were fitted to the Debye model yielded values of the Debye temperature, T-D = 477(56) K for Cr and T-D = 282(16) :K for Cr3%Mn. The difference in the T-D-value can be regarded as evidence that a spin-phonon coupling is different for the incommensurate and commensurate antiferromagnetic magnetic structure of chromium. Copyright (C) EPLA, 2019

Update: 11-Sep-2019

Title:
Al-Cu-Fe quasicrystals as the anode for lithium ion batteries
Authors:
Lan, X; Wang, HJ; Sun, ZH; Jiang, XY Author Full Names: Lan, Xiao; Wang, Haijuan; Sun, Zhanhao; Jiang, Xunyong
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 805 942-946; 10.1016/j.jallcom.2019.07.148 OCT 15 2019
Abstract:
In this paper, Al-Cu-Fe quasicrystal alloy was used as the anode material for lithium-ion batteries. The first specific discharge capacity of quasicrystal was 204 mA h/g. Cyclic voltammetry showed that the oxidation peak of the Al-Cu-Fe quasicrystal was at about 1.4 V. The reduction peak was at 0.3 V. The Al-Cu-Fe quasicrystals had a higher Li-ion diffusion impedance and Warburg impedance in the first cycle. X-ray diffraction analysis demonstrated that Li atoms enter into the quasicrystal structure and can-not fully leave the quasicrystal during the first charge-discharge cycle, which induces an irreversible capacity. (C) 2019 Elsevier B.V. All rights reserved.
Title:
High-pressure structural change in the ferroelectric layered perovskite Sr2Nb2O7
Authors:
Alanis, J; Ojeda-Galvan, HJ; Rodriguez-Aranda, MC; Rodriguez, AG; Garcia, HM; Iniguez, J; Mendoza, ME; Navarro-Contreras, HR Author Full Names: Alanis, Javier; Joazet Ojeda-Galvan, Hiram; Rodriguez-Aranda, M. C.; Rodriguez, A. G.; Moreno Garcia, Harumi; Iniguez, Jorge; Eugenia Mendoza, Maria; Navarro-Contreras, Hugo R.
Source:
PHYSICAL REVIEW B, 100 (5):10.1103/PhysRevB.100.054110 AUG 26 2019
Abstract:
The structural changes of sintered powder samples of perovskite-slab layered polycrystalline Sr2Nb2O7 (SNO) ferroelectric compound subjected to high pressures are here investigated. The samples were prepared using a solid-state reaction in the presence (SNOE) or absence (SNO) of an applied electric field. Density functional theory (DFT) calculations including hydrostatic pressure indicate that SNO's ferroelectricity remains up to 25 GPa in the structure of space group Cmc2(1) derived from the condensation of one zone-center soft phonon. The predicted DFT theoretical structural changes are discussed and compared with the results of the experimental Raman spectra as a function of pressure. The pressure-dependent spectra were recorded from atmospheric pressure up to 11.5 and 13.5 GPa for SNOE and SNO, respectively. Both samples underwent a pressure induced phase transition from an incommensurate to a commensurate state at room temperature, SNO at Pi-c = 6.5 +/- 0.2 GPa, and SNOE at Pi-c = 6.9 +/- 0.3 GPa. The DFT calculations enable the identification of the change in phase to the orthorhombic structure with the space group Cmc2(1). The experimental values for Pi-c are in reasonably good agreement with the theoretical predicted value of similar to 7.3 GPa. After the critical pressures, the number of observable phonons decreases, that is, when the compound adopts a higher symmetry structure, several phonons vanish abruptly in both the SNO and SNOE samples, as expected. The Raman spectra for both samples show hysteresis effects, that is, after the pressure is removed, a few extra lines remain visible, as well as many relative intensity changes and broadenings for some phonon bands. The bulk moduli of the Sr2Nb2O7 before and after Pi-c are calculated resulting in 117.0 and 147.8 GPa, respectively. The Gruneisen parameters of the phonons observed are finally calculated and discussed.
Title:
Spin-Orbital Density Wave and a Mott Insulator in a Two-Orbital Hubbard Model on a Honeycomb Lattice
Authors:
Zhu, Z; Sheng, DN; Fu, L Author Full Names: Zhu, Zheng; Sheng, D. N.; Fu, Liang
Source:
PHYSICAL REVIEW LETTERS, 123 (8):10.1103/PhysRevLett.123.087602 AUG 23 2019
Abstract:
Inspired by the recent discovery of correlated insulating states in twisted bilayer graphene, we study a two-orbital Hubbard model on the honeycomb lattice with two electrons per unit cell. Based on the real-space density matrix renormalization group simulation, we identify a metal-insulator transition around U-c/t = 2.5-3. In the vicinity of U-c, we find strong spin-orbital density wave fluctuations at commensurate wave vectors, accompanied by weaker incommensurate charge density wave fluctuations. The spin-orbital density wave fluctuations are enhanced with increasing system sizes, suggesting the possible emergence of long-range order in the two-dimensional limit. At larger U, our calculations indicate a possible nonmagnetic Mott insulator phase without spin or orbital polarization. Our findings offer new insight into correlated electron phenomena in twisted bilayer graphene and other multiorbital honeycomb materials.
Title:
Pinched P-E hysteresis loops in Ba4Sm2Fe0.5Ti3Nb6.5O30 ceramic with tungsten bronze structure
Authors:
Li, C; Hong, JS; Huang, YH; Ma, X; Fu, MS; Li, J; Liu, XQ; Wu, YJ Author Full Names: Li, Cheng; Hong, Jiang Sheng; Huang, Yu Hui; Ma, Xiao; Fu, Mao Sen; Li, Juan; Liu, Xiao Qiang; Wu, Yong Jun
Source:
APPLIED PHYSICS LETTERS, 115 (8):10.1063/1.5111360 AUG 19 2019
Abstract:
In the present work, single-phase Ba4Sm2Fe0.5Ti3Nb6.5O30 ceramics with a tetragonal tungsten bronze structure (TTB) were synthesized. Pinched polarization-electric field (P-E) hysteresis loops are observed below the Curie temperature (T-c) in the as-synthesized ceramics. The origin of the loops was thoroughly studied using in situ TEM and XRD. The in situ selected area electron diffraction (SAED) patterns showed that the pinched loops originated from the coexistence of polar commensurate and nonpolar incommensurate superlattice reflections. In situ XRD results revealed increasing tetragonality with rising temperature, implying that the enhancement in octahedral tilting was closely related to the commensurate-incommensurate structural modulation.

Update: 5-Sep-2019

Title:
Low temperature magnetic and x-ray diffraction studies of YBa1-xSrxCuFeO5 (x=0, 0.5)
Authors:
Lai, S; Mukherjee, K; Yadav, CS Author Full Names: Lai, Surender; Mukherjee, K.; Yadav, C. S.
Source:
PHYSICA B-CONDENSED MATTER, 570 191-193; 10.1016/j.physb.2019.06.034 OCT 1 2019
Abstract:
We report low temperature magnetic and structural properties of Sr doped layered perovskite material YBaCuFeO5. YBaCuFeO5 is the antiferromagnetic compound with commensurate to incommensurate transition temperature at 200 K. Low temperature x-ray diffraction shows the lattice contraction effect with decreasing temperature. Below 15 K a strong bifurcation between the ZFC and FC curves has been observed in YBa0.5Sr0.5CuFeO5, which may arise due to lattice contraction effect which changes the interaction between the spin and the lattice.
Title:
Unique crystal structures and their applications as materials for Li1+x-yM1-x-3yTix+4yO3 (M = Nb or Ta, 0.07 <= x <= 0.33, 0 <= y <= 0.175)
Authors:
Nakano, H Author Full Names: Nakano, Hiromi
Source:
ADVANCED POWDER TECHNOLOGY, 30 (10):2003-2013; 10.1016/j.apt.2019.04.034 OCT 2019
Abstract:
In the Li2O-M2O5-TiO2 (M = Nb or Ta) system, Li1+x-yM1-x-3yTix+4yO3 (LMT) forms with a superstructure known as the M-phase, in which the periodical intergrowth layers are inserted in a matrix having a trigonal structure of LiMO3. We have been investigating this unique material focusing on its crystal structure, photoluminescence, and electrical properties. First, the formation area of the superstructure was compared between Nb- and Ta-systems and the difference was accurately analyzed. Second, to apply this unique material as a host material of phosphor, we synthesized new phosphors with various emission colors. Red phosphor, having a high PL intensity with an internal quantum efficiency of 98%, was successfully synthesized and used as a host material of the solid solution for the Ta system. Its high value was the result of the large centroid-to-cation distance of the Eu3+ position in the [(Li, Eu)O-12] polyhedral. Further still, toward application of the unique qualities of an electro-ceramic, we successfully fabricated oriented balk ceramics for the Nb system by slip casting in a strong magnetic field of 12 T. As a result, anisotropic electric properties were found along the c-axis, which were caused by the super-structure. We first clarified the mechanism showing that the anisotropic Qf value was due to anisotropic electron conductivity and anisotropic bonding strength within the superstructure. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
Title:
Structural, thermodynamic, thermal, and electron transport properties of single-crystalline LaPt2Si2
Authors:
Falkowski, M; Dolezal, P; Andreev, AV; Duverger-Nedellec, E; Havela, L Author Full Names: Falkowski, M.; Dolezal, P.; Andreev, A., V; Duverger-Nedellec, E.; Havela, L.
Source:
PHYSICAL REVIEW B, 100 (6):10.1103/PhysRevB.100.064103 AUG 20 2019
Abstract:
LaPt2Si2 in a single-crystalline form was subjected to structure, thermodynamic, thermal, and electron transport studies with a special emphasis on the structure phase transition appearing at T = 85 K. X-ray diffraction proves the noncentrosymmetric tetragonal structure of CaBe2Ge2-type (space group P4/nmm). The transition manifests as a small step of opposite sign in both lattice parameters, leaving almost no volume change. c decreases and a increases in the low-T phase, but the change of the c/a ratio does not exceed 0.1%. Additional periodicity, related to the supposed charge density wave (CDW) state, can be related to satellites corresponding to the wave vector q approximate to (0.36, 0, 0), which start to grow with temperature decreasing below 175 K and almost vanish (or relocate from the investigated ab plane) below the 85 K transition. Electrical resistivity reveals that the 85 K transition is hysteretic in temperature, with the difference between heating and cooling being almost 10 K, proving the first-order type of the transition. The transition dramatically enhances resistivity in the low-T state, pointing to a formation of a pseudogap. This, however, does allow a superconducting state, arising below T-c = 1.6 K. The temperature dependence up upper critical field is not compatible with the weak coupling BCS theory. Strong anisotropy of electronic structure and its dramatic changes at the structure transition are manifest also in thermal expansion and thermoelectric power. The Sommerfeld coefficient gamma = 7.8 mJ mol(-1) K-2 and Debye temperature of 205 K could be derived at low temperatures, but the specific heat has a strongly non-Debye like T dependence, which can be ascribed to a low-energy Einstein mode.
Title:
Superconducting phase diagram and nontrivial band topology of structurally modulated Sn1-xSbx
Authors:
Liu, B; Xiao, CC; Zhu, QQ; Wu, JF; Cui, YW; Wang, HD; Wang, ZC; Lu, YH; Ren, Z; Cao, GH Author Full Names: Liu, Bin; Xiao, Chengcheng; Zhu, Qinqing; Wu, Jifeng; Cui, Yanwei; Wang, Hangdong; Wang, Zhicheng; Lu, Yunhao; Ren, Zhi; Cao, Guang-han
Source:
PHYSICAL REVIEW MATERIALS, 3 (8):10.1103/PhysRevMaterials.3.084603 AUG 19 2019
Abstract:
We report the discovery of superconductivity in binary alloy Sn1-xSbx with x in the range of 0.43 to 0.6, which possesses a modulated rhombohedral structure due to the incommensurate ordering of Sn and Sb layers along the c axis. The specific heat measurements indicate a weakly coupled, fully gapped superconducting state in this homogeneity range with a maximum bulk T-c of 1.58 K at x = 0.46, though the electronic specific heat and Hall coefficients remain nearly x independent. The nonmonotonic dependence of the bulk T-c is discussed in relation to the effects of Sb-layer intercalation between the [Sn4Sb3] seven-layer lamellae that are the essential building blocks for superconductivity. On the other hand, a zero-resistivity transition is found to take place well above the bulk superconducting transition, and the corresponding T-c increases monotonically with x from 2.06 K to 3.29 K. This contrast, together with the uniform elements distribution revealed by energy dispersive x-ray mapping, implies that the resistive transition is due to the strain effect at the grain boundary rather than the compositional inhomogeneity. The first-principles calculations on the representative composition Sn 4 Sb 3 (x = 0.43) indicate that it is topologically nontrivial similar to Sb, but with different Z(2) invariants (0;111). Our results not only identify a second superconducting region in the Sn-Sb phase diagram, but also provide a viable platform to study the interplay between structural modulation, nontrivial band topology, and superconductivity.
Title:
Depth dependent ferroelectric to incommensurate/commensurate antiferroelectric phase transition in epitaxial lanthanum modified lead zirconate titanate thin films
Authors:
Gao, M; Tang, X; Dai, S; Li, JF; Viehland, D Author Full Names: Gao, Min; Tang, Xiao; Dai, Steve; Li, Jiefang; Viehland, D.
Source:
APPLIED PHYSICS LETTERS, 115 (7):10.1063/1.5113720 AUG 12 2019
Abstract:
Transmission electron microscopy was used to investigate the coexistence of ferroelectricity (FE) and antiferroelectricity (AFE) in (001) and (011) (Pb0.97, La0.02) (Zr0.95, Ti0.05) O3 (PLZT) epitaxial thin films. The depth resolved selected area electron diffraction (SAED) results revealed that the AFE phase was located in the near interface region, whereas the FE phase was found in the near surface region. A thickness dependent lattice parameter distribution was calculated using the SAED data, and a decrease in the c/a ratio was found to correlate with the transition from AFE to FE stability. Additionally, commensurate and incommensurate modulations in AFE PLZT were identified based on the observation of various superlattice reflections.

Update: 28-Aug-2019

Title:
Significantly improved cycling stability for electrochemical hydrogen storage in Ti1.4V0.6Ni alloy with TiN
Authors:
Yu, L; Lin, J; Liang, F; Wang, LM; Chang, LM; Wang, FK; Li, N Author Full Names: Yu, Lu; Lin, Jing; Liang, Fei; Wang, Limin; Chang, Limin; Wang, Fangkuo; Li, Na
Source:
MATERIALS RESEARCH BULLETIN, 118 10.1016/j.materresbull.2019.110509 OCT 2019
Abstract:
Ti1.4V0.6Ni alloy contained icosahedral quasicrystals can be electrochemically charged and discharged with the maximum capacity of approximately 270 mAh g(-1), however this alloy shows poor cycling stability, making it difficult to develop the practical application. Here, new TiN-added Ti1.4V0.6Ni composites are prepared by ball-milling. The electrochemical performance of the composites as negative active ingredient of Nickel-metal hydride(Ni-MH) battery is compared with Ti1.4V0.6Ni. Benefiting from the excellent catalysts for HER, electrical conductivity and resistance to oxidation/corrosion of TiN, TiN-added Ti1.4V0.6Ni composites exhibit excellent cycling stability as well as charge retention(89.7% after 24 h relaxation). The cycling capacity retention rate for these electrodes is approximately 80% after a preliminarytest of 50 continuous cycles. But meanwhile, the maxium discharge capacity falls into about 250 g(-1), and the electrocatalytic activity improvement is hightly demanded. This work presents a practical method for using TiN as an additive for enhancing the cycling stability of hydrogen storage alloy.
Title:
Whirling spin order in the quasicrystal approximant Au72Al14Tb
Authors:
Sato, TJ; Ishikawa, A; Sakurai, A; Hattori, M; Avdeev, M; Tamura, R Author Full Names: Sato, Taku J.; Ishikawa, Asuka; Sakurai, Akira; Hattori, Masashi; Avdeev, Maxim; Tamura, Ryuji
Source:
PHYSICAL REVIEW B, 100 (5):10.1103/PhysRevB.100.054417 AUG 13 2019
Abstract:
A neutron powder diffraction experiment has been performed on the quasicrystal approximant Au72Al14Tb14, a body-centered-cubic crystal of icosahedral spin clusters. The long-range antiferromagnetic order was confirmed at the transition temperature T-N = 10.4 K. The magnetic structure consists of noncoplanar whirling spins on the icosahedral clusters, arranged in an antiferroic manner. A simple icosahedral spin-cluster model with uniaxial anisotropy accounts well the whirling spin order as well as the in-field metamagnetic transition, indicating that the icosahedral symmetry is essential.
Title:
Theory of quantum oscillations in quasicrystals: Quantizing spiral Fermi surfaces
Authors:
Spurrier, S; Cooper, NR Author Full Names: Spurrier, Stephen; Cooper, Nigel R.
Source:
PHYSICAL REVIEW B, 100 (8):10.1103/PhysRevB.100.081405 AUG 13 2019
Abstract:
We show that electronic materials with disallowed rotational symmetries that enforce quasiperiodic order can exhibit quantum oscillations and that these are generically associated with exotic "spiral Fermi surfaces." These Fermi surfaces are self-intersecting, and characterized by a winding number of their surface tangent-a topological invariant-that is larger than one. We compute the nature of the quantum oscillations in two experimentally relevant settings which give rise to spiral Fermi surfaces: a "nearly-free-electron" quasicrystal, and 30 degrees twisted bilayer graphene.
Title:
The incommensurately modulated structures of volcanic plagioclase: displacement, ordering and phase transition
Authors:
Jin, SY; Xu, HF; Wang, XP; Zhang, DO; Jacobs, R; Morgan, D Author Full Names: Jin, Shiyun; Xu, Huifang; Wang, Xiaoping; Zhang, Dongzho; Jacobs, Ryan; Morgan, Dane
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 75 643-656; SI 10.1107/S2052520619006243 4 AUG 2019
Abstract:
Four basaltic phenocryst samples of plagioclase, with compositions ranging from An(48) (andesine) to An(64) (labradorite), have been studied with single-crystal X-ray and neutron diffraction techniques. The samples were also subjected to a heating experiment at 1100 degrees C for two weeks in an effort to minimize the Al-Si ordering in their structures. The average and the modulated structures of the samples (before and after the heating experiment) were compared, in order to understand the mechanism of the phase transition from the disordered C (1) over bar structure to the e-plagioclase structure. A comparison between the structures from neutron and X-ray diffraction data shows that the < T-O > distance does not solely depend on the Al occupancy as previously thought. A dramatic decrease of the Al-Si ordering is observed after heating at 1100 degrees C for two weeks for all four samples, with an obvious change in the intensities of the satellite reflections (e-reflections) in the diffraction pattern. Evident changes in the modulation period were also observed for the more calcic samples. No obvious change in the Ca-Na ordering was observed after the heating experiment. An in situ heating X-ray diffraction experiment was carried out on the andesine sample (An(48)) to study the change in the satellite intensity at high temperature. A dramatic weakening of the satellite peaks was observed between 477 degrees C and 537 degrees C, which strongly supports the displacive nature of the initiation of e2 ordering. Rigid-Unit Mode (RUM) analysis of the plagioclase structure suggests the initial position of the e-reflections is determined by the anti-RUMs in the framework.
Title:
Daliranite, PbHgAs2S5: determination of the incommensurately modulated structure and revision of the chemical formula
Authors:
Lanza, AE; Gemmi, M; Bindi, L; Mugnaioli, E; Paar, WH Author Full Names: Lanza, Arianna E.; Gemmi, Mauro; Bindi, Luca; Mugnaioli, Enrico; Paar, Werner H.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 75 711-716; SI 10.1107/S2052520619007340 4 AUG 2019
Abstract:
The incommensurately modulated crystal structure of the mineral daliranite has been determined using 3D electron diffraction data obtained on nanocrystalline domains. Daliranite is orthorhombic with a = 21, b = 4.3, c = 9.5 angstrom and shows modulation satellites along c. The solution of the average structure in the Pnma space group together with energy-dispersive X-ray spectroscopy data obtained on the same domains indicate a chemical formula of PbHgAs2S5, which has one S fewer than previously reported. The crystal structure of daliranite is built from columns of face-sharing PbS8 bicapped trigonal prisms laterally connected by Hg[2+4] polyhedra and (As23+S5)(4-) groups. The excellent quality of the electron diffraction data allows a structural model to be built for the modulated structure in superspace, which shows that the modulation is due to an alternated occupancy of a split As site.

Update: 22-Aug-2019

Title:
Comparison of quantum spin Hall states in quasicrystals and crystals
Authors:
Huang, HQ; Liu, F Author Full Names: Huang, Huaqing; Liu, Feng
Source:
PHYSICAL REVIEW B, 100 (8):10.1103/PhysRevB.100.085119 AUG 8 2019
Abstract:
We theoretically study the quantum spin Hall states in an Ammann-Beenker-type octagonal quasicrystal and a periodic snub-square crystal, both sharing the same basic building blocks. Although the bulk states show significant differences in localization and transport properties, the topological phases manifest similarly in the two systems. This indicates the robustness of the topological properties regardless of symmetry and periodicity. We characterize the topological nature of the two systems with a nonzero topological invariant (spin Bott index B-s and Z(2) invariant), robust metallic edge states, and quantized conductance. In spite of some quantitative differences, the topological phase diagram of the two systems also exhibits similar behaviors, indicating that the topological phase transition is mainly determined by similar interactions in the two systems regardless of their structural difference. This is also reflected by the observation that the transition point between the normal insulator and the quantum spin Hall state in both systems follows a universal linear scaling relation for topological phase transitions.
Title:
The origin of the modulated structure in Sr2CuO3+delta (delta=0.4): [CuO2] in-plane oxygen vacancy or apical oxygen vacancy?
Authors:
Shen, X; Cao, LP; Zhao, JF; Wang, WP; Liu, QQ; Yao, Y; Li, JJ; Gu, CZ; Chen, MW; Jin, CQ; Yu, RC Author Full Names: Shen, Xi; Cao, Li-Peng; Zhao, Jian-Fa; Wang, Wei-Peng; Liu, Qing-Qing; Yao, Yuan; Li, Jun-Jie; Gu, Chang-Zhi; Chen, Ming-Wei; Jin, Chang-Qing; Yu, Ri-Cheng
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 10.1111/jace.16662
Abstract:
We propose the question of the modulated structures of copper oxide is caused by the [CuO2] in-plane oxygen vacancy or apical oxygen vacancy. Sr2CuO3+delta single-crystal samples were prepared using high-temperature and high-pressure methods. The major phase of Sr2CuO3+delta (delta = 0.4) single-crystal system is found to be constituted by the 5 root 2 a modulated structure with the Fmmm space group, which originates from the [CuO2] in-plane oxygen vacancy appearing in octahedral Cu-O. Besides, the presence of the [CuO2] in-plane oxygen vacancy may obliterate the superconductivity of the system. Experimental results deduce that the oxygen vacancy may appear in the apical oxygen sites in high-temperature copper oxide superconductors.
Title:
Formation of an Intermediate Valence Icosahedral Quasicrystal in the Au-Sn-Yb System
Authors:
Yamada, T; Nakamura, Y; Watanuki, T; Machida, A; Mizumaki, M; Nitta, K; Sato, A; Matsushita, Y; Tsai, AP Author Full Names: Yamada, Tsunetomo; Nakamura, Yoko; Watanuki, Tetsu; Machida, Akihiko; Mizumaki, Masaichiro; Nitta, Kiyofumi; Sato, Akira; Matsushita, Yoshitaka; Tsai, An-Pang
Source:
INORGANIC CHEMISTRY, 58 (14):9181-9186; 10.1021/acs.inorgchem.9b00801 JUL 15 2019
Abstract:
We report on the formation of a new icosahedral quasicrystal (iQC) in the Au-Sn-Yb alloy system. This iQC has a primitive icosahedral lattice with a lattice constant a(ico) of 0.5447(7) nm and a composition that was determined to be Au60.0Sn26.7Yb13.3. X-ray absorption spectroscopy measurement of the near Yb L-3 edge demonstrates that the Yb valence in the iQC is an intermediate valence between divalent (4f(14)) and trivalent (4f(13)) at ambient pressure and was determined to be 2.18+. The results are compared to those for a corresponding 2/1 cubic approximant crystal. The formation of this new iQC is discussed in terms of the atomic size factor (delta) and the valence electron-to-atom ratio (e/a).

Update: 15-Aug-2019

Title:
V-51-NMR study on the S=1/2 square lattice antiferromagnet K2V3O8
Authors:
Takeda, H; Yasuoka, H; Yoshida, M; Takigawa, M; Ghimire, NJ; Mandrus, D; Sales, BC Author Full Names: Takeda, H.; Yasuoka, H.; Yoshida, M.; Takigawa, M.; Ghimire, N. J.; Mandrus, D.; Sales, B. C.
Source:
PHYSICAL REVIEW B, 100 (5):10.1103/PhysRevB.100.054406 AUG 5 2019
Abstract:
Static and dynamic properties of the quasi-two-dimensional antiferromagnet K2V3O8 have been investigated by V-51-NMR experiments on nonmagnetic V5+ sites. Above the structural transition temperature T-S = 115 K, NMR spectra are fully compatible with the P4bm space-group symmetry. The formation of superstructure below T-S causes splitting of the NMR lines, which get broadened at lower temperatures so that individual peaks are not well resolved. Evolution of NMR spectra with magnetic field along the c axis below the magnetic transition temperature T-N similar to 4 K is qualitatively consistent with a simple Neel order and a spin-flop transition. However, a broad feature of the spectra does not rule out possible incommensurate spin structure. The spin-lattice relaxation rate 1/T-1 below T-N shows huge enhancement for a certain range of magnetic field, which is independent of temperature and attributed to cross relaxation due to anomalously large nuclear spin-spin coupling between V5+ and magnetic V4+ sites. The results indicate strong gapless spin fluctuations, which could arise from incommensurate orders or complex spin textures.
Title:
Interpretation of diffuse scattering using superspace crystallography
Authors:
Schmidt, EM; Neder, RB Author Full Names: Schmidt, Ella Mara; Neder, Reinhard B.
Source:
PHYSICAL REVIEW B, 100 (5):10.1103/PhysRevB.100.054201 AUG 2 2019
Abstract:
Single-crystal diffuse scattering is generally interpreted using correlation parameters that describe probabilities for certain configurations on a local scale. In this paper we present an interpretation of diffuse maxima using a disordered superspace approach. In (D + d)-dimensional superspace two modulation functions are disordered along the superspace axis a(s,i) for i = 1, . . . , D, while the periodicity along the internal dimensions is maintained. This simple approach allows the generation of substitutionally disordered model structures that show diffuse maxima of any width at any position in reciprocal space. The extinction rules that are introduced by superspace symmetry are also fulfilled by the diffuse maxima from structures generated using the disordered superspace approach. In this paper we demonstrate the disordered superspace approach using a simple two-dimensional binary substitutionally disordered system. The extension of the approach to (3 + d)-dimensional superspace is trivial. The treatment of displacement and magnetic disorder as well as size-effect-like distortions in a similar manner is possible.
Title:
Conduction electrons in aperiodic versus periodic structures: An ESR study of quasicrystalline i-Y(Gd)-Cd and its approximant Y(Gd)Cd-6
Authors:
Cabrera-Baez, M; Avila, MA; Rettori, C Author Full Names: Cabrera-Baez, M.; Avila, M. A.; Rettori, C.
Source:
PHYSICAL REVIEW B, 100 (1):10.1103/PhysRevB.100.014207 JUL 31 2019
Abstract:
A formal description of collective electronic states in condensed-matter systems lacking long-range periodicity remains a theoretical challenge. To experimentally explore the differences in electronic and magnetic behavior between metallic quasicrystals (QCs) and their conventional crystalline analogs [quasicrystal approximants (QCAs)], we have grown single crystals of Y1-xGdx-Cd6 (QCA) together with their QC counterparts i-Y1-xGdx-Cd for x = 0.006, 0.01, 0.1, and 1.00, and we carried out comparative T-dependent electron spin resonance (ESR) measurements. On the high Gd concentration side, x = 1.00, we confirm that GdCd6 adopts an antiferromagnetic ground state below T-N similar to 22 K, whereas i-Gd-Cd presents spin-glass-like behavior showing similar local and dynamical properties from the point of view of ESR. For the diluted samples, our ESR experimental results show similar local conduction electron polarization behavior at the Gd3+ site in all QC/QCA pairs investigated, supporting the validity of using QCAs as periodic representations of QCs in terms of short-range electronic interactions. However, there is a measurable difference in the Korringa relaxation rate (spin-flip relaxation process between the localized Gd3+ 4f electron and the delocalized s-type conduction electrons at the Fermi surface) between the QC/QCA pairs probably associated with the lack of periodicity. We expect that our comparative ESR study may provide support and motivation for the development of new theoretical approaches toward a generalized band-structure theory, contemplating condensed-matter systems beyond the scope of traditional periodicity.

Update: 8-Aug-2019

Title:
Elastic Properties of a FeGe2 Single Crystal
Authors:
Zainullina, RI; Milyaev, MA Author Full Names: Zainullina, R. I.; Milyaev, M. A.
Source:
PHYSICS OF THE SOLID STATE, 61 (7):1278-1283; 10.1134/S1063783419070321 JUL 2019
Abstract:
The report presents the results of studying the temperature dependences of the velocities of propagation of longitudinal and torsion waves and the internal friction in a tetragonal FeGe2 single crystal along crystallographic axes [100], [110], and [001]. At temperatures of magnetic phase transitions of T-1 approximate to 263 K and T-2 approximate to 289 K an abrupt decrease of sound velocities is detected. A high anisotropy of the internal friction is observed in the region of existence of an incommensurate magnetic structure (T-1 <= T <= T-2).
Title:
Transition Kinetics of Self-Assembled Supramolecular Dodecagonal Quasicrystal and Frank-Kasper sigma Phases in AB(n) Dendron-Like Giant Molecules
Authors:
Feng, XY; Liu, GX; Guo, D; Lang, KN; Zhang, RM; Huang, JH; Su, ZB; Li, YW; Huang, MJ; Li, T; Cheng, SZD Author Full Names: Feng, Xueyan; Liu, Gengxin; Guo, Dong; Lang, Kening; Zhang, Ruimeng; Huang, Jiahao; Su, Zebin; Li, Yiwen; Huang, Mingjun; Li, Tao; Cheng, Stephen Z. D.
Source:
ACS MACRO LETTERS, 8 (7):875-881; 10.1021/acsmacrolett.9b00287 JUL 2019
Abstract:
A series of noncrystalline AB dendron-like giant molecules DPOSS MPOSSn (n = 2-6, DPOSS: hydrophilic polyhedral oligomeric silsesquioxane (POSS) cage; MPOSS: hydrophobic POSS cage) were synthesized. These samples present a thermodynamically stable phase formation sequence from the hexagonal cylinder phase (plane group of P6mm), to the Frank Kasper (F-K) A15 phase (space group of Pm (3) over barn), and further to the F-K sigma phase (space group of P4(2)/mnm), with increasing the number of MPOSS in a single molecule (n, from 2 to 6). Moreover, for DPOSS MPOSS5 and DPOSS-MPOSS6, an intriguing dodecagonal quasicrystal (DQC) structure has been identified and revealed as a kinetic favorable metastable phase at lower temperatures, while the thermodynamically stable phase is the a phase. The detailed investigation of the transition kinetics between the DQC and a phase in these samples makes it possible to identify how the self-assembly directs the phase transition in terms of molecular and supramolecular aspects.

Update: 1-Aug-2019

Title:
TEM study of incommensurate superstructure in Pb1-0.5xNbx((Zr0.52Sn0.48)(0.955)Ti-0.045)(1-x)O-3 ceramics with 0-1 switching characteristic strain and high energy storage density
Authors:
Lyu, CG; Liu, YF; Lyu, YN; Qian, H; Li, M; Chen, FJ; Xi, H Author Full Names: Lyu, Chongguang; Liu, Yunfei; Lyu, Yinong; Qian, Hao; Li, Min; Chen, Fujun; Xi, Hao
Source:
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 30 (13):12375-12381; 10.1007/s10854-019-01595-4 JUL 2019
Abstract:
Pb1-0.5xNbx((Zr0.52Sn0.48)(0.955)Ti-0.045)(1-x)O-3(PNZST-100x (x=0.01, 0.02, 0.03, 0.04)) antiferroelectric (AFE) ceramics were prepared using a solid-state method. X-ray diffraction analysis indicates a structural evolution from the tetragonal phase to the pseudocubic phase. When x=0.02, the ceramic exhibits an enhanced energy storage density of 1.37J/cm(3), and a strain, with 0-1 switching characteristics, of 0.22%. Selected-area electron diffraction (SAED), high-resolution transmission electron microscopy imaging, and in-situ TEM analyses indicate that there are two kinds of superlattice reflections, including the 1/2(hkl) superlattice reflection (h, k, and l: all odd) and 1/6.67(a+b) one-dimensional incommensurate superlattice reflections. The origin of the 1/2(hkl) superlattice reflection was the tilting of a(-)a(-)a(-) oxygen octahedra. Therefore, the 1/2(hkl) reflections were no longer superlattice reflections, but fundamental reflections in the trigonal system; hence, the reciprocal vector was re-expressed as H, where h, k, and l are integers and (-h+k+l)=3n. The incommensurate structure of the PNZST-2 ceramic originated from the displacement of Pb2+.
Title:
Bridging the local configurations and crystalline counterparts of bulk metallic glass by nanocalorimetry
Authors:
Zhao, BG; Yang, B; Rodriguez-Viejo, J; Wu, MN; Schick, C; Zhai, QJ; Gao, YL Author Full Names: Zhao, Bingge; Yang, Bin; Rodriguez-Viejo, Javier; Wu, Mannan; Schick, Christoph; Zhai, Qijie; Gao, Yulai
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 8 (4):3603-3611; 10.1016/j.jmrt.2019.05.023 JUL-AUG 2019
Abstract:
The structural understanding of crystallization in bulk metallic glasses (BMGs) has attracted much attention while rapid crystallization occurring under controllable conditions is less involved. In this study, a Ce68Al10Cu20Co2 (at.%) BMG was thermally devitrified by differential scanning calorimetry (DSC) and nanocalorimetry. At a heating rate of 10 K/min by DSC, AlCe3 and Ce are the major crystalline phases after devitrification while Al13Co4 quasicrystals and Ce are the dominant phases in the crystallization products at a heating rate of 5000 K/s by nanocalorimetry. Attributing to the covalent-like bond in Al-Co atom pairs, Al13Co4 quasicrystals precipitate in the primary crystallization and work as the precursors associating local atomic configurations in the glassy state with crystalline phases after crystallization. Attributing to the enhanced mobility of Cu atoms, compositional redistribution occurs in the as-cast sample. On nanocalorimetry heating, an unambiguous discrepancy in the nucleation and growth of the nano-sized Al13Co4 quasicrystals is thus triggered, contributing to an obvious difference in the crystal size. This research unveils the distinct crystallization behaviors of Ce-based BMG on rapid heating. The formation of quasicrystals demonstrates the multi-stage crystallization on rapid heating and bridges the structural gap between local atomic configurations of metallic glasses and crystalline phases. (C) 2019 The Authors. Published by Elsevier B.V.

Update: 25-Jul-2019

Title:
New stable icosahedral quasicrystal in the system Al-Cu-Co-Fe
Authors:
Klyueva, M; Shulyatev, D; Andreev, N; Tabachkova, N; Sviridova, T; Suslov, A Author Full Names: Klyueva, Maria; Shulyatev, Dmitry; Andreev, Nikolay; Tabachkova, Natalia; Sviridova, Tatiana; Suslov, Alexey
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 801 473-477; 10.1016/j.jallcom.2019.06.056 SEP 15 2019
Abstract:
Based on the conceptual Al-Cu-(Fe + Co) phase diagram we found an optimal initial composition and developed a method to grow Al-Cu-Fe-Co single-grain quasicrystals. Our original two-stage cooling process includes (i) fast cooling of the melt down to the quasicrystalline single phase region with rate of similar to 165 K/h to prevent growing of nonquasicrystalline phases in the melt, and (ii) slow cooling down with rate of similar to 2-3 K/h to grow large (mm-size) single-grain quasicrystals. As a result a new stable quaternary Al-based icosahedral quasicrystal has been obtained. The chemical composition of the grown quasicrystal determined by both the energy dispersive X-ray analysis and inductively coupled plasma mass spectrometry was Al64.36Cu22.20CO3.05Fe10.39. Powder XRD and selected area electron diffraction were carried out for the phase identification and confirmed the icosahedral structure. The temperature dependencies of the electrical resistance measured on the oriented samples in the temperature range of 1.4 K-300 K is typical for icosahedral quasicrystals. (C) 2019 Elsevier B.V. All rights reserved.
Title:
Direct observation of growth and stability of Al-Cu-Fe quasicrystal thin films
Authors:
Parsamehr, H; Yang, CL; Liu, WT; Chen, SW; Chang, SY; Chen, LJ; Tsai, AP; Lai, CH Author Full Names: Parsamehr, Hadi; Yang, Chun-Liang; Liu, Wei-Ting; Chen, Shi-Wei; Chang, Shou-Yi; Chen, Lih-Juann; Tsai, An Pang; Lai, Chih-Huang
Source:
ACTA MATERIALIA, 174 1-8; 10.1016/j.actamat.2019.05.024 AUG 1 2019
Abstract:
Al-Cu-Fe based quasicrystal thin films exhibit unique surface and mechanical properties. To better understand the formation of the quasicrystal thin films, we observe direct growth of quasicrystals, prepared in a multilayer Al-Cu-Fe thin films with subsequent heat treatment, by in-situ synchrotron x-ray diffraction and in-situ transmission electron microscopy during heating and cooling. Using these two methods, we show that the ternary phase is more thermodynamically stable compared to the binary phases at temperature higher than 470 degrees C during the heating process, and quasicrystal formation occurs during the cooling process, specifically at 660 degrees C, after the sample has reached a liquid state. To distinguish quasicrystal from approximant crystals in the obtained thin film samples, we use high resolution x-ray diffraction to analyze the sample at room temperature. We reveal that the peak broadening increases monotonically along the twofold, threefold, and fivefold high-symmetry directions with the physical scattering vector but does not have systematic dependence on the phason momentum, which suggests that the thin film sample is indeed a quasicrystal instead of approximant crystals and it is almost free of phason strain. Our study provides a complete understanding of the growth mechanism for thin film Al-Cu-Fe quasicrystals, which is of particular importance for developing versatile applications of quasicrystal thin films. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Enhanced electrochemical hydrogen storage performance of Ti49Zr26Ni25 alloy by doping with Pd nanoparticles deposited MWCNTs
Authors:
Zhang, L; Zhang, YN; Lv, DF; Liu, H; Zhao, JX; Chen, P; Liu, WQ Author Full Names: Zhang, Lei; Zhang, Yinan; Lv, Dongfang; Liu, Heng; Zhao, Jianxun; Chen, Peng; Liu, Wanqiang
Source:
SOLID STATE SCIENCES, 94 138-144; 10.1016/j.solidstatesciences.2019.06.007 AUG 2019
Abstract:
Mechanical alloying and subsequent annealing are used to fabricate the Ti49Zr26Ni25 quasicrystal. A complexation-reduction method is employed to obtain the Pd deposited multiwall carbon nanotubes (Pd/MWCNTs). Composite of Ti49Zr26Ni25 mixed with Pd/MWCNTs is obtained via ball-milling. The composite alloy combines the characteristics of Pd in conjunction with the advantages of MWCNTs. Pd exhibits outstanding electrocatalytic activity and MWCNTs provide high conductivity and large specific surface area. The electrochemical performance and kinetics properties of the alloy electrodes for Ni/MH secondary batteries are studied. A maximum discharge capacity of 274.6 mAh/g is achieved for Ti49Zr26Ni25 + Pd/MWCNTs, remarkably higher than that for original Ti49Zr26Ni25 (208.9 mAh/g). In addition, the composite shows improved cyclic stability and high-rate dischargeability. The synergistic effect of Pd and MWCNTs can decrease charge-transfer resistance and accelerate the hydrogen transmission, thus improving the reaction kinetics and electrochemical activity of the electrode.
Title:
Conventional superconductivity in quasicrystals
Authors:
Araujo, RN; Andrade, EC Author Full Names: Araujo, Ronaldo N.; Andrade, Eric C.
Source:
PHYSICAL REVIEW B, 100 (1):10.1103/PhysRevB.100.014510 JUL 11 2019
Abstract:
Motivated by a recent experimental observation of superconductivity in the Al-Zn-Mg quasicrystal, we study the low-temperature behavior of electrons moving in the quasiperiodic potential of the Ammann-Beenker tiling in the presence of a local attraction. We employ the Bogoliubov-de Gennes approach for approximants of different sizes and determine the local pairing amplitude Delta(i) as well its spatial average, Delta(0), the superconducting order parameter. Due to the lack of periodicity of the octagonal tiling, the resulting superconducting state is inhomogeneous, but we find no evidence of the superconductivity islands, as observed in disordered systems, with Delta(i) -> 0 at T-c for all sites. In the weak-coupling regime, we find that the superconducting order parameter depends appreciably on the approximant size only if the Fermi energy sits at a pseudogap in the noninteracting density of states, with Delta(0) decreasing as the system size increases. These results are in line with the experimental observations for the Al-Zn-Mg quasicrystal, and they suggest that, despite their electronic structure, quasicrystals are prone to display conventional BCS-like superconductivity.
Title:
Tomonaga-Luttinger Liquid Spin Dynamics in the Quasi-One-Dimensional Ising-Like Antiferromagnet BaCo2V2O8
Authors:
Faure, Q; Takayoshi, S; Simonet, V; Grenier, B; Mansson, M; White, JS; Tucker, GS; Ruegg, C; Lejay, P; Giamarchi, T; Petit, S Author Full Names: Faure, Quentin; Takayoshi, Shintaro; Simonet, Virginie; Grenier, Beatrice; Mansson, Martin; White, Jonathan S.; Tucker, Gregory S.; Ruegg, Christian; Lejay, Pascal; Giamarchi, Thierry; Petit, Sylvain
Source:
PHYSICAL REVIEW LETTERS, 123 (2):10.1103/PhysRevLett.123.027204 JUL 10 2019
Abstract:
Combining inelastic neutron scattering and numerical simulations, we study the quasi-one-dimensional Ising anisotropic quantum antiferromagnet BaCo2V2O8 in a longitudinal magnetic field. This material shows a quantum phase transition from a Neel ordered phase at zero field to a longitudinal incommensurate spin density wave at a critical magnetic field of 3.8 T. Concomitantly, the excitation gap almost closes and a fundamental reconfiguration of the spin dynamics occurs. These experimental results are well described by the universal Tomonaga-Luttinger liquid theory developed for interacting spinless fermions in one dimension. We especially observe the rise of mainly longitudinal excitations, a hallmark of the unconventional low-field regime in Ising-like quantum antiferromagnetic chains.
Title:
Structural and electronic properties of the incommensurate host-guest Bi-III phase
Authors:
Kartoon, D; Makov, G Author Full Names: Kartoon, D.; Makov, G.
Source:
PHYSICAL REVIEW B, 100 (1):10.1103/PhysRevB.100.014104 JUL 9 2019
Abstract:
At high pressure, bismuth acquires a complex incommensurate host-guest structure, only recently discovered. Characterizing the structure and properties of this incommensurate phase from first principles is challenging owing to its nonperiodic nature. In this study we use large-scale density functional theory calculations to model commensurate approximants to the Bi-III phase, and in particular to describe the atomic modulations with respect to their ideal positions, shown here to strongly affect the electronic structure of the lattice and its stability. The equation of state and range of stability of Bi-III are reproduced in excellent agreement with experiment using a fully relativistic model. We demonstrate the importance of employing large unit cells for the accurate description of the geometric and electronic configuration of Bi-III. In contrast, accurate description of the equation of state of bismuth is found to be primarily sensitive to the choice of pseudopotential and exchange-correlation function, while almost completely insensitive to the commensurate approximation.
Title:
Effect of heat treatment on the microstructure and micromechanical properties of the rapidly solidified Mg61.7Zn34Gd4.3 alloy containing icosahedral phase
Authors:
Luo, WB; Xue, ZY; Mao, WM Author Full Names: Luo, Wen-bo; Xue, Zhi-yong; Mao, Wei-min
Source:
INTERNATIONAL JOURNAL OF MINERALS METALLURGY AND MATERIALS, 26 (7):869-877; 10.1007/s12613-019-1799-4 JUL 2019
Abstract:
In this paper, the microstructure evolution of the rapidly solidified (RS) Mg61.7Zn34Gd4.3 (at%, atomic ratio) alloy at high temperatures was investigated. The hardness and elastic modulus of the main precipitated phases were also analyzed and compared with those of the alpha-Mg matrix on the basis of nanoindentation tests. The results show that the RS alloy consists of either a petal-like icosahedral quasicrystal (IQC) phase (similar to 20 mu m) and block-shaped H1 phase (similar to 15 mu m) or IQC particles with an average grain size of similar to 107 nm as well as a small proportion of amorphous phase, which mainly depends on the holding time at the liquid temperature and the thickness of the ribbons. The IQC phase gradually transforms at 400 degrees C to a short-rod-shaped mu-phase (Mg28.6Zn63.8Gd7.7) with a hexagonal structure. The hardness of the IQC phase is higher than that of H1 phase, and both phases exhibit a higher hardness than the alpha-Mg matrix and the mu-phase. The elasticity of the H1 phase is superior to that of the alpha-Mg matrix. The IQC phase possesses a higher elastic modulus than H1 phase. The easily formed H1 phase exhibits the poorest plastic deformation capacity among these phases but a higher elastic modulus than the alpha-Mg matrix.

Update: 17-Jul-2019

Title:
Comprehensive study of the magnetic phase transitions in Tb3Co combining thermal, magnetic and neutron diffraction measurements
Authors:
Herrero, A; Oleaga, A; Gubkin, AF; Frontzek, MD; Salazar, A; Baranov, NV Author Full Names: Herrero, A.; Oleaga, A.; Gubkin, A. F.; Frontzek, M. D.; Salazar, A.; Baranov, N., V
Source:
INTERMETALLICS, 111 10.1016/j.intermet.2019.106519 AUG 2019
Abstract:
A comprehensive study of the magnetic phase transitions in Tb3Co has been undertaken combining different techniques. Using single crystal neutron diffraction in the paramagnetic state a weak crystal structure distortion from the room temperature orthorhombic structure of the Fe3C type described with the Pnma space group toward structure with lower symmetry has been observed with cooling below 100 K. At 81 K there is a second order phase transition to an antiferromagnetic incommensurate phase with the propagation vector k = (0.155, 0, 0). As derived from thermal diffusivity measurements, the critical exponents for this transition are very close to the 3D-Heisenberg universality class, proving that the magnetic interactions are short-range but with a deviation from perfect isotropy due to crystal field effects. At T-2 approximate to 70 K there is another magnetic phase transition to a ferromagnetic state whose character is shown to be weakly first order. The low temperature magnetic state has a non-coplanar ferromagnetic structure with strong ferromagnetic components of Tb magnetic moments along the crystallographic c-axis. The application of an external magnetic field B = 2 T along the c crystallographic axis suppresses the incommensurate antiferromagnetic phase and gives rise to the ferromagnetic phase. The magnetic entropy peak change as well as the refrigerant capacity indicate that Tb3Co is a competitive magnetocaloric material in this temperature range.
Title:
Significantly improved plasticity of bulk metallic glasses by introducing quasicrystal within high energy glass matrix
Authors:
Liu, BC; Zhang, QD; Wang, HJ; Li, XY; Zu, FQ Author Full Names: Liu, Bao-Chuan; Zhang, Qi-Dong; Wang, Hui-Juan; Li, Xiao-Yun; Zu, Fang-Qiu
Source:
INTERMETALLICS, 111 10.1016/j.intermet.2019.106504 AUG 2019
Abstract:
Many studies consistently report that quasicrystal-BMG (bulk metallic glass) composites usually exhibit limited plasticity. In this work, however, we demonstrate that quasicrystal embedded in high energy glass matrix could remarkably improve the plasticity of BMGs. By the method, a Zr-based quasicrystal-BMG composite successfully exhibits > 50.0% compressive plasticity and > 6.6% bending strain, which is much higher than similar to 3.0% compressive plasticity in the monolithic as-cast BMG. After introducing quasicrystal within high energy glass matrix, the lower formation energy and difficulty to propagate of shear bands contribute to the enhanced plasticity. This work provides a new strategy to overcome the brittleness of BMGs and greatly promotes the practical value of quasicrystal in improving plasticity of BMGs.
Title:
Microstructural evolution and age-hardening behavior of quasicrystal-reinforced Mg-Dy-Zn alloy
Authors:
Bi, GL; Han, YX; Jiang, J; Jiang, CH; Li, YD; Ma, Y Author Full Names: Bi, Guang-Li; Han, Yu-Xiang; Jiang, Jing; Jiang, Chun-Hong; Li, Yuan-Dong; Ma, Ying
Source:
RARE METALS, 38 (8):739-745; 10.1007/s12598-018-1089-8 AUG 2019
Abstract:
Microstructural evolution and age-hardening behavior of Mg-2Dy-6Zn (at%) alloy during solid-solution and aging treatment were investigated. The microstructure of as-cast alloy is composed of -Mg, Mg3DyZn6 (I) phase, Mg3Dy2Zn3 (W) phase, Mg(Zn,Dy) phase and a small amount of Mg0.97Zn0.03 phases. After solid-solution treatment (480 degrees C, 12h), all the I phases and most W phases dissolve into -Mg matrix and the remainder W phases transform into Mg(Dy,Zn) phase and MgDy3 phase. During aging treatment, I phase and small amounts of W phases co-precipitate from -Mg matrix, respectively. The alloy exhibits a peak hardness of HV 77.5 at 200 degrees C for 8h. The excellent age-hardening behavior of alloy is mainly attributed to the co-precipitation strengthening of I and W phases.
Title:
Microstructure and mechanical properties of AZ31 magnesium alloy reinforced by I-phase
Authors:
Wu, HR; Du, WB; Li, SB; Liu, K; Wang, ZH Author Full Names: Wu, Hai-Rong; Du, Wen-Bo; Li, Shu-Bo; Liu, Ke; Wang, Zhao-Hui
Source:
RARE METALS, 38 (8):733-738; 10.1007/s12598-014-0390-4 AUG 2019
Abstract:
The particles of Mg-Zn-Gd icosahedral quasi-crystal master alloy were added into the AZ31 alloy by the repeated plastic working (RPW) process in order to improve the mechanical properties of the AZ31 alloy at room temperature. The microstructure and tensile properties of composites were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and tensile testing machine at room temperature. The results suggest that the RPW process can effectively refine the matrix and make the I-phase particles distribute uniformly. The ultimate tensile strength and the yield strength of the composites reach their maximum values of 362.3 and 330.5MPa, respectively, when the amount of I-phase particles added is 10%. Meanwhile, the elongation of the composites decreases sharply.
Title:
Disordered Jahn-Teller-Polaron States in the Simple Perovskite Manganite Ca(1-x)La(x)nO(3) with 0.15 <= x <= 0.28
Authors:
Endo, T; Goto, T; Inoue, Y; Koyama, Y Author Full Names: Endo, Tomoki; Goto, Takamasa; Inoue, Yasuhide; Koyama, Yasumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (7):10.7566/JPSJ.88.074708 JUL 15 2019
Abstract:
Among orbital-ordered states in manganites with strongly correlated electronic systems, both the C-type orbital-ordered (Ctype-OO) state and the charge- and orbital-ordered (COO) state have been reported in the simple perovskite Ca1-xLaxMnO3 (CLMO) with 0.15 <= x <= 0.28. To understand their formation from the disordered Pnma (DO) state with orthorhombic symmetry, the crystallographic features of prepared CLMO samples with 0.15 <= x <= 0.28 were examined mainly by transmission electron microscopy. When the temperature was lowered from the orthorhombic DO state for 0.15 <= x <= 0.23, referred to as Region I, the Ctype-OO state with monoclinic-P2(1)/m symmetry appeared via a disordered Jahn-Teller polaron (DJTP) state, which exhibited characteristic diffuse scattering around each DO reflection in electron diffraction patterns. For 0.23 <= x <= 0.28 as Region II, cooling from the DO state resulted in the appearance of the COO state via a similar DJTP state. In patterns obtained from the COO state, satellite reflections characterizing the state were confirmed to be due to both transverse and longitudinal lattice modulations. It was also found that the DJTP states in Regions I and II were present in T-N >= T >= T-Ct(yp)e-OO and T >= T-COO), respectively, and were identified as the precursor states, which appear prior to the formation of the Ctype-OO and COO states.
Title:
Emergent symmetries in block copolymer epitaxy
Authors:
Ding, Y; Gadelrab, KR; Rodriguez, KM; Huang, HJ; Ross, CA; Alexander-Katz, A Author Full Names: Ding, Yi; Gadelrab, Karim R.; Rodriguez, Katherine Mizrahi; Huang, Hejin; Ross, Caroline A.; Alexander-Katz, Alfredo
Source:
NATURE COMMUNICATIONS, 10 10.1038/s41467-019-10896-5 JUL 5 2019
Abstract:
The directed self-assembly (DSA) of block copolymers (BCPs) has shown promise in fabricating customized two-dimensional (2D) geometries at the nano- and meso-scale. Here, we discover spontaneous symmetry breaking and superlattice formation in DSA of BCP. We observe the emergence of low symmetry phases in high symmetry templates for BCPs that would otherwise not exhibit these phases in the bulk or thin films. The emergence phenomena are found to be a general behavior of BCP in various template layouts with square local geometry, such as 4(4) and 3(2)434 Archimedean tilings and octagonal quasicrystals. To elucidate the origin of this phenomenon and confirm the stability of the emergent phases, we implement self-consistent field theory (SCFT) simulations and a strong-stretching theory (SST)-based analytical model. Our work demonstrates an emergent behavior of soft matter and draws an intriguing connection between 2-dimensional soft matter self-assembly at the mesoscale and inorganic epitaxy at the atomic scale.
Title:
Magnetic phase diagram of the quantum spin chain compound SrCo2V2O8: a single-crystal neutron diffraction study
Authors:
Shen, L; Zaharko, O; Obirk, J; Jellyman, E; He, Z; Blackburn, E Author Full Names: Shen, L.; Zaharko, O.; Birk, J. O.; Jellyman, E.; He, Z.; Blackburn, E.
Source:
NEW JOURNAL OF PHYSICS, 21 10.1088/1367-2630/ab2b7a JUL 3 2019
Abstract:
We explore magnetic order in the quantum spin chain compound SrCo2V2O8 up to 14.9 T and down to 50 mK, using single-crystal neutron diffraction. Upon cooling in zero-field, commensurate antiferromagnetic (C-AFM) order with modulation vector k(C) = (0, 0, 1) develops below T-N similar or equal to 5.0 K. Applying an external magnetic field (H parallel to c axis) destabilizes this C-AFM order, leading to an order-disorder transition between T-N and similar to 1.5 K. Below 1.5 K, a commensurate to incommensurate (IC-AFM) transition occurs at 3.9 T, above which the magnetic reflections can be indexed by k(1C) = (0, 0,1 +/- delta l). The incommensurability N scales monotonically with H until the IC-AFM order disappears around 7.0 T. Magnetic reflections modulated by k(C) emerge again at higher fields. While the characters of the C-AFM, IC-AFM and the emergent AFM order in SrCo2V2O8 appear to fit the descriptions of the Neel, longitudinal spin density wave and transverse AFM order observed in the related compound BaCo2V2O8, our results also reveal several unique signatures that are not present in the latter, highlighting the inadequacy of mean-field theory in addressing the complex magnetic order in systems of this class.
Title:
X-ray magnetic diffraction under high pressure
Authors:
Wang, YS; Rosenbaum, TF; Feng, Y Author Full Names: Wang, Yishu; Rosenbaum, T. F.; Feng, Yejun
Source:
IUCRJ, 6 507-520; 10.1107/S2052252519007061 4 JUL 2019
Abstract:
Advances in both non-resonant and resonant X-ray magnetic diffraction since the 1980s have provided researchers with a powerful tool for exploring the spin, orbital and ion degrees of freedom in magnetic solids, as well as parsing their interplay. Here, we discuss key issues for performing X-ray magnetic diffraction on single-crystal samples under high pressure (above 40 GPa) and at cryogenic temperatures (4 K). We present case studies of both non-resonant and resonant X-ray magnetic diffraction under pressure for a spin-flip transition in an incommensurate spin-density-wave material and a continuous quantum phase transition of a commensurate all-in-all-out antiferromagnet. Both cases use diamond-anvil-cell technologies at third-generation synchrotron radiation sources. In addition to the exploration of the athermal emergence and evolution of antiferromagnetism discussed here, these techniques can be applied to the study of the pressure evolution of weak charge order such as charge-density waves, antiferro-type orbital order, the charge anisotropic tensor susceptibility and charge superlattices associated with either primary spin order or softened phonons.
Title:
Identification of Phase Transitions and Metastability in Dynamically Compressed Antimony Using Ultrafast X-Ray Diffraction
Authors:
Coleman, AL; Gorman, MG; Briggs, R; McWilliams, RS; McGonegle, D; Bolme, CA; Gleason, AE; Fratanduono, DE; Smith, RF; Galtier, E; Lee, HJ; Nagler, B; Granados, E; Collins, GW; Eggert, JH; Wark, JS; McMahon, MI Author Full Names: Coleman, A. L.; Gorman, M. G.; Briggs, R.; McWilliams, R. S.; McGonegle, D.; Bolme, C. A.; Gleason, A. E.; Fratanduono, D. E.; Smith, R. F.; Galtier, E.; Lee, H. J.; Nagler, B.; Granados, E.; Collins, G. W.; Eggert, J. H.; Wark, J. S.; McMahon, M. I.
Source:
PHYSICAL REVIEW LETTERS, 122 (25):10.1103/PhysRevLett.122.255704 JUN 28 2019
Abstract:
Ultrafast x-ray diffraction at the LCLS x-ray free electron laser has been used to resolve the structural behavior of antimony under shock compression to 59 GPa. Antimony is seen to transform to the incommensurate, host-guest phase Sb-II at similar to 11 GPa, which forms on nanosecond timescales with ordered guest-atom chains. The high-pressure bcc phase Sb-III is observed above similar to 15 GPa, some 8 GPa lower than in static compression studies, and mixed Sb-III/liquid diffraction are obtained between 38 and 59 GPa. An additional phase which does not exist under static compression, Sb-I', is also observed between 8 and 12 GPa, beyond the normal stability field of Sb-I, and resembles Sb-I with a resolved Peierls distortion. The incommensurate Sb-II high-pressure phase can be recovered metastably on release to ambient pressure, where it is stable for more than 10 ns.
Title:
Maximum supercooling studies in Ti39.5Zr39.5Ni21, Ti40Zr30Ni30, and Zr80Pt20 liquids-Connecting liquid structure and the nucleation barrier
Authors:
Sellers, ME; Van Hoesen, DC; Gangopadhyay, AK; Kelton, KF Author Full Names: Sellers, M. E.; Van Hoesen, D. C.; Gangopadhyay, A. K.; Kelton, K. F.
Source:
JOURNAL OF CHEMICAL PHYSICS, 150 (20):10.1063/1.5096188 MAY 28 2019
Abstract:
Almost three quarters of a century ago, Charles Frank proposed that the deep supercooling observed in metallic liquids is due to icosahedral short-range order (ISRO), which is incompatible with the long-range order of crystal phases. Some evidence in support of this hypothesis had been published previously. However, those studies were based on a small population of maximum supercooling measurements before the onset of crystallization. Here, the results of a systematic statistical study of several hundred maximum supercooling measurements on Ti39.5Zr39.5Ni21, Ti40Zr30Ni30, and Zr80Pt20 liquids are presented. Previous X-Ray and neutron scattering studies have shown that the structures of these liquid alloys contain significant amounts of ISRO. The results presented here show a small work of critical cluster formation (W* = 31-40 k(B)T) from the analysis of the supercooling data for the Ti39.5Zr39.5Ni21 liquid, which crystallizes to a metastable icosahedral quasicrystal. A much larger value (W* = 54-79 k(B)T and W* = 60-99 k(B)T) was obtained for the Ti40Zr30Ni30 and Zr80Pt20 liquids, respectively, which do not crystallize to an icosahedral quasicrystal. Taken together, these results significantly strengthen the validity of Frank's hypothesis. Published under license by AIP Publishing.
Title:
Chemical Bonding and Physical Properties in Quasicrystals and Their Related Approximant Phases: Known Facts and Current Perspectives
Authors:
Barber, EM Author Full Names: Macia Barber, Enrique
Source:
APPLIED SCIENCES-BASEL, 9 (10):10.3390/app9102132 MAY 2 2019
Abstract:
Quasicrystals are a class of ordered solids made of typical metallic atoms but they do not exhibit the physical properties that usually signal the presence of metallic bonding, and their electrical and thermal transport properties resemble a more semiconductor-like than metallic character. In this paper I first review a number of experimental results and numerical simulations suggesting that the origin of the unusual properties of these compounds can be traced back to two main features. For one thing, we have the formation of covalent bonds among certain atoms grouped into clusters at a local scale. Thus, the nature of chemical bonding among certain constituent atoms should play a significant role in the onset of non-metallic physical properties of quasicrystals bearing transition-metal elements. On the other hand, the self-similar symmetry of the underlying structure gives rise to the presence of an extended chemical bonding network due to a hierarchical nesting of clusters. This novel structural design leads to the existence of quite diverse wave functions, whose transmission characteristics range from extended to almost localized ones. Finally, the potential of quasicrystals as thermoelectric materials is discussed on the basis of their specific transport properties.
Title:
STATISTICAL DESCRIPTION OF DIFFRACTION PATTERN OF APERIODIC CRYSTALS
Authors:
Wolny, J; Buganski, I; Pytlik, L; Strzalka, R Author Full Names: Wolny, J.; Buganski, I; Pytlik, L.; Strzalka, R.
Source:
ARCHIVES OF METALLURGY AND MATERIALS, 64 (2):721-725; 10.24425/amm.2019.127604 2019
Abstract:
Modern crystallography faces a demanding challenge of describing atomic structure and diffraction pattern of quasicrystals, which, after 30 years of Shechtman's discovery, is still an open field of research. The classical approach based on the Braggs and Laue equations in three-dimensional space is useless, because the direct and the reciprocal lattices cannot be introduced for aperiodic systems. A standard solution to this problem, applied by number of scientists, is to retrieve periodicity in high dimensions. This is a purely mathematical approach with some difficulties from a point of view of physics. It is mathematically elegant, but not applicable to all aperiodic systems (e.g. Thue-Morse or Rudin-Shapiro sequences). It meets also a serious trouble in a proper description of structural defects, like phasons. In our opinion the most successful alternative to the multidimensional description is a statistical method of diffractional and structural analysis of aperiodic systems, also known as the average unit cell approach (AUC). In this work an application of the AUC method to selected aperiodic systems, including modulated structures, quasicrystals and covering clusters, is discussed in the form of a mini-review. A reader can find more details in the cited references.
Title:
Electronic properties of incommensurately modulated novel and complex materials
Authors:
Martino, E; Arakcheeva, A; Autes, G; Katrych, S; Yazyev, OV; Moll, PJW; Akrap, A; Forro, L Author Full Names: Martino, Edoardo; Arakcheeva, Alla; Autes, Gabriel; Katrych, Sergiv; Yazyev, Oleg V.; Moll, Philip J. W.; Akrap, Aim; Forro, Laszlo
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E96-E96; S 10.1107/S2053273318093798 AUG 2018
Title:
Investigation of the structure of the modulated doubly ordered perovskite NaLaCoWO6 and its reversible phase transition with a colossal temperature hysteresis
Authors:
Cohn, CV; Zuo, P; Darie, C; Klein, H Author Full Names: Cohn, Claire V.; Zuo, Peng; Darie, Celine; Klein, Holger
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E51-E51; S 10.1107/S2053273318094421 AUG 2018
Title:
Electron diffraction tomography of modulated minerals: the crystal structure of daliranite
Authors:
Gemmi, M; Lanza, A; Mugnaioli, E; Bindi, L; Paar, WH Author Full Names: Gemmi, Mauro; Lanza, Arianna; Mugnaioli, Enrico; Bindi, Luca; Paar, Werner H.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E321-E322; S 10.1107/S2053273318090356 AUG 2018
Title:
Application of the Generalized Penrose Tiling to the structure refinement of AICuRh decagonal quasicrystal
Authors:
Strzalka, R; Buganski, L; Chodyn, M; Wolny, J Author Full Names: Strzalka, Radoslaw; Buganski, Lreneusz; Chodyn, Maciej; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E98-E98; S 10.1107/S2053273318093762 AUG 2018
Title:
Multidimensional crossed cube tilings
Authors:
Ben-Abraham, S Author Full Names: Ben-Abraham, Shelomo
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E332-E332; S 10.1107/S2053273318090186 AUG 2018
Title:
Transitions toward complex electronic states and superperiodic structures in P4W16O56
Authors:
Duverger-Nedellec, E; Pautrat, A; Perez, O Author Full Names: Duverger-Nedellec, Elen; Pautrat, Alain; Perez, Olivier
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E95-E95; S 10.1107/S2053273318093816 AUG 2018
Title:
Exploring modulation in molecular crystals at low temperatures
Authors:
Sztylko, M; Hoser, A Author Full Names: Sztylko, Marcin; Hoser, Anna
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E327-E327; S 10.1107/S2053273318090289 AUG 2018
Title:
Aperidic structures and luminescent properties in the scheelite family
Authors:
Morozov, V; Abakumov, A; Hadermann, J; Khaikina, E; Deynekol, D; Lazoryak, B; Leonidov, I; Batuk, D; Batuk, M Author Full Names: Morozov, Vladimir; Abakumov, Artem; Hadermann, Joke; Khaikina, Elena; Deynekol, Dina; Lazoryak, Bogdan; Leonidov, Ivan; Batuk, Dmitry; Batuk, Maria
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E94-E94; S 10.1107/S2053273318093828 AUG 2018
Title:
On the symmetry of incommensurate magnetic structures
Authors:
Perez-Mato, JM; Elcoro, L; Madariaga, G; Aroyo, MI Author Full Names: Manuel Perez-Mato, J.; Elcoro, Luis; Madariaga, Gotzon; Aroyo, Mois I.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E100-E101; S 10.1107/S2053273318093737 AUG 2018
Title:
AlCuRh decagonal quasicrystal - new techniques for the refinement
Authors:
Buganski, I; Strzalka, R; Wolny, J Author Full Names: Buganski, Ireneusz; Strzalka, Radoslaw; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E328-E328; S 10.1107/S2053273318090265 AUG 2018
Title:
Clusters in the Al13TM4 quasicrystalline approximants : role on the surface structures and properties
Authors:
Gaudry, E Author Full Names: Gaudry, Emilie
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E96-E97; S 10.1107/S2053273318093786 AUG 2018

Update: 11-Jul-2019

Title:
Low-temperature thermal conductivity and magnetic transitions of the kagome-staircase compound Ni3V2O8
Authors:
Zhao, ZY; Li, QJ; Liu, XG; Rao, X; Che, HL; Chu, LG; He, ZZ; Zhao, X; Sun, XF Author Full Names: Zhao, Z. Y.; Li, Q. J.; Liu, X. G.; Rao, X.; Che, H. L.; Chu, L. G.; He, Z. Z.; Zhao, X.; Sun, X. F.
Source:
PHYSICAL REVIEW B, 99 (22):10.1103/PhysRevB.99.224428 JUN 25 2019
Abstract:
The kagome-staircase compound Ni3V2O8 is an attractive multiferroic material exhibiting rich phase diagrams. However, the magnetic properties and magnetic transitions have been studied only above 1.3 K. In this work, we study the thermal conductivity kappa of Ni3V2O8 single crystals at low temperatures down to 0.3 K and in magnetic fields up to 14 T. In zero field, the magnetic transitions from the low-temperature incommensurate (LTI) phase to the commensurate phase (C) and then to a second commensurate phase (C' yield anomalies in kappa(T) curves at T-LC = 3.7 K and T-CC' = 2.0 K, respectively, which indicates a significant phonon scattering by the critical spin fluctuations. When the field is applied along the a axis, the field dependence of kappa displays four anomalies associated with different magnetic transitions and reveals an undetected magnetic state at subkelvin temperatures. In addition, the kappa(B) curves are found to depend not only on the history but also on the magnitude of the applied field. When the field is applied along the b axis, a high-field phase located above the LTI and high-temperature incommensurate phases is revealed.
Title:
Stacking sequence variations in vaterite resolved by precession electron diffraction tomography using a unified superspace model
Authors:
Steciuk, G; Palatinus, L; Rohlicek, J; Ouhenia, S; Chateigner, D Author Full Names: Steciuk, Gwladys; Palatinus, Lukas; Rohlicek, Jan; Ouhenia, Salim; Chateigner, Daniel
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-019-45581-6 JUN 24 2019
Abstract:
As a metastable phase, vaterite is involved in the first step of crystallization of several carbonate-forming systems including the two stable polymorphs calcite and aragonite. Its complete structural determination would consequently shed important light to understand scaling formation and biomineralization processes. While vaterite's hexagonal substructure (a(0) similar to 4.1 angstrom and c(0) similar to 8.5 angstrom) and the organization of the carbonate groups within a single layer is known, conflicting interpretations regarding the stacking sequence remain and preclude the complete understanding of the structure. To resolve the ambiguities, we performed precession electron diffraction tomography (PEDT) to collect single crystal data from 100 K to the ambient temperature. The structure was solved ab initio and described over all the temperature range using a unified modulated structure model in the superspace group C12/c1(alpha 0 gamma)00 with a = a(0) = 4.086(3) angstrom, b = root 3a(0) = 7.089(9) angstrom, c = c(0) = 8.439(9) angstrom, alpha=beta=gamma=90 degrees and q = 2/3a* + gamma c*. At 100 K the model presents a pure 4-layer stacking sequence with gamma = 1/2 whereas at the ambient temperature, ordered stacking faults are introduced leading to gamma < 1/2. The model was refined against PEDT data using the dynamical refinement procedure including modulation and twinning as well as against x-ray powder data by the Rietveld refinement.
Title:
Effect of exchange interaction on electronic instabilities in the honeycomb lattice: A functional renormalization group study
Authors:
O, SJ; Kim, YH; Rim, HY; Pak, HC; Im, SJ Author Full Names: O, Song-Jin; Kim, Yong-Hwan; Rim, Ho-Yong; Pak, Hak-Chol; Im, Song-Jin
Source:
PHYSICAL REVIEW B, 99 (24):10.1103/PhysRevB.99.245140 JUN 21 2019
Abstract:
The impact of local and nonlocal density-density interactions on the electronic instabilities in the honeycomb lattice is widely investigated. Some early studies proposed the emergence of interaction-induced topologically nontrivial phases, but recently, it was denied in several works including renormalization group calculations with refined momentum resolution. We use the truncated unity functional renormalization group to study the many-body instabilities of electrons on the half-filled honeycomb lattice, focusing on the effect of the exchange interaction. We show that varying the next-nearest-neighbor repulsion and nearest-neighbor exchange integral can lead to diverse ordered phases, namely, the quantum spin Hall, the spin-Kekule, and some spin- and charge-density-wave phases. The quantum spin Hall phase can be induced by a combination of the ferromagnetic exchange and pair hopping interactions. Another exotic phase, the spin-Kekule phase, develops in a very small region of the parameter space considered. We encounter the three-sublattice charge-density-wave phase in a large part of the parameter space. It is replaced by the incommensurate charge density wave when increasing the exchange integral. In order to reduce the computational effort, we derive the explicit symmetry relations for the bosonic propagators of the effective interaction and propose a linear-response-based approach for identifying the form factor of order parameter. Their efficiencies are confirmed by numerical calculations in our work.
Title:
Suppression of charge density wave order by disorder in Pd-intercalated ErTe3
Authors:
Straquadine, JAW; Weber, F; Rosenkranz, S; Said, AH; Fisher, AIR Author Full Names: Straquadine, J. A. W.; Weber, F.; Rosenkranz, S.; Said, A. H.; Fisher, And I. R.
Source:
PHYSICAL REVIEW B, 99 (23):10.1103/PhysRevB.99.235138 JUN 19 2019
Abstract:
Disorder is generically anticipated to suppress long range charge density wave (CDW) order. We report transport, thermodynamic, and scattering experiments on PdxErTe3, a model CDW system with disorder induced by intercalation. The pristine parent compound (x = 0) shows two separate, mutually perpendicular, incommensurate unidirectional CDW phases setting in at 270 K and 165 K. In this work we present measurements on a finely-spaced series of single crystal samples, in which we track the suppression of signatures corresponding to these two parent transitions as the Pd concentration increases. At the largest values of x, we observe complete suppression of long range CDW order in favor of superconductivity. We also report evidence from electron and x-ray diffraction which suggests a tendency toward short-range ordering along both wave vectors which persists even well above the crossover temperature and comment on the origin and consequences of this effect. Based on this work, PdxErTe3 appears to provide a promising model system for the study of the interrelation of charge order and superconductivity in the presence of quenched disorder, for pseudotetragonal materials.
Title:
Commensurate Nb2Zr5O15: Accessible Within the Field Nb2ZrxO2x+5 After All
Authors:
Wiedemann, D; Orthmann, S; Muhlbauer, MJ; Lerch, M Author Full Names: Wiedemann, Dennis; Orthmann, Steven; Muehlbauer, Martin J.; Lerch, Martin
Source:
CHEMISTRYOPEN, 8 (4):447-450; 10.1002/open.201900043 APR 2019
Abstract:
Doped niobium zirconium oxides are applied in field-effect transistors and as special-purpose coatings. Whereas their material properties are sufficiently known, their crystal structures remain widely uncharacterized. Herein, we report on the comparably mild sol-gel synthesis of Nb2Zr5O15 and the elucidation of its commensurately modulated structure via neutron diffraction. We describe the structure using the most appropriate superspace as well as the convenient supercell approach. It is part of an -PbO2-homeotypic field with the formula Nb2ZrxO2x+5, which has previously been reported only for x5.1, and is closely related to the structure of Hf3Ta2O11. The results, supported by X-ray diffraction and additional synthesis experiments, are contextualized within the existing literature. Via the sol-gel route, metastable Nb-Zr-O compounds and their heavier congeners are accessible that shed light on possible structures of these commercially utilized materials.

Update: 27-Jun-2019

Title:
Growth of layered Lu(2)Fe(3)O(7 )and Lu3Fe4O10 single crystals exhibiting long-range charge order via the optical floating-zone method
Authors:
Hammouda, SS; Angst, M Author Full Names: Hammouda, S. S.; Angst, M.
Source:
JOURNAL OF CRYSTAL GROWTH, 521 50-54; 10.1016/j.jcrysgro.2019.06.003 SEP 1 2019
Abstract:
We report the controlled growth of single crystals of intercalated layered Lu1+n Fe2+nO4+3n-delta(n = 1,2) with different oxygen stoichiometries delta. For the first time crystals sufficiently stoichiometric to exhibit superstructure reflections in X-ray diffraction attributable to charge ordering were obtained. The estimated correlation lengths tend to be smaller than for not intercalated LuFe2O4. For Lu2Fe3O7, two different superstructures were observed, one an incommensurate zigzag pattern similar to previous observations by electron diffraction, the other an apparently commensurate pattern with (1/31/30) propagation. Implications for the possible charge order in the bilayers are discussed. Magnetization measurements suggest reduced magnetic correlations and the absence of an antiferromagnetic phase.
Title:
Synthesis and characterization of Sn reinforced Al-Cu-Fe quasicrystalline matrix nanocomposite by mechanical milling
Authors:
Shadangi, Y; Shivam, V; Singh, MK; Chattopadhyay, K; Basu, J; Mukhopadhyay, NK Author Full Names: Shadangi, Yagnesh; Shivam, Vikas; Singh, Manish Kumar; Chattopadhyay, Kausik; Basu, Joysurya; Mukhopadhyay, N. K.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 797 1280-1287; 10.1016/j.jallcom.2019.05.128 AUG 15 2019
Abstract:
The influence of mechanical milling (MM), primarily on microstructure and phase evolution in Al62.5Cu25Fe12.5 (at%) quasicrystalline (IQC) matrix reinforced with varying volume fraction of Sn has been investigated by means of X-ray diffraction (XRD), scanning & transmission electron microscopy (SEM and TEM) and differential scanning calorimetry (DSC) methods. It was observed that with increasing the milling duration, the IQC phase transforms to crystalline B2 phase [Al (Cu, Fe) and Pm3m, a = 0.29 nm]. In SEM and TEM analysis, it was found that both IQC and Sn particles are refined during MM. The XRD and TEM results confirm the formation nanostructured matrix consisting of nanocrystalline B2 phase along with minor IQC phase reinforced with ultrafine grained Sn particles after 40 h of MM. The STEM-EDS results show a homogenous distribution of elements (Al, Cu, Fe). The Sn particles were immiscible in a matrix consisting of B2 and IQC phase as indicated by XRD and TEM investigations. (C) 2019 Elsevier B.V. All rights reserved.
Title:
Comprehensive magnetic phase diagrams of the polar metal Ca-3(Ru0.95Fe0.05)(2)O-7
Authors:
Lei, SM; Chikara, S; Puggioni, D; Peng, J; Zhu, MZ; Gu, MQ; Zhao, WW; Wang, Y; Yuan, YK; Akamatsu, H; Chan, MHW; Ke, XL; Mao, ZQ; Rondinelli, JM; Jaime, M; Singleton, J; Weickert, F; Zapf, VS; Gopalan, V Author Full Names: Lei, Shiming; Chikara, Shalinee; Puggioni, Danilo; Peng, Jin; Zhu, Mengze; Gu, Mingqiang; Zhao, Weiwei; Wang, Yu; Yuan, Yakun; Akamatsu, Hirofumi; Chan, Moses H. W.; Ke, Xianglin; Mao, Zhiqiang; Rondinelli, James M.; Jaime, Marcelo; Singleton, John; Weickert, Franziska; Zapf, Vivien S.; Gopalan, Venkatraman
Source:
PHYSICAL REVIEW B, 99 (22):10.1103/PhysRevB.99.224411 JUN 10 2019
Abstract:
Polar metals exist as a rather unique class of materials as they combine two seemingly mutually exclusive properties (polar order and metallicity) in one system. So far only a few polar metals have been unambiguously identified; the magnetic ones are exceptionally rare. Here we investigate a 5% Fe-doped polar metal Ca3Ru2O7, via electrical transport, magnetization, microstrain, and optical second-harmonic generation measurements. We report the full magnetic phase diagrams (in the field-temperature space) for magnetic field H parallel to a and H parallel to b, which exhibit distinct field-dependent magnetizations behavior. In particular, for H parallel to a we found a ferromagnetic incommensurate spin structure, which is absent in the pure Ca3Ru2O7. We propose a microscopic spin model to understand this behavior, highlighting the role of Fe doping in tipping the delicate balance of the underlying exchange-interaction energy in this system.
Title:
Experimental realization of a semiconducting quasicrystalline approximant in Al-Si-Ru system by band engineering
Authors:
Iwasaki, Y; Kitahara, K; Kimura, K Author Full Names: Iwasaki, Yutaka; Kitahara, Koichi; Kimura, Kaoru
Source:
PHYSICAL REVIEW MATERIALS, 3 (6):10.1103/PhysRevMaterials.3.061601 JUN 7 2019
Abstract:
We found that an Al-Si-Ru cubic quasicrystalline approximant has a semiconducting band structure by performing an orbital analysis based on density functional theory. These semiconducting transport properties have been confirmed in an experimentally synthesized sample. The temperature dependences of the electrical conductivity and the Seebeck coefficient were consistent with the trends of an intrinsic semiconductor with a band gap of 0.15 eV above 350 K. The lattice thermal conductivity had a low value of approximately 1.0 W m(-1) K-1 above 400 K, which is close to the theoretical minimum.
Title:
Incommensurate magnetism in K2MnS2-xSex and prospects for tunable frustration in a triangular lattice of pseudo-1D spin chains
Authors:
Bhutani, A; Behera, P; McAuliffe, RD; Cao, HB; Huq, A; Kirkham, MJ; dela Cruz, CR; Woods, T; Shoemaker, DP Author Full Names: Bhutani, Ankita; Behera, Piush; McAuliffe, Rebecca D.; Cao, Huibo; Huq, Ashfia; Kirkham, Melanie J.; dela Cruz, Clarina R.; Woods, Toby; Shoemaker, Daniel P.
Source:
PHYSICAL REVIEW MATERIALS, 3 (6):10.1103/PhysRevMaterials.3.064404 JUN 5 2019
Abstract:
We report a detailed investigation of K2MnS2 and K2MnSe2 from the K2MnS2 structure type and their magnetic solid solution K2MnS2-xSex and find that compounds of this structure type consist of strongly coupled pseudo-one-dimensional antiferromagnetic chains that collectively represent a frustrated two-dimensional triangular antiferromagnet. Bulk samples of K2MnS2-xSex with 0 <= x <= 2 are characterized using x-ray diffraction, neutron diffraction, magnetization, and heat-capacity measurements. An incommensurate cycloid magnetic structure with a magnetic propagation vector k = [0.58 0 1] is observed for all samples in K2MnS2-xSex, and the ordering is robust despite a 12% increase in cell volume. Geometric frustration of chains results in incommensurability along a and a two-step magnetic transition. The varying geometries accessible in compounds of this structure type are presented as promising avenues to tune frustration.
Title:
Emergent localization in dodecagonal bilayer quasicrystals
Authors:
Park, MJ; Kim, HS; Lee, S Author Full Names: Park, Moon Jip; Kim, Hee Seung; Lee, SungBin
Source:
PHYSICAL REVIEW B, 99 (24):10.1103/PhysRevB.99.245401 JUN 4 2019
Abstract:
Long range order in the absence of translational symmetry gives rise to drastic revolution of our common knowledge in condensed-matter physics. Quasicrystals, as such an unconventional system, became a plethora to test our insights and to find exotic states of matter. In particular, electronic properties in quasicrystals have gotten lots of attention along with their experimental realization and controllability in twisted bilayer systems. In this work, we study how quasicrystalline order in bilayer systems can induce unique localization of electrons without any extrinsic disorders. We focus on the dodecagonal quasicrystal that has been demonstrated in twisted bilayer graphene system in recent experiments. In the presence of a small gap, we show the localization generically occurs due to the nonperiodic nature of quasicrystals, which is evidenced by the inverse participation ratio and the energy-level statistics. We understand the origin of such localization by approximating the dodecagonal quasicrystals as an impurity scattering problem.
Title:
Study of Penrose Tiling Using Parameterization Method
Authors:
Shutov, AV; Maleev, AV Author Full Names: Shutov, A. V.; Maleev, A. V.
Source:
CRYSTALLOGRAPHY REPORTS, 64 (3):376-385; 10.1134/S1063774519030234 MAY 2019
Abstract:
A new description of Penrose tiling, based on parameterization of tiling rhombuses, has been obtained. A method making it possible to describe clusters and coordination environments in Penrose tiling in terms of parameters is developed. The parameters of all possible types of the first coordination environments in Penrose tiling are found. A new proof is obtained that the form of layer-by-layer growth of Penrose tiling is a regular decagon, and the vertices of this decagon are calculated.

Update: 19-Jun-2019

Title:
Control of wave propagation response using quasi crystals: A formulation based on spectral finite element
Authors:
Chellappan, V; Gopalakrishnan, S; Mani, V Author Full Names: Chellappan, Vinita; Gopalakrishnan, S.; Mani, V
Source:
MECHANICS OF ADVANCED MATERIALS AND STRUCTURES, 26 (7):579-600; 10.1080/15376494.2017.1410901 APR 3 2019
Abstract:
This paper presents wave propagation studies in quasi crystal structures and quasi crystal reinforced aluminium structures. The analysis is performed using frequency domain spectral finite element formulation. The analysis considers different 2-D decagonal and 3-D icosahedral quasi crystals. First, wave propagation analysis of quasi crystal structure alone is performed and the propagation of phonon and phason modes for different quasi crystals are studied. The study includes the propagation of axial and transverse wave responses in these quasi crystals. The study has found that the amplitude of the phason modes is very small compared to the phonon modes and the increase of the phason mode content (through increase in R) increases the phason mode amplitude, without affecting the phonon mode amplitudes. It is shown that the dominant axial phonon mode is non-dispersive and the dominant flexural phonon mode is dispersive. In the next study, the aluminium beam structure is reinforced with different quasi crystals in different configurations and the wave propagation of axial and transverse responses are studied. For all the combinations of quasi crystal aluminium beam combination, there is substantial suppression of responses both for the axial and the bending responses. Unsymmetrical configuration produces substantial non-dominant phonon modes which propagate dispersively. It is found that for a symmetric bi-morph configuration, the response is reduced significantly, about 68% and 75% for axial loading and 80% and 78% for flexural loading, respectively, for the 2-D decagonal quasi crystal and the 3-D icosahedral quasi crystal.
Title:
Microstructure and mechanical behavior of Al92Fe3Cr2X3 (X = Ce, Mn, Ti, and V) alloys processed by centrifugal force casting
Authors:
Koga, GY; Silva, AMBE; Wolf, W; Kiminami, CS; Bolfarini, C; Botta, WJ Author Full Names: Koga, Guilherme Yuuki; Branquinho e Silva, Ana Martha; Wolf, Witor; Kiminami, Claudio Shyinti; Bolfarini, Claudemiro; Botta, Walter Jose
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 8 (2):2092-2097; 10.1016/j.jmrt.2018.12.022 APR 2019
Abstract:
Microstructural and mechanical characterization of Al92Fe3Cr2X3 (X = Ce, Mn, Ti, and V) alloys were performed. The alloys were processed by a method that uses centrifugal force to cast the samples into a rotating copper mold. Microstructural characterization was carried out by means of x-ray diffraction, scanning electron microscopy, and differential scanning calorimetry. Compressive tests at room and at 300 degrees C were performed in selected samples to evaluate their mechanical properties. Microstructural characterization showed the formation of quasicrystalline phases as well as other intermetallic phases embedded within an Al-FCC matrix. The Ce-containing alloy exhibited promising results regarding quasicrystalline phase formation and stability as well as with respect to its mechanical properties at high temperatures. The quasicrystalline phase of this alloy appears to be stable up to 545 degrees C when the DSC reveals an exothermic transformation. In addition, the presence of a eutectic structure surrounding the Al-FCC grains enhanced the mechanical strength of this alloy. At 300 degrees C, the Ce-containing alloy showed yield strength and ultimate tensile strength of 180 MPa and 360 MPa, respectively. If compared to a commercial aluminum alloy 2024 at the T6 condition, close to 300 degrees C, the alloy studied here showed an increase of more than 4 times in the yield strength, and almost 7 times in the ultimate tensile strength. The high thermal stability and mechanical properties at high temperatures of this alloy open interesting possibilities for further studies and future applications of this Al-Fe-Cr-Ce alloy. (C) 2019 Published by Elsevier Editora Ltda. on behalf of Brazilian Metallurgical, Materials and Mining Association.
Title:
Effect of I(Mg3YZn6)-, W(Mg3Y2Zn3)- and LPSO(Mg12ZnY)- phases on tensile work-hardening and fracture behaviors of rolled Mg-Y-Zn alloys
Authors:
Yang, JY; Kim, WJ Author Full Names: Yang, Jun Yeong; Kim, Woo Jin
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 8 (2):2316-2325; 10.1016/j.jmrt.2019.04.016 APR 2019
Abstract:
The effects of secondary phases (W,Mg3Y2Zn3), long-period stacking-ordered (LPSO, Mg12ZnY) and icosahedral (I, Mg3YZn6) phases on the tensile properties and work- hardening behavior of Mg-Y-Zn alloys (Mg-1.32Zn-1.79Y, ZW12; Mg-4.4Zn-2.2Y, ZW42; and microstructures were studied at room temperature. The volume fractions of LPSO, W and I-phase in ZW12, ZW42 and ZW51 were 4.7, 6.3 and 4.8%, respectively. The rolled alloys exhibited a similar level of yield strength but different work hardening characteristics and tensile fracture behavior. The rolled ZW51 with I-phase particles exhibited the highest work-hardening rate and the largest tensile elongation (with ductile fracture). The ZW42 with W-phase particles exhibited a work-hardening rate slightly lower than that of the rolled ZW51, despite having the larger amount of secondary phase, and premature fracture occurred far before neck formation in ZW42, while fracture occured after neck formation occurred far before neck formation in ZW42, while fracture occured after neck formation in ZW51. The fractured surface showed that the coherent interface between the I-phase and Mg matrix phase is significantly more resistant to cracking than is the incoherent interface between the W-phase and Mg matrix phase. The rolled ZW12 with LPSO-phase, forming a coherent interface with the Mg matrix phase, exhibited a considerably lower work hardening rate than the rolled ZW51, though they had the similar amounts of secondary phase. Thus, the uniform strain of the rolled ZW12 was quite small compared with that of the rolled ZW51, though fracture occurred after necking in both alloys. The same work-hardening and tensile elongation behaviors were retained after annealing treatment on the rolled alloys. (C) 2019 The Authors. Published by Elsevier B.V.
Title:
Synthesis and Investigation of Quaternary Quasi-Crystalline Phase in Al - Cu - Fe - Cr Alloys
Authors:
Wang, YF; Hou, H; Zhao, YH; Tian, JZ Author Full Names: Wang, Yifan; Hou, Hua; Zhao, Yuhong; Tian, Jinzhong
Source:
METAL SCIENCE AND HEAT TREATMENT, 60 (11-12):770-776; 10.1007/s11041-019-00354-w MAR 2019
Abstract:
Formation of a quasi-crystalline phase under rapid solidification and heat treatment of alloys of the Al - Cu - Fe - Cr system is studied. The study is performed by x-ray diffractometry, optical, scanning and transmission electron microscopy and differential scanning calorimetry. It is shown that the quasi-crystalline Al65Cu20Fe10Cr5 phase is a mixture of icosahedral and decagonal phases. The substitution of iron with chromium destabilizes the icosahedral I-phase and promotes formation of a decagonal d-phase. After quenching from 880 degrees C, the Al64Cu24Fe10Cr2 alloy acquires a pure I-phase, and the Al64Cu24Fe8Cr4 alloy acquires a d-phase.

Update: 13-Jun-2019

Title:
Charge density wave and lock-in transitions of CuV2S4
Authors:
Ramakrishnan, S; Schonleber, A; Hubschle, CB; Eisele, C; Schaller, AM; Rekis, T; Bui, NHA; Feulner, F; van Smaalen, S; Bag, B; Ramakrishnan, S; Tolkiehn, M; Paulmann, C Author Full Names: Ramakrishnan, Sitaram; Schoenleber, Andreas; Huebschle, Christian B.; Eisele, Claudio; Schaller, Achim M.; Rekis, Toms; Nguyen Hai An Bui; Feulner, Florian; van Smaalen, Sander; Bag, Biplab; Ramakrishnan, Srinivasan; Tolkiehn, Martin; Paulmann, Carsten
Source:
PHYSICAL REVIEW B, 99 (19):10.1103/PhysRevB.99.195140 MAY 23 2019
Abstract:
The three-dimensional charge density wave (CDW) compound CuV2S4 is known to undergo phase transitions at similar to 91 and similar to 50 K. Employing single-crystal x-ray diffraction on an annealed crystal, we confirm the formation of an incommensurate CDW at T-CDW approximate to 91 K, and we establish the nature of the transition at Tlock-in approximate to 50 K as a lock-in transition toward a threefold superstructure. As-grown crystals develop the same incommensurate CDW as the annealed crystal does, but they fail to go through the lock-in transition. Instead, the length of the modulation wave vector continues to decrease down to low temperatures in as-grown crystals. These findings are corroborated by distinct temperature dependencies of the electrical resistivity, magnetic susceptibility, and specific heat measured on as-grown and annealed crystals. A superspace model for the crystal structure of the incommensurate CDW suggests that the formation of extended vanadium clusters is at the origin of the CDW. In the lock-in phase, short and long V-V distances persist, but clusters now percolate the entire crystal. The lowering toward orthorhombic symmetry appears to be responsible for the precise pattern of short and long V-V distances. However, the orthorhombic lattice distortion is nearly zero for the annealed crystal, while it is visible for the as-grown material, again suggesting the role of lattice defects in the latter.
Title:
Magnons in a Quasicrystal: Propagation, Extinction, and Localization of Spin Waves in Fibonacci Structures
Authors:
Lisiecki, F; Rychly, J; Kuswik, P; Glowinski, H; Klos, JW; Gross, F; Trager, N; Bykova, I; Weigand, M; Zelent, M; Goering, EJ; Schutz, G; Krawczyk, M; Stobiecki, F; Dubowik, J; Grafe, J Author Full Names: Lisiecki, Filip; Rychly, Justyna; Kuswik, Piotr; Glowinski, Hubert; Klos, Jaroslaw W.; Gross, Felix; Traeger, Nick; Bykova, Iuliia; Weigand, Markus; Zelent, Mateusz; Goering, Eberhard J.; Schuetz, Gislea; Krawczyk, Maciej; Stobiecki, Feliks; Dubowik, Janusz; Graefe, Joachim
Source:
PHYSICAL REVIEW APPLIED, 11 (5):10.1103/PhysRevApplied.11.054061 MAY 22 2019
Abstract:
Magnonic quasicrystals exceed the possibilities of spin-wave (SW) manipulation offered by regular magnonic crystals, because of their more complex SW spectra with fractal characteristics. Here, we report the direct x-ray microscopic observation of propagating SWs in a magnonic quasicrystal, consisting of dipolar coupled permalloy nanowires arranged in a one-dimensional Fibonacci sequence. SWs from the first and second band as well as evanescent waves from the band gap between them are imaged. Moreover, additional mini band gaps in the spectrum are demonstrated, directly indicating an influence of the quasiperiodicity of the system. Finally, the localization of SW modes within the Fibonacci crystal is shown. The experimental results are interpreted using numerical calculations and we deduce a simple model to estimate the frequency position of the magnonic gaps in quasiperiodic structures. The demonstrated features of SW spectra in one-dimensional magnonic quasicrystals allow utilizing this class of metamaterials for magnonics and make them an ideal basis for future applications.
Title:
Changes in spin and lattice dynamics induced by magnetic and structural phase transitions in multiferroic SrMn7O12
Authors:
Kamba, S; Goian, V; Kadlec, F; Nuzhnyy, D; Kadlec, C; Vit, J; Borodavka, F; Glazkova, IS; Belik, AA Author Full Names: Kamba, Stanislav; Goian, Veronica; Kadlec, Filip; Nuzhnyy, Dmitry; Kadlec, Christelle; Vit, Jakub; Borodavka, Fedir; Glazkova, Iana S.; Belik, Alexei A.
Source:
PHYSICAL REVIEW B, 99 (18):10.1103/PhysRevB.99.184108 MAY 20 2019
Abstract:
SrMn7O12 is a recently synthesized homolog of multiferroic CaMn7O12. Upon cooling, SrMn7O12 undergoes a series of structural and magnetic phase transitions from cubic to rhombohedral symmetry, and to an incommensurately modulated crystal structure, which is connected with charge and orbital ordering of the Mn cations. We report infrared, terahertz, and Raman spectra of SrMn7O12 ceramics reflecting corresponding changes in phonon selection rules, including new phonons appearing in spin-order-induced ferroelectric phases. The observed phonon activities are compared with the predictions from the factor-group analysis. In the high-temperature phase, more phonons are observed than the number predicted for the cubic symmetry. This is explained by the presence of rhombohedral clusters in the cubic phase. The strongest variations occur in THz spectra near the two magnetic phase transitions, at T-N1 = 87 K and T-N2 = 63 K. These activate new modes in the spectra, with resonance frequencies and intensities changing with temperature and magnetic field. Below T-N2, we observed a transfer of oscillator strengths from low-frequency phonons to these excitations, which we assign to electromagnons.
Title:
Microstructure and Mechanical Properties of Extruded Mg-7Sn-5Zn-xAl (x=0, 1, 2 and 3 wt.%) Alloy
Authors:
Jiang, J; Li, TQ; Bi, GL; Yan, FY; Cao, C; Li, YD; Ma, Y Author Full Names: Jiang, Jing; Li, Tingqu; Bi, Guang-Li; Yan, Feng-Yun; Cao, Chi; Li, Yuan-Dong; Ma, Ying
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 28 (5):2672-2680; 10.1007/s11665-019-04053-8 MAY 2019
Abstract:
Microstructure and mechanical properties of extruded Mg-7Sn-5Zn-xAl (x=0, 1, 2 and 3 wt.%) alloy were investigated. The as-cast Mg-7Sn-5Zn alloy mainly comprised alpha-Mg dendrites, Mg2Sn and nanosized Mg-Zn phases in a Mg matrix, whereas the quasicrystal (icosahedral (I)) phase precipitated with the addition of Al. After extrusion, the grain size decreased due to dynamic recrystallization and the resulting particles were crushed and distributed along the extrusion direction. The highest tensile strength was exhibited by the extruded Mg-7Sn-5Zn-2Al alloy, which had a yield strength, ultimate tensile strength and elongation to failure of 198, 343 MPa and 18.7%, respectively. The high tensile strength was mainly attributed to grain refinement and precipitation strengthening of the Mg2Sn and icosahedral phases.

Update: 6-Jun-2019

Title:
The influence of the incommensurately modulated structure on the physical properties of Fe1.35Ge
Authors:
Jacimovic, J; Popcevic, P; Arakcheeva, A; Pattison, P; Pisoni, A; Katrych, S; Prsa, K; Berger, H; Smontara, A; Forro, L Author Full Names: Jacimovic, J.; Popcevic, P.; Arakcheeva, A.; Pattison, P.; Pisoni, A.; Katrych, S.; Prsa, K.; Berger, H.; Smontara, A.; Forro, L.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 794 108-113; 10.1016/j.jallcom.2019.04.159 JUL 25 2019
Abstract:
Single crystal growth by chemical vapour transport has resulted samples with Fe1.35Ge stoichiometry. Structural study has shown that the large number of vacancies introduces an incommensuately modulated structure. The electrical resistivity is in the 200 mu Omega cm range at room temperature, and although the ferromagnetic transition temperature at 425 K is clearly visible, it hardly varies down to 4.2 K. It is suggested that the large number of vacancies (and the incommensurate modulation) introduce a strong backscattering, and the system is at the brink of a Mooij correlation. The thermal conductivity and Seebeck coefficient carry also the consequences of the high concentration of vacancies. (c) 2019 Elsevier B.V. All rights reserved.
Title:
Annealing induced precipitation of nanoscale icosahedral quasicrystals in aluminum based alloy
Authors:
Mochugovskiy, A; Tabachkova, N; Mikhaylovskaya, A Author Full Names: Mochugovskiy, Andrey; Tabachkova, Natalia; Mikhaylovskaya, Anastasia
Source:
MATERIALS LETTERS, 247 200-203; 10.1016/j.matlet.2019.03.126 JUL 15 2019
Abstract:
This study analyzes the precipitation phenomenon in the Al-3%Mg-1%Mn alloy and shows that low-temperature annealing at 360 degrees C enables the decomposition of an as-cast Mn-enriched supersaturated solid solution and precipitation of the quasicrystalline icosahedral phase. Icosahedrons are predominantly formed heterogeneously on the dislocations and dislocation walls. Precipitates with quasicrystalline structure contain Al and Mn, free of Si, and their size varies in a range of 17-71 nm. The Ashby-Brown contrast and the ordered positions of the precipitate and matrix reflections in the SAED and in high-resolution TEM images suggest partial coherency of the quasicrystalline precipitates and aluminum matrix. (C) 2019 Elsevier B.V. All rights reserved.
Title:
Incommensurate Magnetism Near Quantum Criticality in CeNiAsO
Authors:
Wu, S; Phelan, WA; Liu, L; Morey, JR; Tutmaher, JA; Neuefeind, JC; Huq, A; Stone, MB; Feygenson, M; Tam, DW; Frandsen, BA; Trump, B; Wan, C; Dunsiger, SR; McQueen, TM; Uemura, YJ; Broholm, CL Author Full Names: Wu, Shan; Phelan, W. A.; Liu, L.; Morey, J. R.; Tutmaher, J. A.; Neuefeind, J. C.; Huq, Ashfia; Stone, Matthew B.; Feygenson, M.; Tam, David W.; Frandsen, Benjamin A.; Trump, Benjamin; Wan, Cheng; Dunsiger, S. R.; McQueen, T. M.; Uemura, Y. J.; Broholm, C. L.
Source:
PHYSICAL REVIEW LETTERS, 122 (19):10.1103/PhysRevLett.122.197203 MAY 15 2019
Abstract:
We report the discovery of incommensurate magnetism near quantum criticality in CeNiAsO through neutron scattering and zero field muon spin rotation. For T < T-N1 = 8.7(3) K, a second order phase transition yields an incommensurate spin density with a wave vector k = (0.44(4), 0, 0). For T < T-N2 = 7.6(3) K, we find coplanar commensurate order with a moment of 0.37(5)mu(B), reduced to 30% of the saturation moment of the vertical bar +/- 1/2 > Kramers doublet ground state, which we establish through inelastic neutron scattering. Muon spin rotation in CeNiAs1-xPxO shows the commensurate order only exists for x <= 0.1 so we infer the transition at x(c) = 0.4(1) is between an incommensurate longitudinal spin density wave and a paramagnetic Fermi liquid.
Title:
Magnetic Phase Transitions to an Incommensurate Magnetic Structure in FeGe2 Compound
Authors:
Men'shenin, VV Author Full Names: Men'shenin, V. V.
Source:
PHYSICS OF THE SOLID STATE, 61 (3):421-432; 10.1134/S1063783419030211 MAR 2019
Abstract:
A symmetry analysis of possible magnetic structures in an incommensurate magnetic phase in FeGe2 compound, resulted from phase transitions from the paramagnetic phase, was performed based on a phenomenological consideration. It is shown that two possible approaches to a such an analysis, the first of which uses the magnetic representation of the space group, and the second one is based on the expansion of the magnetic moment in basis functions of irreducible representations of the space group of the paramagnetic phase, yield the same results. Space group irreducible representations are determined, according to which the transition to an incommensurate structure can occur. The set of these representations appears identical in both approaches. Ginzburg-Landau functionals for analyzing the transitions according to these representations are written. A renormalization group analysis of the second-order phase transitions from the paramagnetic state to the incommensurate magnetic structure is performed. It is shown that a helical magnetic structure can arise in the incommensurate phase as a result of two second-order phase transitions at the transitions temperature.

Update: 29-May-2019

Title:
Preparation of bulk metallic glasses by modifying local structure of icosahedral quasicrystals
Authors:
Li, ZJ; Pan, SP; Zhang, SH; Feng, SD; Li, MZ; Liu, RP; Tian, YJ; Wang, LM Author Full Names: Li, Zijing; Pan, Shaopeng; Zhang, Suhong; Feng, Shidong; Li, Maozhi; Liu, Riping; Tian, Yongjun; Wang, Li-min
Source:
INTERMETALLICS, 109 97-104; 10.1016/j.intermet.2019.03.007 JUN 2019
Abstract:
An attempt is carried out to design metallic glasses by modifying the local structure of icosahedral quasicrystals. A series of metallic glasses are prepared by introducing beryllium to the quasicrystal former, Zr40Ti40Ni20, and the maximum diameter of the glasses reaches 20 mm. A phase transformation diagram is constructed for the alloys of (Zr40Ti40Ni20)(100-x)Be-x, revealing the transition from stable crystal to quasicrystal and then to metallic glasses with the increased Be content. This study shows a connection between the formation of metallic glasses and the specific thermodynamics of the initially precipitated quasicrystals. Interestingly, both improvements in the forming ability for glasses and quasicrystals are observed over a wide composition range. Ab initio molecular dynamic simulations show the evolution of the structural features of the metallic melts for the optimised glass forming region, which guarantee the primary precipitation of quasicrystal.
Title:
Formation and stability of complex metallic phases including quasicrystals explored through combinatorial methods
Authors:
Wolf, W; Kube, SA; Sohn, S; Xie, YJ; Cha, JJ; Scanley, BE; Kiminami, CS; Bolfarini, C; Botta, WJ; Schroers, J Author Full Names: Wolf, Witor; Kube, Sebastian A.; Sohn, Sungwoo; Xie, Yujun; Cha, Judy J.; Ellen Scanley, B.; Kiminami, Claudio S.; Bolfarini, Claudemiro; Botta, Walter J.; Schroers, Jan
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-019-43666-w MAY 9 2019
Abstract:
Aluminum-based quasicrystals typically form across narrow composition ranges within binary to quaternary alloys, which makes their fabrication and characterization challenging. Here, we use combinatorial approaches together with fast characterization techniques to study a wide compositional range including known quasicrystal forming compositions. Specifically, we use magnetron cosputtering to fabricate libraries of similar to 140 Al-Cu-Fe and similar to 300 Al-Cu-Fe-Cr alloys. The alloys compositions are measured through automated energy dispersive X-ray spectroscopy. Phase formation and thermal stability are investigated for different thermal processing conditions (as-sputtered and annealed at 400 degrees C, 520 degrees C and 600 degrees C for Al-Cu-Fe libraries; annealed at 600 degrees C for Al-Cu-Fe-Cr libraries) using automated X-ray diffraction and transmission electron microscopy. In both systems the compositional regions across which the quasicrystalline phase forms are identified. In particular, we demonstrate that the quasicrystalline phase forms across an unusually broad composition range in the Al-Cu-Fe-Cr system. Additionally, some of the considered alloys vitrify during sputtering, which also allows us to study their nucleation behavior. We find that phases with polytetrahedral symmetry, such as the icosahedral quasicrystal and the lambda-Al13Fe4 phase, exhibit higher nucleation rates but lower growth rates, as compared to other phases with a lower degree of polytetrahedral order. Altogether, the here used combinatorial approach is powerful to identify compositional regions of quasicrystals.
Title:
Lattice Discontinuities of 1T-TaS2 across First Order Charge Density Wave Phase Transitions
Authors:
Wang, W; Dietzel, D; Schirmeisen, A Author Full Names: Wang, Wen; Dietzel, Dirk; Schirmeisen, Andre
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-019-43307-2 MAY 8 2019
Abstract:
Transition metal dichalcogenides are lamellar materials which can exhibit unique and remarkable electronic behavior due to effects of electron-electron and electron-phonon coupling. Among these materials, 1T-tantalum disulfide (1T-TaS2) has spurred considerable interest, due to its multiple first order phase transitions between different charge density wave (CDW) states. In general, the basic effects of charge density wave formation in 1T-TaS2 can be attributed to in plane re-orientation of Ta-atoms during the phase transitions. Only in recent years, an increasing number of studies has also emphasized the role of interlayer interaction and stacking order as a crucial aspect to understand the specific electronic behavior of 1T-TaS2, especially for technological systems with a finite number of layers. Obviously, continuously monitoring the out of plane expansion of the sample can provide direct inside into the rearrangement of the layer structure during the phase transition. In this letter, we therefore investigate the c-axis lattice discontinuities of 1T-TaS2 by atomic force microscopy (AFM) method under ultra-high vacuum conditions. We find that the c-axis lattice experiences a sudden contraction across the nearly-commensurate CDW (NC-CDW) phase to commensurate CDW (C-CDW) phase transition during cooling, while an expansion is found during the transition from the C-CDW phase to a triclinic CDW phase during heating. Thereby our measurements reveal, how higher order C-CDW phase can favor a more dense stacking. Additionally, our measurements also show subtler effects like e.g. two expansion peaks at the start of the transitions, which can provide further insight into the mechanisms at the onset of CDW phase transitions.
Title:
Crystal Structure and Photoluminescence Properties of an Incommensurate Phase in EuO- and P2O5-Doped Ca2SiO4
Authors:
Hiramatsu, Y; Michiue, Y; Funahashi, S; Hirosaki, N; Banno, H; Urushihara, D; Asaka, T; Fukuda, K Author Full Names: Hiramatsu, Yuya; Michiue, Yuichi; Funahashi, Shiro; Hirosaki, Naoto; Banno, Hiroki; Urushihara, Daisuke; Asaka, Toru; Fukuda, Koichiro
Source:
INORGANIC CHEMISTRY, 58 (9):6155-6160; 10.1021/acs.inorgchem.9b00408 MAY 6 2019
Abstract:
We have for the first time clarified the incommensurately modulated crystal structure as well as the photoluminescence properties of Eu2+ -activated Ca2SiO4 solid solution, the chemical formula of which is (Ca1.88Eu0.012+square(0.11))-(Si0.78P0.22)O-4, where square denotes vacancies in Ca sites with the replacement of Si4+ by P5+. The emission spectrum upon the 335 nm excitation showed a relatively broad band centered at ca. 490 nm and a full width at half-maximum of ca. 80 nm. The crystal structure was made up of the four types of beta-Ca2SiO4-like layers with one type of interlayer. The incommensurate modulation with superspace group Pnma(0 beta 0)00s was induced by the long-range stacking order of these layers. The modulation wavevector was 0.27404(2) x b*, with the basic unit-cell dimensions being a = 0.68355(2) nm, b = 0.54227(2) nm, and c = 0.93840(3) nm (Z = 4). The basic structure contained two nonequivalent Ca sites. One site was fully occupied by Ca2+ and free from Eu2+ in the overall incommensurate structure. The occupational modulation at the other site was so significant that the sum of site occupation factors for Ca2+ and Eu2+ as low as 0.5 was seen at the interlayer. This site was too large for accommodation of Ca2+ but was suitable for Eu2+. Thus, the Eu2+ ions would exclusively concentrate at the relevant site, which would cause the emission peak of the incommensurate phase to be shifted to the shorter wavelength ranges as compared with those of the other commensurate phases such as beta and alpha'(L).
Title:
Synthesis and Atomic Structure of the Yb-Ga-Au 1/1 Quasicrystal Approximant
Authors:
Yamada, T; Kurihara, T; Prots, Y; Sato, A; Matsushita, Y; Grin, Y; Tsai, AP Author Full Names: Yamada, Tsunetomo; Kurihara, Takuya; Prots, Yurii; Sato, Akira; Matsushita, Yoshitaka; Grin, Yuri; Tsai, An Pang
Source:
INORGANIC CHEMISTRY, 58 (9):6320-6327; 10.1021/acs.inorgchem.9b00513 MAY 6 2019
Abstract:
The Yb-Ga-Au 1/1 quasicrystal approximant (AP) composition ranges from Yb14.0Ga20.6Au65.4 to Yb-14.8Ga46.3Au38.9, and single crystals of the 1/1 AP having the composition Yb13.8Ga26.1Au60.1 were obtained by the self-flux technique. X-ray structural analysis demonstrated that the atomic structure [space group Im (3) over bar; a = 14.6889(9) angstrom] can be described by the body-centered packing of Tsai-type rhombic triacontahedron (RTH) clusters. The positional disorder in these clusters, interpreted as the average of an orientationally disordered tetrahedron and triangle, results in positional disorder in the outer shells. The elemental distributions and positions of mixtures of Au and Ga atoms in the RTH clusters correspond to those in the isostructural Yb15Al36Au49 1/1 AP.
Title:
Na3Sm(PO4)(2):(3+1)-dimensional commensurately modulated structure model and photoluminescence properties
Authors:
Zhang, RJ; Zhao, D; Zhong, Q; Xue, YL; Huang, GX Author Full Names: Zhang, Rui-Juan; Zhao, Dan; Zhong, Qiu; Xue, Ya-Li; Huang, Guang-Xu
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 234 (5):281-289; 10.1515/zkri-2018-2095 MAY 2019
Abstract:
For the first time, we determined the detailed crystal structure of Na3Sm(PO4)(2) using single crystal X-ray diffraction and established the commensurately modulated structure model using the superspace formalism. The structure adopts a (3+1)-dimensional superspace group Pca2(1)(0 beta 0)000 with the modulation vector q=1/3b*. At the same time, the photoluminescent properties of Na3Sm(PO4)(2) sintered at different temperatures between 800 and 1200 degrees C were studied. Under near-UV excitation (402 nm), Na3Sm(PO4)(2) shows intense characteristic emission bands of Sm3+ (561, 596, 642 nm) with the CIE coordinate of (0.5709, 0.4282), corresponding to orange color. The excitation spectrum covers a wide range from 350 nm to 470 nm, which indicates that Na3Sm(PO4)(2) can be efficiently activated by near-UV or visuable LED ship.
Title:
Influence of Ni Alloying on the Precipitation of Quasicrystal Phase in As-Cast Mg96.5Zn1Y1.5Mn1 Alloy
Authors:
Zhu, W; Liu, W; Zhang, YG; Ma, QQ; Zhang, JS; Xu, CX Author Full Names: Zhu, Wei; Liu, Wei; Zhang, Yong Gang; Ma, Qiang Qiang; Zhang, Jinshan; Xu, Chunxiang
Source:
ADVANCED ENGINEERING MATERIALS, 21 (4):10.1002/adem.201801238 APR 2019
Abstract:
Ni alloying is first adopted to explore the precipitation of quasicrystal phase (I phase) in Mg96.5Zn1Y1.5Mn1 alloy containing LPSO structure and W phase during solidification. Results show the component of I phase is Mg-3(Zn, Ni)(6)Y-1 which mainly distributes near the W phase. Besides, during the formation of I phase, Ni acts as Zn to participate in the precipitation process of I phase, making up for the deficiency of Zn. Meanwhile, an excellent strength-ductility balance with ultimate tensile strength (210MPa) and elongation (9.5%) is greatly optimized.
Title:
The Effect of Composition on the Formation of a BCC Approximant in Ti-Cr-Al-Si-O Alloys
Authors:
Firstov, SA; Gorban, VF; Karpets, MV; Krapivka, MO; Rokytska, OA; Samelyuk, AV Author Full Names: Firstov, S. A.; Gorban, V. F.; Karpets, M. V.; Krapivka, M. O.; Rokytska, O. A.; Samelyuk, A. V.
Source:
POWDER METALLURGY AND METAL CERAMICS, 57 (11-12):731-739; 10.1007/s11106-019-00038-3 MAR 2019
Abstract:
The microstructure, phase composition, and mechanical properties of Ti-Cr-Al-Si-O alloys in ascast state and after annealing at 800 degrees C have been studied. The as-cast alloys with 50 and 60 at.% Ti have two phases: a 1/1 (TiCrSi) cubic approximant of the quasicrystalline phase and an intermetallic Cr2Ti(C14) Laves phase in different ratios. The as-cast alloy with a high titanium amount (72 at.%) contains three phases: a 1/1(TiCrSi) approximant and two -Ti and -Ti solid solutions. The effect of annealing on the phase composition of the alloys has been studied. After annealing, the alloys with the lowest (50 at.%) and highest (72 at.%) Ti contents change their phase composition with the formation of Ti5Si3 silicide, while the alloy with 60 at.% Ti exhibits high thermal stabilityits phase composition remains unchanged. The changes in hardness of the starting and annealed alloys have been examined by automatic indentation. The highest hardness, 11.7 GPa, is shown by the as-cast Ti72Cr20Al2Si2(SiO2)(4) alloy. The hardness of the annealed Ti50Cr30Al13Si2(SiO2)(5) alloy increases to 14.8 GPa.

Update: 22-May-2019

Title:
Formation and crystallographic orientation study of quasicrystal, 2/1 and 1/1 approximants in Cd-Mg-Y system using electron backscatter diffraction (EBSD)
Authors:
Labib, F; Ohhashi, S; Tsai, AP Author Full Names: Labib, Farid; Ohhashi, Satoshi; Tsai, An-Pang
Source:
PHILOSOPHICAL MAGAZINE, 99 (12):1528-1550; 10.1080/14786435.2019.1585589 JUN 18 2019
Abstract:
A partial isothermal ternary phase diagram of the Cd-Mg-Y system including icosahedral quasicrystal (i-QC) and 1/1 approximant (APP) was obtained at 673 K. The stability of the i-QC and APPs in terms of composition and temperature was studied, as a result of which the 2/1 APP phase was discovered at 773 K. Moreover, the i-QC phase was found to be stable at lower Y concentrations of similar to 12-13 at.%, as compared to the 1/1 APP, which showed similar to 15-16 at.% Y. Single i-QC, 2/1 and 1/1 APP grains were also synthesized applying centrifuging system. Electron backscatter diffraction (EBSD) characterization of the obtained i-QC and APPs revealed almost the same Kikuchi patterns for the i-QC and 2/1 APP, indicating high resemblance of their structures. However, the Kikuchi pattern acquired from the 1/1 APP was distinguishable from the one obtained from the i-QC as it showed split bands. The occurrence of the split bands was associated with significant deviation from a perfect icosahedral symmetry. This was also confirmed by analysing calculated electron diffraction and Kikuchi patterns along pseudo-five-fold axes of the 2/1 and 1/1 APPs. Finally, orientation relationships between the i-QC, 1/1 APP and alpha-Mg were investigated by analysing acquired EBSD Kikuchi patterns from the respective domains. Accordingly, three perpendicular two-fold axes of the i-QC and {100} axes of the 1/1 APP occur along three mutually orthogonal {0001}, {10-10} and {11-20} axes of the alpha-Mg.
Title:
Effect of Ca Doping on Modulated Structures in Multiferroic Bi1-xCaxFeO3
Authors:
Hiroyama, T; Hirata, A; Inoue, Y; Horibe, Y; Koyama, Y Author Full Names: Hiroyama, Takumi; Hirata, Akihiko; Inoue, Yasuhide; Horibe, Yoichi; Koyama, Yasumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (5):10.7566/JPSJ.88.054601 MAY 15 2019
Abstract:
The crystallographic features of Bi1-xCaxFeO3 samples with x = 0.10, 0.15, 0.20, and 0.30 compositions are investigated by transmission electron microscopy. Perovskite-based modulated structures are found in all the samples except for the x = 0.10 sample where a rhombohedral R3c BiFeO3-type structure is observed at room temperature. The in situ heating experiment indicates that the modulated structure appears even in the x = 0.10 sample at 673K or higher. At room temperature, the modulation direction is found to change at approximately x = 0.20. The models of the modulated structures are constructed by introducing periodic antiphase boundaries in terms of the M-3-type rotational displacements of the FeO6 octahedra. The electron diffraction patterns simulated from the models are in good agreement with the experimental results. The composition dependence of the modulated structures is also discussed.
Title:
Preparation and electro-catalytic activity of nanoporous palladium by dealloying rapidly-quenched Al70Pd17Fe13 quasicrystalline alloy
Authors:
Liu, XY; Wang, YM; Qiang, JB; Wang, BL; Ma, DG; Zhang, W; Dong, C Author Full Names: Liu, Xin-yi; Wang, Ying-min; Qiang, Jian-bing; Wang, Bao-lin; Ma, Dian-guo; Zhang, Wei; Dong, Chuang
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 29 (4):785-790; 10.1016/S1003-6326(19)64988-5 APR 2019
Abstract:
The formation of nanoporous Pd was studied by electro-chemical dealloying a rapidly-quenched Al70Pd17Fe13 quasicrystal alloy in dilute NaCl aqueous solution, and the electro-catalytic activity of the nanoporous Pd towards methanol electro-oxidation was evaluated by cyclic voltammetry in 1 mol/L KOH solution. XRD and TEM analyses revealed that nano-decomposition of quasicrystal grains occurred in the initial stage of dealloying, and the fully dealloyed sample was composed of FCC-Pd phase. Scanning electron microscopy observation indicated that a maze-like nanoporous pattern was formed in the dealloyed sample, consisting of percolated pores of 5-20 nm in diameter in a skeleton of randomly-orientated Pd nano-ligaments with a uniform thickness of similar to 5 nm. A retention of similar to 12 at.% Al in the Pd nano-ligments was determined by energy dispersive X-ray spectroscopy (EDS). The nanoporous Pd demonstrated obvious electro-catalytic activity towards methanol electro-oxidation in alkaline environment.
Title:
Analytic Solutions to Two-Dimensional Decagonal Quasicrystals with Defects Using Complex Potential Theory
Authors:
Cao, HB; Shi, YQ; Li, W Author Full Names: Cao, Haobai; Shi, Yiqing; Li, Wu
Source:
CRYSTALS, 9 (4):10.3390/cryst9040209 APR 2019
Abstract:
An analytical treatment for two-dimensional point group 10 mm decagonal quasicrystals with defects was suggested based on the complex potential method. On the basis of the assumption of linear elasticity, two new conformal maps were applied to two examples: the first was an arc with an elliptic notch inner surface in a decagonal quasicrystal, where the complex potentials could be exactly obtained; and the second was concerned with a decagonal point group 10 mm quasicrystalline strip weakened by a Griffith crack, which was subjected to a pair of uniform static pressures. Using the basic idea underlying crack theory, the extent of the stress intensity factors was analytically estimated. If the height was allowed to approach infinity, these results can be turned into the known results of an ordinary crystal with only phonon elastic parameters when the phason and phonon-phason elastic constants are eliminated.
Title:
Y3Ru2-x-A Representative of a Composite Modulated Family of Intermetallics
Authors:
Lidin, S; Folkers, L Author Full Names: Lidin, Sven; Folkers, Laura
Source:
CRYSTALS, 9 (4):10.3390/cryst9040189 APR 2019
Abstract:
The compound Y3Ru2-x was synthesized from the elements and the structure was solved from single crystal synchrotron data. The high quality of the data allowed the determination of the incommensurate ordering of the compound, previously reported as disordered, with respect to the second subsystem. The compound crystallizes in the super space group X-3(00)0 with the q-vector axial along c*, q = 00, = 0.4276(7) and the centering vectors (1/3 2/3 0 1/3), (2/3 1/3 0 2/3).
Title:
Formation of ethylene-vinyl acetate composites filled with Al-Cu-Fe and Al-Cu-Cr quasicrystallline particles
Authors:
Tcherdyntsev, VV; Stepashkin, AA; Chukov, DI; Olifirov, LK; Senatov, FS Author Full Names: Tcherdyntsev, Victor V.; Stepashkin, Andrey A.; Chukov, Dilyus, I; Olifirov, Leonid K.; Senatov, Fedor S.
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 18 (1):572-589; 10.1016/j.jmrt.2018.05.008 JAN-MAR 2019
Abstract:
Icosahedral Al65Cu23Fe12 and decagonal Al73Cu11Cr16 quasicrystalline powders were synthesized by the mechanical alloying and subsequent annealing. Morphology evolution at mechanical alloying of Al-based powders was found to be determined by competition between cold welding and fracture mechanisms. Mechanical alloying results in formation of coarse agglomerates consisting of fine particles. The chemical binding between the polymer matrix and quasicrystals, destruction of agglomerated at extrusion, and the uniform distribution of quasicrystals over the polymer melt were provided by surface treatment of quasicrystalline particles with silanes. The highly filled (up to 60 wt%) ethylene-vinyl acetate/quasicrystals composites were obtained, and their rheological characteristics were studied. It was shown that the fluidity of the melt is retained at a high level providing uniform distribution of quasicrystalline particles over the polymer. (C) 2018 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda.
Title:
Study of the surface properties of the epoxy/quasicrystal composite
Authors:
Barros, TPD; Cavalcante, DGD; de Oliveira, DF; Caluete, RE; de Lima, SJG Author Full Names: dos Santos Barros, Thayza Pacheco; de Lima Cavalcante, Danielle Guedes; de Oliveira, Danniel Ferreira; Caluete, Rafael Evaristo; Guedes de Lima, Severino Jackson
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 18 (1):590-598; 10.1016/j.jmrt.2018.04.015 JAN-MAR 2019
Abstract:
This work consists of the study of the surface and Hardness properties of epoxy/quasicrystal (QC) composites. The composites had volumetric proportions of 1%, 10%, 20% and 30%, where the comparison was made between the composites and the pure epoxy resin. Techniques of Shore D Hardness, Thermogravimetric Analysis Techniques, Roughness Test, Contact Angle Analysis and Scanning Electron Microscopy (SEM) were used. Wettability test allowed to analyze the surface of the composite under the influence of two liquids: saline water and paraffinic oil. Regarding the composite and the pure resin, the contact angle increased when the liquid used in the test was saline water and decreased when exposed to paraffinic oil. It could be ensured that this small variation of the contact angles in relation to the increase of the composition occurred due to the influence of the roughness. In relation to saline water, the roughness has operated in order to prevent the liquid from spreading on the composite. As for paraffinic oil, it influenced in an opposite way, absorbing the oil and reducing the angle formed. When analyzing the pure quasicrystal, the effect was contrary to that of the composite: when it was exposed to saline water the contact angle decreased, on the other hand when exposed to paraffinic oil the resulting angle increased. This effect is related to the low polarity of the Quasicrystal, which when exposed to an apolar liquid tends to repel, thus forming a greater contact angle. Through this study it is concluded that it was possible to obtain a composite QC/Epoxy with greater hardness and still maintain its surface characteristics. (C) 2018 Published by Elsevier Editora Ltda. on behalf of Brazilian Metallurgical, Materials and Mining Association.

Update: 15-May-2019

Title:
Density Wave Probes Cuprate Quantum Phase Transition
Authors:
Webb, TA; Boyer, MC; Yin, Y; Chowdhury, D; He, Y; Kondo, T; Takeuchi, T; Ikuta, H; Hudson, EW; Hoffman, JE; Hamidian, MH Author Full Names: Webb, Tatiana A.; Boyer, Michael C.; Yin, Yi; Chowdhury, Debanjan; He, Yang; Kondo, Takeshi; Takeuchi, T.; Ikuta, H.; Hudson, Eric W.; Hoffman, Jennifer E.; Hamidian, Mohammad H.
Source:
PHYSICAL REVIEW X, 9 (2):10.1103/PhysRevX.9.021021 MAY 1 2019
Abstract:
In cuprates, the strong correlations in proximity to the antiferromagnetic Mott insulating state give rise to an array of unconventional phenomena beyond high-temperature superconductivity. Developing a complete description of the ground-state evolution is crucial to decoding the complex phase diagram. Here we use the structure of broken translational symmetry, namely, d-form factor charge modulations in (Bi, Pb)(2) (Sr, La)(2)CuO6+delta as a probe of the ground-state reorganization that occurs at the transition from truncated Fermi arcs to a large Fermi surface. We use real space imaging of nanoscale electronic inhomogeneity as a tool to access a range of dopings within each sample, and we definitively validate the spectral gap Delta as a proxy for local hole doping. From the Delta dependence of the charge modulation wave vector, we discover a commensurate-to-incommensurate transition that is coincident with the Fermi-surface transition from arcs to large hole pocket, demonstrating the qualitatively distinct nature of the electronic correlations governing the two sides of this quantum phase transition. Furthermore, the doping dependence of the incommensurate wave vector on the overdoped side is at odds with a simple Fermi-surface-driven instability.
Title:
Reprogrammability and Scalability of Magnonic Fibonacci Quasicrystals
Authors:
Lisiecki, F; Rychly, J; Kuswik, P; Glowinski, H; Klos, JW; Gross, F; Bykova, I; Weigand, M; Zelent, M; Goering, EJ; Schutz, G; Gubbiotti, G; Krawczyk, M; Stobiecki, F; Dubowik, J; Grafe, J Author Full Names: Lisiecki, Filip; Rychly, Justyna; Kuswik, Piotr; Glowinski, Hubert; Klos, Jaroslaw W.; Gross, Felix; Bykova, Iuliia; Weigand, Markus; Zelent, Mateusz; Goering, Eberhard J.; Schuetz, Gisela; Gubbiotti, Gianluca; Krawczyk, Maciej; Stobiecki, Feliks; Dubowik, Janusz; Graefe, Joachim
Source:
PHYSICAL REVIEW APPLIED, 11 (5):10.1103/PhysRevApplied.11.054003 MAY 1 2019
Abstract:
Magnonic crystals are systems that can be used to design and tune the dynamic properties of magnetization. Here, we focus on one-dimensional Fibonacci magnonic quasicrystals. We confirm the existence of collective spin waves propagating through the structure as well as dispersionless modes; the reprogammability of the resonance frequencies, dependent on the magnetization order; and dynamic spin-wave interactions. With the fundamental understanding of these properties, we lay a foundation for the scalable and advanced design of spin-wave band structures for spintronic, microwave, and magnonic applications.
Title:
Incommensurate 2k(F) density wave quantum criticality in two-dimensional metals
Authors:
Halbinger, J; Pimenov, D; Punk, M Author Full Names: Halbinger, Johannes; Pimenov, Dimitri; Punk, Matthias
Source:
PHYSICAL REVIEW B, 99 (19):10.1103/PhysRevB.99.195102 MAY 1 2019
Abstract:
We revisit the problem of two-dimensional metals in the vicinity of a quantum phase transition to incommensurate Q = 2k(F) charge-density-wave order, where the order-parameter wave vector Q connects two hot spots on the Fermi surface with parallel tangents. Earlier theoretical works argued that such critical points are potentially unstable, if the Fermi surface at the hot spots is not sufficiently flat. Here we perform a controlled, perturbative renormalization-group analysis and find a stable fixed point corresponding to a continuous quantum phase transition, which exhibits a strong dynamical nesting of the Fermi surface at the hot spots. We derive scaling forms of correlation functions at the critical point and discuss potential implications for experiments with transition-metal dichalcogenides and rare-earth tellurides.
Title:
Quasicrystalline electronic states in 30 degrees rotated twisted bilayer graphene
Authors:
Moon, P; Koshino, M; Son, YW Author Full Names: Moon, Pilkyung; Koshino, Mikito; Son, Young-Woo
Source:
PHYSICAL REVIEW B, 99 (16):10.1103/PhysRevB.99.165430 APR 29 2019
Abstract:
The recently realized bilayer graphene system with a twist angle of 30 degrees offers a new type of quasicrystal which unites the dodecagonal quasicrystalline nature and graphene's relativistic properties. Here, we introduce a concise theoretical framework that fully respects both the dodecagonal rotational symmetry and the massless Dirac nature, to describe the electronic states of the system. We find that the electronic spectrum consists of resonant states labeled by 12-fold quantized angular momentum, together with the extended relativistic states. The resulting quasiband structure is composed of the nearly flat bands with spiky peaks in the density of states, where the wave functions exhibit characteristic patterns which fit to the fractal inflations of the quasicrystal tiling. We also demonstrate that the 12-fold resonant states appear as spatially localized states in a finite-size geometry, which is another hallmark of quasicrystal. The theoretical method introduced here is applicable to a broad class of "extrinsic quasicrystals" composed of a pair of two-dimensional crystals overlaid on top of the other with incommensurate configurations.

Update: 8-May-2019

Title:
Effect of thermal treatment upon the structure incommensurability and magnetism of the spin chain oxide Sr3CaMn2CoO9+delta
Authors:
Seikh, MM; Caignaert, V; Sakly, N; Perez, O; Raveau, B; Hardy, V Author Full Names: Seikh, Md. Motin; Caignaert, Vincent; Sakly, Nahed; Perez, Olivier; Raveau, Bernard; Hardy, Vincent
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 790 572-576; 10.1016/j.jallcom.2019.03.183 JUN 25 2019
Abstract:
Spin chain oxides with different incommensurate hexagonal composite structures have been obtained for a same cationic composition according to the formula Sr3CaMn2CoO9+delta by varying the thermal treatments in air. The cell parameters of these oxides, a-9.5 angstrom, c(1)similar to 2.5 angstrom and c(2)similar to 3.8 angstrom, decrease as the deviation from commensurability increases, i.e. as gamma = c(1)/c(2) decreases and falls away from 2/3. All the investigated samples exhibit a signature typical of single-ion magnet (SIM), as well as a competition between single-chain magnet (SCM) and short-range ordering (SRO) responses. The balance between the latter two features turns out to be clearly affected by the thermal treatment. The sample quenched at 1450 degrees C, which structure is almost commensurate (gamma = 0.6659, close to 2/3), exhibits a SCM behavior without sizeable indication of SRO, whereas, for the samples annealed at 1300 degrees C or furnace cooled from 1400 degrees C with an incommensurate structure (gamma = 0.6622-0.6631), the SRO character is strongly reinforced. These changes in the magnetic response are assumed to originate from incorporation of extra oxygen into the commensurate stoichiometric Sr3CaMn2CoO9 oxide, leading to the replacement of some trimeric units built up of two octahedra and one trigonal prism (Oh(2)Tp) by tetrameric units (Oh(3)Tp) containing one additional octahedron, with a concomitant appearance of cationic vacancies in the trigonal prismatic sites. (C) 2019 Elsevier B.V. All rights reserved.
Title:
Many-beam dynamical scattering simulations for scanning and transmission electron microscopy modalities for 2D and 3D quasicrystals
Authors:
Singh, S; Lenthe, WC; De Graef, M Author Full Names: Singh, Saransh; Lenthe, William C.; De Graef, Marc
Source:
PHILOSOPHICAL MAGAZINE, 10.1080/14786435.2019.1605217
Abstract:
We present a general theory of electron scattering from both 2D and 3D quasicrystals, applicable to both transmission (forescatter) and scanning (backscatter) geometries. Specifically, simulations of conventional zone axis diffraction patterns, convergent beam diffraction patterns and electron backscatter diffraction for decagonal AlNiCo are presented. As expected, the geometry of the diffraction pattern is similar to kinematical patterns, but the intensity distributions show strong dynamical effects in all the modalities. Experimental electron backscatter diffraction patterns for AlNiCo are compared to simulated patterns for this 2D quasicrystalline structure as well as one of its crystalline monoclinic approximant phases, CoAl. While the simulated patterns from the quasicrystalline and approximant phases are very similar to the experimental patterns, direct comparison shows a better agreement with the decagonal phase.
Title:
Looking for alternatives to the superspace description of icosahedral quasicrystals
Authors:
Madison, AE; Madison, PA Author Full Names: Madison, A. E.; Madison, P. A.
Source:
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, 475 (2221):10.1098/rspa.2018.0667 JAN 2019
Abstract:
A multiple-cell approach is discussed as a possible alternative to the higher dimensional crystallography of icosahedral quasicrystals. It is based on the Socolar-Steinhardt tiling combined with the quasi-unit cell model. Quasi-unit cells fill the space without gaps and overlappings similar to those in periodic crystals. Similarly, the atoms can occupy general and special positions. The alloy stoichiometry and the packing density can be calculated through the relative tile frequencies, which in turn are determined as the components of the Perron-Frobenius eigenvector of the corresponding substitution matrix. The calculation of the diffraction pattern reduces to the Perron projection of a special matrix, the entries of which reflect the contribution of each type of quasi-unit cell to the coherent scattering.

Update: 2-May-2019

Title:
Characterization of aluminium matrix compositesreinforced by Al-Cu-Fe-Cr quasicrystalline particles
Authors:
Yuan, Y; Hou, H; Zhao, YH; Yan, F Author Full Names: Yuan, Ye; Hou, Hua; Zhao, Yuhong; Yan, Feng
Source:
MATERIALS RESEARCH EXPRESS, 6 (7):10.1088/2053-1591/ab15a4 JUL 2019
Abstract:
The Al63Cu25Fe9Cr3 quasicrystalline was prepared by conventional casting method. The microstructures and phase composition of Al63Cu25Fe12 quasi-crystalline and Al65Cu20Fe10Cr5 phases were characterized by XRD and SEM. Aluminium based composites was fabricated by using the Al63Cu25Fe9Cr3 quasicrystalline particles as the reinforcing phase and ZL101 as matrix with mechanical stirring. The effects of quasicrystals content, on the microstructure and mechanical properties of the obtained composite, were investigated. The results show that the as-cast quasicrystalline material is composed of d-phase(Al65Cu20Fe10Cr5), I-phase(Al63Cu25Fe12), lambda-Al3Fe, beta-AlFe3 and a small amount of eta-AlCu, theta-Al2Cu phases. After heat treatment, the quasicrystalline intermediate alloy composition tends to quasicrystal phase. In the composite material, the diffusion between the quasicrystalline and the matrix alloy caused the decomposition of the structure of quasicrystalline phase. With the increase of quasicrystalline content, the tensile strength of the composites increases. However, addition of the Cr element changes the acicular beta-Fe(Al80-85Fe6-9Si10-15) phase into a manlike or bone-like alpha-Fe(Al80-85Fe4-8Si6-8Cr3-5) phase which increases the elongation of the composite. The best comprehensive mechanical properties corresponded to the 7 wt% quasicrystalline particles. Strengthening mechanism of quasicrystal reinforced aluminum matrix composites, a model that model considers the dislocation strengthening mechanism and the effect of load transfers mechanism on the tensile strength of composites. This theory calculates the tensile strength of quasicrystalline reinforced aluminum matrix composites and verifies the effectiveness of the model through experiments.
Title:
Effect of selective post-aging treatment on subsurface damage of quasicrystal reinforced Al composite manufactured by selective laser melting
Authors:
Kang, N; El Mansori, M; Lu, JL; Lin, X; Huang, WD Author Full Names: Kang, N.; El Mansori, M.; Lu, J. L.; Lin, X.; Huang, W. D.
Source:
WEAR, 426 934-941; 10.1016/j.wear.2018.12.048 B APR 30 2019
Abstract:
In this work, Al-Fe-Cr quasicrystal reinforced Al matrix composite was in-situ prepared by using selective laser melting from powder mixture of Al-Cu-Fe-Cr quasicrystal and pure Al. The effect of selective post-aging treatment on microstructure and mechanical properties were determined with focus on the metastable phases. The microstructural analysis, which was determined by X-ray diffraction and scanning electron microscopy, indicates that the Al-based intermetallic is precipitated from supersaturated alpha-Al after the aging process. Moreover, the compression tests were performed on the samples in form of dense and lattice structures (50% porosity). The elastic modules of dense and lattice structural samples reduce from 21.3 GPa and 4.4-14.6 GPa and 3.6 GPa by using a low cooling-rated aging process. After aging process, the compressive deformation behavior of dense part changes from elastic-plastic-fracture mode to elastic-plastic-densification mode. On the other hand, the failure mechanism of lattice structural sample changes from rapid-single-stage to slow-double-stage with an improvement of the strain at failure.
Title:
Unconventional Charge Density Wave Order in the Pnictide Superconductor Ba(Ni1-xCox)(2)As-2
Authors:
Lee, S; de la Pena, G; Sun, SXL; Mitrano, M; Fang, YZ; Jang, HY; Lee, JS; Eckberg, C; Campbell, D; Collini, J; Paglione, J; de Groot, FMF; Abbamonte, P Author Full Names: Lee, Sangjun; de la Pena, Gilberto; Sun, Stella X-L; Mitrano, Matteo; Fang, Yizhi; Jang, Hoyoung; Lee, Jun-Sik; Eckberg, Chris; Campbell, Daniel; Collini, John; Paglione, Johnpierre; de Groot, F. M. F.; Abbamonte, Peter
Source:
PHYSICAL REVIEW LETTERS, 122 (14):10.1103/PhysRevLett.122.147601 APR 12 2019
Abstract:
Ba(Ni1-xCox)(2)As-2 is a structural homologue of the pnictide high temperature superconductor, Ba(Fe1-xCox)(2)As-2, in which the Fe atoms are replaced by Ni. Superconductivity is highly suppressed in this system, reaching a maximum T-c = 2.3 K, compared to 24 K in its iron-based cousin, and the origin of this T-c suppression is not known. Using x-ray scattering, we show that Ba(Ni1-xCox)(2)As-2 exhibits a unidirectional charge density wave (CDW) at its triclinic phase transition. The CDW is incommensurate, exhibits a sizable lattice distortion, and is accompanied by the appearance of alpha Fermi surface pockets in photoemission [B. Zhou et al., Phys. Rev. B 83, 035110 (2011)], suggesting it forms by an unconventional mechanism. Co doping suppresses the CDW, paralleling the behavior of antiferromagnetism in iron-based superconductors. Our study demonstrates that pnictide superconductors can exhibit competing CDW order, which may be the origin of T-c suppression in this system.
Title:
Electron diffraction study of crystal structures of (Sr1-xBax)(2)Nb2O7
Authors:
Aryal, B; Morikawa, D; Tsuda, K; Tsukada, S; Akishige, Y; Terauchi, M Author Full Names: Aryal, Bikas; Morikawa, Daisuke; Tsuda, Kenji; Tsukada, Shinya; Akishige, Yukikuni; Terauchi, Masami
Source:
PHYSICAL REVIEW MATERIALS, 3 (4):10.1103/PhysRevMaterials.3.044405 APR 12 2019
Abstract:
Selected-area electron diffraction and convergent-beam electron diffraction (CBED) techniques are used to reveal the Ba doping effect on the crystal structure of (Sr1-xBax)(2)Nb2O7 [SBN(x)] in the temperature range from 293 to 693 K. Ba doping of Sr2Nb2O7 (SN) causes weakening of the incommensurate modulation and deviation from the C-centered lattice. On the other hand, symmetries of fundamental reflections in CBED patterns of SBN(x) are seen to be the same as those of SN, showing a small structural deviation from Cmc2(1). Crystal symmetries above and below the temperature of a relaxorlike dielectric anomaly in SBN (x = 0.32) at 465 K remain unchanged. CBED experiments with a nanometer-sized electron probe do not show any indication of the presence of a nanodomain around this temperature. However, the presence of a few-micron-sized polar-inversion domains is found at around 573 K in SBN (x = 0.32). The origin of the reported relaxorlike dielectric anomaly in SBN (x = 0.32) is discussed on the basis of the experimental results of CBED.

Update: 25-Apr-2019

Title:
Influence of Ir Additions and Icosahedral Short Range Order (ISRO) on Nucleation and Growth Kinetics in Au-20.5Wt Pct Cu-4.5Wt PctAg Alloy
Authors:
Zollinger, J; Rouat, B; Guyon, J; Pillai, SK; Rappaz, M Author Full Names: Zollinger, J.; Rouat, B.; Guyon, J.; Pillai, S. K.; Rappaz, M.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 50A (5):2279-2288; 10.1007/s11661-019-05176-2 MAY 2019
Abstract:
Based on detailed EBSD analyses, Kurtuldu et al. (Acta Mater. 70:240-248, 2014) have explained the grain refinement of Au-12.5 wt pctCu-12.5 wt pctAg (yellow gold) by the addition of minute amounts of Ir in terms of icosahedral quasicrystal (iQC)-mediated nucleation, i.e., Ir induced the formation of Icosahedral short range order (ISRO) of atoms in the liquid, leading to the formation of iQC on which the fcc-phase forms. In the present contribution, we show that: (i) this mechanism is also responsible of the grain refinement in Au-20.5 wt pctCu-4.5 wt pctAg (pink gold) with Ir addition; (ii) ISRO also influences the morphology and growth kinetics of the fcc phase: at solidification rate of a few mm/s, 100 dendrites are replaced by a cellular-type morphology growing along 111 when 100 wt ppm of Ir is added to the melt; (iii) iQC-mediated nucleation is accompanied by a spinodal decomposition of the liquid, which is revealed at high cooling rate by the formation of Cu-rich particles or dendrites, some of them being also twinned, in parallel to iQC-mediated grain refinement and twin formation. (C) The Minerals, Metals & Materials Society and ASM International 2019
Title:
Structural evolution of La2Ti2O7 at elevated temperatures
Authors:
Ishizawa, N; Ninomiya, K; Wang, J Author Full Names: Ishizawa, Nobuo; Ninomiya, Keisuke; Wang, Jun
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 75 10.1107/S2052520619002105 2 APR 2019
Abstract:
Structural evolution of a La2Ti2O7 ferroelectric compound possessing perovskite-type slabs at elevated temperatures was investigated using the single-crystal X-ray diffraction technique. The monoclinic low-temperature phase (L) transformed into the orthorhombic high-temperature phase (H) via an incommensurately modulated phase (IC) between similar to 989 and similar to 1080 K. The L-IC transition was considered to be of the first order, with the L+IC two-phase co-existing region between similar to 989 and similar to 1027 K. The structure of IC was determined from the (3+1)-dimensional superspace representation with a modulation vector q = alpha a(o) (alpha similar or equal to 0.49), where a o is the a-axis vector of the basic cell. The structural modulation originated from the variation of the tilt angle of the TiO6 octahedra in the perovskite-type slab in association with small positional displacements of La atoms. The IC-H transition took place at -1080 K and was close to the second order. During the IC-H transition, nanoscale flat plate domains having either a cell twin of the L-type structural modules or a cell twin of the alternating H- and L-type structural modules began to appear in the approximant structure of IC. The thickness of the flat plate domains then grew rapidly along the modulation vector in proportion to (1/2-alpha)(-1) as alpha approached 1/2 with decreasing temperature. In the two-phase L+IC co-existing region, the IC phase consisting of the two types of cell twins was gradually replaced with the low-temperature monoclinic phase L, which is not cell twinned but rather twinned macroscopically by the L-type structural modules.

Update: 17-Apr-2019

Title:
Distortion analysis of crystalline and locally quasicrystalline 2D photonic structures with grazing-incidence small-angle X-ray scattering
Authors:
Pfluger, M; Soltwisch, V; Xavier, J; Probst, J; Scholze, F; Becker, C; Krumrey, M Author Full Names: Pflueger, Mika; Soltwisch, Victor; Xavier, Jolly; Probst, Juergen; Scholze, Frank; Becker, Christiane; Krumrey, Michael
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 52 322-331; 10.1107/S1600576719001080 2 APR 2019
Abstract:
In this study, grazing-incidence small-angle X-ray scattering (GISAXS) is used to collect statistical information on dimensional parameters in an area of 20 x 15 mm on photonic structures produced by nanoimprint lithography. The photonic structures are composed of crystalline and locally quasicrystalline two-dimensional patterns with structure sizes between about 100 nm and 10 mu m to enable broadband visible light absorption for use in solar-energy harvesting. These first GISAXS measurements on locally quasicrystalline samples demonstrate that GISAXS is capable of showing the locally quasicrystalline nature of the samples while at the same time revealing the long-range periodicity introduced by the lattice design. The scattering is described qualitatively in the framework of the distorted-wave Born approximation using a hierarchical model mirroring the sample design, which consists of a rectangular and locally quasicrystalline supercell that is repeated periodically to fill the whole surface. The nanoimprinted samples are compared with a sample manufactured using electron-beam lithography and the distortions of the periodic and locally quasiperiodic samples are quantified statistically. Owing to the high sensitivity of GISAXS to deviations from the perfect lattice, the misalignment of the crystallographic axes was measured with a resolution of 0.015 degrees, showing distortions of up to +/- 0.15 degrees in the investigated samples.
Title:
Effects of semisolid treatment and ECAP on the microstructure and mechanical properties of Mg-6.52Zn-0.95Y alloy with icosahedral phase
Authors:
Li, KN; Zhang, YB; Zeng, Q; Huang, GH; Ji, B; Yin, DD Author Full Names: Li, K. N.; Zhang, Y. B.; Zeng, Q.; Huang, G. H.; Ji, B.; Yin, D. D.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 751 283-291; 10.1016/j.msea.2019.02.083 MAR 28 2019
Abstract:
The microstructure evolutions and mechanical properties of Mg-6.52Zn-0.95Y (wt%) alloy with icosahedral phase (I-phase) by semisolid treatment and equal channel angular processing (ECAP) were systematically investigated. After semisolid treatment, lamellar ultra-fine eutectic phases with spacing of 100 +/- 19 nm formed at the grain boundaries. After subsequent 4 passes ECAP, fine grains (2.9 +/- 0.4 gm) were obtained and the lamellar eutectic phases were fragmented into 50-500 nm granular particles. The best comprehensive mechanical properties with ultimate tensile strength (UTS) of 385 +/- 18 MPa, tensile yield strength (TYS) of 290 +/- 3 MPa and elongation to failure (EL) of 22.0 +/- 1.6% were obtained by the combination of semisolid treatment and subsequent 2 passes ECAP at 300 degrees C followed by 2 passes ECAP at 200 degrees C, compared with that by the initial alloy. The improvement of mechanical properties results from combined effects of the grain refinement, dispersion of nanoscale I-phase particles and weakened basal texture. In addition, the I-phase particles contributed to the grain refinement during dynamic recrystallization by particle stimulated nucleation (PSN), which contributed to both strength and ductility. The average Schmid factor (SF) of basal slip increased from 0.2 to 0.4 after semisolid treatment and ECAP processing, which benefit the ductility.
Title:
Influence of cobalt substitution on the magnetism of NiBr2
Authors:
Rai, BK; Christianson, AD; Mandrus, D; May, AF Author Full Names: Rai, Binod K.; Christianson, Andrew D.; Mandrus, David; May, Andrew F.
Source:
PHYSICAL REVIEW MATERIALS, 3 (3):10.1103/PhysRevMaterials.3.034005 MAR 25 2019
Abstract:
Co-substituted Ni1-xCoxBr2 (0 <= x <= 1) single crystals were synthesized using vapor transport. The physical properties of the crystals were characterized by x-ray powder diffraction, magnetization, and specific-heat measurements. Room-temperature x-ray powder diffraction data indicate that a change from the CdCl2 structure type to the CdI2 structure type occurs within 0.56 < x < 0.76. NiBr2 has a commensurate antiferromagnetic phase below TN approximate to 46 K and an incommensurate magnetic ground state below TIC approximate to 20 K. Both magnetic transitions are affected by cobalt substitution, and the incommensurate phase transition is present up to at least x = 0.56. The evolution of magnetism has been studied as a function of cobalt content and is summarized in the temperature-composition phase diagram.
Title:
A neutron diffraction demonstration of long-range magnetic order in the quasicrystal approximant DyCd6
Authors:
Ryan, DH; Cadogan, JM; Kong, T; Canfield, PC; Goldman, AI; Kreyssig, A Author Full Names: Ryan, D. H.; Cadogan, J. M.; Kong, T.; Canfield, P. C.; Goldman, A. I.; Kreyssig, A.
Source:
AIP ADVANCES, 9 (3):10.1063/1.5079991 MAR 2019
Abstract:
We have used neutron powder diffraction to demonstrate the existence of long-range antiferromagnetic order of Ising-like Dy moments in the DyCd6 quasicrystal approximant phase. This cubic compound undergoes a slight distortion to a monoclinic cell at low temperatures. The Neel temperature is 18.0(2) K and the magnetic order of the Dy sublattice may be described in the parent cubic Im (3) over bar structure using a combination of two propagation vectors, k(1) = [0 0 0] and k(2) = [1/2 0 1/2], yielding 'anti-I' order. Alternatively, when referred to the monoclinic C2/c cell, the magnetic structure may be described by a single propagation vector: k = [1 0 0]. (C) 2019 Author(s).
Title:
Modulated magnetic structure in Fe-57 doped orthorhombic YbMnO3: A Mossbauer study
Authors:
Duttine, M; Wattiaux, A; Balima, F; Decorse, C; Moutaabbid, H; Ryan, DH; Bonville, P Author Full Names: Duttine, Mathieu; Wattiaux, Alain; Balima, Felix; Decorse, Claudia; Moutaabbid, Hicham; Ryan, D. H.; Bonville, Pierre
Source:
AIP ADVANCES, 9 (3):10.1063/1.5077005 MAR 2019
Abstract:
In the orthorhombic manganites o-RMnO3, where R is a heavy rare earth (R = Gd-Yb), the Mn3+ sublattice is known to undergo two magnetic transitions. The low temperature phase has an antiferromagnetic structure (collinear or elliptical), which has been well characterized by neutron diffraction in most of these compounds. The intermediate phase, occurring in a narrow temperature range (a few K), is documented for R = Gd-Ho as a collinear modulated structure, incommensurate with the lattice spacings. We report here on a Fe-57 Mossbauer study of 2% Fe-57 doped o-YbMnO3, where the spin only Fe3+ ion plays the role of a magnetic probe. From the analysis of the shape of the magnetic hyperfine Mossbauer spectra, we show that the magnetic structure of the intermediate phase in o-YbMnO3 (38.0 K < T < 41.5 K) is also modulated and incommensurate. (C) 2019 Author(s).

Update: 10-Apr-2019

Title:
Relaxing Kondo-screened Kramers doublets in CeRhSi3
Authors:
Pasztorova, J; Howell, A; Songvilay, M; Sarte, PM; Rodriguez-Rivera, JA; Arevalo-Lopez, AM; Schmalzl, K; Schneidewind, A; Dunsiger, SR; Singh, DK; Petrovic, C; Hu, R; Stock, C Author Full Names: Pasztorova, J.; Howell, A.; Songvilay, M.; Sarte, P. M.; Rodriguez-Rivera, J. A.; Arevalo-Lopez, A. M.; Schmalzl, K.; Schneidewind, A.; Dunsiger, S. R.; Singh, D. K.; Petrovic, C.; Hu, R.; Stock, C.
Source:
PHYSICAL REVIEW B, 99 (12):10.1103/PhysRevB.99.125144 MAR 25 2019
Abstract:
CeRhSi3 is a superconductor under pressure coexisting with a weakly antiferromagnetic phase characterized by a Bragg peak at (q) over right arrow (0) = (similar to 0.2, 0, 0.5) [N. Aso et al., J. Magn. Magn. Mater. 310, 602 (2007)]. The compound is also a heavy-fermion material with a large specific heat coefficient gamma = 110 mJ mol(-1) K-2 and a high Kondo temperature of T-K = 50 K, indicating CeRhSi3 is in a strongly Kondo screened state. We apply high-resolution neutron spectroscopy to investigate the magnetic fluctuations in the normal phase, at ambient pressures, and at low temperatures. We measure a commensurate dynamic response centered around the (Q) over right arrow = (0, 0, 2) position that gradually evolves to H similar to 0.2 with decreasing temperature and/or energy transfers. The response is broadened both in momentum and energy and is not reminiscent of sharp spin wave excitations found in insulating magnets where the electrons are localized. We parametrize the excitation spectrum and temperature dependence using a heuristic model utilizing the random-phase approximation to couple relaxing Ce3+ ground-state Kramers doublets with a Kondo-like dynamic response. With a Ruderman-Kittel-Kasuya-Yosida exchange interaction within the ab plane and an increasing single-site susceptibility, we can qualitatively reproduce the neutron spectroscopic results in CeRhSi3 and, namely, the trade-off between scattering at commensurate and incommensurate positions. We suggest that the antiferromagnetic phase in CeRhSi3 is driven by weakly correlated relaxing localized Kramers doublets and that CeRhSi3 at ambient pressures is on the border between a Rudderman-Kittel-Yosida antiferromagnetic state and a Kondo-screened phase where static magnetism is predominately absent.

Update: 4-Apr-2019

Title:
Analysis solution method for 3D planar crack problems of two-dimensional hexagonal quasicrystals with thermal effects
Authors:
Li, Y; Zhao, MH; Qin, QH; Fan, CY Author Full Names: Li, Yuan; Zhao, MingHao; Qin, Qing-Hua; Fan, CuiYing
Source:
APPLIED MATHEMATICAL MODELLING, 69 648-664; 10.1016/j.apm.2019.01.004 MAY 2019
Abstract:
An analysis solution method (ASM) is proposed for analyzing arbitrarily shaped planar cracks in two-dimensional (2D) hexagonal quasicrystal (QC) media. The extended displacement discontinuity (EDD) boundary integral equations governing three-dimensional (3D) crack problems are transferred to simplified integral-differential forms by introducing some complex quantities. The proposed ASM is based on the analogy between these EDD boundary equations for 3D planar cracks problems of 2D hexagonal QCs and those in isotropic thermoelastic materials. Mixed model crack problems under combined normal, tangential and thermal loadings are considered in 2D hexagonal QC media. By virtue of ASM, the solutions to 3D planar crack problems under various types of loadings for 2D hexagonal QCs are formulated through comparison to the corresponding solutions of isotropic thermoelastic materials which have been studied intensively and extensively. As an application, analytical solutions of a penny-shaped crack subjected uniform distributed combined loadings are obtained. Especially, the analytical solutions to a penny-shaped crack subjected to the anti-symmetric uniform thermal loading are first derived for 2D hexagonal QCs. Numerical solutions obtained by EDD boundary element method provide a way to verify the validity of the presented formulation. The influences of phonon-phason coupling effect on fracture parameters of 2D hexagonal QCs are assessed. (C) 2019 Elsevier Inc. All rights reserved.
Title:
Rational Design and Self-Assembly of Two-Dimensional, Dodecagonal DNA Quasicrystals
Authors:
Liu, LF; Li, Z; Li, YL; Mao, CD Author Full Names: Liu, Longfei; Li, Zhe; Li, Yulin; Mao, Chengde
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141 (10):4248-4251; 10.1021/jacs.9b00843 MAR 13 2019
Abstract:
Quasicrystals are a class of materials with long-range order but no translational periodicity. Though many quasicrystals have been discovered, rational design and engineering of quasicrystals remain a great challenge. Herein, we have developed a rational strategy to assemble two-dimensional (2D), dodecagonal quasicrystals from branched DNA nanomotifs. The key of our strategy is to balance the rigidity and flexibility of the motifs, which is controlled by the introduction of interbranch "bridges". By fine-tuning the experimental conditions, we are able to predictably produce either 2D quasicrystals or conventional crystals. This study presents a rational design, prediction and realization of quasicrystal formation.

Update: 27-Mar-2019

Title:
Spinodal decomposition in a melt-spun Cu-15Ni-8Sn alloy
Authors:
Kondo, S; Nakashima, H; Morimura, T Author Full Names: Kondo, Shin-ichiro; Nakashima, Hiromichi; Morimura, Takao
Source:
PHYSICA B-CONDENSED MATTER, 560 244-254; 10.1016/j.physb.2019.01.030 MAY 1 2019
Abstract:
We investigate the spinodal decomposition process in a melt-spun Cu-15Ni-8Sn alloy using X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron diffraction analyses. In the XRD measurements, an aging treatment of more than 300 min at 350 degrees C was required to obtain the (200) sidebands. TEM observations of the melt-spun samples aged at 350 degrees C for 40, 60, and 300 min showed a modulated structure with a wavelength too small to be detected by TEM and aging for about 1200 min was required for the clear appearance of a modulated structure. The electron diffraction patterns showed only the disordered fcc phase with no satellite structures in the sample aged for 20 min at 350 degrees C, which implied that no spinodal decomposition occurred. Aging for 40 min at 350 degrees C was required before the super-lattice reflection of DO22 was observed. These experimental results indicate that the decomposition process in the melt-spun alloy was slow initially.
Title:
Analytical and numerical investigations of noncollinear magnetic ordering in the frustrated delafossite CuCrO2
Authors:
Albaalbaky, A; Kvashnin, Y; Patte, R; Ledue, D Author Full Names: Albaalbaky, Ahmed; Kvashnin, Yaroslav; Patte, Renaud; Ledue, Denis
Source:
PHYSICAL REVIEW B, 99 (10):10.1103/PhysRevB.99.104415 MAR 12 2019
Abstract:
The magnetic propagation vector in delafossite CuCrO2 with classical Heisenberg spins is calculated analytically as a function of exchange interactions up to fourth-nearest neighbors. Exchange interactions are estimated by a series of density functional theory calculations for several values of lattice distortion. Our calculations show that the magnetic propagation vector is directly affected by the considered distortions providing different stable commensurate or incommensurate magnetic configurations. A realistic set of exchange interactions corresponding to a 0.1% lattice distortion yields the experimental ground state with an incommensurate propagation vector q similar to (0.329, 0.329, 0). We find that a very weak antiferromagnetic interlayer interaction favors an incommensurate ordering even in the absence of lattice distortion. Moreover, the exchange energy of a magnetic configuration of a finite crystal of CuCrO2 with periodic boundary conditions is derived analytically. Based on that, highly accurate Monte Carlo simulations performed on CuCrO2 confirm both the proposed analytical calculations and the density functional theory estimations, where we obtain excellent convergence toward the experimental ground state with a magnetic propagation vector q = (0.3288, 0.3288, 0).
Title:
Size effect of soft phonon dispersion in nanosized ferroics
Authors:
Morozovska, AN; Eliseev, EA Author Full Names: Morozovska, Anna N.; Eliseev, Eugene A.
Source:
PHYSICAL REVIEW B, 99 (11):10.1103/PhysRevB.99.115412 MAR 11 2019
Abstract:
Using Landau-Ginsburg-Devonshire theory, we derive and analyze analytical expressions for the frequency dispersion of soft phonon modes in nanosized ferroics and perform numerical calculations for a thin SrTiO3 film. We revealed the pronounced "true" size effect in the dependence of soft phonon spatial dispersion on the film thickness and predict that it can lead to the "apparent" or "false" size effect of dynamic flexoelectric coupling constants. Also, we derived analytical expressions describing the influence of finite size effect on the appearance and properties of the incommensurate spatial modulation induced by the static flexoelectric effect in ferroic thin films. To verify the theoretical predictions experimental measurements of the soft phonon dispersion in nanosized ferroics seem urgent.
Title:
Magnetic-field-induced incommensurate to collinear spin order transition in NiBr2
Authors:
Babu, S; Prokes, K; Huang, YK; Radu, F; Mishra, SK Author Full Names: Babu, S.; Prokes, K.; Huang, Y. K.; Radu, F.; Mishra, S. K.
Source:
JOURNAL OF APPLIED PHYSICS, 125 (9):10.1063/1.5066625 MAR 7 2019
Abstract:
The triangular spin lattice of NiBr2 is a canonical example of the frustrated helimagnet that shows a collinear commensurate antiferromagnetic to an incommensurate spin helix phase transition on cooling. Herein, we have studied a self-flux grown NiBr2 single crystal by neutron diffraction and low temperature magnetization measurements at fields up to 14 T. Experimental findings enable the deduction of the driving force responsible for the spin spiral ordering. The neutron diffraction data reveal satellite peaks representing characteristic features of an incommensurate magnetic state. The satellites develop symmetrically below T-N = 44.0(1) K, replacing the main magnetic reflections. Interestingly, a field-induced incommensurate to commensurate spin phase transition has been successfully demonstrated, which enforces the spin helix to restore the high temperature compensated antiferromagnetic structure. This reorientation can be described by a spin-flop in the (a-b) basal plane of a triangular spin lattice system. The findings offer a novel way for spin helix control of incommensurate phases, having immense scientific and technological implications in the next generation data storage devices.

Update: 20-Mar-2019

Title:
Isothermal section of Ga-Co-Cu phase diagram at 830 degrees C and its peculiarities
Authors:
Priputen, P; Drienovsky, M; Noga, P; Kusy, M; Cernickova, I; Janovec, J Author Full Names: Priputen, P.; Drienovsky, M.; Noga, P.; Kusy, M.; Cernickova, I; Janovec, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 785 1173-1179; 10.1016/j.jallcom.2019.01.288 MAY 15 2019
Abstract:
Recently, the Ga-based ternary alloys have gained interest for the possibility of finding new quasicrystals. Inspired by the previously reported decagonal and icosahedral quasicrystals identified in the Ga50Co25Cu25 alloy at 830 degrees C, the phase equilibria of 27 alloys of various composition were investigated in this work. Based on the obtained results, an isothermal section of the Ga-Co-Cu phase diagram at 830 degrees C was proposed. However, neither decagonal nor icosahedral quasicrystals were found to be stable at 830 degrees C, but instead of that, a superalloy-like structure was found in the Ga35Co25Cu40 alloy consisting of beta-GaCo and beta-GaCug-GaCu. (C) 2019 Elsevier B.V. All rights reserved.
Title:
Band gap closure, incommensurability and molecular dissociation of dense chlorine
Authors:
Dalladay-Simpson, P; Binns, J; Pena-Alvarez, M; Donnelly, ME; Greenberg, E; Prakapenka, V; Chen, XJ; Gregoryanz, E; Howie, RT Author Full Names: Dalladay-Simpson, Philip; Binns, Jack; Pena-Alvarez, Miriam; Donnelly, Mary-Ellen; Greenberg, Eran; Prakapenka, Vitali; Chen, Xiao-Jia; Gregoryanz, Eugene; Howie, Ross T.
Source:
NATURE COMMUNICATIONS, 10 10.1038/s41467-019-09108-x MAR 8 2019
Abstract:
Diatomic elemental solids are highly compressible due to the weak interactions between molecules. However, as the density increases the intra-and intermolecular distances become comparable, leading to a range of phenomena, such as structural transformation, molecular dissociation, amorphization, and metallisation. Here we report, following the crystallization of chlorine at 1.15(30) GPa into an ordered orthorhombic structure (oC8), the existence of a mixed-molecular structure (mC8, 130(10)-241(10) GPa) and the concomitant observation of a continuous band gap closure, indicative of a transformation into a metallic molecular form around 200(10) GPa. The onset of dissociation of chlorine is identified by the observation of the incommensurate structure (i-oF4) above 200(10) GPa, before finally adopting a monatomic form (oI2) above 256(10) GPa.
Title:
Resonantly hybridized excitons in moire superlattices in van der Waals heterostructures
Authors:
Alexeev, EM; Ruiz-Tijerina, DA; Danovich, M; Hamer, MJ; Terry, DJ; Nayak, PK; Ahn, S; Pak, S; Lee, J; Sohn, JI; Molas, MR; Koperski, M; Watanabe, K; Taniguchi, T; Novoselov, KS; Gorbachev, RV; Shin, HS; Fal'ko, VI; Tartakovskii, AI Author Full Names: Alexeev, Evgeny M.; Ruiz-Tijerina, David A.; Danovich, Mark; Hamer, Matthew J.; Terry, Daniel J.; Nayak, Pramoda K.; Ahn, Seongjoon; Pak, Sangyeon; Lee, Juwon; Sohn, Jung Inn; Molas, Maciej R.; Koperski, Maciej; Watanabe, Kenji; Taniguchi, Takashi; Novoselov, Kostya S.; Gorbachev, Roman V.; Shin, Hyeon Suk; Fal'ko, Vladimir I.; Tartakovskii, Alexander I.
Source:
NATURE, 567 (7746):81-+; 10.1038/s41586-019-0986-9 MAR 7 2019
Abstract:
Atomically thin layers of two-dimensional materials can be assembled in vertical stacks that are held together by relatively weak van der Waals forces, enabling coupling between monolayer crystals with incommensurate lattices and arbitrary mutual rotation(1,2). Consequently, an overarching periodicity emerges in the local atomic registry of the constituent crystal structures, which is known as a moire superlattice(3). In graphene/hexagonal boron nitride structures(4), the presence of a moire superlattice can lead to the observation of electronic minibands(5-7), whereas in twisted graphene bilayers its effects are enhanced by interlayer resonant conditions, resulting in a superconductor-insulator transition at magic twist angles(8). Here, using semiconducting heterostructures assembled from incommensurate molybdenum diselenide (MoSe2) and tungsten disulfide (WS2) monolayers, we demonstrate that excitonic bands can hybridize, resulting in a resonant enhancement of moire superlattice effects. MoSe2 and WS2 were chosen for the near-degeneracy of their conduction-band edges, in order to promote the hybridization of intra- and interlayer excitons. Hybridization manifests through a pronounced exciton energy shift as a periodic function of the interlayer rotation angle, which occurs as hybridized excitons are formed by holes that reside in MoSe2 binding to a twist-dependent superposition of electron states in the adjacent monolayers. For heterostructures in which the monolayer pairs are nearly aligned, resonant mixing of the electron states leads to pronounced effects of the geometrical moire pattern of the heterostructure on the dispersion and optical spectra of the hybridized excitons. Our findings underpin strategies for bandstructure engineering in semiconductor devices based on van der Waals heterostructures(9).
Title:
Redox behaviour and solid solubility of cerium ortho-niobates
Authors:
Harris, CM; Skinner, SJ Author Full Names: Harris, Cassandra M.; Skinner, Stephen J.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 271 135-143; 10.1016/j.jssc.2018.12.042 MAR 2019
Abstract:
Using Ce L-III edge X-ray absorption near edge spectroscopy (XANES), it is shown that acceptor dopants introduced to cerium members of the rare earth ortho-niobate series, Ce1-xSrxNbO4 +/- delta and Ce1-xSrxNbO4 +/- delta, are charge compensated by the formation of holes on the cerium sublattice. These spectroscopic studies are complemented by structural studies, using X-ray and neutron powder diffraction, determining that the solubility limit of the strontium and calcium dopants within the CeNbO4+delta structure is similar to 10% and similar to 30% respectively. Under oxidising conditions, the Ce3+/Ce4+ redox couple facilitates reversible redox processes, and it is observed that the Ce1-xSrxNbO4 +/- delta and Ce1-xSrxNbO4 +/- delta materials form commensurate and incommensurately modulated oxygen hyperstoichiometric phases as a function of temperature. Under reducing atmospheres, this redox activity is suppressed, and charge-compensating Ce4+ holes are annihilated.
Title:
Kinetics of a Phonon-Mediated Laser-Driven Structural Phase Transition in Sn2P2Se6
Authors:
Kubli, M; Savoini, M; Abreu, E; Burganov, B; Lantz, G; Huber, L; Neugebauer, MJ; Boie, L; Esposito, V; Bothschafter, EM; Parchenko, S; Grubel, S; Porer, M; Rittmann, J; Beaud, P; Staub, U; Yabashi, M; Tanaka, Y; Katayama, T; Togashi, T; Kohutych, AA; Vysochanskii, YM; Johnson, SL Author Full Names: Kubli, Martin; Savoini, Matteo; Abreu, Elsa; Burganov, Bulat; Lantz, Gabriel; Huber, Lucas; Neugebauer, Martin J.; Boie, Larissa; Esposito, Vincent; Bothschafter, Elisabeth M.; Parchenko, Sergii; Gruebel, Sebastian; Porer, Michael; Rittmann, Jochen; Beaud, Paul; Staub, Urs; Yabashi, Makina; Tanaka, Yoshikazu; Katayama, Tetsuo; Togashi, Tadashi; Kohutych, Anton A.; Vysochanskii, Yulian M.; Johnson, Steven L.
Source:
APPLIED SCIENCES-BASEL, 9 (3):10.3390/app9030525 FEB 1 2019
Abstract:
We investigate the structural dynamics of the incommensurately modulated phase of Sn2P2Se6 by means of time-resolved X-ray diffraction following excitation by an optical pump. Tracking the incommensurable distortion in the time domain enables us to identify the transport effects leading to a complete disappearance of the incommensurate phase over the course of 100 ns. These observations suggest that a thin surface layer of the high-temperature phase forms quickly after photo-excitation and then propagates into the material with a constant velocity of 3.7 m/s. Complementary static structural measurements reveal previously unreported higher-order satellite reflection in the incommensurate phase. These higher-order reflections are attributed to cubic vibrational terms in the Hamiltonian.
Title:
Wood-Derived Dietary Fibers Promote Beneficial Human Gut Microbiota
Authors:
La Rosa, SL; Kachrimanidou, V; Buffetto, F; Pope, PB; Pudlo, NA; Martens, EC; Rastall, RA; Gibson, GR; Westereng, B Author Full Names: La Rosa, Sabina Leanti; Kachrimanidou, Vasiliki; Buffetto, Fanny; Pope, Phillip B.; Pudlo, Nicholas A.; Martens, Eric C.; Rastall, Robert A.; Gibson, Glenn R.; Westereng, Bjerge
Source:
MSPHERE, 4 (1):10.1128/mSphere.00554-18 JAN-FEB 2019
Abstract:
Woody biomass is a sustainable and virtually unlimited source of hemicellulosic polysaccharides. The predominant hemicelluloses in softwood and hardwood are galactoglucomannan (GGM) and arabinoglucuronoxylan (AGX), respectively. Based on the structure similarity with common dietary fibers, GGM and AGX may be postulated to have prebiotic properties, conferring a health benefit on the host through specific modulation of the gut microbiota. In this study, we evaluated the prebiotic potential of acetylated GGM (AcGGM) and highly acetylated AGX (AcAGX) obtained from Norwegian lignocellulosic feedstocks in vitro. In pure culture, both substrates selectively promoted the growth of Bifidobacterium, Lactobacillus, and Bacteroides species in a manner consistent with the presence of genetic loci for the utilization of beta-manno-oligosaccharides/beta-mannans and xylo-oligosaccharides/ xylans. The prebiotic potential of AcGGM and AcAGX was further assessed in a pH-controlled batch culture fermentation system inoculated with healthy adult human feces. Results were compared with those obtained with a commercial fructo-oligosaccharide (FOS) mixture. Similarly to FOS, both substrates significantly increased (P < 0.05) the Bifidobacterium population. Other bacterial groups enumerated were unaffected with the exception of an increase in the growth of members of the Bacteroides-Prevotella group, Faecalibacterium prausnitzii, and clostridial cluster IX (P < 0.05). Compared to the other substrates, AcGGM promoted butyrogenic fermentation whereas AcAGX was more propiogenic. Although further in vivo confirmation is necessary, these results demonstrate that both AcGGM and AcAGX from lignocellulosic feedstocks can be used to direct the promotion of beneficial bacteria, thus exhibiting a promising prebiotic ability to improve or restore gut health. IMPORTANCE The architecture of the gut bacterial ecosystem has a profound effect on the physiology and well-being of the host. Modulation of the gut microbiota and the intestinal microenvironment via administration of prebiotics represents a valuable strategy to promote host health. This work provides insights into the ability of two novel wood-derived preparations, AcGGM and AcAGX, to influence human gut microbiota composition and activity. These compounds were selectively fermented by commensal bacteria such as Bifidobacterium, Bacteroides-Prevotella, F. prausnitzii, and clostridial cluster IX spp. This promoted the microbial synthesis of acetate, propionate, and butyrate, which are beneficial to the microbial ecosystem and host colonic epithelial cells. Thus, our results demonstrate potential prebiotic properties for both AcGGM and AcAGX from lignocellulosic feedstocks. These findings represent pivotal requirements for rationally designing intervention strategies based on the dietary supplementation of AcGGM and AcAGX to improve or restore gut health.

Update: 13-Mar-2019

Title:
Mechanics of dislocations and metadislocations in quasicrystals and their approximants: power invariance and balance
Authors:
Mariano, PM Author Full Names: Mariano, Paolo Maria
Source:
CONTINUUM MECHANICS AND THERMODYNAMICS, 31 (2):373-399; 10.1007/s00161-018-0690-2 MAR 2019
Abstract:
We discuss the mechanics of a single dislocation in quasicrystals. We account for dislocation's core by means of a non-constant line energy. Above all, we focus attention on the origin of the balance equations involving the pertinent bulk and line actions. We derive all balances, including those of configurational actions along the dislocation line,from a unique invariance requirement for the so-called relative power; it is an axiom that furnishes also the action-reaction principle for the standard traction and the phason one, as well as the standard Cauchy theorem and, in addition, the existence of phason stress and self-action. The theoretical scheme presented here includes the description of the large core of metadislocations in quasicrystal's approximants (complex metallic alloys). Each metadislocation features thousands of atoms per unit thickness in the direct vicinity of the core, a circumstance suggesting to consider it as a sort of micro-rod, a view adopted in the present paper. In fact, from an abstract point of view, the results presented here describe the motion of a rod within a body with vectorial microstructure.
Title:
Principles of weakly ordered domains in intermetallics: the cooperative effects of atomic packing and electronics in Fe2Al5
Authors:
Vinokur, AI; Hilleke, KP; Fredrickson, DC Author Full Names: Vinokur, Anastasiya, I; Hilleke, Katerina P.; Fredrickson, Daniel C.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 297-306; 10.1107/S2053273318017461 2 MAR 2019
Abstract:
Many complex intermetallic structures feature a curious juxtaposition of domains with strict 3D periodicity and regions of much weaker order or incommensurability. This article explores the basic principles leading to such arrangements through an investigation of the weakly ordered channels of Fe2Al5. It starts by experimentally confirming the earlier crystallographic model of the high-temperature form, in which nearly continuous columns of electron density corresponding to disordered Al atoms emerge. Then electronic structure calculations on ordered models are used to determine the factors leading to the formation of these columns. These calculations reveal electronic pseudogaps near 16 electrons/Fe atom, an electron concentration close to the Al-rich side of the phase's homogeneity range. Through a reversed approximation Molecular Orbital (raMO) analysis, these pseudogaps are correlated with the filling of 18-electron configurations on the Fe atoms with the support of isolobal sigma Fe-Fe bonds. The resulting preference for 16 electrons/Fe requires a fractional number of Al atoms in the Fe2Al5 unit cell. Density functional theory-chemical pressure (DFT-CP) analysis is then applied to investigate how this nonstoichiometry is accommodated. The CP schemes reveal strong quadrupolar distributions on the Al atoms of the channels, suggestive of soft atomic motions along the undulating electron density observed in the Fourier map that allow the Al positions to shift easily in response to compositional changes. Such a combination of preferred electron counts tied to stoichiometry and continuous paths of CP quadrupoles could provide predictive indicators for the emergence of channels of disordered or incommensurately spaced atoms in intermetallic structures.
Title:
Ted Janssen and aperiodic crystals
Authors:
de Boissieu, M Author Full Names: de Boissieu, Marc
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 273-280; 10.1107/S2053273318016765 2 MAR 2019
Abstract:
This article reviews some of Ted Janssen's (1936-2017) major contributions to the field of aperiodic crystals. Aperiodic crystals are long-range ordered structures without 3D lattice translations and encompass incommensurately modulated phases, incommensurate composites and quasicrystals. Together with Pim de Wolff and Aloysio Janner, Ted Janssen invented the very elegant theory of superspace crystallography that, by adding a supplementary dimension to the usual 3D space, allows for a deeper understanding of the atomic structure of aperiodic crystals. He also made important contributions to the understanding of the stability and dynamics of aperiodic crystals, exploring their fascinating physical properties. He constantly interacted and collaborated with experimentalists, always ready to share and explain his detailed understanding of aperiodic crystals.
Title:
A side-by-side comparison of the solidification dynamics of quasicrystalline and approximant phases in the Al-Co-Ni system
Authors:
Han, I; Xiao, XH; Sun, HP; Shahani, AJ Author Full Names: Han, Insung; Xiao, Xianghui; Sun, Haiping; Shahani, Ashwin J.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 281-296; 10.1107/S2053273318017114 2 MAR 2019
Abstract:
Quasicrystals and their approximants have triggered widespread interest due to the challenge of solving their complex crystal structures as well as their possibly exceptional properties. The structural motifs of approximants are similar to those of the corresponding quasicrystals, but to what extent are their crystallization pathways the same? Unfortunately, there have been very few in situ experimental investigations to answer this question. Here, by leveraging the high penetrating power of hard X-rays, synchrotron-based X-ray tomography was conducted in order to capture the nucleation and growth of a decagonal quasicrystal and its related approximant. The combination of data-driven computational analysis with new thermodynamic databases allowed the characterization, with high precision, of the constitutional and kinetic driving forces for crystallization. The experimental results prove that the growth of both crystals from a liquid is dominated by first-order kinetics. Nevertheless, and somewhat surprisingly, significant differences were observed in their rates of nucleation and growth. The reasons for such divergent behaviours are discussed in light of contemporary theories of intermetallic crystallization.
Title:
Phason-flips refinement of and multiple-scattering correction for the d-AlCuRh quasicrystal
Authors:
Ruganski, I; Strzalka, R; Wolny, J Author Full Names: Ruganski, Ireneusz; Strzalka, Radoslaw; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 352-361; 10.1107/S2053273318017254 2 MAR 2019
Abstract:
The origin of the characteristic bias observed in a logarithmic plot of the calculated and measured intensities of diffraction peaks for quasicrystals has not yet been established. Structure refinement requires the inclusion of weak reflections; however, no structural model can properly describe their intensities. For this reason, detailed information about the atomic structure is not available. In this article, a possible cause for the characteristic bias, namely the lattice phason flip, is investigated. The derivation of the structure factor for a tiling with inherent phason flips is given and is tested for the AlCuRh decagonal quasicrystal. Although an improvement of the model is reported, the bias remains. A simple correction term involving a redistribution of the intensities of the peaks was tested, and successfully removed the bias from the diffraction data. This new correction is purely empirical and only mimics the effect of multiple scattering. A comprehensive study of multiple scattering requires detailed knowledge of the diffraction experiment geometry.
Title:
Aperiodic order coming of age: from inorganic materials to dynamic protein superstructures
Authors:
Borgstahl, G; Goldman, AI; Thiel, PA Author Full Names: Borgstahl, Gloria; Goldman, Alan I.; Thiel, Patricia A.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 212-213; 10.1107/S2053273319001165 2 MAR 2019
Title:
Full real-space analysis of a dodecagonal quasicrystal
Authors:
Schenk, S; Zollner, EM; Krahn, O; Schreck, B; Hammer, R; Forster, S; Widdra, W Author Full Names: Schenk, Sebastian; Zollner, Eva Maria; Krahn, Oliver; Schreck, Berit; Hammer, Rene; Foerster, Stefan; Widdra, Wolf
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 307-313; 10.1107/S2053273319000056 2 MAR 2019
Abstract:
The atomically resolved real-space structure of a long-range-ordered dodecagonal quasicrystal is determined based on scanning tunnelling microscopy. For the BaTiO3-derived oxide quasicrystal which spontaneously forms on a Pt(111) surface, 8100 atomic positions have been determined and are compared with an ideal Niizeki-Gahler tiling. Although the Niizeki-Gahler tiling has a complex three-element structure, the abundance of the triangle, square and rhomb tiling elements in the experimental data closely resembles the ideal frequencies. Similarly, the frequencies of all possible next-neighbour tiling combinations are, within the experimental uncertainty, identical to the ideal tiling. The angular and orientational distributions of all individual tiling elements show the characteristics of the dodecagonal quasicrystal. In contrast, the analysis of the orientation of characteristic and more complex tiling combinations indicates the partial decomposition of the quasicrystal into small patches with locally reduced symmetry. These, however, preserve the long-range quasicrystal coherence. The symmetry reduction from dodecagonal to sixfold is assigned to local interaction with the threefold substrate. It leads to atomic flips which preserve the number of quasicrystal tiling elements.
Title:
Characterizing modulated structures with first-principles calculations: a unified superspace scheme of ordering in mullite
Authors:
Klar, PB; Etxebarria, I; Madariaga, G Author Full Names: Klar, Paul Benjamin; Etxebarria, Inigo; Madariaga, Gotzon
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 260-272; 10.1107/S2053273319000846 2 MAR 2019
Abstract:
The benefit of computational methods applying density functional theory for the description and understanding of modulated crystal structures is investigated. A method is presented which allows one to establish, improve and test superspace models including displacive and occupational modulation functions from firstprinciples calculations on commensurate structures. The total energies of different configurations allow one to distinguish stable and less stable structure models. The study is based on a series of geometrically optimized superstructures of mullite (A(l4+2x)Si(2-2x)O(10-x)) derived from the superspace group Pham(alpha 01/2)0ss. Despite the disordered and structurally complex nature of mullite, the calculations on ordered superstructures are very useful for determining the ideal Al/Si ordering in mullite, extracting atomic modulation functions as well as understanding the SiO2-Al2O3 phase diagram. The results are compared with experimentally established models which confirm the validity and utility of the presented method.
Title:
Phase diagram of the Kondo model on the zigzag ladder
Authors:
Peschke, M; Woelk, LM; Potthoff, M Author Full Names: Peschke, Matthias; Woelk, Lena-Marie; Potthoff, Michael
Source:
PHYSICAL REVIEW B, 99 (8):10.1103/PhysRevB.99.085140 FEB 27 2019
Abstract:
The effect of next-nearest-neighbor hopping t(2) on the ground-state phase diagram of the one-dimensional Kondo lattice is studied with density-matrix renormalization-group techniques and by comparing with the phase diagram of the classical-spin variant of the same model. For a finite t(2), i.e., for a zigzag-ladder geometry, indirect antiferromagnetic interactions between the localized spins are geometrically frustrated. We demonstrate that t(2) at the same time triggers several magnetic phases which are absent in the model with nearest-neighbor hopping only. For strong J, we find a transition from antiferromagnetic to incommensurate magnetic short-range order, which can be understood entirely in the classical-spin picture. For weaker J, a spin-dimerized phase emerges, which spontaneously breaks the discrete translation symmetry. The phase is not accessible to perturbative means but is explained, on a qualitative level, by the classical-spin model as well. Spin dimerization alleviates magnetic frustration and is interpreted as a key to understand the emergence of quasi-long-range spiral magnetic order, which is found at weaker couplings. The phase diagram at weak J, with gapless quasi-long-range order on top of the twofold degenerate spin-dimerized ground state, competing with a nondegenerate phase with gapped spin (and charge) excitations, is unconventional and eludes an effective low-energy spin-only theory.
Title:
Gauge theory for the cuprates near optimal doping
Authors:
Sachdev, S; Scammell, HD; Scheurer, MS; Tarnopolsky, G Author Full Names: Sachdev, Subir; Scammell, Harley D.; Scheurer, Mathias S.; Tarnopolsky, Grigory
Source:
PHYSICAL REVIEW B, 99 (5):10.1103/PhysRevB.99.054516 FEB 25 2019
Abstract:
We describe the phase diagram of a 2+1-dimensional SU(2) gauge theory of fluctuating incommensurate spin density waves for the hole-doped cuprates. Our primary assumption is that all low-energy fermionic excitations are gauge neutral and electron-like, while the spin density wave order is fractionalized into Higgs fields transforming as adjoints of the gauge SU(2). The confining phase of the gauge theory is a conventional Fermi liquid with a large Fermi surface (and its associated d-wave superconductor). There is a quantum phase transition to a Higgs phase describing the "pseudogap" at lower doping. Depending on the quartic terms in the Higgs potential, the Higgs phase exhibits one or more of charge density wave, Ising-nematic, time-reversal odd scalar spin chirality, and Z(2) topological orders. It is notable that the emergent broken symmetries in our theory of fluctuating spin density waves coincide with those observed in diverse experiments. For the electron-doped cuprates, the spin density wave fluctuations are at wave vector (pi, pi), and then the corresponding SU(2) gauge theory only has a crossover between the confining and Higgs regimes, with an exponentially large confinement scale deep in the Higgs regime. On the Higgs side, for both the electron- and hole-doped cases, and at scales shorter than the confinement scale (which can be infinite when Z(2) topological order is present), the electron spectral function has a "fractionalized Fermi liquid" form with small Fermi surfaces. We also describe the deconfined quantum criticality of the Higgs transition in the limit of a large number of Higgs flavors, and perturbatively discuss its coupling to fermionic excitations.
Title:
Spin dynamics and field-induced magnetic phase transition in the honeycomb Kitaev magnet alpha-Li2IrO3
Authors:
Choi, S; Manni, S; Singleton, J; Topping, CV; Lancaster, T; Blundell, SJ; Adroja, DT; Zapf, V; Gegenwart, P; Coldea, R Author Full Names: Choi, Sungkyun; Manni, S.; Singleton, J.; Topping, C., V; Lancaster, T.; Blundell, S. J.; Adroja, D. T.; Zapf, V; Gegenwart, P.; Coldea, R.
Source:
PHYSICAL REVIEW B, 99 (5):10.1103/PhysRevB.99.054426 FEB 25 2019
Abstract:
The layered honeycomb iridate alpha-Li2IrO3 displays an incommensurate magnetic structure with counter-rotating moments on nearest-neighbor sites, proposed to be stabilized by strongly frustrated anisotropic Kitaev interactions between spin-orbit entangled Ir4+ magnetic moments. Here we report powder inelastic neutron scattering measurements that observe sharply dispersive low-energy magnetic excitations centered at the magnetic ordering wave vector, attributed to Goldstone excitations of the incommensurate order, as well as an additional intense mode above a gap Delta similar or equal to 2.3 meV. Zero-field muon-spin relaxation measurements show clear oscillations in the muon polarization below the Ned temperature T-N similar or equal to 15 K with a time-dependent profile consistent with bulk incommensurate long-range magnetism. Pulsed-field magnetization measurements observe that only about half the saturation magnetization value is reached at the maximum field of 64 T. A clear anomaly near 25 T indicates a transition to a phase with reduced susceptibility. The transition field has a Zeeman energy comparable to the zero-field gapped mode, suggesting gap suppression as a possible mechanism for the field-induced transition.
Title:
Static response of functionally graded multilayered one-dimensional hexagonal piezoelectric quasicrystal plates using the state vector approach
Authors:
Huang, YZ; Li, Y; Yang, LZ; Gao, Y Author Full Names: Huang, Yun-zhi; Li, Yang; Yang, Lian-zhi; Gao, Yang
Source:
JOURNAL OF ZHEJIANG UNIVERSITY-SCIENCE A, 20 (2):133-147; 10.1631/jzus.A1800472 FEB 2019
Abstract:
The effect of the non-homogeneity of material properties has been considered the important variation mechanism in the static responses of quasicrystal structures, but the existing theoretical model for it is unable to simulate the material change format beyond the exponential function. In this paper, we create a new model of functionally graded multilayered 1D piezoelectric quasicrystal plates using the state vector approach, in which varying functionally graded electro-elastic properties can be extended from exponential to linear and higher order in the thickness direction. Based on the state equations, an analytical solution for a single plate has been derived, and the result for the corresponding multilayered case is obtained utilizing the propagator matrix method. The present study shows, in particular, that coefficient orders of two varying functions (the power function and the exponential function) of the material gradient provide the ability to tailor the mechanical behaviors in the system's phonon, phason, and electric fields. Moreover, the insensitive points of phonon stress and electric potential under functionally graded effects in the quasicrystal layer are observed. In addition, the influences of stacking sequences and discontinuity of horizontal stress are explored in the simulation by the new model. The results are very useful for the design and understanding of the characterization of functionally graded piezoelectric quasicrystal materials in their applications to multilayered systems.
Title:
Elasto-hydrodynamics of quasicrystals with a crack under sudden impacts
Authors:
Zhou, YB; Li, XF Author Full Names: Zhou, Y. -B.; Li, X. -F.
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 98 (10):419-436; 10.1080/09500839.2019.1566796 2018
Abstract:
In this paper, a mode-III crack in one-dimensional (1D) hexagonal quasicrystals subjected to anti-plane impact loading is analyzed. The elasto-hydrodynamics of quasicrystals is adopted, where the phonon field obeys wave equation, and the phason field obeys diffusion equation. By introducing a new auxiliary function, the coupled wave-diffusion equations are converted to a single higher-order partial differential equation. With the aid of the Laplace transform, an associated mixed initial-boundary value problem is reduced to two sets of dual integral equations, and then transformed into two coupled Fredholm integral equations of the second kind. Numerical results of transient phonon and phason stress intensity factors and crack-centre displacement jump are obtained through the numerical inversion of the Laplace transform and are presented graphically to show the influences of the phason.

Update: 7-Mar-2019

Title:
Neutron diffraction study of a metallic kagome lattice, Tb3Ru4Al12
Authors:
Rayaprol, S; Hoser, A; Iyer, KK; Upadhyay, SK; Sampathkumaran, EV Author Full Names: Rayaprol, Sudhindra; Hoser, Andreas; Iyer, Kartik K.; Upadhyay, Sanjay K.; Sampathkumaran, E. V.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 477 83-87; 10.1016/j.jmmm.2018.12.104 MAY 1 2019
Abstract:
We present the results of neutron diffraction studies on polycrystals of a metallic kagome lattice, Tb3Ru4Al12, reported recently to undergo reentrant magnetism, with the onset of long range antiferromagnetic order below (T-N = 22 K) and spin-glass features below about 17 K. The present results reveal long-range antiferromagnetic order of an incommensurate type with the moments oriented along c-axis at all temperatures below T-N. There are however notable changes in the T-dependence of propagation vector along b-axis across 17 K. An observation of interest is that there is no decrease of intensity of magnetic Bragg peaks on entrance into the glassy phase (that is, below 17 K). This finding suggests that the magnetism of this compound is an exotic one.
Title:
Charge orbital and spin ordering transitions in La1-xSrxMnO3+delta(x=0.67 & 0.71)
Authors:
Shahee, A; Kaushik, SD; Lalla, NP Author Full Names: Shahee, Aga; Kaushik, S. D.; Lalla, N. P.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 782 277-287; 10.1016/j.jallcom.2018.11.404 APR 25 2019
Abstract:
Structural and magnetic phase-transitions in La1-xSrxMnO3+delta (x = 0.67 & 0.71) have been studied employing x-ray diffraction, neutron diffraction and transmission electron microscopy (TEM) in conjunction with electrical-transport and magnetic studies. These studies reveal a cubic to incommensurate (IC) charge-ordered (CO) tetragonal phase-transition in both the samples with k-vector varying with temperature and thus indicates charge density wave-like nature. Followed by magnetic transition from paramagnetic phase to incommensurate antiferromagnetic phase. The nearly equal expansion of the a,b axes in the ab plane and the contraction of the c-axis (i.e. type-I Jahn-Teller distortion (JTD)) indicate that the CO is accompanied by a planer ferro-ordering of 3d(x2-y2) orbitals in the ab plan, which is different from haring-bone type ordering of 3d(3x2-r2)/3d(3y2-r2) orbitals, commonly observed in narrow bandwidth CO manganites. For x = 0.71, a second phase-transition from type-I JTD-CO phase (c < a) to charge disorder type-II JTD tetragonal phase (c > a) was observed. Through EDAX analysis in TEM, a nanoscale marginal composition difference has been observed to lead to nanoscale phase-coexistence. These studies have revealed first microscopic evidence of CO and nano-scale multiphase coexistence in La1-xSrxMnO3+delta with x = 0.67 & 0.71. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Negative refraction in quasicrystalline multilayered metamaterials
Authors:
Morini, L; Eyzat, Y; Gei, M Author Full Names: Morini, Lorenzo; Eyzat, Yoann; Gei, Massimiliano
Source:
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 124 282-298; 10.1016/j.jmps.2018.10.016 MAR 2019
Abstract:
Inspired by some recent results in elastodynamics of layered composites, we address here the problem of an antiplane elastic wave obliquely incident at the interface between a substrate and a periodic laminate with a quasicrystalline structure (generated by the Fibonacci substitution rule). The angles of refraction of the transmitted modes are computed by combining the transfer matrix method with the normal mode decomposition and evaluating the direction of the average Poynting vector. It is shown that, with respect to a periodic classical bilayer, on the one hand, beyond a certain frequency threshold, high order Fibonacci laminates can provide negative refraction for a wider range of angles of incidence, on the other, they allow negative wave refraction at lower frequencies. The outcome strongly relies on the Floquet-Bloch dynamic analysis of this class of laminates that is performed thoroughly. It is revealed that the corresponding spectra have a self-similar character linked to the specialisation of the Kohmoto's invariant, a function of the frequency that was recently studied by the authors for periodic one-dimensional quasicrystalline-generated waveguides. This function is able to explain two types of scaling occurring in dispersion diagrams. The attained results represent an important advancement towards the realisation of multilayered quasicrystalline metamaterials with the aim to control negatively refracted elastic waves. (C) 2018 Elsevier Ltd. All rights reserved.
Title:
Excess specific heat from the gapped sliding phonon modes in the incommensurate composite crystal Sr14Cu24O41
Authors:
Bag, R; Hazra, S; Kini, RN; Singh, S Author Full Names: Bag, Rabindranath; Hazra, Soumitra; Kini, Rajeev N.; Singh, Surjeet
Source:
PHYSICAL REVIEW B, 99 (5):10.1103/PhysRevB.99.054305 FEB 13 2019
Abstract:
We show that the low-temperature specific heat (C-p) of the incommensurate chain-ladder system {CuO2}(alpha){Sr2Cu2O3} = Sr14Cu24O41 (for alpha = 10/7) shows a rather large excess contribution of nonmagnetic origin. Diluted Al doping at the Cu site or annealing the crystal in an O-2 atmosphere suppresses this feature considerably. Using THz time-domain spectroscopy, we relate the occurrence of excess specific heat to the presence of very low-energy (similar to 1 meV) gapped phonon modes that originate from the sliding motion of oppositely charged {CuO2} chain and {Sr2Cu2O3} ladder sheets past each other.
Title:
Critical Properties of the Anisotropic Ising Model with Competitive Interactions in the Region of a Phase Transition from the Modulated Phase to the Paramagnetic One
Authors:
Murtazaev, AK; Ibaev, ZG Author Full Names: Murtazaev, A. K.; Ibaev, Zh. G.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 127 (6):1040-1045; 10.1134/S106377611812021X DEC 2018
Abstract:
Monte Carlo methods are used to study the anisotropic Ising model with competing interactions in the region of the phase transition from the modulated to the paramagnetic phase. Using histogram analysis of Monte Carlo data and the theory of finite-size scaling, it is shown that the transition from the modulated state to the paramagnetic one is a second-order phase transition. The critical parameters and temperatures of phase transitions in this region are calculated. It is shown that the modulated-paramagnetic phase transition cannot be described within the framework of the known universality classes of critical behavior.

Update: 27-Feb-2019

Title:
Microstructure and mechanical properties of an aluminum alloy reinforced by Al-Ni-Co-Mn quasi-crystalline
Authors:
Yuan, Y; Hou, H; Zhao, YH; Yan, F; Zhang, Y Author Full Names: Yuan, Ye; Hou, Hua; Zhao, Yu Hong; Yan, Feng; Zhang, Yu
Source:
MATERIALS RESEARCH EXPRESS, 6 (5):10.1088/2053-1591/ab014c MAY 2019
Abstract:
The Al72Ni13Co10Mn5 quasi-crystalline was prepared by conventional casting method. The microstructures and the phase composition of Al72Ni12Co16 quasi-crystalline, Al70Ni11Co12Mn7 and Al2Ni phases were characterized by XRD, SEM and DSC. The (Al72Ni13Co10Mn5)p/ZL101A aluminium based composite was fabricated by using the Al72Ni13Co10Mn5 quasicrystals particles as the reinforcing phase and ZL101A as the matrix with electromagnetic stirring. The results showed that the Al72Ni13Co10Mn5 is a QC(quasi-crystalline) phase and the hardness of Al72Ni13Co10Mn5 is higher than d-Al72Ni12Co16; the as-cast (Al72Ni13Co10Mn5)p/ZL101A composites are composed of alpha-Al, eutectic Si, theta, gamma and phi phase. With the increase of reinforcing particle fraction, the changed order for the morphology of coralline Si as follows: coral distribution -> partially converted into strips strip -> or thick sheet. The changes of mechanical properties were studied by tensile test and the resulting crystalline phase gamma and phi phases contribute to the improvement of the mechanical properties of the composite. After adding 4%wt% quasicrystalline particles, the tensile strength increased by 20.3%. However, when additional increased to 7 wt% will cause agglomeration and clusters of the theta phase, which leads to the decrease of the mechanical properties.
Title:
Analysis of migration maps and features of magnetic properties of LiNi0.9M0.1PO4 (M = Co, Mn) single crystals
Authors:
Urusova, N; Semkin, M; Kratochvilova, M; Barykina, J; Volegov, A; Park, JG; Lee, S; Pirogov, A Author Full Names: Urusova, N.; Semkin, M.; Kratochvilova, M.; Barykina, J.; Volegov, A.; Park, J. -G.; Lee, S.; Pirogov, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 781 571-581; 10.1016/j.jallcom.2018.12.089 APR 15 2019
Abstract:
Lithium orthophosphates of the LiMPO4 type (M = Ni, Co, Fe, and Mn) gain intensive development due to the potential applications as electrodes for lithium-ion batteries. The other remarkable property of LiMPO4 is the multiferroicity. We present a study of the crystal structure and magnetic properties, refined anisotropic thermal coefficients and Li-ion migration maps of the LiNi0.9M0.1PO4(M = Co, Mn) single crystals and compared results for the undoped LiNiPO4 and LiMnPO4 ones. All samples have been synthesized by the flux method. In LiNi0.9M0.1PO4(M = Co, Mn), doping increases the lattice constants, unit cell volume, valence bonds, and the anisotropic thermal coefficients. By means of X-ray diffraction and the program package TOPOS, the Li-cation migration maps were obtained. The Li-ions move along the [010] direction which can be clearly visualized in the mixed-metal LiNi0.9 M0.1PO4(M = Co, Mn) single crystals. It was found that the 10% doping of LiNiPO4 by cobalt ions leads to a decrease in the formation temperature and to the suppression of the incommensurate phase. The 10% doping of manganese ions increases the transition temperature, while the temperature range of the incommensurate phase narrows. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Magnetic properties of RCuAl3 (R = Pr and Nd) compounds
Authors:
Klicpera, M; Fikacek, J; Vlaskova, K; Puente-Orench, I; Divis, M; Javorsky, P Author Full Names: Klicpera, Milan; Fikacek, Jan; Vlaskova, Kristina; Puente-Orench, Ines; Divis, Martin; Javorsky, Pavel
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 781 1189-1197; 10.1016/j.jallcom.2018.12.077 APR 15 2019
Abstract:
( )Magnetic properties of PrCuAl3 and NdCuAl3 single crystals, adopting the tetragonal BaNiSn3 -structure-type, are reported. Our magnetization and specific heat measurements revealed no magnetic ordering in PrCuAl3, while NdCuAl3 orders antiferromagnetically below T-N = 2.45 K. The paramagnetic regime was investigated for both analogues revealing (i) the a-axis as the easy direction of magnetization with (ii) a relatively high uniaxial anisotropy energy of 13.2 meV for PrCuAl3 compared to a smaller value of 4.7 meV for NdCuAl3. The measured data are well explained by rare-earth ground state multiplet splitting in crystal electric field. A powder neutron diffraction experiment confirmed PrCuAl3 to remain paramagnetic down to 1.5 K. On the other hand, NdCuAl3 orders antiferromagnetically below T-N with an incommensurate magnetic structure described by two propagation vectors k(1) = (1/3 - delta(1), 0, 0) and k(2) = (1/7 - delta 2 , 1/7 - delta(2) , 0), where delta(1) = 0.035(1) and delta(2) = 0.007(1). The magnetic moments (of both magnetic modulations) are arranged within the basal plane with a small z-component moment allowed by the symmetry. Our results are discussed with respect to other RCuAl3 compounds. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Spontaneous and induced magnetic phase transitions in Tb0.9Er0.1Ni5
Authors:
Lee, HJ; Choi, YN; Lukoyanov, AV; Gerasimov, EG; Pirogov, AN Author Full Names: Lee, H-J; Choi, Y-N; Lukoyanov, A., V; Gerasimov, E. G.; Pirogov, A. N.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 475 593-601; 10.1016/j.jmmm.2018.12.004 APR 1 2019
Abstract:
Magnetic and neutron powder diffraction measurements have been carried out on Tb0.9Er0.1Ni5 intermetallic compound. The intermetallide crystallizes in the hexagonal CaCu5-type structure and possesses a long-range magnetic order at temperatures below 22 K. A fan-like magnetic structure is described by two propagation vectors: k(1) = 0 and k(2) = 2 pi/c(0, 0, 0.036), at 20 K. The total Tb-ion magnetic moment has the ferromagnetic and modulated components. The latter is a transverse spin wave. When the sample is cooled at a temperature below 8 K, the module of the k(2) vector does not change and is equal to k(2) = 2 pi/c(0, 0, 0.027). An "in-commensurate - lock-in" magnetic transition takes place at 8 K. The k(2) vector exhibits a temperature hysteresis of about (5-6) K, whereas the intensities of Bragg reflections and satellites do not show up appreciable changes. When an external magnetic field is applied to the sample, the satellites and the module of the k(2) vector decrease, while the Bragg intensities increase. The sample becomes a ferromagnetic at a field of similar to 2 kOe, and the Tb-ion magnetic moment is equal to 8.3 mu(B). A general notion of the Tb0.9Er0.1Ni5 magnetic state evolution with an external field is given using the field dependence of the background intensity in diffraction patterns. First principle calculations for TbNi5 and Tb0.9Er0.1Ni5 are performed including the 4f states into the orbital basis and accounting for strong electronic correlations and spin-orbital coupling. This allowed obtaining both spin and orbital moments of the effective Tb-ion moment and estimating also the value of Tb-Tb exchange interaction.
Title:
Direct observation of incommensurate magnetism in Hubbard chains (vol 565, pg 56, 2018)
Authors:
Salomon, G; Koepsell, J; Vijayan, J; Hilker, TA; Nespolo, J; Pollet, L; Bloch, I; Gross, C Author Full Names: Salomon, Guillaume; Koepsell, Joannis; Vijayan, Jayadev; Hilker, Timon A.; Nespolo, Jacopo; Pollet, Lode; Bloch, Immanuel; Gross, Christian
Source:
NATURE, 566 (7743):E5-E5; 10.1038/s41586-019-0906-z FEB 14 2019
Title:
Honeycomb lattice type charge density wave associated with interlayer Cu ions ordering in 1T-CuxTiSe2
Authors:
Kitou, S; Kobayashi, S; Kaneko, T; Katayama, N; Yunoki, S; Nakamura, T; Sawa, H Author Full Names: Kitou, Shunsuke; Kobayashi, Shintaro; Kaneko, Tatsuya; Katayama, Naoyuki; Yunoki, Seiji; Nakamura, Toshikazu; Sawa, Hiroshi
Source:
PHYSICAL REVIEW B, 99 (8):10.1103/PhysRevB.99.081111 FEB 11 2019
Abstract:
The phase transition phenomenon in a semimetallic 1T-TiSe2. has attracted attention as an excitonic insulator. However, as the phase transition accompanying superlattice peaks has the q vector connecting the Fermi surfaces of the three-dimensional shape of hole and electron pockets, it also assumes the charge density wave (CDW) state owing to the electron-phonon interaction. To understand the electronic state at the low temperature, control of the chemical potential was attempted by electronic doping through Cu+ intercalation. Physical properties measurements and synchrotron x-ray diffraction experiments in CuxTiSe2 (x = 0-0.35) were performed. The phase transition was determined to occur as a cooperative phenomenon between the honeycomb lattice type CDW corresponding to the nesting vector and the ordered state of the Cu+ ions between TiSe2 layers at a specific doping amount (x = 1/3). The behavior of Cu+ ions in highly doped regions suggests the occurrence of a two-dimensional liquid-solid state transition based on the temperature dependence of the x-ray diffuse scattering.
Title:
Crystallographic Relationship between the nu (Mn82Si18) and H (Mn7Si2V) Phases in the Mn-Si-V Alloy System
Authors:
Nakayama, K; Kurihara, D; Koyama, Y Author Full Names: Nakayama, Kei; Kurihara, Daichi; Koyama, Yasumasa
Source:
MATERIALS TRANSACTIONS, 59 (7):1051-1056; 10.2320/matertrans.MD201712 2018
Abstract:
There are the intermetallic-compound nu (Mn82Si18) and H (Mn7Si2V) phases in the Mn-Si-V alloy system. These two phases can be regarded as approximant phases of the dodecagonal quasicrystal, and their crystal structures involve similar structural hierarchies consisting of dodecagonal atomic columns and giant dodecagonal structural units. To understand the crystallographic relationship between these approximant phases, we examined their crystallographic features mainly by transmission electron microscopy. It was found that there is a simple orientation relationship of N(001)(nu)//N(0001)(H) and N(010)(nu)//N(01<(1)overbar>0)(H) between the nu and H structures. In addition, H-structure regions have an antiphase boundary with a pi phase shift along a column axis as a structural defect. A notable feature of the antiphase boundary is that it consists of decagonal columns, not dodecagonal columns present in the H structure, where both 11 dodecagonal columns and eight decagonal columns form one dodecagonal unit in the nu structure. The nu structure can thus be produced in the following two steps. First, eight outer dodecagonal columns in each dodecagonal unit in the H structure are replaced by eight decagonal columns. The second step is the periodic introduction of antiphase boundaries, consisting of decagonal columns present in the replacement.

Update: 20-Feb-2019

Title:
Benefits of intermediate-layer formation at the interface of Nb/Cu and Ta/Cu explosive clads
Authors:
Parchuri, P; Kotegawa, S; Yamamoto, H; Ito, K; Mori, A; Hokamoto, K Author Full Names: Parchuri, PradeepK.; Kotegawa, Shota; Yamamoto, Hajime; Ito, Kazuhiro; Mori, Akihisa; Hokamoto, Kazuyuki
Source:
MATERIALS & DESIGN, 166 10.1016/j.matdes.2019.107610 MAR 15 2019
Abstract:
A systematic, comparative study was carried out to quantitatively characterize the bending strength of wavy interfaces with and without an intermediate layer (IL) in Nb/Cu and Ta/Cu explosive clads. The clads having wavy interfaces with and without an IL were obtained at horizontal high and low collision velocities (HCV and LCV) in the explosive welding, respectively. The stress-strain curves of all the clads were similar in three-point bending tests, but the clads with an IL exhibited higher bending stress than those without an IL. Moreover, cracks were observed in the Nb plate of Nb/Cu clads without an IL, but nocracks in that with an IL. TEM observation confirmed coexistence of ultrafine refractory metal and Cu phases in the ILs. In addition, the Ta-Cu-based intermetallic compound or dodecagonal quasicrystal, which is a non-equilibrium phase, were also observed along with coexistence of Ta and Cu phases in the ILs of Ta/Cu interface. Cladding at HCV and a lower collision angle assisted in resultant less strain in refractory metal plates near the joint interfaces than those at LCV, due to IL formation. The ILs assisted in obtainment of interfaces of higher hardness, leading to higher bending-stress clads without losing large elongation. (C) 2019 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.
Title:
Formation and temporal evolution of modulated structure in high Nb-containing lamellar gamma-TiAl alloy
Authors:
Ren, GD; Dai, CR; Mei, W; Sun, J; Lu, S; Vitos, L Author Full Names: Ren, Guo-dong; Dai, Cheng-ren; Mei, Wei; Sun, Jian; Lu, Song; Vitos, Levente
Source:
ACTA MATERIALIA, 165 215-227; 10.1016/j.actamat.2018.11.041 FEB 15 2019
Abstract:
The formation and temporal evolution of the modulated structure in a lamellar gamma-based Ti-45Al-8.5Nb alloy have been investigated by transmission electron microscopy (TEM) in combination with first-principles theory in this work. The results show that the Nb-rich O phase as a constituent of the modulated structure is thermodynamically stable below 650 degrees C in the alpha(2) lamellae. The morphology of the O phase variants changes from thin plate-like shape with a low volume fraction at initial annealing to rectangle/square shape with a high volume fraction after a prolonged annealing, and the retransformed alpha(2), named as alpha(2-II) hereafter, emerges at intersections of the variants with two orthogonal habit planes due to their elastic interactions. The partitioning coefficient of Nb between the O phase and alpha(2) is about 2 at 600 degrees C. The diffusion coefficient of Nb derived from growth kinetics of the O phase is about (1.3 +/- 0.2) x 10(-22) m(2)s(-1) in the alpha(2) lamellae. Significant precipitation hardening effect of the O phase has been revealed for the alpha(2) lamellae and gamma/(alpha(2)+O) lamellar microstructure, which is supposed to be attributed to refining the alpha(2) lamellae associated with elastic strain energy from the alpha(2) -> O phase transformation and introducing the interface between the modulated lamella and adjacent gamma phase. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Room temperature structure and transport properties of the incommensurate modulated LaNb0.88W0.12O4.06
Authors:
Li, C; Pramana, SS; Skinner, SJ Author Full Names: Li, Cheng; Pramana, Stevin S.; Skinner, Stephen J.
Source:
DALTON TRANSACTIONS, 48 (5):1633-1646; 10.1039/c8dt03958e FEB 7 2019
Abstract:
The crystal structure of a (3 + 2)D incommensurate modulated LaNb0.88W0.12O4.06 phase, a novel oxygen ionic conductor, is refined using a combination of synchrotron X-ray diffraction and electron diffraction data. The superspace group I2/c(alpha(1)0(gamma 1))00(alpha(2)0(gamma 2))00 (a = 5.4131(1) angstrom, b = 11.6432(2) degrees, c = 5.2963(1) angstrom, beta = 91.540(1)degrees, q(1) = 0.2847(5)a* + 0.1098(9)c* and q(2) = -0.1266(9)a* + 0.2953(1)c*) was chosen for the refinement. Similar to other scheelite type modulated structures, the modulation of LaNb0.88W0.12O4.06 stems from the cation occupancy ordering in the xz plane. To facilitate the modulated cation sub-lattice, and to compensate for the difference in their size and charge, the B site polyhedra are distorted by stretching the B-O bond lengths. Consequently, an extension in the B site coordination number from 6 to 8 is observed in the modulated phase. An interconnected 3D network of BOx polyhedra, similar to that of modulated CeNbO4.25, is obtained as a result of the structure modulation, which is not available in the unmodulated parent structure. Tracer diffusivity measurements indicate that the composition is an oxygen ion conductor, which relies on an intersticalcy conduction mechanism. Oxygen tracer diffusivity of 2.46 x 10(-9) cm(2) s(-1), at 750 degrees C is reported.
Title:
In-Situ observation of local atomic structure of Al-Cu-Fe quasicrystal formation
Authors:
Parsamehr, H; Lu, YJ; Lin, TY; Tsai, AP; Lai, CH Author Full Names: Parsamehr, Hadi; Lu, Ying-Jiu; Lin, Tzu-Ying; Tsai, An-Pang; Lai, Chih-Huang
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-018-37644-x FEB 4 2019
Abstract:
The phase and local environment, neighbouring atoms and coordination numbers (CN), for an Al-Cu-Fe multilayer were studied during heating (to 800 degrees C) and cooling (to room temperature) processes using in-situ X-Ray diffraction (XRD) and in-situ X-ray absorption spectroscopy (XAS) techniques to investigate the formation of Al-Cu-Fe quasicrystals (QCs). In-situ XRD clarified the transition of the omega-Al7Cu2Fe phase to a liquid state at the high temperature which transformed into the QC phase during cooling. The in-situ XAS showed a relatively small shift in distance between Cu-Al and Fe-Al during the phase evolution from RT to 700 degrees C. The distance between Cu-Cu, however, showed a significant increase from omega-phase at 700 degrees C to the liquid state at 800 degrees C, and this distance was maintained after QC formation. Furthermore, the CN of Fe-Al was changed to N = 9 during cooling. Through our observations of changes in CN, atomic distances and the atomic environment, we propose the local structural ordering of the quasicrystalline phase originated from a liquid state via omega-phase. In this study, we give a clear picture of the atomic environment from the crystalline to the quasicrystalline phase during the phase transitions, which provides a better understanding of the synthesis of functional QC nanomaterials.
Title:
Enhancing Morphology and Separation Performance of Polyamide 6,6 Membranes By Minimal Incorporation of Silver Decorated Graphene Oxide Nanoparticles
Authors:
Mahmoudi, E; Ng, LY; Ang, WL; Chung, YT; Rohani, R; Mohammad, AW Author Full Names: Mahmoudi, Ebrahim; Ng, Law Yong; Ang, Wei Lun; Chung, Ying Tao; Rohani, Rosiah; Mohammad, Abdul Wahab
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-018-38060-x FEB 4 2019
Abstract:
Nanomaterials can be incorporated in the synthesis of membrane to obtain mixed-matrix membrane with marked improvement in properties and performance. However, stability and dispersion of the nanomaterials in the membrane matrix, as well as the need to use high ratio of nanomaterials for obvious improvement of membrane properties, remain a major hurdle for commercialization. Hence, this study aims to investigate the improvement of polyamide 6,6 membrane properties with the incorporation of silver nanoparticles decorated on graphene oxide (Ag-GO) nanoplates and at the same time focus is given to the issues above. Graphene oxide nanoplates were synthesized using the modified Hummers' method and decorated with silver before embedded into the polyamide 6,6 matrix. Physicochemical characterizations were conducted on both nanoplates and the mixed-matrix Ag-GO polyamide 6,6 membrane. The issues of Ag agglomeration and leaching were not observed, which could be attributed to the decoration of Ag on GO that helped to disperse the nanomaterials and provided a better anchor point for the attachment of Ag nanoparticles. The synthesized membrane showed marked improvement regarding flux (135% increment) and antifouling (40% lower irreversible fouling), which could be ascribed to the more negative charge of membrane surface (-14 +/- 6 to -31 +/- 3.8 mV) and hydrophilicity (46% enhancement) of the membranes. With minimal embedment of Ag nanoparticles, the membrane showed superior antibacterial property where the E. coli bacteria could not form a single colony on the membrane surface. Overall, the decoration of Ag on GO nanoplates could be a promising approach to resolve the agglomeration and leaching issues as well as reduce the amount of precious Ag in the synthesis of Ag-GO polyamide 6,6 membrane.
Title:
Energy-dispersive Laue experiments with X-ray tube and PILATUS detector: precise determination of lattice constants
Authors:
Kurdzesau, F Author Full Names: Kurdzesau, Fiodar
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 52 72-93; 10.1107/S1600576718017193 1 FEB 2019
Abstract:
A PILATUS detector in combination with a conventional sealed X-ray tube was used for the development of the energy-dispersive Laue diffraction technique, which can be applied for precise measurements of single-crystal lattice constants in transmission and reflection modes without moving the sample. Exploiting the ability of PILATUS detectors to suppress counting of X-ray photons below a certain energy threshold allows one to recover the wavelength of diffracted Bragg reflections, reconstruct the three-dimensional reciprocal-space pattern, index X-ray diffraction peaks, and find the orientation and lattice parameters of the crystal without any a priori information about the sample. By making some geometrical assumptions and using a set of fast in situ calibration procedures, it is possible to simultaneously refine lattice constants and hardware correction factors, which simplifies the sample preparation and measurement strategies. Several samples [silicon, quartz, fluorite (CaF2), o-Al13Co4 quasicrystal approximant, Laves (MgZn2) and Bergman (Mg-32(Al,Zn)(49)) phases] were studied with the developed technique, and 0.01 angstrom and 0.1 degrees precisions were routinely reached for lattice vector lengths and angles, respectively. The use of the developed methods is only limited by the energy resolution of the PILATUS detector, where lattice vectors with >27 angstrom length cannot be reliably resolved.
Title:
Damping Properties of As-Cast Mg-Zn-Y Alloy with / Phase
Authors:
Wan, DQ; Hu, YL; Li, ZM; Ye, ST Author Full Names: Wan Diqing; Hu Yinglin; Li Zhumin; Ye Shuting
Source:
RARE METAL MATERIALS AND ENGINEERING, 48 (1):71-76; JAN 2019
Abstract:
A conventional casting method was adopted to fabricate the alloys of Mg-Zn-Y, in which the dendritic morphology and its relation to the damping properties of as-cast Mg-Zn-Y alloy were studied based on the typical Mg93Zn6Y1 alloy containing icosahedral quasicrystal phase. By controlling the pouring temperature, the stirring speed and stirring time, the dendritic morphology with different parameters was obtained. The results show that the microstructure of the as-cast Mg93Zn6Y1 mainly consists of alpha-Mg dendritic crystal and icosahedral quasicrystal phase. After stirring, the primary alpha-Mg dendritic gradually have fractal characteristics in faith, and its size changes, affecting the damping capacity. The mechanism was discussed.
Title:
Porous Al63Cu25Fe12 quasicrystals covered with (Al11.5Fe13.9Cu19.7)O-54.9 nanosheets
Authors:
Zhang, F; Guo, HJ; Wang, LL; Ma, HK; Li, H; Zhang, L; He, ZB Author Full Names: Zhang, Fan; Guo, Huijie; Wang, Leilei; Ma, Haikun; Li, Hua; Zhang, Lei; He, Zhangbing
Source:
MATERIALS CHARACTERIZATION, 147 165-172; 10.1016/j.matchar.2018.10.026 JAN 2019
Abstract:
Porous Al63Cu25Fe12 quasicrystal alloys with the surfaces and the wall of pores covered with abundant (Al11.5Fe13.9Cu19.7)O-54.9 nanosheets were successfully fabricated through the combination of powder metallurgy and dealloying in NaOH solutions. Their compositions, microscopic morphology, and crystal structures were investigated using energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. We found that the composite of porous Al63Cu25Fe12 quasicrystal alloys and (Al11.5Fe13.9Cu19.7)O-54.9 nanosheets shows high catalytic performances in hydrogen production by methanol steam reforming at relatively low temperatures. X-ray photoelectron spectroscopy was used to analyze the catalytic mechanisms, and Cu was found to be the key element in this catalytic reaction.

Update: 13-Feb-2019

Title:
Helical Ordering of Spin Trimers in a Distorted Kagome Lattice of Gd3Ru4Al12 Studied by Resonant X-ray Diffraction
Authors:
Matsumura, T; Ozono, Y; Nakamura, S; Kabeya, N; Ochiai, A Author Full Names: Matsumura, Takeshi; Ozono, Yusaku; Nakamura, Shintaro; Kabeya, Noriyuki; Ochiai, Akira
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (2):10.7566/JPSJ.88.023704 FEB 15 2019
Abstract:
Successive magnetic phase transitions at T-1 = 17.5 K and T-2 = 18.5 K in Gd3Ru4Al12, with a distorted kagome lattice of Gd ions, is studied using resonant X-ray diffraction with polarization analysis. It has been suggested that in this compound the S = 7/2 spins on the nearest-neighbor Gd-triangle form a ferromagnetic trimer and the Gd lattice can be effectively considered as an antiferromagnetic triangular lattice of S = 21/2 spin trimers [S. Nakamura et al., Phys. Rev. B 98, 054410 (2018)]. We show that the magnetic order in this system is described by an incommensurate wave vector q similar to (0.27,0, 0), which varies slightly with temperature. In the low temperature phase below T-1, the experimental results are well explained by considering that the spin timers form a helical order with both the c-axis and c-plane components. In the intermediate phase above T-1 the c-axis component vanishes, resulting in a sinusoical structure within the c-plane. The sinusoidal-helical transition at T-1, can be regarded as an ordering of chiral degree of freedom, which is degenerate in the intermediate phase.
Title:
Long-period structural modulation on the global length scale as the characteristic feature of the morphotropic phase boundaries in the Na0.5Bi0.5TiO3 based lead-free piezoelectrics
Authors:
Das Adhikary, G; Khatua, DK; Senyshyn, A; Ranjan, R Author Full Names: Das Adhikary, Gobinda; Khatua, Dipak Kumar; Senyshyn, Anatoliy; Ranjan, Rajeev
Source:
ACTA MATERIALIA, 164 749-760; 10.1016/j.actamat.2018.11.016 FEB 1 2019
Abstract:
The inherent structural disorder has a profound effect on the dielectric, ferroelectric and the electromechanical response of the Na0.5Bi0.5TiO3 (NBT) based lead-free piezoelectrics. While analogous to the lead-based classical morphotropic phase boundary (MPB) systems the existence of MPB has been recognized in some derivatives of NBT displaying enhanced electromechanical response, there is a lack of clarity on the structural state of the MPB compositions on NBT-based systems on the global length scale. We have examined this issue on the well known MPB system (1-x)Na0.5Bi0.5TiO3-(x)K0.5Bi0.5TiO3(NBT-KBT) by carrying out structural investigations on local and global length scales using Eu+3 photoluminiscence and high-resolution neutron powder diffraction techniques, respectively. Our study reveals that the MPB of this system is characterized by the onset of a long-period modulated structure with a periodicity of similar to 40 angstrom on the global scale. Temperature depedent neutron diffraction study revealed that the intermediate temperature P4bm phase which appears in NBT is suppressed for the MPB composition. The MPB composition rather develops a long-period modulated phase on cooling from the cubic phase. The ergodic-nonergodic relaxor ferroelectric transition occurs within this long-period modulated phase. In the non-ergodic regime, however, strong electric field irreversibly transforms the long-period modulated phase to the rhombohedral ferroelectric (R3c). We demonstrate that thermal depolarization of this system is a distinct structural event characterized by the system losing its field-induced long range rhombohedral (R3c) coherence and transforming back to the long-period modulated phase. Our study suggests that the long-period modulated phase is the primary structural feature of the MPB compositions in NBT-based piezoelectrics. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Symmetry-changing commensurate-incommensurate solid transition in the He-4 monolayer on 6,6,12-graphyne
Authors:
Ahn, J; You, M; Lee, G; Volkoff, T; Kwon, Y Author Full Names: Ahn, Jeonghwan; You, Mujin; Lee, Gwangyoung; Volkoff, Tyler; Kwon, Yongkyung
Source:
PHYSICAL REVIEW B, 99 (2):10.1103/PhysRevB.99.024113 JAN 30 2019
Abstract:
Path-integral Monte Carlo calculations have been carried out to investigate physical properties of a He-4 monolayer adsorbed on a single 6,6,12-graphyne sheet, which is one of the graphyne families possessing a rectangular symmetry. To characterize elusive quantum phases of an adsorbed He-4 monolayer on 6,6,12-graphyne, we model the He-4-graphyne interaction by the pairwise sum of empirical He-4-C interatomic potentials. At partially filled He-4 coverages, we identify three commensurate solids of the C-3/4, C-4/4, and C-6/4 structures from the two-dimensional density distribution. These solids show the rectangular symmetry inherited from the symmetry of 6,6,12-graphyne, which were confirmed with the analysis of their static structure factors. At high helium coverages near its completion, the He-4 monolayer is predicted to exhibit a transition from a rectangular commensurate structure to a triangular incommensurate structure, after going through inhomogeneous structures mixed with domains of triangular and rectangular orderings. This symmetry-changing transition has not been observed in He-4 monolayers adsorbed on other carbon substrates.
Title:
Microstructure, texture evolution and tensile properties of extruded Mg-4.58Zn-2.6Gd-0.16Zr alloy
Authors:
Xiao, L; Yang, GY; Chen, JM; Luo, SF; Li, JH; Jie, WQ Author Full Names: Xiao, Lei; Yang, Guangyu; Chen, Jieming; Luo, Shifeng; Li, Jiehua; Jie, Wanqi
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 744 277-289; 10.1016/j.msea.2018.11.142 JAN 28 2019
Abstract:
Microstructure, texture evolution and mechanical properties of extruded Mg-4.58Zn-2.6Gd-0.18Zr alloy were investigated at extrusion temperatures of 260 degrees C, 280 degrees C and 300 degrees C, extrusion ratios of 10, 15 and 30, and ram speeds of 3 mm s(-1) and 6 mm s(-1), respectively. The results indicated that the as-cast experimental alloy was composed of alpha-Mg matrix, coarse alpha-Mg + W(Mg3Zn3Gd2) eutectic and icosahedral quasicrystalline I(Mg3Zn6Gd) phase. A small amount of undissolved W phases were detected after the homogenization treatment at 505 degrees C up to 16 h, while most I phase dissolved into the alpha-Mg matrix. The initial crystallites before extrusion were randomly oriented, and showed a typical random texture. After extrusions, all samples exhibited a bimodal microstructure consisting of fine Dynamic recrystallization (DRX) grains and coarse elongated un-DRX grains, and the formation of ultra-fine DRX grains only occurred in the sample with an extrusion ratio of 10 at 260 degrees C, 3 mm s(-1), which was caused by the solute segregation in homogenized billets and non-uniformly distributed W phase during the extrusion process. A fiber texture with {0002} planes and < 1210 > directions paralleled to the extrusion direction was observed to be dominant in all the extruded samples. Furthermore, the increase of extrusion ratio was found to be beneficial for the DRX process and refinement of grain size, and the maximum texture intensity was accordingly weakened, which resulted in a decrease of tensile yield strength but an increase of elongation. With increasing the extrusion temperature or ram speed, both the grain size and DRX fraction gradually increased. Consequently, the texture was randomized and the maximum texture intensity decreased, which led to a reduction of the elongation and tensile yield strength. The tensile failure behaviors under different extrusion conditions were found to be related with the contraction twin lamellas formed in the un-DRX grains and the string-like W phases.
Title:
Comparing the anomalous Hall effect and the magneto-optical Kerr effect through antiferromagnetic phase transitions in Mn3Sn
Authors:
Balk, AL; Sung, NH; Thomas, SM; Rosa, PFS; McDonald, RD; Thompson, JD; Bauer, ED; Ronning, F; Crooker, SA Author Full Names: Balk, A. L.; Sung, N. H.; Thomas, S. M.; Rosa, P. F. S.; McDonald, R. D.; Thompson, J. D.; Bauer, E. D.; Ronning, F.; Crooker, S. A.
Source:
APPLIED PHYSICS LETTERS, 114 (3):10.1063/1.5066557 JAN 21 2019
Abstract:
In the non-collinear antiferromagnet Mn3Sn, we compare simultaneous measurements of the anomalous Hall effect (AHE) and the magneto-optical Kerr effect (MOKE) through two magnetic phase transitions: the high-temperature paramagnetic/antiferromagnetic (AF) phase transition at the Neel temperature (T-N approximate to 420 K) and a lower-temperature incommensurate magnetic ordering at T-1 approximate to 270 K. While both the AHE and MOKE are sensitive to the same underlying symmetries of the AF non-collinear spin order, we find that the transition temperatures measured by these two techniques unexpectedly differ by approximately 10 K. Moreover, the applied magnetic field at which the AF order reverses is significantly larger when measured by MOKE than when measured by AHE. These results point to a difference between the bulk and surface magnetic properties of Mn3Sn. Published under license by AIP Publishing.
Title:
Quasicrystal nucleation and Z module twin growth in an intermetallic glass-forming system
Authors:
Hornfeck, W; Kobold, R; Kolbe, M; Conrad, M; Herlach, D Author Full Names: Hornfeck, Wolfgang; Kobold, Raphael; Kolbe, Matthias; Conrad, Matthias; Herlach, Dieter
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-018-06597-0 OCT 3 2018
Abstract:
While quasicrystals possess long-range orientational order they lack translation periodicity. Considerable advancements in the elucidation of their structures and formative principles contrast with comparatively uncharted interrelations, as studies bridging the spatial scales from atoms to the macroscale are scarce. Here, we report on the homogeneous nucleation of a single quasicrystalline seed from the undercooled melt of glass-forming NiZr and its continuous growth into a tenfold twinned dendritic microstructure. Observing a series of crystallization events on electrostatically levitated NiZr confirms homogeneous nucleation. Mapping the microstructure with electron backscatter diffraction suggests a unique, distortion-free structure merging a common structure type of binary alloys with a spiral growth mechanism resembling phyllotaxis. A general geometric description, relating all atomic loci, observed by atomic resolution electron microscopy, to a pentagonal Z module, explains how the seed's decagonal long-range orientational order is conserved throughout the symmetry breaking steps of twinning and dendritic growth.
Title:
Waves in one-dimensional quasicrystalline structures: dynamical trace mapping, scaling and self-similarity of the spectrum
Authors:
Morini, L; Gei, M Author Full Names: Morini, Lorenzo; Gei, Massimiliano
Source:
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 119 83-103; 10.1016/j.jmps.2018.06.007 OCT 2018
Abstract:
Harmonic axial waves in quasiperiodic-generated structured rods are investigated. The focus is on infinite bars composed of repeated elementary cells designed by adopting generalised Fibonacci substitution rules, some of which represent examples of one-dimensional quasicrystals. Their dispersive features and stop/pass band spectra are computed and analysed by imposing Floquet-Bloch conditions and exploiting the invariance properties of the trace of the relevant transfer matrices. We show that for a family of generalised Fibonacci substitution rules, corresponding to the so-called precious means, an invariant function of the circular frequency, the Kohmoto's invariant, governs self-similarity and scaling of the stop/pass band layout within defined ranges of frequencies at increasing generation index. Other parts of the spectrum are instead occupied by almost constant ultrawide band gaps. The Kohmoto's invariant also explains the existence of particular frequencies, named canonical frequencies, associated with closed orbits on the geometrical three-dimensional representation of the invariant. The developed theory represents an important advancement towards the realisation of elastic quasicrystalline metamaterials. (C) 2018 Elsevier Ltd. All rights reserved.

Update: 6-Feb-2019

Title:
Observation of the nesting and defect-driven 1D incommensurate charge density waves phase in the 2D system
Authors:
Matetskiy, AV; Denisov, NV; Hsing, CR; Wei, CM; Zotov, AV; Saranin, AA Author Full Names: Matetskiy, A., V; Denisov, N., V; Hsing, C. R.; Wei, C. M.; Zotov, A., V; Saranin, A. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 31 (11):10.1088/1361-648X/aaf9ea MAR 20 2019
Abstract:
We report on the low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) study of the (Bi, Na)/Si(111) root 3 x root 3 reconstruction that is known to possess Fermi surface with apparently good nesting. We found that defects on this surface produce a one-dimensional-like pattern with the periodicity of 8.2 +/- 0.4 angstrom that is incommensurate with the root 3 x root 3 lattice period. The dI/dV mapping analysis reveals an occurrence of the k-dependent branch associated with quasi-particle interference and the k-independent branch associated with the nesting vector connecting the parallel segments of the (Bi,Na)/Si(111) root 3 x root 3 Fermi surface, the fingerprint of the charge-density-wave (CDW) phase. The STS data demonstrates that development of the CDW phase leads to reducing electron density of states at the Fermi level.
Title:
Coherent photo-induced phonon emission in the charge-density-wave state of K0.3MoO3
Authors:
Rabia, K; Meng, F; Thomson, MD; Bykov, M; Merlin, R; van Smaalen, S; Roskos, HG Author Full Names: Rabia, K.; Meng, F.; Thomson, M. D.; Bykov, M.; Merlin, R.; van Smaalen, S.; Roskos, H. G.
Source:
NEW JOURNAL OF PHYSICS, 21 10.1088/1367-2630/aaf81f JAN 18 2019
Abstract:
We report on the observation of coherent terahertz (THz) emission from the quasi-one-dimensional charge-density wave (CDW) system, blue bronze (K0.3MoO3), upon photo-excitation with ultrashort near-infrared optical pulses. The emission contains a broadband, low-frequency component due to the photo-Dember effect, which is present over the whole temperature range studied (30-300 K), as well as a narrow-band doublet centered at 1.5 THz, which is only observed in the CDW state and results from the generation of coherent transverse-optical phonons polarized perpendicular to the incommensurate CDW b-axis. As K0.3MoO3 is centrosymmetric, the lowest-order generation mechanism which can account for the polarization dependence of the phonon emission involves either a static surface field or quadrupolar terms due to the optical field gradients at the surface. This phonon signature is also present in the ground-state conductivity, and decays in strength with increasing temperature to vanish above T similar to 100 K, i.e. significantly below the CDW transition temperature. The temporal behavior of the phonon emission can be well described by a simple model with two coupled modes, which initially oscillate with opposite polarity.

Update: 23-Jan-2019

Title:
On the Characterization of a Hitherto Unreported Icosahedral Quasicrystal Phase in Additively Manufactured Aluminum Alloy AA7075
Authors:
Kairy, SK; Gharbi, O; Nicklaus, J; Jiang, D; Hutchinson, CR; Birbilis, N Author Full Names: Kairy, S. K.; Gharbi, O.; Nicklaus, J.; Jiang, D.; Hutchinson, C. R.; Birbilis, N.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 50A (2):529-533; 10.1007/s11661-018-5025-1 FEB 2019
Abstract:
Aluminum alloy AA7075 (Al-Zn-Mg-Cu) specimens were prepared using selective laser melting, also known as powder bed fusion additive manufacturing. In the as-manufactured state, which represents a locally rapidly solidified condition, the prevalence of a previously unreported icosahedral quasicrystal with 5-fold symmetry was observed. The icosahedral quasicrystal, which has been termed -phase (nu-phase), was comprised of Zn, Cu, and Mg.
Title:
Topological Landscape of Competing Charge Density Waves in 2H-NbSe2
Authors:
Gye, G; Oh, E; Yeom, HW Author Full Names: Gye, Gyeongcheol; Oh, Eunseok; Yeom, Han Woong
Source:
PHYSICAL REVIEW LETTERS, 122 (1):10.1103/PhysRevLett.122.016403 JAN 9 2019
Abstract:
Despite decades of studies of the charge density wave (CDW) of 2H-NbSe2, the origin of its incommensurate CDW ground state has not been understood. We discover that the CDW of 2H-NbSe2 is composed of two different, energetically competing, structures. The lateral heterostructures of two CDWs are entangled as topological excitations, which give rise to a CDW phase shift and the incommensuration without a conventional domain wall. A partially melted network of topological excitations and their vertices explain an unusual landscape of domains. The unconventional topological role of competing phases disclosed here can be widely applied to various incommensuration or phase coexistence phenomena in materials.

Update: 17-Jan-2019

Title:
Anisotropic transient thermoelasticity analysis in a two-dimensional decagonal quasicrystal using meshless local Petrov-Galerkin (MLPG) method
Authors:
Hosseini, SM; Sladek, J; Sladek, V Author Full Names: Hosseini, Seyed Mahmoud; Sladek, Jan; Sladek, Vladimir
Source:
APPLIED MATHEMATICAL MODELLING, 66 275-295; 10.1016/j.apm.2018.09.024 FEB 2019
Abstract:
The meshless local Petrov-Galerkin (MLPG) method is employed for anisotropic transient thermoelasticity analysis of 2D decagonal quasicrystals (QCs) subjected to transient thermal and mechanical shock loadings. The wave type model and the elasto-hydrodynamic model are applied to derive the phonon and phason governing equations, respectively. The temperature affects only the phonon field. To find the temperature distributions on the assumed 2D domain, the anisotropic heat conduction problem is solved using the MLPG method. Also, the MLPG method is successfully employed to obtain the transient behaviors of both phonon and phason displacements by solving the governing equations in local integral equations (LIEs) forms. Making use a unit step function as the test functions in the local weak-form of governing equations, we derived the local integral equations (LIEs) considered on small subdomains identical with support domains of test functions around each node. The radial basis functions are used for approximation of the spatial variation of field variables. The Laplace-transform technique is utilized to discretize the time variations. (C) 2018 Elsevier Inc. All rights reserved.
Title:
Direct observation of incommensurate magnetism in Hubbard chains
Authors:
Salomon, G; Koepsell, J; Vijayan, J; Hilker, TA; Nespolo, J; Pollet, L; Bloch, I; Gross, C Author Full Names: Salomon, Guillaume; Koepsell, Joannis; Vijayan, Jayadev; Hilker, Timon A.; Nespolo, Jacopo; Pollet, Lode; Bloch, Immanuel; Gross, Christian
Source:
NATURE, 565 (7737):56-+; 10.1038/s41586-018-0778-7 JAN 3 2019
Abstract:
The interplay between magnetism and doping is at the origin of exotic strongly correlated electronic phases and can lead to novel forms of magnetic ordering. One example is the emergence of incommensurate spin-density waves, which have wavevectors that do not belong to the reciprocal lattice. In one dimension this effect is a hallmark of Luttinger liquid theory, which also describes the low-energy physics of the Hubbard model(1). Here we use a quantum simulator that uses ultracold fermions in an optical lattice(2-8) to directly observe such incommensurate spin correlations in doped and spin-imbalanced Hubbard chains using fully spin- and density-resolved quantum gas microscopy. Doping is found to induce a linear change in the spin-density wavevector, in excellent agreement with predictions from Luttinger theory. For non-zero polarization we observe a reduction in the wavevector with magnetization, as expected from the antiferromagnetic Heisenberg model in a magnetic field. We trace the microscopic-scale origin of these incommensurate correlations to holes, doublons (double occupancies) and excess spins, which act as delocalized domain walls for the antiferromagnetic order. In addition, by inducing interchain coupling we observe fundamentally different spin correlations around doublons and suppression of incommensurate magnetism at finite (low) temperature in the two-dimensional regime(9). Our results demonstrate how access to the full counting statistics of all local degrees of freedom can be used to study fundamental phenomena in strongly correlated many-body physics.
Title:
Crystal structure of the high-temperature form of the trisulfide Cs2S3 and the (3+1)D modulated structure of the telluride K37Te28
Authors:
Stuble, P; Berroth, A; Wortelkamp, F; Rohr, C Author Full Names: Stueble, Pirmin; Berroth, Angela; Wortelkamp, Fritz; Roehr, Caroline
Source:
ZEITSCHRIFT FUR NATURFORSCHUNG SECTION B-A JOURNAL OF CHEMICAL SCIENCES, 74 (1):33-47; SI 10.1515/znb-2018-0168 JAN 2019
Abstract:
The high-temperature polymorph of the trisulfide Cs2S3, which has been synthesized from Cs2S2 and elemental sulfur, crystallizes in a new structure type (monoclinic, space group P2(1)/c, a = 999.97(4), b = 1029.30(5), c = 2642.07(12) pm, beta = 90.083(2)degrees, Z = 16, R1 = 0.0324). The structure contains four crystallographically independent angled S-3(2-) trisulfide ions with S-S distances of 205.7-208.3 pm. The distorted b.c.c. packing of the anions and their insertion in the five-membered rings of 3.5(3) + 3.5.3.5. (1:1) Cs nets are similarly found in the r.t. form (Cmc2(1), K2S3-type structure) and the two polymorphs differ mainly in the orientation of the S-3 groups. The second title compound, K37Te28, was synthesized from stoichiometric melts of the elements. It forms a complex (3 + 1)D modulated tetragonal structure (space group I4(1)/amd (00 sigma(3))s0s0, q=(0, 0, 0.5143), a = 1923.22(2), c = 2626.66(4) pm, Z = 4, R1(all) = 0.0837). According to K37Te28 = K-37[Te(1X)](8)[Te(2X)(2)](6)[Te(3X)(8)] the structure contains three different types of Te anions: The two crystallographically different isolated telluride anions [Te(1X)](2-) are coordinated by 9/10 K+ cations. Three [Te(2X)(2)](2-) dumbbells (d(Te-Te) = 277.9/286.4 pm) are arranged to 'hexamers'. The Te(31) and Te(32) atoms are located in columns of face-sharing K square antiprisms. Their z position modulation, which is accompanied by a smaller shift of the surrounding K+ cations, results in the decomposition of the [Te(3X)(8)](2) chain in a sequence vertical bar:Te-3-Te-2-Te-2-Te-3-Te-2-Te-2-Te-2:vertical bar of dumbbells Te-2(2-) (d(Te-Te) = 304 pm) and hypervalent linear trimers Te-3(4- )(d(Te-Te) = 325 pm).
Title:
A Yoffe-type moving crack in one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Zhou, YB; Li, XF Author Full Names: Zhou, Y. -B.; Li, X. -F.
Source:
APPLIED MATHEMATICAL MODELLING, 65 148-163; 10.1016/j.apm.2018.08.005 JAN 2019
Abstract:
A Yoffe-type moving crack in one-dimensional hexagonal piezoelectric quasicrystals is considered. The Fourier transform technique is used to solve a moving crack problem under the action of antiplane shear and inplane electric field. Full elastic stresses of phonon and phason fields and electric fields are derived for a crack running with constant speed in the periodic plane. Obtained results show that the coupled elastic fields inside piezoelectric quasicrystals depend on the speed of crack propagation, and exhibit the usual square-root singularity at the moving crack tip. Electric field and phason stresses do not have singularity and electric displacement and phonon stresses have the inverse square-root singularity at the crack tip for a permeable crack. The field intensity factors and energy release rates are obtained in closed form. The crack velocity does not affect the field intensity factors, but alters the dynamic energy release rate. Bifurcation angle of a moving crack in a 1D hexagonal piezoelectric quasicrystal is evaluated from the viewpoint of energy balance. Obtained results are helpful to better understanding crack advance in piezoelectric quasicrystals. (C) 2018 Elsevier Inc. All rights reserved.
Title:
The origin of the polar symmetry in huebnerite-type multiferroics
Authors:
Park, SH; Behal, D; Pedersen, B Author Full Names: Park, So-Hyun; Behal, David; Pedersen, Bjoern
Source:
PHYSICA B-CONDENSED MATTER, 551 118-121; 10.1016/j.physb.2017.11.034 DEC 15 2018
Abstract:
The magnetic structure of the multiferroic phase AF2 of huebnerite (MnWO4) has been re-investigated based on the polar space group P2, instead of P2/c widely accepted in literature. The site character between two independent sites for Mn2+, Mn-a and Mn-b, fairly differs from each other in terms of bond valence sums. This hidden intrinsic dipole moment is the true origin of the chiral magnetic order in AF2 in the polar superspace group P2.1' (alpha, 1/2, gamma)0s. From structure refinements using single crystal neutron diffraction data at 10 K the ellipticity of the spin helix could be determined to be 0.92 and 0.77 at Mn-a and Mn-b, respectively. The different contributions of two chiral spin-textures to electric polarisation microscopically measurable in the b axis (P-b) could be estimated with P-b (Mn-a) = 22.8 mu Cm-2 and P-b (Mn-b) = 12.2 mu Cm-2.

Update: 9-Jan-2019

Title:
Lattice Modulation and Structural Phase Transition in the Antiferromagnet EuAl4
Authors:
Shimomura, S; Murao, H; Tsutsui, S; Nakao, H; Nakamura, A; Hedo, M; Nakama, T; Onuki, Y Author Full Names: Shimomura, Susumu; Murao, Hiroki; Tsutsui, Satoshi; Nakao, Hironori; Nakamura, Ai; Hedo, Masato; Nakama, Takao; Onuki, Yoshichika
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (1):10.7566/JPSJ.88.014602 JAN 15 2019
Abstract:
X-ray diffraction measurements on the antiferromagnet EuAl4 using synchrotron radiation have revealed that satellite peaks characterized by an incommensurate wave vector (0, 0, zeta) with zeta approximate to 0.18 appear below 145.1 K, suggesting the formation of a charge density wave. The value of zeta shows an inflection at an antiferromagnetic transition temperature of 15.4K, and it changes discontinuously at lower antiferromagnetic transition temperatures of 12.2 and 10.0K. The antiferromagnetic transition at 12.2 K is accompanied by a structural transition from the modulated structure on a tetragonal lattice to that on a lattice with lower symmetry such as an orthorhombic one.
Title:
Unique Helical Magnetic Order and Field-Induced Phase in Trillium Lattice Antiferromagnet EuPtSi
Authors:
Kaneko, K; Frontzek, MD; Matsuda, M; Nakao, A; Munakata, K; Ohhara, T; Kakihana, M; Haga, Y; Hedo, M; Nakama, T; Onuki, Y Author Full Names: Kaneko, Koji; Frontzek, Matthias D.; Matsuda, Masaaki; Nakao, Akiko; Munakata, Koji; Ohhara, Takashi; Kakihana, Masashi; Haga, Yoshinori; Hedo, Masato; Nakama, Takao; Onuki, Yoshichika
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (1):10.7566/JPSJ.88.013702 JAN 15 2019
Abstract:
Magnetic transition phenomena in cubic chiral antiferromagnet EuPtSi with T-N = 4.0 K were investigated by means of single crystal neutron diffraction. At 0.3 K in the ground state, magnetic peaks emerge at positions represented by an ordering vector q(1) = (0.2, 0.3, 0) and its cyclic permutation. Upon heating, an additional magnetic peak splitting with hysteresis was uncovered at around T-N* similar to 2.5 K, indicating the presence of a first-order commensurate incommensurate transition with q(1)* = (0.2, 0.3, delta) (delta(max) similar or equal to 0.04) at T-N*. A half-polarized neutron scattering experiment for polarization parallel to the scattering vector revealed that polarization antiparallel to the scattering vector has stronger intensity in both magnetic phases. This feature clarifies the single chiral character of the helical structure with moments lying perpendicular to the ordering vector in both ordered states. Under a vertical magnetic field of 1.2 T for B parallel to [1, 1, 1] at 1.9 K entering into the so-called A phase, magnetic peaks form characteristic hexagonal patterns in the equatorial scattering plane around nuclear peaks. An ordering vector q(A) similar or equal to (+/- 0.09, +/- 0.20, -/+ 0.28) of the A-phase has similar periodic length as q(1), and could be the hallmark of a formation of skyrmion lattice in EuPtSi.
Title:
Hyperuniformity and anti-hyperuniformity in one-dimensional substitution tilings
Authors:
Oguz, EC; Socolar, JES; Steinhardt, PJ; Torquato, S Author Full Names: Oguz, Erdal C.; Socolar, Joshua E. S.; Steinhardt, Paul J.; Torquato, Salvatore
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 3-13; 10.1107/S2053273318015528 1 JAN 2019
Abstract:
This work considers the scaling properties characterizing the hyperuniformity (or anti-hyperuniformity) of long-wavelength fluctuations in a broad class of one-dimensional substitution tilings. A simple argument is presented which predicts the exponent alpha governing the scaling of Fourier intensities at small wavenumbers, tilings with alpha > 0 being hyperuniform, and numerical computations confirm that the predictions are accurate for quasiperiodic tilings, tilings with singular continuous spectra and limit-periodic tilings. Quasiperiodic or singular continuous cases can be constructed with alpha arbitrarily close to any given value between -1 and 3. Limit-periodic tilings can be constructed with alpha between -1 and 1 or with Fourier intensities that approach zero faster than any power law.
Title:
k-eIsocoronal tilings
Authors:
Taganap, E; De Las Penas, MLA Author Full Names: Taganap, Eduard; Antonette De Las Penas, Ma. Louise
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 94-106; 10.1107/S2053273318013992 1 JAN 2019
Abstract:
In this article, a framework is presented that allows the systematic derivation of planar edge-to-edge k-isocoronal tilings from tile-s-transitive tilings, s <= k. A tiling T is k-isocoronal if its vertex coronae form k orbits or k transitivity classes under the action of its symmetry group. The vertex corona of a vertex x of T is used to refer to the tiles that are incident to x. The k-isocoronal tilings include the vertex-k-transitive tilings (k-isogonal) and k-uniform tilings. In a vertex-k-transitive tiling, the vertices form k transitivity classes under its symmetry group. If this tiling consists of regular polygons then it is k-uniform. This article also presents the classification of isocoronal tilings in the Euclidean plane.

Update: 4-Jan-2019

Title:
Spatially localized quasicrystalline structures
Authors:
Subramanian, P; Archer, AJ; Knobloch, E; Rucklidge, AM Author Full Names: Subramanian, P.; Archer, A. J.; Knobloch, E.; Rucklidge, A. M.
Source:
NEW JOURNAL OF PHYSICS, 20 10.1088/1367-2630/aaf3bd DEC 14 2018
Abstract:
Soft matter systems have been observed to self-assemble, over a range of system parameters, into quasicrystalline structures. The resulting quasicrystals (QCs) may minimize the free energy, and be in thermodynamic coexistence with the liquid state. At such state points, the likelihood of finding the presence of spatially localized states with quasicrystalline structure within the liquid is increased. Here we report the first examples of metastable spatially localized QCs of varying sizes in both two and three dimensions. Implications of these results for the nucleation of quasicrystalline structures are discussed. Our conclusions apply to a broad class of soft matter systems and more generally to continuum systems exhibiting quasipatterns.

Update: 20-Dec-2018

Title:
Accurate Determination of Composite Crystal Structure of Incommensurately Modulated Sr14Cu24O41 Using the Akaike Information Criterion
Authors:
Gotoh, Y Author Full Names: Gotoh, Yoshito
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 87 (12):10.7566/JPSJ.87.124601 DEC 15 2018
Abstract:
The composite crystal structure of the spin-ladder compound Sr14Cu24O41 has been reinvestigated using the Akaike information criterion (AIC) to solve the possible overfitting of atomic positions in our previous work [Phys. Rev. B 68. 224108 (2003)]. The minimizing AIC method using the same data as before removes the splitting behavior of the Cu-O bonds along the one-dimensional Cu-O chain in the two-legged Cu2O3 ladder and reveals the importance of the Cu-O-Cu rung with a strong Cu-O bond. Nonsymmetric paths of hole transfer from the O atom in the CuO2 chain to the Cu-O-Cu rung in the ladder have been elucidated by the resulting new modulated structure. Bond-valence sum analysis of the modulated CuO2 substructure of Sr(14)Cu(24)O(41 )shows the role of large displacive modulation of the O atom in the CuO2 chain and the valence fluctuation of Cu atom with a periodicity almost 200 times that of the average CuO2 lattice. There is no discommensuration of the < Cu2+>-< Cu3+>-< Cu2+> arrangements in the CuO2 chain. The incommensurability between the average substructures is characterized as sigma = (0 0 0.6995) and the chemical formula should be exactly expressed as (Sr2Cu2O3)(0.6995)CuO2.
Title:
Magnetic order in the rare-earth ferroborate CeFe3(BO3)(4)
Authors:
Hayashida, S; Asai, S; Kato, D; Hasegawa, S; Avdeev, M; Cao, HB; Masuda, T Author Full Names: Hayashida, Shohei; Asai, Shinichiro; Kato, Daiki; Hasegawa, Shunsuke; Avdeev, Maxim; Cao, Huibo; Masuda, Takatsugu
Source:
PHYSICAL REVIEW B, 98 (22):10.1103/PhysRevB.98.224405 DEC 4 2018
Abstract:
We have studied the magnetic order of the rare-earth ferroborate CeFe3(BO3)(4) through the thermodynamic and the neutron diffraction measurements. The heat capacity and the magnetic susceptibility revealed antiferromagnetic magnetic ordering at 29 K. In the neutron powder diffraction data, we observed the magnetic Bragg peaks indexed by the commensurate (CM) propagation vector k(CM) = (0, 0, 3/2) and the incommensurate (ICM) vector k(ICM) = (0, 0, 3/2+delta). The incommensurability delta increases with decreasing the temperature, and is evaluated to be 0.04556(16) at 3.7 K. Magnetic structure analysis reveals that the magnetic moments aligning in the ab plane form the collinear antiferromagnetic structure having k(CM)( )and helical structure having k(ICM). Detailed measurements of the magnetic susceptibility exhibit an additional anomaly at 27 K. Furthermore, the temperature dependence of the neutron diffraction profile on the single-crystal sample shows that the ICM and CM ordering occurs at 29 and 26 K, respectively. These results suggest a phase separation state between the collinear and helical structures. The multiferroicity of CeFe3(BO3)(4) is discussed on the basis of the determined magnetic structure.
Title:
A seed-based structural model for constructing rhombic quasilattice with 7-fold symmetry
Authors:
Ajlouni, R Author Full Names: Ajlouni, Rima
Source:
STRUCTURAL CHEMISTRY, 29 (6):1875-1883; 10.1007/s11224-018-1169-2 DEC 2018
Abstract:
A seed-based theoretical model with built-in local degree of freedom for constructing rhombic quasilattice with 7-fold symmetry is presented. This new approach mitigates a key limitation with existing structural models for describing quasicrystals, which do not incorporate atomic fluctuations or phasonic flips in their approaches. Here, we propose a structural model that works in concert with the seed-initiated nucleation growth models of quasicrystals and incorporates a degree of flexibility that allows the lattice to rearrange locally without affecting the global long-range order. This approach suggests that the position of high-symmetry motifs locally and globally is defined by one long-range framework and not based on local rules (i.e., inflation, deflation, substitution, matching, overlapping, etc.). The proposed model is based on building a hierarchical network that allows the self-similar quasilattice to expand infinitely without any gaps, overlaps, or mismatches. The use of a global relational logic provides scientists, artists, and teachers with a simple method for creating a wide variety of complicated hierarchical quasilattice formations without the need for any specialized software or complicated mathematics and could possibly provide a deeper understanding of how the atoms interact to form their complicated long-range quasicrystalline formations.
Title:
Light-Tunable 1T-TaS2 Charge-Density-Wave Oscillators
Authors:
Zhu, C; Chen, Y; Liu, FC; Zheng, SJ; Li, XB; Chaturvedi, A; Zhou, JD; Fu, QD; He, YM; Zeng, QS; Fan, HJ; Zhang, H; Liu, WJ; Yu, T; Liu, Z Author Full Names: Zhu, Chao; Chen, Yu; Liu, Fucai; Zheng, Shoujun; Li, Xiaobao; Chaturvedi, Apoorva; Zhou, Jiadong; Fu, Qundong; He, Yongmin; Zeng, Qingsheng; Fan, Hong Jin; Zhang, Hua; Liu, Wen Jun; Yu, Ting; Liu, Zheng
Source:
ACS NANO, 12 (11):11203-11210; 10.1021/acsnano.8b05756 NOV 2018
Abstract:
w External stimuli-controlled phase transitions are essential for fundamental physics and design of functional devices. Charge density wave (CDW) is a metastable collective electronic phase featured by the periodic lattice distortion. Much attention has been attracted to study the external control of CDW phases. Although much work has been done in the electric field-induced CDW transition, the study of the role of Joule heating in the phase transition is insufficient. Here, using the Raman spectroscopy, the electric-field-driven phase transition is in situ observed in the ultrathin 1T-TaS2. By quantitative evaluation of the Joule heating effect in the electric-field-induced CDW transition, it is shown that Joule heating plays a secondary role in the nearly commensurate (NC) to incommensurate (IC) CDW transition, while it dominants the IC-NC CDW transition, providing a better understanding of the electric field-induced phase transition. More importantly, at room temperature, light illumination can modulate the CDW phase and thus tune the frequency of the ultrathin 1T-TaS2 oscillators. This light tunability of the CDW phase transition is promising for multifunctional device applications.
Title:
Thermal behavior of modulated hauyne from Eifel, Germany: In situ high-temperature single-crystal X-ray diffraction study
Authors:
Kuribayashi, T; Aoki, S; Nagase, T Author Full Names: Kuribayashi, Takahiro; Aoki, Satoshi; Nagase, Toshiro
Source:
JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES, 113 (1):51-55; 10.2465/jmps.161114d FEB 2018
Abstract:
In-situ high-temperature single-crystal X-ray diffraction experiments on modulated hauyne obtained from Ei-fel, Germany, were conducted to re-evaluate its thermal behavior. The linearity of its thermal expansion is lost between 600 and 700 degrees C. Satellite peaks, indicating the modulated structure, were clearly observed up to 600 degrees C, but disappeared at 700 degrees C. These results indicate that the modulated hauyne structure changed in this temperature region. In addition, according to the observation of X-ray oscillation images taken at ambient conditions, the modulated structure of the sample heat-treated below 1000 degrees C remained unchanged, whereas modulation of the parent crystal structure changed when the sample was heat-treated above 1000 degrees C. This structural change to the unique modulated structure can be attributed to be the possible rearrangement of Al/Si distribution in the tetrahedral sites forming the framework.

Update: 12-Dec-2018

Title:
In-situ synthesis of aluminum/nano-quasicrystalline Al-Fe-Cr composite by using selective laser melting
Authors:
Kang, N; El Mansori, M; Lin, X; Guittonneau, F; Liao, HL; Huang, WD; Coddet, C Author Full Names: Kang, N.; El Mansori, M.; Lin, X.; Guittonneau, F.; Liao, H. L.; Huang, W. D.; Coddet, C.
Source:
COMPOSITES PART B-ENGINEERING, 155 382-390; 10.1016/j.compositesb.2018.08.108 DEC 15 2018
Abstract:
In this research, Al-Fe-Cr quasicrystal (QC) reinforced Al-based metal matrix composites were in-situ manufactured by using selective laser melting (SLM) from the powder mixture. The parametrical optimization based on our previous work was performed with focus on laser scanning speed. From the optimized parameters, an almost dense (99.7%) free-crack sample was fabricated with an ultra-fine microstructure. A phase transition from decagonal QC Al65Cu25Fe10Cr5 to icosahedral QC Al91Fe4Cr5 could be observed as laser scanning speed decreases. Differential scanning calorimetry curves show that the QC phase is quiet stable until 500 degrees C. And then, the effects of annealing temperature on the microstructural and mechanical properties were determined. The results indicate that the recrystallization and growth behavior of alpha-Al grains could be prevented by QC particle during annealing. Furthermore, the growth of QC particle, which tends to form a porous structure, leads an improvement of Young modulus and decline of ductility.
Title:
Syntheses, modulated crystal structures of Ba6-2xU2+xAg4Se12 (x=0 and 0.5), and crystal structure and spectroscopy of Sr4Th2.78Cu4S12
Authors:
Mesbah, A; Prakash, J; Beard, JC; Malliakas, CD; Lebegue, S; Ibers, JA Author Full Names: Mesbah, Adel; Prakash, Jai; Beard, Jessica C.; Malliakas, Christos D.; Lebegue, Sebastien; Ibers, James A.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 268 30-35; 10.1016/j.jssc.2018.08.025 DEC 2018
Abstract:
Single crystals of Ba6-2xU2+xAg4Se12 (x = 0 and 0.5) and Sr4Th2.78Cu4S12 were obtained by standard solid-state chemistry methods at 1173 K. The Ba6-2xU2+xAg4Se12 structures are modulated. They were solved and refined in the monoclinic C2(alpha 0 gamma)0 super space group. The structure consists of layers formed by the connection of USe6 and AgSe4 polyhedra. The incommensurate nature of the structure arises from the disorder among Ba atoms and U atoms in the layers. The crystal structure of the Sr4Th2.78Cu4S12 was solved in space group Pmn2(1) of the orthorhombic system. The refinement of the structure reveals three partially occupied Th sites. The connection of ThS7 and CuS4 polyhedra form a channel structure filled by Sr atoms. From optical measurements Sr4Th2.78Cu4S12 is a semiconductor with an indirect band gap of 2.27(2) eV.
Title:
Basic and charge density wave modulated structures of NbS3-II
Authors:
Zupanic, E; van Midden, HJP; van Midden, MA; Sturm, S; Tchernychova, E; Pokrovskii, VY; Zybtsev, SG; Nasretdinova, VF; Zaitsev-Zotov, SV; Chen, WT; Pai, WW; Bennett, JC; Prodan, A Author Full Names: Zupanic, E.; van Midden, H. J. P.; van Midden, M. A.; Sturm, S.; Tchernychova, E.; Pokrovskii, V. Ya; Zybtsev, S. G.; Nasretdinova, V. F.; Zaitsev-Zotov, S., V; Chen, W. T.; Pai, Woei Wu; Bennett, J. C.; Prodan, A.
Source:
PHYSICAL REVIEW B, 98 (17):10.1103/PhysRevB.98.174113 NOV 27 2018
Abstract:
The basic and the charge density wave (CDW) structures of the monoclinic NbS3-II polymorph were studied by synchrotron x-ray diffraction, ab initio calculations, simulation of electron diffraction patterns, and by atomic-resolution transmission electron and low-temperature scanning tunneling microscopies. It is confirmed that the basic structure belongs to the space group P2(1)/ m and is described with a unit cell, formed of four pairs of symmetry-related trigonal prismatic (TP) columns [a(0) = 0.96509(8) nm, b(0) = 0.33459(2) nm, c(0) = 1.9850(1) nm, and beta(0) = 110.695(4)degrees]. The incommensurate components of the two CDWs, (q) over bar (1) = (0, 0.298, 0) and (q) over bar (2) = (0, 0.352, 0), are related as (q) over bar (1b) + 2q(2b) approximate to 1. Both CDWs form their own modulation patterns with unit cells (a(m) = 2a(0), b(m) = b(0)/q(jb), c(m) = c(0), beta(m) = beta(0)) and are ordered along adjacent isosceles TP columns either pairwise or with both columns modulated by either the (q) over bar (1) or (q) over bar (2) CDW only. The CDWs are ordered according to one of the two possible modulation pattern space groups, Cm or C2/ m. If considered as long-period commensurate, the entire modulated structure with both CDWs included is described within experimental error with an enlarged unit cell (a = 2a(0), b = 37b(0), c = c(0), and beta = beta(0)) and with all atoms displaced from their average positions in accord with the specified modulation pattern.
Title:
Crystal and Magnetic Structures and Properties of (Lu1-xMnx)MnO3 Solid Solutions
Authors:
Zhang, L; Donni, A; Pomjakushin, VY; Yamaura, K; Belik, AA Author Full Names: Zhang, Lei; Donni, Andreas; Pomjakushin, Vladimir Y.; Yamaura, Kazunari; Belik, Alexei A.
Source:
INORGANIC CHEMISTRY, 57 (22):14073-14085; 10.1021/acs.inorgchem.8b01470 NOV 19 2018
Abstract:
(Lu1-xMnx)MnO3 solid solutions, having the perovskite-type structure and Pnma space group, with 0 <= x <= 0.4 were synthesized by a high-pressure, high temperature method at 6 GPa and about 1670 K from Lu2O3 and Mn2O3. Their crystal and magnetic structures were studied by neutron powder diffraction. The degree of octahedral MnO6 tilting decreases in (Lu1-xMnx)MnO3 with increasing x. Only the incommensurate (IC) spin structure with a propagation vector of k = (k(0), 0, 0) and k(0) approximate to 0.44 remains in (Lu0.9Mn0.1)MnO3 in the whole temperature range below the Neel temperature T-N = 36 K, and the commensurate noncollinear E-type structure that has been reported in the literature for undoped o-LuMnO3 is not observed. (Lu1-xMnx)MnO3 samples with 0.2 <= x <= 0.4 have a ferrimagnetic structure with a propagation vector of k = (0, 0, 0) and ferromagnetic (FM) ordering of Mn3+ and Mn4+ cations at the B site, which are antiferromagnetically coupled to a noncollinear predominantly FM arrangement of Mn2+ at the A site. The ferrimagnetic Curie temperature, T-C, increases monotonically from 67 K for x = 0.2 to 118 K for x = 0.4. Magnetic and dielectric properties of (Lu1-xMnx)MnO3 and a composition-temperature phase diagram are also reported.
Title:
At the Gates: The Tantalum-Rich Phase Hf3Ta2O11 and its Commensurately Modulated Structure
Authors:
Wiedemann, D; Ludtke, T; Palatinus, L; Willinger, E; Willinger, MG; Muhlbauer, MJ; Lerch, M Author Full Names: Wiedemann, Dennis; Luedtke, Tobias; Palatinus, Lukas; Willinger, Elena; Willinger, Marc G.; Muehlbauer, Martin J.; Lerch, Martin
Source:
INORGANIC CHEMISTRY, 57 (22):14435-14442; 10.1021/acs.inorgchem.8b02642 NOV 19 2018
Abstract:
Generic mixtures in the system (Zr,Hf)O-2-(Nb,Ta)(2)O-5 are employed as tunable gate materials for field-effect transistors. Whereas production processes and target compositions are well-defined, resulting crystal structures are vastly unexplored. In this study, we summarize the sparse reported findings and present the new phase Hf3Ta2O11 as synthesized via a sol-gel route. Its commensurately modulated structure represents the hitherto unknown, metal(V)-richest member of the family (Zr,Hf)(x)(Nb,Ta)(2)O2x+5. Based on electron, neutron, and X-ray diffraction, the crystal structure is described within modern superspace [Hf1.2Ta0.8O4.4 Z = 2, a = 4.7834(13), b = 5.1782(17), c = 5.064(3) angstrom, q = 1/5c*, orthorhombic, superspace group Xmcm(00 gamma)s00] and supercell formalisms [Hf3Ta2O11, Z = 4, a = 4.7834(13), b = 5.1782(17), c = 25.320(13) angstrom, orthorhombic, space group Pbnm]. Transmission electron microscopy shows the microscopic structure from film-like aggregates down to atomic resolution. Cation ordering within the different available coordination environments is possible, but no significant hint at it is found within the limits of standard diffraction techniques. Hf3Ta2O11 is an unpredicted compound in the above-mentioned oxide systems, in which stability ranges have been disputably fuzzy and established only by syntheses via solid-state routes so far.
Title:
Magnetic structure of a non-centrosymmetric CePtSi3
Authors:
Ueta, D; Yoshida, M; Ikeda, Y; Liu, Y; Hong, T; Masuda, T; Yoshizawa, H Author Full Names: Ueta, D.; Yoshida, M.; Ikeda, Y.; Liu, Y.; Hong, T.; Masuda, T.; Yoshizawa, H.
Source:
AIP ADVANCES, 8 (11):10.1063/1.5042736 NOV 2018
Abstract:
Neutron diffraction experiments have been performed on single crystalline samples of CePtSi3. We found that the incommensurate magnetic propagation vector tau(1) = (+/- 0.283, 0, 0) in the phase I (2.2 similar to 4.8 K) switches to the commensurate vectors tau(2) = (+/- 0.25, 0, 0) and tau(3) = (+/- 0.25, 0, +/- 1) in the phase III (similar to 2.8 K) at zero field. Although the magnetic structure of CePtSi3 in the phase I is a spin density wave similar to those in CeRhSi3, CeIrSi3, and CePdSi3, the magnetic structure in the phase III is commensurate unlike other CeTSi3 (T = Rh, Ir, Pd) compounds. (c) 2018 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license

Update: 5-Dec-2018

Title:
New Ti-based bulk metallic glasses with exceptional glass forming ability
Authors:
Lin, SF; Liu, DM; Zhu, ZW; Li, D; Fu, HM; Zhuang, YX; Zhang, HW; Li, H; Wang, AM; Zhang, HF Author Full Names: Lin, Shifeng; Liu, Dingming; Zhu, Zhengwang; Li, Dan; Fu, Huameng; Zhuang, Yanxin; Zhang, Hongwei; Li, Hong; Wang, Aimin; Zhang, Haifeng
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 502 71-75; 10.1016/j.jnoncrysol.2018.06.038 DEC 15 2018
Abstract:
New Ti-based bulk metallic glasses (BMGs) of Ti32.8+xZr30.2-xNi5.3Cu9Be22.7 (3 <= vertical bar X vertical bar <= 15, at.%) with large size were prepared. The results reveal that the forming of primary icosahedral quasicrystal phase (I-phase) and the enthalpy of the primary crystallization (Delta H-1) were closely related to the glass forming abilities (GFAs). Thecrystallization product of the metallic glass alloys at primary crystallization state is a metastable I-phase. It is demonstrated that apparent activation energy for crystallization obtained by fitting the Kissinger equation at T-x temperature increases with the increase of Ti concentration, while GFAs deteriorate. The Delta H-1 of metallic glasses declines with the increase of Ti concentration. The Ti32.8+XZr30.2-XNi5.3Cu9Be22.7 possess high similar compressive fracture strength of about 1800 MPa, which is one of the best options as structural materials on account of high specific strength and low cost.
Title:
Magnetic ordering in multiferroic SmMn2O5 and GdMn2O5 studied by resonant soft x-ray scattering
Authors:
Ishii, Y; Horio, S; Yamamoto, H; Noda, Y; Nakao, H; Murakami, Y; Kimura, H Author Full Names: Ishii, Y.; Horio, S.; Yamamoto, H.; Noda, Y.; Nakao, H.; Murakami, Y.; Kimura, H.
Source:
PHYSICAL REVIEW B, 98 (17):10.1103/PhysRevB.98.174428 NOV 21 2018
Abstract:
Resonant soft x-ray scattering was used to study the magnetic ordering of the multiferroic materials SmMn2O5 and GdMn2O5. In the case of SmMn2O5, the results confirm that antiferromagnetic ordering of Mn magnetic moments occurs with magnetic propagation vector q(M) = (1/2, 0, 1/3 + delta') in the incommensurate magnetic phase, followed by the appearance of the commensurate magnetic phase with q(M) = (1/2, 0, 0) as the temperature is decreased. The energy spectrum around Mn L-II(,)III edges suggests that the Mn ions adopt unique electronic states in the CM phase of SmMn2O5. No evidence was found for spin polarization of oxygen ions through 2p-3d orbital hybridization between oxygen and Mn ions in this compound, although this phenomenon is clearly evident in GdMn2O5 and other RMn2O5 (R = Y, Er, Tb) compounds. The energy spectra around O K edge strongly suggest that electronic polarization resulting from charge transfer between oxygen and Mn ions has little contribution to the ferroelectricity while lattice distortion likely plays a key role in promoting ferroelectricity in SmMn2O5.
Title:
Synthesis of an Al-Mn-Based Alloy Containing In Situ-Formed Quasicrystals and Evaluation of Its Mechanical and Corrosion Properties
Authors:
Naglic, I; Samardzija, Z; Delijic, K; Kobe, S; Leskovar, B; Markoli, B Author Full Names: Naglic, Iztok; Samardzija, Zoran; Delijic, Kemal; Kobe, Spomenka; Leskovar, Blaz; Markoli, Bostjan
Source:
JOM, 70 (11):2698-2703; 10.1007/s11837-018-2945-6 NOV 2018
Abstract:
An Al-Mn alloy with additions of copper, magnesium, and silicon was prepared and cast into a copper mold. It contains in situ-formed icosahedral quasicrystals (iQCs), as confirmed by electron backscatter diffraction. The aim of this work is to present the mechanical and corrosion properties of this alloy and compare its properties with some conventional commercial materials. The compressive strength and compressive yield strength were 751MPa and 377MPa, while the compressive fracture strain was 19%. It was observed that intensive shearing caused the final fracture of the specimens and the fractured iQC dendrites still showed cohesion with the -Al matrix. The polarization resistance and corrosion rate of the artificially aged alloy were 7.30k and 1.2m/year. The evaluated properties are comparable to conventional, discontinuously reinforced aluminum metal-matrix composites and structural wrought aluminum alloys.
Title:
Influence of Minor Additions on Icosahedral Short-Range Order (ISRO) and Its Consequences on Nucleation and Solidification Growth Kinetics in fcc Alloys
Authors:
Zollinger, J; Rappaz, M Author Full Names: Zollinger, J.; Rappaz, M.
Source:
TRANSACTIONS OF THE INDIAN INSTITUTE OF METALS, 71 (11):2635-2638; SI 10.1007/s12666-018-1411-z NOV 2018
Abstract:
The present contribution reviews the recent progress related to the influence of icosahedral short-range order (ISRO) and icosahedral quasicrystal (iQC) formation on the solidification of fcc alloys through minor solute element additions. From intensive crystallographic analysis of multi-twinned region in as-cast Al-based and Au-based fcc alloys, it has been shown recently that a so-called iQC-mediated nucleation mechanism occurs when a few hundred ppm of Cr and Ir, respectively, are added to the melt (Kurtuldu et al. in Acta Mater 61(19):7098-7108, 2013; Acta Mater 70:240-248, 2014). Similarly, it appears that the growth directions of dendrites in Al-Zn/Cr are also influenced by ISRO in the liquid, thus showing an attachment kinetics effect (Kurtuldu in Influence of trace elements on the nucleation and solidification morphologies of fcc alloys and relationship with icosahedral quasicrystal formation, 2014). Similar observations have been made recently in pink gold alloys with Ir additions, when the solidification speed is increased (Zollinger et al. in Acta Mater, 2018).

Update: 28-Nov-2018

Title:
Effect of Cu and Mn content on solidification microstructure, T-phase formation and mechanical property of Al-Cu-Mn alloys
Authors:
Dar, SM; Liao, HC; Xu, AQ Author Full Names: Dar, Soban Muddassir; Liao, Hengcheng; Xu, Aiqun
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 774 758-767; 10.1016/j.jallcom.2018.09.362 FEB 5 2019
Abstract:
Solidification microstructure of two AlCuMn alloys (Alloy-1: Al-1.6Cu-0.3Mn, Alloy-2: Al-2.2Cu-0.8Mn) and their precipitation behavior during solutionizing and aging treatments were investigated by optical microscopy, X-ray diffraction, Scanning and Transmission Electron Microscopies. The influence of Cu/Mn content and ratio on mechanical properties was also discussed in this study. Results reveal that Cu/Mn content and ratio have considerable influence on the solidification microstructure of these alloys. In Alloy-1 with low Cu/Mn content and ratio, only small amount of theta-CuAl2 and T-phase (Al20Cu2Mn3) are formed within the interdendritic regions and grains boundaries during solidification. But in Alloy-2 with high Cu/Mn content and ratio, a great amount of bone-like and round multiphase structure is observed in interdendritic regions, which consists of alpha-Al, theta-CuAl2 and Al13Cu4Mn3 phases. The Al13Cu4Mn3 phase in multiphase structure is demonstrated to be an icosahedral quasicrystalline phase (I-phase). The formation of I-phase in a conventional casting of AlCuMn alloy is related to the stabilizing effect of Fe. Cu/Mn content and ratio also have considerable influence on precipitation behavior of AlCuMn alloy during solutionizing and aging treatment. In Alloy-2, two morphologies of T-phase are formed: large particulate one is transformed from the instability decomposition of I-phase at high temperature and the fine rod-like is precipitated from supersaturated Al solid solution. And further aging does not lead to new precipitates. At each test temperature, both the YS and UTS of Alloy-2 are higher than that of Alloy-1 which is related to the formation of a great amount of T-phase particles during solution treatment. (C) 2018 Published by Elsevier B.V.
Title:
Effect of refinement of grains and icosahedral phase on hot compressive deformation and processing maps of Mg-Zn-Y magnesium alloys with different volume fractions of icosahedral phase
Authors:
Kwak, TY; Kim, WJ Author Full Names: Kwak, T. Y.; Kim, W. J.
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 35 (1):181-191; 10.1016/j.jmst.2018.06.019 JAN 2019
Abstract:
The effect of the volume fraction of I-phase on the hot compressive behavior and processing maps of the extruded Mg-Zn-Y alloys was examined, and the obtained results were compared with those of the cast alloys in a previous work. The average grain sizes, fractions of dynamically recrystallized (DRXed) grains, and sizes of DRXed grains of the extruded alloys after compressive deformation were significantly smaller, higher and smaller, respectively, than those of the cast alloys after compressive deformation under the same experimental conditions. This was because the microstructures of the extruded alloys, having much more grain boundaries and more refined I-phase particles than the cast alloys, provided a larger number of nucleation sites for dynamic recrystallization than those of the cast alloys. The constitutive equations for high-temperature deformation of the extruded and cast alloys could be derived using the same activation energy for plastic flow, which was close to the activation energy for lattice diffusion in magnesium. Compared with the cast alloys, the onset of the power law breakdown (PLB) occurred at larger Zener-Holloman (Z) parameter values in the extruded alloys. This was because the extruded alloys had finer initial grain sizes and higher fractions of finer DRXed grains compared to the cast alloys, such that the onset of PLB caused by creation of excessive concentrations of deformation-induced vacancies was delayed to a higher strain rate and a lower temperature. The flow-stress difference between the extruded alloys and the cast alloys could be attributed to the difference in the fraction of DRXed grains. According to the processing maps, the extruded alloys exhibited higher power dissipation efficiency and flow stability than the cast alloys. This agreed with the microstructural observations. (C) 2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
Title:
Electronic structure of commensurate, nearly commensurate, and incommensurate phases of 1T-TaS2 by angle-resolved photoelectron spectroscopy, scanning tunneling spectroscopy, and density functional theory
Authors:
Lutsyk, I; Rogala, M; Dabrowski, P; Krukowski, P; Kowalczyk, PJ; Busiakiewicz, A; Kowalczyk, DA; Lacinska, E; Binder, J; Olszowska, N; Kopciuszynski, M; Szalowski, K; Gmitra, M; Stepniewski, SR; Jalochowski, M; Kolodziej, JJ; Wysmolek, A; Klusek, Z Author Full Names: Lutsyk, I; Rogala, M.; Dabrowski, P.; Krukowski, P.; Kowalczyk, P. J.; Busiakiewicz, A.; Kowalczyk, D. A.; Lacinska, E.; Binder, J.; Olszowska, N.; Kopciuszynski, M.; Szalowski, K.; Gmitra, M.; Stepniewski, S. R.; Jalochowski, M.; Kolodziej, J. J.; Wysmolek, A.; Klusek, Z.
Source:
PHYSICAL REVIEW B, 98 (19):10.1103/PhysRevB.98.195425 NOV 19 2018
Abstract:
The electronic structure of 1T-TaS2 showing a metal-insulator transition and a sequence of different charge density wave (CDW) transformations was discussed in the frame of variable temperature angle-resolved photoelectron spectroscopy (ARPES), scanning tunneling spectroscopy (STS), and density functional theory (DFT) calculations. For the commensurate charge density wave phase (CCDW) the Mott gap was estimated to be 0.4 eV and energy gaps Delta(CCDW,1), Delta(CCDW,2), Delta(B3-HHB), Delta(B4-B3) were observed. For the nearly commensurate charge density wave phase (NCCDW), the reminiscent of higher and lower Hubbard bands and a very pronounced electronic state associated with the parabolic band at the (Gamma) over bar point in the Brillouin zone were identified. The incommensurate charge density wave phase (ICCDW) showed a high value of local density of states at the Fermi level and a very pronounced edge of the metallic surface state located in the range of 0.15-0.20 eV above the Fermi level. The obtained STS and ARPES results were consistent with our theoretical calculations performed within DFT formalism including spin-orbit coupling.
Title:
Femtosecond diffraction studies of solid and liquid phase changes in shock-compressed bismuth
Authors:
Gorman, MG; Coleman, AL; Briggs, R; McWilliams, RS; McGonegle, D; Bolme, CA; Gleason, AE; Galtier, E; Lee, HJ; Granados, E; Sliwa, M; Sanloup, C; Rothman, S; Fratanduono, DE; Smith, RF; Collins, GW; Eggert, JH; Wark, JS; McMahon, MI Author Full Names: Gorman, M. G.; Coleman, A. L.; Briggs, R.; McWilliams, R. S.; McGonegle, D.; Bolme, C. A.; Gleason, A. E.; Galtier, E.; Lee, H. J.; Granados, E.; Sliwa, M.; Sanloup, C.; Rothman, S.; Fratanduono, D. E.; Smith, R. F.; Collins, G. W.; Eggert, J. H.; Wark, J. S.; McMahon, M. I.
Source:
SCIENTIFIC REPORTS, 8 10.1038/s41598-018-35260-3 NOV 16 2018
Abstract:
Bismuth has long been a prototypical system for investigating phase transformations and melting at high pressure. Despite decades of experimental study, however, the lattice-level response of Bi to rapid (shock) compression and the relationship between structures occurring dynamically and those observed during slow (static) compression, are still not clearly understood. We have determined the structural response of shock-compressed Bi to 68 GPa using femtosecond X-ray diffraction, thereby revealing the phase transition sequence and equation-of-state in unprecedented detail for the first time. We show that shocked-Bi exhibits a marked departure from equilibrium behavior - the incommensurate Bi-III phase is not observed, but rather a new metastable phase, and the Bi-V phase is formed at significantly lower pressures compared to static compression studies. We also directly measure structural changes in a shocked liquid for the first time. These observations reveal new behaviour in the solid and liquid phases of a shocked material and give important insights into the validity of comparing static and dynamic datasets.

Update: 21-Nov-2018

Title:
A contribution to the ternary phase diagrams of Al with Co, Rh and Ir
Authors:
Grushko, B Author Full Names: Grushko, B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 772 399-408; 10.1016/j.jallcom.2018.09.066 JAN 25 2019
Abstract:
Phase equilibria were studied in Al-Co-Rh above 50 at.% Al at 1100 and 1000 degrees C and above 70 at.% Al at 900 degrees C; in Al-Co-Ir above 50 at.% Al at 1100 degrees C and above 70 at.% Al at 900 degrees C; in Al-Ir-Rh above 50 at.% Al at 1150 degrees C and above 70 at.% Al at 900 degrees C. Wide phase regions extended along about constant Al are common in these ternary alloy systems. A continuous ternary region was observed between isostructural Al9Co2, Al9Rh2 and Al9Ir2 (theta-phase), another region between Al5Co2 and Al5Rh2 (H-phase), and at elevated temperatures also between Al2.63Rh and Al2.75Ir (C-phase). The binary regions forming around equiatomic AlCo, AlRh and AlIr are probably connected by continuous ternary regions. The C-phase was found to extend up to at least 8 at.% Co in Al-Co-Rh and up to 10 at.% Co in Al-Co-Ir. The H-phase was found to extend up to at least 8 at.% Ir in Al-Co-Ir. The ternary extensions of m-Al13Co4 achieved similar to 11 at.% Ir and similar to 15 at.% Rh, and those of the Al-Co Z-phase up to similar to 4 at.% Ir and similar to 10 at.% Rh. O-Al13Co4 was found to dissolve up to similar to 2 at.% Rh or Ir. M-Al13Co4 was not observed at ternary compositions. The Al-Rh epsilon-region containing both epsilon(6) and epsilon(16) was found to extend up to similar to 8.5 at.% Co and up to similar to 20 at.% Ir, while the Al-Rh V-phase was found to extend up to 5.5 at.% Co and at least 13 at.% Ir. Of the Al-Ir phases, the phi-phase was found to dissolve up to 5 at.% Rh, and the chi-phase up to at least 12 at.% Rh but only similar to 5 at.% Co. Al3Ir was found to dissolve up to similar to 14.5 at.% Co but very little Rh. No ternary phases were revealed in Al-Ir-Rh. A ternary E-phase (Pbma, a = 2.3555, b = 1.6497, c = 2.0035 nm) was exposed around similar to Al77Co8Rh15. The same structure was also revealed at similar to Al77Co10.5-16.0Ir12.5-7.0. In addition, Al-Co-Ir contains ternary phases V, epsilon, W and D. The Al-Co-Ir V-phase and epsilon-phase are structurally interrelated with the Al-Rh V-phase and epsilon-phase, respectively. The former is formed at similar to Al71Co17.5Ir11.5, the latter at Al76Co7.5-10.5Ir16.5-13.5. The W-phase (Pmn2(1), a = 2.3736, b = 0.8153, c = 2.0757 nm for Al73Co21Ir6) occupies a region inside similar to Al73.0-71.5Co19.0-22Ir5.0-9.0 at 1100 degrees C and decomposes between 1000 and 1100 degrees C. At 1150 degrees C the same compositional region belongs to a decagonal D-phase, while at 1100 degrees C this phase exists at similar to Al74.5Co17.5-21.0Ir8.0-4.5 and at 900 degrees C around similar to Al74.5Co19,5Ir6.0. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Mechanical properties and Hall-Petch relationship of the extruded Mg-Zn-Y alloys with different volume fractions of icosahedral phase
Authors:
Kwak, TY; Kim, WJ Author Full Names: Kwak, T. Y.; Kim, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 770 589-599; 10.1016/j.jallcom.2018.08.121 JAN 5 2019
Abstract:
The effect of the volume fraction (0.6-8.4%) of the icosahedral phase (I-phase) on the microstructure, texture and mechanical properties of extruded Mg-Zn-Y alloys was examined. During extrusion, the eutectic and divorced eutectic I-phase in the cast microstructures was broken into small particles, and the particles were dispersed along the extrusion direction, forming parallel particle bands. The broken Iphase particles promoted grain refinement via a particle-stimulated nucleation mechanism and led to basal texture weakening through dynamic recrystallization. The work hardening rate increased with an increase in the volume fraction of I-phase. However, the strength decreased with an increase in the volume fraction of I-phase due to the texture softening effect. To incorporate the texture softening effect into the Hall-Petch relation, a modified Hall-Petch equation, which simultaneously considers the effects of grain size and texture on strength, was developed using the Schmid factors for basal slip. The proposed equation predicts smaller Hall-Petch slope, friction stress and yield strength with easier activation of basal slip, agreeing with the experimental observations. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Neutron Diffraction Studies on Valence Ordering Compound YbPd
Authors:
Oyama, K; Sugishima, M; Tanabe, K; Mitsuda, A; Wada, H; Ohoyama, K; Matsukawa, T; Yoshida, Y; Hoshikawa, A; Ishigaki, T; Iwasa, K Author Full Names: Oyama, Kohei; Sugishima, Masaki; Tanabe, Kousuke; Mitsuda, Akihiro; Wada, Hirofumi; Ohoyama, Kenji; Matsukawa, Takeshi; Yoshida, Yukihiko; Hoshikawa, Akinori; Ishigaki, Toru; Iwasa, Kazuaki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 87 (11):10.7566/JPSJ.87.114705 NOV 15 2018
Abstract:
The magnetic structure of YbPd was determined for a newly synthesized strain-free sample by neutron diffraction techniques. The sinusoidal magnetic structure characterized by an incommensurate wave vector k = (0.080 0 0.32) is observed in the magnetic-ordered phase between T-3 = 1.9K and T-4 = 0.5 K, which is composed of the magnetic-moment amplitude of 0.3 mu(B) parallel to the alpha-axis in the tetragonal crystal-structure phase. The modulated magnetic structure is consistent with the previously proposed Yb-ion valence ordered structure appearing below T-2 = 105 K, which consists of the periodic arrangement of magnetic and nonmagnetic Yb ions.
Title:
Unravelling Incommensurate Magnetism and Its Emergence in Iron-Based Superconductors
Authors:
Christensen, MH; Andersen, BM; Kotetes, P Author Full Names: Christensen, Morten H.; Andersen, Brian M.; Kotetes, Panagiotis
Source:
PHYSICAL REVIEW X, 8 (4):10.1103/PhysRevX.8.041022 NOV 9 2018
Abstract:
We focus on a broad class of tetragonal itinerant systems sharing a tendency towards the spontaneous formtion of incommensurate magnetism with ordering wave vectors Q(1,)(2) = (pi - delta, 0)/(0, pi - delta) or Q(1,2) = (pi, delta) 1 (-delta, pi). Employing a Landau approach, we obtain the generic magnetic phase diagram and identify the leading instabilities near the paramagnetic-magnetic transition. Nine distinct magnetic phases exist that either preserve or violate the assumed C-4 symmetry of the paramagnetic phase. These are single-and double-Q phases consisting of magnetic stripes, helices, and whirls, either in an individual or coexisting manner. These nine phases can be experimentally distinguished by polarized neutron scattering, or, e.g., by combining measurements of the induced charge order and magnetoelectric coupling. Within two representative five-orbital models, suitable for BaFe2As2 and LaFeAsO, we find that the incommensurate magnetic phases we discuss here are accessible in iron-based superconductors. Our investigation unveils a set of potential candidates for the unidentified C-2-symmetric magnetic phase that was recently observed in Ba1-xNaxFe2As2. Among the phases stabilized we find a spin-whirl crystal, which is a textured magnetic C-4-symmetric phase. The possible experimental observation of textured magnetic orders in iron-based superconductors opens new directions for realizing intrinsic topological superconductors.
Title:
Angle-dependent magnetization dynamics with mirror-symmetric excitations in artificial quasicrystalline nanomagnet lattices
Authors:
Bhat, VS; Grundler, D Author Full Names: Bhat, V. S.; Grundler, D.
Source:
PHYSICAL REVIEW B, 98 (17):10.1103/PhysRevB.98.174408 NOV 6 2018
Abstract:
We report angle-dependent spin-wave spectroscopy on aperiodic quasicrystalline magnetic lattices, i.e., Ammann, Penrose P2 and P3 lattices made of large arrays of interconnected Ni80Fe20 nanobars. Spin-wave spectra obtained in the nearly saturated state contain distinct sets of resonances with characteristic angular dependencies for applied in-plane magnetic fields. Micromagnetic simulations allow us to attribute detected resonances to mode profiles with specific mirror symmetries. Spectra in the reversal regime show systematic emergence and disappearance of spin-wave modes indicating reprogrammable magnonic characteristics.
Title:
Angle-dependent magnetoresistance as a sensitive probe of the charge density wave in quasi-one-dimensional semimetal Ta2NiSe7
Authors:
He, JM; Wen, LB; Wu, YS; Liu, JY; Tang, GX; Yang, YS; Xing, H; Mao, ZQ; Sun, H; Liu, Y Author Full Names: He, Jiaming; Wen, Libin; Wu, Yueshen; Liu, Jinyu; Tang, Guoxiong; Yang, Yusen; Xing, Hui; Mao, Zhiqiang; Sun, Hong; Liu, Ying
Source:
APPLIED PHYSICS LETTERS, 113 (19):10.1063/1.5058182 NOV 5 2018
Abstract:
The behavior of charge density waves (CDWs) in an external magnetic field is dictated by both orbital and Pauli (Zeeman) effects. A quasi-one-dimensional (Q1D) system features Q1D Fermi surfaces that allow these effects to be distinguished, which in turn can provide a sensitive probe to the underlying electronic states. Here, we studied the field dependence of an incommensurate CDW in a transition-metal chalcogenide Ta2NiSe7 with a Q1D chain structure. The angle-dependent magnetoresistance (MR) is found to be very sensitive to the relative orientation between the magnetic field and the chain direction. With an applied current fixed along the b axis (the chain direction), the angle-dependent MR shows a striking change of the symmetry below T-CDW only for a rotating magnetic field in the ac plane. In contrast, the symmetry axis remains unchanged for other configurations (H in ab and be planes). The orbital effect conforms to the lattice symmetry, while the Pauli effect in the form of mu B-B/(h) over barv(F) can be responsible for such symmetry change, provided that the Fermi velocity v(F) is significantly anisotropic and the nesting vector changes in a magnetic field, which is corroborated by our first-principles calculations. Our results show that the angle-dependent MR is a sensitive transport probe of CDW and can be useful for the study of lowdimensional systems in general. Published by AIP Publishing.
Title:
Previously unknown quasicrystal periodic approximant found in space
Authors:
Bindi, L; Pham, J; Steinhardt, PJ Author Full Names: Bindi, Luca; Pham, Joyce; Steinhardt, Paul J.
Source:
SCIENTIFIC REPORTS, 8 10.1038/s41598-018-34375-x NOV 2 2018
Abstract:
We report the discovery of Al34Ni9Fe2, the first natural known periodic crystalline approximant to decagonite (Al71Ni24Fe5), a natural quasicrystal composed of a periodic stack of planes with quasiperiodic atomic order and ten-fold symmetry. The new mineral has been approved by the International Mineralogical Association (IMA 2018-038) and officially named proxidecagonite, which derives from its identity to periodic approximant of decagonite. Both decagonite and proxidecagonite were found in fragments from the Khatyrka meteorite. Proxidecagonite is the first natural quasicrystal approximant to be found in the Al-Ni-Fe system. Within this system, the decagonal quasicrystal phase has been reported to transform at similar to 940 degrees C to Al-13(Fe,Ni)(4), Al-3(Fe,Ni)(2) and the liquid phase, and between 800 and 850 degrees C to Al-13(Fe,Ni)(4),Al-3(Fe,Ni) and Al-3(Fe,Ni)(2). The fact that proxidecagonite has not been observed in the laboratory before and formed in a meteorite exposed to high pressures and temperatures during impact-induced shocks suggests that it might be a thermodynamically stable compound at high pressure. The most prominent structural motifs are pseudo-pentagonal symmetry subunits, such as pentagonal bipyramids, that share edges and corners with trigonal bipyramids and which maximize shortest Ni-Al over Ni-Ni contacts.

Update: 14-Nov-2018

Title:
A tenfold twin of the CrB structure type
Authors:
Hornfeck, W Author Full Names: Hornfeck, Wolfgang
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 659-672; 10.1107/S2053273318011828 6 NOV 2018
Abstract:
NiZr crystallized from an amorphous matrix or solidified from an undercooled melt exhibits a tenfold twinned microstructure, which is explained by an ideal twin model utilizing special geometric properties of the CrB structure type. The model is unique in several ways: (i) it contains no adjustable parameters other than a scaling factor accounting for the smallest interatomic distance; (ii) it features an irrational shift in the translational part of the twin operation; and (iii) it has many traits commonly observed for quasicrystals, connected to the occurrence of decagonal long-range orientational order, making NiZr the first experimental example of the recently introduced concept of Z-module twinning. It is shown how these remarkable properties of the tenfold twin's structure model are related to one another and founded in number theory as well as in the mathematical theory of aperiodic order.
Title:
Thermal evolution of quasi-one-dimensional spin correlations within the anisotropic triangular lattice of alpha-NaMnO2
Authors:
Dally, RL; Chisnell, R; Harriger, L; Liu, YH; Lynn, JW; Wilson, SD Author Full Names: Dally, Rebecca L.; Chisnell, Robin; Harriger, Leland; Liu, Yaohua; Lynn, Jeffrey W.; Wilson, Stephen D.
Source:
PHYSICAL REVIEW B, 98 (14):10.1103/PhysRevB.98.144444 OCT 31 2018
Abstract:
Magnetic order on the spatially anisotropic triangular lattice of alpha-NaMnO2 is studied via neutron diffraction measurements. The transition into a commensurate, collinear antiferromagnetic ground state with k = (0.5, 0.5, 0) was found to occur below T-N = 22 K. Above this temperature, the transition is preceded by the formation of a coexisting, short-range ordered, incommensurate state below T-IC = 45 K whose two-dimensional propagation vector evolves toward k = (0.5, 0.5) as the temperature approaches T-N. At high temperatures (T > T-IC), quasielastic scattering reveals one-dimensional spin correlations along the nearest-neighbor Mn-Mn "chain direction" of the MnO6 planes. Our data are consistent with the predictions of a mean-field model of Ising-like spins on an anisotropic triangular lattice, as well as the predominantly one-dimensional Heisenberg spin Hamiltonian reported for this material.
Title:
Quasicrystal Tilings in Three Dimensions and Their Empires
Authors:
Hammock, D; Fang, F; Irwin, K Author Full Names: Hammock, Dugan; Fang, Fang; Irwin, Klee
Source:
CRYSTALS, 8 (10):10.3390/cryst8100370 OCT 2018
Abstract:
The projection method for constructing quasiperiodic tilings from a higher dimensional lattice provides a useful context for computing a quasicrystal's vertex configurations, frequencies, and empires (forced tiles). We review the projection method within the framework of the dual relationship between the Delaunay and Voronoi cell complexes of the lattice being projected. We describe a new method for calculating empires (forced tiles) which also borrows from the dualisation formalism and which generalizes to tilings generated projections of non-cubic lattices. These techniques were used to compute the vertex configurations, frequencies and empires of icosahedral quasicrystals obtained as a projections of the D-6 and Z(6) lattices to R-3 and we present our analyses. We discuss the implications of this new generalization.

Update: 8-Nov-2018

Title:
Effect of Ca Concentration on Microstructure and Mechanical Properties of As-Cast and As-Extruded Quasicrystal-Strengthened Mg-7.2Zn-2.4Gd Alloy
Authors:
Sun, JC; Ma, YL; Miao, HW; Li, KJ; Li, CH; Huang, H Author Full Names: Sun, Jianchun; Ma, Yilong; Miao, Hongwei; Li, Kejian; Li, Chunhong; Huang, Hua
Source:
ADVANCES IN MATERIALS SCIENCE AND ENGINEERING, 10.1155/2018/9138753 2018
Abstract:
Quasicrystal-strengthened Mg-Zn-RE (RE = rare-earth element) alloys have been investigated extensively due to their excellent mechanical properties. Here, we prepare quasicrystal-strengthened Mg-7.2Zn-2.4Gd (wt.%) alloy with different concentrations of Ca addition (0, 0.16, 0.32, and 0.64 wt.%) by traditional gravity casting, followed by extrusion at 573 K with the extrusion ratio of 9:1. lhe microstructure and room temperature tensile properties of as-cast and as-extruded alloys are characterized. With the addition of the trace amount of Ca, the I-phase tends to transfer into W-phase due to the appearance of Mg2Ca and Mg6Zn3Ca2. As a consequence, the mechanical properties of the as-cast Ca containing alloys are downgraded. After extrusion, in comparison to the as-cast alloys, microstructure of the four types of alloys is refined and mechanical property is enhanced greatly. With the increasing of Ca concentration, the grain size is decreased gradually. However, the yield strength of the alloys is decreased to about 230 MPa and then up to 269 MPa, while the elongation increases first from 12.9% to 13.6% yet then decreases to 9.9%.

Update: 1-Nov-2018

Title:
Identification of the incommensurate structure transition in biphenyl by Raman scattering
Authors:
Zhang, K; Chen, XJ Author Full Names: Zhang, Kai; Chen, Xiao-Jia
Source:
SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 206 202-206; 10.1016/j.saa.2018.07.104 JAN 5 2019
Abstract:
Raman scattering measurements are performed on crystalline biphenyl at low temperatures. The properties of the vibrational modes focused on the intra- and intermolecular terms are analyzed in detail. Nearly all of the vibration modes exhibit hardening and simultaneously sharpen with decreasing temperature, whereas the modes at around 250 cm(-1) and 1280 cm(-1) soften their energies as temperature is decreased. Moreover, all the internal modes have anomalous reversals at around 45 K on the frequencies, widths, and intensities, and below 45 K, several new internal modes appear. Results of the analyses indicate that the reemergence of the interring tilt angle of the molecules at 45 K has a significant impact on the vibrational properties of biphenyl. Our work thus paves interesting and essential groundwork for the further study of biphenyl. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Magnetic phase coexistence in DyNiAl4
Authors:
White, R; Hutchison, WD; Avdeev, M Author Full Names: White, R.; Hutchison, W. D.; Avdeev, M.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 469 30-34; 10.1016/j.jmmm.2018.08.011 JAN 1 2019
Abstract:
The magnetic structure and properties of the rare earth intermetallic DyNiAl4 have been determined. Two magnetic phase transitions have been observed at T-N = 20.2(1) K and T-N, = 14.6(1) K. Analysis via neutron diffraction has revealed that these correspond to the formation of two distinct magnetic phases, a low temperature collinear antiferromagnetic phase with k(C) = (0, 1, 0) and a higher temperature incommensurate phase with k(I) = ( 0.1745(6), 1, 0.0313(6)). The incommensurate phase consists of a sinusoidal modulation of the magnetic moment along the a- and c-axis directions. In addition, both of these phases have been found to coexist between 14.5 K and 16.1 K.
Title:
A New Class of Ordered Structure Between Crystals and Quasicrystals
Authors:
Qin, GW; Xie, HB; Pan, HC; Ren, YP Author Full Names: Qin Gaowu; Xie Hongbo; Pan Hucheng; Ren Yuping
Source:
ACTA METALLURGICA SINICA, 54 (11):1490-1502; SI 10.11900/0412.1961.2018.00357 NOV 11 2018
Abstract:
This paper briefly reviews the development and research history of strutures of the solid matters, and highlight two new strcutures of precipitates in Mg alloys found by our group recently. (1) The isothermally aged (Mg, In)(2)Ca "Laves phase" contains two separate unit cells promoting the formation of five tiling patterns. The bonding of these patterns leads to the generation of the present phase but without any six-fold rotational symmetry in a long-range on the (0001)(L) basal plane, constrainted by the Penrose geometrical rule, completely different from the known Laves phases. (2) The MgZn five-fold nanodomain structure is self-assembled by two separate unit cells (72 degrees rhombus structure: MgZn2, and 72 degrees equilateral hexagon structure: MgZn) under the Penrose geomotrical constraints, containing 2D five-fold symmetry locally and short-range ordered C14 and C15 Laves structures. These two special structures without any translational symmetry on the normal plane while periodical arrangement along the normal direction, are a new class of intermediate structures between crystals and quasicrystals. And thus, they does not belong to any crystals or 2D ordered structures in quasicrystals or quasicrystal approximants.
Title:
Landau levels in quasicrystals
Authors:
Fuchs, JN; Mosseri, R; Vidal, J Author Full Names: Fuchs, Jean-Noel; Mosseri, Remy; Vidal, Julien
Source:
PHYSICAL REVIEW B, 98 (16):10.1103/PhysRevB.98.165427 OCT 19 2018
Abstract:
Two-dimensional tight-binding models for quasicrystals made of plaquettes with commensurate areas are considered. Their energy spectrum is computed as a function of an applied perpendicular magnetic field. Landau levels are found to emerge near band edges in the zero-field limit. Their existence is related to an effective zero-field dispersion relation valid in the continuum limit. For quasicrystals studied here, an underlying periodic crystal exists and provides a natural interpretation to this dispersion relation. In addition to the slope (effective mass) of Landau levels, we also study their width as a function of the magnetic flux and identify two fundamental broadening mechanisms: (i) tunneling between closed cyclotron orbits and (ii) individual energy displacement of states within a Landau level. Interestingly, the typical broadening of the Landau levels is found to behave algebraically with the magnetic field with a nonuniversal exponent.
Title:
Influence of the magnetic field on the stability of the multiferroic conical spin arrangement of Mn0.80Co0.20WO4
Authors:
Urcelay-Olabarria, I; Ressouche, E; Ivanov, VY; Skumryev, V; Wang, Z; Skourski, Y; Balbashov, AM; Popov, YF; Vorob'ev, GP; Qureshi, N; Garcia-Munoz, JL; Mukhin, AA Author Full Names: Urcelay-Olabarria, I.; Ressouche, E.; Ivanov, V. Y.; Skumryev, V.; Wang, Z.; Skourski, Y.; Balbashov, A. M.; Popov, Yu. F.; Vorob'ev, G. P.; Qureshi, N.; Garcia-Munoz, J. L.; Mukhin, A. A.
Source:
PHYSICAL REVIEW B, 98 (13):10.1103/PhysRevB.98.134430 OCT 17 2018
Abstract:
The evolution of the low temperature antiferromagnetic conical (characterized by two, commensurate and incommensurate propagation vectors), and the high temperature collinear spin arrangements of the 20% Co-doped MnWO4 multiferroic has been studied in the presence of magnetic field up to 60 T by means of macroscopic magnetic and pyroelectric measurements, and by neutron diffraction experiments in fields up to 12 T on a single crystal. The complete magnetoelectric phase diagrams for magnetic fields along distinct magnetic directions with respect to the spin structure have been constructed up to magnetic field values exceeding those necessary to induce a spin-flip transition into the paramagnetic state. The differences in the topology of the diagrams are discussed. The obtained results might be common for other magnetic materials possessing conical antiferromagnetic structures.
Title:
Grain extraction and microstructural analysis method for two-dimensional poly and quasicrystalline solids
Authors:
Hirvonen, P; La Boissoniere, GM; Fan, ZY; Achim, CV; Provatas, N; Elder, KR; Ala-Nissila, T Author Full Names: Hirvonen, Petri; La Boissoniere, Gabriel Martine; Fan, Zheyong; Vasile Achim, Cristian; Provatas, Nikolas; Elder, Ken R.; Ala-Nissila, Tapio
Source:
PHYSICAL REVIEW MATERIALS, 2 (10):10.1103/PhysRevMaterials.2.103603 OCT 16 2018
Abstract:
While the microscopic structure of defected solid crystalline materials has significant impact on their physical properties, efficient and accurate determination of a given polycrystalline microstructure remains a challenge. In this paper, we present a highly generalizable and reliable variational method to achieve this goal for two-dimensional crystalline and quasicrystalline materials. The method is benchmarked and optimized successfully using a variety of large-scale systems of defected solids, including periodic structures and quasicrystalline symmetries to quantify their microstructural characteristics, e.g., grain size and lattice misorientation distributions. We find that many microstructural properties show universal features independent of the underlying symmetries.
Title:
Structure and hydrogen absorption properties of Ti53Zr27Ni20(Pd,V) quasicrystals
Authors:
Lee, SH; Kim, J Author Full Names: Lee, Sang-hwa; Kim, Jaeyong
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 43 (41):19130-19140; 10.1016/j.ijhydene.2018.08.141 OCT 11 2018
Abstract:
The structure and hydrogen absorption properties of Pd and V doped TiZrNi quasicrystals were investigated in terms of the equilibrium vapor pressure of hydrogen, and the results were compared with those of undoped samples. Rapidly quenched Ti53Zr27Ni2o alloys formed quasicrystals and absorbed hydrogen H/M (hydrogen to host metal atom ratio) value of 1.79 at room temperature. This was attributed to their structure, which contains mostly tetrahedral interstitial sites that are chemically formed by atoms having a high affinity with hydrogen. However, the relatively low equilibrium vapor pressure of hydrogen, 0.14 Torr at 300 degrees C, prevents TiZrNi quasicrystals for the practical application on energy storage materials. To overcome this limitation, we replaced Ti with Pd and V to increase the vapor pressure of hydrogen and investigated the properties of hydrogen absorption behaviors. Results of XRD measurements revealed that the quasicrystal structure was maintained by the replacement of Ti with a maximum of 8 at. % of Pd and V. Total amounts of the absorbed hydrogen decreased from 1.33 to 1.06 and to 1.12 of the H/M values when the Ti was replaced by 8 at. % of Pd and V, respectively, at 300 degrees C. The pressure-composition-temperature data measured using an automatic gas-handling system revealed that the equilibrium vapor pressure increased from 0.14 to 0.21 and to 0.56 Torr at H/M value of 0.5 when Ti atoms were replaced by 8 at. % Pd, and V, respectively, without the appearance of an impurity phase. Our results demonstrate that the replacement of Ti with Pd and V is an effective method to increase the equilibrium vapor pressure of hydrogen without a phase transformation in a TiZrNi quasicrystal system. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Update: 24-Oct-2018

Title:
Coupling between Ho and Mn/Cr moments and its influence on the structural and magnetic properties of HoMn1-xCrxO3 (0 < x <= 1) compounds
Authors:
Prakash, P; Singh, R; Mishra, SK; Prajapat, CL; Kumar, A; Das, A Author Full Names: Prakash, Pulkit; Singh, Ripandeep; Mishra, S. K.; Prajapat, C. L.; Kumar, A.; Das, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 465 70-80; 10.1016/j.jmmm.2018.05.080 NOV 1 2018
Abstract:
The effect of doping non Jahn-Teller (JT) Cr3+ ion on the crystallographic structure and magnetic ordering has been studied in a series of polycrystalline compounds HoMn1-xCrxO3 (0 < x <= 1). These compounds crystallize in a mixture of hexagonal and orthorhombic phases for x < 0.125 whereas the orthorhombic phase is present for all higher concentrations. It is observed that Cr doping leads to decrease in the mismatch of the bond length in Mn-O-6 octahedra indicating reduction in the static orbital ordering due to JT effect. In addition, doping with Cr3+ introduces ferromagnetic Mn3+-O-Cr3+ interactions in an antiferromagnetic matrix consisting of Mn3+-OMn3+ and Cr3+-O-Cr3+ interactions. A change in the magnetic structure from Gamma(4) (A(x)F(y)G(z)) to Gamma(2) (C(x)G(y)F(z)) is observed in samples with x > 0.75, which is attributed to the anisotropic interactions between the Ho3+ and Cr3+ spins. An incommensurate magnetic order corresponding to the wave vector (0.4, 0, 0) is observed in the orthorhombic phase associated with the x = 0.05 sample. The hexagonal phase in the Mn-rich end exhibits a reduced magnetic ordering temperature of 55 K and a spin reorientation at 15 K, in comparison to h-HoMnO3. The temperature variation of dielectric data shows weak magnetodielectric coupling in these compounds.
Title:
Old and New Insights into Structure and Properties of Eu-2[SiO4]
Authors:
Funk, C; Koher, J; Lazar, I; Kajewski, D; Roleder, K; Nuss, J; Bussmann-Holder, A; Bamberger, H; van Slageren, J; Enseling, D; Justel, T; Schleid, T Author Full Names: Funk, Christian; Koeher, Juergen; Lazar, Iwona; Kajewski, Dariusz; Roleder, Krystian; Nuss, Juergen; Bussmann-Holder, Annette; Bamberger, Heiko; van Slageren, Joris; Enseling, David; Juestel, Thomas; Schleid, Thomas
Source:
CRYSTAL GROWTH & DESIGN, 18 (10):6316-6325; 10.1021/acs.cgd.8b01265 OCT 2018
Abstract:
Lemon-yellow single crystals of Eu-2[SiO4] were obtained by reaction of elemental europium with Eu2O3 in the presence of SiO2 carried out in evacuated silica ampules at 1373 K for 48 h followed by constant cooling to room temperature with 120 K per hour. Eu-2[SiO4] crystallizes at room temperature in the larnite-type structure of beta-Ca-2[SiO4] (monoclinic, P2(1)/n) with parameters a = 565.02(5), b = 709.15(6), c = 975.84(8) pm, beta = 92.614(3)degrees for Z = 4. At 452 K it undergoes a reversible phase transition to an incommensurate structure similar to the isotypic compounds Sr-2[SiO4] and K-2[SeO4]. The phase transition energy was determined to 0.54(2) J.g(-1) by DSC measurements and temperature dependent birefringence measurements show that the phase transition exhibits a significant hysteresis. Refinements of the structure of Eu-2[SiO4] based on single crystal X-ray diffraction data show that the high temperature modification crystallizes in the orthorhombic space group Pnma(alpha 00)0ss with a = 710.16(6), b = 566.93(5), c = 977.13(8) pm, and an incommensurate modulation along [100] with a modulation vector t = [0.293(4), 0, 0]. Eu-2[SiO4] exhibits a bright yellow photoluminescence and its permittivity increases substantially above 300 K. Magnetic susceptibility and EPR measurements show that Eu-2[SiO4] becomes ferromagnetic below 7 K with a g factor of 1.993.
Title:
Development of Mg-Zn-Y-Ca alloys containing icosahedral quasicrystal phase through trace addition of Y
Authors:
Nie, KB; Kang, XK; Deng, KK; Guo, YC; Han, JG; Zhu, ZH Author Full Names: Nie, Kaibo; Kang, Xinkai; Deng, Kunkun; Guo, Yachao; Han, Jungang; Zhu, Zhihao
Source:
JOURNAL OF MATERIALS RESEARCH, 33 (18):2806-2816; 10.1557/jmr.2018.267 SEP 28 2018
Abstract:
In this work, three Mg-Zn-Y-Ca alloys reinforced by icosahedral quasicrystal phase through trace Y addition were extruded at a low temperature of 503 K. With increasing the contents of Zn and Y, the grain size of the as-extruded alloy was significantly reduced while both the size and volume fraction of nanosized precipitates were increased. The grain refinement in the Mg-Zn-Y-Ca alloy was related to dynamical recrystallization during extrusion and the pinning effect of nanosized precipitates on the grain boundaries. After extrusion, the yield strength (YS) and ultimate tensile strength (UTS) of the three alloys were significantly increased. The YS of 294.0 MPa, UTS of 337.5 MPa, and elongation of 10.6% were obtained in the case of Mg-2.09Zn-0.26Y-0.12Ca (at.%) alloys. The improvement in the mechanical properties could mainly be due to the grain boundary strengthening and Orowan strengthening. The as-cast alloy exhibited a typical cleavage fracture while the as-extruded alloy possessed a mixture fracture of dimple fracture and cracking along the twinning.
Title:
Correlation between the atomic configurations and the amorphous-to-icosahedral phase transition in metallic glasses
Authors:
Geng, GH; Yan, ZJ; Hu, Y; Wang, Z; Ketov, SV; Eckert, J Author Full Names: Geng, Guihong; Yan, Zhijie; Hu, Yong; Wang, Zhi; Ketov, Sergey V.; Eckert, Juergen
Source:
JOURNAL OF MATERIALS RESEARCH, 33 (18):2775-2783; 10.1557/jmr.2018.187 SEP 28 2018
Abstract:
Positron annihilation spectroscopy and differential scanning calorimetry were used to evaluate the changes of the atomic configurations in Zr-based metallic glasses (MGs) due to alloying and plastic deformation. The correlation between the atomic configurations of MGs and the amorphous-to-icosahedral phase transition due to heating was investigated. The results indicate that the free volume frozen in the as-cast Zr60Al15Ni25, Zr65Al7.5Ni10Cu17.5, and Zr65Al7.5Ni10Cu17.5Ag5 MGs substantially decreases in sequence. More excess free volume is introduced in Zr65Al7.5Ni10Cu17.5Ag5 MG due to cold rolling and milling. The annihilation of free volume due to alloying considerably stabilizes the icosahedral structure of MGs, which enhances the nucleation and growth of quasicrystals upon heating. However, the nucleation and growth of quasicrystals are considerably suppressed in Zr65Al7.5Ni10Cu17.5Ag5 MG due to cold rolling and milling, during which the more introduced excess free volume results in substantial destruction of short-range order with 5-fold symmetry. The present work further provides direct evidence for the prevalence of icosahedral short-range order in MGs.

Update: 17-Oct-2018

Title:
Correlation between crystallographic and microstructural features and low hysteresis behavior in Ni50.0Mn35.25In14.75 melt-spun ribbons
Authors:
Yan, HL; Sanchez-Valdes, CF; Zhang, YD; Llamazares, JLS; Li, ZB; Yang, B; Esling, C; Zhao, X; Zuo, L Author Full Names: Yan, Haile; Sanchez-Valdes, C. F.; Zhang, Yudong; Sanchez Llamazares, J. L.; Li, Zongbin; Yang, Bo; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 767 544-551; 10.1016/j.jallcom.2018.07.063 OCT 30 2018
Abstract:
In this work, crystallographic, microstructural and magnetocaloric investigations were performed on textured Ni50Mn35.25In14.75 melt-spun ribbons with low thermal (6 K) and magnetic-field induced hysteresis (-0.731 kg(-1) at 2 T) and moderate maximum magnetic entropy change Delta S-M(max)(11 J kg(-1) K-1 at 5 T) at room temperature (302 K). The austenite in the ribbons crystallizes into a L2(1) structure, whereas martensite has a monoclinic incommensurate 6 M modulated structure as determined with the super space theory. By means of electron backscatter diffraction technique, the morphological and crystallographic features of microstructure were systematically characterized. Ribbons possess a fine microstructure with an average grain size (initial austenite phase) of around 10 mu m, whereas the 6 M martensite has a self-accommodated microstructure with 4 kinds of twin-related martensite variants. During inverse martensitic transformation, the austenite prefers to nucleate at the grain boundaries of initial austenite. By means of cofactor conditions and crystallographic orientation analyses, the good geometrical compatibility between austenite and martensite was confirmed. Based on the crystal structure and microstructure information obtained, the reason of the low thermal hysteresis was discussed. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Exceptionally large areas of local tenfold symmetry in decagonal Al59Cr21Fe10Si10
Authors:
Ma, HK; He, ZB; Hou, LG; Steurer, W Author Full Names: Ma, Haikun; He, Zhanbing; Hou, Longgang; Steurer, Walter
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 765 753-756; 10.1016/j.jallcom.2018.05.084 OCT 15 2018
Abstract:
The decagonal diffraction symmetry of a decagonal quasicrystal (DQC) results from its particular auto-correlation (Patterson) function. Structural subunits ('clusters') with decagonal symmetry may exist but do not need to exist. By atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), we observed the so far largest tenfold symmetric structural subunits in decagonal Al59Cr21Fe10Si10 scaling up to 5.2 nm. This amazing result provides direct experimental evidence how the local tenfold symmetry of DQCs is expanded to a larger size. (C) 2018 Published by Elsevier B.V.
Title:
Formation and microstructure of quasicrystals in suction cast Al-6wt.% Mn alloys with additions of nickel and iron elements
Authors:
Chen, Z; Xie, B; Fan, Q Author Full Names: Chen, Z.; Xie, B.; Fan, Q.
Source:
MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, 49 (10):1236-1244; 10.1002/mawe.201700128 OCT 2018
Abstract:
The formation and microstructure of quasicrystals in suction cast Al-6wt.% Mn-2wt.% TM (TM=Ni, Fe) alloys were investigated by transmission electron microscopy, scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The suction cast Al-6wt.% Mn-2wt.% Ni alloy consists of a single decagonal phase of Al56Mn11Ni2, whereas the Al-6wt.% Mn alloy with 2wt.% iron addition comprises a primitive icosahedral phase and a decagonal phase of Al40Mn7Fe2. Thus, the addition of nickel or iron favors quasicrystal formation in the suction cast Al-6wt.% Mn alloys. Based on a 4:1 matching ratio of aluminum atoms to heavier atoms, the approximate electron to atom ratio is 1.85 in two decagonal phases of Al56Mn11Ni2 and Al40Mn7Fe2. Various morphologies of quasicrystals with a size of more than 5m were observed in the microstructure of suction cast Al-6wt.% Mn-2wt.% TM (TM=Ni, Fe) alloys. The decagonal Al40Mn7Fe2 phase nucleates epitaxially and grows on the icosahedral phase.
Title:
Nonuniformly Loaded Stack of Antiplane Shear Cracks in One-Dimensional Piezoelectric Quasicrystals
Authors:
Tupholme, GE Author Full Names: Tupholme, G. E.
Source:
ADVANCES IN MATERIALS SCIENCE AND ENGINEERING, 10.1155/2018/4847837 2018
Abstract:
Representations in a closed form are derived, using an extension to the method of dislocation layers, for the phonon and phason stress and electric displacement components in the deformation of one-dimensional piezoelectric quasicrystals by a nonuniformly loaded stack of parallel antiplane shear cracks. Their dependence upon the polar angle in the region close to the tip of a crack is deduced, and the field intensity factors then follow. These exhibit that the phenomenon of crack shielding is dependent upon the relative spacing of the cracks. The analogous analyses, that have not been given previously, involving non-piezoelectric or non-quasicrystalline or simply elastic materials can be straightforwardly considered as special cases. Even when the loading is uniform and the crack is embedded in a purely elastic isotropic solid, no explicit representations have been available before for the components of the field at points other than directly ahead of a crack. Typical numerical results are graphically displayed.

Update: 3-Oct-2018

Title:
Magnetic structures of the rare-earth quadruple perovskite manganites RMn7O12
Authors:
Johnson, RD; Khalyavin, DD; Manuel, P; Zhang, L; Yamaura, K; Belik, AA Author Full Names: Johnson, R. D.; Khalyavin, D. D.; Manuel, P.; Zhang, L.; Yamaura, K.; Belik, A. A.
Source:
PHYSICAL REVIEW B, 98 (10):10.1103/PhysRevB.98.104423 SEP 19 2018
Abstract:
We report a neutron powder diffraction study of RMn7O12 quadruple perovskite manganites with R = La, Ce, Nd, Sm, and Eu. We show that in all measured compounds concomitant magnetic ordering of the A and B manganese sublattices occurs on cooling below the Neel temperature. The respective magnetic structures are collinear, with one uncompensated Mn3+ moment per formula unit as observed in bulk magnetization measurements. We show that both LaMn7O12 and NdMn7O12 undergo a second magnetic phase transition at low temperature, which introduces a canting of the B-site sublattice moments that is commensurate in LaMn7O12 and incommensurate in NdMn7O12. This spin canting is consistent with a magnetic instability originating in the B-site orbital order. Furthermore, NdMn7O12 displays a third magnetic phase transition at which long-range ordering of the Nd sublattice modifies the periodicity of the incommensurate spin canting. Our results demonstrate a rich interplay between transition-metal magnetism, orbital order, and the crystal lattice, which may be fine-tuned by cation substitution and rare-earth magnetism.
Title:
Quantum Spin Hall Effect and Spin Bott Index in a Quasicrystal Lattice
Authors:
Huang, HQ; Liu, F Author Full Names: Huang, Huaqing; Liu, Feng
Source:
PHYSICAL REVIEW LETTERS, 121 (12):10.1103/PhysRevLett.121.126401 SEP 17 2018
Abstract:
Despite the rapid progress in the field of the quantum spin Hall (QSH) effect, most of the QSH systems studied up to now are based on crystalline materials. Here we propose that the QSH effect can be realized in quasicrystal lattices (QLs). We show that the electronic topology of aperiodic and amorphous insulators can be characterized by a spin Bott index B-s. The nontrivial QSH state in a QL is identified by a nonzero spin Bott index B-s = 1, associated with robust edge states and quantized conductance. We also map out a topological phase diagram in which the QSH state lies in between a normal insulator and a weak metal phase due to the unique wave functions of QLs. Our findings not only provide a better understanding of electronic properties of quasicrystals but also extend the search of the QSH phase to aperiodic and amorphous materials that arc experimentally feasible.

Update: 26-Sep-2018

Title:
Unraveling the complex magnetic structure of multiferroic pyroxene NaFeGe2O6: A combined experimental and theoretical study
Authors:
Ding, L; Manuel, P; Khalyavin, DD; Orlandi, F; Tsirlin, AA Author Full Names: Ding, Lei; Manuel, Pascal; Khalyavin, Dmitry D.; Orlandi, Fabio; Tsirlin, Alexander A.
Source:
PHYSICAL REVIEW B, 98 (9):10.1103/PhysRevB.98.094416 SEP 14 2018
Abstract:
Magnetic order and the underlying magnetic model of the multiferroic pyroxene NaFeGe2O6 are systematically investigated by neutron powder diffraction, thermodynamic measurements, density-functional band-structure calculations, and Monte Carlo simulations. Upon cooling, NaFeGe2O6 first reveals one-dimensional spin-spin correlations in the paramagnetic state below about 50 K, uncovered by magnetic diffuse scattering. The sinusoidal spin-density wave with spins along the a direction sets in at 13 K, followed by the cycloidal configuration with spins lying in the (ac) plane below 11.6 K. Microscopically, the strongest magnetic coupling runs along the structural chains, J(1) similar or equal to 12 K, which is likely related to the one-dimensional spin-spin correlations. The interchain couplings J(2) similar or equal to 3.8 K and J(3) similar or equal to 2.1 K are energetically well balanced and compete, thus giving rise to the incommensurate order, in sharp contrast to other transition-metal pyroxenes, in which one type of the interchain couplings prevails. The magnetic model of NaFeGe2O6 is further completed by the weak single-ion anisotropy along the a direction. Our results resolve the earlier controversies regarding the magnetic order in NaFeGe2O6 and establish relevant symmetries of the magnetic structures. These results, combined with symmetry analysis, enable us to identify the possible mechanisms of the magnetoelectric coupling in this compound. We also elucidate microscopic conditions for the formation of incommensurate magnetic order in pyroxenes.
Title:
Phase Formation of Mg-Zn-Gd Alloys on the Mg-rich Corner
Authors:
Luo, L; Liu, Y; Duan, M Author Full Names: Luo, Lan; Liu, Yong; Duan, Meng
Source:
MATERIALS, 11 (8):10.3390/ma11081351 AUG 2018
Abstract:
The phase constitutions of as-cast magnesium (Mg)-Zn-Gd alloys (Zn/Gd = 0.25 similar to 60, Zn 0 similar to 10 at.%, Gd 0 similar to 2 at.%, 48 samples) were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Mg-Zn-Gd phase diagram focused on the Mg-rich corner (with up to 20 at.% Zn, 10 at.% Gd) has been set up. Five regions can be classified as follows: (I) alpha-Mg+W-phase+(binary compounds), (II) alpha-Mg+W-phase+I-phase(+binary compounds), (III) alpha-Mg+I-phase(+binary compounds), (IV) alpha-Mg+binary compounds, and (V) alpha-Mg. The phase diagram has been verified by solidification behaviors observation using differential thermal analysis (DTA). Moreover, the structures of I-phase and W-phase in the alloy were explored in details. In terms of the Hume-Rothery rules, I-phase is confirmed as FK-type quasicrystalline with a chemical stoichiometry as Mg30 +/- 1Zn62Gd8 +/- 1 (at.%). The composition and lattice parameter aW-phase (fcc structure, m (3) over barm) are affected by the composition of Mg-Zn-Gd alloys, especially by the Zn/Gd ratio of alloys. This work would be instructive for the design of Mg-Zn-Gd alloys to obtain the phase components, and then selected the strengthening ways, which could adjust its mechanical properties.

Update: 19-Sep-2018

Title:
Microstructure evolution, mechanical properties and diffusion behaviour of Mg-6Zn-2Gd-0.5Zr alloy during homogenization
Authors:
Xiao, L; Yang, GY; Liu, Y; Luo, SF; Jie, WQ Author Full Names: Xiao, Lei; Yang, Guangyu; Liu, Yang; Luo, Shifeng; Jie, Wanqi
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 34 (12):2246-2255; 10.1016/j.jmst.2018.05.003 DEC 2018
Abstract:
The microstructure evolution and mechanical properties of Mg-6Zn-2Gd-0.5Zr alloy during homogenization treatment were investigated. The as-cast alloy was found to be composed of dendritic primary alpha-Mg matrix, alpha-Mg +W (Mg3Zn3Gd2) eutectic along grain boundaries, and icosahedral quasicrystalline I (Mg3Zn6Gd) phase within alpha-Mg matrix. During homogenization process, alpha-Mg +W (Mg3Zn3Gd2) eutectic and I phase gradually dissolved into alpha-Mg matrix, while some rod-like rare earth hydrides (GdH2) formed within alpha-Mg matrix. Both the tensile yield strength and the elongation showed a similar tendency as a function of homogenization temperature and holding time. The optimized homogenization parameter was determined to be 505 degrees C for 16 h according to the microstructure evolution. Furthermore, the diffusion kinetics equation of the solute elements derived from the Gauss model was established to predict the segregation ratio of Gd element as a function of holding time, which was proved to be effective to evaluate the homogenization effect of the experimental alloy. (C) 2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
Title:
Role of nanosize icosahedral quasicrystal of Mg-Al and Mg-Ca alloys in avoiding crystallization of liquid Mg: Ab initio molecular dynamics study
Authors:
Debela, TT; Abbas, HG Author Full Names: Debela, Tekalign T.; Abbas, Hafiz Ghulam
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 499 173-182; 10.1016/j.jnoncrysol.2018.07.010 NOV 1 2018
Abstract:
We have used highly accurate first-principles molecular dynamics simulations to explore the structural (both topological and chemical ordering) evolution during solidification of Mg90Ca10 and MgaoAlio liquids upon cooling. Using various structural analysis methods, we find that local atomic structure of both amorphous alloys are characterized by major distorted and perfect icosahedral symmetry. The fraction of fivefold icosahedra around Mg atoms in Mg-Ca alloy is higher than in Mg-Al alloy. Eutectic Mg90Ca50 alloy shows strong chemical short range order, which further increases upon cooling. In contrast, Mg90Al10 shows weak chemical short range ordering which seems to show weak temperature dependency behavior. The fraction of fivefold icosahedral symmetry, which is responsible for geometrical frustration, and the atomic size are responsible for the dynamic slowdown and causing glassy formation.
Title:
A Brownian quasi-crystal of pre-assembled colloidal Penrose tiles
Authors:
Wang, PY; Mason, TG Author Full Names: Wang, Po-Yuan; Mason, Thomas G.
Source:
NATURE, 561 (7721):94-+; 10.1038/s41586-018-0464-9 SEP 6 2018
Abstract:
Penrose's pentagonal P2 quasi-crystal(1-4) is a beautiful, hierarchically organized multiscale structure in which kite-and dart-shaped tiles are arranged into local motifs, such as pentagonal stars, which are in turn arranged into various close-packed superstructural patterns that become increasingly complex at larger length scales. Although certain types of quasi-periodic structure have been observed in hard and soft matter, such structures are difficult to engineer, especially over large areas, because generating the necessary, highly specific interactions between constituent building blocks is challenging. Previously reported soft-matter quasi-crystals of dendrimers(5), triblock copolymers(6), nanoparticles(7) and polymeric micelles(8) have been limited to 12- or 18-fold symmetries. Because routes for self-assembling complex colloidal building blocks(9-11) into low-defect dynamic superstructures remain limited(12), alternative methods, such as using optical and directed assembly, are being explored(13,14). Holographic laser tweezers(15) and optical standing waves(16) have been used to hold microspheres in local quasi-crystalline arrangements, and magnetic microspheres of two different sizes have been assembled into local five-fold-symmetric quasi-crystalline arrangements in two dimensions(17). But a Penrose quasi-crystal of mobile colloidal tiles has hitherto not been fabricated over large areas. Here we report such a quasi-crystal in two dimensions, created using a highly parallelizable method of lithographic printing and subsequent release of pre-assembled kite- and dart-shaped tiles into a solution-dispersion containing a depletion agent. After release, the positions and orientations of the tiles within the quasi-crystal can fluctuate, and these tiles undergo random, Brownian motion in the monolayer owing to frequent collisions between neighbouring tiles, even after the system reaches equilibrium. Using optical microscopy, we study both the equilibrium fluctuations of the system at high tile densities and also the 'melting' of the pattern as the tile density is lowered. At high tile densities we find signatures of a five-fold pentatic liquid quasi-crystalline phase, analogous to a six-fold hexatic liquid crystal. Our fabrication approach is applicable to tiles of different sizes and shapes, and with different initial positions and orientations, enabling the creation of two-dimensional quasi-crystalline systems (and other systems that possess multiscale complexity at high tile densities) beyond those of current self-or directed-assembly methods(18-20). We anticipate that our approach for generating lithographically pre-assembled monolayers could be extended to create three-dimensional Brownian systems of fluctuating particles with custom-designed shapes through holographic lithography(21,22) or stereolithography(23).

Update: 6-Sep-2018

Title:
Effects of Mg-Zn-Y quasicrystal addition on the microstructures, mechanical performances and corrosion behaviors of as-cast AM60 magnesium alloy
Authors:
Jia, P; Wu, M; Zhang, JY; Hu, X; Teng, XY; Zhao, DG; Wei, T; Dong, DH; Liu, Q; Wang, Y Author Full Names: Jia, Peng; Wu, Ming; Zhang, Jinyang; Hu, Xun; Teng, Xinying; Zhao, Degang; Wei, Tao; Dong, Dehua; Liu, Qing; Wang, Yi
Source:
MATERIALS RESEARCH EXPRESS, 5 (10):10.1088/2053-1591/aada70 OCT 2018
Abstract:
In this work, the as-cast Mg-50Zn-5Y (mass fraction) master alloy containing Mg42Zn50Y8(mole fraction) icosahedral quasicrystal phase (I-phase) was prepared. The influences of addition amount of the Mg-50Zn-5Y master alloy on the microstructure, mechanical performances and corrosion properties of AM60 alloys were studied, aiming to investigate the structure-activity relationship for optimizing the microstructures and properties of AM60 alloys. The results indicated that the continuous reticulation structure could be broken and the precipitated phases could be significantly refined by adding the Mg-50Zn-5Y quasicrystal master alloy. The quasicrystal-reinforced AM60 alloys exhibited better mechanical properties and corrosion resistance than unmodified one. The modified AM60 alloy with 6 wt% of the Mg-50Zn-5Y quasicrystal master alloy had the optimal mechanical performances and corrosion resistance such as a Brinell hardness of 74 HB (increased by 37.0%), an ultimate tensile strength of 205 MPa (increased by 24.3%), a yield strength of 99 MPa (increased by 32.0%) as well as a corrosion rate of 1.35 x 10(-2)mm.year(-1)(decreased by 93.1%). The broken of the continuous reticulation structure and the refinement of the precipitated phases were responsible for the improvement of mechanical performances and corrosion resistance.
Title:
Preparation and electrochemical hydrogen storage properties of MWCNTs-doped Ti49Zr26Ni25 alloy containing quasicrystal phase
Authors:
Liu, H; Zhai, XJ; Li, Z; Tao, X; Liu, WQ; Zhao, JX; Jiang, DY; Gao, S Author Full Names: Liu, Heng; Zhai, Xiaojie; Li, Zhe; Tao, Xing; Liu, Wanqiang; Zhao, Jianxun; Jiang, Dayong; Gao, Shang
Source:
SOLID STATE SCIENCES, 83 17-22; 10.1016/j.solidstatesciences.2018.06.012 SEP 2018
Abstract:
Mechanical alloying technique and subsequent annealing were used to prepare the Ti49Zr26Ni25 quasicrystal. Composite materials of multi-walled carbon nanotubes (MWCNT5) doped Ti49Zr26Ni25 alloys were obtained via ball-milling to improve the hydrogen storage performance of Ti49Zr26Ni25. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were used to analyze the structural properties of the samples. The phase structures of the composite alloys were composed of icosahedral quasicrystal phase and Ti2Ni-type phase. Smaller alloy particles were obtained after doping MWCNT5. Moreover, a three-electrode battery system was carried out to test the electrochemical properties. The composites showed higher discharge capacity, stronger HRD, better cyclic stability and lower charge-transfer resistance than the original Ti49Zr26Ni25 alloy. In the composite electrodes, the optimal discharge capacity of 254.2 mAh/g and the highest capacity retention of 63.1% were achieved for 5 wt% additive content of MWCNTs. The electro-catalytic function of MWCNT5, the reduction of particle size and raise of specific surface area for Ti49Zr26Ni25 alloy may provide larger electrochemically accessible area and rapid channel for hydrogen transportation, which are crucial for improving the electrochemical performance of the alloy.
Title:
A molecular overlayer with the Fibonacci square grid structure
Authors:
Coates, S; Smerdon, JA; McGrath, R; Sharma, HR Author Full Names: Coates, Sam; Smerdon, Joseph A.; McGrath, Ronan; Sharma, Hem Raj
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-018-05950-7 AUG 24 2018
Abstract:
Quasicrystals differ from conventional crystals and amorphous materials in that they possess long-range order without periodicity. They exhibit orders of rotational symmetry which are forbidden in periodic crystals, such as five-, ten-, and twelve-fold, and their structures can be described with complex aperiodic tilings such as Penrose tilings and Stampfli-Gaehler tilings. Previous theoretical work explored the structure and properties of a hypothetical four-fold symmetric quasicrystal-the so-called Fibonacci square grid. Here, we show an experimental realisation of the Fibonacci square grid structure in a molecular overlayer. Scanning tunnelling microscopy reveals that fullerenes (C-60) deposited on the two-fold surface of an icosahedral Al-Pd-Mn quasicrystal selectively adsorb atop Mn atoms, forming a Fibonacci square grid. The site-specific adsorption behaviour offers the potential to generate relatively simple quasicrystalline overlayer structures with tunable physical properties and demonstrates the use of molecules as a surface chemical probe to identify atomic species on similar metallic alloy surfaces.

Update: 29-Aug-2018

Title:
Incommensurate phase of the stuffed tridymite derivative BaSrFe4O8
Authors:
Ishii, Y; Kawaguchi, S; Asai, K; Mori, S Author Full Names: Ishii, Y.; Kawaguchi, S.; Asai, K.; Mori, S.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 265 314-318; 10.1016/j.jssc.2018.06.007 SEP 2018
Abstract:
We demonstrate a new modulation for a high-temperature polymorph of BaSrFe4O8 via synchrotron powder X-ray diffraction and transmission electron microscopy (TEM) experiments. Although the powder X-ray diffraction pattern was successfully analyzed using a structure model of space group Pnna, an unusually large isotropic atomic displacement parameter (U-iso) was observed for the O1 atom. A split atom model that was applied to the O1 site and the adjacent Ba/Sr site, both of which are on the two-fold axis along the c-axis, indicated that positional disorder occurred in these atoms along the c-axis. The electron diffraction pattern and high-resolution TEM observations combined with the structure refinements revealed an incommensurate structure with a modulation vector q = 0.4270(1)a* and a displacement vector perpendicular to the alpha-axis, which gave rise to the large U-iso value of the O1 atom. The modulation observed in this study may be a signature of structural instability, which has commonly been discussed in the stuffed tridymite-type oxides.
Title:
Spontaneous and field-induced magnetic phase transitions in Dy2Co3Al9: Effects of exchange frustration
Authors:
Gorbunov, DI; Henriques, MS; Qureshi, N; Ouladdiaf, B; Mejia, CS; Gronemann, J; Andreev, AV; Petricek, V; Green, EL; Wosnitza, J Author Full Names: Gorbunov, D. I.; Henriques, M. S.; Qureshi, N.; Ouladdiaf, B.; Mejia, C. Salazar; Gronemann, J.; Andreev, A. V.; Petricek, V.; Green, E. L.; Wosnitza, J.
Source:
PHYSICAL REVIEW MATERIALS, 2 (8):10.1103/PhysRevMaterials.2.084406 AUG 15 2018
Abstract:
Due to the long-range oscillatory character of RKKY exchange interactions, for Dy2Co3Al9 there exist positive and negative couplings between the Dy magnetic moments that lead to magnetic frustration. As a result, the ground state can be easily perturbed, and the system displays a number of spontaneous and field-induced phase transitions. We performed magnetization, magnetic-susceptibility, specific-heat, and electrical-resistivity measurements as well as neutron-diffraction experiments on a single crystal. We find two transitions to distinct incommensurate antiferromagnetic phases at 6.2 and 5.2 K that evolve to a commensurate phase at 3.7 K. In applied magnetic field, new phases emerge. Field-dependent magnetization exhibits a multistep metamagnetic process with sharp transitions accompanied by pronounced magnetoresistance changes. The large number of phases and their complex magnetic structures suggest that the physical properties of Dy2Co3Al9 are ruled by exchange frustration in the presence of a large magnetocrystalline anisotropy.
Title:
Effect of Mg-Based Quasicrystals Addition on Microstructure and Mechanical Properties of AM50 Magnesium Alloy
Authors:
Ma, DZ; Wang, F; Wang, Z; Liu, Z; Mao, PL Author Full Names: Ma Dezhi; Wang Feng; Wang Zhi; Liu Zheng; Mao Pingli
Source:
RARE METAL MATERIALS AND ENGINEERING, 47 (7):2166-2171; JUL 2018
Abstract:
The Mg-48Zn-13Y (MZY) quasicrystal master alloy with high volume fraction of the quasicrystalline phase was prepared by a conventional solidification method. The influences of the MZY quasicrystal on microstructures and mechanical properties of AM50 alloys were investigated by OM, SEM, EDS, XRD and tensile tests. The results indicate that with addition of the MZY quasicrystal to AM50 alloy, the Mg3Zn6Y quasicrystal phase can be retained in AM50 matrix alloy, and the microstructures are obviously refined. The beta phase in the microstructures is changed from coarse and continuous net-like to discontinuous strip-like and granular, and the amount is decreased. When the content of the MZY quasicrystal is 6%, the microstructure is greatly refined, and the ultimate tensile strength, yield strength and elongation of the alloy reach to the maximum, 202.92 MPa, 100.57 MPa and 10.8%, respectively, which are improved by 24.59%, 74.9% and 66.15%, respectively, compared with those of AM50 alloy. Mechanical properties of AM50 magnesium alloy can be improved significantly by addition of the MZY quasicrystal, which results from the microstructure refinement, the optimization of the morphology and amount of the beta phase, and the dispersion strengthening effect of the quasicrystal phase having good wettability with the magnesium alloy substrate.

Update: 22-Aug-2018

Title:
Formation of modulated structures induced by oxygen vacancies in alpha-Fe2O3 nanowires
Authors:
Li, T; Feng, HL; Wang, YQ; Wang, C; Zhu, WH; Yuan, L; Zhou, GW Author Full Names: Li, Tao; Feng, Honglei; Wang, Yiqian; Wang, Chao; Zhu, Wenhui; Yuan, Lu; Zhou, Guangwen
Source:
JOURNAL OF CRYSTAL GROWTH, 498 10-16; 10.1016/j.jcrysgro.2018.05.031 SEP 15 2018
Abstract:
Two modulated structures caused by long-range ordering of oxygen vacancies have been observed in alpha-Fe2O3 nanowires (NWs) produced after oxidation of Fe, one being ten times (30 (3) over bar0) interplanar spacing and the other being six times (11 (2) over bar0) interplanar spacing. Both types of oxygen vacancy ordering structures have a similar modulation periodicity of 1.45 or 1.50 nm with corresponding atomic ratios of Fe and O (Fe/O) of 0.7407 and 0.7273, respectively. The Fe/O ratios in the NWs with oxygen-vacancy ordering are very close to that of Fe3O4 (0.7500). The similar Fe/O ratio between NWs and Fe3O4 may explain the similar modulation periodicity of different oxygen-vacancy orderings. Electron energy-loss spectroscopy studies show that the Fe/O ratio of NWs is close to that of Fe3O4 when oxygen atoms are not sufficient, which makes the NWs energetically favorable. The elucidation of the mechanism governing the formation of the modulated structures in alpha-Fe2O3 NWs is critical for controlling the microstructure and correspondingly physicochemical properties of NWs.
Title:
Investigation of a nano-scale, incommensurate, modulated domain in a Ti-Fe alloy
Authors:
Zheng, YF; Huber, D; Fraser, HL Author Full Names: Zheng, Yufeng; Huber, Daniel; Fraser, Hamish L.
Source:
SCRIPTA MATERIALIA, 154 220-224; 10.1016/j.scriptamat.2018.06.010 SEP 2018
Abstract:
The microstructure of a Ti-Fe compositional gradient sample was investigated using transmission electron microscopy (TEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Different combinations of phases were observed to form depending on the local concentration of Fe. Interestingly, a nano-scale incommensurate modulated domain was detected in the alloy containing approximately 13.8 to 33.9 wt% Fe using selected area diffraction (SAD). The observed disordered structure with no fixed long range periodicity in the nano-scale incommensurate modulated domain in aberration-corrected HAADF-STEM imaging was found not related to the shuffle mechanism of the to phase. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Electronic phase separation and magnetic-field-induced phenomena in molecular multiferroic (ND4)(2)FeCl5 center dot D2O
Authors:
Tian, W; Cao, HB; Clune, AJ; Hughey, KD; Hong, T; Yan, JQ; Agrawal, HK; Singleton, J; Sales, BC; Fishman, RS; Musfeldt, JL; Fernandez-Baca, JA Author Full Names: Tian, W.; Cao, H. B.; Clune, Amanda J.; Hughey, Kendall D.; Hong, Tao; Yan, J. -Q.; Agrawal, Harish K.; Singleton, John; Sales, B. C.; Fishman, Randy S.; Musfeldt, J. L.; Fernandez-Baca, J. A.
Source:
PHYSICAL REVIEW B, 98 (5):10.1103/PhysRevB.98.054407 AUG 8 2018
Abstract:
Electronic phase separation has been increasingly recognized as an important phenomenon in understanding many of the intriguing properties displayed in transition metal oxides. It is believed to produce fascinating functional properties in otherwise chemically homogenous electronic systems, e.g., colossal magnetoresistance manganites and high-T-c cuprates. While many well-known electronically phase-separated systems are oxides, it has been argued that the same phenomenon should occur in other electronic systems with strong competing interactions. Here we report the observation of electronic phase separation in molecular (ND4)(2)FeCl5 center dot D2O, a type-II multiferroic. We show that two magnetic phases, one of which is commensurate and the other of which is incommensurate, coexist in this material. Their evolution under applied magnetic field produces emergent properties. In particular, our measurements reveal a field-induced exotic state linked to a direct transition from a paraelectric/paramagnetic phase to a ferroelectric/antiferromagnetic phase, a collective phenomenon that hasn't been seen in other magnetic multiferroics.
Title:
Incommensurately Modulated Structures in Zr-rich PZT: Periodic Nanodomains, Reciprocal Configuration, and Nucleation
Authors:
Fu, ZQ; Chen, XF; Lu, P; Zhu, CX; Nie, HC; Xu, FF; Wang, GS; Dong, XL Author Full Names: Fu, Zhengqian; Chen, Xuefeng; Lu, Ping; Zhu, Chenxi; Nie, Henchang; Xu, Fangfang; Wang, Genshui; Dong, Xianlin
Source:
CRYSTAL GROWTH & DESIGN, 18 (8):4395-4402; 10.1021/acs.cgd.8b00369 AUG 2018
Abstract:
Zr-rich PZT is one of the most representative materials with compositions located at the ferroelectric-antiferroelectric (FE-AFE) phase boundary. The study of its incommensurately modulated structure (IMS) is of fundamental importance in understanding the origin of its high-performance stored-energy properties and phase transformation between FE and AFE. In this study, the structural features of the IMS were investigated in detail by transmission electron microscopy. The IMS appears as submicron domains assembled by periodic arrays of two-dimensional nanodomains along a <111> direction with the domain width of about 30 {111} spacings. The nanodomains have dual attributes of both antiphase domains and electric domains. The displacement vector across the periodic antiphase boundaries was determined to be R = [001]. The reciprocal lattice of IMS was constructed and characterized by a set of strong basic reflections of pseudocubic unit cell together with 1/2{ooe} superlattice reflections where 1/2(ooe) superlattice reflections (located on the (001) reciprocal planes) do not split, while both 1/2(eoo) and 1/2(oeo) superlattice reflections (located on (100) and (010) reciprocal planes, respectively) split. In addition, the growth process of IMS and the visibility conditions for the periodic nanodomains and superlattice reflections splitting are presented.
Title:
Modulation in charge ordering structure of ferroelectric YbFe2O4 by magnetic ordering
Authors:
Nagata, T; Ikeda, N Author Full Names: Nagata, T.; Ikeda, N.
Source:
AIP ADVANCES, 8 (7):10.1063/1.5026921 JUL 2018
Abstract:
We report the modulation in charge ordering structure of ferroelectric YbFe2O4 by magnetic ordering from x-ray diffraction experiments and magnetic measurements. The incommensurate modulation was observed on (n n 3m+3/2) type diffraction signal around magnetic ordering temperature where n and m are integer. The modulation was also observed on charge ordering signal, indicating spin-charge coupling. The incommensurate modulation was observed only on (n/3 n/3 3m) type charge ordering signal. This selectivity can be explained by polar charge ordering models. (C) 2018 Author(s).

Update: 15-Aug-2018

Title:
Research on the formation of M1-type alite doped with MgO and SO3-A route to improve the quality of cement clinker with a high content of MgO
Authors:
Zhou, H; Gu, XM; Sun, JF; Yu, ZQ; Huang, H; Wang, QQ; Shen, XD Author Full Names: Zhou, Hao; Gu, Xiaomei; Sun, Jinfeng; Yu, Zhuqing; Huang, Hong; Wang, Qianqian; Shen, Xiaodong
Source:
CONSTRUCTION AND BUILDING MATERIALS, 182 156-166; 10.1016/j.conbuildmat.2018.06.078 SEP 10 2018
Abstract:
This paper discusses the effect of SO3 dopants on the M-1 polymorph formation and mechanical properties of alite containing a high content of MgO. The structure of the M-1 alite is identified by XRD, high-temperature XRD and TEM analysis. A characteristic XRD pattern of M-1 alite doped with MgO and SO3 is determined, and TEM results show that M-1 alite has an incommensurate modulated structure feature with 2.4 times the subcell dimension along [(2) over bar1 0 ](H)* and could be expressed as ha* + kb* + lc* + m/[2.4 (-2a* + b*)], where m = +/- 1. The First-Principles method is used to simulate the structure of M-1 alite, and the calculated Delta Cohesive Energy is approximately 11-12 eV between the M-1 and M-3 alite. Quantitative analysis is performed by the Rietveld method. The SO3/MgO (mass ratio from SO3 to MgO) and M-1% in alite (M1-C3S%/M1-C3S%+M3-C3S% x 100%) are shown to have a strong linear relationship, which can be defined as M1-C3S%/M1-C3S%+M3-C3S% x 100% = 24.73 + 108.11 * SO3/MgO (%). Mechanical properties results show that appropriate SO3 dopant can improve the compressive strength of alite containing high MgO while over dosed SO3 will lead to a contrary effect because of the decomposition of alite. The relationship between M-1% in the alite and the compressive strengths at different ages is also given. The optimal M-1% in alite is approximately 68% and the best SO3/MgO ratio is approximately 0.43 because the compressive strength could be maximized at each age. (C) 2018 Elsevier Ltd. All rights reserved.
Title:
Incommensurately Modulated Structures and Luminescence Properties of the AgxSm(2-x)/3WO4 (x=0.286, 0.2) Scheelites as Thermographic Phosphors
Authors:
Morozov, V; Deyneko, D; Basoyich, O; Khaikina, EG; Spassky, D; Morozov, A; Chernyshev, V; Abakumov, A; Hadermann, J Author Full Names: Morozov, Vladimir; Deyneko, Dina; Basoyich, Olga; Khaikina, Elena G.; Spassky, Dmitry; Morozov, Anatolii; Chernyshev, Vladimir; Abakumov, Artem; Hadermann, Joke
Source:
CHEMISTRY OF MATERIALS, 30 (14):4788-4798; 10.1021/acs.chemmater.8b02029 JUL 24 2018
Abstract:
Ag+ for Sm3+ substitution in the scheelite-type AgxSm(2-x)/3 square(1-2x)/3WO4 tungstates has been investigated for its influence on the cation-vacancy ordering and luminescence properties. A solid state method was used to synthesize the x = 0.286 and x = 0.2 compounds, which exhibited (3 + 1)D incommensurately modulated structures in the transmission electron microscopy study. Their structures were refined using high resolution synchrotron powder X-ray diffraction data. Under near-ultraviolet light, both compounds show the characteristic emission lines for (4)G(5/2) -> H-6(J) (J = 5/2, 7/2, 9/2, and 11/2) transitions of the Sm3+ ions in the range 550-720 nm, with the J = 9/2 transition at the similar to 648 nm region being dominant for all photoluminescence spectra. The intensities of the (4)G(5/2) -> H-6(9/2) and (4)G(5/2) -> H-6(7/2) bands have different temperature dependencies. The emission intensity ratios (R) for these bands vary reproducibly with temperature, allowing the use of these materials as thermographic phosphors.

Update: 8-Aug-2018

Title:
Effects of Microstructure of Quasicrystal Alloys on Their Mechanical and Tribological Performance
Authors:
Lee, K; Dai, W; Naugle, D; Liang, H Author Full Names: Lee, Kyungjun; Dai, Wei; Naugle, Donald; Liang, Hong
Source:
JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, 140 (5):10.1115/1.4039528 SEP 2018
Abstract:
The current design of materials against wear considers hardness as the sole material property. As a result, the brittleness associated with increased hardness leads to severe damage. The purpose of this research is to understand the nature of conflicts between hardness and toughness of a new alloy composite. First, we designed Al-Cu-Fe alloys containing crystal structures of lambda, beta, and quasi-crystalline i-phase. These and their combination with others lead to a set of alloys with various hardness and fracture toughness. Experimental study was carried out using a noble and hard tungsten carbide (WC) ball against sample disks. The WC ball did not produce any wear. The wear rate of those alloys was found to be dependent not only on their hardness, but also the toughness, an alternative to the well-accepted Archard-based equations.
Title:
Re-entrant charge order in overdoped (Bi,Pb)(2.12)Sr1.88CuO6+delta outside the pseudogap regime
Authors:
Peng, YY; Fumagalli, R; Ding, Y; Minola, M; Caprara, S; Betto, D; Bluschke, M; De Luca, GM; Kummer, K; Lefrancois, E; Salluzzo, M; Suzuki, H; Le Tacon, M; Zhou, XJ; Brookes, NB; Keimer, B; Braicovich, L; Grilli, M; Ghiringhelli, G Author Full Names: Peng, Y. Y.; Fumagalli, R.; Ding, Y.; Minola, M.; Caprara, S.; Betto, D.; Bluschke, M.; De Luca, G. M.; Kummer, K.; Lefrancois, E.; Salluzzo, M.; Suzuki, H.; Le Tacon, M.; Zhou, X. J.; Brookes, N. B.; Keimer, B.; Braicovich, L.; Grilli, M.; Ghiringhelli, G.
Source:
NATURE MATERIALS, 17 (8):697-+; 10.1038/s41563-018-0108-3 AUG 2018
Abstract:
In the underdoped regime, the cuprate high-temperature superconductors exhibit a host of unusual collective phenomena, including unconventional spin and charge density modulations, Fermi surface reconstructions, and a pseudogap in various physical observables. Conversely, overdoped cuprates are generally regarded as conventional Fermi liquids possessing no collective electronic order. In partial contradiction to this widely held picture, we report resonant X-ray scattering measurements revealing incommensurate charge order reflections for overdoped (Bi,Pb)(2.12)Sr1.88CuO6+delta (Bi2201), with correlation lengths of 40-60 lattice units, that persist up to temperatures of at least 250 K. The value of the charge order wavevector decreases with doping, in line with the extrapolation of the trend previously observed in underdoped Bi2201. In overdoped materials, however, charge order coexists with a single, unreconstructed Fermi surface without nesting or pseudogap features. The discovery of re-entrant charge order in Bi2201 thus calls for investigations in other cuprate families and for a reconsideration of theories that posit an essential relationship between these phenomena.
Title:
Incommensurate atomic and magnetic modulations in the spin-frustrated beta-NaMnO2 triangular lattice
Authors:
Orlandi, F; Aza, E; Bakaimi, I; Kiefer, K; Klemke, B; Zorko, A; Arcon, D; Stock, C; Tsibidis, GD; Green, MA; Manuel, P; Lappas, A Author Full Names: Orlandi, Fabio; Aza, Eleni; Bakaimi, Ioanna; Kiefer, Klaus; Klemke, Bastian; Zorko, Andrej; Arcon, Denis; Stock, Christopher; Tsibidis, George D.; Green, Mark A.; Manuel, Pascal; Lappas, Alexandros
Source:
PHYSICAL REVIEW MATERIALS, 2 (7):10.1103/PhysRevMaterials.2.074407 JUL 24 2018
Abstract:
The layered beta-NaMnO2, a promising Na-ion energy-storage material, has been investigated for its triangular lattice capability to promote complex magnetic configurations that may release symmetry restrictions for the coexistence of ferroelectric and magnetic orders. The complexity of the neutron powder diffraction patterns underlines that the routinely adopted commensurate structural models are inadequate. Instead, a single-phase superspace symmetry description is necessary, demonstrating that the material crystallizes in a compositionally modulated q = (0.077(1), 0, 0) structure. Here Mn3+ Jahn-Teller distorted MnO6 octahedra form corrugated layer stacking sequences of the beta-NaMnO2 type, which are interrupted by flat sheets of the alpha-like oxygen topology. Spontaneous long-range collinear antiferromagnetic order, defined by the propagation vector k = (1/2,1/2,1/2), appears below T-N1 = 200 K. Moreover, a second transition into a spatially modulated proper-screw magnetic state (k +/- q) is established at T-N2 = 95 K, with an antiferromagnetic order parameter resembling that of a two-dimensional (2D) system. The evolution of Na-23 NMR spin-lattice relaxation identifies a magnetically inhomogeneous state in the intermediate T region (T-N2 < T < T-N1), while its strong suppression below T-N2 indicates that a spin gap opens in the excitation spectrum. High-resolution neutron inelastic scattering confirms that the magnetic dynamics are indeed gapped (Delta similar to 5 meV) in the low-temperature magnetic phase, while simulations on the basis of the single-mode approximation suggest that Mn spins residing on adjacent antiferromagnetic chains, establish sizable 2D correlations. Our analysis points out that novel structural degrees of freedom promote cooperative magnetism and emerging dielectric properties in this nonperovskite type of manganite.

Update: 1-Aug-2018

Title:
Easy-plane XY spin fluctuations in the cycloidal magnet UPtGe studied via field-orientation-dependent Pt-195 NMR
Authors:
Tokunaga, Y; Nakamura, A; Aoki, D; Shimizu, Y; Homma, Y; Honda, F; Sakai, H; Hattori, T; Kambe, S Author Full Names: Tokunaga, Y.; Nakamura, A.; Aoki, D.; Shimizu, Y.; Homma, Y.; Honda, F.; Sakai, H.; Hattori, T.; Kambe, S.
Source:
PHYSICAL REVIEW B, 98 (1):10.1103/PhysRevB.98.014425 JUL 23 2018
Abstract:
Pt-195 NMR measurements have been performed on a single crystal of the uranium-based compound UPtGe, which is the only 5f system known to possess an incommensurate helical (cycloidal) structure below T-N = 50 K. Knight shift measurement confirmed the isotropic character of the static spin susceptibilities in hexagonal-like ac crystal planes of the EuAuGe-type crystal structure. The hyperfine coupling constants were also found to be isotropic in the planes, estimated to be 59 kOe/mu B. Nuclear relaxation rate (1/T-1) measurement revealed the development of the antiferromagnetic spin fluctuations with XY character confined to the hexagonal-like plane below 200 K. The results present a clear contrast to the Ising anisotropy of the fluctuations in ferromagnetic superconductors UCoGe and URhGe.
Title:
Imaging the magnetic structures of artificial quasicrystal magnets using resonant coherent diffraction of circularly polarized X-rays
Authors:
Sung, D; Jung, C; Cho, BG; Jo, W; Han, HS; Lee, KS; Bhat, V; Farmer, B; De Long, LE; Lee, KB; Keavney, DJ; Lee, DR; Song, C Author Full Names: Sung, Daeho; Jung, Chulho; Cho, Byeong-Gwan; Jo, Wonhyuk; Han, Hee-Sung; Lee, Ki-Suk; Bhat, Vinayak; Farmer, Barry; De Long, L. E.; Lee, Ki Bong; Keavney, D. J.; Lee, Dong Ryeol; Song, Changyong
Source:
NANOSCALE, 10 (27):13159-13164; 10.1039/c8nr03733g JUL 21 2018
Abstract:
Unraveling nanoscale spin structures has long been an important activity addressing various scientific interests, that are also readily adaptable to technological applications. This has invigorated the development of versatile nanoprobes suitable for imaging specimens under native conditions. Here we have demonstrated the resonant coherent diffraction of an artificial quasicrystal magnet with circularly polarized X-rays. The nanoscale magnetic structure was revealed from X-ray speckle patterns by comparing with micromagnetic simulations, as a step toward understanding the intricate relationship between the chemical and spin structures in an aperiodic quasicrystal lattice. Femtosecond X-ray pulses from free electron lasers are expected to immediately extend the current work to nanoscale structure investigations of ultrafast spin dynamics, surpassing the present spatio-temporal resolution.
Title:
Structure and properties of composites based on polyphenylene sulfide reinforced with Al-Cu-Fe quasicrystalline particles
Authors:
Chukov, DI; Stepashkin, AA; Tcherdyntsev, VV; Olifirov, LK; Kaloshkin, SD Author Full Names: Chukov, D. I.; Stepashkin, A. A.; Tcherdyntsev, V. V.; Olifirov, L. K.; Kaloshkin, S. D.
Source:
JOURNAL OF THERMOPLASTIC COMPOSITE MATERIALS, 31 (7):882-895; 10.1177/0892705717729015 JUL 2018
Abstract:
Structural, mechanical, and thermal properties of polyphenylene sulfide (PPS) filled with Al-Cu-Fe quasicrystals particles were studied. It was shown that the introducing of quasicrystalline fillers into the polymer matrix results in the increase in Young's modulus, hardness, and toughness of the polymer. Quasicrystalline fillers can improve thermal properties of PPS, including heat resistance index, Vicat softening temperature, thermal diffusivity, and thermal conductivity.
Title:
Cylindrical bending analysis of a layered two-dimensional piezoelectric quasicrystal nanoplate
Authors:
Li, Y; Yang, LZ; Gao, Y; Pan, EN Author Full Names: Li, Yang; Yang, Lianzhi; Gao, Yang; Pan, Ernian
Source:
JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES, 29 (12):2660-2676; 10.1177/1045389X18770920 JUL 2018
Abstract:
The piezoelectric effect is a significant property of quasicrystal. In this article, the exact solution is derived for a layered piezoelectric quasicrystal nanoplate with nonlocal effect in cylindrical bending. Based on the nonlocal theory and the pseudo-Stroh formalism, the exact solution for a homogeneous simply supported nanoplate is obtained. With the aid of the propagator matrix, the exact solution for a multilayered nanoplate is achieved. Numerical examples are carried out to reveal the influences of span-to-thickness ratio, nonlocal parameter, and stacking sequence on piezoelectric quasicrystal nanoplates with their top surface subjected to two loadings. One is a z-direction mechanical loading and the other is an electric potential loading. These results can be served as benchmarks for the design, numerical modeling, and simulation of layered two-dimensional piezoelectric quasicrystal nanoplates under cylindrical bending.
Title:
EVOLUTION OF THE PHASES OF QUASICRYSTALLINE ALLOYS ICOSAHEDRAL/DECAGONAL Al62.2Cu25.3Fe12.5/Al65Ni15Co20 AND OXIDATIVE BEHAVIOR
Authors:
Jamshidi, LCLA; Rodbari, RJ Author Full Names: Lucena Agostinho Jamshidi, Lourdes Cristina; Rodbari, Reza Jamshidi
Source:
JOURNAL OF THE CHILEAN CHEMICAL SOCIETY, 63 (2):3928-3933; 10.4067/s0717-97072018000203928 JUN 2018
Abstract:
In this paper, we present an approach and investigation on the evolution of the icosahedral and decagonal phases of quasicrystalline alloys Al62.2Cu25.3Fe12.5 E Al65Ni15Co20, the oxidation behavior in them. The quantification of the quasicrystalline and crystalline phases present in the quasicrystals provides important information in the mass transport by diffusion, as well as the phase transformations that occurred. For this purpose, X-ray diffraction (XRD) and Rietveld Method Quantification, Scanning Electron Microscopy (SEM) / Dispersive Energy Spectroscopy (EDS), Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis). The results showed structural aspects of the two compositions of quasicrystals, these were elaborated and obtained in an arc induction furnace. The oxidation of the alloy Al62.2Cu25.3Fe12.5 showed intermetallic phases with associations of the elements of the alloy and above 735 degrees C was observed that the crystalline phase is stable in the icosahedral phase. The quasicrystals Al65Ni15Co20, with the interaction of oxygen, happens in the surface of symmetry 10 times plane perpendicular vector. The formation of a thin film of the aluminum oxide with a well ordered hexagonal shape structure, with a domain opposite the decagonal phase with lateral size at about 35 angstrom.
Title:
Electric-field-induced phase transition and pinched P-E hysteresis loops in Pb-free ferroelectrics with a tungsten bronze structure
Authors:
Li, K; Zhu, XL; Liu, XQ; Ma, X; Sen Fu, M; Kroupa, J; Kamba, S; Chen, XM Author Full Names: Li, Kun; Zhu, Xiao Li; Liu, Xiao Qiang; Ma, Xiao; Sen Fu, Mao; Kroupa, Jan; Kamba, Stanislav; Chen, Xiang Ming
Source:
NPG ASIA MATERIALS, 10 10.1038/s41427-018-0013-x APR 5 2018
Abstract:
Antiferroelectrics are of interest due to their high potential for energy storage. Here, we report the discovery of pinched, polarization-vs.-electric field (P-E) hysteresis loops in the lead-free tungsten bronze ferroelectrics Ba4Sm2Ti4Nb6O30 and Ba4Eu2Ti4Nb6O30, while a broad, single P-E hysteresis loop was observed in the analogue compound Ba4Nd2Ti4Nb6O30. Pinched P-E loops are similar to antiferroelectric hysteresis loops, but in perovskites, they are mostly caused by an extrinsic, internal bias field due to defects, which block domain wall motion. We show that the pinched P-E loops are caused by an intrinsic effect, i.e., by the electric-field-induced phase transition from a non-polar incommensurate to a polar commensurately modulated crystal structure. The in situ electron diffraction results show the coexistence of commensurate polar structural modulation and incommensurate non-polar modulation during the ferroelectric transition and within the ferroelectric phase below the transition temperature. This phase coexistence is the reason for the small remanent polarization. An external electric field transforms the incommensurate component into a commensurate one, and the polarization increases. This new mechanism for pinched P-E hysteresis loops in ferroelectrics not only indicates a new direction for the development of Pb-free ferroelectric materials for energy storage but also significantly contributes to the physical understanding of ferroelectricity in materials with a tungsten bronze structure.

Update: 26-Jul-2018

Title:
Charge density wave phase, Mottness, and ferromagnetism in monolayer 1T-NbSe2
Authors:
Pasquier, D; Yazyev, OV Author Full Names: Pasquier, Diego; Yazyev, Oleg V.
Source:
PHYSICAL REVIEW B, 98 (4):10.1103/PhysRevB.98.045114 JUL 10 2018
Abstract:
The recently investigated 1T polymorph of monolayer NbSe2 revealed an insulating behavior suggesting a star-of-David phase with root 13 x root 13 periodicity associated with a Mott insulator, reminiscent of 1 T-TaS2. We examine this novel two-dimensional material from first principles. We find an instability towards the formation of an incommensurate charge density wave (CDW) and establish the star-of-David phase as the most stable commensurate CDW. The Mottness in the star-of-David phase is confirmed and studied at various levels of theory: the spin-polarized generalized gradient approximation (GGA) and its extension involving the on-site Coulomb repulsion (GGA+U), as well as the dynamical mean-field theory. Finally, we estimate Heisenberg exchange couplings in this material and find a weak nearest-neighbor ferromagnetic coupling, at odds with most Mott insulators. We point out the close resemblance between this star-of-David phase and flat-band ferromagnetism models.
Title:
Multi-orbital nature of the spin fluctuations in Sr2RuO4
Authors:
Boehnke, L; Werner, P; Lechermann, F Author Full Names: Boehnke, Lewin; Werner, Philipp; Lechermann, Frank
Source:
EPL, 122 (5):10.1209/0295-5075/122/57001 JUN 2018
Abstract:
The spin susceptibility of strongly correlated Sr2RuO4 is known to display a rich structure in reciprocal space, with a prominent peak at Q(i) = (0.3,0.3,0). It is still debated if the resulting incommensurate spin-density-wave fluctuations foster unconventional superconductivity at low temperature or compete therewith. By means of density functional theory combined with dynamical mean-field theory, we reveal the realistic multi-orbital signature of the (dynamic) spin susceptibility beyond existing weak-coupling approaches. The experimental fluctuation spectrum up to 80 meV is confirmed by theory. Furthermore, the peak at Q(i) is shown to carry nearly equal contributions from each of the Ru(4d)-t(2)g orbitals, pointing to a cooperative effect resulting in the dominant spin fluctuations. Copyright (C) EPLA, 2018
Title:
Quasicrystal seen to superconduct
Authors:
Jarman, S Author Full Names: Jarman, Sam
Source:
PHYSICS WORLD, 31 (5):4-4; MAY 2018

Update: 18-Jul-2018

Title:
Persistent low-energy phonon broadening near the charge-order q vector in the bilayer cuprate Bi2Sr2CaCu2O8+delta
Authors:
He, Y; Wu, S; Song, Y; Lee, WS; Said, AH; Alatas, A; Bosak, A; Girard, A; Souliou, SM; Ruiz, A; Hepting, M; Bluschke, M; Schierle, E; Weschke, E; Lee, JS; Jang, H; Huang, H; Hashimoto, M; Lu, DH; Song, D; Yoshida, Y; Eisaki, H; Shen, ZX; Birgeneau, RJ; Yi, M; Frano, A Author Full Names: He, Y.; Wu, S.; Song, Y.; Lee, W-S; Said, A. H.; Alatas, A.; Bosak, A.; Girard, A.; Souliou, S. M.; Ruiz, A.; Hepting, M.; Bluschke, M.; Schierle, E.; Weschke, E.; Lee, J-S; Jang, H.; Huang, H.; Hashimoto, M.; Lu, D-H; Song, D.; Yoshida, Y.; Eisaki, H.; Shen, Z-X; Birgeneau, R. J.; Yi, M.; Frano, A.
Source:
PHYSICAL REVIEW B, 98 (3):10.1103/PhysRevB.98.035102 JUL 2 2018
Abstract:
We report a persistent low-energy phonon broadening around qB similar to 0.28 reciprocal lattice unit (r.l.u.)along the Cu-O bond direction in the high-T-c cuprate Bi2Sr2CaCu2O8+delta (Bi-2212). We show that such broadening exists both inside and outside the conventional charge-density wave (CDW) phase, via temperature-dependent measurements in both underdoped and heavily overdoped samples. Combining inelastic hard x-ray scattering, diffuse scattering, angle-resolved photoemission spectroscopy, and resonant soft x-ray scattering at the Cu L-3-edge, we exclude the presence of a CDW in the heavily overdoped Bi-2212 similar to that observed in the underdoped systems. Finally, we discuss the origin of such anisotropic low-energy phonon broadening and its potential precursory role to the CDW phase in the underdoped region.
Title:
Exploiting superspace to clarify vacancy and Al/Si ordering in mullite
Authors:
Klar, PB; Etxebarria, I; Madariaga, G Author Full Names: Klar, Paul Benjamin; Etxebarria, Inigo; Madariaga, Gotzon
Source:
IUCRJ, 5 497-509; 10.1107/S2052252518007467 4 JUL 2018
Abstract:
Synchrotron single-crystal X-ray diffraction has revealed diffuse scattering alongside sharp satellite reflections for different samples of mullite (Al4+2xSi2-2xO10-x). Structural models have been developed in (3+1)-dimensional superspace that account for vacancy ordering and Al/Si ordering based on harmonic modulation functions. A constraint scheme is presented which explains the crystal-chemical relationships between the split sites of the average structure. The modulation amplitudes of the refinements differ significantly by a factor of similar to 3, which is explained in terms of different degrees of ordering, i.e. vacancies follow the same ordering principle in all samples but to different extents. A new approach is applied for the first time to determine Al/Si ordering by combining density functional theory with the modulated volumes of the tetrahedra. The presence of Si-Si diclusters indicates that the mineral classification of mullite needs to be reviewed. A description of the crystal structure of mullite must consider both the chemical composition and the degree of ordering. This is of particular importance for applications such as advanced ceramics, because the physical properties depend on the intrinsic structure of mullite.
Title:
Sr2Pt8-x As: a layered incommensurately modulated metal with saturated resistivity
Authors:
Martino, E; Arakcheeva, A; Autes, G; Pisoni, A; Bachmann, MD; Modic, KA; Helm, T; Yazyev, OV; Moll, PJW; Forro, L; Katrych, S Author Full Names: Martino, Edoardo; Arakcheeva, Alla; Autes, Gabriel; Pisoni, Andrea; Bachmann, Maja D.; Modic, Kimberly A.; Helm, Toni; Yazyev, Oleg, V; Moll, Philip J. W.; Forro, Laszlo; Katrych, Sergiy
Source:
IUCRJ, 5 470-477; 10.1107/S2052252518007303 4 JUL 2018
Abstract:
The high-pressure synthesis and incommensurately modulated structure are reported for the new compound Sr2Pt8-xAs, with x = 0.715 (5). The structure consists of Sr2Pt3 As layers alternating with Pt-only corrugated grids. Ab initio calculations predict a metallic character with a dominant role of the Pt d electrons. The electrical resistivity (rho) and Seebeck coefficient confirm the metallic character, but surprisingly, rho showed a near-flat temperature dependence. This observation fits the description of the Mooij correlation for electrical resistivity in disordered metals, originally developed for statistically distributed point defects. The discussed material has a long-range crystallographic order, but the high concentration of Pt vacancies, incommensurately ordered, strongly influences the electronic conduction properties. This result extends the range of validity of the Mooij correlation to long-range ordered incommensurately modulated vacancies. Motivated by the layered structure, the resistivity anisotropy was measured in a focused-ion-beam micro-fabricated well oriented single crystal. A low resistivity anisotropy indicates that the layers are electrically coupled and conduction channels along different directions are intermixed.
Title:
A Markov theoretic description of stacking-disordered aperiodic crystals including ice and opaline silica
Authors:
Hart, AG; Hansen, TC; Kuhs, WF Author Full Names: Hart, A. G.; Hansen, T. C.; Kuhs, W. F.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 357-372; 10.1107/S2053273318006083 4 JUL 2018
Abstract:
This article reviews the Markov theoretic description of one-dimensional aperiodic crystals, describing the stacking-faulted crystal polytype as a special case of an aperiodic crystal. Under this description the centrosymmetric unit cell underlying a topologically centrosymmetric crystal is generalized to a reversible Markov chain underlying a reversible aperiodic crystal. It is shown that for the close-packed structure almost all stackings are irreversible when the interaction reichweite s > 4. Moreover, the article presents an analytic expression of the scattering cross section of a large class of stacking-disordered aperiodic crystals, lacking translational symmetry of their layers, including ice and opaline silica (opal CT). The observed stackings and their underlying reichweite are then related to the physics of various nucleation and growth processes of disordered ice. The article discusses how the derived expressions of scattering cross sections could significantly improve implementations of Rietveld's refinement scheme and compares this Q-space approach with the pair-distribution function analysis of stacking-disordered materials.
Title:
Primitive substitution tilings with rotational symmetries
Authors:
Say-awen, ALD; De las Penas, MLAN; Frettloh, D Author Full Names: Say-awen, April Lynne D.; De las Penas, Ma Louise Antonette N.; Frettloeh, Dirk
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 388-398; 10.1107/S2053273318006745 4 JUL 2018
Abstract:
This work introduces the idea of symmetry order, which describes the rotational symmetry types of tilings in the hull of a given substitution. Definitions are given of the substitutions sigma(6) and sigma(7) which give rise to aperiodic primitive substitution tilings with dense tile orientations and which are invariant under six- and sevenfold rotations, respectively; the derivation of the symmetry orders of their hulls is also presented.
Title:
A phenomenological model for structural phase transitions in incommensurate alkane/urea inclusion compounds
Authors:
Couzi, M; Guillaume, F; Harris, KDM Author Full Names: Couzi, Michel; Guillaume, Francois; Harris, Kenneth D. M.
Source:
ROYAL SOCIETY OPEN SCIENCE, 5 (6):10.1098/rsos.180058 JUN 2018
Abstract:
n-Alkane/urea inclusion compounds are crystalline materials in which n-alkane 'guest' molecules are located within parallel one-dimensional 'host' tunnels formed by a helical hydrogen-bonded arrangement of urea molecules. The periodic repeat distance of the guest molecules along the host tunnels is incommensurate with the periodic repeat distance of the host substructure. The structural properties of the high-temperature phase of these materials (phase I), which exist at ambient temperature, are described by a (3 + l)-dimensional superspace. Recent publications have suggested that, in the prototypical incommensurate composite systems, n-nonadecane/urea and n-hexadecane/urea, two low-temperature phases II and 'III' exist and that one or both of these phases are described by a (3 + 2)dimensional superspace. We present a phenomenological model based on symmetry considerations and developed in the frame of a pseudo-spin-phonon coupling mechanism, which accounts for the mechanisms responsible for the I <-> II <-> 'III' phase sequence. With reference to published experimental data, we demonstrate that, in all phases of these incommensurate materials, the structural properties are described by (3 + l)-dimensional superspace groups. Around the temperature of the II <-> 'III' transition, the macroscopic properties of the material are not actually associated with a phase transition, but instead represent a 'crossover' between two regimes involving different couplings between relevant order parameters.
Title:
Microstructural analysis, micro-hardness and wear resistance properties of quasicrystalline Al-Cu-Fe coatings on Ti-6Al-4V alloy
Authors:
Fatoba, OS; Akinlabi, SA; Akinlabi, ET; Gharehbaghi, R Author Full Names: Fatoba, O. S.; Akinlabi, S. A.; Akinlabi, E. T.; Gharehbaghi, R.
Source:
MATERIALS RESEARCH EXPRESS, 5 (6):10.1088/2053-1591/aaca70 JUN 2018
Abstract:
The need for engineering components with suitable functionality under harsh wear and aggressive environment subjected to high risk of deterioration, has led to the demand for surface treatment processes and high-performance materials. Ti-6Al-4V is one of the mostly used titanium alloys with more than 70% of the industrial applications in the aerospace, marine and automotive industries. Despite the exceptional properties of Ti-6Al-4V alloy, their low hardness, high susceptibility to corrosion, poor thermal stability and poor tribological properties have limited their viability in the field of engineering. In this research, laser metal deposition technique by incorporating quasicrystal-line Al-Cu-Fe coatings can be very beneficial in enhancing the surface properties of Ti-6Al-4V alloy. A 3 kW continuous wave ytterbium laser system (YLS) attached to a KUKA robot which controls the movement of the cladding process was utilized for the fabrication of the coatings. The titanium alloy cladded surfaces were investigated for its microstructure, mechanical and wear resistance properties at different laser processing conditions. The obtained results illustrated that geometrical properties height and width of the deposit increase with an increase in laser power. Increase in scanning speed results in a decrease in the geometrical properties. Ti reacted with increased amount of Al and Fe and less amount of Cu powders to form Al2Ti, Fe0.975Ti, Al0.9Fe3.1Ti0.025 and AlCu2Ti. The optimum performances were obtained for an alloy composition of Ti-6A-4V/Al-Cu-5Fe composite, at laser power of 800 W and scanning speed of 1.0 m min(-1). Its performance enhancement compared to the unprotected substrate comprised a significant increase in hardness from 302 to 2740 HV which translates to 89.14% in hardness values above that of the substrate. Coatings with higher hardness levels were achieved mainly due to the larger fraction of hard-intermetallic phases at lower laser scanning speeds. Finally, Ti-6Al-4V/Al-Cu-5Fe coating at laser power of 800 W and scanning speed of 1.0 m min(-1) shows the highest wear resistance performance compared to the substrate. Ti-6Al-4V/ Al-Cu-5Fe coating was 2.8 times the wear resistance performance of the substrate.

Update: 11-Jul-2018

Title:
Al-Fe-Ge: New ternary compounds and phase equilibria at 800 degrees C
Authors:
Reisinger, GR; Effenberger, HS; Richter, KW Author Full Names: Reisinger, Gabriel R.; Effenberger, Herta S.; Richter, Klaus W.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 762 849-857; 10.1016/j.jallcom.2018.05.214 SEP 25 2018
Abstract:
The isothermal sections of Al-Fe-Ge at 800 degrees C and 780 degrees C were studied by a combination of SEM/EDX with X-ray powder diffraction. Two new ternary compounds were structurally characterised by means of single-crystal XRD measurements: Al3-xFeGe2+x, I4/mcm, a = 6.2303(11) angstrom, c = 9.710(2) angstrom, V = 376.9 angstrom(3), Z = 4, R-int = 0.031, wR(2) = 0.038 and Al1+xFeGe1-x, Fddd, a = 8.627(2) angstrom, b = 4.9139(8) angstrom, c = 16.369(3) angstrom, V = 693.9 angstrom(3), Z = 16, R-int = 0.039, wR(2) = 0.053, which crystallise in the Ga5Pd and CuMg2 structure types, respectively. Considerable solid solution ranges mainly based on Al/Ge substitution were found for all binary and ternary phases present in this section. An apparently incommensurate superstructure of Al5Fe2 is triggered by Ge-additions. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Liquid Exfoliation of Icosahedral Quasicrystals
Authors:
Yadav, TP; Woellner, CF; Sinha, SK; Sharifi, T; Apte, A; Mukhopadhyay, NK; Srivastava, ON; Vajtai, R; Galvao, DS; Tiwary, CS; Ajayan, PM Author Full Names: Yadav, Thakur Prasad; Woellner, Cristiano F.; Sinha, Shyam K.; Sharifi, Tiva; Apte, Amey; Mukhopadhyay, Nilay Krishna; Srivastava, Onkar Nath; Vajtai, Robert; Galvao, Douglas S.; Tiwary, Chandra Sekhar; Ajayan, Pulickel M.
Source:
ADVANCED FUNCTIONAL MATERIALS, 28 (26):10.1002/adfm.201801181 JUN 27 2018
Abstract:
The realization of quasicrystals has attracted a considerable attention due to their unusual structures and properties. The concept of quasicrystals in the atomically thin materials is even more appealing due to the in-plane covalent bonds and weak interlayer interactions. Here, it is demonstrated that 2D quasicrystals can be created/isolated from bulk phases because of long-range interlayer ordered aperiodic arrangements. An ultrasonication-assisted exfoliation of polygrained icosahedral Al-Pd-Mn quasicrystals at room temperature shows the formation of a large area of mono- and few layers in threefold quasicrystalline plane. The formation of these layers from random grain orientation consistently indicates that the threefold plane is most stable in comparison to the twofold and fivefold planes in icosahedral clusters. The above experimental observations are further supported with help of theoretical simulations. The mono- and few-layered aperiodic planes render plentiful active sites for the catalysis of hydrogen evolution reaction. The threefold 2D quasicrystalline plane exhibits a hydrogen evolution reaction overpotential of approximate to 100 mV (160 times less than bulk counterpart) and long-term durability. These systems constitute the first demonstration of quasicrystalline monolayer ordering in a free-standing thin layer without requiring the support of periodic or aperiodic substrate.
Title:
Light Localization in Local Isomorphism Classes of Quasicrystals
Authors:
Lin, C; Steinhardt, PJ; Torquato, S Author Full Names: Lin, Chaney; Steinhardt, Paul J.; Torquato, Salvatore
Source:
PHYSICAL REVIEW LETTERS, 120 (24):10.1103/PhysRevLett.120.247401 JUN 14 2018
Abstract:
We study a continuum of photonic quasicrystal heterostructures derived from local isomorphism (LI) classes of pentagonal quasicrystal tilings. These tilings are obtained by direct projection from a five-dimensional hypercubic lattice. We demonstrate that, with the sole exception of the Penrose LI class, all other LI classes result in degenerate, effectively localized states, with precisely predictable and tunable properties (frequencies, frequency splittings, and densities). We show that localization and tunability are related to a mathematical property of the pattern known as "restorability," i.e., whether the tiling can be uniquely specified given only a set of rules that fix all allowed clusters smaller than some bound.
Title:
First-principles study of elastic and slip properties of non-canonical beta-based Al-Cu-Fe approximants
Authors:
Medvedeva, NI; Shalaeva, EV Author Full Names: Medvedeva, N. I.; Shalaeva, E. V.
Source:
PHILOSOPHICAL MAGAZINE, 98 (23):2135-2150; 10.1080/14786435.2018.1478145 2018
Abstract:
Ab initio calculations were carried out to compare the mechanical properties of beta-based non-canonical Al-Cu-Fe approximants of quasicrystals with cubic (beta), monoclinic (eta) and orthorhombic (xi 1, xi 2) structures, which all demonstrate high strengthening. The aim was to elucidate the competitive effects of the eta- and xi-ordering and iron content on deformation behaviour of these phases. We found that the Young's modulus, polycrystalline shear modulus, mechanical stability and shear elastic modulus G(n,m) for different slip planes decrease for beta-Al50Cu1-xFex with lowering iron content, but they grow from beta-Al50Cu31.25Fe18.75 to the ordered eta-Al50Cu45Fe5, and xi 2-Al45.5Cu50Fe4.5 that indicates a growing resistance to plastic deformation due to ordering and agrees well with our experimental finding. The preferable slip systems were predicted based on the calculated generalised stacking fault (GSF) energies in beta-(Cu,Fe)Al and eta-(Cu,Fe)Al with similar Fe concentration. The GSF energies confirmed also that the strengthening observed in eta-phase is related to ordering rather than the Fe effect in consistence with a stronger covalent bonding in eta-phase.
Title:
Interpretation of some Yb-based valence-fluctuating crystals as approximants to a dodecagonal quasicrystal
Authors:
Ishimasa, T; Mihalkovic, M; Deguchi, K; Sato, NK; de Boissieu, M Author Full Names: Ishimasa, Tsutomu; Mihalkovic, Marek; Deguchi, Kazuhiko; Sato, Noriaki K.; de Boissieu, Marc
Source:
PHILOSOPHICAL MAGAZINE, 98 (22):2018-2034; 10.1080/14786435.2018.1470339 2018
Abstract:
The hexagonal ZrNiAl-type (space group: P (6) over bar 2m) and the tetragonal Mo2FeB2-type (space group: P4/mbm) structures, which are formed in the same Yb-based alloys and exhibit physical properties related to valence-fluctuation, can be regarded as approximants of a hypothetical dodecagonal quasicrystal. Using Pd-Sn-Yb system as an example, a model of quasicrystal structure has been constructed, of which five-dimensional crystal (space group: P12/mmm, a(DD) = 5.66 angstrom and c = 3.72 angstrom) consists of four types of acceptance regions located at the following crystallographic sites; Yb [0 0 0 0 0], Pd[1/3 0 1/3 0 1/2], Pd[1/3 1/3 1/3 1/3 0] and Sn[1/2 00 1/2 1/2]. In the three-dimensional space, the quasicrystal is composed of three types of columns, of which c-projections correspond to a square, an equilateral triangle and a three-fold hexagon. They are fragments of two known crystals, the hexagonal alpha-YbPdSn and the tetragonal Yb2Pd2Sn structures. The model of the hypothetical quasicrystal may be applicable as a platform to treat in a unified manner the heavy fermion properties in the two types of Yb-based crystals.

Update: 4-Jul-2018

Title:
Evolution of Magneto-Orbital order Upon B-Site Electron Doping in Na1-xCaxMn7O12 Quadruple Perovskite Manganites
Authors:
Johnson, RD; Mezzadri, F; Manuel, P; Khalyavin, DD; Gilioli, E; Radaelli, PG Author Full Names: Johnson, R. D.; Mezzadri, F.; Manuel, P.; Khalyavin, D. D.; Gilioli, E.; Radaelli, P. G.
Source:
PHYSICAL REVIEW LETTERS, 120 (25):10.1103/PhysRevLett.120.257202 JUN 19 2018
Abstract:
We present the discovery and refinement by neutron powder diffraction of a new magnetic phase in the Na1-xCaxMn7O12 quadruple perovskite phase diagram, which is the incommensurate analogue of the wellknown pseudo-CE phase of the simple perovskite manganites. We demonstrate that incommensurate magnetic order arises in quadruple perovskites due to the exchange interactions between A and B sites. Furthermore, by constructing a simple mean field Heisenberg exchange model that generically describes both simple and quadruple perovskite systems, we show that this new magnetic phase unifies a picture of the interplay between charge, magnetic, and orbital ordering across a wide range of compounds.
Title:
Magnetoelastic phase diagram of TbNi2B2C
Authors:
Toft-Petersen, R; Jensen, TBS; Jensen, J; von Zimmermann, M; Sloth, S; Isaksen, FW; Christensen, NB; Chen, YZ; Siemensmeyer, K; Kawano-Furukawa, H; Takeya, H; Abrahamsen, AB; Andersen, NH Author Full Names: Toft-Petersen, Rasmus; Jensen, Thomas Bagger Stibius; Jensen, Jens; von Zimmermann, Martin; Sloth, Steffen; Isaksen, Frederik Werner; Christensen, Niels Bech; Chen, Yunzhong; Siemensmeyer, Konrad; Kawano-Furukawa, Hazuki; Takeya, Hiroyuki; Abrahamsen, Asger Bech; Andersen, Niels Hessel
Source:
PHYSICAL REVIEW B, 97 (22):10.1103/PhysRevB.97.224417 JUN 15 2018
Abstract:
The magnetic phase diagram of the quaternary borocarbide TbNi2B2C is investigated by direct means and by studying magnetically induced modifications of the crystal structure. Detailed superconducting quantum interference device measurements reveal a complex phase diagram with five distinct magnetic phases. The phase boundaries aremapped out comprehensively. Synchrotron hard x-raymeasurements in appliedmagnetic fields are employed to probe the magnetoelastic distortions throughout the phase diagram. The determination of the wave vectors of these field-induced lattice deformations suggests a range of commensurate spin-slip-type magnetic structures at low temperatures with wave vectors of the form (q, 0,0) with q = 6/11 and 5/9. The proposed magnetic structures yield values of magnetization well in-line with observations. The scattering intensity due to the magnetoelastic deformations exhibits a drastic jump at the phase boundary at 1.3 T and low temperatures.
Title:
Lattice Correspondence and Growth Structures of Monoclinic Mg4Zn7 Phase Growing on an Icosahedral Quasicrystal
Authors:
Singh, A; Rosalie, JM Author Full Names: Singh, Alok; Rosalie, Julian M.
Source:
CRYSTALS, 8 (5):10.3390/cryst8050194 MAY 2018
Abstract:
Mg4Zn7 phase, with a monoclinic unit cell, a layered structure and a unique axis showing pseudo-tenfold symmetry, grows over icosahedral quasicrystalline phase in a manner similar to a decagonal quasicrystal. In this study, the relationship of this phase to icosahedral quasicrystal is brought out by a transmission electron microscopy study of Mg4Zn7 phase growing on icosahedral phase in a cast Mg-Zn-Y alloy. Lattice correspondences between the two phases have been determined by electron diffraction. Planes related to icosahedral fivefold and pseudo-twofold symmetry are identified. Possible orthogonal cells bounded by twofold symmetry-related planes have been determined. Mg4Zn7 phase growing on an icosahedral phase exhibits a number of planar faults parallel to the monoclinic axis, presumably to accommodate the quasiperiodicity at the interface. Two faults were identified, which were on {200} and {201} planes. Their structures have been determined by high resolution imaging in TEM. They produce two different unit cells at the interface.
Title:
Crystallographic features of the approximant H (Mn7Si2V) phase in the Mn-Si-V alloy system
Authors:
Nakayama, K; Komatsuzaki, T; Koyama, Y Author Full Names: Nakayama, Kei; Komatsuzaki, Takumi; Koyama, Yasumasa
Source:
PHILOSOPHICAL MAGAZINE, 98 (20):1823-1847; 10.1080/14786435.2018.1459058 2018
Abstract:
The intermetallic compound H (Mn7Si2V) phase in the Mn-Si-V alloy system can be regarded as an approximant phase of the dodecagonal quasicrystal as one of the two-dimensional quasicrystals. To understand the features of the approximant H phase, in this study, the crystallographic features of both the H phase and the (sigma H) reaction in Mn-Si-V alloy samples were investigated, mainly by transmission electron microscopy. It was found that, in the H phase, there were characteristic structural disorders with respect to an array of a dodecagonal structural unit consisting of 19 dodecagonal atomic columns. Concretely, penetrated structural units consisting of two dodecagonal structural units were presumed to be typical of such disorders. An interesting feature of the (sigma H) reaction was that regions with a rectangular arrangement of penetrated structural units (RAPU) first appeared in the sigma matrix as the initial state, and H regions were then nucleated in contact with RAPU regions. The subsequent conversion of RAPU regions into H regions eventually resulted in the formation of the approximant H state as the final state. Furthermore, atomic positions in both the H structure and the dodecagonal quasicrystal were examined using a simple plane-wave model with 12 plane waves.

Update: 27-Jun-2018

Title:
Photoinduced discommensuration of the commensurate charge-density wave phase in 1T-TaS2
Authors:
Tanimura, K Author Full Names: Tanimura, Katsumi
Source:
PHYSICAL REVIEW B, 97 (24):10.1103/PhysRevB.97.245115 JUN 11 2018
Abstract:
The dynamics induced by femtosecond-laser excitation of the commensurate phase of the charge-density wave (CDW) in 1T -TaS2 have been studied using both time-resolved electron diffraction and the time-resolved spectroscopy of coherent-phonon dynamics. Electron diffraction results show that the commensurate CDW phase is transformed into a new phase with CDW order that is similar to the nearly commensurate phase with threshold-type transition rates; the threshold excitation density of 0.2 per 13 Ta atoms is evaluated. Coherent-phonon spectroscopy results show that, together with the amplitude mode of CDW with a frequency of 2.41 THz, two other modes with frequencies of 2.34 and 2.07 THz are excited in the photoexcited commensurate CDW phase over a timescale of several tens of picoseconds after excitation. Spectroscopic, temporal, and excitation-intensity dependent characteristics of the three coherent phonons reveal that a photoinduced decomposition of the commensurate CDW order into an ensemble of domains with different CDW orders is induced before the CDW-phase transition occurs. The physics underlying the photoinduced decomposition and evolution into discommensurations responsible for the CDW-order transformation are discussed.
Title:
Adaptive modulation in the Ni2Mn1.4In0.6 magnetic shape-memory Heusler alloy
Authors:
Devi, P; Singh, S; Dutta, B; Manna, K; D'Souza, SW; Ikeda, Y; Suard, E; Petricek, V; Simon, P; Werner, P; Chadhov, S; Parkin, SSP; Felser, C; Pandey, D Author Full Names: Devi, P.; Singh, Sanjay; Dutta, B.; Manna, K.; D'Souza, S. W.; Ikeda, Y.; Suard, E.; Petricek, V; Simon, P.; Werner, P.; Chadhov, S.; Parkin, Stuart S. P.; Felser, C.; Pandey, D.
Source:
PHYSICAL REVIEW B, 97 (22):10.1103/PhysRevB.97.224102 JUN 11 2018
Abstract:
The origin of incommensurate structural modulation in Ni-Mn based Heusler-type magnetic shape-memory alloys (MSMAs) is still an unresolved issue in spite of intense focus on it due to its role in the magnetic field induced ultrahigh strains. In the archetypal MSMA Ni2MnGa, the observation of "nonuniform displacement" of atoms from their mean positions in the modulated martensite phase, premartensite phase, and charge density wave as well as the presence of phason broadening of satellite peaks has been taken in support of the electronic instability model linked with a soft acoustic phonon. We present here results of a combined high-resolution synchrotron x-ray powder diffraction (SXRPD) and neutron powder diffraction (NPD) study on Ni2Mn1.4In0.6 using a (3+1)D superspace group approach, which reveals not only uniform atomic displacements in the modulated structure of the martensite phase with physically acceptable ordered magnetic moments in the antiferromagnetic phase at low temperatures, but also the absence of any premartensite phase and phason broadening of the satellite peaks. Our HRTEM studies and first-principles calculations of the ground state also support uniform atomic displacements predicted by powder diffraction studies. All these observations suggest that the structural modulation in the martensite phase of Ni(2)Mn(1.4)In(0.6 )MSMA can be explained in terms of the adaptive phase model. The present study underlines the importance of superspace group analysis using complementary SXRPD and NPD in understanding the physics of the origin of modulation as well as the magnetic and the modulated ground states of the Heusler-type MSMAs. Our work also highlights the fact that the mechanism responsible for the origin of modulated structure in different Ni-Mn based MSMAs may not be universal and it must be investigated thoroughly in different alloy compositions.
Title:
Breakdown of Magnetic Order in the Pressurized Kitaev Iridate beta-Li2IrO3
Authors:
Majumder, M; Manna, RS; Simutis, G; Orain, JC; Dey, T; Freund, F; Jesche, A; Khasanov, R; Biswas, PK; Bykova, E; Dubrovinskaia, N; Dubrovinsky, LS; Yadav, R; Hozoi, L; Nishimoto, S; Tsirlin, AA; Gegenwart, P Author Full Names: Majumder, M.; Manna, R. S.; Simutis, G.; Orain, J. C.; Dey, T.; Freund, F.; Jesche, A.; Khasanov, R.; Biswas, P. K.; Bykova, E.; Dubrovinskaia, N.; Dubrovinsky, L. S.; Yadav, R.; Hozoi, L.; Nishimoto, S.; Tsirlin, A. A.; Gegenwart, P.
Source:
PHYSICAL REVIEW LETTERS, 120 (23):10.1103/PhysRevLett.120.237202 JUN 8 2018
Abstract:
Temperature-pressure phase diagram of the Kitaev hyperhoneycomb iridate beta-Li2IrO3 is explored using magnetization, thermal expansion, magnetostriction, and muon spin rotation measurements, as well as single-crystal x-ray diffraction under pressure and ab initio calculations. The Neel temperature of beta-Li2IrO3 increases with the slope of 0.9 K/GPa upon initial compression, but the reduction in the polarization field Hc reflects a growing instability of the incommensurate order. At 1.4 GPa, the ordered state breaks down upon a first-order transition, giving way to a new ground state marked by the coexistence of dynamically correlated and frozen spins. This partial freezing in the absence of any conspicuous structural defects may indicate the classical nature of the resulting pressure-induced spin liquid, an observation paralleled to the increase in the nearest-neighbor off-diagonal exchange Gamma under pressure.
Title:
Dynamically enhanced magnetic incommensurability: Effects of local dynamics on nonlocal spin correlations in a strongly correlated metal
Authors:
Vilardi, D; Taranto, C; Metzner, W Author Full Names: Vilardi, Demetrio; Taranto, Ciro; Metzner, Walter
Source:
PHYSICAL REVIEW B, 97 (23):10.1103/PhysRevR.97.235110 JUN 7 2018
Abstract:
We compute the spin susceptibility of the two-dimensional Hubbard model away from half-filling, and analyze the impact of frequency-dependent vertex corrections as obtained from the dynamical mean field theory (DMFT). We find that the local dynamics captured by the DMFT vertex strongly affects nonlocal spin correlations, and thus the momentum dependence of the spin susceptibility. While the widely used random-phase approximation yields commensurate Neel-type antiferromagnetism as the dominant instability over a wide doping range, the vertex corrections favor incommensurate ordering wave vectors away from(pi,pi). Our results indicate that the connection between the magnetic ordering wave vector and the Fermi surface geometry, familiar for weakly interacting systems, can hold in a strongly correlated metal, too.
Title:
Structural phase transitions in YPtGe2 and GdPtGe2
Authors:
Janka, O; Hoffmann, RD; Heying, B; Pottgen, R Author Full Names: Janka, Oliver; Hoffmann, Rolf-Dieter; Heying, Birgit; Poettgen, Rainer
Source:
DALTON TRANSACTIONS, 47 (17):6075-6088; 10.1039/c8dt00815a MAY 7 2018
Abstract:
The germanides YPtGe2 and GdPtGe2 were synthesized from REGe2 precursor compounds and platinum by arc-melting and their structures were studied on the basis of temperature-dependent single crystal X-ray diffraction data. At room temperature both germanides adopt the orthorhombic YIrGe2 type structure, space group Immm, with enhanced U-11 displacement parameters for the Ge1 atoms. Below 174 and 145 K, respectively, satellite reflections emerge in the diffraction patterns, giving rise to modulations. The low-temperature structures were refined in the superspace group Pnnn(1/2,1/2,gamma)qq0 (48.1.11.3). The structural phase transition is also evident in the magnetic susceptibility, specific heat and resistivity data. The high-and low-temperature modifications are discussed on the basis of a group-subgroup scheme.

Update: 20-Jun-2018

Title:
Preparation and nanoscopic plastic deformation of toughened Al-Cu-Fe-based quasicrystal/vanadium multilayered coatings
Authors:
Chang, SY; Chen, BJ; Hsiao, YT; Wang, DS; Chen, TS; Leu, MS; Lai, HJ Author Full Names: Chang, Shou-Yi; Chen, Bo-Jien; Hsiao, Yu-Ting; Wang, Ding-Shiang; Chen, Tai-Sheng; Leu, Ming-Sheng; Lai, Hong-Jen
Source:
MATERIALS CHEMISTRY AND PHYSICS, 213 277-284; 10.1016/j.matchemphys.2018.04.045 JUL 1 2018
Abstract:
Ductile vanadium layers were alternately deposited with brittle aluminum-copper-iron-based quasicrystal-alloy layers to form multilayered coatings. The in-situ transmission electron microscopic observations of nanopillar compression revealed that the as-deposited single-layered amorphous aluminum-copper-iron alloy slightly deformed via shear banding. After annealing at 800 degrees C, brittle quasicrystal and intermetallic compounds were formed, so the single-layered coating cracked and peeled. In comparison, the multilayered coatings were effectively toughened. The multilayered nanopillars plastically deformed via dislocation activities and were work hardened owing to confined dislocation gliding. The as-deposited multilayered structure (amorphous alloy/crystalline vanadium) had a low 10% flow stress of 1.72 GPa, while the annealed multilayered structure (quasicrystal/vanadium) presented a high flow stress of 2.58 GPa owing to quasicrystal strengthening. Dislocation clusters were in-situ observed to glide laterally in the crystalline vanadium layers and move vertically through the vanadium and quasicrystal layers, yielding an improved plasticity. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Growth of two-dimensional decagonal colloidal quasicrystals
Authors:
Martinsons, M; Schmiedeberg, M Author Full Names: Martinsons, M.; Schmiedeberg, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 30 (25):10.1088/1361-648X/aac503 JUN 27 2018
Abstract:
The growth of quasicrystals, i.e. structures with long-range positional order but no periodic translational symmetry, is more complex than the growth of periodic crystals. By employing Brownian dynamics simulations in two dimensions for colloidal particles that interact according to an isotropic pair potential with two incommensurate lengths, we study the growth of quasicrystalline structures by sequentially depositing particles at their surface. We quantify the occurrence of quasicrystalline order as a function of the temperature and the rate of added particles. In addition, we explore defects like local triangular order or gaps within the quasicrystalline structure. Furthermore, we analyze the shapes of the surfaces in grown structures which tend to build straight lines along the symmetry axes of the quasicrystal. Finally, we identify phasonic flips which are rearrangements of the particles due to additional degrees of freedom. The number of phasonic flips decreases with the distance to the surface.
Title:
Identification of a secondary phase Ga2O3(ZnO)m in Ga-doped ZnO thermoelectric materials by a (3+1)-dimensional superspace model
Authors:
Michiue, Y; Mori, T Author Full Names: Michiue, Yuichi; Mori, Takao
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 51 924-927; 10.1107/S1600576718004119 3 JUN 2018
Abstract:
A unified structure model for the homologous compounds Ga2O3(ZnO)(m) in (3 + 1)-dimensional superspace was modified by refinements for samples of Ga2O3:ZnO = 1:n (n = 15, 23, 28, 33, 38). The first-order sine terms in the modulation functions decreased with increasing phase index m. The diffraction intensities of the thermoelectric material Ga2O3:ZnO = 1:98 were best fitted by a two-phase model containing the wurtzite structure (Ga-doped ZnO) and the homologous compound Ga2O3(ZnO)(s), where s = 38.
Title:
Commensurate versus incommensurate charge ordering near the superconducting dome in Ir1-xPtxTe2 revealed by resonant x-ray scattering
Authors:
Takubo, K; Yamamoto, K; Hirata, Y; Wadati, H; Mizokawa, T; Sutarto, R; He, F; Ishii, K; Yamasaki, Y; Nakao, H; Murakami, Y; Matsuo, G; Ishii, H; Kobayashi, M; Kudo, K; Nohara, M Author Full Names: Takubo, K.; Yamamoto, K.; Hirata, Y.; Wadati, H.; Mizokawa, T.; Sutarto, R.; He, F.; Ishii, K.; Yamasaki, Y.; Nakao, H.; Murakami, Y.; Matsuo, G.; Ishii, H.; Kobayashi, M.; Kudo, K.; Nohara, M.
Source:
PHYSICAL REVIEW B, 97 (20):10.1103/PhysRevB.97.205142 MAY 31 2018
Abstract:
The electronic-structural modulations of Ir1-xPtxTe2 (0 <= x <= 0.12) have been examined by resonant elastic x-ray scattering (REXS) and resonant inelastic x-ray scattering (RIXS) techniques at both the Ir and Te edges. Charge-density-wave-like superstructures with wave vectors of Q = (1/5 0 - 1/5), (1/8 0 - 1/8), and (1/6 0 - 1/6) are observed on the same sample of IrTe2 at the lowest temperature, the patterns of which are controlled by the cooling speeds. In contrast, superstructures around Q = (1/5 0 - 1/5) are observed for doped samples (0.02 <= x <= 0.05). The superstructure reflections persist to higher Pt substitution than previously assumed, demonstrating that a charge-density wave (CDW) can coexist with superconductivity. The analysis of the energy-dependent REXS and RIXS line shape reveals the importance of the Te 5p state rather than the Ir 5d states in the formation of the spatial modulation of these systems. The phase diagram reexamined in this work suggests that the CDW incommensurability may correlate with the emergence of superconducting states such as CuxTiSe2 and LixTaS2.
Title:
Dipole-dipole interactions and incommensurate order in perovskite structures
Authors:
Burkovsky, RG Author Full Names: Burkovsky, R. G.
Source:
PHYSICAL REVIEW B, 97 (18):10.1103/PhysRevB.97.184109 MAY 31 2018
Abstract:
Dipole-dipole (DD) interactions are known to play an important role in conditioning ferroelectricity in ABO(3) perovskite crystals. Their possible role in conditioning nonferroelectric (inhomogeneous) cation ordering is presently unexplored. I analyze the energy of DD interactions in perovskite structure for different inhomogeneous spatial patterns of electric dipoles localized at the lattice sites. I show that DD interactions can favor inhomogeneous ordering when other terms of the Hamiltonian allow large total polarizability of A sites, comparably large total polarizability of oxygen sites in A-O planes, and relatively weak total polarizability of oxygen sites in the B-O direction. These conditions are naturally expected in PbZrO3 crystals, for which the reason behind antiferroelectric and incommensurate inhomogeneous ordering is currently being debated.
Title:
Magnetic structure of Ho0.5Y0.5Mn6Sn6 compound studied by powder neutron diffraction
Authors:
Li, XY; Peng, LC; He, LH; Zhang, SY; Yao, JL; Zhang, Y; Wang, FW Author Full Names: Li, X-Y.; Peng, L-C.; He, L-H.; Zhang, S-Y.; Yao, J-L.; Zhang, Y.; Wang, F-W.
Source:
JOURNAL OF APPLIED PHYSICS, 123 (20):10.1063/1.5029707 MAY 28 2018
Abstract:
The crystallographic and magnetic structures of the HfFe6Ge6-type compound Ho0.5Y0.5Mn6Sn6 have been studied by powder neutron diffraction and in-situ Lorentz transmission electron microscopy. Besides the nonlinear thermal expansion of lattice parameters, an incommensurate conical spiral magnetic structure was determined in the temperature interval of 2-340 K. A spin reorientation transition has been observed from 50 to 300 K, where the alignment of the c-axis component of magnetic moments of the Ho sublattice and the Mn sublattice transfers from ferrimagnetic to ferromagnetic. Published by AIP Publishing.

Update: 13-Jun-2018

Title:
A study on spherical particles in Al65Cu20Fe15 alloy prepared by arc melting
Authors:
Li, CF; Carey, C; Li, DQ; Caputo, M; Bouch, R; Hampikian, H Author Full Names: Li, Chunfei; Carey, Christopher; Li, Dingqiang; Caputo, Matthew; Bouch, Ronald; Hampikian, Helen
Source:
MATERIALS CHARACTERIZATION, 140 162-171; 10.1016/j.matchar.2018.03.050 JUN 2018
Abstract:
Al-Cu-Fe alloys are important due to reports that stable icosahedral quasicrystalline phase with composition in the vicinity of Al65Cu20Fe15 can be prepared. However, it has been widely reported that the as-prepared alloy, very often by arc-melting, is porous, consisting of particles with different morphologies. Among these, one type of particles of a spherical shape is considered as pure cubic beta phase in previous reports. In this research, this spherical particle was studied using a Scanning Electron Microscope, Energy Dispersive X-ray Spectroscopy, Transmission Electron Microscope, and Electron Diffraction. It was found that the particles are not single phase, consisting of icosahedral quasicrystalline grains embedded inside single crystal matrix of tau phase. Additionally, there are places where the tau phase appears to have out-most layer enriched in Cu. The surface of the particles is faceted and the facets can be classified to three types according to their detailed structures. A close examination and analysis led to the conclusion that these three types are parallel to the atomic planes of {1 1 0}, {1 1 1}, and {1 0 0}, respectively. A model for the spherical particle formation is suggested and the reasons for the formation of facets are discussed. This report is valuable in clarifying some discrepancies in previous reports, and in understanding the phase development in an Al-Cu-Fe alloy system.

Update: 6-Jun-2018

Title:
Coexistence of charge density wave and incommensurate antiferromagnetism in the cubic phase of DyGe2.85 synthesised under high pressure
Authors:
Salamatin, DA; Sidorov, VA; Kichanov, SE; Velichkov, A; Salamatin, AV; Fomicheva, LN; Kozlenko, DP; Nikolaev, AV; Menzel, D; Budzynski, M; Tsvyashchenko, AV Author Full Names: Salamatin, D. A.; Sidorov, V. A.; Kichanov, S. E.; Velichkov, A.; Salamatin, A. V.; Fomicheva, L. N.; Kozlenko, D. P.; Nikolaev, A. V.; Menzel, D.; Budzynski, M.; Tsvyashchenko, A. V.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 755 10-14; 10.1016/j.jallcom.2018.04.319 JUL 30 2018
Abstract:
A novel metastable phase of DyGe2.85 synthesised in the AuCu3-structure under high pressure, has been studied by means of the magnetic susceptibility and electrical resistivity measurements (under the pressure P <= 3.1 GPa), neutron powder diffraction and time-differential gamma-gamma perturbed angular correlations (TDPAC) using Cd-111 nuclear probes. Two distinct phase transitions have been found in this compound as the temperature is lowered. We assign the first transition occurring at the temperature T-CDW = 80 K with charge density wave formation and the second transition at T-N approximate to 18 K with an antiferromagnetic spiral ordering of Dy magnetic moments, and discuss a close relationship between them. (C) 2018 Elsevier B.V. All rights reserved.
Title:
PERFECTLY ORDERED QUASICRYSTALS AND THE LITTLEWOOD CONJECTURE
Authors:
Haynes, A; Koivusalo, H; Walton, J Author Full Names: Haynes, Alan; Koivusalo, Henna; Walton, James
Source:
TRANSACTIONS OF THE AMERICAN MATHEMATICAL SOCIETY, 370 (7):4975-4992; 10.1090/tran/7136 JUL 2018
Abstract:
Linearly repetitive cut and project sets are mathematical models for perfectly ordered quasicrystals. In a previous paper we presented a characterization of linearly repetitive cut and project sets. In this paper we extend the classical definition of linear repetitivity to try to discover whether or not there is a natural class of cut and project sets which are models for quasicrystals which are better than 'perfectly ordered'. In the positive direction, we demonstrate an uncountable collection of such sets (in fact, a collection with large Hausdorff dimension) for every choice of dimension of the physical space. On the other hand, we show that, for many natural versions of the problems under consideration, the existence of these sets turns out to be equivalent to the negation of a well-known open problem in Diophantine approximation, the Littlewood conjecture.
Title:
Improved electrochemical hydrogen storage capacity of Ti45Zr38Ni17 quasicrystal by addition of ZrH2
Authors:
Zhao, JX; Zhai, XJ; Tao, X; Li, Z; Wang, QS; Liu, WQ; Wang, LM Author Full Names: Zhao, Jianxun; Zhai, Xiaojie; Tao, Xing; Li, Zhe; Wang, Qingshuang; Liu, Wanqiang; Wang, Limin
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 34 (6):995-998; 10.1016/j.jmst.2017.10.006 JUN 2018
Abstract:
Ti45Zr38Ni17 + xZrH(2) (x = 5, 10, 15 and 20 wt%) composite materials are produced by ball milling for 20 min. The results of XRD measurement show that the composite materials contain icosahedral quasicrystal phase (I-phase), FCC phase with a Ti2Ni type crystal and C14 Laves phase. After adding ZrH2, the composite materials include not only the individual phases mentioned above, but also the ZrH phase. These composite materials are used as the negative electrode material of the nickel-metal hydride batteries. The electrochemical hydrogen storage characteristics of the material after adding ZrH is investigated. The Ti45Zr38Ni17 + xZrH(2) (x = 5, 10, 15 and 20 wt%) composite material has reached the maximum discharge capacity (83.2 mA h/g) when x equals 10. This maximum discharge capacity is much higher than that of Ti(45)Zr(38)Ni(17 )alloy without ZrH. After adding ZrH2, the high-rate discharge ability and the cycling stability are enhanced simultaneously. The improvement of the electrochemical properties can be attributed to the synergistic effects of ZrH2, and the synergistic effects in the composite electrodes are probably attributed to the entry of most of hydrogen atoms from weakly bond strength of the Zr-H to the I-phase structure in electrochemical reaction. (C) 2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
Title:
Epitaxial growth of a metastable icosahedral quasicrystal on a stable icosahedral quasicrystal substrate
Authors:
Leskovar, B; Sturm, S; Samardzija, Z; Ambrozic, B; Markoli, B; Naglic, I Author Full Names: Leskovar, Blaz; Sturm, Saso; Samardzija, Zoran; Ambrozic, Bojan; Markoli, Bostjan; Naglic, Iztok
Source:
SCRIPTA MATERIALIA, 150 92-95; 10.1016/j.scriptamat.2018.03.014 JUN 2018
Abstract:
This study confirms that the stable icosahedral quasicrystal (iQc) phase Al65Cu20Fe15(iQc-AlCuFe) can serve as a substrate for the nucleation of the metastable iQc-AlMnSi phase formed in rapidly solidified Al-Mn-Si alloys. The results reveal that a continuous, thin layer of the metastable iQc-AlMnSi phase can be formed on a stable iQc-AlCuFe particle. Electron backscatter diffraction patterns and selected-area electron diffraction patterns confirmed that epitaxy exists between the stable and the metastable iQc phases. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Magnetic field induced evolution of intertwined orders in the Kitaev magnet beta-Li2IrO3
Authors:
Rousochatzakis, I; Perkins, NB Author Full Names: Rousochatzakis, Ioannis; Perkins, Natalia B.
Source:
PHYSICAL REVIEW B, 97 (17):10.1103/PhysRevB.97.174423 MAY 24 2018
Abstract:
Recent scattering experiments in the 3D Kitaev magnet beta-Li2IrO3 have shown that a relatively weak magnetic field along the crystallographic b axis drives the system from its incommensurate counter-rotating order to a correlated magnet, with a significant uniform 'zigzag' component superimposing the magnetization along the field. Here it is shown that the zigzag order is not emerging from its linear coupling to the field (via a staggered, off-diagonal element of the g tensor) but from its intertwining with the incommensurate order and the longitudinal magnetization. The emerging picture explains all qualitative experimental findings at zero and finite fields, including the rapid decline of the incommensurate order with field and the so-called intensity sum rule. The latter are shown to be independent signatures of the smallness of the Heisenberg exchange J, compared to the Kitaev coupling K and the off-diagonal anisotropy Gamma. Remarkably, in the regime of interest, the field H* at which the incommensurate component vanishes, depends essentially only on J, which allows us to extract an estimate of J similar or equal to 4 K from reported measurements of H*. We also comment on recent experiments in pressurized beta-Li2IrO3 and conclude that J decreases with pressure.
Title:
Polarized neutron scattering study of the multiple order parameter system NdB4
Authors:
Metoki, N; Yamauchi, H; Matsuda, M; Fernandez-Baca, JA; Watanuki, R; Hagihala, M Author Full Names: Metoki, N.; Yamauchi, H.; Matsuda, M.; Fernandez-Baca, J. A.; Watanuki, R.; Hagihala, M.
Source:
PHYSICAL REVIEW B, 97 (17):10.1103.PhysRevB.97.174416 MAY 17 2018
Abstract:
Neutron polarization analysis has been carried out in order to clarify the magnetic structures of multiple order parameter f-electron system NdB4. We confirmed the noncollinear "all-in all-out" structure (Gamma(4)) of the in-plane moment, which is in good agreement with our previous neutron powder diffraction study. We found that the magnetic moment along the c-axis m(c) showed diagonally antiferromagnetic structure (Gamma(10)), inconsistent with previously reported "vortex" structure (Gamma(2)). The microscopic mixture of these two structures with (q) over right arrow 0 = (0,0,0) appears in phase II and remains stable in phases III and IV, where an incommensurate modulation coexists. The unusual magnetic ordering is phenomenologically understood via Landau theory with the primary order parameter Gamma(4) coupled with higher-order secondary order parameter Gamma(10). The magnetic moments were estimated to be 1.8 +/- 0.2 and 0.2 +/- 0.05 mu B at T = 7.5 K for Gamma(4) and Gamma(10), respectively. We also found along-penod incommensurate modulation of the (q) over right arrow1 = (0,0,1 /2) antiferromagnetic structure of m(c) with the propagation (q) over right arrow (s1)= (0.14, 0.14, 0.1) and <(q) over right arrow>(s2) = (0.2,0,0.1) in phase III and IV, respectively. The amplitude of sinusoidal modulation was about m(c) = 1.0 +/- 0.2 mu B at T=1.5 K. The local (0,0,1 /2) structure consists of in-plane ferromagnetic and out-of-plane antiferromagnetic coupling of m(c), opposite to the coexisting Gamma(10). The m(c) of Gamma(10) is significantly enhanced up to 0.6 mu B at T=1.5 K, which is accompanied by the incommensurate modulations. The Landau phenomenological approach indicates that the higher-order magnetic and/or multipole interactions based on the pseudoquartet f-electron state play important roles.
Title:
Structural and electronic properties of the alkali metal incommensurate phases
Authors:
Woolman, G; Robinson, VN; Marques, M; Loa, I; Ackland, GJ; Hermann, A Author Full Names: Woolman, Gavin; Robinson, Victor Naden; Marques, Miriam; Loa, Ingo; Ackland, Graeme J.; Hermann, Andreas
Source:
PHYSICAL REVIEW MATERIALS, 2 (5):10.1103/PhysRevMaterials.2.053604 MAY 11 2018
Abstract:
Under pressure, the alkali elements sodium, potassium, and rubidium adopt nonperiodic structures based on two incommensurate interpenetrating lattices. While all elements form the same "host" lattice, their "guest" lattices are all distinct. The physical mechanism that stabilizes these phases is not known, and detailed calculations are challenging due to the incommensurability of the lattices. Using a series of commensurate approximant structures, we tackle this issue using density functional theory calculations. In Na and K, the calculations prove accurate enough to reproduce not only the stability of the host-guest phases, but also the complicated pressure dependence of the host-guest ratio and the two guest-lattice transitions. We find Rb-IV to be metastable at all pressures, and suggest it is a high-temperature phase. The electronic structure of these materials is unique: they exhibit two distinct, coexisting types of electride behavior, with both fully localized pseudo anions and electrons localized in 1D wells in the host lattice, leading to low conductivity. While all phases feature pseudogaps in the electronic density of states, the perturbative free-electron picture applies to Na, but not to K and Rb, due to significant d-orbital population in the latter.

Update: 23-May-2018

Title:
Dzyaloshinskii-Moriya interaction and magnetic anisotropies in Uranium compounds
Authors:
Sandratskii, LM Author Full Names: Sandratskii, L. M.
Source:
PHYSICA B-CONDENSED MATTER, 536 512-515; 10.1016/j.physb.2017.11.014 MAY 1 2018
Abstract:
We report on the first-principles study of complex noncollinear magnetic structures in Uranium compounds. We contrast two cases. The first is the periodic magnetic structure of U2Pd2In with exactly orthogonal atomic moments, the second is an incommensurate plane spiral structure of UPtGe where the angle between atomic moments of nearest neighbors is also close to 90 degrees. We demonstrate that the hierarchy of magnetic interactions leading to the formation of the magnetic structure is opposite in the two cases. In U2Pd2In, the magnetic anisotropy plays the leading role, followed by the Dzyaloshinskii-Moriya interaction (DMI) interaction specifying the chirality of the structure. Here, the interatomic exchange interaction does not play important role. In UPtGe the hierarchy of the interactions is opposite. The leading interaction is the interatomic exchange interaction responsible for the formation of the incommensurate spiral structure followed by the DMI responsible for the selected chirality of the helix. The magnetic anisotropy is very weak that is a prerequisite for keeping the distortion of the helical structure weak.
Title:
Magnetic excitations in the orbital disordered phase of MnV2O4
Authors:
Matsuura, K; Sagayama, H; Uehara, A; Nii, Y; Kajimoto, R; Kamazawa, K; Ikeuchi, K; Ji, S; Abe, N; Arima, TH Author Full Names: Matsuura, Keisuke; Sagayama, Hajime; Uehara, Amane; Nii, Yoichi; Kajimoto, Ryoichi; Kamazawa, Kazuya; Ikeuchi, Kazuhiko; Ji, Sungdae; Abe, Nobuyuki; Arima, Taka-hisa
Source:
PHYSICA B-CONDENSED MATTER, 536 372-376; 10.1016/j.physb.2017.09.085 MAY 1 2018
Abstract:
We have investigated the temperature dependence of magnetic dynamics in a spinel-type vanadium oxide MnV2O4 by inelastic neutron scattering. The scattering intensity of excitation around 20 meV disappears in the collinear intermediate-temperature cubic-ferrimagnetic phase, which reveals that this excitation should be peculiar to the orbital ordered phase. We have found a weakly dispersive mode emergent from a non-integer wavevector (1.4,1.4,0) at 56 K, which lies in the cubic-ferrimagnetic phase between non-coplanar ferrimagnetic and paramagnetic phases. This indicates that the probable presence of an incommensurate instability in the simple collinear structure.
Title:
Magnetic and thermodynamic studies on the charge and spin ordering in the highly-doped La2-xSrxCoO4
Authors:
Yoshida, M; Ueta, D; Ikeda, Y; Yokoo, T; Itoh, S; Yoshizawa, H Author Full Names: Yoshida, Masahiro; Ueta, Daichi; Ikeda, Yoichi; Yokoo, Tetsuya; Itoh, Shinichi; Yoshizawa, Hideki
Source:
PHYSICA B-CONDENSED MATTER, 536 338-341; 10.1016/j.physb.2017.10.081 MAY 1 2018
Abstract:
We report magnetic studies on the charge and spin ordering in La2-xSrxCoO4 for x = 1/3, 0.60, and 0.75. The magnetic susceptibility displays a clear cusp which we attribute to a spin glass freezing transition in all three compositions stduied. The behaviors of the evaluated effective magnetic moment and Curie-Weiss temperature indicate that the antiferromagnetic (AFM) interaction among Co2+ ions surrounded by the non-magnetic Co3+ weakens with increasing the doping concentration x. In addition, we have found that the incommensurate AFM short range order is frozen at T-g which is further below the onset temperature TIC of the neutron intensity of the incommensurate AFM correlation.
Title:
Detailed study of the structure of the low-energy magnetic excitations in overdoped La1.75Sr0.25CuO4
Authors:
Ikeuchi, K; Kikuchi, T; Nakajima, K; Kajimoto, R; Wakimoto, S; Fujita, M Author Full Names: Ikeuchi, Kazuhiko; Kikuchi, Tatsuya; Nakajima, Kenji; Kajimoto, Ryoichi; Wakimoto, Shuichi; Fujita, Masaki
Source:
PHYSICA B-CONDENSED MATTER, 536 717-719; 10.1016/j.physb.2017.11.022 MAY 1 2018
Abstract:
To examine the detailed structure of low-energy magnetic excitations in a high-transition-temperature superconducting cuprate with heavily hole-doping, we performed inelastic neutron scattering experiments on La1.75Sr0.25CuO4. We observed clear dispersion relations of the previously reported incommensurate (IC) magnetic correlations at Qtet = (0.5 +/- d, 0.5)/(0.5, 0.5 +/- delta) [1]. In addition, we show the emergence of continuum magnetic excitations with a ring shape centered at G point Q(tet) = (0.5, 0.5) in a constant energy spectrum at Gamma = 50K. The radius of the ring (r = 0.109) is smaller than the incommensurability (delta = 0.118). This suggests that the origin of the ring-like excitations is different from that of the IC magnetic correlations, and the low-energy magnetic excitations of the La2-xSrxCuO4 system are inherently composed of these two kinds of excitations.
Title:
Fluctuation effects at the onset of the 2k(F) density wave order with one pair of hot spots in two-dimensional metals
Authors:
Sykora, J; Holder, T; Metzner, W Author Full Names: Sykora, Jachym; Holder, Tobias; Metzner, Walter
Source:
PHYSICAL REVIEW B, 97 (15):10.1103/PhysRevB.97.155159 APR 30 2018
Abstract:
We analyze quantum fluctuation effects at the onset of charge or spin density wave order in two-dimensional metals with an incommensurate 2k(F) wave vector connecting a single pair of hot spots on the Fermi surface. We compute the momentum and frequency dependence of the fermion self-energy near the hot spots to leading order in a fluctuation expansion (one loop). Non-Fermi liquid behavior with anomalous frequency scaling and a vanishing quasiparticle weight is obtained. The momentum dependence yields a divergent renormalization of the Fermi velocity and a flattening of the Fermi surface near the hot spots. Going beyond the leading-order calculation, we find that the one-loop result is not self-consistent. We show that any momentum-independent self-energy with a non-Fermi liquid frequency exponent wipes out the peak of the polarization function at the 2k(F) wave vector, and thus destroys the mechanism favoring 2k(F) density waves over those with generic wave vectors. However, a 2k(F) density wave quantum critical point might survive in presence of a sufficiently flat renormalized Fermi surface.
Title:
Refinement of the Modulated Structures of Pb-Free and Pb-Doped Bi-2223 HTSC
Authors:
Shcherban, O; Akselrud, L; Giannini, E; Gladyshevskii, R Author Full Names: Shcherban, O.; Akselrud, L.; Giannini, E.; Gladyshevskii, R.
Source:
ACTA PHYSICA POLONICA A, 133 (4):1027-1029; 10.12693/APhysPolA.133.1027 APR 2018
Abstract:
The incommensurate modulated structures of Pb-free and Pb-doped Bi-2223 phases were refined on single crystal X-ray diffraction data.

Update: 16-May-2018

Title:
First-principles study of giant thermoelectric power in incommensurate TlInSe2
Authors:
Ishikawa, M; Nakayama, T; Wakita, K; Shim, YG; Mamedov, N Author Full Names: Ishikawa, M.; Nakayama, T.; Wakita, K.; Shim, Y. G.; Mamedov, N.
Source:
JOURNAL OF APPLIED PHYSICS, 123 (16):10.1063/1.5011337 APR 28 2018
Abstract:
Ternary thallium compound TlInSe2 exhibits a giant Seebeck effect below around 410 K, where Tl atoms form one dimensional incommensurate (IC) arrays. To clarify the origin of large thermoelectric power in the IC phase, the electronic properties of Tl-atom super-structured TlInSe2 were studied using the first-principles calculations. It was shown that the super-structures induce strong binding states between Se-p orbitals in the nearest neighboring layers and produce large density of states near lower conduction bands, which might be one of the origins to produce large thermoelectric power. Published by AIP Publishing.
Title:
The Effect of Doping on the Corrosion Behavior of Quasi-Crystalline Alloys in the Al-Cu-Fe-Cr System
Authors:
Chugunov, DB; Klyuchagina, AN; Meshkov, LL; Osipov, AK Author Full Names: Chugunov, D. B.; Klyuchagina, A. N.; Meshkov, L. L.; Osipov, A. K.
Source:
PROTECTION OF METALS AND PHYSICAL CHEMISTRY OF SURFACES, 54 (2):301-307; 10.1134/S2070205118020041 MAR 2018
Abstract:
The electrochemical behavior of five alloys of variable compositions in the Al65Cu25Fe10-N... Cr (N...) system in dependence on the number of QC phases in acidic and alkaline media has been investigated by the potentiodynamic method. It has been established that the samples' corrosion stabilities increase along with the increase of the solution pH. Higher stability was manifested by alloys with a predominant quasi-crystalline (dexagonal and icosahedral) structural component.

Update: 9-May-2018

Title:
Field-induced magnetic phase transitions and metastable states in Tb3Ni
Authors:
Gubkin, AF; Wu, LS; Nikitin, SE; Suslov, AV; Podlesnyak, A; Prokhnenko, O; Prokes, K; Yokaichiya, F; Keller, L; Baranov, NV Author Full Names: Gubkin, A. F.; Wu, L. S.; Nikitin, S. E.; Suslov, A. V.; Podlesnyak, A.; Prokhnenko, O.; Prokes, K.; Yokaichiya, F.; Keller, L.; Baranov, N. V.
Source:
PHYSICAL REVIEW B, 97 (13):10.1103/PhysRevB.97.134425 APR 26 2018
Abstract:
In this paper we report the detailed study of magnetic phase diagrams, low-temperature magnetic structures, and the magnetic field effect on the electrical resistivity of the binary intermetallic compound Tb3Ni. The incommensurate magnetic structure of the spin-density-wave type described with magnetic superspace group P112(1)/a1'(ab0)0ss and propagation vector k(IC) = [0.506, 0.299,0] was found to emerge just below Neel temperature T-N = 61 K. Further cooling below 58 K results in the appearance of multicomponent magnetic states: (i) a combination of k(1) = [1/2, 1/2, 0] and k(IC) in the temperature range 51 < T < 58 K; (ii) a mixed magnetic state of k(IC), k(1), and k(2) = [1/2, 1/4, 0] with the partially locked-in incommensurate component in the temperature range 48 < T < 51 K; and (iii) a low-temperature magnetic structure that is described by the intersection of two isotropy subgroups associated with the irreducible representations of two coupled primary order parameters (OPs) k(2) = [1/2, 1/4, 0] and k(3) = [1/2, 1/3, 0] and involves irreducible representations of the secondary OPs k(1) = [1/2, 1/2, 0] and k(4) = [1/2, 0, 0] below 48 K. An external magnetic field suppresses the complex low-temperature antiferromagnetic states and induces metamagnetic transitions towards a forced ferromagnetic state that are accompanied by a substantial magnetoresistance effect due to the magnetic superzone effect. The forced ferromagnetic state induced after application of an external magnetic field along the b and c crystallographic axes was found to be irreversible below 3 and 8 K, respectively.
Title:
Improved electrochemical hydrogen storage performance of Ti49Zr26Ni25 quasicrystal alloy by doping with mesoporous alpha-Fe2O3 particles
Authors:
Liu, H; Zhai, XJ; Li, Z; Tao, X; Liu, WQ; Zhao, JX Author Full Names: Liu, Heng; Zhai, Xiaojie; Li, Zhe; Tao, Xing; Liu, Wanqiang; Zhao, Jianxun
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 43 (15):7447-7455; 10.1016/j.ijhydene.2018.02.149 APR 12 2018
Abstract:
A Ti49Zr26Ni25 quasicrystal alloy was prepared by mechanical alloying and subsequent annealing. Mesoporous alpha-Fe2O3 particles were obtained via a hydro-thermal procedure using chitosan as the template. Composites of Ti49Zr26Ni25 mixed with different amounts of mesoporous alpha-Fe2O3 were synthesized to enhance the electrochemical properties of Ti49Zr26Ni25. The structural characteristics of the alloy and composites were investigated using XRD, SEM, TEM and BET analysis. The electrochemical properties of the composite electrodes were tested using a three-electrode battery system at room temperature. The discharge capacities for the composites were higher than those for the Ti49Zr26Ni25 alloy and reached a maximum (259.6 mAh/g) for 5% additive content of alpha-Fe2O3. Moreover, the composites showed enhanced high-rate dischargeability. The capacity decay rate and charge-transfer resistance decreased after alpha-Fe2O3 loading. The preferable performance of the composite alloys may be attributed to the doping of mesoporous alpha-Fe2O3, which may play a catalytic effect in the kinetics of the electrochemical reactions. The large surface area and mesoporous structure of alpha-Fe2O3 may also be advantageous for rapid transmission of hydrogen in the interior of the alloy, thus improving the discharge capacity of the alloy electrode. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Update: 2-May-2018

Title:
The Tetrachloridoaurates(III) of Zinc(II) and Cadmium(II)
Authors:
Landvogt, C; Beck, J Author Full Names: Landvogt, Christian; Beck, Johannes
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 644 (7):391-396; 10.1002/zaac.201700455 APR 17 2018
Abstract:
The first salt-like compounds of dications with [AuCl4](-) anions are reported. The compounds Zn[AuCl4](2)(AuCl3)(1.115) (1) and Cd[AuCl4](2) (2) are obtained from reactions of MCl2 (M = Zn, Cd) and elemental gold in liquid chlorine at ambient temperature under autogenous pressure and subsequent annealing at 230 degrees C. The structure of 1 represents an incommensurately modulated composite [superspace group C2/c(0)0s] built of two subsystems. The first subsystem contains chains of zinc(II) tetrachloridoaurate(III), which feature a slightly distorted octahedral coordination of Zn and can be described by the Niggli formula (1){Zn[AuCl4](1/1)[AuCl4](2/2)}. The second subsystem consists of Au2Cl6 molecules, which are located in channels built up by the first subsystem. The structural parameters of the hosted Au2Cl6 molecules show only small deviations from neat AuCl3. The crystal structure of Cd[AuCl4](2) (2) consists of chains built of Cd2+ ions coordinated by bridging [AuCl4](-) anions and alternating Cd-Au sequence. Cd has a distorted octahedral coordination environment.

Update: 25-Apr-2018

Title:
Large-sized quasi-crystals with continuously adjustable compositions
Authors:
Li, ZJ; Zhao, LR; Pan, SP; Fan, CZ; Qiang, JB; Dong, C; Wang, LM Author Full Names: Li, Zijing; Zhao, Linran; Pan, Shaopeng; Fan, Changzeng; Qiang, Jianbing; Dong, Chuang; Wang, Li-Min
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 746 356-360; 10.1016/j.jallcom.2018.02.341 MAY 25 2018
Abstract:
The quasi-crystal-forming alloys with adjustable compositions were prepared by element-addition to a pre-existing pure quasi-crystalline system. The protocol alloy Zr40Ti40Ni20 was chosen as the parent alloy, and beryllium was used as the additive element. The quasi-crystal forming ability was found to be enhanced with Be content within a wide composition range of (Zr40Ti40Ni20)(100-x)Be-x (0 <= x <= 16). A maximum size of up to 10mm in diameter of pure quasi-crystalline rod was attained at a composition of (Zr40Ti40Ni20)(84)Be-16. Structural analyses show that Be-addition continuously reduces the interplanar spacing. The mechanism of the enhanced quasi-crystal forming ability was also discussed. (c) 2018 Elsevier B.V. All rights reserved.
Title:
Effects of crystalline electronic field and onsite interorbital interaction in Yb-based quasicrystal and approximant crystal
Authors:
Watanabe, S; Miyake, K Author Full Names: Watanabe, Shinji; Miyake, Kazumasa
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 30 (18):10.1088/1361-648X/aab817 MAY 10 2018
Abstract:
To get an insight into a new type of quantum critical phenomena recently discovered in the quasicrystal Yb15Al34Au51 and approximant crystal (AC) Yb14Al35Au51 under pressure, we discuss the property of the crystalline electronic field (CEF) at Yb in the AC and show that uneven CEF levels at each Yb site can appear because of the Al/Au mixed sites. Then we construct the minimal model for the electronic state on the AC by introducing the onsite Coulomb repulsion between the 4f and 5d orbitals at Yb. Numerical calculations for the ground state shows that the lattice constant dependence of the Yb valence well explains the recent measurement done by systematic substitution of elements of Al and Au in the quasicrystal and AC, where the quasicrystal Yb15Al34Au51 is just located at the point from where the Yb-valence starts to change drastically. Our calculation convincingly demonstrates that this is indeed the evidence that this material is just located at the quantum critical point of the Yb-valence transition.
Title:
Partially-devitrified icosahedral quasicrystalline phase in Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 amorphous alloys with near equi-atomic compositions
Authors:
Takeuchi, A; Amiya, K; Yubuta, K Author Full Names: Takeuchi, A.; Amiya, K.; Yubuta, K.
Source:
MATERIALS CHEMISTRY AND PHYSICS, 210 245-250; SI 10.1016/j.matchemphys.2017.10.057 MAY 1 2018
Abstract:
Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 alloys were investigated for their possibility to be formed into a high-entropy alloy (HEA) with a quasicrystalline (QC) structure that contains an icosahedral-(I-) phase. The melt-spun alloys quenched at a circumference speed of 39 m/s were formed into an amorphous single phase. The amorphous alloys annealed up to a temperature between the first and second crystallization temperatures exhibited mixed phases of I- and remaining amorphous phases. Observation of the Zr30Hf30Ni15Cu10Ti15 amorphous alloy heated up to 745 K with transmission electron microscope revealed the presence of precipitates with diameters ranging 10-20 nm. Nano-beam diffraction demonstrated that the precipitates were identified to be the I-phase with the five-, three and two-fold symmetries. The Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 alloys were not formed into a single quasicrystalline phase as HEAs, but the discussions of the current and early experimental data led to provide the way to approach high-entropy quasicrystalline alloys (HE-QCs). (C) 2017 Elsevier B.V. All rights reserved.
Title:
Phase diagram of antimony up to 31 GPa and 835 K
Authors:
Coleman, AL; Stevenson, M; McMahon, MI; Macleod, SG Author Full Names: Coleman, A. L.; Stevenson, M.; McMahon, M. I.; Macleod, S. G.
Source:
PHYSICAL REVIEW B, 97 (14):10.1103/PhysRevB.97.144107 APR 13 2018
Abstract:
X-ray powder diffraction experiments using resistively heated diamond anvil cells have been conducted in order to establish the phase behavior of antimony up to 31 GPa and 835 K. The dip in the melting curve at 5.7 GPa and 840 K is identified as the triple point between the Sb-I, incommensurate Sb-II, and liquid phases. No evidence of the previously reported simple cubic phase was observed. Determination of the phase boundary between Sb-II and Sb-III suggests the existence of a second triple point in the region of 13 GPa and 1200 K. The incommensurate composite structure of Sb-II was found to remain ordered to the highest temperatures studies-no evidence of disordering of the guest-atom chains was observed. Indeed, the modulation reflections that arise from interactions between the host and guest subsystems were found to be present to the highest temperatures, suggesting such interactions remain relatively strong in Sb even in the presence of increased thermal motion. Finally, we show that the incommensurately modulated structure recently reported as giving an improved fit to diffraction data from incommensurate Ba-IV can be rejected as the structure of Sb-II using a simple density argument.
Title:
Phase transitions in ferroelectric 4-amino-pyridinium tetrachloroantimonate(III) - revisited
Authors:
Gagor, A Author Full Names: Gagor, Anna
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 74 217-225; 10.1107/S2052520618003669 2 APR 2018
Abstract:
New X-ray diffraction studies on the crystal structure of ferroelectric [4-NH2C5H4NH][SbCl4] indicate that in the broad temperature range from 240 to 304 K covering the three intermediate phases, the crystal structure is modulated. Phase II is incommensurately modulated with modulation vector q = beta b*, beta varying from 0.60 to 0.66 and monoclinic C2/c(0 beta 0)s0 superspace group. Ferroelectric phase III is commensurate with q = 2/3b* and Cc(0 beta 0)0 symmetry. Polar phase IV is incommensurately modulated with beta varying from 0.66 to 0.70 and Cc(0 beta 0)0 superspace group. In all phases only first-order satellites are observed along the b* direction. Two types of periodic deformation are present in the structure of modulated phases. The 4-aminopyridinium cations are subjected to occupation modulation whereas [SbCl4](n)(-) chains are displacively modulated. The paraelectric-ferroelectric phase transition is an example of the incommensurate-commensurate transition of the lock-in type. A new mechanism for this transformation is proposed.
Title:
Revisiting the I(1)over-bar structures of high-temperature Ca-rich plagioclase feldspar - a single-crystal neutron and X-ray diffraction study
Authors:
Jin, SY; Wang, XP; Xu, HF Author Full Names: Jin, Shiyun; Wang, Xiaoping; Xu, Huifang
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 74 152-164; 10.1107/S2052520618003219 2 APR 2018
Abstract:
The I (1) over bar structures of four natural Ca-rich plagioclase feldspars formed at high temperature were analysed using single-crystal neutron and X-ray diffraction. The neutron time-of-flight Laue diffractometer at the ORNL Spallation Neutron Source (Tennessee, USA) combined with a single-crystal X-ray diffraction instrument were able to reveal some new details about these already intensively studied structures. The split oxygen atoms refined from the neutron diffraction data show the underlying mechanism of Ca-Na ordering and the anisotropic P (1) over bar ordering along the c-axis. The compositional ranges covered by the samples studied are quite rare for I (1) over bar structures. The incommensurately modulated e2 structure of some plagioclase samples can easily be confused with an I (1) over bar structure from the diffraction pattern, which puts some previously published I (1) over bar structures into question. An incomplete phase diagram for Ca-rich plagioclase feldspar is proposed to explain the rarity of the I (1) over bar structure in this compositional range, and a time-temperature-transformation diagram for the composition similar to An(66) is provided accordingly.

Update: 18-Apr-2018

Title:
Incommensurately modulated phase and charge ordering transition in nanocrystalline Nd0.5Sr0.5MnO3 perovskite
Authors:
Shankar, U; Pandey, R; Singh, AK Author Full Names: Shankar, Uma; Pandey, Rishikesh; Singh, Akhilesh Kumar
Source:
JOURNAL OF APPLIED PHYSICS, 123 (12):10.1063/1.5007199 MAR 28 2018
Abstract:
We report here the "incommensurate modulated" phase along with the ferromagnetic character in nanocrystalline Nd0.5Sr0.5MnO3 perovskite. The Rietveld analysis of powder X-ray diffraction data reveals that the structure of nanocrystalline Nd0.5Sr0.5MnO3 ceramic can be described as a modulated phase in the monoclinic structure with space group Pm and lattice parameters a(m) approximate to 2a(o), b(m) approximate to b(o), and c(m) approximate to 3c(o), where a(o), b(o), and c(o) correspond to the lattice parameters of the parent ortho-rhombic structure for the bulk sample at room temperature. Increasing the crystallite size converts the modulated monoclinic structure to an orthorhombic structure with the Imma space group for the bulk Nd0.5Sr0.5MnO3 sample. The magnetic measurements on nanocrystalline samples reveal ferromagnetic behaviour and the absence of charge ordering transition at low temperatures. The nanocrystalline samples also exhibit Griffith phase like behaviour near the paramagnetic to ferromagnetic phase transition. The Powder X-ray diffraction study of bulk Nd0.5Sr0.5MnO3 in the temperature range of 13 K-300K reveals the transition from the orthorhombic to the monoclinic structure in the P2(1)/m space group with the coexistence of the two phases in a wide temperature range below room temperature. Published by AIP Publishing.

Update: 11-Apr-2018

Title:
Thermal transport properties, magnetic susceptibility and neutron diffraction studies of the (Cr100-xAlx)(95)Mo-5 alloy system
Authors:
Muchono, B; Sheppard, CJ; Venter, AM; Prinsloo, ARE Author Full Names: Muchono, B.; Sheppard, C. J.; Venter, A. M.; Prinsloo, A. R. E.
Source:
PHYSICA B-CONDENSED MATTER, 537 212-224; 10.1016/j.physb.2018.02.018 MAY 15 2018
Abstract:
Previous electrical resistivity (rho) and specific heat (C-P) studies on the ternary (Cr100-xAlx)(95)Mo-5 alloy system suggested that it harbours two quantum critical points (QCPs). This study reports comprehensive investigations of this alloy system through Seebeck coefficient oSthorn, thermal conductivity (kappa) magnetic susceptibility o.thorn and neutron diffraction oNDthorn measurements in the concentration range 0 <= x 8.6. The results of (kappa) and (chi) show that spin-density-wave (SDW) antiferromagnetism is suppressed to temperatures below 2 K for concentrations in the range 1.4 <= x <= 4.4. Plots of dS= dT in the limit as T -> 2 K depict two minima, i. e. just above x = 1.4 and 4.4. This parameter has been used as a key indicator of quantum critical behaviour (QCB) in Cr alloys. Analyses against the Nordheim-Gorter relationship demonstrates a positive slope for the incommensurate (I) SDW alloys and a negative slope for the commensurate (C) SDW alloys. Extrapolations of these two slopes intercept at a concentration of 3.2 at.% Al indicating the occurrence of band structure modifications when Al is added into the Cr95Mo5 base alloy. The Lorenz number oLthorn for the alloys with x = 0 and 0.5 shows interesting anomalous behaviour associated with band structure effects and SDW magnetic ordering. ND measurements as a function of temperature confirm that alloys with x < 1.4 order in the incommensurate (I) SDW phase whilst alloys with x > 4.4 show commensurate (C) SDW order. Power law fits of the form T-N alpha(1.40 - x)(0.35) (+/-0.05) for the ISDW to P phase transition and T-N alpha (x- 4. 40)(0.63) (+/-0.03) for the P to CSDW phase transition rendered the critical exponents 0: 35 +/- 0: 05 and 0: 63 +/- 0: 03 respectively. Overall the results of S,.,. and ND corroborate the existence of two QCPs at x approximate to 1.4 and 4.4.
Title:
Microphases deriving from Ba2ZrF8 structure type: II: Crystal structure of Sr17Zr9F70 and Sr(17.145)ZT(9)F(70.29)
Authors:
Laval, JP; Rafik, H; Trolliard, G Author Full Names: Laval, Jean-Paul; Rafik, Hamid; Trolliard, Gilles
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 260 151-158; 10.1016/j.jssc.2018.01.005 APR 2018
Abstract:
In the domain Sr1-xZrxF2+2 (x) studied at 670 degrees C between the limits 0.333 <= x <= 0.353, Sr2ZrF8 (x = 0.333) cannot be obtained under our synthesis conditions but a new phase Sr17Zr9F70 (x = 0.346) is characterized which clearly shows a great analogy with Ba2ZrF8 and Pb2ZrF8 already described. It presents the same Pnma space group and derives from this basic type by the relation: a = 28.812(10) angstrom = 3 x a(Ba2ZrF8); b = 16.566(6) angstrom = 3 x b(Ba2ZrF8); c = 11.433(4)angstrom = c(Ba2ZrF8). The superlattice along a results from a change in the step of zigzag parallel rows of respectively Sr cations and ZrF8 polyhedra. The zigzag step is not composition-dependent but more likely depends on the size of the M2+ cation. The superlattice along b results from an ordered creation of Sr vacancies of multiplicity m = 3 (1 vacancy for 3 Sr) in some Sr raws which changes the Sr/Zr ratio from 2/1 to 1.889/1 (x = 0.346). Then the superstructure along b accommodates the change in stoichiometry in Sr within this phase from Sr18Zr9F72 (9 x "Sr2ZrF8") to Sr17Zr9F70. A second structure of close composition (x = 0.344) shows that the vacant Sr site can be partially occupied in a disordered way by a small proportion of Sr, giving a composition slightly closer to "Sr2ZrF8". Compared to Sr17Zr8F70, the over-stoichiometry mechanism is a solid solution model. For Zr contents comprised between x = 0.346 and 0.353, a series of modulated phases corresponding to various more or less ordered sequences of Sr cations and Sr vacancies along b are characterized by electron diffraction and TEM lattice imaging. They can be interpreted as intermediate between limit phases Sr17Zr9F70 (x = 0.346) and Sr11Zr6F46 (x = 0.353), of respective multiplicities m = 3 and m = 2 along the same b direction and of modulation vectors q = 1/3b* and q = 1/2b*. Several modulated phases with q modulation vector comprised between 1/3 b* and 1/2 b* can be characterized.
Title:
Stairlike Aurivillius Phases in the Pseudobinary Bi5Nb3O15-ABi(2)Nb(2)O(9) (A = Ba and Sr) System: A Comprehensive Analysis Using Superspace Group Formalism
Authors:
Steciuk, G; Barrier, N; Pautrat, A; Boullay, P Author Full Names: Steciuk, Gwladys; Barrier, Nicolas; Pautrat, Alain; Boullay, Philippe
Source:
INORGANIC CHEMISTRY, 57 (6):3107-3115; 10.1021/acs.inorgchem.7b03026 MAR 19 2018
Abstract:
We report the possibility of extending the so-called stairlike Aurivilius phases in the pseudobinary Bi5Nb3O15-ABi(2)Nb(2)O(9) (A = Ba and Sr) over a wide range of compositions. These phases are characterized by a discontinuous stacking of [Bi2O2] slabs and perovskite blocks, leading to long-period intergrowths stabilized as a single phase. When analyses from precession electron diffraction tomography and Xray and neutron powder diffraction are combined, the monoclinic incommensurately modulated structure with q = alpha a* + gamma c* previously proposed for the ABi(7)Nb(5)O(24) composition could be generalized to the Bi5Nb3O15-ABi(2)Nb(2)O(9) (A = Ba and Sr) compounds. Considering the compositions expressed as (A,Bi)(1-x)NbxO3-3x, the stacking sequence associated with compositions ranging from x = 2/5 to 3/8 is governed by the component gamma of the modulation vector and can be predicted following a Farey tree hierarchy independently to the A cation. The length of the steps, characteristic of the stairlike nature, is controlled by the alpha component and depends on the substitution ratio A/Bi and the nature of A (A = Ba and Sr). This study highlights the compositional flexibility of stairlike Aurivillius phases.
Title:
Kinetically Controlled Formation and Decomposition of Metastable [(BiSe)(1+delta)](m)[TiSe2](m) Compounds
Authors:
Lygo, AC; Hamann, DM; Moore, DB; Merrill, DR; Ditto, J; Esters, M; Orlowicz, J; Wood, SR; Johnson, DC Author Full Names: Lygo, Alexander C.; Hamann, Danielle M.; Moore, Daniel B.; Merrill, Devin R.; Ditto, Jeffrey; Esters, Marco; Orlowicz, Jacob; Wood, Suzannah R.; Johnson, David C.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 140 (9):3385-3393; 10.1021/jacs.7b13398 MAR 7 2018
Abstract:
Preparing homologous series of compounds allows chemists to rapidly discover new compounds with predictable structure and properties. Synthesizing compounds within such a series involves navigating a free energy landscape defined by the interactions within and between constituent atoms. Historically, synthesis approaches are typically limited to forming only the most thermodynamically stable compound under the reaction conditions. Presented here is the synthesis, via self-assembly of designed precursors, of isocompositional incommensurate layered compounds[(BiSe)(1+delta)](m)[TiSe2](m) , with m = 1, 2, and 3. The structure of the BiSe bilayer in the m = 1 compound is not that of the binary compound, and this is the first example of compounds where a BiSe layer thicker than a bilayer in heterostructures has been prepared. Specular and in-plane X-ray diffraction combined with high-resolution electron microscopy data was used to follow the formation of the compounds during low-temperature annealing and the subsequent decomposition of the m = 2 and 3 compounds into [(BiSe)(1+delta)](1)[TiSe2](1) at elevated temperatures. These results show that the structure of the precursor can be used to control reaction kinetics, enabling the synthesis of kinetically stable compounds that are not accessible via traditional techniques. The data collected as a function of temperature and time enabled us to schematically construct the topology of the free energy landscape about the local free energy minima for each of the products.
Title:
The Mystery of the Auln 1:1 Phase and Its Incommensurate Structural Variations
Authors:
Folkers, LC; Simonov, A; Wang, F; Lidin, S Author Full Names: Folkers, Laura C.; Simonov, Arkadiy; Wang, Fei; Lidin, Sven
Source:
INORGANIC CHEMISTRY, 57 (5):2791-2796; 10.1021/acs.inorgchem.7b03206 MAR 5 2018
Abstract:
In this communication, the AuIn 1:1 phase (Naturwissenschaften, 1953, 40, 437, DOI: 10.1007/BF00590353), and its ordering behavior at various temperatures is investigated. To enable the growth of a X-ray suitable specimen, a tempering routine was established by the interpretation of a differential scanning calorimetry (DSC) study. In this way, good quality single crystals were grown and measured at the Crystal beamline at Synchrotron SOLEIL. From the acquired data, three variations of this structure could be found at temperatures of 400 degrees C and 300 degrees C and room temperature, with differing degrees of incommensurate modulation. Diffuse scattering found at 400 degrees C was interpreted with the help of a three-dimensional difference pair distribution function (3D-Delta PDF) study.
Title:
Formation of Quasicrystalline Phases and Their Close Approximants in Cast Al-Mn Base Alloys Modified by Transition Metals
Authors:
Stan-Glowinska, K Author Full Names: Stan-Glowinska, Katarzyna
Source:
CRYSTALS, 8 (2):10.3390/cryst8020061 FEB 2018
Abstract:
The aim of the presented research was to study the influence of Cr, Co, Ni, and Cu additions on the formation of quasicrystalline particles in the 94Al-6Mn base alloy during casting at intermediate cooling rates. Based on the obtained results, Cu and Ni enhance quasicrystalline phase nucleation compared to the unmodified binary composition. In the case of Cu addition, formation of a quasicrystalline phase takes place along whole thickness of the prepared casting, but its fraction and morphology depends on the cooling rates present in different parts of the sample. Based on the previous works on the beneficial effect of Fe addition, a quaternary alloy containing both Fe and Cu was prepared to evaluate the effect of the simultaneous presence of these elements on the microstructure of the obtained castings.
Title:
Possible nucleus of the Bergman cluster in the Zn-Mg-Y alloy system
Authors:
Nakayama, K; Nakagawa, M; Koyama, Y Author Full Names: Nakayama, Kei; Nakagawa, Masaya; Koyama, Yasumasa
Source:
PHILOSOPHICAL MAGAZINE, 98 (3):219-236; 10.1080/14786435.2017.1400703 2018
Abstract:
To understand the formation of the Bergman cluster in the F-type icosahedral quasicrystal (IQ), crystallographic relations between the quasicrystal and the intermetallic-compound H and Zn23Y6 phases in the ZnMgY alloy system were investigated mainly by transmission electron microscopy. It was found that, although sample rotations of about 1 degrees were required to obtain simple crystallographic relations, the orientation relationship was established among the cubic-Fmm Zn23Y6 structure, the hexagonal-P6(3)/mmc H structure and the F-type IQ; that is, [(1) over bar 1 3](c) // the five-fold axis in the IQ // N(2 (1) over bar(1) over bar0)(H), and [1 1 1](c) // the two-fold axis in the IQ // N(0 5 (5) over bar3)(H), where N(h k m l)(H) means the normal direction of the (h k m l)(H) plane in the H structure. The correspondences between atomic positions in the Bergman cluster and in the Zn23Y6 structure and between those in the cluster and in the H structure were investigated on the basis of the established relationship. As a result, an assembly of six short-penetrated-decagonal columns was identified as an appropriate nucleus in the formation of the Bergman cluster from these two structures.

Update: 4-Apr-2018

Title:
Spin wave propagation spectra in Octonacci one-dimensional magnonic quasicrystals
Authors:
Valeriano, AP; Costa, CH; Bezerra, CG Author Full Names: Valeriano, Analine P.; Costa, Carlos H.; Bezerra, Claudionor G.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 456 228-235; 10.1016/j.jmmm.2018.02.042 JUN 15 2018
Abstract:
In this paper, we study spin wave propagation in quasiperiodic magnonic superlattices that follow the so-called Octonacci quasiperiodic sequence, where the N-th stage can be obtained through the recurrence rule S-N = SN-1SN-2SN-1, for N >= 3, and starting with S-1 = A and S-2 = B. The multilayered magnonic nanostructure is composed of two simple cubic ferromagnetic materials, labeled A and B, which interact through bilinear and biquadratic exchange couplings at their interfaces. The ferromagnetic materials are described by the Heisenberg model, and a transfer matrix treatment is employed, with the calculations performed for the exchange-dominated regime, taking the random phase approximation (RPA) into account. The obtained numerical results show the effects of both (i) the Octonacci quasiperiodic sequence and (ii) the biquadratic exchange coupling on the band structure and transmission spectra of spin waves. Comparisons are also performed with the spectra found in other periodic and quasiperiodic structures. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Building 2D quasicrystals from 5-fold symmetric corannulene molecules
Authors:
Kalashnyk, N; Ledieu, J; Gaudry, E; Cui, C; Tsai, AP; Fournee, V Author Full Names: Kalashnyk, Nataliya; Ledieu, Julian; Gaudry, Emilie; Cui, Can; Tsai, An-Pang; Fournee, Vincent
Source:
NANO RESEARCH, 11 (4):2129-2138; 10.1007/s12274-017-1830-x APR 2018
Abstract:
The formation of long-range ordered aperiodic molecular films on quasicrystalline substrates is a new challenge that provides an opportunity for further surface functionalization. This aim can be realized through the smart selection of molecular building blocks, based on symmetry-matching between the underlying quasicrystal and individual molecules. It was previously found that the geometric registry between the C-60 molecules and the 5- and 10-fold surfaces was key to the growth of quasiperiodic organic layers. However, an attempt to form a quasiperiodic C-60 network on i-Ag-In-Yb substrates was unsuccessful, resulting in disordered molecular films. Here we report the growth of 5-fold symmetric corannulene C20H10 molecules on the 5-fold surfaces of i-Ag-In-Yb quasicrystals. Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) revealed long-range quasiperiodic order and 5-fold rotational symmetry in self-assembled corannulene films. Recurrent decagonal molecular rings were seen, resulting from the decoration of specific adsorption sites with local pentagonal symmetry by corannulenes, adsorbed with their bowl-openings pointing away from the surface. They were identified as (Ag, In)-containing rhombic triacontahedral (RTH) cluster centers and pentagonal Yb motifs, which cannot be occupied simultaneously due to steric hindrance. It is proposed that symmetry-matching between the molecule and specific substrate sites drives this organization. Alteration of the molecular rim by the introduction of CH substituents appeared to increase molecule mobility on the potential energy surface and facilitate trapping at these specific sites. This finding suggests that rational selection of molecular moiety enables the templated self-assembly of molecules leading to an ordered aperiodic corannulene layer.
Title:
SU(5) grand unified theory, its polytopes and 5-fold symmetric aperiodic tiling
Authors:
Koca, M; Koca, NO; Al-Siyabi, A Author Full Names: Koca, Mehmet; Koca, Nazife Ozdes; Al-Siyabi, Abeer
Source:
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS, 15 (4):10.1142/S0219887818500561 APR 2018
Abstract:
We associate the lepton-quark families with the vertices of the 4D polytopes 5-cell (0001) (A4) and the rectified 5-cell (0100) (A4) derived from the SU(5) Coxeter-Dynkin diagram. The off-diagonal gauge bosons are associated with the root polytope (1001) A(4) whose facets are tetrahedra and the triangular prisms. The edge-vertex relations are interpreted as the SU(5) charge conservation. The Dynkin diagram symmetry of the SU(5) diagram can be interpreted as a kind of particle-antiparticle symmetry. The Voronoi cell of the root lattice consists of the union of the polytopes (1000) (A4) + (0100) (A4) + (0010) (A4) + (0001) (A4) whose facets are 20 rhombohedra. We construct the Delone (Delaunay) cells of the root lattice as the alternating 5-cell and the rectified 5-cell, a kind of dual to the Voronoi cell. The vertices of the Delone cells closest to the origin consist of the root vectors representing the gauge bosons. The faces of the rhombohedra project onto the Coxeter plane as thick and thin rhombs leading to Penrose-like tiling of the plane which can be used for the description of the 5-fold symmetric quasicrystallography. The model can be extended to SO(10) and even to SO(11) by noting the Coxeter-Dynkin diagram embedding A(4) subset of D-5 subset of B-5. Another embedding can be made through the relation A(4) subset of D-5 subset of E-6 for more popular GUT's. Appendix A includes the quaternionic representations of the Coxeter-Weyl groups W(A(4)) subset of W(H-4) which can be obtained directly from W(E-8) by projection. This leads to relations of the SU(5) polytopes with the quasicrystallography in 4D and E-8 polytopes. Appendix B discusses the branching of the polytopes in terms of the irreducible representations of the Coxeter-Weyl group W(A(4)) approximate to S-5.
Title:
Charge Order and Superconductivity in Underdoped YBa2Cu3O7-delta under Pressure
Authors:
Putzke, C; Ayres, J; Buhot, J; Licciardello, S; Hussey, NE; Friedemann, S; Carrington, A Author Full Names: Putzke, Carsten; Ayres, Jake; Buhot, Jonathan; Licciardello, Salvatore; Hussey, Nigel E.; Friedemann, Sven; Carrington, Antony
Source:
PHYSICAL REVIEW LETTERS, 120 (11):10.1103/PhysRevLett.120.117002 MAR 16 2018
Abstract:
In underdoped cuprates, an incommensurate charge density wave (CDW) order is known to coexist with superconductivity. A dip in T-c at the hole doping level where the CDW is strongest (n(p) similar or equal to 0.12) suggests that CDW order may suppress superconductivity. We investigate the interplay of charge order with superconductivity in underdoped YBa2Cu3O7-d(delta) by measuring the temperature dependence of the Hall coefficient R-H(T) at high magnetic field and at high hydrostatic pressure. We find that, although pressure increases T-c by up to 10 K at 2.6 GPa, it has very little effect on R-H(T). This suggests that pressure, at these levels, only weakly affects the CDW and that the increase in T-c with pressure cannot be attributed to a suppression of the CDW. We argue, therefore, that the dip in T-c at n(p) similar or equal to 0.12 at ambient pressure is probably not caused by the CDW formation.

Update: 28-Mar-2018

Title:
Simultaneous localization of photons and phonons in defect-free dodecagonal phoxonic quasicrystals
Authors:
Xu, BH; Wang, Z; Tan, YX; Yu, TB Author Full Names: Xu, Bihang; Wang, Zhong; Tan, Yixiang; Yu, Tianbao
Source:
MODERN PHYSICS LETTERS B, 32 (7):10.1142/S0217984918500963 MAR 10 2018
Abstract:
In dodecagonal phoxonic quasicrytals (PhXQCs) with a very high rotational symmetry, we demonstrate numerically large phoxonic band gaps (PhXBGs, the coexistence of photonic and phononic band gaps). By computing the existence and dependence of PhXBGs on the choice of radius of holes, we find that PhXQCs can possess simultaneous photonic and phononic band gaps over a rather wide range of geometric parameters. Furthermore, localized modes of THz photons and tens of MHz phonons may exist inside and outside band gaps in defect-free PhXQCs. The electromagnetic and elastic field can be confined simultaneously around the quasicrytals center and decay in a length scale of several basic cells. As a kind of quasiperiodic structures, 12-fold PhXQCs provide a good candidate for simultaneously tailoring electromagnetic and elastic waves. Moreover, these structures exhibit some interesting characteristics due to the very high symmetry.

Update: 21-Mar-2018

Title:
Two spin-canting textures in the antiferromagnetic phase AF1 of MnWO4 based on the new polar atomistic model in P2
Authors:
Park, SH; Liu, BQ; Behal, D; Pedersen, B; Schneidewind, A Author Full Names: Park, S-H; Liu, B-Q; Behal, D.; Pedersen, B.; Schneidewind, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 30 (13):10.1088/1361-648X/aaaeae APR 4 2018
Abstract:
The low temperature antiferromagnetic (AF) phase of MnWO4 (the so-called AF1 phase) exhibits different spin-canting configurations at two Mn2+ sublattices of the (3 + 1)-dimensional magnetic structure. The suggested superspace group P2.1'(alpha, 1/2, gamma)0s is a significant consequence of the polar space group P2 true for the nuclear structure of MnWO4. Density functional theory calculations showed that its ground state prefers this two spin-canting system. The structural difference between two independent atomic sites for Mn (Mn-a, Mn-b) is too small to allow microscopically detectable electric polarisation. However, this hidden intrinsic polar character allows AF1 two commensurately modulated spin-canting textures. This is considered as the prerequisite onset of the improper ferroelectricity enhanced by the helical spin order in the multiferroic phase AF2 of MnWO4.
Title:
The incommensurately modulated crystal structure of roshchinite, Cu0.09Ag1.04Pb0.65Sb2.82As0.37S6.08
Authors:
Makovicky, E; Stoger, B; Topa, D Author Full Names: Makovicky, Emil; Stoger, Berthold; Topa, Dan
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 233 (3-4):255-267; 10.1515/zkri-2017-2126 MAR 2018
Abstract:
The Pb-Ag-Sb sulfide roshchinite, Cu0.09Ag1.04Pb0.65Sb2.82As0.37S6.08, is a lillianite homologue N = 4 with a complex incommensurate superstructure in the 8.46 angstrom direction of the orthorhombic crystal lattice with a 19.0804(1) angstrom, b 8.4591(2) angstrom and c 12.9451(3) angstrom, superspace group Pbcn(0 sigma(2)0)00s, q = 0.41458(3) b*. A structure solution and refinement in (3+1) superspace, based on 10,019 observed reflections and 437 refined parameters was terminated at R-obs (wR) equal to 7.27 (8.07)% using satellites up to second order; R-obs is 4.82 for main reflections only. The Pb atoms in trigonal coordination prisms on planes of unit-cell twinning are semiperiodically replaced by antimony. The marginal columns of (311)(PbS) slabs of the Sb-Ag based structure which is based on PbS-like topology contain Sb, Ag(Cu) and mixed Ag/Sb sites in a complicated sequence. Central portions of the slabs are occupied by Sb-S crankshaft chains, best exposed on the (100) PbS planes, which run diagonally across the slabs. In these planes, in their majority the chains display Sb3S4 form and two opposing orientations, zig-zagging along the [010] direction. Every six chains, a parallel configuration of two chains occurs, but occasionally this interval is reduced to five chains. This, together with related compositional changes in the Pb- and Ag-Sb column, explains the one-dimensionally incommensurate character of roshchinite. Modestly elevated contents of As replacing Sb are the probable reason of modulation and non-commensurability in roshchinite.
Title:
The (3+3) commensurately modulated structure of the uranyl silicate mineral swamboite-(Nd), Nd-0.333[(UO2)(SiO3OH)](H2O)(2.41)
Authors:
Plasil, J; Petricek, V; Locock, AJ; Skoda, R; Burns, PC Author Full Names: Plasil, Jakub; Petricek, Vaclav; Locock, Andrew J.; Skoda, Radek; Burns, Peter C.
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 233 (3-4):223-231; 10.1515/zkri-2017-2119 MAR 2018
Abstract:
The uranyl mineral swamboite has been redefined to swamboite-(Nd) and its structure has been solved and refined as a commensurate structure in six-dimensional superspace. The structure is monoclinic, superspace group P2(1)/m(a1, b1, g1) 00(-a1, b1, g1) 00 (a2,0,g2)0s, cell parameters a = 6.6560(3), b = 6.9881(5), c = 8.8059(6), c = 11.3361(16) angstrom, beta = 102.591(5)degrees, modulation wave-vectors q(1) = 1/3 1/3 0; q(2) = - 1/3 1/3 0; q(3) = 1/2 0 1/2. The structure was refined from 8717 reflections to a final R = 0.0610. The model includes modulation both of atomic positions and displacement parameters, as well as occupancy waves. The structure is based upon uranyl-silicate sheets of uranophane topology alternating with an inter-layer of partly occupied Nd3+ sites and H2O molecules. The strong (3 + 3) dimensional modulation of the structure originates from the distribution of the Nd-dominated sites and further accommodation of the suitable geometry within the sheets and charge distribution within the structure. The separation distances between the corres-ponding occupied Nd sites are rationals of the super-cell vectors corresponding to the modulation vectors of the structure. The case of swamboite-(Nd) is the first example of a modulated structure within the oxysalts of U6+.
Title:
Frustration and thermalization in an artificial magnetic quasicrystal
Authors:
Shi, D; Budrikis, Z; Stein, A; Morley, SA; Olmsted, PD; Burnell, G; Marrows, CH Author Full Names: Shi, Dong; Budrikis, Zoe; Stein, Aaron; Morley, Sophie A.; Olmsted, Peter D.; Burnell, Gavin; Marrows, Christopher H.
Source:
NATURE PHYSICS, 14 (3):309-+; 10.1038/s41567-017-0009-4 MAR 2018
Abstract:
Artificial frustrated systems offer a playground to study the emergent properties of interacting systems. Most work to date has been on spatially periodic systems, known as artificial spin ices when the interacting elements are magnetic. Here we have studied artificial magnetic quasicrystals based on quasiperiodic Penrose tiling patterns of interacting nanomagnets. We construct a low-energy configuration from a step-by-step approach that we propose as a ground state. Topologically induced emergent frustration means that this configuration cannot be constructed from vertices in their ground states. It has two parts, a quasione- dimensional 'skeleton' that spans the entire pattern and is capable of long-range order, surrounding ` flippable' clusters of macrospins that lead to macroscopic degeneracy. Magnetic force microscopy imaging of Penrose tiling arrays revealed superdomains that are larger for more strongly coupled arrays, especially after annealing the array above its blocking temperature.
Title:
Coordination numbers of the vertex graph of a Penrose tiling
Authors:
Shutov, A; Maleev, A Author Full Names: Shutov, Anton; Maleev, Andrey
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 112-122; 10.1107/S2053273318000062 2 MAR 2018
Abstract:
A new approach to study coordination shells and coordination sequences of quasiperiodic graphs is suggested. The structure of the coordination shells in the vertex graph of a Penrose tiling is described. An asymptotic formula for its coordination numbers is obtained. An essentially different behaviour of the coordination numbers for even and odd shells is revealed.
Title:
Deformation Behavior and Structure of i-Al-Cu-Fe Quasicrystalline Alloy in Vicinity of Nanoindenter Indentation
Authors:
Shalaeva, EV; Selyanin, IO; Smirnova, EO; Smirnov, SV; Novachek, DD Author Full Names: Shalaeva, E. V.; Selyanin, I. O.; Smirnova, E. O.; Smirnov, S. V.; Novachek, D. D.
Source:
PHYSICS OF THE SOLID STATE, 60 (2):312-319; 10.1134/S1063783418020233 FEB 2018
Abstract:
The nanoindentation tests have been carried out for the quasicrystalline polygrain Al62.4Cu25.3Fe12.3 alloy with the icosahedral structure i; the load P-displacement h diagrams have been used to estimate the contributions of plastic deformation (monotonic and intermittent), and the structures of the transverse microscopic sections have been studied in the vicinity of indentations by electron microscopy. It is shown that several systems of deformation bands are formed in the elasto-plastic zone in the vicinity of the indentations along the close-packed planes of the i lattice with the five-fold and two-fold symmetry axes; the bands often begin from cracks and manifest the signs of the dislocation structure. The traces of the phase transformation with the formation of the beta-phase areas are observed only in a thin layer under an indenter. The effects of intermittent deformation are up to 50% of the total inelastic deformation and are related to the plastic behavior of the quasicrystal-activation and passage of deformation bands and also the formation of undersurface micro- and nanosized cracks.

Update: 14-Mar-2018

Title:
Melt holding time as an important factor on the formation of quasicrystal phase in Mg67Zn30Gd3 alloy
Authors:
Zhang, JY; Jia, P; Zhao, DG; Teng, XY Author Full Names: Zhang, Jinyang; Jia, Peng; Zhao, Degang; Teng, Xinying
Source:
PHYSICA B-CONDENSED MATTER, 533 28-32; 10.1016/j.physb.2017.12.052 MAR 15 2018
Abstract:
In the present work, the content of icosahedral quasicrystal phase (I-phase) and melt holding time shows a mono peak curve: a small amount of I-phase and lots of Mg-3(Gd, Zn) phase are presented for t < 21 min, however a great deal of I-phase is observed for t > 21 min, and the volumetric fraction of I-phase has the maximum of 49.50% for t = 41 min. This strategy of formation of quasicrystal phase makes us realize that melt thermal treatment could significantly affect the phase types in Mg-Zn-Gd alloy.
Title:
Multi-q Mesoscale Magnetism in CeAuSb2
Authors:
Marcus, GG; Kim, DJ; Tutmaher, JA; Rodriguez-Rivera, JA; Birk, JO; Niedermeyer, C; Lee, H; Fisk, Z; Broholm, CL Author Full Names: Marcus, Guy G.; Kim, Dae-Jeong; Tutmaher, Jacob A.; Rodriguez-Rivera, Jose A.; Birk, Jonas Okkels; Niedermeyer, Christof; Lee, Hannoh; Fisk, Zachary; Broholm, Collin L.
Source:
PHYSICAL REVIEW LETTERS, 120 (9):10.1103/PhysRevLett.120.097201 FEB 28 2018
Abstract:
We report the discovery of a field driven transition from a single-q to multi-q spin density wave (SDW) in the tetragonal heavy fermion compound CeAuSb2. Polarized along c, the sinusoidal SDW amplitude is 1.8(2)mu(B)/Ce for T << T-N = 6.25(10)K with a wave vector q(1) = (eta, eta, 1/2) [eta = 0.136(2)]. For H parallel to c, harmonics appearing at 2q(1) evidence a striped magnetic texture below mu H-degrees(1) = 2.78(1)T. Above H-1, these are replaced by coupled harmonics at q(1) + q(2) = (2 eta, 0, 0) + c* until mu H-degrees(2) = 5.42(5)T, where satellites vanish and magnetization nonlinearly approaches saturation at 1.64(2)mu(B)/Ce for mu H-degrees approximate to 7T.
Title:
High-strength Mg-6Zn-1Y-1Ca (wt%) alloy containing quasicrystalline I-phase processed by a powder metallurgy route
Authors:
Medina, J; Perez, P; Garces, G; Stark, A; Schell, N; Adeva, P Author Full Names: Medina, J.; Perez, P.; Garces, G.; Stark, A.; Schell, N.; Adeva, P.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 715 92-100; 10.1016/j.msea.2017.12.111 FEB 7 2018
Abstract:
A high-strength Mg-6Zn-1Y-1Ca (wt%) alloy has been processed by a powder metallurgy route. Rapidly solidified powders with a particle size below 100 tun were used as a way for preventing formation of ternary MgZnCa compounds during subsequent extrusion at 250 degrees C. The microstructure of the extruded alloy consists of an ultrafine-grain magnesium matrix, with an average grain size of 444 nm, embedding a high volume fraction of fine I-phase particles aligned along the extrusion direction. The alloy combines an excellent ductility (14% of elongation to failure) with a high strength (ultimate strength of 469 MPa and yield stress of 461 MPa) at room temperature, mainly due to grain size refinement (around 70% of the yield stress). The strength is kept high up to 150 degrees C (yield stress of 279 MPa). Above this temperature, the mechanical strength falls to very low values but the ability to deform plastically is considerably enhanced, exhibiting superplastic behaviour from 200 to 350 degrees C, with a maximum elongation of 477% at 350 degrees C.
Title:
Parallels in Structural Chemistry between the Molecular and Metallic Realms Revealed by Complex Intermetallic Phases
Authors:
Fredrickson, DC Author Full Names: Fredrickson, Daniel C.
Source:
ACCOUNTS OF CHEMICAL RESEARCH, 51 (2):248-257; 10.1021/acs.accounts.7b00625 FEB 2018
Abstract:
CONSPECTUS: The structural diversity of intermetallic phases poses a great challenge to chemical theory and materials design. In this Account, two examples are used to illustrate how a focus on the most complex of these structures (and their relationships to simpler ones) can reveal how chemical principles underlie structure for broad families of compounds. First, we show how experimental investigations into the Fe-Al-Si system, inspired by host-guest like features in the structure of Fe25Al78Si20, led to a theoretical approach to deriving isolobal analogies between molecular and intermetallic compounds and a more general electron counting rule. Specifically, the Fe(8)Al(17.6)Si(7.4)compound obtained in these syntheses was traced to a fragmentation of the fluorite-type structure (as adopted by NiSi2), driven by the maintenance of 18-electron configurations on the transition metal centers.& para;& para;The desire to quickly generalize these conclusions to a broader range of phases motivated the formulation of the reversed approximation Molecular Orbital (raMO) approach. The application of raMO to a diverse series of compounds allowed us recognize the prevalence of electron pair sharing in multicenter functions isolobal to classical covalent bonds and to propose the 18 - n electron rule for transition metal-main group (T-E) intermetallic compounds. These approaches provided a framework for understanding the 14-electron rule of the Nowotny Chimney Ladder phases, a temperature-driven phase transition in GdCoSi2, and the bcc-structure of group VI transition metals.& para;& para;In the second story, we recount the development of the chemical pressure approach to analyzing atomic size and packing effects in intermetallic structures. We begin with how the stability of the Yb2Ag7-type structure of Ca2Ag7 over the more common CaCu(5 )type highlights the pressing need for approaches to assessing the role of atomic size in crystal structures, and inspired the development of the DFT-Chemical Pressure (CP) method. Examples of structural phenomena elucidated by this approach are then given, including the Y/Co(2 )dumbbell substitution in the Th2Zn17-type phase Y2Co17, and local icosahedral order in the Tsai-type quasicrystal approximant CaCd6. We next discuss how deriving relationships between the CP features of a structure and its phonon modes provided a way of both validating the method and visualizing how local arrangements can give rise to soft vibrational modes. The themes of structural mechanisms for CP relief and soft atomic motions merge in the discovery and elucidation of the incommensurately modulated phase CaPd5. In the conclusion of this Account, we propose combining raMO and CP methods for focused predictions of structural phenomena.
Title:
In Situ Synthesis and Single Crystal Synchrotron X-ray Diffraction Study of ht-Sn3Sb2: An Example of How Complex Modulated Structures Are Becoming Generally Accessible
Authors:
Lidin, S; Folkers, LC Author Full Names: Lidin, Sven; Folkers, Laura C.
Source:
ACCOUNTS OF CHEMICAL RESEARCH, 51 (2):223-229; 10.1021/acs.accounts.7b00508 FEB 2018
Abstract:
Recent developments in X-ray sources and detectors and the parallel development of software for nonstandard crystallography has made analysis of very complex structural problems accessible to nonexperts. Here, we report the successful solution of the structure of ht-Sn3Sb2, an analysis that presents several challenges but that is still manageable in a relatively straightforward way. This compound exists only in a narrow temperature regime and undergoes an unquenchable phase transformation on cooling to room temperature; it contains two elements with close to identical scattering factors, and the structure is incommensurately modulated with four symmetry dependent modulation wave vectors. In this study, an attempt was first made to synthesize the title compound by in-house crystal growth in the stability region of ht-Sn3Sb2, followed by cooling to room temperature. This is known to produce mutiply twinned stistaite and elemental tin, and this sample, freshly prepared, was then reheated in situ at the single crystal materials beamline Crystal at the synchrotron Soleil. This method was unsuccessful as reheating the sample led to loss of Sn from stistaite as revealed by a change in the measured modulation wave vector. The compound was instead successfully synthesized in situ at the beamline by the topochemical reaction of single crystalline stistaite and liquid tin. A well-formed crystal of stistaite was enclosed in a quartz capillary together with a large excess of tin and heated above the melting point of tin but below the melting point of ht-Sn3Sb2. The structure was probed by sychrotron X-ray diffraction using a wavelength close to the absorption edge of Sn to maximize elemental contrast. In the diffraction patterns, first order satellites were observed, making the structure of ht-Sn3Sb2 incommensurately modulated. Further analysis exposes four q-vectors running along the body diagonals of the cubic unit cell (q(1)' = alpha alpha alpha, q(2)' = -alpha alpha -alpha, q3' = -alpha -alpha alpha, q(4)' = alpha-alpha-alpha). To facilitate the analysis, the q vectors were instead treated as axial (q(1) = alpha 0 0, q(2) = 0 alpha 0, q(3) = 0 0 alpha) and an F-type extinction condition for satellites was introduced so that only reflections with hklmnp, mnp all odd or all even, were considered. Further, the modulation functions F(q(i)) were set to zero, and only modulation functions of the type F(q(i)') were refined. The final model uses the four modulation functions, F(q(1)'), F(q(2)'), F(q(3)'), and F(q(4)'), to model occupancy Sn/Sb and positional modulation. The model shows a structure that comprises small NaCl type clusters, typically 7 x 7 x 7 atoms in extension, interspersed between single layers of elemental tin. The terminating layers of tin are slightly puckered, emulating an incipient deformation toward the structure of the layers perpendicular to the [001] direction in elemental tin. It is notable that this model is complementary to that of stistaite. In stistaite, two-dimensionally infinite slabs of rock salt are interspersed between layers of antimony along the trigonal [001] direction, so that the terminating Sb layers are the puckered bilayers typical for elemental Sb. Since all modulation functions are simple first-order harmonics, the structural model describes a locally disordered and most probably dynamic ordering.

Update: 7-Mar-2018

Title:
Shear localization and size-dependent strength of YCd6 quasicrystal approximant at the micrometer length scale
Authors:
Song, G; Kong, T; Dusoe, KJ; Canfield, PC; Lee, SW Author Full Names: Song, Gyuho; Kong, Tai; Dusoe, Keith J.; Canfield, Paul C.; Lee, Seok-Woo
Source:
JOURNAL OF MATERIALS SCIENCE, 53 (9):6980-6990; 10.1007/s10853-018-2043-8 MAY 2018
Abstract:
Mechanical properties of materials are strongly dependent of their atomic arrangement as well as the sample dimension, particularly at the micrometer length scale. In this study, we investigated the small-scale mechanical properties of single-crystalline YCd6, which is a rational approximant of the icosahedral Y-Cd quasicrystal. In situ microcompression tests revealed that shear localization always occurs on {101} planes, but the shear direction is not constrained to any particular crystallographic directions. Furthermore, the yield strengths show the size dependence with a power law exponent of 0.4. Shear localization on {101} planes and size-dependent yield strength are explained in terms of a large interplanar spacing between {101} planes and the energetics of shear localization process, respectively. The mechanical behavior of the icosahedral Y-Cd quasicrystal is also compared to understand the influence of translational symmetry on the shear localization process in both YCd6 and Y-Cd quasicrystal micropillars. The results of this study will provide an important insight in a fundamental understanding of shear localization process in novel complex intermetallic compounds.
Title:
Precipitation of binary quasicrystals along dislocations
Authors:
Yang, ZQ; Zhang, LF; Chisholm, MF; Zhou, XZ; Ye, HQ; Pennycook, SJ Author Full Names: Yang, Zhiqing; Zhang, Lifeng; Chisholm, Matthew F.; Zhou, Xinzhe; Ye, Hengqiang; Pennycook, Stephen J.
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-018-03250-8 FEB 23 2018
Abstract:
Dislocations in crystals naturally break the symmetry of the bulk, introducing local atomic configurations with symmetries such as fivefold rings. But dislocations do not usually nucleate aperiodic structure along their length. Here we demonstrate the formation of extended binary quasicrystalline precipitates with Penrose-like random-tiling structures, beginning with chemical ordering within the pentagonal structure at cores of prismatic dislocations in Mg-Zn alloys. Atomic resolution observations indicate that icosahedral chains centered along [0001] pillars of Zn interstitial atoms are formed templated by the fivefold rings at dislocation cores. They subsequently form columns of rhombic and elongated hexagonal tiles parallel to the dislocation lines. Quasicrystalline precipitates are formed by random tiling of these rhombic and hexagonal tiles. Such precipitation may impact dislocation glide and alloy strength.
Title:
From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca-Au-Al: In Situ Variable-Temperature Transformation
Authors:
Pham, J; Meng, FQ; Lynn, M; Ma, T; Kreyssig, A; Kramer, MJ; Goldman, AI; Miller, GJ Author Full Names: Pham, Joyce; Meng, Fanqiang; Lynn, Matthew.; Ma, Tao; Kreyssig, Andreas; Kramer, Matthew J.; Goldman, Alan I.; Miller, Gordon J.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 140 (4):1337-1347; 10.1021/jacs.7b10358 JAN 31 2018
Abstract:
The irreversible transformation from an icosahedral quasicrystal (i-QC) CaAu4.39Al1.61 to its cubic 2/1 crystalline approximant (CA) Ca13Au56.31 Al-(3)(21.69) (CaAu4.33(1)Al1.67, Pa (3) over bar (No. 205); Pearson symbol: cP728; a = 23.8934(4)), starting at similar to 570 degrees C and complete by similar to 650 degrees C, is discovered from in situ, high-energy, variable-temperature powder X-ray diffraction (PXRD), thereby providing direct experimental evidence for the relationship between QCs and their associated CAs. The new cubic phase crystallizes in a Tsai-type approximant structure under the broader classification of polar intermetallic compounds, in which atoms of different electronegativities, viz., electronegative Au + Al vs electropositive Ca, are arranged in concentric shells. From a structural chemical perspective, the outermost shell of this cubic approximant may be described as interpenetrating and edge-sharing icosahedra, a perspective that is obtained by splitting the traditional structural description of this shell as a 92-atom rhombic triacontahedron into an 80-vertex cage of primarily Au [Au59.86(2)Al17.14 square(3.00)] and an icosahedral shell of only Al [Al-10.5 square(1.5)]. Following the proposal that the cubic 2/1 CA approximates the structure of the i-QC and on the basis of the observed transformation, an atomic site analysis of the 2/1 CA, which shows a preference to maximize the number of heteroatomic Au-Al nearest neighbor contacts over homoatomic Al-Al contacts, implies a similar outcome for the i-QC structure. Analysis of the most intense reflections in the diffraction pattern of the cubic 2/1 CA that changed during the phase transformation shows correlations with icosahedral symmetry, and the stability of this cubic phase is assessed using valence electron counts. According to electronic structure calculations, a cubic 1/1 CA, "Ca24Au88Al (64)" (CaAu3.67Al2.67) is proposed.

Update: 1-Mar-2018

Title:
On the kinetic and equilibrium shapes of icosahedral Al71Pd19Mn10 quasicrystals
Authors:
Senabulya, N; Xiao, XH; Han, I; Shahani, AJ Author Full Names: Senabulya, Nancy; Xiao, Xianghui; Han, Insung; Shahani, Ashwin J.
Source:
SCRIPTA MATERIALIA, 146 218-221; 10.1016/j.scriptamat.2017.11.049 MAR 15 2018
Abstract:
The dynamics of growth and relaxation of icosahedral single quasicrystals in a liquid phase were investigated using in situ synchrotron-based X-ray tomography. Our 4D studies (i.e., space- and time-resolved) provide direct evidence that indicates the growth process of an Al71Pd19Mn10 quasicrystal is governed predominantly by bulk transport rather than attachment kinetics. This work is in agreement with theoretical predictions, which show that the pentagonal dodecahedron is not the minimum energy structure in Al-Pd-Mn icosahedral quasicrystals, but merely a growth shape characterized by non-zero anisotropic velocity. This transient shape transforms into a truncated dodecahedral Archimedian polyhedron once equilibrium has been attained. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
A Cesium Rare-Earth Silicate Cs3RESi6O15 (RE = Dy-Lu, Y, In): The Parent of an Unusual Structural Class Featuring a Remarkable 57 angstrom Unit Cell Axis
Authors:
Terry, R; Vinton, D; McMillen, CD; Kolis, JW Author Full Names: Terry, Rylan; Vinton, Daniel; McMillen, Colin D.; Kolis, Joseph W.
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 57 (8):2077-2080; 10.1002/anie.201708798 FEB 19 2018
Abstract:
The structure of Cs3RESi6O15, where RE=Dy-Lu, Y, In, is unusual in that it contains octahedrally coordinated rare-earth ions; their relative orientation dictates the structure, as they rotate about the c-axis supported by the cyclic Si6O15 framework. The repeat unit of the rotation is eight units generating a very long (ca. 57 angstrom) unit cell axis. This unusual repeat unit is created by the structural flexibility of the hexasilicate ring, which is in turn affected by the size of the rare earth ion as well as the size of alkali ion residing within the silicate layers. Previous work showed for the smaller Sc3+ ion, the rotation of the octahedra is not sufficient to achieve closure at an integral repeat unit and an incommensurate structure results. The products are prepared as large, high quality single crystals using a high-temperature (650 degrees C) hydrothermal method with CsOH and F- mineralizers. The presence of fluoride is essential to the formation of the product.
Title:
Enhancement and destruction of spin-Peierls physics in a one-dimensional quantum magnet under pressure
Authors:
Rotundu, CR; Wen, JJ; He, W; Choi, Y; Haskel, D; Lee, YS Author Full Names: Rotundu, Costel R.; Wen, Jiajia; He, Wei; Choi, Yongseong; Haskel, Daniel; Lee, Young S.
Source:
PHYSICAL REVIEW B, 97 (5):10.1103/PhysRevB.97.054415 FEB 15 2018
Abstract:
The application of pressure reveals a rich phase diagram for the quantum S = 1/2 spin chain material TiOCl. We performed x-ray diffraction on single-crystal samples in a diamond-anvil cell down to T = 4 K and pressures up to 14.5 GPa. Remarkably, the magnetic interaction scale increases dramatically with increasing pressure, as indicated by the high onset temperature of the spin-Peierls phase. The spin-Peierls phase was probed at similar to 6 GPa up to 215 K but possibly extends in temperature to above T = 300 K, indicating the possibility of a quantum singlet state at room temperature. Near the critical pressure for the transition to the more metallic phase, coexisting phases are exemplified by incommensurate order in two directions. Further comparisons are made with the phase diagrams of related spin-Peierls systems that display metallicity and superconductivity under pressure.
Title:
Effect of imperfections on the hyperuniformity of many-body systems
Authors:
Kim, J; Torquato, S Author Full Names: Kim, Jaeuk; Torquato, Salvatore
Source:
PHYSICAL REVIEW B, 97 (5):10.1103/PhysRevB.97.054105 FEB 12 2018
Abstract:
A hyperuniform many-body system is characterized by a structure factor S(k) that vanishes in the small-wave-number limit or equivalently by a local number variance sigma(2)(N) (R) associated with a spherical window of radius R that grows more slowly than R-d in the large-R limit. Thus, the hyperuniformity implies anomalous suppression of long-wavelength density fluctuations relative to those in typical disordered systems, i.e., sigma(2)(N) (R) similar to R-d as R -> infinity. Hyperuniform systems include perfect crystals, quasicrystals, and special disordered systems. Disordered hyperuniform systems are amorphous states of matter that lie between a liquid and crystal [S. Torquato et al., Phys. Rev. X 5, 021020 (2015)], and have been the subject of many recent investigations due to their novel properties. In the same way that there is no perfect crystal in practice due to the inevitable presence of imperfections, such as vacancies and dislocations, there is no "perfect" hyperuniform system, whether it is ordered or not. Thus, it is practically and theoretically important to quantitatively understand the extent to which imperfections introduced in a perfectly hyperuniform system can degrade or destroy its hyperuniformity and corresponding physical properties. This paper begins such a program by deriving explicit formulas for S(k) in the small-wave-number regime for three types of imperfections: (1) uncorrelated point defects, including vacancies and interstitials, (2) stochastic particle displacements, and (3) thermal excitations in the classical harmonic regime. We demonstrate that our results are in excellent agreement with numerical simulations. We find that "uncorrelated" vacancies or interstitials destroy hyperuniformity in proportion to the defect concentration p. We show that "uncorrelated" stochastic displacements in perfect lattices can never destroy the hyperuniformity but it can be degraded such that the perturbed lattices fall into class III hyperuniform systems, where sigma(2)(N) (R) similar to Rd-alpha as R -> infinity and 0 < alpha < 1. By contrast, we demonstrate that certain "correlated" displacements can make systems nonhyperuniform. For a perfect (ground-state) crystal at zero temperature, increase in temperature T introduces such correlated displacements resulting from thermal excitations, and thus the thermalized crystal becomes nonhyperuniform, even at an arbitrarily low temperature. It is noteworthy that imperfections in disordered hyperuniform systems can be unambiguously detected. Our work provides the theoretical underpinnings to systematically study the effect of imperfections on the physical properties of hyperuniform materials.
Title:
Magnetoelectric and Raman spectroscopic studies of monocrystalline MnCr2O4
Authors:
Lin, GT; Wang, YQ; Luo, X; Ma, J; Zhuang, HL; Qian, D; Yin, LH; Chen, FC; Yan, J; Zhang, RR; Zhang, SL; Tong, W; Song, WH; Tong, P; Zhu, XB; Sun, YP Author Full Names: Lin, G. T.; Wang, Y. Q.; Luo, X.; Ma, J.; Zhuang, H. L.; Qian, D.; Yin, L. H.; Chen, F. C.; Yan, J.; Zhang, R. R.; Zhang, S. L.; Tong, W.; Song, W. H.; Tong, P.; Zhu, X. B.; Sun, Y. P.
Source:
PHYSICAL REVIEW B, 97 (6):10.1103/PhysRevB.97.064405 FEB 12 2018
Abstract:
MnCr2O4 that exhibits spin frustration and complex spiral spin order is of great interest from both fundamental as well as application-oriented perspectives. Unlike CoCr2O4, whose ground state presents the coexistence of commensurate spiral spin order (CSSO) and ferroelectric order, MnCr2O4 shows no multiferroicity. One reason is that the spiral spin order is highly sensitive to the oxygen concentration in MnCr2O4. Here, we have successfully grown high-quality single-crystalline MnCr2O4 by the chemical vapor transport method. We observe a first-order magnetic transition from the incommensurate spiral spin order (ICSSO) at 19.4 K to the CSSO at 17.4 K. This magnetic transition is verified by magnetization, specific heat, and magnetoelectric measurements, which also confirm that the ground state exhibits the coexistence of the CSSO and magnetoelectricity below 17.4 K. Interestingly, the temperature evolution of Raman spectra between 5.4 and 300 K suggests that the structure remains the same. We also find that the phase-transition temperature of the CSSO decreases as applied magnetic field increases up to 45 kOe.
Title:
Magnetic state selected by magnetic dipole interaction in the kagome antiferromagnet NaBa2Mn3F11
Authors:
Hayashida, S; Ishikawa, H; Okamoto, Y; Okubo, T; Hiroi, Z; Avdeev, M; Manuel, P; Hagihala, M; Soda, M; Masuda, T Author Full Names: Hayashida, Shohei; Ishikawa, Hajime; Okamoto, Yoshihiko; Okubo, Tsuyoshi; Hiroi, Zenji; Avdeev, Maxim; Manuel, Pascal; Hagihala, Masato; Soda, Minoru; Masuda, Takatsugu
Source:
PHYSICAL REVIEW B, 97 (5):10.1103/PhysRevB.97.054411 FEB 12 2018
Abstract:
We haved studied the ground state of the classical kagome antiferromagnet NaBa2Mn3F11. Strong magnetic Bragg peaks observed for d spacings shorter than 6.0 angstrom were indexed by the propagation vector of k(0) = (0,0,0). Additional peaks with weak intensities in the d-spacing range above 8.0 angstrom were indexed by the incommensurate vector of k(1) = [0.3209(2), 0.3209(2), 0] and k(2) = [0.3338(4), 0.3338(4), 0]. Magnetic structure analysis unveils a 120 degrees. structure with the tail-chase geometry having k(0) modulated by the incommensurate vector. A classical calculation of the Heisenberg kagome antiferromagnet with antiferromagnetic second-neighbor interaction, for which the ground state a k(0) 120 degrees. degenerated structure, reveals that the magnetic dipole-dipole (MDD) interaction including up to the fourth neighbor terms selects the tail-chase structure. The observed modulation of the tail-chase structure is attributed to a small perturbation such as the long-range MDD interaction or the interlayer interaction.
Title:
Magnetic structure of the swedenborgite CaBa(Co3Fe)O-7 derived by unpolarized neutron diffraction and spherical neutron polarimetry
Authors:
Qureshi, N; Diaz, MTF; Chapon, LC; Senyshyn, A; Schweika, W; Valldor, M Author Full Names: Qureshi, N.; Diaz, M. T. Fernandez; Chapon, L. C.; Senyshyn, A.; Schweika, W.; Valldor, M.
Source:
PHYSICAL REVIEW B, 97 (6):10.1103/PhysRevB.97.064404 FEB 9 2018
Abstract:
We present a study that combines polarized and unpolarized neutrons to derive the magnetic structure of the swedenborgite compound CaBa(Co3Fe)O-7. Integrated intensities from a standard neutron diffraction experiment and polarization matrices from spherical neutron polarimetry have been simultaneously analyzed revealing a complex order, which differs from the usual spin configurations on a kagome lattice. We find that the magnetic structure is well described by a combination of two one-dimensional representations corresponding to themagnetic superspace symmetry P2(1)' and it consists of spins rotating around an axis close to the [110] direction. Due to the propagation vector q = (1/300), this modulation has cycloidal and helicoidal character rendering this system a potential multiferroic. The resulting spin configuration can be mapped onto the classical root 3 x root 3 structure of a kagome lattice, and it indicates an important interplay between the kagome and the triangular layers of the crystal structure.
Title:
Atomic channel occupation in disordered eta-Al5Fe2 and in two of its low-temperatures phases, eta '' and eta '''
Authors:
Becker, H; Leineweber, A Author Full Names: Becker, Hanka; Leineweber, Andreas
Source:
INTERMETALLICS, 93 251-262; 10.1016/j.intermet.2017.09.021 FEB 2018
Abstract:
High-temperature, disordered n-Al5Fe2 intermetallic and its low-temperature long-range ordered structures have been investigated in the whole homogeneity range from 70.6 to 73.0 at.% Al based on selected area electron diffraction data and powder X-ray diffraction data. Using these data, the channel site occupation in the disordered eta phase has been revised and a composition-dependent model with mixed occupation of the channels by both Al and Fe atoms was derived. It leads to an average number of atoms per channel and unit cell of approx. 1.5 in the whole homogeneity range. Below about 350 degrees C, four different phases exhibiting long-range order of the channel atoms appear to exist. Here the atomic ordering in the Al-poorest and Al-richest of these low-temperature phases, eta '' and eta ''' is reported. Both these phases can be characterized as incommensurately modulated composite crystal structures. Thereby, in both phases, the first composite subsystem contains atoms of the framework structure generating channels which are filled by atoms described by the second composite subsystem. The subsystems of the eta '' phase have orthorhombic superspace groups Xmcm(00g)0s0 and Inunm(00g)0s0 keeping the basic metric of the parent eta phase. The subsystems of the eta ''' can be described by the monoclinic superspace groups P2(1)/c(0b0)00 and P2(1)/c(0b0)s0 providing a lattice correspondence a(m) = 1/2(a + b), b(m) = c and c(m) = a +b to the orthorhombic parent eta phase. Although the number of atoms per channel is approx. 1.5 in eta '' and eta ''' phases, the channels are differently correlated with each other which is attributed to different Fe content in the channels inherited from the channel occupation in the disordered eta phase.
Title:
Observation of a dodecagonal oxide quasicrystal and its complex approximant in the SrTiO3-Pt(111) system
Authors:
Schenk, S; Forster, S; Meinel, K; Hammer, R; Leibundgut, B; Paleschke, M; Pantzer, J; Dresler, C; Schumann, FO; Widdra, W Author Full Names: Schenk, Sebastian; Foerster, Stefan; Meinel, Klaus; Hammer, Rene; Leibundgut, Bettina; Paleschke, Maximilian; Pantzer, Jonas; Dresler, Christoph; Schumann, Florian O.; Widdra, Wolf
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (13):10.1088/1361-648X/aa5bdb APR 5 2017
Abstract:
We report on the formation of a SrTiO3-derived dodecagonal oxide quasicrystal (OQC) at the interface to Pt(111). This is the second observation of a two-dimensional quasicrystal in the class of oxides. The SrTiO3-derived OQC exhibits strong similarities to the BaTiO3-derived OQC with respect to the local tiling geometry. However, the characteristic length scale of the SrTiO3-derived OQC is 1.8% smaller. Coexisting with the OQC a large scale approximant structure with a monoclinic unit cell is identified. It demonstrates the extraordinary level of complexity that oxide approximant structures can reach.

Update: 21-Feb-2018

Title:
A non-uniformly loaded anti-plane crack embedded in a half-space of a one-dimensional piezoelectric quasicrystal
Authors:
Tupholme, G Author Full Names: Tupholme, G. E.
Source:
MECCANICA, 53 (4-5):973-983; 10.1007/s11012-017-0759-1 MAR 2018
Abstract:
Closed-form representations are obtained using an extension of the classical continuous dislocation layer method combined with a method of images for the components of the phonon and phason stress and electric displacement fields around a generally loaded strip crack in a half-space of one-dimensional hexagonal piezoelectric quasicrystalline material parallel to its free surface. Representative numerical data are presented graphically.
Title:
Similar local order in disordered fluorite and aperiodic pyrochlore structures
Authors:
Shamblin, J; Tracy, CL; Palomares, RI; O'Quinn, EC; Ewing, RC; Neuefeind, J; Feygenson, M; Behrens, J; Trautmann, C; Lang, M Author Full Names: Shamblin, Jacob; Tracy, Cameron L.; Palomares, Raul I.; O'Quinn, Eric C.; Ewing, Rodney C.; Neuefeind, Joerg; Feygenson, Mikhail; Behrens, Jason; Trautmann, Christina; Lang, Maik
Source:
ACTA MATERIALIA, 144 60-67; 10.1016/j.actamat.2017.10.044 FEB 1 2018
Abstract:
A major challenge to understanding the response of materials to extreme environments (e.g., nuclear fuels/waste forms and fusion materials) is to unravel the processes by which a material can incorporate atomic-scale disorder, and at the same time, remain crystalline. While it has long been known that all condensed matter, even liquids and glasses, possess short-range order, the relation between fully-ordered, disordered, and aperiodic structures over multiple length scales is not well understood. For example, when defects are introduced (via pressure or irradiation) into materials adopting the pyrochlore structure, these complex oxides either disorder over specific crystallographic sites, remaining crystalline, or become aperiodic. Here we present neutron total scattering results characterizing the irradiation response of two pyrochlores, one that is known to disorder (Er2Sn2O7) and the other to amorphize (Dy2Sn2O7) under ion irradiation. The results demonstrate that in both cases, the local pyrochlore structure is transformed into similar short range configurations that are best fit by the orthorhombic weberite structure, even though the two compositions have distinctly different structures, aperiodic vs. disordered-crystalline, at longer length scales. Thus, a material's resistance to amorphization may not depend primarily on local defect formation energies, but rather on the structure's compatibility with meso-scale modulations of the local order in a way that maintains long-range periodicity. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Cesium immobilization in (Ba,Cr)-hollandites: Effects on structure
Authors:
Tumurugoti, P; Sundaram, SK; Misture, ST Author Full Names: Tumurugoti, Priyatham; Sundaram, S. K.; Misture, Scott T.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 258 72-78; 10.1016/j.jssc.2017.10.008 FEB 2018
Abstract:
Hollandites with compositions Ba1.15-xCs2xCr2.3Ti5.7O16 (0 <= x <= 1.15) intended for the immobilization of cesium (Cs) from nuclear waste have been prepared, characterized, and analyzed for Cs retention properties. Sol-gel synthesized powders were used for structural characterization using a combination of X-ray, neutron, and electron diffraction techniques. Phase-pure hollandites adopting tetragonal (I4/m) or monoclinic symmetry (I2/m) were observed to form in the compositional range 0 <= x <= 0.4. Structural models for the compositions, x = 0, 0.15, and 0.25 were developed from Rietveld analysis of powder diffraction data. Refined anisotropic displacement parameters (beta(ij)) for the Ba and Cs ions in the hollandite tunnels indicate local disorder of Ba/Cs along the tunnel direction. In addition, weak superlattice reflections were observed in X-ray and electron diffraction patterns that were due to the compositional modulation i.e., ordering of ions and vacancies along tunnel direction. Our overall observations suggest the phase-pure hollandites studied assumed supercell structures with ordered tunnel cations, which in turn have positional disorder in individual supercells.
Title:
Phase relations in the pseudo ternary system In2O3-TiO2-BO (B: Zn, Co and Ni) at 1200 degrees C in air
Authors:
Brown, F; Jacobo-Herrera, IE; Alvarez-Montano, VE; Kimizuka, N; Hirano, T; Sekine, R; Denholme, SJ; Miyakawa, N; Kudo, A; Iwase, A; Michiue, Y Author Full Names: Brown, Francisco; Edmundo Jacobo-Herrera, Ivan; Emmanuel Alvarez-Montano, Victor; Kimizuka, Noboru; Hirano, Tomonosuke; Sekine, Ryotaro; Denholme, Saleem J.; Miyakawa, Nobuaki; Kudo, Akihiko; Iwase, Akihide; Michiue, Yuichi
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 258 865-875; 10.1016/j.jssc.2017.12.020 FEB 2018
Abstract:
Phase relations in the pseudo ternary systems In2O3-TiO2-ZnO, In2O3-TiO2-CoO and In2O3-TiO2-NiO at 1200 degrees C in air were determined by means of a classic quenching method. In6Ti6BO22 (B: Zn, Co and Ni) which has the monoclinic In(Fe1/4Ti3/4)O-27/8-type of structure with a 4-dimensional super space group exists in a stable form. There exist homologous phases In1-x(Ti1/2Zn1/2)(1-x)O-3(ZnO)(m) (m: natural number, 0 m (No. 166) for m = odd or P63/mmc (No. 194) for m = even in space group. Lattice constants for each of the homologous compounds as a hexagonal setting and In6Ti6BO22 as the monoclinic system were determined by means of the powder X-ray diffraction method at room temperature. The temperature dependence of resistivity for In1-x(Ti1/2Zn1/2)(1-x)(ZnO)(4) (0.15 <= x <= 1) showed semiconducting like behavior for all samples examined at T(K) = 2-300. The resistivity increased systematically with decreasing x (0.7 <= x <= 1), and it was found that samples where x <= 0.7 became insulators. The optical band gap E-g (eV) of In1+x(Ti1/2Zn1/2)(1-x)(ZnO)(4) has been estimated from the diffuse reflection spectra for the whole range of x (0.15 <= x <= 1). A minimum value of 2.0717 eV for x = 1 and a maximum one of 3.066 eV for x = 0.15 were observed. Dependence of the crystal structures of the InAO(3)(BO), In(Ti1/2B1/2)O-3(B'O) and stability of In6Ti6BO22 upon the constituent cations in the pseudo quaternary system In2O3-TiO2-A(2)O(3)-BO (A: Fe, Ga and Cr; B, B': Mg, Zn, Co, Ni, Ca and Sr) were discussed in terms of their ionic radii and site preference effects.
Title:
Hybrid aluminium matrix composites containing boron carbide and quasicrystals: manufacturing and characterisation
Authors:
Khan, M; Zulfaqar, M; Ali, F; Subhani, T Author Full Names: Khan, Mahmood; Zulfaqar, Muhammad; Ali, Fahad; Subhani, Tayyab
Source:
MATERIALS SCIENCE AND TECHNOLOGY, 33 (16):1955-1963; 10.1080/02670836.2017.1342017 2017
Abstract:
Hybrid composites of boron carbide (B4C) and Al62.5Cu25Fe12.5 quasicrystals (QCs) were prepared by ball milling and pressureless sintering in aluminium matrix to investigate their individual and hybrid effects on microstructural and mechanical properties. Hybrid composite contained B4C and QCs in 3 wt-% each, making a total of 6 wt-%. For reference, specimens of pure aluminium and two composites containing 6 wt-% B4C and 6 wt-% QCs were prepared. Microstructural characterisation was performed using optical, scanning electron microscopy and X-ray diffraction, while evaluation of mechanical properties was carried out by hardness and compression tests. Uniform dispersion of reinforcements in composites was observed along with significant increase in the mechanical properties. The composite containing 6 wt-% QCs demonstrated the highest hardness, while the hybrid composite showed better compressive properties.
Title:
Microstructure and mechanical properties of Mg-Zn-Y alloy under a steady magnetic field
Authors:
Zhang, L; Jin, F; Zhan, W; Hu, PH; Zhou, Q Author Full Names: Zhang, L.; Jin, F.; Zhan, W.; Hu, P. H.; Zhou, Q.
Source:
MATERIALS SCIENCE AND TECHNOLOGY, 33 (18):2197-2202; 10.1080/02670836.2017.1353662 2017
Abstract:
This study examined the effect of steady magnetic field on the microstructure and mechanical properties of Mg-Zn-Y alloy reinforced by icosahedral quasicrystal phase. Results show that the microstructure of Mg-Zn-Y alloy was further refined as the magnetic field intensity increased. However, the primary alpha-Mg gradually became coarse over a certain value. No significant effect on the refinement of icosahedral quasicrystal phase was observed. The (10 (1) over bar1) plane of the alloy treated by steady magnetic field was substituted by the (0002) plane as the primary plane. The (10 (1) over bar2) plane was intensified gradually as the intensity of the magnetic field increased. The mechanical properties of Mg-Zn-Y alloy also improved with steady magnetic field treatment.

Update: 15-Feb-2018

Title:
Relaxor nature in Ba5RZr3Nb7O30 (R = La, Nd, Sm) tetragonal tungsten bronze new system
Authors:
Feng, WB; Zhu, XL; Liu, XQ; Fu, MS; Ma, X; Jia, SJ; Chen, XM Author Full Names: Feng, Wen Bin; Zhu, Xiao Li; Liu, Xiao Qiang; Fu, Mao Sen; Ma, Xiao; Jia, Shu Jing; Chen, Xiang Ming
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 101 (4):1623-1631; 10.1111/jace.15332 APR 2018
Abstract:
Ba5RZr3Nb7O30(R=La, Nd, Sm) lead-free relaxor ferroelectrics were prepared by a standard solid-state reaction process, and the influence of A and B site ion occupation on the dielectric characteristics especially the relaxor nature were investigated systematically. Tetragonal tungsten bronze structure with space group P4/mbm was determined for all compositions, ion cross distribution by Ba2+ and R3+ in A1 site was observed, while A2 site was only occupied by Ba2+. Selected area electron diffraction patterns confirmed the existence of incommensurate superlattice modulation. Furthermore, temperature and frequency dependences of the dielectric properties showed a broad permittivity peak with strong frequency dispersion, following well the Vogel-Fulcher relationship. The maximum dielectric constant temperature increased gradually with decreasing A1 site ion size. Slim P-E hysteresis loops were obtained at room temperature for all compositions. Meanwhile, micro ferroelectric domains were observed in Ba5SmZr3Nb7O30. For Ba4R2Zr4Nb6O30 and Ba5RZr3Nb7O30 (R=Nd, Sm), the transition from normal ferroelectric to relaxor behavior originates from the increased t(A1), which is a result of cross distribution at A1 site. Compared with Ba5RTi3Nb7O30, Zr substitution at B site enhances the relaxor nature.
Title:
Crystallite size effect on the monoclinic deformation of the bcc crystal structure of chromium
Authors:
Przenioslo, R; Fabrykiewicz, P; Sosnowska, I; Wardecki, D; Slawinski, WA; Playford, HY; Hempelmann, R; Bukowski, M Author Full Names: Przenioslo, R.; Fabrykiewicz, P.; Sosnowska, I.; Wardecki, D.; Slawinski, W. A.; Playford, H. Y.; Hempelmann, R.; Bukowski, M.
Source:
PHYSICA B-CONDENSED MATTER, 530 183-190; 10.1016/j.physb.2017.10.086 FEB 1 2018
Abstract:
The modulated spin density wave magnetic orderings observed in chromium suggests that the crystal structure of chromium cannot be described by the cubic space group Im3m. Our experimental studies of polycrystalline and nanocrystalline chromium by synchrotron radiation (SR) and neutron powder diffraction show a hkl-dependent Bragg peak broadening which can be interpreted by the low-symmetry monoclinic space group P2(1)/n instead of the high symmetry cubic space group Im3m. Themonoclinic angle is beta(m) = 90.05(1)degrees and 90.29(1)degrees for polycrystalline Cr and nanocrystalline Cr, respectively. The relative monoclinic distortion observed in chromium is 5 times larger than those reported for several oxides: BiFeO3, alpha-Fe2O3, Cr2O3 and calcite. The symmetry of the magnetic transverse spin density wave (TSDW) and the longitudinal spin density wave (LSDW) observed in Cr are described by using the superspace groups P2(1)/n(0 beta 0)00 and P2'(1)/n'(0 beta 0)00, respectively. These superspace groups describe both the magnetic modulations and the atomic position modulations reported in the literature. The monoclinic symmetry of chromium is a robust effect which is observed in the paramagnetic as well as in the TSDW and LSDW phases.

Update: 7-Feb-2018

Title:
Field-induced magnetic phase transitions and memory effect in bilayer ruthenate Ca3Ru2O7 with Fe substitution
Authors:
Zhu, M; Hong, T; Peng, J; Zou, T; Mao, ZQ; Ke, X Author Full Names: Zhu, M.; Hong, T.; Peng, J.; Zou, T.; Mao, Z. Q.; Ke, X.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 30 (7):10.1088/1361-648X/aaa626 FEB 21 2018
Abstract:
Bilayer ruthenate Ca-3(Ru(1-x)Fex)(2)O-7 (x = 0.05) exhibits an incommensurate magnetic soliton lattice driven by the Dzyaloshinskii-Moriya interaction. Here we report complex field-induced magnetic phase transitions and memory effect in this system via single-crystal neutron diffraction and magnetotransport measurements. We observe first-order incommensurateto- commensurate magnetic transitions upon applying the magnetic field both along and perpendicular to the propagation axis of the incommensurate spin structure. Furthermore, we find that the metastable states formed upon decreasing the magnetic field depend on the temperature and the applied field orientation. We suggest that the observed field-induced metastability may be ascribable to the quenched kinetics at low temperature.
Title:
Two superstructures of Ce3Rh4Ge4
Authors:
Vosswinkel, D; Hoffmann, RD; Svitlyk, V; Hermes, W; Greiwe, M; Niehaus, O; Chevalier, B; Matar, SF; Al Alam, AF; Nakhl, M; Ouaini, N; Pottgen, R Author Full Names: Vosswinkel, Daniel; Hoffmann, Rolf-Dieter; Svitlyk, Volodymyr; Hermes, Wilfried; Greiwe, Magnus; Niehaus, Oliver; Chevalier, Bernard; Matar, Samir F.; Al Alam, Adel F.; Nakhl, Michel; Ouaini, Naim; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 233 (2):81-95; 10.1515/zkri-2017-2092 FEB 2018
Abstract:
Two different samples of Ce3Rh4Ge4 were synthesized from different starting compositions by melting of the elements in an arc-melting furnace followed by annealing sequences in a sealed tantalum ampoule in a muffle furnace. The structures of two different stacking variants were refined on the basis of temperature dependent single-crystal X-ray diffractometer data. At high temperature Ce3Rh4Ge4 adopts the U3Ni4Si4 type structure with strongly enhanced anisotropic displacement parameters for the Rh1 atoms. For the two different crystals, additional reflections start to appear at different temperatures. The first crystal showed additional reflections already at room temperature (stacking variant I) and the second one showed additional reflections emerging below 270 K (stacking variant II). Stacking variant I could be described with the (3 + 1)D superspace group I2/m(alpha 0 gamma)00; alpha = 1/2a*, gamma = 1/2c*; (Z = 2), 1252 F-2 values, 48 variables, wR = 0.0306 for the main and wR = 0.0527 for 440 1st order satellite reflections, similar to Pr3Rh4Ge4. For stacking variant II the (3 + 1) D superspace group is Immm(alpha 00)00s; alpha = 1/2a*; (Z = 2). The structure could be refined with 1261 F-2 values, 53 variables and residuals of wR = 0.0331 for the main reflections and wR = 0.1755 (R1(obs) = 0.0788) for the 1st order satellite reflections, [a = 406.2(1), b = 423.7(1) and c = 2497.1(1) pm]. The commensurate description could be transformed to a three-dimensional (3D)supercell with space group Pnma and Z = 4: a = 812.5(1), b = 423.7(1), c = 2497.1(2) pm, 1261 F-2 values, 69 variables and wR = 0.0525. The relation of the U3Ni4Si4 type structure, the (3 + 1) D modulated and the 3D supercells are discussed on the basis of group-subgroup schemes. Ab initio electronic structure calculations are in line with the diffraction experiments, revealing the lowest total energy for the Pnma phase.
Title:
Incommensurate Phonon Anomaly and the Nature of Charge Density Waves in Cuprates
Authors:
Miao, H; Ishikawa, D; Heid, R; Le Tacon, M; Fabbris, G; Meyers, D; Gu, GD; Baron, AQR; Dean, MPM Author Full Names: Miao, H.; Ishikawa, D.; Heid, R.; Le Tacon, M.; Fabbris, G.; Meyers, D.; Gu, G. D.; Baron, A. Q. R.; Dean, M. P. M.
Source:
PHYSICAL REVIEW X, 8 (1):10.1103/PhysRevX.8.011008 JAN 18 2018
Abstract:
While charge density wave (CDW) instabilities are ubiquitous to superconducting cuprates, the different ordering wave vectors in various cuprate families have hampered a unified description of the CDW formation mechanism. Here, we investigate the temperature dependence of the low-energy phonons in the canonical CDW-ordered cuprate La1.875Ba0.125CuO4. We discover that the phonon softening wave vector associated with CDW correlations becomes temperature dependent in the high-temperature precursor phase and changes from a wave vector of 0.238 reciprocal lattice units (r.l.u.) below the ordering transition temperature to 0.3 r.l.u. at 300 K. This high-temperature behavior shows that "214"-type cuprates can host CDW correlations at a similar wave vector to previously reported CDW correlations in non-214-type cuprates such as YBa2Cu3O6+delta. This indicates that cuprate CDWs may arise from the same underlying instability despite their apparently different low-temperature ordering wave vectors.
Title:
The partial substitution of Y with Gd on microstructures and mechanical properties of as-cast and as-extruded Mg-10Zn-6Y-0.5Zr alloy
Authors:
Jiang, HS; Qiao, XG; Zheng, MY; Wu, K; Xu, C; Kamado, S Author Full Names: Jiang, H. S.; Qiao, X. G.; Zheng, M. Y.; Wu, K.; Xu, C.; Kamado, S.
Source:
MATERIALS CHARACTERIZATION, 135 96-103; 10.1016/j.matchar.2017.11.025 JAN 2018
Abstract:
Mg-10Zn-6Y-0.5Zr (wt%) alloy and Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy with medium RE content have been fabricated by conventional casting and indirect extrusion. The as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy shows a bimodal microstructure containing dynamic recrystallized (DRXed) grains with average grain size of 2 mu m and deformed regions. In addition to the fragmented W phase particle bands distributing along the extrusion direction, large amount of nano W phase and small amount of nano beta(2)' phase are precipitated in the matrix. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy exhibits completely dynamic recrystallized microstructure with average grain size of 3 mu m. The broken W phase particles are distributed homogeneously in the matrix. Icosahedral quasicrystal phase layer is observed at the surface of some W phase particles in the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr alloy. The as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy exhibits yield strength of 341 MPa, ultimate tensile strength of 368 MPa and elongation to failure of 6.8%. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy shows lower yield strength of 247 MPa, ultimate tensile strength of 330 MPa and higher elongation to failure of 19.8%. The higher strength in the as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy is mainly attributed to higher area fraction of unDRXed regions with strong texture and the precipitation of nano W and beta(2)' phase. The fully recrystallized microstructure with weak texture and the formation of icosahedral quasi crystal phases with good coherent bond with alpha-Mg contribute to the good ductility of the as-extruded Mg-10Zn3Y-3Gd-0.5Zr alloy.

Update: 1-Feb-2018

Title:
Comment on "The true structural periodicities and superspace group descriptions of the prototypical incommensurate composite materials: Alkane/urea inclusion compounds" by Couzi M. et al
Authors:
Toudic, B; Guerin, L; Mariette, C; Frantsuzov, I; Rabiller, P; Ecolivet, C; Janssen, T; Hollingsworth, MD Author Full Names: Toudic, B.; Guerin, L.; Mariette, C.; Frantsuzov, I.; Rabiller, P.; Ecolivet, C.; Janssen, T.; Hollingsworth, Mark D.
Source:
EPL, 119 (6):10.1209/0295-5075/119/66004 SEP 2017

Update: 25-Jan-2018

Title:
Discovery of superconductivity in quasicrystal
Authors:
Kamiya, K; Takeuchi, T; Kabeya, N; Wada, N; Ishimasa, T; Ochiai, A; Deguchi, K; Imura, K; Sato, NK Author Full Names: Kamiya, K.; Takeuchi, T.; Kabeya, N.; Wada, N.; Ishimasa, T.; Ochiai, A.; Deguchi, K.; Imura, K.; Sato, N. K.
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-017-02667-x JAN 11 2018
Abstract:
Superconductivity is ubiquitous as evidenced by the observation in many crystals including carrier-doped oxides and diamond. Amorphous solids are no exception. However, it remains to be discovered in quasicrystals, in which atoms are ordered over long distances but not in a periodically repeating arrangement. Here we report electrical resistivity, magnetization, and specific-heat measurements of Al-Zn-Mg quasicrystal, presenting convincing evidence for the emergence of bulk superconductivity at a very low transition temperature of T-c congruent to 0: 05 K. We also find superconductivity in its approximant crystals, structures that are periodic, but that are very similar to quasicrystals. These observations demonstrate that the effective interaction between electrons remains attractive under variation of the atomic arrangement from periodic to quasiperiodic one. The discovery of the superconducting quasicrystal, in which the fractal geometry interplays with superconductivity, opens the door to a new type of superconductivity, fractal superconductivity.
Title:
Unidirectional spin density wave state in metallic (Sr1-xLax)(2)IrO4
Authors:
Chen, X; Schmehr, JL; Islam, Z; Porter, Z; Zoghlin, E; Finkelstein, K; Ruff, JPC; Wilson, SD Author Full Names: Chen, Xiang; Schmehr, Julian L.; Islam, Zahirul; Porter, Zach; Zoghlin, Eli; Finkelstein, Kenneth; Ruff, Jacob P. C.; Wilson, Stephen D.
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-017-02647-1 JAN 9 2018
Abstract:
Materials that exhibit both strong spin-orbit coupling and electron correlation effects are predicted to host numerous new electronic states. One prominent example is the J(eff) = 1/2 Mott state in Sr2IrO4, where introducing carriers is predicted to manifest high temperature superconductivity analogous to the S = 1/2 Mott state of La2CuO4. While bulk super-conductivity currently remains elusive, anomalous quasiparticle behaviors paralleling those in the cuprates such as pseudogap formation and the formation of a d-wave gap are observed upon electron-doping Sr2IrO4. Here we establish a magnetic parallel between electron-doped Sr2IrO4 and hole-doped La2CuO4 by unveiling a spin density wave state in electron-doped Sr2IrO4. Our magnetic resonant X-ray scattering data reveal the presence of an incommensurate magnetic state reminiscent of the diagonal spin density wave state observed in the monolayer cuprate (La1-xSrx)(2)CuO4. This link supports the conjecture that the quenched Mott phases in electron-doped Sr2IrO4 and hole-doped La2CuO4 support common competing electronic phases.
Title:
Lattice Distortions in TlInSe2 Thermoelectric Material Studied by X-Ray Absorption Fine Structure
Authors:
Hosokawa, S; Stellhorn, JR; Ikemoto, H; Mimura, K; Wakita, K; Mamedov, N Author Full Names: Hosokawa, Shinya; Stellhorn, Jens Ruediger; Ikemoto, Hiroyuki; Mimura, Kojiro; Wakita, Kazuki; Mamedov, Nazim
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 215 (1):10.1002/pssa.201700416 JAN 2018
Abstract:
Tl L-II and In K X-ray absorption fine structure (XAFS) measurements were performed on a TlInSe2 thermoelectric material in the temperature range of 25-300K including the incommensurate-commensurate phase transition temperature of about 135K. Most of the bond lengths obtained from the present XAFS measurements are in good agreement with existing X-ray diffraction data at room temperature, while only the Tl-Tl correlation shows inconsistent values indicating the commensurate properties of the Tl chains expected from the thermodynamic properties. The present XAFS data clearly support positional fluctuations of the Tl atoms found in three-dimensional atomic images reconstructed from X-ray fluorescence holography.
Title:
Hyperuniformity variation with quasicrystal local isomorphism class (vol 29, 204003, 2017)
Authors:
Lin, C; Steinhardt, PJ; Torquato, S Author Full Names: Lin, C.; Steinhardt, P. J.; Torquato, S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (47):10.1088/1361-648X/aa8430 NOV 29 2017

Update: 17-Jan-2018

Title:
Spin waves in planar quasicrystal of Penrose tiling
Authors:
Rychly, J; Mieszczak, S; Klos, JW Author Full Names: Rychly, J.; Mieszczak, S.; Klos, J. W.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 450 18-23; 10.1016/j.jmmm.2017.03.029 MAR 15 2018
Abstract:
We investigated two-dimensional magnonic structures which are the counterparts of photonic quasicrystals forming Penrose tiling. We considered the slab composed of Ni (or Py) disks embedded in Fe (or Co) matrix. The disks are arranged in quasiperiodic Penrose-like structure. The infinite quasicrystal was approximated by its rectangular section with periodic boundary conditions applied. This approach allowed us to use the plane wave method to find the frequency spectrum of eigenmodes for spin waves and their spatial profiles. The calculated integrated density of states shows more distinctive magnonic gaps for the structure composed of materials of high magnetic contrast (Ni and Fe) and relatively high filling fraction. This proves the impact of quasiperiodic long-range order on the spectrum of spin waves. We also investigated the localization of spin wave eingenmodes resulting from the quasiperiodicity of the structure. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Defects in Static Elasticity of Quasicrystals
Authors:
Xu, Q; Lu, J; Li, W Author Full Names: Xu, Qin; Lu, Jing; Li, Wu
Source:
CRYSTALS, 7 (12):10.3390/cryst7120373 DEC 2017
Abstract:
A review on mathematical elasticity of quasicrystals is given. In this review, the focus is on various defects of quasicrystals. Dislocation and crack are two classes of typical topological defects, while their existence has great influence on the mechanical behavior of quasicrystals. The analytic and numerical solutions of dislocations and crack in quasicrystals are the core of the static and dynamic elasticity theory, and this paper gives a comprehensive review on the solutions for dislocations and crack with different configurations in different various important quasicrystalline systems. We review some results in linear elasticity of quasicrystals, referring to different boundary value problems. We also add some new achievements.
Title:
Structurally Complex Frank-Kasper Phases and Quasicrystal Approximants: Electronic Origin of Stability
Authors:
Degtyareva, VF; Afonikova, NS Author Full Names: Degtyareva, Valentina F.; Afonikova, Natalia S.
Source:
CRYSTALS, 7 (12):10.3390/cryst7120359 DEC 2017
Abstract:
Metal crystals with tetrahedral packing are known as Frank-Kasper phases, with large unit cells with the number of atoms numbering from hundreds to thousands. The main factors of the formation and stability of these phases are the atomic size ratio and the number of valence electrons per atom. The significance of the electronic energy contribution is analyzed within the Fermi sphere-Brillouin zone interaction model for several typical examples: Cu4Cd3, Mg2Al3 with over a thousand atoms per cell, and for icosahedral quasicrystal approximants with 146-168 atoms per cell. Our analysis shows that to minimize the crystal energy, it is important that the Fermi sphere (FS) is in contact with the Brillouin zones that are related to the strong diffraction peaks: the zones either inscribe the FS or are circumscribed by the FS creating contact at edges or vertices.

Update: 11-Jan-2018

Title:
Influence of Ag replacement on supercooled liquid region and icosahedral phase precipitation of Zr65Al7.5Ni10Cu17.5-xAgx (x=0-17.5 at%) glassy alloys
Authors:
Li, MM; Inoue, A; Han, Y; Kong, FL; Zhu, SL; Shalaan, E; Al-Marzouki, F Author Full Names: Li, M. M.; Inoue, A.; Han, Y.; Kong, F. L.; Zhu, S. L.; Shalaan, E.; Al-Marzouki, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 735 1712-1721; 10.1016/j.jallcom.2017.11.203 FEB 25 2018
Abstract:
The glass transition phenomenon for Zr65Al7.5Ni10Cu17.5-xAgx (x = 5-17.5 at%) glassy alloys was observed in the Ag content range below about 15% and the icosahedral phase precipitated as the heating-induced primary phase in the limited Ag content range. In the higher Ag content range where glass transition is not clearly observed, the primary precipitation phase changed to mixed phases of tetragonal Zr3Ag + tetragonal Zr2Ni + hexagonal Zr4Al3. The good correspondence between the appearance of glass transition and the icosahedral phase precipitation was recognized in the multicomponent glassy alloys containing the immiscible type atomic pairs of Ni-Ag and Cu-Ag. Although neither glass transition nor supercooled liquid region is observed for Zr65Al7.5Ni10Ag17.5 and no icosahedral phase is formed, a modified Zr65Al7.5Ni17.5Ag10 alloy with higher Ni/Ag content ratio exhibits glass transition and supercooled liquid region and the primary precipitates also changes to an icosahedral phase. The good correspondence can be interpreted on the basis of the previous knowledge that the appearance of glass transition and supercooled liquid state originates from icosahedral-like medium range ordered atomic configurations. Besides, the 6% Ag-containing alloy keeps high glass-forming ability which is high enough to form a bulk glassy alloy rod of 6 mm by suction casting. The close correlation between the appearance of glass transition phenomenon and the primary precipitation of icosahedral phase is expected to provide a useful knowledge on the role of icosahedral-like atomic configuration in the achievement of bulk glass-forming ability through the stabilization of supercooled liquid. (C) 2017 Elsevier B.V. All rights reserved.
Title:
The role of hydrogen bonds in order-disorder transition of a new incommensurate low temperature phase beta-[Zn-(C7H4NO4)(2)]center dot 3H(2)O
Authors:
Tabatabaee, M; Poupon, M; Eigner, V; Vanek, P; Dusek, M Author Full Names: Tabatabaee, Masoumeh; Poupon, Morgane; Eigner, Vaclav; Vanek, Premysl; Dusek, Michal
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 233 (1):17-25; 10.1515/zkri-2016-2013 JAN 2018
Abstract:
The room temperature structure with P2(1)/c symmetry of the zinc(II) complex of pyridine-2,6-dicarboxylic acid was published by Okabe and Oya (N. Okabe, N. Oya, Copper(II) and zinc(II) complexes of pyridine-2,6-dicarboxylic acid. Acta Crystallogr. C. 2000, 56, 305). Here we report crystal structure of the low temperature phase beta-[Zn(pydcH)(2)]center dot 3H(2)O, pydc = C7H3NO4, resulting from the phase transition around 200 K. The diffraction pattern of the low temperature phase revealed satellite reflections, which could be indexed with q-vector 0.4051(10)b* corresponding to (3 + 1)D incommensurately modulated structure. The modulated structure was solved in the superspace group X2(1)/c(0b0)s0, where X stands for a nonstandard centring vector (1/2, 0, 0, 1/2), and compared with the room temperature phase. It is shown that hydrogen bonds are the main driving force of modulation.
Title:
Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO3
Authors:
Rosenberg, AJ; Katmis, F; Kirtley, JR; Gedik, N; Moodera, JS; Moler, KA Author Full Names: Rosenberg, Aaron J.; Katmis, Ferhat; Kirtley, John R.; Gedik, Nuh; Moodera, Jagadeesh S.; Moler, Kathryn A.
Source:
PHYSICAL REVIEW MATERIALS, 1 (7):10.1103/PhysRevMaterials.1.074406 DEC 15 2017
Abstract:
The combination of ferromagnets with topological superconductors or insulators allows for new phases of matter that support excitations such as chiral edge modes and Majorana fermions. EuS, a wide-bandgap ferromagnetic insulator with a Curie temperature around 16 K, and SrTiO3 (STO), an important substrate for engineering heterostructures, may support these phases. We present scanning superconducting quantum interference device measurements of EuS grown epitaxially on STO that reveal micron-scale variations in ferromagnetism and paramagnetism. These variations are oriented along the STO crystal axes and only change their configuration upon thermal cycling above the STO cubic-to-tetragonal structural transition temperature at 105 K, indicating that the observed magnetic features are due to coupling between EuS and the STO tetragonal structure. We speculate that the STO tetragonal distortions may strain the EuS, altering the magnetic anisotropy on a micron scale. This result demonstrates that local variation in the induced magnetic order from EuS grown on STO needs to be considered when engineering new phases of matter that require spatially homogeneous exchange.

Update: 13-Dec-2017

Title:
Mechanical and surface properties of Aluminum-Copper-Iron quasicrystal thin films
Authors:
Parsamehr, H; Chang, SY; Lai, CH Author Full Names: Parsamehr, Hadi; Chang, Shou-Yi; Lai, Chih-Huang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 732 952-957; 10.1016/j.jallcom.2017.10.229 JAN 25 2018
Abstract:
We show quasicrystal formation by annealing multilayers of Al, Cu and Fe. The mechanical and surface properties of quasicrystals are affected by the parameters of annealing process. Here, multilayer Al-Cu-Fe thin film samples with different compositions were sputtered on Si/SiO2 substrates and subjected to a two-step annealing process for different durations (5, 10 and 15 h). X-ray diffraction analyses indicated that the 15-h annealed sample had a sharper quasicrystal peak, which was more stable than any other phases. From the XRD data, the amount of each phase was calculated; the sample with longer annealing duration revealed a high amount of phi-phase (84.3% crystallinity of quasicrystal) with a small amount of cubic Al-50 (CuFe) (50) phase. Nanoindentation tests and contact angle measurements showed that this sample also had the greatest hardness (similar to 11 GPa) and the highest contact angle (127 degrees), respectively. (C) 2017 Elsevier B.V. All rights reserved.
Title:
The formation of quasicrystals in Al-Cu-Fe-(M=Cr, Ni) melt-spun ribbons
Authors:
Wolf, W; Coury, FG; Kaufman, MJ; Bolfarini, C; Kiminami, CS; Botta, WJ Author Full Names: Wolf, W.; Coury, F. G.; Kaufman, M. J.; Bolfarini, C.; Kiminami, C. S.; Botta, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 731 1288-1294; 10.1016/j.jallcom.2017.09.139 JAN 15 2018
Abstract:
The influence of Cr and Ni additions in rapidly-solidified Al-Cu-Fe alloys was investigated. Four compositions, namely, Al64Cu20Fe13Ni3, Al63Cu18Fe10Ni9, Al65Cu22Fe10Cr3 and Al67Cu20Fe5Cr8 were selected based on a methodology in which the average valence electron per atom (e/a) ratio of the ternary Al-Cu-Fe quasicrystal was maintained constant. Melt-spun ribbons of all four alloys were produced and then examined by X-ray diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy. The results indicate that the Al-Cu-Fe icosahedral quasicrystalline phase has limited solubility for Ni such that with increasing Ni content, the fraction of the quasicrystalline phase decreased drastically and two primitive B2 cubic phases were formed instead. Additions of Cr resulted in the formation of a decagonal quasicrystal at the expense of the icosahedral phase. At 3 at% Cr, both icosahedral and decagonal phases were observed, with the former having the major volume fraction. For the alloy containing 8 at% Cr, only the decagonal phase was observed. (C) 2017 Elsevier B.V. All rights reserved.

Update: 7-Dec-2017

Title:
In-situ neutron diffraction of a quasicrystal-containing Mg alloy interpreted using a new polycrystal plasticity model of hardening due to {10.2} tensile twinning
Authors:
Agnew, SR; Singh, A; Calhoun, CA; Mulay, RP; Bhattacharyya, JJ; Somekawa, H; Mukai, T; Clausen, B; Wu, PD Author Full Names: Agnew, S. R.; Singh, A.; Calhoun, C. A.; Mulay, R. P.; Bhattacharyya, J. J.; Somekawa, H.; Mukai, T.; Clausen, B.; Wu, P. D.
Source:
INTERNATIONAL JOURNAL OF PLASTICITY, 100 34-51; 10.1016/j.ijplas.2017.09.005 JAN 2018
Abstract:
Due to the excellent balance of strength and ductility exhibited by some Mg-Zn-RE (Y subgroup rare earth element) alloys, which contain icosahedral quasicrystalline precipitates, it is of interest to examine their deformation mechanisms. The internal strain evolution Mg-3at%Zn-0.5 at%Y with 4 vol% i-phase was measured using in-situ neutron diffraction. The extruded samples exhibit an initially weak <10.0> parallel to extrusion direction "rod texture," distinct from the normally strong texture of extruded Mg alloys, but the grain size is unexceptional (16.7 +/- 2.1 mu m). The initially weak texture contributes to a nearly symmetric yielding response between tension and compression. The hardening responses are asymmetric, however, since {10.2} extension twinning is significantly more active during compressive straining, despite the initially weak texture. In-situ neutron diffraction tension and compression experiments parallel to the extrusion direction, together with elasto-plastic self-consistent (EPSC) crystal plasticity modeling, reveal the strength and hardening behavior of individual slip and twinning modes. The previously published twinning-detwinning (TDT) model is implemented within the EPSC framework, and it is proven effective for describing the observed, mild tension-compression asymmetry. This is not possible with previous EPSC-based models of twinning. Finally, the description of hardening within the TDT model is modified, in order to accurately describe the evolution of internal strains within the twins. (C) 2017 Elsevier Ltd. All rights reserved.
Title:
Revealing the Topology of Quasicrystals with a Diffraction Experiment
Authors:
Dareau, A; Levy, E; Aguilera, MB; Bouganne, R; Akkermans, E; Gerbier, F; Beugnon, J Author Full Names: Dareau, A.; Levy, E.; Aguilera, M. Bosch; Bouganne, R.; Akkermans, E.; Gerbier, F.; Beugnon, J.
Source:
PHYSICAL REVIEW LETTERS, 119 (21):10.1103/PhysRevLett.119.215304 NOV 22 2017
Abstract:
Topological properties of crystals and quasicrystals is a subject of recent and growing interest. This Letter reports an experiment where, for certain quasicrystals, these properties can be directly retrieved from diffraction. We directly observe, using an interferometric approach, all of the topological invariants of finite-length Fibonacci chains in their diffraction pattern. We also quantitatively demonstrate the stability of these topological invariants with respect to structural disorder.
Title:
Rational Design of a Commensurate (3+3)-D Modulated Structure within the Fast-Ion Conducting Stabilized delta-Bi2O3 Series
Authors:
Wind, J; Polt, J; Zhang, Z; Blom, DA; Vogt, T; Withers, RL; Ling, CD Author Full Names: Wind, Julia; Polt, Julia; Zhang, Zhaoming; Blom, Douglas A.; Vogt, Thomas; Withers, Ray L.; Ling, Chris D.
Source:
CHEMISTRY OF MATERIALS, 29 (21):9171-9181; 10.1021/acs.chemmater.7b03012 NOV 14 2017
Abstract:
We report the systematic design, preparation, and characterization of the first commensurate member of the oxide-ionic conducting, (3 + 3)-D modulated, Type II phases of doped delta-Bi2O3. The incommensurate Type II modulation vector epsilon was previously described as continuously variable, but high-resolution synchrotron X-ray powder diffraction data show that close to the composition Bi23CrNb3O45, it "locks in" to epsilon = 1/3. The space group of the resulting 3 X 3 X 3 fluorite type supercell was found to be F $(4) over bar $ 3m by selected-area electron diffraction, and the structure was solved and Rietveld-refined against neutron powder diffraction data in conjunction with local structural information from X-ray absorption spectroscopy, high-resolution transmission electron microscopy, and ab initio geometry optimization calculations. The result unambiguously validates the crystal-chemical model of the Type II phases as being based on the local ordering of oxygen around transition metals M into tetrahedral clusters of MO6 octahedra and isolated MO4 tetrahedra, separating relatively disordered fluorite-type regions that facilitate the highest oxide-ionic conduction among transition metal-doped delta-Bi2O3 phases.

Update: 30-Nov-2017

Title:
Structural signature and size-dependent mechanical response of frozen-in icosahedral phase in bulk metallic glasses
Authors:
Chang, HJ; Oh, HS; Lee, JI; Park, ES Author Full Names: Chang, Hye Jung; Oh, Hyun Seok; Lee, Je In; Park, Eun Soo
Source:
MATERIALS & DESIGN, 138 129-139; 10.1016/j.matdes.2017.10.049 JAN 15 2018
Abstract:
In the present study, we report structural signature and size-dependent mechanical response of frozen-in icosahedral phase (I-phase) embedded in Zr-(Ti, Nb, Al)-(Cu, Ni) bulkmetallic glass (BMG)-forming alloys, which exhibit a narrowcomposition range overlapping between glass and I-phase forming region. Thus, the different sizes of the I-phase from tens of nanoscale precipitates to enhanced icosahedral short-range order in MG matrix can be obtained by controlling cooling history. I-phase particles with tens of nanoscale in BMGs do not contribute to extrinsic ductility due to limited blocking of the propagation of shear band. The shear band passes through the particle, splitting it into two pieces. On the other hand, BMGs with enhanced icosahedral short-range order, which can be evaluated by EXAFS analysis as well as calorimetric signal during isothermal annealing, exhibit enhanced ductility without strength reduction. Indeed, we examine the cut-off size of strain bursts and deformation dynamics of shear-avalanches through the statistical analysis of serration behavior. Icosahedral short-range order (ISRO)-embedded MGs exhibit weakened jammed state of the self-organized deformed zones, which results in the formation of numerous catastrophic deformed zones under relatively chaotic dynamics, and consequently multiple shear bands. These results would help deepen our understanding of the underlying mechanism that determines intrinsic ductility in BMGs via frozen-in ISRO, and ultimately give us a guideline for the design of promising BMGs with improved intrinsic ductility by manipulating local structural instability. (C) 2017 Elsevier Ltd. All rights reserved.
Title:
Model refinement of quasicrystals
Authors:
Wolny, J; Buganski, I; Strzalka, R Author Full Names: Wolny, Janusz; Buganski, Ireneusz; Strzalka, Radoslaw
Source:
CRYSTALLOGRAPHY REVIEWS, 24 (1):22-64; 10.1080/0889311X.2017.1340276 2018
Abstract:
From the discovery of quasicrystals, exhibiting rotational symmetries forbidden by the classical crystallography, the idea of a quasicrystalline geometry spreads out to a great variety of scientific fields, including soft matter physics, optics, or nanotechnology. However, the atomic structure of quasicrystals is still unclear and many questions are unanswered, including the most peculiar one asked by Per Bak: Where are the atoms?' [Icosahedral crystals: where are the atoms? Phys Rev Lett. 1986;56:861-864]. To answer those questions, more detailed structural analysis needs to be done. Two approaches to the structural description and refinement are used for aperiodic crystals: the higher dimensional method, well established in the community, and the statistical method. We introduce the essence of the crystallography of quasicrystals, giving the historical background and fundamentals of the higher dimensional modelling, but focus is put on the details and application of the statistical approach. We present also a case study of the decagonal Al-Cu-{Co,Ir,Rh} phase, which is an example of the crystal structure solved using the statistical method. In the last chapter, a brief discussion of the recently developed approach of a phasonic corrective factor, alongside the effect of phonons on the atomic distribution function, is given.
Title:
Hall effect in cuprates with an incommensurate collinear spin-density wave
Authors:
Charlebois, M; Verret, S; Foley, A; Simard, O; Senechal, D; Tremblay, AMS Author Full Names: Charlebois, M.; Verret, S.; Foley, A.; Simard, O.; Senechal, D.; Tremblay, A. -M. S.
Source:
PHYSICAL REVIEW B, 96 (20):10.1103/PhysRevB.96.205132 NOV 16 2017
Abstract:
The presence of incommensurate spiral spin-density waves (SDW) has been proposed to explain the p (hole doping) to 1 + p jump measured in the Hall number n(H) at a doping p*. Here we explore incommensurate collinear SDW as another possible explanation of this phenomenon, distinct from the incommensurate spiral SDW proposal. We examine the effect of different SDW strengths and wave vectors, and we find that the n(H) similar to p behavior is hardly reproduced at low doping. Furthermore, the calculated n(H) and Fermi surfaces give characteristic features that should be observed; thus, the lack of these features in experiment suggests that the incommensurate collinear SDW is unlikely to be a good candidate to explain the n(H) similar to p observed in the pseudogap regime.
Title:
Shock Synthesis of Decagonal Quasicrystals
Authors:
Oppenheim, J; Ma, C; Hu, J; Bindi, L; Steinhardt, PJ; Asimow, PD Author Full Names: Oppenheim, J.; Ma, C.; Hu, J.; Bindi, L.; Steinhardt, P. J.; Asimow, P. D.
Source:
SCIENTIFIC REPORTS, 7 10.1038/s41598-017-15229-4 NOV 15 2017
Abstract:
The Khatyrka meteorite contains both icosahedral and decagonal quasicrystals. In our previous studies, icosahedral quasicrystals have been synthesized and recovered from shock experiments at the interface between CuAl5 and stainless steel 304 alloys. In this study, we report a new shock recovery experiment aimed at synthesizing decagonal quasicrystals similar to decagonite, natural Al71Ni24Fe5. Aluminum 2024 and permalloy 80 alloys were stacked together and shocked in a stainless steel 304 recovery chamber. Abundant decagonal quasicrystals of average composition Al73Ni19Fe4Cu2Mg0.6Mo0.4Mn0.3 with traces of Si and Cr were found along the recovered interface between the Al and permalloy. The experiment also synthesized AlNiFe alloy with the B2 (CsCl-type) structure and the metastable Al9Ni2 phase. We present chemical (scanning electron microscopy and electron microprobe) and structural (electron backscatter diffraction and transmission electron microscopy) characterization of the recovered phases and discuss the implications of this shock synthesis for the stability of quasicrystals during high-pressure shocks and for the interpretation of the phase assemblage found in Khatyrka.
Title:
Unusual Long-Range Ordering Incommensurate Structural Modulations in an Organic Molecular Ferroelectric
Authors:
Sun, ZH; Li, J; Ji, CM; Sun, JL; Hong, MC; Luo, JH Author Full Names: Sun, Zhihua; Li, Jian; Ji, Chengmin; Sun, Junliang; Hong, Maochun; Luo, Junhua
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 139 (44):15900-15906; 10.1021/jacs.7b08950 NOV 8 2017
Abstract:
The incommensurate (IC) behaviors of ferroelectrics have been widely investigated in inorganic oxides as an exciting branch for aperiodic materials, whereas it still remains a great challenge to achieve such intriguing effects in organic systems. Here, we present that successive ordering of dynamic dipoles in an organic molecular ferroelectric, N-isopropylbenzylaminium trichloroacetate (1), enables unusual incommensurately modulated structures between its paraelectric phase and ferroelectric phase. In particular, 1 exhibits three distinct IC states coupling with a long-range ordering modulation. That is, the incommensurately modulated lattice is similar to 7 times as large as its periodic prototype, and the IC structure is well solved using a (3 + 1)D superspace group with the modulated wavevector q = (0, 0, 0.1589). To the best of our knowledge, 1 is the first organic ferroelectric showing such a long-range ordering IC structural modulation. In addition, structural analyses reveal that slowing down dynamic motions of anionic moieties accounts for its modulation behaviors, which also results in dramatic reorientation of dipolar moments and concrete ferroelectric polarization of 1 (similar to 0.65 mu C/cm(2)). The combination of unique IC structural modulations and ferroelectricity makes 1 a potential candidate for the assembly of an artificially modulated lattice, which will allow for a deep understanding of the underlying chemistry and physics of aperiodic materials.

Update: 23-Nov-2017

Title:
Frustrated spin-1/2 ladder with ferro- and antiferromagnetic legs
Authors:
Maiti, D; Dey, D; Kumar, M Author Full Names: Maiti, Debasmita; Dey, Dayasindhu; Kumar, Manoranjan
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 446 170-176; 10.1016/j.jmmm.2017.09.025 JAN 15 2018
Abstract:
Two-leg spin-1/2 ladder systems consisting of a ferromagnetic leg and an antiferromagnetic leg are considered where the spins on the legs interact through antiferromagnetic rung couplings J(1). These ladders can have two geometrical arrangements either zigzag or normal ladder and these systems are frustrated irrespective of their geometry. This frustration gives rise to incommensurate spin density wave, dimer and spin fluid phases in the ground state. The magnetization in the systems decreases linearly with J(1)(2), and the systems show an incommensurate phase for 0.0 < J(1) < 1.0. The spin-spin correlation functions in the incommensurate phase follow power law decay which is very similar to Heisenberg antiferromagnetic chain in external magnetic field. In large J(1) limit, the normal ladder behaves like a collection of singlet dimers, whereas the zigzag ladder behaves as a one dimensional spin-1/2 antiferromagnetic chain. (C) 2017 Elsevier B.V. All rights reserved.

Update: 15-Nov-2017

Title:
New State of Matter: Heavy Fermion Systems, Quantum Spin Liquids, Quasicrystals, Cold Gases, and High-Temperature Superconductors
Authors:
Shaginyan, VR; Stephanovich, VA; Msezane, AZ; Schuck, P; Clark, JW; Amusia, MY; Japaridze, GS; Popov, KG; Kirichenko, EV Author Full Names: Shaginyan, V. R.; Stephanovich, V. A.; Msezane, A. Z.; Schuck, P.; Clark, J. W.; Amusia, M. Ya.; Japaridze, G. S.; Popov, K. G.; Kirichenko, E. V.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS, 189 (5-6):410-450; 10.1007/s10909-017-1801-3 DEC 2017
Abstract:
We report on a new state of matter manifested by strongly correlated Fermi systems including various heavy fermion (HF) metals, two-dimensional quantum liquids such as He films, certain quasicrystals, and systems behaving as quantum spin liquids. Generically, these systems can be viewed as HF systems or HF compounds, in that they exhibit typical behavior of HF metals. At zero temperature, such systems can experience a so-called fermion condensation quantum phase transition (FCQPT). Combining analytical considerations with arguments based entirely on experimental grounds, we argue and demonstrate that the class of HF systems is characterized by universal scaling behavior of their thermodynamic, transport, and relaxation properties. That is, the quantum physics of different HF compounds is found to be universal, emerging irrespective of the individual details of their symmetries, interactions, and microscopic structure. This observed universal behavior reveals the existence of a new state of matter manifest in HF compounds. We propose a simple, realistic model to study the appearance of flat bands in two-dimensional ensembles of ultracold fermionic atoms, interacting with coherent resonant light. It is shown that signatures of these flat bands may be found in peculiarities in their thermodynamic and spectroscopic properties. We also show that the FCQPT, in generating flat bands and altering Fermi surface topology, is an essential progenitor of the exotic behavior of the overdoped high-temperature superconductors represented by , whose superconductivity differs from that predicted by the classical Bardeen-Cooper-Schrieffer theory. The theoretical results presented are in good agreement with recent experimental observations, closing the colossal gap between these empirical findings and Bardeen-Cooper-Schrieffer-like theories.

Update: 9-Nov-2017

Title:
High electrochemical performance of nanoporous Fe3O4/CuO/Cu composites synthesized by dealloying Al-Cu-Fe quasicrystal
Authors:
Liu, H; Wang, XL; Wang, JX; Xu, H; Yu, WS; Dong, XT; Zhang, HB; Wang, LM Author Full Names: Liu, Huan; Wang, Xinlu; Wang, Jinxian; Xu, Hang; Yu, Wensheng; Dong, Xiangting; Zhang, Hongbo; Wang, Limin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 729 360-369; 10.1016/j.jallcom.2017.09.111 DEC 30 2017
Abstract:
Quasicrystal, an attractive type of material with special physical and chemical properties, has been considered as one of the most promising functional materials. Herein, Al65Cu23Fe12 quasicrystal precursor alloy ribbons were prepared by arc-melting subsequently melt-spinning under a protective argon atmosphere. Unique Fe3O4/CuO/Cu with bicontinuous ligaments and nanopore channels structure was fabricated by a facile one-step chemical dealloying method in 2 M NaOH solutions at room temperature with controlled dealloying times (12 h, 24 h, 48 h, and 96 h). X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) analysis, transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM) are employed to study the crystal structure and microstructural evolution of these Fe3O4/CuO/Cu composites. The unique composites combined both advantages of Fe3O4/CuO with high capacities and Cu with excellent conductive as anode material for lithium ion batteries. Remarkably, the successful integration of Fe3O4, CuO and Cu as well as the specific 3D ligament-pore structure, which could alleviate the volume changes during the repeating charge and discharge cycles, endowed the as-prepared electrode material with higher reversible capacity, excellent cycle life, and good rate performance due to the synergetic effect. Cyclic voltammetry (CV) and galvanostatic chargeedischarge measurements had been aimed at evaluating the lithium storage performances of the Fe3O4/CuO/Cu composites. A high specific capacity of 738.4 mAh g(-1) could be achieved up to 550 cycles at a current density of 200 mA g(-1). Therefore, the as synthesized Fe3O4/CuO/Cu composites exhibit excellent electrochemical stability and reactivity, which might open a new avenue to explore the application of quasicrystals. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Phase transitions of Cu3+xSi observed by temperature-dependent x-ray powder diffraction
Authors:
Correa, CA; Poupon, M; Kopecek, J; Kral, R; Zemenova, P; Lecourt, J; Barrier, N; Brazda, P; Klementova, M; Palatinus, L Author Full Names: Correa, Cinthia Antunes; Poupon, Morgane; Kopecek, Jaromir; Kral, Robert; Zemenova, Petra; Lecourt, Jerome; Barrier, Nicolas; Brazda, Petr; Klementova, Mariana; Palatinus, Lukas
Source:
INTERMETALLICS, 91 129-139; 10.1016/j.intermet.2017.07.003 DEC 2017
Abstract:
Phases in the system Cu3+xSi were analyzed by temperature-dependent x-ray powder diffraction and differential scanning calorimetry on samples with nominal composition Cu74Si26 and Cu78Si22 in the temperature range between 30 degrees C and 700 degrees C. Contrary to previous works, which report three phases in the system, we identified six distinct phases, labeled, in order of increasing temperature, eta"', eta", eta(3) eta(2), eta(1),. All these phases can be indexed with a similar basic unit cell. However, each phase has a different superstructure or modulation vectors.
Title:
Z-module defects in crystals
Authors:
Sirindil, A; Quiquandon, M; Gratias, D Author Full Names: Sirindil, Abdullah; Quiquandon, Marianne; Gratias, Denis
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 73 427-437; 10.1107/S2053273317013882 6 NOV 2017
Abstract:
An analysis is presented of the new types of defects that can appear in crystalline structures where the positions of the atoms and the unit cell belong to the same Z-module, i.e. are irrational projections of an N > 3-dimensional (N-D) lattice Lambda as in the case of quasicrystals. Beyond coherent irrationally oriented twins already discussed in a previous paper [Quiquandon et al. (2016). Acta Cryst. A72, 55-61], new two-dimensional translational defects are expected, the translation vectors of which, being projections of nodes of Lambda, have irrational coordinates with respect to the unitcell reference frame. Partial dislocations, called here module dislocations, are the linear defects bounding these translation faults. A specific case arises when the Burgers vector B is the projection of a non-zero vector of Lambda that is perpendicular to the physical space. This new kind of dislocation is called a scalar dislocation since, because its Burgers vector in physical space is zero, it generates no displacement field and has no interaction with external stress fields and other dislocations.
Title:
The monoclinic superstructure of the M2Pt6Al15 series (M = Ca, Sc, Y, La, Lu)
Authors:
Radzieowski, M; Stegemann, F; Hoffmann, RD; Janka, O Author Full Names: Radzieowski, Mathis; Stegemann, Frank; Hoffmann, Rolf-Dieter; Janka, Oliver
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 232 (10):675-687; 10.1515/zkri-2017-2050 OCT 2017
Abstract:
The five ternary intermetallic compounds M2Pt6Al15 (M = Ca, Sc, Y, La, Lu) were prepared from the elements by arc-melting. The crystal structure was determined via single crystal X-ray diffraction. The title compounds crystallize in a superstructure of the RE0.67Pt2Al5 type structure (P6(3)/mmc) in the monoclinic crystal system with space group P12(1)/m1 (Sc2Pt6Al15 : a= 734.19(2), b = 1628.96(10), c = 734.19(2) pm, beta = 119.999(3)degrees; wR = 0.0356, 3034 F-2 values, 68 variables). The superstructure can be derived by the superspace formalism using (3 + 2)D or (3 + 1)D interpretations of the diffraction data. The structural relation to the subcell structure is discussed on the basis of a group-subgroup scheme. In the crystal structure strongly bonded [Pt2Al4](delta-) slabs are alternatingly stacked with ordered layers containing M atoms and Al-3 triangles.
Title:
Modeling of dodecagonal quasicrystal lattices
Authors:
Smolyakov, AV; Girzhon, VV Author Full Names: Smolyakov, A. V.; Girzhon, V. V.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 125 (3):443-450; 10.1134/S1063776117080106 SEP 2017
Abstract:
We consider a method for constructing dodecagonal quasi-lattices, which involves the recurrent multiplication of the initial group of sites that are vertices of a regular dodecagon. The algorithm of modeling of reciprocal lattices of dodecagonal quasicrystals has been analyzed. The proposed modeling method is compared with the traditional projection method. We have performed indexing of the diffraction pattern from dodecagonal quasicrystals, which is analogous to indexing proposed by Cahn for icosahedral quasicrystals. The ambiguity of the choice of the basis vectors of the quasicrystal reciprocal lattice has been considered.

Update: 1-Nov-2017

Title:
Phase equilibria in the nominally Al65Cu23Fe12 system at 3, 5 and 21 GPa: Implications for the quasicrystal-bearing Khatyrka meteorite
Authors:
Stagno, V; Bindi, L; Steinhardt, PJ; Fei, YW Author Full Names: Stagno, Vincenzo; Bindi, Luca; Steinhardt, Paul J.; Fei, Yingwei
Source:
PHYSICS OF THE EARTH AND PLANETARY INTERIORS, 271 47-56; 10.1016/j.pepi.2017.08.005 OCT 2017
Abstract:
Two of the three natural quasiperiodic crystals found in the Khatyrka meteorite show a composition within the Al-Cu-Fe system. Icosahedrite, with formula Al63Cu24Fe13, coexists with the new Al62Cu31Fe2 quasicrystal plus additional Al-metallic minerals such as stolperite (AlCu), kryachkoite [(AlCu)(6)(Fe, Cu)], hollisterite (AlFe3), khatyrkite (Al2Cu) and cupalite (AlCu), associated to high-pressure phases like ringwoodite/ahrensite, coesite, and stishovite. These high-pressure minerals represent the evidence that most of the Khatyrka meteoritic fragments formed at least at 5 GPa and 1200 degrees C, if not at more extreme conditions. On the other hand, experimental studies on phase equilibria within the representative Al-Cu Fe system appear mostly limited to ambient pressure conditions, yet. This makes the interpretation of the coexisting mineral phases in the meteoritic sample quite difficult. We performed experiments at 3,5 and 21 GPa and temperatures of 800-1500 degrees C using the multi-anvil apparatus to investigate the phase equilibria in the Al65Cu23Fe12 system representative of the first natural quasicrystal, icosahedrite. Our results, supported by single-crystal X-ray diffraction and analyses by scanning electron microscopy, confirm the stability of icosahedrite at high pressure and temperature along with additional coexisting Al-bearing phases representative of khatyrkite and stolperite as those found in the natural meteorite. One reversal experiment performed at 5 GPa and 1200 degrees C shows the formation of the icosahedral quasicrystal from a pure Al, Cu and Fe mixture, a first experimental synthesis of icosahedrite under those conditions. Pressure appears to not play a major role in the distribution of Al, Cu and Fe between the coexisting phases, icosahedrite in particular. Results from this study extend our knowledge on the stability of icosahedral AlCuFe at higher temperature and pressure than previously examined, and provide a new constraint on the stability of icosahedrite. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Elevated temperature mechanical behaviour of nanoquasicrystalline Al93Fe3Cr2Ti2 alloy and composites
Authors:
Pedrazzini, S; Galano, M; Audebert, F; Smith, GDW Author Full Names: Pedrazzini, S.; Galano, M.; Audebert, F.; Smith, G. D. W.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 705 352-359; 10.1016/j.msea.2017.08.075 SEP 29 2017
Abstract:
Rapidly solidified nano-quasicrystalline Al93Fe3Cr2Ti2 at% alloy has previously shown outstanding tensile and compressive strength and microstructural stability up to elevated temperatures. Despite this, no study had previously assessed the effect of plastic deformation at elevated temperature to simulate thermal-mechanical forging processes for the production of engineering components. The present work analysed bars consisting of a nano-quasicrystalline Al93Fe3Cr2Ti2 at% alloy matrix, with the addition of 10 and 20 vol% pure Al ductilising fibres, produced through gas atomisation and warm extrusion. The microstructure was made primarily of nanometre-sized icosahedral particles in an alpha-Al matrix. Compression tests were performed across a range of temperatures and strain rates. The measured yield strength at 350 degrees C was over 3x that of "high strength" 7075 T6 Al alloy, showing outstanding thermal stability and mechanical performance. However, the microstructure was shown by XRD to undergo a phase transformation which resulted in the decomposition of the icosahedral phase around 500 degrees C into more stable intermetallic phases. Serrated flow associated with dynamic strain ageing was observed and a semi-quantitative analysis matching elemental diffusion speeds with dislocation speed at specific strain rates was performed, which tentatively identified Ti as the solute species responsible within the selected range of temperatures and strain rates.

Update: 26-Oct-2017

Title:
The Construction of Nonlinear Elasticity Tensors for Crystals and Quasicrystals
Authors:
Astapov, Y; Khristich, D; Markin, A; Sokolova, M Author Full Names: Astapov, Yuri; Khristich, Dmitrii; Markin, Alexey; Sokolova, Marina
Source:
INTERNATIONAL JOURNAL OF APPLIED MECHANICS, 9 (6):10.1142/S1758825117500806 SEP 2017
Abstract:
The problem of construction of constitutive relations in nonlinear elasticity theory for crystals and quasicrystals is associated with finding the construction of the structure of tensors of elastic modules of 2nd and 3rd orders. In the case of linear constitutive relations, the problem is entirely solved for crystals and some quasicrystals. In the case of nonlinear relations, the quantity of nonzero elastic modules of the 3rd order is known only for some classes of crystals. The problem of construction of nonlinear constitutive relations for quasicrystal materials has not been considered. In this article, representations of linear and nonlinear elastic properties of crystals and quasicrystals in the form of decompositions by special invariant tensor bases are considered. This allows us to concretize constitutive relations for icosahedral and axial quasicrystals. It is shown that axial quasicrystals' behavior towards elastic properties coincides with transversal-isotropic materials. Icosahedral quasicrystals' behavior matches with the isotropic materials' one. On the basis of the obtained decompositions of nonlinear elasticity tensors for axial quasicrystals having a symmetry plane and for graphene films with and without defects, the analysis of their mechanical behavior at some types of loading is fulfilled. It is shown that differences in the behavior of these materials appear only in the second order effects.

Update: 20-Oct-2017

Title:
Formation of incommensurate long-range magnetic order in the Dzyaloshinskii-Moriya antiferromagnet Ba-2 CuGe2O7 studied by neutron diffraction
Authors:
Muhlbauer, S; Brandl, G; Mansson, M; Garst, M Author Full Names: Muehlbauer, S.; Brandl, G.; Mansson, M.; Garst, M.
Source:
PHYSICAL REVIEW B, 96 (13):10.1103/PhysRevB.96.134409 OCT 6 2017
Abstract:
Neutron diffraction on a triple-axis spectrometer and a small-angle neutron scattering instrument is used to study the magnetic phase transition in tetragonal Ba2CuGe2O7 at zero magnetic field. In addition to the incommensurate cycloidal antiferromagnetic (AFM) long-range order, we establish that weak incommensurate ferromagnetism (FM) also arises below the transition temperature T-N identified by sharp Bragg peaks close to the Gamma point. The intensities of both the incommensurate AFM and FM Bragg peaks vanish abruptly at T-N, which is indicative of a weak first-order transition. Above TN, evidence is presented that the magnetic intensity within the tetragonal (a, b) plane is distributed on a ring in momentum space whose radius is determined by the incommensurate wave vector of the cycloidal order. We speculate that the associated soft fluctuations are at the origin of the weak first-order transition in the spirit of a scenario proposed by Brazovskii.
Title:
Low-temperature behaviour of K2Sc[Si2O6]F: determination of the lock-in phase and its relationships with fresnoite-and melilite-type compounds
Authors:
Hejny, C; Bindi, L Author Full Names: Hejny, C.; Bindi, L.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 923-930; 10.1107/S2052520617010241 5 OCT 2017
Abstract:
K2Sc[Si2O6]F exhibits, at room temperature, a (3 + 2)-dimensional incommensurately modulated structure [a = 8.9878 (1), c = 8.2694 (2) angstrom, V = 668.01 (2) angstrom(3); superspace group P4(2)/mnm(alpha, alpha,0) 000s(-alpha, alpha,0) 0000] with modulation wave-vectors q(1) = 0.2982 (4)(a* + b*) and q(2) = 0.2982 (4)(-a* + b*). Its low-temperature behaviour has been studied by single-crystal X-ray diffraction. Down to 45 K, the irrational component alpha of the modulation wave-vectors is quite constant varying from 0.2982 (4) (RT), through 0.2955 (8) (120 K), 0.297 (1) (90 K), 0.298 (1) (75 K), to 0.299 (1) (45 K). At 25 K it approaches the commensurate value of one-third [i.e. 0.332 (3)]: thus indicating that the incommensurate-commensurate phase transition takes place between 45 K and 25 K. The commensurate lock-in phase of K2Sc[Si2O6] F has been solved and refined with a 3 x 3 x 1 supercell compared with the tetragonal incommensurately modulated structure stable at room temperature. This corresponds to a 3 x 1 x 3 supercell in the pseudo-orthorhombic monoclinic setting of the low-temperature structure, space group P2/m, with lattice parameters a = 26.786 (3), b = 8.245 (2) c = 26.824 (3) angstrom, beta = 90.00 (1)degrees. The structure is a mixed tetrahedral-octahedral framework composed of chains of [ScO4F2] octahedra that are interconnected by [Si4O12] rings with K atoms in fourfold to ninefold coordination. Distorted [ScO4F2] octahedra are connected to distorted Si tetrahedra to form octagonal arrangements closely resembling those observed in the incommensurate structure of fresnoite-and melilite-type compounds.
Title:
A commensurately modulated structure of parabutlerite, (FeSO4)-S-III(OH)center dot 2H(2)O
Authors:
Plasil, J; Petricek, V; Majzlan, J Author Full Names: Plasil, Jakub; Petricek, Vaclav; Majzlan, Juraj
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 856-862; 10.1107/S2052520617007156 5 OCT 2017
Abstract:
Parabutlerite, orthorhombic (FeSO4)-S-III(OH)center dot 2H(2)O, has been reinvestigated using single-crystal X-ray diffraction. The structure of parabutlerite is commensurately modulated, with a = 20.0789 (8), b = 7.4024 (7), c = 7.2294 (15) angstrom and q = 0.4b*. The superstructure has been determined, using a superspace approach, as having the superspace group Pnma(0 beta 0)s0s and t(0) = 1/20, and refined to R = 0.0295 for 2392 main reflections with I > 3 sigma(I). The structure consists of infinite chains of Fe octahedra that are linked via vertices (OH groups); these chains are encased from both sides by SO4 tetrahedra. The displacive modulation of atoms in parabutlerite is connected with a tilt of the chains around the b axis towards the adjacent chains due to the accommodation of an energetically more favorable hydrogen-bond geometry.
Title:
Structural changes of relaxor ferroelectric Sr0.52Ba0.48Nb2O6 (SBN52) on quenching and reheating
Authors:
Graetsch, HA Author Full Names: Graetsch, Heribert A.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 820-826; 10.1107/S2052520617007880 5 OCT 2017
Abstract:
Quenching of Sr0.52Ba0.48Nb2O6 (SBN52) from temperatures above 700 degrees C causes small modifications in the strontium distribution over the large cation sites (Me1 and Me2), changed off-centre shifts of the Nb atoms and slightly increased modulation amplitudes. The higher disorder of cation incorporation can explain the enhanced ferroelectric properties. The quenched structural disorder can be healed by reheating followed by slow cooling. A change of the modulation dimension on quenching such as for CaxBa1-xNb2O6 (CBN) mixed crystals was not observed.
Title:
Incommensurately modulated structure of morpholinium tetrafluoroborate and configurational versus chemical entropies at the incommensurate and lock-in phase transitions
Authors:
Noohinejad, L; van Smaalen, S; Petricek, V; Schoenleber, A Author Full Names: Noohinejad, Leila; van Smaalen, Sander; Petricek, Vaclav; Schoenleber, Andreas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 836-843; 10.1107/S2052520617009398 5 OCT 2017
Abstract:
Morpholinium tetrafluoroborate, [C4H10NO](+)[BF4](-), belongs to a class of ferroelectric compounds ABX(4). However, [C4H10NO](+)[BF4](-) does not develop ferroelectric properties because the incommensurate phase below T-c,T-I = 153 K is centrosymmetric with superspace group Pnam(sigma(1)00)00s and sigma(1) = 0.42193 (12) at T = 130 K; the threefold superstructure below T-c,T-II = 117-118 K possesses the acentric but non-ferroelectric space group P2(1)2(1)2(1). At ambient conditions, [C4H10NO](+)[BF4](-) comprises orientationally disordered [BF4](-) anions accommodated in cavities between four morpholinium cations. A structure model for the incommensurately modulated phase, which involves modulated orientational ordering of [BF4](-) together with modulated distortions and displacements of the morpholinium ions is reported. A mechanism is proposed for the phase transitions, whereby at low temperatures morpholinium cations are shaped around the tetrafluoroborate anion in order to optimize the interactions with one orientation of this anion and, thus, forcing [BF4](-) into this orientation. This mechanism is essentially different from a pure order-disorder phase transition. It is supported by consideration of the transition entropy. The difference in configurational entropy between the disordered and incommensurate phases has been computed from the structure models. It is shown to be much smaller than the experimental transition entropy reported by Owczarek et al. [Chem. Phys. (2011), 381, 11-20]. These features show that the order-disorder contribution is only a minor contribution to the transition entropy and that other factors, such as conformational changes, play a larger role in the phase transitions.
Title:
Flexocoupling-induced soft acoustic modes and the spatially modulated phases in ferroelectrics
Authors:
Morozovska, AN; Glinchuk, MD; Eliseev, EA; Vysochanskii, YM Author Full Names: Morozovska, Anna N.; Glinchuk, Maya D.; Eliseev, Eugene A.; Vysochanskii, Yulian M.
Source:
PHYSICAL REVIEW B, 96 (9):10.1103/PhysRevB.96.094111 SEP 29 2017
Abstract:
Using the Landau-Ginzburg-Devonshire theory and one component approximation, we examined the conditions of the soft acoustic phonon mode (A-mode) appearance in a ferroelectric (FE) depending on the magnitude of the flexoelectric coefficient f and temperature T. If the flexocoefficient f is equal to the temperature-dependent critical value f(cr)(T) at some temperature T = T-IC, theA-mode frequency tends to zero atwave vector k = k(0)(cr), and the spontaneous polarization becomes spatially modulated in the temperature rangeT < T-IC, where T-IC is turned into the transition temperature to the incommensurate spatially modulated phase (SMP). When f > f(cr)(T-IC), the A-mode becomes zero for two wave vectors k = k(1,2)(cr), and does not exist in the range of wave vectors k(1)(cr) < k < k(2)(cr), indicating the transition to SMP. The corresponding temperature dependence of the dielectric susceptibility is in agreement with experimental data in ferroics with SMPs. This gives us a background to predict flexocoupling-induced soft acoustic amplitudon-type modes in FEs with SMPs of type II. The available experimental results on neutron scattering in organic incommensurate FE betaine calcium chloride dihydrate are in semiquantitative agreement with our theoretical results.
Title:
The Equivalence Between Unit-Cell Twinning and Tiling in Icosahedral Quasicrystals
Authors:
Prodan, A; Hren, RD; van Midden, MA; van Midden, HJP; Zupanic, E Author Full Names: Prodan, Albert; Hren, Ram Dusic; van Midden, Marion A.; van Midden, Herman J. P.; Zupanic, Erik
Source:
SCIENTIFIC REPORTS, 7 10.1038/s41598-017-12669-w SEP 29 2017
Abstract:
It is shown that tiling in icosahedral quasicrystals can also be properly described by cyclic twinning at the unit cell level. The twinning operation is applied on the primitive prolate golden rhombohedra, which can be considered a result of a distorted face-centered cubic parent structure. The shape of the rhombohedra is determined by an exact space filling, resembling the forbidden five-fold rotational symmetry. Stacking of clusters, formed around multiply twinned rhombic hexecontahedra, keeps the rhombohedra of adjacent clusters in discrete relationships. Thus periodicities, interrelated as members of a Fibonacci series, are formed. The intergrown twins form no obvious twin boundaries and fill the space in combination with the oblate golden rhombohedra, formed between clusters in contact. Simulated diffraction patterns of the multiply twinned rhombohedra and the Fourier transform of an extended model structure are in full accord with the experimental diffraction patterns and can be indexed by means of three-dimensional crystallography. The alternative approach is fully compatible to the rather complicated descriptions in a hyper-space.

Update: 12-Oct-2017

Title:
Influence of chemical leaching on Al-Cu-Co decagonal quasicrystals
Authors:
Mishra, SS; Pandey, SK; Yadav, TP; Srivastava, ON Author Full Names: Mishra, S. S.; Pandey, Sunita K.; Yadav, T. P.; Srivastava, O. N.
Source:
MATERIALS CHEMISTRY AND PHYSICS, 200 23-32; 10.1016/j.matchemphys.2017.07.068 OCT 1 2017
Abstract:
In the present investigation, the chemical leaching of the poly-grain Al65Cu15Co20 and Al65Cu20Co15 decagonal quasicrystalline alloys have been studied. The polished surfaces of as-cast Al65Cu15Co20 and Al65Cu20Co15 alloys have been leached by 10 moltlitre (mol/L) concentrated NaOH alkaline solutions. The X-ray diffraction, Scanning electron microscopy and Transmission electron microscopy techniques have been used for the structural and microstructural characterization of the samples and the chemical composition were characterized using Energy-dispersive X-ray spectroscopy. Chemical leaching exclusively removes the Al from the surfaces of the Al65Cu15Co20 and Al65Cu20Co15 decagonal quasicrystalline alloys, consequentially the formation of porous structure containing nano size particles of Cu, Co and Co3O4 have been observed on the leached surface. The leached surface of Al65Cu15Co20 was more porous compared to Al65Cu20Co15 alloy, however the size of the precipitated nano-particles i.e. Cu, Co and Co3O4 were smaller in the case of Al65Cu20Co15 alloy. The elemental mapping through energy dispersive X-ray spectroscopy suggests that the distribution of Cu and Co were formed on the leached surface, however in some regions the oxygen was also detected. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Bronze-mean hexagonal quasicrystal
Authors:
Dotera, T; Bekku, S; Ziherl, P Author Full Names: Dotera, Tomonari; Bekku, Shinichi; Ziherl, Primoz
Source:
NATURE MATERIALS, 16 (10):987-+; 10.1038/NMAT4963 OCT 2017
Abstract:
The most striking feature of conventional quasicrystals is their non-traditional symmetry characterized by icosahedral, dodecagonal, decagonal or octagonal axes(1-6). The symmetry and the aperiodicity of these materials stem from an irrational ratio of two or more length scales controlling their structure, the best-known examples being the Penrose(7,8) and the Ammann-Beenker(9,10) tiling as two-dimensional models related to the golden and the silver mean, respectively. Surprisingly, no other metallic-mean tilings have been discovered so far. Here we propose a self-similar bronze-mean hexagonal pattern, which may be viewed as a projection of a higher-dimensional periodic lattice with a Koch-like snowflake projection window. We use numerical simulations todemonstrate that a disordered variant(11) of this quasicrystal can be materialized in soft polymeric colloidal particles with a core-shell architecture(12-17). Moreover, by varying the geometry of the pattern we generate a continuous sequence of structures, which provide an alternative interpretation of quasicrystalline approximants observed in several metal-silicon alloys(18).
Title:
Layer-by-layer growth of vertex graph of Penrose tiling
Authors:
Shutov, AV; Maleev, AV Author Full Names: Shutov, A. V.; Maleev, A. V.
Source:
CRYSTALLOGRAPHY REPORTS, 62 (5):683-691; 10.1134/S1063774517050194 SEP 2017
Abstract:
The growth form for the vertex graph of Penrose tiling is found to be a regular decagon. The lower and upper bounds for this form, coinciding with it, are strictly proven. A fractal character of layer-by-layer growth is revealed for some subgraphs of the vertex graph of Penrose tiling.

Update: 28-Sep-2017

Title:
Metastable quasicrystals in Al-Mn alloys containing copper, magnesium and silicon
Authors:
Naglic, I; Samardzija, Z; Delijic, K; Kobe, S; Dubois, JM; Leskovar, B; Markoli, B Author Full Names: Naglic, Iztok; Samardzija, Zoran; Delijic, Kemal; Kobe, Spomenka; Dubois, Jean-Marie; Leskovar, Blaz; Markoli, Bostjan
Source:
JOURNAL OF MATERIALS SCIENCE, 52 (23):13657-13668; 10.1007/s10853-017-1477-8 DEC 2017
Abstract:
We prepared three Al-Mn-based alloys with different copper, magnesium and silicon contents by casting into cylindrical copper molds. All the alloys exhibited primary metastable quasicrystals (QCs). In order to confirm the presence of either primary decagonal QCs (dQCs) or icosahedral QCs (iQCs) and to determine their compositions, the castings were characterized by means of light microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), electron-backscatter diffraction and X-ray diffraction. The dQCs are present in the Al-Mn-based alloys containing copper. In the case of the combined presence of copper and magnesium, iQCs are present in the edge region and dQCs are present in the central region. In the alloy containing copper, magnesium and silicon, iQCs are present in the casting. The average metallic radius (AMR) and electron-to-atom ratio of these primary phases were calculated by taking into account the composition of these primary phases, as determined by EDS. The AMR shows different values in the cases of dQCs and iQCs. Equal mean values of the AMR were found in iQCs with markedly different compositions. Furthermore, all the metastable QCs in this work show electron concentrations close to 2.6.
Title:
Tricritical wings and modulated magnetic phases in LaCrGe3 under pressure
Authors:
Kaluarachchi, US; Bud'ko, SL; Canfield, PC; Taufour, V Author Full Names: Kaluarachchi, Udhara S.; Bud'ko, Sergey L.; Canfield, Paul C.; Taufour, Valentin
Source:
NATURE COMMUNICATIONS, 8 10.1038/s41467-017-00699-x SEP 15 2017
Abstract:
Experimental and theoretical investigations on itinerant ferromagnetic systems under pressure have shown that ferromagnetic quantum criticality is avoided either by a change of the transition order, becoming of the first order at a tricritical point, or by the appearance of modulated magnetic phases. In the first case, the application of a magnetic field reveals a wing-structure phase diagram as seen in itinerant ferromagnets such as ZrZn2 and UGe2. In the second case, no tricritical wings have been observed so far. Here, we report on the discovery of wing-structure as well as the appearance of modulated magnetic phases in the temperature-pressure-magnetic field phase diagram of LaCrGe3. Our investigation of LaCrGe3 reveals a double-wing structure indicating strong similarities with ZrZn2 and UGe2. But, unlike these simpler systems, LaCrGe3 also shows modulated magnetic phases similar to CeRuPO. This finding provides an example of an additional possibility for the phase diagram of metallic quantum ferromagnets.
Title:
Periodic layers of a dodecagonal quasicrystal and a floating hexagonal crystal in sedimentation-diffusion equilibria of colloids
Authors:
Pattabhiraman, H; Dijkstra, M Author Full Names: Pattabhiraman, Harini; Dijkstra, Marjolein
Source:
JOURNAL OF CHEMICAL PHYSICS, 147 (10):10.1063/1.4993521 SEP 14 2017
Abstract:
We investigate the behaviour of a system of colloidal particles interacting with a hard-core and a repulsive square shoulder potential under the influence of a gravitational field using event-driven Brownian dynamics simulations. We use a fixed square shoulder diameter equal to 1.4 times the hardcore diameter of the colloids, for which we have previously calculated the equilibrium phase diagram considering two-dimensional disks [H. Pattabhiraman et al., J. Chem. Phys. 143, 164905 (2015) and H. Pattabhiraman and M. Dijkstra, J. Phys.: Condens. Matter 20, 094003 (2017)]. The parameters in the simulations are chosen such that the pressure at the bottom of the sediment facilitates the formation of phases in accordance with the calculated phase diagram of the two-dimensional system. It is surprising that we observe the formation of layers with dodecagonal, square, and hexagonal symmetries at the relevant pressures in the three-dimensional sedimentation column. In addition, we also observe a re-entrant behaviour exhibited by the colloidal fluid phase, engulfing a hexagonal crystal phase, in the sedimentation column. In other words, a floating crystal is formed between the colloidal fluid regions. Published by AIP Publishing.

Update: 21-Sep-2017

Title:
Interaction between infinitely many dislocations and a semi-infinite crack in one-dimensional hexagonal quasicrystal
Authors:
Liu, GT; Yang, LY Author Full Names: Liu, Guan-Ting; Yang, Li-Ying
Source:
CHINESE PHYSICS B, 26 (9):10.1088/1674-1056/26/9/094601 AUG 2017
Abstract:
By means of analytic function theory, the problems of interaction between infinitely many parallel dislocations and a semi-infinite crack in one-dimensional hexagonal quasicrystal are studied. The analytic solutions of stress fields of the interaction between infinitely many parallel dislocations and a semi-infinite crack in one-dimensional hexagonal quasicrystal are obtained. They indicate that the stress concentration occurs at the dislocation source and the tip of the crack, and the value of the stress increases with the number of the dislocations increasing. These results are the development of interaction among the finitely many defects of quasicrystals, which possesses an important reference value for studying the interaction problems of infinitely many defects in fracture mechanics of quasicrystal.

Update: 13-Sep-2017

Title:
On the microstructure, hardness and wear behavior of Al-Fe-Cr quasicrystal reinforced Al matrix composite prepared by selective laser melting
Authors:
Kang, N; Fu, YQ; Coddet, P; Guelorget, B; Liao, HL; Coddet, C Author Full Names: Kang, Nan; Fu, Yingqing; Coddet, Pierre; Guelorget, Bruno; Liao, Hanlin; Coddet, Christian
Source:
MATERIALS & DESIGN, 132 105-111; 10.1016/j.matdes.2017.06.060 OCT 15 2017
Abstract:
Al91Fe4Cr5 quasicrystal (QC) reinforced alpha-Al matrix composite materials from the mixture of pure aluminum and Al65Cu20Fe10Cr5 QC powders were prepared by Selective Laser Melting (SLM) which can produce parts with sophisticated form and fine microstructure with near-zeromaterial waste. The effects of process parameters (such as laser power and scanning speed) on the microstructure, hardness and wear behavior of SLMed composites were investigated with a special focus on the size and morphology of Al91Fe4Cr5 QC reinforcement. After laser melting process, an Al-rich QC phase (Al91Fe4Cr5) is formed. The grain size increases and its morphology changes from spherical to irregular with increment of laser power. Additionally, the sample obtained at relatively low laser power presents a mixed microstructure (partially melted QC, micro-QC and nano-QC) and high wear resistance. The instrumented indentation tests indicate that the partially melted QC particle present higher hardness than that of the other structure in the composite. Moreover, the wear mechanism changes from oxidation to delamination as the laser power increases. (C) 2017 Elsevier Ltd. All rights reserved.
Title:
First Observation of Heavy Fermion Behavior in Ce-Based Icosahedral Approximant
Authors:
Imura, K; Nobe, K; Deguchi, K; Matsunami, M; Miyazaki, H; Yasui, A; Ikenaga, E; Sato, NK Author Full Names: Imura, Keiichiro; Nobe, Kohei; Deguchi, Kazuhiko; Matsunami, Masaharu; Miyazaki, Hidetoshi; Yasui, Akira; Ikenaga, Eiji; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 86 (9):10.7566/JPSJ.86.093702 SEP 15 2017
Abstract:
Since the discovery of unconventional quantum criticality in the Au-Al-Yb quasicrystal and pressure-induced quantum criticality in its approximant, quasicrystals and approximants with an icosahedral cluster of atoms have attracted much attention. Here we report magnetic, thermodynamic, transport, and hard x-ray photoemission spectroscopy experiments on the Ce-based approximant Ag-In-Ce. These results indicate the heavy fermion behavior of the 4f electrons and provide convincing evidence of a magnetic phase transition into a spin-glass-like short-rangeordered state at a low temperature. The Ag-In-Ce alloy is the first Ce-based heavy fermion approximant to a Tsai-type quasicrystal. Reflecting its unique crystal structure, the approximant shows an electrical resistivity distinct from that of traditional Kondo lattices.
Title:
Formation pathways of mesoporous silica nanoparticles with dodecagonal tiling
Authors:
Sun, Y; Ma, K; Kao, T; Spoth, KA; Sai, H; Zhang, DH; Kourkoutis, LF; Elser, V; Wiesner, U Author Full Names: Sun, Yao; Ma, Kai; Kao, Teresa; Spoth, Katherine A.; Sai, Hiroaki; Zhang, Duhan; Kourkoutis, Lena F.; Elser, Veit; Wiesner, Ulrich
Source:
NATURE COMMUNICATIONS, 8 10.1038/s41467-017-00351-8 AUG 15 2017
Abstract:
Considerable progress in the fabrication of quasicrystals demonstrates that they can be realized in a broad range of materials. However, the development of chemistries enabling direct experimental observation of early quasicrystal growth pathways remains challenging. Here, we report the synthesis of four surfactant-directed mesoporous silica nanoparticle structures, including dodecagonal quasicrystalline nanoparticles, as a function of micelle pore expander concentration or stirring rate. We demonstrate that the early formation stages of dodecagonal quasicrystalline mesoporous silica nanoparticles can be preserved, where precise control of mesoporous silica nanoparticle size down to <30 nm facilitates comparison between mesoporous silica nanoparticles and simulated single-particle growth trajectories beginning with a single tiling unit. Our results reveal details of the building block size distributions during early growth and how they promote quasicrystal formation. This work identifies simple synthetic parameters, such as stirring rate, that may be exploited to design other quasicrystal-forming self-assembly chemistries and processes.
Title:
X-ray Study of Phason Strains in an AlCuFeMn Decagonal Phase
Authors:
Yang, W; Ando, T; Yamamoto, K Author Full Names: Yang, Wang; Ando, Tomoyo; Yamamoto, Kazuki
Source:
MATERIALS TRANSACTIONS, 58 (6):847-851; 10.2320/matertrans.M2016446 2017
Abstract:
The peak profiles, shifts, and splittings of Bragg reflections, which are inherent in the phason strain of a quasicrystal, are carefully examined using a precise powder X-ray diffraction method for a wide range of different AlCuFeMn alloys and annealing temperatures. Based on the peak-shift dependences of the Bragg reflections on the phason momentum Q(perpendicular to), two kinds of new approximant phases are identifled. These phases have linear phason strains theta(1) = tau(-6) and theta(2) = tau(-5), and theta(1) = tau(-10) and theta(2) =tau(-5), corresponding to lattice spacings a=3.814 nm and b = 2.005 nm, and a = 9.985 nm and b = 2.005 nm in the quasiperiodic plane of the orthorhombic system, respectively.

Update: 6-Sep-2017

Title:
Quantum incommensurate skyrmion crystals and commensurate to in-commensurate transitions in cold atoms and materials with spin-orbit couplings in a Zeeman field
Authors:
Sun, FD; Ye, JW; Liu, WM Author Full Names: Sun, Fadi; Ye, Jinwu; Liu, Wu-Ming
Source:
NEW JOURNAL OF PHYSICS, 19 10.1088/1367-2630/aa7ce5 AUG 16 2017
Abstract:
In this work, we study strongly interacting spinor atoms in a lattice subject to a two dimensional (2d) anisotropic Rashba type of spin orbital coupling (SOC) and an Zeeman field. We find the interplay between the Zeeman field and the SOC provides a new platform to host rich and novel classes of quantum commensurate and in-commensurate phases, excitations and phase transitions. These commensurate phases include two collinear states at low and high Zeeman field, two co-planar canted states at mirror reflected SOC parameters respectively. Most importantly, there are non-coplanar incommensurate Skyrmion (IC-SkX) crystal phases surrounded by the four commensurate phases. New excitation spectra above all the five phases, especially on the IC-SKX phase are computed. Three different classes of quantum commensurate to in-commensurate transitions from the IC-SKX to its four neighboring commensurate phases are identified. Finite temperature behaviors and transitions are discussed. The critical temperatures of all the phases can be raised above that reachable by current cold atom cooling techniques simply by tuning the number of atoms N per site. In view of recent impressive experimental advances in generating 2d SOC for cold atoms in optical lattices, these new many-body phenomena can be explored in the current and near future cold atom experiments. Applications to various materials such as MnSi, Fe-0.5 Co0.5Si, especially the complex incommensurate magnetic ordering in Li2IrO3 are given.

Update: 30-Aug-2017

Title:
Atomic-scale configurations of variant twin boundaries of a pseudo-decagonal quasicrystal approximant in Al60Cr20Fe10Si10 alloy
Authors:
Ma, HK; Li, H; He, ZB Author Full Names: Ma, Haikun; Li, Hua; He, Zhanbing
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 723 736-742; 10.1016/j.jallcom.2017.06.183 NOV 5 2017
Abstract:
Twin boundaries (TBs) of decagonal quasicrystal approximants generally exhibit structural characteristics that are peculiar compared with traditional crystals with small lattice parameters. Herein, the TBs of the orthorhombic (3/2,2/1) 2 decagonal approximant in the quaternary Al60Cr20Fe10Si10 alloy were investigated, and four types of ( 101) TBs were found using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. The structural features of these TBs at the atomic level were revealed and the corresponding projected structural models along the pseudo-tenfold axis were proposed and discussed. These results demonstrate that the diversifications of the TBs of decagonal approximants are closely related to the rich combinations of substructural blocks, and this may trigger further interest in the planar defects present in other decagonal approximants. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Continual approach at T=0 in the mean field theory of incommensurate magnetic states in the frustrated Heisenberg ferromagnet with an easy axis anisotropy
Authors:
Martynov, SN; Tugarinov, VI; Martynov, AS Author Full Names: Martynov, S. N.; Tugarinov, V. I.; Martynov, A. S.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 440 47-49; 10.1016/j.jmmm.2016.12.086 OCT 15 2017
Abstract:
The algorithm of approximate solution was developed for the differential equation describing the anharmonical change of the spin orientation angle in the model of ferromagnet with the exchange competition between nearest and next nearest magnetic neighbors and the easy axis exchange anisotropy. The equation was obtained from the collinearity constraint on the discrete lattice. In the low anharmonicity approximation the equation is resulted to an autonomous form and is integrated in quadratures. The obvious dependence of the angle velocity and second derivative of angle from angle and initial condition was derived by expanding the first integral of the equation in the Taylor series in vicinity of initial condition. The ground state of the soliton solutions was calculated by a numerical minimization of the energy integral. The evaluation of the used approximation was made for a triple point of the phase diagram.
Title:
Hierarchical porous CoNi/CoO/NiO composites derived from dealloyed quasicrystals as advanced anodes for lithium-ion batteries
Authors:
Liu, H; Wang, XL; Wang, JX; Xu, H; Yu, WS; Dong, XT; Zhang, HB; Wang, LM Author Full Names: Liu, Huan; Wang, Xinlu; Wang, Jinxian; Xu, Hang; Yu, Wensheng; Dong, Xiangting; Zhang, Hongbo; Wang, Limin
Source:
SCRIPTA MATERIALIA, 139 30-33; 10.1016/j.scriptamat.2017.06.011 OCT 2017
Abstract:
Three-dimensional (3D) hierarchical porous CoNi/CoO/NiO composites have been elaborately designed by selectively dealloying of Al-Ni-Co quasicrystals (QCs) alloy. The CoNi/CoO/NiO electrode combines the excellent conductivity and strong stability of CoNi with the high theoretical capacities of CoO/NiO together. When applied as anode materials for lithium-ion batteries (LIBs), the CoNi/CoO/NiO delivers a high specific capacity of 578 mAh g(-1) at a current density of 200 mA g(-1) after 600 cycles. Furthermore, this facile and efficient strategy not only provides an opportunity for rational designing advanced battery anodes, but also open a promising avenue to explore the application of QCs. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Interplay of phase sequence and electronic structure in the modulated martensites of Mn2NiGa from first-principles calculations
Authors:
Kundu, A; Gruner, ME; Siewert, M; Hucht, A; Entel, P; Ghosh, S Author Full Names: Kundu, Ashis; Gruner, Markus E.; Siewert, Mario; Hucht, Alfred; Entel, Peter; Ghosh, Subhradip
Source:
PHYSICAL REVIEW B, 96 (6):10.1103/PhysRevB.96.064107 AUG 14 2017
Abstract:
We investigate the relative stability, structural properties, and electronic structure of various modulated martensites of the magnetic shape memory alloy Mn2NiGa by means of density functional theory. We observe that the instability in the high-temperature cubic structure first drives the system to a structure where modulation shuffles with a period of six atomic planes are taken into account. The driving mechanism for this instability is found to be the nesting of the minority band Fermi surface, in a similar way to that established for the prototype system Ni2MnGa. In agreement with experiments, we find 14M modulated structures with orthorhombic and monoclinic symmetries having energies lower than other modulated phases with the same symmetry. In addition, we also find energetically favorable 10M modulated structures which have not been observed experimentally for this system yet. The relative stability of various martensites is explained in terms of changes in the electronic structures near the Fermi level, affected mostly by the hybridization of Ni and Mn states. Our results indicate that the maximum achievable magnetic field-induced strain in Mn2NiGa would be larger than in Ni2MnGa. However, the energy costs for creating nanoscale adaptive twin boundaries are found to be one order of magnitude higher than that in Ni2MnGa.
Title:
Latest trends in quasicrystal research
Authors:
Takemori, N; Singh, A Author Full Names: Takemori, Nayuta; Singh, Alok
Source:
CURRENT SCIENCE, 113 (3):377-379; AUG 10 2017
Title:
Universal self-assembly of one-component three-dimensional dodecagonal quasicrystals
Authors:
Ryltsev, R; Chtchelkatchev, N Author Full Names: Ryltsev, Roman; Chtchelkatchev, Nikolay
Source:
SOFT MATTER, 13 (29):5076-5082; 10.1039/c7sm00883j AUG 7 2017
Abstract:
Using molecular dynamics simulations, we study computational self-assembly of one-component threedimensional dodecagonal (12-fold) quasicrystals in systems with two-length-scale potentials. Existing criteria for three-dimensional quasicrystal formation are quite complicated and rather inconvenient for particle simulations. So to localize numerically the quasicrystal phase, one should usually simulate over a wide range of system parameters. We show how to universally localize the parameter values at which dodecagonal quasicrystal order may appear for a given particle system. For that purpose, we use a criterion recently proposed for predicting decagonal quasicrystal formation in one-component two-length-scale systems. The criterion is based on two dimensionless effective parameters describing the fluid structure which are extracted from the radial distribution function. The proposed method allows reduction of the time spent for searching the parameters favoring a certain solid structure for a given system. We show that the method works well for dodecagonal quasicrystals; this result is verified on four systems with different potentials: the Dzugutov potential, the oscillating potential which mimics metal interactions, the repulsive shoulder potential describing effective interactions for the core/shell model of colloids and the embedded-atom model potential for aluminum. Our results suggest that the mechanism of dodecagonal quasicrystal formation is universal for both metallic and soft-matter systems and it is based on competition between interparticle scales.

Update: 23-Aug-2017

Title:
How to assign a (3+1)-dimensional superspace group to an incommensurately modulated biological macromolecular crystal
Authors:
Porta, J; Lovelace, J; Borgstahl, GEO Author Full Names: Porta, Jason; Lovelace, Jeff; Borgstahl, Gloria E. O.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 50 1200-1207; 10.1107/S1600576717007294 4 AUG 2017
Abstract:
Periodic crystal diffraction is described using a three-dimensional (3D) unit cell and 3D space-group symmetry. Incommensurately modulated crystals are a subset of aperiodic crystals that need four to six dimensions to describe the observed diffraction pattern, and they have characteristic satellite reflections that are offset from the main reflections. These satellites have a non-integral relationship to the primary lattice and require q vectors for processing. Incommensurately modulated biological macromolecular crystals have been frequently observed but so far have not been solved. The authors of this article have been spearheading an initiative to determine this type of crystal structure. The first step toward structure solution is to collect the diffraction data making sure that the satellite reflections are well separated from the main reflections. Once collected they can be integrated and then scaled with appropriate software. Then the assignment of the superspace group is needed. The most common form of modulation is in only one extra direction and can be described with a (3 + 1) D superspace group. The (3 + 1) D superspace groups for chemical crystallographers are fully described in Volume C of International Tables for Crystallography. This text includes all types of crystallographic symmetry elements found in small-molecule crystals and can be difficult for structural biologists to understand and apply to their crystals. This article provides an explanation for structural biologists that includes only the subset of biological symmetry elements and demonstrates the application to a real-life example of an incommensurately modulated protein crystal.
Title:
Microstructural and crystallographic characteristics of modulated martensite, non-modulated martensite, and pre-martensitic tweed austenite in Ni-Mn-Ga alloys
Authors:
Zhou, L; Schneider, MM; Giri, A; Cho, K; Sohn, Y Author Full Names: Zhou, Le; Schneider, Matthew M.; Giri, Anit; Cho, Kyu; Sohn, Yongho
Source:
ACTA MATERIALIA, 134 93-103; 10.1016/j.actamat.2017.05.050 AUG 1 2017
Abstract:
A combinatorial approach using diffusion couples and TEM analyses was carried out to investigate the composition-dependent martensitic transformation in NiMnGa alloys. The compositions cover a large portion of the off-stoichiometric Ni2MnGa compositions and some Mn-rich compositions. Crystallographic variations of the martensitic phase, including non-modulated (NM) martensite, modulated (5M or 7M) martensite, and austenitic phase were identified in the diffusion couples and investigated with respect to their microstructure and crystallography. The 5M and 7M martensitic structures were only found near the interphase boundary between austenite and martensite, while the NM martensitic structures were found mostly away from the interphase boundary. The tetragonality ratio (c/a) for NM martensite generally increases with e/a ratio, but was also dependent on the composition. The habit plane and martensitic microstructure that consists of twinned variants with differing orientations were documented using electron diffraction. The pre-martensitic state was observed in the austenitic phase that was located near the interphase boundary between austenite and martensite, with distinctive tweed microstructure and a strain field originating from the local lattice distortions. The combinatorial approach proves to be efficient and systematic in studying the composition-dependent martensitic transformation in NiMnGa alloys and can be potentially applied to other shape memory alloys. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Crystal structures of eta ''-Cu3+xSi and eta '''-Cu3+xSi
Authors:
Correa, CA; Perez, O; Kopecek, J; Brazda, P; Klementova, M; Palatinus, L Author Full Names: Correa, Cinthia Antunes; Perez, Olivier; Kopecek, Jaromir; Brazda, Petr; Klementova, Mariana; Palatinus, Lukas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 767-774; SI 10.1107/S2052520617006163 4 AUG 2017
Abstract:
The binary phase diagram of Cu-Si is unexpectedly complex in the vicinity of Cu3+xSi. The low-temperature region contains three closely related incommensurately modulated phases denoted, in order of increasing temperature of stability, eta''', eta '' and eta'. The structure analysis of eta' has been reported previously [Palatinus et al. (2011). Inorg. Chem. 50, 3743]. Here the structure model for the phases eta '' and eta''' is reported. The structures could be solved in superspace, but no superspace structure model could be constructed due to the complexity of the modulation functions. Therefore, the structures were described in a supercell approximation, which involved a 4 x 4 x 3 supercell for the eta '' phase and a 14 x 14 x 3 supercell for the eta''' phase. Both structures are very similar and differ only by a subtle symmetry lowering from eta '' to eta'''. A comparison of the structure models of eta '' and eta''' with the reported structure of eta' suggests that the reported structure model of eta' contains an incorrect assignment of atomic types.

Update: 17-Aug-2017

Title:
Local cluster networks and the number of valence states in aluminium-transition metal face-centred icosahedral quasicrystals
Authors:
Kitahara, K; Kimura, K Author Full Names: Kitahara, Koichi; Kimura, Kaoru
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 232 (7-9):507-513; 10.1515/zkri-2016-2035 JUL 2017
Abstract:
Coordination environments of a special class of clusters which are related to the valence states in aluminium-transition metal face-centred icosahedral quasicrystals were analysed on the basis of the six-dimensional model of Katz and Gratias for the atomic sites and that of Yamamoto for the centres of the clusters. The number of the clusters per atom in the model (approximate to 0.263) is comparable with that of Al-Cu-Ir cubic approximant crystal (approximate to 0.258), and it indicates that the model reasonably represents the distribution of the clusters. We identified all the possible local cluster networks of short distances, which are related to the inter-cluster bonds, and evaluated the number of the valence states by assuming two possible configurations of inter-cluster bonds. The number of the valence states per atom was derived as a function of the fraction of transition-metal atoms, and the value is in good agreement with that expected from the compositions of real quasicrystals. Notably, the number of the part of the valence states which do not depend on the fraction of transition-metal atoms is numerically similar to the electron to atom ratio known as e/ a, which is phenomenologically related to the stability of quasicrystals.
Title:
Anisotropic electrical, thermal and magnetic properties of Al13Ru4 decagonal quasicrystalline approximant
Authors:
Wencka, M; Vrtnik, S; Kozelj, P; Jaglicic, Z; Gille, P; Dolinsek, J Author Full Names: Wencka, Magdalena; Vrtnik, Stanislav; Kozelj, Primoz; Jaglicic, Zvonko; Gille, Peter; Dolinsek, Janez
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 232 (7-9):647-652; 10.1515/zkri-2016-2039 JUL 2017
Abstract:
We present measurements of the anisotropic electrical and thermal transport coefficients (the electrical resistivity, the thermoelectric power, the thermal conductivity), the magnetization and the specific heat of the Al13Ru4 monoclinic approximant to the decagonal quasicrystal, in comparison to the isostructural Al13Fe4. The electrical and thermal transport parameters of Al13Ru4 were found to exhibit significant anisotropy, qualitatively similar to that found previously in the Al13Fe4 (P. Popcevic, et al., Phys. Rev. B 2010, 81, 184203). The crystallographic b direction, corresponding to the stacking direction of the (a,c) atomic planes, is the most conducting direction for the electricity and heat. The thermopower is strongly anisotropic with a complicated temperature dependence, exhibiting maxima, minima, crossovers and sign change. The electronic density of states (DOS) at the Fermi energy is reduced to 35% of the DOS of Al metal. The magnetic susceptibility is diamagnetic and the diamagnetism is by a factor of 2 stronger for the magnetic field along the stacking b direction.s

Update: 3-Aug-2017

Title:
Three-Dimensional Modeling of Quasicrystal Structures from X-ray Diffraction: An Icosahedral Al-Cu-Fe Alloy
Authors:
Hong, ST Author Full Names: Hong, Seung-Tae
Source:
INORGANIC CHEMISTRY, 56 (13):7354-7359; 10.1021/acs.inorgchem.7b00245 JUL 3 2017
Abstract:
Quasicrystals (QCs) are well-ordered but aperiodic crystals with classically forbidden symmetries (such as 5-fold). High-dimensional (HD) crystallography is a standard method to locate atom positions explicitly. However, in practice, it is still challenging because of its complexity. Here, we report a new simple approach to three-dimensional (3D) atomic modeling derived from X-ray diffraction data, and apply it to the icosahedral QC Al0.63Cu0.25Fe0.12. Electron density maps were calculated directly from 3D diffraction data indexed with noninteger (fractional) numbers as measured, with proper phases; each of 2(5) = 32 possible phase assignments for the five strongest reflections was used for Fourier synthesis. This resulted in an initial phasing model based on chemically sensible electron density maps. The following procedure was exactly the same as that used to determine ordinary crystal structures, except that fractional indices were assigned to the reciprocal vectors relative to the three orthogonal 2-fold axes in icosahedral (I-h) symmetry to which the observed diffraction data conformed. Finally, similar to 30 000 atoms were located within a sphere of a,similar to 48 angstrom radius. Structural motifs or basic repeating units with a hierarchical nature can be found. Isolated icosahedral clusters are surrounded by a concentric dodecahedron, beyond which there is a concentric truncated icosahedron. These are strikingly similar to those obtained via HI) crystallography, but show very clear real-space relationships between the clusters.
Title:
Microstructural and Mechanical Characterization of Hybrid Aluminum Matrix Composite Containing Boron Carbide and Al-Cu-Fe Quasicrystals
Authors:
Khan, M; Zulfaqar, M; Ali, F; Subhani, T Author Full Names: Khan, Mahmood; Zulfaqar, Muhammad; Ali, Fahad; Subhani, Tayyab
Source:
METALS AND MATERIALS INTERNATIONAL, 23 (4):813-822; 10.1007/s12540-017-6619-7 JUL 2017
Abstract:
Hybrid aluminum matrix composites containing particles of boron carbide and quasicrystals were manufactured to explore the combined effect of reinforcements on microstructural evolution and mechanical performance of the composites. The particles were incorporated at a loading of 6 wt% each making a total of 12 wt% reinforcement in pure aluminum. For comparison, two composites containing individually reinforced 12 wt% particles were also prepared along with a reference specimen of pure aluminum. Ball milling technique was employed to mix the composite constituents. The green bodies of composite powders were prepared by uniaxial pressing at room temperature followed by consolidation by pressureless sintering under inert atmosphere. The microstructural characterization was performed using scanning electron microscopy while phase identification was carried out by X-ray diffraction. The mechanical characterization was performed by Vickers hardness and compression tests. Hybrid composites showed increased compressive properties while the composites containing solely quasicrystals demonstrated improved hardness. The increase in mechanical performance was related to the microstructural evolution due to the presence and uniform dispersion of binary particles.
Title:
Orthorhombic intermediate phase originating from {110} nanotwinning in Ni50.0Mn28.7Ga21.3 modulated martensite
Authors:
Straka, L; Drahokoupil, J; Vertat, P; Kopecek, J; Zeleny, M; Seiner, H; Heczko, O Author Full Names: Straka, Ladislav; Drahokoupil, Jan; Vertat, Petr; Kopecek, Jaromir; Zeleny, Martin; Seiner, Hanus; Heczko, Oleg
Source:
ACTA MATERIALIA, 132 335-344; 10.1016/j.actamat.2017.04.048 JUN 15 2017
Abstract:
The temperature evolution of the structure of Ni50.0Mn28.7Ga21.3, single crystals exhibiting magnetic shape memory effect was investigated near the martensitic transformation by X-ray diffraction. Upon heating, five-layered modulated monoclinic martensite (10M) with a = 0.5974 nm, b = 0.5949 nm, c = 0.5589 nm, and 7 = 90.34 at room temperature (297 K) changed to an intermediate (10M') phase with a = b = 0.5945 nm, c = 0.5616 nm, and gamma = 90.25 degrees at a few tenths of kelvin below the transformation to austenite at T-A = 327 K. This previously unreported 10M' phase between 10M martensite and austenite can be described as orthorhombic using axes diagonal to the original a and b axes derived from the cubic L2(1) cell. Upon cooling, the phase remained stable in a broader temperature interval down to temperature T = 318 K at which it transformed back to monoclinic 10M structure with a not equal b. The transformation temperature coincided with the martensitic transformation temperature T-M = 318 K. The SEM observations and theoretical X-ray diffraction calculations indicate that the intermediate phase is actually the nanotwinned original 10M phase. This {110} nanotwinning with approximate to 20 nm mean twin width originates from the complex hierarchical branching on the austenite nucleus-martensite interface. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Influence of Fe addition on the formation of a quasicrystalline phase in bulk Al-rich Al-Mn base alloys
Authors:
Stan-Glowinska, K; Litynska-Dobrzynska, L; Rogal, L Author Full Names: Stan-Glowinska, K.; Litynska-Dobrzynska, L.; Rogal, L.
Source:
MATERIALS CHARACTERIZATION, 128 203-208; 10.1016/j.matchar.2017.04.006 JUN 2017
Abstract:
This work evaluates the effect of Fe addition on the formation of a quasicrystalline phase in the 94A1-6Mn base alloys obtained by wedge casting. Different Mn to Fe ratios (1, 1.4, 2, 5) were used to estimate Fe content that leads to formation of a quasicrystalline icosahedral phase (I-phase) at the selected Al concentration (94 at.%). Based on the obtained results, Fe enhances I-phase nucleation in the studied ternary alloys compared to the non modified binary composition. Although the maximum thickness of the cast wedge at which the I -phase was formed in the prepared alloys varied with Fe content, its nucleation was always limited to a certain range of cooling rates above 10(3) K/s. Hardness increased significantly for areas composed of Al matrix and I -phase particles. The highest HV values were obtained for parts of castings where the microstructure consisted of very fine I-phase/A1 eutectic.

Update: 26-Jul-2017

Title:
Effects of hot-compaction on the structure and properties of Al-Mn-Fe-X alloys strengthened with quasi-crystalline icosahedral phase
Authors:
Stan-Glowinska, K; Litynska-Dobrzynska, L; Kania, B; Dutkiewicz, J; Rogal, L; Skuza, W; Wojewoda-Budka, J; Gordillo, MA; Wiezorek, JM Author Full Names: Stan-Glowinska, K.; Litynska-Dobrzynska, L.; Kania, B.; Dutkiewicz, J.; Rogal, L.; Skuza, W.; Wojewoda-Budka, J.; Gordillo, M. A.; Wiezorek, J. M.
Source:
MATERIALS & DESIGN, 126 162-173; 10.1016/j.matdes.2017.04.043 JUL 15 2017
Abstract:
Melt-spun ribbons of Al91Mn6Fe2X1 (X= Mn, Mo, V) were used as a feedstock to obtain bulk materials by mechanical milling and subsequent hot-pressing compaction. Modifications of the chemical composition of the Al-Fe-Mn base ternary alloy with the transition metals Mo and V facilitated hot-compaction based preparation of bulk samples with microstructures that retained significant fractions of the quasicrystalline I-phase. The transition metal modified bulk alloy samples exhibited enhanced values of compressive strength and high hardness.
Title:
EXISTENCE RESULTS IN THE LINEAR DYNAMICS OF QUASICRYSTALS WITH PHASON DIFFUSION AND NONLINEAR GYROSCOPIC EFFECTS
Authors:
Bisconti, L; Mariano, PM Author Full Names: Bisconti, Luca; Mariano, Paolo Maria
Source:
MULTISCALE MODELING & SIMULATION, 15 (2):745-767; 10.1137/15M1049580 2017
Abstract:
Quasicrystals are characterized by quasi-periodic arrangements of atoms. The description of their mechanics involves deformation and a (so-called phason) vector field accounting at macroscopic scale for local phase changes, due to atomic flips necessary to match quasi periodicity under the action of the external environment. Here we discuss the mechanics of quasicrystals, commenting on a shift from its initial formulation, as standard elasticity in a space with dimension twice the ambient one, to a more elaborated setting, which seems to account more deeply for the physics at hand. In the new setting we tackle two problems. First we discuss the linear dynamics of quasicrystals including a phason diffusion. We prove existence of weak solutions and their uniqueness under rather general boundary and initial conditions. We then consider phason rotational inertia, nonlinearly coupled with the curl of the macroscopic velocity, and prove once again existence of weak solutions to the pertinent balance equations.

Update: 19-Jul-2017

Title:
Towards the growth of single quasicrystalline grains in Al-Cu-(Fe,Cr) alloys after mechanical alloying and subsequent high temperature heating
Authors:
Salimon, AI; Stepashkin, AA; Tcherdyntsev, VV; Olifirov, LK; Klyueva, MV; Kaloshkin, SD Author Full Names: Salimon, A. I.; Stepashkin, A. A.; Tcherdyntsev, V. V.; Olifirov, L. K.; Klyueva, M. V.; Kaloshkin, S. D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 720 95-104; 10.1016/j.jallcom.2017.05.249 OCT 5 2017
Abstract:
Coarse grains growth in Al65Cu23Fe12 and Al73Cu11Cr16 mechanically alloyed powders was studied. Heating up to 950 degrees C and further rapid cooling produces a range of single quasicrystalline grains having different sizes, shapes and the degree of perfection. In the Al-Cu-Fe system both secondary recrystallization in the solid state and crystallization from liquid state were found. Contrary to the mechanism of nucleation in the liquid state and further growth of nuclei we demonstrate another mechanism - the ready nuclei which survived after the short heating are incorporating the molten material, which results in the formation of perfectly shaped single grains. In the Al-Cu-Cr system only secondary recrystallization in the solid state and no crystallization from liquid state were found. (C) 2017 Elsevier B.V. All rights reserved.

Update: 13-Jul-2017

Title:
Analysis of cracks in one-dimensional hexagonal quasicrystals with the heat effect
Authors:
Fan, CY; Yuan, YP; Pan, YB; Zhao, MH Author Full Names: Fan, CuiYing; Yuan, YanPeng; Pan, YiBo; Zhao, MingHao
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 120 146-156; 10.1016/j.ijsolstr.2017.04.036 AUG 1 2017
Abstract:
The extended displacement discontinuity (EDD) method is proposed to analyze cracks in the periodical plane of one-dimensional (1D) hexagonal quasicrystals with the heat effect. Based on the operator theory and the Fourier transform, the fundamental solutions for EDDs are derived, where the EDD5 include phonon and phason displacement discontinuities and the temperature discontinuity. The EDD boundary integral equation method is used to analyze the singularities of the near-crack tip fields, and the extended stress intensity factor (ESIF) expressions are obtained in terms of the EDD5 across the crack faces. The EDD boundary element method is proposed to calculate the ESIFs of cracks in 1D hexagonal quasicrystals. COMSOL software is used to validate the developed method. The influences of applied mechanical and heat loads on cracks in a finite plate are investigated. (C) 2017 Elsevier Ltd. All rights reserved.

Update: 6-Jul-2017

Title:
On magnetism in the quasicrystalline Ti45Zr38Ni17 alloy
Authors:
Czub, J; Przewoznik, J; Zywczak, A; Takasaki, A; Hoser, A; Gondek, L Author Full Names: Czub, J.; Przewoznik, J.; Zywczak, A.; Takasaki, A.; Hoser, A.; Gondek, L.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 470 108-111; 10.1016/j.jnoncrysol.2017.05.007 AUG 15 2017
Abstract:
Magnetism of 3D quasicrystals is extensively researched, mainly for rare-earth or iron-based alloys. In this contribution, magnetic properties of the icosahedral Ti45Zr38Ni17 quasicrystal are reported. Namely, the results of magnetometric and neutron diffraction studies in the broad temperature ranges of 1.5-300 K and 2-700 K respectively are discussed. The magnetometric studies reveal that the alloy exhibits an extremely weak ferromagnetic signal, however it is associated with the traces of nickel clusters at the grains boundaries. The neutron scattering studies, including diffraction in external magnetic field, indicate no possibility of long-rage magnetic ordering in the icosahedral Ti45Zr38Ni17 alloy. According to our studies, the investigated material exhibits Pauli-like paramagnetic behaviour.
Title:
Effects of calcium, manganese and cerium-rich mischmetal additions on the mechanical properties of extruded Mg-Zn-Y alloy reinforced by quasicrystalline I-phase
Authors:
Medina, J; Perez, P; Garces, G; Adeva, P Author Full Names: Medina, Judit; Perez, Pablo; Garces, Gerardo; Adeva, Paloma
Source:
MATERIALS CHARACTERIZATION, 129 195-206; 10.1016/j.matchar.2017.04.033 JUL 2017
Abstract:
The effect of calcium, manganese and cerium mischmetal additions on the mechanical properties of the extruded Mg-6Zn-1Y (wt%) alloy reinforced by quasicrystalline I-phase has been investigated. The tensile behaviour at room temperature can be rationalized on the basis of microstructural changes induced by the different elements added to the ternary alloy. The highest yield stress value corresponds to the material modified with cerium-rich mischmetal. Manganese addition leads to the best balance between strength and ductility while calcium addition has a negligible effect on the mechanical properties of ternary alloy. The analysis of the contributions of the different strengthening mechanisms operating during deformation reveals that grain size refinement is the main hardening contribution in all alloys mechanism followed by the strengthening due to coarse second phases. The hardening due to basal texture conferred by the existence of coarse non-recrystallized grains depends on the overall hardening induced by the rest of strengthening mechanisms.
Title:
Imaging quasiperiodic electronic states in a synthetic Penrose tiling
Authors:
Collins, LC; Witte, TG; Silverman, R; Green, DB; Gomes, KK Author Full Names: Collins, Laura C.; Witte, Thomas G.; Silverman, Rochelle; Green, David B.; Gomes, Kenjiro K.
Source:
NATURE COMMUNICATIONS, 8 10.1038/ncomms15961 JUN 22 2017
Abstract:
Quasicrystals possess long-range order but lack the translational symmetry of crystalline solids. In solid state physics, periodicity is one of the fundamental properties that prescribes the electronic band structure in crystals. In the absence of periodicity and the presence of quasicrystalline order, the ways that electronic states change remain a mystery. Scanning tunnelling microscopy and atomic manipulation can be used to assemble a two-dimensional quasicrystalline structure mapped upon the Penrose tiling. Here, carbon monoxide molecules are arranged on the surface of Cu(111) one at a time to form the potential landscape that mimics the ionic potential of atoms in natural materials by constraining the electrons in the two-dimensional surface state of Cu(111). The real-space images reveal the presence of the quasiperiodic order in the electronic wave functions and the Fourier analysis of our results links the energy of the resonant states to the local vertex structure of the quasicrystal.
Title:
Static charge-density-wave order in the superconducting state of La2-xBaxCuO4
Authors:
Thampy, V; Chen, XM; Cao, Y; Mazzoli, C; Barbour, AM; Hu, W; Miao, H; Fabbris, G; Zhong, RD; Gu, GD; Tranquada, JM; Robinson, IK; Wilkins, SB; Dean, MPM Author Full Names: Thampy, V.; Chen, X. M.; Cao, Y.; Mazzoli, C.; Barbour, A. M.; Hu, W.; Miao, H.; Fabbris, G.; Zhong, R. D.; Gu, G. D.; Tranquada, J. M.; Robinson, I. K.; Wilkins, S. B.; Dean, M. P. M.
Source:
PHYSICAL REVIEW B, 95 (24):10.1103/PhysRevB.95.241111 JUN 21 2017
Abstract:
Charge-density-wave (CDW) correlations feature prominently in the phase diagram of the cuprates, motivating competing theories of whether fluctuating CDW correlations aid superconductivity or whether static CDW order coexists with superconductivity in inhomogeneous or spatially modulated states. Here we report Cu L-edge resonant x-ray photon correlation spectroscopy measurements of CDW correlations in superconducting La2-xBaxCuO4, x = 0.11. Static CDW order is shown to exist in the superconducting state at low temperatures and to persist up to at least 85% of the CDW transition temperature. We discuss the implications of our observations for how nominally competing order parameters can coexist in the cuprates.
Title:
High-field magnetization and magnetic phase diagram of alpha-Cu2V2O7
Authors:
Gitgeatpong, G; Suewattana, M; Zhang, SW; Miyake, A; Tokunaga, M; Chanlert, P; Kurita, N; Tanaka, H; Sato, TJ; Zhao, Y; Matan, K Author Full Names: Gitgeatpong, G.; Suewattana, M.; Zhang, Shiwei; Miyake, A.; Tokunaga, M.; Chanlert, P.; Kurita, N.; Tanaka, H.; Sato, T. J.; Zhao, Y.; Matan, K.
Source:
PHYSICAL REVIEW B, 95 (24):10.1103/PhysRevB.95.245119 JUN 16 2017
Abstract:
High-field magnetization of the spin-1/2 antiferromagnet alpha-Cu2V2O7 was measured in pulsed magnetic fields of up to 56 T in order to study its magnetic phase diagram. When the field was applied along the easy axis (the a axis), two distinct transitions were observed at H-c1 = 6.5 T and H-c2 = 18.0 T. The former is a spin-flop transition typical for a collinear antiferromagnet and the latter is believed to be a spin-flip transition of canted moments. The canted moments, which are induced by the Dzyaloshinskii-Moriya interactions, anti-align for H-c1 < H < H-c2 due to the anisotropic exchange interaction that favors the antiferromagnetic arrangement along the a axis. Above H-c2, the Zeeman energy of the applied field overcomes the antiferromagnetic anisotropic interaction and the canted moments are aligned along the field direction. Density functional theory was employed to compute the exchange interactions, which were used as inputs for quantum Monte Carlo calculations and then further refined by fitting to the magnetic susceptibility data. Contrary to our previous report in Phys. Rev. B 92, 024423 (2015), the dominant exchange interaction is between the third nearest-neighbor spins, which form zigzag spin chains that are coupled with one another through an intertwining network of the nonnegligible nearest and second nearest-neighbor interactions. In addition, elastic neutron scattering under the applied magnetic fields of up to 10 T reveals the incommensurate helical spin structure in the spin-flop state.
Title:
Ultrafast Formation of a Charge Density Wave State in 1T-TaS2: Observation at Nanometer Scales Using Time-Resolved X-Ray Diffraction
Authors:
Laulhe, C; Huber, T; Lantz, G; Ferrer, A; Mariager, SO; Grubel, S; Rittmann, J; Johnson, JA; Esposito, V; Lubcke, A; Huber, L; Kubli, M; Savoini, M; Jacques, VLR; Cario, L; Corraze, B; Janod, E; Ingold, G; Beaud, P; Johnson, SL; Ravy, S Author Full Names: Laulhe, C.; Huber, T.; Lantz, G.; Ferrer, A.; Mariager, S. O.; Grubel, S.; Rittmann, J.; Johnson, J. A.; Esposito, V.; Lubcke, A.; Huber, L.; Kubli, M.; Savoini, M.; Jacques, V. L. R.; Cario, L.; Corraze, B.; Janod, E.; Ingold, G.; Beaud, P.; Johnson, S. L.; Ravy, S.
Source:
PHYSICAL REVIEW LETTERS, 118 (24):10.1103/PhysRevLett.118.247401 JUN 16 2017
Abstract:
Femtosecond time-resolved x-ray diffraction is used to study a photoinduced phase transition between two charge density wave (CDW) states in 1T-TaS2, namely the nearly commensurate (NC) and the incommensurate (I) CDW states. Structural modulations associated with the NC-CDW order are found to disappear within 400 fs. The photoinduced I-CDW phase then develops through a nucleation and growth process which ends 100 ps after laser excitation. We demonstrate that the newly formed I-CDW phase is fragmented into several nanometric domains that are growing through a coarsening process. The coarsening dynamics is found to follow the universal Lifshitz-Allen-Cahn growth law, which describes the ordering kinetics in systems exhibiting a nonconservative order parameter.
Title:
Analysis of a three-dimensional arbitrarily shaped interface crack in a one-dimensional hexagonal thermo-electro-elastic quasicrystal bi-material. Part 1: Theoretical solution
Authors:
Zhao, MH; Dang, HY; Fan, CY; Chen, ZT Author Full Names: Zhao, MingHao; Dang, HuaYang; Fan, CuiYing; Chen, ZengTao
Source:
ENGINEERING FRACTURE MECHANICS, 179 59-78; 10.1016/j.engfracmech.2017.04.019 JUN 15 2017
Abstract:
The extended displacement discontinuity boundary integral-differential equation method is adapted to analyze a three-dimensional interface crack of arbitrary shape in a one-dimensional, hexagonal thermo-electro-elastic quasicrystals bi-material. The extended displacement discontinuities include phonon and phason displacement discontinuities, electric potential discontinuity, as well as temperature discontinuity across the interface crack; while the extended stresses represent phonon and phason stresses, electric displacement and heat flux, respectively. An analysis method is proposed based on the analogy between the governing equations for one-dimensional hexagonal electro-thermo-elastic quasicrystals and three-dimensional transversely isotropic magnetoelectrothermoelastic media. By using the analogy method, the fundamental solutions for unit-point extended displacement discontinuities on the interface are obtained. Using the superposition principal, the extended displacement discontinuity boundary integral-differential equations are established. The singular indices and the singular behaviors of the near crack border fields are studied, and the combined extended stress intensity factors (SIFs) are derived in terms of the EDDs. (c) 2017 Elsevier Ltd. All rights reserved.
Title:
Study on structure variations of incommensurately modulated labradorite feldspars with different cooling histories
Authors:
Jin, SY; Xu, HF Author Full Names: Jin, Shiyun; Xu, Huifang
Source:
AMERICAN MINERALOGIST, 102 (6):1328-1339; 10.2138/am-2017-6003 JUN 2017
Abstract:
The incommensurately modulated structures of three intermediate plagioclase feldspars with compositions of similar to An(51) are determined by single-crystal X-ray diffraction analyses. The samples selected cover a range of different cooling rate, from relatively fast to extremely slow. The structures show various ordering states that are directly correlated with the cooling histories of the samples. The slowest cooled sample shows an e1 structure with strong density modulation, along with nanoscale exsolution lamellae. The fastest cooled sample displays an e2 structure, without second-order satellite reflections (f-reflections) and density modulation. The sample with intermediate cooling rate shows a less ordered e1 structure with weak density modulation, but the modulation period and orientation are the same as in e2 structure. The comparison of the structures with the same composition reveals the ordering process and phase transitions during the cooling of plagioclase within the compositional range of Boggild intergrowth. New parameters from modulation waves can be used for quantifying the ordering state of plagioclase feldspars. Proposed phase relationship and T-T-T diagram for similar to An(51) plagioclase feldspars are illustrated for explaining the relationship among Cl, e1 and e2 structures, and relative cooling rates of their host rocks.
Title:
Enhanced electrochemical hydrogen storage performance of Ti-V-Ni composite employing NaAlH4
Authors:
Liang, F; Lin, J; Wu, YM; Wang, LM Author Full Names: Liang, Fei; Lin, Jing; Wu, Yaoming; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 42 (21):14633-14640; 10.1016/j.ijhydene.2017.04.202 MAY 25 2017
Abstract:
The Ti1.41V0.6Ni doped with NaAlH4 composites were prepared by ball-milling method and the phase composition and electrochemical hydrogen storage properties of the composites were investigated. The phase contains icosahedral quasicrystalline (i-phase), Ti2Ni and V based solid-solution phase primarily. The NaAlH4 phase is not evident for the composite, and the NaAlH4 phase should be decomposed to help form porous structure on the surface of the composites. The electrochemical hydrogen storage properties of composites has been enhanced with doped NaAlH4, and the maximum electrochemical hydrogen discharge capacity is 299.2 mAh/g, and keeps above 220 mAh/g after 80 cycles for 1 wt.% doping. The high-rate discharge ability of the composite electrode could achieve 79.8% at the discharge current density of 240 mA/g compared with that of 30 mA/g. The enhancement could be attributed to decoration of the composites surface, increase of entropy variation and improvement of H-kinetics on the strength of new porous structure in the composites. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Effect of Icosahedral Phase on Crystallographic Texture and Mechanical Anisotropy of Mg-4%Li Based Alloys
Authors:
Li, CQ; Xu, DK; Yu, S; Sheng, LY; Han, EH Author Full Names: Li, C. Q.; Xu, D. K.; Yu, S.; Sheng, L. Y.; Han, E. H.
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 33 (5):475-480; 10.1016/j.jmst.2016.10.003 MAY 2017
Abstract:
Through investigating and comparing the microstructure and mechanical properties of the as-extruded Mg alloys Mg-4%Li and Mg-4%Li-6%Zn-1.2%Y (in wt%), it demonstrates that although the formation of I-phase (Mg3Zn6Y, icosahedral structure) could weaken the crystallographic texture and improve the mechanical strength, the mechanical anisotropy in terms of strength remains in Mg-4%Li-6%Zn-1.2%Y alloy. Failure analysis indicates that for the Mg-4%Li alloy, the fracture surfaces of the tensile samples tested along transverse direction (TD) contain a large number of plastic dimples, whereas the fracture surface exhibits quasi-cleavage characteristic when tensile samples were tested along extrusion direction (ED). For the Mg-4%Li-6%Zn-1.2%Y alloy, typical ductile fracture surfaces can be observed in both "TD" and "ED" samples. Moreover, due to the zonal distribution of broken I-phase particles, the fracture surface of "TD" samples is characterized by the typical "woody fracture". Copyright (C) 2017, The editorial office of Journal of Materials Science & Technology. Published by Elsevier Limited.

Update: 29-Jun-2017

Title:
Heat capacity, resistivity, and angular dependent magnetization studies of single crystal Nd1+epsilon Fe4B4 for epsilon approximate to 1/7
Authors:
Conner, BS; Susner, MA; Lampen-Kelley, P; May, AF; McGuire, MA; Yan, JQ; Sales, BC Author Full Names: Conner, B. S.; Susner, M. A.; Lampen-Kelley, P.; May, A. F.; McGuire, M. A.; Yan, J. -Q.; Sales, B. C.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 435 100-106; 10.1016/j.jmmm.2017.04.002 AUG 1 2017
Abstract:
Advances in crystal growth have allowed for synthesis of large single crystals of Nd1+epsilon Fe4B4, a wellknown phase with a modulated structure. As a result we are able to report heat capacity and resistivity measurements on a single crystal Nd1+epsilon Fe4B4 sample with a distribution of epsilon that skews towards the solubility limit of Nd near epsilon approximate to 1/7. Heat capacity measurements show evidence of crystal field splitting at temperatures higher than the long-range ferromagnetic Curie temperature. Heat capacity, resistivity, and magnetization measurements all confirm a Curie temperature of 7 K which is lower than previously reported values in the Nd1+epsilon Fe4B4 system. We also perform measurements of the angular dependence of the magnetization and discover behavior associated with the magnetic anisotropy that is inconsistent with the simple description previously proposed. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Fe-57 Mossbauer study of unusual magnetic structure of multiferroic 3R-AgFeO2
Authors:
Sobolev, A; Rusakov, V; Moskvin, A; Gapochka, A; Belik, A; Glazkova, I; Akulenko, A; Demazeau, G; Presniakov, I Author Full Names: Sobolev, A.; Rusakov, V.; Moskvin, A.; Gapochka, A.; Belik, A.; Glazkova, I.; Akulenko, A.; Demazeau, G.; Presniakov, I.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (27):10.1088/1361-648X/aa70ae JUL 12 2017
Abstract:
We report new results of a Fe-57 Mossbauer study of hyperfine magnetic interactions in the layered multiferroic 3R-AgFeO2 demonstrating two magnetic phase transitions at TN1 and TN2. The asymptotic value beta* approximate to 0.34 for the critical exponent obtained from the temperature dependence of the hyperfine field H-hf(T) at Fe-57 the nuclei below TN1 approximate to 14 K indicates that 3R-AgFeO2 shows quasi-3D critical behavior. The spectra just above TN1 (TN1 < T < T* approximate to 41 K) demonstrate a relaxation behavior due to critical spin fluctuations which indicates the occurrence of short-range correlations. At the intermediate temperature range, TN2 < T < TN1, the Fe-57 Mossbauer spectra are described in terms of collinear spin-density-waves (SDW) with the inclusion of many high-order harmonics, indicating that the real magnetic structure of the ferrite appears to be more complicated than a pure sinusoidally modulated SDW. Below T < TN2 approximate to 9 K, the hyperfine field Hhf reveals a large spatial anisotropy (Delta H-anis approximate to 30 kOe) which is related with a local intra-cluster (FeO6) spin-dipole term that implies a conventional contribution of the polarized oxygen ions. We proposed a simple two-parametric formula to describe the dependence of H-anis on the distortions of the (FeO6) clusters. Analysis of different mechanisms of spin and hyperfine interactions in 3R-AgFeO2 and its structural analogue CuFeO2 points to a specific role played by the topology of the exchange coupling and the oxygen polarization in the delafossite-like structures.
Title:
Quantitative atomic force microscopy
Authors:
Songen, H; Bechstein, R; Kuhnle, A Author Full Names: Soengen, Hagen; Bechstein, Ralf; Kuehnle, Angelika
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (27):10.1088/1361-648X/aa6f8b JUL 12 2017
Abstract:
A variety of atomic force microscopy (AFM) modes is employed in the field of surface science. The most prominent AFM modes include the amplitude modulation (AM) and the frequency modulation (FM) mode. Over the years, different ways for analyzing data acquired with different AFM modes have been developed, where each analysis is usually based on mode-specific assumptions and approximations. Checking the validity of the seemingly different approximations employed in the various analysis methods can be a tedious task. Moreover, a straightforward comparison of data analyzed with different methods can, therefore, be challenging. Here, we combine the existing evaluation methods which have been separately developed for the different AFM modes and present a unifying set of three equations. These three AFM equations allow for a straightforward analysis of AFM data within the harmonic approximation, regardless of the AFM mode. The three AFM equations provide the three and only pieces of information about the tip-sample force available within the harmonic approximation. We demonstrate the generality of our approach by quantitatively analyzing three-dimensional AFM data obtained in both the AM and FM mode.
Title:
Engineering of many-body Majorana states in a topological insulator/s-wave superconductor heterostructure
Authors:
Hung, HH; Wu, JS; Sun, K; Chiu, CK Author Full Names: Hung, Hsiang-Hsuan; Wu, Jiansheng; Sun, Kuei; Chiu, Ching-Kai
Source:
SCIENTIFIC REPORTS, 7 10.1038/s41598-017-02493-7 JUN 14 2017
Abstract:
We study a vortex chain in a thin film of a topological insulator with proximity-induced superconductivity-a promising platform to realize Majorana zero modes (MZMs)-by modeling it as a two-leg Majorana ladder. While each pair of MZMs hybridizes through vortex tunneling, we hereby show that MZMs can be stabilized on the ends of the ladder with the presence of tilted external magnetic field and four-Majorana interaction. Furthermore, a fruitful phase diagram is obtained by controlling the direction of magnetic field and the thickness of the sample. We reveal many-body Majorana states and interaction-induced topological phase transitions and also identify trivialsuperconducting and commensurate/ incommensurate charge-density-wave states in the phase diagram.
Title:
Crossover from an incommensurate singlet spiral state with a vanishingly small spin gap to a valence-bond solid state in dimerized frustrated ferromagnetic spin chains
Authors:
Agrapidis, CE; Drechsler, SL; van den Brink, J; Nishimoto, S Author Full Names: Agrapidis, Clio Efthimia; Drechsler, Stefan-Ludwig; van den Brink, Jeroen; Nishimoto, Satoshi
Source:
PHYSICAL REVIEW B, 95 (22):10.1103/PhysRevB.95.220404 JUN 13 2017
Abstract:
Motivated by the magnetic properties of the spin-chain compounds LiCuSbO4 equivalent to LiSbCuO4 and Rb2Cu2Mo3O12, we study the ground state of the Heisenberg chain with dimerized nearest-neighbor ferromagnetic (FM) (J(1), J'(1) < 0) and next-nearest-neighbor antiferromagnetic (J(2) > 0) couplings. Using the density-matrix renormalization group technique and spin-wave theory, we find a first-order transition between a fully polarized FM and an incommensurate spiral state at 2 alpha = beta/(1 + beta), where alpha is the frustration ratio J(2)/|J(1)| and beta the degree of dimerization J'(1)/J(1). In the singlet spiral state the spin-gap is vanishingly small in the vicinity of the FM transition, corresponding to a situation of LiCuSbO4. For larger alpha, corresponding to Rb2Cu2Mo3O12, and smaller beta there is a crossover from this frustration induced incommensurate state to an Affleck-Lieb-Kennedy-Tasaki-type valence-bond solid state with substantial spin gaps.
Title:
Deformation behavior and texture randomization of Mg-Zn-Gd alloys reinforced with icosahedral quasicrystal
Authors:
Huang, H; Miao, HW; Yuan, GY; Chen, CL; Zhang, H; Pei, J; Wang, ZC Author Full Names: Huang, Hua; Miao, Hongwei; Yuan, Guangyin; Chen, Chunlin; Zhang, Hua; Pei, Jia; Wang, Zhongchang
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 108 (6):455-464; 10.3139/146.111500 JUN 2017
Abstract:
We report hot deformation behavior of icosahedral quasicrystalline phase reinforced Mg-1.50Zn-0.25Gd (at.%) alloys fabricated by a traditional gravity casting approach. The exponential law constitutive equation is applied to describe their flow stress behavior and the average activation energy is determined to be 187.70 kJ mol(-1). We also find that I-phase forms and grows in the alloys when the deformation strain is increasingly applied and that twinning contributes to high basal texture at early stage of deformation. Basal texture is weakened when the applied strain is strong owing to the dynamic recrystallization and also to the particle stimulation nucleation (PSN) effects of I-phase at late stage of deformation. High temperature is found to contribute to recrystallization but restrain I-phase precipitation and also weaken PSN effects of I-phase. Moreover, we find that a large strain rate not only promotes non-basal dislocation glide/twinning but also contributes to basal texture randomization, while a moderate strain rate is harmful for deformation due to the generation of strong basal texture. Furthermore, I-phase is found to be more effective for basal texture randomization than other strengthening secondary phases in Mg alloys, which is due to the presence of many orientation relationships and also because the interface between I-phase and Mg matrix is coherent or semi-coherent.
Title:
On the Mechanisms of Modulation of Crystal Structures
Authors:
Borisov, SV; Magarill, SA; Pervukhina, NV Author Full Names: Borisov, S. V.; Magarill, S. A.; Pervukhina, N. V.
Source:
CRYSTALLOGRAPHY REPORTS, 62 (3):349-354; 10.1134/S1063774517030038 MAY 2017
Abstract:
Based on the assumption that crystal structures of a number of sulfides are the result of modulation of cationic lattices by anionic lattices, the versions of their conjugation in direct and reciprocal spaces have been analyzed using common translational lattices. The concept of this phenomenon, developed within the superspace formalism, is supplemented by a proposed interpretation of the real modulation of the structures.

Update: 21-Jun-2017

Title:
Magnetism of PrFeAsO parent compound for iron-based superconductors: Mossbauer spectroscopy study
Authors:
Komedera, K; Pierzga, A; Blachowski, A; Ruebenbauer, K; Budziak, A; Katrych, S; Karpinski, J Author Full Names: Komedera, K.; Pierzga, A.; Blachowski, A.; Ruebenbauer, K.; Budziak, A.; Katrych, S.; Karpinski, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 717 350-355; 10.1016/j.jallcom.2017.05.049 SEP 15 2017
Abstract:
Mossbauer spectroscopy measurements were performed for the temperature range between 4.2 K and 300 K in a transmission geometry applying 14.41-keV resonant line in Fe-57 for PrFeAsO the latter being a parent compound of the iron-based superconductors belonging to the '1111' family. It was found that an itinerant 3d magnetic order develops at about 165 K and it is accompanied by an orthorhombic distortion of the chemical unit cell. A complete longitudinal 3d incommensurate spin density wave (SDW) order develops at about 140 K. Transferred hyperfine magnetic field generated by the praseodymium magnetic order on iron nuclei is seen at 12.8 K and below, i.e., below magnetic order of praseodymium magnetic moments. It is oriented perpendicular to the field of SDW on iron nuclei. The shape of SDW is almost rectangular at low temperatures and it transforms into roughly triangular form around "nematic" transition at about 140 K. Praseodymium magnetic order leads to the substantial enhancement of SDW due to the large orbital contribution to the magnetic moment of praseodymium. A transferred field indicates presence of strong magnetic susceptibility anisotropy in the [b-c] plane while following rotation of praseodymium magnetic moments in this plane with lowering temperature. It was found that "nematic" phase region is a region of incoherent spin density wavelets typical for a critical region. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Stacking order dynamics in the quasi-two-dimensional dichalcogenide 1T-TaS2 probed with MeV ultrafast electron diffraction
Authors:
Le Guyader, L; Chase, T; Reid, AH; Li, RK; Svetin, D; Shen, X; Vecchione, T; Wang, XJ; Mihailovic, D; Durr, HA Author Full Names: Le Guyader, L.; Chase, T.; Reid, A. H.; Li, R. K.; Svetin, D.; Shen, X.; Vecchione, T.; Wang, X. J.; Mihailovic, D.; Durr, H. A.
Source:
STRUCTURAL DYNAMICS, 4 (4):10.1063/1.4982918 JUL 2017
Abstract:
Transitions between different charge density wave (CDW) states in quasi-twodimensional materials may be accompanied also by changes in the inter-layer stacking of the CDW. Using MeV ultrafast electron diffraction, the out-of-plane stacking order dynamics in the quasi-two-dimensional dichalcogenide 1T-TaS2 is investigated for the first time. From the intensity of the CDW satellites aligned around the commensurate l = 1/6 characteristic stacking order, it is found out that this phase disappears with a 0.3 ps time constant. Simultaneously, in the same experiment, the emergence of the incommensurate phase, with a slightly slower 2.0 ps time constant, is determined from the intensity of the CDW satellites aligned around the incommensurate l = 1/3 characteristic stacking order. These results might be of relevance in understanding the metallic character of the laser-induced metastable "hidden" state recently discovered in this compound. (C) 2017 Author(s).
Title:
Dynamic diffraction effects and coherent breathing oscillations in ultrafast electron diffraction in layered 1T-TaSeTe
Authors:
Wei, LL; Sun, SS; Guo, C; Li, ZW; Sun, K; Liu, Y; Lu, WJ; Sun, YP; Tian, HF; Yang, HX; Li, JQ Author Full Names: Wei, Linlin; Sun, Shuaishuai; Guo, Cong; Li, Zhongwen; Sun, Kai; Liu, Yu; Lu, Wenjian; Sun, Yuping; Tian, Huanfang; Yang, Huaixin; Li, Jianqi
Source:
STRUCTURAL DYNAMICS, 4 (4):10.1063/1.4979643 JUL 2017
Abstract:
Anisotropic lattice movements due to the difference between intralayer and interlayer bonding are observed in the layered transition-metal dichalcogenide 1T-TaSeTe following femtosecond laser pulse excitation. Our ultrafast electron diffraction investigations using 4D-transmission electron microscopy (4D-TEM) clearly reveal that the intensity of Bragg reflection spots often changes remarkably due to the dynamic diffraction effects and anisotropic lattice movement. Importantly, the temporal diffracted intensity from a specific crystallographic plane depends on the deviation parameter s, which is commonly used in the theoretical study of diffraction intensity. Herein, we report on lattice thermalization and structural oscillations in layered 1T-TaSeTe, analyzed by dynamic diffraction theory. Ultrafast alterations of satellite spots arising from the charge density wave in the present system are also briefly discussed. (C) 2017 Author(s).
Title:
Magnetic structures and excitations in CePd2(Al,Ga)(2) series: Development of the "vibron" states
Authors:
Klicpera, M; Boehm, M; Dolezal, P; Mutka, H; Koza, MM; Rols, S; Adroja, DT; Orench, IP; Rodriguez-Carvajal, J; Javorsky, P Author Full Names: Klicpera, M.; Boehm, M.; Dolezal, P.; Mutka, H.; Koza, M. M.; Rols, S.; Adroja, D. T.; Orench, I. Puente; Rodriguez-Carvajal, J.; Javorsky, P.
Source:
PHYSICAL REVIEW B, 95 (8):10.1103/PhysRevB.95.085107 FEB 3 2017
Abstract:
CePd2Al2-xGax compounds crystallizing in the tetragonal CaBe2Ge2-type structure (space group P4/nmm) and undergoing a structural phase transition to an orthorhombic structure (Cmme) at low temperatures were studied by means of neutron scattering. The amplitude-modulated magnetic structure of CePd2Al2 is described by an incommensurate propagation vector (k) over right arrow = (delta(x), 1/2 + delta(y), 0) with delta(x) = 0.06 and delta(y) = 0.04. The magnetic moments order antiferromagnetically within the ab planes stacked along the c axis and are arranged along the direction close to the orthorhombic a axis with a maximum value of 1.5(1) mu(B)/Ce3+. CePd2Ga2 reveals a magnetic structure composed of two components: the first is described by the propagation vector (k) over right arrow (1) = (1/2,1/2,0), and the second one propagates with (k) over right arrow (2) = (0,1/2,0). The magnetic moments of both components are aligned along the same direction-the orthorhombic [100] direction-and their total amplitude varies depending on the mutual phase of magnetic moment components on each Ce site. The propagation vectors (k) over right arrow (1) and (k) over right arrow (2) describe also the magnetic structure of substituted CePd2Al2-xGax compounds, except the one with x = 0.1. CePd2Al1.9Ga0.1 with magnetic structure described by (k) over right arrow and (k) over right arrow (1) stays on the border between pure CePd2Al2 and the rest of the series. Determined magnetic structures are compared with other Ce 112 compounds. Inelastic neutron scattering experiments disclosed three nondispersive magnetic excitations in the paramagnetic state of CePd2Al2, while only two crystal field (CF) excitations are expected from the splitting of ground state J = 5/2 of the Ce3+ ion in a tetragonal/orthorhombic point symmetry. Three magnetic excitations at 1.4, 7.8, and 15.9 meV are observed in the tetragonal phase of CePd2Al2. A structural phase transition to an orthorhombic structure shifts the first excitation up to 3.7 meV, while the other two excitations remain at almost the same energy. The presence of an additional magnetic peak is discussed and described within the Thalmeier-Fulde CF-phonon coupling (i.e., magnetoelastic coupling) model generalized to the tetragonal point symmetry. The second parent compound CePd2Ga2 does not display any sign of additional magnetic excitation. The expected two CF excitations were observed. The development of magnetic excitations in the CePd2Al2-xGax series is discussed and crystal field parameters determined.
Title:
Sr1/2Ce5/14 square 1/7WO4: a new modulated ternary scheelite compound
Authors:
dos Passos, RHD; Arab, M; de Souza, CP; Leroux, C Author Full Names: Damascena dos Passos, Rafael Hernandez; Arab, Madjid; de Souza, Carlson Pereira; Leroux, Christine
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 466-473; 10.1107/S2052520617002827 3 JUN 2017
Abstract:
For the first time, a ternary tetragonal scheelite structure tungstate with strontium and cerium cations, (Sr, Ce)WO4, was synthesized. As much as 35% Ce could be inserted into the structure, leaving 1/7 of the (Sr, Ce) cation sites vacant. Partial ordering of Sr and Ce, with atomic displacements, were shown by high-resolution electron microscopy. Two-dimensional incommensurate modulations occur in this material, in small domains 20 nm in size. The band gap of this compound is significantly lower than the band gap of SrWO4 and this was related to the distortions of WO4 and (Sr,Ce)O-8 polyhedra. The band gap value of 3.2 eV makes Sr1/2Ce5/14 square 1/7WO4 a promising candidate for violet luminescence.
Title:
Could incommensurability in sulfosalts be more common than thought? The case of meneghinite, CuPb13Sb7S24
Authors:
Bindi, L; Petricek, V; Biagioni, C; Plasil, J; Moelo, Y Author Full Names: Bindi, Luca; Petricek, Vaclav; Biagioni, Cristian; Plasil, Jakub; Moelo, Yves
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 369-376; 10.1107/S2052520617002657 3 JUN 2017
Abstract:
The structure of meneghinite (CuPb13Sb7S24), from the Bottino mine in the Apuan Alps (Italy), has been solved and refined as an incommensurate structure in four-dimensional superspace. The structure is orthorhombic, superspace group Pnma(0 beta 0)00s, cell parameters a = 24.0549 (3), b = 4.1291 (6), c = 11.3361 (16) angstrom, modulation vector q = 0.5433 (4) b*. The *structure* was refined from 6604 reflections to a final R = 0.0479. The model includes modulation of both atomic positions and displacement parameters, as well as occupational waves. The driving forces stabilizing the modulated structure of meneghinite are linked to the occupation modulation of Cu and some of the Pb atoms. As a consequence of the Cu/[] and Pb/Sb modulations, three-to sevenfold coordinations of the M cations (Pb/Sb) occur in different parts of the structure. The almost bimodal distribution of the occupation of Cu/[] and Pb/Sb at M5 conforms with the coupled substitution Sb3+ + [] -> Pb2+ + Cu+, thus corroborating the hypothesis deduced previously for the incorporation of copper in the meneghinite structure. The very small departure (similar to 0.54 versus 0.50) from the commensurate value of the modulation raises the question of whether other sulfosalts considered superstructures have been properly described, and, in this light, if incommensurate modulation in sulfosalts could be much more common than thought.
Title:
Ordered vacancy distribution in 2/1 mullite: a superspace model
Authors:
Klar, PB; de la Pinta, N; Lopez, GA; Etxebarria, I; Breczewski, T; Madariaga, G Author Full Names: Klar, Paul B.; de la Pinta, Noelia; Lopez, Gabriel A.; Etxebarria, Inigo; Breczewski, Tomasz; Madariaga, Gotzon
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 377-388; 10.1107/S2052520617001652 3 JUN 2017
Abstract:
A mullite single crystal with composition Al4.84Si1.16O9.58 (2) exhibiting sharp satellite reflections was investigated by means of X-ray diffraction. For the refinement of a superspace model in the superspace group Pbam(alpha 01/2)0ss different scale factors for main and satellite reflections were used in order to describe an ordered mullite structure embedded in a disordered polymorph. The ordered fraction of the mullite sample exhibits a completely ordered vacancy distribution and can be described as a block structure of vacancy blocks (VBs) that alternate with vacancy-free blocks (VFBs) along a and c. The incommensurate nature of mullite originates from a modulation of the block size, which depends on the composition. The displacive modulation is analyzed with respect to the vacancy distribution and a possible Al/Si ordering scheme is derived, although the measurement itself is not sensitive to the Al/Si distribution. An idealized, commensurate approximation for 2/1 mullite is also presented. Comparison of the ordered superspace model with different preceding models reconciles many key investigations of the last decades with partly contradicting conclusions, where mullite was usually treated as either ordered or disordered instead of considering simultaneously different states of order.

Update: 15-Jun-2017

Title:
Enhancement in magnetocaloric properties of NiMnGa alloy through stoichiometric tuned phase transformation and magneto-thermal transitions
Authors:
Dey, S; Roy, RK; Ghosh, M; Mallick, AB; Mitra, A; Panda, AK Author Full Names: Dey, Sushmita; Roy, R. K.; Ghosh, M.; Mallick, A. Basu; Mitra, A.; Panda, A. K.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 439 305-311; 10.1016/j.jmmm.2017.04.088 OCT 1 2017
Abstract:
The investigation is focussed on phase generation and magnetocaloric properties of a series of Ni77-XMnXGa23 (x = 22, 23, 24, 25, 27) alloys prepared through arc melting furnace. With increase in Mn content, the alloys showed systematic transition from a non-modulated martensite (NM) to a fully austenitic parent phase through an appearance and coexistence of modulated (M) structure. Intermediate Mn containing alloy (#Mn-24) not only displayed high magnetic entropy change (Delta S-M) of -7.7 J/kg(-1)K(-1) but also large Refrigerant Capacity (RC) of 169 J.Kg(-1) at magnetic field change of 3 T compared to other alloys. The coexisting martensite (NM, M) and parent austenite as well as overlapping thermomagnetic and structural transformation was deliverable through tuning of alloy chemistry wherein Ni was systematically substituted by Mn. Transmission electron microscopy (TEM) supported the proposition with existence of martensite plates of different morphology in Mn-24 alloy exhibiting superior magnetocaloric properties. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Interlayer coupling and electronic structure of misfit-layered bismuth-based cobaltites
Authors:
Takakura, S; Yamamoto, I; Tanaka, E; Azuma, J; Maki, M Author Full Names: Takakura, Sho-ichi; Yamamoto, Isamu; Tanaka, Eishi; Azuma, Junpei; Maki, Makoto
Source:
PHYSICAL REVIEW B, 95 (19):10.1103/PhysRevB.95.195166 MAY 30 2017
Abstract:
The [Bi2M2O4](p) CoO2 materials (M = Ca, Sr, and Ba) were studied to clarify the effect of the lattice incommensurability on electronic properties using angle-resolved photoemission spectroscopy and transmission electron microscopy (TEM). Results show that the insulating behavior is characterized by a spectral weight for binding energies higher than 2.0 eV. Moreover, the spectral shape is modified as a function of the incident photon energy, demonstrating a close relationship between the electrical properties and interlayer coupling. TEM results show that the effect of the lattice mismatch differs for different misfit parameters p. We therefore conclude that the carrier concentration and the chemical environment at the misfit interface, which depend on the degree of incommensurability, mutually determine the electronic properties of the system.
Title:
Fracture analysis of one-dimensional hexagonal quasicrystals: Researches of a finite dimension rectangular plate by boundary collocation method
Authors:
Cheng, JX; Sheng, DF; Shi, PP Author Full Names: Cheng Jiaxing; Sheng Dongfa; Shi Pengpeng
Source:
JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY, 31 (5):2373-2383; 10.1007/s12206-017-0434-4 MAY 2017
Abstract:
As an important supplement and development to crystallography, the applications about quasicrystal materials have played a core role in many fields, such as manufacturing and the space industry. Due to the sensitivity of quasicrystals to defects, the research on the fracture problem of quasicrystals has attracted a great deal of attention. We present a boundary collocation method to research fracture problems for a finite dimension rectangular one-dimensional hexagonal quasicrystal plate. Because mode I and mode II problems for onedimensional hexagonal quasicrystals are like that for the classical elastic materials, only the anti-plane problem is discussed in this paper. The correctness of the present numerical method is verified through a comparison of the present results and the existing results. And then, the size effects on stress field, stress intensity factor and energy release rate are discussed in detail. The obtained results can provide valuable references for the fracture behavior of quasicrystals.
Title:
Interplay between charge density wave and antiferromagnetic order in GdNiC2
Authors:
Hanasaki, N; Shimomura, S; Mikami, K; Nogami, Y; Nakao, H; Onodera, H Author Full Names: Hanasaki, N.; Shimomura, S.; Mikami, K.; Nogami, Y.; Nakao, H.; Onodera, H.
Source:
PHYSICAL REVIEW B, 95 (8):10.1103/PhysRevB.95.085103 FEB 2 2017
Abstract:
The correlation between the charge density wave (CDW) and f local moments is observed in GdNiC2 by means of x-ray diffraction in a magnetic field. Various kinds of electronic states exist in the magnetic field. The intensity of the CDW peak changes in the successive transitions and the commensurate-incommensurate transition of the CDW takes place as well. The successive transitions are explained in terms of a cooperative effect of the Peierls instability and the spin Friedel oscillation, in which the antiferromagnetic order of the f local moments is coupled to the spin density wave coexisting with the CDW of the conduction electron.
Title:
Effects of oxygen-deficiency on crystal structure, dielectric and ferroelectric properties in Sr5SmTi3+2xNb7-2xO30-x with tungsten bronze structure
Authors:
Deng, BL; Zhu, XL; Liu, XQ; Chen, XM Author Full Names: Deng, Bao Li; Zhu, Xiao Li; Liu, Xiao Qiang; Chen, Xiang Ming
Source:
RSC ADVANCES, 7 (44):27370-27376; 10.1039/c7ra03870d 2017
Abstract:
Oxygen-deficient tungsten bronze ceramics with general formula Sr5SmTi3+ 2xNb7-2xO30-x (x = 0, 0.1, 0.25) are prepared. The effects of oxygen deficiency on the crystal structure, dielectric and ferroelectric properties are investigated. With increasing oxygen deficiency, the crystal structure becomes less stable and the lattice shrinks, while the ferroelectricity is weakened, and the low temperature relaxation enhanced. Commensurate superlattices observed in Sr5SmTi3+ 2xNb7-2xO30-x , corresponding to the onset of the ferroelectric transition as reported previously. In compositions with x = 0.1 and 0.25, two factors that Asite cross occupancies and disturbance of oxygen vacancies on the ferroelectric order are noticed and related to the change from ferroelectric behavior to diffuse one. Three orders of incommensurate superlattice reflections are observed in x = 0.1 and 0.25 compositions. The first-order incommensurate superlattice reflections appear at positions (h + 1/4 - delta, k + 1/4 - delta, l + 1/2), reflecting the common feature in tungsten bronzes with relaxor or diffuse ferroelectric nature. The second-order incommensurate superlattice reflections are observed on the (00l) (l = 0, 1, 2, 3,.) planes around the (h + 1/2, k + 1/2, l) positions, while the third-order incommensurate superlattice reflections are observed on the (00l) (l = 1/2, 3/2,.) planes, by the side of the first-order ones. The appearance of higher-order is believed to reduce the high structural energy induced by the oxygen deficiency.

Update: 7-Jun-2017

Title:
Copper nanocubes on Al65Cu20Fe15 quasicrystalline surface
Authors:
Yadav, TP; Mishra, SS; Srivastava, ON Author Full Names: Yadav, T. P.; Mishra, S. S.; Srivastava, O. N.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 712 134-138; 10.1016/j.jallcom.2017.04.058 JUL 25 2017
Abstract:
A simple leaching method was developed to synthesize Cu nanocubes having edge length in the range of 50-80 nm on a quasicrystalline surface. The Al65Cu20Fe15(at%) quasicrystalline ribbons (similar to 2 mm wide, 5 cm long and similar to 20 mu m thick) have been synthesized by melt spinning techniques. The copper nanocubes were formed by leaching these quasicrystalline ribbons with a 5 M aqueous solution of NaOH. Leaching was performed at various times ranging from 1 to 8 hours (h). The samples were characterized using x-ray diffraction, scanning and transmission electron microscopy as well as energy-dispersive x-ray spectroscopy which confirm the presence of copper nanocubes on the surface of quasicrystal after 8 h of leaching. (C) 2017 Elsevier B.V. All rights reserved.
Title:
An investigation on selective laser melting of Al-Cu-Fe-Cr quasicrystal: From single layer to multilayers
Authors:
Fu, YQ; Kang, N; Liao, HL; Gao, Y; Coddet, C Author Full Names: Fu, Yingqing; Kang, Nan; Liao, Hanlin; Gao, Yang; Coddet, Christian
Source:
INTERMETALLICS, 86 51-58; 10.1016/j.intermet.2017.03.012 JUL 2017
Abstract:
In this study, the effects of processing parameters on the microstructure of Al-Cu-Fe-Cr quasicrystalline (QC) coatings fabricated by selective laser melting (SLM) are investigated. A qualitative analysis on the XRD patterns indicates that the phase composition for the SLM processed coating mainly consisted of Al-Cu-Fe-Cr quasicrystals and alpha-Al (CuFeCr) solid solution, and with increasing laser energy input or coating thickness, the volume fraction of QC i-Al91Fe4Cr5 reduced and those of QC d-Al65Cu20Fe10Cr5 and crystalline 0-Al2Cu increased. The formation of cracks during the coating building procedure from single layer to multilayers is also discussed. For the coatings with the same layer number, the pores and balling particles diminish as laser power increases, due to the growth of melting degree. At the early stage of fabrication, with increment of layer number (or coating thickness), pores and balling particles decrease considerably because the molten pool solidified more "slowly". However, after the layer number increases continuously from 10 to 20, the porosity no longer decreases, and some big size pores, micro-cracks and fractures appear, especially for the sample obtained at lower laser power. A wavy-like pattern composed chiefly of Al and QC phases, is formed at the interfacial region between substrate and coating due to Marangoni effect. (C) 2017 Elsevier Ltd. All rights reserved.
Title:
Salt fog corrosion behavior in a powder-processed icosahedral-phase-strengthened aluminum alloy
Authors:
Watson, TJ; Gordillo, MA; Ernst, AT; Bedard, BA; Aindow, M Author Full Names: Watson, T. J.; Gordillo, M. A.; Ernst, A. T.; Bedard, B. A.; Aindow, M.
Source:
CORROSION SCIENCE, 121 133-138; 10.1016/j.corsci.2017.03.010 JUN 2017
Abstract:
The pitting corrosion resistance has been evaluated for a powder-processed Al-Cr-Mn-Co-Zr alloy which contains approximate to 35% by volume of an icosahedral quasi-crystalline phase and a little Al9Co2 in an Al matrix. ASTM standard salt fog exposure tests show that the alloy exhibits far lower corrosion pit densities and depths than commercial high-strength aerospace Al alloys under the same conditions. Electron microscopy data show that the salt fog exposure leads to the selective oxidation of the face-centered cubic Al matrix around the other phases, and to the development of a porous outer oxide scale. (C) 2017 Elsevier Ltd. All rights reserved.
Title:
Strain modulated ferromagnetic to antiferromagnetic transition in FeRh/BaTiO3 (001) heterostructures
Authors:
Chen, JH; Ma, J; Zhang, YJ; Bao, SY; Wu, L; Liu, C; Nan, CW Author Full Names: Chen, Jiahui; Ma, Jing; Zhang, Yujun; Bao, Shanyong; Wu, Liang; Liu, Chen; Nan, Ce-Wen
Source:
JOURNAL OF APPLIED PHYSICS, 121 (19):10.1063/1.4983361 MAY 21 2017
Abstract:
We report the elastically induced magnetic phase transition of FeRh thin films on BaTiO3 (001) at the successive phase transitions of BaTiO3, which is accompanied by abrupt variations of magnetization and resistance of FeRh at saturated magnetic fields. In-situ X-ray diffraction at different temperatures reveal that the compressive strains are induced accompanied by the tetragonal to orthorhombic and the orthorhombic to rhombohedral structural phase transition of BaTiO3 during cooling, due to the changes in the lattice constant and domain structure in different phases. The compressive strain further stabilizes the antiferromagnetic phase of FeRh and accounts for the magnetization and resistance changes. Published by AIP Publishing.
Title:
Dimensional Crossover in a Charge Density Wave Material Probed by Angle-Resolved Photoemission Spectroscopy
Authors:
Nicholson, CW; Berthod, C; Puppin, M; Berger, H; Wolf, M; Hoesch, M; Monney, C Author Full Names: Nicholson, C. W.; Berthod, C.; Puppin, M.; Berger, H.; Wolf, M.; Hoesch, M.; Monney, C.
Source:
PHYSICAL REVIEW LETTERS, 118 (20):10.1103/PhysRevLett.118.206401 MAY 18 2017
Abstract:
High-resolution angle-resolved photoemission spectroscopy data reveal evidence of a crossover from one-dimensional (1D) to three-dimensional (3D) behavior in the prototypical charge density wave (CDW) material NbSe3. In the low-temperature 3D regime, gaps in the electronic structure are observed due to two incommensurate CDWs, in agreement with x-ray diffraction and electronic-structure calculations. At higher temperatures we observe a spectral weight depletion that approaches the power-law behavior expected in one dimension. From the warping of the quasi-1D Fermi surface at low temperatures, we extract the energy scale of the dimensional crossover. This is corroborated by a detailed analysis of the density of states, which reveals a change in dimensional behavior dependent on binding energy. Our results offer an important insight into the dimensionality of excitations in quasi-1D materials.
Title:
Effect of Atomic Disorder and Temperature on Incommensurate Helical Spin Waves in the Anderson-Hubbard Model
Authors:
Groshev, AG; Arzhnikov, AK Author Full Names: Groshev, A. G.; Arzhnikov, A. K.
Source:
PHYSICS OF THE SOLID STATE, 59 (5):890-897; 10.1134/S1063783417050146 MAY 2017
Abstract:
Based on the single-band t-t' Anderson-Hubbard model, the effect of disorder on the parameters and ranges of existence of incommensurate helical spin waves is studied. The problem is solved within the functional integration theory in static approximation, taking into account longitudinal fluctuations of the magnetic moment. Magnetic phase diagrams and parameters of incommensurate helical spin waves are obtained as functions of temperatures and electron and impurity concentrations. It is shown that disorder can lead to the first-order transition from the antiferromagnetic phase to the (Q, pi) phase and the metal-dielectric transition from antiferromagnetic metal to antiferromagnetic dielectric far from the half-filled band. The results obtained are used to explain the incommensurate magnetic order observed in cuprates in the overdoped mode.

Update: 1-Jun-2017

Title:
The order-disorder evolution in quasicrystals through phason flips
Authors:
Buganski, I; Chodyn, M; Strzalka, R; Wolny, J Author Full Names: Buganski, Ireneusz; Chodyn, Maciej; Strzalka, Radoslaw; Wolny, Janusz
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 710 92-101; 10.1016/j.jallcom.2017.03.251 JUL 5 2017
Abstract:
The problem of incorporating phason flips in the structural investigation of aperiodic systems is still an open question and a challenge in crystallography. Phasons are understood both as atomic fluctuation and positional disorder of the quasicrystalline lattice. Popular correction to diffraction peaks' intensities takes the form of generalized Debye-Waller factor, assuming Gaussian distribution of fluctuations in the perpendicular space of higher-dimensional periodic lattice. Although proven to work in case of random tiling types of structures recent evidence indicates improper handling of peaks with high perpendicular space scattering vector whenever structure is far from random tiling regime. We introduce the concept of a series expansion of the characteristic function of the statistical distribution to properly correct the peaks' intensities with respect to phasonic fluctuations. Calculations are performed upon Penrose tiling. Such approximation of the structure factor works correctly even in cases for which the Debye-Waller correction fails. Even more we investigate transition to random tiling through phason flips by means of the statistical approach which results in interesting scaling properties (ordered -> disordered -> random -> amorphous structure). (C) 2017 Elsevier B.V. All rights reserved.
Title:
Three-dimensional exact electric-elastic analysis of a multilayered two-dimensional decagonal quasicrystal plate subjected to patch loading
Authors:
Yang, LZ; Li, Y; Gao, Y; Pan, E; Waksmanski, N Author Full Names: Yang, Lianzhi; Li, Yang; Gao, Yang; Pan, Ernian; Waksmanski, Natalie
Source:
COMPOSITE STRUCTURES, 171 198-216; 10.1016/j.compstruct.2017.02.036 JUL 1 2017
Abstract:
An exact electric-elastic analysis of a multilayered two-dimensional decagonal quasicrystal plate subjected to patch loading with simply supported boundary conditions is presented. The pseudo-Stroh formalism and propagator matrix method are used to obtain the exact three-dimensional mechanical behaviors of the plate. By expressing the patch loading in the form of a double Fourier series expansion an exact closed-form solution with a concise and elegant expression is deduced. Three different kinds of patch surface loadings are applied to the surface of the plate and the response of the plate is investigated. Comprehensive numerical results are shown for a sandwich plate subjected to the three patch loadings with two different stacking sequences. The results show that the stacking sequences, patch loading areas, and patch loading types have a great influence on the stress, displacement and electric components of the plate. Also, different coupling constants between the phonon and phason fields will influence the physical quantities. The useful features observed from numerical results can be used in the design of composite laminates made of two-dimensional piezoelectric quasicrystals. The numerical results can also serve as a reference in convergence studies of other numerical methods and for verification of existing or future plate theories. (C) 2017 Elsevier Ltd. All rights reserved.
Title:
Non-close-packed three-dimensional quasicrystals
Authors:
Damasceno, PF; Glotzer, SC; Engel, M Author Full Names: Damasceno, Pablo F.; Glotzer, Sharon C.; Engel, Michael
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (23):10.1088/1361-648X/aa6cc1 JUN 14 2017
Abstract:
Quasicrystals are frequently encountered in condensed matter. They are important candidates for equilibrium phases from the atomic scale to the nanoscale. Here, we investigate the computational self-assembly of four quasicrystals in a single model system of identical particles interacting with a tunable isotropic pair potential. We reproduce a known icosahedral quasicrystal and report a decagonal quasicrystal, a dodecagonal quasicrystal, and an octagonal quasicrystal. The quasicrystals have low coordination number or occur in systems with mesoscale density variations. We also report a network gel phase.
Title:
Exchange bias and strain effect co-modulated magnetic symmetry in La0.6Sr0.4MnO3/orthorhombic-YMnO3 multiferroic heterostructures
Authors:
Zheng, DX; Gong, JL; Jin, C; Li, P; Feng, LF; Bai, HL Author Full Names: Zheng, Dongxing; Gong, Junlu; Jin, Chao; Li, Peng; Feng, Liefeng; Bai, Haili
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 50 (21):10.1088/1361-6463/aa69ab JUN 1 2017
Abstract:
The exchange bias and strain effect co-modulated magnetic symmetry in all oxide La0.6Sr0.4MnO3 (LSMO) and orthorhombic YMnO3 (YMO) multiferroic heterostructures were studied. Because of the lattice mismatch between the LSMO and YMO layers, the LSMO layer exhibits a 90 degrees rotation growth on the YMO layer. The strain induced growth not only leads to a 90 degrees phase shift in the anisotropic magnetoresistance (AMR) curves, but also brings a two-fold symmetric magnetoelastic coupling energy along the LSMO [1 1 0] direction. With the incorporation of magnetoelastic coupling energy and exchange coupling energy, the exchange bias induced torque shows a phase shift and causes the asymmetry of the peak position and value in the AMR curves. This work illustrates a modulated magnetic symmetry in ferromagnetic/multiferroic systems by interfacial exchange coupling and strain effect, which will benefit the design of magnetoelectric devices.
Title:
Influence of Cr on local order and dynamic properties of liquid and undercooled Al-Zn alloys
Authors:
Pasturel, A; Jakse, N Author Full Names: Pasturel, A.; Jakse, N.
Source:
JOURNAL OF CHEMICAL PHYSICS, 146 (18):10.1063/1.4982887 MAY 14 2017
Abstract:
Using ab initio molecular dynamics, we present a systematic study of structural and transport properties of liquid Al90Zn10 and Al83Zn10Cr7 alloys. In the liquid phase, we find that Cr additions promote the formation of a heterogeneous local ordering characterized by a strong five-fold symmetry (icosahedral short-range order (ISRO)) around Cr atoms. In the undercooled phase, we observe the extension of ISRO to icosahedral medium-range order (IMRO) length scale referring to Cr atoms. In examining dynamic properties, we show that this Cr induced structural heterogeneity leads to a substantial decoupling of Cr diffusion from the diffusion of Al and Zn components by a factor of 3 at 1000 K, the liquidus temperature. Below this temperature, the formation of IMRO gives rise to a non-Arrhenian temperature dependence of diffusivity and viscosity, a breakdown of the Stokes-Einstein relation, as well as the onset of dynamic heterogeneities. Using the isoconfigurational ensemble method, we evidence that the structural origin of dynamics heterogeneities is clearly related to IMRO. Finally we discuss the role of IMRO in a quasicrystal-enhanced nucleation mechanism discovered recently in Al-Zn-Cr alloys. Published by AIP Publishing.
Title:
Evidence of cross-cutting and redox reaction in Khatyrka meteorite reveals metallic-Al minerals formed in outer space
Authors:
Lin, C; Hollister, LS; MacPherson, GJ; Bindi, L; Ma, C; Andronicos, CL; Steinhardt, PJ Author Full Names: Lin, Chaney; Hollister, Lincoln S.; MacPherson, Glenn J.; Bindi, Luca; Ma, Chi; Andronicos, Christopher L.; Steinhardt, Paul J.
Source:
SCIENTIFIC REPORTS, 7 10.1038/s41598-017-01445-5 MAY 9 2017
Abstract:
We report on a fragment of the quasicrystal-bearing CV3 carbonaceous chondrite Khatyrka recovered from fine-grained, clay-rich sediments in the Koryak Mountains, Chukotka (Russia). We show higher melting-point silicate glass cross-cutting lower melting-point Al-Cu-Fe alloys, as well as unambiguous evidence of a reduction-oxidation reaction history between Al-Cu-Fe alloys and silicate melt. The redox reactions involve reduction of FeO and SiO2 to Fe and Fe-Si metal, and oxidation of metallic Al to Al2O3, occurring where silicate melt was in contact with Al-Cu-Fe alloys. In the reaction zone, there are metallic Fe and Fe-Si beads, aluminous spinel rinds on the Al-Cu-Fe alloys, and Al2O3 enrichment in the silicate melt surrounding the alloys. From this and other evidence, we demonstrate that Khatyrka must have experienced at least two distinct events: first, an event as early as 4.564 Ga in which the first Al-Cu-Fe alloys formed; and, second, a more recent impact-induced shock in space that led to transformations of and reactions between the alloys and the meteorite matrix. The new evidence firmly establishes that the Al-Cu-Fe alloys (including quasicrystals) formed in outer space in a complex, multi-stage process.
Title:
Competing Phases Involving Spin-State and Ligand Structural Orderings in a Multistable Two-Dimensional Spin Crossover Coordination Polymer
Authors:
Zhang, DP; Trzop, E; Valverde-Munoz, FJ; Pineiro-Lopez, L; Munoz, MC; Collet, E; Real, JA Author Full Names: Zhang, Daopeng; Trzop, Elzbieta; Valverde-Munoz, Francisco J.; Pineiro-Lopez, Lucia; Munoz, M. Carmen; Collet, Eric; Real, Jose A.
Source:
CRYSTAL GROWTH & DESIGN, 17 (5):2736-2745; 10.1021/acs.cgd.7b00218 MAY 2017
Abstract:
Competition between spin-crossover and structural ligand ordering is identified as responsible for multistability and generation of six different phases in a rigid two-dimensional coordination polymer formulated {Fe-II[Hg-II(SCN)(3)](2) mu-(4,4'-bipy)(2)}(n) (1) (4,4'-bipy = 4,4'-bipyridine). The structure of 1 consists of infinite linear [Fe(mu-4,4'-bipy)](n)(2n+) chains linked by in situ formed {[Hg-II(SCN)(3)](2)(mu-4,4'-bipy)}(2n-) anionic dimers. The thermal dependence of the high-spin fraction, his, features four magnetic phases defined by steps following the sequence gamma(HS) = 1 (phase 1) <-> gamma(HS) = 1/2 (phase 2) <-> gamma(HS) approximate to 1/3 (phase 3) <-> gamma(HS) = 0 (phase 4) These four magnetic states are consistent with structural ordering stemming from the different commensurate or incommensurate high and low-spin populations [HS] <-> [HS:LS], <-> approximate to [HS:2LS] <-> [LS1] inferred from single crystal-analysis. Furthermore, two additional phases are generated at low temperature. One, LS2 (gamma(HS) = 0, phase 5); is due to spontaneous symmetry breaking of the : LS-1 state below 85 K The other results from irradiating the low-temperature-LS2 Phase at 15 K with red light to photogenerate a HS phase of low symmetry (HS*) (gamma(HS) = 1, phase 6). Detailed structural studies of the six phases-unravd the pivotal role-played by the internal dihedral angle of the 4,4'-bipy ligands in the microscopic. mechanism responsible for multistability and multistep behavior in 1.
Title:
Theory of charge density wave depinning by electromechanical effect
Authors:
Quemerais, P Author Full Names: Quemerais, P.
Source:
EPL, 117 (5):10.1209/0295-5075/117/57004 MAR 2017
Abstract:
We discuss the first theory for the depinning of low-dimensional, incommensurate, charge density waves (CDWs) in the strong electron-phonon (e-p) regime. Arguing that most real CDWs systems invariably develop a gigantic dielectric constant (GDC) at very low frequencies, we propose an electromechanical mechanism which is based on a local field effect. At zero electric field and large enough e-p coupling the structures are naturally pinned by the lattice due to its discreteness, and develop modulation functions which are characterized by discontinuities. When the electric field is turned on, we show that it exists a finite threshold value for the electric field above which the discontinuities of the modulation functions vanish due to CDW deformation. The CDW is then free to move. The signature of this pinning/depinning transition as a function of the increasing electric field can be directly observed in the phonon spectrum by using inelastic neutrons or X-rays experiments. Copyright (C) EPLA, 2017

Update: 25-May-2017

Title:
Mechanical alloying as a solid state route for fabrication of Al-Cu-M(=Fe, Cr) quasicrystalline phases
Authors:
Salimon, AI; Shevchukov, AP; Stepashkin, AA; Tcherdyntsev, VV; Olifirov, LK; Kaloshkin, SD Author Full Names: Salimon, A. I.; Shevchukov, A. P.; Stepashkin, A. A.; Tcherdyntsev, V. V.; Olifirov, L. K.; Kaloshkin, S. D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 707 315-320; 10.1016/j.jallcom.2016.11.173 JUN 15 2017
Abstract:
Almost single phase quasicrystalline powders consisting of icosahedral Al65Cu23Fe12 and decagonal Al73Cu11Cr16 phases were produced by mechanical alloying (MA) and subsequent heat-treatment. Microstructure, particle size distribution, chemical and phase composition of crystalline powder precursors forming under MA from elemental powders of Al, Cu, Fe and Cr were investigated. Phase transformations leading to formation of quasicrystals during heating of precursors were determined by differential thermal analysis and X-ray diffraction. The growth of quasicrystalline grains studied by SEM is discussed. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Effect of Cr addition on the formation of the decagonal quasicrystalline phase of a rapidly solidified Al-Ni-Co alloy
Authors:
Wolf, W; Sitta, BO; Martini, LM; Jorge, AM; Bolfarini, C; Kiminami, CS; Botta, WJ Author Full Names: Wolf, W.; Sitta, B. O.; Martini, L. M.; Jorge, A. M., Jr.; Bolfarini, C.; Kiminami, C. S.; Botta, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 707 41-45; 10.1016/j.jallcom.2016.10.050 JUN 15 2017
Abstract:
The influence of Cr addition in a rapidly solidified Al-Ni-Co alloy was investigated. Melt spun samples of atomic composition Al71Ni20Co9, Al72Ni19Co7Cr2 and Al72Ni20Co5Cr3 were studied by X-ray diffraction and transmission electron microscopy. Aiming to develop quasicrystalline compositions enriched in corrosion resistant elements such as Cr and Ni this work presents, for the first time, the effect of Cr addition on the quasicrystalline phase formation of a high-Ni Al-Ni-Co rapidly solidified alloy chosen to be within the range of formation of the decagonal quasicrystalline phase observed in this ternary system. The composition of the quaternary alloys was chosen by reducing the Co content in favor of Cr on the ternary alloy and keeping the average valence electron per atom (e/a) around 1.86. The phase constitution of the ternary alloy consisted of the decagonal phase along with two intermetallic phases, Al3Ni and Al3Ni2. The addition of Cr resulted in the formation of a second quasicrystalline decagonal phase, rich in Cr. This was due to the low Cr solubility on the ternary Al-Ni-Co decagonal and intermetallic phases, which rejected Cr and resulted on the formation of the Cr-rich quasicrystal. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Characterization of nano-quasicrystal-formation in correlation to the local structure in Zr-based metallic glasses containing Pd
Authors:
Saida, J; Yamada, R; Kozikowski, P; Imafuku, M; Sato, S; Ohnuma, M Author Full Names: Saida, Junji; Yamada, Rui; Kozikowski, Pawel; Imafuku, Muneyuki; Sato, Shigeo; Ohnuma, Masato
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 707 46-50; 10.1016/j.jallcom.2016.10.270 JUN 15 2017
Abstract:
The effect of a noble metal (Pd) on the local atomic structure of the glassy state and the transformation behavior of quasicrystal (QC) precipitation in Zr-70(Cu and Ni)(30-x)Pd-x (x = 0, 5, 10, 20) alloys were investigated. A QC phase precipitates in Zr-Cu glassy alloys at Pd concentrations of 5-20 at.% and in Zr-Ni glassy alloys at Pd concentrations of 10-20 at.%. The radial distribution function (RDF) indicates a change in the local atomic structure upon the addition of Pd. The QC phase is abruptly formed from the glassy structure above a certain temperature. The activation energy for nucleation is much larger than that for the precipitation of conventional intermetallic compounds. The QC growth is suddenly suppressed when their diameter reaches approximately 20 nm. The cooperative motion of icosahedral clusters as the precipitation mechanism was discussed. It was assumed that QC nucleus has a Zr-centered icosahedral medium-range order (MRO) as its core, and it grows by the aggregation of surrounding small icosahedral clusters. Noble metals might play a role of stabilizing the individual Zr-centered icosahedral MROs. (C) 2016 Elsevier B.V. All rights reserved.
Title:
On the lubricity of transition metal dichalcogenides: an ab initio study
Authors:
Irving, BJ; Nicolini, P; Polcar, T Author Full Names: Irving, Benjamin J.; Nicolini, Paolo; Polcar, Tomas
Source:
NANOSCALE, 9 (17):5597-5607; 10.1039/c7nr00925a MAY 7 2017
Abstract:
Owing to specific characteristics engendered by their lamellar structures, transition metal dichalcogenides are posited as being some of the best dry lubricants available. Herein, we report a density functional investigation into the sliding properties and associated phenomena of these materials. Calculated potential energy and charge transfer profiles are used to highlight the dependence of shear strength on chemical composition and bilayer orientation (sliding direction). Furthermore, our calculations underscore the intrinsic relationship between incommensurate crystals and the oft-touted superlubric behaviour of molybdenum disulfide.
Title:
Domain state of the axial next-nearest-neighbor Ising model in two dimensions
Authors:
Matsubara, F; Shirakura, T; Suzuki, N Author Full Names: Matsubara, Fumitaka; Shirakura, Takayuki; Suzuki, Nobuo
Source:
PHYSICAL REVIEW B, 95 (17):10.1103/PhysRevB.95.174409 MAY 5 2017
Abstract:
We have examined the spin ordering of an axial next-nearest-neighbor Ising model in two dimensions (2D) near above the antiphase (< 2 > phase). We considered an N-R-replica system and calculated an overlap function qm between different replicas, having used a cluster heat bath Monte Carlo method. We determined transition temperature between the < 2 > phase and a floating incommensurate (IC) phase as T-C2/J = 0.89 +/- 0.01 with frustration ratio k(= -J(2)/J(1)) = 0.6. We found that the spin state at T greater than or similar to T-C2 may be called a domain state, because the spin structure is characterized by a sequentially arranged four types of domains with different < 2 > structures. In the domain state, the 2D XY symmetry of the spin correlation in the IC phase weakly breaks, and the diversity of the spin arrangement increases as T -> T-C2. The Binder ratio gL exhibits a depression at T similar to T-C2 and the quasiperiodic spin structure, which is realized in the IC phase, becomes diverse at T greater than or similar to T-C2. We discussed that the domain state is stable against the thermal fluctuation which brings a two-stage development of the spin structure at low temperatures.
Title:
NMR determination of an incommensurate helical antiferromagnetic structure in EuCo2As2
Authors:
Ding, QP; Higa, N; Sangeetha, NS; Johnston, DC; Furukawa, Y Author Full Names: Ding, Q. -P.; Higa, N.; Sangeetha, N. S.; Johnston, D. C.; Furukawa, Y.
Source:
PHYSICAL REVIEW B, 95 (18):10.1103/PhysRevB.95.184404 MAY 5 2017
Abstract:
We report Eu-153, As-75, and Co-59 nuclear magnetic resonance (NMR) results on EuCo2As2 single crystal. Observations of Eu-153 and As-75 NMR spectra in zero magnetic field at 4.3 K below an antiferromagnetic (AFM) ordering temperature T-N = 45 K and its external magnetic field dependence clearly evidence an incommensurate helical AFM structure in EuCo2As2. Furthermore, based on Co-59 NMR data in both the paramagnetic and the incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector k = (0,0,0.73 +/- 0.07)2 pi/c, where c is the c lattice parameter. Thus the incommensurate helical AFM state was characterized by only NMR data with model-independent analyses, showing NMR to be a unique tool for determination of the spin structure in incommensurate helical AFMs.
Title:
The interaction between a screw dislocation and a wedge-shaped crack in one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Jiang, LJ; Liu, GT Author Full Names: Jiang, Li-Juan; Liu, Guan-Ting
Source:
CHINESE PHYSICS B, 26 (4):10.1088/1674-1056/26/4/044601 APR 2017
Abstract:
Based on the fundamental equations of piezoelasticity of quasicrystal material, we investigated the interaction between a screw dislocation and a wedge-shaped crack in the piezoelectricity of one-dimensional hexagonal quasicrystals. Explicit analytical solutions are obtained for stress and electric displacement intensity factors of the crack, as well as the force on dislocation. The derivation is based on the conformal mapping method and the perturbation technique. The influences of the wedge angle and dislocation location on the image force are also discussed. The results obtained in this paper can be fully reduced to some special cases already available or deriving new ones.

Update: 18-May-2017

Title:
Nucleation of recrystallized magnesium grains over quasicrystalline phase during severe plastic deformation of a Mg-Zn-Y alloy at room temperature
Authors:
Singh, A; Basha, DA; Somekawa, H; Tsuchiya, K Author Full Names: Singh, Alok; Basha, Dudekula Aithaf; Somekawa, Hidetoshi; Tsuchiya, Koichi
Source:
SCRIPTA MATERIALIA, 134 80-84; 10.1016/j.scriptamat.2017.02.039 JUN 2017
Abstract:
We show by high pressure torsion at room temperature and transmission electron microscopy that nucleation of recrystallized alpha-Mg grains occurs preferentially over quasicrystalline i-phase particles at an early stage of recrystallization in a Mg-3.0Zn-0.5Y (at%) alloy. alpha-Mg grains nucleated on i-phase surfaces by torsional rotation N = 1/2 (at 5GPa pressure), and show definite orientation relationships with the i-phase. These orientation relationships are asymmetrical variations of those reported for as-cast and extruded alloys. The nucleated grains show a planar interface with the i-phase and are often faceted as they grow into a yet unrecrystallized matrix. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Effects of grain boundaries and defects on anisotropic magnon transport in textured Sr14Cu24O41
Authors:
Chen, X; Jarvis, K; Sullivan, S; Li, YT; Zhou, JS; Shi, L Author Full Names: Chen, Xi; Jarvis, Karalee; Sullivan, Sean; Li, Yutao; Zhou, Jianshi; Shi, Li
Source:
PHYSICAL REVIEW B, 95 (14):10.1103/PhysRevB.95.144310 APR 27 2017
Abstract:
The strong spin-spin exchange interaction in some low-dimensional magnetic materials can give rise to a high group velocity and thermal conductivity contribution from magnons. Examples are the incommensurate layered compounds (Sr,Ca,La)(14)Cu24O41. The effects of grain boundaries and defects on quasi-one-dimensional magnon transport in these compounds are not well understood. Here we report the microstructural and anisotropic thermal transport properties of textured Sr14Cu24O41, which is prepared by solid-state reaction followed by spark plasma sintering. Transmission electron microscopy clearly reveals nanolayered grains and the presence of dislocations and planar defects. The thermal conductivity contribution and mean free paths of magnons in the textured samples are evaluated with the use of a kinetic model for one-dimensional magnon transport and found to be suppressed significantly compared to single crystals at low temperatures. The experimental results can be explained by a one-dimensional magnon-defect scattering model, provided that the magnon-grain boundary scattering mean free path in the anisotropic magnetic structure is smaller than the average length of these nanolayers along the c axis. The finding suggests low transmission coefficients for energy-carrying magnons across grain boundaries.
Title:
Tuning the competing phases of bilayer ruthenate Ca3Ru2O7 via dilute Mn impurities and magnetic field
Authors:
Zhu, M; Peng, J; Tian, W; Hong, T; Mao, ZQ; Ke, X Author Full Names: Zhu, M.; Peng, J.; Tian, W.; Hong, T.; Mao, Z. Q.; Ke, X.
Source:
PHYSICAL REVIEW B, 95 (14):10.1103/PhysRevB.95.144426 APR 21 2017
Abstract:
We have systematically investigated the evolution of the magnetic structure of the bilayer ruthenate Ca-3(Ru1-xMnx)(2)O-7 induced uponMndoping. For 0 < x <= 0.03, thematerials exhibit the same spin structure as that of the parent compound at low temperature, while an incommensurate cycloidal magnetic structure emerges at T slightly above the metal-insulator transition (MIT) temperature (T-MIT). In contrast, for x >= 0.04 the ground state becomes a G-type antiferromagnetic Mott insulator. Furthermore, we have observed magnetic-field-induced transitions in Ca-3(Ru0.96Mn0.04)(2)O-7, which is positioned at the phase boundary. Below T-MIT, the magnetic transition is accompanied by a structural transition, as well as a dramatic change in the electronic properties from a Mott insulator to a localized phase. On the contrary, an incommensurate-to-commensurate spin structure transition is observed for T-MIT < T < T-ICM. Our results suggest strong competing magnetic tendencies in this bilayer ruthenate system that are very susceptible to 3d transition-metal substitution and magnetic field.
Title:
Kitaev-Heisenberg model in a magnetic field: Order-by-disorder and commensurate-incommensurate transitions
Authors:
Chern, GW; Sizyuk, Y; Price, C; Perkins, NB Author Full Names: Chern, Gia-Wei; Sizyuk, Yuriy; Price, Craig; Perkins, Natalia B.
Source:
PHYSICAL REVIEW B, 95 (14):10.1103/PhysRevB.95.144427 APR 21 2017
Abstract:
We present a theoretical study of field-induced magnetic phases in the honeycomb Kitaev-Heisenberg model, which is believed to describe the essential physics of Mott insulators with strong spin-orbit coupling such as A(2)IrO(3) and alpha-RuCl3. We obtain a rich finite temperature phase diagram in which the competition between the Zeeman coupling and thermal fluctuations gives rise to both collinear zigzag phases and noncoplanar magnetic orders. Our large-scale classical Monte Carlo simulations also unveil intriguing commensurate-incommensurate transitions and multiple-Q incommensurate phases at high field. Experimental implications are also discussed.
Title:
Field-induced metastability of the modulation wave vector in a magnetic soliton lattice
Authors:
Zhu, M; Peng, J; Hong, T; Prokes, K; Zou, T; Mao, ZQ; Ke, X Author Full Names: Zhu, M.; Peng, J.; Hong, T.; Prokes, K.; Zou, T.; Mao, Z. Q.; Ke, X.
Source:
PHYSICAL REVIEW B, 95 (13):10.1103/PhysRevB.95.134429 APR 19 2017
Abstract:
We present magnetic-field-induced metastability of the magnetic soliton lattice in a bilayer ruthenate Ca-3(Ru1-xFex)(2)O-7(x = 0.05) through single-crystal neutron diffraction study. We show that the incommensurability of the modulation wave vector at zero field strongly depends on the history of magnetic field at low temperature, and that the equilibrium ground state can be achieved by warming above a characteristic temperature Tg similar to 37 K. We suggest that such metastability might be associated with the domain wall pinning by the magnetic Fe dopants.
Title:
Incommensurate magnetic order in a quasicubic structure of the double-perovskite compound Sr2NiIrO6
Authors:
Rolfs, K; Toth, S; Pomjakushina, E; Adroja, DT; Khalyavin, D; Conder, K Author Full Names: Rolfs, K.; Toth, S.; Pomjakushina, E.; Adroja, D. T.; Khalyavin, D.; Conder, K.
Source:
PHYSICAL REVIEW B, 95 (14):10.1103/PhysRevB.95.140403 APR 10 2017
Abstract:
In Sr2NiIrO6, a metastable compound, the magnetic structure could be elucidated. The magnetic susceptibility data of the compound suggests a three-dimensional Heisenberg behavior. Moreover, neutron diffraction reveals a novel incommensurate magnetic order, requiring exchange interactions beyond second neighbor to stabilize this phase. An incommensurate propagation vector of k = (0, k, k) with k = 0.356 was observed in such a pseudocubic system. This can be an example of how to induce an incommensurate ground state and a possible type-II multiferroicity in double perovskites.
Title:
Emergent incommensurate correlations in frustrated ferromagnetic spin-1 chains
Authors:
Lee, HJ; Choi, M; Jeon, GS Author Full Names: Lee, Hyeong Jun; Choi, MooYoung; Jeon, Gun Sang
Source:
PHYSICAL REVIEW B, 95 (2):10.1103/PhysRevB.95.024424 JAN 23 2017
Abstract:
We study frustrated ferromagnetic spin-1 chains, where the ferromagnetic nearest-neighbor coupling competes with the antiferromagnetic next-nearest-neighbor coupling. We use the density-matrix renormalization group to obtain the ground states. Through the analysis of spin-spin correlations we identify the double Haldane phase as well as the ferromagnetic phase. It is shown that the ferromagnetic coupling leads to incommensurate correlations in the double Haldane phase. Such short-range correlations transform continuously into the ferromagnetic instability at the transition to the ferromagnetic phase. We also compare the results with the spin-1/2 and classical spin systems and discuss the string orders in the system.

Update: 10-May-2017

Title:
Formation of a quasicrystalline phase in Al-Mn base alloys cast at intermediate cooling rates
Authors:
Stan-Glowinska, K; Rogal, L; Goral, A; Wierzbicka-Miernik, A; Wojewoda-Budka, J; Schell, N; Litynska-Dobrzynska, L Author Full Names: Stan-Glowinska, Katarzyna; Rogal, Lukasz; Goral, Anna; Wierzbicka-Miernik, Anna; Wojewoda-Budka, Joanna; Schell, Norbert; Litynska-Dobrzynska, Lidia
Source:
JOURNAL OF MATERIALS SCIENCE, 52 (13):7794-7807; 10.1007/s10853-017-1011-z JUL 2017
Abstract:
Al-rich 94Al-6Mn and 94Al-4Mn-2Fe alloys were suction-cast to evaluate the feasibility of obtaining bulk quasicrystal-strengthened Al-alloys at intermediate cooling rates alloyed with non-toxic, easily accessible and affordable additions. The influence of different cooling rates on the potential formation of a quasicrystalline phase was examined by means of scanning and transmission electron microscopy, X-ray diffraction and differential scanning calorimetry. Increased cooling rates in the thinnest castings entailed a change in sample phase composition. The highest cooling rates turned out to be insufficient to form an icosahedral quasicrystalline phase (I-phase) in the binary alloy. Instead, an orthorhombic approximant phase occurred (L-phase). The addition of Fe to the 94Al-6Mn binary alloy enhanced the formation of a quasicrystalline phase. At intermediate cooling rates of 10(2)-10(3) K/s, various metastable phases were formed, including decagonal and icosahedral quasicrystals and their approximants. Rods (1 mm in diameter) composed of I-phase particles embedded in Al matrix exhibited a hardness of 1.5 GPa, much higher than the 1.1 GPa of 94Al-6Mn.
Title:
Magnetic texturing due to the partial ordering of Fe+3 and Cu+2 in NdBaCuFeO5
Authors:
Pissas, M Author Full Names: Pissas, M.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 432 224-230; 10.1016/j.jmmm.2017.01.083 JUN 15 2017
Abstract:
The crystal and magnetic structure of the oxygen deficient double perovskite NdBaCuFeO5 was studied, using neutron powder diffraction data. The structure was refined from neutron powder diffraction data using the space groups P4/ mmm and P4mm. For 2 K <= T <= T-N2 = 260 K three families of magnetic Bragg peaks exist. These peaks can be indexed with commensurate propagation vectors k(1) = [1/2 1/2 1/2 ], k(2) = [1/2 1/2 0] and the incommensurate k(3) = [1/2 1/2 0.4] Above T-N2 only magnetic Bragg peaks originated from k(1) and k(2) propagation, were observed. The incommensurate magnetic structure can be attributed to a circular inclined spiral ordering as in YBaCuFeO5 compound. (C)2017 Elsevier B. V. All rights reserved.
Title:
Hyperuniformity variation with quasicrystal local isomorphism class
Authors:
Lin, C; Steinhardt, PJ; Torquato, S Author Full Names: Lin, C.; Steinhardt, P. J.; Torquato, S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (20):10.1088/1361-648X/aa6944 MAY 24 2017
Abstract:
Hyperuniformity is the suppression of long-wavelength density fluctuations, relative to typical structurally disordered systems. In this paper, we examine how the degree of hyperuniformity [(Lambda) over bar (infinity)] in quasicrystals depends on the local isomorphism class. By studying the continuum of pentagonal quasicrystal tilings obtained by direct projection from a five-dimensional hypercubic lattice, we find that (Lambda) over bar (infinity) is dominantly determined by the local distribution of vertex environments (e.g. as measured by Voronoi cells) but also exhibits a non-negligible dependence on the restorability. We show that the highest degree of hyperuniformity [smallest (Lambda) over bar (infinity)] corresponds to the Penrose local isomorphism class. The difference in the degree of hyperuniformity is expected to affect physical characteristics, such as transport properties.
Title:
Structure and magnetism in the bond-frustrated spinel ZnCr2Se4
Authors:
Zajdel, P; Li, WY; van Beek, W; Lappas, A; Ziolkowska, A; Jaskiewicz, S; Stock, C; Green, MA Author Full Names: Zajdel, P.; Li, W. -Y.; van Beek, W.; Lappas, A.; Ziolkowska, A.; Jaskiewicz, S.; Stock, C.; Green, M. A.
Source:
PHYSICAL REVIEW B, 95 (13):10.1103/PhysRevB.95.134401 APR 3 2017
Abstract:
The crystal and magnetic structures of stoichiometric ZnCr2Se4 have been investigated using synchrotron x-ray and neutron powder diffraction, muon spin relaxation (mu SR), and inelastic neutron scattering. Synchrotron x-ray diffraction shows a spin-lattice distortion from the cubic Fd (3) over barm spinel to a tetragonal I4(1)/amd lattice below T-N = 21 K, where powder neutron diffraction confirms the formation of a helical magnetic structure with magnetic moment of 3.04( 3) mu(B) at 1.5 K, close to that expected for high-spin Cr3+. mu SR measurements show prominent local spin correlations that are established at temperatures considerably higher (< 100 K) than the onset of long-range magnetic order. The stretched exponential nature of the relaxation in the local spin-correlation regime suggests a wide distribution of depolarizing fields. Below T-N, unusually fast (> 100 mu s(-1)) muon relaxation rates are suggestive of rapid site hopping of the muons in static field. Inelastic neutron scattering measurements show a gapless mode at an incommensurate propagation vector of k = [000.4648( 2)] in the low-temperature magnetic ordered phase that extends to 0.8 meV. The dispersion is modeled by a two-parameter Hamiltonian, containing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions with a J(nnn)/J(nn) = -0.337.
Title:
Enhancement of Mechanical Properties of Aluminum and 2124 Aluminum Alloy by the Addition of Quasicrystalline Phases
Authors:
Wolf, W; Aliaga, LCR; Travessa, DN; Afonso, CRM; Bolfarini, C; Kiminami, CS; Botta, WJ Author Full Names: Wolf, Witor; Rodriguez Aliaga, Luis Cesar; Travessa, Dilermando Nagle; Moreira Afonso, Conrado Ramos; Bolfarini, Claudemiro; Kiminami, Claudio Shyinti; Botta, Walter Jose
Source:
MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS, 19 74-79; 1 10.1590/1980-5373-MR-2016-0088 DEC 2016
Abstract:
A structural and mechanical characterization of pure aluminum and 2124 T6 aluminum alloy reinforced with quasicrystalline phases of composition Al65Cu20Fe15 and Al70.5Pd21Mn8.5 (% at.) were performed. The quasicrystalline phases were synthesized by arc melting and then milled to produce powder of the alloys, which were then mechanical mixed with the starting powders of aluminum and 2124 aluminum alloy. The composites were produced by hot extrusion of a mechanical mixture containing 20% (% wt.) of the reinforcing phases on the metallic matrix. The structural characterization of the composites was carried out by X- ray diffraction, scanning electron microscopy and transmission electron microscopy. Mechanical characterization was carried out by Vickers hardness measurements and torsion tests at room temperature. The pure aluminum/ quasicrystal composite showed the presence of the same phases from the starting powder mixture while for the 2124 aluminum alloy/Al65Cu20Fe15 the quasicrystalline phase transformed to the tetragonal w-Al7Cu2 Fe during the solution heat treatment. Mechanical strength of the composites presented a substantial increase in comparison to the original matrix metal. While the equivalent ultimate tensile strength of the Al/ quasicrystal composites reached values up to 215MPa and Vickers hardness up to 60HV, the 2124/ quasicrystal composites reached values up to 670MPa and Vickers hardness up to 190HV.

Update: 4-May-2017

Title:
Incommensurately modulated twin structure of nyerereite Na1.64K0.36Ca(CO3)(2)
Authors:
Bolotina, NB; Gavryushkin, PN; Korsakov, AV; Rashchenko, SV; Seryotkin, YV; Golovin, AV; Moine, BN; Zaitsev, AN; Litasov, KD Author Full Names: Bolotina, Nadezhda B.; Gavryushkin, Pavel N.; Korsakov, Andrey V.; Rashchenko, Sergey V.; Seryotkin, Yurii V.; Golovin, Alexander V.; Moine, Bertrand N.; Zaitsev, Anatoly N.; Litasov, Konstantin D.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 276-284; SI 10.1107/S2052520616020680 2 APR 2017
Abstract:
The incommensurately modulated twin structure of nyerereite Na1.64K0.36Ca(CO3)(2) has been first determined in the (3 + 1)- dimensional symmetry group Cmcm(alpha 00)00s with modulation vector q = 0.383a*. Unit-*cell* values are a = 5.062 (1), b = 8.790 (1), c = 12.744 (1) angstrom. Three orthorhombic components are related by threefold rotation about [001]. Discontinuous crenel functions are used to describe the occupation modulation of Ca and some CO3 groups. The strong displacive modulation of the O atoms in vertexes of such CO3 groups is described using x- harmonics in crenel intervals. The Na, K atoms occupy mixed sites whose occupation modulation is described in two ways using either complementary harmonic functions or crenels. The nyerereite structure has been compared both with the commensurately modulated structure of K-free Na2Ca(CO3)(2) and with the widely known incommensurately modulated structure of gamma-Na2CO3.
Title:
IN SITU TEM STUDY OF PRECIPITATION IN A QUASICRYSTAL-STRENGTHENED Al-ALLOY
Authors:
Boncina, T; Zupanic, F Author Full Names: Boncina, T.; Zupanic, F.
Source:
ARCHIVES OF METALLURGY AND MATERIALS, 62 (1):5-9; 10.1515/amm-2017-0001 2017
Abstract:
Precipitation kinetics and mechanisms within an Al-Mn-Be-Cu quasicrystal strengthened alloy at 300 degrees C were studied using in-situ transmission electron microscopy. The alloy was cast into a copper mould. Quasicrystalline precipitates formed throughout the Al-rich solid solution, whilst heterogeneous formations of Al2Cu and T-phase occurred on icosahedral quasicrystalline particles formed during solidification. The formation of quasicrystalline particles and T-phase was limited by manganese diffusivity, whilst that of Al2Cu by copper diffusivity. The precipitation produced only a small hardening effect.

Update: 27-Apr-2017

Title:
Effect of cation vacancies on the crystal structure and luminescent properties of Ca0.85-1.5xGdxEu0.1 square 0.05+0.5xWO4(0 <= x <= 0.567) scheelite-based red phosphors
Authors:
Batuk, D; Batuk, M; Morozov, VA; Meert, KW; Smet, PF; Poelman, D; Abakumov, AM; Hadermann, J Author Full Names: Batuk, Dmitry; Batuk, Maria; Morozov, Vladimir A.; Meert, Katrien W.; Smet, Philippe F.; Poelman, Dirk; Abakumov, Artem M.; Hadermann, Joke
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 706 358-369; 10.1016/j.jallcom.2017.02.154 JUN 5 2017
Abstract:
The Ca0.85-1.5xGdxEu0.1+0.05 square 0.5xWO4(0 <= x <= 0.567) series of cation-deficient scheelites is investigated to unveil the influence of the cation vacancies on the crystal structure and luminescent properties. The concentration of the vacancies is varied by the heterovalent substitution of Gd3+ for Ca2+, keeping the concentration of the Eu3+ luminescent centers constant in all compounds of the series. The crystal structure of the materials is studied using a combination of transmission electron microscopy and synchrotron X-ray powder diffraction. At low vacancy concentration (x - 0.1, 0.2), cations and cation vacancies are randomly distributed in the structure, and the materials preserve the I4(1)/alpha symmetry of the parent scheelite structure [x = 0.1: a = 5.25151(1) angstrom, c = 11.39479(2) angstrom; x = 0.2: a = 5.25042(1) angstrom, c = 11.41335(2) angstrom]. At higher concentration, the cation-vacancy ordering gives rise to incommensurately modulated structures. The x = 0.3 structure has a (3 + 2) D tetragonal symmetry [superspace group I4(1)/alpha(alpha,beta, 0)00(-beta,alpha,0)00, a = 5.24700(1) angstrom, c = 11.45514(3) angstrom, q(1) = 0.51637(14)a* + 0.80761(13)b*, q(2) = -0.80761a* + 0.51637b*]. At x = 0.4, the scheelite basic cell undergoes a monoclinic distortion with the formation of the (3 + 1) D structure [superspace group I-2/b(alpha,beta,0)00, a = 5.23757(1) angstrom, b = 5.25035(1) angstrom, c = 11.45750(2) angstrom, gamma = 90.5120(2) angstrom, q = 0.54206(8)a* + 0.79330(8)b*]. In both structures, the antiphase Ca and (Gd, Eu) occupancy modulations indicate that the ordering between the A cations and vacancies also induces partial Ca/(Gd, Eu) cation ordering. Further increase of the Gd3+ content up to x = 0.567 leads to the formation of a monoclinic phase (space group C2/c) with the Eu2/ 3WO4-type structure. Despite the difference in the cation-vacancy ordering patterns, all materials in the series demonstrate very similar quantum efficiency and luminescence decay lifetimes. However, the difference in the local coordination environment of the A cation species noticeably affects the line width and the multiplet splitting of the 4f(6)-4f(6) transitions. (C) 2017 Elsevier B.V. All rights reserved.
Title:
New quantum criticality revealed under pressure
Authors:
Watanabe, S; Miyake, K Author Full Names: Watanabe, Shinji; Miyake, Kazumasa
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS, 56 (5):3 10.7567/JJAP.56.05FA01 MAY 2017
Abstract:
Unconventional quantum critical phenomena observed in Yb-based periodic crystals such as YbRh2Si2 and beta-YbAlB4 have been one of the central issues in strongly correlated electron systems. The common criticality has been discovered in the quasicrystal Yb15Au51Al34, which surprisingly persists under pressure at least up to P = 1.5GPa. The T/H scaling where the magnetic susceptibility can be expressed as a single scaling function of the ratio of the temperature T to the magnetic field H has been discovered in the quasicrystal, which is essentially the same as that observed in beta-YbAlB4. Recently, the T/ H scaling as well as the common criticality has also been observed even in the approximant crystal Yb15Au51Al34 under pressure. The theory of critical Yb-valence fluctuation gives a natural explanation for these striking phenomena in a unified way. (C) 2017 The Japan Society of Applied Physics
Title:
International Journal of Biological Macromolecules
Authors:
Abidi, M; Iram, A; Furkan, M; Naeem, A Author Full Names: Abidi, Minhal; Iram, Afshin; Furkan, Mohammad; Naeem, Aabgeena
Source:
INTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES, 98 459-468; 10.1016/1flbiomac.2017.01.086 MAY 2017
Abstract:
Glucoamylase (EC 3.2.1.3) from Aspergillus niger possesses 31% alpha-helix, 36% beta structure and rest aperiodic structure. A transition of glucoamylase structure in the presence of varying concentrations of glyoxal (GO) and trifluoroethanol (TFE) was studied by using multi-methodological approaches. At 20% GO, glucoamylase exists as molten globule state as evident by high tryptophan and ANS fluorescence, retention of secondary structure and loss of native tertiary structure. This state precedes the onset of the aggregation process and maximum is achieved at the highest concentration i.e. at 90% of GO. In parallel study TFE, on increasing concentration up to 25% induces secondary structure transformation leading to accumulation of intermolecular 13 sheets, altered tryptophan environment, high ANS and ThT fluorescence resulting in the formation of glucoamylase aggregates. Isothermal titration calorimetric curve is sigmoidal, indicating the weak binding of GO/TFE and glucoamylase. TEM studies showed that glucoamylase exists as globular and amorphous aggregates at 90% glyoxal and 25% TFE respectively. Further, TFE at 70% causes inhibition of enzyme aggregates; the majority of secondary structures observed at this concentration are a helices. Alpha helices being the main key player relocates glucoamylase native environment as evident by CD, FTIR and TEM. Hence induction of 6 sheet promotes protein aggregation and a helices inhibits protein aggregation. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Enhanced thermal stability of a quasicrystalline phase in rapidly solidified Al-Mn-Fe-X alloys
Authors:
Stan-Glowinska, K; Litynska-Dobrzynska, L; Morgiel, J; Goral, A; Gordillo, MA; Wiezorek, JM Author Full Names: Stan-Glowinska, K.; Litynska-Dobrzynska, L.; Morgiel, J.; Goral, A.; Gordillo, M. A.; Wiezorek, J. M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 702 216-228; 10.1016/j.jallcom.2016.12383 APR 25 2017
Abstract:
A series of rapidly solidified Al-Mn-Fe-X alloys, where X is one of Mo, W or V, were prepared using a melt spinning technique. Microstructures of obtained ribbons comprised of an aluminium solid solution matrix containing metastable quasicrystalline particles of icosahedral type (I-phase). Micro-analytical studies by X-ray diffraction, transmission and scanning transmission electron microscopy after various heat treatments, including in situ TEM heating experiments, have been performed to elucidate details of the I-phase decomposition mechanisms. Results of these investigations and values of activation energies of the transition calculated based on differential scanning calorimeter measurements indicated that V modified alloys exhibit significantly increased thermal stability of the I-phase relative to Mo- and W modified alloys and the un-modified ternary Al-Mn-Fe benchmark. In V-modified alloys the quasicrystalline particle transformations resulted in formation of the Al-45(Mn, Fe, V)(7) intermetallic phase, while the Ally(Mn, Fe, X = Mo, W) crystalline product formed during annealing of Mo- and W-modified alloys. Notably, the Al-45(Mn, Fe, V)(7) intermetallic phase shows considerable structural similarity to the quasi crystalline I-phase. This correlates with a small value of measured heat release during the I-phase decomposition and implies the stabilization of icosahedral structural ordering by V addition. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Non-collinear magnetic structure of manganese quadruple perovskite CdMn7O12
Authors:
Guo, H; Fernandez-Daz, MT; Zhou, L; Yin, Y; Long, Y; Komarek, AC Author Full Names: Guo, H.; Fernandez-Daz, M. T.; Zhou, L.; Yin, Y.; Long, Y.; Komarek, A. C.
Source:
SCIENTIFIC REPORTS, 7 10.1038/srep45939 APR 5 2017
Abstract:
We report on the magnetic structure of CdMn7O12 determined by powder neutron diffraction. We were able to measure the magnetic structure of this Cd containing and highly neutron absorbing material by optimizing the sample geometry and by blending the CdMn7O12 with Aluminum powder. Below its Neel temperature TN1 all magnetic reflections can be indexed by a single commensurate propagation vector k = (0, 0, 1). This is different to the case of CaMn7O12 where the propagation vector is incommensurate and where an in-plane helical magnetic structure has been found. We observe a commensurate noncollinear magnetic structure in CdMn7O12 with in-plane aligned magnetic moments resembling the ones in CaMn7O12. However, the commensurate propagation vector prevents the appearance of a helical magnetic structure in CdMn7O12. Finally, we also observe a third structural phase transition below similar to 60 K that can be attributed to phase separation.
Title:
Incommensurate atomic density waves in the high-pressure IVb phase of barium
Authors:
Arakcheeva, A; Bykov, M; Bykova, E; Dubrovinsky, L; Pattison, P; Dmitriev, V; Chapuis, G Author Full Names: Arakcheeva, Alla; Bykov, Maxim; Bykova, Elena; Dubrovinsky, Leonid; Pattison, Phil; Dmitriev, Vladimir; Chapuis, Gervais
Source:
IUCRJ, 4 152-157; 10.1107/S2052252517000264 2 MAR 2017
Abstract:
The host-guest structures of elements at high pressure discovered a decade ago still leave many open questions due to the lack of precise models based on full exploitation of the diffraction data. This concerns in particular Ba IV, which is stable in the range 12-45 GPa. With the example of phase Ba IVb, which is characterized here for the first time, a systematic analysis is presented of possible host-guest structure models based on high-quality single-crystal diffraction data obtained with synchrotron radiation at six different pressures between 16.5 and 19.6 GPa. It is shown that a new incommensurately modulated (IM) structure model better fits the experimental data. Unlike the composite models which are commonly reported for the Ba IV phases, the IM model reveals a density wave and its pressure-dependent evolution. The crucial role played by the selected model in the interpretation of structure evolution under pressure is discussed. The findings give a new experimental basis for a better understanding of the nature of host-guest structures.
Title:
Breakthrough in the high-pressure structures of Ba based on full exploitation of aperiodic symmetry
Authors:
Boldyreva, EV Author Full Names: Boldyreva, Elena V.
Source:
IUCRJ, 4 104-105; 10.1107/S2052252517001427 2 MAR 2017
Title:
Ordering effect on the mechanical, electronic and magnetic properties of the beta-based non-canonical approximant phases: beta-Al50Cu33Fe17, eta-Al50Cu44Fe6 and phi-Al47.5Cu49.5Fe3
Authors:
Shalaeva, EV; Medvedeva, NI; Prekul, AF; Smirnova, EO; Smirnov, SV; Shchegolikhina, NI; Selyanin, IO Author Full Names: Shalaeva, E. V.; Medvedeva, N. I.; Prekul, A. F.; Smirnova, E. O.; Smirnov, S. V.; Shchegolikhina, N. I.; Selyanin, I. O.
Source:
PHILOSOPHICAL MAGAZINE, 97 (13):1024-1046; 10.1080/14786435.2017.1287970 A 2017
Abstract:
Using transmission electron microscopy and X-ray diffraction, we established that the ordered eta 1-Al50Cu44Fe6 and phi-Al47.5Cu49.5Fe3 (Fmm2) alloys with nano-sized domain structure are formed by slowly cooling, whereas beta-solid solutions with a short-range order were found in quenched states. The phi'-modification which exhibits the additional long-period superstructure was also observed in Al47.5Cu49.5Fe3. The studies of low temperature magnetic susceptibility and heat capacity did not reveal any another phase transitions in these alloys. The indentation test showed that hardness and Young's modulus consistently grow as beta-Al50Cu33Fe17 -> eta 1-Al50Cu44Fe6 -> (phi+phi')-Al47.5Cu49.5Fe3 and approach to those in icosahedral phase. The same trend in the Young's modulus was obtained for alloys containing beta-solid solution with a short-range order. Ab initio calculations, however, predicted the opposite tendency in cubic beta-Al50Cu50-xFex with a decrease in x, which was explained by the weakening of the covalent Fe 3d-Al sp bonding. This discrepancy between the results for beta- and ordered phases, we related to a crucial effect of ordering which is accompanied by a progressive distortion of cubic local structure in the series beta-Al50Cu33Fe17 -> eta 1-Al50Cu44Fe6 -> phi-Al47.5Cu49.5Fe3. As we demonstrated for eta-Al(Cu,Fe), these distortions lead to the strengthening of the both covalent FeAl and Cu-Al bonds and the higher modules.
Title:
Enhancement of Mechanical Properties of Aluminum and 2124 Aluminum Alloy by the Addition of Quasicrystalline Phases
Authors:
Wolf, W; Aliaga, LCR; Travessa, DN; Afonso, CRM; Bolfarini, C; Kiminami, CS; Botta, WJ Author Full Names: Wolf, Witor; Rodriguez Aliaga, Luis Cesar; Travessa, Dilermando Nagle; Moreira Afonso, Conrado Ramos; Bolfarini, Claudemiro; Kiminami, Claudio Shyinti; Botta, Walter Jose
Source:
MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS, 19 74-79; 1 10.1590/1980-5373-MR-2016-0088 DEC 2016
Abstract:
A structural and mechanical characterization of pure aluminum and 2124 T6 aluminum alloy reinforced with quasicrystalline phases of composition Al65Cu20Fe15 and Al70.5Pd21Mn8.5 (% at.) were performed. The quasicrystalline phases were synthesized by arc melting and then milled to produce powder of the alloys, which were then mechanical mixed with the starting powders of aluminum and 2124 aluminum alloy. The composites were produced by hot extrusion of a mechanical mixture containing 20% (% wt.) of the reinforcing phases on the metallic matrix. The structural characterization of the composites was carried out by X- ray diffraction, scanning electron microscopy and transmission electron microscopy. Mechanical characterization was carried out by Vickers hardness measurements and torsion tests at room temperature. The pure aluminum/ quasicrystal composite showed the presence of the same phases from the starting powder mixture while for the 2124 aluminum alloy/Al65Cu20Fe15 the quasicrystalline phase transformed to the tetragonal w-Al7Cu2 Fe during the solution heat treatment. Mechanical strength of the composites presented a substantial increase in comparison to the original matrix metal. While the equivalent ultimate tensile strength of the Al/ quasicrystal composites reached values up to 215MPa and Vickers hardness up to 60HV, the 2124/ quasicrystal composites reached values up to 670MPa and Vickers hardness up to 190HV.

Update: 20-Apr-2017

Title:
Geometry of adaptive martensite in Ni-Mn- based Heusler alloys
Authors:
Niemann, R; Fahler, S Author Full Names: Niemann, Robert; Faehler, Sebastian
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 703 280-288; 10.1016/j.jallcom.2017.01.189 MAY 5 2017
Abstract:
Modulated martensites play an important role in magnetic shape memory alloys, because all functional properties are closely connected to the twin microstructure and the phase boundary. The nature of the modulated martensites is still unclear. One approach is the concept of adaptive martensite, which regards all modulated phases as nanotwinned microstructures. In this article, we use the Ni-Mn-based shape memory alloys as an example to show the geometric rationale behind this concept using analytic equations based on the phenomenological theory of martensite. This could enhance discussions about the implications of the adaptive martensite by showing the exact relations between the various unit cells used to describe the structure. We use the concept to discuss the compatibility at the habit plane, the nature of high-order twin boundaries and the dependence of the lattice constants on the different types of modulation. (C) 2017 Elsevier B.V. All rights reserved.

Update: 13-Apr-2017

Title:
Magnetic ordering and dielectric relaxation in the double perovskite YBaCuFeO5
Authors:
Lai, YC; Du, CH; Lai, CH; Liang, YH; Wang, CW; Rule, KC; Wu, HC; Yang, HD; Chen, WT; Shu, GJ; Chou, FC Author Full Names: Lai, Yen-Chung; Du, Chao-Hung; Lai, Chun-Hao; Liang, Yu-Hui; Wang, Chin-Wei; Rule, Kirrily C.; Wu, Hung-Cheng; Yang, Hung-Duen; Chen, Wei-Tin; Shu, G. J.; Chou, F-C
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (14):10.1088/1361-648X/aa5708 APR 12 2017
Abstract:
Using magnetization, dielectric constant, and neutron diffraction measurements on a high quality single crystal of YBaCuFeO5 (YBCFO), we demonstrate that the crystal shows two antiferromagnetic transitions at T-N1 similar to 475 K and T-N2 similar to 175 K, and displays a giant dielectric constant with a characteristic of the dielectric relaxation at T-N2. It does not show the evidence of the electric polarization for the crystal used for this study. The transition at T-N1 corresponds with a paramagnetic to antiferromagnetic transition with a magnetic propagation vector doubling the unit cell along three crystallographic axes. Upon cooling, at T-N2, the commensurate spin ordering transforms to a spiral magnetic structure with a propagation vector of (h/2 k/2 l/2 +/- delta), where h, k, and l are odd, and the incommensurability d is temperature dependent. Around the transition boundary at T-N2, both commensurate and incommensurate spin ordering coexist.
Title:
Stability of icosahedral quasicrystals in a simple model with two-length scales
Authors:
Jiang, K; Zhang, PW; Shi, AC Author Full Names: Jiang, Kai; Zhang, Pingwen; Shi, An-Chang
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (12):10.1088/1361-648X/aa586b MAR 29 2017
Abstract:
The phase behaviour of a free energy functional with two length scales is examined by comparing the free energy of different candidate phases including three-dimensional icosahedral quasicrystals. Accurate free energy of the quasicrystals has been obtained using the recently developed projection method. The results reveal that the icosahedral quasicrystal and body-centred-cubic spherical phase are the stable ordered phases of the model. Furthermore, the difference between the results obtained from the projection method and the one-mode approximation has been analyzed in detail. The present study extends previous results on two-dimensional systems, demonstrating that the interactions between density waves at two length scales can stabilize two-and three-dimensional quasicrystals.
Title:
Effects of Cu addition on the microstructure and mechanical properties of as-cast and heat treated Mg-6Zn-4Al magnesium alloy
Authors:
Zhu, SZ; Luo, TJ; Zhang, TG; Li, YJ; Yang, YS Author Full Names: Zhu, Shaozhen; Luo, Tianjiao; Zhang, Tingan; Li, Yingju; Yang, Yuansheng
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 689 203-211; 10.1016/j.msea.2017.02.061 MAR 24 2017
Abstract:
The microstructure and mechanical properties of as-cast and heat treated Mg-6Zn-4Al-xCu (x=0, 0.5, 1.0 and 1.5 wt%) alloys were investigated in this work. The results show that the grain sizes of the alloys decrease considerably with increasing Cu addition, and the eutectics are refined with 0.5% Cu addition. The icosahedral quasi-crystalline phase is observed in Mg-6Zn-4Al and Cu-containing alloys, and the MgAlCu phase forms in the Cu-containing alloys because of Cu addition. Compared with Mg-6Zn-4Al alloy, the Cu-containing alloys exhibit improved age-hardening response during single-aging treatment. In addition, high-density fine precipitates are formed in the matrix during double-aging treatment, resulting in remarkable improvement of the tensile strength. The double aged Mg-6Zn-4Al-0.5Cu alloy shows the relatively optimal tensile properties. The yield strength, ultimate tensile strength and elongation are 202 MPa, 312 MPa and 7%, respectively, which is attributed to the combined effects of fine grains and the uniform distribution of high-density fine precipitates. It is noticed that the ductility of as-aged Cu-containing alloys is lower than that of the as-aged Mg-6Zn-4Al alloy due to the stress concentration during the tensile stress caused by the residual phases distributed along the grain boundaries after solution treatment.
Title:
Phase behaviour of quasicrystal forming systems of core-corona particles
Authors:
Pattabhiraman, H; Dijkstra, M Author Full Names: Pattabhiraman, Harini; Dijkstra, Marjolein
Source:
JOURNAL OF CHEMICAL PHYSICS, 146 (11):10.1063/1.4977934 MAR 21 2017
Abstract:
Using Monte Carlo simulations and free-energy calculations, we study the phase behaviour of a two-dimensional system of particles interacting with a hard core of diameter sigma(HD) and a repulsive square shoulder potential. The interest in this system lies in the formation of quasicrystals of different symmetries at specific square-shoulder widths delta as previously reported by Dotera et al. [Nature 506, 208 (2014)]. However, an insight into other possible periodic phases formed in these systems and the thermodynamic stability of both the periodic and quasicrystal phases is yet to be addressed. Here, we study the phase behaviour and map out the phase diagrams for three different shoulder widths delta = 1.27 sigma(HD), 1.40 sigma(HD), and 1.60 sigma(HD), where octadecagonal, dodecagonal, and decagonal quasicrystals were previously reported. In addition, we verify the thermodynamic stability of these quasicrystals with respect to their periodic approximants. In general, we find that the system at all three shoulder widths forms hexagonal phases in two distinct density ranges due to the two characteristic length scales in the interaction potential. Further, we find that the dodecagonal and octadecagonal quasicrystals are stable in between two crystal phase regimes. In contrast, the decagonal quasicrystal is not bounded by a low-density crystal phase regime due to the lower density of this quasicrystal. From the free-energy calculations, we find indications that the decagonal and dodecagonal quasicrystals are thermodynamically stable with respect to their approximants, and the octadecagonal quasicrystal is stabilised by a configurational entropy contribution. Published by AIP Publishing.
Title:
Enhancement of Ferroelectricity for Orthorhombic (TB0.861Mn0.121)MnO3-delta by Copper Doping
Authors:
Deng, JM; Farid, MA; Zhang, M; Yang, AM; Zhang, HX; Zhang, H; Tian, GF; Wu, MM; Liu, LJ; Sun, JL; Li, GB; Liao, FH; Lin, JH Author Full Names: Deng, Jianming; Farid, Muhammad Asim; Zhang, Meng; Yang, Aimei; Zhang, Hongxing; Zhang, Hao; Tian, Gengfang; Wu, Meimei; Liu, Laijun; Sun, Junliang; Li, Guobao; Liao, Fuhui; Lin, Jianhua
Source:
INORGANIC CHEMISTRY, 56 (6):3475-3482; 10.1021/acs.inorgchem.6b03024 MAR 20 2017
Abstract:
Copper-doped (Tb0.861MnO0.121)Mn0(3-delta) has been synthesized by the conventional solid state reaction method. X-ray, neutron, and electron diffraction data indicate that they crystallize in Pnma space group at room temperature. Two magnetic orderings are found for this series by neutron diffraction. One is the ICAM (incommensurate canted antiferromagnetic) ordering of Mn with a wave vector q(Mn) = (similar to 0.283, 0, 0) with a approximate to 5.73A,b approximate to 5.31 A, and c approximate to 7.41 A, and the other is the CAM (canted antiferromagneiic) ordering of both Tb and Mn in the magnetic space group Pn'a2(1)' with a approximate to 5.73 A, b approximate to 5.31 A, and c approximate to 7:41 A. A dielectric peak around 40 K is found for the samples doped with Cu, which is higher than that for orthorhombic TbMnO3.
Title:
Opening a nodal gap by fluctuating spin-density wave in lightly doped La2-xSrxCuO4
Authors:
Kapon, I; Ellis, DS; Drachuck, G; Bazalitski, G; Weschke, E; Schierle, E; Strempfer, J; Niedermayer, C; Keren, A Author Full Names: Kapon, Itzik; Ellis, David S.; Drachuck, Gil; Bazalitski, Galina; Weschke, Eugen; Schierle, Enrico; Strempfer, Joerg; Niedermayer, Christof; Keren, Amit
Source:
PHYSICAL REVIEW B, 95 (10):10.1103/PhysRevB.95.104512 MAR 14 2017
Abstract:
We investigate whether the spin or charge degrees of freedom are responsible for the nodal gap in underdoped cuprates by performing inelastic neutron scattering and x-ray diffraction measurements on La2-xSrxCuO4, which is on the edge of the antiferromagnetic phase. We found that a fluctuating incommensurate spin-density wave (SDW) with a bottom part of an hourglass dispersion exists even in this magnetic sample. The strongest component of these fluctuations diminishes at the same temperature where the nodal gap opens. X-ray scattering measurements on the same crystal show no signature of a charge-density wave (CDW). Therefore, we suggest that the nodal gap in the electronic band of this cuprate opens due to fluctuating SDW with no contribution from CDW.
Title:
E-type noncollinear magnetic ordering in multiferroic o-LuMnO3
Authors:
Mukherjee, S; Donni, A; Nakajima, T; Mitsuda, S; Tachibana, M; Kitazawa, H; Pomjakushin, V; Keller, L; Niedermayer, C; Scaramucci, A; Kenzelmann, M Author Full Names: Mukherjee, Saumya; Donni, Andreas; Nakajima, Taro; Mitsuda, Setsuo; Tachibana, Makoto; Kitazawa, Hideaki; Pomjakushin, Vladimir; Keller, Lukas; Niedermayer, Christof; Scaramucci, Andrea; Kenzelmann, Michel
Source:
PHYSICAL REVIEW B, 95 (10):10.1103/PhysRevB.95.104412 MAR 13 2017
Abstract:
Multiferroic orthorhombic o-LuMnO3 exhibits large ferroelectric polarization induced by an E-type magnetic order. Recently, the E-type magnetic phase in LuMnO3 was proposed to feature magnetic moments tilted away from the collinear ordering. We employed neutron diffraction to determine the symmetry of the magnetic order in o-LuMnO3. We observed that below T-N = 39 K, the Mn3+ spins order into an incommensurate amplitudemodulated phase that obeys the Pbnm crystal symmetry and is paraelectric. The incommensurate phase locks into a commensurate phase at T-C = 35.5 K described by a fully antiferromagnetic and noncollinear E-type order. This noncollinear E-type ordering breaks the spatial inversion symmetry and induces a spontaneous polarization at TC. At T = 2 K, an appreciably large electric polarization was observed similar to that of other orthorhombic manganites featuring E-type magnetic order. We also present a Pbnm symmetry-allowed Dzyaloshinskii-Moriya interaction that explains the noncollinear E-type order in the commensurate phase. These results are in qualitative agreement with the type of distortions from collinear E-type antiferromagnetic order found using Monte Carlo simulation for rare-earth manganites
Title:
Sodium layer chiral distribution and spin structure of Na2Ni2TeO6 with a Ni honeycomb lattice
Authors:
Karna, SK; Zhao, Y; Sankar, R; Avdeev, M; Tseng, PC; Wang, W; Shu, GJ; Matan, K; Guo, GY; Chou, FC Author Full Names: Karna, Sunil K.; Zhao, Y.; Sankar, R.; Avdeev, M.; Tseng, P. C.; Wang, W.; Shu, G. J.; Matan, K.; Guo, G. Y.; Chou, F. C.
Source:
PHYSICAL REVIEW B, 95 (10):10.1103/PhysRevB.95.104408 MAR 8 2017
Abstract:
The nature of Na ion distribution, diffusion path, and the spin structure of P2-type Na2Ni2TeO6 with a Ni honeycomb lattice has been explored. The nuclear density distribution of Na ions reveals a two-dimensional (2D) chiral pattern within Na layers without breaking the original 3D crystal symmetry, which has been achieved uniquely via an inverse Fourier transform (iFT)-assisted neutron-diffraction technique. The Na diffusion pathway described by the calculated isosurface of the Na ion bond valence sum (BVS) map is found consistent to a chiral diffusion mechanism. The Na site occupancy and Ni2+ spin ordering were examined in detail with the neutron diffraction, magnetic susceptibility, specific heat, thermal conductivity, and transport measurements. Signatures of both strong incommensurate (ICM) and weak commensurate (CM) antiferromagnetic (AFM) spin ordering were identified in the polycrystalline sample studied, and the CM-AFM spin ordering was confirmed by using a single-crystal sample through the k scan in the momentum space corresponding to the AFM peak of (1/2,0,1).
Title:
Formation of the Structure and Physicomechanical Properties of a Quasicrystalline Al-Cu-Fe Alloy upon Plasma Spraying
Authors:
Lepeshev, AA; Karpov, IV; Ushakov, AV Author Full Names: Lepeshev, A. A.; Karpov, I. V.; Ushakov, A. V.
Source:
PHYSICS OF THE SOLID STATE, 59 (3):438-442; 10.1134/S1063783417030210 MAR 2017
Abstract:
Quasicrystalline coatings prepared under various thermal conditions of spraying have been studied. Initial quasicrystalline powders with dispersion of 10-50 mu m were prepared in a low-pressure arc discharge plasma. The coatings have been sprayed on copper rings using a swinging plasmatron. It is found that the increase in the quenching rate of melt droplets increases the chemical homogeneity and leads to formation of nanostructured formations. The precipitation of nanostructured grains (d < 100 nm) in the sprayed alloy leads to an increase in the mechanical characteristics (hardness, deformation, and ductility) and can be considered as an additional factor of hardening of the material.
Title:
Mossbauer Studies of Spatial Spin-Modulated Structure and Hyperfine Interactions in Multiferroic (BiFe0.10Fe0.85Cr0.05O3)-Fe-57
Authors:
Pokatilov, VS; Rusakov, VS; Sigov, AS; Belik, AA; Matsnev, ME; Komarov, AE Author Full Names: Pokatilov, V. S.; Rusakov, V. S.; Sigov, A. S.; Belik, A. A.; Matsnev, M. E.; Komarov, A. E.
Source:
PHYSICS OF THE SOLID STATE, 59 (3):443-449; 10.1134/S1063783417030271 MAR 2017
Abstract:
Results of Mossbauer investigations on Fe-57 nuclei in multiferroic material (BiFe0.10Fe0.85Cr0.05O3)-Fe-57 in the temperature range from 5.2 to 300 K are presented. Bulk rhombohedral samples were obtained by solid-state synthesis at high pressure. Mossbauer spectra were analyzed using the model of spatial incommensurate spin-modulated structure of the cycloidal type. Information on the influence of substituting Cr cations for Fe cations on hyperfine spectral parameters was obtained: the shift and quadrupolar shift of a Mossbauer line, and isotropic and anisotropic contributions into the hyperfine magnetic field. The anharmonicity parameter m of the spatial spin-modulated structure increases almost 1.7 times at 5.2 K when BiFeO3 is doped with chromium. The data on m were used for calculation of the uniaxial magnetic anisotropy constants and their temperature dependences for pure and chromium-doped BiFeO3.ß

Update: 6-Apr-2017

Title:
Charge Density Wave in the New Polymorphs of RE2Ru3Ge5 (RE = Pr, Sm, Dy)
Authors:
Bugaris, DE; Malliakas, CD; Han, F; Calta, NP; Sturza, M; Krogstad, MJ; Osborn, R; Rosenkranz, S; Ruff, JPC; Trimarchi, G; Bud'ko, SL; Balasubramanian, M; Chung, DY; Kanatzidis, MG Author Full Names: Bugaris, Daniel E.; Malliakas, Christos D.; Han, Fei; Calta, Nicholas P.; Sturza, Mihai; Krogstad, Matthew J.; Osborn, Raymond; Rosenkranz, Stephan; Ruff, Jacob P. C.; Trimarchi, Giancarlo; Bud'ko, Sergey L.; Balasubramanian, Mahalingam; Chung, Duck Young; Kanatzidis, Mercouri G.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 139 (11):4130-4143; 10.1021/jacs.7b00284 MAR 22 2017
Abstract:
A new polymorph of the RE2Ru3Ge5 (RE = Pr, Sm, Dy) compounds has been grown as single crystals via an indium flux. These compounds crystallize in tetragonal space group P4/mnc with the Sc2Fe3Si5-type structure, having lattice parameters a = 11.020(2) angstrom and c = 5.853(1) angstrom for RE = Pr, a = 10.982(2) angstrom and c = 5.777(1) angstrom for RE = Sm, and a = 10.927(2) angstrom and c = 5.697(1) angstrom for RE = Dy. These materials exhibit a structural transition at low temperature, which is attributed to an apparent charge density wave (CDW). Both the high-temperature average crystal structure and the low-temperature incommensufately Modulated crystal structure (for Sm2Ru3Ge5 as a representative) have been solved. The charge density wave order is manifested by periodic distortions of the one-dimensional zigzag Ge chains. From X-ray diffraction, charge transport (electrical resistivity, Hall effect, magnetoresistance), magnetic measurements, and heat capacity, the ordering temperatures (T-CDW) observed, in the Pr and Sm analogues are similar to 200 and similar to 175 K, respectively. The charge transport measurement results indicate an electronic state transition happening simultaneously with the CDW transition. X-ray absorption near-edge spectroscopy (XANES) and electronic band structure results are also reported.
Title:
Improved tensile properties of an equal channel angular pressed (ECAPed) Mg-8Sn-6Zn-2A1 alloy by prior aging treatment
Authors:
Cheng, WL; Tian, L; Wang, HX; Bian, LP; Yu, H Author Full Names: Cheng, Weili; Tian, Liang; Wang, Hongxia; Bian, Liping; Yu, Hui
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 687 148-154; 10.1016/jansea.2017.01.054 FEB 27 2017
Abstract:
This paper demonstrates that aging prior to ECAP (APE) can greatly enhance the tensile properties of an ECAPed Mg-8Sn-6Zn-2(wt%)Al (TZA862) alloy. Both fine Mg2Sn and icosahedral quasicrystal phase (I -phase) precipitates that formed during the APE treatment could reduce the average size of dynamically recrystallized (DRXed) grains as well as increase the fraction of fine particles after ECAP. Furthermore, the APE treatment resulted in increased basal texture intensity as well as a decreased amount of large non-deformed particles. Therefore, the tensile strength and ductility of ECAPed TZA862 alloy were improved simultaneously by the APE treatment.
Title:
Subpicometer-scale atomic displacements and magnetic properties in the oxygen-isotope substituted multiferroic DyMnO3
Authors:
Narayanan, N; Graham, PJ; Reynolds, N; Li, F; Rovillain, P; Hester, J; Kimpton, J; Yethiraj, M; McIntyre, GJ; Hutchison, WD; Ulrich, C Author Full Names: Narayanan, N.; Graham, P. J.; Reynolds, N.; Li, F.; Rovillain, P.; Hester, J.; Kimpton, J.; Yethiraj, M.; McIntyre, G. J.; Hutchison, W. D.; Ulrich, C.
Source:
PHYSICAL REVIEW B, 95 (7):10.1103/PhysRevB.95.075154 FEB 27 2017
Abstract:
We have investigated DyMn O-16(3) and its isotopically substituted counterpart DyMn O-18(3) by neutron powder diffraction, x-ray diffraction, and heat capacity measurements to investigate the mechanism leading to its magnetically induced electric polarization. O-18 isotope substitution does not influence the magnetic ordering temperature of the Mn ions T-N,(Mn) or the multiferroic ordering temperature T-l coinciding with the onset of the spin spiral phase; however, it does reduce the ordering temperature of Dy into its incommensurate magnetic state T-N,T-Dy from 7.0(1) K to 5.9(1) K. The temperature dependence of the magnetic propagation vector, q(IC), changes with O-18 substitution, while T-l remains almost constant, independent of q(IC). Pronounced changes in the lattice parameters occur at the various phase transitions. Furthermore, distinct subpicometer-scale distortions of the MnO6 octahedra and displacements of the Dy ions are observed below the ferroelectric phase transition at T-l in both samples, pointing toward the mechanism for electric polarization and its coupling to the orbital degrees of freedom.
Title:
Hyperuniformity of quasicrystals
Authors:
Oguz, EC; Socolar, JES; Steinhardt, PJ; Torquato, S Author Full Names: Oguz, Erdal C.; Socolar, Joshua E. S.; Steinhardt, Paul J.; Torquato, Salvatore
Source:
PHYSICAL REVIEW B, 95 (5):10.1103/PhysRevB.95.054119 FEB 23 2017
Abstract:
Hyperuniform systems, which include crystals, quasicrystals, and special disordered systems, have attracted considerable recent attention, but rigorous analyses of the hyperuniformity of quasicrystals have been lacking because the support of the spectral intensity is dense and discontinuous. We employ the integrated spectral intensity Z(k) to quantitatively characterize the hyperuniformity of quasicrystalline point sets generated by projection methods. The scaling of Z(k) as k tends to zero is computed for one-dimensional quasicrystals and shown to be consistent with independent calculations of the variance, sigma(2)(R), in the number of points contained in an interval of length 2R. We find that one-dimensional quasicrystals produced by projection from a two-dimensional lattice onto a line of slope 1/tau fall into distinct classes determined by the width of the projection window. For a countable dense set of widths, Z(k) similar to k(4); for all others, Z(k) similar to k(2). This distinction suggests that measures of hyperuniformity define new classes of quasicrystals in higher dimensions as well.
Title:
Field-induced reentrant magnetoelectric phase in LiNiPO4
Authors:
Toft-Petersen, R; Fogh, E; Kihara, T; Jensen, J; Fritsch, K; Lee, J; Granroth, GE; Stone, MB; Vaknin, D; Nojiri, H; Christensen, NB Author Full Names: Toft-Petersen, Rasmus; Fogh, Ellen; Kihara, Takumi; Jensen, Jens; Fritsch, Katharina; Lee, Jooseop; Granroth, Garrett E.; Stone, Matthew B.; Vaknin, David; Nojiri, Hiroyuki; Christensen, Niels Bech
Source:
PHYSICAL REVIEW B, 95 (6):10.1103/PhysRevB.95.064421 FEB 21 2017
Abstract:
Using pulsed magnetic fields up to 30 T we have measured the bulk magnetization and electrical polarization of LiNiPO4 and have studied its magnetic structure by time-of-flight neutron Laue diffraction. Our data establish the existence of a reentrant magnetoelectric phase between 19 T and 21 T. We show that a magnetized version of the zero field commensurate structure explains the magnetoelectric response quantitatively. The stability of this structure suggests a field-dependent spin anisotropy. Above 21 T, amagnetoelectrically inactive, short-wavelength incommensurate structure is identified. Our results demonstrate the combination of pulsed fields with epithermal neutron Laue diffraction as a powerful method to probe even complex phase diagrams in strong magnetic fields.
Title:
Cell-quintupling: Structural phase transition in a molecular crystal, bis(trans-4-butylcyclohexyl) methanol
Authors:
Saito, K; Ikeda, T; Yamamura, Y; Saitoh, H; Hishida, M; Kobayashi, Y; Fujita, T; Ichikawa, J Author Full Names: Saito, Kazuya; Ikeda, Takaaki; Yamamura, Yasuhisa; Saitoh, Hideki; Hishida, Mafumi; Kobayashi, Yutaro; Fujita, Takeshi; Ichikawa, Junji
Source:
JOURNAL OF CHEMICAL PHYSICS, 146 (7):10.1063/1.4976318 FEB 21 2017
Abstract:
Astructural phase transition at 151.6 K of the title compound [bis(trans-4-butylcyclohexyl) methanol] is examined by X-ray diffraction crystallography, Fourier-transform infrared spectroscopy, and adiabatic calorimetry. A general consideration on possible superstructures indicates that a single modulation wave is sufficient to drive this cell-quintupling transition. The entropy of transition determined calorimetrically indicates that two conformations are dominant in the room-temperature phase in contrast to the fivefold disorder expected from the structure of the low-temperature phase. Published by AIP Publishing.
Title:
Four-Dimensional Incommensurate Modulation and Luminescent Properties of Host Material Na3La(PO4)(2)
Authors:
Zhao, D; Ma, FX; Ma, SQ; Zhang, AY; Nie, CK; Huang, M; Zhang, L; Fan, YC Author Full Names: Zhao, Dan; Ma, Fa-Xue; Ma, Shu-Qi; Zhang, Ai-Yun; Nie, Cong-Kui; Huang, Min; Zhang, Lei; Fan, Yun-Chang
Source:
INORGANIC CHEMISTRY, 56 (4):1835-1845; 10.1021/acs.inorgchem.6b02241 FEB 20 2017
Abstract:
A series of orthophosphates Na(3)Ln(PO4)(2) (Ln = lanthanoids) have for a long time been known as good luminescent materials, yet their crystal structures have not been studied in full detail. In this work, compound Na3La(PO4)(2) was prepared using molten salt (flux) method and for the first time was structurally determined on X-ray single-crystal diffraction data. Interestingly, it crystallizes in the four-dimensional incommensurately modulated structure with orthorhombic superspace group Pca(21)(0 beta 0)000 and modulation wave vector q = 0.387b*. Furthermore, to evaluate the potentiality of Na3La(PO4)(2) to be used as a luminescent host material, 5 mol % Eu3+, Tb3+, and Dy3+ doped phosphors were prepared, respectively. The excitation spectra, emission spectra, decay time, quantum efficiency, and the color purity of prepared phosphors, Na3La0.95Eu0.05(PO4)(2), Na3La0.95Tb0.05(PO4)(2), and Na3La0.95Dy0.05(PO4)(2), were studied.
Title:
Anomalous lattice compression and magnetic ordering in CuO at high pressures: A structural study and first-principles calculations
Authors:
Kozlenko, DP; Druzbicki, K; Kichanov, SE; Lukin, EV; Liermann, HP; Glazyrin, KV; Savenko, BN Author Full Names: Kozlenko, D. P.; Druzbicki, K.; Kichanov, S. E.; Lukin, E. V.; Liermann, H. -P.; Glazyrin, K. V.; Savenko, B. N.
Source:
PHYSICAL REVIEW B, 95 (5):10.1103/PhysRevB.95.054115 FEB 17 2017
Abstract:
The structural and magnetic properties of multiferroic CuO have been studied by means of neutron and x-ray powder diffraction at pressures up to 11 and 38 GPa, respectively, and by first-principles theoretical calculations. Anomalous lattice compression is observed, with enlargement of the lattice parameter a, reaching a maximum at P = 13 GPa, followed by its reduction at higher pressures. The lattice distortion of the monoclinic structure at high pressures is accompanied by a progressive change of the oxygen coordination around Cu atoms from the square fourfold towards the octahedral sixfold coordination. The pressure-induced evolution of the structural properties and electronic structure of CuO was successfully elucidated in the framework of full-electronic density functional theory calculations with range-separated HSE06, and meta-generalized gradient approximation hybrid M06 functionals. The antiferromagnetic (AFM) ground state with a propagation vector q = (0.5,0, -0.5) remains stable in the studied pressure range. From the obtained structural parameters, the pressure dependencies of the principal superexchange magnetic interactions were analyzed, and the pressure behavior of the Neel temperature as well as the magnetic transition temperature from the intermediate incommensurate AFM multiferroic state to the commensurate AFM ground state were evaluated. The estimated upper limit of the Neel temperature at P = 38 GPa is about 260 K, not supporting the previously predicted existence of the multiferroic phase at room temperature and high pressure.
Title:
Fabrication of a Quasicrystal Electrode at a Low Processing Temperature via Electrohydrodynamic and Transfer Printing for use in Multifunctional Electronics
Authors:
Park, S; Park, S; Park, S; Ryu, H; Park, JJ Author Full Names: Park, Seoungwoong; Park, Siyong; Park, Sangki; Ryu, Hochung; Park, Jong-Jin
Source:
ADVANCED ELECTRONIC MATERIALS, 3 (2):10.1002/aelm.201600440 FEB 2017
Abstract:
Fabrication of a quasicrystal electrode at a low processing temperature via electrohydrodynamic and transfer printing for use in multifunctional electronics is demonstrated using an electrohydrodynamic narrow nozzle-to-substrate distance printing method to obtain a quasicrystal electrode (transferred electrode), which can increase electrode durability with a better surface roughness and lower processing cost with low-temperature processing, for use in multifunctional electronics.
Title:
Dynamic response of an icosahedral quasi-crystalline medium with a Griffith crack under mechanical loadings
Authors:
Qiao, LP; Wu, L; Fan, TY Author Full Names: Qiao, Liangping; Wu, Li; Fan, Tianyou
Source:
ADVANCES IN MECHANICAL ENGINEERING, 9 (2):10.1177/1687814016688850 FEB 1 2017
Abstract:
Elastodynamic response of three-dimensional icosahedral quasi-crystals under mechanical loadings is presented in this article. Two kinds of cases are considered here, in which the plane problem and anti-plane problem are included. The phonon and phason elastic fundamental fields along with their coupling effect in crack analysis are explicitly presented in terms of the theoretical and numerical analyses. Using the finite difference method, some numerical results of stresses, displacements, and normalized dynamic stress intensity factor are obtained. By comparing the results of quasi-crystals, this article reveals the influence of phonon and phason elastic fundamental fields, which occupy an important position in dynamic deformation behavior of quasi-crystals. Of course, phonon-phason coupling effect also should not be neglected.

Update: 30-Mar-2017

Title:
Shield-like tile and its application to the decagonal quasicrystal-related structures in Al-Cr-Fe-Si alloys
Authors:
Li, H; Ma, HK; Hou, LG; Guo, MX; He, ZB Author Full Names: Li, Hua; Ma, Haikun; Hou, Longgang; Guo, Mingxing; He, Zhanbing
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 701 494-498; 10.1016/j.jallcom.2017.01.105 APR 15 2017
Abstract:
A shield-like tile (SLT) consisting of one star tile and two hexagon tiles was used as one structural block to describe the tilings of quasicrystal approximants in our previous work [J. All. Compds. 647 (2015) 797- 801.] because of its merits compared with the hexagon-boat-star model. In this paper, we aim to elucidate the rules of connection and the orientations of SLTs. Two examples of high-angle annular dark field scanning transmission electron microscopy images are provided to support these rules. The SLT orientation mapping of the quasicrystal-related structures along the pseudo-tenfold axis was achieved, and the structural characterizations were revealed intuitively. Furthermore, some new quasicrystal approximants were discussed based on the changeable rows of SLTs. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Nanoquasicrystalline Al-Fe-Cr-Ti alloy matrix/gamma-Al2O3 nanocomposite powders: The effect of the ball milling process
Authors:
Xu, W; Galano, M; Audebert, F Author Full Names: Xu, W.; Galano, M.; Audebert, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 701 342-349; 10.1016/j.jallcom.2016.11.412 APR 15 2017
Abstract:
Quasicrystalline aluminium alloys and aluminium based nanocomposites with the advantage of high strength over commercial aluminium alloys have been studied for many years. In this work a nano-quasicrystalline Al-Fe-Cr-Ti alloy powder and a nanocomposite consisting of a mixture of a nano-quasicrystalline alloy and nanosize gamma-Al2O3 powders were produced through mechanical milling with different milling speeds. It has been observed that a higher milling time or milling speed can improve the homogeneity of the gamma-Al2O3 distribution. The alpha-Al crystallite size decreases and the hardness increases with the milling time. The smallest crystallite size (14 nm) and the highest hardness value (638 HV10g) were obtained for the nanocomposite after 30 h of milling at 250 rpm. As the alpha-Al crystallite size is the main change in the microstructure during the ball milling process, the change in the hardness of the milled powders was found to follow a Hall-Fetch type relation with an exponent of 0.25. (C) 2016 Published by Elsevier B.V.
Title:
The effect of temperature, interaction range, and pair potential on the formation of dodecagonal quasicrystals in core-corona systems
Authors:
Pattabhiraman, H; Dijkstra, M Author Full Names: Pattabhiraman, Harini; Dijkstra, Marjolein
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (9):10.1088/1361-648X/aa5530 MAR 8 2017
Abstract:
A two-dimensional dodecagonal quasicrystal was previously reported by Dotera et al (2014 Nature 506 208) in a system of particles interacting with a hard core of diameter s and a repulsive square shoulder of diameter delta = 1.40 sigma. In the current work, we examine the formation of this quasicrystal using bond orientational order parameters, correlation functions and tiling distributions. We find that this dodecagonal quasicrystal forms from a fluid phase. We further study the effect of the width of the repulsive shoulder by simulating the system over a range of values of d. For the range of densities and temperatures considered, we observe the formation of the dodecagonal quasicrystal between delta = 1.30 sigma and 1.44 sigma. We also study the effect of shape of the interaction potential by simulating the system using three other interaction potentials with two length scales, namely hard-core plus a linear ramp, modified exponential, or Buckingham (exp-6) potential. We observe the presence of the quasicrystal in all three systems. However, depending on the shape of the potential, the formation of the quasicrystal takes place at lower temperatures (or higher interaction strengths). Using free-energy calculations, we demonstrate that the quasicrystal is thermodynamically stable in the square-shoulder and linear-ramp system.
Title:
New insights into the multiferroic properties of Mn3TeO6
Authors:
Ivanov, SA; Ritter, C; Nordblad, P; Tellgren, R; Weil, M; Carolus, V; Lottermoser, T; Fiebig, M; Mathieu, R Author Full Names: Ivanov, S. A.; Ritter, C.; Nordblad, P.; Tellgren, R.; Weil, M.; Carolus, V.; Lottermoser, Th; Fiebig, M.; Mathieu, R.
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 50 (8):10.1088/1361-6463/aa5621 MAR 1 2017
Abstract:
Mn3TeO6 has a trigonal corundum related structure (space group R (3) over bar), and orders in an incommensurate antiferromagnetic (AFM) structure at T-N approximate to 24 K. A weak ferroelectric order below T* similar to 21 K has recently been reported. In order to investigate possible structural changes below T-N leading to the observed dipole order, we have performed a detailed study of the crystal and magnetic structures of Mn3TeO6 using neutron powder diffraction (NPD) in the temperature range of 5-40 K. Complementary low-temperature second harmonic generation (SHG) measurements were performed in order to confirm the reported dipole order at T*. No change in the rhombohedral symmetry associated with a possible displacive phase transition at T* was observed in the long-range *structural* correlations, and it appears that Mn3TeO6 keeps the same incommensurately modulated magnetic spin structure with the propagation vector k = (0; 0; 0.43) in the whole temperature range from 5 to 24 K.
Title:
Competing electronic instabilities of extended Hubbard models on the honeycomb lattice: A functional renormalization group calculation with high-wave-vector resolution
Authors:
de la Pena, DS; Lichtenstein, J; Honerkamp, C Author Full Names: de la Pena, D. Sanchez; Lichtenstein, J.; Honerkamp, C.
Source:
PHYSICAL REVIEW B, 95 (8):10.1103/PhysRevB.95.085143 FEB 27 2017
Abstract:
We investigate the quantum many-body instabilities for electrons on the honeycomb lattice at half filling with extended interactions, motivated by a description of graphene and related materials. We employ a recently developed fermionic functional renormalization group scheme, which allows for highly resolved calculations of wave-vector dependences in the low-energy effective interactions. We encounter the expected anti-ferromagnetic spin densitywave for a dominant on-site repulsion between electrons, and charge orderwith different modulations for dominant pure nth nearest-neighbor repulsive interactions. Novel instabilities towards incommensurate charge density waves take place when nonlocal density interactions among several bond distances are included simultaneously. Moreover, for more realistic Coulomb potentials in graphene including enough nonlocal terms there is a suppression of charge order due to competition effects between the different charge ordering tendencies, and if the on-site term fails to dominate, the semimetallic state is rendered stable. The possibility of a topological Mott insulator being the favored tendency for dominating second-nearest-neighbor interactions is not realized in our results with high momentum resolution.
Title:
Quasiperiodic Frank-Kasper phases derived from the square-triangle dodecagonal tiling
Authors:
Sadoc, JF; Mosseri, R Author Full Names: Sadoc, Jean-Francois; Mosseri, Remy
Source:
STRUCTURAL CHEMISTRY, 28 (1):63-73; SI 10.1007/s11224-016-0846-2 FEB 2017
Abstract:
Frank-Kasper (F-K) phases form an important set of large-cell crystalline structures describing many intermetallic alloys. They are usually described in term of their atomic environments, with atoms having 12, 14, 15 and 16 neighbours, coded into the canonical Z(p) cells (with p the coordination number), the case p = 12 corresponding to a local icosahedral environment. In addition, the long-range structure is captured by the geometry of a network (called either "major skeleton" or "disclination network") connecting only the non-icosahedral sites (with p 6 not equal 12). Another interesting description, valid for the so-called layered F-K phases, amounts to give simple rules to decorate specific periodic 2d tilings made of triangles and squares and eventually get the 3d periodic F-K phases. Quasicrystalline phases can sometime be found in the vicinity, in the phase diagram, of the F-K crystalline alloys; it is therefore of interest to understand whether and how the standard F-K construction rules can be generalized on top of an underlying quasiperiodic structure. It is in particular natural to investigate how well square-triangle quasiperiodic tilings with dodecagonal symmetry, made of square and (equilateral) triangles, can be used as building frames to generate some F-K-like quasicrystalline structures. We show here how to produce two types of such structures, which are quasiperiodic in a plane and periodic in the third direction, and containing (or not) Z(16) sites.
Title:
Are periodicity and symmetry the properties of a discrete space? (On one paradox of cellular automata)
Authors:
Shevchenko, VY; Krivovichev, SV Author Full Names: Shevchenko, Vladimir Ya; Krivovichev, Sergey V.
Source:
STRUCTURAL CHEMISTRY, 28 (1):45-50; SI 10.1007/s11224-016-0844-4 FEB 2017
Abstract:
We consider a three-color cellular automaton (CA) that acts on a square lattice. In ternary numeral system, the CA has the number 111010011111110111011102010, which corresponds to 3704707887996 in the decimal system. With the finite size of the input row, CA-3704707887996 generates aperiodic structures with repeating self-similar patterns. In order to investigate the formation of periodic patterns by the CA-3704707887996, the input row was used that represents a periodic structure containing variable number of cells. The behavior of the CA-3704707887996 work for the input rows with periods up to 21 cells was studied. All generated patterns were analyzed from the viewpoint of their periodicity along the vertical direction. It was found out that the behavior of the system depending upon the length (l(input)) and structure of the periodic input row is strongly nonlinear. The complexity C of a pattern considered as a size of a unit cell increases exponentially with the increasing l(input) value and can be described by the function C = 1.8986 exp [0.3334 l(input)], with the correlation coefficient R-2 = 0.8967. As a rule, initially the CA generates a metastable aperiodic structure and then adopts a stable regime of generation of a stable periodic pattern. The abstract properties of the CA-3704707887996 have several important consequences for structural chemistry: (1) relatively simple schemes of local interactions of particles may result in the formation of very complex structures depending upon the initial conditions and abstract properties of the interactions; (2) symbolic complexity of the generated patterns increases exponentially depending upon the structure of initial conditions; (3) under certain initial conditions, explosive fluctuations of complexity are possible that lead to the formation of giant superstructures with extremely large periods; and (4) under certain conditions, the border between aperiodic and periodic structures virtually disappears.
Title:
Generalized reciprocal vector sets
Authors:
Gomez-Rodriguez, A; Aragon, JL Author Full Names: Gomez-Rodriguez, A.; Aragon, J. L.
Source:
STRUCTURAL CHEMISTRY, 28 (1):235-238; SI 10.1007/s11224-016-0848-0 FEB 2017
Abstract:
In this work, we present a short review on generalized reciprocal vectors, a field created by Alan L. Mackay. In particular, we discuss the concept of generalized reciprocal vectors, its relation with eutactic stars used in quasicrystallography and their calculation using Moore-Penrose pseudoinverses. Additionally, we propose a plain Gaussian algorithm for this same purpose.
Title:
Tiling approach for the description of the sevenfold symmetry in quasicrystals
Authors:
Madison, AE Author Full Names: Madison, A. E.
Source:
STRUCTURAL CHEMISTRY, 28 (1):57-62; SI 10.1007/s11224-016-0793-y FEB 2017
Abstract:
An example of substitution rules for the construction of heptagonal rhombic tilings is proposed. Rigorous inflation/deflation rules make it possible to expand the tiling up to infinity without additional ad hoc rearrangements. The derived tilings are self-similar and consist of characteristic patterns with seven-pointed stars surrounded by similar seven-pointed stars.
Title:
Mackay clusters and beyond in icosahedral quasicrystals seen from 6D space
Authors:
Sirindil, A; Quiquandon, M; Gratias, D Author Full Names: Sirindil, Abdullah; Quiquandon, Marianne; Gratias, Denis
Source:
STRUCTURAL CHEMISTRY, 28 (1):123-132; SI 10.1007/s11224-016-0843-5 FEB 2017
Abstract:
It is a great pleasure and honour for us to participate to the celebration of the 90th birthday of Alan Mackay, one of the most inspired crystallographers of our time who has been the authentic predecessor of the quasicrystal discovery. We discuss here several ways to construct Mackay-type atomic clusters and others for describing quasicrystalline structures from the standard 6D framework. We show that they are several simple solutions for both the 6D natural cluster and the original Mackay derivation that are consistent with special points of the basic icosahedral 6D lattice and the actually determined clusters in usual cubic 1/1 approximants of the icosahedral phases. This technique works as well for describing the two first shells of the so-called Bergman clusters but the situation is far more complicated for the so-called Tsai cluster that cannot be directly obtained from the icosahedral cut and projection of the simple 6D lattice special points without significantly large differences in the radii of the various orbits with respect to their actual positions in the YbCd icosahedral-type alloys. This shows that the 6D approach using special points as locations of the mean atomic surfaces-although very efficient for constructing initial simple models of the icosahedral phases-requires subsequent refinement techniques, especially in the actual locations and sizes of the various atomic orbits of the implied clusters, for leading to final acceptable structural models.
Title:
Kurt Bruckner's view on the Penrose tiling
Authors:
Steurer, W; Arlitt, S Author Full Names: Steurer, Walter; Arlitt, Sabine
Source:
STRUCTURAL CHEMISTRY, 28 (1):51-56; SI 10.1007/s11224-016-0790-1 FEB 2017
Abstract:
We demonstrate the potential of Kurt Bruckner's 'addition algorithm', which is based on the substitution rule for the generation of the Robinson triangle tiling, a variant of the Penrose tiling. The artist Kurt Bruckner developed his straightforward approach intuitively for the creation of quasiperiodic ornaments. This versatile method can be used for the construction of achiral, homochiral and racemic quasiperiodic ornaments, as well as for the generation of decorated two-level (two-color) Penrose tilings. Therefore, the underlying tiling is always the same kind of Penrose tiling, which is invariant under the action of specific mirror and black/white mirror operations in contrast to unit tiles that are decorated in specific ways. Compared to the underlying classical substitution method the advantage of Kurt Bruckner's approach is its simplicity and versatility for the creation of decorated tilings. Using a vector graphics editor, large and arbitrarily complex quasiperiodic ornaments can be easily generated manually.
Title:
Generalizing crystallography: a tribute to Alan L. Mackay at 90
Authors:
Hargittai, I Author Full Names: Hargittai, Istvan
Source:
STRUCTURAL CHEMISTRY, 28 (1):1-16; SI 10.1007/s11224-016-0766-1 FEB 2017
Abstract:
Alan L. Mackay, one of the rare generalists of our time, was a disciple and follower of J. Desmond Bernal. Mackay has contributed decisively to the development of the science of structures and taught generations to look at the broader picture when determining crystal and molecular structures. He was constantly seeking coherence and regularities in observations and in thought experiments and was aiming at creating concepts on the basis of those regularities. His inquiries prompted him to predict the existence of regular but not periodic crystal structures that are known today as quasicrystals.
Title:
The philosophical significance of Alan Mackay's theoretical discovery of quasicrystals
Authors:
Gilead, A Author Full Names: Gilead, Amihud
Source:
STRUCTURAL CHEMISTRY, 28 (1):249-256; SI 10.1007/s11224-016-0742-9 FEB 2017
Abstract:
Dan Shechtman was the first to discover an actual quasicrystal (on April 8, 1982). He was, however, not the first to discover the pure possibility of this novel structure (the theoretical discovery), which had been excluded from the range of the possibilities of crystals (as it had been fixed by both theoretical and empirical means in the beginning of the twentieth century). Penrose and Mackay, in particular, had contributed to the discovery of the pure possibilities of quasicrystals quite some time before their actual discovery. These pure possibilities are mathematical-structural, and like purely mathematical entities, they do not exist spatiotemporally and causally, whereas actual quasicrystals exist only spatiotemporally and causally. The pure possibilities of quasicrystals do not depend on their actualities, and without them, these actualities would have been theoretically groundless, meaningless, and could not be correctly identified if at all. Hence, Mackay's contribution to the meaning and theoretical basis of the discovery of actual quasicrystals is indispensable.
Title:
Microstructure and electrical resistivity in the GdNi5-xCux intermetallic series
Authors:
Bajorek, A; Chelkowska, G Author Full Names: Bajorek, Anna; Chelkowska, Grazyna
Source:
JOURNAL OF RARE EARTHS, 35 (1):71-78; 10.1016/S1002-0721(16)60176-X JAN 2017
Abstract:
The effect of the Ni/Cu substitution on the electrical resistivity and microstructure of the polycrystalline GdNi5-xCux series was studied. The value of temperature of phase transition (T-ph) estimated from temperature dependence of electrical resistance varied non-linearly across copper doping from 32.5 K (x=0.0) to 29.1 K (x=5.0). The value of residual resistivity (rho(o)) estimated at low temperature range decreased from 27.28 mu Omega cm (x=0.0) to 9.44 mu Omega cm (x=5.0), which was discussed as the influence of microstructure. In order to describe the temperature dependence of resistivity rho(T) a variety of approaches were applied due to different scattering mechanisms occurring at high and low temperature ranges. The change within rho(T) curvature was evidenced at low temperature range across copper doping. The temperature variation of the resistivity was quite peculiar for Cu-rich compounds (x=4.8, x=5.0), which might be correlated with the incommensurate magnetic structure derived from the weakly negative interaction between the nearest neighbours of Gd. The correlation between microstructure and resistivity was observed.

Update: 16-Mar-2017

Title:
Interfacial free energy and medium range order: Proof of an inverse of Frank's hypothesis
Authors:
Lee, GW; Cho, YC; Lee, B; Kelton, KF Author Full Names: Lee, Geun Woo; Cho, Yong Chan; Lee, Byeongchan; Kelton, Kenneth F.
Source:
PHYSICAL REVIEW B, 95 (5):10.1103/PhysRevB.95.054202 FEB 13 2017
Abstract:
We study the relation of crystal-liquid interfacial free energy and medium range order in the quasicrystal-forming Ti37Zr42Ni21 liquid from undercooling experiment and ab initio molecular dynamics (MD) simulation. Adding a small amount of Ag to the liquid significantly reduces the degree of undercooling, which is suggestive of small interfacial free energy, and thus very similar atomic configuration between the liquid and the icosahedral quasicrystal phases. Using ab initioMDstudy, we find that Ag atoms predominantly form a bond with Zr atoms in the short range and, further, Ag-Zr pairs are extended in the liquid, as amedium range orderwhich is identical to the global structural feature reported recently [Liu et al., Phys. Rev. Lett. 105, 155501 (2010)]. This result may expect extremely small undercooling if the icosahedral medium range order exists in a liquid forming an icosahedral quasicrystal, which implies the ambiguity of clear distinction of heterogeneous and homogeneous nucleation.
Title:
Non-Fermi surface nesting driven commensurate magnetic ordering in Fe-doped Sr(2)RuO4
Authors:
Zhu, M; Shanavas, KV; Wang, Y; Zou, T; Sun, WF; Tian, W; Garlea, VO; Podlesnyak, A; Matsuda, M; Stone, MB; Keavney, D; Mao, ZQ; Singh, DJ; Ke, X Author Full Names: Zhu, M.; Shanavas, K. V.; Wang, Y.; Zou, T.; Sun, W. F.; Tian, W.; Garlea, V. O.; Podlesnyak, A.; Matsuda, M.; Stone, M. B.; Keavney, D.; Mao, Z. Q.; Singh, D. J.; Ke, X.
Source:
PHYSICAL REVIEW B, 95 (6):10.1103/PhysRevB.95.054413 FEB 10 2017
Abstract:
Sr2RuO4, an unconventional superconductor, is known to possess an incommensurate spin-density wave instability driven by Fermi surface nesting. Here we report a static spin-density wave ordering with a commensurate propagation vector q(c) = ( 0.25 0.25 0) in Fe-doped Sr2RuO4, despite the magnetic fluctuations persisting at the incommensurate wave vectors q(ic) = ( 0.30.3L) as in the parent compound. The latter feature is corroborated by the first-principles calculations, which showthat Fe substitution barely changes the nesting vector of the Fermi surface. These results suggest that in addition to the known incommensurate magnetic instability, Sr2RuO4 is also in proximity to a commensurate magnetic tendency that can be stabilized via Fe doping.
Title:
Non-Fermi surface nesting driven commensurate magnetic ordering in Fe-doped Sr2RuO4
Authors:
Zhu, M; Shanavas, KV; Wang, Y; Zou, T; Sun, WF; Tian, W; Garlea, VO; Podlesnyak, A; Matsuda, M; Stone, MB; Keavney, D; Mao, ZQ; Singh, DJ; Ke, X Author Full Names: Zhu, M.; Shanavas, K. V.; Wang, Y.; Zou, T.; Sun, W. F.; Tian, W.; Garlea, V. O.; Podlesnyak, A.; Matsuda, M.; Stone, M. B.; Keavney, D.; Mao, Z. Q.; Singh, D. J.; Ke, X.
Source:
PHYSICAL REVIEW B, 95 (5):10.1103/PhysRevB.95.054413 FEB 10 2017
Abstract:
Sr2RuO4, an unconventional superconductor, is known to possess an incommensurate spin-density wave instability driven by Fermi surface nesting. Here we report a static spin-density wave ordering with a commensurate propagation vector q(c) = (0.25 0.25 0) in Fe-doped Sr2RuO4, despite the magnetic fluctuations persisting at the incommensurate wave vectors q(ic) = (0.30.3L) as in the parent compound. The latter feature is corroborated by the first-principles calculations, which show that Fe substitution barely changes the nesting vector of the Fermi surface. These results suggest that in addition to the known incommensurate magnetic instability, Sr2RuO4 is also in proximity to a commensurate magnetic tendency that can be stabilized via Fe doping.
Title:
Incommensurate charge ordered states in the t-t '-J model
Authors:
Choubey, P; Tu, WL; Lee, TK; Hirschfeld, PJ Author Full Names: Choubey, Peayush; Tu, Wei-Lin; Lee, Ting-Kuo; Hirschfeld, P. J.
Source:
NEW JOURNAL OF PHYSICS, 19 10.1088/1367-2630/19/1/013028 JAN 20 2017
Abstract:
We study the incommensurate charge ordered states in the t-t'-J model using the Gutzwiller mean field theory on large systems. In particular, we explore the properties of incommensurate charge modulated states referred to as nodal pair density waves (nPDW) in the literature. nPDW states intertwine site and bond charge order with modulated d-wave pair order, and are characterized by a nonzero amplitude of uniform pairing; they also manifest a dominant intra-unit cell d-density wave form factor. To compare with a recent scanning tunneling microscopy (STM) study (Hamidian et al 2015 Nat. Phys. 12 150) of the cuprate superconductor BSCCO-2212, we compute the continuum local density of states (LDOS) at a typicalSTM tip height using the Wannier function based approach. By Fourier transforming Cu and O sub-lattice LDOS we also obtain bias-dependent intra-unit cell form factors and spatial phase difference. We find that in then PDW state the behavior of form factors and spatial phase difference as a function of energy agrees remarkably well with the experiment. This is in contrast to commensurate charge modulated states, which we show do not agree with experiment. We propose that then PDW states are good candidates for the charge density wave phase observed in the superconducting state of underdoped cuprates.

Update: 9-Mar-2017

Title:
Tuning Crystal Structures and Thermoelectric Properties through Al Doping in ReSi1.75
Authors:
Wang, F; Veremchuk, I; Lidin, S Author Full Names: Wang, Fei; Veremchuk, Igor; Lidin, Sven
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 2017 (1):47-55; 10.1002/ejic.201600792 JAN 2017
Abstract:
Binary rhenium silicide, ReSi1.75, and its aluminium-doped variants have been synthesized. Their crystal structures were characterized by X-ray diffraction, solved and refined through the use of superspace group models. The binary un-doped ReSi1.75 is a commensurate (supercell) structure of the previously well-known MoSi2-type structure. Al doping renders an incommensurate structure that was solved and refined, and reported for the first time. The thermoelectric properties of these compounds were also measured, including their electrical resistivities, thermal conductivities, and Seebeck coefficients. Compared with the commensurate structure of binary ReSi1.75, the Al-doped incommensurate phase exhibits lower lattice thermal conductivity, lower electrical resistivity, a higher Seebeck coefficient, and ultimately a much higher figure of merit (ZT). The cause of the structural incommensuration by Al doping was studied through the use of first-principle calculations. The relationship between the incommensurability and the improved thermoelectric properties is also discussed.
Title:
The true structural periodicities and superspace group descriptions of the prototypical incommensurate composite materials: Alkane/urea inclusion compounds
Authors:
Couzi, M; Guillaume, F; Harris, KDM; Palmer, BA; Christensen, K; Collins, SP Author Full Names: Couzi, Michel; Guillaume, Francois; Harris, Kenneth D. M.; Palmer, Benjamin A.; Christensen, Kirsten; Collins, Stephen P.
Source:
EPL, 116 (5):10.1209/0295-5075/116/56001 DEC 2016
Abstract:
The prototypical family of incommensurate composite materials are the n-alkane/urea inclusion compounds, in which n-alkane guest molecules are arranged in a periodic manner along one-dimensional tunnels in a urea host structure, with an incommensurate relationship between the periodicities of the host and guest substructures along the tunnel. We develop interpretations of the structural periodicities, superspace group descriptions and symmetry properties of the low-temperature phases of n-alkane/urea inclusion compounds, based in part on a high-resolution synchrotron single-crystal X-ray diffraction study of n-nonadecane/urea. Specifically, we prove that, on passing from phase I to phase II, the C-centering of the orthohexagonal unit cell is lost for both the host and guest substructures, and that the symmetries of all phases I, II and III are described completely by (3+1)-dimensional superspace groups. Copyright (C) EPLA, 2016
Title:
Commensurate-incommensurate transition and domain wall dynamics of adsorbed overlayers on a honeycomb substrate
Authors:
Elder, KR; Achim, CV; Granato, E; Ying, SC; Ala-Nissila, T Author Full Names: Elder, K. R.; Achim, C. V.; Granato, E.; Ying, S. C.; Ala-Nissila, T.
Source:
EPL, 116 (5):10.1209/0295-5075/116/56002 DEC 2016
Abstract:
We introduce an effective one-mode phase-field crystal model for studying the commensurate-incommensurate transition and domain wall dynamics of the (root 3 x root 3) R30 degrees. phase found in systems such as Xe/Pt(111), or Xe and Kr on graphite. The model allows us to study large systems where the domain walls can be separated over large macroscopic distances and at the same time incorporate the microscopic details of the domain wall structures. The resulting phase diagram shows that an intermediate stripe incommensurate phase always separates the commensurate phase from the honeycomb incommensurate phases. The energy of the domain wall crossing is investigated. We also find that near a step edge, the domain walls tend to align perpendicularly to the step edge, in agreement with recent experimental observations. Copyright (C) EPLA, 2016
Title:
Thermoelectric properties of layered calcium cobaltite Ca3Co4O9 from hybrid functional first-principles calculations
Authors:
Lemal, S; Varignon, J; Bilc, DI; Ghosez, P Author Full Names: Lemal, Sebastien; Varignon, Julien; Bilc, Daniel I.; Ghosez, Philippe
Source:
PHYSICAL REVIEW B, 95 (7):10.1103/PhysRevB.95.075205 FEB 9 2017
Abstract:
Using a combination of first-principles calculations based on density functional theory and Boltzmann semiclassical transport theory, we compute and study the properties of pristine layered calcium cobaltite Ca3Co4O9. We model the system with the B1WC hybrid functional. Two supercells of increasing size which approximate the incommensurate crystallographic structure of the compound are studied and we determine their structural, magnetic, and electronic properties. It is found that the B1WC hybrid functional is appropriate to reproduce the structural, electronic, and magnetic properties, which are then extensively discussed. From the electronic band structure, the Seebeck (S) and electrical resistivity (rho) tensors are computed using Boltzmann transport theory within the constant relaxation-time approximation. The differences between the diagonal components are detailed and reveal a strong in-plane anisotropy of the properties. The qualitative behavior of the averaged in-plane properties, S-// and rho(//), is consistent with the measurements reported in the literature. Our calculation clarifies and provides a broad picture of the evolution of the thermoelectric properties with both carrier density and temperature, and suggests that the change in S-// and rho(//) around 100 K is not necessarily related to the magnetic transitions occurring around 100 K.
Title:
Quasicrystalline nanocrystal superlattice with partial matching rules
Authors:
Ye, XC; Chen, J; Irrgang, ME; Engel, M; Dong, AG; Glotzer, SC; Murray, CB Author Full Names: Ye, Xingchen; Chen, Jun; Irrgang, M. Eric; Engel, Michael; Dong, Angang; Glotzer, Sharon C.; Murray, Christopher B.
Source:
NATURE MATERIALS, 16 (2):214-219; 10.1038/NMAT4759 FEB 2017
Abstract:
Expanding the library of self-assembled superstructures provides insight into the behaviour of atomic crystals and supports the development of materials with mesoscale order(1,2). Here we build on recent findings of soft matter quasicrystals (3-6) and report a quasicrystalline binary nanocrystal superlattice that exhibits correlations in the form of partial matching rules reducing tiling disorder. We determine a three-dimensional structure model through electron tomography(7,8) and direct imaging of surface topography. The 12-fold rotational symmetry of the quasicrystal is broken in sublayers, forming a random tiling of rectangles, large triangles and small triangles with 6-fold symmetry. We analyse the geometry of the experimental tiling and discuss factors relevant for the stabilization of the quasicrystal. Our joint experimental-computational study demonstrates the power of nanocrystal superlattice engineering and further narrows the gap between the richness of crystal structures found with atoms and in soft matter assemblies.

Update: 22-Feb-2017

Title:
Critical scattering and incommensurate phase transition in antiferroelectric PbZrO3 under pressure
Authors:
Burkovsky, RG; Bronwald, I; Andronikova, D; Wehinger, B; Krisch, M; Jacobs, J; Gambetti, D; Roleder, K; Majchrowski, A; Filimonov, AV; Rudskoy, AI; Vakhrushev, SB; Tagantsev, AK Author Full Names: Burkovsky, R. G.; Bronwald, I.; Andronikova, D.; Wehinger, B.; Krisch, M.; Jacobs, J.; Gambetti, D.; Roleder, K.; Majchrowski, A.; Filimonov, A. V.; Rudskoy, A. I.; Vakhrushev, S. B.; Tagantsev, A. K.
Source:
Scientific Reports, 7 10.1038/srep41512 JAN 30 2017
Abstract:
Antiferroelectric lead zirconate is the key ingredient in modern ferroelectric and piezoelectric functional solid solutions. By itself it offers opportunities in new-type non-volatile memory and energy storage applications. A highly useful and scientifically puzzling feature of this material is the competition between the ferro- and antiferroelectric phases due to their energetic proximity, which leads to a challenge in understanding of the critical phenomena driving the formation of the antiferroelectric structure. We show that application of hydrostatic pressure drastically changes the character of critical lattice dynamics and enables the soft-mode-driven incommensurate phase transition sequence in lead zirconate. In addition to the long known cubic and antiferroelectric phases we identify the new non-modulated phase serving as a bridge between the cubic and the incommensurate phases. The pressure effect on ferroelectric and incommensurate critical dynamics shows that lead zirconate is not a single-instability-driven system.
Title:
Observation of a Charge Density Wave Incommensuration Near the Superconducting Dome in CuxTiSe2
Authors:
Kogar, A; de la Pena, GA; Lee, S; Fang, Y; Sun, SXL; Lioi, DB; Karapetrov, G; Finkelstein, KD; Ruff, JPC; Abbamonte, P; Rosenkranz, S Author Full Names: Kogar, A.; de la Pena, G. A.; Lee, Sangjun; Fang, Y.; Sun, S. X. -L.; Lioi, D. B.; Karapetrov, G.; Finkelstein, K. D.; Ruff, J. P. C.; Abbamonte, P.; Rosenkranz, S.
Source:
PHYSICAL REVIEW LETTERS, 118 (2):10.1103/PhysRevLett.118.027002 JAN 11 2017
Abstract:
X-ray diffraction was employed to study the evolution of the charge density wave (CDW) in CuxTiSe2 as a function of copper intercalation in order to clarify the relationship between the CDW and superconductivity. The results show a CDWincommensuration arising at an intercalation value coincident with the onset of superconductivity at around x = 0.055(5). Additionally, it was found that the charge density wave persists to higher intercalant concentrations than previously assumed, demonstrating that the CDW does not terminate inside the superconducting dome. A charge density wave peak was observed in samples up to x = 0.091(6), the highest copper concentration examined in this study. The phase diagram established in this work suggests that charge density wave incommensuration may play a role in the formation of the superconducting state.

Update: 16-Feb-2017

Title:
Multiple quasicrystal approximants with the same lattice parameters in Al-Cr-Fe-Si alloys
Authors:
He, ZB; Li, H; Ma, HK; Li, GW Author Full Names: He, Zhanbing; Li, Hua; Ma, Haikun; Li, Guowu
Source:
SCIENTIFIC REPORTS, 7 10.1038/srep40510 JAN 13 2017
Abstract:
By means of atomic-resolution high-angle annular dark-field scanning transmission electron microscopy, we found three types of giant approximants of decagonal quasicrystal in Al-Cr-Fe-Si alloys, where each type contains several structural variants possessing the same lattice parameters but different crystal structures. The projected structures of these approximants along the pseudo-tenfold direction were described using substructural blocks. Furthermore, the structural relationship and the plane crystallographic groups in the (a, c) plan of these structural variants was also discussed. The diversity of quasicrystal approximants with the same lattice parameters was shown to be closely related to the variety of shield-like tiles and their tiling patterns.
Title:
A general algorithm for generating isotropy subgroups in superspace
Authors:
Stokes, HT; Campbell, BJ Author Full Names: Stokes, Harold T.; Campbell, Branton J.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 73 4-13; 10.1107/S2053273316017629 1 JAN 2017
Abstract:
This paper presents a general algorithm for generating the isotropy subgroups of superspace extensions of crystallographic space groups involving arbitrary superpositions of multi-k order parameters from incommensurate and commensurate k vectors. Several examples are presented in detail in order to illuminate each step of the algorithm. The practical outcome is that one can now start with any commensurate parent crystal structure and generate a structure model for any conceivable incommensurate modulation of that parent, fully parameterized in terms of order parameters of irreducible representations at the relevant wavevectors. The resulting modulated structures have (3 + d)-dimensional superspace-group symmetry. Because incommensurate structures are now commonly encountered in the context of many scientifically and technologically important functional materials, the opportunity to apply the powerful methods of group representation theory to this broader class of structural distortions is very timely.
Title:
To superspace and beyond
Authors:
Senn, MS Author Full Names: Senn, Mark S.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 73 1-3; 10.1107/S2053273316019902 1 JAN 2017

Update: 8-Feb-2017

Title:
Field-induced magnetic states in holmium tetraboride
Authors:
Brunt, D; Balakrishnan, G; Wildes, AR; Ouladdiaf, B; Qureshi, N; Petrenko, OA Author Full Names: Brunt, D.; Balakrishnan, G.; Wildes, A. R.; Ouladdiaf, B.; Qureshi, N.; Petrenko, O. A.
Source:
PHYSICAL REVIEW B, 95 (2):10.1103/PhysRevB.95.024410 JAN 11 2017
Abstract:
A study of the zero field and field induced magnetic states of the frustrated rare earth tetraboride HoB4 has been carried out using single crystal neutron diffraction complemented by magnetization measurements. In zero field, HoB4 shows magnetic phase transitions at T-N1 = 7.1 K to an incommensurate state with a propagation vector (delta, delta, delta'), where delta = 0.02 and delta' = 0.43 and at T-N2 = 5.7 K to a noncollinear commensurate antiferromagnetic structure. Polarized neutron diffraction measurements in zero field have revealed that the incommensurate reflections, albeit much reduced in intensity, persist down to 1.5 K despite antiferromagnetic ordering at 5.7 K. At lower temperatures, application of a magnetic field along the c axis initially re-establishes the incommensurate phase as the dominant magnetic state in a narrow field range, just prior to HoB4 ordering with an up-up-down ferrimagnetic structure characterized by the (h k 1/3)-type reflections between 18 and 24 kOe. This field range is marked by the previously reported M/M-sat = 1 3 magnetization plateau, which we also see in our magnetization measurements. The region between 21 and 33 kOe is characterized by the increase in the intensity of the antiferromagnetic reflections, such as (100), the maximum of which coincides with the appearance of the narrow magnetization plateau with M/M-sat approximate to 3/5. Further increase of the magnetic field results in the stabilization of a polarized state above 33 kOe, while the incommensurate reflections are clearly present in all fields up to 59 kOe. We propose the H-T phase diagram of HoB4 for the H parallel to c containing both stationary and transitionary magnetic phases which overlap and show significant history dependence.
Title:
Gapped excitation in dense Kondo lattice CePtZn
Authors:
Harriger, L; Disseler, SM; Gunasekera, J; Rodriguez-Rivera, J; Pixley, J; Manfrinetti, P; Dhar, SK; Singh, DK Author Full Names: Harriger, L.; Disseler, S. M.; Gunasekera, J.; Rodriguez-Rivera, J.; Pixley, J.; Manfrinetti, P.; Dhar, S. K.; Singh, D. K.
Source:
PHYSICAL REVIEW B, 95 (4):10.1103/PhysRevB.95.041102 JAN 10 2017
Abstract:
We report on neutron scattering and muon spin relaxation measurements of dense Kondo lattice CePtZn. The system develops long-range incommensurate magnetic order as the temperature is reduced below T-N = 1.75 K. Interestingly, a Q-independent gap at E = 0.65 meV in the energy spectrum is found to co-exist with the long-range magnetic order. The gap persists to a very high temperature of T similar or equal to 100 K. The Q-independent characteristic and its persistence to high temperature hint that the gapped excitation may be manifesting the excited state of the ground-state doublet of the crystal-field energy levels. However, the observed broadness in the linewidth with distinct temperature and field dependencies makes it a nontrivial phenomenon. Qualitative analysis of the experimental data suggests the possible co-existence of a local critical behavior, which is onset near the critical field of H similar or equal to 3 T, with the crystal-field excitation in the dynamic properties.
Title:
Mixed-mode crack tip loading and crack deflection in 1D quasicrystals
Authors:
Wang, Z; Scheel, J; Ricoeur, A Author Full Names: Wang, Zhibin; Scheel, Johannes; Ricoeur, Andreas
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 122 (12):10.1007/s00339-016-0570-1 DEC 2016
Abstract:
Quasicrystals (QC) are a new class of materials besides crystals and amorphous solids and have aroused much attention of researchers since they were discovered. This paper presents a generalized fracture theory including the J-integral and crack closure integrals, relations between J(1), J(2) and the stress intensity factors as well as the implementation of the near-tip stress and displacement solutions of 1D QC. Different crack deflection criteria, i.e. the J-integral and maximum circumferential stress criteria, are investigated for mixed-mode loading conditions accounting for phonon-phason coupling. One focus is on the influence of phason stress intensity factors on crack deflection angles.

Update: 1-Feb-2017

Title:
Electronic structure and X-ray magnetic circular dichroism in the Ni-Mn-Ga Heusler alloys
Authors:
Antonov, VN; Bekenov, LV; Uba, S; Bonda, A; Uba, L Author Full Names: Antonov, V. N.; Bekenov, L. V.; Uba, S.; Bonda, A.; Uba, L.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 695 1826-1837; 10.1016/j.jallcom.2016.11.016 FEB 25 2017
Abstract:
The electronic structure and X-ray magnetic circular dichroism (XMCD) spectra of the Ni2MnGa and Cu doped Ni2MnGa Heusler alloys were investigated theoretically from first principles, using the fully relativistic Dirac linear MT-orbital (LMTO) band structure method. Densities of valence states, orbital and spin magnetic moments are analyzed and discussed. The electronic and magnetic structure of Ni-Mn-Ga Heusler alloys were investigated for the cubic austenitic and modulated 7M-like incommensurate martensitic phases. The X-ray absorption spectra ( XAS) and XMCD at the Mn, Ni, Ga, and Cu L-2,L-3,L- and Mn, Ni, and Ga K edges were investigated theoretically from first principles. The origin of the XMCD spectra in the Ni2MnGa compound is examined. The ab initio calculations reproduce well experimental XAS and XMCD spectra. The XAS at the Mn L-2,L-3 edges remains mostly unchanged through martensitic phase transition. A fingerprint of the martensitic phase transition has been found in the Ni L-2,L-3 XAS spectra. The experimental Ni L-3 XAS has a pronounced shoulder at the L-3 peak at around 853 eV. This peak is nearly suppressed in the martensitic state in comparison with the austenitic phase due to the lifting of the degeneracy in the Ni 3d related unoccupied electronic states. The XMCD of the martensitic phase is increased compared to the XMCD of the austenite phase at the Ni and Mn L-2,L-3 edges. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Incommensurately modulated structure and spectroscopic properties of CaGd2(MoO4)(4):Ho3+/Yb3+ phosphors for up-conversion applications
Authors:
Lim, CS; Atuchin, VV; Aleksandrovsky, AS; Molokeev, MS; Oreshonkov, AS Author Full Names: Lim, Chang Sung; Atuchin, Victor V.; Aleksandrovsky, Aleksandr S.; Molokeev, Maxim S.; Oreshonkov, Aleksandr S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 695 737-746; 10.1016/j.jallcom.2016.06.134 FEB 25 2017
Abstract:
CaGd2(MoO4)(4):Ho3+/Yb3+ phosphors doped by Ho3+ and Yb3+ (Ho3+ = 0 and 0.05, and Yb3+ = 0, 0.35, 0.40, 0.45 and 0.50) were successfully synthesized by the microwave sol-gel method. The synthesized particles, being formed after heat-treatment at 900 degrees C for 16 h, showed a well crystallized morphology. All compounds are (3 + 2)D incommensurately modulated with superspace group I4(1)/alpha(alpha,beta,0)00(-beta,alpha,0)00. It was found that parameter (alpha(2) + beta(2))(1)/(2) is proportional to cell parameter a for all studied compositions and, therefore, modulation vector k is the same for all known CaRE2(MoO4)(4) compounds. The modulation vector invariance is a specific and valuable feature of this type of the structure. Under the excitation at 980 nm, the doped particles exhibited the yellow emission composed of green (545-nm) and red (655-nm) emission bands due to frequency upconversion (UC). The pump power dependence and CIE chromaticity of the UC emission were evaluated. The shape of UC bands in CaGd2(MoO4)(4):Ho3+/Yb3+ is dependent on the Yb content due to the influence of the crystal field affecting a holmium ion. 13 Raman-active modes of the CaGd2(MoO4)(4) lattice were identified via a comparison of experimental Raman spectra and the lattice dynamics simulation results. Four additional Raman lines were found in the region of stretching vibrations and, at least, two additional modes are present in the bending mode region. These additional modes are ascribed to incommensurate crystal lattice modulation. Luminescence bands of Ho ions are severely broadened due to a statistical disorder in the CaGd2-xYby (MoO4)(4) lattice. (C) 2016 Published by Elsevier B.V.
Title:
Commensurate-incommensurate magnetic phase transition in the new Yb1-xLuxMn6Sn6 compounds
Authors:
Eichenberger, L; Venturini, G; Malaman, B; Nataf, L; Baudelet, F; Mazet, T Author Full Names: Eichenberger, L.; Venturini, G.; Malaman, B.; Nataf, L.; Baudelet, F.; Mazet, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 695 286-293; 10.1016/j.jallcom.2016.10.191 FEB 25 2017
Abstract:
We investigate the magnetic properties of the new Yb1-xLuxMn6Sn6 (0.00 <= x <= 1.00) alloys from AC/DC magnetization and powder neutron diffraction experiments. Room-temperature XANES measurements at Yb L-3 edge indicate that Yb is in an intermediate valent state (upsilon(Yb) similar to 2.6) in the whole Yb1-xLuxMn6Sn6 series. In these compounds only the Mn sublattice magnetically orders with an atomic Mn moment close to m(Mn) similar to 2.2 mu(B) at 2 K throughout the series. Lu substitution yields a crossover from ferromagnetism to antiferromagnetism of the Mn sublattice. In RMn6Sn6 compounds, this is the first time that such transition of the Mn sublattice is induced by substitution on the R site. The enhancement of the antiferromagnetic interactions likely results from modification in valence electron concentration since intermediate valent Yb is replaced by trivalent Lu. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Pushing the limits of crystallography
Authors:
Wolny, J; Buganski, I; Kuczera, P; Strzalka, R Author Full Names: Wolny, Janusz; Buganski, Ireneusz; Kuczera, Pawel; Strzalka, Radoslaw
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 2106-2115; 10.1107/S160057671601637X 6 DEC 2016
Abstract:
A very serious concern of scientists dealing with crystal structure refinement, including theoretical research, pertains to the characteristic bias in calculated versus measured diffraction intensities, observed particularly in the weak reflection regime. This bias is here attributed to corrective factors for phonons and, even more distinctly, phasons, and credible proof supporting this assumption is given. The lack of a consistent theory of phasons in quasicrystals significantly contributes to this characteristic bias. It is shown that the most commonly used exponential Debye-Waller factor for phasons fails in the case of quasicrystals, and a novel method of calculating the correction factor within a statistical approach is proposed. The results obtained for model quasiperiodic systems show that phasonic perturbations can be successfully described and refinement fits of high quality are achievable. The standard Debye-Waller factor for phonons works equally well for periodic and quasiperiodic crystals, and it is only in the last steps of a refinement that different correction functions need to be applied to improve the fit quality.
Title:

Update: 19-Jan-2017

Title:
K8Nb7P7O39: a new type of complicated incommensurately modulated structure and photoluminescence properties of Eu3+-doped solid solutions
Authors:
Zhao, D; Cui, JY; Han, HX; Li, C Author Full Names: Zhao, Dan; Cui, Jun-Yan; Han, Hong-Xian; Li, Can
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 4 (48):11436-11448; 10.1039/c6tc03022j 2016
Abstract:
A new type of potassium niobium phosphate, K8Nb7P7O39, has been prepared and its structure has been determined by single crystal X-ray diffraction analysis. The results show that it crystallizes in a novel (3 + 1)-dimensional incommensurately modulated structure with a triclinic superspace group P (1) over bar(alpha beta gamma)O and modulation vector q = -0.35281a* + 0.17630b* + 0.25807c*. The structure of K8Nb7P7O39 contains [K-3.66](infinity) N, [K-4.34](infinity) N and [Nb7P7O39](infinity) N layers alternately stacked along the c-axis. In this structure, seven not fully occupied K atoms (six of them come from the [K-3.66](infinity) N layer and the remaining one comes from the [K-4.34]infinity N layer) are thought to be the dominant factors in driving the structural modulation. The strong occupational modulation in combination with positional modulation of these seven K atoms can be described by crenel-type modulation functions. Furthermore, elemental composition, UV-Vis absorption spectrum, SEM morphology and photoluminescence properties induced by Eu3+-doping have been studied for K8Nb7P7O39. The excitation spectrum covers a wide range from 362 to 465 nm and it matches well with the emission of near-UV InGaN-based LED chips and bluish-green LED chips, indicating that K8Nb7P7O39: Eu3+ has potential as a red-emitting phosphor for LED applications.
Title:
Generation of Basis Vectors for Magnetic Structures and Displacement Modes
Authors:
Davies, ZL; Wills, AS Author Full Names: Davies, Z. L.; Wills, A. S.
Source:
ADVANCES IN CONDENSED MATTER PHYSICS, 10.1155/2016/3960145 2016
Abstract:
Increasing attention is being focused on the use of symmetry-adapted functions to describe magnetic structures, structural distortions, and incommensurate crystallography. Though the calculation of such functions iswell developed, significant difficulties can arise such as the generation of too many or too few basis functions to minimally span the linear vector space. We present an elegant solution to these difficulties using the concept of basis sets and discuss previous work in this area using this concept. Further, we highlight the significance of unitary irreducible representations in this method and provide the first validation that the irreducible representations of the crystallographic space groups tabulated by Kovalev are unitary.
Title:
K8Nb7P7O39: a new type of complicated incommensurately modulated structure and photoluminescence properties of Eu3+-doped solid solutions
Authors:
Zhao, D; Cui, JY; Han, HX; Li, C Author Full Names: Zhao, Dan; Cui, Jun-Yan; Han, Hong-Xian; Li, Can
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 4 (48):11436-11448; 10.1039/c6tc03022j 2016
Abstract:
A new type of potassium niobium phosphate, K8Nb7P7O39, has been prepared and its structure has been determined by single crystal X-ray diffraction analysis. The results show that it crystallizes in a novel (3 + 1)-dimensional incommensurately modulated structure with a triclinic superspace group P (1) over bar(alpha beta gamma)O and modulation vector q = -0.35281a* + 0.17630b* + 0.25807c*. The structure of K8Nb7P7O39 contains [K-3.66](infinity) N, [K-4.34](infinity) N and [Nb7P7O39](infinity) N layers alternately stacked along the c-axis. In this structure, seven not fully occupied K atoms (six of them come from the [K-3.66](infinity) N layer and the remaining one comes from the [K-4.34]infinity N layer) are thought to be the dominant factors in driving the structural modulation. The strong occupational modulation in combination with positional modulation of these seven K atoms can be described by crenel-type modulation functions. Furthermore, elemental composition, UV-Vis absorption spectrum, SEM morphology and photoluminescence properties induced by Eu3+-doping have been studied for K8Nb7P7O39. The excitation spectrum covers a wide range from 362 to 465 nm and it matches well with the emission of near-UV InGaN-based LED chips and bluish-green LED chips, indicating that K8Nb7P7O39: Eu3+ has potential as a red-emitting phosphor for LED applications.
Title:
Generation of Basis Vectors for Magnetic Structures and Displacement Modes
Authors:
Davies, ZL; Wills, AS Author Full Names: Davies, Z. L.; Wills, A. S.
Source:
ADVANCES IN CONDENSED MATTER PHYSICS, 10.1155/2016/3960145 2016
Abstract:
Increasing attention is being focused on the use of symmetry-adapted functions to describe magnetic structures, structural distortions, and incommensurate crystallography. Though the calculation of such functions iswell developed, significant difficulties can arise such as the generation of too many or too few basis functions to minimally span the linear vector space. We present an elegant solution to these difficulties using the concept of basis sets and discuss previous work in this area using this concept. Further, we highlight the significance of unitary irreducible representations in this method and provide the first validation that the irreducible representations of the crystallographic space groups tabulated by Kovalev are unitary.

Update: 12-Jan-2017

Title:
Incommensurate spin density wave as a signature of spin-orbit coupling and precursor of topological superconductivity
Authors:
Farrell, A; Wu, PK; Kao, YJ; Pereg-Barnea, T Author Full Names: Farrell, Aaron; Wu, P. -K.; Kao, Y. -J.; Pereg-Barnea, T.
Source:
PHYSICAL REVIEW B, 94 (21):10.1103/PhysRevB.94.214424 DEC 22 2016
Abstract:
On a square lattice, the Hubbard model at half filling reduces to the Heisenberg model and exhibits antiferromagnetism. When doped away from half filling this model gives rise to d-wave superconductivity. This behavior is reminiscent of the phenomenology of the cuprate family with their high T(c)d-wave superconductivity and their antiferromagnetic parent compound. It is therefore interesting to study an extension of the Hubbard model which includes spin orbit coupling. We have previously studied this model away from half filling [see, for example, Farrell and Pereg-Barnea, Phys. Rev. B 89, 035112 (2014)] and found that the addition of spin-orbit coupling and Zeeman field leads to topological superconductivity with d + id pairing function. In this paper we are interested in the 'parent compound' of this state. Namely, we study the half filling, strong coupling limit of the square lattice Hubbard model with spin orbit coupling and Zeeman field. The strong coupling expansion of the model is a spin model which contains compass anisotropy and Dzyaloshinsky-Moriya interaction on top of the usual Heisenberg term. We analyze this spin model classically and find an incommensurate spin density wave (ISDW) for low Zeeman fields. This ISDWhas a wave vector (Q) over right arrow which deviates from (pi, pi) by an amount which is proportional to the spin-orbit coupling and can therefore serve as a signature. We study the stability of the ISDW phase using spin wave theory and find a stable and an unstable region. At higher but moderate Zeeman fields we find a tilted antiferromagnet and a ferromagnet at high Zeeman fields.
Title:
Anisotropic spin fluctuations in Sr2RuO4: Role of spin-orbit coupling and induced strain
Authors:
Cobo, S; Ahn, F; Eremin, I; Akbari, A Author Full Names: Cobo, Sergio; Ahn, Felix; Eremin, Ilya; Akbari, Alireza
Source:
PHYSICAL REVIEW B, 94 (22):10.1103/PhysRevB.94.224507 DEC 14 2016
Abstract:
We analyze the spin anisotropy of themagnetic susceptibility of Sr2RuO4 in the presence of spin-orbit coupling and anisotropic strain using quasi-two-dimensional tight-binding parametrization fitted to the angle-resolved photoemission spectroscopy results. Similar to the previous observations we find the in-plane polarization of the low-q magnetic fluctuations and the out-of-plane polarization of the incommensurate magnetic fluctuation at the nestingwave-vector Q(1) = (2/3 pi, 2/3 pi) but also nearly isotropic fluctuations nearQ(2) = (pi/6, pi/6). Furthermore, one finds that, apart from the high-symmetry direction of the tetragonal Brillouin zone, the magnetic anisotropy is maximal, i. e., chi(xx) not equal chi(yy) not equal chi(zz) reflected in the x polarization of the intraband nestingwave-vectorQ(3) = (pi/2, pi). This is a consequence of the orbital anisotropy of the t(2g) orbitals in momentum space. We also study how the magnetic anisotropy evolves in the presence of the strain and find strong Ising-like ferromagnetic fluctuations near the Lifshitz transition for the xy band.
Title:
Vacancy pairing and superstructure in the high-pressure silicate K1.5Mg2Si2O7H0.5: a new potential host for potassium in the deep Earth
Authors:
Welch, MD; Bindi, L; Petricek, V; Plasil, J Author Full Names: Welch, M. D.; Bindi, L.; Petricek, V.; Plasil, J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 822-827; 10.1107/S2052520616014049 6 DEC 2016
Abstract:
The high-pressure silicate K1.5Mg2Si2O7H0.5, synthesized and characterized by Welch et al. [(2012), Am. Mineral. 97, 1849-1857], has been re-examined with the aim of determining the nature of the superstructure noted in their study. The composition corresponds to a 1:1 combination of KMg2Si2O7H and K2Mg2Si2O7 end-members, but it is not a solid solution. Single-crystal X-ray diffraction data for one of the original K1.5Mg2Si2O7H0.5 crystals synthesized at 16 GPa/1573 K, has been collected using a much longer exposure time in order to improve the intensity statistics of weak superlattice reflections identified by Welch et al. (2012). The superstructure has been determined using a superspace approach as having the superspace group Cmcm(0,beta,0)00s and t(0) = 1/16 with refined parameters a = 8.7623 (10), b = 5.0703 (7), c = 13.2505 (11) angstrom, V = 588.69 (12) angstrom(3). This structure corresponds to one with the conventional space group Pbnm and unit-cell parameters a = 8.7623 (10), b = 20.281 (3), c = 13.2505 (11) angstrom, V=2354.7 (5) angstrom(3) and is based upon a super-sheet motif in which ordering involves rows of pairs of vacant interlayer K sites. This is the third topologically distinct structure type for the KMg2Si2O7H-K2Mg2Si2O7 join and suggests that there is very limited solid solution, and so it can be expected that each of the three structures (P6(3)cm, P (3) over bar 1m and Pbnm) has its own stability field, rather than being part of a continuous compositional series based upon a single structure type. As such, K1.5Mg2Si2O7H0.5 should be considered as a potentially significant host of K in the Earth's mantle.
Title:
Incommensurate density modulation in a Na-rich plagioclase feldspar: Z-contrast imaging and single-crystal X-ray diffraction study
Authors:
Xu, HF; Jin, SY; Noll, BC Author Full Names: Xu, Huifang; Jin, Shiyun; Noll, Bruce C.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 904-915; 10.1107/S205252061601578X 6 DEC 2016
Abstract:
Plagioclase feldspars are the most abundant mineral in the Earth's crust. Intermediate plagioclase feldspars commonly display incommensurately modulated or aperiodic structures. Z-contrast images show both Ca-Na ordering and density modulation. The local structure of lamellae domains has I1-like symmetry. The neighboring lamellae domains are in an inversion twinning relationship. With a state-of-the-art X-ray diffraction unit, second-order satellite reflections (f-reflections) are observed for the first time in andesine (An(45)), a Na-rich e-plagioclase. The f-reflections indicate a structure with a density modulation which is close to a Ca-rich e-plagioclase. The similarity between this e-andesine structure and previously solved e-labradorite structure is confirmed. Refinement of the structure shows density modulation of similar to 7 mol% in compositional variation of the anorthite (An) component. The results from Z-contrast imaging and low-temperature single X-ray diffraction (XRD) provide a structure consistent with density modulation. The discovery of f-reflections in Na-rich e-plagioclase extends the composition range of e1 structure with density modulation to as low as at least An45, which is the lower end of the composition range of Boggild intergrowth. The new result supports the loop-shaped solvus for Boggild intergrowth, below which is a homogenous stable area for e1 structure in the phase diagram. The phase transition between e2 structure without density modulation and e1 structure with density modulation should happen at low temperature. There is a change in modulation period accompanying the phase transition, as well as higher occupancy of AL in the T(1)o site. The andesine with density modulation also indicates extremely slow cooling of its host rock.
Title:
Elasto-Dynamics of Quasicrystals
Authors:
Li, W; Fan, TY Author Full Names: Li, Wu; Fan, Tianyou
Source:
CRYSTALS, 6 (11):10.3390/cryst6110152 NOV 2016
Abstract:
A review on elasto-dynamics of quasicrystals (QCs) and their applications based on mathematical elasticity is given. In this study, recent studies on elasto-dynamics of QCs are reviewed, in which the focus of the problem lies in the role of phason variables and the coupling effect between phonons and phasons in the dynamic deformation process. On summarizing and describing the development of the elastic dynamics of QCs, this review mainly presents theelasto-dynamics of QCs and their application in a variety of research areas, ranging from problems with different QCs, including one-, two-, and three-dimensional QCs to various coupling problems. The plane elasticity and anti-plane elasticity of quasicrystals are included in this review.
Title:
Quasicrystals and Other Aperiodic Structures in Mineralogy
Authors:
Pina, CM; Lopez-Acevedo, V Author Full Names: Pina, Carlos M.; Lopez-Acevedo, Victoria
Source:
CRYSTALS, 6 (11):10.3390/cryst6110137 NOV 2016
Abstract:
In this article, we first present and discuss eighteenth-century descriptions of minerals that contributed decisively to the development of crystallography. Remarkably, these old crystallographic descriptions included morphologies with symmetries incompatible with an internal periodic order of atoms, which, however, have been recognised to be characteristics of quasicrystals. Moreover, we also review a number of studies of minerals with aperiodic crystal structures, including recently reported natural quasicrystals of extra-terrestrial origin. Finally, we discuss the current investigations addressing the search for new quasicrystalline minerals in nature.
Title:
Neutron diffraction study of low-temperature magnetic phase diagram of an isosceles-triangular-lattice Ising antiferromagnet CoNb2O6
Authors:
Kobayashi, S; Mitsuda, S; Hosaka, S; Tamatsukuri, H; Nakajima, T; Koorikawa, H; Prokes, K; Kiefer, K Author Full Names: Kobayashi, S.; Mitsuda, S.; Hosaka, S.; Tamatsukuri, H.; Nakajima, T.; Koorikawa, H.; Prokes, K.; Kiefer, K.
Source:
PHYSICAL REVIEW B, 94 (13):10.1103/PhysRevB.94.134427 OCT 27 2016
Abstract:
A low-temperature magnetic phase diagram under magnetic fields along the orthorhombic a axis of an isosceles-triangular-lattice antiferromagnet CoNb2O6 was investigated through single-crystal neutron diffraction measurements made at temperatures down to T = 0.5K. We produced a phase diagram that consists of three magnetically ordered phases, i.e., the antiferromagnetic (AF), the incommensurate sinusoidal magnetic (IC), and the induced ferromagnetic (IFM) phases, which were characterized by the propagation wave vectors Q = (01/20), (0 q 0), and (0 0 0), respectively. We found that a field-induced ferrimagnetic phase with Q = (01/40) that had been observed by previous neutron diffraction studies down to T = 1.8K [H. Weitzel et al., Phys. Rev. B 62, 12146 (2000)] does not exist as a single equilibrium phase, but rather it always coexists with the other ordered phases near the triple point where the AF, IC, and IFM phases meet. We also found that the relaxation time of the system becomes extremely long below T = 0.6 K in comparison with our observation time; this was considered to possibly be the reason for magnetization plateaus appearing at T = 0.5K. These plateaus have a half-saturation magnetization, from which another field-induced state was inferred in previous magnetization measurements [J. Phys. Soc. Jpn. 63, 2706 (1994)].
Title:
An Icosahedral Quasicrystal and Its 1/0 Crystalline Approximant in the Ca-Au-Al System
Authors:
Pham, J; Kreyssig, A; Goldman, AI; Miller, GJ Author Full Names: Pham, Joyce; Kreyssig, Andreas; Goldman, Alan I.; Miller, Gordon J.
Source:
INORGANIC CHEMISTRY, 55 (20):10425-10437; 10.1021/acs.inorgchem.6b01636 OCT 17 2016
Abstract:
A new icosahedral quasicrystalline phase, CaAu4.5-xAl1.5+x [0.11 <= x <= 0.40(6); CaAu4.4Al1.6, a(QC) = 5.383(4) angstrom, and Pm (3) over bar(5) over bar], and its lowest-order 1/0 cubic crystalline approximant phase, CaAu3+xAl1-x [0 <= x <= 0.31(1); a = 9.0766(5)-9.1261(8) angstrom, Pa (3) over bar (No. 205), and Pearson symbol cP40], have been discovered in the Ca-poor region of the Ca-Au-Al system. In the crystalline approximant, eight [Au3-xAl1+x] tetrahedra fill the unit cell, and each tetrahedron is surrounded by four Ca atoms, thus forming a three-dimensional network of {Ca-4/4[Au3-xAl1+x]} tetrahedral stars. A computational study of Au and Al site preferences concurs with the experimental results, which indicate a preference for near-neighbor Au-Al interactions over Au-Au and Al-Al interactions. Analysis of the electronic density of states and the associated crystal orbital Hamilton population curves was used to rationalize the descriptions of CaAu4.5-xAl1.5+x [0.11 <= x <= 0.46(6)] and CaAu3+xAl1-x [0 <= x <= 0.31(1)] as polar intermetallic species, whereby Ca atoms engage in polar covalent bonding with the electronegative, electron-deficient [Au3-xAl1+x] tetrahedral clusters and the observed phase width of the crystalline approximant.
Title:
Quantum Simulation of a 2D Quasicrystal with Cold Atoms
Authors:
Mace, N; Jagannathan, A; Duneau, M Author Full Names: Mace, Nicolas; Jagannathan, Anuradha; Duneau, Michel
Source:
CRYSTALS, 6 (10):10.3390/cryst6100124 OCT 2016
Abstract:
We describe a way to obtain a two-dimensional quasiperiodic tiling with eight-fold symmetry using cold atoms. One can obtain a series of such optical tilings, related by scale transformations, for a series of specific values of the chemical potential of the atoms. A theoretical model for the optical system is described and compared with that of the well-known cut-and-project method for the Ammann-Beenker tiling. The relation between the two tilings is discussed. This type of cold atom structure should allow the simulation of several important lattice models for interacting quantum particles and spins in quasicrystals.
Title:
Detection of a Cooper-pair density wave in Bi2Sr2CaCu2O8+x
Authors:
Hamidian, MH; Edkins, SD; Joo, SH; Kostin, A; Eisaki, H; Uchida, S; Lawler, MJ; Kim, EA; Mackenzie, AP; Fujita, K; Lee, J; Davis, JCS Author Full Names: Hamidian, M. H.; Edkins, S. D.; Joo, Sang Hyun; Kostin, A.; Eisaki, H.; Uchida, S.; Lawler, M. J.; Kim, E. -A.; Mackenzie, A. P. .; Fujita, K.; Lee, Jinho; Davis, J. C. Seamus
Source:
NATURE, 532 (7599):343-+; 10.1038/nature17411 APR 21 2016
Abstract:
The quantum condensate of Cooper pairs forming a superconductor was originally conceived as being translationally invariant. In theory, however, pairs can exist with finite momentum Q, thus generating a state with a spatially modulated Cooper-pair density(1,2). Such a state has been created in ultracold Li-6 gas(3) but never observed directly in any superconductor. It is now widely hypothesized that the pseudogap phase (4) of the copper oxide superconductors contains such a 'pair density wave' state(5-21). Here we report the use of nanometre-resolution scanned Josephson tunnelling microscopy (22-24) to image Cooper pair tunnelling from a d-wave superconducting microscope tip to the condensate of the superconductor Bi2Sr2CaCu2O8+x. We demonstrate condensate visualization capabilities directly by using the Cooper-pair density variations surrounding zinc impurity atoms(25) and at the Bi2Sr2CaCu2O8+x crystal supermodulation(26). Then, by using Fourier analysis of scanned Josephson tunnelling images, we discover the direct signature of a Cooper-pair density modulation at wavevectors Q(P) approximate to (0.25, 0)2 pi/a(0) and (0, 0.25)2 pi/a(0) in Bi2Sr2CaCu2O8+x. The amplitude of these modulations is about five per cent of the background condensate density and their form factor exhibits primarily s or s' symmetry. This phenomenology is consistent with Ginzburg-Landau theory(5,13,14) when a charge density wave(5,27) with d-symmetry form factor(28-30) and wavevector Q(C) = Q(P) coexists with a d-symmetry superconductor; it is also predicted by several contemporary microscopic theories for the pseudogap phase (18-21).

Update: 4-Jan-2017

Title:
Monoclinic superstructure of Pr3Rh4Ge4
Authors:
Vosswinkel, D; Hoffmann, RD; Greiwe, M; Eul, M; Pottgen, R Author Full Names: Vosswinkel, Daniel; Hoffmann, Rolf-Dieter; Greiwe, Magnus; Eul, Matthias; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (11):641-651; 10.1515/zkri-2016-1992 NOV 2016
Abstract:
Pr3Rh4Ge4 was synthesized by melting of the elements in an arc-melting furnace followed by annealing in a sealed tantalum ampoule in a muffle furnace. Structure refinement was based on temperature dependent single-crystal X-ray diffractometer data. At ambient temperature Pr3Rh4Ge4 adopts the U3Ni4Si4 type structure with strongly enhanced anisotropic displacement parameters for Rh1. Below 230 K additional reflections start to appear and at 110 K the structure could be described with the (3+1)D superspace group I2/m(alpha 0 gamma)00; alpha = 1/2, gamma = 1/2; (Z = 2). This commensurately *modulated structure* could be refined with 1448 F-2 values, 39 variables and residuals of wR = 0.0417 for the main reflections and wR = 0.1520 for the satellites of 1st order, [a = 408.36(2), b = 421.12(3) and c = 2504.4(2) pm]. The commensurate description could be transformed to a 3D supercell with space group A2/m and Z = 4: a = 816.72(2), b = 421.12(3), c = 2537.5(1) pm, beta = 99.26(1)degrees, 1448 F-2 values, 69 variables and wR = 0.0499. The relation of the U3Ni4Si4 type structure, the (3+ 1)D modulated and the 3D supercell is discussed on the basis of a group-subgroup scheme. Temperature dependent magnetic susceptibility data reveal Curie-Weiss paramagnetism with an experimental moment of 3.72(2) mu(B) /Pr atom and a Weiss constant of -12.6(5) K. No magnetic ordering is evident down to 3 K.

Update: 29-Dec-2016

Title:
Collisions in outer space produced an icosahedral phase in the Khatyrka meteorite never observed previously in the laboratory
Authors:
Bindi, L; Lin, C; Ma, C; Steinhardt, PJ Author Full Names: Bindi, Luca; Lin, Chaney; Ma, Chi; Steinhardt, Paul J.
Source:
Scientific Reports, 6 10.1038/srep38117 DEC 8 2016
Abstract:
We report the first occurrence of an icosahedral quasicrystal with composition Al-62.0(8) Cu-31.2(8) Fe-6.8(4), outside the measured equilibrium stability field at standard pressure of the previously reported Al-Cu-Fe quasicrystal (AlxCuyFez, with x between 61 and 64, y between 24 and 26, z between 12 and 13%). The new icosahedral mineral formed naturally and was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite that experienced shock metamorphism, local melting (with conditions exceeding 5 GPa and 1,200 degrees C in some locations), and rapid cooling, all of which likely resulted from impact-induced shock in space. This is the first example of a quasicrystal composition discovered in nature prior to being synthesized in the laboratory. The new composition was found in a grain that has a separate metal assemblage containing icosahedrite (Al63Cu24Fe13), currently the only other known naturally occurring mineral with icosahedral symmetry (though the latter composition had already been observed in the laboratory prior to its discovery in nature). The chemistry of both the icosahedral phases was characterized by electron microprobe, and the rotational symmetry was confirmed by means of electron backscatter diffraction.
Title:
Spin-lattice coupling mediated multiferroicity in (ND4)(2)FeCl5 center dot D2O
Authors:
Tian, W; Cao, H; Wang, J; Ye, F; Matsuda, M; Yan, JQ; Liu, Y; Garlea, VO; Agrawal, HK; Chakoumakos, BC; Sales, BC; Fishman, RS; Fernandez-Baca, JA Author Full Names: Tian, W.; Cao, Huibo; Wang, Jincheng; Ye, Feng; Matsuda, M.; Yan, J. -Q.; Liu, Yaohua; Garlea, V. O.; Agrawal, Harish K.; Chakoumakos, B. C.; Sales, B. C.; Fishman, Randy S.; Fernandez-Baca, J. A.
Source:
PHYSICAL REVIEW B, 94 (21):10.1103/PhysRevB.94.214405 DEC 7 2016
Abstract:
We report a neutron diffraction study of the multiferroic mechanism in (ND4)(2)FeCl5 center dot D2O, a molecular compound that exhibits magnetically induced ferroelectricity. This material exhibits two successive magnetic transitions on cooling: a long-range order transition to an incommensurate (IC) collinear sinusoidal spin state at T-N = 7.3 K, followed by a second transition to an IC cycloidal spin state at T-FE = 6.8 K, the latter of which is accompanied by spontaneous ferroelectric polarization. The cycloid structure is strongly distorted by spin-lattice coupling, as evidenced by the observations of both odd and even higher-order harmonics associated with the cycloid wave vector, and a weak commensurate phase that coexists with the IC phase. The second-order harmonic appears at TFE, thereby providing unambiguous evidence that the onset of the electric polarization is accompanied by a lattice modulation due to spin-lattice interaction. The neutron results, in conjunction with the negative thermal expansion and large magnetostriction observed in Ref. [19], indicate that spin-lattice coupling plays a critical role in the ferroelectric mechanism of (ND4)(2)FeCl5 center dot D2O.
Title:
Hofstadter butterfly of a quasicrystal
Authors:
Fuchs, JN; Vidal, J Author Full Names: Fuchs, Jean-Noel; Vidal, Julien
Source:
PHYSICAL REVIEW B, 94 (20):10.1103/PhysRevB.94.205437 NOV 28 2016
Abstract:
The energy spectrum of a tight-binding Hamiltonian is studied for the two-dimensional quasiperiodic Rauzy tiling in a perpendicular magnetic field. This spectrum known as a Hofstadter butterfly displays a very rich pattern of bulk gaps that are labeled by four integers, instead of two for periodic systems. The role of phason-flip disorder is also investigated in order to extract genuinely quasiperiodic properties. This geometric disorder is found to only preserve main quantum Hall gaps.
Title:
Magnetic field-temperature phase diagrams of multiferroic (Ni0.9Co0.1)(3)V2O8
Authors:
Qureshi, N; Ressouche, E; Mukhin, AA; Ivanov, VY; Barilo, SN; Shiryaev, SV; Skumryev, V Author Full Names: Qureshi, N.; Ressouche, E.; Mukhin, A. A.; Ivanov, V. Yu.; Barilo, S. N.; Shiryaev, S. V.; Skumryev, V.
Source:
PHYSICAL REVIEW B, 94 (17):10.1103/PhysRevB.94.174441 NOV 28 2016
Abstract:
We present macroscopic and neutron diffraction data on multiferroic lightly Co doped Ni3V2O8. The magnetic H-T phase diagrams have been derived from magnetization and electric polarization measurements with field directions parallel to the principal crystallographic axes. While the phase diagram for H parallel to b is very similar to that of the parent compound Ni3V2O8 for the commonly involved phases, the zero-field phases in (Ni0.9Co0.1)(3)V2O8 show a stronger instability for applied magnetic fields along the a or c axis. Neutron single-crystal diffraction revealed the magnetic structure of the field-induced phase for H parallel to c with a collinear spin alignment along the a and b axes for the two magnetically inequivalent sites. A pronounced irreversibility has been observed for the transition between the zero-field spin cycloid and the field-induced phase, which is manifested in a propagation vector change from q = (0.322 0 0) to q = (0.306 0 0), with slight modifications of the magnetic structure after reentering the zero-field phase. The reentrant phase is characterized by a significantly larger b component of the cross-tie site spin, therefore showing remanent features of the high-field phase. For H parallel to a the magnetization data reveal anomalies, one of which was proved to reflect a field-induced transition from the cycloidally to the sinusoidally modulated magnetic structure.

Update: 21-Dec-2016

Title:
Enhancement of glass-forming ability and mechanical property of Zr-based Zr-Al-Ni bulk metallic glasses with addition of Pd
Authors:
Hua, NB; Chen, WZ Author Full Names: Hua, Nengbin; Chen, Wenzhe
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 693 816-824; 10.1016/j.jallcom.2016.09.263 FEB 5 2017
Abstract:
The effects of partial substitution of Ni by Pd in the high-Zr-based Zr65Al10Ni25-xPdx (at.%, x = 0, 5 and 10) alloys on their glass-forming ability (GFA), crystallization kinetics and mechanical property were investigated. The critical diameter for glass formation is increased from 3 mm for Zr65Al10Ni25 alloy to 5 mm for Zr65Al10Ni15Pd10. An icosahedral quasicrystal phase precipitates in the amorphous matrix in the first crystallization step of Zr-Al-Ni-Pd BMGs, implying that strong icosahedral short/medium-range order (IS/MRO) may exist in the Pd-containing alloys. In additional, Pd-bearing Zr-based BMGs present a lower Avrami exponent n indicating the higher stabilization of the supercooled liquid. Moreover, the Zr-Al-Ni-Pd BMGs exhibit larger compressive plasticity, higher notch toughness and Poisson's ratio than those of Zr65Al10Ni25 alloy, which can be correlated with the existence of strong IS/MRO clusters in amorphous phase. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Microstructure evolution and mechanical properties of quasicrystal-reinforced Mg-Zn-Y alloy subjected to ultrasonic vibration
Authors:
Fang, XG; Wu, SS; Lu, SL; Wang, J; Yang, X Author Full Names: Fang, Xiaogang; Wu, Shusen; Lu, Shulin; Wang, Jing; Yang, Xiong
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 679 372-378; 10.1016/j.msea.2016.10.035 JAN 2 2017
Abstract:
Although the icosahedral quasicrystal phase found in Mg-Zn-Y alloys has some outstanding characteristics, the coarse alpha-Mg dendrites and the agglomeration of the secondary phases in as-cast microstructure restrict the improvements in the mechanical properties. In this study, the semisolid slurry of Mg-6Zn-1.4Y alloy was obtained with ultrasonic vibration (UV) treatment and then formed by rheo-squeeze casting (RSC) process. The effects of UV on the microstructure evolution and mechanical properties were systematically investigated. With UV, primary a-Mg grains and the agglomerated Mg-Zn-Y compounds were significantly refined. Notably, a large mass of fine and granular quasicrystal I-phase particles precipitate in the grains at the later stage of solidification. The RSC alloy subjected to 6 W/mL UV exhibited the optimal mechanical properties, with the yield strength of 129 MPa, the ultimate tensile strength of 231 MPa and the elongation of 18.5%. Compared with the samples without UV, they are increased by 18.3%, 14.9% and 55.5%, respectively.
Title:
Intertwined nematic orders in a frustrated ferromagnet
Authors:
Iqbal, Y; Ghosh, P; Narayanan, R; Kumar, B; Reuther, J; Thomale, R Author Full Names: Iqbal, Yasir; Ghosh, Pratyay; Narayanan, Rajesh; Kumar, Brijesh; Reuther, Johannes; Thomale, Ronny
Source:
PHYSICAL REVIEW B, 94 (22):10.1103/PhysRevB.94.224403 DEC 2 2016
Abstract:
We investigate the quantum phases of the frustrated spin-1/2 J(1)-J(2)-J(3) Heisenberg model on the square lattice with ferromagnetic J(1) and antiferromagnetic J(2) and J(3) interactions. Using the pseudofermion functional renormalization group technique, we find an intermediate paramagnetic phase located between classically ordered ferromagnetic, stripy antiferromagnetic, and incommensurate spiral phases. We observe that quantum fluctuations lead to significant shifts of the spiral pitch angles compared to the classical limit. By computing the response of the system with respect to various spin rotation and lattice symmetry-breaking perturbations, we identify a complex interplay between different nematic spin states in the paramagnetic phase. While retaining time-reversal invariance, these phases either break spin-rotation symmetry, lattice-rotation symmetry, or a combination of both. We therefore propose the J(1)-J(2)-J(3) Heisenberg model on the square lattice as a paradigmatic example where different intimately connected types of nematic orders emerge in the same model.
Title:
Cation distribution in nanocrystalline (Co, Ni)Al2O4 Spinel
Authors:
Agarwal, H; Yadav, TP; Srivastava, ON; Shaz, MA Author Full Names: Agarwal, Harshit; Yadav, T. P.; Srivastava, O. N.; Shaz, M. A.
Source:
CERAMICS INTERNATIONAL, 42 (16):19429-19432; 10.1016/j.ceramint.2016.08.193 DEC 2016
Abstract:
In the present study, the cations Co2+/Ni2+ and Al3+ distribution in nanocrystalline (Co, Ni)Al2O4 spinel have been investigated using X-ray and transmission electron microscopy. The nanocrystalline (Co, Ni) Al2O4 spinet has been synthesized using mechanically activated Al70Co15Ni15 quasicrystalline precursor through annealing at 600 degrees C in controlled oxygen atmosphere. The mechanical activation of single phasic decagonal Al70Co15Ni15 quasicrystal was carried out in a high energy attritor ball mill for 40 h with 40:1 ball to powder ratio using toluene as a process control agent. The high resolution x-ray diffraction data has been refined by the Rietveld method using JANA2006 and subsequently, the corresponding structure has been constructed using Diamond4.0. The structure was also confirmed by analysis of transmission electron microscopy linearized diffraction pattern profile of D-values and corresponding plane. These analyses indicate that the cations Co2+ and Ni2+ distributed in the tetrahedral coordinated sites are the dominant species in the normal spinel phase. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Title:
Commensurate Superstructure of the {Cu(NO3)(H2O)}(HTae)(Bpy) Coordination Polymer: An Example of 2D Hydrogen-Bonding Networks as Magnetic Exchange Pathway
Authors:
de Luis, RF; Larrea, ES; Orive, J; Lezama, L; Arriortua, MI Author Full Names: Fernandez de Luis, Roberto; Larrea, Edurne S.; Orive, Joseba; Lezama, Luis; Arriortua, Maria I.
Source:
INORGANIC CHEMISTRY, 55 (22):11662-11675; 10.1021/acs.inorgchem.6b01199 NOV 21 2016
Abstract:
The average and commensurate superstructures of the one-dimensional coordination polymer {Cu(NO3)(H2O)}(HTae)(Bpy) (H(2)Tae = 1,1,2,2-tetraacetylethane, Bpy = 4,4'-bipyridine) were determined by single-crystal X-ray diffraction, and the possible symmetry relations between the space group of the average structure and the superstructure were checked. The crystal structure consists in parallel and oblique {Cu(HTae)(Bpy)} zigzag metal organic chains stacked along the [100] crystallographic direction. The origin of the fivefold c axis in the commensurate superstructure is ascribed to a commensurate modulation of the coordination environment of the copper atoms. The commensurately ordered nitrate groups and coordinated water molecules establish a twodimensional hydrogen-bonding network. Moreover, the crystal structure shows a commensurate to incommensurate transition at room temperature. The release of the coordination water molecules destabilizes the crystal framework, and the compound shows an irreversible structure transformation above 100 degrees C. Despite the loss of crystallinity, the spectroscopic studies indicate that the main building blocks of the crystal framework are retained after the transformation. The hydrogen-bonding network not only plays a crucial role stabilizing the crystal structure but also is an important pathway for magnetic exchange transmission. In fact, the magnetic susceptibility curves indicate that after the loss of coordinated water molecules, and hence the collapse of the hydrogen-bonding network, the weak anti-ferromagnetic coupling observed in the initial compound is broken. The electron paramagnetic resonance spectra are the consequence of the average signals from Cu(II) with different orientations, indicating that the magnetic coupling is effective between them. In fact, X- and Q-band data are reflecting different situations; the X-band spectra show the characteristics of an exchange g-tensor, while the Qband signals are coming from both the exchange and the molecular g-tensors.
Title:
The Moment Series Expansion for Quasicrystal with Phason Disorder
Authors:
Buganski, I; Strzalka, R; Wolny, J Author Full Names: Buganski, I.; Strzalka, R.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):833-835; 10.12693/APhysPolA.130.833 OCT 2016
Abstract:
The novel method for structural analysis of quasicrystals with phason flips is presented. The correction for diffraction peaks' intensities can be made within average unit cell approach by modification of the statistical distribution of atomic positions. Characteristic function of the distribution expanded into moment series, involving only even moments, estimates the envelope function and therefore the flip ratio can be evaluated.
Title:
Crystal Structure of the High Temperature Phase of Strontium Barium Niobate
Authors:
Paszkowski, R; Zubko, M; Wokulska, K; Kusz, J; Dec, J Author Full Names: Paszkowski, R.; Zubko, M.; Wokulska, K.; Kusz, J.; Dec, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):856-858; 10.12693/APhysPolA.130.856 OCT 2016
Abstract:
Pure and undoped strontium-barium niobate Sr0.40Ba0.60Nb2O6 (SBN40) single crystals grown by the Czochralski method were investigated by single crystal X-ray diffraction methods. The study below T-C (429 K for SBN40) confirmed the structure with P4bm space group. Above this temperature the structure transforms into the paraelectric, centrosymmetric one with P4/mbm space group. Analysis of the recorded diffraction patterns allowed to observe several signs of crystal structure modulation. On the registered diffraction images satellite reflections were found. A modulation vector q = (delta, +/-delta,), where delta = 0.3075(6) (at room temperature) was found and it was similar to that occurring in the SBN61. In addition, above the phase transition temperature on the (hk) planes with l integer a weak diffuse scattering was observed.
Title:
Solution and Refinement of Magnetic Structures with Jana2006
Authors:
Petricek, V; Henriques, MS; Dusek, M Author Full Names: Petricek, V.; Henriques, M. S.; Dusek, M.
Source:
ACTA PHYSICA POLONICA A, 130 (4):848-851; 10.12693/APhysPolA.130.848 OCT 2016
Abstract:
The program Jana2006 allows the solution and refinement of regular, twinned, modulated, and composite structures against different diffraction data sets. Recently a new option for solving and refining magnetic structures from powder and single crystal neutron diffraction data has been developed.
Title:
Fitting the Long-Range Order of a Decagonal Quasicrystal
Authors:
Chodyn, M; Kuczera, P; Wolny, J Author Full Names: Chodyn, M.; Kuczera, P.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):845-847; 10.12693/APhysPolA.130.845 OCT 2016
Abstract:
The generalized Penrose tiling is an infinite set of decagonal tilings. It is constructed with the same rhombs (thick and thin) as the conventional Penrose tiling, but its long-range order depends on the so-called shift parameter s is an element of < 0,1). The formula for structure factor, calculated within the average unit cell approach, works in physical space only and is directly dependent on the s parameter. It allows to straightforwardly change the long-range order of the refined structure just by changing the s parameter and keeping the tile decoration unchanged. The possibility and viability of using the shift as one of the refinement parameters during structure refinement was tested for a numerically generated simple binary decagonal quasicrystal.
Title:
Simple Decoration Model of Icosahedral Quasicrystals in Statistical Approach
Authors:
Strzalka, R; Buganski, I; Wolny, J Author Full Names: Strzalka, R.; Buganski, I.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):841-844; 10.12693/APhysPolA.130.841 OCT 2016
Abstract:
The statistical approach based on the average unit cell concept was recently successfully applied to structural modelling of icosahedral quasicrystals. The structure factor for arbitrarily decorated icosahedral structure was derived for model Ammann tiling (3D Penrose tiling). It is a fully physical-space model where no higher-dimensional description is needed. In the present paper we show the application of the model to the so-called simple decoration scheme - atomic decoration in the nodes, at mid-edges and along body-diagonal of structural units of 3D Penrose tiling. By analyzing the obtained calculated diffraction patterns we show the correctness of the model and its applicability to binary and ternary icosahedral phases.
Title:
Phononic and Phasonic Debye-Waller Factors for 1D Quasicrystals
Authors:
Wolny, J; Buganski, I; Strzalka, R Author Full Names: Wolny, J.; Buganski, I.; Strzalka, R.
Source:
ACTA PHYSICA POLONICA A, 130 (4):836-840; 10.12693/APhysPolA.130.836 OCT 2016
Abstract:
The main purpose of crystallography is to solve and refine crystal structures based on measured diffraction data. One of important corrections crucial in the refinement process is the Debye-Waller factor correction for phonons in physical, and phasons in perpendicular space. In our paper we show the limitations of the standard approaches to the Debye-Waller correction in case of quasicrystals and propose new approach based on the statistical method. For the model 1D quasicrystal we show that in case of phonons there is no significant objection against classical (exponential) Debye-Waller factor, however using different forms can slightly improve the results of a refinement. In case of phasons the classical formula gives no rise to the efficiency of the refinement and completely new approach is required. We propose a redefinition of the Debye-Waller factor in terms of the statistical approach and show its effectiveness.
Title:
Precession Electron Diffraction Studies of SrxBa1-xNb2O6 and CaxBa1-xNb2O6 Single Crystals
Authors:
Wspaniala-Rak, J; Zubko, M; Stroz, D; Rak, J; Dec, J Author Full Names: Wspaniala-Rak, J.; Zubko, M.; Stroz, D.; Rak, J.; Dec, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):830-832; 10.12693/APhysPolA.130.830 OCT 2016
Abstract:
Crystal structures of two single crystals SrxBa1-xNb2O6 and CaxBa1-xNb2O6 have been reinvestigated using automated electron diffraction tomography method with beam precession. 3D reciprocal space has been reconstructed based on recorded tilt series. For both samples the crystal structure was refined and the tetragonal symmetry with space group P4bm was confirmed. The three dimensional reciprocal space allowed to observe and to study satellite reflections in both materials.
Title:
FOUR-DIMENSIONAL INCOMMENSURATELY MODULATED STRUCTURE OF THULIUM POLYPHOSPHATE
Authors:
Ma, FX; Zhao, D; Yang, H; Chen, PF; Yang, RJ; Wu, SX Author Full Names: Ma, Fa-Xue; Zhao, Dan; Yang, Hong; Chen, Peng-Fei; Yang, Rui-Juan; Wu, Shan-Xuan
Source:
JOURNAL OF THE CHILEAN CHEMICAL SOCIETY, 61 (2):3005-3008; JUN 2016
Abstract:
Single crystal of rare-earth polyphosphate Tm(PO3)(3) has been grown under high temperature molten-salt method and structurally characterized by single crystal X-ray diffraction analysis. Using the four-dimensional superspace formalism for aperiodic structures, we performed the crystal structure refinement of Tm(PO3)(3) as (3+ 1)-dimensional incommensurately modulated structure with monoclinic superspace group C2/c(0, 0.358,0)s0 and a = 14.0620 (12)angstrom, b = 6.6612 (6) angstrom, c = 10.0191 (9) angstrom, beta = 127.6043 (9)degrees, V = 743.51 (11) angstrom(3), Z = 4, M-r = 405.8, D-c = 3.626 g/cm(3), F(000) = 744, mu((MoKa)) = 12.60 mm(-1), R = 0.048 and omega R = 0.050. The structure features infinite chains of corner-sharing PO4 tetrahedra which are affected by positional modulation running along the b-axis. The final structure model was reasonable and did not show any unusual features.

Update: 14-Dec-2016

Title:
Soft-phonon-driven orbital order in CaMn7O12
Authors:
Souliou, SM; Li, Y; Du, X; Le Tacon, M; Bosak, A Author Full Names: Souliou, S. M.; Li, Y.; Du, X.; Le Tacon, M.; Bosak, A.
Source:
PHYSICAL REVIEW B, 94 (18):10.1103/PhysRevB.94.184309 NOV 22 2016
Abstract:
We use variable-temperature x-ray thermal diffuse scattering and inelastic scattering to investigate the lattice dynamics in single crystals of multiferroic CaMn7O12 which undergo a series of orbital and magnetic transitions at low temperatures. Upon approaching the charge and orbital ordering temperature T-o = 250 K from above, we observe intense diffuse scattering features and a pronounced optical phonon softening centered around the superstructure reflections of the incommensurately modulated structure. The phonon anomaly appears well above T-o and continuously increases upon cooling, following a canonical power-law temperature dependence that confirms the transition at T-o to be of second order and related to a soft-phonon lattice instability. Microscopic mechanisms for the incommensurate charge and orbital ordering based on competing interactions and on momentum-dependent electron-phonon coupling could both account for the observed extended momentum width of the phonon softening. Our results highlight the importance of the lattice interactions in the physics of this magnetically induced ferroelectric system.
Title:
High-Pressure Phase Transformations in TiPO4: A Route to Pentacoordinated Phosphorus
Authors:
Bykov, M; Bykova, E; Hanfland, M; Liermann, HP; Kremer, RK; Glaum, R; Dubrovinsky, L; van Smaalen, S Author Full Names: Bykov, Maxim; Bykova, Elena; Hanfland, Michael; Liermann, Hanns-Peter; Kremer, Reinhard K.; Glaum, Robert; Dubrovinsky, Leonid; van Smaalen, Sander
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 55 (48):15053-15057; 10.1002/anie.201608530 NOV 21 2016
Abstract:
Titanium(III) phosphate, TiPO4, is a typical example of an oxyphosphorus compound containing covalent P-O bonds. Single-crystal X-ray diffraction studies of TiPO4 reveal complex and unexpected structural and chemical behavior as a function of pressure at room temperature. A series of phase transitions lead to the high-pressure phase V, which is stable above 46 GPa and features an unusual oxygen coordination of the phosphorus atoms. TiPO4-V is the first inorganic phosphorus-containing compound that exhibits fivefold coordination with oxygen. Up to the highest studied pressure of 56 GPa, TiPO4-V coexists with TiPO4-IV, which is less dense and might be kinetically stabilized. Above a pressure of about 6 GPa, TiPO4-II is found to be an incommensurately modulated phase whereas a lock-in transition at about 7 GPa leads to TiPO4-III with a fourfold superstructure compared to the structure of TiPO4-I at ambient conditions. TiPO4-II and TiPO4-III are similar to the corresponding low-temperature incommensurate and commensurate magnetic phases and reflect the strong pressure dependence of the spin-Peierls interactions.
Title:
Influence of elastic strain gradient on the upper limit of flexocoupling strength, spatially modulated phases, and soft phonon dispersion in ferroics
Authors:
Morozovska, AN; Eliseev, EA; Scherbakov, CM; Vysochanskii, YM Author Full Names: Morozovska, Anna N.; Eliseev, Eugene A.; Scherbakov, Christian M.; Vysochanskii, Yulian M.
Source:
PHYSICAL REVIEW B, 94 (17):10.1103/PhysRevB.94.174112 NOV 21 2016
Abstract:
Using the Landau-Ginzburg-Devonshire theory, we established the role of the flexoelectric coupling between the gradients of elastic strain and polarization in the stability of spatially modulated phases in ferroics, such as incipient and proper ferroelectrics with commensurate and incommensurate long-range-ordered phases. We included the square of elastic strain gradient in the Landau-Ginzburg-Devonshire functional because this term provides the functional stability for all values of the strain gradient. Analytical expressions for polarization, strain, dielectric susceptibility, and stability threshold were derived for a one-dimensional case. The expressions show that the maximal possible values of the static flexoelectric effect coefficients (upper limits) established by Yudin, Ahluwalia, and Tagantsev without the square of elastic strain gradient and other higher order gradients terms lose their direct meaning. Considering the gradients, the temperature dependent condition for the flexocoupling magnitude exists instead of the upper limits. Also, we established that spatially modulated phases appear and become stable in commensurate ferroelectrics if the flexocoupling constant exceeds a critical value. The critical value depends on the electrostriction and elastic constants, temperature, and gradient coefficients in the Landau-Ginzburg-Devonshire functional. We calculated soft phonon dispersion in commensurate and incommensurate long-range-ordered phases of ferroelectrics with the square of elastic strain gradient, static, and dynamic flexocoupling. It appeared that the dispersion of the optical mode is slightly sensitive to the flexocoupling, and the dispersion of acoustic mode strongly depends on the coupling magnitude. Obtained results demonstrate that nontrivial differences in the dispersion of optical and acoustic modes occur with the change of flexocoupling constant. Therefore, experimental determination of soft phonon dispersion might be very informative to study the influence of strain gradients and flexocoupling on the spatially modulated phase in ferroelectrics with commensurate and incommensurate long-range order.
Title:
MAGNDATA: towards a database of magnetic structures. I. The commensurate case
Authors:
Gallego, SV; Perez-Mato, JM; Elcoro, L; Tasci, ES; Hanson, RM; Momma, K; Aroyo, MI; Madariaga, G Author Full Names: Gallego, Samuel V.; Manuel Perez-Mato, J.; Elcoro, Luis; Tasci, Emre S.; Hanson, Robert M.; Momma, Koichi; Aroyo, Mois I.; Madariaga, Gotzon
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 1750-1776; 10.1107/S1600576716012863 5 OCT 2016
Abstract:
A free web page under the name MAGNDATA, which provides detailed quantitative information on more than 400 published magnetic structures, has been developed and is available at the Bilbao Crystallographic Server (http://www. cryst.ehu.es). It includes both commensurate and incommensurate structures. This first article is devoted to explaining the information available on commensurate magnetic structures. Each magnetic structure is described using magnetic symmetry, i.e. a magnetic space group (or Shubnikov group). This ensures a robust and unambiguous description of both atomic positions and magnetic moments within a common unique formalism. A non-standard setting of the magnetic space group is often used in order to keep the origin and unit-cell orientation of the paramagnetic phase, but a description in any desired setting is possible. Domain-related equivalent structures can also be down-loaded. For each structure its magnetic point group is given, and the resulting constraints on any macroscopic tensor property of interest can be consulted. Any entry can be retrieved as a magCIF file, a file format under development by the International Union of Crystallography. An online visualization tool using Jmol is available, and the latest versions of VESTA and Jmol support the magCIF format, such that these programs can be used locally for visualization and analysis of any of the entries in the collection. The fact that magnetic structures are often reported without identifying their symmetry and/or with ambiguous information has in many cases forced a reinterpretation and transformation of the published data. Most of the structures in the collection possess a maximal magnetic symmetry within the constraints imposed by the magnetic propagation vector(s). When a lower symmetry is realized, it usually corresponds to an epikernel (isotropy subgroup) of one irreducible representation of the space group of the parent phase. Various examples of the structures present in this collection are discussed.
Title:
Temperature and cooling field dependent exchange coupling in [Cr/Gd](5) multilayers
Authors:
Jiao, ZW; Chen, HJ; Jiang, WD; Wang, JF; Yu, SJ; Hou, YL; Lu, B; Ye, QL Author Full Names: Jiao, Z. W.; Chen, H. J.; Jiang, W. D.; Wang, J. F.; Yu, S. J.; Hou, Y. L.; Lu, B.; Ye, Q. L.
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 213 (9):2531-2536; 10.1002/pssa.201600025 SEP 2016
Abstract:
Exchange coupling has been investigated in the [Cr/Gd](5) multilayers deposited at 25, 200, and 400 degrees C, where the Neel temperature (TN) of antiferromagnetic Cr is slightly higher than the Curie temperature (T-C) of ferromagnetic Gd. It was found that the exchange coupling existed not only at T-C < T < T-N, but also above the temperature (T-N) of antiferromagnetic orderings with incommensurate spin-density wave structures transiting to paramagnetic state. These results can be discussed in terms of the crucial role played by the antiferromagnetic spins of Cr with commensurate spin-density wave structures in the vicinity of the Cr/Gd interfaces. Moreover, the exchange coupling of the multilayers grown at different temperatures exhibited different dependencies on the measuring temperature and the cooling field, respectively. Positive exchange bias was observed in the multilayers grown at 200 and 400 degrees C. The interfacial roughness, grain size, and the antiferromagnetic orderings of Cr may be responsible for the anomalous exchange coupling of the multilayers. In addition, the competition between the exchange coupling at Cr/Gd interfaces and the external field-Cr surface magnetic coupling can explain the appearance of negative or positive exchange bias. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Update: 8-Dec-2016

Title:
Self-assembly of two-dimensional binary quasicrystals: a possible route to a DNA quasicrystal
Authors:
Reinhardt, A; Schreck, JS; Romano, F; Doye, JPK Author Full Names: Reinhardt, Aleks; Schreck, John S.; Romano, Flavio; Doye, Jonathan P. K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (1):10.1088/0953-8984/29/1/014006 JAN 11 2017
Abstract:
We use Monte Carlo simulations and free-energy techniques to show that binary solutions of penta-and hexavalent two-dimensional patchy particles can form thermodynamically stable quasicrystals even at very narrow patch widths, provided their patch interactions are chosen in an appropriate way. Such patchy particles can be thought of as a coarse-grained representation of DNA multi-arm 'star' motifs, which can be chosen to bond with one another very specifically by tuning the DNA sequences of the protruding arms. We explore several possible design strategies and conclude that DNA star tiles that are designed to interact with one another in a specific but not overly constrained way could potentially be used to construct soft quasicrystals in experiment. We verify that such star tiles can form stable dodecagonal motifs using oxDNA, a realistic coarse-grained model of DNA.
Title:
Electrochemical and kinetic properties of Ti41.5Zr41.5Ni17 quasicrystal and LiH composite materials
Authors:
Zhai, XJ; Wang, QS; Luo, TH; Zhao, Z; DongyanLiu; Xing, C; Shen, XD; Liu, WQ; LiminWang Author Full Names: Zhai, Xiaojie; Wang, Qingshuang; Luo, Tianhao; Zhao, Zhen; DongyanLiu; Xing, Cheng; Shen, Xiande; Liu, Wanqiang; LiminWang
Source:
MATERIALS RESEARCH BULLETIN, 85 196-201; 10.1016/j.materresbull.2016.09.021 JAN 2017
Abstract:
We report the effect of LiH on the discharge performance of electrodes which are consist of Ti41.5Zr41.5Ni17 quasicrystal in this paper. The Ti41.5Zr41.5Ni17 alloy ribbons are prepared by arc-melting and melt spinning technique subsequently. The final product of Ti41.5Zr41.5Ni17 and LiH composite materials is produced by mechanical alloying (MA) for 20 min, and it is investigated by a three-electrode cell at room temperature. The maximum discharge capacity can achieve 146.6 mAh/g around for Ti41.5Zr41.5Ni17 and LiH composite materials electrode at the first discharge process, which is higher than 96.5 mAh/g of Ti41.5Zr41.5Ni17 quasicrystal at the third discharge process. High-rate dischargeability and cycling stability are improved by adding LiH, which may attribute to the reversible reaction of LiH that enhances the electrochemical reaction activity in the process of electrochemical reaction. The discharge process is also characterized by electrochemical impedance spectroscopy. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
Polarization curling and flux closures in multiferroic tunnel junctions
Authors:
Peters, JJP; Apachitei, G; Beanland, R; Alexe, M; Sanchez, AM Author Full Names: Peters, Jonathan J. P.; Apachitei, Geanina; Beanland, Richard; Alexe, Marin; Sanchez, Ana M.
Source:
NATURE COMMUNICATIONS, 7 10.1038/ncomms13484 NOV 16 2016
Abstract:
Formation of domain walls in ferroelectrics is not energetically favourable in low-dimensional systems. Instead, vortex-type structures are formed that are driven by depolarization fields occurring in such systems. Consequently, polarization vortices have only been experimentally found in systems in which these fields are deliberately maximized, that is, in films between insulating layers. As such configurations are devoid of screening charges provided by metal electrodes, commonly used in electronic devices, it is wise to investigate if curling polarization structures are innate to ferroelectricity or induced by the absence of electrodes. Here we show that in unpoled Co/PbTiO3/(La, Sr)MnO3 ferroelectric tunnel junctions, the polarization in active PbTiO3 layers 9 unit cells thick forms Kittel-like domains, while at 6 unit cells there is a complex flux-closure curling behaviour resembling an incommensurate phase. Reducing the thickness to 3 unit cells, there is an almost complete loss of switchable polarization associated with an internal gradient.
Title:
Semiclassical ground-state phase diagram and multi-Q phase of a spin-orbit-coupled model on triangular lattice
Authors:
Liu, CL; Yu, R; Wang, XQ Author Full Names: Liu, Changle; Yu, Rong; Wang, Xiaoqun
Source:
PHYSICAL REVIEW B, 94 (17):10.1103/PhysRevB.94.174424 NOV 15 2016
Abstract:
Motivated by recent experiments on the frustrated quantum magnetic compound YbMgGaO4, we study an effective spin model on triangular lattice taking into account the effects of the spin-orbit coupling. We determine the classical ground-state phase diagram of this model, which includes a 120 degrees Neel and two collinear antiferromagnetic phases. In the vicinity of the phase boundary between the Neel and collinear phases, we identify three intermediate noncollinear antiferromagnetic phases. In each of them the magnetic moments are ordered at multiple incommensurate wave vector Q values. We further study the effects of quantum fluctuations in this model via a linear spin-wave theory. We find that the spin excitation gap of the noncollinear multi-Q antiferromagnetic states is vanishingly small. We also find that multi-Q states are most fragile against quantum fluctuations, and hence most unstable toward spin liquid phases.
Title:
Effect of cooling rate and Mg addition on the structural evaluation of rapidly solidified Al-20wt%Cu-12wt%Fe alloy
Authors:
Karakose, E; Colak, H Author Full Names: Karakose, Ercan; Colak, Hakan
Source:
MATERIALS CHARACTERIZATION, 121 68-75; 10.1016/j.matchar.2016.09.030 NOV 2016
Abstract:
The present work examines the effect of Mg contents and cooling rate on the morphology and mechanical properties of Al20Cu12Fe quasicrystalline alloy. The microstructure of the alloys was analyzed by scanning electron microscopy and the phase composition was identified by X-ray diffractometry. The melting characteristics were studied by differential thermal analysis under an Ar atmosphere. The mechanical features of the melt-spun and conventionally solidified alloys were tested by tensile-strength test and Vickers micro-hardness test. It was found that the final microstructure of the Al20Cu12Fe samples mainly depends on the cooling rate and Mg contents, which suggests that different cooling rates and Mg contents produce different microstructures and properties. The average grain sizes of the melt spun samples were about 100-300 nm at 35 m/s. The nanosize, dispersed, different shaped quasicrystal particles possessed a remarkable effect to the mechanical characteristics of the rapidly solidified ribbons. The microhardness values of the melt spun samples were approximately 18% higher than those of the conventionally counterparts. (C) 2016 Elsevier Inc. All rights reserved.
Title:
Magnetic structure and effect of magnetic field on its domain structure in magnetoelectric Ba1.3Sr0.7CoZnFe11AlO22
Authors:
Ueda, H; Tanaka, Y; Nakajima, H; Mori, S; Ohta, K; Haruki, K; Hirose, S; Wakabayashi, Y; Kimura, T Author Full Names: Ueda, H.; Tanaka, Y.; Nakajima, H.; Mori, S.; Ohta, K.; Haruki, K.; Hirose, S.; Wakabayashi, Y.; Kimura, T.
Source:
APPLIED PHYSICS LETTERS, 109 (18):10.1063/1.4966623 OCT 31 2016
Abstract:
The magnetic structure and the effect of a magnetic field on its domain structure were investigated in a magnetoelectric Y-type hexaferrite, Ba1.3Sr0.7CoZnFe11AlO22, by means of mapping with a micro-focused and circularly polarized X-ray beam in the resonant X-ray diffraction. It was revealed that this hexaferrite exhibits a magnetic order characterized by two distinct antiferromagnetic components: incommensurate helical and commensurate collinear ones, which can be explained as the development of the so-called alternating longitudinal conical structure. A multidomain state due to the handedness of the helical component, i.e., spin-chirality, is transformed into nearly a mono-domain one by using only a magnetic field. Furthermore, the sign of the spin-chirality in the mono-domain state is reversed by reversing the sign of a magnetic field. These results demonstrate that the spin-chirality in this hexaferrite can be manipulated by a magnetic field alone at room temperature. Published by AIP Publishing.
Title:
Structure and Electrical Conductivity of Ag-Doped TiZrNi Quasicrystals
Authors:
Lee, SH; Park, T; Yi, W; Kim, J Author Full Names: Lee, Sang-Hwa; Park, Taehee; Yi, Whikun; Kim, Jaeyong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 16 (10):10532-10534; 10.1166/jnn.2016.13189 OCT 2016
Abstract:
To investigate the structure and electrical conductivity of Ag-doped TiZrNi quasicrystals, alloys of (Ti53Zr27Ni20)(100) Ag-x(x) (where, x = 0, 4 and 8) were arc-melted and rapidly quenched in an Ar atmosphere. After optimum quenching, the results of the X-ray diffraction (XRD) measurements revealed that the samples have a pure quasicrystal structure. The quasicrystal structure remained to the maximum 8 at.% of Ag without a significant change in the quasi-lattice constant value, 5.12 angstrom. The specific electrical resistance values of the quasicrystals increased from 4.21 to 5.47x10(-4) Omega. cm with increasing Ag contents from 0 to 8 at.% whereas the coherence lengths decreased from 119 to 93 angstrom accordingly. It is interesting to note that the reduction in the electrical conductivity with the increase in Ag contents is mainly due to the structural incoherence factor, not the atomic conductivity of Ag.
Title:
Direct observation of incommensurate structure in Mo3Si
Authors:
Gulec, A; Yu, XX; Taylor, M; Perepezko, JH; Marks, L Author Full Names: Gulec, Ahmet; Yu, Xiaoxiang; Taylor, Matthew; Perepezko, John H.; Marks, Laurence
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 72 660-666; 10.1107/S2053273316012286 6 OCT 2016
Abstract:
Z-contrast imaging, electron diffraction, atom-probe tomography (APT) and density functional theory calculations were used to study the crystal structure of the Mo3Si phase which was previously reported to have an A15 crystal structure. The results showed that Mo3Si has an incommensurate crystal structure with a non-cubic unit cell. The small off-stoichiometry in composition of the sample which was revealed by APT and atomic resolution Z-contrast imaging suggested that site substitution caused the development of split atomic positions, disorder and vacancies.
Title:
Structure determination of modulated structures by powder X-ray diffraction and electron diffraction
Authors:
Zhou, ZY; Palatinus, L; Sun, JL Author Full Names: Zhou, Zhengyang; Palatinus, Lukas; Sun, Junliang
Source:
INORGANIC CHEMISTRY FRONTIERS, 3 (11):1351-1362; 10.1039/c6qi00219f 2016
Abstract:
Since the first discovery and description of materials, whose structures are not periodic, enormous efforts have been made in studying these aperiodic structures. With these efforts including the development of superspace group theory and structure solution algorithms, numerous incommensurately modulated structures which represent the vast majority of known aperiodic structures have been determined with single crystal X-ray diffraction data. However, the determination of modulated structures remains very difficult for polycrystalline materials. Powder X-ray diffraction and electron microscopy techniques yield remarkable information for polycrystalline materials. By combining these two methods, modulated structures of polycrystalline materials that impede solution by conventional methods can be determined. The power of these methods is illustrated with the examples of the determination of modulated structures of polycrystalline materials.

Update: 23-Nov-2016

Title:
Crystallographic Features and State Stability of the Decagonal Quasicrystal in the Al-Co-Cu Alloy System
Authors:
Nakayama, K; Mizutani, A; Koyama, Y Author Full Names: Nakayama, Kei; Mizutani, Akito; Koyama, Yasumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (11):10.7566/JPSJ.85.114602 NOV 15 2016
Abstract:
In the Al-Co-Cu alloy system, both the decagonal quasicrystal with the space group of P (10) over bar m2 and its approximant Al13Co4 phase with monoclinic Cm symmetry are present around 20 at. % Co-10 at. % Cu. In this study, we examined the crystallographic features of prepared Al-(30 - x) at. % Co-x at. % Cu samples mainly by transmission electron microscopy in order to make clear the crystallographic relation between the decagonal quasicrystal and the monoclinic Al13Co4 structure. The results revealed a coexistence state consisting of decagonal quasicrystal and approximant Al13Co4 regions in Al-20 at. % Co-10 at. % Cu alloy samples. With the help of the coexistence state, the orientation relationship was established between the monoclinic Al13Co4 structure and the decagonal quasicrystal. In the determined relationship, the crystallographic axis in the quasicrystal was found to be parallel to the normal direction of the (010) m plane in the Al13Co4 structure, where the subscript m denotes the monoclinic system. Based on data obtained experimentally, the state stability of the decagonal quasicrystal was also examined in terms of the Hume-Rothery (HR) mechanism on the basis of the nearly-free-electron approximation. It was found that a model based on the HR mechanism could explain the crystallographic features such as electron diffraction patterns and atomic arrangements found in the decagonal quasicrystal. In other words, the HR mechanism is most likely appropriate for the stability of the decagonal quasicrystal in the Al-Co-Cu alloy system.
Title:
Prediction of entropy stabilized incommensurate phases in the system MoS2-MoTe2
Authors:
Burton, BP; Singh, AK Author Full Names: Burton, B. P.; Singh, A. K.
Source:
JOURNAL OF APPLIED PHYSICS, 120 (15):10.1063/1.4964868 OCT 21 2016
Abstract:
A first principles phase diagram calculation, that included van der Waals interactions, was performed for the 3D bulk system (1 X).MoS2 (X) . MoTe2. Surprisingly, the predicted phase diagram has at least two ordered phases, at X approximate to 0: 46, even though all calculated formation energies are positive; in a ground-state analysis that examined all configurations with 16 or fewer anion sites. The lower-temperature I-phase is predicted to transform to a higher-temperature I'-phase at T approximate to 500 K, and I0 disorders at T approximate to 730 K. Both these transitions are predicted to be first-order, and there are broad two-phase fields on both sides of the ordered regions. Both the I-and I'-phases are predicted to be incommensurate, i. e., aperiodic: I-phase in three dimensions; and I'-phase in two dimensions.
Title:
Structural transformations in highly oriented seven modulated martensite Ni-Mn-Ga thin films on an Al2O3 (11(2)over-bar0) substrate
Authors:
Sharma, A; Mohan, S; Suwas, S Author Full Names: Sharma, Amit; Mohan, Sangeneni; Suwas, Satyam
Source:
JOURNAL OF MATERIALS RESEARCH, 31 (19):3016-3026; 10.1557/jmr.2016.317 OCT 2016
Abstract:
Highly oriented Ni-Mn-Ga thin film with multiple variants and room temperature orthorhombic martensite structure were prepared on a single crystalline Al2O3 (11 (2) over bar0) substrate by DC magnetron sputtering. X-ray diffraction and rocking curve measurements reveal the film as (202)(7M) oriented with an excellent crystal quality ( = 1.8 degrees). Spot-like pole figures indicate that the Ni-Mn-Ga film grows with a strong in-plane preferred orientation. An in-depth analysis of the measured pole figure reveals the presence of a retained austenite phase in the film. Two phase transformations, M-S approximate to 345 K and T-C approximate to 385 K, are observed and are attributed to first order structural transformation from cubic to orthorhombic, and second order phase transformation from ferromagnetic to paramagnetic, respectively. In situ high temperature x-ray diffraction measurements provide a clear indication of a thermally-induced martensite austenite reversible structural phase transformation in the film. The presence of martensite plates with seven modulated orthorhombic structure and adaptive nano-twins are some of the important microscopic features observed in the film with transmission electron microscopy investigations.

Update: 16-Nov-2016

Title:
A guide to lifting aperiodic structures
Authors:
Baake, M; Ecija, D; Grimm, U Author Full Names: Baake, Michael; Ecija, David; Grimm, Uwe
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (9):507-515; 10.1515/zkri-2016-1982 SEP 2016
Abstract:
The embedding of a given point set with non-crystallographic symmetry into higher-dimensional space is reviewed, with special emphasis on the Minkowski embedding known from number theory. This is a natural choice that does not require an a priori construction of a lattice in relation to a given symmetry group. Instead, some elementary properties of the point set in physical space are used, and explicit methods are described. This approach works particularly well for the standard symmetries encountered in the practical study of quasicrystalline phases. We also demonstrate this with a recent experimental example, taken from a sample with square-triangle tiling structure and (approximate) 12-fold symmetry.
Title:
Effect of Pt addition to Ag-Au bimetallic nanoclusters: A molecular dynamics study of Ag-Au-Pt ternary system
Authors:
Akbarzadeh, H; Shamkhali, AN; Abbaspour, M; Salemi, S; Hajizadeh, Z Author Full Names: Akbarzadeh, Hamed; Shamkhali, Amir Nasser; Abbaspour, Mohsen; Salemi, Sirous; Hajizadeh, Zohreh
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 692 647-657; 10.1016/j.jallcom.2016.09.066 JAN 25 2017
Abstract:
In this work addition of Pt atoms to Ag0.5Au0.5 nanoclusters and formation of Ag0.5-chi Au0.5-chi Pt2 chi (with chi - 0.1, 0.17, 0.2, 0.25, 0.3, and 0.4) and total number of atoms equal to 1415 and 2057 ternary nanoclusters is studied by molecular dynamics simulation. The results indicated that at low concentrations of Pt, nanoclusters exhibit a local-ordered structure in such a way that (Pt-Ag-n-Au-2n) cores are surrounded by extra Ag atoms. By increase of Pt concentration total order of the nanocluster also increases. For nanoclusters with 0.0 < chi(Pt) < 0.4 total order of the system is decreased due to lower concentration of Ag-Pt and Au-Pt interactions. For chi(Pt) - 0.4 system, total order of the nanocluster again increases considerably which represents a Pt-rich nanocluster with some Ag and Au impurity. Also, all nanoclusters with chi(Pt) > 0.0 exhibit an icosahedral-fcc phase transition before melting and temperature of this phase transition is decreased by increase of Pt concentration. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Controlling Magnetic Ordering in Ca1-xEuxCo2As2 by Chemical Compression
Authors:
Tan, XY; Yaroslavtsev, AA; Cao, HB; Geondzhian, AY; Menushenkov, AP; Chernikov, RV; Nataf, L; Garlea, VO; Shatruk, M Author Full Names: Tan, Xiaoyan; Yaroslavtsev, Alexander A.; Cao, Huibo; Geondzhian, Andrey Y.; Menushenkov, Alexey P.; Chernikov, Roman V.; Nataf, Lucie; Garlea, V. Ovidiu; Shatruk, Michael
Source:
CHEMISTRY OF MATERIALS, 28 (20):7459-7469; 10.1021/acs.chemmater.6b03184 OCT 25 2016
Abstract:
To investigate the interplay between electronic structure and itinerant magnetism, Ca1-xEuxCo2As2 solid solutions (x = 0, 0.1, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7, 0.9, 1.0) were prepared by reactions between constituent elements in molten Bi. All of the samples crystallize in the ThCr2Si2 structure type. The crystal structure refinement revealed the formation of Co vacancies, the concentration of which decreases as the Eu content increases. The Eu site exhibits mixed valence in all samples. X-ray absorption near-edge structure spectroscopy revealed that the average Eu oxidation state decreases from +2.17 at 0 < x <= 0.6 to +2.14 at x >= 0.65. The same borderline behavior is observed in magnetic properties. The substitution of Eu for Ca causes the transition from the antiferromagnetic (AFM) ordering of Co moments in CaCo2As2 to ferromagnetic (FM) ordering of Co moments in Ca1-xEuxCo2As2 with 0.1 <= x <= 0.6. At higher Eu content, AFM ordering of Eu moments is observed, whereas the Co sublattice exhibits only paramagnetic behavior. Single-crystal neutron diffraction studies revealed that both Co and Eu sublattices order FM in Ca0.5Eu0.5Co2As2 with the magnetic moments aligned along the tetragonal c axis. In the AFM phases with x >= 0.65, only Eu moments are ordered in a helical spin structure defined by an incommensurate propagation vector k = [00q], with the moment lying in the ab plane. The changes in magnetic behavior are well-justified by the analysis of the electronic density of states and crystal orbital Hamilton population.
Title:
Role of Structure- and Defect Chemistry in High-Performance Thermoelectric Bismuth Strontium Cobalt Oxides
Authors:
Baran, JD; Kepaptsoglou, D; Molinari, M; Kulwongwit, N; Azough, F; Freer, R; Ramasse, QM; Parker, SC Author Full Names: Baran, Jakub D.; Kepaptsoglou, Demie; Molinari, Marco; Kulwongwit, Nuth; Azough, Feridoon; Freer, Robert; Ramasse, Quentin M.; Parker, Stephen C.
Source:
CHEMISTRY OF MATERIALS, 28 (20):7470-7478; 10.1021/acs.chemmater.6b03200 OCT 25 2016
Abstract:
[Bi0.87SrO2](2)[CoO2](1.82) (BSCO) is one of the best p-type thermoelectric oxides but its structural and electronic properties are still poorly understood. BSCO is a misfit-layered compound consisting of an incommensurate stacking of hexagonal CoO2 and double rock-salt BiSrO2 layers. Here we combine experimental and computational approaches to investigate its crystallographic and electronic structure as well as thermoelectric transport properties. Considering different approximations for the subsystems stacking, we present a structural model that agrees well with both bulk and atomic-scale experimental data. This model, which suggests a level of Bi deficiency in the rock-salt layers, is then used to discuss the material's electronic, magnetic, and transport properties. We show that Bi deficiency leads to a band gap opening and increases p-type electronic conductivity due to the formation of Co4+ species that serve as itinerant holes within the predominantly Co3+ framework of the CoO2 layer. We validate these predictions using electron energy loss spectroscopy in the scanning transmission electron microscope. The relationship between the hole-doping mechanism and the changes of the local structure (in particular the level of Bi deficiency) is evaluated. The reliability of the simulations is supported by the calculated temperature dependence of the Seebeck coefficient, in good agreement with experimental measurements.
Title:
Weak coupling of pseudoacoustic phonons and magnon dynamics in the incommensurate spin-ladder compound Sr14Cu24O41
Authors:
Chen, X; Bansal, D; Sullivan, S; Abernathy, DL; Aczel, AA; Zhou, JS; Delaire, O; Shi, L Author Full Names: Chen, Xi; Bansal, Dipanshu; Sullivan, Sean; Abernathy, Douglas L.; Aczel, Adam A.; Zhou, Jianshi; Delaire, Olivier; Shi, Li
Source:
PHYSICAL REVIEW B, 94 (13):10.1103/PhysRevB.94.134309 OCT 21 2016
Abstract:
Intriguing lattice dynamics have been predicted for aperiodic crystals that contain incommensurate substructures. Here we report inelastic neutron scattering measurements of phonon and magnon dispersions in Sr14Cu24O41, which contains incommensurate one-dimensional (1D) chain and two-dimensional (2D) ladder substructures. Two distinct pseudoacoustic phonon modes, corresponding to the sliding motion of one sublattice against the other, are observed for atomic motions polarized along the incommensurate axis. In the long wavelength limit, it is found that the sliding mode shows a remarkably small energy gap of 1.7-1.9 meV, indicating very weak interactions between the two incommensurate sublattices. The measurements also reveal a gapped and steep linear magnon dispersion of the ladder sublattice. The high group velocity of this magnon branch and weak coupling with acoustic and pseudoacoustic phonons can explain the large magnon thermal conductivity in Sr14Cu24O41 crystals. In addition, the magnon specific heat is determined from the measured total specific heat and phonon density of states and exhibits a Schottky anomaly due to gapped magnon modes of the spin chains. These findings offer new insights into the phonon and magnon dynamics and thermal transport properties of incommensurate magnetic crystals that contain low-dimensional substructures.
Title:
Helicity-dependent photocurrent in a Bi2Se3 thin film probed by terahertz emission spectroscopy
Authors:
Hamh, SY; Park, SH; Jerng, SK; Jeon, JH; Chun, SH; Lee, JS Author Full Names: Hamh, Sun Young; Park, Soon-Hee; Jerng, Sahng-Kyoon; Jeon, Jae Ho; Chun, Seung-Hyun; Lee, Jong Seok
Source:
PHYSICAL REVIEW B, 94 (16):10.1103/PhysRevB.94.161405 OCT 20 2016
Abstract:
We investigate photocarrier dynamics in a Bi2Se3 thin film via terahertz (THz) emission spectroscopy. We report amplitude and phase modulations of the emitted THz wave under the variations in a polarization of an input laser beam and sample azimuth. Photon-helicity-dependent responses are manifested in both time and frequency domains, and azimuth dependence of such circular anisotropy exhibits a clear threefold periodicity. We analyze these results based on the symmetry of the bulk and the surface of Bi2Se3 and demonstrate that the observed helicity-dependent photocurrent originates from the circular photon drag effect, namely, linear and angular momentum transfers from photons to photocarriers.
Title:
Crystallographic computing system Jana2006: solution and refinement of twinned structures
Authors:
Petricek, V; Dusek, M; Plasil, J Author Full Names: Petricek, Vaclav; Dusek, Michal; Plasil, Jakub
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (10):583-599; SI 10.1515/zkri-2016-1956 OCT 2016
Abstract:
Twinning is a phenomenon complicating structure analysis of single crystals of standard as well as modulated structures. Jana2006 as a software for advanced structure analysis contains tools for recognition and refinement of twins including most complicated cases of modulated and magnetic structures. In order to efficiently use the tools of Jana2006 related to twinning, we explain the basic terminology and the underlying theory, especially the symmetry of the diffraction patterns affected by twinning. We present typical diffraction patterns of twins and show how twinning can be recognized or detected by various tools and described with twinning matrices. Data processing of twins and ways of how they can be imported to Jana2006 are also discussed. Two examples demonstrate the solution of typical twins: twinning by metric merohedry and twinning by reticular merohedry, followed by the third example demonstrating twinning in a commensurately *modulated structure*. The relationship between the dimensionality of the structure and twinning is discussed, too.

Update: 10-Nov-2016

Title:
Competing magnetic ground states and their coupling to the crystal lattice in CuFe2Ge2
Authors:
May, AF; Calder, S; Parker, DS; Sales, BC; McGuire, MA Author Full Names: May, Andrew F.; Calder, Stuart; Parker, David S.; Sales, Brian C.; McGuire, Michael A.
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep35325 OCT 14 2016
Abstract:
Identifying and characterizing systems with coupled and competing interactions is central to the development of physical models that can accurately describe and predict emergent behavior in condensed matter systems. This work demonstrates that the metallic compound CuFe2Ge2 has competing magnetic ground states, which are shown to be strongly coupled to the lattice and easily manipulated using temperature and applied magnetic fields. Temperature-dependent magnetization M measurements reveal a ferromagnetic-like onset at 228 (1) K and a broad maximum in M near 180 K. Powder neutron diffraction confirms antiferromagnetic ordering below T-N approximate to 175 K, and an incommensurate spin density wave is observed below approximate to 125 K. Coupled with the small refined moments (0.5-1 mu B/Fe), this provides a picture of itinerant magnetism in CuFe2Ge2. The neutron diffraction data also reveal a coexistence of two magnetic phases that further highlights the near-degeneracy of various magnetic states. These results demonstrate that the ground state in CuFe2Ge2 can be easily manipulated by external forces, making it of particular interest for doping, pressure, and further theoretical studies.
Title:
Charge density wave modulation and gap measurements in CeTe3
Authors:
Ralevic, U; Lazarevic, N; Baum, A; Eiter, HM; Hackl, R; Giraldo-Gallo, P; Fisher, IR; Petrovic, C; Gajic, R; Popovic, ZV Author Full Names: Ralevic, U.; Lazarevic, N.; Baum, A.; Eiter, H. -M.; Hackl, R.; Giraldo-Gallo, P.; Fisher, I. R.; Petrovic, C.; Gajic, R.; Popovic, Z. V.
Source:
PHYSICAL REVIEW B, 94 (16):10.1103/PhysRevB.94.165132 OCT 14 2016
Abstract:
We present a study of charge density wave (CDW) ordering in CeTe3 at room temperature using a scanning tunneling microscope and Raman spectroscopy. Two characteristic CDW ordering wave vectors obtained from the Fourier analysis are assessed to be |c* - q| = 4.19 nm(-1) and |q| = 10.26 nm(-1) where |c*| = 2 Pi/c is the reciprocal lattice vector. The scanning tunneling spectroscopy measurements, along with inelastic light ( Raman) scattering measurements, show a CDWgap Delta(max) of approximately 0.37 eV. In addition to the CDW modulation, we observe an organization of the Te sheet atoms in an array of alternating V- and N-shaped groups along the CDW modulation, as predicted in the literature.
Title:
Remarkable Stability of Charge Density Wave Order in La1.875Ba0.125CuO4
Authors:
Chen, XM; Thampy, V; Mazzoli, C; Barbour, AM; Miao, H; Gu, GD; Cao, Y; Tranquada, JM; Dean, MPM; Wilkins, SB Author Full Names: Chen, X. M.; Thampy, V.; Mazzoli, C.; Barbour, A. M.; Miao, H.; Gu, G. D.; Cao, Y.; Tranquada, J. M.; Dean, M. P. M.; Wilkins, S. B.
Source:
PHYSICAL REVIEW LETTERS, 117 (16):10.1103/PhysRevLett.117.167001 OCT 11 2016
Abstract:
The occurrence of charge-density-wave (CDW) order in underdoped cuprates is now well established, although the precise nature of the CDW and its relationship with superconductivity is not. Theoretical proposals include contrasting ideas such as that pairing may be driven by CDW fluctuations or that static CDWs may intertwine with a spatially modulated superconducting wave function. We test the dynamics of CDW order in La1.825Ba0.125CuO4 by using x-ray photon correlation spectroscopy at the CDW wave vector, detected resonantly at the Cu L-3 edge. We find that the CDW domains are strikingly static, with no evidence of significant fluctuations up to 2 (3)/(4) h. We discuss the implications of these results for some of the competing theories.
Title:
Structure of the Al13Co4(100) surface: Combination of surface x-ray diffraction and ab initio calculations
Authors:
Gaudry, E; Chatelier, C; McGuirk, GM; Loli, LNS; de Weerd, MC; Ledieu, J; Fournee, V; Felici, R; Drnec, J; Beutier, G; de Boissieu, M Author Full Names: Gaudry, E.; Chatelier, C.; McGuirk, G. M.; Serkovic Loli, L. N.; de Weerd, M. -C.; Ledieu, J.; Fournee, V.; Felici, R.; Drnec, J.; Beutier, G.; de Boissieu, M.
Source:
PHYSICAL REVIEW B, 94 (16):10.1103/PhysRevB.94.165406 OCT 10 2016
Abstract:
The structure of the quasicrystalline approximant Al13Co4(100) has been determined by surface x-ray diffraction (SXRD) and complementary density-functional-theory (DFT) calculations. Thanks to the use of a two-dimensional pixel detector, which speeds up the data acquisition enormously, an exceptionally large set of experimental data, consisting of 124 crystal truncation rods, has been collected and used to refine this complex structure of large unit cell and low symmetry. Various models were considered for the SXRD analysis. The best fit is consistent with a surface termination at the puckered type of planes but with a depletion of the protruding Co atoms. The surface energy of the determined surface model was calculated using DFT, and it takes a rather low value of 1.09 J/m(2). The results for the atomic relaxation of surface planes found by SXRD or DFT were in excellent agreement. This work opens up additional perspectives for the comprehension of related quasicrystalline surfaces.
Title:
Communication between cation environments in aluminosilicate frameworks: incommensurately modulated crystal structure of an e-plagioclase
Authors:
Fredrickson, RT; Fredrickson, DC Author Full Names: Fredrickson, Rie T.; Fredrickson, Daniel C.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 787-801; 10.1107/S2052520616010350 5 OCT 2016
Abstract:
Despite being one of the most common minerals in the earth's crust the crystal structure of intermediate e-plagioclase remains only partially understood, due in a large part to its complex diffraction patterns including satellite reflections. In this article we present a detailed analysis of the structure of e-plagioclase (An44) using single-crystal X-ray diffraction measured at ambient and low temperature (T = 100 K), in which the full modulated structure is successfully refined. As in earlier studies, the diffraction pattern exhibits strong main a-reflections and weak e-satellite reflections. The average structure could be solved in terms of an albite-like basic cell with the triclinic centrosymmetric and non-centrosymmetric space groups P (1) over bar and P1 (treated in its C (1) over bar and C1 setting, respectively, to follow conventions in the literature), while the incommensurately modulated structure was modeled in (3 + 1) D superspace, employing both the centro-and noncentrosymmetric superspace groups X (1) over bar(alpha beta gamma)0 and X1(alpha beta gamma) 0, where X refers to a special (3 + 1) D lattice centering with centering vectors (0 0 1/2 1/2), (1/2 1/2 0 1/2), and (1/2 1/2 1/2 0). Individual positional and occupational modulations for Ca/Na were refined with deeper insights being revealed in the non-centrosymmetric structure model. Through the structural details emerging from this model, the origin of the modulation can be traced to the communication between Ca/Na site positions through their bridging aluminosilicate (Si/Al) O-4 tetrahedra.
Title:
Charge and spin coupling in magnetoresistive oxygen-vacancy strontium ferrate SrFeO3-delta
Authors:
Lee, SH; Frawley, TW; Yao, CH; Lai, YC; Du, CH; Hatton, PD; Wang, MJ; Chou, FC; Huang, DJ Author Full Names: Lee, S. H.; Frawley, T. W.; Yao, C. H.; Lai, Y. C.; Du, Chao-Hung; Hatton, P. D.; Wang, M. J.; Chou, F. C.; Huang, D. J.
Source:
NEW JOURNAL OF PHYSICS, 18 10.1088/1367-2630/18/9/093033 SEP 20 2016
Abstract:
Using magnetization, conductivity and x-ray scattering measurements, we demonstrate that the giant magnetoresistance of the oxygen-deficient ferrite SrFeO2.875+0.02 is a consequence of the coupling between the charge and spin order parameters and the tetragonal to monoclinic structural distortion. Upon cooling the sample at T similar or equal to 120 K we find a shoulder in both field-cool and zero field cool magnetization data and the simultaneous appearance of incommensurate structural satellites observed using x-ray diffraction. These satellites are shown to be due to incommensurate charge ordering with the high temperature delocalized Fe3.5+ ions becoming localized with a charge disproportion forming an incommensurate charge-ordered phase. Strong resonant enhancement of these satellites at the Fe L-III absorption edge confirms that this charge ordering is occurring at the Fe(2) sites. Further cooling increases the charge order correlation until T similar or equal to 62Kwhere there is a full structural transition from the tetragonal phase to a mononclinic phase. This causes a jump in the charge order wavevector from an incommensurate value of 0.610 to a commensurate ground state position of 5/8. This first-order structural transition displays considerable hysteresis as well as dramatic reductions in the magnetization, resistivity and magnetoresistance. The transition also causes an antiferromagnetic spin-ordering with a doubled unit cell along the c-axis. Well as observing new commensurate magnetic reflections at the Fe-III edge we also observed resonant enhancement at the oxygen K-edge showing considerable hybridization between the Fe 3d and oxygen 2p states at low temperatures. Our results show that the formation of a magnetic long-rage ordered ground state drives the charge ordering from an incommensurate ordering to a commensurate ground state. This is evidence of a strong coupling between the magnetic and charge order parameters which is the basis for the unusual magnetoresistive effects observed at the transition.

Update: 3-Nov-2016

Title:
Ab-initio, Mossbauer spectroscopy, and magnetic study of the approximant Al72Ni9Fe19 to a decagonal Al-Ni-Fe quasicrystal
Authors:
Nejadsattari, F; Stadnik, ZM; Przewoznik, J; Grushko, B Author Full Names: Nejadsattari, Farshad; Stadnik, Zbigniew M.; Przewoznik, Janusz; Grushko, Benjamin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 689 726-732; 10.1016/j.jallcom.2016.08.021 DEC 25 2016
Abstract:
We report the results of ab-initio electronic structure and electric field gradient calculations and of X-ray diffraction, Fe-57 Mossbauer spectroscopy, and magnetic studies of the approximant Al72Ni9Fe19 to a decagonal Al-Ni-Fe quasicrystal. The approximant crystallizes in the hexagonal space group P63/mmc with the lattice parameters a = 7.6989(2) A ($) over circle and c = 7.6724(2) A ($) over circle. A pseudogap in the density of states, centered at similar to 0.30 eV above the Fermi level and with a width of similar to 0.35 eV, is found. Evidence for the covalent nature of the chemical bonding and good metallicity of Al72Ni9Fe19 is provided. The Mossbauer spectra and a 1/T-like dependence of the magnetic susceptibility indicate that Al72Ni9Fe19 is a paramagnet down to 2.0 K. The shape of the Mossbauer spectra is accounted for by a superposition of two quadrupole doublets corresponding to Fe atoms located at two inequivalent crystallographic sites. A sudden change of the quadrupole splittings of the two doublets at similar to 200 K indicates a possible structural phase transition. Excellent agreement between the calculated and measured quadrupole splittings is observed. The Debye temperature of Al72Ni9Fe19 is found to be 431 (3) K. (C) 2016 Elsevier B. V. All rights reserved.
Title:
High temperature phases with wurtzite-derived structure in Zn2LiGaO4-ZnO alloy system
Authors:
Kita, M; Fukada, T; Yamaguchi, S; Omata, T Author Full Names: Kita, Masao; Fukada, Tomoaki; Yamaguchi, Shu; Omata, Takahisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 69-76; 10.1016/j.jallcom.2016.06.249 A DEC 15 2016
Abstract:
We investigated the structural phase transformations of Zn2LiGaO4, which is a quaternary oxide semiconductor with a wide band gap of 4.0 eV, and its alloys with ZnO by using in-situ high-temperature X-ray diffraction (XRD), room-temperature XRD and selected-area electron diffraction of samples quenched from high temperatures of >873 K. Three types of phases with the wurtzite-derived structure were found in the y(Zn2LiGaO4)(1/4)-(1-y)ZnO alloy system. First is the low-temperature phase, phase I, in which constituent cations are ordered similarly to those in a Cd2AgGaS4-type structure. Phase I has an incommensurate modulation vector of 1.04b* and is stable at <1070 K and compositions of 0.96 <= y <= 1 and is stable at room temperature for y = 0.92. The second phase, phase II, appears at intermediate temperatures of 773-1373 K at 0.96 <= y <= 1, and its incommensurate modulation vector is 1.08b*. *Phase* III, which has no long-range cation ordering but still has short-range cation ordering, is stable for 0.92 <= y < 1 at high temperatures and for 0.2 < y < 0.92 from room temperature to high temperatures. We discuss the driving force of the transformations among the three phases in terms of their crystal structure and the mismatch in thermal expansion between -Zn-O-Zn-O- and -Li-O-Ga-O- linkages. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Anisotropy of the electric transport properties of decagonal Al-Cu-Co(Fe) quasicrystals
Authors:
Shulyatev, DA; Klyueva, MV; Devaradjan, U Author Full Names: Shulyatev, D. A.; Klyueva, M. V.; Devaradjan, U.
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 117 (9):883-888; 10.1134/S0031918X16070152 SEP 2016
Abstract:
The method of growth from a melt solution was used to obtain iron-alloyed (0.08 at %) Al-Cu-Co single crystals with a decagonal symmetry. The temperature dependences of the electrical resistivity in magnetic fields of 0-18 T were measured using samples oriented in the periodic direction (rho (p) (T)) and in the quasi-periodic plane (rho (q) (T)). A strong anisotropy of the resistivity was observed; the rho (p) (T) curve is linear, whereas the rho (q) (T) curve is approximated well by a second-order polynomial. A strong anisotropy of the magnetoresistance was also observed; a positive magnetoresistance Delta rho/rho similar to 10(-3) for the current flowing in the quasiperiodic plane; and a weak (close to zero) negative magnetoresistance for the current flowing along the periodic direction.

Update: 27-Oct-2016

Title:
Application of electron backscatter diffraction (EBSD) to quasicrystal-containing microstructures in the Mg-Cd-Yb system
Authors:
Tanaka, R; Ohhashi, S; Fujita, N; Demura, M; Yamamoto, A; Kato, A; Tsai, AP Author Full Names: Tanaka, R.; Ohhashi, S.; Fujita, N.; Demura, M.; Yamamoto, A.; Kato, A.; Tsai, A. P.
Source:
ACTA MATERIALIA, 119 193-202; 10.1016/j.actamat.2016.08.011 OCT 15 2016
Abstract:
We develop a new analysis system for identifying orientation of an icosahedral quasicrystal (iQc) in a SEM installed with an electron backscatter diffraction (EBSD) instrument. The system is successfully applied to determine the orientation of any given iQc grain by reading and assigning the Kikuchi bands obtained with the EBSD. This enables us to analyze relative orientations of iQc and alpha Mg grains in a eutectic structure obtained through a unidirectional solidification process for the Mg-Cd-Yb system. According to EBSD analysis, growth direction of the eutectic structure is shown to be clearly parallel to a two-fold axis of the iQc and {10-10} of alpha Mg, and a unique orientation relationship in iQc and alpha Mg grains is verified in all iQc-alpha Mg coexisting regions. The similarity between primary inter-planar spacings of the iQc and alpha Mg phases is a key factor for stabilizing the interface of two phases and favoring the formation of eutectic structure. This stabilization mechanism is supported by a simple argument on the energetics of a quasiperiodic/periodic lattice interface. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Two-Level Electron Excitations and Distinctive Physical Properties of Al-Cu-Fe Quasicrystals
Authors:
Prekul, A; Shchegolikhina, N Author Full Names: Prekul, Alexandre; Shchegolikhina, Natalya
Source:
CRYSTALS, 6 (9):10.3390/cryst6090119 SEP 2016
Abstract:
This article is not a review in the conventional sense. Rather, it is a monographic study of the implications of detection in Al-Cu-Fe quasicrystals of the electronic heat capacity contributions associated with the two-level electron excitations. Our aim was to reveal correlations between these contributions, on the one hand, and specific features of electron transport, magnetic susceptibility, Hall-effect, tunnelling and optical spectra, on the other hand. It is shown that the full range of these features can be understood in the framework of the unified conceptual scheme based on two-level electron excitations.
Title:
Statistical Approach to Diffraction of Periodic and Non-Periodic Crystals-Review
Authors:
Strzalka, R; Buganski, I; Wolny, J Author Full Names: Strzalka, Radoslaw; Buganski, Ireneusz; Wolny, Janusz
Source:
CRYSTALS, 6 (9):10.3390/cryst6090104 SEP 2016
Abstract:
In this paper, we show the fundamentals of statistical method of structure analysis. Basic concept of a method is the average unit cell, which is a probability distribution of atomic positions with respect to some reference lattices. The distribution carries complete structural information required for structure determination via diffraction experiment regardless of the inner symmetry of diffracting medium. The shape of envelope function that connects all diffraction maxima can be derived as the Fourier transform of a distribution function. Moreover, distributions are sensitive to any disorder introduced to ideal structure-phonons and phasons. The latter are particularly important in case of quasicrystals. The statistical method deals very well with phason flips and may be used to redefine phasonic Debye-Waller correction factor. The statistical approach can be also successfully applied to the peak's profile interpretation. It will be shown that the average unit cell can be equally well applied to a description of Bragg peaks as well as other components of diffraction pattern, namely continuous and singular continuous components. Calculations performed within statistical method are equivalent to the ones from multidimensional analysis. The atomic surface, also called occupation domain, which is the basic concept behind multidimensional models, acquires physical interpretation if compared to average unit cell. The statistical method applied to diffraction analysis is now a complete theory, which deals equally well with periodic and non-periodic crystals, including quasicrystals. The method easily meets also any structural disorder.
Title:
A Review of Transmission Electron Microscopy of Quasicrystals-How Are Atoms Arranged?
Authors:
Li, RT; Li, Z; Dong, ZL; Khor, KA Author Full Names: Li, Ruitao; Li, Zhong; Dong, Zhili; Khor, Khiam Aik
Source:
CRYSTALS, 6 (9):10.3390/cryst6090105 SEP 2016
Abstract:
Quasicrystals (QCs) possess rotational symmetries forbidden in the conventional crystallography and lack translational symmetries. Their atoms are arranged in an ordered but non-periodic way. Transmission electron microscopy (TEM) was the right tool to discover such exotic materials and has always been a main technique in their studies since then. It provides the morphological and crystallographic information and images of real atomic arrangements of QCs. In this review, we summarized the achievements of the study of QCs using TEM, providing intriguing structural details of QCs unveiled by TEM analyses. The main findings on the symmetry, local atomic arrangement and chemical order of QCs are illustrated.
Title:
Elastodynamic Analysis of a Hollow Cylinder with Decagonal Quasicrystal Properties: Meshless Implementation of Local Integral Equations
Authors:
Hosseini, SM; Sladek, J; Sladek, V Author Full Names: Hosseini, Seyed Mahmoud; Sladek, Jan; Sladek, Vladimir
Source:
CRYSTALS, 6 (8):10.3390/cryst6080094 AUG 2016
Abstract:
A meshless approximation and local integral equation (LIE) formulation are proposed for elastodynamic analysis of a hollow cylinder made of quasicrystal materials with decagonal quasicrystal properties. The cylinder is assumed to be under shock loading. Therefore, the general transient elastodynamic problem is considered for coupled phonon and phason displacements and stresses. The equations of motion in the theory of compatible elastodynamics of wave type for phonons and wave-telegraph type for phasons are employed and can be easily modified to the elasto-hydro dynamic equations for quasicrystals (QCs). The angular dependence of the tensor of phonon-phason coupling coefficients handicaps utilization of polar coordinates, when the governing equations would be given by partial differential equations with variable coefficients. Despite the symmetry of the geometrical shape, the local weak formulation and meshless approximation are developed in the Cartesian coordinate system. The response of the cylinder in terms of both phonon and phason stress fields is obtained and studied in detail.
Title:
A ZrNiAl related high-pressure modification of CeRuSn
Authors:
Niehaus, O; Heymann, G; Huppertz, H; Rodewald, UC; Chevalier, B; Matar, SF; Hoffmann, RD; Pottgen, R Author Full Names: Niehaus, Oliver; Heymann, Gunter; Huppertz, Hubert; Rodewald, Ute Ch.; Chevalier, Bernard; Matar, Samir F.; Hoffmann, Rolf-Dieter; Poettgen, Rainer
Source:
DALTON TRANSACTIONS, 45 (36):14216-14229; 10.1039/c6dt02294d 2016
Abstract:
Monoclinic CeRuSn with its own structure type transforms to a high-pressure modification at 11.5 GPa and 1470 K (1000 t press, Walker type module). The structure of the high-pressure phase was refined from X-ray single crystal diffractometer data at room temperature. The HP-CeRuSn subcell structure adopts the ZrNiAl type: P (6) over bar 2m, a = 751.4(3) and c = 394.6(2) pm, wR2 = 0.0787, 310 F-2 values and 15 variables. The Ru2 atoms within the Sn-6 trigonal prisms show a strongly enhanced U-33 parameter. Weak satellite reflections indicate a commensurate modulation: (3 + 1)D superspace group P31m(1/3,1/3,gamma)000, a = 751.4(3) and c = 394.6(2) pm, gamma = -1/3, wR2 = 0.0786, 1584 F-2 values, 32 variables for the main reflections and wR2 = 0.3757 for the satellites of 1st order. A description of this new superstructure variant of the ZrNiAl type is possible in a transformed 3D supercell with the space group R3m and Z = 9. The driving force for formation of the modulation is strengthening of Ru-Sn bonding within the comparatively large Ru@Sn-6 trigonal prisms. Electronic structure calculations point to an almost depleted Ce 4f shell. This is substantiated by temperature-dependent magnetic susceptibility data. Fitting of the data within the inter-configuration fluctuation model (ICF) resulted in cerium valences of 3.41 at 10 K and 3.31 at 350 K. Temperature dependent specific heat data underline the absence of magnetic ordering.

Update: 20-Oct-2016

Title:
Complex magnetic ordering in Tm3Cu4Si4
Authors:
Baran, S; Szytula, A; Kaczorowski, D; Damay, F Author Full Names: Baran, S.; Szytula, A.; Kaczorowski, D.; Damay, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 577-584; 10.1016/j.jallcom.2016.07.241 B DEC 15 2016
Abstract:
Tm3Cu4Si4 crystalizes in the orthorhombic Gd3Cu4Ge4-type crystal structure with trivalent Tm atoms occupying 2(d) and 4(e) Wyckoff sites. Neutron diffraction data shows that at 1.7 K the Tm magnetic moments form a commensurate magnetic structure defined by the propagation vectors (k) over right arrow (2d) = [0,1/2,0] and (k) over right arrow (4e) = [1/4,0,1/2] for the 2(d) and 4(e) sites, respectively. With increasing temperature, the magnetic order in the 4(e) sublattice undergoes near 2.5 K an order-order transition into an incommensurate magnetic structure and then disappears at 2.9 K. Similar changes in the magnetic structure occur in the 2(d) sublattice at 3.3 and 3.8 K, respectively. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Al-rich region of Al-Cu-Mn
Authors:
Grushko, B; Mi, SB Author Full Names: Grushko, B.; Mi, S. B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 957-963; 10.1016/j.jallcom.2016.07.075 B DEC 15 2016
Abstract:
The Al-Cu-Mn alloy system was studied above 45 at.% Al between 550 and 910 degrees C by scanning electron microscopy, powder X-ray diffraction and differential thermal analysis. A wide ternary region of the so-called beta-phase extending along similar to 50 at.% Al was confirmed. It has a CsCl-type structure with a approximate to 0.292-0.298 nm. The total gamma(1)/gamma(2)-region extends from Al-Mn up to similar to 17 at.% Cu and the high-temperature T-Al3Mn phase (Pnma, a approximate to 1.48, b approximate to 1.24, c approximate to 1.25 nm) extends up to similar to 15 at.% Cu. The so-called R-phase (Bbmm, a approximate to 2.41, b approximate to 1.25, c approximate to 0.76 nm) was found to exist in a compositional region of Al74-80Cu5-12.5Mn12.5-18. The ternary phase earlier reported at Al57.9Cu26.3Mn15.8 was confirmed. It exists below 697 degrees C in a compositional region of Al55-58Cu29-Mn-37(7.5-14). The decagonal D-3-phase was concluded to be stable in a compositional region of Al61.5-68.5Cu19-29.5Mn9-16. Below 631 degrees C an fcc phase (a = 0.5814 nm) was revealed around similar to Al60Cu36.5Mn3.5. Partial isothermal sections at 550, 600, 650, 750, 850 and 910 degrees C were constructed. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Microstructural characteristics and mechanical properties of Mg-Zn-Y alloy containing icosahedral quasicrystals phase treated by pulsed magnetic field
Authors:
Zhang, L; Zhou, W; Hu, PH; Zhou, Q Author Full Names: Zhang, L.; Zhou, W.; Hu, P. H.; Zhou, Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 868-874; 10.1016/j.jallcom.2016.07.280 B DEC 15 2016
Abstract:
Pulsed magnetic field (PMF) has been imposed during solidification of Mg-Zn-Y alloy containing icosahedral quasicrystals phase (I-phase) in this work. The effects of vibration power on the solidification microstructure and mechanical properties of Mg93Zn6Y alloy were studied. The results show that the solidification microstructure of the Mg93Zn6Y alloy was further refined with increasing vibration power. The primary alpha-Mg in the alloy treated by PMF was changed from dendrites with the average grain size more than 1 mm untreated by PMF to rosette-like and polyhedral morphology with the average grain size of 122 mm. Moreover, the I-phase was changed from continuous thick skeletal to discontinuous fine reticular and particle-like morphology. The fraction of I-phase in the alloy treated by PMF was also reduced due to the increase of concentrations of Zn and Y elements inside grains. The mechanical properties of Mg93Zn6Y alloy treated by PMF were also improved significantly. The yield strength, ultimate tensile strength and elongation of the alloy treated by PMF at a vibration power of 350 Wat room temperature were 162 MPa, 221 MPa and 1.99%, which were increased by 65%, 66% and 124% respectively, compared to those of the alloy untreated by PMF. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Laser-Induced Charge-Density-Wave Transient Depinning in Chromium
Authors:
Jacques, VLR; Laulhe, C; Moisan, N; Ravy, S; Le Bolloc'h, D Author Full Names: Jacques, V. L. R.; Laulhe, C.; Moisan, N.; Ravy, S.; Le Bolloc'h, D.
Source:
PHYSICAL REVIEW LETTERS, 117 (15):10.1103/PhysRevLett.117.156401 OCT 3 2016
Abstract:
We report on time-resolved x-ray diffraction measurements following femtosecond laser excitation in pure bulk chromium. Comparing the evolution of incommensurate charge-density-wave (CDW) and atomic lattice reflections, we show that, a few nanoseconds after laser excitation, the CDW undergoes different structural changes than the atomic lattice. We give evidence for a transient CDW shear strain that breaks the lattice point symmetry. This strain is characteristic of sliding CDWs, as observed in other incommensurate CDW systems, suggesting the laser-induced CDW sliding capability in 3D systems. This first evidence opens perspectives for unconventional laser-assisted transport of correlated charges.
Title:
Phase transition of solid bismuth under high pressure
Authors:
Chen, HY; Xiang, SK; Yan, XZ; Zheng, LR; Zhang, Y; Liu, SG; Bi, Y Author Full Names: Chen, Hai-Yan; Xiang, Shi-Kai; Yan, Xiao-Zhen; Zheng, Li-Rong; Zhang, Yi; Liu, Sheng-Gang; Bi, Yan
Source:
CHINESE PHYSICS B, 25 (10):10.1088/1674-1056/25/10/108103 OCT 2016
Abstract:
As a widely used pressure calibrator, the structural phase transitions of bismuth from phase I, to phase II, to phase III, and then to phase V with increasing pressure at 300 K have been widely confirmed. However, there are different structural versions for phase III, most of which are determined by x-ray diffraction (XRD) technology. Using x-ray absorption fine structure (XAFS) measurements combined with ab initio calculations, we show that the proposed incommensurate composite structure of bismuth of the three configurations is the best option. An abnormal continuous increase of the nearest-neighbor distance of phase III with elevated pressure is also observed. The electronic structure transformation from semimetal to metal is responsible for the complex behavior of structure transformation.
Title:
Collapse and reappearance of magnetic orderings in spin frustrated TbMnO3 induced by Fe substitution
Authors:
Hong, F; Yue, BB; Wang, JL; Studer, A; Fang, CS; Wang, XL; Dou, SX; Cheng, ZX Author Full Names: Hong, Fang; Yue, Binbin; Wang, Jianli; Studer, Andrew; Fang, Chunsheng; Wang, Xiaolin; Dou, Shixue; Cheng, Zhenxiang
Source:
APPLIED PHYSICS LETTERS, 109 (10):113-117; 10.1063/1.4962465 SEP 5 2016
Abstract:
We studied the temperature dependent magnetic phase evolution in spin frustrated TbMnO3 affected by Fe doping via powder neutron diffraction. With the introduction of Fe (10% and 20%), the long range incommensurate magnetic orderings collapse. When the Fe content is increased to 30%, a long-range antiferromagnetic ordering develops, while a spin reorientation transition is found near 35K from a canted G-type antiferromagnetic ordering to a collinear G-type antiferromagnetic ordering. This work demonstrates the complex magnetic interactions existing in transition metal oxides, which helps to understand the frustrated spin states in other similar systems and design magnetic materials as well. Published by AIP Publishing.

Update: 13-Oct-2016

Title:
Crystallization behavior and mechanical properties of (Al90Fe5Ce5)(100-x)Ti-x amorphous alloys
Authors:
Singh, D; Singh, D; Mandal, RK; Srivastava, ON; Tiwari, RS Author Full Names: Singh, Dharmendra; Singh, Devinder; Mandal, R. K.; Srivastava, O. N.; Tiwari, R. S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 687 990-998; 10.1016/j.jallcom.2016.06.272 DEC 5 2016
Abstract:
The crystallization behavior and mechanical properties of melt-spun (Al90Fe5Ge5)(100-x)Ti-x (x = 0, 4, 8 and 12 at.%) alloys have been investigated. The amorphous phase seems to be stable up to x = 8. The crystallization products for the amorphous alloys with x = 0-8 mainly composed of fcc-Al and icosahedral phases in the glassy matrix. The load dependent hardness behavior of amorphous alloys with and without Ti addition has been studied. The hardness value of the amorphous alloys has been found to be 3.72 and 3.07 GPa for x = 0 and 8 at 100 g load respectively. The annealed ribbons have higher hardness and strength as compared to that of as-synthesized ribbons. The enhanced values of hardness of the (Al90Fe5Ce5)(100-x)Ti-x (x = 0, 4 and 8) alloys are attributed to the combined effects of icosahedral nano particles and Al nanoparticles in amorphous matrix. The absence of cracks around the indentation area up to 500 g of load for amorphous alloys suggests better capability to resist crack propagation in comparison to the annealed alloys. The formation of shear bands around the indentation periphery has been observed. The number of visible shear bands for the as-synthesized ribbons is higher in comparison to those of annealed ribbons. The values of yield strength and Meyer exponent of these alloys are also compared. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Spatially modulated spin structure (SMSS) in BiFeO3-30 years later
Authors:
Sosnowska, IM Author Full Names: Sosnowska, I. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (42):10.1088/0953-8984/28/42/421002 OCT 26 2016
Title:
Martensitic transition, structure and magnetic anisotropy of martensite in Ni-Mn-Sn single crystal
Authors:
Czaja, P; Szczerba, MJ; Chulist, R; Balanda, M; Przewoznik, J; Chumlyakov, YI; Schell, N; Kapusta, C; Maziarz, W Author Full Names: Czaja, P.; Szczerba, M. J.; Chulist, R.; Balanda, M.; Przewoznik, J.; Chumlyakov, Y. I.; Schell, N.; Kapusta, Cz.; Maziarz, W.
Source:
ACTA MATERIALIA, 118 213-220; 10.1016/j.actamat.2016.07.059 OCT 1 2016
Abstract:
The structural and magnetic properties of Ni50Mn37.5Sn12.5 single crystal were investigated. The alloy undergoes martensitic transformation at 308 K from the austenite phase to the structurally modulated tetragonal 4M martensite phase with lattice parameters a(4M) = 6.177 angstrom, c(4M) = 5.669 angstrom. The alloy shows 7.9% pre-strain upon uniaxial compression along the (001) direction, which is near the theoretical 8.2% maximum twinning strain. Magnetization measurements reveal that the magnetic anisotropy of the martensite phase is uniaxial with the easy magnetization axis corresponding to the shortest c axis of the tetragonally distorted unit cell, while its a axis is the hard magnetization direction. The magnetic anisotropy constant K-u saturates at low temperature around 7 x 10(4) j/m(3) and then gradually decreases with increasing temperature as the system approaches the Curie temperature of martensite at 215 K. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Er1.33Pt3Ga8: A modulated variant of the Er4Pt9Al24-structure type
Authors:
Oswald, IWH; Gourdon, O; Bekins, A; Evans, J; Treadwell, LJ; Chan, JY; Macaluso, RT Author Full Names: Oswald, Iain W. H.; Gourdon, Olivier; Bekins, Amy; Evans, Jess; Treadwell, LaRico J.; Chan, Julia Y.; Macaluso, Robin T.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 242 161-167; SI 10.1016/j.jssc.2016.04.009 2 OCT 2016
Abstract:
Single crystals of Er1.33Pt3Ga8 were synthesized in a molten Ga flux. Er1.33Pt3Ga8 can be considered to be a modulated variant of the Er4Pt9Al24-structure type, where the partial occupancies are ordered. Indeed, the presence of weak satellite reflections indicates a complex organization and distribution of the Er and Ga atoms within the [ErGa] slabs. The structure has been solved based on single crystal X-ray diffraction data in the monoclinic superspace group X2/m(0 beta 0)00 with a commensurate modulated vector q=1/3b*. Precession images also indicate diffusion in the perpendicular direction indicating a partial disorder of this arrangement from layer to layer. In addition, Er1.33Pt3Ga8 shows antiferromagnetic ordering at T-N similar to 5 K. (C) 2016 Elsevier Inc. All rights reserved.
Title:
Strong magnetoelastic coupling at the transition from harmonic to anharmonic order in NaFe(WO4)(2) with 3d(5) configuration
Authors:
Holbein, S; Ackermann, M; Chapon, L; Steffens, P; Gukasov, A; Sazonov, A; Breunig, O; Sanders, Y; Becker, P; Bohaty, L; Lorenz, T; Braden, M Author Full Names: Holbein, S.; Ackermann, M.; Chapon, L.; Steffens, P.; Gukasov, A.; Sazonov, A.; Breunig, O.; Sanders, Y.; Becker, P.; Bohaty, L.; Lorenz, T.; Braden, M.
Source:
PHYSICAL REVIEW B, 94 (10):10.1103/PhysRevB.94.104423 SEP 21 2016
Abstract:
The crystal structure of the double tungstate NaFe(WO4)(2) arises from that of the spin-driven multiferroic MnWO4 by inserting nonmagnetic Na layers. NaFe(WO4)(2) exhibits a three-dimensional incommensurate spin-spiral structure at low temperature and zero magnetic field, which, however, competes with commensurate order induced by magnetic field. The incommensurate zero-field phase corresponds to the condensation of a single irreducible representation but it does not imply ferroelectric polarization because spirals with opposite chirality coexist. Sizable anharmonic modulations emerge in this incommensurate structure, which are accompanied by large magnetoelastic anomalies, while the onset of the harmonic order is invisible in the thermal-expansion coefficient. In magnetic fields applied along the monoclinic axis, we observe a first-order transition to a commensurate structure that again is accompanied by large magnetoelastic effects. The large magnetoelastic coupling, a reduction of the b lattice parameter, is thus associated only with the commensurate order. Upon releasing the field at low temperature, the magnetic order transforms to another commensurate structure that considerably differs from the incommensurate low-temperature phase emerging upon zero-field cooling. The latter phase, which exhibits a reduced ordered moment, seems to be metastable.
Title:
Unusual Relaxor Ferroelectric Behavior in Stairlike Aurivillius Phases
Authors:
Steciuk, G; Boullay, P; Pautrat, A; Barrier, N; Caignaert, V; Palatinus, L Author Full Names: Steciuk, Gwladys; Boullay, Philippe; Pautrat, Alain; Barrier, Nicolas; Caignaert, Vincent; Palatinus, Lukas
Source:
INORGANIC CHEMISTRY, 55 (17):8881-8891; 10.1021/acs.inorgchem.6b01373 SEP 5 2016
Abstract:
New ferroelectric layered materials were found in the pseudobinary system Bi5Nb3O15-ABi(2)Nb(2)O(9) (A= Ba, Sr and Pb). Preliminary observations made by transmission electron microscopy indicate that these compounds exhibit a complex incommensurately modulated structure. A (3 + 1)D structural model is obtained using ab initio phasing by charge flipping based on the analysis of precession electron diffraction tomography data. The (3 + 1)D structure is further validated by a refinement against neutron powder diffraction. These materials possess a layered structure with discontinuous [Bi2O2] slabs and perovskite blocks. While these structural units are characteristics of Aurivillius phases, the existence of periodic crystallographic shear planes offers strong similarities with collapsed or stairlike structures known in high-Tc superconductors and related compounds. Using dielectric spectroscopy, we study the phase transitions of these new layered materials. For A = Ba and Sr, a Vogel-Fulcher-like behavior characteristic of the so-called relaxor ferroelectrics is observed and compared to "canonical" relaxors. For A = Sr, the absence of a Bums temperature separated from the freezing temperature appears as a rather unusual behavior.
Title:
An exceptional series of phase transitions in hydrophobic amino acids with linear side chains
Authors:
Gorbitz, CH; Karen, P; Dusek, M; Petricek, V Author Full Names: Gorbitz, Carl Henrik; Karen, Pavel; Dusek, Michal; Petricek, Vaclav
Source:
IUCRJ, 3 341-353; 10.1107/S2052252516010472 5 SEP 2016
Abstract:
The solid-state phase transitions and intermediate structures of S-2-aminobutanoic acid (L-2-aminobutyric acid), S-2-aminopentanoic acid (L-norvaline), S-2-aminohexanoic acid (L-norleucine) and L-methionine between 100 and 470 K, identified by differential scanning calorimetry, have been characterized in a comprehensive single-crystal X-ray diffraction investigation. Unlike other enantiomeric amino acids investigated until now, this group featuring linear side chains displays up to five distinct phases. The multiple transitions between them involve a number of different processes: alteration of the hydrogen-bond pattern, to our knowledge the first example of this observed for an amino acid, sliding of molecular bilayers, seen previously only for racemates and quasiracemates, concerted side-chain rearrangements and abrupt as well as gradual modifications of the side-chain disorder. Ordering of L-norleucine upon cooling even proceeds via an incommensurately modulated structure. L-Methionine has previously been described as being fully ordered at room temperature. An accurate refinement now reveals extensive disorder for both molecules in the asymmetric unit, while two previously unknown phases occur above room temperature.
Title:
Heuristic Description of Magnetoelectricity of Cu2OSeO3
Authors:
Milde, P; Neuber, E; Bauer, A; Pfleiderer, C; Berger, H; Eng, LM Author Full Names: Milde, Peter; Neuber, Erik; Bauer, Andreas; Pfleiderer, Christian; Berger, Helmuth; Eng, Lukas M.
Source:
NANO LETTERS, 16 (9):5612-5618; 10.1021/acs.nanolett.6b02167 SEP 2016
Abstract:
CuO2SeO3 is an insulating material that hosts topologically nontrivial spin whirls, so-called skyrmions, and exhibits magnetoelectric coupling allowing to manipulate these skyrmions by means of electric fields. We report magnetic force microscopy imaging of the real-space spin structure on the surface of a.. bulk single crystal of CuO2SeO3. Based on measurements of the electric polarization using Kelvin-probe force microscopy, we develop a heuristic description of the magnetoelectric properties in CuO2SeO3. The model successfully describes the dependency of the electric polarization on the magnetization in all magnetically modulated phases.

Update: 6-Oct-2016

Title:
Multi-phase quasicrystalline alloys for superior wear resistance
Authors:
Lee, K; Hsu, JL; Naugle, D; Liang, H Author Full Names: Lee, Kyungjun; Hsu, Jialin; Naugle, Donald; Liang, Hong
Source:
MATERIALS & DESIGN, 108 440-447; 10.1016/j.matdes.2016.06.113 OCT 15 2016
Abstract:
Highly wear-resistant alloys are important in many engineering and biomedical applications. In this research, a multi-phase quasicrystal-based alloy was developed using a rapid arc-melting technique. The alloy contains three characteristic phases, hard lambda-Al13Fe4, quasicrystal icosahedral (i-phase), and ductile tau-AlCu. The Vickers micro hardness of each was 828, 795, and 552, respectively, with an overall hardness of 334 (HR15T). Due to the co-existence of these three phases, this alloy exhibits both hardness and ductility. As such, the new material has favorable wear and crack resistance. The approaches used in this study are beneficial for the future design and development of this class of quasicrystalline alloys. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
Quantization of states and strain-induced transformation of charge-density waves in the quasi-one-dimensional conductor TaS3
Authors:
Zybtsev, SG; Pokrovskii, VY Author Full Names: Zybtsev, S. G.; Pokrovskii, V. Ya.
Source:
PHYSICAL REVIEW B, 94 (11):10.1103/PhysRevB.94.115140 SEP 16 2016
Abstract:
We report studies of low-field conductivity, sigma, of nanosized samples of orthorhombic TaS3 as a function of strain, epsilon. The sigma(epsilon) curves show steplike changes associated with the "quantization" of the wave vector, q, of the charge-density wave. Based on the effect we have revealed the change of the q-vector with strain: its in-chain component (normalized by the reciprocal lattice constant) is found to increase with sample stretch. A similar q(epsilon) dependence results from the analysis of the sigma(epsilon) hysteresis for macroscopic samples. This means that the strain-induced anomalies cannot be explained by the transition of the CDW to fourfold commensurability with the pristine lattice (lock-in transition), as it was supposed earlier. We also discuss the metastable length states and the elastic anomalies in TaS3 in light of the observed q(epsilon) dependence.
Title:
Thermoelastic analysis of a two-dimensional decagonal quasicrystal with a conductive elliptic hole
Authors:
Guo, JH; Yu, J; Xing, YM; Pan, EN; Li, LH Author Full Names: Guo, Junhong; Yu, Jing; Xing, Yongming; Pan, Ernian; Li, Lianhe
Source:
ACTA MECHANICA, 227 (9):2595-2607; 10.1007/s00707-016-1657-7 SEP 2016
Abstract:
A general solution in terms of the Stroh-type formalism for quasicrystals is developed for two-dimensional thermoelastic deformation. The solution is then applied to analyze the deformation of a conductive elliptic hole embedded in the decagonal quasicrystal plane which is under a remotely uniform heat flow. The hoop stresses around the elliptic hole are derived in an exact closed form. When the thermal conductivity inside the hole is neglected, the present results are reduced to the existing solutions in the literature. Some numerical examples are provided to show the effects of the geometrical shape of the hole and the thermal conductivity inside the hole on the hoop stresses. The results show that along the hole the variations of the hoop stress of the phonon field are completely different from those of the phason field. Compared to the corresponding insulated case, consideration of a conductive elliptic hole would lead to very different and interesting thermoelastic behaviors.
Title:
Microstructural changes in an extruded Mg-Zn-Y alloy reinforced by quasicrystalline I-phase by small additions of calcium, manganese and cerium-rich mischmetal
Authors:
Medina, J; Perez, P; Garces, G; Tolnai, D; Stark, A; Schell, N; Adeva, P Author Full Names: Medina, J.; Perez, P.; Garces, G.; Tolnai, D.; Stark, A.; Schell, N.; Adeva, P.
Source:
MATERIALS CHARACTERIZATION, 118 186-198; 10.1016/j.matchar.2016.05.019 AUG 2016
Abstract:
The effects of calcium, manganese and cerium-rich mischmetal additions on the microstructure and texture of the extruded Mg-6Zn-1Y (wt.%) alloy have been investigated. The microstructure of the alloys consisted of a magnesium matrix embedding second phase particles aligned along the extrusion direction. The nature and volume fraction of the second phases depended on the alloying element. Thus, Ce-rich mischmetal promoted the formation of T-phase while calcium additions resulted in the formation of a ternary Mg-Zn-Ca compound. Only, manganese additions did not affect the existence of the I-phase present in the ternary alloy. The texture was measured and it was found that calcium addition has a significant effect weakening the extrusion texture. (C) 2016 Elsevier Inc. All rights reserved.
Title:
First Step Towards a Devil's Staircase in Spin-Crossover Materials
Authors:
Trzop, E; Zhang, DP; Pineiro-Lopez, L; Valverde-Munoz, FJ; Munoz, MC; Palatinus, L; Guerin, L; Cailleau, H; Real, JA; Collet, E Author Full Names: Trzop, Elzbieta; Zhang, Daopeng; Pineiro-Lopez, Lucia; Valverde-Munoz, Francisco J.; Carmen Munoz, M.; Palatinus, Lukas; Guerin, Laurent; Cailleau, Herve; Antonio Real, Jose; Collet, Eric
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 55 (30):8675-8679; 10.1002/anie.201602441 JUL 18 2016
Abstract:
The unprecedented bimetallic 2D coordination polymer {Fe[(Hg(SCN)(3))(2)](4,4'-bipy)(2)}(n) exhibits a thermal high-spin (HS)<-> low-spin (LS) staircase-like conversion characterized by a multi-step dependence of the HS molar fraction gamma(HS). Between the fully HS (gamma(HS)= 1) and LS (gamma(HS)= 0) phases, two steps associated with different ordering appear in terms of spin-state concentration waves (SSCW). On the gamma(HS). 0.5 step, a periodic SSCW forms with a HS-LS-HS-LS sequence. On the gamma(HS) approximate to 0.34 step, the 4D superspace crystallography structural refinement reveals an aperiodic SSCW, with a HS-LS sequence incommensurate with the molecular lattice. The formation of these different long-range spatially ordered structures of LS and HS states during the multi-step spin-crossover is discussed within the framework of "Devil's staircase"-type transitions. Spatially modulated phases are known in various types of materials but are uniquely related to molecular HS/LS bistability in this case.
Title:
Atomic-scale mapping of twins and relevant defective structures in Al20Cu2Mn3 decagonal approximant
Authors:
Wang, J; Zhang, B; He, ZB; Wu, B; Ma, XL Author Full Names: Wang, J.; Zhang, B.; He, Z. B.; Wu, B.; Ma, X. L.
Source:
PHILOSOPHICAL MAGAZINE, 96 (23):2457-2467; 10.1080/14786435.2016.1205229 2016
Abstract:
Twins or multiple twins occur frequently in the orthorhombic Al20Cu2Mn3 approximant of decagonal quasi crystal (DQC). Due to the specific structural units, the twins in the Al20Cu2Mn3 approximant usually exhibit the glide-reflection characteristics. Using aberration-corrected transmission electron microscope at the atomic scale, we have observed not only glide-reflection twins but also simple mirror-reflection twins in the Al20Cu2Mn3 approximant. The two twinning modes are found to coexist in the present sample. These twins exhibit variant configurations at the twin boundaries where the tessellations of local subunits are imaged at an atomic scale. At the twin boundaries, diversified tiles such as star-like (S), bowtie-shaped and boat-shaped (B) are observed. The diversified tiles stacking with various manners allow the coexistence of the DQC and the approximant. Furthermore, the variants of B and S tiles are also found.

Update: 29-Sep-2016

Title:
Structure and mechanical properties in a powder-processed icosahedral-phase-strengthened aluminum alloy
Authors:
Watson, TJ; Gordillo, MA; Cernatescu, I; Aindow, M Author Full Names: Watson, Thomas J.; Gordillo, Mauricio A.; Cernatescu, Iuliana; Aindow, Mark
Source:
SCRIPTA MATERIALIA, 123 51-54; 10.1016/j.scriptamat.2016.05.037 OCT 2016
Abstract:
Nanocomposite powder particles of aluminum with dispersed icosahedral quasicrystals were produced by gas atomization from an Al-Cr-Mn-Co-Zr alloy. Bulk dispersion -strengthened material was obtained from the powder by blind-die compaction and forging. The material exhibited an attractive combination of room temperature mechanical properties with a dynamic elastic modulus of 90.5 GPa, a tensile yield strength of 690 MPa with 6% elongation to failure, and a high cycle fatigue life of 109 cycles at 207 MPa applied stress. The material also exhibited significant potential for elevated temperature applications with a modulus of 75 GPa and yield strength of 400 MPa at 300 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
Strengthening mechanisms in an Al-Fe-Cr-Ti nano-quasicrystalline alloy and composites
Authors:
Pedrazzini, S; Galano, M; Audebert, F; Collins, DM; Hofmann, F; Abbey, B; Korsunsky, AM; Lieblich, M; Escorial, AG; Smith, GDW Author Full Names: Pedrazzini, S.; Galano, M.; Audebert, F.; Collins, D. M.; Hofmann, F.; Abbey, B.; Korsunsky, A. M.; Lieblich, M.; Garcia Escorial, A.; Smith, G. D. W.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 672 175-183; 10.1016/j.msea.2016.07.007 AUG 30 2016
Abstract:
We report a study of the structure-processing-property relationships in a high strength Al93Fe3Cr2Ti2 nano-quasicrystalline alloy and composites containing 10 and 20 vol% ductilising pure Al fibres. The superimposed contributions of several different strengthening mechanisms have been modelled analytically using data obtained from systematic characterisation of the monolithic alloy bar. An observed yield strength of 544 MPa has been substantiated from a combination of solid solution strengthening, work hardening, precipitation hardening and Hall-Petch grain size dependent effects. These materials have been shown by other authors in previous published work to be highly sensitive to the size distribution of particles in the powder from which they are made, and the subsequent thermomechanical processing conditions. The processing condition employed in this study provided micron-sized grains with a strong [111] preferential orientation along the extrusion direction and a bimodal size distribution of the icosahedral nano-quasicrystalline precipitates. Both were deemed to be a significant contributor to the high yield strength observed. The addition of pure Al fibres was found to decrease the yield strength linearly with increasing Al content, and to auginent the ductility of the composites. (C) 2016 The Authors. Published by Elsevier B.V.
Title:
Observation and Structure Determination of an Oxide Quasicrystal Approximant
Authors:
Forster, S; Trautmann, M; Roy, S; Adeagbo, WA; Zollner, EM; Hammer, R; Schumann, FO; Meinel, K; Nayak, SK; Mohseni, K; Hergert, W; Meyerheim, HL; Widdra, W Author Full Names: Foerster, S.; Trautmann, M.; Roy, S.; Adeagbo, W. A.; Zollner, E. M.; Hammer, R.; Schumann, F. O.; Meinel, K.; Nayak, S. K.; Mohseni, K.; Hergert, W.; Meyerheim, H. L.; Widdra, W.
Source:
PHYSICAL REVIEW LETTERS, 117 (9):10.1103/PhysRevLett.117.095501 AUG 24 2016
Abstract:
We report on the first observation of an approximant structure to the recently discovered two-dimensional oxide quasicrystal. Using scanning tunneling microscopy, low-energy electron diffraction, and surface x-ray diffraction in combination with ab initio calculations, the atomic structure and the bonding scheme are determined. The oxide approximant follows a 3(2.)4.3.4 Archimedean tiling. Ti atoms reside at the corners of each tiling element and are threefold coordinated to oxygen atoms. Ba atoms separate the TiO3 clusters, leading to a fundamental edge length of the tiling 6.7 angstrom.
Title:
Polymorphism in Zintl Phases ACd(4)Pn(3): Modulated Structures of NaCd(4)Pn(3) with Pn = P, As
Authors:
Grotz, C; Baumgartner, M; Freitag, KM; Baumer, F; Nilges, T Author Full Names: Grotz, Carolin; Baumgartner, Maximilian; Freitag, Katharina M.; Baumer, Franziska; Nilges, Tom
Source:
INORGANIC CHEMISTRY, 55 (15):7764-7776; 10.1021/acs.inorgchem.6b01233 AUG 1 2016
Abstract:
NaCd4P3 and NaCd4As3 were synthesized via short-way transport using the corresponding elements and CdI2 as mineralizer. At room temperature, the two beta-polymorphs adopt the RbCd4As3 structure type which has been recently reported for alkali metal (A)-d(10) transition metal (T)-pnictides (Pn). The title compounds crystallize rhombohedrally in space group R (3) over barm at room temperature and show reversible phase transitions to incommensurately modulated alpha-polymorphs at lower temperatures. The low-temperature phases are monoclinic and can be described in space group Cm(alpha 0 gamma)s with q vectors of q = (-0.04,0,0.34) for alpha-NaCd4P3 and q(1) = (-0.02,0,0.34) for alpha-NaCd4As3. Thermal properties, Raman spectroscopy, and electronic structures have been determined. Both compounds are Zintl phases with band gaps of 1.05 eV for beta-NaCd4P3 and similar to 0.4 eV for beta-NaCd4As3.
Title:
Crystal structure of modulated martensite and crystallographic correlations between martensite variants of Ni50Mn38Sn12 alloy
Authors:
Lin, CQ; Yan, HL; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Lin, Chunqing; Yan, Haile; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 1276-1283; 10.1107/S1600576716010372 4 AUG 2016
Abstract:
A comprehensive study on the crystal structure, the microstructure and the crystallographic features of the martensite in an Ni50Mn38Sn12 alloy has been conducted in the present work. The results show that the martensite possesses a 4O modulated structure. The martensite is organized into broad plates in the original austenite grain. The plates contain irregularly shaped colonies with two characteristic microstructural patterns: a classical lamellar pattern and a herringbone pattern. Crystallographic analyses by scanning electron microscopy/electron backscatter diffraction demonstrate that in each colony there are four orientation variants (A, B, C and D) and they form three types of twins (type I, type II and compound twin). The interfaces between corresponding variants are coincident with their twinning plane K1. The interface planes of the compound twin pairs A&D and B&C can have one or two different orientations, which leads to the two microstructural patterns. The corresponding variants in neighboring colonies within one broad plate (intra-plate colonies) possess close orientations, but the type I and the type II twin relationships are interchanged. The variants in neighboring colonies situated in adjacent plates (inter-plate colonies) are type I or type II twin related but with some angular deviations. The plate interface is defined by the {221} plane of the variant pair with largest thickness. The results of the present work provide comprehensive microstructural and crystallographic information on modulated martensite in NiMnSn alloys that is useful for the understanding of their specific functionalities and helpful for further investigation on property optimization of these materials.
Title:
Superior room-temperature ductility of typically brittle quasicrystals at small sizes
Authors:
Zou, Y; Kuczera, P; Sologubenko, A; Sumigawa, T; Kitamura, T; Steurer, W; Spolenak, R Author Full Names: Zou, Yu; Kuczera, Pawel; Sologubenko, Alla; Sumigawa, Takashi; Kitamura, Takayuki; Steurer, Walter; Spolenak, Ralph
Source:
NATURE COMMUNICATIONS, 7 10.1038/ncomms12261 AUG 2016
Abstract:
The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformation has been found to only be possible at high temperatures or under hydrostatic pressures, and their deformation mechanism at low temperatures is still unclear. Here, we report that typically brittle quasicrystals can exhibit remarkable ductility of over 50% strains and high strengths of similar to 4.5 GPa at room temperature and sub-micrometer scales. In contrast to the generally accepted dominant deformation mechanism in quasicrystals-dislocation climb, our observation suggests that dislocation glide may govern plasticity under high-stress and low-temperature conditions. The ability to plastically deform quasicrystals at room temperature should lead to an improved understanding of their deformation mechanism and application in small-scale devices.
Title:
Magnetism and superconductivity in a quasi-2D anisotropic system doped with charge carriers
Authors:
Palistrant, ME Author Full Names: Palistrant, M. E.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 123 (1):86-97; 10.1134/S1063776116050198 JUL 2016
Abstract:
The theory of multiband superconducting systems with variable density of charge carriers is analyzed. The possibility of emergence of nonphonon high-temperature superconductivity due to the predominance of electron-electron interband interactions over intraband interactions, as well as due to the fact that the thermodynamic and magnetic properties of multiband systems in the superconducting phase differ qualitatively from those of single-band systems, is indicated. Phase transitions in a quasi-2D anisotropic medium upon a change in the carrier concentration, i.e., a transition from the commensurate to the incommensurate state of the spin density wave, are analyzed. Such a transition is observed when the Umklapp processes in the lattice structure are taken into account. These processes facilitate a deviation of wavevector Q of the spin density wave from 2k (F) , as well as a displacement of the bandgap relative to the Fermi surface. This leads to the generation of free charge carriers and the possibility of superconductivity. It is shown that superconductivity accompanies the magnetism. The conditions for the coexistence of these two phenomena are determined.
Title:
Direct imaging of incommensurate wave pockets in the charge-density-wave state of LaTe2
Authors:
Yang, HX; Cai, Y; Ma, C; Li, J; Long, YJ; Chen, GF; Tian, HF; Wei, LL; Li, JQ Author Full Names: Yang, H. X.; Cai, Y.; Ma, C.; Li, J.; Long, Y. J.; Chen, G. F.; Tian, H. F.; Wei, L. L.; Li, J. Q.
Source:
EPL, 114 (6):10.1209/0295-5075/114/67002 JUN 2016
Abstract:
We herein report the study of the atomic structure for a fully incommensurate CDW in LaTe2 using Cs-corrected scanning transmission electron microscopy (STEM). It is directly revealed for the first time that the atomic displacements adopt an incommensurate wave-pocket structure along each Te chain. This pocket structure has a long periodicity determined by the CDW incommensurability. We can use the sinusoidal waves as the first-order approximation to characterize the atomic motions within the pocket pattern, which can yield atomic displacements in good agreement with the theoretical model commonly used for studying CDW. These facts demonstrate that the incommensurate pocket patterns should be an essential structural nature in the CDW states and play a critical role for developing the mechanism of the CDW transitions. Copyright (C) EPLA, 2016

Update: 22-Sep-2016

Title:
Microstructure and Mechanical Properties of Squeeze Casting Quasicrystal Reinforced AZ91D Magnesium Matrix Composites
Authors:
Yang, L; Hou, H; Zhao, YH; Yang, XM Author Full Names: Yang Ling; Hou Hua; Zhao Yuhong; Yang Xiaomin
Source:
RARE METAL MATERIALS AND ENGINEERING, 45 (8):1978-1982; AUG 2016
Abstract:
To improve the mechanical properties of AZ91D alloy, a squeeze casting process was employed to fabricate AZ91D magnesium matrix composites reinforced with stable icosahedral quasicrystal particles which were introduced as Mg-Zn-Y quasicrystal master alloy. The effects of quasicrystal master alloy content on the microstructure and mechanical properties of the composites were investigated. The results show that the squeeze casting process is an effective method to refine grain size. The composites comprise alpha-Mg matrix, beta-Mg17Al12 phases that disperse on grain boundaries and Mg3Zn6Y quasicrystal particles. A stable interface between the quasicrystal particles and the Mg matrix is observed. The composite exhibits the maximum ultimate tensile strength of 194.3 MPa and the maximum elongation of 9.2%, when the mass fraction of quasicrystal master alloy is 5%. The reinforcement mechanism is concluded as fine-grain strengthening and quasicrystal particle strengthening.

Update: 15-Sep-2016

Title:
Fatigue properties and microstructure of quasicrystalline AlFeCrTi alloy
Authors:
Chlupova, A; Chlup, Z; Kruml, T Author Full Names: Chlupova, Alice; Chlup, Zdenek; Kruml, Tomas
Source:
INTERNATIONAL JOURNAL OF FATIGUE, 91 251-256; 10.1016/j.ijfatigue.2016.06.007 1 OCT 2016
Abstract:
Aluminium based material having chemical composition of Al93Fe3Ti2Cr2 (at.%) was prepared by hot extrusion of gas atomised powder. Microstructure consisting of aluminium matrix and icosahedral quasicrystalline particles was investigated by scanning and transmission electron microscopy a X-ray spectroscopy. Size, distribution and inner structure of quasicrystalline particles were determined. When quasicrystalline particles having submicron size were present in the microstructure together with fine-grained aluminium matrix, it resulted in enhancement of mechanical properties. Fatigue experiments were performed in load controlled regime with positive mean stress and fatigue life data for this quasicrystalline material were compared with similar results for commercially available aluminium alloys. Longer fatigue life together with higher fatigue strength reaching value of 350 MPa was observed. It is approx. 100 MPa higher than for commercially produced coarse-grained aluminium alloys. Fractographic observations revealed presence of fish eye fracture patterns and validity of weakest link fracture mechanism acting in this type of material under investigation. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
Quasi-ordered C-60 molecular films grown on the pseudo-ten-fold (100) surface of the Al13Co4 quasicrystalline approximant
Authors:
Fournee, V; Gaudry, E; Ledieu, J; de Weerd, MC; Diehl, RD Author Full Names: Fournee, V.; Gaudry, E.; Ledieu, J.; de Weerd, M-C; Diehl, R. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (35):10.1088/0953-8984/28/35/355001 SEP 7 2016
Abstract:
The growth of C-60 films on the pseudo-ten-fold (1 0 0) surface of the orthorhombic Al13Co4 quasicrystalline approximant was studied experimentally by scanning tunneling microscopy, low-energy electron diffraction and photoemission spectroscopy. The (1 0 0) surface terminates at bulk-planes presenting local atomic configurations with five-fold symmetry-similar to quasicrystalline surfaces. While the films deposited at room temperature were found disordered, high-temperature growth (up to 693 K) led to quasi-ordered molecular films templated on the substrate rectangular unit mesh. The most probable adsorption sites and geometries were investigated by density functional theory (DFT) calculations. A large range of adsorption energies was determined, influenced by both symmetry and size matching at the molecule-substrate interface. The quasi-ordered structure of the film can be explained by C-60 adsorption at the strongest adsorption sites which are too far apart compared to the distance minimizing the intermolecular interactions, resulting in some disorder in the film structure at a local scale. Valence band photoemission indicates a broadening of the molecular orbitals resulting from hybridization between the substrate and overlayer electronic states. Dosing the film at temperature above 693 K led to molecular damage and formation of carbide thin films possessing no azimuthal order with respect to the substrate.
Title:
Exchange anisotropy as mechanism for spin-stripe formation in frustrated spin chains
Authors:
Pregelj, M; Zaharko, O; Herak, M; Gomilsek, M; Zorko, A; Chapon, LC; Bourdarot, F; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Zaharko, O.; Herak, M.; Gomilsek, M.; Zorko, A.; Chapon, L. C.; Bourdarot, F.; Berger, H.; Arcon, D.
Source:
PHYSICAL REVIEW B, 94 (8):10.1103/PhysRevB.94.081114 AUG 29 2016
Abstract:
We investigate the spin-stripe mechanism responsible for the peculiar nanometer modulation of the incommensurate magnetic order that emerges between the vector-chiral and the spin-density-wave phase in the frustrated zigzag spin-1/2 chain compound beta-TeVO4. A combination of magnetic-torque, neutron-diffraction, and spherical-neutron-polarimetry measurements is employed to determine the complex magnetic structures of all three ordered phases. Based on these results, we develop a simple phenomenological model, which exposes the exchange anisotropy as the key ingredient for the spin-stripe formation in frustrated spin systems.
Title:
Electronic structure and magneto-optical Kerr effect spectra of ferromagnetic shape-memory Ni-Mn-Ga alloys: Experiment and density functional theory calculations
Authors:
Uba, S; Bonda, A; Uba, L; Bekenov, LV; Antonov, VN Author Full Names: Uba, S.; Bonda, A.; Uba, L.; Bekenov, L. V.; Antonov, V. N.
Source:
PHYSICAL REVIEW B, 94 (5):10.1103/PhysRevB.94.054427 AUG 25 2016
Abstract:
In this joint experimental and ab initio study, we focused on the influence of the chemical composition and martensite phase transition on the electronic, magnetic, optical, and magneto-optical properties of the ferromagnetic shape-memory Ni-Mn-Ga alloys. The polar magneto-optical Kerr effect (MOKE) spectra for the polycrystalline sample of the Ni-Mn-Ga alloy of Ni60Mn13Ga27 composition were measured by means of the polarization modulation method over the photon energy range 0.8 <= hv <= 5.8 eV in magnetic field up to 1.5 T. The optical properties (refractive index n and extinction coefficient k) were measured directly by spectroscopic ellipsometry using the rotating analyzer method. To complement experiments, extensive first-principles calculations were made with two different first-principles approaches combining the advantages of a multiple scattering Green function method and a spin-polarized fully relativistic linear-muffin-tin-orbital method. The electronic, magnetic, and MO properties of Ni-Mn-Ga Heusler alloys were investigated for the cubic austenitic and modulated 7M-like incommensurate martensitic phases in the stoichiometric and off-stoichiometric compositions. The optical and MOKE properties of Ni-Mn-Ga systems are very sensitive to the deviation from the stoichiometry. It was shown that the ab initio calculations reproduce well experimental spectra and allow us to explain the microscopic origin of the Ni2MnGa optical and magneto-optical response in terms of interband transitions. The band-by-band decomposition of the Ni2MnGa MOKE spectra is presented and the interband transitions responsible for the prominent structures in the spectra are identified.
Title:
Reflection quasilattices and the maximal quasilattice
Authors:
Boyle, L; Steinhardt, PJ Author Full Names: Boyle, Latham; Steinhardt, Paul J.
Source:
PHYSICAL REVIEW B, 94 (6):10.1103/PhysRevB.94.064107 AUG 25 2016
Abstract:
We introduce the concept of a reflection quasilattice, the quasiperiodic generalization of a Bravais lattice with irreducible reflection symmetry. Among their applications, reflection quasilattices are the reciprocal (i.e., Bragg diffraction) lattices for quasicrystals and quasicrystal tilings, such as Penrose tilings, with irreducible reflection symmetry and discrete scale invariance. In a follow-up paper, we will show that reflection quasilattices can be used to generate tilings in real space with properties analogous to those in Penrose tilings, but with different symmetries and in various dimensions. Here we explain that reflection quasilattices only exist in dimensions two, three, and four, and we prove that there is a unique reflection quasilattice in dimension four: the "maximal reflection quasilattice" in terms of dimensionality and symmetry. Unlike crystallographic Bravais lattices, all reflection quasilattices are invariant under rescaling by certain discrete scale factors. We tabulate the complete set of scale factors for all reflection quasilattices in dimension d > 2, and for all those with quadratic irrational scale factors in d = 2.
Title:
Atomic structure of the i-R-Cd quasicrystals and consequences for magnetism
Authors:
Yamada, T; Takakura, H; Kong, T; Das, P; Jayasekara, WT; Kreyssig, A; Beutier, G; Canfield, PC; de Boissieu, M; Goldman, AI Author Full Names: Yamada, T.; Takakura, H.; Kong, T.; Das, P.; Jayasekara, W. T.; Kreyssig, A.; Beutier, G.; Canfield, P. C.; de Boissieu, M.; Goldman, A. I.
Source:
PHYSICAL REVIEW B, 94 (6):10.1103/PhysRevB.94.060103 AUG 15 2016
Abstract:
We report on the six-dimensional (6D) structural refinement of three members of the i-R-Cd quasicrystals (R = Gd, Dy, Tm) via synchrotron x-ray diffraction from single-grain samples, and show that this series is isostructural to the i-YbCd5.7 quasicrystal. However, our refinements suggest that the R occupancy on the Yb icosahedron sites within the Tsai-type atomic cluster is approximately 80%, with the balance taken up by Cd. Similarities between the i-R-Cd series and i-ScZn7.33, and their differences with i-YbCd5.7 and i-Ca15Cd85, indicate that there are at least two subclasses of Tsai-type icosahedral quasicrystals. We further show from x-ray resonant magnetic scattering (XRMS) measurements on a set of closely related Tb1-xYxCd6 1/1 approximants that the dilution of themagnetic R ions on the icosahedron within the Tsai-type cluster by nonmagnetic Y disrupts the commensurate magnetic ordering in the approximant phase.
Title:
Three-Dimensional Icosahedral Phase Field Quasicrystal
Authors:
Subramanian, P; Archer, AJ; Knobloch, E; Rucklidge, AM Author Full Names: Subramanian, P.; Archer, A. J.; Knobloch, E.; Rucklidge, A. M.
Source:
PHYSICAL REVIEW LETTERS, 117 (7):10.1103/PhysRevLett.117.075501 AUG 8 2016
Abstract:
We investigate the formation and stability of icosahedral quasicrystalline structures using a dynamic phase field crystal model. Nonlinear interactions between density waves at two length scales stabilize three-dimensional quasicrystals. We determine the phase diagram and parameter values required for the quasicrystal to be the global minimum free energy state. We demonstrate that traits that promote the formation of two-dimensional quasicrystals are extant in three dimensions, and highlight the characteristics required for three-dimensional soft matter quasicrystal formation.
Title:
Modulated crystal structure of InMo4O6
Authors:
Schultz, P; Simon, A; Oeckler, O Author Full Names: Schultz, Peter; Simon, Arndt; Oeckler, Oliver
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 642-649; SI 10.1107/S205252061600874X 4 AUG 2016
Abstract:
The (3 + 1)-dimensional modulated crystal structure of the metal-rich cluster compound InMo4O6 was solved and refined from single-crystal data in the superspace group P4/mbm(00 gamma)00ss [q = 0, 0, 0.1536 (4); a = 9.6664 (9), c = 2.8645 (3) angstrom; R1(all) = 0.046, wR(all) = 0.076]. The crystal structure is closely related to the NaMo4O6 structure type. It is built from rods of Mo-6 clusters condensed via trans edges. These form channels parallel to [001], in which In-6 and In-7 oligomers alternate. Weak diffuse planes parallel to (001)* interconnect the *satellite* *reflections*; they occur due to two-dimensional rod disorder of the In oligomer chains.
Title:
Magnetic anisotropy in the frustrated spin-chain compound beta-TeVO4
Authors:
Weickert, F; Harrison, N; Scott, BL; Jaime, M; Leitmae, A; Heinmaa, I; Stern, R; Janson, O; Berger, H; Rosner, H; Tsirlin, AA Author Full Names: Weickert, F.; Harrison, N.; Scott, B. L.; Jaime, M.; Leitmae, A.; Heinmaa, I.; Stern, R.; Janson, O.; Berger, H.; Rosner, H.; Tsirlin, A. A.
Source:
PHYSICAL REVIEW B, 94 (6):10.1103/PhysRevB.94.064403 AUG 1 2016
Abstract:
Isotropic and anisotropic magnetic behavior of the frustrated spin-chain compound beta-TeVO4 is reported. Three magnetic transitions observed in zero magnetic field are tracked in fields applied along different crystallographic directions using magnetization, heat capacity, and magnetostriction measurements. Qualitatively different temperature-field diagrams are obtained below 10 T for the field applied along a or b and along c, respectively. In contrast, a nearly isotropic high-field phase emerges above 18 T and persists up to the saturation that occurs around 22.5 T. Upon cooling in low fields, the transitions at T-N1 and T-N2 toward the spin-density-wave and stripe phases are of the second order, whereas the transition at T-N3 toward the helical state is of the first order and entails a lattice component. Our microscopic analysis identifies frustrated J(1)-J(2) spin chains with a sizable antiferromagnetic interchain coupling in the bc plane and ferromagnetic couplings along the a direction. The competition between these ferromagnetic interchain couplings and the helical order within the chain underlies the incommensurate order along the a direction, as observed experimentally. While a helical state is triggered by the competition between J(1) and J(2) within the chain, the plane of the helix is not uniquely defined because of competing magnetic anisotropies. Using high-resolution synchrotron diffraction and Te-125 nuclear magnetic resonance, we also demonstrate that the crystal structure of beta-TeVO4 does not change down to 10 K, and the orbital state of V4+ is preserved.
Title:
Internal field emission nature of the fine structure of tunnel spectra in icosahedral quasicrystals
Authors:
Prekul, AF; Schegolikhina, NI Author Full Names: Prekul, A. F.; Schegolikhina, N. I.
Source:
JETP LETTERS, 103 (9):603-606; 10.1134/S0021364016090071 MAY 2016
Abstract:
Calorimetric and tunnel data for the icosahedral phases of the Al-Cu-Fe system have been jointly analyzed. It has been found that the field-dependent part of the tunnel conductance can be represented as the sum of elementary terms similar in nature to thermal Schottky anomalies. As a result, the features of the fine structure of tunnel spectra in the form of zero-bias anomalies, peaks, and humps can be due to the internal field emission and can indicate a wide distribution of two-level electron traps in the electronic structure of quasicrystals. It was previously assumed that these features constitute a direct image of the density of single-electron states of the conduction band.

Update: 9-Sep-2016

Title:
Long-range charge-density-wave proximity effect at cuprate/manganate interfaces
Authors:
Frano, A; Blanco-Canosa, S; Schierle, E; Lu, Y; Wu, M; Bluschke, M; Minola, M; Christiani, G; Habermeier, HU; Logvenov, G; Wang, Y; van Aken, PA; Benckiser, E; Weschke, E; Le Tacon, M; Keimer, B Author Full Names: Frano, A.; Blanco-Canosa, S.; Schierle, E.; Lu, Y.; Wu, M.; Bluschke, M.; Minola, M.; Christiani, G.; Habermeier, H. U.; Logvenov, G.; Wang, Y.; van Aken, P. A.; Benckiser, E.; Weschke, E.; Le Tacon, M.; Keimer, B.
Source:
NATURE MATERIALS, 15 (8):831-+; 10.1038/NMAT4682 AUG 2016
Abstract:
The interplay between charge density waves (CDWs) and high-temperature superconductivity is currently under intense investigation(1-10). Experimental research on this issue is difficult because CDW formation in bulk copper oxides is strongly influenced by random disorder(11-13), and a long-range-ordered CDW state in high magnetic fields(14-16) is difficult to access with spectroscopic and diffraction probes. Here we use resonant X-ray scattering in zero magnetic field to show that interfaces with the metallic ferromagnet La2/3Ca1/3MnO3 greatly enhance CDW formation in the optimally doped high-temperature superconductor YBa2Cu3O6+delta (delta similar to 1), and that this effect persists over several tens of nanometres. The wavevector of the incommensurate CDW serves as an internal calibration standard of the charge carrier concentration, which allows us to rule out any significant influence of oxygen non-stoichiometry, and to attribute the observed phenomenon to a genuine electronic proximity effect. Long-range proximity effects induced by heterointerfaces thus offer a powerful method to stabilize the charge-density-wave state in the cuprates and, more generally, to manipulate the interplay between different collective phenomena in metal oxides.

Update: 1-Sep-2016

Title:
Electron diffraction study of cobalt-rich Hf-Co
Authors:
Li, XZ; Jin, YL; Wang, MY; Shield, JE; Skomski, R; Sellmyer, DJ Author Full Names: Li, X. -Z.; Jin, Y. -L.; Wang, M. -Y.; Shield, J. E.; Skomski, R.; Sellmyer, D. J.
Source:
INTERMETALLICS, 75 54-61; 10.1016/j.intermet.2016.06.002 AUG 2016
Abstract:
Intermetallic compounds having compositions from HfCo4 to HfCo8 were investigated by transmission electron microscopy, selected-area electron diffraction, and energy-dispersive x-ray spectroscopy. A major crystalline phase, closely related to the orthorhombic Zr2Co11 phase in structure, has been observed in the samples with the composition ranges from HfCo6 to HfCo8. The phase, referred to as either Hf2Co11 or HfCo7 phase in the literature, is actually one common phase, having a broad composition range and referred to as mu-phase in the present paper. In addition to the mu-phase, we have found coexisted fcc-Co phase and a minor Hf2Co7 phase. The Hf6Co23 phase has been identified in the HfCo4 and HfCo5 samples. Tilt-series electron diffraction revealed that the mu-phase is a one-dimensional incommensurate structure, which can be described approximately as B-centered orthorhombic with a = 0.47 nm, b = 0.82 nm, and c = 3.86 nm. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
Low temperature heat capacity and electrical resistivity of the Ti40Zr25Cu12Ni3Be20 glass forming alloy
Authors:
Liu, BB; Ye, F Author Full Names: Liu, Binbin; Ye, Feng
Source:
INTERMETALLICS, 75 31-35; 10.1016/j.intermet.2016.05.010 AUG 2016
Abstract:
Gaining knowledge of electronic structure provides useful information for understanding unique properties of metallic glasses. In this study, low temperature heat capacity and electrical resistivity of the glass forming Ti40Zr25Cu12Ni3Be20 alloy with glassy, quasicrystalline, or crystalline states below 300 K were investigated. The precipitation of the I-phase was revealed in the initial crystallization process of the Ti40Zr25Cu12Ni3Be20 BMG. The glassy state has higher state density at Fermi level than its quasi crystalline or crystalline counterparts, which could be interpreted by the electron localization in glassy state as well as a pseudo-Brillouin zone formed nearby Fermi surface in the quasicrystalline state. None of the three states showed superconductivity phenomenon down to 1.9 K. Temperature dependence of resistivity for both the glassy state and the quasicrystalline state exhibited negative temperature coefficient and was less sensitive to temperature than the crystalline state. The electrical resistivity showed a smaller value for the I-phase than that for the glass due to lower structural integrity of I -phase. Electrical resistivity as well as heat capacity measurements indicated that the electronic structure of the quasi crystalline state is quite similar to glassy state but far from crystalline state. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
2D materials and van der Waals heterostructures
Authors:
Novoselov, KS; Mishchenko, A; Carvalho, A; Neto, AHC Author Full Names: Novoselov, K. S.; Mishchenko, A.; Carvalho, A.; Castro Neto, A. H.
Source:
SCIENCE, 353 (6298):461-+; 10.1126/science.aac9439 JUL 29 2016
Abstract:
The physics of two-dimensional ( 2D) materials and heterostructures based on such crystals has been developing extremely fast. With these new materials, truly 2D physics has begun to appear ( for instance, the absence of long-range order, 2D excitons, commensurate-incommensurate transition, etc.). Novel heterostructure devices-such as tunneling transistors, resonant tunneling diodes, and light-emitting diodes-are also starting to emerge. Composed from individual 2D crystals, such devices use the properties of those materials to create functionalities that are not accessible in other heterostructures. Here we review the properties of novel 2D crystals and examine how their properties are used in new heterostructure devices.

Update: 25-Aug-2016

Title:
Prediction of Host-Guest Na-Fe Intermetallics at High Pressures
Authors:
Zhou, YY; Wang, H; Zhu, CY; Liu, HY; Tse, JS; Ma, YM Author Full Names: Zhou, Yuanyuan; Wang, Hui; Zhu, Chunye; Liu, Hanyu; Tse, John S.; Ma, Yanming
Source:
INORGANIC CHEMISTRY, 55 (14):7026-7032; 10.1021/acs.inorgchem.6b00881 JUL 18 2016
Abstract:
High pressure can fundamentally alter the electronic structure of elemental metals, leading to the unexpected formation of intermetallics with unusual structural features. In the present study, the phase stabilities and structural changes of Na-Fe intermetallics under pressure were studied using unbiased structure searching methods, combined with density functional theory calculations. Two intermetallics with stoichiometries Na3Fe and Na4Fe are found to be thermodynamically stable at pressures above 120 and 155 GPa, respectively. An interesting structural feature is that both have form a host guest-like structure with Na sublattices constructed from small and large polygons similar to the host framework of the self-hosting incommensurate phases observed in Group I and II elements. Apart from the one-dimensional (1D) Fe chains running through the large channels, more interestingly, electrides are found to localize in the small channels between the layers. Electron topological analysis shows secondary bonding interactions between the Fe atoms and the interstitial electrides help to stabilize these structures.

Update: 18-Aug-2016

Title:
Influence of icosahedral short range order on diffusion in liquids: A study on Al-Zn-Cr alloys
Authors:
Kurtuldu, G; Jarry, P; Rappaz, M Author Full Names: Kurtuldu, Guven; Jarry, Philippe; Rappaz, Michel
Source:
ACTA MATERIALIA, 115 423-433; 10.1016/j.actamat.2016.05.051 AUG 15 2016
Abstract:
It has been shown recently that minute additions of Cr in Al-Zn alloys refine the solidified grain structure and induce multiply-twinned grains which can only be explained if the icosahedral symmetry is considered (Kurtuldu et al., 2013). It has been suggested that Cr addition to Al-Zn alloys promotes the formation of icosahedral short-range order (ISRO) in the liquid, leading to the formation of icosahedral quasicrystals (iQC) acting then as a template for the nucleation of the fcc Al-phase. If ISRO exists in liquid Al-Zn-Cr alloys, this should influence diffusion of solute elements in the liquid. The present study focuses on the effect of Cr addition on Zn diffusion in liquid Al-Zn-Cr alloys. The solute diffusion coefficients of Zn and Cr in the liquid were deduced from the solute profiles in the quenched liquid ahead of a planar solid liquid interface. By comparison with the same measurement in Al-Zn alloys, it is shown that Cr indeed slows down the diffusion (and mobility) of Zn atoms, an effect which reinforces the hypothesis of ISRO in Al-Zn liquid induced by Cr. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Structure and microstructure of Ni-Mn-Ga single crystal exhibiting magnetic shape memory effect analysed by high resolution X-ray diffraction
Authors:
Heczko, O; Cejpek, P; Drahokoupil, J; Holy, V Author Full Names: Heczko, Oleg; Cejpek, Petr; Drahokoupil, Jan; Holy, Vaclav
Source:
ACTA MATERIALIA, 115 250-258; 10.1016/j.actamat.2016.05.047 AUG 15 2016
Abstract:
Subtle changes of (micro-) structure can have far-reaching consequences for magnetic shape memory (MSM) effect, also called magnetic induced reorientation (MIR). Detailed X-ray structure analysis using reciprocal mapping of Ni-Mn-Ga single crystals exhibiting MIR at room temperature and prepared in single macrotwin orientation revealed 10M modulated structure. It indicated that the modulation was harmonic, i.e. commensurate, but it also showed that the difference when compared to non commensurate mode or even to adaptive model was very small. The distinction between commensurate and non-commensurate modulation could not be reliably resolved due to large broadening of diffraction peaks. The broadening was caused by small size (less than 100 nm) of structurally coherent L2(1) ordered domains. The small size of these coherent domains is a result of large concentration of antiphase boundaries. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
The 7 x 1 Fermi Surface Reconstruction in a Two-dimensional f-electron Charge Density Wave System: PrTe3
Authors:
Lee, E; Kim, DH; Kim, HW; Denlinger, JD; Kim, H; Kim, J; Kim, K; Min, BI; Min, BH; Kwon, YS; Kang, JS Author Full Names: Lee, Eunsook; Kim, D. H.; Kim, Hyun Woo; Denlinger, J. D.; Kim, Heejung; Kim, Junwon; Kim, Kyoo; Min, B. I.; Min, B. H.; Kwon, Y. S.; Kang, J. -S.
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep30318 JUL 25 2016
Abstract:
The electronic structure of a charge density wave (CDW) system PrTe3 and its modulated structure in the CDW phase have been investigated by employing ARPES, XAS, Pr 4 f RPES, and first-principles band structure calculation. Pr ions are found to be nearly trivalent, supporting the CDW instability in the metallic Te sheets through partial filling. Finite Pr 4 f spectral weight is observed near the Fermi level, suggesting the non-negligible Pr 4 f contribution to the CDW formation through the Pr 4 f-Te 5p hybridization. The two-fold symmetric features in the measured Fermi surface (FS) of PrTe3 are explained by the calculated FS for the assumed 7 x 1 CDW supercell formation in Te sheets. The shadow bands and the corresponding very weak FSs are observed, which originate from both the band folding due to the 3D interaction of Te sheets with neighboring Pr-Te layers and that due to the CDW-induced FS reconstruction. The straight vertical FSs are observed along k(z), demonstrating the nearly 2D character for the near-E-F states. The observed linear dichroism reveals the in-plane orbital character of the near-E-F Te 5p states.

Update: 11-Aug-2016

Title:
Structure and multiferroic properties of multi-doped Bi1-xErxFe0.96Mn0.02Co0.02O3 thin films
Authors:
Zheng, YJ; Tan, GQ; Xia, A; Ren, HJ Author Full Names: Zheng, Yujuan; Tan, Guoqiang; Xia, Ao; Ren, Huijun
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 684 438-444; 10.1016/j.jallcom.2016.05.193 NOV 5 2016
Abstract:
Multiferroic Bi1-xErxFe0.96Mn0.02Co0.02O3 (BExFMCO, x = 0.08-0.12) thin films have been successfully prepared on fluorine doped tin oxide (FTO) substrates by the chemical solution deposition method. The structural characteristics of the thin films were investigated by X-ray diffraction (XRD), Rietveld refinement and Raman spectra, indicating a structural transition from typical rhombohedral-R3c:H (BFO) to two-phase coexistence of triclinic-P1 and orthorhombic-Pbmn (BE0.12FMCO). XPS analyses suggest there is the coexistence of Fe2+ and Fe3+ ions in all the thin films. The multi-doping exhibits small effects on oxygen vacancies due to the complex effects of doping ions. Intensive super exchange between Fe2+ and Fe3+ and the decreased leakage current densities are observed in BE0.1FMCO thin films. Multi-doped thin films show the superior ferroelectric properties with a giant remanent polarization (the BE0.1FMCO thin film with P-r similar to 104.43 mu C/cm(2)). The enhanced ferroelectric properties of BExFMCO thin films can be mainly attributed to the structural transition via doping. The highest magnetization values of M-s similar to 9.78 emu/cm(3) and M-r similar to 2.1 emu/cm(3) are obtained in the BE0.1FMCO thin films, which can be attributed to the super exchange between Fe2+ and Fe3+ ions and the altered space modulated spin structure due to structural transition. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Chemical Pressure-Driven Incommensurability in CaPd5: Clues to High-Pressure Chemistry Offered by Complex Intermetallics
Authors:
Kilduff, BJ; Fredrickson, DC Author Full Names: Kilduff, Brandon J.; Fredrickson, Daniel C.
Source:
INORGANIC CHEMISTRY, 55 (13):6781-6793; 10.1021/acs.inorgchem.6b01124 JUL 4 2016
Abstract:
While composition and pressure are generally considered orthogonal parameters in the synthesis and optimization of solid state materials, their distinctness is blurred by the concept of chemical pressure (CP): microscopic pressure arising from lattice constraints rather than an externally applied force. In this article, we describe the first cycle of an iterative theoretical/experimental investigation into this connection. We begin by theoretically probing the ability of physical pressure to promote structural transitions in CaCu5-type phases that are driven by CP in other systems. Our results point to the instability of the reported CaCu5-type CaPd5 phase to such a transition even at ambient pressure, suggesting that new structural chemistry should arise at only modest pressures. We thus attempted to synthesize CaPd5 as a starting material for high-pressure experiments. However, rather than obtaining the expected CaCu5-type phase, we encountered crystals of an incommensurately modulated variant CaCu5+q/2, whose composition is related to its satellite spacing, q = qb(basic)* with q approximate to 0.44. Its structure was solved and refined in the (3 + 1)D superspace group Cmcm(0 beta 0)s00, revealing CaCu5-type slabs separated by distorted Pd hexagonal nets with an incommensurate periodicity. DFT-CP analysis on a commensurate model for CaPd5+q/2 indicates that the new Pd nets serve to relieve intense negative CPs that the Ca atoms would experience in a CaCu5-type CaPd5 phase but suffer from a desire to contract relative to the rest of the structure. In this way, both the Pd layer substitution and incommensurability in CaPd5+q/2 are anticipated by the CP schemes of simpler model systems, with CP quadrupoles tracing the paths of the favorable atomic motions. This picture offers predictions for how elemental substitution and physical pressure should affect these structural motifs, which could be applicable to the magnetic phase Zr2Co11 whose previously proposed structures show close parallels to CaPd5+q/2.

Update: 4-Aug-2016

Title:
Distributed Hybridization Model for Quantum Critical Behavior in Magnetic Quasicrystals
Authors:
Otsuki, J; Kusunose, H Author Full Names: Otsuki, Junya; Kusunose, Hiroaki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (7):10.7566/JPSJ.85.073712 JUL 15 2016
Abstract:
A quantum critical behavior of the magnetic susceptibility was observed in a quasicrystal containing ytterbium. At the same time, a mixed-valence feature of Yb ions was reported, which appears to be incompatible with the magnetic instability. We derive the magnetic susceptibility by expressing the quasiperiodicity as the distributed hybridization strength between Yb 4f and conduction electrons. Assuming a wide distribution of the hybridization strength, the most f electrons behave as renormalized paramagnetic states in the Kondo or mixed-valence regime, but a small number of f moments remain unscreened. As a result, the bulk magnetic susceptibility exhibits a nontrivial power-law-like behavior, while the average f-electron occupation is that of mixed-valence systems. This model thus resolves two contradictory properties of Yb quasicrystals.
Title:
Incommensurate Magnetic Structure in the Cubic Noncentrosymmetric Ternary Compound Pr5Ru3Al2
Authors:
Makino, K; Okuyama, D; Avdeev, M; Sato, TJ Author Full Names: Makino, Koya; Okuyama, Daisuke; Avdeev, Maxim; Sato, Taku J.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (7):10.7566/JPSJ.85.073705 JUL 15 2016
Abstract:
Magnetic susceptibility and neutron powder diffraction experiments have been performed on the noncentrosymmetric ternary compound Pr5Ru3Al2. The previously reported ferromagnetic transition at 24K was not detected in our improved-quality samples. Instead, magnetic ordering was observed in the DC magnetic susceptibility at T-c similar or equal to 3.8 K. The neutron powder diffraction experiment further indicates that an incommensurate magnetic structure is established below T-c with the magnetic modulation vector q similar or equal to (0.066, 0.066, 0.066) (r.l.u.). A candidate for the magnetic structure is proposed using representation analysis.
Title:
Local growth of icosahedral quasicrystalline tilings
Authors:
Hann, CT; Socolar, JES; Steinhardt, PJ Author Full Names: Hann, Connor T.; Socolar, Joshua E. S.; Steinhardt, Paul J.
Source:
PHYSICAL REVIEW B, 94 (1):10.1103/PhysRevB.94.014113 JUL 14 2016
Abstract:
Icosahedral quasicrystals (IQCs) with extremely high degrees of translational order have been produced in the laboratory and found in naturally occurring minerals, yet questions remain about how IQCs form. In particular, the fundamental question of how locally determined additions to a growing cluster can lead to the intricate long-range correlations in IQCs remains open. In answer to this question, we have developed an algorithm that is capable of producing a perfectly ordered IQC yet relies exclusively on local rules for sequential, face-to-face addition of tiles to a cluster. When the algorithm is seeded with a special type of cluster containing a defect, we find that growth is forced to infinity with high probability and that the resultant IQC has a vanishing density of defects. The geometric features underlying this algorithm can inform analyses of experimental systems and numerical models that generate highly ordered quasicrystals.
Title:
Unique magnetic structure of YbCo2Si2
Authors:
Mufti, N; Kaneko, K; Hoser, A; Gutmann, M; Geibel, C; Krellner, C; Stockert, O Author Full Names: Mufti, N.; Kaneko, K.; Hoser, A.; Gutmann, M.; Geibel, C.; Krellner, C.; Stockert, O.
Source:
PHYSICAL REVIEW B, 94 (4):10.1103/PhysRevB.94.045116 JUL 14 2016
Abstract:
We report on the results of powder and single-crystal neutron diffraction to investigate the magnetic order in YbCo2Si2 below the Neel temperature T-N = 1.7 K in detail. Two different magnetically ordered phases can clearly be distinguished. At lowest temperatures a commensurate magnetic structure with a propagation vector k(1) = (0.25 0.25 1) is found, while the intermediate phase (T > 0.9 K) is characterized by an incommensurate magnetic structure with k(2) = (0.25 0.086 1). The magnetic structure in YbCo2Si2 is in marked contrast to all other known RCo2Si2 compounds (R = rare earth element) likely due to some itineracy of the Yb 4f states being responsible for the magnetism.
Title:
Reinterpretation of the zero-temperature conductivity in icosahedral AlPdRe
Authors:
Rapp, O Author Full Names: Rapp, O.
Source:
PHYSICAL REVIEW B, 94 (2):10.1103/PhysRevB.94.024202 JUL 13 2016
Abstract:
The zero-temperature conductivity sigma(0) of icosahedral (i)-AlPdRe has been found to be simply related to the resistance ratio R = rho(4.2 K)/rho(295 K) by a power law, sigma(0) similar to R (1.74), over four orders of magnitude in sigma(0). This relation includes metallic single grain samples, and polygrain samples of different morphologies which are metallic for small R values, and insulatinglike at large R. Electronic transport properties of single grain i-AlPdRe samples are thus found to be on common ground with polygrain i-AlPdRe. The relation between R and sigma(0) can be qualitatively understood from published band-structure calculations on quasicrystalline approximants.
Title:
Commensurate and incommensurate magnetic order in spin-1 chains stacked on the triangular lattice in Li2NiW2O8
Authors:
Ranjith, KM; Nath, R; Majumder, M; Kasinathan, D; Skoulatos, M; Keller, L; Skourski, Y; Baenitz, M; Tsirlin, AA Author Full Names: Ranjith, K. M.; Nath, R.; Majumder, M.; Kasinathan, D.; Skoulatos, M.; Keller, L.; Skourski, Y.; Baenitz, M.; Tsirlin, A. A.
Source:
PHYSICAL REVIEW B, 94 (1):10.1103/PhysRevB.94.014415 JUL 13 2016
Abstract:
We report the thermodynamic properties, magnetic ground state, and microscopic magnetic model of the spin-1 frustrated antiferromagnet Li2NiW2O8, showing successive transitions at T-N1 similar or equal to 18 K and T-N2 similar or equal to 12.5 K in zero field. Nuclear magnetic resonance and neutron diffraction reveal collinear and commensurate magnetic order with the propagation vector k = (1/2,0,1/2) below T-N2. The ordered moment of 1.8 mu(B) at 1.5 K is directed along [0.89(9), - 0.10(5), - 0.49(6)] and matches the magnetic easy axis of spin-1 Ni2+ ions, which is determined by the scissor-like distortion of the NiO6 octahedra. Incommensurate magnetic order, presumably of spin-density-wave type, is observed in the region between T-N2 and T-N1. Density-functional band-structure calculations put forward a three-dimensional spin lattice with spin-1 chains running along the [01 (1) over bar] direction and stacked on a spatially anisotropic triangular lattice in the ab plane. We show that the collinear magnetic order in Li2NiW2O8 is incompatible with the triangular lattice geometry and thus driven by a pronounced easy-axis single-ion anisotropy of Ni2+.
Title:
Static magnetic order on the metallic triangular lattice in CrSe2 detected by mu+SR
Authors:
Sugiyama, J; Nozaki, H; Umegaki, I; Uyama, T; Miwa, K; Brewer, JH; Kobayashi, S; Michioka, C; Ueda, H; Yoshimura, K Author Full Names: Sugiyama, Jun; Nozaki, Hiroshi; Umegaki, Izumi; Uyama, Takeshi; Miwa, Kazutoshi; Brewer, Jess H.; Kobayashi, Shintaro; Michioka, Chishiro; Ueda, Hiroaki; Yoshimura, Kazuyoshi
Source:
PHYSICAL REVIEW B, 94 (1):10.1103/PhysRevB.94.014408 JUL 7 2016
Abstract:
The magnetic nature of a metallic two-dimensional triangular compound, CrSe2, has been investigated by muon spin rotation and relaxation (mu+SR) measurements using both powder and single crystal samples. It is found that CrSe2 enters into a static antiferromagnetic (AF) ordered state below 157 K (=T-N). Furthermore, the AF state is slightly changed below around 20 K (=T-N2). Based on the analysis of the internal magnetic fields at the muon sites predicted with DFT calculations, collinear AF and helical 120 degrees AF are clearly eliminated for the ground state of CrSe2. The most probable one is an incommensurate spin density wave order.
Title:
Atomic structure and phason modes of the Sc-Zn icosahedral quasicrystal
Authors:
Yamada, T; Takakura, H; Euchner, H; Gomez, CP; Bosak, A; Fertey, P; de Boissieu, M Author Full Names: Yamada, Tsunetomo; Takakura, Hiroyuki; Euchner, Holger; Gomez, Cesar Pay; Bosak, Alexei; Fertey, Pierre; de Boissieu, Marc
Source:
IUCRJ, 3 247-258; 10.1107/S2052252516007041 4 JUL 2016
Abstract:
The detailed atomic structure of the binary icosahedral (i) ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants K-2/K-1 = -0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye-Waller factor, which explains the vanishing of 'high-Q(perp)' reflections.
Title:
Mysteries of icosahedral quasicrystals: how are the atoms arranged?
Authors:
Ishimasa, T Author Full Names: Ishimasa, Tsutomu
Source:
IUCRJ, 3 230-231; 10.1107/S2052252516009842 4 JUL 2016

Update: 28-Jul-2016

Title:
Defects forming the optical absorption edge in TlGaSe2 layered crystal
Authors:
Seyidov, MY; Suleymanov, RA; Sale, Y Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Sale, Yasin
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 96-97 17-21; 10.1016/j.jpcs.2016.04.009 SEP-OCT 2016
Abstract:
In this work, we present the results of optical experiments designed to investigate the changes in optical absorption spectra of TlGaSe2 ferroelectric-semiconductor with incommensurate (INC) phase in experimental conditions where crystal is kept several hours within the INC-phase (the regime of so called "memory" effect). The fundamental absorption of TlGaSe2, experimentally investigated by optical transmission measurements performed in the temperature range 15-300 K. An extraordinary modification of the optical absorption edge in the range of Urbach's tail is discovered as a result of the annealing within the INC-phase. The role of native defects forming the band edge in the observed phenomena in TlGaSe2 is discussed. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
Phase transitions and magnetic structures in MnW1-xMoxO4 compounds (x <= 0.2)
Authors:
Hardy, V; Payen, C; Damay, F; Meddar, L; Josse, M; Andre, G Author Full Names: Hardy, Vincent; Payen, Christophe; Damay, Francoise; Meddar, Lynda; Josse, Michael; Andre, Gilles
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (33):10.1088/0953-8984/28/33/336003 AUG 24 2016
Abstract:
Temperature-dependent specific heat, magnetization and neutron diffraction data have been collected in zero magnetic field for polycrystalline samples of MnW1-xMoxO4 (x <= 0.2) solid solution whose end-member MnWO4 exhibits a magnetoelectric multiferroic phase (AF2 phase) between T-1 approximate to 8 K and T-2 = 12.5 K. In MnW1-xMoxO4, diamagnetic W6+ are replaced with diamagnetic Mo6+ cations and magnetic couplings among Mn2+ (3d(5), S = 5/2) ions are modified due the doping-induced tuning of the orbital hybridization between Mn 3d and O 2p states. It was observed that magnetic phase transition temperatures which are associated with the second-order AF3-to-paramagnetic (T-N) and AF2-to-AF3 (T-2) transitions in pure MnWO4 slightly increase with the Mo content x. Magnetic specific heat data also indicate that the first-order AF1-to-AF2 phase transition at T-1 survives a weak doping x <= 0.05. This latter phase transition becomes invisible above the base temperature 2 K for higher level of doping x >= 0.10. Neutron powder diffraction datasets collected above 1.5 K for a sample of MnW0.8Mo0.2O4 were analyzed using the Rietveld method. The magnetic structure below approximate to 14 K is a helical incommensurate spin order with a temperature-independent propagation vector k = (-0.217(6), 0.5, 0.466(4)). This cycloidal magnetic structure is similar to the polar AF2 structure observed in MnWO4. The AF1 up-up-down-down collinear spin arrangement observed in MnWO4 is absent in our MnW0.8Mo0.2O4 sample.
Title:
Shock synthesis of quasicrystals with implications for their origin in asteroid collisions
Authors:
Asimow, PD; Lin, C; Bindi, L; Ma, C; Tschauner, O; Hollister, LS; Steinhardt, PJ Author Full Names: Asimow, Paul D.; Lin, Chaney; Bindi, Luca; Ma, Chi; Tschauner, Oliver; Hollister, Lincoln S.; Steinhardt, Paul J.
Source:
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 113 (26):7077-7081; 10.1073/pnas.1600321113 JUN 28 2016
Abstract:
We designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the Khatyrka meteorite. At the boundaries among CuAl5, (Mg0.75Fe0.252+)(2)SiO4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline phase displaying face-centered icosahedral symmetry and low phason strain. The compositional range of the icosahedral phase is Al68-73Fe11-16Cu10-12Cr1-4Ni1-2 and extends toward higher Al/(Cu+Fe) and Fe/Cu ratios than those reported for natural icosahedrite or for any previously known synthetic quasicrystal in the Al-Cu-Fe system. The shock-induced synthesis demonstrated in this experiment reinforces the evidence that natural quasicrystals formed during a shock event but leaves open the question of whether this synthesis pathway is attributable to the expanded thermodynamic stability range of the quasicrystalline phase at high pressure, to a favorable kinetic pathway that exists under shock conditions, or to both thermodynamic and kinetic factors.
Title:
Dynamic stabilities of icosahedral-like clusters and their ability to form quasicrystals
Authors:
Liang, XG; Hamid, I; Duan, HM Author Full Names: Liang, Xiaogang; Hamid, Ilyar; Duan, Haiming
Source:
AIP ADVANCES, 6 (6):10.1063/1.4954741 JUN 2016
Abstract:
The dynamic stabilities of the icosahedral-like clusters containing up to 2200 atoms are investigated for 15 metal elements. The clusters originate from five different initial structures (icosahedron, truncated decahedron, octahedron, closed-shell fragment of an HCP structure, and non-closed-shell fragment of an HCP structure). The obtained order of the dynamic stabilities of the icosahedral-like clusters can be assigned to three groups, from stronger to weaker, according to the size ranges involved: (Zr, Al, Ti) > (Cu, Fe, Co, Ni, Mg, Ag) > (Pb, Au, Pd, Pt, Rh, Ir), which correspond to the predicted formation ability of the quasicrystals. Thedifferences of the sequences can be explained by analyzing the parameters of the Gupta-type manybody inter-atomic potentials. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Update: 22-Jul-2016

Title:
Complex incommensurate helicoidal magnetic ordering of EuNiGe3
Authors:
Ryan, DH; Cadogan, JM; Rejali, R; Boyer, CD Author Full Names: Ryan, D. H.; Cadogan, J. M.; Rejali, Rasa; Boyer, C. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (26):10.1088/0953-8984/28/26/266001 JUL 6 2016
Abstract:
Eu-151 Mossbauer spectroscopy and neutron powder diffraction are combined to show that the tetragonal (I4mm #107) compound EuNiGe3 orders magnetically below T-N similar to 14 K and adopts a complex incommensurate helicoidal magnetic structure at 3.6 K, with a propagation vector k =[0.255(1), 0.054(14), 0] and a Eu moment of 7.1(2)mu B. On warming through 6 K an incommensurate sinusoidal modulation develops and dominates the magnetic order by 12 K.

Update: 14-Jul-2016

Title:
Microstructural control and hardening response of Mg-6Zn-0.5Er-0.5Ca alloy
Authors:
Zheng, XB; Liu, K; Wang, ZH; Li, SB; Du, WB Author Full Names: Zheng, Xiao-Bing; Liu, Ke; Wang, Zhao-Hui; Li, Shu-Bo; Du, Wen-Bo
Source:
RARE METALS, 35 (7):526-531; 10.1007/s12598-015-0462-0 JUL 2016
Abstract:
The effects of heat treatment on microstructures and hardening response of Mg-6Zn-0.5Er-0.5Ca (wt%) alloy were investigated by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM) in this paper. The results show that the Mg-6Zn-0.5Er-0.5Ca alloy contains Mg3Zn6Er1 quasicrystalline phase (I-phase) and Ca2Mg6Zn3 phase under as-cast condition. Most of the Ca2Mg6Zn3 phases and I-phases dissolve into matrix during heat treatment at 475 degrees C for 5 h. After the as-solution alloy was aged at 175 degrees C for 36 h, a large amount of MgZn2 precipitate with several nanometers precipitate. It is suggested that the trace addition of Ca results in refining the size of the precipitate, and the presence of the nanoscale MgZn2 phase is the main factor to improve the peak-aged hardness greatly to 87 HV, which increases about 40 % compared with that of as-cast alloy.
Title:
Atomistic simulation of frictional anisotropy on quasicrystal approximant surfaces
Authors:
Ye, ZJ; Martini, A; Thiel, P; Lovelady, HH; McLaughlin, K; Rabson, DA Author Full Names: Ye, Zhijiang; Martini, Ashlie; Thiel, Patricia; Lovelady, Heather H.; McLaughlin, Keith; Rabson, David A.
Source:
PHYSICAL REVIEW B, 93 (23):10.1103/PhysRevB.93.235438 JUN 23 2016
Abstract:
J. Y. Park et al. [Science 309, 1354 (2005)] have reported eight times greater atomic-scale friction in the periodic than in the quasiperiodic direction on the twofold face of a decagonal Al-Ni-Co quasicrystal. We present results of molecular-dynamics simulations intended to elucidate mechanisms behind this giant frictional anisotropy. Simulations of a bare atomic-force-microscope tip on several model substrates and under a variety of conditions failed to reproduce experimental results. On the other hand, including the experimental passivation of the tip with chains of hexadecane thiol, we reproduce qualitatively the experimental anisotropy in friction, finding evidence for entrainment of the organic chains in surface furrows parallel to the periodic direction.
Title:
Magnetic correlations in a periodic Anderson model with nonuniform conduction electron coordination
Authors:
Hartman, N; Chiu, WT; Scalettar, RT Author Full Names: Hartman, N.; Chiu, W. -T.; Scalettar, R. T.
Source:
PHYSICAL REVIEW B, 93 (23):10.1103/PhysRevB.93.235143 JUN 21 2016
Abstract:
The periodic Anderson model is widely studied to understand strong correlation physics and especially the competition of antiferromagnetism and singlet formation. In this paper we extend quantum Monte Carlo work on lattices with uniform numbers of neighbors to geometries in which the conduction electron sites can have variable coordination z. This situation is relevant both to recently discovered magnetic quasicrystals and also to magnetism in doped heavy fermion systems. Our key results are the presence of antiferromagnetic order at weak interorbital hybridization Vfd, and a delay in singlet formation to larger values of Vfd on sites with larger z. The staggered magnetization tends to be larger on sites with higher z, providing insight into the behavior to be expected in crown, dice, and CaVO lattices.
Title:
Weak crystallization theory of metallic alloys
Authors:
Martin, I; Gopalakrishnan, S; Demler, EA Author Full Names: Martin, Ivar; Gopalakrishnan, Sarang; Demler, Eugene A.
Source:
PHYSICAL REVIEW B, 93 (23):10.1103/PhysRevB.93.235140 JUN 20 2016
Abstract:
Crystallization is one of the most familiar, but hardest to analyze, phase transitions. The principal reason is that crystallization typically occurs via a strongly first-order phase transition, and thus rigorous treatment would require comparing energies of an infinite number of possible crystalline states with the energy of liquid. A great simplification occurs when crystallization transition happens to be weakly first order. In this case, weak crystallization theory, based on unbiased Ginzburg-Landau expansion, can be applied. Even beyond its strict range of validity, it has been a useful qualitative tool for understanding crystallization. In its standard form, however, weak crystallization theory cannot explain the existence of a majority of observed crystalline and quasicrystalline states. Here we extend the weak crystallization theory to the case of metallic alloys. We identify a singular effect of itinerant electrons on the form of weak crystallization free energy. It is geometric in nature, generating strong dependence of free energy on the angles between ordering wave vectors of ionic density. That leads to stabilization of fcc, rhombohedral, and icosahedral quasicrystalline (iQC) phases, which are absent in the generic theory with only local interactions. As an application, we find the condition for stability of iQC that is consistent with the Hume-Rothery rules known empirically for the majority of stable iQC; namely, the length of the primary Bragg-peak wave vector is approximately equal to the diameter of the Fermi sphere.
Title:
Effect of MWNTs-addition on cathodic performance of Ti-V-Ni composites for Ni-MH batteries
Authors:
Lin, J; Sun, LS; Liang, F; Wu, YM; Cao, ZY; Wang, LM Author Full Names: Lin, Jing; Sun, Lianshan; Liang, Fei; Wu, Yaoming; Cao, Zhanyi; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 41 (22):9471-9475; 10.1016/j.ijhydene.2016.03.211 JUN 15 2016
Abstract:
Composites of Ti1.4V0.6Ni alloy and various amounts of multiwalled carbon nanotubes (MWNTs) have been synthesized by high energy mechanical ball-milling method. The composites mainly contain icosahedral quasicrystal and TiNi-type phases. In contrast to Ti1.4V0.6Ni, all milled composites have excellent activation properties activated at the first charge/discharge cycle, together with excellent rate discharge abilities. The composites are able to deliver outstanding maximum discharge capacities of 295.5 mAh g(-1) enhanced by 68.2 mAh g(-1) in comparison to Ti1.4V0.6Ni alloy, and good cycling stabilities with capacity retention of more than 40% after 100 charge/discharge cycles higher than Ti1.4V0.6Ni alloy. Experimental and theoretical investigations suggest that the unusual electrochemical performance of this composite is depended on the copacetic electrocatalytic activity of MWNTs addition and the enhancement of hydrogen diffusion progress. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Fundamental solutions and analysis of three-dimensional cracks in one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Fan, CY; Li, Y; Xu, GT; Zhao, MH Author Full Names: Fan, CuiYing; Li, Yuan; Xu, GuangTao; Zhao, MingHao
Source:
MECHANICS RESEARCH COMMUNICATIONS, 74 39-44; 10.1016/j.mechrescom.2016.03.009 JUN 2016
Abstract:
In this study, three-dimensional cracks in one-dimensional hexagonal piezoelectric quasicrystals are investigated. Based on the general solutions and Hankel transform, the fundamental solutions for unit point extended displacement discontinuities (including the phonon and phason displacement discontinuities and the electric potential discontinuity) are derived. The extended displacement discontinuity boundary integral equations for a planar crack of arbitrary shape in the periodic plane of one-dimensional hexagonal piezoelectric quasicrystals are established in terms of the extended displacement discontinuities. Using the boundary integral equation method, the singularities of near-crack border fields are obtained and the stress and electric displacement intensity factors are derived. (C) 2016 Elsevier Ltd. All rights reserved.

Update: 7-Jul-2016

Title:
Characterization of SrBiMn2-xTixO6 perovskites: Local ordering influence on the dielectric and magnetic response
Authors:
Alonso-Dominguez, D; Alvarez-Serrano, I; Lopez, ML; Cuello, GJ; Asensio, E; Garcia-Hernandez, M; Veiga, ML; Pico, C Author Full Names: Alonso-Dominguez, D.; Alvarez-Serrano, I.; Lopez, M. L.; Cuello, Gabriel J.; Asensio, Eloy; Garcia-Hernandez, Mar; Veiga, M. L.; Pico, C.
Source:
CERAMICS INTERNATIONAL, 42 (10):11889-11900; 10.1016/j.ceramint.2016.04.111 AUG 1 2016
Abstract:
Two new phases in the (SrTiO3)-(BiMnO3) perovskite type system were studied. These SrBiMn2-xTixO6 (x=0.5 and 0.75) ceramics were prepared by the liquid-mix method as polycrystalline powders. They were characterized by neutron diffraction (ND), electrical and magnetic measurements and these results were analysed in connection with the x=0.25 phase, previously described by us. Their crystal structures were fitted in the tetragonal 14/mcm space group, with additional superstructure reflections suggesting local ordering. Electron microscopy results revealed these ordering effects are actually present concerning both perovskite sublattices. The electrical response pointed to a mechanism consisting in variable range hopping of polarons. A relaxor ferroelectric behaviour dependent on the pellets thickness was found with T-m in the 140-240 K range. The magnetic structures imply an incommensurable modulation of the magnetic moments along the c or a directions, depending on the substitution degree x. A cluster picture in terms of chemically different nanoregions responsible of the macroscopic response is discussed. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Title:
Quasicrystallinity expressed in two-dimensional coordination networks
Authors:
Urgel, JI; Ecija, D; Lyu, GQ; Zhang, R; Palma, CA; Auwarter, W; Lin, NA; Barth, JV Author Full Names: Urgel, Jose I.; Ecija, David; Lyu, Guoqing; Zhang, Ran; Palma, Carlos-Andres; Auwaerter, Willi; Lin, Nian; Barth, Johannes V.
Source:
NATURE CHEMISTRY, 8 (7):657-662; 10.1038/nchem.2507 JUL 2016
Abstract:
The recognition of quasicrystals, which exhibit long-range order but lack translational symmetry, represented both the introduction of a new class of materials and a transformative breakthrough in crystallography. Concomitant with the exploration of quasicrystallinity, metal-organic architectures emerged as promising and versatile systems with significant application potential. Their building principles have been studied extensively and become manifest in a multitude of intricate amorphous and crystalline phases. To date, however, indications for quasicrystalline order have been elusive in metal-organic coordination networks (MOCNs). Here we employ rare-earth-directed assembly to construct a two-dimensional tiling with quasicrystalline characteristics at a well-defined gold substrate. By careful stoichiometry control over europium centres and functional linkers, we produced a porous network, including the simultaneous expression of four-fold, five-fold and six-fold vertices. The pertaining features were directly inspected by scanning tunnelling microscopy, and the molecule-europium reticulation was recognized as square-triangle tessellation with dodecagonal symmetry. Our findings introduce quasicrystallinity in surface-confined MOCNs with a nanoporous structure and anticipate functionalities that arise from quasicrystalline ordering of the coordinative spheres.
Title:
Microstructure and mechanical properties of aluminium matrix composites reinforced by Al62Cu25.5Fe12.5 melt spun ribbon
Authors:
Litynska-Dobrzynska, L; Mitka, M; Goral, A; Stan-Glowinska, K; Dutkiewicz, J Author Full Names: Litynska-Dobrzynska, Lidia; Mitka, Mikolaj; Goral, Anna; Stan-Glowinska, Katarzyna; Dutkiewicz, Jan
Source:
MATERIALS CHARACTERIZATION, 117 127-133; 10.1016/j.matchar.2016.04.025 JUL 2016
Abstract:
Aluminium matrix composites containing 15, 30 and 50 vol.% of pulverized Al62Cu25.5Fe12.5 (in at.%) melt spun ribbons have been prepared by a vacuum hot pressing (T = 673 K, P = 600 MPa). The microstructure of the initial ribbon and the composites was investigated using X-ray, scanning and transmission electron microscopy. In the as-spun ribbon the quasicrystalline icosahedral phase (i-phase) coexisted with the cubic copper rich beta-Al(Cu, Fe) intermetallic compound. The phase composition of Al-Cu-Fe particles changed after consolidation process and the i-phase transformed partially to the omega-Al70Cu20Fe10 phase. Additionally, the Theta-Al2Cu phase formed at the alpha(Al)/Al-Cu-Fe particle interfaces. With an increase in volume fraction of the reinforcement the hardness of the composites increased up to HV = 180 for the highest amount of added particles. The ultimate compression strength of the same sample reached the value of 545 MPa. (C) 2016 Elsevier Inc. All rights reserved.
Title:
Exploring metamagnetism of single crystalline EuNiGe3 by neutron scattering
Authors:
Fabreges, X; Gukasov, A; Bonville, P; Maurya, A; Thamizhavel, A; Dhar, SK Author Full Names: Fabreges, X.; Gukasov, A.; Bonville, P.; Maurya, A.; Thamizhavel, A.; Dhar, S. K.
Source:
PHYSICAL REVIEW B, 93 (21):10.1103/PhysRevB.93.214414 JUN 15 2016
Abstract:
We present here a neutron diffraction study, both in zero field and as a function of magnetic field, of the magnetic structure of the tetragonal intermetallic EuNiGe3 on a single crystalline sample. This material is known to undergo a cascade of transitions, first at 13.2 K towards an incommensurate modulated magnetic structure, then at 10.5 K to an antiferromagnetic structure. We show here that the low-temperature phase presents a spiral moment arrangement with wave vector k = (1/4, delta, 0). For a magnetic field applied along the tetragonal c axis, the square root of the scattering intensity of the (1 0 1) reflection matches very well the complex metamagnetic behavior of the magnetization along c measured previously. For the magnetic field applied along the b axis, two magnetic transitions are observed below the transition to a fully polarized state.
Title:
Commensurate and incommensurate spin-density waves in heavy electron systems
Authors:
Schlottmann, P Author Full Names: Schlottmann, P.
Source:
AIP ADVANCES, 6 (5):10.1063/1.4942549 MAY 2016
Abstract:
The nesting of the Fermi surfaces of an electron and a hole pocket separated by a nesting vector Q and the interaction between electrons gives rise to itinerant antiferromagnetism. The order can gradually be suppressed by mismatching the nesting and a quantum critical point (QCP) is obtained as the Neel temperature tends to zero. The transfer of pairs of electrons between the pockets can lead to a superconducting dome above the QCP (if Q is commensurate with the lattice, i.e. equal to G/2). If the vector Q is not commensurate with the lattice there are eight possible phases: commensurate and incommensurate spin and charge density waves and four superconductivity phases, two of them with modulated order parameter of the FFLO type. The renormalization group equations are studied and numerically integrated. A re-entrant SDW phase (either commensurate or incommensurate) is obtained as a function of the mismatch of the Fermi surfaces and the magnitude of vertical bar Q - G/2 vertical bar. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Update: 30-Jun-2016

Title:
The Z '=12 superstructure of A-cobalt(III) sepulchrate trinitrate governed by C-H center dot center dot center dot O hydrogen bonds
Authors:
Dey, S; Schonleber, A; Mondal, S; Prathapa, SJ; van Smaalen, S; Larsen, FK Author Full Names: Dey, Somnath; Schoenleber, Andreas; Mondal, Swastik; Prathapa, Siriyara Jagannatha; van Smaalen, Sander; Larsen, Finn Krebs
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 372-380; 10.1107/S2052520616005503 3 JUN 2016
Abstract:
A-Cobalt(III) sepulchrate trinitrate crystallizes in P6(3)22 with Z = 2 (Z' = 1/6) at room temperature. Slabs perpendicular to the hexagonal axis comprise molecules Co(sepulchrate) alternating with nitrate groups A and B. Coordinated by six sepulchrate molecules, highly disordered nitrate groups C are accommodated between the slabs. Here we report the fully ordered, low temperature crystal structure of Co(sep)(NO3)(3). It is found to be a high-Z' structure with Z' = 12 of the 12-fold 6a(h) x root 3b(h) x c(h) superstructure with monoclinic symmetry P2(1) (c unique). Correlations between structural parameters are effectively removed by refinements within the superspace approach. Superstructure formation is governed by a densification of the packing in conjunction with ordering of nitrate group C, the latter assuming different orientations for each of the Z' = 12 independent copies in the superstructure. The Co(sep) moiety exhibits small structural variations over its 12 independent copies, while orientations of nitrate groups A and B vary less than the orientations of the nitrate group C do. Molecular packing in the superstructure is found to be determined by short C-H center dot center dot center dot H-C contacts, with H center dot center dot center dot H distances of 2.2-2.3 angstrom, and by short C H center dot center dot center dot O contacts, with H center dot center dot center dot O distances down to 2.2 angstrom. These contacts presumably represent weak C-H center dot center dot center dot O hydrogen bonds, but in any case they prevent further densification of the structure and strengthening of weak N-H center dot center dot center dot O hydrogen bonds with observed H center dot center dot center dot O distances of 2.4-2.6 angstrom.
Title:
New insight on bismuth cuprates with incommensurate modulated structures
Authors:
Mironov, AV; Petricek, V; Khasanova, NR; Antipov, EV Author Full Names: Mironov, Andrei V.; Petricek, Vaclav; Khasanova, Nellie R.; Antipov, Evgeny V.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 395-403; 10.1107/S2052520616005643 3 JUN 2016
Abstract:
The incommensurate modulated crystal structure of Bi2.27Sr1.73CuO6+delta (2201) phase [a = 5.3874 (5), b = 5.3869 (4), c = 24.579 (3) angstrom; beta = 90.01 (1)degrees, q = 0.2105 (3)a* + 0.538 (4)c*, Z = 4, the (3 + 1) -dimensional monoclinic A2/a(alpha 0 gamma) group] has been refined with R = 0.041, wR = 0.052 from X-ray single-crystal data including up to third-order satellite reflections. The same structure has also been considered as incommensurate composite with a(2) = 2.437, b(2) = 5.387, c(2) = 24.614, beta(2) = 93.06, q(2) = 0.4524a(2)* -0.243c(2)* and the (3 + 1)-dimensional A2/m(alpha 0 gamma)0s group for the second component. Both approaches give quite similar results. The structure possesses oxygen disorder in the oxygen-rich region of the BiO layer. An extra 0 atom is determined in the bridging position shifted similar to 0.6 angstrom from BiO towards the SrO layer. Its presence is the cause of the tremendous increase of the bismuth U-11 atomic displacement parameter in similar to 20% of the unit cells (t = -0.05-0.15). Vacancies are determined in the oxygen site of the SrO layer, which may result in the oxygen content variation with annealing at different oxygen pressures. The total refined oxygen content 6.18 (1) corresponds to the results of chemical analysis.

Update: 23-Jun-2016

Title:
Thermo-mechanical study of bulk glass forming Zr-Cu-Ni-Al alloys
Authors:
Spassov, T; Gyurov, S; Stefanov, G; Rangelov, A; Drenchev, L; Russew, K Author Full Names: Spassov, Tony; Gyurov, Stoyko; Stefanov, Georgi; Rangelov, Antoan; Drenchev, Lyudmil; Russew, Krassimir
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 443 103-107; 10.1016/j.jnoncrysol.2016.04.006 JUL 1 2016
Abstract:
The thermal stability and viscous flow behavior of bulk glass forming Zr(68)Cu(13)Ni(11.5)A(17.5) and Zr69Cu12.5Ni11Al7.5 alloys are studied. The viscosity experimental results are interpreted based on the free volume model (FVM). The values of the obtained model parameters are used to estimate the glass forming ability (GFA) in terms of Angell parameter, and the fracture strength of the alloys based on its correlation with the glass transition temperature (T-g). The viscosity data are compared with DSC measurements. The two glasses, having similar composition, revealed comparable T-g, but one of them (Zr68Cu13Ni11.5Al7.5) showed substantially lower crystallization temperature due to quasicrystals formation. Higher GFA was obtained for Zr69Cu12.5Ni11Al7.5 alloy. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Origin of Quantum Criticality in Yb-Al-Au Approximant Crystal and Quasicrystal
Authors:
Watanabe, S; Miyake, K Author Full Names: Watanabe, Shinji; Miyake, Kazumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (6):10.7566/JPSJ.85.063703 JUN 15 2016
Abstract:
To get insight into the mechanism of emergence of unconventional quantum criticality observed in quasicrystal Yb15Al34Au51, the approximant crystal Yb14Al35Au51 is analyzed theoretically. By constructing a minimal model for the approximant crystal, the heavy quasiparticle band is shown to emerge near the Fermi level because of strong correlation of 4f electrons at Yb. We find that charge-transfer mode between 4f electron at Yb on the 3rd shell and 3p electron at Al on the 4th shell in Tsai-type cluster is considerably enhanced with almost flat momentum dependence. The mode-coupling theory shows that magnetic as well as valence susceptibility exhibits chi similar to T-0.5 for zero-field limit and is expressed as a single scaling function of the ratio of temperature to magnetic field T/B over four decades even in the approximant crystal when some condition is satisfied by varying parameters, e.g., by applying pressure. The key origin is clarified to be due to strong locality of the critical Yb-valence fluctuation and small Brillouin zone reflecting the large unit cell, giving rise to the extremely-small characteristic energy scale. This also gives a natural explanation for the quantum criticality in the quasicrystal corresponding to the infinite limit of the unit-cell size.
Title:
Pressure-Driven Quantum Criticality and T/H Scaling in the Icosahedral Au-Al-Yb Approximant
Authors:
Matsukawa, S; Deguchi, K; Imura, K; Ishimasa, T; Sato, NK Author Full Names: Matsukawa, Shuya; Deguchi, Kazuhiko; Imura, Keiichiro; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (6):10.7566/JPSJ.85.063706 JUN 15 2016
Abstract:
We report on ac magnetic susceptibility measurements under pressure of the Au-Al-Yb alloy, a crystalline approximant to the icosahedral quasicrystal that shows unconventional quantum criticality. In describing the susceptibility as chi(T)(-1) - chi(0)(-1) alpha T-gamma, we find that chi(0)(-1) decreases with increasing pressure and vanishes to zero at the critical pressure P-c similar or equal to 2 GPa, with gamma (similar or equal to 0.5) unchanged. We suggest that this quantum criticality emerges owing to critical valence fluctuations. Above P-c, the approximant undergoes a magnetic transition at T similar or equal to 100 mK. These results are contrasted with the fact that, in the quasicrystal, the quantum criticality is robust against the application of pressure. The applicability of the so-called T/H scaling to the approximant is also discussed.
Title:
d-Density Wave Scenario Description of the New Hidden Charge Order in Cuprates
Authors:
Makhfudz, I Author Full Names: Makhfudz, Imam
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (6):10.7566/JPSJ.85.064701 JUN 15 2016
Abstract:
In this paper, we show that the theory of high T-c superconductivity based on a microscopic model with d-density wave (DDW) scenario in the pseudogap phase is able to reproduce some of the most important features of the recent experimentally discovered hidden charge order in several families of Cuprates. In particular, by computing and comparing energies of charge orders of different modulation directions derived from a full microscopic theory with d-density wave scenario, the axial charge order phi(X(Y)) with wavevector Q = (Q(0), 0)((0, Q(0))) is shown to be unambiguously energetically more favorable over the diagonal charge order phi(X+Y) with wavevector Q = (Q(0), +/- Q(0)) at least in commensurate limit, to be expected also to hold even to more general incommensurate case, in agreement with experiment. The two types of axial charge order phi(X) and phi(Y) are degenerate by symmetry. We find that within the superconducting background, biaxial (checkerboard) charge order is energetically more favorable than uniaxial (stripe) charge order, and therefore checkerboard axial charge order should be the one observed in experiments, assuming a single domain of charge ordered state on each CuO2 plane.
Title:
Superlubricity in quasicrystalline twisted bilayer graphene
Authors:
Koren, E; Duerig, U Author Full Names: Koren, Elad; Duerig, Urs
Source:
PHYSICAL REVIEW B, 93 (20):10.1103/PhysRevB.93.201404 MAY 31 2016
Abstract:
The unique atomic positions in quasicrystals lead to peculiar self-similarity and fractal-like structural morphology. Accordingly, many of the material properties are supposed to manifest exceptional characteristics. In this Rapid Communication, we explain through numerical simulations the fundamental and peculiar aspects of quasicrystals wearless friction manifested in a 30 degrees twisted bilayer graphene system. In particular, the sliding force exhibits a fractal structure with distinct area correlations due to the natural mixture between both periodic and aperiodic lateral modulations. In addition, zero power scaling of the sliding force with respect to the contact area is demonstrated for a geometric sequence of dodecagonal elements.
Title:
Temperature dependences of the electric polarization and wave number of incommensurate structures in multiferroics
Authors:
Pikin, SA Author Full Names: Pikin, S. A.
Source:
CRYSTALLOGRAPHY REPORTS, 61 (3):449-455; 10.1134/S1063774516030214 MAY 2016
Abstract:
It is shown that the electric polarization and wave number of incommensurate modulations, proportional to each other, increase according to the Landau law in spin multiferroic cycloids near the N,el temperature. In this case, the constant magnetization component (including the one for a conical spiral) is oriented perpendicular to the spin incommensurability wave vector. A similar temperature behavior should manifest itself for spin helicoids, the axes of which are oriented parallel to the polarization vector but their spin rotation planes are oriented perpendicular to the antiferromagnetic order plane. When the directions of axes of the magnetization helicoid and polarization vector coincide, the latter is quadratic with respect to magnetization and linearly depends on temperature, whereas the incommensurate-modulation wave number barely depends on temperature. Structural distortions of unit cells for multiferroics of different types determine their axial behavior.

Update: 20-Jun-2016

Title:
Determination of shapes and preferred growth directions of icosahedral quasicrystals from the 2D-sections
Authors:
Zupanic, F; Boncina, T Author Full Names: Zupanic, Franc; Boncina, Tonica
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 681 532-540; 10.1016/j.allcom.2016.04.255 OCT 5 2016
Abstract:
The icosahedral quasicrystalline phases have been present in many alloys either as nearly regular polyhedra or dendrites. This work provides a systematic approach for the determination of shapes of polyhedra with icosahedral symmetry, and the determination of preferred growth directions of icosahedral dendrites from their 2D-sections; i.e. from the surface of polished samples. The possible shapes of polyhedra and dendrites by differently oriented intersecting planes are presented within the icosahedral stereographic triangle. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Incommensurate counterrotating magnetic order stabilized by Kitaev interactions in the layered honeycomb alpha-Li2IrO3
Authors:
Williams, SC; Johnson, RD; Freund, F; Choi, S; Jesche, A; Kimchi, I; Manni, S; Bombardi, A; Manuel, P; Gegenwart, P; Coldea, R Author Full Names: Williams, S. C.; Johnson, R. D.; Freund, F.; Choi, Sungkyun; Jesche, A.; Kimchi, I.; Manni, S.; Bombardi, A.; Manuel, P.; Gegenwart, P.; Coldea, R.
Source:
PHYSICAL REVIEW B, 93 (19):10.1103/PhysRevB.93.195158 MAY 26 2016
Abstract:
The layered honeycomb magnet alpha-Li2IrO3 has been theoretically proposed as a candidate to display unconventional magnetic behaviour associated with Kitaev interactions between spin-orbit entangled j(eff) = 1/2 magnetic moments on a honeycomb lattice. Here we report single crystal magnetic resonant x-ray diffraction combined with powder magnetic neutron diffraction to reveal an incommensurate magnetic order in the honeycomb layers with Ir magnetic moments counterrotating on nearest-neighbor sites. This unexpected type of magnetic structure for a honeycomb magnet cannot be explained by a spin Hamiltonian with dominant isotropic (Heisenberg) couplings. The magnetic structure shares many key features with the magnetic order in the structural polytypes beta- and gamma-Li2IrO3, understood theoretically to be stabilized by dominant Kitaev interactions between Ir moments located on the vertices of three-dimensional hyperhoneycomb and stripyhoneycomb lattices, respectively. Based on this analogy and a theoretical soft-spin analysis of magnetic ground states for candidate spin Hamiltonians, we propose that Kitaev interactions also dominate in alpha-Li2IrO3, indicative of universal Kitaev physics across all three members of the harmonic honeycomb family of Li2IrO3 polytypes.
Title:
Strong enhancement of superconductivity at high pressures within the charge-density-wave states of 2H-TaS2 and 2H-TaSe2
Authors:
Freitas, DC; Rodiere, P; Osorio, MR; Navarro-Moratalla, E; Nemes, NM; Tissen, VG; Cario, L; Coronado, E; Garcia-Hernandez, M; Vieira, S; Nunez-Regueiro, M; Suderow, H Author Full Names: Freitas, D. C.; Rodiere, P.; Osorio, M. R.; Navarro-Moratalla, E.; Nemes, N. M.; Tissen, V. G.; Cario, L.; Coronado, E.; Garcia-Hernandez, M.; Vieira, S.; Nunez-Regueiro, M.; Suderow, H.
Source:
PHYSICAL REVIEW B, 93 (18):10.1103/PhysRevB.93.184512 MAY 24 2016
Abstract:
We present measurements of the superconducting and charge-density-wave (CDW) critical temperatures (T-c and T-CDW) as a function of pressure in the transition metal dichalchogenides 2H-TaSe2 and 2H-TaS2. Resistance and susceptibility measurements show that T-c increases from temperatures below 1 K up to 8.5 K at 9.5 GPa in 2H-TaS2 and 8.2 K at 23 GPa in 2H-TaSe2. We observe a kink in the pressure dependence of T-CDW at about 4 GPa that we attribute to the lock-in transition from incommensurate CDW to commensurate CDW. Above this pressure, the commensurate TCDW slowly decreases, coexisting with superconductivity within our full pressure range.
Title:
Self-lubricating, low-friction, wear-resistant Al-based quasicrystalline coatings
Authors:
de Lima, BASG; Gomes, RM; de Lima, SJG; Dragoe, D; Barthes-Labrousse, MG; Kouitat-Njiwa, R; Dubois, JM Author Full Names: Silva Guedes de Lima, Bruno Alessandro; Gomes, Rodinei Medeiros; Guedes de Lima, Severino Jackson; Dragoe, Diana; Barthes-Labrousse, Marie-Genevieve; Kouitat-Njiwa, Richard; Dubois, Jean-Marie
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 17 (1):71-79; 10.1080/14686996.2016.1152563 2016
Abstract:
After gas atomization, a quasicrystalline powder based on aluminium was used to prepare a thick coating by high-velocity oxygen-fuel flame torch spraying. This layer was deposited on top of a bond-coat layer on a steel plate. A post-spraying annealing treatment turned the two layers to their stable state, a.-brass crystal and an icosahedral quasicrystal, respectively. The projection parameters were selected in such a way that the coating behaved like a self-lubricating material, which offered very good wear resistance (duration of pin-on-disk tests superior to 5 km with negligible material loss) and low friction (mu <= 6% against sintered tungsten carbide), in contrast to the state of the art. This property was achieved thanks to, on the one hand, excellent bonding to the substrate via the bound coat, and on the other hand, presence at the boundaries between quasicrystalline flakes of a mixture of both threefold and fourfold coordinated carbon originating from spray processing. Application to hard materials used in mechanical devices is appealing, especially because soft, lubricating additives may not be needed, thus considerably increasing the lifetime of the devices and reducing waste of materials.

Update: 8-Jun-2016

Title:
Evolution of the magnetic structure of TbRu2Al10 in applied field
Authors:
White, R; Hutchison, WD; Mizushima, T; Studer, AJ Author Full Names: White, R.; Hutchison, W. D.; Mizushima, T.; Studer, A. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 679 169-176; 10.1016/j.jallcom.2016.04.039 SEP 15 2016
Abstract:
TbRu2Al10 is found to undergo two magnetic phase transitions as a function of temperature and three as a function of applied field at low temperature. The Tb3+ magnetic moments order antiferromagnetically along the c-axis at 15.0(3) K, with an incommensurate sinusoidally modulated structure with a propagation vector of k = (0, 0.759(1), 0). At 6.5(3) K the structure switches to square wave order. Analysis of single crystal TbRu2Al10 has revealed that this square wave structure is altered to a 'pulse wave' on application of a 1.30 T magnetic field along the c-axis, with two in fifty of the magnetic moments across the structure changing direction to be aligned parallel with the direction of the field. At 1.85 T a further three moments flip, leading to a duty cycle of 60% and resulting in a total change of one in ten moments from the starting square wave structure. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Two iridates, two models, and two approaches: A comparative study on magnetism in three-dimensional honeycomb materials
Authors:
Lee, EKH; Rau, JG; Kim, YB Author Full Names: Lee, Eric Kin-Ho; Rau, Jeffrey G.; Kim, Yong Baek
Source:
PHYSICAL REVIEW B, 93 (18):10.1103/PhysRevB.93.184420 MAY 17 2016
Abstract:
Two recent theoretical works studied the role of Kitaev interactions in the newly observed incommensurate magnetic order in the hyper-honeycomb (beta-Li2IrO3) and stripy-honeycomb (gamma-Li2IrO3) iridates. Each of these works analyzed a different model (JK Gamma versus coupled zigzag chain model) using a contrasting method (classical versus soft-spin analysis). The lack of commonality between these works precludes meaningful comparisons and a proper understanding of these unusual orderings. In this study, we complete the unfinished picture initiated by these two works by solving both models with both approaches for both three-dimensional (3D) honeycomb iridates. Through comparisons between all combinations of models, techniques, and materials, we find that the bond-isotropic JK Gamma model consistently predicts the experimental phase of beta-Li2IrO3 regardless of the method used, while the experimental phase of gamma-Li2IrO3 can be generated by the soft-spin approach with eigenmode mixing irrespective of the model used. To gain further insights, we solve a one-dimensional (1D) quantum spin-chain model related to both 3D models using the density matrix renormalization group method to form a benchmark. We discover that in the 1D model, incommensurate correlations in the classical and soft-spin analysis survive in the quantum limit only in the presence of the symmetric-off-diagonal exchange Gamma found in the JK Gamma model. The relevance of these results to the real materials is also discussed.

Update: 1-Jun-2016

Title:
Ternary phases forming adjacent to Al3Mn-Al4Mn in Al-Mn-TM (TM = Fe, Co, Ni, Cu, Zn, Pd)
Authors:
Grushko, B; Pavlyuchkov, D; Mi, SB; Balanetskyy, S Author Full Names: Grushko, B.; Pavlyuchkov, D.; Mi, S. B.; Balanetskyy, S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 677 148-162; 10.1016/j.jallcom.2016.03.220 AUG 25 2016
Abstract:
The Al-Mn alloy system contains complex intermetallics in its Al-rich part, and this was the first system where quasiperiodic structures were recognized. In the present work, the solubility of TMs (TM = Fe, Co, Ni, Cu, Zn and Pd) in the stable binaries, the stabilization effect of these elements on the metastable binaries and the formation of ternary compounds are specified and compared. While the solubility of all these TMs in hexagonal mu-Al4Mn and lambda-Al4Mn is low, the high-temperature orthorhombic T-Al3Mn dissolves up to at least 14.5, 12, 16 and 7.5 at.% Fe, Cu, Zn and Pd, respectively. The metastable hexagonal phi-Al10Mn3 is stabilized by Fe, Co and Ni in wide ternary compositional regions, and in Al-Co-Mn such a region propagates up to Al5Co2. In alloys with Fe, Co and Ni, a ternary hexagonal phase isostructural to the Al-Cr-Ni zeta-phase (P6(3)/m, a approximate to 1.76, c approximate to 1.25 nm) is formed along similar to 80 at.% Al, while in alloys with Cu and Pd the orthorhombic so-called R-phase (Bbmm, a approximate to 2.41, b approximate to 1.25, c approximate to 0.76 nm) was found at similar compositions. This structure is also known in Al-Zn-Mn but at much lower-Al Al68Zn14.5Mn17.5, while in the range of 75-80 at.% Al a monoclinic phase isostructural to eta-Al11Cr2 (C2/c, a approximate to 1.76, b approximate to 3.04, c approximate to 1.76 nm, beta approximate to 90 degrees) is formed. In addition to the stable decagonal D-3-phase in Al-Fe-Mn and Al-Pd-Mn reported earlier, the stabilization of binary Al-Mn D-3-phase was revealed around Al64Cu20Mn16. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Medium-range structure and glass forming ability in Zr-Cu-Al bulk metallic glasses
Authors:
Zhang, P; Maldonis, JJ; Besser, MF; Kramer, MJ; Voyles, PM Author Full Names: Zhang, Pei; Maldonis, Jason J.; Besser, M. F.; Kramer, M. J.; Voyles, Paul M.
Source:
ACTA MATERIALIA, 109 103-114; 10.1016/j.actamat.2016.02.006 MAY 1 2016
Abstract:
Fluctuation electron microscopy experiments combined with hybrid reverse Monte Carlo modeling show a correlation between medium-range structure at the nanometer scale and glass forming ability in two Zr-Cu-Al bulk metallic glass (BMG) alloys. Both Zr50Cu35Al15 and Zr50Cu45Al5 exhibit two nanoscale structure types, one icosahedral and the other more crystal-like. In Zr50Cu35Al15, the poorer glass former, the crystal-like structure is more stable under annealing below the glass transition temperature, T-g, than in Zr50Cu45Al5. Variable resolution fluctuation microscopy of the MRO clusters show that in Zr50Cu35Al15 on sub-T-g annealing, the crystal-like clusters shrink even as they grow more ordered, while icosahedral-like clusters grow. Overall, the results suggest that achieving better glass forming ability in this alloy system may depend more on destabilizing crystal-like structures than enhancing non-crystalline structures. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Influence of pre-strain on the aging hardening effect of the Mg-9.02Zn-1.68Y alloy
Authors:
Ye, J; Lin, XP; Zhao, TB; Liu, NN; Xie, HB; Niu, Y; Teng, F Author Full Names: Ye, Jie; Lin, Xiao-ping; Zhao, Tian-bo; Liu, Ning-ning; Xie, Hong-bin; Niu, Yi; Teng, Fei
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 663 49-55; 10.1016/j.msea.2016.03.115 APR 29 2016
Abstract:
The solid-solution state Mg-7.68Zn-1.68Y alloy was pre-compressed before the isothermal aging treatment at 200 degrees C, then the pre-induced twinning and its influence on the aging microstructure and aging hardening effect were investigated using EBSD, TEM and SEM. Results showed that: about 15% (area fraction) lenticular (1012) tensile twinning were induced into the matrix when the alloy was compressed by 3% pre-strain; and when the amount of pre-strain increased, area fraction of twinning would increase, average size of twinning would decrease, morphology and structure of twinning would change: when the pre-strain reached 15%, about 28% (area fraction) of narrow double twinning (10 (1) over bar1)-(10 (1) over bar2)would be induced, while the anamorphosis of double twinning were mostly inter-crossing. In addition, twinning could become an effective substrate for nucleation. And different from precipitates in the matrix, which is rod-shaped beta'(1)1-MgZn2 growing along a certain direction, precipitates in the twin boundaries were granular icosahedral quasi -crystal phase with 5 -times rotational symmetric diffraction pattern. And when the pre-strain was in the range of 3-15%, aging hardening effect increased with pre-strain; when pre-strain were 10-15%, the peak hardness arrived 110HV, 28% improved compared to that of the not pre-deformed one (86HV); when the pre-strain exceeded 20%, the aging hardening effect would decrease. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Determination of the zero-field magnetic structure of the helimagnet MnSi at low temperature
Authors:
de Reotier, PD; Maisuradze, A; Yaouanc, A; Roessli, B; Amato, A; Andreica, D; Lapertot, G Author Full Names: de Reotier, P. Dalmas; Maisuradze, A.; Yaouanc, A.; Roessli, B.; Amato, A.; Andreica, D.; Lapertot, G.
Source:
PHYSICAL REVIEW B, 93 (14):10.1103/PhysRevB.93.144419 APR 22 2016
Abstract:
Below a temperature of approximately 29 K the manganese magnetic moments of the cubic binary compound MnSi order to a long-range incommensurate helical magnetic structure. Here we quantitatively analyze a high-statistic zero-field muon spin rotation spectrum recorded in the magnetically ordered phase of MnSi by exploiting the result of representation theory as applied to the determination of magnetic structures. Instead of a gradual rotation of the magnetic moments when moving along a (111) axis, we find that the angle of rotation between the moments of certain subsequent planes is essentially quenched. It is the magnetization of pairs of planes which rotates when moving along a (111) axis, thus preserving the overall helical structure.
Title:
Incommensurate-commensurate transitions in the monoaxial chiral helimagnet driven by the magnetic field
Authors:
Laliena, V; Campo, J; Kishine, JI; Ovchinnikov, AS; Togawa, Y; Kousaka, Y; Inoue, K Author Full Names: Laliena, Victor; Campo, Javier; Kishine, Jun-Ichiro; Ovchinnikov, Alexander S.; Togawa, Yoshihiko; Kousaka, Yusuke; Inoue, Katsuya
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134424 APR 20 2016
Abstract:
The zero-temperature phase diagram of the monoaxial chiral helimagnet in the magnetic-field plane formed by the components parallel and perpendicular to the helical axis is thoroughly analyzed. The nature of the transition to the commensurate state depends on the angle between the field and the helical axis. For field directions close to the directions parallel or perpendicular to the helical axis the transition is continuous, while for intermediate angles the transition is discontinuous and the incommensurate and commensurate states coexist on the transition line. The continuous and discontinuous transition lines are separated by two tricritical points with specific singular behavior. The location of the continuous and discontinuous lines and of the tricritical points depend strongly on the easy-plane anisotropy, the effect of which is analyzed. For high anisotropy the conical approximation locates the transition line very accurately, although it does not predict the continuous transitions and the tricritical behavior. It is shown that for high anisotropy, as in CrNb3S6, the form of the transition line is universal, that is, independent of the sample, and obeys a simple equation. The position of the tricritical points, which is not universal, is theoretically estimated for a sample of CrNb3S6.
Title:
Low-Temperature Oxidation of Fine UO2 Powders: A Process of Nanosized Domain Development
Authors:
Leinders, G; Pakarinen, J; Delville, R; Cardinaels, T; Binnemans, K; Verwerft, M Author Full Names: Leinders, Gregory; Pakarinen, Janne; Delville, Remi; Cardinaels, Thomas; Binnemans, Koen; Verwerft, Marc
Source:
INORGANIC CHEMISTRY, 55 (8):3915-3927; 10.1021/acs.inorgchem.6b00127 APR 18 2016
Abstract:
The nanostructure and phase evolution in low-temperature oxidized (40-250 degrees C), fine UO2 powders (<200 nm) have been investigated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). The extent of oxidation was also measured via in situ thermogravimetric analysis. The oxidation of fine powders was found to, proceed differently as compared to oxidation of coarse grained UO2. No discrete surface oxide layer was observed and no U3O8 was formed, despite the high degree of oxidation (up to O/U = 2.45). Instead, nanosized (5-15 nm) amorphous nuclei (interpreted as amorphous UO3), unmodulated and modulated U4O9, and a continuous range of U3O7-z phases with varying tetragonal distortion (c/a > 1) were observed. Oxidation involves formation of higher uranium oxides in nanodomains near the grain surface which, initially, have a disordered defect structure ("disordered U4O9"). As oxidation progresses, domain growth increases and the long period modulated structure of U4O9 develops ("ordered U4O9"). A similar mechanism is understood to happen also in U3O7-z.
Title:
Disorder-promoted C-4-symmetric magnetic order in iron-based superconductors
Authors:
Hoyer, M; Fernandes, RM; Levchenko, A; Schmalian, J Author Full Names: Hoyer, Mareike; Fernandes, Rafael M.; Levchenko, Alex; Schmalian, Joerg
Source:
PHYSICAL REVIEW B, 93 (14):10.1103/PhysRevB.93.144414 APR 18 2016
Abstract:
In most iron-based superconductors, the transition to the magnetically ordered state is closely linked to a lowering of structural symmetry from tetragonal (C-4) to orthorhombic (C-2). However, recently, a regime of C-4-symmetric magnetic order has been reported in certain hole-doped iron-based superconductors. This novel magnetic ground state can be understood as a double-Q spin density wave characterized by two order parameters M-1 and M-2 related to each of the two Q vectors. Depending on the relative orientations of the order parameters, either a noncollinear spin-vortex crystal or a nonuniform charge-spin density wave could form. Experimentally, Mossbauer spectroscopy, neutron scattering, and muon spin rotation established the latter as the magnetic configuration of some of these optimally hole-doped iron-based superconductors. Theoretically, low-energy itinerant models do support a transition from single-Q to double-Q magnetic order, but with nearly degenerate spin-vortex crystal and charge-spin density wave states. In fact, extensions of these low-energy models including additional electronic interactions tip the balance in favor of the spin-vortex crystal, in apparent contradiction with the recent experimental findings. In this paper we revisit the phase diagram of magnetic ground states of low-energy multiband models in the presence of weak disorder. We show that impurity scattering not only promotes the transition from C-2 to C-4-magnetic order, but it also favors the charge-spin density wave over the spin-vortex crystal phase. Additionally, in the single-Q phase, our analysis of the nematic coupling constant in the presence of disorder supports the experimental finding that the splitting between the structural and stripe-magnetic transition is enhanced by disorder.
Title:
Low-temperature magnetic phase transitions in the multiferroic Nd0.9Dy0.1Fe3(BO3)(4). Part 1. Transitions induced by magnetic fields directed along the trigonal symmetry axis. Spontaneous transitions with temperature changes
Authors:
Zvyagina, GA; Zhekov, KR; Bilych, IV; Kolodyazhnaya, MP; Zvyagin, AA; Bludov, AN; Pashchenko, VA; Gudim, IA Author Full Names: Zvyagina, G. A.; Zhekov, K. R.; Bilych, I. V.; Kolodyazhnaya, M. P.; Zvyagin, A. A.; Bludov, A. N.; Pashchenko, V. A.; Gudim, I. A.
Source:
LOW TEMPERATURE PHYSICS, 42 (4):273-279; 10.1063/1.4947480 APR 2016
Abstract:
The elastic and magnetic characteristics of single-crystal Nd0.9Dy0.1Fe3(BO3)(4) are studied at low temperatures in zero magnetic field and in external fields H vertical bar vertical bar C-3. The temperature dependences of the acoustic mode velocities and the magnetic susceptibility manifest a transition of the magnetic subsystem into a magnetically ordered state and two successive, spontaneous spin-reorientation phase transitions. The possibility of a spontaneous transition into an incommensurate (spiral) magnetic phase in the crystal is discussed. It is shown that an external magnetic field directed along the trigonal axis of the crystal induces a sequence of spin-reorientation phase transitions. An H-T phase diagram (H vertical bar vertical bar C-3) is constructed for this compound. Published by AIP Publishing.
Title:
3D Morphology and Formation Process of the Icosahedral Quasicrystalline Phase in Rapidly Solidified Al-Mn Alloy
Authors:
Kang, HJ; Hu, ZL; Gao, XX; Chen, ZN; Lu, YP; Jie, JC; Guo, JJ Author Full Names: Kang, Hui-Jun; Hu, Zhong-Lue; Gao, Xiao-Xia; Chen, Zong-Ning; Lu, Yi-Ping; Jie, Jin-Chuan; Guo, Jing-Jie
Source:
ACTA METALLURGICA SINICA-ENGLISH LETTERS, 29 (1):28-31; 10.1007/s40195-015-0357-y JAN 2016
Abstract:
Three-dimensional morphology and formation process of icosahedral quasicrystal phase have been investigated in a melt-spun Al-18Mn alloy (in wt%). Three distinct layers corresponding to varying temperature gradient have been observed on the cross section of the ribbons. 3D morphologies of cellular and dendritic icosahedral phase have been obtained through electro-etching. A model has been proposed to describe the formation process of the icosahedral phase and alpha-Al during the rapid solidification. The icosahedral phases are primarily precipitated from the melt into fine cellular and dendritic particles, and subsequently engulfed by the alpha-Al which propagates in a planar morphology.
Title:
Diffraction pattern of modulated structures described by Bessel functions
Authors:
Wolny, J; Buganski, I; Strzalka, R Author Full Names: Wolny, Janusz; Buganski, Ireneusz; Strzalka, Radoslaw
Source:
PHILOSOPHICAL MAGAZINE, 96 (13):1344-1359; 10.1080/14786435.2016.1161859 2016
Abstract:
We performed detailed analysis of 1D modulated structure (MS) with harmonic modulation within the statistical approach. By applying two-mode Fourier transform, we were able to derive analytically the structure factor for MS with single harmonic modulation component. We confirmed in a very smooth way that ordinary Bessel functions of the first kind define envelopes tuning the intensities of the diffraction peaks. This applies not only to main reflections of the diffraction pattern but also to all satellites. In the second part, we discussed in details the similarities between harmonically modulated structures with multiple modulations and 1D model quasicrystal. The Fourier expansion of the nodes' positions in the Fibonacci chain gives direct numerical definition of the atomic arrangement in MS. In that sense, we can define 1D quasicrystal as a MS with infinite number of harmonic modulations. We prove that characteristic measures (like v(u) relation typical for statistical approach and diffraction pattern) calculated for MS asymptotically approach their counterparts for 1D quasicrystal as large enough number of modulation terms is taken into account.
Title:
The Effect of the Drop Tube Process for the Quasicrystal Fine Particles Formation
Authors:
Takeda, Y; Kawamura, T; Nagayama, K Author Full Names: Takeda, Yuya; Kawamura, Tadaharu; Nagayama, Katsuhisa
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 80 (4):273-279; 10.2320/jinstmet.JBW201506 2016
Abstract:
In general, quasicrystalline structures are produced by liquid quenching using a single roll, Bridgman and Czochralski method, which is typical for the production of single crystals. However, there are few reports of the quasicrystal formation using a containerless process; therefore, the effect of such a process is unclear. In this study, we have investigated the production of quasicrystalline fine particles and the formation ability of Al63Cu25Fe12, Al65Cu20Fe15, and Al70Ni15Co15 ternary alloys using a drop tube apparatus with a free fall length of 2.5 m. In addition, we have aimed to examine the effectiveness of the drop tube process for quasicrystal formation. The formation of dodecahedron crystals, which are considered a quasicrystalline phase, was observed in Al63Cu25Fe12 ternary fine particle samples prepared using the drop tube process under a He atmosphere (1 atm). Based on the heat flux, the calculated results suggested that the icosahedral phase was formed at high cooling rates of similar to 10(5) K/s. In the Al70Ni15Co15 ternary fine particle sample, aggregation of prismatic crystals was observed in the fine particle samples prepared using the drop tube process under an atmosphere of He (1 atm) and Ar (1 atm). Furthermore, formation of prismatic crystals was observed on the surface of fine particle samples prepared under a low-pressure Ar atmosphere (0.5 atm), under which the formation ability of quasicrystals was observed to be the highest. From these results, the formation ability of the Al-Ni-Co-based decagonal phase is suggested to increase with decreasing cooling rates. This result is different from that of the Al-Cu-Fe-based icosahedral quasicrystals.

Update: 27-May-2016

Title:
Self-consistent theory of nanodomain formation on nonpolar surfaces of ferroelectrics
Authors:
Morozovska, AN; Ievlev, AV; Obukhovskii, VV; Fomichov, Y; Varenyk, OV; Shur, VY; Kalinin, SV; Eliseev, EA Author Full Names: Morozovska, Anna N.; Ievlev, Anton V.; Obukhovskii, Vyacheslav V.; Fomichov, Yevhen; Varenyk, Oleksandr V.; Shur, Vladimir Ya.; Kalinin, Sergei V.; Eliseev, Eugene A.
Source:
PHYSICAL REVIEW B, 93 (16):10.1103/PhysRevB.93.165439 APR 28 2016
Abstract:
We propose a self-consistent theoretical approach capable of describing the features of the anisotropic nanodomain formation induced by a strongly inhomogeneous electric field of a charged scanning probe microscopy tip on nonpolar cuts of ferroelectrics. We obtained that a threshold field, previously regarded as an isotropic parameter, is an anisotropic function that is specified from the polar properties and lattice pinning anisotropy of a given ferroelectric in a self-consistent way. The proposed method for the calculation of the anisotropic threshold field is not material specific, thus the field should be anisotropic in all ferroelectrics with the spontaneous polarization anisotropy along the main crystallographic directions. The most evident examples are uniaxial ferroelectrics, layered ferroelectric perovskites, and low-symmetry incommensurate ferroelectrics. Obtained results quantitatively describe the differences at several times in the nanodomain length experimentally observed on X and Y cuts of LiNbO3 and can give insight into the anisotropic dynamics of nanoscale polarization reversal in strongly inhomogeneous electric fields.
Title:
Incommensurate spin correlations in highly oxidized cobaltates La2-xSrxCoO4
Authors:
Li, ZW; Drees, Y; Kuo, CY; Guo, H; Ricci, A; Lamago, D; Sobolev, O; Rutt, U; Gutowski, O; Pi, TW; Piovano, A; Schmidt, W; Mogare, K; Hu, Z; Tjeng, LH; Komarek, AC Author Full Names: Li, Z. W.; Drees, Y.; Kuo, C. Y.; Guo, H.; Ricci, A.; Lamago, D.; Sobolev, O.; Ruett, U.; Gutowski, O.; Pi, T. W.; Piovano, A.; Schmidt, W.; Mogare, K.; Hu, Z.; Tjeng, L. H.; Komarek, A. C.
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep25117 APR 27 2016
Abstract:
We observe quasi-static incommensurate magnetic peaks in neutron scattering experiments on layered cobalt oxides La2-xSrxCoO4 with high Co oxidation states that have been reported to be paramagnetic. This enables us to measure the magnetic excitations in this highly hole-doped incommensurate regime and compare our results with those found in the low-doped incommensurate regime that exhibit hourglass magnetic spectra. The hourglass shape of magnetic excitations completely disappears given a high Sr doping. Moreover, broad low-energy excitations are found, which are not centered at the incommensurate magnetic peak positions but around the quarter-integer values that are typically exhibited by excitations in the checkerboard charge ordered phase. Our findings suggest that the strong inter-site exchange interactions in the undoped islands are critical for the emergence of hourglass spectra in the incommensurate magnetic phases of La2-xSrxCoO4.
Title:
Electronic nature of the lock-in magnetic transition in CeXAl4Si2
Authors:
Gunasekera, J; Harriger, L; Dahal, A; Maurya, A; Heitmann, T; Disseler, SM; Thamizhavel, A; Dhar, S; Singh, DJ; Singh, DK Author Full Names: Gunasekera, J.; Harriger, L.; Dahal, A.; Maurya, A.; Heitmann, T.; Disseler, S. M.; Thamizhavel, A.; Dhar, S.; Singh, D. J.; Singh, D. K.
Source:
PHYSICAL REVIEW B, 93 (15):10.1103/PhysRevB.93.155151 APR 25 2016
Abstract:
We have investigated the underlying magnetism in newly discovered single crystal Kondo lattices CeXAl4Si2, where X = Rh, Ir. We show that the compound undergoes an incommensurate-to-commensurate magnetic transition at T-c = 9.19 K (10.75 K in Ir). The spin correlation in the incommensurate phase is described by a spin density wave configuration of Ce ions, which locks in to the long-range antiferromagnetic order at T = T-c. The analysis of the experimental data, combined with the calculation of the electronic properties, suggests the role of the Fermi surface nesting as the primary mechanism behind this phenomenon.
Title:
Direct imaging of coexisting ordered and frustrated sublattices in artificial ferromagnetic quasicrystals
Authors:
Farmer, B; Bhat, VS; Balk, A; Teipel, E; Smith, N; Unguris, J; Keavney, DJ; Hastings, JT; De Long, LE Author Full Names: Farmer, B.; Bhat, V. S.; Balk, A.; Teipel, E.; Smith, N.; Unguris, J.; Keavney, D. J.; Hastings, J. T.; De Long, L. E.
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134428 APR 25 2016
Abstract:
We have used scanning electron microscopy with polarization analysis and photoemission electron microscopy to image the two-dimensional magnetization of permalloy films patterned into Penrose P2 tilings (P2T). The interplay of exchange interactions in asymmetrically coordinated vertices and short-range dipole interactions among connected film segments stabilize magnetically ordered, spatially distinct sublattices that coexist with frustrated sublattices at room temperature. Numerical simulations that include long-range dipole interactions between sublattices agree with images of as-grown P2T samples and predict a magnetically ordered ground state for a two-dimensional quasicrystal lattice of classical Ising spins.
Title:
Confinement transition to density wave order in metallic doped spin liquids
Authors:
Patel, AA; Chowdhury, D; Allais, A; Sachdev, S Author Full Names: Patel, Aavishkar A.; Chowdhury, Debanjan; Allais, Andrea; Sachdev, Subir
Source:
PHYSICAL REVIEW B, 93 (16):10.1103/PhysRevB.93.165139 APR 25 2016
Abstract:
Insulating quantum spin liquids can undergo a confinement transition to a valence bond solid via the condensation of topological excitations of the associated gauge theory. We extend the theory of such transitions to fractionalized Fermi liquids (FL*): These are metallic doped spin liquids in which the Fermi surfaces only have gauge neutral quasiparticles. Using insights from a duality transform on a doped quantum dimer model for the U(1)-FL* state, we show that projective symmetry group of the theory of the topological excitations remains unmodified, but the Fermi surfaces can lead to additional frustrating interactions. We propose a theory for the confinement transition of Z2-FL* states via the condensation of visons. A variety of confining, incommensurate density wave states are possible, including some that are similar to the incommensurate d-form factor density wave order observed in several recent experiments on the cuprate superconductors.
Title:
Two Kinds of Contact Problems in Dodecagonal Quasicrystals of Point Group 12 mm
Authors:
Zhao, XF; Li, X; Ding, SH Author Full Names: Zhao, Xuefen; Li, Xing; Ding, Shenghu
Source:
ACTA MECHANICA SOLIDA SINICA, 29 (2):167-177; APR 2016
Abstract:
In this paper, two kinds of contact problems in 2-D dodecagonal quasicrystals were discussed using the complex variable function method: one is the finite frictional contact problem, the other is the adhesive contact problem. The analytic expressions of contact stresses in the phonon and phason fields were obtained for a flat rigid punch, which showed that: (1) for the finite frictional contact problem, the contact stress exhibited power-type singularities at the edge of the contact zone; (2) for the adhesive contact problem, the contact stress exhibited oscillatory singularities at the edge of the contact zone. The distribution regulation of contact stress under punch was illustrated; and the low friction property of quasicrystals was verified graphically.
Title:
Structure modulation, band structure, density of states and luminescent properties of columbite-type ZnNb2O6
Authors:
Zhao, D; Ma, FX; Zhang, RJ; Li, FF; Zhang, L; Yang, J; Fan, YC; Xin, X Author Full Names: Zhao, Dan; Ma, Fa-Xue; Zhang, Rui-Juan; Li, Fei-Fei; Zhang, Lei; Yang, Juan; Fan, Yun-Chang; Xin, Xia
Source:
CRYSTENGCOMM, 18 (16):2929-2936; 10.1039/c5ce01828e 2016
Abstract:
Zinc niobate ZnNb2O6, with a columbite-type structure, is a promising dielectric, photocatalytic and luminescent material, but the crystal structure has not been studied in detail. For the first time, we redetermined the crystal structure using single crystal X-ray diffraction and established the commensurately modulated structure model through high-dimensional formalism. The structure features a (3 + 1)-dimensional superspace group Pbcn(alpha 00)00s with the modulation vector q = 1/3a*. At the same time, calculations of the band structure and the density of states were performed using density functional theory to reveal the electronic origins of the optical transitions. In addition, the photoluminescent properties of ZnNb2O6 were studied, showing that a broad emission band at approximately 470 nm can achieve a high quantum efficiency of up to 64% with an optimal sintered temperature of 950 degrees C.

Update: 18-May-2016

Title:
Point contact tunneling spectroscopy of the density of states in Tb-Mg-Zn quasicrystals
Authors:
Escudero, R; Morales, F Author Full Names: Escudero, R.; Morales, F.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 439 46-50; 10.1016/j.jnonaysol.2016.02.019 MAY 1 2016
Abstract:
According to theoretical predictions the quasicrystalline (QC) electronic density of states (DOS) must have a rich and fine spiky structure which actually has resulted elusive. The problem with its absence may be related to poor structural characteristics of the studied specimens, and/or to the non-existence of this spike characteristic. Recent calculations have shown that the fine structure indeed exists, but only for two dimensional approximants phases. The aim of the present study is to show our recent experimental studies with point contact tunnel junction spectroscopy performed in samples of very high quality. The studies were performed in icosahedral QC alloys with composition Tb9Mg35Zn56. We found the presence of a pseudogap feature at the Fermi level, small as compared to the pseudogap of other icosahedral materials. This study made in different spots on the QC shows quite different spectroscopic features, where the observed DOS was a fine non-spiky structure, distinct to theoretical predictions. In some regions of the specimens the spectroscopic features could be related to Kondo characteristics due to Tb magnetic atoms acting as impurities. Additionally, we observed that the spectroscopic features vanished under magnetic field. (C) 2016 Elsevier B.V. All rights reserved.

Update: 12-May-2016

Title:
Quasicrystal as a Catalyst for the Synthesis of Carbon Nanotubes
Authors:
Kajiwara, K; Matsui, Y; Yadav, TP; Mukhopadhyay, NK; Srivastava, ON Author Full Names: Kajiwara, K.; Matsui, Y.; Yadav, T. P.; Mukhopadhyay, N. K.; Srivastava, O. N.
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 16 (3):3084-3089; 10.1166/jnn.2016.12468 MAR 2016
Abstract:
The present report describes the catalytic activity of mechanically activated nano quasicrystalline Al65Cu20Fe15 and related nano crystalline Al50Cu28Fe22 for the synthesis of carbon nanotubes (CNTs). CNTs are synthesized by catalytic decomposition of ethanol through nano quasicrystalline Al65Cu20Fe15 and related crystalline Al50Cu28Fe22 alloys as a catalyst. The synthesized multi-walled CNTs exhibits tube diameter ranging from 5 to 25 nm. The synthesized CNTs are characterized by scanning and transmission electron microscopy. It is found that Al65Cu20Fe15 nanoquasicystal shows better catalytic behaviour as compared to nano-crystalline Al50Cu28Fe22 alloys for decomposition of ethanol during the synthesis of multi-walled CNTs.

Update: 5-May-2016

Title:
Long-period modulated structure and electric-field-induced structural transformation in Na0.5Bi0.5TiO3-based lead-free piezoelectrics
Authors:
Khatua, DK; Senyshyn, A; Ranjan, R Author Full Names: Khatua, Dipak Kumar; Senyshyn, Anatoliy; Ranjan, Rajeev
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134106 APR 14 2016
Abstract:
Na0.5Bi0.5TiO3- based lead-free piezoelectrics exhibiting giant piezostrain are technologically interesting materials for actuator applications. The lack of clarity with regard to the structure of the nonpolar phase of this system has hindered the understanding of the structural mechanism associated with the giant piezostrain and other related phenomena. In this paper, we have investigated the structure and field-induced phase transformation behavior of a model system (0.94 - x) Na0.5Bi0.5TiO3-0.06BaTiO(3)-xK(0.5)Na(0.5)NbO(3) (0.0 <= x <= 0.025). A detailed structural analysis using neutron powder diffraction revealed that the nonpolar phase is neither cubic nor a mixture of rhombohedral (R3c) and tetragonal (P4bm) phases as commonly reported in literature but exhibits a long-period modulated structure, which is most probably of the type root 2 x root 2 x n with n = 16. Our results suggest that the giant piezoelectric strain is associated with a field-induced phase transformation of the long-period modulated structure to rhombohedral R3c structure above a critical field. We also demonstrate that the giant piezostrain is lost if the system retains a fraction of the field-induced R3c phase. A possible correlation among depolarization temperature, giant piezostrain, and its electrical fatigue behavior has also been indicated.
Title:
Temperature-dependent Fermi surface of the misfit cobaltite [Bi2Sr2O4](0.51)CoO2: A comparison with [Bi2Ba2O4](0.50)CoO2
Authors:
Takakura, S; Yamamoto, I; Koga, E; Ichikawa, F; Azuma, J; Maki, M Author Full Names: Takakura, Sho-ichi; Yamamoto, Isamu; Koga, Emi; Ichikawa, Fusao; Azuma, Junpei; Maki, Makoto
Source:
PHYSICAL REVIEW B, 93 (16):10.1103/PhysRevB.93.165118 APR 14 2016
Abstract:
Angle-resolved photoemission spectroscopy has been performed to investigate the Fermi surface (FS) and the electronic structure of misfit cobaltites, by comparing [Bi2Sr2O4](p)CoO2 with [Bi2Ba2O4](0.50)CoO2. In [Bi2Sr2O4](0.51)CoO2, we observed a suppression of spectral weight near the Fermi energy. Nevertheless, the FS can be mapped out by measuring the photoelectron intensity distribution. The FS size changes with temperature. Additionally, results show that the electronic band structure at a higher binding energy was changed by changing the sample temperature. Our results provide insight into the characteristics of the pseudogap state in the misfit-layered cobaltites. The unusual properties are probably related to the local deformations of the incommensurate structure.
Title:
Structure modulations in nonlinear optical (NLO) materials Cs2TB4O9 (T = Ge, Si)
Authors:
Zhou, ZY; Xu, X; Fei, R; Mao, JG; Sun, JL Author Full Names: Zhou, Zhengyang; Xu, Xiang; Fei, Rao; Mao, Jianggao; Sun, Junliang
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 194-200; 10.1107/S2052520615019733 2 APR 2016
Abstract:
Incommensurately modulated borate structures of a new type were studied in detail in the nonlinear optical (NLO) materials Cs2TB4O9 (T = Ge, Si) using single-crystal X-ray diffraction techniques. The structures were solved by the charge-flipping algorithm in the superspace group I2(alpha beta 0)0. The refinement results strongly suggest that the main structure modulation feature of Cs2TB4O9 is the ordering of the O atoms. With these modulated structure models, the unreasonable B-O distances in the average structures were explained as the ordering of BO4 and BO3.
Title:
Melilite-like modulation and temperature-dependent evolution in the framework structure of K2Sc[Si2O6]F
Authors:
Hejny, C; Kahlenberg, V; Eberhard, T; Kruger, H Author Full Names: Hejny, Clivia; Kahlenberg, Volker; Eberhard, Tim; Krueger, Hannes
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 209-222; 10.1107/S2052520615024865 2 APR 2016
Abstract:
The crystal structure of synthetic K2Sc[Si2O6] F has been solved and refined as an incommensurately modulated structure in (3 + 2)-dimensional superspace. This paper describes the tetragonal structure in the superspace group P4(2)/mnm(alpha, alpha,0) 000s(-alpha, alpha,0) 0000 [a = 8.9878 (1), c = 8.2694 (2) angstrom, V = 668.01 (2) angstrom(3)] with modulation wavevectors q(1) = 0.2982 (4)(a* + b*) and q(2) = 0.2982 (4)(-a* + b*). Structure refinement taking into account the modulation of positional and ADP parameters for all atoms from 3074 observed main hkl00 and satellite reflections hklmn of first order with single, m.n = 0, and mixed, m.n = +/- 1, indices converged to a final R value of 0.0514. The structure is a mixed octahedral-tetrahedral framework composed of [ScO4F2] octahedra, [Si4O12] rings and K in variable coordination. Due to the modulation the O atoms move into and out of the first coordination sphere of K leading to a minimum of five and a maximum of 10 interatomic K-O distances up to 3.1 angstrom Although this feature is comparable to observations in modulated fresnoite and melilite group compounds, these structures differ from K2Sc[Si2O6] F with respect to their topology. On temperature increase the intensity of the satellite reflections decreases until they disappear just above 443 K. The high-temperature normal structure, in space group P4(2)/mnm, is identical to the room-temperature average structure of K2Sc[Si2O6]F.

Update: 29-Apr-2016

Title:
Metastable phase formation in ternary Mg-Gd-Zn alloys
Authors:
Grobner, J; Zhu, SM; Nie, JF; Gibson, MA; Schmid-Fetzer, R Author Full Names: Groebner, Joachim; Zhu, Suming; Nie, Jian-Feng; Gibson, Mark A.; Schmid-Fetzer, Rainer
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 675 149-157; 10.1016/j.jallcom.2016.03.106 AUG 5 2016
Abstract:
Two metastable phases have been identified in as-cast Mg-rich Mg-Gd-Zn alloys by TEM characterization. The I-phase was found to have a composition close to Gd11Mg29Zn60 with an icosahedral structure (a(R) = 0.524 nm). The H2-phase, with a composition close to Gd16Mg14Zn70, was identified to have a hexagonal structure (a = 0.937 nm and c = 0.977 nm). An extension of the thermodynamic description of the ternary Mg-Gd-Zn phase diagram to incorporate the formation of these metastable phases has been modelled. Thermodynamic simulation of metastable phase formation has been conducted by suppressing the formation of more stable phases in a constrained Scheil solidification simulation to form I and H2 phases. The results of these solidification simulations are compared with reported as-cast alloy structures. Limiting values for the Gd/Zn atomic ratio, similar to< 0.55 and similar to> 1.4, are found to be crucial for phase selection. An application to Mg-Zn-Gd-Y alloys is discussed briefly. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Phenomenological Magnetic Model in Tsai-Type Approximants
Authors:
Sugimoto, T; Tohyama, T; Hiroto, T; Tamura, R Author Full Names: Sugimoto, Takanori; Tohyama, Takami; Hiroto, Takanobu; Tamura, Ryuji
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (5):10.7566/JPSJ.85.053701 MAY 15 2016
Abstract:
Motivated by the recent discovery of canted ferromagnetism in the Tsai-type approximants Au-Si-REs (RE = Tb, Dy, and Ho), we propose a phenomenological magnetic model reproducing their magnetic structure and thermodynamic quantities. In the model, the cubic symmetry (m (3) over bar) of the approximately regular icosahedra plays a key role in the peculiar magnetic structure determined by a neutron diffraction experiment. Our magnetic model does not only explain magnetic behaviors in the quasicrystal approximants, but also provides a good starting point for the possibility of the coexistence between the magnetic long-range order and the aperiodicity in quasicrystals.
Title:
Low temperature magneto-structural transitions in Mn3Ni20P6
Authors:
Cedervall, J; Beran, P; Vennstrom, M; Danielsson, T; Ronneteg, S; Hoglin, V; Lindell, D; Eriksson, O; Andre, G; Andersson, Y; Nordblad, P; Sahlberg, M Author Full Names: Cedervall, Johan; Beran, Premysl; Vennstrom, Marie; Danielsson, Therese; Ronneteg, Sabina; Hoglin, Viktor; Lindell, David; Eriksson, Olle; Andre, Gilles; Andersson, Yvonne; Nordblad, Per; Sahlberg, Martin
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 237 343-348; 10.1016/j.jssc.2016.02.028 MAY 2016
Abstract:
X-ray and neutron powder diffraction has been used to determine the crystal and magnetic structure of Mn3Ni20P6. The crystal structure can be described as cubic with space group Fm (3) over barm (225) without any nuclear phase transformation within studied temperature interval from room temperature down to 4 K. The magnetic structure of Mn3Ni20P6 is complex with two independent magnetic positions for the Mn atoms and the compound passes three successive magnetic phase transitions during cooling. At 30 K the spins of the Mn atoms on the Wyckoff 4a site (Mn1) order to form a primitive cubic anti ferromagnetic structure with propagation vector k=(0 0 1). Between 29 and 26 K the Mn atoms on the Wyckoff 8c site (Mn2) order independently on already ordered Mn1 magnetic structure forming a commensurate antiferromagnetic structure with propagation vector k= (0 0 1/2) and below 26 K, both Mn positions order to form an incommensurate helical structure with propagation vector k=(0 0 similar to 0.45). Magnetization vs. temperature curve of Mn3Ni20P6 shows a steep increase indicating some magnetic ordering below 230 K and a sharp field dependent anomaly in a narrow temperature range around 30 K. (C) 2016 Elsevier Inc. All rights reserved.
Title:
Europium and manganese magnetic ordering in EuMn2Ge2
Authors:
Ryan, DH; Rejali, R; Cadogan, JM; Flacau, R; Boyer, CD Author Full Names: Ryan, D. H.; Rejali, Rasa; Cadogan, J. M.; Flacau, R.; Boyer, C. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (16):10.1088/0953-8984/28/16/166003 APR 27 2016
Abstract:
The antiferromagnetic structures of both the manganese and europium sublattices in EuMn2Ge2 have been determined using thermal neutron diffraction. T-N(Mn) = 714(5) K with the 3.35(5) mu(B) (at 285 K) Mn moments ordering according to the I4 '/m ' m ' m space group. The Eu order is incommensurate with the 6.1(2) mu(B) (at 3.6 K) Eu moments oriented parallel to the c-axis with a propagation vector of k = [0.153(2) 0 0]. Both neutron diffraction and Eu-151 Mossbauer spectroscopy reveal evidence of magnetic short-range ordering of the Eu sublattice around and above T-N(Eu) similar to 10 K. The ordering temperature of the Eu sublattice is strongly affected by the sample's thermal history and rapid quenching from the melting point may lead to a complete suppression of that ordering.
Title:
Quantum diffusion of electrons in quasiperiodic and periodic approximant lattices in the rare earth-cadmium system
Authors:
Armstrong, NMR; Mortimer, KD; Kong, T; Bud'ko, SL; Canfield, PC; Basov, DN; Timusk, T Author Full Names: Armstrong, N. M. R.; Mortimer, K. D.; Kong, T.; Bud'ko, S. L.; Canfield, P. C.; Basov, D. N.; Timusk, T.
Source:
PHILOSOPHICAL MAGAZINE, 96 (11):1122-1130; 10.1080/14786435.2016.1150612 APR 12 2016
Abstract:
Icosahedral quasicrystals are characterised by the absence of a distinct Drude peak in their low-frequency optical conductivity and the same is true of their crystalline approximants. We have measured the optical conductivity of i-GdCd [GRAPHICS] , an icosahedral quasicrystal, and two approximants, GdCd [GRAPHICS] and YCd [GRAPHICS] . We find that there is a significant difference in the optical properties of these compounds. The approximants have a zero frequency peak, characteristic of a metal, whereas the quasicrystal has a striking minimum. This is the first example where the transport properties of a quasicrystal and its approximant differ in such a fundamental way. Using a generalised Drude model introduced by Mayou, we find that our data are well described by this model. It implies that the quantum diffusion of electron wave packets through the periodic and quasiperiodic lattices is responsible for these dramatic differences: in the approximants, the transport is superdiffusive, whereas the quasicrystals show subdiffusive motion of the electrons.
Title:
Electromagnons, magnons, and phonons in Eu1-xHoxMnO3
Authors:
Chen, ZY; Schmidt, M; Wang, Z; Mayr, F; Deisenhofer, J; Mukhin, AA; Balbashov, AM; Loidl, A Author Full Names: Chen, Zhenyu; Schmidt, M.; Wang, Zhe; Mayr, F.; Deisenhofer, J.; Mukhin, A. A.; Balbashov, A. M.; Loidl, A.
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134406 APR 6 2016
Abstract:
Here we present a detailed study of the terahertz and far-infrared response of the mixed perovskite manganite system Eu1-xHoxMnO3 for holmium concentrations x = 0.1 and 0.3. We compare the magnetic excitations of the four different magnetically ordered phases (A-type antiferromagnetic, sinusoidally modulated collinear, helical phases with spin planes perpendicular to the crystallographic a and c axes). The transition between the two latter phases goes hand in hand with a switching of the ferroelectric polarization from P parallel to a to P parallel to c. Special emphasis is paid to the temperature dependence of the excitations at this transition. We find a significant change of intensity indicating that the exchange-striction mechanism may not be the only mechanism to induce dipolar weight to spin-wave excitations. We also focus on excitations within the incommensurate collinear antiferromagnetic phase and find an excitation close to 40 cm(-1). A detailed analysis of optical weight gives a further unexpected result: In the multiferroic phase with P parallel to c all the spectral weight of the electromagnons comes from the lowest-phonon mode. However, for the phase with the polarization P parallel to a additional spectral weight must be transferred from higher frequencies.
Title:
Effect of platinum substitution on the structural and magnetic properties of Ni2MnGa ferromagnetic shape memory alloy
Authors:
Singh, S; D'Souza, SW; Nayak, J; Caron, L; Suard, E; Chadov, S; Felser, C Author Full Names: Singh, Sanjay; D'Souza, S. W.; Nayak, J.; Caron, L.; Suard, E.; Chadov, S.; Felser, C.
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134102 APR 6 2016
Abstract:
Ni2MnGa exhibits ideal ferromagnetic shape memory properties, however, brittleness and a low-temperature martensite transition hinder its technological applications motivating the search for novel materials showing better mechanical properties as well as higher transition temperatures. In this work, the crystal structure, phase transitions, and the magnetic properties of quaternary Ni2-x Pt-x MnGa(0 <= x <= 1) shape memory alloys were studied experimentally by x-ray diffraction, magnetization measurements, and neutron diffraction and compared to ab initio calculations. Compositions within 0 <= x <= 0.25 exhibit the cubic austenite phase at room temperature. The x approximate to 0.3 composition exhibits a seven-layer modulated monoclinic martensite structure. Within 0.4 <= x <= 1, the system stabilizes in the nonmodulated tetragonal structure. The martensite transition has very narrow thermal hysteresis 0 <= x <= 0.3, which is a typical characteristic of a shape memory alloy. By increasing x, the temperature of the martensite transition increases, while that of the magnetic transition decreases. The x = 1 composition (NiPtMnGa) in the martensite phase undergoes a para-to-ferrimagnetic transition. The saturation magnetization exhibits a nontrivial behavior with increasing up to x approximate to 0.25, above which, it suddenly decreases. Powder neutron diffraction reveals the presence of antisite disorder, with about 17% of the original Ga sites being occupied by Mn. Computations suggest that the antisite disorder triggers an antiferromagnetic coupling between two Mn atoms in different crystallographic positions, resulting into a sudden drop of the saturation magnetization for higher x.
Title:
Comparative study of the field-induced and spontaneous AF2 ' multiferroic phases in MnWO4 and Mn0.90Co0.10WO4 within the magnetic symmetry framework
Authors:
Urcelay-Olabarria, I; Garcia-Munoz, JL; Ressouche, E; Mukhin, AA; Skumryev, V Author Full Names: Urcelay-Olabarria, Irene; Luis Garcia-Munoz, Jose; Ressouche, Eric; Mukhin, Alexander A.; Skumryev, Vassil
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 520-527; 10.1107/S1600576716000881 2 APR 2016
Abstract:
(Mn,Co)WO4 compounds are regarded as reference spin-induced multiferroics. A comparative study is presented here, within the magnetic symmetry framework, of the incommensurate magnetic orders responsible for the ferroelectric phases of (i) MnWO4 under a magnetic field (H vertical bar vertical bar b) and (ii) Mn0.90Co0.10WO4 in the absence of an external field. On the one hand, although these two ferroelectric phases are stabilized under different external physical conditions, both present the same Xc1'(alpha 0 gamma)ss magnetic symmetry and practically the same modulation vector. The magnetic ordering in both phases is an elliptical helix with the magnetic moments (as the polarization vector, P) perpendicular to the b axis, although in most of the ferroelectric compositions of the (Mn,Co)WO4 family the spins rotate in planes containing b (and have P vertical bar vertical bar b). On the other hand, the anisotropy of the resulting magnetic modulations is extraordinarily different in the two phases. This is described and explained in the light of the different anisotropies of Co and Mn ions.
Title:
Structure determination of a pseudo-decagonal quasicrystal approximant by the strong-reflections approach and rotation electron diffraction
Authors:
Singh, D; Yun, YF; Wan, W; Grushko, B; Zou, XD; Hovmoller, S Author Full Names: Singh, Devinder; Yun, Yifeng; Wan, Wei; Grushko, Benjamin; Zou, Xiaodong; Hovmoller, Sven
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 433-441; 10.1107/S1600576716000042 2 APR 2016
Abstract:
The structure of a complicated pseudo-decagonal (PD) quasicrystal approximant in the Al-Co-Ni alloy system, denoted as PD1, was solved by the strong-reflections approach on three-dimensional rotation electron diffraction (RED) data, using the phases from the known PD2 structure. RED shows that the PD1 crystal is primitive and orthorhombic, with a = 37.3, b = 38.8, c = 8.2 angstrom. However, as with other approximants in the PD series, the superstructure reflections (corresponding to c = 8.2 angstrom) are much weaker than those of the main reflections (corresponding to c = 4.1 angstrom), so it was decided to solve the PD1 structure in the smaller primitive unit cell first, i.e. with unit-cell parameters a = 37.3, b = 38.8, c = 4.1 angstrom and space group Pnam. A density map of PD1 was calculated from only the 15 strongest unique reflections. It contained all 31 Co/Ni atoms and many weaker peaks corresponding to Al atoms. The structure obtained from the strong-reflections approach was confirmed by applying direct methods to the complete RED data set. Successive refinement using the RED data set resulted in 108 unique atoms (31 Co/Ni and 77 Al). This is one of the most complicated approximant structures ever solved by electron diffraction. As with other approximants in the PD series, PD1 is built of characteristic 2 nm wheel clusters with fivefold rotational symmetry, which agrees with results from high-resolution electron microscopy images. The simulated electron diffraction patterns for the structure model are in good agreement with the experimental electron diffraction patterns obtained by RED.
Title:
Jacques Friedel and the physics of metals and alloys
Authors:
Villain, J; Lavagna, M; Bruno, P Author Full Names: Villain, Jacques; Lavagna, Mireille; Bruno, Patrick
Source:
COMPTES RENDUS PHYSIQUE, 17 (3-4):276-290; 10.1016/j.crhy.2015.12.010 MAR-APR 2016
Abstract:
This is an introduction to the theoretical physics of metals for students and physicists from other specialities. Certain simple consequences of the Fermi statistics in pure metals are first addressed, namely the Peierls distortion, Kohn anomalies and the Labbe-Friedel distortion. Then the physics of dilute alloys is discussed. The analogy with nuclear collisions was a fruitful starting point, which suggested one should analyze the effects of impurities in terms of a scattering problem with the introduction of phase shifts. Starting from these concepts, Friedel derived a theory of the resistivity of alloys, and a celebrated sum rule relating the phase shifts at the Fermi level to the number of electrons in the impurity, which turned out to play a prominent role later in the context of correlated impurities, as for instance in the Kondo effect. Friedel oscillations are also an important result, related to incommensurate magnetic structures. It is shown how they can be derived in various ways: from collision theory, perturbation theory, self-consistent approximations and Green's function methods. While collision theory does not permit to take the crystal structure into account, which is responsible for electronic bands, those effects can be included in other descriptions, using for instance the tight binding approximation. (C) 2015 The Authors. Published by Elsevier Masson SAS on behalf of Academie des sciences.

Update: 22-Apr-2016

Title:
X-ray study of the anomalous thermal hystereses of the modulation wavevectors in Cs2HgCl4
Authors:
Bagautdinov, B; Shaw, Z; Orlov, A; Aliev, MA Author Full Names: Bagautdinov, Bagautdin; Shaw, Zachery; Orlov, Andrii; Aliev, Marat A.
Source:
PHASE TRANSITIONS, 89 (5):471-479; 10.1080/01411594.2015.1080258 MAY 3 2016
Abstract:
A rich sequence of structural modulations in Cs2HgCl4 as a function of temperature was studied by means of X-ray diffraction. Accurate satellite-position measurements on the cooling and heating paths of the crystal revealed abnormal thermal hystereses for incommensurate phases and coexistences of neighboring commensurate phases. A well-defined X-ray picture of the a-axis modulated phases in the range of 221-184K were observed on the heating path, while the c-axis modulated phases existing below 184K were definitely detected on the cooling path. The proper conditions for a precise phase diagram of Cs2HgCl4 can be correlated with relatively defect-free transformations of a-axis modulations at heating and of c-axis modulations at cooling. The peculiarity of Cs2HgCl4 to switch modulation direction among the a- and c-axes at 184K allows us deliberately accumulate and thus control a majority of mobile defects on the mutually perpendicular (100) or (001) planes by possessing crystal within temperature domain of a- or c-axes modulations, respectively.
Title:
Phase transformation behavior of Cu-10Ni-3Al-0.8Si alloy
Authors:
Shen, LN; Li, Z; Zhao, YY; Wang, Y; Dong, QY; Wang, MY Author Full Names: Shen, Leinuo; Li, Zhou; Zhao, Yuyuan; Wang, Yang; Dong, Qiyi; Wang, Mengying
Source:
MATERIALS CHEMISTRY AND PHYSICS, 173 421-428; 10.1016/j.matchemphys.2016.02.033 APR 15 2016
Abstract:
Microstructure evolution of solution treated Cu-10Ni-3Al-0.8Si alloy aged at different temperatures was investigated and different transformation products were observed: modulated structure resulting from spinodal decomposition, L1(2) ordering of matrix, continuous Ni3Al precipitates, continuous delta-Ni2Si precipitates and discontinuous precipitates. Modulated structure, L1(2) ordering of matrix and micro-twins formed initially at 450 degrees C, while continuous Ni3Al and delta-Ni2Si particles precipitated soon. Increasing temperature led to the formation of discontinuous precipitates, dissolution of Ni3Al and cellular decomposition. The alloy showed excellent over-aging resistance at 450 degrees C because the Ni3Al and delta-Ni2Si precipitates grew very slowly and the addition of silicon hindered the precipitation of the coarsening NiAl phase. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Interplay of charge density wave and multiband superconductivity in 2H-PdxTaSe2
Authors:
Bhoi, D; Khim, S; Nam, W; Lee, BS; Kim, C; Jeon, BG; Min, BH; Park, S; Kim, KH Author Full Names: Bhoi, D.; Khim, S.; Nam, W.; Lee, B. S.; Kim, Chanhee; Jeon, B. -G.; Min, B. H.; Park, S.; Kim, Kee Hoon
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep24068 APR 5 2016
Abstract:
2H-TaSe2 has been one of unique transition metal dichalcogenides exhibiting several phase transitions due to a delicate balance among competing electronic ground states. An unusual metallic state at high-T is sequentially followed by an incommensurate charge density wave (ICDW) state at approximate to 122 K and a commensurate charge density wave (CCDW) state at approximate to 90 K, and superconductivity at T-C similar to 0.14 K. Upon systematic intercalation of Pd ions into TaSe2, we find that CCDW order is destabilized more rapidly than ICDW to indicate a hidden quantum phase transition point at x similar to 0.09-0.10. Moreover, T-C shows a dramatic enhancement up to 3.3 K at x = 0.08, similar to 24 times of T-C in 2H-TaSe2, in proportional to the density of states N(E-F). Investigations of upper critical fields H-C2 in single crystals reveal evidences of multiband superconductivity as temperature-dependent anisotropy factor gamma(H) = H-C2(ab)/HHC2C, quasi-linear increase of H-C2(C) (T), and an upward, positive-curvature in H-C2(ab) (T) near T-C. Furthermore, analysis of temperature-dependent electronic specific heat corroborates the presence of multiple superconducting gaps. Based on above findings and electronic phase diagram vs x, we propose that the increase of N(E-F) and effective electron-phonon coupling in the vicinity of CDW quantum phase transition should be a key to the large enhancement of T-C in PdxTaSe2.
Title:
Synthesis and anisotropic properties of single crystalline Ln(2)Ru(3)Al(15+x) (Ln=Gd, Tb)
Authors:
Morrison, G; Prestigiacomo, J; Haldolaarachchige, N; Rai, BK; Young, DP; Stadler, S; Morosan, E; Chan, JY Author Full Names: Morrison, Gregory; Prestigiacomo, Joseph; Haldolaarachchige, Neel; Rai, Binod K.; Young, David P.; Stadler, Shane; Morosan, Emilia; Chan, Julia Y.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 236 186-194; SI 10.1016/j.jssc.2015.08.009 APR 2016
Abstract:
Single crystals of Ln(2)Ru(3)Al(15+x)(Ln=Gd, Tb) have been grown using the self-flux method under Ru-poor conditions. The structure of the Gd analog is found to be highly dependent on the synthesis method. Gd2Ru3Al15.08 orders antiferromagnetically at 17.5 K. Tb2Ru3Al15.05 enters an antiferromagnetic state at 16.6 K followed by a likely incommensurate-to-commensurate transition at 14.9 K for crystals oriented with HI lab. For crystals oriented with H//c, a broad maximum is observed in the temperature dependent M/H indicative of a highly anisotropic magnetic system with the hard axis in the c-direction. The magnetization as a function of field and magnetoresistance along the ab-direction of Tb2Ru3Al15.05 display a stepwise behavior and indicate strong crystalline electric field effects. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Crystal growth of incommensurate members of 2H-hexagonal perovskite related oxides: Ba4MzPt3-zO9 (M=Co, Ni, Cu, Zn, Mg, Pt)
Authors:
Ferreira, T; Morrison, G; Yeon, J; zur Loye, HC Author Full Names: Ferreira, Timothy; Morrison, Gregory; Yeon, Jeongho; zur Loye, Hans-Conrad
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 236 2-9; SI 10.1016/j.jssc.2015.10.040 APR 2016
Abstract:
Millimeter sized crystals of six oxides of approximate composition Ba4MzPt3-zO9 (M=Co, Ni, Cu, Zn, Mg, Pt) were grown from molten K2CO3 fluxes and found to crystallize in a 2H hexagonal perovskite-related structure type. The compositions of these incommensurate structures, which belong to the A(3n+3m)A'(n) B3m+nO9m+6n family of 2H hexagonal perovskite related oxides, were characterized by X-ray diffraction, energy dispersive spectroscopy, and magnetic susceptibility measurements. The specific synthetic considerations, crystal growth conditions, and magnetic susceptibility measurements are discussed. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Interplay between multiple charge-density waves and the relationship with superconductivity in PdxHoTe3
Authors:
Lou, R; Cai, YP; Liu, ZH; Qian, T; Zhao, LX; Li, Y; Liu, K; Han, ZQ; Zhang, DD; He, JB; Chen, GF; Ding, H; Wang, SC Author Full Names: Lou, Rui; Cai, Yipeng; Liu, Zhonghao; Qian, Tian; Zhao, Lingxiao; Li, Yu; Liu, Kai; Han, Zhiqing; Zhang, Dandan; He, Junbao; Chen, Genfu; Ding, Hong; Wang, Shancai
Source:
PHYSICAL REVIEW B, 93 (11):10.1103/PhysRevB.93.115133 MAR 21 2016
Abstract:
HoTe3, a member of the rare-earth tritelluride (RTe3) family, and its Pd-intercalated compounds, PdxHoTe3, where superconductivity (SC) sets in as the charge-density wave (CDW) transition is suppressed by the intercalation of a small amount of Pd, are investigated using angle-resolved photoemission spectroscopy (ARPES) and electrical resistivity. Two incommensurate CDWs with perpendicular nesting vectors are observed in HoTe3 at low temperatures. With a slight Pd intercalation (x = 0.01), the large CDW gap decreases and the small one increases. The momentum dependence of the gaps along the inner Fermi surface (FS) evolves from orthorhombicity to near tetragonality, manifesting the competition between two CDW orders. At x = 0.02, both CDW gaps decrease with the emergence of SC. Further increasing the content of Pd for x = 0.04 will completely suppress the CDW instabilities and give rise to the maximal SC order. The evolution of the electronic structures and electron-phonon couplings (EPCs) of the multiple CDWs upon Pd intercalation are carefully scrutinized. We discuss the interplay between multiple CDW orders, and the competition between CDW and SC in detail.

Update: 15-Apr-2016

Title:
Cycloid spirals and cycloid cone transition in the HoMn6-xCrxGe6 (T, x) magnetic phase diagramm by neutron diffraction
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Buschow, K. H. J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 408 233-243; 10.1016/j.jmmm.2016.02.018 JUN 15 2016
Abstract:
The structures and magnetic properties of the antiferromagnetic hexagonal pseudo ternary compounds HoMn6-xCrxGe6 (x=1, 1.5 and 2) are studied by neutron diffraction in the temperature range 1.5-300 K. The substitution of nonmagnetic Cr for Mn greatly affects the magnetic properties of HoMn6Ge6 by reducing the ordering temperature from 466 K to 278 K, 205 K and 130 K for (x=0, 1, 1.5 and 2) respectively, increasing the c/a ratio, suppressing the high temperature (HT) commensurate phase with q(2)=(0, 0, 1/2) and changing the high temperature (LT) q(1)=(0, 0, q(1z)) skew spiral rotation plane. HoMn5CrGe6 and HoMn4Cr2Ge6 display in the entire magnetically ordered regime cycloid spiral structures with the wave vector: q=(0, 0, q(z)), q(z) approximate to 0.18(3) r.l.u. and q(z) approximate to 64.8 degrees turn angle. The Ho and Mn/ Cr (001) layers have ferromagnetic arrangements coupled antiferromagnetically. The Ho moments in the z=0 layer are oriented in a direction opposite to the line bisecting the angle 2 phi(Mn) approximate to 2 x 28 degrees of the Mn layers at z = +/-similar to 0.25. This triple unit changes orientation collectively in the direction of q within the (b, c) plane containing the wave vector. Above 50 K, the wave vector length increases linearly from 0.24 to 0.28 (1) r.l.u. below T-N. The HT HoMn4.5Cr1.5Ge6 cycloid spiral, is stable in the range T-t < T < T-N (q(1)=(0,0,q(1z)), q(1z)=0.1711(3) r. I.u., Phi(s), =61.6 degrees at 40 K). At variance to the other compounds, crossing Try 36 K from above, it undergoes a first order magnetoelastic transition from a cycloid HT q(1) to a LT longitudinal cone structure: q(2)=(0, 0, q2z), q2z=0.149 r.l.u., Phi(s)=53.6 degrees and cone angle Phi(c)=47 degrees. The q(1) and q(2) phases coexist in the LT range down to 1.5 K <= T <= T-t in varying amounts with T. This transition is directly manifested by the splitting of the HT magnetic satellites and the increase of characteristic nuclear intensities. The results are summarised in a (T, x) magnetic phase diagram. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Neutron scattering studies of spin-phonon hybridization and superconducting spin gaps in the high-temperature superconductor La2-x(Sr, Ba)(x)CuO4
Authors:
Wagman, JJ; Carlo, JP; Gaudet, J; Van Gastel, G; Abernathy, DL; Stone, MB; Granroth, GE; Kolesnikov, AI; Savici, AT; Kim, YJ; Zhang, H; Ellis, D; Zhao, Y; Clark, L; Kallin, AB; Mazurek, E; Dabkowska, HA; Gaulin, BD Author Full Names: Wagman, J. J.; Carlo, J. P.; Gaudet, J.; Van Gastel, G.; Abernathy, D. L.; Stone, M. B.; Granroth, G. E.; Kolesnikov, A. I.; Savici, A. T.; Kim, Y. J.; Zhang, H.; Ellis, D.; Zhao, Y.; Clark, L.; Kallin, A. B.; Mazurek, E.; Dabkowska, H. A.; Gaulin, B. D.
Source:
PHYSICAL REVIEW B, 93 (9):10.1103/PhysRevB.93.094416 MAR 14 2016
Abstract:
We present time-of-flight neutron scattering measurements on single crystals of La2-xBaxCuO4 (LBCO) with 0 <= x <= 0.095 and La2-xSrxCuO4 (LSCO) with x = 0.08 and 0.11. This range of dopings spans much of the phase diagram relevant to high-temperature cuprate superconductivity, ranging from insulating, three-dimensional commensurate long-range antiferromagnetic order, for x <= 0.02, to two-dimensional (2D) incommensurate antiferromagnetism coexisting with superconductivity for x >= 0.05. Previous work on lightly doped LBCO with x = 0.035 showed a clear enhancement of the inelastic scattering coincident with the low-energy crossings of the highly dispersive spin excitations and quasi-2D optic phonons. The present work extends these measurements across the phase diagram and shows this enhancement to be a common feature to this family of layered quantum magnets. Furthermore, we show that the low-temperature, low-energy magnetic spectral weight is substantially larger for samples with nonsuperconducting ground states relative to any of the samples with superconducting ground states. Spin gaps, suppression of low-energy magnetic spectral weight as a function of decreasing temperature, are observed in both superconducting LBCO and LSCO samples, consistent with previous observations for superconducting LSCO.

Update: 7-Apr-2016

Title:
A Partial Isothermal Section at 1000 A degrees C of Al-Mn-Fe Phase Diagram in Vicinity of Taylor Phase and Decagonal Quasicrystal
Authors:
Priputen, P; Cernickova, I; Lejcek, P; Janickovic, D; Janovec, J Author Full Names: Priputen, P.; Cernickova, I.; Lejcek, P.; Janickovic, D.; Janovec, J.
Source:
JOURNAL OF PHASE EQUILIBRIA AND DIFFUSION, 37 (2):130-134; 10.1007/s11669-015-0432-0 APR 2016
Abstract:
Altogether 19 alloys of an Al-Mn-Fe system with compositions near to the Taylor phase and/or the decagonal quasicrystal were characterised by the x-ray diffraction and the energy-dispersive x-ray spectroscopy coupled with the scanning electron microscopy, after annealing at 1000 A degrees C for 330 h. The obtained experimental results were used to propose a partial isothermal section at 1000 A degrees C of the Al-Mn-Fe phase diagram. The ternary T-phase area of an untypical saddle shape was found to touch the Al-Mn binary one. The gamma(2)- phase was found to be stable between 2 and 30 at.% of Fe at 1000 A degrees C and boundaries between gamma(1)- and gamma(2)-areas are expected to be located very close to the Al-Mn binary.

Update: 1-Apr-2016

Title:
Evidence of multiferroicity in NdMn2O5
Authors:
Chattopadhyay, S; Baledent, V; Damay, F; Gukasov, A; Moshopoulou, E; Auban-Senzier, P; Pasquier, C; Andre, G; Porcher, F; Elkaim, E; Doubrovsky, C; Greenblatt, M; Foury-Leylekian, P Author Full Names: Chattopadhyay, S.; Baledent, V.; Damay, F.; Gukasov, A.; Moshopoulou, E.; Auban-Senzier, P.; Pasquier, C.; Andre, G.; Porcher, F.; Elkaim, E.; Doubrovsky, C.; Greenblatt, M.; Foury-Leylekian, P.
Source:
PHYSICAL REVIEW B, 93 (10):10.1103/PhysRevB.93.104406 MAR 8 2016
Abstract:
Recently, RMn2O5 (R = rare earth, Bi, Y) type multiferroics have drawn considerable attention, because of magnetically induced ferroelectricity along with an extremely large magnetoelectric coupling. Here, we present a detailed study on NdMn2O5 which is a crucial composition between the nonferroelectric PrMn2O5 and ferroelectric SmMn2O5. We report the results of heat capacity, magnetization, dielectric permittivity, and electric polarization measurements along with an accurate description of the structural and microscopic magnetic properties obtained from high resolution x-ray and neutron diffraction studies. We show that NdMn2O5 is ferroelectric, although the magnitude of polarization is much weaker than that of the other multiferroic members. The direction of the polarization is along the crystallographic b axis and its magnitude can be tuned with the application of a magnetic field. Moreover, unlike the other multiferroic members of this series, ferroelectricity in NdMn2O5 emerges in an incommensurate magnetic state. The present study also provides evidence in support of the influence of the rare-earth size on the magnetoelectric phase diagram.
Title:
Thermally and Electrochemically Driven Topotactical Transformations in Sodium Layered Oxides NaxVO2
Authors:
Didier, C; Guignard, M; Suchomel, MR; Carlier, D; Darriet, J; Delmas, C Author Full Names: Didier, Christophe; Guignard, Marie; Suchomel, Matthew R.; Carlier, Dany; Darriet, Jacques; Delmas, Claude
Source:
CHEMISTRY OF MATERIALS, 28 (5):1462-1471; 10.1021/acs.chemmater.5b04882 MAR 8 2016
Abstract:
Phase diagrams and structural transformations in the complex NaxVO2 system have been studied using electrochemical (de)intercalation and in situ and operando high resolution synchrotron powder diffraction. Starting from O'3-Na1/2VO2 obtained by sodium electrochemical deintercalation of O'3-NaVO2, the structural details of irreversible and reversible thermally driven transformations to P'3 and P3 type structures are presented. Subsequently, these P'3-NaxVO(2) phases provide a platform for operando studies exploring the NaxVO2 phase diagram as a function of sodium electrochemical (de) intercalation. In this system, three single phase domains have been found: a line phase P'3-Na1/2VO2, one solid solution for 0.53 <= x <= 0.55 characterized by an incommensurate modulated structure, and a second solid solution for 0.63 <= x <= 0.65 with a defective structure resulting from a random stack of O'3 and P'3 layers. With further sodium intercalation (x > 0.65), the structure irreversibly transforms to the starting parent phase O3-NaVO2. This work reveals new details about the diverse structural polymorphs found in sodium layered oxides used as electrode battery materials and the transitional pathways between them as a function of temperature and composition.
Title:
Tailoring Magnetic Behavior in the Tb-Au-Si Quasicrystal Approximant System
Authors:
Gebresenbut, GH; Andersson, MS; Nordblad, P; Sahlberg, M; Gomez, CP Author Full Names: Gebresenbut, Girma H.; Andersson, Mikael S.; Nordblad, Per; Sahlberg, Martin; Gomez, Cesar Pay
Source:
INORGANIC CHEMISTRY, 55 (5):2001-2008; 10.1021/acs.inorgchem.5b02286 MAR 7 2016
Abstract:
A novel synthesis method, "arc-melting-self-flux", has been developed and a series of five Tsai-type 1/1 approximant crystals in the Tb-Au-Si system have been synthesized. The synthesis method, by employing a temperature program which oscillates near the melting and nucleation points of the approximants, has provided high-quality and large single crystals in comparison to those obtained from the standard arc-melting-annealing and self-flux methods. The atomic structures of the approximants have been determined from single-crystal X-ray diffraction data and described using concentric atomic clusters with icosahedral symmetry. The compounds are nearly isostructural with subtle variations; two types of atomic clusters which mainly vary at their cluster centers are observed. One type contains a Tb site at the center, and the other contains a disordered tetrahedron decorated with Au/Si mixed sites. Both cluster types can be found coexisting in the approximants. The compounds have different average weighted ratios of central Tb to disordered tetrahedron in the bulk material. Furthermore, a strategy for chemically tuning magnetic behavior is presented. Magnetic property measurements on the approximants revealed that the magnetic transition temperature (T-c) decreases as the occupancy of the central Tb site increases. T-c decreased from 11.5 K for 0% occupancy of the central Tb to 8 K for 100% occupancy. Enhanced magneto crystalline anisotropy is observed for the approximants with higher central Tb occupancy in comparison to their low central Tb occupancy counterparts. Hence, the previously reported "ferrimagnetic-like" magnetic structure model remains valid.
Title:
Athermal and deformation-induced omega-phase transformations in biomedical beta-type alloy Ti-9Cr-0.20
Authors:
Liu, HH; Niinomi, M; Nakai, M; Cho, K Author Full Names: Liu, Huihong; Niinomi, Mitsuo; Nakai, Masaaki; Cho, Ken
Source:
ACTA MATERIALIA, 106 162-170; 10.1016/j.actamat.2016.01.008 MAR 2016
Abstract:
The alloy Ti-9Cr-0.20 has been developed as a potential material for implant rods used in spinal fixation applications, since it exhibits good mechanical properties and a remarkably "changeable Young's modulus", which is achieved by suppressing the athermal omega-phase formed upon quenching and enhancing the deformation-induced omega-phase transformation. In this study, athermal and deformation induced omega-phase transformations in Ti-9Cr-0.20 were investigated systematically by transmission electron microscopy. This was done in order to understand the nature of these omega-phase transformations, as well as the specific functionality the "changeable Young's modulus" resulting from them. In solution-treated alloy samples, in addition to ideal omega-structures, structures considered as initial omega-structures associated with incommensurate omega-phase were observed. This might be attributed to the composition heterogeneity, heterogeneity of oxygen distribution, and/or the inhomogeneous distribution of defects such as vacancies and locally strained areas. Following cold rolling, some of the selected area electron diffraction patterns of the alloy showed that the reflections of one omega-variant had increased significantly in intensity while those of the other omega-variant had decreased sharply. This vanishing of one type of variant omega-structures is attributable to two possible mechanisms: (i) a reversal mechanism, under which the particular <111> partial dislocations transform the corresponding omega-variants back into beta-phase or (ii) a re-orientation mechanism, according to which the omega-variants unfavorable with regard to the loading direction re-orient and turn into the preferred omega-variants. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
SrPt2Al2 - A(3+2)D-incommensurately modulated variant of the CaBe2Ge2 type structure
Authors:
Hoffmann, RD; Stegemann, F; Janka, O Author Full Names: Hoffmann, Rolf-Dieter; Stegemann, Frank; Janka, Oliver
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (3):127-142; 10.1515/zkri-2015-1891 MAR 2016
Abstract:
The first ternary compound in the Sr-Pt-Al system, SrPt2Al2, was synthesized by melting of the elements in a sealed niobium tube in a high frequency furnace. The structure of SrPt2Al2 was determined by single-crystal X-ray diffraction on the basis of data sets recorded at 90, 150, 210, 270 and 300 K. The compound crystallizes in an incommensurately modulated (3+2)D structure being related to the tetragonal primitive CaBe2Ge2 type structure. The structure was refined in the orthorhombic superspace group Pmmn(alpha, 0,0) 0s0(0,beta,0) s00 (alpha = 0.222(1) a*, beta = 0.224(1) b*, a = b = 436.89(5), c = 1010.16(13) pm at 90 K) with R-M = 0.0403, R-S,R-1 = 0.0597 and R-S,R-2 = 0.2046. The structural relation with CaBe2Ge2 along with a refinement in the tetragonal superspace group P4/nmm(alpha, 0,0)-0000(0,alpha,0)00s0 is discussed with respect to the temperature dependence of the q-vectors and by group-subgroup relations. The modulation, from the standpoint of the crystal chemistry, is mainly caused by the distortion of the Pt arrangements within the pseudo-tetragonal ab plane.
Title:
The modulated structure of intermediate-valent CeCoGa
Authors:
Niehaus, O; Hoffmann, RD; Chevalier, B; Pottgen, R Author Full Names: Niehaus, Oliver; Hoffmann, Rolf-Dieter; Chevalier, Bernard; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (3):143-153; 10.1515/zkri-2015-1882 MAR 2016
Abstract:
CeCoGa was synthesized by melting of the elements in an arc-melting furnace as well as in a sealed niobium tube in an induction furnace. A further annealing step improves the purity and crystallinity of the samples significantly. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Already at room temperature CeCoGa crystallizes in a superstructure of the HT-CeCoAl type. This superstructure can be described in the (3 + 1)D superspace group C2/m(alpha 0 gamma) 00; alpha = 2/3, gamma = 1/3 with a temperature independent q-vector (Z = 4). For the 300 K data (also for 90 K) the commensurate *modulated structure* could be refined with 1336 F-2 values, 56 variables and residuals of wR = 0.0348 for the main and wR = 0.0605 for the satellites of 1st order [a = 1101.7(1), b = 436.0(1) and c = 482.4(1) pm, beta = 103.2(1)degrees]. Furthermore a description in a transformed 3D supercell with the space group C2/m and Z = 12 is possible. For the 90 K data this 3D supercell was refined with 1289 F-2 values, 56 variables and a residual of wR = 0.0409 [a = 1618.8(1), b = 435.3(1) and c = 1094.1(1) pm, beta = 119.3(1)degrees]. The relation of the HT-CeCoAl type structure, the (3 + 1)D modulated and the 3D supercell structure are discussed on the basis of a group-subgroup relation. By thermal analysis and magnetic measurements the phase transition temperature to the HT-CeCoAl type structure is stated slightly above 475 K. Furthermore intermediate cerium valence was identified by the magnetic susceptibility.
Title:
The estimation of phason flips in 1D quasicrystal from the diffraction pattern
Authors:
Buganski, I; Strzalka, R; Wolny, J Author Full Names: Buganski, Ireneusz; Strzalka, Radoslaw; Wolny, Janusz
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 253 (3):450-457; 10.1002/pssb.201552426 MAR 2016
Abstract:
The statistical approach based on the average unit-cell concept and the envelop functions for the diffraction pattern were used to estimate the number of phason flips in the model 1D quasicrystal (Fibonacci chain). The characteristic function of a statistical distribution expanded to a power series with distribution moments as coefficients can be used to retrieve phases of diffraction peaks. In addition, the number of flips in the structure can be designated in two ways: with the value of the second moment's value and directly from the shape of a probability density function retrieved from the diffraction pattern. In this paper, all calculations are performed for a nondecorated Fibonacci chain. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Schottky effect in the i-Zn-Ag-Sc-Tm icosahedral quasicrystal and its 1/1 Zn-Sc-Tm approximant
Authors:
Jazbec, S; Kashimoto, S; Kozelj, P; Vrtnik, S; Jagodic, M; Jaglicic, Z; Dolinsek, J Author Full Names: Jazbec, S.; Kashimoto, S.; Kozelj, P.; Vrtnik, S.; Jagodic, M.; Jaglicic, Z.; Dolinsek, J.
Source:
PHYSICAL REVIEW B, 93 (5):10.1103/PhysRevB.93.054208 FEB 23 2016
Abstract:
The analysis of low-temperature specific heat of rare-earth (RE)-containing quasicrystals and periodic approximants and consequent interpretation of their electronic properties in the T -> 0 limit is frequently hampered by the Schottky effect, where crystalline electric fields lift the degeneracy of the RE-ion Hund's rule ground state and introduce additional contribution to the specific heat. In this paper we study the low-temperature specific heat of a thulium-containing i-Zn-Ag-Sc-Tm icosahedral quasicrystal and its 1/1 Zn-Sc-Tm approximant, both being classified as "Schottky" systems. We have derived the crystal-field Hamiltonian for pentagonal symmetry of the crystalline electric field, pertinent to the class of Tsai-type icosahedral quasicrystals and their approximants, where the RE ions are located on fivefold axes of the icosahedral atomic cluster. Using the leading term of this Hamiltonian, we have calculated analytically the Schottky specific heat in the presence of an external magnetic field and made comparison to the experimental specific heat of the investigated quasicrystal and approximant. When the low-temperature specific heat C is analyzed in a C/T versus T-2 scale (as it is customarily done for metallic specimens), the Schottky specific heat yields an upturn in the T -> 0 limit that cannot be easily distinguished from a similar upturn produced by the electron-electron interactions in exchange-enhanced systems and strongly correlated systems. Our results show that extraction of the electronic properties of RE-containing quasicrystals from their low-temperature specific heat may be uncertain in the presence of the Schottky effect.
Title:
Mechanical and tribological properties of AlCuFe quasicrystal and Al(Si)CuFe approximant thin films
Authors:
Olsson, S; Broitman, E; Garbrecht, M; Birch, J; Hultman, L; Eriksson, F Author Full Names: Olsson, Simon; Broitman, Esteban; Garbrecht, Magnus; Birch, Jens; Hultman, Lars; Eriksson, Fredrik
Source:
JOURNAL OF MATERIALS RESEARCH, 31 (2):232-240; 10.1557/jmr.2015.384 JAN 28 2016
Abstract:
Multilayered thin films of Al/Cu/Fe have been prepared by magnetron sputtering and annealed into quasicrystalline and approximant phases on Al2O3 and Si substrates, respectively. The nanomechanical and nanotribological properties, such as hardness, elastic modulus, friction, and toughness, have been measured using a triboindenter and analytical methods. The approximant phase was proved to be slightly harder than the quasicrystalline phase with a hardness of about 15.6 GPa, and with a similar elastic modulus of about 258 GPa. These values however decreased rapidly with an increasing amount of Si in the approximant. The indentation toughness of the approximant, <0.1 MPa/m(1/2), was however inferior to that of the quasicrystals with 1.5 MPa/m(1/2). Friction coefficients were measured in a range of 0.10-0.14 for both the quasicrystalline and approximant thin films.

Update: 24-Mar-2016

Title:
Design and Synthesis of a Geopolymer-Enhanced Quasi-Crystalline Composite for Resisting Wear and Corrosion
Authors:
Ozaydin, MF; Liang, H Author Full Names: Ozaydin, M. Fevzi; Liang, Hong
Source:
JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, 138 (2):10.1115/1.4031400 APR 2016
Abstract:
Multiphase composites are attractive for improved mechanical performance and corrosion resistance. In this research, a new composite consisting quasi-crystalline Al75Mn14Si7Fe4 alloy of icosahedral, cubic alpha-AlMnSiFe, monoclinic Al13Fe4 phases, and ferro-silico-aluminate geopolymer was synthesized using rapid solidification and thermal treatment methods. The concentration of icosahedral phase (i-phase) was controlled and the formation of geopolymer was obtained through heat treatment. Characterization showed that the microhardness and wear resistance were increased with the amount of i-phase. The corrosion resistance, on the other hand, was improved with the existence of the geopolymer. This research demonstrates an effective approach in processing a multi-phase composite that has desired properties and performance through multiphase design and composition.
Title:
Coexistence of Incommensurate Magnetism and Superconductivity in the Two-Dimensional Hubbard Model
Authors:
Yamase, H; Eberlein, A; Metzner, W Author Full Names: Yamase, Hiroyuki; Eberlein, Andreas; Metzner, Walter
Source:
PHYSICAL REVIEW LETTERS, 116 (9):10.1103/PhysRevLett.116.096402 MAR 4 2016
Abstract:
We analyze the competition of magnetism and superconductivity in the two-dimensional Hubbard model with a moderate interaction strength, including the possibility of incommensurate spiral magnetic order. Using an unbiased renormalization group approach, we compute magnetic and superconducting order parameters in the ground state. In addition to previously established regions of Neel order coexisting with d-wave superconductivity, the calculations reveal further coexistence regions where superconductivity is accompanied by incommensurate magnetic order.
Title:
Evolution of the charge density wave superstructure in ZrTe3 under pressure
Authors:
Hoesch, M; Garbarino, G; Battaglia, C; Aebi, P; Berger, H Author Full Names: Hoesch, Moritz; Garbarino, Gaston; Battaglia, Corsin; Aebi, Philipp; Berger, Helmuth
Source:
PHYSICAL REVIEW B, 93 (12):10.1103/PhysRevB.93.125102 MAR 1 2016
Abstract:
The material ZrTe3 is a well-known example of an incommensurate periodic lattice distortion (PLD) at low temperatures due to a charge density wave (CDW). Previous studies have found a sharp boundary as a function of pressure between CDW below 5 GPa and bulk superconductivity above this value. We present a study of low-temperature-high-pressure single crystal x-ray diffraction along with ab initio density functional theory calculations. The modulation vector q(CDW) is found to change smoothly with pressure until the PLD is lost. Fermi surface calculations reproduce these changes, but neither these nor the experimental crystal lattice structure show a particular step change at 5 GPa, thus leading to the conclusion that the CDW is lost accidentally by tipping the balance of CDW formation in the Fermi surface nesting that stabilizes it.
Title:
Incommensurate spin-density-wave antiferromagnetism in CeRu2Al2B
Authors:
Bhattacharyya, A; Khalyavin, DD; Kruger, F; Adroja, DT; Strydom, AM; Kockelmann, WA; Hillier, AD Author Full Names: Bhattacharyya, A.; Khalyavin, D. D.; Krueger, F.; Adroja, D. T.; Strydom, A. M.; Kockelmann, W. A.; Hillier, A. D.
Source:
PHYSICAL REVIEW B, 93 (6):10.1103/PhysRevB.93.060410 FEB 29 2016
Abstract:
The newly discovered Ising-type ferromagnet CeRu2Al2B exhibits an additional phase transition at T-N = 14.2 K before entering the ferromagnetic ground state at T-C = 12.8 K. We clarify the nature of this transition through high resolution neutron diffraction measurements. The data reveal the presence of a longitudinal incommensurate spin-density wave (SDW) in the temperature range of T-C < T < T-N. The propagation vector q similar to (0,0,0.148) is nearly temperature independent in this region and discontinuously locks into q = 0 at T-C. Mean-field calculations of an effective Ising model indicate that the modulated SDW phase is stabilized by a strong competition between ferromagnetic and antiferromagnetic exchange interactions. This makes CeRu2Al2B a particularly attractive model system to study the global phase diagram of ferromagnetic heavy-fermion metals under the influence of magnetic frustration.

Update: 17-Mar-2016

Title:
The modulated structures of La2-xPrxO2MnSe2 (0 <= x <= 1) and La2-xNdxO2MnSe2 (0 <= x <= 0.6)
Authors:
Peschke, S; Johrendt, D Author Full Names: Peschke, Simon; Johrendt, Dirk
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (2):89-95; 10.1515/zkri-2015-1883 FEB 2016
Abstract:
The solid solutions La2-xPrxO2MnSe2 (0 <= x <= 1) and La2-xNdxO2MnSe2 (0 <= x <= 0.6) were synthesized in a NaI/KI flux between 800 and 900 degrees C. The selenide oxides adopt a ZrCuSiAs-related structure with modulated [MnSe2](2)(-)- layers which consist of a mixture of edge- and corner-sharing MnSe4/2-tetrahedra. The crystal structures are described with a (3+1)D model in superspace group Cmme(alpha 01/2)0s0. The modulation vector q can be-controlled by partial substitution of La3+ for Pr3+ and Nd3+ via the unit cell volume leading to, amongst others, (La0.55Pr0.45)(2)O2MnSe2 with alpha = 1/6, which allows the projection onto 3D space by using a simple sixfold a axis.
Title:
M2PO3N (M = Ca, Sr): ortho-Oxonitridophosphates with beta-K2SO4 Structure Type
Authors:
Marchuk, A; Schultz, P; Hoch, C; Oeckler, O; Schnick, W Author Full Names: Marchuk, Alexey; Schultz, Peter; Hoch, Constantin; Oeckler, Oliver; Schnick, Wolfgang
Source:
INORGANIC CHEMISTRY, 55 (2):974-982; 10.1021/acs.inorgchem.5b02647 JAN 18 2016
Abstract:
Two novel oxonitridophosphates M2PO3N with M = Ca and Sr were synthesized under high-pressure high-temperature (7 GPa and 1100 degrees C) using the multianvil technique or by solid-state reaction in the silica ampules (1100 degrees C) from amorphous phosphorus oxonitride (PON) and the respective alkaline earth oxides MO (M = Ca, Sr). The products represent the first examples of alkaline earth ortho-oxonitridophosphates containing noncondensed [PO3N](4-) ions. The crystal structures were elucidated by single-crystal X-ray diffraction. Sr2PO3N [space group Pnma (No. 62), Z = 4, a = 7.1519(5) angstrom, b = 5.5778(3) angstrom, c = 9.8132(7) angstrom, R1 = 0.020, wR2 = 0.047] crystallizes in the beta-K2SO4 structure type. The structure of Ca2PO3N was solved and refined in the (3 + 1)D superspace group Pnma(a00)0ss [Z = 4, a = 6.7942(7) angstrom, b = 5.4392(6) angstrom, c = 9.4158(11) angstrom, R1 = 0.041, wR2 = 0.067]. It exhibits an incommensurate modulation along [100] with a modulation vector q = [0.287(5), 0, 0]. Rietveld refinements support the structural models as well as the phase purity of the products. Upon doping with Eu2+, Ca2PO3N exhibits luminescence in the green range (lambda(em) = 525 nm) of the visible spectrum if excited by near-UV light (lambda(exc) = 400 nm).

Update: 11-Mar-2016

Title:
Incommensurate crystal supercell and polarization flop observed in the magnetoelectric ilmenite MnTiO3
Authors:
Silverstein, HJ; Skoropata, E; Sarte, PM; Mauws, C; Aczel, AA; Choi, ES; van Lierop, J; Wiebe, CR; Zhou, HD Author Full Names: Silverstein, Harlyn J.; Skoropata, Elizabeth; Sarte, Paul M.; Mauws, Cole; Aczel, Adam A.; Choi, Eun Sang; van Lierop, Johan; Wiebe, Christopher R.; Zhou, Haidong
Source:
PHYSICAL REVIEW B, 93 (5):10.1103/PhysRevB.93.054416 FEB 19 2016
Abstract:
MnTiO3 has been studied for many decades, but it was only in the last few years that its magnetoelectric behavior had been observed. Here, we use neutron scattering on two separately grown single crystals and two powder samples to show the presence of a supercell that breaks R (3) over bar symmetry. We also present the temperature and field dependence of the dielectric constant and pyroelectric current and show evidence of nonzero off-diagonal magnetoelectric tensor elements (forbidden by R (3) over bar symmetry) followed by a polarization flop accompanying the spin flop transition at mu H-0(SF) = 6.5T. Mossbauer spectroscopy on MnTiO3 gently doped with Fe-57 was used to help shed light on the impact of the supercell on the observed behavior. Although the full supercell structure could not be solved at this time due to a lack of visible reflections, the full scope of the results presented here suggest that the role of local spin-lattice coupling in the magnetoelectric properties of MnTiO3 is likely more important than previously thought.
Title:
Magnetic ordering in pressure-induced phases with giant spin-driven ferroelectricity in multiferroic TbMnO3
Authors:
Terada, N; Khalyavin, DD; Manuel, P; Osakabe, T; Kikkawa, A; Kitazawa, H Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Osakabe, Toyotaka; Kikkawa, Akiko; Kitazawa, Hideaki
Source:
PHYSICAL REVIEW B, 93 (8):10.1103/PhysRevB.93.081104 FEB 16 2016
Abstract:
In order to clarify the mechanism associated with pressure/magnetic-field-induced giant ferroelectric polarization in TbMnO3, this work investigated changes in magnetic ordering brought about by variations in temperature, magnetic field, and pressure. This was accomplished by means of neutron diffraction analyses under high pressures and high magnetic fields, employing a single crystal. The incommensurate magnetic ordering of a cycloid structure was found to be stable below the reported critical pressure of 4.5 GPa. In contrast, a commensurate E-type spin ordering of Mn spins and a noncollinear configuration of Tb spins with k = (0, 1/2,0) appeared above 4.5 GPa. The application of a magnetic field along the a axis (H-parallel to a) under pressure induces a k = (0,0,0) antiferromagnetic structure in the case of Tb spins above H-parallel to a, enhancing the ferroelectric polarization, while the E-type ordering of Mn spins is stable even above the critical field. From the present experimental findings, we conclude that the E-type ordering of Mn spins induces giant ferroelectric polarization through an exchange striction mechanism. The H-parallel to a-induced polarization enhancement can be understood by considering that the polarization, reduced by the polar ordering of Tb moments in a zero field, can be recovered through a field-induced change to nonpolar k = (0,0,0) ordering at H-parallel to a similar to 2 T.
Title:
Alumina nanowire growth by water decomposition and the peritectic reaction of decagonal Al65Cu15Co20 quasicrystals
Authors:
Tellez-Vazquez, JO; Patino-Carachure, C; Rosas, G Author Full Names: Tellez-Vazquez, J. O.; Patino-Carachure, C.; Rosas, G.
Source:
MATERIALS CHARACTERIZATION, 112 155-159; 10.1016/j.matchar.2015.12.023 FEB 2016
Abstract:
In this paper, the results of the Al2O3 nanowires' growth through a chemical reaction between Al and water vapor at 1050 degrees C are presented. Our approach is based on two primary considerations. First, at room temperature, the Al65Cu15Co20 alloy is affected by the following mechanism: 2AI (s) + 3H(2)O (g) -> Al2O3 (s) + H-2 (g). In this reaction, the released hydrogen induces cleavage fracture of the material to form small particles. Second, the Al65Cu15Co20 quasicrystalline phase is transformed on heating to liquid + Al (Cu, Co) cubic phase through a peritectic reaction at 1050 degrees C. The Al-rich liquid then reacts with water vapor, forming Al2O3 nanowires. X-ray diffraction (XRD) analysis shows that the formed nanowires have a hexagonal structure, and infrared analysis further confirms the presence of alpha-Al2O3 phase in the final products. Transmission electron microscopy observations show that nanoparticles are present at the end of nanowires, suggesting the VLS growth mechanism. Elemental analysis by energy dispersive spectroscopy (EDS) indicates that the particles at the tip of the nanowires are mainly formed by Co and Cu alloying elements and small amounts of Al. Electron microscopy observations showed nanowires with diameters ranging from 20 to 70 nm; the average diameter was 37 nm and the nanowire lengths were up to several micrometers. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Structure and reactivity with oxygen of Pr2NiO4+delta: an in situ synchrotron X-ray powder diffraction study
Authors:
Broux, T; Prestipino, C; Bahout, M; Paofai, S; Elkaim, E; Vibhu, V; Grenier, JC; Rougier, A; Bassat, JM; Hernandez, O Author Full Names: Broux, Thibault; Prestipino, Carmelo; Bahout, Mona; Paofai, Serge; Elkaim, Erik; Vibhu, Vaibhav; Grenier, Jean-Claude; Rougier, Aline; Bassat, Jean-Marc; Hernandez, Olivier
Source:
DALTON TRANSACTIONS, 45 (7):3024-3033; 10.1039/c5dt03482e 2016
Abstract:
The promising SOFC cathode material Pr2NiO4.22 has been studied in situ under a pure oxygen atmosphere from 25 to 950 degrees C by high resolution synchrotron X-ray powder diffraction. At room temperature (RT) delta = 0.22(1), the average crystal structure turns out to be monoclinic. The subtle monoclinic distortion (gamma = 90.066(1)degrees at RT), retained up to 460 degrees C, is interpreted in terms of specific tilt schemes of the NiO6 octahedra. It is also shown that Pr2NiO4.22 is incommensurately structurally modulated already at room temperature, in the same manner as the homologous cobaltate La2CoO4.14. The phase transition to the High Temperature Tetragonal (HTT) phase was completed at 480 degrees C without any evidence for the Low Temperature Orthorhombic (LTO) phase allowing clarifying the phase diagram of this K2NiF4-type ternary oxide. Moreover, it turns out that above 800 degrees C, the HTT phase transforms reversibly into two coexisting isomorphous tetragonal phases. The incommensurate modulation subsists up to 950 degrees C, although modified concomitantly with the two abovementioned phase transformations. In addition, the role of kinetics on the decomposition process is highlighted through thermo-gravimetric analyses.

Update: 3-Mar-2016

Title:
Analysis of modulated Ho2PdSi3 crystal structure at Pd K and Ho L absorption edges using resonant elastic X-scattering
Authors:
Nentwich, M; Zschornak, M; Richter, C; Novikov, D; Meyer, DC Author Full Names: Nentwich, Melanie; Zschornak, Matthias; Richter, Carsten; Novikov, Dmitri; Meyer, Dirk C.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (6):10.1088/0953-8984/28/6/066002 FEB 17 2016
Abstract:
Replacing Si atoms with a transition metal in rare earth disilicides results in a family of intermetallic compounds with a variety of complex magnetic phase transitions. In particular, the family R2PdSi3 shows interesting magnetic behavior arising from the electronic interaction of the R element with the transition metal in the Si network, inducing the specific structure of the related phase. Within this series, the highest degree of superstructural order was reported for the investigated representative Ho2PdSi3, although several competing superstructures have been proposed in literature. The diffraction anomalous fine structure (DAFS) method is highly sensitive to the local structure of chosen atoms at specific positions within the unit cell of a crystalline phase. In combination with x-ray absorption fine structure (XAFS), this sophisticated synchrotron method has been applied in the present work to several selected reflections, i.a. a satellite reflection. Extensive electronic modeling was used to test the most relevant structure proposals. The 2 x 2 x 8 superstructure has been strongly confirmed, although a small amount of disorder in the modulation is very probable.
Title:
Effect of LiH on electrochemical hydrogen storage properties of Ti55V10Ni35 quasicrystal
Authors:
Liu, DY; Zhao, Z; Luo, TH; Xing, C; Fei, L; Lin, J; Hou, JH; Jiang, DY; Liu, WQ; Wang, LM Author Full Names: Liu, Dongyan; Zhao, Zhen; Luo, Tianhao; Xing, Cheng; Fei, Liang; Lin, Jing; Hou, Jianhua; Jiang, Dayong; Liu, Wanqiang; Wang, Limin
Source:
SOLID STATE SCIENCES, 52 19-22; 10.1016/j.solidstatesciences.2015.12.002 FEB 2016
Abstract:
The electrochemical hydrogen storage properties and mechanisms of the Ti55V10Ni35 quasicrystal + xLiH(x = 3, 6 and 9 wt.%) system are investigated and discussed in this paper. A composite material in the Ti55V10Ni35 quasicrystal and system has been synthesized moderately by means of mechanical milling under an argon atmosphere, which can avoid reaction of releasing of hydrogen during the process of milling. The results indicate that the addition of LiH significantly improves the electrochemical characteristics of composite material. The maximum discharge capacity increases from 220.1 mAh/g to 292.3 mAh/g on Ti55V10Ni35 + 6 wt.% LiH, and the cycling stability is also enhanced too. In addition, the high rate dischargeability (HRD) is ameliorated remarkably, and the value of HRD value at 240 mA/g rises by 78.1%-87.8% for Ti55V10Ni35 + 6 wt.% LiH alloy electrodes. The improvement of characteristics of the electrochemical hydrogen storage characteristics may be attributed to LiH, which has excellent electrochemical activity. (C) 2015 Elsevier Masson SAS. All rights reserved.
Title:
Synthesis, structure, and magnetic characterization of Cr4US8
Authors:
Ward, MD; Chan, IY; Malliakas, CD; Lee, M; Choi, ES; Ibers, JA Author Full Names: Ward, Matthew D.; Chan, Ian Y.; Malliakas, Christos D.; Lee, Minseong; Choi, Eun Sang; Ibers, James A.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 233 67-74; 10.1016/j.jssc.2015.10.009 JAN 2016
Abstract:
The compound Cr4US8 has been synthesized at 1073 K and its crystal structure has been determined at 100 K. The structure is modulated with a two-fold commensurate supercell. The subcell may be indexed in an orthorhombic cell but weak supercell reflections lead to the monoclinic superspace group P2(1)/c (0 alpha gamma)0s with two Cr sites, one U site, and four S sites. The structure comprises a three-dimensional framework of CrS6 octahedra with channels that are partially occupied by U atoms. Each U atom in these channels is coordinated by eight S atoms in a bicapped trigonal-prismatic arrangement. The magnetic behavior of Cr4US8 is complex. At temperatures above similar to 120 K at all measured fields, there is little difference between field-cooled and zero field-cooled data and chi(T) decreases monotonously with temperature, which is reminiscent of the Curie-Weiss law. At lower temperatures, the temperature dependence of chi(T) is complex and strongly dependent on the magnetic field strength. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Electronic transport in polycrystalline samples of icosahedral phases
Authors:
Vekilov, YK; Chernikov, MA; Dolinichek, Y Author Full Names: Vekilov, Yu. Kh.; Chernikov, M. A.; Dolinichek, Ya.
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 117 (1):16-21; 10.1134/S0031918X15110113 JAN 2016
Abstract:
The low-temperature electronic transport in polycrystals of quasicrystalline phases with an icosahedral structure has been analyzed within the model of the granular electronic system. In this model, the grains (drops) of a metallic icosahedral phase are surrounded by extended defects and grain boundaries, which create an insulating environment. The electron transport in this model is determined by the size quantization of electronic states inside metallic grains, by intergranular tunneling, and by electrostatic barriers. Depending on the temperature and structural state of the system, the hopping conductivity with variable lengths of jumps in the Efros-Shklovskii or Mott regime is observed with predominantly elastic cotunneling. In the case of strong intergranular coupling, the system passes into the metallic regime with the exponential temperature dependence of the electrical conductivity.

Update: 25-Feb-2016

Title:
From an electron micrograph to a postage stamp
Authors:
Hargittai, I Author Full Names: Hargittai, Istvan
Source:
STRUCTURAL CHEMISTRY, 27 (1):5-7; SI 10.1007/s11224-015-0629-1 FEB 2016
Abstract:
Soon following Dan Shechtman's discovery of quasicrystals, Agnes Csanady and her associates started producing beautiful quasicrystals of flowerlike morphology. The image of one of their specimen appeared on the Israeli postage stamp honoring Shechtman's discovery, his Nobel Prize, and the International Year of Crystallography.
Title:
Ultrafast resonant soft x-ray diffraction dynamics of the charge density wave in TbTe3
Authors:
Moore, RG; Lee, WS; Kirchman, PS; Chuang, YD; Kemper, AF; Trigo, M; Patthey, L; Lu, DH; Krupin, O; Yi, M; Reis, DA; Doering, D; Denes, P; Schlotter, WF; Turner, JJ; Hays, G; Hering, P; Benson, T; Chu, JH; Devereaux, TP; Fisher, IR; Hussain, Z; Shen, ZX Author Full Names: Moore, R. G.; Lee, W. S.; Kirchman, P. S.; Chuang, Y. D.; Kemper, A. F.; Trigo, M.; Patthey, L.; Lu, D. H.; Krupin, O.; Yi, M.; Reis, D. A.; Doering, D.; Denes, P.; Schlotter, W. F.; Turner, J. J.; Hays, G.; Hering, P.; Benson, T.; Chu, J. -H.; Devereaux, T. P.; Fisher, I. R.; Hussain, Z.; Shen, Z. -X.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.024304 JAN 25 2016
Abstract:
Understanding the emergence of collective behavior in correlated electron systems remains at the forefront of modern condensed matter physics. Disentangling the degrees of freedom responsible for collective behavior can lead to insights into the microscopic origins of emergent properties and phase transitions. Utilizing an optical pump, resonant soft x-ray diffraction probe we are able to track, in real time, the dynamics of the charge density wave (CDW) in TbTe3, a model system that violates traditional views of a Fermi surface nested CDW. We observe coherent oscillations corresponding to the CDW amplitude mode at 2.4 THz and a coherent optical phonon mode at similar to 1.7 THz. We show how such observations reveal the anisotropic energy optimization between in-plane Te charge density modulations and the three-dimensional lattice coupling.
Title:
Ti-V-Ni with graphene-mixing icosahedral quasicrystalline composites: Preparation, structure and its application in Ni-MH rechargeable batteries
Authors:
Lin, J; Lu, C; Sun, LS; Liang, F; Cao, ZY; Wang, LM Author Full Names: Lin, Jing; Lu, Chong; Sun, Lianshan; Liang, Fei; Cao, Zhanyi; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 41 (2):1098-1103; 10.1016/j.ijhydene.2015.11.067 JAN 12 2016
Abstract:
The Ti-V-Niquasicrystalline was prepared by arc-melting and subsequent melt-spinning technique, and the Ti1.4V0.6Ni + x graphene (x = 3, 5, 7, 10 and 13, wt%) composites were obtained by mechanical ball-milling method. The structures and electrochemical hydrogen storage properties of the composites were investigated. The results showed that, the structures of the composites contained icosahedral quasicrystal, Ti2Ni-type, NiTi and graphene phases. The electrochemical hydrogen storage properties of the composites were improved with graphene addition. The cycling stabilities after 50 charging/discharging cycles of Ti1.4V0.6Ni + x graphene composites were improved obviously, especially the Ti1.4V0.6Ni + 10 graphene composite showed the best cycling stability of 70.3%, increased by 6.5%, compared with the Ti1.4V0.6Ni electrode. The high-rate discharge abilities of the composites were also increased appreciably. The improvement in the hydrogen storage characteristics should own to the proper graphene addition and that could cause copacetic electrocatalytic activity and anti-corrosion ability. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Orientation Relations and Conversion Matrix Between M3 Supercell and Pseudohexagonal Subcell in Tricalcium Silicate Solid Solution
Authors:
Min, HH; Xu, F; Lu, YN; Yang, J; Ding, LF; Su, F; Zhu, JM Author Full Names: Min Hui-Hua; Xu Feng; Lu Yi-Nong; Yang Jing; Ding Lin-Fei; Su Fan; Zhu Jian-Min
Source:
CHINESE JOURNAL OF INORGANIC CHEMISTRY, 32 (1):145-152; JAN 10 2016
Abstract:
A M3 modification of tricalcium silicate (C3S) solid solution was investigated using transmission electron microscope (TEM). Selected area electron diffraction (SAED) patterns and high resolution transmission electron microscopy (HRTEM) images were analyzed based on a pseudohexagonal subcell (Space group R3m; a=0.705 9 nm, b=0.705 5 nm, c=2.492 4 nm, alpha=89.79 degrees,beta=90.04 degrees, gamma=120.14 degrees). Reflections caused by the superstructure were proven to occur along the modulation wave vector [(1) over bar .17](H)(*) with one-dimensional type and could be expressed as ha+kb+lc*+m/[6(-a+b+7C*)], where m=+/- 1,+/- 2 and +/- 3. SAED patterns and HRTEM images based on the M3 supercell (Space group Cm; a=3.310 8 nm, b=0.703 6 nm, c=1.852 1 nm, beta=94.137 degrees) were simulated and finally the orientation relations between M3 supercell and pseudohexagonal subcell were established as follows: (600)(M3), (020)(M3) and (006)(M3) were equivalent to ((1) over bar1 (2) over bar)(H), ((1) over bar(1) over bar0)(H) and ((1) over bar 17)(H)* respectively, and [100](M3)//[(7) over bar7 (2) over bar](H), [010](M3)// [(1) over bar(1) over bar0](H), and [001](M3)//[(1) over bar 11](H): Furthermore, the conversion matrix between M3 supercell and pseudohexagonal subcell was established.
Title:
Soft spherical nanostructures with a dodecagonal quasicrystal-like order
Authors:
Rochal, SB; Konevtsova, OV; Shevchenko, IA; Lorman, VL Author Full Names: Rochal, S. B.; Konevtsova, O. V.; Shevchenko, I. A.; Lorman, V. L.
Source:
SOFT MATTER, 12 (4):1238-1247; 10.1039/c5sm02265g 2016
Abstract:
We develop a theory which predicts curvature-related structural peculiarities of soft spherical nanostructures with a dodecagonal local arrangement of subunits. Spherical templates coated with a thin film of a soft quasicrystal (QC)-forming material constitute the most promising direction to realize these nanostructures. Disordered and perfect spherical nanostructures are simulated using two approaches. The first of them models a random QC-like spherical nanostructure with extended curvature-induced topological defects similar to scars in colloidal spherical crystals. The second approach is inspired by the physics of viral capsids. It deals with the most regular spherical nanostructures with a local QC-like order derived from three well-known planar dodecagonal tilings. We explain how the additional QC-like degrees of freedom assist the nanostructure stabilization and determine the point defect number and location without extended scar formation. Unusual for nanoassemblies snub cube geometry is shown to be the most energetically favorable global organization of these spherical QC nanostructures.
Title:
Thermal conductivity of solid thiophene in an incommensurate orientational state
Authors:
Korolyuk, OA; Krivchikov, AI; Vdovichenko, GA; Romantsova, OO; Horbatenko, YV Author Full Names: Korolyuk, O. A.; Krivchikov, A. I.; Vdovichenko, G. A.; Romantsova, O. O.; Horbatenko, Yu. V.
Source:
LOW TEMPERATURE PHYSICS, 42 (1):68-73; 10.1063/1.4940993 JAN 2016
Abstract:
The thermal conductivity of solid thiophene at equilibrium vapor pressure between 2K < T < 170K, has been measured in a sequence of incommensurate metastable orientationally disordered phases II, II1, II2, and II2g with different degrees of orientational ordering of the molecules. It is found that in phase states II, II1 and II2 with dynamic orientational disorder of the molecules, the thermal conductivity does not depend on the temperature. It is shown that the temperature dependence of the thermal conductivity kappa(T) of orientational glass V-g and II2g (incommensurate) does not have any of the anomalies that are typical for amorphous materials and glasses. The temperature dependence kappa(T) of the incommensurate state of orientational glass II2g is bell-shaped, which is typical for the thermal conductivity of crystals with long-range orientational order. In the II2g state, as temperature drops from T-g to almost 10K, the thermal conductivity increases according to kappa(T) = A/T + B, where the first term describes the input of the propagating phonons, wherein the average length of their mean free path is greater than half of the phonon wavelength. The B term is associated with the input of localized short-wave, or "diffuse" vibrational modes. At low temperatures T <= 7K, kappa(T) proportional to T-3 is observed with increasing temperatures, which corresponds to the boundary scattering of phonons. (C) 2016 AIP Publishing LLC.
Title:
Synthesis of quasi-crystalline phases in the Al-Cu-Fe-Cr system
Authors:
Chugunov, DB; Meshkov, LL; Kalmykov, KB; Osipov, AK Author Full Names: Chugunov, D. B.; Meshkov, L. L.; Kalmykov, K. B.; Osipov, A. K.
Source:
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY, 61 (1):11-17; 10.1134/S003602361601006X JAN 2016
Abstract:
Phase equilibria in the Al-Cu-Fe system alloyed with 5% Cr were studied. Based on the data of X-ray powder diffraction analysis, electron microscopy, and differential thermal analysis, the effect of temperature on i a double dagger" d phase transitions in alloys Al65Cu25Fe5Cr5 and Al70Cu20Fe5Cr5. In the Al-Cu-Fe-Cr system, multiphase structures were detected; these structures are mixtures of quasi-crystalline and approximant phases, the contents and morphologies of which depend on the composition of the initial mixture and the crystallization rate.
Title:
STRUCTURE AND MECHANICAL PROPERTIES OF QUASICRYSTALLINE AND APPROXIMANT PHASES OBTAINED FROM TITANIUM-BASED QUINARY ALLOY
Authors:
Firstov, SA; Gorban', VF; Karpets, MV; Krapivka, NA; Danilenko, NI; Pechkovskii, EP; Rokitskaya, EA Author Full Names: Firstov, S. A.; Gorban', V. F.; Karpets, M. V.; Krapivka, N. A.; Danilenko, N. I.; Pechkovskii, E. P.; Rokitskaya, E. A.
Source:
STRENGTH OF MATERIALS, 47 (6):781-788; 10.1007/s11223-015-9714-3 NOV 2015
Abstract:
The paper presents the investigation of influence of cooling rate and conditions of melt crystallization on the change in phase composition and physical and mechanical properties of alloy Ti60Cr30Al3Si2(SiO2)(5). The influence of thermal treatment on the stability and properties of quasicrystalline and approximant phases is studied. Using the method of high-temperature indentation it is found that the diffusive mechanism of plastic strain of the alloy is strongly observed at 800 degrees C (0.68T(m)).

Update: 18-Feb-2016

Title:
Structural and electrocaloric properties of multiferroic-BiFeO3 doped 0.94Bi(0.5)Na(0.5)TiO(3)-0.06BaTiO(3) solid solutions
Authors:
Zheng, GP; Uddin, S; Zheng, XC; Yang, JH Author Full Names: Zheng, Guang-Ping; Uddin, Sarir; Zheng, Xiucheng; Yang, Junhe
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 663 249-255; 10.1016/j.jallcom.2015.12.056 APR 5 2016
Abstract:
Single-phase (1-x)(0.94Bi(0.5)Na(0.5)TiO(3)-0.06BaTiO(3))-xBiFeO(3) (BNT-BT-xBF, x = 0.05, 0.1 and 0.15) solid solutions are fabricated using a modified citrate method. The structural, ferroelectric and electrocaloric properties are significantly affected by the multiferroic BiFe03 doping, which is found to favor the antiferroelectric (AFE) state of the solid solutions. The dynamic mechanical analysis suggests that the BiFeO3 induced ordering of oxygen octahedrons plays a dominant role in the formation of AFE incommensurate phases and leads to the enhanced negative electrocaloric effect (ECE). A maximum ECE temperature change of 1.65 degrees C under an applied field of 70 kV/cm is observed. It is suggested that the magnetoelectric coupling is effective in enhancing the negative ECE in BNT-BT-xBF. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Indirect assessment of the surface energy of the Al-Cu-Fe quasicrystal
Authors:
de Lima, DCG; Dos Passos, TA; de Weerd, MC; Kenzari, S; Medeiros, RG; de Lima, SJG; Dubois, JM Author Full Names: Guedes de Lima, Danielle Cavalcante; Dos Passos, Tiberio Andrade; de Weerd, Marie-Cecile; Kenzari, Samuel; Medeiros, Rodinei Gomes; Guedes de Lima, Severino Jackson; Dubois, Jean-Marie
Source:
JOURNAL OF MATERIALS SCIENCE, 51 (8):4070-4078; 10.1007/s10853-016-9728-7 APR 2016
Abstract:
This work summarizes an attempt to estimate the surface energy of the stable, icosahedral Al-Cu-Fe quasicrystal (i-ACF hereafter). To this end, samples of i-ACF were prepared by sintering a powder produced by ball milling and heat treating a master ingot of composition Al59Cu25.5Fe12.5B3 (at.%), icosahedral lattice structure, and containing negligibly small amounts of contaminating crystalline phases. This powder was then sintered in the shape of a cylinder appropriate for pin-on-disk tests in ambient air. Variable amounts of either Sn or Bi were added to the powder prior to sintering. These elements do not dissolve in the quasicrystal and form small pockets of pure Sn or Bi that are either isolated or percolating, depending on the added volume of metal. Analysis of pin-on-disk data deduced from tests performed at room temperature allows us to conclude that the surface energy of the quasicrystal itself falls between the respective surface energies of the pure metals: gamma(Bi) a parts per thousand currency sign gamma(QC) a parts per thousand currency sign gamma(Sn) or 0.5 a parts per thousand currency sign gamma(i-ACF) a parts per thousand currency sign 0.8 J/m(2).
Title:
Flexoelectricity, incommensurate phases and the Lifshitz point
Authors:
Pottker, H; Salje, EKH Author Full Names: Poettker, Henning; Salje, Ekhard K. H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (7):10.1088/0953-8984/28/7/075902 FEB 24 2016
Abstract:
The solutions for the minimizers of the energy density f(q, p) = Aq(2) + Bq(4) + p(2) + g(A,B) + beta(q'p-p'q) + vertical bar q'vertical bar(2) + k vertical bar p'vertical bar(2) describe the flexoelectric effect with a flexoelectric coupling coefficient beta. The order parameters q and p can be visualized as strain and polarisation, respectively. The parameter k denotes the ratio of intrinsic length scales for q and p. We show that the structural ground-states include 3 phases, namely the paraelastic state q = p = 0, the ferroelastic state where polarization exists inside and near twin boundaries, and the incommensurate (modulated) phases with a very rich array of structural modulations ranging from nearly pure sine waves to kink arrays and ripple states. The phases coincide in the multicritical Lifshitz point. Linear flexoelectricity p similar to q' is encountered only approximately inside the ferroelastic phase and near the phase boundary between the paraelastic phase and the incommensurate phase. The relationship between the polarisation and the strain gradient is highly non-linear in all other states. The spatial profiles and energy distributions are discussed in detail.
Title:
Muon-spin relaxation study of the double perovskite insulators Sr2BOsO6 (B = Fe, Y, In)
Authors:
Williams, RC; Xiao, F; Thomas, IO; Clark, SJ; Lancaster, T; Cornish, GA; Blundell, SJ; Hayes, W; Paul, AK; Felser, C; Jansen, M Author Full Names: Williams, R. C.; Xiao, F.; Thomas, I. O.; Clark, S. J.; Lancaster, T.; Cornish, G. A.; Blundell, S. J.; Hayes, W.; Paul, A. K.; Felser, C.; Jansen, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (7):10.1088/0953-8984/28/7/076001 FEB 24 2016
Abstract:
We present the results of zero-field muon-spin relaxation measurements made on the double perovskite insulators Sr2BOsO6 (B = Fe, Y, In). Spontaneous muon-spin precession indicative of quasistatic long range magnetic ordering is observed in Sr2FeOsO6 within the AF1 antiferromagnetic phase for temperatures below T-N = 135 +/- 2 K. Upon cooling below T-2 approximate to 67 K the oscillations cease to be resolvable owing to the coexistence of the AF1 and AF2 phases, which leads to a broader range of internal magnetic fields. Using density functional calculations we identify a candidate muon stopping site within the unit cell, which dipole field simulations show to be consistent with the proposed magnetic structure. The possibility of incommensurate magnetic ordering is discussed for temperatures below T-N = 53 K and 25 K for Sr2YOsO6 and Sr2InOsO6, respectively.
Title:
B-cation effect on relaxor behavior and electric properties in Sr2NaNb5-xSbxO15 tungsten bronze ceramics
Authors:
Fan, JY; Yang, B; Wei, LL; Wang, ZM Author Full Names: Fan, Jianyong; Yang, Bian; Wei, Lingling; Wang, Zhongming
Source:
CERAMICS INTERNATIONAL, 42 (3):4054-4062; 10.1016/j.ceramint.2015.11.077 FEB 15 2016
Abstract:
Sr2NaNb5-xSbxO15 ceramics (SNNS, x=0.0, 0.3, 0.5, 1.0) with 'filled' tungsten bronze structure were prepared by the conventional solid-state reaction method. Effects of introducing Sb concentration in B-sites on the microstructure, dielectric and ferroelectric properties were investigated in detail. With increasing of Sb concentration, the crystal structure of SNNS ceramics distorted slightly from the TB orthorhombic Ccm2 phase to tetragonal P4bm phase, and then to paraelectric P4/mbm phase at room temperature. The smaller ionic radius of Sb5+ (0.60 angstrom) compared with that of Nb5+ (0.64 angstrom) contributed to the shrinkage of crystal structure. It was found that accompanying with the introduction of Sb, some unique dielectric and ferroelectric behavior emerged for SNNS ceramics. Only the samples with x < 0.5 showed additional dielectric anomaly in low temperature range, which was attributed to the incommensurate superstructure ICS-associated dielectric dispersion process caused by local structural fluctuation. With increasing of Sb concentration, T-c shifted to lower temperatures, and the diffuse phase transition and relaxor behavior appeared to be exceptionally induced around T-c at higher Sb concentration. The underlying mechanisms of relaxor behavior induced by different Sb concentration in B-sites for SNNS ceramics were clarified in detail. Moreover, the ferroelectric properties deteriorated and even disappeared at higher Sb concentration, because the ceramics showed P4/mbm phase structure as a result of decreasing of T-c to lower than room temperature. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Title:
Glass-like Lattice Thermal Conductivity and Thermoelectric Properties of Incommensurate Chimney-Ladder Compound FeGe gamma
Authors:
Sato, N; Ouchi, H; Takagiwa, Y; Kimura, K Author Full Names: Sato, Naoki; Ouchi, Hideyasu; Takagiwa, Yoshiki; Kimura, Kaoru
Source:
CHEMISTRY OF MATERIALS, 28 (2):529-533; 10.1021/acs.chemmater.5b03952 JAN 26 2016
Abstract:
We have characterized the thermoelectric properties of FeGe gamma which is one of the promising Nowotny chimney-ladder compounds. A glass-like low lattice thermal conductivity below 1.0 W m(-1) K-1 is observed around 373 K because of its complex structural nature, i.e., incommensurate structure. A first-principles band structure calculation implies that a narrow band gap of similar to 0.2 eV is formed near the Fermi level for a hypothetical composition of Fe2Ge3 with a Ru2Sn3-type structure, leading to a large power factor of 1.90 mW m(-1) K-2 near 600 K. The maximum dimensionless figure-of-merit of 0.57 is attractive as a starting point; calculation using the Boltzmann transport equation under a constant relaxation time approximation predicts that a further enhancement of ZT exceeding unity at 600-700 K can be achieved by optimizing the valence electron count per transition metal and further reduction of the lattice thermal conductivity.
Title:
Modulated structures and associated microstructures in the ferroelectric phase of Ba1-xSrxAl2O4 for 0.7 <= x <= 1.0
Authors:
Tsukasaki, H; Ishii, Y; Tanaka, E; Kurushima, K; Mori, S Author Full Names: Tsukasaki, Hirofumi; Ishii, Yui; Tanaka, Eri; Kurushima, Kosuke; Mori, Shigeo
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS, 55 (1):10.7567/JJAP.55.011502 JAN 2016
Abstract:
In order to understand the ferroelectric and ferroelastic phases in Ba1-xSrxAl2O4 for 0.7 <= x <= 1.0, we have investigated the crystal structures and their associated microstructures of the ferroelectric and ferroelastic phases mainly by transmission electron microscopy (TEM) and scanning transmission electron microscopy-high-angle angular dark-field (STEM-HAADF) experiments, combined with powder X-ray diffraction experiments. Electron diffraction experiments showed that the ferroelectric and ferroelastic phases of Ba1-xSrxAl2O4 for 0.7 <= x <= 1.0 should be characterized as a modulated structure with the modulation vector of q = 0, 1/2, 0, whose space group should be monoclinic P2(1). High-resolution TEM experiments revealed that the microstructures in the monoclinic phase can be characterized as twin structures and nanometer-sized planar defects due to the monoclinic structure with the modulated structures, which are responsible for anomalous elastic behaviors and mechanoelectro-optical properties. In addition, subatomic-resolution STEM-HAADF images clearly indicated that the displacement of Al3+ ions involved in the AlO4 tetrahedra should play a crucial role in the formation of the modulated structures and twin structures. (C) 2016 The Japan Society of Applied Physics
Title:
Influence of high energy milling on the microstructure and magnetic properties of the AlCu-Fe phases: the case of the i-Al64Cu23Fe13 quasicrystalline and the omega-Al70Cu20Fe10 crystalline phases
Authors:
Quispe, MP; Landauro, CV; Vergara, MZP; Quispe-Marcatoma, J; Rojas-Ayala, C; Pena-Rodriguez, VA; Baggio-Saitovitch, E Author Full Names: Pillaca Quispe, Mirtha; Landauro, Carlos V.; Pinto Vergara, Milida Z.; Quispe-Marcatoma, Justiniano; Rojas-Ayala, Chachi; Pena-Rodriguez, Victor A.; Baggio-Saitovitch, Elisa
Source:
RSC ADVANCES, 6 (7):5367-5376; 10.1039/c5ra21093c 2016
Abstract:
The effect of mechanical milling in i-Al64Cu23Fe13 quasicrystalline and omega-Al70Cu20Fe10 crystalline phases is systematically investigated in the present work. The Al-Cu-Fe samples were obtained by arc furnace technique and then nanostructured by means of mechanical milling. The results indicate that the solid samples present a weak ferromagnetic behavior at 300 K, showing a saturation magnetization of 0.124 emu g(-1) for the icosahedral phase (i-phase) and 0.449 emu g(-1) for the tetragonal phase (omega phase). These small values could be an indication that only a few percentage of Fe atoms carry magnetic moment. The magnetic response in the nanostructured u-phase increases up to 3.5 times higher than its corresponding solid counterpart. Whereas for the i-phase this increment is about 16 times higher. Moreover, the speed of the variation of the studied physical parameters after reducing the average grain size has been obtained from the exponent (alpha) of a power law fit of the experimental data. The values of a, corresponding to the magnetic response, are slightly different in each phase, which should be related to the different chemical composition and/or the type of long range order. Additionally, we also search for a critical grain size. However, this critical value has not been observed in the studied samples.

Update: 10-Feb-2016

Title:
Magnetic structures in TmPdIn and TmAgSn
Authors:
Baran, S; Szytula, A; Kaczorowski, D; Damay, F Author Full Names: Baran, S.; Szytula, A.; Kaczorowski, D.; Damay, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 662 11-15; 10.1016/j.jallcom.2015.11.200 MAR 25 2016
Abstract:
Low temperature antiferromagnetic structures of TmPdIn and TmAgSn have been derived from powder neutron diffraction data. The magnetic structure of TmPdIn is a commensurate one and related to a propagation vector (k) over right arrow = [1/3, 1/3, 1/2] while the incommensurate sine-modulated structure of TmAgSn is connected with (k) over right arrow = [k(x), -k(x), 0] where k(x) = 0.1314(2). The thulium magnetic moments are constrained within the basal plane and show 'triangular' arrangement. Validity of obtained magnetic structures is discussed on the basis of symmetry analysis. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Mossbauer spectroscopy, magnetic, and ab-initio study of the approximant Al76Ni9Fe15 to a decagonal Al-Ni-Fe quasicrystal
Authors:
Nejadsattari, F; Stadnik, ZM; Przewoznik, J; Grushko, B Author Full Names: Nejadsattari, Farshad; Stadnik, Zbigniew M.; Przewoznik, Janusz; Grushko, Benjamin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 662 612-620; 10.1016/j.jallcom.2015.12.115 MAR 25 2016
Abstract:
The structural, magnetic, and Mossbauer spectral properties of the approximant Al76Ni9Fe15 to a decagonal Al-Ni-Fe quasicrystal, complemented by ab-initio electronic structure and the hyperfine-interaction parameters calculations, are reported. The approximant studied crystallizes in the monoclinic space group C2/m with the lattice parameters a = 15.3898(3) angstrom, b = 8.0840(2) angstrom, c = 12.4169(2) angstrom, and beta = 107.870(2)degrees. The existence of a pseudogap in the calculated electronic density of states slightly above the Fermi level suggests electronic stabilization according to the Hume-Rothery-type mechanism. High metallicity of Al76Ni9Fe15 is predicted. Both the Mossbauer spectra and magnetic susceptibility data indicate that Al76Ni9Fe15 is a paramagnet down to 2.0 K. The presence of the distribution of the electric quadrupole splitting in the Mossbauer spectra measured in the temperature range 4.5-296.1 K is observed. The increase of the average quadrupole splitting with decreasing temperature is well described by a T-3/2 power-law relation. The Debye temperature of Al76Ni9Fe15 is found to be 431(3) K. (C) 2015 Elsevier B.V. All rights reserved.
Title:
The Use and Abuse of Transcranial Magnetic Stimulation to Modulate Corticospinal Excitability in Humans (vol 10, e0144151, 2015)
Authors:
Heroux, ME; Taylor, JL; Gandevia, SC Author Full Names: Heroux, Martin E.; Taylor, Janet L.; Gandevia, Simon C.
Source:
PLOS ONE, 11 (1):10.1371/journal.pone.0147890 JAN 21 2016
Title:
Composition-driven spin glass to ferromagnetic transition in the quasicrystal approximant Au-Al-Gd
Authors:
Ishikawa, A; Hiroto, T; Tokiwa, K; Fujii, T; Tamura, R Author Full Names: Ishikawa, A.; Hiroto, T.; Tokiwa, K.; Fujii, T.; Tamura, R.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.024416 JAN 21 2016
Abstract:
We investigated the composition dependence of the magnetic susceptibility of the quasicrystal approximant Au-Al-Gd. A composition-driven ferromagnetic transition is observed in a quasicrystal approximant, which is attributed to the Ruderman-Kittel-Kasuya-Yosida (RKKY) oscillation via a variation in the Fermi wave vector. The ferromagnetic transition is most simply understood as a result of the close matching of the nearest and second-nearest spin distances with the maximum positions of the RKKY potential. The present work provides an idea that allows us to tailor the magnetic order via the electron concentration in quasicrystal approximants as well as in quasicrystals.
Title:
Complex phase diagram of Ba1-xNaxFe2As2: A multitude of phases striving for the electronic entropy
Authors:
Wang, L; Hardy, F; Bohmer, AE; Wolf, T; Schweiss, P; Meingast, C Author Full Names: Wang, L.; Hardy, F.; Boehmer, A. E.; Wolf, T.; Schweiss, P.; Meingast, C.
Source:
PHYSICAL REVIEW B, 93 (1):10.1103/PhysRevB.93.014514 JAN 19 2016
Abstract:
The low-temperature electronic phase diagram of Ba1-xNaxFe2As2, obtained using high-resolution thermal-expansion and specific-heat measurements, is shown to be considerably more complex than previously reported, containing nine different phases. Besides the magnetic C-2 and reentrant C-4 phases, we find evidence for an additional, presumably magnetic, phase below the usual spin-density-wave transition, as well as a possible incommensurate magnetic phase. All these phases coexist and compete with superconductivity, which is particularly strongly suppressed by the C-4-magnetic phase due to a strong reduction of the electronic entropy available for pairing in this phase.
Title:
Use of frit-disc crucibles for routine and exploratory solution growth of single crystalline samples
Authors:
Canfield, PC; Kong, T; Kaluarachchi, US; Jo, NH Author Full Names: Canfield, Paul C.; Kong, Tai; Kaluarachchi, Udhara S.; Jo, Na Hyun
Source:
PHILOSOPHICAL MAGAZINE, 96 (1):84-92; 10.1080/14786435.2015.1122248 JAN 2 2016
Abstract:
Solution growth of single crystals from high temperature solutions often involves the separation of residual solution from the grown crystals. For many growths of intermetallic compounds, this separation has historically been achieved with the use of plugs of silica wool. Whereas this is generally efficient in a mechanical sense, it leads to a significant contamination of the decanted liquid with silica fibres. In this paper, we present a simple design for frit-disc alumina crucible sets that has made their use in the growth single crystals from high temperature solutions both simple and affordable. An alumina frit-disc allows for the clean separation of the residual liquid from the solid phase. This allows for the reuse of the decanted liquid, either for further growth of the same phase, or for subsequent growth of other, related phases. In this paper, we provide examples of the growth of isotopically substituted TbCd6 and icosahedral i-RCd quasicrystals, as well as the separation of (i) the closely related Bi2Rh3S2 and Bi2Rh3.5S2 phases and (ii) PrZn11 and Pr2Zn17.
Title:
Mn3TeO6 - a new multiferroic material with two magnetic substructures
Authors:
Zhao, L; Hu, ZW; Kuo, CY; Pi, TW; Wu, MK; Tjeng, LH; Komarek, AC Author Full Names: Zhao, Li; Hu, Zhiwei; Kuo, Chang-Yang; Pi, Tun-Wen; Wu, Maw-Kuen; Tjeng, Liu Hao; Komarek, Alexander C.
Source:
PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, 9 (12):730-734; 10.1002/pssr.201510347 DEC 2015
Abstract:
From magnetic susceptibility, dielectric permittivity, electric polarization and specific heat measurements we discover spin-induced ferroelectricity and magnetoelectric coupling in Mn3TeO6 and observe two successive magnetic transitions at low temperatures. A non-ferroelectric intermediate magnetic state occurs below 23 K and a multiferroic ground state emerges below 21 K. Moreover, Mn3TeO6 is a candidate for a multiferroic material where two types of incommensurate spin structures, cycloidal and helical, coexist. Theoretically, both spin substructures may contribute to the macro electric polarization via different mechanisms. This could open new ways of manipulating the ferroelectric polarization in a multiferroic material. (c) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Update: 4-Feb-2016

Title:
Highly modulated structure and upconversion photoluminescence properties of PbGd2(MoO4)(4):Er3+/Yb3+ phosphors
Authors:
Lim, CS Author Full Names: Lim, Chang Sung
Source:
MATERIALS RESEARCH BULLETIN, 75 211-216; 10.1016/j.materresbull.2015.11.058 MAR 2016
Abstract:
Double molybdate of PbGd2-x(MoO4)(4):Er3+/Yb3+ phosphors with the correct doping concentrations of Er3+ and Yb3+ (x= Er3+ + Yb3+, Er3+ = 0.05, 0.1, 0.2 and Yb3+ = 0.2, 0.45) were successfully synthesized by microwave sol-gel process. The highly modulated structure and the upconversion photoluminescence properties were investigated in detail. The synthesized particles, formed after heat-treatment at 900 degrees C for 16 h, showed a well ctystallized morphology with particle sizes of 2-5 mu m. Under excitation at 980 nm, the PbGd1.7(MoO4)(4):Er(0.1)Ybo(0.2) and PbGd1.5(MoO4)(4):Er0.05Yb0.45 particles exhibited a strong 525-nm emission band, a weak 550-nm emission band in the green region, and a very weak 655-nm emission band in the red region. The Raman spectra of the doped particles indicated the disordered structures of PbGd2-x(MoO4)(4) by the incorporation of the Er3+ and Yb3+ ions into the crystal lattice, which resulted in the highly modulated structure as well as a concentration quenching effect of Er3+ ions. (C) 2015 Published by Elsevier Ltd.
Title:
Gabor frames for quasicrystals, K-theory, and twisted gap labeling
Authors:
Kreisel, M Author Full Names: Kreisel, Michael
Source:
JOURNAL OF FUNCTIONAL ANALYSIS, 270 (3):1001-1030; 10.1016/j.jfa.2015.11.011 FEB 1 2016
Abstract:
We study the connection between Gabor frames for quasicrystals, the topology of the hull of a quasicrystal A, and the K-theory of an associated twisted groupoid algebra. In particular, we construct a finitely generated projective module over this algebra, and any multiwindow Gabor frame for A can be used to construct an idempotent representing this module in K-theory. For lattice subsets in dimension two, this allows us to prove a twisted version of Bellissard's gap labeling theorem. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Observation of nonequilibrium behavior near the Lifshitz point in ferroelectrics with incommensurate phase
Authors:
Rushchanskii, KZ; Molnar, A; Bilanych, R; Yevych, R; Kohutych, A; Vysochanskii, YM; Samulionis, V; Banys, J Author Full Names: Rushchanskii, K. Z.; Molnar, A.; Bilanych, R.; Yevych, R.; Kohutych, A.; Vysochanskii, Yu. M.; Samulionis, V.; Banys, J.
Source:
PHYSICAL REVIEW B, 93 (1):10.1103/PhysRevB.93.014101 JAN 14 2016
Abstract:
We have investigated nonequilibrium properties of proper uniaxial Sn2P2(SexS1-x)(6) ferroelectrics with the type II incommensurate phase above Lifshitz point x(LP) similar to 0.28. We performed measurements of dielectric susceptibility in cooling and heating regimes with the rate ranging 0.002-0.1 K/min, as well as high-resolution ultrasound investigation and hypersound Brillouin scattering experiments. For samples with x >= 0.28 clear anomalies are observed at incommensurate second-order transition (T-i) and at first-order lock-in transition (T-c) in the regime of very slow cooling rate, whereas the intermediate incommensurate phase is not observed when the rate is faster than 0.1 K/min. In general, increasing the cooling rate leads to smearing of the anomaly at T-c. We relate this effect to cooling rate dependence of domain-wall concentration and their size: domain width decreases when cooling rate increases. At certain conditions, the size of domain is comparable to the incommensurate phase modulation period, which is in the micrometer range in the vicinity of Lifshitz point and leads to pinning of the modulation period by domain walls.
Title:
Spatial spin-modulated structure and hyperfine interactions of Fe-57 nuclei in multiferroics BiFe1-x T (x) O-3 (T = Sc, Mn; x=0, 0.05)
Authors:
Rusakov, VS; Pokatilov, VS; Sigov, AS; Matsnev, ME; Gapochka, AM; Kiseleva, TY; Komarov, AE; Shatokhin, MS; Makarova, AO Author Full Names: Rusakov, V. S.; Pokatilov, V. S.; Sigov, A. S.; Matsnev, M. E.; Gapochka, A. M.; Kiseleva, T. Yu.; Komarov, A. E.; Shatokhin, M. S.; Makarova, A. O.
Source:
PHYSICS OF THE SOLID STATE, 58 (1):102-107; 10.1134/S1063783416010261 JAN 2016
Abstract:
The results of the Mossbauer studies on Fe-57 nuclei in multiferroics BiFe1-x T (x) O-3 (T = Sc, Mn; x = 0, 0.05) in the temperature range of 5.2-300 K have been presented. The Mossbauer spectra have been analyzed in terms of the model of an incommensurate spatial spin-*modulated structure* of cycloid type. Information has been obtained about the effect of the substitution of Sc and Mn atoms for Fe atoms on the hyperfine parameters of the spectrum: the shift and the quadrupole shift of the Mossbauer line, the isotropic and anisotropic contributions to the hyperfine magnetic field, and also the parameter of anharmonicity of the spatial spin-modulated structure.
Title:
Multilayered sandwich-like architecture containing large-scale faceted Al-Cu-Fe quasicrystal grains
Authors:
Wei, DX; He, ZB Author Full Names: Wei, Dongxia; He, Zhanbing
Source:
MATERIALS CHARACTERIZATION, 111 154-161; 10.1016/j.matchar.2015.11.027 JAN 2016
Abstract:
Faceted quasicrystals are structurally special compared with traditional crystals. Although the application of faceted quasicrystals has been expected, wide-scale application has not occurred owing to the limited exposure of the facets. Using a facile method of heat treatment, we synthesize a multilayered sandwich-like structure with each layer composed of large-scale pentagonal-dodecahedra of Al-Cu-Fe quasicrystals. Moreover, there are channels between the adjacent Al-Cu-Fe layers that serve to increase the exposure of the facets of quasicrystals. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction are used to characterize the multilayered architecture, and the generation mechanisms of this special structure are also discussed. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Effect of applied pressure on microstructure and mechanical properties of Mg-Zn-Y quasicrystal-reinforced AZ91D magnesium matrix composites prepared by squeeze casting
Authors:
Yang, L; Hou, H; Zhao, YH; Yang, XM Author Full Names: Yang, Ling; Hou, Hua; Zhao, Yu-hong; Yang, Xiao-min
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 25 (12):3936-3943; 10.1016/S1003-6326(15)64041-9 DEC 2015
Abstract:
The Mg-Zn-Y quasicrystal-reinforced AZ91D magnesium matrix composites were prepared by squeeze casting process. The effects of applied pressure on microstructure and mechanical properties of the composites were investigated. The results show that squeeze casting process is an effective method to refine the grain. The composites are mainly composed of alpha-Mg, beta-Mg17Al12 and Mg3Zn6Y icosahedral quasicrystal phase (I-phase). With the increase of applied pressure, the contents of beta-Mg17Al12 phase and Mg3Zn6Y quasicrystal particles increase, further matrix grain refinement occurs and coarse dendritic alpha-Mg transforms into equiaxed grain structure. The composite exhibits the maximum ultimate tensile strength and elongation of 194.3 MPa and 9.2% respectively when the applied pressure is 100 MPa, and a lot of dimples appear on the tensile fractography. Strengthening mechanisms of quasicrystal-reinforced AZ91D magnesium matrix composites are chiefly fine-grain strengthening and quasicrystal particles strengthening.

Update: 28-Jan-2016

Title:
Controlling many-body states by the electric-field effect in a two-dimensional material
Authors:
Li, LJ; O'Farrell, ECT; Loh, KP; Eda, G; Ozyilmaz, B; Neto, AHC Author Full Names: Li, L. J.; O'Farrell, E. C. T.; Loh, K. P.; Eda, G.; Ozyilmaz, B.; Neto, A. H. Castro
Source:
NATURE, 529 (7585):185-U129; 10.1038/nature16175 JAN 14 2016
Abstract:
To understand the complex physics of a system with strong electron-electron interactions, the ideal is to control and monitor its properties while tuning an external electric field applied to the system (the electric-field effect). Indeed, complete electric-field control of many-body states in strongly correlated electron systems is fundamental to the next generation of condensed matter research and devices(1-3). However, the material must be thin enough to avoid shielding of the electric field in the bulk material. Two-dimensional materials do not experience electrical screening, and their charge-carrier density can be controlled by gating. Octahedral titanium diselenide (1T-TiSe2) is a prototypical two-dimensional material that reveals a charge-density wave (CDW) and superconductivity in its phase diagram(4), presenting several similarities with other layered systems such as copper oxides(5), iron pnictides(6), and crystals of rare-earth elements and actinide atoms(7). By studying 1T-TiSe2 single crystals with thicknesses of 10 nanometres or less, encapsulated in two-dimensional layers of hexagonal boron nitride, we achieve unprecedented control over the CDW transition temperature (tuned from 170 kelvin to 40 kelvin), and over the superconductivity transition temperature (tuned from a quantum critical point at 0 kelvin up to 3 kelvin). Electrically driving TiSe2 over different ordered electronic phases allows us to study the details of the phase transitions between many-body states. Observations of periodic oscillations of magnetoresistance induced by the Little-Parks effect show that the appearance of superconductivity is directly correlated with the spatial texturing of the amplitude and phase of the superconductivity order parameter, corresponding to a two-dimensional matrix of superconductivity. We infer that this superconductivity matrix is supported by a matrix of incommensurate CDW states embedded in the commensurate CDW states. Our results show that spatially modulated electronic states are fundamental to the appearance of two-dimensional superconductivity.
Title:
Structure of periodic crystals and quasicrystals in ultrathin films of Ba-Ti-O
Authors:
Cockayne, E; Mihalkovic, M; Henley, CL Author Full Names: Cockayne, Eric; Mihalkovic, Marek; Henley, Christopher L.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.020101 JAN 7 2016
Abstract:
We model the remarkable thin-film Ba-Ti-O structures formed by heat treatment of an initial perovskite BaTiO3 thin film on a Pt(111) surface. All structures contain a rumpled Ti-O network with all Ti threefold coordinated with O and with Ba occupying the larger. mainly Ti7O7, pores. The quasicrystal structure is a simple decoration of three types of tiles: square, triangle, and 30 degrees. rhombus, with edge lengths 6.85 angstrom, joined edge-to-edge in a quasicrystalline pattern; observed periodic crystals in ultrathin film Ba-Ti-O are built from these and other tiles. Simulated STM images reproduce the patterns seen experimentally and identify the bright protrusions as Ba atoms. The models are consistent with all experimental observations.
Title:
Ultrafast Metamorphosis of a Complex Charge-Density Wave
Authors:
Haupt, K; Eichberger, M; Erasmus, N; Rohwer, A; Demsar, J; Rossnagel, K; Schwoerer, H Author Full Names: Haupt, Kerstin; Eichberger, Maximilian; Erasmus, Nicolas; Rohwer, Andrea; Demsar, Jure; Rossnagel, Kai; Schwoerer, Heinrich
Source:
PHYSICAL REVIEW LETTERS, 116 (1):10.1103/PhysRevLett.116.016402 JAN 6 2016
Abstract:
Modulated phases, commensurate or incommensurate with the host crystal lattice, are ubiquitous in solids. The transition between such phases involves formation and rearrangement of domain walls and is generally slow. Using ultrafast electron diffraction, we directly record the photoinduced transformation between a nearly commensurate and an incommensurate charge-density-wave phase in 1T-TaS2. The transformation takes place on the picosecond time scale, orders of magnitude faster than previously observed for commensurate-to-incommensurate transitions. The transition speed and mechanism can be linked to the peculiar nanoscale structure of the photoexcited nearly commensurate phase.
Title:
Phase diagram of the Kondo lattice model on the kagome lattice
Authors:
Ghosh, S; Brien, PO; Henley, CL; Lawler, MJ Author Full Names: Ghosh, Shivam; Brien, Patrick O'; Henley, Christopher L.; Lawler, Michael J.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.024401 JAN 4 2016
Abstract:
We consider the potential for novel forms of magnetism arising from the subtle interplay between electrons and spins in the underscreened kagome Kondo lattice model. At weak coupling, we show that incommensurate noncoplanar multiwave vector magnetic orders arise at nearly all fillings and that this results from Fermi surface effects that introduce competing interactions between the spins. At strong coupling, we find that such a complex order survives near half filling despite the presence of ferromagnetism at all other fillings. We show this arises due to state selection among a massive degeneracy of states at infinite coupling. Finally, we show that at intermediate filling only commensurate orders seem to survive, but these orders still include noncoplanar magnetism. So, the mere presence of both local moments and itinerant electrons enables complex orders to form unlike any currently observed in kagome materials.
Title:
Incommensurate to commensurate antiferromagnetism in CeRhAl4Si2: An Al-27 NMR study
Authors:
Sakai, H; Hattori, T; Tokunaga, Y; Kambe, S; Ghimire, NJ; Ronning, F; Bauer, ED; Thompson, JD Author Full Names: Sakai, H.; Hattori, T.; Tokunaga, Y.; Kambe, S.; Ghimire, N. J.; Ronning, F.; Bauer, E. D.; Thompson, J. D.
Source:
PHYSICAL REVIEW B, 93 (1):10.1103/PhysRevB.93.014402 JAN 4 2016
Abstract:
Al-27 nuclear magnetic resonance (NMR) experiments have been performed on a single crystal of CeRhAl4Si2, which is an antiferromagnetic Kondo-lattice compound with successive antiferromagnetic transitions of T-N1 = 14 K and T-N2 = 9 K at zero external field. In the paramagnetic state, the Knight shifts, quadrupolar frequency, and asymmetric parameter of electrical field gradient on the Al sites have been determined, which have local orthorhombic symmetry. The transferred hyperfine coupling constants are also determined. Analysis of the NMR spectra indicates that a commensurate antiferromagnetic structure exists below T-N2, but an incommensurate modulation of antiferromagnetic moments is present in the antiferromagnetic state between T-N1 and T-N2. The spin-lattice relaxation rate suggests that the 4 f electrons behave as local moments at temperatures above T-N1.
Title:
Trapping of Oxygen Vacancies at Crystallographic Shear Planes in Acceptor-Doped Pb-Based Ferroelectrics
Authors:
Batuk, D; Batuk, M; Tsirlin, AA; Hadermann, J; Abakumov, AM Author Full Names: Batuk, Dmitry; Batuk, Maria; Tsirlin, Alexander A.; Hadermann, Joke; Abakumov, Artem M.
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 54 (49):14787-14790; 10.1002/anie.201507729 DEC 1 2015
Abstract:
The defect chemistry of the ferroelectric material PbTiO3 after doping with Fe-III acceptor ions is reported. Using advanced transmission electron microscopy and powder X-ray and neutron diffraction, we demonstrate that even at concentrations as low as circa 1.7% (material composition approximately ABO(2.95)), the oxygen vacancies are trapped into extended planar defects, specifically crystallographic shear planes. We investigate the evolution of these defects upon doping and unravel their detailed atomic structure using the formalism of superspace crystallography, thus unveiling their role in nonstoichiometry in the Pb-based perovskites.

Update: 14-Jan-2016

Title:
Dislocations in icosahedral quasicrystalline phase embedded in hot-deformed Mg alloys
Authors:
Huang, H; Tian, Y; Yuan, GY; Chen, CL; Wang, ZC; Ding, WJ; Inoue, A Author Full Names: Huang, Hua; Tian, Yuan; Yuan, Guangyin; Chen, Chunlin; Wang, Zhongchang; Ding, Wenjiang; Inoue, Akihisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 658 483-487; 10.1016/j.jallcom.2015.10.284 FEB 15 2016
Abstract:
We perform a systematic structural investigation of the I-phase particles embedded in Mg matrix in I-phase-reinforced Mg-3.5Zn-0.6Gd alloy and offer evidence to the presence of dislocations in the I-phase particles. Such dislocations are found to be formed on the (0001) plane of Mg matrix, which is attributed to their slipping into the 5-fold and 2-fold planes of I-phase particles. We also discuss how deformation conditions of wrought Mg alloys affect the deformation behaviors of the I-phase and how deformation behavior of I-phase affect the mechanical properties of wrought Mg alloys. The bonding between the I-phase and Mg matrix was also confirmed to be strong. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Microstructures and phase transformations in as-aged Mn2.04NiGa Heusler alloy
Authors:
Du, ZW; Han, XL; Li, T; Liu, EK; Ma, XD; Xiong, JC; Wu, GH Author Full Names: Du, Z. W.; Han, X. L.; Li, T.; Liu, E. K.; Ma, X. D.; Xiong, J. C.; Wu, G. H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 657 443-449; 10.1016/j.jallcom.2015.10.111 FEB 5 2016
Abstract:
The room-temperature microstructures and phase transformation of Mn2.04NiGa alloy were investigated by transmission electron microscopy (TEM), electron backscattered diffraction (EBSD) and high-angle annular dark field scanning-TEM (HAADF-STEM). The Mn2.04NiGa alloy annealed at 1073 K for 72 h is mainly austenite phase with Hg2CuTi-type structure. After 623 K/72 h ageing, nano-scaled MnNiGa precipitates considered as Ni2In-type hexagonal structure were found by TEM. A crystalline orientation relationship between precipitates and austensite can be described by ((22) over bar4)(A)//(0 (1) over bar 10)(H), [1 (1) over bar0](A)//[2 (11) over bar0](H). These precipitates are accompanying with Mn-rich martensite lamellae. Both non-modulated and nearly 16-layered modulated structures are generally in coexistence in one martensite lath. A crystalline orientation relationship between the ageing-induced martensite and austenite is (111)(A)//(110)(M), [011](A)//[1 (1) over bar2]M. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Origin of modulated phases and magnetic hysteresis in TmB4
Authors:
Wierschem, K; Sunku, SS; Kong, T; Ito, T; Canfield, PC; Panagopoulos, C; Sengupta, P Author Full Names: Wierschem, Keola; Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; Canfield, Paul C.; Panagopoulos, Christos; Sengupta, Pinaki
Source:
PHYSICAL REVIEW B, 92 (21):10.1103/PhysRevB.92.214433 DEC 23 2015
Abstract:
We investigate the low-temperature magnetic phases in TmB4, a metallic quantum magnet on the geometrically frustrated Shastry-Sutherland lattice, using coordinated experimental and theoretical studies. Our results provide an explanation for the appearance of the intriguing fractional plateau in TmB4 and accompanying magnetic hysteresis. Together with observation of the bump in the half plateau, our results support the picture that the magnetization plateau structure in TmB4 is strongly influenced by the zero-field modulated phases. We present a phenomenological model to explain the appearance of the modulated phases and a microscopic Hamiltonian that captures the complete magnetic behavior of TmB4.

Update: 7-Jan-2016

Title:
Magnetic properties and complex magnetic phase diagram in non-centrosymmetric EuRhGe3 and EuIrGe3 single crystals
Authors:
Maurya, A; Bonville, P; Kulkarni, R; Thamizhavel, A; Dhar, SK Author Full Names: Maurya, Arvind; Bonville, P.; Kulkarni, R.; Thamizhavel, A.; Dhar, S. K.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 401 823-831; 10.1016/j.jmmm.2015.10.134 MAR 1 2016
Abstract:
We report the magnetic properties of two Eu based compounds, single crystalline EuIrGe3 and EuRhGe3, inferred from magnetisation, electrical transport, heat capacity and Eu-151 Mossbauer spectroscopy. These previously known compounds crystallise in the non-centrosymmetric, tetragonal, I4 mm, BaNiSn3-type structure. Single crystals of EuIrGe3 and EuRhGe3 were grown using a high temperature solution growth method using In as flux. EuIrGe3 exhibits two magnetic transition temperatures T-N1 = 12.4 K, and T(N)2 = 7.3 K, whereas EuRhGe3 presents a single one at T-N = 12K. Eu-151 Mossbauer spectra show evidence for a cascade of transitions from paramagnetic to incommensurate amplitude modulated followed by an equal moment phase at lower temperature in EuIrGe3. This latter phase alone occurs in EuRhGe3. In both compounds, the magnetisation measured up to 14 T suggests that the equal moment magnetic phase has a spiral spin arrangement. The field induced reorientations are also well documented in the magnetotransport data. A superzone gap is observed for the current density J vertical bar vertical bar [001], which is enhanced by a transverse magnetic field. The magnetic phase diagram constructed from all the data is complex, revealing the presence of many phases in the H - T space. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Structural and magnetic phase transitions in CeCu6-xT(x) (T = Ag, Pd)
Authors:
Poudel, L; de la Cruz, C; Payzant, EA; May, AF; Koehler, M; Garlea, VO; Taylor, AE; Parker, DS; Cao, HB; McGuire, MA; Tian, W; Matsuda, M; Jeen, H; Lee, HN; Hong, T; Calder, S; Zhou, HD; Lumsden, MD; Keppens, V; Mandrus, D; Christianson, AD Author Full Names: Poudel, L.; de la Cruz, C.; Payzant, E. A.; May, A. F.; Koehler, M.; Garlea, V. O.; Taylor, A. E.; Parker, D. S.; Cao, H. B.; McGuire, M. A.; Tian, W.; Matsuda, M.; Jeen, H.; Lee, H. N.; Hong, T.; Calder, S.; Zhou, H. D.; Lumsden, M. D.; Keppens, V.; Mandrus, D.; Christianson, A. D.
Source:
PHYSICAL REVIEW B, 92 (21):10.1103/PhysRevB.92.214421 DEC 15 2015
Abstract:
The structural and the magnetic properties of CeCu6-xAgx(0 <= x <= 0.85) and CeCu6-xPdx (0 <= x <= 0.4) have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of CeCu6-xAgx and CeCu6-xPdx as a function of Ag/Pd composition are reported. The end member, CeCu6, undergoes a structural phase transition from an orthorhombic (Pnma) to a monoclinic (P2(1)/c) phase at 240 K. In CeCu6-xAgx, the structural phase transition temperature (T-s) decreases linearly with Ag concentration and extrapolates to zero at x(S) approximate to 0.1. The structural transition in CeCu6-xPd (x) remains unperturbed with Pd substitution within the range of our study. The lattice constant b slightly decreases with Ag/Pd doping, whereas a and c increase with an overall increase in the unit cell volume. Both systems, CeCu6-xAgx and CeCu6-xPdx, exhibit a magnetic quantum critical point (QCP), at x approximate to 0.2 and x approximate to 0.05, respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector (delta(1) 0 delta(2)), where delta(1) similar to 0.62, delta 2 similar to 0.25, x = 0.125 for CeCu6-xPdx and delta(1) similar to 0.64, delta(2) similar to 0.3, x = 0.3 for CeCu6-xAgx. The magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.
Title:
Overcoming magnetic frustration and promoting half-metallicity in spinel CoCr2O4 by doping with Fe
Authors:
Ganguly, S; Chimata, R; Sanyal, B Author Full Names: Ganguly, Shreemoyee; Chimata, Raghuveer; Sanyal, Biplab
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224417 DEC 14 2015
Abstract:
In this paper, we present a systematic study of the effects of Fe doping on the electronic and magnetic structures of spinel CoCr2O4 by ab initio density functional theory and atomistic spin dynamics calculations. Our calculated magnetic structure for pristine CoCr2O4 correctly reproduces the experimental one with a q-vector of (0.67, 0.67,0.0), establishing the accuracy of the calculated interatomic exchange interactions. We show that the noncollinear spin structure with a nonzero q-vector in the spinel structure is driven towards collinearity by Fe doping by a complex interplay between interatomic exchange interactions. In the inverse spinel structure with 100% Fe doping, a collinear antiferromagnetic order develops along with a half-metallic electronic structure, which evolves due to the chemical disorder between Fe and Co in the B sites described by the coherent potential approximation. This is a comprehensive theoretical study to understand the evolution of magnetic and electronic properties of multiferroic CoCr2O4 doped with Fe.

Update: 31-Dec-2015

Title:
Decoupling of the antiferromagnetic and insulating states in Tb-doped Sr2IrO4
Authors:
Wang, JC; Aswartham, S; Ye, F; Terzic, J; Zheng, H; Haskel, D; Chikara, S; Choi, Y; Schlottmann, P; Custelcean, R; Yuan, SJ; Cao, G Author Full Names: Wang, J. C.; Aswartham, S.; Ye, Feng; Terzic, J.; Zheng, H.; Haskel, Daniel; Chikara, Shalinee; Choi, Yong; Schlottmann, P.; Custelcean, Radu; Yuan, S. J.; Cao, G.
Source:
PHYSICAL REVIEW B, 92 (21):10.1103/PhysRevB.92.214411 DEC 8 2015
Abstract:
Sr2IrO4 is a spin-orbit-coupled insulator with an antiferromagnetic (AFM) transition at T-N = 240 K. We report results of a comprehensive study of single-crystal Sr2Ir1-xTbxO4 (0 <= x <= 0.03). This study found that a mere 3% (x = 0.03) of tetravalent Tb4+ (4f(7)) substituting for Ir4+ (rather than Sr2+) completely suppresses the long-range collinear AFM transition but retains the insulating state, leading to a phase diagram featuring a decoupling of the magnetic interactions and charge gap. The insulating state at x = 0.03 is characterized by an unusually large specific heat at low temperatures and an incommensurate magnetic state having magnetic peaks at (0.95,0,0) and (0,0.95,0) in the neutron diffraction, suggesting a spiral or spin-density-wave order. It is apparent that Tb doping effectively changes the relative strength of the spin-orbit interaction (SOI) and the tetragonal crystal electric field and enhances the Hund's rule coupling that competes with the SOI, and destabilizes the AFM state. However, the disappearance of the AFM is accompanied by no metallic state chiefly because an energy level mismatch for the Ir and Tb sites weakens charge carrier hopping and causes a persistent insulating state. This work highlights an unconventional correlation between the AFM and insulating states in which the magnetic transition plays no critical role in the formation of the charge gap in the iridate.
Title:
Long-range magnetic order in models for rare-earth quasicrystals
Authors:
Thiem, S; Chalker, JT Author Full Names: Thiem, Stefanie; Chalker, J. T.
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224409 DEC 7 2015
Abstract:
We take a two-step theoretical approach to study magnetism of rare-earth quasicrystals by considering Ising spins on quasiperiodic tilings, coupled via Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. First, we compute RKKY interactions from a tight-binding Hamiltonian defined on the two-dimensional quasiperiodic tilings. We find that the magnetic interactions are frustrated and strongly dependent on the local environment. This results in the formation of clusters with strong bonds at certain patterns of the tilings that repeat quasiperiodically. Second, we examine the statistical mechanics of Ising spins with these RKKY interactions, using extensive Monte Carlo simulations. Although models that have frustrated interactions and lack translational invariance might be expected to display spin-glass behavior, we show that the spin system has a phase transition to low-temperature states with long-range quasiperiodic magnetic order. Additionally, we find that in some of the systems spin clusters can fluctuate much below the ordering temperature.
Title:
One-Dimensional Quasicrystals from Incommensurate Charge Order
Authors:
Flicker, F; van Wezel, J Author Full Names: Flicker, Felix; van Wezel, Jasper
Source:
PHYSICAL REVIEW LETTERS, 115 (23):10.1103/PhysRevLett.115.236401 DEC 3 2015
Abstract:
Artificial quasicrystals are nowadays routinely manufactured, yet only two naturally occurring examples are known. We present a class of systems with the potential to be realized both artificially and in nature, in which the lowest energy state is a one-dimensional quasicrystal. These systems are based on incommensurately charge-ordered materials, in which the quasicrystalline phase competes with the formation of a regular array of discommensurations as a way of interpolating between incommensurate charge order at high temperatures and commensurate order at low temperatures. The nonlocal correlations characteristic of the quasicrystalline state emerge from a free-energy contribution localized in reciprocal space. We present a theoretical phase diagram showing that the required material properties for the appearance of such a ground state allow for one-dimensional quasicrystals to form in real materials. The result is a potentially wide class of one-dimensional quasicrystals.
Title:
Disorder in the composite crystal structure of the manganese 'disilicide' MnSi1.73 from powder X-ray diffraction data
Authors:
Akselrud, L; Gil, RC; Wagner-Reetz, M; Grin, Y Author Full Names: Akselrud, L.; Gil, R. Cardoso; Wagner-Reetz, M.; Grin, Yu.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 (6):707-712; SI 10.1107/S2052520615019757 DEC 2015
Abstract:
The crystal structure of the higher manganese silicide MnSi1.7 (known in the literature as HMS) is investigated in samples with different compositions obtained by different techniques at temperatures not higher than 1273 K. Powder X-ray diffraction was applied. The crystal structure is described as incommensurate composite. In addition to the ordered model already known in the literature, the partial disorder in the silicon substructure was detected and described introducing an additional atomic site with a different modulation function.
Title:
Type II Bi-1 (-) xWxO1.5 (+) (1.5x): a (3+3)-dimensional commensurate modulation that stabilizes the fast-ion conducting delta phase of bismuth oxide
Authors:
Wind, J; Auckett, JE; Withers, RL; Piltz, RO; Maljuk, A; Ling, CD Author Full Names: Wind, Julia; Auckett, Josie E.; Withers, Ray L.; Piltz, Ross O.; Maljuk, Andrey; Ling, Chris D.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 (6):679-687; SI 10.1107/S2052520615018351 DEC 2015
Abstract:
The Type II phase in the Bi1 - xWxO1.5 (+) (1.5x) system is shown to have a (3 + 3)-dimensional modulated delta-Bi2O3-related structure, in which the modulation vector epsilon 'locks in' to a commensurate value of 1/3. The structure was refined in a 3 x 3 x 3 supercell against single-crystal Laue neutron diffraction data. Ab initio calculations were used to test and optimize the local structure of the oxygen sublattice around a single mixed Bi/W site. The underlying crystal chemistry was shown to be essentially the same as for the recently refined (3 + 3)-dimensional modulated structure of Type II Bi-1 (-) xNbxO1.5 (+) (x) (Ling et al., 2013), based on a transition from fluorite-type to pyrochlore-type via the appearance of W4O18 'tetrahedra of octahedra' and chains of corner-sharing WO6 octahedra along < 110 >(F) directions. The full range of occupancies on this mixed Bi/W site give a hypothetical solid-solution range bounded by Bi23W4O46.5 (x = 0.148) and Bi22W5O48 (x = 0.185), consistent with previous reports and with our own synthetic and analytical results.
Title:
Determination of the incommensurate modulated structure of Bi2Sr1.6La0.4CuO6+delta by aberration-corrected transmission electron microscopy
Authors:
Ge, BH; Wang, YM; Luo, HQ; Wen, HH; Yu, R; Cheng, ZY; Zhu, J Author Full Names: Ge, Binghui; Wang, Yumei; Luo, Huiqian; Wen, Haihu; Yu, Rong; Cheng, Zhiying; Zhu, Jing
Source:
ULTRAMICROSCOPY, 159 67-72; 10.1016/j.ultramic.2015.08.004 1 DEC 2015
Abstract:
The incommensurate modulated structure (IMS) of Bi2Sr1.6La0.4Cu6+delta (BSLCO) has been studied by aberration-corrected transmission electron microscopy in combination with a high-dimensional (HD) space description. Two images are deconvoluted in the negative Cs imaging (NCSI) and positive Cs imaging (PCSI) modes. Similar results for the IMS have been obtained from two corresponding projected potential maps (PPMs), and the size of the dots representing atoms in the NCSI PPM is found to be smaller than that in the PCSI PPM. Considering that the object size is one of the factors that influence the precision of the structural determination, modulation functions for all unoverlapped atoms in BSLCO were determined on the basis of the NCSI PPM in combination with the HD space description. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Crystal Structure and Thermoelectric Properties of Chimney-Ladder Higher Manganese Silicides
Authors:
Miyazaki, Y Author Full Names: Miyazaki, Yuzuru
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 79 (11):530-537; SI 10.2320/jinstmet.JA201508 2015
Abstract:
Crystal structure, electronic structure and thermoelectric (TE) properties of Nowotny chimney-ladder (NCL) higher manganese silicides (HMSs) are reviewed. According to a (3+1). dimensional superspace approach, HMSs are revealed to belong to incommensurate composite crystals, wherein [Mn] and [Si] subsystems possess an irrational c-axis ratio gamma=c(Mn)/c(Si). The gamma parameter, also represents a stoichiometry of the HMSs as MnSi gamma, dictates the electronic structure, directly relating to a valence electron counting number, VEC. The p-type TE performance can be enhanced by a partial substitution of V, Cr, etc., while n-type HMSs can be obtained by heavily substituting Mn with Fe, etc., to realize VEC > 14. A unique thermal expansion has been discovered at T similar to 800 K, which would deteriorate TE performance and hence to be avoided from a practical application point of view.
Title:
Electronic vs. structural ordering in a manganese(III) spin crossover complex
Authors:
Fitzpatrick, AJ; Trzop, E; Muller-Bunz, H; Dirtu, MM; Garcia, Y; Collet, E; Morgan, GG Author Full Names: Fitzpatrick, Anthony J.; Trzop, Eliza; Mueller-Bunz, Helge; Dirtu, Marinela M.; Garcia, Yann; Collet, Eric; Morgan, Grace G.
Source:
CHEMICAL COMMUNICATIONS, 51 (99):17540-17543; 10.1039/c5cc05129k 2015
Abstract:
A symmetry breaking spin transition in a Mn(III) complex is reported with three structural phases, a high symmetry high temperature S = 2 phase, an intermediate S = 1/S = 2 ordered phase and an aperiodic low temperature phase with S = 1 cations. The aperiodicity is interpreted as resulting from long-range ordering of the NTf2- anions.
Title:
Effects of Initial States on the Spinodal Decomposition of Quenched and Melt-Spun Cu-15Ni-8Sn Alloy
Authors:
Kondo, S; Masusaki, A; Ogawa, K; Morimura, T; Nakashima, H Author Full Names: Kondo, Shin-ichiro; Masusaki, Akinori; Ogawa, Kento; Morimura, Takao; Nakashima, Hiromichi
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 79 (12):664-671; 10.2320/jinstmet.J2015012 2015
Abstract:
We investigate early stages of spinodal decomposition in a melt. spun Cu-15Ni-8Sn alloy (melt-spun samples) by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron diffraction analysis through comparison against a quenched alloy of the same composition (quenched samples). In XRD measurements, no sidebands of (200) planes are found in the melt-spun sample after aging at 350 degrees C for 120 min, whereas they are found in the quenched sample after a heat treatment at 350 degrees C for 60 min. TEM observations of a quenched sample after aging at 350 degrees C for 60 min indicate the presence of a modulated structure (lambda= 5-10 nm) in the matrix, whereas those of a melt-spun sample after the same heat treatment also indicate the presence of a modulated structure (lambda: too small to measure). Electron diffraction patterns reveal satellite structures in both samples, although with superlattice reflections from ordering phases visible in the quenched sample. These differences are presumably due to a difference in the size of clusters present in their respective quenched states; in melt. spun samples, cluster size was much smaller as a result of a high cooling rate (approximate to 8 x 10(5 degrees)C/s).

Update: 24-Dec-2015

Title:
Single-Crystal Neutron Diffraction Study of the Heavy-Electron Superconductor CeNiGe3
Authors:
Ikeda, Y; Ueta, D; Yoshizawa, H; Nakao, A; Munakata, K; Ohhara, T Author Full Names: Ikeda, Yoichi; Ueta, Daichi; Yoshizawa, Hideki; Nakao, Akiko; Munakata, Koji; Ohhara, Takashi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (12):10.7566/JPSJ.84.123701 DEC 15 2015
Abstract:
A single-crystal neutron diffraction study was performed on anomalous antiferromagnetic ordering in the heavyelectron superconductor CeNiGe3. We observed incommensurate magnetic Bragg reflections characterized by the incommensurate propagation vector k(2) = (0, 0.41, 1/2) below the Neel temperature of 5K, but no significant magnetic reflection with the commensurate propagation vector k(1) = (1, 0, 0), at which another magnetic reflection was observed in a previous neutron diffraction study with a polycrystalline sample. From the single-crystal study, we suggest that the magnetic phase of CeNiGe3 at ambient pressure is characterized only by the incommensurate propagation vector k(2).
Title:
Electronic Properties of Incommensurate Atomic Layers
Authors:
Koshino, M; Moon, P Author Full Names: Koshino, Mikito; Moon, Pilkyung
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (12):10.7566/JPSJ.84.121001 DEC 15 2015
Abstract:
We present a brief theoretical overview of electronic properties of incommensurate multilayer systems, i.e., a pair of two-dimensional atomic layers stacked in an arbitrary orientation. We introduce the general theoretical scheme to describe the interlayer interaction between incommensurate crystal structures, and apply the formula to two specific examples, the twisted bilayer graphene and graphene-hBN composite bilayer. In each case, we calculate the electronic band structure and demonstrate that the low-energy electronic properties are significantly modified by the interlayer interaction, particularly when the two lattice structures are close to each other. We also study the energy spectrum and the quantum Hall effect in magnetic fields, where we see that the spectral structure exhibits a fractal nature, as known as the Hofstadter butterfly. We argue about the optical absorption properties of the twisted bilayer graphene and show that the interlayer interaction gives rise to the characteristic spectroscopic features in zero magnetic field and also in strong magnetic field.
Title:
Amorphous hydrides of the Ti45Zr38Ni17-xCox nano-powders
Authors:
Zywczak, A; Rusinek, D; Czub, J; Sikora, M; Stepien, J; Gondek, L; Takasaki, A; Hoser, A Author Full Names: Zywczak, A.; Rusinek, D.; Czub, J.; Sikora, M.; Stepien, J.; Gondek, L.; Takasaki, A.; Hoser, A.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 40 (45):15534-15539; 10.1016/j.ijhydene.2015.09.136 DEC 7 2015
Abstract:
The Ti-Zr-Ni alloys can be synthesized in crystalline, amorphous and quasicrystalline phases. They are produced by mechanical alloying or melt-spinning and they are good candidate materials for hydrogen storage applications. In this communication we modified the Ti45Zr38Ni17 compounds by substituting 3d metals (cobalt) for Ni to obtain amorphous phase. The cobalt atoms are located at the same positions as nickel. We describe a series of phase transitions associated with a hydrogen uptake in the amorphous Ti45Zr38Ni17-xCox alloys that were prepared by mechanical alloying. The investigated alloys exhibited a high capacity for gaseous H-2 reaching 2.2 wt.% at elevated temperatures. It has been found, that the amorphous powders were decomposed into simple hydrides being exposed to H-2 at temperatures above 200 degrees C. In order to overcome that problem, a processing route to obtain the amorphous hydrides was established. The heated amorphous hydrides underwent an unusual and fascinating transformation into the glassy quasicrystal phase with no hydrogen loss. A further temperature increase triggered another structural transformation into the cubic phase, which was associated with hydrogen release from the structure. The crystal structure evolution was characterized by the variety of diffraction techniques. Thermodynamic properties were studied by differential scanning calorimetry and thermal desorption spectroscopy. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Static and quasielastic properties of the spiral magnet Ba2CuGe2O7 studied by neutron resonance spin echo spectroscopy and neutron Larmor labeling
Authors:
Muhlbauer, S; Kindervater, J; Hassler, W Author Full Names: Muehlbauer, S.; Kindervater, J.; Haessler, W.
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224406 DEC 4 2015
Abstract:
We provide a route to use elastic and quasielastic neutron spin echo spectroscopy (Larmor labeling) for a unified approach to study both the static and dynamic properties of incommensurate magnetic structures with small propagation vectors. The archetypal noncentrosymmetric spiral magnet Ba2CuGe2O7 serves as a model system for our study. We show how Larmor labeling can efficiently decouple instrumental wavelength resolution and effective-(Q) over right arrow resolution and give high-precision access to the structural properties of the incommensurate domains of Ba2CuGe2O7.
Title:
Two types of nematicity in the phase diagram of the cuprate superconductor YBa2Cu3Oy
Authors:
Cyr-Choiniere, O; Grissonnanche, G; Badoux, S; Day, J; Bonn, DA; Hardy, WN; Liang, R; Doiron-Leyraud, N; Taillefer, L Author Full Names: Cyr-Choiniere, O.; Grissonnanche, G.; Badoux, S.; Day, J.; Bonn, D. A.; Hardy, W. N.; Liang, R.; Doiron-Leyraud, N.; Taillefer, Louis
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224502 DEC 2 2015
Abstract:
Nematicity has emerged as a key feature of cuprate superconductors, but its link to other fundamental properties such as superconductivity, charge order, and the pseudogap remains unclear. Here we use measurements of transport anisotropy in YBa2Cu3Oy to distinguish two types of nematicity. The first is associated with short-range charge-density-wave modulations in a doping region near p = 0.12. It is detected in the Nernst coefficient, but not in the resistivity. The second type prevails at lower doping, where there are spin modulations but no charge modulations. In this case, the onset of in-plane anisotropy-detected in both the Nernst coefficient and the resistivity-follows a line in the temperature-doping phase diagram that tracks the pseudogap energy. We discuss two possible scenarios for the latter nematicity.
Title:
Direct observation of an optically induced charge density wave transition in 1T-TaSe2
Authors:
Sun, SS; Wei, LL; Li, ZW; Cao, GL; Liu, Y; Lu, WJ; Sun, YP; Tian, HF; Yang, HX; Li, JQ Author Full Names: Sun, Shuaishuai; Wei, Linlin; Li, Zhongwen; Cao, Gaolong; Liu, Y.; Lu, W. J.; Sun, Y. P.; Tian, Huanfang; Yang, Huaixin; Li, Jianqi
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224303 DEC 2 2015
Abstract:
Four-dimensional ultrafast transmission electron microscopy measurements reveal a rich variety of structural dynamic phenomena at a phase transition in the charge density wave (CDW) of 1T-TaSe2. Under photoexcitation, remarkable changes in both the CDW intensity and orientation are clearly observed, associated with the transformation from a commensurate (C) phase into an incommensurate (IC) phase in a time scale of picoseconds. Moreover, the transient states reveal a notable "structural isosbestic point" at a wave vector of q(iso) where the C and IC phases yield their diffracting efficiencies in equal ratio. This observation reveals that the crystal planes parallel to q(iso) adopt a common dynamic feature in the CDW phases throughout whole nonequilibrium transition. The second-order characteristics observed in this nonequilibrium phase transition have also been analyzed based on time-resolved structural data.
Title:
Ancient Metal Mirror Alloy Revisited: Quasicrystalline Nanoparticles Observed
Authors:
Sekhar, JA; Mantri, AS; Yamjala, S; Saha, S; Balamuralikrishnan, R; Rao, PR Author Full Names: Sekhar, J. A.; Mantri, A. S.; Yamjala, S.; Saha, Sabyasachi; Balamuralikrishnan, R.; Rao, P. Rama
Source:
JOM, 67 (12):2976-2983; 10.1007/s11837-015-1524-3 DEC 2015
Abstract:
This article presents, for the first time, evidence of nanocrystalline structure, through direct transmission electron microscopy (TEM) observations, in a Cu-32 wt.% Sn alloy that has been made by an age-old, uniquely crafted casting process. This alloy has been used as a metal mirror for centuries. The TEM images also reveal five-sided projections of nano-particles. The convergent beam nano-diffraction patterns obtained from the nano-particles point to the nano-phase being quasicrystalline, a feature that has never before been reported for a copper alloy, although there have been reports of the presence of icosahedral 'clusters' within large unit cell intermetallic phases. This observation has been substantiated by x-ray diffraction, wherein the observed peaks could be indexed to an icosahedral quasi-crystalline phase. The mirror alloy casting has been valued for its high hardness and high reflectance properties, both of which result from its unique internal microstructure that include nano-grains as well as quasi-crystallinity. We further postulate that this microstructure is a consequence of the raw materials used and the manufacturing process, including the choice of mold material. While the alloy consists primarily of copper and tin, impurity elements such as zinc, iron, sulfur, aluminum and nickel are also present, in individual amounts not exceeding one wt.%. It is believed that these trace impurities could have influenced the microstructure and, consequently, the properties of the metal mirror alloy.
Title:
Mathematical crystallography in the 21st century
Authors:
Senechal, M Author Full Names: Senechal, Marjorie
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 230 (12):691-698; SI 10.1515/zkri-2015-1870 DEC 2015
Abstract:
As crystallography merges with materials science and engineering, mathematical crystallography is growing in new directions, including: Characterizing new materials with unusual properties; Imaging, including but not limited to diffraction; Exploring and exploiting superspaces; Mapping the aperiodic landscape, from chaos to classical periodicity and beyond; Re-modeling the structures of real crystals, both periodic and aperiodic; Modeling self-assembly and self-reorganization on the nanoscale. In short, it's not (just) about space groups and tilings anymore.
Title:
Incommensurate charge density wave modulated by period of Hubbard superlattices
Authors:
Zhang, LL; Huang, J; Duan, CB; Wang, WZ Author Full Names: Zhang, Liang-Liang; Huang, Jin; Duan, Cheng-Bo; Wang, Wei-Zhong
Source:
MODERN PHYSICS LETTERS B, 29 (32):10.1142/S0217984915502085 NOV 30 2015
Abstract:
The charge structure factor of the half-filled Hubbard superlattices with one on-site repulsive site and L-0 free sites per unit cell is investigated numerically. The behaviors of charge structure reveal a kind of evenodd L-0 disparity. For even L-0, we always observe a commensurate charge density wave (CDW). For odd L-0, we observe a commensurateincommensurate CDW transition at a critical on-site repulsion around the particlehole symmetric point. This transition results from the competition between the local charge correlations with odd distance and even distance.
Title:
Incommensurate-commensurate magnetic phase transition in SmRu2Al10
Authors:
Takai, S; Matsumura, T; Tanida, H; Sera, M Author Full Names: Takai, Shun; Matsumura, Takeshi; Tanida, Hiroshi; Sera, Masafumi
Source:
PHYSICAL REVIEW B, 92 (17):10.1103/PhysRevB.92.174427 NOV 30 2015
Abstract:
Magnetic properties of single crystalline SmRu2Al10 have been investigated by electrical resistivity, magnetic susceptibility, and specific heat. We have confirmed the successive magnetic phase transitions at T-N = 12.3 K and T-M = 5.6 K. Resonant x-ray diffraction has also been performed to study the magnetic structures. Below TN, the Sm3+ moments order in an incommensurate structure with q(1) = (0,0.759,0). The magnetic moments are oriented along the orthorhombic b axis, which coincides with the magnetization easy axis in the paramagnetic phase. A very weak third harmonic peak is also observed at q(3) = (0,0.278,0). The transition at T-M is a lock-in transition to the commensurate structure described by q(1) = (0,0.75,0). A well-developed third harmonic peak is observed at q(3) = (0,0.25,0). From the discussion of the magnetic structure, we propose that the long-range RKKY interaction plays an important role, in addition to the strong nearest-neighbor antiferromagnetic interaction.
Title:
Microstructure and High Damping Properties of Mg-Zn-Y Alloys Containing LPSO Phase and I Phase
Authors:
Wan, DQ; Li, JJ; Yu, T Author Full Names: Wan Diqing; Li Junjie; Yu Tian
Source:
RARE METAL MATERIALS AND ENGINEERING, 44 (11):2651-2655; NOV 2015
Abstract:
A high damping Mg-Zn-Y alloy containing LPSO phase and I phase was investigated. The microstructure of a high damping Mg80Y4Zn16 (at%) alloy was examined by optical microscopy (OM) and SEM. Furthermore, the differential thermal analysis (DTA) was used to analyze its phase transformation. Microstructure evolution and damping properties under the conditions of the different solid solution time (3, 6, 9 h) were studied. The results show that the main phase component of the Mg80Y4Zn16 alloy is alpha-Mg, Mg12ZnY (X phase), Mg3Zn6Y (I phase) and Mg10ZnY2 phase (LPSO phase), in which I phase and LPSO phase coexistence is firstly reported. The average damping value of the alloy is 0.03, indicating that it is a high damping alloy. The damping is strain amplitude dependent. The high damping mechanism was also discussed.

Update: 17-Dec-2015

Title:
On the adaptability of 1/1 cubic approximant structure in the Mg-Al-Zn system with the particular example of Mg32Al12Zn37
Authors:
Montagne, P; Tillard, M Author Full Names: Montagne, Pierre; Tillard, Monique
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 656 159-165; 10.1016/j.jallcom.2015.09.201 JAN 25 2016
Abstract:
Intermetallic Mg alloys are of interest in the development of light materials with specific properties and some of them are crystalline approximants of quasicrystalline materials. Mg32Al12Zn37 single crystal structure, cubic, Im (3) over bar, a = 14.1845(1) angstrom, is disordered and belongs to the well known 1/1 approximant structural type commonly called Mg-32(Al1-xZnx)(49) or T-phase. In this family, Mg32Al12Zn37 is a new member remarkable for its very special composition nearby intersection of the 2/1 and 1/1 lines that mark composition domains of cubic 2/1 and 1/1 approximants. Structural features are discussed comparatively with literature data to emphasize the great adaptability through atom disorder of the 1/1 structure. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Icosahedral hydrides of the Ti45Zr38Ni17-xCox nano-powders
Authors:
Zywczak, A; Rusinek, D; Czub, J; Sikora, M; Stepien, J; Gondek, L; Gajewska, M; Takasaki, A; Hoser, A Author Full Names: Zywczak, A.; Rusinek, D.; Czub, J.; Sikora, M.; Stepien, J.; Gondek, L.; Gajewska, M.; Takasaki, A.; Hoser, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 656 702-706; 10.1016/j.jallcom.2015.09.278 JAN 25 2016
Abstract:
In this communication we report the phase transitions associated with a hydrogen uptake in the quasicrystalline Ti45Zr38Ni17-xCox alloys that were prepared by mechanical alloying. The crystal structure evolution of the alloys was characterized by means of the variety of diffraction techniques (X-ray, neutron, and electron) as well as extended X-ray absorption fine structure spectroscopy (EXAFS). That analysis was supported by the results of the thermodynamic measurements, namely differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS). According to the neutron diffraction results, the transformation of the amorphous Ti45Zr38Ni17-xCox phases into the quasicrystalline state starts at the temperature of 475 degrees C. At 525 degrees C the icosahedral phase (the i-phase) is well-developed. At higher temperatures the i-phase transforms into the approximant w-phase and eventually into the cubic phase (the c-phase). The investigated icosahedral nano-powders exhibit a high capacity for gaseous H-2 reaching 2.2 wt.% at elevated temperatures. After a hydrogen uptake, a complex phase constitution including the simple hydrides is evidenced. Although the i-phases form again after hydrogen desorption, they are accompanied by the additional Zr3Co phase. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Thermal diffusivity and 3D-XY critical behavior of ferroelectric semiconductors (PbxSn1-x)(2)P2Se6
Authors:
Shvalya, V; Oleaga, A; Salazar, A; Kohutych, AA; Vysochanskii, YM Author Full Names: Shvalya, V.; Oleaga, A.; Salazar, A.; Kohutych, A. A.; Vysochanskii, Yu. M.
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 88 78-84; 10.1016/j.jpcs.2015.10.004 JAN 2016
Abstract:
An ac photopyroelectric calorimeter has been used to study the thermal diffusivity of the ferroelectric semiconductors family (PbxSn1 (-) (x))(2)P2Se6 (x=0-1) from 30 K to room temperature. Phase transitions have been found for x=0, 0.05, 0.2, 0.47 but not for x=1 in the full temperature range. A continuous phase transition has been found for x=0, 0.05, 0.2 and 0.47 which corresponds to the paraelectric commensurate to incommensurate phase. It has been possible to study the critical behavior of this transition for x=0, 0.05 and the critical parameters obtained have been alpha=-0.019, A(+)/A(-)=1.00 and alpha=-0.026, A(+)/A(-) A(-)=1.03, respectively, having fitted at the same time both the low and high temperature branches of the transition as rigorous critical theory indicates; these results agree with the theoretical prediction from renormalization group theory that this kind of transition complies with the 3D-XY universality class (alpha(theor)=-0.014, A(+)/A(-)=1.06), which has been experimentally confirmed only in a few materials. A first order incommensurate to ferroelectric phase transition has been characterized in x=0, 0.05 at lower temperature. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Planar lattices with tailorable coefficient of thermal expansion and high stiffness based on dual-material triangle unit
Authors:
Wei, K; Chen, HS; Pei, YM; Fang, DN Author Full Names: Wei, Kai; Chen, Haosen; Pei, Yongmao; Fang, Daining
Source:
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 86 173-191; 10.1016/j.jmps.2015.10.004 JAN 2016
Abstract:
The unexpected thermal distortions and failures in engineering raise the big concern about thermal expansion controlling. Thus, design of tailorable coefficient of thermal expansion (CTE) is urgently needed for the materials used in large temperature variation circumstance. Here, inspired by multi-fold rotational symmetry in crystallography, we have devised six kinds of periodic planar lattices, which incorporate tailorable CTE and high specific biaxial stiffness. Fabrication process, which overcame shortcomings of welding or adhesion connection, was developed for the dual-material planar lattices. The analytical predictions agreed well with the CTE measurements. It is shown that the planar lattices fabricated from positive CTE constituents, can give large positive, near zero and even negative CIEs. Furthermore, a generalized stationary node method was proposed for aperiodic lattices and even arbitrary structures with desirable thermal expansion. As an example, aperiodic quasicrystal lattices were designed and exhibited zero thermal expansion property. The proposed method for the lattices of lightweight, robust stiffness, strength and tailorable thermal expansion is useful in the engineering applications. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Magnetic structures of R5Ni2In4 and R11Ni4In9 (R = Tb and Ho): strong hierarchy in the temperature dependence of the magnetic ordering in the multiple rare-earth sublattices
Authors:
Ritter, C; Provino, A; Manfrinetti, P; Pecharsky, VK; Gschneidner, KA; Dhar, SK Author Full Names: Ritter, C.; Provino, A.; Manfrinetti, P.; Pecharsky, V. K.; Gschneidner, K. A., Jr.; Dhar, S. K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (47):10.1088/0953-8984/27/47/476001 DEC 2 2015
Abstract:
The magnetic properties and magnetic structures of the R5Ni2In4 and the microfibrous R11Ni4In9 compounds with R = Tb and Ho have been examined using magnetization, heat capacity, and neutron diffraction data. Rare earth atoms occupy three and five symmetrically inequivalent rare earth sites in R5Ni2In4 and R11Ni4In9 compounds, respectively. As a result of the intra-and inter-magnetic sublattice interactions, the magnetic exchange interactions are different for various rare earth sites; this leads to a cascade of magnetic transitions with a strong hierarchy in the temperature dependence of the magnetic orderings. A transition at T-C = 125 K in Tb5Ni2In4 [kappa(1) = (0, 0, 0)] leads to a ferro/ferrimagnetic order where the magnetic ordering in one of the three R-sublattices leads to the ordering of another one; the third sublattice stays non-magnetic. New magnetic Bragg peaks appearing below T-N = 20 K can be indexed with the incommensurate magnetic propagation vector kappa(2) = (0, 0.636, 1/2); at T-N = 20 K a cycloidal spin order, which acts mostly upon the third R-sublattice, occurs. Ho5Ni2In4 establishes first antiferromagnetism [kappa = (0, 0, 0)] at T-N = 31 K on two R-sublattices; then the system becomes ferro/ferrimagnetic at T-C = 25 K with the third sublattice ordering as well. Tb11Ni4In9 has three magnetic transitions at T-C = 135 K, T-N1 = 35 K and at T-N2 = 20 K; they are respectively coupled to the appearance of different propagation vectors [kappa(1) = (0, 0, 0), kappa(2) = (0, 0, 1/2), kappa(3) = (0, 1, 1/2)], which themselves are operating differently on the five different R-sublattices. Two sublattices remain mostly ferromagnetic down to lowest temperature while the three others are predominantly coupled antiferromagnetically. In Ho11Ni4In9 a purely antiferromagnetic order, described by four different magnetic propagation vectors [kappa(1) = (0, 0.62, 0), kappa(2) = (0, 1, 0), kappa(3) = (0, 0, 1/2), kappa(4) = (0, 1, 1/2)], succeedingly includes all five different sublattices on cooling through transitions at T-N1 = 22 K, T-N2 = 12 K, T-N3 = 8 K and T-N4 = 7 K. The strength of the magnetic interactions of the different sublattices can be linked to structural details for both R5Ni2In4 and R11Ni4In9 compounds.
Title:
Spiral magnetism in the single-band Hubbard model: the Hartree-Fock and slave-boson approaches
Authors:
Igoshev, PA; Timirgazin, MA; Gilmutdinov, VF; Arzhnikov, AK; Irkhin, VY Author Full Names: Igoshev, P. A.; Timirgazin, M. A.; Gilmutdinov, V. F.; Arzhnikov, A. K.; Irkhin, V. Yu
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (44):10.1088/0953-8984/27/44/446002 NOV 11 2015
Abstract:
The ground-state magnetic phase diagram is investigated within the single-band Hubbard model for square and different cubic lattices. The results of employing the generalized non-correlated mean-field (Hartree-Fock) approximation and generalized slave-boson approach by Kotliar and Ruckenstein with correlation effects included are compared. We take into account commensurate ferromagnetic, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often lacking in previous investigations. It is found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistically large Hubbard U by the correlation effects if nesting is absent and van Hove singularities are well away from the paramagnetic phase Fermi level. The magnetic phase separation plays an important role in the formation of magnetic states, the corresponding phase regions being especially wide in the vicinity of half-filling. The details of non-collinear and collinear magnetic ordering for different cubic lattices are discussed.
Title:
Quasicrystals at extreme conditions: The role of pressure in stabilizing icosahedral A(163)Cu(24)Fe(13) at high temperature
Authors:
Stagno, V; Bindi, L; Park, CY; Tkachev, S; Prakapenka, VB; Mao, HK; Hemley, RJ; Steinhardt, PJ; Fei, YW Author Full Names: Stagno, Vincenzo; Bindi, Luca; Park, Changyong; Tkachev, Sergey; Prakapenka, Vitali B.; Mao, H. -K.; Hemley, Russell J.; Steinhardt, Paul J.; Fei, Yingwei
Source:
AMERICAN MINERALOGIST, 100 (11-12):2412-2418; 10.2138/am-2015-5412 NOV-DEC 2015
Abstract:
Icosahedrite, the first natural quasicrystal with composition Al63Cu24Fe13, was discovered in several grains of the Khatyrka meteorite, a CV3 carbonaceous chondrite. The presence of icosahedrite associated with high-pressure phases like ahrensite and stishovite indicates formation at high pressures and temperatures due to an impact-induced shock. Previous experimental studies on the stability of synthetic icosahedral AlCuFe have either been limited to ambient pressure, for which they indicate incongruent melting at similar to 1123 K, or limited to room-temperature, for which they indicate structural stability up to about 35 GPa. These data are insufficient to experimentally constrain the formation and stability of icosahedrite under the conditions of high pressure and temperature that formed the Khatyrka meteorite. Here we present the results of room-temperature, high-pressure diamond-anvil cells measurements of the compressional behavior of synthetic icosahedrite up to 50 GPa. High P-T experiments were also carried out using both laser-heated diamond-anvil cells combined with in situ synchrotron X-ray diffraction (at 42 GPa) and multi-anvil apparatus (at 21 GPa) to investigate the structural evolution and crystallization of possible coexisting phases. The results demonstrate that the quasiperiodic order of icosahedrite is retained over the P-T range explored. We find that pressure acts to stabilize the icosahedral symmetry at temperatures much higher than previously reported. Direct solidification of AlCuFe quasicrystals from an unusual Al-Cu-rich melt is possible but it is limited to a narrow temperature range. Alternatively, quasicrystals may form after crystallization through solid-solid reactions of Al-rich phases. In either case, our results show that quasicrystals can preserve their structure even after hypervelocity impacts spanning a broad range of pressures and temperatures.
Title:
New horizon in quasicrystals
Authors:
Samavat, F; Kiani, M Author Full Names: Samavat, F.; Kiani, M.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (6):935-938; 10.1134/S1063774515060280 NOV 2015
Abstract:
Quasicrystals (QCs) are aperiodic intermetallic alloys that possess a long range positional order. They often exhibit crystallographically forbidden symmetries, most commonly fivefold and tenfold. The forbidden symmetry is related to the fact that the atoms are arranged quasiperiodically. Quasiperiodic translational order has physical consequences. For example, since electrons and phonons in quasicrystals do not encounter a periodic potential, quasicrystals have unusual resistive and elastic properties, and these have been exploited in several applications. The purpose of this introduction is to present certain properties that are relevant to the surface science of quasicrystals, as a launching point for the other articles in this special issue of progress in surface science.
Title:
Penrose tilings as model sets
Authors:
Shutov, AV; Maleev, AV Author Full Names: Shutov, A. V.; Maleev, A. V.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (6):797-804; 10.1134/S1063774515060322 NOV 2015
Abstract:
The Baake construction, based on generating a set of vertices of Penrose tilings as a model set, is refined. An algorithm and a corresponding computer program for constructing an uncountable set of locally indistinguishable Penrose tilings are developed proceeding from this refined construction. Based on an analysis of the parameters of tiling vertices, 62 versions of rhomb combinations at the tiling center are determined. The combinatorial structure of Penrose tiling worms is established. A concept of flip transformations of tilings is introduced that makes it possible to construct Penrose tilings that cannot be implemented in the Baake construction.
Title:
Birefringence of mechanically stressed Rb2ZnCl4 crystals
Authors:
Kurlyak, VY; Stadnyk, VY; Stakhura, VB; Kohut, ZO Author Full Names: Kurlyak, V. Yu.; Stadnyk, V. Yo.; Stakhura, V. B.; Kohut, Z. O.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (6):929-934; 10.1134/S1063774515060164 NOV 2015
Abstract:
The spectral and temperature dependences of the birefringence of mechanically free and uniaxially stressed Rb2ZnCl4 crystals have been investigated. It is shown that annealing a crystal leads to step changes in the birefringence at the phase transition from the incommensurate to commensurate phase, whereas the birefringence of as-prepared crystals changes continuously. It is established that the birefringence of Rb2ZnCl4 crystal is sensitive to uniaxial pressure; however, uniaxial stress does not change the character of its dispersion and temperature dependences. A new "pseudoisotropic" state of this crystal and a baric shift of the points of paraelectric phase-incommensurate phase-commensurate phase transitions to different temperature regions are found.
Title:
Refinement of Thermodynamic Parameters of the Mg24Y5, W and H Phases in the Mg-Zn-Y System
Authors:
Minamoto, S; Horiuchi, T; Miura, S Author Full Names: Minamoto, Satoshi; Horiuchi, Toshiaki; Miura, Seiji
Source:
MATERIALS TRANSACTIONS, 56 (10):60-64; 10.2320/matertrans.MH201418 OCT 2015
Abstract:
The Mg-Zn-Y alloy shows excellent mechanical properties which can be achieved by combining LPSO phase (known as X phase) and an icosahedral quasicrystal phase (land Z phases) in Mg solid solution (a phase). Thermodynamic data for the binary/ternary compounds Mg24Y5, X, Wand H have to be critically assessed to obtain accurate information of three-phase equilibrium in order to understand equilibria among these phases. In this research, we focused on developing CALPHAD (CALculation of PHAse Diagrams) thermodynamic database to evaluate phase diagrams for the Mg-Zn-Y system. Especially thermodynamic models for the Mg24Y5, W and H phases have been determined based on crystallographic data. Then thermodynamic parameters have been assessed to yield experimental data from EPMA/WDS, SEM, TEM and X-Ray diffraction.
Title:
Dielectric Properties and Phase Diagram of (Sr1-xBax)(2)Nb2O7 Single Crystals
Authors:
Akishige, Y; Kamata, M; Tsukada, S Author Full Names: Akishige, Yukikuni; Kamata, Misako; Tsukada, Shinya
Source:
FERROELECTRICS, 485 (1):73-79; SI 10.1080/00150193.2015.1060832 AUG 26 2015
Abstract:
Dielectric constants, epsilon(b) and epsilon(c) along the crystallographic b and c axes respectively, were measured in a temperature range of 10 - 700K on Ba-substituted Sr2Nb2O7 single crystals with different Ba concentrations up to x = 0.32. When x = 0, two dielectric anomalies were observed at T-I = 489K and at T-L = 100K, owing to the incommensurate phase transition and the low-temperature ferroelectric phase transition, respectively. Both T-I and T-L decrease with Ba-content x at initial slopes of ca. -19 and -37K/mol%, respectively, and become broad at x = 0.04 and almost disappear at x = 0.08. Furthermore, Ba-substitution induces a weak and broad dielectric maximum in epsilon(b)' vs. T curve at approximately T-m = 465K for x > 0.2. Phase diagram of this system was proposed.

Update: 10-Dec-2015

Title:
Smearing-type wear behavior of Al62Cu25.5Fe12.5 quasicrystal abrasive on soft metals
Authors:
Chen, YJ; Qiang, JB; Dong, C Author Full Names: Chen, Yongjun; Qiang, Jianbin; Dong, Chuang
Source:
INTERMETALLICS, 68 23-30; 10.1016/j.intermet.2015.09.001 JAN 2016
Abstract:
The abrasive polishing behavior of Al62Cu25.5Fe12.5 quasicrystal on Cu, Al and austenite stainless steel alloys were investigated, to compare with commonly used hard abrasives such as diamond, alumina and silica. The quasicrystal abrasive showed a dominating smearing-type wear mechanism, in sharp contrast to all the other three abrasives, as reflected by large indent size shrinking with respect to surface removal depth. The quasicrystal abrasive polishing, producing a flattened surface with minor depth removal, may open new application fields where low-wearing and fine surface finishing are demanded. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
X-ray diffraction study of the icosahedral AlCuFe quasicrystal at megabar pressures
Authors:
Takagi, S; Kyono, A; Mitani, S; Sugano, N; Nakamoto, Y; Hirao, N Author Full Names: Takagi, Sota; Kyono, Atsushi; Mitani, Saki; Sugano, Neo; Nakamoto, Yuki; Hirao, Naohisa
Source:
MATERIALS LETTERS, 161 13-16; 10.1016/j.matlet.2015.08.057 DEC 15 2015
Abstract:
We report in-situ synchrotron X-ray diffraction study of icosahedral (i)-AlCuFe quasicrystal (QC) at high pressure up to 104 GPa under ambient temperature using the diamond anvil technique. With compression, there is no obvious change of the diffraction pattern within the measured pressure range. Five characteristic peaks from the i-AlCuFe QC maintain up to 104 GPa. The unit cell volume of the i-AlCuFe QC decreases monotonously until 72 GPa. The experimental P-V compression curve below 72 GPa was fitted to the Birch-Murnaghan equation of state with V-0=2023(19) angstrom(3), K-0=131(7) GPa, K'=4.0 (fixed). The resulting EoS parameters are approximately consistent with those observed in previous study. A discontinuous volume change is observed between 72 and 75 GPa. These observed results indicate a phase transition from i-AlCuFe QC to an approximant crystal (AC) which has a similar local atomic arrangement as the QC. This study suggests that i-AlCuFe QC maintains its structure at least up to 72 GPa and then transforms to AC with small displacement of atoms. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Ni coated Ti1.4V0.6Ni composite as the negative electrode in Ni-MH battery
Authors:
Sun, LS; Lin, J; Liang, F; Cao, ZY; Wang, LM Author Full Names: Sun, Lianshan; Lin, Jing; Liang, Fei; Cao, Zhanyi; Wang, Limin
Source:
MATERIALS LETTERS, 161 686-689; 10.1016/j.matlet.2015.09.081 DEC 15 2015
Abstract:
Ti1.4V0.6Ni composite is synthesized by arc-melting and subsequent melt-spinning techniques. An improved electrochemical stability of Ti14V0.6Ni composite is obtained by chemical plating Ni. The phase structures of the composite contain icosahedral quasicrystal phase (i-phase) and TiNi-type phase. Different amount of Ni is coated on the surface of the composite particles. When Ti14V0.6Ni is plated with 19 wt% Ni, the discharge capacity retention ratio is promoted. Ni coating layer inhibits the dissolution of V from the composite and also promotes the high rate discharge property. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Antiphase Boundaries in the Turbostratically Disordered Misfit Compound (BiSe)(1+delta)NbSe2
Authors:
Mitchson, G; Falmbigl, M; Ditto, J; Johnson, DC Author Full Names: Mitchson, Gavin; Falmbigl, Matthias; Ditto, Jeffrey; Johnson, David C.
Source:
INORGANIC CHEMISTRY, 54 (21):10309-10315; 10.1021/acs.inorgchem.5b01648 NOV 2 2015
Abstract:
(BiSe)(1+delta)NbSe2 ferecrystals were synthesized in order to determine whether structural modulation in BiSe layers, characterized by periodic antiphase boundaries and Bi-Bi bonding, occurs. Specular X-ray diffraction revealed the formation of the desired compound with a c-axis lattice parameter of 1.21 nm from precursors with a range of initial compositions and initial periodicities. In-plane X-ray diffraction scans could be indexed as hk0 reflections of the constituents, with a rectangular basal BiSe lattice and a trigonal basal NbSe2 lattice. Electron micrographs showed extensive turbostratic disorder in the samples and the presence of periodic antiphase boundaries (approximately 1.5 nm periodicity) in BiSe layers oriented with the [110] direction parallel to the zone axis of the microscope. This indicates that the structural modulation in the BiSe layers is not due to coherency strain resulting from commensurate in-plane lattices. Electrical transport measurements indicate that holes are the dominant charge carrying species, that there is a weak decrease in resistivity as temperature decreases, and that minimal charge transfer occurs from the BiSe to NbSe2 layers. This is consistent with the lack of charge transfer from the BiX to the TX2 layers reported in misfit layer compounds where antiphase boundaries were observed. This suggests that electronic considerations, i.e., localization of electrons in the Bi-Bi pairs at the antiphase boundaries, play a dominant role in stabilizing the structural modulation.
Title:
Unravelling structural ambiguities in lithium- and manganese-rich transition metal oxides
Authors:
Shukla, AK; Ramasse, QM; Ophus, C; Duncan, H; Hage, F; Chen, GY Author Full Names: Shukla, Alpesh Khushalchand; Ramasse, Quentin M.; Ophus, Colin; Duncan, Hugues; Hage, Fredrik; Chen, Guoying
Source:
NATURE COMMUNICATIONS, 6 10.1038/ncomms9711 OCT 2015
Abstract:
Although Li- and Mn-rich transition metal oxides have been extensively studied as high-capacity cathode materials for Li-ion batteries, the crystal structure of these materials in their pristine state is not yet fully understood. Here we apply complementary electron microscopy and spectroscopy techniques at multi-length scale on well-formed Li-1.2(Ni0.13Mn0.54Co0.13)O-2 crystals with two different morphologies as well as two commercially available materials with similar compositions, and unambiguously describe the structural make-up of these samples. Systematically observing the entire primary particles along multiple zone axes reveals that they are consistently made up of a single phase, save for rare localized defects and a thin surface layer on certain crystallographic facets. More specifically, we show the bulk of the oxides can be described as an aperiodic crystal consisting of randomly stacked domains that correspond to three variants of monoclinic structure, while the surface is composed of a Co- and/or Ni-rich spinel with antisite defects.
Title:
Fermi states and anisotropy of Brillouin zone scattering in the decagonal Al-Ni-Co quasicrystal
Authors:
Rogalev, VA; Groning, O; Widmer, R; Dil, JH; Bisti, F; Lev, LL; Schmitt, T; Strocov, VN Author Full Names: Rogalev, V. A.; Groening, O.; Widmer, R.; Dil, J. H.; Bisti, F.; Lev, L. L.; Schmitt, T.; Strocov, V. N.
Source:
NATURE COMMUNICATIONS, 6 10.1038/ncomms9607 OCT 2015
Abstract:
Quasicrystals (QCs) are intermetallic alloys that have excellent long-range order but lack translational symmetry in at least one dimension. The valence band electronic structure near the Fermi energy E-F in such materials is of special interest since it has a direct relation to their unusual physical properties. However, the Fermi surface (FS) topology as well as the mechanism of QC structure stabilization are still under debate. Here we report the first observation of the three-dimensional FS and valence band dispersions near E-F in decagonal Al70Ni20Co10 (d-AlNiCo) QCs using soft X-ray angle-resolved photoemission spectroscopy. We show that the FS, formed by dispersive Al sp-states, has a multicomponent character due to a large contribution from high-order bands. Moreover, we discover that the magnitude of the gap at the FS related to the interaction with Brillouin zone boundary (Hume-Rothery gap) critically differs for the periodic and quasiperiodic directions.

Update: 3-Dec-2015

Title:
Microstructure and mechanical properties of laser beam welded Al-Li alloy 2060 with Al-Mg filler wire
Authors:
Zhang, XY; Yang, WX; Xiao, RS Author Full Names: Zhang, Xinyi; Yang, Wuxiong; Xiao, Rongshi
Source:
MATERIALS & DESIGN, 88 446-450; 10.1016/j.matdes.2015.08.144 DEC 25 2015
Abstract:
Alloy 2060-T8 is a newly developed high-strength Al-Li alloy for applications in aircraft industry. Crack-free welds were obtained in laser beam welding with 5087 filler wire under optimized welding conditions. In this paper, fusion zone microstructure and joint mechanical properties were investigated. Microstructure typical for the weld metal consists of alpha-Al matrix with a few nanoscale precipitates inside and a coarse icosahedral quasi-crystalline T-2 phase at the dendritic and grain boundaries. The quasicrystalline occurred normally in Al-Li-Cu alloys with higher Li contents. Our investigations show that the icosahedral quasicrystalline phase T-2 phase forms in the laser-welded Al-Li alloy 2060 with lower Li content as a result of segregation and replacement of Mg element. The joint tensile strength in as-welded condition is around 317 MPa, about 63% of that of the base metal, and fracture occurs within the fusion zone. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Explosively welded multilayer Ni-Al composites
Authors:
Bataev, IA; Ogneva, TS; Bataev, AA; Mali, VI; Esikov, MA; Lazurenko, DV; Guo, Y; Jorge, AM Author Full Names: Bataev, I. A.; Ogneva, T. S.; Bataev, A. A.; Mali, V. I.; Esikov, M. A.; Lazurenko, D. V.; Guo, Y.; Jorge Junior, A. M.
Source:
MATERIALS & DESIGN, 88 1082-1087; 10.1016/j.matdes.2015.09.103 DEC 25 2015
Abstract:
In this study, the structure of explosively welded Ni-Al multilayer composites was investigated. In particular, the interface between Ni and Al plates was studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). Continuous interlayers of mixed Al and Ni were found at the interface. The Al and Ni in these zones were heated above their melting temperatures, non-uniformly mixed, and rapidly solidified. Several intermetallic phases, including the decagonal phase and metastable Al9Ni2, were observed in these zones using electron diffraction. A cellular dislocation structure formed in the Ni plates and a polygonized dislocation structure formed in the Al plates due to the extremely high strain rate deformation and heating. Subsequent heat treatment at 620 degrees C led to the rapid formation of stable intermetallic layers at the interfaces. The growth of the intermetallic layers was considerably faster in the explosively welded composite than in the reference sample. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Effect of icosahedral phase on the crystallographic texture and mechanical anisotropy of duplex structured Mg-Li alloys
Authors:
Xu, DK; Li, CQ; Wang, BJ; Han, EH Author Full Names: Xu, D. K.; Li, C. Q.; Wang, B. J.; Han, E. H.
Source:
MATERIALS & DESIGN, 88 88-97; 10.1016/j.matdes.2015.08.123 DEC 25 2015
Abstract:
Through comparing the microstructure and mechanical properties of Mg-6%Li and Mg-6%Li-6%Zn-1.2%Y alloys, the difference in their mechanical anisotropy have been deeply investigated. Due to the formation of I-phase (Mg3Zn6Y, icosohedral structure), the volume fraction of beta-Li phases formed in Mg-6%Li-6%Zn-1.2%Y alloy was two times higher than that in Mg-6%Li alloy even these two alloys having the same Li content. Texture analysis demonstrated that I-phase particle stimulated nucleation of recrystallization (PSN) and the formation of higher volume fraction of beta-Li phases can remarkably weaken the basal texture of alpha-Mg phases, resulting in a very weak mechanical anisotropy. On the contrary, the basal texture of the alpha-Mg phases in Mg-6%Li alloy was quite strong and obvious mechanical anisotropy between differently oriented samples can be observed. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Phase Formation in the Rapidly Solidified Al70-xGaxPd13Mn17 Alloys
Authors:
Yadav, TP; Shaz, MA; Mukhopadhyay, NK; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Shaz, M. A.; Mukhopadhyay, N. K.; Tiwari, R. S.; Srivastava, O. N.
Source:
TRANSACTIONS OF THE INDIAN INSTITUTE OF METALS, 68 (6):1145-1149; 10.1007/s12666-015-0660-3 DEC 2015
Abstract:
In the present investigation, the effect of Ga substitution at Al site on the phase formation and stabilization of decagonal quasicrystalline phase in the rapidly solidified Al70-xGaxPd13Mn17 alloys have been studied by employing X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive x-ray analysis. The as-cast and rapidly solidified alloys with x = 0, 2.5 and 5 have been investigated. The melt-spinning technique has been used for rapid solidification of the as-cast alloys. The alloys up to 5 at.% Ga exhibit the formation of small amount of icosahedral quasicrystalline phases along with major amount of decagonal phase in the rapidly solidied ribbons. The energy dispersive X-ray analysis investigations suggest the homogeneous presence of Ga in the quasicrystalline alloys.
Title:
Three-dimensional charge density wave order in YBa2Cu3O6.67 at high magnetic fields
Authors:
Gerber, S; Jang, H; Nojiri, H; Matsuzawa, S; Yasumura, H; Bonn, DA; Liang, R; Hardy, WN; Islam, Z; Mehta, A; Song, S; Sikorski, M; Stefanescu, D; Feng, Y; Kivelson, SA; Devereaux, TP; Shen, ZX; Kao, CC; Lee, WS; Zhu, D; Lee, JS Author Full Names: Gerber, S.; Jang, H.; Nojiri, H.; Matsuzawa, S.; Yasumura, H.; Bonn, D. A.; Liang, R.; Hardy, W. N.; Islam, Z.; Mehta, A.; Song, S.; Sikorski, M.; Stefanescu, D.; Feng, Y.; Kivelson, S. A.; Devereaux, T. P.; Shen, Z. -X.; Kao, C. -C.; Lee, W. -S.; Zhu, D.; Lee, J. -S.
Source:
SCIENCE, 350 (6263):949-952; 10.1126/science.aac6257 NOV 20 2015
Abstract:
Charge density wave (CDW) correlations have been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured with x-ray scattering at zero and low fields. We combined a pulsed magnet with an x-ray free-electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields of up to 28 tesla. While the zero-field CDW order, which develops at temperatures below similar to 150 kelvin, is essentially two dimensional, at lower temperature and beyond 15 tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW appears around the zero-field superconducting transition temperature; in contrast, the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.
Title:
Tuning of magnetic ordering by Y substitution onto Tb site in the nanocrystalline TbMnO3
Authors:
Chakraborty, KR; Shukla, R; Kaushik, SD; Mukadam, MD; Siruguri, V; Tyagi, AK; Yusuf, SM Author Full Names: Chakraborty, Keka R.; Shukla, Rakesh; Kaushik, S. D.; Mukadam, M. D.; Siruguri, V.; Tyagi, A. K.; Yusuf, S. M.
Source:
JOURNAL OF APPLIED PHYSICS, 118 (16):10.1063/1.4934251 OCT 28 2015
Abstract:
We report the magnetic properties, of nano-crystalline powders Tb1-xYxMnO3 (x = 0, 0.1, 0.2, 0.3 and 0.4), as perceived by neutron diffraction, and elucidate the effect of Tb site substitution on the magnetic structure of TbMnO3. All samples crystallized in the orthorhombic structure conforming to space group Pnma, and exhibited an incommensurate collinear antiferromagnetic ordering of the Mn ions below similar to 40 K. Furthermore, at T <= 20 K, all these samples showed a change in magnetic structure (of Mn moments) to a spiral ordering down to 2K, the lowest measured temperature. For the samples with x = 0, 0.1, and 0.2, a short-ranged two dimensional (2D) ordering of Tb moments was also observed at 2K. However, for the other samples (x-0.3 and 0.4), no magnetic ordering of Tb moments was found down to 2K. So with Y substitution, a crossover from 2D ordering to a disordering of Tb moments was observed. The moments at the Mn site were found to be lower than the full Mn3+(4 mu B) moment for all the samples below 40 K. The magnetic properties of all the samples studied by us in nano form are more pronounced than those of the reported single crystals of same compositions [V. Yu. Ivanov et al., JETP Lett. 91, 392-397 (2010)]. (C) 2015 AIP Publishing LLC.
Title:
Exchange integrals of commensurate and incommensurate structures of MFe4Al8 (M = U, Sc)
Authors:
Recko, K Author Full Names: Recko, K.
Source:
JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17 (9-10):1403-1409; SEP-OCT 2015
Abstract:
The appearance of the commensurability of UFe4Al8 alloy considering incommensurability of ScFe4Al8 compound is analysed on the basis of Heisenberg Hamiltonian. The influence of Dzyaloshinskii - Moriya and Ruderman-Kittel-Kasuya-Yoshida as well as the dipolar interactions as the main reasons of the noncollinearity and incommensurability of the alloys belonging to ThMn12 family is investigated. The values and directions of the spin ordering found by magnetic diffraction are compared to that one's deriving from grand state configurations obtained by a simulated annealing algorithm. The lock-in magnetic modulations due to substitution of scandium by uranium atoms is discussed based on an appropriate exchange constants ratios.
Title:
The Incommensurate Phase Transformation in TlInS2 Ferroelectric
Authors:
Salnik, A; Gololobov, YP; Borovoy, NA Author Full Names: Salnik, A.; Gololobov, Yu. P.; Borovoy, N. A.
Source:
FERROELECTRICS, 484 (1):62-68; SI 10.1080/00150193.2015.1059716 AUG 5 2015
Abstract:
The features of the crystal structure of c and 2c TlInS2 polytypes have been studied by single-crystal X-ray diffraction method in the temperature range 180 K-300 K. In the c polytype the appearance of the incommensurate phase with modulation vector q. d; 0; 0: 25/. dD0: 04/was observed at the temperature of 238 K (on cooling). The active phase formation occurred between 213 K and 217 K. The incommensurability parameter d decreases monotonically to the zero as the temperature approaches 195 K. For the 2c polytype the modulation satellites for both incommensurate and commensurate phases were not observed in the temperature range 180 K-300 K.

Update: 26-Nov-2015

Title:
Superconductivity in the orthorhombic phase of thermoelectric CsPbxBi4-xTe6 with 0.3 <= x <= 1.0
Authors:
Zhang, RX; Yang, HX; Tian, HF; Chen, GF; Wu, SL; Wei, LL; Li, JQ Author Full Names: Zhang, R. X.; Yang, H. X.; Tian, H. F.; Chen, G. F.; Wu, S. L.; Wei, L. L.; Li, J. Q.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 232 50-55; 10.1016/j.jssc.2015.08.050 DEC 2015
Abstract:
Experimental measurements clearly reveal the presence of bulk superconductivity in the CsPbxBi4-xTe6 (0.3 <= x <= 1.0) materials, i.e. the first member of the thermoelectric series of Cs[PbmBi3Te5+m], these materials have the layered orthorhombic structure containing infinite anionic [PbBi3Te6]- slabs separated with Cs+ cations. Temperature dependences of electrical resistivity, magnetic susceptibility, and specific heat have consistently demonstrated that the superconducting transition in Cs0.96Pb0.25Bi3.75Te6.04 occurs at T-c=3.1 K, with a superconducting volume fraction close to 100% at 1.8 K. Structural study using aberration-corrected STEM/TEM reveals a rich variety of microstructural phenomena in correlation with the Pb-ordering and chemical inhomogeneity. The superconducting material CS0.96Pb0.25Bi3.75Te6.04 with the highest T-c shows a clear ordered structure with a modulation wave vector of q approximate to a*/2+c*/1.35 on the a-c plane. Our study evidently demonstrates that superconductivity deriving upon doping of narrow-gap semiconductor is a viable approach for exploration of novel superconductors. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Phason space analysis and structure modelling of 100 angstrom-scale dodecagonal quasicrystal in Mn-based alloy
Authors:
Ishimasa, T; Iwami, S; Sakaguchi, N; Oota, R; Mihalkovic, M Author Full Names: Ishimasa, Tsutomu; Iwami, Shuhei; Sakaguchi, Norihito; Oota, Ryo; Mihalkovic, Marek
Source:
PHILOSOPHICAL MAGAZINE, 95 (33):3745-3767; 10.1080/14786435.2015.1095365 NOV 22 2015
Abstract:
The dodecagonal quasicrystal classified into the five-dimensional space group P12(6)/mmc, recently discovered in a Mn-Cr-Ni-Si alloy, has been analysed using atomic-resolution spherical aberration-corrected electron microscopy, i.e. high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and conventional transmission electron microscopy. By observing along the 12-fold axis, non-periodic tiling consisting of an equilateral triangle and a square has been revealed, of which common edge length is a=4.560 angstrom. These tiles tend to form a network of dodecagons of which size is (2+root 3)a approximate to 17 angstrom in diameter. The tiling was interpreted as an aggregate of 100 angstrom-scale oriented domains of high- and low-quality quasicrystals with small crystallites appearing at their boundaries. The quasicrystal domains exhibited a densely filled circular acceptance region in the phason space. This is the first observation of the acceptance region in an actual dodecagonal quasicrystal. Atomic structure model consistent with the electron microscopy images is a standard Frank-Kasper decoration of the triangle and square tiles that can be inferred from the crystal structures of Zr4Al3 and Cr3Si. Four kinds of layers located at z = 0, +/- 1/4 and 1/2 are stacked periodically along the 12-fold axis, and the atoms at z = 0 and 1/2 form hexagonal anti-prisms consistently with the 12(6)-screw axis. The validity of this structure model was examined by means of powder X-ray diffraction.
Title:
Effect of Ca and CaO on the microstructure and hot compressive deformation behavior of Mg-9.5Zn-2.0Y alloy
Authors:
Kwak, TY; Lim, HK; Kim, WJ Author Full Names: Kwak, T. Y.; Lim, H. K.; Kim, W. J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 648 146-156; 10.1016/j.msea.2015.09.014 NOV 11 2015
Abstract:
In this study, the effect of adding 0.3 wt% Ca to a Mg-9.5Zn-2.0Y alloy with icosahedral (I) phase (Mg3Zn6Y) was examined. The Ca alloying was done by two different routes, either through a master alloy produced with Mg and CaO (which is convenient from the points of view of safety and cost) or by direct addition of powdered Ca to the molten alloy. The small addition of Ca (CaO) effectively increased the ignition temperature of the alloys (by about 90 K), which is promising for fire suppression and safe handling with the molten alloys, but it led to the formation of Ca2Mg5Zn13 phase at grain boundaries or interdendritic interfaces, causing partial melting and intergranular cracking during compressive deformation near similar to 615 K. As a result, the upper limit of hot workability temperature decreased to 598 K, which is lower than that of the Mg-9.5Zn-2.0Y alloy by 125 K. The cast Mg-9.5Zn-2.0Y-03Ca alloys prepared using the two different routes exhibited high similarity in ignition temperature, chemical composition, microstructure, hot compressive behaviors and processing maps, indicating that the use of CaO is as effective as the use of Ca in producing the same quality of Ca containing Mg alloys. The flow stresses during hot compressive deformation and the activation energy for plastic flow remained unaffected by the Ca (CaO) alloying, but decreased the strain rate sensitivity at high strain rates over 10(-3) s(-1) due to the initiation of either power-law breakdown or partial melting by adiabatic heating. Because of this, the Ca containing alloy lost hot workability at high strain rates by comparison to the Ca-free alloy. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Incommensurateness in nanotwinning models of modulated martensites
Authors:
Benesova, B; Frost, M; Kampschulte, M; Melcher, C; Sedlak, P; Seiner, H Author Full Names: Benesova, Barbora; Frost, Miroslav; Kampschulte, Malte; Melcher, Christof; Sedlak, Petr; Seiner, Hanus
Source:
PHYSICAL REVIEW B, 92 (18):10.1103/PhysRevB.92.180101 NOV 6 2015
Abstract:
We study the formation of modulated martensites in ferromagnetic shape memory alloys by a mathematical model originating from the nanotwinning concept. The results show that the incommensurateness, systematically observed in experiments for the modulated phases, may be understood as a precursor effect of the intermartensitic transitions, and its appearance does not contradict the nanotwinning concept itself. The model sufficiently explains the different levels of incommensurateness reported from different experimental observations for the 14-layered and 10-layered martensites of the Ni-Mn-Ga alloy and outlines the mechanism of formation of faults in the stacking sequences of these materials.
Title:
Quantum phase transitions and decoupling of magnetic sublattices in the quasi-two-dimensional Ising magnet Co3V2O8 in a transverse magnetic field
Authors:
Fritsch, K; Ehlers, G; Rule, KC; Habicht, K; Ramazanoglu, M; Dabkowska, HA; Gaulin, BD Author Full Names: Fritsch, K.; Ehlers, G.; Rule, K. C.; Habicht, K.; Ramazanoglu, M.; Dabkowska, H. A.; Gaulin, B. D.
Source:
PHYSICAL REVIEW B, 92 (18):10.1103/PhysRevB.92.180404 NOV 5 2015
Abstract:
The application of a magnetic field transverse to the easy axis, Ising direction in the quasi-two-dimensional kagome staircase magnet, Co3V2O8, induces three quantum phase transitions at low temperatures, ultimately producing a novel high field polarized state, with two distinct sublattices. New time-of-flight neutron scattering techniques, accompanied by large angular access, high magnetic field infrastructure allow the mapping of a sequence of ferromagnetic and incommensurate phases and their accompanying spin excitations. At least one of the transitions to incommensurate phases at mu H-0(c1) similar to 6.25 T and mu H-0(c2) similar to 7 T is discontinuous, while the final quantum critical point at mu H-0(c3) similar to 13 T is continuous.
Title:
Fluctuating orders and quenched randomness in the cuprates
Authors:
Nie, LM; Sierens, LEH; Melko, RG; Sachdev, S; Kivelson, SA Author Full Names: Nie, Laimei; Sierens, Lauren E. Hayward; Melko, Roger G.; Sachdev, Subir; Kivelson, Steven A.
Source:
PHYSICAL REVIEW B, 92 (17):10.1103/PhysRevB.92.174505 NOV 4 2015
Abstract:
We study a quasi-two-dimensional classical Landau-Ginzburg-Wilson effective field theory in the presence of quenched disorder in which incommensurate charge-density wave and superconducting orders are intertwined. The disorder precludes long-range charge-density wave order, but not superconducting or nematic order. We select three representative sets of input parameters and compute the corresponding charge-density wave structure factors using both large-N techniques and classical Monte Carlo simulations. Where nematicity and superconductivity coexist at low temperature, the peak height of the charge-density wave structure factor decreases monotonically as a function of increasing temperature, unlike what is seen in x-ray experiments on YBa2Cu3O6+x. Conversely, where the thermal evolution of the charge-density wave structure factor qualitatively agrees with experiments, the nematic correlation length, computed to one-loop order, is shorter than the charge-density wave correlation length.
Title:
Symmetries and color symmetries of a family of tilings with a singular point
Authors:
Evidente, IF; Felix, RP; Loquias, MJC Author Full Names: Evidente, Imogene F.; Felix, Rene P.; Loquias, Manuel Joseph C.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 583-591; 10.1107/S2053273315016137 6 NOV 2015
Abstract:
Tilings with a singular point are obtained by applying conformal maps on regular tilings of the Euclidean plane and their symmetries are determined. The resulting tilings are then symmetrically colored by applying the same conformal maps on colorings of regular tilings arising from sublattice colorings of the centers of the tiles. In addition, conditions are determined in order that the coloring of a tiling with singularity that is obtained in this manner is perfect.
Title:
Unusual Strong Incommensurate Modulation in a Tungsten-Bronze-Type Relaxor PbBiNb5O15
Authors:
Lin, K; Zhou, ZY; Liu, LJ; Ma, HQ; Chen, J; Deng, JX; Sun, JL; You, L; Kasai, H; Kato, K; Takata, M; Xing, XR Author Full Names: Lin, Kun; Zhou, Zhengyang; Liu, Laijun; Ma, Hongqiang; Chen, Jun; Deng, Jinxia; Sun, Junliang; You, Li; Kasai, Hidetaka; Kato, Kenichi; Takata, Masaki; Xing, Xianran
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137 (42):13468-13471; 10.1021/jacs.5b08230 OCT 28 2015
Abstract:
Pb- or Bi-based perovskite oxides have been widely studied and used because of their large ferroelectric polarization features induced by stereochemically active 6s(2) lone pair electrons. It is intriguing whether this effect could exist in other related systems. Herein, we designed and synthesized a mixed Pb and Bi A site polar compound, PbBiNb5O15, with the TTB framework. The as-synthesized material turns out to be a relaxor with weak macroscopic ferroelectricity but adopts strong local polarizations. What's more, unusual five orders of incommensurate satellite reflections with strong intensities were observed under the electron diffraction, suggesting that the modulation is highly developed with large amplitudes. The structural modulation was solved with a (3 + 1)D superspace group using high-resolution synchrotron radiation combined with anomalous dispersion X-ray diffraction technique to distinguish Pb from Bi. We show that the strong modulation mainly originates from lone-pair driven Pb2+-Bi3+ ordering in the large pentagonal caves, which can suppress the local polarization in x-y plane in long ranges. Moreover, the as-synthesized ceramics display strong relaxor ferroelectric feature with transition temperature near room temperature and moderate dielectric properties, which could be functionalized to be electromechanical device materials.
Title:
On the stability of a quasicrystal and its crystalline approximant in a system of hard disks with a soft corona
Authors:
Pattabhiraman, H; Gantapara, AP; Dijkstra, M Author Full Names: Pattabhiraman, Harini; Gantapara, Anjan P.; Dijkstra, Marjolein
Source:
JOURNAL OF CHEMICAL PHYSICS, 143 (16):10.1063/1.4934499 OCT 28 2015
Abstract:
Using computer simulations, we study the phase behavior of a model system of colloidal hard disks with a diameter sigma and a soft corona of width 1.4 sigma. The particles interact with a hard core and a repulsive square-shoulder potential. We calculate the free energy of the random-tiling quasicrystal and its crystalline approximants using the Frenkel-Ladd method. We explicitly account for the configurational entropy associated with the number of distinct configurations of the random-tiling quasicrystal. We map out the phase diagram and find that the random tiling dodecagonal quasicrystal is stabilised by entropy at finite temperatures with respect to the crystalline approximants that we considered, and its stability region seems to extend to zero temperature as the energies of the defect-free quasicrystal and the crystalline approximants are equal within our statistical accuracy. (C) 2015 AIP Publishing LLC.
Title:
Corrosion Behavior of Psi and beta Quasicrystalline Al-Cu-Fe Alloy
Authors:
Torres, A; Serna, S; Patino, C; Rosas, G Author Full Names: Torres, Alvaro; Serna, Sergio; Patino, Cristobal; Rosas, Gerardo
Source:
ACTA METALLURGICA SINICA-ENGLISH LETTERS, 28 (9):1117-1122; 10.1007/s40195-015-0302-0 SEP 2015
Abstract:
Two nanostructured Al-Cu-Fe alloys, Al64Cu24Fe12 and Al62.5Cu25.2Fe12.3, have been studied. Icosahedral quasicrystalline (psi) Al64Cu24Fe12 and crystalline cubic (beta) Al62.5Cu25.2Fe12.3 cylindrical ingots were first produced using normal casting techniques. High-energy mechanical milling was then conducted to obtain psi icosahedral and beta intermetallic nanostructured powders. Electrochemical impedance spectroscopy, linear polarization resistance, and potentiodynamic polarization were used to investigate the electrochemical corrosion characteristics of the powders in solutions with different pH values. Current density (i(corr)), polarization resistance (R-p), and impedance modulus (vertical bar Z vertical bar) were determined. The results showed that regardless of pH value, increasing the solution temperature enhanced the corrosion resistance of the both phases. However, the electrochemical behavior of the psi phase indicated that its stability depends on the submerged exposure time in neutral and alkaline environments. This behavior was related to the type of corrosion products present on the surfaces of the particles along with the diffusion and charge-transfer mechanisms of the corrosion process.

Update: 19-Nov-2015

Title:
Large coincidence lattice on Au/Fe3O4 incommensurate structure for spintronic applications
Authors:
Munoz-Noval, A; Rubio-Zuazo, J; Salas-Colera, E; Serrano, A; Rubio-Marcos, F; Castro, GR Author Full Names: Munoz-Noval, Alvaro; Rubio-Zuazo, Juan; Salas-Colera, Eduardo; Serrano, Aida; Rubio-Marcos, Fernando; Castro, German R.
Source:
APPLIED SURFACE SCIENCE, 355 698-701; 10.1016/j.apsusc.2015.07.158 NOV 15 2015
Abstract:
The design of metallic hybrid systems for spintronics has been widely studied during the past decade, motivated by the promising technological applications of these materials. Nevertheless, the importance of preserving the native structure and properties of the interfaces is often ignored. Here, we present the fabrication of nanocrystalline Au(001) onto a single oriented Fe3O4 (0 0 1) thin film as a promising hybrid system to develop spintronic devices by growing Au over the Fe3O4 by using a simple one-pot Pulsed Laser Deposition (PLD) approach. The structural coupling between Au nanocrystals and Fe3O4 layer results in the development of an incommensurate structure based on a coincidence lattice of order 35, which preserves the intrinsic properties of the Au nanocrystals, the Fe3O4 matrix and the interface between them. The general strategy described in the present work preserves the structure and main intrinsic properties of the constituting materials, being a fundamental issue for the future development of spintronic devices. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Unoccupied electronic structure of Ni2MnGa ferromagnetic shape memory alloy
Authors:
Maniraj, M; D'Souza, SW; Rai, A; Schlagel, DL; Lograsso, TA; Chakrabarti, A; Barman, SR Author Full Names: Maniraj, M.; D'Souza, S. W.; Rai, Abhishek; Schlagel, D. L.; Lograsso, T. A.; Chakrabarti, Aparna; Barman, S. R.
Source:
SOLID STATE COMMUNICATIONS, 222 1-4; 10.1016/j.ssc.2015.08.003 NOV 2015
Abstract:
Momentum resolved inverse photoemission spectroscopy measurements show that the dispersion of the unoccupied bands of Ni(2)MaGa is significant in the austenite phase. In the martensite phase, it is markedly reduced, which is possibly related to the structural transition to an incommensurate modulated state in the martensite phase. Based on the first principle calculations of the electronic structure of Ni-Mn-Ga, we show that the modification of the spectral shape with surface composition is related to change in the hybridization between the Mn 3d and Ni 3d-like states that dominate the unoccupied conduction band. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Local cluster symmetry of a highly ordered quasicrystalline Al58Cu26Ir16 extracted through multivariate analysis of STEM images
Authors:
Seki, T; Abe, E Author Full Names: Seki, Takehito; Abe, Eiji
Source:
MICROSCOPY, 64 (5):341-349; 10.1093/jmicro/dfv035 OCT 2015
Abstract:
The structure of a highly ordered Al58Cu26Ir16 decagonal quasicrystal (d-QC), which is constructed by a periodic stack of quasiperiodic atomic planes, was investigated using aberration-corrected scanning transmission electron microscopy. The entire quasiperiodic structure can be well described based on the pentagonal Penrose lattice decorated with a decagonal columnar cluster 2 nm across, and the individual clusters apparently showed up with localized atomic disorder to various degree that blurs the underlying cluster symmetry. Multivariate analysis of the cluster images with principal component analysis has successfully extracted two fundamental clusters, which are with definite mirror and 10-fold-rotation symmetries; this is the first solid example of the d-QC composed of multiple fundamental clusters with different symmetry. Consequently, it is found that all the observed variations can be reasonably interpreted by a linear combination between these two fundamental clusters of mirror and 10-fold symmetries, indicating that the possible atomic disorder is strongly restricted by these particular symmetries. Characteristic distributions of the mirror/10-fold clusters on the pentagonal Penrose lattice are also described.

Update: 12-Nov-2015

Title:
Magnetic anisotropy in FeSb studied by Fe-57 Mossbauer spectroscopy
Authors:
Komedera, K; Jasek, AK; Blachowski, A; Ruebenbauer, K; Krzton-Maziopa, A Author Full Names: Komedera, K.; Jasek, A. K.; Blachowski, A.; Ruebenbauer, K.; Krzton-Maziopa, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 399 221-227; 10.1016/j.jmmm.2015.09.076 FEB 1 2016
Abstract:
The Fe1+xSb compound has been synthesized close to stoichiometry with x=0.023(8). The compound was investigated by Fe-57 Mossbauer spectroscopy in the temperature range 4.2-300 K. The anti-ferromagnetic ordering temperature was found as 232 K i.e. much higher than for the less stoichiometric material. Regular iron was found to occupy two different positions in proportion 2:1. They differ by the electric quadrupole coupling constants and both of them exhibit extremely anisotropic electric field gradient tensor (EFG) with the asymmetry parameter eta approximate to 1. The negative component of both EFGs is aligned with the c-axis of the hexagonal unit cell, while the positive component is aligned with the (120) direction. Hence, a model describing deviation from the NiAs P6(3)/mmc symmetry group within Fe-planes has been proposed. Spectra in the magnetically ordered state could be explained by introduction of the incommensurate spin spirals propagating through the iron atoms in the direction of the c-axis with a complex pattern of the hyperfine magnetic fields distributed within a-b plane. Hyperfine magnetic field pattern of spirals due to major regular iron is smoothed by the spin polarized itinerant electrons, while the minor regular iron exhibits hyperfine field pattern characteristic of the highly covalent bonds to the adjacent antimony atoms. The excess interstitial iron orders magnetically at the same temperature as the regular iron, and magnetic moments of these atoms are likely to form two-dimensional spin glass with moments lying in the a-b plane. The upturn of the hyperfine field for minor regular iron and interstitial iron is observed below 80 K. Magneto-elastic effects are smaller than for FeAs, however the recoilless fraction increases significantly upon transition to the magnetically ordered state. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Flat and conical incommensurate magnetic structures in the two-subsystem partially frustrated Heisenberg ferrimagnet
Authors:
Martynov, SN Author Full Names: Martynov, S. N.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 398 121-126; 10.1016/j.jmmm.2015.09.046 JAN 15 2016
Abstract:
The phase transitions into flat and conical incommensurate magnetic structures are considered for a ferrimagnet with the dominant nonfrustrated exchange between the spins in one crystallographic position, competing exchanges between the spins in another position and frustrated exchange between the spins in different positions. The appearance conditions and the temperatures of the second order phase transitions are analytically obtained in the mean field approximation. The first order phase transition between these states is studied and the phase diagrams of temperature vs frustrated exchanges are calculated by the numerical minimization of free energy. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Temperature dependence of the propagation vector in Ni3-xCoxV2O8 with x=0.1 and 0.5
Authors:
Lee, S; Lee, H; Choi, YN; Semkin, MA; Teplykh, AE; Skryabin, YN; Li, WH; Pirogov, AN Author Full Names: Lee, Seongsu; Lee, Heeju; Choi, Yong Nam; Semkin, M. A.; Teplykh, A. E.; Skryabin, Yu. N.; Li, Wen-Hsien; Pirogov, A. N.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 397 225-229; 10.1016/j.jmmm.2015.08.106 JAN 1 2016
Abstract:
We present the susceptibility and neutron diffraction data on multiferroic Ni3-xCoxV2O8 with x=0.1 and 0.5. The temperature dependence of the susceptibility indicates that the magnetic order-disorder transition occurs at T-HTI=8.5 K in both samples. Below T-HTI, the high-temperature incommensurate magnetic structure is realized, which undergoes a transition to the low-temperature incommensurate phase when the sample is cooled. The temperature evolution of the propagation vector k for x=0.1 is very weak, which confirms previous studies showing that substitution of 3.5% Ni ions by Co ions suppresses the explicit temperature dependence of k that is observed in the parent compound. On the other hand, we found that the vector k for x=0.5 exhibits a definite temperature dependence, which differs from the case of the undopal sample (x=0)., (C) 2015 Elsevier By. All rights reserved.
Title:
Microstructure of mechanically alloyed and annealed Al62Cu25.5Fe12.5 powder
Authors:
Mitka, M; Goral, A; Rogal, L; Litynska-Dobrzynska, L Author Full Names: Mitka, Mikolaj; Goral, Anna; Rogal, Lukasz; Litynska-Dobrzynska, Lidia
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 653 47-53; 10.1016/j.jallcom.2015.08.250 DEC 25 2015
Abstract:
The influence of mechanical alloying (MA) of Al62Cu25.5Fe12.5 (at.%) powder obtained with different milling speeds and milling time and subsequent annealing on its microstructure and phase composition was investigated by means X-ray diffraction, scanning and transmission electron microscopy (SEM and TEM) methods. The power was milled in a high energy planetary ball mill at the rotation speed 250, 300 and 350 rpm for 3, 6, 10 and 20 h using WC milling media. The annealing of milled powders was performed at 800 degrees C for 4 h. Nano-quasicrystalline icosahedral phase (i-phase) was obtained in the as-milled powder at a speed 350 rpm, while the lower milling speed resulted in the formation of cubic beta-Al(Cu, Fe) phase. In all annealed powders the i-phase coexisting with the ordered lambda-Al(Cu, Fe) phase and small amount of the l-Al13Fe4 phase has been observed. The highest volume fraction of i-phase was found in the annealed powder milled at 250 rpm. After annealing the grain size increases compared to the as-milled powder. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Fabrication and properties of Ti-Zr-Ni quasicrystal and bulk composite materials by high pressure sintering
Authors:
Han, QG; Zhong, JL; Zhang, Q; Liu, B; Wang, LM Author Full Names: Han, Qi-Gang; Zhong, Ji-Lun; Zhang, Qiang; Liu, Biao; Wang, Li-Min
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 428 62-67; 10.1016/j.jnoncrysol.2015.08.008 NOV 15 2015
Abstract:
The overall composition of Ti40.83Zr40.83Ni18.34 quasicrystal powders that consist of the stable icosahedral phase (I-phase) was prepared by mechanical alloying and the subsequent heat treatment in a vacuum furnace. Then, bulk composite materials (BCMs) with the composition of Ti40.83Zr40.83Ni18.34 I-phase quasicrystal powders and carbonyl nickel powders as metal bonding agent (20 wt.%), have been fabricated by high pressure sintering. The Vickers hardness, compressive strength, deformation at fracture, Young's modulus, and wear resistance of the BCMs have been studied in detail, after being sintered at different pressure and temperature. It indicates that high pressure sintering enables us to produce the BCMs (about 10 mm in diameter and 3 mm in height) with a short sintered time of 10 mm and high pressure of 3.0 GPa. In addition, the optimum sintered condition is 3.0 GPa-600 degrees C, which is beneficial of the improvement of the performances of BCM, such as the Vickers hardness of 389, the compressive strength of 430 MPa, the deformation at fracture of 2.20%, the Young's modulus of 19 GPa, the lowest value of friction coefficient at 0.45 +/- 0.13, and wear mass losses of 024 mm(3). This work shows a promise in practical fabrication of BCM that consist of the stable Ti-Zr-Ni icosahedral quasicrystalline phase may be developed. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Nanosized helical magnetic domains in strongly frustrated Fe3PO4O3
Authors:
Ross, KA; Bordelon, MM; Terho, G; Neilson, JR Author Full Names: Ross, K. A.; Bordelon, M. M.; Terho, G.; Neilson, J. R.
Source:
PHYSICAL REVIEW B, 92 (13):10.1103/PhysRevB.92.134419 OCT 26 2015
Abstract:
Fe3PO4O3 forms a noncentrosymmetric lattice structure (space group R3m) comprising triangular motifs of Fe3+ coupled by strong antiferromagnetic interactions (vertical bar circle dot(CW)vertical bar > 900 K). Neutron diffraction from polycrystalline samples shows that strong frustration eventually gives way to an ordered helical incommensurate structure below T-N = 163 K, with the helical axis in the hexagonal ab plane and a modulation length to similar to 86 angstrom. The magnetic structure consists of an unusual needlelike correlation volume that extends past 900 angstrom along the hexagonal c axis but is limited to similar to 70 angstrom in the ab plane, despite the three-dimensional nature of the magnetic sublattice topology. The small in-plane correlation length, which persists to at least T = T-N/40, indicates a robust blocking of long-range order of the helical magnetic structure, and therefore stable domain walls, or other defect spin textures, must be abundant in Fe3PO4O3. Temperature-dependent neutron powder diffraction reveals small negative thermal expansion below T-N. No change in lattice symmetry is observed on cooling through TN, as revealed by high-resolution synchrotron x-ray diffraction. The previously reported reduced moment of the Fe3+ ions (S = 5/2), mu similar to 4.2 mu(B), is confirmed here through magnetization studies of a magnetically diluted solid solution series of compounds, Fe(3-x)GaxPO4O3, and is consistent with the refined magnetic moment from neutron diffraction 4.14(2) mu(B). We attribute the reduced moment to a modified spin density distribution arising from ligand charge transfer in this insulating oxide.
Title:
Solitonic Spin-Liquid State Due to the Violation of the Lifshitz Condition in Fe1+yTe
Authors:
Materne, P; Koz, C; Rossler, UK; Doerr, M; Goltz, T; Klauss, HH; Schwarz, U; Wirth, S; Rossler, S Author Full Names: Materne, Ph.; Koz, C.; Roessler, U. K.; Doerr, M.; Goltz, T.; Klauss, H. H.; Schwarz, U.; Wirth, S.; Roessler, S.
Source:
PHYSICAL REVIEW LETTERS, 115 (17):10.1103/PhysRevLett.115.177203 OCT 21 2015
Abstract:
A combination of phenomenological analysis and Mossbauer spectroscopy experiments on the tetragonal Fe1+yTe system indicates that the magnetic ordering transition in compounds with higher Fe excess, y >= 0.11, is unconventional. Experimentally, a liquidlike magnetic precursor with quasistatic spin order is found from significantly broadened Mossbauer spectra at temperatures above the antiferromagnetic transition. The incommensurate spin-density wave order in Fe1+yTe is described by a magnetic free energy that violates the weak Lifshitz condition in the Landau theory of second-order transitions. The presence of multiple Lifshitz invariants provides the mechanism to create multidimensional, twisted, and modulated solitonic phases.
Title:
Rare earth ferrites LuFe2O4 +/- x polymorphism, polytypism and metastable phases
Authors:
Hervieu, M; Damay, F; Maignan, A; Martin, C Author Full Names: Hervieu, M.; Damay, F.; Maignan, A.; Martin, C.
Source:
SOLID STATE SCIENCES, 48 A1-A16; 10.1016/j.solidstatesciences.2015.07.013 OCT 2015
Abstract:
This work is a compendium of the structural properties of layered LnFe(2)O(4 +/- x) ferrites, focussed on recently discovered polymorphs and their transitions through five complex commensurate and incommensurate modulated structures. These phases are obtained varying the oxygen content (reversibly from O-4.0 to O-4.5) or applying high pressure (up to 15 GPa). The relationships between the different structures are discussed and models are proposed. These ferrites, which contain magnetic cations and exhibit remarkable 3D flexibility, open the road for magnetic, electric, catalytic or energy materials. (C) 2015 Elsevier Masson SAS. All rights reserved.
Title:
Low temperature oxygen diffusion mechanisms in Nd2NiO4+delta and Pr2NiO4+delta via large anharmonic displacements, explored by single crystal neutron diffraction
Authors:
Ceretti, M; Wahyudi, O; Cousson, A; Villesuzanne, A; Meven, M; Pedersen, B; Bassat, JM; Paulus, W Author Full Names: Ceretti, M.; Wahyudi, O.; Cousson, A.; Villesuzanne, A.; Meven, M.; Pedersen, B.; Bassat, J. M.; Paulus, W.
Source:
JOURNAL OF MATERIALS CHEMISTRY A, 3 (42):21140-21148; 10.1039/c5ta05767a 2015
Abstract:
We investigated the structure of Nd2NiO4+delta and Pr2NiO4+delta by single crystal neutron diffraction studies. While the real structure of both compounds is incommensurate, the scattering density of the respective average structures was explored using the Maximum Entropy Method. Unusually high displacement factors were found for the equatorial and apical oxygen atoms showing respectively large displacement amplitudes towards [001] and [110] with respect to the F-symmetry cell. The shifts of the apical oxygen atoms reach up to 1 angstrom from their average position, corresponding to a 25 degrees tilt of the NiO6 octahedra. At 400 degrees C, i.e. slightly above the orthorhombic-tetragonal phase transition, the anharmonic apical oxygen displacements towards [110] in the commensurate tetragonal parent structure are strongly enhanced, showing a double-well potential and pointing towards the interstitial vacancy sites, creating a quasi continuous shallow energy diffusion pathway between apical and interstitial oxygen sites. These large displacement amplitudes are considered to be - at least partially - of dynamical origin, which is consistent with a phonon assisted diffusion mechanism, already activated at very moderate temperatures.

Update: 5-Nov-2015

Title:
Effects of cyclic extrusion and compression parameters on microstructure and mechanical properties of Mg-1.50Zn-0.25Gd alloy
Authors:
Huang, H; Tang, ZB; Tian, Y; Jia, GZ; Niu, JL; Zhang, H; Pei, J; Yuan, GY; Ding, WJ Author Full Names: Huang, Hua; Tang, Zibo; Tian, Yuan; Jia, Gaozhi; Niu, Jialin; Zhang, Hua; Pei, Jia; Yuan, Guangyin; Ding, Wenjiang
Source:
MATERIALS & DESIGN, 86 788-796; 10.1016/j.matdes.2015.07.155 DEC 5 2015
Abstract:
Mg-1.50Zn-0.25Gd (at.%) alloy reinforced by icosahedral quasicrystalline phase (I-phase) was fabricated and then subjected to cyclic extrusion and compression (CEC) at 250, 300, 350 and 400 degrees C, respectively. The effects of CEC parameters including passes and temperatures on microstructure evolution and room temperature tensile mechanical properties were characterized and discussed. The results show that more passes are beneficial for secondary phase precipitation, grain refinement and basal texture weakening; while moderate temperature is beneficial for secondary phase precipitation and basal texture weakening by particle stimulated recrystallization nucleation (PSN), and lower temperature is beneficial for grain refinement. The alloy has the highest yield strength after CEC at 250 degrees C because of grain refinement and basal texture strengthening, while it has the highest elongation after being processed with 8 passes of CEC due to grain refinement and basal texture weakening. The processing passes have more important effects on microstructure evolution and mechanical properties than that of temperature during CEC. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Evolution of the dense packings of spherotetrahedral particles: from ideal tetrahedra to spheres
Authors:
Jin, WW; Lu, P; Li, SX Author Full Names: Jin, Weiwei; Lu, Peng; Li, Shuixiang
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep15640 OCT 22 2015
Abstract:
Particle shape plays a crucial role in determining packing characteristics. Real particles in nature usually have rounded corners. In this work, we systematically investigate the rounded corner effect on the dense packings of spherotetrahedral particles. The evolution of dense packing structure as the particle shape continuously deforms from a regular tetrahedron to a sphere is investigated, starting both from the regular tetrahedron and the sphere packings. The dimer crystal and the quasicrystal approximant are used as initial configurations, as well as the two densest sphere packing structures. We characterize the evolution of spherotetrahedron packings from the ideal tetrahedron (s = 0) to the sphere (s = 1) via a single roundness parameter s. The evolution can be partitioned into seven regions according to the shape variation of the packing unit cell. Interestingly, a peak of the packing density Phi is first observed at s approximate to 0.16 in the Phi-s curves where the tetrahedra have small rounded corners. The maximum density of the deformed quasicrystal approximant family (Phi approximate to 0.8763) is slightly larger than that of the deformed dimer crystal family (Phi approximate to 0.8704), and both of them exceed the densest known packing of ideal tetrahedra (Phi approximate to 0.8563).
Title:
Neutron diffraction investigation of the H - T phase diagram above the longitudinal incommensurate phase of BaCo2V2O8
Authors:
Grenier, B; Simonet, V; Canals, B; Lejay, P; Klanjsek, M; Horvatic, M; Berthier, C Author Full Names: Grenier, B.; Simonet, V.; Canals, B.; Lejay, P.; Klanjsek, M.; Horvatic, M.; Berthier, C.
Source:
PHYSICAL REVIEW B, 92 (13):10.1103/PhysRevB.92.134416 OCT 20 2015
Abstract:
The quasi-one-dimensional antiferromagnetic Ising-like compound BaCo2V2O8 has been shown to be describable by the Tomonaga-Luttinger liquid theory in its gapless phase induced by a magnetic field applied along the Ising axis. Above 3.9 T, this leads to an exotic field-induced low-temperature magnetic order, made of a longitudinal incommensurate spin-density wave, stabilized by weak interchain interactions. By single-crystal neutron diffraction we explore the destabilization of this phase at a higher magnetic field. We evidence a transition at around 8.5 T towards a more conventional magnetic structure with antiferromagnetic components in the plane perpendicular to the magnetic field. The phase diagram boundaries and the nature of this second field-induced phase are discussed with respect to previous results obtained by means of nuclear magnetic resonance and electron spin resonance, and in the framework of the simple model based on the Tomonaga-Luttinger liquid theory, which obviously has to be refined in this complex system.
Title:
Microscopic adjustment of misfit strain and charge segregation in [Bi2Sr2O4](0.51)CoO2
Authors:
Maki, M; Takakura, S; Nishizaki, T; Ichikawa, F Author Full Names: Maki, Makoto; Takakura, Sho-ichi; Nishizaki, Terukazu; Ichikawa, Fusao
Source:
PHYSICAL REVIEW B, 92 (16):10.1103/PhysRevB.92.165117 OCT 16 2015
Abstract:
From scanning tunneling microscopy of the misfit-layered cobaltate [Bi2Sr2O4](0.51)CoO2 single crystals, we observed structural short corrugations oriented in the direction inclined with respect to the incommensurate axis. Results show that the spatial distribution of the electronic charge density is also modified in relation to the atomic displacement. Our data strongly suggest that the rocksalt structure flexibly mounted on the CoO2 layer affects the electronic properties of this system.
Title:
Phase Diagram of Modulated Structures in Ferroelectric Crystals Based on Quantum Ising Model with Third-Neighbor Interactions
Authors:
Mashiyama, H Author Full Names: Mashiyama, Hiroyuki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (10):10.7566/JPSJ.84.104712 OCT 15 2015
Abstract:
Incommensurate commensurate phase transitions are analyzed using a model derived from the normal coordinate Hamiltonian for a crystal lattice. The Hamiltonian consists of a local self-potential and effective third-neighbor interactions. Free energies of various modulated phases are calculated with a mean-field approximation under the condition that two quantum states within the local potential are important at low temperature. It is demonstrated that the quantum effect works to stabilize the incommensurate phase rather than the commensurate phase. Even at zero temperature, the incommensurate phase can occupy a finite region in the phase diagram. This situation is similar to quantum paraelectricity in some ferroelectrics, and can be expected as a general feature of modulated structures of dielectric crystals. The phase diagram for ferroic first- and third-neighbor interactions but antiferroic second-neighbor interactions is constructed theoretically and is discussed in detail to explain qualitatively the low-temperature behavior of some ferroelectric crystals.
Title:
Competing magnetic and structural states in multiferroic YMn2O5 at high pressure
Authors:
Kozlenko, DP; Dang, NT; Kichanov, SE; Lukin, EV; Pashayev, AM; Mammadov, AI; Jabarov, SH; Dubrovinsky, LS; Liermann, HP; Morgenroth, W; Mehdiyeva, RZ; Smotrakov, VG; Savenko, BN Author Full Names: Kozlenko, D. P.; Dang, N. T.; Kichanov, S. E.; Lukin, E. V.; Pashayev, A. M.; Mammadov, A. I.; Jabarov, S. H.; Dubrovinsky, L. S.; Liermann, H. -P.; Morgenroth, W.; Mehdiyeva, R. Z.; Smotrakov, V. G.; Savenko, B. N.
Source:
PHYSICAL REVIEW B, 92 (13):10.1103/PhysRevB.92.134409 OCT 12 2015
Abstract:
The magnetic, structural, and vibrational properties of YMn2O5 multiferroic have been studied by means of neutron, x-ray powder diffraction, and Raman spectroscopy at pressures up to 6 and 30 GPa, respectively. Application of high pressure, P > 1 GPa, leads to a gradual suppression of the commensurate and incommensurate antiferromagnetic (AFM) phases with a propagation vector q = (1/2,0, q(z) similar to 1/4) and appearance of the commensurate AFM phase with q = (1/2,0,1/2). This observation is sharply contrasting to general trend towards stabilization of commensurate AFM phase with q = (1/2,0,1/4) found in other RMn2O5 compounds upon lattice compression. At P similar to 16 GPa a structural phase transformation accompanied by anomalies in lattice compression and pressure behavior of vibrational modes was observed. The comparative analysis of high-pressure and R-cation radius variation effects clarified a role of particular magnetic interactions in the formation of the magnetic states of RMn2O5 compounds.

Update: 29-Oct-2015

Title:
First-order commensurate-incommensurate magnetic phase transition in the coupled FM spin-1/2 two-leg ladders
Authors:
Jahangiri, J; Hadipour, H; Mandavifar, S; Shayesteh, SF Author Full Names: Jahangiri, J.; Hadipour, H.; Mandavifar, S.; Shayesteh, S. Farjami
Source:
PHYSICA B-CONDENSED MATTER, 476 24-28; 10.1016/j.physb.2015.07.012 NOV 1 2015
Abstract:
We consider the spin-1/2 two-leg ladders with ferromagnetic (FM) interactions along legs and rungs. Using the stochastic series expansion QMC method, we study the low-temperature magnetic behavior of the system. An isolated spin-1/2 FM two-leg ladder is in the gapped saturated FM phase at zero temperature. As soon as the spin-1/2 FM two-leg ladders are connected with antiferromagnetic (AFM) inter-ladder interaction, a first-order commensurate-incommensurate quantum phase transition occurs in the ground state magnetic phase diagram. In fact a jump in the magnetization curve is observed. We found that, coupled spin-1/2 FM two-leg ladders are in a nonmagnetic phase at zero temperature. Applying a magnetic field, the ground state of coupled spin-1/2 FM two-leg ladders remains in the nonmagnetic phase up to a quantum saturate critical field. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Predicting complex mineral structures using genetic algorithms
Authors:
Mohn, CE; Kob, W Author Full Names: Mohn, Chris E.; Kob, Walter
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (42):10.1088/0953-8984/27/42/425201 OCT 28 2015
Abstract:
We show that symmetry-adapted genetic algorithms are capable of finding the ground state of a range of complex crystalline phases including layered- and incommensurate superstructures. This opens the way for the atomistic prediction of complex crystal structures of functional materials and mineral phases.
Title:
Incommensurate modulation and thermal expansion of Sr3B2 (+) Si-x(1) (-) O-x(8) (-) (x/2) solid solutions
Authors:
Volkov, S; Bubnova, R; Bolotina, N; Krzhizhanovskaya, M; Belousova, O; Filatov, S Author Full Names: Volkov, Sergey; Bubnova, Rimma; Bolotina, Nadezhda; Krzhizhanovskaya, Maria; Belousova, Olga; Filatov, Stanislav
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 489-497; 10.1107/S2052520615011713 5 OCT 2015
Abstract:
Crystal structures of Sr3B2 (+) Si-x(1) (-) O-x(8) (- x/2) solid solutions with nominal compositions x = 0.28, 0.53, 0.78 in the Sr3B2SiO8-Sr2B2O5 section of the SrO-B2O3-SiO2 system are refined using single-crystal X-ray diffraction data. Incommensurate structure modulations are mainly associated with various orientations of corner-sharing (B,Si)-polyhedra. Preference is given to the (3 + 2)-dimensional symmetry group Pnma(0 beta gamma)000(0 beta gamma)000 for a single crystal compared with an alternate model of a twin formed by monoclinic components, each of them corresponding to the (3 + 1)-dimensional symmetry group P2(1)/n(0 beta gamma). Single-phase polycrystalline samples of solid solutions are investigated by high-temperature X-ray powder diffraction in air. Orientation preferences of the BO3 units lead to a strong anisotropy of thermal expansion. Negative expansion is observed along the a axis over the temperature range 303-753 K. Anisotropy decreases both on heating and decreasing of the boron content.
Title:
Decagonite, Al71Ni24Fe5, a quasicrystal with decagonal symmetry from the Khatyrka CV3 carbonaceous chondrite
Authors:
Bindi, L; Yao, N; Lin, C; Hollister, LS; Andronicos, CL; Distler, VV; Eddy, MP; Kostin, A; Kryachko, V; MacPherson, GJ; Steinhardt, WM; Yudovskaya, M; Steinhardt, PJ Author Full Names: Bindi, Luca; Yao, Nan; Lin, Chaney; Hollister, Lincoln S.; Andronicos, Christopher L.; Distler, Vadim V.; Eddy, Michael P.; Kostin, Alexander; Kryachko, Valery; MacPherson, Glenn J.; Steinhardt, William M.; Yudovskaya, Marina; Steinhardt, Paul J.
Source:
AMERICAN MINERALOGIST, 100 (10):2340-2343; 10.2138/am-2015-5423 OCT 2015
Abstract:
Decagonite is the second natural quasicrystal, after icosahedrite (Al63Cu24Fe13), and the first to exhibit the crystallographically forbidden decagonal symmetry. It was found as rare fragments up to similar to 60 mu m across in one of the grains (labeled number 126) of the Khatyrka meteorite, a CV3 carbonaceous chondrite. The meteoritic grain contains evidence of a heterogeneous distribution of pressures and temperatures that occurred during impact shock, in which some portions of the meteorite reached at least 5 GPa and 1200 degrees C. Decagonite is associated with Al-bearing trevorite, diopside, forsterite, ahrensite, clinoenstatite, nepheline, coesite, pentlandite, Cu-bearing troilite, icosahedrite, khatyrkite, taenite, Al-bearing taenite, and steinhardtite. Given the exceedingly small size of decagonite, it was not possible to determine most of the physical properties for the mineral. A mean of seven electron microprobe analyses (obtained from three different fragments) gave the formula Al70.2(3)Ni24.5(4)Fe5.3(2), on the basis of 100 atoms. A combined TEM and single-crystal X-ray diffraction study revealed the unmistakable signature of a decagonal quasicrystal: a pattern of sharp peaks arranged in straight lines with 10-fold symmetry together with periodic patterns taken perpendicular to the 10-fold direction. For quasicrystals, by definition, the structure is not reducible to a single three-dimensional unit cell, so neither cell parameters nor Z can be given. The likely space group is P10(5)/mine, as is the case for synthetic A(17)Ni(24)Fe(5). The five strongest powder-diffraction lines [d in angstrom (I/I-0)] are: 2.024 (100), 3.765 (50), 2.051 (45), 3.405 (40), 1.9799 (40). The new mineral has been approved by the IMA-NMNC Commission (IMA2015-017) and named decagonite for the 10-fold symmetry of its structure. The finding of a second natural quasicrystal informs the longstanding debate about the stability and robustness of quasicrystals among condensed matter physicists and demonstrates that mineralogy can continue to surprise us and have a strong impact on other disciplines.
Title:
Secondary phases in quasicrystal-reinforced Mg-3.5Zn-0.6Gd Mg alloy
Authors:
Huang, H; Tian, Y; Yuan, GY; Chen, CL; Wang, ZC; Ding, WJ; Inoue, A Author Full Names: Huang, Hua; Tian, Yuan; Yuan, Guangyin; Chen, Chunlin; Wang, Zhongchang; Ding, Wenjiang; Inoue, Akihisa
Source:
MATERIALS CHARACTERIZATION, 108 132-136; 10.1016/j.matchar.2015.09.005 OCT 2015
Abstract:
The secondary phases in quasicrystal-reinforced Mg-Zn-Gd alloys are investigated by transmission electron microscopy. The orientation relationships between the dendritic I-phase and the Mg matrix are identified to be [1 1 (2) over bar 0](Mg)parallel to[2-fold](I-phase) and (0001)(Mg)parallel to(5-fold)(I-phase). We also find that the dendritic I-phase is brittle along 2-fold, 5-fold, and 3-fold atomic planes during hot extrusion. Moreover, new orientation relations [(1) over bar 101](Mg)parallel to[mirror 2-fold](I-phase) and (0 (1) over bar 1 1)(Mg)parallel to(5-fold)(I-phase) are found between nanoscale I-phase and Mg matrix. The findings have implications for our understanding of excellent mechanical properties of the I-phase-strengthened Mg alloys. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Strain induced incommensurate structures in vicinity of reconstructive phase transitions
Authors:
Korzhenevskii, AL; Dmitriev, V Author Full Names: Korzhenevskii, A. L.; Dmitriev, V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (37):10.1088/0953-8984/27/37/375401 SEP 23 2015
Abstract:
General conditions controlling the formation of incommensurate phases in crystals undergoing reconstructive phase transitions are analyzed in the framework of a model-free phenomenological approach. A universal trend to stabilizing such intermediate phases in the vicinity of reconstructive phase transitions stems from the fact that certain high-order improper Lifshitz invariants reduce at such transformations to ones bi-linearly coupling critical displacement gradients and strains or even to the proper Lifshitz invariant. The approach developed here introduces a universal mechanism for the formation both of premartensite incommensurate phases and complex structures with giant unit cells, as found in some elemental crystals at high pressure.
Title:
Characteristics of 5M modulated martensite in Ni-Mn-Ga magnetic shape memory alloys
Authors:
Cakir, A; Acet, M; Righi, L; Albertini, F; Farle, M Author Full Names: Cakir, A.; Acet, M.; Righi, L.; Albertini, F.; Farle, M.
Source:
AIP ADVANCES, 5 (9):10.1063/1.4932233 SEP 2015
Abstract:
The applicability of the magnetic shape memory effect in Ni-Mn-based martensitic Heusler alloys is closely related to the nature of the crystallographically modulated martensite phase in these materials. We study the properties of modulated phases as a function of temperature and composition in three magnetic shape memory alloys Ni49.8Mn25.0Ga25.2, Ni49.8Mn27.1Ga23.1 and Ni49.5Mn28.6Ga21.9. The effect of substituting Ga for Mn leads to an anisotropic expansion of the lattice, where the b-parameter of the 5M modulated structure increases and the a and c-parameters decrease with increasing Ga concentration. The modulation vector is found to be both temperature and composition dependent. The size of the modulation vector corresponds to an incommensurate structure for Ni49.8Mn25.0Ga25.2 at all temperatures. For the other samples the modulation is incommensurate at low temperatures but reaches a commensurate value of q approximate to 0.400 close to room temperature. The results show that commensurateness of the 5M modulated structure is a special case of incommensurate 5M at a particular temperature. (C) 2015 Author(s).

Update: 22-Oct-2015

Title:
Thermoelectric properties of Tsai-type Au-Al-RE (RE: Yb, Tm, Gd) quasicrystals and approximants
Authors:
Takagiwa, Y; Kimura, K; Sawama, K; Hiroto, T; Nishio, K; Tamura, R Author Full Names: Takagiwa, Y.; Kimura, K.; Sawama, K.; Hiroto, T.; Nishio, K.; Tamura, R.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 652 139-144; 10.1016/j.jallcom.2015.08.081 DEC 15 2015
Abstract:
The thermoelectric properties of Tsai-type Au-Al-RE (RE: Yb, Tm, Gd) icosahedral quasicrystals (QCs) and their approximant crystals (ACs) have been investigated from 373 K to 873 K. Comparison of their thermoelectric properties above room temperature is of great interest since resonant states are likely to be present in the electronic density of states near the Fermi level for the Au-Al-Yb QC, which should influence the thermoelectric properties and, hence, the dimensionless figure of merit. The electrical conductivity of Au-Al-Yb ACs varies significantly, i.e. from 3000 Omega(-1) cm(-1) to 5200 Omega(-1) cm(-1), with changing the Au/Al composition whereas the other compounds have conductivities of similar to 3000 Omega(-1) cm(-1). Such an anomalous behavior of the Au-Al-Yb ACs is understood to be due to the existence of a resonant peak originating from hybridization of Yb f-states and Au/Al sp-states. A maximum power factor of 230 mu Wm(-1) K-2 at 873 K is obtained in 1/1-Au48Al37Yb15 AC, which is significantly higher than those of Al-based icosahedral phases at the same temperature. On the other hand, the room-temperature thermal conductivities for Au-Al-RE compounds range from 3 to 4 W m(-1) K-1, reflecting their complex crystal structures with a large unit cell and mixed and/or partially occupied sites. Consequently, both 1/1-Au50Al35Yb15 and Au48Al37Yb15 ACs have similar maximum figures of merit of 0.014 at 873 K. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Deformation mechanism of Ni54Mn25Ga20.9Gd0.1 high-temperature shape memory alloy
Authors:
Zhang, X; Sui, JH; Cai, W; Liu, QS; Liu, AL Author Full Names: Zhang, Xin; Sui, Jiehe; Cai, Wei; Liu, Qingsuo; Liu, Ailian
Source:
INTERMETALLICS, 67 52-55; 10.1016/j.intermet.2015.07.017 DEC 2015
Abstract:
Ni54Mn25Ga20.9Gd0.1 Polycrystalline high-temperature shape memory alloy displayed high compressive fracture strain of 24.6% and large shape memory effect of 7.5%. However, its deformation mechanism was still unknown. In this paper, the structure revolution characterized by XRD and TEM indicated a new deformation mechanism different before was found. The deformation process of Ni54Mn25Ga20.9Gd0.1 alloy could be divided into four stages, including elastic deformation of non-modulated tetragonal martensite (T), stress-induced T to seven-layered modulated martensite (7 M) transformation, variants reorientation of 7 M, and elastic plastic deformation of reoriented 7 M. The 7 M formed by compression deformation disappeared completely after heating to the temperature above A(f). (C) 2015 Elsevier Ltd. All rights reserved.
Title:
From crystal morphology to molecular and scale crystallography
Authors:
Janner, A; Janssen, T Author Full Names: Janner, A.; Janssen, T.
Source:
PHYSICA SCRIPTA, 90 (8):10.1088/0031-8949/90/8/088007 AUG 2015
Abstract:
A number of topics, ranging from morphology of aperiodic crystals to indexed enclosing forms of axial-symmetric proteins, nucleic acids and viruses, have been selected among those investigated by the authors in 50 years of research. The basic symmetries involved in fields like superspace, molecular and scale crystallography, are considered from a personal point of view in their time evolution. A number of specific subjects follow, chosen among a few highlights and presented according to the experience of the authors: snow crystals, calaverite AuTe2, the incommensurately modulated crystals Rb2ZnBr4, [N(CH3)(4)](2)ZnCl4 and the mitochondrial ferritin.
Title:
Atomic structure of icosahedral quasicrystals: stacking multiple quasi-unit cells
Authors:
Madison, AE Author Full Names: Madison, Alexey E.
Source:
RSC ADVANCES, 5 (97):79279-79297; 10.1039/c5ra13874d 2015
Abstract:
An effective tiling approach is proposed for the structural description of icosahedral quasicrystals based on the original substitution algorithm. The atomic structure of icosahedral quasicrystals may by derived by using the iterative and recursive inflation/deflation procedure with subsequent decoration of quasi-unit cells. The quasi-unit cells are stacked in three-dimensional space face-to-face without any gaps between them producing the whole infinite icosahedral structure in the same manner as the usual periodic crystals are generated by multiplication of their unit cells containing one or more atoms in a specific spatial arrangement. A variety of examples illustrating the efficiency of the general algorithm is presented. Stacking of quasi-unit cells along the five-fold axis, as well as the arrangement of cells normal to the five-fold, three-fold, and two-fold axes are presented. The possible atomic structure of an icosahedral single-component quasicrystal is derived. Three types of inequivalent sites with exact icosahedral symmetry may simultaneously exist in the quasicrystalline structure. The structure of characteristic clusters enforced by the compatibility with the quasicrystalline type of ordering is discussed.

Update: 15-Oct-2015

Title:
Solid-state formation of icosahedral quasicrystals at Zn3Mg3Y2/Mg interfaces in a Mg-Zn-Y alloy
Authors:
Liu, JF; Yang, ZQ; Ye, HQ Author Full Names: Liu, J. F.; Yang, Z. Q.; Ye, H. Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 65-69; 10.1016/j.jallcom.2015.07.254 NOV 25 2015
Abstract:
Solid-state formation of Zn6Mg3Y icosahedral quasicrystals was observed at interfaces between Mg and W-Zn3Mg3Y2 crystals in a Mg-Zn-Y alloy by in situ transmission electron microscopy investigations. The quasicrystals were formed at about 593 K which is about 130 K below the peritectic temperature. Thermally driven interdiffusion of atoms across the W/Mg interface firstly produces local regions with Zn:Mg:Y close to 6:3:1 at the surface of W phase particles, where the cuboctahedral packing of atoms in W phase transforms to icosahedral packing through slight rearrangement of atoms, leading to the nucleation and growth of icosahedral clusters. The icosahedral clusters act as nuclei for the growth of icosahedral quasicrystals. Both valence electron concentration and the densest packing of atoms play important roles in the formation of Zn6Mg3Y quasicrystals. Solid-state formation of icosahedral quasicrystals at W/Mg interfaces provide a feasible way to modify the weakly bonded W/Mg interfaces, which is thus believed to be able to improve the magnesium alloy's mechanical properties. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Properties of Ti40.83Zr40.83Ni18.34 quasicrystalline alloys sintered by Spark Plasma Sintering
Authors:
Han, QG; Chen, ML; Zhang, Q; Sun, LS; Lin, J; Wang, LM Author Full Names: Han, Qi-Gang; Chen, Meng-Lu; Zhang, Qiang; Sun, Lian-Shan; Lin, Jing; Wang, Li-Min
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 154-158; 10.1016/j.jallcom.2015.07.297 NOV 25 2015
Abstract:
The quasicrystalline alloy powders with the composition of Ti40.83Zr40.83Ni18.34 are prepared by mechanical alloying (MA) techniques, and the bulk part is obtained by Spark Plasma Sintering (SPS) method. The structure, mechanical properties, friction and wear properties of the bulk part are investigated. The results showed that the structure of the bulk part is pure icosahedral quasicrystalline phase (I-phase). The Vickers Hardness of the bulk part is 7.03 GPa. The maximum compression strength, the elastic deformation and Young modulus is (662 +/- 50) MPa, 2.7 +/- 0.1% and (30 +/- 3) GPa, respectively. The lowest value of friction coefficient is 0.40 at a normal load of 100 N, a sliding velocity of 10 mm/s, a sliding time of 10 min and an ambient temperature of 293.15 K. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Electrochemical hydrogen storage properties of Ti1.4V0.6Ni alloy comprising quasicrystal coating with Cu
Authors:
Sun, LS; Lin, J; Cao, ZY; Liang, F; Wang, LM Author Full Names: Sun, Lianshan; Lin, Jing; Cao, Zhanyi; Liang, Fei; Wang, Limin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 15-21; 10.1016/j.jallcom.2015.07.252 NOV 25 2015
Abstract:
The Ti1.4V0.6Ni alloy ribbons are prepared by arc-melting and subsequently melt spinning technique. Different percentage compositions of x Cu (x = 1, 3, 5 and 10 wt%) are covered on the surface of the alloy particles utilizing electro-less plating method. The phase structures of the Ti1.4V0.6Ni alloy contain icosahedral quasicrystal phase (I-phase), fcc-Ti2Ni-type phase and bcc-V-based solid solution phase. With increasing x value, the maximum electrochemical hydrogen storage capacity reaches 260 mAh g(-1) when x = 10. After 100 cycles, 23% capacity retention rate is promoted by covering 10 wt% Cu on the alloy than the bare Ti1.4V0.6Ni. Cu offers well electrical conductivity and corrosion resistance, especially it also inhibits the dissolution of V from the alloys. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Investigation on incommensurate modulation structure and T-c in Ca-doped Bi-2201 system
Authors:
Sun, BZ; Zhang, M; Wang, RY; Jiang, YL; Wang, H; Qi, Y Author Full Names: Sun, B. Z.; Zhang, M.; Wang, R. Y.; Jiang, Y. L.; Wang, H.; Qi, Y.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 430-435; 10.1016/j.jallcom.2015.08.015 NOV 25 2015
Abstract:
A series of samples with the nominal composition of Bi2Sr2-xCaxCuO6+delta (x = 0.2, 0.4, 0.6, 0.8, 1.0) ceramics are synthesized by sol-gel growth. The microstructure and the incommensurate modulation structure (IMS) were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. The superconductivity and the onset temperature of superconducting transition (T-c,T-onset) were analysed. In the whole Ca-doping range, an IMS in b-c planes can be identified and the values of T-c,T-onset are all exceed 80 K. With an increase of chi, the b-component of modulation vector q*, the basic *structural* parameters b and c of Bi-2201 phase have a trend of fall first then rise, whereas the c-component of modulation vector, the angle theta between q* and b* vectors and the values of T-c,T-onset are reversely varied. It can be verified that Ca concentration x = 0.6 is an extreme value, at which the distortion of the CuO2 layers makes the concentration of mobile carriers and the value of T-c,(onset) optimizing. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Approximants of Al-Cr-Fe-Si decagonal quasicrystals described by single structural block
Authors:
He, ZB; Wei, DX; Shen, X; Chen, Y; Ma, HK; Wang, LL; Du, K; Yao, Y; Yu, RC Author Full Names: He, Zhanbing; Wei, Dongxia; Shen, Xi; Chen, Yuan; Ma, Haikun; Wang, Leilei; Du, Kui; Yao, Yuan; Yu, Richeng
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 647 797-801; 10.1016/j.jallcom.2015.06.165 OCT 25 2015
Abstract:
The orthorhombic (3/2, 2/1) approximant with a = 3.06 nm, b = 1.23 nm, c = 2.24 nm, and the coexisting (2/1, 3/2) approximant of decagonal quasicrystals with a = 1.90 nm, c = 3.64 nm, and beta congruent to 90 degrees are found in Al-Cr-Fe-Si alloys by aberration-corrected transmission electron microscope. The structural relationships of these two approximants are analyzed and discussed based on the high-angle annular dark-field scanning transmission electron microscopy images at atomic resolution. We find that both of their structural tiling along the [010] direction can be described by one shield-like tile, with the superiority over the previous HBS tiling model due to the clarity. Combining the shield-like tile and HBS tiling model, the domains of approximants are clearly demonstrated. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Incommensurate antiferromagnetism induced by a charge density wave in the cubic phase of TbGe2.85
Authors:
Tsvyashchenko, AV; Salamatin, DA; Sidorov, VA; Petrova, AE; Fomicheva, LN; Kichanov, SE; Salamatin, AV; Velichkov, A; Kozlenko, DR; Nikolaev, AV; Ryasny, GK; Makarova, OL; Menzel, D; Budzynski, M Author Full Names: Tsvyashchenko, A. V.; Salamatin, D. A.; Sidorov, V. A.; Petrova, A. E.; Fomicheva, L. N.; Kichanov, S. E.; Salamatin, A. V.; Velichkov, A.; Kozlenko, D. R.; Nikolaev, A. V.; Ryasny, G. K.; Makarova, O. L.; Menzel, D.; Budzynski, M.
Source:
PHYSICAL REVIEW B, 92 (10):10.1103/PhysRevB.92.104426 SEP 23 2015
Abstract:
Temperature dependencies of the electrical resistivity, magnetic susceptibility, and heat capacity have been obtained in the cubic phase of TbGe2.85 (the AuCu3 structure), synthesized at high pressure. The macroscopic measurements indicate that a charge density wave is formed below 145 K and an antiferromagnetic ordering is realized below 19 K. Hyperfine interaction data obtained with the time differential perturbed angular correlation method with Cd-111 probes inserted in the TbGe2.85 lattice suggest that the charge density wave is incommensurate in the temperature region 19-145 K, but becomes commensurate below 19 K. The neutron diffraction reveals a complex antiferromagnetic spiral structure in the magnetically ordered phase. We discuss relations between the charge density wave and helical ordering in TbGe2.85 and TbPd3.
Title:
Direct evidence of an incommensurate phase in NaNbO3 and its implication in NaNbO3-based lead-free antiferroelectrics
Authors:
Guo, HZ; Shimizu, H; Randall, CA Author Full Names: Guo, Hanzheng; Shimizu, Hiroyuki; Randall, Clive A.
Source:
APPLIED PHYSICS LETTERS, 107 (11):10.1063/1.4930067 SEP 14 2015
Abstract:
Hot-stage in situ transmission electron microscopy was employed to investigate the temperature-induced complex sequence of phase transitions in NaNbO3 polycrystalline. In addition to the commonly recognized P (Pbma) -> R (Pmnm) -> S (Pnmm) phase transitions, incommensurate phases were observed to exist in P and R phase regions. The former (in the P -> R transition region) is coincident with a diffused dielectric peak appearing at similar to 170 degrees C, and the latter (in the R -> S transition region) serves as an intermediate structure to bridge the two sub-phases in the R phase region. The incommensurate phase in the P phase region can be inferred from the polarization current density and differential dielectric permittivity anomalies, and it provides the bridge structure during the electric field-induced polarization reversal and antiferroelectric-to-ferroelectric transition in NaNbO3 solid solutions. (C) 2015 AIP Publishing LLC.
Title:
Structure and electrical properties of tetragonal tungsten bronze Ba2CeFeNb4O15
Authors:
Ma, HQ; Lin, K; Liu, LJ; Yang, BL; Rong, YC; Chen, J; Deng, JX; Kawaguchi, S; Kato, K; Xing, XR Author Full Names: Ma, Hongqiang; Lin, Kun; Liu, Laijun; Yang, Baoling; Rong, Yangchun; Chen, Jun; Deng, Jinxia; Kawaguchi, Shogo; Kato, Kenichi; Xing, Xianran
Source:
RSC ADVANCES, 5 (94):76957-76962; 10.1039/c5ra16115k 2015
Abstract:
The crystal structure and electrical microstructure of a tetragonal tungsten bronze (TTB) ceramic, BaCeFeNb4O15 (BCFN), were investigated by high-resolution synchrotron X-ray powder diffraction (SPD), selected area electron diffraction (SAED), and AC impedance spectroscopy. SPD and SAED reveal that the BCFN has a tetragonal structure with space group P4/mbm, and includes an incommensurate modulated behavior. Impedance and AC conductivity tests in the range of 200-360 degrees C suggest thermally activated electrical behavior which originates from both the bulk and the grain boundary elements of the ceramics. The dielectric relaxation in the grain boundaries is due to the trap-controlled ac conduction around doubly ionized oxygen vacancies while the relaxation of the bulk may be associated with the localized electron hopping between the transition-metal ions. These results could be helpful in understanding the electrical conduction and relaxation processes in Fe-containing TTB-type oxides.

Update: 8-Oct-2015

Title:
Oxygen vacancy ordering and its mobility in YMnO3
Authors:
Zhang, QH; Shen, X; Yao, Y; Wang, YG; Jin, CQ; Yu, RC Author Full Names: Zhang, Q. H.; Shen, X.; Yao, Y.; Wang, Y. G.; Jin, C. Q.; Yu, R. C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 648 253-257; 10.1016/j.jallcom.2015.07.032 NOV 5 2015
Abstract:
Oxygen vacancy (V-O) ordering and its mobility in YMnO3 have been studied via electron-beam irradiation. By controlling the beam intensity, three commensurate (A, B and C-type) and one incommensurate V-O-orderings can be formed. The transformation from the A-type to the C-type ordering has also been revealed, which could be attributed to the migration of V-O from the apical V-O site to the planar V-O site. Further, intense irradiation can introduce more V(O)s and make a breakdown of the ferroelectric displacements of Y ions. These results suggest that the V(O)s in YMnO3 system are highly active in several ordered ways and also have a high mobility. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Evolution of atomic distribution during devitrification of bulk metallic glass investigated by atom probe microscopy
Authors:
Mridha, S; Jaeger, DL; Arora, HS; Banerjee, R; Mukherjee, S Author Full Names: Mridha, Sanghita; Jaeger, David L.; Arora, Harpreet Singh; Banerjee, Rajarshi; Mukherjee, Sundeep
Source:
MATERIALS LETTERS, 158 99-103; 10.1016/j.matlet.2015.05.034 NOV 1 2015
Abstract:
Evolution of atomic distribution during devitrification of a zirconium-based bulk metallic glass, Zr41.2Ti13.8Cu12.5Ni10.0Be22.5, was investigated using three-dimensional atom probe microscopy. Atom probe analysis showed uniform distribution of constituent elements for the as-cast alloy, with no phase separation. The metallic glass was annealed at different temperatures to study the crystallization pathways and the length scale, distribution, and morphology of the phases formed. Devitrification was found to proceed via the formation of a metastable icosahedral phase. The devitrification pathway is explained based on "strong-liquid" behavior of this alloy. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Conduction mechanisms and enhanced multiferroic properties of Sr doped Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 thin films
Authors:
Yan, X; Tan, GQ; Ye, W; Ren, HJ; Xia, A Author Full Names: Yan, Xia; Tan, Guoqiang; Ye, Wei; Ren, Huijun; Xia, Ao
Source:
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 26 (10):7407-7414; 10.1007/s10854-015-3371-y OCT 2015
Abstract:
Pure BiFeO3 (BFO) and Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 (BPSxFMO, x = 0.02-0.05) thin films were deposited on fluorine-doped SnO2 (FTO/glass) substrates by a sol-gel method. The systematic studies of crystalline structure, surface morphologies, leakage conduction mechanisms, ferroelectric and magnetic properties of pure BiFeO3 and Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 thin films were investigated. X-ray diffraction patterns, Rietveld analysis and Raman scattering spectra reveal that the (Pr, Sr and Mn) co-doped BiFeO3 thin films give rise to a trigonal (R3m: R) structure transition with respect to the original rhombohedral structure of pure BiFeO3 film. Fowler-Nordheim tunneling conduction mechanism dominates the leakage current of all the films in the relatively high electric field. The significantly enhanced ferroelectric properties of the Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 thin films were observed in comparison with pure BiFeO3 film. In addition, the BPS2FMO film shows the enhanced ferromagnetism with the saturation magnetization (M (s) similar to 1.97 emu cm(-3)), which is almost three times larger than that of pure BFO film (M (s) similar to 0.67 emu cm(-3)), as a result of the small grain size effect and the collapse of space modulated spin structure by the structure transition.
Title:
Crystalline and Spin Chiralities in Multiferroics with Langasite-type Structure and Fe1-xCoxSi Crystals
Authors:
Pikin, SA; Lyubutin, IS; Dudka, AP Author Full Names: Pikin, S. A.; Lyubutin, I. S.; Dudka, A. P.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (5):729-736; 10.1134/S1063774515050077 SEP 2015
Abstract:
It is shown that, when magnetic ordering occurs in layered iron-containing langasites (sp. gr. P321), one of the reasons for spin chiralities of different signs is the presence of structural chirality (the existence of inversion twins), which, in turn, is due to the nonsymmetricity of these crystals. Spin helicoids arise in these multiferroics at split sites of Fe3+ ions below the N,el point. The direction of electric polarization vectors coincides with the direction of the magnetic helicoid axes because of the piezoelectric properties of these materials. Due to the magnetostriction effects, structural chirality wave vector k (z) exceeds the magnetic helicoid wave vector by a factor of 2: k (z) = 2q (z). The temperatures of transitions to the chiral structural and chiral magnetic states may differ. In particular, if the structural transition initial temperature exceeds the magnetic transition temperature (T-U > T-M ), structural displacements may arise in the absence of magnetism at T-M < T < T-U. In noncentrosymmetric Fe1-xCoxSi crystals (sp. gr. P2(1)3), which are not multiferroics, magnetic chirality is due to the Dzyaloshinski-Moriya interaction. The dependence of the moduli of incommensurate wave number of the corresponding helicoid on the atomic composition of the crystals under consideration is nonmonotonic.

Update: 1-Oct-2015

Title:
Strongly anisotropic and complex magnetic behavior in EuRhGe3
Authors:
Bednarchuk, O; Kaczorowski, D Author Full Names: Bednarchuk, Oleksandr; Kaczorowski, Dariusz
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 646 291-297; 10.1016/j.jallcom.2015.06.125 OCT 15 2015
Abstract:
Single crystals of EuRhGe3 were studied by means of magnetic susceptibility, magnetization, heat capacity, resistivity and magnetoresistance measurements, performed in wide ranges of temperature and magnetic field strength. The compound was characterized as a Curie-Weiss paramagnet, due to divalent Eu ions, that orders antiferromagnetically at T-N = 11.3 K. In the ordered state, EuRhGe3 exhibits strong magnetic anisotropy. The magnetic moments are probably nearly confined within the ab plane of the tetragonal crystallographic unit cell, and the magnetic propagation vector is likely perpendicular to this plane. The bulk thermodynamic and transport data concordantly suggest that in zero magnetic field the magnetic structure of EuRhGe3 is incommensurate with the chemical one and bears an amplitude-modulated character. In external magnetic field applied within the easy magnetization plane, two other magnetic structures were detected, each of them having an antiferromagnetic nature. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Electrochemical synthesis of Co7Ni3 and Co6Ni4 nanorods with controlled crystalline phase. Application to methanol electro-oxidation
Authors:
Vilana, J; Escalera-Lopez, D; Gomez, E; Valles, E Author Full Names: Vilana, Joan; Escalera-Lopez, Daniel; Gomez, Elvira; Valles, Elisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 646 669-674; 10.1016/j.jallcom.2015.06.134 OCT 15 2015
Abstract:
CoNi nanorods with modulated crystalline phase have been synthesised by means of a potentiostatic deposition method, using a single electrolytic bath, by only varying the electrodeposition potential. The growth of the nanorods in the interior on the nanochannels of the membrane is mainly controlled by the limited transport of the Co(II) and Ni(II) ions to the growth front. Two types of CoNi nanorods of several microns long, with similar composition but different crystalline phases depending on the applied potential, have been obtained. The potentials for the electrosynthesis of the nanorods have been selected to induce different deposition rates and, as a consequence, different crystalline phases, hcp for the lower deposition rates and fcc (+hcp) for the highest ones. For each selected potential, the nanorods present the same composition and crystalline phase along the rods. The test of the two types of nanorods for the methanol electro-oxidation demonstrated both the specific electrocatalytic behaviour of each one and the promising behaviour of the nanorods as electrocatalysts in direct methanol fuel cells in basic medium, due to their higher surface/volume ratio than that of thin films and the superior stability than that of nanoparticles. The influence of the crystalline phase in the methanol electro-oxidation has been also corroborated from pure-hcp and pure-fcc CoNi films. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Structural phase transitions in the Ti45Zr38Ni17-xFex nano-alloys and their deuterides
Authors:
Rusinek, D; Czub, J; Niewolski, J; Gondek, L; Gajewska, M; Takasaki, A; Hoser, A; Zywczak, A Author Full Names: Rusinek, D.; Czub, J.; Niewolski, J.; Gondek, L.; Gajewska, M.; Takasaki, A.; Hoser, A.; Zywczak, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 646 90-95; 10.1016/j.jallcom.2015.06.023 OCT 15 2015
Abstract:
The mechanically alloyed Ti-Zr-Ni materials are extensively studied due to their promising properties concerning biomedical, electronic or hydrogen related applications (for example the gaseous hydrogen storage and the MNiH batteries). In this paper we address the very crucial issue of the structural properties and transformations of the amorphous and quasicrystalline Ti45Zr38Ni17-xFex (x = 0, 4, 8) and their hydrides. According to the neutron diffraction results, the transformation of the amorphous Ti45Zr38Ni17 phase into the icosahedral quasicrystalline state (the i-phase) is quasi-continuous and starts at the relatively low temperature of 300 degrees C. At 500 degrees C the i-phase is well-developed. At higher temperatures the i-phase transforms into the approximant w-phase and eventually into the cubic phase (the c-phase). Interestingly, the deuterided i-phase exhibits completely different thermal evolution. Namely, this phase decomposes into the simple intermetallic compounds above 625 degrees C. What is worth-mentioning is that the release of deuterium is strictly related to that structural decomposition. The possibility of hydrogenation of the amorphous Ti45Zr38Ni17-xFe (x) phases with maintaining the amorphous nature of the alloys is the other extremely important field of our interest. We established a processing route to meet our goal. Finally, we show that introducing deuterium triggers an exciting phase transition from the deuterided amorphous phase into the unknown before, partially disordered, quasicrystallinelike phase (the glassy quasicrystal) without releasing of deuterium. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Reassessment of the effects of Ce on quasicrystal formation and microstructural evolution in rapidly solidified Al-Mn alloys
Authors:
Coury, FG; Botta, WJ; Bolfarini, C; Kiminami, CS; Kaufman, MJ Author Full Names: Coury, F. G.; Botta, W. J.; Bolfarini, C.; Kiminami, C. S.; Kaufman, M. J.
Source:
ACTA MATERIALIA, 98 221-228; 10.1016/j.actamat.2015.07.046 OCT 1 2015
Abstract:
Rapidly solidified Al-Mn-Ce alloys have been reported to exhibit desirable properties due to the uniform distribution of quasicrystalline (QC) particles in an Al matrix. In this study, several ternary alloy compositions that encompassed the alloys reported in the previous reports, namely Al-6Mn-2Ce, Al-6Mn-4Ce, AI-8Mn-4Ce, Al-12Mn-2Ce and Al-10Mn-5Ce, were prepared by melt spinning and their microstructures were characterized by electron microscopy and X-ray diffraction. The results are in direct contrast with the previous reports available in the literature in that the formation of QCs was only observed in the Al-12Mn-2Ce alloy; in the others, the dispersed phase was not the QC; rather, the structural and compositional information presented in this paper together with data recently published in the literature enabled a reinterpretation of the effect of Ce on rapidly solidified Al-Mn alloys. The main conclusion is that Ce favors the formation of a ternary metastable phase with approximate stoichiometry Al20Mn2Ce. This phase forms in a wide portion of the Al-rich region of the ternary phase diagram and can even coexist with the QC phase in alloys containing low amounts of Ce; in this case, the QC contains no detectable Ce by TEM/EDS, consistent with the conclusion that Ce does not favor QC formation in contrast to the previous reports. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Discovery of a Sodium-Ordered Form of Na3V2(PO4)(3) below Ambient Temperature
Authors:
Chotard, JN; Rousse, G; David, R; Mentre, O; Courty, M; Masquelier, C Author Full Names: Chotard, Jean-Noel; Rousse, Gwenaelle; David, Renald; Mentre, Olivier; Courty, Matthieu; Masquelier, Christian
Source:
CHEMISTRY OF MATERIALS, 27 (17):5982-5987; 10.1021/acs.chemmater.5b02092 SEP 8 2015
Abstract:
The crystal structure of the NASICON Na3V2(PO4)(3) phase (NVP) has been investigated as a function of temperature. Combining laboratory and synchrotron X-ray powder diffraction with single crystal X-ray diffraction, we demonstrate the presence of four polymorphs of NVP from 30 to 225 degrees C. While the high temperature gamma-NVP crystallizes in the classical rhombohedral cell (S.G. R (3) over barc, a = 8.73382(4) angstrom, c = 21.91438(17) angstrom), the low temperature alpha-NVP undergoes a monoclinic distortion (S.G. C2/c, a = 15.1244(6) angstrom, b = 8.7287(3) angstrom, c = 21.6143(8) angstrom, beta = 90.163(2)degrees) together with an ordering of the Na atoms. In the middle temperature range, two incommensurate modulated structures (beta- and beta '-NVP) are also reported for the first time.
Title:
Intermediate-valent CeCoAl - a commensurate modulated structure with short Ce-Co distances
Authors:
Niehaus, O; Hoffmann, RD; Tence, S; Chevalier, B; Poettgen, R Author Full Names: Niehaus, Oliver; Hoffmann, Rolf-Dieter; Tence, Sophie; Chevalier, Bernard; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 230 (9-10):579-591; 10.1515/zkri-2015-1856 SEP 2015
Abstract:
CeCoAl was synthesized by melting of the elements in a sealed niobium tube in an induction furnace. Annealing of the sample gave access to a single phase sample. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Above 271 K CeCoAl crystallizes in its own structure type in the space group C2/m [a = 1107.4(2), b = 440.6(1) and c = 479.6(1) pm, beta = 104.6(1)degrees]. Data obtained at 300 K lead to 511 F-2 values with 20 variables and a residual of [I >= 3 sigma(I)] wR = 0.0539. Below 271 K satellites give rise to the superspace group C2/m(alpha 0 gamma) 00; alpha = 2/3, gamma = 2/5 with a temperature independent q-vector. For the 90 K data (also for 180 and 220 K) the commensurate modulated structure could be refined with 4817 F-2 values, 129 variables and residuals of wR = 0.0347 (main), wR = 0.1927 (satellites 1st order), wR = 0.1541 (satellites 2nd order) and wR = 0.1768 (satellites 3rd order) [a = 1107.5(1), b = 440.3(1) and c = 479.0(1) pm, beta = 104.7(1)degrees]. For the three temperatures only minor variations of the modulation amplitudes are observed. The relation of the low temperature (3+1)D 3a x 5c approximant and the room temperature 3D structure is discussed on the basis of a group-subgroup relation. By investigation of the heat capacity, the phase transition could be identified as a second order one with a transition temperature of 271 K. Magnetic measurements clearly prove the intermediate cerium valence which is in line with the short Ce-Co distances.
Title:
The birth of time-of-flight (TOF) neutron powder diffraction at pulsed neutron source (invited)
Authors:
Sosnowska, IM Author Full Names: Sosnowska, Izabela M.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 50 (9-10):705-715; 10.1002/crat.201400439 SEP 2015
Abstract:
Behind every improvement there is a story. The early history of the TOF neutron powder diffraction technique is presented. Successes and problems in the application of this technique in material science are reported. Powder diffraction technique is very useful when materials, in a single crystal form, reveal complicated electric and magnetic domain structures. Finding and describing the magnetic structure of multiferroics is the great success of ultra-high resolution TOF neutron diffraction. This unique role of the TOF method in discovery of the modulated magnetic structure of BiFeO3 is presented. To date, the TOF powder neutron diffraction technique gives the richest information on the long period modulated magnetic structure of BiFeO3 and its solid solutions. Determination of magnetic moment direction in a crystal lattice is the unique area of application of the TOF technique. The current status and perspectives of the application of the TOF neutron powder diffraction technique in material science are presented in the review.

Update: 24-Sep-2015

Title:
HREM observation and high-pressure composition isotherm measurement of Ti45Zr38Ni17 quasicrystal powders synthesized by mechanical alloying
Authors:
Tominaga, T; Takasaki, A; Shibato, T; Swierczek, K Author Full Names: Tominaga, Tomoki; Takasaki, Akito; Shibato, Tsuyoshi; Swierczek, Konrad
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 645 S292-S294; 1 10.1016/j.jallcom.2014.12.200 OCT 5 2015
Abstract:
Elemental powders consisted of chemical composition of Ti45Zr38Ni17 were mechanical alloyed and annealed subsequently, and the microstructures were characterized by high-resolution electron microscopy (HREM) and an X-ray diffractometry, and hydrogen absorption and desorption pressure-composition (PC) isotherms were measured at 523 K, 573 K and 623 K by a Sieverts type apparatus. The annealing after mechanical alloying (MA) caused formation of an icosahedral quasicrystal with a Ti2Ni type crystal phases. 5 or 10-fold rotational symmetry, which is prohibited to normal crystals, was observed by HREM in a digital diffractogram and an simulated atomic arrangement derived from the digital diffractogram. The hydrogen storage capacity (hydrogen to metal atom ratio: H/M) at 523 K was about 1.3, which decreased with increasing hydrogenation temperatures. All the PC isotherms were steep, and no plateau pressure was observed. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Hydrogen storage properties for Mg-Zn-Y quasicrystal and ternary alloys
Authors:
Luo, XL; Grant, DM; Walker, GS Author Full Names: Luo, Xuanli; Grant, David M.; Walker, Gavin S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 645 S23-S26; 1 10.1016/j.jallcom.2015.01.266 OCT 5 2015
Abstract:
Three Zn-Mg-Y alloys with nominal compositions of Zn50Mg42Y8 and Zn60Mg30Y10 were prepared by induction melting or gas atomisation. XRD and SEM analysis shows samples ZMY-1 and ZMY-2 consisted of multiple phases including icosahedral quasicrystal (QC) i-phase, hexagonal H-phase and Mg7Zn3, whilst ZMY-3 contained QC only. The hydrogen storage properties of the Zn-Mg-Y quasicrystal and ternary alloys were investigated for the first time. The quasicrystal sample ZMY-3 hydrogenated at 300 degrees C had 0.3 wt.% capacity and the DSC decomposition peak temperature was 503 degrees C. Amongst the three samples, the highest hydrogen storage capacity (0.9 wt.%) and the lowest decomposition peak temperature (445 degrees C) was achieved by sample ZMY-1. The pressure-composition-isotherm (PCI) curve of ZMY-1 sample showed a flat plateau gave a plateau pressure of 3.5 bar at 300 degrees C, which indicates a lower dehydrogenation enthalpy than MgH2. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Electrochemical properties of Ti49Zr26Ni25-xPdx (x=0-6) quasicrystal electrodes produced by mechanical alloying
Authors:
Ariga, Y; Takasaki, A; Kimijima, T; Swierczek, K Author Full Names: Ariga, Youhei; Takasaki, Akito; Kimijima, Tsubasa; Swierczek, Konrad
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 645 S152-S154; 1 10.1016/j.jallcom.2015.01.114 OCT 5 2015
Abstract:
Elemental powders consisted of chemical composition of Ti49Zr26Ni25 Pd-x(x) (x = 0, 1, 3, 6) were mechanically alloyed and annealed subsequently, and the discharge performance of the electrodes was measured by a three-electrode cell at room temperature. The annealing after mechanical alloying caused a formation of the icosahedral quasicrystal phase with a Ti2Ni type crystal, C14 Laves and alpha-Ti/Zr phases. The quasilattice constant increased with increasing amount of Pd substituted for Ni up to 3 at.% due to difference in atomic radius between Pd and Ni. The maximum discharge capacity achieved was about 220 mA h/g from a (Ti49Zr26Ni22Pd3) electrode at the first discharge process. (C) 2015 Elsevier B.V. All rights reserved.
Title:
TEM study of the (SbS)(1+delta)(NbS2)(n), (n=1, 2, 3; delta similar to 1.14, 1.20) misfit layer phases
Authors:
Gomez-Herrero, A; Landa-Canovas, AR; Otero-Diaz, LC Author Full Names: Gomez-Herrero, A.; Landa-Canovas, A. R.; Otero-Diaz, L. C.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 230 357-368; 10.1016/j.jssc.2015.07.029 OCT 2015
Abstract:
In the Sb-Nb-S system four new misfit layer phases have been found and carefully investigated via Transmission Electron Microscopy (TEM). Their structures are of composite modulated structure type with stoichiometries that can be formulated as (SbS)(1+delta)(NbS2)(n); for n=1, delta similar to 1.14 and 1.19; for n=2, delta similar to 1.18 and for n=3, delta similar to 1.19. Selected Area Electron Diffraction (SAED) patterns show an almost commensurate fit between the pseudo-tetragonal (SbS) and the pseudo-orthohexagonal (NbS2)(n) subcells along the misfit direction a, with 3(SbS) approximate to 5(NbS2), being b the same for both sub-lattices and c the stacking direction. For n=1, a commensurate phase with 4a(SbS)=7a(NbS2) has also been observed. In addition to the characteristic misfit and associated modulation of the two sub-structures, a second modulation is also present which appears to be primarily associated with the (SbS) sub-structure of both the n=1 and n=2 phases. High Resolution Transmission Electron Microscopy (HRTEM) images show ordered stacking sequences between the (SbS) and (NbS2)(n) lamellae for each of the four phases, however, disordered intergrowths were also occasionally found. Most of the crystals showed different kinds of twinning defects on quite a fine scale. Many crystals showed curled up edges. In some cases the lamellar crystals were entirely folded giving rise to similar diffraction patterns as found for cylindrical crystals. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Enhancement of superconductivity at the onset of charge-density-wave order in a metal
Authors:
Wang, YX; Chubukov, AV Author Full Names: Wang, Yuxuan; Chubukov, Andrey V.
Source:
PHYSICAL REVIEW B, 92 (12):10.1103/PhysRevB.92.125108 SEP 4 2015
Abstract:
We analyze superconductivity in the cuprates near the onset of an incommensurate charge-density-wave (CDW) order with momentum Q = (Q, 0)/(0, Q), as observed in experiments. We first consider a semiphenomenological charge-fermion model in which hot fermions, separated by Q, attract each other by exchanging soft CDW fluctuations. We find that in a quantum-critical region near the CDW transition, T-c = A (g) over bar (c), where (g) over bar (c) is charge-fermion coupling and Ais the prefactor, which we explicitly compute. We then consider the particular microscopic scenario in which the CDW order parameter emerges as a composite field made of primary spin-density-wave fields. We show that charge-fermion coupling (g) over bar (c) is of the order of spin-fermion coupling (g) over bar (s). As a consequence, superconducting Tc is substantially enhanced near the onset of CDW order. Finally, we analyze the effect of an external magnetic field H. We show that, as H increases, the optimal Tc decreases and the superconducting dome becomes progressively more confined to the CDW quantum-critical point. These results are consistent with experiments.
Title:
Quasiperiodicity and 2D topology in 1D charge-ordered materials
Authors:
Flicker, F; van Wezel, J Author Full Names: Flicker, F.; van Wezel, Jasper
Source:
EPL, 111 (3):10.1209/0295-5075/111/37008 AUG 2015
Abstract:
The mathematical description of 1D quasicrystals has recently been linked to that of 2D quantum Hall states. The topological classification of 1D quasicrystals and the corresponding interpretation of their observed charge transport have been widely discussed. We demonstrate the equivalence of both 1D quasicrystals and 2D quantum Hall states to a mean-field treatment of charge order. Using the fractal nature of the spectrum of charge-ordered states we consider incommensurate order as a limit of commensurate. The topological properties of both are identical, arising from a 2D parameter space of phase and wave vector, and fit into class A of the Tenfold Way. The topological nature of all the systems can be tested by measuring a quantized particle transport upon dragging the charge order. Copyright (C) EPLA, 2015

Update: 17-Sep-2015

Title:
Low temperature superplasticity of ultrafine grained Mg-9.25Zn-1.66Y alloy with an icosahedral quasicrystalline phase
Authors:
Kim, WJ; Yoo, YJ Author Full Names: Kim, W. J.; Yoo, Y. J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 643 47-50; 10.1016/j.msea.2015.07.022 SEP 3 2015
Abstract:
The ultrafine grained Mg-9.25Zn-1.66Y alloy sheet with I-phase prepared by directly applying high-ratio differential speed rolling to the as-cast microstructure exhibited excellent low-temperature super-plasticity (386-888% at 443-473 K) at a moderately high strain rate of 10(-3) s(-1). A criterion for achieving low temperature superplasticity was proposed. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Premartensite to martensite transition and its implications for the origin of modulation in Ni2MnGa ferromagnetic shape-memory alloy
Authors:
Singh, S; Bednarcik, J; Barman, SR; Felser, C; Pandey, D Author Full Names: Singh, Sanjay; Bednarcik, J.; Barman, S. R.; Felser, C.; Pandey, Dhananjai
Source:
PHYSICAL REVIEW B, 92 (5):10.1103/PhysRevB.92.054112 AUG 28 2015
Abstract:
We present results of a temperature-dependent high-resolution synchrotron x-ray powder diffraction study of sequence of phase transitions in Ni2MnGa. Our results show that the incommensurate martensite phase results from the incommensurate premartensite phase and not from the austenite phase assumed in the adaptive phase model. The premartensite phase transforms to the martensite phase through a first order phase transition with coexistence of the two phases in a broad temperature interval (similar to 40 K), discontinuous change in the unit cell volume as also in the modulation wave vector across the transition temperature, and considerable thermal hysteresis in the characteristic transition temperatures. The temperature variation of the modulation wave vector q shows smooth analytic behavior with no evidence for any devilish plateau corresponding to an intermediate or ground state commensurate lock-in phase. The existence of the incommensurate 7M-like modulated structure down to 5 K suggests that the incommensurate 7M-like modulation is the ground state of Ni2MnGa and not the Bain distorted tetragonal L1(0) phase or any other lock-in phase with a commensurate modulation. These findings can be explained within the framework of the soft phonon model.
Title:
KEu(MoO4)(2): Polymorphism, Structures, and Luminescent Properties
Authors:
Morozov, VA; Arakcheeva, AV; Pattison, P; Meert, KW; Smet, PF; Poelman, D; Gauquelin, N; Verbeeck, J; Abakumov, AM; Hadermann, J Author Full Names: Morozov, Vladimir A.; Arakcheeva, Alla V.; Pattison, Philip; Meert, Katrien W.; Smet, Philippe F.; Poelman, Dirk; Gauquelin, Nicolas; Verbeeck, Johan; Abakumov, Artem M.; Hadermann, Joke
Source:
CHEMISTRY OF MATERIALS, 27 (16):5519-5530; 10.1021/acs.chemmater.5b01622 AUG 25 2015
Abstract:
In this paper, with the example of two different polymorphs of KEu(MoO4)(2), the influence of the ordering of the A-cations on the luminescent properties in scheelite related compounds (A',A '') [(B',B '')O-4](m) is investigated. The polymorphs were synthesized using a solid state method. The study confirmed the existence of only two polymorphic forms at annealing temperature range 923-1203 K and ambient pressure: a low temperature anorthic alpha-phase and a monoclinic high temperature beta-phase with an incommensurately *modulated structure*. The *structures* of both polymorphs were solved using transmission electron microscopy and refined from synchrotron powder X-ray diffraction data. The monoclinic beta-KEu(MoO4)(2) has a (3+1)-dimensional incommensurately modulated structure (superspace group I2/b(alpha beta 0)00, a = 5.52645(4) angstrom, b = 5.28277(4) angstrom, c = 11.73797(8) angstrom, gamma = 91.2189(4)degrees, q = 0.56821(2)a*-0.12388(3)b*), whereas the anorthic alpha-phase is (3+1)-dimensional commensurately modulated (superspace group I (1) over bar(alpha beta gamma)0, a = 5.58727(22) angstrom, b = 5.29188(18)angstrom, c = 11.7120(4) angstrom, alpha = 90.485(3)degrees, beta = 88.074(3)degrees, gamma = 91.0270(23)degrees, q = 1/2a* + 1/2c*). In both cases the modulation arises due to Eu/K cation ordering at the A site: the formation of a 2-dimensional Eu3+ network is characteristic for the alpha-phase, while a 3-dimensional Eu3+-framework is observed for the beta-phase structure. The luminescent properties of KEu(MoO4)(2) samples prepared under different annealing conditions were measured, and the relation between their optical properties and their structures is discussed.
Title:
Precipitates in a quasicrystal-strengthened Al-Mn-Be-Cu alloy
Authors:
Zupanic, F; Wang, D; Gspan, C; Boncina, T Author Full Names: Zupanic, Franc; Wang, Di; Gspan, Cristian; Boncina, Tonica
Source:
MATERIALS CHARACTERIZATION, 106 93-99; 10.1016/j.matchar.2015.05.013 AUG 2015
Abstract:
In this work, an Al-Mn-Be-Cu alloy was studied containing a primary and eutectic icosahedral quasicrystalline phase in the as-cast microstructure. Special attention was given to a transmission electron microscopy investigation of precipitates formed within the aluminium solid solution (Al-ss) at different temperatures. At 200 degrees C, only binary Al-Cu precipitates (theta') were formed. At 300 degrees C, icosahedral quasicrystalline (IQC) precipitates prevailed with a crystallographic orientation relationship with the Al-ss. The rods of the T-phase (Al20Mn3Cu2) which were precipitated above 400 degrees C, also had a specific orientation relationship with the Al-ss. The primary and eutectic IQC microstructural constituent started to transform rapidly to the T-phase and Be4Al(Mn,Cu) at 500 degrees C. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Self-assembly of the decagonal quasicrystalline order in simple three-dimensional systems
Authors:
Ryltsev, R; Klumov, B; Chtchelkatchev, N Author Full Names: Ryltsev, Roman; Klumov, Boris; Chtchelkatchev, Nikolay
Source:
SOFT MATTER, 11 (35):6991-6998; 10.1039/c5sm01397f 2015
Abstract:
Using molecular dynamics simulations we show that a one-component system can be driven to a three-dimensional decagonal (10-fold) quasicrystalline state just by purely repulsive, isotropic and monotonic interaction pair potential with two characteristic length scales; no attraction is needed. We found that self-assembly of a decagonal quasicrystal from a fluid can be predicted by two dimensionless effective parameters describing the fluid structure. We demonstrate stability of the results under changes of the potential by obtaining the decagonal order for three particle systems with different interaction potentials, both purely repulsive and attractive, but with the same values of the effective parameters. Our results suggest that soft matter quasicrystals with decagonal symmetry can be experimentally observed for the same systems demonstrating the dodecagonal order for an appropriate tuning of the effective parameters.

Update: 10-Sep-2015

Title:
The Effect of Icosahedral Phase on Dynamic Recrystallization Evolution and Hot Workability of Mg-2.0Zn-0.3Zr-0.2Y Alloy
Authors:
Lv, BJ; Peng, J; Chu, Z Author Full Names: Lv, Bin-Jiang; Peng, Jian; Chu, Zhong
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 24 (9):3502-3512; 10.1007/s11665-015-1604-0 SEP 2015
Abstract:
The effect of Icosahedral phase (I-phase) on hot deformation behavior, dynamic recrystallization (DRX) evolution, and hot workability of Mg-2.0Zn-0.3Zr-0.2Y alloy has been investigated in the temperature range of 300-500 A degrees C and strain rate range of 0.001-1 s(-1) using Gleeble 3500D thermo-mechanical simulator. Based on regression analysis for Arrhenius-type equation of flow behavior, the average activation energy of deformation was determined as Q = 277.8 kJ/mol. The model of DRX evolution is . The DRX model agreed well with the microstructure evolution of the alloy at all deformation conditions. At lower strain rates (0.001-0.01 s(-1)), continuous DRX (CDRX) is the main DRX mechanism that occurred near the original grain boundaries. Twin-dynamic recrystallization (TDRX) began to occur at lower deformation temperatures and higher strain rates (0.1-1 s(-1)). At a deformation temperature range of 250 to 350 A degrees C and a strain rate of 1 s(-1), the main DRX mechanism is TDRX, and the density of twins decreased, and CDRX began to occur near the original grain boundaries. When the deformation temperature increased to 400 A degrees C, TDRX disappeared and CDRX occurred near original grain boundaries and I-phase particles. According to the flow stress behavior and DRX model, the processing maps have exhibited the optimum deformation conditions to be 450 A degrees C and the strain rate range of 0.01-0.001 s(-1).
Title:
Crystal chemistry of layered structures formed by linear rigid silyl-capped molecules
Authors:
Lumpi, D; Kautny, P; Stoger, B; Frohlich, J Author Full Names: Lumpi, Daniel; Kautny, Paul; Stoeger, Berthold; Froehlich, Johannes
Source:
IUCRJ, 2 584-600; 10.1107/S2052252515011665 5 SEP 2015
Abstract:
The crystallization behavior of methylthio-or methylsulfonyl-containing spacer extended Z, Z-bis-ene-yne molecules capped with trimethylsilyl groups obtained by (tandem) thiophene ring fragmentation and of two non-spacer extended analogs were investigated. The rigid and linear molecules generally crystallized in layers whereby the flexibility of the layer interfaces formed by the silyl groups leads to a remarkably rich crystal chemistry. The molecules with benzene and thiophene spacers both crystallized with C2/c symmetry and can be considered as merotypes. Increasing the steric bulk of the core by introduction of ethylenedioxythiophene (EDOT) gave a structure incommensurately modulated in the [010] direction. Further increase of steric demand in the case of a dimethoxythiophene restored periodicity along [010] but resulted in a doubling of the c vector. Two different polytypes were observed, which feature geometrically different layer interfaces (non-OD, order-disorder, polytypes), one with a high stacking fault probability. Oxidation of the methylthio groups of the benzene-based molecule to methylsulfonyl groups led to three polymorphs (two temperature-dependent), which were analyzed by Hirshfeld surface d(e)/d(i) fingerprint plots. The analogously oxidized EDOT-based molecule crystallized as systematic twins owing to its OD polytypism. Shortening of the backbone by removal of the aryl core resulted in an enantiomorphic structure and a further shortening by removal of a methylthio-ene fragment again in a systematically twinned OD polytype.
Title:
Good reproductive preparation method of Li-intercalated hexagonal boron nitride and transmission electron microscopy - Electron energy loss spectroscopy analysis
Authors:
Sumiyoshi, A; Hyodo, H; Sato, Y; Terauchi, M; Kimura, K Author Full Names: Sumiyoshi, A.; Hyodo, H.; Sato, Y.; Terauchi, M.; Kimura, K.
Source:
SOLID STATE SCIENCES, 47 68-72; 10.1016/j.solidstatesciences.2015.04.011 SEP 2015
Abstract:
A Li-intercalated hexagonal boron nitride (Li-h-BNIC) phase was synthesized using a highly reproducible method that involves annealing an Li3N and h-BN mixture at 1220 K. Powder X-ray diffraction, electrical conductivity measurements, transmission electron microscopy (TEM) and electron energy loss spectroscopy were performed. The stacking of BN atomic layers in the Li-h-BNIC phase is not the same as the two-layer stacking periodicity of h-BN. TEM observation suggests the existence of incommensurate periodicity along the intralayer direction. From the low-loss and core-loss spectra, the Li-h-BNIC phase is not metal as predicted by the first-principle calculations. Satellite peaks of 1 s to pi* transition in the B K-edge core-loss spectrum indicate the presence of N atom vacancies modified by O atoms in the h-BN atomic layer. (C) 2015 Elsevier Masson SAS. All rights reserved.
Title:
Cluster-Based Solidification and Growth Algorithm for Decagonal Quasicrystals
Authors:
Kuczera, P; Steurer, W Author Full Names: Kuczera, P.; Steurer, W.
Source:
PHYSICAL REVIEW LETTERS, 115 (8):10.1103/PhysRevLett.115.085502 AUG 21 2015
Abstract:
A novel approach is used for the simulation of decagonal quasicrystal (DQC) solidification and growth. It is based on the observation that in well-ordered DQCs the atoms are largely arranged along quasiperiodically spaced planes parallel to the tenfold axis, running throughout the whole structure in five different directions. The structures themselves can be described as quasiperiodic arrangements of decagonal columnar clusters (cluster covering) that partially overlap in a systematic way. Based on these findings, we define a cluster interaction model within the mean field approximation, with effectively asymmetric interactions ranging beyond the nearest neighbors. In our Monte Carlo simulations, this leads to a long-range ordered quasiperiodic ground state. Indications of two finite-temperature unlocking phase transitions are observed, and are related to the two fundamental length scales that are characteristic for the system.
Title:
Complex variable method for an anti-plane elliptical cavity of one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Yu, J; Guo, JH; Xing, YM Author Full Names: Yu Jing; Guo Junhong; Xing Yongming
Source:
CHINESE JOURNAL OF AERONAUTICS, 28 (4):1287-1295; 10.1016/j.cja.2015.04.013 AUG 2015
Abstract:
Based on the fundamental equations of piezoelasticity of quasicrystal media, using the symmetry operations of point groups, the linear piezoelasticity behavior of one-dimensional (1D) hexagonal quasicrystals is investigated and the piezoelasticity problem of 1D hexagonal quasicrystals is decomposed into two uncoupled problems, i.e., the classical plane elasticity problem of conventional hexagonal crystals and the phonon-phason-electric coupling elasticity problem of 1D hexagonal quasicrystals. The final governing equations are derived for the phonon-phason-electric coupling anti-plane elasticity of 1D hexagonal quasicrystals. The complex variable method for an anti-plane elliptical cavity in 1D hexagonal piezoelectric quasicrystals is proposed and the exact solutions of complex potential functions, the stresses and displacements of the phonon and the phason fields, the electric displacements and the electric potential are obtained explicitly. Reducing the cavity into a crack, the explicit solutions in closed forms of electro-elastic fields, the field intensity factors and the energy release rate near the crack tip are derived. (C) 2015 The Authors.

Update: 27-Aug-2015

Title:
(3+1)-Dimensional incommensurately modulated structure and photoluminescence property of polyphosphate Ho(PO3)(3)
Authors:
Zhao, D; Zhang, RH; Ma, FX; Li, FF Author Full Names: Zhao, Dan; Zhang, Rong-Hua; Ma, Fa-Xue; Li, Fei-Fei
Source:
MATERIALS LETTERS, 157 219-221; 10.1016/j.matlet.2015.05.125 OCT 15 2015
Abstract:
Single-crystal of polyphosphate Ho(PO3)(3) has been prepared under high temperature molten-salt method and its structure has been characterized by single crystal X-ray diffraction analysis. In-commensurately modulated structure of compound Ho(PO3)(3) was perfectly modeled using high-dimensional approach with centrosymmetric superspace group C2/c(0 beta 0)s0 and modulation vector q=0.362b*. The basic structure features infinite 1-D zigzag chains of (PO3)infinity running along the c-axis, which are further interconnected by HoO6 octahedra. Although with high concentration of Ho3+ ion, the emission spectrum shows the characteristic 4f transitions of Ho3+ ion of S-5(2)-> I-5(8) at about 566 nm, making it as a promising green emitting phosphor. (C) 2015 Elsevier B.V. All rights reserved.

Update: 20-Aug-2015

Title:
Field-induced spin density wave and spiral phases in a layered antiferromagnet
Authors:
Stone, MB; Lumsden, MD; Garlea, VO; Grenier, B; Ressouche, E; Samulon, EC; Fisher, IR Author Full Names: Stone, M. B.; Lumsden, M. D.; Garlea, V. O.; Grenier, B.; Ressouche, E.; Samulon, E. C.; Fisher, I. R.
Source:
PHYSICAL REVIEW B, 92 (2):10.1103/PhysRevB.92.020415 JUL 28 2015
Abstract:
We determine the low-field ordered magnetic phases of the S = 1 dimerized antiferromagnet Ba3Mn2O8 using single-crystal neutron diffraction. We find that for magnetic fields between mu H-0 = 8.80 T and 10.56 T applied along the [1 (1) over bar0] direction the system exhibits spin density wave order with incommensurate wave vectors of type (eta,eta,epsilon). For mu H-0 > 10.56 T, the magnetic order changes to a spiral phase with incommensurate wave vectors only along the [hh0] direction. For both field-induced ordered phases, the magnetic moments are lying in the plane perpendicular to the field direction. The nature of these two transitions is fundamentally different: the low-field transition is a second-order transition to a spin density wave ground state, while the one at higher field, toward the spiral phase, is of first order.
Title:
Symmetry-Based Computational Tools for Magnetic Crystallography
Authors:
Perez-Mato, JM; Gallego, SV; Tasci, ES; Elcoro, L; de la Flor, G; Aroyo, MI Author Full Names: Perez-Mato, J. M.; Gallego, S. V.; Tasci, E. S.; Elcoro, L.; de la Flor, G.; Aroyo, M. I. Edited by: Clarke DR
Source:
ANNUAL REVIEW OF MATERIALS RESEARCH, VOL 45, 45 217-248; 10.1146/annurev-matsci-070214-021008 2015 Book Series: Annual Review of Materials Research
Abstract:
In recent years, two important advances have opened new doors for the characterization and determination of magnetic structures. Firstly, researchers have produced computer-readable listings of the magnetic or Shubnikov space groups. Secondly, they have extended and applied the superspace formalism, which is presently the standard approach for the description of nonmagnetic incommensurate structures and their symmetry, to magnetic structures. These breakthroughs have been the basis for the subsequent development of a series of computer tools that allow a more efficient and comprehensive application of magnetic symmetry, both commensurate and incommensurate. Here we briefly review the capabilities of these computation instruments and present the fundamental concepts on which they are based, providing various examples. We show how these tools facilitate the use of symmetry arguments expressed as either a magnetic space group or a magnetic superspace group and allow the exploration of the possible magnetic orderings associated with one or more propagation vectors in a form that complements and goes beyond the traditional representation method. Special focus is placed on the programs available online at the Bilbao Crystallographic Server (http://www. cryst.ehu.es).

Update: 13-Aug-2015

Title:
Thermodynamic Aspects of Homogeneous Nucleation Enhanced by Icosahedral Short Range Order in Liquid Fcc-Type Alloys
Authors:
Rappaz, M; Kurtuldu, G Author Full Names: Rappaz, Michel; Kurtuldu, Gueven
Source:
JOM, 67 (8):1812-1820; 10.1007/s11837-015-1328-5 AUG 2015
Abstract:
We have recently shown that minute solute element additions to liquid metallic alloys can strongly influence the nucleation of the fcc phase and act as a grain refinement method. Electron back-scattered diffraction observations revealed a concomitant increase in the percentage of nearest neighbor (nn) grains that are in a twin relationship. Furthermore, multiple-twinned (MT) nn grain configurations with a fivefold symmetry around a common < 110 > direction have been identified, an occurrence that can be explained when the symmetry of the icosahedron is accounted for. It was then conjectured that a new nucleation mechanism occurs in two steps: first, the formation of small icosahedral quasicrystals in the melt, followed by heteroepitaxy of the fcc phase on facets of these quasicrystals. In the present contribution, based on thermodynamics arguments, it is proposed that the first step occurs by spinodal decomposition of the liquid, in a manner similar to Guinier-Preston zones formation in solid state precipitation, while the second step is a transformation of these quasicrystal precursors into MT-fcc nanocrystals once the driving force for this transformation is sufficient to overcome the fcc-liquid interfacial energy and the elastic strains associated with MT-fcc nanoparticles. This explanation sets up guidelines for finding solute elements and composition ranges that favor this grain refinement mechanism.
Title:
Symmetry of icosahedral quasicrystals
Authors:
Madison, AE Author Full Names: Madison, A. E.
Source:
STRUCTURAL CHEMISTRY, 26 (4):923-942; 10.1007/s11224-014-0559-3 AUG 2015
Abstract:
The concept of infinitely fragmented fractal tiling is proposed for the description of the structure and symmetry of quasicrystals. Fractal tilings may serve as unique "parent" structures for the corresponding local isomorphism class. The generating symmetry elements and some special features of the resulting symmetry groups of the fractal tilings are analyzed. Simple inflation/deflation rules for icosahedral quasicrystals are proposed, and natural local matching rules are derived.
Title:
Incommensurate spin density wave at a ferromagnetic quantum critical point in a three-dimensional parabolic semimetal
Authors:
Murray, JM; Vafek, O; Balents, L Author Full Names: Murray, James M.; Vafek, Oskar; Balents, Leon
Source:
PHYSICAL REVIEW B, 92 (3):10.1103/PhysRevB.92.035137 JUL 21 2015
Abstract:
We explore the ferromagnetic quantum critical point in a three-dimensional semimetallic system with upwardand downward-dispersing bands touching at the Fermi level. Evaluating the static spin susceptibility to leading order in the coupling between the fermions and the fluctuating ferromagnetic order parameter, we find that the ferromagnetic quantum critical point is masked by an incommensurate, longitudinal spin density wave phase. We first analyze an idealized model that, despite having strong spin-orbit coupling, still possesses O(3) rotational symmetry generated by the total angular momentum operator. In this case, the direction of the incommensurate spin density wave propagation can point anywhere, while the magnetic moment is aligned along the direction of propagation. Including symmetry-allowed anisotropies in the fermion dispersion and the coupling to the order parameter field, however, we find that the ordering wavevector instead breaks a discrete symmetry and aligns along either the [111] or [100] direction, depending on the signs and magnitudes of these two types of anisotropy.
Title:
Spin- and Pair-Density-Wave Glasses
Authors:
Mross, DF; Senthil, T Author Full Names: Mross, David F.; Senthil, T.
Source:
PHYSICAL REVIEW X, 5 (3):10.1103/PhysRevX.5.031008 JUL 20 2015
Abstract:
Spontaneous breaking of translational symmetry, known as density-wave order, is common in nature. However, such states are strongly sensitive to impurities or other forms of frozen disorder leading to fascinating glassy phenomena. We analyze impurity effects on a particularly ubiquitous form of broken translation symmetry in solids: a spin-density wave (SDW) with spatially modulated magnetic order. Related phenomena occur in pair-density-wave (PDW) superconductors where the superconducting order is spatially modulated. For weak disorder, we find that the SDW or PDW order can generically give way to a SDWor PDW glass-new phases of matter with a number of striking properties, which we introduce and characterize here. In particular, they exhibit an interesting combination of conventional (symmetry-breaking) and spin-glass (Edwards-Anderson) order. This is reflected in the dynamic response of such a system, which-as expected for a glass-is extremely slow in certain variables, but, surprisingly, is fast in others. Our results apply to all uniaxial metallic SDW systems where the ordering vector is incommensurate with the crystalline lattice. In addition, the possibility of a PDW glass has important consequences for some recent theoretical and experimental work on La2-xBaxCu2O4.
Title:
A magnetocaloric effect arising from a ferromagnetic transition in the martensitic state in Heusler alloy of Ni50Mn36Sb8Ga6
Authors:
Tian, FH; Zeng, YY; Xu, MW; Yang, S; Lu, T; Wang, JQ; Chang, TY; Adil, M; Zhang, Y; Zhou, C; Song, XP Author Full Names: Tian, Fanghua; Zeng, Yuyang; Xu, Minwei; Yang, Sen; Lu, Tao; Wang, Jieqiong; Chang, Tieyan; Adil, Murtaza; Zhang, Yin; Zhou, Chao; Song, Xiaoping
Source:
APPLIED PHYSICS LETTERS, 107 (1):10.1063/1.4926411 JUL 6 2015
Abstract:
We report a magnetocaloric effect with nearly zero thermal hysteresis in Heusler alloy of Ni50Mn36Sb8Ga6 around room temperature due to a ferromagnetic transition in martensitic state (FTMS). The refrigerant capacity value of this ferromagnetic transition in the vicinity of onset temperature T-M(C) can arrive at 163.8 J/kg, much higher than that of first-order magnetically martensitic transition in the same alloy. Such a magnetocaloric effect in FTMS is attributed to a second-order (or a weak first-order) transition from an antiferromagnetic phase with modulated 7M orthorhombic structure to a ferromagnetic phase with modulated 4O orthorhombic structure. (C) 2015 AIP Publishing LLC.

Update: 6-Aug-2015

Title:
Microstructural transformation of quasicrystalline AlFeCrTi extruded bars upon long thermal treatments
Authors:
Garcia-Escorial, A; Natale, E; Cremaschi, VJ; Todd, I; Lieblich, M Author Full Names: Garcia-Escorial, A.; Natale, E.; Cremaschi, V. J.; Todd, I.; Lieblich, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 643 S199-S203; 1 10.1016/j.jallcom.2014.12.164 SEP 15 2015
Abstract:
Bulk Al93Fe3Cr2Ti2 bars extruded from gas atomised powder particles present a microstructure of an aluminium matrix reinforced with a spherical nanoquasicrystalline phase. In this work the evolution of the microstructure of Al93Fe3Cr2Ti2 extruded bars upon heating at 400 degrees C for up to 1000 h is investigated by means of X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. According to our observations we propose that the quasicrystalline alloy evolves in two steps: a first step consists in the decomposition of the supersaturated solid solution of the matrix and the quasicrystals, and a second step in the transformation of the quasicrystals into the equilibrium phases. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Characterization of aluminium matrix composites reinforced by Al-Cu-Fe quasicrystalline particles
Authors:
Litynska-Dobrzynska, L; Dutkiewicz, J; Stan-Glowinska, K; Wajda, W; Dembinski, L; Langlade, C; Coddet, C Author Full Names: Litynska-Dobrzynska, L.; Dutkiewicz, J.; Stan-Glowinska, K.; Wajda, W.; Dembinski, L.; Langlade, C.; Coddet, C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 643 S114-S118; 1 10.1016/j.jallcom.2014.11.125 SEP 15 2015
Abstract:
Aluminium matrix composites were consolidated from elemental Al powder and atomised Al65Cu20Fe15 particles by vacuum hot pressing technique. The spherical Al65Cu20Fe15 particles consisted of icosahedral quasicrystalline dendrites or cells and cubic tau-AlCu(Fe) phase located in interdendritic areas. The composites with different content of the reinforcement particles (20, 40 and 60 wt%) were prepared. All composites showed density about 99% and a good bonding between the Al65Cu20Fe15 particles and the matrix. It was shown that the phase composition of the atomised particles did not change after consolidation for the composite containing 20% and 40% added particles while Al2Cu precipitates formed at the Al/Al65Cu20Fe15 interfaces and inside the matrix in the composite with 60% of Al65Cu20Fe15 particles. With the increase of the volume fraction of the reinforcement in the composite the hardness as well as compressive strength increased reaching the value of 173 HV0.5 and 370 MPa, respectively for 60% of Al65Cu20Fe15 particles. The friction coefficient slightly varied in the range 0.5-0.7 depending on the composition. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Formation of Complex Intermetallics in the Al-Rich Part of Al-Pt-Ru
Authors:
Kapush, D; Samuha, S; Meshi, L; Velikanova, TY; Grushko, B Author Full Names: Kapush, D.; Samuha, S.; Meshi, L.; Velikanova, T. Ya.; Grushko, B.
Source:
JOURNAL OF PHASE EQUILIBRIA AND DIFFUSION, 36 (4):327-332; 10.1007/s11669-015-0385-3 AUG 2015
Abstract:
The study confirmed the stability of the previously reported ternary C-phase (, a = 0.77353(3) nm for Al73.5Pt10Ru16.5), whose composition was found to range between Al73Pt6Ru21 and Al73.5Pt14.5Ru12. The thermodynamically stable decagonal phase was revealed for the first time at 700-900 A degrees C in a small compositional region around Al78Pt6Ru16. It belongs to the D-4 structural type (1.65 nm periodicity in the specific direction). The metastable Al-Pt chi-phase (P31c) is stabilized by the addition of only similar to 1.5 at.% Ru and extends up to similar to 12 at.% Ru. The lattice parameters for Al76Pt18.6Ru5.4 are a = 1.2256(4) and c = 2.7331(4) nm.
Title:
Periodic almost-Schrodinger equation for quasicrystals
Authors:
Blinov, IV Author Full Names: Blinov, Igor V.
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep11492 JUL 24 2015
Abstract:
A new method for finding electronic structure and wavefunctions of electrons in quasiperiodic potential is introduced. To obtain results it uses slightly modified Schrodinger equation in spaces of dimensionality higher than physical space. It enables to get exact results for quasicrystals without expensive non-exact calculations.
Title:
Complex antiferromagnetic structure in the intermediate-valence intermetallic Ce-2 RuZn4
Authors:
Hartwig, S; Prokes, K; Hansen, T; Ritter, C; Gerke, B; Pottgen, R; Mydosh, JA; Forster, T Author Full Names: Hartwig, Steffen; Prokes, Karel; Hansen, Thomas; Ritter, Clemens; Gerke, Birgit; Poettgen, Rainer; Mydosh, J. A.; Foerster, Tobias
Source:
PHYSICAL REVIEW B, 92 (2):10.1103/PhysRevB.92.024420 JUL 17 2015
Abstract:
Neutron powder diffraction experiments were performed on the intermediate-valence Ce-2 RuZn4 intermetallic compound and combined with magnetic bulk measurements including high magnetic field experiments up to 58 T. Previous theoretical studies suggest that only one (here Ce1) out of two inequivalent Ce sites is magnetically active. Ce-2 RuZn4 orders antiferromagnetically at T-N = 2.3 K. The magnetic structure is characterized by an incommensurate propagation vector q(m) = (0.384, 0.384, 1/2). Assuming that the Ce2 site does not carry any substantial moment, Ce1 magnetic moments are confined to the (110)-type planes and transversely modulated with an amplitude of 1.77(3) mu(B).
Title:
Commensurate and incommensurate spin-density waves and the superconductivity dome in heavy electron systems
Authors:
Schlottmann, P Author Full Names: Schlottmann, P.
Source:
PHYSICAL REVIEW B, 92 (4):10.1103/PhysRevB.92.045115 JUL 16 2015
Abstract:
The nesting of the Fermi surfaces of an electron and a hole pocket separated by a nesting vector Q and the interaction between electrons gives rise to itinerant antiferromagnetism. The order can gradually be suppressed by mismatching the nesting and a quantum critical point is obtained as the Neel temperature tends to zero. If the vector Q is commensurate with the lattice (umklapp with Q = G/2), pairs of electrons can be transferred between the pockets and a superconducting dome above the quantum critical point may arise. If the vector Q is not commensurate with the lattice, there are eight phases that need to be considered: commensurate and incommensurate spin and charge density waves and four superconductivity phases, two of them with a modulated order parameter of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type. The renormalization group equations are studied and numerically integrated. The phase diagram is obtained as a function of the mismatch of the Fermi surfaces and the magnitude of vertical bar Q - G/2 vertical bar.
Title:
Non-Fermi-Liquid Behavior in Metallic Quasicrystals with Local Magnetic Moments
Authors:
Andrade, EC; Jagannathan, A; Miranda, E; Vojta, M; Dobrosavljevic, V Author Full Names: Andrade, Eric C.; Jagannathan, Anuradha; Miranda, Eduardo; Vojta, Matthias; Dobrosavljevic, Vladimir
Source:
PHYSICAL REVIEW LETTERS, 115 (3):10.1103/PhysRevLett.115.036403 JUL 14 2015
Abstract:
Motivated by the intrinsic non-Fermi-liquid behavior observed in the heavy-fermion quasicrystal Au51Al34Yb15, we study the low-temperature behavior of dilute magnetic impurities placed in metallic quasicrystals. We find that a large fraction of the magnetic moments are not quenched down to very low temperatures T, leading to a power-law distribution of Kondo temperatures P(T-K) similar to T-K(alpha-1), with a nonuniversal exponent alpha, in a remarkable similarity to the Kondo-disorder scenario found in disordered heavy-fermion metals. For alpha < 1, the resulting singular P(T-K) induces non-Fermi-liquid behavior with diverging thermodynamic responses as T -> 0.

Update: 30-Jul-2015

Title:
Effect of Ti addition on the glass forming ability, crystallization, and plasticity of (Zr64.13Cu15.75Ni10.12Al10)(100-x)Ti-x bulk metallic glasses
Authors:
Shi, B; Xu, YL; Ma, WL; Li, C; Estefania, CV; Li, JG Author Full Names: Shi, Bo; Xu, Yuanli; Ma, Wenli; Li, Chao; Estefania, Carmen Verge; Li, Jiangong
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 639 345-349; 10.1016/j.msea.2015.04.100 JUL 15 2015
Abstract:
A series of (Zr(64.13)Cu(15.7)sNi(10.12)Al(10))(100-x)Ti-x (x=0-7) bulk metallic glasses were prepared by water-cooled copper mold casting method. The glass forming ability, crystallization behavior, and plasticity of the (Zr64.13Cu15.75Ni10.12Al10)(100-x)Ti-x alloys with different Ti contents were studied. The reduced glass transition temperature increases with Ti addition and a maximum value of 0.562 is achieved at x=5, indicating that the glass forming ability increases with Ti addition. Compared with that of one crystallization step for the sample without Ti addition, the Ti (x >= 2) containing alloys exhibit a two-step crystallization behavior. In addition, the initial crystallization temperature decreases from 744 to 684 K as x increases from 0 to 7. Icosahedral quasicrystal phase was found to precipitate in the amorphous matrix in the first crystallization step, implying that strong icosahedral short-range order may exist in the Ti (x >= 2) containing alloys. moreover, the (Zr64.13Cu15.75Ni10.12Al10)(100-x)Ti-x bulk metallic glasses exhibit excellent plasticity, i.e., a plastic engineering strain in compression larger than 80% for x <= 6. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Effects of Al-Cr-Fe Quasicrystal Content on Tribological Properties of Cold-Sprayed Titanium Composite Coatings
Authors:
Khun, NW; Li, RT; Loke, K; Khor, KA Author Full Names: Khun, N. W.; Li, R. T.; Loke, K.; Khor, K. A.
Source:
TRIBOLOGY TRANSACTIONS, 58 (4):616-624; 10.1080/10402004.2014.991860 2015
Abstract:
Titanium (Ti) composite coatings were prepared on commercially available Ti substrates via a cold-spray process. Quasicrystalline Al-Cr-Fe particles were incorporated in the cold-sprayed Ti matrices at different contents to form a new type of wear-resistant Ti composite coating. The tribological properties of the Ti composite coatings were systematically investigated using steel ball-on-disc microtribological testing. The incorporation of 10 wt% Al-Cr-Fe particles gave rise to the higher wear resistance of the Ti composite coating than that of the Ti coating due to the higher wear resistance of the Al-Cr-Fe particles than that of the Ti matrix. As a result, an increase in the Al-Cr-Fe particle content to 20 wt% increased the wear resistance of the Ti composite coating. However, the wear resistance of the Ti composite coating decreased with a further increase in the Al-Cr-Fe particle content to 30 wt% due to the significantly increased volume of micropores in the composite coating. It could be concluded that the Ti composite coating with 20 wt% Al-Cr-Fe particles had the highest wear resistance among the cold-sprayed coatings used in this study.
Title:
Complex physical properties of EuMgSi - a complementary study by neutron powder diffraction and Eu-151 Mossbauer spectroscopy
Authors:
Niehaus, O; Ryan, DH; Flacau, R; Lemoine, P; Chernyshov, D; Svitlyk, V; Cuervo-Reyes, E; Slabon, A; Nesper, R; Schellenberg, I; Pottgen, R Author Full Names: Niehaus, O.; Ryan, D. H.; Flacau, R.; Lemoine, P.; Chernyshov, D.; Svitlyk, V.; Cuervo-Reyes, E.; Slabon, A.; Nesper, R.; Schellenberg, I.; Poettgen, R.
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 3 (27):7203-7215; 10.1039/c5tc01017a 2015
Abstract:
X-ray pure samples of EuMgSi were synthesized by reactions of the elements in sealed niobium tubes using a high frequency and subsequently a resistance furnace. The structure was investigated by single crystal X-ray diffraction: TiNiSi-type, Pnma, a = 769.5(2), b = 455.0(1), c = 836.9(2) pm, wR(2) = 0.033 [I > 2 sigma(I)], and 705 F-2 values with 20 variables. Powder synchrotron radiation diffraction experiments did not reveal any structural changes down to 4.3 K. Magnetic susceptibility data and Eu-151 Mossbauer spectra clearly indicate a stable Eu2+ configuration. Two distinct magnetic anomalies around 12 and 14 K can be observed for different samples with dc- and ac-susceptibility, heat capacity and resistivity measurements. Fitting of hyperfine field splitting as a function of temperature (Eu-151 Mossbauer spectroscopy data) with a Brillouin function also leads to a magnetic ordering around 14 K. Electronic structure calculations in coincidence with the resistivity measurement prove narrow (or nearly zero) gap-semiconducting behaviour. The calculated band gap energy of 0.03 eV should be considered with precautions due to the accuracy of this method. An incommensurate magnetic structure with the propagation vector k = [q(x) approximate to 0.37, 0, 0] was determined using neutron diffraction data at 5.5 K. In consensus of dc- and ac-susceptibility and neutron powder diffraction a complex combination of antiferromagnetic and ferromagnetic interactions, most likely by super-exchange, is confirmed. These cause two magnetic ordering temperatures, though only one independent crystallographic Eu site in terms of the crystal structure is present in EuMgSi.

Update: 23-Jul-2015

Title:
Microstructure and mechanical properties of sand mold cast Mg-4.58Zn-2.6Gd-0.18Zr magnesium alloy after different heat treatments
Authors:
Liu, SJ; Yang, GY; Luo, SF; Jie, WQ Author Full Names: Liu, S. J.; Yang, G. Y.; Luo, S. F.; Jie, W. Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 644 846-853; 10.1016/j.jallcom.2015.05.062 SEP 25 2015
Abstract:
Microstructure and mechanical properties of sand mold cast Mg-4.58Zn-2.6Gd-0.18Zr magnesium alloy after different heat treatments were investigated. As-cast alloy was composed of alpha(Mg) matrix, interdendritic alpha(Mg) + W(Mg3Zn3Gd2) eutectic, icosahedral quasicrystalline I(Mg3Zn6Gd) phase and Mg3Gd particles within alpha(Mg) matrix. After solution treatment at 505 degrees C for 16 h, most of alpha(Mg) + W(Mg3Zn3Gd2) eutectic dissolved into alpha(Mg) matrix, but a new phase, Zn2Zr3, precipitated within alpha(Mg) matrix. The appropriate aging treatment was done at 220 degrees C for 16 h, after which some dispersive fine eutectics re-precipitated along the grain boundary. Furthermore, rod-like beta(1)' and plate-like beta(2)' formed within alpha(Mg) matrix. The ultimate tensile strength, yield strength and elongation of the experimental alloy in the T6 state at room temperature were 280 MPa, 175 MPa and 7.5%, respectively. According to strengthening contribution calculation, it is revealed that both the second phase strengthening and the solid solution strengthening played important roles in improving the mechanical properties after T6 treatment. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Hot compression characteristics and processing maps of a cast Mg-9.5Zn-2.0Y alloy with icosahedral quasicrystalline phase
Authors:
Kwak, TY; Lim, HK; Kim, WJ Author Full Names: Kwak, T. Y.; Lim, H. K.; Kim, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 644 645-653; 10.1016/j.jallcom.2015.04.158 SEP 25 2015
Abstract:
Hot compressive characteristics and processing maps of a cast Mg-9.5Zn-2.0Y alloy with I-phase (ZW92) were studied in the temperature range between 523 and 723 K and in the strain rate range between 10(-3) and 10 s(-1). According to the analysis of deformation behavior, the rate-controlling mechanism governing deformation during entire compression process was lattice diffusion controlled dislocation climb creep and power-law breakdown. Comparison of the processing maps of ZW92 with those of the cast Mg-Zn-Y alloys with different types of intermetallic compounds (W- and long period stacking ordered phases) and the cast Mg-Al-Zn alloy (AZ80) alloy with beta-Mg17Al12 phase in terms of eta values and the domain sizes of the unstable regime indicated that ZW92 exhibited a better hot workability at high strain rates above 1 s-1. This result was attributed to the suppression of power law breakdown in ZW92 due to occurrence of extensive dynamic recrystallization at high strain rates, which was facilitated by the effective fragmentation and dispersion of I-phase during deformation at high strain rates. A fully recrystallized microstructure composed of defect-free fine grains (9.34 mu m) with high fraction of high angle grain boundaries (0.81) was obtained at 623 K - 10 s(-1). (C) 2015 Elsevier B.V. All rights reserved.

Update: 16-Jul-2015

Title:
Structural crossover from nonmodulated to long-period modulated tetragonal phase and anomalous change in ferroelectric properties in the lead-free piezoelectric Na1/2Bi1/2TiO3-BaTiO3
Authors:
Rao, BN; Khatua, DK; Garg, R; Senyshyn, A; Ranjan, R Author Full Names: Rao, Badari Narayana; Khatua, Dipak Kumar; Garg, Rohini; Senyshyn, Anatoliy; Ranjan, Rajeev
Source:
PHYSICAL REVIEW B, 91 (21):10.1103/PhysRevB.91.214116 JUN 29 2015
Abstract:
The highly complex structure-property interrelationship in the lead-free piezoelectric (x) Na1/2Bi1/2TiO3 - (1 - x) BaTiO3 is a subject of considerable contemporary debate. Using comprehensive x-ray, neutron diffraction, dielectric, and ferroelectric studies, we have shown the existence of a new criticality in this system at x = 0.80, i.e., well within the conventional tetragonal phase field. This criticality manifests as a nonmonotonic variation of the tetragonality and coercivity and is shown to be associated with a crossover from a nonmodulated tetragonal phase (for x < 0.8) to a long-period modulated tetragonal phase (for x > 0.80). It is shown that the stabilization of long-period modulation introduces a characteristic depolarization temperature in the system. While differing qualitatively from the two-phase model often suggested for the critical compositions of this system, our results support the view with regard to the tendency in perovskites to stabilize long-period modulated structures as a result of complex interplay of antiferrodistortive modes [Bellaiche and Iniguez, Phys. Rev. B 88, 014104 ( 2013); Prosandeev, Wang, Ren, Iniguez, ands Bellaiche, Adv. Funct. Mater. 23, 234 (2013)].
Title:
Crystal structure, incommensurate magnetic order, and ferroelectricity in Mn1-xCuxWO4 (0 <= x <= 0.19)
Authors:
Kumar, CMN; Xiao, Y; Lunkenheimer, P; Loidl, A; Ohl, M Author Full Names: Kumar, C. M. N.; Xiao, Y.; Lunkenheimer, P.; Loidl, A.; Ohl, M.
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235149 JUN 29 2015
Abstract:
We have carried out a systematic study on the effect of Cu doping on nuclear, magnetic, and dielectric properties in Mn1-xCuxWO4 for 0 <= x <= 0.19 by a synergic use of different techniques, viz, heat capacity, magnetization, dielectric, and neutron powder diffraction measurements. Via heat capacity and magnetization measurements we show that with increasing Cu concentration magnetic frustration decreases, which leads to the stabilization of commensurate magnetic ordering. This was further verified by temperature-dependent unit cell volume changes derived from neutron diffraction measurements which was modeled by the Gruneisen approximation. Dielectric measurements show a low temperature phase transition below about 9-10 K. Furthermore, magnetic refinements reveal no changes below this transition indicating a possible spin-flop transition which is unique to the Cu doped system. From these combined studies we have constructed a magnetoelectric phase diagram of this compound.
Title:
Interplay between magnetic order at Mn and Tm sites alongside the structural distortion in multiferroic films of o-TmMnO3
Authors:
Windsor, YW; Ramakrishnan, M; Rettig, L; Alberca, A; Bothschafter, EM; Staub, U; Shimamoto, K; Hu, Y; Lippert, T; Schneider, CW Author Full Names: Windsor, Y. W.; Ramakrishnan, M.; Rettig, L.; Alberca, A.; Bothschafter, E. M.; Staub, U.; Shimamoto, K.; Hu, Y.; Lippert, T.; Schneider, C. W.
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235144 JUN 26 2015
Abstract:
We employ resonant soft x-ray diffraction to individually study the magnetic ordering of the Mn and the Tm sublattices in single-crystalline films of orthorhombic (o-)TmMnO3. The same magnetic ordering wave vector of (0 q 0) with q approximate to 0.46 is found for both ionic species, suggesting that the familiar antiferromagnetic order of the Mn ions induces a magnetic order on the Tm unpaired 4f electrons. Indeed, intensity variations of magnetic reflections with temperature corroborate this scenario. Calculated magnetic fields at the Tm sites are used as a model magnetic structure for the Tm, which correctly predicts intensity variations at the Tm resonance upon azimuthal rotation of the sample. The model allows ruling out a bc-cycloid modulation of the Mn ions as the cause for the incommensurate ordering, as found in TbMnO3. The structural distortion, which occurs in the ferroelectric phase below T-C, was followed through nonresonant diffraction of structural reflections forbidden by the high-temperature crystal symmetry. The (0 q 0) magnetic reflection appears at the Mn resonance well above T-C, indicating that this reflection is sensitive also to the intermediate sinusoidal magnetic phase. The model presented suggests that the Tm 4f electrons are polarized well above the ferroelectric transition and are possibly not affected by the transition at T-C. The successful description of the induced order observed at the Tm resonance is a promising example for future element-selective studies in which "spectator" ions may allow access to previously unobtainable information about other constituent ions.
Title:
Superspace crystallography: a key to the chemistry and properties
Authors:
Pinheiro, CB; Abakumov, AM Author Full Names: Pinheiro, Carlos Basilio; Abakumov, Artem M.
Source:
IUCRJ, 2 137-154; 10.1107/S2052252514023550 1 JAN 2015
Abstract:
An overview is given of the recent advances in the field of modulated molecular and inorganic crystals with an emphasis on the links between incommensurability, intermolecular and interatomic interactions and, wherever possible, the properties of the materials. The importance of detailed knowledge on the modulated structure for understanding the crystal chemistry and the functional properties of modulated phases is shown using selected examples of incommensurate modulations in organic molecular compounds and inorganic complex oxides.
Title:
A CENTURY OF X-RAY CRYSTALLOGRAPHY AND 2014 INTERNATIONAL YEAR OF X-RAY CRYSTALLOGRAPHY
Authors:
Kojic-Prodic, B Author Full Names: Kojic-Prodic, Biserka
Source:
MACEDONIAN JOURNAL OF CHEMISTRY AND CHEMICAL ENGINEERING, 34 (1):19-32; 2015
Abstract:
The 100(th) anniversary of the Nobel prize awarded to Max von Laue in 1914 for his discovery of diffraction of X-rays on a crystal marked the beginning of a new branch of science - X-ray crystallography. The experimental evidence of von Laue's discovery was provided by physicists W. Friedrich and P. Knipping in 1912. In the same year, W. L. Bragg described the analogy between X-rays and visible light and formulated the Bragg's law, a fundamental relation that connected the wave nature of X-rays and fine structure of a crystal at atomic level. In 1913 the first simple diffractometer was constructed and structure determination started by the Braggs, father and son. In 1915 their discoveries were acknowledged by a Nobel Prize in physics. Since then, X-ray diffraction has been the basic method for determination of three-dimensional structures of synthetic and natural compounds. The three-dimensional structure of a substances defines its physical, chemical, and biological properties. Over the past century the significance of X-ray crystallography has been recognized by about forty Nobel prizes. X-ray structure analysis of simple crystals of rock salt, diamond and graphite, and later of complex biomolecules such as B12-vitamin, penicillin, haemoglobin/myoglobin, DNA, and biomolecular complexes such as viruses, chromatin, ribozyme, and other molecular machines have illustrated the development of the method. Among these big discoveries the double helix DNA structure was an epochal achievement of the 20(th) century. These discoveries, together with many others of the X-ray crystallography, have completely changed our views and helped to develop other new fields of science such as molecular genetics, biophysics, structural molecular biology, material science, and many others. During the last decade, the implementation of free electron X-ray lasers, a new experimental tool, has opened up femtosecond dynamic crystallography. This highly advanced methodology enables to solve the structures and dynamics of the most complex biological assemblies involved in a cell metabolism. The advancements of science and technology over the 20th and 21(st) centuries are of great influence on our views in almost all human activities. The importance of Xray crystallography for science and technology advocates for its high impact on a wide area of research and declares it as a highly interdisciplinary science. In short, crystallography has defined the shape of the modern world. Focusing on single crystal diffraction, this essay tackles only one field of crystallography; the comprehensive review on X-ray crystallography can hardly be fitted into a single article. The aim with this review was to highlight the most striking examples illustrating some of the milestones over the past century.
Title:
A modulation wave approach to the order hidden in disorder
Authors:
Withers, R Author Full Names: Withers, Ray
Source:
IUCRJ, 2 74-84; 10.1107/S2052252514022556 1 JAN 2015
Abstract:
The usefulness of a modulation wave approach to understanding and interpreting the highly structured continuous diffuse intensity distributions characteristic of the reciprocal spaces of the very large family of inherently flexible materials which exhibit ordered 'disorder' is pointed out. It is shown that both longer range order and truly short-range order are simultaneously encoded in highly structured diffuse intensity distributions. The long-range ordered crystal chemical rules giving rise to such diffuse distributions are highlighted, along with the existence and usefulness of systematic extinction conditions in these types of structured diffuse distributions.

Update: 9-Jul-2015

Title:
Microwave sol-gel synthesis and upconversion photoluminescence properties of CaGd2(WO4)(4):Er3+/Yb3+ phosphors with incommensurately modulated structure
Authors:
Lim, CS; Aleksandrovsky, A; Molokeev, M; Oreshonkov, A; Atuchin, V Author Full Names: Lim, Chang Sung; Aleksandrovsky, Aleksandr; Molokeev, Maxim; Oreshonkov, Aleksandr; Atuchin, Victor
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 228 160-166; 10.1016/j.jssc.2015.04.032 AUG 2015
Abstract:
CaGd2-x(WO4)(4):Er3+/Yb3+ phosphors with the doping concentrations of Er3+ and Yb3+ (x=Er3++Yb3+, Er3+=0.05, 0.1, 0.2 and Yb3+=0.2, 0.45) have been successfully synthesized by the microwave sol-gel method. The crystal structure of CaGd2-x(WO4)(4):Er3+/Yb3+ tungstates have been refined, and upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after the heat-treatment at 900 degrees C for 16 h, showed a well crystallized morphology. Under the excitation at 980 nm, CaGd2(WO4)(4):Er3+/Yb3+ particles exhibited a strong 525-nm and a weak 550-nm emission bands in the green region and a very weak 655-nm emission band in the red region. The Raman spectrum of undoped CaGd2(WO4)(4) revealed about 12 narrow lines. The strongest band observed at 903 cm(-1) was assigned to the v(1) symmetric stretching vibration of WO4 tetrahedrons. The spectra of the samples doped with Er and Yb obtained under the 514.5 nm excitation were dominated by Er3+ luminescence preventing the recording of these samples Raman spectra. Concentration quenching of the erbium luminescence at H-2(11/2)-> I-4(15/2) transition is weak in the range of erbium doping level x(Er)=0.05-0.2, while, for transition S-4(3/2)-> 4I(15/2), the signs of concentration quenching become pronounced at x(Er)=0.2. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Direct evidence for stress-induced transformation between coexisting multiple martensites in a Ni-Mn-Ga multifunctional alloy
Authors:
Huang, L; Cong, DY; Wang, ZL; Nie, ZH; Dong, YH; Zhang, Y; Ren, Y; Wang, YD Author Full Names: Huang, L.; Cong, D. Y.; Wang, Z. L.; Nie, Z. H.; Dong, Y. H.; Zhang, Y.; Ren, Y.; Wang, Y. D.
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 48 (26):10.1088/0022-3727/48/26/265304 JUL 8 2015
Abstract:
The structural response of coexisting multiple martensites to stress field in a Ni-Mn-Ga multifunctional alloy was investigated by the in situ high-energy x-ray diffraction technique. Stress-induced transformation between coexisting multiple martensites was observed at 110 K, at which five-layered modulated (5M), seven-layered modulated (7M) and non-modulated (NM) martensites coexist. We found that a tiny stress of as low as 0.5 MPa could trigger the transformation from 5M and 7M martensites to NM martensite and this transformation is partly reversible. Besides the transformation between coexisting multiple martensites, rearrangement of martensite variants also occurs during loading, at least at high stress levels. The present study is instructive for designing advanced multifunctional alloys with easy actuation.
Title:
Quasicrystal dissolution and performance of isothermally heat-treated Mg-Zn-Y alloy
Authors:
Wan, DQ; Luo, X; Liu, YJ; Yu, T Author Full Names: Wan, Di-Qing; Luo, Xian; Liu, Ya-Juan; Yu, Tian
Source:
RARE METALS, 34 (7):452-456; 10.1007/s12598-013-0119-9 JUL 2015
Abstract:
Conventional casting method was employed to prepare Mg-Zn-Y alloy only with alpha-Mg+I-phase; however, the grain size of quasicrystal is quite large in the as-cast state. Therefore, isothermal treatment was applied to refine the quasicrystal phase. The result shows that after the Mg-Zn-Y alloy was isothermally treated at 500 degrees C for several hours, the coarse quasicrystal can be gradually dissolved and thus refined. Generally, the dissolving processes of quasicrystal are slow first and then accelerate; after isothermally treated with 8 h at 500 degrees C, the quasicrystal is almost completely dissolved into the matrix only with 1-5 mu m tiny quasicrystals remained. Refinement of quasicrystal can markedly reduce the wear resistance, but increase the corrosion resistance.
Title:
How important is the {103} plane of stable Ge2Sb2Te5 for phase-change memory?
Authors:
Zhang, W; Zheng, WT; Kim, JG; Cui, XQ; Li, L; Qi, JG; Kim, YJ; Song, SA Author Full Names: Zhang, W.; Zheng, W. T.; Kim, J. -G.; Cui, X. Q.; Li, L.; Qi, J. G.; Kim, Y. -J.; Song, S. A.
Source:
JOURNAL OF MICROSCOPY, 259 (1):10-15; 10.1111/jmi.12242 JUL 2015
Abstract:
Closely correlating with {200} plane of cubic phase, {103} plane of hexagonal phase of Ge2Sb2Te5 plays a crucial role in achieving fast phase change process as well as formation of modulation structures, dislocations and twins in Ge2Sb2Te5. The behaviors of {103} plane of hexagonal phase render the phase-change memory process as a nanoscale shape memory. Lay description Exploring the phase-change mechanism, structures and properties of chalcogenides has been currently one of the hot topics. Ge-Sb-Te chalcogenides are of tremendous technological importance ranging from optical data storage to PRAM. Exhibiting the best performance for DVD-RAM in terms of speed and stability, Ge2Sb2Te5 is currently the most important phase-change alloy. There exist three solid phases in Ge2Sb2Te5: amorphous, metastable rocksalt (FCC) and stable hexagonal (Hex) phases. The whole switching operation in optical data storage and electronic memories is based on the following rapid cycling processes by either laser or electric heating: amorphousFCC (Erase/SET process)Hexliquidamorphous (Write/RESET process). The stable Hex is an indispensable concern to bridge the aforementioned whole cycling framework. In this work, structural correlations between the two crystalline phases were analyzed and the rich structural phenomena were unraveled. Closely correlated with {200} plane of FCC phase, {103} plane of Hex phase of Ge2Sb2Te5 plays a crucial role in achieving fast phase change process as well as formation of modulation structures, dislocations and twins in Ge2Sb2Te5. We propose that from a point view of maintaining the ultra-high transition speed, (103) of Hex phase can effectively facilitate phase-change memory. This leads to a novel concept that phase-change process can be treated as a nanoscale shape-memory, towards essential understanding of the relevant structural features of Ge-Sb-Te chalcogenides.
Title:
Antiferromagnetic Dichroism in a Complex Multisublattice Magnetoelectric CuB2O4
Authors:
Boldyrev, KN; Pisarev, RV; Bezmaternykh, LN; Popova, MN Author Full Names: Boldyrev, K. N.; Pisarev, R. V.; Bezmaternykh, L. N.; Popova, M. N.
Source:
PHYSICAL REVIEW LETTERS, 114 (24):10.1103/PhysRevLett.114.247210 JUN 19 2015
Abstract:
Magnetic control of the crystal chirality was announced by Saito et al. [Phys. Rev. Lett. 101, 117402 (2008)] on the ground of experiments in CuB2O4. This claim has raised a sharp dispute in the literature because it seemed to contradict the fundamental symmetry principles. We settle this dispute on the basis of a high-resolution optical spectroscopy study of excitonic transitions in CuB2O4. We find that a large sublattice-sensitive antiferromagnetic linear dichroism (LD) emerges at the Neel temperature T-N = 21 K and show how it could simulate a "magnetic-field control of the crystal chirality." We prove that the discovered LD is related microscopically to the magnetic Davydov splitting. This LD is highly sensitive to subtle changes in the spin subsystems, which allowed us to observe a splitting of the phase transition into an incommensurate magnetic phase into two transitions (T-1* = 8.5 and T-2* = 7.9 K) and to suggest elliptical spiral structures below T-1*, instead of a simple circular helix proposed earlier.
Title:
Lattice vibrations in the Frenkel-Kontorova model. I. Phonon dispersion, number density, and energy
Authors:
Meng, QP; Wu, LJ; Welch, DO; Zhu, YM Author Full Names: Meng, Qingping; Wu, Lijun; Welch, David O.; Zhu, Yimei
Source:
PHYSICAL REVIEW B, 91 (22):10.1103/PhysRevB.91.224305 JUN 17 2015
Abstract:
We studied the lattice vibrations of two interpenetrating atomic sublattices via the Frenkel-Kontorova (FK) model of a linear chain of harmonically interacting atoms subjected to an on-site potential using the technique of thermodynamic Green's functions based on quantum field-theoretical methods. General expressions were deduced for the phonon frequency-wave-vector dispersion relations, number density, and energy of the FK model system. As the application of the theory, we investigated in detail cases of linear chains with various periods of the on-site potential of the FK model. Some unusual but interesting features for different amplitudes of the on-site potential of the FK model are discussed. In the commensurate structure, the phonon spectrum always starts at a finite frequency, and the gaps of the spectrum are true ones with a zero density of modes. In the incommensurate structure, the phonon spectrum starts from zero frequency, but at a nonzero wave vector; there are some modes inside these gap regions, but their density is very low. In our approximation, the energy of a higher-order commensurate state of the one-dimensional system at a finite temperature may become indefinitely close to the energy of an incommensurate state. This finding implies that the higher-order incommensurate-commensurate transitions are continuous ones and that the phase transition may exhibit a "devil's staircase" behavior at a finite temperature.
Title:
Lattice vibrations in the Frenkel-Kontorova Model. II. Thermal conductivity
Authors:
Meng, QP; Wu, LJ; Welch, DO; Zhu, YM Author Full Names: Meng, Qingping; Wu, Lijun; Welch, David O.; Zhu, Yimei
Source:
PHYSICAL REVIEW B, 91 (22):10.1103/PhysRevB.91.224306 JUN 17 2015
Abstract:
We applied the formulas for the phonon spectral-density function that we presented in the previous paper of this series to analyze the thermal conductivity of the lattice in the framework of the Frenkel-Kontorova (FK) model. We found that two extra mechanisms of phonon scattering (different from the point impurities, three-phonon processes, and boundary scattering typical of all crystals), viz., resonance, and anharmonic scattering, that mainly influences the thermal conductivity of the lattice. The frequencies of resonance scattering are discrete, and their number increases from a finite number to infinity with their transition from the commensurate to the incommensurate state. Changing the amplitude and period of the FK model changes the frequencies and the frequency number of resonance scattering and the intensity of anharmonic scattering. We analyze these changes in detail. Our theory can explain all existing numerical results on this problem and suggest strategies to reduce the thermal conductivity of the lattice of layered materials.
Title:
Characterization of deep level defects and thermally stimulated depolarization phenomena in La-doped TlInS2 layered semiconductor
Authors:
Seyidov, MY; Suleymanov, RA; Mikailzade, FA; Kargin, EO; Odrinsky, AP Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Mikailzade, Faik A.; Kargin, Elif Orhan; Odrinsky, Andrei P.
Source:
JOURNAL OF APPLIED PHYSICS, 117 (22):10.1063/1.4922347 JUN 14 2015
Abstract:
Lanthanum-doped high quality TlInS2 (TlInS2: La) ferroelectric-semiconductor was characterized by photo-induced current transient spectroscopy (PICTS). Different impurity centers are resolved and identified. Analyses of the experimental data were performed in order to determine the characteristic parameters of the extrinsic and intrinsic defects. The energies and capturing cross section of deep traps were obtained by using the heating rate method. The observed changes in the Thermally Stimulated Depolarization Currents (TSDC) near the phase transition points in TlInS2: La ferroelectric-semiconductor are interpreted as a result of self-polarization of the crystal due to the internal electric field caused by charged defects. The TSDC spectra show the depolarization peaks, which are attributed to defects of dipolar origin. These peaks provide important information on the defect structure and localized energy states in TlInS2: La. Thermal treatments of TlInS2: La under an external electric field, which was applied at different temperatures, allowed us to identify a peak in TSDC which was originated from La-dopant. It was established that deep energy level trap BTE43, which are active at low temperature (T <= 156 K) and have activation energy 0.29 eV and the capture cross section 2.2 x 10(-14) cm(2), corresponds to the La dopant. According to the PICTS results, the deep level trap center B5 is activated in the temperature region of incommensurate (IC) phases of TlInS2: La, having the giant static dielectric constant due to the structural disorders. From the PICTS simulation results for B5, native deep level trap having an activation energy of 0.3 eV and the capture cross section of 1.8 x 10(-16) cm(2) were established. A substantial amount of residual space charges is trapped by the deep level localized energy states of B5 in IC-phase. While the external electric field is applied, permanent dipoles, which are originated from the charged B5 deep level defects, are aligned in the direction of the applied electric field and the equilibrium polarization can be reached in a relatively short time. When the polarization field is maintained, while cooling the temperature of sample to a sufficiently low degrees, the relaxation times of the aligned dipoles drastically increases. Practically, frozen internal electric field or electrets states remain inside the TlInS2: La when the applied bias field is switched off. The influence of deep level defects on TSDC spectra of TlInS2: La has been revealed for the first time. (C) 2015 AIP Publishing LLC.
Title:
Coexistence of the spin and electron-hole quantum liquids in frustrated manganites La1-y Sm (y) MnO3+delta
Authors:
Bukhanko, FN; Bukhanko, AF Author Full Names: Bukhanko, F. N.; Bukhanko, A. F.
Source:
PHYSICS OF THE SOLID STATE, 57 (6):1114-1127; 10.1134/S1063783415060062 JUN 2015
Abstract:
The structural, electronic, and magnetic phase transformations induced in the temperature range of 4.2-300 K by the isovalent substitution of the rare-earth Sm3+ ion for the La3+ ion with a larger radius have been investigated in the system of self-doped manganites La1-y Sm (y) MnO3+delta (delta similar to 0.1, 0 a parts per thousand currency sign y a parts per thousand currency sign 1). It has been found using the X-ray diffraction analysis that the substitution La -> Sm is accompanied by a significant increase of the GdFeO3-type and Jahn-Teller-type lattice distortions. At a temperature of 300 K, an increase in the Sm concentration y leads to a concentration phase transition from the pseudocubic O* phase to the orthorhombic O phase, as well as to the appearance of an s-shaped anomaly of the lattice parameter a at concentrations y a parts per thousand yen 0.4 and an anomalous peak in the concentration dependence of the electrical resistance R(y) near y a parts per thousand 0.85. The magnetic T-y-aOE (c) r (A) phase diagrams of the La1-y Sm (y) MnO3+delta system in the temperature range of 4.2-250 K have been constructed according to the results of measurements of the temperature dependences of the direct-current (dc) magnetization M(T). It has been revealed that the samples with y a parts per thousand yen 0.8 exhibit signs of the melting of the A- and CE-type modulated antiferromagnetic (AFM) structures in the form of an anomalous decrease both in the critical temperature of the transition to a frustrated AFM state and in the magnetization of the samples with an increase in the concentration y. The anomalies observed in the temperature dependences of the alternating-current (ac) dielectric permittivity of the La1-y Sm (y) MnO3+delta samples have been explained within the existing concepts of the Bose-Einstein condensation of an electron-hole liquid in the form of metallic droplets in an excitonic insulator.

Update: 2-Jul-2015

Title:
Ni- and Cu-free Ti-based metallic glasses with potential biomedical application
Authors:
Guo, Y; Bataev, I; Georgarakis, K; Jorge, AM; Nogueira, RP; Pons, M; Yavari, AR Author Full Names: Guo, Y.; Bataev, I.; Georgarakis, K.; Jorge, A. M., Jr.; Nogueira, R. P.; Pons, M.; Yavari, A. R.
Source:
INTERMETALLICS, 63 86-96; 10.1016/j.intermet.2015.04.004 AUG 2015
Abstract:
In the present work Ti-Fe-Si and Ti-Fe-Si-X (X = Zr, Pd, Ge) glassy alloys are discussed as potential biomedical materials. Depending on composition and experimental conditions these alloys possess glassy, quasicrystalline or crystalline structure. The glassy state and crystallization behavior of the melt spun ribbons were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and the Hank's solution was used as simulated body fluid for corrosion tests. Ternary Ti-Fe-Si alloys near the Ti65Fe30Si5 eutectic point were prone to form quasicrystals if the cooling rate was not high enough to retain amorphous structure. The compositions on the steeper side of the eutectic point could be vitrified. The results indicate that small additions of Zr can have a positive effect on glass formation, while additions of Ge, Pd may have a detrimental effect by promoting crystallization. Ti Fe Si and Ti Fe Si Zr alloys exhibited high corrosion properties, superior to that of pure Ti and most of Ti-based glassy alloys reported in the literature. Being free of Ni and Cu this group of alloys may be considered for possible biomedical application. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Amorphous-i phase-big cube-amorphous cyclic phase transformation of mechanically alloyed Zr75Ni20Al5 system
Authors:
El-Eskandarany, MS Author Full Names: El-Eskandarany, M. Sherif
Source:
INTERMETALLICS, 63 27-36; 10.1016/j.intermet.2015.01.010 AUG 2015
Abstract:
Cyclic glassy-metastable-glassy phase transformations were investigated during mechanical alloying of Zr75Ni20Al5 powders, using high-energy ball milling technique. After 20 h of continuous milling, a single glassy phase was obtained. The synthesized glassy powder, which is homogeneous in structure and composition, showed a glass transition temperature lied at 510 degrees C and a large supercooled liquid region extended to 86.5 degrees C. This glassy phase, which crystallized through a single sharp exothermic peak at 596.5 degrees C, tended to transformed into icosahedral (i-phase) nano-quasicrystalline grains upon further milling to 30 h. This i-phase showed serious instability against the mechanical deformations generated by the milling tools, and hence transformed into big cube phase with increasing the milling time to 45 h. In a cyclic phase transformation the obtained big cube phase subsequently transformed into the same glassy phase after 60 h of milling. This observed cyclic phase transformation was observed twice upon further milling to 90 h without serious compositional changes. The iron contamination contents in the ball-milled powders had constant values of about 0.16 wt.% and did not change with changing the structure of the powders. The present work shows that this phenomenon does not have any obvious analogues with the periodic redox reactions or with diffusive-reactive phenomena known in chemistry. On the basis of our results, the destabilizing effect of the defects created by the milling media (balls), which leads to the cyclic transformations, depends on the milling time. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Direct observation of solid-state reversed transformation from crystals to quasicrystals in a Mg alloy
Authors:
Liu, JF; Yang, ZQ; Ye, HQ Author Full Names: Liu, Jian-Fang; Yang, Zhi-Qing; Ye, Heng-Qiang
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep09816 JUN 12 2015
Abstract:
Phase transformation of quasicrystals is of interest in various fields of science and technology. Interestingly, we directly observed unexpected solid-state epitaxial nucleation and growth of Zn6Mg3Y icosahedral quasicrystals in a Mg alloy at about 573 K which is about 300 K below the melting point of Zn6Mg3Y, in contrast to formation of quasicrystals through solidification that was usually found in many alloys. Maximizing local packing density of atoms associated with segregation of Y and Zn in Mg adjacent to Mg/Zn3MgY interfaces triggered atomic rearrangement in Mg to form icosahedra coupled epitaxially with surface distorted icosahedra of Zn3MgY, which plays a critical role in the nucleation of icosahedral clusters. A local Zn: Mg: Y ratio close to 6:3:1, corresponding to a valence electron concentration of about 2.15, should have been reached to trigger the formation of quasicrystals at Mg/Zn3MgY interfaces. The solid-state icosahedral ordering in crystals opens a new window for growing quasicrystals and understanding their atomic origin mechanisms. Epitaxial growth of quasicrystals onto crystals can modify the surface/interface structures and properties of crystalline materials.
Title:
Bulk electronic structure of Zn-Mg-Y and Zn-Mg-Dy icosahedral quasicrystals
Authors:
Nayak, J; Maniraj, M; Gloskovskii, A; Krajci, M; Sebastian, S; Fisher, IR; Horn, K; Barman, SR Author Full Names: Nayak, J.; Maniraj, M.; Gloskovskii, A.; Krajci, M.; Sebastian, S.; Fisher, I. R.; Horn, K.; Barman, S. R.
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235116 JUN 11 2015
Abstract:
We use bulk sensitive hard x-ray photoelectron spectroscopy to provide unambiguous evidence for a pseudogap in the density of states around the Fermi level in icosahedral Zn-Mg-Y and Zn-Mg-Dy quasicrystals, in agreement with our density functional theory calculations. The pseudogap in these Zn-based quasicrystals is less pronounced compared to the Al-based ones such as Al-Pd-Mn and Al-Cu-Fe [J. Nayak et al., Phys. Rev. Lett. 109, 216403 ( 2012)]. This observation is in agreement with transport studies that indicate a larger charge carrier concentration in the Zn-based quasicrystals. Compared to Zn-Mg-Dy, the pseudogap is somewhat deeper in Zn-Mg-Y. The larger width of the Mg 1s and Zn 2p core-level spectra in Zn-Mg-Y is explained by different configurations of the local atomic surrounding compared to Zn-Mg-Dy.
Title:
Synthesis, structures and magnetic properties of the dimorphic Mn2CrSbO6 oxide
Authors:
Dos Santos-Garcia, AJ; Solana-Madruga, E; Ritter, C; Avila-Brande, D; Fabelo, O; Saez-Puche, R Author Full Names: Dos Santos-Garcia, Antonio J.; Solana-Madruga, Elena; Ritter, Clemens; Avila-Brande, David; Fabelo, Oscar; Saez-Puche, Regino
Source:
DALTON TRANSACTIONS, 44 (23):10665-10672; 10.1039/c4dt03849e 2015
Abstract:
The perovskite polymorph of Mn2CrSbO6 compound has been synthesized at 8 GPa and 1473 K. It crystallizes in the monoclinic P2(1)/n space group with cell parameters a = 5.2180 (2) angstrom, b = 5.3710(2) angstrom, c = 7.5874(1) angstrom and alpha = 90.36(1)degrees. Magnetic susceptibility and magnetization measurements show the simultaneous antiferromagnetic ordering of Mn2+ and Cr3+ sublattices below T-N = 55 K with a small canting. Low temperature powder neutron diffraction reveals a commensurate magnetic structure with spins confined to the ac-plane and a propagation vector kappa = [1/2 0 1/2]. The thermal treatment of this compound induces an irreversible phase transition to the ilmenite polymorph, which has been isolated at 973 K and crystallizes in R (3) over bar space group with cell parameters a = 5.2084 (4) angstrom and c = 14.4000 (11) angstrom. Magnetic susceptibility, magnetization and powder neutron diffraction data confirm the antiferromagnetic helical ordering of spins in an incommensurate magnetic structure with kappa = [00 0.46] below 60 K, and the temperature dependence of the propagation vector up to kappa = [00 0.54] at about 10 K.
Title:
Ordering effects in the crystal structure and electrochemical properties of the Gd0.5Ba0.5Mn0.5Fe0.5O3-delta perovskite
Authors:
Munoz-Gil, D; Avila-Brande, D; Urones-Garrote, E; Garcia-Martin, S Author Full Names: Munoz-Gil, Daniel; Avila-Brande, David; Urones-Garrote, Esteban; Garcia-Martin, Susana
Source:
DALTON TRANSACTIONS, 44 (23):10867-10874; 10.1039/c4dt03873h 2015
Abstract:
Layered-type ordering and oxygen vacancies ordering are revealed in GdBaMnFeO6-delta perovskite. Selected area electron diffraction and high-resolution transmission electron microscopy results indicate a modulation of the crystal structure. Ba and Gd ordering in (001)(p) layers is confirmed by high angle annular dark field scanning transmission electron microscopy and electron energy-loss spectroscopy. These techniques also revealed formation of layer-stacking defects in the crystals. Direct imaging of the oxygen sublattice is obtained by phase image reconstruction. Location of the oxygen vacancies in the (GdO)(x) layers is achieved by analysis of the intensity of the averaged phase image. Physical properties of the GdBaMnFeO6-delta perovskite, are likely to be strongly affected by its ordering effects and crystal microstructure. In this sense, layered-type GdBaMnFeO6-delta perovskite show better electrochemical properties as cathodes in SOFCs than ion disordered Gd0.5Ba0.5Mn0.5Fe0.5O3-delta perovskite.

Update: 25-Jun-2015

Title:
Symplectic approach for the plane elasticity problem of quasicrystals with point group 10 mm
Authors:
Wang, H; Li, LH; Huang, JJ; Chen, A Author Full Names: Wang, Hua; Li, Lianhe; Huang, Junjie; Chen, Alatancang
Source:
APPLIED MATHEMATICAL MODELLING, 39 (12):3306-3316; 10.1016/j.apm.2014.10.060 JUN 15 2015
Abstract:
The symplectic approach is introduced into the plane elasticity problem of quasicrystals with point group 10 mm. The basic equations of the problem are equivalently written as the Hamiltonian dual equations. It is shown that the generalized eigenvector system of the corresponding Hamiltonian operator matrix is complete in the Cauchy Principal Value (CPV) sense. The analytical solution and related numerical results of the problem are then given. (C) 2014 Elsevier Inc. All rights reserved.
Title:
Magnetic structure and multiferroic coupling in pyroxene NaFeSi2O6
Authors:
Baum, M; Komarek, AC; Holbein, S; Fernandez-Diaz, MT; Andre, G; Hiess, A; Sidis, Y; Steffens, P; Becker, P; Bohaty, L; Braden, M Author Full Names: Baum, M.; Komarek, A. C.; Holbein, S.; Fernandez-Diaz, M. T.; Andre, G.; Hiess, A.; Sidis, Y.; Steffens, P.; Becker, P.; Bohaty, L.; Braden, M.
Source:
PHYSICAL REVIEW B, 91 (21):10.1103/PhysRevB.91.214415 JUN 9 2015
Abstract:
By comprehensive neutron diffraction measurements we have studied the magnetic structure of aegirine (NaFeSi2O6) in and above its multiferroic phase. Natural aegirine exhibits two magnetic transitions into incommensurate magnetic order with a propagation vector of (k) over right arrow (inc) = (0, similar to 0.78,0). Between 9 and 6 K, we find a transverse spin-density wave with moments pointing near the c direction. Below 6 K, magnetic order becomes helical and spins rotate in the ac plane. The same irreducible representation is involved in the two successive transitions. In addition, the ferroelectric polarization (P) over right arrow appearing along the b direction cannot be described by the most common multiferroic mechanism but follows (P) over right arrow proportional to ($) over right arrow (i) x (S) over right arrow (j). Synthetic NaFeSi2O6 does not exhibit the pure incommensurate helical order but shows coexistence of this order with a commensurate magnetic structure. By applying moderate pressure to natural aegirine, we find that the incommensurate magnetic ordering partially transforms to the commensurate one, underlining the nearly degenerate character of the two types of order in NaFeSi2O6.
Title:
Matrix product state approach to a frustrated spin chain with long-range interactions
Authors:
Li, ZH; Wang, AM Author Full Names: Li, Zhi-Hua; Wang, An-Min
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235110 JUN 8 2015
Abstract:
We make extensive simulations over a spin chain model that combines the frustrated J(1) - J(2) spin chain and the long-range nonfrustrated (-1)((r-1))r(-alpha) decay interactions through the variational matrix product state method for both finite and infinite lengths. We study both the ground-state entanglement and phase diagram. We find that it is most entangled in the rotation invariant long-range ordered antiferromagnetic phase, where the entanglement scales approximately logarithmically. We determine the development of the Majudar-Ghosh point to a disorder line from entanglement. And we approximately determine the transition from the dimerized and incommensurate phase of the J(1) - J(2) model to a decoupled phase by studying spin correlation and the dimerization order parameter. Some implications for entanglement in systems with long-range interactions are stated.
Title:
Influence of Ti doping on the incommensurate charge density wave in 1T-TaS2
Authors:
Chen, XM; Miller, AJ; Nugroho, C; de la Pena, GA; Joe, YI; Kogar, A; Brock, JD; Geck, J; MacDougall, GJ; Cooper, SL; Fradkin, E; Van Harlingen, DJ; Abbamonte, P Author Full Names: Chen, X. M.; Miller, A. J.; Nugroho, C.; de la Pena, G. A.; Joe, Y. I.; Kogar, A.; Brock, J. D.; Geck, J.; MacDougall, G. J.; Cooper, S. L.; Fradkin, E.; Van Harlingen, D. J.; Abbamonte, P.
Source:
PHYSICAL REVIEW B, 91 (24):10.1103/PhysRevB.91.245113 JUN 8 2015
Abstract:
We report temperature-dependent transport and x-ray diffraction measurements of the influence of Ti hole doping on the charge density wave (CDW) in 1T-Ta1-xTixS2. Confirming past studies, we find that even trace impurities eliminate the low-temperature commensurate (C) phase in this system. Surprisingly, the magnitude of the in-plane component of the CDW wave vector in the nearly commensurate (NC) phase does not change significantly with Ti concentration, as might be expected from a changing Fermi surface volume. Instead, the angle of the CDWin the basal plane rotates, from 11.9 degrees at x = 0 to 16.4 degrees at x = 0.12. Ti substitution also leads to an extended region of coexistence between incommensurate (IC) and NC phases, indicating heterogeneous nucleation near the transition. Finally, we explain a resistive anomaly originally observed by Di Salvo [F. J. Di Salvo et al., Phys. Rev. B 12, 2220 (1975)] as arising from pinning of the CDW on the crystal lattice. Our study highlights the importance of commensuration effects in the NC phase, particularly at x similar to 0.08.
Title:
Dispersionless Spin Waves and Underlying Field-Induced Magnetic Order in Gadolinium Gallium Garnet
Authors:
d'Ambrumenil, N; Petrenko, OA; Mutka, H; Deen, PP Author Full Names: d'Ambrumenil, N.; Petrenko, O. A.; Mutka, H.; Deen, P. P.
Source:
PHYSICAL REVIEW LETTERS, 114 (22):10.1103/PhysRevLett.114.227203 JUN 2 2015
Abstract:
We report the results of neutron diffraction and inelastic neutron scattering on a powder sample of Gd3Ga5O12 at high magnetic fields. Analysis of the diffraction data shows that in high fields (B greater than or similar to 1.8 T) the spins are not fully aligned, but are canted slightly as a result of the dipolar interaction. The magnetic phase for fields less than or similar to 1.8 T is characterized by antiferromagnetic peaks at (210) and an incommensurate wave vector. The dominant contribution to inelastic scattering at large momentum transfers is from a band of almost dispersionless excitations. We show that these correspond to the spin waves localized on ten site rings, expected on the basis of nearest neighbor exchange interaction, and that the spectrum at high fields B greater than or similar to 1.8 T is well described by a spin wave theory.
Title:
Aperiodic crystals and beyond
Authors:
Grimm, U Author Full Names: Grimm, Uwe
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 258-274; 10.1107/S2052520615008409 3 JUN 2015
Abstract:
Crystals are paradigms of ordered structures. While order was once seen as synonymous with lattice periodic arrangements, the discoveries of incommensurate crystals and quasicrystals led to a more general perception of crystalline order, encompassing both periodic and aperiodic crystals. The current definition of crystals rests on their essentially point-like diffraction. Considering a number of recently investigated toy systems, with particular emphasis on non-crystalline ordered structures, the limits of the current definition are explored.
Title:
Structures beyond superspace
Authors:
Senechal, M Author Full Names: Senechal, Marjorie
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 250-251; 10.1107/S2052520615009907 3 JUN 2015
Title:
The modulated average structure of mullite
Authors:
Birkenstock, J; Petricek, V; Pedersen, B; Schneider, H; Fischer, RX Author Full Names: Birkenstock, Johannes; Petricek, Vaclav; Pedersen, Bjoern; Schneider, Hartmut; Fischer, Reinhard X.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 358-368; 10.1107/S205252061500757X 3 JUN 2015
Abstract:
Homogeneous and inclusion-free single crystals of 2: 1 mullite (Al4.8Si1.2O9.6) grown by the Czochralski technique were examined by X-ray and neutron diffraction methods. The observed diffuse scattering together with the pattern of satellite reflections confirm previously published data and are thus inherent features of the mullite structure. The ideal composition was closely met as confirmed by microprobe analysis (Al-4.82 (3) Si-1.18 (1) O-9.59 (5)) and by average structure refinements. 8 (5) to 20 (13)% of the available Si was found in the T* position of the tetrahedra triclusters. The strong tendencey for disorder in mullite may be understood from considerations of hypothetical superstructures which would have to be n-fivefold with respect to the three-dimensional average unit cell of 2: 1 mullite and n-fourfold in case of 3: 2 mullite. In any of these the possible arrangements of the vacancies and of the tetrahedral units would inevitably be unfavorable. Three directions of incommensurate modulations were determined: q(1) = [0.3137 (2) 0 1/2], q(2) = [0 0.4021 (5) 0.1834 (2)] and q(3) = [0 0.4009 (5) -0.1834 (2)]. The one-dimensional incommensurately modulated crystal structure associated with q1 was refined for the first time using the superspace approach. The modulation is dominated by harmonic occupational modulations of the atoms in the di- and the triclusters of the tetrahedral units in mullite. The modulation amplitudes are small and the harmonic character implies that the modulated structure still represents an average structure in the overall disordered arrangement of the vacancies and of the tetrahedral structural units. In other words, when projecting the local assemblies at the scale of a few tens of average mullite cells into cells determined by either one of the modulation vectors q(1), q(2) or q(3) a weak average modulation results with slightly varying average occupation factors for the tetrahedral units. As a result, the real structure of mullite is locally ordered (as previously known), but on the long-range its average is not completely disordered, the modulated structure of mullite may be denoted the true 'average structure of mullite'.
Title:
Neutron Laue and X-ray diffraction study of a new crystallographic superspace phase in n-nonadecane-urea
Authors:
Zerdane, S; Mariette, C; McIntyre, GJ; Lemee-Cailleau, MH; Rabiller, P; Guerin, L; Ameline, JC; Toudic, B Author Full Names: Zerdane, S.; Mariette, C.; McIntyre, G. J.; Lemee-Cailleau, M. -H.; Rabiller, P.; Guerin, L.; Ameline, J. C.; Toudic, B.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 293-299; 10.1107/S2052520615005442 3 JUN 2015
Abstract:
Aperiodic composite crystals present long-range order without translational symmetry. These materials may be described as the intersection in three dimensions of a crystal which is periodic in a higher-dimensional space. In such materials, symmetry breaking must be described as structural changes within these crystallographic superspaces. The increase in the number of superspace groups with the increase in the dimension of the superspace allows many more structural solutions. This is illustrated in n-nonadecane-urea, revealing a fifth higher-dimensional phase at low temperature.
Title:
One-Third Magnetization Plateau with a Preceding Novel Phase in Volborthite
Authors:
Ishikawa, H; Yoshida, M; Nawa, K; Jeong, M; Kramer, S; Horvatic, M; Berthier, C; Takigawa, M; Akaki, M; Miyake, A; Tokunaga, M; Kindo, K; Yamaura, J; Okamoto, Y; Hiroi, Z Author Full Names: Ishikawa, H.; Yoshida, M.; Nawa, K.; Jeong, M.; Kraemer, S.; Horvatic, M.; Berthier, C.; Takigawa, M.; Akaki, M.; Miyake, A.; Tokunaga, M.; Kindo, K.; Yamaura, J.; Okamoto, Y.; Hiroi, Z.
Source:
PHYSICAL REVIEW LETTERS, 114 (22):10.1103/PhysRevLett.114.227202 JUN 1 2015
Abstract:
We have synthesized high-quality single crystals of volborthite, a seemingly distorted kagome antiferromagnet, and carried out high-field magnetization measurements up to 74 T and V-51 NMR measurements up to 30 T. An extremely wide 1/3 magnetization plateau appears above 28 T and continues over 74 T at 1.4 K, which has not been observed in previous studies using polycrystalline samples. NMR spectra reveal an incommensurate order (most likely a spin-density wave order) below 22 T and a simple spin structure in the plateau phase. Moreover, a novel intermediate phase is found between 23 and 26 T, where the magnetization varies linearly with magnetic field and the NMR spectra indicate an inhomogeneous distribution of the internal magnetic field. This sequence of phases in volborthite bears a striking similarity to those of frustrated spin chains with a ferromagnetic nearest-neighbor coupling J(1) competing with an antiferromagnetic next-nearest-neighbor coupling J(2)
Title:
Pressure-induced normal-incommensurate and incommensurate-commensurate phase transitions in CrOCl
Authors:
Bykov, M; Bykova, E; Dubrovinsky, L; Hanfland, M; Liermann, HP; van Smaalen, S Author Full Names: Bykov, Maxim; Bykova, Elena; Dubrovinsky, Leonid; Hanfland, Michael; Liermann, Hanns-Peter; van Smaalen, Sander
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep09647 MAY 21 2015
Abstract:
The high-pressure behavior of layered CrOCl is shown to be governed by non-bonded interactions between chlorine atoms in relation to a rigid framework composed of Cr and O atoms. The competition between optimizing intra-and interlayer Cl-Cl distances and the general trend towards denser packing defines a novel mechanism for high-pressure phase transitions of inorganic materials. CrOCl possesses an incommensurate phase for 16-51 GPa. Single-crystal x-ray diffraction in a diamond anvil cell provides an accurate description of the evolution of the incommensurate wave with pressure. It thus demonstrates a continuous increase of the amplitude up to 30 GPa, followed by a decrease of the wavelength until a lock-in transition occurs at 51 GPa.
Title:
Magnetism in rare-earth quasicrystals: RKKY interactions and ordering
Authors:
Thiem, S; Chalker, JT Author Full Names: Thiem, Stefanie; Chalker, J. T.
Source:
EPL, 110 (1):10.1209/0295-5075/110/17002 APR 2015
Abstract:
We study magnetism in simple models for rare-earth quasicrystals, by considering Ising spins on a quasiperiodic tiling, coupled via RKKY interactions. Computing these interactions from a tight-binding model on the tiling, we find that they are frustrated and strongly dependent on the local environment. Although such features are often associated with spin glass behaviour, we show using Monte Carlo simulations that the spin system has a phase transition to a low-temperature state with long-range quasiperiodic magnetic order. Copyright (C) EPLA, 2015
Title:
Synthesis and structure of the new pentanary uranium (VI) silicate, K4CaUSi4O14, a member of a structural family related to fresnoite
Authors:
Morrison, G; Smith, MD; Tran, TT; Halasyamani, PS; Loye, HCZ Author Full Names: Morrison, Gregory; Smith, Mark D.; Tran, T. Thao; Halasyamani, P. Shiv; Loye, Hans-Conrad Zur
Source:
CRYSTENGCOMM, 17 (22):4218-4224; 10.1039/c5ce00504c 2015
Abstract:
Single crystals of K4CaUSi4O14 have been grown from a eutectic CaF2-KF flux. K4CaUSi4O14 crystallizes in a new structure which exhibits a 49-fold superstructure believed to be due to a modulation of the uranium and silicon polyhedra. We report the sub-cell of the structure which adopts the tetragonal space group P (4) over bar n2 with lattice parameters a = 9.2862(2) angstrom c = 8.3796(4) angstrom, and V = 722.60(5)angstrom(3). K4CaUSi4O14 is a member of a structural family related to the mineral fresnoite which we describe here. Finally, we report UV-vis absorbance and SHG measurements on the compound, which is non-centrosymmetric.
Title:
The symmetry of the thermoelastic properties of quasicrystals
Authors:
Sokolova, MY; Khristich, DV Author Full Names: Sokolova, M. Yu.; Khristich, D. V.
Source:
PMM JOURNAL OF APPLIED MATHEMATICS AND MECHANICS, 78 (5):524-528; 10.1016/j.jappmathmech.2015.03.012 2014
Abstract:
The thermoelastic properties of quasicrystals, possessing 5-th, 8-th, 10-th and 12-th order rotational axes, not characteristic of crystalline bodies, are considered. Using group analysis, canonical representations of the second and fourth rank tensors, characterizing the properties of quasicrystals, are constructed. The fact that orthogonal, decagonal and dodecagonal quasicrystals belong to the class of transversely isotropic materials and the isotropy of icosahedric quasicrystals and fullerenes are proved. (C) 2015 Elsevier Ltd. All rights reserved.

Update: 18-Jun-2015

Title:
Magnetostructural transitions in Mn-rich Heusler Mn-Ni-In melt-spun ribbons with enhanced magnetocaloric effect
Authors:
Li, HW; Feng, ST; Ren, J; Zhai, QJ; Fu, JX; Luo, ZP; Zheng, HX Author Full Names: Li, Hongwei; Feng, Shutong; Ren, Jian; Zhai, Qijie; Fu, Jianxun; Luo, Zhiping; Zheng, Hongxing
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 391 17-21; 10.1016/j.jmmm.2015.04.098 OCT 1 2015
Abstract:
The magnetostructural transition behavior and magnetocaloric effect of Mn-rich Heusler Mn-Ni-In melt spun ribbons have been investigated in the present study. Experimental results showed that the martensitic transition temperatures decreased by substituting small amounts of Ni with Mn in Mn49+xNi42-xIn9 (x=0,1,2). Within a temperature range from 100 K to 380 K, the Mn(49)Ni(41)ln(9) underwent a martensitic transformation from a paramagnetic L2(1)-type cubic austenite to a ferromagnetic modulated fourteen layered monoclinic (14M) martensite, followed with a ferromagnetic -> weak-magnetic transition in martensite upon cooling. While for both Mn50Ni41In9 and Mn51Ni40In9, the paramagnetic -> ferromagnetic transition in austenite occurred prior to the martensitic transformation upon cooling. Under a magnetic field change of 30 kOe, the maximum magnetic entropy changes of the Mn50Ni41In9 melt spun ribbons were found to be 5.7 J/kg K and -2.3 J/kg K in the vicinity of martensitic transformation and magnetic transition of austenite, respectively. An enhanced total effective refrigeration capacity as high as 184.2 J/kg was obtained in the Mn50Ni41In9 melt spun ribbons. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Microstructure and phase transformation of forged Mg-3.7Zn-0.3Y-0.3Gd quasicrystal alloy
Authors:
Yang, Y; Zhang, K; Ma, ML; Li, XG Author Full Names: Yang, Yang; Zhang, Kui; Ma, Minglong; Li, Xinggang
Source:
JOURNAL OF MATERIALS RESEARCH, 30 (10):1693-1700; 10.1557/jmr.2015.97 MAY 28 2015
Abstract:
An alloy with the composition of Mg-3.7Zn-0.3Y-0.3Gd (in at.%) which contains quasicrystal phase was studied by multiple means. The as-cast alloy has dendritic structure and consists of -Mg, I-phase, W-phase, and Mg-Zn precipitations. The alloy was forged one pass and annealed at 440 degrees C for 4 h, then followed by two passes of compressions. Eutectics were crushed and partially dissolved after deformation and annealing. The tensile strength increased after each forge pass. Submicron scale particles precipitated all around the grains during the deformations, and the amount of precipitations was proportional to the amount of deformations. These precipitated particles were observed by high resolution transmission electron microscopy (TEM). The existence of rhomboid W'-phase with face center cubic (FCC) structure and globular I-phase was confirmed. A quasi-periodicity lamellar phase combined with I-phase was founded, which was considered to be the transient phase between I-phase and I-phase.
Title:
Effect of substrate and orientation on charge ordering behaviors in epitaxial Pr0.5Ca0.35Sr0.15MnO3 films
Authors:
Yang, HW; Wang, C; Cai, RS; Hu, FX; Wang, YQ; Sun, JR Author Full Names: Yang, H. W.; Wang, C.; Cai, R. S.; Hu, F. X.; Wang, Y. Q.; Sun, J. R.
Source:
JOURNAL OF APPLIED PHYSICS, 117 (17):10.1063/1.4913731 MAY 7 2015
Abstract:
The charge ordering (CO) behaviors of Pr0.5Ca0.35Sr0.15MnO3 films grown on STO(100), STO(110) and LAO(100) are systematically investigated by transport measurements and transmission electron microscopy (TEM) examinations. From the transport measurements, the CO transition temperatures of all the three films are much higher than those of the bulk materials, showing that the film strain could enhance the CO transition. From TEM observations, many superlattice spots appear in the electron diffraction patterns taken from the films, indicating the appearance of the CO modulation structures at room temperature. The modulation vectors are determined to be (1/2, 0, 0) for STO (100), (1/2, 1/2, 1/2) for STO (110), and both (0, 1/2, 0) and (1/2, 1/2, 0) for LAO (100). It is shown that both the substrate orientation and the film strain have a great effect on the CO modulation structures. The CO state is much easier to appear in the compressive strain direction which is due to the Mn-O-Mn angle tilting. (C) 2015 AIP Publishing LLC.
Title:
Spin reorientation in multiferroic spinel Co0.5Fe0.5Cr2O4 with Mossbauer spectroscopy
Authors:
Myoung, BR; Kim, CS Author Full Names: Myoung, Bo Ra; Kim, Chul Sung
Source:
JOURNAL OF APPLIED PHYSICS, 117 (17):10.1063/1.4918968 MAY 7 2015
Abstract:
We studied the magnetic properties of multiferroic spinel Co0.5Fe0.5Cr2O4, especially focusing on the spin-ordering, spin-reorientation, and charge re-distribution effects. From the Rietveld refinement analysis, the crystal structure was identified to be a normal cubic spinel of Fd-3m. Based on the temperature-dependent measurements of the magnetization and magnetic hyperfine field (H-hf), Curie temperature (T-C) of Co0.5Fe0.5Cr2O4 was determined to be around 86K where H-hf (sic) 0. From the change of slope in the M-T curve, the conical-spiral magnetic ordering temperature was determined to be 20 K, which coincides with H-hf measurement. Also, we have observed the decrease in the slope of the electric quadrupole splitting (Delta E-Q) curve above 20K, suggesting that the change in Delta E-Q around T-S is originated from charge redistribution due to the spin-relocation associated with the distortion of each tetrahedral site around Fe2+ ion above T-S. This indicates that Co0.5Fe0.5Cr2O4 has the noncollinear conical-spiral spin ordering with incommensurate spin structure below T-S, while above T-S, it has ferrimagnetic spin ordering with commensuration in the collinear state. In addition, the Jahn-teller distortion temperature is measured to be around 155K, since both Delta E-Q and Delta(1) of T-5(2g) band decrease rapidly with increasing temperature and disappear around 155 K. (C) 2015 AIP Publishing LLC.
Title:
Zone-Folded Phonons and the Commensurate-Incommensurate Charge-Density-Wave Transition in 1T-TaSe2 Thin Films
Authors:
Samnakay, R; Wickramaratne, D; Pope, TR; Lake, RK; Salguero, TT; Balandin, AA Author Full Names: Samnakay, R.; Wickramaratne, D.; Pope, T. R.; Lake, R. K.; Salguero, T. T.; Balandin, A. A.
Source:
NANO LETTERS, 15 (5):2965-2973; 10.1021/nl504811s MAY 2015
Abstract:
Bulk 1T-TaSe2 exhibits unusually high charge density wave (CDW) transition temperatures of 600 and 473 K below which the material exists in the incommensurate (I-CDW) and the commensurate (C-CDW) charge-density-wave phases, respectively. The (13)(1/2) x (13)(1/2), C-CDW reconstruction of the lattice coincides with new Raman peaks resulting from zone-folding of phonon modes from middle regions of the original Brillouin zone back to Gamma. The C-CDW transition temperatures as a function of film thickness are determined from the evolution of these new Raman peaks, and they are found to decrease from 473 to 413 K as the film thicknesses decrease from 150 to 35 nm. A comparison of the Raman data with ab initio calculations of both the normal and C-CDW phases gives a consistent picture of the zone-folding of the phonon modes following lattice reconstruction, The Raman peak at similar to 154 cm(-1) originates from the zone-folded phonons in the C-CDW phase. In the I-CDW phase, the loss of translational symmetry coincides with a strong suppression and broadening of the Raman peaks. The observed,change: in the C-CDW transition temperature is consistent with total energy calculations of bulk and monolayer 1T-TaSe2.
Title:
Temperature-Pressure Phase Diagram for Rb2ZnCl4 Crystals
Authors:
Kurlyak, VY; Stadnyk, VY; Stakhura, V Author Full Names: Kurlyak, V. Yu.; Stadnyk, V. Yo.; Stakhura, V.
Source:
JOURNAL OF APPLIED SPECTROSCOPY, 82 (2):228-233; 10.1007/s10812-015-0090-3 MAY 2015
Abstract:
We have studied the effect of uniaxial stress along the principal crystallophysical directions on the temperature variations in the birefringence Delta n (i) and the refractive indices ni for Rb2ZnCl4 crystals in the region of phase transitions from the paraelectric phase to the incommensurate phase and then to the commensurate ferroelectric phase. We have established that Delta n (i) and n (i) are rather sensitive to the action of uniaxial stresses. We have observed a significant pressure-induced shift of the paraelectric - incommensurate - ferroelectric phase transition points in different temperature regions, depending on the direction of the uniaxial compression.

Update: 11-Jun-2015

Title:
Effect of Li on electrochemical properties of Ti1.4V0.6Ni quasicrystal alloy produced by rapid quenching
Authors:
Ouyang, ZT; Liu, K; Shang, JM; Xing, C; Liu, WQ; Wang, LM Author Full Names: Ouyang, Zhongtao; Liu, Kun; Shang, Jinming; Xing, Cheng; Liu, Wanqiang; Wang, Limin
Source:
INTERMETALLICS, 62 50-55; 10.1016/j.intermet.2015.03.010 JUL 2015
Abstract:
The effect of Li on the electrochemical performance of electrodes consisting of Ti1.4V0.6Ni quasicrystal was investigated at room temperature in three-electrode cell set-up. The quasicrystal sample was initially synthesized by arc melting, followed by melt-spinning, and then infiltrated with Li atoms by electroosmosis. According to X-ray diffraction, all ribbon samples were determined to be icosahedral quasicrystal phase (I-phase), V-based solid solution phase with BCC structure and face centered cubic (FCC) phase with Ti2Ni-type structure. After infiltrating some Li atoms into the Ti1.4V0.6Ni quasicrystal lattice under the condition of an electroosmosis current of 0.6 A, we could observe the appearance of Li diffraction peaks. Importantly, the slight shift to the left observed in the diffraction peaks indicated that lattice expansion was caused by the infiltration of Li. The discharge capacity of Ti1.4V0.6Ni-Li material was higher than that of Ti1.4V0.6Ni.The maximum discharge capacity of 307.1 mAh/g was recorded for Ti1.4V0.6Ni Li at a current density of 30 mAh/g. Both high-rate dischargeability and cycling stability were enhanced as a result of infiltrating Li. The lithium could get into the lattice, which resulted in the formation of microspores on surface of alloy, thus improving electrochemical activity of the alloy electrode. At the same time, the electrochemical reaction kinetics of alloy electrodes was also researched. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Synthesis and Characterization of Bulk Al-Cu-Fe Based Quasicrystals and Composites by Spray Forming
Authors:
Mukhopadhyay, NK; Uhlenwinkel, V; Srivastava, VC Author Full Names: Mukhopadhyay, N. K.; Uhlenwinkel, V.; Srivastava, V. C.
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 24 (6):2172-2178; SI 10.1007/s11665-015-1442-0 JUN 2015
Abstract:
The bulk quasicrystalline (QC) materials and their composites have attracted considerable interest due to their promising mechanical properties. In the present investigation, spray forming has been used to synthesize bulk single-phase icosahedral quasicrystals and composites in Al62.5Cu25Fe12.5 system as well as in quaternary system containing 10% Sn. The elemental materials were induction melted under nitrogen cover and a billet of 250 mm in diameter and 350 mm in height was spray formed. The phase constitution of the spray-formed materials showed a bulk single-phase icosahedral quasicrystal as a major phase along with other crystalline phases. A large number of annealing twins were observed in the microstructure in ternary AlCuFe alloys. It is interesting to note that due to addition of Sn, the volume fraction of beta-Al(CuFe) phase was found to increase and annealing twins were almost absent. The hardness of the single-phase AlCuFe alloy and Sn-containing composites was found to be 8.6 and 6.0 GPa, respectively, at a load of 300 g. In general, the hardness decreases with heat treatment at high temperatures. However, in case of Sn-ontaining alloy, hardness increases with low-temperature heat treatment. Long and hair-like cracks (Palmqvist type) are observed to form from the corner of the indentations of the ternary alloys, whereas in Sn-containing composites, the cracks are not sharp and long suggesting the enhancement of fracture toughness in the composites. Attempts have been made to understand the effect of Sn on the evolution of icosahedral phase, other crystalline phases and their composite effects on the mechanical properties.
Title:
Superconductivity and the electronic phase diagram of LaPt2-xGe2+x
Authors:
Maeda, S; Matano, K; Yatagai, R; Oguchi, T; Zheng, GQ Author Full Names: Maeda, S.; Matano, K.; Yatagai, R.; Oguchi, T.; Zheng, Guo-qing
Source:
PHYSICAL REVIEW B, 91 (17):10.1103/PhysRevB.91.174516 MAY 22 2015
Abstract:
In many cases, unconventional superconductivity are realized by suppressing another order parameter, such as charge density wave (CDW) or spin density wave (SDW). This suggests that the fluctuations of these order parameters play an important role in producing superconductivity. LaPt2Ge2 undergoes a tetragonal-to-monoclinic structural phase transition (SPT) at T-s = 394 K, accompanying a double period modulation in the a-axis direction, and superconducts at T-c = 0.41 K. We performed band calculations and found 2D (two dimensional)-like Fermi surfaces with partial nesting. A reduction in the density of states in the monoclinic phase was found in the calculation and confirmed by Pt-195-NMR. We suggest a CDW as a possible cause for the SPT. By changing the stoichiometry between Pt and Ge, we succeeded in suppressing T-s and increasing T-c in LaPt2-xGe2+x. Comparison of La-139- and Pt-195-NMR data reveals moderate fluctuations associated with SPT. From La-139-NQR measurements at zero field, we found that an isotropic superconducting gap is realized in LaPt2-xGe2+x (x = 0.20). We discuss the relationship between superconductivity and the SPT order/fluctuations.
Title:
Oxygen octahedra distortion induced structural and magnetic phase transitions in Bi1-xCaxFe1-xMnxO3 ceramics
Authors:
Kumar, P; Shankhwar, N; Srinivasan, A; Kar, M Author Full Names: Kumar, Pawan; Shankhwar, Nisha; Srinivasan, A.; Kar, Manoranjan
Source:
JOURNAL OF APPLIED PHYSICS, 117 (19):10.1063/1.4921433 MAY 21 2015
Abstract:
The co-doping of Ca and Mn in respective Bi and Fe-sites of BiFeO3 lattice leads to structural transition from rhombohedral (R3c space group) to orthorhombic (Pbnm space group) crystal symmetry. The tilt angle for anti-phase rotation of the oxygen octahedra of BiFeO3 at room temperature is observed to be similar to 13.8 degrees. It decreases with the increase in the co-doping percentage which suggests the composition-driven structural phase transition. The remnant magnetization for sample with 15% of co-doping becomes about 16 times that of BiFeO3. It may be attributed to the suppression of cycloid spin structure and uncompensated spins at the surface of nanocrystallites. Further increase in co-doping percentage results in the sharp reduction of remnant magnetization due to the dominant contribution from the collinear antiferromagnetic ordering in the Pbnm space group. The Arrott plot analysis clearly indicates the composition-driven crossover from the antiferromagnetic to weak ferromagnetic ordering and vice versa. Electron spin resonance results provide the evidence for the composition-driven phase transitions from an incommensurate spin cycloidal modulated state to one with nearly homogeneous spin order. The band gap (2.17 eV) of BiFeO3 measured using UV-Vis spectra was supported by the resonance Raman spectra. (C) 2015 AIP Publishing LLC.
Title:
Coexistence of Charge-Density-Wave and Pair-Density-Wave Orders in Underdoped Cuprates
Authors:
Wang, YX; Agterberg, DF; Chubukov, A Author Full Names: Wang, Yuxuan; Agterberg, Daniel F.; Chubukov, Andrey
Source:
PHYSICAL REVIEW LETTERS, 114 (19):10.1103/PhysRevLett.114.197001 MAY 15 2015
Abstract:
We analyze incommensurate charge-density-wave (CDW) and pair-density-wave (PDW) orders with transferred momenta (+/- Q, 0)/(0, +/- Q) in underdoped cuprates within the spin-fermion model. Both orders appear due to an exchange of spin fluctuations before magnetic order develops. We argue that the ordered state with the lowest energy has nonzero CDW and PDW components with the same momentum. Such a state breaks C-4 lattice rotational symmetry, time-reversal symmetry, and mirror symmetries. We argue that the feedback from CDW/PDW order on fermionic dispersion is consistent with ARPES data. We discuss the interplay between the CDW/PDWorder and d(x2-y2) superconductivity and make specific predictions for experiments.
Title:
Incommensurate Systems as Model Compounds for Disorder Revealing Low-Temperature Glasslike Behavior
Authors:
Remenyi, G; Sahling, S; Biljakovic, K; Staresinic, D; Lasjaunias, JC; Lorenzo, JE; Monceau, P; Cano, A Author Full Names: Remenyi, G.; Sahling, S.; Biljakovic, K.; Staresinic, D.; Lasjaunias, J. -C.; Lorenzo, J. E.; Monceau, P.; Cano, A.
Source:
PHYSICAL REVIEW LETTERS, 114 (19):10.1103/PhysRevLett.114.195502 MAY 14 2015
Abstract:
We show that the specific heat of incommensurately modulated crystals with broken translational periodicity presents similar features at low temperatures to those of amorphous and glass materials. Here we demonstrate that the excess to the constant C-p(T)/T-3 law (or Debye limit) is made up of an upturn below 1 K and of a broad bump at T approximate to 10 K that directly originates from the gapped phase and amplitude modes of the incommensurate structure. We argue that the low-energy dynamics of incommensurate systems constitute a plausible simplification of the landscape of interactions present in glasses, giving rise to their low-temperature anomalies.
Title:
A Crystal-Chemical Framework for Relaxor versus Normal Ferroelectric Behavior in Tetragonal Tungsten Bronzes
Authors:
Zhu, X; Fu, M; Stennett, MC; Vilarinho, PM; Levin, I; Randall, CA; Gardner, J; Morrison, FD; Reaney, IM Author Full Names: Zhu, X.; Fu, M.; Stennett, M. C.; Vilarinho, P. M.; Levin, I.; Randall, C. A.; Gardner, J.; Morrison, F. D.; Reaney, I. M.
Source:
CHEMISTRY OF MATERIALS, 27 (9):3250-3261; 10.1021/acs.chemmater.5b00072 MAY 12 2015
Abstract:
Tetragonal tungsten bronzes (TTBs), an important class of oxides known to exhibit ferroelectricity, undergo complex distortions, including rotations of,oxygen octahedra, which give rise to either incommensurately or commensurately modulated superstructures. Many TTBs display broad, frequency-dependent relaxor dieletric behavior rather than sharper frequency-independent normal ferroelectric anomalies, but the exact reasons that favor a particular type of dielectric response for a given composition remain unclear. In this contribution the influence of incommensurate/commensurate dispiacive modulations on the onset of relaxor/ferroelectric behavior in TTBs is assessed in the context of basic crystal-chemical factors, such as positional disorder, ionic radii and polarizabilities, and point defects. We present a predictive crystal-chemical model that rationalizes composition structure properties relations for a broad range of TTB systems.
Title:
Structural transformation in quasicrystal-forming Al-Cu-Fe alloys
Authors:
Boularas, H; Debili, MY; Alleg, S Author Full Names: Boularas, H.; Debili, M. Y.; Alleg, S.
Source:
METALLURGICAL RESEARCH & TECHNOLOGY, 112 (2):10.1051/metal/2015008 2015
Abstract:
Three Al-Cu-Fe alloys with various iron contents (6 at.%, 12 at.% and 15 at.%), were synthesized by fusion under high-frequency magnetic induction and characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry(DSC). The microstructure evolution was carried out both in the as-quenched state as well after heat treatment at 500 degrees C in relation to iron composition. Particular attention was been paid to the alloy containing 15%, and we were been able to determine by DSC that a massive transformation from crystal (beta) to quasicrystal i-psi (Al6Fe2Cu) occurs for this composition.
Title:
Formation of an Icosahedral Quasicrystal and Its Approximant in Au-Al-Sc System
Authors:
So, YG; Kimoto, K; Edagawa, K Author Full Names: So, Yeong-Gi; Kimoto, Koji; Edagawa, Keiichi
Source:
MATERIALS TRANSACTIONS, 56 (4):495-499; 10.2320/matertrans.M2014421 2015
Abstract:
The formation of the icosahedral (i-) and 1/1-approximant (1/1-) phases in the Au-Al-Sc system has been investigated. A primitive-type i-phase was found to form in an Au45Al40Sc15 alloy. This i-phase was shown to be thermodynamically stable at 973 K. A stable 1/1-phase was found to form at 1173K for compositions of Au44+xAl41-xSc15 (x = 0, 1, 2, 3). High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed that the 1/1-phase consists of Tsai-type icosahedral clusters. Similar local structures were observed in the HAADF-STEM image for the i-phase, indicating that the i-phase consists of Tsai-type clusters identical to the clusters in the 1/1-phase. The composition of the Au-Al-Sc i-phase is consistent with the formation conditions, including those in the valence electrons per atom ratio and in the atomic size factor, which has been shown previously for other Tsai-type i-phases. This fact demonstrates the importance of these conditions for stabilization of Tsai-type i-phases.

Update: 3-Jun-2015

Title:
The study of Al-3(Mn, Pd) crystal and Al-Mn-Pd decagonal quasicrystal by spherical aberration-corrected scanning transmission microscopy and atomic-resolution energy dispersive X-ray spectroscopy
Authors:
Yasuhara, A; Hiraga, K Author Full Names: Yasuhara, Akira; Hiraga, Kenji
Source:
PHILOSOPHICAL MAGAZINE, 95 (14):1511-1523; 10.1080/14786435.2015.1039623 MAY 13 2015
Abstract:
An Al3Mn-type Al-3(Mn, Pd) crystal and an Al-Mn-Pd decagonal quasicrystal (DQC) in an Al70Mn20Pd10 alloy are studied using a spherical aberration (Cs)-corrected scanning transmission electron microscope (STEM) with high-angle annular dark-field (HAADF) and annular bright-field (ABF) techniques, together with atomic-resolution energy dispersive X-ray spectroscopy (EDS). Mn and Pd atomic positions in the Al-3(Mn, Pd) structure projected along the b-axis (pseudo-tenfold rotational axis) are represented by separate bright dots in observed HAADF-STEM images. Besides, Al as well as Mn and Pd atomic positions are represented as dark dots in ABF-STEM images. Most Mn and Pd atomic positions in the Al-3(Mn, Pd) structure can be observed on atomic-resolution EDS maps. On the basis of the good correlation between the STEM images and the EDS maps, and also considering the structure of the Al-3(Mn, Pd) crystal, which was determined by X-ray diffraction using a single crystal, observed HAADF and ABF-STEM images of the Al-Mn-Pd DQC have been interpreted. Pd and Mn atomic positions in the Al-Mn-Pd DQC can be detected on the observed EDS maps. It can be seen that Pd is enriched around the centre of the columnar clusters, having a decagonal section with 2nm in diameter. It can therefore be concluded that Pd plays an important role in the stabilization of the decagonal clusters, which form the Al-Mn-Pd DQC structure.
Title:
The structure of an Al-Rh-Cu decagonal quasicrystal studied by spherical aberration (Cs)-corrected scanning transmission electron microscopy
Authors:
Hiraga, K; Yasuhara, A; Yamamoto, K; Yubuta, K Author Full Names: Hiraga, Kenji; Yasuhara, Akira; Yamamoto, Kazuki; Yubuta, Kunio
Source:
PHILOSOPHICAL MAGAZINE, 95 (14):1524-1535; 10.1080/14786435.2015.1039624 MAY 13 2015
Abstract:
The structure of an Al-Rh-Cu decagonal quasicrystal formed with two quasiperiodic planes along the periodic axis in an Al63Rh18.5Cu18.5 alloy has been studied by spherical aberration (Cs)-corrected high-angle annular detector dark-field (HAADF)- and annular bright-field (ABF)-scanning transmission electron microscopy (STEM). Heavy atoms of Rh and mixed sites (MSs) of Al and Cu atoms projected along the periodic axis can be clearly represented as separate bright dots in observed HAADF-STEM images, and consequently arrangements of Rh atoms and MSs on the two quasiperiodic planes can be directly determined from those of bright dots in the observed HAADF-STEM image. The Rh atoms are arranged in pentagonal tiling formed with pentagonal and star-shaped pentagonal tiles with an edge-length of 0.76nm, and also MSs with a pentagonal arrangement are located in the pentagonal tiles with definite orientations. The star-shaped pentagonal tiles in the pentagonal tiling are arranged in tau(2)(tau: golden ratio)-inflated pentagonal tiling with a bond-length of 2nm. From arrangements of Rh atoms placed in pentagonal tilings with a bond-length of 2nm, which are generated by the projection of a five-dimensional hyper-cubic lattice, occupation domains in the perpendicular space are derived. Al atoms as well as Rh atoms and MSs are represented as dark dots in an observed ABF-STEM image, and arrangements of Al atoms in well-symmetric regions are discussed.

Update: 28-May-2015

Title:
Refinement of the icosahedral quasicrystalline phase and the grain size of Mg-9.25Zn-1.66Y alloy by high-ratio differential speed rolling
Authors:
Kwak, TY; Lim, HK; Han, SH; Kim, WJ Author Full Names: Kwak, T. Y.; Lim, H. K.; Han, S. H.; Kim, W. J.
Source:
SCRIPTA MATERIALIA, 103 49-52; 10.1016/j.scriptamat.2015.03.004 JUL 1 2015
Abstract:
Differential speed rolling was applied to a Mg-9.25Zn-1.66Y alloy with an icosahedral quasicrystalline (I) phase to refine its cast microstructure by severe plastic deformation. The grain size was reduced to gm. A higher speed ratio, which produces a higher shear strain, was more effective in breaking up the eutectic I phase structure and dispersing the broken particles into the matrix. The processed alloy exhibited a high yield stress of 337 MPa and a good elongation of 10.7%. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Evidence for magneto-electric and spin-lattice coupling in PbFe0.5Nb0.5O3 through structural and magneto-electric studies
Authors:
Matteppanavar, S; Rayaprol, S; Singh, K; Reddy, VR; Angadi, B Author Full Names: Matteppanavar, Shidaling; Rayaprol, Sudhindra; Singh, Kiran; Reddy, V. Raghavendra; Angadi, Basavaraj
Source:
JOURNAL OF MATERIALS SCIENCE, 50 (14):4980-4993; 10.1007/s10853-015-9046-5 JUL 2015
Abstract:
Neutron diffraction (ND) studies were carried out on polycrystalline single-phase multiferroic Pb(Fe0.5Nb0.5)O-3 (PFN) in the temperature range of 290-2 K to understand the structural and magnetic properties as a function of temperature. ND data were refined using the Rietveld refinement method for both crystallographic and magnetic structures. The structure at room temperature was found to be monoclinic, in Cm space group. No structural transition was observed till 2 K. At low temperatures (i.e., from T < T (N); T (N) = 155 K), an additional peak appears at scattering vector, Q = 1.35 (-1), indicating the onset of antiferromagnetic ordering. The magnetic structure was found to be commensurate with the crystallographic structure and could be refined using the propagation vector, k = [0.125, 0.5, and 0.5]. Magnetization, ferroelectric P-E loops, and dielectric measurements on PFN reveal a strong anomaly at the antiferromagnetic transition temperature (T (N)) indicating the magneto-electric coupling. The refined temperature-dependent structural parameters such as unit cell volume and monoclinic distortion angle (beta) reveal pronounced anomalies at the magnetic ordering temperature (T (N)), which indicates strong spin-lattice coupling. An anomaly in lattice volume was observed with a small negative thermal expansion below and a large thermal expansion above the T (N), respectively. It shows the occurrence of isostructural phase transition accompanying the magnetic ordering below T (N) 155 K, leading to significant change in ionic polarization, octahedral tilt angle, and lattice strain around T (N). We have used refined atomic positional coordinates from the nuclear and magnetic structures, to obtain ionic polarization. These detailed studies confirm the magneto-electric and spin-lattice coupling in PFN across T-N.
Title:
Pressure-induced successive magnetic and structural phase transitions in Fe1.087Te
Authors:
Jorgensen, JE; Hansen, TC Author Full Names: Jorgensen, Jens-Erik; Hansen, Thomas Christian
Source:
EUROPEAN PHYSICAL JOURNAL B, 88 (5):10.1140/epjb/e2015-50713-6 MAY 11 2015
Abstract:
The crystal and magnetic structures of Fe1.087Te have been studied by neutron powder diffraction in the temperature range from 5 to 170 K at pressures in the range from approximate to 0.8 to approximate to 7 GPa. The p, T-phase diagram contains three phases with monoclinic, orthorhombic and tetragonal symmetry. The monoclinic and orthorhombic phases are both antiferromagnetically ordered and stable at temperatures below approximate to 69 K while the non-magnetic tetragonal phase is stable above this temperature. The monoclinic phase is stable for p less than or similar to 1.2 GPa while the orthorhombic phase is stable for 1.2 less than or similar to p less than or similar to 1.7 GPa and the tetragonal phase becomes stable at higher pressures at the lowest measured temperatures. The magnetic ordering is antiferromagnetic bicollinear and commensurate in the monoclinic phase but incommensurate and pressure dependent in the orthorhombic phase. The pressure-induced collapse of magnetic order at approximate to 1.7 GPa is accompanied by abrupt changes in volume and compressibility, suggestive of a spin state change of the Fe2+ ions in the FeTe layers.
Title:
Amount of valence charge of Al- and Zn-based quasicrystals and related approximant crystals evaluated by chemical shift observations and Bader analysis
Authors:
Koshiya, S; Terauchi, M Author Full Names: Koshiya, S.; Terauchi, M.
Source:
PHILOSOPHICAL MAGAZINE, 95 (13):1462-1470; 10.1080/14786435.2015.1033486 MAY 3 2015
Abstract:
The amounts of decreased charge at Al sites of Al-based (Al-Pd-Cr-Fe, Al-Si-Mn, and Al-Re-Si) and at Zn sites of Zn-based (Zn-Mg-Zr) quasicrystals and approximant crystals were estimated. The evaluation was done by comparisons between chemical shifts experimentally observed by soft-X-ray emission spectroscopy and the amount of valence charge obtained by Bader analysis for first principle calculations of reference materials (Al, alpha-Al2O3, Zn, and ZnO). Decreased charges at Al sites of Al-based quasicrystals and at Zn sites of Zn-based quasicrystals were evaluated to be 1.0-2.5 e(-)/atom and 1.1-1.2 e(-)/atom, respectively. A covalent bonding nature alloy of Al-Re-Si also showed a decrease in valence charge at Al sites.
Title:
Infinitely Adaptive Transition Metal Oxychalcogenides: The Modulated Structures of Ce2O2MnSe2 and (Ce0.78La0.22)(2)O2MnSe2
Authors:
Wang, CH; Ainsworth, CM; Gui, DY; McCabe, EE; Tucker, MG; Evans, IR; Evans, JSO Author Full Names: Wang, Chun-Hai; Ainsworth, Chris M.; Gui, Dong-Yun; McCabe, Emma E.; Tucker, Matthew G.; Evans, Ivana R.; Evans, John S. O.
Source:
CHEMISTRY OF MATERIALS, 27 (8):3121-3134; 10.1021/acs.chemmaer.5b00666 APR 28 2015
Abstract:
This article reports the syntheses, structures, and physical properties of the oxychalcogenides (Ce1-xLax)(2)O2MnSe2 with x = 0-0.7. These materials have a layered structure related to that of the LaOFeAs-derived superconductors but with the transition metal sites 50% occupied. Ce2O2MnSe2 contains alternating layers of composition: [Ce2O2](2+) and [MnSe2](2-). The size mismatch between the layers leads to an incommensurate structure with a modulation vector of q = ae+ Ob*+0.5c* with a = 0.158(1), which can be described with a (3 + 1)D superspace structural model in superspace group Cmme(a,0,(1) / OM [67.12]. There is a strong modulation of Mn site occupancies, leading to a mixture of corner- and edge-sharing MnSe4/2 tetrahedra in the [MnSe2](2-) layers. The modulation vector can be controlled by partial substitution of Ce3+ for larger La3+, and a simple commensurate (Ce0.78La0.22)(2)O2MnSe2 with a = 1/6. The materials respond to the change in relative size of the oxide and chalcogenide blocks by varying the ratio of corner- to edge-sharing tetrahedra. The superspace model lets us unify the structural description of the five different ordering patterns reported to date for different Ln(2)O(2)MSe(2) (Ln = lanthanide) materials. Mn moments in Ce2O2MnSe2 and (Ce0.78La0.22)(2)O2MnSe2 order antiferromagnetically below TN = 150 K, and Ce moments order below similar to 70 K. The magnetic structures of both materials have been determined using neutron diffraction. Both materials are semiconductors; Ce2O2MnSe2 has a = 9 x 10(-6) Omega(-1) cm(-1) at room temperature and an activation energy for charge carrier mobility from RT to 170 degrees C of -,0.4 eV.
Title:
Effect of Pd Substitution on Phase Formation and Stability in Ti-Zr-Ni Quasicrystalline Alloys
Authors:
Huang, HG; Chen, L; Xu, QY Author Full Names: Huang Huogen; Chen Liang; Xu Qinying
Source:
RARE METAL MATERIALS AND ENGINEERING, 44 (4):821-825; APR 2015
Abstract:
Pd can be used as an adding element to improve hydrogenation properties of Ti-Zr-Ni quasicrystalline alloys. However, the action mechanism of Pd addition is unclear yet. The effects of Pd substituting Ti and Zr in Ti45Zr38Ni17 and Ti40Zr40Ni20 alloys were studied by means of XRD, TEM and DSC examination. The results show that icosahedral quasicrystal can be formed purely through 4%similar to 6% Pd substitution for Ti or 4% for Zr in the Ti45Zr38Ni17 alloy, as well as 3%similar to 4% for Ti or possibly below 3% for Zr in the Ti40Zr40Ni20 alloy. This indicates a higher substitution limit for Ti in order for the heritance of the quasicrystal phase. Two derived quasicrystals Ti39Zr38Ni17Pd6 and Ti36Zr40Ni20Pd4 can be transformed into crystalline phases after annealing at 400 degrees C, demonstrating their lower thermo-stabilities in comparison to such Ti-Zr-Ni alloys being stable at about 700 degrees C. Both the replacement tendency and the decrease of the thermostability of quasicrystal phase might be ascribed to appropriate atomic size of Pd.
Title:
X-ray induced lock-in transition of cycloidal magnetic order in a multiferroic perovskite manganite
Authors:
Yamasaki, Y; Nakao, H; Murakami, Y; Nakajima, T; Sampietro, AL; Ohsumi, H; Takata, M; Arima, T; Tokura, Y Author Full Names: Yamasaki, Y.; Nakao, H.; Murakami, Y.; Nakajima, T.; Sampietro, A. Lafuente; Ohsumi, H.; Takata, M.; Arima, T.; Tokura, Y.
Source:
PHYSICAL REVIEW B, 91 (10):10.1103/PhysRevB.91.100403 MAR 24 2015
Abstract:
We report the x-ray photoexcitation effects on cycloidal magnetic order in a multiferroic perovskite-type manganite Gd0.5Tb0.5MnO3. The material exhibits a competition between the P (electric polarization)parallel to a ferroelectric state with the commensurate (C) ab-plane cycloidal and the P parallel to c ferroelectric state with the incommensurate (IC) bc-plane cycloidal spin structure. The phase transition between these two phases can be induced by an application of a magnetic field. We found that the x-ray irradiation can induce the bidirectional and persistent phase transition between IC and C phases. The nonresonant x-ray magnetic diffraction revealed that both the initial and the x-ray induced phases have the bc-plane cycloidal magnetic structure, whereas the magnetic wave number varies between IC and C. The x-ray induced bc-plane cycloidal C phase is thus the hidden multiferroic phase in the Gd1-xTbxMnO3 system, which does not show up with the application of any static field.

Update: 20-May-2015

Title:
High-resolution Brillouin scattering studies of phase transitions in Ca2MgSi2O7 and Ca2ZnSi2O7 silicates
Authors:
Maczka, M; Hanuza, J; Kaminskii, A; Kojima, S Author Full Names: Maczka, Miroslaw; Hanuza, Jerzy; Kaminskii, Alexander; Kojima, Seiji
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 638 34-37; 10.1016/j.jallcom.2015.03.055 JUL 25 2015
Abstract:
Temperature-dependent Micro-Brillouin scattering studies of Ca2MgSi2O7 and Ca2ZnSi2O7 single crystals were performed. Step-like decrease of Brillouin shifts and strong broadening of Brillouin bands corresponding to the c(33) elastic constant were observed at 351 K for Ca2MgSi2O7 and 407 K for Ca2ZnSi2O7. This behavior was attributed to coupling of strain to the square of the order parameter due to structural transitions into incommensurate phases. Analysis of the observed acoustic anomalies showed critical slowing down behavior of the relaxation time characterizing interaction between the order parameter and acoustic phonon. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Investigation of multiferroic behaviour of TbMnO3 nanoplates
Authors:
Acharya, SA; Khule, SM; Gaikwad, VM Author Full Names: Acharya, S. A.; Khule, S. M.; Gaikwad, V. M.
Source:
MATERIALS RESEARCH BULLETIN, 67 111-117; 10.1016/j.materresbull.2015.03.013 JUL 2015
Abstract:
In the present study, hydrothermally prepared TbMnO3 in plates-like morphology at nanoscale are investigated in multiferroic view point. X-ray diffraction study confirms the orthorhombic phase of as-synthesized TbMnO3. Microstructural features studied by Scanning Electron Microscopy and Transmission Electron Microscopy show the plates-like morphology of as-synthesized TbMnO3 at nanoscale. Local distortions investigated by FT-Raman exhibits redshift in T mode by about 20 cm(-1) as compared to that of the single crystal. The redshift in T mode is mainly due to defect by tilting of octahedra and respective changes in bond angle of Mn-O(1)-Mn. This is assigned to the size-morphology induced defects. The temperature dependent zero-field-cooled and field-cooled magnetization are measured at H=50 Oe and in the temperature range 2-300 K. The anomalies in magnetization are obtained at 8 and 42 K. Bifurcation of the ZFC and FC curves are observed very close to magnetic transition temperature 42 K. The 42 K anomaly is related to the sine wave ordering of Mn3+ moment; and 8K anomaly is associated with magnetic ordering of the Tb3+-sublattice propagation vector. The anomalies in the electric properties, epsilon' (T), tan delta (T), which are noticed within the 28K range, coincide with the temperature of incommensurate-commensurate (or lock-in) magnetic transition of TbMnO3. This study confirms that multiferroic behavior is retained in TbMnO3 nanoplates. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Spatial decay of the phason field in quasicrystal linear elasticity
Authors:
Mariano, PM; Salvatori, L Author Full Names: Mariano, Paolo Maria; Salvatori, Luca
Source:
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING, 23 (4):10.1088/0965-0393/23/4/045004 JUN 2015
Abstract:
We present numerical simulations showing that a conservative phason self-action, i.e. the stationary part of the phason diffusion, promotes in quasicrystal linear elasticity the phason spatial decay. The proof of the possible existence of such a phason self-action is based on the invariance requirements of the external power of all actions over a quasicrystal, with respect to isometry-based changes in observers in the physical and phason spaces. The numerical result confirms a 2011 theoretical prevision by Colli and Mariano.
Title:
Phase equilibria and transformations in ternary Mg-Gd-Zn alloys
Authors:
Grobner, J; Kozlov, A; Fang, XY; Zhu, SM; Nie, JF; Gibson, MA; Schmid-Fetzer, R Author Full Names: Groebner, Joachim; Kozlov, Artem; Fang, Xi-Ya; Zhu, Suming; Nie, Jian-Feng; Gibson, Mark A.; Schmid-Fetzer, Rainer
Source:
ACTA MATERIALIA, 90 400-416; 10.1016/j.actamat.2015.02.044 MAY 15 2015
Abstract:
Phase equilibria and transformations in ternary Mg-Gd-Zn alloys were studied experimentally by investigating 22 samples with up to 40 at.% Gd and 60 at.% Zn. These results, combined with a critical review of literature data, were used to develop thermodynamic descriptions of the Gd Zn and the Mg-Gd-Zn systems and to calculate the Mg-Gd-Zn phase diagram in the entire composition range. In the ternary system the hexagonal long-period stacking ordered structure 14H, the hexagonal phase H1, Gd11Mg24Zn64, and five solid solution phases with ternary compositions, GdMg5, GdMg3, GdMg2, Gd(Mg,Zn), and W are found to be stable, whereas the icosahedral phase I, GdMg3Zn6, and other hexagonal phases are metastable. In addition, a new stable phase Gd20Mg19Zn81 with a face-centered cubic structure is identified in the Mg Gd Zn system. Based on the thermodynamic description obtained in this work, the microstructures and phase transformations previously observed in the as-cast, solution heat treated and aged conditions are discussed. It is shown that the current thermodynamic predictions are in good accord with the experimental findings, suggesting the viability of such an approach for the microstructure design of Mg-Gd-Zn alloys. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Spectroscopic study of metallic magnetism in single-crystalline Nb1-yFe2+y
Authors:
Rauch, D; Kraken, M; Litterst, FJ; Sullow, S; Luetkens, H; Brando, M; Forster, T; Sichelschmidt, J; Neubauer, A; Pfleiderer, C; Duncan, WJ; Grosche, FM Author Full Names: Rauch, D.; Kraken, M.; Litterst, F. J.; Suellow, S.; Luetkens, H.; Brando, M.; Foerster, T.; Sichelschmidt, J.; Neubauer, A.; Pfleiderer, C.; Duncan, W. J.; Grosche, F. M.
Source:
PHYSICAL REVIEW B, 91 (17):10.1103/PhysRevB.91.174404 MAY 6 2015
Abstract:
We have investigated single crystals and polycrystals from the series Nb1-yFe2+y, -0.004 <= y <= 0.018, by electron spin resonance, muon spin relaxation, and Mossbauer spectroscopy. Our data establish that at lowest temperatures all samples exhibit bulk magnetic order. Slight Fe excess induces low-moment ferromagnetism, consistent with bulk magnetometry, while Nb-rich and stoichiometric NbFe2 display spin density wave order with small magnetic moment amplitudes of order similar to 0.001-0.01 mu(B)/Fe. This provides microscopic evidence for a modulated magnetic state on the border of ferromagnetism in NbFe2.
Title:
Long-range modulation of a composite crystal in a five-dimensional superspace
Authors:
Guerin, L; Mariette, C; Rabiller, P; Huard, M; Ravy, S; Fertey, P; Nichols, SM; Wang, B; Mannsfeld, SCB; Weber, T; Hollingsworth, MD; Toudic, B Author Full Names: Guerin, Laurent; Mariette, Celine; Rabiller, Philippe; Huard, Michael; Ravy, Sylvain; Fertey, Pierre; Nichols, Shane M.; Wang, Bo; Mannsfeld, Stefan C. B.; Weber, Thomas; Hollingsworth, Mark D.; Toudic, Bertrand
Source:
PHYSICAL REVIEW B, 91 (18):10.1103/PhysRevB.91.184101 MAY 5 2015
Abstract:
The intergrowth crystal of n-tetracosane/urea presents a misfit parameter, defined by the ratio gamma = c(h)/c(g) (c(host)/c(guest)), that is very close to a commensurate value (gamma congruent to 1/3). High-resolution diffraction studies presented here reveal an aperiodic misfit parameter of gamma = 0.3369, which is found to be constant at all temperatures studied. A complex sequence of structural phases is reported. The high temperature phase (phase I) exists in the four-dimensional superspace group P6(1)22(00 gamma). At T-c1 = 179(1) K, a ferroelastic phase transition increases the dimension of the crystallographic superspace. This orthorhombic phase (phase II) is characterized by the five-dimensional (5D) superspace group C222(1)(00 gamma)(10 delta) with a modulation vector a(o)* + c(m)* = a(o)* + delta . c(h)*, in which the supplementary misfit parameter is delta = 0.025(1) in host reciprocal units. This corresponds to the appearance of a modulation of very long period (about 440 +/- 16 angstrom). At T-c2 = 163.0(5) K, a 5D to 5D phase transition leads to the crystallographic superspace group P2(1)2(1)2(1)(00 gamma)(00 delta) with a very similar value of delta. This phase transition reveals a significant hysteresis effect.
Title:
X-ray investigation of lateral hetero-structures of inversion domains in LiNbO3, KTiOPO4 and KTiOAsO4
Authors:
Lyford, TS; Collins, SP; Fewster, PF; Thomas, PA Author Full Names: Lyford, Thomas S.; Collins, Stephen P.; Fewster, Paul F.; Thomas, Pamela A.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 255-267; 10.1107/S2053273315001503 3 MAY 2015
Abstract:
In this paper periodically domain-inverted (PDI) ferroelectric crystals are studied using high-resolution X-ray diffraction. Rocking curves and reciprocal-space maps of the principal symmetric Bragg reflections in LiNbO3 (LN) (Lambda = 5 mu m), KTiOPO4 (KTP) (Lambda = 9 mu m) and KTiOAsO4 (KTA) (Lambda = 39 mu m) are presented. For all the samples strong satellite reflections were observed as a consequence of the PDI structure. Analysis of the satellites showed that they were caused by a combination of coherent and incoherent scattering between the adjacent domains. Whilst the satellites contained phase information regarding the structure of the domain wall, this information could not be rigorously extracted without a priori knowledge of the twinning mechanism. Analysis of the profiles reveals strain distributions of Delta d/d = 1.6 x 10(-4) and 2.0 x 10(-4) perpendicular to domain walls in KTP and LN samples, respectively, and lateral correlation lengths of 63 mu m (KTP), 194 mu m (KTA) and 10 mu m (LN). The decay of crystal truncation rods in LN and KTP was found to support the occurrence of surface corrugations.
Title:
Structure factor for an icosahedral quasicrystal within a statistical approach
Authors:
Strzalka, R; Buganski, I; Wolny, J Author Full Names: Strzalka, Radoslaw; Buganski, Ireneusz; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 279-290; 10.1107/S2053273315001473 3 MAY 2015
Abstract:
This paper describes a detailed derivation of a structural model for an icosahedral quasicrystal based on a primitive icosahedral tiling (three-dimensional Penrose tiling) within a statistical approach. The average unit cell concept, where all calculations are performed in three-dimensional physical space, is used as an alternative to higher-dimensional analysis. Comprehensive analytical derivation of the structure factor for a primitive icosahedral lattice with monoatomic decoration (atoms placed in the nodes of the lattice only) presents in detail the idea of the statistical approach to icosahedral quasicrystal structure modelling and confirms its full agreement with the higher-dimensional description. The arbitrary decoration scheme is also discussed. The complete structure-factor formula for arbitrarily decorated icosahedral tiling is derived and its correctness is proved. This paper shows in detail the concept of a statistical approach applied to the problem of icosahedral quasicrystal modelling.
Title:
Path-independent integral in fracture mechanics of quasicrystals
Authors:
Sladek, J; Sladek, V; Atluri, SN Author Full Names: Sladek, J.; Sladek, V.; Atluri, S. N.
Source:
ENGINEERING FRACTURE MECHANICS, 140 61-71; 10.1016/j.engfracmech.2015.03.039 MAY 2015
Abstract:
Path-independent integrals are successfully utilized for accurate evaluation of fracture parameters in crystalic materials, where atomic arrangement is periodic. In quasicrystals (QC) the atomic arrangement is quasiperiodic in one-, two-or three-directions. The 2-d elastic problem for quasicrystal is described by coupled governing equations for phonon and phason displacements. Conservation laws for quasicrystals are utilized to derive path-independent integrals for cracks. The relation between the energy release and stress intensity factor for a crack under the mode I is given for decagonal QCs. The path-independent integral formulation is valid also for cracks in QCs with continuously varying material properties. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Density functional theory calculations of the turbostratically disordered compound [(SnSe)(1+y)](m)(VSe2)(n)
Authors:
Rudin, SP; Johnson, DC Author Full Names: Rudin, Sven P.; Johnson, David C.
Source:
PHYSICAL REVIEW B, 91 (14):10.1103/PhysRevB.91.144203 APR 30 2015
Abstract:
Among composite materials that layer constituent substances of nanoscale thicknesses, [(SnSe)(1+y)](m)(VSe2)(n) emerges as an example where the constituents retain incommensurate lattice structures. Perpendicular to the stacking direction, the system exhibits random translations and random rotations on average, i.e., turbostratic disorder, with local regions showing twelvefold diffraction patterns. Earlier theoretical work on these structures showed that combining density functional theory with an empirical treatment of the van der Waals interaction gave structural parameters in good agreement with experiment, but no attempt was made to examine the relative orientations. Here we approximate the extended system with one extended constituent and one finite constituent, which allows the treatment of all relative orientations on equal footing. The calculations show how the twelvefold periodicity follows from how the ions of the SnSe layer lock in with favored positions relative to the VSe2 layer, and the associated energy scale supports arguments for the overall turbostratic disorder. The success of this approximation in describing the structural parameters of the extended [(SnSe)(1+y)](m)(VSe2)(n) system encourages its use for other properties and for other similar systems with other chemistries.
Title:
Linear spin wave theory for single-Q incommensurate magnetic structures
Authors:
Toth, S; Lake, B Author Full Names: Toth, S.; Lake, B.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (16):10.1088/0953-8984/27/16/166002 APR 29 2015
Abstract:
Linear spin wave theory provides the leading term in the calculation of the excitation spectra of long-range ordered magnetic systems as a function of 1/root S. This term is acquired using the Holstein-Primakoff approximation of the spin operator and valid for small dS fluctuations of the ordered moment. We propose an algorithm that allows magnetic ground states with general moment directions and single-Q incommensurate ordering wave vector using a local coordinate transformation for every spin and a rotating coordinate transformation for the incommensurability. Finally we show, how our model can determine the spin wave spectrum of the magnetic C-site langasites with incommensurate order.
Title:
Soft chemical control of the crystal and magnetic structure of a layered mixed valent manganite oxide sulfide
Authors:
Blandy, JN; Abakumov, AM; Christensen, KE; Hadermann, J; Adamson, P; Cassidy, SJ; Ramos, S; Free, DG; Cohen, H; Woodruff, DN; Thompson, AL; Clarke, SJ Author Full Names: Blandy, Jack N.; Abakumov, Artem M.; Christensen, Kirsten E.; Hadermann, Joke; Adamson, Paul; Cassidy, Simon J.; Ramos, Silvia; Free, David G.; Cohen, Harry; Woodruff, Daniel N.; Thompson, Amber L.; Clarke, Simon J.
Source:
APL MATERIALS, 3 (4):10.1063/1.4918973 APR 2015
Abstract:
Oxidative deintercalation of copper ions from the sulfide layers of the layered mixed-valent manganite oxide sulfide Sr2MnO2Cu1.5S2 results in control of the copper-vacancy modulated superstructure and the ordered arrangement of magnetic moments carried by the manganese ions. This soft chemistry enables control of the structures and properties of these complex materials which complement mixed-valent perovskite and perovskite-related transition metal oxides. (C) 2015 Author(s).
Title:
Periodic and incommensurately modulated phases in a (2-methylimidazolium) tetraiodobismuthate(III) thermochromic organic-inorganic hybrid
Authors:
Gagor, A; Weclawik, M; Bondzior, B; Jakubas, R Author Full Names: Gagor, A.; Weclawik, M.; Bondzior, B.; Jakubas, R.
Source:
CRYSTENGCOMM, 17 (17):3286-3296; 10.1039/c5ce00046g 2015
Abstract:
A(2-methylimidazolium) tetraiodobismuthate(III) (abbreviated as (2-MIm)BiI4) hybrid undergoes structural phase transition to an incommensurately modulated phase at 308 K. The relative coordinates of the modulation q-vector do not change down to 150 K indicating the stability of the incommensurate crystal packing that may be modeled by the sinusoidal waves of displacements. The transformation is triggered by the deformation of [BiI4-](n) chains which entails ordering of 2-MIm(+) counterions that couple to the anionic substructure via weak hydrogen bond interactions. Differential scanning calorimetry (DSC) and dielectric spectroscopy methods confirm the phase transition at 308 K (phase I -> phase II). Two dielectric relaxation processes that may be assigned to the dynamics of the polar 2-MIm(+) cations are present: a low frequency relaxator close to T-c and a high frequency one in a wide temperature region over phase II. The compound shows significant thermochromism characteristics for direct gap semiconductors. DOS calculations, together with the asymmetric local environment of bismuth ions, imply the presence of the stereo-chemically active bismuth lone pair 6s(2) electrons in both phases.

Update: 14-May-2015

Title:
Magnetic anisotropy in the incommensurate ScFe4Al8 system
Authors:
Recko, K; Dobrzynski, L; Waliszewski, J; Szymanski, K Author Full Names: Recko, K.; Dobrzynski, L.; Waliszewski, J.; Szymanski, K.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 388 82-89; 10.1016/j.jmmm.2015.03.096 AUG 15 2015
Abstract:
Neutron scattering and magnetization data are used for estimation of the spin ordering in ScFe4Al8. Results of experimental measurements are compared with the ground state configurations obtained by simulated annealing algorithms. The origins of the magnetocrystalline anisotropy of the scandium intermetallic alloy and the conditions of the coexistence of two different magnetic modulations as a function of the exchange integrals are discussed. The influence of the dipolar interactions for the noncollinearity and incommensurability in ScFe4Al8 was determined. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Thermal expansion of a Au - Al - Yb intermediate valence quasicrystal
Authors:
Watanuki, T; Kashimoto, S; Ishimasa, T; Machida, A; Yamamoto, S; Tanaka, Y; Mizumaki, M; Kawamura, N; Watanabe, S Author Full Names: Watanuki, T.; Kashimoto, S.; Ishimasa, T.; Machida, A.; Yamamoto, S.; Tanaka, Y.; Mizumaki, M.; Kawamura, N.; Watanabe, S.
Source:
SOLID STATE COMMUNICATIONS, 211 19-22; 10.1016/1.ssc2015.03.008 JUN 2015
Abstract:
The thermal expansion of a Au - Al - Yb intermediate-valence quasicrystal has been studied. X-ray diffraction measurements showed zero thermal expansion below 50 K. By comparison with an isostructural Au - Al - Tm quasicrystal, the contribution of the Yb valence variation was extracted, and it was shown that its negative thermal expansion component compensated for the positive thermal expansion of the original lattice. On cooling, the Yb contribution grew steeply below approximately 155 K down to the lowest experimental temperature of 5 K, due to enlargement of the Yb atomic radius, which was caused by the valence shift toward the divalent state. Additionally, a larger Yb contribution to the thermal expansion was demonstrated in a crystalline approximant to this quasicrystal. The magnitude of this contribution was approximately 1.4 Limes larger than in the case of the quasicrystal itself, resulting in a slight negative thermal expansion below 50 K. A heterogeneous valence model for the quasicrystal that we proposed previously accounts for this magnitude difference. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
The unusual normal state and charge-density-wave order in 2H-NbSe2
Authors:
Koley, S; Mohanta, N; Taraphder, A Author Full Names: Koley, S.; Mohanta, N.; Taraphder, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (18):10.1088/0953-8984/27/18/185601 MAY 13 2015
Abstract:
Competition between collective states like charge-density-wave and superconductivity, unencumbered by the spin degrees of freedom, is played out in some of the transition metal dichalcogenides. Although 2H-NbSe2 has received much less attention than some of the other members of the family (such as 1T-TiSe2 and 2H-TaSe2) of late, it shows superconductivity at 7.2 K and incommensurate charge ordering at 33 K. Recent experiments, notably angle resolved photoemission spectroscopy, have cast serious doubts on the theories based on Fermi surface nesting and electron-phonon interaction. The normal state has been found to be a poor, incoherent metal and remarkably, the coherence increases in the broken symmetry state. From a preformed excitonic liquid scenario, we show that there exists a natural understanding of the experimental data on 2H-NbSe2, based on electron-electron interaction. The collective instabilities, in this scenario, are viewed as a condensation of an incoherent excitonic liquid already present at high temperature.
Title:
Muon spin rotation and neutron scattering study of the noncentrosymmetric tetragonal compound CeAuAl3
Authors:
Adroja, DT; de la Fuente, C; Fraile, A; Hillier, AD; Daoud-Aladine, A; Kockelmann, W; Taylor, JW; Koza, MM; Burzuri, E; Luis, F; Arnaudas, JI; del Moral, A Author Full Names: Adroja, D. T.; de la Fuente, C.; Fraile, A.; Hillier, A. D.; Daoud-Aladine, A.; Kockelmann, W.; Taylor, J. W.; Koza, M. M.; Burzuri, E.; Luis, F.; Arnaudas, J. I.; del Moral, A.
Source:
PHYSICAL REVIEW B, 91 (13):10.1103/PhysRevB.91.134425 APR 24 2015
Abstract:
We have investigated the noncentrosymmetric tetragonal heavy fermion compound CeAuAl3 using muon spin rotation (mu SR), neutron diffraction (ND), and inelastic neutron scattering (INS) measurements. We have also revisited the magnetic, transport, and thermal properties. Themagnetic susceptibility reveals an antiferromagnetic transition at 1.1 K with, possibly, another magnetic transition near 0.18 K. The heat capacity shows a sharp lambda-type anomaly at 1.1 K in zero field, which broadens and moves to a higher temperature in an applied magnetic field. Our zero-field mu SR and ND measurements confirm the existence of a long-range magnetic ground state below 1.2 K. Further, the ND study reveals an incommensurate magnetic order with a magnetic propagation vector k = (0,0,0.52(1)) and a spiral structure of Ce moments coupled ferromagnetically within the ab plane. Our INS study reveals the presence of two well-defined crystal electric field (CEF) excitations at 5.1 and 24.6 meV in the paramagnetic phase of CeAuAl3 that can be explained on the basis of the CEF theory and the Kramer's theorem for a Ce ion having a 4f(1) electronic state. Furthermore, low energy quasielastic excitations show a Gaussian line shape below 30 K compared to a Lorentzian line shape above 30 K, indicating a slowdown of spin fluctuations below 30 K. We have estimated a Kondo temperature of T-K = 3.5 K from the quasielastic linewidth, which is in good agreement with that estimated from the heat capacity. This study also indicates the absence of any CEF-phonon coupling unlike that observed in isostructural CeCuAl3 The CEF parameters, energy level scheme, and their wave functions obtained from the analysis of INS data explain satisfactorily the single crystal susceptibility in the presence of two-ion anisotropic exchange interaction in CeAuAl3.
Title:
One-dimensional chain melting in incommensurate potassium
Authors:
McBride, EE; Munro, KA; Stinton, GW; Husband, RJ; Briggs, R; Liermann, HP; McMahon, MI Author Full Names: McBride, E. E.; Munro, K. A.; Stinton, G. W.; Husband, R. J.; Briggs, R.; Liermann, H. -P.; McMahon, M. I.
Source:
PHYSICAL REVIEW B, 91 (14):10.1103/PhysRevB.91.144111 APR 22 2015
Abstract:
Between 19 and 54 GPa, potassium has a complex composite incommensurate host-guest structure which undergoes two intraphase transitions over this pressure range. The temperature dependence of these host-guest phases is further complicated by the onset of an order-disorder transition in their guest chains. Here, we report single-crystal, quasi-single-crystal, and powder synchrotron x-ray diffraction measurements of this order-disorder phenomenon in incommensurate potassium to 47 GPa and 750 K. The so-called chain melting transition is clearly visible over a 22 GPa pressure range, and there are significant changes in the slope of the phase boundary which divides the ordered and disordered phases, one of which results from the intraphase transitions in the guest structure.
Title:
Structures of spherical viral capsids as quasicrystalline tilings
Authors:
Konevtsova, OV; Lorman, VL; Rochal, SB Author Full Names: Konevtsova, O. V.; Lorman, V. L.; Rochal, S. B.
Source:
PHYSICS OF THE SOLID STATE, 57 (4):810-814; 10.1134/S1063783415040125 APR 2015
Abstract:
Spherical viral shells with icosahedral symmetry have been considered as quasicrystalline tilings. Similarly to known Caspar-Klug quasi-equivalence theory, the presented approach also minimizes the number of conformations necessary for the protein molecule bonding with its neighbors in the shell, but is based on different geometrical principles. It is assumed that protein molecule centers are located at vertices of tiles with identical edges, and the number of different tile types is minimal. Idealized coordinates of nonequivalent by symmetry protein positions in six various capsid types are obtained. The approach describes in a uniform way both the structures satisfying the well-known Caspar-Klug geometrical model and the structures contradicting this model.

Update: 7-May-2015

Title:
The question of intrinsic origin of the metal-insulator transition in i-AlPdRe quasicrystal
Authors:
Delallaye, J; Berger, C Author Full Names: Delallaye, Julien; Berger, Claire
Source:
EUROPEAN PHYSICAL JOURNAL B, 88 (4):10.1140/epjb/e2015-50720-7 APR 15 2015
Abstract:
The icosahedral (i-) AlPdRe is the most resistive quasicrystalline alloy discovered so far. Resistivities (rho) of 1 Omega cm at 4 K and correlated resistance ratios (RRR = rho(4) kappa/rho(300) K) of more than 200 are observed in polycrystalline samples. These values are two orders of magnitude larger than for the isomorphous i-AlPdMn phase. We discuss here the controversial microscopic origin of the i-AlPdRe alloy electrical specificity. It has been proposed that the high resistivity values are due to extrinsic parameters, such as secondary phases or oxygen contamination. From comprehensive measurements and data from the literature including electronic transport correlated with micro structural and micro chemical analysis, we show that on the contrary there is mounting evidence in support of an origin intrinsic to the i-phase. Similarly to the other quasicrystalline alloys, the electrical resistivity of the i-AlPdRe samples depends critically on minute changes in the structural quality and chemical composition. The low resistivity in i-AlPdRe single-grains compared to polycrystaline samples can be explained by difference in chemical composition, heterogeneity and thermal treatment.
Title:
Beyond Entropy: Magnetic Forces Induce Formation of Quasicrystalline Structure in Binary Nanocrystal Superlattices
Authors:
Yang, ZJ; Wei, JJ; Bonville, P; Pileni, MP Author Full Names: Yang, Zhijie; Wei, Jingjing; Bonville, Pierre; Pileni, Marie-Paule
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137 (13):4487-4493; 10.1021/jacs.5b00332 APR 8 2015
Abstract:
Here, it is shown that binary superlattices of Co/Ag nanocrystals with the same size, surface coating, differing by their type of crystallinity are governed by Co-Co magnetic interactions. By using 9 nm amorphous-phase Co nanocrystals and 4 nm polycrystalline Ag nanocrystals at 25 degrees C, triangle-shaped NaCl-type binary nanocrystal superlattices are produced driven by the entropic force, maximizing the packing density. By contrast, using ferromagnetic 9 nm single domain (hcp) Co nanocrystals instead of amorphous-phase Co, dodecagonal quasicrystalline order is obtained, together with less-packed phases such as the CoAg13 (NaZn13-type), CoAg (AuCu-type), and CoAg3 (AuCu3-type) structures. On increasing temperature to 65 degrees C, 9 nm hcp Co nanocrystals become superparamagnetic, and the system yields the CoAg3 (AuCu3-type) and CoAg2 (AlB2-type) structures, as observed with 9 nm amorphous Co nanocrystals. Furthermore, by decreasing the Co nanocrystal size from 9 to 7 nm, stable AlB2-type binary nanocrystal superlattices are produced, which remain independent of the crystallinity of Co nanocrystals with the superparamagnetic state.
Title:
Incommensurate and commensurate modulations of Ba5RTi3Nb7O30 (R = La, Nd) tungsten bronzes and the ferroelectric domain structures
Authors:
Mao, MM; Li, K; Zhu, XL; Chen, XM Author Full Names: Mao, Min Min; Li, Kun; Zhu, Xiao Li; Chen, Xiang Ming
Source:
JOURNAL OF APPLIED PHYSICS, 117 (13):10.1063/1.4916723 APR 7 2015
Abstract:
Incommensurate and commensurate structural modulations of Ba5RTi3Nb7O30 (R=La, Nd) tungsten bronze ceramics were investigated by using a cooling holder equipped transmission electron microscopy in the temperature range from 100 K to 363 K. The incommensurate modulation was observed in both Ba5LaTi3Nb7O30 and Ba5NdTi3Nb7O30 at room temperature, while there was a transition from incommensurate tilted structure to commensurate superstructure for Ba5NdTi3Nb O-7(30) with decreasing temperature. The incommensurate and commensurate modulations were determined by the A-site occupancy of Ba and R cations. The A-site disorder resulted in larger incommensurability parameter delta and the diffusion of the *satellite reflection* spots. The effect of A-site disorder on the coupling between long-range dipolar order and the commensurate modulation was also discussed. The obvious ferroelectric 180 degrees domains with spike-like shape parallel to c axis were observed for Ba5NdTi3Nb7O30, while no macro ferroelectric domain was determined for Ba5LaTi3Nb7O30. (C) 2015 AIP Publishing LLC.
Title:
Periodically distributed objects with quasicrystalline diffraction pattern
Authors:
Wolny, J; Kuczera, P; Strzalka, R Author Full Names: Wolny, Janusz; Kuczera, Pawel; Strzalka, Radoslaw
Source:
APPLIED PHYSICS LETTERS, 106 (13):10.1063/1.4916830 MAR 30 2015
Abstract:
It is possible to construct fully periodically distributed objects with a diffraction pattern identical to the one obtained for quasicrystals. These objects are probability distributions of distances obtained in the statistical approach to aperiodic structures distributed periodically. The diffraction patterns have been derived by using a two-mode Fourier transform-a very powerful method not used in classical crystallography. It is shown that if scaling is present in the structure, this two-mode Fourier transform can be reduced to a regular Fourier transform with appropriately rescaled scattering vectors and added phases. Detailed case studies for model sets 1D Fibonacci chain and 2D Penrose tiling are discussed. Finally, it is shown that crystalline, quasicrystalline, and approximant structures can be treated in the same way. (C) 2015 AIP Publishing LLC.

Update: 30-Apr-2015

Title:
Correlation effects and non-collinear magnetism in the doped Hubbard model
Authors:
Igoshev, PA; Timirgazin, MA; Gilmutdinov, VF; Arzhnikov, AK; Irkhin, VY Author Full Names: Igoshev, P. A.; Timirgazin, M. A.; Gilmutdinov, V. F.; Arzhnikov, A. K.; Irkhin, V. Yu
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 383 2-7; 10.1016/j.jmmm.2014.10.031 JUN 1 2015
Abstract:
The ground-state magnetic phase diagram is investigated for the two- and three-dimensional t-t' Hubbard model. We take into account commensurate ferro-, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often missed in previous investigations. We trace the influence of correlation effects on the stability of both spiral and collinear magnetic order by comparing the results of employing both the generalized non-correlated mean-field (Hartree-Fock) approximation and generalized slave boson approach by Kotliar and Ruckenstein with correlation effects included. We found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistic large Hubbard U, if the correlation effects are taken into account. The electronic phase separation plays an important role in the formation of magnetic states and corresponding regions are wide, especially in the vicinity of half-filling. The details of magnetic ordering for different cubic lattices are discussed. (C) 2014 Elsevier B.V. All rights reserved
Title:
Structural, vibrational, and dielectric properties of Ruddlesden-Popper Ba2ZrO4 from first principles
Authors:
Louis, L; Nakhmanson, SM Author Full Names: Louis, Lydie; Nakhmanson, Serge M.
Source:
PHYSICAL REVIEW B, 91 (13):10.1103/PhysRevB.91.134103 APR 13 2015
Abstract:
Using first-principles computational techniques, we have investigated the structural, vibrational, and dielectric properties of a Ruddlesden-Popper-type layered oxide Ba2ZrO4 subjected to a wide range of biaxial strains emulating epitaxial thin-film environment. Under compressive strains, this compound experiences an incommensurate distortion characterized by planar displacements of individual perovskite slabs away from their high symmetry positions. On the other hand, under increasing epitaxial tension, the original centrosymmetric structure becomes unstable-first, with respect to antiferrodistortive oxygen cage rotations and then also with respect to in-plane polar distortions. Both the incommensurate-to-commensurate and the nonpolar-to-polar phase transformations are accompanied by anomalies of the static dielectric response, however, only in the latter case a divergence of the in-plane dielectric constant is observed. Remarkably, even after the transition into the ferroelectric state (with polarization of up to 0.12 C/m(2) at 3.5% tension) dielectric permittivity of Ba2ZrO4 remains unusually high, which is explained by an emergence of a Goldstone-like excitation in the system manifested through an in-plane libration of the polarization vector. Since Ba2ZrO4 displays a yet poorly understood tendency to absorb small molecules, such as water and CO2, acquiring better insights into the physical underpinnings of its behavior can produce more efficient functional materials for applications in advanced technologies for carbon sequestration.
Title:
Charge-Density Wave in Ca-Intercalated Bilayer Graphene Induced by Commensurate Lattice Matching
Authors:
Shimizu, R; Sugawara, K; Kanetani, K; Iwaya, K; Sato, T; Takahashi, T; Hitosugi, T Author Full Names: Shimizu, Ryota; Sugawara, Katsuaki; Kanetani, Kohei; Iwaya, Katsuya; Sato, Takafumi; Takahashi, Takashi; Hitosugi, Taro
Source:
PHYSICAL REVIEW LETTERS, 114 (14):10.1103/PhysRevLett.114.146103 APR 7 2015
Abstract:
We report the emergence of a charge-density wave (CDW) in Ca-intercalated bilayer graphene (C6CaC6), the thinnest limit of superconducting C6Ca, observed by low-temperature, high-magneticfield scanning tunneling microscopy or spectroscopy, and angle-resolved photoemission spectroscopy. While the possible superconductivity was not observed in epitaxially grown C6CaC6 on a SiC substrate, a CDW order different from that observed on the surface of bulk C6Ca was observed. It is inferred that the CDW state is induced by the potential modulation due to the commensurate lattice matching between the C6CaC6 film and the SiC substrate.
Title:
Microstructure and phase transformation of as-cast and annealed Mg-4Zn-1Y alloy containing quasi-crystal phase
Authors:
Yang, Y; Zhang, K; Li, XG; Li, YJ; Ma, ML; Shi, GL; Yuan, JW Author Full Names: Yang, Yang; Zhang, Kui; Li, Xing-Gang; Li, Yong-Jun; Ma, Ming-Long; Shi, Guo-Liang; Yuan, Jia-Wei
Source:
RARE METALS, 34 (4):239-244; 10.1007/s12598-014-0443-8 APR 2015
Abstract:
By means of optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses, the microstructures of as-cast and heat-treated Mg-4Zn-1Y (wt%) alloy containing quasi-crystal phase were studied. The microstructure of the as-cast alloy consists of alpha-Mg solid solution grains, intermetallic particles and eutectic phases (W-phase and I-phase), and huge grains with serious dendritic segregation are clearly observed. After heat treatment, phase transformation and dissolution occur in the alloy and many phases remain. When the alloy was treated above 410 A degrees C, the eutectic phases transform into spherical shape as the I-phase turns to W-phase. After heat treatment for long time, the alloy is over burnt and the W-phase decomposes to Mg-Y binary phase.
Title:
Microstructural changes in quasicrystalline Al - Mn - Be - Cu alloy after various heat treatments
Authors:
Strekelj, N; Naglic, I; Klancnik, G; Nagode, A; Markoli, B Author Full Names: Strekelj, Neva; Naglic, Iztok; Klancnik, Grega; Nagode, Ales; Markoli, Bostjan
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 106 (4):342-351; 10.3139/146.111195 APR 2015
Abstract:
In this study we investigated the microstructural changes after a variety of heat treatments of the quasicrystalline Al - Mn - Be - Cu alloy. In addition, we report on Vickers microhardness measurements and tensile-test results for the same materials. The samples were produced in a conventional manner, i.e., melting in an electrical resistance furnace in air and a gravitational casting process using a round copper die, which was in the form of a tensile-test specimen with a diameter of 5 mm. After the casting, some of the samples were just solution treated (annealed) and then quenched in water, while others were additionally aged (artificially - T6, or naturally - T4) or directly aged after the casting. In comparison to the as-cast state, the Vickers microhardness values of the aluminum-based matrix and the tensile properties of the samples decreased when just the solution treatment, T4 or T6 treatment was performed. The tensile properties also decreased after the heat treatments. A microstructural inspection revealed that the microstructural changes occurred already during the solution treatment, i.e., the formation of the phases Be4Al(Mn,Cu) and tau(1)-Al29Mn6Cu4 on the approximant H-Al4Mn and quasicrystalline i-phase particles' edges and the occurrence of precipitates in the alpha(Al) matrix. The precipitates that would additionally contribute to the hardening of the alloy did not form. The directly aged samples showed little or no increase in microhardness values in comparison to the as-cast samples, but possibilities of theta '' precipitates being formed from the already saturated matrix after the casting could not be excluded. After all the heat treatments the quasicrystalline i-phase, as a primary and eutectic phase, was preserved.
Title:
Influence of I-phase and W-phase on microstructure and mechanical properties of Mg-8Li-3Zn alloy
Authors:
Wei, GB; Peng, XD; Zhang, B; Hadadzadeh, A; Xu, TC; Xie, WD Author Full Names: Wei, Guo-bing; Peng, Xiao-dong; Zhang, Bao; Hadadzadeh, Amir; Xu, Tian-cai; Xie, Wei-dong
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 25 (3):713-720; 10.1016/S1003-6326(15)63656-1 MAR 2015
Abstract:
Microstructures and mechanical properties of LZ83-xY alloys containing I-phase and W-phase were investigated by XRD, OM, SEM and EDS. The experimental results show that the content of I-phase and W-phase changes by varying Zn/Y mass ratio in the LZ83-xY alloys. The cohesion of I-phase/alpha-Mg eutectic pockets can enhance the strength in the as-cast LZ83-0.5Y and LZ83-1.0Y alloys, while the W-phase has no obvious strengthening effect on the LZ83-1.5Y alloy. In the extruded alloys, the I-phase and W-phase were extruded into the particles with nanoscale size in the beta-Li matrix phase. The dispersion strengthening of W-phase was more obvious because of the higher volume fraction. The ultimate tensile strength of extruded LZ83-1.5Y alloy is up to 238 MPa while the elongation is up to 20%.
Title:
Topological Hofstadter insulators in a two-dimensional quasicrystal
Authors:
Tran, DT; Dauphin, A; Goldman, N; Gaspard, P Author Full Names: Tran, Duc-Thanh; Dauphin, Alexandre; Goldman, Nathan; Gaspard, Pierre
Source:
PHYSICAL REVIEW B, 91 (8):10.1103/PhysRevB.91.085125 FEB 27 2015
Abstract:
We investigate the properties of a two-dimensional quasicrystal in the presence of a uniform magnetic field. In this configuration, the density of states (DOS) displays a Hofstadter-butterfly-like structure when it is represented as a function of the magnetic flux per tile. We show that the low-DOS regions of the energy spectrum are associated with chiral edge states, in direct analogy with the Chern insulators realized with periodic lattices. We establish the topological nature of the edge states by computing the topological Chern number associated with the bulk of the quasicrystal. This topological characterization of the nonperiodic lattice is achieved through a local (real-space) topological marker. This work opens a route for the exploration of topological-insulating materials in a wide range of nonperiodic lattice systems, including photonic crystals and cold atoms in optical lattices.
Title:
The refined theory of 2D quasicrystal deep beams based on elasticity of quasicrystals
Authors:
Gao, Y; Yu, LY; Yang, LZ; Zhang, LL Author Full Names: Gao, Yang; Yu, Lian-Ying; Yang, Lian-Zhi; Zhang, Liang-Liang
Source:
STRUCTURAL ENGINEERING AND MECHANICS, 53 (3):411-427; FEB 10 2015
Abstract:
Based on linear elastic theory of quasicrystals, various equations and solutions for quasicrystal beams are deduced systematically and directly from plane problem of two-dimensional quasicrystals. Without employing ad hoc stress or deformation assumptions, the refined theory of beams is explicitly established from the general solution of quasicrystals and the Lur'e symbolic method. In the case of homogeneous boundary conditions, the exact equations and exact solutions for beams are derived, which consist of the fourth-order part and transcendental part. In the case of non-homogeneous boundary conditions, the exact governing differential equations and solutions under normal loadings only and shear loadings only are derived directly from the refined beam theory, respectively. In two illustrative examples of quasicrystal beams, it is shown that the exact or accurate analytical solutions can be obtained in use of the refined theory.
Title:
Low-Temperature Physical Properties of Single-Crystalline EuCoGe3 and EuRhGe3
Authors:
Bednarchuk, O; Kaczorowski, D Author Full Names: Bednarchuk, O.; Kaczorowski, D.
Source:
ACTA PHYSICA POLONICA A, 127 (2):418-420; FEB 2015
Abstract:
Since a few years europium-based intermetallics have been attracting more and more attention due to their intriguing physical properties with anomalous behaviours in magnetically ordered states. Here, we report on the formation and the bulk physical properties of two tetragonal compounds EuCoGe3 and EuRhGe3, studied on high-quality single-crystalline specimens. In both materials, the Eu ions are in their divalent state, which gives rise to an antiferromagnetic ordering below T-N = 15.4 K and T-N = 11.3 K, respectively. In addition, EuCoGe3 exhibits a successive antiferromagnetic phase transition at T-2 = 13.4 K. Based on some characteristic features in the temperature variations of the magnetic susceptibility, specific heat and electrical resistivity, we suggest that in both germanides an amplitude modulated magnetic structure develops below the respective T-N, with the Eu magnetic moments directed along the crystallographic [001] axis in EuCoGe3 and perpendicular to this direction in EuRhGe3.
Title:
The J(1)-J(2) Model on the Anisotropic Triangular and the Square Lattice: Similarities and Differences
Authors:
Schmidt, B; Thalmeier, P Author Full Names: Schmidt, B.; Thalmeier, P.
Source:
ACTA PHYSICA POLONICA A, 127 (2):324-326; FEB 2015
Abstract:
The Heisenberg model on a triangular lattice is a prime example for a geometrically frustrated spin system. However most experimentally accessible compounds have spatially anisotropic exchange interactions. As a function of this anisotropy, ground states with different magnetic properties can be realized. On the other hand, the J(1)-J(2) model on the square lattice is a well-known example for frustration induced by competing exchange. The classical phase diagrams of the two models are related in a broad range of the control parameter phi - tan(-1)(J(2)/J(1)). In both cases three different types of ground states are realized, each model having a ferromagnetic and an antiferromagnetic region in the phase diagram, and a third phase with columnar magnetic order for the square lattice and an in general incommensurate spiral structure for the triangular lattice. Quantum effects lift degeneracies in the non-FM phases and lead to additional nonmagnetic regions in the phase diagrams. The contribution of zero point fluctuations to ground state energy, wave vector, and ordered moment is discussed.
Title:
Reconstruction of the Exchange Integrals Map of ScFe4Al8 Magnetic Structure
Authors:
Recko, K; Dobrzynski, L; Waliszewski, J; Szymanski, K Author Full Names: Recko, K.; Dobrzynski, L.; Waliszewski, J.; Szymanski, K.
Source:
ACTA PHYSICA POLONICA A, 127 (2):424-426; FEB 2015
Abstract:
The influence of the dipolar as well as crystal field interaction as the main reasons of the noncollineaxity and incommensurability of the 3d-3d-3p alloy belonging to ThMn12 family is investigated. Available data on the single crystal neutron scattering experiments for ScFe4Al8 compound are discussed. The values and directions of the spin ordering found by magnetic diffraction are compared to that one derived from ground state configurations obtained by a simulated annealing algorithm.

Update: 23-Apr-2015

Title:
Crystal structure determination of incommensurate modulated martensite in Ni-Mn-In Hensler alloys
Authors:
Yan, HL; Zhang, YD; Xu, N; Senyshyn, A; Brokmeier, HG; Esling, C; Zhao, X; Zuo, L Author Full Names: Yan, Haile; Zhang, Yudong; Xu, Nan; Senyshyn, Anatoliy; Brokmeier, Heinz-Guenter; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
ACTA MATERIALIA, 88 375-388; 10.1016/j.actamat.2015.01.025 APR 15 2015
Abstract:
The crystal structure of modulated martensite in Mn-rich off-stoichiometric Ni2Mn1.44In0.56 alloy was determined with high-resolution powder neutron diffraction and synchrotron X-ray diffraction in the frame of (3 + 1)-dimensional superspace theory. The average crystal structure and the modulation wave vector were firstly derived by analyzing the reflection separations induced by the martensitic transformation on the basis of the transformation orientation inheritance. This treatment could be applied to predetermine the modulated structures of materials with displacive structural transformation. The crystal structure of modulated martensite was finally refined by the Rietveld method. Results show that the martensite possesses an incommensurate 6M modulated structure of superspace group I2/m(alpha 0 gamma)00, with lattice parameters a= 4.3919(4) angstrom, b = 5.6202(1) angstrom, c = 4.3315(7) angstrom, and beta = 93.044(1)degrees, and the modulation wave vector q = 0.343(7) c.* The detailed site occupations for extra-Mn atoms with respect to the stoichiometric case were investigated by ab initio calculations. The extra-Mn atoms have a preference to be uniformly dispersed. A threefold layered superstructure in the 3-dimensional space was proposed to approximately describe the incommensurate modulated structure. This 6M superstructure model is considered to be representative for off-stoichiometric Ni-(Co)-Mn-In modulated martensite with martensitic transformation around room temperature. The present study is expected to offer an important basis for reliable crystallographic and microstructural characterizations on Ni-Mn-In alloys, so as to understand the underlying mechanisms of their multifunctional magneto-responsive properties. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Magnetic structures in the magnetic phase diagram of Ho2RhIn8
Authors:
Cermak, P; Prokes, K; Ouladdiaf, B; Boehm, M; Kratochvilova, M; Javorsky, P Author Full Names: Cermak, Petr; Prokes, Karel; Ouladdiaf, Bachir; Boehm, Martin; Kratochvilova, Marie; Javorsky, Pavel
Source:
PHYSICAL REVIEW B, 91 (14):10.1103/PhysRevB.91.144404 APR 7 2015
Abstract:
The magnetic phase diagram of the tetragonal Ho2RhIn8 compound has similar features to many related systems, revealing a zero magnetic field AF1 and a field-induced AF2 phases. Details of the magnetic order in the AF2 phase were not reported yet for any of the related compounds. In addition, only the Ho2RhIn8 phase diagram contains a small region of the incommensurate zero-field AF3 phase. We have performed a number of neutron diffraction experiments on single crystals of Ho2RhIn8 using several diffractometers including experiments in both horizontal and vertical magnetic fields up to 4 T. We present details of the magnetic structures in all magnetic phases of the rich phase diagram of Ho2RhIn8. The Ho magnetic moments point along the tetragonal c axis in every phase. The ground-state AF1 phase is characterized by propagation vector k = (1/2,0,0). The more complex ferrimagnetic AF2 phase is described by four propagation vectors k(0) = ( 0,0,0), k(1) = (1/2,0,0), k(2) = ( 0,1/ 2,1/2), k(3) = (1/2,1/2,1/2). The magnetic structure in the AF3 phase is incommensurate with k(AF3) = ( 0.5, delta, 0). Our results are consistent with theoretical calculations based on crystal field theory.
Title:
Taking a closer look for a broader view: combining powder diffraction with electron crystallography for a better understanding of modulated structures
Authors:
Palatinus, L Author Full Names: Palatinus, Lukas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 125-126; 10.1107/S2052520615005910 2 APR 2015
Title:
Resonance-stabilized partial proton transfer in hydrogen bonds of incommensurate phenazine-chloranilic acid
Authors:
Noohinejad, L; Mondal, S; Ali, SI; Dey, S; van Smaalen, S; Schonleber, A Author Full Names: Noohinejad, Leila; Mondal, Swastik; Ali, Sk Imran; Dey, Somnath; van Smaalen, Sander; Schoenleber, Andreas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 228-234; 10.1107/S2052520615004084 2 APR 2015
Abstract:
The co-crystal of phenazine (Phz) and chloranilic acid (H(2)ca) becomes ferroelectric upon cooling through the loss of inversion symmetry. Further cooling results in the development of an incommensurate ferroelectric phase, followed by a lock-in transition towards a twofold superstructure. Here we present the incommensurately modulated crystal structure of Phz-H(2)ca at T = 139 K with a symmetry given by the superspace group P2(1)(1/2 sigma(2) 1/2)0 and sigma(2) = 0.5139. The modulation mainly affects the positions of the protons within half of the intermolecular hydrogen bonds that are responsible for the spontaneous polarization in all three low-temperature phases. Evidence for proton transfer in part of the hydrogen bonds is obtained from the correlated dependence on the phase of the modulation of the lengths of bonds involved in resonance stabilization of the acidic anion, and much smaller variations of bond lengths of atoms not involved in the resonance mechanism. Incommensurability is explained as competition between proton transfer favored for single hydrogen bonds on the basis of pK(a) values and avoiding unfavorable Coulomb repulsion within the lattice of the resulting ionic molecules.
Title:
Synergy between transmission electron microscopy and powder diffraction: application to modulated structures
Authors:
Batuk, D; Batuk, M; Abakumov, AM; Hadermann, J Author Full Names: Batuk, Dmitry; Batuk, Maria; Abakumov, Artem M.; Hadermann, Joke
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 127-143; 10.1107/S2052520615005466 2 APR 2015
Abstract:
The crystal structure solution of modulated compounds is often very challenging, even using the well established methodology of single-crystal Xray crystallography. This task becomes even more difficult for materials that cannot be prepared in a single-crystal form, so that only polycrystalline powders are available. This paper illustrates that the combined application of transmission electron microscopy (TEM) and powder diffraction is a possible solution to the problem. Using examples of anion-deficient perovskites modulated by periodic crystallographic shear planes, it is demonstrated what kind of local structural information can be obtained using various TEM techniques and how this information can be implemented in the crystal structure refinement against the powder diffraction data. The following TEM methods are discussed: electron diffraction (selected area electron diffraction, precession electron diffraction), imaging (conventional high-resolution TEM imaging, high-angle annular dark-field and annular bright-field scanning transmission electron microscopy) and state-of-the-art spectroscopic techniques (atomic resolution mapping using energy-dispersive X-ray analysis and electron energy loss spectroscopy).
Title:
Magnetic ordering and ferroelectricity in multiferroic 2H-AgFeO2: Comparison between hexagonal and rhombohedral polytypes
Authors:
Terada, N; Khalyavin, DD; Manuel, P; Tsujimoto, Y; Belik, AA Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Tsujimoto, Yoshihiro; Belik, Alexei A.
Source:
PHYSICAL REVIEW B, 91 (9):10.1103/PhysRevB.91.094434 MAR 30 2015
Abstract:
Magnetic and dielectric properties of the hexagonal triangular lattice antiferromagnet 2H-AgFeO2 have been studied by neutron diffraction, magnetic susceptibility, specific heat, pyroelectric current, and dielectric constant measurements. The ferroelectric polarization, P similar or equal to 5 mu C/m(2), has been found to appear below 11 K due to a polar nature of the magnetic ground state of the system. In the temperature range of 11 K <= T <= 18 K, an incommensurate spin density wave (ICM1) with the nonpolar magnetic point group mmm1' and the k(1) = (0, q(b)(1),0; q(b)(1) = 0.390-0.405) propagation vector takes place. Below 14 K, a proper screw ordering (ICM2) and k(2) = (0, q(b)(2),0; q(b)(2) = 0.385-0.396) appears as a minor phase which coexists with ICM1 and the ground state down to the lowest measured temperature 5.5 K. No ferroelectric polarization associated with the ICM2 phase was observed in agreement with its nonpolar point group 2221'. Finally, a spiral order with cycloid and proper screw components (ICM3), and k(3) = (q(a)(3), q(b)(3),0; q(a)(3) = 0.0467, q(b)(3) = 0.349) emerges below 11 K as the ground state of the system. Based on the deduced magnetic point group 21', we conclude that the ferroelectric polarization in ICM3 is parallel to the c axis and is caused by the inverse Dzyloshinskii-Moriya effect with p(1) proportional to r(ij) x (S-i x S-j). Unlike the rhombohedral 3R-AgFeO2 polytype, the additional contribution to the macroscopic polarization p(2) proportional to S-i x S-j is not allowed in the present case due to the symmetry constraints imposed by the hexagonal lattice of 2H-AgFeO2.
Title:
Field effects with H vertical bar vertical bar b on the incommensurate magnetic structures of multiferroic MnWO4 studied within the superspace formalism
Authors:
Urcelay-Olabarria, I; Garcia-Munoz, JL; Mukhin, AA Author Full Names: Urcelay-Olabarria, I.; Garcia-Munoz, J. L.; Mukhin, A. A.
Source:
PHYSICAL REVIEW B, 91 (10):10.1103/PhysRevB.91.104429 MAR 30 2015
Abstract:
We investigate the magnetic-field-induced (H vertical bar vertical bar b) transition in the reference improper multiferroic MnWO4 using superspace formalism. The distinct superspace group symmetries are determined from single-crystal neutron diffraction. The study of the full magnetic symmetry of the incommensurate magnetic phases under field provides the keys for understanding its magnetic and ferroelectric behavior up to 12 T. At moderate fields, below the transition, the magnetic modulations of the two Mn sites in the simple cell are independent. At the field-induced transition between multiferroic phases, the electric polarization undergoes a flip from the monoclinic b axis to the ac plane. An additional component in the polarization is predicted along the c axis, due to a point symmetry change from 2(y) 1' to m(y)1'. In contrast with the low-field phase, above the transition the influence of the magnetic field results in the coupling between the magnetic modulations of the two Mn sites of the original monoclinic cell.
Title:
Updating the phase diagram of the archetypal frustrated magnet Gd3Ga5O12
Authors:
Deen, PP; Florea, O; Lhotel, E; Jacobsen, H Author Full Names: Deen, P. P.; Florea, O.; Lhotel, E.; Jacobsen, H.
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.014419 JAN 15 2015
Abstract:
The applied magnetic field and temperature phase diagram of the archetypal frustrated magnet, Gd3Ga5O12, has been reinvestigated using single-crystal magnetometry and polarized neutron diffraction. The updated phase diagram is substantially more complicated than previously reported and can be understood in terms of competing interactions with loops of spins, trimers, and decagons, in addition to competition and interplay between antiferromagnetic, incommensurate, and ferromagnetic order. Several additional distinct phase boundaries are presented. The phase diagram centers around a multiphase convergence to a single point at 0.9 T and similar to 0.35 K, below which, in temperature, a very narrow magnetically disordered region exists. These data illustrate the richness and diversity that arise from frustrated exchange on the three-dimensional hyperkagome lattice.
Title:
Chemical ordering of Co and Ni in a W-(AlCoNi) crystalline approximant related to Al-Co-Ni decagonal quasicrystals studied by atomic resolution energy-dispersive X-ray spectroscopy
Authors:
Yasuhara, A; Hiraga, K Author Full Names: Yasuhara, Akira; Hiraga, Kenji
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 95 (1):52-57; 10.1080/09500839.2015.1006705 JAN 2 2015
Abstract:
A W-(AlCoNi) crystalline approximant, which is closely related to Al-Co-Ni decagonal quasicrystals, in an Al72.5Co20Ni7.5 alloy has been studied by atomic resolution energy-dispersive X-ray spectroscopy (EDS), in an instrument attached to a spherical aberration (Cs)-corrected scanning transmission electron microscope. On high-resolution EDS maps of Co and Ni elements, obtained by integrating many sets of EDS data taken from undamaged areas, chemical ordering of Co and Ni is clearly detected. In the structure of the W-(AlCoNi) phase, consisting of arrangements of transition-metal (TM) atoms located at vertices of pentagonal tilings and pentagonal arrangements of mixed sites (MSs) of TM and Al atoms, Co atoms occupy the TM atom positions with the pentagonal tiling and Ni is enriched in part of the pentagonal arrangements of MSs.

Update: 16-Apr-2015

Title:
Nematic fluctuations and their wave vector in two-dimensional metals
Authors:
Punk, M Author Full Names: Punk, Matthias
Source:
PHYSICAL REVIEW B, 91 (11):10.1103/PhysRevB.91.115131 MAR 17 2015
Abstract:
We revisit the problem of electrons on a square lattice below half-filling close to an Ising-nematic quantum critical point. For Fermi surfaces with sufficiently strong antinodal nesting, the static nematic susceptibility is maximal at the antinodal nesting wave vector within a simple random phase approximation calculation. We present a detailed analysis of the nematic susceptibility within Eliashberg theory and show that the strong interaction between fermions in the antinodal regions shifts the maximum of the nematic susceptibility to slightly larger wave vectors. The corresponding order is akin to the incommensurate charge-density wave with d-wave form factor found recently in some underdoped cuprate materials. At sufficiently high temperatures around T/t similar to 0.1, nematic fluctuations are strongest at zero wave vector.
Title:
Ferroelectricity induced by ferriaxial crystal rotation and spin helicity in a B-site-ordered double-perovskite multiferroic In2NiMnO6
Authors:
Terada, N; Khalyavin, DD; Manuel, P; Yi, W; Suzuki, HS; Tsujii, N; Imanaka, Y; Belik, AA Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Yi, Wei; Suzuki, Hiroyuki S.; Tsujii, Naohito; Imanaka, Yasutaka; Belik, Alexei A.
Source:
PHYSICAL REVIEW B, 91 (10):10.1103/PhysRevB.91.104413 MAR 17 2015
Abstract:
We have performed dielectric measurements and neutron diffraction experiments on the double perovskite In2NiMnO6. A ferroelectric polarization, P similar or equal to 30 mu C/m(2), is observed in a polycrystalline sample below T-N = 26 K where a magnetic phase transition occurs. The neutron diffraction experiment demonstrates that a complex noncollinear magnetic structure with " cycloidal" and " proper screw" components appears below T-N, which has the incommensurate propagation vector k = (k(a),0, k(c); k(a) similar or equal to 0.274, k(c) similar or equal to - 0.0893). The established magnetic point group 21' implies that the macroscopic ferroelectric polarization is along the monoclinic b axis. Recent theories based on the inverse Dzyaloshinskii- Moriya effect allow us to specify two distinct contributions to the polarization of In2NiMnO6. One of them is associated with the cycloidal component, p(1) proportional to r(ij) x (S-i x S-j)(perpendicular to), and the other with the proper screw component, p(2) proportional to [r(ij) center dot ( S-i x S-j)(parallel to)] A. The latter is explained by coupling between spin helicity and " ferriaxial" crystal rotation with macroscopic ferroaxial vector A, characteristic of the B- site ordered perovskite systems with out- of- plane octahedral tilting.
Title:
X-ray standing wave study of Si clusters on a decagonal Al-Co-Ni quasicrystal surface
Authors:
Woodruff, DP; Ledieu, J; Lovelock, KRJ; Jones, RG; Deyko, A; Wearing, LH; McGrath, R; Chaudhuri, A; Li, HI; Su, SY; Mayer, A; Stanisha, NA; Diehl, RD Author Full Names: Woodruff, D. P.; Ledieu, J.; Lovelock, K. R. J.; Jones, Robert G.; Deyko, A.; Wearing, L. H.; McGrath, R.; Chaudhuri, A.; Li, H. I.; Su, S. Y.; Mayer, A.; Stanisha, N. A.; Diehl, R. D.
Source:
PHYSICAL REVIEW B, 91 (11):10.1103/PhysRevB.91.115418 MAR 12 2015
Abstract:
Quantitative adsorption structure determinations on quasicrystals are scarce because most techniques for measuring surface structures are not well suited to the complex and infinite unit cells of quasicrystals. The normal incidence standing x-ray wave field technique presents a solution to these problems because it can be made inherently surface sensitive and does not involve extensive computational effort. We describe a method for applying this technique to adsorbates on quasicrystals, with specific application to a submonolayer of Si atoms on a decagonal Al-Co-Ni surface. We demonstrate the sensitivity of the technique to both adsorption site and geometry, leading to the conclusion that the Si atoms, which form six-atom pentagonal clusters, have an average height of 1.77 +/- 0.05 angstrom above pentagonal hollow sites, with a significant height variation among the Si atoms in the cluster. In particular, the central Si atom sits more deeply than the five surrounding Si atoms, which are, on average, 2.7 angstrom away from the central Si atom. Although this study was performed on a decagonal quasicrystal that is periodic perpendicular to the surface, we describe how the technique can be applied to cases with no periodicity.
Title:
Effect of pointlike impurities on d(x2-y2) charge-density waves in cuprate superconductors
Authors:
Atkinson, WA; Kampf, AP Author Full Names: Atkinson, W. A.; Kampf, A. P.
Source:
PHYSICAL REVIEW B, 91 (10):MAR 12 2015
Abstract:
Many cuprate superconductors possess an unusual charge- ordered phase that is characterized by an approximate dx2 - y2 intraunit cell form factor and a finite modulation wave vector q*. We study the effects of impurities on this charge- ordered phase via a single- band model in which bond order is the analog of charge order in the cuprates. Impurities are assumed to be pointlike and are treated within the self- consistent t- matrix approximation. We show that suppression of bond order by impurities occurs through the local disruption of the dx2 - y2 form factor near individual impurities. Unlike d- wave superconductors, where the sensitivity of Tc to impurities can be traced to a vanishing average of the dx2 - y2 order parameter over the Fermi surface, the response of bond order to impurities is dictated by a few Fermi surface " hotspots." The bond order transition temperature Tbo thus follows a different universal dependence on impurity concentration ni than does the superconducting Tc. In particular, Tbo decreases more rapidly than Tc with increasing ni when there is a nonzero Fermi surface curvature at the hotspots. Based on experimental evidence that the pseudogap is insensitive to Zn doping, we conclude that a direct connection between charge order and the pseudogap is unlikely. Furthermore, the enhancement of stripe correlations in the La- based cuprates by Zn doping is evidence that this charge order is also distinct from stripes.
Title:
Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal
Authors:
Lowe, M; Yadav, TP; Fournee, V; Ledieu, J; McGrath, R; Sharma, HR Author Full Names: Lowe, M.; Yadav, T. P.; Fournee, V.; Ledieu, J.; McGrath, R.; Sharma, H. R.
Source:
JOURNAL OF CHEMICAL PHYSICS, 142 (9):10.1063/1.4913567 MAR 7 2015
Abstract:
The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe3O4 rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol. (C) 2015 AIP Publishing LLC.
Title:
Flux Synthesis, Modulated Crystal Structures, and Physical Properties of REMn0.5SeO (RE = La, Ce)
Authors:
Peschke, S; Nitsche, F; Johrendt, D Author Full Names: Peschke, Simon; Nitsche, Fabian; Johrendt, Dirk
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 641 (3-4):529-536; 10.1002/zaac.201400603 MAR 2015
Abstract:
The selenide oxides REMn0.5SeO (RE = La, Ce) were synthesized by heating RE2O3, RE, Mn, and Se in a NaI/KI flux at 800 degrees C, and their modulated crystal structures determined by X-ray single crystal and powder diffraction {P 1 1 2/n(1/2)0s, Z = 2, LaMn0.5SeO: a = 405.7(1), b = 405.7(1), c = 915.2(1) pm, = 90 degrees, q = [1/10, -1/10, 1/2]; CeMn0.5SeO: a = 402.0(1), b = 401.8(1), c = 910.7(1) pm, = 90.000(4)degrees, q = [0.0789(2), -0.0783(2), 1/2]}. The structures are related to the ZrCuSiAs-type structure with ordered vacancies at the manganese sites. The resulting modulations of the checkerboard pattern in the [Mn0.5Se] layers can be approximated by 10ax10bx2c and 51ax51bx2c supercells in LaMn0.5SeO and CeMn0.5SeO, respectively. Both compounds are insulators. The optical bandgap of LaMn0.5SeO was determined to 2.13 eV from the Kubelka-Munk function. Magnetic measurements indicate antiferromagnetic ordering of the Mn2+ moments with Neel points well above room temperature, as known from related manganese compounds.
Title:
Microstructure and phase compositions of as-cast Mg-3.9Zn-0.6RE (Gd, Y) alloy with different Gd/Y ratios
Authors:
Yang, Y; Zhang, K; Ma, ML; Yuan, JW Author Full Names: Yang, Yang; Zhang, Kui; Ma, Ming-Long; Yuan, Jia-Wei
Source:
RARE METALS, 34 (3):160-163; 10.1007/s12598-014-0444-7 MAR 2015
Abstract:
Mg-Zn-RE (Gd, Y) alloys with different Gd/Y atomic ratios were prepared by conventional casting, and the microstructure of the alloys was studied by multiple means. Icosahedral quasicrystal phases are observed in all alloys. The different Gd/Y atomic ratios affect the microstructures of the alloys irregularly. The alloy with more Gd has large dendritic structure and more complicated phase composition which are composed of I-phase lamellar eutectic, W-phase divorced eutectic, Mg-RE cuboid particles and Mg-Zn binary phases. Other two alloys show similar microstructures and phase compositions with very thin lamellar eutectics which distribute along the interdendritic region, and the lamellar eutectics are formed by I-phase and Mg. The element contents of the I-phases and Mg-RE phases are partially controlled by the Gd/Y atomic ratio.
Title:
Coupling between an incommensurate antiferromagnetic structure and a soft ferromagnet in the archetype multiferroic BiFeO3/cobalt system (vol 91, 014402, 2015)
Authors:
Elzo, M; Moubah, R; Blouzon, C; Sacchi, M; Grenier, S; Belkhou, R; Dhesi, S; Colson, D; Torres, F; Kiwi, M; Viret, M; Jaouen, N Author Full Names: Elzo, Marta; Moubah, Reda; Blouzon, Camille; Sacchi, Maurizio; Grenier, Stephane; Belkhou, Rachid; Dhesi, Sarnjeet; Colson, Dorothee; Torres, Felipe; Kiwi, Miguel; Viret, Michel; Jaouen, Nicolas
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.019903 JAN 30 2015

Update: 9-Apr-2015

Title:
Synthesis and structural analysis of C-60-C-70 two-component fullerene nanowhiskers
Authors:
Konno, T; Wakahara, T; Miyazawa, K Author Full Names: Konno, Toshio; Wakahara, Takatsugu; Miyazawa, Kun'ichi
Source:
JOURNAL OF CRYSTAL GROWTH, 416 41-46; 10.1016/j.jcrysgro.2014.12.016 APR 15 2015
Abstract:
C-60-C-70 two-component fullerene nanowhiskers (C-60-C(70)NWs) were synthesized by liquid-liquid interfacial precipitation (LLIP) using various ratios of C-70 to C-60 and then analyzed using a focused ion beam processing apparatus (FIB-SEM), scanning electron microscopy (SEM). Raman spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, X-ray diffraction (XRD) and high-performance liquid chromatography (HPLC). Both C-60 and C-70 were saturated in the supernatant solutions with fullerene compositions in the mother solutions ranging from 124 mass% C-70 to 73.4 mass% C-70. C-60-C(70)NWs contained a small amount of rhombohedral phase, indicating polymerization of C-60. The solid solubility limit of C-70 in the C-60 matrix was found to be 13.7 mass%. In addition to fine C-60-C(70)NWs, thick C-60-C-70 needle-like crystals were formed. The thick C-60-C-70 needle-like crystals were fractured using a molybdenum probe in the FIB. The fractured surfaces of the C-60-C-70 needle-like crystals showed modulated structures with chemical compositions characteristic of spinodal decomposition. The activation energy of diffusion was determined to be 37.1 kJ/mol. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Broken translational and rotational symmetry via charge stripe order in underdoped YBa2Cu3O6+y
Authors:
Comin, R; Sutarto, R; Neto, EHDS; Chauviere, L; Liang, R; Hardy, WN; Bonn, DA; He, F; Sawatzky, GA; Damascelli, A Author Full Names: Comin, R.; Sutarto, R.; Neto, E. H. da Silva; Chauviere, L.; Liang, R.; Hardy, W. N.; Bonn, D. A.; He, F.; Sawatzky, G. A.; Damascelli, A.
Source:
SCIENCE, 347 (6228):1335-1339; 10.1126/science.1258399 MAR 20 2015
Abstract:
After the discovery of stripelike order in lanthanum-based copper oxide superconductors, charge-ordering instabilities were observed in all cuprate families. However, it has proven difficult to distinguish between unidirectional (stripes) and bidirectional (checkerboard) charge order in yttrium-and bismuth-based materials. We used resonant x-ray scattering to measure the two-dimensional structure factor in the superconductor YBa2Cu3O6+y in reciprocal space. Our data reveal the presence of charge stripe order (i.e., locally unidirectional density waves), which may represent the true microscopic nature of charge modulation in cuprates. At the same time, we find that the well-established competition between charge order and superconductivity is stronger for charge correlations across the stripes than along them, which provides additional evidence for the intrinsic unidirectional nature of the charge order.
Title:
Synchronized collapse and formation of long-period stacking and chemical orders in Mg85Zn6Y9
Authors:
Matsushita, M; Bednarcik, J; Sakata, Y; Akamatsu, S; Nishiyama, N; Michalikoya, J; Yamasaki, M; Kawamura, Y Author Full Names: Matsushita, Masafumi; Bednarcik, Jozef; Sakata, Yuya; Akamatsu, Shutaro; Nishiyama, Norimasa; Michalikoya, Jana; Yamasaki, Michiaki; Kawamura, Yoshihito
Source:
PHYSICA B-CONDENSED MATTER, 461 147-153; 10.1016/j.physb.2014.12.021 MAR 15 2015
Abstract:
Phase transformation of the long period stacking order (LPSO) synchronized with the chemical concentration in Mg85Zn6Y9 has been investigated during both heating and cooling via in situ X-ray diffraction analysis. With increasing temperature, above 800 K, 10H-type LPSO phase collapsed firstly. 10H structural modulation collapsed earlier than the chemical modulation of 5 layers per period. The in plane ordering consisted of aligned L1(2)-type clusters vanished before the collapse of chemical and structural modulation of 18R-type LPSO. After, the chemical and structural modulation of 18R-type LPSO show synchronize collapse. During cooling, the 14H-type LPSO emerged in addition to the 18R-type LPSO. The growths of chemical and structural modulation start at the same temperature. After that, the formation of in plane order consisting of aligned L1(2)-type Zn-Y clusters emerged. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Natural quasicrystal with decagonal symmetry
Authors:
Bindi, L; Yao, N; Lin, C; Hollister, LS; Andronicos, CL; Distler, VV; Eddy, MP; Kostin, A; Kryachko, V; MacPherson, GJ; Steinhardt, WM; Yudovskaya, M; Steinhardt, PJ Author Full Names: Bindi, Luca; Yao, Nan; Lin, Chaney; Hollister, Lincoln S.; Andronicos, Christopher L.; Distler, Vadim V.; Eddy, Michael P.; Kostin, Alexander; Kryachko, Valery; MacPherson, Glenn J.; Steinhardt, William M.; Yudovskaya, Marina; Steinhardt, Paul J.
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep09111 MAR 13 2015
Abstract:
We report the first occurrence of a natural quasicrystal with decagonal symmetry. The quasicrystal, with composition Al71Ni24Fe5, was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite. Icosahedrite, Al63Cu24Fe13, the first natural quasicrystal to be identified, was found in the same meteorite. The new quasicrystal was found associated with steinhardtite (Al38Ni32Fe30), Fe-poor steinhardtite (Al50Ni40Fe10), Al-bearing trevorite (NiFe2O4) and Al-bearing taenite (FeNi). Laboratory studies of decagonal Al71Ni24Fe5 have shown that it is stable over a narrow range of temperatures, 1120 K to 1200 K at standard pressure, providing support for our earlier conclusion that the Khatyrka meteorite reached heterogeneous high temperatures [1100 < T(K) <= 1500] and then rapidly cooled after being heated during an impact-induced shock that occurred in outer space 4.5 Gya. The occurrences of metallic Al alloyed with Cu, Ni, and Fe raises new questions regarding conditions that can be achieved in the early solar nebula.
Title:
Group-theoretical analysis of aperiodic tilings from projections of higher-dimensional lattices B-n
Authors:
Koca, M; Koca, NO; Koc, R Author Full Names: Koca, Mehmet; Koca, Nazife Ozdes; Koc, Ramazan
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 175-185; 10.1107/S2053273314025492 2 MAR 2015
Abstract:
A group-theoretical discussion on the hypercubic lattice described by the affine Coxeter-Weyl group W-a(B-n) is presented. When the lattice is projected onto the Coxeter plane it is noted that the maximal dihedral subgroup D-h of W(B-n) with h = 2n representing the Coxeter number describes the h-fold symmetric aperiodic tilings. Higher-dimensional cubic lattices are explicitly constructed for n = 4, 5, 6. Their rank-3 Coxeter subgroups and maximal dihedral subgroups are identified. It is explicitly shown that when their Voronoi cells are decomposed under the respective rank-3 subgroupsW(A(3)), W(H-2) x W(A(1)) and W(H-3) one obtains the rhombic dodecahedron, rhombic icosahedron and rhombic triacontahedron, respectively. Projection of the lattice B-4 onto the Coxeter plane represents a model for quasicrystal structure with eightfold symmetry. The B-5 lattice is used to describe both fivefold and tenfold symmetries. The lattice B-6 can describe aperiodic tilings with 12-fold symmetry as well as a three-dimensional icosahedral symmetry depending on the choice of subspace of projections. The novel structures from the projected sets of lattice points are compatible with the available experimental data.
Title:
Thermodynamic and neutron diffraction studies on multiferroic NdMn2O5
Authors:
Chattopadhyay, S; Baledent, V; Auban-Senzier, P; Pasquier, C; Doubroysky, C; Greenblatt, M; Foury-Leylekian, P Author Full Names: Chattopadhyay, S.; Baledent, V.; Auban-Senzier, P.; Pasquier, C.; Doubroysky, C.; Greenblatt, M.; Foury-Leylekian, P.
Source:
PHYSICA B-CONDENSED MATTER, 460 214-217; SI 10.1016/j.physb.2014.11.074 MAR 1 2015
Abstract:
Magnetically frustrated RMn2O5 oxides have attracted considerable attention in recent years, because most of the members of this family show spin ordering induced dielectric polarization along with strong magneto-electric coupling. Although the true origin of the ferroelectricity is still a matter of debate, it has been observed that the magneto-electric phase diagram can be substantially tuned with the variation of rare earth elements. In this work, we have chosen NdMn2O5 as the compound of our interest since it lies exactly in between the ferroelectric and non-ferroelectric members of this family and also, because there are few investigations performed on RMn2O5 systems with large rare earth atoms. With the combination of heat capacity, magnetic susceptibility, dielectric permittivity, powder X-ray diffraction, and powder neutron diffraction measurements, it has been found that NdMn2O5 undergoes an incommensurate magnetic ordering around 30 K followed by a possible ferroelectric-like transition at similar to 26 K. Another lock-in kind of magnetic transition appears when the temperature is decreased to similar to 15 K. With further lowering of temperature, an antiferromagnetic ordering, which is presumably associated with the Nd3+, is achieved near 4 K. This study thus sheds light on a new compound of the RMn2O5 series presenting different multiferroic properties. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Generalized Penrose tiling as a quasilattice for decagonal quasicrystal structure analysis
Authors:
Chodyn, M; Kuczera, P; Wolny, J Author Full Names: Chodyn, Maciej; Kuczera, Pawel; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 161-168; 10.1107/S2053273314024917 2 MAR 2015
Abstract:
The generalized Penrose tiling is, in fact, an infinite set of decagonal tilings. It is constructed with the same rhombs (thick and thin) as the conventional Penrose tiling, but its long-range order depends on the so-called shift parameter (s is an element of < 0; 1)). The structure factor is derived for the arbitrarily decorated generalized Penrose tiling within the average unit cell approach. The final formula works in physical space only and is directly dependent on the s parameter. It allows one to straightforwardly change the long-range order of the refined structure just by changing the s parameter and keeping the tile decoration unchanged. This gives a great advantage over the higher-dimensional method, where every change of the tiling (change in the s parameter) requires the structure model to be built from scratch, i.e. the fine division of the atomic surfaces has to be redone.
Title:
Analytical electron microscopy study on gallium nitride systems doped with manganese and iron
Authors:
Meingast, A; Quezada, AN; Devillers, T; Kovacs, A; Albu, M; Fladischer, S; Bonanni, A; Kothleitner, G Author Full Names: Meingast, Arno; Quezada, Andrea Navarro; Devillers, Thibaut; Kovacs, Andras; Albu, Mihela; Fladischer, Stefanie; Bonanni, Alberta; Kothleitner, Gerald
Source:
SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 30 (3):10.1088/0268-1242/30/3/035002 MAR 2015
Abstract:
Modulated structures of gallium nitride (GaN) doped with transition metal ions (here Fe, Mn) are investigated by analytical (scanning) transmission electron microscopy to gain insight into the structural arrangement and chemical composition of the material, known to be critically correlated to the magnetic response and hence the functionality of these technologically relevant systems. Three classes of samples are considered: (i) homogeneous (dilute) (Ga, Mn) N; (ii) delta-Mn-doped (Ga, delta-Mn) N and phase separated (Ga, Fe) N, containing Fe-rich nanocrystals. The combination of various microscopic techniques employed, allows for a quantitative determination of the distribution of the magnetic ions in the samples, providing essential information on the structural and chemical asset of these systems.
Title:
Direct observation of single-electron solitons and Friedel oscillations in a quasi-one dimensional material with incommensurate charge-density waves
Authors:
Brun, C; Brazovskii, S; Wang, ZZ; Monceau, P Author Full Names: Brun, Christophe; Brazovskii, Serguei; Wang, Zhao-Zhong; Monceau, Pierre
Source:
PHYSICA B-CONDENSED MATTER, 460 88-92; SI 10.1016/j.physb.2014.11.046 MAR 1 2015
Abstract:
We have performed scanning tunneling microscopy experiments in the quasi-one dimensional charge density wave (CDW) system NbSe3, where we could image and study in detail individual solitons corresponding to the self-trapping of a single electron. Our analysis shows that the type of soliton we observed is an "Amplitude Soliton", characterized by a vanishing CDW amplitude at the soliton center and by a pi-shift of its phase along the chain direction. Pairs of solitons or multiple solitons were also observed. Such observations could be made only in the high-temperature COW phase. Additionally, one-dimensional Friedel oscillations around charged defects could also be imaged and are found to be superimposed to the COW. The distinction between amplitude solitons and Friedel oscillations can be made without any ambiguity. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Topological Hofstadter insulators in a two-dimensional quasicrystal
Authors:
Tran, DT; Dauphin, A; Goldman, N; Gaspard, P Author Full Names: Tran, Duc-Thanh; Dauphin, Alexandre; Goldman, Nathan; Gaspard, Pierre
Source:
PHYSICAL REVIEW B, 91 (8):10.1103/PhysRevB.91.085125 FEB 27 2015
Abstract:
We investigate the properties of a two-dimensional quasicrystal in the presence of a uniform magnetic field. In this configuration, the density of states (DOS) displays a Hofstadter-butterfly-like structure when it is represented as a function of the magnetic flux per tile. We show that the low-DOS regions of the energy spectrum are associated with chiral edge states, in direct analogy with the Chern insulators realized with periodic lattices. We establish the topological nature of the edge states by computing the topological Chern number associated with the bulk of the quasicrystal. This topological characterization of the nonperiodic lattice is achieved through a local (real-space) topological marker. This work opens a route for the exploration of topological-insulating materials in a wide range of nonperiodic lattice systems, including photonic crystals and cold atoms in optical lattices.
Title:
Effects of Initial States on the Spinodal Decomposition of Quenched and Melt-Spun Cu-15Ni-8Sn Alloy
Authors:
Kondo, SI; Masusaki, A; Ogawa, K; Morimura, T; Nakashima, H Author Full Names: Kondo, Shin-ichiro; Masusaki, Akinori; Ogawa, Kento; Morimura, Takao; Nakashima, Hiromichi
Source:
MATERIALS TRANSACTIONS, 56 (1):23-29; 10.2320/matertrans.M2014234 JAN 2015
Abstract:
We investigate early stages of spinodal decomposition in a melt-spun Cu-15Ni-8Sn alloy (melt-spun samples) by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron diffraction analysis through comparison against a non-melt-spun alloy of the same composition (quenched samples). In XRD measurements, no sidebands of (200) planes are found in the melt-spun sample after aging at 350 degrees C for 120 min, whereas they are found in the quenched sample after a heat treatment at 350 degrees C for 60 min. TEM observations of a quenched sample after aging at 350 degrees C for 60 mm indicate the presence of a modulated structure (lambda = 5-10 nm) in the matrix, whereas those of a melt-spun sample after the same heat treatment also indicate the presence of a modulated structure (lambda: too small to measure). Electron diffraction patterns reveal satellite structures in both samples, although with superlattice reflections from ordering phases visible in the quenched sample. These differences are presumably due to a difference in the size of clusters present in their respective quenched states; in melt-spun samples, cluster size was much smaller as a result of a high cooling rate (approximate to 8 x 10(5)degrees C/s).

Update: 2-Apr-2015

Title:
First-principles study of structurally modulated multiferroic CaMn7O12
Authors:
Cao, K; Johnson, RD; Perks, N; Giustino, F; Radaelli, PG Author Full Names: Cao, Kun; Johnson, Roger D.; Perks, Natasha; Giustino, Feliciano; Radaelli, Paolo G.
Source:
PHYSICAL REVIEW B, 91 (6):10.1103/PhysRevB.91.064422 FEB 27 2015
Abstract:
study the electronic and magnetic structures of multiferroic CaMn7O12 by first-principles calculations, based on the experimentally determined modulated crystal structure. We confirm the presence of a 3d orbital modulation of the Mn2 (Mn3+) sites, previously inferred from the Jahn-Teller crystal distortions. Our results indicate that in the multiferroic phase themagnetic structure of the Mn3 (Mn4+) sites is anharmonically modulated via orbitally mediated coupling with the structural modulation, and that the Dzyaloshinskii-Moriya and exchange striction mechanisms contribute equally to the polarization.
Title:
Disorder from order among anisotropic next-nearest-neighbor Ising spin chains in SrHo2O4
Authors:
Wen, JJ; Tian, W; Garlea, VO; Koohpayeh, SM; McQueen, TM; Li, HF; Yan, JQ; Rodriguez-Rivera, JA; Vaknin, D; Broholm, CL Author Full Names: Wen, J. -J.; Tian, W.; Garlea, V. O.; Koohpayeh, S. M.; McQueen, T. M.; Li, H. -F.; Yan, J. -Q.; Rodriguez-Rivera, J. A.; Vaknin, D.; Broholm, C. L.
Source:
PHYSICAL REVIEW B, 91 (5):10.1103/PhysRevB.91.054424 FEB 26 2015
Abstract:
We describe why Ising spin chains with competing interactions in SrHo2O4 segregate into ordered and disordered ensembles at low temperatures (T). Using elastic neutron scattering, magnetization, and specific heat measurements, the two distinct spin chains are inferred to have Neel (up arrow down arrow up arrow down arrow) and double-Neel (up arrow up arrow down arrow down arrow) ground states, respectively. Below T-N = 0.68(2) K, the Neel chains develop three-dimensional long range order (LRO), which arrests further thermal equilibration of the double-Neel chains so they remain in a disordered incommensurate state for T below T-S = 0.52(2) K. SrHo2O4 distills an important feature of incommensurate low dimensional magnetism: kinetically trapped topological defects in a quasi-d-dimensional spin system can preclude order in d + 1 dimensions.
Title:
Quantum critical behavior in heavily doped LaFeAsO1-xHx pnictide superconductors analyzed using nuclear magnetic resonance
Authors:
Sakurai, R; Fujiwara, N; Kawaguchi, N; Yamakawa, Y; Kontani, H; Iimura, S; Matsuishi, S; Hosono, H Author Full Names: Sakurai, R.; Fujiwara, N.; Kawaguchi, N.; Yamakawa, Y.; Kontani, H.; Iimura, S.; Matsuishi, S.; Hosono, H.
Source:
PHYSICAL REVIEW B, 91 (6):10.1103/PhysRevB.91.064509 FEB 19 2015
Abstract:
We studied the quantum critical behavior of the second antiferromagnetic (AF) phase in the heavily electron-doped high-T-c pnictide, LaFeAsO1-x H-x, by using a As-75 and H-1 nuclear magnetic resonance (NMR) technique. In the second AF phase, we observed a spatially modulated spin-density-wave-like state up to x = 0.6 from the NMR spectral line shape and detected a low-energy excitation gap from the nuclear relaxation time T-1 of As-75. The excitation gap closes at the AF quantum critical point (QCP) at x approximate to 0.49. The superconducting phase in a lower-doping regime contacts the second AF phase only at the AF QCP, and both phases are segregated from each other. The absence of AF critical fluctuations and the enhancement of the in-plane electric anisotropy are key factors for the development of superconductivity.
Title:
Disruption of quantum oscillations by an incommensurate charge density wave
Authors:
Zhang, Y; Maharaj, AV; Kivelson, S Author Full Names: Zhang, Yi; Maharaj, Akash V.; Kivelson, Steven
Source:
PHYSICAL REVIEW B, 91 (8):10.1103/PhysRevB.91.085105 FEB 9 2015
Abstract:
Because a material with an incommensurate charge density wave (ICDW) is only quasiperiodic, Bloch's theorem does not apply and there is no sharply defined Fermi surface. We will show that, as a consequence, there are no quantum oscillations which are truly periodic functions of 1/B (where B is the magnitude of an applied magnetic field). For a weak ICDW, there exist broad ranges of 1/B in which approximately periodic variations occur, but with frequencies that vary inexorably in an unending cascade with increasing 1/B. For a strong ICDW, e.g., in a quasicrystal, no quantum oscillations survive at all. Rational and irrational numbers really are different.
Title:
Direct observation of Ca-Na ordering and structure polarity in Ca-rich intermediate plagioclase feldspar with incommensurate modulated structure
Authors:
Xu, HF Author Full Names: Xu, Huifang
Source:
AMERICAN MINERALOGIST, 100 (2-3):510-515; 10.2138/am-2015-5022 FEB-MAR 2015
Abstract:
Ca-Na ordering and structural polarity of subcells in an intermediate plagioclase with modulated structure have been observed using Z-contrast imaging with an aberration-corrected scanning transmission electron microscope. Neighboring lamellar domains with I1 symmetry are related by inversion twin operation, instead of anti-phase domain boundaries (or APBs) as in all previously reported structure models. The boundaries between lamellar domains have I (1) over bar symmetry instead of C (1) over bar symmetry. Modulated plagioclase has unique Ca-Na and Al-Si ordering structure that is different from those in end-member structures of anorthite and low albite. The modulated structures of intermediate plagioclase are not metastable structures formed during phase transition, but instead thermodynamically stable structures at low temperature due to Ca-Na ordering within the subcells with I1 symmetry.

Update: 26-Mar-2015

Title:
Charge order and resistivity transition of Zn-doped cuprate superconductors
Authors:
de Mello, EVL; Mockli, D Author Full Names: de Mello, E. V. L.; Moeckli, David
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (9):10.1088/0953-8984/27/9/095702 MAR 11 2015
Abstract:
Impurity doping using Zn atoms was largely studied in cuprates because this process substantially reduces the superconducting critical temperature T-c without any effect on the pseudogap onset T*. Earlier theories missed the recently established ubiquitous presence of incommensurate charge modulations in these materials. The charge order is a consequence of a phase separation transition which we describe by a continuity equation of the local free energy density. The Zn atoms generate a local magnetic moment, freezing their neighbors' spins, slowing down the electronic segregation process. Then the Zn-doped properties are that of a granular superconductor whose size of the charge order modulations are dictated by the degree of phase separation.
Title:
Effect of Li on structure and electrochemical hydrogen storage properties of Ti55V10Ni35 quasicrystal alloy
Authors:
Liu, CF; Duan, YH; Ouyang, ZT; Shang, JM; Liu, K; Xing, C; Fu, YG; Liu, WQ; Wang, LM Author Full Names: Liu, Chaofan; Duan, Yuhan; Ouyang, Zhongtao; Shang, Jinming; Liu, Kun; Xing, Cheng; Fu, Yuegang; Liu, Wanqiang; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 40 (7):3015-3022; 10.1016/j.ijhydene.2014.12.133 FEB 23 2015
Abstract:
The Ti55V10Ni35 quasicrystal ribbons are synthesized by arc melting and subsequent melt-spinning technique and then Li atoms are infiltrated into this quasicrystal material by the way of electroosmosis. X-ray diffraction results indicate that the pristine quasicrystal Ti55V10Ni35 mainly consists of the icosahedral quasicrystal (I-phase), V-based solid solution phase with BBC structure and face centered cubic (FCC) phase with Ti2Ni-type structure. After infiltrating some amount of Li atoms into Ti55V10Ni35 quasicrystal lattice voids at different electroosmosis current density (A/mg) of 0.3, 0.6 and 0.9 respectively, phase structure investigations show that the main phase structures do not change greatly except for the additional lithium phase, which demonstrates that Li does not destroy the phase structure of Ti55V10Ni35 quasicrystal. Ti55V10Ni35 alloy shows the best discharge capacity is 219.8 mAh g(-1) at a current density of 30 mA g(-1). The negative electrode made by Ti55V10Ni35 Li quasicrystal alloys (Li atoms are infiltrated into Ti55V10Ni35 quasicrystal alloy at different the electroosmosis current density (A/mg) of 0.3, 0.6 and 0.9 has a maximum discharge capacity of 257.7 mAh g(-1), 301.8 mAh g(-1) and 238.7 mAh g(-1) at a discharge current density of 30 mA g(-1), respectively. And the high rate discharge ability of alloy electrodes is higher than that of Ti55V10Ni35 quasicrystal alloy at 240 mA g(-1). The Effect of Li on structure of Ti55V10Ni35 quasicrystal has been discussed by measuring the place, mass ratio and chemical state that Li infiltrated into quasicrystal Ti55V10Ni35 lattice. In addition, the electrochemical reaction kinetics of Ti55V10Ni35-Li quasicrystal alloy electrodes is also studied by measuring both the electrochemical impedance spectroscopy and hydrogen diffusion coefficient. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Density-matrix renormalization group study of the extended Kitaev-Heisenberg model
Authors:
Shinjo, K; Sota, S; Tohyama, T Author Full Names: Shinjo, Kazuya; Sota, Shigetoshi; Tohyama, Takami
Source:
PHYSICAL REVIEW B, 91 (5):10.1103/PhysRevB.91.054401 FEB 4 2015
Abstract:
We study an extended Kitaev-Heisenberg model including additional anisotropic couplings by using the two-dimensional density-matrix renormalization group method. Calculating the ground-state energy, entanglement entropy, and spin-spin correlation functions, we make a phase diagram of the extended Kitaev-Heisenberg model around the spin-liquid phase. We find a zigzag antiferromagnetic phase, a ferromagnetic phase, a 120. antiferromagnetic phase, and two kinds of incommensurate phases around the Kitaev spin-liquid phase. Furthermore, we study the entanglement spectrum of the model, and we find that entanglement levels in the Kitaev spin-liquid phase are degenerate forming pairs, but those in the magnetically ordered phases are nondegenerate. The Schmidt gap defined as the energy difference between the lowest two levels changes at the phase boundary adjacent to the Kitaev spin-liquid phase. However, we find that phase boundaries between magnetically ordered phases do not necessarily agree with the change of the Schmidt gap.
Title:
Modification of the phase composition and structure of the quasicrystalline Al-Cu-Fe alloy prepared by plasma spraying
Authors:
Lepeshev, AA; Bayukov, OA; Rozhkova, EA; Karpov, IV; Ushakov, AV; Fedorov, LY Author Full Names: Lepeshev, A. A.; Bayukov, O. A.; Rozhkova, E. A.; Karpov, I. V.; Ushakov, A. V.; Fedorov, L. Yu.
Source:
PHYSICS OF THE SOLID STATE, 57 (2):255-259; 10.1134/S1063783415020249 FEB 2015
Abstract:
The structural-phase state of quasicrystalline coatings of the Al-Cu-Fe alloy produced under different thermal conditions of plasma spraying (different contact temperatures T (k) of the substrate) has been investigated. It has been shown that sprayed coatings are heterophase with the dominant content of the icosahedral psi and cubic beta phases, the formation and fractional ratio of which depend on spraying conditions. The distribution of probabilities P(QS) of quadrupole splitting in experimental gamma-resonance spectra has been analyzed. The dependence of hyperfine interaction parameters (QS, A) on spraying conditions of the coating has been established. Five nonequivalent positions of resonant iron atoms, the appearance and filling of which are determined by spraying conditions, have been revealed.
Title:
Incommensurate Structure and Phase Transitions in Epitaxial Multiferroic Films
Authors:
Gareeva, ZV; Popkov, AF; Kulagin, NE; Soloviov, SV; Zvezdin, AK Author Full Names: Gareeva, Z. V.; Popkov, A. F.; Kulagin, N. E.; Soloviov, S. V.; Zvezdin, A. K.
Source:
FERROELECTRICS, 475 (1):1-9; SI 10.1080/00150193.2015.994973 JAN 25 2015
Abstract:
We investigate transformations of space modulated structure in BiFeO3 films induced by change of magnetic anisotropy, strain, or temperature and applied magnetic field. We show that critical field of the transition between incommensurate and commensurate structures is lower in films as compared with single crystals. There are two incommensurate phases at H parallel to[111]: plane and conical cycloidal phases with the second order transition between them. An important feature of this transition is softening of spin wave activation mode localized on spin cycloid. Cycloidal spin wave spectrum contains a countable number of branches, thus BiFeO3 can be considered as a magnonic crystal.

Update: 19-Mar-2015

Title:
Electrochemical hydrogen storage properties of Ti1.4V0.6Ni quasicrystal and TiH composite materials
Authors:
Liu, K; Shang, JM; Ouyang, ZT; Duan, YH; Xing, C; Fu, YG; Liang, F; Lin, J; Liu, WQ; Wang, LM Author Full Names: Liu, Kun; Shang, Jinming; Ouyang, Zhongtao; Duan, Yuhan; Xing, Cheng; Fu, Yuegang; Liang, Fei; Lin, Jing; Liu, Wanqiang; Wang, Limin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 630 158-162; 10.1016/j.jallcom.2015.01.062 MAY 5 2015
Abstract:
In this study, we use arc-melting and subsequent melt-spinning techniques to prepare Ti1.4V0.6Ni alloy ribbons. The Ti1.4V0.6Ni + xTiH (x = 5, 10, 15 and 20 wt.%) mixture powders are obtained by mechanical ball-milling. Also, we investigate the structure and electrochemical hydrogen storage properties of composite materials. Besides I-phase, FCC and BCC phase, the XRD of composite materials indicates it contains TiH phase. After adding TiH, the discharge capacities of Ti1.4V0.6Ni alloy electrode increase first and then decrease with increasing amount of Ti. The achieved maximum discharge capacity is about 339.8 mA h/g (x = 15 wt.%) at the first discharge cycle. Additionally, composite materials lead to significant improvement in the high-rate dischargeability (HRD) as well as the cyclic stability. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Wave propagation of phonon and phason displacement modes in quasicrystals: Determination of wave parameters
Authors:
Chellappan, V; Gopalakrishnan, S; Mani, V Author Full Names: Chellappan, Vinita; Gopalakrishnan, S.; Mani, V.
Source:
JOURNAL OF APPLIED PHYSICS, 117 (5):10.1063/1.4907212 FEB 7 2015
Abstract:
The paper presents the study of wave propagation in quasicrystals. Our interest is in the computation of the wavenumber (k(n)) and group speed (c(g)) of the phonon and phason displacement modes of one, two, and three dimensional quasicrystals. These wave parameter expressions are derived and computed using the elasto-hydrodynamic equations for quasicrystals. For the computation of the wavenumber and group speeds, we use Fourier transform approximation of the phonon and the phason displacement modes. The characteristic equations obtained are a polynomial equation of the wavenumber (k(n)), with frequency as a parameter. The corresponding group speeds (c(g)) for different frequencies are then computed from the wavenumber k(n). The variation of wavenumber and group speeds with frequency is plotted for the 1-D quasicrystal, 2-D decagonal Al-Ni-Co quasicrystals, and 3-D icosahedral Al-Pd-Mn and Zn-Mg-Sc quasicrystals. From the wavenumber and group speeds plots, we obtain the cut-off frequencies for different spatial wavenumber eta(m). The results show that for 1-D, 2-D, and 3-D quasicrystals, the phonon displacement modes are non-dispersive for low values of eta(m) and becomes dispersive for increasing values of eta(m). The cut-off frequencies are not observed for very low values of eta(m), whereas the cut-off frequency starts to appear with increasing eta(m). The group speeds of the phason displacement modes are orders of magnitude lower than that of the phonon displacement modes, showing that the phason modes do not propagate, and they are essentially the diffusive modes. The group speeds of the phason modes are also not influenced by eta(m). The group speeds for the 2-D quasicrystal at 35 kHz is also simulated numerically using Galerkin spectral finite element methods in frequency domain and is compared with the results obtained using wave propagation analysis. The effect of the phonon and phason elastic constants on the group speeds is studied using 3-D icosahedral Al-Pd-Mn and Zn-Mg-Sc quasicrystals. It is also shown that the phason elastic constants and the coupling coefficient do not affect the group speeds of the phonon displacement modes. (C) 2015 AIP Publishing LLC.

Update: 12-Mar-2015

Title:
Spin-Glass Behavior and Incommensurate Modulation in High-Pressure Perovskite BiCr0.5Ni0.5O3
Authors:
Arevalo-Lopez, AM; Dos Santos-Garcia, AJ; Levin, JR; Attfield, JP; Alario-Franco, MA Author Full Names: Arevalo-Lopez, Angel M.; Dos Santos-Garcia, Antonio J.; Levin, Jessica R.; Attfield, J. Paul; Alario-Franco, Miguel A.
Source:
INORGANIC CHEMISTRY, 54 (3):832-836; 10.1021/ic502012p FEB 2 2015
Abstract:
The BiCr0.5Ni0.5O3 perovskite has been obtained at high pressure. Neutron and synchrotron diffraction data show a Pnma orthorhombic structure with a = 5.5947(1) angstrom, b = 7.7613(1) angstrom, and c = 5.3882(1) angstrom at 300 K and random B-site Cr/Ni distribution. Electron diffraction reveals an incommensurate modulation parallel to the b axis. The combination of either Cr-O-Ni (J > 0) or Cr-O-Cr/Ni-O-Ni (J < 0) nearest-neighbor spin interactions results in a random-bond spin-glass configuration. Magnetization, neutron diffraction, and muon-spin-relaxation measurements demonstrate that variations in the local bonding and charge states contribute to the magnetic frustration.
Title:
Structural Modulations in the Rare-Earth Metal Digermanides REAl1-x,Ge-2 (RE = Gd-Tm, Lu, Y; 0.8
Authors:
Zhang, JL; Wang, YM; Bobev, S Author Full Names: Zhang, Jiliang; Wang, Yingmin; Bobev, Svilen
Source:
INORGANIC CHEMISTRY, 54 (3):722-732; 10.1021/ic501002j FEB 2 2015
Abstract:
Rare-earth metal aluminum germanides with the general formula REAl1-xGe2 (RE = Gd, Tb, Dy, Ho, Er, Tm, Lu, and Y) have been synthesized by direct fusion of the corresponding elements. The structures have been studied by single-crystal X-ray diffraction and selected-area electron diffraction (SAED). The average structure represents a randomly stuffed variant of the orthorhombic ZrSi2 structure type, also known as the CeNi1-xSi2 type (Pearson symbol oC16; space group Cmcm). The SAED patterns for selected members of the family suggest the coexistence of commensurate and incommensurate structural modulations. The most prominent model for long-range vacancy ordering is the Tb4FeGe8 type (Pearson symbol mP26; space group P2(1)/n), which is the commensurate 4-fold superstructure of CeNi1-xSi2 (x = 3/4). Short-range correlations cause additional deviations in the 4-fold superlattice. These results shed more light on the structural complexity as a function of the aluminum vacancies and size of the rare-earth metal. Magnetic susceptibility measurements are presented and discussed. The measured ordering temperatures and calculated ones based on empirical rules and Ruderman-Kittel-Kasuya-Yosida interactions are shown to be in close agreement.
Title:
Fabrication and structural characterization of bismuth niobate thin films grown by chemical solution deposition
Authors:
Goncalves, LF; Cortes, JA; Ranieri, MGA; Destro, FB; Ramirez, MA; Simoes, AZ Author Full Names: Goncalves, L. F.; Cortes, J. A.; Ranieri, M. G. A.; Destro, F. B.; Ramirez, M. A.; Simoes, A. Z.
Source:
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 26 (2):1142-1150; 10.1007/s10854-014-2518-6 FEB 2015
Abstract:
Bi3NbO7 (BNO) thin films were deposited on Pt/TiO2/SiO2/Si (100) substrates at room temperature from the polymeric precursor method. X-ray powder diffraction and transmission electron microscopy were used to investigate the formation characteristics and stability range of the tetragonal modification of a fluorite-type solid solution. The results showed that this tetragonal, commensurately modulated phase forms through the intermediate formation of the incommensurately modulated cubic fluorite phase followed by the incommensurate-commensurate transformation. The 200 nm thick BNO films exhibit crystalline structure, a dielectric constant of 170, capacitance density of 200 nF/cm(2), dielectric loss of 0.4 % at 1 MHz, and a leakage current density of approximately 1 x 10(-7) A/cm(2) at 5 V. They show breakdown strength of about 0.25 MV/cm. The leakage mechanism of BNO film in high field conduction is well explained by the Schottky and Poole-Frenkel emission models. The 200 nm thick BNO film is suitable for embedded decoupling capacitor applications directly on a printed circuit board.
Title:
On the Origin of Nanochessboard Super lattices in A-Site-Deficient Ca-Stabilized Nd2/3TiO3
Authors:
Azough, F; Kepaptsoglou, D; Ramasse, QM; Schaffer, B; Freer, R Author Full Names: Azough, Feridoon; Kepaptsoglou, Demie; Ramasse, Quentin M.; Schaffer, Berhnard; Freer, Robert
Source:
CHEMISTRY OF MATERIALS, 27 (2):497-507; 10.1021/cm5036985 JAN 27 2015
Abstract:
A-site deficient Nd2/3TiO3 ceramics stabilized with CaTiO3, with an overall composition of 0.9 Nd2/3TiO3-0.1 CaTiO3, were synthesized by the mixed oxide route. Synchrotron X-ray diffraction was used to identify the basic perovskite structure and revealed cross-type superlattice reflections. An incommensurate superlattice structure with dimensions of a approximate to b approximate to 20ap and c = 2a(p) (where a(p) is the cell parameter for the parent perovskite phase) was identified, giving rise to contrast features resembling a nanochessboard pattern in electron microscopy images. The superlattice was further characterized by aberration-corrected scanning transmission electron microscopy (STEM): atomically resolved lattice images were obtained along ?100? orientations to visualize the A-site (Ca, Nd, and vacancies) and B-site (Ti) cation column intensities, in correlation with observations of the nanochessboard superlattice. Electron energy loss spectroscopy (EELS) was used to precisely determine the distribution of Nd and Ca across the structure, confirming the absence of long-range elemental segregation or phase separation across the nanochessboard superstructure. Closer inspection of the chemical maps in two orthogonal directions, however, suggests the presence of localized ordering of cations and vacancies. The chessboard pattern superlattice is thus likely to be caused by periodic octahedral tilt distortions of the O sublattice, possibly induced by these short-range chemical variations, as a result of a complex interplay between cation and vacancy ordering in three dimensions.
Title:
Cation ordering in A-site-deficient Li-ion conducting perovskites La(1-x)/3LixNbO3
Authors:
Gao, X; Fisher, CAJ; Ikuhara, YH; Fujiwara, Y; Kobayashi, S; Moriwake, H; Kuwabara, A; Hoshikawa, K; Kohama, K; Iba, H; Ikuhara, Y Author Full Names: Gao, Xiang; Fisher, Craig A. J.; Ikuhara, Yumi H.; Fujiwara, Yasuyuki; Kobayashi, Shunsuke; Moriwake, Hiroki; Kuwabara, Akihide; Hoshikawa, Keigo; Kohama, Keiichi; Iba, Hideki; Ikuhara, Yuichi
Source:
JOURNAL OF MATERIALS CHEMISTRY A, 3 (7):3351-3359; 10.1039/c4ta07040b 2015
Abstract:
Cation-deficient perovskites exhibit complex local atomic arrangements which cannot be adequately described by average crystal structure models. By combining reciprocal-space electron diffraction analysis and direct observations of atom positions using state-of-the-art scanning transmission electron microscopy, we clarify the nature of the cation ordering within A-site-deficient perovskite single crystals of La(1-x)/3LixNbO3 (x = 0 and x = 0.04). Both materials are found to have complex modulated crystal structures with two types of A-cation ordering, namely a long-range layer ordering in alternate (001)(p) planes and a short-range (intra-domain) columnar ordering within La-rich (001)(p) layers. The columnar ordering (occupational modulation) produces modulated displacements of Nb and O atoms. It is also found that substitution of even a small amount of Li for La can affect significantly the columnar ordering, leading to a series of structural and microstructural changes that are likely to have a deleterious effect on the Li-ion conductivity of this material.
Title:
Magnetic resonance and spin-reorientation transitions in the Nd0.75Ho0.25Fe3(BO3)(4) multiferroic
Authors:
Kobets, MI; Dergachev, KG; Gnatchenko, SL; Khatsko, EN; Bezmaternykh, LN; Gudim, IA Author Full Names: Kobets, M. I.; Dergachev, K. G.; Gnatchenko, S. L.; Khatsko, E. N.; Bezmaternykh, L. N.; Gudim, I. A.
Source:
LOW TEMPERATURE PHYSICS, 41 (1):75-79; 10.1063/1.4906338 JAN 2015
Abstract:
A presentation of experimental study results obtained by antiferromagnetic resonance (AFMR) of the high-frequency properties of the multiferroic Nd0.75Ho0.25Fe3(BO3)(4) in a broad range of temperatures and frequencies. We studied the effect of substituting the Nd3+ ions with Ho3+, on the resonance properties of the Nd0.75Ho0.25Fe3(BO3)(4) solid solution. In addition, we investigated the particularities of magnetic-field induced spin-reorientation phase transitions for H parallel to c and H parallel to a directions, in which the anisotropy of the magnetic system is measured from "easy-axis" anisotropy to "easy-plane." The AFMR modes of a Fe3+ subsystem are revealed. New information about the most important characteristics of AFM is obtained, including: frequency-field dependence of the AFMR spectrum, gaps in the spin-wave spectrum, effective magnetic anisotropy values, and fields of spin-reorientation transitions. It is shown that "easy-plane" anisotropy prevails in this magnet, with a weak anisotropy in the basal plane. For the first time there are observed features in the AFMR spectra that could be tied to the presence of a spatially modulated spin structure (incommensurate phase) in AFM Nd0.75Ho0.25Fe3(BO3)(4). (C) 2015 AIP Publishing LLC.
Title:
Single-molecule probing of incommensurate biphenyl (vol 36, pg 448, 2010)
Authors:
Pars, M; Palm, V; Kikas, J Author Full Names: Paers, M.; Palm, V.; Kikas, J.
Source:
LOW TEMPERATURE PHYSICS, 41 (1):80-80; 10.1063/1.4906339 JAN 2015
Title:
Effect of shape on the self-assembly of faceted patchy nanoplates with irregular shape into tiling patterns
Authors:
Millan, JA; Ortiz, D; Glotzer, SC Author Full Names: Millan, Jaime A.; Ortiz, Daniel; Glotzer, Sharon C.
Source:
SOFT MATTER, 11 (7):1386-1396; 10.1039/c4sm01612b 2015
Abstract:
Recent reports of the synthesis and assembly of faceted nanoplates with a wide range of shapes and composition motivates the possibility of a new class of two-dimensional materials with specific patterns targeted for a host of exciting properties. Yet, studies of how nanoplate shape controls their assembly knowledge necessary for their inverse design from target structures - has been performed for only a handful of systems. By constructing a general framework in which many known faceted nanoplates may be described in terms of four anisotropy dimensions, we discover design rules to guide future synthesis and assembly. We study via Monte Carlo simulations attractive polygons whose shape is altered systematically under the following four transformations: faceting, pinching, elongation and truncation. We report that (i) faceting leads to regular porous structures (ii) pinching stabilizes complex structures such as dodecagonal quasicrystals (iii) elongation leads to asymmetric phase behavior, where low and high aspect ratio nanoplates self-assemble completely different structures and (iv) low and high degrees of truncation transform a complex self-assembler into a disk-like assembler, providing design ideas that could lead to switchable structures. We provide important insight into how the shape and attractive interactions of a nanoplate can be exploited or designed to target specific classes of structures, including space-filling, porous, and complex tilings.
Title:
Ultrathin Two-Dimensional Inorganic Materials: New Opportunities for Solid State Nanochemistry
Authors:
Sun, YF; Gao, S; Lei, FC; Xiao, C; Xie, Y Author Full Names: Sun, Yongfu; Gao, Shan; Lei, Fengcai; Xiao, Chong; Xie, Yi
Source:
ACCOUNTS OF CHEMICAL RESEARCH, 48 (1):3-12; 10.1021/ar500164g JAN 2015
Abstract:
CONSPECTUS: The ultimate goal of solid state chemistry is to gain a clear correlation between atomic, defect, and electronic structure and intrinsic properties of solid state materials. Solid materials can generally be classified as amorphous, quasicrystalline, and crystalline based on their atomic arrangement, in which crystalline materials can be further divided into single crystals, microcrystals, and nanocrystals. Conventional solid state chemistry mainly focuses on studying single crystals and microcrystals, while recently nanocrystals have become a hot research topic in the field of solid state chemistry. As more and more nanocrystalline materials have been artificially fabricated, the solid state chemistry for studying those nanosolids has become a new subdiscipline: solid state nanochemistry. However, solid state nanochemistry, usually called "nanochemistry" for short, primarily studies the microstructures and macroscopic properties of a nanomaterial's aggregation states. Due to abundant microstructures in the aggregation states, it is only possible to build a simple but imprecise correlation between the microscopic morphology and the macroscopic properties of the nanostructures. Notably, atomically thin two-dimensional inorganic materials provide an ideal platform to establish clear structure-property relationships in the field of solid state nanochemistry, thanks to their homogeneous dispersion without the assistance of a capping ligand. In addition, their atomic structures including coordination number, bond length, and disorder degree of the examined atoms can be clearly disclosed by X-ray absorption fine structure spectroscopy. Also, their more exposed interior atoms would inevitably induce the formation of various defects, which would have a non-negligible effect on their physicochemical properties. Based on the obtained atomic and defect structural characteristics, density-functional calculations are performed to study their electronic structures. Then, after the properties of the individual ultrathin two-dimensional materials or their assembled highly oriented thin film-based nanodevices are measured, the explicit relationship between atomic, defect, and electronic structure and intrinsic properties could be established. In this Account, we focus on our recent advances in the field of solid state nanochemistry, including atomic structure characterization of ultrathin two-dimensional inorganic materials by X-ray absorption fine structure spectroscopy, characterization of their different types of structural defects by positron annihilation spectra and electron spin resonance, and investigation of their electronic structure by density-functional calculations. In addition, we summarize the close correlation between atomic, defect, and electronic structure variations and the optoelectronic, electrical, magnetic, and thermal properties of ultrathin two-dimensional materials. Finally, we also propose the major challenges and opportunities that face solid state nanochemistry. We believe that all the past achievements in ultrathin two-dimensional materials could bring new opportunities for solid state nanochemistry.

Update: 5-Mar-2015

Title:
An enhancement ZT and spin state transition of Ca3Co4O9 with Pb doping
Authors:
Demirel, S; Altin, E; Oz, E; Altin, S; Bayri, A Author Full Names: Demirel, S.; Altin, E.; Oz, E.; Altin, S.; Bayri, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 627 430-437; 10.1016/j.jallcom.2014.11.200 APR 5 2015
Abstract:
We reported the structural, electrical, thermal and magnetic properties of Pb-doped Ca3Co4O9 in the range of 300-5 K. DTA analysis showed that the stability of the Ca3Co4O9 was increased with Pb doping. According to XRD analysis, it is found that Pb ions were successfully doped in the Ca3Co4O9 structure. The temperature of resistivity minima, T-min, increased by increasing the Pb doping level and it is seen that incommensurate spin density wave state becomes more stable with Pb doping. The enhancement of thermopower was explained that Pb doping in Ca sites caused a decrease of Co4+ fraction such that Co4+ ions transformed into Co3+ or Co2+. The room temperature ZT value of the polycrystalline sample reaches about 16 times larger value than that of the un-doped polycrystalline sample which is the promising candidate for high temperatures in the thin film applications. According to magnetic susceptibility measurement, the increase of effective magnetic moment by Pb concentration was explained by spin state transition of Co3+ from low spin to intermediate spin and high spin state together with some orbital angular momentum contribution which comes from T-5(2) term due to a decrease of the ligand field splitting energy. (C) 2014 Elsevier B. V. All rights reserved.
Title:
Localized Electron Magnetism in the Icosahedral Au-Al-Tm Quasicrystal and Crystalline Approximant
Authors:
Nakayama, M; Tanaka, K; Matsukawa, S; Deguchi, K; Imura, K; Ishimasa, T; Sato, NK Author Full Names: Nakayama, Mika; Tanaka, Katsumasa; Matsukawa, Shuya; Deguchi, Kazuhiko; Imura, Keiichiro; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (2):10.7566/JPSJ.84.024721 FEB 15 2015
Abstract:
We report the magnetic, thermal, and transport properties of the Au-Al-Tm quasicrystal, which is isostructural to the first and only quasicrystal Au-Al-Yb that shows a novel quantum critical behavior. The Tm-based quasicrystal undergoes a spin-glass-like freezing below T-f similar to 0.4 K. We also synthesize the Au-Al-Tm approximant to the quasicrystal and find that it shows a similar spin-glass-like freezing below T-f similar to 0.3 K. Both the quasicrystal and the approximant follow the Curie-Weiss law in a wide temperature range above T-f, indicating that the 4f electrons are well localized on the vertices of the icosahedron. The interspin interaction is antiferromagnetic and its magnitude is as small as similar to 1 K. The spin-glass-like freezing is presumably driven by the combined effect of the chemical disorder of Au/Al ions and the frustrated nature of the icosahedron. On the basis of these results, we discuss a possible origin of the unusual quantum criticality observed in the Yb-based system.
Title:
Superconductivity of Au-Ge-Yb Approximants with Tsai-Type Clusters
Authors:
Deguchi, K; Nakayama, M; Matsukawa, S; Imura, K; Tanaka, K; Ishimasa, T; Sato, NK Author Full Names: Deguchi, Kazuhiko; Nakayama, Mika; Matsukawa, Shuya; Imura, Keiichiro; Tanaka, Katsumasa; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (2):10.7566/JPSJ.84.023705 FEB 15 2015
Abstract:
We report the emergence of bulk superconductivity in Au64.0Ge22.0Yb14.0 and Au63.5Ge20.5Yb16.0 below 0.68 and 0.36 K, respectively. This is the first observation of superconductivity in Tsai-type crystalline approximants of quasicrystals. The Tsai-type cluster center is occupied by Au and Ge ions in the former approximant, and by an Yb ion in the latter. For magnetism, the latter system shows a larger magnetization than the former. To explain this observation, we propose a model that the cluster-center Yb ion is magnetic. The relationship between the magnetism and the superconductivity is also discussed.
Title:
Incommensurate magnetic structure, Fe/Cu chemical disorder, and magnetic interactions in the high-temperature multiferroic YBaCuFeO5
Authors:
Morin, M; Scaramucci, A; Bartkowiak, M; Pomjakushina, E; Deng, G; Sheptyakov, D; Keller, L; Rodriguez-Carvajal, J; Spaldin, NA; Kenzelmann, M; Conder, K; Medarde, M Author Full Names: Morin, M.; Scaramucci, A.; Bartkowiak, M.; Pomjakushina, E.; Deng, G.; Sheptyakov, D.; Keller, L.; Rodriguez-Carvajal, J.; Spaldin, N. A.; Kenzelmann, M.; Conder, K.; Medarde, M.
Source:
PHYSICAL REVIEW B, 91 (6):10.1103/PhysRevB.91.064408 FEB 6 2015
Abstract:
Motivated by the recent observations of incommensurate magnetic order and electric polarization in YBaCuFeO5 up to temperatures T-N2 as high as 230 K [B. Kundys et al., Appl. Phys. Lett. 94, 072506 (2009); Y. Kawamura et al., J. Phys. Soc. Jpn 79, 073705 (2010)], we report here for the first time a model for the incommensurate magnetic structure of this material, which we complement with ab initio calculations of the magnetic exchange parameters. Using neutron powder diffraction, we show that the appearance of polarization below TN2 is accompanied by the replacement of the high-temperature collinear magnetic order by a circular inclined spiral with propagation vector k(i) = (1/2,1/2,1/2 +/- q). Moreover, we find that the polarization approximately scales with the modulus of the magnetic modulation vector q down to the lowest temperature investigated (similar to 3 K). Further, we observe occupational Fe/Cu disorder in the FeO5-CuO5 bipyramids, although a preferential occupation of such units by Fe-Cu pairs is supported by the observed magnetic order and by density functional calculations. We calculate exchange coupling constants for different Fe/Cu distributions and show that, for those containing Fe-Cu dimers, the resulting magnetic order is compatible with the experimentally observed collinear magnetic structure [k(c) = (1/2,1/2,1/2), T-N2 > T > T-N1 = 440 K]. Based on these results, we discuss possible origins for the incommensurate modulation and its coupling with ferroelectricity.
Title:
Critical behaviour of Sn2P2S6 and Sn2P2(Se0.28S0.72)(6) crystals under high hydrostatic pressures
Authors:
Zapeka, B; Kostyrko, M; Martynyuk-Lototska, I; Vlokh, R Author Full Names: Zapeka, B.; Kostyrko, M.; Martynyuk-Lototska, I.; Vlokh, R.
Source:
PHILOSOPHICAL MAGAZINE, 95 (4):382-393; 10.1080/14786435.2015.1006295 FEB 1 2015
Abstract:
Basing on the temperature dependences of optical birefringence for Sn2P2S6 and Sn2P2(Se0.28S0.72)(6) crystals subjected to hydrostatic pressures, we prove unambiguously that Sn2P2S6 reveals a tricritical point on its (p, T)- phase diagram with the coordinates (p, T) = (4.3kbar, 259K), so that the second-order phase transition transforms into the first-order one whenever the pressure increases above 4.3kbar. We also find that increasing hydrostatic pressure applied to Sn2P2(Se0.28S0.72)(6) leads to the change in the phase transition character from tricritical to first order. Further increase in the pressure up to ~2.5kbar imposes splitting of the first-order paraelectric-to-ferroelectric phase transition into two phase transitions, a second-order paraelectric-to-incommensurate one and a first-order incommensurate-to-ferroelectric transition.
Title:
Phase Diagram of (Li1-xFex)OHFeSe: A Bridge between Iron Selenide and Arsenide Superconductors
Authors:
Dong, XL; Zhou, HX; Yang, HX; Yuan, J; Jin, K; Zhou, F; Yuan, DN; Wei, LL; Li, JQ; Wang, XQ; Zhang, GM; Zhao, ZX Author Full Names: Dong, Xiaoli; Zhou, Huaxue; Yang, Huaixin; Yuan, Jie; Jin, Kui; Zhou, Fang; Yuan, Dongna; Wei, Linlin; Li, Jianqi; Wang, Xinqiang; Zhang, Guangming; Zhao, Zhongxian
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137 (1):66-69; 10.1021/ja511292f JAN 14 2015
Abstract:
Previous experimental results have shown important differences between iron selenide and arsenide superconductors which seem to suggest that the high-temperature superconductivity in these two subgroups of iron-based families may arise from different electronic ground states. Here we report the complete phase diagram of a newly synthesized superconducting (SC) system, (Li1-xFex)OHFeSe, with a structure similar to that of FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at similar to 127 K. This is the first example to demonstrate such an SDW phase in an FeSe-based superconductor system. Transmission electron microscopy shows that a well-known O5xO5 iron vacancy ordered state, resulting in an AFM order at similar to 500 K in A(y)Fe(2-x)Se(2) (A = metal ions) superconductor systems, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q = 1/2(1,1,0), identical to that seen in the SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature T-c = 40 K). Hence, we conclude that the high-T-c superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors.
Title:
Row of shear cracks moving in one-dimensional hexagonal quasicrystalline materials
Authors:
Tupholme, GE Author Full Names: Tupholme, G. E.
Source:
ENGINEERING FRACTURE MECHANICS, 134 451-458; 10.1016/j.engfracmech.2014.07.002 JAN 2015
Abstract:
Representations for the stress fields created around an infinite row of collinear, antiplane shear cracks moving within one-dimensional hexagonal quasicrystals, and the resulting stress intensity factors and the J-integral, are determined in closed-form and discussed, using an extended method of dislocation layers. The solutions for a finite quasicrystalline plate containing a single moving crack and a plate with a moving edge crack are also provided by this analysis. (C) 2014 Elsevier Ltd. All rights reserved.

Update: 26-Feb-2015

Title:
Electrochemical hydrogen storage properties of TixV65-xNi35 (x=45, 55) alloys produced by rapid-quenching
Authors:
Liu, CF; Liu, WQ; Wang, LM; Liang, F; Lin, J; Shen, Y; Jiang, DY Author Full Names: Liu, Chaofan; Liu, Wanqiang; Wang, Limin; Liang, Fei; Lin, Jing; Shen, Yu; Jiang, Dayong
Source:
MATERIALS LETTERS, 141 291-293; 10.1016/j.matlet.2014.11.108 FEB 15 2015
Abstract:
Electrochemical discharge performances of TixV65-xNi35 (x=45, 55) alloy are measured by electrochemical measurements at galvanostatic conditions, and alloy ribbon is prepared by rapid-quenching under argon atmosphere. XRD analysis of TixV65-xNi35 (x=45) alloy shows that the Ti45V20Ni35 (x=45) is mostly the amorphous phase, V-based solid solution phase with BCC structure phase and a negligible amount of (Ni, V) phase. While x=55, namely the Ti55V10Ni35 alloy, mainly consists of the icosahedral quasicrystal (I-phase), face centered cubic (FCC) phase with Ti2Ni-type structure and V-based solid solution phase with BCC structure phase. In the electrochemical tests, the maximum discharge capacity of Ti45V20Ni35 is about 150.4 mAh/g at a current density of 30 mA/g. However, Ti55V10Ni35 alloy shows that the best discharge capacity is 221.8 mAh/g under the same condition. In addition, it exhibits extraordinary cycling stability of 87.2% at 30 charge-discharge cycles. It can be found that the discharge capacity of the amorphous electrode is lower than those of the I-phase ones under the similar composition levels. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Strain-induced dimensionality crossover of precursor modulations in Ni2MnGa
Authors:
Nie, ZH; Wang, YD; Shang, SL; Zeng, QS; Ren, Y; Liu, DM; Yang, WG; Wang, Y; Liu, ZK Author Full Names: Nie, Zhihua; Wang, Yandong; Shang, Shunli; Zeng, Qiaoshi; Ren, Yang; Liu, Dongmei; Yang, Wenge; Wang, Yi; Liu, Zi-Kui
Source:
APPLIED PHYSICS LETTERS, 106 (2):10.1063/1.4906333 JAN 12 2015
Abstract:
Precursor modulations often occur in functional materials like magnetic shape memory alloys, ferroelectrics, and superconductors. In this letter, we have revealed the underlying mechanism of the precursor modulations in ferromagnetic shape memory alloys Ni2MnGa by combining synchrotron-based x-ray diffraction experiments and first-principles phonon calculations. We discovered the precursor modulations along [011] direction can be eliminated with [001] uniaxial loading, while the precursor modulations or premartensite can be totally suppressed by hydrostatic pressure condition. The TA(2) phonon anomaly is sensitive to stress induced lattice strain, and the entire TA(2) branch is stabilized along the directions where precursor modulations are eliminated by external stress. Our discovery bridges precursor modulations and phonon anomalies, and sheds light on the microscopic mechanism of the two-step superelasticity in precursor martensite. (C) 2015 AIP Publishing LLC.
Title:
Static friction scaling of physisorbed islands: the key is in the edge
Authors:
Varini, N; Vanossi, A; Guerra, R; Mandelli, D; Capozza, R; Tosatti, E Author Full Names: Varini, Nicola; Vanossi, Andrea; Guerra, Roberto; Mandelli, Davide; Capozza, Rosario; Tosatti, Erio
Source:
NANOSCALE, 7 (5):2093-2101; 10.1039/c4nr06521b 2015
Abstract:
The static friction preventing the free sliding of nanosized rare gas solid islands physisorbed on incommensurate crystalline surfaces is not completely understood. Simulations modeled on Kr/Pb(111) highlight the importance and the scaling behavior of the island's edge contribution to static friction.

Update: 19-Feb-2015

Title:
Distinct itinerant spin-density waves and local-moment antiferromagnetism in an intermetallic ErPd2Si2 single crystal
Authors:
Li, HF; Cao, CD; Wildes, A; Schmidt, W; Schmalzl, K; Hou, BY; Regnault, LP; Zhang, C; Meuffels, P; Loser, W; Roth, G Author Full Names: Li, Hai-Feng; Cao, Chongde; Wildes, Andrew; Schmidt, Wolfgang; Schmalzl, Karin; Hou, Binyang; Regnault, Louis-Pierre; Zhang, Cong; Meuffels, Paul; Loeser, Wolfgang; Roth, Georg
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep07968 JAN 22 2015
Abstract:
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q(+/-) = (H +/- 0.557(1), 0, L +/- 0.150(1)) and Q(C) = (H +/- 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd2Si2 single crystal by neutron scattering and establish their respective temperature-and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q(+/-)modulation may be attributed to localized 4f moments while the Q(C) correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd2Si2 represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix.
Title:
Exploring the magnetic phase diagram of dysprosium with neutron diffraction
Authors:
Yu, J; LeClair, PR; Mankey, GJ; Robertson, JL; Crow, ML; Tian, W Author Full Names: Yu, J.; LeClair, P. R.; Mankey, G. J.; Robertson, J. L.; Crow, M. L.; Tian, W.
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.014404 JAN 5 2015
Abstract:
With one of the highest intrinsic magnetic moments (10.6 mu(B)/atom) among the heavy rare-earth elements, dysprosium exhibits a rich magnetic phase diagram, including several modulated magnetic phases. Aided by the Ruderman-Kittel-Kasuya-Yosida interaction, the magnetic modulations propagate coherently over a long range. Neutron diffraction experiments were performed to determine the microscopic magnetic origin of the field induced phases in bulk Dy as a function of temperature, covering regions of the well-known ferromagnetic, helical antiferromagnetic, fan phases, and several possible new phases suggested by previous studies. A short-range ordered fan phase was identified as the intermediate state between ferromagnetism and long-range ordered fan. In a field of 1 T applied along the a axis, the temperature range of a coexisting helix/fan phase was determined. The magnetic phase diagram of Dy was thus refined to include the detailed magnetic origin and the associated phase boundaries. Based on the period of the magnetic modulation and the average magnetization, the evolution of the spin arrangement upon heating was derived quantitatively for the modulated magnetic phases.
Title:
Coupling between an incommensurate antiferromagnetic structure and a soft ferromagnet in the archetype multiferroic BiFeO3/cobalt system
Authors:
Elzo, M; Moubah, R; Blouzon, C; Sacchi, M; Grenier, S; Belkhou, R; Dhesi, S; Colson, D; Torres, F; Kiwi, M; Viret, M; Jaouen, N Author Full Names: Elzo, Marta; Moubah, Reda; Blouzon, Camille; Sacchi, Maurizio; Grenier, Stephane; Belkhou, Rachid; Dhesi, Sarnjeet; Colson, Dorothee; Torres, Felipe; Kiwi, Miguel; Viret, Michel; Jaouen, Nicolas
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.014402 JAN 5 2015
Abstract:
Multiferroic materials are mostly antiferromagnets, often containing incommensurate magnetic arrangements stemming from the magnetoelectric interaction. Using soft x-ray resonant magnetic scattering, we show that these long-range structures induce a magnetization wriggle in cobalt layers deposited on top of BiFeO3 single crystals. This is understood using a simple interface exchange interactions model. It leads to the appearance of a magnetic anisotropy axis, which, in the particular BiFeO3/Co system, can be manipulated using an electric field. More generally, it is demonstrated here that through interfacial magnetic exchange, antiferromagnets can leave an imprint revealing some of their hidden properties, thus providing much richer effects than mere exchange bias.
Title:
Modulated spin structure responsible for the magnetic-field-induced polarization switching in multiferroic TbMn2O5
Authors:
Lee, JH; Jang, HM Author Full Names: Lee, Jung-Hoon; Jang, Hyun Myung
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.014403 JAN 5 2015
Abstract:
Orthorhombic TbMn2O5 (o-TMO) is a well-known multiferroic manganite with the remarkable property of polarization switching at 3 K under a bias magnetic (H) field along the a axis of Pb2(1)m. To theoretically account for this outstanding observation, we have proposed a modulated spin structure under the saturated bias H field by considering the relative strength of the three relevant exchange parameters in o-TMO. The proposed modulated structure based on density-functional theory (DFT) calculations is described in terms of the spin angle phi between the neighboring Mn4+-Mn3+ spin moments on the a-b plane. We have shown that the computed DFT polarization plotted as a function of f satisfactorily accounts for the observed H-field-induced polarization switching. We have further theoretically shown that the square of the critical field strength (H-c) needed for the polarization switching is inversely proportional to the degree of the extrinsic magnetoelectric coupling. The computed partial charge density demonstrates that the H-field-induced polarization switching also accompanies with the switching in the sign of the excess valence-electron density.
Title:
Molecular disorder effects in the thermal conductivity of solid thiophene
Authors:
Vdovichenko, GA; Krivchikov, AI; Korolyuk, OA; Romantsova, OO Author Full Names: Vdovichenko, G. A.; Krivchikov, A. I.; Korolyuk, O. A.; Romantsova, O. O.
Source:
LOW TEMPERATURE PHYSICS, 40 (12):1112-1115; 10.1063/1.4904001 DEC 2014
Abstract:
The temperature dependence of the thermal conductivity kappa(T) of solid thiophene is measured in a sequence of stable orientationally disordered phases with different degrees of orientational ordering of the molecules: in orientational glass (V-g); in phase V with large angular librational molecular vibrations; in incommensurate phase IV with a static orientational disorder; and in orientationally disordered crystalline phase III with dynamic orientational disorder of the molecules. Measurements are made at the saturated vapor pressure in a temperature range of 2-180 K. It is found that the thermal conductivity of thiophene is practically independent of temperature in phases III and V with dynamic orientational disorder of the molecules. In the orientational glass state and in the incommensurate state, the temperature dependence of the thermal conductivity of thiophene has a form typical of crystals with a long-range orientational order. A distinct hysteresis of the thermal conductivity is found at temperatures slightly below the temperature of the transition from phase IV into phase V. (C) 2014 AIP Publishing LLC.

Update: 12-Feb-2015

Title:
Magnetic and structural phase transitions and the tetragonality of thermoelastic martensite in quasi-binary Heusler alloys Ni2+x Mn1-x Ga
Authors:
Pushin, VG; Kourov, NI; Korolev, AV; Marchenkova, EB; Kuranova, NN; Belosludtseva, ES Author Full Names: Pushin, V. G.; Kourov, N. I.; Korolev, A. V.; Marchenkova, E. B.; Kuranova, N. N.; Belosludtseva, E. S.
Source:
PHYSICS OF THE SOLID STATE, 57 (1):45-52; 10.1134/S1063783415010242 JAN 2015
Abstract:
This paper reports on the results of investigations into the structure of martensite and the electronic and magnetic properties of Ni2 + x Mn1 - x Ga alloys in the concentration range 0.12 a parts per thousand currency sign x a parts per thousand currency sign 0.39. The concentration dependences of the critical temperatures and the anomalous behavior of the degree of tetragonal distortion of the martensite have been discussed, as well as the changes in the parameters characterizing the electronic and magnetic subsystems in the thermoelastic martensitic transition L2(1) a dagger' M, which occurs in atomically ordered L2(1)-type alloys upon doping in the range 0.12 a parts per thousand currency sign x a parts per thousand currency sign 0.39 at different temperatures. The temperature and concentration dependences of the magnetic properties have been determined for the state of the single-phase L2(1) austenite (at T > T (C) and A (f)) and martensite (at T > T (C) and M (f)), which undergoes the transition from a modulated 10M- or 14M-type structure to a nonmodulated (NM) tetragonal structure.
Title:
The Synthesis, Structure, and Electrical Characterization of (SnSe)(1.2)TiSe2
Authors:
Merrill, DR; Moore, DB; Ditto, J; Sutherland, DR; Falmbigl, M; Winkler, M; Pernau, HF; Johnson, DC Author Full Names: Merrill, Devin R.; Moore, Daniel B.; Ditto, Jeffrey; Sutherland, Duncan R.; Falmbigl, Matthias; Winkler, Markus; Pernau, Hans-Fridtjof; Johnson, David C.
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, (1):83-91; 10.1002/ejic.201402814 JAN 2015
Abstract:
(SnSe)(1.2)TiSe2 was found to self-assemble from a precursor containing modulated layers of Sn-Se and Ti-Se over a surprisingly large range of layer thicknesses and compositions. The constituent lattices form an alternating layer superstructure with rotational disorder present between the layers. This compound was found to have the highest Seebeck coefficient measured for analogous TiX2 containing misfit layered compounds to date, suggesting potential for low-temperature thermoelectric applications. Electrical characterization suggests that electrons transferred from SnSe to TiSe2 are responsible for the higher carrier concentration observed relative to bulk TiSe2. The transfer of charge from one constituent to the other may provide a mechanism for doping layered dichalcogenides for various applications without negatively affecting carrier mobility.
Title:
Very large thermal rectification in bulk composites consisting partly of icosahedral quasicrystals
Authors:
Takeuchi, T Author Full Names: Takeuchi, Tsunehiro
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (6):10.1088/1468-6996/15/6/064801 DEC 2014
Abstract:
The bulk thermal rectifiers usable at a high temperature above 300 K were developed by making full use of the unusual electron thermal conductivity of icosahedral quasicrystals. The unusual electron thermal conductivity was caused by a synergy effect of quasiperiodicity and by a narrow pseudogap at the Fermi level. The rectification ratio, defined by TRR = vertical bar J(large)vertical bar/vertical bar J(small)vertical bar, reached vary large values exceeding 2.0. This significant thermal rectification would lead to new practical applications for the heat management.

Update: 5-Feb-2015

Title:
Microstructure evolution and mechanical properties of quasicrystal-reinforced Mg-Zn-Gd alloy processed by cyclic extrusion and compression
Authors:
Tian, Y; Huang, H; Yuan, GY; Ding, WJ Author Full Names: Tian, Yuan; Huang, Hua; Yuan, Guangyin; Ding, Wenjiang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 626 42-48; 10.1016/j.jallcom.2014.11.167 MAR 25 2015
Abstract:
Mg-1.5Zn-0.25Gd (at.%) alloy reinforced by icosahedral quasicrystalline phase (I-phase) was fabricated and subjected to cyclic extrusion and compression (CEC) at 350 degrees C to investigate the microstructure evolution during CEC and its effect on the mechanical properties. It is observed that, during CEC, the microstructure of the alloy was greatly refined by dynamic recrystallization (DRX), large numbers of I-phase particles precipitated and then grew up, the texture of the alloy was obviously weakened. These changes in microstructure improved the mechanical properties of the alloy significantly and the alloy processed by 8 passes CEC exhibited outstanding plasticity of 31.4% and moderate yield strength of 161 MPa. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Substitution rules for icosahedral quasicrystals
Authors:
Madison, AE Author Full Names: Madison, Alexey E.
Source:
RSC ADVANCES, 5 (8):5745-5753; 10.1039/c4ra09524c 2015
Abstract:
An original well-defined substitution algorithm on how to construct the icosahedral packings is proposed, simple inflation/deflation rules for icosahedral quasicrystals are described, and natural local matching rules are derived.

Update: 29-Jan-2015

Title:
The modulated antiferromagnetic structures in multiferroic FeVO4: A Fe-57 Mossbauer spectroscopy investigation
Authors:
Colson, D; Forget, A; Bonville, P Author Full Names: Colson, D.; Forget, A.; Bonville, P.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 378 529-534; 10.1016/j.jmmm.2014.11.078 MAR 15 2015
Abstract:
We present an investigation of the two incommensurate magnetic phases in the multiferroic material FeVO4 using magnetic susceptibility and Fe-57 Mossbauer spectroscopy measurements. The susceptibility shows anomalies at the phase transitions at 15.7 and 23 K. We devise Mossbauer lineshapes appropriate for planar elliptical and collinear modulated magnetic structures and show that they reproduce very well the Mossbauer spectra in FeVO4, in full qualitative agreement with a previous neutron diffraction study. Quantitatively, our spectra provide precise determinations of the characteristics of the elliptical and modulated structures which match rather well the neutron diffraction results. We find that the hyperfine field elliptical modulation persists as T -> 0, which we attribute to an anisotropy of the hyperfine interaction since a moment modulation is forbidden at T=0 for a spin only ion like Fe3+. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Crystal Structure of Superconducting 1/1 Cubic Au-Ge-Yb Approximant with Tsai-Type Cluster
Authors:
Deguchi, K; Nakayama, M; Matsukawa, S; Imura, K; Tanaka, K; Ishimasa, T; Sato, NK Author Full Names: Deguchi, Kazuhiko; Nakayama, Mika; Matsukawa, Shuya; Imura, Keiichiro; Tanaka, Katsumasa; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (1):10.7566/JPSJ.84.015002 JAN 15 2015
Abstract:
We report the synthesis of a single-phase sample of the superconducting crystalline approximant Au64.0Ge22.0Yb14.0 and present a structure model refined by Rietveld analysis for X-ray diffraction data.
Title:
Semimetallic Band Structure and Cluster-Based Description of a Cubic Quasicrystalline Approximant in the Al-Cu-Ir System
Authors:
Kitahara, K; Takagiwa, Y; Kimura, K Author Full Names: Kitahara, Koichi; Takagiwa, Yoshiki; Kimura, Kaoru
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (1):10.7566/JPSJ.84.014703 JAN 15 2015
Abstract:
Density functional calculations were performed for a cubic quasicrystalline approximant in the Al-Cu-Ir system. A semimetallic band structure was developed and analyzed on the basis of Wannier functions constructed from the valence and a part of the conduction band manifold. The Wannier functions were s-and p-like orbitals centered on either the centers of conventional clusters or the icosahedron-like vertices of pseudo-Mackay clusters, and d-like orbitals centered on the transition metals. Grouping the orbitals according to their center, we considered a small cluster for each group of the orbitals. Most of the orbitals contribute to the density of states only within the valence bands, i.e., they are valence states. The exceptions are some of p-like orbitals centered on the icosahedron-like vertices of the pseudo-Mackay clusters, and they contribute to both valence and conduction bands. Each of these p-like orbitals forms a covalent bond with one centered on the neighboring small cluster. The resulting bonding and antibonding orbitals are valence and conduction states, respectively. The number of valence bands (173) of our Al39Cu8Ir15 model was then decomposed in terms of the numbers of transition metals (23), clusters (16), and covalent bonds between the clusters (6) as 23 x 5 + 16 x 4 -6 = 173. The description for the valence-band formation may also be applicable to some of the group 13 element-transition metal intermetallic compounds, such as RuAl2.
Title:
Detailed study of the magnetic ordering in FeMnP0.75Si0.25
Authors:
Hoglin, V; Hudl, M; Caron, L; Beran, P; Solby, MH; Nordblad, P; Andersson, Y; Sahlberg, M Author Full Names: Hoglin, Viktor; Hudl, Matthias; Caron, Luana; Beran, Premysl; Solby, Magnus H.; Nordblad, Per; Andersson, Yvonne; Sahlberg, Martin
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 221 240-246; 10.1016/j.jssc.2014.10.013 JAN 2015
Abstract:
Magnetic and crystallographic properties of FeMnP0.75Si0.25 in the hexagonal Fe2P-type structure have been investigated by X-ray powder diffraction, neutron powder diffraction and magnetic measurements. The room temperature diffractograms reveal co-existence of two distinct structural phases in the samples with small, but significant, differences only in the unit cell dimensions. The volume ratio between the two phases is governed by the annealing conditions. One of the phases orders ferromagnetically (T-C=250 K) and the other in an incommensurate antiferromagnetic structure at low temperatures (q(x) = 0.363(1), T-N=150 K). (C) 2014 Elsevier Inc. All rights reserved.
Title:
Multiple twins of a decagonal approximant embedded in S-Al2CuMg phase resulting in pitting initiation of a 2024Al alloy
Authors:
Wang, J; Zhang, B; Zhou, YT; Ma, XL Author Full Names: Wang, J.; Zhang, B.; Zhou, Y. T.; Ma, X. L.
Source:
ACTA MATERIALIA, 82 22-31; 10.1016/j.actamat.2014.09.001 JAN 1 2015
Abstract:
The pitting of Al-Cu-Mg alloy is believed to originate from the local dissolution of S-Al2CuMg particles, and the dissolution activity differs from one particle to another. Nevertheless, the initial site where the dissolution of the S phase preferentially occurs and the cause of the heterogeneity in the electrochemical dissolution activity remain unknown, hindering our understanding of pitting initiation of Al-Cu-Mg alloys. In this work, we have applied in situ ex-environmental transmission electron microscopy and identified a large number of nanosized Al20Cu2Mn3 approximants of the decagonal quasicrystal embedded in the S phase. We find that the S phase with Al20Cu2Mn3 inclusions is more active than those free of the approximants. Such a preference is clarified to result from the decomposition of Al20Cu2Mn3 approximant prior to the dissolution of the S phase. In addition, we also find that the electrochemical behavior of Al20Cu2Mn3 approximants is different. The approximants with multiple twins are more active than those with few planar defects. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
New RMnO3+delta (R=Y, Ho; delta approximate to 0.35) phases with modulated structure
Authors:
Parkkima, O; Malo, S; Hervieu, M; Rautama, EL; Karppinen, M Author Full Names: Parkkima, Outi; Malo, Sylvie; Hervieu, Maryvonne; Rautama, Eeva-Leena; Karppinen, Maarit
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 221 109-115; 10.1016/j.jssc.2014.09.012 JAN 2015
Abstract:
A series of hexagonal RMnO3 (R=Y, Ho-Lu) compounds are first annealed in various highly oxidizing conditions to show that for the largest R constituents, Y and Ho, it is possible to load the phases with large amounts of excess oxygen. Within the oxygen-annealed samples we identify new heavily-oxygenated phases, that is, YMnO3.33 and HoMnO3.34. The former is then thoroughly characterized by thermogravimetric analysis, X-ray diffraction and electron diffraction. These studies evidence a hexagonal sub-cell (a(s) approximate to 3.578 angstrom (a(H)/root 3), c(S)approximate to 11.18 angstrom, space group P6(3)mc) and satellites, associated with two modulation vectors q(1)(->*)approximate to 0.41 a(S)(->*)+ 0.41 b(S)(->*)+1/3 c(S)(->*) and q(2)(->*) = (1/2). The results are interpreted by the formation of a modulated composite structure, resulting from the evolution of the hexagonal parent YMnO3+delta structure toward a reduced pyrochlore-type structure Y2Mn2O7-x, in long-and short-range ordering. (C) 2014 Elsevier Inc. All rights reserved.
Title:
Closely related magnetic and dielectric transitions in the "114" magnetoelectric Zn-doped CaBaCo4O7
Authors:
Seikh, MM; Caignaert, V; Suard, E; Meher, KRSP; Maignan, A; Raveau, B Author Full Names: Seikh, Md Motin; Caignaert, V.; Suard, E.; Meher, K. R. S. Preethi; Maignan, A.; Raveau, B.
Source:
JOURNAL OF APPLIED PHYSICS, 116 (24):10.1063/1.4905033 DEC 28 2014
Abstract:
We report on the impact of zinc doping upon the magneto-electric properties of CaBaCo4O7. We show that the presence of less than 1% Zn at the Co sites decreases T-C from 64K to 48K and generates two magnetic transitions, concomitant with changes of slope of dielectric permittivity, at 54K and 77K, respectively. Powder neutron diffraction and magnetic data show the existence of an incommensurate magnetic phase and a spin-flop transition in this temperature range. The crossover of the magnetodielectric effect of this oxide, from positive below 50K to negative above this temperature emphasizes the primordial role of the incommensurate magnetic phase in the evolution of these properties. (C) 2014 AIP Publishing LLC.
Title:
Tiling Phosphorene
Authors:
Guan, J; Zhu, Z; Tomanek, D Author Full Names: Guan, Jie; Zhu, Zhen; Tomanek, David
Source:
ACS NANO, 8 (12):12763-12768; 10.1021/nn5059248 DEC 2014
Abstract:
We present a scheme to categorize the structure of different layered phosphorene allotropes by mapping their nonplanar atomic structure onto a two-color 2D triangular tiling pattern. In the buckled structure of a phosphorene monolayer, we assign atoms in top positions to dark tiles and atoms in bottom positions to light tiles. Optimum sp(3) bonding is maintained throughout the structure when each triangular tile is surrounded by the same number N of like-colored tiles, with 0 = N = 2. Our ab initio density functional calculations indicate that both the relative stability and electronic properties depend primarily on the structural index N. The proposed mapping approach may also be applied to phosphorene structures with nonhexagonal rings and 2D quasicrystals with no translational symmetry, which we predict to be nearly as stable as the hexagonal network.
Title:
Spatial control of functional properties via octahedral modulations in complex oxide superlattices
Authors:
Moon, EJ; Colby,; Wang, Q; Karapetrova, E; Schleputz, CM; Fitzsimmons, MR; May, SJ Author Full Names: Moon, E. J.; R., Colby; Wang, Q.; Karapetrova, E.; Schlepuetz, C. M.; Fitzsimmons, M. R.; May, S. J.
Source:
NATURE COMMUNICATIONS, 5 10.1038/ncomms6710 DEC 2014
Abstract:
Control of atomic structure, namely the topology of the corner-connected metal-oxygen octahedra, has emerged as an important route to tune the functional properties at oxide interfaces. Here we investigate isovalent manganite superlattices (SLs), [(La0.7Sr0.3MnO3) n/(Eu0.7Sr0.3MnO3) n] x m, as a route to spatial control over electronic bandwidth and ferromagnetism through the creation of octahedral superstructures. Electron energy loss spectroscopy confirms a uniform Mn valence state throughout the SLs. In contrast, the presence of modulations of the MnO6 octahedral rotations along the growth direction commensurate with the SL period is revealed by scanning transmission electron microscopy and X-ray diffraction. We show that the Curie temperatures of the constituent materials can be systematically engineered via the octahedral superstructures leading to a modulated magnetization in samples where the SL period is larger than the interfacial octahedral coupling length scale, whereas a single magnetic transition is observed in the short-period SLs.
Title:
Magnetic structure and domain conversion of the quasi-2D frustrated antiferromagnet CuCrO2 probed by NMR
Authors:
Sakhratov, YA; Svistov, LE; Kuhns, PL; Zhou, HD; Reyes, AP Author Full Names: Sakhratov, Yu A.; Svistov, L. E.; Kuhns, P. L.; Zhou, H. D.; Reyes, A. P.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 119 (5):880-890; 10.1134/S1063776114110181 NOV 2014
Abstract:
We have carried out Cu-63,Cu-65 NMR spectra measurements in a magnetic field up to about 15.5 T on a single crystal of the multiferroic triangular-lattice antiferromagnet CuCrO2. The measurements were performed for perpendicular and parallel orientations of the magnetic field with respect to the c axis of the crystal, and the detailed angle dependence of the spectra on the magnetic field direction in the ab plane was studied. The shape of the spectra can be well described in the model of spiral spin structure proposed by recent neutron diffraction experiments. When the field is rotated perpendicular to the crystal c axis, we observed, directly for the first time, a remarkable reorientation of the spin plane simultaneous with rotation of the incommensurate wavevector, by quantitatively deducing the conversion of the energetically less favorable domain to a more favorable one. At high enough fields parallel to the c axis, the data are consistent with either a field-induced commensurate spiral magnetic structure or an incommensurate spiral magnetic structure with a disorder in the c direction, suggesting that high fields may have influence on interplanar ordering.
Title:
Modeling quasi-lattice with octagonal symmetry
Authors:
Girzhon, VV; Smolyakov, OV; Zakharenko, MI Author Full Names: Girzhon, V. V.; Smolyakov, O. V.; Zakharenko, M. I.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 119 (5):854-860; 10.1134/S1063776114110053 NOV 2014
Abstract:
We prove the possibility to use the method of modeling of a quasi-lattice with octagonal symmetry similar to that proposed earlier for the decagonal quasicrystal. The method is based on the multiplication of the groups of basis sites according to specified rules. This model is shown to be equivalent to the method of the periodic lattice projection, but is simpler because it considers merely two-dimensional site groups. The application of the proposed modeling procedure to the reciprocal lattice of octagonal quasicrystals shows a fairly good matching with the electron diffraction pattern. Similarly to the decagonal quasicrystals, the possibility of three-index labeling of the diffraction reflections is exhibited in this case. Moreover, the ascertained ratio of indices provides information on the intensity of diffraction reflections.
Title:
Single-Crystal Neutron Diffraction Study of Superstructure Ordering and Domain Behaviour in Brownmillerite-Type Ca2Fe2O5
Authors:
Auckett, JE; Studer, AJ; Ling, CD Author Full Names: Auckett, Josie E.; Studer, Andrew J.; Ling, Chris D.
Source:
AUSTRALIAN JOURNAL OF CHEMISTRY, 67 (12):1824-1828; 10.1071/CH14358 2014
Abstract:
We show that large single crystals of brownmillerite-type Ca2Fe2O5 can be grown using the floating-zone method under ambient pressure conditions, provided that the feed rods are pre-annealed to a very high density. Neutron diffraction data collected from these crystals show the emergence of a long-range ordered incommensurate phase at high temperature. The observation of this phase for the first time using neutrons proves that the incommensurate ordering of tetrahedral chains upon heating Ca2Fe2O5 is a truly long-range and bulk phenomenon. The results are used to compare and contrast the structures of Ca2Fe2O5 and Sr2Fe2O5, and are consistent with experimental observations of significantly higher oxide ionic conduction in the latter material.

Update: 21-Jan-2015

Title:
The creation of modulated monoclinic aperiodic composites in n-alkane/urea compounds
Authors:
Mariette, C; Guerin, L; Rabiller, P; Chen, YS; Bosak, A; Popov, A; Hollingsworth, MD; Toudic, B Author Full Names: Mariette, Celine; Guerin, Laurent; Rabiller, Philippe; Chen, Yu-Sheng; Bosak, Alexei; Popov, Alexander; Hollingsworth, Mark D.; Toudic, Bertrand
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):5-11; 10.1515/zkri-2014-1773 JAN 2015
Abstract:
n-Dodecane/urea is a member of the prototype series of n-alkane/urea inclusion compounds. At room temperature, it presents a quasi-one dimensional liquid-like state for the confined guest molecules within the rigid, hexagonal framework of the urea host. At lower temperatures, we report the existence of two other phases. Below T-c=248 K there appears a phase with rank four superspace group P6(1)22(00 gamma), the one typically observed at room temperature in n-alkane/urea compounds with longer guest molecules. A misfit parameter, defined by the ratio gamma=C-h/C-g (C-host/C-guest), is found to be 0.632 +/- 0.005. Below T-c1=123 K, a monoclinic modulated phase is created with a constant shift along c of the guest molecules in adjacent channels. The maximal monoclinic space group for this structure is P12(1)1(alpha 0 gamma). Analogies and differences with n-heptane/urea, which also presents a monoclinic, modulated low-temperature phase, are discussed.
Title:
Incommensurate modulations in stoichiometric Ni2MnGa ferromagnetic shape memory alloy: an overview
Authors:
Singh, S; Barman, SR; Pandey, D Author Full Names: Singh, Sanjay; Barman, S. R.; Pandey, Dhananjai
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):13-22; 10.1515/zkri-2014-1784 JAN 2015
Abstract:
This article presents a brief overview of our recent work on the nature of long period modulation in the premartensite and martensite phases of Ni2MnGa ferromagnetic shape memory alloy using high resolution synchrotron x-ray powder diffraction patterns. The commensurate structure model using the Pnnm space group is unable to account for the peak positions of the satellite reflections that appear due to modulations correctly. LeBail and Rietveld refinements using the (3+1)-D super space group Immm(00 gamma)s00 show that the peak positions of all the reflections, including the satellites, can be explained satisfactorily using incommensurate modulations for both the premartensite and martensite phases. The incommensurate modulation vectors are found to be q=0.33761(5)c*=(1/3+delta(1))c* and 0.43160(3)c*=(3/7+delta(2))c*, where delta(1) and delta(2) are the degrees of incommensuration for the premartensite and martensite phases, respectively. The periodicity of the closest rational approximant of the premartensite and martensite phases are confirmed to be 3 M and 7 M, respectively, in agreement with single crystal diffraction results.
Title:
Insights from STEM and NBED studies into the local structure and growth mechanism of misfit layered compounds prepared using modulated reactants
Authors:
Hausler, I; Atkins, R; Falmbigl, M; Rudin, SP; Neumann, W; Johnson, DC Author Full Names: Haeusler, Ines; Atkins, Ryan; Falmbigl, Matthias; Rudin, Sven P.; Neumann, Wolfgang; Johnson, David C.
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):45-54; 10.1515/zkri-2014-1761 JAN 2015
Abstract:
X-ray diffraction and transmission electron microscopy were used to probe the structure of the misfit compound [(SnSe)(1.15)](1)(VSe2)(1) grown using an elementally modulated precursor. The specular X-ray diffraction pattern contained only 00l reflections, which yielded a c lattice parameter of 1.203(1) nm. Cross-section STEM revealed alternating layers of SnSe and VSe2, in agreement with the structure model refined from the X-ray diffraction pattern using Rietveld refinement. Plan-view transmission electron microscopy revealed the in-plane grain structure of the films, yielding grain sizes in agreement with previously reported in plane X-ray diffraction studies and the cross-section STEM images. The plan view images also contained Moire fringes resulting from grains with different relative tilting on both sides of interfaces as well as Moire fringes resulting from different relative rotations between domains. An energy-filtered nano-beam electron diffraction pattern obtained from at least one domain in the [(SnSe)(1.15)](1) (VSe2)(1) sample investigated in cross section contained a series of resolvable supercell reflections along the c axis that indicated that the supercell c-axis lattice parameter was a multiple of three times that determined using X-ray diffraction. Energy filtered NBED of plan-view samples showed diffraction patterns from select regions with 12-fold symmetry, indicating that the arrangement of the layers is not rotationally random from layer to layer. This suggests that during the self-assembly of the amorphous modulated elemental precursor, the SnSe and VSe2 constituent layers must nucleate off the adjacent interfaces of the growing crystal, yielding layers that are locally rotationally aligned with growing crystal. Different processing conditions during the precursor to crystal self-assembly might enable the domain size and/or the extent of order to be controlled.
Title:
The modulated structure of labradorite
Authors:
Boysen, H; Kek, S Author Full Names: Boysen, Hans; Kek, Stefan
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):23-35; 10.1515/zkri-2014-1749 JAN 2015
Abstract:
The crystal structure of labradorite is characterized by two modulation waves with largely different periods of about 1500 angstrom and 50 angstrom, giving rise to s- and e-satellites, respectively. The problems to determine the true structure by diffraction methods are discussed. Since each s-lamella has its own e-modulation, common experiments are not sufficient. Using only s-satellites around main reflections assumes e-averaged structures of the s-lamellae. On the other hand, using only averaged e-satellites and main reflections integrated over the s-satellites leads to a hypothetical, idealised structure such as if there were no s-modulation. For this reason the analysis of an extensive data set, including e-satellites up to third order, cannot resolve the Ca/Na modulation unambiguously, although the Si/Al modulation can be determined consistently from directly refined occupancies and T-O bond lengths.
Title:
LEED studies on modulated surface structures
Authors:
Moritz, W Author Full Names: Moritz, Wolfgang
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):37-43; 10.1515/zkri-2014-1787 JAN 2015
Abstract:
The problems occurring in structure analyses of modulated surfaces by LEED or X-ray diffraction are briefly discussed. In previous LEED studies of modulated surfaces a commensurate unit cell and Fourier coefficients to describe the modulation function has been used. The wave length of the modulation and the size of the supercell are limited in this way by the computational effort of the multiple scattering calculations. To overcome this problem an approximation is proposed allowing the analysis of commensurate or incommensurate surface modulations with long wave lengths.
Title:
Density-wave instabilities of fractionalized Fermi liquids
Authors:
Chowdhury, D; Sachdev, S Author Full Names: Chowdhury, Debanjan; Sachdev, Subir
Source:
PHYSICAL REVIEW B, 90 (24):10.1103/PhysRevB.90.245136 DEC 22 2014
Abstract:
Recent experiments in the underdoped regime of the hole-doped cuprates have found evidence for an incommensurate charge density-wave state. We present an analysis of the charge ordering instabilities in a metal with antiferromagnetic correlations, where the electronic excitations are coupled to the fractionalized excitations of a quantum fluctuating antiferromagnet on the square lattice. The resulting charge density-wave state emerging out of such a fractionalized Fermi liquid (FL*)has wave vectors of the form (+/- Q(0),0),(0, +/- Q(0)), with a predominantly d-form factor, in agreement with experiments on a number of different families of the cuprates. In contrast, as previously shown, the charge density-wave instability of a nearly antiferromagnetic metal with a large Fermi surface, interacting via short-range interactions, has wave vectors of the type (+/- Q(0), +/- Q(0)). Our results show that the observed charge density-wave appears as a low-energy instability of a fractionalized metallic state linked to the proximity to an antiferromagnetic insulator, and the pseudogap regime can be described by such a metal at least over intermediate length and energy scales.
Title:
BaGe6 and BaGe6-x : Incommensurately Ordered Vacancies as Electron Traps
Authors:
Akselrud, L; Wosylus, A; Castillo, R; Aydemir, U; Prots, Y; Schnelle, W; Grin, Y; Schwarz, U Author Full Names: Akselrud, Lev; Wosylus, Aron; Castillo, Rodrigo; Aydemir, Umut; Prots, Yurii; Schnelle, Walter; Grin, Yuri; Schwarz, Ulrich
Source:
INORGANIC CHEMISTRY, 53 (24):12699-12705; 10.1021/ic5021065 DEC 15 2014
Abstract:
We report the high-pressure high-temperature synthesis of the germanium-based framework compounds BaGe6 (P = 15 GPa, T = 1073 K) and BaGe6-x (P = 10 GPa, T = 1073 K) which are metastable at ambient conditions. In BaGe6-x, partial fragmentation of the BaGe6 network involves incommensurate modulations of both atomic positions and site occupancy. Bonding analysis in direct space reveals that the defect formation in BaGe6-x is associated with the establishment of free electron pairs around the defects. In accordance with the electron precise composition of BaGe6-x for x = 0.5, physical measurements evidence semiconducting electron transport properties which are combined with low thermal conductivity.
Title:
Structural phase transition associated with van Hove singularity in 5d transition metal compound IrTe2
Authors:
Qian, T; Miao, H; Wang, ZJ; Shi, X; Huang, YB; Zhang, P; Xu, N; Zeng, LK; Ma, JZ; Richard, P; Shi, M; Xu, G; Dai, X; Fang, Z; Fang, AF; Wang, NL; Ding, H Author Full Names: Qian, T.; Miao, H.; Wang, Z. J.; Shi, X.; Huang, Y. B.; Zhang, P.; Xu, N.; Zeng, L. K.; Ma, J. Z.; Richard, P.; Shi, M.; Xu, G.; Dai, X.; Fang, Z.; Fang, A. F.; Wang, N. L.; Ding, H.
Source:
NEW JOURNAL OF PHYSICS, 16 10.1088/1367-2630/16/12/123038 DEC 15 2014
Abstract:
We have investigated the electronic states of IrTe2 by using angle-resolved photoemission spectroscopy to elucidate the origin of the structural phase transition. Both the Ir 4f and Te 4d core level spectra exhibit dramatic splitting below the phase transition temperature T-s, suggesting that there exist two inequivalent Ir and Te sites with distinctly different electronic states in the distorted phase. The band related to the saddle points at the Fermi level (E-F) is strongly reconstructed, which removes the van Hove singularity from E-F below T-s. The wavevector connecting the adjacent saddle points is consistent with the in-plane superstructure modulation wavevector. These results indicate that the phase transition in IrTe2 is intimately associated with the saddle points. As the van Hove singularity mainly originates from the Te p(x)+p(y) orbitals, the Te 5p electronic states play a dominant role in the structural phase transition.
Title:
Diagnostics of a spatial spin-modulated structure using nuclear magnetic resonance and Mossbauer spectroscopy
Authors:
Rusakov, VS; Pokatilov, VS; Sigov, AS; Matsnev, ME; Gubaidulina, TV Author Full Names: Rusakov, V. S.; Pokatilov, V. S.; Sigov, A. S.; Matsnev, M. E.; Gubaidulina, T. V.
Source:
JETP LETTERS, 100 (7):463-469; 10.1134/S0021364014190102 DEC 2014
Abstract:
Methods of the diagnostics of the spatial spin-modulated structure of the cycloidal type in multiferroics based on nuclear magnetic resonance and Mossbauer spectroscopy have been considered. It has been established that Mossbauer spectroscopy makes it possible to determine the anharmonicity parameter of the spatial spin-modulated structure of the cycloidal type with no worse accuracy than nuclear magnetic resonance with higher resolution. Mossbauer spectroscopy, being sensitive to the hyperfine quadrupole interaction of the nucleus in the excited state, makes it possible to obtain additional information on the features of the spatial spin-modulated structure.
Title:
Effects of Au-Addition on Plastic Deformation Ability of Zr-Cu-Ni-Al Bulk Metallic Glasses
Authors:
Yamada, M; Yamasaki, T; Fujita, K; Yokoyama, Y; Kim, DH Author Full Names: Yamada, Masahiro; Yamasaki, Tohru; Fujita, Kazutaka; Yokoyama, Yoshihiko; Kim, Do Hyang
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 78 (12):449-458; 10.2320/jinstmet.J2014042 DEC 2014
Abstract:
Effects of Au-addition on plastic deformation ability of Zr-Cu-Ni-Al bulk metallic glasses (BMGs) during compression and tensile tests have been examined. Zr65Cu20Ni5Al10 BMG(Zr-65) and Zr60+xCu22-xNi5Al10Au3(x= 0, 5, 6.5, 8, 9 at.) BMGs (Zr60Au3-Zr69Au3) have been prepared by a tilt casting method. By the Au. addition on the BMGs containing Zr. content of 65 at. and more, precipitation of icosahedral quasicrystalline phase (I. phase) in supercooled liquids was observed, resulting in large increase of viscosity in the supercooled liquids. Compression and tensile tests were carried out in these BMGs under various strain rates of 1 similar to 5x10 (4)/s at room temperature. In the compression test of the Zr65 BMG, plastic strain at fracture was about 10. and only several localized shear bands were observed. In the Zr65Au3 and Zr66.5Au3 BMGs, plastic strains at fracture were largely increased to 20. and above. In these cases, initial plastic strains of about 5. with large number of shear band were observed as macroscopically homogeneous deformation, and successive plastic strains along main shear band was observed. In the tensile test, large plastic strain at fracture of about 0.5% was also observed for the Zr66.5Au3 BMG. By transmission electron microscopic observations of the Au. addition BMGs, precipitation of nano. crystallites having about 10 nm in diameter was observed near the fractured surfaces of the compressive and tensile test specimens. Viscosity of supercooled liquids in shear bands was estimated by the stress. drop of serrations in the compressive stress. strain curves. It is considered that the large increase of the plastic strain is due to the drastic increase of the viscosity of the supercooled liquids formed inside shear bands during plastic deformation.
Title:
Spin reorientation and magnetic structure of HoCo12B6 ferrimagnetic compound
Authors:
Diop, LVB; Isnard, O Author Full Names: Diop, L. V. B.; Isnard, O.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (2):10.1088/0953-8984/27/2/026004 JAN 21 2014
Abstract:
The magnetic phase diagram is determined by combining magnetization measurements, ac susceptibility and neutron diffraction. The crystal and magnetic structures are also investigated. The HoCo12B6 compound exhibits ferrimagnetic behavior below T-C = 147 K. Two antiferromagnetically coupled sublattices cancel out at the compensation temperature T-Comp = 46 K. HoCo12B6 undergoes a spin reorientation transition at T-SR = 76 K; the easy magnetization axis changes from axial to basal plane upon heating. The magnitude of the magnetic moments and their orientation are described and discussed. It is revealed that HoCo12B6 compound exhibits a commensurate magnetic structure below T-SR and an incommensurate one slightly above T-SR. Significantly different magnetic moments have been observed on the two Co crystal sites, a very low magnetic moment of 0.14(mu B) being refined on the Co 18 g position. In addition, the second order crystal electric-field parameter A(2)(0) at the rare-earth site is determined. This result is discussed and used to explain the observed spin reorientation transition by a competition between the Co and Ho sublattice anisotropy.

15-Jan-2015

Title:
A modulation wave approach to the order hidden in disorder
Authors:
Withers, R.
Source:
IUCrJ (2015) 2, 74-84
Abstract:
The usefulness of a modulation wave approach to understanding and interpreting the highly structured continuous diffuse intensity distributions characteristic of the reciprocal spaces of the very large family of inherently flexible materials which exhibit ordered `disorder' is pointed out. It is shown that both longer range order and truly short-range order are simultaneously encoded in highly structured diffuse intensity distributions. The long-range ordered crystal chemical rules giving rise to such diffuse distributions are highlighted, along with the existence and usefulness of systematic extinction conditions in these types of structured diffuse distributions.
Title:
Superspace crystallography: a key to the chemistry and properties
Authors:
Pinheiro, C. B; Abakumov, A. M.
Source:
IUCrJ (2015) 2, 137-154
Abstract:
An overview is given of the recent advances in the field of modulated molecular and inorganic crystals with an emphasis on the links between incommensurability, intermolecular and interatomic interactions and, wherever possible, the properties of the materials. The importance of detailed knowledge on the modulated structure for understanding the crystal chemistry and the functional properties of modulated phases is shown using selected examples of incommensurate modulations in organic molecular compounds and inorganic complex oxides.
Title:
Computational self-assembly of a one-component icosahedral quasicrystal
Authors:
Engel, M; Damasceno, PF; Phillips, CL; Glotzer, SC Author Full Names: Engel, Michael; Damasceno, Pablo F.; Phillips, Carolyn L.; Glotzer, Sharon C.
Source:
NATURE MATERIALS, 14 (1):109-116; 10.1038/NMAT4152 JAN 2015
Abstract:
Icosahedral quasicrystals (IQCs) are a form of matter that is ordered but not periodic in any direction. All reported IQCs are intermetallic compounds and either of face-centred-icosahedral or primitive-icosahedral type, and the positions of their atoms have been resolved from diffraction data. However, unlike axially symmetric quasicrystals, IQCs have not been observed in non-atomic (that is, micellar or nanoparticle) systems, where real-space information would be directly available. Here, we show that an IQC can be assembled by means of molecular dynamics simulations from a one-component system of particles interacting via a tunable, isotropic pair potential extending only to the third-neighbour shell. The IQC is body-centred, self-assembles from a fluid phase, and in parameter space neighbours clathrates and other tetrahedrally bonded crystals. Our findings elucidate the structure and dynamics of the IQC, and suggest routes to search for it and design it in soft matter and nanoscale systems.
Title:
ICOSAHEDRAL QUASICRYSTALS Assembled with one component
Authors:
Boissieu, M Author Full Names: de Boissieu, Marc
Source:
NATURE MATERIALS, 14 (1):18-19; 10.1038/nmat4183 JAN 2015
Title:
Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement
Authors:
de Nijs, B; Dussi, S; Smallenburg, F; Meeldijk, JD; Groenendijk, DJ; Filion, L; Imhof, A; van Blaaderen, A; Dijkstra, M Author Full Names: de Nijs, Bart; Dussi, Simone; Smallenburg, Frank; Meeldijk, Johannes D.; Groenendijk, Dirk J.; Filion, Laura; Imhof, Arnout; van Blaaderen, Alfons; Dijkstra, Marjolein
Source:
NATURE MATERIALS, 14 (1):56-60; 10.1038/NMAT4072 JAN 2015
Abstract:
Icosahedral symmetry, which is not compatible with truly long-range order, canbefoundinmany systems, such as liquids, glasses, atomic clusters, quasicrystals and virus-capsids(1-12). To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential(1,3,6-12). Here, we report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometre- and micrometre-sized colloids, as well as computer simulations, we show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favoured over the bulk face-centred cubic crystal structure (13,14). Our findings provide insights into the interplay between confinement and crystallization and into how these are connected to the formation of icosahedral structures.
Title:
Frustration and multicriticality in the antiferromagnetic spin-1 chain
Authors:
Pixley, JH; Shashi, A; Nevidomskyy, AH Author Full Names: Pixley, J. H.; Shashi, Aditya; Nevidomskyy, Andriy H.
Source:
PHYSICAL REVIEW B, 90 (21):10.1103/PhysRevB.90.214426 DEC 15 2014
Abstract:
The antiferromagnetic spin-1 chain has a venerable history and has been thought to be well understood. Here, we show that inclusion of both next-nearest-neighbor (alpha) and biquadratic (beta) interactions results in a rich phase diagram with a multicritical point that has not been observed before. We study the problem using a combination of the density matrix renormalization group (DMRG), an analytic variational matrix product state wave function, and conformal field theory. For negative beta < beta*, we establish the existence of a spontaneously dimerized phase, separated from the Haldane phase by the critical line alpha(c) (beta) of second-order phase transitions. In the opposite regime, beta > beta*, the transition from the Haldane phase becomes first order into the next-nearest-neighbor (NNN) AKLT phase. Based on the field theoretical arguments and DMRG calculations, we find that these two regimes are separated by a multicritical point (beta*, alpha*) of a different universality class, described by the level-4 SU(2) Wess-Zumino-Witten conformal theory. From the DMRG calculations, we estimate this multicritical point to lie in the range -0.2 < beta* < -0.15 and 0.47 < alpha* < 0.53. We further find that the dimerized and NNN-AKLT phases are separated from each other by a line of first-order phase transitions that terminates at the multicritical point. We establish that transitions out of the Haldane phase into the dimer or NNN-AKLT phases are topological in nature and occur either with or without closing of the bulk gap, respectively. We also study short-range incommensurate-to-commensurate transitions in the resulting phase diagram. Inside the Haldane phase, we show the existence of two incommensurate crossovers: the Lifshitz transition and the disorder transition of the first kind, marking incommensurate correlations in momentum and real space, respectively. Notably, these crossover lines stretch across the entire (beta, alpha) phase diagram, merging into a single incommensurate-to-commensurate transition line for negative beta less than or similar to beta* inside the dimer *phase*. This behavior is qualitatively similar to that seen in classical frustrated two-dimensional spin models, by way of the quantum (1+ 1) D to classical 2D correspondence.
Title:
Isothermal section of Mg-rich corner in Mg-Zn-Al ternary system at 335 degrees C
Authors:
Ren, YP; Sun, SN; Wang, LQ; Guo, Y; Li, HX; Li, S; Qin, GW Author Full Names: Ren, Yu-ping; Sun, Shi-neng; Wang, Li-qing; Guo, Yun; Li, Hong-xiao; Li, Song; Qin, Gao-wu
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 24 (11):3405-3412; 10.1016/S1003-6326(14)63483-X NOV 2014
Abstract:
The phase equilibria and compositions at the Mg-rich corner of the Mg-Zn-Al ternary system at 335 degrees C were systemically investigated through the equilibrated alloy method by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with energy dispersive spectroscopy of X-ray (EDS). It is experimentally testified that the alpha-Mg solid solution is not in equilibrium with the Mg-32(Al, Zn)(49) (tau) ternary intermetallic compound or q quasicrystalline phase, but only in equilibrium with one ternary intermetallic compound Al5Mg11Zn4 (phi). The whole composition range of the phi phase was also obtained at 335 degrees C, i.e., 52.5%-56.4% Mg, 13.6%-24.0% Al, 19.6%-33.9% Zn (mole fraction). The solubility of Al in the MgZn phase is remarkably more than that in the Mg7Zn3 phase, and the maximum is about 8.6% Al. Aluminum and zinc are simultaneously soluble in the alpha-Mg solid solution.
Title:
The alpha <-> beta phase transitions of Zn2P2O7 revisited: existence of an additional intermediate phase with an incommensurately modulated structure
Authors:
Stoger, B; Weil, M; Dusek, M Author Full Names: Stoeger, Berthold; Weil, Matthias; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 539-554; SI 10.1107/S205252061401049X 3 JUN 2014
Abstract:
Zn2P2O7 crystallizes in a thortveitite-like structure and features temperature-dependent polymorphism. At high temperatures (T > 500 K), the aristotype phase beta-Zn2P2O7 (C2/m, Z = 2, a similar or equal to 6.60, b similar or equal to 8.28, c similar or equal to 4.53 angstrom, beta similar or equal to 105.4 degrees) is stable. At lower temperatures the lock-in phase alpha(1)-Zn2P2O7 [at 350 K: I2/c, Z = 12, a = 20.1131 (13), b = 8.2769 (6), c = 9.109 (3) angstrom, beta = 106.338 (16)degrees], a sixfold superstructure with commensurate modulation vector q = (1/3, 0, 1/2), is stable. Between the stability ranges of the alpha(1)- and beta-phases exists the intermediate, *incommensurately modulated* alpha(2)-Zn2P2O7 phase with modulation wavevector q similar or equal to (0.33, 0, 0.40) and C2/m(alpha, 0, gamma)0s superspace group symmetry. The alpha(1) -> alpha(2) lock-in phase transition at T-L = 408 K is of first-order and features virtually no hysteresis. It is immediately followed by the second-order alpha(2) -> beta transition to the non-modulated phase at T-I similar or equal to 430 K. This transformation is sluggish and even at T = 500 K very weak satellite reflections of the alpha(2)- phase were observed. Both phase transitions were analyzed with differential scanning calorimetry and high-temperature powder and single-crystal X-ray diffraction. The crystal structures of the alpha(1)- and alpha(2)- phases were refined from single crystal data collected at T = 350, 400, 405, 410, 415, 420, 425, 430, 450 and 500 K. Different models describing the slow transition from the *incommensurately modulated* alpha(2)- to the non-modulated beta-phase were tested. In the model resulting in the best residuals, the bridging O atom of the [P2O7] group, which is located on a 2/m position in the basic structure, is described as an overlap of an atom ordered in internal space and one atom disordered around the mirror plane. The occupancy of the ordered atom decreases with temperature until at T = 500 K virtually only the disordered atom remains. Simultaneously, the amplitude of the modulation functions of the remaining atoms decreases, so that the T = 500 K structure can be considered as the C2/m aristotype structure, although the diffraction pattern still features *satellite reflections* of first order with very low intensities.
Title:
Understanding the structure details when drying hydrate crystals of pharmaceuticals - interpretations from diffuse scattering and inter-modulation satellites of a partially dehydrated crystal
Authors:
Chan, EJ; Gao, Q; Dabros, M Author Full Names: Chan, E. J.; Gao, Q.; Dabros, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 555-567; SI 10.1107/S2052520614005125 3 JUN 2014
Abstract:
Simplified models for the crystal lattice of the sesquihydrate form of the hemi-sulfate salt of (5S, 6S, 9R)-5-amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohepta[b]py ridin9-yl 4-(2-oxo-2,3-dihydro-1H-imidazol[4,5b]pyridin-1-yl)-1piperidine carboxylate (BMS-927711, C28H29F2N6O3+) are used to calculate diffuse diffraction features in order to develop a mechanistic understanding of the dehydration process with respect to disruption of the lattice, since a Bragg model cannot be established. The model demonstrates that what we observe when the water leaves the crystal is partial transformation from the parent form to a child form (a new form, less hydrated and structurally related to the parent). Yet this 'dried' structure is not a pure phase. It consists of semi-random layers of both child, parent and an interfacial layer which has a *modulated structure* that represents a transitory *phase*. Understanding the fact that a single 'dried' crystal can have the disordered layer structure described as well as understanding mechanistic relationships between the phases involved can have implications in understanding the effect of common large scale bulk drying procedures. During the development of BMS-927711, difficulties did arise during characterization of the dried bulk when using only routine solid-state analysis. The material is now better understood from this diffraction study. The diffraction experiments also reveal intermodulation satellites, which upon interpretation yield even more structural information about the crystal transformation. The model suggests the mechanism of transformation is laminar in which layers of the crystal are driven to approach a stable B-centered supercell phase of lower water content.

Update: 8-Jan-2015

Title:
Incommensurate-to-incommensurate phase transition in Eu metal at high pressures
Authors:
Husband, RJ; Loa, I; Munro, KA; McBride, EE; Evans, SR; Liermann, HP; McMahon, MI Author Full Names: Husband, R. J.; Loa, I.; Munro, K. A.; McBride, E. E.; Evans, S. R.; Liermann, H. -P.; McMahon, M. I.
Source:
PHYSICAL REVIEW B, 90 (21):10.1103/PhysRevB.90.214105 DEC 8 2014
Abstract:
High pressure x-ray powder-diffraction experiments were performed on europium metal up to similar to 70 GPa. Above 38 GPa, europium transforms from the incommensurately modulated Eu-IV phase to a second phase with an incommensurately modulated crystal structure, Eu-V. This is a previously unseen incommensurately modulated to incommensurately modulated transition in the elements at high pressure. High-pressure high-temperature experiments were also performed up to 449 K in order to make an initial estimate of the positions of the phase boundaries of the incommensurate phases.
Title:
Toward the Understanding of Modulation in Molecular Materials: Barluenga's Reagent and its Analogues.
Authors:
Kim, Y; Mckinley, EJ; Christensen, KE; Rees, NH; Thompson, AL Author Full Names: Kim, Yejin; Mckinley, Emma J.; Christensen, Kirsten E.; Rees, Nicholas H.; Thompson, Amber L.
Source:
CRYSTAL GROWTH & DESIGN, 14 (12):6294-6301; 10.1021/cg500983s DEC 2014
Abstract:
Investigations into the phase transition of Barluengas reagent revealed a transient incommensurately modulated phase; the structures are presented herein. To understand the origin of the modulated phase and the chemistry that can affect it, analogues of Barluengas reagent were synthesized and studied. In this context, the halogen and anion can easily be exchanged. Studying different analogues led to the development of the Ratchet Model to describe the behavior in the solid state leading to a better understanding of modulation in this class of molecular crystal structure.
Title:
Breakdown of the Fermi arcs in underdoped cuprates by incommensurate charge density waves
Authors:
Gor'kov, LP Author Full Names: Gor'kov, L. P.
Source:
JETP LETTERS, 100 (6):403-406; 10.1134/S0021364014180040 NOV 2014
Abstract:
Interactions between the coherent excitations on disconnected arcs along a "bare" Fermi surface (the socalled Fermi arcs FAs) seen by angle-resolved photo emission spectroscopy (ARPES) in several underdoped (UD) cuprates and incommensurate charge density wave (IC CDW) ordering at lowering of the temperature have been studied. The carriers on FAs scatter strongly on the short-wavelength potential of CDW. The large momentum transfer relates FAs with the electronic states lying deeply under the chemical potential thus involving into consideration the Fermi liquid interactions. At low temperatures IC CDW may fully destroy low lying excitations on the Fermi arcs, leaving electrons on the pocket at the I" point as the only charged elementary excitations in the CDW phase in UD cuprates. The results infer competition between superconducting and CDW order parameters.
Title:
Magnetic shape memory effect and highly mobile twin boundaries
Authors:
Heczko, O Author Full Names: Heczko, O.
Source:
MATERIALS SCIENCE AND TECHNOLOGY, 30 (13A):1559-1578; 10.1179/1743284714Y.0000000599 NOV 2014
Abstract:
The magnetic shape memory effect can be classified as an example of the multiferroic effect combining ferro-elasticity and (ferro) magnetism. After short overview of all known effects the focus is on magnetic field induced structure reorientation (MIR) in the martensite of Ni-Mn-Ga. In this material giant deformations of up to 12% have been observed in moderate magnetic fields. The phenomenology of the effect is first discussed and a model presented. The properties of Ni-Mn-Ga relevant to MIR are then considered. One necessary condition for MIR is a highly mobile twin boundary or interface between two differently oriented martensite variants (ferroelastic domains). In 10M modulated martensite, two types of mobile twin boundary (type I and type II) are observed with complex layered microstructures consisting of a hierarchy of twinning systems. The boundaries strongly differ according to the magnitude and temperature dependence of the twinning stress. Finally, the nature of these boundaries and their different behaviour is reviewed.
Title:
Linear magneto-optical effect in the incommensurate phase of antiferromagnetic LiNiPO4
Authors:
Kharchenko, YM; Miloslavskaya, OV; Kharchenko, MF Author Full Names: Kharchenko, Yu. M.; Miloslavskaya, O. V.; Kharchenko, M. F.
Source:
LOW TEMPERATURE PHYSICS, 40 (11):1029-1031; 10.1063/1.4901407 NOV 2014
Abstract:
A linear magneto-optical effect, birefringence of linearly polarized light that is directly proportional to magnetic field strength, is observed in magnetoelectric crystals of the orthophosphate LiNiPO4. This effect is especially pronounced in the incommensurate antiferromagnetic phase of the crystal. The linear magneto-optical effect indicates that the magnetic symmetry groups of the incommensurate, as well as the commensurate, phases of antiferromagnetic LiNiPO4 lack an anti-inversion operation. This fact is consistent with the existence of ultraweak ferromagnetism in the crystal and indicates that this antiferromagnet has more complicated magnetic structures than those found in neutron diffraction experiments. (C) 2014 AIP Publishing LLC.
Title:
Mechanical Alloying of Al73Cu11Cr16 Alloy from Ion Irradiated Powders
Authors:
Medvedeva, EV; Tcherdyntsev, VV; Makhin'ko, FF; Gushchina, NV; Ovchinnikov, VV Author Full Names: Medvedeva, E. V.; Tcherdyntsev, V. V.; Makhin'ko, F. F.; Gushchina, N. V.; Ovchinnikov, V. V.
Source:
ACTA PHYSICA POLONICA A, 126 (4):979-983; OCT 2014
Abstract:
Al73Cu11Cr16 alloys were prepared by mechanical alloying of the irradiated by Ar+ ions elemental powders. Evolution of alloy structure at ball milling, as well as during the further annealing, was investigated using X-ray diffraction and differential scanning calorimetry. It was shown that ball milling leads to the Cu dissolution in Al and Cr and to the formation of Al2Cu intermetallic phase. An increase of the milling duration leads to an increase of the Al2Cu phase content in the samples. Ion irradiation of initial elemental powders results in an increase of their interaction rate at milling. In the case of irradiated powders using as initial materials, a content of Al2Cu phase after milling is higher than in the case of using non-irradiated elemental powders. No effect of irradiation of initial elemental powders on the phase transformation at heating was observed. The annealing results in the decomposition of Al- and Cr-based supersaturated solid solutions. An increase in the Al2Cu phase content at heating was observed only in the samples, which were milled for 4 h. In the samples milled for 14 h, nearly no increase in Al2Cu phase content at heating was observed. Heating up to 500-600 degrees C results in the single-phase decagonal quasicrystalline phase formation for all of the studied samples.

Update: 1-Jan-2015

Title:
Brillouin scattering, DSC, dielectric and X-ray diffraction studies of phase transitions in antiferroelectric PbHfO3:Sn
Authors:
Maczka, M; Kim, TH; Gagor, A; Jankowska-Sumara, I; Majchrowski, A; Kojima, S Author Full Names: Maczka, Miroslaw; Kim, Tae Hyun; Gagor, Anna; Jankowska-Sumara, Irena; Majchrowski, Andrzej; Kojima, Seiji
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 622 935-941; 10.1016/j.jallcom.2014.11.020 FEB 15 2015
Abstract:
Specific heat, dielectric, powder X-ray diffraction and Brillouin scattering studies of phase transitions in antiferroelectric PbHf0.975Sn0.025O3 crystal were performed. The specific heat data revealed clear anomalies at T-1 = 473.5 and T-2 = 426.3 K on cooling, which could be attributed to onset of first order phase transitions from the paraelectric (PE) phase to an intermediate antiferroelectric phase (AFE2) and the AFE2 phase to another antiferroelectric phase (AFE1), respectively. The estimated entropy changes at T-1 and T-2 pointed to mainly an order-disorder and displacive character of these transitions, respectively. X-ray diffraction data showed a complex superstructure of the intermediate phase with a = 11.895(6) angstrom, b = 11.936(4) angstrom, c = 8.223(3)angstrom at 453 K. Brillouin studies revealed pronounced softening of longitudinal acoustic (LA) mode in the PE phase associated with its broadening. The broadening and softening exhibited maximum values at T-1. Additional acoustic anomalies, that is, abrupt frequency shifts for LA and transverse acoustic (TA) modes were also observed at T-2. Brillouin scattering data also showed presence of a broad central peak (CP) that exhibited highest intensity at T-1. The observed temperature dependences of acoustic modes and CP indicate order-disorder character of the FE to AFE2 phase transition and importance of polar precursor clusters in the PE phase. The obtained data also suggest that the intermediate antiferroelectric phases in Sn4+ doped PbHfO3 and PbZrO3 may have very similar structures with incommensurate modulations. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Atomic structure solution of the complex quasicrystal approximant Al77Rh15Ru8 from electron diffraction data
Authors:
Samuha, S; Mugnaioli, E; Grushko, B; Kolb, U; Meshi, L Author Full Names: Samuha, Shmuel; Mugnaioli, Enrico; Grushko, Benjamin; Kolb, Ute; Meshi, Louisa
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 999-1005; 10.1107/S2052520614022033 6 DEC 2014
Abstract:
The crystal structure of the novel Al77Rh15Ru8 phase (which is an approximant of decagonal quasicrystals) was determined using modern direct methods (MDM) applied to automated electron diffraction tomography (ADT) data. The Al77Rh15Ru8 E-phase is orthorhombic [Pbma, a = 23.40 (5), b = 16.20 (4) and c = 20.00 (5) angstrom] and has one of the most complicated intermetallic structures solved solely by electron diffraction methods. Its structural model consists of 78 unique atomic positions in the unit cell (19 Rh/Ru and 59 Al). Precession electron diffraction (PED) patterns and high-resolution electron microscopy (HRTEM) images were used for the validation of the proposed atomic model. The structure of the E-phase is described using hierarchical packing of polyhedra and a single type of tiling in the form of a parallelogram. Based on this description, the structure of the E-phase is compared with that of the epsilon(6)-phase formed in Al-Rh-Ru at close compositions.
Title:
Field-Induced Spin-Flop in Antiferromagnetic Semiconductors with Commensurate and Incommensurate Magnetic Structures: Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS)
Authors:
Brant, JA; dela Cruz, C; Yao, JL; Douvalis, AP; Bakas, T; Sorescu, M; Aitken, JA Author Full Names: Brant, Jacilynn A.; dela Cruz, Clarina; Yao, Jinlei; Douvalis, Alexios P.; Bakas, Thomas; Sorescu, Monica; Aitken, Jennifer A.
Source:
INORGANIC CHEMISTRY, 53 (23):12265-12274; 10.1021/ic5011693 DEC 1 2014
Abstract:
Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS), which are among the first magnetic semiconductors with the wurtz-kesterite structure, exhibit antiferromagnetism with TN 6 and 4 K, respectively. Both compounds undergo a conventional metamagnetic transition that is accompanied by a hysteresis; a reversible spin-flop transition is dominant. On the basis of constant-wavelength neutron powder diffraction data, we propose that LIGS and LITS exhibit collinear magnetic structures that are commensurate and incommensurate with propagation vectors k(m) = [(1)/(2), (1)/(2), (1)/(2)] and [0, 0, 0.546(1)], respectively. The two compounds exhibit similar magnetic phase diagrams, as the critical fields are temperature-dependent. The nuclear structures of the bulk powder samples were verified using time-of-flight neutron powder diffraction along with synchrotron X-ray powder diffraction. (57)Fe and (119)Sn Mossbauer spectroscopy confirmed the presence of Fe2+ and Sn4+ as well as the number of crystallographically unique positions. LIGS and LITS are semiconductors with indirect and direct bandgaps of 1.42 and 1.86 eV, respectively, according to optical diffuse-reflectance UV-vis-NIR spectroscopy.
Title:
Structure and Magnetic Behaviours of Melt-Spun Ti1.4V0.6Ni Alloy Containing Icosahedral Quasicrystalline Phase
Authors:
Hu, W; Yin, C; Ma, ZY; Liu, WQ; Wang, LM Author Full Names: Hu, W.; Yin, C.; Ma, Z. Y.; Liu, W. Q.; Wang, L. M.
Source:
ASIAN JOURNAL OF CHEMISTRY, 26 (17):5821-5823; A SEP 2014
Abstract:
The ribbons of Ti1.4V0.6Ni and TiVNi alloys were synthesized by arc-melting and subsequent melt-spinning techniques. The structures and magnetic properties were investigated. The results showed that the icosahedral quasicrystal (I-phase), Ti2Ni-type face centered cubic (FCC) phase and body centered cubic (BCC) structural solid solution phase existed in Ti1.4V0.6Ni alloy and the Ti2Ni-type FCC phase and BCC solid solution phase presented in TiVNi alloy. The relationships of M-H (magnetization -magnetic field) and M-T (magnetization-temperature) of the alloy ribbons were investigated by using SQUID (superconductivity quantum interference device). The results demonstrated that the magnetic behaviour was different, which is the Ti1.4V0.6Ni alloy ribbons exhibited higher ferromagnetic properties than those of TiVNi alloy ribbons both at 15 and 300 K.

Update: 25-Dec-2014

Title:
In situ transmission electron microscopy investigation of quasicrystal-crystal transformations in Mg-Zn-Y alloys
Authors:
Liu, JF; Yang, ZQ; Ye, HQ Author Full Names: Liu, J. F.; Yang, Z. Q.; Ye, H. Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 621 179-188; 10.1016/j.jallcom.2014.09.177 FEB 5 2015
Abstract:
Evolution of icosahedral quasicrystals (IQC) in Mg-Zn-Y alloys during annealing was investigated by in situ transmission electron microscopy (TEM), in combination with differential thermal analysis and X-ray diffraction. In bulk samples, the IQC phase transformed to face-centered cubic phase W and hexagonal phase H at 720 K and 727 K, respectively. In TEM samples, IQC started to transform to W at 673 K and H at 688 K during heating, and H transformed to W at 623 K on cooling. Quantitative analysis of the in situ transformation process reveals that growth of both H and W is controlled by diffusion, agreeing with the Avrami's model. The transformed products have specific orientation relationships with the parent phases: 3-fold(IQC)//[0001](H)//[111](W) and 2- fold(IQC)//11 (2) over bar0](H)//[0 (1) over bar1](W). The specific orientation relationships are attributed to close structural correlation among icosahedron, distorted icosahedron and cuboctahedron in IQC, H and W phases. The close structure relationship among IQC, H and W phases on the unit-cell level plays an important role in the phase transformations. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Microstructure and tensile properties of as-extruded Mg-Li-ZnGd alloys reinforced with icosahedral quasicrystal phase
Authors:
Zhang, Y; Zhang, J; Wu, GH; Liu, WC; Zhang, L; Ding, WJ Author Full Names: Zhang, Yang; Zhang, Jie; Wu, Guohua; Liu, Wencai; Zhang, Liang; Ding, Wenjiang
Source:
MATERIALS & DESIGN, 66 162-168; 10.1016/j.matdes.2014.10.049 A FEB 5 2015
Abstract:
Mg-Li-Zn-Gd alloys reinforced with icosahedral quasicrystal phase (I-phase) were prepared by casting and deformed by hot extrusion. The microstructure and tensile properties of as-extruded Mg-Li-Zn-Gd alloys were investigated. It is found that I-phase formed in as-cast Mg-Li-Zn-Gd alloys and was broken into small particles during extrusion. After hot extrusion, both alpha-Mg and beta-Li phases were elongated along the extrusion direction. Dynamic recrystallization occurred in as-extruded Mg-Li-Zn-Gd alloys. Compared with Mg-9Li (L9) alloy, the improvement in mechanical properties especially the tensile strength of the as-extruded Mg-Li-Zn-Gd alloys was mainly ascribed to the formation of I-phase and their volume fraction. Moreover, the finely recrystallized grain structure can also attribute to the strength enhancement of the alloy. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
Field dependence of the magnetic structure of TbMn2O5
Authors:
Chatterji, T; Brown, PJ Author Full Names: Chatterji, T.; Brown, P. J.
Source:
JOURNAL OF APPLIED PHYSICS, 116 (20):10.1063/1.4902840 NOV 28 2014
Abstract:
The evolution of the magnetic propagation vector of the magnetically ordered phases of TbMn2O5 has been studied as a function of magnetic field applied parallel to both [010] and [100] axes. The results have been used to construct (H, T) phase diagrams showing the regions of stability of the three distinct phases IC1, C, and IC2 known to exist in zero field. Application of magnetic field along [010] increases the stability range of the commensurate C phase at the expense of the two incommensurate phases IC1 and IC2, whereas applying the field along [100] has the opposite effect. The evolution with field of the magnetic structure of the C phase has been determined from the integrated intensities of sets of magnetic reflections measured with different field values. With the field along [010], there are no significant changes in structure in fields up to 6 T. Applying the field parallel to [100] leads to an apparently continuous increase in the z component of the propagation vector from 0.25 in zero field to approximate to 0.3 in 6 T. This change is accompanied by increasing ferromagnetic polarisation of the Tb sublattices. Polarised neutron measurements made on the fundamental reflections show that there is no significant ferromagnetic polarisation of any the Mn sublattices in fields of up to 6 T. (C) 2014 AIP Publishing LLC.
Title:
Structural Evolution of GdBaCo2O5+delta (delta=7/18) at Elevated Temperatures
Authors:
Ishizawa, N; Asaka, T; Kudo, T; Fukuda, K; Yasuhara, A; Abe, N; Arima, T Author Full Names: Ishizawa, Nobuo; Asaka, Toru; Kudo, Tatsunari; Fukuda, Koichiro; Yasuhara, Akira; Abe, Nobuyuki; Arima, Taka-hisa
Source:
CHEMISTRY OF MATERIALS, 26 (22):6503-6517; 10.1021/cm503132e NOV 25 2014
Abstract:
The structural chemistry of the double-layered perovskite-type gadolinium barium cobaltate, GdBaCo2O5+delta (0 < delta < 1/2), is not well-known, in comparison to the representative end-member phases alpha at delta = 0 and beta at delta = 1/2. This study unveils the structural evolution of the room-temperature stable phase gamma at delta = 7/18, using in situ single-crystal X-ray diffraction at elevated temperatures and electron microscopy. The gamma phase is essentially charge-ordered with Co3+ and Co2+ in a ratio of 8:1 and is incommensurately modulated in the five-dimensional superspace. The approximant of the modulated structure reveals the presence of island-like charge-ordered square cell domains interleaved with a discommensurate zone. The gamma phase underwent a reversible first-order phase transition at similar to 380 K to the commensurate phase beta, without any change in composition at delta = 7/18. The charge ordering of Co in gamma ceased in beta, in combination with a redistribution of oxygen atoms (O3) in the [GdO delta] layer and a change in the spin state of Co. Further heating of beta induced partial oxygen detachment at similar to 700 K, causing a change in d from 7/18 (similar to 0.389) to 0.19 in the nitrogen flow atmosphere. The crystal irreversibly turned into a tetragonal prototypal phase a. A peristaltic oxygen transport mechanism in GdBaCo2O5+delta (0 <= delta <= 1/2) accompanied by electron transfer and resulting in polaronic local structure relaxation is also proposed. This mechanism underpins a usefulness of the compound for application to solid oxide fuel cells as revealed in recent years.

Update: 18-Dec-2014

Title:
Automated effective band structures for defective and mismatched supercells
Authors:
Brommer, P; Quigley, D Author Full Names: Brommer, Peter; Quigley, David
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (48):10.1088/0953-8984/26/48/485501 DEC 3 2014
Abstract:
In plane-wave density functional theory codes, defects and incommensurate structures are usually represented in supercells. However, interpretation of E versus (k) over right arrow band structures is most effective within the primitive cell, where comparison to ideal structures and spectroscopy experiments are most natural. Popescu and Zunger recently described a method to derive effective band structures (EBS) from supercell calculations in the context of random alloys. In this paper, we present bs_sc2pc, an implementation of this method in the CASTEP code, which generates an EBS using the structural data of the supercell and the underlying primitive cell with symmetry considerations handled automatically. We demonstrate the functionality of our implementation in three test cases illustrating the efficacy of this scheme for capturing the effect of vacancies, substitutions and lattice mismatch on effective primitive cell band structures.
Title:
Wear assessment of composite surface layers in Al-6Mg alloy reinforced with AlCuFe quasicrystalline particles: Effects of particle size, microstructure and hardness
Authors:
Mordyuk, BN; Prokopenko, GI; Milman, YV; Iefimov, MO; Grinkevych, KE; Sameljuk, AV; Tkachenko, IV Author Full Names: Mordyuk, B. N.; Prokopenko, G. I.; Milman, Yu. V.; Iefimov, M. O.; Grinkevych, K. E.; Sameljuk, A. V.; Tkachenko, I. V.
Source:
WEAR, 319 (1-2):84-95; 10.1016/j.wear.2014.07.011 NOV 15 2014
Abstract:
Aluminium alloys reinforced with ceramic, intermetallic or quasicrystalline particles can fill the needs of automotive and aerospace industries due to their superior properties. In this paper, near-surface layers in Al-6Mg alloy specimens were modified using an ultrasonic impact treatment (UIT) process, which induces mechanical mixing of matrix and reinforces quasicrystalline (QC) Al63Cu25Fe12 particles to be introduced into a zone of severe plastic deformation. The wear and friction behaviours of the matrix alloy and QC reinforced layers were investigated in quasi-static and dynamic conditions with particular attention to the effects of QC particles size and test type on wear resistance and microhardness of subsurface composite layers in Al-6Mg alloy. XRD and SEM analyses show that the layers of 40-50 mu m dispersed fine QC(F) (0.5-3 mu m) or coarse QC(C) (similar to 15 mu m) particles, with volume fractions V-f of about 9% and 22%, respectively. In comparison to the annealed Al-6Mg alloy, noticeable increment in wear resistance was registered only for the composite layer reinforced with QC(F) particles. On the contrary, the QC(C) particles being fractured at the fabrication process and/or at the wear tests facilitate three-body abrasive wear conditions and deteriorate the wear resistance of the alloy. SEM and confocal laser microscopy show changes in wear mechanism from microcutting/ploughing in the QC(F) reinforced layer to microcracking/fracturing in the case of QC(C) reinforcement. Fine QC(F) particles are preferred for better wear resistance both at the quasi-static and dynamic conditions. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Photocatalytic and magnetic behaviors of BiFeO3 thin films deposited on different substrates
Authors:
Xu, HM; Wang, HC; Shen, Y; Lin, YH; Nan, CW Author Full Names: Xu, Hao-Min; Wang, Huan-Chun; Shen, Yang; Lin, Yuan-Hua; Nan, Ce-Wen
Source:
JOURNAL OF APPLIED PHYSICS, 116 (17):10.1063/1.4901066 NOV 7 2014
Abstract:
Single phase polycrystalline BiFeO3 thin films were grown on three different substrates via chemical solution deposition. Our results indicate that the band gap of as-prepared BiFeO3 films can be tuned (2.02-2.67eV) by the grain size effects caused by the substrates. These BiFeO3 films show good photocatalytic properties by the degradation of Congo red solution under visible-light irradiation (lambda>400 nm). Additionally, weak ferromagnetic behaviors can be observed at room temperature in all the films, which should be correlated to the destruction of the incommensurate cycloid spin structure of BiFeO3 phase and the coexistence of Fe3+ and Fe2+ as confirmed by X-ray photoelectron spectroscopy. (C) 2014 AIP Publishing LLC.
Title:
Formation of less-known structurally complex zeta(b) and orthorhombic quasicrystalline approximant epsilon(n) on solidification of selected Al-Pd-Cr alloys
Authors:
Adamech, M; Cernickova, I; Duriska, L; Kolesar, V; Drienovsky, M; Bednarcik, J; Svoboda, M; Janovec, J Author Full Names: Adamech, M.; Cernickova, I.; Duriska, L.; Kolesar, V.; Drienovsky, M.; Bednarcik, J.; Svoboda, M.; Janovec, J.
Source:
MATERIALS CHARACTERIZATION, 97 189-198; 10.1016/j.matchar.2014.10.001 NOV 2014
Abstract:
The evolution of phases was investigated on cooling of Al71Pd24Cr5, Al73Pd20Cr7, and Al73Pd23Cr4 alloys from 1350 degrees C down to ambient temperature with the rate of 10 degrees C.min(-1). To perform the investigation, differential thermal analysis, synchrotron X-ray powder diffraction, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy were used. In all the investigated alloys structurally complex phases epsilon(n) (epsilon(6) + epsilon(28)) and zeta(b), as well as the delta-phase were identified. Based on the results of differential thermal analysis, sequences of phase transformations were determined. The Al71Pd24Cr4 alloy started to solidify at 1031.4 degrees C through beta. Primary dendrites of zeta(b) were observed in Al73Pd20Cr7 and Al73Pd23Cr4 alloys. In the second step of solidification delta and/or zeta(b) were formed. The peritectic reaction, liquid + zeta(b) + delta -> epsilon(n) + zeta(b) + delta, leading to the formation of the quasicrystalline approximant epsilon(n) (epsilon(6) + epsilon(28)) took place in the final step of solidification at approximately 792 degrees C. (C) 2014 Published by Elsevier Inc.
Title:
Microstructure and compression deformation behavior in the quasicrystal-reinforced Mg-8Zn-1Y alloy solidified under super-high pressure
Authors:
Dong, Y; Lin, XP; Xu, R; Zheng, RG; Fan, ZB; Liu, SJ; Wang, Z Author Full Names: Dong Yun; Lin Xiaoping; Xu Rui; Zheng Runguo; Fan Zhibin; Liu Shijun; Wang Zhe
Source:
JOURNAL OF RARE EARTHS, 32 (11):1048-1055; 10.1016/S1002-0721(14)60182-4 NOV 2014
Abstract:
The microstructure of Mg-8Zn-1Y alloy solidified under super-high pressure was analyzed through X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). And, compression deformation behavior at room-temperature was studied. The results showed that the microstructure of Mg-8Zn-1Y alloy solidified under ambient pressure and super-high pressure was both mainly composed of alpha-Mg and quasicrystal I-Mg3Zn6Y. Solidification under super-high pressure contributed to refining solidified microstructure and changing morphology of the intergranular second phase. The morphology of intergranular second phase (quasicrystal I-Mg3Zn6Y) was transformed from continuous network (ambient pressure) to long island (high pressure) and finally to granular (super-high pressure) with the increase in pressure. The compressive strength, yield strength and rupture strain of the samples solidified under ambient pressure were significantly improved from 262.6 MPa, 244.4 MPa and 13.3% to 437.3 MPa, 368.9 MPa and 24.7% under the pressure of 6 GPa, respectively. Under ambient pressure, cleavage plane on compressive fracture was large and smooth. When it was solidified under the pressure ranging from 4 to 6 GPa, cleavage plane on compressive fracture was small and coarse. In addition, dimple, tear ridge and lobate patterns existed.
Title:
Anti-plane problem analysis for icosahedral quasicrystals under shear loadings
Authors:
Li, W; Chai, YZ Author Full Names: Li Wu; Chai Yu-Zhen
Source:
CHINESE PHYSICS B, 23 (11):10.1088/1674-1056/23/11/116201 NOV 2014
Abstract:
The present paper is concerned with the longitudinal shear elasticity of three-dimensional icosahedral quasicrystals. By virtue of the Dugdale hypothesis along with the method of complex potential theory, it involves two defect problems of the icosahedral quasicrystals. The first one is the calculation of stress intensity factors and the size of the cohesive force zone in a half-infinite crack. Meanwhile, the crack tip tearing displacements can be exactly derived. The other is the demonstration of the generalized stress intensity factors induced by a sharp V-notch as an extension of a crack. The generalized E-integral around the notch tip gives the energy release rate when the V-notch degenerates into a crack. Apart from their own usefulness in carrying out some simplified crack analyses, the results obtained in this work can particularly serve as a basis for fracture mechanics of anti-plane defect problems of icosahedral quasicrystals.
Title:
Tailoring microstructure of Mg-Zn-Y alloys with quasicrystal and related phases for high mechanical strength
Authors:
Singh, A Author Full Names: Singh, Alok
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (4):10.1088/1468-6996/15/4/044803 AUG 2014
Abstract:
The occurrence of a stable icosahedral (i-) phase, which is quasicrystalline with an icosahedral (fivefold) symmetry, on the equilibrium phase diagram of Mg-Zn-RE (RE = Y, Gd, Tb, Dy, Ho or Er) alloys opened up an interesting possibility of developing a new series of magnesium alloys for structural applications. Alloys based on the i-phase have been studied for the past 14 years. Ultra-high strengths combined with good ductility have been shown. Here we show two strategies for tailoring microstructures for very high strengths in Mg-Zn-Y alloys. One of them involves strengthening by a fine distribution of rod-like beta(')(1) precipitates, where the matrix grain size is not critical. The alloy is solutionized at a high temperature of 480 degrees C to dissolve a large part of the i-phase, followed by a high temperature extrusion (similar to 430 degrees C) and a low temperature ageing to reprecipitate phases with fine size distribution. At first, phase transformations involved in this procedure are described. The closeness of the structure of the beta(')(1) precipitates to the i-phase is brought out. By this procedure, tensile yield strengths of over 370 MPa are obtained in grain sizes of 20 mu m. In another strategy, the alloys are chill cast and then extruded at low temperatures of about 250 degrees C. Ultra-fine grains are produced by enhanced recrystallization due to presence of the i-phase. At the same time nano-sized precipitates are precipitated dynamically during extrusion from the supersaturated matrix. Ultra-high tensile strengths of up to 400 MPa are obtained in combination with ductility of 12 to 16%. Analysis of the microstructure shows that strengthening by the i-phase occurs by enhanced recrystallization during extrusion. It produces ultra-fine grain sizes to give very high strengths, and moderate texture for good ductility. Fine distribution of the i-phase and precipitates contribute to strengthening and provide microstructre stability. Ultra-high strength over a very wide range of grain sizes is thus demonstrated, by utilizing different strengthening effects.
Title:
Metallic-covalent bonding conversion and thermoelectric properties of Al-based icosahedral quasicrystals and approximants
Authors:
Takagiwa, Y; Kimura, K Author Full Names: Takagiwa, Yoshiki; Kimura, Kaoru
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (4):10.1088/1468-6996/15/4/044802 AUG 2014
Abstract:
In this article, we review the characteristic features of icosahedral cluster solids, metallic-covalent bonding conversion (MCBC), and the thermoelectric properties of Al-based icosahedral quasicrystals and approximants. MCBC is clearly distinguishable from and closely related to the well-known metal-insulator transition. This unique bonding conversion has been experimentally verified in 1/1-AlReSi and 1/0-Al12Re approximants by the maximum entropy method and Rietveld refinement for powder x-ray diffraction data, and is caused by a central atom inside the icosahedral clusters. This helps to understand pseudogap formation in the vicinity of the Fermi energy and establish a guiding principle for tuning the thermoelectric properties. From the electron density distribution analysis, rigid heavy clusters weakly bonded with glue atoms are observed in the 1/1-AlReSi approximant crystal, whose physical properties are close to icosahedral Al-Pd-TM (TM: Re, Mn) quasicrystals. They are considered to be an intermediate state among the three typical solids: metals, covalently bonded networks (semiconductor), and molecular solids. Using the above picture and detailed effective mass analysis, we propose a guiding principle of weakly bonded rigid heavy clusters to increase the thermoelectric figure of merit (ZT) by optimizing the bond strengths of intra-and intericosahedral clusters. Through element substitutions that mainly weaken the inter-cluster bonds, a dramatic increase of ZT from less than 0.01 to 0.26 was achieved. To further increase ZT, materials should form a real gap to obtain a higher Seebeck coefficient.
Title:
Magnetism in icosahedral quasicrystals: current status and open questions
Authors:
Goldman, AI Author Full Names: Goldman, Alan I.
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (4):10.1088/1468-6996/15/4/044801 AUG 2014
Abstract:
Progress in our understanding of the magnetic properties of R-containing icosahedral quasicrystals (R = rare earth element) from over 20 years of experimental effort is reviewed. This includes the much studied R-Mg-Zn and R-Mg-Cd ternary systems, as well as several magnetic quasicrystals that have been discovered and investigated more recently including Sc-Fe-Zn, R-Ag-In, Yb-Au-Al, the recently synthesized R-Cd binary quasicrystals, and their periodic approximants. In many ways, the magnetic properties among these quasicrystals are very similar. However, differences are observed that suggest new experiments and promising directions for future research.

Update: 11-Dec-2014

Title:
Structural and electrical properties of a new ([SnSe](1.16))(1)(NbSe2)(1) polytype
Authors:
Alemayehu, MB; Falmbigl, M; Grosse, C; Ta, K; Fischer, SF; Johnson, DC Author Full Names: Alemayehu, Matti B.; Falmbigl, Matthias; Grosse, Corinna; Ta, Kim; Fischer, Saskia F.; Johnson, David C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 619 861-868; 10.1016/j.jallcom.2014.09.084 JAN 15 2015
Abstract:
A new polytype of the misfit layer compound ([SnSe](1.16))(1)(NbSe2)(1) with extensive rotational disorder was prepared from designed modulated elemental reactants. This polytype, previously referred to as a ferecrystal due to the extensive rotational disorder, formed over a range of compositions and precursor thicknesses and the resulting c-axis lattice parameters ranged from 1.2210(4) to 1.2360(4) nm. These values bracket the value published for the crystalline misfit layer compound prepared at high temperature. The a- and b-axis in-plane lattice parameters of both the SnSe and NbSe2 constituents were incommensurate, which differs from the misfit layer compound formed via high temperature reaction that has a common b-axis lattice parameter for the two constituents. The in-plane area per unit cell of the ferecrystal is 1-2% larger than the compound formed at high temperature. The ferecrystalline ([SnSe](1.16))(1)(NbSe2)(1) compound is 1.6 times more conductive than the misfit layer compound. Hall effect measurements indicate that the ferecrystal is a p-type metal and that the higher conductivity is a consequence of higher mobility of carriers in the ferecrystalline compound. (C) 2014 Elsevier B.V. All rights reserved.
Title:
The Al-rich region of the Al-Fe-Mn alloy system
Authors:
Balanetskyy, S; Pavlyuchkov, D; Velikanova, T; Grushko, B Author Full Names: Balanetskyy, S.; Pavlyuchkov, D.; Velikanova, T.; Grushko, B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 619 211-220; 10.1016/j.jallcom.2014.08.232 JAN 15 2015
Abstract:
Phase equilibria in the Al-rich region of the Al-Fe-Mn alloy system were studied at 1070, 1020, 950, 875, 800, 740, 695 and 650 degrees C. The continuous region of the bcc solid solution was estimated between the Al-Mn and Al-Fe terminals. Also the isostructural high-temperature Al-Mn and Al-Fe gamma(1)- phases (gamma-brass type structure) form continuous regions. The Al6Mn, high-temperature T-Al11Mn4 and low-temperature gamma(2) phases dissolve up to 9.0, 14.5 and 31.0 at.% Fe, respectively, while the M-Al13Fe4, Al5Fe2 and Al2Fe phases dissolve up to 15.5, 11.5 and 10.0 at.% Mn, respectively. The thermodynamically stable decagonal D-3-phase with periodicity of 1.25 nm in the specific direction and two periodic intermetallics designated phi(P6(3)/mmc; a = 0.7554, c = 0.7872 nm) and kappa (P6(3)/m; a = 1.7630, c = 1.2506 nm) were identified. An additional ternary phase of unknown structure was also revealed. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Neutron and X-ray Scattering Studies of Rb2CoCl4 and Successive Phase Transition in A(2)BX(4)-type Crystals
Authors:
Shigematsu, H; Nishiyama, K; Kawamura, Y; Mashiyama, H Author Full Names: Shigematsu, Hirotake; Nishiyama, Katsura; Kawamura, Yukihiko; Mashiyama, Hiroyuki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 83 (12):10.7566/JPSJ.83.124601 DEC 15 2014
Abstract:
Soft phonon modes, which are related to the normal-incommensurate phase transition at T-i = 294 K and the lowest-temperature phase transition at T-3 = 66 K in Rb2CoCl4, have been measured by inelastic neutron scattering. For the normal-incommensurate phase transition, phonon dispersion curves have been determined in the low-temperature commensurate phases, and the phase mode has been observed far below T-i. The soft mode is fully overdamped above T-i. Moreover, another soft phonon mode, which contributes to the phase transition at T3, has been observed. Furthermore, the space group of the lowest phase is directly confirmed to be C1c1 by verifying extinction rules of X-ray diffraction. It has been recognized that the ratio of the ionic radius of A(+) to the average bond length B-X in the tetrahedral BX42- ion can control the phase transition sequence. Rb2CoCl4 belongs to the group in which this ratio is in the range from 0.69 to 0.85, and the transition temperature decreases loosely with increasing the lattice parameter ratio c(0)/a(0), where a(0) and c(0) are the lattice parameters of the normal phase.
Title:
Controllable 3D morphology and growth mechanism of quasicrystalline phase in directionally solidified Al-Mn-Be alloy
Authors:
Kang, HJ; Wang, TM; Lu, YP; Jie, JH; Li, XZ; Su, YQ; Guo, JJ Author Full Names: Kang, Huijun; Wang, Tongmin; Lu, Yiping; Jie, Jinchuan; Li, Xinzhong; Su, Yanqing; Guo, Jingjie
Source:
JOURNAL OF MATERIALS RESEARCH, 29 (21):2547-2555; 10.1557/jmr.2014.287 NOV 14 2014
Abstract:
Three-dimensional (3D) morphological evolution and growth mechanisms of primary I-phase particles have been investigated in directionally solidified Al-6Mn-2.5Be (wt%) alloy at a wide range of growth rates (100-1500 mu m/s). At relatively low growth rates (100-600 mu m/s), the I-phase particles exhibit faceted growth with strong anisotropy, forming a hierarchical flower-like aggregate with icosahedral morphological symmetry composed of several attached irregular polyhedrons or pentagonal dodecahedrons. At higher growth rates (e.g., 1000 mu m/s), the interface of the I-phases becomes unstable along the edges and corners of the pentagonal dodecahedron, thereby arousing growth perturbations. Correspondingly, a transition from faceted to nonfaceted growth occurs with increasing growth rate. Further increase of the growth rate leads to the formation of I-phase columnar dendrites' preferential growth along the 3-fold axis. The configurations of the flower-like aggregates can be adequately illustrated by a geometrical model in terms of the perfect and elongated pentagonal dodecahedrons. A growth mechanism for the flower-like aggregates has been proposed based on the clear understanding of the 3D morphological evolution of the I-phase particles.
Title:
Commensurate structural modulation in the charge- and orbitally ordered phase of the quadruple perovskite (NaMn3)Mn4O12
Authors:
Prodi, A; Daoud-Aladine, A; Gozzo, F; Schmitt, B; Lebedev, O; van Tendeloo, G; Gilioli, E; Bolzoni, F; Aruga-Katori, H; Takagi, H; Marezio, M; Gauzzi, A Author Full Names: Prodi, A.; Daoud-Aladine, A.; Gozzo, F.; Schmitt, B.; Lebedev, O.; van Tendeloo, G.; Gilioli, E.; Bolzoni, F.; Aruga-Katori, H.; Takagi, H.; Marezio, M.; Gauzzi, A.
Source:
PHYSICAL REVIEW B, 90 (18):10.1103/PhysRevB.90.180101 NOV 10 2014
Abstract:
By means of synchrotron x-ray and electron diffraction, we studied the structural changes at the charge order transition T-CO = 176 K in the mixed-valence quadruple perovskite (NaMn3)Mn4O12. Below T-CO we find satellite peaks indicating a commensurate structural modulation with the same propagation vector q = ( 1/2,0,-1/2) of the CE magnetic structure that orders at low temperatures, similarly to the case of simple perovskites such as La0.5Ca0.5MnO3. In the present case, the modulated structure, together with the observation of a large entropy change at T-CO, gives evidence of a rare case of full Mn3+/Mn4+ charge and orbital order, consistent with the Goodenough-Kanamori model.
Title:
Noncoplanar and Counterrotating Incommensurate Magnetic Order Stabilized by Kitaev Interactions in gamma-Li2IrO3
Authors:
Biffin, A; Johnson, RD; Kimchi, I; Morris, R; Bombardi, A; Analytis, JG; Vishwanath, A; Coldea, R Author Full Names: Biffin, A.; Johnson, R. D.; Kimchi, I.; Morris, R.; Bombardi, A.; Analytis, J. G.; Vishwanath, A.; Coldea, R.
Source:
PHYSICAL REVIEW LETTERS, 113 (19):10.1103/PhysRevLett.113.197201 NOV 6 2014
Abstract:
Materials that realize Kitaev spin models with bond-dependent anisotropic interactions have long been searched for, as the resulting frustration effects are predicted to stabilize novel forms of magnetic order or quantum spin liquids. Here, we explore the magnetism of gamma-Li2IrO3, which has the topology of a three-dimensional Kitaev lattice of interconnected Ir honeycombs. Using magnetic resonant x-ray diffraction, we find a complex, yet highly symmetric incommensurate magnetic structure with noncoplanar and counterrotating Ir moments. We propose a minimal Kitaev-Heisenberg Hamiltonian that naturally accounts for all key features of the observed magnetic structure. Our results provide strong evidence that gamma-Li2IrO3 realizes a spin Hamiltonian with dominant Kitaev interactions.
Title:
Original Crystal-Chemical Behaviors in (Ba,Sr)(2)Ln(Fe,Nb,Ta)(5)O-15 Tetragonal Tungsten Bronze: Anion-Driven Properties Evidenced by Cationic Substitutions
Authors:
Josse, M; Heijboer, P; Albino, M; Molinari, F; Porcher, F; Decourt, R; Michau, D; Lebraud, E; Veber, P; Velazquez, M; Maglione, M Author Full Names: Josse, Michael; Heijboer, Pierre; Albino, Marjorie; Molinari, Flora; Porcher, Florence; Decourt, Rodolphe; Michau, Dominique; Lebraud, Eric; Veber, Philippe; Velazquez, Matias; Maglione, Mario
Source:
CRYSTAL GROWTH & DESIGN, 14 (11):5428-5435; 10.1021/cg5006049 NOV 2014
Abstract:
From room-temperature composite multiferroics to relaxor to ferroelectric crossovers, many original behaviors were recently evidenced in compounds and/or solid solutions related to the Ba(2)LnFeNb(4)O(15) (Ln = rare earth) family of tetragonal tungsten bronze (TTB) materials. We show how an empirical crystal chemistry approach, while yielding unexpected results, allowed for a better understanding of these original and sometimes specific behaviors. A survey of the dielectric properties of four solid solutions derived from the Ba2NdFeNb4O15 ferroelectric TTB is presented. We also show how the diversity of compositions and chemical substitution patterns unveils the anionic driving force behind the relaxor to ferroelectric crossovers. We finally discuss the probable involvement of aperiodic modulations in these crossovers and the fact that these modulations may constitute an additional degree of freedom to control the properties of TTB structured functional materials.
Title:
Twelvefold symmetric quasicrystallography from the lattices F-4, B-6 and E-6
Authors:
Koca, NO; Koca, M; Koc, R Author Full Names: Koca, Nazife O.; Koca, Mehmet; Koc, Ramazan
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 70 605-615; 10.1107/S2053273314015812 6 NOV 2014
Abstract:
One possible way to obtain the quasicrystallographic structure is the projection of the higher-dimensional lattice into two- or three-dimensional subspaces. Here a general technique applicable to any higher-dimensional lattice is introduced. The Coxeter number and the integers of the Coxeter exponents of a Coxeter-Weyl group play a crucial role in determining the plane onto which the lattice is to be projected. The quasicrystal structures display the dihedral symmetry of order twice that of the Coxeter number. The eigenvectors and the corresponding eigenvalues of the Cartan matrix are used to determine the set of orthonormal vectors in n-dimensional Euclidean space which lead to suitable choices for the projection subspaces. The maximal dihedral subgroup of the Coxeter-Weyl group is identified to determine the symmetry of the quasicrystal structure. Examples are given for 12-fold symmetric quasicrystal structures obtained by projecting the higher-dimensional lattices determined by the affine Coxeter-Weyl groups W-a(F-4), W-a(B-6) and W-a(E-6). These groups share the same Coxeter number h = 12 with different Coxeter exponents. The dihedral subgroup D-12 of the Coxeter groups can be obtained by defining two generators R-1 and R-2 as the products of generators of the Coxeter-Weyl groups. The reflection generators R-1 and R-2 operate in the Coxeter planes where the Coxeter element R1R2 of the Coxeter-Weyl group represents the rotation of order 12. The canonical (strip, equivalently, cut-and-project technique) projections of the lattices determine the nature of the quasicrystallographic structures with 12-fold symmetry as well as the crystallographic structures with fourfold and sixfold symmetry. It is noted that the quasicrystal structures obtained from the lattices W-a(F-4) and W-a(B-6) are compatible with some experimental results.
Title:
A study of one-dimensional incommensurate modulated structure determination in high-resolution transmission electron microscopy
Authors:
Li, XM; Ge, BH; Li, FH; Luo, HQ; Wen, HH Author Full Names: Li, Xueming; Ge, Binghui; Li, Fanghua; Luo, Huiqian; Wen, Haihu
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 70 563-571; 10.1107/S2053273314012005 6 NOV 2014
Abstract:
The methods for determining incommensurate modulated structures (IMSs) in high-resolution transmission electron microscopy have been studied and improved to a level more perfect than before. This is demonstrated by means of the IMS determination for Bi2.31Sr1.69CuO6+ as an example. First, as previously, the projected potential map (PPM) of the IMS with resolution 0.2nm was obtained after image deconvolution from a [100] image. Secondly, the resolution of the PPM was enhanced to 0.1nm through phase extension combined with the electron-diffraction data so that the substitutional and displacive modulation functions could be determined. Thirdly, a (2+1)- dimensional structure model that corresponds to the [100] projected IMS was built for calculating the related partial structure factors that were utilized to correct the experimental electron-diffraction intensities for both main and satellite reflections. After three cycles of diffraction-intensity correction and phase extension, all unoverlapped atoms projected along the [100] direction in Bi2.31Sr1.69CuO6+ were resolved, and the modulations of substitution and displacement could be observed clearly. The substitution of Bi for Sr atoms at the Sr(O) columns was seen in the final PPM and verified by high-dimensional image simulation.
Title:
Dielectric Studies of Thiourea, SC(NH2)(2), Embedded into Molecular Sieves
Authors:
Baryshnikov, SV; Charnaya, EV; Milinskiy, AY Author Full Names: Baryshnikov, S. V.; Charnaya, E. V.; Milinskiy, A. Yu.
Source:
FERROELECTRICS, 471 (1):109-117; 10.1080/00150193.2014.963428 OCT 26 2014
Abstract:
Studies of temperature dependences of linear permittivity and third harmonic generation were carried out for ferroelectric thiourea, SC(NH2)(2), particles embedded into molecular sieves SBA-15 and \MC\M-41 with pore sizes of 7.5nm and 4.0nm, respectively. Temperatures of the ferroelectric phase transition and transition from the incommensurate phase into paraphase were shown to be higher than in bulk thiourea. The shifts of the transitions increased with decreasing pore size. Both phase transitions were strongly diffused. The obtained data evidenced that the third harmonic generation can be used to find temperatures of the diffused ferroelectric transition.

Update: 4-Dec-2014

Title:
B19 phase in Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy
Authors:
Song, L; Xu, XJ; You, L; Liang, YF; Lin, JP Author Full Names: Song, L.; Xu, X. J.; You, L.; Liang, Y. F.; Lin, J. P.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 618 305-310; 10.1016/j.jallcom.2014.08.137 JAN 5 2015
Abstract:
The B19 phase is widely observed in the alpha(2) laths in Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy, forming a modulated structure together with the alpha(2) phase. The distortion between the alpha(2) and B19 phases exists only along the [1 (1) over bar 0 0](alpha 2) direction and is very difficult to detect. Thin gamma laths precipitate regularly within the alpha(2) + B19 structure to accommodate the lattice misfit, whereas the sizes of the gamma laths are limited to a small scale. The B19 phase, however, is unstable and was eliminated after annealing at 900 degrees C for 30 min, followed by air-cooling. The pure alpha(2) phase observed in the air-cooled sample is not in the equilibrium state. The B19 phase can be a stable phase in some temperatures below 900 degrees C but be repressed under rapid cooling. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Microstructure of an Al-Mn-Be-B alloy
Authors:
Zupanic, F; Boncina, T Author Full Names: Zupanic, F.; Boncina, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 617 174-179; 10.1016/j.jallcom.2014.07.212 DEC 25 2014
Abstract:
The aim of this work was to determine the effect of boron on the solidification and processes taking place during heat treatment of an Al-Mn-Be-based alloy. Several phases formed upon slow cooling of the investigated alloy Al89Mn2Be2B7: BeB12, AlBeB, T-Al15Mn3Be2, Al6Mn and aluminium solid solution (Al-ss). An icosahedral quasicrystalline phase (IQC) was formed during rapid solidification by melt spinning; partly dissolving Be and B, while the remaining Be and B precipitated as a ternary compound AlBeB. The primary IQC persisted within the microstructure up to 400 degrees C, whilst at temperatures above 450 degrees C the initial microstructure started to transform quickly into AlBeB, Al6Mn and Al-ss, which appeared to be the stable phases below the alloy's solidus temperature. The hardness remained almost unchanged up to 400 degrees C, whilst at temperatures above 450 degrees C it dropped abruptly. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Incommensurate structure of a new Nowotny phase in Fe-Ge system
Authors:
Li, WF; Li, Y; Ma, XL; Zhang, ZD Author Full Names: Li, Wanfeng; Li, Ying; Ma, Xiuliang; Zhang, Zhidong
Source:
MATERIALS CHEMISTRY AND PHYSICS, 148 (3):490-493; 10.1016/j.matchemphys.2014.08.023 DEC 15 2014
Abstract:
We studied post-annealed Fe-Ge alloy by X-ray diffraction and transmission electron microscopy. A new Nowotny chimney ladder phase has been discovered in such Fe-Ge system. The crystal structure and the composition have been calculated based on selected area electron diffraction. The formation of the incommensurate structure is attributed to the shrinkage of the Ge sublattice to meet the 14 electrons rule. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Hydrogen Absorption and Structural Analysis of TiZrNiV Quasicrystals
Authors:
Lee, SH; Jo, Y; Kim, J Author Full Names: Lee, Sang-Hwa; Jo, Youngsoo; Kim, Jaeyong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 14 (12):9373-9376; 10.1166/jnn.2014.10126 DEC 2014
Abstract:
Ti-based quasicrystals are known to store a high capacity of hydrogen exceeding the density of liquid hydrogen. Because TiZrNi quasicrystals contain a large number of tetrahedral sites formed with Ti and Zr atoms that are chemically favorable to hydrogen, these materials retain strong advantages for hydrogen storage applications in structurally and chemically. In fact, TiZrNi quasicrystals are known to absorb hydrogen maximum of the hydrogen to host metal ratio (H/M) value of near 2.0. The critical disadvantage, however, is that the equilibrium vapor pressure of hydrogen is very low (less than 1 Torr). To overcome this engineering drawback, we added a small amount of vanadium (V) in Ti53-XZr27Ni20Vx, alloys (where x = 0 to 15) and rapidly quenched the molten ingots to form quasicrystals, and investigated the effects of V in terms of changes of structure, the H/M values, and an equilibrium vapor pressure of hydrogen. As the results, an equilibrium vapor pressure significantly increased from 0.84 to 2.16 Torr while the maximum H/M value decreased from 1.32 to 1.11 as increasing x = 0 to 8. After hydrogenation, the main peaks shifted evenly to the lower angle of 2 theta in X-ray diffraction patterns with uniform expansion of the quasilattice constants which demonstrates that hydrogen atoms homogeneously diffused into the samples. A Laves phase starts to form at x = 13 and the samples completely transformed to the phase at x = 15 suggesting the similarity between the quasicrystal and the Laves phase.
Title:
The electronic structure and magnetism of CaFeAs2: First principles calculations
Authors:
Wang, GT; Shi, XB; Zhang, L; Yi, X Author Full Names: Wang, Guangtao; Shi, Xianbiao; Zhang, Lin; Yi, Xia
Source:
SOLID STATE COMMUNICATIONS, 200 61-65; 10.1016/j.ssc.2014.09.025 DEC 2014
Abstract:
The electronic structure, magnetism and Fermi surface (FS) nesting of the recently discovered superconductive parent material CaFeAs2 are studied by the first-principles, based on the GGA and GGA+U methods. In the nonmagnetic state, the density of states at the Fermi level are mostly derived from the d(xy), d(yz) and d(zx) orbits, just like LaOFeAs. The Fermi surfaces consist of four hole like FS sheets around the Gamma-point, two electron like sheets near the Brillouin zone corner M-point, and small pockets near X-point. The hole like Fermi surfaces will strongly overlap with the electron like FS sheets, if they are shifted by the q-vector q = (pi, pi, 0). Such FS nesting will induce the magnetic instability and spin density wave (SDW), which has been confirmed to be more stable than other states by the calculated total energy. The calculated bare susceptibility chi(0)(q) peaked at M-point, and was obviously suppressed with the electron doping. This explains the emergence of the superconductivity in the electron-doped compound Ca1-xLaxFeAs2, because the electron doping suppressed the SDW and induced the superconductivity. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
Superspace application on magnetic structure analysis of the Pb2MnWO6 double perovskite system
Authors:
Orlandi, F; Righi, L; Ritter, C; Pernechele, C; Solzi, M; Cabassi, R; Bolzoni, F; Calestani, G Author Full Names: Orlandi, Fabio; Righi, Lara; Ritter, Clemens; Pernechele, Chiara; Solzi, Massimo; Cabassi, Riccardo; Bolzoni, Fulvio; Calestani, Gianluca
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 2 (43):9215-9223; 10.1039/c4tc01450b NOV 21 2014
Abstract:
The commensurate crystal structure of the magnetic phase occurring below 7 K of the multiferroic Pb2MnWO6 perovskite has been solved by the introduction of the superspace approach. This lead based double perovskite is characterized by a complex ferrielectric non-centrosymmetric nuclear structure with orthorhombic symmetry stable in a wide temperature range. As indicated from the analysis of powder neutron diffraction data, the low temperature antiferromagnetic structure showing a propagation vector kappa = [1/4 0 0] is stabilized by a multi-step process involving the evolution from incommensurate to commensurate spin ordering with a concomitant change of the magnetic symmetry. The determination of the Pb2MnWO6 magnetic structure offers a meaningful example of the superspace application and provides a detailed phase diagram of the involved magnetic states. Nowadays this ordered perovskite could be considered as a new type of multiferroic material combining ferrielectric properties and a long period antiferromagnetic structure.
Title:
Synthesis and crystal structure of a series of incommensurately modulated composite oxohalide compounds
Authors:
Zimmermann, I; Corgnet, A; Johnsson, M; Lidin, S Author Full Names: Zimmermann, Iwan; Corgnet, Alexis; Johnsson, Mats; Lidin, Sven
Source:
DALTON TRANSACTIONS, 43 (42):15812-15817; 10.1039/c4dt02084g NOV 14 2014
Abstract:
Transparent, needle-like single crystals of the isostructural compounds [Sb4O7+3 delta X4][Zn-3](1+delta) = CL Br, I) delta approximate to 0.2 were obtained from chemical reactions in evacuated and sealed silica tubes. First, the average structure was solved in P211n but the model refined poorly and a lowering of the symmetry to the 3 + 1 dimensional space group P2(1)(alpha 0 gamma)0 gave a significantly better fit to the data. This model used second order positional modulations for all the atoms. Whereas Sb, Cl (Br, I) and most 0 positions were well behaved, there was a mismatch with Zn that was better described in a sub-cell, thus yielding a composite structure. The composite nature of the structure leads to a charge imbalance that is compensated by oxygen vacancies.
Title:
Complex magnetic ordering in CeGe1.76 studied by neutron diffraction
Authors:
Jayasekara, WT; Tian, W; Hodovanets, H; Canfield, PC; Bud'ko, SL; Kreyssig, A; Goldman, AI Author Full Names: Jayasekara, W. T.; Tian, W.; Hodovanets, H.; Canfield, P. C.; Bud'ko, S. L.; Kreyssig, A.; Goldman, A. I.
Source:
PHYSICAL REVIEW B, 90 (13):10.1103/PhysRevB.90.134423 OCT 29 2014
Abstract:
Neutron diffraction measurements on a single crystal of CeGe1.76 reveal a complex series of magnetic transitions at low temperature. At T-N approximate to 7 K, there is a transition from a paramagnetic state at higher temperature to an incommensurate magnetic structure characterized by a magnetic propagation vector ( 0 0 tau) with tau approximate to 1/4 and the magnetic moment along the a axis of the orthorhombic unit cell. Below T-LI approximate to 5 K, the magnetic structure locks in to a commensurate structure with tau = 1/4 and the magnetic moment remains along the a axis. Below T* approximate to 4 K, we find additional half-integer and integer indexed magnetic Bragg peaks consistent with a second commensurately ordered antiferromagnetic state.
Title:
Feedback of superconducting fluctuations on charge order in the underdoped cuprates
Authors:
Chowdhury, D; Sachdev, S Author Full Names: Chowdhury, Debanjan; Sachdev, Subir
Source:
PHYSICAL REVIEW B, 90 (13):10.1103/PhysRevB.90.134516 OCT 24 2014
Abstract:
Metals interacting via short-range antiferromagnetic fluctuations are unstable to sign-changing superconductivity at low temperatures. For the cuprates, this leading instability leads to the well-known d-wave superconducting state. However, there is also a secondary instability to an incommensurate charge-density wave, with a predominantly d-wave form factor, arising from the same antiferromagnetic fluctuations. Recent experiments in the pseudogap regime of the hole-doped cuprates have found strong evidence for such a charge-density wave order and, in particular, the predicted d-wave form factor. However, the observed wave vector of the charge order differs from the leading instability in Hartree-Fock theory, and is that of a subleading instability. In this paper, we examine the feedback of superconducting fluctuations on these different charge-density wave states, and find that over at least a small temperature window, they prefer the experimentally observed wave vector.
Title:
Non-Fermi-liquid behavior at the onset of incommensurate 2k(F) charge- or spin-density wave order in two dimensions
Authors:
Holder, T; Metzner, W Author Full Names: Holder, Tobias; Metzner, Walter
Source:
PHYSICAL REVIEW B, 90 (16):10.1103/PhysRevB.90.161106 OCT 21 2014
Abstract:
We analyze the influence of quantum critical fluctuations on single-particle excitations at the onset of incommensurate 2k(F) charge- or spin-density wave order in two-dimensional metals. The case of a single pair of hot spots at high symmetry positions on the Fermi surface needs to be distinguished from the case of two hot spot pairs. We compute the fluctuation propagator and the electronic self-energy perturbatively in leading order. The energy dependence of the single-particle decay rate at the hot spots obeys non-Fermi-liquid power laws, with an exponent 2/3 in the case of a single hot spot pair, and exponent one for two hot spot pairs. The prefactors of the linear behavior obtained in the latter case are not particle-hole symmetric.
Title:
Structural and magnetic dynamics in the magnetic shape-memory alloy Ni2MnGa
Authors:
Mariager, SO; Dornes, C; Johnson, JA; Ferrer, A; Grubel, S; Huber, T; Caviezel, A; Johnson, SL; Eichhorn, T; Jakob, G; Elmers, HJ; Beaud, P; Quitmann, C; Ingold, G Author Full Names: Mariager, S. O.; Dornes, C.; Johnson, J. A.; Ferrer, A.; Gruebel, S.; Huber, T.; Caviezel, A.; Johnson, S. L.; Eichhorn, T.; Jakob, G.; Elmers, H. J.; Beaud, P.; Quitmann, C.; Ingold, G.
Source:
PHYSICAL REVIEW B, 90 (16):10.1103/PhysRevB.90.161103 OCT 10 2014
Abstract:
Magnetic shape-memory Heusler alloys are multiferroics stabilized by the correlations between electronic, magnetic, and structural order. To study these correlations we use time-resolved x-ray diffraction and magneto-optical Kerr effect experiments to measure the laser induced dynamics in a Heusler alloy Ni2MnGa film and reveal a set of time scales intrinsic to the system. We observe a coherent phonon which we identify as the amplitudon of the modulated structure and an ultrafast phase transition leading to a quenching of the incommensurate modulation within 300 fs with a recovery time of a few ps. The thermally driven martensitic transition to the high temperature cubic phase proceeds via nucleation within a few ps and domain growth limited by the speed of sound. The demagnetization time is 320 fs, which is comparable to the quenching of the structural modulation.
Title:
Fine structure of the incommensurate antiferromagnetic fluctuations in single-crystalline LiFeAs studied by inelastic neutron scattering
Authors:
Qureshi, N; Steffens, P; Lamago, D; Sidis, Y; Sobolev, O; Ewings, RA; Harnagea, L; Wurmehl, S; Buchner, B; Braden, M Author Full Names: Qureshi, N.; Steffens, P.; Lamago, D.; Sidis, Y.; Sobolev, O.; Ewings, R. A.; Harnagea, L.; Wurmehl, S.; Buechner, B.; Braden, M.
Source:
PHYSICAL REVIEW B, 90 (14):10.1103/PhysRevB.90.144503 OCT 8 2014
Abstract:
We present an inelastic neutron scattering study on single-crystalline LiFeAs devoted to the characterization of the incommensurate antiferromagnetic fluctuations at Q = (0.5 +/- delta, 0.5 -/+ delta, ql). Time-of-flight measurements show the presence of these magnetic fluctuations up to an energy transfer of 60 meV, while polarized neutrons in combination with a longitudinal polarization analysis on a triple-axis spectrometer prove the pure magnetic origin of this signal. The normalization of the magnetic scattering to an absolute scale yields that magnetic fluctuations in LiFeAs are by a factor of 8 weaker than the resonance signal in nearly optimally Co-doped BaFe2As2, although a factor of 2 is recovered due to the split peaks owing to the incommensurability. The longitudinal polarization analysis indicates weak spin-space anisotropy with a slightly stronger out-of-plane component between 6 and 12 meV. Furthermore, our data suggest a fine structure of the magnetic signal most likely arising from superposing nesting vectors.
Title:
CeCu2Ge2: Challenging our understanding of quantum criticality
Authors:
Zeng, B; Zhang, QR; Rhodes, D; Shimura, Y; Watanabe, D; Baumbach, RE; Schlottmann, P; Ebihara, T; Balicas, L Author Full Names: Zeng, B.; Zhang, Q. R.; Rhodes, D.; Shimura, Y.; Watanabe, D.; Baumbach, R. E.; Schlottmann, P.; Ebihara, T.; Balicas, L.
Source:
PHYSICAL REVIEW B, 90 (15):10.1103/PhysRevB.90.155101 OCT 3 2014
Abstract:
In the zero temperature limit, the zero-point quantum fluctuations of certain degrees of freedom (or quantum criticality) are claimed to describe the collective fluctuations of systems undergoing a second-order phase transition. To date, some of the best studied examples of quantum phase transitions, and concomitant anomalous physical behavior, involve f-electron magnetism in heavy-fermion metals, where quantum criticality (QC) is ascribed to either the suppression of a spin-density wave (SDW) ground state or the Kondo effect. Here, we unveil evidence for a quantum phase transition in CeCu2Ge2 which displays both an incommensurate SDW ground state, and a strong renormalization of the quasiparticle effective masses (mu) due to the Kondo effect. For all angles theta between an external magnetic field (H) and the crystallographic c axis, the application of H leads to the suppression of the SDW state through a second-order phase transition at a theta-dependent critical field H-p(theta) leading to the observation of small Fermi surfaces (FSs) in the paramagnetic state. For the H vertical bar vertical bar c axis, these FSs are characterized by light mu's pointing also to the suppression of the Kondo effect at H-p with, surprisingly, no experimental evidence for QC. But as H is rotated towards the a axis, these mu's increase considerably becoming undetectable for theta > 56 degrees between H and the c axis. Around H-p(a) similar to 30 T the resistivity becomes alpha T which, coupled to the divergence of mu, indicates the existence of a field-induced QC point at H-p(a) (T = 0 K). This observation, suggesting FS hot spots associated with the SDW nesting vector, is at odds with current QC scenarios for which the continuous suppression of all relevant energy scales at H-p(theta, T) should lead to a line of quantum-critical points in the H-theta plane. Finally, we show that the complexity of its magnetic phase diagram(s) makes CeCu2Ge2 an ideal system to explore field-induced quantum tricritical and QC end points.
Title:
Competing Exchange Interactions on the Verge of a Metal-Insulator Transition in the Two-Dimensional Spiral Magnet Sr3Fe2O7
Authors:
Kim, JH; Jain, A; Reehuis, M; Khaliullin, G; Peets, DC; Ulrich, C; Park, JT; Faulhaber, E; Hoser, A; Walker, HC; Adroja, DT; Walters, AC; Inosov, DS; Maljuk, A; Keimer, B Author Full Names: Kim, J. -H.; Jain, Anil; Reehuis, M.; Khaliullin, G.; Peets, D. C.; Ulrich, C.; Park, J. T.; Faulhaber, E.; Hoser, A.; Walker, H. C.; Adroja, D. T.; Walters, A. C.; Inosov, D. S.; Maljuk, A.; Keimer, B.
Source:
PHYSICAL REVIEW LETTERS, 113 (14):10.1103/PhysRevLett.113.147206 OCT 3 2014
Abstract:
We report a neutron scattering study of the magnetic order and dynamics of the bilayer perovskite Sr3Fe2O7, which exhibits a temperature-driven metal-insulator transition at 340 K. We show that the Fe4+ moments adopt incommensurate spiral order below T-N = 115 K and provide a comprehensive description of the corresponding spin-wave excitations. The observed magnetic order and excitation spectra can be well understood in terms of an effective spin Hamiltonian with interactions ranging up to third-nearest-neighbor pairs. The results indicate that the helical magnetism in Sr3Fe2O7 results from competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions whose strengths become comparable near the metal-insulator transition. They thus confirm a decades-old theoretical prediction and provide a firm experimental basis for models of magnetic correlations in strongly correlated metals.
Title:
Oxide ion distribution, vacancy ordering and electrical behaviour in the Bi3NbO7-Bi3YbO6 pseudo-binary system
Authors:
Leszczynska, M; Liu, X; Wrobel, W; Malys, M; Dygas, JR; Norberg, ST; Hull, S; Krok, F; Abrahams, I Author Full Names: Leszczynska, M.; Liu, X.; Wrobel, W.; Malys, M.; Dygas, J. R.; Norberg, S. T.; Hull, S.; Krok, F.; Abrahams, I.
Source:
JOURNAL OF MATERIALS CHEMISTRY A, 2 (43):18624-18634; 10.1039/c4ta03225j 2014
Abstract:
Oxide ion distribution, vacancy ordering and electrical conductivity has been examined in the Nb/Yb double substituted bismuth oxide based system Bi3Nb1-xYbxO7-x, using X-ray and neutron powder diffraction, reverse Monte Carlo modelling of total neutron scattering data and a. c. impedance spectroscopy. Transference number measurements confirm the system to be predominantly ionically conducting above ca. 450 degrees C. Niobium rich compositions show incommensurate ordering of the fluorite subcell, while increasing ytterbium content results in a commensurate fluorite, with fully disordered cation and anion sublattices. Oxide ion distribution shows both compositional and thermal dependencies. The latter is discussed with respect to its effect on the thermal variation of cubic lattice parameter. Substitution of bismuth by niobium and ytterbium in the cation sublattice of bismuth oxide leads to the creation of Frenkel interstitial oxide ions, which increase the tetrahedral vacancy concentration. The high vacancy concentration is confirmed in both Rietveld and RMC analyses of neutron data. Examination of vacancy ordering, in the x - 0.6 composition, indicates a favouring of < 100 > vacancy pair alignment.

Update: 26-Nov-2014

Title:
Magnetic properties of nanoscaled paramelaconite Cu4O3-x (x=0.0 and 0.5)
Authors:
Djurek, D; Prester, M; Drobac, D; Ivanda, M; Vojta, D Author Full Names: Djurek, D.; Prester, M.; Drobac, Dj.; Ivanda, M.; Vojta, D.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 373 183-187; JAN 1 2015
Abstract:
Pure paramelaconite Cu4O3-x has been prepared in the form of nanoparticles with 56 nm in diameter. This mixed valency oxide crystallizes in a tetragonal lattice with 4 unit formulae and forms a pyrochlore structure which manifests in two stoichiometric forms; Cu4O3 and Cu4O2.5, the latter form having two oxygen vacancies per unit cell. Magnetic lattice consists of Cu spin 1/2, and both stoichiometric forms obey transition to the antiferromagnetic state at T-N=45-55 K. Defect free Cu4O3 is indicated by an inversion symmetry and exhibits both antiferromagnetic and ferromagnetic state, where the latter is supposedly due to the superexchange interaction in Cu-O(1n)-Cu bonds. An additional magnetic transition was observed in Cu4O3 at T=120 K, probably as a result of an incommensurate ordering. Absence of an inversion symmetry in the oxygen defect Cu4O2.5 results in a long range Dzyaloshinsky-Moriya interaction accompanied by the strong superparamagnetism. (C) 2014 Elsevier B.V. All rights reserved
Title:
Interacting magnetic cluster-spin glasses and strain glasses in Ni-Mn based Heusler structured intermetallics
Authors:
Entel, P; Gruner, ME; Comtesse, D; Sokolovskiy, VV; Buchelnikov, VD Author Full Names: Entel, Peter; Gruner, Markus E.; Comtesse, Denis; Sokolovskiy, Vladimir V.; Buchelnikov, Vasiliy D.
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 251 (10):2135-2148; SI 10.1002/pssb.201451059 OCT 2014
Abstract:
Magnetic Ni-Mn based Heusler intermetallics show complex magnetic behavior in connection with martensitic transformations (see, for instance, the phase diagram of Ni-Co-Mn-Sn on the right-hand side). The cubic austenitic phase at high temperature shows long-range ferromagnetic order which can considerably be weakened by the appearance of competing antiferromagnetic interactions which are induced by Mn excess and chemical disorder. With decreasing temperature a martensitic/magnetostructural transformation takes place from cubic to non-modulated/modulated tetragonal/monoclinic or orthorhombic structure, where long-range ferromagnetic order can no longer be maintained, leading to superparamagnetic behavior. At still lower temperatures superparamagnetism changes to superspin glass because of strong competition of ferromagnetic and antiferromagnetic interactions and chemical disorder. In addition, disorder and local structural distortions can lead to strain glass in austenite, as observed for some nonmagnetic martensitic systems. The magnetic intermetallics are of technological importance in view of their functional properties involving magnetic shape-memory and exchangebias effects as well as magnetocaloric effects. The ` ferroic cooling' is of particular relevance since it avoids the use of ozone-depleting and greenhouse chemicals compared with conventional fluid-compression technology. Experimental phase diagram of Ni50-xCoxMn39Sn11 for 0 <= x <= 10. Here, TC is the Curie temperature of austenite; at T-M the system transforms to paramagnetic martensite and at T-S to superparamagnetic martensite (SPM) and then to superspin-glass martensite (SSG) at T-P. The possible strainglass phases (labeled by question marks) are predicted because of kinetic arrest phenomena and local distortions associated with the magnetostructural transition and ergodicity breaking by field-cooling/zero-field-cooling experiments. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Elastic fields around a nanosized elliptic hole in decagonal quasicrystals
Authors:
Li, LH; Yun, GH Author Full Names: Li Lian-He; Yun Guo-Hong
Source:
CHINESE PHYSICS B, 23 (10):10.1088/1674-1056/23/10/106104 OCT 2014
Abstract:
Based on the variational principle, a continuum theory of surface elasticity and new boundary conditions for quasicrystals is proposed. The effect of the residual surface stress on a decagonal quasicrystal that is weakened by a nanoscale elliptical hole is considered. The explicit expressions for the hoop stress along the edge of the hole are obtained using the Stroh formalism. The results show that the residual surface stress and the shape of the hole have a significant effect on the elastic state around the hole.
Title:
Two-coupled structural modulations in charge-density-wave state of SrPt2As2 superconductor
Authors:
Wang, L; Wang, Z; Shi, HL; Chen, Z; Chiang, FK; Tian, HF; Yang, HX; Fang, AF; Wang, NL; Li, JQ Author Full Names: Wang Li; Wang Zhen; Shi Hong-Long; Chen Zhen; Chiang Fu-Kuo; Tian Huan-Fang; Yang Huai-Xin; Fang Ai-Fang; Wang Nan-Lin; Li Jian-Qi
Source:
CHINESE PHYSICS B, 23 (8):10.1088/1674-1056/23/8/086103 AUG 2014
Abstract:
Transmission electron microscopy (TEM) study of SrPt2As2 reveals two incommensurate modulations appearing in the charge-density-wave (CDW) state below T-CDW approximate to 470 K. These two structural modulations can be well explained in terms of condensations of two-coupled phonon modes with wave vectors of q(1) = 0.62a on the a-b* plane and q(2) = 0.23a on the a-c* plane. The atomic displacements occur along the b-axis direction for q(1) and along the c-axis direction for q(2), respectively. Moreover, the correlation between q(1) and q(2) can be generally written as q(1) = (q(2) + a*)/2 in the CDW state, suggesting the presence of essential coupling between q(1) and q(2). A small fraction of Ir doping on the Pt site in Sr(Pt1-xIrx)(2)As-2 (x < 0.06) could moderately change these CDW modulations and also affect their superconductivities.

Update: 19-Nov-2014

Title:
The use of Nb in rapid solidified Al alloys and composites
Authors:
Audebert, F; Galano, M; Saporiti, F Author Full Names: Audebert, F.; Galano, M.; Saporiti, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 615 S621-S626; 1 10.1016/j.jallcom.2013.12.129 DEC 5 2014
Abstract:
The worldwide requirements for reducing the energy consumption and pollution have increased the demand of new and high performance lightweight materials. The development of nanostructured Al-based alloys and composites is a key direction towards solving this demand. High energy prices and decreased availability of some alloying elements open up the opportunity to use non-conventional elements in Al alloys and composites. In this work the application of Nb in rapid solidified Al-based alloys and Al alloys matrix composites is reviewed. New results that clarify the effect of Nb on rapid solidified Al alloys and composites are also presented. It is observed that Nb stabilises the icosahedral Al-Fe/Cr clusters, enhances the glass forming ability and shifts the icosahedral phase decomposition towards higher temperatures. Nb provides higher corrosion resistance with respect to the pure Al and Al-Fe-RE (RE: rare earth) alloys in the amorphous and crystalline states. The use of Nb as a reinforcement to produce new Al alloy matrix composites is explored. It is observed that Nb provides higher strength, ductility and toughness to the nanoquasicrystalline matrix composite. Nb appears as a new key element that can improve several properties in rapid solidified Al alloys and composites. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Effect of Ti, Zr and Hf addition on microstructure and properties of rapidly solidified Al-Mn-Fe alloy
Authors:
Stan, K; Litynska-Dobrzynska, L; Ochin, P; Garzel, G; Wierzbicka-Miernik, A; Wojewoda-Budka, J Author Full Names: Stan, K.; Litynska-Dobrzynska, L.; Ochin, P.; Garzel, G.; Wierzbicka-Miernik, A.; Wojewoda-Budka, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 615 S607-S611; 1 10.1016/j.jallcom.2013.11.160 DEC 5 2014
Abstract:
In this work, the influence of alloying elements Ti, Zr and Hf on microstructure and properties of Al91Mn7Fe2 melt spun ribbons, strengthened with quasicrystalline particles was studied. It was found that Zr improves significantly the microhardness of the alloy in as spun state by precipitation of metastable L1(2)-Al3Zr phase in matrix grains. Both Hf and Zr additions retain higher microhardness values after annealing at 673 K by formation of stable Al3X precipitates, even though the quasicrystalline phase being the main strengthening phase in the alloy starts to decompose. Comparison of the results from differential scanning calorimetry, thermo-mechanical analysis and microhardness measurements after annealing showed correlation between phase transformations and mechanical properties. Based on TEM studies, drop of microhardness and increase in Young's modulus with temperature for all samples was attributed to significant change in samples microstructure, especially to decomposition of quasicrystalline particles and formation of different intermetallic phases. (C) 2013 Elsevier B.V. All rights reserved.
Title:
High-resolution electron microscopy and electron diffraction of perovskite-type superconducting copper oxides
Authors:
Oku, T Author Full Names: Oku, Takeo
Source:
NANOTECHNOLOGY REVIEWS, 3 (5):413-444; SI 10.1515/ntrev-2014-0003 OCT 2014
Abstract:
High-resolution electron microscopy and electron diffraction are quite useful for structural characterization of perovskite-type superconducting copper oxides on the atomic scale. Valuable information on the crystal structures and the microstructures could be obtained from observed high-resolution images if severe conditions such as thinner crystals and definite defocus values are satisfied. The structure images and electron diffraction patterns include information not only on accurate atomic coordinates of cations but also on ordered arrangements of oxygen atoms and oxygen vacancies. Crystal structures of the various perovskite-type copper oxides were analyzed from the observed structure images. Modulated structures, defects, intergowth, surfaces, and interfaces were also investigated.
Title:
Dual-phase glassy/nanoscale icosahedral phase materials in Cu-Zr-Ti-Pd system alloys
Authors:
Louzguine-Luzgin, DV; Churyumov, AY Author Full Names: Louzguine-Luzgin, Dmitri V.; Churyumov, A. Yu.
Source:
MATERIALS CHARACTERIZATION, 96 6-12; 10.1016/j.matchar.2014.07.014 OCT 2014
Abstract:
The present work is devoted to an investigation of the formation kinetics, stability and homogeneity area of the nanoscale icosahedral phase formed on heating in the dual-phase glassy/quasicrystalline phase Cu-Zr-Ti-Pd alloys. The data obtained indicate that the Cu-Zr-Ti-Pd icosahedral phase is not a Cu-rich part of the compositional homogeneity area of the Zr-Cu-Pd one. Moreover, Ti, as well as Pd, is found to be an important element stabilizing quasicrystalline phase in the Cu-Zr-Ti-Pd alloys. The formation criteria for Cu- and Zr/Hf-based icosahedral phases are discussed based on the quasilattice constant to average atomic diameter ratio. Deviation from a certain ratio leads to destabilization of the icosahedral phase. By using the isothermal calorimetry traces transformation kinetics above and below the glass-transition region was analyzed. Some difference in the transformation kinetics above and below the glass-transition region allows us to suggest that possible structure changes occur upon glass-transition. (C) 2014 Elsevier Inc. All rights reserved.
Title:
Partially amorphous (metamict) titanite: a silicate mineral in a natural radiation induced non-equilibrium phase
Authors:
Beirau, T Author Full Names: Beirau, Tobias
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 229 (8):543-549; 10.1515/zkri-2014-1745 AUG 2014
Abstract:
The present review will give a brief overview mainly focused on studies during the past 5 years on the mineral titanite (end-member composition CaTiSiO5) which could incorporate radioactive elements in its crystal structure. Aspects of investigations were the structural damage resulting from the radioactive decay, the thermally induced recrystallization process and the elastic properties of the mineral. During the radiation induced damage process, namely the metamictization, titanite becomes partially amorphous with coexisting defect enriched crystalline and aperiodic regions. Within these crystalline regions a P2(1)/c to C2/c phase transition (similar to at 500 K) occurs. Resulting from radiation induced structural damage, titanite shows elastic properties close to those of titanite glass. During recrystallization on annealing an initial softening of the titanite structure takes place (up to temperature similar to 950 K) resulting from the formation of soft interfaces. Thermal annealing at higher temperatures leads to increasing structural order and the hardening of the mineral.

Update: 13-Nov-2014

Title:
Multicomponent and High Entropy Alloys
Authors:
Cantor, B Author Full Names: Cantor, Brian
Source:
ENTROPY, 16 (9):4749-4768; 10.3390/e16094749 SEP 2014
Abstract:
This paper describes some underlying principles of multicomponent and high entropy alloys, and gives some examples of these materials. Different types of multicomponent alloy and different methods of accessing multicomponent phase space are discussed. The alloys were manufactured by conventional and high speed solidification techniques, and their macroscopic, microscopic and nanoscale structures were studied by optical, X-ray and electron microscope methods. They exhibit a variety of amorphous, quasicrystalline, dendritic and eutectic structures.
Title:
Structural origin of the different devitrification behaviors between ZrCu and ZrPd metallic glasses
Authors:
Huang, P; Zou, DH; Guo, GQ; Yang, L Author Full Names: Huang, Po; Zou, De-Hui; Guo, Gu-Qing; Yang, Liang
Source:
EPL, 107 (6):10.1209/0295-5075/107/66002 SEP 2014
Abstract:
The microstructures of Zr70Pd30 and Zr70Cu30 metallic glasses (MGs) were investigated via the synchrotron radiation techniques combined with the reverse Monte Carlo simulations. It is revealed that, compared with Zr70Cu30, Zr70Pd30 has more fruitful icosahedral-like clusters, which have a relatively high geometrical regularity closer to that of the ideal icosahedron. Therefore, clusters in Zr70Pd30 are prone to change into the structural units of icosahedral quasicrystal phase. This should be the structural origin of the amorphous-to-quasicrystal transformation found in Zr70Pd30 while such phase change never appears when heating Zr70Cu30 MG. This work provides an understanding of the devitrification mechanism from the atomic level in this class of glassy materials. Copyright (C) EPLA, 2014
Title:
The alpha <-> beta phase transitions of Zn2P2O7 revisited: existence of an additional intermediate phase with an incommensurately modulated structure
Authors:
Stoger, B; Weil, M; Dusek, M Author Full Names: Stoeger, Berthold; Weil, Matthias; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 539-554; SI 10.1107/S205252061401049X 3 JUN 2014
Abstract:
Zn2P2O7 crystallizes in a thortveitite-like structure and features temperature-dependent polymorphism. At high temperatures (T > 500 K), the aristotype phase beta-Zn2P2O7 (C2/m, Z = 2, a similar or equal to 6.60, b similar or equal to 8.28, c similar or equal to 4.53 angstrom, beta similar or equal to 105.4 degrees) is stable. At lower temperatures the lock-in phase alpha(1)-Zn2P2O7 [at 350 K: I2/c, Z = 12, a = 20.1131 (13), b = 8.2769 (6), c = 9.109 (3) angstrom, beta = 106.338 (16)degrees], a sixfold superstructure with commensurate modulation vector q = (1/3, 0, 1/2), is stable. Between the stability ranges of the alpha(1)- and beta-phases exists the intermediate, incommensurately modulated alpha(2)-Zn2P2O7 phase with modulation wavevector q similar or equal to (0.33, 0, 0.40) and C2/m(alpha, 0, gamma)0s superspace group symmetry. The alpha(1) -> alpha(2) lock-in phase transition at T-L = 408 K is of first-order and features virtually no hysteresis. It is immediately followed by the second-order alpha(2) -> beta transition to the non-modulated phase at T-I similar or equal to 430 K. This transformation is sluggish and even at T = 500 K very weak satellite reflections of the alpha(2)-phase were observed. Both phase transitions were analyzed with differential scanning calorimetry and high-temperature powder and single-crystal X-ray diffraction. The crystal structures of the alpha(1)- and alpha(2)-phases were refined from single crystal data collected at T = 350, 400, 405, 410, 415, 420, 425, 430, 450 and 500 K. Different models describing the slow transition from the incommensurately modulated alpha(2)- to the non-modulated beta-phase were tested. In the model resulting in the best residuals, the bridging O atom of the [P2O7] group, which is located on a 2/m position in the basic structure, is described as an overlap of an atom ordered in internal space and one atom disordered around the mirror plane. The occupancy of the ordered atom decreases with temperature until at T = 500 K virtually only the disordered atom remains. Simultaneously, the amplitude of the modulation functions of the remaining atoms decreases, so that the T = 500 K structure can be considered as the C2/m aristotype structure, although the diffraction pattern still features satellite reflections of first order with very low intensities.
Title:
Understanding the structure details when drying hydrate crystals of pharmaceuticals - interpretations from diffuse scattering and inter-modulation satellites of a partially dehydrated crystal
Authors:
Chan, EJ; Gao, Q; Dabros, M Author Full Names: Chan, E. J.; Gao, Q.; Dabros, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 555-567; SI 10.1107/S2052520614005125 3 JUN 2014
Abstract:
Simplified models for the crystal lattice of the sesquihydrate form of the hemi-sulfate salt of (5S, 6S, 9R)-5-amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohepta[b]py ridin9-yl 4-(2-oxo-2,3-dihydro-1H-imidazol[4,5b]pyridin-1-yl)-1piperidine carboxylate (BMS-927711, C28H29F2N6O3+) are used to calculate diffuse diffraction features in order to develop a mechanistic understanding of the dehydration process with respect to disruption of the lattice, since a Bragg model cannot be established. The model demonstrates that what we observe when the water leaves the crystal is partial transformation from the parent form to a child form (a new form, less hydrated and structurally related to the parent). Yet this 'dried' structure is not a pure phase. It consists of semi-random layers of both child, parent and an interfacial layer which has a modulated structure that represents a transitory phase. Understanding the fact that a single 'dried' crystal can have the disordered layer structure described as well as understanding mechanistic relationships between the phases involved can have implications in understanding the effect of common large scale bulk drying procedures. During the development of BMS-927711, difficulties did arise during characterization of the dried bulk when using only routine solid-state analysis. The material is now better understood from this diffraction study. The diffraction experiments also reveal intermodulation satellites, which upon interpretation yield even more structural information about the crystal transformation. The model suggests the mechanism of transformation is laminar in which layers of the crystal are driven to approach a stable B-centered supercell phase of lower water content.

Update: 5-Nov-2014

Title:
High temperature X-ray diffraction study on incommensurate composite crystal MnSi gamma - (3+1)-dimensional superspace approach
Authors:
Kikuchi, Y; Nakajo, T; Hayashi, K; Miyazaki, Y Author Full Names: Kikuchi, Y.; Nakajo, T.; Hayashi, K.; Miyazaki, Y.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 616 263-267; 10.1016/j.jallcom.2014.07.106 DEC 15 2014
Abstract:
The (3 + 1)-dimensional crystal structure of a higher manganese silicide (MnSi gamma) phase is revealed using in situ high temperature powder X-ray diffraction (XRD) above room temperature. The compound consists of two tetragonal subsystems of [Mn] and [Si] with an irrational c-axis ratio gamma = c(Mn)/c(Si). The in situ XRD results show that the MnSi gamma phase is stable, in a vacuum of similar to 1 Pa, up to 1093 K and partially decomposes into the monosilicide (MnSi) phase with further increase in temperature. Refined a- and c(Mn)-axis lengths increase linearly and the thermal expansion coefficients are comparable with those of typical metallic electrode materials. In contrast, c(Si)-axis length changes its increment against temperature at T-BD similar to 773 K. As a result, the temperature dependence of gamma starts to decrease gradually above T-BD, from 1.7387(1) (at 773 K) to 1.7244(1) (at 1173 K). This finding implies that the MnSi gamma phase consecutively changes its irrational composition above T-BD, a typical temperature where the silicides exhibit a maximum figure-of-merit. An increase in hole carrier concentration is expected according to the valence electron counting concept. Although the nearest Mn-Mn and Mn-Si distances increase monotonically with temperature, the nearest Si-Si distance much increases by similar to 0.05 angstrom from 2.439(4) angstrom at 773 K to 2.493(7) angstrom at 1173 K. The latter increase is considered to be caused by the introduction of excited electron carriers into the anti-bonding orbital, due to the bipolar diffusion (BD). (C) 2014 Elsevier B.V. All rights reserved.
Title:
Effects of S-Se substitution and magnetic field on magnetic order in Fe0.5Ti(S,Se)(2) layered compounds
Authors:
Gubkin, AF; Sherokalova, EM; Keller, L; Selezneva, NV; Proshkin, AV; Proskurina, EP; Baranov, NV Author Full Names: Gubkin, A. F.; Sherokalova, E. M.; Keller, L.; Selezneva, N. V.; Proshkin, A. V.; Proskurina, E. P.; Baranov, N. V.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 616 148-154; 10.1016/j.jallcom.2014.06.195 DEC 15 2014
Abstract:
Powder neutron diffraction and specific heat measurements have been employed to study the evolution of an antiferromagnetic (AFM) structure in the intercalated Fe0.5TiS2-ySey compounds with S-Se substitution and under application of a magnetic field. In Fe0.5TiS2 (y = 0), the magnetic structure just below T-N similar or equal to 140 K is incommensurate while it becomes commensurate with further cooling below T-t similar or equal to 125 K. The presence of two magnetic phase transitions at T-t and T-N in Fe0.5TiS2 is confirmed by specific heat measurements. The field-induced AFM-FM transitions occurring in Fe0.5TiS2 within temperature interval T-t < T < T-N and below T-t are evidenced by neutron diffraction measurements under application of a magnetic field. Unlike Fe0.5TiS2 having a quadruplicated AFM structure, the compounds with the Se concentrations y > 0.5 are observed to exhibit an AFM structure with the doubled magnetic unit cell along a and c crystallographic directions of the monoclinic crystal lattice (I12/m1 space group). In the transition region around the critical Se concentration y(c) approximate to 0.5, the magnetic structure of Fe0.5TiS2-ySey is found to be incommensurate. The appearance of the AFM order with decreasing temperature in Fe0.5TiS2-ySey is accompanied by anisotropic deformations of the crystal lattice. At low temperatures, the Fe magnetic moments in all Fe0.5TiS2-ySey form an angle 14-16 degrees to the c crystallographic direction, which can be ascribed to the crystal field effects and spin-orbit couplings. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Cu3Sn - understanding the systematic absences
Authors:
Muller, CJ; Lidin, S Author Full Names: Muller, Carola J.; Lidin, Sven
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 879-887; 10.1107/S205252061401806X 5 OCT 2014
Abstract:
The intermetallic compound Cu3Sn has previously been described as a long-period antiphase boundary superstructure of the Cu3Ti structure type. While the compound itself has been reported as a tenfold and an eightfold superstructure, ternary doped alloys show shorter repetitions. Interestingly, the diffraction patterns of these compounds show noncrystallographic absences that cannot be explained using the superstructure models. Since the compound exhibits phase broadening, these models are not satisfactory because the paucity of observed data does not allow for a refinement of the composition. Here, an alternative, superspace model in the orthorhombic space group Xmcm(0 beta 0)000 is proposed, with the centering vectors (0,0,0,0) and (1/2,0,0,1/2). The presence of the non-crystallographic absences is explained as a result of a dominating occupational modulation that is accompanied by a weaker displacive modulation. In consistency with the EDXS results, the composition has been refined to Cu3 + xSn from single-crystal X-ray diffraction data. It is further demonstrated that by varying the length and the direction of the modulation wavevector in the superspace model, the ternary Cu3Sn compounds and other colored hexagonal close packing (h.c.p.) structures can be produced.
Title:
Mackay icosahedron explaining orientation relationship of dispersoids in aluminium alloys
Authors:
Muggerud, AMF; Li, YJ; Holmestad, R; Andersen, SJ Author Full Names: Muggerud, Astrid Marie F.; Li, Yanjun; Holmestad, Randi; Andersen, Sigmund J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 888-896; 10.1107/S2052520614017880 5 OCT 2014
Abstract:
The orientation relations (ORs) of the cubic icosahedral quasicrystal approximant phase alpha-Al(Fe,Mn)Si have been studied after low temperature annealing of a 3xxx wrought aluminium alloy by transmission electron microscopy. From diffraction studies it was verified that the most commonly observed OR for the alpha-Al(Fe,Mn)Si dispersoids is [1 (1) over bar1]alpha // [1 (1) over bar1]Al, (5 (2) over bar(7) over bar)alpha // (011)Al. This orientation could be explained by assuming that the internal Mackay icosahedron (MI) in the alpha-phase has a fixed orientation in relation to Al, similar to that of the icosahedral quasi-crystals existing in this alloy system. It is shown that mirroring of the normal-to-high-symmetry icosahedral directions of the MI explains the alternative orientations, which are therefore likely to be caused by twinning of the fixed MI. Only one exception was found, which was related to the Bergman icosahedron internal to the T-phase of the Al-Mg-Zn system.
Title:
The ac-magnetic susceptibility and dielectric response of complex spin ordering processes in Mn3O4
Authors:
Thota, S; Singh, K; Nayak, S; Simon, C; Kumar, J; Prellier, W Author Full Names: Thota, Subhash; Singh, Kiran; Nayak, Sanjib; Simon, Ch.; Kumar, Jitendra; Prellier, Wilfrid
Source:
JOURNAL OF APPLIED PHYSICS, 116 (10):10.1063/1.4895054 SEP 14 2014
Abstract:
We report a meticulous study of the ac-magnetization dynamics (chi(ac)(T)), relative dielectric permittivity epsilon(r)(T), and magneto-dielectric (Delta epsilon(r)/epsilon(r)(H)) response of various complex magnetic transitions that occur below the ferrimagnetic Neel temperature T-N of Mn3O4. Besides the known sequence of transitions at T-N similar to 42.75 K, T-1 similar to 39 K, and T-2 similar to 34 K, the existence of a new anomaly reported recently at 38 K (T*) has been successfully probed by chi(ac)(T) and epsilon(r)(T) measurements. The effect of external dc-bias fields (H-DC) and driving frequency (f) on the above mentioned transitions has been investigated in consonance with the epsilon(r)(T) and Delta epsilon(r)/epsilon(r)(T, H) results. For the first time, we observed a clear hysteresis of about 5.15 K in the zero-field epsilon(r)(T) across the incommensurate-to-commensurate transition T-2 similar to 34 K, which provides evidence to the first-order nature of this transition. The Arrott plot (H/M vs. M-2) criterion has been used to distinguish the nature of all the sequential transitions that take place below T-N. (C) 2014 AIP Publishing LLC.
Title:
Structural changes and microstructures in stuffed tridymite-type compounds Ba1-xSrxAl2O4
Authors:
Tanaka, E; Ishii, Y; Teukasaki, H; Taniguchi, H; Mori, S Author Full Names: Tanaka, Eri; Ishii, Yui; Teukasaki, Hirofumi; Taniguchi, Hiroki; Mori, Shigeo
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS, 53 (9):SI 10.7567/JJAP.53.09PB01 SEP 2014
Abstract:
Crystal structures and microstructures in Ba1-xSrxAl2O4 solid solutions between the end members of BaAl2O4 and SrAl2O4 have been carefully investigated by powder X-ray diffraction, electron diffraction and transmission electron microscopy (TEM) imaging experiments. With the help of fast Fourier transform (FFT) calculation, high-resolution TEM images suggested that diffuse streaks along three equivalent (110) directions in the (001) plane, which appear in the P6(3) structure of Ba1-xSrxAl2O4 for x = 0.4, originate from the large structural fluctuation of the AlO4 tetrahedral network. On the other hand, the monoclinic P2(1) structure in Ba1-xSrxAl2O4 with x = 0.7 was found to consist of a modulated structure with q = 0,1/2,0. The present experimental results reveal that a structural phase boundary exists at approximately x = 0.6 between the P6(3) structure with a large structural fluctuation and a monoclinic P2(1) phase with the single-q modulated structure. (C) 2014 The Japan Society of Applied Physics
Title:
Strongly localized modes in one-dimensional defect-free magnonic quasicrystals
Authors:
Chen, CH; Qiu, RZ; Chang, CH; Hsueh, WJ Author Full Names: Chen, C. H.; Qiu, R. Z.; Chang, C. H.; Hsueh, W. J.
Source:
AIP ADVANCES, 4 (8):10.1063/1.4892164 AUG 2014
Abstract:
Signal storage in magnonic quasicrystals using a slow spin-wave mode, rather than the quasinormal mode of traditional periodic magnonic crystals, is proposed, which is analogous to the slow light mode in the field of optics. Compared to traditional materials, richer and more wavelength-selective sharp resonances are achieved using the quasicrystals with a fewer number of layers, because of the peculiar fractal transmission spectra of quasicrystals. The number of sharp resonance and the quality factor for the sharp resonances in the transmission spectra also increases as the generation order of the magnonic quasicrystal increases. This generic nature allows the storage of signals using spin wave, for a wide range of quasiperiodic systems. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
Title:
Crystal structure and magnetic properties of Bi(0.8)A(0.2)FeO(3) (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy
Authors:
Rangi, M; Agarwal, A; Sanghi, S; Singh, R; Meena, SS; Das, A Author Full Names: Rangi, Manisha; Agarwal, Ashish; Sanghi, Sujata; Singh, Ripandeep; Meena, S. S.; Das, A.
Source:
AIP ADVANCES, 4 (8):10.1063/1.4893241 AUG 2014
Abstract:
Bi(0.8)A(0.2)FeO(3) (A = La, Ca, Sr, Ba) multiferroics were studied using x-ray, neutron diffraction and magnetization techniques. All the samples crystallized in rhombohedral structure with space group R3c. The compounds exhibit antiferromagnetic (AFM) ordering at 300 K and no evidence of further structural or magnetic transition was observed on lowering of temperature below it. The magnetic structure of these substituted compounds are found to be collinear G-type AFM structure as against the non collinear incommensurate magnetic structure reported in the case of parent compound. The moments on Fe at 6 K are aligned along the a-axis in the case of Ca-doped sample. With increase in the ionic radii of dopant, the moments are found to be aligned in the ac plane and the angle of tilt away from the a-axis increases. The observed change in the magnetic structure with substitution is attributed to the intrinsic structural distortion as evidenced by the change in the bond angle (Fe-O-Fe) and bond distances (Bi-O, Fe-O). It has been found that heterovalent substitution A(2+) results in the formation of oxygen vacancies in the parent lattices as the possibility of Fe4+ ruled out by Mossbauer spectra recorded at room temperature. Higher value of remnant magnetization (0.4187 emu/g) and coercivity (4.7554kOe) is observed in Bi0.8Ba0.2FeO3 sample in comparison to other substituted samples revealing a strong correlation between ionic radii and magnetization. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
Title:
The alpha <-> beta phase transitions of Zn2P2O7 revisited: existence of an additional intermediate phase with an incommensurately modulated structure
Authors:
Stoger, B; Weil, M; Dusek, M Author Full Names: Stoeger, Berthold; Weil, Matthias; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 539-554; SI 10.1107/S205252061401049X 3 JUN 2014
Abstract:
Zn2P2O7 crystallizes in a thortveitite-like structure and features temperature-dependent polymorphism. At high temperatures (T > 500 K), the aristotype phase beta-Zn2P2O7 (C2/m, Z = 2, a similar or equal to 6.60, b similar or equal to 8.28, c similar or equal to 4.53 angstrom, beta similar or equal to 105.4 degrees) is stable. At lower temperatures the lock-in phase alpha 1-Zn2P2O7 [at 350 K: I2/c, Z = 12, a = 20.1131 (13), b = 8.2769 (6), c = 9.109 (3) angstrom, beta = 106.338 (16)degrees], a sixfold superstructure with commensurate modulation vector q = (1/3, 0, 1/2), is stable. Between the stability ranges of the alpha(1)- and beta-phases exists the intermediate, *incommensurately modulated* alpha(2)-Zn2P2O7 phase with modulation wavevector q similar or equal to (0.33, 0, 0.40) and C2/m(alpha, 0, gamma)0s superspace group symmetry. The alpha(1) -> alpha(2) lock-in phase transition at T-L = 408 K is of first-order and features virtually no hysteresis. It is immediately followed by the second-order alpha(2) -> beta transition to the non-modulated phase at T-I similar or equal to 430 K. This transformation is sluggish and even at T = 500 K very weak satellite reflections of the alpha(2)- phase were observed. Both phase transitions were analyzed with differential scanning calorimetry and high-temperature powder and single-crystal X-ray diffraction. The crystal structures of the alpha(1)- and alpha(2)- phases were refined from single crystal data collected at T = 350, 400, 405, 410, 415, 420, 425, 430, 450 and 500 K. Different models describing the slow transition from the *incommensurately modulated* alpha(2)- to the non-modulated beta-phase were tested. In the model resulting in the best residuals, the bridging O atom of the [P2O7] group, which is located on a 2/m position in the basic structure, is described as an overlap of an atom ordered in internal space and one atom disordered around the mirror plane. The occupancy of the ordered atom decreases with temperature until at T = 500 K virtually only the disordered atom remains. Simultaneously, the amplitude of the modulation functions of the remaining atoms decreases, so that the T = 500 K structure can be considered as the C2/m aristotype structure, although the diffraction pattern still features *satellite reflections* of first order with very low intensities.
Title:
Understanding the structure details when drying hydrate crystals of pharmaceuticals - interpretations from diffuse scattering and inter-modulation satellites of a partially dehydrated crystal
Authors:
Chan, EJ; Gao, Q; Dabros, M Author Full Names: Chan, E. J.; Gao, Q.; Dabros, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 555-567; SI 10.1107/S2052520614005125 3 JUN 2014
Abstract:
Simplified models for the crystal lattice of the sesquihydrate form of the hemi-sulfate salt of (5S,6S,9R)-5-amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohep ta[b]pyridin9-yl 4-(2-oxo-2,3-dihydro-1H-imidazol[4,5b] pyridin-1-yl)-1-piperidine carboxylate (BMS-927711, C28H29F2N6O3+) are used to calculate diffuse diffraction features in order to develop a mechanistic understanding of the dehydration process with respect to disruption of the lattice, since a Bragg model cannot be established. The model demonstrates that what we observe when the water leaves the crystal is partial transformation from the parent form to a child form (a new form, less hydrated and structurally related to the parent). Yet this 'dried' structure is not a pure phase. It consists of semi-random layers of both child, parent and an interfacial layer which has a modulated structure that represents a transitory phase. Understanding the fact that a single 'dried' crystal can have the disordered layer structure described as well as understanding mechanistic relationships between the phases involved can have implications in understanding the effect of common large scale bulk drying procedures. During the development of BMS-927711, difficulties did arise during characterization of the dried bulk when using only routine solid-state analysis. The material is now better understood from this diffraction study. The diffraction experiments also reveal intermodulation satellites, which upon interpretation yield even more structural information about the crystal transformation. The model suggests the mechanism of transformation is laminar in which layers of the crystal are driven to approach a stable B-centered supercell phase of lower water content.
Title:
Studies on icosahedral Ag-In-Yb: a prototype for Tsai-type quasicrystals
Authors:
Cui, C; Shimoda, M; Tsai, AP Author Full Names: Cui, Can; Shimoda, Masahiko; Tsai, An Pang
Source:
RSC ADVANCES, 4 (87):46907-46921; 10.1039/c4ra07980a 2014
Abstract:
Tsai-type icosahedral quasicrystals (i-QCs) are present in numerous alloy systems. Among them, the icosahedral Ag-In-Yb quasicrystal (i-Ag-In-Yb) is regarded as a prototype for studying various features of QCs, such as crystalline structure and physical properties, due to its good average structural order, good stability both in air and in ultra-high vacuum, amenability to growth of large single grains, and lack of elements with high vapor pressure or toxicity. Here we present a review on recent studies of i-Ag-In-Yb, including studies on bulk structure, crystal growth, physical properties, surface structure and thin film growth on quasicrystalline surface. We believe the results will encourage studies on other QCs.

Update: 29-Oct-2014

Title:
Fusion: a General Framework for Hierarchical Tilings
Authors:
Frank, NP Author Full Names: Frank, N. P.
Source:
ACTA PHYSICA POLONICA A, 126 (2):461-466; AUG 2014
Abstract:
One well studied way to construct quasicrystalline tilings is via inflate-and-subdivide (a.k.a. substitution) rules. These produce self-similar tilings the Penrose, octagonal, and pinwheel tilings are famous examples. We present a different model for generating hierarchical tilings we call "fusion rules". Inflate-and-subdivide rules are a special case of fusion rules, but general fusion rules are more flexible and allow for defects, changes in geometry, and even constrained randomness. A condition that produces homogeneous structures and a method for computing frequency for fusion tiling spaces are discussed.
Title:
Quasicrystal-Polymer Composites for Additive Manufacturing Technology
Authors:
Kenzari, S; Bonina, D; Degiovanni, A; Dubois, JM; Fournee, V Author Full Names: Kenzari, S.; Bonina, D.; Degiovanni, A.; Dubois, J. M.; Fournee, V.
Source:
ACTA PHYSICA POLONICA A, 126 (2):449-452; AUG 2014
Abstract:
We present a new niche application of quasicrystalline powders that leads to a commercially successful development of polymer-matrix composites. The process is based upon selective laser sintering, which is one of the current most powerful additive manufacturing technologies in use in the mechanical industries. Characteristics of the materials produced, such as porosity, friction and wear against hard steel, are evaluated and compared to the state of the art. Insight into the production of metal-matrix composites, using a variant of the technology, is also given.
Title:
Electronic Properties and Complexity of Al-Based Complex Metallic Alloys
Authors:
Dubois, JM; Belin-Ferre, E Author Full Names: Dubois, J. -M.; Belin-Ferre, E.
Source:
ACTA PHYSICA POLONICA A, 126 (2):453-457; AUG 2014
Abstract:
As a consequence of their structural complexity, the electron transport properties of Al-based complex metallic alloys scale as simple power laws of the number of atoms in the primitive unit cell. Furthermore, presence in energy space of localised, d-like states below the Fermi level is systematically observed, even in the absence of any transition metal constituting element. The relative intensity of this contribution to the total density of states correlates with the structural complexity of the compound. Thus, complexity plays a key role, via Hume-Rothery, hybridization effects and most probably hopping, in the selection, formation and stability of Al-based complex metallic alloys. The results are interpreted in terms of self-organized criticality. In order to promote discussion about the essence of the quasicrystalline state ("why are the atoms where they are?"), a speculative model is suggested.
Title:
Hyperbolic Icosahedral Tilings by Buckyballs
Authors:
Luck, R; Frettloh, D Author Full Names: Lueck, R.; Frettloeh, D.
Source:
ACTA PHYSICA POLONICA A, 126 (2):524-526; AUG 2014
Abstract:
Hyperbolic icosabedral filings by Hockyballs with 4 or 8 Buckyballs sharing a vertex are considered as an example of tilings by Archimedean polyhedra. Representation requires Poincare balls; colour symmetry may be derived by GAP. Colour symmetries preserving both rotation and reflection symmetry as well as only rotation symmetry are discussed.
Title:
Leaching Effect on Multiple Surfaces of a Single Grain Decagonal Al-Ni-Co Quasicrystal
Authors:
Lowe, M; Gille, P; McGrath, R; Sharma, HR Author Full Names: Lowe, M.; Gille, P.; McGrath, R.; Sharma, H. R.
Source:
ACTA PHYSICA POLONICA A, 126 (2):520-523; AUG 2014
Abstract:
We have studied the effect of leaching treatments on the surface microstructure and chemical composition on the two different twofold surfaces, (10000) and (10 (1) over bar 00), and the tenfold surface (00001) of a decagonal (d-) Al-Ni-Co quasicrystal. A sample exposing the three surfaces was leached with NaOH solution and then studied using atomic force microscopy and scanning electron microscopy combined with energy dispersive X-ray analysis. The leaching treatment preferentially removes the Al present in the crystal surface leaving a mixture of transition metal and their associated oxides. The high symmetry, tenfold axis was found to be less resistant to leaching than either of the twofold axes, providing further information regarding the effect of crystallographic direction on leaching kinetic.
Title:
Fermi Surface-Brillouin Zone Interactions in 2/1-2/1-2/1 Bergman-Type Approximant Na27Au27Ga31
Authors:
Mizutani, U; Sato, H; Inukai, M; Zijlstra, ES; Lin, Q; Corbett, JD; Miller, GJ Author Full Names: Mizutani, U.; Sato, H.; Inukai, M.; Zijlstra, E. S.; Lin, Q.; Corbett, J. D.; Miller, G. J.
Source:
ACTA PHYSICA POLONICA A, 126 (2):535-538; AUG 2014
Abstract:
The X-ray diffraction studies on a newly synthesized Na26Au25Ga29 single crystal revealed the formation of a single phase 2/1-2/1-2/1 Bergman-type approximant and the presence of Au/Ga mixed occupancies in its unit cell containing 680 atoms. The structure model of the 2/1-2/1-2/1 approximant with composition Na27Au27Ga31 was constructed by eliminating the chemical disorder with a minimum sacrifice of composition displacement. The full potential linearized augmented plane wave electronic structure calculations with subsequent full potential linearized augmented plane wave-Fourier analysis were performed for the 2/1-2/1-2/1 approximant Na27Au27Ga31 with space group Pa (3) over bar. The square of the Fermi diameter (2kF)(2), electrons per atom ratio e/a and the critical reciprocal lattice vector vertical bar G vertical bar(2) are determined. A shallow pseudogap at the Fermi level was interpreted as originating from interference of electrons having (2kF)(2) = 109.2 +/- 1.0 with sets of lattice planes with vertical bar G vertical bar(2)s centered at 108. The effective e/a value for the compound is found to be 1.76 in good agreement with 1.73 derived from a composition average of (e/a)Na = 1.0, (e/a)Au = 1.0 and (e/a)Ga = 3.0.
Title:
Aperiodicity in Equilibrium Systems: Between Order and Disorder
Authors:
van Enter, ACD Author Full Names: van Enter, A. C. D.
Source:
ACTA PHYSICA POLONICA A, 126 (2):621-624; AUG 2014
Abstract:
Spatial aperiodicity occurs in various models and materials. Although today the most well-known examples occur in the area of quasicrystals, other applications might also be of interest. Here we discuss some issues related to the notion and occurrence of aperiodic order in equilibrium statistical mechanics. In particular, we consider some spectral characterisations, and shortly review what is known about the occurrence of aperiodic order in lattice models at zero and nonzero temperatures. At the end some more speculative connections to the theory of (spin-)glasses are indicated.
Title:
Nanoquasicrystalline Phase in Mechanically Alloyed and Heat-Treated Al73Cu11Cr16
Authors:
Sviridova, TA; Shevchukov, AP; Shelekhov, EV; Diakonov, DL; Gorshenkov, MV; Kaloshkin, SD; Tcherdyntsev, VV; Li, Z; Fan, G Author Full Names: Sviridova, T. A.; Shevchukov, A. P.; Shelekhov, E. V.; Diakonov, D. L.; Gorshenkov, M. V.; Kaloshkin, S. D.; Tcherdyntsev, V. V.; Li, Z.; Fan, G.
Source:
ACTA PHYSICA POLONICA A, 126 (2):599-602; AUG 2014
Abstract:
X-ray diffraction analysis, scanning and transmission electron microscopy, thermal analysis and measurement of chemical composition were implemented to determine structure, thermal stability and chemical composition of the decagonal quasicrystal in Al73Cu11Cr16 alloy produced by long-term mechanical alloying of elemental powders followed by annealing at 700 C. According to the TEM investigation such a technique permits to produce a single-phase nanostructural quasicrystal with grain size about 60 nm. Differential thermal analysis revealed that the decagonal phase does not exist above 923 degrees C and undergoes incongruent two-stage melting coming to the end at 1100 degrees C.
Title:
Periodic Series of Peaks in Diffraction Patterns of Aperiodic Structures
Authors:
Wolny, J; Kozakowski, B; Kuczera, P; Pytlik, L; Strzalka, R; Wnek, A Author Full Names: Wolny, J.; Kozakowski, B.; Kuczera, P.; Pytlik, L.; Strzalka, R.; Wnek, A.
Source:
ACTA PHYSICA POLONICA A, 126 (2):625-628; AUG 2014
Abstract:
Quasicrystals are aperiodic structures with no periodicity both in direct and reciprocal space. The diffraction pattern of quasicrystals consists however of the periodic series of peaks in the scattering vector space. The intensities of the peaks of all series reduced in a proper way build up the so-called envelope function common for the whole pattern. The Fourier transformed envelope gives the average unit cell which is the statistical distribution of atomic positions in physical space. The distributions lifted to high dimensions correspond to atomic surfaces - the basic concept of structural quasicrystals modeling within higher-dimensional approach.
Title:
Electronic Structure and Transport in Approximants of the Penrose Tiling
Authors:
de Laissardiere, GT; Szallas, A; Mayou, D Author Full Names: de Laissardiere, G. Trambly; Szallas, A.; Mayou, D.
Source:
ACTA PHYSICA POLONICA A, 126 (2):617-620; AUG 2014
Abstract:
We present numerical calculations of electronic structure and transport in the Penrose approximants. The electronic structure of perfect approximants shows a spiky density of states and a tendency to localization that is more pronounced in the middle of the band. Near the band edges the behavior is more similar to that of free electrons. These calculations of band structure and in particular the band scaling suggest an anomalous quantum diffusion when compared to normal ballistic crystals. This is confirmed by a numerical calculation of quantum diffusion which shows a crossover from normal ballistic propagation at long times to anomalous, possibly insulator-like, behavior at short times. The time scale t* (E) for this crossover is computed for several approximants and is detailed. The consequences for electronic conductivity are discussed in the context of the relaxation time approximation. The metallic-like or non-metallic-like behavior of the conductivity is dictated by the comparison between the scattering time due to defects and the time scale t* (E).
Title:
Characterization of Rapidly Solidified Al65Cu20Fe15 Alloy in Form of Powder or Ribbon
Authors:
Litynska-Dobrzynska, L; Dutkiewicz, J; Stan-Glowinska, K; Dembinski, L; Coddet, C; Ochin, P Author Full Names: Litynska-Dobrzynska, L.; Dutkiewicz, J.; Stan-Glowinska, K.; Dembinski, L.; Coddet, C.; Ochin, P.
Source:
ACTA PHYSICA POLONICA A, 126 (2):512-515; AUG 2014
Abstract:
The Al65Cu20Fe15 alloy has been prepared by conventional casting to the mould and by melt spinning or atomisation techniques. The melt spun ribbon was in the form of fragmented, brittle flakes, atomized powder has spherical shape with average size 17.2 mu m. It was found that icosahedral I-phase was the main phase in all types of prepared samples. In the conventionally cast alloy the following phases have been identified additionally: lambda-Al13Fe4, tau-AlCu(Fe) and eta(2)-AlCu. In the melt-spun ribbon the formation of eta(2) is avoided, while in the atomised powder the I-phase coexists with small amount of copper rich tau-phase. In the cast ingot the I-phase form as a product of peritectic reaction lambda + L, while in the ribbon and in the powder quasicrystal solidified from the undercooled melt as primary phase and next metastable cubic tau-AlCu(Fe) was formed at the interdendritic areas. Single I-phase grains of the sizes about 1 mu m are observed in the ribbon close to the wheel side.
Title:
N-H center dot center dot center dot O and C-H center dot center dot center dot F hydrogen bonds in the incommensurately modulated crystal structure of adamantan-1-ammonium 4-fluorobenzoate
Authors:
Schonleber, A; van Smaalen, S; Weiss, HC; Kesel, AJ Author Full Names: Schoenleber, Andreas; van Smaalen, Sander; Weiss, Hans-Christoph; Kesel, Andreas J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 652-659; 10.1107/S2052520614007707 4 AUG 2014
Abstract:
At low temperatures the organic salt adamantan-1-ammonium 4-fluorobenzoate, C10H18N+center dot C7H4FO2-, possesses an incommensurately modulated crystal structure. The effect of the modulation on the atomic arrangement and intermolecular interactions is studied by analysing single-crystal X-ray diffraction data within the (3 + 1)-dimensional superspace approach and superspace group P2(1)/n(alpha 0 gamma)00. The modulation strongly affects the position of the atoms as well as their atomic displacement parameters. Nevertheless, the molecular cations and anions are built by rigid moieties, which vary their orientation with respect to each other as a function of the phase of the modulation t. Cations and anions are connected into slabs by dense N-H center dot center dot center dot O and C-H center dot center dot center dot F hydrogen-bonded networks, which are characterized by being rather rigid and which show only a little variation as a function of the phase of the modulation t.
Title:
Formation of the Icosahedral Al-Cu-Fe Phase by Solid State Reaction
Authors:
Shulyatev, DA; Nigmatulin, AS; Chernikov, MA; Klyueva, MV; Shaitura, DS; Golovkova, EA Author Full Names: Shulyatev, D. A.; Nigmatulin, A. S.; Chernikov, M. A.; Klyueva, M. V.; Shaitura, D. S.; Golovkova, E. A.
Source:
ACTA PHYSICA POLONICA A, 126 (2):581-584; AUG 2014
Abstract:
Al-Cu-Fe alloys with a nominal composition of Al63Cu24Fe13, Al62Cu25.5Fe12.5 and Al65Cu20Fe15 have been fabricated by solid-state reaction at 550, 650, and 750 degrees C. The synthesized alloys mainly consist of icosahedral Al65Cu20Fe15, body-centered cubic beta-AlFe(Cu) and monoclinic lambda-Al13Fe4 phases. After synthesis under optimal conditions the fraction of the icosahedral phase was 100, 80, and 85 weight per cent in Al63Cu24Fe13, Al62Cu25.5Fe12.5, and Al65Cu20Fe15, respectively.
Title:
Inhomogeneous Electronic Localization in Icosahedral Quasicrystals
Authors:
Prekul, A; Schegolikhina, N; Shalaeva, E Author Full Names: Prekul, A.; Schegolikhina, N.; Shalaeva, E.
Source:
ACTA PHYSICA POLONICA A, 126 (2):556-559; AUG 2014
Abstract:
Experimental results indicating that the electronic inhomogeneity may be a fundamental property of icosahedral quasicrystals and their approximants are presented.
Title:
Direct and Reciprocal Space Properties of the Generalized Penrose Tiling
Authors:
Chodyn, M; Kuczera, P; Wolny, J Author Full Names: Chodyn, M.; Kuczera, P.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 126 (2):442-445; AUG 2014
Abstract:
We have constructed a generalized Penrose tiling by the cut-and-project method and compared its structure with that of the regular Penrose tiling. We derived the structure factor of the generalized Penrose tiling and applied it to calculate the diffraction pattern of a non-decorated structure.
Title:
Development of Composites with Icosahedral Phase in Al-Cu-Fe Quasicrystalline Alloys Obtained by the Bridgman Method
Authors:
Krawczyk, J Author Full Names: Krawczyk, J.
Source:
ACTA PHYSICA POLONICA A, 126 (2):501-504; AUG 2014
Abstract:
The composites were obtained by the Bridgman method through solidification of Al61Cu27Fe12 alloy (numbers indicate at.%). The microstructure of composites with crystal matrix and quasicrystal reinforcement was studied. The crystalline beta-phase was the matrix and the quasicrystaline i-phase was the reinforcement of obtained composites. The shape and spatial distribution of reinforcement fibres were specified. Some geometrical relations of the fibres arrangement were defined. Obtained composite samples were subjected to X-ray phase analysis, optical, and scanning electron microscopy observations, chemical microanalysis and the Laue diffraction.
Title:
Structure of decagonal Al-Ni-Rh
Authors:
Logvinovich, D; Simonov, A; Steurer, W Author Full Names: Logvinovich, Dmitry; Simonov, Arkadiy; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 732-742; 10.1107/S2052520614010750 4 AUG 2014
Abstract:
The crystal structure of the decagonal phase in the system Al-Ni-Rh (d-Al-Ni-Rh) was analyzed in the five-dimensional embedding approach based on single-crystal synchrotron X-ray diffraction data. The structure can be described as a quasiperiodic packing of partially overlapping decagonal and pentagonal columnar clusters with similar to 21 angstrom diameter and similar to 4 angstrom period along the tenfold axis.
Title:
Evolution of the beta Phase Flux Dissolution during Quasicrystal Formation
Authors:
Surowiec, M; Bogdanowicz, W; Sozanska, M Author Full Names: Surowiec, M.; Bogdanowicz, W.; Sozanska, M.
Source:
ACTA PHYSICA POLONICA A, 126 (2):594-596; AUG 2014
Abstract:
This study focuses mainly on the verification of a peritectic reaction during the crystallization of quasicrystals. The beta and lambda phases apparently provide the necessary material for crystallization of the quasicrystalline psi phase. We present results of an experimental visualization of the evolution of the flux dissolution process of the high temperature beta phase. Solidified droplets of the beta phase, formed primarily by the surface tension of the liquid within a bubble or a shrinkage, after crumbling during the flux dissolution may contribute to the quasicrystal formation process according to a peritectic reaction: beta(c) + lambda + L ->psi where beta(c) denotes the crumbled beta phase immersed in the liquid.
Title:
Compositions of Al-Based Quasicrystals Interpreted by Cluster Formulae
Authors:
Chen, H; Qiang, JB; Wang, YM; Dong, C Author Full Names: Chen, H.; Qiang, J. B.; Wang, Y. M.; Dong, C.
Source:
ACTA PHYSICA POLONICA A, 126 (2):446-448; AUG 2014
Abstract:
It is known previously that bulk metallic glass compositions satisfy cluster formulae [cluster](glue atom)(1,3) of 24 valence electrons as deduced from our cluster-resonance model. In the present work, it is further shown that compositions of Al-based binary and ternary quasicrystals are also explained by 24-electron cluster formulae of the types [icosahedron](glue atom)(0,1), where the icosahedral cluster is identified from a corresponding crystalline approximant according to dense atomic packing and cluster isolation criteria, and the glue atom site is either vacant for an icosahedral quasicrystal or equal to one for a decagonal quasicrystal. Ternary quasicrystals are formulated with the same formulae as their basic binary ones but the icosahedron shell sites are substituted by third elements. The 24-electron cluster formulae are then the chemical and electronic structural units of quasicrystals, mimicking the molecular formulae of chemical substances.
Title:
An Icosahedral Quasicrystal as a Packing of Regular Tetrahedra
Authors:
Fang, F; Kovacs, J; Sadler, G; Irwin, K Author Full Names: Fang, F.; Kovacs, J.; Sadler, G.; Irwin, K.
Source:
ACTA PHYSICA POLONICA A, 126 (2):458-460; AUG 2014
Abstract:
We present the construction of a dense, quasicrystalline packing of regular tetrahedra with icosahedral symmetry. This quasicrystalline packing was achieved through two independent approaches. The first approach originates in the Elser Sloane 4D quasicrystal. A 3D slice of the quasicrystal contains a few types of prototiles. An initial structure is obtained by decorating these prototiles with tetrahedra. This initial structure is then modified using the Elser Sloane quasicrystal itself as a guide. The second approach proceeds by decorating the prolate and oblate rhombohedra in a 3-dimensional Ammann tiling. The resulting quasicrystal has a packing density of 59.783%. We also show a variant of the quasicrystal that has just 10 "plane classes" (compared with the 190 of the original), defined as the total number of distinct orientations of the planes in which the faces of the tetrahedra are contained. This small number of plane classes was achieved by a certain "golden rotation" of the tetrahedra.
Title:
Transport Properties of the Au-Al-Yb Quasicrystal and Approximant under Hydrostatic Pressure
Authors:
Matsukawa, S; Tanaka, K; Nakayama, M; Kunikata, S; Deguchi, K; Imura, K; Ishimasa, T; Sato, NK Author Full Names: Matsukawa, S.; Tanaka, K.; Nakayama, M.; Kunikata, S.; Deguchi, K.; Imura, K.; Ishimasa, T.; Sato, N. K.
Source:
ACTA PHYSICA POLONICA A, 126 (2):527-530; AUG 2014
Abstract:
The mixed-valence Au-Al-Yb quasicrystal exhibits unusual quantum criticality. Its crystalline approximant behaves like a conventional heavy fermion metal. Due to these novel features, they have attracted much attention recently. To examine the sample dependence of this new type of materials, we have prepared several samples and measured the electrical resistivity both at ambient and high pressures as well as the magnetic susceptibility at ambient pressure. The residual resistivity ratio of the quasicrystals is almost sample independent while the power law exponent n of the electrical resistivity varies from sample to sample. The effective magnetic moment p(eff) of the quasicrystals is also sample dependent, ranging from about 3.4 to 3.9 mu(B)/Yb, and these values are all smaller than the free Yb3+ ion value, confirming the mixed-valence nature. Although the magnitude of n and p(eff) is sample-dependent, the principal feature of the mixed-valence is confirmed in all the samples studied thus far. A combination of these results indicates correlation between n and p(eff) suggesting that the 4f electrons may contribute to a scattering mechanism of the conduction electrons. External pressure increases the magnitude of the electrical resistivity and decreases the index n of both the quasicrystal and the approximant. Up to the highest pressure measured in the present study no experimental evidence for a phase transition was found.
Title:
Topology of the Random Fibonacci Tiling Space
Authors:
Gahler, F; Miro, E Author Full Names: Gaehler, F.; Miro, E.
Source:
ACTA PHYSICA POLONICA A, 126 (2):564-567; AUG 2014
Abstract:
We look at the topology of the tiling space of locally random Fibonacci substitution, which is defined as a -> ba with probability p, a -> ab with probability 1-p and b -> a for 0 < p < 1. We show that its Cech cohomology group is not finitely generated, in contrast to the case where random substitutions are applied globally.
Title:
Coincidences of a Shifted Hexagonal Lattice and the Hexagonal Packing
Authors:
Arias, JCH; Gabinete, ED; Loquias, MJC Author Full Names: Arias, J. C. H.; Gabinete, E. D.; Loquias, M. J. C.
Source:
ACTA PHYSICA POLONICA A, 126 (2):516-519; AUG 2014
Abstract:
A geometric study of twin and grain boundaries in crystals and quasicrystals is achieved via coincidence site lattices and coincidence site modules, respectively. Recently, coincidences of shifted lattices and multilattices (i.e. finite unions of shifted copies of a lattice) have been investigated. Here, we solve the coincidence problem for a shifted hexagonal lattice. This result allows us to analyze the coincidence isometrics of the hexagonal packing by viewing the hexagonal packing as a multilattice.
Title:
From Colorings to Weavings
Authors:
Miro, E; Garciano, A; Zambrano, A Author Full Names: Miro, E.; Garciano, A.; Zambrano, A.
Source:
ACTA PHYSICA POLONICA A, 126 (2):560-563; AUG 2014
Abstract:
We present a methodology for constructing weavings from 2-colorings of the plane. In particular, we consider tilings T of the plane by triangles and their corresponding triangle groups G. We derive 2-colorings of T using the index 2 subgroups of G.
Title:
Structure Model for Icosahedral Quasicrystal Based on Ammann Tiling
Authors:
Strzalka, R; Wolny, J Author Full Names: Strzalka, R.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 126 (2):585-587; AUG 2014
Abstract:
We derive a structure model for icosahedral quasicrystals. The model is based on a statistical approach involving the concept of average unit cell. This approach enables limiting calculations to real space as opposed to higher-dimensional analysis involving to unphysical atomic surface modeling. We start with the three-dimensional Ammann tiling with its two rhombohedral prototiles. For monoatomic decoration of the lattice nodes the perfect agreement with the higher-dimensional description was recently shown. In this paper we discuss the shape of the average unit cell and the first attempts for decoration scheme.
Title:
RKKY Interactions and Low-Temperature Behaviour of Spins in Quasiperiodic Tilings
Authors:
Thiem, S Author Full Names: Thiem, S.
Source:
ACTA PHYSICA POLONICA A, 126 (2):613-616; AUG 2014
Abstract:
We study the structure of the Ruderman Kittel Kasuya Yosida interactions for selected quasiperiodic tilings. The interaction energies between the magnetic impurities in these systems are computed by a continued fraction expansion for the Green function of the conduction electrons. Based on these results we study the alignment of the magnetic moments in the Ammann Beenker tiling by Monte Carlo simulations. In particular, we are interested in the structure of the magnetic ground state and the low-temperature behaviour for the Ising model.
Title:
Proceedings of the 12th International Conference on Quasicrystals (ICQ12) Krakow, Poland, September 1-6, 2013 Preface
Authors:
Wolny, J; Surowiec, M Author Full Names: Wolny, Janusz; Surowiec, Marian
Source:
ACTA PHYSICA POLONICA A, 126 (2):429-429; AUG 2014
Title:
Tight-Binding Models in a Quasiperiodic Optical Lattice
Authors:
Jagannathan, A; Duneau, M Author Full Names: Jagannathan, A.; Duneau, M.
Source:
ACTA PHYSICA POLONICA A, 126 (2):490-492; AUG 2014
Abstract:
This paper describes how one can use four standing wave laser fields to realize a two dimensional optical quasicrystal with eight-fold symmetry, closely related to the well-known octagonal or Ammann-Beenker tiling quasicrystal. We describe the structure and we outline the main features of an effective tight-binding model for atoms in this optical quasicrystal. Such a system, if realized experimentally, should provide valuable insights into the quantum properties of quasicrystals.
Title:
Recent Progress in Mathematical Diffraction
Authors:
Grimm, U; Baake, M Author Full Names: Grimm, U.; Baake, M.
Source:
ACTA PHYSICA POLONICA A, 126 (2):474-478; AUG 2014
Abstract:
A brief summary of recent developments in mathematical diffraction theory is given. Particular emphasis is placed on systems with aperiodic order and continuous spectral components. We restrict ourselves to some key results and refer to the literature for further details.
Title:
Tiling Vertices and the Spacing Distribution of Their Radial Projection
Authors:
Jakobi, T Author Full Names: Jakobi, T.
Source:
ACTA PHYSICA POLONICA A, 126 (2):493-496; AUG 2014
Abstract:
The Fourier-based diffraction approach is an established method to extract order and symmetry properties from a given point set. We want to investigate a different method for planar sets which works in direct space and relies on reduction of the point set information to its angular component relative to a chosen reference frame. The object of interest is the distribution of the spacings of these angular components, which can for instance be encoded as a density function on R+. In fact, this radial projection method is not entirely new, and the most natural choice of a point set, the integer lattice Z(2), is already well understood. We focus on the radial projection of aperiodic point sets and study the relation between the resulting distribution and properties of the underlying tiling, like symmetry, order and the algebraic type of the inflation multiplier.
Title:
F-AlCoPdGe Alloy with Three Types of Pseudo-Mackay Clusters
Authors:
Sugiyama, K; Yubuta, K; Yokoyama, Y; Suzuki, S; Simura, R Author Full Names: Sugiyama, K.; Yubuta, K.; Yokoyama, Y.; Suzuki, S.; Simura, R.
Source:
ACTA PHYSICA POLONICA A, 126 (2):588-593; AUG 2014
Abstract:
The structure of an F-AlCoPdGe alloy was determined by single-crystal X-ray diffraction analysis: space group Pa (3) over bar (No. 205), Pearson symbol cP1128-142.4, a = 24.4338(4) angstrom; R1 = 0.0526 for the observed 5106 reflections with Fo > 4.0 sigma(F-0). The F-AlCoPdGe alloy exhibited three types of pseudo-Mackay clusters (pMCs). The first shell of the Co(13)-pMC at 24d indicated a coordination polyhedron typically found in Al Co binary approximants; the second shell was a combination of an M icosahedron and an Al icosidodecahedron, where M is a mixed site of Pd and/or Co. The first shell of the Co(14)-pMC at 4b consisted of 20 partially occupied Al positions arranged in a dodecahedral fashion; its second shell was also composed of an M icosahedron and an Al icosidodecahedron. The first shell of the Al(18)-pMC at 4a consisted of a combination of an M cube and an Al octahedron, resulting in the rhombic dodecahedral arrangement; its outer shell structure was similar to those of the other pMCs. The structure of the F-AlCoPdGe phase comprised an arrangement of these three types of pMCs together with interstitially placed Al icosahedra around the Pd/Al(1) and Pd/Al(2) sites.
Title:
Phason Contribution to the Dislocation Loop Bias in Quasicrystals
Authors:
Lavrova, GN; Turkin, AA; Bakai, AS Author Full Names: Lavrova, G. N.; Turkin, A. A.; Bakai, A. S.
Source:
ACTA PHYSICA POLONICA A, 126 (2):505-507; AUG 2014
Abstract:
We develop a model of the absorption of vacancies and self-interstitial atoms by dislocation loops and associated phason defects in quasicrystals under irradiation. The capture efficiency and the bias of the loop for radiation point defects are evaluated for variable loop sizes. Numerical calculation of these quantities is performed for comparison. It is shown that phason defects decrease the total bias of the dislocation loop in a quasicrystal.
Title:
Surface Decorations of Al-Cu-Fe and Al-Cu-Co Single Quasicrystals
Authors:
Surowiec, M; Bogdanowicz, W; Krawczyk, J; Sozanska, M Author Full Names: Surowiec, M.; Bogdanowicz, W.; Krawczyk, J.; Sozanska, M.
Source:
ACTA PHYSICA POLONICA A, 126 (2):597-598; AUG 2014
Abstract:
We studied surface decorations of faceted icosahechal Al-Cu-Fe and decagonal Al-Cu-Co single quasicrystals by the scanning electron microscopy using primary and secondary electrons. Both types of single quasicrystals exhibited decorations on their facets, however the character of the decorations was totally different. Three kinds of decorations has been developed. On icosahech-al Al60Cu26Fe14 quasicrystals we found three kinds of decorations: cellular, cavity type and fractal-like. There was no evident difference in chemical composition between the inner dodecahedra and the decorations of all types. Surface decorations found on decagonal Al73.5Cu17.5Co9 quasicrystals formed a kind of irregular dench-itic stars on the separate bright islands.
Title:
The Structure of the (100) Surface of Ag-In-Gd 1/1 Approximant
Authors:
Hars, SS; Sharma, HR; Smerdon, JA; Yadav, TP; Tamura, R; Shimoda, M; McGrath, R Author Full Names: Hars, S. S.; Sharma, H. R.; Smerdon, J. A.; Yadav, T. P.; Tamura, R.; Shimoda, M.; McGrath, R.
Source:
ACTA PHYSICA POLONICA A, 126 (2):479-481; AUG 2014
Abstract:
Scanning tunneling microscopy is employed to characterise the structure and morphology of the (100) surface of the Ag-In-Gd 1/1 approximant. The surface prepared by the usual method of sputter-annealing produces stepterrace structure. Observed step heights are consistent with the lattice constant of the bulk. Scanning tunneling microscopy on terraces reveals cluster-like protrusions arranged with a square unit cell as expected from the bulk. It has not been possible to assign the terraces to the specific bulk planes because of lack of atomic resolution on terraces.
Title:
Quotient Cohomology of Certain 1-and 2-Dimensional Substitution Tiling Spaces
Authors:
Bugarin, EP; Gahler, F Author Full Names: Bugarin, E. P.; Gaehler, F.
Source:
ACTA PHYSICA POLONICA A, 126 (2):438-441; AUG 2014
Abstract:
The quotient cohomology of tiling spaces is a topological invariant that relates a tiling space to one of its factors, viewed as topological dynamical systems. In particular, it is a relative version of the tiling cohomology that distinguishes factors of tiling spaces. In this work, the quotient cohomologies within certain families of substitution tiling spaces in 1 and 2 dimensions are determined. Specifically, the quotient cohomologies for the family of the generalised Thue Morse sequences and generalised chair tilings are presented.
Title:
Incommensurate modulations of relaxor ferroelectric Ca0.24Ba0.76Nb2O6 (CBN24) and Ca0.31Ba0.69Nb2O6 (CBN31)
Authors:
Graetsch, HA; Pandey, CS; Schreuer, J; Burianek, M; Muhlberg, M Author Full Names: Graetsch, Heribert A.; Pandey, Chandra Shehkar; Schreuer, Juergen; Burianek, Manfred; Muehlberg, Manfred
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 743-749; 10.1107/S2052520614011676 4 AUG 2014
Abstract:
CBN crystals show a one- and a two-dimensionally modulated modification. The former is isotypic with orthorhombic Ba4Na2Nb10O30 and the latter with the tetragonal tungsten bronze type of crystal structure. The orthorhombic form irreversibly transforms to the tetragonal polymorph at the ferroelectric phase transition near 603 K. Orthorhombic and tetragonal CBN24 slightly differ in the distribution of the Ba and Ca atoms over the incompletely filled Me1 and Me2 sites. The tetragonal symmetry is further broken in orthorhombic CBN24 by different amplitudes of the positional modulations of O atoms which are symmetrically equivalent in the TTB structure. A similar orthorhombic phase of CBN31 could be obtained by quenching from 1473 K.
Title:
Magnetic Properties of Icosahedral (Au,Cu)-Al-Yb Quasicrystals
Authors:
Oki, S; Hiroto, T; Muro, Y; Tamura, R Author Full Names: Oki, S.; Hiroto, T.; Muro, Y.; Tamura, R.
Source:
ACTA PHYSICA POLONICA A, 126 (2):553-555; AUG 2014
Abstract:
We have synthesized Cu-substituted (Au,Cu) Al Yb quasicrystals in order to investigate the relationship between the quasilattice constant and the magnetic property. The quasilattice constant a R is found to decrease as Au is replaced by Cu, and the maximum reduction of 2.18% in aR was observed for x = 0.60 in (Au1-xCux)(49)Al34Yb17. Magnetic measurements of (Au1-xCux)(49)Al34Yb17 (x = 0, 0.10, 0.20, 0.50) show that the intermediate-valence state of Yb persists in all the studied compositions. The effective magnetic moment is found to depend on (r) over bar /a(R) rather than on the quasilattice constant a(R). This suggests that f/ari can be regarded as a measure of the chemical pressure induced on the Yb atoms.
Title:
Electric-Elastic Field Induced by a Straight Dislocation in One-Dimensional Quasicrystals
Authors:
Yang, LZ; Gao, Y; Pan, E; Waksmanski, N Author Full Names: Yang, L. -Z.; Gao, Y.; Pan, E.; Waksmanski, N.
Source:
ACTA PHYSICA POLONICA A, 126 (2):467-470; AUG 2014
Abstract:
By using the generalized Stroh formalism, the electric-elastic field induced by a straight dislocation parallel to a periodic axis of a one-dimensional quasicrystal is obtained. The derivation is concise and the solution is in an exact closed form. As an illustration, the electric-elastic fields around a straight dislocation in a one-dimensional hexagonal quasicrystal are studied. Besides the interesting numerical results presented, the generalized Stroh formalism can be applied to more complicated dislocation problems in quasicrystals.
Title:
Tsai-Type Quasicrystal and Its Approximant in Au-Al-Tm Alloys
Authors:
Tanaka, K; Tanaka, Y; Ishimasa, T; Nakayama, M; Matsukawa, S; Deguchi, K; Sato, NK Author Full Names: Tanaka, K.; Tanaka, Y.; Ishimasa, T.; Nakayama, M.; Matsukawa, S.; Deguchi, K.; Sato, N. K.
Source:
ACTA PHYSICA POLONICA A, 126 (2):603-607; AUG 2014
Abstract:
A P-type icosahedral quasicrystal with a six-dimensional lattice parameter a(6D) = 7.411 angstrom is formed as an equilibrium phase in Au-Al-Tm alloy, of which composition was analyzed to be Au(46)AL(38)Tm(16) by electron probe microanalysis. This quasicrystal is observed as a predominant phase in both as-cast and Au49Al34Tm17 alloys annealed at 910 degrees C, and as one of main phases in the alloy slowly cooled from 1020 degrees C. A 1/1 approximant, Au48Al38Tm14, is also formed near the composition of the quasicrystal. This is a body-centered cubic structure (space group: /m(3)) with a lattice parameter a = 14.458 angstrom that is an isostructure to the recently reported 1/1 Tsai-type approximant in Au-Al-Yb. This approximant is characterized by disorderly arranged four Au-Al atoms centered at the Tsai-type cluster, presence of atoms at 8c site, and chemical ordering of Au and Al at sites forming a partial triacontahedron.
Title:
Temperature Dependence of Ag Film Roughening during Deposition on Quasicrystal and Approximant Surfaces
Authors:
Unal, B; Evans, JW; Thiel, PA Author Full Names: Uenal, B.; Evans, J. W.; Thiel, P. A.
Source:
ACTA PHYSICA POLONICA A, 126 (2):608-612; AUG 2014
Abstract:
The temperature (T) dependence of roughening as assessed by scanning tunneling microscopy is compared for growth of Ag films on an 5-fold icosahedral Al-Pd-Mn quasicrystal surface and on an xi'-approximant. Growth on the quasicrystal corresponds to a version of the Volmer Weber growth, but modified by quantum size effects, and also by kinetic smoothening at low T and low coverages (theta). Growth on the approximant corresponds to a version of the Stranski Krastanov growth modified by kinetic roughening at low T and low theta. For larger theta, i.e., for thicker films, distinct behavior is observed.
Title:
Colloidal Trajectories in Two-Dimensional Light-Induced Quasicrystals with 14-Fold Symmetry due to Phasonic Drifts
Authors:
Martinsons, M; Sandbrink, M; Schmiedeberg, M Author Full Names: Martinsons, M.; Sandbrink, M.; Schmiedeberg, M.
Source:
ACTA PHYSICA POLONICA A, 126 (2):568-571; AUG 2014
Abstract:
Quasicrystals are structures that are not periodic but possess a long range positional order. They can have any rotational symmetry including those that are forbidden in periodic crystals. The symmetry is classified by the point group and the rank D. In quasicrystals, phasons as additional hydrodynamic modes cause correlated rearrangements of the particles. The number of phasonic degrees of freedom depends on the rank. For colloidal quasicrystals that are induced by laser fields, specific phasonic displacements can be realized by changing the phases of the laser beams in a well-determined way. The arising trajectories of colloids in two-dimensional light-induced colloidal quasicrystals with rank D = 4 have already been analyzed in detail. Here, we analyze the colloidal trajectories in two-dimensional quasicrystals with 14-fold symmetry having rank D = 6. We observe complex paths of the colloids consisting of straight and winding lines as well as jumps.
Title:
Structure of an Al-Fe-Ni Decagonal Quasicrystal Studied by Cs-Corrected STEM
Authors:
Yasuhara, A; Yamamoto, K; Yubuta, K; Hiraga, K Author Full Names: Yasuhara, A.; Yamamoto, K.; Yubuta, K.; Hiraga, K.
Source:
ACTA PHYSICA POLONICA A, 126 (2):637-640; AUG 2014
Abstract:
The structure of an Al-Fe-Ni decagonal quasicrystal with two quasiperiodic planes along the periodic axis in an Al72Ni24Fe4 alloy has been examined by spherical aberration (Cs)-corrected scanning transmission electron microscopy with high-angle annular dark-field and annular bright-field techniques. The transition-metal atoms and mixed sites (MSs) of Al and transition-metal atoms are represented as separated bright dots in the observed high-angle annular dark-field scanning transmission electron microscopy images, and consequently the arrangements of transition-metal atoms and mixed sites on the two quasiperiodic planes can be directly determined. The transition-metal atoms are arranged on a pentagonal tiling of an edge-length of 0.76 nm. The close examination of observed annular bright-field- and high-angle annular dark-field scanning transmission electron microscopy images indicates the existence of large decagonal columnar clusters with 3.2 nm diameter, and their arrangement on pentagonal, thin rhombic and squashed hexagonal tiles with an edge-length of 3.2 nm. The arrangements of transition-metal atoms in these three tiles are placed on an ideal pentagonal tiling with an edge-length of 3.2 nm, which is generated by the projection of a five-dimensional hyper-cubic lattice. The vertices are denoted by 5D hyper-cubic indices and then they are projected on the occupation domains in perpendicular space. The arrangement of Al atoms as well as transition-metal atoms and mixed sites in the large decagonal atom cluster with about 3.2 nm diameter is interpreted from the observed high-angle annular dark-field- and annular bright-field scanning transmission electron microscopy ABF-STEM images.
Title:
Tiling Spaces of Taylor-Socolar Tilings
Authors:
Lee, JY Author Full Names: Lee, J. -Y.
Source:
ACTA PHYSICA POLONICA A, 126 (2):508-511; AUG 2014
Abstract:
The Taylor Socolar tiling has been introduced as an aperiodic mono-tile tiling. We consider a tiling space which consists of all the tilings that are locally indistinguishable from a Taylor-Socolar tiling and study its structure. It turns out that there is a bijective map between the space of the Taylor-Socolax tilings and a compact Abelian group of a Q-adic space ((Q) over bar) except at a dense set of points of measure 0 in ((Q) over bar). From this we can derive that the Taylor Socolar tilings have quasicrystalline structures. We make a parity tiling from the Taylor Socolar tiling identifying all the rotated versions of a tile in the Taylor-Socolax tiling by white tiles and all the reflected versions of the tile by gray tiles. It turns out that the Taylor-Socolax tiling is mutually locally derivable from this parity tiling.
Title:
Aperiodic crystals and superspace concepts
Authors:
Janssen, T; Janner, A Author Full Names: Janssen, T.; Janner, A.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 617-651; 10.1107/S2052520614014917 4 AUG 2014
Abstract:
For several decades the lattice periodicity of crystals, as shown by Laue, was considered to be their essential property. In the early sixties of the last century compounds were found which for many reasons should be called crystals, but were not lattice periodic. This opened the field of aperiodic crystals. An overview of this development is given. Many materials of this kind were found, sometimes with very interesting properties. In the beginning the development was slow, but the number of structures of this type increased enormously. In the meantime hundreds of scientists have contributed to this field using a multi-disciplinary approach.
Title:
Finite Element Method for Static Problems of Cubic Quasicrystals
Authors:
Yang, LZ; He, FM; Gao, Y Author Full Names: Yang, L. -Z.; He, F. -M.; Gao, Y.
Source:
ACTA PHYSICA POLONICA A, 126 (2):471-473; AUG 2014
Title:
Curie Temperature and Density of States at the Fermi Level for Al-Cu-Fe Phases: beta-Solid State
Authors:
Shalaeva, EV; Prekul, AF; Shchegolikhina, NI; Medvedeva, NI Author Full Names: Shalaeva, E. V.; Prekul, A. F.; Shchegolikhina, N. I.; Medvedeva, N. I.
Source:
ACTA PHYSICA POLONICA A, 126 (2):572-576; AUG 2014
Abstract:
A consistent reduction in the absolute value of the negative paramagnetic Curie temperature was found in a series of Al-Cu-Fe phases: beta(CsCl)- solid state solution, noncanonical approximant (eta-AlCu(Fe) phase), rational approximants (P1+P2-pentagonal phases) and icosahechal quasicrystal. For these Al-Cu-Fe phases, the decrease in the Curie temperature correlates with a reduction of the density of states at the Fermi level which was estimated from the low-temperature heat capacity measurements and first-principles calculations. The observed correlation was related to the antiferromagnetic indirect exchange interaction (Ruderman Kittel Kasuya Yosida interaction) between the localized magnetic moments on Fe induced by the intrinsic structural defects in the Al-Cu-Fe phases. The weakening of Fe 3d-Al s,p hybridization owing to the intrinsic structural defects such as vacancies, antisite defects and distortions of coordination polyhedrons is suggested to be the main mechanism of appearance of localized magnetic moments on Fe atoms.
Title:
Shape Limit in Triangular Spiral Tilings
Authors:
Sushida, T; Hizume, A; Yamagishi, Y Author Full Names: Sushida, T.; Hizume, A.; Yamagishi, Y.
Source:
ACTA PHYSICA POLONICA A, 126 (2):633-636; AUG 2014
Abstract:
Phyllotaxis is the study of arrangements of leafs and florets. The topology of triangular spiral (multiple) tilings with opposed parastichy pairs is intimately related to the phyllotaxis theory and continued fractions. It is shown that, if the divergence angle of the genetic spiral is given as a quadratic irrational and fixed, then the limit set of the shape parameters of triangular tiles, as the parastichy numbers tend to infinity, is a finite set. In particular, the limit is the golden section if the divergence angle is 'ultimately golden'.
Title:
Inverse Hall Petch Like Mechanical Behaviour in Nanophase Al-Cu-Fe Quasicrystals: A New Phenomenon
Authors:
Mukhopadhyay, NK; Ali, F; Scudino, S; Khoshkhoo, MS; Stoica, M; Srivastava, VC; Uhlenwinkel, V; Vaughan, G; Suryanarayana, C; Eckert, J Author Full Names: Mukhopadhyay, N. K.; Ali, F.; Scudino, S.; Khoshkhoo, M. Samadi; Stoica, M.; Srivastava, V. C.; Uhlenwinkel, V.; Vaughan, G.; Suryanarayana, C.; Eckert, J.
Source:
ACTA PHYSICA POLONICA A, 126 (2):543-548; AUG 2014
Abstract:
The structural and mechanical stability of quasicrystals are important issues due to their potential for possible applications at high temperatures and stresses. The aim of the present work is, therefore, to review the earlier works on conventional crystalline and quasicrystalline materials and also to report the results and the analysis on the Hall Petch and inverse Hall Petch like behavior of nanoquasicrystalline Al62.5Cu25Fe12.5 alloys. It was observed that, at large grain sizes, the hardness increases with decreasing grain size, exhibiting the conventional Hall Petch relationship, whereas for smaller grains, inverse Hall Petch behavior was identified. The inverse Hall Fetch behavior in the nanoquasicrystalline phase could be attributed to thermally activated shearing of the grain boundaries, leading to grain boundary sliding in nanostructures of quasicrystalline grains. These results were analyzed based on the dislocation pile-up model as well as the grain boundary shearing models applicable to nanomaterials.
Title:
Leaching of Al-Based Polygrain Quasicrystalline and Related Crystalline Surfaces
Authors:
Yadav, TP; Mishra, SS; Pandey, SK; Singh, D; Lowe, M; Tamura, R; Mukhopadhyay, NK; Srivastava, ON; McGrath, R; Sharma, HR Author Full Names: Yadav, T. P.; Mishra, S. S.; Pandey, S. K.; Singh, D.; Lowe, M.; Tamura, R.; Mukhopadhyay, N. K.; Srivastava, O. N.; McGrath, R.; Sharma, H. R.
Source:
ACTA PHYSICA POLONICA A, 126 (2):629-632; AUG 2014
Abstract:
In the present investigation, we have studied leaching on polygrain Al-based quasicrystalline (i-Al63Cu25Fe12) as well as crystalline (B2 phase; Al55Cu30Fe15) alloy surfaces using a 10 mole NaOH solution. The surface was leached at varying times from 30 mm to 8 h and subsequently characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis. Leaching of the samples for 30 min generated a homogeneous layer. However further leaching for 1-8 h yielded nano-size particles on the surface. Spherical microstructure has been observed on the Al-Cu-Fe crystalline surface whereas on the quasicrystalline surface a petal-like microstructure appeared. The implications of the evolution of different microstructures in the context of structure, stability and activity are discussed. The results are compared with the microstructure of leached polygrained samples containing a mixture of different surface orientations.

Update: 23-Oct-2014

Title:
Influence of yttrium content on phase formation and strain hardening behavior of Mg-Zn-Mn magnesium alloy
Authors:
Tahreen, N; Zhang, DF; Pan, FS; Jiang, XQ; Li, C; Li, DY; Chen, DL Author Full Names: Tahreen, N.; Zhang, D. F.; Pan, F. S.; Jiang, X. Q.; Li, C.; Li, D. Y.; Chen, D. L.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 615 424-432; 10.1016/j.jallcom.2014.06.211 DEC 5 2014
Abstract:
The aim of this study was to identify the effect of yttrium (Y) addition on the phase development and strain hardening behavior of an extruded Mg-Zn-Mn (ZM31) magnesium alloy. The addition of a small amount (0.3 wt.%) of Y in the alloy led to the formation of icosahedral quasicrystalline I (Mg3YZn6) phase. Both I-phase and W-phase (Mg3Y2Zn3) were present in the extruded ZM31+3.2Y alloy, while long period stacking ordered (LPSO) X-phase (Mg12YZn) and Mg24Y5 were observed in the extruded ZM31+6Y alloy. The Y addition significantly refined grains in the extruded state. The presence of I-phase in the extruded ZM31+0.3Y alloy increased hardness, compressive yield strength, and Stage B strain hardening rate. The extruded ZM31+3.2Y alloy exhibited a lower hardness and Stage B hardening rate due to the formation of W-phase. Both extruded ZM31+0.3Y and ZM31+3.2Y alloys showed a yield point phenomenon with an initial negative strain hardening rate. The extruded ZM31+6Y alloy had a high hardness and compressive yield strength without Stage B hardening, suggesting a change of major deformation mode from twinning to slip mainly due to the role of LPSO X-phase. After solution treatment and aging, the hardness and compressive yield strength gradually increased with increasing Y content, while the strain hardening exponent and the extent of Stage B strain hardening decreased due to the dissolution of I- and W-phases and the presence of LPSO X-phase. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Synthesis of an icosahedral quasicrystalline phase in the Al-Cu-Fe system via mechanical activation
Authors:
Chugunov, DB; Filippova, SE; Portnoi, VK; Meshkov, LL Author Full Names: Chugunov, D. B.; Filippova, S. E.; Portnoi, V. K.; Meshkov, L. L.
Source:
INORGANIC MATERIALS, 50 (11):1083-1092; 10.1134/S0020168514110053 NOV 2014
Abstract:
A quasicrystalline compound of composition Al64Cu24Fe12 has been prepared through mechanical activation. We have studied the morphology of powder particles after heat treatment under various conditions, identified the sequence of phase transformations in Al-Cu-Fe alloys in the stability region of the ico-phase, and optimized conditions for the preparation of powders containing the maximum possible percentage of the quasicrystalline phase.
Title:
Dielectric properties of the ferroelectric composite (NaNO2)(0.9)/(BaTiO3)(0.1)
Authors:
Baryshnikov, S; Stukova, E; Koroleva, E Author Full Names: Baryshnikov, S.; Stukova, E.; Koroleva, E.
Source:
COMPOSITES PART B-ENGINEERING, 66 190-193; 10.1016/j.compositesb.2014.05.005 NOV 2014
Abstract:
The temperature and frequency dependences of dielectric properties of the ferroelectric composite (NaNO2)(0.9)/(BaTiO3)(0.1) have been studied. It was shown that in the composites the mutual influence of the components may lead to the expansion of incommensurate phase existence in NaNO2. The greatest contribution to the low-frequency dielectric constant of the composite is due to the Maxwell-Wagner polarization. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
Magnetic structure of the Eu2+ moments in superconducting EuFe2(As1-xPx)(2) with x=0.19
Authors:
Nandi, S; Jin, WT; Xiao, Y; Su, Y; Price, S; Schmidt, W; Schmalzl, K; Chatterji, T; Jeevan, HS; Gegenwart, P; Bruckel, T Author Full Names: Nandi, S.; Jin, W. T.; Xiao, Y.; Su, Y.; Price, S.; Schmidt, W.; Schmalzl, K.; Chatterji, T.; Jeevan, H. S.; Gegenwart, P.; Brueckel, Th.
Source:
PHYSICAL REVIEW B, 90 (9):10.1103/PhysRevB.90.094407 SEP 9 2014
Abstract:
The magnetic structure of the Eu2+ moments in the superconducting EuFe2(As1-xPx)(2) sample with x = 0.19 has been determined using neutron scattering. We conclude that the Eu2+ moments are aligned along the c direction below T-C = 19.0(1) K with an ordered moment of 6.6(2) mu(B) in the superconducting state. An impurity phase similar to the underdoped phase exists within the bulk sample which orders antiferromagnetically below T-N = 17.0(2) K. We found no indication of iron magnetic order, nor any incommensurate magnetic order of the Eu2+ moments in the sample.
Title:
Structure of a crystalline approximant related to Al-Co-Ni decagonal quasicrystals studied by spherical aberration (Cs)-corrected scanning transmission electron microscopy and atomic-resolution energy dispersive X-ray spectroscopy
Authors:
Yasuhara, A; Yubuta, K; Hiraga, K Author Full Names: Yasuhara, Akira; Yubuta, Kunio; Hiraga, Kenji
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 94 (9):539-547; 10.1080/09500839.2014.944604 2014
Abstract:
Six types of decagonal quasicrystals (DQCs) found in Al-Co-Ni alloys with a wide compositional ratio of Co/Ni are considered to be stabilized by chemical ordering of Co and Ni, but the elucidation of this ordering has never been performed on alloys containing neighbouring elements Co and Ni. In order to examine the chemical ordering, an Al-Co-Ni crystalline phase, the PD3c phase, which is an important approximant for understanding the structures of ordered Al-Co-Ni DQCs, in an Al71.5Co16Ni12.5 alloy has been studied by spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM) and atomic-resolution energy dispersive X-ray spectroscopy (EDXS). From the combination of observed high-angle annular dark-field and annular bright-field STEM observations, an atomic arrangement of the crystalline approximant can be directly derived. The chemical ordering of Co and Ni in the arrangement of transition-metal (TM) atoms and mixed sites (MSs) of TM and Al atoms can be clearly detected on atomic-resolution EDXS maps obtained with the special technique. Co atoms are located at the TM atom positions arranged in pentagonal tiling with a bond length of 0.76 nm, whereas Ni is enriched in the MSs located in pentagonal tiles of Co atoms. It can be concluded that the change of an area ratio of Co-rich clusters to Ni-rich MSs produces various types of DQCs with different compositional Ni/Co ratios.

Update: 15-Oct-2014

Title:
Incommensurate helical spin ground states on the hollandite lattice
Authors:
Mandal, S; Andreanov, A; Crespo, Y; Seriani, N Author Full Names: Mandal, S.; Andreanov, A.; Crespo, Y.; Seriani, N.
Source:
PHYSICAL REVIEW B, 90 (10):10.1103/PhysRevB.90.104420 SEP 24 2014
Abstract:
We present a model of classical Heisenberg spins on a hollandite lattice, which has been developed to describe the magnetic properties of alpha-MnO2 and similar compounds. The model has only nearest-neighbor interacting spins, however, the strength and the sign of spin-spin interactions is anisotropic and depends on the nature of the bonds. Our analysis shows that the hollandite lattice supports four different incommensurate and helical magnetic ground states depending on the relative strengths and signs of spin-spin interactions. We show that the incommensurate helical ground states appear due to the geometrical frustration present in the model. We demonstrate that each of the four helical incommensurate magnetic phases are continuously connected to four different collinear antiferromagnetic ground states as the strength of spin-spin interaction along some bonds is increased. The present results give support to the presence of helical states that have been previously suggested experimentally for hollandite compounds. We provide an in-depth analysis of the magnetic form factors for each helical phase and describe how it could be used to identify each of these phases in neutron diffraction experiments.
Title:
Spiral order in the honeycomb iridate Li2IrO3
Authors:
Reuther, J; Thomale, R; Rachel, S Author Full Names: Reuther, Johannes; Thomale, Ronny; Rachel, Stephan
Source:
PHYSICAL REVIEW B, 90 (10):10.1103/PhysRevB.90.100405 SEP 12 2014
Abstract:
The honeycomb iridates A(2)IrO(3) (A = Na, Li) constitute promising candidate materials to realize the Heisenberg-Kitaev model (HKM) in nature, hosting unconventional magnetic as well as spin-liquid phases. Recent experiments suggest, however, that Li2IrO3 exhibits a magnetically ordered state of incommensurate spiral type which has not been identified in the HKM. We show that these findings can be understood in the context of an extended Heisenberg-Kitaev scenario satisfying all tentative experimental evidence: (i) the maximum of the magnetic susceptibility is located inside the first Brillouin zone, (ii) the Curie-Weiss temperature is negative relating to dominant antiferromagnetic fluctuations, and (iii) significant second-neighbor spin exchange is involved.
Title:
Magnetic and nonmagnetic phases in doped AB(2) t-J Hubbard chains
Authors:
Montenegro, RR; Coutinho, MD Author Full Names: Montenegro-Filho, R. R.; Coutinho-Filho, M. D.
Source:
PHYSICAL REVIEW B, 90 (11):10.1103/PhysRevB.90.115123 SEP 11 2014
Abstract:
We discuss the rich phase diagram of doped AB(2) t-J chains by using data from density matrix renormalization group and exact diagonalization techniques. The J vs delta (hole doping) phase diagram exhibits regions of itinerant ferrimagnetism, incommensurate, resonating valence bond and Nagaoka states, phase separation, and Luttinger liquid (LL) physics. Several features are highlighted, such as the modulated ferrimagnetic structure, the occurrence of Nagaoka spin polarons in the underdoped regime and small values of J = 4t(2)/U, where t is the first-neighbor hopping amplitude and U is the on-site repulsive Coulomb interaction, incommensurate structures with nonzero magnetization, and strong-coupling LL physics in the high-doped regime. We also verify that relevant findings are in agreement with the corresponding findings in square and n-leg ladder lattices. In particular, we mention the instability of Nagaoka ferromagnetism against J and delta.
Title:
Renormalization group analysis of a fermionic hot-spot model
Authors:
Whitsitt, S; Sachdev, S Author Full Names: Whitsitt, Seth; Sachdev, Subir
Source:
PHYSICAL REVIEW B, 90 (10):10.1103/PhysRevB.90.104505 SEP 10 2014
Abstract:
We present a renormalization group (RG) analysis of a fermionic "hot-spot" model of interacting electrons on the square lattice. We truncate the Fermi-surface excitations to linearly dispersing quasiparticles in the vicinity of eight hot spots on the Fermi surface, with each hot spot separated from another by the wave vector (pi, pi). This is motivated by the importance of these Fermi-surface locations to the onset of antiferromagnetic order; however, we allow for all possible quartic interactions between the fermions, and also for all possible ordering instabilities. We compute the RG equations for our model, which depend on whether or not the hot spots are perfectly nested, and relate our results to earlier models. We also compute the RG flow of the relevant order parameters for both Hubbard and J, V interactions, and present our results for the dominant instabilities in the nested and non-nested cases. In particular, we find that non-nested hot spots with J, V interactions have competing singlet d(x2) (-) (y2) superconducting and d-form factor incommensurate density wave instabilities. We also investigate the enhancement of incommensurate density waves near experimentally observed wave vectors, and find dominant d-form factor enhancement for a range of couplings.
Title:
Formation of Tsai-type 1/1 approximants in In-Pd-RE (RE: rare earth metal) alloys
Authors:
So, YG; Saruhashi, F; Kimoto, K; Tamura, R; Edagawa, K Author Full Names: So, Yeong-Gi; Saruhashi, Fukuaki; Kimoto, Koji; Tamura, Ryuji; Edagawa, Keiichi
Source:
PHILOSOPHICAL MAGAZINE, 94 (26):2980-2991; 10.1080/14786435.2014.944607 2014
Abstract:
The formation of the 1/1 crystal approximant phase (1/1 phase) to the icosahedral phase (i phase) in In-Pd-RE (RE: rare earth metal) systems has been investigated. A new series of 1/1 phases were found in In53Pd33RE14 (RE; Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm) alloys. For Y, Sm, Gd, Tb, Dy, and Ho, the 1/1 phases were found in annealed alloys, indicating that they are thermodynamically stable. The atomic structure of the 1/1 phases was directly observed by high-angle annular dark-field imaging performed via scanning transmission electron microscopy, revealing that the 1/1 phases consisted of a periodic arrangement of Tsai-type icosahedral clusters. Further, the atomic size effect on i phase formation, as well as formation conditions previously reported for other Tsai-type i and 1/1 phases were examined. It was found that the ratio of the atomic radius of base metals such as In and Pd affects i phase formation. Moreover, the appropriate range of the radius ratio for i phase formation was narrower than that for 1/1 phase formation.

Update: 9-Oct-2014

Title:
The triplite-triploidite supergroup: structural modulation in wagnerite, discreditation of magniotriplite, and the new mineral hydroxylwagnerite
Authors:
Chopin, C; Armbruster, T; Grew, ES; Baronnet, A; Leyx, C; Medenbach, O Author Full Names: Chopin, Christian; Armbruster, Thomas; Grew, Edward S.; Baronnet, Alain; Leyx, Catherine; Medenbach, Olaf
Source:
EUROPEAN JOURNAL OF MINERALOGY, 26 (4):553-565; 10.1127/0935-1221/2014/0026-2386 AUG 2014
Abstract:
Electron-microprobe analysis, single-crystal X-ray diffraction with an area detector, and high-resolution transmission electron microscopy show that minerals related to wagnerite, triplite and triploidite, which are monoclinic Mg, Fe and Mn phosphates with the formula Me2+ 2PO4(F,OH), constitute a modulated series based on the average triplite structure. Modulation occurs along b and may be commensurate with (2b periodicity) or incommensurate but generally close to integer values (similar to 3b, similar to 5b, similar to 7b, similar to 9b), i.e. close to polytypic behaviour. As a result, the Mg- and F-dominant minerals magniotriplite and wagnerite can no longer be considered polymorphs of Mg2PO4F, i.e., there is no basis for recognizing them as distinct species. Given that wagnerite has priority (1821 vs. 1951), the name magniotriplite should be discarded in favour of wagnerite. Hydroxylwagnerite, end-member Mg2PO4OH, occurs in pyrope megablasts along with talc, clinochlore, kyanite, rutile and secondary apatite in two samples from lenses of pyrope-kyanite-phengite-quartz-schist within metagranite in the coesite-bearing ultrahigh-pressure metamorphic unit of the Dora-Maira Massif, western Alps, Vallone di Gilba, Val Varaita, Piemonte, Italy. Electron microprobe analyses of holotype hydroxylwagnerite and of the crystal with the lowest F content gave in wt%: P2O5 44.14, 43.99; SiO2 0.28, 0.02; SO3 -, 0.01; TiO2 0.20, 0.16; Al2O3 0.06, 0.03; MgO 48.82, 49.12; FeO 0.33, 0.48; MnO 0.01, 0.02; CaO 0.12, 0.10; Na2O 0.01, -; F 5.58, 4.67; H2O (calc) 2.94, 3.36; -O = F 2.35, 1.97; Sum 100.14, 99.98, corresponding to (Mg1.954Fe0.007Ca0.003Ti0.004Al0.002Na0.001)(Sigma=1.971)(P1.003Si0.008) (Sigma=1.011)O-4(OH0.526F0.474)(Sigma=1) and (Mg1.971Fe0.011Ca0.003Ti0.003Al0.001)(Sigma=1.989)(P1.002Si0.001)(Sigma= 1.003)O-4(OH0.603F0.397)(Sigma=1), respectively. Due to the paucity of material, H2O could not be measured, so OH was calculated from the deficit in F assuming stoichiometry, i.e., by assuming F + OH = 1 per formula unit. Holotype hydroxylwagnerite is optically biaxial (+), alpha 1.584(1), beta 1.586(1), gamma 1.587(1) (589 nm); 2V(Z) (meas.) = 43(2)degrees; orientation Y = b. Single-crystal X-ray diffraction gives monoclinic symmetry, space group P2(1)/c, a = 9.646(3) angstrom, b = 12.7314(16) angstrom, c = 11.980(4) angstrom, beta = 108.38(4)degrees, V = 1396.2(8) angstrom(3,) Z = 16, i.e., hydroxylwagnerite is the OH-dominant analogue of wagnerite [beta-Mg2PO4(OH)] and a high-pressure polymorph of althausite, holtedahlite, and alpha- and epsilon-Mg2PO4(OH). We suggest that the group of minerals related to wagnerite, triplite and triploidite constitutes a triplite-triploidite super-group that can be divided into F-dominant phosphates (triplite group), OH-dominant phosphates (triploidite group), O-dominant phosphates (stanekite group) and an OH-dominant arsenate (sarkinite). The distinction among the three groups and a potential fourth group is based only on chemical features, i.e., occupancy of anion or cation sites. The structures of these minerals are all based on the average triplite structure, with a modulation controlled by the ratio of Mg, Fe2+, Fe3+ and Mn2+ ionic radii to (O,OH,F) ionic radii.
Title:
Orbital correlations and dimensional crossover in epitaxial Pr0.5Ca0.5MnO3/La0.5Sr0.5MnO3 superlattices
Authors:
Wadati, H; Okamoto, J; Garganourakis, M; Scagnoli, V; Staub, U; Sakai, E; Kumigashira, H; Sugiyama, T; Ikenaga, E; Nakamura, M; Kawasaki, M; Tokura, Y Author Full Names: Wadati, H.; Okamoto, J.; Garganourakis, M.; Scagnoli, V.; Staub, U.; Sakai, E.; Kumigashira, H.; Sugiyama, T.; Ikenaga, E.; Nakamura, M.; Kawasaki, M.; Tokura, Y.
Source:
NEW JOURNAL OF PHYSICS, 16 10.1088/1367-2630/16/7/073044 JUL 30 2014
Abstract:
We studied the charge-orbital ordering in the superlattice of charge-ordered insulating Pr0.5Ca0.5MnO3 and ferromagnetic metallic La0.5Sr0.5MnO3 by resonant soft x-ray diffraction (RSXD) and hard x-ray photoemission spectroscopy (HXPES). A temperature-dependent incommensurability is found in the orbital ordering by RSXD. In addition, a large hysteresis is observed that is caused by phase competition between the insulating charge ordered and metallic ferromagnetic states. No magnetic phase transitions are observed in contrast to pure Pr0.5Ca0.5MnO3 thin films, confirming the unique character of the superlattice. Mn 2p HXPES spectra revealed a hysteresis in the metalicity, supporting the picture of phase competition. The deviation from the commensurate orbital order can be directly related to the decrease of ordered-layer thickness that leads to dimensional crossover from three-dimensional to two-dimensional orbital ordering.

Update: 1-Oct-2014

Title:
Unusual doping effect of non-magnetic ion on magnetic properties of CuFe1-xGaxO2
Authors:
Shi, LR; Jin, Z; Chen, BR; Xia, NM; Zuo, HK; Wang, YS; Ouyang, ZW; Xia, ZC Author Full Names: Shi, Liran; Jin, Zhao; Chen, Borong; Xia, Nianming; Zuo, Huakun; Wang, Yeshuai; Ouyang, Zhongwen; Xia, Zhengcai
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 372 7-11; 10.1016/j.jmmm.2014.07.014 DEC 2014
Abstract:
The structural and magnetic properties of nonmagnetic Ga3+ ion doped CuFe1-xGaxO2 (x=0, 0.02, 0.03, and 0.05) single crystal samples have been investigated. In pulsed high magnetic fields, the field-induced multi-step transitions were observed in all the samples. Compared with pure CuFeO2, the transition temperatures, critical magnetic fields decrease and the magnetic hysteresis of the doped samples become small, which may result from the partial release of the spin frustration and the changes of the magnetic coupling both inter- and intra-planes due to the Ga3+ dopant. The magnetization measurements show an abnormal dilution behavior, especially in a lower temperature region, the magnetic moment was enhanced due to the nonmagnetic Ga3+ ion doping, the enhancement becomes more obviously in the sample with the Ga3+ doping level of x=0.03. These results may connected with the substitution of nonmagnetic Ga3+ ions destroying the stability of ground state and affecting the stability of the ferroelectricity incommensurate phase. Based on the experimental results, a super-cell model and their magnetic diagram were assumed. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Composition dependent phase stability of Ni-Mn-Ga alloys studied by ab initio calculations
Authors:
Xu, N; Raulot, JM; Li, ZB; Zhang, YD; Bai, J; Peng, W; Meng, XY; Zhao, X; Zuo, L; Esling, C Author Full Names: Xu, N.; Raulot, J. M.; Li, Z. B.; Zhang, Y. D.; Bai, J.; Peng, W.; Meng, X. Y.; Zhao, X.; Zuo, L.; Esling, C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 614 126-130; 10.1016/j.jallcom.2014.06.079 NOV 25 2014
Abstract:
Composition dependent phase stability of Ni-Mn-Ga magnetic shape memory alloys was studied by first-principles density-functional calculations. It is demonstrated that the three kinds of doping (Ni substitution for Mn, Ni for Ga, and Mn for Ga) destabilize all the three structures. However, Ni-doping relatively stabilizes the non-modulated martensite (NM) with simple tetragonal crystal structure, whereas proper Mn-doping relatively stabilizes the monoclinic seven-layered modulated (7M) martensite with monoclinic structure. Comparing the energy difference between the parent and the product phases, we found that martensitic transformation experiences much larger driving force than that of the intermar-tensitic transformation. Chemical bonds between Ni and Mn are observed not only with the stoichiometric Mn, but also with the excess ones. Bonds between Ni and Mn in modulated martensite is stronger than that of the non-modulated martensite, which is beneficial to the stability of the modulated martensite. The present result provides useful information for further development of magnetic shape memory alloys that is difficult to be obtained from experiments. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Impact of Quenched Oxygen Disorder on Charge Density Wave Order in YBa2Cu3O6+x
Authors:
Achkar, AJ; Mao, X; McMahon, C; Sutarto, R; He, F; Liang, RX; Bonn, DA; Hardy, WN; Hawthorn, DG Author Full Names: Achkar, A. J.; Mao, X.; McMahon, Christopher; Sutarto, R.; He, F.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Hawthorn, D. G.
Source:
PHYSICAL REVIEW LETTERS, 113 (10):10.1103/PhysRevLett.113.107002 SEP 4 2014
Abstract:
The competition between superconductivity and charge density wave (CDW) order in underdoped cuprates has now been widely reported, but the role of disorder in this competition has yet to be fully resolved. A central question is whether disorder sets the length scale of the CDW order, for instance by pinning charge density fluctuations or disrupting an otherwise long-range order. Using resonant soft x-ray scattering, we investigate the sensitivity of CDW order in YBa2Cu3O6+x (YBCO) to varying levels of oxygen disorder. We find that quench cooling YBCO6.67 (YBCO6.75) crystals to destroy their o-V and o-VIII (o-III) chains decreases the intensity of the CDW superlattice peak by a factor of 1.9 (1.3), but has little effect on the CDW correlation length, incommensurability, and temperature dependence. This reveals that while quenched oxygen disorder influences the CDW order parameter, the spatial extent of the CDW order is insensitive to the level of quenched oxygen disorder and may instead be a consequence of competition with superconductivity.
Title:
Cation Ordering and Flexibility of the BO42- Tetrahedra in Incommensurately Modulated CaEu2(BO4)(4) (B = Mo, W) Scheelites
Authors:
Abakumov, AM; Morozov, VA; Tsirlin, AA; Verbeeck, J; Hadermann, J Author Full Names: Abakumov, Artem M.; Morozov, Vladimir A.; Tsirlin, Alexander A.; Verbeeck, Johan; Hadermann, Joke
Source:
INORGANIC CHEMISTRY, 53 (17):9407-9415; 10.1021/ic5015412 SEP 1 2014
Abstract:
The factors mediating cation ordering in the scheelite-based molybdates and tungstates are discussed on the basis of the incommensurately modulated crystal structures of the CaEu2(BO4)(4) (B = Mo, W) red phosphors solved from high-resolution synchrotron powder X-ray diffraction data. Monoclinic CaEu2(WO4)(4) adopts a (3 + 1)-dimensionally modulated structure [superspace group I2/b(alpha beta 0)00, a = 5.238 73(1)A, b = 5.266 35(1) A, c = 11.463 19(9) A, gamma = 91.1511(2)degrees, q = 0.56153(6)a* + 0.7708(9)b*, R-F = 0.050, R-p = 0.069], whereas tetragonal CaEu2(MoO4)(4) is (3 + 2)-dimensionally modulated [superspace group I4(1)/ a(alpha beta 0)00(-beta alpha 0)00, a = 5.238 672(7) A, c = 11.548 43(2) A, q(1) = 035331(8)a* + 0.82068(9)b*, q(2) = -0.82068(9)a* + 0.55331(8)b*, R-F = 0.061, R-p = 0.082]. In both cases the modulation arises from the ordering of the Ca/Eu cations and the cation vacancies at the A-sublattice of the parent scheelite ABO(4) structure. The cation ordering is incomplete and better described with harmonic rather than with steplike occupational modulation functions. The structures respond to the variation of the effective charge and cation size at the A-position through the flexible geometry of the MoO42- and WO42- tetrahedra demonstrating an alternation of stretching the B-O bond lengths and bending the O-B-O bond angles. The tendency towards A-site cation ordering in scheelites is rationalized using the difference in ionic radii and concentration of the A-site vacancies as parameters and presented in the form of a structure map.
Title:
Controlled Self-Assembly of Periodic and Aperiodic Cluster Crystals
Authors:
Barkan, K; Engel, M; Lifshitz, R Author Full Names: Barkan, Kobi; Engel, Michael; Lifshitz, Ron
Source:
PHYSICAL REVIEW LETTERS, 113 (9):10.1103/PhysRevLett.113.098304 AUG 28 2014
Abstract:
Soft particles are known to overlap and form stable clusters that self-assemble into periodic crystalline phases with density-independent lattice constants. We use molecular dynamics simulations in two dimensions to demonstrate that, through a judicious design of an isotropic pair potential, one can control the ordering of the clusters and generate a variety of phases, including decagonal and dodecagonal quasicrystals. Our results confirm analytical predictions based on a mean-field approximation, providing insight into the stabilization of quasicrystals in soft macromolecular systems, and suggesting a practical approach for their controlled self-assembly in laboratory realizations using synthesized soft-matter particles.
Title:
Quantum spin chain as a potential realization of the Nersesyan-Tsvelik model
Authors:
Balz, C; Lake, B; Luetkens, H; Baines, C; Guidi, T; Abdel-Hafiez, M; Wolter, AUB; Buchner, B; Morozov, IV; Deeva, EB; Volkova, OS; Vasiliev, AN Author Full Names: Balz, C.; Lake, B.; Luetkens, H.; Baines, C.; Guidi, T.; Abdel-Hafiez, M.; Wolter, A. U. B.; Buechner, B.; Morozov, I. V.; Deeva, E. B.; Volkova, O. S.; Vasiliev, A. N.
Source:
PHYSICAL REVIEW B, 90 (6):10.1103/PhysRevB.90.060409 AUG 25 2014
Abstract:
It is well established that long-range magnetic order is suppressed in magnetic systems whose interactions are low dimensional. The prototypical example is the S-1/2 Heisenberg antiferromagnetic chain (S-1/2 HAFC) whose ground state is quantum critical. In real S-1/2 HAFC compounds interchain coupling induces long-range magnetic order although with a suppressed ordered moment and reduced Neel temperature compared to the Curie-Weiss temperature. Recently, it was suggested that order can also be suppressed if the interchain interactions are frustrated, as for the Nersesyan-Tsvelik model. Here, we study the new S-1/2 HAFC, (NO)[Cu(NO3)(3)]. This material shows extreme suppression of order which furthermore is incommensurate revealing the presence of frustration consistent with the Nersesyan-Tsvelik model.
Title:
Excess-hole induced high temperature polarized state and its correlation with the multiferroicity in single crystalline DyMnO3
Authors:
Zou, T; Dun, ZL; Cao, HB; Zhu, MZ; Coulter, D; Zhou, HD; Ke, XL Author Full Names: Zou, Tao; Dun, Zhiling; Cao, Huibo; Zhu, Mengze; Coulter, Daniel; Zhou, Haidong; Ke, Xianglin
Source:
APPLIED PHYSICS LETTERS, 105 (5):10.1063/1.4892470 AUG 4 2014
Abstract:
Controlling the ferroelectricity and magnetism in multiferroic materials has been an important research topic. We report the formation of a highly polarized state in multiferroic DyMnO3 single crystals which develops well above the magnetic transition temperatures, and we attribute it to the thermally stimulated depolarization current effect of excess holes forming Mn4+ ions in the system. We also show that this high temperature polarized state intimately correlates with the lower temperature ferroelectric state that is induced by the incommensurate spiral magnetic order of Mn spins. This study demonstrates an efficient approach to tune the multiferroicity in the manganite system. (C) 2014 AIP Publishing LLC.
Title:
Short-range cluster spin glass near optimal superconductivity in BaFe2-xNixAs2
Authors:
Lu, XY; Tam, DW; Zhang, CL; Luo, HQ; Wang, M; Zhang, R; Harriger, LW; Keller, T; Keimer, B; Regnault, LP; Maier, TA; Dai, PC Author Full Names: Lu, Xingye; Tam, David W.; Zhang, Chenglin; Luo, Huiqian; Wang, Meng; Zhang, Rui; Harriger, Leland W.; Keller, T.; Keimer, B.; Regnault, L. -P.; Maier, Thomas A.; Dai, Pengcheng
Source:
PHYSICAL REVIEW B, 90 (2):10.1103/PhysRevB.90.024509 JUL 11 2014
Abstract:
High-temperature superconductivity in iron pnictides occurs when electrons are doped into their antiferromagnetic (AF) parent compounds. In addition to inducing superconductivity, electron doping also changes the static commensurate AF order in the undoped parent compounds into short-range incommensurate AF order near optimal superconductivity. Here we use neutron scattering to demonstrate that the incommensurate AF order in BaFe2-xNixAs2 is not a spin-density wave arising from the itinerant electrons in nested Fermi surfaces, but is consistent with a cluster spin glass in the matrix of the superconducting phase. Therefore, optimal superconductivity in iron pnictides coexists and competes with a mesoscopically separated cluster spin glass phase, much different from the homogeneous coexisting AF and superconducting phases in the underdoped regime.

Update: 24-Sep-2014

Title:
Exchange bias in non-collinear spin-spiral system Co(Cr1-xCox)(2)O-4(x=0.0-0.1)
Authors:
Padam, R; Ravi, S; Ramakrishnan, S; Grover, AK; Pal, D Author Full Names: Padam, R.; Ravi, S.; Ramakrishnan, S.; Grover, A. K.; Pal, D.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 371 144-148; 10.1016/j.jmmm.2014.07.052 DEC 2014
Abstract:
We report structural and magnetic properties of Co(Cr1-xCox)(2)O-4 (x = 0.0-0.1). The thermal hysteresis has been observed both across magnetostructural transition (T-S) and lock-in transition (T-L). We observe noticeable Exchange bias (EB) only below the lock-in transition, T-L. The value or coercivity also shows the dramatical increase below T-L. These results have been discussed in the context or incommensurate to commensurate non-collinear spin-spiral transitions across T-L. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Exact diagonalization study of the anisotropic triangular lattice Heisenberg model using twisted boundary conditions
Authors:
Thesberg, M; Sorensen, ES Author Full Names: Thesberg, Mischa; Sorensen, Erik S.
Source:
PHYSICAL REVIEW B, 90 (11):10.1103/PhysRevB.90.115117 SEP 8 2014
Abstract:
The spin-1/2 anisotropic triangular model, which is believed to describe the materials Cs2CuCl4 and Cs2CuBr4, among others, is dominated by incommensurate spiral physics and is thus extremely resistant to numerical analysis on small system sizes. In this paper, we use twisted boundary conditions and exact diagonalization techniques to study the ground state of this model as a function of exchange parameter strength. With these boundary conditions we are able to extract the inter-and intrachain ordering q vectors for the J '/J < 1 region finding very close agreement with recent DMRG results on much larger systems. Our results suggest a phase transition between a long-range incommensurate spiral ordered phase, and a more subtle phase with short-range spiral correlations with the q vector describing the incommensurate correlations varying smoothly through the transition. In the latter phase correlations between next-nearest chains exhibit an extremely close competition between predominantly antiferromagnetic and ferromagnetic correlations. Further analysis suggests that the antiferromagnetic next-nearest chain correlations may be slightly stronger than the ferromagnetic ones. This difference is found to be slight but in line with previous renormalization group predictions of a collinear antiferromagnetic ordering in this region.
Title:
Unoccupied electronic states of icosahedral Al-Pd-Mn quasicrystals: Evidence of image potential resonance and pseudogap
Authors:
Maniraj, M; Rai, A; Barman, SR; Krajci, M; Schlagel, DL; Lograsso, TA; Horn, K Author Full Names: Maniraj, M.; Rai, Abhishek; Barman, S. R.; Krajci, M.; Schlagel, D. L.; Lograsso, T. A.; Horn, K.
Source:
PHYSICAL REVIEW B, 90 (11):10.1103/PhysRevB.90.115407 SEP 5 2014
Abstract:
We study the unoccupied region of the electronic structure of the fivefold symmetric surface of an icosahedral (i) Al-Pd-Mn quasicrystal. A feature that exhibits parabolic dispersion with an effective mass of (1.15 +/- 0.1)m(e) and tracks the change in the work function is assigned to an image potential resonance because our density functional calculation shows an absence of band gap in the respective energy region. We show that Sn grows pseudomorphically on i-Al-Pd-Mn as predicted by density functional theory calculations, and the energy of the image potential resonance tracks the change in the work function with Sn coverage. The image potential resonance appears much weaker in the spectrum from the related crystalline Al-Pd-Mn surface, demonstrating that its strength is related to the compatibility of the quasiperiodic wave functions in i-Al-Pd-Mn with the free-electron-like image potential states. Our investigation of the energy region immediately above E-F provides unambiguous evidence for the presence of a pseudogap, in agreement with our density functional theory calculations.
Title:
Quantitative Adsorbate Structure Determination for Quasicrystals Using X-Ray Standing Waves
Authors:
Diehl, RD; Li, HI; Su, SY; Mayer, A; Stanisha, NA; Ledieu, J; Lovelock, KRJ; Jones, RG; Deyko, A; Wearing, LH; McGrath, R; Chaudhuri, A; Woodruff, DP Author Full Names: Diehl, R. D.; Li, H. I.; Su, S. Y.; Mayer, A.; Stanisha, N. A.; Ledieu, J.; Lovelock, K. R. J.; Jones, Robert G.; Deyko, A.; Wearing, L. H.; McGrath, R.; Chaudhuri, A.; Woodruff, D. P.
Source:
PHYSICAL REVIEW LETTERS, 113 (10):10.1103/PhysRevLett.113.106101 SEP 3 2014
Abstract:
The quantitative structure determination of adsorbed species on quasicrystal surfaces has so far appeared to present insurmountable problems. The normal incidence standing x-ray wave field technique offers a simple solution, without extensive data sets or large computations. Its application to quasicrystals raises several conceptual difficulties that are related to the phase problem in x-ray diffraction. We demonstrate their solution for the case of Si atoms adsorbed on the decagonal Co-rich modification of the Al-Co-Ni quasicrystal to determine the local structure, comprising 6-atom clusters in particular hollow sites.
Title:
Nonmagnetic Impurity Effect on Magnetic Phase Transitions in an Isosceles Triangular Lattice Ising Chain Antiferromagnet CoNb2O6
Authors:
Nakajima, T; Mitsuda, S; Okano, H; Inomoto, Y; Kobayashi, S; Prokes, K; Gerischer, S; Smeibidl, P Author Full Names: Nakajima, Taro; Mitsuda, Setsuo; Okano, Hidekazu; Inomoto, Yu; Kobayashi, Satoru; Prokes, Karel; Gerischer, Sebastian; Smeibidl, Peter
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 83 (9):10.7566/JPSJ.83.094723 SEP 2014
Abstract:
We have investigated nonmagnetic impurity effect on the H-parallel to c-T magnetic phase diagram of an isosceles triangular lattice Ising antiferromagnet CoNb2O6, by means of neutron diffraction measurements using single crystals of Co1-x-MgxNb2O6 with x = 0, 0.004, and 0.008. We have found that the commensurate antiferromagnetic (AF) ground state disappears by substituting only 0.8% of nonmagnetic Mg2+ ions for the magnetic Co2+ ions. On the other hand, the phase boundaries between the other phases, namely the field-induced ferrimagnetic phase, thermally-induced incommensurate (IC) magnetic phase and the paramagnetic phase, are hardly affected by the small amount of nonmagnetic substitution. We have also performed Monte Carlo simulations for the isosceles triangular lattice Ising model to understand the extremely high sensitivity to the nonmagnetic substitution. Consequently, we have revealed that the disappearance of the AF phase is not because the small amount of nonmagnetic impurities destabilize the AF phase, but because the phase transition from the IC phase to the AF phase is strongly suppressed by a pinning effect due to the impurities.
Title:
Possible coupling between magnons and phonons in multiferroic CaMn7O12
Authors:
Kadlec, F; Goian, V; Kadlec, C; Kempa, M; Vanek, P; Taylor, J; Rols, S; Prokleska, J; Orlita, M; Kamba, S Author Full Names: Kadlec, Filip; Goian, Veronica; Kadlec, Christelle; Kempa, Martin; Vanek, Premysl; Taylor, Jon; Rols, Stephane; Prokleska, Jan; Orlita, Milan; Kamba, Stanislav
Source:
PHYSICAL REVIEW B, 90 (5):10.1103/PhysRevB.90.054307 AUG 28 2014
Abstract:
Spin and lattice dynamics of CaMn7O12 ceramics were investigated using infrared, THz, and inelastic neutron scattering (INS) spectroscopies in the temperature range 2 to 590 K, and, at low temperatures, in applied magnetic fields of up to 12 T. On cooling, we observed phonon splitting accompanying the structural phase transition at T-C = 450 K as well as the onset of the incommensurately modulated structure at 250 K. In the two antiferromagnetic phases below T-N1 = 90 K and T-N2 = 48 K, several infrared-active excitations emerge in the meV range; their frequencies correspond to the maxima in the magnon density of states obtained by INS. At the magnetic phase transitions, these modes display strong anomalies and, for some of them, a transfer of dielectric strength from the higher-frequency phonons is observed. We propose that these modes are electromagnons. Remarkably, at least two of these modes remain active also in the paramagnetic phase; for this reason, we call them paraelectromagnons. In accordance with this observation, quasielastic neutron scattering revealed short-range magnetic correlations persisting within temperatures up to 500 K above T-N1.
Title:
Structural, magnetic, and dielectric studies on Gd0.7Y0.3MnO3
Authors:
Sarguna, RM; Sridharan, V; Samatham, SS; Ganesan, V; Bhardwaj, S; Awasthi, AM; Mukadam, MD; Yusuf, SM; Sinha, AK; Subramanian, N Author Full Names: Sarguna, R. M.; Sridharan, V.; Samatham, S. Shanmukharao; Ganesan, V.; Bhardwaj, S.; Awasthi, A. M.; Mukadam, M. D.; Yusuf, S. M.; Sinha, A. K.; Subramanian, N.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (34):10.1088/0953-8984/26/34/345901 AUG 27 2014
Abstract:
Structural, magnetic, specific heat, and dielectric studies were carried out on Y substituted (30 at. %) GdMnO3 compound as a function of temperature. Anomalies occur at similar to 41 and 18 K, in the specific heat measurements and are ascribed to paramagnetic, to sinusoidal incommensurate antiferromagnetic transition (ICAFM) and ICAFM to commensurate antiferromagnetic transitions, respectively. Changes in the lattice parameters across these temperatures indicate magneto-elastic coupling present in the compound. However, in the dielectric measurements, an anomaly at 18 K alone is observed and is ascribed to a ferroelectric transition, giving rise to spontaneous ferroelectric ordering at low temperatures. This observation is supported by an anomaly in lattice parameters, across the transition temperature. From the frequency dependent dielectric studies, a strong coupling between Gd3+ and Mn3+ magnetic sublattices is inferred and Y substitution results in substantial changes in the relaxation process compared to that of GdMnO3.
Title:
Uniaxial-pressure control of geometrical spin frustration in an Ising antiferromagnet CoNb2O6 via anisotropic deformation of the isosceles lattice
Authors:
Kobayashi, S; Hosaka, S; Tamatsukuri, H; Nakajima, T; Mitsuda, S; Prokes, K; Kiefer, K Author Full Names: Kobayashi, S.; Hosaka, S.; Tamatsukuri, H.; Nakajima, T.; Mitsuda, S.; Prokes, K.; Kiefer, K.
Source:
PHYSICAL REVIEW B, 90 (6):10.1103/PhysRevB.90.060412 AUG 26 2014
Abstract:
We report neutron diffraction measurement results for an Ising antiferromagnet CoNb2O6 under uniaxial pressure along the geometrically frustrated isosceles-triangular-lattice direction. We find that an onset incommensurate wave number at the Neel temperature increases with pressure from 0.378 to 0.411 at 400 MPa. The observations suggest that the anisotropic deformation of the lattice by the uniaxial pressure significantly modifies the spin frustration, leading to an increase in the nearest-neighbor to next-nearest-neighbor interaction ratio from 1.33 to 1.81.
Title:
Phases of a Triangular-Lattice Antiferromagnet Near Saturation
Authors:
Starykh, OA; Jin, W; Chubukov, AV Author Full Names: Starykh, Oleg A.; Jin, Wen; Chubukov, Andrey V.
Source:
PHYSICAL REVIEW LETTERS, 113 (8):10.1103/PhysRevLett.113.087204 AUG 21 2014
Abstract:
We consider 2D Heisenberg antiferromagnets on a triangular lattice with spatially anisotropic interactions in a high magnetic field close to the saturation. We show that this system possesses a rich phase diagram in a field or anisotropy plane due to competition between classical and quantum orders: an incommensurate noncoplanar spiral state, which is favored classically, and a commensurate coplanar state, which is stabilized by quantum fluctuations. We show that the transformation between these two states is highly nontrivial and involves two intermediate phases-the phase with coplanar incommensurate spin order and the one with noncoplanar double-Q spiral order. The transition between the two coplanar states is of commensurate-incommensurate type, not accompanied by softening of spin-wave excitations. We show that a different sequence of transitions holds in triangular antiferromagnets with exchange anisotropy, such as Ba3CoSb2O9.
Title:
Competing charge, spin, and superconducting orders in underdoped YBa2Cu3Oy
Authors:
Hucker, M; Christensen, NB; Holmes, AT; Blackburn, E; Forgan, EM; Liang, RX; Bonn, DA; Hardy, WN; Gutowski, O; von Zimmermann, M; Hayden, SM; Chang, J Author Full Names: Huecker, M.; Christensen, N. B.; Holmes, A. T.; Blackburn, E.; Forgan, E. M.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Gutowski, O.; v Zimmermann, M.; Hayden, S. M.; Chang, J.
Source:
PHYSICAL REVIEW B, 90 (5):10.1103/PhysRevB.90.054514 AUG 21 2014
Abstract:
To explore the doping dependence of the recently discovered charge-density-wave (CDW) order in YBa2Cu3Oy, we present a bulk-sensitive high-energy x-ray study for several oxygen concentrations, including strongly underdoped YBa2Cu3O6.44. Combined with previous data around the so-called 1/8 doping, we show that bulk CDW order exists at least for hole concentrations (p) in the CuO2 planes of 0.078 less than or similar to p less than or similar to 0.132. This implies that CDW order exists in close vicinity to the quantum critical point for spin-density-wave (SDW) order. In contrast to the pseudogap temperature T*, the onset temperature of CDW order decreases with underdoping to T-CDW similar to 90 K in YBa2Cu3O6.44. Together with a weakened order parameter this suggests a competition between CDW and SDW orders. In addition, the CDW order in YBa2Cu3O6.44 shows the same type of competition with superconductivity as a function of temperature and magnetic field as samples closer to p = 1/8. At low p the CDW incommensurability continues the previously reported linear increasing trend with underdoping. In the entire doping range the in-plane correlation length of the CDW order in b axis direction depends only very weakly on the hole concentration, and appears independent of the type and correlation length of the oxygen-chain order. The onset temperature of the CDW order is remarkably close to a temperature T-dagger that marks the maximum of 1/(T1T) in planar Cu-63 NQR/NMR experiments, potentially indicating a response of the spin dynamics to the formation of the CDW. Our discussion of these findings includes a detailed comparison to the charge stripe order in La2-xBaxCuO4.
Title:
Resonant x-ray scattering study of charge-density wave correlations in YBa2Cu3O6+x
Authors:
Blanco-Canosa, S; Frano, A; Schierle, E; Porras, J; Loew, T; Minola, M; Bluschke, M; Weschke, E; Keimer, B; Le Tacon, M Author Full Names: Blanco-Canosa, S.; Frano, A.; Schierle, E.; Porras, J.; Loew, T.; Minola, M.; Bluschke, M.; Weschke, E.; Keimer, B.; Le Tacon, M.
Source:
PHYSICAL REVIEW B, 90 (5):10.1103/PhysRevB.90.054513 AUG 21 2014
Abstract:
We report the results of a comprehensive study of charge-density wave (CDW) correlations in untwinned YBa2Cu3O6+x single crystals with 0.4 <= x <= 0.99 using CuL3 edge resonant x-ray scattering (RXS). Evidence of CDW formation is found for 0.45 <= x <= 0.93 (hole-doping levels 0.086 less than or similar to p less than or similar to 0.163), but not for samples with x <= 0.44 (p less than or similar to 0.084) that exhibit incommensurate spin-density-wave order, and in slightly overdoped samples with x = 0.99 (p similar to 0.19). This suggests the presence of two proximate zero-temperature CDW critical points at p(c1) similar to 0.08 and p(c2) similar to 0.18. Remarkably, pc(2) is close to the doping level that is optimal for superconductivity. The CDW reflections are observed at incommensurate in-plane wave vectors (delta(a), 0) and (0, delta(b)) with delta(a) less than or similar to delta(b). Both delta(a) and delta(b) decrease linearly with increasing doping, in agreement with recent reports on Bi-based high-T-c superconductors, but in sharp contrast to the behavior of the La2-x(Ba,Sr)(x)CuO4 family. The CDW intensity and correlation length exhibit maxima at p similar to 0.12, coincident with a plateau in the superconducting transition temperature T-c. The onset temperature of the CDW reflections depends nonmonotonically on p, with a maximum of similar to 160 K for p similar to 0.12. The RXS reflections exhibit a uniaxial intensity anisotropy. Whereas in strongly underdoped samples the reflections at (delta(a), 0) are much weaker than those at (0, delta(b)), the anisotropy is minimal for p similar to 0.12, and reversed close to optimal doping. We further observe a depression of CDW correlations upon cooling below T-c, and (for samples with p >= 0.09) an enhancement of the signal when an external magnetic field up to 6 T is applied in the superconducting state. For samples with p similar to 0.08, where prior work has revealed a field-enhancement of incommensurate magnetic order, the RXS signal is field independent. This supports a previously suggested scenario in which incommensurate charge and spin orders compete against each other, in addition to individually competing against superconductivity [Blanco-Canosa et al., Phys. Rev. Lett. 110, 187001 (2013)]. We discuss the relationship of these results to prior observations of "stripe" order in La2-x(Ba,Sr)(x)CuO4, the "pseudogap" phenomenon, superconducting fluctuations, and quantum oscillations, as well as their implications for the mechanism of high-temperature superconductivity.
Title:
High-resolution synchrotron x-ray powder diffraction study of the incommensurate modulation in the martensite phase of Ni2MnGa: Evidence for nearly 7M modulation and phason broadening
Authors:
Singh, S; Petricek, V; Rajput, P; Hill, AH; Suard, E; Barman, SR; Pandey, D Author Full Names: Singh, Sanjay; Petricek, V.; Rajput, Parasmani; Hill, Adrian H.; Suard, E.; Barman, S. R.; Pandey, Dhananjai
Source:
PHYSICAL REVIEW B, 90 (1):10.1103/PhysRevB.90.014109 JUL 31 2014
Abstract:
The modulated structure of the martensite phase of Ni2MnGa is revisited using high-resolution synchrotron x-ray powder diffraction measurements, which reveal higher-order *satellite reflections* up to the third order and phason broadening of the satellite peaks. The structure refinement, using the (3+1) dimensional superspace group approach, shows that the *modulated structure* of Ni2MnGa can be described by orthorhombic *superspace* group Immm(00 gamma)s00 with lattice parameters a = 4.218 61(2) angstrom, b = 5.546 96(3) angstrom, and c = 4.187 63(2) angstrom, and an incommensurate modulation wave vector q = 0.431 60(3)c* = (3/7 + delta)c*, where delta = 0.003 03(3) is the degree of incommensuration of the modulated structure. Additional satellite peak broadening, which could not be accounted for in terms of the anisotropic strain broadening based on a lattice parameter distribution, has been modeled in terms of phasons using fourth-rank covariant strain-tensor representation for incommensurate structures. The simulation of single-crystal diffraction patterns from the refined structural parameters unambiguously reveals a rational approximant structure with 7M modulation. The inhomogeneous displacement of different atomic sites on account of incommensurate modulation and the presence of phason broadening clearly rule out the adaptive phase model proposed recently by Kaufmann et al. [S. Kaufmann, U. K. Rossler, O. Heczko, M. Wuttig, J. Buschbeck, L. Schultz, and S. Fahler, Phys. Rev. Lett. 104, 145702 (2010)] and suggest that the modulation in Ni2MnGa originates from soft-mode phonons.
Title:
Charge-density-wave order with momentum (2Q,0) and (0,2Q) within the spin-fermion model: Continuous and discrete symmetry breaking, preemptive composite order, and relation to pseudogap in hole-doped cuprates
Authors:
Wang, YX; Chubukov, A Author Full Names: Wang, Yuxuan; Chubukov, Andrey
Source:
PHYSICAL REVIEW B, 90 (3):10.1103/PhysRevB.90.035149 JUL 31 2014
Abstract:
We analyze charge order in hole-doped cuprates within the the spin-fermion model. We show that a magnetically mediated interaction, which is known to give rise to d-wave superconductivity and charge order with momentum along zone diagonal, also gives rise to charge order with momenta Q(x) = (2Q,0) and Q(y) = (0,2Q) consistent with the experiments. We show that an instability towards Delta(Q)(k) = < c(k+Q)(dagger)c(k-Q)> with Q = Q(x) or Q(y) is a threshold phenomenon, but the dimensionless spin-fermion coupling is above the threshold, if the magnetic correlation length xi exceeds a certain critical value. At a critical xi, the onset temperature for the charge order terminates at a quantum-critical point distant from the magnetic one. We argue that the charge order with Q(x) or Q(y) changes sign under k -> k + (pi, pi), but vertical bar Delta(Q)(k)vertical bar not equal vertical bar Delta(Q)(k+(pi,pi))vertical bar. In real space, such an order has both bond and site components; the bond one is larger. We further argue that Delta(Q)(k) and Delta(Q)(-k) are not equivalent, and their symmetric and antisymmetric combinations describe, in real space, incommensurate density modulations and incommensurate bond current, respectively. We derive the Ginzburg-Landau functional for four-component U(1) order parameters Delta(Q)(k) with Q = Q(x) or Q(y) and analyze it first in mean-field theory and then beyond mean field. Within mean field we find two types of charge-density-wave (CDW) states, I and II, depending on system parameters. In state I, density and current modulations emerge with the same Q = Q(x) or Q(y), breaking Z(2) lattice rotational symmetry, and differ in phase by +/-pi/2. The selection of pi/2 or -pi/2 additionally breaks Z(2) time-reversal symmetry, such that the total order parameter manifold is U(1) x Z(2) x Z(2). In state II, density and current modulations emerge with different Q and the order parameter manifold is U(1) x U(1) x Z(2), where in the two realizations of state II, Z(2) corresponds to either lattice rotational or time-reversal symmetry breaking. We extend the analysis beyond mean field and argue that discrete symmetries get broken before long-range charge order sets in. For state I, which, we argue, is related to hole-doped cuprates, we show that, upon lowering the temperature, the system first breaks Z(2) lattice rotational symmetry (C-4 -> C-2) at T = T-n and develops a nematic order, then breaks Z(2) time-reversal symmetry at T-t < T-n and locks the relative phase between density and current fluctuations, and finally breaks U(1) symmetry of a common phase of even and odd components of Delta(Q)(k) at T = T-CDW < T-t < T-n and develops a true charge order. We argue that at a mean field, T-CDW is smaller than superconducting T-SC, but preemptive composite order lifts T-CDW and reduces T-SC such that at large xi charge order develops prior to superconductivity. We obtain the full phase diagram and present quantitative comparison of our results with ARPES data for hole-doped cuprates.
Title:
Metastable host-guest structure of carbon
Authors:
Zhu, Q; Feya, OD; Boulfelfel, SE; Oganov, AR Author Full Names: Zhu, Q.; Feya, O. D.; Boulfelfel, S. E.; Oganov, A. R.
Source:
JOURNAL OF SUPERHARD MATERIALS, 36 (4):246-256; 10.3103/S1063457614040030 JUL 2014
Abstract:
A family of metastable host-guest structures, the prototype of which is a tetragonal tP9 structure with 9 atoms per cell has been found. It is composed of an 8-atoms tetragonal host, with atoms filling channels oriented along the c-axis. The tP9 structure has a strong analogy with the recently discovered Ba-IV- and Rb-IV-type incommensurate structures. By considering modulations of the structure due to the variations of the host/guest ratio, it has been concluded that the most stable representative of this family of structures has a guest/host ratio of 2/3 and 26 atoms in the unit cell (space group P4(2)/m). This structure is 0.39 eV/atom higher in energy than diamond. We predict it to have band gap 4.1 eV, bulk modulus 384 GPa, and hardness 61-71 GPa. Due to the different local environments of the host and guest atoms, we considered the possibility of replacing carbon atoms in the guest sublattice by Si atoms in the tP9 prototype and study the properties of the resulting compound SiC8, which was found to have remarkably high bulk modulus 361.2 GPa and hardness 46.2 GPa.

Update: 18-Sep-2014

Title:
Ordered vacancies in the commensurately modulated structure of SrPt1.833 square Sn-0.167(2)
Authors:
Schwickert, C; Hoffmann, RD; Winter, F; Pottgen, R Author Full Names: Schwickert, Christian; Hoffmann, Rolf-Dieter; Winter, Florian; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 229 (7):525-535; 10.1515/zkri-2014-1759 2014
Abstract:
The stannide SrPt1.833 square Sn-0.167(2) was synthesized from the elements in a sealed niobium tube in a high-frequency furnace. Its structure was determined by and refined on the basis of single crystal X-ray diffraction data at 300 and 90K. The refinement of 1177/1169 F-2 values with 34/37 variables leads to residuals [I >= 3 sigma(I)] R-M=0.026 (375) and R-S=0.075 (53)/R-M=0.0211 (408) and R-S=0.0503 (128) for the 300/90 K data sets, respectively. SrPt1.833 square Sn-0.167(2) crystallizes with an orthorhombic (3+1)D structure with the supercentered superspace group C(c)mme(O beta O)sOO [beta=1/3 b*, a=655.25(15), b=656.7(4), c=2062.3(5) pm]. It is related to the tetragonal CaBe2Ge2 type structure. The crystal chemistry is described and the structure solution is discussed based on (3+2)D-(3+1)D-3D group-subgroup relations in the Barnighausen formalism. Sn-119 Mossbauer spectra at ambient temperature and 78 K revealed a single signal with isomer shifts of delta=1.78(1) and delta=1.83(1) mm s(-1) with quadropole splitting of Delta E-Q=0.71(1) and 0.86(1) mm s(-1), respectively reflecting the low-symmetric site symmetry of the tin atoms. SrPt1.833 square Sn-0.167(2) was classified as a Pauliparamagnet by magnetic susceptibility measurements. Its specific heat capacity is C-pm=121.4(1) J mol(-1)K(-1) at 300 K.

Update: 11-Sep-2014

Title:
Temperature dependence of the electrical resistivity of Mg-Zn-Y quasicrystal alloy
Authors:
Geng, JW; Teng, XY; Zhou, GR; Zhao, DG Author Full Names: Geng, Jiwei; Teng, Xinying; Zhou, Guorong; Zhao, Degang
Source:
MATERIALS LETTERS, 132 334-337; 10.1016/j.matlet.2014.06.076 OCT 1 2014
Abstract:
Resistivity of Mg63.5Zn34Y2.5 alloy including icosahedral quasicrystalline phase (I-phase) was measured. It shows that the quasicrystal alloy has a negative temperature coefficient of resistivity (TCR) before melting of I-phase. The TCR shows a reversible transition at similar to 1073 K during heating and cooling processes, involving evolution of icosahedral short-range orders (ISROs) inheriting from I-phase. The pre-existing ISROs act as templates in liquid and promote the nucleation of I-phase. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Pairing Symmetry, Spin Gap, and More in HTSC Cuprates
Authors:
Dayan, M Author Full Names: Dayan, Moshe
Source:
JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 27 (9):1973-1981; 10.1007/s10948-014-2549-5 SEP 2014
Abstract:
This work is based on the double correlated linear aggregations of holes in checkerboard geometry. It is proved that the pairing function symmetry is -d (x2 - y2), as been observed experimentally. It is also shown that there is a "superconductive spin gap" for the observation of the magnetic incommensurate modulation peaks, in agreement with the experiment. In addition, the unperturbed Hamiltonian and its related propagator are reanalyzed and modified.
Title:
Evidence of a short-range incommensurate d-wave charge order from a fermionic two-loop renormalization group calculation of a 2D model with hot spots
Authors:
de Carvalho, VS; Freire, H Author Full Names: de Carvalho, Vanuildo S.; Freire, Hermann
Source:
ANNALS OF PHYSICS, 348 32-49; 10.1016/j.aop.2014.05.009 SEP 2014
Abstract:
The two-loop renormalization group (RG) calculation is considerably extended here for the two-dimensional (2D) fermionic effective field theory model, which includes only the so-called "hot spots" that are connected by the spin-density-wave (SDW) ordering wavevector on a Fermi surface generated by the 2D t - t' Hubbard model at low hole doping. We compute the Callan-Symanzik RG equation up to two loops describing the flow of the single-particle Green's function, the corresponding spectral function, the Fermi velocity, and some of the most important order-parameter susceptibilities in the model at lower energies. As a result, we establish that - in addition to dearly dominant SDW correlations - an approximate (pseudospin) symmetry relating a short-range incommensurate d-wave charge order to the d-wave superconducting order indeed emerges at lower energy scales, which is in agreement with recent works available in the literature addressing the 2D spin-fermion model. We derive implications of this possible electronic phase in the ongoing attempt to describe the phenomenology of the pseudogap regime in underdoped cuprates. (C) 2014 Elsevier Inc. All rights reserved.
Title:
Long range ordered magnetic and atomic structures of the quasicrystal approximant in the Tb-Au-Si system
Authors:
Gebresenbut, G; Andersson, MS; Beran, P; Manuel, P; Nordblad, P; Sahlberg, M; Gomez, CP Author Full Names: Gebresenbut, Girma; Andersson, Mikael Svante; Beran, Premysl; Manuel, Pascal; Nordblad, Per; Sahlberg, Martin; Gomez, Cesar Pay
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (32):10.1088/0953-8984/26/32/322202 AUG 13 2014
Abstract:
The atomic and magnetic structure of the 1/1 Tb(14)Au(70)Si(16) quasicrystal approximant has been solved by combining x-ray and neutron diffraction data. The atomic structure is classified as a Tsai-type 1/1 approximant with certain structural deviations from the prototype structures; there are additional atomic positions in the so-called cubic interstices as well as in the cluster centers. The magnetic property and neutron diffraction measurements indicate the magnetic structure to be ferrimagnetic-like below 9 K in contrast to the related Gd(14)Au(70)Si(16) structure that is reported to be purely ferromagnetic.
Title:
Structure of Bergman-type W-TiZrNi approximants to quasicrystal, analyzed by lattice inversion method
Authors:
Huang, H; Meng, DQ; Lai, XC; Liu, TW; Long, Y; Hu, QM Author Full Names: Huang, H.; Meng, D. Q.; Lai, X. C.; Liu, T. W.; Long, Y.; Hu, Q. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (31):10.1088/0953-8984/26/31/315003 AUG 6 2014
Abstract:
The combined interatomic pair potentials of TiZrNi, including Morse and Inversion Gaussian, are successfully built by the lattice inversion method. Some experimental controversies on atomic occupancies of sites 6-8 in W-TiZrNi are analyzed and settled with these inverted potentials. According to the characteristics of composition and site preference occupancy of W-TiZrNi, two stable structural models of W-TiZrNi are proposed and the possibilities are partly confirmed by experimental data. The stabilities of W-TiZrNi mostly result from the contribution of Zr atoms to the phonon densities of states in lower frequencies.
Title:
Self-similarity and self-inversion of quasicrystals
Authors:
Madison, AE Author Full Names: Madison, A. E.
Source:
PHYSICS OF THE SOLID STATE, 56 (8):1706-1716; 10.1134/S1063783414080162 AUG 2014
Abstract:
The discovery of quasicrystals played a revolutionary role in the condensed matter science and forced to renounce the dogma of the classical crystallography that the regular filling of the space by identical blocks is reduced solely to the Fedorov space groups. It is shown that aperiodic crystals, apart from the similarity, exhibit the self-inversion property. In a broadened sense, the self-inversion implies the possible composition of the inversion with translations, rotations, and homothety, whereas pure reflection by itself in a circle can be absent as an independent symmetry element. It is demonstrated that the symmetry of aperiodic tilings is described by Schottky groups (which belong to a particular type of Kleinian groups generated by the linear fractional Mobius transformations); in the theory of aperiodic crystals, the Schottky groups play the same role that the Fedorov groups play in the theory of crystal lattices. The local matching rules for the Penrose fractal tiling are derived, the problem of choice of the fundamental region of the group of motions of a quasicrystal is discussed, and the relation between the symmetry of aperiodic tilings and the symmetry of constructive fractals is analyzed.
Title:
Charge density wave fluctuations in La2-xSrxCuO4 and their competition with superconductivity
Authors:
Croft, TP; Lester, C; Senn, MS; Bombardi, A; Hayden, SM Author Full Names: Croft, T. P.; Lester, C.; Senn, M. S.; Bombardi, A.; Hayden, S. M.
Source:
PHYSICAL REVIEW B, 89 (22):10.1103/PhysRevB.89.224513 JUN 19 2014
Abstract:
We report hard (14 keV) x-ray diffraction measurements on three compositions (x = 0.11,0.12,0.13) of the high-temperature superconductor La2-xSrxCuO4. All samples show charge density wave (CDW) order with onset temperatures in the range 51-80 K and ordering wave vectors close to (0.23,0,0.5). The CDW is strongest with the longest in-plane correlation length near 1/8 doping. On entering the superconducting state the CDW is suppressed, demonstrating the strong competition between the charge order and superconductivity. CDW order coexists with incommensurate magnetic order and the wave vectors of the two modulations have the simple relationship delta(charge) = 2 delta(spin). The intensity of the CDW Bragg peak tracks the intensity of the low-energy (quasielastic) spin fluctuations. We present a phase diagram of La2-xSrxCuO4 including the pseudogap phase, CDW, and magnetic order.

Update: 3-Sep-2014

Title:
Effect of microstructure on strength and ductility of high strength quasicrystal phase dispersed Mg-Zn-Y alloys
Authors:
Singh, A; Osawa, Y; Somekawa, H; Mukai, T Author Full Names: Singh, Alok; Osawa, Yoshiaki; Somekawa, Hidetoshi; Mukai, Toshiji
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 611 242-251; 10.1016/j.msea.2014.05.091 AUG 12 2014
Abstract:
Recently, magnesium alloys with a dispersion of quasicrystalline icosahedral i-phase have been shown to exhibit very high strengths combined with ductility. However, effect of the i-phase and its amount has not been investigated comprehensively. To make a systematic investigation, two alloys of composition Mg-6x Zn-x Y, where x=0.5 and 1 at%, were chill cast and extruded at three different temperatures to produce various grain sizes with a dispersion of i-phase. The extruded alloys were tested in tension and compression. Very fine grains of micron and submicron size have been obtained, resulting in very high yield strengths of up to about 400 MPa accompanied by total elongations of over 12%. Microstructural features such as precipitation and texture have been studied, and mechanical properties such as strength and ductility in tension and compression have been determined. As the grain size is refined, depending on the alloy composition and extrusion temperature, the texture is also modified, such that a higher strength resulting from finer grain size is accompanied by a reasonable elongation, of over 12%. In aged condition the Hall-Petch plots for tensile and compressive yield strengths are nearly parallel, with slopes in the range of 237-307 MPa mu m(-1/2). The Hall-Petch slopes of critically resolved shear stress of slip and twinning are nearly the same at about 63 MPa mu m(-1/2). (C) 2014 Elsevier B.V. All rights reserved.
Title:
Effect of annealing on the microstructure and mechanical properties of Mg-2.5Zn-0.5Y alloy
Authors:
Zhang, L; Liu, Z; Mao, PL Author Full Names: Zhang, Li; Liu, Zheng; Mao, Ping-li
Source:
INTERNATIONAL JOURNAL OF MINERALS METALLURGY AND MATERIALS, 21 (8):779-784; 10.1007/s12613-014-0971-0 AUG 2014
Abstract:
The microstructure and mechanical properties of extruded Mg-2.5Zn-0.5Y alloy before and after annealing treatments were investigated. The as-extruded alloy exhibits a yield tensile strength (YTS) of 305.9 MPa and an ultimate tensile strength (UTS) of 354.8 MPa, whereas the elongation is only 4%. After annealing, the YTS and UTS decrease to 150 MPa and 240 MPa, respectively, and the elongation increases to 28%. Interestingly, the annealed alloy maintains an acceptable stress level even after a much higher ductility is achieved. These excellent mechanical properties stem from the combined effects of fine alpha-Mg dynamic recrystallization (DRX) grains and a homogeneously distributed icosahedral quasicrystalline phase (I-phase) in the alpha-Mg DRX grains. In particular, the superior ductility originates from the coherent interface of I-phase and alpha-Mg and from the formation of the secondary twin {10 (1) over bar 1}-{10 (1) over bar 2}(38 degrees < 1 <(2)over bar> 10>) in the tension twin {10 (1) over bar 2}.
Title:
Ferroelectricity of Phenazine-Chloranilic Acid at K
Authors:
Noohinejad, L; Mondal, S; Wolfel, A; Ali, SI; Schonleber, A; van Smaalen, S Author Full Names: Noohinejad, Leila; Mondal, Swastik; Woelfel, Alexander; Ali, Sk Imran; Schoenleber, Andreas; van Smaalen, Sander
Source:
JOURNAL OF CHEMICAL CRYSTALLOGRAPHY, 44 (8):387-393; 10.1007/s10870-014-0527-1 AUG 2014
Abstract:
The co-crystal of phenazine (Phz) and chloroanilic acid is ferroelectric below the temperature K (FE-I phase). Upon cooling, two more phase transitions involve a further reduction of symmetry, until Phz-Hca is triclinic in the second ferroelectric phase (FE-II phase) stable below 137 K. Ferroelectricity in all low-temperature phases is believed to be related to partial proton transfer within the hydrogen bonds between the molecules Phz and . Here we present the crystal structure of the FE-II phase at K. Experimental positions of hydrogen atoms indicate that ferroelectricity is mainly governed by half of the hydrogen-bonded chains, whereby proton transfer is observed within one of the two hydrogen bonds in which each molecule participates. A simple point charge model quantitatively reproduces the polarisation of this material. However, a possible contribution to the polarisation is proposed of the O-HN hydrogen bonds of the second half of the mixed chains, which show elongated O-H bonds similar to those in the FE-I phase. The twofold superstructure with symmetry was successfully solved as commensurately modulated structure employing the monoclinic superspace group . The latter shows that the distortions at low temperatures follow a single normal mode of the space group of the FE-I phase, and it thus explains that the direction of the polarisation remains close to the monoclinic axis, despite the lowering towards triclinic symmetry.
Title:
Structure of an Al-Cu-Co Decagonal Quasicrystal Studied by Cs-Corrected STEM
Authors:
Yubuta, K; Yamamoto, K; Yasuhara, A; Hiraga, K Author Full Names: Yubuta, Kunio; Yamamoto, Kazuki; Yasuhara, Akira; Hiraga, Kenji
Source:
MATERIALS TRANSACTIONS, 55 (6):866-870; 10.2320/matertrans.M2014008 JUN 2014
Abstract:
The structure of an Al-Cu-Co decagonal quasicrystal (DQC) with two quasiperiodic planes in an annealed Al64Cu22Co14 alloy has been studied by spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM) with high-angle annular detector dark-field (HAADF) and annular bright-field (ABF) techniques. The observed HAADF-STEM images taken with the incident beam parallel to the periodic axis clearly represent individual transition-metal (TM) Cu/Co atoms and mixed sites (MSs) of Al and TM atoms as separated bright dots, and consequently arrangements of TM atoms and MSs on the two quasiperiodic planes can be directly determined. The TM atoms on the two quasiperiodic planes are arranged in pentagonal tiling with an edge-length of 0.76nm, and also the TM atoms and MSs are located at vertices of Penrose tiling with an edge-length of 0.25 nm, and so they are arranged with a bond orientational order (BOO). Pentagonal frames with definite directions in the pentagonal tiling of TM atoms are also arranged in tau(2)-inflated pentagonal tiling with an edge-length of 2 nm. Arrangements of TM atoms derived from the observed HAADF-STEM image are placed in ideal pentagonal Penrose tiling with an edge-length of 2 nm, which is generated by the projection of five-dimensional (5D) hyper-cubic lattice, and are projected on occupation domains (ODs) in the perpendicular space. The arrangement of Al atoms and TM atoms and MSs in a well-symmetric region is interpreted from the observed HAADF- and ABF-STEM images.

Update: 28-Aug-2014

Title:
Effect of group 5 elements on the formation and corrosion behavior of Ti-based BMG matrix composites reinforced by icosahedral quasicrystalline phase
Authors:
Debnath, MR; Chang, HJ; Fleury, E Author Full Names: Debnath, Mukta Rani; Chang, Hye-Jung; Fleury, Eric
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 612 134-142; 10.1016/j.jallcom.2014.05.049 NOV 5 2014
Abstract:
The addition of a low concentration of group 5 elements to the Ti40Zr29Be16Cu8Ni7 BMG alloys resulted in the formation of particles with icosahedral quasiciystalline symmetry of different size and volume fraction embedded in BMG matrices. Since the i-phase is known for its excellent corrosion resistance, the properties of the TM-containing Ti-based BMGs, with 0 <= TM <= 5 at.%, have been investigated in aerated 1 M H2SO4 + 2 ppm F- solution with 80 degrees C by means of potentio-dynamic, potentio-static and chemical immersion. The addition of 3 at.% Ta provided an alloys with properties similar to those of Ti-6Al-4V alloy in a solution simulating the environment of a bipolar plate in polymer electrolyte membrane. The high corrosion resistances of the in situ BMG matrix composites are attributed to the similarity in the composition of the i-phase and amorphous matrices as well as the formation of protective oxide layers rich in Ti, Zr and V/Ta/Nb. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Magnetic ordering of ScMn6Ge6 by neutron diffraction
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Buschow, K. H. J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 369 243-248; 10.1016/j.jmmm.2014.06.052 NOV 2014
Abstract:
The compound ScMn6Ge6 (Hffe(6)Ge(6)-type, P6/mmm) orders antiferromagnetically below T-N=516 K. Neutron powder diffraction at various temperatures 1.5-309 K shows the existence of two distinct magnetic ordering ranges described by the commensurate q(1)=(0, 0, 1/2) and the incommensurate q(2)=(0, 0, q(z)) vectors: (i) the HT (high temperature) T-t approximate to 100 K < T < 309 K range described by cut, corresponds to an easy axis antiferromagnetic stacking of the Mn ferromagnetic (0 0 1) layers ( + - - +) at z(Mn) similar to 1/4, 3/4, 5/4, 7/4, the Mn moments being confined to the c-axis. (ii) The LT (low temperature) T-t > T > 1.5 K range has an easy double-cone incommensurately modulated structure described by two vectors (q(1), q(2)). At 1.5 K q(2)=(0, 0, 0.405(1)), the spiral angle is Phi=145.8 degrees the cone half angle is a alpha approximate to 8 degrees and the ordered moment value mu(Mn)=2.12(2)mu(B) is the same as for the isomorphic RMn6Ge6 (R=heavy rare earth) compounds. The 1.5 K q(2) satellites are very weak as the in-plane moment component measures only 0.31 mu(B). (C) 2014 Elsevier B.V. All rights reserved
Title:
Magnetic transitions in the spin-5/2 frustrated magnet BiMn2PO6 and strong lattice softening in BiMn2PO6 and BiZn2PO6 below 200 K
Authors:
Nath, R; Ranjith, KM; Roy, B; Johnston, DC; Furukawa, Y; Tsirlin, AA Author Full Names: Nath, R.; Ranjith, K. M.; Roy, B.; Johnston, D. C.; Furukawa, Y.; Tsirlin, A. A.
Source:
PHYSICAL REVIEW B, 90 (2):10.1103/PhysRevB.90.024431 JUL 30 2014
Abstract:
The crystallographic, magnetic, and thermal properties of polycrystalline BiMn2PO6 and its nonmagnetic analog BiZn2PO6 are investigated by x-ray diffraction, magnetization M, magnetic susceptibility., heat capacity C-p, and P-31 nuclear magnetic resonance (NMR) measurements versus applied magnetic field H and temperature T as well as by density-functional band theory and molecular-field calculations. Both compounds show a strong monotonic lattice softening on cooling, where the Debye temperature decreases by a factor of two from Theta(D) similar to 650 K at T = 300 K to Theta(D) similar to 300 K at T = 2 K. The chi(T) data for BiMn2PO6 above 150 K follow a Curie-Weiss law with a Curie constant consistent with a Mn+2 spin S = 5/2 with g factor g = 2 and an antiferromagnetic (AFM) Weiss temperature theta(CW) similar or equal to -78 K. The. data indicate long-range AFM ordering below T-N similar or equal to 30 K, confirmed by a sharp lambda-shaped peak in C-p(T) at 28.8 K. The magnetic entropy at 100 K extracted from the C-p(T) data is consistent with spin S = 5/2 for the Mn+2 cations. The band-theory calculations indicate that BiMn2PO6 is an AFM compound with dominant interactions J(1)/k(B) similar or equal to 6.7 K and J(3)/k(B) similar or equal to 5.6 K along the legs and rungs of a Mn two-leg spin-ladder, respectively. However, sizable and partially frustrating interladder couplings lead to an anisotropic three-dimensional magnetic behavior with long-range AFM ordering at T-N similar or equal to 30 K observed in the chi, C-p, and NMR measurements. A second magnetic transition at approximate to 10 K is observed from the chi and NMR measurements but is not evident in the C-p data. The C-p data at low T suggest a significant contribution from AFM spin waves moving in three dimensions and the absence of a spin-wave gap. A detailed analysis of the NMR spectra indicates commensurate magnetic order between 10 and 30 K, while below 10 K additional features appear that may arise from an incommensurate modulation and/or spin canting. The commensurate order is consistent with microscopic density functional calculations that yield a collinear Neel-type AFM spin arrangement both within and between the ladders, despite the presence of multiple weak interactions frustrating this magnetic structure of the Mn spins. Frustration for AFM ordering and the one-dimensional spatial anisotropy of the three-dimensional spin interactions are manifested in the frustration ratio f = |theta(CW)|/T-N similar or equal to 2.6, indicating a suppression of T-N from 68 K in the absence of these effects to the observed value of about 30 K in BiMn2PO6.
Title:
Icosahedral AlCuFe quasicrystal at high pressure and temperature and its implications for the stability of icosahedrite
Authors:
Stagno, V; Bindi, L; Shibazaki, Y; Tange, Y; Higo, Y; Mao, HK; Steinhardt, PJ; Fei, YW Author Full Names: Stagno, Vincenzo; Bindi, Luca; Shibazaki, Yuki; Tange, Yoshinori; Higo, Yuji; Mao, H. -K.; Steinhardt, Paul J.; Fei, Yingwei
Source:
SCIENTIFIC REPORTS, 4 10.1038/srep05869 JUL 29 2014
Abstract:
The first natural-occurring quasicrystal, icosahedrite, was recently discovered in the Khatyrka meteorite, a new CV3 carbonaceous chondrite. Its finding raised fundamental questions regarding the effects of pressure and temperature on the kinetic and thermodynamic stability of the quasicrystal structure relative to possible isochemical crystalline or amorphous phases. Although several studies showed the stability at ambient temperature of synthetic icosahedral AlCuFe up to similar to 35 GPa, the simultaneous effect of temperature and pressure relevant for the formation of icosahedrite has been never investigated so far. Here we present in situ synchrotron X-ray diffraction experiments on synthetic icosahedral AlCuFe using multianvil device to explore possible temperature-induced phase transformations at pressures of 5 GPa and temperature up to 1773 K. Results show the structural stability of i-AlCuFe phase with a negligible effect of pressure on the volumetric thermal expansion properties. In addition, the structural analysis of the recovered sample excludes the transformation of AlCuFe quasicrystalline phase to possible approximant phases, which is in contrast with previous predictions at ambient pressure. Results from this study extend our knowledge on the stability of icosahedral AlCuFe at higher temperature and pressure than previously examined, and provide a new constraint on the stability of icosahedrite.
Title:
Effects of Y on Microstructures and Properties of Mg-Zn-Y Alloys Prepared by Conventional Solidification
Authors:
Yang, L; Zhao, YH; Hou, H; Yang, XM Author Full Names: Yang Ling; Zhao Yuhong; Hou Hua; Yang Xiaomin
Source:
RARE METAL MATERIALS AND ENGINEERING, 43 (7):1754-1758; JUL 2014
Abstract:
Mg-45Zn-xY (x=1.0, 4.0, 5.5, 8.0 wt%) alloys were prepared by a conventional solidification technique. The influences of Y on microstructures and properties of Mg-45Zn-xY alloys were investigated by means of SEM, EDS, OM, TEM, XRD, DSC and hardness tests. The formation mechanism of quasicrystal was also analyzed. The results show that microstructures of Mg-45Zn-xY alloys consist of alpha-Mg particle or dendritic crystal, petal-like Mg3Zn6Y quasicrystalline phase (I-phase), lamellar (I-phase+alpha-Mg) eutectic structure and Mg7Zn3 phase. The morphology, the amount and distribution of quasicrystalline phase are closely related to the content of Y. With the increase of Y content, the amount of petal-like quasicrystalline phase increases and when Y content is 5.5 wt%, the alloy has the most petal-like quasicrystalline phase and its hardness reaches the maximum value of HB 1557 MPa. When Y content is 8.0 wt%, the petal-like quasicrystalline phase disappears. Quasicrystalline phase exists in two forms: eutectic structure and petal-like structure, and the special morphology of petal-like structure is the result of icosahedron's growth along five-axis direction.
Title:
Incommensurate Phases of the MgSiF6 center dot 6H(2)O Crystals: EPR and Group-Theoretical Studies
Authors:
Skrylnik, PG; Ziatdinov, AM Author Full Names: Skrylnik, Peter G.; Ziatdinov, Albert M.
Source:
APPLIED MAGNETIC RESONANCE, 45 (7):623-640; 10.1007/s00723-014-0542-6 JUL 2014
Abstract:
The group-theoretical study of the structural phase transition to incommensurate state of MgSiF6 center dot 6H(2)O crystals, revealed by the electron paramagnetic resonance (EPR) method, as well as analysis of the EPR results, are presented. The consideration of temperature dependences of Mn2+ admixture ion EPR spectrum symmetry and parameters leads to the conclusion that at T-i1 = 370 +/- 0.3 K they undergo second-order structural phase transition to incommensurately modulated state, the order parameter of this transition may be the angle of [Mg(H2O)(6)](2+) octahedra rotation around crystal C-3 axis. At temperature decreasing below Ti1 the gradual transformation of plane-wave modulation of lattice displacements into soliton mode occurs, which is interrupted by the first-order phase transition at T-i2 = 343 +/- 0.3 K accompanied by abrupt decrease in modulation amplitude. At T-c = 298.5 +/- 0.3 K the first-order improper ferroelastic phase transition into monoclinic phase occurs. The group-theoretical analysis of the phase transition at T-i1 in the investigated crystals, carried out for the first time, has shown that the existence of the *incommensurately modulated* *phase* is conditioned by the fundamental reasons (presence of Lifshitz invariant). The conclusions of this analysis on the nature of order parameter, the structural motifs of incommensurate phase and the possible character of temperature evolution of the structure are in agreement with the EPR investigation data.
Title:
Effects of Water-Cooling on Quasicrystal Formation of As-Cast Mg-Zn-Zr-Y Alloys and the Microstructure
Authors:
Lu, BJ; Peng, J; Han, W; Tang, AT; Pan, FS Author Full Names: Lu Binjiang; Peng Jian; Han Wei; Tang Aitao; Pan Fusheng
Source:
RARE METAL MATERIALS AND ENGINEERING, 43 (7):1643-1648; JUL 2014
Abstract:
Mg-Zn-Zr-Y alloys containing quasicrystal phase were prepared by an as-cast method with water-cooling. On this base, the effects of different Zn and Y content (the same Zn/Y ratio) on microstructure and micro-hardness were also discussed. The results show that the increase of cooling rate by water-cooling can increase the volume fraction of quasicrystal phase (I-phase, Mg3YZn6) of Mg-Zn-Zr-Y alloy. The decreasing of grain sizes of the as-cast alloy is due to the increase of constitutional supercooling by Y addition. The solid solubility of Zn in alpha-Mg matrix mainly affects the hardness of the matrix, and the hardness of I-phase is much higher than that of the matrix. The liquidus temperature decreases substantially while the solid temperature does not change with Y addition, which weakens the hot cracking tendency of the ingot due to the decrease of freezing range.

Update: 21-Aug-2014

Title:
Room temperature inverse magnetocaloric effect in Pd substituted Ni50Mn37Sn13 Heusler alloys
Authors:
Saha, R; Nigam, AK Author Full Names: Saha, Ritwik; Nigam, A. K.
Source:
PHYSICA B-CONDENSED MATTER, 448 263-266; 10.1016/j.physb.2014.04.011 SEP 1 2014
Abstract:
The structural, magnetic and magnetocaloric effects for Ni50-xPdxMn37Sn13 Heusler alloys have been investigated around both structural and magnetic transitions. The room temperature X-ray diffraction indicates 10 M modulated martensitic structure with an orthorhombic unit cell for x=0 and 1. However, the superstructure reflections for x=2 alloy imply that the pattern is related to the L2(1) phase. The maximum entropy change occurring at the martensitic transition is found to be 21 j kg(-1) K-1 for Ni50Mn37Sn13 alloy around room temperature. Despite the smaller change in entropy around room temperature, 3.8 times larger value of refrigerant capacity (184.6 jfkg) is achieved for 2% substitution of Pd, due to occurrence of magnetic entropy change in a broader temperature region. (C) 2014 Elsevier B.V. All rights reserved,
Title:
Friction and solid-solid adhesion on complex metallic alloys
Authors:
Dubois, JM; Belin-Ferre, E Author Full Names: Dubois, Jean-Marie; Belin-Ferre, Esther
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (3):10.1088/1468-6996/15/3/034804 JUN 2014
Abstract:
The discovery in 1987 of stable quasicrystals in the Al-Cu-Fe system was soon exploited to patent specific coatings that showed reduced friction in ambient air against hard antagonists. Henceforth, it was possible to develop a number of applications, potential or commercially exploited to date, that will be alluded to in this topical review. A deeper understanding of the characteristics of complex metallic alloys (CMAs) may explain why material made of metals like Al, Cu and Fe offers reduced friction; low solid-solid adhesion came later. It is linked to the surface energy being significantly lower on those materials, in which translational symmetry has become a weak property, that is determined by the depth of the pseudo-gap at the Fermi energy. As a result, friction is anisotropic in CMAs that builds up according to the translation symmetry along one direction, but is aperiodic along the other two directions. A review is given in this article of the most salient data found along these lines during the past two decades or so.

Update: 14-Aug-2014

Title:
Orthorhombic Zr2Co11 phase revisited
Authors:
Li, XZ; Zhang, WY; Sellmyer, DJ; Zhao, X; Nguyen, MC; Wang, CZ; Ho, KM Author Full Names: Li, X. -Z.; Zhang, W. Y.; Sellmyer, D. J.; Zhao, X.; Nguyen, M. C.; Wang, C. Z.; Ho, K. M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 611 167-170; 10.1016/j.jallcom.2014.05.072 OCT 25 2014
Abstract:
The structure of the orthorhombic Zr2Co11 phase was revisited in the present work. Selected-area electron diffraction (SAED) and high-resolution electron microscopy (HREM) techniques were used to investigate the structure. They show the orthorhombic Zr2Co11 phase has a 1-D incommensurate modulated structure. The structure can be approximately described as a B-centered orthorhombic lattice. The lattice parameters of the orthorhombic Zr2Co11 phase have been determined by a tilt series of SAED patterns. A hexagonal network with a modulation wave has been observed in the HREM image and the hexagonal motif is considered as the basic structural unit. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Magnetic and transport properties of i-R-Cd icosahedral quasicrystals (R=Y, Gd-Tm)
Authors:
Kong, T; Budko, SL; Jesche, A; McArthur, J; Kreyssig, A; Goldman, AI; Canfield, PC Author Full Names: Kong, Tai; Budko, Sergey L.; Jesche, Anton; McArthur, John; Kreyssig, Andreas; Goldman, Alan I.; Canfield, Paul C.
Source:
PHYSICAL REVIEW B, 90 (1):10.1103/PhysRevB.90.014424 JUL 18 2014
Abstract:
We present a detailed characterization of the recently discovered i-R-Cd (R = Y, Gd-Tm) binary quasicrystals by means of x-ray diffraction, temperature-dependent dc and ac magnetization, temperature-dependent resistance, and temperature-dependent specific heat measurements. Structurally, the broadening of x-ray diffraction peaks found for i-R-Cd is dominated by frozen-in phason strain, which is essentially independent of R. i-Y-Cd is weakly diamagnetic and manifests a temperature-independent susceptibility. i-Gd-Cd can be characterized as a spin glass below 4.6 K via dc magnetization cusp, a third order nonlinear magnetic susceptibility peak, a frequency-dependent freezing temperature, and a broad maximum in the specific heat. i-R-Cd (R = Ho-Tm) is similar to i-Gd-Cd in terms of features observed in thermodynamic measurements. i-Tb-Cd and i-Dy-Cd do not show a clear cusp in their zero-field-cooled dc magnetization data, but instead show a more rounded, broad local maximum. The resistivity for i-R-Cd is of order 300 mu Omega cm and weakly temperature dependent. The characteristic freezing temperatures for i-R-Cd (R = Gd-Tm) deviate from the de Gennes scaling, in a manner consistent with crystal electric field splitting induced local moment anisotropy.
Title:
Switching of the magnetic order in CeRhIn5-xSnx in the vicinity of its quantum critical point
Authors:
Raymond, S; Buhot, J; Ressouche, E; Bourdarot, F; Knebel, G; Lapertot, G Author Full Names: Raymond, S.; Buhot, J.; Ressouche, E.; Bourdarot, F.; Knebel, G.; Lapertot, G.
Source:
PHYSICAL REVIEW B, 90 (1):10.1103/PhysRevB.90.014423 JUL 18 2014
Abstract:
We report neutron diffraction experiments performed in the tetragonal antiferromagnetic heavy fermion system CeRhIn5-xSnx in its (x, T) phase diagram up to the vicinity of the critical concentration x(c) approximate to 0.40, where long range magnetic order is suppressed. The propagation vector of the magnetic structure is found to be k(IC) = (1/2,1/2,k(l)) with k(l) increasing from k(l) = 0.298 to k(l) = 0.410 when x increases from x = 0 to x = 0.26. Surprisingly, for x = 0.30, the order has changed drastically and a commensurate antiferromagnetism with k(C) = (1/2,1/2,0) is found. This concentration is located in the proximity of the quantum critical point where superconductivity is expected.
Title:
Transformation between spin-Peierls and incommensurate fluctuating phases of Sc-doped TiOCl
Authors:
Zhang, J; Wolfel, A; Bykov, M; Schonleber, A; van Smaalen, S; Kremer, RK; Williamson, HL Author Full Names: Zhang, Jian; Woelfel, Alexander; Bykov, Maxim; Schoenleber, Andreas; van Smaalen, Sander; Kremer, Reinhard K.; Williamson, Hailey L.
Source:
PHYSICAL REVIEW B, 90 (1):10.1103/PhysRevB.90.014415 JUL 15 2014
Abstract:
Single crystals of ScxTi1-xOCl (x = 0.005) have been grown by the vapor phase transport technique. Specific heat measurements prove the absence of phase transitions for 4-200 K. Instead, an excess entropy is observed over a range of temperatures that encompasses the incommensurate phase transition at 90 K and the spin-Peierls transition at 67 K of pure TiOCl. Temperature-dependent x-ray diffraction on ScxTi1-xOCl gives broadened diffraction maxima at incommensurate positions between T-cl = 61.5 (3) and similar to 90 K, and at commensurate positions below 61.5 K. These results are interpreted as due to the presence of an incommensurate phase without long-range order at intermediate temperatures, and of a highly disturbed commensurate phase without long-range order at low temperatures. The commensurate phase is attributed to a fluctuating spin-Peierls state on an orthorhombic lattice. The monoclinic symmetry and local structure of the fluctuations are equal to the symmetry and structure of the ordered spin-Peierls state of TiOCl. A novel feature of ScxTi1-xOCl (x = 0.005) is a transformation from one fluctuating phase (the incommensurate phase at intermediate temperatures) to another fluctuating phase (the spin-Peierls-like phase). This transformation is not a phase transition occurring at a critical temperature, but it proceeds gradually over a temperature range of similar to 10 K wide. The destruction of long-range order requires much lower levels of doping in TiOCl than in other low-dimensional electronic crystals, like the canonical spin-Peierls compound CuGeO3. An explanation for the higher sensitivity to doping has not been found, but it is noticed that it may be the result of an increased two-dimensional character of the doped magnetic system. The observed fluctuating states with long correlation lengths are reminiscent of Kosterlitz-Thouless-type phases in two-dimensional systems.
Title:
Magnetocaloric effect in multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2(Fe0.92Al0.08)(12)O-22
Authors:
Xu, WF; Yang, J; Shen, YD; Bai, W; Zhang, YY; Liu, J; Tang, K; Wang, Z; Duan, CG; Tang, XD; Chu, JH Author Full Names: Xu, Wenfei; Yang, Jing; Shen, Yude; Bai, Wei; Zhang, Yuanyuan; Liu, Jia; Tang, Kai; Wang, Zhi; Duan, Chun-Gang; Tang, Xiaodong; Chu, Junhao
Source:
AIP ADVANCES, 4 (6):10.1063/1.4883235 JUN 2014
Abstract:
Magnetocaloric effect is investigated in multiferroic Ba0.5Sr1.5Zn2(Fe0.92Al0.08)(12)O-22 ceramic with Y-type hexagonal system. Three magnetic transitions, from alternating longitudinal conical to mixed conical at similar to 240 K, to ferrimagnetic at similar to 297 K, further to paramagnetic at similar to 702 K, are unambiguously determined. Furthermore, obvious MCE is shown, and the maximum values of the magnetic entropy change and relative cooling power are evaluated to be 1.53 JKg(-1)K(-1) and 280 JKg(-1) for a field change of 7 T, respectively. In addition, inverse MCE is also observed, which might be associated with the first-order magnetic phase transition between two incommensurate longitudinal conical phases. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Update: 7-Aug-2014

Title:
Crystal structure, disorder and composition of the 2/1 approximant in the Al-Mg-Zn system revisited
Authors:
Berthold, R; Mihalkovic, M; Burkhardt, U; Prots, Y; Amarsanaa, A; Kreiner, G Author Full Names: Berthold, Rico; Mihalkovic, Marek; Burkhardt, Ulrich; Prots, Yurii; Amarsanaa, Altangerel; Kreiner, Guido
Source:
INTERMETALLICS, 53 67-84; 10.1016/j.intermet.2014.02.022 OCT 2014
Abstract:
The tau(1) and tau(2) phases in the Al-Mg-Zn system are famous examples for complex intermetallic alloy phases. They are 1/1 and 2/1 approximants of a quasicrystalline phase. The crystal structure of the tau(2) phase has been studied several times but the reported results are inconsistent. In this work, the tau(2) phase has been investigated in order to determine the homogeneity range at 330 degrees C and 360 degrees C and to revisit its crystal structure. The tau(2) phase is a ternary solid solution phase, which is able to vary its composition by about 5 at.% Al, 2 at.% Mg and 6 at.% Zn at 330 degrees C. Heterogeneous equilibria with the five phases Phi, tau(1), beta, MB21Zn25 and (Mg) have been observed. The Zn-rich beta phase is a new intermetallic compound with a large cubic unit cell. At 360 degrees C, the variation of the Zn content is slightly larger (8 at.%) and the two phases Phi and (Mg) are exchanged in heterogeneous equilibria by a liquid and a quasicrystalline phase. The crystal structure of the tau(2) phase has been studied at the composition Al15.4Mg42.0Zn42.6 by a combined refinement of X-ray and neutron data. Total energy calculations at 0 K reveal two stable variants at the compositions Al14.8Mg40.8Zn44.4 and Al13.0Mg40.8Zn46.2. The chemical and structural disorder can be illustrated with the help of a Henley-Elser decoration of a canonical cell tiling. The crystal data are close to those reported previously reported by Spiekermann, but not in agreement with the results of Sugiyama et al. and Lin et al., which have reported compositions outside the homogeneity range. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
Nanoscale icosahedral quasicrystal phase precipitation mechanism during annealing for Mg-Zn-Gd-based alloys
Authors:
Tian, Y; Huang, H; Yuan, GY; Chen, CL; Wang, ZC; Ding, WJ Author Full Names: Tian, Yuan; Huang, Hua; Yuan, Guangyin; Chen, Chunlin; Wang, Zhongchang; Ding, Wenjiang
Source:
MATERIALS LETTERS, 130 236-239; 10.1016/j.matlet.2014.05.131 SEP 1 2014
Abstract:
We have performed a systematic transmission electron microscopy study of precipitated particles in Mg-Zn-Gd-based alloys after annealing. We find that the Mg-Zn phases and ellipsoidal-shaped icosahedral quasicrystal phases (I-phase) are precipitated and distributed by partition in the grains, which can be attributed to the composition segregation of the alloying elements in the as-cast alloys. The content of alloying element is found to be crucial to the precipitation of nanoscale I-phase. The nanoscale I-phase ranges in size from a few to dozens of nanometers, revealing that the precipitation process satisfies the classical nucleation and growth theory. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Crystal structure and potential interstitial oxide ion conductivity of LnNbO(4) and LnNb(0.92) W0.08O4.04 (Ln = La, Pr, Nd)
Authors:
Li, C; Bayliss, RD; Skinner, SJ Author Full Names: Li, Cheng; Bayliss, Ryan D.; Skinner, Stephen J.
Source:
SOLID STATE IONICS, 262 530-535; SI 10.1016/j.ssi.2013.12.023 SEP 1 2014
Abstract:
Single phase LnNbO(4) and LnNb(0.92) W0.08O4.04 (Ln = La, Pr and Nd) were prepared via solid state reaction. The crystal structure of the materials has been investigated by X-ray diffraction and Rietveld refinement. PrNb0.92 W0.08O4.04 and NdNb0.92 W0.08O4.04 were found to have the same crystal structure as the parent phases whereas LaNb0.92W0.08O4.04 has a modulated structure. Electrical conductivity was studied by AC impedance spectroscopy. Substantial improvements in total conductivity were achieved by W doping on the B-site, with LaNb0.92 W0.08O4.04 having the highest overall conductivity of 3.0 x 10(-3) Scm(-1) at 800 degrees C. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Mesenchymal stromal cell transplantation modulates neuroinflammatory milieu in amyotrophic lateral sclerosis
Authors:
Connick, P; Chandran, S Author Full Names: Connick, Peter; Chandran, Siddharthan
Source:
CYTOTHERAPY, 16 (8):1031-1032; 10.1016/j.jcyt.2014.06.001 AUG 2014
Title:
Crystallographic insights into the intermartensitic transformation in Ni-Mn-Ga alloys
Authors:
Li, ZB; Yang, B; Zhang, YD; Esling, C; Zou, NF; Zhao, X; Zuo, L Author Full Names: Li, Zongbin; Yang, Bo; Zhang, Yudong; Esling, Claude; Zou, Naifu; Zhao, Xiang; Zuo, Liang
Source:
ACTA MATERIALIA, 74 9-17; 10.1016/j.actamat.2014.04.025 AUG 1 2014
Abstract:
Ferromagnetic shape memory alloys such as Ni-Mn-Ga usually undergo intermartensitic transformation upon cooling or heating. Here, an attempt is made to explore the microstructural features and orientation relationships associated with the intermartensitic transformation from seven-layered modulated (7M) martensite to non-modulated (NM) martensite in a polycrystalline Ni53Mn22Ga25 alloy. Based on electron backscatter diffraction analysis, it is demonstrated that the intermartensitic transformation proceeds in an in-plate manner (through atomic reshuffling and lattice distortion) with specific orientation relationships between the two martensitic phases, i.e. (0 0 1)(7M)//(1 1 2)(NM) and [1 0 0](7M)//[1 1 (1) over bar](NM) as well as (0 0 1)(7M)//(1 1 2)(NM) and [(1) over bar 0 0](7M)//[1 1 (1) over bar](NM), accompanied by the thickening of martensite plates and the surface relief effect. Consequently, one 7M variant (plate) evolves into one NM plate consisting of two twin-related fine variants, and four differently oriented 7M variants in one variant group result in a total of eight NM variants. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Phonon and thermal transport properties of the misfit-layered oxide thermoelectric Ca3Co4O9 from first principles
Authors:
Rebola, A; Klie, RF; Zapol, P; Ogut, S Author Full Names: Rebola, Alejandro; Klie, Robert F.; Zapol, Peter; Oeguet, Serdar
Source:
APPLIED PHYSICS LETTERS, 104 (25):10.1063/1.4885389 JUN 23 2014
Abstract:
The full phonon spectra of two rational approximants to the incommensurate thermoelectric oxide material Ca3Co4O9 (CCO) are calculated from first principles within density functional theory (DFT) and its DFT + U extension. The computed phonon dispersion curves are then used to evaluate the constant volume heat capacity, as well as the full and partial (subsystem-projected) lattice thermal conductivity of CCO. The results are discussed in terms of the effects of the Hubbard U on the computed properties, the size of the rational approximants used to model CCO, the relative contributions of the two subsystems that comprise the misfit-layered material, and the anisotropic nature of the computed thermal conductivity. We obtain good agreement with available experimental data. (C) 2014 AIP Publishing LLC.
Title:
Mapping of strained graphene into one-dimensional Hamiltonians: Quasicrystals and modulated crystals
Authors:
Naumis, GG; Roman-Taboada, P Author Full Names: Naumis, Gerardo G.; Roman-Taboada, Pedro
Source:
PHYSICAL REVIEW B, 89 (24):10.1103/PhysRevB.89.241404 JUN 11 2014
Abstract:
The electronic properties of graphene under any arbitrary uniaxial strain field are obtained by an exact mapping of the corresponding tight-binding Hamiltonian into an effective one-dimensional modulated chain. For a periodic modulation, the system displays a rich behavior, including quasicrystals and modulated crystals with a complex spectrum, including gaps and peaks at the Fermi energy and localization transitions. All these features are explained by the incommensurate or commensurate nature of the potential, which leads to a dense filling by diffraction spots of the reciprocal space in the former case. The essential features of strain are made specially clear by analyzing a special momenta that uncouples the model into dimers.
Title:
Hidden one-dimensional spin modulation in a three-dimensional metal
Authors:
Feng, YJ; Wang, JY; Palmer, A; Aguiar, JA; Mihaila, B; Yan, JQ; Littlewood, PB; Rosenbaum, TF Author Full Names: Feng, Yejun; Wang, Jiyang; Palmer, A.; Aguiar, J. A.; Mihaila, B.; Yan, J. -Q.; Littlewood, P. B.; Rosenbaum, T. F.
Source:
NATURE COMMUNICATIONS, 5 10.1038/ncomms5218 JUN 2014
Abstract:
Pressure can transform a transparent material into an opaque one, quench the moments in a magnet and force solids to flow like liquids. At 15 GPa, the pressure found 500 km below the earth's surface, the semiconductors silicon and germanium superconduct. Yet, at this same pressure, we show here that the magnetism in metallic GdSi remains completely robust even as it shrinks by one-seventh of its volume. Non-resonant X-ray magnetic diffraction in a specially designed diamond anvil cell, combined with band structure calculations, reveal the stability of the incommensurate spin density wave, which can be traced to a persistently nested portion of the Fermi surface that becomes increasingly one-dimensional under pressure. A cooperative interaction between nested, itinerant spins and local magnetic moments provides the organizing principle for the modulated magnetic order, salient both for its insights into the role of topology in ordered states and its potential functionality.
Title:
Electronic and magnetic properties of BiFeO3 with intrinsic defects: First-principles prediction
Authors:
Yang, RP; Lin, SX; Fang, XG; Qin, MH; Gao, XS; Zeng, M; Liu, JM Author Full Names: Yang Rui-Peng; Lin Si-Xian; Fang Xiao-Gong; Qin Ming-Hui; Gao Xing-Sen; Zeng Min; Liu Jun-Ming
Source:
CHINESE PHYSICS B, 23 (6):10.1088/1674-1056/23/6/067102 JUN 2014
Abstract:
The electronic structure, magnetism, and dielectric functions of BiFeO3 with intrinsic vacancies, including Bi-, Fe-, and O-vacancies (denoted as V-Fe, V-Bi, and V-O, respectively) are investigated using the first-principles density functional theory plus U calculations. It is revealed that the structural distortions associated with those vacancies impose significant influences on the total density of state and magnetic behaviors. The existence of V-Bi favors the excitation of the O-2p state into the band gap at 0.4 eV, while the O-2p and Fe-3d orbitals are co-excited into the band gap around 0.45 eV in V-Fe. Consequently, a giant net magnetic moment of 1.96 mu(B) is generated in VFe, and a relatively small moment of 0.13 mu B is induced in V-Bi, whereas VO seems magnetically inactive. The giant magnetic moment generated in V-Fe originates from the suppression of the spatially modulated antiferromagnetic spin structure. Furthermore, V-Fe and V-Bi have strong influences on dielectric function, and induce some strong peaks to occur in the lower energy level. In contrast, V-O has a small effect.
Title:
Impact-induced shock and the formation of natural quasicrystals in the early solar system
Authors:
Hollister, LS; Bindi, L; Yao, N; Poirier, GR; Andronicos, CL; MacPherson, GJ; Lin, C; Distler, VV; Eddy, MP; Kostin, A; Kryachko, V; Steinhardt, WM; Yudovskaya, M; Eiler, JM; Guan, YB; Clarke, JJ; Steinhardt, PJ Author Full Names: Hollister, Lincoln S.; Bindi, Luca; Yao, Nan; Poirier, Gerald R.; Andronicos, Christopher L.; MacPherson, Glenn J.; Lin, Chaney; Distler, Vadim V.; Eddy, Michael P.; Kostin, Alexander; Kryachko, Valery; Steinhardt, William M.; Yudovskaya, Marina; Eiler, John M.; Guan, Yunbin; Clarke, Jamil J.; Steinhardt, Paul J.
Source:
NATURE COMMUNICATIONS, 5 10.1038/ncomms5040 JUN 2014
Abstract:
The discovery of a natural quasicrystal, icosahedrite (Al63Cu24Fe13), accompanied by khatyrkite (CuAl2) and cupalite (CuAl) in the CV3 carbonaceous chondrite Khatyrka has posed a mystery as to what extraterrestrial processes led to the formation and preservation of these metal alloys. Here we present a range of evidence, including the discovery of high-pressure phases never observed before in a CV3 chondrite, indicating that an impact shock generated a heterogeneous distribution of pressures and temperatures in which some portions reached at least 5GPa and 1,200 degrees C. The conditions were sufficient to melt Al-Cu-bearing minerals, which then rapidly solidified into icosahedrite and other Al-Cu metal phases. The meteorite also contains heretofore unobserved phases of iron-nickel and iron sulphide with substantial amounts of Al and Cu. The presence of these phases in Khatyrka provides further proof that the Al-Cu alloys are natural products of unusual processes that occurred in the early solar system.
Title:
Networks of superconducting nano-puddles in 1/8 doped YBa2Cu3O6.5+y controlled by thermal manipulation
Authors:
Ricci, A; Poccia, N; Campi, G; Coneri, F; Barba, L; Arrighetti, G; Polentarutti, M; Burghammer, M; Sprung, M; Zimmermann, MV; Bianconi, A Author Full Names: Ricci, Alessandro; Poccia, Nicola; Campi, Gaetano; Coneri, Francesco; Barba, Luisa; Arrighetti, Gianmichele; Polentarutti, Maurizio; Burghammer, Manfred; Sprung, Michael; Zimmermann, Martin V.; Bianconi, Antonio
Source:
NEW JOURNAL OF PHYSICS, 16 10.1088/1367-2630/16/5/053030 MAY 14 2014
Abstract:
While it is known that the nature and the arrangement of defects in complex oxides have an impact on the material functionalities, little is known about control of superconductivity by oxygen interstitial organization in cuprates. Here we report direct compelling evidence for the control of T-c by manipulation of the superconducting granular networks of nanoscale puddles, made of ordered oxygen stripes, in a single crystal of YBa2Cu3O6.5+y with average formal hole doping p close to 1/8. Upon thermal treatments we were able to switch from a first network of oxygen defect striped puddles with OVIII modulation ((qOVIII)(a*) = (h + 3/8, k, 0) and (qOVIII)(a*) = (h + 5/8, k, 0)) to a second network characterized by OXVI modulation ((qOXVI)(a*) = (h + 7/16, k, 0) and (qox-VI)(a*) = (h + 9/16, k, 0)) and finally to a third network with puddles of OV periodicity ((qOV)(a*) = (4/10, 1, 0) and (qOV)(a*) = (6/10, 1, 0)). We map the microscopic spatial evolution of the out of plane OVIII, OXVI and OV puddle nanosize distribution via scanning micro-diffraction measurements. In particular, we calculated the number of oxygen chains (n) and the charge density (hole concentration p) inside each puddle, analyzing areas of 160 x 80 mu m(2), and recording 12 800 diffraction patterns to reconstruct each spatial map. The high spatial inhomogeneity shown by all the reconstructed spatial maps reflects the intrinsic granular structure that characterizes cuprates and iron chalcogenides, disclosing the presence of several complex networks of coexisting superconducting domains with different lattice modulations, charge densities and gaps as in the proposed multi-gap scenario called superstripes.
Title:
Internal Friction of an Ag-In-Yb Icosahedral Quasicrystal
Authors:
Handa, K; So, YG; Kamimura, Y; Tamura, R; Edagawa, K Author Full Names: Handa, Kenma; So, Yeong-Gi; Kamimura, Yasushi; Tamura, Ryuji; Edagawa, Keiichi
Source:
MATERIALS TRANSACTIONS, 55 (5):754-757; 10.2320/matertrans.M2013448 MAY 2014
Abstract:
Internal friction has been measured for an Ag-In-Yb Tsai-type icosahedral (i-) quasicrystal to investigate an energy-dissipation mechanism by phason relaxation, possibly operating in quasicrystals. A fairly large peak of the magnitude Q(-1) approximate to 0.022 was observed, which was shown to be of the thermally-activated relaxation type. The frequency factor and activation enthalpy were evaluated to be 10(20)s(-1) and 2.6 x 10(-19)J (1.6 eV), respectively. The observed peak was analyzed on the assumption that it is of phason-origin. The magnitude of the phonon-phason coupling constant was estimated to be 0.008 mu (mu: shear modulus), based on the model of the phonon-phason elastodynamics previously proposed. This value is comparable to those previously reported for Mackay-type i-phases such as i-Al-Pd-Mn and i-Al-Cu-Fe.

Update: 31-Jul-2014

Title:
Growth Modes of Quasicrystals
Authors:
Achim, CV; Schmiedeberg, M; Lowen, H Author Full Names: Achim, C. V.; Schmiedeberg, M.; Loewen, H.
Source:
PHYSICAL REVIEW LETTERS, 112 (25):10.1103/PhysRevLett.112.255501 JUN 26 2014
Abstract:
The growth of quasicrystals, i.e., aperiodic structures with long-range order, seeded from the melt is investigated using a dynamical phase field crystal model. Depending on the thermodynamic conditions, two different growth modes are detected, namely defect-free growth of the stable quasicrystal and a mode dominated by phasonic flips which are incorporated as local defects into the grown structure such that random tilinglike ordering emerges. The latter growth mode is unique to quasicrystals and can be verified in experiments on one-component mesoscopic systems.
Title:
Commensurate-incommensurate magnetic phase transition in the Fe-doped bilayer ruthenate Ca3Ru2O7
Authors:
Ke, X; Peng, J; Tian, W; Hong, T; Zhu, M; Mao, ZQ Author Full Names: Ke, X.; Peng, J.; Tian, W.; Hong, Tao; Zhu, M.; Mao, Z. Q.
Source:
PHYSICAL REVIEW B, 89 (22):10.1103/PhysRevB.89.220407 JUN 23 2014
Abstract:
Neutron diffraction studies have revealed an uncommon commensurate-incommensurate magnetic phase transition with decreasing temperature in the (similar to 5%) Fe-doped bilayer ruthenate Ca-3(Ru,Fe)(2)O-7. An incommensurate phase formed of a cycloidal spiral spin structure coexists with a commensurate one below the phase transition at 42 K and persists down to the lowest temperature, accompanied by higher-order magnetic satellite peaks which indicate the formation of a magnetic soliton lattice. We ascribe these findings to the competing magnetic interactions in this system. This study demonstrates an effective approach to tune novel magnetic and electronic properties of ruthenates via 3d magnetic transition-metal substitution.
Title:
Charge- and spin-density waves observed through their spatial fluctuations by coherent and simultaneous x-ray diffraction
Authors:
Jacques, VLR; Pinsolle, E; Ravy, S; Abramovici, G; Le Bolloc'h, D Author Full Names: Jacques, V. L. R.; Pinsolle, E.; Ravy, S.; Abramovici, G.; Le Bolloc'h, D.
Source:
PHYSICAL REVIEW B, 89 (24):10.1103/PhysRevB.89.245127 JUN 23 2014
Abstract:
Spatial fluctuations of spin-density wave (SDW) and charge-density wave (CDW) in chromium have been compared by combining coherent and simultaneous x-ray diffraction experiments. Despite their close relationship, spatial fluctuations of the spin and of the charge-density waves display a very different behavior: the satellite reflection associated to the charge density displays speckles while the spin one displays an impressive long-range order. This observation is hardly compatible with the commonly accepted magneto-elastic origin of CDW in chromium and is more consistent with a purely electronic scenario where CDW is the second harmonic of SDW. A BCS model taking into account a second-order nesting predicts correctly the existence of a CDW and explains why the CDW is more sensitive to punctual defects.
Title:
On Symplectic Analysis for the Plane Elasticity Problem of Quasicrystals with Point Group 12 mm
Authors:
Wang, H; Chen, JR; Zhang, XY Author Full Names: Wang, Hua; Chen, Jianrui; Zhang, Xiaoyu
Source:
ABSTRACT AND APPLIED ANALYSIS, 10.1155/2014/367018 2014
Abstract:
The symplectic approach, the separation of variables based on Hamiltonian systems, for the plane elasticity problem of quasicrystals with point group 12 mm is developed. By introducing appropriate transformations, the basic equations of the problem are converted to two independent Hamiltonian dual equations, and the associated Hamiltonian operator matrices are obtained. The study of the operator matrices shows the feasibility of the method. Without any assumptions, the general solution is presented for the problem with mixed boundary conditions.

Update: 24-Jul-2014

Title:
Modulating the Li+/Ni2+ replacement and electrochemical performance optimizing of layered Lithium-rich Li1.2Ni0.2Mn0.6O2 by minor Co dopant
Authors:
Huang, XL; Wang, M; Che, RC Author Full Names: Huang, Xiaolan; Wang, Min; Che, Renchao
Source:
JOURNAL OF MATERIALS CHEMISTRY A, 2 (25):9656-9665; 10.1039/c4ta01217h JUL 7 2014
Abstract:
The influences of the Li+/Ni2+ replacement modulated by minor Co dopant on cyclic capacity and rate performance of lithium-rich cathode material Li1.2Ni0.2-z/2Mn0.6-z/2CozO2 (z = 0, 0.02, 0.04, 0.10) were investigated from the microstructural point of view by comprehensive techniques of high-resolution transmission electron microscopy (HRTEM) imaging, atomic-resolution electron energy loss spectroscopy (EELS), selected-area electron diffraction (SAED), and X-ray diffraction (XRD). It is found that Co played a vital role in decreasing the Li+/Ni2+ replacement ratio in the hexagonal layered Li1 2Ni0.2-z/2Mn0.6-z/2CozO2 (R (3) over barm), which is closely related to the electrochemical performance. An evident cationic ordering in the transition metal layers and a stacking sequence vertical to the Li+ diffusion orientation were observed in the Li1.2Ni0.2-z/2Mn0.6-z/2CozO2 (z > 0) system rather than in the Li1.2Ni0.2Mn0.6O2 system. Compared with Li1.2Ni0 2Mn0.6O2, Li1.2Ni0.18Mn0.58Co0.04O2 showed excellent electrochemical performance with increase in discharge capacity to 288.3 mA h g(-1) from 166.3 mA h g(-1), improvement in capacity retention to 98.6% from 73.9% at a current density of 0.1 C after 40 cycles, and enhancement in capacity to 161.4 mA h g(-1) from 113 mA h g(-1) at a higher rate of 2 C. The largest interlayer spacing (0.218 nm of O-Li-O layer), highest proportion of Mn4+ ion component, and the most remarkable superstructure diffraction spots were found for Li1.2Ni0.18Mn0.58Co0.04O2 among all specimens, as confirmed by XRD refinement, EELS, HRTEM, and SAED. Three superstructure vectors modulated by 1/4 (q) over right arrow, 2/4 (q) over right arrow, 3/4 (q) over right arrow ((q) over right arrow = [0 (1) over bar1]) were simultaneously observed for Li1.2Ni0.18Mn0.58Co0.04O2, indicating a high degree of ordering. Our findings might shed new insights into the understanding of the Li+/Ni2+ replacement by doping minor amounts of Co for optimizing the electrochemical performance in Li-ion batteries cathode material from the microstructural point of view.
Title:
Al-Cr-Fe phase diagram. Isothermal Sections in the region above 50 at% Al
Authors:
Pavlyuchkov, D; Przepiorzynski, B; Kowalski, W; Velikanova, TY; Grushko, B Author Full Names: Pavlyuchkov, D.; Przepiorzynski, B.; Kowalski, W.; Velikanova, T. Ya.; Grushko, B.
Source:
CALPHAD-COMPUTER COUPLING OF PHASE DIAGRAMS AND THERMOCHEMISTRY, 45 194-203; 10.1016/j.calphad.2013.12.007 JUN 2014
Abstract:
The Al-Cr-Fe phase diagram was studied in the compositional range of 50-100 at% Al and partial isothermal sections were determined at 1160, 1100, 1075, 1042, 1000, 900, 800 and 700 degrees C In the low-Al part of the studied compositional region the isostructural high-temperature Al-Cr and Al-Fe gamma(1)- phases form a continuous region of solid solutions. Both binary Al13Fe4 and Al5Fe2 were found to dissolve up to 6.5 at% Cr while Al2Fe was found to extend up to 4.1 at% Cr. The solid solutions based on the Al-Cr gamma(2) and mu phases were determined to reach 35.2 and 1.3 at% Fe, respectively. The dissolution of Cr in the Al-Fe binaries only slightly influences their Al concentrations, while the Al-Cr binaries exhibit decreasing Al concentration with increasing Fe concentration. The Al-Cr eta-phase dissolves up to 5 at% Fe, which results in a sharp decrease of its Al concentration and increase of melting temperatures. The earlier reported existence of a ternary decagonal D-3-phase and three complex periodic phases O-1, H and e was confirmed and their compositions at different temperatures were specified. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Atomic clusters and atomic surfaces in icosahedral quasicrystals
Authors:
Quiquandon, M; Portier, R; Gratias, D Author Full Names: Quiquandon, Marianne; Portier, Richard; Gratias, Denis
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 70 229-238; 10.1107/S2053273314004665 3 MAY 2014
Abstract:
This paper presents the basic tools commonly used to describe the atomic structures of quasicrystals with a specific focus on the icosahedral phases. After a brief recall of the main properties of quasiperiodic objects, two simple physical rules are discussed that lead one to eventually obtain a surprisingly small number of atomic structures as ideal quasiperiodic models for real quasicrystals. This is due to the fact that the atomic surfaces (ASs) used to describe all known icosahedral phases are located on high-symmetry special points in six-dimensional space. The first rule is maximizing the density using simple polyhedral ASs that leads to two possible sets of ASs according to the value of the six-dimensional lattice parameter A between 0.63 and 0.79 nm. The second rule is maximizing the number of complete orbits of high symmetry to construct as large as possible atomic clusters similar to those observed in complex intermetallic structures and approximant phases. The practical use of these two rules together is demonstrated on two typical examples of icosahedral phases, i-AlMnSi and i-CdRE (RE = Gd, Ho, Tm). (C) 2014 International Union of Crystallography
Title:
Fluorinated mixed valence Fe(II)-Fe(III) phosphites with channels templated by linear tetramine chains. Structural and magnetic implications of partial replacement of Fe(II) by Co(II)
Authors:
Orive, J; de Luis, RF; Fernandez, JR; Legarra, E; Plazaola, F; Arriortua, MI Author Full Names: Orive, Joseba; de Luis, Roberto Fernandez; Fernandez, Jesus Rodriguez; Legarra, Estibaliz; Plazaola, Fernando; Arriortua, Maria I.
Source:
CRYSTENGCOMM, 16 (27):6066-6079; 10.1039/c4ce00264d 2014
Abstract:
Three new fluorinated mixed valence Fe(II)-Fe(III) phosphites were synthesized by employing mild hydrothermal conditions. (H(4)baepn) (0.5)[(Fe2.3Fe1.7II)-Fe-III(H2O)(2)(HPO3)(4)-((x+y))(HPO4)x(PO4)yF(4)] (x similar or equal to 0.13, y similar or equal to 0.3) (1) (baepn = N,N'-bis(2-aminoethyl)-1,3-propanediamine (C7N4H20)) and the Co(II)-substituted phase with the formula (H(4)baepn)(0.5)[(Fe2.0FeI0.71Co1.29II)-Fe-III-Co-I(H2O)(2)(HPO3)(4-x)(H PO4)xF(4)] (x similar or equal to 0.38) (2) were studied by single crystal X-ray diffraction. The phase with the major content of Co(II), (H(4)baepn)(0.5)[(Fe2.0Fe0.62Co1.38II)-Fe-III-Co-II(H2O)(2)(HPO3)(4-x)(H PO4)xF(4)] (x similar or equal to 0.38) (3) was obtained as a polycrystalline powder and studied by Rietveld refinement by using the structural model of 2. These compounds were characterized by ICP-Q-MS, thermogravimetric and thermodiffractometric analyses, and XPS, IR, UV/ vis and Mssbauer spectroscopy. The single crystal data indicate that phases 1 and 2 crystallize in the P2(1)/c space group with lattice parameters a = 13.6808(4), b = 12.6340(2), c = 12.7830(3) angstrom and beta = 116.983(4)degrees for 1 and a = 13.6823(4), b = 12.6063(3), c = 12.7535(4) angstrom and beta = 116.988(4)degrees for 2, with Z = 4. The reciprocal space of 1 shows satellite reflections with a modulation wavevector q = 0.284(2)a* which indicate an *incommensurate* long-range order. The average structure of these compounds is built up by a 3D lattice constructed by inorganic layers of Fe(III) chains and Fe(II) and Co(II) dimers joined by phosphite groups partially substituted by HPO4 and PO4 tetrahedral groups. These anionic layers stack along the [100] direction encapsulating linear tetramines in eight-membered open channels involving host-guest interactions. Magnetic measurements of 1 and 3 showed antiferromagnetic coupling as the major interactions, exhibiting a weak ferromagnetic component together with a spin glass transition at low temperature in the case of 1. Heat capacity measurements showed a small anomaly at 20.5 K for 1 and a sharp magnetic peak at 28 K for 3. Unexpectedly, the small anomaly observed in 1 increased with the magnetic field and became better defined.

Update: 10-Jul-2014

Title:
Pressure-induced polar phases in multiferroic delafossite CuFeO2
Authors:
Terada, N; Khalyavin, DD; Manuel, P; Osakabe, T; Radaelli, PG; Kitazawa, H Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Osakabe, Toyotaka; Radaelli, Paolo G.; Kitazawa, Hideaki
Source:
PHYSICAL REVIEW B, 89 (22):10.1103/PhysRevB.89.220403 JUN 13 2014
Abstract:
The pressure effect on the frustrated magnetic system CuFeO2 exhibiting multiferroic behavior has been studied by means of time-of-flight single crystal neutron diffraction combined with a hybrid-anvil-type pressure cell. The nonpolar collinear magnetic ground state (CM1 phase) with propagation vector k = (0, 1/2, 1/2) turns into a proper screw magnetic ordering with incommensurate modulation k = (0, q, 1/2; q similar or equal to 0.4) and a polar 21 ' magnetic point group (ICM2 phase), between 3 and 4 GPa. This spin structure is similar to the ferroelectric phase induced by magnetic field or chemical doping under ambient pressure. Above, 4 GPa, a magnetic phase (ICM3) appears, with an incommensurate propagation vector that is unique for the CuFeO2 system, k = (qa, qb, qc; qa similar or equal to 0, qb similar or equal to 0.34, qc similar or equal to 0.43). This propagation vector at the general point results in triclinic magnetic symmetry which implies an admixture of both cycloidal and proper screw spin configurations. The ICM3 phase is stable in a narrow pressure range, and above 6 GPa, the spin-density collinear structure (ICM1 phase), similar to the first ordered state at ambient pressure, takes place. Comparing the degree of lattice distortions among the magnetic phases observed at ambient pressure, we discuss the origin of the pressure-induced magnetic phase transitions in CuFeO2.
Title:
Synthesis of [(SnSe)(1.16-1.09)](1)[(NbxMo1-x)Se-2](1) Ferecrystal Alloys
Authors:
Westover, RD; Atkins, RA; Ditto, JJ; Johnson, DC Author Full Names: Westover, Richard D.; Atkins, Ryan A.; Ditto, Jeffrey J.; Johnson, David C.
Source:
CHEMISTRY OF MATERIALS, 26 (11):3443-3449; 10.1021/cm500720x JUN 10 2014
Abstract:
Modification of the modulated elemental reactant method allowed the first reported synthesis of quaternary [(MX)(z)](m)[(TxT'(1-x))X-2](n), compounds with controlled compositions. Metastable ferecrystal compounds, [(SnSe)(1.16-1.09)](1)[(NbxMo1-x)Se-2](1) with x = 0, 0.26, 0.49, 0.83, and 1, were synthesized and characterized by X-ray diffraction, electron probe microanalysis (EPMA), and scanning transmission electron microscopy (STEM). Misfit layer dichalcogenide analogues, showing controlled alloying of the dichalcogenide layers, have not been reported. Changes in lattice parameters, as a function of x, were similar to literature observations for the (NbxMo1-x)Se-2 system. The c-lattice parameters of the ferecrystal alloys decreased linearly from 12.53(2) angstrom for [(SnSe)(1.09)](1)(MoSe2)(1) to 12.27(2) angstrom for [(SnSe)(1.6)](1)(NbSe2)(1). The a-lattice parameters of the dichalcogenide constituent increased from 3.329(8) angstrom for [(SnSe)(1.09)](1)(MoSe2)(1) to 3.461(4) angstrom for [(SnSe)(1.6)](1)(NbSe2)(1). The a-lattice parameter of the rocksalt constituent remained constant resulting in a linear increase in misfit parameter with increased Nb content. Temperature dependent electrical resistivity measurements showed a transition from semiconducting to metallic behavior as the Nb content of the alloys increased.
Title:
Conduction-band electronic structure of 1T-TaS2 revealed by angle-resolved inverse-photoemission spectroscopy
Authors:
Sato, H; Arita, M; Utsumi, Y; Mukaegawa, Y; Sasaki, M; Ohnishi, A; Kitaura, M; Namatame, H; Taniguchi, M Author Full Names: Sato, Hitoshi; Arita, Masashi; Utsumi, Yuki; Mukaegawa, Yutaka; Sasaki, Minoru; Ohnishi, Akimasa; Kitaura, Mamoru; Namatame, Hirofumi; Taniguchi, Masaki
Source:
PHYSICAL REVIEW B, 89 (15):10.1103/PhysRevB.89.155137 APR 28 2014
Abstract:
We have investigated the conduction-band electronic structure of 1T-TaS2 in the incommensurate (IC) and commensurate (C) charge-density-wave (CDW) phases by means of angle-resolved inverse-photoemission spectroscopy (ARIPES) along the Gamma (A)-M (L) direction. In the ARIPES spectra for the ICCDW phase, a continuous and dispersive Ta 5d band is clearly observed near the Fermi level (E-F). For the CCDW phase, on the other hand, the Ta 5d band splits up and down into two manifolds around the M (L) point, reflecting formation of the root 13 x root 13 superstructure of the Ta plane. In addition, the CCDW-ARIPES spectrum around the M (L) points exhibits a shoulder structure at 0.7 eV above E-F, ascribed to the upper Hubbard band folded from the Gamma (Lambda) point. We have also observed an energy gap of similar to 100 meV in the unoccupied density of states in the CCDW phase.

Update: 2-Jul-2014

Title:
Development of Very High Strength and Ductile Dilute Magnesium Alloys by Dispersion of Quasicrystal Phase
Authors:
Singh, A; Osawa, Y; Somekawa, H; Mukai, T; Parrish, CJ; Shih, DS Author Full Names: Singh, Alok; Osawa, Yoshiaki; Somekawa, Hidetoshi; Mukai, Toshiji; Parrish, Catherine J.; Shih, Donald S.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 45A (8):3232-3240; 10.1007/s11661-013-2056-5 JUL 2014
Abstract:
Very high strengths, with tensile yield strength from 377 to 405 MPa, combined with elongation to failure of over 12 pct, have been achieved in Mg-Zn-Y dilute alloys by direct extrusion. Alloys Mg-6xZn-xY, where x = 0.2, 0.35, and 0.5 (at. pct) were chill cast in a steel mold and direct extruded at a temperature in the range 508 K to 528 K (235 A degrees C to 255 A degrees C), which produced an average grain size of about 1 mu m. Quasicrystalline i-phase particles were dispersed in the matrix with size ranging from 50 nm to 1 mu m. In addition, high density of nano-precipitates of average size 15 nm was dispersed in matrix. Thus we have developed magnesium alloys of very high strength combined with ductility by a simple process using extrusion with very little addition of yttrium. (C) The Minerals, Metals & Materials Society and ASM International 2013
Title:
Localization and Impact of Pb-Non-Bonded Electronic Pair on the Crystal and Electronic Structure of Pb2YSbO6
Authors:
Larrogola, SA; Alonso, JA; de la Pena-O'Shea, VA; Sheptyakov, D; Pomjakushin, V; Fernandez-Diaz, MT; Pedregosa, JC Author Full Names: Larregola, Sebastian A.; Alonso, Jose A.; de la Pena-O'Shea, Victor A.; Sheptyakov, Denis; Pomjakushin, Vladimir; Fernandez-Diaz, Maria T.; Pedregosa, Jose C.
Source:
INORGANIC CHEMISTRY, 53 (11):5609-5618; 10.1021/ic500278y JUN 2 2014
Abstract:
The synthesis and crystal structure evolution of the double perovskite Pb2YSbO6 is reported for the first time. The structure has been analyzed in the temperature range between 100 and 500 K by using a combination of synchrotron and neutron powder diffraction. This compound shows two consecutive first order phase transformations as previously observed for a subgroup of Pb2RSbO6 perovkites (R = rare earths). The thermodynamic parameters associated with the phase transitions were calculated using differential scanning calorimetry (DSC), and the role of the diverse cations of the structure was studied from DFT calculations for the room temperature polymorph. The crystal structure evolves from a C2/c monoclinic structure (a(-)b(-)b(-) tilting system in Glazer's notation) to another monoclinic P2(1)/n (a(-)a(-)b(+))phase with an incommensurate modulation and finally to a cubic Fm (3) over barm perovskite (a(0)a(0)a(0)). The highly distorted nature of the room temperature crystal structure seems to be driven by the polarization of the Pb lone pair which shows a marked local effect in the atomic spatial arrangements. Moreover, the lone pairs have been localized from DFT calculations and show an antiferroelectric ordering along the b monoclinic axis.
Title:
Emergence of charge density wave domain walls above the superconducting dome in 1T-TiSe2
Authors:
Joe, YI; Chen, XM; Ghaemi, P; Finkelstein, KD; de la Pena, GA; Gan, Y; Lee, JCT; Yuan, S; Geck, J; MacDougall, GJ; Chiang, TC; Cooper, SL; Fradkin, E; Abbamonte, P Author Full Names: Joe, Y. I.; Chen, X. M.; Ghaemi, P.; Finkelstein, K. D.; de la Pena, G. A.; Gan, Y.; Lee, J. C. T.; Yuan, S.; Geck, J.; MacDougall, G. J.; Chiang, T. C.; Cooper, S. L.; Fradkin, E.; Abbamonte, P.
Source:
NATURE PHYSICS, 10 (6):421-425; 10.1038/NPHYS2935 JUN 2014
Abstract:
Superconductivity in so-called unconventional superconductors is nearly always found in the vicinity of another ordered state, such as antiferromagnetism, charge density wave (CDW), or stripe order. This suggests a fundamental connection between superconductivity and fluctuations in some other order parameter. To better understand this connection, we used high-pressure X-ray scattering to directly study the CDW order in the layered dichalcogenide TiSe2, which was previously shown to exhibit superconductivity when the CDW is suppressed by pressure(1) or intercalation of Cu atoms(2). We succeeded in suppressing the CDW fully to zero temperature, establishing for the first time the existence of aquantum critical point (QCP) at P-c = 5.1 +/- 0.2 GPa, which is more than 1 GPa beyond the end of the superconducting region. Unexpectedly, at P = 3 GPa we observed a reentrant, weakly first order, incommensurate phase, indicating the presence of a Lifshitz tricritical point somewhere above the superconducting dome. Our study suggests that superconductivity in TiSe2 may not be connected to the QCP itself, but to the formation of CDW domain walls.
Title:
The alpha <-> beta phase transitions of Zn2P2O7 revisited: existence of an additional intermediate phase with an incommensurately modulated structure
Authors:
Stoger, B; Weil, M; Dusek, M Author Full Names: Stoeger, Berthold; Weil, Matthias; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 539-554; SI 10.1107/S205252061401049X 3 JUN 2014
Abstract:
Zn2P2O7 crystallizes in a thortveitite-like structure and features temperature-dependent polymorphism. At high temperatures (T > 500 K), the aristotype phase beta-Zn2P2O7 (C2/m, Z = 2, a similar or equal to 6.60, b similar or equal to 8.28, c similar or equal to 4.53 angstrom, beta similar or equal to 105.4 degrees) is stable. At lower temperatures the lock-in phase alpha(1)-Zn2P2O7 [at 350 K: I2/c, Z = 12, a = 20.1131 (13), b = 8.2769 (6), c = 9.109 (3) angstrom, beta = 106.338 (16)degrees], a sixfold superstructure with commensurate modulation vector q = (1/3, 0, 1/2), is stable. Between the stability ranges of the alpha(1)- and beta-phases exists the intermediate, incommensurately modulated alpha(2)-Zn2P2O7 phase with modulation wavevector q similar or equal to (0.33, 0, 0.40) and C2/m(alpha, 0, gamma)0s superspace group symmetry. The alpha(1) -> alpha(2) lock-in phase transition at T-L = 408 K is of first-order and features virtually no hysteresis. It is immediately followed by the second-order alpha(2) -> beta transition to the non-modulated phase at T-I similar or equal to 430 K. This transformation is sluggish and even at T = 500 K very weak satellite reflections of the alpha(2)- phase were observed. Both phase transitions were analyzed with differential scanning calorimetry and high-temperature powder and single-crystal X-ray diffraction. The crystal structures of the alpha(1)- and alpha(2)- phases were refined from single crystal data collected at T = 350, 400, 405, 410, 415, 420, 425, 430, 450 and 500 K. Different models describing the slow transition from the incommensurately modulated alpha(2)- to the non-modulated beta-phase were tested. In the model resulting in the best residuals, the bridging O atom of the [P2O7] group, which is located on a 2/m position in the basic structure, is described as an overlap of an atom ordered in internal space and one atom disordered around the mirror plane. The occupancy of the ordered atom decreases with temperature until at T = 500 K virtually only the disordered atom remains. Simultaneously, the amplitude of the modulation functions of the remaining atoms decreases, so that the T = 500 K structure can be considered as the C2/m aristotype structure, although the diffraction pattern still features satellite reflections of first order with very low intensities.
Title:
Phase transformation and mechanical properties of as-cast Ti41.5Zr41.5Ni17 quasicrystalline composites
Authors:
Park, GH; Hong, SH; Kim, JT; Park, HJ; Seo, Y; Suh, JY; Hong, S; Park, JM; Kim, KB Author Full Names: Park, G. H.; Hong, S. H.; Kim, J. T.; Park, H. J.; Seo, Y.; Suh, J. Y.; Hong, S.; Park, J. M.; Kim, K. B.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 392 6-10; 10.1016/j.jnoncryso1.2014.03.024 JUN 1 2014
Abstract:
Phase transformation behavior of the quasicrystalline icosahedral phase (I-phase) and mechanical properties in a Ti41.5Zr41.5Ni17, alloy have been investigated using suction-casted bulk samples with various sample sizes (phi = 2, 3 and 5 mm). For 2 and 3 mm diameter rod samples, micrometer size dendritic beta-(Ti,Zr) phases are precipitated in the matrix and continuously I-phases are developed in the vicinity of the primary beta-(Ti,Zr) phases. With further increase of the sample size (i.e. decrease of cooling rate; phi = 5 mm), the length scale and volume fraction of primary beta-(Ti,Zr) dendritic phase are continuously increased and the constitution of matrix phase is changed from I-phase to eutectic lamella composed of bcc beta-(Ti,Zr) and hcp C14 Laves phases. The characterization of mechanical properties was carried out by compression and microhardness tests at room temperature. Depending on the selection, size and volume fraction of constituent phases, the values of hardness and compressive fracture strength are varied. The fracture surface morphologies of failed samples exhibit cleavage and quasi-cleavage patterns revealing the typical brittle failure characteristics. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Commensurate-incommensurate transition in graphene on hexagonal boron nitride
Authors:
Woods, CR; Britnell, L; Eckmann, A; Ma, RS; Lu, JC; Guo, HM; Lin, X; Yu, GL; Cao, Y; Gorbachev, RV; Kretinin, AV; Park, J; Ponomarenko, LA; Katsnelson, MI; Gornostyrev, YN; Watanabe, K; Taniguchi, T; Casiraghi, C; Gao, HJ; Geim, AK; Novoselov, KS Author Full Names: Woods, C. R.; Britnell, L.; Eckmann, A.; Ma, R. S.; Lu, J. C.; Guo, H. M.; Lin, X.; Yu, G. L.; Cao, Y.; Gorbachev, R. V.; Kretinin, A. V.; Park, J.; Ponomarenko, L. A.; Katsnelson, M. I.; Gornostyrev, Yu. N.; Watanabe, K.; Taniguchi, T.; Casiraghi, C.; Gao, H-J.; Geim, A. K.; Novoselov, K. S.
Source:
NATURE PHYSICS, 10 (6):451-456; 10.1038/NPHYS2954 JUN 2014
Abstract:
When a crystal is subjected to a periodic potential, under certain circumstances it can adjust itself to follow the periodicity of the potential, resulting in a commensurate state. Of particular interest are topological defects between the two commensurate phases, such as solitons and domain walls. Here we report a commensurate-incommensurate transition for graphene on top of hexagonal boron nitride (hBN). Depending on the rotation angle between the lattices of the two crystals, graphene can either stretch to adapt to a slightly different hBN periodicity (for small angles, resulting in a commensurate state) or exhibit little adjustment (the incommensurate state). In the commensurate state, areas with matching lattice constants are separated by domain walls that accumulate the generated strain. Such soliton-like objects are not only of significant fundamental interest, but their presence could also explain recent experiments where electronic and optical properties of graphene-hBN heterostructures were observed to be considerably altered.
Title:
Understanding the structure details when drying hydrate crystals of pharmaceuticals - interpretations from diffuse scattering and inter-modulation satellites of a partially dehydrated crystal
Authors:
Chan, EJ; Gao, Q; Dabros, M Author Full Names: Chan, E. J.; Gao, Q.; Dabros, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 555-567; SI 10.1107/S2052520614005125 3 JUN 2014
Abstract:
Simplified models for the crystal lattice of the sesquihydrate form of the hemi-sulfate salt of (5S, 6S, 9R)-5-amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohepta[b]py ridin9-yl 4-(2-oxo-2,3-dihydro-1H-imidazol[4,5b]pyridin-1-yl)-1piperidine carboxylate (BMS-927711, C28H29F2N6O3+) are used to calculate diffuse diffraction features in order to develop a mechanistic understanding of the dehydration process with respect to disruption of the lattice, since a Bragg model cannot be established. The model demonstrates that what we observe when the water leaves the crystal is partial transformation from the parent form to a child form (a new form, less hydrated and structurally related to the parent). Yet this 'dried' structure is not a pure phase. It consists of semi-random layers of both child, parent and an interfacial layer which has a modulated structure that represents a transitory phase. Understanding the fact that a single 'dried' crystal can have the disordered layer structure described as well as understanding mechanistic relationships between the phases involved can have implications in understanding the effect of common large scale bulk drying procedures. During the development of BMS-927711, difficulties did arise during characterization of the dried bulk when using only routine solid-state analysis. The material is now better understood from this diffraction study. The diffraction experiments also reveal intermodulation satellites, which upon interpretation yield even more structural information about the crystal transformation. The model suggests the mechanism of transformation is laminar in which layers of the crystal are driven to approach a stable B-centered supercell phase of lower water content.
Title:
Solidification Process and Formation of Quasi-crystal Phase in Mg-6Zn-1Y Alloy under Pressure in the Order of GPa
Authors:
Dong, Y; Lin, XP; Xu, R; Liu, SJ; Tian, SS Author Full Names: Dong Yun; Lin Xiaoping; Xu Rui; Liu Shijun; Tian Shasha
Source:
RARE METAL MATERIALS AND ENGINEERING, 43 (5):1117-1122; MAY 2014
Abstract:
The solidification path in the Mg-6Zn-1Y alloy was calculated by FactSage thermodynamic software and Mg-database. The solidification process and the formation of quasi-crystal phase in the Mg-6Zn-1Y alloy were analyzed using OM, SEM equipped with EDS, XRD, and DSC. The results show that the microstructure of the alloy solidified under the ambient pressure is consisted of the lamellar quasi-crystal I-Mg3YZn6 distributed in the interdendritic region of the coarse alpha-Mg dendrite and the thermodynamic calculation is well agreed with the experimental analyses of the solidification process. The microstructure of the super-fined dendrite can be obtained and the morphology of interdendritic lamellar phases can be improved when the alloy solidifies under super-high pressure in the order of GPa. The transition of dendritic morphology occurs from interdendritic network or banding to "long island" as well as "granule" with the increasing of solidified pressure. In particular, the amount of interdendritic quasi-crystal I-Mg3YZn6 increases remarkably and the volume fraction of the phase is up to 40%. Meanwhile, the new ternary Mg-Zn-Y phase with high Y content is dispersively distributed in the matrix with the size in the order of nanometer.
Title:
Crystallographic Computing System JANA2006: General features
Authors:
Petricek, V; Dusek, M; Palatinus, L Author Full Names: Petricek, Vaclav; Dusek, Michal; Palatinus, Lukas
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 229 (5):345-352; 10.1515/zkri-2014-1737 2014
Abstract:
JANA2006 is a freely available program for structure determination of standard, modulated and magnetic samples based on X-ray or neutron single crystal/powder diffraction or on electron diffraction. The system has been developed for 30 years from specialized tool for refinement of modulated structures to a universal program covering standard as well as advanced crystallography. The aim of this article is to describe the basic features of JANA2006 and explain its scope and philosophy. It will also serve as a basis for future publications detailing tools and methods of JANA.
Title:
The incommensurate crystal structure of the Pd(5)b(1-z) phase; B ordering driven by elastic interaction between B atoms
Authors:
Leineweber, A; Berger, TG; Udyansky, A; Bugaev, VN; Duppel, V Author Full Names: Leineweber, Andreas; Berger, Tilmann Georg; Udyansky, Alexander; Bugaev, Volodymyr N.; Duppel, Viola
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 229 (5):353-367; 10.1515/zkri-2013-1710 2014
Abstract:
The atomic structure of the incommensurate Pd5B1-z phase has been analysed in detail by selected area electron diffraction and neutron-powder diffraction. That structure is based on a close-packed cubic arrangement of Pd atoms with the B atoms occupying the octahedral sites in a long-range ordered fashion. The ordering pattern of B is an incommensurately modulated one with a modulation vector of a length which changes with the B content (similar to PdB0.18-0.19) to adapt the ordering pattern continuously to the actual composition. The structure can be conceived to be constituted from "isolated" BPd6 units (also occurring in the previously reported Pd6B phase) and edge-sharing B2Pd10 octahedra units, which occur in a ratio reflecting the actual B content. As predicted on the basis of elastic interactions between B atoms, nearest neighbour B-B pairs occur (the B2Pd10 double octahedra units) in the structure of the Pd5B1-z phase, whereas occurrence of second-nearest neighbour B-B pairs is avoided. For the ideal composition Pd5B the crystal structure of the Pd5B1-z, phase corresponds to that of monoclinic UCl5 with U playing the role of B and Cl that of Pd.

Update: 25-Jun-2014

Title:
Al-based metal matrix composites reinforced with Al-Cu-Fe quasicrystalline particles: Strengthening by interfacial reaction
Authors:
Ali, F; Scudino, S; Anwar, MS; Shahid, RN; Srivastava, VC; Uhlenwinkel, V; Stoica, M; Vaughan, G; Eckert, J Author Full Names: Ali, F.; Scudino, S.; Anwar, M. S.; Shahid, R. N.; Srivastava, V. C.; Uhlenwinkel, V.; Stoica, M.; Vaughan, G.; Eckert, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 607 274-279; 10.1016/j.jallcom.2014.04.086 SEP 15 2014
Abstract:
The interfacial reaction between the Al matrix and the Al62.5Cu25Fe12.5 quasicrystalline (QC) reinforcing particles to form the Al7Cu2Fe omega-phase has been used to further enhance the strength of the Al/QC composites. The QC-to-omega phase transformation during heating was studied by in situ X-ray diffraction using a high-energy monochromatic synchrotron beam, which permits to follow the structural evolution and to correlate it with the mechanical properties of the composites. The mechanical behavior of these transformation-strengthened composites is remarkably improved as the QC-to-x phase transformation progresses: the yield strength increases from 195 MPa for the starting material reinforced exclusively with QC particles to 400 MPa for the material where the QC-to-x reaction is complete. The reduction of the matrix ligament size resulting from the increased volume fraction of the reinforcing phase during the transformation can account for most of the observed improvement in strength, whereas the additional strengthening can be ascribed to the possible presence of nanosized omega-phase particles as well as to the improved interfacial bonding between matrix and particles caused by the compressive stresses arising in the matrix. (C0 2014 Elsevier B.V. All rights reserved.
Title:
Field-induced incommensurate phase in the strong-rung spin ladder with ferromagnetic legs
Authors:
Yamaguchi, H; Miyagai, H; Yoshida, M; Takigawa, M; Iwase, K; Ono, T; Kase, N; Araki, K; Kittaka, S; Sakakibara, T; Shimokawa, T; Okubo, T; Okunishi, K; Matsuo, A; Hosokoshi, Y Author Full Names: Yamaguchi, H.; Miyagai, H.; Yoshida, M.; Takigawa, M.; Iwase, K.; Ono, T.; Kase, N.; Araki, K.; Kittaka, S.; Sakakibara, T.; Shimokawa, T.; Okubo, T.; Okunishi, K.; Matsuo, A.; Hosokoshi, Y.
Source:
PHYSICAL REVIEW B, 89 (22):10.1103/PhysRevB.89.220402 JUN 9 2014
Abstract:
We report magnetization, specific heat, and NMR measurements of 3-Br-4-F-V [=3-(3-bromo-4-fluorophenyl)-1,5-diphenylverdazyl], a strong-rung S = 1/2 Heisenberg spin ladder with ferromagnetic leg interactions. We explain the magnetic and thermodynamic properties based on the strong-rung regime. Furthermore, we find a field-induced successive phase transition in the specific heat and the nuclear spin-lattice relaxation rate 1/T-1. F-19-NMR spectra for higher-and lower-temperature phases indicate partial magnetic order and incommensurate long-range order, respectively, evidencing the presence of frustration due to weak interladder couplings.
Title:
Raman study of phonons in CaMn7O12: Effects of structural modulation and structural transition
Authors:
Iliev, MN; Hadjiev, VG; Gospodinov, MM; Nikolova, RP; Abrashev, MV Author Full Names: Iliev, M. N.; Hadjiev, V. G.; Gospodinov, M. M.; Nikolova, R. P.; Abrashev, M. V.
Source:
PHYSICAL REVIEW B, 89 (21):10.1103/PhysRevB.89.214302 JUN 5 2014
Abstract:
Polarized Raman spectra of oriented CaMn7O12 single crystals have been studied in a broad temperature range (5-500 K) covering the crystallographic, ferroelectric, and magnetic transitions. From the spectra obtained at room temperature (RT) 10 out of the total 12 Raman active 6A(g) + 6E(g) modes of the trigonal R (3) over bar phase have been identified and assigned to definite atomic motions in close comparison to results of lattice-dynamics modeling. With the decrease in temperature below 250 K some Raman bands split, and additional spectral features, not expected for the R (3) over bar structure, arise well above the magnetic transitions near 90 and 50 K. Their appearance, however, correlates with the transformation due to incommensurate structural modulation revealed by recent x-ray and neutron-diffraction studies. As temperature increases above RT the intensity of the Raman lines strongly decreases, and entering the high-temperature Im (3) over bar phase the spectrum transforms its shape to that expected for a structure with disordered Jahn-Teller distortions.
Title:
Concomitant charge-density-wave and unit-cell-doubling structural transitions in Dy5Ir4Si10
Authors:
Lee, MH; Chen, CH; Tseng, CM; Lue, CS; Kuo, YK; Yang, HD; Chu, MW Author Full Names: Lee, M. H.; Chen, C. H.; Tseng, C. M.; Lue, C. S.; Kuo, Y. K.; Yang, H. D.; Chu, M. -W.
Source:
PHYSICAL REVIEW B, 89 (19):10.1103/PhysRevB.89.195142 MAY 29 2014
Abstract:
The tetragonal rare-earth transition-metal silicide system with three-dimensional crystallographic structure R5T4Si10, where R is Dy, Ho, Er, Tm, and Lu, and T = Ir and Rh, has been shown to exhibit fascinating charge-density-wave (CDW) phase transitions, a phenomenon largely found in otherwise low-dimensional systems. In this study, we report the investigations of CDW in Dy5Ir4Si10 at different temperatures using transmission electron microscopy techniques including electron diffraction and dark-field imaging. Incommensurate superlattice spots along the c axis were observed in the electron-diffraction patterns when the sample was cooled below the CDW transition temperature at similar to 208 K. CDW becomes commensurate with further cooling and configurations of CDW dislocations convincingly show that the CDW phase transition is accompanied by a concomitant cell-doubling crystallographic structural phase transition. Intriguingly, the cell-doubling transition is featured by a broken inversion symmetry along the c axis and a disparity in the CDW-modulation vectors with opposite signs, which gives rise to two sets of CDW domains with reversed contrasts. The profound physics underlining this notable domain-contrast behavior is discussed.
Title:
Neutron powder diffraction and Mossbauer spectroscopy (Sn-119 and Gd-155) studies of the CeScSi-type GdMgSn and GdMgPb compounds
Authors:
Lemoine, P; Lee-Hone, NR; Ryan, DH; Verniere, A; Malaman, B; Le Caer, G Author Full Names: Lemoine, P.; Lee-Hone, N. R.; Ryan, D. H.; Verniere, A.; Malaman, B.; Le Caer, G.
Source:
PHYSICAL REVIEW B, 89 (17):10.1103/PhysRevB.89.174428 MAY 28 2014
Abstract:
The magnetic structures of the CeScSi-type GdMgSn and GdMgPb compounds have been studied by both neutron powder diffraction and Mossbauer spectroscopy (Sn-119 and Gd-155). The neutron diffraction results show that the two compounds adopt incommensurate antiferromagnetic structures at 5.4 K with propagation vectors (k) over right arrow = [0.910,0.077,0] for GdMgSn and (k) over right arrow = [0.892,0,0] for GdMgPb. The magnetic moments lie in the basal plane, which is confirmed by both Sn-119 and Gd-155 Mossbauer spectroscopy. Mossbauer spectroscopy refinements and simulations reveal that the magnetic structure of GdMgSn is cycloidal at low temperature and undergoes a transition to a modulated magnetic structure above T similar to 40 K. A similar magnetic transition is inferred for GdMgPb. The magnetic structures of GdMgSn and GdMgPb are compared with those of other CeScSi-type compounds.
Title:
Magnetic and ferroelectric orderings in multiferroic alpha-NaFeO2
Authors:
Terada, N; Khalyavin, DD; Perez-Mato, JM; Manuel, P; Prabhakaran, D; Daoud-Aladine, A; Radaelli, PG; Suzuki, HS; Kitazawa, H Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Perez-Mato, Juan M.; Manuel, Pascal; Prabhakaran, Dharmalingam; Daoud-Aladine, Aziz; Radaelli, Paolo G.; Suzuki, Hiroyuki S.; Kitazawa, Hideaki
Source:
PHYSICAL REVIEW B, 89 (18):10.1103/PhysRevB.89.184421 MAY 28 2014
Abstract:
The triangular based antiferromagnet alpha-NaFeO2 has been studied by magnetization, dielectric, and neutron diffraction measurements as a function of temperature and magnetic field. The appropriate (H - T) phase diagram was constructed revealing a complex behavior due to a competition between several magnetic phases. In zero field, the system undergoes a sequence of magnetostructural transitions; initially from paramagnetic R (3) over bar m1' phase to the incommensurate spin density wave (ICM1) at T-N1 = 11 K with the nonpolar (3 + 1) magnetic superspace group C2/m1' (0, beta, 1/2)s0s, then, below T-N2 = 7.5 K, the ICM1 phase coexists with the polar cycloidal ordering (ICM2) possessing the Cm1'(0, beta, 1/2)0s superspace symmetry and finally the commensurate collinear ordering (CM) with the nonpolar magnetic space group P(a)2(1)/m develops below T-N3 = 5.5 K as the ground state of the system. A small amount of ICM2 coexists with the ICM1 and CM phases resulting in a nonzero measured polarization below T-N2. Magnetic field destabilizes the collinear ground state and promotes the polar ICM2 phase resulting in a drastic increase of the polarization. The symmetry of the zero field cycloidal structure allows the two orthogonal components p(1) proportional to r(ij) x (S-i x S-j) and p(2) proportional to S-i x S-j to contribute to the macroscopic polarization through the inverse DM effect. The applied magnetic field reduces the symmetry of the ICM2 phase down to the triclinic P-1(alpha, beta, gamma)0, resulting in admixture of another cycloidal and helical components both generating magnetic field switchable polarization p(3) perpendicular to p(1) and p(2).
Title:
Influence of the Structure on the Properties of NaxEuy(MoO4)(z) Red Phosphors
Authors:
Morozov, VA; Lazoryak, BI; Shmurak, SZ; Kiselev, AP; Lebedev, OI; Gauquelin, N; Verbeeck, J; Hadermann, J; Van Tendeloo, G Author Full Names: Morozov, Vladimir A.; Lazoryak, Bogdan I.; Shmurak, Semen Z.; Kiselev, Aleksander P.; Lebedev, Oleg I.; Gauquelin, Nicolas; Verbeeck, Johan; Hadermann, Joke; Van Tendeloo, Gustaaf
Source:
CHEMISTRY OF MATERIALS, 26 (10):3238-3248; 10.1021/cm500966g MAY 27 2014
Abstract:
Scheelite related compounds (A',A '')(n)[(B',B '')O-4](m) with B', B '' = W and/or Mo are promising new materials for red phosphors in pc-WLEDs (phosphor-converted white-light-emitting-diode) and solid-state lasers. Cation substitution in CaMoO4 of Ca2+ by the combination of Na+ and Eu3+, with the creation of A cation vacancies, has been investigated as a factor for controlling the scheelite-type structure and the luminescent properties. Na5Eu(MoO4)(4) and NaxEu(2-x)/33+square(2-x)/3MoO4 (0.138 <= x <= 0.5) phases with a scheelite-type structure were synthesized by the solid state method; their structural characteristics were investigated using transmission electron microscopy. Contrary to powder synchrotron X-ray diffraction before, the study by electron diffraction and high resolution transmission electron microscopy in this paper revealed that Na0.286Eu0.571MoO4 has a (3 + 2)D incommensurately modulated structure and that (3 + 2)D incommensurately modulated domains are present in Na0.200Eu0.600MoO4. It also confirmed the (3 + 1)D incommensurately modulated character of Na(0.138)Eu(0.621)Mo04. The luminescent properties of all phases under near-ultraviolet (n-UV) light have been investigated. The excitation spectra of these phosphors show the strongest absorption at about 395 nm, which matches well with the commercially available n-UV-emitting GaN-based LED chip. The emission spectra indicate an intense red emission due to the D-5(0) -> F-7(2) transition of Eu3+, with local minima in the intensity at Na0.286Eu0.571MoO4 and Na0.200Eu0.600MoO4 for similar to 613 nm and similar to 616 nm bands. The phosphor Na5Eu(MoO4)(4) shows the brightest red light emission among the phosphors in the Na2MoO4-Eu2/3MoO4 system and the maximum luminescence intensity of Na5Eu(MoO4)(4) (lambda(ex) = 395 nm) in the D-5(0) -> F-7(2) transition region is close to that of the commercially used red phosphor YVO4:Eu3+ (lambda(ex) = 326 nm). Electron energy loss spectroscopy measurements revealed the influence of the structure and Na/Eu cation distribution on the number and positions of bands in the UV-optical-infrared regions of the EELS spectrum.

Update: 19-Jun-2014

Title:
Acid-Base Chemistry in the Formation of Mackay-Type Icosahedral Clusters: mu(3)-Acidity Analysis of Sc-Rich Phases of the Sc-Ir System
Authors:
Guo, YM; Stacey, TE; Fredrickson, DC Author Full Names: Guo, Yiming; Stacey, Timothy E.; Fredrickson, Daniel C.
Source:
INORGANIC CHEMISTRY, 53 (10):5280-5293; 10.1021/ic500510s MAY 19 2014
Abstract:
The crystal structures of intermetallic phases offer a wealth of geometrical features (helices, multishelled clusters, and host guest motifs) whose formation has yet to be explained or predicted by chemical theory. A recently developed extension of the acid base concept to metallic systems, the mu(3)-acidity model, provides an avenue for developing this understanding for intermetallics formed from transition metals. In this Article, we illustrate how this approach can be used to understand one of the most striking geometrical entities to emerge in intermetallic chemistry, the Mackay cluster of icosahedral quasicrystals. We present mu(3)-acidity analyses, based on DFT-calibrated Huckel calculations, for a series of Sc-Ir intermetallics: ScIr (CsCl-type), Sc2Ir (Ti2Ni-type), Sc11Ir4, and the Mackay cluster containing phases Sc57Ir13 and Sc44Ir7. We begin by illustrating that a mu(3)-acidity model correctly predicts that each of these phases is stable relative to disproportionation into their neighboring compounds when a common set of Huckel parameters and d-orbital occupancies is used. Next, we explain these results by developing a relationship between the distance distribution of homoatomic contacts within an atom's coordination sphere and the mu(3)-neutralization it experiences. For a given average homoatomic distance, the role of heteroatomic contacts is higher when the distribution of homoatomic contacts is narrower. This effect is key to the strength of the acid base neutralization of the Sc-rich phases, where the Sc atoms find a scarcity of Ir atoms from which to obtain neutralization. Under these circumstances, Sc-Ir contacts should be maximized, whereas the number and distance variations of the Sc Sc contacts should be minimized. These expectations are borne out by the observed crystal structures. In particular, the Mackay clusters of Sc57Ir13 and Sc44Ir7, in which a central Ir atom is icosahedrally coordinated by a pentagonal dodecahedral array of face-sharing Sc octahedra, represent a natural way of merging the competing needs for enhancing Sc-Ir interactions while diminishing those between the Sc atoms.
Title:
Crystalline and quasicrystalline allotropes of Pb formed on the fivefold surface of icosahedral Ag-In-Yb
Authors:
Sharma, HR; Smerdon, JA; Nugent, PJ; Ribeiro, A; McLeod, I; Dhanak, VR; Shimoda, M; Tsai, AP; McGrath, R Author Full Names: Sharma, H. R.; Smerdon, J. A.; Nugent, P. J.; Ribeiro, A.; McLeod, I.; Dhanak, V. R.; Shimoda, M.; Tsai, A. P.; McGrath, R.
Source:
JOURNAL OF CHEMICAL PHYSICS, 140 (17):10.1063/1.4873596 MAY 7 2014
Abstract:
Crystalline and quasicrystalline allotropes of Pb are formed by evaporation on the fivefold surface of the icosahedral (i) Ag-In-Yb quasicrystal under ultra-high vacuum. Lead grows in three dimensional quasicrystalline order and subsequently forms fivefold-twinned islands with the fcc(111) surface orientation atop of the quasicrystalline Pb. The islands exhibit specific heights (magic heights), possibly due to the confinement of electrons in the islands. We also study the adsorption behavior of C-60 on the two allotropes of Pb. Scanning tunneling microcopy reveals that a high corrugation of the quasicrystalline Pb limits the diffusion of the C-60 molecules and thus produces a disordered film, similar to adsorption behavior of the same molecules on the clean substrate surface. However, the sticking coefficient of C-60 molecules atop the Pb islands approaches zero, regardless of the overall C-60 coverage. (C) 2014 AIP Publishing LLC.
Title:
Icosahedral quasicrystals solids with an elliptic hole under uniform heat flow
Authors:
Li, LH; Liu, GT Author Full Names: Li Lian-He; Liu Guan-Ting
Source:
CHINESE PHYSICS B, 23 (5):10.1088/1674-1056/23/5/056101 MAY 2014
Abstract:
The complex variable method for solving the two-dimensional thermal stress problem of icosahedral quasicrystals is stated. The closed-form solutions for icosahedral quasicrystals containing an elliptical hole subjected to a remote uniform heat flow are obtained. When the hole degenerates into a crack, the explicit solutions for the stress intensity factors is presented.
Title:
Finite size specimens with cracks of icosahedral Al-Pd-Mn quasicrystals
Authors:
Yang, LZ; Andreas, R; He, FM; Gao, Y Author Full Names: Yang Lian-Zhi; Andreas, Ricoeur; He Fan-Min; Gao Yang
Source:
CHINESE PHYSICS B, 23 (5):10.1088/1674-1056/23/5/056102 MAY 2014
Abstract:
Icosahedral quasicrystals are the most important and thermodynamically stable in all about 200 kinds of quasicrystals currently observed. Beyond the scope of classical elasticity, apart from a phonon displacement field, there is a phason displacement field in the elasticity of the quasicrystal, which induces an important effect on the mechanical properties of the material and makes an analytical solution difficult to obtain. In this paper, a finite element algorithm for the static elasticity of icosahedral quasicrystals is developed by transforming the elastic boundary value problem of the icosahedral quasicrystals into an equivalent variational problem. Analytical and numerical solutions for an icosahedral Al-Pd-Mn quasicrystal cuboid subjected to a uniaxial tension with different phonon-phason coupling parameters are given to verify the validity of the numerical approach. A comparison between the analytical and numerical solutions of the specimen demonstrates the accuracy and efficiency of the present algorithm. Finally, in order to reveal the fracture behavior of the icosahedral Al-Pd-Mn quasicrystal, a cracked specimen with a finite size of matter is investigated, both with and without phonon-phason coupling. Meanwhile, the geometry factors are calculated, including the stress intensity factor and the crack opening displacement for the finite-size specimen. Computational results reveal the importance of phonon-phason coupling effect on the icosahedral Al-Pd-Mn quasicrystal. Furthermore, the finite element procedure can be used to solve more complicated boundary value problems.
Title:
A Novel Approach to Improve Properties of BiFeO3 Nanomultiferroics
Authors:
Arya, G; Kotnala, RK; Negi, NS Author Full Names: Arya, Ghanshyam; Kotnala, Ravinder K.; Negi, Nainjeet Singh
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 97 (5):1475-1480; 10.1111/jace.12782 MAY 2014
Abstract:
In this study we report the synthesis of Bi1-xInxFe1-yTiyO3 (0x0.1, 0y0.05) nanoparticles by a simple cost effective solution combustion method. Pure BFO samples shows distorted rhombohedral perovskite structure with space group R3c which is also supported by Fourier transform infrared spectra study. The codoping of In and Ti at A-B sites of BFO (BIFTO) partially distorts the crystal structure, increases the lattice strain, reduces the average particle size (14nm), and increases the Fe3+/Fe2+ ratio which significantly affect the observed results. The saturation magnetization increases significantly upon codoping (4.60emu/gm) by about 12 times than that of pure BFO (0.4emu/gm). The improved ferromagnetic properties upon codoping is further manifestated in large value of linear magnetoelectric coupling coefficient (4.8mV/cmOe) which further provides an indirect evidence for the collapse of space modulated spin structure. The activation energy increases with codoping (0.68eV), although less than 1eV which indicates that the conduction is still dominated by charged defects.
Title:
Coupled Skyrmion Sublattices in Cu2OSeO3
Authors:
Langner, MC; Roy, S; Mishra, SK; Lee, JCT; Shi, XW; Hossain, MA; Chuang, YD; Seki, S; Tokura, Y; Kevan, SD; Schoenlein, RW Author Full Names: Langner, M. C.; Roy, S.; Mishra, S. K.; Lee, J. C. T.; Shi, X. W.; Hossain, M. A.; Chuang, Y. -D.; Seki, S.; Tokura, Y.; Kevan, S. D.; Schoenlein, R. W.
Source:
PHYSICAL REVIEW LETTERS, 112 (16):10.1103/PhysRevLett.112.167202 APR 25 2014
Abstract:
We report the observation of a Skyrmion lattice in the chiral multiferroic insulator Cu2OSeO3 using Cu L-3-edge resonant soft x-ray diffraction. We observe the unexpected existence of two distinct Skyrmion sublattices that arise from inequivalent Cu sites with chemically identical coordination numbers but different magnetically active orbitals. The Skyrmion sublattices are rotated with respect to each other, implying a long wavelength modulation of the lattice. The modulation vector is controlled with an applied magnetic field, associating this moirelike phase with a continuous phase transition. Our findings will open up a new class of science involving manipulation of quantum topological states.
Title:
Quasicrystal-reinforced Mg alloys
Authors:
Kim, YK; Kim, WT; Kim, DH Author Full Names: Kim, Young Kyun; Kim, Won Tae; Kim, Do Hyang
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (2):10.1088/1468-6996/15/2/024801 APR 2014
Abstract:
The formation of the icosahedral phase (I-phase) as a secondary solidification phase in Mg-Zn-Y and Mg-Zn-Al base systems provides useful advantages in designing high performance wrought magnesium alloys. The strengthening in two-phase composites (I-phase + alpha-Mg) can be explained by dispersion hardening due to the presence of I-phase particles and by the strong bonding property at the I-phase/matrix interface. The presence of an additional secondary solidification phase can further enhance formability and mechanical properties. In Mg-Zn-Y alloys, the co-presence of I and Ca2Mg6Zn3 phases by addition of Ca can significantly enhance formability, while in Mg-Zn-Al alloys, the co-presence of the I-phase and Mg2Sn phase leads to the enhancement of mechanical properties. Dynamic and static recrystallization are significantly accelerated by addition of Ca in Mg-Zn-Y alloy, resulting in much smaller grain size and more random texture. The high strength of Mg-Zn-Al-Sn alloys is attributed to the presence of finely distributed Mg2Sn and I-phase particles embedded in the alpha-Mg matrix.
Title:
Complex metallic alloys as new materials for additive manufacturing
Authors:
Kenzari, S; Bonina, D; Dubois, JM; Fournee, V Author Full Names: Kenzari, Samuel; Bonina, David; Dubois, Jean Marie; Fournee, Vincent
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (2):10.1088/1468-6996/15/2/024802 APR 2014
Abstract:
Additive manufacturing processes allow freeform fabrication of the physical representation of a three-dimensional computer-aided design (CAD) data model. This area has been expanding rapidly over the last 20 years. It includes several techniques such as selective laser sintering and stereolithography. The range of materials used today is quite restricted while there is a real demand for manufacturing lighter functional parts or parts with improved functional properties. In this article, we summarize recent work performed in this field, introducing new composite materials containing complex metallic alloys. These are mainly Al-based quasicrystalline alloys whose properties differ from those of conventional alloys. The use of these materials allows us to produce light-weight parts consisting of either metal-matrix composites or of polymer-matrix composites with improved properties. Functional parts using these alloys are now commercialized.
Title:
On the equations of motion of dislocations in quasicrystals
Authors:
Agiasofitou, E; Lazar, M Author Full Names: Agiasofitou, Eleni; Lazar, Markus
Source:
MECHANICS RESEARCH COMMUNICATIONS, 57 27-33; 10.1016/j.mechrescom.2014.01.006 APR 2014
Abstract:
In this work we investigate the theory of dynamics of dislocations in quasicrystals. We consider three models: the elastodynamic model of wave type, the elasto-hydrodynamic model, and the elastodynamic model of wave-telegraph type. Similarities and differences between the three models are pointed out and discussed. Using the framework of linear incompatible elastodynamic theory, the equations of motion of dislocations are deduced for these three models. Especially, the equations of motion for the phonon and phason elastic distortion tensors and elastic velocity vectors are derived, where the source fields are given in terms of the phonon and phason dislocation density and dislocation current tensors in analogy to the classical theory of elastodynamics of dislocations. The equations of motion for the displacement fields are also obtained. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
A New Mechanism of the Incommensurate Phase Transition
Authors:
Ishibashi, Y; Iwata, M Author Full Names: Ishibashi, Y.; Iwata, M.
Source:
FERROELECTRICS, 461 (1):1-9; SI 10.1080/00150193.2014.889521 MAR 12 2014
Abstract:
A new mechanism of incommensurate (INC) phase transition will be mentioned. The INC phase may be stabilized by freezing of a soft mode on the [k, k, 0] or [k, k, 1/2] branch induced by the parabolic splitting of the doubly degenerate modes at the Brillouin zone boundary (1/2, 1/2, 0) or (1/2, 1/2, 1/2). A simple model theory of the incommensurate phase transition of this type is proposed, which easily reproduces a special feature for the INC phase that the macroscopic symmetry changes at the INC phase transition.

Update: 11-Jun-2014

Title:
EuNiGe3, an anisotropic antiferromagnet
Authors:
Maurya, A; Bonville, P; Thamizhavel, A; Dhar, SK Author Full Names: Maurya, A.; Bonville, P.; Thamizhavel, A.; Dhar, S. K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (21):10.1088/0953-8984/26/21/216001 MAY 28 2014
Abstract:
Single crystals of EuNiGe3, crystallizing in the non-centrosymmetric BaNiSn3-type structure, were grown using In flux, enabling us to explore the anisotropic magnetic properties, which was not possible with previously reported polycrystalline samples. The EuNiGe3 single crystalline sample is found to order antiferromagnetically at 13.2 K, as revealed from the magnetic susceptibility, heat capacity and electrical resistivity data. The low temperature magnetization M (H) is distinctly different for the field parallel to the ab-plane and c-axis; the ab-plane magnetization varies almost linearly with the field before the occurrence of an induced ferromagnetic (FM) phase (spin-flip) at 6.2 Tesla. On the other hand M (H) along the c-axis is accompanied by two metamagnetic transitions followed by a spin-flip at 4.1 T. A model including anisotropic exchange and dipole-dipole interactions reproduces the main features of magnetization plots but falls short of full representation. (H,T) phase diagrams have been constructed for the field applied along the principal directions. From the Eu-151 Mssbauer spectra, we determine that the 13.2 K transition leads to an incommensurate antiferromagnetic (AFM) intermediate phase followed by a transition near 10.5 K to a commensurate AFM configuration.
Title:
Sign of canted ferromagnetism in the quasicrystal approximants Au-SM-R (SM = Si, Ge and Sn/R = Tb, Dy and Ho)
Authors:
Hiroto, T; Tokiwa, K; Tamura, R Author Full Names: Hiroto, T.; Tokiwa, K.; Tamura, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (21):10.1088/0953-8984/26/21/216004 MAY 28 2014
Abstract:
Magnetic susceptibility and magnetization of the quasicrystal approximants Au-SM-R (SM = Si, Ge or Sn / R = Gd, Tb, Dy or Ho) are investigated. Ferromagnetic transitions are observed in all of these compounds, in contrast to the spin-glass behavior reported in similar compounds, Ag-In-R (R = Eu, Gd, Tb or Dy). Au-SM-Gd (SM = Si, Ge or Sn) exhibit a simple ferromagnetic transition at 22.5, 13 and 9 K, respectively, whereas Au-Si-(Tb, Dy or Ho) show indications of a canted ferromagnetic transition at 8.3, 5.9 and 3.8 K, respectively. The latter are attributed to a crystal electric field effect that is absent in the Gd-bearing compounds. The ferromagnetic behavior in Au-SM-R may be understood to be a consequence of the short R-R distances compared to those for Cd-R and Ag-In-R.
Title:
Chemical shifts of metallic and non-metallic Al-Re-Si approximant crystals studied by EELS and SXES
Authors:
Koshiya, S; Terauchi, M; Takagiwa, Y; Yamada, K; Kanazawa, I; Kimura, K Author Full Names: Koshiya, S.; Terauchi, M.; Takagiwa, Y.; Yamada, K.; Kanazawa, I.; Kimura, K.
Source:
PHILOSOPHICAL MAGAZINE, 94 (15):1711-1718; 10.1080/14786435.2014.894648 MAY 24 2014
Abstract:
Chemical shifts of approximant crystals of 1/0-Al12Re (1/0-metallic), 1/1-Al73Re15Si12 (1/1-metallic) and 1/1-Al73Re17Si10 (1/1-non-metallic) were examined by using electron energy-loss spectroscopy (EELS) and soft-X-ray emission spectroscopy (SXES). Al L-shell excitation EELS spectra of these alloys showed an apparent chemical shift only for the 1/1-non-metallic alloy to the larger binding energy side by 0.2 eV. Al-K alpha, Re-M alpha and Si-K alpha emission SXES spectra also showed a shift to the larger binding energy side only for 1/1-non-metallic alloy. 1/0-metallic and 1/1-metallic alloys did not show any chemical shift in EELS and SXES experiments. Chemical shifts were observed only in larger binding energy side compared with pure materials. This implies the decrease of valence charge at constituent atomic sites of 1/1-non-metallic alloy compared with 1/0-metallic, 1/1-metallic and pure materials. The decreased charges should distribute intermetallic sites, which should be related to a formation of covalent bonding among Al atomic sites reported by maximum-entropy method (MEM)/Rietveld analysis on this material. This relation between chemical shift and covalent bonding nature of this approximant alloy may support the presence of covalent bonding in Al-based quasicrystals.
Title:
Structural Phase Transition and Microstructures in Stuffed Tridymite-Type Compounds; Ba(Al, Fe)(2)O-4
Authors:
Mori, S; Katsumura, S; Ozaki, T; Tanaka, E; Ishii, Y; Kurushima, K; Kubota, Y; Taniguchi, H Author Full Names: Mori, S.; Katsumura, S.; Ozaki, T.; Tanaka, E.; Ishii, Y.; Kurushima, K.; Kubota, Y.; Taniguchi, H.
Source:
FERROELECTRICS, 464 (1):116-121; SI 10.1080/00150193.2014.893160 MAY 19 2014
Abstract:
We have investigated structural phase transition and changes of microstrucrtures in BaAl2O4 with the tridymite tetrahedral framework structure by transmission electron microscopy experiments in the temperature range between 100K and 298K. In our polycrystalline samples the transition from the paraelectric phase with the P6(3)22 space group to the ferroelectric (FE) phase took place around 250K, which accompanies with the appearance of the modulated structure with the three equivalent modulation wave vectors, q = 1/2. Real-space images revealed that the FE phase should consist of nanodomains with the 10 similar to 20nm size. In addition, it is revealed that partial substitution of Fe3+ for Al3+ in BaAl2O4 induced structural phase transition to the modulated structure with q = 1/3 around x similar to 0.50 in Ba(Al1-xFex)(2)O-4.
Title:
Influence of flexoelectric coupling on domain patterns in ferroelectrics
Authors:
Ahluwalia, R; Tagantsev, AK; Yudin, P; Setter, N; Ng, N; Srolovitz, DJ Author Full Names: Ahluwalia, Rajeev; Tagantsev, Alexander K.; Yudin, Petr; Setter, Nava; Ng, Nathaniel; Srolovitz, David J.
Source:
PHYSICAL REVIEW B, 89 (17):10.1103/PhysRevB.89.174105 MAY 14 2014
Abstract:
Using Ginzburg-Landau theory and two-dimensional (2D) phase field simulations, we analyze the influence of flexoelectric coupling on the domain patterns in ferroelectrics. The phase field simulations predict that a high strength of the flexoelectric coupling leads to formation of a fine structure in domain patterns in ferroelectrics. The fine structure forms when the coupling strength exceeds a critical value and is related to local transition into an incommensurate phase. Depending on the parameters, a structure with stripe patterns with antiparallel polarizations or another one, not seen before, with two-dimensional arrays of alternating vortices is found. Complex domain configurations with coexisting phases and unusual domain walls between them are observed. Although the incommensurate phase does not form for weaker couplings, the influence of flexoelectricity on bulk domain patterns can still be significant. The results of the calculations are rationalized using an analytical model. Directions for the modulation wave vectors in the fine structure are found in the framework of a linear analysis, while the type of the structure-stripes or vortices-is determined by anharmonicity.
Title:
Ab-initio tiling and atomic structure for decagonal ZnMgY quasicrystal
Authors:
Mihalkovic, M; Richmond-Decker, J; Henley, CL; Oxborrow, M Author Full Names: Mihalkovic, M.; Richmond-Decker, J.; Henley, C. L.; Oxborrow, M.
Source:
PHILOSOPHICAL MAGAZINE, 94 (14):1529-1541; 10.1080/14786435.2014.888499 MAY 13 2014
Abstract:
We discover the detailed atomic structure of -MgZnY, a stable decagonal quasicrystal alloy of the layered Frank-Kasper type, and related phases, using the 'tiling and decoration' approach. The atoms have invariable sites in the rectangle and triangle tiles of a 10-fold-symmetric planar tiling. To discover the lowest-energy structures, we combine the methods of density functional theory (DFT) total energy calculations, empirical oscillating pair potentials (fitted to DFT), fitting effective Hamiltonians for tilings, and discovering optimum tiling structures using a nonlocal tile-reshuffling algorithm. We find a family of almost stable binary compounds with varying composition, including the decagonal quasicrystal and the known MgZn; in addition, we show the ternary versions can be stable: -MgZnY at high temperature, and -MgZnSc even at .
Title:
Spin fluctuations and frustrated magnetism in multiferroic FeVO4
Authors:
Zhang, J; Ma, L; Dai, J; Zhang, YP; He, ZZ; Normand, B; Yu, WQ Author Full Names: Zhang, J.; Ma, L.; Dai, J.; Zhang, Y. P.; He, Zhangzhen; Normand, B.; Yu, Weiqiang
Source:
PHYSICAL REVIEW B, 89 (17):10.1103/PhysRevB.89.174412 MAY 12 2014
Abstract:
We report V-51 nuclear magnetic resonance (NMR) studies on single crystals of the multiferroic material FeVO4. The high-temperature Knight shift shows Curie-Weiss behavior K-51 = a/(T + theta), with a large Weiss constant theta approximate to 116 K. However, the V-51 spectrum shows no ordering near these temperatures, splitting instead into two peaks below 65 K, which suggests only short-ranged magnetic order on the NMR time scale. Two magnetic transitions are identified from peaks in the spin-lattice relaxation rate 1/T-51(1) at temperatures T-N1 approximate to 19 K and T-N2 approximate to 13 K, which are lower than the estimates obtained from polycrystalline samples. In the low-temperature incommensurate spiral state, the maximum ordered moment is estimated as 1.95 mu(B)/Fe, or 1/3 of the local moment. Strong low-energy spin fluctuations are also indicated by the unconventional power-law temperature dependence 1/T-51(1) proportional to T-2. The largeWeiss constant, short-range magnetic correlations far above T-N1, small ordered moment, significant low-energy spin fluctuations, and incommensurate ordered phases all provide explicit evidence for strong magnetic frustration in FeVO4.
Title:
Ferro-Orbital Ordering Transition in Iron Telluride Fe1+yTe
Authors:
Fobes, D; Zaliznyak, IA; Xu, ZJ; Zhong, RD; Gu, GD; Tranquada, JM; Harriger, L; Singh, D; Garlea, VO; Lumsden, M; Winn, B Author Full Names: Fobes, David; Zaliznyak, Igor A.; Xu, Zhijun; Zhong, Ruidan; Gu, Genda; Tranquada, John M.; Harriger, Leland; Singh, Deepak; Garlea, V. Ovidiu; Lumsden, Mark; Winn, Barry
Source:
PHYSICAL REVIEW LETTERS, 112 (18):10.1103/PhysRevLett.112.187202 MAY 9 2014
Abstract:
Fe1+yTe with y less than or similar to 0.05 exhibits a first-order phase transition on cooling to a state with a lowered structural symmetry, bicollinear antiferromagnetic order, and metallic conductivity, dp/dT > 0. Here, we study samples with y = 0.09(1), where the frustration effects of the interstitial Fe decouple different orders, leading to a sequence of transitions. While the lattice distortion is closely followed by incommensurate magnetic order, the development of bicollinear order and metallic electronic coherence is uniquely associated with a separate hysteretic first-order transition, at a markedly lower temperature, to a phase with dramatically enhanced bond-order wave (BOW) order. The BOW state suggests ferro-orbital ordering, where electronic delocalization in ferromagnetic zigzag chains decreases local spin and results in metallic transport.
Title:
Hardness of Al-based quasicrystals evaluated via cluster-plus-glue-atom model
Authors:
Chen, H; Luo, LJ; Qiang, JB; Wang, YM; Dong, C Author Full Names: Chen, Hua; Luo, Lingjie; Qiang, Jianbing; Wang, Yingmin; Dong, Chuang
Source:
PHILOSOPHICAL MAGAZINE, 94 (13):1463-1477; 10.1080/14786435.2014.887863 MAY 3 2014
Abstract:
In this paper, the hardness of ternary Al-based quasicrystals was assessed through an application of the cluster-plus-glue-atom model. In this model, any structure is decomposed into a first-neighbour strongly bonded cluster part and second-neighbour weakly bonded glue-atom part so that the overall structural information is condensed into a local structural unit [cluster](glue atom)(x). For quasicrystals, the averaged local units are formulated as [icosahedron] TM0,1(Transition Metal) and could be visualized as single icosahedron packing. Then, the hardness of quasicrystals was related to the rupture of weak inter-cluster bonds. Typically, theoretical hardness values of 8-9 GPa were obtained using 19 broken inter-cluster bonds, which accounts for about half of all the surface bonds of an icosahedron in the Mackay-type environment. The unit cluster formulas would act as rigid units during deformation and cracking.
Title:
Templated Quasicrystalline Molecular Ordering
Authors:
Smerdon, JA; Young, KM; Lowe, M; Hars, SS; Yadav, TP; Hesp, D; Dhanak, VR; Tsai, AP; Sharma, HR; McGrath, R Author Full Names: Smerdon, J. A.; Young, K. M.; Lowe, M.; Hars, S. S.; Yadav, T. P.; Hesp, D.; Dhanak, V. R.; Tsai, A. P.; Sharma, H. R.; McGrath, R.
Source:
NANO LETTERS, 14 (3):1184-1189; 10.1021/nl403947b MAR 2014
Abstract:
Quasicrystals are materials with long-range ordering but no periodicity. We report scanning tunneling microscopy (STM) observations of quasicrystalline molecular layers on 5-fold quasicrystal surfaces. The molecules adopt positions and orientations on the surface consistent with the quasicrystalline ordering of the substrate. Carbon-60 adsorbs atop sufficiently separated Fe atoms on icosahedral Al-Cu-Fe to form a unique quasicrystalline lattice, whereas further C-60 molecules decorate remaining surface Fe atoms in a quasi-degenerate fashion. Pentacene (Pn) adsorbs at 10-fold symmetric points around surface-bisected rhombic triacontahedral the first demonstrations of quasicrystalline molecular ordering on clusters in icosahedral Ag-In-Yb. These systems constitute a template.

Update: 5-Jun-2014

Title:
Icosahedral quasicrystal-enhanced nucleation of the fcc phase in liquid gold alloys
Authors:
Kurtuldu, G; Sicco, A; Rappaz, M Author Full Names: Kurtuldu, Gueven; Sicco, Alberto; Rappaz, Michel
Source:
ACTA MATERIALIA, 70 240-248; 10.1016/j.actamat.2014.02.037 MAY 15 2014
Abstract:
Although the grain refinement of yellow gold alloys with Jr has been used in industry and known for nearly half a century, the basic mechanism is still unknown. The present contribution shows that the mechanism is the same as that evidenced recently in Al-Zn alloys, when small amounts of Cr (1000 ppm) are added to the melt (Kurtuldu et al., 2013). The reduced face-centered cubic (fcc) crystal size, the abnormal fraction of twin, or near-twin, grain boundaries and the 5-fold symmetry crystallographic orientation of multiple nearestneighbor grains reproduce the symmetry of icosahedral quasicrystals (iQCs) with the following heteroepitaxial relationships: {111}(fcc)< 110 >(fcc) perpendicular to 3-fold/2-fold symmetry axes of iQCs. While iQCs and the approximant stable Al45Cr7 phase, which contains several 5-fold symmetry building blocks in its unit cell, are known to exist in Al Cr alloys, no such phases have been reported for yellow gold +Ir. Nevertheless, when minute amounts of Jr ( less than or similar to 200 ppm) are added to the gold alloy melt, it is shown that the grain refinement from 248 to 30 mu m is accompanied by a spectacular increase in the fraction of twinned grain boundaries, i.e. from less than 1% without Jr to 11% with 200 ppm Ir. Furthermore, up to 9 grains have been shown to reproduce the six 5-fold symmetry axes of the icosahedron, while many other grain configurations exhibit this heteroepitaxial relationship with the icosahedron or interlocked icosahedron. This confirms that fcc crystals can form in a supercooled liquid by heteroepitaxial growth from an iQC template. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd.
Title:
Magneto-optical spectroscopy of ferromagnetic shape-memory Ni-Mn-Ga alloy
Authors:
Veis, M; Beran, L; Zahradnik, M; Antos, R; Straka, L; Kopecek, J; Fekete, L; Heczko, O Author Full Names: Veis, M.; Beran, L.; Zahradnik, M.; Antos, R.; Straka, L.; Kopecek, J.; Fekete, L.; Heczko, O.
Source:
JOURNAL OF APPLIED PHYSICS, 115 (17):10.1063/1.4867754 MAY 7 2014
Abstract:
Magneto-optical properties of single crystal of Ni50.1Mn28.4Ga21.5 magnetic shape memory alloy in martensite and austenite phase were systematically studied. Crystal orientation was approximately along {100} planes of parent cubic austenite. At room temperature, the sample was in modulated 10M martensite phase and transformed to cubic austenite at 323 K. Spectral dependence of polar magneto-optical Kerr effect was obtained by generalized magneto-optical ellipsometry with rotating analyzer in the photon energy range from 1.2 to 4 eV, and from room temperature to temperature above the Curie point. The Kerr rotation spectra exhibit prominent features typical for complexes containing Mn atoms. Significant spectral changes during transformation to austenite can be explained by different optical properties caused by changes in density of states near the Fermi energy. (C) 2014 AIP Publishing LLC.
Title:
Ferromagnetic resonance study of eightfold artificial ferromagnetic quasicrystals
Authors:
Bhat, VS; Sklenar, J; Farmer, B; Woods, J; Ketterson, JB; Hastings, JT; De Long, LE Author Full Names: Bhat, V. S.; Sklenar, J.; Farmer, B.; Woods, J.; Ketterson, J. B.; Hastings, J. T.; De Long, L. E.
Source:
JOURNAL OF APPLIED PHYSICS, 115 (17):10.1063/1.4859035 MAY 7 2014
Abstract:
We have performed broadband (10 MHz-18 GHz) and narrowband (9.7 GHz) ferromagnetic resonance (FMR) measurements on permalloy thin films patterned with quasiperiodic Ammann tilings having eightfold rotational symmetry. We observed highly reproducible mode structures in the low-frequency, hysteretic regime in which domain walls and unsaturated magnetization textures exist. A minimum of 10 robust modes were observed in patterned samples, compared to the single uniform mode observed in unpatterned permalloy films. The field dependence and approximate eightfold rotational symmetry of the FMR spectra are in good agreement with micromagnetic simulations that confirm the importance of patterning for controlling static and dynamic magnetic response. (C) 2014 AIP Publishing LLC.
Title:
Growth mechanism of an icosahedral quasicrystal and solute partitioning in a Mg-rich Mg-Zn-Y alloy
Authors:
Geng, JW; Teng, XY; Zhou, GR; Zhao, DG; Leng, JF Author Full Names: Geng, Jiwei; Teng, Xinying; Zhou, Guorong; Zhao, Degang; Leng, Jinfeng
Source:
JOURNAL OF MATERIALS RESEARCH, 29 (8):942-949; 10.1557/jmr.2014.81 APR 28 2014
Abstract:
The growth mechanism of an icosahedral quasicrystal and solute partitioning in a Mg-rich Mg-Zn-Y alloy were investigated. It is found that the preferred growth directions of the icosahedral quasicrystalline phase (I-phase) are along 5-fold axes and the planes perpendicular to the 5-fold axes grow in a facet manner. Due to the local compositional change at the solid/liquid interface, the planar growth is gradually replaced by cellular growth. During the nucleation of the primary I-phase, on a microscale, the distribution of the Y element is changed and concentrated along 5-fold directions in the remaining liquid. If the cooling rate is relatively slow, there will be more Y element in the remaining liquid after the formation of the primary I-phase. It causes that (I-phase + alpha-Mg) eutectic structures form around the primary I-phase. Almost all the Y element is exhausted after this stage. Especially, under a relatively slow cooling rate, the solute partitioning occurs during the growth process of the primary I-phase, which leads to the microshrinkage cavity and crack defects at the edge of the primary I-phase.
Title:
Spin density waves in the Hubbard model: A DMFT approach
Authors:
Peters, R; Kawakami, N Author Full Names: Peters, Robert; Kawakami, Norio
Source:
PHYSICAL REVIEW B, 89 (15):10.1103/PhysRevB.89.155134 APR 24 2014
Abstract:
We analyze spin density waves (SDWs) in the Hubbard model on a square lattice within the framework of inhomogeneous dynamical mean field theory (IDMFT). Doping the half-filled Hubbard model results in a change of the antiferromagnetic Neel state, which exists exactly at half filling, to a phase of incommensurate SDWs. Previous studies of this phase mainly rely on static mean field calculations. In this paper, we will use large-scale IDMFT calculations to study properties of SDWs in the Hubbard model. A great advantage of IDMFT over static mean field approaches is the inclusion of local screening effects and the easy access to dynamical correlation functions. Furthermore, this technique is not restricted to the Hubbard model, but can be easily used to study incommensurate phases in various strongly correlated materials.
Title:
Unusual spin fluctuations and magnetic frustration in olivine and non-olivine LiCoPO4 detected by P-31 and Li-7 nuclear magnetic resonance
Authors:
Baek, SH; Klingeler, R; Neef, C; Koo, C; Buchner, B; Grafe, HJ Author Full Names: Baek, S. -H.; Klingeler, R.; Neef, C.; Koo, C.; Buechner, B.; Grafe, H. -J.
Source:
PHYSICAL REVIEW B, 89 (13):10.1103/PhysRevB.89.134424 APR 24 2014
Abstract:
We report P-31 and Li-7 nuclear magnetic resonance (NMR) studies in new non-olivine LiZnPO4-type LiCoPO4tetra microcrystals, where the Co2+ ions are tetrahedrally coordinated. Olivine LiCoPO4, which was directly transformed from LiCoPO4tetra by an annealing process, was also studied and compared. The uniform bulk magnetic susceptibility and the P-31 Knight shift obey the Curie-Weiss law for both materials with a high spin Co2+ (3d(7), S = 3/2), but the Weiss temperature Theta and the effective magnetic moment mu(eff) are considerably smaller in LiCoPO4tetra. The spin-lattice relaxation rate T-1(-1) reveals a quite different nature of the spin dynamics in the paramagnetic state of both materials. Our NMR results imply that strong geometrical spin frustration occurs in tetrahedrally coordinated LiCoPO4, which may lead to the incommensurate magnetic ordering.
Title:
Structural Diversity of Hydrogen-Bonded Networks of [Co(NH3)(6)](3+) Complex Cations and Acetylenedicarboxylic Acid Anions
Authors:
Seidel, RW; Goddard, R; Gramm, V; Ruschewitz, U Author Full Names: Seidel, Ruediger W.; Goddard, Richard; Gramm, Verena; Ruschewitz, Uwe
Source:
ZEITSCHRIFT FUR NATURFORSCHUNG SECTION B-A JOURNAL OF CHEMICAL SCIENCES, 69 (3):277-288; 10.5560/ZNB.2014-3272 MAR 2014
Abstract:
The crystal structure of [Co(NH3)(6)](ADC)(HADC) center dot 2 H2O (1) (ADC(2-) = acetylenedicarboxylate) (P2(1)/n, Z = 4) was mistakenly described as containing the [Co(H2O)(6)](3+) ion [I. Stein, U. Ruschewitz, Z. Nattuforsch. 2011, 66b, 471-478]. A revision is reported. While attempting to reproduce 1, we isolated phase-pure crystalline material of [Co(NH3)(6)]Cl-2(HADC) center dot H2O (2), the crystal structure of which was also reported in the article above. Upon standing in the aqueous mother liquor at room temperature for several days, the needle-shaped crystals of 2 disappear, while block-shaped crystals of the formerly unknown compound [Co(NH3)(6)](ADC)(HADC) (3) grow. Satellite peaks in the X-ray diffraction frames indicate that the crystal structure is incommensurately modulated. Dissolving crystals of 3 in water at elevated temperature leads to plate-shaped crystals of the new compound [Co(NH3)(6)](2) (ADC)(3) center dot 3 H2O (4) upon slow cooling to room temperature. Compounds 2-4 were investigated by elemental analysis, powder X-ray diffraction and infrared spectroscopy. Structural characterization of 4 by single-crystal X-ray analysis was also achieved (P (1) over bar, Z = 2). Complex 1, however, could not be reproduced.

Update: 29-May-2014

Title:
Mg-doped Bi0.8Ca0.2FeO3 with enhanced ferromagnetic properties
Authors:
Xu, JL; Xie, D; Yin, C; Feng, TT; Zhang, XW; Zhao, HM; Li, G; Ren, TL; Guan, YJ; Gao, XS; Pan, W Author Full Names: Xu, Jianlong; Xie, Dan; Yin, Cong; Feng, Tingting; Zhang, Xiaowen; Zhao, Haiming; Li, Gang; Ren, Tian-Ling; Guan, Yujie; Gao, Xingsen; Pan, Wei
Source:
MATERIALS LETTERS, 122 139-142; 10.1016/j.matlet.2014.01.127 MAY 1 2014
Abstract:
We report the structural and enhanced ferromagnetic properties of Mg doped Bi0.8Ca0.2FEO3 ceramics. Oxygen vacancies are introduced into Bi0.8Ca0.2Fe1-xMgxO3 ceramics doping confirmed by XRD and Raman spectra, which induce a significantly enhanced macroscopic ferromagnetism from antiferromagnetism to ferromagnetism. The enhanced ferromagnetism can be ascribed to the creation of unbalanced Fe3+ spins induced by the collapse of the space modulated cycloidal spin structure and relative long-range coupling mediated by the oxygen vacancies trapped localized electrons. The improved ferromagnetic properties obtained by co-doping demonstrate the possibility of bulk BFO in practical multiferroic applications. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Mechanical and damping properties of thermal treated Mg-Zn-Y-Zr alloys reinforced with quasicrystal phase
Authors:
Ma, R; Dong, XP; Yan, BS; Chen, SQ; Li, ZB; Pan, Z; Ling, HJ; Fan, ZT Author Full Names: Ma, Rong; Dong, Xuanpu; Yan, Bangsong; Chen, Shuqun; Li, Zhangbo; Pan, Zhang; Ling, Hongjiang; Fan, Zitian
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 602 11-18; 10.1016/j.msea.2014.02.055 APR 25 2014
Abstract:
The effects of annealing, T4 and T6 heat treatment on microstructure, mechanical properties and damping capacities of a quasicrystal-reinforced Mg-Zn-Y-Zr alloy (the ZWK3 alloy) were investigated in this study. The structural results show that the Mg0.97Zn0.03 phase could transform to Mg7Zn3 phase during annealing and only primary phase and the I-Mg3YZn6 quasicrystal phase exist in the T4 treated ZWK3 alloy. Further aging in T6 treatment precipitates a large amount of nanoscaled MgZn2 phase. The thermal treatment could improve the tensile strength of the ZWK3 alloy greatly, while a large reduction in elongation and high strain amplitude damping are obtained compared with that of the as-cast alloy. In spite of this, the damping values of three heat treated ZWK3 alloys all exceed 0.01, representing our studied alloys still belong to high damping magnesium alloys. Decrease of mobility of dislocations, resulting from tanglement and pinning, is responsible for damping decline. We also find that twins only observed in the T6 treated ZWK3 alloy could produce new damping sources besides dislocation. (C) 2014 Published by Elsevier B.V.
Title:
Effect of Mg-Zn-Nd Quasicrystal Addition on Corrosion Resistance of AZ91 Alloys
Authors:
Zhao, ZW; Teng, XY; Zhou, GR; Leng, JF; Geng, JW Author Full Names: Zhao Zhenwei; Teng Xinying; Zhou Guorong; Leng Jinfeng; Geng Jiwei
Source:
RARE METAL MATERIALS AND ENGINEERING, 43 (4):791-795; APR 2014
Abstract:
The purpose of this study is to improve the corrosion resistance of AZ91 alloys through adding different contents of Mg-Zn-Nd quasicrystal master alloy. The microstructure and the corrosion behavior of AZ91 alloys with addition of Mg-Zn-Nd (MZN) quasicrystal master alloy were investigated by scanning electron microscopy (SEM) equipped with electron dispersive spectroscopy (EDS), X-ray diffractometry (XRD), mass loss tests and potentiodynamic polarization measurements. The results show that the microstructures of AZ91 alloys are significantly refined, and the morphology of beta-Mg17Al12 phase changes from a continuous net to a discrete net or even to particles after adding MZN quasicrystal master alloy. Moreover, the amount of beta-Mg17Al12 phase is reduced. The alloy with 6wt% MZN quasicrystal master alloy has the best corrosion resistance, and the corrosion rate is 0.8 (mg.cm(-2))/d, only 1/15 of that of common AZ91 alloy, but the excessive MZN quasicrystal master alloy could result in a poorer corrosion resistance of AZ91 alloy.
Title:
Penrose nanotiles: design of the thin and thick rhomb molecules to self-assemble into a quasicrystal
Authors:
Laikov, DN Author Full Names: Laikov, Dimitri N.
Source:
RSC ADVANCES, 4 (34):17925-17930; 10.1039/c4ra01354a 2014
Abstract:
New organic molecules are designed, with synthesis in mind, to fit the shape of the thin and thick rhombs of the Penrose tiling and selfassemble by hydrogen bonding into nearly flat sheets (that may stack face-to-face) following the matching rules.

Update: 22-May-2014

Title:
Mechanical properties of Al-Cu-Fe quasicrystalline and crystalline phases: An analogy
Authors:
Laplanche, G; Bonneville, J; Joulain, A; Gauthier-Brunet, V; Dubois, S Author Full Names: Laplanche, G.; Bonneville, J.; Joulain, A.; Gauthier-Brunet, V.; Dubois, S.
Source:
INTERMETALLICS, 50 54-58; 10.1016/j.intermet.2014.02.004 JUL 2014
Abstract:
The mechanical properties of the omega-Al7Cu2Fe crystalline phase have been investigated over a large temperature range (650-1000 K). Despite of its antinomic structure with the icosahedral Al-Cu-Fe quasicrystalline phase, i.e. periodic vs non-periodic, its mechanical properties are very similar to those of the quasicrystalline phase, which strongly suggest similar deformation mechanisms. Consequently, as for the quasicrystalline structure, we propose that dislocation climb might control the plastic deformation of the omega-phase. However, in the present case, the specificities of the quasiaystalline structure cannot be invoked to justify the predominance of dislocation climb, which questions the role of quasiperiodicity on dislocation mobility. We suggest that this deformation mode certainly results from specific non-planar extensions of the dislocation core. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
Crystal structures of orthorhombic, hexagonal, and cubic compounds of the Sm(x)Yb(2-x)TiO5 series
Authors:
Aughterson, RD; Lumpkin, GR; Reyes, MD; Sharma, N; Ling, CD; Gault, B; Smith, KL; Avdeev, M; Cairney, JM Author Full Names: Aughterson, Robert D.; Lumpkin, Gregory R.; Reyes, Massey de Los; Sharma, Neeraj; Ling, Christopher D.; Gault, Baptiste; Smith, Katherine L.; Avdeev, Maxim; Cairney, Julie M.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 213 182-192; 10.1016/j.jssc.2014.02.029 MAY 2014
Abstract:
A series of single phase compounds with nominal stoichiometry Sm(x)Yb(2-x)TiO5 (x=2,1.4, 1, 0.6, and 0) have been successfully fabricated to generate a range of crystal structures covering the most common polymorphs previously discovered in the Ln(2)TiO(5) series (Ln=lanthanides and yttrium). Four of the five samples have not been previously fabricated in bulk, single phase form so their crystal structures are refined and detailed using powder synchrotron and single crystal x-ray diffraction, neutron diffraction and transmission electron microscopy. Based on the phase information from diffraction data, there are four crystal structure types in this series; orthorhombic Pnma, hexagonal P6(3)/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. The cubic materials show modulated structures with variation between long and short range ordering and the variety of diffraction techniques were used to describe these complex crystal structure types. Crown Copyright (C) 2014 Published by Elsevier Inc. All rights reserved.
Title:
Local Crystal Structure of Antiferroelectric Bi2Mn4/3Ni2/3O6 in Commensurate and Incommensurate Phases Described by Pair Distribution Function (PDF) and Reverse Monte Carlo (RMC) Modeling
Authors:
Szczecinski, RJ; Chong, SY; Chater, PA; Hughes, H; Tucker, MG; Claridge, JB; Rosseinsky, MJ Author Full Names: Szczecinski, Robert J.; Chong, Samantha Y.; Chater, Philip A.; Hughes, Helen; Tucker, Matthew G.; Claridge, John B.; Rosseinsky, Matthew J.
Source:
CHEMISTRY OF MATERIALS, 26 (7):2218-2232; 10.1021/cm4038439 APR 8 2014
Abstract:
The functional properties of materials can arise from local structural features that are not well determined or described by crystallographic methods based on long-range average structural models. The room temperature (RT) structure of the Bi perovskite Bi2Mn4/3Ni2/3O6 has previously been modeled as a locally polar structure where polarization is suppressed by a long-range incommensurate antiferroelectric modulation. In this study we investigate the short-range local structure of Bi2Mn4/3Ni2/3O6, determined through reverse Monte Carlo (RMC) modeling of neutron total scattering data, and compare the results with the long-range incommensurate structure description. While the incommensurate structure has equivalent B site environments for Mn and Ni, the local structure displays a significantly Jahn-Teller distorted environment for Mn3+. The local structure displays the rock-salt-type Mn/Ni ordering of the related Bi2MnNiO6 high pressure phase, as opposed to Mn/Ni clustering observed in the long-range average incommensurate model. RMC modeling reveals short-range ferroelectric correlations between Bi3+ cations, giving rise to polar regions that are quantified for the first time as existing within a distance of approximately 12 A. These local correlations persist in the commensurate high temperature (HT) phase, where the long-range average structure is nonpolar. The local structure thus provides information about cation ordering and B site structural flexibility that may stabilize Bi3+ on the A site of the perovskite structure and reveals the extent of the local polar regions created by this cation.
Title:
Spin Exchange and Magnetic Dipole Dipole Interactions Leading to the Magnetic Superstructures of MAs2O6 (M = Mn, Co, Ni)
Authors:
Koo, HJ; Whangbo, MH Author Full Names: Koo, Hyun-Joo; Whangbo, Myung-Hwan
Source:
INORGANIC CHEMISTRY, 53 (7):3812-3817; 10.1021/ic500156e APR 7 2014
Abstract:
The three isostructural magnetic oxides MAs2O6 (M = Mn, Co, Ni) containing high-spin M2+ ions undergo a long-range antiferromagnetic ordering below 30 K, but their ordered magnetic structures are not identical. While CoAs2O6 and NiAs2O6 adopt the commensurate superstructure of q(1) = (0, 0, 1/2), MnAs2O6 has the incommensurate superstructure of q(2) = (0.055, 0.389, 0.136). The cause for this difference was examined by calculating their spin exchange and magnetic dipole-dipole interaction energies. In CoAs2O6 and NiAs2O6, the strongest M-O center dot center dot center dot O-M spin exchange, J(1), dominates over other exchanges, hence leading to the q(1) superstructure. For MnAs2O6, the spin exchanges are not a deciding factor leading to its magnetic superstructure, being all weak and comparable in strengths, but the magnetic dipole-dipole interactions are.

Update: 14-May-2014

Title:
Effect of different element doping on the structure and magnetic properties of composite crystal Sr-14(Cu1-xMx)(24)O-41 (M=Zn, Ni, Co)
Authors:
Wang, J; Zou, HM; Li, Y; Xie, H; Hu, N; Wang, LL; Shi, J Author Full Names: Wang, Jun; Zou, Huamin; Li, Yang; Xie, Hui; Hu, Ni; Wang, Lili; Shi, Jing
Source:
PHYSICA B-CONDENSED MATTER, 441 6-11; 10.1016/j.physb.2014.01.045 MAY 15 2014
Abstract:
The Zn2+, Ni2+ and Co3+ doped Sr-14(Cu1 - xMx)(24)O-41 composite crystals were synthesized by a standard solid state reaction method. The temperature dependence of magnetic properties was measured for every sample. The Curie coefficient, Weiss temperature, number of dimers in CuO2 chain per formula unit (Lu.) and dimer coupling constant are obtained by fitting the temperature dependence of the magnetic susceptibility. Meantime, selected area electron diffraction patter no (EDPs) show that the diffraction spots corresponding to the CuO2 chain substnicture are extended to streaks along a and b directions for all the samples, while the diffraction spots produced merely by the Cu2O3 ladder substructure are still very sharp. This means that the periodicities of chains in a and b directions are partially destroyed upon doping of Zn, Ni and Co due to that the initial phase of each chain becomes a random variable. Considering the effect of different ions substitution for Cu on the magnetic susceptibility, it is found that the degree of initial phase disorder is related to the order degree of magnetic sequence in CuO2 chain. For the un-doped sample, the decoupling of (timers is weak, the magnetic sequence is slightly destroyed, and the streaks in EDP are also very weak, which implies the degree of initial phase disorder in CuO2 chain is very low. When Zn2+ and Ni2+ ions are doped, the number of dimers per Eu, decreases, and the intensity of diffraction streaks increases. Furthermore, when the high spin magnetic ions Co3+ are doped, the number of holes in Sr-14(Cu1- xCox)(24)O-41 decreases, the magnetic sequence is destroyed very seriously, and the spots in EDP are extended to streaks almost completely. The phenomenon that the diffraction spots of CuO2 chain extend to streaks in EDP appears as evidence that the magnetic sequence in the CuO2 chain is destroyed by doping of Zn, Ni, Co. (C) 2014 Elsevier BA/. All rights reserved.
Title:
Mg-based bulk metallic glass composite containing in situ microsized quasicrystalline particles
Authors:
Zhao, YY; Men, H; Estevez, D; Liu, Y; Wang, XM; Li, RW; Chang, CT Author Full Names: Zhao, Yuan-Yun; Men, He; Estevez, Diana; Liu, Yan; Wang, Xinmin; Li, Run-Wei; Chang, Chuntao
Source:
SCRIPTA MATERIALIA, 78-79 21-24; 10.1016/j.scriptamat.2014.01.019 MAY 2014
Abstract:
A novel in situ forming Mg66Zn29Ca4Y1 composite comprising microsized icosahedral quasicrystal phase (I-phase) particles dispersed within a Mg-based metallic glass matrix was synthesized. The size and volume fraction of the I-phase particles are similar to 25-35 mu m and similar to 10%, respectively. The I-phase particles can noticeably improve both the strength and plasticity of the composite. The mechanism of the hard I-phase particles on the deformation and fracture behaviors of the composite and the synthesis strategy of the composite are discussed. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
The 1D Spin-1/2 XXZ Model in Transverse Uniform and Staggered Magnetic Fields
Authors:
Moradmard, H; Naseri, MS; Mahdavifar, S Author Full Names: Moradmard, H.; Naseri, M. Shahri; Mahdavifar, S.
Source:
JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 27 (5):1265-1271; 10.1007/s10948-013-2429-4 MAY 2014
Abstract:
We have studied the ground state magnetic phase diagram of the one-dimensional anisotropic spin-1/2 XXZ model in the presence of transverse uniform and staggered magnetic fields. We have suggested that the presence study can be applied to a real magnet with the Dzyaloshinskii-Moriya interaction. In the absence of the staggered magnetic field, the phase diagram is divided into four regions. Using the numerical Lanczos method, we have done an accurate numerical experiment. We have presented a detailed numerical analysis of the low energy spectrum and the ground state magnetic phase diagram. Our numerical results show the staggered-field-induced effects depend on in which one of the four regions the system is. In one of the regions, we have identified two quantum phase transitions, which belong to the universality class of the commensurate-incommensurate phase transition.
Title:
Formation mechanism of quasicrystals at the nanoscale during hot compression of Mg alloys
Authors:
Huang, H; Tian, Y; Yuan, GY; Chen, CL; Ding, WJ; Wang, ZC Author Full Names: Huang, Hua; Tian, Yuan; Yuan, Guangyin; Chen, Chunlin; Ding, Wenjiang; Wang, Zhongchang
Source:
SCRIPTA MATERIALIA, 78-79 61-64; 10.1016/j.scriptamat.2014.01.035 MAY 2014
Abstract:
A comprehensive transmission electron microscopy investigation was conducted to gain insights into how the secondary phases in Mg-1.50Zn-0.25Gd alloys are transformed during hot compression. It was found that needle-like Mg4Zn7 phases precipitate in Mg matrix, yet vanish during compression, forming nano-quasicrystals. These nano-quasicrystals are found to nucleate on the Mg4Zn7 phase with orientation relationships [1 1 (2) over bar 0](Mg) parallel to [(1) over bar 0 7](Mg4Zn7) parallel to [2-fold](I-phase), indicating that the crystal phase can transform to the quasicrystalline phase. The formation mechanism of the quasicrystals in Mg alloys at the nanoscale is also discussed. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
The Splitting of SDW State into Commensurable and Incommensurables Ones and the Peculiarities of the Behavior of Thermodynamic Quantities in a Magnetic Field Arbitrarily Oriented to Magnetization in Quasi Two-Dimensional Systems
Authors:
Palistrant, ME; Ursu, VA; Calalb, M Author Full Names: Palistrant, M. E.; Ursu, V. A.; Calalb, M.
Source:
JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 27 (5):1299-1308; 10.1007/s10948-013-2431-x MAY 2014
Abstract:
The quasi-two-dimensional system in which magnetism is caused by spin density wave (SDW) with an anisotropic energy spectrum (with defined impurity concentration x) is examined. The wave vector is supposed to be different from 2k (F) and the umklapp scattering (U-processes) is taken into account. The system is placed in a magnetic field arbitrarily oriented with respect to the vector . The basic equations for order parameters are obtained and the system of these equations is transformed taking into account the U-processes. The particular cases and and the case of small arbitrarily oriented magnetic fields are examined in detail. The conditions of the system transition to commensurable and incommensurable SDW state are analyzed. The phase diagram (T,x) at H=0 is traced. The influence of the magnetic field on the temperature of magnetic transition is researched and the aspect of the phase diagram in magnetic field in the cases H (z) H (sigma) =0 is presented. The longitudinal magnetic susceptibility chi (ayen) which demonstrates that at x < x (c) the temperature behavior is similar to the case when the system has a gap, and at x > x (c) to a gapless case. At x similar to x (c) in the dependence X (ayen)(T) a local maximum appears. The influence of the energy spectrum anisotropy on the system's properties is researched. Also the angular anisotropy of the quantity chi (ayen) at different values of T and x is determined.
Title:
Brillouin zone labelling for quasicrystals
Authors:
Gambaudo, JM; Vignolo, P Author Full Names: Gambaudo, Jean-Marc; Vignolo, Patrizia
Source:
NEW JOURNAL OF PHYSICS, 16 10.1088/1367-2630/16/4/043013 APR 15 2014
Abstract:
We propose a scheme to determine the energy-band dispersion of quasicrystals that does not require any periodic approximation and directly provides the correct structure of the extended Brillouin zones. From the gap labelling viewpoint, this allows us to transpose the measurement of the integrated density of states with that of the effective Brillouin zone areas, which are uniquely determined by the position of the Bragg peaks. Moreover, we show that the Bragg vectors can be determined by stability analysis of the law of recurrence used to generate the quasicrystal. Our analysis of gap labelling in the quasimomentum space opens the way to experimental proof of gap labelling itself within the framework of optics experiments, polaritons, or with ultracold atoms.

Update: 7-May-2014

Title:
High-pressure synthesis, crystal chemistry and physics of perovskites with small cations at the A site
Authors:
Belik, AA; Yi, W Author Full Names: Belik, Alexei A.; Yi, Wei
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (16):10.1088/0953-8984/26/16/163201 APR 23 2014
Abstract:
ABO(3) perovskites with small cations at the A site (A = Sc3+, In3+ and Mn2+ and B = Al3+ and transition metals) are reviewed. They extend the corresponding families of perovskites with A(3+) = Y, La-Lu, and Bi and A(2+) = Cd, Ca, Sr and Ba and exhibit the largest structural distortions. As a result of these large distortions, they show, in many cases, distinct structural and magnetic properties. These are manifested in: B-site-ordered monoclinic structures of ScMnO3 and 'InMnO3'; an unusual superstructure of ScRhO3 and InRhO3; antiferromagnetic ground states and multiferroic properties of Sc2NiMnO6 and In2NiMnO6; two magnetic transitions in ScCrO3 and InCrO3 with very close transition temperatures; a Pnma-to-P-1 structural transition and k = (1/2, 0, 1/2) magnetic ordering in ScVO3; and incommensurate magnetic ordering of Mn2+ spins in metallic MnVO3. A large number of simple ScBO3, InBO3 and MnBO3 perovskites has not been synthesized yet, and the number of experimental and theoretical works on each known ScBO3, InBO3 and MnBO3 perovskites counts to only one or two (except for ScAlO3). The synthesis, crystal chemistry and physics of perovskites with small cations at the A site is an emerging field in perovskite science.
Title:
Phase formation and stability of quasicrystal/alpha-Mg interfaces in the Mg-Cd-Yb system
Authors:
Ohhashi, S; Suzuki, K; Kato, A; Tsai, AP Author Full Names: Ohhashi, S.; Suzuki, K.; Kato, A.; Tsai, A. P.
Source:
ACTA MATERIALIA, 68 (15):116-126; 10.1016/j.actamat.2014.01.009 APR 2014
Abstract:
Phase formation involving icosahedral quasicrystals (iQc) in the Mg-Cd-Yb system was investigated. The phase diagrams obtained revealed that the iQc is in equilibrium with either (Mg, Cd)(2)Yb or an alpha-Mg phase over a wide composition range at 673 K. A eutectic reaction, where the melt decomposed to a rod-like lamella structure consisting of iQc and alpha-Mg phases was observed for Mg68Cd24Yb8 at 735 K. High-angle annular dark-field scanning transmission microscopy observation of the iQc in Mg96Cd3Yb1 verified the atomic positions of the Yb icosahedra and confirmed that the i-MgCdYb is isostructural to the i-CdYb. The formation of the eutectic structure is responsible for the high stability of the iQc/alpha-Mg interfaces because of good lattice matching; which is coincident interplanar spacing over several planes for the two phases. This coincidence in interplanar spacing was further confirmed in the real atomic structure, for which the twofold planes of the iQc, and the [0002] and [2-1-10] planes of alpha-Mg are dominant factors in determining the stability of the interfaces. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
QUASICRYSTALS Making ends meet
Authors:
Verberck, B Author Full Names: Verberck, Bart
Source:
NATURE PHYSICS, 10 (4):246-246; 10.1038/nphys2944 APR 2014
Title:
Effect of aluminum on the microstructure and properties of two refractory high-entropy alloys
Authors:
Senkov, ON; Senkova, SV; Woodward, C Author Full Names: Senkov, O. N.; Senkova, S. V.; Woodward, C.
Source:
ACTA MATERIALIA, 68 (15):214-228; 10.1016/j.actamat.2014.01.029 APR 2014
Abstract:
The microstructure, phase composition and mechanical properties of the AlMo0.5NbTa0.5TiZr and Al0.4Hf0.6NbTaTiZr high-entropy alloys are reported. The AlMo0.5NbTa0.5TiZr alloy consists of two body-centered cubic (bcc) phases with very close lattice parameters, a(1) = 326.8 pm and a(2) = 332.4 pm. One phase was enriched with Mo, Nb and Ta and another phase was enriched with Al and Zr. The phases formed nano-lamellae modulated structure inside equiaxed grains. The alloy had a density of rho = 7.40 g cm(-3) and Vickers hardness H-v = 5.8 GPa. Its yield strength was 2000 MPa at 298 K and 745 MPa at 1273 K. The Al0.4Hf0.6NbTaTiZr had a single-phase bcc structure, with the lattice parameter a= 336.7 pm. This alloy had a density rho = 9.05 g cm(-3), Vickers microhardness H-v = 4.9 GPa, and its yield strength at 298 K and 1273 K was 1841 MPa and 298 MPa, respectively. The properties of these Al-containing alloys were compared with the properties of the parent CrMo0.5NbTa0.5TiZr and HfNbTaTiZr alloys and the beneficial effects from the Al additions on the microstructure and properties were outlined. A thermodynamic calculation of the solidification and equilibrium phase diagrams was conducted for these alloys and the calculated results were compared with the experimental data. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Crystallographic account of nano-scaled intergrowth of M2B-type borides in nickel-based superalloys
Authors:
Hu, XB; Zhu, YL; Ma, XL Author Full Names: Hu, X. B.; Zhu, Y. L.; Ma, X. L.
Source:
ACTA MATERIALIA, 68 (15):70-81; 10.1016/j.actamat.2014.01.002 APR 2014
Abstract:
M2B-type borides in nickel-based superalloys containing boron subjected to long-term aging treatments were investigated by means of analytical transmission electron microscopy. Contrast analysis and electron diffraction show that the boride precipitations have dual-phase structures (I4/mcm, C16; Fddd, C-b) with a high density of stacking faults. The faulted planes and displacement vectors are determined as (110)(C16) and [1 (1) over bar1](C16)/4 in C16 structure and (100)(Cb) and [011](Cb)/4 in C-b structure. Structural models based on a polyhedron of square anti-prisms are proposed not only to rationalize the stacking faults, 60 degrees rotation twin and the intergrowth of structural variants, but also to interpret the newly observed structure in M2B-type borides. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Structural phase transitions of robust insulating Bi1-xLaxFe1-yTiyO3 multiferroics
Authors:
Zhang, LL; Yu, J; Itoh, M Author Full Names: Zhang, Linlin; Yu, Jian; Itoh, Mitsuru
Source:
JOURNAL OF APPLIED PHYSICS, 115 (12):10.1063/1.4869743 MAR 28 2014
Abstract:
In contrast to leaky BiFeO3, of which two structural phase transitions of cycloidal modulated antiferromagnetic-paramagnetic and ferroelectric-paraelectric are observed below 850 degrees C, chemical co-substitution to form Bi1-xLaxFe1-yTiyO3 ternary solid solution makes these multiferroic ceramics become robust insulating low dielectric loss and exhibit rich structural phase transitions. Differential thermal analysis and temperature-dependent X-ray diffraction measurements probe four first-order structural phase transitions, e. g., T-H = 305 degrees C, T-N = 365 degrees C, T-C = 810 degrees C, and T-S = 830 degrees C observed in the Bi0.98La0.02Fe0.99Ti0.01O3 system, which are reasonably attributed to Brazovskii-type cycloidal modulated antiferromagnetic-helimagnetic (at T-H) and helimagnetic-paramagnetic (at T-N) magnetic phase transitions, ferroelectric-paraelectric (at T-C) and rhombohedral-cubic (at T-S) structural phase transitions, respectively. Magnetic phase transition temperatures change a little but ferroelectric and lattice structural phase transition temperatures decrease gradually with increasing co-substitution up to composition-induced rhombohedral-(pseudo-)cubic structural phase boundary. The first-order nature of magnetic phase transition and emergence of helimagnetic phase were attributed to Ti3+ d(1) magnetic disorder distribution in the Fe3+ d(5) -O-Fe3+ d(5) chains, while the first-order nature becomes weak with increasing co-substitution, owing to decreased ferroelectric rhombohedral lattice distortion. An intermediate rhombohedral paraelectric phase is discovered intervening between ferroelectric rhombohedral and paraelectric cubic phase, of which the temperature range defined by difference between TC and TS increases with increasing co-substitution. It was found that TC and TS are able to be predicted quantitatively by reduced mass of unit cell. These findings enrich our understanding of ferroic phase transitions and advance designing novel high temperature multiferroic compounds. (C) 2014 AIP Publishing LLC.
Title:
Dynamic behavior of magnetoelectric coupling of CuFeO2 induced by a high magnetic field
Authors:
Xia, NM; Shi, LR; Xia, ZC; Chen, BR; Jin, Z; Wang, YS; Ouyang, ZW; Zuo, HK; Shen, YN Author Full Names: Xia, Nianming; Shi, Liran; Xia, Zhengcai; Chen, Borong; Jin, Zhao; Wang, Yeshuai; Ouyang, Zhongwen; Zuo, Huakun; Shen, Yining
Source:
JOURNAL OF APPLIED PHYSICS, 115 (11):10.1063/1.4868578 MAR 21 2014
Abstract:
Magnetoelectric effects and their dynamic behavior in a CuFeO2 single crystal grown by the floating zone technique are investigated at low temperature in pulsed high magnetic fields. Experimental results show that the magnetization, dielectric polarization, and magnetoelectric coupling are anisotropic. In the magnetization, a field-induced multi-step-like transition with hysteresis is observed, in which the critical magnetic fields are independent of the field sweep rate. In the dielectric polarization, the field-induced dielectric polarization with hysteresis (or partial irreversible) is only observed in the incommensurate-noncollinear phase. In particular, no obvious spontaneous dielectric polarization is observed in the lower magnetic field regime. Using a pulsed high magnetic field with various magnetic field strength and field sweep rates, the coupling behavior between the magnetic moment and the dielectric polarization is investigated. Experimental results show that the dielectric polarization is weakly related to the field sweep rate. In the field-decreasing branch, the magnetic field is higher, the magnetic field region of the dielectric polarization remains is lower, indicating that the pulsed high magnetic field has an effect on the enhancement of the spontaneous dielectric polarization. (C) 2014 AIP Publishing LLC.

Update: 1-May-2014

Title:
An exact solution for a multilayered two-dimensional decagonal quasicrystal plate
Authors:
Yang, LZ; Gao, Y; Pan, E; Waksmanski, N Author Full Names: Yang, Lian-Zhi; Gao, Yang; Pan, Ernian; Waksmanski, Natalie
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 51 (9):1737-1749; 10.1016/j.ijsolstr.2014.01.018 MAY 1 2014
Abstract:
By extending the pseudo-Stroh formalism to two-dimensional decagonal quasicrystals, an exact closed-form solution for a simply supported and multilayered two-dimensional decagonal quasicrystal plate is derived in this paper. Based on the different relations between the periodic direction and the coordinate system of the plate, three internal structure cases for the two-dimensional quasicrystal layer are considered. The propagator matrix method is also introduced in order to treat efficiently and accurately the multilayered cases. The obtained exact closed-form solution has a concise and elegant expression. Two homogeneous quasicrystal plates and a sandwich plate made of a two-dimensional quasicrystal and a crystal with two stacking sequences are investigated using the derived solution. Numerical results show that the differences of the periodic direction have strong influences on the stress and displacement components in the phonon and phason fields; different coupling constants between the phonon and phason fields will also cause differences in physical quantities; the stacking sequences of the multilayer plates can substantially influence all physical quantities. The exact closed-form solution should be of interest to the design of the two-dimensional quasicrystal homogeneous and laminated plates. The numerical results can also be employed to verify the accuracy of the solution by numerical methods, such as the finite element and difference methods, when analyzing laminated composites made of quasicrystals. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
Np-237 Mossbauer effect study on NpFeAsO
Authors:
Gaczynski, P; Klimczuk, T; Walker, H; Springell, R; Colineau, E; Eloirdi, R; Griveau, JC; Caciuffo, R Author Full Names: Gaczynski, P.; Klimczuk, T.; Walker, H.; Springell, R.; Colineau, E.; Eloirdi, R.; Griveau, J-C; Caciuffo, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (15):10.1088/0953-8984/26/15/156002 APR 16 2014
Abstract:
We report Np-237 Mossbauer measurements on NpFeAsO. The Np atoms were found to occupy only one crystallographic site. The value of the isomer shift (delta similar to 9.1 mm s(-1) versus NpAl2) indicates a 5f(4) electronic configuration (Np3+ ions). The magnetic ordering of the Np sublattice below 60 K is established and the saturated ordered magnetic moment is determined to be 1.73 mu(B) at 3.6 K. The unique set of hyperfine parameters exclude a modulated magnetic structure or spin waves on the Np site. The neptunium magnetic moments mu(Np) are found to lie along the tetragonal c-axis.
Title:
High-temperature structural study of decagonal Al-Cu-Rh
Authors:
Kuczera, P; Wolny, J; Steurer, W Author Full Names: Kuczera, Pawel; Wolny, Janusz; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 306-314; 10.1107/S2052520613032575 2 APR 2014
Abstract:
The structure of decagonal Al-Cu-Rh has been studied as a function of temperature by in-situ single-crystal X-ray diffraction in order to contribute to the discussion on energy or entropy stabilization of quasicrystals. The experiments were performed at 293, 1223, 1153, 1083 and 1013 K. A common subset of 1460 unique reflections was used for the comparative structure refinements at each temperature. A comparison of the high-temperature datasets suggests that the best quasiperiodic ordering should exist between 1083 and 1153 K. However, neither the refined structures nor the phasonic displacement parameter vary significantly with temperature. This indicates that the phasonic contribution to entropy does not seem to play a major role in the stability of this decagonal phase in contrast to other kinds of structural disorder, which suggests that, in this respect, this decagonal phase would be similar to other complex intermetallic high-temperature phases.
Title:
Moroccan ornamental quasiperiodic patterns constructed by the multigrid method
Authors:
Aboufadil, Y; Thalal, A; Raghni, MAE Author Full Names: Aboufadil, Youssef; Thalal, Abdelmalek; El Idrissi Raghni, My Ahmed
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 47 630-641; 10.1107/S1600576714001691 2 APR 2014
Abstract:
The similarity between the structure of Islamic decorative patterns and quasicrystals has aroused the interest of several crystallographers. Many of these patterns have been analysed by different approaches, including various kinds of ornamental quasiperiodic patterns encountered in Morocco and the Alhambra (Andalusia), as well as those in the eastern Islamic world. In the present work, the interest is in the quasiperiodic patterns found in several Moroccan historical buildings constructed in the 14th century. First, the zellige panels (fine mosaics) decorating the Madrasas (schools) Attarine and Bou Inania in Fez are described in terms of Penrose tiling, to confirm that both panels have a quasiperiodic structure. The multigrid method developed by De Bruijn [Proc. K. Ned. Akad. Wet. Ser. A Math. Sci. (1981), 43, 39-66] and reformulated by Gratias [Tangente (2002), 85, 34-36] to obtain a quasiperiodic paving is then used to construct known quasiperiodic patterns from periodic patterns extracted from the Madrasas Bou Inania and Ben Youssef (Marrakech). Finally, a method of construction of heptagonal, enneagonal, tetradecagonal and octadecagonal quasiperiodic patterns, not encountered in Moroccan ornamental art, is proposed. They are built from tilings (skeletons) generated by the multigrid method and decorated by motifs obtained by craftsmen.
Title:
The quasiperiodic average structure of highly disordered decagonal Zn-Mg-Dy and its temperature dependence
Authors:
Ors, T; Takakura, H; Abe, E; Steurer, W Author Full Names: Ors, Taylan; Takakura, Hiroyuki; Abe, Eiji; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 315-330; 10.1107/S2052520614001115 2 APR 2014
Abstract:
A single-crystal X-ray diffraction structure analysis of decagonal Zn-Mg-Dy, a Frank-Kasper-type quasicrystal, was performed using the higher-dimensional approach. For this first Frank-Kasper (F-K) decagonal quasicrystal studied so far, significant differences to the decagonal Al-TM-based (TM: transition metal) phases were found. A new type of twofold occupation domain is located on certain edge centers of the five-dimensional unit cell. The structure can be described in terms of a two-cluster model based on a decagonal cluster (similar to 23 angstrom diameter) arranged on the vertices of a pentagon-Penrose tiling (PPT) and a star-like cluster covering the remaining space. This model is used for the five-dimensional refinements, which converged to an R value of 0.126. The arrangement of clusters is significantly disordered as indicated by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In order to check the structure and stability at higher temperatures, in-situ high-temperature (HT) single-crystal X-ray diffraction experiments were conducted at 598 and 648 K (i.e. slightly below the decomposition temperature). The structure does not change significantly, however, the best quasiperiodic order is found at 598 K. The implication of these results on the stabilization mechanism of quasicrystals is discussed.
Title:
LiZn4-x (x=0.825) as a (3+1)-dimensional modulated derivative of hexagonal close packing
Authors:
Pavlyuk, V; Chumak, I; Akselrud, L; Lidin, S; Ehrenberg, H Author Full Names: Pavlyuk, Volodymyr; Chumak, Ihor; Akselrud, Lev; Lidin, Sven; Ehrenberg, Helmut
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 212-217; 10.1107/S2052520613030709 2 APR 2014
Abstract:
The (3+1)-dimensional modulated structure of the LiZn4 - x (x = 0.825) binary compound has been determined in the superspace. The compound crystallizes in the orthorhombic superspace group Cmcm(alpha 00)0s0 with a = 2.7680 (6), b = 4.7942 (6), c = 4.3864 (9) angstrom, modulation wavevector: q similar or equal to 4/7a*. The structure is a derivative from the hexagonal close packing. The cubo-octahedron as a coordination polyhedron (c.n. = 12) is typical for all atoms. Bonding between atoms is explored by means of the TB-LMTO-ASA program package. The absence of strong interatomic interactions in LiZn4 - x is the main reason for the possible structure transformations.
Title:
Charge Density Wave Accompanied by Spin Density Wave in Mn3Si
Authors:
Tomiyoshi, S; Ohsumi, H; Kobayashi, H; Yamamoto, A Author Full Names: Tomiyoshi, Shoichi; Ohsumi, Hiroyuki; Kobayashi, Hisao; Yamamoto, Akiji
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 83 (4):10.7566/JPSJ.83.044715 APR 2014
Abstract:
The displacement modulation due to the charge density wave (CDW) in Mn3Si, which occurs as second harmonics of the spin density wave (SDW), has been investigated by synchrotron x-ray diffraction and the existence of CDW below Neel temperature of 23 K has been confirmed. High resolution measurement revealed the splitting of the satellite peaks deviating very little from the [111] axis toward [110] direction, suggesting the possibility of a single or double q CDW state. The temperature dependence of the satellites indicates the existence of the phase transition at T-t = 8.5 K, in agreement with the neutron diffraction result [Phys. Rev. B 73, 224416 (2006)]. The analysis of reflection intensities using a single q model, which is a limiting case of no splitting, shows that in both phases Si and Mn-II have larger displacement than that of Mn-I. The formation of single and double q SDWs and their nesting mechanism are discussed.
Title:
Superspace description of wagnerite-group minerals (Mg,Fe,Mn)(2)(PO4)(F,OH)
Authors:
Lazic, B; Armbruster, T; Chopin, C; Grew, ES; Baronnet, A; Palatinus, L Author Full Names: Lazic, Biljana; Armbruster, Thomas; Chopin, Christian; Grew, Edward S.; Baronnet, Alain; Palatinus, Lukas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 243-258; 10.1107/S2052520613031247 2 APR 2014
Abstract:
Reinvestigation of more than 40 samples of minerals belonging to the wagnerite group (Mg, Fe, Mn)(2)(PO4)(F,OH) from diverse geological environments worldwide, using single-crystal X-ray diffraction analysis, showed that most crystals have incommensurate structures and, as such, are not adequately described with known polytype models (2b), (3b), (5b), (7b) and (9b). Therefore, we present here a unified superspace model for the structural description of periodically and aperiodically modulated wagnerite with the (3+1)-dimensional superspace group C2/c(0 beta 0)s0 based on the average triplite structure with cell parameters a similar or equal to 12.8, b similar or equal to 6.4, c similar or equal to 9.6 angstrom, beta similar or equal to 117 degrees and the modulation vectors q = beta b*. The superspace approach provides a way of simple modelling of the positional and occupational modulation of Mg/Fe and F/OH in wagnerite. This allows direct comparison of crystal properties.
Title:
The Tenth Ewald Prize and aperiodic crystals
Authors:
Mukhopadhyay, NK Author Full Names: Mukhopadhyay, N. K.
Source:
CURRENT SCIENCE, 106 (6):793-793; MAR 25 2014
Title:
Rheological properties of palygorskite-bentonite and sepiolite-bentonite mixed clay suspensions
Authors:
Chemeda, YC; Christidis, GE; Khan, NMT; Koutsopoulou, E; Hatzistamou, V; Kelessidis, VC Author Full Names: Chemeda, Yadeta C.; Christidis, George E.; Khan, N. M. Tauhid; Koutsopoulou, Eleni; Hatzistamou, Vicky; Kelessidis, Vassilios C.
Source:
APPLIED CLAY SCIENCE, 90 165-174; 10.1016/j.clay.2013.12.013 MAR 2014
Abstract:
This study examines the influence of layer charge and smectite content on the rheological properties of mixed bentonite-palygorskite suspensions. Eight bentonite samples containing smectite with layer charge ranging between 0.38 and 0.54 e/huc were used to prepare 5% w/v mixed palygorskite-bentonite aqueous suspension at pH 7. The influence of smectite on the apparent viscosity and yield point of palygorskite suspensions depends on the proportion of the smectite in the mixture and the layer charge and charge localization of the smectite. The interaction between the two end member clay minerals is maximum at low percentage (10 to 20%) of bentonite in the mixture. Low charge and high charge smectite tended to improve and deteriorate, respectively, the yield point and apparent viscosity of the suspension. This behaviour seemed to be related to the influence of layer charge of smectite on the degree of delamination and the thickness of smectite quasicrystals, which consequently determine the number of particles involved in the interaction and the strength of particle-particle linkages. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Frequency dependence of the characteristic temperatures in PbSc0.5Ta0.36Nb0.14O3 relaxor ferroelectrics crystals seen via acoustic emission
Authors:
Dul'kin, E; Mihailova, B; Gospodinov, M; Roth, M Author Full Names: Dul'kin, E.; Mihailova, B.; Gospodinov, M.; Roth, M.
Source:
JOURNAL OF APPLIED PHYSICS, 115 (8):10.1063/1.4864036 FEB 28 2014
Abstract:
PbSc0.5Ta0.36Nb0.14O3 relaxor ferroelectrics crystals were investigated in a wide temperature range of 200-700K using acoustic emission. The intermediate temperature T* as well as the Burns temperature T-d were successfully detected at 480K and 581 K, respectively. Another acoustic emission burst was detected at T-n(l) similar to 211K, which is below the temperature of the dielectric-permittivity maximum T-m similar to 257K but it is accompanied by a slight anomaly in the dielectric permittivity. T-n(l) is attributed to the low-temperature boundary of an incommensurately modulated antiferroelectric phase transition taking place over a temperature range. All characteristic temperatures exhibit frequency dispersion in the range of 0.1-10 kHz, which is considerably stronger for T* and T-d than for T-m and T-n(l). In addition, T-n(l) depends linearly on frequency, whereas both T* and T-d resemble the non-linear frequency dependence of Tm typical of relaxors. The nature of the frequency dispersion of T* and T-d is discussed from the viewpoint of complex behavior of low-energy polar modes intrinsic of relaxor ferroelectrics. (C) 2014 AIP Publishing LLC.
Title:
In-situ high-pressure X-ray diffraction on the Zn6Sc 1/1 periodic cubic approximant to a quasicrystal
Authors:
Yamada, T; Garbarino, G; Takakura, H; Gomez, CP; Tamura, R; de Boissieu, M Author Full Names: Yamada, Tsunetomo; Garbarino, Gaston; Takakura, Hiroyuki; Gomez, Cesar Pay; Tamura, Ryuji; de Boissieu, Marc
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 229 (3):230-235; SI 10.1515/zkri-2013-1684 2 2014
Abstract:
The Zn6Sc 1/1 cubic approximant to a quasicrystal has been studied in-situ at high pressures by single-crystal X-ray diffraction. This phase can be described as a bcc packing of Tsai-type icosahedral clusters whose center is occupied by a disordered Zn-4 tetrahedron. At ambient pressure the Zn6Sc undergoes a structural phase transition at 159 K to a monoclinic superstructure in which the Zn-4 tetrahedra are orientationally ordered along the [101] direction of the high-temperature bcc phase. In the pressure range up to 35 GPa, two new superstructures have been observed. The second phase corresponds to a four-fold pseudo cubic superstructure, i.e. a very large unit cell with a lattice parameter of about 5.5 nm. The resulting pressure-temperature phase diagram is different from that of Cd6Yb, which was reported by Watanuki et al. (2006).

Update: 23-Apr-2014

Title:
Bulk synthesis by spray forming of Al-Cu-Fe and Al-Cu-Fe-Sn alloys containing a quasicrystalline phase
Authors:
Srivastava, VC; Huttunen-Saarivirta, E; Cui, C; Uhlenwinkel, V; Schulz, A; Mukhopadhyay, NK Author Full Names: Srivastava, V. C.; Huttunen-Saarivirta, E.; Cui, C.; Uhlenwinkel, V.; Schulz, A.; Mukhopadhyay, N. K.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 597 258-268; 10.1016/j.jallcom.2014.01.241 JUN 5 2014
Abstract:
In this study, Al-Cu-Fe alloys without and with the addition of Sn and containing a quasicrystalline phase were spray deposited. The spray-deposited bulk materials were characterized in terms of microstructure and hardness. The results showed that the Al62.5Cu25Fe12.5 alloy contains the icosahedral quasicrystalline phase (i-phase) along with the minor lambda-Al13Fe4 phase, whereas the Al62.5Cu25Fe12.5 + Sn alloy contains five phases: the major i-phase and the crystalline phases of Sn, theta-Al2Cu, lambda-Al13Fe4 and beta-AlFe(Cu) phases. These results have been corroborated by X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM) and differential scanning calorimetry (DSC). The hardness value of the Al-Cu-Fe alloy reached 10.5 GPa at 50 g load and then decreased steadily with increase in the applied load, while that for Al-Cu-Fe-Sn alloy it was originally somewhat lower, then decreased dramatically with slight increase in the applied load but stayed constant with further load increase. The hardness indentations in Al-Cu-Fe alloy introduced cracking in the material, whereas in the case of Al-Cu-Fe-Sn alloy the Sn-rich areas inhibited the crack growth. The present study provides an insight into the mechanism of phase and microstructural evolutions during spray forming of the studied alloys. Furthermore, the role of Sn in terms of microstructure and properties is highlighted. (C) 2014 Elsevier B. V. All rights reserved.
Title:
Exotic Magnetism on the Quasi-fcc Lattices of the d(3) Double Perovskites La2NaB ' O-6 (B ' = Ru, Os)
Authors:
Aczel, AA; Baker, PJ; Bugaris, DE; Yeon, J; Loye, HCZ; Guidi, T; Adroja, DT Author Full Names: Aczel, A. A.; Baker, P. J.; Bugaris, D. E.; Yeon, J.; Loye, H. -C. Zur; Guidi, T.; Adroja, D. T.
Source:
PHYSICAL REVIEW LETTERS, 112 (11):10.1103/PhysRevLett.112.117603 MAR 20 2014
Abstract:
We find evidence for long-range and short-range (zeta = 70 angstrom at 4 K) incommensurate magnetic order on the quasi-face-centered-cubic (fcc) lattices of the monoclinic double perovskites La2NaRuO6 and La2NaOsO6, respectively. Incommensurate magnetic order on the fcc lattice has not been predicted by mean field theory, but may arise via a delicate balance of inequivalent nearest neighbor and next nearest neighbor exchange interactions. In the Ru system with long-range order, inelastic neutron scattering also reveals a spin gap Delta similar to 2.75 meV. Magnetic anisotropy is generally minimized in the more familiar octahedrally coordinated 3d(3) systems, so the large gap observed for La2NaRuO6 may result from the significantly enhanced value of spin-orbit coupling in this 4d(3) material.
Title:
Influence of the thickness of [N(CH3)(4)](2)Zn0.75Mn0.25Cl4 crystal on the *phase-*transition temperature
Authors:
Sveleba, SA; Karpa, IV; Katerynchuk, IM; Kunyo, IM; Phitsych, EI Author Full Names: Sveleba, S. A.; Karpa, I. V.; Katerynchuk, I. M.; Kunyo, I. M.; Phitsych, E. I.
Source:
CRYSTALLOGRAPHY REPORTS, 59 (2):229-237; 10.1134/S1063774514020266 MAR 2014
Abstract:
The change in the phase-transition temperature of [N(CH3)(4)](2)Zn0.75Mn0.25Cl4 crystal as a function of its size (3500 mu m-1 mu m) has been investigated. It is established that a decrease in crystal sizes along the spontaneous-polarization axis is accompanied by several effects: a shift of the initial *phase-*incommensurate phase transition point to higher temperatures, an increase in the temperature range of existence of incommensurate phase, an increase in the temperature range of existence of metastable states of incommensurate structure, the occurrence of new long-period commensurate phases, and an increase in *phase-*transition temperature hysteresis at T (c) and T (3). The possibility that a size effect exists in the phase diagram of this crystal is discussed.
Title:
Modulated quasi-two-dimensional antiferromagnetic structures in La1-y Nd (y) MnO3+delta manganites
Authors:
Bukhanko, FN Author Full Names: Bukhanko, F. N.
Source:
PHYSICS OF THE SOLID STATE, 56 (3):473-486; 10.1134/S106378341403007X MAR 2014
Abstract:
The structural, electronic, and magnetic phase transitions induced by the isovalent substitution of the rare-earth Nd3+ ion for the La3+ ion with a larger radius have been investigated in the system of self-doped manganites La1 - y Nd (y) MnO3 + delta (0 a parts per thousand currency sign y a parts per thousand currency sign 1; delta similar to 0.1). For the average radius of the ions in A-sites of the lattice aOE (c) r (A) > aOE (c) 1.19 (y > 0.5), the phenomena revealed in the manganites are as follows: the ordering of Mn e (g) orbitals, the transition from the pseudocubic O* phase to the orthorhombic O' phase, the opening of the dielectric Jahn-Teller gap, the frustration of the collinear ferromagnetic (FM) state, and the transition from the lowtemperature canted FM to canted antiferromagnetic (AFM) state of Mn spins. It is assumed that, in samples with neodymium concentrations y = 0.9 and 1.0 (aOE (c) r (A) > a parts per thousand 1.16 ) at temperatures T < 12 K, there coexist A- and E-type modulated AFM states similar to the sinusoidal and helical structures of Mn spins, which were previously studied in RMnO3 multiferroics. The magnetic T-H phase diagrams of these samples are characteristic of quasi-two-dimensional antiferromagnets with a very low (zero) magnetic anisotropy in the ab planes. Under these conditions, the phase transition from the A-type AFM phase to the spin-flop state occurs in a relatively weak magnetic field. The AFM ordering of the Nd magnetic moments with a critical phase transition temperature T (Nd) a parts per thousand OE 6 K is induced in magnetic fields with a strength H a parts per thousand yen 3.5 kOe. For the NdMnO3 + delta manganite in a magnetic field H = 10.7 kOe, the curves M(T) are characterized by additional very narrow peaks near temperatures T (1) a parts per thousand OE 4.5 K and T (2) a parts per thousand OE 5 K. The additional features revealed for the first time in the magnetization near T = 0 are assumed to be caused by the quantization of the spectrum of free holes in the ab planes by a strong magnetic field.
Title:
Electronic band structure and Fermi surfaces of the quasi-two-dimensional monophosphate tungsten bronze, P4W12O44
Authors:
Paul, S; Ghosh, A; Sato, T; Sarma, DD; Takahashi, T; Wang, E; Greenblatt, M; Raj, S Author Full Names: Paul, S.; Ghosh, A.; Sato, T.; Sarma, D. D.; Takahashi, T.; Wang, E.; Greenblatt, M.; Raj, S.
Source:
EPL, 105 (4):10.1209/0295-5075/105/47003 FEB 2014
Abstract:
The electronic structure of quasi-two-dimensional monophosphate tungsten bronze, P4W12O44, has been investigated by high-resolution angle-resolved photoemission spectroscopy and density functional theoretical calculations. Experimental electron-like bands around Gamma point and Fermi surfaces have similar shapes as predicted by calculations. Fermi surface mapping at different temperatures shows a depletion of density of states at low temperature in certain flat portions of the Fermi surfaces. These flat portions of the Fermi surfaces satisfy the partial nesting condition with incommensurate nesting vectors q(1) and q(2), which leads to the formation of charge density waves in this phosphate tungsten bronzes. The setting up of charge density wave in these bronzes can well explain the anomaly observed in its transport properties. Copyright (C) EPLA, 2014

Update: 17-Apr-2014

Title:
Local orderings in long-range-disordered bismuth-layered intergrowth structure
Authors:
Zhang, FQ; Li, YX; Gu, H; Gao, X Author Full Names: Zhang, Faqiang; Li, Yongxiang; Gu, Hui; Gao, Xiang
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 212 165-170; 10.1016/j.jssc.2014.01.031 APR 2014
Abstract:
A series of intergrowth bismuth-layered (Bi3TiNbO9)(2)(Bi4Ti3O12) (2(2)3) ceramics were prepared by conventional solid-state reaction to study the characteristics of the local orderings in long-range-disordered intergrowth structures. High-resolution high-angle annular dark-field (HAADF) imaging reveals the intergrowth structure composed of mixtures of -23-, -223-, -2223- and -22- sequences, while the -223- structure is the thermodynamic stable state of this intergrowth system. It was confirmed by the crystals of recurrent -223- structure prepared by self-flux method and the nature of the local ordering was discussed from their differences in repeating units. The statistics show that when repeating units reach 4 or higher, the independent -223- intergrowth ordering emerges clearly among the competing associated orderings. We infer it is the kinetic factor that induces local compositional variance to result in long-range disordered intergrowth structures. (C) 2014 Elsevier Inc. All rights reserved.
Title:
Angular Fluctuations of a Multicomponent Order Describe the Pseudogap of YBa2Cu3O6+x
Authors:
Hayward, LE; Hawthorn, DG; Melko, RG; Sachdev, S Author Full Names: Hayward, Lauren E.; Hawthorn, David G.; Melko, Roger G.; Sachdev, Subir
Source:
SCIENCE, 343 (6177):1336-1339; 10.1126/science.1246310 MAR 21 2014
Abstract:
The hole-doped cuprate high-temperature superconductors enter the pseudogap regime as their superconducting critical temperature, T-c, falls with decreasing hole density. Recent x-ray scattering experiments in YBa2Cu3O6+x observe incommensurate charge-density wave fluctuations whose strength rises gradually over a wide temperature range above T-c, but then decreases as the temperature is lowered below T-c. We propose a theory in which the superconducting and charge-density wave orders exhibit angular fluctuations in a six-dimensional space. The theory provides a natural quantitative fit to the x-ray data and can be a basis for understanding other characteristics of the pseudogap.
Title:
Magnetic ordering in TmGa
Authors:
Cadogan, JM; Stewart, GA; Perez, SM; Cobas, R; Hansen, BR; Avdeev, M; Hutchison, WD Author Full Names: Cadogan, J. M.; Stewart, G. A.; Perez, S. Munoz; Cobas, R.; Hansen, B. R.; Avdeev, M.; Hutchison, W. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (11):10.1088/0953-8984/26/11/116002 MAR 19 2014
Abstract:
We have determined the magnetic structure of the intermetallic compound TmGa by high-resolution neutron powder diffraction and Tm-169 Mossbauer spectroscopy. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure and its magnetic structure is characterized by magnetic order of the Tm sublattice along the a-axis. The initial magnetic ordering occurs at 15(1) K and yields an incommensurate antiferromagnetic structure described by the propagation vector k1 = [0.0.275(2)0]. At 12 K the dominant ferromagnetic ordering of the Tm sublattice along the a-axis develops in what appears to be a first-order transition. At 3 K the magnetic structure of TmGa is predominantly ferromagnetic but a weakened incommensurate component remains. The ferromagnetic Tm moment reaches 6.7(2) mu B at 3 K and the amplitude of the remaining incommensurate component is 2.7(4) mu B. The Tm-169 hyperfine magnetic field at 5 K is 631(1) T.
Title:
RESEARCH PROGRESS OF FIVE-FOLD SYMMETRY CLUSTERS
Authors:
Li, GF; Shu, XY; Liu, JW Author Full Names: Li, G. F.; Shu, X. Y.; Liu, J. W.
Source:
REVIEWS ON ADVANCED MATERIALS SCIENCE, 36 (1):21-28; FEB 2014
Abstract:
Since 1984, Shechtman et al. published a paper which marked the discovery of quasicrystals. The local five fold symmetry (LFFS) structure is becoming an unsocial hero, who walks a muricated way against classical crystallography. As well known, the LFFS clusters have largely potential application prospect in catalysis, in recomposing physical, mechanical and thermal performance of bulk metallic glasses, in composing "super atom" materials, in some creative manufacture technologies of crystal metal from amorphous straightly. In this paper, we summarize the ubiquitous existence, particularity, performance and research progress of LFFS clusters in metallic glasses, and put forward some urgent problems.
Title:
Comprehensive study of the spin-charge interplay in antiferromagnetic La-2 - xSrxCuO4
Authors:
Drachuck, G; Razzoli, E; Bazalitski, G; Kanigel, A; Niedermayer, C; Shi, M; Keren, A Author Full Names: Drachuck, Gil; Razzoli, Elia; Bazalitski, Galina; Kanigel, Amit; Niedermayer, Christof; Shi, Ming; Keren, Amit
Source:
NATURE COMMUNICATIONS, 5 10.1038/ncomms4390 FEB 2014
Abstract:
The origin of the pseudogap and its relationship with superconductivity in the cuprates remains vague. In particular, the interplay between the pseudogap and magnetism is mysterious. Here we investigate the newly discovered nodal gap in hole-doped cuprates using a combination of three experimental techniques applied to one, custom made, single crystal. The crystal is an antiferromagnetic La2 - xSrxCuO4 with x = 1.92%. We perform angle-resolved photoemission spectroscopy measurements as a function of temperature and find: quasi-particle peaks, Fermi surface, anti-nodal gap and below 45 K a nodal gap. Muon spin rotation measurements ensure that the sample is indeed antiferromagnetic and that the doping is close, but below, the spin-glass phase boundary. We also perform elastic neutron scattering measurements and determine the thermal evolution of the commensurate and incommensurate magnetic order, where we find that a nodal gap opens well below the commensurate ordering at 140 K, and close to the incommensurate spin density wave ordering temperature of 30 K.

Update: 9-Apr-2014

Title:
A novel quasicrystal-resin composite for stereolithography
Authors:
Sakly, A; Kenzari, S; Bonina, D; Corbel, S; Fournee, V Author Full Names: Sakly, Adnene; Kenzari, Samuel; Bonina, David; Corbel, Serge; Fournee, Vincent
Source:
MATERIALS & DESIGN, 56 280-285; 10.1016/j.matdes.2013.11.025 APR 2014
Abstract:
Laser stereolithography (SL) is an additive manufacturing technology which is increasingly being used to produce customized end-user parts of any complex shape. It requires the use of a photo-curable resin which can be loaded with ceramic powders or carbon fibers to produce composite parts. However, the range of available materials compatible with the SL process is rather limited. In particular, photo-curable resins reinforced by metal particles are difficult to process, because of fundamental limitations related to the high reflectivity of intermetallics in the UV-visible range. In this work, the unique properties of Al-based quasicrystalline alloys are being used to develop a new UV-curable resin reinforced by such metal particles. The optical properties of the quasicrystalline particles and of the filled resin are studied and they are found to be compatible with the SL process. The volume fraction of the filler particles in the liquid resin is optimized to increase the polymerization depth while preserving suitable rheological behaviour. Finally, 3D composite parts are being built by SL. The composite parts have improved mechanical properties compared to the unfilled resin (higher hardness, reduced wear losses and lower friction coefficient) and compete favourably with the other commercial photo-curable resins. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Elastic field in an infinite medium of one-dimensional hexagonal quasicrystal with a planar crack
Authors:
Li, XY Author Full Names: Li, X. -Y.
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 51 (6):1442-1455; 10.1016/j.ijsolstr.2013.12.030 MAR 15 2014
Abstract:
This present work is concerned with planar cracks embedded in an infinite space of one-dimensional hexagonal quasicrystals. The potential theory method together with the general solutions is used to develop the framework of solving the crack problems in question. The model problems of three common planar cracks (a penny-shaped crack, an external circular crack and a half-infinite crack) are solved in a systematic manner. The phonon and phason elastic fundamental fields along with some important parameters in crack analysis are explicitly presented in terms of elementary functions. Several examples are given to show the applications of the present fundamental solutions. The validity of the present solutions is discussed both analytically and numerically. The derived analytical solutions of crack will not only play an important role in understanding the phonon-phason coupling behavior in quasicrystals, but also serve as benchmarks for future numerical studies and simplified analyses. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Pressure effect on magnetism and multiferroicity in Mn2GeO4
Authors:
Honda, T; Aoyama, T; White, JS; Strassle, T; Keller, L; Kenzelmann, M; Honda, F; Miyake, A; Shimizu, K; Wakabayashi, Y; Kimura, T Author Full Names: Honda, T.; Aoyama, T.; White, J. S.; Straessle, Th; Keller, L.; Kenzelmann, M.; Honda, F.; Miyake, A.; Shimizu, K.; Wakabayashi, Y.; Kimura, T.
Source:
PHYSICAL REVIEW B, 89 (10):10.1103/PhysRevB.89.104405 MAR 10 2014
Abstract:
The effect of high pressure exceeding 6 GPa on magnetism and multiferroicity was investigated for the olivine Mn2GeO4 that shows successive magnetic transitions at ambient pressure and a ferroelectric ground state driven by spin- spiral order. We measured heat capacity, dielectric constant, and electric polarization at various pressures using a diamond anvil cell. The pressure evolution of the magnetic structures was also investigated by powder neutron diffraction measurements using a Paris- Edinburgh press. We found that all of the magnetic transition temperatures are enhanced monotonically by applying pressure. Furthermore, the spin- driven ferroelectricity persists up to about 6 GPa but suddenly vanishes by 6.3 GPa. A consistent description of all data is achieved if an incommensurate- commensurate phase transition occurs with pressurization and causes the suppression of ferroelectricity. We discuss the origin of the observed pressure effects on the magnetism and multiferroicity in Mn2GeO4 in terms of a pressure- induced change in the superexchange magnetic interactions.
Title:
Observation of a new type of magnetic excitations in NdFe3(BO3)(4) ferroborate
Authors:
Kobets, M; Dergachev, K; Kovalev, A; Gnatchenko, S; Khatsko, E Author Full Names: Kobets, M.; Dergachev, K.; Kovalev, A.; Gnatchenko, S.; Khatsko, E.
Source:
LOW TEMPERATURE PHYSICS, 40 (2):151-155; 10.1063/1.4865568 FEB 2014
Abstract:
AFMR spectra of single crystal NdFe3(BO3)(4) are studied over frequencies of 15-32.2 GHz and temperatures of 2.17-10 K in fields H
Title:
Activation of Al-Cu-Fe quasicrystalline surface: fabrication of a fine nanocomposite layer with high catalytic performance
Authors:
Kameoka, S; Tanabe, T; Satoh, F; Terauchi, M; Tsai, AP Author Full Names: Kameoka, Satoshi; Tanabe, Toyokazu; Satoh, Futami; Terauchi, Masami; Tsai, An Pang
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (1):10.1088/1468-6996/15/1/014801 FEB 2014
Abstract:
A fine layered nanocomposite with a total thickness of about 200 nm was formed on the surface of an Al63Cu25Fe12 quasicrystal (QC). The nanocomposite was found to exhibit high catalytic performance for steam reforming of methanol. The nanocomposite was formed by a self-assembly process, by leaching the Al-Cu-Fe QC using a 5 wt% Na2CO3 aqueous solution followed by calcination in air at 873 K. The quasiperiodic nature of the QC played an important role in the formation of such a structure. Its high catalytic activity originated from the presence of highly dispersed copper and iron species, which also suppressed the sintering of nanoparticles.

Update: 3-Apr-2014

Title:
Anomalous triple point effects in the spin-density-wave Cr1-xAlx alloy system
Authors:
Sheppard, CJ; Prinsloo, ARE; Alberts, HL; Muchono, B; Strydom, AM Author Full Names: Sheppard, C. J.; Prinsloo, A. R. E.; Alberts, H. L.; Muchono, B.; Strydom, A. M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 595 164-177; 10.1016/j.jallcom.2014.01.129 MAY 15 2014
Abstract:
It was recently suggested that for the Cr1-xAlx alloy system the Sommerfeld specific heat coefficient (gamma) as a function of x may peak at the triple point (TP) concentration (x(t)) of the x-T magnetic phase diagram. The TP at (x(t), T-t) represents the intersection point of three magnetic phase transition lines at which incommensurate (I) and commensurate (C) spin-density-wave (SDW) phases are expected to coexist with the paramagnetic (P) phase. A comprehensive experimental study on the physical properties of single crystalline Cr1-xAlx alloys in the concentration range 0 <= x <= 0.034, that encloses x(t), is reported here for further investigations of the above conjecture and possible anomalous behaviour in other physical properties near x(t). The measurements include the electrical resistivity (rho), Seebeck coefficient (S), specific heat (C-p), Hall coefficient (R-H), magnetic susceptibility (chi) and thermal conductivity (kappa). All these properties, except for kappa, depict anomalous temperature and concentration dependencies of SDW origin for x close to x(t). The present study indicates a value of x(t) rather close to x = 0.022. The x-dependence of gamma exhibits an extraordinary large and sharp peak near this concentration. This observation is interpreted as indication that the temperature of the TP is likely situated at 0 K. A new magnetic phase diagram is therefore proposed for the Cr1-xAlx alloy system for x in the region of x(t). This study presents novel experimental evidence of exceptional anomalous magnetic behaviour around the TP concentration of the Cr1-xAlx system. It should incite similar studies on other Cr alloy systems with a TP on their magnetic phase diagrams. (C) 2014 Elsevier B. V. All rights reserved.
Title:
Magnetic properties of LaCo12B6 compound as probed by neutron diffraction and by magnetization study under high pressures
Authors:
Diop, LVB; Arnold, Z; Isnard, O; Kamarad, J Author Full Names: Diop, L. V. B.; Arnold, Z.; Isnard, O.; Kamarad, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 593 163-168; 10.1016/j.jallcom.2013.12.216 APR 25 2014
Abstract:
The magnetic properties have been studied by magnetization measurements and the crystal and magnetic structure investigated by neutron diffraction. It is shown that LaCo12B6 compound exhibits an incommensurate conical type magnetic structure. Significantly different magnetic moments have been observed on the two Co crystal sites. The ambient pressure data are compared to that of YCo12B6 isotype and Landau coefficients have been derived from the magnetization curves for both compounds as well as their temperature dependence. The LaCo12B6 compound undergoes a transition from ordered to paramagnetic state at 160 K. The volume dependence of intrinsic magnetic properties of the LaCo12B6 compound has been determined by studies under hydrostatic pressure up to 10 kbar in temperature range 5-200 K. Both the Curie temperature T-C and the spontaneous magnetization M-S decreases with increasing pressure. The observed decrease of M-S with pressure (dM(S)/dp = -7.4 x 10(-3) mu(B)/kbar at 5 K) can be attributed to the pressure induced decrease of Co magnetic moments. The decrease of T-C with pressure (dT(C)/dp = -0.49 K/kbar) is comparable to the decrease observed on RCo12B6 compounds with non-magnetic R and can be attributed to the volume dependence of Co-Co exchange interactions. The remarkable role of the hybridization as a consequence of small distances between Co and B atoms could be a background of this rather unexpected volume stability of magnetic properties. (C) 2014 Elsevier B.V. All rights reserved.
Title:
(3+1)-dimensional crystal and antiferromagnetic structures in CeRuSn
Authors:
Prokes, K; Petricek, V; Ressouche, E; Hartwig, S; Ouladdiaf, B; Mydosh, JA; Hoffmann, RD; Huang, YK; Pottgen, R Author Full Names: Prokes, K.; Petricek, V.; Ressouche, E.; Hartwig, S.; Ouladdiaf, B.; Mydosh, J. A.; Hoffmann, R-D; Huang, Y-K; Poettgen, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (12):10.1088/0953-8984/26/12/122201 MAR 26 2014
Abstract:
At 320 K, the crystal structure of CeRuSn is commensurate with the related CeCoAl-type of structure by the doubling of the c lattice parameter. However, with lowering the temperature it becomes incommensurate with x and z position parameters at all three elemental sites being modulated as one moves along the c-axis. The resulting crystal structure can be conveniently described within the superspace formalism in (3 + 1) dimensions. The modulation vector, after initially strong temperature dependence, approaches a value close to q(nuc) = (0 0 0.35). Below T-N = 2.8 (1) K, CeRuSn orders antiferromagnetically with a propagation vector q(mag) = (0 0 0.175), i.e. with the magnetic unit cell doubled along the c-axis direction with respect to the incommensurate crystal structure. Ce moments appear to be nearly collinear, confined to the a-c plane, forming ferromagnetically coupled pairs. Their magnitudes are modulated between 0.11 and 0.95 mu B as one moves along the c-axis.
Title:
Self-assembly of hydrogen-bonded two-dimensional quasicrystals
Authors:
Wasio, NA; Quardokus, RC; Forrest, RP; Lent, CS; Corcelli, SA; Christie, JA; Henderson, KW; Kandel, SA Author Full Names: Wasio, Natalie A.; Quardokus, Rebecca C.; Forrest, Ryan P.; Lent, Craig S.; Corcelli, Steven A.; Christie, John A.; Henderson, Kenneth W.; Kandel, S. Alex
Source:
NATURE, 507 (7490):86-+; 10.1038/nature12993 MAR 6 2014
Abstract:
The process of molecular self-assembly on solid surfaces is essentially one of crystallization in two dimensions, and the structures that result depend on the interplay between intermolecular forces and the interaction between adsorbates and the underlying substrate(1). Because a single hydrogen bond typically has an energy between 15 and 35 kilojoules per mole, hydrogen bonding can be a strong driver of molecular assembly; this is apparent from the dominant role of hydrogen bonding in nucleic-acid base pairing, as well as in the secondary structure of proteins. Carboxylic acid functional groups, which provide two hydrogen bonds, are particularly promising and reliable in creating and maintaining surface order, and self-assembled monolayers of benzoic acids produce structure that depends on the number and relative placement of carboxylic acid groups(2-6). Here we use scanning tunnelling microscopy to study self-assembled monolayers of ferrocenecarboxylic acid (FcCOOH), and find that, rather than producing dimeric or linear structures typical of carboxylic acids, FcCOOH forms highly unusual cyclic hydrogen-bonded pentamers, which combine with simultaneously formed FcCOOH dimers to form two-dimensional quasicrystallites that exhibit local five-fold symmetry and maintain translational and rotational order (without periodicity) for distances of more than 400 angstroms.
Title:
Ordering and growth of rare gas films (Xe, Kr, Ar, and Ne) on the pseudo-ten-fold quasicrystalline approximant Al13Co4(100) surface
Authors:
Petucci, J; Karimi, M; Huang, YT; Curtarolo, S; Diehl, RD Author Full Names: Petucci, J.; Karimi, M.; Huang, Y-T; Curtarolo, S.; Diehl, R. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (9):10.1088/0953-8984/26/9/095003 MAR 5 2014
Abstract:
Adsorption of the rare gases Kr, Ar, and Ne on the complex alloy surface Al13Co4(100) was studied using grand canonical Monte Carlo (GCMC) computer simulations. This surface is an approximant to the ten-fold decagonal Al-Ni-Co quasicrystalline surface, on which rare gas adsorption was studied previously. Comparison of adsorption results on the periodic Al13Co4(100) surface with those of the quasiperiodic Al-Ni-Co surface indicates some similarities, such as layer-by-layer growth, and some dissimilarities, such as the formation of Archimedes tiling phases (Mikhael et al 2008 Nature 454 501, Shechtman et al 1984 Phys. Rev. Lett. 53 1951, Macia 2006 Rep. Prog. Phys. 69 397, Schmiedeberg et al 2010 Eur. Phys. J. E 32 25-34, Kromer et al 2012 Phys. Rev. Lett. 108 218301, Schmiedeberg and Stark 2008 Phys. Rev. Lett. 101 218302). The conditions under which Archimedes tiling phases (ATP) emerge on Al13Co4(100) are examined and their presence is related to the gas-gas and gas-surface interaction parameters.
Title:
What periodicities can be found in diffraction patterns of quasicrystals?
Authors:
Wolny, J; Kozakowski, B; Kuczera, P; Pytlik, L; Strzalka, R Author Full Names: Wolny, Janusz; Kozakowski, Bartlomiej; Kuczera, Pawel; Pytlik, Lucjan; Strzalka, Radoslaw
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 70 181-185; 10.1107/S2053273313034384 2 MAR 2014
Abstract:
The structure of quasicrystals is aperiodic. Their diffraction patterns, however, can be considered periodic. They are composed solely of series of peaks which exhibit a fully periodic arrangement in reciprocal space. Furthermore, the peak intensities in each series define the so-called 'envelope function'. A Fourier transform of the envelope function gives an average unit cell, whose definition is based on the statistical distribution of atomic coordinates in physical space. If such a distribution is lifted to higher-dimensional space, it becomes the so-called atomic surface - the most fundamental feature of higher-dimensional analysis.
Title:
Hydrogen storage properties of Ti1.4V0.6Ni + x Mg (x=1-3, wt.%) alloys
Authors:
Lin, J; Mang, F; Wu, YM; Liu, WQ; Wang, LM Author Full Names: Lin, Jing; Mang, Fei; Wu, Yaoming; Liu, Wanqiang; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 39 (7):3313-3319; 10.1016/j.ijhydene.2013.12.059 FEB 25 2014
Abstract:
We prepared Ti1.4V0.6Ni ribbons by arc-melting and subsequent melt-spinning techniques. Ti1.4V0.6Ni + x Mg (x = 1, 1.5, 2, 2.5 and 3, wt.%) composite alloys were obtained by the mechanical ball-milling method. The structures and hydrogen storage properties of alloys were investigated. Ti1.4V0.6Ni + x Mg composite alloys contained icosahedral quasicrystalline phase, Ti2Ni-type phase, beta-Ti solid-solution phase and metallic Mg. The electrochemical and gaseous hydrogen storage properties of alloys were improved with Mg addition. Ti1.4V0.6Ni + 2 Mg alloy showed maximum electrochemical discharge capacity of 282.5 mAh g(-1) as well as copacetic high-rate discharge ability of 82.3% at the discharge current density of 240 mA g(-1) compared with that of 30 mA g(-1), and the cycling life achieved above 200 mAh g(-1) after 50 consecutive cycles of charging and discharging. The hydrogen absorption/desorption properties of Ti1.4V0.6Ni + x Mg (x = 1, 2 and 3, wt.%) alloys were better than Ti1.4V0.6Ni. Ti1.4V0.6Ni + 3 Mg alloy also exhibited a favorable hydrogen absorption capacity of 1.53 wt.%. The improvement in the hydrogen storage characteristics caused by adding Mg may be ascribed to better hydrogen diffusion and anti-corrosion ability. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Chemical pressure effects on structural, dielectric and magnetic properties of solid solutions Mn3-xCoxTeO6
Authors:
Ivanov, SA; Mathieu, R; Nordblad, P; Ritter, C; Tellgren, R; Golubko, N; Mosunov, A; Politova, ED; Weil, M Author Full Names: Ivanov, S. A.; Mathieu, R.; Nordblad, P.; Ritter, C.; Tellgren, R.; Golubko, N.; Mosunov, A.; Politova, E. D.; Weil, M.
Source:
MATERIALS RESEARCH BULLETIN, 50 42-56; 10.1016/j.materresbull.2013.10.016 FEB 2014
Abstract:
The effects of Co2+ doping on the structural, magnetic and dielectric properties of the multiferroic frustrated antiferromagnet Mn3TeO6 have been investigated. Ceramic samples of the solid solution series Mn3-xCoxTeO6 were prepared by a solid-state reaction route. X-ray and neutron powder diffraction and electron microscopy techniques were combined with calorimetric, dielectric and magnetic measurements to investigate the dependence of the crystal structure and physical properties on temperature and composition. It is shown that the compounds with x <= 2.4 adopt the trigonal corundum-related structure of pure Mn3TeO6 (space group 18) in the temperature range 5-295 K and that the lattice parameters a and c and the unit-cell volume V decrease linearly with increasing Co2+ concentration. The low-temperature magnetic susceptibility and heat capacity data evidence the antiferromagnetic ordering of all samples. The Neel temperature linearly increases with Co2+ concentration x. Curie-Weiss fits of the high temperature susceptibility indicate that the magnetic frustration decreases with x. The derived magnetic structure of Mn3TeO6 can be described as an incommensurately modulated magnetic spin state with k = [0, 0, k(z)] and an elliptical spin-spiral order of spins within the chains of MnO6 octahedra. With increasing Co2+ concentration the propagation vector kz changes from 0.453 (x = 0) to 0.516 (x = 2.4). The magnetic anisotropy changes as well, leading to a reorientation of the spiral-basal plane. A possible coexistence of long-range order of electrical dipoles and magnetic moments in Mn3-xCoxTeO6 is discussed. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Observation of exchange bias below incommensurate antiferromagnetic (ICAFM) to canted A-type antiferromagnetic (cAAFM) transition in nanocrystalline orthorhombic EuMnO3
Authors:
Das, R; Poddar, P Author Full Names: Das, Raja; Poddar, Pankaj
Source:
RSC ADVANCES, 4 (21):10614-10618; 10.1039/c3ra45435e 2014
Abstract:
Detailed ac and dc magnetic properties of orthorhombic EuMnO3 were studied using a nanocrystalline powder sample. Orthorhombic EuMnO3 nanoparticles of 45 nm average size were synthesised using a hydrothermal method. Zero field cooled (ZFC) and field cooled (FC) magnetisation shows anomalies at similar to 53, 44 and 24 K attributed to paramagnetic (PM) to an incommensurate antiferromagnetic phase (ICAFM), ICAFM to a canted A-type antiferromagnetic order (cAAFM) and spin reorientation transitions, respectively. No indication of a PM to ICAFM transition was observed in either the real or imaginary part of ac magnetisation. The real part of the ac magnetisation curve showed a peak at similar to 24.7 K and anomalies at similar to 46.8 and 21.8 K were observed in the imaginary part of ac magnetisation. Reduction in the width of the thermal hysteresis between the field cooling and heating magnetisation curve was observed with the nanocrystallites (similar to 1 K) compared with the bulk phase (similar to 3 K) EuMnO3. Isothermal magnetisation showed a large value of the exchange bias (2799 Oe at 3 K) below the ICAFM to cAAFM transition temperature.
Title:
Lattice dynamical signature of charge density wave formation in underdoped YBa2Cu3O6+x
Authors:
Bakr, M; Souliou, SM; Blanco-Canosa, S; Zegkinoglou, I; Gretarsson, H; Strempfer, J; Loew, T; Lin, CT; Liang, R; Bonn, DA; Hardy, WN; Keimer, B; Le Tacon, M Author Full Names: Bakr, M.; Souliou, S. M.; Blanco-Canosa, S.; Zegkinoglou, I.; Gretarsson, H.; Strempfer, J.; Loew, T.; Lin, C. T.; Liang, R.; Bonn, D. A.; Hardy, W. N.; Keimer, B.; Le Tacon, M.
Source:
PHYSICAL REVIEW B, 88 (21):10.1103/PhysRevB.88.214517 DEC 31 2013
Abstract:
We report a detailed Raman scattering study of the lattice dynamics in detwinned single crystals of the underdoped high-temperature superconductor YBa2Cu3O6+x (x = 0.75, 0.6, 0.55, and 0.45). Whereas at room temperature the phonon spectra of these compounds are similar to that of optimally doped YBa2Cu3O6.99, additional Raman-active modes appear upon cooling below similar to 170-200Kin underdoped crystals. The temperature dependence of these new features indicates that they are associated with the incommensurate charge density wave state recently discovered using synchrotron x-ray scattering techniques on the same single crystals. Raman scattering thus has the potential to explore the evolution of this state under extreme conditions.

Update: 26-Mar-2014

Title:
Valence Change Driven by Constituent Element Substitution in the Mixed-Valence Quasicrystal and Approximant Au-Al-Yb
Authors:
Matsukawa, S; Tanaka, K; Nakayama, M; Deguchi, K; Imura, K; Takakura, H; Kashimoto, S; Ishimasa, T; Sato, NK Author Full Names: Matsukawa, Shuya; Tanaka, Katsumasa; Nakayama, Mika; Deguchi, Kazuhiko; Imura, Keiichiro; Takakura, Hiroyuki; Kashimoto, Shiro; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 83 (3):10.7566/JPSJ.83.034705 MAR 2014
Abstract:
Quantum criticality has been considered to be specific to crystalline materials such as heavy fermions. Very recently, however, the Tsai-type quasicrystal Au51Al34Yb15 has been reported to show unusual quantum critical behavior. To obtain a deeper understanding of this new material, we have searched for other Tsai-type cluster materials. Here, we report that the metal alloys Au44Ga41Yb15 and Ag47Ga38Yb15 are members of the 1/1 approximant to the Tsai-type quasicrystal and that both possess no localized magnetic moment. We suggest that the Au-Al-Yb system is located near the border of the divalent and trivalent states of the Yb ion; we also discuss a possible origin of the disappearance of magnetism, associated with the valence change, by the substitution of the constituent elements.
Title:
Ordering and dynamical properties of superbright C-60 molecules on Ag(111)
Authors:
Li, HI; Abreu, GJP; Shukla, AK; Fournee, V; Ledieu, J; Loli, LNS; Rauterkus, SE; Snyder, MV; Su, SY; Marino, KE; Diehl, RD Author Full Names: Li, H. I.; Abreu, G. J. P.; Shukla, A. K.; Fournee, V.; Ledieu, J.; Loli, L. N. Serkovic; Rauterkus, S. E.; Snyder, M. V.; Su, S. Y.; Marino, K. E.; Diehl, R. D.
Source:
PHYSICAL REVIEW B, 89 (8):10.1103/PhysRevB.89.085428 FEB 28 2014
Abstract:
C-60 monolayers grown on Ag(111) at room temperature form incommensurate lattices that convert into a commensurate (2 root 3 x 2 root 3)R30 degrees phase upon annealing. The C-60 molecules in the commensurate phase have been observed to exist in three different states on Ag(111), namely bright, dim, and superbright (SB). All three species are in dynamical equilibrium at 280 < T < 440 K. The bright and dim species were the subject of an earlier low-energy electron diffraction study that determined their geometries on the surface and the dynamics of the switching between those two states. The study presented here takes a closer look at the SB molecules, which appear and disappear at temperature-dependent rates with a measured activation barrier of 1.5 eV. The SB molecules in the commensurate phase comprise about 0.5% of the molecules and have a spatially random distribution. The evidence suggests that the formation of the three different states of C-60 on Ag(111) is a result of stress imposed by the substrate as the C-60 adopts the commensurate spacing that is slightly smaller than its natural spacing. In the incommensurate phases, there is no bright-dim contrast, but SB C-60 molecules form and organize into ordered arrays that appear to correspond to the moire patterns that are produced by the mutually incommensurate lattices. This suggests that the substrate responds to the nonuniform forces imposed by the C-60 molecules by producing raised islands of Ag atoms at the vertices of the moire structure. A similar island structure may account for the SB molecules in the commensurate phase.
Title:
Nanotubes from Chalcogenide Misfit Compounds: Sn-S and Nb-Pb-S
Authors:
Radovsky, G; Popovitz-Biro, R; Stroppa, DG; Houben, L; Tenne, R Author Full Names: Radovsky, Gal; Popovitz-Biro, Ronit; Stroppa, Daniel G.; Houben, Lothar; Tenne, Reshef
Source:
ACCOUNTS OF CHEMICAL RESEARCH, 47 (2):406-416; 10.1021/ar400138h FEB 18 2014
Abstract:
Carbon fullerenes and nanotubes revolutionized understanding of the reactivity of nanoscale compounds. Subsequently, our group and others discovered analogous inorganic compounds with hollow, dosed nanostructures. Such inorganic nanostructures offer many applications, particularly in the energy and electronics industries. One way to create inorganic nanostructures is via misfit layered compounds (MLC), which are stacks of alternating two-dimensional molecular slabs, typically held together via weak van der Waals forces. They contain "misfits" in their a-b plane structures that can make them unstable, leading to collapse of the slabs into tubular nanostructures. For example, metal chalcogenide MLCs of the general formula (MX)(1+y)/TX2 (M = Sn, Pb, Bi, Sb, and other rare earths; T= Sn, Ti, V, Cr, Nb,Ta, etc; X = S or Se) consist of a superstructure of alternating layers where the MX unit belongs to a (distorted NaCl) orthorhombic symmetry group (O), the TX2 layer possesses trigonal (T) or octahedral symmetry, and the two layers are held together via both van der Waals and polar forces. A misfit in the a axis or both a and b axes of the two sublattices may lead to the formation of nanostructures as the lattices relax via scrolling. Previous research has also shown that the abundance of atoms with dangling bonds in the rims makes nanoparticles of compounds with layered structure unstable in the planar form, and they tend to fold into hollow closed structures such as nanotubes. This Account shows that combining these two triggers, misfits and dangling bond annihilation in the slab rims, leads to new kinds of nanotubes from MLCs. In particular, we report the structure of two new types of nanotubes from misfits, namely, the SnS/SnS2 and PbS/NbS2 series. To decipher the complex structures of these nanotubes, we use a range of methods: high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED) analyses, scanning electron microscopy (SEM), and Cs-corrected scanning transmission electron microscopy (STEM) in the high-angle annular dark-field mode (HAADF). In both new types, the lattice mismatch between the two alternating sublayers dictates the relative layer-stacking order and leads to a variety of chiral tubular structures. In particular, the incommensuration (a type of misfit) of the SnS2/SnS system in both the (in plane) a and b directions leads to a variety of relative in-plane orientation and stacking orders along the common c-axis. Thus the SnS/SnS2 nanotubes form superstructures with the sequence O-T and O-T-T, and mixtures thereof. We also report nanotubes of the misfit layered compound (PbS)(1.14)NbS2, and of NbS2 intercalated with Pb atoms, with the chemical formula PbNbS2. Thus, the possibility to use two kinds of folding mechanisms jointly offers a new apparatus for the synthesis of unique 1-D nanostructures of great complexity and a potentially large diversity of physicochemical properties.
Title:
On the nature of phase transitions in the tetragonal tungsten bronze GdK2Nb5O15 ceramics
Authors:
Gagou, Y; Amira, Y; Lukyanchuk, I; Mezzane, D; Courty, M; Masquelier, C; Yuzyuk, YI; El Marssi, M Author Full Names: Gagou, Y.; Amira, Y.; Lukyanchuk, I.; Mezzane, D.; Courty, M.; Masquelier, C.; Yuzyuk, Yu. I.; El Marssi, M.
Source:
JOURNAL OF APPLIED PHYSICS, 115 (6):10.1063/1.4865741 FEB 14 2014
Abstract:
Phase transitions in gadolinium potassium niobate GdK2Nb5O15 (GKN) ceramics have been investigated by x-ray diffraction, dielectric susceptibility, differential scanning calorimetry, and Raman scattering. The results of our complementary studies show that GKN exhibits two phase transitions at T-c1 = 238 degrees C and T-c2 = 375 degrees C attributed to the ferroelectric-antiferroelectric-paraelectric (FE-AFE-PE) phase transitions. According to the x-ray diffraction analysis, the FE and PE phases were refined in the polar P4bm and centrosymmetric P4/mbm space groups. For the intermediate phase, the structure is refined in the space group P4nc with doubling of the c unit cell parameter, which is compatible with an AFE phase. This result was confirmed by Raman spectroscopy since new low-frequency lines are activated in the AFE phase due to the Brillouin zone-folding effect, typical for the modulated phases. The presence of the AFE phase between the FE and PE phases and the complex nature of tetragonal tungsten bronze crystal structure can explain the large thermal hysteresis observed at the FE-AFE transition between heating and cooling cycle and the strong depression of the Curie-Weiss temperature T-0. The semi-phenomenological Ising-like model based on the obtained experimental data is proposed to account for the observed FE-AFE-PE transition sequence. (C) 2014 AIP Publishing LLC.
Title:
High magnetic field evolution of ferroelectricity in CuCrO2
Authors:
Mun, E; Frontzek, M; Podlesnyak, A; Ehlers, G; Barilo, S; Shiryaev, SV; Zapf, VS Author Full Names: Mun, Eundeok; Frontzek, M.; Podlesnyak, A.; Ehlers, G.; Barilo, S.; Shiryaev, S. V.; Zapf, Vivien S.
Source:
PHYSICAL REVIEW B, 89 (5):10.1103/PhysRevB.89.054411 FEB 12 2014
Abstract:
CuCrO2 offers insights into the different types of spiral magnetic orderings that can form spontaneously due to frustration in triangular-lattice antiferromagnets. We explore the magnetic phase diagram up to 65 T along all the principal axes, and also use electric polarization to probe changes in the spiral order at high magnetic fields. It is known that at zero magnetic field a proper-screw spiral of the Cr S = 3/2 spins forms that in turn induces electric polarization with six possible orientations in the ab plane. Applied magnetic fields in the (hard) ab plane have been shown to induce a transition to cycloidal-spiral magnetic order above 5.3 T in those domains that have spins perpendicular to the applied magnetic field. We show that the cycloidal order remains unchanged all the way up to 65 T, which is one quarter of the extrapolated saturation magnetization. On the other hand, for magnetic fields along the (easy) c axis, we observe a transition in the electric polarization near 45 T, and it is followed by a series of steps and/or oscillations in the electric polarization. The data are consistent with a proper-screw-to-cycloidal transition that is pushed from 5.3 to 45 T by easy-axis anisotropy, and is in turn followed by stretching of the magnetic spiral through commensurate and incommensurate wave vectors. This work also highlights the ability of the magnetically induced electric polarization to probe complex magnetic orders in regimes of phase space that are difficult to reach with neutron diffraction.
Title:
Self-generation of dissipative solitons in magnonic quasicrystal active ring resonator
Authors:
Grishin, SV; Beginin, EN; Morozova, MA; Sharaevskii, YP; Nikitov, SA Author Full Names: Grishin, S. V.; Beginin, E. N.; Morozova, M. A.; Sharaevskii, Yu. P.; Nikitov, S. A.
Source:
JOURNAL OF APPLIED PHYSICS, 115 (5):10.1063/1.4864133 FEB 7 2014
Abstract:
Self-generation of dissipative solitons in the magnonic quasicrystal (MQC) active ring resonator is studied theoretically and experimentally. The developed magnonic crystal has quasiperiodic Fibonacci type structure. Frequency selectivity of the MQC together with the parametric three-wave decay of magnetostatic surface spin wave (MSSW) leads to the dissipative soliton self-generation. The transfer matrix method is used to describe MQC transmission responses. Besides, the model of MQC active ring resonator is suggested. The model includes three coupled differential equations describing the parametric decay of MSSW and two differential equations of linear oscillators describing the frequency selectivity of MQC. Numerical simulation results of dissipative soliton self-generation are in a fair agreement with experimental data. (C) 2014 AIP Publishing LLC.
Title:
Spin-density-wave ordering in Ca0.5Sr1.5RuO4 studied by neutron scattering
Authors:
Kunkemoller, S; Nugroho, AA; Sidis, Y; Braden, M Author Full Names: Kunkemoeller, S.; Nugroho, A. A.; Sidis, Y.; Braden, M.
Source:
PHYSICAL REVIEW B, 89 (4):10.1103/PhysRevB.89.045119 JAN 14 2014
Abstract:
The spin-density-wave ordering in Ca0.5Sr1.5RuO4 was studied by polarized and unpolarized neutron diffraction experiments. Below about 20 K Ca0.5Sr1.5RuO4 exhibits quasistatic correlations at exactly the incommensurate wave vector at which pure Sr2RuO4 shows strong inelastic fluctuations driven by Fermi-surface nesting. The magnetic character of the signal and the orientation of the ordered moments along the c direction can be ascertained by neutron polarization analysis. The magnetic ordering at low temperature is very similar to that found upon minor Ti substitution of Sr2RuO4, underlining that this incommensurate spin density wave is the dominant magnetic instability of the unconventional superconductor Sr2RuO4.
Title:
Vector-spin-chirality order in a dimerized frustrated spin-1/2 chain
Authors:
Ueda, H; Onoda, S Author Full Names: Ueda, Hiroshi; Onoda, Shigeki
Source:
PHYSICAL REVIEW B, 89 (2):10.1103/PhysRevB.89.024407 JAN 10 2014
Abstract:
A frustrated spin-1/2 XXZ chain model comprising a ferromagnetic nearest-neighbor coupling with the bond alternation, J(1)(1 +/- delta) < 0, and an antiferromagnetic second-neighbor exchange coupling J(2) > 0 is studied at zero and weak magnetic fields by means of density-matrix renormalization-group calculations of order parameters, correlation functions, and the entanglement entropy, as well as an Abelian bosonization analysis. At zero magnetic field, the bond alternation delta > 0 suppresses the gapless phase characterized by a vector-chiral (VC) long-range order (LRO) and a quasi-LRO of an incommensurate spin spiral, whereas this phase occupies a large region in the space of J(1)/J(2) and the easy-plane exchange anisotropy for delta = 0 [S. Furukawa et al., Phys. Rev. Lett. 105, 257205 (2010)]. Then, four gapped phases are found to appear as the exchange anisotropy varies from the SU(2)-symmetric case to the U(1)-symmetric case: the Haldane dimer (D+) phase with the same sign of the x, y- and z-component dimer order parameters, two VC dimer (VCD+/VCD-) phases with the sign of the z-component dimer order parameter being unaltered/reversed, and the even-parity dimer (D-) phase. At small magnetic fields, a field-induced ring-exchange interaction, which is proportional to a staggered scalar chirality and a magnetic flux penetrating the associated triangle, drives a transition from the D- phase into a VC-Neel-dimer (VCND) phase, but not from the D+ phase. This VCND phase is stable up to the large magnetic field at which the Zeeman term closes the spin gap. A possible relevance to Rb2Cu2Mo3O12 is discussed.
Title:
Collective modes in quasi-one-dimensional charge-density wave systems probed by femtosecond time-resolved optical studies
Authors:
Schaefer, H; Kabanov, VV; Demsar, J Author Full Names: Schaefer, H.; Kabanov, V. V.; Demsar, J.
Source:
PHYSICAL REVIEW B, 89 (4):10.1103/PhysRevB.89.045106 JAN 6 2014
Abstract:
The interplay between the electronic and structural subsystems has strong implications on the character of collective excitations in cooperative systems. Their detailed understanding can provide important information on the coupling mechanisms and coupling strengths in such systems. With the recent developments in femtosecond time-resolved optical probes, numerous advantages with respect to conventional time-integrated probes have been put forward. Owing to their high dynamic range, high-frequency resolution, fast data acquisition, and an inherent access to phases of coherent excitations, they provide direct access to the interplay between various degrees of freedom. In this paper, we present a detailed analysis of time-resolved optical data on blue bronzes (K0.3MoO3 and Rb0.3MoO3), prototype quasi-one-dimensional charge-density wave (CDW) systems. Numerous coherent (Raman active) modes appear upon the phase transition into the CDW state. We analyze the temperature dependence of mode frequencies, their damping times, as well as their oscillator strengths and phases using the time-dependent Ginzburg-Landau model. We demonstrate that these low-temperature modes are a result of linear coupling between the Fermi surface nesting driven modulation of the conduction electron density and the normal-state phonons at the CDW wave vector, and determine their coupling strengths. Moreover, we are able to identify the nature of excitation of these coupled modes, as well as the nature of the probing mechanisms in this type of experiments. We demonstrate that in incommensurate CDW systems, femtosecond optical excitation initially suppresses the electronic density modulation, while the reflectivity changes at frequencies far above the CDW induced gap in the single-particle excitation spectrum are governed by the modulation of interband transitions caused by lattice motion. This approach can be readily extended to more complex systems with spatially modulated ground states.
Title:
Wear and Friction Properties of Mg-Zn-Y Alloy with Dispersion of Quasi-Crystalline Phase
Authors:
Somekawa, H; Shimoda, A; Hirayama, T; Matsuoka, T; Mukai, T Author Full Names: Somekawa, Hidetoshi; Shimoda, Atsushi; Hirayama, Tomoko; Matsuoka, Takashi; Mukai, Toshiji
Source:
MATERIALS TRANSACTIONS, 55 (7):216-219; 10.2320/matertrans.M2013301 JAN 2014
Abstract:
The wear and friction properties of the Mg-Zn-Y alloys with a dispersion of the quasi-crystalline phase were investigated using the pin-on-disk configuration. The wear loss rates and the friction coefficient were obtained to be 1.95 x 10(-5)mm(3)/mm and 0.26 in the casted alloy, 1.75 x 10(-5)mm(3)/mm and 0.24 in the heat-treated alloy, 2.40 x 10(-5)mm(3)/mm and 0.24 in the extruded alloy, respectively, under the dry wear condition. An effective method to enhance the wear properties in the magnesium alloys was determined to be a homogenous distribution of the quasi-crystalline phase in the coarse-grained matrix. Meanwhile, the grain refinement was not suitable due to grain boundary sliding, i.e., materials softening.
Title:
Geometrically frustrated magnetism of spins on icosahedral clusters: The Gd3Au13Sn4 quasicrystalline approximant
Authors:
Kozelj, P; Jazbec, S; Vrtnik, S; Jelen, A; Dolinsek, J; Jagodic, M; Jaglicic, Z; Boulet, P; de Weerd, MC; Ledieu, J; Dubois, JM; Fournee, V Author Full Names: Kozelj, P.; Jazbec, S.; Vrtnik, S.; Jelen, A.; Dolinsek, J.; Jagodic, M.; Jaglicic, Z.; Boulet, P.; de Weerd, M. C.; Ledieu, J.; Dubois, J. M.; Fournee, V.
Source:
PHYSICAL REVIEW B, 88 (21):10.1103/PhysRevB.88.214202 DEC 26 2013
Abstract:
By investigating the magnetism of spins on a quasiperiodic lattice, we present an experimental study of static and dynamic magnetic properties, specific heat, and magnetic entropy of the Gd3Au13Sn4 quasicrystalline approximant. The magnetic sublattice of Gd3Au13Sn4 is a periodic arrangement of nonoverlapping spin clusters of almost perfect icosahedral symmetry, where gadolinium localized f magnetic moments are distributed on equilateral triangles. The absence of disorder on the magnetic sublattice and the antiferromagnetic (AFM) interactions between the nearest-neighbor spins distributed on triangles result in geometrical frustration of spin-spin interactions. Thus, the Gd3Au13Sn4 phase can be viewed as a prototype site-ordered, geometrically frustrated spin system on icosahedral clusters. The zero-field-cooled and field-cooled magnetic susceptibilities, the alternating current susceptibility, the thermoremanent magnetization, the memory effect, the magnetic specific heat, and the magnetic entropy all show that the spin system undergoes at low temperatures a transition to a nonergodic state at the spin freezing temperature T-f approximate to 2.8 K. Below this, the ergodicity is broken on the experimental timescale, because the thermally activated correlation times for the spin reorientations become macroscopically long. The magnetic state achieved at low temperatures by continuous cooling in low magnetic fields is likely a superposition of (1) metastable states with randomly frozen spins that have no long-range order yet undergo gradual spin-freezing dynamics and (2) an AFM-like magnetically ordered state with critical slowing dynamics. The magnetic properties of the site-ordered, geometrically frustrated Gd3Au13Sn4 system are discussed in comparison to site-disordered spin glasses that contain both randomness and frustration.

Update: 20-Mar-2014

Title:
The incommensurate modulations of stoichiometric Ni2MnGa
Authors:
Mariager, SO; Huber, T; Ingold, G Author Full Names: Mariager, S. O.; Huber, T.; Ingold, G.
Source:
ACTA MATERIALIA, 66 192-198; 10.1016/j.actamat.2013.11.077 MAR 2014
Abstract:
We use X-ray diffraction to confirm that the 5M phase of the stoichiometric Hensler alloy Ni2MnGa has an incommensurate modulation with wavevector q = [0.428 0.428 0]. We find the crystal to be macroscopically twinned with a structure well described by the theory of martensitic phase transitions, though theoretical calculations of the X-ray diffraction rule out the existence of an adaptive phase. The premartensite phase is found to be slightly incommensurate with q =[0.341 0.341 0]. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Pressure-Induced Quantum Critical and Multicritical Points in a Frustrated Spin Liquid
Authors:
Thede, M; Mannig, A; Mansson, M; Huvonen, D; Khasanov, R; Morenzoni, E; Zheludev, A Author Full Names: Thede, M.; Mannig, A.; Mansson, M.; Huevonen, D.; Khasanov, R.; Morenzoni, E.; Zheludev, A.
Source:
PHYSICAL REVIEW LETTERS, 112 (8):10.1103/PhysRevLett.112.087204 FEB 25 2014
Abstract:
The quantum spin-liquid compound (C4H12N2)Cu2Cl6 is studied by muon spin relaxation under hydrostatic pressures up to 23.6 kbar. At low temperatures, pressure-induced incommensurate magnetic order is detected beyond a quantum critical point at P-c similar to 4.3 kbar. An additional phase transition to a different ordered phase is observed at P-1 similar to 13.4 kbar. The data indicate that the high-pressure phase may be a commensurate one. The established (P-T) phase diagram reveals the corresponding pressure-induced multicritical point at P-1, T-1 = 2.0 K.
Title:
Generic Spin Model for the Honeycomb Iridates beyond the Kitaev Limit
Authors:
Rau, JG; Lee, EKH; Kee, HY Author Full Names: Rau, Jeffrey G.; Lee, Eric Kin-Ho; Kee, Hae-Young
Source:
PHYSICAL REVIEW LETTERS, 112 (7):10.1103/PhysRevLett.112.077204 FEB 20 2014
Abstract:
Recently, realizations of Kitaev physics have been sought in the A(2)IrO(3) family of honeycomb iridates, originating from oxygen-mediated exchange through edge-shared octahedra. However, for the j(eff) = 1/2 Mott insulator in these materials, exchange from direct d-orbital overlap is relevant, and it was proposed that a Heisenberg term should be added to the Kitaev model. Here, we provide the generic nearest-neighbor spin Hamiltonian when both oxygen-mediated and direct overlap are present, containing a bond-dependent off-diagonal exchange in addition to Heisenberg and Kitaev terms. We analyze this complete model using a combination of classical techniques and exact diagonalization. Near the Kitaev limit, we find new magnetic phases, 120 degrees and incommensurate spiral order, as well as extended regions of zigzag and stripy order. Possible applications to Na2IrO3 and Li2IrO3 are discussed.
Title:
Origin of {332} twinning in metastable beta-Ti alloys
Authors:
Tobe, H; Kim, HY; Inamura, T; Hosoda, H; Miyazaki, S Author Full Names: Tobe, Hirobumi; Kim, Hee Young; Inamura, Tomonari; Hosoda, Hideki; Miyazaki, Shuichi
Source:
ACTA MATERIALIA, 64 345-355; 10.1016/j.actamat.2013.10.048 FEB 2014
Abstract:
In this paper, the origin of {3 3 2}< 1 1 (3) over bar > twinning, which is a unique twinning mode in metastable beta-Ti alloys, was investigated. The possible twinning modes in metastable beta-Ti alloys are derived by considering lattice instability in addition to the theory of the crystallography of deformation twinning. In order to consider lattice instability in the body-centered-cubic (bcc) structure, a modulated structure was proposed. We then clarify how the modulated structure facilitates {3 3 2}< 1 1 (3) over bar > twinning preferentially compared to other possible twinning modes by evaluating the magnitude of twinning shear and the complexity of shuffle. It was found that the lattice instability makes {1 1 2}<(1) over bar (1) over bar 1 > twinning, which is a major twinning mode observed in alloys with stable bcc structure, unlikely to occur because the lattice modulation causes additional shuffling to form the {1 1 2}<(1) over bar (1) over bar 1 > twin. It was also found that {3 3 2}<(1) over bar (1) over bar 3 > twinning is the most possible twinning mode in the modulated structure in terms of the magnitude of twinning shear and the complexity of shuffle. The new formation model of the {3 3 2} < 1 1 (3) over bar > twin presented in this study can explain how the lattice instability preferentially activates the {3 3 2}< 1 1 (3) over bar > twinning in metastable beta-Ti alloys. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Growth and Characterization of Ba(2)LnFeNb(4)O(15) (Ln = Pr, Nd, Sm, Eu) Relaxor Single Crystals
Authors:
Albino, M; Veber, P; Pechev, S; Labrugere, C; Velazquez, M; Maglione, M; Josse, M Author Full Names: Albino, Marjorie; Veber, Philippe; Pechev, Stanislav; Labrugere, Christine; Velazquez, Matias; Maglione, Mario; Josse, Michael
Source:
CRYSTAL GROWTH & DESIGN, 14 (2):500-512; 10.1021/cg401181j FEB 2014
Abstract:
Ba(2)LnFeNb(4)O(15) (Ln = Pr, Nd, Sm, and Eu) single crystals were grown from high-temperature solution under controlled atmosphere. Chemical, structural, and dielectric characterizations were performed on four crystals with tetragonal tungsten bronze (TTB) structure. The main difference between the four crystals' compositions is the proportion of rare-earth, as well as vacancies, located in the square site. All crystals displayed an incommensurately modulated structure at room temperature in the paraelectric state. The corresponding basic structures were refined using the P4/mbm space group (R = 0.0274; 0.0416; 0.0328; 0.0357 for Ln = Pr, Nd, Sm, and Eu, respectively). Examination of the structural parameters confirmed the central role played by square-shaped channels in the crystal chemistry of these materials. All crystals display a relaxor behavior with T-m (1 MHz) ranging from 110 to 270 K. The chemical, structural, and physical properties of the crystals are discussed and compared, for the latter, with those of corresponding ceramics.
Title:
Effect of mechanical processing on the stability of metastable icosahedral quasicrystalline nanoparticles in zirconium and hafnium based metallic glasses
Authors:
Li, CF; Li, DQ; Solomon, V; Bauer, M; McCauley, T; Berrier, S Author Full Names: Li, Chunfei; Li, Dingqiang; Solomon, Virgil; Bauer, Michael; McCauley, Tyler; Berrier, Shannon
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 381 68-72; 10.1016/j.jnoncrysol.2013.09.023 DEC 1 2013
Abstract:
Metastable icosahedral quasicrystalline nanoparticles precipitate in the initial crystallization processes of some selected zirconium and hafnium based metallic glasses. All such particles reported so far are embedded in residual glassy matrix. It is predicted that, if these are separated as free standing particles, they can be applied in a variety of fields. Breaking the suitably annealed metallic glasses to small pieces by mechanical approaches is considered to be the first step toward this goal. The result of such an attempt is reported here. Several previously reported metallic glasses such as Zr70Cu27.5Rh2.5 and Hf69.5Al7.5Ni11Cu12 have been abraded by using regular sandpapers and diamond papers, scraped with diamond scratchers, and sliced by using microtome. Thus obtained small pieces have been examined by Scanning Electron Microscope, Transmission Electron Microscope, and Energy Dispersive X-ray Spectroscopy. It has been revealed that the mechanical breaking processes cause an undesired phase transformation Of the quasicrystalline nanoparticles to the crystalline phases. The reason for this undesired phase transformation was analyzed and the appropriate procedures to avoid this negative effect for future work were suggested. (C) 2013 Elsevier B.V. All rights reserved.

Update: 12-Mar-2014

Title:
Understanding the multiple magnetic structures of the intermetallic compound NdMn1.4Co0.6Si2
Authors:
Halder, M; Bera, AK; Kumar, A; Keller, L; Yusuf, SM Author Full Names: Halder, Madhumita; Bera, A. K.; Kumar, Amit; Keller, L.; Yusuf, S. M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 592 86-91; 10.1016/j.jallcom.2013.12.247 APR 15 2014
Abstract:
Magnetic phases for the intermetallic compound NdMn1.4Co0.6Si2 have been investigated at various temperatures by dc magnetization, neutron diffraction and neutron depolarization. Our study shows multiple magnetic phase transitions with temperature (T) over 1.5-300 K. In agreement with dc-magnetization and neutron depolarization results, the temperature dependence of the neutron diffraction patterns shows five distinct regions with different magnetic phases. These temperature regions are (i) T >= 215 K, (ii) 215 K > T >= 50 K, (iii) 50 K > T >= 40 K, (iv) 40 K > T > 15 K, and (v) T <= 15 K. The corresponding magnetic structures are paramagnetic, commensurate collinear antiferromagnetic (AFM-I), incommensurate AFM (AFM-II), mixed ferromagnetic and AFM (FM + AFM-II), and incommensurate AFM (AFM-II), respectively. (C) 2014 Elsevier B.V. All rights reserved.
Title:
The elastodynamic model of wave-telegraph type for quasicrystals
Authors:
Agiasofitou, E; Lazar, M Author Full Names: Agiasofitou, Eleni; Lazar, Markus
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 51 (5):923-929; 10.1016/j.ijsolstr.2013.11.016 MAR 1 2014
Abstract:
In this work we propose the elastodynamic model of wave-telegraph type for the description of dynamics of quasicrystals. Phonons are represented by waves, and phasons by waves damped in time and propagating with finite velocity. Therefore, the equations of motion for the phonon fields are of wave type and for the phason fields are of telegraph type. The proposed model constitutes a unified theory in the sense that already established models in the literature can be recovered as asymptotic cases of it. The equations of motion for the displacement fields in the theory of incompatible and compatible elastodynamics of wave-telegraph type of quasicrystals are derived. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Anomalous electronic transport in quasicrystals and related complex metallic alloys
Authors:
de Laissardiere, GT; Mayou, D Author Full Names: de Laissardiere, Guy Trambly; Mayou, Didier
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):70-81; 10.1016/j.crhy.2013.09.010 JAN 2014
Abstract:
We analyse the transport properties in approximants of quasicrystals alpha-AlMnSi, 1/1-AlCuFe and for the complex metallic phase lambda-AlMn. These phases present strong analogies in their local atomic structures and are related to existing quasicrystalline phases. Experimentally, they present unusual transport properties with low conductivities and a mix of metallic-like and insulating-like characteristics We compute the band structure and the quantum diffusion in the perfect structure without disorder and introduce simple approximations that allow us to treat the effect of disorder. Our results demonstrate that the standard Bloch-Boltzmann theory is not applicable to these intermetallic phases. Indeed their dispersion relations are flat, indicating small band velocities, and corrections to quantum diffusion, which are not taken into account in the semi-classical Bloch-Boltzmann scheme, become dominant. We call this regime the small velocity regime. A simple relaxation time approximation to treat the effect of disorder allows us to reproduce the main experimental facts on conductivity qualitatively and even quantitatively. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Prolegomena of quasicrystals
Authors:
Friedel, J Author Full Names: Friedel, Jacques
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):3-5; 10.1016/j.crhy.2013.09.001 JAN 2014
Abstract:
The first published observations of quasicrystals in metallic alloys were in harmony with the increasing complexity of the structural description of possible solid phases, due to specific properties of the magnetic and electric charges of electrons. This led to the complex crystal phases of Frank and Kasper and Meyer's prediction of quasicrystalline structures with original diffraction properties in the reciprocal space and local symmetries not allowed for crystals. The initial works on two-dimensional tilings by Penrose and others clarified the problems involved. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Crystal chemistry and chemical order in ternary quasicrystals and approximants
Authors:
Gomez, CP; Tsai, AP Author Full Names: Gomez, Cesar Pay; Tsai, An Pang
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):30-39; 10.1016/j.crhy.2013.10.007 JAN 2014
Abstract:
In this work we review our current understanding of structure, stability and formation of icosahedral quasicrystals and approximants. The work has special emphasis on Cd-Yb type phases, but several concepts are generalized to other families of icosahedral quasicrystals and approximants. The paper handles topics such as chemical order and site preference at the cluster level for ternary phases, valence electron concentration and its influence on formation and composition, fundamental building blocks and cluster linkages, and the similarities and differences between different families of icosahedral quasicrystals and approximants. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Dynamics of quasicrystals
Authors:
Janssen, T; de Boissieu, M Author Full Names: Janssen, Ted; de Boissieu, Marc
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):58-69; 10.1016/j.crhy.2013.09.011 JAN 2014
Abstract:
The (lattice) dynamics of quasicrystals differs in many aspects from that of lattice periodic systems. This they have in common with other aperiodic crystals. The dynamics of quasicrystals is discussed here in the context of these general aperiodic crystals, but the special features of quasicrystals are stressed. The lattice dynamics is now fairly well understood. Especially for aperiodic crystals, there are excitations related to the possibility to describe the systems in superspace. These 'phasons' are discussed in particular. (C) 2013 Published by Elsevier Masson SAS on behalf of Academie des sciences.
Title:
Surfaces of quasicrystals
Authors:
Ledieu, J; Fournee, V Author Full Names: Ledieu, Julian; Fournee, Vincent
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):48-57; 10.1016/j.crhy.2013.09.009 JAN 2014
Abstract:
The remarkable surface properties of quasicrystals have motivated extensive investigations of their intrinsic atomic and electronic structures. In this article, we summarize some of the main conclusions obtained so far. We also describe adsorption experiments where quasiperiodic surfaces are used as templates to grow thin films with novel structures. Finally we discuss some of their useful properties of current interest. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Decagonal quasicrystals - What has been achieved?
Authors:
Steurer, W; Deloudi, S Author Full Names: Steurer, Walter; Deloudi, Sofia
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):40-47; 10.1016/j.crhy.2013.09.007 JAN 2014
Abstract:
Where are we now, 25 years after the discovery of the first stable decagonal quasicrystal (DQC)? In this critical review, the status of research into these axial quasicrystals, which are quasiperiodic in two dimensions and periodic along the third, is discussed, and some of the open questions are addressed. We conclude that the structures of DQC are essentially known now, a few of them even as a function of temperature. Some hypotheses concerning DQC formation, growth and stability have still to be confirmed. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Quasicrystals, model sets, and automatic sequences
Authors:
Allouche, JP; Meyer, Y Author Full Names: Allouche, Jean-Paul; Meyer, Yves
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):6-11; 10.1016/j.crhy.2013.09.002 JAN 2014
Abstract:
We survey mathematical properties of quasicrystals, first from the point of view of harmonic analysis, then from the point of view of morphic and automatic sequences. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
About the atomic structures of icosahedral quasicrystals
Authors:
Quiquandon, M; Gratias, D Author Full Names: Quiquandon, Marianne; Gratias, Denis
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):18-29; 10.1016/j.crhy.2013.09.008 JAN 2014
Abstract:
This paper is a survey of the crystallographic methods that have been developed these last twenty five years to decipher the atomic structures of the icosahedral stable quasicrystals since their discovery in 1982 by D. Shechtman. After a brief recall of the notion of quasiperiodicity and the natural description of Z-modules in 3-dim as projection of regular lattices in N > 3-dim spaces, we give the basic geometrical ingredients useful to describe icosahedral quasicrystals as irrational 3-dim cuts of ordinary crystals in 6-dim space. Atoms are described by atomic surfaces (ASs) that are bounded volumes in the internal (or perpendicular) 3-dim space and the intersections of which with the physical space are the actual atomic positions. The main part of the paper is devoted to finding the major properties of quasicrystalline icosahedral structures. As experimentally demonstrated, they can be described with a surprisingly few high symmetry ASs located at high symmetry special points in 6-dim space. The atomic structures are best described by aggregations and intersections of high symmetry compact interpenetrating atomic clusters. We show here that the experimentally relevant clusters are derived from one generic cluster made of two concentric triacontahedra scaled by tau and an external icosidodecahedron. Depending on which ones of the orbits of this cluster are eventually occupied by atoms, the actual atomic clusters are of type Bergman, Mackay, Tsai and others.... (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Dislocations and mechanical properties of icosahedral quasicrystals
Authors:
Mompiou, F; Caillard, D Author Full Names: Mompiou, Frederic; Caillard, Daniel
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):82-89; 10.1016/j.crhy.2013.09.003 JAN 2014
Abstract:
In this article we interpret the mechanical properties of icosahedral quasicrystals with the dislocation theory. After having defined the concept of dislocation in a periodic crystal, we extend this notion to quasicrystals in the 6-dimensional space. We show that perfect dislocations and imperfect dislocations trailing a phason fault can be defined and observed in transmission electron microscopy (TEM). In-situ straining TEM experiments at high temperature show that dislocations move solely by climb, a non-conservative motion-requiring diffusion. This behavior at variance with that of crystals which deform mainly by glide is explained by the atypical nature of the atomic structure of icosahedral quasicrystals. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Quasicrystals and atomic clusters
Authors:
Guyot, P; Audier, M Author Full Names: Guyot, Pierre; Audier, Marc
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):12-17; 10.1016/j.crhy.2013.10.005 JAN 2014
Abstract:
Historically, two principal approaches exist to determine the quasicrystal atomic structures: one is derived directly from diffraction experiments, using cut and projection of higher dimensional space-representation techniques; the other one takes use of the similarity between so-called approximant crystalline phases, observed to co-exist with quasicrystals. The known structure of these phases is shown to be the starting point of building a quasicrystal model in terms of constitutive polyatomic clusters of icosahedral symmetry. It requires to apply inflation properties of quasiperiodicity, and decoration of elementary building tiles. One example is detailed and discussed, in terms of a two-cluster model, in the case of AlLiCu. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Spin wave spectra and spatially modulated structures in BiFeO3
Authors:
Popkov, AF; Kulagin, NE; Soloviov, SV; Gareeva, ZV; Zvezdin, AK Author Full Names: Popkov, A. F.; Kulagin, N. E.; Soloviov, S. V.; Gareeva, Z. V.; Zvezdin, A. K.
Source:
LOW TEMPERATURE PHYSICS, 40 (1):58-64; 10.1063/1.4862464 JAN 2014
Abstract:
The spin wave spectra of antiferromagnetic BiFeO3-type multiferronics are analyzed theoretically. The presence of a spatially modulated cycloidal antiferromagnetic structure leads to a countable number of frequency branches of two oscillatory modes (Goldstone and activation) for spin waves propagating along a cycloid. When there is no magnetic field and anisotropy, the magnon spectrum is characterized by the absence of frequency gaps. The spectral features of the spin oscillations with changing anisotropy and application of a magnetic field are identified and the limits on the existence of an antiferromagnetic cycloid are established up to its transformation into a conical structure. In the transverse direction the spin oscillations have a mixed character which indicates that the cycloid is stable with respect to bending throughout its domain of existence. (C) 2014 AIP Publishing LLC.

Update: 26-Feb-2014

Title:
Lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and the cubic 1/1-approximant Zn6Sc
Authors:
Euchner, H; Yamada, T; Rols, S; Ishimasa, T; Ollivier, J; Schober, H; Mihalkovic, M; de Boissieu, M Author Full Names: Euchner, H.; Yamada, T.; Rols, S.; Ishimasa, T.; Ollivier, J.; Schober, H.; Mihalkovic, M.; de Boissieu, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (5):10.1088/0953-8984/26/5/055402 FEB 5 2014
Abstract:
A comparison of periodic approximants and their quasicrystalline counterparts offers the opportunity to better understand the structure, physical properties and stabilizing mechanisms of these complex phases. We present a combined experimental and computational study of the lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and compare these to the lattice dynamics of the cubic 1/1-approximant Zn6Sc. The two phases, quasicrystal and approximant, are built up from the same atomic clusters, which are packed either quasiperiodically or on a body centered cubic lattice, respectively. Using inelastic neutron scattering and atomic scale simulations, we show that the vibrational spectra of these three systems are very similar, however, they contain a clear signature of the increasing structural complexity from approximant to quasicrystal.
Title:
A complex pseudo-decagonal quasicrystal approximant, Al-37(Co,Ni)(15.5), solved by rotation electron diffraction
Authors:
Singh, D; Yun, YF; Wan, W; Grushko, B; Zou, XD; Hovmoller, S Author Full Names: Singh, Devinder; Yun, Yifeng; Wan, Wei; Grushko, Benjamin; Zou, Xiaodong; Hovmoller, Sven
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 47 215-221; 10.1107/S1600576713029294 1 JAN 2014
Abstract:
Electron diffraction is a complementary technique to single-crystal X-ray diffraction and powder X-ray diffraction for structure solution of unknown crystals. Crystals too small to be studied by single-crystal X-ray diffraction or too complex to be solved by powder X-ray diffraction can be studied by electron diffraction. The main drawbacks of electron diffraction have been the difficulties in collecting complete three-dimensional electron diffraction data by conventional electron diffraction methods and the very time-consuming data collection. In addition, the intensities of electron diffraction suffer from dynamical scattering. Recently, a new electron diffraction method, rotation electron diffraction (RED), was developed, which can overcome the drawbacks and reduce dynamical effects. A complete three-dimensional electron diffraction data set can be collected from a sub-micrometre-sized single crystal in less than 2 h. Here the RED method is applied for ab initio structure determination of an unknown complex intermetallic phase, the pseudo-decagonal (PD) quasicrystal approximant Al-37.0(Co,Ni)(15.5), denoted as PD2. RED shows that the crystal is F-centered, with a = 46.4, b = 64.6, c = 8.2 angstrom. However, as with other approximants in the PD series, the reflections with odd l indices are much weaker than those with l even, so it was decided to first solve the PD2 structure in the smaller, primitive unit cell. The basic structure of PD2 with unit-cell parameters a = 23.2, b = 32.3, c = 4.1 angstrom and space group Pnmm has been solved in the present study. The structure with c = 8.2 angstrom will be taken up in the near future. The basic structure contains 55 unique atoms (17 Co/Ni and 38 Al) and is one of the most complex structures solved by electron diffraction. PD2 is built of characteristic 2 nm wheel clusters with fivefold rotational symmetry, which agrees with results from high-resolution electron microscopy images. Simulated electron diffraction patterns for the structure model are in good agreement with the experimental electron diffraction patterns obtained by RED.
Title:
Co-4 clusters in the high-temperature phase La18Co28In3
Authors:
Galadzhun, YV; Rodewald, UC; Svitlyk, V; Kalychak, Y; Pottgen, R Author Full Names: Galadzhun, Yaroslav V.; Rodewald, Ute Ch.; Svitlyk, Volodymyr; Kalychak, Yaroslav; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 228 (12):650-655; 10.1524/zkri.2013.1695 2013
Abstract:
The metal-rich indide La18Co28In3 was synthesized by melting of the elements in a high-frequency furnace and characterized by X-ray diffraction on powders and single crystals. This high-temperature phase crystallizes with a new structure type: 14/mmm, a = 1432.56(8), c = 984.35(6) pm, wR(2) = 0.1054, 1027 F-2 values, 43 variables at 295 K. The structure is built up by a complex three-dimensional network of Co-4 tetrahedra which arc condensed via further cobalt atoms with a broad range of Co-Co distances (242-262 pin). This network leaves larger channels which are filled by the lanthanum and indium centered polyhedra. The two crystallographically independent indium atoms have exclusively lanthanum neighbors within the channels. They form infinite (In-In2-In2) chains along c with mill In1-In2 and In2-In2 distances of 332 and 319 pm, respectively. These chains are only weakly bonded to their lanthanum neighbors with La-In distances ranging from 344 to 368 pm. Both indium sites show enhanced displacements along the c axis. Temperature dependent diffraction studies and similarities to the incommensurate La1.18Rh3In2 structure are discussed.

Update: 19-Feb-2014

Title:
Double symmetry breaking in TmFe4Ge2 compared to RFe4Ge2 (R=Y, Lu, Er, Ho, Dy) magnetic behaviour
Authors:
Schobinger-Papamantellos, P; Buschow, KHJ; Rodriguez-Carvajal, J Author Full Names: Schobinger-Papamantellos, P.; Buschow, K. H. J.; Rodriguez-Carvajal, J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 355 104-120; 10.1016/j.jmmm.2013.11.020 APR 2014
Abstract:
TmFe4Ge(2) undergoes a double magneto-elastic first order transition at T-N,T-C where the high temperature (HT) tetragonal phase disproportionate into two distinct orthorhombic low temperature (LT) phases with commensurate and incommensurate magnetic wave vectors respectively: P4(2)/mnm (HT) T-N, T-C -> Cmmm q(1) = (0, 1/2, 0) + Pnnm (q(2) = (0, q(y), 0), q(y) approximate to 2/11(LT) Neutron diffraction shows the relative portions of the LT Cmmm and Pnnm competing phases change linearly with T. The amount of the majority IIT phase Nom (54% at 30 K) decreases linearly to 30% clown to 10 K in favour of the Cmmm phase that dominates the range 26-1.5 K. The Tm moments point along the c-axis in both phases while the Fe moments have canted arrangements. The mu(Tm) = 3.54(3) mu(B)/atom at 15 K is strongly reduced below the Tm3+ free ion value g(J)J = 7 mu(B) for the q(1) phase. The q(2) phase corresponds to a 3D canted sinusoidal arrangement. The results are summarised on a phase diagram and compared to the findings in RFe4Ge2 (R = Y, Lu, Er, Ho, Dy) that are reviewed. The multitude of transition paths occurring in those systems arise from the competing magnetoelastic mechanisms involving the R-crystal field anisotropy, the exchange interactions R-R, R-Fe, Fe-Fe of the two sublattices and their coupling to the lattice strain. The geometrical frustration emerging from the compact tetrahedral Fe arrangement with antiferromagnetic interactions leads to 2D and 3D canted, incommensurate and nonmagnetic states. The Cmmm transition is triggered by dominating R-R and R-Fe interactions becoming stronger at LT while the Pnnm phase is promoted by Fe-Fe and R-Fe interactions that prevail at HT. Included is also the magnetic structure of the ferromagnetic impurity phase Fe3Ge. (C) 2013 Elsevier B.V. All rights reserved
Title:
The structural stability and magnetic properties of the ferromagnetic Heusler alloy Ni-Mn-Sn: A first principle investigation
Authors:
Wang, X; Shang, JX; Wang, FH; Jiang, CB; Xu, HB Author Full Names: Wang, Xu; Shang, Jia-Xiang; Wang, Fu-He; Jiang, Cheng-Bao; Xu, Hui-Bin
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 355 173-179; 10.1016/j.jmmm.2013.12.017 APR 2014
Abstract:
The phase stability and magnetic properties of the cubic phase L2(1) and modulated four- and five layered orthorhombic (40. 5M) and unmodulated tetragonal (L1(0)) martensite of Ni-Mn-Sn alloys are investigated using the first-principle calculations. The results show that for Ni2Mn1+xSn1-x the martensite phases can be stable only at x >= 0.05. The stability of L2(1) phase decreases while it increases for L1(0) with the increasing of Mn contents. The anti-ferromagnetic order is stable for both L2(1) and martensite phases. The modulated 5M and 40 structures are determined accurately and the displacement of the atoms exhibits a sine-like oscillation along the stacking direction. Furthermore, a regular oscillation can also be observed in the distribution of the magnetic moments. With the analysis of the electronic structures, the origin of the effect of the modulation on the system can be explained. The modulation induced displacement of the atoms enhances the charge accumulation between the Ni and Mn/Mn', which lead to a stronger interaction and more structural stability. Accordingly, the calculated results may help in gaining the comprehensive and detailed information on the structural and magnetic properties of the modulated martensite structures, for better understanding of the basic transformation in Ni-Mn-Sn alloys. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Giant frictional dissipation peaks and charge-density-wave slips at the NbSe2 surface
Authors:
Langer, M; Kisiel, M; Pawlak, R; Pellegrini, F; Santoro, GE; Buzio, R; Gerbi, A; Balakrishnan, G; Baratoff, A; Tosatti, E; Meyer, E Author Full Names: Langer, Markus; Kisiel, Marcin; Pawlak, Remy; Pellegrini, Franco; Santoro, Giuseppe E.; Buzio, Renato; Gerbi, Andrea; Balakrishnan, Geetha; Baratoff, Alexis; Tosatti, Erio; Meyer, Ernst
Source:
NATURE MATERIALS, 13 (2):173-177; 10.1038/NMAT3836 FEB 2014
Abstract:
Understanding nanoscale friction and dissipation is central to nanotechnology(1-4). The recent detection of the electronicfriction drop caused by the onset of superconductivity in Nb (ref. 5) by means of an ultrasensitive non-contact pendulum atomic force microscope (AFM) raised hopes that a wider variety of mechanical-dissipation mechanisms become accessible. Here, we report a multiplet of AFM dissipation peaks arising a few nanometres above the surface of NbSe2-a layered compound exhibiting an incommensurate chargedensity wave (CDW). Each peak appears at a well-defined tip-surface interaction force of the order of a nanonewton, and persists up to 70 K, where the short-range order of CDWs is known to disappear. Comparison of the measurements with a theoretical model suggests that the peaks are associated with local, tip-induced 2 pi phase slips of the CDW, and that dissipation maxima arise from hysteretic behaviour of the CDW phase as the tip oscillates at specific distances where sharp local slips occur.
Title:
A new modulated structure in Sr2CuO3+delta superconductor synthesized under high pressure
Authors:
Liu, Y; Shen, X; Liu, QQ; Li, X; Feng, SM; Yu, RC; Uchida, S; Jin, CQ Author Full Names: Liu, Y.; Shen, X.; Liu, Q. Q.; Li, X.; Feng, S. M.; Yu, R. C.; Uchida, S.; Jin, C. Q.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 497 34-37; 10.1016/j.physc.2013.09.004 FEB 2014
Abstract:
A Sr2CuO3+delta superconductor with a new modulated structure has been synthesized using high pressure technique. Two superconducting transitions with Tc similar to 75 K and similar to 48 K respectively were found in Sr2CuO3+delta superconductor. The superconducting volume fraction is calculated to be 85% at 2 K, which is much higher than anyone else reported before. A new type of modulated phase with a periodicity of 2 root 2a(p) x 2 root 2a(p) x c(p) of Pmmm symmetry is found in the sample by using transmission electron microscopy. Our experimental results suggest that the new Pmmm modulated phase is responsible for superconductivity with Tc at 48 K, while C2/m modulated phase for that with Tc at 75 K found previously. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Partial Spin Ordering and Complex Magnetic Structure in BaYFeO4: A Neutron Diffraction and High Temperature Susceptibility Study
Authors:
Thompson, CM; Greedan, JE; Garlea, VO; Flacau, R; Tan, M; Nguyen, PHT; Wrobel, F; Derakhshan, S Author Full Names: Thompson, Corey M.; Greedan, John E.; Garlea, V. Ovidiu; Flacau, Roxana; Tan, Malinda; Nguyen, Phuong-Hieu T.; Wrobel, Friederike; Derakhshan, Shahab
Source:
INORGANIC CHEMISTRY, 53 (2):1122-1127; 10.1021/ic4026798 JAN 20 2014
Abstract:
The novel iron-based compound, BaYFeO4, crystallizes in the Pnma space group with two distinct Fe3+ sites, that are alternately corner-shared [FeO5](7-) square pyramids and [FeO6](9-) octahedra, forming into [Fe4O18](24-) rings, which propagate as columns along the b-axis. A recent report shows two discernible antiferromagnetic (AFM) transitions at 36 and 48 K in the susceptibility, yet heat capacity measurements reveal no magnetic phase transitions at these temperatures. An upturn in the magnetic susceptibility measurements up to 400 K suggests the presence of short-range magnetic behavior at higher temperatures. In this Article, variable-temperature neutron powder diffraction and high-temperature magnetic susceptibility measurements were performed to clarify the magnetic behavior. Neutron powder diffraction confirmed that the two magnetic transitions observed at 36 and 48 K are due to long-range magnetic order. Below 48 K, the magnetic structure was determined as a spin-density wave (SDW) with a propagation vector, k = (0, 0, 1/3), and the moments along the b-axis, whereas the structure becomes an incommensurate cycloid [k = (0, 0, 0.35)] below 36 K with the moments within the bc-plane. However, for both cases the ordered moments on Fe3+ are only of the order similar to 3.0 mu(B), smaller than the expected values near 4.5 mu(B), indicating that significant components of the Fe moments remain paramagnetic to the lowest temperature studied, 6 K. Moreover, new high-temperature magnetic susceptibility measurements revealed a peak maximum at similar to 550 K indicative of short-range spin correlations. It is postulated that most of the magnetic entropy is thus removed at high temperatures which could explain the absence of heat capacity anomalies at the long-range ordering temperatures. Published spin dimer calculations, which appear to suggest a k = (0, 0, 0) magnetic structure, and allow for neither low dimensionality nor geometric frustration, are inadequate to explain the observed complex magnetic structure.
Title:
Labile Degree of Disorder in Bismuth-Oxophosphate Compounds: Illustration through Three New Structural Types
Authors:
Aliev, A; Endara, D; Huve, M; Colmont, M; Roussel, P; Delevoye, L; Tran, TT; Halasyamani, PS; Mentre, O Author Full Names: Aliev, A.; Endara, D.; Huve, M.; Colmont, M.; Roussel, P.; Delevoye, L.; Tran, T. T.; Halasyamani, P. S.; Mentre, O.
Source:
INORGANIC CHEMISTRY, 53 (2):861-871; 10.1021/ic402930d JAN 20 2014
Abstract:
Here, we analyze the crystal structures of three new Bi/M oxophosphates, focusing on the ambiguity between order and disorder in different structural subunits. The three structures are original but systematically built on the assembly of O(Bi,M)(4) tetrahedra into various 1D-oxocenterd units, separated by PO4 groups that create cationic channels. Two main subunits show versatile degrees of disorder, i.e., the cationic channels and some of the terminal O(Bi,M)(4) entities. (a) In the compound [Bi-2(Bi1.56K0.44)O-dis(3)]K-0.88(dis)(PO4)(2), the K/K and K/Bi disorder is total on both nano- and micro-sized domains. (b) In the incommensurately modulated [Bi-10(Bi similar to 0.5Cd similar to 0.5)(8)O-dis(16)](Bi0.6Cd0.8)(2)(ord)(PO4)(8), only the cationic channels show an ordered Bi/Cd arrangement which can be modified by minor stoichiometric changes between domains. (c) In [Bi18Zn10O21](ord)zn(5)(ord)(PO4)(14), both subunits are almost perfectly ordered (complex Bi/Zn sequence) into a 7-fold supercell, but this order strongly depends on the observation scale and is mainly lost in micronic-grains also due to slight compositional changes. However, the refined noncentrosymmetric organization is maintained (SHG tests) in the bulk. The relative stability of ordered versus disordered sites is discussed on the basis of the existence of two possible mixed sites and probably depends on the M chemical nature. Disorder was characterized by use of solid-state P-31 NMR probing for the first two cases. Finally, the observed disordered or long periodicities along the infinite dimension suggest the sketch of a periodic/rigid skeleton of O(Bi,M)(4) units with counterions filling the interspace in more or less disordered arrangements.

Update: 5-Feb-2014

Title:
Effects of minor Gd addition on microstructures and mechanical properties of the high strain-rate rolled Mg-Zn-Zr alloys
Authors:
Yu, HY; Yan, HG; Chen, JH; Su, B; Zheng, Y; Shen, YJ; Ma, ZJ Author Full Names: Yu, Haiyang; Yan, Hongge; Chen, Jihua; Su, Bin; Zheng, Yi; Shen, Yanjin; Ma, Zhaojie
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 757-765; 10.1016/j.jallcom.2013.10.005 FEB 15 2014
Abstract:
Effects of minor Gd addition (0, 0.2, 0.5 and 0.8 mass%) on microstructure and mechanical properties of the high strain-rate rolled (HSRR) Mg-5.5Zn-0.6Zr-based alloys are investigated by OM, XRD, SEM, TEM and mechanical testing. The Mg-5.5Zn-0.6Zr alloy consists of the alpha-Mg matrix and the Mg7Zn3 phase. Minor Gd addition can effectively refine grains and change phase compositions. The quasicrystal I-phases (Mg-Zn-Gd ternary phase) are formed and mainly aggregated along the grain boundaries in the Mg-5.5Zn-0.6Zr-based alloys with minor Gd addition. The amount of the I-phase increases with the increase of Gd addition, but the amount of the Mg7Zn3 phase decreases. With the Gd addition up to 0.8 mass%, the main phases of the alloy are the alpha-Mg matrix and I-phases. The Gd addition can reduce the stacking fault energy of the alpha-Mg matrix and thus promote the dynamic recrystallization (DRX) during the HSRR process. The broken quasicrystal I-phase particles resulted from the HSRR process play a role in promoting the nucleation of DRX, inhibiting the growth of the DRX grains and refining grains. Meanwhile, the dispersion strengthening and precipitation strengthening of the I-phase particles contribute to the enhanced strength. The as-rolled Mg-5.5Zn-0.6Zr-0.8Gd alloy exhibits an optimal strength-ductility balance, with the ultimate tensile strength of 327 MPa, the yield strength of 242 MPa and the elongation to rupture of 22%, respectively. The addition of Gd can effectively weaken the recrystallization texture and modify the tensile fracture mechanism from quasi-cleavage to ductile. (C) 2013 Elsevier B. V. All rights reserved.
Title:
Electronic density of states and metastability of icosahedral Au-Al-Yb quasicrystal
Authors:
Jazbec, S; Vrtnik, S; Jaglicic, Z; Kashimoto, S; Ivkov, J; Popcevic, P; Smontara, A; Kim, HJ; Kim, JG; Dolinsek, J Author Full Names: Jazbec, S.; Vrtnik, S.; Jaglicic, Z.; Kashimoto, S.; Ivkov, J.; Popcevic, P.; Smontara, A.; Kim, Hae Jin; Kim, Jin Gyu; Dolinsek, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 343-348; 10.1016/j.jallcom.2013.10.073 FEB 15 2014
Abstract:
The recently discovered icosahedral quasicrystal (i-QC) in the ternary Au-Al-Yb system at the composition Au51Al34Yb15 is formed only in as-cast alloys and is metastable with decomposition to other crystalline phases upon annealing at 700 degrees C. Measuring the electronic transport coefficients (electrical resistivity, thermoelectric power, Hall coefficient), magnetic susceptibility and specific heat, we addressed the question of metastability of the i-Au-Al-Yb quasicrystalline phase by reconstructing the shape of the electronic density of states (DOS) in the vicinity of Fermi level epsilon(F) with the aim to find out whether there exists a pseudogap in the DOS that could contribute to electronic stabilization of the icosahedral phase. The results have revealed that the DOS in the vicinity of epsilon(F) exhibits a pronounced valley on a 100 meV energy scale with a sharp feature on a 10 meV scale, both being centered almost exactly at epsilon(F). This pseudogap is apparently not wide enough to ensure sufficient electronic energy gain of the order of a few 10 kJ/mol needed for the electronic stabilization of the icosahedral phase. A possible origin of metastability of the i-Au-Al-Yb quasicrystal and thermodynamic stability of its 1/1 cubic approximant of very similar composition is discussed. The sharp feature in the DOS at epsilon(F) is proposed to originate from indirect interaction between localized Yb f-moments due to overlap of their polarization clouds in the presence of hybridization of the f and s states, which leads to a sharp resonance peak. (C) 2013 Elsevier B. V. All rights reserved.

Update: Nezname datum (ma se nacist z hlavicek e-mailu)

Title:
Magnetic ordering in NdMn2O5 studied by the neutron diffraction
Authors:
Zobkalo, IA; Gavrilov, SV; Nyi, NZS; Barilo, SN; Shiryaev, SV Author Full Names: Zobkalo, I. A.; Gavrilov, S. V.; Nyi, N. Z. Saw; Barilo, S. N.; Shiryaev, S. V.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 354 85-89; 10.1016/j.jmmm.2013.10.034 MAR 2014
Abstract:
The magnetic ordering in NdMn2O5 single crystal has been studied by the neutron scattering, including XYZ-polarization analysis. At T-N approximate to 30 K the onset of the long-range magnetic order with incommensurate wave vector k = (0.5 0 similar to 0.36) is observed. Below 30 K two magnetic phases are observed with propagation vectors close to each other: k(1)=(0.5 0 k(z1)), k(2)=(0.5 0 k(z2)). k(z1), k(z2) components increase monotonously with temperature decrease down to 25 K, then remain to be constant with values k(z1)=0.384(2), k(z2)=0.395(2). Two reorientation transitions were observed at similar to 20 K and at similar to 5 K. (C) 2013 Published by Elsevier B.V.
Title:
Interpretation of magnetoelectric phase states using the praphase concept and exchange symmetry
Authors:
Ter-Oganessian, NV; Sakhnenko, VP Author Full Names: Ter-Oganessian, N. V.; Sakhnenko, V. P.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (3):10.1088/0953-8984/26/3/036003 JAN 22 2014
Abstract:
The majority of magnetoelectric crystals show complex temperature-magnetic field or temperature-pressure phase diagrams with alternating antiferromagnetic incommensurate, magnetoelectric, and commensurate phases. Such phase diagrams occur as a result of successive magnetic instabilities with respect to different order parameters, which usually transform according to different irreducible representations (IRs) of the space group of the crystal. Therefore, in order to build a phenomenological theory of phase transitions in such magnetoelectrics one has to employ several order parameters and assume the proximity of various instabilities on the thermodynamic path. In this work we analyze the magnetoelectrics MnWO4, CuO, NaFeSi2O6, NaFeGe2O6, Cu3Nb2O8, alpha-CaCr2O4 and FeTe2O5Br using the praphase concept and the symmetry of the exchange Hamiltonian. We find that in all the considered cases the appearing magnetic structures are described by IRs entering into a single exchange multiplet, whereas in the cases of MnWO4 and CuO by a single IR of the space group of the praphase structure. Therefore, one can interpret the complex phase diagrams of magnetoelectrics as induced by a single IR either of the praphase or of the symmetry group of the exchange Hamiltonian. Detailed temperature-magnetic field phase diagrams of MnWO4 and CuO for certain field directions are obtained and the magnetic structures of the field-induced phases are determined.
Title:
Temperature hysteresis of magnetic phase transitions in Tb1-xCexMn2O5 (x = 0, 0.20, 0.25)
Authors:
Zobkalo, IA; Gavrilov, SV; Sanina, VA; Golovenchits, EI Author Full Names: Zobkalo, I. A.; Gavrilov, S. V.; Sanina, V. A.; Golovenchits, E. I.
Source:
PHYSICS OF THE SOLID STATE, 56 (1):51-56; 10.1134/S1063783414010405 JAN 2014
Abstract:
The temperature evolution of the magnetic structure of multiferroics Tb1 - x Ce (x) Mn2O5 (x = 0, 0.20, 0.25) has been investigated using the neutron scattering methods. It has been found that, despite the qualitative similarity of the magnetic states and the series of phase transitions for pure TbMn2O5 (TMO) and doped crystals Tb1 - x Ce (x) Mn2O5 (TCMO, x = 0.20 and 0.25), there are significant differences in their properties. In contrast to TMO, where there are three magnetic phases, TCMO can include two magnetic phases that coexist in a wide temperature range and exhibit a rather wide temperature hysteresis. One of these phases with wave vector k (1) = (0.5, 0, k (z1)), k (z1) = 0.25, is commensurate and arises at temperatures below T (N) similar to 39 K (for x = 0.2) and T (N) similar to 38 K (x = 0.25). The second phase is incommensurate with wave vector k (2) = (1/2, 0, k (z2)), k (z2) = 0.256(2), and appears upon cooling at T = 21 K (x = 0.2) and T = 19 K (x = 0.25). Upon further cooling to 16 K, the component k (z2) increases to 0.292(2) and then remains constant. The component k (z1) increases to the value of 0.280(2) upon cooling in the range from 15 to 10 K and then remains constant down to 1.5 K. With an increase in the temperature, the components k (z1) and k (z2) undergo reverse changes to their initial values, but these changes occur at temperatures 7 K higher than those observed with a decrease in the temperature. For TMO, two phases also coexist, but the temperature hysteresis in this case is considerably smaller than for TCMO. This is explained by different densities of domain walls and different sizes of domains in pure and doped crystals.
Title:
Spatially modulated magnetic structure of AgFeO2: Mossbauer study on Fe-57 nuclei
Authors:
Rusakov, VS; Presnyakov, IA; Sobolev, AV; Gapochka, AM; Matsnev, ME; Belik, AA Author Full Names: Rusakov, V. S.; Presnyakov, I. A.; Sobolev, A. V.; Gapochka, A. M.; Matsnev, M. E.; Belik, A. A.
Source:
JETP LETTERS, 98 (9):544-550; 10.1134/S0021364013220098 JAN 2014
Abstract:
The results of the Mossbauer study of ferrite AgFeO2 manifesting multiferroic properties (at T a parts per thousand currency sign T (N2)) have been presented. The hyperfine interaction parameters of Fe-57 nuclei have been analyzed in a wide temperature range including the points of two magnetic phase transitions (T (N2) a parts per thousand 7-9 K and T (N1) a parts per thousand 15-16 K). It has been shown that the Mossbauer spectra of the Fe-57 nuclei are sensitive to the variations of the character of the magnetic ordering of Fe3+ ions in the studied ferrite. The results of the model identification of a series of spectra (4.7 K a parts per thousand currency sign T a parts per thousand currency sign T (N2)) under the assumption of the cycloid magnetic structure of ferrite AgFeO2 have been presented. The analysis of the results has been performed in comparison with the literature data for other oxide multiferroics.

Update: 23-Jan-2014

Title:
Magnetic Order in Ce0.95Nd0.05CoIn5: The Q-Phase at Zero Magnetic Field
Authors:
Raymond, S; Ramos, SM; Aoki, D; Knebel, G; Mineev, VP; Lapertot, G Author Full Names: Raymond, Stephane; Ramos, Scheilla M.; Aoki, Dai; Knebel, Georg; Mineev, Vladimir P.; Lapertot, Gerard
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 83 (1):10.7566/JPSJ.83.013707 JAN 2014
Abstract:
We report neutron scattering experiment results revealing the nature of the magnetic order occurring in the heavy fermion superconductor Ce0.95Nd0.05CoIn5. In this system, an antiferromagnetic state is stabilized at a temperature below the superconducting transition one. We evidence that it is an incommensurate order and its propagation vector is found to be identical to that of the magnetic field induced antiferromagnetic order occurring in the stoichiometric superconductor CeCoIn5, the so-called Q-phase. The commonality between these two cases suggests that d-wave superconductivity is playing a key role for the formation of this kind of magnetic order. The proposed mechanism is the enhancement of the nesting condition by an order parameter with nodes in the nesting area.

Update: 16-Jan-2014

Title:
Depth dependent order/disorder transitions in iron-rich thin films grown on i-Al-Pd-Mn studied by medium energy ion scattering
Authors:
Noakes, TCQ; Parle, J; Nugent, P; Sharma, HR; Smerdon, JA; Bailey, P; McGrath, R Author Full Names: Noakes, T. C. Q.; Parle, J.; Nugent, P.; Sharma, H. R.; Smerdon, J. A.; Bailey, P.; McGrath, R.
Source:
SURFACE SCIENCE, 620 59-64; 10.1016/j.susc.2013.09.023 FEB 2014
Abstract:
This paper reports a medium energy ion scattering study of the room temperature deposition of Fe on the fivefold surface of i-Al70Pd21Mn9. At low coverage (similar to 1 ML) growth results in a disordered alloy film with significant Al content. At higher coverage (similar to 11 ML) again an alloy film is formed, but this time with an average composition that slowly varies through the film but is close to stoichiometric Fe3Al. This composition is consistent with magnetic ordering which has been observed in previous experiments on this system. Structural analysis indicates five domains of bcc-like structure in the film, which is oriented with (110) type planes parallel to the five-fold quasicrystal surface. There is a distinct structural transition within the film between a compressed layer near the surface and a slightly expanded layer directly above the quasicrystalline substrate. The sub-surface layer has considerable disorder and the change in layer spacing is attributed to this order/disorder transition within the film. Annealing to 300 degrees C for 10 min induces a small amount of further up-diffusion of Al into the film and also some segregation of Al to the surface, although structurally the film remains essentially unchanged, with the order/disorder transition occurring at a similar depth. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.
Title:
Icosahedral gold-platinum alloy nanocrystals in hollow silica: a highly active and stable catalyst for Ullmann reactions
Authors:
Wu, XL; Tan, LF; Chen, D; Meng, XW; Tang, FQ Author Full Names: Wu, Xiaoli; Tan, Longfei; Chen, Dong; Meng, Xianwei; Tang, Fangqiong
Source:
CHEMICAL COMMUNICATIONS, 50 (5):539-541; 10.1039/c3cc46383d 2014
Abstract:
Icosahedral Au-Pt alloy nanocrystals are prepared in porous hollow silica nanospheres via a hydrothermal method without using capping agents. These nanoparticles with unique shape and structure exhibit excellent catalytic activity and stability in Ullmann reactions.
Title:
Sintering, structure, and physicomechanical properties of Al-Cu-Fe quasicrystals compacted at high pressure
Authors:
Ekimov, EA; Sirotinkin, VP; Petrzhik, MI; Gromnitskaya, EL Author Full Names: Ekimov, E. A.; Sirotinkin, V. P.; Petrzhik, M. I.; Gromnitskaya, E. L.
Source:
INORGANIC MATERIALS, 50 (1):52-57; 10.1134/S002016851401004X JAN 2014
Abstract:
Bulk samples of Al-Cu-Fe quasicrystals with excellent mechanical and tribological properties were prepared by high-pressure compaction followed by pressureless sintering. Cold pressing at 8-9 GPa was shown to cause severe plastic deformation of the Al-Cu-Fe quasicrystals.
Title:
Interfacial magnetism and exchange coupling in BiFeO3-CuO nanocomposite
Authors:
Chakrabarti, K; Sarkar, B; Ashok, VD; Das, K; Chaudhuri, SS; De, SK Author Full Names: Chakrabarti, Kaushik; Sarkar, Babusona; Ashok, Vishal Dev; Das, Kajari; Chaudhuri, Sheli Sinha; De, S. K.
Source:
NANOTECHNOLOGY, 24 (50):10.1088/0957-4484/24/50/505711 DEC 20 2013
Abstract:
Ferromagnetic BiFeO3 nanocrystals of average size 9 nm were used to form a composite with antiferromagnetic CuO nanosheets, with the composition (x) BiFeO3/(100 - x )CuO, x D 0, 20, 40, 50, 60, 80 and 100. The dispersion of BiFeO3 nanocrystals into the CuO matrix was confirmed by x-ray diffraction and transmission electron microscopy. The ferromagnetic ordering as observed in pure BiFeO3 occurs mainly due to the reduction in the particle size as compared to the wavelength (62 nm) of the spiral modulated spin structure of the bulk BiFeO3. Surface spin disorder of BiFeO3 nanocrystals gives rise to an exponential behavior of magnetization with temperature. Strong magnetic exchange coupling between the BiFeO3 nanocrystal and the CuO matrix induces an interfacial superparamagnetic phase with a blocking temperature of about 80 K. Zero field and field cooled magnetizations are analyzed by a ferromagnetic core and disordered spin shell model. The temperature dependence of the calculated saturation magnetization exhibits three magnetic contributions in three temperature regimes. The BiFeO3/CuO nanocomposites reveal an exchange bias effect below 170 K. The maximum exchange bias field HEB is 1841 Oe for x D 50 at 5 K under field cooling of 50 kOe. The exchange bias coupling results in an increase of coercivity of 1934 Oe at 5 K. Blocked spins within an interfacial region give rise to a remarkable exchange bias effect in the nanocomposite due to strong magnetic exchange coupling between the BiFeO3 nanocrystals and the CuO nanosheets.
Title:
Universal emergence of spatially modulated structures induced by flexoantiferrodistortive coupling in multiferroics
Authors:
Eliseev, EA; Kalinin, SV; Gu, YJ; Glinchuk, MD; Khist, V; Borisevich, A; Gopalan, V; Chen, LQ; Morozovska, AN Author Full Names: Eliseev, Eugene A.; Kalinin, Sergei V.; Gu, Yijia; Glinchuk, Maya D.; Khist, Victoria; Borisevich, Albina; Gopalan, Venkatraman; Chen, Long-Qing; Morozovska, Anna N.
Source:
PHYSICAL REVIEW B, 88 (22):10.1103/PhysRevB.88.224105 DEC 19 2013
Abstract:
We proved the existence of a universal flexoantiferrodistortive coupling as a necessary complement to the well-known flexoelectric coupling. The coupling is universal for all antiferrodistortive systems and can lead to the formation of incommensurate, spatially modulated phases in multiferroics. Our analysis can provide a self-consistent mesoscopic explanation for a broad range of modulated domain structures observed experimentally in multiferroics.
Title:
Analysis of Structure and P-c-T Curve of Hydrogenated Ti53Zr27-xNi20Pdx Quasicrystals
Authors:
Jo, Y; Lee, SH; Shin, HS; Kim, J Author Full Names: Jo, Youngsoo; Lee, Sang-Hwa; Shin, Hong Sik; Kim, Jaeyong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 13 (12):7959-7962; 10.1166/jnn.2013.8124 DEC 2013
Abstract:
The potential application of TiZrNi quasicrystals was evaluated by measuring the pressure-composition-temperature curves after replacing Zr by Pd to the limit maintaining the host structure for the samples made with Ti53Zr27-xNi20Pdx, where 0 <= x <= 8. The results of X-ray diffraction data revealed that the samples keep the pure quasicrystal structure to the maximum value of x = 8. All diffracted peaks uniformly shifted to the low angle of 2 theta in X-ray diffraction pattern suggesting that hydrogen atoms homogeneously diffuse in the quasicrystals and uniformly expand the quasilattice constants without modification of the structure. After hydrogenation at elevated temperature, the quasi-lattice constants increased from 5.12 to 5.34 angstrom for the samples made with x = 0 without appearing an impurity phase. When Zr was replaced by 8 at.% of Pd, the equilibrium vapor pressures significantly increased to 3.41 from 0.41 Torr at 300 degrees C although the total amount of hydrogen decreased as increasing Pd concentration. These results demonstrate that Pd will play a critical role in application for the TiZrNi quasicrystals as hydrogen storage materials.
Title:
Effect of Ce on electrochemical properties of the TiVNi quasicrystal material as an anode for Ni/MH batteries
Authors:
Liu, WQ; Duan, Q; Liang, F; Lin, J; Jiang, DY; Wang, LM Author Full Names: Liu, Wanqiang; Duan, Qian; Liang, Fei; Lin, Jing; Jiang, Dayong; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 38 (34):14810-14815; 10.1016/j.ijhydene.2013.09.015 NOV 13 2013
Abstract:
In order to investigate effect of Ce on electrochemical properties of the Ti1.4V/Ni-0.6 quasi-crystal, (Ti1.4V0.6Ni)(99.4)Ce-0.6 alloy ribbon is prepared by arc melting and subsequent melt-spinning technique. The electrochemical properties of the Ti1.4V0.6Ni and (Ti1.4V0.6Ni)(99.4)Ce-0.6 are studied as negative electrode for nickel-metal hydride batteries in aqueous KOH solution. The structures of the alloys were characterized by XRD and TEM. Phase structure investigations of the (Ti1.4V0.6Ni)(99) Ce-4(0.6) show that alloy mainly consist of the icosahedral quasicrystal (I-phase) and face centered cubic (FCC) phase with Ti2Ni-type structure. The electrochemical measurements demonstrated that the negative electrode made by (Ti1.4V0.6Ni)(99.4)Ce-0.6 alloy showed an improved electrochemical reversibility and a considerably higher charge-discharge capacity when compared to the Ce-free base alloy. Its maximum discharge capacity is about 300 mAh/g, which is higher than that of Ti1.4V0.6Ni, and remains 270 mAh/g after 30 cycles at a current density of 30 mA/g. The discharge process is also characterized by electrochemical impedance spectroscopy. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Update: 8-Jan-2014

Title:
Metastable primary precipitation phases in multicomponent glass forming Fe-base alloys with metalloids
Authors:
Lyasotsky, IV; Dyakonova, NB; Dyakonov, DL Author Full Names: Lyasotsky, I. V.; Dyakonova, N. B.; Dyakonov, D. L.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 S20-S23; 1 10.1016/j.jallcom.2013.03.112 FEB 15 2014
Abstract:
Structure transformations at the initial stages of devitrification have been investigated for alloys with good glass forming ability on the base of Fe-B-Si, Fe-P-C, Fe-P-B-C systems with various additions. Systematization of the metastable phases formed in these alloys showed that: (a) metastable phases at the initial stages of crystallization are tetrahedrally close packed (TCP) or aperiodic structures and possess compositions close to the mean composition of the alloy; (b) the observed TCP phases belong to one family of structures related to alpha-Mn for essentially different types of alloying systems, having in common a high glass forming ability; (c) for alloys based on the same system with different small alloying additions, structure of the metastable phase can change within this family of related phases. The obtained results show that Fe-based metallic glasses with metalloids are not essentially different from metal-metal type glasses. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Vitrification and devitrification processes in metallic glasses
Authors:
Louzguine-Luzgin, DV Author Full Names: Louzguine-Luzgin, D. V.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 S2-S8; 1 10.1016/j.jallcom.2012.09.057 FEB 15 2014
Abstract:
The phenomenon of vitrification on cooling, also called the glass-transition still remains not fully understood. Recent studies by different techniques were performed in order to shed light on this and on the converse phenomenon of devitrification. Devitrification may either lead to the formation of a supercooled liquid, a crystal(s) or a quasicrystal(s). The present paper is a review of recent findings on the processes of vitrification and devitrification in metallic glasses. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Development of antifriction composites based on polypyromellitimide matrix
Authors:
Olifirov, LK; Kaloshkin, SD; Tcherdyntsev, VV; Danilov, VD Author Full Names: Olifirov, L. K.; Kaloshkin, S. D.; Tcherdyntsev, V. V.; Danilov, V. D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 S446-S450; 1 10.1016/j.jallcom.2013.02.119 FEB 15 2014
Abstract:
A method of polypyromellitimide powder production from PM-A film was proposed and a possibility of fabricating bulk composites based on polypyromellitimide matrix was investigated. The powders were prepared by the treatment of PM-A films in a planetary ball mill. The compositions based on polypyromellitimide containing additives of Al65Cu23Fe12 quasicrystals, graphite, polytetrafluoroethylene and PI-PR-20 polyimide were prepared by the solid-state mixing in an IKA M20 batch mill. The bulk samples were fabricated by the compression molding technique. Thus produced materials were characterized by using the methods of sieve analysis, scanning electron microscopy, Fourier-transform infrared spectroscopy, dynamo-mechanical analysis and tribological tests. It was found that the PM-A polypyromellitimide powder had a low sinterability and, therefore, the bulk samples of unfilled PM-A and also the composites based on PM-A containing additives of Al65Cu23Fe12 quasicrystals, graphite and polytetrafluoroethylene exhibited a high brittleness and show unstable behavior in the tribological tests. It was found that an addition of 15 wt.% PI-PR-20 polyimide improved the sinterability of PM-A and also provides excellent antifriction properties. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Microstructure and mechanical properties of a Mg-Zn-Y alloy produced by a powder metallurgy route
Authors:
Asgharzadeh, H; Yoon, EY; Chae, HJ; Kim, TS; Lee, JW; Kim, HS Author Full Names: Asgharzadeh, H.; Yoon, E. Y.; Chae, H. J.; Kim, T. S.; Lee, J. W.; Kim, H. S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 S95-S100; 1 10.1016/j.jallcom.2012.10.108 FEB 15 2014
Abstract:
In this paper, a bulk Mg-Zn-Y alloy reinforced by quasicrystalline particles was produced by hot extrusion of rapidly-solidified powders. MgZn4.3Y0.7 powders with different particle sizes were prepared by an inert gas atomizer and then extruded at 380 degrees C with extrusion ratios of 10:1, 15:1, and 20:1. Microstructural studies were performed using an optical microscope, scanning electron microscope, transmission electron microscope, and X-ray diffraction. The mechanical strength and hardness of the extruded materials were enhanced by employing finer Mg alloy powders. More uniform deformation of powders in extruded billets with good tensile properties was achieved at higher extrusion ratios, especially for finer powders. The high strength of the MgZn4.3Y0.7 alloy was preserved at elevated temperatures due to the presence of icosahedral phase nanoparticles. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Decagonal quasicrystalline phase in as-cast and mechanically alloyed Al-Cu-Cr alloys
Authors:
Shevchukov, AP; Sviridova, TA; Kaloshkin, SD; Tcherdyntsev, VV; Gorshenkov, MV; Churyukanova, MN; Zhang, D; Li, Z Author Full Names: Shevchukov, A. P.; Sviridova, T. A.; Kaloshkin, S. D.; Tcherdyntsev, V. V.; Gorshenkov, M. V.; Churyukanova, M. N.; Zhang, D.; Li, Z.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 S391-S394; 1 10.1016/j.jallcom.2013.02.043 FEB 15 2014
Abstract:
Microstructure and phase composition of three Al-rich as-cast alloys of Al-Cu-Cr system were investigated by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The decagonal quasi-crystalline phase is contained in all alloys under study and has grains with faceted shape, its composition lies in the range of 71-73 at.% Al, 11-12 at.% Cu and 15-18 at.% Cr. The heating in calorimeter of the mechanically alloyed Al73Cu11Cr16 powder up to 600 degrees C leads to the formation of the pure decagonal phase. Total thermal effect in the temperature range 250-600 degrees C corresponding to the quasicrystalline phase formation is about 15 kJ/mol. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Effect of Mo on stability of quasicrystalline phase in Al-Mn-Fe alloy
Authors:
Stan, K; Litynska-Dobrzynska, L; Labar, JL; Goral, A Author Full Names: Stan, Katarzyna; Litynska-Dobrzynska, Lidia; Labar, Janos L.; Goral, Anna
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 S395-S399; 1 10.1016/j.jallcom.2012.12.013 FEB 15 2014
Abstract:
Microstructure evolution in rapidly solidified Al91Mn6Fe2Mo1 ribbons after annealing was investigated using X-ray diffraction, scanning electron microscopy and analytical transmission electron microscopy including in situ heating experiment in TEM. As spun ribbons consisted of icosahedral quasicrystalline particles enriched in Fe, Mn and Mo embedded in an aluminium matrix. A small amount of quasicrystals containing Fe and Mn which coexisted with the Al-3(Fe, Mn) phase was also observed between the aluminium grains. Further annealing experiments and subsequent analysis of microstructure changes in the sample showed that the quasicrystalline particles underwent a transformation into stable crystalline phases at temperatures which depended on their composition. It was observed that quasicrystals enriched in Mn and Fe transformed at much lower temperatures than primary quasicrystals with Mo content. It was noticed that two different crystalline phases formed in dependence on the temperature of annealing. The Al-6(Mn, Fe) phase appeared first at the quasicrystal/matrix interface. At higher temperature, the Al-12(Mn, Mo) phase formed due to reaction of the Al-6(Mn, Fe) phase with the aluminium matrix. Microstructural and DSC investigations showed that addition of molybdenum improved thermal stability of the quasicrystals in Al-Mn-Fe system. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Effect of mechanical milling on electrochemical properties of Ti45Zr38xNi17+x (x=0, 8) quasicrystals produced by rapid-quenching
Authors:
Baster, D; Takasaki, A; Kuroda, C; Hanc, E; Lee, SH; Swierczek, K; Szmyd, JS; Kim, JY; Molenda, J Author Full Names: Baster, Dominika; Takasaki, Aldto; Kuroda, Chihiro; Hanc, Emil; Lee, Sang-Hwa; Swierczek, Konrad; Szmyd, Janusz S.; Kim, Jae-Yong; Molenda, Janina
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 580 S238-S242; 1 10.1016/j.jallcom.2013.03.272 DEC 15 2013
Abstract:
The effect of mechanical milling on the discharge performance of electrodes consisting of Ti45Zr38-xNi17+x (x = 0, 8) quasictystals, which were produced by a rapid-quenching, was investigated at room temperature in three-electrode cell set-up. All of the obtained ribbons were identified to contain mostly icosahedral (i) quasicrystal phase (i-phase). The measured discharge capacity for Ti45Zr30Ni25 material was higher than the one for Ti45Zr38Ni17. The maximum discharge capacity equal 86 mA h g(-1) was achieved for Ti45Zr30Ni25, which was mechanically milled for 15 h. This value was obtained at the third discharge process. The recorded discharge performance was quite stable on cycling up to 30 cycles for Ti45Zr38Ni17 material, but slight decrease after 15th cycle was observed for Ti45Zr30Ni25 phase. It should be highlighted that the quasioystal i-phase remained stable also after 25 h of mechanical milling for both studied materials. However, a formation of (Ti, Zr)H-2 hydride phase was observed after charge/discharge cycles for both of the materials. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Hydrogen storage characteristics of Ti45Zr38Ni17-xCox (x=4, 8) alloy and quasicrystal powders produced by mechanical alloying
Authors:
Takasaki, A; Zywczak, A; Gondek, L; Figiel, H Author Full Names: Takasaki, Akito; Zywczak, A.; Gondek, L.; Figiel, H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 580 S216-S218; 1 10.1016/j.jallcom.2013.03.145 DEC 15 2013
Abstract:
The effect of substitution of Co for Ni on hydrogen storage characteristics of Ti-Zr-Ni/Co powders (Ti-45- Zr38Ni17-xCox (x = 4, 8)) produced by mechanical alloying (MA) was investigated. The final product after MA was amorphous for all the powders, but subsequent annealing caused the formation of the icosahedral quasicrystal (i) phase with a Ti2Ni type crystal and a C14 like Laves phases. The amount of i-phase decreased, and reversely those of Ti2Ni and the Laves phases increased with increasing the amount of Co. After hydrogenation at 573 K and at an initial hydrogen pressure of 3.8 MPa, the maximum hydrogen concentration for the annealed powders reached was about 58 at%, and all the phases in the powders transformed to metallic hydrides ((Zr,Ti)H-2, Ni(Zr,Ti)H-3 and Co(Zr,Ti)H-3). Because of the formation of several hydrides, accelerated hydrogen desorption occurred at several temperatures. The activation energies for hydrogen desorption varied from about 70 kJ/mol to 180 kJ/mol. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Electrochemical properties of Ti45-xZr30+xNi25 (x=4, 0, 4) quasicrystal and amorphous electrodes produced by mechanical alloying
Authors:
Ariga, Y; Takasaki, A; Kuroda, C; Kulka, A Author Full Names: Ariga, Youhei; Takasaki, Akito; Kuroda, Cihiro; Kulka, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 580 S251-S254; 1 10.1016/j.jallcom.2013.03.224 DEC 15 2013
Abstract:
The effect of substitution of Zr for Ti on the discharge performance of electrodes consisted of Ti45-xZr30+xNi25 (x = -4, 0, 4) powders produced by mechanical alloying (MA) and subsequent annealing was investigated by a three-electrode cell at room temperature. All the powders after MA were amorphous, but a subsequent annealing caused the formation of the icosahedral (i) quasicrystal phase with a Ti2Ni type crystal phase as the second phase. The discharge capacities for both the amorphous and the i-phase electrodes decreased with increasing amount of Zr substituted for Ti. The maximum discharge capacity achieved was about 130 mA h/g from a (Ti49Zr26Ni25) i-phase electrode at the first discharge process. The discharge capacities of the amorphous electrodes were lower than those of the i-phase ones if the composition levels were alike. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Physical, Mechanical, and Tribological Properties of Quasicrystalline Al-Cu-Fe Coatings Prepared by Plasma Spraying
Authors:
Lepeshev, AA; Rozhkova, EA; Karpov, IV; Ushakov, AV; Fedorov, LY Author Full Names: Lepeshev, A. A.; Rozhkova, E. A.; Karpov, I. V.; Ushakov, A. V.; Fedorov, L. Yu.
Source:
PHYSICS OF THE SOLID STATE, 55 (12):2531-2536; 10.1134/S1063783413120202 DEC 2013
Abstract:
The physical, mechanical, and tribological properties of quasicrystalline coatings based on the Al65Cu23Fe12 alloy prepared by plasma spraying have been investigated. The specific features of the phase formation due to the competitive interactions of the icosahedral psi and cubic beta phases have been elucidated. A correlation between the microhardness and the content of the icosahedral phase in the coating has been determined. The decisive role of the quasicrystalline phase in the formation of high tribological characteristics of the coatings has been revealed and tested.
Title:
Measurement of Unique Magnetic and Superconducting Phases in Oxygen-Doped High-Temperature Superconductors La2-xSrxCuO4+y
Authors:
Udby, L; Larsen, J; Christensen, NB; Boehm, M; Niedermayer, C; Mohottala, HE; Jensen, TBS; Toft-Petersen, R; Chou, FC; Andersen, NH; Lefmann, K; Wells, BO Author Full Names: Udby, L.; Larsen, J.; Christensen, N. B.; Boehm, M.; Niedermayer, Ch.; Mohottala, H. E.; Jensen, T. B. S.; Toft-Petersen, R.; Chou, F. C.; Andersen, N. H.; Lefmann, K.; Wells, B. O.
Source:
PHYSICAL REVIEW LETTERS, 111 (22):10.1103/PhysRevLett.111.227001 NOV 25 2013
Abstract:
We present a combined magnetic neutron scattering and muon spin rotation study of the nature of the magnetic and superconducting phases in electronically phase separated La2-xSrxCuO4+y, x = 0.04, 0.065, 0.09. For all samples, we find long- range modulated magnetic order below TN similar or equal to Tc = 39 K. In sharp contrast to oxygen- stoichiometric La-2 -xSrxCuO4, we find that the magnetic propagation vector as well as the ordered magnetic moment is independent of Sr content and consistent with that of the "striped" cuprates. Our study provides direct proof that superoxygenation in La2-xSrxCuO4+y allows the spin stripe ordered phase to emerge and phase separate from superconducting regions with the hallmarks of optimally doped oxygen- stoichiometric La2-xSrxCuO4.

Update: 25-Dec-2013

Title:
Differently mobile twin boundaries and magnetic shape memory effect in 10 M martensite of Ni-Mn-Ga
Authors:
Heczko, O; Kopecek, J; Straka, L; Seiner, H Author Full Names: Heczko, O.; Kopecek, J.; Straka, L.; Seiner, H.
Source:
MATERIALS RESEARCH BULLETIN, 48 (12):5105-5109; SI 10.1016/j.materresbull.2013.04.034 DEC 2013
Abstract:
We investigated twin boundaries with sharply different mobility or twinning stress in five-layered modulated (10 M) martensite of Ni-Mn-Ga exhibiting magnetic shape memory effect or magnetically induced reorientation. Different mobility is ascribed to the different microstructures of the macrotwin planar interface. In monoclinic approximation the mobile boundaries are of Type 1 and Type 11 with complex microstructure of adjoining variants. These boundaries respond differently to magnetic field. For Type II boundary the reorientation takes place at very low field 250 Oe. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
New Roles for Icosahedral Clusters in Intermetallic Phases: Micelle-like Segregation of Ca-Cd and Cu-Cd Interactions in Ca10Cd27Cu2
Authors:
Hadler, AB; Harris, NA; Fredrickson, DC Author Full Names: Hadler, Amelia B.; Harris, Nicholas A.; Fredrickson, Daniel C.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 135 (46):17369-17378; 10.1021/ja407291t NOV 20 2013
Abstract:
Despite significant progress in the structural characterization of the quasicrystalline state, the chemical origins of long- and short-range icosahedral order remain mysterious and a subject of debate. In this Article, we present the crystal structure of a new complex intermetallic phase, Ca10Cd27Cu2 (mC234.24), whose geometrical features offer clues to the driving forces underlying the icosahedral clusters that occur in Bergman-type quasicrystals. Ca10Cd27Cu2 adopts a C-centered monoclinic superstructure of the 1/1 Bergman approximant structure, in which [110] layers of Bergman clusters in the 1/1 structure are separated through the insertion of additional atoms (accompanied by substantial positional disorder). An examination of the coordination environments of Ca and Cu (in the ordered regions) reveals that the structure can be viewed as a combination of coordination polyhedra present in the nearest binary phases in the Ca-Cd-Cu compositional space. A notable feature is the separation of Ca-Cd and Cu-Cd interactions, with Bergman clusters emerging as Ca-Cd Friauf polyhedra (derived from the MgZn2-type CaCd2 phase) encapsulate a Cu-Cd icosahedron similar to those appearing in Cu2Cd5. DFT chemical pressure calculations on nearby binary phases point to the importance of this segregation of Ca-Cd and Cu-Cd interactions. The mismatch in atomic size between Cu and Cd leads to an inability to satisfy Ca Cu and Ca Cd interactions simultaneously in the Friauf polyhedra of the nearby Laves phase CaCd2. The relegation of the Cu atoms to icosahedra prevents this frustration while nucleating the formation of Bergman clusters.
Title:
Grain size softening effect in Al62.5Cu25Fe12.5 nanoquasicrystals
Authors:
Mukhopadhyay, NK; Ali, F; Scudino, S; Khoshkhoo, MS; Stoica, M; Srivastava, VC; Uhlenwinkel, V; Vaughan, G; Suryanarayana, C; Eckert, J Author Full Names: Mukhopadhyay, N. K.; Ali, F.; Scudino, S.; Khoshkhoo, M. Samadi; Stoica, M.; Srivastava, V. C.; Uhlenwinkel, V.; Vaughan, G.; Suryanarayana, C.; Eckert, J.
Source:
APPLIED PHYSICS LETTERS, 103 (20):10.1063/1.4831737 NOV 11 2013
Abstract:
Inverse Hall-Petch (IHP) behavior in nano-quasicrystalline Al62.5Cu25Fe12.5 is reported. Powders with varying grain sizes were produced by mechanical milling of spray-formed quasicrystals. The hardness of the milled powders increased with decreasing grain size down to about 40 nm and decreased with further refinement, demonstrating the IHP behavior. This critical grain size was found to be larger compared to other metallic nanocrystalline alloys. This IHP behaviour has been attributed to the structural complexity in quasicrystals and to thermally activated shearing events of atoms at the grain boundaries. (C) 2013 AIP Publishing LLC.
Title:
Influence of Cr on the nucleation of primary Al and formation of twinned dendrites in Al-Zn-Cr alloys: Can icosahedral solid clusters play a role?
Authors:
Kurtuldu, G; Jarry, P; Rappaz, M Author Full Names: Kurtuldu, Gueven; Jarry, Philippe; Rappaz, Michel
Source:
ACTA MATERIALIA, 61 (19):7098-7108; 10.1016/j.actamat.2013.07.056 NOV 2013
Abstract:
The equiaxed solidification of Al-20 wt.% Zn alloys revealed an unexpectedly large number of fine grains which are in a twin, or near-twin, relationship with their nearest neighbors when minute amounts of Cr (1000 ppm) are added to the melt. Several occurrences of neighboring grains sharing a nearly common < 1 1 0 > direction with a fivefold symmetry multi-twinning relationship have been found. These findings are a very strong indication that the primary face-centered cubic Al phase forms on either icosahedron quasicrystals or nuclei of the parent stable Al45Cr7 phase, which exhibits several fivefold symmetry building blocks in its large monoclinic unit cell. They are further supported by thermodynamic calculations and by grains sometimes exhibiting orientations compatible with the so-called interlocked icosahedron. These results are important, not only because they provide an explanation of the nucleation of twinned dendrites in Al alloys, a topic that has remained unclear over the past 60 years despite several recent investigations, but also because they identify a so far neglected nucleation mechanism in aluminum alloys, which could also apply to other metallic systems. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Templated three-dimensional growth of quasicrystalline lead
Authors:
Sharma, HR; Nozawa, K; Smerdon, JA; Nugent, PJ; McLeod, I; Dhanak, VR; Shimoda, M; Ishii, Y; Tsai, AP; McGrath, R Author Full Names: Sharma, H. R.; Nozawa, K.; Smerdon, J. A.; Nugent, P. J.; McLeod, I.; Dhanak, V. R.; Shimoda, M.; Ishii, Y.; Tsai, A. P.; McGrath, R.
Source:
NATURE COMMUNICATIONS, 4 10.1038/ncomms3715 NOV 2013
Abstract:
Quasicrystals, materials with aperiodic long-range order, have been found in intermetallics, soft materials such as colloids and supermolecules, and also in two-dimensional monolayer films. Here we present the first example of three-dimensional growth of a single-element quasicrystalline film. Using a hitherto unexplored template, the icosahedral Ag-In-Yb quasi-crystal, and various experimental techniques combined with theoretical calculations of adsorption energies, we find that lead atoms deposited on the surface occupy the positions of atoms in the rhombic triacontahedral cluster, the building block of the substrate, and thus grow in layers with different heights and adsorption energies. We show that the adlayer-adlayer interaction is crucial for stabilizing this epitaxial quasicrystalline structure. The finding opens an avenue for further investigation of the impact of the aperiodic atomic order over periodic order on the physical and chemical properties of materials.
Title:
About the reason of electric polarization flop in TbMnO3
Authors:
Chupis, IE; Kovtun, HA Author Full Names: Chupis, I. E.; Kovtun, H. A.
Source:
APPLIED PHYSICS LETTERS, 103 (18):10.1063/1.4824929 OCT 28 2013
Abstract:
The phenomenological analysis of incommensurate magnetic states in multiferroic TbMnO3 in magnetic field along the modulation wave vector is provided. The incommensurate state of manganese spins after the polarization flop (reorientation of electric polarization by 90 degrees) is assumed. The key role of magnetic anisotropic energy of the fourth order in polarization flop and existence of tricritical point on the phase diagram is shown. The competition between different terms of the fourth order of anisotropic energy is a reason of the reorientation of spin cycloid plane, leading to polarization flop. Calculated phase diagram is in a good agreement with the experimental data. (c) 2013 AIP Publishing LLC.
Title:
Rosette patterns - a common description for both crystalline and quasicrystalline structures
Authors:
Ruhnow, M Author Full Names: Ruhnow, M.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 48 (9):612-621; 10.1002/crat.201300175 SEP 2013
Abstract:
Crystalline structures are generally considered to be the normal case and quasicrystals a rare peculiarity. An attempt has been made to find a generalized view for both of these long range ordered atomic arrangements. It has been shown that they can be understood in terms of an angle-periodic rosette pattern. The three-dimensional wall paper design patterns, normally used to describe crystalline structures, are a large subgroup of this rosette pattern supergroup, which have the additional characteristics of translational periodicity. The topic is dealt with from a combined crystallographic and solid state physics point of view. The covalent bonding in the quasicrystals is an important prerequisite for their appearance. (C) 2013 WILEY- VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
The parameters that play role in numerical parameter variation in two-center holographic recording in photorefractive lithium niobate (LiNbO3) and strontium barium niobate (SrxBa1-xNb2O6)
Authors:
Demirbilek, R; Kilic, M Author Full Names: Demirbilek, Riza; Kilic, Mehmet
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 210 (8):1641-1646; 10.1002/pssa.201228800 AUG 2013
Abstract:
We have conducted a numerical study of the dependence of nonvolatile data storage on the holographic parameter variation for a two-center holographic recording (TCHR) process. Parameters of the photorefractive crystals and the experimental conditions such as the electron mobility in the conduction band, the level concentrations, the electron-recombination coefficients, the bulk photovoltaic coefficient, the spatial period of modulation, the dielectric constant, and the modulation depth are studied numerically. The results of the numerical calculations showed that the significant parameters are the electron mobility in the conduction band, the electron-recombination coefficient, and the concentrations of the dopant levels (levels created due to the dopants) in the TCHR process. It seems that the electron-recombination coefficient for deep levels plays a more important role than the other parameters.
Title:
1-Periodic Nanostructures
Authors:
Diudea, MV; Bucila, VR; Proserpio, DM Author Full Names: Diudea, Mircea V.; Bucila, Virginia R.; Proserpio, Davide M.
Source:
MATCH-COMMUNICATIONS IN MATHEMATICAL AND IN COMPUTER CHEMISTRY, 70 (2):545-564; 2013
Abstract:
Triply periodic structures are the usual subjects of crystallographic studies while the objects of these are the crystals or reticulations. There are amorphous materials with no ordered atomic arrays and some ordered structures with no translational periodicity, eventually called quasicrystals. This study presents a variety of five-fold symmetry molecular networks with 1-periodicity. The construction and topology (the genus calculation included) of these structures is described in terms of the net parameters, in a crystallographic manner.

Update: 18-Dec-2013

Title:
Production of Al-Cu-Fe metallic foams without foaming agents or space holders
Authors:
Suarez, MA; Figueroa, IA; Gonzalez, G; Lara-Rodriguez, GA; Novelo-Peralta, O; Alfonso, I; Calvo, IJ Author Full Names: Suarez, M. A.; Figueroa, I. A.; Gonzalez, G.; Lara-Rodriguez, G. A.; Novelo-Peralta, O.; Alfonso, I.; Calvo, I. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 585 318-324; 10.1016/j.jallcom.2013.08.015 FEB 5 2014
Abstract:
This investigation presents a study on the intrinsic formation of Al68Cu20Fe12 alloy foams, i.e. without the need of foaming agents or space holders. This alloy was slowly solidified in the furnace crucible, producing a multiphase microstructure, mainly composed by the lambda-Al13Fe4, I-icosahedral, theta-Al2Cu and omega-Al7Cu2Fe phases. Several heat treatments were carried out to a number of as-cast alloy samples in order to produce foams with porosities above 60%. The microstructure, thermal properties, pore morphology and porosity were characterized by means of SEM, DTA, Image analyzer and Archimedes principle, respectively. The highest amount of macro porosity of up to 65% and a density of 1.5 g/cm(3) in the treated sample were found at 900 degrees C for 360 min. At this temperature, a highly porous structure formed mainly by the lambda-Al13Fe4, I-icosahedral and omega-Al7Cu2Fe phase was obtained. The proposed mechanism for the intrinsic porosity formation is based on the high amount of liquid phase generated by the melting of the Cu-rich phases and the peritectic reaction. The reaction between the lambda-Al13Fe4 and the liquid phases formed the highly dense omega-Al7Cu2Fe and I-icosahedral phases. Thus, the space that is left behind caused the highly porous structure in this material. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Effect of quasicrystal phase on mechanical properties and damping capacities of Mg-Zn-Y-Zr alloys
Authors:
Ma, R; Dong, XP; Chen, SQ; Pan, Z; Ling, HJ; Fan, ZT Author Full Names: Ma, Rong; Dong, Xuanpu; Chen, Shuqun; Pan, Zhang; Ling, Hongjiang; Fan, Zitian
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 587 328-335; 10.1016/j.msea.2013.07.035 DEC 10 2013
Abstract:
Four Mg-5x%Zn-x%Y-0.6%Zr alloys reinforced with the I-Mg3YZn6 quasiaystal phase were fabricated by introducing Zn and Y elements into Mg-0.6%Zr alloys under conventional solidification condition. Due to the coherent lattice relationship between the I-Mg3YZn6 phase and the alpha-Mg matrix, the grain sizes of the Mg-Zn-Y-Zr alloys are obviously refined and the tensile strengths are largely improved to a maximum value of 216 MPa. The fracture mechanism transformed from cleavage fracture to quasi-cleavage fracture with increasing amount of I-Mg3YZn6 phase. The damping capacities of the Mg-Zn-Y-Zr alloys decrease with the increasing I-Mg3YZn6 phase and the damping behavior can be explained with the G-L dislocation model. The forming of the I-Mg3YZn6 phase makes more grain boundaries, phases and interfaces generate in the alloys. And the dislocation densities in the alloys hardly changes as little residual stress or entanglement of dislocation generates at the interface between the I-Mg3YZn6 phase and the alpha-Mg matrix. So the damping values are reduced accordingly with the strong pinning points on dislocations increasing tremendously. (C) 2013 Published by Elsevier B.V.
Title:
Interplay of Charge-Density Wave and Magnetic Order in Ternary Rare-Earth Nickel Carbides, RNiC2 (R = Pr and Nd)
Authors:
Yamamoto, N; Kondo, R; Maeda, H; Nogami, Y Author Full Names: Yamamoto, Nobuki; Kondo, Ryusuke; Maeda, Hiroyuki; Nogami, Yoshio
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (12):10.7566/JPSJ.82.123701 DEC 2013
Abstract:
The electrical and structural properties of NdNiC2 and PrNiC2 are examined in single-crystalline samples in order to investigate the interplay of charge-density wave (CDW) and magnetic order in ternary rare-earth nickel carbides, RNiC2, where R is a rare-earth element. PrNiC2 (no magnetic order down to 1.5 K) and NdNiC2 [antiferromagnetic (AF) transition at 17.2 K] show resistance anomalies at 89 and 121 K, respectively, which are revealed to be CDW transitions by observing X-ray satellite reflections. NdNiC2 also shows a gradual decrease in both resistivity and CDW amplitude below the Neel temperature. In the AF phase, the magnetoresistance sharply decreases where a ferromagnetic (FM) order occurs, which is realized above the spin-flop magnetic field. These results clearly suggest that the relationships between CDW and magnetic order in RNiC2 depend on whether the magnetic order is AF or FM.
Title:
Competing Magnetic Anisotropy Fields and Double Polarization Flops in Multiferroic Mn1-xCoxWO4
Authors:
Song, YS; Chung, JH; Chun, SH; Kim, KH; Schefer, J Author Full Names: Song, Young-Sang; Chung, Jae-Ho; Chun, Sae Hwan; Kim, Kee Hoon; Schefer, Juerg
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (12):10.7566/JPSJ.82.124716 DEC 2013
Abstract:
We report the cobalt doping dependencies of the ferroelectric polarization and underlying incommensurate spiral magnetic ordering in multiferroic Mn1-xCoxWO4 (0 <= x < 0.18). The spiral ordering changed its rotational plane upon cobalt doping (x similar to 0.1), followed by heliconical ordering at higher doping (x > 0.15). These consecutive changes were accompanied by simultaneous 90 degrees flops of ferroelectric polarizations. Such doping dependencies are driven by the competitions between the anisotropy fields of MnWO4 and CoWO4, the spatial distributions of which are nearly orthogonal to each other. We propose a model that can consistently describe the two consecutive flops based on a combined picture of magnetic anisotropy and biquadratic exchange.
Title:
Theory of Antiferromagnetic Order in High-T-c Oxides: An Approach Based on Ginzburg-Landau Expansion
Authors:
Hayashi, M; Tanuma, Y; Kuboki, K Author Full Names: Hayashi, Masahiko; Tanuma, Yasunari; Kuboki, Kazuhiro
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (12):10.7566/JPSJ.82.124705 DEC 2013
Abstract:
The mean-field phase diagram of antiferromagnetic order in t-J model has been examined, using the free energy obtained by Ginzburg-Landau (GL) expansion. We extended the usual GL theory in two ways: First, we have included higher order terms with respect to the spatial derivative (or wave number) to incorporate the incommensurate antiferromagnetic order. Second, we have also included higher order terms with respect to the order parameter amplitude, in order to treat the first order phase transition between paramagnetic and antiferromagnetic phase, which appears at some doping rates. We found the possibility of tricritical point and critical endpoint in the magnetic phase diagram of the high-T-c oxides associated with the commensurate and incommensurate antiferromagnetic order. The possible effects of thermal fluctuations and randomness (spin glass) are also discussed qualitatively based on the GL free energy.
Title:
Ultrathin quasicrystals
Authors:
Taroni, A Author Full Names: Taroni, Andrea
Source:
NATURE MATERIALS, 12 (12):1080-1080; DEC 2013
Title:
Complex magnetic couplings in Co3TeO6
Authors:
Wang, CW; Lee, CH; Li, CY; Wu, CM; Li, WH; Chou, CC; Yang, HD; Lynn, JW; Huang, QZ; Harris, AB; Berger, H Author Full Names: Wang, Chin-Wei; Lee, Chi-Hung; Li, Chi-Yen; Wu, Chun-Ming; Li, Wen-Hsien; Chou, Chih-Chieh; Yang, Hung-Duen; Lynn, Jeffrey W.; Huang, Qingzhen; Harris, A. Brooks; Berger, Helmuth
Source:
PHYSICAL REVIEW B, 88 (18):10.1103/PhysRevB.88.184427 NOV 26 2013
Abstract:
We report powder and single-crystal neutron diffractionmeasurements, combinedwith x-ray powder diffraction data, to unravel the complex magnetic phase diagram and exchange coupling in Co3TeO6. The magnetic structures of the various phases differ markedly from those proposed by Ivanov et al. [Mater. Res. Bull. 47, 63 (2012)] on the basis of only powder diffraction data. The dominant exchange interactions are identified by considering the geometrical arrangement of severely distorted CoO6 octahedra and CoO4 tetrahedra, which naturally divide into two different types of layers, one of which consists of zigzag chains. These zigzag chains are the first to develop magnetic order at T-M1 = 26 K, which is incommensurate in nature. The other separate layer of Co spins develops antiferromagnetic order of Gamma 4 symmetry at zero wave vector at T-M2 = 19.5 K. Our results are consistent with the previous findings of a spontaneous polarization below T-M3 = 18 K. Our neutron powder diffraction data indicate that the increase in the single-crystal (600) Bragg peak is due to a relief of extinction rather than to magnetic effects associated with the observed anomalous variation in the incommensurate wave vector at T-M4 = 16 K. The commensurate order parameter is shown to have a small dependence on the applied electric field, whereas no such effect is found for the incommensurate ordering. Below T-M3, the thermal expansion is negative, and it also exhibits anomalies at T-M2 and T-M4. A symmetry analysis and comprehensive phase diagram are given.
Title:
Electronic phase separation in iron pnictides
Authors:
Sboychakov, AO; Rozhkov, AV; Kugel, KI; Rakhmanov, AL; Nori, F Author Full Names: Sboychakov, A. O.; Rozhkov, A. V.; Kugel, K. I.; Rakhmanov, A. L.; Nori, Franco
Source:
PHYSICAL REVIEW B, 88 (19):10.1103/PhysRevB.88.195142 NOV 22 2013
Abstract:
A mechanism for electronic phase separation in iron pnictides is proposed. It is based on the competition between commensurate and incommensurate spin-density-wave phases in a system with an imperfect doping-dependent nesting of a multisheeted Fermi surface. We model the Fermi surface by two elliptical electron pockets and three circular hole pockets. The interaction between a charge carrier in a hole band and a carrier in an electron band leads to the formation of spin-density-wave order. The commensurate spin density wave in the parent compound transforms to the incommensurate phase when doping is introduced. We show that, for certain parameter values, the uniform state is unstable with respect to phase separation. The resulting inhomogeneous state consists of regions of commensurate and incommensurate spin-density-wave phases. Our results are in qualitative agreement with recent observations of incommensurate spin density waves and electronic inhomogeneity in iron pnictides.
Title:
Incommensurate Modulation and Luminescence in the CaGd2(1-x)Eu-2x(MoO4)(4(1-y))(WO4)(4y) (0 <= x <= 1, 0 <= y <= 1) Red Phosphors
Authors:
Morozov, VA; Bertha, A; Meert, KW; Van Rompaey, S; Batuk, D; Martinez, GT; Van Aert, S; Smet, PF; Raskina, MV; Poelman, D; Abakumov, AM; Hadermann, J Author Full Names: Morozov, Vladimir A.; Bertha, Anne; Meert, Katrien W.; Van Rompaey, Senne; Batuk, Dmitry; Martinez, Gerardo T.; Van Aert, Sandra; Smet, Philippe F.; Raskina, Maria V.; Poelman, Dirk; Abakumov, Artem M.; Hadermann, Joke
Source:
CHEMISTRY OF MATERIALS, 25 (21):4387-4395; 10.1021/cm402729r NOV 12 2013
Abstract:
Scheelite related compounds (A',A '') [(B',B '')O-4], with B', B '' = W and/or Mo are promising new light-emitting materials for photonic applications, including phosphor converted LEDs (light-emitting diodes). In this paper, the creation and ordering of A-cation vacancies and the effect of cation substitutions in the scheelite-type framework are investigated as a factor for controlling the scheelite-type structure and luminescent properties. CaGd2(1-x)Eu2x(MoO4)(4(1-y))(WO4)(4y) (0 <= x <= 1, 0 <= y <= 1) solid solutions with scheelite-type structure were synthesized by a solid state method, and their structures were investigated using a combination of transmission electron microscopy techniques and powder X-ray diffraction. Within this series all complex molybdenum oxides have (3 + 2)D incommensurately modulated structures with superspace group I4(1)/a(alpha,beta,0)00(-beta,alpha,0)00, while the structures of all tungstates are (3 + 1)D incommensurately modulated with superspace group I2/b(alpha beta 0)00. In both cases the modulation arises because of cation-vacancy ordering at the A site. The prominent structural motif is formed by columns of A-site vacancies running along the c-axis. These vacant columns occur in rows of two or three aligned along the [110] direction of the scheelite subcell. The replacement of the smaller Gd3+ by the larger Eu3+ at the A-sublattice does not affect the nature of the incommensurate modulation, but an increasing replacement of Mo6+ by W6+ switches the modulation from (3 + 2)D to (3 + 1)D regime. Thus, these solid solutions can be considered as a model system where the incommensurate modulation can be monitored as a function of cation nature while the number of cation vacancies at the A sites remain constant upon the isovalent cation replacement. All compounds' luminescent properties were measured, and the optical properties were related to the structural properties of the materials. CaGd2(1-x)(MoO4)(4(1-y))(WO4)(4y) phosphors emit intense red light dominated by the D-5(0)-F-7(2) transition at 612 nm, along with other transitions from the D-5(1) and D-5(0) excited states. The intensity of the 5D0-7F2 transition reaches a maximum at x = 0.5 for y = 0 and 1.
Title:
Crystal structures of X-phase in the Sb-Te binary alloy system
Authors:
Kifune, K; Fujita, T; Tachizawa, T; Kubota, Y; Yamada, N; Matsunaga, T Author Full Names: Kifune, K.; Fujita, T.; Tachizawa, T.; Kubota, Y.; Yamada, N.; Matsunaga, T.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 48 (11):1011-1021; 10.1002/crat.201300252 NOV 2013
Abstract:
It is well known that the Sb-Te binary system has a large number of incommensurately or commensurately modulated structures between Sb and Sb2Te3 compounds. These structures, which are long-period trigonal stacking structures, possess their own modulation period , according to their composition in the thermal equilibrium. However, the structure of sputtered Sb-Te films with various compositions between the two compounds at both ends formed in a non-thermal equilibrium showed smaller values, than those expected from their compositions without exception. A smaller value implies that its structure is closer to that of Sb with the shortest period in all Sb-Te modulated structures. With increase in temperature, all these transient structures with smaller , however, became stable, accompanying an increase of to acquire their original modulated structures.

Update: 12-Dec-2013

Title:
Effect of quasicrystalline phase on improving the corrosion resistance of a duplex structured Mg-Li alloy
Authors:
Xu, DK; Han, EH Author Full Names: Xu, D. K.; Han, E. H.
Source:
SCRIPTA MATERIALIA, 71 21-24; 10.1016/j.scriptamat.2013.09.025 JAN 15 2014
Abstract:
The in situ formation of I-phase improves the corrosion resistance of the duplex structured Mg-6% Li alloy. Corrosion attack on the surfaces of Mg-6% Li alloy is very inhomogeneous and severe pits and filiform corrosion clearly occur on the surfaces after immersion in 0.1 M NaCl solution. For the I-phase-containing Mg-6% Li-6% Zn-1.2% Y alloy, the corrosion attack is homogeneous and no severe pits and filiform corrosion can be observed. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Modulated crystal structure of Pr2SbO2
Authors:
Magdysyuk, OV; Nuss, J; Jansen, M Author Full Names: Magdysyuk, Oxana V.; Nuss, Juergen; Jansen, Martin
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 69 547-555; 10.1107/S2052519213029436 6 DEC 2013
Abstract:
The crystal structure of commensurately modulated Pr2SbO2 was solved in the orthorhombic superspace group Immm(0 beta 0)000, q = 3/4b*, a = 13.5790 (15), b = 3.9818 (18), c = 4.0041 (18) angstrom (T = 40 K) from a crystal twinned by reticular pseudomerohedry applying the twin law (1 0 0, 0 0 1, 0-10), corresponding to a rotation by 90 degrees along the reciprocal a axis. The formation of Zintl- type Sb2--Sb2- dumbbells in Pr-2(3+) Sb2-O22- is considered to be accountable for its semiconducting properties, as observed previously. The space group for the three- dimensional commensurate super-cell a = 13.5790 (15), b = 15.9272 (18), c = 4.0041 (18) angstrom (T = 40 K) is Pmnm.
Title:
Spin-Peierls distortions in TiPO4
Authors:
Bykov, M; Zhang, J; Schonleber, A; Wolfel, A; Ali, SI; van Smaalen, S; Glaum, R; Koo, HJ; Whangbo, MH; Reuvekamp, PG; Law, JM; Hoch, C; Kremer, RK Author Full Names: Bykov, Maxim; Zhang, Jian; Schoenleber, Andreas; Woelfel, Alexander; Ali, Sk Imran; van Smaalen, Sander; Glaum, R.; Koo, H. -J.; Whangbo, M. -H.; Reuvekamp, P. G.; Law, J. M.; Hoch, C.; Kremer, R. K.
Source:
PHYSICAL REVIEW B, 88 (18):10.1103/PhysRevB.88.184420 NOV 19 2013
Abstract:
On the basis of single-crystal x-ray diffraction we show that TiPO4 undergoes a spin-Peierls distortion below 74.5(5) K, with a dimerization of the Ti chains along the c axis. Between 74.5(5) and 111.6(3) K, TiPO4 develops an incommensurate (IC) phase with temperature-dependent q vector (sigma(1),0,0). Density functional calculations strongly suggest that the IC phase results from a frustration of the lock-in spin-Peierls transition due to the competition of three energetically almost degenerate crystal structures and elastic coupling of the Ti chains via the bridging PO4 units. The phase transition into the IC phase is of second order, but the lock-in transition into the spin-Peierls distortion below 74.5 K is of weak first order in nature.
Title:
Crystal and Magnetic Structure in Co-Substituted BiFeO3
Authors:
Sosnowska, I; Azuma, M; Przenioslo, R; Wardecki, D; Chen, WT; Oka, K; Shimakawa, Y Author Full Names: Sosnowska, Izabela; Azuma, Masaki; Przenioslo, Radoslaw; Wardecki, Dariusz; Chen, Wei-tin; Oka, Kengo; Shimakawa, Yuichi
Source:
INORGANIC CHEMISTRY, 52 (22):13269-13277; 10.1021/ic402427q NOV 18 2013
Abstract:
Ultra-high-resolution neutron diffraction studies of BiFe0.8Co0.2O3 show a transition from a cycloidal space modulated spin structure at T = 10 K to a collinear G-type antiferromagnetic structure at T = 120 K. The model of antiparallel directions of Fe3+ and Co3+ magnetic moments at the shared Wyckoff position describes well the observed neutron diffraction intensities. On heating above RT, the crystal structure of BiFe0.8Co0.2O3 changes from a rhombohedral R3c to a monoclinic Cm. At 573 K only the Cm phase is present. The collinear C-type antiferromagnetic structure is present in the Cm phase of BiFe0.8Co0.2O3 at RT after annealing.
Title:
Problem Solving with Pentagons: Tsai-Type Quasicrystal as a Structural Response to Chemical Pressure
Authors:
Berns, VM; Fredrickson, DC Author Full Names: Berns, Veronica M.; Fredrickson, Daniel C.
Source:
INORGANIC CHEMISTRY, 52 (22):12875-12877; 10.1021/ic402412k NOV 18 2013
Abstract:
Even after significant advances in the structural characterization of quasicrystals-phases whose diffraction patterns combine the sharp peaks normally associated with lattice periodicity and rotational symmetries antithetical to such periodicity this new form of long-range order remains enigmatic. Here, we present DFT-chemical pressure calculations on the Tsai-type quasicrystal approximant CaCd6, which reveal how its icosahedral clusters can be traced to simple CaCu5-type (hP6) intermetallics. The results indicate that the Tsai-type clusters emerge from an atomic-size-driven transformation from planar arrangements to spherical clusters, recalling the relationship between graphene and C-60.
Title:
Incommensurately Modulated delta ''-Au1+xCd2-x Formed by an Unquenchable Phase Transformation from the gamma-Brass delta '-Phase
Authors:
Jana, PP; Lidin, S Author Full Names: Jana, Partha P.; Lidin, Sven
Source:
INORGANIC CHEMISTRY, 52 (22):12980-12985; 10.1021/ic4013608 NOV 18 2013
Abstract:
The synthesis and structural determination of the compound delta"-Au1-xCd2-x, (0.07 <= x <= 0.08) is reported. The structure may be formally derived from that of xi-CoZn13, but elemental ordering causes an incommensurate modulation as determined by single-crystal X-ray diffraction at room temperature. The compound delta"-Au3.23Cd5.76 crystallizes in the monoclinic super space group C2/m(0 beta 1/2)00 with lattice parameters a = 14.790(2) angstrom, b = 8.251(1) angstrom, c = 12.744(1) angstrom, beta = 115.182(9)degrees and a q-vector q = (0 beta 1/2), beta = 0.579b*. The delta ''-phase is stable up to 652(1) K.
Title:
Interlayer Magnetoresistance due to Chiral Soliton Lattice Formation in Hexagonal Chiral Magnet CrNb3S6
Authors:
Togawa, Y; Kousaka, Y; Nishihara, S; Inoue, K; Akimitsu, J; Ovchinnikov, AS; Kishine, J Author Full Names: Togawa, Y.; Kousaka, Y.; Nishihara, S.; Inoue, K.; Akimitsu, J.; Ovchinnikov, A. S.; Kishine, J.
Source:
PHYSICAL REVIEW LETTERS, 111 (19):10.1103/PhysRevLett.111.197204 NOV 7 2013
Abstract:
We investigate the interlayer magnetoresistance (MR) along the chiral crystallographic axis in the hexagonal chiral magnet CrNb3S6. In a region below the incommensurate-commensurate phase transition between the chiral soliton lattice and the forced ferromagnetic state, a negative MR is obtained in a wide range of temperature, while a small positive MR is found very close to the Curie temperature. Normalized data of the negative MR almost falls into a single curve and is well fitted by a theoretical equation of the soliton density, meaning that the origin of the MR is ascribed to the magnetic scattering of conduction electrons by a nonlinear, periodic, and countable array of magnetic soliton kinks.
Title:
Superspace approach to high pressure superstructures
Authors:
Bykov, M; Bykova, E; Hanfland, M; Liermann, HP; van Smaalen, S Author Full Names: Bykov, Maxim; Bykova, Elena; Hanfland, Michael; Liermann, Hanns-Peter; van Smaalen, Sander
Source:
HIGH PRESSURE RESEARCH, 33 (3):501-510; SI 10.1080/08957959.2013.822076 AUG 20 2013
Abstract:
Single-crystal X-ray diffraction in a diamond anvil cell has proven to be a powerful tool for studying matter at extreme conditions. Displacive zone-boundary phase transitions between a high-symmetry low pressure structure and a low-symmetry high pressure superstructure represent a significant part of pressure-induced processes. However, the analysis of such superstructures is usually complicated by low angular resolution and limited reciprocal space coverage. This leads to unfavorable data/parameter ratio during the structure solution and refinement. The superspace approach is an established method to describe commensurately modulated structures, however it is not often applied to high pressure phase transitions. Here, we discuss the advantages of the superspace approach for the description and crystal-chemical analysis of high pressure superstructures. The main ideas of this approach are illustrated by the examples of isostructural FeOCl and CrOCl, forming different superstructures above 15 GPa.
Title:
Determining complex crystal structures from high pressure single-crystal diffraction data collected on synchrotron sources
Authors:
McMahon, MI; Loa, I; Stinton, GW; Lundegaard, LF Author Full Names: McMahon, M. I.; Loa, I.; Stinton, G. W.; Lundegaard, L. F.
Source:
HIGH PRESSURE RESEARCH, 33 (3):485-500; SI 10.1080/08957959.2013.831087 AUG 20 2013
Abstract:
As part of a Long Term Project, single-crystal diffraction techniques have been developed for use at the high pressure beamlines ID09 and ID27 at the European Synchrotron Radiation Facility, and have been utilised to determine the crystal structures of various high pressure phases, including those with incommensurate structures, at both high and low temperatures. The same techniques have also been used to determine the structures of high pressure phases at the SRS, Diamond and Petra-III synchrotron sources. In this paper, we describe technical details of the methods developed, and describe some of the considerations necessary for planning experiments and collecting and processing the data. We then illustrate the quality of data that can be obtained, and the complexity of the structures that can be refined, using recent results obtained from complex high pressure phases of N-2 and Ba.
Title:
The Anisotropic Glassy Properties of Decagonal Quasicrystals
Authors:
Anghel, DV; Churochkin, DV Author Full Names: Anghel, Dragos-Victor; Churochkin, Dmitry V.
Source:
ADVANCES IN CONDENSED MATTER PHYSICS, 10.1155/2013/419202 2013
Abstract:
We use an extended version of the standard tunnelingmodel to explain the anisotropic sound absorption in decagonal quasicrystals. The glassy properties are determined by an ensemble of two level systems (TLSs), arbitrarily oriented. The TLS is characterized by a 3 x 3 symmetric tensor, [T], which couples to the strain field, [S], through a 3 x 3 x 3 x 3 tensor of coupling constants, [R]. The structure of [R] reflects the symmetry of the quasicrystal. We also analyze the probability distributions of the elements of [T] in this particular model for a better understanding of the characteristics of "isotropic" and "anisotropic" distributions of the ensemble of TLSs. We observe that the distribution of the elements is neither simple nor intuitive and therefore it is difficult to guess it a priory, using qualitative arguments based on the symmetry properties.

Update: 4-Dec-2013

Title:
Numerical methods for quasicrystals
Authors:
Jiang, K; Zhang, PW Author Full Names: Jiang, Kai; Zhang, Pingwen
Source:
JOURNAL OF COMPUTATIONAL PHYSICS, 256 428-440; 10.1016/j.jcp.2013.08.034 JAN 1 2014
Abstract:
Quasicrystals are one kind of space-filling structures. The traditional crystalline approximant method utilizes periodic structures to approximate quasicrystals. The errors of this approach come from two parts: the numerical discretization, and the approximate error of Simultaneous Diophantine Approximation which also determines the size of the domain necessary for accurate solution. As the approximate error decreases, the computational complexity grows rapidly, and moreover, the approximate error always exits unless the computational region is the full space. In this work we focus on the development of numerical method to compute quasicrystals with high accuracy. With the help of higher-dimensional reciprocal space, a new projection method is developed to compute quasicrystals. The approach enables us to calculate quasicrystals rather than crystalline approximants. Compared with the crystalline approximant method, the projection method overcomes the restrictions of the Simultaneous Diophantine Approximation, and can also use periodic boundary conditions conveniently. Meanwhile, the proposed method efficiently reduces the computational complexity through implementing in a unit cell and using pseudospectral method. For illustrative purpose we work with the Lifshitz-Petrich model, though our present algorithm will apply to more general systems including quasicrystals. We find that the projection method can maintain the rotational symmetry accurately. More significantly, the algorithm can calculate the free energy density to high precision. (C) 2013 Elsevier Inc. All rights reserved.
Title:
Crystal-quasicrystal transition depending on cooling rates in directionally solidified Al-3Mn-7Be (at.%) alloy
Authors:
Kang, HJ; Li, XZ; Wang, TM; Liu, DM; Su, YQ; Hu, ZL; Guo, JJ; Fu, HZ Author Full Names: Kang, Huijun; Li, Xinzhong; Wang, Tongmin; Liu, Dongmei; Su, Yanqing; Hu, Zhonglve; Guo, Jingjie; Fu, Hengzhi
Source:
INTERMETALLICS, 44 101-105; 10.1016/j.intermet.2013.09.004 JAN 2014
Abstract:
The transition of primary phases from the crystalline approximant phase to icosahedral quasicrystal phase (I-phase) is observed in the directional solidified Al-3Mn-7Be (at.%) alloy. The structures of I-phase and approximant phases are characterized by SEM, TEM and HRTEM. The addition of Be significantly enhances the formation ability of I-phase, combining with the directional solidification method where the growth rates and temperature gradients can be separately controlled, giving rise to a promising way to prepare quasicrystal-reinforced Al-matrix composite. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Switching kinetics of the ferroelectric transition in K2SeO4 studied by stroboscopic gamma-ray diffraction
Authors:
Leist, J; Gibhardt, H; Eckold, G Author Full Names: Leist, J.; Gibhardt, H.; Eckold, G.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (46):10.1088/0953-8984/25/46/465901 NOV 20 2013
Abstract:
The kinetics of the ferroelectric lock-in transition in potassium selenate (K2SeO4) was studied on a millisecond timescale using high-resolution gamma-ray diffraction. A large change of the line width and wavevector of the first order satellite is observed during the switching process. This is attributed to a loss of long-range order under the influence of the electric field. In addition, the incommensurate phase is stabilized by the pulsed field and the transition to the pure commensurate phase is shifted to lower temperatures. Strains that may build up during the rapid switching process are supposed to be the reason for this behaviour.
Title:
Short-range order and singularities of the electronic structure of icosahedral quasicrystals
Authors:
Prekul, AF; Shchegolikhina, NI Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.
Source:
PHYSICS OF THE SOLID STATE, 55 (11):2260-2266; 10.1134/S106378341311019X NOV 2013
Abstract:
For icosahedral phases of the Al-Cu-Fe system, components of the electrical conductivity, magnetic susceptibility, Hall effect, and heat capacity associated with thermally induced charge carriers for the first time have been considered jointly over a wide temperature range. It has been shown that the full range of thermal effects can be understood in the framework of the unified concept, which is based on an inhomogeneous system of two-level electronic excitations. A model of the inhomogeneous electronic state and the mechanism of its formation with the dominant role of short-range order have been proposed.
Title:
"Bite like a Rottweiler"
Authors:
Remenyi, C; Koster, V; Shechtman, D Author Full Names: Remenyi, Christian; Koester, Vera; Shechtman, Dan
Source:
NACHRICHTEN AUS DER CHEMIE, 61 (11):1107-1108; 10.1002/nadc.201390359 NOV 2013
Abstract:
2011 Nobel prize laureate Dan Shechtman talks about quasicrystals, jewelry and being stubborn.
Title:
Lamellar structure and nanomechanical properties of quasicrystalline Al-Cu-Fe alloys
Authors:
Shalaeva, EV; Chernyshev, YV; Smirnova, EO; Smirnov, SV Author Full Names: Shalaeva, E. V.; Chernyshev, Yu. V.; Smirnova, E. O.; Smirnov, S. V.
Source:
PHYSICS OF THE SOLID STATE, 55 (11):2205-2214; 10.1134/S106378341311022X NOV 2013
Abstract:
The kinetics of structural phase transformations in quasicrystal-forming Al-Cu-Fe alloys with compositions in the region of stability of the icosahedral (i) phase has been investigated. It has been shown that, depending on the development of metastable transformations i -> pentagonal phases P1 and P2, a homogeneous lamellar structure (i + P1 + P2) or a polygrain i-phase is formed in the alloys. The P-h diagrams obtained upon nanoindentation, atomic force microscopy, and scanning electron microscopy of indentations have demonstrated signs of elasto-plastic deformation of the alloys with lamellar and polygrain icosahedral structures. It has been found that, in contrast to the polygrain icosahedral alloys with a normal size effect of nanoindentation, the alloys with a lamellar structure are characterized by a nonmonotonic dependence of the hardness (H) on the maximum load (P (max)) and exhibit the effect of strain hardening in the range of loads 50 mN a parts per thousand currency sign P (max) < 500 mN. The strain hardening is considered as the result of resistance exerted by boundaries of the lamellar structure to the development of plastic deformation.
Title:
beta-Technetium Dichloride: Solid-State Modulated Structure, Electronic Structure, and Physical Properties
Authors:
Malliakas, CD; Poineau, F; Johnstone, EV; Weck, PF; Kim, E; Scott, BL; Forster, PM; Kanatzidis, MG; Czerwinski, KR; Sattelberger, AP Author Full Names: Malliakas, Christos D.; Poineau, Frederic; Johnstone, Erik V.; Weck, Philippe F.; Kim, Eunja; Scott, Brian L.; Forster, Paul M.; Kanatzidis, Mercouri G.; Czerwinski, Kenneth R.; Sattelberger, Alfred P.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 135 (42):15955-15962; 10.1021/ja408459k OCT 23 2013
Abstract:
A second polymorph of technetium dichloride, beta-TcCl2, has been synthesized from the reaction of Tc metal and chlorine in a sealed tube at 450 degrees C. The crystallographic structure and physical properties of beta-TcCl2 have been investigated. The structure of beta-TcCl2 consists of infinite chains of face sharing [Tc2Cl8] units; within a chain, the Tc Tc vectors of two adjacent [Tc2Cl8] units are ordered in the long-range where perpendicular and/or parallel arrangement of Tc Tc vectors yields a modulated structure. Resistivity and Seebeck measurements performed on a beta-TcCl2 single crystal indicate the compound to be a p-type semiconductor while a magnetic susceptibility measurement shows technetium dichloride to be diamagnetic. A band gap of 0.12(2) eV was determined by reflectance spectroscopy measurements. Theoretical calculations at the density functional level were utilized for the investigation of other possible stable forms of TcCl2.

Update: 27-Nov-2013

Title:
de Haas-van Alphen effect and Fermi surface properties of single-crystal CrB2
Authors:
Brasse, M; Chioncel, L; Kunes, J; Bauer, A; Regnat, A; Blum, CGF; Wurmehl, S; Pfleiderer, C; Wilde, MA; Grundler, D Author Full Names: Brasse, M.; Chioncel, L.; Kunes, J.; Bauer, A.; Regnat, A.; Blum, C. G. F.; Wurmehl, S.; Pfleiderer, C.; Wilde, M. A.; Grundler, D.
Source:
PHYSICAL REVIEW B, 88 (15):10.1103/PhysRevB.88.155138 OCT 31 2013
Abstract:
We report the angular dependence of three distinct de Haas-van Alphen (dHvA) frequencies of the torque magnetization in the itinerant antiferromagnet CrB2 at temperatures down to 0.3 K and magnetic fields up to 14 T. Comparison with the Fermi surface calculations considering an incommensurate cycloidal magnetic order suggests that two of the observed dHvA oscillations arise from electronlike Fermi surface sheets formed by bands with strong B-p(x,y) character. The third orbit could correspond to a Cr-d derived Fermi surface sheet. The measured effective masses of these Fermi surface sheets display strong enhancements of a factor of about 2 over the calculated band masses which can be attributed to electron-phonon coupling and electronic correlations. Signatures of further heavy d-electron bands that are predicted by the calculations are not observed in the temperature and field range studied. In the view that the B-p bands are at the heart of conventional high-temperature superconductivity in the isostructural MgB2, we consider possible implications of our findings for nonmagnetic CrB2 and an interplay of itinerant antiferromagnetism with superconductivity.
Title:
Effect of Lone-Electron-Pair Cations on the Orientation of Crystallographic Shear Planes in Anion-Deficient Perovskites
Authors:
Batuk, D; Batuk, M; Abakumov, AM; Tsirlin, AA; McCammon, C; Pubrovinsky, L; Hadermann, J Author Full Names: Batuk, Dmitry; Batuk, Maria; Abakumov, Artem M.; Tsirlin, Alexander A.; McCammon, Catherine; Pubrovinsky, Leonid; Hadermann, Joke
Source:
INORGANIC CHEMISTRY, 52 (17):10009-10020; 10.1021/ic4012845 SEP 2 2013
Abstract:
Factors affecting the structure and orientation of the crystallographic shear (CS) planes in anion-deficient perovskites were investigated using the (Pb1-,Srz),-xFe(1+x),,, "perovskites as a model system. The isovalent substitution of Sr2+ for Pb2+ highlights the-influence of the A cation electronic strUcture because these cations exhibit very close ionic radii. Two compositional ranges have been identified in the system: 0.05 <= z <= 0.2, where the CS plane orientation gradually varies but stays close to (203)p, and 0.3 <= z <= 0.45 with (101)p CS,planes. The incommensurately modulated structure of Pb0.792Sro.,68Fel.0,002.629 was refined from neutron powder diffraction data using the (3+ 1)D approach (space group X2/rn(alpha 0(gamma)), X -= C / 2, V2, I/2), a = 3.9512(1) A, b = 3.9483(1) A, c =3.9165(1) k, = 93.268(2)6, q =0.0879(1)a* +0.1276(1)c*, R-F = 0.023, R-p = 0.029, and T = 900 K). A comparison of the compounds with different CS planes indicates that the orientation of the CS planes is governed mainly by the stereochemical "activity of the lone-electron-pair cations inside the perovskite blocks.
Title:
Magnetic Tri-Axial Grain Alignment Achieved in Bismuth-Based Cuprate Superconductors
Authors:
Horii, S; Nagai, R; Yamaki, M; Maeda, T; Shimoyama, J; Doi, T Author Full Names: Horii, Shigeru; Nagai, Ryotaro; Yamaki, Momoko; Maeda, Toshihiko; Shimoyama, Jun-ichi; Doi, Toshiya
Source:
APPLIED PHYSICS EXPRESS, 6 (9):10.7567/APEX.6.093102 SEP 2013
Abstract:
We demonstrate the tri-axial magnetic alignment of Bi2Sr2CaCu2Oy [Bi2212] and Bi1.7Pb0.35Sr2Ca2Cu3Oy [(Bi1.7Pb0.35)2223] and report the semi-quantitative tri-axial magnetic anisotropy of Bi2212. A modulated rotating magnetic field of 10 tesla achieved degrees of in-plane and c-axis orientations of <9 and similar to 4 degrees, respectively. Conversion of magnetization axes of Bi2212 by slight Er-doping suggests that the incommensurate modulated crystal structures observed in the Bi-based cuprates induced generation of weak but strictly tri-axial magnetic anisotropy. Our present results indicate the possibility of fabricating tri-axially grain-oriented bulks and thick films without applying epitaxial growth methods, such as melt solidification and thin-film deposition. (c) 2013 The Japan Society of Applied Physics

Update: 20-Nov-2013

Title:
Microscopic coexistence of a two-component incommensurate spin density wave with superconductivity in underdoped NaFe0.983Co0.017As
Authors:
Oh, S; Mounce, AM; Lee, JA; Halperin, WP; Zhang, CL; Carr, S; Dai, PC; Reyes, AP; Kuhns, PL Author Full Names: Oh, Sangwon; Mounce, A. M.; Lee, Jeongseop A.; Halperin, W. P.; Zhang, C. L.; Carr, S.; Dai, Pengcheng; Reyes, A. P.; Kuhns, P. L.
Source:
PHYSICAL REVIEW B, 88 (13):10.1103/PhysRevB.88.134518 OCT 25 2013
Abstract:
We have performed As-75 and Na-23 nuclear magnetic resonance (NMR) measurements on a single crystal of NaFe0.9835Co0.0165As and found microscopic coexistence of superconductivity with a two-component spin density wave (SDW). Using Na-23 NMRwemeasured the spatial distribution of local magnetic fields. The SDWwas found to be incommensurate with a major component having magnetic moment (similar to 0.2 mu(B)/Fe) and a smaller component with magnetic moment (similar to 0.02 mu(B)/Fe). Spin lattice relaxation experiments reveal that this coexistence occurs at a microscopic level.
Title:
Electron doping evolution of the magnetic excitations in BaFe2-xNixAs2
Authors:
Luo, HQ; Lu, XY; Zhang, R; Wang, M; Goremychkin, EA; Adroja, DT; Danilkin, S; Deng, GC; Yamani, Z; Dai, PC Author Full Names: Luo, Huiqian; Lu, Xingye; Zhang, Rui; Wang, Meng; Goremychkin, E. A.; Adroja, D. T.; Danilkin, Sergey; Deng, Guochu; Yamani, Zahra; Dai, Pengcheng
Source:
PHYSICAL REVIEW B, 88 (14):10.1103/PhysRevB.88.144516 OCT 25 2013
Abstract:
We use inelastic neutron scattering (INS) spectroscopy to study the magnetic excitations spectra throughout the Brillouin zone in electron-doped iron pnictide superconductors BaFe2-xNixAs2 with x = 0.096,0.15,0.18. While the x = 0.096 sample is near optimal superconductivity with T-c = 20 K and has coexisting static incommensurate magnetic order, the x = 0.15,0.18 samples are electron overdoped with reduced T-c of 14 and 8 K, respectively, and have no static antiferromagnetic (AF) order. In previous INS work on undoped (x = 0) and electron optimally doped (x = 0.1) samples, the effect of electron doping was found to modify spin waves in the parent compound BaFe2As2 below similar to 100 meV and induce a neutron spin resonance at the commensurate AF ordering wave vector that couples with superconductivity. While the new data collected on the x = 0.096 sample confirm the overall features of the earlier work, our careful temperature dependent study of the resonance reveals that the resonance suddenly changes its Q width below T-c similar to that of the optimally hole-doped iron pnictides Ba0.67K0.33Fe2As2. In addition, we establish the dispersion of the resonance and find it to change from commensurate to transversely incommensurate with increasing energy. Upon further electron doping to overdoped iron pnictides with x = 0.15 and 0.18, the resonance becomes weaker and transversely incommensurate at all energies, while spin excitations above similar to 100 meV are still not much affected. Our absolute spin excitation intensity measurements throughout the Brillouin zone for x = 0.096,0.15,0.18 confirm the notion that the low-energy spin excitation coupling with itinerant electron is important for superconductivity in these materials, even though the high-energy spin excitations are weakly doping dependent.
Title:
Stable All-Nitrogen Metallic Salt at Terapascal Pressures
Authors:
Sun, J; Martinez-Canales, M; Klug, DD; Pickard, CJ; Needs, RJ Author Full Names: Sun, Jian; Martinez-Canales, Miguel; Klug, Dennis D.; Pickard, Chris J.; Needs, Richard J.
Source:
PHYSICAL REVIEW LETTERS, 111 (17):10.1103/PhysRevLett.111.175502 OCT 24 2013
Abstract:
The phase diagram and equation of state of dense nitrogen are of interest in understanding the fundamental physics and chemistry under extreme conditions, including planetary processes, and in discovering new materials. We predict several stable phases of nitrogen at multi-TPa pressures, including a P4/nbm structure consisting of partially charged N-2(delta+) pairs and N-5(delta-) tetrahedra, which is stable in the range 2.5-6.8 TPa. This is followed by a modulated layered structure between 6.8 and 12.6 TPa, which also exhibits a significant charge transfer. The P4/nbm metallic nitrogen salt and the modulated structure are stable at high pressures and temperatures, and they exhibit strongly ionic features and charge density distortions, which is unexpected in an element under such extreme conditions and could represent a new class of nitrogen materials. The P-T phase diagram of nitrogen at TPa pressures is investigated using quasiharmonic phonon calculations and ab initio molecular dynamics simulations.
Title:
Magnetic Structures of LiMBO3 (M = Mn, Fe, Co) Lithiated Transition Metal Borates
Authors:
Tao, L; Neilson, JR; Melot, BC; McQueen, TM; Masquelier, C; Rousse, G Author Full Names: Tao, Liang; Neilson, James R.; Melot, Brent C.; McQueen, Tyrel M.; Masquelier, Christian; Rousse, Gwenaelle
Source:
INORGANIC CHEMISTRY, 52 (20):11966-11974; 10.1021/ic401671m OCT 21 2013
Abstract:
The magnetic ordering within LiMBO3 compounds (M = Mn, Fe, and Co) has been explored re by magnetization measurements and neutron powder diffraction. For all M, an incommensurately ordered magnetic phase is established on cooling, followed by a change to a commensurate long-range antiferromagnetic state below T-N2 = 12(1) K for LiMnBO3, T-N2 = 25(1) K for LiFeBO3, and T-N2 = 12(1) K for LiCoBO3. For LiMnBO3, the magnetic ordering at T = 2 K exhibits a propagation vector k = (1, 0, 0) and consists of antiferromagnetic chains that are coupled antiferromagnetically to each other, the magnetic moments being oriented along the [001] direction. In contrast, the magnetic order at T=2 K in LiFeBO3 and LiCoBO3 exhibits a propagation vector of k = (1/2, 1/2, 1/2) and consists of ferromagnetic chains that are antiferromagnetically coupled. The magnetic moments lie roughly along the [02 (3) over bar] direction within the bc plane for LiFeBO3, and along the [30 (1) over bar] direction within the ac plane for LiCoBO3. The moment orientations in both LiMnBO3 and LiFeBO3 suggest an Ising character arising from unquenched orbital momentum due to unusual trigonal bipyrimidal coordination environments. No evidence of Ising behavior is found in the case of LiCoBO3.
Title:
Magnetic fluctuations and effective magnetic moments in gamma-iron due to electronic structure peculiarities
Authors:
Igoshev, PA; Efremov, AV; Poteryaev, AI; Katanin, AA; Anisimov, VI Author Full Names: Igoshev, P. A.; Efremov, A. V.; Poteryaev, A. I.; Katanin, A. A.; Anisimov, V. I.
Source:
PHYSICAL REVIEW B, 88 (15):10.1103/PhysRevB.88.155120 OCT 18 2013
Abstract:
Applying the local density and dynamical mean field approximations to paramagnetic gamma-iron we revisit the problem of the theoretical description of its magnetic properties in a wide temperature range. We show that contrary to alpha-iron, the frequency dependence of the electronic self-energy has a quasiparticle form for both t(2g) and e(g) states. In the temperature range T = 1200-1500 K, where gamma-iron exists in nature, this substance can be nevertheless characterized by temperature-dependent effective local moments, which yield relatively narrow peaks in the real part of the local magnetic susceptibility as a function of frequency. At the same time, at low temperatures gamma-iron (which is realized in precipitates) is better described in terms of the itinerant picture. In particular, the nesting features of the Fermi surfaces yield the maximum of the static magnetic susceptibility at the incommensurate wave vector q(max) belonging in the direction q(X) - q(W) (q(X) (2 pi/a)(1,0,0), q(W) (2 pi/a)(1,1/2,0), a is a lattice parameter) in agreement with the experimental data. This state is found, however, to compete closely with the states characterized by magnetic wave vectors along the directions q(X) - q(L) - q(K), where q(L) (2 pi/a)(1/2,1/2,1/2), q(K) (2 pi/a)(3/4,3/4,0). From the analysis of the uniform magnetic susceptibility we find that contrary to alpha-iron, the Curie-Weiss law is not fulfilled in a broad temperature range, although the inverse susceptibility is nearly linear in the moderate-temperature region (1200-1500 K). The nonlinearity of the inverse uniform magnetic susceptibility in a broader temperature range is due to the density of states peak located close to the Fermi level. The effective exchange integrals in the paramagnetic phase are estimated on the base of momentum-dependent susceptibility.
Title:
Hartree-Fock Ground State Phase Diagram of Jellium
Authors:
Baguet, L; Delyon, F; Bernu, B; Holzmann, M Author Full Names: Baguet, L.; Delyon, F.; Bernu, B.; Holzmann, M.
Source:
PHYSICAL REVIEW LETTERS, 111 (16):10.1103/PhysRevLett.111.166402 OCT 14 2013
Abstract:
We calculate the ground state phase diagram of the homogeneous electron gas in three dimensions within the Hartree-Fock approximation and show that broken symmetry states are energetically favored at any density against the homogeneous Fermi gas state with isotropic Fermi surface. At high density, we find metallic spin-unpolarized solutions where electronic charge and spin density form an incommensurate crystal having more crystal sites than electrons. For r(s) -> 0, our solutions approach pure spin-density waves, whereas the commensurate Wigner crystal is favored at lower densities, r(s) greater than or similar to 3.4. Decreasing the density, the system undergoes several structural phase transitions with different lattice symmetries. The polarization transition occurs around r(s) approximate to 8.5.
Title:
System-dependent melting behavior of icosahedral anti-Mackay nanoalloys
Authors:
Oderji, HY; Behnejad, H; Ferrando, R; Ding, HB Author Full Names: Oderji, Hassan Yousefi; Behnejad, Hassan; Ferrando, Riccardo; Ding, Hongbin
Source:
RSC ADVANCES, 3 (44):21981-21993; 10.1039/c3ra43401j 2013
Abstract:
Anti-Mackay icosahedral clusters of composition Ag32M13, where M is either Cu, Ni, or Co, have been recently shown to possess special structural stability both by calculations and experiments. These nanoalloys assume a core-shell arrangement, with an icosahedral core of 13 M atoms surrounded by an Ag shell of anti-Mackay structure. In this paper we study the melting of these three nanoalloys, showing that, despite the close similarity of the structures, melting takes place through quite different mechanisms. In particular, we find that Ag32Co13 and Ag32Ni13 present a premelting phenomenon which involves only the shell of the cluster while the core melts at higher temperatures, in agreement with previous calculations. On the contrary, in Ag32Cu13, melting occurs through stages that involve the shell and the core at the same time. These findings are rationalized in terms of the different features of the energy landscape of these nanoalloys. Our simulations, in which special care has been devoted to avoid non-ergodicity problems, show also that the particles keep their core-shell structures even in the liquid phase, indicating an incomplete miscibility of Ag with Ni, Co or Cu at the nanoscale up to quite high temperatures.

Update: 13-Nov-2013

Title:
The Influence of Alloying Elements on Adhesive Properties of Epoxy-Quasicrystal Composites
Authors:
Altidis, JD; Lima, SJG; Torres, SM; Lima, BASG; Medeiros, ES; de Barros, S Author Full Names: Altidis, J. D.; Lima, S. J. G.; Torres, S. M.; Lima, B. A. S. G.; Medeiros, E. S.; de Barros, S.
Source:
JOURNAL OF ADHESION, 90 (1):41-49; SI 10.1080/00218464.2013.806212 JAN 2 2014
Abstract:
Quasicrystals (QC) are materials that exhibit good surface properties such as high hardness, low surface energy, low friction coefficient, and good resistance to oxidation and corrosion. Despite these properties, QC alloys are highly brittle, discouraging their uses in applications requiring mechanical stresses. Hence, the development of composites using quasicrystalline materials as reinforcement to ductile matrices is an interesting alternative. In this work, Al-Cu-Fe quasicrystals were used as a reinforcement to epoxy resin in order improve adhesion with metallic substrates. Adhesive properties were evaluated by single lap joint (SLJ) tests and the QC/epoxy interface was analyzed by scanning electron microscopy (SEM). Aluminum, copper, and iron, individual elements, were used to investigate the contribution of each element to the adhesive. Results show that it was possible to significantly enhance adhesion properties when 25% QC was added to epoxy and that the effect of QC amount on SLJ bond strength did not follow a linear trend. Moreover, the contribution of each alloying element was important to explain the influence of QC addition on adhesive properties of the epoxy-based composites.
Title:
Uniaxial-Pressure Effects on Spin-Driven Lattice Distortions in Geometrically Frustrated Magnets CuFe1-xGaxO2 (x=0, 0.035)
Authors:
Nakajima, T; Iguchi, Y; Tamatsukuri, H; Mitsuda, S; Yamasaki, Y; Nakao, H; Terada, N Author Full Names: Nakajima, Taro; Iguchi, Yusuke; Tamatsukuri, Hiromu; Mitsuda, Setsuo; Yamasaki, Yuichi; Nakao, Hironori; Terada, Noriki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (11):10.7566/JPSJ.82.114711 NOV 2013
Abstract:
The triangular lattice antiferromagnet CuFeO2 (CFO) is a spin-lattice coupled system, whose magnetic phase transitions are accompanied by crystal lattice distortions to relieve the geometrical spin frustration. Recent neutron diffraction and magnetic susceptibility measurements on CFO have revealed that the application of uniaxial pressure (up to 100 MPa) in the triangular lattice plane shifts the magnetic phase transition temperatures to higher values [Nakajima et al.: J. Phys. Soc. Jpn. 81 (2012) 094710]. In the present study, we have performed synchrotron radiation x-ray diffraction measurements on CFO and CuFe1-xGaxO2 (CFGO) with x = 0.035 under applied uniaxial pressure in order to directly observe the uniaxial-pressure effects on the lattice. As a result, we have revealed that the applied uniaxial pressure certainly affects the crystal structure so that the structural transition temperatures increase as well as the magnetic phase transition temperatures. We have also found that CFO exhibits a pronounced lattice instability in the vicinity of the phase transition from the paramagnetic phase with a trigonal structure to an incommensurate magnetic phase with a monoclinic structure. In addition, the present results for CFGO (x = 0.035) have revealed that the lattice instability is suppressed by the substitution of a small amount of nonmagnetic Ga3+ ions for the magnetic Fe3+ ions. This indicates that the spin degree of freedom plays an important role in the lattice instability in this system.
Title:
Incommensurate Crystallography
Authors:
Chapuis, G Author Full Names: Chapuis, Gervais
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 620-621; 10.1107/S010876731301951X 6 NOV 2013
Title:
Ferromagnetism and re-entrant spin-glass transition in quasicrystal approximants Au-SM-Gd (SM = Si, Ge)
Authors:
Hiroto, T; Gebresenbut, GH; Gomez, CP; Muro, Y; Isobe, M; Ueda, Y; Tokiwa, K; Tamura, R Author Full Names: Hiroto, T.; Gebresenbut, G. H.; Gomez, C. Pay; Muro, Y.; Isobe, M.; Ueda, Y.; Tokiwa, K.; Tamura, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (42):10.1088/0953-8984/25/42/426004 OCT 23 2013
Abstract:
Magnetic susceptibility and specific heat measurements on quasicrystalline approximants Au-Si-Gd and Au-Ge-Gd reveal that a ferromagnetic (FM) transition occurs at T-c = 22.5(5) K for Au-Si-Gd and at T-c = 13(1) K for Au-Ge-Gd, which are the first examples of ferromagnetism in crystalline approximants. In addition, a re-entrant spin-glass (RSG) transition is observed at T-RSG = 3.3 K for Au-Ge-Gd in contrast to Au-Si-Gd. The different behaviors are understood based on the recent structural models reported by Gebresenbut et al (2013 J. Phys.: Condens. Matter 25 135402). The RSG transition in Au-Ge-Gd is attributed to a random occupation of the center of the Gd-12 icosahedron by Gd atoms; a central Gd spin hinders the long-range FM order.
Title:
QUASICRYSTALLINE OXIDES
Authors:
[Anonymous] Author Full Names: [Anonymous]
Source:
CHEMICAL & ENGINEERING NEWS, 91 (41):30-30; OCT 14 2013
Title:
TRANSPORT PROPERTIES IN MISFIT-LAYERED Ca2Co2O5 COMPOUND
Authors:
Lan, JL; Zhan, B; Lin, YH; Nan, CW; Liu, YC Author Full Names: Lan, Jinle; Zhan, Bin; Lin, Yuan-Hua; Nan, Ce-Wen; Liu, Yao-Chun
Source:
FUNCTIONAL MATERIALS LETTERS, 6 (5):10.1142/S1793604713400018 OCT 2013
Abstract:
The low temperature transport and magnetic properties were investigated in the misfit-layered Ca2Co2O5 compound. The compound exhibits incommensurate spin-density-wave (SDW) state in the d(chi)(-1)/dT curve at 20K, which is confirmed by the resistivity (rho) characterization. The resistivity shows an upturn from metallic to insulating behavior at TM-I (130 K) and strong Fermi liquid behaviors with rho similar to T-2 relation between TM-I and T*(225 K). The Seebeck coefficient shows abnormal temperature dependence at T-p (40 K), which is suggested to origin from the long order of atomic in [Ca2CoO3] sublayer and spin fluctuation of Co ions. Moreover, large Seebeck coefficient (120 mu V/K) and low thermal conductivity (2.5 W/mK) were obtained at room temperature, indicating that it is a promising p-type thermoelectric material for energy conversion.
Title:
Non-centro-symmetric electron diffraction pattern of icosahedral quasicrystal induced by combination of linear phason strain and curvature of Ewald sphere
Authors:
Xiong, DX; Lu, L; Wang, JB; Zhao, DS; Sun, YF Author Full Names: Xiong, Dongxia; Lu, Lu; Wang, Jianbo; Zhao, Dongshan; Sun, Yufeng
Source:
MICRON, 52-53 45-48; 10.1016/j.micron.2013.08.004 SEP-OCT 2013
Abstract:
Non-centro-symmetric characteristics are observed in the experimental electron diffraction patterns (EDPs) from the icosahedral quasicrystalline precipitates in ZrAlNiCuNb alloys. Different from the well-known breaking of the Friedel's law, where a strong dynamical effect will reveal in EDPs the concealed non-centro-symmetry originated from the crystal structures themselves, the current results can be interpreted in terms of changes in deviation parameters due to a delicate combination of the linear phason strain characteristic of quasicrystals and the curvature of Ewald sphere. After taking this effect into consideration, the corresponding simulated EDPs fit quite well to the experimental data. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Structural and magnetic characterization of the intermartensitic phase transition in NiMnSn Heusler alloy ribbons
Authors:
Llamazares, JLS; Flores-Zuniga, H; Rios-Jara, D; Sanchez-Valdes, CF; Garcia-Fernandez, T; Ross, CA; Garcia, C Author Full Names: Sanchez Llamazares, J. L.; Flores-Zuniga, H.; Rios-Jara, D.; Sanchez-Valdes, C. F.; Garcia-Fernandez, T.; Ross, C. A.; Garcia, C.
Source:
JOURNAL OF APPLIED PHYSICS, 113 (17):10.1063/1.4800836 MAY 7 2013
Abstract:
Phase transitions and structural and magnetic properties of rapidly solidified Ni50Mn38Sn12 alloy ribbons have been studied. Ribbon samples crystallize as a single-phase, ten-layered modulated (10M) monoclinic martensite with a columnar-grain microstructure and a magnetic transition temperature of 308 K. By decreasing the temperature, martensite undergoes an intermartensitic phase transition around 195 K. Above room temperature, the high temperature martensite transforms into austenite. Below 100 K, magnetization hysteresis loops shift along the negative H-axis direction, confirming the occurrence of an exchange bias effect. On heating, the thermal dependence of the coercive field H-C shows a continuous increase, reaching a maximum value of 1017 Oe around 50 K. Above this temperature, H-C declines to zero around 195 K. But above this temperature, it increases again up to 20 Oe falling to zero close to 308 K. The coercivity values measured in both temperature intervals suggest a significant difference in the magnetocrystalline anisotropy of the two martensite phases. (C) 2013 AIP Publishing LLC.

Update: 7-Nov-2013

Title:
Bending analyses of 1D orthorhombic quasicrystal plates
Authors:
Sladek, J; Sladek, V; Pan, E Author Full Names: Sladek, J.; Sladek, V.; Pan, E.
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 50 (24):3975-3983; 10.1016/j.ijsolstr.2013.08.006 NOV 2013
Abstract:
The meshless Petrov-Galerkin method (MLPG) is applied to plate bending analysis in 1D orthorhombic quasicrystals (QCs) under static and transient dynamic loads. The Bak and elasto-hydrodynamic models are applied for phason governing equation in the elastodynamic case. The phason displacement for the orthorhombic QC in the first-order shear deformation plate theory depends only on the in-plane coordinates on the mean plate surface. Nodal points are randomly distributed over the mean surface of the considered plate. Each node is the center of a circle surrounding this node. The coupled governing partial differential equations are satisfied in a weak-form on small fictitious subdomains. The spatial variations of the phonon and phason displacements are approximated by the moving least-squares (MLS) scheme. After performing the spatial MLS approximation, a system of ordinary differential equations (ODEs) for nodal unknowns is obtained. The system of the ODEs of the second order is solved by the Houbolt finite-difference scheme. Our numerical examples demonstrate clearly the effect of the coupling parameter on both static and dynamic phonon/phason deflections. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Competition Between Antiferromagnetism and Ferromagnetism in Sr2RuO4 Probed by Mn and Co Doping
Authors:
Ortmann, JE; Liu, JY; Hu, J; Zhu, M; Peng, J; Matsuda, M; Ke, X; Mao, ZQ Author Full Names: Ortmann, J. E.; Liu, J. Y.; Hu, J.; Zhu, M.; Peng, J.; Matsuda, M.; Ke, X.; Mao, Z. Q.
Source:
SCIENTIFIC REPORTS, 3 10.1038/srep02950 OCT 15 2013
Abstract:
Spin-triplet superconductivity in Sr2RuO4 has attracted enormous interest. Like other unconventional superconductors, superconductivity in Sr2RuO4 is in close proximity to magnetic instability. Undoped Sr2RuO4 exhibits incommensurate antiferromagnetic (AFM) fluctuations, which can evolve into static, short-range AFM order via Ti doping. Moreover, weak ferromagnetic (FM) coupling in Sr2RuO4 has also been suggested by NMR/neutron scattering experiments and studies on Ca2-xSrxRuO4 and Sr2-yLayRuO4, implying orbital dependent magnetism. We report bulk static, short-range FM order in Sr2RuO4 triggered by <2% Co doping, showing superconductivity in Sr2RuO4 is much closer to FM instability than previously reported in Ca2-xSrxRuO4. We also find Mn doping can effectively establish incommensurate AFM order, with T-N similar to 50 K for 3% Mn doping. These new results place Sr2RuO4 in a unique situation where superconductivity lies directly on the borderline of two distinct magnetic states, highlighting the important role of competing magnetic fluctuations in determining superconducting properties of Sr2RuO4.
Title:
Quasicrystalline structure formation in a classical crystalline thin-film system
Authors:
Forster, S; Meinel, K; Hammer, R; Trautmann, M; Widdra, W Author Full Names: Foerster, Stefan; Meinel, Klaus; Hammer, Rene; Trautmann, Martin; Widdra, Wolf
Source:
NATURE, 502 (7470):215-+; 10.1038/nature12514 OCT 10 2013
Abstract:
The discovery of quasicrystals(1)-crystalline structures that show order while lacking periodicity-forced a paradigm shift in crystallography. Initially limited to intermetallic systems(1-4), the observation of quasicrystalline structures has recently expanded to include 'soft' quasicrystals in the fields of colloidal and supermolecular chemistry(5-9). Here we report an aperiodic oxide that grows as a two-dimensional quasicrystal on a periodic single-element substrate. On a Pt(111) substrate with 3-fold symmetry, the perovskite barium titanate BaTiO3 forms a high-temperature interface-driven structure with 12-fold symmetry. The building blocks of this dodecagonal structure assemble with the theoretically predicted Stampfli-Gahler tiling(10,11) having a fundamental length-scale of 0.69 nm. This example of interface-driven formation of ultrathin quasicrystals from a typical periodic perovskite oxide potentially extends the quasicrystal concept to a broader range of materials. In addition, it demonstrates that frustration at the interface between two periodic materials can drive a thin film into an aperiodic quasicrystalline phase, as proposed previously(12). Such structures might also find use as ultrathin buffer layers for the accommodation of large lattice mismatches in conventional epitaxy(13).
Title:
Magnetic orders, excitations, and phase transitions in Fe1+yTe
Authors:
Chen, G; Choi, S; Radzihovsky, L Author Full Names: Chen, G.; Choi, S.; Radzihovsky, L.
Source:
PHYSICAL REVIEW B, 88 (16):10.1103/PhysRevB.88.165117 OCT 10 2013
Abstract:
We study the magnetic properties of Fe1+yTe, a parent compound of the iron-based high-temperature superconductors. Motivated by recent neutron scattering experiments, we show that a spin S = 1 exchange model, supplemented by a single-ion spin anisotropy, accounts well for the experimentally observed low-temperature magnetic phase diagram, that exhibits a commensurate bicollinear order at low Fe dopings (y less than or similar to 0.12) and an incommensurate spin-spiral order at high Fe dopings (y greater than or similar to 0.12). We suggest that the commensurate incommensurate transition at y similar or equal to 0.12 is due to the competition between the exchange interaction and the local spin anisotropy. At low Fe dopings, the single-ion spin anisotropy is strong and pins the spins along the easy axis, which, together with the spatially anisotropic exchanges, induces a unusual bicollinear commensurate magnetic order. The low-energy spin-wave excitation is gapped due to the explicit breaking of spin-rotational symmetry by the local spin anisotropy. At high Fe dopings, the single-ion anisotropy is weak, and the exchange favors an incommensurate coplanar state. The incommensurate magnetic wave vector averages out the spin anisotropy so that a gapless low-energy spin-wave excitation is obtained. We also analyze the low-energy hydrodynamic model and use it to describe the magnetostructural transition and the static and dynamical spin structure factors across the magnetic ordering transitions.
Title:
Evolution of incommensurate spin order with magnetic field and temperature in the itinerant antiferromagnet GdSi
Authors:
Feng, YJ; Silevitch, DM; Wang, JY; Palmer, A; Woo, N; Yan, JQ; Islam, Z; Suslov, AV; Littlewood, PB; Rosenbaum, TF Author Full Names: Feng, Yejun; Silevitch, D. M.; Wang, Jiyang; Palmer, A.; Woo, Nayoon; Yan, J. -Q.; Islam, Z.; Suslov, A. V.; Littlewood, P. B.; Rosenbaum, T. F.
Source:
PHYSICAL REVIEW B, 88 (13):10.1103/PhysRevB.88.134404 OCT 7 2013
Abstract:
GdSi exhibits spin-density-wave (SDW) order arising from the cooperative interplay of sizeable local moments and a partially nested Fermi sea of itinerant electrons. Using magnetotransport, magnetization, and nonresonant magnetic x-ray diffraction techniques, we determine the H-T phase diagrams of GdSi for magnetic fields up to 21 T, where antiferromagnetic order is no longer stable, and field directions along each of the three major crystal axes. While the incommensurate magnetic ordering vector that characterizes the SDW is robust under magnetic field, the multiple spin structures of this compound are highly flexible and rotate relative to the applied field via either canting or spin-flop processes. The antiferromagnetic spin densities always arrange themselves transverse to the applied magnetic field direction. The phase diagrams are delineated by two types of phase boundaries: one separates a collinear from a planar spin structure associated with a lattice structural transition, and the other defines a spin flop transition that is only weakly temperature dependent. The major features of the phase diagrams along each of the crystal axes can be explained by the combination of local moment and global Fermi surface physics at play.
Title:
Critical behavior of RMn2O5 oxides near the magnetic phase transition to a structure incommensurate in two spatial directions
Authors:
Men'shenin, VV Author Full Names: Men'shenin, V. V.
Source:
PHYSICS OF THE SOLID STATE, 55 (10):2051-2056; 10.1134/S1063783413100235 OCT 2013
Abstract:
A phase transition from the paramagnetic state to the long-period magnetic structure in RMn2O5 oxides with the star of the wave vector determining the incommensurability of long-range magnetic order in two spatial directions has been investigated. An effective Hamiltonian of the system that allows one to describe this transition in the framework of the renormalization group approach has been constructed. It has been shown that there is a stable critical point of transformations of this group at which there occurs a second-order phase transition. The critical indices have been found. The obtained results have been compared with the results for phase transitions occurring in these oxides in accordance with the star of the wave vector, which provides incommensurability in one of the spatial directions. It has been found that fluctuations of the four-component order parameter due to the low spatial symmetry of these compounds do not change the order of the phase transition, which was found in terms of the Landau theory.
Title:
Effects of Strain and Ordering of Rare-Earth Element Moments on Magnetic-Reordering in Orthorhombic Multiferroic Manganites
Authors:
Hsiao, YF; Lai, JY; Lin, JY; Fang, HW; Hung, YT; Luo, CW; Wu, KH; Uen, TM; Lin, JY; Juang, JY Author Full Names: Hsiao, Yen-Fu; Lai, Jun-Yo; Lin, Jun-Yu; Fang, Hau-Wei; Hung, Yi-Tse; Luo, Chih-Wei; Wu, Kaung-Hsiung; Uen, Tzeng-Ming; Lin, Jiunn-Yuan; Juang, Jenh-Yih
Source:
APPLIED PHYSICS EXPRESS, 6 (10):10.7567/APEX.6.103201 OCT 2013
Abstract:
Orthorhombic multiferroic manganite thin films with various orientations and strain states were prepared to show the effects of anisotropic strain and antiferromagnetic (AFM) ordering of rare-earth f-electrons on the orientation of the incommensurate-to-commensurate AFM reordering. Systematic analyses suggest that the low-temperature AFM ordering of the rare-earth f-electrons may have played a decisive role in causing the orientation changes in AFM reordering, although the b-axis strain does have a significant influence on the zero-field magnetization behaviors. (C) 2013 The Japan Society of Applied Physics
Title:
Mechanical properties of the icosahedral phase reinforced duplex Mg-Li alloy both at room and elevated temperatures
Authors:
Xu, DK; Zu, TT; Yin, M; Xu, YB; Han, EH Author Full Names: Xu, D. K.; Zu, T. T.; Yin, M.; Xu, Y. B.; Han, E. H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 582 161-166; 10.1016/j.jallcom.2013.08.020 JAN 5 2013
Abstract:
Through investigating tensile properties of the duplex Mg-Li alloys with and without I-phase (Mg3Zn6Y, icosahedral quasicrystal structure) tested both at ambient and elevated temperatures, it demonstrates that I-phase can not only improve the tensile strength at room temperature, but also be beneficial for the mechanical improvement at elevated temperatures. Based on the microstructural observations of the sample surfaces before and after tests, the I-phase particles can effectively suppress the plastic flow of beta phase at 220 degrees C, resulting in the I-phase reinforced duplex Mg-Li alloy having higher mechanical properties at elevated temperatures. (c) 2013 Elsevier B.V. All rights reserved.
Title:
Arrangements of Transition-Metal Atoms in Three Types of Al-Co-Ni Decagonal Quasicrystals Studied by Cs-Corrected HAADF-STEM
Authors:
Hiraga, K; Yasuhara, A Author Full Names: Hiraga, K.; Yasuhara, A.
Source:
MATERIALS TRANSACTIONS, 54 (4):493-497; 10.2320/matertrans.M2012340 2013
Abstract:
Three types of Al-Co-Ni decagonal quasicrystals in Al72.5Co11Ni16.5, Al71Co14.5Ni14.5 and Al71.5Co16Ni12.5 alloys have been examined by Cs-corrected high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM), which has an enough resolution to represent individual TM atoms as bright dots in observed images of decagonal quasicrystals. On the basis of the structure of a W-(AlNiCo) crystalline approximant, transition-metal (TM) atoms and mixed sites (MSs) of Al and TM atoms are separately distinguished in HAADF-STEM images. Most of TM atoms are arranged with pentagonal tilings of a bond-length of 0.76 nm, and MSs are located inside of pentagonal frames with definite orientations. All of the TM atoms and MSs are located at lattice points of a Penrose lattice of an edge-length of 0.25 nm, and arranged with a bond-orientational order. The present result shows that the structures of Al-Co-Ni decagonal quasicrystals should be characterized as BOO arrangements of transition-metal atoms, instead of previous models of BOO arrangements of 2 nm atom clusters.

Update: 31-Oct-2013

Title:
Role of magnetic chirality in polarization flip upon a commensurate-incommensurate magnetic phase transition in YMn2O5
Authors:
Wakimoto, S; Kimura, H; Sakamoto, Y; Fukunaga, M; Noda, Y; Takeda, M; Kakurai, K Author Full Names: Wakimoto, Shuichi; Kimura, Hiroyuki; Sakamoto, Yuma; Fukunaga, Mamoru; Noda, Yukio; Takeda, Masayasu; Kakurai, Kazuhisa
Source:
PHYSICAL REVIEW B, 88 (14):10.1103/PhysRevB.88.140403 OCT 10 2013
Abstract:
We have performed simultaneous measurements of magnetic chirality by using polarized neutrons and electric polarization along the b axis of single crystals of YMn4+(Mn1-xGax)O-3+(5) with x = 0.047 and 0.12, in which nonmagnetic Ga ions dilute Mn3+ spins. The x = 0.047 sample exhibits high-temperature incommensurate (HT-ICM), commensurate (CM), and low-temperature incommensurate (LT-ICM) magnetic phases in order of decreasing temperature, whereas the x = 0.12 sample exhibits only HT-ICM and LT-ICM phases. Here, the CM and LT-ICM phases are ferroelectric and weak ferroelectric, respectively. Measurements conducted under zero-field heating after various field-cooling conditions evidence that the microscopic mechanisms of the spin-driven ferroelectricity in the CM and LT-ICM phases are different: The magnetic chirality of Mn4+ cycloidal spins plays a dominant role in the LT-ICM phase, whereas the magnetic exchange striction by the Mn4+-Mn3+ chain plays a dominant role in the CM phase. The polarization of YMn2O5 flips upon a CM to LT-ICM phase transition because the ferroelectricity driven by the magnetic chirality and the exchange striction provides opposite directions of polarization.
Title:
Magnetic and structural properties near the Lifshitz point in Fe1+xTe
Authors:
Rodriguez, EE; Sokolov, DA; Stock, C; Green, MA; Sobolev, O; Rodriguez-Rivera, JA; Cao, H; Daoud-Aladine, A Author Full Names: Rodriguez, E. E.; Sokolov, D. A.; Stock, C.; Green, M. A.; Sobolev, O.; Rodriguez-Rivera, Jose A.; Cao, H.; Daoud-Aladine, A.
Source:
PHYSICAL REVIEW B, 88 (16):10.1103/PhysRevB.88.165110 OCT 7 2013
Abstract:
We construct a phase diagram of the parent compound Fe1+xTe as a function of interstitial iron x in terms of the electronic, structural, and magnetic properties. For a concentration of x < 10%, Fe1+xTe undergoes a "semimetal" to metal transition at approximately 70 K that is also first-order and coincident with a structural transition from a tetragonal to a monoclinic unit cell. For x approximate to 14%, Fe1+xTe undergoes a second-order phase transition at approximately 58 K corresponding to a semimetal to semimetal transition along with a structural orthorhombic distortion. At a critical concentration of x approximate to 11%, Fe1+xTe undergoes two transitions: the higher-temperature one is a second-order transition to an orthorhombic phase with incommensurate magnetic ordering and temperature-dependent propagation vector, while the lower-temperature one corresponds to nucleation of a monoclinic phase with a nearly commensurate magnetic wave vector. While both structural and magnetic transitions display similar critical behavior for x < 10% and near the critical concentration of x approximate to 11%, samples with large interstitial iron concentrations show a marked deviation between the critical response indicating a decoupling of the order parameters. Analysis of temperature dependent inelastic neutron data reveals incommensurate magnetic fluctuations throughout the Fe1+xTe phase diagram are directly connected to the "semiconductor"-like resistivity above T-N and implicates scattering from spin fluctuations as the primary reason for the semiconducting or poor metallic properties. The results suggest that doping driven Fermi surface nesting maybe the origin of the gapless and incommensurate spin response at large interstitial concentrations.
Title:
Observation of atomic scale compositional and displacive modulations in incommensurate melilite electrolytes
Authors:
Wei, FX; Williams, T; An, T; Baikie, T; Kloc, C; Wei, J; White, T Author Full Names: Wei, Fengxia; Williams, Tim; An, Tao; Baikie, Tom; Kloc, Christian; Wei, Jun; White, Tim
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 203 291-296; 10.1016/j.jssc.2013.04.039 JUL 2013
Abstract:
The paradigm that functional materials are adequately described as three-dimensional crystal structures is not universally tenable. Gallate melilites are efficient oxide ion conductors at intermediate temperatures (similar to 750 degrees C) with non-rational crystallographic modulations presumed to play a key role in significantly enhancing oxygen mobility. Lattice distortions associated with incommensuration are usually extrapolated from diffraction analysis of volumes greatly exceeding the scale of modulation. Therefore, opportunities for making direct nanometric measurements are exceptionally valuable for correlating structure with function. In [CaLn](2)[Ga](2)[Ga2O7](2) (Ln=Nd, La) melilites, atomic displacive and compositional modulation waves can be imaged by high angle annular dark field and bright field scanning transmission electron microscopy with contrast quantified through electron scattering simulation. Here, we present atomic scale observations of (3+2)-dimensional modulations in gallate melilites which expands our understanding of the ion conduction mechanism and provides guidance for enhancing the performance of solid oxide fuel cells through crystal chemical tailoring. (C) 2013 Elsevier Inc. All rights reserved.

Update: 23-Oct-2013

Title:
SWAXS analysis on some quasicrystalline alloys: Nanoclusters and nanoaggregates
Authors:
Tukel, C; Ide, S; Yildirim, L; Erbudak, M Author Full Names: Tukel, Caner; Ide, Semra; Yildirim, Leyla; Erbudak, Mehmet
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 581 860-866; 10.1016/j.jallcom.2013.07.175 DEC 25 2013
Abstract:
Mesoscopic structure of two decagonal quasicrystalline samples, Al-Co-Ni and Al-Co-Cu, is investigated by XRD and SEM. Simultaneous SAXS and WAXS (SWAXS) measurements give information on the shape, size, and pair-distance distributions of nanometer-size aggregates contained in the analyzed volume. Decagonal single quasicrystal structures, quasicrystalline approximants, and nanometer-size domain structures are found to coexist in the samples. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Characterisation of nano-sized Al-Mn-(Mg) particles in AZ91 and their effect on Mg17Al12 precipitation
Authors:
Zeng, R; Chiu, Y; Jones, IP Author Full Names: Zeng, R.; Chiu, Y.; Jones, I. P.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 579 34-38; 10.1016/j.jallcom.2013.04.179 DEC 5 2013
Abstract:
Al-Mn-(Mg) particles in the size range of 20-200 nm have been found in a sand cast AZ91 magnesium alloy. Their morphologies, chemical composition and structures were investigated using transmission electron microscopy. It was found that these particles have a chemical composition of (Al6.52Mn)(1-x)Mg-x (x < 0.13) and a decagonal quasi-crystalline structure. These particles were stable during a solution treatment at 420 degrees C for 72 h and acted as preferential nucleation sites for Mg17Al12 precipitates during the subsequent ageing. The potential effect of these Al-Mn-(Mg) particles on the strengthening of AZ91 magnesium alloys is discussed. (c) 2013 Elsevier B.V. All rights reserved.
Title:
C6H4S2AsCl: description and interpretation of an incommensurately modulated molecular crystal structure
Authors:
Bakus, RC; Atwood, DA; Parkin, S; Brock, CP; Petricek, V Author Full Names: Bakus, Ronald C., II; Atwood, David A.; Parkin, Sean; Brock, Carolyn P.; Petricek, Vaclav
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 69 496-508; 10.1107/S205251921301782X 5 OCT 2013
Abstract:
Crystals of 2-chloro-benzo-1,3,2-dithiarsole have a strongly modulated structure that can be solved and refined with relative ease in a P (1) over bar, Z' = 17 approximate supercell but that is better described as incommensurate. Two conventional refinements (different superstructure approximations that differ in the placement of their crystallographic inversion centers) and a (3 + 1)-dimensional superspace refinement are all nearly equally successful, at least as measured by the usual agreement factors; the data integration, however, shows that the incommensurate description is preferable. The overall packing is determined by the stacking of the aromatic rings and probably by the segregation of As and Cl atoms to give short As center dot center dot center dot Cl contacts. A refinement of the average (Z' = 1) structure shows that there are two basic orientations of the C6S2 plane, but that those orientations must be correlated in several directions to avoid impossibly short intermolecular contacts. Along the modulation vector q the orientation of the C6S2 plane varies smoothly, but q is not a direction in which the molecules are in contact. Along the directions in which the molecules are in contact the orientation of the C6S2 plane alternates; there are also positional shifts. The single modulation q relieves packing problems in several different directions well enough that crystals that diffract well can be grown.
Title:
Dzyaloshinskii-Moriya driven helical-butterfly structure in Ba3NbFe3Si2O14
Authors:
Scagnoli, V; Huang, SW; Garganourakis, M; de Souza, RA; Staub, U; Simonet, V; Lejay, P; Ballou, R Author Full Names: Scagnoli, V.; Huang, S. W.; Garganourakis, M.; de Souza, R. A.; Staub, U.; Simonet, V.; Lejay, P.; Ballou, R.
Source:
PHYSICAL REVIEW B, 88 (10):10.1103/PhysRevB.88.104417 SEP 18 2013
Abstract:
We have used soft x-ray magnetic diffraction at the Fe3+ L-2,L-3 edges to examine to what extent the Dzyaloshinsky-Moriya interaction in Ba3NbFe3Si2O14 influences its low-temperature magnetic structure. A modulated component of the moments along the c axis is present, adding to the previously proposed helical magnetic configuration of coplanar moments in the a, b plane. This leads to a "helical-butterfly" structure and suggests that both the multiaxial in-plane and the uniform out-of-plane Dzyaloshinsky-Moriya vectors are relevant. A nonzero orbital magnetic signal is also observed at the oxygen K edge, which reflects the surprisingly strong hybridization between iron 3d and oxygen 2p states, given the nominal spherical symmetry of the Fe3+ half-filled shell.
Title:
Rotational disorder of bis(mesitylene)vanadium in channels of a triazine inclusion compound
Authors:
Barbon, A; Hauser, J; Berger, R; Brustolon, M; Hulliger, J Author Full Names: Barbon, Antonio; Hauser, Juerg; Berger, Ricarda; Brustolon, Marina; Hulliger, Juerg
Source:
CRYSTENGCOMM, 15 (40):8110-8115; 10.1039/c3ce41102h 2013
Abstract:
Electron paramagnetic resonance (EPR) was applied to study rotational disorder of bis(mesitylene)vanadium (VBM, S = 1/2) in channels of 2,4,6-tris(4-Br-phenoxy)-1,3,5-triazine. To ensure a magnetically dilute system, decamethylbis(cyclopentadienyl) ruthenium was used as a main guest to fill the channels. X-ray diffraction confirmed inclusion formation, resulting in an incommensurate host-guest system. EPR spectra were measured using prismatic single crystals oriented to have B-o either parallel to the channel axis c or at any angle in between c and the perpendicular direction. Temperature-dependent spectra were recorded down to 80 K. The analysis revealed two types of paramagnetic guest entities, i.e. VBM (I) and VBM (II). Both showed dynamical effects due to a reorientational motion. VBM (I) is confined to show a molecular axis z distributed around c by a small angle (+/- 1.25 degrees), whereas for VBM (II) the distribution is completely disordered. The reorientational motions are frozen at low temperature giving for VBM (II) a powder-like EPR spectrum. Analysing EPR intensities allowed us to conclude that the ratio of (I)/(II) species is of the order of 1.5.

Update: 17-Oct-013

Title:
Phases in the Al-Corner of the Al-Mn-Be System
Authors:
Zupanic, F; Markoli, B; Naglic, I; Weingartner, T; Meden, A; Boncina, T Author Full Names: Zupanic, Franc; Markoli, Bostjan; Naglic, Iztok; Weingaertner, Tobias; Meden, Anton; Boncina, Tonica
Source:
MICROSCOPY AND MICROANALYSIS, 19 (5):1308-1316; 10.1017/S1431927613001852 OCT 2013
Abstract:
This work studied the phases in the Al corner of the Al-Mn-Be phase diagram in the as-cast state and heat-treated conditions. Metallographic investigations, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy were used for identifying the phases. The Be contents in the identified phases were precisely determined using Auger electron spectroscopy. The results indicated that Al6Mn does not dissolve Be, whilst lambda-Al4Mn dissolves up to 7 at.% Be. The average composition of the T phase, which is normally designated as Al15Mn3Be2, was 72 at.% Al, 19 at.% Mn, and 9 at.% Be. The phase with the nominal composition Be4AlMn contained more Al than Mn. The atomic ratio Al: Mn was between 1.3: 1 and 2: 1. The hexagonal Be-rich phase did not dissolve any Al and Mn. The icosahedral quasicrystalline (IQC) phase contained up to 45 at.% Be. The compositions of T phase, lambda-Al4Mn, IQC, and Be4AlMn may vary, however, the ratio (Al + Be):Mn remained constant, and was close either to four or six indicating substitution of Al atoms with Be atoms in these phases.
Title:
Experimental Study of Al-Co-Cu Phase Diagram in Temperature Range of 800-1050 A degrees C
Authors:
Priputen, P; Liu, TY; Cernickova, I; Janickovic, D; Kolesar, V; Janovec, J Author Full Names: Priputen, P.; Liu, T. Y.; Cernickova, I.; Janickovic, D.; Kolesar, V.; Janovec, J.
Source:
JOURNAL OF PHASE EQUILIBRIA AND DIFFUSION, 34 (5):425-429; 10.1007/s11669-013-0253-y OCT 2013
Abstract:
Partial isothermal sections of the Al-Co-Cu phase diagram at 800, 1020, and 1050 A degrees C were proposed based on both literature data and own experimental results. By means of x-ray diffraction, electron backscattered diffraction, electron diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopy altogether five phases (Al5Co2, m-Al13Co4, D, B2, and rapidly solidified liquid) were identified in a number of investigated alloys falling within compositional ranges Al58-67Co18-34Cu7-20. The single-phase area corresponding in the isothermal sections to the decagonal quasicrystalline phase (D) was found to reduce in size, and to shift to lower Cu and higher Al bulk contents, both with increasing temperature. The single-phase m and Al5Co2 areas showed only small temperature-dependent changes in size and location. Moreover, an increase in temperature caused both a slow decrease of the copper solubility in B2 and an increase of the liquid stability.
Title:
Direction of atom displacement in incommensurate state of Ti-32Pd-18Fe shape memory alloy
Authors:
Todai, M; Fukuda, T; Kakeshita, T Author Full Names: Todai, Mitsuharu; Fukuda, Takashi; Kakeshita, Tomoyuki
Source:
MATERIALS LETTERS, 108 293-296; 10.1016/j.matlet.2013.07.018 OCT 1 2013
Abstract:
Displacement of atoms causing diffuse satellites in a Ti-32Pd-18Fe alloy (in at%) has been investigated by transmission electron microscopy (TEM). In this alloy, diffuse satellites appear at incommensurate positions given by g(B2)+q when the zone axis is [111] and [001], but they are missing when [110]. This results imply that the satellites appear because of a transverse wave with a propagation vector of q similar to 1/5 * and displacement in (110) direction. Possibly, this transverse wave occurs as a result of phonon softening of the TA(2) phonon branch, which is a common feature for B2-type Ti-based shape memory alloys. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Dynamic spin correlations in the frustrated cubic phase of MnV2O4
Authors:
Chung, JH; Song, YS; Kim, JH; Suzuki, T; Katsufuji, T; Matsuda, M; Lee, SH Author Full Names: Chung, Jae-Ho; Song, Young-Sang; Kim, J. -H.; Suzuki, T.; Katsufuji, T.; Matsuda, M.; Lee, S. -H.
Source:
PHYSICAL REVIEW B, 88 (9):10.1103/PhysRevB.88.094430 SEP 23 2013
Abstract:
The ferrimagnetic spinel MnV2O4 undergoes an orbital-induced cubic-to-tetragonal distortion at T-YK = 58 K, below which noncollinear commensurate ferrimagnetic ordering occurs. Using inelastic neutron scattering, we investigated low-energy dynamics in its cubic phase above TYK. We observed two types of coexisting short-range magnetic excitations: the dispersive spin waves centered around the Brillouin-zone centers, k(0) = (0, 0, 0), and quasielastic spin fluctuations centered at incommensurate wave vectors, k(incom) = (xi,xi, 0). The coexistence of the two distinct features can be understood as a dynamic realization of the conical spiral order observed in cubic spinels such as CoCr2O4.
Title:
Fabrication and magnetic properties of single-crystalline La0.33Pr0.34Ca0.33MnO3/MgO nanowires
Authors:
Li, L; Li, H; Zhai, XF; Zeng, CG Author Full Names: Li, Lin; Li, Hui; Zhai, Xiaofang; Zeng, Changgan
Source:
APPLIED PHYSICS LETTERS, 103 (11):10.1063/1.4819828 SEP 9 2013
Abstract:
Single crystalline La0.33Pr0.34Ca0.33MnO3/MgO core-shell nanowires with diameters about tens of nanometers are synthesized by a two-step process. Structure and morphology characterizations confirm the epitaxial growth of La0.33Pr0.34Ca0.33MnO3 shell layers on MgO core layers. Clear interfaces are observed between the core and shell layers. Magnetic measurements suggest the existence of electronic phase separation in the one dimensional nanowires similar to the bulk. However, the nanowires exhibit significantly increased amount of magnetically frozen phase and increased coercivity, which are attributed to the strongly modulated magnetic structure in the one dimensional structure. (C) 2013 AIP Publishing LLC.
Title:
AlCuFe(Cr) and AlCoFeCr coatings for improvement of elevated temperature oxidation resistance of a near-alpha titanium alloy
Authors:
Moskalewicz, T; Dubiel, B; Wendler, B Author Full Names: Moskalewicz, Tomasz; Dubiel, Beata; Wendler, Bogdan
Source:
MATERIALS CHARACTERIZATION, 83 161-169; 10.1016/j.matchar.2013.06.018 SEP 2013
Abstract:
In this work, an AlCuFe, AlCuFeCr and AlCoFeCr multicomponent coatings were deposited on a near-alpha titanium alloy, TIMETAL 834, by a non-reactive magnetron sputtering. A microstructure, phase composition, coatings adhesion to the substrate, micro-mechanical properties and oxidation resistance were investigated. The AlCuFe coating was quasicrystalline and consisted of icosahedral psi-Al65Cu20Fe15 phase grains. The AlCuFeCr coating consisted mainly of decagonal d-AlCuFeCr phase and some Al6.1Cu1.2Ti2.7 phase grains. The AlCoFeCr coating microstructure was composed of AlCrFe2 nanocrystals embedded in an Al13Co4 matrix. It was established that all multicomponent coatings exhibit higher hardness and elastic moduli than the titanium alloy substrate. Among all investigated coatings, the AlCoFeCr one exhibits the best adhesion to the substrate. It was found that a very brittle, non-protective scale formed on the uncoated alloy during isothermal oxidation consisted of TiO2 (rutile) grains. The oxidation resistance of the TIMETAL 834 alloy at elevated temperature (750 degrees C) was significantly improved by the coatings deposition. The smallest weight gain during oxidation test, 82% lower than in the case of uncoated sample, was found for the AlCoFeCr coated alloy. The microstructure investigation of the specimen after oxidation test was performed by SEM and TEM. It was found that the improvement of oxidation resistance of TIMETAL 834 by the coatings deposited in the present work is mainly due to an occurrence of the protective alpha-Al2O3 scale. (C) 2013 Elsevier Inc. All rights reserved.
Title:
Incommensurate magnetic structures in rhombohedral Heisenberg antiferromagnet
Authors:
Martynov, SN Author Full Names: Martynov, S. N.
Source:
JETP LETTERS, 98 (1):19-23; 10.1134/S0021364013140099 SEP 2013
Abstract:
The phase diagram of the ground state has been calculated for a rhombohedral antiferromagnet of the R3m symmetry with frustrated exchange in the base plane and competition of exchanges between the nearest and next-nearest planes. The diagram contains phases of collinear antiferromagnetic ordering of various types separated by five incommensurate magnetic states of the helicoidal type, differing in the ordering type and in the direction of the modulation vector. The commensurate and incommensurate phases converge at multi-critical points lying on a line corresponding to an antiferromagnet with an undistorted simple cubic lattice.
Title:
Icosahedral stereographic projections in three dimensions for use in dark field TEM
Authors:
Bourdillon, AJ Author Full Names: Bourdillon, Antony J.
Source:
MICRON, 51 21-25; 10.1016/j.micron.2013.06.004 AUG 2013
Abstract:
Thermodynamics require that rapidly cooled crystals and quasicrystals are relatively defective. Yet, without convenient 3-dimensional indexation both at crystal poles and in diffraction planes, or Kikuchi maps, it is difficult to identify the defects by dark field transmission electron microscopy. For two phase Al6Mn, these maps are derived. They relate i-Al6Mn to the standard face centered cubic, matrix crystals. An example of their usefulness in determining interfacial characteristics is described. Indices are integral powers on an irrational number. (c) 2013 Elsevier Ltd. All rights reserved.
Title:
Bond Order in Two-Dimensional Metals with Antiferromagnetic Exchange Interactions
Authors:
Sachdev, S; La Placa, R Author Full Names: Sachdev, Subir; La Placa, Rolando
Source:
PHYSICAL REVIEW LETTERS, 111 (2):10.1103/PhysRevLett.111.027202 JUL 9 2013
Abstract:
We present an unrestricted Hartree-Fock computation of charge-ordering instabilities of two-dimensional metals with antiferromagnetic exchange interactions, allowing for arbitrary ordering wave vectors and internal wave functions of the particle-hole pair condensate. We find that the ordering has a dominant d symmetry of rotations about lattice points for a range of ordering wave vectors, including those observed in recent experiments at low temperatures on YBa2Cu3Oy. This d symmetry implies the charge ordering is primarily on the bonds of the Cu lattice, and we propose incommensurate bond order parameters for the underdoped cuprates. The field theory for the onset of Neel order in a metal has an emergent pseudospin symmetry which "rotates" d-wave Cooper pairs to particle-hole pairs [M. A. Metlitski and S. Sachdev, Phys. Rev. B82, 075128 ( 2010)]; our results show that this symmetry has consequences even when the spin correlations are short ranged and incommensurate.

Update: 9-Oct-2013

Title:
Scanning tunneling microscopy of a polygrain Al-Pd-Re quasicrystal: study of the relative surface stability
Authors:
Tamura, R; Yadav, TP; McLeod, IM; Hesp, D; Young, KM; Nakamura, T; Nishio, K; Dhanak, VR; McGrath, R; Sharma, HR Author Full Names: Tamura, R.; Yadav, T. P.; McLeod, I. M.; Hesp, D.; Young, K. M.; Nakamura, T.; Nishio, K.; Dhanak, V. R.; McGrath, R.; Sharma, H. R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (39):10.1088/0953-8984/25/39/395007 OCT 2 2013
Abstract:
Scanning tunneling microscopy and x-ray photoemission spectroscopy on a polygrain icosahedral (i-) Al-Pd-Re quasicrystal (QC) show the formation of the twofold surfaces with symmetry and composition expected from the bulk. The predominant occurrence of the twofold surface on the polygrain i-QC having random grain orientation, as well as preferential formation of terrace edges, kinks and voids along the twofold axes, consistently indicates that the twofold surface, which has the highest atomic density, is the most stable among all the crystallographic planes.
Title:
Topological equivalence of crystal and quasicrystal band structures
Authors:
Madsen, KA; Bergholtz, EJ; Brouwer, PW Author Full Names: Madsen, Kevin A.; Bergholtz, Emil J.; Brouwer, Piet W.
Source:
PHYSICAL REVIEW B, 88 (12):10.1103/PhysRevB.88.125118 SEP 11 2013
Abstract:
A number of recent articles have reported the existence of topologically nontrivial states and associated end states in one-dimensional incommensurate lattice models that would usually only be expected in higher dimensions. Using an explicit construction, we here argue that the end states have precisely the same origin as their counterparts in commensurate models and that incommensurability does not in fact provide a meaningful connection to the topological classification of systems in higher dimensions. In particular, we show that it is possible to smoothly interpolate between states with commensurate and incommensurate modulation parameters without closing the band gap and without states crossing the band gap.
Title:
Optical spectroscopy and electronic structure of the face-centered icosahedral quasicrystals Zn-Mg-R (R = Y, Ho, Er)
Authors:
Karpus, V; Tumenas, S; Suchodolskis, A; Arwin, H; Assmus, W Author Full Names: Karpus, V.; Tumenas, S.; Suchodolskis, A.; Arwin, H.; Assmus, W.
Source:
PHYSICAL REVIEW B, 88 (9):10.1103/PhysRevB.88.094201 SEP 9 2013
Abstract:
Results of optical spectroscopy studies of the face-centered icosahedral (fci) single-grain Zn-Mg-Y, Zn-Mg-Ho, and Zn-Mg-Er quasicrystals (QCs) are presented. The dielectric function of the QCs was measured in the 0.01-6 eV spectral range by IR-UV spectroscopic ellipsometry and far infrared reflection spectroscopy techniques. A theoretical scheme of optical conductivity calculations is extended to account for the Fermi level positions within and below a pseudogap. The model of the QC electron energy spectrum, based on a band structure hypothesis, is suggested, which treats the electronic subsystem as a nearly free electron gas affected by intersections of the Fermi surface with several families of Bragg planes. The experimental optical spectra are reproduced in detail by theoretical calculations carried out within the framework of the model. The parameters of the electron energy spectrum deduced from an analysis of optical data are close to those previously determined in an analysis of fci Zn-Mg-R valence band photoemission spectra.
Title:
Atom probe tomography investigation of lath boundary segregation and precipitation in a maraging stainless steel
Authors:
Thuvander, M; Andersson, M; Stiller, K Author Full Names: Thuvander, Mattias; Andersson, Marcus; Stiller, Krystyna
Source:
ULTRAMICROSCOPY, 132 265-270; 10.1016/j.ultramic.2012.10.014 SEP 2013
Abstract:
Lath boundaries in a maraging stainless steel of composition 13Cr-8Ni-2Mo-2Cu-1Ti-0.7Al-0.3Mn-0.2Si-0.03C (at%) have been investigated using atom probe tomography following aging at 475 degrees C for up to 100 h. Segregation of Mo, Si and P to the lath boundaries was observed already after 5 min or aging, and the amount or segregation increases with aging time At lath boundaries also precipitation or eta-Ni-3(Ti, Al) and Cu-rich 9R, in contact with each other, takes place. These co-precipitates grow with time and because of coarsening the area number density decreases. After 100 h or aging a similar to 5 nm thick film-like precipitation of a Mo-rich phase was observed at the lath boundaries. From the composition or the film it is suggested that the phase in question is the quasicrystalline R' phase. The film is perforated with Cu-rich OR and eta-Ni-3(Ti, Al) co-precipiLaLes. Not all precipitate types present in the matrix do precipitate at the lath boundaries; the Si-containing G phase and gamma'-Ni-3(Ti, Al, Si) and the Cr-rich alpha' phase were not observed at the lath boundaries. (C) 2012 Elsevier B.V. All rights reserved.

Update: 3-Oct-2013

Title:
Nanoquasicrystalline Al-Fe-Cr-Nb alloys produced by powder metallurgy
Authors:
Audebert, F; Galano, M; Rios, CT; Kasama, H; Peres, M; Kiminami, C; Botta, WJ; Bolfarini, C Author Full Names: Audebert, F.; Galano, M.; Triveno Rios, C.; Kasama, H.; Peres, M.; Kiminami, C.; Botta, W. J.; Bolfarini, C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 577 650-657; 10.1016/j.jallcom.2013.06.162 NOV 15 2013
Abstract:
Nano-quasicrystalline Al-Fe-Cr based alloys produced by rapid solidification processes exhibit high strength at elevated temperatures. Nevertheless, the quasicrystalline particles in these systems become unstable at high temperature limiting the industrial applications. In early works, it was observed that the use of Nb or Ta increases the stability of the Al-Fe-Cr quasicrystalline phase delaying the microstructural transformation to higher temperatures. Thus, these nano-quasicrystalline Al-based alloys have become promising new high strength material to be used at elevated temperatures in the automotive and aeronautical industries. In previous works, nano-quasicrystalline Al-Fe-Cr-Nb based alloys were obtained by rapid solidification using the melt-spinning technique. In order to obtain bulk alloys for industrial applications other fabrication routes such as powder production by gas atomization followed by compaction and extrusion are required. In the present work, the production of Al-Fe-Cr-Nb based alloys by powder atomization at laboratory scale was investigated. The powders obtained were sieved in different ranges of sizes and the microstructures were characterised by means of X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive of X-ray analysis. Mechanical properties have been measured by compression tests at room temperature and at 250 degrees C. It was observed that a very high temperature is required to produce these alloys by gas atomization; the icosahedral quasicrystalline phase can be retained after the atomization in powder sizes typically under 75 mu m, and also after the extrusion at 375 degrees C. The extruded bars were able to retain a very high strength at elevated temperature, around 60% of the yield stress at room temperature, in contrast with the 10-30% typically obtained for many commercial Al alloys. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Microstructure transformations in the heat-treated Mg-Zn-Y alloy
Authors:
Geng, JW; Teng, XY; Zhou, GR; Zhao, DG Author Full Names: Geng, Jiwei; Teng, Xinying; Zhou, Guorong; Zhao, Degang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 577 498-506; 10.1016/j.jallcom.2013.07.009 NOV 15 2013
Abstract:
Mg-Zn-Y icosahedral quasicrystals have been prepared from the Mg63.5Zn34Y2.5 (at.%) alloy by copper and steel molds casting respectively. The phase transformations under different heat treatments have been investigated successively. Although the cooling rates of the two samples are quite different, the icosahedral quasicrystalline (I-phase) can precipitate from liquid directly almost at the same temperature. The eutectic structure (alpha-Mg + I-phase) forms at the later stage, while the Mg7Zn3 phase forms under a larger cooling rate (copper mold). Moreover, with a lower cooling speed, micro shrinkage cavities and cracks are easily caused by solute partitioning at the edge of petals-like I-phase. The volume fraction of I-phase is effectively increased after heat treatment at 350 degrees C for 50 h because I-phase can grow further in a facet manner during the heat treatment process. The I-phase in the Mg63.5Zn34Y2.5 alloy is thermodynamically unstable at 420 degrees C, and therefore transformations of the I-phase to the W or H-phase occur due to slow transformation kinetics and low thermodynamics driving force. In addition, few decagonal quasicrystalline phases (D-phases) can form on the I-phase/Mg7Zn3 interface. Atomic diffusion and concentration also play a crucial role in these transformations. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Relative orientation of the magnetic moments in modulated multiferroic CaMn7O12
Authors:
Przenioslo, R; Wardecki, D; Slawinski, W; Sosnowska, I; Keller, L Author Full Names: Przenioslo, Radoslaw; Wardecki, Dariusz; Slawinski, Wojciech; Sosnowska, Izabela; Keller, Lukas
Source:
PHYSICA B-CONDENSED MATTER, 428 27-29; 10.1016/j.physb.2013.07.008 NOV 1 2013
Abstract:
The modulated magnetic ordering in the multiferroic manganite CaMn7O12 has been studied by using the neutron powder diffraction technique. The relative orientation of the magnetic moments of Mn4+ and Mn3+ ions located in Mn3 sublattice at (0,0,112) and Mn2 sublattice at (112,0,112) is shown to be antiparallel, i.e. their relative orientation angle Phi=pi. This result differs from that given by other authors who propose another relative orientation with a value of Phi=0.84(4)pi. The relative orientation angle is an important parameter used in model studies based on effective hamiltonians. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Origin of the phase transition in IrTe2: Structural modulation and local bonding instability
Authors:
Cao, HB; Chakoumakos, BC; Chen, X; Yan, JQ; McGuire, MA; Yang, H; Custelcean, R; Zhou, HD; Singh, DJ; Mandrus, D Author Full Names: Cao, Huibo; Chakoumakos, Bryan C.; Chen, Xin; Yan, Jiaqiang; McGuire, Michael A.; Yang, Hui; Custelcean, Radu; Zhou, Haidong; Singh, David J.; Mandrus, David
Source:
PHYSICAL REVIEW B, 88 (11):10.1103/PhysRevB.88.115122 SEP 12 2013
Abstract:
We used x-ray and neutron diffraction to determine the low-temperature structure of IrTe2. A structural modulation was observed with a wave vector of k = (1/5,0,1/5) below T-s approximate to 285 K, accompanied by a structural transition from a trigonal to a triclinic lattice. We also performed first-principles calculations for high-temperature and low-temperature structures, which elucidate the nature of the phase transition and the low-temperature structure. A local bonding instability associated with the Te 5p states is likely the origin of the structural phase transition in IrTe2.
Title:
EFFECT OF ALLOYING ELEMENTS ON MICROSTRUCTURE AND PROPERTIES OF Al-Mn-Fe RIBBON
Authors:
Stan, K; Litynska-Dobrzynska, L; Ochin, P; Wierzbicka-Miernik, A; Goral, A; Wojewoda-Budka, J Author Full Names: Stan, K.; Litynska-Dobrzynska, L.; Ochin, P.; Wierzbicka-Miernik, A.; Goral, A.; Wojewoda-Budka, J.
Source:
ARCHIVES OF METALLURGY AND MATERIALS, 58 (2):341-346; 10.2478/v10172-012-0195-0 2013
Abstract:
Influence of Ti, V, Cr, Zr, and Mo additions on microstructure and mechanical properties of the Al91Mn7Fe2 quasicrystalline alloy produced by the melt spinning technique has been studied. It was found that the microstructure of obtained all ribbons was similar and consists of spherical or dendritic icosahedral quasicrystalline particles embedded in an aluminium matrix coexisting with small fraction of intermetallic phase. Comporing DSC curves obtained for each sample it was observed that the alloy with Mo addition exhibits the best thermal stability among prepared alloys. Addition of molybdenum caused a significant shift of the main exothermic peak corresponding to temperature of quasicrystalline phase decomposition from 450 degrees C for ternary alloy to about 550 degrees C for quaternary composition. Microhardness measured for all prepared alloys were similar with the mean value of about 200 HV only alloy with Zr addition exhibited higher microhardness of about 270 HV caused by strengthening effect of Zr localized in the grains of aluminium matrix.

Update: 26-Sep-2013

Title:
STM and XPS investigation of the oxidation of the Al-4(Cr,Fe) quasicrystal approximant
Authors:
Parle, JK; Beni, A; Dhanak, VR; Smerdon, JA; Schmutz, P; Warde, M; Barthes-Labrousse, MG; Bauer, B; Gille, P; Sharma, HR; McGrath, R Author Full Names: Parle, J. K.; Beni, A.; Dhanak, V. R.; Smerdon, J. A.; Schmutz, P.; Warde, M.; Barthes-Labrousse, M. -G.; Bauer, B.; Gille, P.; Sharma, H. R.; McGrath, R.
Source:
APPLIED SURFACE SCIENCE, 283 276-282; 10.1016/j.apsusc.2013.06.101 OCT 15 2013
Abstract:
The oxidation of the Al-4(Cr, Fe) quasicrystal approximant has been studied using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM data indicate that the initial oxidation on the (1 0 0) surface proceeds in a highly ordered fashion. Oxygen preferentially adsorbs onto the surface of terraces, and step edges remain intact. The STM images show ordered stripes after initial oxidation. XPS data indicate that only Al is oxidised, with at least two oxidation states present. The Cr and Fe peaks remain unchanged. The oxidation of Al, rather than Cr or Fe, is consistent with the enthalpies of formation for each oxide. The stripes visible on the STM images are therefore identified to be the initial stages of aluminium oxide formation. XPS performed after higher O-2 exposure indicates that the (1 0 0) termination shows hindered Al oxide film thickness growth rates compared to the (0 1 0) and (0 0 1) surfaces. Crown Copyright (c) 2013 Published by Elsevier B.V. All rights reserved.
Title:
Excellent mechanical properties of an ultrafine-grained quasicrystalline strengthened magnesium alloy with multi-modal microstructure
Authors:
Huang, H; Yuan, GY; Chen, CL; Ding, WJ; Wang, ZC Author Full Names: Huang, Hua; Yuan, Guangyin; Chen, Chunlin; Ding, Wenjiang; Wang, Zhongchang
Source:
MATERIALS LETTERS, 107 181-184; 10.1016/j.matlet.2013.06.006 SEP 15 2013
Abstract:
In this study, we have developed an excellent mechanical properties of an ultrafine-grained quasicrystalline strengthened magnesium alloys by conventional extruding as-casted Mg-1.5Zn-0.25Gd (at%) ingot at 373 K with an extrusion ratio of about 9:1. After extrusion, multi-modal microstructure was formed, i.e. exhibited large deformed grains surrounded by fine dynamical recrystallization grains and the mean grain sizes smaller than I pal. The extruded sample shows excellent tensile properties at ambient temperature with ultimate tensile strength of 417 MPa, 0.2% proof stress of 395 MPa and elongation to failure of 8.3%. The notable improvement in strength mainly attributed to the grain refinement, dense distribution of the fine precipitates inside the fine dynamical recrystallization grains and the high intensity of typical basal texture. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Layered pnictide-oxide Na(2)Ti(2)Pn(2)O (Pn = As, Sb): a candidate for spin density waves
Authors:
Yan, XW; Lu, ZY Author Full Names: Yan, Xun-Wang; Lu, Zhong-Yi
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (36):10.1088/0953-8984/25/36/365501 SEP 11 2013
Abstract:
From first-principles calculations, we have studied the electronic and magnetic structures of compound Na(2)Ti(2)Pn(2)O (Pn = As or Sb), whose crystal structure is a bridge between or a combination of those of high-T-c superconducting cuprates and iron pnictides. We find that in the ground state Na2Ti2As2O is a novel blocked checkerboard antiferromagnetic semiconductor with a small band gap of about 0.15 eV. In contrast, Na2Ti2Sb2O is a bi-collinear antiferromagnetic semimetal, with a small moment of about 0.5 mu B around each Ti atom. We show that there is a strong Fermi surface nesting in Na(2)Ti(2)Pn(2)O, and we verify that the blocked checkerboard and bi-collinear antiferromagnetic states both are the spin density waves induced by the Fermi surface nesting. A tetramer structural distortion is found in company with the formation of a blocked checkerboard antiferromagnetic order, in good agreement with the experimentally observed commensurate structural distortion but with space group symmetry retained after the anomaly happens.
Title:
Phonon and magnon Raman scattering in CuB2O4
Authors:
Ivanov, VG; Abrashev, MV; Todorov, ND; Tomov, V; Nikolova, RP; Litvinchuk, AP; Iliev, MN Author Full Names: Ivanov, V. G.; Abrashev, M. V.; Todorov, N. D.; Tomov, V.; Nikolova, R. P.; Litvinchuk, A. P.; Iliev, M. N.
Source:
PHYSICAL REVIEW B, 88 (9):10.1103/PhysRevB.88.094301 SEP 3 2013
Abstract:
The Brillouin-zone-center phonons and two-magnon excitations in CuB2O4 are studied experimentally by polarized Raman spectroscopy. Most of the expected modes are clearly pronounced and their symmetry unambiguously identified from the polarization selection rules. The experimentally observed transverse optical phonon frequencies are in good agreement with those obtained by means of density functional theory. The two-magnon scattering band is centered at 82 cm(-1) and is clearly identified at temperatures below the Neel temperature T-N. The spectral shape of the two-magnon band confirms the existing theoretical models of magnon dispersion in the commensurate phase of CuB2O4 and suggests an exchange integral of J = 33 cm(-1) (48 K) between the nearest-neighbor Cu(A) ions. The quantitative line-shape analysis of the two-magnon band evidences for additional magnon self-energy contributions below the temperature T* of the commensurate-to-incommensurate phase transition.
Title:
Anisotropic Spin Fluctuations in the Quasi One-Dimensional Frustrated Magnet LiCuVO4
Authors:
Nawa, K; Takigawa, M; Yoshida, M; Yoshimura, K Author Full Names: Nawa, Kazuhiro; Takigawa, Masashi; Yoshida, Makoto; Yoshimura, Kazuyoshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (9):10.7566/JPSJ.82.094709 SEP 2013
Abstract:
We report results of NMR experiments on a single crystal of the quasi one-dimensional frustrated magnet LiCuVO4 The NMR spectra of Li-7 and V-51 nuclei indicate a helical spin order in a magnetic field of 4 T with the helical spin plane perpendicular to the field and a spin-density-wave (SDW) order at 10 T with modulation in the magnitude of the moments aligned along the field, in agreement with earlier reports. The nuclear spin-lattice relaxation rate 1/T-1 at V-51 nuclei, which is selectively coupled to the transverse spin fluctuations perpendicular to the field, shows a pronounced peak near the helical ordering temperature in the field of 4 T applied along the a-axis. In the field of 10 T, however, such a peak is absent. Instead 1/T-1 at Li-7 nuclei probing longitudinal spin fluctuations shows divergent behavior towards the SDW ordering temperature. These results are qualitatively consistent with the theoretical description that the SDW correlation is due to bound magnon pairs, which produce an energy gap in the transverse spin excitation spectrum.
Title:
Field-induced phase transitions in the helimagnet Ba2CuGe2O7
Authors:
Chovan, J; Marder, M; Papanicolaou, N Author Full Names: Chovan, J.; Marder, M.; Papanicolaou, N.
Source:
PHYSICAL REVIEW B, 88 (6):10.1103/PhysRevB.88.064421 AUG 26 2013
Abstract:
We present a theoretical study of the two-dimensional spiral antiferromagnet Ba2CuGe2O7 in the presence of an external magnetic field. We employ a suitable nonlinear sigma model to calculate the T = 0 phase diagram and the associated low-energy spin dynamics for arbitrary canted magnetic fields, in general agreement with experiment. In particular, when the field is applied parallel to the c axis, a previously anticipated Dzyaloshinskii-type incommensurate-to-commensurate phase transition is actually mediated by an intermediate phase, in agreement with our earlier theoretical prediction confirmed by the recent observation of the so-called double-k structure. The sudden pi/2 rotations of the magnetic structures observed in experiment are accounted for by a weakly broken U(1) symmetry of our model. Finally, our analysis suggests a nonzero weak-ferromagnetic component in the underlying Dzyaloshinskii-Moriya anisotropy, which is important for quantitative agreement with experiment.
Title:
Landau theory of crystallization and self-assembly of octagonal quasicrystals
Authors:
Konevtsova, OV; Rochal, SB; Lorman, VL Author Full Names: Konevtsova, O. V.; Rochal, S. B.; Lorman, V. L.
Source:
PHYSICS OF THE SOLID STATE, 55 (8):1596-1601; 10.1134/S1063783413080143 AUG 2013
Abstract:
The theory of crystallization of quasicrystal structures that does not use the concept of multidimensional crystallography for describing the quasicrystal order has been proposed. It has been shown using the structure of the MnSiAl octagonal quasicrystal as an example that the coordinates of the sites in the corresponding quasicrystal lattice can be calculated by conditional minimization of the Landau free energy. The abandonment of the unconditional minimization of the free energy has been justified by special features of the local atomic order in the considered structure. The proposed theory gives a new physical meaning to the traditional concepts of multidimensional crystallography and can also be used for explaining the formation of quasicrystal structures with other quasicrystal lattices.

Update: 19-Sep-2013

Title:
Powder neutron diffraction study of HoCoGa5
Authors:
Kobayashi, R; Kaneko, K; Wakimoto, S; Chi, SX; Sanada, N; Watanuki, R; Suzuki, K Author Full Names: Kobayashi, Riki; Kaneko, Koji; Wakimoto, Shuichi; Chi, Songxue; Sanada, Naoyuki; Watanuki, Ryuta; Suzuki, Kazuya
Source:
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 63 (3):337-340; SI 10.3938/jkps.63.337 AUG 2013
Abstract:
We have studied successive magnetic transitions of HoCoGa5 at T (N1) = 9.6 K and T (N2) = 7.5 K by using powder neutron diffraction. Apparent superlattice peaks were observed at temperatures below T (N1). With further decreases temperature, the patterns exhibit a substantial change at temperatures below T (N2). The observed magnetic peaks at 8 K (AntiFerromagnetic InCommensurate (AFIC) phase: T (N2) aOE (c) T < T (N1)) can be represented by the propagation vector q (L) = (1/2 0 tau) with tau = 0.35(2). In contrast, the magnetic structure becomes commensurate with q (C) = (1/2 0 1/2) at 4 K (AntiFerromagnetic Commensurate (AFC) phase: T < T (N2)). The temperature dependence of magnetic intensity shows an apparent temperature hysteresis at T (N2), indicates a first-order transition at T (N2). Analysis of the integrated intensity at 4 K reveals that the Ho moment with a size of 8.6(2) A mu(B), oriented parallel to the c-axis in the AFC phase. While the successive transitions of HoCoGa5 are different from those of TbCoGa5, the magnetic structure in the AFC phase of HoCoGa5 is the same as the AF (I) (Tb) of TbCoGa5, and may indicate an additional transition at a lower temperature in HoCoGa5.
Title:
Structural and Magnetic Phase Transitions in the A(n)B(n)O(3n-2) Anion-Deficient Perovskites Pb2Ba2BiFe5O13 and Pb1.5Ba2.5Bi2Fe6O16
Authors:
Abakumov, AM; Batuk, M; Tsirlin, AA; Tyablikov, OA; Sheptyakov, DV; Filimonov, DS; Pokholok, KV; Zhidal, VS; Rozova, MG; Antipov, EV; Hadermann, J; Van Tendeloo, G Author Full Names: Abakumov, A. M.; Batuk, M.; Tsirlin, A. A.; Tyablikov, O. A.; Sheptyakov, D. V.; Filimonov, D. S.; Pokholok, K. V.; Zhidal, V. S.; Rozova, M. G.; Antipov, E. V.; Hadermann, J.; Van Tendeloo, G.
Source:
INORGANIC CHEMISTRY, 52 (14):7834-7843; 10.1021/ic3026667 JUL 15 2013
Abstract:
Novel anion-deficient perovskite-based ferrites Pb2Ba2BiFe5O13 and Pb1.5Ba2.5Bi2Fe6O16 were synthesized by solid-state reaction in air. Pb2Ba2BiFe5O13 and Pb1.5Ba2.5Bi2Fe6O16 belong to the perovskite-based A(n)B(n)O(3n-2) homologous series with n = 5 and 6, respectively, with a unit cell related to the perovskite subcell a(p) as a(p)root 2 x a(p) x na(p) root 2. Their structures are derived from the perovsldte one by slicing it with 1/2[110](p)((1) over bar 01)(p) crystallographic shear (CS) planes. The CS operation results in ((1) over bar 01)(p)-shaped perovsldte blocks with a thickness of (n - 2) FeO6 octahedra connected to each other through double chains of edge-sharing FeO5 distorted tetragonal pyramids which can adopt two distinct mirror-related configurations. Ordering of chains with a different configuration provides an extra level of structure complexity. Above T approximate to 750 K for Pb2Ba2BiFe5O13 and T approximate to 400 K for Pb1.5Ba2.5Bi2Fe6O16 the chains have a disordered arrangement. On cooling, a second-order structural phase transition to the ordered state occurs in both compounds. Symmetry changes upon phase transition are analyzed using a combination of superspace crystallography and group theory approach. Correlations between the chain ordering pattern and octahedral tilting in the perovskite blocks are discussed. Pb2Ba2BiFe5O13 and Pb1.5Ba2.5Bi2Fe6O16 undergo a transition into an antiferromagnetically (AFM) ordered state, which is characterized by a G-type AFM ordering of the Fe magnetic moments within the perovsldte blocks. The AFM perovsldte blocks are stacked along the CS planes producing alternating FM and AFM-aligned Fe-Fe pairs. In spite of the apparent frustration of the magnetic coupling between the perovskite blocks, all n = 4, 5, 6 A(n)Fe(n)O3(n-2) (A = Pb, Bi, Ba) feature robust antiferromagnetism with similar Neel temperatures of 623-632 K.
Title:
Surface-enhanced charge-density-wave instability in underdoped Bi2Sr2-xLaxCuO6+delta
Authors:
Rosen, JA; Comin, R; Levy, G; Fournier, D; Zhu, ZH; Ludbrook, B; Veenstra, CN; Nicolaou, A; Wong, D; Dosanjh, P; Yoshida, Y; Eisaki, H; Blake, GR; White, F; Palstra, TTM; Sutarto, R; He, F; Pereira, AF; Lu, Y; Keimer, B; Sawatzky, G; Petaccia, L; Damascelli, A Author Full Names: Rosen, J. A.; Comin, R.; Levy, G.; Fournier, D.; Zhu, Z. -H.; Ludbrook, B.; Veenstra, C. N.; Nicolaou, A.; Wong, D.; Dosanjh, P.; Yoshida, Y.; Eisaki, H.; Blake, G. R.; White, F.; Palstra, T. T. M.; Sutarto, R.; He, F.; Pereira, A. Frano; Lu, Y.; Keimer, B.; Sawatzky, G.; Petaccia, L.; Damascelli, A.
Source:
NATURE COMMUNICATIONS, 4 10.1038/ncomms2977 JUL 2013
Abstract:
Neutron and X-ray scattering experiments have provided mounting evidence for spin and charge ordering phenomena in underdoped cuprates. These range from early work on stripe correlations in Nd-LSCO to the latest discovery of charge-density-waves in YBa2Cu3O6 + x. Both phenomena are characterized by a pronounced dependence on doping, temperature and an externally applied magnetic field. Here, we show that these electron-lattice instabilities exhibit also a previously unrecognized bulk-surface dichotomy. Surface-sensitive electronic and structural probes uncover a temperature-dependent evolution of the CuO2 plane band dispersion and apparent Fermi pockets in underdoped Bi-2 Sr2-x La-x CuO6 + delta (Bi2201), which is directly associated with an hitherto-undetected strong temperature dependence of the incommensurate superstructure periodicity below 130 K. In stark contrast, the structural modulation revealed by bulk-sensitive probes is temperature-independent. These findings point to a surface-enhanced incipient charge-density-wave instability, driven by Fermi surface nesting. This discovery is of critical importance in the interpretation of single-particle spectroscopy data, and establishes the surface of cuprates and other complex oxides as a rich playground for the study of electronically soft phases.

Update: 12-Sep-2013

Title:
Two-dimensional alloy of immiscible Pb and Sn atoms on Ru(0001)
Authors:
Yuhara, J; Ishikawa, Y; Matsui, T Author Full Names: Yuhara, J.; Ishikawa, Y.; Matsui, T.
Source:
SURFACE SCIENCE, 616 131-136; 10.1016/j.susc.2013.05.018 OCT 2013
Abstract:
We investigated the atomic arrangements and phase diagrams of single and binary two-dimensional (2D) films of Pb and Sn on Ru(0001) using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). The Pb films formed the (root 7 x root 7) and c(2 x 4) structures in the saturated and unsaturated coverages, respectively, and their arrangements of Pb atoms were identified as hexagonal and rectangular structures. The Sn films formed the c(2 x 8) and incommensurate ("root 6 x root 3"), namely IC-1, at low coverages. Upon increasing the coverage, the IC-1 phase transformed into the commensurate (root 7 x root 3) structure and gradually extended to an incommensurate ("root 10 x root 3") structure, namely IC-2, at saturated coverages. The atomic arrangements of the Sn atoms were primarily rectangular-like structures. The 2D binary film exhibited an incommensurate structure close to (root 7 x root 7) at the Pb and Sn coverages of 0.15 +/- 0.05 ML and 0.40 +/- 0.05 ML, respectively. Atomically resolved STM images of the 2D binary films revealed a highly ordered hexagonal arrangement of Pb and Sn atoms with an average composition of PbSn3. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Antiferromagnetic order and the structural order-disorder transition in the Cd6Ho quasicrystal approximant
Authors:
Kreyssig, A; Beutier, G; Hiroto, T; Kim, MG; Tucker, GS; de Boissieu, M; Tamura, R; Goldman, AI Author Full Names: Kreyssig, Andreas; Beutier, Guillaume; Hiroto, Takanobu; Kim, Min Gyu; Tucker, Gregory S.; de Boissieu, Marc; Tamura, Ryuji; Goldman, Alan I.
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 93 (9):512-520; 10.1080/09500839.2013.815375 SEP 1 2013
Abstract:
It has generally been accepted that the orientational ordering of the Cd-4 tetrahedron within the Cd6R quasicrystal approximants is kinetically inhibited for R=Ho, Er, Tm and Lu by steric constraints. Our high-resolution X-ray scattering measurements of the Cd6Ho quasicrystal approximant, however, reveal an abrupt (first-order) transition to a monoclinic structure below T-S=178K for samples that have aged' at room temperature for approximately one year, reopening this question. Using X-ray resonant magnetic scattering at the Ho L-3-edge we have elucidated the nature of the antiferromagnetic ordering below T-N=8.5K in Cd6Ho. The magnetic Bragg peaks are found at the charge forbidden H+K+L=2n+1 positions, referenced to the high-temperature body-centred cubic structure. In general terms, this corresponds to antiferromagnetic arrangements of the Ho moments on adjacent clusters in the unit cell as previously found for Cd6Tb.
Title:
Local structure and hyperfine interactions of Fe-57 in NaFeAs studied by Mossbauer spectroscopy
Authors:
Presniakov, I; Morozov, I; Sobolev, A; Roslova, M; Boltalin, A; Son, V; Volkova, O; Vasiliev, A; Wurmehl, S; Buchner, B Author Full Names: Presniakov, I.; Morozov, I.; Sobolev, A.; Roslova, M.; Boltalin, A.; Son, V.; Volkova, O.; Vasiliev, A.; Wurmehl, S.; Buechner, B.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (34):10.1088/0953-8984/25/34/346003 AUG 28 2013
Abstract:
Detailed Fe-57 Mossbauer spectroscopy measurements on superconducting NaFeAs powder samples have been performed in the temperature range 13 K <= T < 300 K. The Fe-57 spectra recorded in the paramagnetic range (T > T-N approximate to 46 K) are discussed supposing that most of the Fe2+ ions are located in distorted (FeAs4) tetrahedra of NaFeAs phase, while an additional minor (< 10%) component of the spectra corresponds to impurity or intergrowth NaFe2As2 phase with a nominal composition near NaFe2As2. Our results reveal that the structural transition (T-S approximate to 55 K) has a weak effect on the electronic structure of iron ions, while at T <= T-N the spectra show a continuous distribution of hyperfine fields H-Fe. The shape of these spectra is analyzed in terms of two models: (i) an incommensurate spin density wave modulation of iron magnetic structure, (ii) formation of a microdomain structure or phase separation. It is shown that the hyperfine parameters obtained using these two methods have very similar values over the whole temperature range. Analysis of the temperature dependence H-Fe (T) with the Bean-Rodbell model leads to zeta = 1.16 +/- 0.05, suggesting that the magnetic phase transition is first order in nature. A sharp evolution of the V-ZZ(T) and eta(T) parameters of the full Hamiltonian of hyperfine interactions near T approximate to (T-N, T-S) is interpreted as a manifestation of the anisotropic electron redistribution between the d(xz)-, d(yz)- and d(xy)-orbitals of the iron ions.
Title:
Surface modification of Mg-67-Zn-30-Y-3 quasicrystal alloy by high current pulsed electron beam
Authors:
Gao, B; Hao, Y; Tu, GF; Li, SW; Yu, FX; Zuo, L; Hu, L Author Full Names: Gao, Bo; Hao, Yi; Tu, Ganfeng; Li, Shiwei; Yu, Fuxiao; Zuo, Liang; Hu, Liang
Source:
SURFACE & COATINGS TECHNOLOGY, 229 42-45; 10.1016/j.surfcoat.2012.06.026 AUG 25 2013
Abstract:
The HCPEB (high current pulsed electron beam) irradiation gives rise to rapid heating, melting and cooling of material surfaces, thereby improving surface properties of materials. In this paper, the surfaces of a Mg67Zn30Y3 quasicrystal alloy (Zn 50.86 wt.%, Y 7.02 wt.%, Mg balance) were bombarded by HCPEB. The surface microstructure variations of the Mg67Zn30Y3 alloy before and after HCPEB treatment were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The results show that the initial structure of the Mg67Zn30Y3 alloy consists of matrix Mg7Zn3, rich Mg phase (alpha-Mg) and quasicrystal Mg3Zn6Y. Under multiple HCPEB treatments, the phase boundaries become indistinct. The chemical composition of the surface layer tends to be a homogeneous distribution due to interdiffusion of alloying elements. Mg largely dissolved in the matrix by analyzing XRD patterns, causing the formation of supersaturated solid solution in surface layer. Besides, a nano-structured quasiaystal layer (grain size of 10-30 nm) is obtained after HCPEB treatment. By wear tests, the wear resistance of the HCPEB-treated samples is improved by a factor of 1.2 compared with that of the initial sample and the main reason can be attributed to the formation of a metastable structure during the HCPEB process. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Valence ordering in the intermediate-valence magnet YbPd
Authors:
Takahashi, R; Honda, T; Miyake, A; Kagayama, T; Shimizu, K; Ebihara, T; Kimura, T; Wakabayashi, Y Author Full Names: Takahashi, Ryo; Honda, Takashi; Miyake, Atsushi; Kagayama, Tomoko; Shimizu, Katsuya; Ebihara, Takao; Kimura, Tsuyoshi; Wakabayashi, Yusuke
Source:
PHYSICAL REVIEW B, 88 (5):10.1103/PhysRevB.88.054109 AUG 19 2013
Abstract:
An x-ray diffraction study reveals the valence-ordering structure in an intermediate-valence magnet YbPd with a CsCl structure. The valence of the Yb ions forms an incommensurate structure, characterized by the wave vector (+/- 0.07 +/- 0.07 1/2) below 130 K. At 105 K, the incommensurate structure turns into a commensurate structure, characterized by the wave vector (0 0 1/2). Based on the resonant x-ray diffraction spectra of the superlattice reflections, the valences of the Yb ions below 105 K are found to be 3+ and 2.6+. The origin of the long-wavelength modulation is discussed with the aid of an Ising model having next-nearest-neighbor interaction.
Title:
Phase transitions and their co-existence in TlGaSe2-TlCrS2(Se-2) systems
Authors:
Veliyev, RG; Seyidov, MHY; Kerimova, EM; Sadykhov, RZ; Asadov, YG; Seyidov, FM; Gasanov, NZ Author Full Names: Veliyev, R. G.; Seyidov, Mir Hasan Yu; Kerimova, E. M.; Sadykhov, R. Z.; Asadov, Yu G.; Seyidov, F. M.; Gasanov, N. Z.
Source:
BULLETIN OF MATERIALS SCIENCE, 36 (4):693-698; 10.1007/s12034-013-0530-8 AUG 2013
Abstract:
Investigation of dielectric properties of layered compound, TlGaSe2, showed that it is a ferroelectric (T (c) = 105 center dot 5 K) with an intermediate incommensurate phase (T (i) = 114 center dot 5 K). Our magnetic studies of layered compounds, TlCrS2 and TlCrSe2, for the first time revealed that the magnetic phase transition in these compounds are quasi two-dimensional ferromagnetic in nature and magnetic characteristics are T (C) = 90 K, T = 115 K, mu (eff) = 3 center dot 26 mu (B) and T (C) = 105 K, T = 120 K, mu (eff) = 3 center dot 05 mu (B) , respectively. Using the method of DTA, areas of homogeneous and heterogeneous coexistence of ferroelectric and ferromagnetic phase transitions in the systems, TlGaSe2-TlCrS2 and TlGaSe (2)-TlCrSe2, were identified. The low-dimensional solid solutions and eutectic alloys in these systems can be used as basic materials for plenty of functional recorders.
Title:
On the special points on the (P,T,x)- phase diagram for Sn2P2(Se x S1- x )(6) crystals: acoustic studies of Sn2P2(Se0.28S0.72)(6)
Authors:
Mys, O; Martynyuk-Lototska, I; Zapeka, B; Vlokh, R Author Full Names: Mys, O.; Martynyuk-Lototska, I.; Zapeka, B.; Vlokh, R.
Source:
PHILOSOPHICAL MAGAZINE, 93 (6):648-660; FEB 1 2013
Abstract:
On the basis of temperature dependences of the acoustic wave velocity and the acoustic attenuation in Sn2P2(Se0.28S0.72)(6) crystals under normal conditions and hydrostatic pressures, we show that increasing pressure causes these crystals to move away from the tricritical point and enter into the region of first-order phase transitions (PTs) in (P,T,x)-space. Still higher hydrostatic pressures lead to an increase in the attenuation of the acoustic wave with the velocity v(22) and broadening of its anomaly in the PT region, thus hinting at splitting of the PT, with the appearance of an intermediate incommensurate phase approximately at P=3.3kbar. We offer a (P,T,x)- phase diagram for the solid solutions Sn2P2(Se (x) S1- (x) )(6), which includes two special lines of PTs, tricritical and triple ones, which can intersect at the Lifshitz point at negative hydrostatic pressures. The variations of the surface of acoustic wave velocities occurring with changing temperature are obtained for Sn2P2(Se0.28S0.72)(6) crystals under the atmospheric pressure.
Title:
On the special points on the (P,T,x)- phase diagram for Sn2P2(Se x S1- x )6 crystals: acoustic studies of Sn2P2(Se0.28S0.72)(6)
Authors:
Mys, O; Martynyuk-Lototska, I; Zapeka, B; Vlokh, R Author Full Names: Mys, O.; Martynyuk-Lototska, I.; Zapeka, B.; Vlokh, R.
Source:
PHILOSOPHICAL MAGAZINE, 93 (6):648-660; 10.1080/14786435.2012.728010 FEB 1 2013
Abstract:
On the basis of temperature dependences of the acoustic wave velocity and the acoustic attenuation in Sn2P2(Se0.28S0.72)(6) crystals under normal conditions and hydrostatic pressures, we show that increasing pressure causes these crystals to move away from the tricritical point and enter into the region of first-order phase transitions (PTs) in (P,T,x)-space. Still higher hydrostatic pressures lead to an increase in the attenuation of the acoustic wave with the velocity v(22) and broadening of its anomaly in the PT region, thus hinting at splitting of the PT, with the appearance of an intermediate incommensurate phase approximately at P=3.3kbar. We offer a (P,T,x)- phase diagram for the solid solutions Sn2P2(Se (x) S1- (x) )(6), which includes two special lines of PTs, tricritical and triple ones, which can intersect at the Lifshitz point at negative hydrostatic pressures. The variations of the surface of acoustic wave velocities occurring with changing temperature are obtained for Sn2P2(Se0.28S0.72)(6) crystals under the atmospheric pressure.
Title:
A review of phase transitions in RbIn-molybdate
Authors:
Zapart, MB; Zapart, W Author Full Names: Zapart, Maria B.; Zapart, Wlodzimierz
Source:
NUKLEONIKA, 58 (3):365-370; 2013
Abstract:
The paper gives a brief review of the results of EPR temperature studies of RbIn(MoO4)(2) crystal. A sequence of several structural phase transitions has been found in this crystal in the temperature region 84-163 K. The transition at T-1 = 163 K leads to an incommensurate triply modulated state, whereas ferroelastic phases start below T-2 = 143 K. All the low temperature phases in the temperature region 84-143 K are examples of simultaneously ferroelastic and incommensurate ones. The transition observed at T-5 = 84 K seems to suppress the ferroelastic properties of the crystal.
Title:
Elliptic holes in octagonal quasicrystals
Authors:
Li, LH Author Full Names: Li Lian-He
Source:
CHINESE PHYSICS B, 22 (1):10.1088/1674-1056/22/1/016102 JAN 2013
Abstract:
The stress potential function theory for the plane elasticity of octagonal quasicrystals is developed. By introducing stress functions, a large number of basic equations involving the elasticity of octagonal quasicrystals are reduced to a single partial differential equation. Furthermore, we develop the complex variable function method (Lekhnitskii method) for anisotropic elasticity theory to that for quasicrystals. With the help of conformal transformation, an exact solution for the elliptic hole of quasicrystals is presented. The solution of the Griffith crack problem, as a special case of the results, is obtained. As a consequence, the phonon stress intensity factor is derived analytically.

Update: 5-Sep-2013

Title:
Crystal and magnetic structure of TbFe0.25Ge2 compound
Authors:
Gil, A; Hoser, A; Penc, B; Szytula, A Author Full Names: Gil, A.; Hoser, A.; Penc, B.; Szytula, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 344 167-170; 10.1016/j.jmmm.2013.05.055 OCT 2013
Abstract:
The crystal and magnetic structure of polycrystalline TbFe0.25Ge2 sample have been determined. X-ray and neutron diffraction studies indicate that this compound has the orthorhombic CeNiSi2-type crystal structure (space group Cmcm). The magnetic ordering, based on the neutron diffraction data in low temperature, is described by two components: a collinear antiferromagnetic G-type and a cosine-wave modulated one. In the collinear G-type structure the Tb magnetic moment is equal to 3.81(5) mu(B) and it is parallel to the c-axis. The modulated structure is described by the propagation vector k=(0.460(8), 0, 0.305(1)), the Tb magnetic moment equals 7.75(8) mu(B), lies in b-c and forms an angle 23(2)degrees with the c-axis. The collinear component decreases to zero at 22.6 K while the modulated one at 190.8 K. (C) 2013 Elsevier BY. All rights reserved.
Title:
Magnetic ordering in GdNi2B2C revisited by resonant x-ray scattering: Evidence for the double-q model
Authors:
Normile, PS; Rotter, M; Detlefs, C; Jensen, J; Canfield, PC; Blanco, JA Author Full Names: Normile, P. S.; Rotter, M.; Detlefs, C.; Jensen, J.; Canfield, P. C.; Blanco, J. A.
Source:
PHYSICAL REVIEW B, 88 (5):10.1103/PhysRevB.88.054413 AUG 14 2013
Abstract:
Recent theoretical efforts aimed at understanding the nature of antiferromagnetic ordering in GdNi2B2C predicted double-q ordering. Here we employ resonant elastic x-ray scattering to test this theory against the formerly proposed, single-q ordering scenario. Our study reveals a satellite reflection associated with a mixed-order component propagation wave vector, viz., (q(a),2q(b), 0) with q(b) = q(a) approximate to 0.55 reciprocal lattice units, the presence of which is incompatible with single-q ordering but is expected from the double-q model. A (3q(a),0,0) wave vector (i.e., third-order) satellite is also observed, again in line with the double-q model. The temperature dependencies of these along with that of a first-order satellite are compared with calculations based on the double-q model and reasonable qualitative agreement is found. By examining the azimuthal dependence of first-order satellite scattering, we show the magnetic order to be, as predicted, elliptically polarized at base temperature and find the temperature dependence of the "out of a-b plane" moment component to be in fairly good agreement with calculation. Our results provide qualitative support for the double-q model and thus in turn corroborate the explanation for the "magnetoelastic paradox" offered by this model.
Title:
Observation of a reentrant phase transition in incommensurate potassium
Authors:
Lundegaard, LF; Stinton, GW; Zelazny, M; Guillaume, CL; Proctor, JE; Loa, I; Gregoryanz, E; Nelmes, RJ; McMahon, MI Author Full Names: Lundegaard, L. F.; Stinton, G. W.; Zelazny, M.; Guillaume, C. L.; Proctor, J. E.; Loa, I.; Gregoryanz, E.; Nelmes, R. J.; McMahon, M. I.
Source:
PHYSICAL REVIEW B, 88 (5):10.1103/PhysRevB.88.054106 AUG 14 2013
Abstract:
The phase transitions in the host-guest composite structure of potassium have been determined between 19 and 54 GPa by a combination of x-ray powder and single-crystal diffraction. The guest component of the incommensurate composite phase K-III undergoes an "intraphase" transition at 30.0(7) GPa from a C-centered tetragonal structure to an A-centered orthorhombic form. At 39.7(5) GPa, the guest component undergoes a reentrant transition back to the C-centered tetragonal form. This is the first such reentrant transition observed in the composite structures of the elements. The transition in the guest at 30.0(7) GPa is preceded by a loss of the c-glide symmetry of the host component of the structure, and this is not recovered until some 3 GPa after the reentrant transition at 39.7 GPa.
Title:
Controlled Magnetic Reversal in Permalloy Films Patterned into Artificial Quasicrystals
Authors:
Bhat, VS; Sklenar, J; Farmer, B; Woods, J; Hastings, JT; Lee, SJ; Ketterson, JB; De Long, LE Author Full Names: Bhat, V. S.; Sklenar, J.; Farmer, B.; Woods, J.; Hastings, J. T.; Lee, S. J.; Ketterson, J. B.; De Long, L. E.
Source:
PHYSICAL REVIEW LETTERS, 111 (7):10.1103/PhysRevLett.111.077201 AUG 12 2013
Abstract:
We have patterned novel Permalloy thin films with quasicrystalline Penrose P2 tilings and measured their dc magnetization and ferromagnetic resonance absorption. Reproducible anomalies in the hysteretic, low-field data signal a series of abrupt transitions between ordered magnetization textures, culminating in a smooth evolution into a saturated state. Micromagnetic simulations compare well to experimental dc hysteresis loops and ferromagnetic resonance spectra and indicate that systematic control of magnetic reversal and domain wall motion can be achieved via tiling design, offering a new paradigm of magnonic quasicrystals.
Title:
Caged clusters in Al11Ir4: Structural transition and insulating phase
Authors:
Mihalkovic, M; Henley, CL Author Full Names: Mihalkovic, Marek; Henley, C. L.
Source:
PHYSICAL REVIEW B, 88 (6):10.1103/PhysRevB.88.064201 AUG 2 2013
Abstract:
Using pair potentials fitted to an ab initio database, combined with replica-exchange simulated annealing, we show that the complex, quasicrystal-related Al11Ir4 compound contains a nonstandard version of the "pseudo-Mackay" icosahedral cluster, with nonicosahedral inner Al10Ir and/or Al9Ir clusters that exist in various orientations and account for partial occupancies in the reported structure. We found two different compositions with different orientationally ordered grounds, each doubling the (cubic) unit cell and each reached by a first-order thermal transition. One of these is metallic and the other is insulating.
Title:
Computing Phase Diagrams for a Quasicrystal-Forming Patchy-Particle System
Authors:
Reinhardt, A; Romano, F; Doye, JPK Author Full Names: Reinhardt, Aleks; Romano, Flavio; Doye, Jonathan P. K.
Source:
PHYSICAL REVIEW LETTERS, 110 (25):10.1103/PhysRevLett.110.255503 JUN 20 2013
Abstract:
We introduce an approach to computing the free energy of quasicrystals, which we use to calculate phase diagrams for systems of two-dimensional patchy particles with five regularly arranged patches that have previously been shown to form dodecagonal quasicrystals. We find that the quasicrystal is a thermodynamically stable phase for a wide range of conditions and remains a robust feature of the system as the potential's parameters are varied. We also demonstrate that the quasicrystal is entropically stabilized over its crystalline approximants.
Title:
Elliptic holes in octagonal quasicrystals
Authors:
Li, LH Author Full Names: Li Lian-He
Source:
CHINESE PHYSICS B, 22 (1):10.1088/1674-1056/22/1/016102 JAN 2013
Abstract:
The stress potential function theory for the plane elasticity of octagonal quasicrystals is developed. By introducing stress functions, a large number of basic equations involving the elasticity of octagonal quasicrystals are reduced to a single partial differential equation. Furthermore, we develop the complex variable function method (Lekhnitskii method) for anisotropic elasticity theory to that for quasicrystals. With the help of conformal transformation, an exact solution for the elliptic hole of quasicrystals is presented. The solution of the Griffith crack problem, as a special case of the results, is obtained. As a consequence, the phonon stress intensity factor is derived analytically.

Update: 29-Aug-2013

Title:
Microstructure, texture and mechanical properties of as-extruded Mg-Zn-Er alloys
Authors:
Wang, QF; Du, WB; Liu, K; Wang, ZH; Li, SB; Wen, K Author Full Names: Wang, Qingfeng; Du, Wenbo; Liu, Ke; Wang, Zhaohui; Li, Shubo; Wen, Kai
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 581 31-38; 10.1016/j.msea.2013.05.055 OCT 1 2013
Abstract:
In the present work, the microstructure, texture and mechanical properties of the as-extruded Mg-xZn-yEr (x=3, 6 and 9; y=0.5,1 and 1.5; x/y= 6) alloys were investigated. The results showed that the I-phase in the as-cast alloys was destroyed and lots of nano-scale quasicrystalline particles were precipitated within the matrix during hot extrusion process. With the increase in the volume fraction of the primary I-phase, the particle-stimulated nucleation (PSN) of recrystallization was activated. It was suggested that the recrystallization via PSN should lead to the nucleation of new grains with a high orientation mismatch to the parent grains, making the texture gradually weaken. Significant strengthening is achieved in the Mg-9Zn-1.5Er alloy, of which the ultimate tensile strength (sigma(b)) and the yield tensile strength (sigma(0.2)) were 319 MPa and 192 MPa, respectively, with an elongation of 22.3%. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Effect of pretreatment and annealing on microstructure and mechanical properties of Mg-1.5Zn-0.25Gd (at%) alloys reinforced with quasicrystal
Authors:
Huang, H; Chen, CL; Wang, ZC; Li, YP; Yuan, GY Author Full Names: Huang, Hua; Chen, Chunlin; Wang, Zhongchang; Li, Yunping; Yuan, Guangyin
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 581 73-82; 10.1016/j.msea.2013.06.003 OCT 1 2013
Abstract:
Mg-1.5Zn-025Gd-based alloys containing the icosahedral quasicrystalline phase (I-phase) were fabricated to investigate the effect of heat treatment on the microstructure, mechanical properties and anisotropy of the as-extruded alloys. The results show that compared with the samples extruded without homogenized annealing, the samples extruded after homogenized annealing show larger grains, lower strength and elongation, which can be attributed to the secondary-phase particles precipitated in the matrix after homogenized annealing and to the fact that only a few volume fraction of nano-scale I-phase is precipitated in the matrix during extrusion. Moreover, the anisotropy is mitigated in the alloys extruded at as-cast condition because of the grain refinement and the I-phase precipitation. We also find that after annealing at 473 K or 673 K, yield strength decreases while the elongation increases slightly, indicating that annealing has a small effect on the improvement of room-temperature strength, especially the one at relatively higher temperature. The choice of appropriate annealing temperature only imposes a little impact on the ductility enhancement of the extruded samples. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Modulated structure of Lu4AlCu2B9O23 from low-temperature single-crystal X-ray data
Authors:
Bolotina, N; Plachinda, P; Belokoneva, E Author Full Names: Bolotina, Nadezhda; Plachinda, Paul; Belokoneva, Elena
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 69 329-335; 10.1107/S2052519213014231 4 AUG 2013
Abstract:
A second-order phase transition with both displacive and disorder mechanisms was discovered in Lu4AlCu2B9O23 using single-crystal X-ray diffraction techniques by cooling down the sample to 110 K. Low-temperature structure modulations are mainly associated with Cu atoms surrounded by O atoms. The fivefold asymmetric environment leads to a special copper position splitting into a pair of general ones so that four O atoms coordinate each of them. Each copper site is 50% occupied at room temperature, but at lower temperature statistical disorder gives occupation and displacive modulations with a wavevector of q = 0.132c*. Tetragonal P (4) over bar2(1)m symmetry of the non-modulated phase transforms into an orthorhombic (3+1)-dimensional symmetry, P2(1)2(1)2(00 gamma)00s, whereas the (4) over bar axis becomes the twinning axis.
Title:
Symmetry Rule of the Landau Free Energy in the Phonon-Originating Phase Transition
Authors:
Kubo, H; Khazaei, M Author Full Names: Kubo, Hiroshi; Khazaei, Mohammad
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (8):10.7566/JPSJ.82.084601 AUG 2013
Abstract:
We propose a pseudopotential model of the Landau free energy. A novel symmetry rule is manifested in the microscopic description of the model. Followed by ab initio calculations, a method of analyzing the mechanism of a weakly first-order phase transition is established. The model is applied to the pre-omega phase transition in Zr metal and in Zr-20% Nb (Zr-20Nb) alloy. The criterion is elucidated for the commensurate (C) omega-to-incommensurate (IC) omega phase transition by estimating the soliton (anti-omega phase wall) formation energy of the IC omega phase. The quantitative calculation of the reaction path in the thermodynamical potential field has explained the crystal structural difference of the pre-omega phase between Zr metal (C structure) and Zr-20Nb alloy (IC structure). The results of the phase stability are summarized in a energy-phase diagram.
Title:
Phonon anomalies and lattice dynamics in the superconducting oxychlorides Ca2-xCuO2Cl2
Authors:
d'Astuto, M; Yamada, I; Giura, P; Paulatto, L; Gauzzi, A; Hoesch, M; Krisch, M; Azuma, M; Takano, M Author Full Names: d'Astuto, Matteo; Yamada, Ikuya; Giura, Paola; Paulatto, Lorenzo; Gauzzi, Andrea; Hoesch, Moritz; Krisch, Michael; Azuma, Masaki; Takano, Mikio
Source:
PHYSICAL REVIEW B, 88 (1):10.1103/PhysRevB.88.014522 JUL 24 2013
Abstract:
We present a comprehensive study of the phonon dispersion in an underdoped, superconducting Ca2-xCuO2Cl2 crystal. We interpret the results using lattice dynamical calculations based on a shell model, and we compare the results to other hole-doped cuprates, in particular, to the ones isomorphic to La2-xSrxCuO4 (LSCO). We found that an anomalous dip in the Cu-O bond stretching dispersion develops in oxychlorides with a simultaneous marked broadening of the mode. The broadening is maximum at approximate to[pi/(2a) 0 0], which corresponds to the charge-modulation propagation vector. Our analysis also suggests that screening effects in calculations may cause an apparent cosine-shaped bending of the Cu-O bond-stretching dispersion along both the (q 0 0) and (q q 0) directions, which is not observed on the data close to optimal doping. This observation suggests that the discrepancy between experimental data and ab initio calculations on this mode originates from an overestimation of the doping effects on the mode.
Title:
The electronic structure and magnetism of BaTi2Sb2O
Authors:
Wang, GT; Zhang, HP; Zhang, L; Liu, C Author Full Names: Wang, Guangtao; Zhang, Huiping; Zhang, Lin; Liu, Chang
Source:
JOURNAL OF APPLIED PHYSICS, 113 (24):10.1063/1.4812489 JUN 28 2013
Abstract:
The electronic structure and magnetic structures of recently discovered BaTi2Sb2O were studied from first-principles calculations. In the nonmagnetic state, the density of states at the Fermi level are mostly derived from the d(z2); d(x2-y2), and d(xy) orbitals. The Fermi surface (FS) consists of three sheets. The first FS sheet (along X-R line) will nest with the third FS sheet (along M-A line) by the q-vector (q) over right arrow (1) = (pi/a, 0, 0) or (q) over right arrow (2) = (0, pi/a, 0) shift. The calculated bare susceptibility chi(0)(q) peaked at X-point, rather than at the M-point in the FeAs-based superconductor. Such peaked susceptibility induces the spin density wave, and the magnetic ground state is nearly two degenerate antiferromagnetism the bi-collinear antiferromagnetism (AF3) or the blocked checkerboard antiferromagnetism (AF4). The peak of susceptibility chi(0)(q) is obviously suppressed and become slightly in-commensurate with hole doping, but increased with electron doping. When the spin fluctuation is suppressed, the superconductivity appears. This can explain that why the superconductivity appears only in the hole-doped compounds, not in the electron-doped ones. (C) 2013 AIP Publishing LLC.
Title:
Interaction of a dislocation with an elliptical hole in icosahedral quasicrystals
Authors:
Li, LH; Liu, GT Author Full Names: Li, Lian He; Liu, Guan Ting
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 93 (3):142-151; 10.1080/09500839.2012.752883 MAR 1 2013
Abstract:
The interaction between a dislocation and an elliptical hole in icosahedral quasicrystals is considered. An explicit expression for the complex potential is derived using the extended Stroh formalism. Based on the conformal mapping method and a perturbation technique, closed-form solutions are obtained. The field intensity factors at a crack tip and the image forces on the dislocation arising from the crack are calculated. The effects of phonon-phason elastic coupling on the mechanical behavior are also observed.

Update: 21-Aug-2013

Title:
Lead nitroprusside: A new precursor for the synthesis of the multiferroic Pb2Fe2O5, an anion-deficient perovskite
Authors:
Gil, DM; Nieva, G; Franco, DG; Gomez, MI; Carbonio, RE Author Full Names: Gil, Diego M.; Nieva, Gladys; Franco, Diego G.; Ines Gomez, Maria; Carbonio, Raul E.
Source:
MATERIALS CHEMISTRY AND PHYSICS, 141 (1):355-361; 10.1016/j.matchemphys.2013.05.022 AUG 15 2013
Abstract:
In order to investigate the formation of multiferroic oxide Pb2Fe2O5, the thermal decomposition of Pb [Fe(CN)(5)NO] has been studied. The complex precursor and the thermal decomposition products were characterized by IR and Raman spectroscopy, thermal analysis, powder X-ray diffraction (PXRD), scanning electron microscopy and magnetic measurements. The crystal structure of Pb[Fe(CN)(5)NO] was refined by Rietveld analysis. It crystallizes in the orthorhombic system, space group Pnma. The thermal decomposition in air produces highly pure Pb2Fe2O5 as final product. This oxide is an anion deficient perovskite with an incommensurate superstructure. The magnetic measurements confirm that Pb2Fe2O5 shows a weak ferromagnetic signal probably due to disorder in the perfect antiferromagnetic structure or spin canting. The estimated ordering temperature from the fit of a phenomenological model was 520 K. The SEM images reveal that the thermal decomposition of Pb[Fe(CN)(5)NO] produces Pb2Fe2O5 with small particle size. (C) 2013 Elsevier B.V. All rights reserved.
Title:
QUASICRYSTALS Model structures
Authors:
de Boissieu, M Author Full Names: de Boissieu, Marc
Source:
NATURE MATERIALS, 12 (8):692-693; 10.1038/nmat3725 AUG 2013
Title:
A family of binary magnetic icosahedral quasicrystals based on rare earths and cadmium
Authors:
Goldman, AI; Kong, T; Kreyssig, A; Jesche, A; Ramazanoglu, M; Dennis, KW; Bud'ko, SL; Canfield, PC Author Full Names: Goldman, Alan I.; Kong, Tai; Kreyssig, Andreas; Jesche, Anton; Ramazanoglu, Mehmet; Dennis, Kevin W.; Bud'ko, Sergey L.; Canfield, Paul C.
Source:
NATURE MATERIALS, 12 (8):714-718; 10.1038/NMAT3672 AUG 2013
Abstract:
Examples of stable binary icosahedral quasicrystals are relatively rare, and at present there are no known examples featuring localized magnetic moments. These would represent an ideal model system for attaining a deeper understanding of the nature of magnetic interactions in aperiodic lattices. Here we report the discovery of a family of at least seven rare earth icosahedral binary quasicrystals, i-R-Cd (R = Gd to Tm, Y), six of which bear localized magnetic moments. Our work highlights the importance of carefully motivated searches through phase space(1) and supports the proposal that, like icosahedral Sc12Zn88 (ref. 2), binary quasicrystalline phases may well exist nearby known crystalline approximants, perhaps as peritectically forming compounds with very limited liquidus surfaces, offering very limited ranges of composition/temperature for primary solidification.
Title:
Pseudo-Fivefold Diffraction Symmetries in Tetrahedral Packing
Authors:
Lee, S; Henderson, R; Kaminsky, C; Nelson, Z; Nguyen, J; Settje, NF; Schmidt, JT; Feng, J Author Full Names: Lee, Stephen; Henderson, Ryan; Kaminsky, Corey; Nelson, Zachary; Jeffers Nguyen; Settje, Nick F.; Schmidt, Joshua Teal; Feng, Ji
Source:
CHEMISTRY-A EUROPEAN JOURNAL, 19 (31):10244-10270; 10.1002/chem.201203758 JUL 29 2013
Abstract:
We review the way in which atomic tetrahedra composed of metallic elements pack naturally into fused icosahedra. Orthorhombic, hexagonal, and cubic intermetallic crystals based on this packing are all shown to be united in having pseudo-fivefold rotational diffraction symmetry. A unified geometric model involving the 600-cell is presented: the model accounts for the observed pseudo-fivefold symmetries among the different Bravais lattice types. The model accounts for vertex-, edge-, polygon-, and cell-centered fused-icosahedral clusters. Vertex-centered and edge-centered types correspond to the well-known pseudo-fivefold symmetries in I-h and D-5h quasicrystalline approximants. The concept of a tetrahedrally-packed reciprocal space cluster is introduced, the vectors between sites in this cluster corresponding to the principal diffraction peaks of fused-icosahedrally-packed crystals. This reciprocal-space cluster is a direct result of the pseudosymmetry and, just as the real-space clusters, can be rationalized by the 600-cell. The reciprocal space cluster provides insights for the Jones model of metal stability. For tetrahedrally-packed crystals, Jones zone faces prove to be pseudosymmetric with one another. Lower and upper electron per atom bounds calculated for this pseudosymmetry-based Jones model are shown to accord with the observed electron counts for a variety of Group 10-12 tetrahedrally-packed structures, among which are the four known Cu/Cd intermetallic compounds: CdCu2, Cd-3 Cu-4, Cu-5 Cd-8, and Cu3Cd10. The rationale behind the Jones lower and upper bounds is reviewed. The crystal structure of Zn11Au15Cd23, an example of a 1: 1 MacKay cubic quasicrystalline approximant based solely on Groups 10-12 elements is presented. This compound crystallizes in Im (3) over bar (space group no. 204) with a= 13.842(2) angstrom. The structure was solved with R-1= 3.53%, I> 2 sigma;= 5.33%, all data with 1282/0/38 data/restraints/parameters.

Update: 15_Aug_2013

Title:
On importance of higher non-linear interactions in the theory of type II incommensurate systems
Authors:
Korda, VY; Berezovsky, SV; Molev, AS; Korda, LP; Klepikov, VF Author Full Names: Korda, V. Yu.; Berezovsky, S. V.; Molev, A. S.; Korda, L. P.; Klepikov, V. F.
Source:
PHYSICA B-CONDENSED MATTER, 425 31-33; 10.1016/j.physb.2013.05.021 SEP 15 2013
Abstract:
We reveal that the role of the higher non-linear local interactions in the conventional theoretical models developed to describe phase transitions in type II incommensurate systems is underestimated. Their consistent consideration in the thermodynamic potential expansion allows one to remove key contradictions in explanation of the experimental data for ferroelectric Sn2P2Se6 in the vicinity of the modulated-commensurate phase transition point. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Topological floating phase in a spatially anisotropic frustrated Ising model
Authors:
Kalz, A; Chitov, GY Author Full Names: Kalz, Ansgar; Chitov, Gennady Y.
Source:
PHYSICAL REVIEW B, 88 (1):10.1103/PhysRevB.88.014415 JUL 16 2013
Abstract:
We present results for the ordering process of a two-dimensional Ising model with anisotropic frustrating next-nearest-neighbor interactions. We concentrate on a specific wide temperature and parameter region to confirm the existence of two particular phases of the model. The first phase is an incommensurate algebraically ordered (floating) phase emerging at the transition from the paramagnetic high-temperature phase. Then the model undergoes a transition to an antiferromagnetically ordered second phase with diagonal ferromagnetic stripes [ordering wave vector q = (pi/2, pi/2)]. We analyze the unconventional features appearing in several observables, e.g., energy, structure factors, and correlation functions, by means of extensive Monte Carlo simulations and examine carefully the influence of the lattice sizes. For the analytical study of the intermediate phase the Villain-Bak theory is adapted for the present model. Combining both the numerical and analytical work we present the quantitative phase diagram of the model, and, in particular, argue in favor of an intermediate topological floating phase.
Title:
Frustrated Octahedral Tilting Distortion in the Incommensurately Modulated Li3xNd2/3-xTiO3 Perovskites
Authors:
Abakumov, AM; Erni, R; Tsirlin, AA; Rossell, MD; Batuk, D; Nenert, G; Van Tendeloo, G Author Full Names: Abakumov, Artem M.; Erni, Rolf; Tsirlin, Alexander A.; Rossell, Marta D.; Batuk, Dmitry; Nenert, Gwilherm; Van Tendeloo, Gustaaf
Source:
CHEMISTRY OF MATERIALS, 25 (13):2670-2683; 10.1021/cm4012052 JUL 9 2013
Abstract:
Perovskite-structured titanates with layered A-site ordering form remarkably complex superstructures. Using transmission electron microscopy, synchrotron X-ray and neutron powder diffraction, and ab initio structure relaxation, we present the structural solution of the incommensurately modulated Li3xNd2/3-xTiO3 perovskites (x = 0.05, superspace group Pmmm(alpha(1),1/2,0)000(1/2,beta(2) 0)000, a = 3.831048(5) angstrom, b = 3.827977(4) angstrom, c = 7.724356(8) angstrom, q(1) = 0.45131(8)a* + 1/2b*, q(2) = 1/2a* + 0.41923(4)b*). In contrast to earlier conjectures on the nanoscale compositional phase separation in these materials, all peculiarities of the superstructure can be understood in terms of displacive modulations related to an intricate octahedral tilting pattern. It involves fragmenting the pattern of the out-of-phase tilted TiO6 octahedra around the a- and b-axes into antiphase domains, superimposed on the pattern of domains with either, pronounced or suppressed in-phase tilt component around the c-axis. The octahedral tilting competes with the second order Jahn-Teller distortion of the TiO6 octahedra. This competition is considered as the primary driving force for the modulated structure. The A cations are suspected to play a role in this modulation affecting it mainly through the tolerance factor and the size variance. The reported crystal structure calls for a revision of the structure models proposed for the family of layered A-site ordered perovskites exhibiting a similar type of modulated structure.
Title:
Dissipative soliton generation in an active ring resonator based on magnonic quasicrystal with Fibonacci type structure
Authors:
Grishin, SV; Beginin, EN; Sharaevskii, YP; Nikitov, SA Author Full Names: Grishin, S. V.; Beginin, E. N.; Sharaevskii, Yu. P.; Nikitov, S. A.
Source:
APPLIED PHYSICS LETTERS, 103 (2):10.1063/1.4813411 JUL 8 2013
Abstract:
This study reports on the experimental investigations of a magnetostatic surface wave (MSSW) propagation in a magnonic quasicrystal (MQC) with Fibonacci type structure. It is shown that such structure has a greater number of band gaps and narrower pass bands located between them than a periodic structure. These features of the MQC and three-wave decay of the MSSW are used in a MQC active ring resonator for the eigenmode selection and dissipative soliton self-generation. (C) 2013 AIP Publishing LLC.
Title:
Critical exponents of ferroelectric transitions in modulated SrTiO3: Consequences of quantum fluctuations and quenched disorder
Authors:
Wang, JX; Liu, MF; Yan, ZB; Liu, JM Author Full Names: Wang Jing-Xue; Liu Mei-Feng; Yan Zhi-Bo; Liu Jun-Ming
Source:
CHINESE PHYSICS B, 22 (7):10.1088/1674-1056/22/7/077701 JUL 2013
Abstract:
The ferroelectric transitions of several SrTiO3-based ferroelectrics are investigated experimentally and theoretically, with special attention to the critical scaling exponents associated with the phase transitions, in order to understand the competition among quantum fluctuations (QFs), quenched disorder, and ferroelectric ordering. Two representative systems with sufficiently strong QFs and quenched disorders in competition with the ferroelectric ordering are investigated. We start from non-stoichiometric SrTiO3 (STO) with the Sr/Ti ratio deviating slightly from one, which is believed to maintain strong QFs. Then, we address Ba/Ca co-doped Sr1-x(Ca0.6389Ba0.3611)(x)TiO3 (SCBT) with the averaged Sr-site ionic radius identical to the Sr2+ ionic radius, which is believed to offer remarkable quenched disorder associated with the Sr-site ionic mismatch. The critical exponents associated with polarization P and dielectric susceptibility e, respectively, as functions of temperature T close to the critical point T-c, are evaluated. It is revealed that both non-stoichiometric SrTiO3 and SCBT exhibit much bigger critical exponents than the Landau mean-field theory predictions. These critical exponents then decrease gradually with increasing doping level or deviation of Sr/Ti ratio from one. A transverse Ising model applicable to the Sr-site doped STO (e.g., Sr1-xCaxTiO3) at low level is used to explain the observed experimental data. It is suggested that the serious deviation of these critical exponents from the Landau theory predictions in these STO-based systems is ascribed to the significant QFs and quenched disorder by partially suppressing the long-range spatial correlation of electric dipoles around the transitions. The present work thus sheds light on our understanding of the critical behaviors of ferroelectric transitions in STO in the presence of quantum fluctuations and quenched disorder, whose effects have been demonstrated to be remarkable.
Title:
The composite modulated structure of cupropearceite and cupropolybasite and its behavior toward low temperature
Authors:
Bindi, L; Schaper, AK; Kurata, H; Menchettii, S Author Full Names: Bindi, Luca; Schaper, Andreas K.; Kurata, Hiroki; Menchettii, Silvio
Source:
AMERICAN MINERALOGIST, 98 (7):1279-1284; 10.2138/am.2013.4380 JUL 2013
Abstract:
Cupropearceite, [(Cu3.51Ag2.50Fe0.01)(Sigma 6.02)(AS(1.72)Sb(0.24))(Sigma 1.96)S-7[Ag9CuS4], and cupropolybasite, [(Cu3.82Ag2.42Zn0.02Pb0.01)(Sigma 6.27)(Sb1.19As0.73)(Sigma 1.92)S-7][Ag9CuS4], both exhibit fast-ion conduction at very low temperatures. The structural relationship between the various phases is not fully understood as yet and is addressed in this study. Samples of these materials were studied by means of synchrotron radiation at room temperature and transmission electron microscopy at room temperature and low temperature (both liquid N-2 and liquid He) to have a better understanding of the stabilization of the fast-ion conducting form at low and ultra-low temperature in these minerals. The study at room temperature did not evidence any doubling of unit-cell parameters with respect to the basic Tac unit cell, of the type typically observed for minerals of the pearceite-polybasite group. On the other hand, relatively strong and well-defined satellite reflections relating to the pseudo-hexagonal arrangement of the Ag+ ions at G +/- similar to 1.39(1) < 110 >* positions of the reciprocal space, where G represents the average structure Bragg reflections, were clearly observed. Although this seems to suggest that the Ag+ ion distribution can adequately be described by a two-dimensional displacive modulation of the average P (3) over bar ml structure (Tac polytype) with the incommensurate modulation wave vectors of the *satellite reflections* q(1) = similar to 0.39(1) (a(F)* + b(F)*) and q(2) = similar to 0.39(I)(a(F)* - b(F)*), where the subscript F indicates the framework substructure, the structure observed is better described as a composite modulated structure because of the intensity asymmetry of the satellite reflections. Low-temperature TEM investigations show that the satellites are still present at both 90 and 4.2 K, with a remarkable temperature-dependent shift in their positions giving rise to a variation of the coefficient a of the modulation vectors from 0.39 at room temperature, trough similar to 0.40 at 90 K to similar to 0.5 at 4.2 K. Thus, the incommensurate modulation, strengthened by the very low temperature, approaches almost the alpha similar to 0.5 value, indicative of a commensurate modulation. The 4.2 K structure could thus be a low-temperature commensurate superstructure ("lock-in phase"), observed for the first time in the minerals of the pearceite-polybasite group.
Title:
Concentrational *commensurate-*incommensurate magnetic phase transition in Y1-x Tb (x) Mn6Sn6
Authors:
Bogdanov, SG; Mushnikov, NV; Terent'ev, PB; Gerasimov, EG; Grogor'ev, SV; Okorokov, AI; Chetverikov, YO; Ekerleb, G; Pranzas, K; Pirogov, AN Author Full Names: Bogdanov, S. G.; Mushnikov, N. V.; Terent'ev, P. B.; Gerasimov, E. G.; Grogor'ev, S. V.; Okorokov, A. I.; Chetverikov, Yu. O.; Ekerleb, G.; Pranzas, K.; Pirogov, A. N.
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 114 (7):566-572; 10.1134/S0031918X13070028 JUL 2013
Abstract:
The magnetic state of Y1 - x Tb (x) Mn6Sn6 (with x a parts per thousand currency sign 0.25) alloy is studied at different temperatures and magnetic fields by neutron diffraction. The alloy with x (c) = 0.22 exhibits an incommensurate-to-commensurate structure phase transition. The transition is accompanied by a decrease in the unit-cell volume. The weak dependence of the intensity of satellites on the x concentration and the monotonic displacement of their angular positions with increasing x allow us to conclude that the antiferromagnet -> ferrimagnet transition occurs through the uniform magnetic state. The incommensurate phase in YMn6Sn6 exhibits four satellites, which are observed in the low-angle range of X-ray diffraction pattern and demonstrate different behavior with changing temperature. At 293 K, the antiferromagnet -> ferromagnet transition in the Y1 -x Tb (x) Mn6Sn6 compound can be induced by applied magnetic field, in particular, the field mu(0) H = 0.3 T induces the transition in Tb0.15Y0.85Mn6Sn6.
Title:
Synthesis, Structure, and Properties of Turbostratically Disordered (PbSe)(1.18)(TiSe2)(2)
Authors:
Moore, DB; Beekman, M; Disch, S; Zschack, P; Hausler, I; Neumann, W; Johnson, DC Author Full Names: Moore, Daniel B.; Beekman, Matt; Disch, Sabrina; Zschack, Paul; Haeusler, Ines; Neumann, Wolfgang; Johnson, David C.
Source:
CHEMISTRY OF MATERIALS, 25 (12):2404-2409; 10.1021/cm400090f JUN 25 2013
Abstract:
Synthesis and structural characterization of a turbostratically disordered polymorph of (PbSe)(1.18)(TiSe2)(2) is reported. The structure of this compound consists of an intergrowth between one distorted rock salt structured PbSe bilayer and two transition metal dichalcogenide structured Se-Ti-Se trilayers. In addition to the lattice mismatch, there is extensive rotational disorder between these constituents. The electrical resistivity of (PbSe)(1.18)(TiSe2)(2) is a factor of 9 lower at room temperature, and the Seebeck coefficient is almost double that reported for the crystalline misfit layered compound analogue.

Update: 8-Aug-2013

Title:
Impact of beryllium additions on thermal and mechanical properties of conventionally solidified and melt-spun Al-4.5 wt.%Mn-x wt.%Be (x=0, 1, 3, 5) alloys
Authors:
Oz, T; Karakose, E; Keskin, M Author Full Names: Oz, Turan; Karakose, Ercan; Keskin, Mustafa
Source:
MATERIALS & DESIGN, 50 399-412; 10.1016/j.matdes.2013.03.024 SEP 2013
Abstract:
The influence of beryllium (Be) addition on the quasicrystal-forming ability, thermal and mechanical properties of Al-4.5 wt.%Mn-x wt.%Be (x = 0, 1, 3, 5) alloys was investigated in this study. Quasicrystalline Al-Mn-Be alloys were synthesized by the conventionally casting and melt spinning techniques. The microstructures of the samples were characterized by scanning electron microscopy (SEM) and the phase composition was identified by X-ray diffractometry (XRD). The phase transition during the solidification process was studied by differential scanning calorimetry (DSC) and differential thermal analysis (DTA) under an Ar atmosphere. The mechanical properties of the conventionally solidified (CS) and melt-spun (MS) samples were measured by a Vickers micro-hardness indenter and tensile-strength tests. The Al-4.5 wt.%Mn alloy has a hexagonal structure and minor dendritic icosahedral quasicrystalline phase (IQC) precipitates surrounded by an alpha-Al matrix. Addition of Be into the Al-4.5 wt.%Mn alloy generates intermetallic Be4AlMn and IQC phases with the extinction of the hexagonal phase, and the fraction of IQC increases continuously with the increase in Be content. A considerable improvement in microhardness and tensile strength values was observed due to the addition of Be in different percentages into the composition. (c) 2013 Elsevier Ltd. All rights reserved.
Title:
Band gaps and transmission spectra in generalized Fibonacci sigma(p, q) one-dimensional magnonic quasicrystals
Authors:
Costa, CHO; Vasconcelos, MS Author Full Names: Costa, C. H. O.; Vasconcelos, M. S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (28):10.1088/0953-8984/25/28/286002 JUL 17 2013
Abstract:
We employ a microscopic theory to investigate spin wave (magnon) propagation through their dispersion and transmission spectra in magnonic crystals arranged to display deterministic disorder. In this work the quasiperiodic arrangement investigated is the well-known generalized Fibonacci sequence, which is characterized by the sigma(p, q) parameter, where p and q are non-zero integers. In order to determine the bulk modes and transmission spectra of the spin waves, the calculations are carried out for the exchange dominated regime within the framework of the Heisenberg model and taking into account the random phase approximation. We have considered magnetic materials that have a ferromagnetic order, and the transfer-matrix treatment is applied to simplify the algebra. The results reveal that spin wave spectra display a rich and interesting magnonic pass- and stop-bands structures, including an almost symmetric band gap distribution around of a mid-gap frequency, which depends on the Fibonacci sequence type.
Title:
Two-dimensional incommensurate and three-dimensional commensurate magnetic order and fluctuations in La2-xBaxCuO4
Authors:
Wagman, JJ; Van Gastel, G; Ross, KA; Yamani, Z; Zhao, Y; Qiu, Y; Copley, JRD; Kallin, AB; Mazurek, E; Carlo, JP; Dabkowska, HA; Gaulin, BD Author Full Names: Wagman, J. J.; Van Gastel, G.; Ross, K. A.; Yamani, Z.; Zhao, Y.; Qiu, Y.; Copley, J. R. D.; Kallin, A. B.; Mazurek, E.; Carlo, J. P.; Dabkowska, H. A.; Gaulin, B. D.
Source:
PHYSICAL REVIEW B, 88 (1):10.1103/PhysRevB.88.014412 JUL 12 2013
Abstract:
We present neutron-scattering measurements on single crystals of lightly doped La2-xBaxCuO4, with 0 <= x <= 0.035. These reveal the evolution of the magnetism in this prototypical doped Mott insulator from a three-dimensional (3D) commensurate (C) antiferromagnetic ground state, which orders at a relatively high T-N, to a two-dimensional (2D) incommensurate (IC) ground state with finite-ranged static correlations, which appear below a relatively low effective T-N. At low temperatures, the 2D IC magnetism coexists with the 3D C magnetism for doping concentrations as low as similar to 0.0125. We find no signal of a 3D C magnetic ground state by x similar to 0.025, consistent with the upper limit of x similar to 0.02 observed in the sister family of doped Mott insulators, La2-xSrxCuO4. The 2D IC ground states observed for 0.0125 <= x <= 0.035 are diagonal, and are rotated by 45 degrees within the orthorhombic basal plane compared with those previously reported for samples with superconducting ground states: La2-xBaxCuO4, with 0.05 <= x <= 0.095. We construct a phase diagram based solely on magnetic order-parameter measurements, which displays much of the complexity of standard high-temperature superconductivity phase diagrams discussed in the literature. Analysis of high-energy resolution inelastic neutron scattering at moderately low temperatures shows a progressive depletion of the very low-energy dynamic magnetic susceptibility as x increases from 0.0125 to 0.035. This low-energy, dynamic susceptibility falls off with increasing temperature on a scale much higher than the effective 2D IC T-N appropriate to these materials. Appreciable dynamic 2D IC magnetic fluctuations inhabit much of the "pseudogap" regime of the phase diagram.
Title:
Incommensurate spin spiral of the geometrically-frustrated antiferromagnet CdCr2O4
Authors:
Chung, JH; Song, YS; Park, S; Ueda, H; Ueda, Y; Lee, SH Author Full Names: Chung, Jae-Ho; Song, Young Sang; Park, Sungil; Ueda, Hiroaki; Ueda, Yutaka; Lee, Seung-Hun
Source:
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 62 (12):1900-1904; 10.3938/jkps.62.1900 JUL 2013
Abstract:
CdCr2O4 is a cubic spinel with geometrically-frustrated antiferromagnetic interactions between Cr3+ ions. We investigated the structural and magnetic phase transitions in powder samples by using magnetization and neutron diffraction measurements. An antiferromagnetic phase transition was observed at T (N) = 8.1 K, below which the crystallographic unit cell was tetragonal (c < a = b). Its incommensurate antiferromagnetic ordering below T (N) resembles dimerized spin chains in the ab planes with the propagation vector k = (0, 0.088, 1). We argue that the Dzyaloshinskii-Moriya interaction and the magnetic frustration play important roles in establishing the observed magnetic ordering.
Title:
Ho-doping effect on the incommensurate magnetic order in La1.88Sr0.12CuO4
Authors:
Fujita, M; Enoki, M; Tsutsumi, K; Iikubo, S; Yamada, K Author Full Names: Fujita, Masaki; Enoki, Masanori; Tsutsumi, Kenji; Iikubo, Satoshi; Yamada, Kazuyoshi
Source:
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 62 (12):1840-1843; 10.3938/jkps.62.1840 JUL 2013
Abstract:
We have performed elastic neutron scattering experiments on the superconductor La1.85Ho0.03Sr0.12CuO4 to study the effect of substitution of a cation with a large magnetic moment at La site on the static spin correlation. In the Ho-free sample with a hole concentration of 0.12, the spatially-modulated magnetic order is known to be stabilized at temperature below T (spin) similar to 30 K. In the present Ho-doped sample, we found the appearance of magnetic peaks at (0.5, 0.5 +/- 0.119, 0) positions below T (spin) similar to 35 K, which is similar to the observation in the pristine sample. Furthermore, the volume-corrected intensities in the Ho-free and Ho-doped samples are comparable, suggesting a negligible effect of Ho-substitution at La sites. These results are quite a contrast to the huge enhancement of the magnetic intensity and the increase of T (spin) by substituting a comparable amounts of magnetic Fe3+ ions onto CuO2 planes. Therefore, the stability of the stripe order induced by the cation substitution is sensitive to the site at which the substitution occurs.
Title:
Molecular dynamics simulation of radiation damage in CaCd6 quasicrystal cubic approximant up to 10 keV
Authors:
Chen, PH; Avchachov, K; Nordlund, K; Pussi, K Author Full Names: Chen, P. H.; Avchachov, K.; Nordlund, K.; Pussi, K.
Source:
JOURNAL OF CHEMICAL PHYSICS, 138 (23):10.1063/1.4811183 JUN 21 2013
Abstract:
Due to the peculiar nature of the atomic order in quasicrystals, examining phase transitions in this class of materials is of particular interest. Energetic particle irradiation can provide a way to modify the structure locally in a quasicrystal. To examine irradiation-induced phase transitions in quasicrystals on the atomic scale, we have carried out molecular dynamics simulations of collision cascades in CaCd6 quasicrystal cubic approximant with energies up to 10 keV at 0 and 300 K. The results show that the threshold energies depend surprisingly strongly on the local coordination environments. The energy dependence of stable defect formation exhibits a power-law dependence on cascade energy, and surviving defects are dominated by Cd interstitials and vacancies. Only a modest effect of temperature is observed on defect survival, while irradiation temperature increases lead to a slight increase in the average size of both vacancy clusters and interstitial clusters. (C) 2013 AIP Publishing LLC.
Title:
The Structure of an Al-Co-Ni Decagonal Quasicrystal in an Al72Co8Ni20 Alloy Studied by Cs-Corrected Scanning Transmission Electron Microscopy
Authors:
Hiraga, K; Yasuhara, A Author Full Names: Hiraga, K.; Yasuhara, A.
Source:
MATERIALS TRANSACTIONS, 54 (5):720-724; 10.2320/matertrans.M2012333 MAY 2013
Abstract:
The structure of an Al-Co-Ni decagonal quasicrystal in an Al72Co8Ni20 alloy has been examined by Cs-corrected high-angle annular detector dark-field (HAADF)- and annular bright-field (ABF)-scanning transmission electron microscopy (STEM) observations with the incident beam parallel to the periodic axis. Observed ABF- and HAADF-STEM images clearly show the existence of large columnar clusters of a decagonal section with an about 3.2 nm in diameter and their arrangement with bond-orientational order (BOO) of a bond-length of 3.2 nm. Individual transition-metal (TM) atoms and mixed sites (MSs) of Al and TM atoms are represented as separated bright dots in observed HAADF-STEM images, and consequently arrangements of TM atoms and MSs on two quasiperiodic planes can be directly determined. The TM atoms and MSs are located at lattice points of a Penrose lattice with an edge-length of 0.25 nm, and so they are arranged with BOO on the two quasiperiodic planes. An atomic arrangement including Al atoms in the 3.2 nm cluster is speculated from observed HAADF- and ABF-STEM images.
Title:
Cu/Te substitution effects on superconductivity and microstructure of phase-separated K0.8Fe1.75Se2
Authors:
Wang, Z; Cai, Y; Wang, ZW; Sun, ZA; Yang, HX; Tian, HF; Ma, C; Zhang, B; Li, JQ Author Full Names: Wang, Z.; Cai, Y.; Wang, Z. W.; Sun, Z. A.; Yang, H. X.; Tian, H. F.; Ma, C.; Zhang, B.; Li, J. Q.
Source:
EPL, 102 (3):10.1209/0295-5075/102/37010 MAY 2013
Abstract:
Two series of K0.8Fe1.75-xCuxSe2 (0 <= x <= 0.15) and K0.8Fe1.75Se2-yTey (0 <= y <= 0.5) single crystals of nominal composition have been prepared and their physical properties and microstructural features have been studied. Resistivity measurements demonstrate that the superconducting transition temperature decreases gradually with the increase of the substitution level and zero resistivity finally disappears in both systems. Systematic TEM, SEM and XRD structural analyses, in combination with the magnetic experimental data, reveal a rich variety of structural phenomena resulting from different types of substitution. Cu substitution gives rise to the volume of a new non-superconducting Cu-rich phase with modulation q(3) = 1/3[2a* + b*] coexisting with the q(2) = 1/2[a* + b*] superconducting stripe domain. With the increase of the ratio of the new non-superconducting phase along with doping, the superconducting path is finally cut off, and results in the absence of zero resistivity. In contrast, the absence of superconductivity in Te-substituted materials is correlated with the complete disappearance of the q2 superconducting phase due to the suppression of phase separation. Copyright (C) EPLA, 2013

Update: 1-Aug-2013

Title:
Hall, Seebeck, and Nernst Coefficients of Underdoped HgBa2CuO4+delta : Fermi-Surface Reconstruction in an Archetypal Cuprate Superconductor
Authors:
Doiron-Leyraud, N; Lepault, S; Cyr-Choiniere, O; Vignolle, B; Grissonnanche, G; Laliberte, F; Chang, J; Barisic, N; Chan, MK; Ji, L; Zhao, X; Li, Y; Greven, M; Proust, C; Taillefer, L Author Full Names: Doiron-Leyraud, Nicolas; Lepault, S.; Cyr-Choiniere, O.; Vignolle, B.; Grissonnanche, G.; Laliberte, F.; Chang, J.; Barisic, N.; Chan, M. K.; Ji, L.; Zhao, X.; Li, Y.; Greven, M.; Proust, C.; Taillefer, Louis
Source:
PHYSICAL REVIEW X, 3 (2):10.1103/PhysRevX.3.021019 JUN 28 2013
Abstract:
Charge-density-wave order has been observed in cuprate superconductors whose crystal structure breaks the square symmetry of the CuO2 planes, such as orthorhombic YBa2Cu3Oy (YBCO), but not so far in cuprates that preserve that symmetry, such as tetragonal HgBa2CuO4+delta (Hg1201). We have measured the Hall (R-H), Seebeck (S), and Nernst (nu) coefficients of underdoped Hg1201 in magnetic fields large enough to suppress superconductivity. The high-field R-H(T) and S(T) are found to drop with decreasing temperature and become negative, as also observed in YBCO at comparable doping. In YBCO, the negative R-H and S are signatures of a small electron pocket caused by Fermi-surface reconstruction, attributed to charge-density-wave modulations observed in the same range of doping and temperature. We deduce that a similar Fermi-surface reconstruction takes place in Hg1201, evidence that density-wave order exists in this material. A striking similarity is also found in the normal-state Nernst coefficient nu(T), further supporting this interpretation. Given the model nature of Hg1201, Fermi-surface reconstruction appears to be common to all hole-doped cuprates, suggesting that density-wave order is a fundamental property of these materials.
Title:
Common quantum phase transition in quasicrystals and heavy-fermion metals
Authors:
Shaginyan, VR; Msezane, AZ; Popov, KG; Japaridze, GS; Khodel, VA Author Full Names: Shaginyan, V. R.; Msezane, A. Z.; Popov, K. G.; Japaridze, G. S.; Khodel, V. A.
Source:
PHYSICAL REVIEW B, 87 (24):10.1103/PhysRevB.87.245122 JUN 24 2013
Abstract:
Extraordinary new materials named quasicrystals and characterized by noncrystallographic rotational symmetry and quasiperiodic translational properties have attracted scrutiny. Study of quasicrystals may shed light on the most basic notions related to the quantum critical state observed in heavy-fermion metals. We show that the electronic system of some quasicrystals is located at the fermion condensation quantum phase transition without tuning. In that case the quasicrystals possess the quantum critical state with the non-Fermi-liquid behavior which in magnetic fields transforms into the Landau Fermi-liquid one. Remarkably, the quantum critical state is robust despite the strong disorder experienced by the electrons. We also demonstrate for the first time that quasicrystals exhibit the typical scaling behavior of their thermodynamic properties such as the magnetic susceptibility, and belong to the famous family of heavy-fermion metals. Our calculated thermodynamic properties are in good agreement with recent experimental observations.
Title:
Avoided Quantum Criticality and Magnetoelastic Coupling in BaFe2-xNixAs2
Authors:
Lu, XY; Gretarsson, H; Zhang, R; Liu, XR; Luo, HQ; Tian, W; Laver, M; Yamani, Z; Kim, YJ; Nevidomskyy, AH; Si, QM; Dai, PC Author Full Names: Lu, Xingye; Gretarsson, H.; Zhang, Rui; Liu, Xuerong; Luo, Huiqian; Tian, Wei; Laver, Mark; Yamani, Z.; Kim, Young-June; Nevidomskyy, A. H.; Si, Qimiao; Dai, Pengcheng
Source:
PHYSICAL REVIEW LETTERS, 110 (25):10.1103/PhysRevLett.110.257001 JUN 18 2013
Abstract:
We study the structural and magnetic orders in electron-doped BaFe2-xNixAs2 by high-resolution synchrotron x-ray and neutron scatterings. Upon Ni doping x, the nearly simultaneous tetragonal-to-orthorhombic structural (T-s) and antiferromagnetic (T-N) phase transitions in BaFe2As2 are gradually suppressed and separated, resulting in T-s > T-N with increasing x, as was previously observed. However, the temperature separation between T-s and T-N decreases with increasing x for x >= 0.065, tending toward a quantum bicritical point near optimal superconductivity at x approximate to 0.1. The zero-temperature transition is preempted by the formation of a secondary incommensurate magnetic phase in the region 0: 088 less than or similar to x less than or similar to 0.104, resulting in a finite value of T-N approximate to T-c + 10 K above the superconducting dome around x approximate to 0.1. Our results imply an avoided quantum critical point, which is expected to strongly influence the properties of both the normal and superconducting states.
Title:
Characteristic chemical shifts of quasicrystalline Zn-Mg-Zr alloys studied by EELS and SXES
Authors:
Koshiya, S; Terauchi, M; Ohhashi, S; Tsai, AP Author Full Names: Koshiya, S.; Terauchi, M.; Ohhashi, S.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE, 93 (18):2250-2258; 10.1080/14786435.2013.765994 JUN 1 2013
Abstract:
Chemical shifts of the constituent atoms of primitive icosahedral quasicrystal (P-QC), face-centred icosahedral quasicrystal (F-QC) and 1/1-approximant (1/1-AP) of F-QC Zn-Mg-Zr alloys were investigated for the first time using high energy-resolution electron energy-loss spectroscopy (EELS) and soft-X-ray emission spectroscopy (SXES). Among Zn M-shell and Mg L-shell excitation EELS spectra of P-QC, F-QC and 1/1-AP alloys, only the quasicrystalline alloys showed a chemical shift towards the larger binding energy side. In Zn-L and Zr-L emission SXES spectra, the P-QC and F-QC alloys showed a chemical shift towards larger binding energy side. The magnitudes of the shifts in the Zn-L emission spectra of the quasicrystalline alloys were almost the same as for ZnO. These results strongly suggest a decrease in valence charge in quasicrystalline states. Therefore, it should be concluded that bonding in quasicrystalline states involves a characteristic increase in covalency compared with bonding in corresponding approximant and standard metal crystals.
Title:
Microstructure of bilayer manganite PrCa2Mn2O7 showing charge/orbital ordering
Authors:
He, ZB; Tian, H; Deng, GC; Xu, Q; Van Tendeloo, G Author Full Names: He, Zhanbing; Tian, He; Deng, Guochu; Xu, Qiang; Van Tendeloo, Gustaaf
Source:
APPLIED PHYSICS LETTERS, 102 (21):10.1063/1.4807758 MAY 27 2013
Abstract:
The microstructure of the charge/orbital ordering Ruddleden-Popper phase PrCa2Mn2O7 was studied by transmission electron microscopy along both the [001] and the [110] orientation. Three coexisting charge/orbital ordering phases CO1, CO2, and CO3 were observed along the [001] orientation at room temperature. Different from the one-dimensional modulation in the CO1 and CO2 phase, the CO3 phase is characterized by two sets of mutually perpendicular structural modulations. From [110] high angle annular dark field-scanning transmission electron microscopy, we found that the Pr atoms locate in-between the bilayer MnO6 octahedra, which is different from the previous reports. (C) 2013 AIP Publishing LLC.
Title:
Nanocrystallization of Coarse Primary Phases in Al- and Mg-Based Alloys Induced by HCPEB Treatment
Authors:
Gao, B; He, JD; Tu, GF; Hu, L Author Full Names: Gao Bo; He Jidong; Tu Ganfeng; Hu Liang
Source:
JOURNAL OF NANOMATERIALS, 10.1155/2013/815384 2013
Abstract:
This paper reports on a phenomenon associated with high-current pulsed electron beam (HCPEB) treatment: surface nanocrystallization of coarse primary phase in hypereutectic Al17.5Si and quasicrystal alloys after multiple pulses of HCPEB irradiation. The HCPEB treatment induces superfast heating and diffusion of alloying elements and heterogeneous nucleation in a melting solution, followed by rapid solidification and cooling of the material surfaces. Consequently, nanostructured surface layers can be achieved easily. Nano-Si phase and nano-quasicrystal phase formation on the modified surface layer of hypereutectic Al17.5Si alloy and quasicrystal alloy (Mg37Zn60Y3) show a potential for surface nanocrystallization of materials with enhanced properties by HCPEB treatment.

Update: 24-Jul-2013

Title:
Magnetic lock-in phase transition in Tb0.95Er0.05Ni5 driven by low magnetic fields
Authors:
Lee, H; Choi, YN; Pirogov, AN; Kazantsev, VA; Gerasimov, EG Author Full Names: Lee, Heeju; Choi, Y. N.; Pirogov, A. N.; Kazantsev, V. A.; Gerasimov, E. G.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 341 129-132; 10.1016/j.jmmm.2013.04.010 SEP 2013
Abstract:
The magnetic properties of a mixed inter-metallic compound, Tb0.95Er0.05Ni5, were investigated using a neutron diffraction method at low temperatures. These compounds were known to have a successive magnetic phase transition from the paramagnetic state at high temperature to a lock-in phase at low temperature through intermediate phases, i.e., PM(paramagnetic)-FM(ferromagnetic)-IC(incommensurate)-L(lock-in) in reverse order of temperature. A meta-magnetic phase transition between an IC phase and a FM phase at 9 K was observed with the critical field, H-MT similar to 200 mT. A new magnetic phase between the new phase (lock-in phase) and an IC phase has been observed. From the field dependence of the Bragg reflections and their satellite peaks at low temperatures (3-12 K), weak field driven first-order magnetic phase transitions were recorded at six fixed temperatures. The critical magnetic field decreases exponentially with the temperature. From these experimental results, we obtained a magnetic phase diagram of Tb0.95Er0.05Ni5 at a low temperature region for the first time. (c) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
Title:
Thermodynamic and transport properties of RSn2 (R=Tb-Tm, Lu, Y) single crystals
Authors:
Zhao, LL; Mehlman, MS; Besara, T; Siegrist, T; Morosan, E Author Full Names: Zhao, Liang L.; Mehlman, Michael S.; Besara, Tiglet; Siegrist, Theo; Morosan, E.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 341 6-16; 10.1016/j.jmmm.2013.03.033 SEP 2013
Abstract:
We report the anisotropic magnetization, heat capacity and resistivity measurements for isostructural RSn2 (R=Tb-Tm, Lu, Y) single crystals. The R=Tb-Tm compounds exhibit long range antiferromagnetic ordering with T-N ranging from 26.3 K to 3.6 K. An additional incommensurate-to-commensurate transition at a lower critical temperature T-1 is observed for R=Tb-Ho. Field-induced metamagnetic transitions have also been observed for all magnetic rare earth compounds. The resistivity has a typical metallic character with a relatively high residual resistivity ratio. Both the AFM ordering temperature and spin disordered resistivity scale with the de Gennes factor. The magnetic heat capacity data indicate partially lifted ground state degeneracies associated with crystal electric field splitting. (c) 2013 Elsevier B.V. All rights reserved.
Title:
Elastic constants of incommensurate solid He-4 from diffusion Monte Carlo simulations
Authors:
Cazorla, C; Lutsyshyn, Y; Boronat, J Author Full Names: Cazorla, Claudio; Lutsyshyn, Yaroslav; Boronat, Jordi
Source:
PHYSICAL REVIEW B, 87 (21):10.1103/PhysRevB.87.214522 JUN 28 2013
Abstract:
We study the elastic properties of incommensurate solid He-4 in the limit of zero temperature. Specifically, we calculate the pressure dependence of the five elastic constants (C-11, C-12, C-13, C-33, and C-44), longitudinal and transversal speeds of sound, and the T = 0 Debye temperature of incommensurate and commensurate hcp He-4 using the diffusion Monte Carlo method. Our results show that under compression, the commensurate crystal is globally stiffer than the incommensurate, however at pressures close to melting (i.e., P similar to 25 bar) some of the elastic constants accounting for strain deformations of the hcp basal plane (C-12 and C-13) are slightly larger in the incommensurate solid. Also, we find that upon the introduction of tiny concentrations of point defects, the shear modulus of He-4 (C-44) undergoes a small reduction.
Title:
Three-dimensional Dirac fermions in quasicrystals as seen via optical conductivity
Authors:
Timusk, T; Carbotte, JP; Homes, CC; Basov, DN; Sharapov, SG Author Full Names: Timusk, T.; Carbotte, J. P.; Homes, C. C.; Basov, D. N.; Sharapov, S. G.
Source:
PHYSICAL REVIEW B, 87 (23):10.1103/PhysRevB.87.235121 JUN 17 2013
Abstract:
The optical conductivity of quasicrystals is characterized by two features not seen in ordinary metallic systems. There is an absence of the Drude peak and the interband conductivity rises linearly from a very low value up to normal metallic levels over a wide range of frequencies. The absence of a Drude peak has been attributed to a pseudogap at the Fermi surface but a detailed explanation of the linear behavior has not been found. Here we show that the linear conductivity, which seems to be universal in all Al based icosahedral quasicrystal families, as well as their periodic approximants, follows from a simple model that assumes that the entire Fermi surface is gapped except at a finite set of Dirac points. There is no evidence of a semiconducting gap in any of the materials suggesting that the Dirac spectrum is massless, protected by topology leading to a Weyl semimetal. This model gives rise to a linear conductivity with only one parameter, the Fermi velocity. This picture suggests that decagonal quasicrystals should, like graphene, have a frequency independent conductivity, without a Drude peak. This is in accord with the experimental data as well.
Title:
Incommensurability and spin dynamics in the low-temperature phases of Ni3V2O8
Authors:
Ehlers, G; Podlesnyak, AA; Hahn, SE; Fishman, RS; Zaharko, O; Frontzek, M; Kenzelmann, M; Pushkarev, AV; Shiryaev, SV; Barilo, S Author Full Names: Ehlers, G.; Podlesnyak, A. A.; Hahn, S. E.; Fishman, R. S.; Zaharko, O.; Frontzek, M.; Kenzelmann, M.; Pushkarev, A. V.; Shiryaev, S. V.; Barilo, S.
Source:
PHYSICAL REVIEW B, 87 (21):10.1103/PhysRevB.87.214418 JUN 17 2013
Abstract:
Magnetic order and low-energy spin dynamics in the zero field ground state of Ni3V2O8 are revealed in elastic and inelastic neutron scattering experiments. Neutron diffraction shows that below T = 2.3 K the Ni2+ moments (spin S = 1) order in a cycloid pattern with incommensurate wave vector k(ICM) = (0,1, tau), where tau = 0.4030 +/- 0.0004, which is superimposed on a commensurate antiferromagnetic spin arrangement with k(CM) = (0,0,0). Three spin wave modes are discerned below E similar to 3 meV in inelastic measurements and qualitatively described by a model Hamiltonian that involves near neighbor exchange, local anisotropy, and a small biquadratic coupling between the spine and cross-tie sites. Results from both elastic and inelastic scattering experiments suggest that the two sublattices on spine and cross-tie sites are largely decoupled.
Title:
Field-induced phase transitions and phase diagrams in BiFeO3-like multiferroics
Authors:
Gareeva, ZV; Popkov, AF; Soloviov, SV; Zvezdin, AK Author Full Names: Gareeva, Z. V.; Popkov, A. F.; Soloviov, S. V.; Zvezdin, A. K.
Source:
PHYSICAL REVIEW B, 87 (21):10.1103/PhysRevB.87.214413 JUN 12 2013
Abstract:
We explore incommensurate magnetic structures and phase diagrams of multiferroics through accurate micromagnetic analysis, taking into account the spin flexoelectric interaction (the so-called Lifshitz invariant). We consider BiFeO3 single crystals and epitaxial films grown on (111) substrates. The main control parameters of these systems are the magnetic field, magnetic anisotropy, and, in the case of thin films, epitaxial strain. We construct phase diagrams representing stability regions for the homogeneous magnetic states and incommensurate structures for two geometries of the field (parallel to the principal crystal axis H parallel to C-3 and perpendicular to this direction H perpendicular to C-3). It is shown that the direction of applied magnetic field substantially affects the magnetic phases, the properties of incommensurate structures, and the character of phase transitions. A conical type of cycloidal ordering is revealed to exist during the transition from the incommensurate cycloidal structure to the homogeneous magnetic state. Constructed phase diagrams provide the combination of control parameters required to suppress the cycloidal ordering. Our results show that the critical magnetic field for suppression of the cycloid is lower in thin films than in single crystals, and can also be lowered by appropriate selection of applied magnetic field orientation. These results provide a stronger understanding of the complex magnetic ordering in BiFeO3 and can be useful for strain engineering of new multiferroic materials on demand.
Title:
X-ray Diffraction Study of BaTiO3/(Ba1-xSrx)TiO3 Artificial Superlattices
Authors:
Zakharchenko, IN; Bunina, OA; Maslova, OA; Yuzyuk, YI; Ortega, N; Kumar, A; Katiyar, RS Author Full Names: Zakharchenko, I. N.; Bunina, O. A.; Maslova, O. A.; Yuzyuk, Yu. I.; Ortega, N.; Kumar, A.; Katiyar, R. S.
Source:
FERROELECTRICS, 444 (1):1-8; 10.1080/00150193.2013.785833 JAN 1 2013
Abstract:
We report x-ray diffraction investigation of two sets of artificial BaTiO3/Ba1-xSrxTiO3 (BT/BST-x) superlattices (SLs) grown on MgO substrates. The first set of SLs was deposited with the constant periodicity (about 150 angstrom) and the variable Ba/Sr content in BST layers. In the second set, the modulation period was varied between 30 angstrom < < 110 angstrom while Ba content was equal 0 in BST layers. It is shown that, fabrication of the artificial SLs with variable composition of the constituting layers even with large modulation period may provide enhanced variation of the ferroelectric properties comparing to the SLs with variable layers thickness.

Update: 17-Jul-2013

Title:
Incommensurate crystallography without additional dimensions
Authors:
Kocian, P Author Full Names: Kocian, Philippe
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 374-387; 10.1107/S0108767313005990 4 JUL 2013
Abstract:
It is shown that the Euclidean group of translations, when treated as a Lie group, generates translations not only in Euclidean space but on any space, curved or not. Translations are then not necessarily vectors (straight lines); they can be any curve compatible with the parameterization of the considered space. In particular, attention is drawn to the fact that one and only one finite and free module of the Lie algebra of the group of translations can generate both modulated and non-modulated lattices, the modulated character being given only by the parameterization of the space in which the lattice is generated. Moreover, it is shown that the diffraction pattern of a structure is directly linked to the action of that free and finite module. In the Fourier transform of a whole structure, the Fourier transform of the electron density of one unit cell (i.e. the structure factor) appears concretely, whether the structure is modulated or not. Thus, there exists a neat separation: the geometrical aspect on the one hand and the action of the group on the other, without requiring additional dimensions.
Title:
Tabulation of irreducible representations of the crystallographic space groups and their superspace extensions
Authors:
Stokes, HT; Campbell, BJ; Cordes, R Author Full Names: Stokes, Harold T.; Campbell, Branton J.; Cordes, Ryan
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 388-395; 10.1107/S0108767313007538 4 JUL 2013
Abstract:
New tables of irreducible representations (IRs) are introduced for the 230 crystallographic space groups (SGs) in three-dimensional space, at both special and non-special k vectors, and for their extensions to (3 + d)-dimensional superspace ('superspace-extended SGs' or SSESGs). Neither a tabulation of SG IR matrices for non-special k vectors nor a tabulation of SSESG IR matrices for d > 1 have been previously published. These tabulations are made possible by a new form in which the IR matrices of SGs are separated as a product of a translation part T and a point-operation part P, and where the IR matrices of SSESGs are separated as a product of a phase-shift part Q and a point-operation part P-s. Both T and Q have a simple prescribed form that does not need to be tabulated. Also, the new IR matrices are in a convenient block form which allows one to see by inspection which parts of the matrices and the associated order parameters belong to which arm of the star of k. In addition to complex IR matrices, real physically irreducible representation (PIR) matrices are tabulated. The new IR and PIR tables are available on the ISO-IR website (http://stokes.byu.edu/iso/irtables.php) in both convenient human-readable and computer-readable forms.
Title:
Signatures of quantum criticality in the thermopower of Ba(Fe1-xCox)(2)As-2
Authors:
Arsenijevic, S; Hodovanets, H; Gaal, R; Forro, L; Bud'ko, SL; Canfield, PC Author Full Names: Arsenijevic, S.; Hodovanets, H.; Gaal, R.; Forro, L.; Bud'ko, S. L.; Canfield, P. C.
Source:
PHYSICAL REVIEW B, 87 (22):10.1103/PhysRevB.87.224508 JUN 18 2013
Abstract:
We demonstrate that the thermopower (S) can be used to probe the spin fluctuations (SFs) in proximity to the quantum critical point (QCP) in Fe-based superconductors. The sensitivity of S to the entropy of charge carriers allows us to observe an increase of S/T in Ba(Fe1-x Co-x)(2)As-2 close to the spin-density-wave (SDW) QCP. This behavior is due to the coupling of low-energy conduction electrons to two-dimensional SFs, similar to heavy-fermion systems. The low-temperature enhancement of S/T in the Co substitution range 0.02 < x < 0.1 is bordered by two Lifshitz transitions, and it corresponds to the superconducting region, where a similarity between the electron and nonreconstructed hole pockets exists. The maximal S/T is observed in proximity to the *commensurate-to-*incommensurate SDW transition, for critical x(c) approximate to 0.05, close to the highest superconducting T-c. This analysis indicates that low-T thermopower is influenced by critical spin fluctuations which are important for the superconducting mechanism.
Title:
Disorder line and incommensurate floating phases in the quantum Ising model on an anisotropic triangular lattice
Authors:
Iglovikov, VI; Scalettar, RT; Singh, RRP; Oitmaa, J Author Full Names: Iglovikov, V. I.; Scalettar, R. T.; Singh, R. R. P.; Oitmaa, J.
Source:
PHYSICAL REVIEW B, 87 (21):10.1103/PhysRevB.87.214415 JUN 13 2013
Abstract:
We present a quantum Monte Carlo study of the Ising model in a transverse field on a square lattice with nearest-neighbor antiferromagnetic exchange interaction J and one diagonal second-neighbor interaction J', interpolating between square-lattice (J' = 0) and triangular-lattice (J' = J) limits. At a transverse field of B-x = J, the disorder line first introduced by Stephenson [J. Math. Phys. 5, 1009 (1964)], where the correlations go from Neel to incommensurate, meets the zero-temperature axis at J' approximate to 0.7 J. Strong evidence is provided that the incommensurate phase at larger J', at finite temperatures, is a floating phase with power-law decaying correlations. We sketch a general phase-diagram for such a system and discuss how our work connects with the previous quantum Monte Carlo work by Isakov and Moessner [Phys. Rev. B 68, 104409 (2003)] for the isotropic triangular lattice (J' = J). For the isotropic triangular lattice, we also obtain the entropy function and constant entropy contours using a mix of quantum Monte Carlo, high-temperature series expansions and high-field expansion methods and show that phase transitions in the model in the presence of a transverse field occur at very low entropy.
Title:
Doping dependence of the spin excitations in the Fe-based superconductors Fe1+yTe1-xSex
Authors:
Christianson, AD; Lumsden, MD; Marty, K; Wang, CH; Calder, S; Abernathy, DL; Stone, MB; Mook, HA; McGuire, MA; Sefat, AS; Sales, BC; Mandrus, D; Goremychkin, EA Author Full Names: Christianson, A. D.; Lumsden, M. D.; Marty, K.; Wang, C. H.; Calder, S.; Abernathy, D. L.; Stone, M. B.; Mook, H. A.; McGuire, M. A.; Sefat, A. S.; Sales, B. C.; Mandrus, D.; Goremychkin, E. A.
Source:
PHYSICAL REVIEW B, 87 (22):10.1103/PhysRevB.87.224410 JUN 12 2013
Abstract:
The Fe1+yTe1-xSex series of materials is one of the prototype families of Fe-based superconductors. To provide further insight into these materials, we present systematic inelastic neutron scattering measurements of the low-energy spin excitations for x = 0.27, 0.36, 0.40, and 0.49. These measurements show an evolution of incommensurate spin excitations towards the (1/2,1/2,0) wave vector with doping. Concentrations (x = 0.40 and 0.49) which exhibit the most robust superconducting properties have spin excitations closest to (1/2,1/2,0) and also exhibit a strong spin resonance in the spin excitation spectrum below T-c. The resonance signal appears to be closer to (1/2,1/2,0) than the underlying spin excitations. We discuss the possible relationship between superconductivity and spin excitations at the (1/2,1/2,0) wave vector and the role that interstitial Fe may play.
Title:
Electronic Instability in a Zero-Gap Semiconductor: The Charge-DensityWave in (TaSe4)(2)I
Authors:
Tournier-Colletta, C; Moreschini, L; Autes, G; Moser, S; Crepaldi, A; Berger, H; Walter, AL; Kim, KS; Bostwick, A; Monceau, P; Rotenberg, E; Yazyev, OV; Grioni, M Author Full Names: Tournier-Colletta, C.; Moreschini, L.; Autes, G.; Moser, S.; Crepaldi, A.; Berger, H.; Walter, A. L.; Kim, K. S.; Bostwick, A.; Monceau, P.; Rotenberg, E.; Yazyev, O. V.; Grioni, M.
Source:
PHYSICAL REVIEW LETTERS, 110 (23):10.1103/PhysRevLett.110.236401 JUN 4 2013
Abstract:
We report a comprehensive study of the paradigmatic quasi-1D compound (TaSe4)(2)I performed by means of angle-resolved photoemission spectroscopy (ARPES) and first-principles electronic structure calculations. We find it to be a zero-gap semiconductor in the nondistorted structure, with non-negligible interchain coupling. Theory and experiment support a Peierls-like scenario for the charge-density wave formation below T-CDW = 263 K, where the incommensurability is a direct consequence of the finite interchain coupling. The formation of small polarons, strongly suggested by the ARPES data, explains the puzzling semiconductor-to-semiconductor transition observed in transport at T-CDW.
Title:
Synthesis, structure and electrical properties of a new tin vanadium selenide
Authors:
Atkins, R; Disch, S; Jones, Z; Haeusler, I; Grosse, C; Fischer, SF; Neumann, W; Zschack, P; Johnson, DC Author Full Names: Atkins, Ryan; Disch, Sabrina; Jones, Zachary; Haeusler, Ines; Grosse, Corinna; Fischer, Saskia F.; Neumann, Wolfgang; Zschack, Paul; Johnson, David C.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 202 128-133; 10.1016/j.jssc.2013.03.008 JUN 2013
Abstract:
The turbostratically disordered misfit layer compound (SnSe)(1.15)VSe2 was synthesized and structurally characterized. Electrical transport measurements suggest this compound undergoes a charge or spin density wave (CDW or SDW) transition, which has not been observed in previous misfit layer compounds. The (SnSe)(1.15)VSe2 compound, created through the modulated elemental reactants technique, contains highly oriented intergrowths of SnSe bilayers and VSe2 structured Se-V-Se trilayers with abrupt interfaces between them perpendicular to the c-axis. X-ray diffraction data and transmission electron microscope images show that each constituent has in-plane crystallinity but that there is a random rotational disorder between the constituent layers. Temperature-dependent electrical resistivity data and Hall measurements are consistent with (SnSe)(1.15)VSe2 being a metal, however an abrupt increase in the resistivity occurs between 30 and 100 K. The carrier concentration decreases by approximately 1 carrier per vanadium atom during this temperature interval. (C) 2013 Elsevier Inc. All rights reserved.
Title:
Microstructure and Physical Properties of Two Charge Density Wave States in NbSe3 Nanowires
Authors:
Shi, HL; Yang, HX; Tian, HF; Wang, ZW; Qin, YB; Song, YJ; Luo, MT; Wang, WZ; Li, JQ Author Full Names: Shi, Honglong; Yang, Huaixin; Tian, Huanfang; Wang, Zhiwei; Qin, Yunbin; Song, Yuanjun; Luo, Minting; Wang, Wenzhong; Li, Jianqi
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 13 (6):4123-4128; 10.1166/jnn.2013.7472 JUN 2013
Abstract:
The whisker-like niobium triselenide (NbSe3) nanowires were synthesized using the traditional solid state reaction. X-ray diffraction experiment suggested the monoclinic structure (P2(1)/m), and crystal morphology analysis indicated that the band-like shape is the stable morphology. Two charge density wave (CDW) states were observed at around 140 K and 50 K, respectively, and the nonlinear effect was detected in the CDW states from the R-T and I-V measurements. The doped Fe atoms, as pinning centers, play an important role in the nonlinear properties of the CDW state. Electron diffraction and HRTEM experiments were carried out at different temperatures in order to investigate the structural features and their evolution. The sets of incommensurate modulation spots with modulation vector q(1) similar to (h, k 0.243, I) appeared below 145 K, and other sets of complex superstructure spots with modulation vector q(2) similar to (h, k + 0.3, I + 1.3424), q(3) similar to (h, k-0.3137, 1.5685), = (1/3, k, 1) and q(5) = (0.5, 0.25, 0.5) were observed at [1 0 0] and [3 0 1] zone axis at about 20 K, respectively, suggesting the complex inconnmensurately modulated structures in this material.
Title:
Structural Properties in Incommensurately Modulated Spinel Compound CuV2S4
Authors:
Kawaguchi, S; Ishibashi, H; Tsuji, N; Kim, J; Kato, K; Takata, M; Kubota, Y Author Full Names: Kawaguchi, Shogo; Ishibashi, Hiroki; Tsuji, Naruki; Kim, Jungeun; Kato, Kenichi; Takata, Masaki; Kubota, Yoshiki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (6):10.7566/JPSJ.82.064603 JUN 2013
Abstract:
We have studied the incommensurate crystal structure of the spinel compound CuV2S4 at low temperatures using the synchrotron powder diffraction technique. The powder diffraction pattern at 70 K shows that the splitting of the fundamental 800 reflection peak and the weak superlattice reflections with a modulation vector q similar to 3/4[110] due to the structural phase transition at 90 K were observed. It is found that the crystal structure at 70 K has an orthorhombic unit cell with the superspace-group Imm2(0 beta 0) with a modulation vector q = 0.7391(5)b*. By Rietveld analysis including the *incommensurate* *modulation* along the b-axis, large static atomic displacements were found at the positions of V atoms, suggesting that V atoms play an important role in a charge-density wave (CDW) transition. The atomic displacements indicate that V1 atoms at the 4c site form dimers along the a-axis, suggesting that a commensurate CDW forms along the a-axis. Furthermore, the V2 atoms at the 4d site tend to approach V1 dimers, giving rise to the formation of V clusters such as trimers and tetramer-like clusters. The arrangements of V clusters form a pattern along the b-axis with a period of nearly four fundamental cells, which may induce the formation of an incommensurate CDW along the b-axis.
Title:
Mechanically driven phase transformation in single phase Al62.5Cu25Fe12.5 quasi-crystals: Effect of milling intensity
Authors:
Ali, F; Scudino, S; Gorantla, SM; Srivastava, VC; Shahid, HR; Uhlenwinkel, V; Stoica, M; Vaughan, G; Mukhopadhyay, NK; Eckert, J Author Full Names: Ali, F.; Scudino, S.; Gorantla, S. M.; Srivastava, V. C.; Shahid, H. R.; Uhlenwinkel, V.; Stoica, M.; Vaughan, G.; Mukhopadhyay, N. K.; Eckert, J.
Source:
ACTA MATERIALIA, 61 (10):3819-3830; 10.1016/j.actamat.2013.03.020 JUN 2013
Abstract:
In this work the effect of mechanical milling on the structure, thermal stability and hardness of single phase Al62.5Cu25Fe12.5 icosahedral quasi-crystals has been investigated for different milling intensities. The results indicate that, irrespective of the milling intensity used, the quasi-crystals transform to a body-centered cubic (bcc) phase during milling. This transformation starts when the grain size of the QC phase is about 10 nm, which represents the critical grain size initiating the phase transformation. Upon heating the milled powder displays grain growth of the bcc phase at low temperatures, followed by transformation to the original icosahedral QC phase at higher temperatures. The phase transformations occurring during milling and subsequent annealing have a remarkable effect on the indentation hardness, which can be tuned within a wide range (7-10 GPa) as a function of the volume fractions of the different phases. This suggests that a composite material with optimized mechanical properties can be produced by appropriate thermo-mechanical treatments. (c) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Composition-dependent ground state of martensite in Ni-Mn-Ga alloys
Authors:
Li, ZB; Xu, N; Zhang, YD; Esling, C; Raulot, JM; Zhao, X; Zuo, L Author Full Names: Li, Zongbin; Xu, Nan; Zhang, Yudong; Esling, Claude; Raulot, Jean-Mare; Zhao, Xiang; Zuo, Liang
Source:
ACTA MATERIALIA, 61 (10):3858-3865; 10.1016/j.actamat.2013.03.024 JUN 2013
Abstract:
For Ni-Mn-Ga alloys, giant magnetic-field-induced strains may be achieved in a modulated martensitic state, offering attractive chances for academic and practical exploration. However, the metastability of modulated martensite imposes a severe constraint on the capacity of these alloys as promising materials for sensors and actuators. In the present work, we conduct both experimental examinations and ab initio calculations to seek potential remedies of this critical problem through composition tuning. Results show that, for Group II alloys having modulated martensite at reasonable temperatures, the increase in Ni addition results in an enhanced tendency to the formation of non-modulated (NM) martensite, whereas the proper Mn addition leads to the stabilization of seven-layered modulated (7M) martensite, which serves as the structural ground state of martensite. By correlating the microstructural evolutions with the two-stage phase transformation (i.e. austenite -> 7M martensite -> NM martensite), it is demonstrated that the 7M martensite possesses lower energy barriers in terms of the lattice distortion of parent austenite and the interfacial energy of martensitic variants, which plays a vital role in bridging the austenite to NM martensite transformation. This result is expected to provide useful information for the design of these new functional materials. (c) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
High-Field Magnetism of the S = 5/2 Triangular-Lattice Antiferromagnet CuFe1-xGaxO2 (x=0-0.028)
Authors:
Fujita, T; Kimura, S; Kida, T; Kotetsu, T; Hagiwara, M Author Full Names: Fujita, Takahito; Kimura, Shojiro; Kida, Takanori; Kotetsu, Takahiro; Hagiwara, Masayuki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (6):10.7566/JPSJ.82.064712 JUN 2013
Abstract:
We have performed multifrequency electron spin resonance (ESR), electric polarization, and magnetization measurements on single crystals of the triangular-lattice antiferromagnet CuFe1-xGaxO2 (x = 0.000-0.028) in high magnetic fields. We compared ESR results with the other results (electric polarization and magnetization measurements) to clarify the origin of the expansion of a ferroelectric and incommensurate (FEIC) phase induced by the doping of nonmagnetic Ga3+ ions. We observed a rapid increase in the ESR linewidth and a large shift of the transition field from a four-sublattice collinear phase to the FEIC phase accompanied with a magnetization jump and a spontaneous electric polarization with slight doping of Ga3+ ions. We have found that the ESR linewidth is highly correlated with this shift. As a result, we have succeeded in explaining the origin of the expansion of the FEIC phase as well as the change of the transition field induced by broadening of the lowest excitation branch with an increase in Ga content.
Title:
Icosahedral quasicrystalline (Ti1.6V0.4Ni)(100-x)Sc-x alloys: Synthesis, structure and their application in Ni-MH batteries
Authors:
Hu, W; Yi, JH; Zheng, BJ; Wang, LM Author Full Names: Hu, Wen; Yi, Jianhong; Zheng, Biju; Wang, Limin
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 202 1-5; 10.1016/j.jssc.2013.03.006 JUN 2013
Abstract:
Thanks to the revolutionary discovery of 5-fold symmetry contributed by Shechtman, quasicrystal is now recognized as another solid-state existing form. As the second largest class of quasicrystals, titanium-based icosahedral quasicrystals are very promising for hydrogen storage applications owing to their inherent abundant interstitial sites and favorable hydrogen-metal chemistry. In this context, (Ti1.6V0.4Ni)(100-x)Sc-x (x=0.5-6) quaternary icosahedral quasicrystals have been successfully synthesized via arc-melting and subsequent melt-spinning techniques, and then their electrochemical performance toward hydrogen is explored. When the molar ratio of Sc addition is under 1%, a maximum discharge capacity of about 270 mA h g(-1) can be delivered. With further increasing Sc amount to 6%, good cycling stability as well as significantly retarded self-discharge rate (capacity retention 94% after 24 h relaxation) is observed. But meanwhile, the discharge capacities fall into 250-240 mA h g(-1), and the electrocatalytic activity improvement is highly demanded. (C) 2013 Elsevier Inc. All rights reserved.
Title:
Superconductivity Induced by Breaking Te-2 Dimers of AuTe2
Authors:
Kudo, K; Ishii, H; Takasuga, M; Iba, K; Nakano, S; Kim, J; Fujiwara, A; Nohara, M Author Full Names: Kudo, Kazutaka; Ishii, Hiroyuki; Takasuga, Masaya; Iba, Keita; Nakano, Seiya; Kim, Jungeun; Fujiwara, Akihiko; Nohara, Minoru
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (6):10.7566/JPSJ.82.063704 JUN 2013
Abstract:
Mineral calaverite AuTe2 is a layered compound with an incommensurately modulated structure. The modulation is characterized by the formation of molecular-like Te-2 dimers. We have found that the breaking of Te-2 dimers that occurs in Au1-xPtxTe2 results in the emergence of superconductivity at T-c = 4.0 K.

Update: 11-Jul-2013

Title:
THE MULTIFERROIC PROPERTIES OF Bi(Fe1/2Cr1/2)O-3 COMPOUND
Authors:
Zhu, JL; Yang, HX; Feng, SM; Wang, LJ; Liu, QQ; Jin, CQ; Wang, XH; Li, LT; Yu, J Author Full Names: Zhu, J. L.; Yang, H. X.; Feng, S. M.; Wang, L. J.; Liu, Q. Q.; Jin, C. Q.; Wang, X. H.; Li, L. T.; Yu, J.
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 27 (15):SI 10.1142/S0217979213620233 JUN 20 2013
Abstract:
Dense Bi(Fe1/2Cr1/2)O-3 ceramics with R 3c crystal structure were synthesized by solid-state reaction under high pressure. Transmission electron microscope observations revealed an incommensurable superstructure along < 110 > direction. Magnetization measurements indicated a transition to a cooperative magnetic state below similar to 130 K. Dielectric properties of Bi(Fe1/2Cr1/2)O-3 showed a dielectric constant anomaly located at similar to 140 K indicating the giant dielectric relaxation in multiferroic Bi(Fe1/2Cr1/2)O-3 compound, which can be explained by the enhanced conductivity and possible Maxwell-Wagner contribution. Large dielectric frequency dispersion was observed at 140-185 K, and was supposed to be a thermal activated intrinsic process.
Title:
Magnetic phase diagrams, domain switching, and quantum phase transition of the quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8
Authors:
Niesen, SK; Kolland, G; Seher, M; Breunig, O; Valldor, M; Braden, M; Grenier, B; Lorenz, T Author Full Names: Niesen, S. K.; Kolland, G.; Seher, M.; Breunig, O.; Valldor, M.; Braden, M.; Grenier, B.; Lorenz, T.
Source:
PHYSICAL REVIEW B, 87 (22):10.1103/PhysRevB.87.224413 JUN 14 2013
Abstract:
In the effective Ising spin-1/2 antiferromagnetic chain system BaCo2V2O8 the magnetic-field influence is highly anisotropic. For magnetic fields along the easy axis c, the Neel order is strongly suppressed already at low fields and an incommensurate order is entered above 4 T. We present a detailed study of the magnetic phase diagrams for different magnetic field directions, which are derived from magnetization data, high-resolution thermal expansion, and magnetostriction measurements as well as from the thermal conductivity. Zero-field thermal-expansion data reveal that the magnetic transition is accompanied by an orthorhombic distortion within the ab plane. Under ambient conditions the crystals are heavily twinned, but the domain orientation can be influenced either by applying uniaxial pressure or a magnetic field along the [100] direction. In addition, our data reveal a pronounced in-plane magnetic anisotropy for fields applied within the ab plane. For H parallel to [110], the magnetic field influence on T-N is weak, whereas for magnetic fields applied along [100], T-N vanishes at about 10 T and the zero-field Neel order is completely suppressed as is confirmed by neutron diffraction data. The second-order phase transition strongly suggests a quantum critical point being present at H similar or equal to 10 T parallel [100].
Title:
Coexistence of spiral magnetic state and weak ferromagnetism in a multiferroic, cross-controlled by external magnetic and electric fields
Authors:
Lyubutin, IS; Pikin, SA Author Full Names: Lyubutin, I. S.; Pikin, S. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (23):10.1088/0953-8984/25/23/236001 JUN 12 2013
Abstract:
The influence of external magnetic and electric fields on the properties of a multiferroic with a helical magnetic structure is described. Thermodynamics of the phase transition from the antiferromagnetic ferroelectric to the new magnetic state is described for a multiferroic with a perovskite-type structure. In this magnetic state a spiral spin structure and weak ferromagnetism can exist simultaneously. Such a state is a result of the first-order phase transition at a certain temperature below T-N when, due to the Dzyaloshinskii-Moriya effect, a helical magnetic structure occurs. In this state the vectors of electrical polarization and the helicoid of magnetic moments in perovskites are mutually perpendicular and lie in the basic (ab) plane perpendicular to the main c axis. In this case an additional electrical polarization proportional to the square of magnetization appears in the (ab) plane which reduces the common polarization of the ferroelectric. It is shown that a weak ferromagnetic moment m occurs along the c axis in an applied magnetic field in addition to a modulated magnetic structure appearing in the (ab) plane. The dependence of these phenomena on the applied electric field is considered. It is shown that a sign-alternating electric field causes a linear-in-the-field variation of the magnetic moment opposite in sign to the electric field variation (i.e., the greater is the electric field, the smaller is the magnetic moment m). The observed hysteresis phenomena determining the temperature ranges of overheating and overcooling of each phase under applied magnetic and electrical fields are explained.
Title:
Magnetic phase diagram of Sr3Fe2O7-delta
Authors:
Peets, DC; Kim, JH; Dosanjh, P; Reehuis, M; Maljuk, A; Aliouane, N; Ulrich, C; Keimer, B Author Full Names: Peets, D. C.; Kim, J. -H.; Dosanjh, P.; Reehuis, M.; Maljuk, A.; Aliouane, N.; Ulrich, C.; Keimer, B.
Source:
PHYSICAL REVIEW B, 87 (21):10.1103/PhysRevB.87.214410 JUN 10 2013
Abstract:
Magnetometry, electrical transport, and neutron scattering measurements were performed on single crystals of the Fe4+-containing perovskite-related phase Sr3Fe2O7-delta as a function of oxygen content. Although both the crystal structure and electron configuration of this compound are closely similar to those of well-studied ruthenates and manganates, it exhibits very different physical properties. The fully oxygenated compound (delta = 0) exhibits a charge-disproportionation transition at T-D = 340 K, and an antiferromagnetic transition at T-N = 115 K. For temperatures T <= T-D, the material is a small-gap insulator; the antiferromagnetic order is incommensurate, which implies competing exchange interactions between the Fe4+ moments. The fully deoxygenated compound (delta = 1) is highly insulating, and its Fe3+ moments exhibit commensurate antiferromagnetic order below T-N similar to 600 K. Compounds with intermediate delta exhibit different order with lower T-N, likely as a consequence of frustrated exchange interactions between Fe3+ and Fe4+ sublattices. A previous proposal that the magnetic transition temperature reaches zero is not supported.
Title:
Chemistry, morphology and structural characteristics of synthetic Al-Ni and Al-Co-lizardites
Authors:
Bentabol, M; Cruz, MDR Author Full Names: Bentabol, Maria; Ruiz Cruz, Maria Dolores
Source:
APPLIED CLAY SCIENCE, 77-78 68-78; 10.1016/j.clay.2013.04.001 JUN 2013
Abstract:
Al-Ni and Al-Co lizardites have been synthesized at hydrothermal conditions. The two phases display different morphologies: thin, dominantly curved platelets (Al-Ni); and stacks of very thin platy particles (Al-Co). The X-ray diffraction and transmission/analytical electron microscopy studies have been used to make accurate distinctions among different structural types and chemical populations. Al-Ni bearing lizardite includes a 1M polytype and probably very subordinate amounts of chlorite. Al-Co bearing lizardite includes two 1M polytypes with different cell-parameters, one of these consisting of an apparently modulated structure. Chemically, Al-Ni- and specially Al-Co lizardite consist of a mixture of two populations with tetrahedral compositions similar to Si1.8Al0.2 and Si-2.0. In contrast with previously described Al-rich serpentines, our serpentines are characterized by an asymmetrical Al distribution, with Al-VI on the order of 1.0 atom per formula u nit. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Structural transformation and enhancement in magnetic properties of single-phase Bi1-xPrxFeO3 nanoparticles
Authors:
Srivastav, SK; Gajbhiye, NS; Banerjee, A Author Full Names: Srivastav, Simant Kumar; Gajbhiye, N. S.; Banerjee, A.
Source:
JOURNAL OF APPLIED PHYSICS, 113 (20):10.1063/1.4807928 MAY 28 2013
Abstract:
Single-phase Bi1-xPrxFeO3 (x = 0.0, 0.05, and 0.10) nanoparticles have been synthesized by propylene glycol-gel route at a temperature of 400 degrees C. Rietveld refinement of X-ray diffraction data and Raman spectra reflect a structural phase transition from rhombohedral for x = 0 to triclinic for x = 0.10. Magnetic measurements reveal that Pr-doped BiFeO3 nanoparticles for x = 0.10 have enhanced remnant magnetization about 10 times as compared to pure BiFeO3 nanoparticles. It has been shown by Fe-57 Mossbauer spectroscopy that the observed enhancement in magnetic properties of BiFeO3 with Pr doping is mainly due to suppression of modulated spiral spin structure near x = 0.10 and not due to Fe multiple valence, i.e., oxygen deficiency. (C) 2013 AIP Publishing LLC.
Title:
Precession Electron Diffraction Tomography for Solving Complex Modulated Structures: the Case of Bi5Nb3O15
Authors:
Boullay, P; Palatinus, L; Barrier, N Author Full Names: Boullay, Philippe; Palatinus, Lukas; Barrier, Nicolas
Source:
INORGANIC CHEMISTRY, 52 (10):6127-6135; 10.1021/ic400529s MAY 20 2013
Abstract:
The crystal structure of the ID incommensurately modulated phase Bi5Nb3O15 [superspace group X2mb(0b0)000, a = 5.46781(7) angstrom, b = 5.47381(8) angstrom, c = 41.9005(5) angstrom, and q = 0.17588(8)b*] is solved by *electron* *diffraction* using a tomography technique combined with precession of the *electron* beam. The (3 + 1)D structure is further validated by a refinement against powder X-ray diffraction (PXRD). A coherent picture of the true nature of this compound is obtained, conciliating experimental observations made by different groups using transmission electron microscopy and PXRD. Bi5Nb3O15 does not have a mixed-layer Aurivillius-type structure but does contain structural elements, [Bi2O2](2+) slabs, and perovsldte-like blocks, characteristic of Aurivillius phases. The presence of aperiodic crystallographic shear planes (CSPs) along the modulated direction b leads to the formation of an original layered structure containing both continuous and discontinuous [Bi2O2](2+) and perovskite-like octahedral layers. Between CSPs, the stacking of these two structural elements exhibits an unprecedented nonuniform sequence referring to Aurivillius phases.
Title:
Structure, Atomistic Simulations, and Phase Transition of Stoichiometric Yeelimite
Authors:
Cuesta, A; De la Torre, AG; Losilla, ER; Peterson, VK; Rejmak, P; Ayuela, A; Frontera, C; Aranda, MAG Author Full Names: Cuesta, Ana; De la Torre, Angeles G.; Losilla, Enrique R.; Peterson, Vanessa K.; Rejmak, Pawel; Ayuela, Andres; Frontera, Carlos; Aranda, Miguel A. G.
Source:
CHEMISTRY OF MATERIALS, 25 (9):1680-1687; 10.1021/cm400129z MAY 14 2013
Abstract:
Yeelimite, Ca-4[Al6O12]SO4, is outstanding as an aluminate sodalite, being the framework of these type of materials flexible and dependent on ion sizes and anion ordering/disordering. On the other hand, yeelimite is also important from an applied perspective as it is the most important phase in calcium sulfoaluminate cements. However, its crystal structure is not well studied. Here, we characterize the room temperature crystal structure of stoichiometric yeelimite through joint Rietveld refinement using neutron and Xray powder diffraction data coupled with chemical soft-constraints. Our structural study shows that yeelimite has a lower symmetry than that of the previously reported tetragonal system, which we establish to likely be the acentric orthorhombic space group Pcc2, with a root 2a x root 2a X a superstructure based on the cubic sodalite structure. Final unit cell values were a = 13.0356(7) angstrom, b = 13.0350(7) angstrom, and c = 9.1677(2) angstrom. We determine several structures using density functional theory calculations, with the lowest energy structure being Pcc2 in agreement with our experimental result. Yeelimite undergoes a reversible phase transition to a higher-symmetry phase which has been characterized to occur at 470 degrees C by thermodiffractometry. The higher-symmetry phase is likely cubic or pseudocubic possessing an incommensurate superstructure, as suggested by our theoretical calculations which show a phase transition from an orthorhombic to a tetragonal structure. Our theoretical study also predicts a pressure-induced phase transition to a cubic structure of space group 1 (4) under bar 3m. Finally, we show that our reported crystal structure of yeelimite enables better mineralogical phase analysis of commercial calcium sulfoaluminate cements, as shown by R-F values for this phase, 6.9% and 4.8% for the previously published orthorhombic structure and for the one reported in this study, respectively.
Title:
Elastohydrodynamic problems in quasicrystal elasticity theory and wave propagation
Authors:
Li, XF Author Full Names: Li, X. F.
Source:
PHILOSOPHICAL MAGAZINE, 93 (13):1500-1519; 10.1080/14786435.2012.745655 MAY 1 2013
Abstract:
Elastohydrodynamic problems of decagonal quasicrystals are analysed where the phonon field obeys wave equation and the phason field obeys diffusive wave equation. Basic equations are solved in the quasiperiodic plane and periodic plane, respectively. Final governing equations of dynamic behaviours of decagonal quasicrystals are obtained. A general solution is derived in terms of introduced three auxiliary functions, where two individually satisfy a fourth-order partial differential equation and one satisfies a second-order hyperbolic diffusion equation. Using the derived governing equations, elastic waves propagating in the quasiperiodic plane and a plane containing the period axis are analysed. Secular equations are obtained. It is found that differing from conventional crystals, at least four branches of elastic waves exist when the phononphason coupling is present. Moreover, acoustic waves have attenuation during wave propagation. Phason fluctuations exhibit! exponential decaying behaviour due to kinematic viscosity and damping. The phase speeds are isotropic in the quasiperiodic plane and anisotropic in a plane with the periodic axis. The section of the slowness surfaces is plotted.
Title:
Hydrogen Absorption Study of Ti-based Alloys Performed by Melt-spinning
Authors:
Ribeiro, RM; Lemus, LF; dos Santos, DS Author Full Names: Ribeiro, R. M.; Lemus, L. F.; dos Santos, D. S.
Source:
MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS, 16 (3):679-682; 10.1590/S1516-14392013005000049 MAY-JUN 2013
Abstract:
The hydrogen absorption and desorption of Ti53Zr27Ni20 icosahedral quasicrystal (ICQ) and Ti50Ni50 shape memory alloy (SMA) melt-spun ribbons was studied. Samples were exposed to hydrogen gas at 623 K and 4 MPa for 1000 minutes. The total capacity of hydrogen obtained for Ti53Zr27Ni20 and Ti50Ni50 was 3.2 and 2.4 wt. % respectively. The Thermal Desorption Spectrometry (TDS) of the hydrogenated alloys shows that both alloys start to desorb hydrogen around 750 K. X-ray diffraction (XRD) patterns, performed after hydrogenation, indicate a complete amorphization of the Ti53Zr27Ni20 i-phase alloy, while the Ti50Ni50 alloy remained crystalline after hydride formation.

Update: 4-Jul-2013

Title:
(3+1)D superspace description of the incommensurate modulation in the premartensite phase of Ni2MnGa: a high resolution synchrotron x-ray powder diffraction study
Authors:
Singh, S; Nayak, J; Rai, A; Rajput, P; Hill, AH; Barman, SR; Pandey, D Author Full Names: Singh, Sanjay; Nayak, J.; Rai, Abhishek; Rajput, Parasmani; Hill, Adrian H.; Barman, S. R.; Pandey, Dhananjai
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (21):10.1088/0953-8984/25/21/212203 MAY 29 2013
Abstract:
Le Bail and Rietveld analysis of high resolution synchrotron x-ray powder diffraction (SXRPD) data shows unambiguous signatures of the failure of the commensurate 3M modulation model. Using (3 + 1) dimensional superspace group formalism, we have not only confirmed the incommensurate modulation in the premartensite phase with a modulation wavevector of q = 0.337 61(5)c* but also determined the superspace group (Immm(00 gamma)s00), atomic positions and amplitude of modulations for the incommensurate premartensite phase of Ni2MnGa for the first time. Our results may have important implications in the understanding of the martensitic transition and hence the magnetic field induced strains.
Title:
Cu/Te substitution effects on superconductivity and microstructure of phase-separated K0.8Fe1.75Se2
Authors:
Wang, Z; Cai, Y; Wang, ZW; Sun, ZA; Yang, HX; Tian, HF; Ma, C; Zhang, B; Li, JQ Author Full Names: Wang, Z.; Cai, Y.; Wang, Z. W.; Sun, Z. A.; Yang, H. X.; Tian, H. F.; Ma, C.; Zhang, B.; Li, J. Q.
Source:
EPL, 102 (3):10.1209/0295-5075/102/37010 MAY 2013
Abstract:
Two series of K0.8Fe1.75-xCuxSe2 (0 <= x <= 0.15) and K0.8Fe1.75Se2-yTey (0 <= y <= 0.5) single crystals of nominal composition have been prepared and their physical properties and microstructural features have been studied. Resistivity measurements demonstrate that the superconducting transition temperature decreases gradually with the increase of the substitution level and zero resistivity finally disappears in both systems. Systematic TEM, SEM and XRD structural analyses, in combination with the magnetic experimental data, reveal a rich variety of structural phenomena resulting from different types of substitution. Cu substitution gives rise to the volume of a new non-superconducting Cu-rich phase with modulation q(3) = 1/3[2a* + b*] coexisting with the q(2) = 1/2[a* + b*] superconducting stripe domain. With the increase of the ratio of the new non-superconducting phase along with doping, the superconducting path is finally cut off, and results in the absence of zero resistivity. In contrast, the absence of superconductivity in Te-substituted materials is correlated with the complete disappearance of the q2 superconducting phase due to the suppression of phase separation. Copyright (C) EPLA, 2013
Title:
Discovery of stable icosahedral quasicrystals: progress in understanding structure and properties
Authors:
Tsai, AP Author Full Names: Tsai, An-Pang
Source:
CHEMICAL SOCIETY REVIEWS, 42 (12):5352-5365; 10.1039/c3cs35388e 2013
Abstract:
The geometrical concept and structural framework of quasicrystals (QCs) were established shortly after the discovery of QCs. Specifically, the static and dynamic properties of the atoms and the electronic structures of quasiperiodic lattices were theoretically developed. Experimental studies lagged behind theoretical progress due to the lack of suitable samples. This situation changed with the discovery of several highly ordered stable QCs. Studies of these new QCs have provided new insights into the structure and properties of QCs. This article chronologically reviews the discoveries of various stable icosahedral QCs and subsequent studies that determined their structures, properties, and stabilization mechanisms.

Update: 26-Jun-2013

Title:
Magnetic field and pressure effects on magnetism of bond-frustrated ZnCr2S4
Authors:
Xie, YM; Yang, ZR; Zhang, ZT; Shen, C; Li, L; Ling, LS; Pi, L; Sun, YP; Zhang, YH Author Full Names: Xie, Y. M.; Yang, Z. R.; Zhang, Z. T.; Shen, C.; Li, L.; Ling, L. S.; Pi, L.; Sun, Y. P.; Zhang, Y. H.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 339 81-83; 10.1016/j.jmmm.2013.03.010 AUG 2013
Abstract:
In this paper, magnetic field and hydrostatic pressure effects on magnetism of ZnCr2S4 were investigated. Upon cooling the sample at 0.5 T to 2 K then warming back, the magnetization displays irreversibility between the cooling and warming sequence at temperatures around incommensurate-commensurate antiferromagnetic transition T-N2. With increasing magnetic field or hydrostatic pressure, the irreversibility is gradually suppressed, although the thermal hysteresis is shifted to higher temperatures under pressure. The observed thermal hysteresis is attributed to a structural transition and evolution of different magnetic phases upon cooling and warming. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Solidification and microstructure of as-cast Mg65Zn32Y3 quasicrystal alloy
Authors:
Geng, JW; Teng, XY; Zhou, GR; Zhao, ZW Author Full Names: Geng, Jiwei; Teng, Xinying; Zhou, Guorong; Zhao, Zhenwei
Source:
PHYSICA B-CONDENSED MATTER, 420 64-69; 10.1016/j.physb.2013.03.035 JUL 1 2013
Abstract:
Stable icosahedral quasicrystal with a nominal composition of Mg30Zn60Y10 (at%) was prepared by an as-cast method. Applying X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques, the equilibrium solidification microstructures of Mg65Zn32Y3 (at%) quasicrystal alloy in Mg-rich corner of the Mg-Zn-Y system was investigated. Since resistivity is one of the physical properties sensitive to structures, it is suggested that there is a reversible temperature-induced solid-liquid structural transition. Quasicrystal possesses quasi-periodic lattice structure and especial electronic structure, which indicates the resistivity of Mg65Zn32Y3 quasicrystal alloy will change greatly during the melting or solidification processes. The temperature dependence on resistivity exhibits a clear turning point. Measuring resistivity-temperature curve (rho-T curve) and comparing with differential scanning calorimetry (DSC) first time, a study on the solidifi cation process of quasicrystal was carried out. The icosahedral quasicrystalline phase (I-phase) surrounded by eutectic microstructure (alpha-Mg+decagonal quasicrystalline phase (D-phase)) is reported first time. During the solidification process, the I-phase is formed at about 423 degrees C undergoing a peritectic reaction, and decagonal quasicrystal eutectic microstructure is formed at the later stage. The phase involved in this peritectic reaction has a composition of Mg28.93M46.62Y24.35 (W-phase). Furthermore, the quasicrystals with various characteristics morphologies exist some degree micro-segregation. And the microsegregation phenomenon in rod-like quasicrystalline phase is more serious than that in petals-like quasicrystalline phase. (c) 2013 Elsevier B.V. All rights reserved.
Title:
Simulation of modulated protein crystal structure and diffraction data in a supercell and in superspace
Authors:
Lovelace, JJ; Simone, PD; Petricek, V; Borgstahl, GEO Author Full Names: Lovelace, Jeffrey J.; Simone, Peter D.; Petricek, Vaclav; Borgstahl, Gloria E. O.
Source:
ACTA CRYSTALLOGRAPHICA SECTION D-BIOLOGICAL CRYSTALLOGRAPHY, 69 1062-1072; 10.1107/S0907444913004630 6 JUN 2013
Abstract:
The toolbox for computational protein crystallography is full of easy-to-use applications for the routine solution and refinement of periodic diffraction data sets and protein structures. There is a gap in the available software when it comes to aperiodic crystallographic data. Current protein crystallography software cannot handle modulated data, and small-molecule software for aperiodic crystallography cannot work with protein structures. To adapt software for modulated protein data requires training data to test and debug the changed software. Thus, a comprehensive training data set consisting of atomic positions with associated modulation functions and the modulated structure factors packaged as both a three-dimensional supercell and as a modulated structure in (3+1)D superspace has been created. The (3+1)D data were imported into Jana2006; this is the first time that this has been performed for protein data.
Title:
Structural phase transition and related electronic properties in quasi-one-dimensional (NbSe4)(10/3)
Authors:
Zubko, M; Kusz, J; Prodan, A; Sturm, S; van Midden, HJP; Bennett, JC; Dubin, G; Zupanic, E; Bohm, H Author Full Names: Zubko, Maciej; Kusz, Joachim; Prodan, Albert; Sturm, Saso; van Midden, Herman J. P.; Bennett, J. Craig; Dubin, Grzegorz; Zupanic, Erik; Boehm, Horst
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 69 229-237; 10.1107/S2052519213010336 3 JUN 2013
Abstract:
The real crystal structure of the (NbSe4)(10/3)I charge density wave (CDW) compound is studied by simulation of the X-ray diffuse scattering. The average structure of the low-temperature twinned phase is determined and the phase transition is attributed to the formation of a CDW. The diffuse streaking, present in X-ray diffraction patterns above and below the transition at T = 282 K, is shown to be a projection of diffuse concentric rings perpendicular to the c* direction. The simulated patterns, based on a mismatch model between infinite NbSe4 chains, correlated by I atoms, are in good accordance with the experimental patterns. In addition to the experiments, the electronic properties of the high-and the low-temperature phases are calculated with the extended Huckel tight-binding method. The Fermi surfaces of the average structures above and below the phase transition appear very similar. Their shapes support a nesting instability and a CDW for! mation. The weak incommensurate CDW satellites, present below the phase transition, are at 100 K properly described by a modulation wavevector q = [0.06 (1), 0, 0.55 (1)].
Title:
Observation of Electronic Inhomogeneity and Charge Density Waves in a Bilayer La2-2xSr1+2xMn2O7 Single Crystal
Authors:
Kim, J; Huang, JW; Zhou, JS; Goodenough, JB; Zheng, H; Mitchell, JF; de Lozanne, A Author Full Names: Kim, Jeehoon; Huang, Junwei; Zhou, J. -S.; Goodenough, J. B.; Zheng, H.; Mitchell, J. F.; de Lozanne, Alex
Source:
PHYSICAL REVIEW LETTERS, 110 (21):10.1103/PhysRevLett.110.217203 MAY 20 2013
Abstract:
We employed a scanning tunneling microscope to image the (001) surface topography and local density of states (LDOS) in La2-2xSr1+2xMn2O7 (x = 0.32, LSMO) single crystals below the Curie temperature (T-C approximate to 120 K). The LDOS maps revealed a stripelike modulation propagating along the tetragonal a axis with a wavelength of about 16 angstrom, which is indicative of a charge density wave (CDW). The observed CDW in the x = 0.32 sample is far from the Fermi surface nesting instability as compared with the data of angle resolved photoemission spectroscopy in an x = 0.40 sample. The stripe model developed previously for cuprates can explain the observed CDW in our LSMO sample, indicating that competing interactions between localized and itinerant phases are the origin of the spatial modulations present intrinsically in cuprates and manganites.
Title:
Structural and magnetic characterization of the intermartensitic phase transition in NiMnSn Heusler alloy ribbons
Authors:
Llamazares, JLS; Flores-Zuniga, H; Rios-Jara, D; Sanchez-Valdes, CF; Garcia-Fernandez, T; Ross, CA; Garcia, C Author Full Names: Sanchez Llamazares, J. L.; Flores-Zuniga, H.; Rios-Jara, D.; Sanchez-Valdes, C. F.; Garcia-Fernandez, T.; Ross, C. A.; Garcia, C.
Source:
JOURNAL OF APPLIED PHYSICS, 113 (17):10.1063/1.4800836 MAY 7 2013
Abstract:
Phase transitions and structural and magnetic properties of rapidly solidified Ni50Mn38Sn12 alloy ribbons have been studied. Ribbon samples crystallize as a single-phase, ten-layered modulated (10M) monoclinic martensite with a columnar-grain microstructure and a magnetic transition temperature of 308 K. By decreasing the temperature, martensite undergoes an intermartensitic phase transition around 195 K. Above room temperature, the high temperature martensite transforms into austenite. Below 100 K, magnetization hysteresis loops shift along the negative H-axis direction, confirming the occurrence of an exchange bias effect. On heating, the thermal dependence of the coercive field H-C shows a continuous increase, reaching a maximum value of 1017 Oe around 50 K. Above this temperature, H-C declines to zero around 195 K. But above this temperature, it increases again up to 20 Oe falling to zero close to 308 K. The coercivity values measured in both temperature intervals suggest a significant difference in the magnetocrystalline anisotropy of the two martensite phases. (C) 2013 AIP Publishing LLC.
Title:
Coexistence of incommensurate and commensurate spiral orders and pressure effect on polycrystalline CoCr2O4
Authors:
Chen, XL; Yang, ZR; Xie, YM; Huang, ZH; Ling, LS; Zhang, SL; Pi, L; Sun, YP; Zhang, YH Author Full Names: Chen, Xuliang; Yang, Zhaorong; Xie, Yuanmiao; Huang, Zhonghao; Ling, Langsheng; Zhang, Shile; Pi, Li; Sun, Yuping; Zhang, Yuheng
Source:
JOURNAL OF APPLIED PHYSICS, 113 (17):10.1063/1.4796172 MAY 7 2013
Abstract:
In this paper, we have investigated the magnetism of multiferroic CoCr2O4. With decreasing temperature, CoCr2O4 first undergoes a ferrimagnetic transition at T-C then a long-range spiral spin transition at T-S followed by a magnetic lock-in transition at T-L. Coercive force manifests different slopes in different magnetic phases. Upon cooling the sample at 100 Oe to 5 K then warming back, the magnetization displays irreversibility between the cooling and warming sequence at temperatures below T-L. The irreversible behavior under the thermal-cycling is inert to magnetic field up to 45 kOe, indicating the coexistence of incommensurate and commensurate spiral orders. Both T-S and T-L are increased with the application of high pressure, which implies that the magnetic frustration is enhanced upon the shrinkage of lattice. The spin-lattice coupling is also revealed by infrared spectrum. (C) 2013 American Institute of Physics.
Title:
Magnetic structure of GdNiSn
Authors:
Lee-Hone, NR; Lemoine, P; Ryan, DH; Verniere, A; Malaman, B Author Full Names: Lee-Hone, N. R.; Lemoine, P.; Ryan, D. H.; Verniere, A.; Malaman, B.
Source:
JOURNAL OF APPLIED PHYSICS, 113 (17):10.1063/1.4793642 MAY 7 2013
Abstract:
The magnetic structure of the TiNiSi-type GdNiSn compound has been studied by both Gd-155 Mossbauer spectrocopy and neutron powder diffraction. The results suggest a square-wave modulated magnetic structure characterized by the propagation vector k = [0.426, 0.351, 0] and Gd magnetic moments of 6.52(15) mu B (at 3.6 K) oriented along the c-axis. The results are compared with those of the isotypic RNiSn compounds and with the possible magnetic structures of GdNiSn proposed from earlier Gd-155 Mossbauer work. (C) 2013 American Institute of Physics.
Title:
Growth and Characterization of Centimeter-Sized Ba2LaFeNb4O15 Crystals from High-Temperature Solution under a Controlled Atmosphere
Authors:
Albino, M; Veber, P; Castel, E; Velazquez, M; Schenk, K; Chapuis, G; Lahaye, M; Pechev, S; Maglione, M; Josse, M Author Full Names: Albino, Marjorie; Veber, Philippe; Castel, Elias; Velazquez, Matias; Schenk, Kurt; Chapuis, Gervais; Lahaye, Michel; Pechev, Stanislav; Maglione, Mario; Josse, Michael
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, (15):2817-2825; 10.1002/ejic.201300008 MAY 2013
Abstract:
Centimeter-sized single crystals of Ba2LaFeNb4O15 were grown from a high-temperature solution by using LiBO2 flux and a sealed platinum assembly. The obtained single crystals display the same physical properties as their ceramic counterparts. A frequency-dependent dielectric permittivity maximum was found (Tm = 100 K at 5 kHz), which indicates relaxor behavior. Magnetic susceptibility measurements revealed purely paramagnetic behavior between 10 and 350 K. X-ray diffraction measurements of Ba2LaFeNb4O15 single crystals revealed an incommensurate structure at room temperature with a bidimensional modulation characterized by vectors q1 = (, , 1/2) and q2 = (, , 1/2) with = 0.295(1). This crystal growth method offers a promising elaboration route to centimeter-sized crystals of niobate-based compounds, which may not be grown from the pure liquid phase, especially those with a tetragonal tungsten bronze (TTB) structure.

Update: 19-Jun-2013

Title:
Momentum-Dependent Charge Correlations in YBa2Cu3O6+delta Superconductors Probed by Resonant X-Ray Scattering: Evidence for Three Competing Phases
Authors:
Blanco-Canosa, S; Frano, A; Loew, T; Lu, Y; Porras, J; Ghiringhelli, G; Minola, M; Mazzoli, C; Braicovich, L; Schierle, E; Weschke, E; Le Tacon, M; Keimer, B Author Full Names: Blanco-Canosa, S.; Frano, A.; Loew, T.; Lu, Y.; Porras, J.; Ghiringhelli, G.; Minola, M.; Mazzoli, C.; Braicovich, L.; Schierle, E.; Weschke, E.; Le Tacon, M.; Keimer, B.
Source:
PHYSICAL REVIEW LETTERS, 110 (18):10.1103/PhysRevLett.110.187001 MAY 1 2013
Abstract:
We use resonant x-ray scattering to determine the momentum-dependent charge correlations in YBa2Cu3O6.55 samples with highly ordered chain arrays of oxygen acceptors (ortho-II structure). The results reveal nearly critical, biaxial charge density wave (CDW) correlations at in-plane wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length are enhanced as superconductivity is weakened by an external magnetic field. Analogous experiments are carried out on a YBa2Cu3O6.6 crystal with a dilute concentration of spinless (Zn) impurities, which had earlier been shown to nucleate incommensurate magnetic order. Compared to pristine crystals with the same doping level, the CDW amplitude and correlation length are found to be strongly reduced. These results indicate a three-phase competition between spin-modulated, charge-modulated, and superconducting states in underdoped YBa2Cu3O6+del! ta.
Title:
Commensurate and incommensurate states of a spin density wave in a quasi-two-dimensional system with an anisotropic energy spectrum in an external magnetic field of arbitrary direction relative to magnetization
Authors:
Palistrant, ME; Ursu, VA Author Full Names: Palistrant, M. E.; Ursu, V. A.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 116 (4):641-656; 10.1134/S1063776113040080 APR 2013
Abstract:
A theory of thermodynamic properties of a spin density wave (SDW) in a quasi-two-dimensional system (with a preset impurity concentration x) is constructed. We choose an anisotropic dispersion relation for the electron energy and assume that external magnetic field H has an arbitrary direction relative to magnetic moment M (Q) . The system of equations defining order parameters M (Q) (z) , M (Q) (sigma) , M (z) , and M (sigma) is constructed and transformed with allowance for the Umklapp processes. Special cases when H aEuro- M (Q) and H aSyen M (Q) (H (Z) H (sigma) = 0) are considered in detail as well as cases of weak fields H of arbitrary direction. The condition for the transition of the system to the commensurate and incommensurate states of the SDW is analyzed. The concentration dependence of magnetic transition temperature T (M) is calculated, and the components of the order parameter for the incommensurate phase are determined. The phase diagram (T,similar to x) is constructed. The effect of the magnetic field on magnetic transition temperature T (M) is analyzed for H (Z) H (sigma) = 0, and longitudinal magnetic susceptibility chi aEuro- is calculated; this quantity demonstrates the temperature dependence corresponding to a system with a gap for x < x (c) and to a gapless state for x > x (c) . In the immediate vicinity of the critical impurity concentration (x similar to x (c) ), the temperature dependence of the magnetic susceptibility acquires a local maximum. The effect of anisotropy of the electron energy spectrum on the investigated physical quantities is also analyzed.

Update: 12-Jun-2013

Title:
Conspicuous variation of the lattice unit cell in the pavonite homologous series and its relation with cation/anion occupational modulations
Authors:
Perez-Mato, JM; Elcoro, L; Makovicky, E; Topa, D; Peticek, V; Madariaga, G Author Full Names: Perez-Mato, J. M.; Elcoro, Luis; Makovicky, Emil; Topa, Dan; Petricek, Vaclav; Madariaga, Gotzon
Source:
MATERIALS RESEARCH BULLETIN, 48 (6):2166-2174; 10.1016/j.materresbull.2013.02.008 JUN 2013
Abstract:
The pavonites is a homologous series of sulfosalts with galena-like modules of variable size. A survey of their unit cells reveals that they are severely constrained by the metrics of an underlying common average sublattice. The unit cell of any compound of the series accommodates with high precision an integer number of approximately equal subcells. This explains a peculiar non-uniform variation of the unit cell parameters within the series and evidences that the interface between the galena-like modules, despite having a very different topology, approximately maintains the subperiodicity of the modules, and must therefore be subject to strong steric restrictions. It also implies that cations and anions occupy the nodes of the observed common underlying average sublattice according to a striking alternate cation/anion occupational modulation. This is the starting point for a description of these materials as modulated structures, which can make a proficient use of the approximate atomic positional non-crystallographic correlations caused by their modular character. Under this approach only four parameters suffice to define a realistic approximate model of any member of the series. A full structural characterization of any of the compounds only requires the determination of additional small/smooth modulations. As an example, the case of the P-7 pavonite Ag3Bi6.2Pb0 8S12, is analyzed. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Short- and long-range ordering during the phase transition of the Zn6Sc 1/1 cubic approximant
Authors:
Yamada, T; Euchner, H; Gomez, CP; Takakura, H; Tamura, R; de Boissieu, M Author Full Names: Yamada, Tsunetomo; Euchner, Holger; Gomez, Cesar Pay; Takakura, Hiroyuki; Tamura, Ryuji; de Boissieu, Marc
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (20):10.1088/0953-8984/25/20/205405 MAY 22 2013
Abstract:
Using in situ x-ray scattering and synchrotron radiation, we have experimentally elucidated the mechanism of the cubic to monoclinic phase transition in the Zn6Sc 1/1 approximant to an icosahedral quasicrystal. The high-temperature cubic phase is described as a bcc packing of a large Tsai-type icosahedral cluster whose center is occupied by an orientationally disordered Zn-4 tetrahedron. A clear monoclinic distortion has been found to take place within 2 K around T-c = 157 K, in excellent agreement with the observed anomalies in the electrical resistivity and heat capacity. Also, a rapid variation of the super-structure reflection intensity is observed. The low-temperature monoclinic phase, as determined by single-crystal x-ray diffraction at 40 K, has been confirmed to consist of ordered Zn-4 tetrahedra, oriented in an anti-parallel way along the [(1) over bar 01] direction. Above T-c, a diffuse scattering signal is observed at the position of the super-structure reflections, which evidences that a short-range ordering of the Zn-4 tetrahedra takes place. In a way similar to a second-order phase transition, the correlation length describing this short-range ordering increases rapidly when the temperature diminishes and almost diverges when the temperature is close to T-c, going from 200 angstrom at 220 K to reach the very large value of 1200 angstrom at 161 K. Finally, using single-crystal x-ray diffraction, the atomic structure of the low-temperature monoclinic super-structure (space group C2/c) could be solved. The ordering of the Zn-4 tetrahedra is accompanied by a strong distortion of the surrounding shells.
Title:
Magnetic and crystal structure determination of Mn2FeSbO6 double perovskite
Authors:
Dos Santos-Garcia, AJ; Ritter, C; Solana-Madruga, E; Saez-Puche, R Author Full Names: Dos Santos-Garcia, A. J.; Ritter, C.; Solana-Madruga, E.; Saez-Puche, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (20):10.1088/0953-8984/25/20/206004 MAY 22 2013
Abstract:
The perovskite form of the Mn2FeSbO6 oxide has been obtained at 5.5 GPa and 1523 K. X-ray and neutron diffraction data reveal that this compound crystallizes in the monoclinic P2(1)/n space group with a = 0.5234 nm, b = 0.5389 nm, c = 0.7642 nm and beta = 90.372 degrees lattice parameters. AC and DC magnetic susceptibility measurements suggest the existence of a complex magnetic behavior below 200 K. The magnetic structure has been determined and can be described on the basis of an elliptical spiral with an incommensurate propagation vector, k = [0, 0.426, 0], where the magnetic moments of 2Mn(2+) and Fe3+ cations are confined to the ac-plane.
Title:
A (3+3)-Dimensional "Hypercubic" Oxide-Ionic Conductor: Type II Bi2O3-Nb2O5
Authors:
Ling, CD; Schmid, S; Blanchard, PER; Petricek, V; McIntyre, GJ; Sharma, N; Maljuk, A; Yaremchenko, AA; Kharton, VV; Gutmann, M; Withers, RL Author Full Names: Ling, Chris D.; Schmid, Siegbert; Blanchard, Peter E. R.; Petricek, Vaclav; McIntyre, Garry J.; Sharma, Neeraj; Maljuk, Andrey; Yaremchenko, Aleksey A.; Kharton, Vladislav V.; Gutmann, Matthias; Withers, Ray L.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 135 (17):6477-6484; 10.1021/ja3109328 MAY 1 2013
Abstract:
The high-temperature cubic form of bismuth oxide, delta-Bi2O3, is the best intermediate-temperature oxide-ionic conductor known. The most elegant way of stabilizing delta-Bi2O3 to room temperature, while preserving a large part of its conductivity, is by doping with higher valent transition metals to create wide solid-solutions fields with exceedingly rare and complex (3 + 3)-dimensional incommensurately modulated "hypercubic" structures. These materials remain poorly understood because no such structure has ever been quantitatively solved and refined, due to both the complexity of the problem and a lack of adequate experimental data. We have addressed this by growing a large (centimeter scale) crystal using a novel refluxing floating-zone method, collecting high-quality single-crystal neutron diffraction data, and treating its structure together with X-ray diffraction data within the superspace symmetry formalism. The structure can be understood as an "inflated" pyrochlore, in which corner-connected NbO6 octahedral chains move smoothly apart to accommodate the solid solution. While some oxide vacancies are ordered into these chains, the rest are distributed throughout a continuous three-dimensional network of wide delta-Bi2O3-like channels, explaining the high oxide-ionic conductivity compared to commensurately modulated phases in the same pseudobinary system.
Title:
Correlation between structures and properties in (Zr65Cu15Ni10Al10)(90)Nb-10 alloys
Authors:
Zhang, JL; Wang, YM; Shek, CH Author Full Names: Zhang, Ji Liang; Wang, Ying Min; Shek, Chan Hung
Source:
JOURNAL OF MATERIALS RESEARCH, 28 (9):1218-1223; 10.1557/jmr.2013.22 MAY 2013
Abstract:
A quasicrystal (QC)-based alloy composite was made by copper mold casting under a low-vacuum level condition at the bulk metallic glass (BMG)- forming composition (Zr65Cu15Al10Ni10)(90)Nb-10. The QC alloy consisted of a majority of icosahedral quasicrystal phase and a small amount Zr-rich glassy phase. Under uniaxial compression at room temperature, the BMG alloy exhibits a certain plastic strain; the QC alloy is much stronger but brittle. The icosahedral glass model was used to describe the I-phase structure. The structure-property relations of the BMG and QC alloys are discussed assuming the common preferential icosahedral atomic structure in both cases and the existence of local glue structure in the BMG structure.
Title:
Symmetry of Quasicrystals
Authors:
Madison, AE Author Full Names: Madison, A. E.
Source:
PHYSICS OF THE SOLID STATE, 55 (4):855-867; 10.1134/S1063783413040185 APR 2013
Abstract:
The definition of an aperiodic crystal (quasicrystal) as a solid that is characterized by the forbidden symmetry suggests the existence of an unsolved problem, because, in a mutually exclusive manner, it appeals to the fundamental theorem of classical crystallography. Using the Penrose tiling as an example, we have investigated the symmetry properties of aperiodic tilings for the purpose to establish the allowed symmetry groups of quasicrystals. The filling of the Euclidean space according to an aperiodic law is considered as the action of an infinite number of group elements on a fundamental domain in the non-Euclidean space. It is concluded that all locally equivalent tilings have a common "parent" structure and, consequently, the same symmetry group. An idealized object, namely, an infinitely refined tiling, is introduced. It is shown that the symmetry operations of this object are operations of the similarity (rotational homothety). A positive answer is given to the question about a possible composition of operations of the similarity with different singular points. It is demonstrated that the transformations of orientation-preserving aperiodic crystals are isomorphic to a discrete subgroup of the Mobius group PSL(2, C); i.e., they can be realized as discrete subgroups of the full group of motions in the Lobachevsky space. The problem of classification of the allowed types of aperiodic tilings is reduced to the procedure of enumeration of the aforementioned discrete subgroups.

Update: 5-Jun-2013

Title:
Pd2Cd11-delta (0.21 <= delta <= 0.51)-a partly disordered gamma-brass type phase and Pd0.238Cd0.762-a gamma-brass related incommensurate phase in the palladium-cadmium system
Authors:
Jana, PP; Lidin, S Author Full Names: Jana, Partha Pratim; Lidin, Sven
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 201 244-249; 10.1016/j.jssc.2013.01.044 MAY 2013
Abstract:
The Cd rich part of the Cd-Pd phase diagram was reassessed by means of synthesis and single crystal and powder X-ray diffraction. The region contains two phases that have been reported to have substantial compositional widths, Cd11Pd2 and Cd4Pd. The phase Cd11Pd2 that has previously been reported to be a disordered gamma-brass crystallizing is space group P (4) over bar 3m is here shown to crystallize in I (4) over bar 3m and the mechanism for compositional variation is explained. The phase Pd4Cd has previously been shown to constitute a phase field or a phase bundle of modulated structures and here we determine the structure of a compound Pd0.238Cd0.762 which crystallizes in the orthorhombic superspace group Fmmm(alpha 00)0s0 (F=[(1/2, 1/2, 0, 0); (1/2, 0, 1/2, 0); (0, 1/2, 1/2, 0)] with the fundamental cell dimensions a=4.687(2) angstrom, b=10.000(1) angstrom, c=14.140(2) angstrom, q=0.6432(6)a*. (C) 2013 Elsevier Inc. All rights reserved.
Title:
Magnetic transition in K4Cu4OCl10: A model system of three-dimensional spin-1/2 tetrahedra
Authors:
Fujihala, M; Zheng, XG; Morodomi, H; Kawae, T; Watanabe, I Author Full Names: Fujihala, Masayoshi; Zheng, Xu-Guang; Morodomi, Hiroki; Kawae, Tatsuya; Watanabe, Isao
Source:
PHYSICAL REVIEW B, 87 (14):10.1103/PhysRevB.87.144425 APR 30 2013
Abstract:
Isolated spin tetrahedral systems with weak intertetrahedral couplings, as have been reported for Cu2Te2O5X2 (X = Cl, Br) and the related compound Cu4Te5O12Cl4, have received much attention recently because they represent an interesting class of magnets that consist of weakly coupled magnetic clusters and, in particular, they can directly demonstrate the interplay of intertetrahedral couplings with built-in tetrahedral frustration. However, there is much debate about the structural low dimensionality of the Cu-Te-O-Cl(Br) compounds and its effect on the magnetism of the material. Here, we present a model spin tetrahedral system K4Cu4OCl10, with almost isotropic magnetic coupling within the tetrahedron and three-dimensional connection of the tetrahedra. The system enters a spin-singlet state with a susceptibility maximum at T-max = 11 K, and then enters an antiferromagnetic order at T-N = 4.4 K. The ratio T-N/T-max = 0.40 is close to the T-N/T-max = 0.38 for Cu2Te2O5Br2, which is viewed as an indicator of closeness to quantum criticality. Evidence in muon-spin rotation or relaxation suggests an incommensurate ordering. This work shows that the previously revealed ground state in anisotropically structured Cu2Te2O5X2 compounds also exists in an isotropic spin tetrahedral system. DOI: 10.1103/PhysRevB.87.144425

Update: 30-May-2013

Title:
Phase Diagrams of He-4 on Flat and Curved Environments
Authors:
Gordillo, MC; Boronat, J Author Full Names: Gordillo, M. C.; Boronat, J.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS, 171 (5-6):606-612; 10.1007/s10909-012-0790-5 JUN 2013
Abstract:
By means of diffusion Monte Carlo calculations, we obtained the phase diagrams of a first and second layer of He-4 on graphene and on the outside of different isolated armchair carbon nanotubes with radii in the range 3.42 to 10.85 . That corresponds to tubes between the (5, 5) and (16, 16) in standard nomenclature. In both cases, the ground state is either a liquid (second layer on graphene and on nanotubes whose radii is greater than similar to 7 ) or an incommensurate solid (for thinner tubes). In the former case, upon a density increase, the system undergoes a first-order phase transition to another incommensurate solid. A study of the influence of the C-He potential (isotropic or anisotropic) on the phase diagrams is also presented.
Title:
Effect of Icosahedral Quasicrystalline Fraction and Extrusion Ratio on Microstructure, Mechanical Properties, and Anisotropy of Mg-Zn-Gd-Based Alloys
Authors:
Huang, H; Yuan, GY; Wang, ZC; Chen, CL; Ding, WJ Author Full Names: Huang, Hua; Yuan, Guangyin; Wang, Zhongchang; Chen, Chunlin; Ding, Wenjiang
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 44A (6):2725-2734; 10.1007/s11661-013-1609-y JUN 2013
Abstract:
We have fabricated three types of Mg-Zn-Gd-based alloys containing the icosahedral quasicrystalline phase (I-phase) to investigate how volume fraction of the I-phase and extrusion ratio can have an impact on the microstructure, mechanical properties, and anisotropy of the as-extruded alloys. We find that grains are refined and that the ultimate tensile strength and elongation are improved as either the volume fraction of I-phase or the extrusion ratio is increased, which can be attributed to the secondary phase particle stimulate recrystallization nucleation and restrained grain boundary motion. Moreover, anisotropy is mitigated in all of the alloys as either the I-phase fraction or the extrusion ratio is increased owing to the coeffect of texture weakening and grain refinement as well as to the effect of I-phase on twinning. We also find that with the increase in the amount of the I-phase, the yield strength (YS) is decreased for the alloys extruded at a low ratio owing to the texture weakening, yet it is increased for the alloys extruded at high ratio owing to the strengthening originating from the I-phase and refined grains. The mechanical properties are improved for the alloys extruded at high ratio, which is due to their fine grains and uniform microstructure.
Title:
H-2 Physisorbed on Graphane
Authors:
Carbonell-Coronado, C; de Soto, F; Cazorla, C; Boronat, J; Gordillo, MC Author Full Names: Carbonell-Coronado, C.; de Soto, F.; Cazorla, C.; Boronat, J.; Gordillo, M. C.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS, 171 (5-6):619-625; 10.1007/s10909-012-0828-8 JUN 2013
Abstract:
We study the zero-temperature phase diagrams of H-2 adsorbed on the three structures predicted for graphane (chair, boat and washboard graphane), using a diffusion Monte Carlo technique. Graphane is the hydrogenated version of graphene, in which each carbon atom changes its hybridization to sp (3) and forms a covalent bond with a hydrogen atom. Our results show that the ground state of H-2 adsorbed on all three types of graphane is a solid, similar to the structures found both for H-2 and D-2 on graphene. When the H-2 density increases, the system undergoes a first order phase transition to a triangular incommensurate solid. This change is direct in the case of washboard graphane, but indirect via different commensurate structures in the other cases. The total hydrogen weight percentage on the three graphane types in their ground states is in the range 10 % to 12 %, depending on if one or both graphane surfaces are covered with H-2.
Title:
Structural and Superfluid Properties of the He-4 Monolayer on a C-28 Molecule
Authors:
Kim, B; Kwon, Y Author Full Names: Kim, Byeongjoon; Kwon, Yongkyung
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS, 171 (5-6):599-605; 10.1007/s10909-012-0732-2 JUN 2013
Abstract:
We have performed path-integral Monte Carlo calculations to study the adsorption of N He-4 atoms on a single C-28 fullerene molecule. Radial density distributions show a layer-by-layer growth of He-4 with the first adlayer being located at a distance of 5.3 from the center of C-28. The monolayer is found to show a commensurate structure at N=16 with each of the 16 adsorption sites on the molecular surface being occupied by one He-4 atom. As more helium atoms are adsorbed beyond N=16, the adlayer is in a mixed state consisting of 4 localized atoms at the hexagonal faces and the other atoms delocalized over the pentagonal faces. Another structurally-ordered state is observed at N=32, where the helium layer shows the same crystalline structure with an icosahedral symmetry as observed for 32 He-4 atoms on a C-60 molecule. It is found that more He-4 atoms can be squeezed into the first layer to disrupt this icosahedral structure when enough He-4 atoms are added in the second layer. Finally we observe the reentrant superfluid response of the monolayer with superfluidity being quenched completely at the ordered states of N=16 and 32.
Title:
Investigation of the electromagnon excitations in the multiferroic TbMn2O5
Authors:
Petit, S; Baledent, V; Doubrovsky, C; Lepetit, MB; Greenblatt, M; Wanklyn, B; Foury-Leylekian, P Author Full Names: Petit, S.; Baledent, V.; Doubrovsky, C.; Lepetit, M. B.; Greenblatt, M.; Wanklyn, B.; Foury-Leylekian, P.
Source:
PHYSICAL REVIEW B, 87 (14):10.1103/PhysRevB.87.140301 APR 25 2013
Abstract:
Multiferroic materials in which magnetism and ferroelectricity coexist are a time-honored subject of study, opening the route for the next generation of electronic devices. Understanding the pronounced interplay between these properties is a current challenge, especially for the realization of multiferroic devices. One of the largest reversible magnetoelectric couplings has been evidenced in TbMn2O5, the reference compound of the so-called RMn2O5 multiferroics. The origin of this strong coupling has been intensively studied from the static properties. Here we report an inelastic neutron scattering investigation of the dynamic properties in this famous compound. Our work sheds light on the electromagnon, a hybrid mode theoretically predicted in multiferroics, which couples magnetic excitations with polar lattice degrees of freedom. We were able to determine in TbMn2O5 the exchange constants of a model Heisenberg Hamiltonian and to identify the spin excitation that transforms in the electromagnon on passing from the ferroelectric and magnetically collinear phase to the low temperature incommensurate and weakly ferroelectric one. Our results point to the unusual feature of the dynamic magnetoelectric coupling in this series of multiferroics. DOI: 10.1103/PhysRevB.87.140301
Title:
Phase transitions in europium at high pressures
Authors:
Husband, RJ; Loa, I; Stinton, GW; Ackland, GJ; McMahon, MI Author Full Names: Husband, R. J.; Loa, I.; Stinton, G. W.; Ackland, G. J.; McMahon, M. I.
Source:
HIGH PRESSURE RESEARCH, 33 (1):158-164; 10.1080/08957959.2013.775280 MAR 1 2013
Abstract:
For several decades, x-ray diffraction studies on europium (Eu) metal at high pressure were complicated by the presence of a rhombo-hedral contaminant phase, hR6, which has been recognised as such only recently. Using x-ray powder diffraction, we have determined the hR6 contaminant to undergo a phase transition to a cubic phase, cI12, at 34.8(12)GPa. Consideration of the volume per Eu atom of the two contaminant phases at the same pressure suggests that they have different stoichiometries or chemical compositions. We also report a phase transition in pure Eu from the incommensurately-modulated Eu-IV phase to Eu-V between 38 and 42GPa.

Update: 22-May-2013

Title:
Magnetism of the chromium thio-spinels Fe1-xCuxCr2S4 studied using muon spin rotation and relaxation
Authors:
Kalvius, GM; Krimmel, A; Wappling, R; Hartmann, O; Litterst, FJ; Wagner, FE; Tsurkan, V; Loidl, A Author Full Names: Kalvius, G. M.; Krimmel, A.; Wappling, R.; Hartmann, O.; Litterst, F. J.; Wagner, F. E.; Tsurkan, V.; Loidl, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (18):10.1088/0953-8984/25/18/186001 MAY 8 2013
Abstract:
Powder samples of Fe1-xCuxCr2S4 with x = 0, 0.2, 0.5, 0.8 were studied, between 5 and 300 K. The results reveal that for x < 1, the magnetic order in the series is more varied than the simple collinear ferrimagnetic structure traditionally assumed to exist everywhere from the Curie point to T -> 0. In FeCr2S4 several ordered magnetic phases are present, with the ground state likely to have an incommensurate cone-like helical structure. Fe0.8Cu0.2Cr2S4 is the compound for which simple collinear ferrimagnetism is best developed. In Fe0.5Cu0.5Cr2S4 the ferrimagnetic spin structure is not stable, causing spin reorientation around 90 K. In Fe0.2Cu0.8Cr2S4 the ferrimagnetic structure is at low temperatures considerably distorted locally, but with rising temperature this disorder shows a rapid reduction, coupled to increased spin fluctuation rates. In summary, the present data show that the changes induced by the replacement of Fe by Cu have more profound influences on the magnetic properties of the Fe1-xCuxCr2S4 compounds than merely a shift of Curie temperature, saturation magnetization and internal field magnitude.
Title:
Incommensurate phases in the statistical theory of the crystalline state
Authors:
Golovko, VA Author Full Names: Golovko, V. A.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 341-354; 10.1107/S0108767313003619 3 MAY 2013
Abstract:
The paper is devoted to the elaboration of a mathematical apparatus for studying second-order phase transitions, both commensurate and incommensurate, and the properties of emerging phases on the basis of the approach in equilibrium statistical mechanics proposed earlier by the author. It is shown that the preliminary symmetry analysis for a concrete crystal can be performed analogously with the one in the Landau phenomenological theory of phase transitions. The analysis enables one to deduce a set of transcendental equations that describe the emerging phases and corresponding phase transitions. The treatment of an incommensurate phase is substantially complicated because the symmetry of the phase cannot be described in terms of customary space groups. For this reason, a strategy of representing the incommensurate phase as the limit of a sequence of long-period commensurate phases whose period tends to infinity is worked out.
Title:
Periodic entanglement I: networks from hyperbolic reticulations
Authors:
Evans, ME; Robins, V; Hyde, ST Author Full Names: Evans, Myfanwy E.; Robins, Vanessa; Hyde, Stephen T.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 241-261; 10.1107/S0108767313001670 3 MAY 2013
Abstract:
High-symmetry free tilings of the two-dimensional hyperbolic plane (H-2) can be projected to genus-3 3-periodic minimal surfaces (TPMSs). The three-dimensional patterns that arise from this construction typically consist of multiple catenated nets. This paper presents a construction technique and limited catalogue of such entangled structures, that emerge from the simplest examples of regular ribbon tilings of the hyperbolic plane via projection onto four genus-3 TPMSs: the P, D, G(yroid) and H surfaces. The entanglements of these patterns are explored and partially characterized using tools from TOPOS, GAVROG and a new tightening algorithm.
Title:
Quasirandom quasicrystals
Authors:
Hornfeck, W Author Full Names: Hornfeck, Wolfgang
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 355-364; 10.1107/S0108767313005412 3 MAY 2013
Abstract:
Two-dimensional point sets derived from pairs of quasirandom numbers generated by the bit-reversal method introduced by van der Corput exhibit features well known from the quasiperiodic binary substitution tilings derived from the rhombic tilings of Penrose and Ammann-Beenker. The concept of geometric discrepancy, a measure describing the uniformity of distribution of quasirandom sequences or point sets, is discussed from the perspective of structural chemistry.
Title:
Cluster-packing geometry for Al-based F-type icosahedral alloys
Authors:
Fujita, N; Takano, H; Yamamoto, A; Tsai, AP Author Full Names: Fujita, Nobuhisa; Takano, Hikari; Yamamoto, Akiji; Tsai, An-Pang
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 322-340; 10.1107/S0108767313005035 3 MAY 2013
Abstract:
This paper presents a new, highly stable, periodic approximant to the Al-based F-type icosahedral quasicrystals, i-Al-Pd-TM (TM = transition metals). The structure of this intermetallic Al-Pd-Cr-Fe compound is determined ab initio using single-crystal X-ray diffraction, where the space group is identified to be Pa (3) over bar and the lattice constant 40.5 angstrom. The structure is well described as a dense packing of clusters of two kinds, which are called the pseudo-Mackay-type and the mini-Bergman-type clusters. Adjacent clusters can be markedly interpenetrated, while the structure requires no glue atoms to fill in the gaps between the clusters. It is shown that the clusters are centred at the vertices of a canonical cell tiling, which corresponds to a 2 x 2 x 2 superstructure of Henley's cubic 3/2 packing, and that the parity of each vertex determines the kind of associated cluster. The proper quasi-lattice constant for describing the cluster packing is 1/tau (tau = golden mean) times the conventional one used to describe Al-based P-type icosahedral alloys. The superstructure ordering of the present approximant turns out to be of a different kind from the P-type superstructure ordering previously reported in i-Al-Pd-Mn. The present results will greatly improve the understanding of atomic structures of F-type icosahedral quasicrystals and their approximants.
Title:
Crack analysis in decagonal quasicrystals by the MLPG
Authors:
Sladek, J; Sladek, V; Krahulec, S; Zhang, C; Wunsche, M Author Full Names: Sladek, J.; Sladek, V.; Krahulec, S.; Zhang, Ch.; Wuensche, M.
Source:
INTERNATIONAL JOURNAL OF FRACTURE, 181 (1):115-126; 10.1007/s10704-013-9825-4 MAY 2013
Abstract:
A meshless method based on the local Petrov-Galerkin approach is proposed to solve initial-boundary-value crack problems in decagonal quasicrystals. These quasicrystals belong to the class of two-dimensional (2-d) quasicrystals, where the atomic arrangement is quasiperiodic in a plane, and periodic in the perpendicular direction. The ten-fold symmetries occur in these quasicrystals. The 2-d crack problem is described by a coupling of phonon and phason displacements. Both stationary governing equations and dynamic equations represented by the Bak's model with oscillations for phasons are analyzed here. Nodal points are spread on the analyzed domain, and each node is surrounded by a small circle for simplicity. The spatial variation of phonon and phason displacements is approximated by the moving least-squares scheme. After performing the spatial integrations, one obtains a system of ordinary differential equations for certain nodal unknowns. That system is solved numerically by the Houbolt finite-difference scheme as a time-stepping method.
Title:
Effects of frustration on magnetic excitations in a two-leg spin-ladder system
Authors:
Sugimoto, T; Mori, M; Tohyama, T; Maekawa, S Author Full Names: Sugimoto, Takanori; Mori, Michiyasu; Tohyama, Takami; Maekawa, Sadamichi
Source:
PHYSICAL REVIEW B, 87 (15):10.1103/PhysRevB.87.155143 APR 24 2013
Abstract:
We theoretically study the magnetic excitations in a frustrated two-leg spin-ladder system, in which antiferromagnetic exchange interactions act on the nearest-neighbor and next-nearest-neighbor bonds in the leg direction, and on the nearest-neighbor bonds in the rung direction. A dynamical spin correlation function at zero temperature is calculated using the dynamical density-matrix renormalization-group method for possible magnetic phases, i.e., columnar-dimer and rung-singlet phases. The columnar-dimer phase is characterized by multispinon excitations with a spin gap, whereas the rung-singlet phase is dominated by the triplet excitation in the rung direction. One major difference found between these two phases appears in the spectral weight of magnetic excitations, in particular, the bonding and antibonding modes in the rung direction. Therefore, we can distinguish one phase from the other by the difference in the spectral weight. Furthermore, we examine the effect of frustration on both modes in the rung-singlet phase with a perturbation theory from the strong coupling limit. The antibonding mode is shown to be stable against frustration, and a wave number with minimum excitation energy is shifted from being commensurate to being incommensurate. In contrast, the bonding mode is merged into the continuum excitation of multiple triplet excitations by increasing frustration. By comparing our results with inelastic neutron scattering experiments for BiCu2PO6, the magnitude of the magnetic exchange interactions and the ground state will be determined. DOI: 10.1103/PhysRevB.87.155143
Title:
Spin Density Wave Fluctuations and p-Wave Pairing in Sr2RuO4
Authors:
Huo, JW; Rice, TM; Zhang, FC Author Full Names: Huo, Jia-Wei; Rice, T. M.; Zhang, Fu-Chun
Source:
PHYSICAL REVIEW LETTERS, 110 (16):10.1103/PhysRevLett.110.167003 APR 18 2013
Abstract:
Recently, a debate has arisen over which of the two distinct parts of the Fermi surface of Sr2RuO4 is the active part for the chiral p-wave superconductivity exhibited. Early theories proposed p-wave pairing on the two-dimensional gamma band, whereas a recent proposal focuses on the one-dimensional (alpha, beta) bands whose nesting pockets are the source of the strong incommensurate spin density wave (SDW) fluctuations. We apply a renormalization group theory to study quasi-one-dimensional repulsive Hubbard chains and explain the form of SDW fluctuations, reconciling the absence of long-range order with their nesting Fermi surface. The mutual exclusion of p-wave pairing and SDW fluctuations in repulsive Hubbard chains favors the assignment of the two-dimensional gamma band as the source of p-wave pairing. DOI: 10.1103/PhysRevLett.110.167003
Title:
On similarity of structure of icosahedral viral capsids and shells of metallic nanoclusters
Authors:
Shevchenko, VY; Blatov, VA; Ilyushin, GD Author Full Names: Shevchenko, V. Ya.; Blatov, V. A.; Ilyushin, G. D.
Source:
GLASS PHYSICS AND CHEMISTRY, 39 (2):101-104; 10.1134/S1087659613020144 MAR 2013
Abstract:
TOPOS software has been applied for searching for topological types of viral capsids-virus shells generated by self-assembly of proteins into geometrically ordered structure (VIPERdb database). Three topological capsid types that characterize packing of capsomeres (1) in the form of 12-vertex icosahedron (its vertex are occupied with pentamers), (2) in the form of 32-vertex polyhedron (12-pentamers + 20-hexamers), and (3) in the form of 62-vertex polyhedron (12-pentamers + 50-hexamers) have been outlined. The three mentioned polyhedral shells have been presented in the form of graphs of edge nets and applied for searching for relevant nanocluster fragments in the developed database of intermetallic compounds (25808 structures). It has been established that local structures in the form of icosahedral shells can be met in 6403 (27.1%) intermetallic compounds. Thirty-two atom shells have been found in 469 (2.0%) intermetallic compounds; furthermore, they are always the second shells of Bergman nanoclusters where the first shell is icosahedron. Sixty-two atom polyhedral shells in intermetallic compounds have not been found in intermetallic compounds; however, a modified 110-atom shell has been obtained on its basis, which is a polyhedron with 72 pentagonal faces. Such a shell has been established in 18 intermetallic compounds, including quasicrystal approximants AlCa3Cd17, CaCd6, Eu3Cd19, HfNi2.15Ca3.85, etc.
Title:
Phason-induced dynamics of colloidal particles on quasicrystalline substrates
Authors:
Kromer, JA; Schmiedeberg, M; Roth, J; Stark, H Author Full Names: Kromer, Justus A.; Schmiedeberg, Michael; Roth, Johannes; Stark, Holger
Source:
EUROPEAN PHYSICAL JOURNAL E, 36 (3):10.1140/epje/i2013-13025-0 MAR 2013
Abstract:
Phasons are special hydrodynamic modes that occur in quasicrystals. The trajectories of particles due to a phasonic drift were recently studied by Kromer et al. (Phys. Rev. Lett. 108, 218301 (2012)) for the case where the particles stay in the minima of a quasicrystalline potential. Here, we study the mean motion of colloidal particles in quasicrystalline laser fields when a phasonic drift or displacement is applied and also consider the cases where the colloids cannot follow the potential minima. While the mean square displacement is similar to the one of particles in a random potential with randomly changing potential wells, there also is a net drift of the colloids that reverses its direction when the phasonic drift velocity is increased. Furthermore, we explore the dynamics of the structural changes in a laser-induced quasicrystal during the rearrangement process that is caused by a steady phasonic drift or an instantaneous phasonic displacement.
Title:
Crystal-Structure Studies of Mononuclear Iron(II) Complexes with Two-Step Spin Crossover: [Fe{5-NO2-sal-N(1,4,7,10)}] Revisited
Authors:
Kusz, J; Nowak, M; Gutlich, P Author Full Names: Kusz, Joachim; Nowak, Maria; Guetlich, Philipp
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, (5-6):832-842; SI 10.1002/ejic.201201467 FEB 2013
Abstract:
In the region of the spin transition of spin-crossover (SCO) compounds there coexist molecules in both high-spin (HS) and low-spin (LS) states. In the case of two-step spin transition, theoretical predictions and computer simulations have shown that HS and LS complex molecules should be ordered in the plateau region. Several examples that support this hypothesis are already presented in the literature. Herein, we discuss a mononuclear complex of iron(II) with two-step spin transition in terms of long-range ordering of HS and LS molecules. In such compounds, spin transition is associated with the formation of a superstructure. However, previous studies of the [Fe{5-NO2-sal-N(1,4,7,10)}] [5-NO2-sal-N(1,4,7,10) = 5-nitrosalicylaldehyde-1,4,7,10-tetraazadecane] coordination complex have not revealed the occurrence of the satellite reflections in the SCO plateau region as a typical sign of the formation of a superstructure. Re-investigations of this complex by using strong X-ray sources and a charge-coupled device (CCD) camera show that satellite reflections appear in the plateau region. This is evidence that also in this case the superstructure is formed in the plateau region with long-range ordering of the HS and LS molecules. The two-step spin transition is connected to the change of the conformer and a dramatic change in the hydrogen-bonding system.

Update: 15-May-2013

Title:
A modulated structure derived from the sigma phase in the Mo-Ni-Re system
Authors:
Yaqoob, K; Guenee, L; Cerny, R; Joubert, JM Author Full Names: Yaqoob, Khurram; Guenee, Laure; Cerny, Radovan; Joubert, Jean-Marc
Source:
INTERMETALLICS, 37 42-45; 10.1016/j.intermet.2013.01.018 JUN 2013
Abstract:
The crystal structure identification of a new Mo-Ni-Re phase was carried out. The chemical characterisation of the studied composition was performed with the help of electron probe microanalysis (EPMA) whereas X-ray diffraction (XRD) and single crystal diffraction techniques were used for structural characterisation. The characterisation results revealed that this new Mo-Ni-Re phase has a modulated phase structure. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Structural evolution and magnetization enhancement of Bi1-xTbxFeO3
Authors:
Zhang, J; Wu, YJ; Chen, XK; Chen, XJ Author Full Names: Zhang, Jing; Wu, Yu-Jie; Chen, Xiao-Kun; Chen, Xiao-Jia
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 74 (6):849-853; 10.1016/j.jpcs.2013.01.030 JUN 2013
Abstract:
The structural, vibrational, and magnetic properties of well prepared Bi1-xTbxFeO3 (x=0-0.2) powders are investigated by combining the X-ray diffraction, Raman scattering, and magnetometry measurements. It is found that partial substitution of Tb (10-12.5%) in Bi site results in a structural transformation from the rhombohedral R3c symmetry to the orthorhombic Pnma phase, accompanied by a ferroelectric-paraelectric phase transition. The magnetization of Bi1-xTbxFeO3 first gradually increases before reaching maximum at the polar-nonpolar phase boundary and then decreases for x >= 0.125 until x=0.20. The enhancement of the remnant magnetization is attributed to the suppression of the space-modulated spin structure in the rhombohedral R3c phase. Meanwhile, the reduction of the remnant magnetization in the orthorhombic Pnma phase is suggested to result from the establishment of well parallel antiferromagnetic ordering. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Evolution of magnetic and crystal structures in the multiferroic FeTe2O5Br
Authors:
Pregelj, M; Jeglic, P; Zorko, A; Zaharko, O; Apih, T; Gradisek, A; Komelj, M; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Jeglic, P.; Zorko, A.; Zaharko, O.; Apih, T.; Gradisek, A.; Komelj, M.; Berger, H.; Arcon, D.
Source:
PHYSICAL REVIEW B, 87 (14):10.1103/PhysRevB.87.144408 APR 9 2013
Abstract:
Neutron diffraction and nuclear quadrupole resonance (NQR) measurements were employed to investigate magnetic order in the nonferroelectric phase preceding the low-temperature multiferroic state in FeTe2O5Br. Refinement of the neutron diffraction data and simulations of Br-79,Br-81 NQR spectra reveal that the incommensurate magnetic ordering in the nonferroelectric state comprises amplitude-modulated magnetic moments, similar to that seen in the multiferroic state. The two ordered states differ in the orientation of the magnetic moments and phase shifts between modulation waves. Surprisingly, all symmetry restrictions for the electric polarization are absent in both states. The different ferroelectric responses of the two states are thus argued to arise from the differences in the phase shifts between certain modulation waves, which cancel out in the nonferrolectric state. DOI: 10.1103/PhysRevB.87.144408
Title:
Binary Superlattices from Colloidal Nanocrystals and Giant Polyoxometalate Clusters
Authors:
Bodnarchuk, MI; Erni, R; Krumeich, F; Kovalenko, MV Author Full Names: Bodnarchuk, Maryna I.; Erni, Rolf; Krumeich, Frank; Kovalenko, Maksym V.
Source:
NANO LETTERS, 13 (4):1699-1705; 10.1021/nl4002475 APR 2013
Abstract:
We report a new kind of long-range ordered binary superlattices comprising atomically defined inorganic clusters and colloidally synthesized nanocrystals. In a model system, we combined surfactant-encapsulated, nearly spherical giant polyoxometalate clusters containing 2.9 nm polyoxomolybdate or 2.5 nm polyoxovanadomolybdate cores with monodisperse colloidal semiconductor nanocrystals (PbS, CdSe, PbS/CdS; 4-11 nm). The results are rationalized on the basis of dense packing principles of sterically stabilized particles with predominantly hard-spherelike interparticle interactions. By varying the size-ratios and relative concentrations of constituents, we obtained known thermodynamically stable binary packings of hard-spheres such as NaCl, AlB2, and NaZn13 lattices and also CaCu5-type lattice and aperiodic quasicrystals with 12-fold symmetry. These results suggest that other kinds of cluster materials such as fullerenes and magic-sized metallic and semiconductor clusters can also be integrated into supramolecular assemblies with nanocrystals. Furthermore, synergistic effects are expected from the combination of redox and catalytic properties of polyoxometalates with excitonic and plasmonic properties of inorganic nanocrystals.
Title:
Microstructure and mechanical properties of as-cast and solution-treated Mg-Zn-Gd-based alloys reinforced with quasicrystals
Authors:
Huang, H; Yuan, GY; Tong, J; Ding, WJ Author Full Names: Huang, Hua; Yuan, Guangyin; Tong, Jian; Ding, Wenjiang
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 104 (4):380-385; 10.3139/146.110880 APR 2013
Abstract:
The microstructure and mechanical properties of as-cast and solution-treated Mg-xZn-yGd (x/y = 6, at.%) alloys reinforced with quasicrystals have been investigated. The results indicate that with the increase in the alloying elements contents, the dendritic microstructure is refined, the corresponding strength gradually increased, and the elongation gradually decreased as the increase in the second phase sizes leads to stress concentration under as-cast and solution-treated conditions. For as-cast alloys, micro-cracks originated in the alpha-Mg matrix and quasicrystals interface. The fracture mode exhibits intergranular fracture characteristics. After solution treatment, the yield strength decreased, and the ultimate tensile strength and elongation increased clearly due to the Mg2Zn3 phase dissolution and the second phase sizes decreasing. The fracture mode changes to transgranular fracture.
Title:
Linear perturbation renormalization group method for Ising-like spin systems
Authors:
Sznajd, J Author Full Names: Sznajd, J.
Source:
CONDENSED MATTER PHYSICS, 16 (1):10.5488/CMP.16.13704 2013
Abstract:
The linear perturbation group transformation (LPRG) is used to study the thermodynamics of the axial next-nearest-neighbor Ising model with four spin interactions (extended ANNNI) in a field. The LPRG for weakly interacting Ising chains is presented. The method is used to study finite field para-ferrimagnetic phase transitions observed in layered uranium compounds, UAs1-xSex, UPd2Si2 or UNi2Si2. The above-mentioned systems are made of ferromagnetic layers and the spins from the nearest-neighbor and next-nearest-neighbor layers are coupled by the antiferromagnetic interactions J(1) < 0 and J(2) < 0, respectively. Each of these systems exhibits a triple point in which two ordered phases (ferrimagnetic and incommensurate) meet the paramagnetic one, and all undergo the high field phase transition from para- to ferrimagnetic (+ + -) phase. However, if in UAs1-xSex the para-ferri phase transition is of the first order as expected from the symmetry reason, in UT2Si2 (T = Pd, Ni) this transition seems to be a continuous one, at least in the vicinity of the multicritical point. Within the MFA, the critical character of the finite field para-ferrimagnetic transition at least at one isolated point can be described by the ANNNI model supplemented by an additional, e.g., four-spin interaction. However, in LPRG approximation for the ratio kappa = J(2)/J(1) around 0.5 there is a critical value of the field for which an isolated critical point also exists in the original ANNNI model. The positive four-spin interaction shifts the critical point towards higher fields and changes the shape of the specific heat curve. In the latter case for the fields small enough, the specific heat exhibits two-peak structure in the paramagnetic phase.
Title:
Influence of heat treatment on electrochemical properties of Ti1.4V0.6Ni alloy electrode containing icosahedral quasicrystalline phase
Authors:
Liu, WQ; Zhang, SS; Wang, LM Author Full Names: Liu Wan-qiang; Zhang Shan-shan; Wang Li-min
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 22 (12):3034-3038; 10.1016/S1003-6326(11)61567-7 DEC 2012
Abstract:
The structures and electrochemical properties of the Ti1.4V0.6Ni ribbon before and after heat treatment are investigated systematically. The structure of the sample is characterized by X-ray powder diffraction analysis. Electrochemical properties including the discharge capacity, the cyclic stability and the high-rate discharge ability are tested. X-ray powder diffraction analysis shows that after heat treatment at 590 degrees C for 30 min, all samples mainly consist of the icosahedral quasicrystal phase (I-phase), Ti2Ni phase (FCC), V-based solid solution phase (BCC) and C14 Laves phase (hexagonal). Electrochemical measurements show that the maximum discharge capacity of the alloy electrode after heat treatment is 330.9 mA.h/g under the conditions that the discharge current density is 30 mA/g and the temperature is 30 degrees C. The result indicates that the cyclic stability and the high-rate discharge ability are all improved. In addition, the electrochemical kinetics of the alloy electrode is also studied by electrochemical impedance spectroscopy (EIS) and hydrogen diffusion coefficient (D).

Update: 8-May-2013

Title:
Monophosphate tungsten bronzes with pentagonal tunnels: reinvestigation through the peephole of the superspace
Authors:
Perez, O; Elcoro, L; Perez-Mato, JM; Petricek, V Author Full Names: Perez, Olivier; Elcoro, Luis; Perez-Mato, J. M.; Petricek, Vaclav
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 69 122-136; 10.1107/S0108768113002826 2 APR 2013
Abstract:
The large family of monophosphate tungsten bronzes with pentagonal tunnels (MPTBp), (PO2)4(WO3)2m with m ranging from 4 to 14, can be considered as modular structures via a description with (PO2)2(WO3)m modules related together by a symmetry operation and alternating along the z axis. Following the success of the application of the superspace for the description of the lillianites homologous series, a (3+1)-dimensional superspace model is efficiently defined to unify the structural analysis of the MPTBp. The (3+1)-dimensional model reveals hidden common characteristics such as the symmetry. An evaluation of the model for six well known members of the series was carried out from experimental data collected to this aim.
Title:
Control of magnetic interaction and ferroelectricity by nonmagnetic Ga substitution in multiferroic YMn2O5
Authors:
Kimura, H; Sakamoto, Y; Fukunaga, M; Hiraka, H; Noda, Y Author Full Names: Kimura, H.; Sakamoto, Y.; Fukunaga, M.; Hiraka, H.; Noda, Y.
Source:
PHYSICAL REVIEW B, 87 (10):10.1103/PhysRevB.87.104414 MAR 29 2013
Abstract:
We have studied the effects of substituting nonmagnetic Ga3+ for Mn3+ on dielectric and magnetic properties in multiferroic YMn2O5. Upon Ga substitution, whereby only the Mn3+ ions are selectively replaced, the commensurate magnetic phase eventually disappeared owing to the disconnection of the magnetic interaction between Mn3+ and Mn4+ ions. In contrast, the low-temperature incommensurate magnetic phase is hardly affected by Ga substitution. Precise crystal structure analyses of Ga-substituted YMn2O5 have revealed that the bonds between Mn ions along the ab plane changed markedly with increasing Ga concentration, while those along the c axis did not change at all. This indicates that the magnetic interactions along the ab plane were altered dramatically, while those along the c axis were robust against Ga substitution. From the dielectric and magnetic phase diagrams as a function of Ga substitution, we conclude that the electric polarization is predominantly induced by exchange-striction in the commensurate magnetic phase, and by an inverse Dzyaloshinskii-Moriya interaction in the incommensurate phase. DOI: 10.1103/PhysRevB.87.104414

Update: 2-May-2013

Title:
X-Ray Diffraction Observations of a Charge-Density-Wave Order in Superconducting Ortho-II YBa2Cu3O6.54 Single Crystals in Zero Magnetic Field
Authors:
Blackburn, E; Chang, J; Hucker, M; Holmes, AT; Christensen, NB; Liang, RX; Bonn, DA; Hardy, WN; Rutt, U; Gutowski, O; von Zimmermann, M; Forgan, EM; Hayden, SM Author Full Names: Blackburn, E.; Chang, J.; Huecker, M.; Holmes, A. T.; Christensen, N. B.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Ruett, U.; Gutowski, O.; v Zimmermann, M.; Forgan, E. M.; Hayden, S. M.
Source:
PHYSICAL REVIEW LETTERS, 110 (13):10.1103/PhysRevLett.110.137004 MAR 28 2013
Abstract:
X-ray diffraction measurements show that the high-temperature superconductor YBa2Cu3O6.54, with ortho-II oxygen order, has charge-density-wave order in the absence of an applied magnetic field. The dominant wave vector of the charge density wave is q(CDW) = (0, 0.328(2), 0.5), with the in-plane component parallel to the b axis (chain direction). It has a similar incommensurability to that observed in ortho-VIII and ortho-III samples, which have different dopings and oxygen orderings. Our results for ortho-II contrast with recent high-field NMR measurements, which suggest a commensurate wave vector along the a axis. We discuss the relationship between spin and charge correlations in YBa2Cu3Oy and recent high-field quantum oscillation, NMR, and ultrasound experiments. DOI: 10.1103/PhysRevLett.110.137004
Title:
Spin and Dipole Ordering in Ni2InSbO6 and Ni2ScSbO6 with Corundum-Related Structure
Authors:
Ivanov, SA; Mathieu, R; Nordblad, P; Tellgren, R; Ritter, C; Politova, E; Kaleva, G; Mosunov, A; Stefanovich, S; Weil, M Author Full Names: Ivanov, S. A.; Mathieu, R.; Nordblad, P.; Tellgren, R.; Ritter, C.; Politova, E.; Kaleva, G.; Mosunov, A.; Stefanovich, S.; Weil, M.
Source:
CHEMISTRY OF MATERIALS, 25 (6):935-945; 10.1021/cm304095s MAR 26 2013
Abstract:
The complex metal oxides Ni2InSbO6 (NISO) and Ni2ScSbO6 (NSSO) have been prepared in the form of polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties of the compounds were investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric, and magnetic measurements. The compounds adopt a trigonal structure, space group R3, of the corundum related Ni3TeO6 (NTO) type. Only one of the octahedral Ni positions (Ni(2)) of the NTO structure was found to be occupied by In (Sc). NTO has noncentrosymmetric structure and is ferroelectric below 1000 K; dielectric and second harmonic measurements suggest that also NISO and NSSO are correspondingly ferroelectric. Magnetization measurements signified antiferromagnetic ordering below T-N = 60 K (NSSO) and 76 K (NISO). The magnetic structure is formed by two antiferromagnetically coupled incommensurate helices with the spiral axis along the b-axis and propagation vector k = [0, k(y),0] with k(y) = 0.036(1) (NSSO) and k(y) = 0.029(1) (NISO). The observed structural and magnetic properties of NISO and NSSO are discussed and compared with those of NTO.

Update: 25-Apr-2013

Title:
Antiferromagnetic order in TmRhGa
Authors:
Baran, S; Hoser, A; Szytula, A Author Full Names: Baran, S.; Hoser, A.; Szytula, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 335 97-100; 10.1016/j.jmmm.2013.01.039 JUN 2013
Abstract:
Magnetic properties of ternary TmRhGa intermetallic compound were investigated by means of ac and dc magnetic susceptibility, dc magnetization and neutron diffraction at low-temperatures. The compound is an antiferromagnet with the Neel temperature equal to 3.9(2) K. At 1.5 K the Tm magnetic moments form an incommensurate sine-wave modulated structure (propagation vector (k) over right arrow = [0,0.4222(3),0]) with amplitude of modulation equal to 7.15(11)mu(B). The moments are parallel to the c-axis. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Primary Transformation Kinetics in Zr-Al-Ni-Cu-Pd Bulk Metallic Glass Correlated with Relaxation State
Authors:
Saida, J; Setyawan, AD Author Full Names: Saida, Junji; Setyawan, Albertus D.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 44A (5):1998-2003; 10.1007/s11661-012-1321-3 MAY 2013
Abstract:
The primary transformation kinetics of nanoicosahedral quasicrystalline (QC) phase formation were investigated in Zr65Al7.5Ni10Cu12.5Pd5 bulk metallic glass (BMG) in various relaxation states. A less relaxed (unrelaxed) BMG exhibited higher activation energy for atomic diffusion in the glassy structure than that of a relaxed one, which represents a change in the nucleation and grain growth kinetics of the primary phase with the relaxation state. Actually, the grain growth rate of a QC particle near the crystallization temperature was approximately 1 x 10(-9) m/s in the less relaxed BMGs, which was less than half of that in the relaxed BMGs. In contrast, the calculated homogeneous nucleation rate significantly increased in the less relaxed samples. It increased with the volume fraction transformed in the early stage. It is concluded that the relaxation state of glassy alloys markedly affects the primary transformation kinetics. The current study also indicates a necessity of development of the relaxation state for structure controlling in industrial applications of BMGs. DOI: 10.1007/s11661-012-1321-3 (C) The Minerals, Metals & Materials Society and ASM International 2012
Title:
Anionic Depolymerization Transition in IrTe2
Authors:
Oh, YS; Yang, JJ; Horibe, Y; Cheong, SW Author Full Names: Oh, Yoon Seok; Yang, J. J.; Horibe, Y.; Cheong, S. -W.
Source:
PHYSICAL REVIEW LETTERS, 110 (12):10.1103/PhysRevLett.110.127209 MAR 22 2013
Abstract:
Selenium substitution drastically increases the transition temperature of iridium ditelluride (IrTe2) to a diamagnetic superstructure from 278 to 560 K. Transmission electron microscopy experiments revealed that this enhancement is accompanied by the evolution of nonsinusoidal structure modulations from q = 1/5(10 (1) over bar) to q = 1/6(10 (1) over bar) types. These comprehensive results are consistent with the concept of the destabilization of polymeric Te-Te bonds at the transition, the temperature of which is increased by chemical and hydrostatic pressure and by the substitution of Te with the more electronegative Se. This temperature-induced depolymerization transition in IrTe2 is unique in crystalline inorganic solids. DOI: 10.1103/PhysRevLett.110.127209
Title:
Antiferromagnetic ordering in a mixed-valent cerium compound CeRuSn
Authors:
Prokes, K; Mydosh, JA; Prokhnenko, O; Stein, WD; Landsgesell, S; Hermes, W; Feyerherm, R; Pottgen, R Author Full Names: Prokes, K.; Mydosh, J. A.; Prokhnenko, O.; Stein, W. -D.; Landsgesell, S.; Hermes, W.; Feyerherm, R.; Poettgen, R.
Source:
PHYSICAL REVIEW B, 87 (9):10.1103/PhysRevB.87.094421 MAR 22 2013
Abstract:
We report the results of extensive neutron powder diffraction experiments on a ternary compound CeRuSn in a temperature range from 2 to 520 K. At room temperature CeRuSn orders in a monoclinic structure that is related to the CeCoAl type by the doubling of the c-axis parameter caused by the splitting of the original single sites for each element into two sites. Upon cooling a very broad hysteretic structural transition has been observed in CeRuSn leading to the presence of higher-ordered variants having multiple c-axis parameters. Depending on the temperatures, one or the other variant seems to be more stable, but the sample as a whole becomes multiphase. We find also evidence for further symmetry lowering at low temperatures. CeRuSn is found to exhibit an antiferromagnetic order below T-N = 2.8(1) K. The order is described by two incommensurate propagation vectors q(1) = (0,0, approximate to 0.30) and q(2) = (0,0, approximate to 0.43) with respect to the doubled crystal structure variant. Although the details of themagnetic structure remain elusive, the best agreement has been found for a complicated distorted cycloidal magnetic structure with Ce moments of approximate to 0.7 mu(B) being confined to the ac plane. DOI: 10.1103/PhysRevB.87.094421
Title:
Mercury Bismuth Chalcohalides, Hg(3)Q(2)Bi(2)Cl(8) (Q = S, Se, Te): Syntheses, Crystal Structures, Band Structures, and Optical Properties
Authors:
Wibowo, AC; Malliakas, CD; Chung, DY; Im, J; Freeman, AJ; Kanatzidis, MG Author Full Names: Wibowo, Arief C.; Malliakas, Christos D.; Chung, Duck Young; Im, Jino; Freeman, Arthur J.; Kanatzidis, Mercouri G.
Source:
INORGANIC CHEMISTRY, 52 (6):2973-2979; 10.1021/ic3023826 MAR 18 2013
Abstract:
Three quaternary mercury bismuth chalcohalides, Hg(3)Q(2)Bi(2)Cl(8) (Q = S, Se, Te), are reported along with their syntheses, crystal structures, electronic band structures, and optical properties. The compounds are structurally similar with a layer comprised of a hole perforated sheet network of [Hg(3)Q(2)](2+) (Q = S and Te) that forms by fused cyclohexane, chairlike Hg(6)Q(6) rings. The cationic charge in the network is balanced by edge-sharing monocapped trigonal-prismatic anions of [Bi2Cl8](2-) that form a two-dimensional network located between layers. Compound 1, Hg(3)Q(2)Bi(2)Cl(8), crystallizes in the monoclinic space group C12/m1 with a = 12.9381(9) angstrom, b = 7.3828(6) angstrom, c = 9.2606(6) angstrom, and beta = 116.641(5)degrees. Compound 2, Hg(3)Q(2)Bi(2)Cl(8), crystallizes in the monoclinic space group C12/c1 with a = 17.483(4) angstrom, b = 7.684(2) angstrom, c = 13.415(3) angstrom, and beta = 104.72(3)degrees. The crystals of the Hg(3)Q(2)Bi(2)Cl(8) analogue exhibit complex modulations and structural disorder, which complicated its structural refinement. Compounds 1 and 2 melt incongruently and show band gaps of 3.26 and 2.80 eV, respectively, which are in a good agreement with those from band-structure density functional theory calculations.
Title:
The Modulated Structure of Co3Al4Si2: Incommensurability and Co-Co Interactions in Search of Filled Octadecets
Authors:
Fredrickson, RT; Fredrickson, DC Author Full Names: Fredrickson, Rie T.; Fredrickson, Daniel C.
Source:
INORGANIC CHEMISTRY, 52 (6):3178-3189; 10.1021/ic302650r MAR 18 2013
Abstract:
Incommensurate modulations are increasingly being recognized as a common phenomenon in solid-state compounds ranging from inorganic materials to molecular crystals. The origins of such modulations are often mysterious, but appear to be as diverse as the compounds in which they arise. In this Article, we describe the crystal structure and bonding of Co3Al4Si2, the delta phase of the Co-Si-Al system, whose modulated structure can be traced to a central concept of inorganic chemistry: the 18 electron rule. The structure is monoclinic, conforming to the 3 + 1D superspace group C/2m(0 beta 0)s0. The basis of the crystal structure is a rod packing of columns of the fluorite (CaF2) type, a theme that is shared by the recently determined structure of Fe8Al17.4Si7.6. The columns are arranged into sheets, within which the fluorite structure's primitive cubic network of Si/Al atoms continues uninterrupted from column to column. Between the sheets, layers of interstitial Si/Al atoms occur, some of which are arranged with a periodicity incommensurate with that of the fluorite-type columns. Strong modulations in the interstitial layers result. Electronic structure calculations, using a DFT-calibrated Huckel model on a commensurate approximate structure, reveal that the complex pattern of atoms within these interstitial layers serves to distribute Si/Al atoms around the Co atoms in order to reach 18 electron counts (filled octadecets). Central to this bonding scheme is the covalent sharing of electron pairs between Co atoms. The shared electron pairs occupy orbitals that are isolobal to classical Co-Co sigma and pi bonds, but whose stability is tied to multicenter character involving bridging Si/Al atoms. Through these features, Co3Al4Si2 expands the structural and electronic manifestations of the 18 electron rule in solid-state inorganic compounds.
Title:
Quasicrystals: a brief history of the impossible
Authors:
Steinhardt, PJ Author Full Names: Steinhardt, Paul J.
Source:
RENDICONTI LINCEI-SCIENZE FISICHE E NATURALI, 24 S85-S91; 1 10.1007/s12210-012-0203-3 MAR 2013
Abstract:
The 30-year history of quasicrystals is one in which, time after time, the conventional scientific view about what is possible has been proven wrong. First, quasicrystals were thought to be mathematically impossible; then, physically impossible; then, impossible unless synthesised in the laboratory under carefully controlled conditions. One by one, these strongly held views have been disproven, the last only recently as the result of the discovery of a natural quasicrystal found in a meteorite dating back to the formation of the solar system. This paper is a brief personal perspective on this history of misunderstanding and discovery.
Title:
The aperiodic nature of incommensurately modulated structures
Authors:
Chapuis, G; Arakcheeva, A Author Full Names: Chapuis, Gervais; Arakcheeva, Alla
Source:
RENDICONTI LINCEI-SCIENZE FISICHE E NATURALI, 24 S77-S84; 1 10.1007/s12210-012-0221-1 MAR 2013
Abstract:
The discovery of aperiodic crystals is perhaps one of the most important event which has changed our vision on crystalline architectures since the discovery of diffraction 100 years ago. It was the merit of a Dutch crystallographer, P.M. de Wolff, to interpret their diffraction pattern as a three dimensional projection of a higher dimensional reciprocal lattice, idea which led directly to the generalization of the concept of crystal. Aperiodic crystals are currently described as periodic objects in higher-dimensional space, i.e. the superspace and their structures can be described in terms of 3-d cuts. Incommensurate structures, composite structures and quasicrystals all belong to aperiodic structures. Many interesting properties of superspace have been discovered which are also directly applicable to crystals in the conventional sense, i.e. crystals with 3-d periodicity. In particular the concept of structure type can be extended for a better understanding of structure relations. The notion of solid solution has also benefited from superspace considerations. Moreover, superspace is a very powerful tool for a better understanding of structure-property relations in material science, e.g. luminescence properties could be directly associated to the description of structures in superspace. Recently, this concept has been used for the prediction of new structural modifications including polytypes and even polytypic modifications of a well-known pharmaceutical product.
Title:
Effects of phase dislocations on the charge density wave dynamics in quasi-one-dimensional conductors
Authors:
Habiballah, N; Qjani, M; Arbaoui, A; Dumas, J Author Full Names: Habiballah, N.; Qjani, M.; Arbaoui, A.; Dumas, J.
Source:
SYNTHETIC METALS, 164 52-54; 10.1016/j.synthmet.2012.12.027 JAN 15 2013
Abstract:
We report in this letter a numerical simulations study of the effects of phase dislocations on the dynamic properties of charge density waves (CDW) conductors, using the one-dimensional Fukuyama, Lee and Rice (FLR) model for a weakly pinned incommensurate CDW. The results show that the CDW phase dislocations affect the local dynamical properties of CDW. (c) 2013 Elsevier B.V. All rights reserved.
Title:
Structure Determination of gamma-Brass-Related Composite Structures in the Ni-Zn System: A Guided Tour by a (3+1)-Dimensional Space Description
Authors:
Jana, PP; Lidin, S Author Full Names: Jana, Partha Pratim; Lidin, Sven
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, (1):91-98; 10.1002/ejic.201200780 JAN 2013
Abstract:
Three incommensurately modulated gamma-brass-related composite structures in the Ni-Zn system have been solved from Xray single crystal diffraction data using a 3+1 dimensional super space description. The compounds at the end points of the compositional domain NiZn3-delta (-0.09 <= delta <= 0.34) and NiZn3.30 crystallize in the orthorhombic superspace group Fmmm(alpha 00) 0s0 {F = [(1/2, 1/2, 0, 0); (1/2, 0, 1/2, 0); (0, 1/2, 1/2, 0)]} with the following fundamental cell dimensions a = 4.165(1) angstrom, b = 8.883(2) angstrom, c = 12.545(3) angstrom, q approximate to 0.6311a*; a = 4.161(2) angstrom, b = 8.876(3) angstrom, c = 12.535(4) angstrom, q approximate to 0.6314a* and a = 4.177(2) angstrom, b = 8.899(1) angstrom, c = 12.570(2) angstrom, q approximate to 0.6378a*.

Update: 17-Apr-2013

Title:
Characterization of mobile type I and type II twin boundaries in 10M modulated Ni-Mn-Ga martensite by electron backscatter diffraction
Authors:
Chulist, R; Straka, L; Lanska, N; Soroka, A; Sozinov, A; Skrotzki, W Author Full Names: Chulist, R.; Straka, L.; Lanska, N.; Soroka, A.; Sozinov, A.; Skrotzki, W.
Source:
ACTA MATERIALIA, 61 (6):1913-1920; 10.1016/j.actamat.2012.12.012 APR 2013
Abstract:
Mobile type I and type II twin boundaries mediating the magnetic field-induced strain in five-layered modulated (10M) Ni-Mn-Ga martensite were analyzed by electron backscatter diffraction. Taking into account the slight monoclinic distortion of the pseudo-tetragonal lattice, the electron backscatter diffraction study reveals domains of 0.01-1 mm thickness adjacent to the type I and type II twin boundaries. The domains differing in the modulation direction are {1 0 0) compound twins and their effect on twinning stress is discussed. Detailed analysis of type II twin boundary reveals that the domains are further internally twinned by compound {1 1 0) twins 1-15 mu m in size. An additional example of a complex twin microstructure combining type I and type II twin boundaries is presented. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Unconventional Magnetostructural Transition in CoCr2O4 at High Magnetic Fields
Authors:
Tsurkan, V; Zherlitsyn, S; Yasin, S; Felea, V; Skourski, Y; Deisenhofer, J; von Nidda, HAK; Wosnitza, J; Loidl, A Author Full Names: Tsurkan, V.; Zherlitsyn, S.; Yasin, S.; Felea, V.; Skourski, Y.; Deisenhofer, J.; von Nidda, H. -A. Krug; Wosnitza, J.; Loidl, A.
Source:
PHYSICAL REVIEW LETTERS, 110 (11):10.1103/PhysRevLett.110.115502 MAR 12 2013
Abstract:
The magnetic-field and temperature dependencies of the ultrasound propagation and magnetization of single-crystalline CoCr2O4 have been studied in static and pulsed magnetic fields up to 14 and 62 T, respectively. Distinct anomalies with significant changes in the sound velocity and attenuation are found in this spinel compound at the onset of long-range incommensurate-spiral-spin order at T-s = 27 K and at the transition from the incommensurate to the commensurate states at T-l = 14 K, evidencing strong spin-lattice coupling. While the magnetization evolves gradually with the field, steplike increments in the ultrasound clearly signal a transition into a new magnetostructural state between 6.2 and 16.5 K and at high magnetic fields. We argue that this is a high-symmetry phase with only the longitudinal component of the magnetization being ordered, while the transverse helical component remains disordered. This phase is metastable in an extended H - T phase space. DOI: 10.1103/PhysRevLett.110.115502
Title:
Microstructure and corrosion behavior of rapidly solidified Mg-Zn-Y alloys
Authors:
Nam, SW; Kim, WT; Kim, DH; Kim, TS Author Full Names: Nam, S. W.; Kim, W. T.; Kim, D. H.; Kim, T. S.
Source:
METALS AND MATERIALS INTERNATIONAL, 19 (2):205-209; 10.1007/s12540-013-2010-5 MAR 2013
Abstract:
The effect of a minor change in alloy composition on the microstructure and corrosion properties of melt spun Mg98.3-xZnxY1.7 ribbons with x=9-12 is studied by X-ray diffractometry, differential scanning calorimetry, transmission electron microscopy and a dynamic polarization test. The ribbon specimens with x=9-10 revealed an in-situ composite microstructure consisting of icosahedral quasicrystalline phase (I-phase) particles distributed in an alpha-Mg matrix. The ribbon specimens with x=11 and 12 contained a minor MgZn2 phase together with an alpha-Mg phase and I-phase. With increasing Zn content, the corrosion potential increased because of a mixed potential effect, but the formation of a MgZn2 phase deteriorated the corrosion property through preferential attack, causing an irregular boundary between the corrosion product and the substrate. These results indicate that it is important to control alloy chemistry not to form the MgZn2 phase in developing an I-phase strengthened Mg-Zn-Y alloy for structural applications.
Title:
Effect of substrate orientation on charge ordering behavior in Sm0.5Ca0.5MnO3 epitaxial films
Authors:
Li, CY; Wang, YQ; Cai, RS; Chen, YZ; Sun, JR Author Full Names: Li, C. Y.; Wang, Y. Q.; Cai, R. S.; Chen, Y. Z.; Sun, J. R.
Source:
MATERIALS LETTERS, 95 70-73; 10.1016/j.matlet.2012.12.097 MAR 1 2013
Abstract:
The effect of anisotropic strain induced by SrTiO3 (STO) substrate with different orientations on charge ordering (CO) behavior in epitaxial Sm0.5Ca0.5MnO3 (SCMO) films was investigated using cross-sectional transmission electron microscopy at 103 K. Incommensurate modulated structure caused by CO transition was observed in the SCMO film grown on a [101]-oriented STO substrate while none were found for SCMO film grown on a [100]-oriented STO substrate. This distinctive orientation-dependent CO transition is correlated with anisotropic strain in the films induced by lattice mismatch, confirming the previous results for growth on different substrates. (C) 2013 Elsevier B.V. All rights reserved.

Update: 10-Apr-2013

Title:
Field induced incommensurate-to-commensurate magnetic phase transition in Ca3Co1.8Fe0.2O6: a neutron diffraction study
Authors:
Yusuf, SM; Jain, A; Keller, L Author Full Names: Yusuf, S. M.; Jain, Anil; Keller, L.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (14):10.1088/0953-8984/25/14/146001 APR 10 2013
Abstract:
Neutron powder diffraction experiments have been performed to investigate the nature of magnetic ordering, as a function of temperature (1.5-100 K) and magnetic field (0, 2 and 4 T), in the compound Ca3Co1.8Fe0.2O6. In zero applied field, the compound orders magnetically in the incommensurate spin density wave (SDW) structure (T-N similar to 20 K). Under an applied field of similar to 2 T, an incommensurate-to-commensurate magnetic phase transition has been observed. With a further increase in the magnetic field (similar to 4 T), the commensurate magnetic structure transforms into a ferrimagnetic structure. In zero applied field, magnetic short-range ordering (SRO) coexists with the SDW long-range ordering (LRO) at all temperatures below T-N. In an applied magnetic field (2 and 4 T), SRO is converted into LRO only over the temperature range 12-20 K; however, below similar to 12 K, an increase in the volume fraction of the SRO has been observed. The correlation length for the SRO (below similar to 12 K) also gets affected by the application of a field.
Title:
Structural Phase Transition and Magnetic-Field Effect on the Modulated Structure in GdBaCo2O5+delta (delta < 0.5)
Authors:
Asaka, T; Abe, N; Kudo, T; Fukuda, K; Kimoto, K; Matsui, Y; Ishizawa, N; Arima, T Author Full Names: Asaka, T.; Abe, N.; Kudo, T.; Fukuda, K.; Kimoto, K.; Matsui, Y.; Ishizawa, N.; Arima, T.
Source:
PHYSICAL REVIEW LETTERS, 110 (12):10.1103/PhysRevLett.110.125502 MAR 19 2013
Abstract:
We investigated the crystal structures of an ordered perovskite-type cobaltate, GdBaCo2O5+delta (delta < 0.5), at elevated temperatures by transmission electron microscopy. Above the magnetic ordering temperature, we observed a first-order structural phase transition between the low-temperature tetragonal 3a(p) x 3a(p) and high-temperature orthorhombic 1a(p) x 2a(p) superstructure phases (where a(p) is the perovskite-unit cell). Upon the application of a magnetic field, an incommensurate phase emerges around the structural phase-transition temperature, which indicates a magnetic-field-induced structural phase transition via no magnetic ordering in the ordered perovskite-type cobaltate. DOI: 10.1103/PhysRevLett.110.125502
Title:
Entropic Commensurate-Incommensurate Transition
Authors:
Nikola, N; Hexner, D; Levine, D Author Full Names: Nikola, Nikolai; Hexner, Daniel; Levine, Dov
Source:
PHYSICAL REVIEW LETTERS, 110 (12):10.1103/PhysRevLett.110.125701 MAR 19 2013
Abstract:
The equilibrium properties of a minimal tiling model are investigated. The model has extensive ground state entropy, with each ground state having a quasiperiodic sequence of rows. It is found that the transition from the ground state to the high temperature disordered phase proceeds through a sequence of periodic arrangements of rows, in analogy with the commensurate-incommensurate transition. We show that the effective free energy of the model resembles the Frenkel-Kontorova Hamiltonian, but with temperature playing the role of the strength of the substrate potential, and with the competing lengths not explicitly present in the basic interactions. DOI: 10.1103/PhysRevLett.110.125701
Title:
Stabilized helical spin order and multiferroic phase coexistence in MnWO4: Consequence of 4d Ru substitution of Mn
Authors:
Yu, HW; Liu, MF; Li, X; Li, L; Lin, L; Yan, ZB; Liu, JM Author Full Names: Yu, H. W.; Liu, M. F.; Li, X.; Li, L.; Lin, L.; Yan, Z. B.; Liu, J. -M.
Source:
PHYSICAL REVIEW B, 87 (10):10.1103/PhysRevB.87.104404 MAR 11 2013
Abstract:
Most earlier work on the effect of chemical substitution in multiferroic MnWO4 has focused on the 3d transition metal substitution of Mn. In this paper, we investigate the Ru substitution of Mn in polycrystalline Mn1-xRux/2 WO4 in order to unveil the consequence of 4d transition metal substitution in terms of magnetic transitions and ferroelectricity. It is found that the Ru substitution substantially reshuffles the magnetic frustration and stabilizes the incommensurate helical spin-order phase (AF2) by partially suppressing the collinear spin-order phase (AF1 phase). The coexistence of the AF2 and AF1 phases at low temperature is suggested. Consequently, the ferroelectric polarization is remarkably enhanced, accompanied with significant response of the polarization to magnetic field. It is argued that the structural distortion and enhanced spin-orbital coupling associated with the Ru substitution may be responsible for this ferroelectricity enhancement. DOI: 10.1103/PhysRevB.87.104404
Title:
A Dugdale-Barenblatt model for a strip with a semi-infinite crack embedded in decagonal quasicrystals
Authors:
Li, W; Xie, LY Author Full Names: Li Wu; Xie Ling-Yun
Source:
CHINESE PHYSICS B, 22 (3):10.1088/1674-1056/22/3/036201 MAR 2013
Abstract:
The present study is to determine the solution of a strip with a semi-infinite crack embedded in decagonal quasicrystals, which transforms a physically and mathematically daunting problem. Then cohesive forces are incorporated into a plastic strip in the elastic body for nonlinear deformation. By superposing the two linear elastic fields, one is evaluated with internal loadings and the other with cohesive forces, the problem is treated in Dugdale-Barenblatt manner. A simple but yet rigorous version of the complex analysis theory is employed here, which involves a conformal mapping technique. The analytical approach leads to the establishment of a few equations, which allows the exact calculation of the size of cohesive force zone and the most important physical quantity in crack theory: stress intensity factor. The analytical results of the present study may be used as the basis of fracture theory of decagonal quasicrystals.
Title:
Geometry of metadislocations in approximants of quasicrystals
Authors:
Gratias, D; Quiquandon, M; Caillard, D Author Full Names: Gratias, Denis; Quiquandon, Marianne; Caillard, Daniel
Source:
PHILOSOPHICAL MAGAZINE, 93 (1-3):304-313; SI 10.1080/14786435.2012.706372 JAN 1 2013
Abstract:
We propose a simple geometrical definition of metadislocations based on the N-dim description of quasicrystals and their approximants, as being the traces of quasicrystalline dislocations with a non-zero component of their N-dim Burgers vector in the perpendicular space of the approximant. Examples are given in the octagonal canonical tiling.

Update: 3-Apr-2013

Title:
Syntheses optimization, structural and thermoelectric properties of 1/1 Tsai-type quasicrystal approximants in RE-Au-SM systems (RE = Yb, Gd and SM = Si, Ge)
Authors:
Gebresenbut, GH; Tamura, R; Eklof, D; Gomez, CP Author Full Names: Gebresenbut, Girma Hailu; Tamura, Ryuji; Eklof, Daniel; Gomez, Cesar Pay
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (13):10.1088/0953-8984/25/13/135402 APR 3 2013
Abstract:
Yb-Cd (Tsai-type) quasicrystals constitute the largest icosahedral quasicrystal family where Yb can be replaced by other rare earth elements (RE) and Cd by pairs of p- and d-block elements. YbCd6 is a prototype 1/1 Tsai-type approximant phase which has a similar local structure to the Yb-Cd quasicrystal. In this study, the syntheses of Yb15.78Au65.22Ge19.00, Gd14.34Au67.16Ge18.5 and Gd14.19Au69.87Si15.94 Tsai-type 1/1 quasicrystal approximants are optimized using the self-flux technique. The crystal structures of the compounds are refined by collecting single crystal x-ray diffraction data. The structural refinements indicated that the compounds are essentially isostructural with some differences at their cluster centers. The basic polyhedral cluster unit in all the three compounds can be described by concentric shells of icosahedra symmetry and of disordered tetrahedra and/or a rare earth atom at the cluster center. Furthermore, the thermoelectric properties of the compounds are probed and their dimensionless figures of merit are calculated at different temperatures. A significant difference is observed in their thermoelectric properties, which could arise due to the slight difference in their crystal structure and chemical composition, as we move from Ge to Si and/or Gd to Yb. Therefore, this study shows the systematic effect of the chemical substitution of structurally similar materials on their thermoelectric properties.
Title:
Impact of intermetallic precipitates on the tribological and/or corrosion performance of cast aluminium alloys: a short review
Authors:
Culliton, D; Betts, AJ; Kennedy, D Author Full Names: Culliton, D.; Betts, A. J.; Kennedy, D.
Source:
INTERNATIONAL JOURNAL OF CAST METALS RESEARCH, 26 (2):65-71; 10.1179/1743133612Y.0000000038 APR 2013
Abstract:
The role of various intermetallic precipitates (IMPs), or secondary phase particles, in governing the wear and corrosion performance characteristics of cast aluminium alloys is outlined in this brief review. Such alloys are especially important in transport applications where their low weight, low cost and recyclability make them very attractive. However, alloy wear and/or corrosion behaviour often limit their industrial application, and more work needs to be carried out to extend their use into other areas. Careful control of IMP nucleation and growth rates may be beneficial, especially in alloys exposed to corrosive environments. Silicon, copper and magnesium are all important elements for enhanced mechanical strength and tribological performance but often to the detriment of alloy corrosion resistance. Other elements such as iron may also play a significant role in deleterious IMP formation. Use of dispersoids based on novel (quasicrystals) seed alloys with similar lattice characteristics to the alpha-Al matrix may result in further exploitation of these alloys.
Title:
An x-ray scattering study of Sn2P2S6: absence of incommensurate phase up to 1 GPa
Authors:
Ondrejkovic, P; Guennou, M; Kempa, M; Vysochanskii, Y; Garbarino, G; Hlinka, J Author Full Names: Ondrejkovic, P.; Guennou, M.; Kempa, M.; Vysochanskii, Y.; Garbarino, G.; Hlinka, J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (11):10.1088/0953-8984/25/11/115901 MAR 20 2013
Abstract:
The ferroelectric phase transition in a semiconductor Sn2P2S6 single crystal has been studied by means of high-resolution synchrotron x-ray diffraction in the pressure-temperature range where an incommensurate modulated phase has been anticipated for many years. In contrast with the predictions, the present measurements reveal only a direct ferroelectric-paraelectric phase transition close to T = 100 K, p = 1.1 GPa. In the vicinity of this phase transition, a characteristic critical diffuse scattering was observed, but no satellite peaks could be resolved there. It is concluded that the earlier hypothesis about the presence of an incommensurate phase and associated Lifshitz point in the temperature-pressure phase diagram of Sn2P2S6 is incorrect.
Title:
Tetrahedron dynamics in the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and the cubic 1/1-approximant Zn6Sc
Authors:
Euchner, H; Yamada, T; Rols, S; Ishimasa, T; Kaneko, Y; Ollivier, J; Schober, H; Mihalkovic, M; de Boissieu, M Author Full Names: Euchner, H.; Yamada, T.; Rols, S.; Ishimasa, T.; Kaneko, Y.; Ollivier, J.; Schober, H.; Mihalkovic, M.; de Boissieu, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (11):10.1088/0953-8984/25/11/115405 MAR 20 2013
Abstract:
A comparison of periodic approximants and their quasicrystalline counterparts offers the opportunity to better understand the structure, physical properties and stabilizing mechanisms of these complex phases. We present a combined experimental and molecular dynamics study of the lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and compare it to recently published results obtained for the cubic 1/1-approximant Zn6Sc [1]. Both phases, quasicrystal and approximant, are built up from large atomic clusters which contain a tetrahedral shell at the cluster centre and are packed either quasiperiodically or on a bcc lattice. Using quasielastic neutron scattering and atomic scale simulations, we show that in the quasicrystal the tetrahedra display a dynamics similar to that observed in the 1/1-approximant: the tetrahedra behave as a 'single molecule' and reorient dynamically on a timescale of the order of a few ps. The tetrahedra reorientation is accompanied by a large distortion of the surrounding cluster shells which provide a unique dynamical flexibility to the quasicrystal. However, whereas in the 1/1-approximant the tetrahedron reorientation is observed down to T-c = 160 K, where a phase transition takes place, in the quasicrystal the tetrahedron dynamics is gradually freezing from 550 to 300 K, similarly to a glassy system.
Title:
On the Structure of alpha-BiFeO3
Authors:
Wang, H; Yang, CX; Lu, J; Wu, MM; Su, J; Li, K; Zhang, JR; Li, GB; Jin, TN; Kamiyama, T; Liao, FH; Lin, JH; Wu, YC Author Full Names: Wang, Hui; Yang, Chengxu; Lu, Jun; Wu, Meimei; Su, Jie; Li, Kuo; Zhang, Junrong; Li, Guobao; Jin, Tounan; Kamiyama, Takashi; Liao, Fuhui; Lin, Jianhua; Wu, Yicheng
Source:
INORGANIC CHEMISTRY, 52 (5):2388-2392; 10.1021/ic302047z MAR 4 2013
Abstract:
Polycrystalline and monocrystalline alpha-BiFeO3 crystals have been synthesized by solid state reaction and flux growth method, respectively. X-ray, neutron, and electron diffraction techniques are used to study the crystallographic and magnetic structure of alpha-BiFeO3. The present data show that alpha-BiFeO3 crystallizes in space group PI with a = 0.563 17(1) nm, b = 0.563 84(1) nm, c = 0.563 70(1) nm, alpha = 59.33(1)degrees, beta = 59.35(1)degrees, gamma = 59.38(1)degrees, and the magnetic structure of alpha-BiFeO3 can be described by space group PI with magnetic modulation vector in reciprocal space q = 0.0045a* - 0.0045b*, which is the magnetic structure model proposed by I. Sosnowska(1) applied to the new PI crystal symmetry of alpha-BiFeO3
Title:
Indentation on one-dimensional hexagonal quasicrystals: general theory and complete exact solutions
Authors:
Wu, YF; Chen, WQ; Li, XY Author Full Names: Wu, Y. F.; Chen, W. Q.; Li, X. Y.
Source:
PHILOSOPHICAL MAGAZINE, 93 (8):858-882; 10.1080/14786435.2012.735772 MAR 1 2013
Abstract:
This paper presents a general account of the indentation responses of a one-dimensional hexagonal quasicrystal half-space pressed by an axisymmetric rigid punch. Based on Green's functions of the half-space subjected to point sources on the surface, the mixed boundary value problem is transformed to integral equations and solved exactly using the results of the potential theory method. Explicit expressions for the generalised pressures and indentation forces are derived for three common indenters (cylinder, cone and approximate sphere) in a systematic manner. For conical and spherical indenters, relations between the contact radius and indentation loads are determined. The coupling phononphason fields in the half-space under indentation are accurately expressed in terms of elementary functions. Numerical calculations are performed and discussions on related physical phenomena are given. The present exact solutions can serve as benchmarks for approximate or numerical analyses and can guide the experimental characterisation of material properties of quasicrystals.
Title:
Incommensurate antiferromagnetism in a pure spin system via cooperative organization of local and itinerant moments
Authors:
Feng, YJ; Wang, JY; Silevitch, DM; Mihaila, B; Kim, JW; Yan, JQ; Schulze, RK; Woo, N; Palmer, A; Ren, Y; van Wezel, J; Littlewood, PB; Rosenbaum, TF Author Full Names: Feng, Yejun; Wang, Jiyang; Silevitch, D. M.; Mihaila, B.; Kim, J. W.; Yan, J. -Q.; Schulze, R. K.; Woo, Nayoon; Palmer, A.; Ren, Y.; van Wezel, Jasper; Littlewood, P. B.; Rosenbaum, T. F.
Source:
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 110 (9):3287-3292; 10.1073/pnas.1217292110 FEB 26 2013
Abstract:
Materials with strong correlations are prone to spin and charge instabilities, driven by Coulomb, magnetic, and lattice interactions. In materials that have significant localized and itinerant spins, it is not obvious which will induce order. We combine electrical transport, X-ray magnetic diffraction, and photoemission studies with band structure calculations to characterize successive anti-ferromagnetic transitions in GdSi. GdSi has both sizable local moments and a partially nested Fermi surface, without confounding contributions from orbital effects. We identify a route to incommensurate order where neither type of moment dominates, but is rooted in cooperative feedback between them. The nested Fermi surface of the itinerant electrons induces strong interactions between local moments at the nesting vector, whereas the ordered local moments in turn provide the necessary coupling for a spin-density wave to form among the itinerant electrons. This mechanism echoes the cooperative interactions between electrons and ions in charge-density-wave materials, and should be germane across a spectrum of transition-metal and rare-earth intermetallic compounds.
Title:
Morphology-controlled synthesis, characterization, and luminescence properties of KEu(MoO4)(2) microcrystals
Authors:
Wu, T; Liu, YF; Lu, YN; Wei, L; Gao, H; Chen, H Author Full Names: Wu, Tao; Liu, Yunfei; Lu, Yinong; Wei, Ling; Gao, Hong; Chen, Hu
Source:
CRYSTENGCOMM, 15 (14):2761-2768; 10.1039/c3ce27073d 2013
Abstract:
Large-scale one-dimensional (1D) rod-like and octagonal-like KEu(MoO4)(2) microcrystals were successfully synthesized by a simple, environmental friendly, and low cost molten salt method using halons (KCl or KBr) as flux. The as-prepared products were characterized by X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED) and photoluminescence (PL) spectrometry. The results show that the reaction parameters, including reaction temperature and reaction time, played important roles on the phase structures and morphologies of the final products. The possible growth process of 1D rod-like KEu(MoO4)(2) was proposed based on the time-dependent shape evolution and HRTEM analysis, which followed oriented aggregation and Ostwald ripening. The results of SAED and HRTEM investigations indicated an incommensurate modulated structure in the rod-like KEu(MoO4)(2), and all the reflections can be expressed as ha* + kb* + lc* + mq, where m is an integer, and modulated vector q = 0.182b* + 0.156c*. Room temperature photoluminescence spectra of KEu(MoO4)(2) microcrystals reveal a strong red emission via D-5(0) -> F-7(2) transition at 615 nm, and the 1D rod-like microcrystals own the enhanced intensity compared with the octagonal-like ones.
Title:
Synthesis, growth and characterization of 4-bromo-4 '-nitrobenzylidene aniline (BNBA): a novel nonlinear optical material with a (3+1)-dimensional incommensurately modulated structure
Authors:
Subashini, A; Leela, S; Ramamurthi, K; Arakcheeva, A; Stoeckli-Evans, H; Petricek, V; Chapuis, G; Pattison, P; Reji, P Author Full Names: Subashini, Ashokkumar; Leela, Sundararaman; Ramamurthi, Kandasamy; Arakcheeva, Alla; Stoeckli-Evans, Helen; Petricek, Vaclav; Chapuis, Gervais; Pattison, Philip; Reji, Philip
Source:
CRYSTENGCOMM, 15 (13):2474-2481; 10.1039/c3ce26663j 2013
Abstract:
The organic nonlinear optical material of 4-bromo-4'-nitrobenzylidene aniline (BNBA, C13H9BrN2O2), a new derivative of benzylideneaniline family, was synthesized and purified by repeated recrystallization. Single crystals of BNBA were grown in acetone solvent by slow evaporation at room temperature. Its (3+1-)dimensional incommensurately modulated structure was elucidated from single crystal X-ray diffraction data obtained at 173 K. The non-centrosymmetric structure was solved and refined in the monoclinic superspace group A2(alpha 0 gamma)0; the unit cell parameters are a = 10.5217(10) angstrom, b = 16.2535(16) angstrom, c = 7.4403(7) angstrom, beta = 110.709(7)degrees, modulation vector q = 0.0658(1)a(star)-0.2658(1)c(star). At 290 K, the structure is partially disordered, however, the local structure of domains is identical to that at 173 K. The H-1 and C-13 NMR and Fourier Transform Infrared and FT-Raman spectroscopic studies confirmed the molecular structure. The Kurtz powder second-harmonic generation (SHG) test reveals that the SHG efficiency of BNBA is about 9.4 times higher than that of potassium dihydrogen phosphate. According to the thermogravimetric, differential thermal and differential scanning calorimetric analyses, BNBA is a stable phase starting from room temperature and up to the melting point, 436 K. The optical nonlinearity of BNBA was investigated at 532 nm using 5 ns laser pulses, employing the open aperture Z-scan technique.

Update: 27-Mar-2013

Title:
Critical phenomena in higher dimensional spaces: The hexagonal-to-orthorhombic phase transition in aperiodic n-nonadecane/urea
Authors:
Mariette, C; Guerin, L; Rabiller, P; Ecolivet, C; Garcia-Orduna, P; Bourges, P; Bosak, A; de Sanctis, D; Hollingsworth, MD; Janssen, T; Toudic, B Author Full Names: Mariette, C.; Guerin, L.; Rabiller, P.; Ecolivet, C.; Garcia-Orduna, P.; Bourges, P.; Bosak, A.; de Sanctis, D.; Hollingsworth, Mark D.; Janssen, T.; Toudic, B.
Source:
PHYSICAL REVIEW B, 87 (10):10.1103/PhysRevB.87.104101 MAR 4 2013
Abstract:
Upon cooling, the aperiodic inclusion compound n-nonadecane/urea presents a hexagonal-to-orthorhombic group-subgroup phase transition at T-cl that increases the structure's superspace dimensionality from four to five. This paper reports on pretransitional phenomena in such a high-dimensional space, generalizing the critical results previously reported at a lower dimensionality. Very high-resolution diffraction data reveal anomalously large correlation lengths along the aperiodic direction, with all correlation lengths diverging at T-cl. This could be explained by low-frequency phason excitations that soften at T-cl at the critical wave vector, in accordance with an increase in the critical diffuse scattering intensity. DOI: 10.1103/PhysRevB.87.104101
Title:
The composite structure of mixed tau-(Ag, Cu)(x)V2O5 bronzes Evidence for T dependant guest-species ordering and mobility
Authors:
Hermes, W; Dolle, M; Rozier, P; Lidin, S Author Full Names: Hermes, Wilfred; Dolle, Mickael; Rozier, Patrick; Lidin, Sven
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 199 84-89; 10.1016/j.jssc.2012.11.029 MAR 2013
Abstract:
The complex structural behavior of tau-[AgCu](similar to 0.92)V4O10 has been elucidated by single crystal X-ray diffraction and thermal analysis. The tau-phase region is apparently composed of several distinct phases and this study identifies at least three: tau(1rt) tau(2rt) and tau(1t), tau(1rt) and tau(2rt) have slightly different compositions and crystal habits. Both phases transform to Tit at low temperature. The room temperature modification tau(1rt) crystallizes in an incommensurately modulated structure with monoclinic symmetry C2(0 beta 1/2) [equivalent to no 5.4, B2(01/2 gamma) in the Intnl. Tables for Crystallography, Volume C] and the cell parameters a=11.757(4) angstrom, b=3.6942(5) angstrom c = 9.463(2) beta=114.62(2)degrees and the q-vector (0 0.92 1/2), but it is more convenient to transform this to a setting with a non-standard centering X=(1/2 1/20 0; 0 0 1/2 1/2; 1/2 1/2 1/2 1/2;) and an axial q vector (00.92 0). The structure features a vanadate host lattice with Cu and Ag guests forming an incommensurate composite. The structural data indicates perfect Ag/Cu ordering. At low temperature this modification is replaced by a triclinic phase characterized by two independent q-vectors. The tau(2rt) phase is similar to the low temperature modification tau(lt) but the satellite reflections are generally more diffuse. (C) 2012 Elsevier Inc. All rights reserved.

Update: 20-Mar-2013

Title:
Influence of gamma ' nanometric particles on martensitic transformation and twinning structure of L1(0) martensite in Co-Ni-Ga ferromagnetic shape memory single crystals
Authors:
Kireeva, IV; Pons, J; Picornell, C; Chumlyakov, YI; Cesari, E; Kretinina, IV Author Full Names: Kireeva, I. V.; Pons, J.; Picornell, C.; Chumlyakov, Yu. I.; Cesari, E.; Kretinina, I. V.
Source:
INTERMETALLICS, 35 60-66; 10.1016/j.intermet.2012.10.018 APR 2013
Abstract:
Ageing treatments at 620 K performed in ferromagnetic Co49Ni21Ga30 shape memory single crystals have been found to generate dense dispersions of nanometric gamma' precipitates in the austenitic matrix. These particles have a strong influence on the B2-L1(0) martensitic transformation, decreasing the overall transformation temperatures and enhancing the transformation range (difference between the temperatures for start and finish of transformation) and hysteresis. The martensitic microstructure is strongly affected as well, in such a way that the thickness of martensitic twins depends on the size and shape of particles (spherical or elongated). The results indicate that, in case of precipitation of spherical particles with diameters similar to 3-5 nm, the martensitic twins can absorb the particles and the twin thickness is still considerably larger than the precipitate diameter, while growth of larger and elongated particles with a length of 10-25 nm leads to the formation of tiny twins in between the particles with thickness of similar to 3-4 nm. These small martensite twins present an additional internal modulation and satellite spots in the diffraction pattern. (C) 2012 Elsevier Ltd. All rights reserved.
Title:
Distribution of cations at two tetrahedral sites in Ca2MgSi2O7-Ca2Fe3+AlSiO7 series synthetic melilite and its relation to incommensurate structure
Authors:
Hamada, M; Akasaka, M Author Full Names: Hamada, Maki; Akasaka, Masahide
Source:
PHYSICS AND CHEMISTRY OF MINERALS, 40 (3):259-270; 10.1007/s00269-013-0566-8 MAR 2013
Abstract:
Synthetic melilites on the join Ca2MgSi2O7 (Ayenkermanite: Ak)-Ca2Fe3+AlSiO7 (ferrialuminium gehlenite: FAGeh) were studied using X-ray powder diffraction and Fe-57 Mossbauer spectroscopic methods to determine the distribution of Fe3+ between two different tetrahedral sites (T1 and T2), and the relationship between ionic substitution and incommensurate (IC) structure. Melilites were synthesized from starting materials with compositions of Ak(100), Ak(80)FAGeh(20), Ak(70)FAGeh(30) and Ak(50)FAGeh(50) by sintering at 1,170-1,350 A degrees C and 1 atm. The average chemical compositions and end-member components, Ak, FAGeh and Geh (Ca2Al2SiO7), of the synthetic melilites were Ca2.015Mg1.023Si1.981O7 (Ak(100)), Ca2.017Mg0.788Fe (0.187) (3+) Al0.221Si1.791O7 (Ak(78)FAGeh(19)Geh(3)), Ca1.995Mg0.695Fe (0.258) (3+) Al0.318Si1.723O7 (Ak(69)FAGeh(25)Geh(6)) and Ca1.982Mg0.495Fe (0.449) (3+) Al0.519Si1.535O7 (Ak(49)FAGeh(44)Geh(7)), respectively. Rietveld refinements using X- ray powder diffraction data measured using CuK (alpha) -radiation at room temperature converged successfully with goodness-of-fits of 1.15-1.26. The refined Fe occupancies at the T1 and T2 sites and the Mg and Si contents determined by electron microprobe analysis gave the site populations of [0.788Mg + 0.082Fe(3+) + 0.130Al](T1)[0.104Fe(3+) + 0.104Al + 1.792Si](T2) for Ak(78)FAGeh(19)Geh(3), [0.695Mg + 0.127Fe(3+) + 0.178Al](T1)[0.132Fe(3+) + 0.144Al + 1.724Si](T2) for Ak(69)FAGeh(25)Geh(6) and [0.495Mg + 0.202Fe(3+) + 0.303Al](T1)[0.248Fe(3+) + 0.216Al + 1.536Si](T2) for Ak(49)FAGeh(44)Geh(7) (apfu: atoms per formula unit), respectively. The results indicate that Fe3+ is distributed at both the T1 and the T2 sites. The mean T1-O distance decreases with the substitution of Fe3+ + Al3+ for Mg2+ at the T1 site, whereas the mean T2-O distance increases with substitution of Fe3+ + Al3+ for Si4+ at the T2 site, causing decrease in the a dimension and increase in the c dimension. However, in spite of the successful Rietveld refinements for the X-ray powder diffraction data measured using CuK (alpha)-radiation at room temperature, each Bragg reflection measured using CuK (alpha 1)-radiation at room temperature showed weak shoulders, which were not observed in those measured at 200 A degrees C. The Mossbauer spectra of the melilites measured at room temperature consist of two doublets assigned to Fe3+ at the T1 site and two or three doublets to Fe3+ at the T2 site, implying the existence of multiple T1 and T2 sites with different site distortions. These facts can be interpreted in terms of the IC structure in all synthetic melilites at room temperature, respectively. The results of Mossbauer analysis indicate that the IC structure in melilite is caused by not only known multiple T1 site, but also multiple T2 site at room temperature.
Title:
Energy-dependent crossover from anisotropic to isotropic magnetic dispersion in lightly doped La1.96Sr0.04CuO4
Authors:
Matsuda, M; Granroth, GE; Fujita, M; Yamada, K; Tranquada, JM Author Full Names: Matsuda, M.; Granroth, G. E.; Fujita, M.; Yamada, K.; Tranquada, J. M.
Source:
PHYSICAL REVIEW B, 87 (5):10.1103/PhysRevB.87.054508 FEB 21 2013
Abstract:
Inelastic neutron-scattering experiments have been performed on lightly doped La1.96Sr0.04CuO4, which shows diagonal incommensurate spin correlations at low temperatures. We previously reported that this crystal, with a single orthorhombic domain, exhibits the "hourglass" dispersion at low energies [Phys. Rev. Lett. 101, 197001 (2008)]. In this paper, we investigate in detail the energy evolution of the magnetic excitations up to 65 meV. It is found that the anisotropic excitations at low energies, dispersing only along the spin modulation direction, cross over to an isotropic, conical dispersion that resembles spin waves in the parent compound La2CuO4. The change from twofold to full symmetry on crossing the waist of the hourglass reproduces behavior first identified in studies of underdoped YBa2Cu3O6+x. We discuss the significance of these results. DOI: 10.1103/PhysRevB.87.054508
Title:
Wavefunctions, quantum diffusion, and scaling exponents in golden-mean quasiperiodic tilings
Authors:
Thiem, S; Schreiber, M Author Full Names: Thiem, Stefanie; Schreiber, Michael
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (7):10.1088/0953-8984/25/7/075503 FEB 20 2013
Abstract:
We study the properties of wavefunctions and the wavepacket dynamics in quasiperiodic tight-binding models in one, two, and three dimensions. The atoms in the one-dimensional quasiperiodic chains are coupled by weak and strong bonds aligned according to the Fibonacci sequence. The associated d-dimensional quasiperiodic tilings are constructed from the direct product of d such chains, which yields either the hypercubic tiling or the labyrinth tiling. This approach allows us to consider fairly large systems numerically. We show that the wavefunctions of the system are multifractal and that their properties can be related to the structure of the system in the regime of strong quasiperiodic modulation by a renormalization group (RG) approach. We also study the dynamics of wavepackets to get information about the electronic transport properties. In particular, we investigate the scaling behaviour of the return probability of the wavepacket with time. Applying again the RG approach we show that in the regime of strong quasiperiodic modulation the return probability is governed by the underlying quasiperiodic structure. Further, we also discuss lower bounds for the scaling exponent of the width of the wavepacket and propose a modified lower bound for the absolute continuous regime.
Title:
Correlating scanning tunneling spectroscopy with the electrical resistivity of Al-based quasicrystals and approximants
Authors:
Mader, R; Widmer, R; Groning, P; Steurer, W; Groning, O Author Full Names: Maeader, Ruben; Widmer, Roland; Groening, Pierangelo; Steurer, Walter; Groening, Oliver
Source:
PHYSICAL REVIEW B, 87 (7):10.1103/PhysRevB.87.075425 FEB 19 2013
Abstract:
We present detailed low-temperature scanning tunneling spectroscopy (STS) investigations of the local electronic density of states (DOS) on the fivefold and twofold i-Al70Pd21Mn9; pseudo tenfold. xi'-Al72Pd25Mn3; tenfold d-Al77Ni17Co6; twofold-(12110) d-Al72.9Ni10.4Co16.7; (100) Y-Al75.8Ni2.1Co22.1; and (111) Al surface in the range of +/- 1 eV around the Fermi energy. All these quasicrystals and approximants exhibit the theoretically predicted electronic pseudogap. We observe no evidence for a correlation between the depth of this pseudogap, as measured by STS, and the remarkably high electrical resistivity of the investigated quasicrystals and approximants. A parametrization of the spatial variability of STS spectra is introduced as a measure of the magnitude of the electron localization for a given system. The resulting (S) over cap parameter is found to be proportional to the square root of the electrical resistivity. This finding supports the validity of interpreting spatial variations of fine-structure features in the STS spectra of Al-based quasicrystals and approximants in terms of electron localization. DOI: 10.1103/PhysRevB.87.075425
Title:
Phase separation of antiferromagnetic ground states in systems with imperfect nesting
Authors:
Rakhmanov, AL; Rozhkov, AV; Sboychakov, AO; Nori, F Author Full Names: Rakhmanov, A. L.; Rozhkov, A. V.; Sboychakov, A. O.; Nori, Franco
Source:
PHYSICAL REVIEW B, 87 (7):10.1103/PhysRevB.87.075128 FEB 19 2013
Abstract:
We analyze the phase diagram for a system of weakly coupled electrons having an *electron-* and a hole-band with imperfect nesting. Namely, both bands have spherical Fermi surfaces, but their radii are slightly different, with a mismatch proportional to the doping. Such a model is used to describe the antiferromagnetism of chromium and its alloys, pnictides, AA-stacked graphene bilayers, as well as other systems. Here we show that the uniform ground state of this model is unstable with respect to electronic phase separation in a wide range of model parameters. Physically, this instability occurs due to the competition between commensurate and incommensurate antiferromagnetic states and could be of importance for other models with imperfect nesting. DOI: 10.1103/PhysRevB.87.075128
Title:
Nb-Nb Interactions Define the Charge Density Wave Structure of 2H-NbSe2
Authors:
Malliakas, CD; Kanatzidis, MG Author Full Names: Malliakas, Christos D.; Kanatzidis, Mercouri G.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 135 (5):1719-1722; 10.1021/ja3120554 FEB 6 2013
Abstract:
2H-NbSe2 is a canonical Charge-Density-Wave (CDW) layered material the structural details of which remained elusive. We report the detailed structure of 2H-NbSe2 below the CDW transition using a (3 + 2)-dimensional crystallographic approach on single crystal X-ray diffraction data collected at 15 K. Intensities of main reflections as well as CDW satellites of first order were measured. Quantitative information about the magnitude of the structural distortions and clustering of Nb atoms were extracted from the refined model. The Nb-Nb distances were found to distort between 3.4102(8) and 3.4928(8) angstrom in the CDW phase from the average undistorted distance of 3.4583(4) angstrom.
Title:
Precipitation of quasicrystal approximant phases in an Al-Mg-Cu-Ge alloy
Authors:
Xia, JH; Sha, G; Chen, ZG; Liao, XZ; Liu, HW; Ringer, SP Author Full Names: Xia, J. H.; Sha, G.; Chen, Z. G.; Liao, X. Z.; Liu, H. W.; Ringer, S. P.
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 93 (2):77-84; 10.1080/09500839.2012.745016 FEB 1 2013
Abstract:
Cube-shaped precipitates in the peak-aged Al4.0Mg1.5Cu0.25Ge (wt.%) alloy were found to exhibit a pseudo five-fold symmetry in their electron diffraction patterns along the ?110? and ?113? zone axes of the Al matrix. These strengthening precipitates, designated as the Z, possess a structure in a transition state from an icosahedral quasicrystal phase to a face-centred cubic (FCC) quasicrystal approximant phase. After prolonged ageing, the Z phase transforms into the FCC equilibrium Z phase having atoms in a periodic icosahedral arrangement.
Title:
Stabilization of Decatellurium Molecules in Isolated and Concatenated Clusters
Authors:
Gunther, A; Isaeva, A; Ruck, M Author Full Names: Guenther, Anja; Isaeva, Anna; Ruck, Michael
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 639 (2):254-260; SI 10.1002/zaac.201200430 FEB 2013
Abstract:
Black, shiny crystals of the molecular cluster compounds (Te10)[M(TeX4)(TeX3)]2 (M/X = Rh/Cl (1), Ir/Br (2)), (Te10)[Ru(TeI4)(TeI2)]2 (3), (Te10)[M(TeI4)(TeI2)]2(TeI4)(Te2I2) (M = Rh (4), Ir (5)) as well as the one-dimensional cluster polymer (Te10I2)[Ir(TeI4)]2(Te4)I2 (6) were synthesized by melting reactions of an electron-rich transition metal M (M = Ru, Rh, Ir) with tellurium and TeX4 (X = Cl, Br, I). X-ray diffraction on single-crystals revealed that the compounds crystallize in the triclinic space group type P$\bar{1}$. 4 and 5 show [3+1]-dimensional modulations of their structures. All compounds contain binuclear complexes with central -4:4-bridging Te10 units and terminal halogenidotellurate(II) groups. Each of the transition metal cations is in a slightly distorted octahedral coordination by six tellurium atoms; the two [MTe6] octahedra share a common edge. With the tellurium atoms acting as electron-pair donors, the 18 electron rule is fulfilled for the electrophilic M atoms. The central tricyclo[5.1.1.13, 5]-decatellurium molecule consists of two ecliptically stacked Te4 rings, which are linked through two tellurium atoms. The symmetric or asymmetric 3c4e bonds along these almost linear bridges are in analogy to polyanionic forms of tellurium, while the tricyclic conformation is stabilized by the strong bonding to the transition-metal cations. Multi-center bonding (3c4e) is also present in the terminal square [Te+IIX4]2 and the T-shaped [Te+IIX3] groups. The crystal structures of 4 and 5 are organized in layers of (Te10)[M(TeI4)(TeI2)]2n+ clusters (n 2) that are quite robust upon oxidation or reduction as shown by molecular calculations. These clusters alternate with incommensurately modulated layers that probably consist of TeI42 anions and a previously unknown Te2I2 molecule. The uncertainty arises primarily from equal scattering powers of I and Te atoms as well as from the known flexibility of the electron count of the Te10 unit. In 6, neutral Te4 rings concatenate (Te10I2)[Ir(TeI4)]2 clusters into chains, which run parallel to the a axis.
Title:
Magnetoelectric coupling driven by inverse magnetostriction in multiferroic BiMn3Mn4O12
Authors:
Gauzzi, A; Rousse, G; Mezzadri, F; Calestani, GL; Andre, G; Bouree, F; Calicchio, M; Gilioli, E; Cabassi, R; Bolzoni, F; Prodi, A; Bordet, P; Marezio, M Author Full Names: Gauzzi, A.; Rousse, G.; Mezzadri, F.; Calestani, G. L.; Andre, G.; Bouree, F.; Calicchio, M.; Gilioli, E.; Cabassi, R.; Bolzoni, F.; Prodi, A.; Bordet, P.; Marezio, M.
Source:
JOURNAL OF APPLIED PHYSICS, 113 (4):10.1063/1.4789350 JAN 28 2013
Abstract:
Inserting both polar A and magnetic B ions in a same crystalline phase, such as A = Bi3+, B = Fe3+ or Mn3+ in simple perovskites ABO(3), has been successful in achieving multiferroic properties with large ferroelectric and magnetic orders. However, modest magnetoelectric couplings have been hitherto reported, thus preventing any application for future electronics. By means of neutron diffraction, we found a large uniform C-type modulation of an E-type antiferromagnetic structure of the Mn3+ ions in the quadruple perovskite BiMn3Mn4O12. A symmetry analysis indicates that this modulation is induced by the internal strain created by the polar Bi3+ ion, which gives evidence of a large magnetoelectric coupling driven by inverse magnetostriction. This modulation is indeed absent in the isomorphic and isovalent compound LaMn3Mn4O12 containing the nonpolar La3+ ion. Our analysis indicates that this coupling mechanism is effective owing to the symmetry-limited structural distortions and inhomogeneities characteristic of the quadruple perovskite structure, thus preventing the release of the strain. We conclude that internal strain is a key control parameter to achieve large magnetoelectric couplings in proper ferroelectrics. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789350]

Update: 14-Mar-2013

Title:
Magnetic structures of Er5Rh4Ge10 compound
Authors:
Penc, B; Hofmann, M; Sikora, W; Szytula, A Author Full Names: Penc, B.; Hofmann, M.; Sikora, W.; Szytula, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 332 114-117; 10.1016/j.jmmm.2012.11.036 APR 2013
Abstract:
A powder neutron diffraction measurement of Er5Rh4Ge10 is reported. This compound crystallizes in the tetragonal Sc5Co4Si10-type structure (space group P4/mbm) in which the Er atoms occupy three different sites. The neutron diffraction measurements indicate antiferromagnetic order with the Neel temperature T-N=5.5 K. Below T-N an additional phase transition connected with the change of the magnetic structure is observed at 4.3 K. At low temperatures the Er moments form a sine-wave modulated structure with the propagation vector k=(1/4, 1/4, 0) for 1.5 K < T < 4.2 K and (113, 113, 0) for 4.2 K up to T-N. The values of the magnetic moments are different in the different sublattices and all are parallel to the c-axis. Determined magnetic structures are compared to the results from symmetry analysis. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Fifty years of aperiodic crystals (vol A68, pg 667, 2012)
Authors:
Janssen, T Author Full Names: Janssen, T.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 207-207; 10.1107/S0108767313000238 Part 2 MAR 2013
Title:
Convex polyhedral tilings hidden in crystals and quasicrystals
Authors:
Oda, T Author Full Names: Oda, Tadao
Source:
REVISTA DE LA REAL ACADEMIA DE CIENCIAS EXACTAS FISICAS Y NATURALES SERIE A-MATEMATICAS, 107 (1):123-143; SI 10.1007/s13398-012-0078-2 MAR 2013
Abstract:
Alattice in a Euclidean space gives rise to facet-to-facet and space-filling convex polyhedral tilings called the Voronoi tiling and its dual Delaunay tiling of the Euclidean space. Given a subspace of the Euclidean space, we develop a systematic way of constructing facet-to-facet and space-filling convex polyhedral tilings of the subspace called the Namikawa tilings, which are generalization of the Delaunay tiling. Our results here amplify the author's previous work with Seshadri that was obtained as a by-product of Geometric Invariant Theory in algebraic geometry. In the orthonormal setting where the lattice is spanned by an orthonormal basis of the ambient Euclidean space, the method of Namikawa tilings turns out to be the "cut and project" method relevant not only to periodic convex polyhedral tilings hidden in crystals but also to aperiodic convex polyhedral tilings hidden in quasicrystals. In another paper, the author showed that a Voronoi tiling is hidden in the "standard realization", in the sense of Kotani and Sunada, of crystals in the case of maximal abelian covering of finite graphs. In this connection, we give an affirmative answer to a question raised by Kotani to the effect that the crystal lies in the 1-skeleton of a nondegenerate convex polyhedral tiling that is a subdivision of the Voronoi tiling appearing in the other paper of the author.
Title:
Multidimensional paperfolding systems
Authors:
Ben-Abraham, SI; Quandt, A; Shapira, D Author Full Names: Ben-Abraham, Shelomo I.; Quandt, Alexander; Shapira, Dekel
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 123-130; 10.1107/S010876731204531X Part 2 MAR 2013
Abstract:
Algorithms for constructing aperiodic structures produce templates for the nanofabrication of arrays for applications in photonics, phononics and plasmonics. Here a general multidimensional recursion rule is presented for the regular paperfolding structure by straightforward generalization of the one-dimensional rule. As an illustrative example the two-dimensional version of the paperfolding structure is explicitly constructed, its symbolic complexity referred to rectangles computed and its Fourier transform shown. The paperfolding structures readily yield novel 'paperfolding' tilings. Explicit formulas are put forward to count the number of folds in any dimension. Finally, possible generalizations of the dragon curve are discussed.
Title:
Enhanced fatigue durability of Al-6 Mg alloy by applying ultrasonic impact peening: Effects of surface hardening and reinforcement with AlCuFe quasicrystalline particles
Authors:
Mordyuk, BN; Prokopenko, GI; Milman, YV; Iefimov, MO; Sameljuk, AV Author Full Names: Mordyuk, B. N.; Prokopenko, G. I.; Milman, Yu V.; Iefimov, M. O.; Sameljuk, A. V.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 563 138-146; 10.1016/j.msea.2012.11.061 FEB 15 2013
Abstract:
Composite layer reinforced with quasicrystalline (QC) Al63Cu25Fe12 particles was fabricated on the surface of Al-6 Mg alloy specimens by ultrasonic impact peening (UIP). Stress-controlled fatigue response of the specimens was studied and compared with those for the annealed and UIP-treated specimens. The notch effect of the UIP induced surface roughness calculated in terms of the stress concentration factor does not exceed similar to 10%. XRD, OM and SEM analyses were used to characterize formed surface layers and fatigue fracture surfaces. Surface composite layer of 40-50 mu m thick contains the homogeneously dispersed QC particles (the volume fraction V-f similar to 0.15) trapped by high compressive residual stresses. The layer demonstrates almost triple increase in microhardness comparing to that for the annealed alloy and twice exceeding of that for the UIP-treated specimen. Superior fatigue endurance of Al-6 Mg alloy after the UIP process and the UIP-induced f! ormation of the composite layer is explained by sub-surface fatigue cracks' initiation promoted with high compressive residual stresses and tight interfacial bonding of QC reinforcement and the matrix alloy. The improved fatigue behavior of the UIP-treated specimens in both the low cycle and high cycle regimes can be ensured by combination of the following favorable characteristics: (i) sufficiently high ductility and resistance to fatigue damage and crack growth in the core parent material along with (ii) superior fatigue strength supported by high microhardness and compressive stresses in the surface layer, which contains fine grained matrix and/or uniformly distributed and tightly bonded QC reinforcements. (c) 2012 Elsevier B.V. All rights reserved.
Title:
Chiral magnetism and helimagnons in a pyrochlore antiferromagnet
Authors:
Choi, ES; Chern, GW; Perkins, NB Author Full Names: Choi, Eunsong; Chern, Gia-Wei; Perkins, Natalia B.
Source:
PHYSICAL REVIEW B, 87 (5):10.1103/PhysRevB.87.054418 FEB 15 2013
Abstract:
Recent neutron scattering measurements on the spinel CdCr2O4 revealed a rare example of helical magnetic order in geometrically frustrated pyrochlore antiferromagnet. The spin spiral characterized by an incommensurate wave vector Q = 2 pi( 0, delta, 1) with delta approximate to 0.09 is accompanied by a tetragonal distortion. Here we conduct a systematic study on the magnetic ground state resulting from the interplay between the Dzyaloshinskii-Moriya interaction and further neighbor exchange couplings, two of the most important mechanisms for stabilizing incommensurate spin orders. We compute the low-energy spin-wave spectrum based on a microscopic spin Hamiltonian and find a dispersion relation characteristic of the helimagnons. By numerically integrating the Landau-Lifshitz-Gilbert equation with realistic model parameters, an overall agreement between experiment and the numerical spectrum, lending further support to the view that a softened optical phonon triggers the magnetic transition and endows the lattice a chirality. DOI: 10.1103/PhysRevB.87.054418
Title:
Spin-Nematic and Spin-Density-Wave Orders in Spatially Anisotropic Frustrated Magnets in a Magnetic Field
Authors:
Sato, M; Hikihara, T; Momoi, T Author Full Names: Sato, Masahiro; Hikihara, Toshiya; Momoi, Tsutomu
Source:
PHYSICAL REVIEW LETTERS, 110 (7):10.1103/PhysRevLett.110.077206 FEB 15 2013
Abstract:
We develop a microscopic theory of finite-temperature spin-nematic orderings in three-dimensional spatially anisotropic magnets consisting of weakly coupled frustrated spin-1/2 chains with nearest-neighbor and next-nearest-neighbor couplings in a magnetic field. Combining a field theoretical technique with density-matrix renormalization group results, we complete finite-temperature phase diagrams in a wide magnetic-field range that possess spin-bond-nematic and incommensurate spin-density-wave ordered phases. The effects of a four-spin interaction are also studied. The relevance of our results to quasi-one-dimensional edge-shared cuprate magnets such as LiCuVO4 is discussed. DOI: 10.1103/PhysRevLett.110.077206
Title:
Manipulating Majorana fermions in quantum nanowires with broken inversion symmetry
Authors:
Liu, XJ; Lobos, AM Author Full Names: Liu, Xiong-Jun; Lobos, Alejandro M.
Source:
PHYSICAL REVIEW B, 87 (6):10.1103/PhysRevB.87.060504 FEB 15 2013
Abstract:
We study a Majorana-carrying quantum wire, driven into a trivial phase by breaking the spatial inversion symmetry with a tilted magnetic field. Interestingly, we predict that a supercurrent applied in the proximate superconductor is able to restore the topological phase and therefore the Majorana end states. Using Abelian bosonization, we further confirm this result in the presence of electron-electron interactions and show a profound connection of this phenomenon to the commensurate-incommensurate transition in one-dimensional doped Mott insulators. These results have important applications in, e. g., realizing a supercurrent-assisted braiding of Majorana fermions, which proves highly useful in topological quantum computation with realistic Majorana networks. DOI: 10.1103/PhysRevB.87.060504
Title:
Field-induced magnetic behavior in quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8: A single-crystal neutron diffraction study
Authors:
Canevet, E; Grenier, B; Klanjsek, M; Berthier, C; Horvatic, M; Simonet, V; Lejay, P Author Full Names: Canevet, E.; Grenier, B.; Klanjsek, M.; Berthier, C.; Horvatic, M.; Simonet, V.; Lejay, P.
Source:
PHYSICAL REVIEW B, 87 (5):10.1103/PhysRevB.87.054408 FEB 13 2013
Abstract:
BaCo2V2O8 is a nice example of a quasi-one-dimensional quantum spin system that can be described in terms of Tomonaga-Luttinger liquid physics. This is explored in the present study where the magnetic field-temperature phase diagram is thoroughly established up to 12 T using single-crystal neutron diffraction. The transition from the Neel phase to the incommensurate longitudinal spin density wave (LSDW) phase through a first-order transition, as well as the critical exponents associated with the paramagnetic-Neel phase transition, and the magnetic order both in the Neel and in the LSDW phase are determined, thus providing a stringent test for the theory. DOI: 10.1103/PhysRevB.87.054408
Title:
Incomplete Devil's Staircase in the Magnetization Curve of SrCu2(BO3)(2)
Authors:
Takigawa, M; Horvatic, M; Waki, T; Kramer, S; Berthier, C; Levy-Bertrand, F; Sheikin, I; Kageyama, H; Ueda, Y; Mila, F Author Full Names: Takigawa, M.; Horvatic, M.; Waki, T.; Kraemer, S.; Berthier, C.; Levy-Bertrand, F.; Sheikin, I.; Kageyama, H.; Ueda, Y.; Mila, F.
Source:
PHYSICAL REVIEW LETTERS, 110 (6):10.1103/PhysRevLett.110.067210 FEB 8 2013
Abstract:
We report on NMR and torque measurements on the frustrated quasi-two-dimensional spin-dimer system SrCu2(BO3)(2) in magnetic fields up to 34 T that reveal a sequence of magnetization plateaus at 1/8, 2/15, 1/6, and 1/4 of the saturation and two incommensurate phases below and above the 1/6 plateau. The magnetic structures determined by NMR involve a stripe order of triplets in all plateaus, suggesting that the incommensurate phases originate from proliferation of domain walls. We propose that the magnetization process of SrCu2(BO3)(2) is best described as an incomplete devil's staircase. DOI: 10.1103/PhysRevLett.110.067210
Title:
Varied linear phason strain and its induced domain structure in quasicrystalline precipitates of Zr-Al-Ni-Cu-Nb bulk metallic glass matrix composites (vol 27, pg 3041, 2012)
Authors:
Lu, L; Xiong, DX; Wang, JB; Zhao, DS; Sun, YF Author Full Names: Lu, Lu; Xiong, Dongxia; Wang, Jianbo; Zhao, Dongshan; Sun, Yufeng
Source:
JOURNAL OF MATERIALS RESEARCH, 28 (4):658-658; 10.1557/jmr.2012.427 FEB 2013
Title:
Hydrodynamic structure factor for two-dimensional decagonal quasicrystals
Authors:
Chatzopoulos, A; Trebin, HR; Ishii, Y Author Full Names: Chatzopoulos, Andreas; Trebin, Hans-Rainer; Ishii, Yasushi
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 250 (2):291-304; 10.1002/pssb.201248275 FEB 2013
Abstract:
The dynamic and static structure factors for two-dimensional decagonal quasicrystals (QCs) are calculated based on the hydrodynamic model. Explicit formulae with algebraic decay, which is characteristic in lower dimensions, are obtained. The sound-wave and diffusive-mode contributions are analyzed separately. It is shown that the phononphason coupling yields the characteristic anisotropy in the structure factors. If one assumes the phasonic diffusion constant of the order of magnitude typical for metallic QCs, however, the phasonic contribution is expected only at very small frequencies and hence more likely to be observed in the time domain than in the frequency domain.
Title:
Hidden ferromagnetic order in underdoped cuprates
Authors:
Seibold, G; Capati, M; Di Castro, C; Grilli, M; Lorenzana, J Author Full Names: Seibold, G.; Capati, M.; Di Castro, C.; Grilli, M.; Lorenzana, J.
Source:
PHYSICAL REVIEW B, 87 (3):10.1103/PhysRevB.87.035138 JAN 30 2013
Abstract:
We study a model for low-doped cuprates where holes aggregate into oriented stripe segments which have a magnetic vortex and antivortex at the extremes. We argue that due to the interaction between segments a ferronematic state with macroscopic polarization is stabilized. This state can be characterized as a charge nematic which, due to the net polarization, breaks inversion symmetry and also exhibits an incommensurate spin modulation. Our calculation can reproduce the doping-dependent spin structure factor of lanthanum cuprates in excellent agreement with experiment and allows to rationalize experiments in which the incommensurability has an order-parameter-like temperature dependence. DOI: 10.1103/PhysRevB.87.035138
Title:
Synthesis, Structural Characterization, and Physical Properties of the Early Rare-Earth Metal Digermanides REGe2-x (x approximate to 1/4) [RE = La-Nd, Sm]. A Case Study of Commensurately and Incommensurately Modulated Structures
Authors:
Zhang, JL; Tobash, PH; Pryz, WD; Buttey, DJ; Hur, N; Thompson, JD; Sarrao, JL; Bobev, S Author Full Names: Zhang, Jiliang; Tobash, Paul H.; Pryz, William D.; Buttey, Douglas J.; Hur, Namjung; Thompson, Joe D.; Sarrao, John L.; Bobev, Svilen
Source:
INORGANIC CHEMISTRY, 52 (2):953-964; 10.1021/ic3021645 JAN 21 2013
Abstract:
Rare-earth metal germanides with the general formula RE4Ge2 (RE = La, Ce, Pr, Nd, Sm) have been synthesized using the In-flux technique. Their structures have been established from single-crystal and powder X-ray diffraction, and the structural elucidation has been aided by electron diffraction. These compounds represent superstructures of the alpha-ThSi2 structure type through the long- and/or short-range vacancy ordering. RE4Ge7 (RE = Pr, Nd, Sm) appear to be commensurately modulated 4-fold superstructure of REGe2-x (x = 1/4), while coexistence of commensurate and incommensurate modulation is revealed in the La- and Ce-analogues. These results shed more light on the structural evolution of the REGe2-x phases as function of the vacancy concentration and nature of the rare-earth metal. Measurements of the magnetic susceptibilities on well-characterized single-crystals show ferromagnetic, antiferromagnetic, and even spin-glass-like behaviors. Mean-field theory is used to evaluate the correlations between structural and magnetic property data. Measurements on the electrical resistivities and the heat capacities are also presented and discussed.
Title:
Effects of heat treatment on microstructure and mechanical properties of Mg-5Zn-0.63Er alloy
Authors:
Zhao, XF; Li, SB; Wang, QF; Du, WB; Liu, K Author Full Names: Zhao, Xian-feng; Li, Shu-bo; Wang, Qing-feng; Du, Wen-bo; Liu, Ke
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 23 (1):59-65; 10.1016/S1003-6326(13)62429-2 JAN 2013
Abstract:
The microstructure evolution of the Mg-5Zn-0.63Er (mass fraction, %) alloy containing quasicrystalline phase (I-phase) under the as-cast condition was investigated via different heat treatments. The results show that apart from the precipitation of the W-phase particles, the I-phase almost dissolves into the matrix after solid solution treatment at 480 degrees C for 10 h (T4 state). The solution-treated alloy was aged at 175 degrees C for 6-100 h (T6 state). The ultimate tensile strength of the peak-aged alloy is approximately 261 MPa companying with an elongation of 10.5%. The improvement of the tensile strength is mainly attributed to the presence of the rod-like MgZn2 particles.

Update: 7-Mar-2013

Title:
Room temperature structure and multiferroic properties in Bi0.7La0.3FeO3 ceramics
Authors:
Carvalho, TT; Fernandes, JRA; de la Cruz, JP; Vidal, JV; Sobolev, NA; Figueiras, F; Das, S; Amaral, VS; Almeida, A; Moreira, JA; Tavares, PB Author Full Names: Carvalho, T. T.; Fernandes, J. R. A.; Perez de la Cruz, J.; Vidal, J. V.; Sobolev, N. A.; Figueiras, F.; Das, S.; Amaral, V. S.; Almeida, A.; Agostinho Moreira, J.; Tavares, P. B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 554 97-103; 10.1016/j.jallcom.2012.11.018 MAR 25 2013
Abstract:
Single phase Bi0.7La0.3FeO3 ceramic samples were successfully synthesized by sol-gel combustion and co-precipitation methods, performing a final sintering at 820-870 degrees C from 10 up to 180 min. Rietveld refinements of the XRD data detected small satellite peaks that were successfully indexed by an incommensurated modulated structure model. Lanthanum doping improves magnetic response, reduces the leakage current and dielectric losses. The piezoelectric coefficient was reported for the first time in the Bi0.7La0.3FeO3 composition. (C) 2012 Elsevier B. V. All rights reserved.
Title:
Acene adsorption on a Fibonacci-modulated Cu film
Authors:
Young, KM; Smerdon, JA; Sharma, HR; Lahti, M; Pussi, K; McGrath, R Author Full Names: Young, K. M.; Smerdon, J. A.; Sharma, H. R.; Lahti, M.; Pussi, K.; McGrath, R.
Source:
PHYSICAL REVIEW B, 87 (8):10.1103/PhysRevB.87.085407 FEB 6 2013
Abstract:
The adsorption of pentacene (Pn) on the fivefold surface of an i-Al-Pd-Mn quasicrystal and on a one-dimensionally aperiodic Cu multilayer formed thereon is observed with scanning tunneling microscopy. The molecule has a strong interaction with the clean quasicrystal surface, leading to the formation of a disordered layer. On the Cu film, a molecular layer assembles, with the Cu rows acting as a template. At lower coverages, there is a repulsive interaction between the molecules, leading to a dispersed homogeneous arrangement. At higher coverages, the steric interaction of the Pn molecules counterbalances the aperiodic template, which results in a short-range periodic "checkerboard" arrangement of molecules. Density functional theory calculations using lower order acenes are used to probe the details of the interactions with the aperiodic Cu surface and it is found that adsorption with molecules parallel to Cu rows is preferred, in agreement with experimental results. DOI: 10.1103/PhysRevB.87.085407
Title:
Thermal study of the interplay between spin and lattice in CoCr2O4 and CdCr2O4
Authors:
Kitani, S; Tachibana, M; Taira, N; Kawaji, H Author Full Names: Kitani, Suguru; Tachibana, Makoto; Taira, Naoya; Kawaji, Hitoshi
Source:
PHYSICAL REVIEW B, 87 (6):10.1103/PhysRevB.87.064402 FEB 4 2013
Abstract:
The interplay between spin and lattice degrees of freedom in the spinels CoCr2O4 and CdCr2O4 has been investigated by heat capacity and thermal expansion measurements. In CoCr2O4, sharp anomalies are observed at the magnetic phase transition temperatures of 13, 26, and 93 K. A large pressure dependence of the transition temperature at 13 K, which is calculated from the heat capacity and thermal expansion, indicates strong spin-lattice coupling in the incommensurate phase. This result provides the possibility of the reduction of lattice symmetry from cubic at the phase transition. In CdCr2O4, negative thermal expansion due to spin-lattice coupling emerges in temperature from 140 to 45 K, which is followed by strong positive thermal expansion at lower temperature. The magnetostructural transition at 7.8 K is observed as a large anomaly with an indication for a large pressure dependence of the transition temperature. The unusual thermal expansion suggests the importance of other perturbations besides exchange interactions between Cr ions for the formation of the spin clusters. Our results demonstrate that thermal measurements can help to further understand the frustrated systems with strong spin-lattice coupling. DOI: 10.1103/PhysRevB.87.064402
Title:
Superionic transitions and conductivity anisotropy in Na4.6FeP2O8.6F0.4 single crystals
Authors:
Sorokin, NI Author Full Names: Sorokin, N. I.
Source:
PHYSICS OF THE SOLID STATE, 55 (2):306-308; 10.1134/S1063783413020315 FEB 2013
Abstract:
The cation conductivity in the directions parallel (sigma(aEuro-[001])) and perpendicular (sigma(aSyen[001])) to the [001] crystallographic direction of Na4.6FeP2O8.6F0.4 single crystals has been investigated at 293-734 K. The specific features of the ionic conductivity have been studied near two phase transitions at T (tr, 1) similar to 450 K and T (tr, 2) similar to 545 K. At T = T (tr, 1), the activation enthalpy for the dependences sigma(aEuro-[001])(T) and sigma(aSyen[001])(T) decreases from 0.45 +/- 0.01 to 0.33 +/- 0.02 eV, and the sigma(aEuro-[001])(T) curve has a jump of the ionic conductivity by a factor of almost two at T = T (tr, 2); the jump is related to a manifestation of commensurate modulation of the crystal structure. In the Na4.6FeP2O8.6F0.4 crystals, the ionic transport is anisotropic with the ratio sigma(aEuro-[001])/sigma(aSyen[001]) = 7.7, 5.2, and 6.6 at 293 K (T < T (tr, 1)), 500 K (T (tr, 1) < T < T (tr, 2)), and 700 K (T < T (tr, 2)), respectively. The mechanism of cation conductivity in the Na4.6FeP2O8.6F0.4 crystals is discussed.
Title:
Electronic spectra of [N(CH3)(4)](2)CoCl4 microcrystals in thin films
Authors:
Karpa, IV; Sveleba, SA; Katerynchuk, IN; Kunyo, IM; Phitsych, EI; Shymkiv, RM; Furgala, YM Author Full Names: Karpa, I. V.; Sveleba, S. A.; Katerynchuk, I. N.; Kunyo, I. M.; Phitsych, E. I.; Shymkiv, R. M.; Furgala, Yu. M.
Source:
JOURNAL OF APPLIED SPECTROSCOPY, 79 (6):888-895; 10.1007/s10812-013-9690-y JAN 2013
Abstract:
Optical absorption spectroscopy was used to study [N(CH3)(4)](2)CoxZn1-xCl4 (x = 0.75, 0.50, 0.25) and [N(CH3)(4)](2)CoCl4 microcrystals in the thickness range 10 a parts per thousand currency sign d < 100 mu m. Weakening of the crystal field was observed with a decrease in the [N(CH3)(4)](2)CoCl4 crystal thickness. Both the reason for the dependence of the absorption band shifts in the visible region on the [N(CH3)(4)](2)CoCl4 crystal thickness and the manifestation of a size effect in crystals with an incommensurate superstructure were considered.
Title:
Elliptic holes in octagonal quasicrystals
Authors:
Li, LH Author Full Names: Li Lian-He
Source:
CHINESE PHYSICS B, 22 (1):10.1088/1674-1056/22/1/016102 JAN 2013
Abstract:
The stress potential function theory for the plane elasticity of octagonal quasicrystals is developed. By introducing stress functions, a large number of basic equations involving the elasticity of octagonal quasicrystals are reduced to a single partial differential equation. Furthermore, we develop the complex variable function method (Lekhnitskii method) for anisotropic elasticity theory to that for quasicrystals. With the help of conformal transformation, an exact solution for the elliptic hole of quasicrystals is presented. The solution of the Griffith crack problem, as a special case of the results, is obtained. As a consequence, the phonon stress intensity factor is derived analytically.

Update: 28-Feb-2013

Title:
A composite based on Fe substituted TiVNi alloy: Synthesis, structure and electrochemical hydrogen storage property
Authors:
Liu, WQ; Kawabe, Y; Liang, F; Okuyama, R; Lin, J; Wang, LM Author Full Names: Liu, Wanqiang; Kawabe, Yoshiteru; Liang, Fei; Okuyama, Ryoichi; Lin, Jing; Wang, Limin
Source:
INTERMETALLICS, 34 18-22; 10.1016/j.intermet.2012.11.001 MAR 2013
Abstract:
The TiV(1-x)NiFex (x = 0, 0.1, 0.2, 0.3 and 0.4) alloy ribbons are synthesized by arc-melting and subsequent melt-spinning techniques. The structure of the alloys is characterized by XRD. The electrochemical properties including the maximum discharge capacity, cyclic stability and the high rate dischargeability, etc. are tested. The results show that the structure of all TiVNi alloy mainly consists of the icosahedral quasicrystal (I-phase), Ti2Ni-type face centered cubic (FCC) phase and body centered cubic (BCC) solid solution phase. After adding some amount of Fe to TiVNi alloys, for TiV0.9NiFe0.1 (x = 0.1) alloy, the XRD pattern is characterized by the FCC and the BCC phase, while the structure of TiV1-xNiFex alloys (x = 0.2, 0.3 and 0.4) consists of the BCC solid solution phase alloy. The maximum discharge capacity of the alloy electrodes increases firstly and then decreases with increasing x, the same as the high-rate dischargeability. The optimal value of C-240/C-30 is 84.2%, corresponding to x being 0.2 and the discharge current density is 240 mA/g. In addition, the electrochemical reaction kinetics of the alloy electrodes is also studied by electrochemical impedance spectroscopy and hydrogen diffusion coefficient (D). (C0 2012 Elsevier Ltd. All rights reserved.
Title:
Incommensurate structure of GdBaCo2O5+delta (delta similar to 0.38)
Authors:
Ishizawa, N; Asaka, T; Kudo, T; Fukuda, K; Abe, N; Arima, T Author Full Names: Ishizawa, N.; Asaka, T.; Kudo, T.; Fukuda, K.; Abe, N.; Arima, T.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 198 532-541; 10.1016/j.jssc.2012.11.004 FEB 2013
Abstract:
The incommensurate structure of the GdBaCo2O5+delta (delta similar to 0.38) paramagnetic phase was studied using the single-crystal X-ray diffraction. The basic structure of the compound is a double-layered perovskite with an alternating layer sequence of [GdO delta]-[CoO2]-[BaO]-[CoO2] along the c axis. The crystal belongs to the five-dimensional superspace group P4/mmm(alpha 00)0000(0 alpha 0)0000, alpha=0.3368(1), with a 1 x 1 x 2-type tetragonal fundamental unit cell of alpha=3.8934(1) angstrom and c=7.5267(1)angstrom. The structure was refined to R=0.028 for all the observed 2216 reflections with I > 3 sigma(I), including 331 main reflections (R=0.017), 1039 observed first-order satellites (R=0.033), and 846 observed second-order satellites (R=0.045). The crystal has oxygen deficiency that occurs only in the [GdO delta] layer; however, it causes many positional modulations of the constituent atoms throughout the crystal in association with a valence fluctuation of Co between the divalent and trivalent states. Because the value of alpha was very close to 1/3, the structure was also investigated using both the commensurately modulated approach and the conventional three-dimensional approach assuming a 3 x 3 x 2 supercell of P4/mmm symmetry. These approaches successfully reproduced a prime structure of the compound that consists of intersecting CoO5 pyramidal arrays parallel to alpha or b axes. The bond valence sum and the charge neutrality principle suggested that the divalent and trivalent cobalt cations are distributed in an ordered way. The incommensurate approach also indicated the possible presence of a local disorder having a structural similarity with that of a high-temperature modification. (c) 2012 Elsevier Inc. All rights reserved.
Title:
Particle and crystallite size effects on the modulated structure of multiferroic CaMn7O12
Authors:
Slawinski, W; Przenioslo, R; SosnowskaA, I; Wardecki, D; Fitch, AN; Bieringer, M; Jasinski, JB Author Full Names: Slawinski, Wojciech; Przenioslo, Radoslaw; SosnowskaA, Izabela; Wardecki, Dariusz; Fitch, Andy N.; Bieringer, Mario; Jasinski, Jacek B.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 198 392-398; 10.1016/j.jssc.2012.10.024 FEB 2013
Abstract:
A systematic study of the atomic position modulation in polycrystalline CaMn7O12 with different particle sizes (determined from scanning electron microscopy) and crystallite sizes (determined from X-ray diffraction) is reported. The morphology and phase composition are characterised by scanning electron microscopy, selected area electron diffraction and energy dispersive X-ray spectroscopy. The crystal structure and the atomic position modulation in polycrystalline CaMn7O12 samples are explored with high-resolution synchrotron radiation based powder X-ray diffraction. The modulation vector and the modulation amplitudes observed at T=10 K do not change as a function of particle size, crystallite size and microstrain fluctuations. In addition, we report and discuss the formation of the additional CaMn4O8 nanowire phase during high temperature annealing. (C) 2012 Elsevier Inc. All rights reserved.
Title:
Frustration by competing interactions in the highly distorted double perovskites La2NaB ' O-6 (B ' = Ru, Os)
Authors:
Aczel, AA; Bugaris, DE; Li, L; Yan, JQ; de la Cruz, C; zur Loye, HC; Nagler, SE Author Full Names: Aczel, A. A.; Bugaris, D. E.; Li, L.; Yan, J-Q; de la Cruz, C.; zur Loye, H-C; Nagler, S. E.
Source:
PHYSICAL REVIEW B, 87 (1):10.1103/PhysRevB.87.014435 JAN 31 2013
Abstract:
The usual classical behavior of S = 3/2, B-site ordered double perovskites generally results in simple, commensurate magnetic ground states. In contrast, combined magnetic susceptibility, heat capacity, and neutron powder diffraction measurements for the S = 3/2 systems La2NaB'O-6 (B' = Ru, Os) reveal an incommensurate magnetic ground state for La2NaRuO6 and a drastically suppressed ordered moment for La2NaOsO6. This behavior is attributed to the large monoclinic structural distortions of these double perovskites. The distortions have the effects of creating inequivalent nearest neighbor (NN) superexchange interactions and weakening them on average, possibly to an energy scale that is comparable with the average next nearest neighbor (NNN) superexchange. The exotic ground states in these materials can then arise from a competition between some combination of inequivalent NN and NNN exchange interactions, providing an unusual mechanism for achieving frustration in the double perovskite family. DOI: 10.1103/PhysRevB.87.014435
Title:
Effect of high pressure on the crystal structure, magnetic, and vibrational properties of multiferroic RbFe(MoO4)(2)
Authors:
Kozlenko, DP; Kichanov, SE; Lukin, EV; Dang, NT; Dubrovinsky, LS; Bykova, EA; Kamenev, KV; Liermann, HP; Morgenroth, W; Shapiro, AY; Savenko, BN Author Full Names: Kozlenko, D. P.; Kichanov, S. E.; Lukin, E. V.; Dang, N. T.; Dubrovinsky, L. S.; Bykova, E. A.; Kamenev, K. V.; Liermann, H. -P.; Morgenroth, W.; Shapiro, A. Ya.; Savenko, B. N.
Source:
PHYSICAL REVIEW B, 87 (1):10.1103/PhysRevB.87.014112 JAN 22 2013
Abstract:
The structural, magnetic, and vibrational properties of RbFe(MoO4) 2 have been studied by means of x-ray and neutron powder diffraction, magnetic susceptibility measurements, and Raman spectroscopy at pressures up to 10 GPa. The gradual structural phase transition from the initial trigonal P (3) over bar m1 phase to the monoclinic C2/c phase via the intermediate P (3) over bar phase was observed at P similar to 1 GPa. The triangular antiferromagnetic order with a propagation vector q = (1/3, 1/3, q(z)) in the suppressed trigonal phase remains incommensurate, and the q(z) value increases from 0.45 to 0.48 in the pressure range 0- 2 GPa at T = 2 K. The pressure coefficient of the Neel temperature is equal to (1/T-N)dT(N)/dP = 0.09 GPa(-1). No evidence of the formation of the long-range magnetic order in the monoclinic phase was found. The pressure dependencies of the vibrational modes for the trigonal and monoclinic phases were obtained.
Title:
Optical features of A(2)BX(4) ferroic nanocomposites with the incommensurate phase
Authors:
Lakshminarayana, G; Plucinski, KJ Author Full Names: Lakshminarayana, G.; Plucinski, K. J.
Source:
MATERIALS LETTERS, 91 345-347; 10.1016/j.matlet.2012.09.116 JAN 15 2013
Abstract:
In this paper, we report on the experimental studies of optical birefringence of A(2)BX(4) (K2ZnCl4, Rb2ZnCl4, and K2SeO4) type of crystals in a wide temperature range which show para-electric, ferroelectric properties with incommensurate phases for the 633 nm wavelength. We found that with the decrease of the nanocrystallite sizes, temperature range of the incommensurate phase is enhanced. At the same time the ferroelectricity disappeared at crystallite sizes below 8 nm due to nano-confinement effects which change the electron-phonon anharmonic interactions which are responsible for such kinds of phase transitions. Additional superposition of the external electric field leads to drastic changes in the relative amount of the ferroelectrics and incommensurate phases. The effect is explained within the Landau-Ginzburg phenomenological approach with Lifshitz invariant. Additional confirmation of the observed effects was obtained by optical second harmonic generation. During the decrease of the nanocrystallite sizes below 12 nm there occurs some harmonic soliton waves which are propagated in several directions parallel to the crystallographic axes. Despite the absence of the long-range disorder there occurs some non-centrosymmetry. (c) 2012 Elsevier B.V. All rights reserved.
Title:
Modulated crystal structures of phases VII and V in (NH4)(3)H(SO4)(2). Neutron Laue diffraction
Authors:
McIntyre, GJ; Smirnov, LS; Baranov, AI; Dolbinina, VV; Frontasyeva, MV; Pavlov, SS; Pankratova, YS Author Full Names: McIntyre, G. J.; Smirnov, L. S.; Baranov, A. I.; Dolbinina, V. V.; Frontasyeva, M. V.; Pavlov, S. S.; Pankratova, Yu. S.
Source:
CRYSTALLOGRAPHY REPORTS, 58 (1):78-80; 10.1134/S1063774513010239 JAN 2013
Abstract:
A study of the crystal structure of the phases VII and V of (NH4)(3)H(SO4)(2) by mean of neutron Laue diffraction was carried out at temperatures from 5 to 300 K. It is found that the crystal structures of phases VII and V are incommensurately modulated with different periods, and that the phase transition from phase VII to phase V is of first order.
Title:
Size effects in [N(CH3)(4)](2)Zn0.58Cu0.42Cl4 crystals
Authors:
Sveleba, SA; Karpa, IV; Katerynchuk, IN; Furgala, YM; Semotyuk, OV; Kunyo, IM; Fitsych, EI; Pankivskyi, YI Author Full Names: Sveleba, S. A.; Karpa, I. V.; Katerynchuk, I. N.; Furgala, Yu. M.; Semotyuk, O. V.; Kunyo, I. M.; Fitsych, E. I.; Pankivskyi, Yu. I.
Source:
CRYSTALLOGRAPHY REPORTS, 58 (1):122-128; 10.1134/S1063774513010124 JAN 2013
Abstract:
The temperature dependences of birefringence in thin [N(CH3)(4)](2)Zn0.58Cu0.42Cl4 crystals in the thickness range 20 x 10(-6) a parts per thousand currency sign d a parts per thousand currency sign 500 a dagger 3/4 10(-6) m have been investigated. An increase in the temperatures of the parent phase-incommensurate phase and incommensurate phase-ferroelectric phase transitions has been found. The reasons for the shift in the phase transition temperatures with a decrease in the thickness of [N(CH3)(4)](2)Zn0.58Cu0.42Cl4 crystal and the size effect in crystals with an incommensurate superstructure are discussed.

Update: 21-Feb-2013

Title:
Structural, tribological and resistivity studies of Ga substituted (Al71-xGax) Pd21Mn8 icosahedral and other intermetallic phases
Authors:
Bohra, M; de Weerd, MC; Fournee, V; Mandal, RK; Mukhopadhyay, NK; Chatterjee, R; Sastry, GVS Author Full Names: Bohra, Murtaza; de Weerd, M. C.; Fournee, Vincent; Mandal, R. K.; Mukhopadhyay, N. K.; Chatterjee, Ratnamala; Sastry, G. V. S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 551 274-278; 10.1016/j.jallcom.2012.09.130 FEB 25 2013
Abstract:
We report the formation of icosahedral phase in Al-71 xGaxPd21Mn8 (x = 0, 4, 6, 8, and 10 at.%) by adopting powder metallurgical route. Such a variation in Ga substitution in the alloy composition gave rise to a nearly single phase face centred icosahedral phase for x = 6. All other Ga substituted compositions displayed formation of intermetallic phases in addition to the icosahedral quasicrystals. The 6d hypercubic lattice parameter for the Ga substituted icosahedral phase is higher than that of Al71Pd21Mn8 composition. The change in the lattice parameter is non-monotonic. Such a change in lattice parameter has been explained based on the mixed valence states of Ga on Al site. The electrical resistivity of x = 6 sample is comparable to those of earlier studies pertaining to flux grown icosahedral composition of Al(Ga) PdMn alloy. Further, x = 6 sample has displayed highest value of static friction coefficient. This has been understood in terms of the shift of Fermi level from the pseudo-gap location owing to mixed valence states of Ga. (C) 2012 Elsevier B. V. All rights reserved.
Title:
Generalization of the Mooij correlation to quasicrystals
Authors:
Rapp, O Author Full Names: Rapp, O.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (6):10.1088/0953-8984/25/6/065701 FEB 13 2013
Abstract:
The Mooij correlation has been generalized to include quasicrystals. The average temperature dependence of the electrical resistivity rho(T), as estimated from the difference rho(4.2 K)-rho(295 K), was found to be correlated with rho(295 K) over seven orders of magnitude. This relation remains robust for modifications of the samples such as approximants, single grain samples, and samples with properties that vary strongly with annealing. An interesting subset of data is metallic alloys of the type Al-Cu-M (M = Li, Li(Mg), Cu Ru, Os), where rho(4.2 K)-rho(295 K) similar to [rho(295 K)](2).
Title:
Magnetic structures and physical properties of Tm3Cu4Ge4 and Tm3Cu4Sn4
Authors:
Baran, S; Kaczorowski, D; Szytula, A; Gil, A; Hoser, A Author Full Names: Baran, S.; Kaczorowski, D.; Szytula, A.; Gil, A.; Hoser, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (6):10.1088/0953-8984/25/6/066012 FEB 13 2013
Abstract:
Tm3Cu4Ge4 crystallizes in the orthorhombic Gd3Cu4Ge4-type crystal structure (space group Immm) whereas Tm3Cu4Sn4 crystallizes in a distorted variant of this structure (monoclinic space group C2/m). The compounds were studied by means of neutron diffraction, specific heat, electrical resistivity and magnetic measurements. Analysis of experimental data revealed the presence of an antiferromagnetic order below 2.8 K in both compounds. In Tm3Cu4Ge4 the magnetic unit cell is doubled in respect to the crystal unit cell and the magnetic structure can be described by a propagation vector (k) over right arrow = [0, 1/2, 0]. A larger magnetic unit cell was found in Tm3Cu4Sn4, given by a propagation vector (k) over right arrow = [1/2, 1/2, 0] (for simplicity the orthorhombic description is used for both the germanide and the stannide). Close to 2 K, in each compound an incommensurate antiferromagnetic order develops. This low-temperature magnetic phase is characterized by a propagation vector (k) over right arrow = [1/4, 0, k(z)], where k(z) is close to 0.49 and 0.47 in Tm3Cu4Ge4 and Tm3Cu4Sn4, respectively. The antiferromagnetic phase transitions are clearly seen in the bulk magnetic and specific heat data of both compounds.
Title:
The charge-flipping algorithm in crystallography
Authors:
Palatinus, L Author Full Names: Palatinus, Lukas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 69 1-16; 10.1107/S0108768112051361 Part 1 FEB 2013
Abstract:
The charge-flipping algorithm (CFA) is a member of the diverse family of dual-space iterative phasing algorithms. These algorithms use alternating modifications in direct and reciprocal space to find a solution to the phase problem. The current state-of-the-art CFA is reviewed and it is put in the context of related dual-space algorithms with relevance for crystallography. The CFA has found applications in many crystallographic problems. The principal applications in various fields are described with sections devoted to routine structure solution, the solution of complex structures from powder diffraction data, the solution of incommensurately modulated crystals and quasicrystals, macromolecular crystallography and single-particle imaging.
Title:
Ultrafast filling of an electronic pseudogap in an incommensurate crystal
Authors:
Brouet, V; Mauchain, J; Papalazarou, E; Faure, J; Marsi, M; Lin, PH; Taleb-Ibrahimi, A; Le Fevre, P; Bertran, F; Cario, L; Janod, E; Corraze, B; Phuoc, VT; Perfetti, L Author Full Names: Brouet, V.; Mauchain, J.; Papalazarou, E.; Faure, J.; Marsi, M.; Lin, P. H.; Taleb-Ibrahimi, A.; Le Fevre, P.; Bertran, F.; Cario, L.; Janod, E.; Corraze, B.; Phuoc, V. Ta; Perfetti, L.
Source:
PHYSICAL REVIEW B, 87 (4):10.1103/PhysRevB.87.041106 JAN 28 2013
Abstract:
We investigate the quasiperiodic crystal (LaS)(1.196)VS2 by angle and time resolved photoemission spectroscopy. The dispersion of electronic states is in qualitative agreement with the band structure calculated for the VS2 slab without incommensurate distortion. Nonetheless, the spectra display a temperature dependent pseudogap instead of quasiparticle crossing. The sudden photoexcitation at 50 K induces a partial filling of the electronic pseudogap within less than 80 fs. The electronic energy flows into the lattice modes on a comparable time scale. We attribute this surprisingly short time scale to a very strong electron-phonon coupling to the incommensurate distortion. This result sheds light on the electronic localization arising in aperiodic structures and quasicrystals. DOI: 10.1103/PhysRevB.87.041106
Title:
Magnetoelectric responses induced by domain rearrangement and spin structural change in triangular-lattice helimagnets NiI2 and CoI2
Authors:
Kurumaji, T; Seki, S; Ishiwata, S; Murakawa, H; Kaneko, Y; Tokura, Y Author Full Names: Kurumaji, T.; Seki, S.; Ishiwata, S.; Murakawa, H.; Kaneko, Y.; Tokura, Y.
Source:
PHYSICAL REVIEW B, 87 (1):10.1103/PhysRevB.87.014429 JAN 25 2013
Abstract:
Dielectric and magnetic properties have been investigated for single crystals of triangular-lattice antiferromagnets NiI2 and CoI2. For NiI2, the proper screw spin order with the magnetic modulation vector q similar to (0.138, 0, 1.457) induces electric polarization (P) along the in-plane direction with respect to the triangular lattice basal plane. The P shows monotonic increase as a function of the poling magnetic field (H) along the in-plane direction, suggesting the H-induced rearrangement of the multiferroic domain out of six possible domains. For CoI2, both in-plane and out-of-plane components of P emerge in the helimagnetic ground state, in which two cycloidal magnetic phases with q(1) = (1/12, 1/12, 1/2) and q(2) = (1/8, 0, 1/2) are supposed to coexist. The application of the in-plane H induces two-step metamagneticlike transitions, which probably goes through another ferroelectric helimagnetic phase as well as a paraelectric spin-collinear phase. Such distinctive magnetoelectric responses in the two simple triangular lattice antiferromagnets demonstrate that even a slight difference in the balance of magnetic interactions leads to a dramatic change of resultant magnetoelectric response in frustrated magnets. DOI: 10.1103/PhysRevB.87.014429
Title:
Effects of quasicrystal formation on the crystallization of (Ti36.1Zr33.2Ni5.8Be24.9)(100-x)Cu-x (x=5, 7, 9, 11, 13, 15, 17) metallic glasses
Authors:
Sha, PF; Zhu, ZW; Tang, MQ; Fu, HM; Li, ZK; Li, H; Wang, AM; Zhang, HW; Zhang, HF; Hu, ZQ Author Full Names: Sha, P. F.; Zhu, Z. W.; Tang, M. Q.; Fu, H. M.; Li, Z. K.; Li, H.; Wang, A. M.; Zhang, H. W.; Zhang, H. F.; Hu, Z. Q.
Source:
JOURNAL OF APPLIED PHYSICS, 113 (3):10.1063/1.4775836 JAN 21 2013
Abstract:
The crystallization behaviors of the (Ti36.1Zr33.2Ni5.8Be24.9)(100-x)Cu-x (x = 5, 7, 9, 11, 13, 15, 17; at. %) metallic glasses are investigated under both the continuous heating and isothermal conditions by the differential scanning calorimetry. Quasicrystals are found in the crystallization products under both conditions by X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. The evolution of the primary crystallization products of these alloys is discussed in detail. The effects of the increasing distortion energy of the icosahedral shortrange order with the increasing Cu content in the(Ti36.1Zr33.2Ni5.8Be24.9)(100-x)Cu-x (x = 5, 7, 9, 11, 13, 15, 17) alloys are found to be responsible for the evolution of the crystallization products. The isothermal crystallization kinetics deviates from the Johnson-Mehl-Avrami-Kolmogoroff (JMAK) model. A modified JMAK model with an impingement parameter is found to be suitable for the isothermal crystallization kinetics of the current alloys. The effects of quasicrystal formation on the crystallization kinetics are disscussed in detail. And it is found that the isothermal crystallization kinetics are influenced by both of the "soft impingement" effect and the formation of the quasicrystals. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4775836]
Title:
Aperiodic crystals
Authors:
Mukhopadhyay, NK Author Full Names: Mukhopadhyay, N. K.
Source:
CURRENT SCIENCE, 103 (12):1392-1394; DEC 25 2012
Title:
Toward theories of friction and adhesion on quasicrystals
Authors:
Rabson, DA Author Full Names: Rabson, D. A.
Source:
PROGRESS IN SURFACE SCIENCE, 87 (9-12):253-271; 10.1016/j.progsurf.2012.10.001 SEP-DEC 2012
Abstract:
It has long been known that quasicrystal surfaces show low sliding friction and adhesion, features that have led to practical applications, notably in cookware. Several mechanisms have been proposed for how quasiperiodicity might result in low friction and low adhesion. These include mechanical characteristics (stiffness and hardness), electronic properties, phonon propagation, surface topography at atomic length scales, and relatively irrational spacings between the atoms of the two sliding surfaces ("superlubricity"). Recent work by Park et al. finds an eightfold anisotropy in the coefficient of sliding friction between a decagonal quasicrystal surface and a passivated probe. This giant anisotropy epitomizes in a single experiment the difference between periodicity and aperiodicity, yet theoretical explanations of the effect remain controversial. (C) 2012 Elsevier Ltd. All rights reserved.

Update: 13-Feb-2013

Title:
Effects of Ag addition on crystallization, microstructure and mechanical properties of Zr-Cu-Ni-Al-Ag bulk metallic glasses
Authors:
Zhou, W; Lin, X; Li, JF Author Full Names: Zhou, W.; Lin, X.; Li, J. F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 552 102-106; 10.1016/j.jallcom.2012.10.101 MAR 5 2013
Abstract:
The composition dependences of crystallization, microstructure and mechanical properties have been investigated. When the Ag content is in the range of 0-8 at%, the BMGs with two or three-step of crystallization process exhibit remarkable plasticity, of which primary phase is an icosahedral phase. However, when the Ag concentration reaches 12-16 at%, the BMGs with single-step of crystallization mode display relatively limited plasticity, whose precipitation phase is Zr2Cu and/or Zr2Ni intermetallic compounds. Structural analyses reveal that the presence of icosahedral medium-range order clusters, which, in turn leads to the heterogeneity of free volume distribution, is responsible for the improvement of plasticity. The present results suggest that, under appropriate microstructural design by the introduction of icosahedral medium-range order clusters, BMG has extensive application prospect as structural material. (C) 2012 Elsevier B. V. All rights reserved.
Title:
Cimetidine, C10H16N6S, form C: crystal structure and modelling of polytypes using the superspace approach
Authors:
Arakcheeva, A; Pattison, P; Bauer-Brandl, A; Birkedal, H; Chapuis, G Author Full Names: Arakcheeva, Alla; Pattison, Philip; Bauer-Brandl, Annette; Birkedal, Henrik; Chapuis, Gervais
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 46 (1):99-107; 10.1107/S0021889812048133 FEB 2013
Abstract:
The H2 antagonist cimetidine forms many polymorphs, several of which have resisted structural analysis thus far. Using single-crystal X-ray measurements obtained from synchrotron radiation, the crystal structure of cimetidine form C has been solved. This layered structure crystallizes in space group C2/c with an unusually large lattice parameter, a = 82.904 angstrom. The thickness of each layer L is equal to a' = a/6 = 13.82 angstrom, and a = 6a' originates from a sixfold LLLL'L'L' sequence with L and L' differing by 0.5b. This packing is reminiscent of polytypic stacking in metals. A (3 + 1)-dimensional superspace model is derived and used to explain and predict many polytypic modifications. This model is characterized by (i) the (3 + 1)-dimensional symmetry group X2/c(alpha 0 gamma)00, where X = 0 1/2 0 1/2; (ii) the lattice parameter a' and modulation vector q = 1/n(a'*); (iii) the atomic positions of a single molecule of cimetidine form C; (iv) the primary variable, 1/n. The model reproduces the previously solved structure, the 6M polytype, and generates the related polytypes nM with lattice parameter a(nM) = na' for n = 1, 2, 3, 4 and 5. A comparison of powder X-ray diffraction patterns available for cimetidine form C with those simulated for the nM polytypes suggests that the powder samples published previously probably contain a mixture of various polytypes.
Title:
Incommensurate magnetic structures of multiferroic MnWO4 studied within the superspace formalism
Authors:
Urcelay-Olabarria, I; Perez-Mato, JM; Ribeiro, JL; Garcia-Munoz, JL; Ressouche, E; Skumryev, V; Mukhin, AA Author Full Names: Urcelay-Olabarria, I.; Perez-Mato, J. M.; Ribeiro, J. L.; Garcia-Munoz, J. L.; Ressouche, E.; Skumryev, V.; Mukhin, A. A.
Source:
PHYSICAL REVIEW B, 87 (1):10.1103/PhysRevB.87.014419 JAN 15 2013
Abstract:
The magnetic structures of the incommensurate phases of the prototypic multiferroic MnWO4 are analyzed using superspace symmetry formalism. This approach shows in a very simple way the relation between the magnetic symmetry of the incommensurate phases and any tensorial property, such as ferroelectricity. The magnetic structures have been redetermined by single-crystal neutron diffraction experiments, which revealed fine details of the AF3 and AF2 magnetic structures. The spin modulations of the two manganese ions of the basic unit cell are symmetry-related in the paraelectric incommensurate-magnetic structure (AF3)-they are not forced to be collinear but they must have opposite chirality-while in the multiferroic phase (AF2) they become symmetry independent. It is due to this symmetry break that the electric polarization arises along the b axis. DOI: 10.1103/PhysRevB.87.014419
Title:
New Layered Tin(II) Thiophosphates ASnPS(4) (A = K, Rb, Cs): Synthesis, Structure, Glass Formation, and the Modulated CsSnPS4
Authors:
Banerjee, S; Malliakas, CD; Kanatzidis, MG Author Full Names: Banerjee, Santanu; Malliakas, Christos D.; Kanatzidis, Mercouri G.
Source:
INORGANIC CHEMISTRY, 51 (21):11562-11573; 10.1021/ic301456m NOV 5 2012
Abstract:
The layered compounds KSnPS4 (1), RbSnPS4 (2), and CsSnPS4 (3) were synthesized using the chalcophosphate flux technique at high temperature and are rare examples of divalent Sn(II) thiophosphates. Orange polyhedral crystals of compound 1 crystallize in the monoclinic space group P2(1)/c with a = 6.6673(13) angstrom, b = 11.9697(24) angstrom, c = 8.7604(18), and beta=127.347(8)degrees in a 2-dimensional layered structure. Compound 2 is isostructural to 1. Yellow block shaped crystals of compound 3 crystallize in the monoclinic superspace group P2(1)(alpha beta 0)0 with a commensurate q-vector at 1/4a* + 1/4c* with a = 18.0477(14) angstrom, b = 6.2021(5) angstrom, and c = 6.8415(5) angstrom. The structure of all three compounds contains SnS3 pyramids, which is an extremely rare solid state chalcogenide coordination environment. All three compounds are semiconductors having well-defined band-gaps between 2.0 and 2.2 eV. The compounds are congruently melting and can be obtained as glasses by rapid quenching of the melt, which subsequently crystallize upon heating.

Update: 6-Feb-2013

Title:
Single crystal growth of antiferromagnetic Mn3Si by a two-phase RF floating-zone method
Authors:
Hermann, R; Wendrock, H; Rodan, S; Rossler, UK; Blum, CGF; Wurmehl, S; Buchner, B Author Full Names: Hermann, R.; Wendrock, H.; Rodan, S.; Roessler, U. K.; Blum, C. G. F.; Wurmehl, S.; Buechner, B.
Source:
JOURNAL OF CRYSTAL GROWTH, 363 1-6; 10.1016/j.jcrysgro.2012.09.029 JAN 15 2013
Abstract:
The floating-zone growth of massive intermetallic single crystals is very often unsuccessful due to unfavorable solidliquid interface geometry and insufficient mixing of the melt which depends on the flow in the molten zone. A tailored magnetic two-phase stirrer system with radio frequency (RF) heating has been developed which enables the control of the melt flow by a significant change of the flow field. The magnetic system was used for the crystal growth of the Heusler compound Mn3Si due to their interesting properties such an itinerant antiferromagnetic and incommensurate spin-density wave state. The grown crystals were oriented and cut to samples with the crystallographic orientations (100) and (110) normal to a plane. Measurements of the temperature dependence of magnetization and specific heat are discussed in terms of contributions of other thermodynamic phases and phase transitions. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Microstructure and mechanical properties of double continuously extruded Mg-Zn-Gd-based magnesium alloys
Authors:
Huang, H; Yuan, GY; Chu, ZH; Ding, WJ Author Full Names: Huang, Hua; Yuan, Guangyin; Chu, Zhenhua; Ding, Wenjiang
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 560 241-248; 10.1016/j.msea.2012.09.063 JAN 10 2013
Abstract:
Double continuous extrusion (DCE) is proposed here as a novel thermomechanical process which means that the sample is continuously extruded twice by one process. The microstructures and mechanical properties of Mg98Zn1.92Gd0.08 (at%, Alloy 1) and Mg96.83Zn2.7Gd0.47 (at%, Alloy 2) after conventional extrusion and DCE at 373 K were investigated. The results show that the major secondary phase in Alloy 1 is Mg2Zn3 and that in Alloy 2 is icosahedral quasicrystals phase (I-phase). After DCE, the microstructure is refined, and the average grain sizes of the both alloys are smaller than 1 mu m, and this further improves the mechanical properties. Both the alloys exhibit excellent mechanical properties, and the ultimate tensile strength, yield strength and elongation to failure are 434 MPa, 410 MPa and 14.6%, respectively, for Alloy 1; and 444 MPa, 417 MPa and 13.1%, respectively, for Alloy 2. The possible strengthening mechanisms were discussed and it was found that DCE is an effective method for Mg-based alloys strengthening by grain refinement and secondary phase dispersion. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Different microstructures of mobile twin boundaries in 10 M modulated Ni-Mn-Ga martensite
Authors:
Heczko, O; Straka, L; Seiner, H Author Full Names: Heczko, O.; Straka, L.; Seiner, H.
Source:
ACTA MATERIALIA, 61 (2):622-631; 10.1016/j.actamat.2012.10.007 JAN 2013
Abstract:
The morphology and microstructure of a single, macroscopically straight twin interface with a twinning stress of about 1 MPa was analysed in detail by differential interference contrast optical microscopy and X-ray diffraction. The interface was identified as a Type I macrotwin boundary between two variants with a/b-laminates and constant modulation direction, in contrast with a highly mobile twinned interface consisting of Type II macrotwin boundary segments with changing modulation direction and a/b-laminate reported earlier. Theoretical analysis using elastic continuum theory shows that only pure Type I or Type II boundaries are fully compatible with a/b-laminate. Other hypothetical twin microstructures combining these two mobile interfaces are shown to be incompatible to various degrees. A weakly incompatible combination of Type I and II boundaries was experimentally observed. The large difference in mobility between Type I and Type II macrotwin boundaries cr! eated at the same location of the same sample indicates that the mobility depends on the internal structure of these boundaries. A possible origin of this different mobility is discussed. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
A new cluster-based cubic phase in the Al-Cu-Ir system
Authors:
Dshemuchadse, J; Kuczera, P; Steurer, W Author Full Names: Dshemuchadse, Julia; Kuczera, Pawel; Steurer, Walter
Source:
INTERMETALLICS, 32 337-343; 10.1016/j.intermet.2012.08.027 JAN 2013
Abstract:
The structure of the intermetallic phase cF244-Al63.3Cu12.3Ir24.4, a superstructure of a 1/0-approximant to an icosahedral quasicrystal, was determined by single-crystal X-ray diffraction. It can be described as a packing of endohedral clusters with a significant amount of disorder in the innermost shells. Similarities to the structures of related intermetallic compounds and quasicrystal approximants are discussed. (C) 2012 Elsevier Ltd. All rights reserved.
Title:
Roles of icosahedral and crystal-like order in the hard spheres glass transition
Authors:
Leocmach, M; Tanaka, H Author Full Names: Leocmach, Mathieu; Tanaka, Hajime
Source:
NATURE COMMUNICATIONS, 3 10.1038/ncomms1974 JUL 2012
Abstract:
A link between structural ordering and slow dynamics has recently attracted much attention from the context of the origin of glassy slow dynamics. Candidates for such structural order are icosahedral, exotic amorphous and crystal-like. Each type of order is linked to a different scenario of glass transition. Here we experimentally access local structural order in polydisperse hard spheres by particle-level confocal microscopy. We identify the key structures as icosahedral and FCC-like order, both statistically associated with slow particles. However, when approaching the glass transition, the icosahedral order does not grow in size, whereas crystal-like order grows. It is the latter that governs the dynamics and is linked to dynamic heterogeneity. This questions the direct role of the local icosahedral ordering in glassy slow dynamics and suggests that the growing length scale of structural order is essential for the slowing down of dynamics and t! he non-local cooperativity in particle motion.

Update: 31-Jan-2013

Title:
Spin density wave in (FexV3-x)S-4 and the coexistence of normal and condensate states: A Mossbauer study
Authors:
Embaid, BP; Gonzalez-Jimenez, F Author Full Names: Embaid, B. P.; Gonzalez-Jimenez, F.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 330 134-140; 10.1016/j.jmmm.2012.10.030 MAR 2013
Abstract:
Iron-vanadium sulfides of the monoclinic system FexV3-xS4 (1.0 <= x <= 2.0) have been investigated by Fe-57 Mossbauer Spectroscopy in the temperature range 30-300 K. Incommensurate spin density waves (SDW) have been found in this system. An alternative treatment of the spectra allows a direct measurement of the temperature evolution of condensate density of the SDW state which follows the Maki-Virosztek formula. For composition (x=1.0) the SDW condensate is unpinned while for compositions (x > 1.0) the SDW condensate is pinned. Possible causes of the pinning-unpinning SDW will be discussed. (C) 2012 Elsevier B.V. All rights reserved.
Title:
An x-ray absorption spectroscopy study of Ni-Mn-Ga shape memory alloys
Authors:
Sathe, VG; Dubey, A; Banik, S; Barman, SR; Olivi, L Author Full Names: Sathe, V. G.; Dubey, Aditi; Banik, Soma; Barman, S. R.; Olivi, L.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (4):10.1088/0953-8984/25/4/046001 JAN 30 2013
Abstract:
The austenite to martensite phase transition in Ni-Mn-Ga ferromagnetic shape memory alloys was studied by extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) spectroscopy. The spectra at all the three elements', namely, Mn, Ga and Ni, K-edges in several Ni-Mn-Ga samples (with both Ni and Mn excess) were analyzed at room temperature and low temperatures. The EXAFS analysis suggested a displacement of Mn and Ga atoms in opposite direction with respect to the Ni atoms when the compound transforms from the austenite phase to the martensite phase. The first coordination distances around the Mn and Ga atoms remained undisturbed on transition, while the second and subsequent shells showed dramatic changes indicating the presence of a modulated structure. The Mn rich compounds showed the presence of antisite disorder of Mn and Ga. The XANES results showed remarkable changes in the unoccupied partial density of states corresponding to Mn and Ni, while the electronic structure of Ga remained unperturbed across the martensite transition. The post-edge features in the Mn K-edge XANES spectra changed from a double peak like structure to a flat peak like structure upon phase transition. The study establishes strong correlation between the crystal structure and the unoccupied electronic structure in these shape memory alloys.
Title:
The impact of oxygen on the morphology of gas-phase prepared Au nanoparticles
Authors:
Pohl, D; Surrey, A; Schultz, L; Rellinghaus, B Author Full Names: Pohl, D.; Surrey, A.; Schultz, L.; Rellinghaus, B.
Source:
APPLIED PHYSICS LETTERS, 101 (26):10.1063/1.4773203 DEC 24 2012
Abstract:
We present an easy procedure for the synthesis of single crystalline gold nanoparticles with a mean diameter of 4 nm using a DC-sputtering in an argon-oxygen gas mixture. Morphology population statistics have been determined to quantify the influence of oxygen. It is found that the particles undergo a structural transition from predominantly icosahedral to single crystalline particles with increasing amount of oxygen. Aberration-corrected high-resolution transmission electron microscopy investigation proves that likewise prepared single crystalline nanoparticles are defect and oxygen free. In contrast, the icosahedral particles prepared with pure argon show the presence of edge dislocations pointing to an energetic disfavoring already at these relatively small particle sizes. This morphology control of clean and uncovered Au nanoparticles provides a high application potential, e. g., for studying the influence of the particle morphology on plasmonic and catalytic propert! ies. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773203]
Title:
Aperiodic Spin State Ordering of Bistable Molecules and Its Photoinduced Erasing
Authors:
Collet, E; Watanabe, H; Brefuel, N; Palatinus, L; Roudaut, L; Toupet, L; Tanaka, K; Tuchagues, JP; Fertey, P; Ravy, S; Toudic, B; Cailleau, H Author Full Names: Collet, E.; Watanabe, H.; Brefuel, N.; Palatinus, L.; Roudaut, L.; Toupet, L.; Tanaka, K.; Tuchagues, J. -P.; Fertey, P.; Ravy, S.; Toudic, B.; Cailleau, H.
Source:
PHYSICAL REVIEW LETTERS, 109 (25):10.1103/PhysRevLett.109.257206 DEC 21 2012
Abstract:
We describe a novel type of ordering phenomenon associated with the incommensurate occupational modulation of bistable molecular magnetic state in a spin-crossover material. This unusual type of aperiodicity resulting from the ordering of multistable electronic states opens new possibilities for addressing such materials by light. Here we show that light can switch the crystal from four-to three-dimensional periodic structure. Mixing aperiodicity, multistability, and photoinduced phenomena opens new perspectives for directing complex order and function in material science. DOI: 10.1103/PhysRevLett.109.257206
Title:
Structural incommensurate modulation rule in hexagonal Ba(Ti1-xMx)O3-delta (M = Mn, Fe) multiferroics
Authors:
Wei, XK; Zhang, QH; Jin, CQ; Yu, RC Author Full Names: Wei, X. K.; Zhang, Q. H.; Jin, C. Q.; Yu, R. C.
Source:
AIP ADVANCES, 2 (4):10.1063/1.4766181 DEC 2012
Abstract:
The structural incommensurate modulation (SIM) rule in hexagonal Ba(Ti1-xMx)O3-delta (1/18 <= x <= 1/3, M = Mn, Fe) multiferroic ceramics is investigated using transmission electron microscope (TEM). Our systematic analysis on the modulation characteristics in the electron diffraction patterns, especially along [001] direction, reveals that three types of anti-phase domain boundaries (APBs) dominate the SIMs. According to the derived APB models, the calculated oxygen vacancies at both O1 (face sharing) and O2 (corner sharing) sites qualitatively agree quite well with our previous results. Analysis on the high-resolution TEM images reveals that complex dislocation structures also play important roles in the formation of the SIMs. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4766181]
Title:
Evidence for a monoclinic incommensurate superstructure in modulated martensite
Authors:
Li, ZB; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Zongbin; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
ACTA MATERIALIA, 60 (20):6982-6990; 10.1016/j.actamat.2012.09.001 DEC 2012
Abstract:
Structural modulation of martensitic phases is regarded as a prerequisite for magnetically or electrically induced reversible strains in shape-memory alloys. Controversy surrounds the crystal structure of modulated martensite. Here, we explore this critical issue through combined spatially resolved microstructural and crystallographic characterizations of a polycrystalline Ni53Mn22Ga25 alloy, by comparing the high-resolution Kikuchi patterns with those predicted according to various hypotheses-7M(IC) or nanotwin combination structure-on the modulated martensite. Detailed analysis has demonstrated that the modulated martensite plates may possess a monoclinic incommensurate superstructure, other than the nanotwinned tetragonal non-modulated structure. Such an incommensurate superstructure can generate a more favorable plate interface configuration for field-driven twinning/detwinning, capable of producing large reversible actuation strain. Moreover, the thermodynamically metastable modulated martensite may transform into the non-modulated martensite by further local lattice distortion, which would degrade the magnetic shape-memory effect. By taking into account the microstructure-property correlation, the ambiguity concerning the modulated martensitic structure could be clarified, which is essential to the understanding of the stability of modulated martensitic phases and their functionality as shape-memory materials. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 23-Jan-2013

Title:
Structure of Turbostratically Disordered Misfit Layer Compounds [(PbSe)0.99]1[WSe2]1, [(PbSe)1.00]1[MoSe2]1, and [(SnSe)1.03]1[MoSe2]1
Authors:
Smeller, MM; Heideman, CL; Lin, QY; Beekman, M; Anderson, MD; Zschack, P; Anderson, IM; Johnson, DC Author Full Names: Smeller, Mary M.; Heideman, Colby L.; Lin, Qiyin; Beekman, Matt; Anderson, Michael D.; Zschack, Paul; Anderson, Ian M.; Johnson, David C.
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 638 (15):2632-2639; SI 10.1002/zaac.201200408 DEC 2012
Abstract:
The structures of three new misfit layer compounds, [(PbSe)0.99]1[WSe2]1, [(PbSe)1.00]1[MoSe2]1, and [(SnSe)1.03]1[MoSe2]1, prepared as thin films from designed elementally modulated reactant precursors, have been investigated by synchrotron X-ray diffraction and scanning transmission electron microscopy. This is the second report of a misfit layer compound based on tin selenide and the first structure determinations of tungsten- and molybdenum-containing misfit layer compounds. The compounds have mismatches in both the a- and b-axis (in-plane) lattice parameters of the component structural units, which result in misfit parameters, d, both greater and smaller than zero. Pole figures of hk0-type reflections indicate that c-axis-oriented (basal plane) dichalcogenide-structured units are randomly oriented within the a-b plane. The widths of diffraction peaks of type hk0, 00l, and hkl (h, k ? 0; l ? 0) indicate coherence lengths of approximately (6 to 7) nm within the a-b plane, the full thickness of the film along the c-axis, and (1 to 2) nm in mixed-index directions, respectively, consistent with random rotational disorder between the constituents, commonly termed turbostratic disorder in the clay literature. The intensities of 00l- and hk0-type diffraction peaks were modeled to determine the structure of atomic planes along the c axis and the projection of the constituent structures onto the a-b plane, respectively.
Title:
High-pressure effects on Ti-Zr-Ni metallic glass and its corresponding quasicrystal
Authors:
Fang, YK; Jiang, JZ Author Full Names: Fang, Yuankan; Jiang, Jianzhong
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 358 (23):3212-3215; 10.1016/j.jnoncrysol.2012.09.022 DEC 1 2012
Abstract:
The room-temperature high-pressure effects on Ti38Zr38Ni24 metallic glass and its corresponding icosahedral quasicrystal have been investigated by in-situ angle-dispersive synchrotron radiation. It is demonstrated that the thermodynamic metastable metallic glass and icosahedral quasicrystal retain their structures up to 42.9 and 46.0 GPa. respectively. For the Ti38Zr38Ni24 quasicrystal, disorders are likely developed during compression. However, no special behaviors are detected in its amorphous counterpart although thermal analyses suggest that the metallic glass is possibly in microquasicrystalline nature. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Allowable irreducible representations of the point groups with five-fold rotational axes
Authors:
Rao, KRM; Simhachalam, B; Rao, PH Author Full Names: Rao, Rama Mohana K.; Simhachalam, B.; Rao, Hemagiri P.
Source:
PRAMANA-JOURNAL OF PHYSICS, 79 (6):1533-1541; 10.1007/s12043-012-0334-1 DEC 2012
Abstract:
Allowable irreducible representations of the point groups with five-fold rotations - that represent the symmetry of the quasicrystals in two and three dimensions - are derived by employing the little group technique in conjunction with the solvability property. The point groups D and are taken to illustrate the method.
Title:
High-Pressure Syntheses of Lanthanide Polysulfides and Polyselenides LnX1.9 (Ln = Gd-Tm, X = S, Se)
Authors:
Muller, CJ; Schwarz, U; Doert, T Author Full Names: Mueller, Carola J.; Schwarz, Ulrich; Doert, Thomas
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 638 (15):2477-2484; SI 10.1002/zaac.201200304 DEC 2012
Abstract:
The polysulfides LnS1.9 and polyselenides LnSe1.9 of the lanthanide metals from gadolinium to thulium were prepared by high-pressure high-temperature synthesis. The compounds adopt the tetragonal CeSe1.9 structure type in space group P42/n (No. 86) with lattice parameters of 8.531 angstrom = a = 8.654 angstrom and 15.563 angstrom = c = 15.763 angstrom for the sulfides and 8.869 angstrom = a = 9.076 angstrom and 16.367 angstrom = c = 16.611 angstrom for the selenides. The atomic pattern consists of puckered double slabs [LnX]+ and planar chalcogenide layers with ten possible chalcogen positions, of which eight are occupied by chalcogen atoms forming dinuclear X22 dianions, one by a single X2 ion and one remaining vacant. This resembles a v5x5?x?2 superstructure of the ZrSSi aristotype. Structural relationships to the aristotype and the related lanthanide polychalcogenides LnX2d (Ln = LaTm, X = STe, d = 0 0.3) are discussed. The samples synthesized under high-pressure conditions (p > 1 GPa) decompose slowly under release of sulfur or selenium at ambient conditions. The crystal structure of a partially degraded thulium-polysulfide sample can be described as an incommensurate variant of the original TmS1.9 motif. Additionally, the isostructural ternary compound Gd(S1xSex)1.9 was synthesized and characterized by powder X-ray diffraction.

Update: 16-Jan-2013

Title:
P2-NaxVO2 system as electrodes for batteries and electron-correlated materials
Authors:
Guignard, M; Didier, C; Darriet, J; Bordet, P; Elkaim, E; Delmas, C Author Full Names: Guignard, Marie; Didier, Christophe; Darriet, Jacques; Bordet, Pierre; Elkaim, Erik; Delmas, Claude
Source:
NATURE MATERIALS, 12 (1):74-80; 10.1038/NMAT3478 JAN 2013
Abstract:
Layered oxides are the subject of intense studies either for their properties as electrode materials for high-energy batteries or for their original physical properties due to the strong electronic correlations resulting from their unique structure. Here we present the detailed phase diagram of the layered P2-NaxVO2 system determined from electrochemical intercalation/deintercalation in sodium batteries and in situ X-ray diffraction experiments. It shows that four main single-phase domains exist within the 0.5 <= x <= 0.9 range. During the sodium deintercalation (intercalation), they differ from one another in the sodium/vacancy ordering between the VO2 slabs, which leads to commensurable or incommensurable superstructures. The electrochemical curve reveals that three peculiar compositions exhibit special structures for x = 1/2, 5/8 and 2/3. The detailed structural characterization of the P2-Na1/2VO2 phase shows that the Na+ ions are perfectly ordered to minimize Na+/Na+ electrostatic repulsions. Within the VO2 layers, the vanadium ions form pseudo-trimers with very short V-V distances (two at 2.581 angstrom and one at 2.687 angstrom). This original distribution leads to a peculiar magnetic behaviour with a low magnetic susceptibility and an unexpected low Curie constant. This phase also presents a first-order structural transition above room temperature accompanied by magnetic and electronic transitions. This work opens up a new research domain in the field of strongly electron-correlated materials. From the electrochemical point of view this system may be at the origin of an entire material family optimized by cationic substitutions.
Title:
Electrochemical hydrogen storage characteristics of TiVNi-quasicrystalline composite materials
Authors:
Liu, WQ; Zhang, SS; Hu, W; Wang, LM Author Full Names: Liu, Wanqiang; Zhang, Shanshan; Hu, Wen; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF NANOTECHNOLOGY, 10 (1-2):80-88; 10.1504/IJNT.2013.050884 2013
Abstract:
The Ti1.4V0.6Ni ribbon alloy and VTZN (V5Ti9Zr26.7Ni38Cr5Mn16Sn0.3) alloy ingot are prepared by melt- spinning technique and induction levitation melting technique, respectively. The Ti1.4V0.6Ni + 20 wt.% VTZN mixture powders are synthesised by ball-milling the above prepared alloy ingots, and their structures and the electrochemical hydrogen storage properties are investigated. It is found that the icosahedral quasicrystal, FCC and BCC structural solid solution phase are all presented in the composite material. The maximum electrochemical discharge capacity of the composite electrode is 308.2 mAh/g at the discharge current density of 30 mA/g and 303 K. In addition, the electrode made of Ti1.4V0.6Ni and AB(3) composite holds better high- rate discharge ability than that of Ti1.4V0.6Ni.
Title:
Equivalence of superspace groups
Authors:
van Smaalen, S; Campbell, BJ; Stokes, HT Author Full Names: van Smaalen, Sander; Campbell, Branton J.; Stokes, Harold T.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 75-90; 10.1107/S0108767312041657 Part 1 JAN 2013
Abstract:
An algorithm is presented which determines the equivalence of two settings of a (3 + d)-dimensional superspace group (d = 1, 2, 3). The algorithm has been implemented as a web tool findssg on SSG(3 + d)D, providing the transformation of any user-given superspace group to the standard setting of this superspace group in SSG(3 + d)D. It is shown how the standard setting of a superspace group can be directly obtained by an appropriate transformation of the external-space lattice vectors (the basic structure unit cell) and a transformation of the internal-space lattice vectors (new modulation wavevectors are linear combinations of old modulation wavevectors plus a three-dimensional reciprocal-lattice vector). The need for non-standard settings in some cases and the desirability of employing standard settings of superspace groups in other cases are illustrated by an analysis of the symmetries of a series of compounds, comparing published and standard settings and the transformations between them. A compilation is provided of standard settings of compounds with two-and three-dimensional modulations. The problem of settings of superspace groups is discussed for incommensurate composite crystals and for chiral superspace groups.
Title:
Spatially modulated antiferromagnetic structures in a multiferroic with biaxial anisotropy
Authors:
Popkov, AF; Solov'ev, SV; Kulagin, NE; Zvezdin, AK Author Full Names: Popkov, A. F.; Solov'ev, S. V.; Kulagin, N. E.; Zvezdin, A. K.
Source:
SEMICONDUCTORS, 46 (13):1568-1572; 10.1134/S1063782612130155 DEC 2012
Abstract:
Possible types of spatially modulated periodic antiferromagnetic structures in a uniaxial rhombohedral multiferroic with BiFeO3 crystal symmetry are studied depending on the ratio of the parameters of uniaxial and basal anisotropy and on magnetoelectric coupling. DOI: 10.1134/S1063782612130155
Title:
Room Temperature Modulated Structure of Ca and K co-Doped LaMnO3
Authors:
Hou, CM; Huang, KK; Hu, B; Yuan, HM; Feng, SH Author Full Names: Hou Chang-min; Huang Ke-ke; Hu Bin; Yuan Hong-ming; Feng Shou-hua
Source:
CHEMICAL RESEARCH IN CHINESE UNIVERSITIES, 28 (5):784-787; SEP 2012
Abstract:
A series of perovskite compounds of La1-x-yCaxKyMnO3 was prepared by hydrothermal disproportionation reaction of MnO2. The three oxidation states of manganese(Mn3+, Mn4+ and Mn5+) can stably exist in the compounds. Under room temperature conditions, twice and three times modulated structure produced by the charge ordering can be observed by X-ray diffraction (XRD), select area electron diffraction (SAED) and high resolution transmission electron microscopy (HR-TEM). The splits of the diffraction peaks of the single crystals confirmed by synchrotron X-ray diffraction experiment are in accordance with those of the powder sample. The existence of the different oxidation states of Mn3+, Mn4+ and Mn5+ can be considered to be the dominating reason of the complicated room temperature modulated structure.

Update: 9-Jan-2013

Title:
Rapidly solidified high-temperature aluminum alloys. I. Structure
Authors:
Krainikov, AV; Neikov, OD Author Full Names: Krainikov, A. V.; Neikov, O. D.
Source:
POWDER METALLURGY AND METAL CERAMICS, 51 (7-8):399-411; 10.1007/s11106-012-9448-8 NOV 2012
Abstract:
The paper examines the phase composition of a number of high-temperature aluminum alloys formed in rapid solidification. The main strengthening phases and associated phase transitions in Al-Fe-Ce, Al-Fe-Cr-(TM), Al-Cr-Zr(Mn), and Al-Fe-V(Mo)-Si alloys have been studied. The phase composition of the alloys is shown to be critically dependent on the cooling rate. High-temperature materials are particularly sensitive to the solidification rate since they are doped by nonsoluble elements. Fine quasicrystalline phases, which make a significant contribution to strengthening at low and high temperatures, are present in rapidly solidified materials doped with iron. Besides these phases, Al3TM intermetallics characterized by high thermal stability and low coarsening rate play an important role in modern materials.
Title:
Morphology Evolution of MZY Quasicrystal Particle in AZ91 Alloy Strengthened by MZY Quasicrystal Alloy
Authors:
Liu, T; Teng, XY; Liu, LY; Zhao, ZW Author Full Names: Liu Teng; Teng Xinying; Liu Liyan; Zhao Zhenwei
Source:
RARE METAL MATERIALS AND ENGINEERING, 41 28-31; 2 SEP 2012
Abstract:
The influence of holding time on the microstructures of MZY quasicrystal particle in AZ91 alloy strengthened by quasicrystals alloy was studied using SEM equipped with energy dispersive spectrometer (EDS). The results show that holding time could obviously influence the microstructures of MZY quasicrystal particle in AZ91 alloy strengthened by quasicrystals alloy. When holding time is within 2 min, the five petals-like quasicrystals could be left well in AZ91 matrix alloy; for the holding time of 4 min, the smooth petal's top of Mg3Zn6Y quasicrystal particle becomes sharp and its petals change for polygons; as holding time of 6 similar to 8 min, the petals of Mg3Zn6Y quasicrystals particle begin to desquamate, the phenomena of groomed fracture would appear in a single petals; for the holding time of 10 min and more, the petals of Mg3Zn6Y quasicrystal particle are not obvious and the petals with stamen form the oval quasicrystal particles.

Update: 2-Jan-2013

Title:
Temperature-dependent IR and Raman scattering studies of phase transitions in K2MgWO2 (PO4)(2)
Authors:
Maczka, M; Majchrowski, A; Hanuza, J; Kojima, S Author Full Names: Maczka, M.; Majchrowski, A.; Hanuza, J.; Kojima, S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (2):10.1088/0953-8984/25/2/025901 JAN 16 2013
Abstract:
Temperature-dependent Raman scattering and IR experiments were performed on K2MgWO2(PO4)(2), which is derived from KTP by the replacement of two Ti4+ ions with Mg2+ and W6+ cations. These studies revealed significant changes in phonon properties of these materials with increasing temperature due to the onset of phase transitions at 436, 537 and 637 K. Analysis of the obtained data showed that disordering processes in the sublattice of potassium ions play a significant role in the mechanism of these phase transitions. However, these transitions are also accompanied by weak tilts of the nearly rigid PO4, WO6 and MgO6 groups. Present results also provide strong arguments that the phase transition at 637 K can be classified as occurring from the normal high-temperature phase with D-4 point symmetry into a modulated or incommensurate phase with the same D-4 point symmetry. Our results also show that the order disorder (displacive) contribution to the phase transition mechanism is significantly stronger (weaker) in K2MgWO2(PO4)(2) when compared to KTP.
Title:
Light wave states in quasiperiodic metallic structures
Authors:
Wang, K Author Full Names: Wang, Kang
Source:
PHYSICAL REVIEW B, 86 (23):10.1103/PhysRevB.86.235110 DEC 10 2012
Abstract:
We investigate the light wave states in the octagonal and decagonal quasiperiodic metallic structures by considering their respective approximants at different orders. The mechanisms underlying the light wave behaviors are studied in relation to various structure parameters and configurations. We show that the formation of the first passbands, that delimit the photonic band gaps and determine the plasma gaps, involves only the lowest frequency resonance modes inside the fat tiles, and that light localization occurs due to resonances in high symmetry local centers as well as in the fragments of such centers, formed by the skinny tiles. The structure filling rate affects the localized state frequencies relative to the first passbands, as well as the plasma frequency levels, by modulating the frequency levels of the resonance modes and the widths of the passbands. The results of this study can be generalized to other metallic quasiperiodic and related structures.
Title:
Neutron scattering study of ferroelectric Sn2P2S6 under pressure
Authors:
Ondrejkovic, P; Kempa, M; Vysochanskii, Y; Saint-Gregoire, P; Bourges, P; Rushchanskii, KZ; Hlinka, J Author Full Names: Ondrejkovic, P.; Kempa, M.; Vysochanskii, Y.; Saint-Gregoire, P.; Bourges, P.; Rushchanskii, K. Z.; Hlinka, J.
Source:
PHYSICAL REVIEW B, 86 (22):10.1103/PhysRevB.86.224106 DEC 7 2012
Abstract:
Ferroelectric phase transition in the semiconductor Sn2P2S6 single crystal has been studied by means of neutron scattering in the pressure-temperature range adjacent to the anticipated tricritical Lifshitz point (p approximate to 0.18 GPa, T approximate to 296 K). The observations reveal a direct ferroelectric-paraelectric phase transition in the whole investigated pressure range (0.18-0.6 GPa). These results are in a clear disagreement with phase diagrams assumed in numerous earlier works, according to which a hypothetical intermediate incommensurate phase extends over several or even tens of degrees in the 0.5 GPa pressure range. Temperature dependence of the anisotropic quasielastic diffuse scattering suggests that polarization fluctuations present above T-C are strongly reduced in the ordered phase. Still, the temperature dependence of the ((2) over bar 00) Bragg reflection intensity at p = 0.18 GPa can be remarkably well modeled assuming the order-parameter amplitude growth according to the power law with logarithmic corrections predicted for a uniaxial ferroelectric transition at the tricritical Lifshitz point.
Title:
Unusual Urbach tail in TlGaSe2 ferroelectric-semiconductor with incommensurate phase
Authors:
Seyidov, MY; Suleymanov, RA; Sale, Y Author Full Names: Seyidov, MirHasan Yu; Suleymanov, Rauf A.; Sale, Yasin
Source:
JOURNAL OF APPLIED PHYSICS, 112 (10):10.1063/1.4765736 NOV 15 2012
Abstract:
An analysis of temperature behavior of optical absorption edge is performed for TlGaSe2 ferroelectric-semiconductor with incommensurate phase. Unusual behavior of the Urbach tail manifested by the shift of the absorption edge toward the higher energies with increasing temperature was observed. It was shown that such behavior is due to the specific temperature interval where Urbach energy decreases with the temperature. This interval corresponds to the incommensurate phase-commensurate phase transition region. Unusual behavior of the Urbach energy can be explained interpreting the incommensurate phase as some type of disordered state, and TlGaSe2 crystal as a disordered semiconductor with controllable disorder. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765736]
Title:
Formation of Al67Cu23Fe10 quasicrystals by microwave heating
Authors:
Mihoc, C; Schick, D; Lutgens, M; Lathe, C; Burkel, E Author Full Names: Mihoc, Carmen; Schick, Daniel; Luetgens, Matthias; Lathe, Christian; Burkel, Eberhard
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 103 (11):1340-1344; 10.3139/146.110786 NOV 2012
Abstract:
The present work was carried out to compare the formation of single icosahedral phase during conventional heating and microwave processing. Al67Cu23Fe10 alloy powder was synthesized from high purity (99.9%) powder elements by mechanical alloying. Differential scanning calorimetry combined with in-situ synchrotron energy dispersive X-ray diffraction was used to identify the main solid state reactions and the phase evolution of the powders. Inductive microwave processing in the magnetic field anti-node was performed to obtain the quasicrystalline phase in only a few seconds. Due to the rapid cooling of the sample it was possible to stabilize the icosahedral phase against its competing quasicrystalline approximants. Laboratory X-ray diffraction analysis was used to characterise the atomic structure of the specimen and scanning electron microscopy was used to characterise the microstructure after the microwave processing.

Update: 27-Dec-2012

Title:
Vanishing of the metal-insulator Peierls transition in pressurized BaVS3
Authors:
Bernu, S; Fertey, P; Itie, JP; Berger, H; Foury-Leylekian, P; Pouget, JP Author Full Names: Bernu, S.; Fertey, P.; Itie, J. -P.; Berger, H.; Foury-Leylekian, P.; Pouget, J. -P.
Source:
PHYSICAL REVIEW B, 86 (23):10.1103/PhysRevB.86.235105 DEC 5 2012
Abstract:
BaVS3 presents a metal-to-insulator (MI) transition at ambient pressure due to the stabilization of a 2k(F) commensurate charge density wave (CDW) Peierls ground state built on the dz(2) V orbitals. The MI transition vanishes under pressure at a quantum critical point (QCP) where the electronic properties exhibit a non-Fermi liquid behavior. In this paper, we determine the CDW phase diagram under pressure and show that it combines both the vanishing of the second-order Peierls transition and a commensurate-incommensurate first-order delocking transition of the 2k(F) wave vector. We explain quantitatively the drop of the MI critical temperature by the decrease of the electron-hole pair lifetime of the CDW condensate due to an enhancement of the hybridization between the dz(2) and e(t(2g)) levels of the V under pressure.
Title:
Interfacial energies on quasicrystals
Authors:
Braides, A; Causin, A; Solci, M Author Full Names: Braides, Andrea; Causin, Andrea; Solci, Margherita
Source:
IMA JOURNAL OF APPLIED MATHEMATICS, 77 (6):816-836; SI 10.1093/imamat/hxs046 DEC 2012
Abstract:
We consider nearest-neighbour ferromagnetic energies defined on a quasicrystal modeled following the so-called cut-and-project approach as a portion of a regular lattice contained in a possibly irrational stripe defined as a neighborhood of a k-dimensional subspace in an n-dimensional space. The overall properties of this system are described by an effective surface energy on a k-dimensional space obtained as Gamma-limit of the scaled discrete energies.
Title:
Confirmation of the Random Tiling Hypothesis for a Decagonal Quasicrystal
Authors:
Kiselev, A; Engel, M; Trebin, HR Author Full Names: Kiselev, Alexander; Engel, Michael; Trebin, Hans-Rainer
Source:
PHYSICAL REVIEW LETTERS, 109 (22):10.1103/PhysRevLett.109.225502 NOV 29 2012
Abstract:
Mechanisms that stabilize quasicrystals are much discussed but not finally resolved. We confirm the random tiling hypothesis and its predictions in a fully atomistic decagonal quasicrystal model by calculating the free energy and the phason elastic constants over a wide range of temperatures. The Frenkel-Ladd method is applied for the phonon part, and an approach of uncorrelated phason flips is applied for the configurational part. When lowering the temperature, a phase transition to an approximant occurs. Close to the transition temperature, one of the phason elastic constants becomes soft.
Title:
Molecular dynamics simulation of reversibly self-assembling shells in solution using trapezoidal particles
Authors:
Rapaport, DC Author Full Names: Rapaport, D. C.
Source:
PHYSICAL REVIEW E, 86 (5):10.1103/PhysRevE.86.051917 Part 1 NOV 29 2012
Abstract:
The self-assembly of polyhedral shells, each constructed from 60 trapezoidal particles, is simulated using molecular dynamics. The spatial organization of the component particles in this shell is similar to the capsomer proteins forming the capsid of a T = 1 virus. Growth occurs in the presence of an atomistic solvent and, under suitable conditions, achieves a high yield of complete shells. The simulations provide details of the structure and lifetime of the particle clusters that appear as intermediate states along the growth pathway, and the nature of the transitions between them. In certain respects the growth of size-60 shells from trapezoidal particles resembles the growth of icosahedral shells from triangular particles studied previously, with reversible bonding playing a major role in avoiding incorrect assembly, although the details differ due to particle shape and bond organization. The strong preference for maximal bonding exhibited by the triangular pa! rticle clusters is also apparent for trapezoidal particles, but this is now confined to early growth and is less pronounced as shells approach completion along a variety of pathways.
Title:
Vortex dynamics in ferromagnetic superconductors: Vortex clusters, domain walls, and enhanced viscosity
Authors:
Lin, SZ; Bulaevskii, LN; Batista, CD Author Full Names: Lin, Shi-Zeng; Bulaevskii, Lev N.; Batista, Cristian D.
Source:
PHYSICAL REVIEW B, 86 (18):10.1103/PhysRevB.86.180506 NOV 28 2012
Abstract:
We demonstrate that there is a long-range vortex-vortex attraction in ferromagnetic superconductors due to polarization of the magnetic moments. Vortex clusters are then stabilized in the ground state for low vortex densities. The motion of vortex clusters driven by the Lorentz force excites magnons. This regime becomes unstable at a threshold velocity above which domain walls are generated for slow relaxation of the magnetic moments and the vortex configuration becomes modulated. This dynamics of vortices and magnetic moments can be probed by transport measurements.
Title:
Self-Similar Micron-Size and Nanosize Drops of Liquid Generated by Surface Acoustic Waves
Authors:
Taller, D; Go, DB; Chang, HC Author Full Names: Taller, Daniel; Go, David B.; Chang, Hsueh-Chia
Source:
PHYSICAL REVIEW LETTERS, 109 (22):10.1103/PhysRevLett.109.224301 NOV 27 2012
Abstract:
A planar surface acoustic wave on a solid substrate and its radiated sound into a static liquid drop produce time-averaged, exponentially decaying acoustic and electric Maxwell pressures near the contact line. These localized contact-line pressures are shown to generate two sequences of hemispherical satellite droplets at the tens of microns and submicron scales, both obeying self-similar exponential scaling but with distinct exponents that correspond to viscous dissipation and field leakage length scales, respectively. The acoustic pressure becomes dominant when the film thickness exceeds (1/4 pi) of the surface acoustic wave wavelength and it affects the shape and stability of the mother drop. The Maxwell pressure of the nanodrops, which exceeds ten atmospheres, is sensitive to the contact angle.
Title:
Persistent Spin Dynamics Intrinsic to Amplitude-Modulated Long-Range Magnetic Order
Authors:
Pregelj, M; Zorko, A; Zaharko, O; Arcon, D; Komelj, M; Hillier, AD; Berger, H Author Full Names: Pregelj, M.; Zorko, A.; Zaharko, O.; Arcon, D.; Komelj, M.; Hillier, A. D.; Berger, H.
Source:
PHYSICAL REVIEW LETTERS, 109 (22):10.1103/PhysRevLett.109.227202 NOV 27 2012
Abstract:
An incommensurate elliptical helical magnetic structure in the frustrated coupled-spin-chain system FeTe2O5Br is surprisingly found to persist down to 53(3) mK (T/T-N similar to 1/200), according to neutron scattering and muon spin relaxation. In this state, finite spin fluctuations at T -> 0 are evidenced by muon depolarization, which is in agreement with specific-heat data indicating the presence of both gapless and gapped excitations. We thus show that the amplitude-modulated magnetic order intrinsically accommodates contradictory persistent spin dynamics and long-range order and can serve as a model structure to investigate their coexistence.
Title:
Effects of icosahedral phase formation on the microstructure and mechanical improvement of Mg alloys: A review
Authors:
Xu, DK; Han, EH Author Full Names: Xu, D. K.; Han, E. H.
Source:
PROGRESS IN NATURAL SCIENCE-MATERIALS INTERNATIONAL, 22 (5):364-385; 10.1016/j.pnsc.2012.09.005 OCT 2012
Abstract:
Icosahedral phase (I-phase) is a relatively excellent strengthening phase in Mg alloys. Depending on their volume fraction, the yield strength of Mg-Zn-Y-Zr alloys can vary from 150 to 450 MPa at room temperature. Recently, the formation of I-phase has been considered as one of the most effective methods for developing high strength lightweight Mg alloys for automotive and aerospace applications. In this review article, a series of research work about I-phase containing Mg alloys have been systematically investigated including I-phase formation mechanism and their effects on mechanical properties of Mg alloys. Particular emphases have been given to: (1) Structure of I-phase and its orientation relationship with the alpha-Mg matrix. (2) Influence of alloying elements and solidification conditions on I-phase formation. (3) Effects of I-phase on microstructural evolution and mechanical improvement of Mg-Zn-Y-(Zr) alloys. Moreover, the applications of I-phase for the mechanical improvement of other Mg alloys such as AZ91 and super-lightweight Mg-Li alloys are also reviewed. (c) 2012 Chinese Materials Research Society. Production and hosting by Elsevier Ltd. All rights reserved.
Title:
CHARACTERIZATION OF AS-SPUN AND ANNEALED Al-Mn-Fe RIBBONS
Authors:
Stan, K; Litynska-Dobrzynska, L; Goral, A; Wierzbicka-Miernik, A Author Full Names: Stan, K.; Litynska-Dobrzynska, L.; Goral, A.; Wierzbicka-Miernik, A.
Source:
ARCHIVES OF METALLURGY AND MATERIALS, 57 (3):651-656; 10.2478/v10172-012-0069-5 2012
Abstract:
Microstructure of conventionally cast and melt spun Al91Mn7Fe2 alloy was examined by X-ray diffraction, SEM and TEM techniques. Three different phases were found in a mould cast ingot: Al-6(Mn, Fe), Al-4(Mn, Fe) and aluminium solid solution. Rapidly quenched ribbons cast using melt spinning technique with different speed values of rotating wheel: 25, 30 and 36 m/s had average width in a range of 30-50 mu m. It was found that ribbons contain quasicrystalline particles with different sizes and shapes including large dendrites in a range of micrometers and smaller spherical particles below 1 mu m embedded in an aluminium matrix. Composition of these particles was similar to the Al-4(Mn, Fe) phase. Also quasicrystals in the form of eutectic were observed with slightly different composition close to the Al-6(Mn, Fe) phase. All observed particles revealed 2, 3 and 5- fold symmetry, typical for icosahedral quasicrystals. Increase in microhardness up to 274 HV for melt spun ribbon comparing to 141 HV for the as-cast ingot was observed due to a change in phase composition and refinement of the phases. Thermal stability of quasicrystalline phase in the ribbon was examined by annealing in different temperatures. Temperatures for thermal treatment were chosen based on DSC curve which contains the exothermic peak in the temperature range 300-500 degrees C. Analysis of ribbons annealed for 30 minutes at 400 degrees C showed that transformation of quasicrystals to stable crystalline phase starts at quasicrystal/Al-matrix interfaces. After annealing for 4 hours at 500 degrees C only the Al-6(Mn, Fe) phase and aluminium solid solution were observed in the ribbon microstructure.

Update: 20-Dec-2012

Title:
Compositional uniformity, domain patterning and the mechanism underlying nano-chessboard arrays
Authors:
Gonzalez, S; Perez-Mato, JM; Elcoro, L; Garcia, A; Withers, RL; Bourgeois, L Author Full Names: Gonzalez, Santiago; Perez-Mato, J. M.; Elcoro, Luis; Garcia, Alberto; Withers, Ray L.; Bourgeois, Laure
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (49):10.1088/0953-8984/24/49/495301 DEC 12 2012
Abstract:
We propose that systems exhibiting compositional patterning at the nanoscale, so far assumed to be due to some kind of ordered phase segregation, can be understood instead in terms of coherent, single phase ordering of minority motifs, caused by some constrained drive for uniformity. The essential features of this type of arrangement can be reproduced using a superspace construction typical of uniformity-driven orderings, which only requires the knowledge of the modulation vectors observed in the diffraction patterns. The idea is discussed in terms of a simple two-dimensional lattice-gas model that simulates a binary system in which the dilution of the minority component is favoured. This simple model already exhibits a hierarchy of arrangements similar to the experimentally observed nano-chessboard and nano-diamond patterns, which are described as occupational modulated structures with two independent modulation wavevectors and simple step-like occupation modulation functions.
Title:
HAADF-STEM study of chemical ordering in Al-Pd-Sc 1/1-crystal approximant
Authors:
So, YG; Nagao, M; Nagai, T; Kimoto, K Author Full Names: So, Yeong-Gi; Nagao, Masahiro; Nagai, Takuro; Kimoto, Koji
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 543 7-11; 10.1016/j.jallcom.2012.07.119 DEC 5 2012
Abstract:
The atomic structure of the Al54Pd31Sc15 1/1-crystal approximant to the icosahedral quasicrystal has been studied using high-angle annular dark-field (HAADF) imaging in a scanning transmission electron microscopy (STEM). HAADF imaging directly reveals that the 1/1-phase has a periodic arrangement of Tsai-type atomic clusters, which consist of three successive shells with icosahedral symmetry as well as a disordered tetrahedron at the cluster center. In the 1/1-phase, the chemical ordering of Al and Pd is observed in the glue sites between the clusters, similar to that of Al and Au in the recently discovered Al35Au51Yb14 1/1-phase, indicating a common structural feature of ternary Tsai-type approximants. Moreover, the preferential introduction of structural disorder into the second dodecahedral shell is observed in the HAADF images, which causes symmetry breaking of the 1/1-phase. On the basis of a comparison with the experimental and simulated images, a preliminary model for the atomic structure of the 1/1-phase is presented. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Comparative structural study of decagonal quasicrystals in the systems Al-Cu-Me (Me = Co, Rh, Ir)
Authors:
Kuczera, P; Wolny, J; Steurer, W Author Full Names: Kuczera, Pawel; Wolny, Janusz; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 578-589; 10.1107/S0108768112041134 Part 6 DEC 2012
Abstract:
A comparative single-crystal X-ray diffraction structure analysis of the family of Al-Cu-Me (Me = Co, Rh and Ir) decagonal quasicrystals is presented. In contrast to decagonal Al-Cu-Co, the other two decagonal phases do not show any structured disorder diffuse scattering indicating a higher degree of order. Furthermore, the atomic sites of Rh and Ir can be clearly identified, while Cu and Co cannot be distinguished because of their too similar atomic scattering factors. The structure models, derived from charge-flipping/low-density elimination results, were refined within the tiling-decoration method but also discussed in the five-dimensional embedding approach. The basic structural building units of the closely related structures are decagonal clusters with 33 angstrom diameter, which are consistent with the available electron-microscopic images. The refined structure models agree very well with the experimental data.
Title:
Varied linear phason strain and its induced domain structure in quasicrystalline precipitates of Zr-Al-Ni-Cu-Nb bulk metallic glass matrix composites
Authors:
Lu, L; Xiong, DX; Wang, JB; Zhao, DS; Sun, YF Author Full Names: Lu, Lu; Xiong, Dongxia; Wang, Jianbo; Zhao, Dongshan; Sun, Yufeng
Source:
JOURNAL OF MATERIALS RESEARCH, 27 (23):3041-3048; 10.1557/jmr.2012.351 DEC 2012
Abstract:
Quasicrystalline precipitates in ZrAlNiCuNb alloy were systematically studied by transmission electron microscopy. It was found that precipitates always contain various linear phason strains. By electron diffraction analysis, two types of linear phason strain with two different directions perpendicular to the incident beam described by strain matrices with only one nonzero element were identified. After measuring the deviations of diffraction spots and quantitatively fitting against their perpendicular components of the reciprocal lattice vectors, the phason strain matrices were obtained. Domain structures formed as a result of linear phason strain variants along directions with equal probability. Electron diffraction and high-resolution electron imaging provide supportive evidence of this result.
Title:
Quantum critical state in a magnetic quasicrystal
Authors:
Deguchi, K; Matsukawa, S; Sato, NK; Hattori, T; Ishida, K; Takakura, H; Ishimasa, T Author Full Names: Deguchi, Kazuhiko; Matsukawa, Shuya; Sato, Noriaki K.; Hattori, Taisuke; Ishida, Kenji; Takakura, Hiroyuki; Ishimasa, Tsutomu
Source:
NATURE MATERIALS, 11 (12):1013-1016; 10.1038/NMAT3432 DEC 2012
Abstract:
Quasicrystals are metallic alloys that possess long-range, aperiodic structures with diffraction symmetries forbidden to conventional crystals. Since the discovery of quasicrystals by Schechtman et al. in 1984(1), there has been considerable progress in resolving their geometric structure. For example, it is well known that the golden ratio of mathematics and art occurs over and over again in their crystal structure. However, the characteristic properties of the electronic states-whether they are extended as in periodic crystals or localized as in amorphous materials-are still unresolved. Here we report the first observation of quantum (T = 0) critical phenomena of the Au-Al-Yb quasicrystal-the magnetic susceptibility and the electronic specific heat coefficient arising from strongly correlated 4f electrons of the Yb atoms diverge as T -> 0. Furthermore, we observe that this quantum critical phenomenon is robust against hydrostatic pressure. By contrast, there is no such divergence in a crystalline approximant, a phase whose composition is close to that of the quasicrystal and whose unit cell has atomic decorations (that is, icosahedral clusters of atoms) that look like the quasicrystal. These results clearly indicate that the quantum criticality is associated with the unique electronic state of the quasicrystal, that is, a spatially confined critical state. Finally we discuss the possibility that there is a general law underlying the conventional crystals and the quasicrystals.
Title:
Structural transformation of Sb-based high-speed phase-change material
Authors:
Matsunaga, T; Kojima, R; Yamada, N; Kubota, Y; Kifune, K Author Full Names: Matsunaga, Toshiyuki; Kojima, Rie; Yamada, Noboru; Kubota, Yoshiki; Kifune, Kouichi
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 559-570; 10.1107/S0108768112039961 Part 6 DEC 2012
Abstract:
The crystal structure of a phase-change recording material (the compound Ag3.4In3.7Sb76.4Te16.5) enclosed in a vacuum capillary tube was investigated at various temperatures in a heating process using a large Debye-Scherrer camera installed in BL02B2 at SPring-8. The amorphous phase of this material turns into a crystalline phase at around 416 K; this crystalline phase has an A7-type structure with atoms of Ag, In, Sb or Te randomly occupying the 6c site in the space group. This structure was maintained up to around 545 K as a single phase, although thermal expansion of the crystal lattice was observed. However, above this temperature, phase separation into AgInTe2 and Sb-Te transpired. The first fragment, AgInTe2, reliably maintained its crystal structure up to the melting temperature. On the other hand, the atomic configuration of the Sb-Te gradually varied with increasing temperature. This gradual structural transformation can be described as a continuous growth of the modulation period gamma.
Title:
Bulk Electronic Structure of Quasicrystals
Authors:
Nayak, J; Maniraj, M; Rai, A; Singh, S; Rajput, P; Gloskovskii, A; Zegenhagen, J; Schlagel, DL; Lograsso, TA; Horn, K; Barman, SR Author Full Names: Nayak, J.; Maniraj, M.; Rai, Abhishek; Singh, Sanjay; Rajput, Parasmani; Gloskovskii, A.; Zegenhagen, J.; Schlagel, D. L.; Lograsso, T. A.; Horn, K.; Barman, S. R.
Source:
PHYSICAL REVIEW LETTERS, 109 (21):10.1103/PhysRevLett.109.216403 NOV 20 2012
Abstract:
We use hard x-ray photoemission to resolve a controversial issue regarding the mechanism for the formation of quasicrystalline solids, i.e., the existence of a pseudogap at the Fermi level. Our data from icosahedral fivefold Al-Pd-Mn and Al-Cu-Fe quasicrystals demonstrate the presence of a pseudogap, which is not observed in surface sensitive low energy photoemission because the spectrum is affected by a metallic phase near the surface. In contrast to Al-Pd-Mn, we find that in Al-Cu-Fe the pseudogap is fully formed; i.e., the density of states reaches zero at E-F indicating that it is close to the metal-insulator phase boundary.
Title:
Magnetic phase transitions in PrMn2O5: Importance of ion-size threshold size effects in RMn2O5 compounds (R = rare earth)
Authors:
Doubrovsky, C; Andre, G; Gukasov, A; Auban-Senzier, P; Pasquier, CR; Elkaim, E; Li, M; Greenblatt, M; Damay, F; Foury-Leylekian, P Author Full Names: Doubrovsky, C.; Andre, G.; Gukasov, A.; Auban-Senzier, P.; Pasquier, C. R.; Elkaim, E.; Li, M.; Greenblatt, M.; Damay, F.; Foury-Leylekian, P.
Source:
PHYSICAL REVIEW B, 86 (17):10.1103/PhysRevB.86.174417 NOV 19 2012
Abstract:
A detailed investigation of the thermodynamic, structural, and magnetic properties of high quality polycrystalline PrMn2O5 samples are presented. In contrast with members of the RMn2O5 family with smaller rare-earth ions, PrMn2O5 is not ferroelectric and does not undergo a transition to an incommensurate (q(x), 0, q(z)) magnetic phase: It exhibits two magnetic transitions, corresponding to commensurate magnetic orderings at T-1 = 25 +/- 1 K and T-2 = 18 +/- 1 K. These two magnetic transitions are characterized by two orthogonal propagation vectors q(1) = (1/2,0,0) and q(2) = (0,0,1/2), respectively, which coexist below (T)2. The refinement of the neutron data show that Mn3+ order primarily at T-1, following q(1); below T-2, the Mn4+ sublattice orders following q(2).
Title:
Effects of hydrogen on the magnetic properties of TiZrNi quasicrystals
Authors:
Shin, H; Lee, SH; Jo, Y; Kim, J Author Full Names: Shin, Hongsik; Lee, Sang-hwa; Jo, Youngsoo; Kim, Jaeyong
Source:
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 61 (9):1541-1544; 10.3938/jkps.61.1541 NOV 2012
Abstract:
The magnetic properties of hydrogenated metastable TiZrNi quasicrystals and their structures were studied. After hydrogenation, the quasi-lattice constants uniformly increased from 5.12 to 5.40 with a narrower peak width in X-ray diffraction, suggesting that hydrogen atoms diffuse homogeneously in different pieces of the metallic ribbon samples. The magnetization values measured by using a superconducting quantum interference device (SQUID) revealed that the magnetic susceptibilities of the hydrogenated quasicrystals strongly depended on the temperature so that the enhanced magnetic coercivities at low temperatures (< 9 K) were the result of a combination of hydrogen and temperature while the reduced magnetization values at temperatures above 9 K were attributed to the structural factor rather than the temperature. In fact, hydrogen contributes to the significant decrease in the magnetization values from 0.0236 to 0.0163 emu/g at room temperature. The reasons for the decreased magnetization after hydrogenation are understood to be the reduced interactions of magnetic moments between Ni atoms induced by the lattice expansion after hydrogen absorption.

Update: 12-Dec-2012

Title:
Transformation and slip behavior of Ni2FeGa
Authors:
Sehitoglu, H; Wang, J; Maier, HJ Author Full Names: Sehitoglu, H.; Wang, J.; Maier, H. J.
Source:
INTERNATIONAL JOURNAL OF PLASTICITY, 39 61-74; 10.1016/j.ijplas.2012.05.011 DEC 2012
Abstract:
Ni2FeGa is a relatively new shape memory alloy (SMA) and exhibits superior characteristics compared to other SMAs. Its favorable properties include low transformation stress, high reversible strains and small hysteresis. The first stage of stress-induced martensitic transformation is from a cubic to a modulated monoclinic phase. The energy barriers associated with the transformation from L2(1) (cubic) to modulated martensite (10M-martensite) incorporating shear and shuffle are established via atomistic simulations. In addition, the slip resistance in the [111] direction and the dissociation of full dislocations into partials as well as slip in the [001] direction are studied. The unstable stacking fault energy barriers for slip by far exceeded the transformation transition state barrier permitting transformation to occur with little irreversibility. Experiments at the mesa-scale on single crystals and transmission electron microscopy were conducted to provide further proof of the pseudoelastic (reversible) behavior and the presence of anti-phase boundaries. The results have implications for design of new shape memory alloys that possess low energy barriers for transformation coupled with high barriers for dislocation slip. (c) 2012 Elsevier Ltd. All rights reserved.
Title:
Variational Iteration Method for the Time-Fractional Elastodynamics of 3D Quasicrystals
Authors:
Yaslan, HC Author Full Names: Yaslan, H. Cerdik
Source:
CMES-COMPUTER MODELING IN ENGINEERING & SCIENCES, 86 (1):29-38; JUL 2012
Abstract:
This paper presents the approximate analytical solutions to the time fractional differential equations of elasticity for 3D quasicrystals with initial conditions. These equations are written in the form of a vector partial differential equation of the second order. The time fractional vector partial differential equations with initial conditions are solved by variational iteration method (VIM). The fractional derivatives are described in the Caputo sense. Numerical example shows that the proposed method is quite effective and convenient for solving kinds of time fractional system of partial differential equations.

Update: 6-Dec-2012

Title:
Complex magnetic order in Pr2Pd3Ge5: a single crystal study
Authors:
Anand, VK; Thamizhavel, A; Ramakrishnan, S; Hossain, Z Author Full Names: Anand, V. K.; Thamizhavel, A.; Ramakrishnan, S.; Hossain, Z.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (45):10.1088/0953-8984/24/45/456003 NOV 14 2012
Abstract:
We have investigated the magnetic and electronic transport properties of single crystal Pr2Pd3Ge5 grown by the Czochralski method. Complex magnetic behaviour (multiple magnetic transitions) is clearly seen in this compound from the magnetic susceptibility chi(T), isothermal magnetization M(H)and electrical resistivity rho(T) data. For the magnetic field applied along the crystallographic c-axis (H parallel to [001]) the chi(T) data exhibit two sharp transitions at 6.9 and 6.3 K and a broad hump near 8 K. Four anomalies at 8.0, 7.3, 6.2 and 4.9 K are observed for the magnetic field along both a- and b-directions (H parallel to [100] and H parallel to [010]). Further, the ordered state chi(T) presents a large anisotropy with an easy axis along the c-axis. The presence of magnetocrystalline anisotropy is also inferred from the isothermal M(H) data. The M(H) data measured at 1.9 K for H parallel to [001] exhibit a step-like increase due to field-induced metamagnetic transitions at H-c1(c) = 2.0 T and H-c2(c) = 4.0 T. For H parallel to [100] and H parallel to [010] sharp step-like field-induced metamagnetic transitions occur at H-c1(a) = H-c1(b) = 1.6 T and H-c2(a) = H-c2(b) = 1.8 T which are accompanied by a weak S-shaped spin-flop metamagnetic transition at H-c3(a) = H-c3(b) similar to 4 T. We have extracted the H-T phase diagram from the M(H) data collected at different temperatures in the magnetically ordered state which shows the existence of three magnetic phases below T-N for H parallel to [100] and H parallel to [010], and two magnetic phases for H parallel to [001]. A sharp transition due to the onset of long range antiferromagnetic order is also seen in the rho(T) data which also exhibit anisotropic behaviour. The observation of an upturn near T-N in the rho(T) data suggests the formation of a super-zone gap and hence the existence of incommensurate magnetic structure. Further, in the ordered state, the rho(T) data present a gap in the excitation spectrum of magnons with a characteristic energy gap Delta similar to 0.23 meV.
Title:
The atomic structure of the threefold surface of the icosahedral Ag-In-Yb quasicrystal
Authors:
Cui, C; Nugent, PJ; Shimoda, M; Ledieu, J; Fournee, V; Tsai, AP; McGrath, R; Sharma, HR Author Full Names: Cui, C.; Nugent, P. J.; Shimoda, M.; Ledieu, J.; Fournee, V.; Tsai, A. P.; McGrath, R.; Sharma, H. R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (44):10.1088/0953-8984/24/44/445011 NOV 7 2012
Abstract:
We report a study of the atomic structure of the threefold icosahedral (i-)Ag-In-Yb quasicrystal surface using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The LEED confirms that the surface exhibits quasicrystalline long-range order with the threefold symmetry expected from the bulk. The STM reveals large atomically flat terraces separated by steps of different heights. A comparison of atomically resolved STM images for the terraces and the step-height distribution with the bulk structure of isostructural i-Cd-Yb shows that the terraces are formed at bulk planes intersecting the centers of the rhombic triacontahedral clusters that make up the bulk structure of the system. However, the stability of particular terraces may be influenced by the density of atoms in the interstices (glue atoms that bind the clusters) in the terraces and also by the chemical environment in the underlying atomic plane. The surface exhibits screw dislocations, which is explained in terms of a continuous atomic density along the threefold axis.
Title:
Modeling the strengthening effect of Al-Cu-Fe quasicrystalline particles in Al-based metal matrix composites
Authors:
Ali, F; Scudino, S; Liu, G; Srivastava, VC; Mukhopadhyay, NK; Khoshkhoo, MS; Prashanth, KG; Uhlenwinkel, V; Calin, M; Eckert, J Author Full Names: Ali, F.; Scudino, S.; Liu, G.; Srivastava, V. C.; Mukhopadhyay, N. K.; Khoshkhoo, M. Samadi; Prashanth, K. G.; Uhlenwinkel, V.; Calin, M.; Eckert, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 536 S130-S133; 1 10.1016/j.jallcom.2011.12.022 SEP 25 2012
Abstract:
In this work, a model that simultaneously considers the combined strengthening contributions of load bearing, dislocation strengthening and matrix ligament size effects, which has been found to accurately describe the mechanical behavior of Al-based composites reinforced with complex intermetallic particles (Scudino et al. (2009) [8]), has been used to predict the mechanical properties of Al-based metal matrix composites containing different amounts of Al62.5Cu25Fe12.5 quasicrystalline reinforcing particles. The present results further demonstrate the validity of this model and confirm the importance of the characteristic matrix ligament size for explaining the strengthening effect of the composites containing large volume fractions of reinforcement. (c) 2011 Elsevier B.V. All rights reserved.

Update: 29-Nov-2012

Title:
Thermally induced structural changes in incommensurate calcium barium niobate Ca0.28Ba0.72Nb2O6 (CBN28)
Authors:
Graetsch, HA; Schreuer, J; Burianek, M; Muhlberg, M Author Full Names: Graetsch, H. A.; Schreuer, J.; Burianek, M.; Muehlberg, M.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 196 255-266; 10.1016/j.jssc.2012.06.028 DEC 2012
Abstract:
The incommensurately modulated crystal structure of relaxor ferroelectric CBN28 was refined at elevated temperatures up to 330 degrees C in the 3+2 dimensional superspace group P4bm(alpha alpha 1/2, -alpha alpha 1/2). The structural modulations mainly consisting of cooperative tilting of NbO6 octahedra and an occupational modulation of the large cation site Me2 persist beyond the diffuse ferroelectric transition with slightly reduced amplitudes. A change of symmetry was not observed. Both symmetrically non-equivalent NbO6 octahedra are distorted by off center shifts of the Nb atoms in the same direction along the tetragonal c-axis. The displacements of the Nb atoms are gradually reduced with increasing temperatures until one of the Nb atoms crosses the center of its coordination polyhedron near the transition temperature T-M adopting an uncompensated anti-ferroelectric configuration. This change is accompanied by enhanced thermal motions of the Nb atoms along the c-axis. Structural distortions and electric polarization do not completely vanish at TM but may persist in fluctuating polar nanodomains. (C) 2012 Elsevier Inc. All rights reserved.
Title:
Collective pinning dynamics of charge-density waves in 1T-TaS2
Authors:
Su, JD; Sandy, AR; Mohanty, J; Shpyrko, OG; Sutton, M Author Full Names: Su, Jun-Dar; Sandy, Alec R.; Mohanty, Jyoti; Shpyrko, Oleg G.; Sutton, Mark
Source:
PHYSICAL REVIEW B, 86 (20):10.1103/PhysRevB.86.205105 NOV 5 2012
Abstract:
Using high-resolution x-ray scattering and x-ray photon correlation spectroscopy (XPCS), we have investigated the structure and dynamics of charge density wave (CDW) dynamics in pure and titanium-doped 1T-TaS2. Time-averaged scattering measurements of pure and doped samples reveal that 1T-TaS2 is a weakly pinned two-dimensional CDW system. Using XPCS, we find that after long anneals the CDW domain structure in the incommensurate phase is pinned and stable against spontaneous fluctuations thus rejecting phasons as spontaneous excitations in higher-dimensional CDW systems. By examining the dynamics of deeply quenched samples upon heating, we find that metastable CDW configurations collectively rearrange in a nonequilibrium manner. For nominally pure samples, we determine an energy barrier to relaxation of 4600 K that is considerably greater than that found for lower-dimensional CDWs.
Title:
Phason strained quasicrystalline and crystalline precipitates in Zr-Al-Ni-Cu-Nb bulk metallic glass matrix composites
Authors:
Xiong, DX; Wang, JB; Lu, L; Zhao, DS; Sun, YF Author Full Names: Xiong, Dongxia; Wang, Jianbo; Lu, Lu; Zhao, Dongshan; Sun, Yufeng
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 358 (22):3007-3011; 10.1016/j.jnoncrysol.2012.07.031 NOV 1 2012
Abstract:
Quasicrystalline and crystalline precipitates in isothermally annealed bulk metallic glass (Zr65Al10Ni10Cu15)(93)Nb-7 are investigated by transmission electron microscopy techniques. The great majority of the precipitates are icosahedral quasicrystal with primitive icosahedral lattice. The linear phason strain widely existed in the quasicrystal phase is determined quantitatively by electron diffraction analysis. Precise measuring of the diffraction spots' deviation and the quantitative data fitting provides the phason strain matrix. Besides, nano-scaled crystallite inclusions are confirmed as rutile TiO2 assembling with (10 (1) over bar) twinning. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Magnetoelastic coupling in the incommensurate antiferromagnetic phase of FeOCl
Authors:
Zhang, J; Wolfel, A; Li, L; van Smaalen, S; Williamson, HL; Kremer, RK Author Full Names: Zhang, Jian; Woelfel, Alexander; Li, Liang; van Smaalen, Sander; Williamson, Hailey L.; Kremer, Reinhard K.
Source:
PHYSICAL REVIEW B, 86 (13):10.1103/PhysRevB.86.134428 OCT 26 2012
Abstract:
The antiferromagnetic phase transition of FeOCl has been studied by temperature-dependent x-ray-diffraction experiments, magnetic susceptibility, heat capacity, and dielectric measurements. The magnetic phase transition is found to be accompanied by a monoclinic lattice distortion, affecting the angle gamma between crystallographic axes parallel to the layers comprising the quasi-two-dimensional magnetic system. The temperature-dependent magnitude of gamma shows the phase transition to be of second order. Satellite reflections occur in x-ray diffraction with twice the magnetic modulation wave vector. These positions are temperature dependent, providing evidence for an incommensurate character of the magnetic order. The observed Neel temperature is T-N = 81.0 (2) K.
Title:
Complex metallic alloys: new materials for rapid manufacturing
Authors:
Kenzari, S; Bonina, D; Dubois, JM; Fournee, V Author Full Names: Kenzari, Samuel; Bonina, David; Dubois, Jean Marie; Fournee, Vincent
Source:
ACTUALITE CHIMIQUE, (366):36-41; SEP 2012
Abstract:
Complex metallic alloys: new materials for rapid manufacturing Rapid manufacturing processes allow freeform fabrication of the physical representation of a three dimensional CAD data model. This area has been expanding rapidly over the last twenty years. It includes several rapid prototyping techniques such as selective laser sintering and stereolithography. The range of materials used today is quite restricted while there is a real demand for manufacturing lighter functional parts. This article summarizes recent works performed in this field at the Jean Lamour Institute, introducing new materials based on complex metallic alloys. These are mainly Al-based alloys that are weakly periodic - or even aperiodic in the case of quasicrystals - whose properties differ from those of conventional alloys. The use of these materials allows us to produce light-weight parts consisting of either metal-intermetallic composites or of polymer-based composites with improved properties. Functional parts using these alloys are now commercialized.

Update: 22-Nov-2012

Title:
Fifty years of aperiodic crystals
Authors:
Janssen, T Author Full Names: Janssen, T.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 68 667-674; 10.1107/S0108767312033715 Part 6 NOV 2012
Abstract:
Historians often have debates about the beginning and end of a certain era. The same discussion can be had about the history of aperiodic crystals. There are reasons to claim that in 2012 one may celebrate the 50th anniversary of this field. A short description is given of the development of this branch of crystallography. It is argued that the most important point in its history is the discovery of quasicrystals, which has been recognized by awarding the Nobel Prize in Chemistry 2011 to Dan Shechtman.
Title:
Effects of Transition Metal Substitutions on the Incommensurability and Spin Fluctuations in BaFe2As2 by Elastic and Inelastic Neutron Scattering
Authors:
Kim, MG; Lamsal, J; Heitmann, TW; Tucker, GS; Pratt, DK; Khan, SN; Lee, YB; Alam, A; Thaler, A; Ni, N; Ran, S; Bud'ko, SL; Marty, KJ; Lumsden, MD; Canfield, PC; Harmon, BN; Johnson, DD; Kreyssig, A; McQueeney, RJ; Goldman, AI Author Full Names: Kim, M. G.; Lamsal, J.; Heitmann, T. W.; Tucker, G. S.; Pratt, D. K.; Khan, S. N.; Lee, Y. B.; Alam, A.; Thaler, A.; Ni, N.; Ran, S.; Bud'ko, S. L.; Marty, K. J.; Lumsden, M. D.; Canfield, P. C.; Harmon, B. N.; Johnson, D. D.; Kreyssig, A.; McQueeney, R. J.; Goldman, A. I.
Source:
PHYSICAL REVIEW LETTERS, 109 (16):10.1103/PhysRevLett.109.167003 OCT 19 2012
Abstract:
The spin fluctuation spectra from nonsuperconducting Cu-substituted, and superconducting Co-substituted, BaFe2As2 are compared quantitatively by inelastic neutron scattering measurements and are found to be indistinguishable. Whereas diffraction studies show the appearance of incommensurate spin-density wave order in Co and Ni substituted samples, the magnetic phase diagram for Cu substitution does not display incommensurate order, demonstrating that simple electron counting based on rigid-band concepts is invalid. These results, supported by theoretical calculations, suggest that substitutional impurity effects in the Fe plane play a significant role in controlling magnetism and the appearance of superconductivity, with Cu distinguished by enhanced impurity scattering and split-band behavior.
Title:
Deuterium storage of Ti40Zr40Ni20 icosahedral quasicrystal
Authors:
Huang, HG; Liu, TW; Zhang, Z; Ye, XQ; Luo, LZ; Zhang, XD Author Full Names: Huang, Huogen; Liu, Tianwei; Zhang, Zhi; Ye, Xiaoqiu; Luo, Lizhu; Zhang, Xiangdong
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 37 (20):15204-15209; 10.1016/j.ijhydene.2012.07.127 OCT 2012
Abstract:
Ti40Zr40Ni20 icosashedral quasicrystal was observed to load hydrogen in a much lower capacity than similar Ti-Zr-Ni alloys. To verify the result, the alloy is further studied by using deuterium instead of hydrogen in this work. With a home-made gas-solid reaction system, XRD and XPS techniques, the investigation was conducted on deuterium absorption and desorption properties of Ti40Zr40Ni20 alloy and its phase stability during the deuteration course. It is shown that the quasicrystal can load deuterium rapidly in an elevated volume of 11.5 mmol.D-2/g.M (D-2 denotes deuterium molecular and M the metal). After the full storage of deuterium, the quasicrystal phase remained, however the quasilattice expanded at a rate of 6.28%, revealing the occurrence of severe quasilattice stress. The solution of deuterium in the alloy caused the increase of binding energy of the metal elements, as much as 0.4 eV for Ti, 0.6 eV for Zr and 0.1 eV for Ni, which reflects the location of deuterium near Ti and Zr. The deuterium release was very slow at low temperature and could be complete at least above 610 degrees C. Based on the gained results, the quasilattice shrink would be more reasonable to explain the big difficulty of the desorption. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Attainment of quasicrystalline phase in Al-Cu-Fe alloy via melting and mechanical alloying
Authors:
Esquivel, R; Suarez, MA; Diaz-Barriga, L; Chavez, F Author Full Names: Esquivel, Rosalba; Suarez, Miguel A.; Diaz-Barriga, Lucia; Chavez, Federico
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 103 (9):1137-1143; 10.3139/146.110808 SEP 2012
Abstract:
Al62Cu25.5Fe12.5 (A) and Al65Cu20Fe15 (B) alloys were fabricated via melting and experimentally studied in both as-cast and annealed conditions. Alloy (B) was also fabricated using mechanical alloying and an annealing treatment. The melted alloys were characterized to investigate the distribution of alloying elements Fe and Cu on the icosahedral and coexisting phases, as well as the hardness of all phases. The as-cast alloys showed the highest amount of icosahedral phase with up to 47 % of ingot (A), but this increased after heat treatment to 99% and 75% of ingots in (A) and (B) alloys respectively. During heat treatment the iron content was increased in all phases, while the copper content decreased. As a consequence, the hardness of the icosahedral phase increased by 23% in (A) Al62Cu25.5Fe12.5 alloy and 33% in (B) Al65Cu20Fe15 alloy. On the other hand, the effect of heat treatment on samples obtained from mechanical alloying caused a modification in the iron and copper contents, leading to the formation of iron-rich phases such as lambda-(Al,Cu)(13)Fe-4 phase for all milling times and the icosahedral phase after 35 h.
Title:
Mechanical behavior of the cold-rolled Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 metallic glass-quasicrystalline composite
Authors:
Beitelschmidt, D; Scudino, S; Prashanth, KG; Kuhn, U; Eckert, J Author Full Names: Beitelschmidt, Denise; Scudino, Sergio; Prashanth, Konda Gokuldoss; Kuehn, Uta; Eckert, Juergen
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 103 (9):1113-1116; 10.3139/146.110783 SEP 2012
Abstract:
The as-cast Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 glass-quasicrystalline composite exhibits high strength, good elasticity but no macroscopic room temperature plastic deformability. Significant improvement in plastic deformability to a strain of about 5% can be achieved after cold-rolling of the as-cast material. This behavior can be ascribed the anisotropic and inhomoeeneous stress distribution developing during the mechanical test along with the creation of an extensive system of shear bands.
Title:
Conventional and Stuffed Bergman-Type Phases in the Na-Au-T (T=Ga, Ge, Sn) Systems: Syntheses, Structures, Coloring of Cluster Centers, and Fermi Sphere-Brillouin Zone Interactions
Authors:
Lin, QS; Smetana, V; Miller, GJ; Corbett, JD Author Full Names: Lin, Qisheng; Smetana, Volodymyr; Miller, Gordon J.; Corbett, John D.
Source:
INORGANIC CHEMISTRY, 51 (16):8882-8889; 10.1021/ic300866q AUG 20 2012
Abstract:
Bergman-type phases in the Na-Au-T (T = Ga, Ge, and Sn) systems were synthesized by solid-state means and structurally characterized by single-crystal X-ray diffraction studies. Two structurally related (1/1) Bergman phases were found in the Na-Au-Ga system: (a) a conventional Bergman-type (CB) structure, Na26AuxGa54-x, which features empty innermost icosahedra, as refined with x = 18.1 (3), Im (3) over bar, a = 14.512(2) angstrom, and Z = 2; (b) a stuffed Bergman-type (SB) structure, Na26AuyGa55-y, which contains Ga-centered innermost icosahedra, as refined with y = 36.0 (1), Im (3) over bar, a = 14.597(2) angstrom, and Z = 2. Although these two subtypes have considerable phase widths along with respective tie lines at Na approximate to 32.5 and 32.1 atom %, they do not merge into a continuous solid solution. Rather, a quasicrystalline phase close to the Au-poor CB phase and an orthorhombic derivative near the Au-rich SB phase lie between them. In contrast, only Au-rich SB phases exist in the Ge and Sn systems, in which the innermost icosahedra are centered by Au rather than Ge or Sn. These were refined for Na26Au40.93(5)Ge14.07(5) (Im (3) over bar, a = 14.581(2) angstrom, and Z = 2) and Na26Au39.83(6)Sn15.17(6) (Im (3) over bar, a = 15.009(2) angstrom, and Z = 2), respectively. Occupations of the centers of Bergman clusters are rare. Such centering and coloring correlate with the sizes of the neighboring icosahedra, the size ratios between electropositive and electronegative components, and the values of the average valence electron count per atom (e/a). Theoretical calculations revealed that all of these phases are Hume-Rothery phases, with evident pseudogaps in the density of states curves that arise from the interactions between Fermi surface and Brillouin zone boundaries corresponding to a strong diffraction intensity.

Update: 14-Nov-2012

Title:
Distinct Charge Orders in the Planes and Chains of Ortho-III-Ordered YBa2Cu3O6+delta Superconductors Identified by Resonant Elastic X-ray Scattering
Authors:
Achkar, AJ; Sutarto, R; Mao, X; He, F; Frano, A; Blanco-Canosa, S; Le Tacon, M; Ghiringhelli, G; Braicovich, L; Minola, M; Sala, MM; Mazzoli, C; Liang, RX; Bonn, DA; Hardy, WN; Keimer, B; Sawatzky, GA; Hawthorn, DG Author Full Names: Achkar, A. J.; Sutarto, R.; Mao, X.; He, F.; Frano, A.; Blanco-Canosa, S.; Le Tacon, M.; Ghiringhelli, G.; Braicovich, L.; Minola, M.; Sala, M. Moretti; Mazzoli, C.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Keimer, B.; Sawatzky, G. A.; Hawthorn, D. G.
Source:
PHYSICAL REVIEW LETTERS, 109 (16):10.1103/PhysRevLett.109.167001 OCT 17 2012
Abstract:
Recently, charge density wave (CDW) order in the CuO2 planes of underdoped YBa2Cu3O6+delta was detected using resonant soft x-ray scattering. An important question remains: is the chain layer responsible for this charge ordering? Here, we explore the energy and polarization dependence of the resonant scattering intensity in a detwinned sample of YBa2Cu3O6.75 with ortho-III oxygen ordering in the chain layer. We show that the ortho-III CDW order in the chains is distinct from the CDWorder in the planes. The ortho-III structure gives rise to a commensurate superlattice reflection at Q = [0.33 0 L] whose energy and polarization dependence agrees with expectations for oxygen ordering and a spatial modulation of the Cu valence in the chains. Incommensurate peaks at [0.30 0 L] and [0 0.30 L] from the CDW order in the planes are shown to be distinct in Q as well as their temperature, energy, and polarization dependence, and are thus unrelated to the structure of the chain layer. Moreover, the energy dependence of the CDW order in the planes is shown to result from a spatial modulation of energies of the Cu 2p to 3d(x2-y2) transition, similar to stripe-ordered 214 cuprates.
Title:
Magnetic Field Splitting of the Spin Resonance in CeCoIn5
Authors:
Stock, C; Broholm, C; Zhao, Y; Demmel, F; Kang, HJ; Rule, KC; Petrovic, C Author Full Names: Stock, C.; Broholm, C.; Zhao, Y.; Demmel, F.; Kang, H. J.; Rule, K. C.; Petrovic, C.
Source:
PHYSICAL REVIEW LETTERS, 109 (16):10.1103/PhysRevLett.109.167207 OCT 17 2012
Abstract:
Neutron scattering in strong magnetic fields is used to show the spin resonance in superconducting CeCoIn5 (T-c = 2.3 K) is a doublet. The underdamped resonance ((h) over bar Gamma = 0.069 +/- 0.019 meV) Zeeman splits into two modes at E-+/- = (h) over bar Omega(0) +/- mu H-B mu 0 with alpha = 0.96 +/- 0: 05. A linear extrapolation of the lower peak reaches zero energy at 11.2 +/- 0.5 T, near the critical field for the incommensurate "Q phase." Kenzelmann et al. [Science 321, 1652 (2008)] This, taken with the integrated weight and polarization of the low-energy mode (E-), indicates that the Q phase can be interpreted as a Bose condensate of spin excitons.
Title:
Magnetic ordering and multiferroicity in MnI2
Authors:
Wu, XX; Cai, YX; Xie, Q; Weng, HM; Fan, H; Hu, JP Author Full Names: Wu, Xianxin; Cai, Yingxiang; Xie, Qing; Weng, Hongming; Fan, Heng; Hu, Jiangping
Source:
PHYSICAL REVIEW B, 86 (13):10.1103/PhysRevB.86.134413 OCT 15 2012
Abstract:
Density-functional calculations are carried out to investigate incommensurate magnetic structures and ferroelectric polarization in the newly discovered multiferroic material MnI2. The exchange interactions among local moments on Mn are parameterized by mapping the mean-field Heisenberg model on to the total energy difference of several magnetic ordering states. The experimentally observed noncollinear magnetic states are well reproduced by using this model and exchange interaction parameters. The direction of polarization experimentally measured is also consistent with the result derived from the symmetry analysis of the magnetically ordered state. In particular, we find that the interplane magnetic exchange coupling is pivotal to the emergence of the spiral magnetic structure. This noncollinear magnetic structure, combined with spin-orbit coupling mainly from I ions, is responsible for the appearance of ferroelectric polarization.
Title:
Metal-insulator transition in the Hubbard model with incommensurate magnetic structures
Authors:
Timirgazin, MA; Arzhnikov, AK; Irkhin, VY Author Full Names: Timirgazin, M. A.; Arzhnikov, A. K.; Irkhin, V. Yu
Source:
JETP LETTERS, 96 (3):171-175; 10.1134/S002136401215012X OCT 2012
Abstract:
The metal-insulator transition for the square, simple cubic, and body centered cubic lattices has been studied within the Hubbard model at half-filling taking into account nearest- and next-nearest-neighbor electron hopping. Both staggered antiferromagnetic and incommensurate magnetic states (spin-spiral wave) have been considered. The inclusion of the latter states for the three-dimensional lattices does not change the general pattern of the metal-insulator transition, but opens the fundamentally new possibility of the metal-insulator transition of the first order between the magnetically ordered states for the square lattice.

Update: 7-Nov-2012

Title:
Extra-electron induced covalent strengthening and generalization of intrinsic ductile-to-brittle criterion
Authors:
Niu, HY; Chen, XQ; Liu, PT; Xing, WW; Cheng, XY; Li, DZ; Li, YY Author Full Names: Niu, Haiyang; Chen, Xing-Qiu; Liu, Peitao; Xing, Weiwei; Cheng, Xiyue; Li, Dianzhong; Li, Yiyi
Source:
SCIENTIFIC REPORTS, 2 10.1038/srep00718 OCT 9 2012
Abstract:
Traditional strengthening ways, such as strain, precipitation, and solid-solution, come into effect by pinning the motion of dislocation. Here, through first-principles calculations we report on an extra-electron induced covalent strengthening mechanism, which alters chemical bonding upon the introduction of extra-valence electrons in the matrix of parent materials. It is responsible for the brittle and high-strength properties of Al12W-type compounds featured by the typical fivefold icosahedral cages, which are common for quasicrystals and bulk metallic glasses (BMGs). In combination with this mechanism, we generalize ductile-to-brittle criterion in a universal hyperbolic form by integrating the classical Pettifor's Cauchy pressure with Pugh's modulus ratio for a wide variety of materials with cubic lattices. This study provides compelling evidence to correlate Pugh's modulus ratio with hardness of materials and may have implication for understanding the intrinsic brittleness of quasicrystals and BMGs.
Title:
Effect of A-site La and Ba doping on threshold field and characteristic temperatures of PbSc0.5Ta0.5O3 relaxor studied by acoustic emission
Authors:
Dul'kin, E; Mihailova, B; Gospodinov, M; Roth, M Author Full Names: Dul'kin, E.; Mihailova, B.; Gospodinov, M.; Roth, M.
Source:
JOURNAL OF APPLIED PHYSICS, 112 (6):10.1063/1.4752400 SEP 15 2012
Abstract:
The structural transitions in Pb1-xLaxSc(1+x)/2Ta(1-x)/2O3, x = 0.08 (PLST) relaxor crystals were studied by means of acoustic emission (AE) under an external electric field (E) and compared with those observed in pure PbSc0.5Ta0.5O3 (PST) and Pb0.78Ba0.22Sc0.5Ta0.5O3 (PBST) [E. Dul'kin et al., EPL 94, 57002 (2011)]. Similar to both the PST and PBST compounds, in zero field PLST exhibits AE corresponding to a para-to-antiferroelectric incommensurate phase transition at T-n = 276 K, lying in the vicinity of dielectric temperature maximum (T-m). This AE signal exhibits a nontrivial behavior when applying E resembling the electric-field-dependence of T-n previously observed for both the PST and PBST, namely, T-n initially decreases with the increase of E, attains a minimum at a threshold field E-th = 0.5 kV/cm, accompanied by a pronounced maximum of the AE count rate (N) over dot = 12 s(-1), and then starts increasing as E enhances. The similarities and difference between PST, PLST, and PBST with respect to T-n, E-th, and (N) over dot are discussed from the viewpoint of three mechanisms: (i) chemically induced random local electric field due to the extra charge on the A-site ion, (ii) disturbance of the system of stereochemically active lone-pair electrons of Pb2+ by the isotropic outermost electron shell of substituting ion, and (iii) change in the tolerance factor and elastic field to the larger ionic radius of the substituting A-site ion due to the different radius of the substituting ion. The first two mechanisms influence the actual values of T-n and E-th, whereas the latter is shown to affect the normalized (N) over dot, indicating the fractions undergoing a field-induced crossover from a modulated antiferroelectric to a ferroelectric state. Creation of secondary random electric field, caused by doping-induced A-site-O ionic chemical bonding, is discussed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752400]
Title:
Diffraction study of bending-induced polysynthetic twins in 10M modulated Ni-Mn-Ga martensite
Authors:
Chulist, R; Sozinov, A; Straka, L; Lanska, N; Soroka, A; Lippmann, T; Oertel, CG; Skrotzki, W Author Full Names: Chulist, R.; Sozinov, A.; Straka, L.; Lanska, N.; Soroka, A.; Lippmann, T.; Oertel, C-G.; Skrotzki, W.
Source:
JOURNAL OF APPLIED PHYSICS, 112 (6):10.1063/1.4754017 SEP 15 2012
Abstract:
Detailed conventional and synchrotron x-ray and electron backscatter diffraction experiments were performed to investigate bending-induced polysynthetic twins in a Ni-Mn-Ga single crystal with five-layered (10M) martensite crystal structure. It was proved that the twin microstructure produced in such a way is composed of type I twins. The type I twins exhibit a relatively high twinning stress of about 0.8 MPa, which limits the performance of bending-induced twins in magnetic actuation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754017]

Update: 31-Oct-2012

Title:
Ordering and dynamics of the central tetrahedron in the 1/1 Zn6Sc periodic approximant to quasicrystal
Authors:
Euchner, H; Yamada, T; Schober, H; Rols, S; Mihalkovic, M; Tamura, R; Ishimasa, T; de Boissieu, M Author Full Names: Euchner, Holger; Yamada, Tsunetomo; Schober, Helmut; Rols, Stephane; Mihalkovic, Marek; Tamura, Ryuji; Ishimasa, Tsutomu; de Boissieu, Marc
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (41):10.1088/0953-8984/24/41/415403 OCT 17 2012
Abstract:
Periodic approximants to quasicrystals offer a unique opportunity to better understand the structure, physical properties and stabilizing mechanisms of their quasicrystal counterparts. We present a detailed study of the order-disorder phase transition occurring at about 160 K in the Zn6Sc cubic approximant to the icosahedral quasicrystal i-MgZnSc. This transition goes along with an anti-parallel ordering of the tetrahedra located at the centres of large atomic clusters, which are packed on a bcc lattice. Single crystal x-ray diffuse scattering shows that the tetrahedra display pre-transitional short range ordering above T-c (Yamada et al 2012 in preparation). Using quasielastic neutron scattering (QENS) we clearly evidence this short range order to be dynamical in nature above T-c. The QENS data are consistent with a model of tetrahedra 'jumping' between almost equivalent positions, which is supported by molecular dynamics simulations. This demonstrates a unique dynamical flexibility of the Zn6Sc structure even at room temperature.
Title:
Spin polarized and density modulated phases in symmetric electron-electron and electron-hole bilayers
Authors:
Kumar, K; Moudgil, RK Author Full Names: Kumar, Krishan; Moudgil, R. K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (41):10.1088/0953-8984/24/41/415601 OCT 17 2012
Abstract:
We have studied symmetric electron-electron and electron-hole bilayers to explore the stable homogeneous spin phase and the feasibility of inhomogeneous charge-/spin-density ground states. The former is resolved by comparing the ground-state energies in states of different spin polarizations, while the latter is resolved by searching for a divergence in the wavevector-dependent static charge/spin susceptibility. For this endeavour, we have used the dielectric approach within the self-consistent mean-field theory of Singwi et al. We find that the inter-layer interactions tend to change an abrupt spin-polarization transition of an isolated layer into a nearly gradual one, even though the partially spin-polarized phases are not clearly stable within the accuracy of our calculation. The transition density is seen to decrease with a reduction in layer spacing, implying a suppression of spin polarization by inter-layer interactions. Indeed, the suppression shows up distinctly in the spin susceptibility computed from the spin-polarization dependence of the ground-state energy. However, below a critical layer spacing, the unpolarized liquid becomes unstable against a charge-density-wave (CDW) ground state at a density preceding full spin polarization, with the transition density for the CDW state increasing on further reduction in the layer spacing. Due to attractive e-h correlations, the CDW state is found to be more pronounced in the e-h bilayer. On the other hand, the static spin susceptibility diverges only in the long-wavelength limit, which simply represents a transition to the homogeneous spin-polarized phase.
Title:
Magnetic ordering phenomena of interacting quantum spin Hall models
Authors:
Reuther, J; Thomale, R; Rachel, S Author Full Names: Reuther, Johannes; Thomale, Ronny; Rachel, Stephan
Source:
PHYSICAL REVIEW B, 86 (15):10.1103/PhysRevB.86.155127 OCT 15 2012
Abstract:
The two-dimensional Hubbard model defined for topological band structures exhibiting a quantum spin Hall effect poses fundamental challenges in terms of phenomenological characterization and microscopic classification. In the limit of infinite coupling U at half filling, the spin model Hamiltonians resulting from a strong-coupling expansion show various forms of magnetic ordering phenomena depending on the underlying spin-orbit coupling terms. We investigate the infinite-U limit of the Kane-Mele-Hubbard model with z-axis intrinsic spin-orbit coupling as well as its generalization to a generically multidirectional spin-orbit term which has been claimed to account for the physical scenario in monolayer Na2IrO3. We find that the axial spin symmetry which is kept in the former but broken in the latter has a fundamental impact on the magnetic phase diagram as we vary the spin-orbit coupling strength. While the Kane-Mele spin model shows a continuous evolution from conventional honeycomb Neel to XY antiferromagnetism which avoids the frustration imposed by the increased spin-orbit coupling, the multidirectional spin-orbit term induces a commensurate to incommensurate transition at intermediate coupling strength, and yields a complex spiral state with a 24 site unit cell in the limit of infinite spin-orbit coupling. From our findings, we conjecture that in the case of broken axial spin symmetry there is a large propensity for an additional phase at sufficiently large spin-orbit coupling and intermediate U.
Title:
The structure of dodecagonal (Ta,V)(1.6)Te imaged by phase-contrast scanning transmission electron microscopy
Authors:
Krumeich, F; Muller, E; Wepf, RA; Conrad, M; Reich, C; Harbrecht, B; Nesper, R Author Full Names: Krumeich, F.; Mueller, E.; Wepf, R. A.; Conrad, M.; Reich, C.; Harbrecht, B.; Nesper, R.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 194 106-112; 10.1016/j.jssc.2012.04.050 OCT 2012
Abstract:
While HRTEM is the well-established method to characterize the structure of dodecagonal tantalum (vanadium) telluride quasicrystals and their periodic approximants, phase-contrast imaging performed on an aberration-corrected scanning transmission electron microscope (STEM) represents a favorable alternative. The (Ta,V)(151)Te-74 clusters, the basic structural unit in all these phases, can be visualized with high resolution. A dependence of the image contrast on defocus and specimen thickness has been observed. In thin areas, the projected crystal potential is basically imaged with either dark or bright contrast at two defocus values close to Scherzer defocus as confirmed by image simulations utilizing the principle of reciprocity. Models for square-triangle tilings describing the arrangement of the basic clusters can be derived from such images. (C) 2012 Elsevier Inc. All rights reserved.
Title:
Incommensurate Orbital Modulation behind Ferroelectricity in CuFeO2
Authors:
Tanaka, Y; Terada, N; Nakajima, T; Taguchi, M; Kojima, T; Takata, Y; Mitsuda, S; Oura, M; Senba, Y; Ohashi, H; Shin, S Author Full Names: Tanaka, Yoshikazu; Terada, Noriki; Nakajima, Taro; Taguchi, Munetaka; Kojima, Taro; Takata, Yasutaka; Mitsuda, Setsuo; Oura, Masaki; Senba, Yasunori; Ohashi, Haruhiko; Shin, Shik
Source:
PHYSICAL REVIEW LETTERS, 109 (12):10.1103/PhysRevLett.109.127205 SEP 19 2012
Abstract:
CuFeO2 is one of the multiferroic materials and is the first case that the electric polarization is not explained by the magnetostriction model or the spin-current model. We have studied this material using soft x-ray resonant diffraction and found that superlattice reflection 0 1 - 2q 0 appears in the ferroelectric and incommensurate magnetic ordered phase at the Fe L-2,L-3 absorption edges and moreover that the rotation of the x-ray polarization such as from sigma to pi or from pi to sigma is allowed at this reflection. These findings definitely provide direct evidence that the 3d t(2g down arrow) orbital state of Fe ions has a long-range order in the ferroelectric state. The spin-orbit interaction in Fe ions plays a crucial role to the ferroelectricity in CuFeO2, coupling two nontrivial spin and orbital orders, both of which break the crystal symmetry.
Title:
Structural Impact of Platinum on the Incommensurably Modulated gamma-Brass Related Composite Structure Pd15Zn54
Authors:
Jana, PP; Lidin, S Author Full Names: Jana, Partha P.; Lidin, Sven
Source:
INORGANIC CHEMISTRY, 51 (18):9893-9901; 10.1021/ic301326p SEP 17 2012
Abstract:
The crystal structure of three incommensurately modulated gamma-brass related composite structures in the Pd-Zn-Pt system has been solved from X-ray single crystal diffraction data using a 3 + 1-dimensional super space description. The compounds PtxPd15-xZn54 (x approximate to 6, 7, 10) crystallize in orthorhombic superspace group Fmmm(alpha 00)0s0 (F = [(1/2, 1/2, 0, 0); (1/2, 0, 1/2, 0); (0, 1/2, 1/2, 0)] with the following fundamental cell dimensions: a = 4.265(1) angstrom, b = 9.132(1) angstrom, c = 12.928(2) angstrom, q approximate to 0.629a*; a = 4.284(1) angstrom, b = 9.151(2) angstrom, c = 12.948(4) angstrom, q approximate to 0.628a*; and a = 4.288(1) angstrom, b = 9.140(4) angstrom, c = 12.926(7) angstrom, q approximate to 0.627a*. Each structure is built by two sub-lattices-pentagonal antiprismatic columns parallel to [100] and a zigzag chain of Zn atoms running along the center of the column.
Title:
Structural Modulation and Phase Transitions in La2CoO4.14 Investigated by Synchrotron X-ray and Neutron Single-Crystal Diffraction
Authors:
Le Dreau, L; Prestipino, C; Hernandez, O; Schefer, J; Vaughan, G; Paofai, S; Perez-Mato, JM; Hosoya, S; Paulus, W Author Full Names: Le Dreau, Loic; Prestipino, Carmelo; Hernandez, Olivier; Schefer, Juerg; Vaughan, Gavin; Paofai, Serge; Perez-Mato, Juan Manuel; Hosoya, Shoichi; Paulus, Werner
Source:
INORGANIC CHEMISTRY, 51 (18):9789-9798; 10.1021/ic301165a SEP 17 2012
Abstract:
We report a combined synchrotron X-ray and neutron diffraction study on as-grown La2CoO4.14 single-crystal from 10 to 470 K. Unprecedented structural features in terms of a (3 + 2)D incommensurate modulation have been detected and characterized in the Low Temperature Orthorhombic (LTO) phase already at room temperature despite the complex twinning that was unravelled. A new intermediate phase between the LTO and High Temperature Tetragonal (HTT) phases has been observed for the first time (in the range of 413-433 K). The transformation from LTO to this so-called HTLO (High Temperature Less Orthorhombic) phase is associated to a lowering of orthorhombicity and a loss of one modulation vector, yielding a (3 + 1)D incommensurate modulation. Conversely, above 433 K the HTT phase appears as nonmodulated but exhibits a strong dynamic disorder of CoO6 octahedra, which has been characterized in detail by reconstruction of nuclear densities via the Maximum Entropy Method (MEM).
Title:
Topological States and Adiabatic Pumping in Quasicrystals
Authors:
Kraus, YE; Lahini, Y; Ringel, Z; Verbin, M; Zilberberg, O Author Full Names: Kraus, Yaacov E.; Lahini, Yoav; Ringel, Zohar; Verbin, Mor; Zilberberg, Oded
Source:
PHYSICAL REVIEW LETTERS, 109 (10):10.1103/PhysRevLett.109.106402 SEP 4 2012
Abstract:
The unrelated discoveries of quasicrystals and topological insulators have in turn challenged prevailing paradigms in condensed-matter physics. We find a surprising connection between quasicrystals and topological phases of matter: (i) quasicrystals exhibit nontrivial topological properties and (ii) these properties are attributed to dimensions higher than that of the quasicrystal. Specifically, we show, both theoretically and experimentally, that one-dimensional quasicrystals are assigned two-dimensional Chern numbers and, respectively, exhibit topologically protected boundary states equivalent to the edge states of a two-dimensional quantum Hall system. We harness the topological nature of these states to adiabatically pump light across the quasicrystal. We generalize our results to higher-dimensional systems and other topological indices. Hence, quasicrystals offer a new platform for the study of topological phases while their topology may better explain their surface properties.
Title:
Incommensurate Sinusoidal Oxygen Modulations in Layered Manganites La1-xSr1+xMnO4 (x >= 0.5)
Authors:
Garcia, J; Herrero-Martin, J; Subias, G; Blasco, J; Andreu, JS; Sanchez, MC Author Full Names: Garcia, Joaquin; Herrero-Martin, Javier; Subias, Gloria; Blasco, Javier; Andreu, J. S.; Concepcion Sanchez, M.
Source:
PHYSICAL REVIEW LETTERS, 109 (10):10.1103/PhysRevLett.109.107202 SEP 4 2012
Abstract:
We have studied the incommensurate-ordered phase in overdoped La0.4Sr1.6MnO4 by resonant x-ray diffraction at the Mn K edge. Weak resonant superlattice (h +/- 0.2 h +/- 0.2 0) and (h +/- 0.4 h +/- 0.4 0) reflections of the tetragonal structure were found below similar to 240 K. The energy, azimuth angle, and polarization dependencies of the resonant scattering have revealed sinusoidal modulations of the oxygen motions that are transverse and longitudinal to the tetragonal [110] direction. This result discards (Mn3+, Mn4+)-like stripe-type order but point to a charge-density-modulation picture.
Title:
The Crystalline Structure of O-AlFePd
Authors:
Sugiyama, K; Obata, T; Hiraga, K Author Full Names: Sugiyama, Kazumasa; Obata, Tatsuo; Hiraga, Kenji
Source:
MATERIALS TRANSACTIONS, 53 (8):1357-1362; 10.2320/matertrans.M2012130 AUG 2012
Abstract:
The structure of O-AlFePd has been analyzed by single-crystal X-ray diffraction, yielding space group Cmca (No. 64), a = 0.8130(1) nm, b = 1.5474(2) nm, c = 2.3868(4) nm, atoms/cell = 204, F(000) = 3339, D-eal, = 5.621 Mg m(-3) and R = 0.0294 for the 2117 observed reflections with F-obs > 4.0 sigma(F-obs). The structure consists of four Fe sites, one Fe/Pd mixed site, and fifteen Al sites, and the corresponding structural formula is Al-13(Fe,Pd)(4) (Z = 8). The O-AlFePd phase is a new type of approximant of decagonal quasicrystals with a periodicity of 0.8 nm, and the alternation of flat and puckered layers at an interval of about 0.2 nm is the fundamental structural feature. The structure could be also described by a linkage of pentagonal atom columns similar to that found in monoclinic Al13Fe4. Nevertheless, the columnar linkage for the O-AlFePd phase is unique, and this allows us to advance an idea explaining the fine (001) glide twins freque ntly found in the Al13Fe4 phase. [doi:10.2320/matertrans.M2012130]

Update: 25-Oct-2012

Title:
SHAPES OF THE ICOSAHEDRAL QUASICRYSTALLINE PHASE IN MELT-SPUN RIBBONS
Authors:
Boncina, T Author Full Names: Boncina, T.
Source:
METALURGIJA, 52 (1):65-67; JAN-MAR 2013
Abstract:
The shapes of icosahedral quasicrystalline (IQC) particles were determined in melt-spun ribbons of alloys based on the Al-Mn-Be alloy system. The sizes of the quasicrystalline particles ranged from a few tenths of nanometres up to 1 mu m. Therefore, different methods were employed for characterizing their shapes: projection of quasicrystalline particles using transmission electron microscopy (TEM), cross-sections of IQCs on metallographically polished surfaces, and observation of deep-etched samples and extracted particles using a scanning electron microscope (SEM). It was discovered that icosahedral quasicrystalline particles preferentially grow in three-fold directions and have a tendency for faceting and adopting the shape of a pentagonal dodecahedron. The evolution of quasicrystalline shapes is systematically presented.
Title:
On the fundamental equations of piezoelasticity of quasicrystal media
Authors:
Altay, G; Dokmeci, MC Author Full Names: Altay, Gulay; Dokmeci, M. Cengiz
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 49 (23-24):3255-3262; 10.1016/j.ijsolstr.2012.06.016 NOV 15 2012
Abstract:
The three-dimensional fundamental equations of elasticity of quasicrystals with extension to quasi-static electric effect are expresses in both differential and variational invariant forms for a regular region of quasicrystal material. The principle of conservation of energy is stated for the regular region and the constitutive relations are obtained for the piezoelasticity of material. A theorem is proved for the uniqueness in solutions of the fundamental equations by means of the energy argument. The sufficient boundary and initial conditions are enumerated for the uniqueness. Hamilton's principle is stated for the regular region and a three-field variational principle is obtained under some constraint conditions. The constraint conditions, which are generally undesirable in computation, are removed by applying an involutory transformation. Then, a unified variational principle is obtained for the regular region, with one or more fixed internal surface of discontinuity. The variational principle operating on all the field variables generates all the fundamental equations of piezoelasticity of quasicrystals under the symmetry conditions of the phonon stress tensor and the initial conditions. The resulting equations, which are expressible in any system of coordinates and may be used through simultaneous approximation upon all the field variables in a direct method of solutions, pave the way to the study of important dislocation, fracture and interface problems of both elasticity and piezoelasticity of quasicrystal materials. (C) 2012 Elsevier Ltd. All rights reserved.
Title:
Neutron scattering studies on stripe phases in non-cuprate materials
Authors:
Ulbrich, H; Braden, M Author Full Names: Ulbrich, Holger; Braden, Markus
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 481 31-45; 10.1016/j.physc.2012.04.039 NOV 2012
Abstract:
Several non-cuprates layered transition-metal oxides exhibit clear evidence for stripe ordering of charges and magnetic moments. Therefore, stripe order should be considered as the typical consequence of doping a layered Mott insulator, but only in cuprates stripe order or fluctuating stripes coexist with metallic properties. A linear relationship between the charge concentration and the incommensurate structural and magnetic modulations can be considered as the finger print of stripe ordering with localized degrees of freedom. In nickelates and in cobaltates with K2NiF4 structure, doping suppresses the nearest-neighbor antiferromagnetism and induces stripe order. The higher amount of doping needed to induce stripe phases in these non-cuprates series can be attributed to reduced charge mobility. Also manganites exhibit clear evidence for stripe phases with further enhanced complexity, because orbital degrees of freedom are involved. Orbital ordering is the key element of stripe order in manganites since it is associated with the strongest structural distortion and with the perfectly fulfilled relation between doping and incommensurability. Magnetic excitations in insulating stripe phases exhibit strong similarity with those in the cuprates, but only for sufficiently short magnetic correlation lengths reflecting well-defined magnetic stripes that are only loosely coupled. (C) 2012 Elsevier B. V. All rights reserved.
Title:
Transmission electron microscopy observations of structural modulation in the phase transition from alpha-Zr to omega-Zr induced by shear strain
Authors:
Shen, X; Yu, PF; Jing, Q; Yao, Y; Gu, L; Wang, YG; Duan, XF; Yu, RC; Liu, RP Author Full Names: Shen, X.; Yu, P. F.; Jing, Q.; Yao, Y.; Gu, L.; Wang, Y. G.; Duan, X. F.; Yu, R. C.; Liu, R. P.
Source:
SCRIPTA MATERIALIA, 67 (7-8):653-656; 10.1016/j.scriptamat.2012.07.017 OCT 2012
Abstract:
Pure alpha-Zr samples were processed using unconstrained die sets at 5 and 6 GPa with different numbers of revolutions. The microstructural characteristics of Zr deformed by high pressure torsion was studied using transmission electron microscopy. It was found that shear strain can induce distortion of the hcp structure, which can, in addition, give rise to a variety of modulated structures. Most importantly, one possible phase transition route from alpha-Zr to omega-Zr is proposed involving intermediate steps with structural modulations. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Heliconical magnetic order and field-induced multiferroicity of the Co2Y-type hexaferrite Ba0.3Sr1.7Co2Fe12O22
Authors:
Lee, HB; Chun, SH; Shin, KW; Jeon, BG; Chai, YS; Kim, KH; Schefer, J; Chang, H; Yun, SN; Joung, TY; Chung, JH Author Full Names: Lee, Hak Bong; Chun, Sae Hwan; Shin, Kwang Woo; Jeon, Byung-Gu; Chai, Yi Sheng; Kim, Kee Hoon; Schefer, Juerg; Chang, Hun; Yun, Sae-Na; Joung, Tae-Young; Chung, Jae-Ho
Source:
PHYSICAL REVIEW B, 86 (9):10.1103/PhysRevB.86.094435 SEP 27 2012
Abstract:
Using magnetoelectric measurements and neutron diffraction, we investigated multiferroic properties of Co2Y hexaferrite Ba0.3Sr1.7Co2Fe12O22 in zero and finite magnetic field (H perpendicular to c). Upon zero-field cooling, a longitudinal heliconical magnetic structure was observed below 280 K, which involves incommensurate planar helical ordering. When the magnetic field was applied perpendicular to its c axis, electric polarization was observed and the incommensurate ordering was replaced by a commensurate one as commonly observed in other hexaferrites. Electric polarization remained at its maximum during field reversal at 10 K, which indicates that magnetic anisotropy within the basal planes stabilizes the field-induced electric polarization.
Title:
In search of natural quasicrystals
Authors:
Steinhardt, PJ; Bindi, L Author Full Names: Steinhardt, Paul J.; Bindi, Luca
Source:
REPORTS ON PROGRESS IN PHYSICS, 75 (9):10.1088/0034-4885/75/9/092601 SEP 2012
Abstract:
The concept of quasicrystals was first introduced twenty-eight years ago and, since then, over a hundred types have been discovered in the laboratory under precisely controlled physical conditions designed to avoid crystallization. Yet the original theory suggested that quasicrystals can potentially be as robust and stable as crystals, perhaps even forming naturally. These considerations motivated a decade-long search for a natural quasicrystal culminating in the discovery of icosahedrite (Al63Cu24Fe13), an icosahedral quasicrystal found in a rock sample composed mainly of khatyrkite (crystalline (Cu,Zn)Al-2) labeled as coming from the Koryak Mountains of far eastern Russia. In this paper, we review the search and discovery, the analysis showing the sample to be of extraterrestrial origin and the initial results of an extraordinary geological expedition to the Koryak Mountains to seek further evidence.
Title:
Beats in the Magnetic Modulation of Multiferroic CaMn7O12
Authors:
Slawinski, W; Przenioslo, R; Sosnowska, I; Chrobak, A Author Full Names: Slawinski, Wojciech; Przenioslo, Radoslaw; Sosnowska, Izabela; Chrobak, Artur
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 81 (9):10.1143/JPSJ.81.094708 SEP 2012
Abstract:
The modulated magnetic ordering and the atomic position modulation are studied in the case of the multiferroic CaCuxMn7-xO12 by neutron and SR powder diffraction methods. Below the magnetic transition temperature of T-N2 = 50 K both orderings are described by using the magnetic superspace group R31'(00 gamma)ts. For the magnetic ordering two different incommensurate modulation vectors are used: (0, 0, q(m)(1)) and (0, 0, q(m)(2)). For the atomic position modulation only one modulation vector is needed (0, 0, q(p)). The magnetic ordering is of helical screw-type showing beats in the magnetic moment spatial distribution. The values of q(m)(1) and q(m)(2) change with temperature below T-N2 = 50 K but the average value fulfil the relation (1/2)(q(m)(1) + q(m)(2)) = (1/2)q(p) = const: This relation underlines the importance of the magnetoelastic coupling in CaCuxMn7-xO12 compounds below T-N2 = 50 K.
Title:
Uniaxial-Pressure Control of Magnetic Phase Transitions in a Frustrated Magnet CuFe1-xGaxO2 (x=0, 0.018)
Authors:
Nakajima, T; Mitsuda, S; Takahashi, K; Yoshitomi, K; Masuda, K; Kaneko, C; Honma, Y; Kobayashi, S; Kitazawa, H; Kosaka, M; Aso, N; Uwatoko, Y; Terada, N; Wakimoto, S; Takeda, M; Kakurai, K Author Full Names: Nakajima, Taro; Mitsuda, Setsuo; Takahashi, Keiichiro; Yoshitomi, Keisuke; Masuda, Kazuya; Kaneko, Chikafumi; Honma, Yuki; Kobayashi, Satoru; Kitazawa, Hideaki; Kosaka, Masashi; Aso, Naofumi; Uwatoko, Yoshiya; Terada, Noriki; Wakimoto, Shuichi; Takeda, Masayasu; Kakurai, Kazuhisa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 81 (9):10.1143/JPSJ.81.094710 SEP 2012
Abstract:
We have investigated effects of applied uniaxial pressure (p) on magnetic phase transitions in a triangular lattice antiferromagnet CuFeO2 (CFO) and a slightly Ga-substituted compound CuFe1-xGaxO2 (CFGO) with x = 0.018. We have performed neutron diffraction, spherical neutron polarimetry, magnetic susceptibility and pyroelectric measurements under p up to 100 MPa applied on the [1 (1) over bar0] surfaces of the single crystal samples. As a result, we have revealed that in both of CFO and CFGO (x = 0.018), the application of p significantly increases the transition temperature from the paramagnetic phase to a collinear incommensurate antiferromagnetic phase, at which these systems exhibit a crystal structural distortion associated with the magnetic ordering. This suggests that the application of p beaks equilateral symmetry of the triangular lattice above the original transition temperature, and partially relieves geometrical spin frustration, which generally suppresses long-range magnetic orderings even at low temperatures. In CFGO (x = 0.018), we have also found that the ferroelectric helimagnetic phase, which originally shows up as an intermediate phase in zero pressure, partly remains down to low temperatures under applied p. These results have demonstrated that uniaxial pressure can be an effective tool to control magnetic phase transitions in frustrated magnets.
Title:
Doping Effect on Interlocked Ferroelectric and Structural Antiphase Domains in YMnO3
Authors:
Kobayashi, K; Koyama, T; Kamo, H; Togawa, Y; Horibe, Y; Cheong, SW; Mori, S Author Full Names: Kobayashi, Keisuke; Koyama, Tsukasa; Kamo, Hideki; Togawa, Yoshihiko; Horibe, Yoichi; Cheong, Sang Wook; Mori, Shigeo
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS, 51 (9):SI 10.1143/JJAP.51.09LE09 Part 2 SEP 2012
Abstract:
Changes in ferroelectric and structural antiphase domain structure by the partial substitution of nonmagnetic Ti4+ ions at the Mn site were investigated carefully by electron diffraction, dark-field imaging, and high-resolution lattice imaging experiments. The ferroelectric and structural antiphase domains are revealed to be mutually interlocked in YMnO3 and, on the other hand, when x was increased up to x similar to 0.30 in YMn1-xTixO3, the ferroelectric domains disappeared and the size of the structural antiphase domains decreased to approximately 10nm at x similar to 0.30. High-resolution lattice images clearly demonstrate the coexisting state of nanodomains characterized by the modulated structure due to the structural trimerization and the nonmodulated structures. Our experimental results suggest that a partial substitution of Ti4+ ions suppressed the ferroelectric displacement along the [001] direction and the correlation length of the Mn3+ trimerization decreased. (c) 2012 The Japan Society of Applied Physics
Title:
The Formation of Quasicrystal Phase in Al-Cu-Fe System By Mechanical Alloying
Authors:
Travessa, DN; Cardoso, KR; Wolf, W; Jorge, AM; Botta, WJ Author Full Names: Travessa, Dilermando Nagle; Cardoso, Katia Regina; Wolf, Witor; Jorge, Alberto Moreira, Jr.; Botta, Walter Jose
Source:
MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS, 15 (5):749-752; 10.1590/S1516-14392012005000046 SEP-OCT 2012
Abstract:
In order to obtain quasicrystalline (QC) phase by mechanical alloying (MA) in the Al-Cu-Fe system, mixtures of elementary Al, Cu and Fe in the proportion of 65-20-15 (at. %) were produced by high energy ball milling (HEBM). A very high energy type mill (spex) and short milling times (up to 5 hours) were employed. The resulting powders were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). QC phase was not directly formed by milling under the conditions employed in this work. However, phase transformations identified by DSC analysis reveals that annealing after HEBM possibly results in the formation of the psi QC phase.
Title:
Modulated structure and molecular dissociation of solid chlorine at high pressures
Authors:
Li, PF; Gao, GY; Ma, YM Author Full Names: Li, Peifang; Gao, Guoying; Ma, Yanming
Source:
JOURNAL OF CHEMICAL PHYSICS, 137 (6):10.1063/1.4742152 AUG 14 2012
Abstract:
Among diatomic molecular halogen solids, high pressure structures of solid chlorine (Cl-2) remain elusive and least studied. We here report first-principles structural search on solid Cl-2 at high pressures through our developed particle-swarm optimization algorithm. We successfully reproduced the known molecular Cmca phase (phase I) at low pressure and found that it remains stable up to a high pressure 142 GPa. At 150 GPa, our structural searches identified several energetically competitive, structurally similar, and modulated structures. Analysis of the structural results and their similarity with those in solid Br-2 and I-2, it was suggested that solid Cl-2 adopts an incommensurate modulated structure with a modulation wave close to 2/7 in a narrow pressure range 142-157 GPa. Eventually, our simulations at >157 GPa were able to predict the molecular dissociation of solid Cl-2 into monatomic phases having body centered orthorhombic (bco) and face-centered cubic (fcc) structures, respectively. One unique monatomic structural feature of solid Cl-2 is the absence of intermediate body centered tetragonal (bct) structure during the bco -> fcc transition, which however has been observed or theoretically predicted in solid Br-2 and I-2. Electron-phonon coupling calculations revealed that solid Cl-2 becomes superconductors within bco and fcc phases possessing a highest superconducting temperature of 13.03 K at 380 GPa. We further probed the molecular Cmca -> incommensurate phase transition mechanism and found that the softening of the A(g) vibrational (rotational) Raman mode in the Cmca phase might be the driving force to initiate the transition. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4742152]
Title:
Magnetic Properties of Hydrogen-Included TiZrNiPd Quasicrystals
Authors:
Shin, H; Lee, SH; Jo, Y; Kim, JY Author Full Names: Shin, Hongsik; Lee, Sang-Hwa; Jo, Youngsoo; Kim, Jae-Yong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 12 (7):6085-6088; 10.1166/jnn.2012.6318 JUL 2012
Abstract:
Quasicrystals prepared by rapid quenching of Pd-added TiZrNi ingots were hydrogenated, and effects of hydrogen for magnetic properties were compared with the unhydrogenated ones under magnetic fields from -10000 to 10000 Oe. The magnetization values obtained from vibrating sample magnetometer (VSM) were analyzed with the combination of powder X-ray diffraction (XRD) data. While its contribution is larger than that of Pd, hydrogen decreases the magnetic moments of both Pd-doped and undoped quasicrystals. As increasing the amount of absorbed hydrogen which is represented by H/M (hydrogen to host metal atom ratio) values from 0 to 1.19, the magnetization values of Ti53Zr27Ni20 quasicrystals measured at 10000 Oe significantly decreased from 0.301 to 0.212 emu/g. A careful analysis of XRD data demonstrated that the reduced interactions of magnetic dipole moments between Ni atoms, as the product of the expansion of the quasilattice constants after hydrogenation, are responsible for the decreased magnetization values in hydrogenated TiZrNiPd quasicrystal samples.
Title:
Properties- and applications of quasicrystals and complex metallic alloys
Authors:
Dubois, JM Author Full Names: Dubois, Jean-Marie
Source:
CHEMICAL SOCIETY REVIEWS, 41 (20):6760-6777; 10.1039/c2cs35110b 2012
Abstract:
This article aims at an account of what is known about the potential for applications of quasicrystals and related compounds, the so-called family of Complex Metallic Alloys (CMAs double dagger). Attention is focused at aluminium-based CMAs, which comprise a large number of crystalline compounds and quasicrystals made of aluminium alloyed with transition metals (like Fe or Cu) or normal metals like Mg. Depending on composition, the structural complexity varies from a few atoms per unit cell up to thousands of atoms. Quasicrystals appear then as CMAs of ultimate complexity and exhibit a lattice that shows no periodicity anymore in the usual 3-dimensional space. Properties change dramatically with lattice complexity and turn the metal-type behaviour of simple Al-based crystals into a far more complex behaviour, with a fingerprint of semi-conductors that may be exploited in various applications, potential or realised. An account of the ones known to the author is given in the light of the relevant properties, namely light absorption, reduced adhesion and friction, heat insulation, reinforcement of composites for mechanical devices, and few more exotic ones. The role played by the search for applications of quasicrystals in the development of the field is briefly addressed in the concluding section.
Title:
Dislocations in icosahedral quasicrystals
Authors:
Feuerbacher, M Author Full Names: Feuerbacher, Michael
Source:
CHEMICAL SOCIETY REVIEWS, 41 (20):6745-6759; 10.1039/c2cs35150a 2012
Abstract:
Dislocations in quasicrystals, as a direct result of the lack of translational symmetry in these materials, possess various salient features. The Burgers vector of a dislocation in an icosahedral quasicrystal is a 6-dimensional vector, which reflects the fact that the dislocation, besides the phonon-type strain field analogous to dislocations in ordinary crystals, is associated inseparably with a further type of defect, the phasons. Phasons are critically involved in the formation and motion of dislocations in quasicrystals and govern the macroscopic plastic behaviour of these materials. In this article the properties of dislocations in icosahedral quasicrystals are comprehensively reviewed, starting from a continuum-mechanical description, via core-structure simulation, to their full experimental characterization. The experimental results presented address the icosahedral phases in the well explored systems Al-Pd-Mn and Zn-Mg-Dy.
Title:
Electron microscopy of quasicrystals - where are the atoms?
Authors:
Abe, E Author Full Names: Abe, Eiji
Source:
CHEMICAL SOCIETY REVIEWS, 41 (20):6787-6798; 10.1039/c2cs35303b 2012
Abstract:
Quasicrystals represent aperiodically ordered form of solids with symmetries long thought forbidden in nature. Since their discovery, the fundamental key question has been "where are the atoms?" in these novel aperiodic solids, and electron microscopy has indeed provided images of real atomic arrangements in quasicrystals. In this tutorial review, we describe the microscopic view of quasicrystals using state-of-the-art scanning transmission electron microscopy, providing intriguing details that had never been unveiled by the early diffraction-based structural analyses.
Title:
Fascinating quasicrystals
Authors:
Steurer, W Author Full Names: Steurer, Walter
Source:
CHEMICAL SOCIETY REVIEWS, 41 (20):6717-6718; 10.1039/c2cs90077g 2012
Title:
Electrical and thermal transport properties of icosahedral and decagonal quasicrystals
Authors:
Dolinsek, J Author Full Names: Dolinsek, Janez
Source:
CHEMICAL SOCIETY REVIEWS, 41 (20):6730-6744; 10.1039/c2cs35036j 2012
Abstract:
Electrical and thermal transport properties of quasicrystals are reviewed on the examples of i-Ag-In-Yb and i-Al-Cu-Fe icosahedral phases and d-Al-Co-Ni decagonal phase. Using samples of single-grain morphology and high structural quality, and performing the measurements along well-defined crystallographic directions, the following basic questions in the context of physical properties of quasicrystals are addressed, both experimentally and theoretically: (1) are the unusual transport properties of quasicrystals introduced by the quasiperiodicity of the structure or are they a consequence of complex local atomic order with no direct relationship to the quasiperiodicity; (2) what is the role of the electronic structure of quasicrystals in their electronic transport properties, especially the pseudogap in the electronic density of states in the vicinity of the Fermi energy; (3) what is the anisotropy of the transport coefficients along different crystallographic directions for icosahedral and decagonal quasicrystals and (4) what are the true intrinsic properties of quasicrystalline phases?
Title:
Mathematical diffraction of aperiodic structures
Authors:
Baake, M; Grimm, U Author Full Names: Baake, Michael; Grimm, Uwe
Source:
CHEMICAL SOCIETY REVIEWS, 41 (20):6821-6843; 10.1039/c2cs35120j 2012
Abstract:
Kinematic diffraction is well suited for a mathematical approach via measures, which has substantially been developed since the discovery of quasicrystals. The need for further insight emerged from the question of which distributions of matter, beyond perfect crystals, lead to pure point diffraction, hence to sharp Bragg peaks only. More recently, it has become apparent that one also has to study continuous diffraction in more detail, with a careful analysis of the different types of diffuse scattering involved. In this review, we summarise some key results, with particular emphasis on non-periodic structures. We choose an exposition on the basis of characteristic examples, while we refer to the existing literature for proofs and further details.
Title:
Comments on the Unsettled Problems Related to the Origin of the Incommensurate Phase of Quartz
Authors:
Shigenari, T; Abe, K; Yajima, M; Nagamine, M; Semagin, D; Aslanyan, TA; Dmitriev, SV Author Full Names: Shigenari, T.; Abe, K.; Yajima, M.; Nagamine, M.; Semagin, D.; Aslanyan, T. A.; Dmitriev, S. V.
Source:
FERROELECTRICS, 433 1-11; 10.1080/00150193.2012.678098 2012
Abstract:
It is shown that there are several experimental and theoretical results which are not compatible with the currently accepted model for the incommensurate (INC) phase of quartz. In this paper, we comment on the unsettled problems obtained from the light scattering spectra and computational simulations related to the new model for the INC phase.
Title:
Adhesion Tests Using Epoxy Quasicrystal Composites
Authors:
Altidis, JD; Lima, SJG; Gomes, RM; Sampaio, EM; Torres, SM; De Barros, S Author Full Names: Altidis, J. D.; Lima, S. J. G.; Gomes, R. M.; Sampaio, E. M.; Torres, S. M.; De Barros, S.
Source:
JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY, 26 (10-11):1443-1451; 10.1163/156856111X618317 2012
Abstract:
Quasicrystals (QC) are usually complex metal alloys with atypical structures. Due to their physical, mechanical and surface properties, quasicrystals have been widely studied. Although methods to manufacture quasicrystalline materials are well known, much effort has been expended in obtaining suitable quasicrystalline materials for use in industry. As quasicrystalline materials are very brittle, they are usually used in powder form as a reinforcement for additives in composites as well as in coating technology. In this work, Al-Cu-Fe quasicrystalline powder was used as a reinforcement in epoxy resin and the influence of the quasicrystal particles incorporation on the adhesive properties of the epoxy was investigated. Single lap joints (SLJ) adhesion tests were performed in order to assess the shear mode bond strength. Results show that the effect of QC reinforcement is not linear with respect to the adherence of the composites. (C) Koninklijke Brill NV, Leiden, 2012

Update: 17-Oct-2012

Title:
Magnetic order and spin-flop transitions in the cobalt-doped multiferroic Mn1-xCoxWO4
Authors:
Ye, F; Chi, SX; Fernandez-Baca, JA; Cao, HB; Liang, KC; Wang, YQ; Lorenz, B; Chu, CW Author Full Names: Ye, Feng; Chi, Songxue; Fernandez-Baca, Jaime A.; Cao, Huibo; Liang, K. -C.; Wang, Yaqi; Lorenz, Bernd; Chu, C. W.
Source:
PHYSICAL REVIEW B, 86 (9):10.1103/PhysRevB.86.094429 SEP 24 2012
Abstract:
We present a comprehensive single-crystal neutron diffraction investigation of the Mn1-xCoxWO4 with 0.02 <= x <= 0.30. At lower concentration x <= 0.05, the system is quickly driven into the multiferroic phase with spin structure forming an elliptical spiral order similar to the parent compound. The reduction of electric polarization is ascribed to the tilting of the spiral plane. For x similar to 0.075, the magnetic structure undergoes a spin-flop transition that is characterized by a sudden rotation of the spin helix envelope into the ac plane. This spin structure persists for concentration up to x = 0.15, where additional competing magnetic orders appear at low temperature. For 0.17 <= x <= 0.30, the system experiences another spin-flop transition and recovers the low-x spiral spin configuration. A simple commensurate spin structure with (q) over right arrow = (0.5,0,0) is found to coexist with the incommensurate spiral order. The complex evolution of magnetic structure in Co doped MnWO4 contrasts sharply with other transition metal ion doped Mn(1-x)A(x)WO(4) (A = Zn, Mg, Fe) where the chemical substitutions stabilize only one type of magnetic structure. The rich phase diagram of Mn1-xCoxWO4 results from the interplay between magnetic frustration and spin anisotropy of the Co ions.
Title:
Composition and local atomic arrangement of decagonal Al-Co-Cu quasicrystal surfaces
Authors:
Zenkyu, R; Yuhara, J; Matsui, T; Zaman, SS; Schmid, M; Varga, P Author Full Names: Zenkyu, R.; Yuhara, J.; Matsui, T.; Zaman, S. Shah; Schmid, M.; Varga, P.
Source:
PHYSICAL REVIEW B, 86 (11):10.1103/PhysRevB.86.115422 SEP 17 2012
Abstract:
We investigated the composition of decagonal Al-Co-Cu surface by Auger electron spectroscopy (AES) and low-energy ion scattering (LEIS). The surface composition after annealing was Al richer and Co poorer compared to that after sputtering or bulk composition. Two types of the characteristic clusters were observed by scanning tunneling microscopy (STM) and no bias voltage dependence of the image was observed. On the other hand, scanning tunneling spectroscopy revealed a subtle difference of local density of states in unoccupied states between different sites. Structural optimization using ab initio calculations based on density functional theory (DFT) was performed on several compositional models, which are based on the W-(AlCoNi) bulk model. The surface structures of two types of the characteristic clusters were determined by comparison of the STM image and the simulated image of the structures obtained by DFT. The topmost layer was composed of Al and Cu atoms, and the compositional ratio was consistent with the AES and LEIS results.
Title:
Magnetic and Neutron Diffraction Studies of the Polycrystalline and Nanoparticle TbMnO3
Authors:
Bazela, W; Dul, M; Dyakonov, V; Gondek, L; Hoser, A; Hoffmann, JU; Penc, B; Szytula, A; Kravchenko, Z; Nosalev, I; Zarzycki, A Author Full Names: Bazela, W.; Dul, M.; Dyakonov, V.; Gondek, L.; Hoser, A.; Hoffmann, J. -U.; Penc, B.; Szytula, A.; Kravchenko, Z.; Nosalev, I.; Zarzycki, A.
Source:
ACTA PHYSICA POLONICA A, 122 (2):384-390; AUG 2012
Abstract:
This paper reports on investigations of magnetic properties, crystal and magnetic structures on TbMnO3 prepared in various ways, namely, as conventional polycrystalline sample and two nano particle specimens (synthesized with a sol gel method at temperatures of 800 and 850 degrees C). The X-ray and neutron diffraction data confirm the orthorhombic crystal structure (space group Pbnm, No. 62) without noticeable differences of the lattice parameters for poly- and nanocompounds. For the polycrystalline sample, a subsequent ordering of the Mn and Tb sublattices with decreasing temperature was observed. Namely, the Mn sublattice exhibits a modulated magnetic structure with the propagation vector k = (0, k(x), 0) in between 41-5 K. Below T = 21 K, a change from a collinear (A(y) mode) into non-collinear (A(y)G(z) mode) structure was evidenced. Further decreasing of temperature below 10 K results in magnetic ordering of the Tb sublattice (modulated G(x)A(y)F(z) mode). For nanoparticle compounds, magnetic ordering in the Mn and Tb sublattices is described by propagation vector k = (0, k(y), 0), with k(y) components higher than observed for polycrystalline sample. The magnetic ordering in the Mn sublattice is described by a collinear A(y) mode down to 1.6 K where the Tb moment becomes ordered (G(x)A(y) mode). The observed broadening of the Bragg peaks connected to the Tb sublattice suggests the cluster-like character of its magnetic structure.

Update: 10-Oct-2012

Title:
Magnetic structure of the Sm5Ge4-type Tb2Ti3Ge4
Authors:
Morozkin, AV; Nirmala, R; Malik, SK; Isnard, O Author Full Names: Morozkin, A. V.; Nirmala, R.; Malik, S. K.; Isnard, O.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (23):4030-4033; 10.1016/j.jmmm.2012.07.009 NOV 2012
Abstract:
The orthorhombic Sm5Ge4-type Tb2Ti3Ge4 shows square modulated non-collinear magnetic ordering with wave vector K=[+/- 1/3, 1/2, 1/2] at 2 K. The terbium magnetic moments lie in the bc plane and magnetic moment value of 7.5(2) mu(B)/Tb is obtained at 2 K. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Oxygen displacements and magnetoelectric coupling in LuMnO3
Authors:
Tong, P; Louca, D; Lee, N; Cheong, SW Author Full Names: Tong, P.; Louca, Despina; Lee, Nara; Cheong, S. -W.
Source:
PHYSICAL REVIEW B, 86 (9):10.1103/PhysRevB.86.094419 SEP 14 2012
Abstract:
The hexagonal multiferroic LuMnO3 transforms to the P6(3)cm symmetry upon entering the ferroelectric phase. Using neutron diffraction and the pair density function analysis, it is shown that short-range local atomic distortions are present, calling for a lower symmetry, such as the P6(3), for the following reasons. With cooling, the MnO5 bipyramid tilting becomes more enhanced than previously determined. This splits the in-plane Mn-O-Mn angles especially below T-N, leading to inequivalent magnetic coupling constants J between the in-plane Mn ions. Additionally, below T-N, several weak incommensurate magnetic phases appear in response to the reminiscent frustration from the triangular Mn lattice. The complex magnetic structure may be the driving mechanism for the lower crystal symmetry.
Title:
Impact of dynamic orbital correlations on magnetic excitations in the normal state of iron-based superconductors
Authors:
Lee, WC; Lv, WC; Tranquada, JM; Phillips, PW Author Full Names: Lee, Wei-Cheng; Lv, Weicheng; Tranquada, J. M.; Phillips, Philip W.
Source:
PHYSICAL REVIEW B, 86 (9):10.1103/PhysRevB.86.094516 SEP 14 2012
Abstract:
We show here that orbital degrees of freedom produce a distinct signature in the magnetic excitation spectrum of iron-based superconductors above the magnetic ordering temperature. Because d(xz) and d(yz) orbitals are strongly connected with Fermi surface topology, the nature of magnetic excitations can be modified significantly due to the presence of either static or fluctuating orbital correlations. Within a five-orbital itinerant model, we show that static orbital order generally leads to an enhancement of commensurate magnetic excitations even when the original Fermi surface lacks nesting at (pi,0) or (0,pi). When long-range orbital order is absent, Gaussian fluctuations beyond the standard random-phase approximation capture the effects of fluctuating orbital correlations on the magnetic excitations. We find that commensurate magnetic excitations can also be enhanced if the orbital correlations are strong. Our results offer a natural explanation for the incommensurate-to-commensurate transformation observed in a recent neutron scattering measurement (Xu et al., arXiv:1201.4404), and we propose that this unusual transformation is an important signature to distinguish orbital from spin physics in the normal state of pnictides. Implications for the magnetic and superconducting states are discussed.
Title:
Effects of Al substitution on the multiferroic properties of TbMnO3
Authors:
Cuartero, V; Blasco, J; Rodriguez-Velaman, JA; Garcia, J; Subias, G; Ritter, C; Stankiewicz, J; Canadillas-Delgado, L Author Full Names: Cuartero, Vera; Blasco, Javier; Alberto Rodriguez-Velaman, J.; Garcia, Joaquin; Subias, Gloria; Ritter, Clemens; Stankiewicz, Jolanta; Canadillas-Delgado, Laura
Source:
PHYSICAL REVIEW B, 86 (10):10.1103/PhysRevB.86.104413 SEP 10 2012
Abstract:
The effect of a small substitution of Mn with Al in TbMnO3 has been studied. We report results of heat capacity, magnetization, and dielectric constant studies in TbMn1-xAlxO3 compounds (x <= 0.1). Al has the same valence as substituted Mn but is nonmagnetic and its small size gives rise to microstructural strain which affects the multiferroic properties of the parent compound. Long-range antiferromagnetic ordering is observed in all compounds but the transition temperature decreases as the Al content increases. TbMn0.95Al0.05O3 exhibits a ferroelectric phase transition which is absent in TbMn0.9Al0.1O3. The dielectric constant of the latter compound reveals a relaxor behavior suggesting the presence of nanosize polar domains for this compound. A neutron diffraction study on a single crystal of TbMn0.9Al0.1O3 reveals that Mn shows a sinusoidal incommensurate ordering down to low temperature. Tb moments exhibit an incommensurate short-range ordering but the application of a magnetic field leads to metamagnetic transitions. In particular, a field parallel to the b axis induces a commensurate long-range ordering of Tb of type CxFy. The magnetic field also affects the magnetic structure of Mn3+ moments at low temperature which develop an incommensurate cycloid ordering in the ab plane. This result suggests that dilution of a magnetic multiferroic with a small nonmagnetic atom might yield materials with a relaxor to ferroelectric transition driven by a magnetic field.
Title:
MESOPOROUS SILICA Holey quasicrystals
Authors:
Tolbert, SH Author Full Names: Tolbert, Sarah H.
Source:
NATURE MATERIALS, 11 (9):749-751; 10.1038/nmat3414 SEP 2012

Update: 3-Oct-2012

Title:
Determining the magnetic ground state of TbNi5 single crystal using polarized neutron scattering technique
Authors:
Pirogov, AN; Bogdanov, SG; Lee, S; Park, JG; Choi, YN; Lee, H; Grigorev, SV; Sikolenko, VV; Sherstobitova, EA; Schedler, R Author Full Names: Pirogov, A. N.; Bogdanov, S. G.; Lee, Seongsu; Park, Je-Geun; Choi, Y. -N.; Lee, H.; Grigorev, S. V.; Sikolenko, V. V.; Sherstobitova, E. A.; Schedler, R.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (22):3811-3816; 10.1016/j.jmmm.2012.06.019 NOV 2012
Abstract:
The TbNi5 compound shows an interesting magnetic phase transition with an incommensurate structure below 23 K, whose true nature remains unresolved. In order to solve this question, we have carried out polarized neutron diffraction experiments by measuring temperature and field dependence of the intensities of satellites and Bragg reflections. From the temperature dependence of both satellite peaks and Bragg reflection, we demonstrated that it has only one magnetic structure at a given temperature. Furthermore, unlike previous reports, we found that both ferromagnetic and modulated components of the Tb ion magnetic moments should be collinear to each other. Our data also show strong depolarisation effects that are most likely to arise from domain structure of ferromagnetic component. A critical field, which destroyers a modulated magnetic structure is found to be lower than a field value to saturate the ferromagnetic component, in which the intensity of Bragg ferromagnetic r! eflections reaches saturation. (C) 2012 Elsevier By. All rights reserved.
Title:
Intermediate-valence icosahedral Au-Al-Yb quasicrystal
Authors:
Watanuki, T; Kashimoto, S; Kawana, D; Yamazaki, T; Machida, A; Tanaka, Y; Sato, TJ Author Full Names: Watanuki, Tetsu; Kashimoto, Shiro; Kawana, Daichi; Yamazaki, Teruo; Machida, Akihiko; Tanaka, Yukinori; Sato, Taku J.
Source:
PHYSICAL REVIEW B, 86 (9):10.1103/PhysRevB.86.094201 SEP 10 2012
Abstract:
A quasiperiodic intermediate-valence (IV) system is realized in an icosahedral Au-Al-Yb quasicrystal. X-ray absorption spectroscopy near the Yb L-3 edge indicates that quasiperiodically arranged Yb ions assume a mean valence of 2.61, between a divalent state (4f(14), J = 0) and a trivalent one (4f(13), J = 7/2). Magnetization measurements demonstrate that the 4f holes in this quasicrystal have a localized character. The magnetic susceptibility shows a Curie-Weiss behavior above similar to 100 K with an effective magnetic moment of 3.81 mu(B) per Yb. Moreover, a crystalline approximant to this quasicrystal is an IV compound. We propose a heterogeneous IV model for the quasicrystal, whereas the crystalline approximant is most likely a homogeneous IV system. At temperatures below similar to 10 K, specific heat and magnetization measurements reveal non-Fermi-liquid behavior in both the quasicrystal and its crystalline approximant without either doping, pressure, or field tuning.
Title:
Spin density wave and superconductivity in CaFe1-xCoxAsF studied by nuclear magnetic resonance
Authors:
Tsutsumi, S; Fujiwara, N; Matsuishi, S; Hosono, H Author Full Names: Tsutsumi, S.; Fujiwara, N.; Matsuishi, S.; Hosono, H.
Source:
PHYSICAL REVIEW B, 86 (6):10.1103/PhysRevB.86.060515 AUG 29 2012
Abstract:
We performed nuclear magnetic resonance measurements to investigate the evolution of spin-density-wave (SDW) and superconducting (SC) states upon electron doping in CaFe1-xCoxAsF, which exhibits an intermediate phase diagram between those of LaFeAsO1-xFx and Ba(Fe1-xCox)(2)As-2. We found that homogeneous coexistence of the incommensurate SDW and SC states occurs only in a narrow doping region around the crossover regime, which supports S+--wave symmetry. However, only the structural phase transition survives upon further doping, which agrees with predictions from orbital fluctuation theory. The transitional features upon electron doping imply that both spin and orbital fluctuations are involved in the superconducting mechanism.
Title:
Europium-IV: An Incommensurately Modulated Crystal Structure in the Lanthanides
Authors:
Husband, RJ; Loa, I; Stinton, GW; Evans, SR; Ackland, GJ; McMahon, MI Author Full Names: Husband, R. J.; Loa, I.; Stinton, G. W.; Evans, S. R.; Ackland, G. J.; McMahon, M. I.
Source:
PHYSICAL REVIEW LETTERS, 109 (9):10.1103/PhysRevLett.109.095503 AUG 27 2012
Abstract:
High-resolution x-ray powder-diffraction experiments were performed on europium metal at high pressure up to 50 GPa. At variance with previous reports, the hcp phase of Eu was observed to be stable not only to 18 GPa, but to 31.5 GPa. At 31.5(5) GPa, europium transforms to a phase (Eu-IV) with an incommensurately modulated monoclinic crystal structure with superspace group C2/c(q(1)0q(3))00. This new phase was observed to be stable to similar to 37.0 GPa, where another phase transition was observed. Eu-IV is the first phase in the lanthanide elements with an incommensurate crystal structure.
Title:
Micrometer-sized quasicrystals in the Al85Ni5Y6Co2Fe2 metallic glass: A TEM study and a brief discussion on the formability of quasicrystals in bulk and marginal glass-forming alloys
Authors:
Yan, M; Wang, JQ; Kong, C; Schaffer, GB; Qian, M Author Full Names: Yan, M.; Wang, J. Q.; Kong, C.; Schaffer, G. B.; Qian, M.
Source:
JOURNAL OF MATERIALS RESEARCH, 27 (16):2131-2139; 10.1557/jmr.2012.140 AUG 2012
Abstract:
Large quasicrystals up to similar to 10 mu m in size with a volume fraction of similar to 30% have been identified in a nitrogen gas-atomized marginal glass-forming alloy Al85Ni5Y6Co2Fe2 by detailed transmission electron microscopy. The formation of the large quasicrystal (Q) phase is discussed through the configuration of the valence electrons of its constituent elements, and the thermodynamic and kinetic factors associated with the solidification of this marginal glass-forming alloy during gas atomization. The finding leads to an important inference that marginal glass-forming alloys could be ideal systems for the formation of bulk quasicrystals under appropriate kinetic conditions. The Q phase is stable up to similar to 500 degrees C and decomposes thereafter. The activation energy for the decomposition of the Q phase is similar to the self-diffusion of Al. Two new intermetallic phases associated with the formation and decomposition of the Q phase have also been identified and characterized.

Update: 26-Sep-2012

Title:
X-ray diffraction study on the microstructure of a Mg-Zn-Y alloy consolidated by high-pressure torsion
Authors:
Jenei, P; Gubicza, J; Yoon, EY; Kim, HS Author Full Names: Jenei, Peter; Gubicza, Jeno; Yoon, Eun Yoo; Kim, Hyoung Seop
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 539 32-35; 10.1016/j.jallcom.2012.05.100 OCT 25 2012
Abstract:
Mg95Zn4.3Y0.7 (at.%) alloy powder produced by an inert gas-atomizer was consolidated by high-pressure torsion (HPT) at room temperature and 373 K. The phase composition and the microstructure were investigated by X-ray diffraction and the microstructural parameters were correlated to the yield strength. HPT-processing yielded an ultrafine-grained microstructure with high dislocation density, leading to a large yield strength of the samples. Both the gas-atomized powder and the consolidated samples contained an icosahedral Mg3YZn6 phase (I-phase) besides the main phase of alpha-Mg. It turned out that the I-phase dispersoids strengthen the consolidated material indirectly by increasing the dislocation density due to their pinning effect. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Epitaxial Bi allotropes on quasicrystal surfaces as templates for adsorption of pentacene and fullerene
Authors:
Sharma, HR; Smerdon, JA; Young, KM; McGrath, R Author Full Names: Sharma, H. R.; Smerdon, J. A.; Young, K. M.; McGrath, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (35):10.1088/0953-8984/24/35/354012 SEP 5 2012
Abstract:
The growth of Bi on surfaces of Al-based quasicrystals yields a quasicrystalline monolayer which is followed by the formation of crystalline islands of various forms depending on coverage, deposition flux and substrate temperature. We have used the Bi thin films consisting of both crystalline and quasicrystalline allotropes as substrates to study the deposition of C-60 and pentacene molecules. Scanning tunneling microscopy (STM) reveals substrate-dependent differences in molecular adsorption.
Title:
Crystallization and compressive behaviors of Ti40Zr25Ni8Cu9Be18 BMG cast from different liquid states
Authors:
Zhou, X; Kou, HC; Wang, J; Li, JS; Zhou, L Author Full Names: Zhou, Xun; Kou, Hongchao; Wang, Jun; Li, Jinshan; Zhou, Lian
Source:
INTERMETALLICS, 28 45-50; 10.1016/j.intermet.2012.03.061 SEP 2012
Abstract:
The initial microstructure of Ti40Zr25Ni8Cu9Be18 metallic glass is sensitive to preparation condition. The Ti40Zr25Ni8Cu9Be18 metallic glasses, prepared at different liquid temperature by copper mold casting, would possess different first crystallization product because of difference in initial microstructure. During first crystallization, Crystallization product is mainly metastable icosahedral phase for metallic glass prepared at relative low liquid temperature. However, the mixture of alpha-Ti + icosahedral + unknown phase precipitates from metallic glass prepared at relative high liquid temperature. Moreover, the difference in initial microstructure also has a significant influence on compressive properties. Ti40Zr25Ni8Cu9Be18 metallic glasses prepared at relative low temperature exhibit better plasticity. One of important reasons is that dominant icosahedral short range order (SRO) increases shear viscosity of shear band, and the possibility of catastrophic failure caused by fast and continuous slide of shear band is depressed. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.

Update: 20-Sep-2012

Title:
Magnetic dilution and steric effects in the multiferroic delafossite CuCrO2
Authors:
Pachoud, E; Singh, K; Breard, Y; Martin, C; Andre, G; Hardy, V; Simon, C; Maignan, A Author Full Names: Pachoud, E.; Singh, K.; Breard, Y.; Martin, C.; Andre, G.; Hardy, V.; Simon, Ch.; Maignan, A.
Source:
PHYSICAL REVIEW B, 86 (5):10.1103/PhysRevB.86.054437 AUG 21 2012
Abstract:
In order to get to the bottom of substitution effects reported in CuCrO2 delafossite, structural, magnetic, and electric properties of several CuCr1-xMxO2 series, where M3+ is a S = 0 cation (M3+ = Al3+, Ga3+, Sc3+, Rh3+), have been investigated. It is shown that the homogeneity of the substitution is element dependent and is particularly difficult to achieve for the smallest Al3+ cation. Ferroelectricity and dielectric properties are found to depend on the x value, but also on the nature of M: The largest substitution effects are observed for the larger elements, owing to the decrease of the Cr3+-Cr3+ interaction resulting from the enlargement of the in-plane lattice parameter. However, the magnetic structures of CuCr0.9Ga0.1O2 and CuCr0.9Rh0.1O2, revealed close to that of CuCrO2 by neutron diffraction, demonstrate the great stability of this antiferromagnetic incommensurate structure against the presence of {M3+, S = 0} cations. This emphasizes the very different nature of the magnetic ground state of CuCrO2, as compared to CuFeO2, despite their common structural characteristics.
Title:
Magnetoelectric properties in orthorhombic Nd1-xYxMnO3: Neutron diffraction experiments
Authors:
Landsgesell, S; Prokes, K; Ouladdiaf, B; Klemke, B; Prokhnenko, O; Hepp, B; Kiefer, K; Argyriou, DN Author Full Names: Landsgesell, S.; Prokes, K.; Ouladdiaf, B.; Klemke, B.; Prokhnenko, O.; Hepp, B.; Kiefer, K.; Argyriou, D. N.
Source:
PHYSICAL REVIEW B, 86 (5):10.1103/PhysRevB.86.054429 AUG 20 2012
Abstract:
In this paper we investigate the complex transformation of the magnetoelectric properties from the collinear A-type phase to the multiferroic noncollinear spin cycloid in the solid solution Nd1-xYxMnO3 from compositions of x = 0.3 to 0.55 in single crystal samples. Neutron diffraction experiments at the structural phase transition (x = 0.35 to 0.45) reveal the coexistence of the A-type order and several incommensurate orders, varying with composition and temperature.
Title:
Magnetic and electronic orderings in orthorhombic RMnO3 (R = Tm, Lu) studied by resonant soft x-ray powder diffraction
Authors:
Garganourakis, M; Bodenthin, Y; de Souza, RA; Scagnoli, V; Donni, A; Tachibana, M; Kitazawa, H; Takayama-Muromachi, E; Staub, U Author Full Names: Garganourakis, M.; Bodenthin, Y.; de Souza, R. A.; Scagnoli, V.; Doenni, A.; Tachibana, M.; Kitazawa, H.; Takayama-Muromachi, E.; Staub, U.
Source:
PHYSICAL REVIEW B, 86 (5):10.1103/PhysRevB.86.054425 AUG 17 2012
Abstract:
Resonant soft x-ray powder diffraction experiments on orthorhombic TmMnO3 and LuMnO3 are presented. Experiments were performed in the vicinity of the Tm M-5 and the Mn L-2,L-3 edges to study the Tm and Mn magnetic moments, respectively. These experiments show that for the heavy rare-earth perovskite with an E-type ordered ground state, the Tm magnetic moments order already in the nonferroelectric incommensurate magnetic phase. Additionally, deviations from the collinear E-type Mn magnetic structure at low temperatures are found for both compounds. These experiments show the power of resonant soft x-ray diffraction, extended to polycrystalline 4f materials.
Title:
Antiferrodistortive phase transition in EuTiO3
Authors:
Goian, V; Kamba, S; Pacherova, O; Drahokoupil, J; Palatinus, L; Dusek, M; Rohlicek, J; Savinov, M; Laufek, F; Schranz, W; Fuith, A; Kachlik, M; Maca, K; Shkabko, A; Sagarna, L; Weidenkaff, A; Belik, AA Author Full Names: Goian, V.; Kamba, S.; Pacherova, O.; Drahokoupil, J.; Palatinus, L.; Dusek, M.; Rohlicek, J.; Savinov, M.; Laufek, F.; Schranz, W.; Fuith, A.; Kachlik, M.; Maca, K.; Shkabko, A.; Sagarna, L.; Weidenkaff, A.; Belik, A. A.
Source:
PHYSICAL REVIEW B, 86 (5):10.1103/PhysRevB.86.054112 AUG 17 2012
Abstract:
X-ray diffraction, dynamical mechanical analysis, and infrared reflectivity studies revealed an antiferrodistortive phase transition in EuTiO3 ceramics. Near 300 K, the perovskite structure changes from cubic Pm (3) over barm to tetragonal I4/mcm due to antiphase tilting of oxygen octahedra along the c axis (a(0)a(0)c(-) in Glazer notation). The phase transition is analogous to SrTiO3. However, some ceramics as well as single crystals of EuTiO3 show different infrared reflectivity spectra bringing evidence of a different crystal structure. In such samples, electron diffraction revealed an incommensurate tetragonal structure with modulation wave vector q similar or equal to 0.38 a*. Extra phonons in samples with modulated structure are activated in the IR spectra due to folding of the Brillouin zone. We propose that defects such as Eu3+ and oxygen vacancies strongly influence the temperature of the phase transition to antiferrodistortive phase as well as the tendency to incommensurate modulation in EuTiO3.
Title:
Multiple magnetic structures of correlated Ce ions in intermetallic CeAu2Ge2
Authors:
Singh, DK; Thamizhavel, A; Lynn, JW; Dhar, SK; Hermann, T Author Full Names: Singh, D. K.; Thamizhavel, A.; Lynn, J. W.; Dhar, S. K.; Hermann, T.
Source:
PHYSICAL REVIEW B, 86 (6):10.1103/PhysRevB.86.060405 AUG 13 2012
Abstract:
Neutron diffraction measurements on a high quality single crystal of CeAu2Ge2 reveal two magnetic structures that coexist with commensurate long-range antiferromagnetic order below the Neel temperature T-N similar or equal to 14 K. The magnetic structures, which exhibit distinct temperature and field dependencies, are described by both commensurate and incommensurate magnetic structures and introduce a new region in the H-T phase diagram. These experimental observations provide important information for developing a universal understanding of the magnetic properties of this class of Ce-based CeX2M2 (X = Cu, Ag, Au; M = Ge, Si) compounds, which are prototypes for exploring quantum phase transitions, and their interplay with unconventional superconductivity.
Title:
QUASICRYSTALS: Tile at random
Authors:
Klopper, A Author Full Names: Klopper, Abigail
Source:
NATURE PHYSICS, 8 (8):582-582; AUG 2012
Title:
Nanosize icosahedral quasicrystal in Mg90Ca10 glass: An ab initio molecular dynamics study
Authors:
Durandurdu, M Author Full Names: Durandurdu, Murat
Source:
JOURNAL OF CHEMICAL PHYSICS, 137 (3):10.1063/1.4736581 JUL 21 2012
Abstract:
Rapid solidification of Mg90Ca10 from its liquid state is studied by means of an ab initio molecular dynamics technique, and its local structure is investigated by various analyzing methods. The liquid and amorphous states are found to have slightly different short range order even though the perfect and defective icosahedral bonding environments are major bonding elements of both liquid and amorphous states. Perfect icosahedrons with a small frequency exist in the liquid state, more develop during the cooling process and they become the leading building units in the glass state, indicating an icosahedral short range order in Mg90Ca10 glass. Also the linked icosahedrons lead to an icosahedral medium range order. Furthermore, an ordered arrangement of some icosahedrons in the hexagonal symmetry is observed in the glass model, representing a nanoscale icosahedral quasicrystalline phase in Mg90Ca10 glass. (C) 2012 American Institute of Physics. [http://dx.do! i.org/10.1063/1.4736581]
Title:
THERMAL STABILITY OF Al-Mn-Be MELT-SPUN RIBBONS
Authors:
Lojen, G; Boncina, T; Zupanic, F Author Full Names: Lojen, Gorazd; Boncina, Tonica; Zupanic, Franc
Source:
MATERIALI IN TEHNOLOGIJE, 46 (4):329-333; JUL-AUG 2012
Abstract:
As with other kinds of finely dispersed, small particles, icosahedral quasicrystals (IQCs) also have a distinct strengthening effect, which can be utilised to enhance the mechanical properties of aluminium alloys. In Al-Mn-Be alloys, IQCs already form at moderate cooling rates, which can be utilised when using some conventional casting processes, like mould or injection casting. In this case, however, crystalline intermetallic phases are also present and the mechanical properties are inferior to those of two-phase alpha(Al)-IQC alloys. Two-phase microstructures are feasible using rapid solidification techniques, e.g., melt spinning. Further processing often involves technologies (consolidation, extrusion etc.), which include the influence of heat. The alloy must not be overheated in order to preserve the strengthening effect of the metastable IQC-particles. In this investigation the Al-Mn-Be alloy was melt-spun using a free-jet melt spinner. Subsequently, the thermal stability of the IQCs was explored by annealing the ribbons for 24 h at different temperatures. The samples were examined in the as-cast and heat-treated conditions using a dual-beam, scanning electron microscope (SEM-FIB). X-ray diffraction (XRD) and differential scanning calorimetry (DSC). It was discovered that in the as-cast condition, the ribbons had a two-phase microstructure, consisting of an alpha(Al) matrix and finely dispersed IQCs. During annealing at temperatures up to 400 degrees C, the IQCs did not decompose and the phase composition remained unchanged. Annealing at 500 degrees C and at higher temperatures caused a decomposition of the IQCs, and only the crystalline intennetallic phases Al6Mn and Be4AlMn could be found in the alpha(Al) matrix.

Update: 12-Sep-2012

Title:
Structural Modulation in the High Capacity Battery Cathode Material LiFeBO3
Authors:
Janssen, Y; Middlemiss, DS; Bo, SH; Grey, CP; Khalifah, PG Author Full Names: Janssen, Yuri; Middlemiss, Derek S.; Bo, Shou-Hang; Grey, Clare P.; Khalifah, Peter G.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 134 (30):12516-12527; 10.1021/ja301881c AUG 1 2012
Abstract:
The crystal structure of the promising Li-ion battery cathode material LiFeBO3 has been redetermined based on the results of single crystal X-ray diffraction data. A commensurate modulation that doubles the periodicity of the lattice in the a-axis direction is observed. When the structure of LiFeBO3 is refined in the 4-dimensional superspace group C2/c(alpha 0 gamma)00, with alpha = 1/2 and gamma = 0 and with lattice parameters of a = 5.1681 angstrom, b = 8.8687 angstrom, c = 10.1656 angstrom, and beta = 91.514 degrees, all of the disorder present in the prior C2/c structural model is eliminated and a long-range ordering of 1D chains of corner-shared LiO4 is revealed to occur as a result of cooperative displacements of Li and O atoms in the c-axis direction. Solid-state hybrid density functional theory calculations find that the modulation stabilizes the LiFeBO3 structure by 1.2 kJ/mol (12 meV/f.u.), and that the modulation disappears after delithiation to form a structurally related FeBO3 phase. The band gaps of LiFeBO3 and FeBO3 are calculated to be 3.5 and 3.3 eV, respectively. Bond valence sum maps have been used to identify and characterize the important Li conduction pathways, and suggest that the activation energies for Li diffusion will be higher in the modulated structure of LiFeBO3 than in its unmodulated analogue.
Title:
Spontaneous formation of filamentary Cd whiskers and degradation of CdMgYb icosahedral quasicrystal under ambient conditions
Authors:
Lu, L; Wang, JB; Zheng, H; Zhao, DS; Wang, RH; Gui, JN Author Full Names: Lu, Lu; Wang, Jianbo; Zheng, He; Zhao, Dongshan; Wang, Renhui; Gui, Jianian
Source:
JOURNAL OF MATERIALS RESEARCH, 27 (14):1895-1904; 10.1557/jmr.2012.136 JUL 2012
Abstract:
The whiskers spontaneously grown in Cd-Mg-Yb alloy containing icosahedral quasicrystal as dominant phase have been investigated by electron microscopy. It is found that: (i) the whiskers are mainly composed of Cd with growth direction along, <<(2)over bar>110>(Cd). CdO particles are frequently observed on surfaces of whiskers and the alloy, indicating the importance of the oxidation process during the whisker growth; (ii) there exist four types of orientation relationship between Cd and CdO. The interfaces between them are shown to accommodate large lattice misfit, which is well explained by near coincidence site lattice model; (iii) nanosized Cd particles are observed to aggregate around the whisker root, providing a convincing experimental evidence for the long-range atomic diffusion. Our study offers a unique opportunity to unveil the relationship between unstability of quasicrystal structure and whisker formation and may have some implications for oxidation process of me! tals.

Update: 5-Sep-2012

Title:
Incommensurate Modulated Structures in the Ta2O5-Al2O3 System
Authors:
Schmid, S; Fung, V Author Full Names: Schmid, Siegbert; Fung, Veronica
Source:
AUSTRALIAN JOURNAL OF CHEMISTRY, 65 (7):851-859; 10.1071/CH12080 2012
Abstract:
Members of the (1 - x)Ta2O5 center dot xAl(2)O(3) series were synthesized, and the structures investigated using synchrotron X-ray powder diffraction and neutron powder diffraction data for the first time. Structural models were developed and refined using the Rietveld method and a [3 + 1] dimensional incommensurately modulated composite structure approach with a composition dependent modulation vector q, and superspace group Xmmm(0 beta 0)s00. Displacive atomic modulation functions across the (1 - x)Ta(2)O(5 center dot)xAl(2)O(3) series were found to be very similar, and strongly resemble those for the Ta2O5-WO3 system, in line with the notion that there are structure types in higher dimensional space just as there are in 3D space. Bond valence sum calculations and bond distance plots showed that the introduction of the modulation to the structural model generally led to more favourable bond valence sum values and bond distances. Fourier difference plots were examined, and the occupational modulation of aluminium refined to determine that the aluminium atoms preferentially occupy the octahedral sites.

Update: 29-Aug-2012

Title:
Effect of microalloying on the formation and stability of the Ti-Zr-Ni icosahedral quasicrystal
Authors:
Lee, GW; Gangopadhyay, AK; Kelton, KF Author Full Names: Lee, G. W.; Gangopadhyay, A. K.; Kelton, K. F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 537 171-174; 10.1016/j.jallcom.2012.05.040 OCT 5 2012
Abstract:
The influence of small additions of Cu, Ag, Au, Pt, Pb, and Si on the formation and stabilization of Ti-Zr-Ni icosahedral quasicrystal (i-phase) are discussed. Among these elements, only the addition of Ag improved the stability and formability of the i-phase, significantly. A small amount of supercooling and the nucleation and growth of only the i-phase from the liquid during levitation melting experiments signal the presence of well developed extended icosahedral short range order (ISRO) in the liquid. These results are explained in terms of a better atomic size ratio of Ag to Zr to form ISRO. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Electrochemical properties of Ti-based Quasicrystal and ZrV2 Laves phase alloy composite materials as negative electrode for Ni-MH secondly batteries
Authors:
Liu, WQ; Liang, F; Zhang, SS; Lin, J; Wang, XL; Wang, LM Author Full Names: Liu, Wanqiang; Liang, Fei; Zhang, Shanshan; Lin, Jing; Wang, Xinlu; Wang, Limin
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 358 (15):1846-1849; 10.1016/j.jnoncrysol.2012.05.035 AUG 1 2012
Abstract:
The Ti1.4V0.6Ni alloy ribbon is prepared by arc melting and subsequent melt-spinning technique. The ZrV2 alloy is prepared by arc melting and annealing at 1250k for 80 h. The structure and electrochemical properties of the Ti1.4V0.6Ni and their ball-milled composites with annealed ZrV2 are investigated. Phase structure investigations of the composites show that alloys mainly consist of the icosahedral quasicrystal (I-phase), C14 Laves phase with a hexagonal structure, C15 Laves phase with cubic structure, V-based solid solution phase with BCC structure and face centered cubic (FCC) phase with Ti2Ni-type structure. The negative electrode made by composite alloys has a maximum discharge capacity of 360.3 mAh/g at a current density of 30 mA/g and a high rate discharge ability of 82.7% at 240 mA/g. The cyclic stability of the negative electrode made of Ti1.4V0.6Ni and annealed ZrV2 composite is higher than that of Ti1.4V0.6Ni. The mechanism for the capacity loss of the alloy electrodes during charge and discharge cycling has been studied in this paper. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Multiferroic FeTe2O5Br: Alternating spin chains with frustrated interchain interactions
Authors:
Pregelj, M; Jeschke, HO; Feldner, H; Valenti, R; Honecker, A; Saha-Dasgupta, T; Das, H; Yoshii, S; Morioka, T; Nojiri, H; Berger, H; Zorko, A; Zaharko, O; Arcon, D Author Full Names: Pregelj, M.; Jeschke, H. O.; Feldner, H.; Valenti, R.; Honecker, A.; Saha-Dasgupta, T.; Das, H.; Yoshii, S.; Morioka, T.; Nojiri, H.; Berger, H.; Zorko, A.; Zaharko, O.; Arcon, D.
Source:
PHYSICAL REVIEW B, 86 (5):10.1103/PhysRevB.86.054402 AUG 1 2012
Abstract:
A combination of density functional theory calculations, many-body model considerations, and magnetization and electron-spin-resonance measurements shows that the multiferroic FeTe2O5Br should be described as a system of alternating antiferromagnetic S = 5/2 chains with strong Fe-O-Te-O-Fe bridges weakly coupled by two-dimensional frustrated interactions, rather than the previously reported tetramer model. The peculiar temperature dependence of the incommensurate magnetic vector can be explained in terms of interchain exchange striction being responsible for the emergent net electric polarization.

Update: 22-Aug-2012

Title:
Growth of large-grain Ag-In-Yb icosahedral quasicrystals and approximant crystals
Authors:
Cui, C; Tsai, AP Author Full Names: Cui, Can; Tsai, An Pang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 536 91-93; 10.1016/j.jallcom.2012.05.031 SEP 25 2012
Abstract:
Large-grain quasicrystals and approximant crystals are desirable for the physical properties and surface properties study. In this letter, we present a study on the growth of large-grain icosahedral quasicrystals and 2/1 and 1/1 approximant crystals of Ag-In-Yb alloy using a facile self-flux method in indium-rich melt-solution. The as-grown samples show facets along 5-, 3- and 2-fold planes in the quasicrystal sample, whereas the 1/1 approximant crystal exhibits facets along {1 0 0} and {1 1 0} planes and the 2/1 approximant crystal along the {1 1 1} planes. The facets are considered to be thermodynamically favorite planes in the above crystals and they offer valuable information for understanding the surface stability in icosahedral quasicrystals. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Unified (3+1)-dimensional superspace description of the 2212-type stair-like [Bi2Sr3Fe2O9](m)[Bi4Sr6Fe2O16] family of compounds
Authors:
Elcoro, L; Perez, O; Perez-Mato, JM; Petricek, V Author Full Names: Elcoro, Luis; Perez, Olivier; Perez-Mato, J. M.; Petricek, Vaclav
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 341-355; 10.1107/S0108768112018095 Part 4 AUG 2012
Abstract:
The (3 + 1)-dimensional superspace approach is applied to describe and refine a series of sheared compounds related to layered high T-c superconducting oxides. Two commensurate members (m = 4, 5) of the 2212 stair-like [Bi2Sr3Fe2O9](m)-[ Bi4Sr6Fe2O16] family of compounds, previously studied using single-crystal diffraction data, are analyzed. A common average unit cell has been identified and a composition-dependent modulation wavevector is proposed. The model is built using only three independent atomic domains, one for the metal atoms and two for the O atoms. The three Sr, Bi and Fe species are described using close-connected crenel-like functions forming a continuous atomic domain along the internal space. The two oxygen domains are represented by crenel functions and the displacive modulation functions are built up by Legendre polynomials recently implemented in the program JANA2006. Surprisingly, the results of the refinements show a striking similarity of the displacive modulations for the two compounds analyzed, indicating that a unique model can be used to describe the correlations between the atomic displacements of the 2212 stair-like series. This final model is then applied to predict the structure of new members of the family.
Title:
Solitonic lattice and Yukawa forces in the rare-earth orthoferrite TbFeO3
Authors:
Artyukhin, S; Mostovoy, M; Jensen, NP; Le, D; Prokes, K; de Paula, VG; Bordallo, HN; Maljuk, A; Landsgesell, S; Ryll, H; Klemke, B; Paeckel, S; Kiefer, K; Lefmann, K; Kuhn, LT; Argyriou, DN Author Full Names: Artyukhin, Sergey; Mostovoy, Maxim; Jensen, Niels Paduraru; Le, Duc; Prokes, Karel; de Paula, Vincius G.; Bordallo, Heloisa N.; Maljuk, Andrey; Landsgesell, Sven; Ryll, Hanjo; Klemke, Bastian; Paeckel, Sebastian; Kiefer, Klaus; Lefmann, Kim; Kuhn, Luise Theil; Argyriou, Dimitri N.
Source:
NATURE MATERIALS, 11 (8):694-699; 10.1038/NMAT3358 AUG 2012
Abstract:
The random fluctuations of spins give rise to many interesting physical phenomena, such as the 'order-from-disorder' arising in frustrated magnets and unconventional Cooper pairing in magnetic superconductors. Here we show that the exchange of spin waves between extended topological defects, such as domain walls, can result in novel magnetic states. We report the discovery of an unusual incommensurate phase in the orthoferrite TbFeO3 using neutron diffraction under an applied magnetic field. The magnetic modulation has a very long period of 340 angstrom at 3 K and exhibits an anomalously large number of higher-order harmonics. These domain walls are formed by Ising-like Tb spins. They interact by exchanging magnons propagating through the Fe magnetic sublattice. The resulting force between the domain walls has a rather long range that determines the period of the incommensurate state and is analogous to the pion-mediated Yukawa interaction between protons and neutrons in nuclei.
Title:
Structure refinement and superspace description of the system Bi2(n+2)MonO6(n+1) (n=3, 4, 5 and 6)
Authors:
Bereciartua, PJ; Zuniga, FJ; Perez-Mato, JM; Petricek, V; Vila, E; Castro, A; Rodriguez-Carvajal, J; Doyle, S Author Full Names: Bereciartua, P. J.; Zuniga, F. J.; Perez-Mato, J. M.; Petricek, V.; Vila, E.; Castro, A.; Rodriguez-Carvajal, J.; Doyle, S.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 323-340; 10.1107/S0108768112017478 Part 4 AUG 2012
Abstract:
The system Bi(2(n + 2))MonO(6(n + 1)) is described within the superspace formalism. Two superspace models are proposed for the different members of this family, depending on the parity of the parameter n. The superspace model for the odd members is constructed through the embedding of the cationic distribution of the member with n = 3, and the modification of a superspace model previously proposed for the compound Bi2MoO6. However, this model cannot be applied to the even members of the family. Performing the appropriate transformations, a suitable superspace model for the even members is obtained. The atomic structure of the different compounds of the family have been refined through the Rietveld method combining synchrotron X-ray and neutron powder diffraction data.
Title:
Effect of Cu on rapidly solidified Al-Mn-Be alloy
Authors:
Zupanic, F; Lojen, G; Barba, L; Boncina, T Author Full Names: Zupanic, F.; Lojen, G.; Barba, L.; Boncina, T.
Source:
MATERIALS CHARACTERIZATION, 70 48-54; 10.1016/j.matchar.2012.05.002 AUG 2012
Abstract:
The microstructure of an Al-Mn-Be-Cu alloy was characterised after melt spinning and heat-treatment at different temperatures. The optimised melt-spinning parameters made it possible to obtain ribbons with thicknesses ranging from 30 to 200 mu m, having a microstructure composed of a supersaturated Al-rich solid solution, finely dispersed icosahedral quasicrystalline (IQC) particles, and a small fraction of Al2Cu. The finest dispersion of the IQC-particles, and consequently the highest microhardness, was obtained on the wheel-side. The initial microstructure started to decompose at temperatures around 400 degrees C. The IQC-phase was replaced by the intermetallic compounds tau(1)-Al29Mn6Cu4 and Be4Al(Mn,Cu). The maximum hardness of the ribbons, which was approximately 50% higher than in the as-cast state, was attained after heat treatment at 400 degrees C, and could be attributed to the fine dispersion of tau(1)-Al29Mn6Cu4 and IQC-particles. (C) 2012 Elsevier Inc. All rights reserved.
Title:
[Ni(MeCN)(H2O)(2)(NO3)(2)]center dot(15-crown-5)center dot MeCN: detailed study of a four-phase sequence that includes an intermediate modulated phase
Authors:
Siegler, MA; Parkin, S; Brock, CP Author Full Names: Siegler, Maxime A.; Parkin, Sean; Brock, Carolyn Pratt
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 389-400; 10.1107/S0108768112018319 Part 4 AUG 2012
Abstract:
A sequence of four phases has been found for an acetonitrile-solvated co-crystal with 15-crown-5 of the nickel complex [acetonitrilediaqua-kappa O-1-nitrato-kappa O-2-nitratonickel(II)]. The structure could be determined at intervals of ca 10 K in the range 90-273 K because crystals remain single through the three transitions. In phase (I) (T >= ca 240 K; P2(1)/m, Z' = 1/2), there is extensive disorder, which is mostly resolved in phase (III) (ca 230-145 K; P2(1)/c, Z' = 1). Phase (IV) (ca 145-90 K, and probably below; P (1) over bar, Z' = 2) is ordered. Phase (II) (ca 238-232 K) is modulated, but the satellite reflections are too weak to allow the structure to be determined within its stability range by standard methods. Most crystals that were flash-cooled from room temperature to 90 K have a metastable P2(1), Z' = 5 superstructure that (at least in a commensurate approximation) was identified as similar to the structure of phase (II) by comparison of reconstructed reciprocal-lattice slices and by analogy with the phase behavior of the very similar compound [Ni(H2O)(6)](NO3)(2)center dot(15-crown-5)center dot 2H2O [Siegler et al. (2011). Acta Cryst. B67, 486-498]. In the phase (II) structure slab-like regions that are like the disordered phase (I) structure alternate with regions of similar shape and size that are like the more ordered phase (III) structure.
Title:
Two types of adjacent dimer layers in the low-temperature phase of BaCuSi2O6
Authors:
Sheptyakov, DV; Pomjakushin, VY; Stern, R; Heinmaa, I; Nakamura, H; Kimura, T Author Full Names: Sheptyakov, D. V.; Pomjakushin, V. Yu.; Stern, R.; Heinmaa, I.; Nakamura, H.; Kimura, T.
Source:
PHYSICAL REVIEW B, 86 (1):10.1103/PhysRevB.86.014433 JUL 30 2012
Abstract:
The low-temperature crystal structure of BaCuSi2O6 has been investigated with high-resolution synchrotron x-ray and neutron powder diffraction techniques and has been found to be on average (ignoring the incommensurate modulation) orthorhombic, with the most probable space group Ibam. The Cu-Cu dimers in this material are forming two types of layerswith distinctly different interatomic distances. Subtle changes also modify the partially frustrated interlayer Cu-Cu exchange paths. The present results corroborate the interpretation of low-temperature nuclear magnetic resonance and inelastic neutron scattering data in terms of distinct dimer layers.
Title:
High CO2 and H-2 Uptake in an Anionic Porous Framework with Amino-Decorated Polyhedral Cages
Authors:
Zhai, QG; Lin, QP; Wu, T; Wang, L; Zheng, ST; Bu, XH; Feng, PY Author Full Names: Zhai, Quan-Guo; Lin, Qipu; Wu, Tao; Wang, Le; Zheng, Shou-Tian; Bu, Xianhui; Feng, Pingyun
Source:
CHEMISTRY OF MATERIALS, 24 (14):2624-2626; 10.1021/cm301322b JUL 24 2012
Title:
Phase stability of Ni-2(Mn1-xFex)Ga: A first-principles study
Authors:
Luo, HB; Hu, QM; Li, CM; Yang, R; Johansson, B; Vitos, L Author Full Names: Luo, Hu-Bin; Hu, Qing-Miao; Li, Chun-Mei; Yang, Rui; Johansson, Borje; Vitos, Levente
Source:
PHYSICAL REVIEW B, 86 (2):10.1103/PhysRevB.86.024427 JUL 23 2012
Abstract:
Ni-2(Mn1-xFex)Ga ferromagnetic shape memory alloy shows unusual composition-dependent martensitic transformation temperature (T-M), namely, T-M decreases with increasing e/a ratio. In hope of understanding this unusual behavior, we investigated the composition dependence of the heat of formation (H-f) and shear elastic modulus (C') of the cubic austenite as well as the stability of the five-layer modulated (5M) tetragonal martensite relative to the austenite, using first-principles exact muffin-tin orbital method in combination with coherent potential approximation. Our calculations demonstrated that H-f of the austenite increases with the Fe content x. C' increases slightly with x up to 0.05 but decreases thereafter. The composition dependence of both H-f and C' cannot fully account for the trend of T-M against x although such correlations have been proposed in literature for other Ni-Mn-Ga based alloys. The structure of 5M martensite phase of Ni-2(Mn1-xFex)Ga wit! h 0 < x < 0.2 is determined by optimizing both the shear (changing c/a) and wavelike shuffle of atoms in (110) planes along [1 (1) over bar0] direction adopting the experimentally determined modulation function. The energy difference Delta E-AM between the austenite and 5M phases decreases with increasing x up to 0.05, following the lower Delta E-AM corresponding to lower T-M rule. However, with x larger than 0.05, Delta E-AM increases, against the experimental T-M similar to x behavior. We propose that, if taking the temperature effect and the spin-orbital coupling into account, the Delta E-AM similar to x curve might be altered and may explain the unusual composition dependence of Ni-2(Mn1-xFex)Ga.
Title:
Effect of Trivalent Additions and Processing on Structural and Magnetic Transitions in Ni-Mn-Ga Ferromagnetic Shape Memory Alloys
Authors:
Mathur, RP; Singh, RK; Ray, S; Ghosal, P; Chandrasekaran, V Author Full Names: Mathur, R. P.; Singh, R. K.; Ray, S.; Ghosal, P.; Chandrasekaran, V.
Source:
DEFENCE SCIENCE JOURNAL, 62 (4):252-260; JUL 2012
Abstract:
Ferromagnetic shape memory Ni50Mn30Ga15Al5-xBx (x = 0, 1, and 4) alloys were prepared by vacuum arc melting and subsequent heat-treatment as well as by melt spinning to investigate the effect of trivalent element additions in ternary Ni-Mn-Ga alloys. The heat-treated alloys containing Al were reported to possess a modulated martensite structure, however alloy containing both Al and B showed a loss of modulated structure in martensite formed. The rapidly solidified alloys on the other hand showed the formation of a similar modulated structure without composition change in alloys containing Al and the alloys containing Al and B. In addition, the former showed a presence of an amorphous phase with latter showing crystalline boron rich phases. The magnetisation of the B containing alloys in both the processing technique was however very low, showing lower magnetic exchange interaction in such alloys.
Title:
Exchange coupling and helical spin order in the triangular lattice antiferromagnet CuCrO2 using first principles
Authors:
Jiang, XF; Liu, XF; Wu, YZ; Han, JR Author Full Names: Jiang Xue-Fan; Liu Xian-Feng; Wu Yin-Zhong; Han Jiu-Rong
Source:
CHINESE PHYSICS B, 21 (7):10.1088/1674-1056/21/7/077502 JUL 2012
Abstract:
The magnetic and electronic properties of the geometrically frustrated triangular antiferromagnet CuCrO2 are investigated by first principles through density functional theory calculations within the generalized gradient approximations (GGA)+U scheme. The spin exchange interactions up to the third nearest neighbours in the ab plane as well as the coupling between adjacent layers are calculated to examine the magnetism and spin frustration. It is found that CuCrO2 has a natural two-dimensional characteristic of the magnetic interaction. Using Monte-Carlo simulation, we obtain the Neel temperature to be 29.9 K, which accords well with the experimental value of 24 K. Based on non-collinear magnetic structure calculations, we verify that the incommensurate spiral-spin structure with (110) spiral plane is believable for the magnetic ground state, which is consistent with the experimental observations. Due to intra-layer geometric spin frustration, parallel helical-spin chains arise along the a, b, or a + b directions, each with a screw-rotation angle of about 120 degrees. Our calculations of the density of states show that the spin frustration plays an important role in the change of d-p hybridization, while the spin-orbit coupling has a very limited influence on the electronic structure.
Title:
Defect structure and electrical conductivity in the pseudo-binary system Bi3TaO7-Bi3NbO7
Authors:
Struzik, M; Liu, X; Abrahams, I; Krok, F; Malys, M; Dygas, JR Author Full Names: Struzik, M.; Liu, X.; Abrahams, I.; Krok, F.; Malys, M.; Dygas, J. R.
Source:
SOLID STATE IONICS, 218 25-30; 10.1016/j.ssi.2012.05.005 JUN 22 2012
Abstract:
A study of electrical and structural characteristics of compositions in the Bi3Ta1-xNbxO7 system, using X-ray and neutron powder diffraction and AC impedance spectroscopy, is presented. The electrical conductivity increases with increasing niobium content. A full solid solution is observed which adopts an incommensurately ordered pseudo-cubic fluorite structure (type II). Analysis of the defect structure of the x=0.50 composition shows chains of niobate/tantalate octahedra as a likely structural motif. A small degree of non-linearity in the thermal expansion of the cubic subcell lattice parameter is observed. (C) 2012 Elsevier B.V. All rights reserved.

Update: 8-Aug-2012

Title:
Dodecagonal tiling in mesoporous silica
Authors:
Xiao, CH; Fujita, N; Miyasaka, K; Sakamoto, Y; Terasaki, O Author Full Names: Xiao, Changhong; Fujita, Nobuhisa; Miyasaka, Keiichi; Sakamoto, Yasuhiro; Terasaki, Osamu
Source:
NATURE, 487 (7407):349-353; 10.1038/nature11230 JUL 19 2012
Abstract:
Recent advances in the fabrication of quasicrystals in soft matter systems have increased the length scales for quasicrystals (1) into the mesoscale range (20 to 500 angstroms). Thus far, dendritic liquid crystals (2), ABC-star polymers(3), colloids(4) and inorganic nanoparticles(5) have been reported to yield quasicrystals. These quasicrystals offer larger length scales than intermetallic quasicrystals (a few angstroms)(1,6), thus potentially leading to optical applications through the realization of a complete photonic bandgap induced via multiple scattering of light waves in virtually all directions(7-9). However, the materials remain far from structurally ideal, in contrast to their intermetallic counterparts, and fine control over the structure through a self-organization process has yet to be attained. Here we use the well-established self-assembly of surfactant micelles to produce a new class of mesoporous silicas, which exhibit 12-fold (dodecagonal) symmetry in both electron diffraction and morphology. Each particle reveals, in the 12-fold cross-section, an analogue of dodecagonal quasicrystals in the centre surrounded by 12 fans of crystalline domains in the peripheral part. The quasicrystallinity has been verified by selected-area electron diffraction and quantitative phason strain analyses on transmission electron microscope images obtained from the central region. We argue that the structure forms through a non-equilibrium growth process, wherein the competition between different micellar configurations has a central role in tuning the structure. A simple theoretical model successfully reproduces the observed features and thus establishes a link between the formation process and the resulting structure.
Title:
Field-induced incommensurate spin structure of TbNiAl4
Authors:
Hutchison, WD; Goossens, DJ; Whitfield, RE; Studer, AJ; Nishimura, K; Mizushima, T Author Full Names: Hutchison, W. D.; Goossens, D. J.; Whitfield, R. E.; Studer, A. J.; Nishimura, K.; Mizushima, T.
Source:
PHYSICAL REVIEW B, 86 (1):10.1103/PhysRevB.86.014412 JUL 13 2012
Abstract:
TbNiAl4 exhibits incommensurate and commensurate magnetic ordering as a function of temperature. As a function of applied field it undergoes a series of magnetic phase transitions. The first of these transitions, into an intermediate spin arrangement, is the source of a large inverse magnetocaloric effect, an unusual result given that an aligning field is being applied. This has potential uses in magnetic cooling. Here, single-crystal neutron diffraction with applied magnetic field is used to obtain the intermediate field spin arrangement in TbNiAl4. We find that not only does the applied field drive the system from commensurate to incommensurate ordering, but that the phase transition shows hysteresis such that a mixed state simultaneously showing commensurate and incommensurate antiferromagnetic ordering, along with ferromagnetism, can be obtained.
Title:
Structure of a new ternary compound with high magnesium content, so-called Gd13Ni9Mg78
Authors:
Couillaud, S; Gaudin, E; Weill, F; Gomez, S; Stan, C; Plante, D; Miraglia, S; Bobet, JL Author Full Names: Couillaud, S.; Gaudin, E.; Weill, F.; Gomez, S.; Stan, C.; Plante, D.; Miraglia, S.; Bobet, J. L.
Source:
ACTA MATERIALIA, 60 (10):4144-4151; 10.1016/j.actamat.2012.04.012 JUN 2012
Abstract:
The magnesium-rich composition Gd13Ni9Mg78 was synthesized from its constituent elements in sealed tantalum tubes in an induction furnace. X-ray diffraction, electron probe microanalysis and dark-field transmission electron microscopy (TEM) images revealed a new compound with a composition ranging from Gd10-15Ni8-12Mg72-78 and low crystallinity. In order to increase the crystallinity, different experimental conditions were investigated for numerous compounds with the initial composition Gd13Ni9Mg78. In addition, several heat treatments (from 573 to 823 K) and cooling rates (from room temperature quenched down to 2 K h(-1)) have been tested. The best crystallinity was obtained for the slower cooling rates ranging from 2 to 6 K h(-1). From the more crystallized compounds, the structure was partially deduced using TEM and an average cubic structure with lattice parameter a = 4.55 A could be assumed. A modulation along both a and b axis with vectors of modulation q1 = 0.42a* and q2 = 0.42b* was observed. This compound, so-called Gd13Ni9Mg78, absorbs around 3 wt.% of hydrogen at 603 K, 30 bars and a reasonable degree of reversibility is possible, because after the first hydrogenation, irreversible decomposition into MgH2, GdH2 and NiMg2H4 has been shown. The pathway of the reaction is described herein. The powder mixture after decomposition shows an interesting kinetics for magnesium without ball milling. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
ANALYSIS OF QUASICRYSTAL GENERATION IN CONVENTIONALLY SOLIDIFIED AL-CU-FE ALLOYS
Authors:
Varga, B; Fazakas, E; Varga, KL Author Full Names: Varga, Bela; Fazakas, Eva; Varga, K. Lalos
Source:
METALURGIA INTERNATIONAL, 17 (8):27-30; 2012
Abstract:
The paper analyzes the structure of Al-Cu-Fe alloys solidified by chill casting. The non-equilibrium structure that results after casting is transformed into a quasicrystal structure by grinding and heat treatment by annealing. Structural analyses were conducted by X-rays, optical microscopy and dilatometry. Dilatometric determinations revealed the peritectic reactions underlying the metastable to stable quasicrystal structure transformation. In the areas five of phase transformations the physical dilatation coefficient ranges between 13.10(-6) and 17.10(-6) K-1.

Update: 1-Aug-2012

Title:
Atomic structure of quasicrystals
Authors:
de Boissieu, M Author Full Names: de Boissieu, Marc
Source:
STRUCTURAL CHEMISTRY, 23 (4):965-976; 10.1007/s11224-012-0004-4 AUG 2012
Abstract:
The 2011 Nobel Prize in chemistry has been awarded to Dan Shechtman for his discovery of quasicrystals. The discovery has indeed been a breakthrough in crystallography and solid state physics and chemistry. After a brief introduction to the subject, we review some of the recent advances in the understanding of the atomic structure of icosahedral quasicrystals and in particular for the binary Cd-Yb type quasicrystal. Thanks to a combined analysis of periodic approximant, high quality synchrotron data, and the superspace approach, a detailed insight in the crystal chemistry of this binary quasicrystal has been achieved.
Title:
On non-Euclidean crystallography, some football manifolds
Authors:
Molnar, E Author Full Names: Molnar, Emil
Source:
STRUCTURAL CHEMISTRY, 23 (4):1057-1069; 10.1007/s11224-012-0041-z AUG 2012
Abstract:
In polyhedral crystallography, non-Euclidean possibilities come into considerations as well. The so-called football manifolds appearing in the Bolyai-Lobachevskian hyperbolic space (H (3)) can model "fullerens" very probably. This may give us the feeling that-in atomic measure-space can wear non-Euclidean structures, e.g., hyperbolic (H (3)), spherical (S (3)) and other ones, respectively. Such phenomena as pentagonal or decagonal symmetry and the discovery of quasicrystals might strengthen these impressions. We examine here some Archimedean solids: (4, 6, 6) in E (3) (the truncated octahedron in the classical Euclidean space, for analogue as motivation, Fig. 1); (5, 6, 6) the "real football" (now in H (3), Fig. 2, from Molnar in Proceedings of International Conference on Differential Geometry and Its Applications, 1988), (3, 10, 10) in H (3) (Fig. 3 from Molnar in the previous Proceedings); an extra solid (4, 6, 8) with two manifolds on it in H (3) (Figs. 4, 5), published first time in this paper. Furthermore (3, 8, 8) will be realized in the spherical space S (3) (Fig. 6). We can study this classical example as a simple non-Euclidean one also for motivation to our method (see also Molnar in Acta Cryst A61:542-552, 2005, as an introductory paper). Each of them will be a manifold, i.e., it can be endowed with an appropriate face pairing (topological glueing), so that every point has a ball-like neighborhood in the corresponding space, especially of constant curvature, but completely in the classical analogy. In addition, each manifold will be compact (bounded and closed) whose fundamental group can be generated by two screw motions.
Title:
Cluster packing from a higher dimensional perspective
Authors:
Steurer, W; Deloudi, S Author Full Names: Steurer, Walter; Deloudi, Sofia
Source:
STRUCTURAL CHEMISTRY, 23 (4):1115-1120; 10.1007/s11224-011-9864-2 AUG 2012
Abstract:
The way to find the optimum packing of quasicrystal-constituting clusters is discussed based on the projected-cell approach. We illustrate why the quasiperiodic arrangement of partially overlapping clusters with decagonal or icosahedral symmetry is the most efficient one, by relating it to the packing of unit cells in hypercubic lattices.
Title:
Phase diagram of the Dzyaloshinskii-Moriya helimagnet Ba2CuGe2O7 in canted magnetic fields
Authors:
Muhlbauer, S; Gvasaliya, S; Ressouche, E; Pomjakushina, E; Zheludev, A Author Full Names: Muehlbauer, S.; Gvasaliya, S.; Ressouche, E.; Pomjakushina, E.; Zheludev, A.
Source:
PHYSICAL REVIEW B, 86 (2):10.1103/PhysRevB.86.024417 JUL 13 2012
Abstract:
The evolution of different magnetic structures of noncentrosymmetric Ba2CuGe2O7 is systematically studied as a function of the orientation of the magnetic field H. Neutron diffraction in combination with measurements of magnetization and specific heat show a virtually identical behavior of the phase diagram of Ba2CuGe2O7 for H confined in both the (1,0,0) and (1,1,0) plane. The existence of a recently proposed incommensurate double-k AF-cone phase is confirmed in a narrow range for H close to the tetragonal c axis. For large angles enclosed by H and the c axis, a complexly distorted nonsinusoidal magnetic structure has recently been observed. We show that its critical field H-c systematically increases for larger canting. Measurements of magnetic susceptibility and specific heat finally indicate the existence of an incommensurate/commensurate transition for H approximate to 9T applied in the basal (a, b) plane and agree with a nonplanar, distort! ed cycloidal magnetic structure.
Title:
FMR determination of the period of an incommensurate magnetic structure in chiral organometallic crystals
Authors:
Mushenok, FB; Kirman, MV; Koplak, OV; Morgunov, RB Author Full Names: Mushenok, F. B.; Kirman, M. V.; Koplak, O. V.; Morgunov, R. B.
Source:
PHYSICS OF THE SOLID STATE, 54 (7):1358-1362; 10.1134/S1063783412070281 JUL 2012
Abstract:
A sequence of maxima of microwave absorption has been found in the ferromagnetic resonance (FMR) spectra of the chiral molecular ferrimagnet [Mn{(R/S)-pn}](2)[Mn{(R/S)-pn}(2)(H2O)][Cr(CN)(6)](2), which, as is shown, corresponds to the spin-soliton resonance. It has been established that this sequence corresponds to an incommensurate magnetic structure induced by the competition between the symmetric and antisymmetric exchange interactions. On the basis of the FMR spectra and their dependence on the temperature, the parameters of the modulated magnetic structure have been estimated.

Update: 25-Jul-2012

Title:
Tailoring martensitic transformation and martensite structure of NiMnIn alloy by Ga doping In
Authors:
Liu, ZH; Li, GT; Wu, ZG; Ma, XQ; Liu, Y; Wu, GH Author Full Names: Liu, Z. H.; Li, G. T.; Wu, Z. G.; Ma, X. Q.; Liu, Y.; Wu, G. H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 535 120-123; 10.1016/j.jallcom.2012.04.088 SEP 15 2012
Abstract:
The martensitic transformation and the martensite crystal structure of alloys Ni50Mn34In16 xGax (x = 0, 2, 4, 6, 8, 10, 12, 14, 16) have been investigated in this study. The studied alloys, with cubic L2(1) phase (x = 0, 2), seven-layered modulated (14 M) martensite phase (x = 4, 6, 8), and non-modulated (NM) martensite phase (x = 10, 12, 14, 16), exhibit martensitic transformation with critical temperature increasing linearly from 238 K for x = 0 to 486 K for x = 16. The linearity coefficient is estimated to be similar to 15 K per at.% of Ga. With regards to the lattice parameters, a elongates, whereas b and c contract as the austenite phase transformed to 14 M martensite phase. While, it turns to c elongates, a and b contract as austenite transformed to NM martensite phase. It is found that the unit cell volume decreases with increasing Ga content, which contributes to the increase of transformation temperature with Ga content. A maximum strain of 12% is predicted through the lattice distortion in 14 M martensite. Magnetic measurement shows the Curie temperature for martensite increases with Ga content. (C) 2012 Elsevier B.V. All rights reserved.
Title:
The effect of nanoquasicrystals on mechanical properties of as-extruded Mg-Zn-Gd alloy
Authors:
Huang, H; Kato, H; Chen, CL; Wang, ZC; Yuan, GY Author Full Names: Huang, Hua; Kato, Hidemi; Chen, Chunlin; Wang, Zhongchang; Yuan, Guangyin
Source:
MATERIALS LETTERS, 79 281-283; 10.1016/j.matlet.2012.04.018 JUL 15 2012
Abstract:
The Mg-3.5Zn-0.6Gd (at. %) alloy was prepared and homogenized at 673 K for 8 h, and then extruded at 523 K with an extrusion ratio of 9:1. The rnicrostructure and mechanical properties of the extruded alloy have been investigated. lcosahedral quasicrystalline phase (I-phase) existed in extruded Mg-Zn-Gd-based alloys in two morphologies: (1) micron-scale I-phase formed in the solidification, (2) nano-scale ellipsoid-shape I-phase particles precipitated in the extrusion process. A definite orientation relationship and good atomic match between I-phase and alpha-Mg matrix were directly observed by conventional and high-resolution transmission electron microscopy (HRTEM), which contribute to the high tensile strength of 308 MPa and the large plasticity of 16.4%. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Ti1.4V0.6Ni quasicrystal and its composites with xV(18)Ti(15)Zr(18)Ni(29)Cr(5)Co(7)Mn alloy used as negative electrode materials for the nickel-metal hydride (Ni-MH) secondary batteries
Authors:
Liu, WQ; Zhang, SS; Wang, LM Author Full Names: Liu, Wanqiang; Zhang, ShanShan; Wang, Limin
Source:
MATERIALS LETTERS, 79 122-124; 10.1016/j.matlet.2012.04.040 JUL 15 2012
Abstract:
This study examined the structure and electrochemical hydrogen storage characteristics of the Ti1.4V0.6Ni quasicrystal and their ball-milled composites with V18Ti15Zr18Ni29Cr5Co7 alloy. It is found by XRD that composite material alloys consist of the icosahedral quasicrystal (I-phase), C14 Laves phase with a hexagonal structure and a V-based solid solution phase with a BCC structure and a face centered cubic (FCC) phase with a Ti2Ni-type structure. The maximum discharge capacity of the alloy electrodes increases with increasing V18Ti15Zr18Ni29Cr5Co7 in the Ti1.4V0.6Ni alloy when using such composite materials as Ni-MH battery anodes under the condition that the discharge current density is 30 mA g(-1) at 303 K. Also, composite materials lead to significant improvement in the high-rate dischargeability (HRD) as well as the cyclic stability. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Neutron scattering studies of spin excitations in superconducting Rb0.82Fe1.68Se2
Authors:
Wang, MY; Li, CH; Abernathy, DL; Song, Y; Carr, SV; Lu, XY; Li, SL; Yamani, Z; Hu, JP; Xiang, T; Dai, PC Author Full Names: Wang, Miaoyin; Li, Chunhong; Abernathy, D. L.; Song, Yu; Carr, Scott V.; Lu, Xingye; Li, Shiliang; Yamani, Zahra; Hu, Jiangping; Xiang, Tao; Dai, Pengcheng
Source:
PHYSICAL REVIEW B, 86 (2):10.1103/PhysRevB.86.024502 JUL 5 2012
Abstract:
We use inelastic neutron scattering to show that superconducting (SC) rubidium iron selenide Rb0.82Fe1.68Se2 exhibits antiferromagnetic (AF) spin excitations near the in-plane wave vector Q = (pi, 0) identical to that for iron arsenide superconductors. Moreover, we find that these excitations change from incommensurate to commensurate with increasing energy and occur at the expense of spin waves associated with the coexisting root 5 x root 5 block AF phase. Since these spin excitations cannot come from Fermi surface nesting based on angle resolved photoemission experiments, our results indicate the presence of local moments in SC Rb0.82Fe1.68Se2 that may have a similar origin as the hourglass-like spin excitations in copper oxide superconductors.
Title:
Magnetic order tuned by Cu substitution in Fe1.1-zCuzTe
Authors:
Wen, JS; Xu, ZJ; Xu, GY; Lumsden, MD; Valdivia, PN; Bourret-Courchesne, E; Gu, GD; Lee, DH; Tranquada, JM; Birgeneau, RJ Author Full Names: Wen, Jinsheng; Xu, Zhijun; Xu, Guangyong; Lumsden, M. D.; Valdivia, P. N.; Bourret-Courchesne, E.; Gu, Genda; Lee, Dung-Hai; Tranquada, J. M.; Birgeneau, R. J.
Source:
PHYSICAL REVIEW B, 86 (2):10.1103/PhysRevB.86.024401 JUL 2 2012
Abstract:
We study the effects of Cu substitution in Fe1.1Te, the nonsuperconducting parent compound of the iron-based superconductor, Fe1+yTe1-xSex, utilizing neutron scattering techniques. It is found that the structural and magnetic transitions, which occur at similar to 60 K without Cu, are monotonically depressed with increasing Cu content. By 10% Cu for Fe, the structural transition is hardly detectable, and the system becomes a spin glass below 22 K, with a slightly incommensurate orderingwave vector of (0.5 - delta, 0, 0.5) with delta being the incommensurability of 0.02, and correlation length of 12 angstrom along the a axis and 9 angstrom along the c axis. With 4% Cu, both transition temperatures are at 41 K, though short-range incommensurate order at (0.42, 0, 0.5) is present at 60K. With further cooling, the incommensurability decreases linearly with temperature down to 37 K, below which there is a first-order transition to a long-range almost-commensurate antiferromagnetic structure. A spin anisotropy gap of 4.5 meV is also observed in this compound. Our results show that the weakly magnetic Cu has a large effect on the magnetic correlations; it is suggested that this is caused by the frustration of the exchange interactions between the coupled Fe spins.

Update: 18-Jul-2012

Title:
A possible generalization of the phenomenological theory of phase transitions in type II ferroelectrics with incommensurate phase
Authors:
Korda, VY; Berezovsky, SV; Molev, AS; Korda, LP; Klepikov, VF Author Full Names: Korda, V. Yu.; Berezovsky, S. V.; Molev, A. S.; Korda, L. P.; Klepikov, V. F.
Source:
PHYSICA B-CONDENSED MATTER, 407 (17):3388-3393; 10.1016/j.physb.2012.04.043 SEP 1 2012
Abstract:
We develop a generalized phenomenological theory of the paraelectric - incommensurate - commensurate phase transitions in type II ferroelectrics. The linear temperature dependence of the sixth-power term coefficient in the thermodynamic potential expansion is proposed. Contrary to the pre-existing theoretical approaches, the developed model eliminates a number of long-standing problems in the theory of type II ferroelectrics and can provide a correct description of the experimental data on the temperature dependence of the properties of type II ferroelectrics in the incommensurate phase. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Magnetic properties and magnetic structures of the CeScSi-type RMgPb (R=Ce-Nd, Sm, Gd-Tm) compounds
Authors:
Lemoine, P; Verniere, A; Venturini, G; Mareche, JF; Capelli, S; Malaman, B Author Full Names: Lemoine, P.; Verniere, A.; Venturini, G.; Mareche, J. F.; Capelli, S.; Malaman, B.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (19):2937-2952; 10.1016/j.jmmm.2012.03.037 SEP 2012
Abstract:
Investigations made by powder X-ray diffraction, magnetic measurements and neutron powder diffraction on the CeScSi-type ternary magnesium plumbides RMgPb (R=Ce-Nd, Sm, Gd-Tm) are reported. Macroscopic magnetic measurements performed in the 2-300 K temperature range show that these compounds follow a Curie-Weiss law in the paramagnetic state (except SmMgPb) and behave antiferromagnetically at low temperature (T-N <= 61 K). Field dependence of the magnetization performed at 5 K evidence metamagnetic-like behaviors (H-crit < 7 T). Neutron powder diffraction evidenced complex antiferromagnetic structures in fair agreement with the magnetic data. PrMgPb and NdMgPb compounds present a commensurate antiferromagnetic structure, while (Tb-Er)MgPb are characterized by incommensurate sine-wave modulated magnetic structure down to lower temperature or square-wave magnetic structure due to appearance of higher odd integer harmonics. CeMgPb and TmMgPb evidence more complex sine-wave modulated magnetic structures, never encountered with the CeScSi-type structure, characterized by two propagation vectors. These results are discussed and compared with those of the isotypic RMgSn compounds. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Modeling of Incommensurate omega Structure in the Zr-Nb Alloys
Authors:
Tang, B; Cui, YW; Chang, H; Kou, HC; Li, JS; Zhou, L Author Full Names: Tang, Bin; Cui, Y. -W.; Chang, Hui; Kou, Hongchao; Li, Jinshan; Zhou, Lian
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 43A (8):2581-2586; 10.1007/s11661-012-1214-5 AUG 2012
Abstract:
Kanzaki force induced by substitutional solutes was introduced as a composition-dependent oscillating defect field in the Ginzburg-Landau model to simulate the pre-transition structure preceding the beta-to-omega phase transformation. A three-dimensional (3-D) modulated incommensurate structure of the omega phase composed of alternating omega and beta phases was predicted to be present in the moderately concentrated Zr-Nb alloys. The modeling work suggests that the Kanzaki force acts as a resistance that generates and retains the incommensurate structure of the omega phase.
Title:
Enhanced microhardness of mechanically activated carbon-quasicrystal composite
Authors:
Yadav, TP; Singh, D; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Singh, Devinder; Tiwari, R. S.; Srivastava, O. N.
Source:
MATERIALS LETTERS, 80 5-8; 10.1016/j.matlet.2012.04.034 AUG 1 2012
Abstract:
In this work, Al65Cu20Fe15 icosahedral quasicrystal and mechanically activated carbon (graphite) composite have been investigated. The low intensity milling (100 rpm) of quasicrystalline phase with mechanically activated carbon (MAC) showed to conserve the quasicrystalline (QC) phase as well as the small amount of nano crystalline B2 phase. Mechanical behavior of the sintered samples (200 degrees C) showed an increase in the hardness of the composite materials up to 5 at.% of MAC. The hardness value is nearly 0.37 times higher than that for stable Al-Cu-Fe quasicrystal. The high hardness value may be attributed to the microstructural variation resulting due to 5 at.% MAC addition. This work has demonstrated the possibility of producing MAC-QC composite materials with acceptable and reliable properties. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Microstructure and properties of extruded rapidly solidified AlCr4.7Fe1.1Si0.3 (at.%) alloys
Authors:
Cavojsky, M; Balog, M; Dvorak, J; Illekova, E; Svec, P; Krizik, P; Janickovic, D; Simancik, F Author Full Names: Cavojsky, Miroslav; Balog, Martin; Dvorak, Jiri; Illekova, Emilia; Svec, Peter; Krizik, Peter; Janickovic, Dusan; Simancik, Frantisek
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 549 233-241; 10.1016/j.msea.2012.04.051 JUL 15 2012
Abstract:
The rapidly solidified AlCr4.7Fe1.1Si0.3 (at.%) alloy produced at large scale by direct extrusion of gas atomised powders was investigated. Hot-extrusion yielded sound compacts and did not create any major structural changes compared to the as-atomised state. Microstructural characterisation of the as-extruded material revealed submicron scale alpha-Al grains with an embedded Al7Cr crystalline phase and traces of a nano-scale quasicrystalline Al84.6Cr15.4 Phase. The long-term thermal stability up to 300 degrees C of compacts was proven. The thermal stability of compacts was accompanied by high mechanical properties, especially high strength and Young's modulus, and creep performance up to 300 degrees C. The same material was prepared by laboratory scale extrusion of cryo-chopped melt-spun ribbons as a reference material. No major differences in the structure or properties of the industrially prepared material were observed compared to the reference material. (c) 2012 Elsevier B.V. All rights reserved.
Title:
The microstructural evolution and superplastic behavior at low temperatures of Mg-5.00Zn-0.92Y-0.16Zr (wt.%) alloys after hot extrusion and ECAP process
Authors:
Xu, SW; Zheng, MY; Kamado, S; Wu, K Author Full Names: Xu, S. W.; Zheng, M. Y.; Kamado, S.; Wu, K.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 549 60-68; 10.1016/j.msea.2012.03.116 JUL 15 2012
Abstract:
In this study, equal channel angular pressing (ECAP) was applied to a hot-extruded Mg-5.00Zn-0.92Y-0.16Zr (wt.%) alloy to produce an ultrafine-grained a-Mg structure of 0.6 mu m with uniformly distributed fine quasicrystal Mg3YZn6 particles. The basal planes in the as-ECAPed alloy were inclined approximately 45 degrees to the ECAP direction (EPD); thus, a high Schmid factor of 0.36 for (0 0 0 1)< 1 1 (2) over bar 0 > basal slip along EPD was obtained. Then, the superplastic behavior at low temperatures of 150-250 degrees C and initial strain rates of 1.67 x 10(-3) s(-1)-1.67 x 10(-1) s(-1) of the as-ECAPed alloy was investigated and compared with that of the as-extruded alloy. The microstructural development, texture evolution and cracking behavior during tensile tests were systemically investigated by electron backscattered diffraction (EBSD) analysis. During the tensile test along the EPD, the basal planes in the as-ECAPed alloy specimen were tilted approximately 15 degrees away from the original position; thus, the basal planes were still in a position favorable for the basal slip along the EPD. As a result, a maximum elongation of 865% was obtained at 200 degrees C and a strain rate of 1.67 x 10(-3) s(-1), as a result of this favored basal texture and the excellent thermal stability of the ultrafine-grained structure. This optimum superplastic temperature of 200 degrees C is much lower than that obtained for other Mg-Zn-Y-(Zr) alloys. In contrast, for the as-extruded alloy specimen, superplastic behavior did not occur until the critical condition of 250 degrees C and a strain rate of 1.67 x 10(-3) s(-1). Below this temperature and strain rate, the strong extrusion basal texture was maintained, and the cracks in the hot-worked coarse region (or un-DRXed region) were observed nucleating mainly associated with the formation of a 38 degrees {1 0 (1) over bar 1}-{1 0 (1) over bar 2} double twin. At this temperature and strain rate, the hot-work! ed coarse regions were significantly refined by the dynamic re! covery a nd the following recrystallization process. In the case, the formation of a double twin was prevented and the facture was delayed. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.
Title:
The polarizability model for ferroelectricity in perovskite oxides
Authors:
Bussmann-Holder, A Author Full Names: Bussmann-Holder, Annette
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (27):10.1088/0953-8984/24/27/273202 JUL 11 2012
Abstract:
This article reviews the polarizability model and its applications to ferroelectric perovskite oxides. The motivation for the introduction of the model is discussed and nonlinear oxygen ion polarizability effects and their lattice dynamical implementation outlined. While a large part of this work is dedicated to results obtained within the self-consistent-phonon approximation, nonlinear solutions of the model are also handled, which are of interest to the physics of relaxor ferroelectrics, domain wall motions, and incommensurate phase transitions. The main emphasis is to compare the results of the model with experimental data and to predict novel phenomena.
Title:
Polarized IR and Raman spectra of Ca2MgSi2O7, Ca2ZnSi2O7 and Sr2MgSi2O7 single crystals: Temperature-dependent studies of commensurate to incommensurate and incommensurate to normal phase transitions
Authors:
Hanuza, J; Ptak, M; Maczka, M; Hermanowicz, K; Lorenc, J; Kaminskii, AA Author Full Names: Hanuza, J.; Ptak, M.; Maczka, M.; Hermanowicz, K.; Lorenc, J.; Kaminskii, A. A.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 191 90-101; 10.1016/j.jssc.2012.02.051 JUL 2012
Abstract:
IR and Raman spectra of Ca2MgSi2O7. Ca2ZnSi2O7 and Sr2MgSi2O7 oriented single crystals and powders have been measured. The temperature dependence of phonons has been established in the 4-650 K range. Discussion of the results has been performed on the basis of factor group approach for the tetragonal P (4) over bar2(1)m (D(2)(3)d) space group with Z=2. The assignment of the bands observed to the internal and external modes has been made on their polarization behaviour, phonon energy calculations and literature data. The evidences of the LO-TO splitting and commensurate (C) to incommensurate (IC) as well as incommensurate (IC) to normal (N) phase transitions have been found. As a representative example, the results obtained for the spontaneous Raman scattering have also been used in the discussion of the stimulated Raman spectra of Ca2ZnSi2O7. (C) 2012 Elsevier Inc. All rights reserved.
Title:
Nanoscale modulations in (KLa)(CaW)O-6 and (NaLa)(CaW)O-6
Authors:
Licurse, MW; Borisevich, AY; Davies, PK Author Full Names: Licurse, Mark W.; Borisevich, Albina Y.; Davies, Peter K.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 191 220-224; 10.1016/j.jssc.2012.03.026 JUL 2012
Abstract:
Complex nanoscale modulations are identified in two new A-site ordered perovskites, (KLa)(CaW)O-6 and (NaLa)(CaW)O-6. In (KLa)(CaW)O-6, selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) show an incommensurate nanocheckerboard modulation with similar to 9.4 x 9.4a(p) periodicity (a(p) approximate to 4 angstrom for the cubic perovskite aristotype). For (NaLa)(CaW)O-6 a one-dimensional modulation is observed with a similar to 16(1 1 0)a(p) repeat; the < 1 1 0 > orientation of the nanostripes is different from the < 1 0 0 > stripes observed in other mixed A-site systems. Studies using high temperature x-ray diffraction suggest the formation of the complex modulations is associated with small deviations from the ideal 1:1:1:1 stoichiometry of the (A(+)La(3+))(CaW)O-6 phases. Z-contrast images acquired on an aberration-corrected microscope provide evidence for deviations from stoichiometry with a similar to 1:15 periodic arrangement of La-4/3(CaW)O-6:(NaLa)(CaW)O-6 nano-phases. (C) 2012 Elsevier Inc. All rights reserved.
Title:
The fluorite related modulated structures of the Gd-2(Zr2-xCex)O-7 solid solution: An analogue for Pu disposition
Authors:
Reid, DP; Stennett, MC; Hyatt, NC Author Full Names: Reid, D. P.; Stennett, M. C.; Hyatt, N. C.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 191 2-9; 10.1016/j.jssc.2011.12.039 JUL 2012
Abstract:
We present an overview of the Gd-2(Zr2-xCex)O-7 phase diagram, of interest as a model system for ceramic disposition of Pu (with Ce as a Pu surrogate). The fluorite related structures of this solid solution were determined using a modulated structure approach, to identify the underlying cation and vacancy ordering mechanisms from analysis of key satellite reflections in selected zone axis electron diffraction patterns. This revealed the formation of four structure types: pyrochlore for x < 0.25, defect fluorite for 0.5 < x < 0.75, an incommensurate C*-type structure for x=1.00, and a C-type structure for x > 1.50. X-ray absorption (XAS) and electron energy loss (EELS) spectra confirmed the presence of Ce4+ as the dominant species in compositions across this system, remaining analogous to Pu4+. (C) 2012 Elsevier Inc. All rights reserved.
Title:
Texture Modification by Addition of Ca in Mg-Zn-Y Alloy
Authors:
Kyeong, JS; Kim, JK; Lee, MJ; Park, YB; Kim, WT; Kim, DH Author Full Names: Kyeong, Joon Seok; Kim, Jeong Kyun; Lee, Myung Jae; Park, Yong Bum; Kim, Won Tae; Kim, Do Hyang
Source:
MATERIALS TRANSACTIONS, 53 (5):991-994; 10.2320/matertrans.M2011401 MAY 2012
Abstract:
The secondary solidification phase of icosahedral (I-) phase in rolled Mg-Zn-Y alloy is replaced with 1 + Ca2Mg6Zn3 phases by addition of Ca. Addition of Ca in Mg-Zn-Y alloy significantly accelerates dynamic and static recrystallization resulting in much fine grain size and more random texture. EBSD analysis indicates that the presence of Ca in the alpha-Mg solid solution matrix may play a role in weakening of basal texture rather than particle stimulation nucleation effect by the second solidification phases. [doi:10.2320/matertrans.M2011401]
Title:
Microstructural evolutions and hardness during heat treatment of Al64Cu20Fe12Si4 quasicrystal alloy
Authors:
Karakose, E; Keskin, M Author Full Names: Karakose, Ercan; Keskin, Mustafa
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 92 (7):314-326; 10.1080/09500839.2012.669056 2012
Abstract:
The microhardness and microstructural characteristics and subsequent heat treatment of conventionally solidified Al64Cu20Fe12Si4 quasicrystal were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS), differential thermal analysis (DTA), and Vickers microhardness tester. XRD analysis indicated that the conventionally solidified samples showed a quasicrystalline icosahedral phase (i-phase) together with cubic beta-AlFe, tetragonal theta-Al2Cu, and monoclinic lambda-A(13)Fe(4) crystal phases. However, the i-phase together with cubic beta-AlFe and monoclinic lambda-A(13)Fe(4) phases observed heat threaded samples. As-cast and subsequently heat-treated quasicrystal samples were measured using a microhardness test device. Vickers microindentation tests were carried out on the heat-treated quasicrystal samples with the load ranging from 1 to 500 mN at room temperature. The melting point of the i-phase was determined as 900 degrees C by DTA examinations.

Update: 11-Jul-2012

Title:
The magnetoelectric effect due to local noncentrosymmetry
Authors:
Sakhnenko, VP; Ter-Oganessian, NV Author Full Names: Sakhnenko, V. P.; Ter-Oganessian, N. V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (26):10.1088/0953-8984/24/26/266002 JUL 4 2012
Abstract:
Magnetoelectrics often possess ions located in noncentrosymmetric surroundings. Based on this fact we suggest a microscopic model of magnetoelectric interaction and show that the spin-orbit coupling leads to spin-dependent electric dipole moments of the electron orbitals of these ions, which results in non-vanishing polarization for certain spin configurations. The approach accounts for the macroscopic symmetry of the unit cell and is valid for both commensurate and complex incommensurate magnetic structures. The model is illustrated by the examples of MnWO4, MnPS3 and LiNiPO4. Application to other magnetoelectrics is discussed.
Title:
Formation and rotation of skyrmion crystal in the chiral-lattice insulator Cu2OSeO3
Authors:
Seki, S; Kim, JH; Inosov, DS; Georgii, R; Keimer, B; Ishiwata, S; Tokura, Y Author Full Names: Seki, S.; Kim, J. -H.; Inosov, D. S.; Georgii, R.; Keimer, B.; Ishiwata, S.; Tokura, Y.
Source:
PHYSICAL REVIEW B, 85 (22):10.1103/PhysRevB.85.220406 JUN 22 2012
Abstract:
Small-angle neutron scattering experiments were performed on a bulk single crystal of chiral-lattice multiferroic insulator Cu2OSeO3. In the absence of an external magnetic field, helical spin order with magnetic modulation vector q parallel to < 001 > was identified. When a magnetic field is applied, a triple-q magnetic structure emerges normal to the field in the A phase just below the magnetic ordering temperature T-c, which suggests the formation of a triangular lattice of skyrmions. Notably, the favorable q direction in the A phase changes from q parallel to < 110 > to q parallel to < 001 > upon approaching T-c. Near the phase boundary between these two states, the external magnetic field induces a 30 degrees rotation of the skyrmion lattice. This suggests a delicate balance between the magnetic anisotropy and the spin texture near T-c, such that even a small perturbation significantly affects the ordering pattern of the skyrmions.
Title:
High-field NMR of the quasi-one-dimensional antiferromagnet LiCuVO4
Authors:
Buttgen, N; Kuhns, P; Prokofiev, A; Reyes, AP; Svistov, LE Author Full Names: Buettgen, N.; Kuhns, P.; Prokofiev, A.; Reyes, A. P.; Svistov, L. E.
Source:
PHYSICAL REVIEW B, 85 (21):10.1103/PhysRevB.85.214421 JUN 20 2012
Abstract:
We report on NMR studies of the quasi-one-dimensional (1D) frustrated S = 1/2 chain cuprate LiCuVO4 in magnetic fields H up to mu H-0 = 30 T (approximate to 70% of the saturation field H-sat). NMR spectra in fields higher than H-c2 (mu H-0(c2) approximate to 7.5 T) and temperatures T < T-N can be described within the model of a spin-modulated phase in which the magnetic moments are aligned parallel to the applied field H and their values alternate sinusoidally along the magnetic chains. Based on theoretical concepts about frustrated 1D S = 1/2 chains, the field dependence of the modulation strength of the magnetic structure is deduced from our experiments. Relaxation time T-2 measurements of the V-51 nuclei show that T-2 depends on the particular position of the probing V-51 nucleus with respect to the magnetic copper moments within the 1D chains: the largest T-2 value is observed for the vanadium nuclei which are right next to the magnetic Cu2+ ion with the largest ordered magnetic moment. This observation is in agreement with the expectation for the spin-modulated magnetic structure. The (H, T) magnetic phase diagram of LiCuVO4 is discussed.
Title:
Surface scaling properties of decagonal quasicrystals under nonequilibrium vertical growth
Authors:
Jeong, HC; Kim, JM Author Full Names: Jeong, Hyeong-Chai; Kim, Jin Min
Source:
PHYSICAL REVIEW E, 85 (6):10.1103/PhysRevE.85.061118 Part 1 JUN 20 2012
Abstract:
Restricted solid-on-solid (RSOS) growth models are studied on two different decagonal quasicrystal lattices, namely the Penrose tiling lattice and the random tiling lattice. There exist two types of growth blocks-fat and skinny tiles-which may have different sticking probabilities. We found that the RSOS growths on both lattices belong to the Kardar-Parisi-Zhang universality class when they have the same sticking probabilities in spite of the lack of periodicity in the substrates. However, when they have tile-type dependent sticking probabilities, the RSOS models on two lattices may produce different scaling behaviors. Growth on Penrose tiling shows that the roughness exponent is around 0.4 while that on random tiling is around 0.49. Our observation may provide an effective way to investigate the bulk structures of decagonal quasicrystals.
Title:
Conical antiferromagnetic order in the ferroelectric phase of Mn0.8Co0.2WO4 resulting from the competition between collinear and cycloidal structures
Authors:
Urcelay-Olabarria, I; Ressouche, E; Mukhin, AA; Ivanov, VY; Balbashov, AM; Garcia-Munoz, JL; Skumryev, V Author Full Names: Urcelay-Olabarria, I.; Ressouche, E.; Mukhin, A. A.; Ivanov, V. Yu.; Balbashov, A. M.; Garcia-Munoz, J. L.; Skumryev, V.
Source:
PHYSICAL REVIEW B, 85 (22):10.1103/PhysRevB.85.224419 JUN 19 2012
Abstract:
Evolution of competing commensurate collinear (AF4) and incommensurate cycloidal (AF2) magnetic structures in Mn0.8Co0.2WO4 multiferroic was studied by neutron diffraction, magnetic, and pyroelectric characterization measurements. In contrast to pure and slightly Co doped MnWO4, the antiferromagnetic AF4 collinear phase [k(1) = (1/2,0,0)] inherent to the pure CoWO4 was observed below N ' eel temperature T-N approximate to 20 K in Mn0.8Co0.2WO4. This collinear order survives down to the lowest temperature reached in the experiments (2 K) even after the appearance of the second (cycloidal AF2) spin order below T-FE approximate to 8.5 K [k(2) = (-0.211, 1/2, 0.452)]. Ferroelectric polarization along b axis was revealed below T-FE in the low temperature conical phase resulting from the superposition of the AF4 and AF2 spin structures. The arrangement of the spins after the two successive magnetic transitions are thoroughly described. In particular, we found that spins in the AF4 phase are aligned along the easy direction in the ac plane (similar to 142 degrees with respect to the c* axis), while the cycloidal AF2 spin order is developed in the magnetically hard directions, perpendicular to the easy one, and consequently the T-FE decreases compared to the pure MnWO4.
Title:
Large magneto (thermo) dielectric effect in multiferroic orthorhombic LuMnO3
Authors:
Wang, LJ; Chai, YS; Feng, SM; Zhu, JL; Manivannan, N; Jin, CQ; Gong, ZZ; Wang, XH; Li, LT Author Full Names: Wang, L. J.; Chai, Y. S.; Feng, S. M.; Zhu, J. L.; Manivannan, N.; Jin, C. Q.; Gong, Z. Z.; Wang, X. H.; Li, L. T.
Source:
JOURNAL OF APPLIED PHYSICS, 111 (11):10.1063/1.4722299 JUN 1 2012
Abstract:
We have investigated the relation between ferroelectric and magnetic orders of orthorhombic (o-) LuMnO3 ceramics. The increase of dielectric constant e exceeds 82% near incommensurate to commensurate E-type antiferromagnetic (AFM) spin ordering transition temperature T-L, reflecting a large magneto (thermo) dielectric response. Meanwhile, distinct anomalies and thermal hysteresis behavior are observed near this temperature in both temperature dependence of epsilon and specific heat C-p, indicating a strong coupling between FE and magnetic orders in o-LuMnO3. Comparing to o-HoMnO3, TmMnO3, and YbMnO3 with similar E-type AFM ground state, o-LuMnO3 has the largest magneto (thermo) dielectric effect (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4722299]
Title:
The story of Nobel-winning 'quasicrystals'
Authors:
Malhotra, R Author Full Names: Malhotra, Richa
Source:
CURRENT SCIENCE, 102 (10):1356-1357; MAY 25 2012

Update: 4-Jul-2012

Title:
In-situ investigation of the icosahedral Al-Cu-Fe phase formation in thin films
Authors:
Haidara, F; Duployer, B; Mangelinck, D; Record, MC Author Full Names: Haidara, F.; Duployer, B.; Mangelinck, D.; Record, M. -C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 534 47-51; 10.1016/j.jallcom.2012.04.036 SEP 5 2012
Abstract:
This work is an investigation of the formation by reactive diffusion at high temperatures of the icosahedral phase, i-Al62.5Cu25Fe12.5, in thin films. The samples were prepared by sputtering at room temperature. The elements Al, Cu and Fe were sequentially deposited onto oxidized silicon substrates. The two following stacking sequences, Al/Cu/Fe and Al/Fe/Cu, were investigated. The phase formation was studied using in situ resistivity, in situ X-ray Diffraction and Differential Scanning Calorimetry measurements. Whatever the stacking sequence, the sequences of phase formation evidenced during the heating treatment are similar. However the temperatures of formation for the first phases that are formed are different; they are higher in the case of the Al/Fe/Cu stacking sequence. (C) 2012 Elsevier B. V. All rights reserved.
Title:
Reactivity of metal-containing monomers 71. Synthesis of nanosized quasicrystals and related metallopolymer composites
Authors:
Aldoshin, SM; Dzhardimalieva, GI; Pomogailo, AD; Abuzin, YA Author Full Names: Aldoshin, S. M.; Dzhardimalieva, G. I.; Pomogailo, A. D.; Abuzin, Yu. A.
Source:
RUSSIAN CHEMICAL BULLETIN, 60 (9):1871-1879; 10.1007/s11172-011-0282-9 SEP 2012
Abstract:
The methods for the preparation of quasicrystalline intermetallic compounds in the protective matrix in the systems Al65Cu22Fe13 and Al54Cu9Mg37 were developed. They are formed both earlier and from elements during the formation of a metallopolymer composite material. Three methods of preparation are optimal: from low-dimensional powders of quasicrystals and film-forming polymers, by the in situ formation of quasicrystals during the thermal decomposition of the corresponding precursors, and via the thermal polymerization of metal-containing monomers (components of quasicrystals) followed by the controlled pyrolysis of the metallopolymers that formed. The metallopolymer composite obtained by the incorporation of Al63Cu22Fe13 into the high-density polyethylene or polyacrylamide matrix affords up to 10 wt.% cubic phase of beta-Al-50(Cu,Fe)(50). The products of thermal decomposition of the low-molecular-weight precursors are a mixture of the quasicrystalline (Al65Cu22Fe13) and crystalline (cubic beta-Al-50(Cu,Fe)(50) and tetragonal omega-Al7Cu2Fe, Al2Cu) phases. The thermolysis of the metallo-polymer composition yields a finely dispersed powder, whose main component is an alloy Al7Cu3Mg6 with an admixture of the Al2CuMg phase.
Title:
Multilayer thin film growth on crystalline and quasicrystalline surfaces: A phase-field crystal study
Authors:
Muralidharan, S; Khodadad, R; Sullivan, E; Haataja, M Author Full Names: Muralidharan, Srevatsan; Khodadad, Raika; Sullivan, Ethan; Haataja, Mikko
Source:
PHYSICAL REVIEW B, 85 (24):10.1103/PhysRevB.85.245428 JUN 14 2012
Abstract:
In this paper, we explore the effects of misfit strain fields on both heterogeneous nucleation behavior and anisotropic growth of islands at submonolayer coverages and compositional patterning at complete monolayer coverage via simulations of a phase-field crystal model. In particular, deposition on top of a herringbone structure and quasicrystalline (QC) substrate are considered, the former representing a system with spatially periodic misfit strain fields arising from the presence of surface dislocations, and the latter representing a system which inherently possesses a wide range of local, aperiodic misfit patterns. In the case of single-component systems, we demonstrate that misfit strain fields lead to heterogeneous nucleation behavior and anisotropic island growth. In the case of QC substrate, a wide range of morphologies, such as coexistence of locally hexagonally ordered atomic clusters within a larger scale arrangement with overall QC symmetry and so-called "starfish" aggregates, is observed in a pure system at submonolayer coverages when the adlayer-substrate interaction strength and lattice mismatch are tuned. In the case of bulk-immiscible binary systems at complete monolayer coverage, strain-stabilized compositional domains emerge at low line tension values for both substrates. Interestingly, the compositional domains on the QC substrate inherit their symmetries at sufficiently low line tension values, while at larger line tension values, the domain structure begins to resemble the classical spinodal microstructure. Such domain structures should be readily observable in colloidal systems in which attractive interparticle and particle-substrate interactions can be tuned.
Title:
Coexistence and Competition of the Short-Range Incommensurate Antiferromagnetic Order with the Superconducting State of BaFe2-xNixAs2
Authors:
Luo, HQ; Zhang, R; Laver, M; Yamani, Z; Wang, M; Lu, XY; Wang, MY; Chen, YC; Li, SL; Chang, S; Lynn, JW; Dai, PC Author Full Names: Luo, Huiqian; Zhang, Rui; Laver, Mark; Yamani, Zahra; Wang, Meng; Lu, Xingye; Wang, Miaoyin; Chen, Yanchao; Li, Shiliang; Chang, Sung; Lynn, Jeffrey W.; Dai, Pengcheng
Source:
PHYSICAL REVIEW LETTERS, 108 (24):10.1103/PhysRevLett.108.247002 JUN 12 2012
Abstract:
Superconductivity in the iron pnictides develops near antiferromagnetism, and the antiferromagnetic (AF) phase appears to overlap with the superconducting phase in some materials such as BaFe2-xTxAs2 (where T = Co or Ni). Here we use neutron scattering to demonstrate that genuine long-range AF order and superconductivity do not coexist in BaFe2-xNixAs2 near optimal superconductivity. In addition, we find a first-order-like AF-to-superconductivity phase transition with no evidence for a magnetic quantum critical point. Instead, the data reveal that incommensurate short-range AF order coexists and competes with superconductivity, where the AF spin correlation length is comparable to the superconducting coherence length.
Title:
Stable icosahedral phase in Mg44Zn44Gd12 alloy
Authors:
Wang, XD; Du, WB; Wang, ZH; Liu, K; Li, SB Author Full Names: Wang Xudong; Du Wenbo; Wang Zhaohui; Liu Ke; Li Shubo
Source:
JOURNAL OF RARE EARTHS, 30 (5):503-506; 10.1016/S1002-0721(12)60080-5 MAY 2012
Abstract:
The microstructure of the as-cast Mg44Zn44Gd12 alloy was investigated by using X-ray diffraction (XRD), differential scanning (DSC), scanning electron microscopy (SEM) and a detailed transmission electron microscope. The XRD, DSC and SEM results indicated that the as-cast Mg44Zn44Gd12 alloy were mainly composed of three types of phases: the primary solidification phase, the dendritic phase and the eutectic phase. The primary solidification phase had an icosahedral structure. The dendritic phase was the W-phase, and eutectic structure phase was the Mg7Zn3 phase. Microstructures of icosahedral phase (I-phase), W-phase and Mg7Zn3 phase in Mg44Zn44Gd12 alloy were investigated. The results indicated that the I-phase in Mg44Zn44Gd12 alloy was a face-centered icosahedral quasicrystal with stoichiometric composition of Mg42Zn50Gd8 which had an excellent thermal stability up to 420 degrees C. The solid solution of Gd Gradually decreased during solidification, which played an important role in activating the formation of Mg7Zn3 phase and W-phase from icosahedral phases.

Update: 27-Jun-2012

Title:
Dynamic mechanical relaxation and loss in the incommensurate phase of quartz
Authors:
Peng, Z; Chien, SY; Redfern, SAT Author Full Names: Peng, Z.; Chien, S-Y; Redfern, S. A. T.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (25):10.1088/0953-8984/24/25/255403 JUN 27 2012
Abstract:
The dynamic mechanical properties of quartz have been studied as a function of temperature across the alpha-beta phase transition and in the vicinity of the incommensurate (IC) phase on cooling from the beta phase. The mechanical response of the IC phase shows strong anelasticity for measurement of Young's modulus (closely related to C-11 in our geometry) with modulated stress driven at 1 Hz. The dynamic shear modulus does not show similar strong effects in its imaginary component, although a very weak anomaly is barely detectable in the real part of the modulus. Our results indicate that the incommensurate microstructures within the quartz transition interval are susceptible to dilatational stress with relaxation times around 1 s.
Title:
Soft-mode-driven lattice instabilities in Cs2HgCl4 crystal: phenomenological treatment and far-infrared spectroscopy of the structurally modulated phases
Authors:
Shchur, Y; Kamba, S; Parasyuk, OV; Kityk, AV Author Full Names: Shchur, Ya; Kamba, S.; Parasyuk, O. V.; Kityk, A. V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (24):10.1088/0953-8984/24/24/245901 JUN 20 2012
Abstract:
This paper reports a comprehensive phenomenological description and experimental infrared (IR) investigations of the soft-mode-driven lattice instabilities into various commensurately and incommensurately modulated phases of Cs2HgCl4 crystals. Our theoretical analysis shows that the lattice instabilities along the a and c crystallographic directions are related to low-frequency transverse optical (TO) phonon branches of Sigma(2) and Lambda(3) symmetry, respectively, which merge together in the center of the Brillouin zone at the point of B-3g symmetry. As the temperature decreases both branches fall down, leading first to the direct condensation of the soft TO Sigma(2) mode in the symmetric Sigma direction (k parallel to a*). On the other hand, coupling of the TO and transverse acoustic (TA) modes of Lambda(3) symmetry causes, at somewhat lower temperatures, a series of frozen modulated commensurate and incommensurate states developing along the symmetric 3 direction (k parallel to c*). Polarized far-infrared (FIR) reflectivity spectra (15-600 cm(-1)) of Cs2HgCl4 crystals were measured in a broad temperature region, 10-297 K. Despite a rich sequence of structurally modulated phases existing above 163 K we observed rather moderate temperature evolution of IR spectra where only a few new modes of different polarizations have been activated. However, the commensurately modulated phases occurring below 163 K made an essential impact on the spectra of all three polarizations. The process of activation of both the Raman- and the IR-active phonons in the structurally modulated phases is subjected to the phenomenological analysis.
Title:
Electronic properties of PrNi1-xCuxAl compounds
Authors:
Fikacek, J; Javorsky, P; Vejpravova, J; Prchal, J; Kastil, J; Nenert, G; Santava, E Author Full Names: Fikacek, J.; Javorsky, P.; Vejpravova, J.; Prchal, J.; Kastil, J.; Nenert, G.; Santava, E.
Source:
PHYSICAL REVIEW B, 85 (21):10.1103/PhysRevB.85.214410 JUN 8 2012
Abstract:
We report on the evolution of magnetic properties in the PrNi1-xCuxAl series investigated by measurements of magnetization, AC susceptibility, specific heat, and powder neutron diffraction. For compounds with a low Cu content, we observe antiferromagnetic incommensurate structures characterized by propagation vector k = (1/20q) having q = 0.416 +/- 0.002 and 0.428 +/- 0.006 in the case of x = 0.1 and 0.2, respectively. A commensurate antiferromagnetic structure with k = (1/20 1/2) then appears in compounds with x = 0.4 and 0.5, which is followed by a spin-glass state with short-range correlations in the Cu-rich part of the series. The short-range magnetic correlations have an antiferromagnetic character with a propagation vector close to the one observed in the magnetically ordered PrCuAl. Investigations of the spin relaxation phenomena by use of the frequency-dependent AC susceptibility revealed that a spin-glass-like state develops at low temperatures with evidence of collective clustering. A crystal-field energy scheme, deduced from specific heat data, is characterized by a quasidoublet ground state in the whole series.
Title:
Incommensurate spin density wave versus local magnetic inhomogeneities in Ba(Fe1-xNix)(2)As-2: a Fe-57 Mossbauer spectral study
Authors:
Olariu, A; Bonville, P; Rullier-Albenque, F; Colson, D; Forget, A Author Full Names: Olariu, A.; Bonville, P.; Rullier-Albenque, F.; Colson, D.; Forget, A.
Source:
NEW JOURNAL OF PHYSICS, 14 10.1088/1367-2630/14/5/053044 MAY 29 2012
Abstract:
We report Fe-57 Mossbauer spectral results in pure and doped Ba(Fe1-xNix)(2)As-2 with x = 0.01 and 0.03. We show that all these materials present a first-order magnetic transition towards a magnetically ordered state. In the doped compounds, a broad distribution of Fe hyperfine fields is present in the magnetic phase. We successfully fit the Mossbauer data in Ba(Fe1-xNix)(2)As-2 in the framework of two different models: (i) an incommensurate spin density wave (IC-SDW); (ii) a dopant-induced perturbation of the Fe polarization, recently proposed to interpret As-75 NMR data in Ba(Fe1-xNix)(2)As-2, which is valid only in the very dilute limit x = 0.01. Moreover, we show here that these NMR data can also be successfully analysed in terms of the 'incommensurate model' for all doping contents by using the parameters obtained from the Mossbauer spectral analysis. Therefore it is not possible to rule out the presence of an IC-SDW on the basis of the As-75 NMR data.
Title:
Structural studies of the P-T phase diagram of sodium niobate
Authors:
Jabarov, SG; Kozlenko, DP; Kichanov, SE; Belushkin, AV; Mammadov, AI; Savenko, BN; Mekhtieva, RZ; Lathe, C Author Full Names: Jabarov, S. G.; Kozlenko, D. P.; Kichanov, S. E.; Belushkin, A. V.; Mammadov, A. I.; Savenko, B. N.; Mekhtieva, R. Z.; Lathe, C.
Source:
JOURNAL OF SURFACE INVESTIGATION-X-RAY SYNCHROTRON AND NEUTRON TECHNIQUES, 6 (3):546-551; 10.1134/S1027451012060250 MAY 2012
Abstract:
The crystal structure of sodium niobate (NaNbO3) has been investigated by energy-dispersive X-ray diffraction at high pressures (up to 4.3 GPa) in the temperature range 300-1050 K. At normal conditions, NaNbO3 has an orthorhombic structure with Pbcm symmetry (antiferroelectric P phase). Upon heating, sodium niobate undergoes a series of consecutive transitions between structural modulated phases P-R-S-T(1)-T(2)-U; these transitions manifest themselves as anomalies in the temperature dependences of the positions and widths of diffraction peaks. Application of high pressure leads to a decrease in the temperatures of the structural transitions to the R, S, T(1), T(2), and U phases with different baric coefficients. A phase diagram for sodium niobate has been build in the pressure range 0-4.3 GPa and the temperature range 300-1050 K. The dependences of the unit-cell parameters and volume on pressure and temperature have been obtained. The bulk modulus and the volume coefficients of thermal expansion have been calculated for different structural modulated phases of sodium niobate. A phase transition (presumably, from the antiferroelectric orthorhombic P phase to the ferroelectric rhombohedral N phase) has been observed at high pressure (P = 1.6 GPa) and room temperature.
Title:
Deformation twinning in Ni2MnGa
Authors:
Pond, RC; Muntifering, B; Mullner, P Author Full Names: Pond, R. C.; Muntifering, B.; Muellner, P.
Source:
ACTA MATERIALIA, 60 (9):3976-3984; 10.1016/j.actamat.2012.03.045 MAY 2012
Abstract:
Deformation twinning is investigated in the martensitic phase of a Ni46.75Mn34Ga19.25 (at.%) alloy. X-ray and electron diffraction are used to establish the crystallography of the non-modulated tetragonal martensite, and transmission electron microscopy is employed to deduce the twinning parameters. It is convenient to define the twinning parameters with respect to a "monoclinic" unit cell, designated 2M: then K-1, eta(1), K-2, and eta(2) are (001), [100], (100), and [001] respectively. The Burgers vector of the active twinning disconnections is close to 1/6[100] and the disconnections are associated with steps of height d((002)). These defects are expected to be highly mobile since their motion does not require atomic shuffling. It is shown that periodic arrangements of two layer twins produce modulated crystal structures, such as 14M. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 20-Jun-2012

Title:
EDMA: a computer program for topological analysis of discrete electron densities
Authors:
Palatinus, L; Prathapa, SJ; van Smaalen, S Author Full Names: Palatinus, Lukas; Prathapa, Siriyara Jagannatha; van Smaalen, Sander
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 45 575-580; 10.1107/S0021889812016068 Part 3 JUN 2012
Abstract:
EDMA is a computer program for topological analysis of discrete electron densities according to Bader's theory of atoms in molecules. It locates critical points of the electron density and calculates their principal curvatures. Furthermore, it partitions the electron density into atomic basins and integrates the volume and charge of these atomic basins. EDMA can also assign the type of the chemical element to atomic basins based on their integrated charges. The latter feature can be used for interpretation of ab initio electron densities obtained in the process of structure solution. A particular feature of EDMA is that it can handle superspace electron densities of aperiodic crystals in arbitrary dimensions. EDMA first generates real-space sections at a selected set of phases of the modulation wave, and subsequently analyzes each section as an ordinary three-dimensional electron density. Applications of EDMA to model electron densities have shown that the relative accuracy of the positions of the critical points, the electron densities at the critical points and the Laplacian is of the order of 10(-4) or better.

Update: 13-Jun-2012

Title:
Microstructure and mechanical properties of a Mg-Zn4.3Y0.7 alloy powder reinforced by quasi-crystalline particles
Authors:
Chae, HJ; Kim, BS; Do Kim, Y; Kim, TS Author Full Names: Chae, Hong Jun; Kim, Bum-Sung; Do Kim, Young; Kim, Taek-Soo
Source:
MATERIALS LETTERS, 77 63-66; 10.1016/j.matlet.2012.02.074 JUN 15 2012
Abstract:
Rapidly solidified (RS) Mg-Zn4.3Y0.7 alloy powders were prepared by using a gas atomization device, followed by the warm extrusion. The microstructure and mechanical properties were analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), and the constituent phases were characterized using X-ray diffraction (XRD). The microstructure of the powders indicated that the icosahedral Mg3YZn6 (I-Phase) quasi-crystals were distributed in the alpha-Mg matrix. I-phases on the order of 0.5 mu m were generally formed along the grain boundaries. The powders were extruded with an area reduction ratio to identify the extrusion behavior. As the extrusion ratio increased from 10:1 to 15:1 and 20:1, the microstructures had a more uniform distribution of the I-phase and showed increased mechanical properties, such as tensile strength and elongation. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Interaction between graphene and nickel(111) surfaces with commensurate and incommensurate orientational relationships
Authors:
Shibuta, Y; Elliott, JA Author Full Names: Shibuta, Yasushi; Elliott, James A.
Source:
CHEMICAL PHYSICS LETTERS, 538 112-117; 10.1016/j.cplett.2012.04.048 JUN 11 2012
Abstract:
The interaction energy between a rigid defect-free graphene sheet and a fixed Ni(111) surface with respect to rotational and translational displacements is examined using an empirical bond order potential. The Rosei (hollow site) structure, and others in which metal atoms are adjacent to hollow sites in graphene, give rise to global and local energy minima, respectively, whereas the interaction energy is almost constant for incommensurate structures. Only a few degrees rotation from the Rosei structure substantially diminishes the energy barrier for translational displacement. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Dy-0.64{Dy-5[Fe2C9]}: A complex carbide with a composite structure
Authors:
Davaasuren, B; Dashjav, E; Kniep, R; Kreiner, G; Schnelle, W; Akselrud, L; van Smaalen, S; Wolfel, A Author Full Names: Davaasuren, Bambar; Dashjav, Enkhtsetseg; Kniep, Ruediger; Kreiner, Guido; Schnelle, Walter; Akselrud, Lev; van Smaalen, Sander; Woelfel, Alexander
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 190 73-79; 10.1016/j.jssc.2012.02.008 JUN 2012
Abstract:
The ternary carbide Dy-5.64[Fe2C9] has been prepared by high temperature synthesis from the elements. The compound forms as a composite structure with two partial structures, {Dy-5[Fe2C9]} and (Dy-0.64) crystallizing in space groups Pnam and Pbam, respectively. The lattice parameters a=2934.63(9) pm and 6=1263.63(5) pm for the two partial structures are identical, whereas the c lattice parameters for {Dy-5[Fe2C9]} (c(H)=504.14(3) pm) and {Dy-0.64} (c(G)=1056.01(5) pm) are different. This gives rise to a modulated structure in the (3+1)D superspace group Pnam(00g) with q=c(H)/c(G)=0.4775. The refinement converged to R(F) values below 0.055 for each partial structure using harmonic and Crenel functions. The compound is a bad metallic conductor and represents a new structure type composed of Dy3+ species embedded in a matrix of discrete planar FeC(C-2)(2) units and edge-sharing Fe(C-2)(4) tetrahedra forming infinite chains Fe(C-2)(4/2) running along the c axis. (C) 2012 Elsevier Inc. All rights reserved.
Title:
Neutron diffraction and electrical transport studies on the incommensurate magnetic phase transition in holmium at high pressures
Authors:
Thomas, SA; Uhoya, WO; Tsoi, GM; Wenger, LE; Vohra, YK; Chesnut, GN; Weir, ST; Tulk, CA; dos Santos, AM Author Full Names: Thomas, Sarah A.; Uhoya, Walter O.; Tsoi, Georgiy M.; Wenger, Lowell E.; Vohra, Yogesh K.; Chesnut, Gary N.; Weir, Samuel T.; Tulk, Christopher A.; dos Santos, Antonio M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (21):10.1088/0953-8984/24/21/216003 MAY 30 2012
Abstract:
Neutron diffraction and electrical transport measurements have been made on the heavy rare earth metal holmium at high pressures and low temperatures in order to elucidate its transition from a paramagnetic (PM) to a helical antiferromagnetic (AFM) ordered phase as a function of pressure. The electrical resistance measurements show a change in the resistance slope as the temperature is lowered through the antiferromagnetic Neel temperature. The temperature of this antiferromagnetic transition decreases from approximately 122 K at ambient pressure at a rate of -4.9 K GPa(-1) up to a pressure of 9 GPa, whereupon the PM-to-AFM transition vanishes for higher pressures. Neutron diffraction measurements as a function of pressure at 89 and 110 K confirm the incommensurate nature of the phase transition associated with the antiferromagnetic ordering of the magnetic moments in a helical arrangement and that the ordering occurs at similar pressures as determined from the resistance results for these temperatures.
Title:
Neutron diffraction study of spin and charge ordering in SrFeO3-delta
Authors:
Reehuis, M; Ulrich, C; Maljuk, A; Niedermayer, C; Ouladdiaf, B; Hoser, A; Hofmann, T; Keimer, B Author Full Names: Reehuis, M.; Ulrich, C.; Maljuk, A.; Niedermayer, Ch.; Ouladdiaf, B.; Hoser, A.; Hofmann, T.; Keimer, B.
Source:
PHYSICAL REVIEW B, 85 (18):10.1103/PhysRevB.85.184109 MAY 22 2012
Abstract:
We report a comprehensive neutron diffraction study of the crystal structure and magnetic order in a series of single-crystal and powder samples of SrFeO3-delta in the vacancy range 0 <= delta <= 0.23. The data provide detailed insights into the interplay between the oxygen vacancy order and the magnetic structure of this system. In particular, a crystallographic analysis of data on Sr8Fe8O23 revealed a structural transition between the high-temperature tetragonal and a low-temperature monoclinic phase with a critical temperature T = 75 K, which originates from charge ordering on the Fe sublattice and is associated with a metal-insulator transition. Our experiments also revealed a total of seven different magnetic structures of SrFeO3-delta in this range of delta, only two of which namely an incommensurate helix state in SrFeO3 and a commensurate, collinear antiferromagnetic state in Sr4Fe4O11) had been identified previously. We present a detailed refinement of some of the magnetic ordering patterns and discuss the relationship between the magnetotransport properties of SrFeO3-delta samples and their phase composition and magnetic microstructure.
Title:
Crystal Chemistry of Melilite [CaLa](2)[Ga](2)[Ga2O7](2): a Five Dimensional Solid Electrolyte
Authors:
Wei, FX; Baikie, T; An, T; Kloc, C; Wei, J; White, T Author Full Names: Wei, Fengxia; Baikie, Tom; An, Tao; Kloc, Christian; Wei, Jun; White, Tim
Source:
INORGANIC CHEMISTRY, 51 (10):5941-5949; 10.1021/ic300585t MAY 21 2012
Abstract:
Melilite-type [A(2)](2)[B-I](2)[(B2O7)-O-II](2) gallates are promising ion conducting electrolytes for deployment in solid oxide fuel cells. Single crystals of [CaLa](2)[Ga](2)[Ga2O7](2), grown in an optical floating zone furnace, were investigated using a combination of transmission electron microscopy and single crystal X-ray diffraction. Strong anisotropic displacements of oxygen arise from the structural misfit between the interlayer Ca/La cations and the [Ga]-[Ga2O7] tetrahedral layers. A model employing two-dimensional modulation achieves bond lengths and bond angles that preserve satisfactory bond valence sums throughout the structure. The melilite belongs to the tetragonal superspace group P (4) over bar2(1)m(alpha, alpha, 0)00s((alpha) over bar, alpha, 0)000, alpha = 0.2160(5), with a subcell metric of a = 7.9383(2) angstrom, c = 5.2641(3) angstrom, onto which modulation vectors are superimposed: q(1) = alpha (a* + b*), q(2) = alpha (-a* + b*). Both displacive (cation and anion) and occupational (cation) modulations contribute to incommensuration. The analysis of structural adjustments that accompany changes in temperature and composition provides assurance that the crystal chemical model is correct. By better understanding the flexibility of this modulated structure a rational approach toward crystallochemical optimization of electrolyte performance by enhancing oxygen mobility becomes feasible.
Title:
Conductivity and incommensurate antiferromagnetism of Fe1.02Se0.10Te0.90 under pressure
Authors:
Katayama, N; Matsubayashi, K; Nomura, Y; Ji, S; Leao, J; Green, MA; Sato, TJ; Uwatoko, Y; Fujita, M; Yamada, K; Arita, R; Lee, SH Author Full Names: Katayama, N.; Matsubayashi, K.; Nomura, Y.; Ji, S.; Leao, J.; Green, M. A.; Sato, T. J.; Uwatoko, Y.; Fujita, M.; Yamada, K.; Arita, R.; Lee, S. -H.
Source:
EPL, 98 (3):10.1209/0295-5075/98/37002 MAY 2012
Abstract:
By performing resistivity, bulk susceptibility and neutron diffraction on single crystals of Fe1.02Se0.10Te0.90 under pressure, we show that an external pressure can enhance both conductivity and magnetism simultaneously. Surprisingly, the pressure-induced magnetic order is nearly three-dimensional, and incommensurate along both the c-axis and the a-axis, which is accompanied by a structural phase separation. Our powder neutron diffraction data show that the Fe(Se, Te)(4) tetrahedron becomes more regular under pressure, which is consistent with the enhancement of the metallicity but is counterintuitive to the three-dimensional magnetic order. Copyright (C) EPLA, 2012

Update: 6-Jun-2012

Title:
In-situ phase transformation studies of Ni48Mn39In13 melt-spun ribbons
Authors:
Kumar, DMR; Rao, DVS; Rao, NVR; Raja, MM; Singh, RK; Suresh, KG Author Full Names: Kumar, D. M. Raj; Rao, D. V. Sridhara; Rao, N. V. Rama; Raja, M. Manivel; Singh, R. K.; Suresh, K. G.
Source:
INTERMETALLICS, 25 126-130; 10.1016/j.intermet.2012.01.029 JUN 2012
Abstract:
The phase transformation in Ni48Mn39In13 melt-spun ribbons has been studied by employing in-situ transmission electron microscopy (TEM) techniques. At room temperature, the investigations showed the martensite phase consisting of plates with internal stacking faults. This phase exhibited the presence of 7M and 5M modulations. In addition, a small volume fraction of the austenite phase was observed. Upon in-situ heating from room temperature to 95 degrees C, the martensite phase transformed to austenite phase. However, in the subsequent cooling-heating cycles, the martensite phase was retained at high temperature. We discuss our experimental observations and the possible mechanisms for the stabilization of the martensite phase due to thermal cycling. (c) 2012 Elsevier Ltd. All rights reserved.
Title:
Structure of (Ga2O3)(2)(ZnO)(13) and a unified description of the homologous series (Ga2O3)(2)(ZnO)(2n+1)
Authors:
Michiue, Y; Kimizuka, N; Kanke, Y; Mori, T Author Full Names: Michiue, Yuichi; Kimizuka, Noboru; Kanke, Yasushi; Mori, Takao
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 250-260; 10.1107/S0108768112016084 Part 3 JUN 2012
Abstract:
The structure of (Ga2O3)(2)(ZnO)(13) has been determined by a single-crystal X-ray diffraction technique. In the monoclinic structure of the space group C2/m with cell parameters a = 19.66 (4), b = 3.2487 (5), c = 27.31 (2) angstrom, and beta = 105.9 (1)degrees, a unit cell is constructed by combining the halves of the unit cell of Ga2O3(ZnO)(6) and Ga2O3(ZnO)(7) in the homologous series Ga2O3(ZnO)(m). The homologous series (Ga2O3)(2)(ZnO)(2n+1) is derived and a unified description for structures in the series is presented using the (3 + 1)-dimensional superspace formalism. The phases are treated as compositely modulated structures consisting of two subsystems. One is constructed by metal ions and another is by O ions. In the (3 + 1)-dimensional model, displacive modulations of ions are described by the asymmetric zigzag function with large amplitudes, which was replaced by a combination of the sawtooth function in refinements. Similarities and differences between the two ho! mologous series (Ga2O3)(2)(ZnO)(2n+1) and Ga2O3(ZnO)(m) are clarified in (3 + 1)-dimensional superspace. The validity of the (3 + 1)-dimensional model is confirmed by the refinements of (Ga2O3)(2)(ZnO)(13), while a few complex phenomena in the real structure are taken into account by modifying the model.
Title:
Helical screw type magnetic structure of the multiferroic CaMn7O12 with low Cu-doping
Authors:
Slawinski, W; Przenioslo, R; Sosnowska, I; Petricek, V Author Full Names: Slawinski, W.; Przenioslo, R.; Sosnowska, I.; Petricek, V.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 240-249; 10.1107/S0108768112008038 Part 3 JUN 2012
Abstract:
The modulated crystal structure and modulated magnetic ordering of the multiferroic CaCuxMn7-xO12 is studied by analysing neutron and synchrotron-radiation (SR) powder diffraction data with a model based on the magnetic super-space group R31'(00 gamma)ts. Both atomic position modulations and magnetic modulations are described with the modulation vector (0, 0, q). The magnetic ordering is a screw-type circular helix where the magnetic moments are perpendicular to the c direction. The temperature dependence of the modulation vector length and the ordered magnetic moments of Mn3+ and Mn4+ ions is given between T = 50 K and the Neel temperature T-N similar or equal to 90 K. The atomic position modulation length L-p and the magnetic modulation length L-m fulfil the relation L-m = 2L(p) at all temperatures between 50 K and T-N.
Title:
Dodecagonal Quasicrystalline Morphology in a Poly(styrene-b-isoprene-b-styrene-b-ethylene oxide) Tetrablock Terpolymer
Authors:
Zhang, JW; Bates, FS Author Full Names: Zhang, Jingwen; Bates, Frank S.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 134 (18):7636-7639; 10.1021/ja301770v MAY 9 2012
Abstract:
A dodecagonal quasicrystalline (QC) morphology is identified in a poly(styrene-b-isoprene-bstyrene-b-ethylene oxide) (SISO) tetrablock terpolymer based on evidence provided by transmission electron microscopy (TEM), small-angle X-ray scattering, and dynamic mechanical spectroscopy measurements. The QC state occurs at temperatures between those associated with simple hexagonal order (HEX) and the sigma-phase (P4(2)/mnm), T-HEX < T-QC < T-sigma, where T-ODT, is the order-disorder transition temperature. All three morphologies are formed from spherical domains containing an 0 core surrounded by a shell of S that screens unfavorable segment segment interactions with an I-rich matrix. TEM analysis reveals a QC morphology with 12-fold rotational symmetry but devoid of long-range translational order, along with locally coordinated structures consistent with dodecagonal quasicrystalline approximants. The SISO molecular architecture decouples control over the domain shape and interdomain interactions, leading to a multiplicity of packing symmetries.
Title:
Na2/7Gd4/7MoO4: a Modulated Scheelite-Type Structure and Conductivity Properties
Authors:
Morozov, V; Arakcheeva, A; Redkin, B; Sinitsyn, V; Khasanov, S; Kudrenko, E; Raskina, M; Lebedev, O; Van Tendeloo, G Author Full Names: Morozov, V.; Arakcheeva, A.; Redkin, B.; Sinitsyn, V.; Khasanov, S.; Kudrenko, E.; Raskina, M.; Lebedev, O.; Van Tendeloo, G.
Source:
INORGANIC CHEMISTRY, 51 (9):5313-5324; 10.1021/ic300221m MAY 7 2012
Abstract:
Scheelite-type compounds with the general formula (A1,A2)(n)[(B1,B2)O-4](m) (2/3 <= n/m <= 3/2) are the subject of large interest owing to their stability, relatively simple preparation, and optical properties. The creation of cation vacancies (square) in the scheelite-type framework and the ordering of A cations and vacancies can be a new factor in controlling the scheelite-type structure and properties. For a long time, cation-deficient Nd3+:M2/7Gd4/7 square 1/7MoO4 (M = Li, Na) compounds were considered as potential lasers with diode pumping. They have a defect scheelite-type 3D structure (space group I4(1)/a) with a random distribution of Li+(Na+), Gd3+, and vacancies in the crystal. A Na2/7Gd4/7MoO4 single crystal with scheelite-type structure has been grown by the Czochralski method. Transmission electron microscopy revealed that Na2/7Gd4/7MoO4 has a (3 + 2)D incommensurately modulated structure. The (3 + 2)D incommensurately modulated scheelite-type cation-deficient structure of Na2/7Gd4/7MoO4 [super space group (I4) over bar (alpha-beta 0,beta alpha 0)00] has been solved from single-crystal diffraction data. The solution of the (3 + 2)D incommensurately modulated structure revealed the partially disordered distribution of vacancies and Na and Gd cations. High-temperature conductivity measurements performed along the [100] and [001] orientation of the single crystal revealed that the conductivity of Na2/7Gd4/7MoO4 at T = 973 K equals sigma = 1.13 X 10(-5) Omega(-1) cm(-1).
Title:
Influence of the Grain Size on the Magnetic Properties of TbMnO3
Authors:
Bazela, W; Dul, M; Dyakonov, V; Gondek, L; Hoser, A; Hoffmann, JU; Penc, B; Szytula, A; Kravchenko, Z; Nosalev, I; Zarzycki, A Author Full Names: Bazela, W.; Dul, M.; Dyakonov, V.; Gondek, L.; Hoser, A.; Hoffmann, J-U; Penc, B.; Szytula, A.; Kravchenko, Z.; Nosalev, I.; Zarzycki, A.
Source:
ACTA PHYSICA POLONICA A, 121 (4):785-788; APR 2012
Abstract:
The magnetic properties including magnetic structure of poly and nano samples of TbMnO3 are determined. All the samples investigated are antiferromagnets. In these samples the Mn ad Tb moments order antiferromagnetically at different temperatures and form modulated magnetic structure described by the propagation vector k=(k(x),0,0) with different value of k(x) for the Mn and Tb sublattices. Comparison of the data for poly and nano samples indicates the decrease of the moment and increase of the k(x) component of propagation vector in the nano specimens. The wide Bragg peak related to the Tb sublattice suggests that the magnetic order has the claster-like character. The magnetic moments value in both sublattices is smaller, whereas the k(x) values are larger for nano samples.
Title:
Electronic structure of two-dimensional hexagonal diselenides: Charge density waves and pseudogap behavior
Authors:
Kuchinskii, EZ; Nekrasov, IA; Sadovskii, MV Author Full Names: Kuchinskii, E. Z.; Nekrasov, I. A.; Sadovskii, M. V.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 114 (4):671-680; 10.1134/S1063776112020252 APR 2012
Abstract:
We theoretically study the electronic structure (spectral functions and Fermi surfaces) of incommensurate pseudogap and charge density wave (CDW) and commensurate CDW phases of quasi-two-dimensional diselenides 2H-TaSe2 and 2H-NbSe2. The incommensurate pseudogap regime is described within the scenario based on short-range-order CDW fluctuations, considered within the static Gaussian random field model. In contrast, e.g., to high- (c) cuprates, layered dichalcogenides have several different CDW scattering vectors and an electronic spectrum with two bands at the Fermi level. For this, we present a theoretical background for the description of multiple scattering processes within a multiple-band electronic spectrum. Theoretical spectral functions and Fermi surfaces thus obtained are compared with recent ARPES experimental data, demonstrating rather good qualitative agreement.
Title:
Residual stress in as-deposited Al-Cu-Fe-B quasicrystalline thin films
Authors:
Polishchuk, S; Boulet, P; Mezin, A; de Weerd, MC; Weber, S; Ledieu, J; Dubois, JM; Fournee, V Author Full Names: Polishchuk, Sergey; Boulet, Pascal; Mezin, Andre; de Weerd, Marie-Cecile; Weber, Sylvain; Ledieu, Julian; Dubois, Jean-Marie; Fournee, Vincent
Source:
JOURNAL OF MATERIALS RESEARCH, 27 (5):837-844; 10.1557/jmr.2011.415 MAR 2012
Abstract:
The residual stress in Al-Cu-Fe-B quasicrystalline thin films has been characterized by x-ray diffraction and the curvature method. Films with thicknesses in a range from 0.55 to 2.6 mu m were deposited using magnetron sputtering on Si(100) substrates maintained at a temperature of 560 degrees C. It is found that the tensile stress in uncracked films as determined by the curvature method is close to that measured by a modified sin(2)psi method using main diffraction peaks of the icosahedral structure and corresponds approximately to 1.1 GPa. This value is close to that of the thermal stress estimated from the mismatch between thermal expansion coefficients of the film and substrate, suggesting that thermal stress is the main source of residual stress. Increasing film thickness results in the development of cracks and partial delamination of the film, accompanied by the sudden decrease of the stress. The fracture toughness of the quasicrystalline films is estimated between 1.5 and 1.9 MPa root m.

Update: 30-May-2012

Title:
Observation of a possible charge-density-wave transition in cubic Ce3Co4Sn13
Authors:
Lue, CS; Liu, HF; Hsu, SL; Chu, MW; Liao, HY; Kuo, YK Author Full Names: Lue, C. S.; Liu, H. F.; Hsu, S. -L.; Chu, M. W.; Liao, H. Y.; Kuo, Y. K.
Source:
PHYSICAL REVIEW B, 85 (20):10.1103/PhysRevB.85.205120 MAY 11 2012
Abstract:
We report an observation of a first-order phase transition in Ce3Co4Sn13 by means of the specific heat, electrical resistivity, Seebeck coefficient, and thermal conductivity, as well as Co-59 nuclear magnetic resonance (NMR) measurements. The phase transition has been evidenced by marked features near T-o similar or equal to 155 K in all measured physical quantities except for magnetic susceptibility. This excludes a magnetic origin for the observed phase transition. In addition, x-ray diffraction results below and above T-o confirm the absence of a structural change, suggesting that the peculiar phase transition is possibly related to an electronic origin and/or electron-lattice coupling such as the formation of a charge density wave (CDW). As a matter of fact, the disappearance of the double-peak feature of 59Co NMR central lines below T-o can be realized as the spatial modulation of the electric field gradient due to incommensurate CDW superlattices. Also, a distinct peak found in the spin-lattice relaxation rate near T-o manifests a phase transition and its feature can be accounted for by the thermally driven normal modes of the CDW. From the NMR analyses, we obtained a consistent picture that the change of electronic structures below T-o is mainly due to the weakening of p-d hybridization. Such an effect could result in possible electron-lattice instability and, thus, the formation of a CDW state in Ce3Co4Sn13.
Title:
Tuning in magnetic modes in Tb(CoxNi1-x)(2)B2C: From longitudinal spin-density waves to simple ferromagnetism
Authors:
ElMassalami, M; Takeya, H; Ouladdiaf, B; Maia, R; Gomes, AM; Paiva, T; dos Santos, RR Author Full Names: ElMassalami, M.; Takeya, H.; Ouladdiaf, B.; Maia Filho, R.; Gomes, A. M.; Paiva, T.; dos Santos, R. R.
Source:
PHYSICAL REVIEW B, 85 (17):10.1103/PhysRevB.85.174412 MAY 9 2012
Abstract:
Neutron diffraction and thermodynamic techniques were used to probe the evolution of the magnetic properties of Tb(CoxNi1-x)(2)B2C. A succession of magnetic modes was observed as x is varied: the longitudinal modulated (k) over right arrow = (0.55,0,0) state at x = 0 is transformed into a collinear (k) over right arrow = (1/2,0,1/2) antiferromagnetic state at x = 0.2, 0.4 then into a transverse c-axis modulated (k) over right arrow = (0,0,1/3) mode at x = 0.6, and finally into a simple ferromagnetic structure at x = 0.8 and 1. Concomitantly, the low-temperature orthorhombic distortion of the tetragonal unit cell at x = 0 is reduced smoothly such that for x >= 0.4 only a tetragonal unit cell is manifested. Though predicted theoretically earlier, this is the first observation of the (k) over right arrow = (0,0,1/3) mode in borocarbides; our findings of a succession of magnetic modes upon increasing x also find support from a recently proposed theoretical model. The implication of these findings and their interpretation on the magnetic structure of the RM2B2 C series are also discussed.
Title:
Landau theory for the phase diagram of multiferroic Mn1-x(Fe,Zn,Mg)(x)WO4
Authors:
Matityahu, S; Aharony, A; Entin-Wohlman, O Author Full Names: Matityahu, Shlomi; Aharony, Amnon; Entin-Wohlman, Ora
Source:
PHYSICAL REVIEW B, 85 (17):10.1103/PhysRevB.85.174408 MAY 8 2012
Abstract:
We present a theoretical analysis of the temperature magnetic field concentration phase diagram of the multiferroic Mn1-xMxWO4 (M = Fe, Zn, Mg), which exhibits three ordered phases, with collinear and noncollinear incommensurate and with a commensurate magnetic order. The middle phase is also ferroelectric. The analysis uses a semiphenomenological Landau theory based on a Heisenberg Hamiltonian with a single-ion anisotropy. With a small number of adjustable parameters, the Landau theory gives an excellent fit to all three transition lines as well as the magnetic and the ferroelectric order parameters. The fit of the magnetic and ferroelectric order parameters is further improved by including the effect of fluctuations near the transitions. We demonstrate the highly frustrated nature of these materials and suggest a simple explanation for the dramatic effects of doping with different magnetic ions at the Mn sites. The model enables an examination of different sets of exchange couplings that were proposed by a number of groups. Small discrepancies are probably a consequence of small errors in the experimental magnetic parameters. In addition, using the Ginzburg criterion, we estimate the temperature range in which fluctuations of the order parameters become important.
Title:
Low temperature anomalous field effect in SrxBa1-xNb2O6 uniaxial relaxor ferroelectric seen via acoustic emission
Authors:
Dul'kin, E; Kojima, S; Roth, M Author Full Names: Dul'kin, E.; Kojima, S.; Roth, M.
Source:
JOURNAL OF APPLIED PHYSICS, 111 (8):10.1063/1.3702888 APR 15 2012
Abstract:
Sr0.75Ba0.25Nb2O6 [100]-oriented uniaxial tungsten bronze relaxor crystals have been studied by means of dedicated acoustic emission during their thermal cycling in 150-300K temperature range under dc electric field (E). A 1st order transition in a modulated incommensurate tetragonal phase has been successfully detected at T-m(i) = 198 K on heating and T-m(i) = 184 K on cooling, respectively. As field E enhances, a thermal hysteresis gradually narrows and vanishes in the critical point at E-th = 0.31 kV/cm, above which a phase transition becomes to 2nd order. The T-m(i)(E) dependence looks as a V-shape dip, not similar that previously has been looked as a smeared minimum between both the two polar and nonpolar tetragonal phases near T-m = 220 divided by 230K in the same crystals (Dul'kin et al., J Appl. Phys. 110, 044106 (2011)). Due to such a V-shape dip is characteristic for Pb-based multiaxial perovskite relaxor, a rhombohedral phase is waited to be induced by a field E in the critical point temperature range. The emergence of this rhombohedral phase as a crucial evidence of an orthorhombic phase presumably existing within the modulated incommensurate tetragonal phase in tungsten bronze SrxBa1-xNb2O6 relaxor is discussed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3702888]
Title:
TEM microstructure of rapidly solidified Mg-6Zn-1Y-1Ce alloy
Authors:
Yang, WP; Guo, XF; Lu, ZX Author Full Names: Yang Wen-peng; Guo Xue-feng; Lu Zheng-xin
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 22 (4):786-792; 10.1016/S1003-6326(11)61246-6 APR 2012
Abstract:
Rapidly solidified (RS) Mg-6Zn-1Y-1Ce ribbons were prepared by single roller melt-spinning technique. Transmission electron microscopy and energy dispersive X-ray spectroscopy were employed to characterize the microstructure of RS ribbons. The results show that there is high density of particles distributed within grains and at grain boundaries in the region near wheel side. The particle density is decreased in the middle region and free surface region. The alloy is predominantly composed of supersaturated alpha-Mg solid solution, T phase and W phase; meanwhile, a few icosahedral quasicrystalline and Mg4Zn7 particles are also observed. The T phase is confirmed having a body-centered orthorhombic structure that is transformed from the body-centered tetragonal structure Mg12Ce phase due to the partial substitution of Mg atoms by Zn.
Title:
First-principles study on superconductivity of simple cubic, modulated and simple hexagonal phases in phosphorus
Authors:
Nakanishi, A; Ishikawa, T; Nagara, H; Shimizu, K; Katayama-Yoshida, H Author Full Names: Nakanishi, Akitaka; Ishikawa, Takahiro; Nagara, Hitose; Shimizu, Katsuya; Katayama-Yoshida, Hiroshi
Source:
HIGH PRESSURE RESEARCH, 32 (1):3-10; 10.1080/08957959.2011.644664 2012
Abstract:
Superconducting properties of simple cubic (sc), modulated, and simple hexagonal (sh) phases in phosphorus are investigated from first-principles. The superconducting transition temperature decreases through the phase transition from the sc phase to the modulated phase. The superconductivity survives in the modulated phase, which indicates the coexistence of the superconducting state and a charge density wave (CDW) if the modulated structure in phosphorus is caused by CDW. In the modulated phase, phonon modes which show strong electron-phonon coupling lie along the direction of a modulation wave vector. By further compression through phase transition from the modulated phase to the sh phase, the transition temperature increases again. The variation in the transition temperature can be correlated to the variation of the density of states at the Fermi level.

Update: 23-May-2012

Title:
Incommensurate SDW in cuprates
Authors:
Niksic, G; Kupcic, I; Sunko, DK; Barisic, S Author Full Names: Niksic, G.; Kupcic, I.; Sunko, D. K.; Barisic, S.
Source:
PHYSICA B-CONDENSED MATTER, 407 (11):1799-1802; 10.1016/j.physb.2012.01.033 JUN 1 2012
Abstract:
The incommensurate antiferromagnetism (AF) in metallic underdoped cuprates is interpreted with several complementary approaches, unified by a consistent disambiguation of the copper and oxygen degrees of freedom. Collinear (with respect to the copper lattice) peaks in the neutron response at low frequency are due to the oxygen-dominated arcs, while the diagonal peaks at high frequency or low doping come from the copper-dominated vH points. The latter switch from collinear to diagonal as the frequency increases. The direct O-O overlap induces an AF which is weaker and thermodynamically preferred to the AF of strongly localized copper sites, and which coexists with Fermi arcs. A theoretical understanding of the strongly k-dependent AF gap observed in ARPES and STM measurements is proposed. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Pinning and depinning process of an incommensurate CDW as revealed by coherent X-ray diffraction
Authors:
Pinsolle, E; Le Bolloc'h, D; Kirova, N; Jacques, VLR; Shinchenko, AA; Monceau, P Author Full Names: Pinsolle, E.; Le Bolloc'h, D.; Kirova, N.; Jacques, V. L. R.; Shinchenko, A. A.; Monceau, P.
Source:
PHYSICA B-CONDENSED MATTER, 407 (11):1848-1851; 10.1016/j.physb.2012.01.046 JUN 1 2012
Abstract:
Experiments on the coherent X-ray diffraction, and their modeling, have been performed on the Charge Density Wave (CDW) system NbSe3. The 2k(F) satellite reflection associated with the CDW has been measured with respect to external dc currents. Below the threshold current, reflection displays several fringes in the transverse direction which disappear when the threshold current is exceeded. In the sliding state, the transverse satellite profile has a form of two nonsymmetric peaks, one of them being centered at the same position as below the threshold and another one being shifted. The shift of the longitudinal peak position below the threshold current and the nonsymmetric peak in the transverse direction above the threshold one is interpreted as the influence of strong linear defect like a crystal step present on the sample surface, combined with induced arrays of dislocations. Coherent X-rays provide a new access to processes in a CDW driven by an external force in a random pinning potential. (C) 2012 Published by Elsevier B.V.
Title:
High-pressure X-ray diffraction study of 1T-TaS2
Authors:
Ravy, S; Laulhe, C; Itie, JP; Fertey, P; Corraze, B; Salmon, S; Cario, L Author Full Names: Ravy, Sylvain; Laulhe, Claire; Itie, Jean-Paul; Fertey, Pierre; Corraze, Benoit; Salmon, Sabrina; Cario, Laurent
Source:
PHYSICA B-CONDENSED MATTER, 407 (11):1704-1706; 10.1016/j.physb.2012.01.011 JUN 1 2012
Abstract:
We present a room temperature high-pressure X-ray diffraction study of the layered compound 1T-TaS2 up to 20 GPa. This material is known to exhibit a variety of structural phase transitions that are ascribed to the stabilization of charge density wave states. It has been recently shown that at pressures larger than 3 GPa and up to 25 GPa, 1T-TaS2 becomes superconductor below about 5 K. It was suggested that this superconductivity coexists with different CDW states, an hypothesis that can be tested by X-ray diffraction. Our first results at room temperature show that at around 1.9 GPa, the nearly-commensurate (NCCDW) phase transforms into a phase similar to the high temperature incommensurate phase (ICCDW). Above 9 GPa, we show the existence of another IC phase, still discernable up to 20 GPa despite the pressure-induced crystal damage above 13 GPa. These results are consistent with resistivity measurements, but call for a complete exploration of the P-T phase diagram of 1T-TaS2. (c) 2012 Elsevier B.V. All rights reserved.
Title:
"Quantization" of the q-vector in microcrystals of K0.3MoO3 and NbSe3
Authors:
Zybtsev, SG; Pokrovskii, VY; Zaitsev-Zotov, SV Author Full Names: Zybtsev, S. G.; Pokrovskii, V. Ya.; Zaitsev-Zotov, S. V.
Source:
PHYSICA B-CONDENSED MATTER, 407 (11):1810-1812; 10.1016/j.physb.2012.01.036 JUN 1 2012
Abstract:
We report steps of conductivity between discrete conducting states in microsamples of quasi-one-dimensional conductors K0.3MoO3 and NbSe3. The steps reveal single phase-slip events, and the discrete states reveal "quantization" of the wave vector q of the charge-density wave. The "quantization" is observed due to the coherence of the CDW within the sample volume and tight boundary conditions at the contacts. The distribution of steps in temperature gives the temperature dependences of the q-vectors, while the steps' height provides the carriers' mobilities. For the case of NbSe3 we give the 1st direct confirmation of the extremely high mobility of the "pocket" holes at low temperatures. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Microstructure and magnetocaloric effect of melt-spun Ni52Mn26Ga22 ribbon
Authors:
Li, ZB; Llamazares, JLS; Sanchez-Valdes, CF; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Z. B.; Sanchez Llamazares, J. L.; Sanchez-Valdes, C. F.; Zhang, Y. D.; Esling, C.; Zhao, X.; Zuo, L.
Source:
APPLIED PHYSICS LETTERS, 100 (17):10.1063/1.4704780 APR 23 2012
Abstract:
Microstructural features and magnetocaloric properties of Ni52Mn26Ga22 melt-spun ribbons were studied. Results show that there are four types of differently oriented variants of seven-layered modulated (7M) martensite at room temperature, being twin-related one another and clustered in colonies. Due to the coupled magnetic and structural transformations between parent austenite and 7M martensite, the melt-spun ribbons exhibit a significant magnetocaloric effect. At an applied magnetic field of 5 T, an absolute maximum value of the isothermal magnetic entropy change of 11.4 J kg(-1) K-1 is achieved with negligible hysteresis losses. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704780]
Title:
Microstructure properties and microhardness of rapidly solidified Al64Cu20Fe12Si4 quasicrystal alloy
Authors:
Karakose, E; Keskin, M Author Full Names: Karakose, Ercan; Keskin, Mustafa
Source:
METALS AND MATERIALS INTERNATIONAL, 18 (2):257-263; 10.1007/s12540-012-2017-3 APR 2012
Abstract:
This paper presents differences in the microstructure and microhardness properties of conventional casting (ingot) and rapidly solidified Al64Cu20Fe12Si4 quasicrystal (QC) alloys. The phases present in the Al64Cu20Fe12Si4 ingot alloy were determined to be icosahedral quasicrystalline (IQC) Psi-Al65Cu20Fe15, cubic beta-AlFe, tetragonal theta-Al2Cu, and monoclinic lambda-A1(3)Fe(4) phases, whereas only IQC Psi-Al65Cu20Fe15 and cubic beta-AlFe phases were identified in the rapidly solidified alloy. The microhardness value of the melt spun alloy was measured to be approximately 790 kg/mm(2). Microhardness increases with increasing solidification rates.
Title:
Nanocrystalline Intermetallics in Al-Cu-Fe-Cr Decagonal Quasicrystalline Alloy
Authors:
Yadav, TP; Mukhopadhyay, NK; Srivastava, ON Author Full Names: Yadav, T. P.; Mukhopadhyay, N. K.; Srivastava, O. N.
Source:
MATERIALS AND MANUFACTURING PROCESSES, 27 (6):620-625; 10.1080/10426914.2011.593246 2012
Abstract:
In the present investigation, an Al-Cu-Fe-Cr decagonal quasicrystalline alloy synthesized by a slow-cooling technique was mechanically milled in a high-energy ball mill for various times ranging up to 100 hours under liquid hexane medium at the speed of 400 rpm with a ball to powder ratio of 40:1. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential thermal analysis (DTA), and energy-dispersive x-ray analysis (EDX) were employed to characterize the as-cast, milled, and annealed samples. Powders milled for more than 10 h contained predominantly the B2-type nano-crystalline phase with a lattice parameter of similar to 0.29 nm. The 100 h milled powder was annealed in air at 500 degrees C for 20-40 h. It was observed that 40 h annealed sample shows the best yield for the fabrication of nanospinel. The processing technique could be optimized to manufacture the composites of nano-quasicrystal, nano-B2, and nanospinels. These materials may be further investigated as a suitable material for pigment industries.

Update: 16-May-012

Title:
Preparation of Al-Cu-Fe-(Sn,Si) quasicrystalline bulks by laser multilayer cladding
Authors:
Feng, LP; Fleury, E; Zhang, GS Author Full Names: Feng, Li-ping; Fleury, Eric; Zhang, Guo-sheng
Source:
INTERNATIONAL JOURNAL OF MINERALS METALLURGY AND MATERIALS, 19 (5):434-440; 10.1007/s12613-012-0575-5 MAY 2012
Abstract:
(Al65Cu20Fe15)(100-x)Sn-x (x=0, 12, 20, 30) and Al57Si10Cu18Fe15 powders were cladded on a medium carbon steel (45# steel) substrate by laser multilayer cladding, respectively. The phases and properties of the produced quasicrystalline bulks were investigated. It was found that the main phases in the Al65Cu20Fe15 sample were crystalline lambda-Al13Fe4 and icosahedral quasicrystal together with a small volume fraction of theta-Al2Cu phase. The volume fraction of icosahedral phase decreased as the Sn content in the (Al65Cu20Fe15)(100-x)Sn-x samples increased owing to the formation of beta-CuSn phase. The increase of Sn content improved the brittleness of the quasicrystal samples. The morphology of the solidification microstructure in the Al57Si10Cu18Fe15 sample changed from elongated shape to spherical shape due to the addition of Si. The nanohardness of the laser multilayer cladded quasicrystal samples was equal to that of the as-cast sample prepared by vacuum quenching. In terms of hardness, the laser cladded Al57Si10Cu18Fe15 quasicrystalline alloy has the highest value among all the investigated samples.
Title:
Competition between commensurate and incommensurate magnetic ordering in Fe1+yTe
Authors:
Parshall, D; Chen, G; Pintschovius, L; Lamago, D; Wolf, T; Radzihovsky, L; Reznik, D Author Full Names: Parshall, D.; Chen, G.; Pintschovius, L.; Lamago, D.; Wolf, Th; Radzihovsky, L.; Reznik, D.
Source:
PHYSICAL REVIEW B, 85 (14):10.1103/PhysRevB.85.140515 APR 26 2012
Abstract:
The Fe1+yTe1-xSex compounds belong to the family of iron-based high-temperature superconductors, in which superconductivity often appears upon doping antiferromagnetic parent compounds. Unlike other Fe-based superconductors (in which the antiferromagnetic order is at the Fermi-surface nesting wave vector [1/2, 1/2, 1]), Fe1+yTe orders at a different wave vector, [1/2, 0, 1/2]. Furthermore, the ordering wave vector depends on y, the occupation of interstitial sites with excess iron; the origin of this behavior is controversial. Using inelastic neutron scattering on Fe1.08Te, we find incommensurate magnetic fluctuations above the Neel temperature, even though the ordered state is bicollinear and commensurate with gapped spin waves. This behavior can be understood in terms of a competition between commensurate and incommensurate order, which we explain as a lock-in transition caused by the magnetic anisotropy.
Title:
Structures and Magnetism of La1-xSrxMnO3-(0.5+x)/2 (0.67 <= x <= 1) Phases
Authors:
Dixon, E; Hadermann, J; Hayward, MA Author Full Names: Dixon, Edward; Hadermann, Joke; Hayward, Michael A.
Source:
CHEMISTRY OF MATERIALS, 24 (8):1486-1495; 10.1021/cm300199b APR 24 2012
Abstract:
Topotactic reduction of La1-xSrxMnO3 (0.67 <= x <= 1) phases with sodium hydride yields a series of isoelectronic materials of composition La1-xSrxMnO3-(0.5+x)/2. Lanthanum rich members of the series (0.67 <= x <= 0.83) adopt anion deficient perovskite structures with a 6-layer -OTOOT'O- stacking sequence of sheets of octahedra/square-based pyramids (O) and sheets of tetrahedra (T). The strontium rich members of the series (0.83 <= x <= 1) incorporate "step defects" into this 6-layer structure in which the OTOOT'O stacking sequence is converted into either OOTOOT' or TOOT'OO at a defect plane which runs perpendicular to the [201] lattice plane. The step defects appear to provide a mechanism to relieve lattice strain and accommodate additional anion deficiency in phases with x > 0.83. Magnetization and neutron diffraction data indicate La1-xSrxMnO3-(0.5+x)/2 phases adopt antiferromagnetically ordered states at low-temperature in which the ordered arrangement of magnetic spins is incommensurate with the crystallographic lattice.
Title:
Antiferromagnetic order in the quasicrystal approximant Cd6Tb studied by x-ray resonant magnetic scattering
Authors:
Kim, MG; Beutier, G; Kreyssig, A; Hiroto, T; Yamada, T; Kim, JW; de Boissieu, M; Tamura, R; Goldman, AI Author Full Names: Kim, M. G.; Beutier, G.; Kreyssig, A.; Hiroto, T.; Yamada, T.; Kim, J. W.; de Boissieu, M.; Tamura, R.; Goldman, A. I.
Source:
PHYSICAL REVIEW B, 85 (13):10.1103/PhysRevB.85.134442 APR 24 2012
Abstract:
We have used x-ray resonant magnetic scattering at the Tb L-2 edge to elucidate the nature of magnetic ordering in Cd6Tb, a 1/1 approximant closely related to the Cd-Mg-R ( R = rare earth) icosahedral alloys. Below T-N approximate to 24 K, the ordered moments associated with the icosahedral clusters at the corners and body center of the pseudocubic unit cell are antiferromagnetically correlated, and long-range magnetic order is realized.
Title:
Mullite and mullite-type crystal structures
Authors:
Fischer, RX; Gaede-Kohler, A; Birkenstock, J; Schneider, H Author Full Names: Fischer, Reinhard X.; Gaede-Koehler, Andrea; Birkenstock, Johannes; Schneider, Hartmut
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 103 (4):402-407; 10.3139/146.110713 APR 2012
Abstract:
Synthetic mullites (Al4+2xSi2-2xO10-x) belong to one of the most important groups of ceramic materials. Their crystal structure consists of chains of edge-sharing AlO6 octahedra interconnected by tetrahedral double chains of TO4 (T = Al, Si) tetrahedra. The occurrence of oxygen vacancies is associated with the formation of triclusters of TO4 groups. The distribution of oxygen vacancies and the distribution of Al and Si on the tetrahedral sites are partially ordered yielding an incommensurately modulated crystal structure with satellite reflections in diffraction patterns. The number of symmetrically independent distribution patterns of oxygen vacancies is given for a 2 x 2 x 2 and a 3 x 3 x 2 superstructure model. Many other compounds have chain structures similar to mullite. These compounds are assigned to subgroups, all derived from a hypothetical tetragonal aristotype structure.
Title:
Incommensurate structures in a two-subsystem partially frustrated ferrimagnet
Authors:
Martynov, SN Author Full Names: Martynov, S. N.
Source:
JETP LETTERS, 95 (4):188-192; 10.1134/S0021364012040066 APR 2012
Abstract:
A new incommensurate magnetic structure with a locally triangular orientation of spins has been proposed for a two-subsystem magnet with frustrated intersystem exchange and competition between exchanges in one of the subsystems. When the temperature is lowered, this structure appears from the antiferromagnetic state after a first-order phase transition. It transfers to the Yafet-Kittel triangular structure when the threshold conditions for the exchange interactions are fulfilled. An increase in the length of the frustrated exchange bonds leads to the appearance of an incommensurate phase with the local antiferromagnetic orientation of the sublattices in each subsystem between the commensurate antiferromagnetic and Yafet-Kittel phases.
Title:
Shift and Broadening of Surface Polaritons of Sapphire upon Deposition of a Quasicrystalline Film
Authors:
Novikova, NN; Ol'shanskii, ED; Teplov, AA; Shaitura, DS; Yakovlev, VA Author Full Names: Novikova, N. N.; Ol'shanskii, E. D.; Teplov, A. A.; Shaitura, D. S.; Yakovlev, V. A.
Source:
PHYSICS OF THE SOLID STATE, 54 (3):573-577; 10.1134/S1063783412030213 MAR 2012
Abstract:
The influence of a quasicrystalline Al-Pd-Re film on the shift and broadening of surface polaritons of a substrate (sapphire) has been studied. Measurements have been performed both on a sample containing only the quasicrystalline phase and on a sample which, in addition to the quasicrystalline phase, contains the crystalline (metallic) phase. The complex dielectric function of the films in the mid-IR region (650-800 cm(-1)) has been estimated.
Title:
Dielectric Characteristics and Phase Transitions in Tl(InS2)(1-x)(FeSe2)(x) Solid Solutions
Authors:
Sheleg, AU; Hurtavy, VG; Mustafaeva, SN; Kerimova, EM; Shautsova, VV Author Full Names: Sheleg, A. U.; Hurtavy, V. G.; Mustafaeva, S. N.; Kerimova, E. M.; Shautsova, V. V.
Source:
PHYSICS OF THE SOLID STATE, 54 (3):607-610; 10.1134/S1063783412030304 MAR 2012
Abstract:
This paper reports on a study of the electrical conductivity and permittivity of Tl(InS2)(1 - x)(FeSe2)(x) crystals as functions of composition and temperature. It has been found that the permittivity decreases in magnitude, while the electrical conductivity increases with increasing x. Crystals Tl(InS2)(1 - x)(FeSe2)(x) have been observed to undergo a sequence of phase transitions characteristic of TlInS2, which manifests itself in formation of anomalies in the sigma = f(T) and epsilon = f(T) temperature dependences. It has been shown that as x increases, the phase transition temperatures decrease, while the temperature region within which the incommensurate phase persists broadens slightly.

Update: 10-May-2012

Title:
First-principles study of the atomic and electronic structures of misfit-layered calcium cobaltite (Ca2CoO3)(CoO2)(1.62) using rational approximants
Authors:
Rebola, A; Klie, R; Zapol, P; Ogut, S Author Full Names: Rebola, Alejandro; Klie, Robert; Zapol, Peter; Oeguet, Serdar
Source:
PHYSICAL REVIEW B, 85 (15):10.1103/PhysRevB.85.155132 APR 19 2012
Abstract:
The atomic and electronic structures of the misfit-layered thermoelectric oxide material Ca3Co4O9 are investigated using detailed first-principles computations performed within the framework of density functional theory (DFT) and its DFT + U extension to account for electron correlations. The structure of Ca3Co4O9, composed of two incommensurate subsystems-a distorted rocksalt-type Ca2CoO3 layer sandwiched between hexagonal CoO2 layers-is modeled by means of Fibonacci rational approximants with systematically increasing unit cells. We show that good agreement with photoemission and transport experiments can be obtained regarding the contribution of the two subsystems to states near the Fermi level, when electron correlations are taken into account with a Hubbard U. The size of the rational approximant plays a secondary role in the analysis; the relatively "small" structure of composition (Ca2CoO3)(6)(CoO2)(10) represents a good model for investigating the atomic and electron ic properties of Ca3Co4O9. Within the DFT + U formalism, the metallic conductivity of Ca3Co4O9 is shown to result from itinerant holes in the hexagonal CoO2 layers, in which the Co atoms are predicted to have a mixed valence of Co4+ with similar to 30% concentration and Co3+ with similar to 70% concentration, both in low-spin configurations. In most cases, the resulting electronic structures show very good agreement with available data from transport and magnetic measurements.
Title:
The Incommensurately Modulated Structures of the Perovskites NaCeMnWO6 and NaPrMnWO6
Authors:
Garcia-Martin, S; King, G; Nenert, G; Ritter, C; Woodward, PM Author Full Names: Garcia-Martin, Susana; King, Graham; Nenert, Gwilherm; Ritter, C.; Woodward, Patrick M.
Source:
INORGANIC CHEMISTRY, 51 (7):4007-4014; 10.1021/ic202071n APR 2 2012
Abstract:
The structures of the doubly ordered perovskites NaCeMnWO6 and NaPrMnWO6, with rock salt ordering of the Mn2+ and W6+ B-site cations and layered ordering of the Na+ and (Ce3+/Pr3+) A-site cations, have been studied by transmission electron microscopy, electron diffraction, neutron and synchrotron X-ray powder diffraction. Both compounds possess incommensurately modulated crystal structures. In NaCeMnWO6 the modulation vector (with reference to the ideal ABX(3) perovskite subcell) is q approximate to 0.067a* (similar to 58.7 angstrom) and in NaPrMnWO6 q approximate to 0.046a* (similar to 85.3 angstrom). In both compounds the superstructures are primarily the two-dimensional chessboard type, although some crystals of NaCeMnWO6 were found with one-dimensional stripes. In some crystals of NaPrMnWO6 there is a coexistence of chessboards and stripes. Modeling of neutron diffraction data shows that octahedral tilting plays an important role in the structural modulation.
Title:
Planar defects in the icosahedral phase in quasicrystal-forming AlCuFe alloys
Authors:
Shalaeva, EV; Prekul, AF; Nazarova, SZ; Khiller, VV Author Full Names: Shalaeva, E. V.; Prekul, A. F.; Nazarova, S. Z.; Khiller, V. V.
Source:
PHYSICS OF THE SOLID STATE, 54 (4):699-707; 10.1134/S1063783412040257 APR 2012
Abstract:
Electron microscopy has revealed that, upon the formation of a stable icosahedral (i) AlCuFe phase, there arise a large number of planar defects. The revealed defects are nanometer-sized coherent intergrowths of the P1-pentagonal approximant. It has been found that the formation of these defects is the result of a nonequilibrium intermediate transformation. The intergrowths are located in the planes with the fivefold symmetry axis and give rise to an elastic-strain state of the i-phase. Analysis of the diffraction contrast has revealed the presence of phason and phonon atomic displacements due to the mismatch between the quasiperiodic (i-phase) and periodic (P1-phase) lattices. The formed structure exhibits a higher electrical resistance as compared to the i-phase and has been considered as a model state of the imperfect icosahedral phase with preferred phonon displacements.
Title:
Theory of linear, nonlinear and dynamic fracture for quasicrystals
Authors:
Fan, TY; Tang, ZY; Chen, WQ Author Full Names: Fan, Tian-You; Tang, Zhi-Yi; Chen, Wei-Qiu
Source:
ENGINEERING FRACTURE MECHANICS, 82 185-194; 10.1016/j.engfracmech.2011.12.009 MAR 2012
Abstract:
In this paper, fracture theory of quasicrystalline material is presented, concerning with linear, nonlinear and dynamic fracture problems for different quasicrystal systems observed to date. Main attention is however paid to three-dimensional icosahedral quasicrystals and two-dimensional decagonal quasicrystals, which play the central role in the new kind of materials. Relevant experimental results are also discussed. (C) 2012 Elsevier Ltd. All rights reserved.

Update: 3-May-2012

Title:
Vacancy-like defects associated with icosahedral phase in Mg-Y-Nd-Zr alloys modified by the addition of Zn
Authors:
Cizek, J; Vlcek, M; Smola, B; Stulikova, I; Prochazka, I; Kuzel, R; Jager, A; Lejcek, P Author Full Names: Cizek, J.; Vlcek, M.; Smola, B.; Stulikova, I.; Prochazka, I.; Kuzel, R.; Jaeger, A.; Lejcek, P.
Source:
SCRIPTA MATERIALIA, 66 (9):630-633; 10.1016/j.scriptamat.2012.01.054 MAY 2012
Abstract:
Positron lifetime spectroscopy combined with other techniques was employed for the structural characterization of Mg-Y-Nd-Zr (WE43) alloy modified by the addition of Zn. A quasicrystalline icosahedral phase was formed in the alloy, thereby strengthening it. Vacancy-like defects characterized by a positron lifetime of similar to 300 ps were also found, although such defects are not present in WE43 alloy without Zn. This testifies that vacancy-like defects are associated with the quasicrystalline phase. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Structure of UMo4O14 oxide
Authors:
Zakharov, ND; Pippel, E; Hillebrand, R; Werner, P Author Full Names: Zakharov, N. D.; Pippel, E.; Hillebrand, R.; Werner, P.
Source:
PROGRESS IN NUCLEAR ENERGY, 57 150-154; SI 10.1016/j.pnucene.2011.10.012 MAY 2012
Abstract:
The structure and composition of UMo4O14 synthesized by solid state reaction method have been investigated by High Resolution Transmission Electron Microscopy (HRTEM), High Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM), Selected Area Electron Diffraction SAED, and energy Dispersive X-ray microanalysis (EDX). The unit cell is orthorhombic, Cccm (66), a = 0.732, b = 3.247, c = 0.81, alpha = 90.0, beta = 90.0, gamma = 90.0. It comprises 2 layers of U and Mo cations. Each following layer is shifted relatively to the previous one by vector a/2. The infinite layers of composition Mo2O7 running perpendicular to b direction can be easily distinguished in the image. These double MoO3 octahedra wide slabs are typical for U-Mo oxides. They are linked to each other by another MoO3 octahedra and infinite one octahedral wide slab, forming a two rows of hexagonal coordinated bi-pyramids occupied by...U-O-Mo-O... strings. One of characteristic features of the UMo4O14 phase is the incommensurate modulation observed in some crystals. The goal of this paper is to reveal three-dimensional atomic structure of U-Mo oxide and to clarify in what way it depends on U/Mo composition. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Magnetic superspace groups and symmetry constraints in incommensurate magnetic phases
Authors:
Perez-Mato, JM; Ribeiro, JL; Petricek, V; Aroyo, MI Author Full Names: Perez-Mato, J. M.; Ribeiro, J. L.; Petricek, V.; Aroyo, M. I.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (16):10.1088/0953-8984/24/16/163201 APR 25 2012
Abstract:
Superspace symmetry has been for many years the standard approach for the analysis of non-magnetic modulated crystals because of its robust and efficient treatment of the structural constraints present in incommensurate phases. For incommensurate magnetic phases, this generalized symmetry formalism can play a similar role. In this context we review from a practical viewpoint the superspace formalism particularized to magnetic incommensurate phases. We analyse in detail the relation between the description using superspace symmetry and the representation method. Important general rules on the symmetry of magnetic incommensurate modulations with a single propagation vector are derived. The power and efficiency of the method is illustrated with various examples, including some multiferroic materials. We show that the concept of superspace symmetry provides a simple, efficient and systematic way to characterize the symmetry and rationalize the structural and physical properties of incommensurate magnetic materials. This is especially relevant when the properties of incommensurate multiferroics are investigated.
Title:
Heat transport of the quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8 in longitudinal and transverse fields
Authors:
Zhao, ZY; Liu, XG; He, ZZ; Wang, XM; Fan, C; Ke, WP; Li, QJ; Chen, LM; Zhao, X; Sun, XF Author Full Names: Zhao, Z. Y.; Liu, X. G.; He, Z. Z.; Wang, X. M.; Fan, C.; Ke, W. P.; Li, Q. J.; Chen, L. M.; Zhao, X.; Sun, X. F.
Source:
PHYSICAL REVIEW B, 85 (13):10.1103/PhysRevB.85.134412 APR 5 2012
Abstract:
The very-low-temperature thermal conductivity (kappa) is studied for BaCo2V2O8, a quasi-one-dimensional Ising-like antiferromagnet exhibiting an unusual magnetic-field-induced order-to-disorder transition. The nearly isotropic transport in the longitudinal field indicates that the magnetic excitations scatter phonons rather than conduct heat. The field dependence of kappa shows a sudden drop at similar to 4 T, where the system undergoes the transition from the Neel order to the incommensurate state. Another dip at lower field of similar to 3 T indicates an unknown magnetic transition, which is likely due to the spin-flop transition. Moreover, the kappa(H) in the transverse field shows a very deep valleylike feature, which moves slightly to higher field and becomes sharper upon lowering the temperature. This indicates a magnetic transition induced by the transverse field, which however is not predicted by the present theories for this low-dimensional spin system.
Title:
Electrical and Magnetic Properties of Quasicrystal Approximants RCd6 (R: Rare Earth)
Authors:
Mori, A; Ota, H; Yoshiuchi, S; Iwakawa, K; Taga, Y; Hirose, Y; Takeuchi, T; Yamamoto, E; Haga, Y; Honda, F; Settai, R; Onuki, Y Author Full Names: Mori, Akinobu; Ota, Hisashi; Yoshiuchi, Shingo; Iwakawa, Ken; Taga, Yuki; Hirose, Yusuke; Takeuchi, Tetsuya; Yamamoto, Etsuji; Haga, Yoshinori; Honda, Fuminori; Settai, Rikio; Onuki, Yoshichika
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 81 (2):10.1143/JPSJ.81.024720 FEB 2012
Abstract:
We measured the electrical resistivity, magnetic susceptibility, magnetization, and specific heat of the quasicrystal approximants RCd6 (R: rare earth, Y-Lu) with a body-centered cubic (bcc) crystal structure. Single crystals were grown by the Cd-self flux method and annealing method. We confirmed that the structural order-disorder transition is realized at about 160K when the lattice constant a is larger than 15.481 angstrom in YCd6, namely, for R = Pr, Nd, Sm, Gd, Tb, Dy, and Yb. At lower temperatures, RCd6 compounds, except non-4f reference compounds YCd6 and LuCd6, and a divalent compound YbCd6, are found to order antiferromagnetically. We clarified that the structural order-disorder transition has a great influence on the magnetic ordering and transport properties. The Neel temperature of RCd6 (R: Nd, Sm, Tb, and Dy) with the structural order-disorder transition is appreciably higher than the de Gennes scaling normalized by the Neel temperature of GdCd6, while the the Neel temperature of RCd6 (R: Ho, Er, and Tm) without the structural transition approximately follows the de Gennes scaling. Moreover, the electrical resistivity of RCd6 with the structural transition decreases monotonically below the Neel temperature, while it increases below the Neel temperature and a large residual resistivity remains at low temperatures in RCd6 without the structural transition. The contribution of an Einstein oscillator to the phonon specific heat is also discussed in YCd6 and LuCd6.
Title:
Solidification of tin on quasicrystalline surfaces
Authors:
Singh, A; Somekawa, H; Matsushita, Y; Tsai, AP Author Full Names: Singh, Alok; Somekawa, H.; Matsushita, Y.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE, 92 (9):1106-1128; 10.1080/14786435.2011.640646 2012
Abstract:
A two-phase alloy of beta-Sn and Al63Cu25Fe12 quasicrystal produced by melt-spinning was annealed and aged to form various microstructures of tin in a quasicrystalline (QC) or microcrystalline (MC) matrix. The morphology and structure of the interfaces was studied by scanning and transmission electron microscopy and was related to melting and solidification behavior of tin studied by differential scanning calorimetry. In a MC matrix the tin phase occurred as nanoparticles and solidified with an undercooling of about 35 degrees C. In a QC matrix, tin formed intergranular layers on faceted matrix grains. Tin showed multiple solidification peaks in undercooling ranging from 8 degrees C to 43 degrees C, indicating several distinct nucleation sites which compete with each other and are selected kinetically. The interfacial energy (depending on the structural state of the matrix) had a more dominating effect on the solidification of tin than the size, shape and the distribution of the tin particles. It was also concluded that solidification of tin is easier on quasicrystalline surfaces than on aluminum.

Update: 26-Apr-2012

Title:
Fractal spectra in generalized Fibonacci one-dimensional magnonic quasicrystals
Authors:
Costa, CHO; Vasconcelos, MS; Barbosa, PHR; Barbosa, FF Author Full Names: Costa, C. H. O.; Vasconcelos, M. S.; Barbosa, P. H. R.; Barbosa Filho, F. F.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (14):2315-2323; 10.1016/j.jmmm.2012.02.123 JUL 2012
Abstract:
In this work we carry out a theoretical analysis of the spectra of magnons in quasiperiodic magnonic crystals arranged in accordance with generalized Fibonacci sequences in the exchange regime, by using a model based on a transfer-matrix method together random-phase approximation (RPA). The generalized Fibonacci sequences are characterized by an irrational parameter sigma(p,q), which rules the physical properties of the system. We discussed the magnonic fractal spectra for first three generalizations, i.e., silver, bronze and nickel mean. By varying the generation number, we have found that the fragmentation process of allowed bands makes possible the emergence of new allowed magnonic bulk bands in spectra regions that were magnonic band gaps before, such as which occurs in doped semiconductor devices. This interesting property arises in one-dimensional magnonic quasicrystals fabricated in accordance to quasiperiodic sequences, without the need to introduce some de ferent atomic layer or defect in the system. We also make a qualitative and quantitative investigations on these magnonic spectra by analyzing the distribution and magnitude of allowed bulk bands in function of the generalized Fibonacci number F-n and as well as how they scale as a function of the number of generations of the sequences, respectively. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Study on phase stability and oxide ion conductivity in the BIAGVOX system
Authors:
Al-Areqi, NAS; Beg, S; Al-Alas, A Author Full Names: Al-Areqi, Niyazi A. S.; Beg, Saba; Al-Alas, Ahlam
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 73 (6):730-734; 10.1016/j.jpcs.2012.01.009 JUN 2012
Abstract:
A novel oxide ion conductor, BIAGVOX formulated as Bi4AgxV2-xO11-(2x)-delta is obtained by substituting a fraction (x) of V5+ by Ag+ in Bi4V2O11 samples of the BIAGVOX system in the composition range, 0.05 <= x <= 0.30 were synthesized using the standard solid-state reaction. XRPD, FT-IR, DTA and AC impedance spectroscopy were used for the investigation of the correlation between the structural phase stability and oxide ion performance of the BIAGVOX materials. It has been found that orthorhombic, beta, and incommensurate tetragonal, gamma' were stabilized at room temperature for compositions with x <= 0.15 and x >= 0.20, respectively. The enthalpy of beta ->gamma and gamma ->gamma transition exhibited a general drop with increasing Ag content and a minimum transition temperature was observed for x = 0.20. However, the oxide ion conductivity at lower temperatures remarkably increased in composition stability ranges of beta- and gamma-phase, while a maximum conductivity was reported for the high temperature gamma-phase at x = 0.15. However, the low temperature conductivity, sigma(300)degrees c measured for x = 0.30 was found to be comparable with the maximum ionic conductivity of the BICUVOX system reported for x = 0.20 at the same temperature. (C) 2012 Elsevier Ltd. All rights reserved.
Title:
Two-dimensional charge fluctuation in beta-Na0.33V2O5
Authors:
Ohwada, K; Yamauchi, T; Fujii, Y; Ueda, Y Author Full Names: Ohwada, Kenji; Yamauchi, Touru; Fujii, Yasuhiko; Ueda, Yutaka
Source:
PHYSICAL REVIEW B, 85 (13):10.1103/PhysRevB.85.134102 APR 6 2012
Abstract:
We have investigated the critical phenomena of the metal-to-insulator (MI) transition of beta-Na0.33V2O5. The critical exponent beta of 0.226(3) and anisotropic diffuse scattering suggest that the MI transition of beta-Na0.33V2O5 is two dimensional in nature and that the dimension of the order parameter is not Ising. The non-Ising-like order parameter indicates that the MI transition is not a simple order-disorder type such as that of alpha'-NaV2O5 but charge-density-wave like, where the valence at each V site is continuous and the arrangement is modulated. This closely corresponds to the situation predicted by neutron diffraction measurements [Nagai et al., J. Phys. Soc. Jpn. 74, 1297 (2005)] and NMR measurements [Itoh et al., Phys. Rev. B 74, 054434 (2006)].
Title:
Phase transitions and incommensurability in the layered semiconductor TlInS2-an NMR study
Authors:
Panich, AM; Mogilyansky, D; Sardarly, RM Author Full Names: Panich, A. M.; Mogilyansky, D.; Sardarly, R. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (13):10.1088/0953-8984/24/13/135901 APR 4 2012
Abstract:
We report on the first NMR study of powder and single crystal samples of thallium indium sulfide, TlInS2. The crystal under study is a pure single-layer TlInS2 polytype. Our findings show that transformation from the high temperature paraelectric phase to the low temperature ferroelectric phase occurs via an incommensurate phase that exists in the temperature range from T-c = 192 K to T-i = 205 K. On approaching the phase transition at T-i from above, the crystal exhibits a soft mode behavior. A discrepancy in the literature data on the phase transitions in TlInS2 is discussed and ascribed to polytypism of the TlInS2 crystals.
Title:
Morphology of monolayer films on quasicrystalline surfaces from the phase field crystal model
Authors:
Rottler, J; Greenwood, M; Ziebarth, B Author Full Names: Rottler, Joerg; Greenwood, Michael; Ziebarth, Benedikt
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (13):10.1088/0953-8984/24/13/135002 APR 4 2012
Abstract:
We present a computational study of the morphology of adsorbed monolayers on quasicrystalline surfaces with five-and seven-fold symmetry. The phase field crystal model is employed to first simulate the growth of the quasicrystal surfaces and then to elastically couple a two-dimensional film to the substrate. We find several distinct pseudomorphic phases that depend on the position of adsorption sites as well as the strength of the monolayer/substrate interaction, and quantify them by computing local order parameters. In qualitative agreement with recent experiments using colloids in quasiperiodic light fields, we find that the formation of quasicrystalline order is greatly inhibited on seven-fold surfaces.
Title:
Unified minimum effective model of magnetic properties of iron-based superconductors
Authors:
Hu, JP; Xu, B; Liu, WM; Hao, NN; Wang, YP Author Full Names: Hu, Jiangping; Xu, Bao; Liu, Wuming; Hao, Ning-Ning; Wang, Yupeng
Source:
PHYSICAL REVIEW B, 85 (14):10.1103/PhysRevB.85.144403 APR 3 2012
Abstract:
Iron-based superconductors exhibit many different antiferromagnetically ordered ground states. We construct a minimum effective magnetic model that displays all magnetic phases. This model also captures three incommensurate magnetic phases as well, two of which have been observed experimentally. The model characterizes the nature of phase transitions between the different magnetic phases and explains a variety of magnetic properties, such as spin-wave spectra and electronic nematism. Most importantly, by unifying the understanding of magnetism, we cast insight on the key ingredients of magnetic interactions that are critical to the occurrence of superconductivity.
Title:
Incommensurate modulation of calcium barium niobate (CBN28 and Ce:CBN28)
Authors:
Graetsch, HA; Pandey, CS; Schreuer, J; Burianek, M; Muhlberg, M Author Full Names: Graetsch, Heribert A.; Pandey, Chandra Shekhar; Schreuer, Juergen; Burianek, Manfred; Muehlberg, Manfred
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 101-106; Part 2 10.1107/S0108768111054863 APR 2012
Abstract:
The incommensurately modulated crystal structures of Ca0.28Ba0.72Nb2O6 (CBN28) and Ce0.02Ca0.25Ba0.72Nb2O6 (Ce:CBN28) were refined in the supercentred setting X4bm(AA0,-AA0) of the 3 + 2-dimensional superspace group P4bm(aa(1/2),-aa(1/2)). Both compounds are isostructural with a tetragonal tungsten bronze-type structure. The modulation of CBN28 consists of a wavy distribution of Ba and Ca atoms as well as vacancies on the incompletely occupied Me2 site with 15-fold oxygen coordination. The occupational modulation is coupled with a modulation of the atomic displacement parameters and a very weak modulation of the positional parameters of Me2. The surrounding O atoms show strong displacive modulations with amplitudes up to ca 0.2 angstrom owing to the cooperative tilting of the rigid NbO6 octahedra. The Me1 site with 12-fold coordination and Nb atoms are hardly affected by the modulations. Only first-order satellites were observed and the modulations are described by first-order harmonics. In Ce:CBN28 cerium appears to be located on both the Me2 and Me1 sites. Wavevectors and structural modulations are only weakly modified upon substitutional incorporation of 0.02 cerium per formula unit of calcium.
Title:
Effective Electron Correlation and Spin Density Fluctuation in Iron-Based Fluorides SrFe1-xCoxAsF (x=0, 0.125)
Authors:
Wang, W; Sun, JF; Li, SW Author Full Names: Wang, Wei; Sun, Jiafa; Li, Suwen
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS, 167 (1-2):83-89; 10.1007/s10909-012-0597-4 APR 2012
Abstract:
Using first-principles calculation, we study effective electron correlation and spin density fluctuation in iron-based fluorides SrFe1-xCoxAsF (x = 0, 0.125). We obtain the observed magnetic moment of Fe atom with a strongly attractive electron correction. Whereas, different from the parent compound, the density of state of superconducting SrFe1-xCoxAsF (x = 0.125) near to the Fermi energy is reduced for both signs of effective electron correlation, and suggests strong instability there. In addition, spin density fluctuation resulted from the effective correlation exists in Co-doped compound, may propagate in the form of collective excitation and manifest as spin fluctuation with specific q-vector in momentum space.
Title:
Quasicrystal-polymer composites for selective laser sintering technology
Authors:
Kenzari, S; Bonina, D; Dubois, JM; Fournee, V Author Full Names: Kenzari, S.; Bonina, D.; Dubois, J. M.; Fournee, V.
Source:
MATERIALS & DESIGN, 35 691-695; 10.1016/j.matdes.2011.10.032 MAR 2012
Abstract:
Selective laser sintering (SLS) process is a layered manufacturing technique used for building functional parts from 3D computer-aided design. Materials compatible with SLS usually consist of polymer-based composites reinforced by metal or ceramic particles. We have investigated a new composite powder compatible with the SLS technology and containing AlCuFeB quasicrystalline filler particles. The processed parts show reduced friction and improved wear resistance compared to other composites used in SLS technology. In addition, the functional parts contain almost no porosity and are leak-tight allowing their direct use in many fluidic applications. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Effect of Zn/Er weight ratio on phase formation and mechanical properties of as-cast Mg-Zn-Er alloys
Authors:
Li, H; Du, WB; Li, SB; Wang, ZH Author Full Names: Li, Han; Du, Wenbo; Li, Shubo; Wang, Zhaohui
Source:
MATERIALS & DESIGN, 35 259-265; 10.1016/j.matdes.2011.10.002 MAR 2012
Abstract:
The results of X-ray diffraction (XRD), differential scanning calorimetry (DSC) and microstructure observations have shown that various Zn/Er weight ratio leads to different phase compositions in the investigated alloys. The composition range for the formation of icosahedral quasicrystalline (I-phase) and face-centered cubic phase (W-phase) in Mg-rich corner is obtained. The Zn/Er weight ratio adjusting from 10 to 6 results in the formation of I-phase exclusively as main secondary phase in the as-cast Mg-Zn-Er alloys. However, when the ratio is less than 0.8, it is mainly contributed to the precipitation of W-phase. When the ratio is in the range from 1 to 4, I-phase coexisting with W-phase is inclined to be formed. The results of tensile tests suggest that the as-cast Mg-5Zn-5.0Er alloy with I-phase and W-phase possesses the highest ultimate strength (UTS). It is concluded that UTS and elongation rate (ER) of as-cast Mg-Zn-Er alloys with I-phase as the main secondary phase are excellent. The UTS of the alloys with coexistence of I-phase and W-phase show the tendency of increasing firstly then decreasing with the increasing volume fraction of W-phase. The UTS declines when W-phase completely replaces I-phase in the alloy. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Magnetic enhancement across a ferroelectric-antiferroelectric phase boundary in Bi1-xNdxFeO3
Authors:
Wu, YJ; Chen, XK; Zhang, J; Chen, XJ Author Full Names: Wu, Yu-Jie; Chen, Xiao-Kun; Zhang, Jing; Chen, Xiao-Jia
Source:
JOURNAL OF APPLIED PHYSICS, 111 (5):10.1063/1.3693531 MAR 1 2012
Abstract:
The structural and magnetic properties of well-prepared Bi1-xNdxFeO3 (0 <= x <= 0.2) powders are investigated by combining x-ray diffraction, Raman scattering spectra, and magnetic measurements. Structural symmetric breaking from rhombohedral R3c to orthorhombic Pnma at the substituted Nd concentration of x = 0.125-0.15, accompanying a ferroelectric-antiferroelectric phase transition, is identified from x-ray diffraction patterns and Raman scattering spectra. The magnetization enhancement of Bi1-xNdxFeO3 is observed before approaching ferroelectric-antiferroelectric phase boundary conditions (0 <= x <= 0.15). We consider that such enhancement results from the destruction of the spin cycloid accompanying the structural transition. At x > 0.15, the magnetization decreases, which is probably attributable to further degradation of the space modulated spin structure, allowing a more perfect antiferromagnetic ordering. (C) 2012 American In! stitute of Physics. [http://dx.doi.org/10.1063/1.3693531]
Title:
Formation and properties of Zr-based bulk quasicrystalline alloys with high strength and good ductility (Retraction of vol 15, pg 2195, 2000)
Authors:
Inoue, A; Zhang, T; Saida, J; Matsushita, M Author Full Names: Inoue, Akihisa; Zhang, Tao; Saida, Junji; Matsushita, Mitsuhide
Source:
MATERIALS TRANSACTIONS, 53 (2):FEB 2012
Title:
Praphase Concept for the Phenomenological Description of Magnetoelectrics
Authors:
Sakhnenko, VP; Ter-Oganessian, NV Author Full Names: Sakhnenko, V. P.; Ter-Oganessian, N. V.
Source:
CRYSTALLOGRAPHY REPORTS, 57 (1):112-117; 10.1134/S1063774511060241 JAN 2012
Abstract:
Complex cascades of phase transitions with the alternation of antiferromagnetic, incommensurate, and magnetoelectric phases are observed in most crystals having magnetoelectric properties. The entire variety of observed phase transitions in numerous recent works is described by introducing several order parameters which are sequentially "condensed" with a decrease in temperature. The possibility of introducing the praphase concept into consideration to reduce the number of order parameters and interpret rich phase diagrams due to the smaller number of instabilities is demonstrated by the examples of MnWO4 and CuO magnetoelectrics. This approach is also used in the phenomenological description of the phase transitions in the BiFeO3 ferroelectromagnetic with the cubic phase of the perovskite structure as a starting point.

Update: 19-Apr-2012

Title:
Structural transformations in quasicrystals induced by higher dimensional lattice transitions
Authors:
Indelicato, G; Keef, T; Cermelli, P; Salthouse, DG; Twarock, R; Zanzotto, G Author Full Names: Indelicato, Giuliana; Keef, Tom; Cermelli, Paolo; Salthouse, David G.; Twarock, Reidun; Zanzotto, Giovanni
Source:
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, 468 (2141):1452-1471; 10.1098/rspa.2011.0680 MAY 8 2012
Abstract:
We study the structural transformations induced, via the cut-and-project method, in quasicrystals and tilings by lattice transitions in higher dimensions, with a focus on transition paths preserving at least some symmetry in intermediate lattices. We discuss the effect of such transformations on planar aperiodic Penrose tilings, and on three-dimensional aperiodic Ammann tilings with icosahedral symmetry. We find that locally the transformations in the aperiodic structures occur through the mechanisms of tile splitting, tile flipping and tile merger, and we investigate the origin of these local transformation mechanisms within the projection framework.
Title:
Study of the structure and physical properties of quasicrystals using large scale facilities
Authors:
de Boissieu, M Author Full Names: de Boissieu, Marc
Source:
COMPTES RENDUS PHYSIQUE, 13 (3):207-217; 10.1016/j.crhy.2011.11.008 APR 2012
Abstract:
Quasicrystals have been puzzling scientists since their discovery. In this article we review some of the recent advances in this field and show how the use of large scale facilities has brought in decisive information for the understanding of their structure and physical properties. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Interplay between the magnetic and electric degrees of freedom in multiferroic Co3TeO6
Authors:
Li, WH; Wang, CW; Hsu, D; Lee, CH; Wu, CM; Chou, CC; Yang, HD; Zhao, Y; Chang, S; Lynn, JW; Berger, H Author Full Names: Li, Wen-Hsien; Wang, Chin-Wei; Hsu, Daniel; Lee, Chi-Hung; Wu, Chun-Ming; Chou, Chih-Chieh; Yang, Hung-Duen; Zhao, Yang; Chang, Sung; Lynn, Jeffrey W.; Berger, Helmuth
Source:
PHYSICAL REVIEW B, 85 (9):10.1103/PhysRevB.85.094431 MAR 28 2012
Abstract:
Neutron diffraction, magnetic susceptibility, specific heat, and dielectric constant measurements of single-crystal Co3TeO6 have been measured to study the interplay between the ferroelectricity and magnetic order. Long-range incommensurate magnetic order develops below T-M1 = 26 K, which is followed by three additional zero-field phase transitions at T-M2 = 19.5 K, T-M3 = 18 K, and T-M4 = 16 K where the incommensurate order changes and commensurate order develops. In magnetic fields up to 14 T we find that the magnetic intensities and incommensurate wave vector are dramatically altered as ferroelectricity develops, with a fifth abrupt transition around 10 T. The overall behavior characterizes Co3TeO6 as a type-II multiferroic.
Title:
Triangular-lattice anisotropic dimerized Heisenberg antiferromagnet: Stability and excitations of the quantum paramagnetic phase
Authors:
Doretto, RL; Vojta, M Author Full Names: Doretto, R. L.; Vojta, Matthias
Source:
PHYSICAL REVIEW B, 85 (10):10.1103/PhysRevB.85.104416 MAR 26 2012
Abstract:
Motivated by experiments on nonmagnetic triangular-lattice Mott insulators, we study one candidate paramagnetic phase, namely the columnar dimer (or valence-bond) phase. We apply variants of the bond-operator theory to a dimerized and spatially anisotropic spin-1/2 Heisenberg model and determine its zero-temperature phase diagram and the spectrum of elementary triplet excitations (triplons). Depending on model parameters, we find that the minimum of the triplon energy is located at either a commensurate or an incommensurate wave vector. Condensation of triplons at this commensurate-incommensurate transition defines a quantum Lifshitz point, with effective dimensional reduction that possibly leads to nontrivial paramagnetic (e.g., spin-liquid) states near the closing of the triplet gap. We also discuss the two-particle decay of high-energy triplons, and we comment on the relevance of our results for the organic Mott insulator (EtMeP)-P-3[Pd(dmit)(2)]! (2).
Title:
Commensurate-incommensurate magnetic phase transition induced in TbNi5 by an external magnetic field
Authors:
Bogdanov, SG; Gerasimov, EG; Skryabin, YN; Sherstobitova, EA; Sikolenko, VV; Schedler, R; Pirogov, AN Author Full Names: Bogdanov, S. G.; Gerasimov, E. G.; Skryabin, Yu N.; Sherstobitova, E. A.; Sikolenko, V. V.; Schedler, R.; Pirogov, A. N.
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 113 (3):228-232; 10.1134/S0031918X12030052 MAR 2012
Abstract:
Neutron-diffraction studies of a single crystal of TbNi5 have been performed. Temperature and field dependences of the intensities of the Bragg reflection (001) and magnetic satellites (001)(-) and (001)(+) have been determined. In the temperature range of 7-10 K, sharp changes in the intensities of both the Bragg reflection and its satellites have been revealed. A conclusion is made that these changes are due to the existence of a magnetic transition from an incommensurate into a lock-in structure. It has been found that at 11 K an external magnetic field mu(0) H = 0.1 T oriented along the [100] axis induces the same magnetic state of the crystal as its cooling to 7 K in the absence of a field. In an external magnetic field mu(0) H = 0.4 T, there occurs a magnetic transition from the incommensurate phase with a wave vector k = 2 pi/c (0, 0, 0.18) into a commensurate ferromagnetic phase with k = 0. In the ferromagnetic phase, an increase in the field from 0.4 to 0.6 T is accompanied by an increase in the intensity of the ferromagnetic reflection (001) by a factor of 1.6. This indicates the existence of strong fluctuations of the magnetization at 0.4 T.
Title:
Evolution of spin-modulated magnetic compound Bi(1-x)SrxFeO3
Authors:
Gippius, AA; Tkachev, AV; Gervits, NE; Pokatilov, VS; Konovalova, AO; Sigov, AS Author Full Names: Gippius, A. A.; Tkachev, A. V.; Gervits, N. E.; Pokatilov, V. S.; Konovalova, A. O.; Sigov, A. S.
Source:
SOLID STATE COMMUNICATIONS, 152 (6):552-556; 10.1016/j.ssc.2011.12.028 MAR 2012
Abstract:
BiFeO3 is a perovskite-like compound with magnetic and electrical long-range order with antiferromagnetic transition temperature about 670 K. It has space modulated magnetic structure of cycloidal type with the period lambda = 620 +/- 20 angstrom incommensurate with the lattice parameter leading to specific NMR line shape. Substitution of strontium for bismuth atoms destroys the space modulated structure. Several samples with substitution of strontium for bismuth Bi1-xSrxFeO3 were studied by means of zero field NMR and Mossbauer spectroscopy. A significant broadening of Fe-57 NMR spectrum was observed at x = 0.10 while Mossbauer spectroscopy demonstrates this effect at x = 0.07. This phenomena evidence for the destruction of the spatial modulated magnetic structure at x similar to 0.07-0.10 by the heterovalent substitution of strontium for bismuth without the destruction of crystal rhombohedral structure. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Morphotropic Phase Boundary, Weak Ferromagnetism, and Strong Piezoelectric Effect in Bi1-xCaxFeO3-x/2 Compounds
Authors:
Troyanchuk, IO; Karpinsky, DV; Bushinsky, MV; Kovetskaya, MI; Efimova, EA; Eremenko, VV Author Full Names: Troyanchuk, I. O.; Karpinsky, D. V.; Bushinsky, M. V.; Kovetskaya, M. I.; Efimova, E. A.; Eremenko, V. V.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 113 (6):1025-1031; 10.1134/S1063776111140196 DEC 2011
Abstract:
The crystal structure and magnetic and piezoelectric properties of the Bi1-xCaxFeO3-x/2 system (x <= 0.2) are studied. The crystal-structure transformations occur in the following sequence: rhombohedral (R3c) polar phase (x <= 0.06) -> modulated polar phase (0.07 <= x <= 0.1) -> modulated antipolar phase (0.11 <= x <= 0.14). The modulated polar and antipolar phases are weakly ferromagnetic with a spontaneous magnetization of 0.25 G cm(3)/g (x = 0.09). In the polar weak ferromagnet with x = 0.09, a uniform piezoelectric response 2.5 times stronger than in the initial BiFeO3 compound is detected by the piezoelectric force microscopy.

Update: 11-Apr-2012

Title:
Statistical mechanics of two dimensional tilings
Authors:
Kaatz, FH; Estrada, E; Bultheel, A; Sharrock, N Author Full Names: Kaatz, Forrest H.; Estrada, Ernesto; Bultheel, Adhemar; Sharrock, Noel
Source:
PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS, 391 (10):2957-2963; 10.1016/j.physa.2012.01.013 MAY 15 2012
Abstract:
Reduced dimensionality in two dimensions is a topic of current interest. We use model systems to investigate the statistical mechanics of ideal networks. The tilings have possible applications such as the 2D locations of pore sites in nanoporous arrays (quantum dots), in the 2D hexagonal structure of graphene, and as adsorbates on quasicrystalline crystal surfaces. We calculate the statistical mechanics of these networks, such as the partition function, free energy, entropy, and enthalpy. The plots of these functions versus the number of links in the finite networks result in power law regression. We also determine the degree distribution, which is a combination of power law and rational function behavior. In the large-scale limit, the degree of these 2D networks approaches 3, 4, and 6, in agreement with the degree of the regular tilings. In comparison, a Penrose tiling has a degree also equal to about 4. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Imaging the coexistence of a superconducting phase and a charge-density modulation in the K0.73Fe1.67Se2 superconductor using a scanning tunneling microscope
Authors:
Cai, P; Ye, C; Ruan, W; Zhou, XD; Wang, AF; Zhang, M; Chen, XH; Wang, YY Author Full Names: Cai, Peng; Ye, Cun; Ruan, Wei; Zhou, Xiaodong; Wang, Aifeng; Zhang, Meng; Chen, Xianhui; Wang, Yayu
Source:
PHYSICAL REVIEW B, 85 (9):10.1103/PhysRevB.85.094512 MAR 23 2012
Abstract:
We report scanning tunneling microscopy studies of the local structural and electronic properties of the iron selenide superconductor K0.73Fe1.67Se2 with T-C = 32 K. On the atomically resolved FeSe surface, we observe a well-defined superconducting gap and the microscopic coexistence of a charge-density modulation with root 2 x root 2 periodicity with respect to the original Se lattice. We propose that a possible origin of the pattern is the electronic superstructure caused by the block-antiferromagnetic ordering of the iron moments. The widely expected iron vacancy ordering is not observed, indicating that it is not a necessary ingredient for superconductivity in the intercalated iron selenides.
Title:
A molecular "phase ordering" phase transition leading to a modulated aperiodic composite in n-heptane/urea
Authors:
Mariette, C; Huard, M; Rabiller, P; Nichols, SM; Ecolivet, C; Janssen, T; Alquist, KE; Hollingsworth, MD; Toudic, B Author Full Names: Mariette, C.; Huard, M.; Rabiller, P.; Nichols, Shane M.; Ecolivet, C.; Janssen, Ted; Alquist, Keith E., III; Hollingsworth, Mark D.; Toudic, B.
Source:
JOURNAL OF CHEMICAL PHYSICS, 136 (10):10.1063/1.3692329 MAR 14 2012
Abstract:
n-Heptane/urea is an aperiodic inclusion compound in which the ratio of host and guest repeats along the channel axis is very close to unity and is found to have a constant value (0.981) from 280 K to 90 K. Below 280 K, two phase transitions are observed. The first (T-c1 = 145 K) is a ferroelastic phase transition that generates superstructure reflections for the host while leaving the guest with 1D order. The second (T-c2 = 130 K) is a "phase ordering" transition to a four-dimensional structure (P2(1)11(0 beta gamma)) with pronounced host-guest intermodulation and a temperature dependent phase shift between guests in adjacent channels. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3692329]

Update: 5-Apr-2012

Title:
Fixed-point tile sets and their applications
Authors:
Durand, B; Romashchenko, A; Shen, A Author Full Names: Durand, Bruno; Romashchenko, Andrei; Shen, Alexander
Source:
JOURNAL OF COMPUTER AND SYSTEM SCIENCES, 78 (3):731-764; 10.1016/j.jcss.2011.11.001 MAY 2012
Abstract:
An aperiodic tile set was first constructed by R. Berger while proving the undecidability of the domino problem. It turned out that aperiodic tile sets appear in many fields, ranging from logic (the Entscheidungsproblem) to physics (quasicrystals). We present a new construction of an aperiodic tile set that is based on Kleene's fixed-point construction instead of geometric arguments. This construction is similar to J. von Neumann's self-reproducing automata: similar ideas were also used by P. Gacs in the context of error-correcting computations. This construction is rather flexible, so it can be used in many ways. We show how it can be used to implement substitution rules, to construct strongly aperiodic tile sets (in which any tiling is far from any periodic tiling), to give a new proof for the undecidability of the domino problem and related results, to characterize effectively closed one-dimensional subshifts in terms of two-dimensional subshifts of finite type (an ! improvement of a result by M. Hochman), to construct a tile set that has only complex tilings, and to construct a "robust" aperiodic tile set that does not have periodic (or close to periodic) tilings even if we allow some (sparse enough) tiling errors. For the latter, we develop a hierarchical classification of points in random sets into islands of different ranks. Finally, we combine and modify our tools to prove our main result: There exists a tile set such that all tilings have high Kolmogorov complexity even if (sparse enough) tiling errors are allowed. Some of these results were included in the DLT extended abstract (Durand et al., 2008 [9]) and in the ICALP extended abstract (Durand et al., 2009 [10]). (C) 2011 Elsevier Inc. All rights reserved.
Title:
Empirical oscillating potentials for alloys from ab initio fits and the prediction of quasicrystal-related structures in the Al-Cu-Sc system
Authors:
Mihalkovic, M; Henley, CL Author Full Names: Mihalkovic, Marek; Henley, C. L.
Source:
PHYSICAL REVIEW B, 85 (9):10.1103/PhysRevB.85.092102 MAR 19 2012
Abstract:
By fitting to a database of ab initio forces and energies, we can extract pair potentials for alloys with a simple six-parameter analytic form including Friedel oscillations, which give a remarkably faithful account of many complex intermetallic compounds. Furthermore, such potentials are combined with a method of discovering complex zero-temperature structures with hundreds of atoms per cell, given only the composition and the constraint of known lattice parameters, using molecular-dynamics quenches. We apply this approach to structure prediction in the Al-Cu-Sc quasicrystal-related system.
Title:
Magnetic Frustration in a Quantum Spin Chain: The Case of Linarite PbCuSO4(OH)(2)
Authors:
Willenberg, B; Schapers, M; Rule, KC; Sullow, S; Reehuis, M; Ryll, H; Klemke, B; Kiefer, K; Schottenhamel, W; Buchner, B; Ouladdiaf, B; Uhlarz, M; Beyer, R; Wosnitza, J; Wolter, AUB Author Full Names: Willenberg, B.; Schaepers, M.; Rule, K. C.; Suellow, S.; Reehuis, M.; Ryll, H.; Klemke, B.; Kiefer, K.; Schottenhamel, W.; Buechner, B.; Ouladdiaf, B.; Uhlarz, M.; Beyer, R.; Wosnitza, J.; Wolter, A. U. B.
Source:
PHYSICAL REVIEW LETTERS, 108 (11):10.1103/PhysRevLett.108.117202 MAR 16 2012
Abstract:
We present a combined neutron diffraction and bulk thermodynamic study of the natural mineral linarite PbCuSO4(OH)(2), this way establishing the nature of the ground-state magnetic order. An incommensurate magnetic ordering with a propagation vector k = (0, 0.186, 1/2) was found below T-N = 2.8 K in a zero magnetic field. The analysis of the neutron diffraction data yields an elliptical helical structure, where one component (0.638 mu(B)) is in the monoclinic ac plane forming an angle with the a axis of 27(2)degrees, while the other component (0.833 mu(B)) points along the b axis. From a detailed thermodynamic study of bulk linarite in magnetic fields up to 12 T, applied along the chain direction, a very rich magnetic phase diagram is established, with multiple field-induced phases, and possibly short-range-order effects occurring in high fields. Our data establish linarite as a model compound of the frustrated one-dimensional spin chain, with ferromagnetic nearest-neighbor ! and antiferromagnetic next-nearest-neighbor interactions. Long-range magnetic order is brought about by interchain coupling 1 order of magnitude smaller than the intrachain coupling.
Title:
Inelastic Neutron-Scattering Measurements of Incommensurate Magnetic Excitations on Superconducting LiFeAs Single Crystals
Authors:
Qureshi, N; Steffens, P; Drees, Y; Komarek, AC; Lamago, D; Sidis, Y; Harnagea, L; Grafe, HJ; Wurmehl, S; Buchner, B; Braden, M Author Full Names: Qureshi, N.; Steffens, P.; Drees, Y.; Komarek, A. C.; Lamago, D.; Sidis, Y.; Harnagea, L.; Grafe, H. -J.; Wurmehl, S.; Buechner, B.; Braden, M.
Source:
PHYSICAL REVIEW LETTERS, 108 (11):10.1103/PhysRevLett.108.117001 MAR 12 2012
Abstract:
Magnetic correlations in superconducting LiFeAs were studied by elastic and by inelastic neutron-scattering experiments. There is no indication for static magnetic ordering, but inelastic correlations appear at the incommensurate wave vector (0.5 +/- delta, 0.5 -/+ delta, 0) with delta similar to 0.07 slightly shifted from the commensurate ordering observed in other FeAs-based compounds. The incommensurate magnetic excitations respond to the opening of the superconducting gap by a transfer of spectral weight.
Title:
Fermi-edge polaritons in Bragg multiple-quantum-well structures
Authors:
Averkiev, NS; Glazov, MM; Voronov, MM Author Full Names: Averkiev, N. S.; Glazov, M. M.; Voronov, M. M.
Source:
SOLID STATE COMMUNICATIONS, 152 (5):395-398; 10.1016/j.ssc.2011.12.002 MAR 2012
Abstract:
The polariton propagation in one-dimensional photonic crystals and quasicrystals based on highly doped quantum-well structures has been theoretically studied. The superradiant and photonic crystal regimes have been considered and expressions for band gap edges for light waves in the Bragg structures have been obtained. The reflection and absorption spectra of such systems have been calculated and the so-called two-wave approximation to their study has been applied. The optical properties of the doped multiple-quantum-well structures are compared with those of undoped ones. (C) 2011 Elsevier Ltd. All rights reserved.

Update: 29_Mar_2012

Title:
Effect of yttrium addition on the formation and mechanical properties of Ti-Zr-Ni-Cu bulk quasicrystalline alloys
Authors:
Wang, XL (Wang, Xinlu); Zhang, SS (Zhang, Shanshan); Wang, LD (Wang, Lidong); Liu, WQ (Liu, Wanqiang); Wu, YM (Wu, Yaoming); Wang, LM (Wang, Limin) Author Full Names: Wang, XL (Wang, Xinlu); Zhang, SS (Zhang, Shanshan); Wang, LD (Wang, Lidong); Liu, WQ (Liu, Wanqiang); Wu, YM (Wu, Yaoming); Wang, LM (Wang, Limin)
Source:
JOURNAL OF ALLOYS AND COMPOUNDS Volume: 522 Pages: 96-100 DOI: 10.1016/j.jallcom.2012.01.096 Published: MAY 5 2012
Abstract:
The effect of yttrium (Y) on the structure and mechanical properties of the as-cast (Ti48Zr36Ni14Cu2)(1-x)Y-x (x = 0, 0.01 and 0.02) bulk quasicrystalline alloys was investigated. These alloys were mainly composed of icosahedral quasicrystalline phase (i-phase) accompanied by minor hexagonal C14 Laves phase and solid-solution. beta-(Ti/Zr) phase. The characterization on their mechanical properties had been carried out by means of microhardness indentation and compression tests at room temperature. The microhardness test showed that the toughness of them was much better than many other i-phase alloys because no obvious crack was detected even at the load of 4.9 N. The compressive fracture strengths first increased and then decreased with increasing x, and the highest strength was 1350 MPa when x = 0.01, it was 210 MPa higher than the without Y alloy. These results reveal that an appropriate amount of Y addition would enhance the mechanical properties of the bulk i-phase alloy. (C) 2012 Elsevier B. V. All rights reserved.
Title:
Kinetic control of structural and magnetic states in LuBaCo4O7
Authors:
Avci, S (Avci, S.); Chmaissem, O (Chmaissem, O.); Zheng, H (Zheng, H.); Huq, A (Huq, A.); Khalyavin, DD (Khalyavin, D. D.); Stephens, PW (Stephens, P. W.); Suchomel, MR (Suchomel, M. R.); Manuel, P (Manuel, P.); Mitchell, JF (Mitchell, J. F.) Author Full Names: Avci, S (Avci, S.); Chmaissem, O (Chmaissem, O.); Zheng, H (Zheng, H.); Huq, A (Huq, A.); Khalyavin, DD (Khalyavin, D. D.); Stephens, PW (Stephens, P. W.); Suchomel, MR (Suchomel, M. R.); Manuel, P (Manuel, P.); Mitchell, JF (Mitchell, J. F.)
Source:
PHYSICAL REVIEW B Volume: 85 Issue: 9 Article Number: 094414 DOI: 10.1103/PhysRevB.85.094414 Published: MAR 9 2012
Abstract:
The RBaCo4O7 (R = Ca, Y, Tb, Ho, Tm, Yb, Lu) compounds provide a novel topology for studying the competition between triangular geometry and magnetic order. Here, we report the structural and magnetic behavior of the Lu member of this series via neutron and synchrotron x-ray diffraction, magnetization, and resistivity measurements. We determined sequential phase transitions and a strong competition between a stable and a metastable low-temperature state that critically depends on controlled cooling rates and the associated heat removal kinetics. No evidence for long-range ordered magnetism was detected by neutron diffraction at any temperature. However, very slow spin dynamics are evidenced by time-dependent neutron diffraction measurements and can be explained by several competing magnetic phases with incommensurate short-range correlations coexisting in this material.
Title:
Coupling of replicate order-parameters in incommensurate multiferroics
Authors:
Mettout, B (Mettout, Bruno); Toledano, P (Toledano, Pierre) Author Full Names: Mettout, B (Mettout, Bruno); Toledano, P (Toledano, Pierre)
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER Volume: 24 Issue: 8 Article Number: 086002 DOI: 10.1088/0953-8984/24/8/086002 Published: FEB 29 2012
Abstract:
I The specific properties of incommensurate multiferroic phases resulting from the coupling of order-parameter replicates are worked out using the illustrative example of iron vanadate. The phase difference between the order-parameter copies induces an additional broken symmetry phase corresponding to the lowest symmetry of the system and varies critically at the transition to the multiferroic phase. It reflects the temperature dependence of the angle between paired spins in the antiferromagnetic spiral structure. Expressing the transition order-parameters in terms of spin-density waves allows us to show that isotropic exchange interactions contribute to the stabilization of the ferroelectric phase.
Title:
Commensurate-incommensurate transition of He-4 adsorbed on a single C-60 molecule
Authors:
Shin, H (Shin, Hyeondeok); Kwon, Y (Kwon, Yongkyung) Author Full Names: Shin, H (Shin, Hyeondeok); Kwon, Y (Kwon, Yongkyung)
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER Volume: 24 Issue: 8 Article Number: 086002 DOI: 10.1088/0953-8984/24/8/086002 Published: FEB 29 2012
Abstract:
The specific properties of incommensurate multiferroic phases resulting from the coupling of order-parameter replicates are worked out using the illustrative example of iron vanadate. The phase difference between the order-parameter copies induces an additional broken symmetry phase corresponding to the lowest symmetry of the system and varies critically at the transition to the multiferroic phase. It reflects the temperature dependence of the angle between paired spins in the antiferromagnetic spiral structure. Expressing the transition order-parameters in terms of spin-density waves allows us to show that isotropic exchange interactions contribute to the stabilization of the ferroelectric phase.

Update: 22-Mar-2012

Title:
Quasicrystal discovery-from NBS/NIST to Stockholm
Authors:
Hargittai, B; Hargittai, I Author Full Names: Hargittai, Balazs; Hargittai, Istvan
Source:
STRUCTURAL CHEMISTRY, 23 (2):301-306; 10.1007/s11224-012-9953-x APR 2012
Abstract:
There were ideal conditions in 1982 at the NBS/NIST for the kind of exploratory research that led Dan Shechtman to the quasicrystal discovery. Almost thirty years later, in 2011, Shechtman received the Nobel Prize for this achievement. What happened in between these two dates has been covered quite extensively elsewhere. But it is intriguing to learn more about the very beginning. Then, the festivities in Stockholm added to our seeing the story in a fuller perspective.
Title:
Structural aspects of the relaxation process in spin crossover solids: Phase separation, mapping of lattice strain, and domain wall structure
Authors:
Nicolazzi, W; Pillet, S Author Full Names: Nicolazzi, W.; Pillet, S.
Source:
PHYSICAL REVIEW B, 85 (9):10.1103/PhysRevB.85.094101 MAR 2 2012
Abstract:
We present a nonequilibrium study of the relaxation process in spin crossover solids using numerical simulations of a recently introduced two-variable elastic Ising-like model. We analyze the structural lattice distortions accompanying the relaxation from the metastable high-spin to the ground low-spin state as a function of cooperativity. In the highly cooperative case, a sigmoidal relaxation behavior of the high-spin fraction n(HS) is described, and it occurs jointly with a structural phase separation process. The mean lattice spacing follows a similar sigmoidal trend, owing to the interplay between electronic and lattice variables in the Hamiltonian. Weakly cooperative systems are characterized by single exponential relaxations of the high-spin fraction, the corresponding structural transformation proceeds homogeneously with a progressive relaxation of the mean lattice spacing. Long relaxation tail effects are also observed. We highlight the development of lattice strain accompanying the spin transition, and show that structural phase rebuilding proceeds in the late stage of the relaxation by releasing residual strain. Under specific conditions, a temporal decoupling between the electronic and lattice variables is observed, which may have direct applications for interpreting time-resolved spectroscopic or diffraction experiments and for elucidating unusual structural behaviors, such as the development of superstructures, modulated structures, or transient phases.
Title:
Similarity and Coincidence Isometries for Modules
Authors:
Glied, S Author Full Names: Glied, Svenja
Source:
CANADIAN MATHEMATICAL BULLETIN-BULLETIN CANADIEN DE MATHEMATIQUES, 55 (1):98-107; 10.4153/CMB-2011-076-x MAR 2012
Abstract:
The groups of (linear) similarity and coincidence isometries of certain modules Gamma in d-dimensional Euclidean space, which naturally occur in quasicrystallography, are considered. It is shown that the structure of the factor group of similarity modulo coincidence isometrics is the direct sum of cyclic groups of prime power orders that divide d. In particular, if the dimension d is a prime number p, the factor group is an elementary abelian p-group. This generalizes previous results obtained for lattices to situations relevant in quasicrystallography.
Title:
Pb3TeCo3V2O14: A Potential Multiferroic Co Bearing Member of the Dugganite Series
Authors:
Silverstein, HJ; Cruz-Kan, K; Hallas, AM; Zhou, HD; Donaberger, RL; Hernden, BC; Bieringer, M; Choi, ES; Hwang, JM; Wills, AS; Wiebe, CR Author Full Names: Silverstein, H. J.; Cruz-Kan, K.; Hallas, A. M.; Zhou, H. D.; Donaberger, R. L.; Hernden, B. C.; Bieringer, M.; Choi, E. S.; Hwang, J. M.; Wills, A. S.; Wiebe, C. R.
Source:
CHEMISTRY OF MATERIALS, 24 (4):664-670; 10.1021/cm202502p FEB 28 2012
Abstract:
Polycrystalline Pb3TeCo3V2O14, a structural analogue of the multiferroic Ba3NbFe3Si2O14, was synthesized and characterized using X-ray diffraction, magnetic susceptibility, specific heat, dielectric constant, and neutron diffraction. Magnetic susceptibility, specific heat capacity measurements, and bond valence analysis confirmed that the V5+ ion is nonmagnetic, while Co2+ is in its high spin state (S = 3/2). Two magnetic transitions were seen at T-N1 = 8.6 K and T-N2 = 6.0 K where the spins first adopt a magnetic structure with propagation vector (k) over right arrow = (0.752,0,1/2) and reorder into a commensurate structure with propagation vector (k) over right arrow = (5/6,5/6,1/2). Changes in the dielectric constant at both magnetic phase transitions suggest that magnetoelectric coupling exists in Pb3TeCo3V2O14.
Title:
Scanning-Tunneling Microscope Imaging of Single-Electron Solitons in a Material with Incommensurate Charge-Density Waves
Authors:
Brazovskii, S; Brun, C; Wang, ZZ; Monceau, P Author Full Names: Brazovskii, Serguei; Brun, Christophe; Wang, Zhao-Zhong; Monceau, Pierre
Source:
PHYSICAL REVIEW LETTERS, 108 (9):10.1103/PhysRevLett.108.096801 FEB 27 2012
Abstract:
We report on scanning-tunneling microscopy experiments in a charge-density wave (CDW) system allowing visually capturing and studying in detail the individual solitons corresponding to the self-trapping of just one electron. This "Amplitude Soliton'' is marked by vanishing of the CDW amplitude and by the pi shift of its phase. It might be the realization of the spinon-the long-sought particle (along with the holon) in the study of science of strongly correlated electronic systems. As a distinct feature we also observe one-dimensional Friedel oscillations superimposed on the CDW which develop independently of solitons.
Title:
THE DISCOVERY OF THE FIRST NATURAL QUASICRYSTAL A New Era for Mineralogy?
Authors:
Bindi, L; Steinhardt, PJ Author Full Names: Bindi, Luca; Steinhardt, Paul J.
Source:
ELEMENTS, 8 (1):13-14; 10.2113/gselements.8.1.13 FEB 2012
Abstract:
For nearly two centuries, a basic tenet of geology and solid state physics was that pure substances form crystals, periodic arrangements of atoms with a restricted set of possible symmetries. For example, the rigorous mathematical theorems of crystallography derived over 100 years ago strictly forbid solids with five-fold symmetry axes. Then, in 1984, Dan Shechtman, Ilan Blech, Denis Gratias, and John Cahn (Shechtman et al. 1984) reported the discovery of a puzzling man-made alloy of aluminum and manganese that produces a diffraction pattern of sharp spots like a crystal, but with the symmetry of an icosahedron.
Title:
Magnetic structure of the modulated martensite phase in Ni-Mn-Ga ferromagnetic shape memory alloys
Authors:
Singh, RK; Raja, MM; Mathur, RP; Shamsuddin, M Author Full Names: Singh, R. K.; Raja, M. Manivel; Mathur, R. P.; Shamsuddin, M.
Source:
MATERIALS CHEMISTRY AND PHYSICS, 132 (1):104-108; 10.1016/j.matchemphys.2011.11.003 JAN 16 2012
Abstract:
The magnetic structure of the seven layered (7 M) modulated martensite phases in Mn-rich Ni-Mn-Ga alloys was studied using Mossbauer spectroscopy. The Mossbauer results clearly demonstrate that in contrast to the non-modulated tetragonal structure two new magnetic sublattices exists for the 7M orthorhombic martensite phase. Based on the unit cell symmetry and atomic coordination, the additional magnetic sublattices have been assigned to the Ni site. The variation in the magnetic properties of the martensite phases has been related to the underlying magnetic structure. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Structural and Mechanical Characterization of Zr58.5Ti8.2Cu14.2Ni11.4Al7.7 Bulk Metallic Glass
Authors:
Prashanth, KG; Scudino, S; Khoshkhoo, MS; Surreddi, KB; Stoica, M; Vaughan, G; Eckert, J Author Full Names: Prashanth, Konda G.; Scudino, Sergio; Khoshkhoo, Mohsen Samadi; Surreddi, Kumar B.; Stoica, Mihai; Vaughan, Gavin; Eckert, Juergen
Source:
MATERIALS, 5 (1):1-11; 10.3390/ma5010001 JAN 2012
Abstract:
Thermal stability, structure and mechanical properties of the multi-component Zr58.5Ti8.2Cu14.2Ni11.4Al7.7 bulk metallic glass have been studied in detail. The glassy material displays good thermal stability against crystallization and a fairly large supercooled liquid region of 52 K. During heating, the alloy transforms into a metastable icosahedral quasicrystalline phase in the first stage of crystallization. At high temperatures, the quasicrystalline phase undergoes a transformation to form tetragonal and cubic NiZr2-type phases. Room-temperature compression tests of the as-cast sample show good mechanical properties, namely, high compressive strength of about 1,630 MPa and fracture strain of 3.3%. This is combined with a density of 6.32 g/cm(3) and values of Poisson's ratio and Young's modulus of 0.377 and 77 GPa, respectively. The mechanical properties of the glass can be further improved by cold rolling. The compressive strength rises to 1,780 MPa a! nd the fracture strain increases to 8.3% for the material cold-rolled to a diameter reduction of 10%.
Title:
Fabrication and Corrosion Resistance of Mg-Zn-Y-based Nano-quasicrystals Alloys
Authors:
Wang, ZF; Zhao, WM; Qin, CL; Cui, Y Author Full Names: Wang, Zhifeng; Zhao, Weimin; Qin, Chunling; Cui, Yan
Source:
MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS, 15 (1):51-56; 10.1590/S1516-14392012005000004 JAN-FEB 2012
Abstract:
A wedge-shaped copper mold was used to fabricate micro quasicrystals (QCs). Stable Mg-Zn-Y-based nano-QCs were directly synthesized through this simple route instead of crystallization from metallic glasses or complicated forming processes at high temperature. The study showed that on the tips of the wedge-shaped ingots, the minimum diameter of nano-QCs approach to 4 similar to 6 nm. The main size of nano-QCs is about 10 similar to 30 nm. The maximum microhardness of QCs has been dramatically improved to about HV440 which increased by about 280% compared with that of the petal-like QCs fabricated under common cast iron mold cooling conditions. Possessing a certain negative enthalpy of mixing and existence of Frank-Kasper-type phases determined the formation of Mg-Zn-Y-based nano-QCs. The further electrochemical studies showed that Mg71Zn26Y2Cu1 nano-QC alloy possess high corrosion resistance in simulated seawater and its corrosion resistance is much better than those of the Mg72Zn26Y2 and Mg71Zn26Y2Cu0.5Ni0.5 nano-QC alloys.

Update: 7-Mar-2012

Title:
Continuous magnetic and structural phase transitions in Fe1+yTe
Authors:
Zaliznyak, IA; Xu, ZJ; Wen, JS; Tranquada, JM; Gu, GD; Solovyov, V; Glazkov, VN; Zheludev, AI; Garlea, VO; Stone, MB Author Full Names: Zaliznyak, I. A.; Xu, Z. J.; Wen, J. S.; Tranquada, J. M.; Gu, G. D.; Solovyov, V.; Glazkov, V. N.; Zheludev, A. I.; Garlea, V. O.; Stone, M. B.
Source:
PHYSICAL REVIEW B, 85 (8):10.1103/PhysRevB.85.085105 FEB 13 2012
Abstract:
We report a sequence of continuous phase transformations in iron telluride, Fe1+yTe with y = 0.10(1), which is observed by combining neutron diffraction, magnetic susceptibility, and specific-heat measurements on single-crystal samples. While a gradual increase of magnetic scattering near the wave vector (0.5,0,0.5) is seen below T approximate to 70 K, a temperature where the discontinuous first-order magnetostructural phase transition is found in systems with small y (less than or similar to 0.06), the reduction of the lattice symmetry in Fe1.1Te only occurs at T-s approximate to 63 K. Below T-N approximate to 57.5 K, the long-range magnetic order develops, the incommensurate wave vector Q(m) of which varies with temperature. Finally, at T-m less than or similar to 45 K, the system enters the low-T phase, where Q(m) is locked at approximate to (0.48,0,0.5). We conclude that these instabilities are weak compared to the strength of the underlying interactions, and we suggest that the impact of the Fe interstitials on the transitions can be treated with random-field models.
Title:
Defect-induced spin-glass magnetism in incommensurate spin-gap magnets
Authors:
Andrade, EC; Vojta, M Author Full Names: Andrade, E. C.; Vojta, M.
Source:
EPL, 97 (3):10.1209/0295-5075/97/37007 FEB 2012
Abstract:
We study magnetic order induced by non-magnetic impurities in quantum paramagnets with incommensurate host spin correlations. In contrast to the well-studied commensurate case where the defect-induced magnetism is spatially disordered but non-frustrated, the present problem combines strong disorder with frustration and, consequently, leads to spin-glass order. We discuss the crossover from strong randomness in the dilute limit to more conventional glass behavior at larger doping, and numerically characterize the robust short-range order inherent to the spin-glass phase. We relate our findings to magnetic order in both BiCu2PO6 and YBa2Cu3O6.6 induced by Zn substitution. Copyright (C) EPLA, 2012
Title:
QUASICRYSTALS Unearthly beauty
Authors:
Trabesinger, A Author Full Names: Trabesinger, Andreas
Source:
NATURE PHYSICS, 8 (2):112-112; FEB 2012

Update: 29-Feb-2012

Title:
Fermi surface reconstruction in CeTe2 induced by charge density waves investigated via angle resolved photoemission
Authors:
Kang, JS; Kim, DH; Lee, HJ; Hwang, J; Lee, HK; Kim, HD; Min, BH; Lee, KE; Kwon, YS; Kim, JW; Kim, K; Kim, BH; Min, BI Author Full Names: Kang, J-S.; Kim, D. H.; Lee, H. J.; Hwang, Jihoon; Lee, Han-Koo; Kim, H-D; Min, B. H.; Lee, K. E.; Kwon, Y. S.; Kim, J. W.; Kim, Kyoo; Kim, B. H.; Min, B. I.
Source:
PHYSICAL REVIEW B, 85 (8):10.1103/PhysRevB.85.085104 FEB 10 2012
Abstract:
Electronic structures of a charge-density wave (CDW) system CeTe2-xSbx (x = 0, 0.05) have been investigated by employing angle-resolved photoemission spectroscopy (ARPES) and the first-principles electronic and phonon band-structure methods. The observed Fermi surface (FS) agrees very well with the calculated FS for the undistorted CeTe2 both in shapes and sizes. The metallic states crossing the Fermi level (E-F) are observed in ARPES even in the CDW state. The carriers near E-F have mainly the Te(1) 5p character, with a negligible contribution from Ce 4f states. The supercell (shadow) bands and the corresponding very weak FSs are found to arise from band folding due to the interaction of Te(1) layers with Ce-Te(2) layers. We found that the CDW modulation vector is along Gamma-X (Q(CDW) approximate to X), which is not coincident with the most prominent FS nesting vector.
Title:
Examining the structure and bonding in complex oxides using aberration-corrected imaging and spectroscopy
Authors:
Klie, RF; Qiao, Q; Paulauskas, T; Ramasse, Q; Oxley, MP; Idrobo, JC Author Full Names: Klie, R. F.; Qiao, Q.; Paulauskas, T.; Ramasse, Q.; Oxley, M. P.; Idrobo, J. C.
Source:
PHYSICAL REVIEW B, 85 (5):10.1103/PhysRevB.85.054106 FEB 10 2012
Abstract:
Our ability to directly characterize the atomic and electronic structures is crucial to developing a fundamental understanding of structure-property relationships in complex-oxide materials. Here, we examine one specific example, the misfit-layered thermoelectric material Ca3Co4O9, which exhibits a high Seebeck coefficient governed by spin-entropy transport as well as hopping-mediated electron transport. However, the role of oxygen and its bonding with cobalt in thermoelectric transport remains unclear. We use atomic-resolution annular bright-field imaging to directly image the oxygen sublattice and to combine our experimental data with multislice image calculations to find that the oxygen atoms in the CoO2 subsystem are highly ordered, while the oxygen-atomic columns are displaced in the Ca2CoO3 subsystem. Atomic-column-resolved electron energy-loss spectroscopy and spectrum image calculations are used to quantify the bonding in the different subsystems of! incommensurate Ca3Co4O9. We find that the holes in the CoO2 subsystem are delocalized, which could be responsible for the p-type conductivity found in the CoO2 subsystem.
Title:
Giant Improper Ferroelectricity in the Ferroaxial Magnet CaMn7O12
Authors:
Johnson, RD; Chapon, LC; Khalyavin, DD; Manuel, P; Radaelli, PG; Martin, C Author Full Names: Johnson, R. D.; Chapon, L. C.; Khalyavin, D. D.; Manuel, P.; Radaelli, P. G.; Martin, C.
Source:
PHYSICAL REVIEW LETTERS, 108 (6):10.1103/PhysRevLett.108.067201 FEB 6 2012
Abstract:
In rhombohedral CaMn7O12, an improper ferroelectric polarization of magnitude 2870 mu Cm-2 is induced by an incommensurate helical magnetic structure that evolves below T-N1 = 90 K. The electric polarization was found to be constrained to the high symmetry threefold rotation axis of the crystal structure, perpendicular to the in-plane rotation of the magnetic moments. The multiferroicity is explained by the ferroaxial coupling mechanism, which in CaMn7O12 gives rise to the largest magnetically induced, electric polarization measured to date.
Title:
The effect of Li-substitution on the M-phases of AgNbO3
Authors:
Khan, HU; Sterianou, I; Miao, S; Pokorny, J; Reaney, IM Author Full Names: Khan, H. U.; Sterianou, I.; Miao, S.; Pokorny, J.; Reaney, I. M.
Source:
JOURNAL OF APPLIED PHYSICS, 111 (2):10.1063/1.3677871 JAN 15 2012
Abstract:
Ceramics in the solid solution, LixAg1-xNbO3 (LAN) with 0 <= x <= 0.20, have been synthesized by the mixed oxide method. X-ray diffraction (XRD) revealed that only compositions with x <= 0.05 were single phase which were indexed according to Pbcm symmetry with a unit cell, root 2a(p) x root 2a(p) x 4a(p) (where a(p) is the fundamental perovskite lattice parameter). For compositions with x >= 0.1, second phase peaks attributed to LiNbO3 were observed and the matrix phase transformed to a metrically rhombohedral structure according to XRD. A phase transition at 0.05 < x <= 0.1 was confirmed by Raman spectroscopy and electron diffraction but the latter technique revealed superstructure reflections for x >= 0.1 at +/- 1/6{00l} and 1/2{ooo} +/- 1/6{00l} (where o = odd). These support the premise that Li doping invokes a new complex modulated tilt system with a root 2a(p) x root 2a(p) x 6a(p) unit cell rather than root 2a(p) x root 2a(p) x 4a(p) (Pbcm). Reflections of the type +/- 1/6{00l} are, however, streaked along the inverted right perpendicular001inverted left perpendicular direction indicating that the structure may be incommensurate or only partially ordered. The appearance of the root 2a(p) x root 2a(p) x 6a(p) structure is associated with strong asymmetry in the peak in permittivity attributed to the M-3-M-2 and a decrease in intensity of the peak in permittivity associated with the M-2-M-1 transition. Slim polarization versus field curves characteristic of weak ferroelectricity were observed for compositions with x <= 0.05 but for higher values of x the loops were unsaturated albeit with larger remanent polarization. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3677871]
Title:
Structural phase transitions of FeCo and FeNi nanoparticles: A molecular dynamics study
Authors:
Meng, LJ; Peng, XY; Zhang, KW; Tang, C; Zhong, JX Author Full Names: Meng, L. J.; Peng, X. Y.; Zhang, K. W.; Tang, C.; Zhong, J. X.
Source:
JOURNAL OF APPLIED PHYSICS, 111 (2):10.1063/1.3675275 JAN 15 2012
Abstract:
We have investigated the structural phase transition of FeCo and FeNi nanoparticles by molecular dynamics (MD) simulation using the generalized embedded atom potential (GEAM). It is found that the phase varies with the atomic compositions and annealing processes. By using the Honeycutt and Andersen index (HA index), bond order parameters (BOP) and pair correlation function (PCF), we found that a BCC to defective icosahedra phase transition occurs in the FeCo nanoparticle when Co composition is increased to about 60 at %. In the FeNi nanoparticle, three phases have been identified, namely, the BCC phase, the mixed BCC/FCC phase, and the multilayer defective icosahedral phase, which correspond to the Ni compositions of 0-20 at %, 20-70 at %, and 70-100 at %, respectively. Our simulations have well reproduced the phase transition points and most of the phases observed in recent experiments. (C) 2012 American Institute of Physics. [doi:10.1063/1.3! 675275]
Title:
Effect of Thermal Fluctuations on Magnetic Phase Separation and on the Parameters of Spin-Spiral Waves
Authors:
Arzhnikov, AK; Groshev, AG Author Full Names: Arzhnikov, A. K.; Groshev, A. G.
Source:
JETP LETTERS, 94 (9):703-707; 10.1134/S002136401121003X JAN 2012
Abstract:
Effects of temperature on magnetic phase separation and on the parameters of spin-spiral waves are studied. The study is performed using the two-dimensional single-band Hubbard model and the Hubbard-Stratonovich transformation. Both commensurate (antiferromagnetic, ferromagnetic) and incommensurate (spiral) magnetic phases are considered. The problem is solved using the static approximation with allowance for transverse fluctuations of the magnetic moment. It is shown that the temperature significantly affects the collinear and spiral magnetic phases. With an increase in the temperature, the phase-separation region near the half-filling is sufficiently reduced and substituted by the antiferromagnetic phase. The results are used for the interpretation of the magnetic properties of cuprates.

Update: 23-Feb-2012

Title:
Evidence of oxygen-dependent modulation in LuFe2O4
Authors:
Bourgeois, J; Hervieu, M; Poienar, M; Abakumov, AM; Elkaim, E; Sougrati, MT; Porcher, F; Damay, F; Rouquette, J; Van Tendeloo, G; Maignan, A; Haines, J; Martin, C Author Full Names: Bourgeois, J.; Hervieu, M.; Poienar, M.; Abakumov, A. M.; Elkaim, E.; Sougrati, M. T.; Porcher, F.; Damay, F.; Rouquette, J.; Van Tendeloo, G.; Maignan, A.; Haines, J.; Martin, C.
Source:
PHYSICAL REVIEW B, 85 (6):10.1103/PhysRevB.85.064102 FEB 6 2012
Abstract:
A polycrystalline sample of LuFe2O4 has been investigated by means of powder synchrotron x-ray and neutron diffraction and transmission electron microscopy (TEM), along with Mossbauer spectroscopy and transport and magnetic properties. A monoclinic distortion is unambiguously evidenced, and the crystal structure is refined in the monoclinic C2/m space group [a(M) = 5.9563(1) angstrom, b(M) = 3.4372(1) angstrom, c(M) = 8.6431(1) angstrom, beta = 103.24(1)degrees]. Along with the previously reported modulations distinctive of the charge-ordering (CO) of the iron species, a new type of incommensurate order is observed, characterized by a vector (q) over right arrow (1) = alpha(1)(a) over right arrow (M)* + gamma(1)(c) over right arrow (M)* (with alpha(1) congruent to 0.55, gamma(1) congruent to 0.13). In situ heating TEM observations from 300 to 773 K confirm that the satellites associated with (q) over right arrow (1) vanish completely, only at a temperature significantly higher than the CO temperature. This incommensurate modulation has a displacive character and corresponds primarily to a transverse displacive modulation wave of the Lu cations position, as revealed by the high resolution, high angle annular dark field scanning TEM images and in agreement with synchrotron data refinements. Analyses of vacuum-annealed samples converge toward the hypothesis of a new ordering mechanism, associated with a tiny oxygen deviation from the O-4 stoichiometry.
Title:
Embedded atom method potentials for Al-Pd-Mn phases
Authors:
Schopf, D; Brommer, P; Frigan, B; Trebin, HR Author Full Names: Schopf, Daniel; Brommer, Peter; Frigan, Benjamin; Trebin, Hans-Rainer
Source:
PHYSICAL REVIEW B, 85 (5):10.1103/PhysRevB.85.054201 FEB 3 2012
Abstract:
A novel embedded atom method (EAM) potential for the Xi phases of Al-Pd-Mn has been determined with the force-matching method. Different combinations of analytic functions were tested for the pair and transfer part. The best results are obtained if one allows for oscillations on two different length scales. These potentials stabilize structure models of the Xi phases and describe their energy with high accuracy. Simulations at temperatures up to 1200 K show very good agreement with ab initio results with respect to stability and dynamics of the system.
Title:
Composition dependent elastic modulus and phase stability of Ni2MnGa based ferromagnetic shape memory alloys
Authors:
Hu, QM; Luo, HB; Li, CM; Vitos, L; Yang, R Author Full Names: Hu QingMiao; Luo HuBin; Li ChunMei; Vitos, Levente; Yang Rui
Source:
SCIENCE CHINA-TECHNOLOGICAL SCIENCES, 55 (2):295-305; 10.1007/s11431-011-4670-z FEB 2012
Abstract:
Ni2MnGa based ferromagnetic alloys are ideal candidates for applications such as actuators, magnetic refrigerators or magnetostrictive transducers due to their attractive properties such as magnetic field induced shape memory effect and large magnetocaloric effect. The properties of these alloys (e.g., the martensitic transformation temperature T (M) ) sensitively depend on the composition. Understanding the composition dependence of these properties so as to design the alloy as desired is one of the main research topics in this area. In recent years, we have investigated the composition dependent elastic modulus and phase stability of Ni2MnGa-based alloys by using a first-principles method, in hope of clarifying their connection to the properties of these alloys. In this article, we review the main results of our investigations. We show that the tetragonal shear modulus C' is a better predictor of the composition dependent T (M) than the number of valence electrons per atom! (e/a) since the general T (M) similar to C' correlation works for some of the alloys for which the T (M) similar to e/a correlation fails, although there exist several cases for which both the general T (M) similar to C' and T (M)similar to e/a correlations break down. Employing the experimentally determined modulation function, the complex 5-layer modulated (5M) structure of the martensite of Ni2MnGa and the Al-doping effect on it are studied. We find that the shuffle and shear of the 5M structure are linearly coupled. The relative stability of the austenite and the martensites is examined by comparing their total energies. The non-modulated martensite beta aEuro(3)aEuro(2) with the tetragonality of the unit cell c/a > 1 is shown to be globally stable whereas the 5M martensite with c/a < 1 is metastable. The critical Al atomic fraction over which the martensitic transformation between the 5M martensite and austenite cannot occur is predicted to be 0.26, in reasonable agreement with experimental findings.
Title:
Helical scattering signatures of strain and electronic textures in YbFe2O4 from three-dimensional reciprocal-space imaging
Authors:
Hearmon, AJ; Prabhakaran, D; Nowell, H; Fabrizi, F; Gutmann, MJ; Radaelli, PG Author Full Names: Hearmon, Alexander J.; Prabhakaran, Dharmalingam; Nowell, Harriott; Fabrizi, Federica; Gutmann, Matthias J.; Radaelli, Paolo G.
Source:
PHYSICAL REVIEW B, 85 (1):10.1103/PhysRevB.85.014115 JAN 27 2012
Abstract:
The insulating ternary oxide YbFe2O4 displays an unusual frustration-driven incommensurate charge-ordering (CO) transition, linked to possible ferroelectricity. Based on high-resolution synchrotron data, we report a detailed structural model showing that the CO phase is an incommensurate charge-density wave and cannot be ferroelectric, since the electrical dipole moments are also incommensurately modulated. The change between continuous and "spotty" helices of scattering at the CO transition is attributed to three-dimensional fluctuations of the direction of the ordering wave vector.
Title:
Atomic-Scale Imaging and Quantification of Electrical Polarisation in Incommensurate Antiferroelectric Lanthanum-Doped Lead Zirconate Titanate
Authors:
MacLaren, I; Villaurrutia, R; Schaffer, B; Houben, L; Pelaiz-Barranco, A Author Full Names: MacLaren, Ian; Villaurrutia, Rafael; Schaffer, Bernhard; Houben, Lothar; Pelaiz-Barranco, Aime
Source:
ADVANCED FUNCTIONAL MATERIALS, 22 (2):261-266; 10.1002/adfm.201101220 JAN 25 2012
Abstract:
Lanthanum doping of zirconium rich lead zirconate titanate gives rise to incommensurate, long-period antiferroelectric structures. The structure of two stacking sequences in this incommensurate phase is determined using quantitative analysis of high-resolution scanning transmission electron microscopy images, with the lead atom positions located with an exceptional precision of about 6 pm. This allows the estimation of local polarisation variations across the stacking units, and the polarisation varies in an approximately sinusoidal fashion along the stacking direction. The measured peak Pb atom displacements of about 28 pm and peak polarisation values of about 60 mu C cm-2 match extremely well to reported values for the commensurate antiferroelectric PbZrO3 phase.
Title:
Origin of the Large Polarization in Multiferroic YMnO3 Thin Films Revealed by Soft- and Hard-X-Ray Diffraction
Authors:
Wadati, H; Okamoto, J; Garganourakis, M; Scagnoli, V; Staub, U; Yamasaki, Y; Nakao, H; Murakami, Y; Mochizuki, M; Nakamura, M; Kawasaki, M; Tokura, Y Author Full Names: Wadati, H.; Okamoto, J.; Garganourakis, M.; Scagnoli, V.; Staub, U.; Yamasaki, Y.; Nakao, H.; Murakami, Y.; Mochizuki, M.; Nakamura, M.; Kawasaki, M.; Tokura, Y.
Source:
PHYSICAL REVIEW LETTERS, 108 (4):10.1103/PhysRevLett.108.047203 JAN 24 2012
Abstract:
We investigated the magnetic structure of an orthorhombic YMnO3 thin film by resonant soft x-ray and hard x-ray diffraction. We observed a temperature-dependent incommensurate magnetic reflection below 45 K and a commensurate lattice-distortion reflection below 35 K. These results demonstrate that the ground state is composed of coexisting E-type and cycloidal states. Their different ordering temperatures clarify the origin of the large polarization to be caused by the E-type antiferromagnetic states in the orthorhombic YMnO3 thin film.
Title:
Quasicrystals or - for What The Nobel Prize in Chemistry Was Awarded in 2011
Authors:
Michalcova, A Author Full Names: Michalcova, Alena
Source:
CHEMICKE LISTY, 106 (1):55-57; 2012
Abstract:
Quasicrystals are aperiodic objects in three dimensional space which exhibit 5-, 8-, 10 a 12- fold rotational symmetry forbidden in classical crystallography. They were discovered by Daniel Shechtman in rapidly solidified AlMn14 alloy in 1982. He managed to get over initial dislike of scientists community and for his significant work he was awarded The Nobel Prize in Chemistry 2011.
Title:
Magnetic phase transitions in the NdFe3(BO3)(4) multiferroic
Authors:
Zvyagina, GA; Zhekov, KR; Bilych, IV; Zvyagin, AA; Gudim, IA; Temerov, VL Author Full Names: Zvyagina, G. A.; Zhekov, K. R.; Bilych, I. V.; Zvyagin, A. A.; Gudim, I. A.; Temerov, V. L.
Source:
LOW TEMPERATURE PHYSICS, 37 (12):1010-1020; 10.1063/1.3674182 DEC 2011
Abstract:
Low-temperature studies of the behavior of the sound velocity and attenuation of acoustic modes have been performed on a single crystal NdFe3(BO3)(4) Transitions of the magnetic subsystem to the antiferromagnetically ordered state at T-N approximate to 30.6 K have been revealed in the temperature behavior of the elastic characteristics. The features in the temperature behavior of elastic characteristics of the neodymium ferroborate and its behavior in the external magnetic field, applied in the basic plane of the crystal, permit us to suppose that the transition to an incommensurate spiral phase is realized in the system. This phase transition behaves as the first order one. H-T phase diagrams for the cases H parallel to a and H parallel to b have been constructed. The phenomenological theory, which explains observed features, has been developed. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3674182]

Update: 15-Feb-2012

Title:
Evidence for the extraterrestrial origin of a natural quasicrystal
Authors:
Bindi, L; Eiler, JM; Guan, YB; Hollister, LS; MacPherson, G; Steinhardt, PJ; Yao, N Author Full Names: Bindi, Luca; Eiler, John M.; Guan, Yunbin; Hollister, Lincoln S.; MacPherson, Glenn; Steinhardt, Paul J.; Yao, Nan
Source:
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 109 (5):1396-1401; 10.1073/pnas.1111115109 JAN 31 2012
Abstract:
We present evidence that a rock sample found in the Koryak Mountains in Russia and containing icosahedrite, an icosahedral quasicrystalline phase with composition Al(63)Cu(24)Fe(13), is part of a meteorite, likely formed in the early solar system about 4.5 Gya. The quasicrystal grains are intergrown with diopside, forsterite, stishovite, and additional metallic phases [khatyrkite (CuAl(2)), cupalite (CuAl), and beta-phase (AlCuFe)]. This assemblage, in turn, is enclosed in a white rind consisting of diopside, hedenbergite, spinel (MgAl(2)O(4)), nepheline, and forsterite. Particularly notable is a grain of stishovite (from the interior), a tetragonal polymorph of silica that only occurs at ultrahigh pressures (>= 10 Gpa), that contains an inclusion of quasicrystal. An extraterrestrial origin is inferred from secondary ion mass spectrometry (18)O/(16)O and (17)O/(16)O measurements of the pyroxene and olivine intergrown with the metal that show them to have isotopic compositions unlike any terrestrial minerals and instead overlap those of anhydrous phases in carbonaceous chondrite meteorites. The spinel from the white rind has an isotopic composition suggesting that it was part of a calcium-aluminum-rich inclusion similar to those found in CV3 chondrites. The mechanism that produced this exotic assemblage is not yet understood. The assemblage (metallic copper-aluminum alloy) is extremely reduced, and the close association of aluminum (high temperature refractory lithophile) with copper (low temperature chalcophile) is unexpected. Nevertheless, our evidence indicates that quasicrystals can form naturally under astrophysical conditions and remain stable over cosmic timescales, giving unique insights on their existence in nature and stability.
Title:
Femtosecond Dynamics of the Collinear-to-Spiral Antiferromagnetic Phase Transition in CuO
Authors:
Johnson, SL; de Souza, RA; Staub, U; Beaud, P; Mohr-Vorobeva, E; Ingold, G; Caviezel, A; Scagnoli, V; Schlotter, WF; Turner, JJ; Krupin, O; Lee, WS; Chuang, YD; Patthey, L; Moore, RG; Lu, D; Yi, M; Kirchmann, PS; Trigo, M; Denes, P; Doering, D; Hussain, Z; Shen, ZX; Prabhakaran, D; Boothroyd, AT Author Full Names: Johnson, S. L.; de Souza, R. A.; Staub, U.; Beaud, P.; Moehr-Vorobeva, E.; Ingold, G.; Caviezel, A.; Scagnoli, V.; Schlotter, W. F.; Turner, J. J.; Krupin, O.; Lee, W. -S.; Chuang, Y. -D.; Patthey, L.; Moore, R. G.; Lu, D.; Yi, M.; Kirchmann, P. S.; Trigo, M.; Denes, P.; Doering, D.; Hussain, Z.; Shen, Z. -X.; Prabhakaran, D.; Boothroyd, A. T.
Source:
PHYSICAL REVIEW LETTERS, 108 (3):10.1103/PhysRevLett.108.037203 JAN 19 2012
Abstract:
We report on the ultrafast dynamics of magnetic order in a single crystal of CuO at a temperature of 207 K in response to strong optical excitation using femtosecond resonant x-ray diffraction. In the experiment, a femtosecond laser pulse induces a sudden, nonequilibrium increase in magnetic disorder. After a short delay ranging from 400 fs to 2 ps, we observe changes in the relative intensity of the magnetic ordering diffraction peaks that indicate a shift from a collinear commensurate phase to a spiral incommensurate phase. These results indicate that the ultimate speed for this antiferromagnetic reorientation transition in CuO is limited by the long-wavelength magnetic excitation connecting the two phases.
Title:
Chiral Quasicrystalline Order and Dodecahedral Geometry in Exceptional Families of Viruses
Authors:
Konevtsova, OV; Rochal, SB; Lorman, VL Author Full Names: Konevtsova, O. V.; Rochal, S. B.; Lorman, V. L.
Source:
PHYSICAL REVIEW LETTERS, 108 (3):10.1103/PhysRevLett.108.038102 JAN 19 2012
Abstract:
On the example of exceptional families of viruses we (i) show the existence of a completely new type of matter organization in nanoparticles, in which the regions with a chiral pentagonal quasicrystalline order of protein positions are arranged in a structure commensurate with the spherical topology and dodecahedral geometry, (ii) generalize the classical theory of quasicrystals (QCs) to explain this organization, and (iii) establish the relation between local chiral QC order and nonzero curvature of the dodecahedral capsid faces.
Title:
The success story of crystallography
Authors:
Schwarzenbach, D Author Full Names: Schwarzenbach, Dieter
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 227 (1):52-62; 10.1524/zkri.2012.1453 2012
Abstract:
Diffractionists usually place the birth of crystallography in 1912 with the first X-ray diffraction experiment of Friedrich, Knipping and Laue. This discovery propelled the mathematical branch of mineralogy to global importance and enabled crystal structure determination. Knowledge of the geometrical structure of matter at atomic resolution had revolutionary consequences for all branches of the natural sciences: physics, chemistry, biology, earth sciences and material science. It is scarcely possible for a single person in a single article to trace and appropriately value all of these developments. This article presents the limited, subjective view of its author and a limited selection of references. The bulk of the article covers the history of X-ray structure determination from the NaCl structure to aperiodic structures and macromolecular structures. The theoretical foundations were available by 1920. The subsequent success of crystallography was then due to the development of diffraction equipment, the theory of the solution of the phase problem, symmetry theory and computers. The many structures becoming known called for the development of crystal chemistry and of data banks. Diffuse scattering from disordered structures without and with partial long-range order allows determination of short-range order. Neutron and electron scattering and diffraction are also mentioned.
Title:
ELECTRONIC SPECTRA AND PHASE TRANSITIONS IN THIN [N(CH(3))(4)](2)CuCl(4) MICROCRYSTALS
Authors:
Shymkiv, RM; Sveleba, SA; Karpa, IV; Katerynchuk, IN; Kunyo, IM; Phitsych, EI Author Full Names: Shymkiv, R. M.; Sveleba, S. A.; Karpa, I. V.; Katerynchuk, I. N.; Kunyo, I. M.; Phitsych, E. I.
Source:
JOURNAL OF APPLIED SPECTROSCOPY, 78 (6):823-828; JAN 2012
Abstract:
Optical absorption spectra in thin [N(CH(3))(4)](2)CuCl(4) crystals in the thickness range 10 mu m <= d < 00 mu m have been studied. Strengthening of the crystal field has been found with a decrease in the [N(CH(3))(4)](2)CuCl(4) crystal size. The reasons for absorption band shifts in the visible region depending on the [N(CH(3))(4)](2)CuCl(4) crystal thickness and the manifestation of a size effect in crystals with an incommensurate superstructure are discussed.
Title:
Quasicrystal as a Reinforcement Material in Magnesium Alloys
Authors:
Chang, HJ; Kim, WT; Kim, DH Author Full Names: Chang, Hye Jung; Kim, Won Tae; Kim, Do Hyang
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1176-1184; SI 10.1002/ijch.201100133 DEC 2011
Abstract:
The existence of the two-phase region (icosahedral phase (I-phase) + a-Mg) in the Mg-rich corner of the Mg-Zn-Y system indicates that composites consisting of I-phase and ductile a-Mg can be fabricated by a simple solidification process. Alloys with a range of combined strength and ductility can be designed by changing the fraction of the I-phase. Strengthening in proportion with increasing the volume fraction of I-phase can be explained by the effect of dispersion hardening due to the presence of finely dispersed I-phase particles. When quasicrystals exist in the a-Mg matrix as a second phase in Mg-Zn-Y alloys, the quasicrystals are stable against coarsening during thermomechanical processes such as hot rolling and high-temperature forming, due to the low interfacial energy of the quasicrystals with the a-Mg crystalline matrix, which provides strong bonding properties at the I-phase/matrix interface. Therefore, quasicrystal-reinforced Mg-Zn-Y alloys exhibit a much better combination of mechanical properties and formability than commercially used alloys such as AZ31 and AZ 61.
Title:
A Cluster-Resonance Criterion for Al-TM Quasicrystal Compositions
Authors:
Chen, H; Qiang, JB; Wang, Q; Wang, YM; Dong, C Author Full Names: Chen, Hua; Qiang, Jianbing; Wang, Qing; Wang, Yingmin; Dong, Chuang
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1226-1234; SI 10.1002/ijch.201100139 DEC 2011
Abstract:
Compositions of binary Al-TM (TM=Cr to Ni) quasicrystals are interpreted with a unified cluster formula [icosahedron](glue)1 using the newly developed clusterresonance model and the e/a formalism. The icosahedra are chosen from the corresponding approximants by considering large radial atomic density, high degree of isolation, and narrow distribution of the shell atoms. Icosahedral quasicrystals are expressed by an icosahedron plus one averaged icosahedron atom as the glue atom [icosahedron](icosahedron/13)1, characterized by e/a similar to 1.831.85, while decagonal quasicrystals are expressed by an icosahedron plus one TM atom, with e/a similar to 1.711.78. The total electrons accommodated in unit cluster formulas of different Al-TM quasicrystals have the same value approaching 24, which implies that the cluster formulas are both chemical and electronic structural units.
Title:
Gas-Surface Interactions on Quasicrystals
Authors:
Curtarolo, S; Setyawan, W; Diehl, RD Author Full Names: Curtarolo, Stefano; Setyawan, Wahyu; Diehl, Renee D.
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1304-1313; SI 10.1002/ijch.201100129 DEC 2011
Abstract:
To commemorate the awarding of the Nobel Prize for Chemistry to Daniel Shechtman for his discovery of quasicrystals, this paper reviews our recent studies of the interaction of rare gases and hydrocarbon gases with the tenfold surface of quasicrystalline decagonal Al-Co-Ni.
Title:
Phonons and Phasons in Icosahedral Quasicrystals
Authors:
de Boissieu, M Author Full Names: de Boissieu, Marc
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1292-1303; SI 10.1002/ijch.201100131 DEC 2011
Abstract:
The discovery of quasicrystals not only has changed our view on long-range order, but was a breakthrough for solid state physics and chemistry, since the Bloch theorem can no longer be applied. We review some of the results obtained for icosahedral quasicrystals for lattice dynamics and phonons, as well as for phason modes, which are diffusive excitations characteristic of the quasicrystalline state.
Title:
Decagonal Quasicrystals and Approximants: Two-Dimensional or Three-Dimensional Solids?
Authors:
Dolinsek, J; Smontara, A Author Full Names: Dolinsek, Janez; Smontara, Ana
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1246-1256; SI 10.1002/ijch.201100132 DEC 2011
Abstract:
Crystallographic structures of decagonal quasicrystals (d-QCs) are traditionally described as a periodic stacking of atomic planes with quasiperiodic in-plane atomic order, so that d-QCs are considered to be two-dimensional (2D) quasicrystals, whereas they are periodic crystals in the third dimension. Similar stacked-layer structures are observed also in the periodic decagonal approximant phases. In this review paper, we consider the dimensionality of the chemical bonding network in the d-QCs and their approximants on the basis of electrical resistivity. By comparing the anisotropic resistivity along the stacking- and the in-plane directions of a series of decagonal approximants with different numbers of atomic layers within one periodicity unit (the two-layer Y-Al-Co-Ni, the four-layer o-Al13Co4, Al13Fe4 and Al13(Fe,Ni)4, and the six-layer Al4(Cr,Fe) and T-Al3(Mn,Fe)) and of a two-layer d-Al-Co-Ni decagonal quasicrystal, we show that universally, the stacking direction perpendicular to the atomic planes is always the most conducting one. Since the in-plane electrical resistivities are of the same order of magnitude as the resistivity along the stacking direction, this confirms the 3D character of the investigated solids. The stacked-layer description in terms of 2D atomic planes should therefore be regarded as a convenient geometrical approach to describe the complex structures of the d-QCs and their approximants, whereas their physical properties are those of true 3D solids.
Title:
So Useful, Those Quasicrystals
Authors:
Dubois, JM Author Full Names: Dubois, Jean-Marie
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1168-1175; SI 10.1002/ijch.201100149 DEC 2011
Abstract:
For years, the community working on quasicrystals in many countries in the world was expecting the ultimate recognition of its contribution to the advancement of crystal chemistry, solid-state physics, mathematics, and other fields. Nearly thirty years after the initial discovery, it was finally awarded in October 2011 to Prof. Danny Shechtman by the Nobel Committee for Physics and Chemistry. Many, most often independent, achievements contributed to this success. The purpose of this article is to chronicle the role played by the applications of quasicrystals and related compounds in the development of the field and its financing by governmental institutions as well as private companies. Those applications, potential or realized, have made the field of quasicrystals comprehensible to the general public and to decision makers all over the world, including in Stockholm, in spite of its rather complicated high-dimensional crystallographic background, and in spite of the absolute opposition that a great chemist manifested against it in its infancy.
Title:
Metadislocations in Complex Metallic Alloys and their Relation to Dislocations in Icosahedral Quasicrystals
Authors:
Feuerbacher, M; Heggen, M Author Full Names: Feuerbacher, Michael; Heggen, Marc
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1235-1245; SI 10.1002/ijch.201100142 DEC 2011
Abstract:
Complex metallic alloys and quasicrystals are closely related. Both possess icosahedral local order, but while in quasicrystals the long-range order and hence the macroscopic structure is also icosahedral, in complex metallic alloys a periodic structure with large lattice parameters is formed. Metadislocations are novel and highly complex structural defects in complex metallic alloys. Focusing on metadislocations in e-type phases, we will review the basic geometric concepts of metadislocations and the relation between the number of phason planes, Burgers vector, and the elastic energy. The properties of dislocations in icosahedral Al-Pd-Mn will briefly be recalled and discussed in relation to metadislocations.
Title:
Thin Film Growth on Quasicrystalline Surfaces
Authors:
Fournee, V; Ledieu, J; Shimoda, M; Krajci, M; Sharma, HR; McGrath, R Author Full Names: Fournee, Vincent; Ledieu, Julian; Shimoda, Masahiko; Krajci, Marian; Sharma, Hem-Raj; McGrath, Ronan
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1314-1325; SI 10.1002/ijch.201100141 DEC 2011
Abstract:
The surfaces of quasicrystals have proved to be a very interesting playground for thin film growth. They offer a complex potential energy surface where heterogeneous nucleation of islands at specific quasilattice sites is frequently observed. These islands tend to locally adopt the symmetry of the quasicrystalline substrate. For some specific adsorbates, a complete 2-dimensional quasiperiodic metal overlayer is even formed. Other interesting phenomena are also observed in the multilayer regime. This includes the formation of novel structures, like 1-dimensional quasiperiodic Cu films or Bi allotropes, the formation of nanoscale crystalline domains with 5-fold rotational epitaxy, or the occurrence of quantum size effects influencing the film morphology. This article presents a short review of some of the achievements in thin film growth on quasicrystalline surfaces that the discovery of quasicrystals by Dan Shechtman has enabled.
Title:
Electrons in Quasicrystals
Authors:
Grimm, U Author Full Names: Grimm, Uwe
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1257-1262; SI 10.1002/ijch.201100143 DEC 2011
Abstract:
Quasicrystals, discovered by Dan Shechtman in 1982, provide unique materials with long-range aperiodic order. Their electronic structure and the electronic transport in quasicrystalline alloys has been a focus of research, motivated by trying to understand the formation and stability of quasicrystals, and their pronounced transport anomalies. This brief review on the motion of electrons concentrates on one perspective of this problem. It focuses on results obtained for simple models which capture the essence of the aperiodic order, rather than on results which attempt a realistic description of quasicrystalline alloys by employing empirical interaction potentials.
Title:
Dan Shechtman's Quasicrystal Discovery in Perspective
Authors:
Hargittai, I Author Full Names: Hargittai, Istvan
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1144-1152; SI 10.1002/ijch.201100137 DEC 2011
Abstract:
Dan Shechtmans discovery of quasicrystals brought about a paradigm change in chemistry, physics, materials science, and other areas of science and engineering. Although superficially it could be looked at as a serendipitous event, Shechtmans curiosity and drive played equal parts with serendipity in this discovery. Shechtman was a lonely discoverer, again, seemingly detached from the main stream of generalized crystallography for which his contribution was a milestone. Generalized crystallography is the science of structures without restrictions structures beyond crystals.1 The discovery of quasicrystals can be seen as written into the history of ideas that have much extended our views about the tools of our scientific inquiry and the materials we aim at producing and utilizing. This review augments a recent Editorial in the August 2011 issue of Structural Chemistry about the lessons of the quasicrystal discovery2 and a book chapter about Dan Shechtmans traits as a discoverer and about his road to the discovery.3
Title:
Dodecagonal Quasicrystals Still in Progress
Authors:
Ishimasa, T Author Full Names: Ishimasa, Tsutomu
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1216-1225; SI 10.1002/ijch.201100134 DEC 2011
Abstract:
The dodecagonal quasiperiodic order is rather rare in the material world, but has been observed in various systems from alloys to aggregates of cylindrical polymers and in a wide range of dimensions. They exhibit uniaxial 12-fold diffraction symmetry, and have common structural properties originating from the arrangement of structural units on a squaretriangle tiling. All dodecagonal quasicrystals known so far were classified into the so-called random-tiling type and not into a mathematically ideal quasiperiodic type. The observed dodecagonal quasicrystals deviated from the ideal state with respect to the limited size of their quasicrystalline region and their structural inhomogeniety. This may be caused by the structural metastability that prevents synthesis of high quality quasicrystals. The effort toward an ideal dodecagonal quasicrystal, in particular in alloys, is reviewed here. There may be two key points: one is taking advantage of the entropy for stabilization, namely the tiling configurational entropy, and the other is taking advantage of so-called second generation tiles scaled up by a factor of 2+v3 as observed in Ta1.6Te quasicrystal and Mn-Si-(Cr, V) approximant systems.
Title:
Symmetry Breaking and Order in the Age of Quasicrystals
Authors:
Lifshitz, R Author Full Names: Lifshitz, Ron
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1156-1167; SI 10.1002/ijch.201100156 DEC 2011
Abstract:
The discovery of quasicrystals has changed our view of some of the most basic notions related to the condensed state of matter. Before the age of quasicrystals, it was believed that crystals break the continuous translation and rotation symmetries of the liquid-phase into a discrete lattice of translations, and a finite group of rotations. Quasicrystals, on the other hand, possess no such symmetriesthere are no translations, nor, in general, are there any rotations, leaving them invariant. Does this imply that no symmetry is left, or that the meaning of symmetry should be revised? We review this and other questions related to the liquid-to-crystal symmetry-breaking transition using the notion of indistinguishability. We characterize the order-parameter space, describe the different elementary excitations, phonons and phasons, and discuss the nature of dislocationskeeping in mind that we are now living in the age of quasicrystals.
Title:
Some Aspects of Stability and Nanophase Formation in Quasicrystals during Mechanical Milling
Authors:
Mukhopadhyay, NK; Yadav, TP Author Full Names: Mukhopadhyay, N. K.; Yadav, Thakur Prasad
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1185-1196; SI 10.1002/ijch.201100145 DEC 2011
Abstract:
Non-equilibrium processing and other related techniques can activate quasicrystalline structures to a higher energy level and enable them to attain various stable/metastable structures. During mechanical milling of quasicrystalline alloys, the stability of the complex structures is of immense importance from a scientific and technological point of view. The evolution of nanoquasicrystalline, nanocrystalline, and amorphous phases and their composites has been observed in the course of milling. The experimental results for mechanical alloying of elemental powders (required for the synthesis of quasicrystals) and mechanical milling of quasicrystals are discussed. The salient features observed in quasicrystals during other non-equilibrium processing are highlighted. Nanospinel formation from the Al-based quasicrystalline precursor is mentioned.
Title:
Chemical Bonding in Al5Co2: The Electron Localizability-Electron Density Approach
Authors:
Ormeci, A; Grin, Y Author Full Names: Ormeci, Alim; Grin, Yuri
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1349-1354; SI 10.1002/ijch.201100147 DEC 2011
Abstract:
Al5Co2 is an intermetallic compound which can be considered as an approximant of the quasicrystalline decagonal phases. Chemical bonding in Al5Co2 is investigated by using the electron localizabilityelectron density approach. The analysis reveals that two atomic clusters, one three dimensional, the other planar, can be identified on the basis of two-centre bonds that are formed around the shortest AlCo distances. These clusters and one of the Al types interact through multi-centre bonds, indicating that both covalent and metallic interactions coexist in Al5Co2.
Title:
Heat Transport in Aluminum-Based Quasicrystals i-AlPdMn, i-AlCuFe, and d-AlCoNi
Authors:
Popcevic, P; Stanic, D; Bihar, Z; Bilusic, A; Smontara, A Author Full Names: Popcevic, Petar; Stanic, Denis; Bihar, Zeljko; Bilusic, Ante; Smontara, Ana
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1340-1348; SI 10.1002/ijch.201100150 DEC 2011
Abstract:
We present a semi-quantitative model used to analyze thermal conductivity data of single-grain aluminum-based icosahedral i-AlPdMn and i-AlFeCu, and decagonal d-AlCoNi quasicrystals in the quasiperiodic plane. The analysis is based on the validity of the WiedemannFranz law and applicability of the Debye model of quasilattice thermal conductivity at low temperatures, where the main phonon scattering centers are assumed to be structural defects in the form of the stacking faults and phenomenological quasiumklapp. At high temperature, electron and quasilattice contributions underestimate the data. This has motivated us to consider two possible additional heat-carrying channels: the activation of localized lattice vibrations and modifications of the WiedemannFranz law.
Title:
Crystal Twins Revisited
Authors:
Senechal, MW Author Full Names: Senechal, Marjorie Wikler
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1153-1155; SI 10.1002/ijch.201100135 DEC 2011
Abstract:
Just as quasicrystals demanded a new definition of crystal, they demand that we redefine crystal twins.
Title:
The generalized Kahler geometry of N = (2,2) WZW-models
Authors:
Sevrin, A; Staessens, W; Terryn, D Author Full Names: Sevrin, Alexander; Staessens, Wieland; Terryn, Dimitri
Source:
JOURNAL OF HIGH ENERGY PHYSICS, (12):10.1007/JHEP12(2011)079 DEC 2011
Abstract:
N = (2, 2), d = 2 supersymmetric non-linear s-models provide a physical realization of Hitchin's and Gualtieri's generalized Kahler geometry. A large subclass of such models are comprised by WZW-models on even-dimensional reductive group manifolds. In the present paper we analyze the complex structures, type changing, the superfield content and the affine isometries compatible with the extra supersymmetry. The results are illustrated by an exhaustive discussion of the N = (2, 2) WZW-models on S(3) x S(1) and S(3) x S(3) where various aspects of generalized Kahler and Calabi-Yau geometry are verified and clarified. The examples illustrate a slightly weaker definition for an N = (2, 2) superconformal generalized Kahler geometry compared to that for a generalized Calabi-Yau geometry.
Title:
Properties of Cd-Based Binary Quasicrystals and Their 1/1 Approximants
Authors:
Tamura, R Author Full Names: Tamura, Ryuji
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1263-1274; SI 10.1002/ijch.201100138 DEC 2011
Abstract:
Electronic and structural properties of Cd-based binary quasicrystals (QCs) and their 1/1 approximants (APs) without chemical disorder are overviewed in terms of electronic states, electronic transport, and phase transitions. A pseudogap in the electronic density of states (DOS) as well as hybridization effect between sp and d states are discussed for both the QCs and their 1/1 APs in comparison with theoretical calculations. In contrast with the cases of ternary stable QCs, the resistivity of the Cd5.7Yb QC exhibits a positive temperature coefficient at low temperatures, which is regarded as an indication of an intrinsic metallic nature of the QC. A unique structural phase transition has been observed at low temperatures (LT) for a series of 1/1 Cd6M APs, which is interpreted as an orientational transition of a tetrahedron residing at the center of the Tsai-type icosahedral cluster. In most of the cases, the LT superstructure is understood as an antiferromagnetic ordering of the tetrahedra along a < 110 > direction of the high-temperature bcc phase. The transition is classified as a non-diffusive orderdisorder transition, which has not been observed in metallic alloys before.
Title:
Guest Editorial: Quasicrystals
Authors:
Thiel, PA Author Full Names: Thiel, Patricia A.
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1141-1142; SI 10.1002/ijch.201100127 DEC 2011
Title:
A Distinctive Feature of the Surface Structure of Quasicrystals: Intrinsic and Extrinsic Heterogeneity
Authors:
Thiel, PA; Unal, B; Jenks, CJ; Goldman, AI; Canfield, PC; Lograsso, TA; Evans, JW; Quiquandon, M; Gratias, D; Van Hove, MA Author Full Names: Thiel, Patricia A.; Uenal, Baris; Jenks, Cynthia J.; Goldman, Alan I.; Canfield, Paul C.; Lograsso, Thomas A.; Evans, James W.; Quiquandon, Marianne; Gratias, Denis; Van Hove, Michel A.
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1326-1339; SI 10.1002/ijch.201100148 DEC 2011
Abstract:
This paper reviews a feature of atomically-clean quasicrystal surfaces that distinguishes them from surfaces of crystalline materials. That feature is a high degree of heterogeneity among different terraces, and among structurally-identical adsorption sites. The heterogeneity can be both structural and chemical in origin. A large variability is expected even for a surface which is perfectly bulk-terminated, and we call this intrinsic heterogeneity. Additional variability can derive from the surface preparation process, which can yield metastable structures. We call this extrinsic heterogeneity. Experimental evidence is given for both cases. This heterogeneity can be an important factor in understanding and predicting surface phenomena such as chemisorption.
Title:
Liquid Quasicrystals
Authors:
Ungar, G; Percec, V; Zeng, XB; Leowanawat, P Author Full Names: Ungar, Goran; Percec, Virgil; Zeng, Xiangbing; Leowanawat, Pawaret
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1206-1215; SI 10.1002/ijch.201100151 DEC 2011
Abstract:
In the first part, this brief review discusses the discovery of the first example of supramolecular dendritic liquid quasicrystal, which represents also the first example of soft quasicrystal. In the second part, we show that soft quasicrystals generated from supramolecular spheres are scattered through libraries of self-assembling dendrons, dendrimers, and dendronized polymers. The supramolecular spheres forming soft quasicrystals are generated via at least two different mechanisms, and are chiral. Generation of quasicrystals from other organic building blocks is also discussed. Finally, potential applications in electronics, sensors, and as ionic liquid-based nanoreactors are also mentioned.
Title:
Quasicrystals: Substances with special Structures
Authors:
Welter, K Author Full Names: Welter, Kira
Source:
CHEMIE IN UNSERER ZEIT, 45 (6):366-367; 10.1002/ciuz.201190088 DEC 2011
Title:
Real Space Structure Factor for Different Quasicrystals
Authors:
Wolny, J; Kozakowski, B; Kuczera, P; Strzalka, R; Wnek, A Author Full Names: Wolny, Janusz; Kozakowski, Bartlomiej; Kuczera, Pawel; Strzalka, Radoslaw; Wnek, Anna
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1275-1291; SI 10.1002/ijch.201100144 DEC 2011
Abstract:
The statistical approach to the description of aperiodic structures using the concept of the so called Average Unit Cell (AUC) is presented. The use of this method is shown for 1D, 2D, and 3D structures. We start with the presentation of the basic ideas for 1D simple sinusoidal modulation (1q) and the Fibonacci chain (a 1D model of a quasicrystalline structure). Up to now the AUC concept has been most thoroughly studied for 2D decagonal quasicrystals. The idea of structure factor derivation for the decorated Penrose tiling, a quasilattice for the description of decagonal quasicrystals, is presented. Two examples of structure refinement of decagonal phases from the Al-Ni-Co system are discussed. The potential of the cluster description of decagonal structures is also presented. The AUC construction and structure factor derivation is shown for the 3D AmmanKramerNeri tiling, which is a model quasilattice for the description of icosahedral phases. The AUC concept can also be extended to structures with singular-continuous Fourier spectrum. An example for the 1D ThueMorse sequence is studied.
Title:
On finite symmetry groups of some models of three-dimensional quasicrystals
Authors:
Artamonov, VA; Sanchez, S Author Full Names: Artamonov, V. A.; Sanchez, S.
Source:
SIBERIAN MATHEMATICAL JOURNAL, 52 (6):969-979; 10.1134/S0037446611060024 NOV 2011
Abstract:
We give a full description of the finite symmetry groups of the cut-and-project model for three-dimensional quasicrystals under the assumption that the phase space dimension is at most 3.

Update: 9-Feb-2012

Title:
Structural and magnetic properties of Mn(3-x)Cd(x)TeO(6) (x=0, 1, 1.5 and 2)
Authors:
Ivanov, SA; Mathieu, R; Nordblad, P; Politova, E; Tellgren, R; Ritter, C; Proidakova, V Author Full Names: Ivanov, S. A.; Mathieu, R.; Nordblad, P.; Politova, E.; Tellgren, R.; Ritter, C.; Proidakova, V.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (8):1637-1644; 10.1016/j.jmmm.2011.12.027 APR 2012
Abstract:
Mn(3)TeO(6) exhibits a corundum-related A(3)TeO(6) structure and a complex magnetic structure involving two magnetic orbits for the Mn atoms [Ivanov et al., 2011 [3]]. Mn(3-x)Cd(x)TeO(6) (x = 0, 1, 1.5, and 2) ceramics were synthesized by solid state reaction and investigated using X-ray powder diffraction, electron microscopy, and calorimetric and magnetic measurements. Cd(2+) replaces Mn(2+) cations without greatly affecting the structure of the compound. The Mn and Cd cations were found to be randomly distributed over the A-site. Magnetization measurements indicated that the samples order antiferromagnetically at low temperature with a transition temperature that decreases with increasing Cd doping. The nuclear and magnetic structure of one specially prepared (114)Cd containing sample: Mn(1.5) (114)Cd(1.5)TeO(6), was studied using neutron powder diffraction over the temperature range 2-295 K. Mn(1.5) (114)Cd(1.5)TeO(6) was found to order in an incommensurate helical magnetic structure, very similar to that of Mn(3)TeO(6) [Ivanov et al., 2011 [3]]. However, with a lower transition temperature and the extension of the ordered structure confined to order 240(10) angstrom. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Effect of Mn substitution on crystal structure and magnetic properties of Bi(1-x)Pr(x)FeO(3) multiferroics
Authors:
Khomchenko, VA; Troyanchuk, IO; Kovetskaya, MI; Kopcewicz, M; Paixao, JA Author Full Names: Khomchenko, V. A.; Troyanchuk, I. O.; Kovetskaya, M. I.; Kopcewicz, M.; Paixao, J. A.
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 45 (4):10.1088/0022-3727/45/4/045302 FEB 1 2012
Abstract:
Mn substitution-driven structural and magnetic phase evolution in the predominantly antiferromagnetic polar rhombohedral (space group R3c) and weak ferromagnetic antipolar orthorhombic (space group Pnam) phases of the Bi(1-x)Pr(x)FeO(3) perovskites was studied by x-ray diffraction, (57)Fe Mossbauer spectroscopy and magnetometry techniques at room temperature. Mn doping was found to effectively modify both the initial structures to stabilize a new phase demonstrating incommensurable modulation. Magnetic behaviour of the Mn-containing samples changes in correlation with the evolution of their structural state. Within the compositional range of the rhombohedrally distorted compounds, the manganese substitution gives rise to suppression of the dominant antiferromagnetic interaction. In the weak ferromagnetic doping-induced phase, a gradual decrease in room temperature spontaneous magnetization takes place with increasing Mn content.
Title:
Influence of Y on the phase composition and mechanical properties of as-extruded Mg-Zn-Y-Zr magnesium alloys
Authors:
Wang, JF; Song, PF; Gao, S; Wei, YY; Pan, FS Author Full Names: Wang, Jingfeng; Song, Pengfei; Gao, Shan; Wei, Yiyun; Pan, Fusheng
Source:
JOURNAL OF MATERIALS SCIENCE, 47 (4):2005-2010; 10.1007/s10853-011-5998-2 FEB 2012
Abstract:
The influence of Y on the microstructure, phase composition and mechanical properties of the extruded Mg-6Zn-xY-0.6Zr (x = 0, 1, 2, 3 and 4, in wt%) alloys has been investigated and compared by optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer and tensile testing. The increase in Y content has shown grain refinement effects on the microstructure morphologies of the extruded alloys. However, when the content of Y exceeds 2.2 wt%, the grain refinement effect of the Y is not obvious any more with the increase of the Y content. The quasicrystal I-phase (Mg(3)YZn(6)), face-centred cubic structure W-phase (Mg(3)Y(2)Zn(3)) and a long period stacking ordered (LPSO) X-phase (Mg(12)YZn) can precipitate in different ranges of Y/Zn ratio (in at.%) when the Y content in the Mg-Zn-Y-Zr alloys is varied. Comparison of the mechanical properties of the alloys showed that the different ternary Mg-Zn-Y phases have different strengthening and toughening effects on the Mg-Zn-Y-Zr alloys in the following order: X-phase > I-phase > W-phase > MgZn(2).
Title:
Atomic ordering in Au-(42 to 50) at.% Pd: A diffuse scattering and first-principles investigation
Authors:
Schonfeld, B; Sax, CR; Ruban, AV Author Full Names: Schoenfeld, B.; Sax, C. R.; Ruban, A. V.
Source:
PHYSICAL REVIEW B, 85 (1):10.1103/PhysRevB.85.014204 JAN 24 2012
Abstract:
Atomic ordering in Au-Pd alloys was studied by diffuse x-ray scattering and first-principles methods. Diffuse scattering was done of a single crystal of Au-48 at.% Pd that was aged at 703 K for 24 days. The weakly modulated short-range-order scattering exhibits diffuse maxima with an incommensurate wave vector, which can be related to a Fermi-surface nesting mechanism. From effective pair interaction parameters determined by the inverse Monte Carlo method, a one-dimensional long-period superstructure of the CH structure, LPS1, was found for AuPd. Concurrent electronic-structure calculations of the effective cluster interaction (ECI) parameters indicated the presence of another closely related superstructure, LPS2, at 0 K. At the same time, direct first-principles calculations of the total energies of the CH structure and further one-dimensional long-period superstructures predicted the stabilization of LPS4. Although the energy differences between these structures are small and a complex behavior of the effective interactions is expected due to the Fermi-surface nesting, experimental data and theoretical results both support the stabilization of a long-period superstructure of the CH structure for AuPd at 0 K. The ECI parameters determined by the screened generalized perturbation method also predicted a ground-state structure different from Au(7)Pd(5), previously obtained from cluster expansion calculations. Its energetic preference was confirmed by direct total-energy calculations.
Title:
Intrinsic anisotropic magnetic, electrical, and thermal transport properties of d-Al-Co-Ni decagonal quasicrystals
Authors:
Bobnar, M; Jeglic, P; Klanjsek, M; Jaglicic, Z; Wencka, M; Popcevic, P; Ivkov, J; Stanic, D; Smontara, A; Gille, P; Dolinsek, J Author Full Names: Bobnar, M.; Jeglic, P.; Klanjsek, M.; Jaglicic, Z.; Wencka, M.; Popcevic, P.; Ivkov, J.; Stanic, D.; Smontara, A.; Gille, P.; Dolinsek, J.
Source:
PHYSICAL REVIEW B, 85 (2):10.1103/PhysRevB.85.024205 JAN 20 2012
Abstract:
To address the questions on the anisotropy of bulk physical properties of decagonal quasicrystals and the intrinsic physical properties of the d-Al-Co-Ni phase, we investigated the anisotropic magnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient, and the thermal conductivity of a d-Al-Co-Ni single crystal of exceptional structural quality. Superior structural order on the local scale of atomic clusters was confirmed by (27)Al nuclear magnetic resonance spectroscopy. The measurements were performed in the 10-fold periodic direction of the structure and in three specific crystallographic directions within the quasiperiodic plane, corresponding to the 2 and 2' twofold symmetry directions and their bisector. The specific heat, being a scalar quantity, was determined as well. The measurements of the second-rank bulk tensorial properties confirm the theoretical prediction that a solid of decagonal point group symmetry should exhibit isotropic physical properties within the quasiperiodic plane and anisotropy between the in-plane and the 10-fold directions. d-Al-Co-Ni is an anisotropic diamagnet with stronger diamagnetism for the magnetic field in the 10-fold direction. Electrical and thermal transport is strongly metallic in the 10-fold direction but largely suppressed within the quasiperiodic plane, the main reason being the lack of translational periodicity that hinders the propagation of electrons and phonons in a nonperiodic lattice. The third-rank Hall-coefficient tensor shows sign-reversal anisotropy related to the direction of the magnetic field when applied in the 10-fold direction or within the quasiperiodic plane. The observed anisotropy is not a peculiarity of quasicrystals but should be a general feature of solids with broken translational periodicity in two dimensions.
Title:
Structural and magnetic transitions in the crystalline approximant Cd(6)Sm
Authors:
Tamura, R; Muro, Y; Hiroto, T; Yaguchi, H; Beutier, G; Takabatake, T Author Full Names: Tamura, R.; Muro, Y.; Hiroto, T.; Yaguchi, H.; Beutier, G.; Takabatake, T.
Source:
PHYSICAL REVIEW B, 85 (1):10.1103/PhysRevB.85.014203 JAN 20 2012
Abstract:
Electrical resistivity, specific heat, magnetic susceptibility, and magnetization of the crystalline approximant Cd(6)Sm are investigated in a temperature range 1.8-300 K. Both structural and magnetic transitions are clearly evidenced. A sharp structural phase transition is observed at T(c) = 179 K in the electrical resistivity as well as in the specific heat, which is attributed to orientational ordering of the Cd(4) tetrahedron located at the center of the icosahedral cluster. In addition, three successive magnetic transitions are found at T(M1) = 12.5, T(M2) = 10.2, and T(M3) = 6.5 K. The anomaly at T(M1) is attributed to an antiferromagnetic transition, whereas those at T(M2) and T(M3) are to ferrimagnetic transitions. The observation of the ferrimagnetic orders indicates that (pseudo) icosahedra made of localized Sm spins have a nonzero net magnetic moment, and the moments of the magnetic clusters form a long-range magnetic order.
Title:
Zn-induced spin dynamics in overdoped La(2-x)Sr(x)Cu(1-y)Zn(y)O(4)
Authors:
Wilson, SD; Yamani, Z; Dhital, C; Freelon, B; Freeman, PG; Fernandez-Baca, JA; Yamada, K; Wakimoto, S; Buyers, WJL; Birgeneau, RJ Author Full Names: Wilson, Stephen D.; Yamani, Z.; Dhital, Chetan; Freelon, B.; Freeman, P. G.; Fernandez-Baca, J. A.; Yamada, K.; Wakimoto, S.; Buyers, W. J. L.; Birgeneau, R. J.
Source:
PHYSICAL REVIEW B, 85 (1):10.1103/PhysRevB.85.014507 JAN 17 2012
Abstract:
Spin fluctuations and the local spin susceptibility in isovalently Zn-substituted La(2-x)Sr(x)Cu(1-y)Zn(y)O(4) (x = 0.25, y approximate to 0.01) are measured via inelastic neutron-scattering techniques. As Zn(2+) is substituted onto the Cu(2+)-sites, an anomalous enhancement of the local spin susceptibility chi ''(omega) appears due to the emergence of a commensurate antiferromagnetic excitation centered at wave vector Q = (pi, pi, 0) that coexists with the known incommensurate spin-density wave excitations at Q(HK) = (pi +/- delta, pi),(pi, pi +/- delta). Our results support a picture of Zn-induced antiferromagnetic (AF) fluctuations appearing through a local staggered polarization of Cu(2+) spins, and the simultaneous suppression of T(c) as AF fluctuations are slowed in proximity to Zn impurities suggests the continued importance of high-energy AF fluctuations at the far overdoped edge of superconductivity in the cuprates.
Title:
Structural phase transitions in SrRh(2)As(2)
Authors:
Zinth, V; Petricek, V; Dusek, M; Johrendt, D Author Full Names: Zinth, V.; Petricek, V.; Dusek, M.; Johrendt, D.
Source:
PHYSICAL REVIEW B, 85 (1):10.1103/PhysRevB.85.014109 JAN 17 2012
Abstract:
SrRh(2)As(2) crystallizes with three polymorphs derived from the tetragonal ThCr(2)Si(2)-type structure and exhibits structural phase transitions comparable to those of BaFe(2)As(2), a parent compound of iron-based superconductors. The structure of alpha-SrRh(2)As(2) is monoclinic (a = 421.2(1) pm, b = 1105.6(2) pm, c = 843.0(1) pm, beta = 95 degrees) and was refined as a twin in the space group P2(1)/c with R1 = 0.0928. beta-SrRh(2)As(2) crystallizes with a modulated structure in the (3 + 1)-dimensional superspace group Fmmm(10 gamma)s00 (a = 1114.4(3) pm, b = 574.4(2) pm, and c = 611.5(2) pm) and an incommensurable modulation vector q = (1, 0, 0.3311(4)). High-temperature single-crystal diffraction experiments confirm the tetragonal ThCr(2)Si(2)-type structure for gamma-SrRh(2)As(2) at 623 K. Electronic band structure calculations indicate that the structural distortion in a-SrRh2As2 is caused by strong Rh-Rh bonding interactions within the layers and has therefore no magnetic origin as suggested for isotypic BaFe(2)As(2).
Title:
Quantum spin fluctuations for a distorted incommensurate spiral
Authors:
Fishman, RS Author Full Names: Fishman, Randy S.
Source:
PHYSICAL REVIEW B, 85 (2):10.1103/PhysRevB.85.024411 JAN 12 2012
Abstract:
Quantum spin fluctuations are investigated for the distorted incommensurate spiral state of a geometrically frustrated triangular-lattice antiferromagnet. With increasing easy axis anisotropy, the average reduction of the spin amplitude by quantum fluctuations is suppressed but the spiral also becomes more distorted. Quantum fluctuations enhance both the wave vector of the distorted spiral and the critical anisotropy above which it undergoes a first-order transition into a collinear state. An experimental technique is proposed to isolate the effects of quantum fluctuations from the classical distortion of the spiral. This analysis is applied to the elliptical spiral state of doped CuFeO(2).
Title:
Monte Carlo and variational calculations of the magnetic phase diagram of CuFeO(2)
Authors:
Fishman, RS; Brown, G; Haraldsen, JT Author Full Names: Fishman, Randy S.; Brown, Gregory; Haraldsen, Jason T.
Source:
PHYSICAL REVIEW B, 85 (2):10.1103/PhysRevB.85.020405 JAN 12 2012
Abstract:
Monte-Carlo and variational calculations are used to revise the phase diagram of the magnetically frustrated material CuFeO(2). For fields 50 < H < 65T, a new spin-flop phase is predicted between a canted 3-sublattice phase and the conventional conical spin-flop phase. With wave vector Q approximate to (0.8 pi, 0.43 pi), this phase is commensurate in the x direction but incommensurate in the y direction. A canted 5-sublattice phase is predicted between the multiferroic phase and either a collinear 5-sublattice phase for pure CuFeO(2) or a canted 3-sublattice phase for Al- or Ga-doped CuFeO(2).
Title:
Temperature-dependent multi-k magnetic structure in multiferroic Co(3)TeO(6)
Authors:
Ivanov, SA; Tellgren, R; Ritter, C; Nordblad, P; Mathieu, R; Andre, G; Golubko, NV; Politova, ED; Weil, M Author Full Names: Ivanov, S. A.; Tellgren, R.; Ritter, C.; Nordblad, P.; Mathieu, R.; Andre, G.; Golubko, N. V.; Politova, E. D.; Weil, M.
Source:
MATERIALS RESEARCH BULLETIN, 47 (1):63-72; 10.1016/j.materresbull.2011.10.003 JAN 2012
Abstract:
A complex magnetic order of the multiferroic compound Co(3)TeO(6) has been revealed by neutron powder diffraction studies on ceramics and crushed single crystals. The compound adopts a monoclinic structure (s.g. C2/c) in the studied temperature range 2-300 K but exhibits successive antiferromagnetic transitions at low temperature. Incommensurate antiferromagnetic order with the propagation vector k(1) = (0, 0.485, 0.055) sets in at 26 K. A transition to a second antiferromagnetic structure with k(2) = (0, 0, 0) takes place at 21.1 K. Moreover, a transition to a commensurate antiferromagnetic structure with k(3) = (0, 0.5, 0.25) occurs at 17.4 K. The magnetic structures have been determined by neutron powder diffraction using group theory analysis as a preliminary tool. Different coordinations of the Co(2+) ions involved in the low-symmetry C2/c structure of Co(3)TeO(6) render the exchange-interaction network very complex by itself. The observed magnetic phase transformations are interpreted as an evidence of competing magnetic interactions. The temperature dependent changes in the magnetic structure, derived from refinements of high-resolution neutron data, are discussed and possible mechanisms connected with the spin reorientations are described. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Mn substitution-driven structural and magnetic phase evolution in Bi(1-x)Sm(x)FeO(3) multiferroics
Authors:
Khomchenko, VA; Troyanchuk, IO; Kovetskaya, MI; Paixao, JA Author Full Names: Khomchenko, V. A.; Troyanchuk, I. O.; Kovetskaya, M. I.; Paixao, J. A.
Source:
JOURNAL OF APPLIED PHYSICS, 111 (1):10.1063/1.3676205 JAN 1 2012
Abstract:
X-ray diffraction and magnetization measurements of the Bi(0.9)Sm(0.1)Fe(1-y)Mn(y)O(3) and Bi(0.86)Sm(0.14)Fe(1-z)Mn(z)O(3) (y <= 0.4, z <= 0.3) series were carried out in order to follow the effect of Mn doping on the room temperature crystal structure and magnetic properties of Sm-substituted BiFeO(3). Initially polar rhombohedral Bi(0.9)Sm(0.1)FeO(3) compound (space group R3c) was shown to undergo the Mn-substitution driven structural transformation into the orthorhombic Pnam phase at y similar to 0.2. Further increasing of the Mn content stabilizes the modified structural phase demonstrating the features of incommensurability. In the Bi(0.86)Sm(0.14)Fe(1-z)Mn(z)O(3) series, the initially dominant antipolar orthorhombic Pnam phase transforms toward the nonpolar Pnma structure (z similar to 0.3). Changes of the main magnetic state (from mixed antiferromagnetic/weak ferromagnetic to weak ferromagnetic) were found to correlate with the rhombohedral-to-orthorhombic transition; however, within the compositional range of the orthorhombically distorted compounds, the room temperature spontaneous magnetization rapidly decreases with increasing Mn content. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676205]
Title:
Structural Defects in Periodic and Quasicrystalline Binary Nanocrystal Superlattices
Authors:
Bodnarchuk, MI; Sheychenko, EV; Talapin, DV Author Full Names: Bodnarchuk, Maryna I.; Sheychenko, Elena V.; Talapin, Dmitri V.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133 (51):20837-20849; 10.1021/ja207154v DEC 28 2011
Abstract:
Binary nanocrystal superlattices (BNSLs) emerge as an important class of man-made materials where components and functionalities can be added, tuned, or combined in a predictable manner. These amazingly complex structures spontaneously self-assemble from colloidal solutions containing binary mixtures of functional (semiconducting, magnetic, plasmonic, etc.) nanocrystals. Further developments of the BNSL-based materials require a deep understanding and control over BNSL formation and structural perfection. Like any solid, BNSL can contain different kinds of structural defects. It is well-known that defects can have a tremendous effect on the material's behavior. Defect engineering is used to modify and improve many of the mechanical, electrical, magnetic, and optical properties of conventional solids. In this work, we provide the first systematic analysis of structural defects in various BNSL structures. We used BNSLs as a platform for studying structural defects in both periodic (crystalline) and aperiodic (quasicrystalline) lattices, as well as for direct imaging of the interfaces between crystalline and quasicrystalline domains. Such direct observation of local imperfections in complex multicomponent lattices provides a unique insight into the fundamental aspects of crystal formation.

Update: 1-Feb-2012

Title:
Neutron powder diffraction study of the ternary RMgSn (R=Ce-Nd, Tb-Tm, Yb) compounds
Authors:
Lemoine, P; Verniere, A; Venturini, G; Capelli, S; Malaman, B Author Full Names: Lemoine, P.; Verniere, A.; Venturini, G.; Capelli, S.; Malaman, B.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (6):961-976; 10.1016/j.jmmm.2011.09.035 MAR 2012
Abstract:
The ternary intermetallic RMgSn compounds are studied by neutron powder diffraction. The CeScSi-type PrMgSn and NdMgSn compounds present a commensurate antiferromagnetic structure, while the (Tb-Tm)MgSn are characterized by an incommensurate sine-wave modulated magnetic structure, which can tend to a square-modulated arrangement at low temperature due to appearance of higher odd integer harmonics. The TiNiSi-type CeMgSn compound is also characterized by an incommensurate sine-wave modulated magnetic structure, while PrMgSn exhibits a ferromagnetic arrangement with a canting at low temperature. Finally, the ZrNiAl-type YbMgSn compound evidences no magnetic ordering. These results are discussed and compared with those published for the other CeScSi-type compounds. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Modeling of decagonal quasicrystal lattice
Authors:
Girzhon, VV; Kovalyova, VM; Smolyakov, OV; Zakharenko, MI Author Full Names: Girzhon, V. V.; Kovalyova, V. M.; Smolyakov, O. V.; Zakharenko, M. I.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 358 (2):137-144; 10.1016/j.jnoncrysol.2011.09.017 JAN 15 2012
Abstract:
The model of the reciprocal lattice of decagonal quasicrystal has been proposed. It is based on the multiplication of the basis sites' groups according to the proposed rules. This model was shown to provide the information not only on the reciprocal sites location, but also on the intensity of the appropriated diffraction reflections. The physical justification of the proposed model correctness has been provided on the base of projection of six-dimensional hyperlattice onto the three-dimensional space. The possibility of three-indices labeling of the diffraction reflections of decagonal quasicrystals has been exhibited. (C) 2011 Elsevier B.V. All rights reserved.
Title:
The luminescence of Na(x)Eu((2-x)/3)(3+)MoO(4) scheelites depends on the number of Eu-clusters occurring in their incommensurately modulated structure
Authors:
Arakcheeva, A; Logvinovich, D; Chapuis, G; Morozov, V; Eliseeva, SV; Bunzli, JCG; Pattison, P Author Full Names: Arakcheeva, Alla; Logvinovich, Dmitry; Chapuis, Gervais; Morozov, Vladimir; Eliseeva, Svetlana V.; Buenzli, Jean-Claude G.; Pattison, Philip
Source:
CHEMICAL SCIENCE, 3 (2):384-390; 10.1039/c1sc00289a 2012
Abstract:
Scheelite related compounds with general formula M(n)(XO(4))(m) are the subject of hefty interest owing to their optical properties, stability and relatively simple preparation. Eu(3+)-containing scheelites are considered as red-emitting phosphors and the main factors affecting their luminescence are thought to be chemical composition and particle size while the influence of their structure is generally ignored. Here we report eight compounds from the Na(x)Eu((2-x)/3)MoO(4) series prepared by conventional solid-state reaction and present a detailed analysis of their crystal structures. Six of them have modulated structures, a common feature of SRCs, in which dopant Eu(3+) ions are orderly distributed. Moreover, different amounts of Eu(3+) dimers are detected in the modulated structures, characterized by weak satellite reflections appearing in the lower angle part of the XRD patterns. These reflections are indexed and incorporated into Rietveld's refinement using superspace (3 + 1)-dimension symmetry. The remarkable feature of the compounds is that the characteristic luminescence parameters, overall (Q(L)(Eu)) and intrinsic (Q(Eu)(Eu)) quantum yields, Eu((5)D(0)) lifetimes, and sensitization efficiencies (eta(sens)), correlate with the number of Eu(3+) aggregates, but not directly with the composition x of the materials. This provides an efficient tool for understanding and controlling the luminescence properties of scheelite related compounds.
Title:
The success story of crystallography
Authors:
Schwarzenbach, D Author Full Names: Schwarzenbach, Dieter
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 68 57-67; Part 1 10.1107/S0108767311030303 JAN 2012
Abstract:
Diffractionists usually place the birth of crystallography in 1912 with the first X-ray diffraction experiment of Friedrich, Knipping and Laue. This discovery propelled the mathematical branch of mineralogy to global importance and enabled crystal structure determination. Knowledge of the geometrical structure of matter at atomic resolution had revolutionary consequences for all branches of the natural sciences: physics, chemistry, biology, earth sciences and material science. It is scarcely possible for a single person in a single article to trace and appropriately value all of these developments. This article presents the limited, subjective view of its author and a limited selection of references. The bulk of the article covers the history of X-ray structure determination from the NaCl structure to aperiodic structures and macromolecular structures. The theoretical foundations were available by 1920. The subsequent success of crystallography was then due to the development of diffraction equipment, the theory of the solution of the phase problem, symmetry theory and computers. The many structures becoming known called for the development of crystal chemistry and of data banks. Diffuse scattering from disordered structures without and with partial long-range order allows determination of short-range order. Neutron and electron scattering and diffraction are also mentioned.
Title:
Direct Preparation of Nano-Quasicrystals via a Water-Cooled Wedge-Shaped Copper Mould
Authors:
Wang, ZF; Zhao, WM; Qin, CL; Cui, Y; Fan, SL; Jia, JQ Author Full Names: Wang, Zhifeng; Zhao, Weimin; Qin, Chunling; Cui, Yan; Fan, Shenglei; Jia, Junqing
Source:
JOURNAL OF NANOMATERIALS, 10.1155/2012/708240 2012
Abstract:
We have successfully synthesized multicomponent Mg-based nano-quasicrystals (nano-QCs) through a simple route by using a water-cooled wedge-shaped copper mould. Nanoscale QCs are prepared directly on tip of wedge-shaped castings. The further study shows that nano-QCs in the Mg(71)Zn(26)Y(2)Cu(1) alloy show well microhardness of greater than HV450. Electrochemical properties of three kinds of quasicrystal alloys are investigated in simulated seawater. The Mg(71)Zn(26)Y(2)Cu(1) nano-QC alloy presents the best corrosion resistance in this study for the formation of well-distributed nano-QC phases (1 similar to 5 nm) and polygonal Mg(2)(Cu,Y) nanophases (40 similar to 50 nm).
Title:
Potts Model with the Simplest Modulated Phase
Authors:
Ganikhodjaev, N; Temir, S; Akin, H; Uguz, S Author Full Names: Ganikhodjaev, Nasir; Temir, Seyit; Akin, Hasan; Uguz, Selman
Source:
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 59 (5):2971-2979; 10.3938/jkps.59.2971 NOV 2011
Abstract:
We study the phase diagrams for the Potts model on the Bethe lattice with competing nearest-neighbor interactions J(1) and ternary interactions J(p) and J(t). At vanishing temperature, the phase diagram is fully determined for all values and signs of J(p)/J(1) and J(t)/J(1); in particular, we show that the phase diagrams contain ferromagnetic, paramagnetic and < 2 > phases only; i.e., the set of modulated phases consists of the < 2 > phase only for J(1) > 0 and J(p)/J(1) < 0. We verify that values of T/J(1) in the very narrow strip -0.11 < T/J(1) < 0 with -J(p)/J(1) < 0 favor the modulated phase, which is either a commensurate phase with a very large period or an incommensurate phase. The transition lines are obtained from stability conditions, and characteristic points in the phase diagram are analyzed by using numerical iterations. Also the wavevectors versus temperature are plotted for some critical points in the modulated phases.
Title:
Materials Researcher Dan Shechtman receives Nobel Prize for discovery of quasicrystals
Authors:
[Anonymous] Author Full Names: [Anonymous]
Source:
MRS BULLETIN, 36 (11):849-849; 10.1557/mrs.2011.284 NOV 2011

Update: 25-Jan-2012

Title:
Microstructure evolution of Zr(65)Al(7.5)Cu(12.5)Ni(10)Ag(5) bulk metallic glass due to rolling and its influence on the thermal stability
Authors:
Yan, ZJ; Yan, J; Hu, Y; Hao, WX Author Full Names: Yan, Z. J.; Yan, J.; Hu, Y.; Hao, W. X.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 513 75-79; 10.1016/j.jallcom.2011.09.083 FEB 5 2012
Abstract:
X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM) are employed to investigate the microstructure evolution of Zr(65)Al(7.5)Cu(12.5)Ni(10)Ag(5) bulk metallic glass subjected to rolling at room temperature. The strain rates are controlled to be 10(-4)-10(-3) s(-1). The results show that the plastic deformation during rolling behaves as an inhomogeneous mode with the characteristic of shear bands, which results in the two-state characteristic of atomic movement from competition between the ordering and disordering processes. The icosahedron-like clusters precipitate in the transition regions between the shear bands and the amorphous matrix, and they tend to aggregate into nano-sized orders. The results of DSC indicate that the onset precipitation temperature of I-phase during heating of the metallic glass obviously decreases due to rolling. However, the time window for the completion of amorphous-to-icosahedral phase transformation is evidently lengthened. The microstructure evolution during rolling and its influence on the thermal stability are discussed. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Incommensurate magnetic order in TbTe(3)
Authors:
Pfuner, F; Gvasaliya, SN; Zaharko, O; Keller, L; Mesot, J; Pomjakushin, V; Chu, JH; Fisher, IR; Degiorgi, L Author Full Names: Pfuner, F.; Gvasaliya, S. N.; Zaharko, O.; Keller, L.; Mesot, J.; Pomjakushin, V.; Chu, J-H; Fisher, I. R.; Degiorgi, L.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (3):10.1088/0953-8984/24/3/036001 JAN 25 2012
Abstract:
We report a neutron diffraction study of the magnetic phase transitions in the charge-density wave (CDW) TbTe(3) compound. We discover that in the paramagnetic phase there are strong 2D-like magnetic correlations, consistent with the pronounced anisotropy of the chemical structure. A long-range incommensurate magnetic order emerges in TbTe(3) at T(mag1) = 5.78 K as a result of continuous phase transitions. We observe that near the temperature T(mag1) the magnetic Bragg peaks appear around the position (0, 0, 0.24) (or its rational multiples), that is fairly close to the propagation vector. 0; 0; 0 : 29 associated with the CDW phase transition in TbTe(3). This suggests that correlations leading to the long-range magnetic order in TbTe(3) are linked to the modulations that occur in the CDW state.
Title:
Magnetic properties of sigma- and hexagonal-Mn(76)Si(18)Cr(6) approximant phases of a dodecagonal quasicrystal
Authors:
Kashimoto, S; Kocjan, A; Jaglicic, Z; Jazbec, S; Iga, H; Ishimasa, T; Dolinsek, J Author Full Names: Kashimoto, S.; Kocjan, A.; Jaglicic, Z.; Jazbec, S.; Iga, H.; Ishimasa, T.; Dolinsek, J.
Source:
PHYSICAL REVIEW B, 84 (22):10.1103/PhysRevB.84.224201 DEC 19 2011
Abstract:
The tetragonal sigma phase and the hexagonal (hex) phase in the Mn-Si-V(Cr) transition-metal-alloy systems are stable approximant phases of a dodecagonal (12-fold) quasicrystal that can be prepared in bulk quantities. We have synthesized samples of the sigma and hex phases of composition Mn(76)Si(18)Cr(6) and determined their magnetic properties. In the sigma-Mn(76)Si(18)Cr(6), a spin-freezing transition to a canonical spin-glass phase was detected below T(f) approximate to 8 K, characterized by a maximum in the zero-field-cooled susceptibility, a frequency-dependent cusp in the ac susceptibility, M(H) hysteresis, and ultraslow time decay of the thermoremanent magnetization. In contrast, no spin-glass transition was observed in the hex-Mn(76)Si(18)Cr(6) phase down to the lowest investigated temperature of 2 K. The analysis of the susceptibility has shown that the coupling of spins in both phases is antiferromagnetic (AFM), but the coupling strength is considerably stronger in the sigma phase. Since both phases are structurally described by the triangle-square tiling scheme related to that of the dodecagonal quasicrystal, which imposes geometric frustration of the AFM-coupled spins on triangles, the absence of spin-glass transition in the hex-Mn(76)Si(18)Cr(6) could be due to shifting of this transition below the lowest temperature of our experimental setup, as a consequence of weaker spin coupling and smaller moment sizes in the hex phase. In both investigated samples, tiny Mn(3)O(4) inclusions that undergo a transition to a ferrimagnetic phase at T(C) approximate to 42 K were detected in the magnetic signal. Geometric frustration of interactions between the AFM-coupled spins placed at the vertices of the triangle-square tiling should be a general feature of dodecagonal quasicrystals and their approximants, so that spin-glass-type ordering is expected to occur quite commonly in the dodecagonal phases.
Title:
Deformed triangular lattice antiferromagnets in a magnetic field: Role of spatial anisotropy and Dzyaloshinskii-Moriya interactions
Authors:
Griset, C; Head, S; Alicea, J; Starykh, OA Author Full Names: Griset, Christian; Head, Shane; Alicea, Jason; Starykh, Oleg A.
Source:
PHYSICAL REVIEW B, 84 (24):10.1103/PhysRevB.84.245108 DEC 12 2011
Abstract:
Recent experiments on the anisotropic spin-1/2 triangular antiferromagnet Cs(2)CuBr(4) have revealed a remarkably rich phase diagram in applied magnetic fields, consisting of an unexpectedly large number of ordered phases. Motivated by this finding, we study the role of three ingredients-spatial anisotropy, Dzyaloshinskii-Moriya interactions, and quantum fluctuations-on the magnetization process of a triangular antiferromagnet, coming from the semiclassical limit. The richness of the problem stems from two key facts: (1) the classical isotropic model with a magnetic field exhibits a large accidental ground-state degeneracy and (2) these three ingredients compete with one another and split this degeneracy in opposing ways. Using a variety of complementary approaches, including extensive Monte Carlo numerics, spin-wave theory, and an analysis of Bose-Einstein condensation of magnons at high fields, we find that their interplay gives rise to a complex phase diagram consisting of numerous incommensurate and commensurate phases. Our results shed light on the observed phase diagram for Cs(2)CuBr(4) and suggest a number of future theoretical and experimental directions that will be useful for obtaining a complete understanding of this material's interesting phenomenology.
Title:
Structure and Morphology of Induction-Melted Higher Manganese Silicide
Authors:
Zhou, AJ; Cui, HG; Li, JZ; Zhao, XB Author Full Names: Zhou Ai-Jun; Cui Heng-Guan; Li Jing-Ze; Zhao Xin-Bing
Source:
ACTA PHYSICO-CHIMICA SINICA, 27 (12):2915-2919; 10.3866/PKU.WHXB20112915 DEC 2011
Abstract:
Field emission scanning microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDXS) were used to study the morphology and composition of secondary phase precipitations in induction-melted higher manganese silicide (HMS). Striations of the secondary phase were observed in individual HMS crystals with an average interval of 5-30 pm and a thickness of similar to 30 nm. The chemical composition of the striations was examined and found to be MnSi, which was observed as an amorphous phase by high resolution transmission electron microscopy (HRTEM). The crystal structure of HMS was determined by selective area electron diffraction (SAED) and the results indicated a single Mn(4)Si(7) phase in the as-prepared material and no other incommensurate HMS phases were found. After ball milling and hot pressing many defects and stress fields were observed in the HMS by transmission electron microscope (TEM), which differentiated substantially from the morphology of the as-melted HMS.
Title:
Phase diagram of hard tetrahedra
Authors:
Haji-Akbari, A; Engel, M; Glotzer, SC Author Full Names: Haji-Akbari, Amir; Engel, Michael; Glotzer, Sharon C.
Source:
JOURNAL OF CHEMICAL PHYSICS, 135 (19):10.1063/1.3651370 NOV 21 2011
Abstract:
Advancements in the synthesis of faceted nanoparticles and colloids have spurred interest in the phase behavior of polyhedral shapes. Regular tetrahedra have attracted particular attention because they prefer local symmetries that are incompatible with periodicity. Two dense phases of regular tetrahedra have been reported recently. The densest known tetrahedron packing is achieved in a crystal of triangular bipyramids (dimers) with a packing density of 4000/4671 approximate to 85.63%. In simulation a dodecagonal quasicrystal is observed; its approximant, with periodic tiling (3.4.3(2).4), can be compressed to a packing fraction of 85.03%. Here, we show that the quasicrystal approximant is more stable than the dimer crystal for packing densities below 84% using Monte Carlo computer simulations and free energy calculations. To carry out the free energy calculations, we use a variation of the Frenkel-Ladd method for anisotropic shapes and thermodynamic integ ration. The enhanced stability of the approximant can be attributed to a network substructure, which maximizes the free volume (and hence the wiggle room) available to the particles and facilitates correlated motion of particles, which further contributes to entropy and leads to diffusion for packing densities below 65%. The existence of a solid-solid transition between structurally distinct phases not related by symmetry breaking - the approximant and the dimer crystal - is unusual for hard particle systems. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3651370]
Title:
Formation of Icosahedral Quasicrystals and 1/1 Crystal Approximants in Al-Pd-RE (RE: Rare Earth Metals) Systems
Authors:
So, YG; Yoshikawa, T; Saruhashi, F; Edagawa, K; Tamura, R Author Full Names: So, Yeong-Gi; Yoshikawa, Takuro; Saruhashi, Fukuaki; Edagawa, Keiichi; Tamura, Ryuji
Source:
MATERIALS TRANSACTIONS, 52 (11):2011-2015; 10.2320/matertrans.M2011162 NOV 2011
Abstract:
We have investigated the formation of an icosahedral quasicrystal (i-phase) and its 1/1-crystal approximant (1/1-phase) in the (Al, Ga)-Pd-RE (Rare earth metals) systems. Consequently, the Ga-Pd-Sc 1/1-phase, the Al-Pd-RE (RE = Yb, Tin and Er) 1/1-phase and the Al-Pd-Yb i-phase have been newly found by the substitution of Al for Ga, or Sc for other RE in the constituent elements of the Al(54)Pd(30)Sc(16) i-phase previously reported. For the i- and the 1/1-phases studied in this work, the number of valence electrons per atom (e/a) ratio is 2.10 and the atomic radius ratio of the rare earth element to that of the other base elements is in the range 1.15-1.24, which fulfilled the formation conditions previously reported for other Tsai-type i-phases. On the other hand, the stability of the i-phases becomes lower with increasing the atomic radii of the RE elements, which indicates that the atomic radius ratio plays important role in the formation of the Al-Pd-RE i- and 1/1-phases. [doi:10.2320/matertrans.M2011162]
Title:
Ti/Pr(0.7)Ca(0.3)MnO(3)/La(0.67)Sr(0.33)MnO(3)/Pt heterostructures
Authors:
Wang, ZW; Zhang, J; Li, HW; Dong, CY; Zhao, J; Zhao, X; Chen, W Author Full Names: Wang Zhong-Wei; Zhang Jian; Li Hong-Wei; Dong Chun-Ying; Zhao Jing; Zhao Xu; Chen Wei
Source:
ACTA PHYSICA SINICA, 60 (11):NOV 2011
Abstract:
Ti/Pr(0.7)Ca(0.3)MnO(3)/Pt and Ti/Pr(0.7)Ca(0.3)MnO(3)/La(0.67)Sr(0.33)MnO(3)/Pt heterostructures are prepared using a pulsed laser deposition (PLD) technique, and the resistive switching of the heterostructures is investigated. The Ti/Pr(0.7)Ca(0.3)MnO(3)/La(0.67)Sr(0.33)MnO(3)/Pt heterostructure, which has a La(0.67)Sro(0.33)MnO(3) modulation layer, shows superior characteristics of resistive switching. In particular, the switching ratio and the fatigue properties are improved greatly in this heterostructure. The mechanism of resistive switching in Ti/Pr(0.7)Ca(0.3)MnO(3)/La(0.67)Sr(0.33)MnO(3)/Pt heterostructure is also discussed in this paper.

Update: 19-Jan-2012

Title:
Evolution of the commensurate and incommensurate magnetic phases of the S=3/2 kagome staircase Co(3)V(2)O(8) in an applied field
Authors:
Helton, JS; Chen, Y; Bychkov, GL; Barilo, SN; Rogado, N; Cava, RJ; Lynn, JW Author Full Names: Helton, Joel S.; Chen, Ying; Bychkov, Georgii L.; Barilo, Sergei N.; Rogado, Nyrissa; Cava, Robert J.; Lynn, Jeffrey W.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (1):10.1088/0953-8984/24/1/016003 JAN 11 2012
Abstract:
Single crystal neutron diffraction studies have been performed on the S = 3/2 kagome staircase compound Co(3)V(2)O(8) with a magnetic field applied along the magnetization easy-axis ((H) over right arrow parallel to(a) over right arrow). Previous zero- field measurements (Chen Y et al 2006 Phys. Rev. B 74 014430) reported a rich variety of magnetic phases, with a ferromagnetic ground state as well as incommensurate, transversely polarized spin density wave (SDW) phases (with a propagation vector of (k) over right arrow = (0 delta 0)) interspersed with multiple commensurate lock-in transitions. The magnetic phase diagram with ((H) over right arrow parallel to(a) over right arrow) adds further complexity. For small applied fields, mu(0)H approximate to 0.05 T, the commensurate lock-in phases are destabilized in favor of the incommensurate SDW ones, while slightly larger applied fields restore the commensurate lock-in phase with delta = 1/2 and yield a new commensurate phase with delta = 2/5. For measurements in an applied field, higher-order scattering is observed that corresponds to the second harmonic.
Title:
Microstructures and mechanical properties of quasicrystal reinforced AZ31 matrix composites
Authors:
Wang, XD; Du, WB; Wang, ZH; Liu, K; Li, SB Author Full Names: Wang, Xudong; Du, Wenbo; Wang, Zhaohui; Liu, Ke; Li, Shubo
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 530 446-451; 10.1016/j.msea.2011.09.110 DEC 15 2011
Abstract:
In order to improve the mechanical properties of AZ31 alloys, the repeated plastic working process was employed to fabricate the AZ31-based composites reinforced with stable icosahedral quasicrystal particles. The microstructure of the composites has been investigated by XRD, SEM, TEM and HREM, and their mechanical properties have also been studied. The results showed that the RPW process reduced the grain size significantly, and the average grain size was only about 500 nm after 200 cycles of RPW. A good metallurgical bond interface between the quasicrystal particles and the Mg matrix was found in their crystallographic orientation relationship of (1 0 (1) over bar 0)(mg)//2-f. The composites exhibited the maximum yield tensile strength of 334 MPa and the maximum ultimate tensile strength of 372 MPa at room temperature, respectively. The enhanced mechanical properties were attributed to the strengthening effect of quasicrystal particles and the refined microstructure. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Effects of the commensurability and disorder on friction for the system Xe/Cu
Authors:
Franchini, A; Bortolani, V; Santoro, G; Xheka, K Author Full Names: Franchini, A.; Bortolani, V.; Santoro, G.; Xheka, K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 23 (48):10.1088/0953-8984/23/48/484004 DEC 7 2011
Abstract:
We present molecular dynamics simulations of static friction for a monolayer of Xe deposited on a thick slab of Cu for two different geometries. The interaction potential between Xe and Cu has been derived from DFT calculations. The first geometry is the commensurate adsorption geometry (root 3 x root 3)R30 degrees suggested by LEED, corresponding to a coverage 1/3, where all Xe atoms are on top positions. The second one corresponds to a coverage 0.36 and is characterized by a large surface unit cell, containing 9 Xe atoms in different disordered positions. This large unit cell mimics an incommensurate case. Our analysis points out the effect of the order/disorder in tribological properties of a realistic three-dimensional system.
Title:
Resonant tunneling in GaAs/Al(x)Ga(1-x)As superlattices with aperiodic potential profiles
Authors:
Djelti, R; Aziz, Z; Bentata, S; Besbes, A Author Full Names: Djelti, R.; Aziz, Z.; Bentata, S.; Besbes, A.
Source:
SUPERLATTICES AND MICROSTRUCTURES, 50 (6):659-666; 10.1016/j.spmi.2011.09.007 DEC 2011
Abstract:
Using the exact Airy function formalism and the transfer-matrix technique, we have numerically investigated in this paper the effect of intentional correlations in spatial disorder on transmission properties of one-dimensional superlattices. Such systems consist of two different structures randomly distributed along the growth direction, with the additional constraint that barriers (wells) of one kind always appear in triply. It is shown that the intentional correlations in disorder and superlattices structural parameters are responsible to obtain resonant tunneling in aperiodic structure. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Structure, electrical and magnetic property investigations on dense Fe-doped hexagonal BaTiO(3)
Authors:
Wei, XK; Su, YT; Sui, Y; Zhang, QH; Yao, Y; Jin, CQ; Yu, RC Author Full Names: Wei, X. K.; Su, Y. T.; Sui, Y.; Zhang, Q. H.; Yao, Y.; Jin, C. Q.; Yu, R. C.
Source:
JOURNAL OF APPLIED PHYSICS, 110 (11):10.1063/1.3658813 DEC 1 2011
Abstract:
Hexagonal Ba(Ti(1-x)Fe(x))O(3-delta) (x = 1/6, 1/3) ceramics treated with post annealing are specifically synthesized to explore the origin mechanism of the unusual ferromagnetism in the doped system. X-ray diffraction refinements and transmission electron microscope experiments reveal that their structures are incommensurately modulated owing to simultaneous oxygen vacancies at both O1 and O2 sites. Consequently, coexisting weak ferrielectricity and weak ferromagnetism are presented at room temperature. Analysis on their leakage current plot reveals that their conduction follows trap-filled limit model. In combination with the magnetism studies on 5 mol% Fe-doped crystals [Phys. Rev. B 83, 144407 (2011)], the reduction of ferromagnetism with an increase of conductivity suggests that dynamic exchanges of trapped electrons among the bound magnetic polarons attribute to the intrinsic ferromagnetism. (C) 2011 American Institute of Physics. [doi:10.1063/1.3658813]
Title:
Analytic solutions to a finite width strip with a single edge crack of two-dimensional quasicrystals
Authors:
Li, W Author Full Names: Li Wu
Source:
CHINESE PHYSICS B, 20 (11):10.1088/1674-1056/20/11/116201 NOV 2011
Abstract:
In this paper, we investigate the well-known problem of a finite width strip with a single edge crack, which is useful in basic engineering and material science. By extending the configuration to a two-dimensional decagonal quasicrystal, we obtain the analytic solutions of modes I and II using the transcendental function conformal mapping technique. Our calculation results provide an accurate estimate of the stress intensity factors K(I) and K(II), which can be expressed in a quite simple form and are essential in the fracture theory of quasicrystals. Meanwhile, we suggest a generalized cohesive force model for the configuration to a two-dimensional decagonal quasicrystal. The results may provide theoretical guidance for the fracture theory of two-dimensional decagonal quasicrystals.
Title:
On a Realistic Growth Mechanism for Quasicrystals
Authors:
Steurer, W Author Full Names: Steurer, Walter
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 637 (13):1943-1947; SI 10.1002/zaac.201100210 NOV 2011
Abstract:
Simple rules are discussed that can guide under realistic conditions the growth of quasicrystals. We propose a two-step mechanism where the well-known overlap rules for the fundamental atomic clusters are complemented by the new layer-continuation rule. This rule demands that the sets of atomic layers, crisscrossing each atomic cluster according to its eigensymmetry, have to be continued across all other clusters formed during the growth process. On one hand, this combined growth rule is local because each fundamental cluster already defines the overlap rules as well as the basic set of atomic layers. On the other hand, it is global because the framework of atomic layers originating locally from each cluster extends infinitely. The layer-continuation rule guides the attachment of atoms to the growing quasicrystal and assists the overlap rules, which are at the high temperatures, where crystal growth takes place, only weakly supported by specific atomic arrangements in the shared cluster volumes.
Title:
Proton NMR study of the organic metal kappa-(BETS)(2)Mn[N(CN)(2)](3)
Authors:
Vyaselev, OM; Kushch, ND; Yagubskii, EB Author Full Names: Vyaselev, O. M.; Kushch, N. D.; Yagubskii, E. B.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 113 (5):835-841; 10.1134/S106377611114010X NOV 2011
Abstract:
Magnetic properties of the organic conductor kappa-(BETS)(2)Mn[N(CN)(2)](3) above and below the temperature of the metal-insulator transition that occurs at T (MI) a parts per thousand 25 K are studied by (1)H NMR. The proton spectrum is shown to be determined by the static dipolar fields from Mn(2+) localized moments, while the (1)H spin-lattice relaxation is dominated by fluctuating fields from Mn(2+) electrons. The NMR data, both static (the spectra) and dynamic (the spin-lattice relaxation), indicate the freezing of Mn(2+) moments into a short-range or an incommensurate long-range antiferromagnetic order below T (MI).
Title:
A Study of the Formation of Ln(2+x)Me(2-x)O(7-x/2) (Ln = Gd, Dy; Me = Zr, Hf) Nanocrystals
Authors:
Popov, VV; Zubavichus, YV; Petrunin, VF; Menushenkov, AP; Kashurnikova, OV; Korovin, SA; Chernikov, RV; Yaroslavtsev, AA Author Full Names: Popov, V. V.; Zubavichus, Ya. V.; Petrunin, V. F.; Menushenkov, A. P.; Kashurnikova, O. V.; Korovin, S. A.; Chernikov, R. V.; Yaroslavtsev, A. A.
Source:
GLASS PHYSICS AND CHEMISTRY, 37 (5):512-520; 10.1134/S1087659611050117 OCT 2011
Abstract:
It has been established that the process of producing the Ln(2+x)Me(2-x)O(7-x/2) (Ln = Gd, Dy; Me = Zr, Hf) nanocrystals by calcination of hydroxides, which, in turn, have been produced by coprecipitation of metal salts, includes several stages. At the beginning, the X-ray amorphous structure of the precursors remains unchanged during dehydration; during subsequent heating to 600-700 degrees C, nanocrystals with a disordered fluorite structure begin to be formed. An increase in the temperature above 700 degrees C leads to an increase in the size of crystallites (coherent scattering regions). This process is accompanied by changes occurring in their local structure. In the nanocrystalline powders of Cd(2)Hf(2)O(7) and Gd(2)Zr(2)O(7) synthesized at 1200 degrees C (6 h), the pyrochlore-type superstructure with the lattice parameters doubled relative to fluorite has been revealed. It has also been found that, possibly, the Dy(2)HfO(5) sample at 1600 degrees C (3 h) has a modulated structure.

Update: 11-Jan-2012

Title:
Ordered fluorite phases in the Bi(2)O(3)-Ta(2)O(5) system: A structural and electrical investigation
Authors:
Struzik, M; Malys, M; Wrobel, W; Abrahams, I; Krok, F; Dygas, JR Author Full Names: Struzik, M.; Malys, M.; Wrobel, W.; Abrahams, I.; Krok, F.; Dygas, J. R.
Source:
SOLID STATE IONICS, 202 (1):22-29; 10.1016/j.ssi.2011.08.009 NOV 2 2011
Abstract:
Structure and electrical behaviour are reported for the system Bi(1-x)Ta(x)O(1.5+x) (0.167 <= x <= 0.250). In the compositional range 0.200 < x <= 0.250 an incommensurately modulated pseudo-cubic phase (type II) is observed, with the appearance of a larger pseudo-cubic phase in the region 0.167 <= x <= 0.200. Structural analysis of the type II phases by neutron diffraction reveals subtle changes in the oxide ion distribution with temperature, associated with changes in the incommensurate modulation parameter. Analysis of the defect structure of the type II phase reveals chains of tantalate octahedra as a likely structural motif. It is proposed that these chains facilitate an electronic contribution to total conductivity at low temperatures through electron hopping along the chains. Changes in oxide ion vacancy ordering may explain the observed non-linear behaviour in the thermal expansion of lattice parameter and Arrhenius plots of total conductivity. (C) 2011 Elsevier B.V. A! ll rights reserved.

Update: 4-Jan-2012

Title:
Nobel Prize in Chemistry honors the discovery of quasicrystals
Authors:
Smart, AG Author Full Names: Smart, Ashley G.
Source:
PHYSICS TODAY, 64 (12):17-20; DEC 2011

Update: 29-Dec-2011

Title:
Microscopically derived Ginzburg-Landau theory for magnetic order in the iron pnictides
Authors:
Brydon, PMR; Schmiedt, J; Timm, C Author Full Names: Brydon, P. M. R.; Schmiedt, Jacob; Timm, Carsten
Source:
PHYSICAL REVIEW B, 84 (21):10.1103/PhysRevB.84.214510 DEC 7 2011
Abstract:
We examine the competition of the observed stripe spin density wave (SDW) with other commensurate and incommensurate SDW phases in a two-band model of the pnictides. Starting from this microscopic model, we rigorously derive an expansion of the free energy in terms of the different order parameters at the mean-field level. We show that three distinct commensurate SDW states are possible and study their appearance as a function of the doping and the electronic structure. We show that the stripe phase is generally present, but its extent in the phase diagram depends strongly upon the number of hole Fermi pockets that are nested with the electron Fermi pockets. Electron pockets competing for the same portion of a hole pocket play a crucial role. We discuss the relevance of our results for the antiferromagnetism of the pnictides.
Title:
(57)Fe Mossbauer spectroscopy studies of CaFe(4)As(3)
Authors:
Nowik, I; Felner, I; Karki, AB; Jin, R Author Full Names: Nowik, I.; Felner, I.; Karki, A. B.; Jin, R.
Source:
PHYSICAL REVIEW B, 84 (21):10.1103/PhysRevB.84.212402 DEC 7 2011
Abstract:
We report on the (57)Fe Mossbauer spectroscopy and direct-current magnetization studies of orthorhombic CaFe(4)As(3), which undergoes two magnetic transitions with the formation of spin density wave at T(N1) = 88 K (incommensurate) and T(N2) = 26 K (commensurate). The magnetic Mossbauer spectroscopy spectra below T(N1) are composed of four subspectra attributed to the four in-equivalent Fe crystallographic sites: three Fe ions in the divalent state (Fe(2+)) and one as Fe(1+). However, the magnetic lines are much broader than that below T(N2), indicating an incommensurate magnetic state. In the paramagnetic state, the Mossbauer spectroscopy spectra are composed of three doublets; one of them is related to Fe(1+). Evidence for spin fluctuations above T(N1) is observed.
Title:
Atomic dynamics and interatomic interaction in quasicrystals
Authors:
Parshin, PP; Zemlyanov, MG; Brand, RA Author Full Names: Parshin, P. P.; Zemlyanov, M. G.; Brand, R. A.
Source:
CRYSTALLOGRAPHY REPORTS, 56 (7):1145-1148; 10.1134/S1063774511070285 DEC 2011
Abstract:
The previous experimental data on the partial spectra of thermal atomic vibrations in icosahedral (Al(62)Cu(25.5)Fe(12.5)) and decagonal (Al(71.3)Ni(24)Fe(4.7)) quasicrystals have been used to perform a comparative analysis of the atomic dynamics features and determine the role that Al, Cu, Ni, and Fe atoms play in the formation of interatomic interaction in the alloys studied. A physical model of the decagonal quasicrystal structure is proposed.
Title:
Atomic packing and short-to-medium range order evolution of Zr-Pd metallic glass
Authors:
Qi, L; Liu, M; Zhang, SL; Zhang, XY; Tan, CL Author Full Names: Qi Li; Liu Mei; Zhang ShiLiang; Zhang XinYu; Tan ChunLin
Source:
CHINESE SCIENCE BULLETIN, 56 (36):3908-3911; 10.1007/s11434-011-4841-0 DEC 2011
Abstract:
A larger-scale Zr(70)Pd(30) alloy system has been simulated using molecular dynamics (MD) to investigate structure evolution in Zr(70)Pd(30) metallic glass. The simulated pair distribution function of Zr(70)Pd(30) metallic glass agrees well with the experimental results. Voronoi polyhedron analysis indicates that the icosahedra are not randomly distributed in space, but form characteristic intercrossed icosahedral clusters with medium-range order. Intercrossed icosahedral clusters are the dominant local configurations in Zr(70)Pd(30) metallic glass and probably cause the quasicrystalline phase discovered in Zr(70)Pd(30) metallic glass.
Title:
Highly mobile twinned interface in 10 M modulated Ni-Mn-Ga martensite: Analysis beyond the tetragonal approximation of lattice
Authors:
Straka, L; Heczko, O; Seiner, H; Lanska, N; Drahokoupil, J; Soroka, A; Fahler, S; Hanninen, H; Sozinov, A Author Full Names: Straka, L.; Heczko, O.; Seiner, H.; Lanska, N.; Drahokoupil, J.; Soroka, A.; Faehler, S.; Hanninen, H.; Sozinov, A.
Source:
ACTA MATERIALIA, 59 (20):7450-7463; 10.1016/j.actamat.2011.09.020 DEC 2011
Abstract:
The huge strains that Ni-Mn-Ga magnetic shape memory alloys can achieve are usually described in a tetragonal unit cell approximation of a five-layered modulated (10 M) crystal structure. Here we analyze the impact of a slight orthorhombic and monoclinic distortion of the 10 M structure in Ni(50.2)Mn(28.3)Ga(21.5)at(.%) single crystal. Combining dedicated experiments to probe the microstructure, structure and mechanical properties with calculation using elastic continuum theory, we prove the existence of fine a/b-laminates within modulation macrotwins of the order of 100 micrometers in size. This complex twin microstructure containing a Type II macrotwin interface is associated with an extraordinarily low twinning stress of between 0.05 and 0.3 MPa, while Type I twins exhibit twinning stress of about 1 MPa. The findings provide important guidelines for designing the martensitic microstructure for more efficient actuators. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Phase evolution and magnetic property of Bi(1-x)Ho(x)FeO(3) powders
Authors:
Wu, YJ; Zhang, J; Chen, XK; Chen, XJ Author Full Names: Wu, Yu-Jie; Zhang, Jing; Chen, Xiao-Kun; Chen, Xiao-Jia
Source:
SOLID STATE COMMUNICATIONS, 151 (24):1936-1940; 10.1016/j.ssc.2011.09.020 DEC 2011
Abstract:
The structural, vibrational, and magnetic properties of well prepared Bi(1-x)Ho(x)FeO(3) (x = 0-0.175) powders are investigated by combining X-ray diffraction, Raman scattering, and magnetometry measurements. A structural symmetry breaking from the rhombohedral R3c to orthorhombic Pnma between x = 0.10 and 0.125 is identified from the X-ray and Raman measurements, accompanying a ferroelectric-paraelectric phase transition. The remnant magnetization of Bi(1-x)Ho(x)FeO(3) is enhanced before approaching the ferroelectric-paraelectric phase boundary, and then it slightly decreases until x = 0.175. Such enhancement (0 <= x <= 0.10) is suggested to result from the destruction of the spin cycloid structure. The decrease in the remnant magnetization with higher substitution concentration is due to the further destruction in the space modulated spin structure allowing a more perfect antiferromagnetic ordering. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Incommensurate Antiferromagnetic Insulating State in (MDT-TS)(AuI(2))(x)
Authors:
Yoshioka, H; Seo, H; Otsuka, Y Author Full Names: Yoshioka, Hideo; Seo, Hitoshi; Otsuka, Yuichi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 80 (12):10.1143/JPSJ.80.123702 DEC 2011
Abstract:
We theoretically study the metal-insulator transition in a molecular conductor (MDT-TS)(AuI(2))(x) composed with an incommensurate ratio (x = 0.441), where the conduction band originated from the HOMO of donor MDT-TS molecules is incommensurately filled. We consider a two-dimensional Hubbard model taking account of anisotropic transfer integrals in the donor layer, under a periodic potential due to the anions (AuI(2))(-) which mismatches the donor lattice period, and investigate the ground state within mean-field approximation. An antiferromagnetic insulating state with induced charge disproportionation is obtained in the large U and delta region; the symmetry in the charge sector is unchanged from the paramagnetic metallic state realized at small U and delta, therefore this state corresponds to the incommensurate Mott insulating state predicted previously [H. Yoshioka et al.: J. Phys. Soc. Jpn. 74 (2005) 1922] based on a simplified one-dimensional model.
Title:
Complex magnetoelastic properties in the frustrated kagome-staircase compounds (Co(1-x)Ni(x))(3)V(2)O(8)
Authors:
Zhang, Q; Knafo, W; Adelmann, P; Schweiss, P; Grube, K; Qureshi, N; Wolf, T; von Lohneysen, HV; Meingast, C Author Full Names: Zhang, Q.; Knafo, W.; Adelmann, P.; Schweiss, P.; Grube, K.; Qureshi, N.; Wolf, Th.; v. Loehneysen, H.; Meingast, C.
Source:
PHYSICAL REVIEW B, 84 (18):10.1103/PhysRevB.84.184429 NOV 28 2011
Abstract:
High-resolution heat-capacity and thermal-expansion measurements on single crystals of the kagome-staircase compounds (Co(1-x)Ni(x))(3)V(2)O(8) are presented. The parent compounds Co(3)V(2)O(8) and Ni(3)V(2)O(8) undergo a sequence of first-and second-order magnetic phase transitions. The low-temperature (T <= 40 K) magnetic entropy evolves monotonically with the doping content x from the full value expected for Ni(2+) S = 1 magnetic moments in Ni(3)V(2)O(8) to only half the value expected for Co(2+) S = 3/2 moments in Co(3)V(2)O(8). The thermal-expansion coefficients alpha(i) (i = a, b, and c) show a strong anisotropy for all (Co(1-x)Ni(x))(3)V(2)O(8) compounds. The low temperature expansivities indicate that Co doping (Ni doping) yields changes similar to uniaxial pressures along a or b (c). Linear Gruneisen parameters Gamma(i) are extracted for the three main axes i and are found to exhibit a complex temperature and doping dependence. For each axis, Gamma(i) and alpha(i) exhibit a sign change at low temperature at the critical concentration x(c) similar or equal to 0.25 where the incommensurate magnetic propagation vector changes. Our study motivates further investigations to understand how the multiple and complex parameters such as magnetic frustration, magnetic anisotropy, and mixture of S = 1 and 3/2 ions affect the rich magnetoelastic properties of (Co(1-x)Ni(x))(3)V(2)O(8).
Title:
Investigation of the Formation of Quasicrystalline Al(70)-Pd(20)-Re(10) Phase in situ during Annealing
Authors:
Makhotkin, IA; Yakunin, SN; Seregin, AY; Shaitur, DS; Tsetlin, MB; Tereshchenko, EY Author Full Names: Makhotkin, I. A.; Yakunin, S. N.; Seregin, A. Yu.; Shaitur, D. S.; Tsetlin, M. B.; Tereshchenko, E. Yu.
Source:
CRYSTALLOGRAPHY REPORTS, 56 (5):871-874; 10.1134/S106377451105018X SEP 2011
Abstract:
The change in the phase composition of thin-film layered AlPdRe nanostructures during annealing, which led to the formation of a quasicrystalline layer, has been studied in situ. It is shown that the Al(3)Pd phase is formed at a temperature above 260 degrees C, which transforms into the AlPd phase at 580 degrees C, and the icosahedral quasicrystalline Al-Pd-Re phase is formed at 680 degrees C. DOI: 10.1134/S106377451105018X

Update: 22-Dec-2011

Title:
Determination of the orientation relationship between austenite and 5M modulated martensite in Ni-Mn-Ga alloys
Authors:
Li, ZB; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Zongbin; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 44 1222-1226; Part 6 10.1107/S0021889811043366 DEC 2011
Abstract:
The microstructural and crystallographic characteristics of 5M martensite in an Ni(50)Mn(28)Ga(22) alloy were investigated by electron backscatter diffraction (EBSD) analysis. The microstructure of 5M martensite observed at room temperature can be characterized by broad plates with alternately distributed fine lamellae (variants). With the accurate EBSD orientation measurements and by application of monoclinic superstructure information, four twin-related variants in one broad plate were identified. On the basis of the correct orientation data of martensite variants acquired from the EBSD measurements, the more favourable orientation relationship between austenite and 5M martensite was revealed to be the Pitsch relation with (101)(A)//(1 (2) over bar(5) over bar)(5M) and [10 (1) over bar](A)//[(5) over bar(5) over bar1](5M) by detailed crystallographic calculation without residual austenite.
Title:
Mossbauer investigations of crystalline and quasicrystalline Al(3)(Mn, Fe) compounds
Authors:
Ali, K; Reissner, M; Steiner, W; Feuerbacher, M Author Full Names: Ali, K.; Reissner, M.; Steiner, W.; Feuerbacher, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 23 (47):10.1088/0953-8984/23/47/475501 NOV 30 2011
Abstract:
(57)Fe Mossbauer and magnetic measurements are reported on Taylor phase compounds T-Al(3)(Mn, Fe), which can be seen as complex metallic alloys. The orthorhombic unit cell contains 156 atoms. These investigations are further extended to Al(71)Mn(19)Fe(10) crystallizing as a decagonal quasicrystal. Common to both structures are layers, which are oriented perpendicular to the b axis in the crystalline or to the periodic axis in the quasicrystalline compound, allowing the formation of characteristic building blocks. At low temperatures for all samples spin glass behavior is observed with freezing temperatures T(f) increasing with Fe content. Above T(f) the (57)Fe Mossbauer spectra were analyzed by a superposition of two subspectra with intensity ratio around 75: 25, which can be allocated to Fe substituted on Mn sites surrounded either by Al and Mn or solely by Al with Mn only at the edge of the nearest neighbor shell. For both subspectra quadrupole splitting and center shift do not change significantly with Fe content and with structure. Below T(f) broad hyperfine field distributions with non-vanishing contributions at zero hyperfine field are present. Magnetic and electrostatic hyperfine interactions are governed by length scales which are determined by the very similar interatomic configurations forming the T-Al(3)Mn phase as well as the decagonal compound. The presence of long range atomic order is of less importance.
Title:
Coexistence of the long-range and short-range magnetic order components in SrEr(2)O(4)
Authors:
Hayes, TJ; Balakrishnan, G; Deen, PP; Manuel, P; Chapon, LC; Petrenko, OA Author Full Names: Hayes, T. J.; Balakrishnan, G.; Deen, P. P.; Manuel, P.; Chapon, L. C.; Petrenko, O. A.
Source:
PHYSICAL REVIEW B, 84 (17):10.1103/PhysRevB.84.174435 NOV 23 2011
Abstract:
Single-crystal neutron diffraction reveals two distinct components to the magnetic ordering in geometrically frustrated SrEr(2)O(4). One component is a long-range ordered k = 0 structure which appears below T(N) = 0.75 K. Another component is a short-range incommensurate structure which manifests itself by the presence of a strong diffuse scattering signal. On cooling from higher temperatures down to 0.06 K, the partially ordered component does not undergo a pronounced phase transition. The magnetic moments in the long-range commensurate and short-range incommensurate structures are predominantly pointing along the [001] and [100] axes, respectively. The unusual coexistence of two magnetic structures is probed using both unpolarized and XYZ-polarized neutron scattering techniques. The observed diffuse scattering pattern can be satisfactorily reproduced with a classical Monte Carlo simulation by using a simple model based on a ladder of triangles.

Update: 7-Dec-2011

Title:
Successive magnetic transitions and static magnetic order in RCoAsO (R = La, Ce, Pr, Nd, Sm, Gd) confirmed by muon-spin rotation and relaxation
Authors:
Sugiyama, J; Mansson, M; Ofer, O; Kamazawa, K; Harada, M; Andreica, D; Amato, A; Brewer, JH; Ansaldo, EJ; Ohta, H; Michioka, C; Yoshimura, K Author Full Names: Sugiyama, Jun; Mansson, Martin; Ofer, Oren; Kamazawa, Kazuya; Harada, Masashi; Andreica, Daniel; Amato, Alex; Brewer, Jess H.; Ansaldo, Eduardo J.; Ohta, Hiroto; Michioka, Chishiro; Yoshimura, Kazuyoshi
Source:
PHYSICAL REVIEW B 84 (18): 10.1103/PhysRevB.84.184421 NOV 16 2011
Abstract:
The presence of antiferromagnetic (AF) order seems to be a common feature for the parent compounds of cuprate as well as some pnictide high-temperature superconductors. In order to search for antiferromagnetic order in the closely related rare-earth cobalt arsenic oxides (RCoAsO), we have measured muon-spin rotation and relaxation (mu(+)SR) spectra on a series of powder samples with R = La, Ce, Pr, Nd, Sm, and Gd. It was found that, besides GdCoAsO, all the other five compounds enter into a static ferromagnetic ordered phase below around 70 K (=T(C)), while additional transitions into a static AF ordered phase were found for NdCoAsO and SmCoAsO. For GdCoAsO, a static ferrimagnetic phase appeared below 60.5 K and then an incommensurate spin-density-wave ordered phase followed below 3.2 K. The AF spin structure was also found to strongly depend on R.
Title:
Degenerate Quasicrystal of Hard Triangular Bipyramids
Authors:
Haji-Akbari, A; Engel, M; Glotzer, SC Author Full Names: Haji-Akbari, Amir; Engel, Michael; Glotzer, Sharon C.
Source:
PHYSICAL REVIEW LETTERS 107 (21): 10.1103/PhysRevLett.107.215702 NOV 15 2011
Abstract:
We report a degenerate quasicrystal in Monte Carlo simulations of hard triangular bipyramids each composed of two regular tetrahedra sharing a single face. The dodecagonal quasicrystal is similar to that recently reported for hard tetrahedra [Haji-Akbari et al., Nature (London) 462, 773 (2009)] but degenerate in the pairing of tetrahedra, and self-assembles at packing fractions above 54%. This notion of degeneracy differs from the degeneracy of a quasiperiodic random tiling arising through phason flips. Free energy calculations show that a triclinic crystal is preferred at high packing fractions.
Title:
Low-temperature structure of xi '-Al-Pd-Mn optimized by ab initio methods
Authors:
Frigan, B; Santana, A; Engel, M; Schopf, D; Trebin, HR; Mihalkovic, M Author Full Names: Frigan, Benjamin; Santana, Alejandro; Engel, Michael; Schopf, Daniel; Trebin, Hans-Rainer; Mihalkovic, Marek
Source:
PHYSICAL REVIEW B 84 (18): 10.1103/PhysRevB.84.184203 NOV 14 2011
Abstract:
We have studied and resolved occupancy correlations in the existing average structure model of the complex metallic alloy xi'-Al-Pd-Mn [Boudard et al., Philos. Mag. A 74, 939 (1996)], which has approximately 320 atoms in the unit cell and many fractionally occupied sites. Model variants were constructed systematically in a tiling-decoration approach and subjected to simulated annealing by use of both density functional theory and molecular dynamics with empirical potentials. To obtain a measure for thermodynamic stability, we reproduce the Al-Pd-Mn phase diagram at T = 0 K, and derive an enthalpy of formation for each structure. Our optimal structure resolves a cloud of fractionally occupied sites in pseudo-Mackay clusters. In particular, we demonstrate the presence of rotational degrees of freedom of an Al(9) inner shell, which is caged within two icosahedrally symmetric outer shells Al(30) and Pd(12). Outside these clusters, the chemical ordering on a chain of three nearby sites surprisingly breaks the inversion symmetry of the surrounding structure, and couples to an Al/vacancy site nearby. Our refined tiling-decoration model applies to any structure within the epsilon-phases family, including the metastable decagonal quasicrystalline phase.
Title:
Order in a spatially anisotropic triangular antiferromagnet
Authors:
Ghamari, S; Kallin, C; Lee, SS; Sorensen, ES Author Full Names: Ghamari, Sedigh; Kallin, Catherine; Lee, Sung-Sik; Sorensen, Erik S.
Source:
PHYSICAL REVIEW B 84 (17): 10.1103/PhysRevB.84.174415 NOV 14 2011
Abstract:
The phase diagram of the spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice of weakly coupled chains, a model relevant to Cs(2)CuCl(4), is investigated using a renormalization group analysis, which includes marginal couplings important for connecting to numerical studies of this model. In particular, the relative stability of incommensurate spiral spin-density order and collinear antiferromagnetic order is studied. While incommensurate spiral order is found to exist over most of the phase diagram in the presence of a Dzyaloshinskii-Moriya (DM) interaction, at small interchain and extremely weak DM couplings, collinear antiferromagnetic order can survive. Our results imply that Cs(2)CuCl(4) is well within the part of the phase diagram where spiral order is stable. The implications of the renormalization group analysis for numerical studies, many of which have found spin-liquidlike behavior, are discussed.
Title:
Mixed Acoustic Phonons and Phase Modes in an Aperiodic Composite Crystal
Authors:
Toudic, B; Lefort, R; Ecolivet, C; Guerin, L; Currat, R; Bourges, P; Breczewski, T Author Full Names: Toudic, B.; Lefort, R.; Ecolivet, C.; Guerin, L.; Currat, R.; Bourges, P.; Breczewski, T.
Source:
PHYSICAL REVIEW LETTERS 107 (20): 10.1103/PhysRevLett.107.205502 NOV 9 2011
Abstract:
Aperiodic crystals which are long range ordered materials present original dynamics features due to the lack of translational symmetry formally implying the nonvalidity of the Brillouin zone concept. This Letter reports the observation by neutron scattering of an overdamped acousticlike mode at a Bragg peak position in a n-alkane-urea inclusion crystal. This result implies the existence of a gap in the dispersion branch. The gap and anomalous damping of these collective modes are discussed in terms of specific dynamics and interaction in aperiodic materials.
Title:
Comment on "Origin of Friction Anisotropy on a Quasicrystal Surface" Reply
Authors:
Filippov, AE; Vanossi, A; Urbakh, M Author Full Names: Filippov, Aleksander E.; Vanossi, Andrea; Urbakh, Michael
Source:
PHYSICAL REVIEW LETTERS 107 (20): 10.1103/PhysRevLett.107.209402 NOV 8 2011
Title:
Comment on "Origin of Friction Anisotropy on a Quasicrystal Surface"
Authors:
McLaughlin, K; Rabson, D; Thiel, P Author Full Names: McLaughlin, K.; Rabson, D.; Thiel, P.
Source:
PHYSICAL REVIEW LETTERS 107 (20): 10.1103/PhysRevLett.107.209401 NOV 8 2011
Title:
Magnetic Structures of Pr(0.8)Lu(0.2)Mn(2)Ge(2) and Pr(0.6)Lu(0.4)Mn(2)Ge(2)
Authors:
Wang, JL; Studer, AJ; Campbell, SJ; Kennedy, SJ; Zeng, R; Dou, SX; Wu, GH Author Full Names: Wang, J. L.; Studer, A. J.; Campbell, S. J.; Kennedy, S. J.; Zeng, R.; Dou, S. X.; Wu, G. H.
Source:
IEEE TRANSACTIONS ON MAGNETICS 47 (10): 2893-2896 10.1109/TMAG.2011.2151180 OCT 2011
Abstract:
The magnetic structures of Pr(0.8)Lu(0.2)Mn(2)Ge(2) and Pr(0.6)Lu(0.4)Mn(2)Ge(2) have been determined by neutron powder diffraction over the temperature range 10-450 K. On cooling from the paramagnetic region the Mn sublattice of Pr(0.8)Lu(0.2)Mn(2)Ge(2) orders in a similar manner to PrMn(2)Ge(2) with first ab-plane intralayer antiferromagnetism (AFI) below T(N)(intra) similar to 397 K followed by canted ferromagnetism (Fmc) at T(C)(inter) similar to 330 K and then a conical (Fmi) spin structure below T(c/c) similar to 192 K. The transition at T(C)(Pr) = 35 K with related enhancement in magnetization, is assigned to the additional ferromagnetic contribution of the Pr sublattice leading to the combined (Fmc+F(Pr)). For Pr(0.6)Lu(0.4)Mn(2)Ge(2) the transition from PM to AFI occurs at T(N)(intra) similar to 375 K while the canted ferromagnetic (Fmc) state forms at T(C)(intra) similar to 321 K. The increased Lu concentration of Pr(0.6)Lu(0.4)Mn(2)Ge(2) destroys the incommensurate Fmi conical spin structure of Pr(0.8)Lu(0.4)Mn(2)Ge(2). Rather, in common with similar mixed RT(2)X(2) systems (e.g., La(1-x)Y(x)Mn(2)Si(2), La(1-x)Pr(x)Mn(2)Si(2)), the Pr(0.6)Lu(0.4)Mn(2)Ge(2) compound exhibits co-existence of the AFmc and Fmc phases on cooling from the pure Fmc state. Transformation to the combined ferromagnetic state (Fmc+F(Pr)) takes place on c-axis ordering of the Pr sublattice at T(C)(Pr) similar to 31 K. In the region of phase co-existence, the Fmc unit cell is larger than the AFmc unit cell indicating strong magneto-structural coupling with a change of the lattice inducing a change of the magnetic state.
Title:
Three-dimensional reconstruction of the atomic arrangement of icosahedral quasicrystals by binary discrete tomography
Authors:
Ishibashi, Y; Sugiura, H; Saitoh, K; Tanaka, N Author Full Names: Ishibashi, Y.; Sugiura, H.; Saitoh, K.; Tanaka, N.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2519-2527 SI 10.1080/14786435.2010.523717 2011
Abstract:
A three-dimensional reconstruction of the structure of icosahedral quasicrystals from high-resolution transmission electron microscope images observed along high-symmetry zone-axis projections is studied. As in discrete tomography, the quasicrystalline structure is treated as a discrete set of atoms arranged on the icosahedral lattice, including atom flip sites, which is a structural disorder originating from the degrees of freedom in the internal space. The occupancy of the atoms on each site of the lattice is determined using only the zone-axis projection images without any knowledge of the image intensity. Simulation studies using icosahedral model lattices composed of several thousands of atoms were carried out to test the present reconstruction method. In the case of the ideal icosahedral lattice, a reconstruction rate of 90% is achieved from 10 projection images and a reconstruction rate of 99% is achieved from 18 projections. The reconstruction rate degrades when the projection images are misaligned. Reconstruction of the three-dimensional distribution of the atom flips is discussed.

Update: 30-Nov-2011

Title:
Double-k phase of the Dzyaloshinskii-Moriya helimagnet Ba(2)CuGe(2)O(7)
Authors:
Muhlbauer, S; Gvasaliya, SN; Pomjakushina, E; Zheludev, A Author Full Names: Muehlbauer, S.; Gvasaliya, S. N.; Pomjakushina, E.; Zheludev, A.
Source:
PHYSICAL REVIEW B 84 (18): 10.1103/PhysRevB.84.180406 NOV 10 2011
Abstract:
Neutron diffraction is used to reinvestigate the magnetic phase diagram of the noncentrosymmetric tetragonal antiferromagnet Ba(2)CuGe(2)O(7). An incommensurate double-k magnetic phase is detected near the commensurate-incommensurate phase transition. This phase is stable only for field closely aligned with the fourfold symmetry axis. The results emphasize the inadequacy of existing theoretical models for this unique material, and points to additional terms in the Hamiltonian or lattice effects.
Title:
Conductivity of icosahedral AlPdRe
Authors:
Rapp, O; Poon, SJ Author Full Names: Rapp, O.; Poon, S. J.
Source:
PHYSICAL REVIEW B 84 (17): 10.1103/PhysRevB.84.174206 NOV 10 2011
Abstract:
The electrical conductivity sigma(T) of icosahedral (i) AlPdRe has been studied in order to address current problems and controversies. Two new approaches are presented. The temperature T(0) below which variable range hopping occurs was estimated directly from d sigma(T)/dT, avoiding the problem of the finite sigma(0) in i-AlPdRe. Secondly, sigma(T) is compared in detail for samples with radically different defects and morphologies. The temperature dependence of sigma(T) is found to be independent of these varying sample conditions. This finding rules out some proposed conduction mechanisms.
Title:
Symmetry and magnetic field driven transitions in the 2D triangular lattice compound RbFe(MoO(4))(2)
Authors:
Ribeiro, JL; Perez-Mato, JM Author Full Names: Ribeiro, J. L.; Perez-Mato, J. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (44): 10.1088/0953-8984/23/44/446003 NOV 9 2011
Abstract:
The temperature versus magnetic field phase diagram of the 2D triangular lattice and multiferroic compound RbFe(MoO(4))(2) is analysed from the point of view of symmetry. The paramagnetic space group and its irreducible representations are used in order to obtain the magnetic symmetry of the possible modulated phases and characterize the restrictions imposed by this symmetry on the corresponding magnetic structures. Superspace symmetry is considered in the case of incommensurate phases. It is shown that the experimentally observed phases correspond to different isotropy subgroups originating in the same irreducible representation of the paramagnetic symmetry group. The relevant couplings between the primary transverse spin modulation and the electric polarization, the in-plane magnetization and the secondary longitudinal magnetic modulation are discussed. The mechanisms for the destabilization of the improper ferroelectric chiral phase and the origin of the different orienta! tion of the spins with respect to the external field in the two collinear phases are analysed from a symmetry based perspective.
Title:
Quasicrystals - Interfaces to Hyperspace
Authors:
Steurer, W Author Full Names: Steurer, Walter
Source:
NACHRICHTEN AUS DER CHEMIE 59 (11): 1035-1038 NOV 2011

Update: 23-Nov-2011

Title:
Microstructure development and properties of the AlCuFe quasicrystalline coating on near-alpha titanium alloy
Authors:
Moskalewicz, T; Kot, M; Wendler, B Author Full Names: Moskalewicz, T.; Kot, M.; Wendler, B.
Source:
APPLIED SURFACE SCIENCE 258 (2): 848-859 10.1016/j.apsusc.2011.09.013 NOV 1 2011
Abstract:
A protective quasicrystalline AlFeCu coating was deposited on TIMETAL 834 substrate by nonreactive magnetron sputtering in order to improve resistance of the alloy to oxidation. Microstructure characterisation of the substrate and the coating was performed by analytical scanning-and transmission electron microscopy as well as X-ray diffractometry. Depending on annealing temperature and time, the deposited coating (2.7 mu m thick) has a different microstructure. The coating in Specimen 1 (annealed 600 degrees C/4 h in vacuum) consisted of two zones: outer, composed of Al(5)Fe(2) and Al(2)Cu(3) phases and inner, in which only quasicrystalline psi phase was present. The coating in Specimen 2 (annealed 600 degrees C/4 h + 700 degrees C/2 h in vacuum) was fully quasicrystalline and consisted of icosahedral psi phase. Both coatings exhibit higher microhardness than the substrate material. It was established that the applied surface treatment essentially improves oxidation resistance of the alloy tested at 750 degrees C during 250 h in static air. Sample weight gain was 60% lower than in the case of uncoated sample. Oxide scale spallation occurred for uncoated alloy while the coated one did not show any spallation. It was found that the very brittle scale formed during oxidation on the uncoated alloy was consisting of TiO(2), while that on the coated one consisted mainly of alpha-Al(2)O(3). (C) 2011 Elsevier B. V. All rights reserved.
Title:
Lead adsorption on the Al(13)Co(4)(100) surface: heterogeneous nucleation and pseudomorphic growth
Authors:
Addou, R; Shukla, AK; Villaseca, SA; Gaudry, E; Deniozou, T; Heggen, M; Feuerbacher, M; Widmer, R; Groning, O; Fournee, V; Dubois, JM; Ledieu, J Author Full Names: Addou, R.; Shukla, A. K.; Villaseca, S. Alarcon; Gaudry, E.; Deniozou, Th; Heggen, M.; Feuerbacher, M.; Widmer, R.; Groening, O.; Fournee, V.; Dubois, J-M; Ledieu, J.
Source:
NEW JOURNAL OF PHYSICS 13 10.1088/1367-2630/13/10/103011 OCT 11 2011
Abstract:
We have investigated the adsorption of Pb atoms on the (100) surface of an orthorhombic Al(13)Co(4) crystal at 300 and 573K substrate temperatures. This complex metallic alloy is an approximant to the decagonal Al-Ni-Co quasicrystal. At submonolayer coverage and at 300 K, Pb adatoms remain highly mobile and adsorb preferentially within the hollow site situated in between adjacent Al pentagonal clusters present at the surface. These experimental findings are supported by ab initio calculations based on density functional theory (DFT). For both temperature regimes, Pb adsorption leads to the formation of pseudomorphic monolayers above which the high adsorbate mobility prohibits the growth of additional layers. For the high-temperature deposition, we propose a structural model for the Pb film and discuss its relationship with the underneath substrate.

Update: 16-Nov-2011

Title:
Magnetic and thermal properties of Er(75)Dy(25) single crystals
Authors:
Khan, M; Schlagel, DL; Lograsso, TA; Gschneidner, KA; Pecharsky, VK Author Full Names: Khan, Mahmud; Schlagel, D. L.; Lograsso, T. A.; Gschneidner, K. A., Jr.; Pecharsky, V. K.
Source:
PHYSICAL REVIEW B 84 (13): 10.1103/PhysRevB.84.134424 OCT 18 2011
Abstract:
We report on an experimental study of the thermal and magnetic properties of Er(75)Dy(25) single crystals with magnetic fields applied parallel to the [0001] and [10 (1) over bar0] directions. The [0001] direction is the easy axis of magnetization, while the [10 (1) over bar0] direction is the hard axis of magnetization. Three major transitions are observed in the heat capacity, magnetization, and alternating current magnetic susceptibility data. A first-order transition is observed at similar to 30 K, and two second-order transitions occur at similar to 45 and similar to 110 K. The H-T phase diagrams constructed from the experimental data reveal that several magnetic phases, including ferromagnetic cone, ferromagnetic fan, and c axis-modulated phases, exist in an Er(75)Dy(25) single crystal. Both similarities and dissimilarities are observed in the H-T phase diagrams of Er(75)Dy(25) when compared to the H-T phase diagrams of pure Er single crystals.

Update: 10-Nov-2011

Title:
Electrical transport and anomalous structural behavior of alpha-Eu(2) (MoO(4))(3) at high temperature
Authors:
Guzman-Afonso, C; Torres, ME; Gonzalez-Silgo, C; Sabalisck, N; Gonzalez-Platas, J; Matesanz, E; Mujica, A Author Full Names: Guzman-Afonso, C.; Torres, M. E.; Gonzalez-Silgo, C.; Sabalisck, N.; Gonzalez-Platas, J.; Matesanz, E.; Mujica, A.
Source:
SOLID STATE COMMUNICATIONS 151 (22): 1654-1658 10.1016/j.ssc.2011.08.009 NOV 2011
Abstract:
The study of XRD patterns of alpha-Eu(2)(MoO(4))(3) modulated scheelite reveals an anomalous behavior of its lattice parameter a in the range of temperatures from 473 to 973 K. We have analyzed the real part of the complex conductivity in the frequency range from 0.1 to 10,000 kHz and the temperature range from 550 to 900 K, and found that it follows a universal dielectric response. Detailed analysis of the temperature dependence of the adjusted parameters within this model shows that, in a temperature range, the dominant mechanism of electrical transport is due to the overlapping of large polarons. Rietveld refinements were performed using symmetry adapted modes at 523, 723 and 923 Kin order to study the thermal dependence of the distortion from the scheelite structure and to interpret the structural effects that favor the formation of polarons. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
New type of incommensurate magnetic ordering in Mn(3)TeO(6)
Authors:
Ivanov, SA; Nordblad, P; Mathieu, R; Tellgren, R; Ritter, C; Golubko, NV; Politova, ED; Weil, M Author Full Names: Ivanov, S. A.; Nordblad, P.; Mathieu, R.; Tellgren, R.; Ritter, C.; Golubko, N. V.; Politova, E. D.; Weil, M.
Source:
MATERIALS RESEARCH BULLETIN 46 (11): 1870-1877 10.1016/j.materresbull.2011.07.041 NOV 2011
Abstract:
The complex metal oxide Mn(3)TeO(6) exhibits a corundum related structure and has been prepared both in forms of single crystals by chemical transport reactions and of polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties have been investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric and magnetic measurements. At room temperature this compound adopts a trigonal structure, space group R (3) over bar with a = 8.8679(1) angstrom. c = 10.6727(2) angstrom. A long-range magnetically ordered state is identified below 23 K. An unexpected feature of this magnetic structure is several types of Mn-chains. Under the action of the incommensurate magnetic propagation vector k = [0, 0, 0.4302(1)] the unique Mn site is split into two magnetically different orbits. One orbit forms a perfect helix with the spiral axis along the c-axis while the other orbit has a sine wave character along the c-axis. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Structural stability and magnetic properties of Bi(1-x)La(Pr)(x)FeO(3) solid solutions
Authors:
Karpinsky, DV; Troyanchuk, IO; Mantytskaya, OS; Khomchenko, VA; Kholkin, AL Author Full Names: Karpinsky, D. V.; Troyanchuk, I. O.; Mantytskaya, O. S.; Khomchenko, V. A.; Kholkin, A. L.
Source:
SOLID STATE COMMUNICATIONS 151 (22): 1686-1689 10.1016/j.ssc.2011.08.002 NOV 2011
Abstract:
In this work, X-ray diffraction data taken on Bi(1-x)La(x)FeO(3) solid solutions are used to verify the following structural phase transitions: "polar rhombohedral-antipolar orthorhombic" at x approximate to 0.16 and "commensurate-incommensurate" within the orthorhombic phase at x approximate to 0.18. In contrast, in the Bi(1-x)Pr(x)FeO(3) series, the polar rhombohedral phase transforms into an antipolar orthorhombic one at x >= 0.13. The polar rhombohedral phase near the morphotropic phase boundary exhibits an isothermal transformation into an antipolar orthorhombic phase, though the transformation occurs much faster in the case of La-doped compounds. The incommensurate structural phase was not detected in Bi(1-x)Pr(x)FeO(3) solid solutions. The ternary structural phase diagram is constructed for (Bi, La, Pr)FeO(3) systems. In addition, the polar rhombohedral phase exhibits a magnetic field-induced transition from the modulated antiferromagnetic state into a homogeneous weak ferromagnetic state whereas the antipolar phase is a weak ferromagnetic state in the absence of an external field. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Seeing is Believing: Quasicrystals and the Demise of Perfect Order
Authors:
Balaram, P Author Full Names: Balaram, P.
Source:
CURRENT SCIENCE 101 (8): 981-982 OCT 25 2011
Title:
Electrical, magnetic, and thermal properties of the single-grain Ag(42)In(42)Yb(16) icosahedral quasicrystal: Experiment and modeling
Authors:
Bobnar, M; Vrtnik, S; Jaglicic, Z; Wencka, M; Cui, C; Tsai, AP; Dolinsek, J Author Full Names: Bobnar, M.; Vrtnik, S.; Jaglicic, Z.; Wencka, M.; Cui, Can; Tsai, An Pang; Dolinsek, J.
Source:
PHYSICAL REVIEW B 84 (13): 10.1103/PhysRevB.84.134205 OCT 17 2011
Abstract:
We have investigated the anisotropy of physical properties (themagnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient, and the thermal conductivity) of single-grain icosahedral i-Ag(42)In(42)Yb(16) quasicrystal along the two-, three-, and fivefold symmetry directions of the crystallographic structure. The specific heat, being a scalar quantity, was determined as well. The symmetry analysis predicts that the tensorial physical properties reduce to scalars for the ideal icosahedral symmetry. The experiments have shown that the anisotropy of the electronic transport coefficients of i-Ag(42)In(42)Yb(16) is either small enough to be considered within the range of the experimental uncertainty (the electrical resistivity and the thermal conductivity) or negligible (the Seebeck and the Hall coefficients). The anisotropy of the magnetization and magnetic susceptibility was also found small, originating from different Yb(3+) magnetic fractions (of the order 10(-3) of all Yb atoms) determined along the three symmetry directions. Our experimental results support the consideration that perfect icosahedral quasicrystals should be isotropic solids regarding their physical properties, unlike decagonal quasicrystals that are strongly anisotropic. Theoretical reproduction of the temperature-dependent electron transport coefficients of i-Ag(42)In(42)Yb(16) by a spectral conductivity model was another aim of this paper.
Title:
Structural evolution of one-dimensional spin-ladder compounds Sr(14-x)Ca(x)Cu(24)O(41) with Ca doping and related evidence of hole redistribution
Authors:
Deng, GC; Pomjakushin, V; Petricek, V; Pomjakushina, E; Kenzelmann, M; Conder, K Author Full Names: Deng, Guochu; Pomjakushin, Vladimir; Petricek, Vaclev; Pomjakushina, Ekaterina; Kenzelmann, Michel; Conder, Kazimierz
Source:
PHYSICAL REVIEW B 84 (14): 10.1103/PhysRevB.84.144111 OCT 17 2011
Abstract:
Incommensurate crystal structures of spin-ladder series Sr(14-x)Ca(x)Cu(24)O(41) (x = 3, 7, 11, and 12.2) were characterized by powder neutron scattering method and refined using the superspace group Xmmm(00 gamma)ss0 [ equivalent to superspace group Fmmm(0, 0, 1 + gamma)ss0; X stands for nonstandard centering (0, 0, 0, 0), (0, 1/2, 1/2, 1/2), (1/2, 1/2, 0, 0), (1/2, 0, 1/2, 1/2)] with a modulated structure model. The Ca doping effects on the lattice parameters, atomic displacement, Cu-O distances, Cu-O bond angles, and Cu bond valence sum were characterized. The refined results show that the CuO(4) planar units in both chain and ladder sublattices become closer to square shape with an increase of Ca doping. The Cu bond valence sum calculation provided new evidence for the charge transfer from the chains to ladders (approximately 0.16 holes per Cu from x = 0 to 12.2). The charge transfer was attributed to two different mechanisms: (a) the Cu-O bond distance shrinkage on the ladder and (b) increase of the interaction between two sublattices, resulting in Cu-O bonding between the chains and ladders. The low-temperature structural refinement resulted in the similar conclusion with a slight charge backflow to the chains.
Title:
Germanium Selenophosphates: The Incommensurately Modulated 1/infinity[Ge(4-x)P(x)Se(12)(4-)] and the Molecular [Ge(2)P(2)Se(14)](6-)
Authors:
Morris, CD; Malliakas, CD; Kanatzidis, MG Author Full Names: Morris, Collin D.; Malliakas, Christos D.; Kanatzidis, Mercouri G.
Source:
INORGANIC CHEMISTRY 50 (20): 10241-10248 10.1021/ic201249w OCT 17 2011
Abstract:
The new germanium selenophosphates K(4)Ge(4-x)P(x)Se(12) (1) and Rb(6)Ge(2)P(2)Se(14) (2) are reported. The former is a one-dimensional metastable compound synthesized using the polychalcogenide flux method that crystallizes in the monoclinic space group P2(1)/c with lattice parameters a = 6.7388(7) angstrom, b = 13.489(1) angstrom, c = 6.3904(6) angstrom, and beta = 91.025(8)degrees. At a glance, a mixed Ge(4+)/P(5+) tetrahedral site and disordered Se position are found among the corner sharing tetrahedra that make up the polymeric anion. After careful examination, the structure was found to be incommensurately modulated and a single q-vector of q = 0.4442(6)a* + 0.3407(6)c* was determined after annealing single crystals below their decomposition point for 30d. The latter compound contains the new discrete molecular anion [Ge(2)P(2)Se(14)](6-) and crystallizes in P (1) over bar with lattice parameters a = 7.2463(8) angstrom, b = 9.707(1)angstrom, c = 11.987(1)angstrom, alpha = 79.516(9)degrees, beta = 89.524(9)degrees, and gamma = 68.281(9)degrees. Both compounds are semiconductors with band gaps of 1 and 2 being 1.9 eV and 2.2 eV, respectively.
Title:
XRD and HREM studies from the decomposition of icosahedral AlCuFe single-phase by high-energy ball milling
Authors:
Patino-Carachure, C; Tellez-Vazquez, O; Rosas, G Author Full Names: Patino-Carachure, C.; Tellez-Vazquez, O.; Rosas, G.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (41): 10036-10039 10.1016/j.jallcom.2011.08.026 OCT 13 2011
Abstract:
In this investigation the Al(64)Cu(24)Fe(12) alloy was melted in an induction furnace and solidified under normal casting conditions. In order to obtain the icosahedral phase (i-phase) in a single-phase region, the as-cast sample was subject to a heat treatment at 700 degrees C under argon atmosphere. Subsequently, the i-phase was milled for different times in order to evaluate phase stability under heavy deformation. X-ray diffraction (XRD) and high-resolution electron microscopy (HREM) analysis were conducted to the structural characterization of ball-milled powders. XRD results indicated a reduction in quasicrystal size during mechanical ball milling to about 30 h. HREM analysis revealed the presence of aperiodic nanodomains, for example, with apparent fivefold symmetry axis. Therefore, the i-phase remains stable over the first 30 h of ball-milling time. However, among 30-50 h of mechanical milling the i-phase transforms progressively into beta-cubic phase. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Vacancies and atomic processes in intermetallics - From crystals to quasicrystals and bulk metallic glasses
Authors:
Schaefer, HE; Baier, F; Muller, MA; Reichle, KJ; Reimann, K; Rempel, AA; Sato, K; Ye, F; Zhang, XY; Sprengel, W Author Full Names: Schaefer, Hans-Eckhardt; Baier, Falko; Mueller, Markus A.; Reichle, Klaus J.; Reimann, Klaus; Rempel, Andrey A.; Sato, Kiminori; Ye, Feng; Zhang, Xiangyi; Sprengel, Wolfgang
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 248 (10): 2290-2299 10.1002/pssb.201147103 OCT 2011
Abstract:
A review is given on atomic vacancies in intermetallic compounds. The intermetallic compounds cover crystalline, quasicrystalline, and bulk metallic glass (BMG) structures. Vacancies can be specifically characterized by their positron lifetimes, by the coincident measurement of the Doppler broadening of the two quanta emitted by positron-electron annihilation, or by time-differential dilatometry. By these techniques, high concentrations and low mobilities of thermal vacancies were found in open-structured B2 intermetallics such as FeAl or NiAl, whereas the concentrations of vacancies are low and their mobilities high in close-packed structure as, e.g., L1(2)-Ni(3)Al. The activation volumes of vacancy formation and migration are determined by high-pressure experiments. The favorable sublattice for vacancy formation is found to be the majority sublattice in Fe(61)Al(39) and in MoSi(2). In the icosahedral quasicrystal Al(70)Pd(21)Mn(9) the thermal vacancy concentration is low, whereas in the BMG Zr(57)Cu(15.4)Ni(12).(6)Nb(3)Al(10) thermal vacancies are found in high concentrations with low mobilities. This may determine the basic mechanisms of the glass transition. Making use of the experimentally determined vacancy data, the main features of atomic diffusion studies in crystalline intermetallics, in quasicrystals, and in BMGs can be understood. Manfred Fahnle and his group have substantially contributed to the theoretical understanding of vacancies and diffusion mechanisms in intermetallics. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Grain size effect on the phase transformations of higher manganese silicide thermoelectric materials: An in situ energy dispersive x-ray diffraction study
Authors:
Zhou, AJ; Zhu, TJ; Zhao, XB; Mueller, E Author Full Names: Zhou, Aijun; Zhu, Tiejun; Zhao, Xinbing; Mueller, Eckhard
Source:
JOURNAL OF MATERIALS RESEARCH 26 (15): 1900-1906 10.1557/jmr.2011.80 AUG 2011
Abstract:
Phase structures of microscale and nanoscale higher manganese silicides (HMSs) were investigated using in situ energy dispersive x-ray diffraction at high temperatures or/and high pressure. A few phase transformations accompanied with the presence of MnSi phase were observed in different temperature regions, which were associated with the interevolution of several incommensurate HMS phases. It was found that in nanostructured HMS, the interevolution of HMS was remarkable and accelerated compared to that in the micropowders. Meanwhile, high pressure was able to influence these phase transformations due to giant strain in the materials. The phase transformations were discussed from thermodynamic aspects with respect to the different formation enthalpy of Mn-Si system and the large surface energy and structural instability of the nanopowders.
Title:
Surprising luminescent properties of the polyphosphates Ln(PO(3))(3): Eu (Ln = Y, Gd, Lu)
Authors:
Hoppe, HA; Kazmierczak, K; Kacprzak, S; Schellenberg, I; Pottgen, R Author Full Names: Hoeppe, Henning A.; Kazmierczak, Karolina; Kacprzak, Sylwia; Schellenberg, Inga; Poettgen, Rainer
Source:
DALTON TRANSACTIONS 40 (39): 9971-9976 10.1039/c1dt10043b 2011
Abstract:
The optical emission properties of the lanthanoid catena-polyphosphates Ln(PO(3))(3) (Ln = Y, Gd, Lu) doped with europium were investigated. Incommensurately modulated b-Y(PO(3))(3) : Eu (super space group Cc (0 vertical bar 0.364 vertical bar 0)0) and Gd(PO(3))(3) : Eu (space group I2/a) show the usual emission characteristics of Eu(3+), while in Lu(PO(3))(3) : Eu (space group Cc) the europium is unprecedentedly partially reduced to the divalent state, as proven by both a broad emission band at 406 nm excited at 279 nm and an EPR spectroscopic investigation. (151)Eu-Mossbauer spectroscopy showed that only a very small part of the europium is reduced in Lu(PO(3))(3) : Eu. An explanation for this unusual behaviour is given.

Update: 3-Nov-2011

Title:
Coexistence of superconductivity and incommensurate magnetic order
Authors:
Ptok, A; Maska, MM; Mierzejewski, M Author Full Names: Ptok, Andrzej; Maska, Maciej M.; Mierzejewski, Marcin
Source:
PHYSICAL REVIEW B 84 (9): 10.1103/PhysRevB.84.094526 SEP 26 2011
Abstract:
The influence of incommensurate spin-density waves (SDW) on superconductivity in unconventional superconductors is studied by means of the Bogolubov-de Gennes (BdG) equations. Exploiting translational symmetries of a magnetically ordered two-dimensional system, we propose an approach that allows to solve the BdG equations on much larger clusters than it is usually possible for inhomogeneous systems. Applying this approach, we demonstrate that the presence of incommensurate spin-density waves induces real-space inhomogeneity of the superconducting order parameter even in the absence of external magnetic field. In this case, a homogeneous order parameter of the Bardeen-Cooper-Schrieffer-type superconducting state is slightly modulated, or equivalently, a small fraction of the charge carriers form Cooper pairs with nonzero total momentum. However, when a sufficiently strong magnetic field is applied, the homogeneous component of the order parameter is suppressed and the system transits to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, where the order parameter oscillates changing sign. We show that for s-wave pairing, the presence of external magnetic field diminishes the destructive influence of the SDW order on superconductivity. A simple explanation of this effect is also proposed.
Title:
Spontaneous phase transitions in magnetic films with a modulated structure
Authors:
Arzamastseva, GV; Evtikhov, MG; Lisovskii, FV; Mansvetova, EG Author Full Names: Arzamastseva, G. V.; Evtikhov, M. G.; Lisovskii, F. V.; Mansvetova, E. G.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 113 (3): 450-458 10.1134/S1063776111080024 SEP 2011
Abstract:
The influence of monoperiodic and biperiodic bias fields on the nucleation of domain structures in quasi-uniaxial magnetic films near the Curie point has been studied experimentally. The main types of observed nonuniform magnetic moment distributions have been established and chains of a devil's staircase phase transitions are shown to be realized when the films are slowly cooled.
Title:
Electrochemical properties of Ti(45)Zr(38-x)Ni(17+x) (0 <= x <= 8) quasicrystals produced by rapid-quenching
Authors:
Takasaki, A; Kuroda, C; Lee, SH; Kim, JY Author Full Names: Takasaki, Akito; Kuroda, Chihiro; Lee, Sang-Hwa; Kim, Jae-Yong
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 S782-S785 2 10.1016/j.jallcom.2010.11.042 SEP 2011
Abstract:
Discharge performances of Ti(45)Zr(38-x)Ni(17+x) (0 <= x <= 8) ribbons produced by rapid-quenching were measured by a three-electrode cell at room temperature, and the effect of substitution of Ni for Zr was investigated. All the ribbons after rapid-quenching were mostly the icosahedral (i) quasicrystal phase with a negligible amount of C14 Laves phase (hcp). The discharge capacity increased with increasing amount of Ni substituted for Zr. The maximum discharge capacity achieved was about 90 mAh/g from (Ti(45)Zr(30)Ni(25)) ribbon after substitution of Ni for Zr. The discharge performance was almost stable against the charge/discharge cycle (until 15 cycles) for all the ribbons, and the i-phase structure was also stable even after the 15th charge/discharge cycle. No metal hydride formation was observed. (C) 2010 Elsevier B.V. All rights reserved.

Update: 27-Oct-2011

Title:
Low-temperature evolution of the modulated magnetic structure in the ferroelectric antiferromagnet BiFeO(3)
Authors:
Sosnowska, I; Przenioslo, R Author Full Names: Sosnowska, I.; Przenioslo, R.
Source:
PHYSICAL REVIEW B 84 (14): 10.1103/PhysRevB.84.144404 OCT 3 2011
Abstract:
High-resolution time-of-flight neutron diffraction studies of the magnetic ordering in the multiferroic BiFeO(3) are presented. Our results show that the cycloidal modulated ordering proposed earlier [I. Sosnowska, T. Peterlin-Neumaier, and E. Steichele, J. Phys. C 15, 4835 (1982)] is stable between 10 and 295 K. The concept of the anharmonic character of the magnetic modulation in BiFeO(3) that was used for the interpretation of NMR, Raman, and THz spectroscopy studies of BiFeO(3) is discussed. The influence of the anharmonic modulation on the magnetic contributions to the BiFeO(3) neutron diffraction patterns is presented. Our experimental data can be described by assuming anharmonic effects with m < 0.25. We propose a method for the anharmonicity strength evaluation based on neutron diffraction data.
Title:
Five-Dimensional Incommensurate Structure of the Melilite Electrolyte [CaNd](2)[Ga](2)[Ga(2)O(7)](2)
Authors:
Wei, FX; Baikie, T; An, T; Schreyer, M; Kloc, C; White, TJ Author Full Names: Wei, Fengxia; Baikie, Tom; An, Tao; Schreyer, Martin; Kloc, Christian; White, Tim J.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 133 (38): 15200-15211 10.1021/ja206441x SEP 28 2011
Abstract:
Melilite-type gallium oxides are potential intermediate temperature electrolytes for solid oxide fuel cells. Single crystals of [CaNd](2)[Ga](2)[Ga(2)O(7)](2) grown using an optical floating zone furnace have been investigated using transmission electron microscopy and powder and single-crystal X-ray diffraction. The anion array topologically conforms to a [(3.5.4.5)(2), 3.5.3.5] network that contains distorted pentagonal tunnels. The distortion is necessary to achieve space filling and accommodate structural misfit between the layers. Satisfactory bond lengths and angles are obtained through two-dimensional modulation in the tetragonal based plane, leading to five-dimensional symmetry in the superspace group P (4) over bar2(1)m(alpha,alpha,0)00s((a) over bar ,a,0)000, alpha = 0.2319(2), with modulation vectors q(1) = alpha(a* + b*) and q(2) = alpha(-a* + b*). Both displacive and occupational modulations are found. Through this mechanism, melilites are primed to accommodate mobile oxygen interstitials, suggesting a rational approach to crystallochemical tailoring that will enhance ionic diffusion and optimize electrolyte performance.

Update: 20-Oct-2011

Title:
Damping properties in Mg-Zn-Y alloy with dispersion of quasicrystal phase particle
Authors:
Somekawa, H; Watanabe, H; Mukai, T Author Full Names: Somekawa, Hidetoshi; Watanabe, Hiroyuki; Mukai, Toshiji
Source:
MATERIALS LETTERS 65 (21-22): 3251-3253 10.1016/j.matlet.2011.07.001 NOV 2011
Abstract:
The effect of the interface structure between the matrix and the particle on the damping capacity was investigated using Mg-Zn and Mg-Zn-Y alloys in this study. The damping capacity was not affected by the interface structure at room temperature. However, the onset of temperature, which was higher in the Mg-Zn-Y alloy than in the Mg-Zn alloy despite their similar grain sizes, increased the damping capacity through grain boundary relaxation by grain boundary sliding. Compared to the Mg-Zn alloy, the existence of the quasicrystal phase particles, which had the coherent interface with low interface energy, was likely to have suppressed and delayed the grain boundary sliding in the Mg-Zn alloy. (C) 2011 Elsevier By. All rights reserved.
Title:
Ti-Doping to Reduce Conductivity in Bi(0.85)Nd(0.15)FeO(3) Ceramics
Authors:
Kalantari, K; Sterianou, I; Karimi, S; Ferrarelli, MC; Miao, S; Sinclair, DC; Reaney, IM Author Full Names: Kalantari, Kambiz; Sterianou, Iasmi; Karimi, Sarah; Ferrarelli, Matthew C.; Miao, Shu; Sinclair, Derek C.; Reaney, Ian M.
Source:
ADVANCED FUNCTIONAL MATERIALS 21 (19): 3737-3743 10.1002/adfm.201100191 OCT 7 2011
Abstract:
In 2009, Karimi et al. reported that Bi(1-x)Nd(x)FeO(3) 0.15 <= x <= 0.25 exhibited a PbZrO(3) (PZ)-like structure. These authors presented some preliminary electrical data for the PZ-like composition but noted that the conductivity was too high to obtain radio-frequency measurements representative of the intrinsic properties. In this study, Bi(0.85)Nd(0.15)Fe(1-y)Ti(y)O(3) (0 <= y <= 0.1) were investigated, in which Ti acted as a donor dopant on the B-site. In contrast to the original study of Karimi et al., X-ray diffraction (XRD) of Bi(0.85)Nd(0.15)FeO(3) revealed peaks which were attributed to a mixture of PZ-like and rhombohedral structures. However, as the Ti (0 < y <= 0.05) concentration increased, the rhombohedral peaks disappeared and all intensities were attributed to the PZ-like phase. For y = 0.1, broad XRD peaks indicated a significant decrease in effective diffracting volume. Electron diffraction confirmed that the PZ-like phase was dominant for y <= 0.05, but for y = 0.1, an incommensurate structure was present, consistent with the broadened XRD peaks. The substitution of Fe(3+) by Ti(4+) decreased the dielectric loss at room temperature from >0.3 to <0.04 for all doped compositions, with a minimum (0.015) observed for y = 0.03. The decrease in dielectric loss was accompanied by a decrease in the room temperature bulk conductivity from similar to 1 mS cm(-1) to < 1 mu S cm(-1) and an increase in bulk activation energy from 0.29 to >1 eV. Plots of permittivity (epsilon(r)) versus temperature for 0.01 <= y <= 0.05 revealed a step rather than a peak in epsilon(r) on heating at the same temperature determined for the antiferroelectric-paraelectric phase transition by differential scanning calorimetry. Finally, large electric fields were applied to all doped samples which resulted in a linear dependence of polarisation on the electric field similar to that obtained for PbZrO(3) ceramics under equivalent experimental conditions.
Title:
Detailed structure of the low-energy magnetic dispersion of the diagonal incommensurate phase in La(1.975)Sr(0.025)CuO(4)
Authors:
Matsuda, M; Fernandez-Baca, JA; Fujita, M; Yamada, K; Tranquada, JM Author Full Names: Matsuda, M.; Fernandez-Baca, J. A.; Fujita, M.; Yamada, K.; Tranquada, J. M.
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.104524 SEP 30 2011
Abstract:
Inelastic neutron scattering experiments have been performed on lightly doped La(1.975)Sr(0.025)CuO(4), which contains a hole concentration slightly higher than the critical concentration for three-dimensional long-range antiferromagnetic order. We previously found that the magnetic excitation spectrum in the insulating phase with a diagonal incommensurate spin modulation has similarities to that in the superconducting regime, where the spin modulation is bond parallel. In this study, we investigate the excitations in detail around Ecross, at which the excitations become most nearly commensurate. It is found that both the magnitude and the anisotropy of the momentum width of the excitations change abruptly at Ecross. Our experimental results suggest that the magnetic excitations rising from the pair of (diagonally) incommensurate wave vectors merge at Ecross into isotropic excitations.
Title:
Magnetic excitations in the geometric frustrated multiferroic CuCrO(2)
Authors:
Frontzek, M; Haraldsen, JT; Podlesnyak, A; Matsuda, M; Christianson, AD; Fishman, RS; Sefat, AS; Qiu, Y; Copley, JRD; Barilo, S; Shiryaev, SV; Ehlers, G Author Full Names: Frontzek, M.; Haraldsen, J. T.; Podlesnyak, A.; Matsuda, M.; Christianson, A. D.; Fishman, R. S.; Sefat, A. S.; Qiu, Y.; Copley, J. R. D.; Barilo, S.; Shiryaev, S. V.; Ehlers, G.
Source:
PHYSICAL REVIEW B 84 (9): 10.1103/PhysRevB.84.094448 SEP 28 2011
Abstract:
In this paper detailed neutron scattering measurements of the magnetic excitation spectrum of CuCrO(2) in the ordered state below T(N1) = 24.2 K are presented. The spectra are analyzed using a model Hamiltonian which includes intralayer exchange up to the next-next-nearest neighbor and interlayer exchange. We obtain a definite parameter set and show that exchange interaction terms beyond the next-nearest neighbor are important to describe the inelastic excitation spectrum. The magnetic ground state structure generated with our parameter set is in agreement with the structure proposed for CuCrO(2) from the results of single crystal diffraction experiments previously published. We argue that the role of the interlayer exchange is crucial to understand the incommensurability of the magnetic structure as well as the spin-charge coupling mechanism.
Title:
Effects of chemical doping and pressure on CaFe(4)As(3)
Authors:
Zhao, LL; Kim, SK; McCandless, GT; Torikachvili, MS; Canfield, PC; Chan, JY; Morosan, E Author Full Names: Zhao, Liang L.; Kim, S. K.; McCandless, Gregory T.; Torikachvili, Milton S.; Canfield, P. C.; Chan, Julia Y.; Morosan, E.
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.104444 SEP 28 2011
Abstract:
The effects of chemical doping by P, Yb, Co, and Cu, and hydrostatic pressure on CaFe(4)As(3), were studied on single-crystalline samples. While the former two dopants substitute the nonmagnetic ions, the latter two partially occupy the Fe sites within the magnetic sublattice. The incommensurate spin density wave (IC-SDW) ordering at T(N) similar to 88 K in CaFe(4)As(3) changes only by up to similar to 40% with doping and applied pressure. Thus the IC-SDW state appears more robust than in the layered Fe pnictides. The commensurate SDW (C-SDW) state below T(2) similar to 26 K is suppressed in the Co-doped series, while it moves up in temperature in the P-, Yb-, and Cu-doped compounds. A new magnetic phase transition is observed at an intermediate temperature T(3) in Ca(Fe(1-x)Co(x))(4)As(3). Resistivity and magnetization measurements on CaFe(4)As(3) were performed under hydrostatic pressure up to 5 GPa, showing a systematic decrease of T(N) and a domelike phase boundary at T(2) up to p(c) similar to 2.10 GPa. At higher pressures, a possible structural phase transition occurs, marked by a slowly increasing transition temperature. A phase diagram is shown to compare the effects of chemical doping and pressure.
Title:
Ordering and growth of Xe films on the 10-fold quasicrystalline approximant Al(13)Co(4)(100) surface
Authors:
Shin, H; Karimi, M; Setyawan, W; Curtarolo, S; Diehl, RD Author Full Names: Shin, Heekeun; Karimi, M.; Setyawan, W.; Curtarolo, S.; Diehl, R. D.
Source:
PHYSICAL REVIEW B 84 (11): 10.1103/PhysRevB.84.115454 SEP 27 2011
Abstract:
Xe adsorption on the (100) surface of the complex alloy Al(13)Co(4) has been carried out using low-energy electron diffraction (LEED) and grand canonical Monte Carlo (GCMC) simulations. This surface is an approximant to the 10-fold surface of decagonal Al-Ni-Co, on which Xe adsorption has been studied previously. The adsorption behavior on the periodic surface is largely similar to that on the quasicrystal (layer-by-layer growth, hexagonal ordering near the onset of the second-layer adsorption), but it also has some differences, such as the complete lack of registry of the Xe layer with the substrate structure in the hexagonal phase, and a high sensitivity of the Xe epitaxial direction to trace impurities. In the simulations, an ordering transition was observed between the low-density and high-density monolayer regimes that involves a uniaxial compression of the monolayer film.

Update: 13-Oct-2011

Title:
Quinary icosahedral quasicrystalline Ti-V-Ni-Mn-Cr alloy: A novel anode material for Ni-MH rechargeable batteries
Authors:
Hu, W; Wang, LD; Wang, LM Author Full Names: Hu, Wen; Wang, Lidong; Wang, Limin
Source:
MATERIALS LETTERS 65 (19-20): 2868-2871 10.1016/j.matlet.2011.06.059 OCT 2011
Abstract:
The substitution of manganese and chromium for 6 at.% nickel in Ti(1.6)V(0.4)Ni leads the rapid quenching synthesis of quinary icosahedral phase (i-phase) evidenced by the observations of 2-. 3- and 5-fold symmetries. As negative electrode in Ni-MH battery, the quinary Ti-V-Ni-Mn-Cr i-phase can deliver a maximum discharge capacity of 278 mAh g(-1) at 30 mA g(-1) larger than that of Ti(1.6)V(0.4)Ni master alloy anode owing to Mn and/or Cr doping. After a preliminary test of 30 consecutive cycles the cycling capacity retention rate (CR%) is 80%. The strong chemisorption of hydrogen shown in cyclic voltammetric (CV) response indicates that the electrocatalytic activity improvement for the i-phase negative electrode is highly demanded. (C) 2011 Elsevier B.V. All rights reserved.

Update: 6-Oct-2011

Title:
Modulated superconductivity due to vacancy and magnetic order in A(y)Fe(2-x/2)Se(2) [A = Cs, K, (Tl,Rb), (Tl,K)] iron-selenide superconductors
Authors:
Das, T; Balatsky, AV Author Full Names: Das, Tanmoy; Balatsky, A. V.
Source:
PHYSICAL REVIEW B 84 (11): 10.1103/PhysRevB.84.115117 SEP 19 2011
Abstract:
We present a calculation of a "modulated" superconducting state in iron-selenide superconductors. The zero-momentum d-wave pairing breaks the translational symmetry of the conventional BaFe(2)Se(2)-like crystal of the I4/mmm space group. This pairing state becomes compatible when the Fe vacancies form an ordered state and the crystal symmetry changes to a low-temperature I4/m one. For the specific case of an incommensurate vacancy order at Q(v) = (1/5, 3/5) in K(0.82(2))Fe(1.626(3))Se(2), we find that it induces a block checkerboard antiferromagnetic phase at wave vector Q(m) = 4Q(v). The coexistence of vacancy order and magnetic order leads to a reconstructed ground state which naturally couples to the d-wave superconductivity in a uniform phase in what we propose will be a general coupling for all iron-selenide superconductors. Our results agree with numerous experimental data available to date. We thus suggest that the incommensurability leads to a uniform coexistence of multiple phases as a viable alternative to a nanoscale phase separation in high-T(c) superconductors and play an important role in the enhancement of superconductivity.
Title:
Disordered polyhalide anion effect on the Fermi surface of the incommensurate organic superconductor (MDT-TSF)I(0.77)Br(0.52)
Authors:
Kawamoto, T; Mori, T; Enomoto, K; Konoike, T; Terashima, T; Uji, S; Kitagawa, H; Takimiya, K; Otsubo, T Author Full Names: Kawamoto, Tadashi; Mori, Takehiko; Enomoto, Kengo; Konoike, Takako; Terashima, Taichi; Uji, Shinya; Kitagawa, Hiroshi; Takimiya, Kazuo; Otsubo, Tetsuo
Source:
PHYSICAL REVIEW B 84 (9): 10.1103/PhysRevB.84.094518 SEP 19 2011
Abstract:
The effect of disorder in polyhalide anions is investigated in terms of the degree of charge transfer and the Fermi surface in the incommensurate organic superconductor (MDT-TSF)I(0.77)Br(0.52), where MDT-TSF is methylenedithio-tetraselenafulvalene. The Raman spectra suggest that the infinite polyhalide chains include the asymmetric trihalide anion I(2)Br(-) and that the degree of charge transfer from the donor molecule to the anion is 0.429, estimated from the lattice constants. The Shubnikov-de Haas (SdH) oscillation is in good agreement with this charge transfer degree. The beating behavior of the SdH oscillation gives a large interlayer transfer integral, which is consistent with a corrugated conducting sheet structure. The randomness of the disordered anions reduces the periodicity of the incommensurate anion potential; this destroys the Fermi surface reconstruction by the incommensurate anion potential. The factor dominating the superconducting transition temperature is not the randomness of the polyhalide anions but the effective cyclotron mass enhancement, i.e., the many-body effect.
Title:
Persistent multiferroicity without magnetoelectric effects in CuO
Authors:
Wang, F; Zou, T; Liu, Y; Yan, LQ; Sun, Y Author Full Names: Wang, Fen; Zou, Tao; Liu, Yi; Yan, Li-Qin; Sun, Young
Source:
JOURNAL OF APPLIED PHYSICS 110 (5): 10.1063/1.3636106 SEP 1 2011
Abstract:
Multiferroicity and magnetoelectric effects in CuO have been investigated by measurements of magnetization, dielectric constant, and electric polarization with and without magnetic fields. Dielectric anomalies which indicate ferroelectric transitions were observed at two magnetic transition temperatures. Ferroelectric polarization was well detected in the incommensurate spiral phase. However, both dielectric constant and polarization have little changes in a 7 T magnetic field. Our study suggests that although with a high multiferroic temperature, the spiral spin structure in CuO is very stable and the induced ferroelectricity sustains even in a high magnetic field, which results in little magnetoelectric effects. (C) 2011 American Institute of Physics. [doi:10.1063/1.3636106]

Update: 28-Sep-2011

Title:
Metamagnetism and soliton excitations in the modulated ferromagnetic Ising chain CoV(2)O(6)
Authors:
Kimber, SAJ; Mutka, H; Chatterji, T; Hofmann, T; Henry, PF; Bordallo, HN; Argyriou, DN; Attfield, JP Author Full Names: Kimber, Simon A. J.; Mutka, Hannu; Chatterji, Tapan; Hofmann, Tommy; Henry, Paul F.; Bordallo, Heloisa N.; Argyriou, Dimitri N.; Attfield, J. Paul
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.104425 SEP 15 2011
Abstract:
We report a combination of physical property and neutron scattering measurements for polycrystalline samples of the one-dimensional spin-chain compound CoV(2)O(6). Heat capacity measurements show that an effective S = 1/2 state is found at low temperatures and that magnetic fluctuations persist up to similar to 6T(N). Above T(N) = 6.3 K, measurements of the magnetic susceptibility as a function of T and H show that the nearest-neighbor exchange is ferromagnetic. In the ordered state, we have discovered a crossover from a metamagnet with strong fluctuations between 5 K and T(N) to a state with a 1/3 magnetization plateau at 2 < T < 5 K. We use neutron powder diffraction measurements to show that the antiferromagnetic state has incommensurate long-range order and inelastic time-of-flight neutron scattering to examine the magnetic fluctuations as a function of temperature. Above T(N), we find two broad bands between 3.5 and 5 meV and thermally activated low-energy features which correspond to transitions within these bands. These features show that the excitations are deconfined solitons rather than the static spin reversals predicted for a uniform ferromagnetic Ising spin chain. Below T(N), we find a ladder of states due to the confining effect of the internal field. A region of weak confinement below T(N), but above 5 K, is identified which may correspond to a crossover between two- and three-dimensional magnetic ordering.
Title:
Effect of dimension on charge order domain in Ruddlesden-Popper manganites
Authors:
Nagao, M; Nagai, T; Hara, T; Kimoto, K Author Full Names: Nagao, M.; Nagai, T.; Hara, T.; Kimoto, K.
Source:
PHYSICA B-CONDENSED MATTER 406 (17): 3192-3195 10.1016/j.physb.2011.05.024 SEP 1 2011
Abstract:
The charge order (CO) domains of dimensionally controlled manganites Pr(1-x)Ca(x)MnO(3) and Pr(1-x)Ca(1+x) MnO(4) (x=0.5, 0.6 and 0.67), which have three-dimensional (3D) and two-dimensional (2D) Mn-O networks, respectively, have been studied by transmission electron microscopy (TEM). Although the electron diffraction data show similar dependences of the modulation wave vector on hole doping x, there are distinctive differences between the 3D and 2D systems in terms of the CO domain sizes. In the 2D system, the TEM images show that the domain size is almost constant irrespective of hole doping x. On the other hand, in the 3D system, the domain size of the incommensurate CO for x=0.6 is much smaller than those of the commensurate CO for x=0.5 and 0.67. Namely, in the 3D system, the CO states are strongly influenced by the incommensurability for the parent lattice. This difference indicates that the dimension of the Mn-O network plays a crucial role in the CO domain and suggests that the electron-lattice coupling of the 3D system is stronger than that of the 2D system. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Effect of chemical composition on the microstructure and hardness of Al-Cu-Fe alloy
Authors:
Suarez, MA; Esquivel, R; Alcantara, J; Dorantes, H; Chavez, JF Author Full Names: Suarez, M. A.; Esquivel, R.; Alcantara, J.; Dorantes, H.; Chavez, J. F.
Source:
MATERIALS CHARACTERIZATION 62 (9): 917-923 10.1016/j.matchar.2011.06.009 SEP 2011
Abstract:
Four Al-Cu-Fe alloys with compositions; a) Al(65)Cu(20)Fe(15), b) Al(64)Cu(22.5)Fe(13.5), c) Al(61)Cu(26)Fe(13) and d) Al(62)Cu(25.5)Fe(12.5), where the icosahedral phase is present, have been experimentally studied in both as-cast and annealed conditions in order to investigate the effect of chemical composition on the percentage of icosahedral phase and the changes in hardness of the alloy and each phase. It was found that the a) Al(65)Cu(20)Fe(15) and b) Al(64)cu(22.5)Fe(13.5) alloys, which present the highest Fe content, showed the largest amount of lambda-Al(13)Fe(4) phase as well as the highest hardness in all phases. In contrast, the same alloys developed the lowest amount of icosahedral phase after heat treatment. The c) Al(61)Cu(26)Fe(13) and d) Al(62)Cu(25.5)Fe(12.5) alloys had a better response to heat treatment, reaching amounts of icosahedral phase up to 87% and 99% respectively. The hardness of phases after heat treatment increased with respect to alloys in as-! cast condition, the hardness of icosahedral phase increased between 20% and 25%, while the hardness of lambda-Al(13)Fe(4) phase increased 9%. The icosahedral phase of annealed a) Al(65)Cu(20)Fe(15) alloy was the toughest with a hardness value of 844HV. (c) 2011 Elsevier Inc. All rights reserved.
Title:
Fermi-surface reconstruction by stripe order in cuprate superconductors
Authors:
Laliberte, F; Chang, J; Doiron-Leyraud, N; Hassinger, E; Daou, R; Rondeau, M; Ramshaw, BJ; Liang, R; Bonn, DA; Hardy, WN; Pyon, S; Takayama, T; Takagi, H; Sheikin, I; Malone, L; Proust, C; Behnia, K; Taillefer, L Author Full Names: Laliberte, F.; Chang, J.; Doiron-Leyraud, N.; Hassinger, E.; Daou, R.; Rondeau, M.; Ramshaw, B. J.; Liang, R.; Bonn, D. A.; Hardy, W. N.; Pyon, S.; Takayama, T.; Takagi, H.; Sheikin, I.; Malone, L.; Proust, C.; Behnia, K.; Taillefer, Louis
Source:
NATURE COMMUNICATIONS 2 10.1038/ncomms1440 AUG 2011
Abstract:
The origin of pairing in a superconductor resides in the underlying normal state. In the cuprate high-temperature superconductor YBa(2)Cu(3)Oy (YBCO), application of a magnetic field to suppress superconductivity reveals a ground state that appears to break the translational symmetry of the lattice, pointing to some density-wave order. Here we use a comparative study of thermoelectric transport in the cuprates YBCO and La(1.8-x)Eu(0.2)Sr(x)CuO(4) (Eu-LSCO) to show that the two materials exhibit the same process of Fermi-surface reconstruction as a function of temperature and doping. The fact that in Eu-LSCO this reconstruction coexists with spin and charge modulations that break translational symmetry shows that stripe order is the generic non-superconducting ground state of hole-doped cuprates.
Title:
RELATIONSHIP BETWEEN CHEMICAL AND ICOSAHEDRAL LOCAL ORDERINGS IN Al-Ni-Fe MELTS
Authors:
Roik, AS; Samsonnikov, AV; Kazimirov, VP; Sokol'skii, VE Author Full Names: Roik, A. S.; Samsonnikov, A. V.; Kazimirov, V. P.; Sokol'skii, V. E.
Source:
JOURNAL OF STRUCTURAL CHEMISTRY 52 (2): 310-318 APR 2011
Abstract:
An X-ray diffraction study and simulation of the structure of ternary Al(81.6)Ni(14.9)Fe(3.5), Al(71.6)Ni(23)Fe(5.4), and Al(61.1)Ni(31.1)Fe(7.3) melts by the reverse Monte Carlo method are conducted. An analysis of the structural models of melts is performed by the Voronoi-Delaunay partition. It is shown that the prepeak on the structure factor curves in the diffraction vector range of 13 nm(-1) to 22 nm(-1) is due to two factors: chemical ordering of atoms and non-crystalline close packing. The origin of the icosahedral short-range order in the melts as one of the variants of ordering of atoms in non-crystalline close packed clusters is discussed.

Update: 22-Sep-2011

Title:
Spatial inhomogeneity and planar symmetry breaking of the lattice incommensurate supermodulation in the high-temperature superconductor Bi(2)Sr(2)CaCu(2)O(8+y)
Authors:
Poccia, N; Campi, G; Fratini, M; Ricci, A; Saini, NL; Bianconi, A Author Full Names: Poccia, Nicola; Campi, Gaetano; Fratini, Michela; Ricci, Alessandro; Saini, Naurang L.; Bianconi, Antonio
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.100504 SEP 12 2011
Abstract:
Using scanning micro-x-ray diffraction we report a mixed real and reciprocal space visualization of the spatial heterogeneity of the lattice incommensurate supermodulation in a single crystal of Bi(2)Sr(2)CaCu(2)O(8+y) with T(c) = 84 K. The mapping shows an amplitude distribution of the supermodulation with large lattice fluctuations at a microscale with similar to 50% amplitude variation. The angular distribution of the supermodulation amplitude in the a-b plane shows a lattice chiral symmetry, forming a left-handed oriented striped pattern. The spatial correlation of the supermodulation is well described by a compressed exponential with an exponent of 1.5 +/- 0.3 and a correlation length of similar to 50 mu m, showing intrinsic lattice disorder in high-temperature superconductors.
Title:
Magnetic structure and electric field effects in multiferroic YMn(2)O(5)
Authors:
de Souza, RA; Staub, U; Scagnoli, V; Garganourakis, M; Bodenthin, Y; Huang, SW; Garcia-Fernandez, M; Ji, S; Lee, SH; Park, S; Cheong, SW Author Full Names: de Souza, R. A.; Staub, U.; Scagnoli, V.; Garganourakis, M.; Bodenthin, Y.; Huang, S. -W.; Garcia-Fernandez, M.; Ji, S.; Lee, S. -H.; Park, S.; Cheong, S. -W.
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.104416 SEP 9 2011
Abstract:
The magnetic structure of multiferroic RMn(2)O(5) (R = Y, Er) has been investigated by means of resonant soft x-ray diffraction. Energy, temperature, and azimuthal angle scans were performed in addition to reciprocal space maps on the magnetic reflection in the different magnetic phases of YMn(2)O(5). We also investigated the orbital magnetic moment at the oxygen K-edge for RMn(2)O(5) with both, R = Y and R = Er compositions. These moments reflect the strong hybridization between Mn 3d and oxygen 2p states. Experiments with applied electric fields are additionally presented, showing that the helical component of the magnetic structure in the CM phase of YMn(2)O(5) can be reversed by the application of an electric field. However, the incommensurate magnetic reflection in the high-temperature phase is unaffected. Interestingly, this is observed only in the presence of a small electrical current, indicative of a current-induced/-enhanced switching of magnetic domains.

Update: 16-Sep-2011

Title:
Magnetoelectric Ordering of BiFeO(3) from the Perspective of Crystal Chemistry
Authors:
Volkova, LM; Marinin, DV Author Full Names: Volkova, L. M.; Marinin, D. V.
Source:
JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM 24 (7): 2161-2177 10.1007/s10948-011-1178-5 OCT 2011
Abstract:
In this paper we examine the role of crystal chemistry factors in creating conditions for formation of magnetoelectric ordering in BiFeO(3). It is generally accepted that the main reason of the ferroelectric distortion in BiFeO(3) is concerned with a stereochemical activity of the Bi lone pair. However, the lone pair is stereochemically active in the paraelectric orthorhombic -phase as well. We demonstrate that a crucial role in emerging of phase transitions of the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order types belongs to the change of the degree of the lone pair stereochemical activity-its consecutive increase with the temperature decrease. Using the structural data, we calculated the sign and strength of magnetic couplings in BiFeO(3) in the range from 945 A degrees C down to 25 A degrees C and found the couplings, which undergo the antiferromagnetic -> aEuro parts per thousand ferromagnetic transition with the temperature decrease and give rise to the antiferromagnetic ordering and its delay in regard to temperature, as compared to the ferroelectric ordering. We discuss the reasons of emerging of the spatially modulated spin structure and its suppression by doping with La(3+).
Title:
Antiferromagnetic Order in Pauli-Limited Unconventional Superconductors
Authors:
Kato, Y; Batista, CD; Vekhter, I Author Full Names: Kato, Yasuyuki; Batista, C. D.; Vekhter, I.
Source:
PHYSICAL REVIEW LETTERS 107 (9): 10.1103/PhysRevLett.107.096401 AUG 26 2011
Abstract:
We develop a theory of the coexistence of superconductivity (SC) and antiferromagnetism (AFM) in CeCoIn(5). We show that in Pauli-limited nodal superconductors the nesting of the quasiparticle pockets induced by Zeeman pair breaking leads to incommensurate AFM with the magnetic moment normal to the field. We compute the phase diagram and find a first order transition to the normal state at low temperatures, the absence of normal state AFM, and the coexistence of SC and AFM at high fields, in agreement with experiments. We also predict the existence of a new double-Q magnetic phase.
Title:
PHOTOINDUCED CHANGES IN THE SPACE-MODULATED MAGNETIC ORDER OF A FeBO(3):Mg SINGLE CRYSTAL
Authors:
Dzhuraev, DR; Sokolov, BY; Faiziev, SS Author Full Names: Dzhuraev, D. R.; Sokolov, B. Yu.; Faiziev, Sh. Sh.
Source:
RUSSIAN PHYSICS JOURNAL 54 (3): 382-385 AUG 2011
Abstract:
An effect of nonpolarized white light on the modulated magnetic structure of a FeBO(3):Mg single crystal, which arises in this light-plane weak ferromagnet in the low temperature range during technical magnetization, has been revealed. It has been found that the degree of the light action on the magnetic state of FeBO(3):Mg depends both on its duration and on the orientation of the spontaneous magnetization vector M of the crystal during illumination. Interpretation of the results obtained has been performed in the context of the "magnetic ripple" theory on the assumption that the absorbed light induces additional uniaxial magnetic anisotropy in the easy plane of the crystal and that the anisotropy axis is collinear to the vector M during illumination.
Title:
Ordered and disordered states in NiAs/Ni(2)In-type Ni(1+delta)Sn: Crystallography and order formation
Authors:
Leineweber, A Author Full Names: Leineweber, Andreas
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 102 (7): 861-873 10.3139/146.110540 JUL 2011
Abstract:
An overview on the occupational order disorder behaviour of NiAs/Ni(2)In-type Ni(1+delta)Sn alloys is given. This order disorder behaviour leads to the occurrence of one disordered high-temperature phase HT and three different low-temperature phases LT, LT' and LT". The low-temperature phases, forming in different compositional regimes, are characterised by long-range order of Ni atoms against vacancies on trigonal-bipyramidal sites formed by Sn, leading to a commensurate superstructure in LT whereas LT' and LT" are incommensurate. Different order disorder related phase transformation were monitored by X-ray powder diffraction. In particular during the formation of long-range order starting from disordered HT-Ni(1+delta)Sn, non-equilibrium crystal structures and microstructures evolve prior to formation of the ideally established equilibrium low-temperature phases. Quantitative analysis of the transformation kinetics including determination of activation energies was done by X-ray powder diffraction. The activation energies of the different processes can be related with the mobility of the Ni atoms in the crystal structure.

Update: 8-Sep-2011

Title:
First-principles investigations of the five-layer modulated martensitic structure in Ni(2)Mn(Al(x)Ga(1-x)) alloys
Authors:
Luo, HB; Li, CM; Hu, QM; Kulkova, SE; Johansson, B; Vitos, L; Yang, R Author Full Names: Luo, H. B.; Li, C. M.; Hu, Q. M.; Kulkova, S. E.; Johansson, B.; Vitos, L.; Yang, R.
Source:
ACTA MATERIALIA 59 (15): 5938-5945 10.1016/j.actamat.2011.06.002 SEP 2011
Abstract:
In this paper, the five-layer modulated (5M) martensitic structures of Ni(2)Mn(Al(x)Ga(1-x)), with x = 0, 0.1 and 0.2, are investigated by the use of the exact muffin-tin orbital method in combination with the coherent potential approximation. The 5M martensite is modeled by varying c/a (shear) and wave-like displacements of the atoms on (1 1 0) plane (shuffle) scaled by eta according to Martynov and Kokorin (J. Phys. III 2, 739 (1992)). For Ni(2)MnGa, we obtain 5M martensite with equilibrium c/a of 0.92 and eta of 0.08, in reasonable agreement with the experiment results (0.94 and 0.06, respectively). c/a and eta are linearly coupled to each other. Al-doping increases c/a and decreases eta, but the linear c/a similar to eta coupling remains. Comparing the total energies of the 5M martensite and L2(1) austenite, we find that the martensite is more stable than the austenite. Al-doping increases the relative stability of the austenite and finally becomes energetically degenerated with the 5M martensite at an Al atomic fraction (x) of about 0.26. The relative phase stability is analyzed based on the calculated density of states. The calculated total magnetic moments mu(0) as a function of c/a exhibit a maximum around the equilibrium c/a. Al-doping reduces mu(0) (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Unraveling the Perplexing Structure of the Zeolite SSZ-57
Authors:
Baerlocher, C; Weber, T; McCusker, LB; Palatinus, L; Zones, SI Author Full Names: Baerlocher, Christian; Weber, Thomas; McCusker, Lynne B.; Palatinus, Lukas; Zones, Stacey I.
Source:
SCIENCE 333 (6046): 1134-1137 10.1126/science.1207466 AUG 26 2011
Abstract:
Previous high-resolution x-ray powder diffraction and transmission electron microscopy studies of the zeolite SSZ-57 could not fully elucidate the structural basis for its puzzling adsorption behavior, which appears to be intermediate between that of a medium-(10-ring) and a large-pore (12-ring) zeolite. Now by applying advanced crystallographic techniques (structure solution in four-dimensional space and interpretation of three-dimensional diffuse scattering by Monte Carlo simulation) and crystal chemistry considerations to high-quality single-crystal x-ray diffraction data collected on a microcrystal (about 2 micrometers by 2 micrometers by 8 micrometers), we have been able to derive a comprehensive description of its silicate framework structure. The framework is related to that of ZSM-11 but is commensurately modulated along the c axis (P (4) over bar m2, a = b = 20.091 angstrom, c = 110.056 angstrom) to yield a structure with a 12-ring:10-ring ratio of 1:15. Disorder of the 12-rings results in a three-dimensional 10-ring channel system with large isolated pockets. The structure helps to clarify the material's catalytic activity.
Title:
GOVERNING EQUATIONS AND GENERAL SOLUTIONS OF PLANE ELASTICITY OF TWO-DIMENSIONAL DECAGONAL QUASICRYSTALS
Authors:
Gao, Y; Shang, LG Author Full Names: Gao, Yang; Shang, Lan-Ge
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B 25 (20): 2769-2778 10.1142/S0217979211101065 AUG 10 2011
Abstract:
Two-dimensional problem is systematically investigated for the coupled equations in two-dimensional decagonal quasicrystals, and three general solutions are presented by an operator method. To simplify governing equations, each general solution shall take three different forms expressed in terms of three displacement functions, which satisfy partial three differential equations of second order. To illustrate its utility, the closed-form solutions are obtained for problems of point phonon forces and phason force acting at the apex of a quasicrystal wedge, all in terms of the general solutions. Furthermore, these solutions can be degenerated to those of problems of point forces applied on the boundary of a quasicrystal half-plane.
Title:
Martensitic transformation in rapidly solidified Heusler Ni(49)Mn(39)Sn(12) ribbons
Authors:
Zheng, HX; Wu, DZ; Xue, SC; Frenzel, J; Eggeler, G; Zhai, QJ Author Full Names: Zheng, Hongxing; Wu, Dianzhen; Xue, Sichuang; Frenzel, Jan; Eggeler, Gunther; Zhai, Qijie
Source:
ACTA MATERIALIA 59 (14): 5692-5699 10.1016/j.actamat.2011.05.044 AUG 2011
Abstract:
In the present work, the microstructure evolution and kinetics of the martensitic transformation are investigated in as-spun and annealed ribbons of Heusler Ni(49)Mn(39)Sn(12) using electron microscopy, X-ray diffraction and differential scanning calorimetry. Both ribbons undergo a reversible martensitic transformation during thermal cycling and the low-temperature martensite is confirmed to be a modulated four-layered orthorhombic (4O) structure through in situ cooling transmission electronic microscopy investigation. The annealing effect on the martensitic transformation behavior is discussed from the viewpoints of electron concentration, Mn-Mn inter-atomic distance, atomic order degree and grain size. A strong cooling-rate dependence of phase transition kinetics is found and the mechanism is analyzed. The satisfactory reproducibility obtained during thermal cycling test of this alloy ribbons offers great potential for practical applications. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Antiferromagnet-Long-Period Structure Phase Transition in RMn(2)O(5) Oxides
Authors:
Men'shenin, VV; Nikolaev, VV; Dmitriev, AV Author Full Names: Men'shenin, V. V.; Nikolaev, V. V.; Dmitriev, A. V.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 112 (1): 25-35 10.1134/S0031918X11010315 JUL 2011
Abstract:
An analysis of the magnetic phase transition from an antiferromagnetic into an incommensurate phase in oxides RMn(2)O(5) has been performed. It has been shown that this is a second-order phase transition and that it can occur through one of complete irreducible representations of the space group Pbam, i.e., without a decrease in the symmetry of the crystal lattice. It has been established that the decrease in the electric polarization of the oxides in this transition is due to the development of long-period magnetic ordering.

Update: 31-Aug-2011

Title:
Magnetic correlation in the square-lattice spin system (CuBr)Sr(2)Nb(3)O(10): A neutron diffraction study
Authors:
Yusuf, SM; Bera, AK; Ritter, C; Tsujimoto, Y; Ajiro, Y; Kageyama, H Author Full Names: Yusuf, S. M.; Bera, A. K.; Ritter, C.; Tsujimoto, Yoshihiro; Ajiro, Yoshitami; Kageyama, Hiroshi
Source:
PHYSICAL REVIEW B 84 (6): 10.1103/PhysRevB.84.064407 AUG 18 2011
Abstract:
Magnetic correlation in the quantum S = 1/2 square-lattice system (CuBr) Sr(2)Nb(3)O(10) has been studied by neutron diffraction. A novel commensurate in-plane, helical antiferromagnetic (AFM) ordering, characterized by the propagation vector k = (0 3/8 1/2), has been confirmed from the appearance of magnetic Bragg peaks below T(N) similar to 7.5 K. The ordered moment at 2 K is found to be 0.79(7) mu B/Cu(2+)-ion. The observed helical AFM structure differs from the ground state predicted theoretically from the J(1)-J(2) model as well as from experimentally reported states for other quantum S = 1/2 square-lattice systems. However, the observed helical magnetic structure can be described in a J(1)-J(2)-J(3) model. Under a 4.5 T magnetic field, the spin-order changes drastically and is characterized by the propagation vector k(1) = (0 1/3 0.446) and a probable k(2) = (0 0 0) vector.
Title:
Mechanical properties of clusters in quasicrystal approximants: The example of the 1/1 Al-Cu-Fe approximant
Authors:
Jung, DY; Steurer, W Author Full Names: Jung, Daniel Y.; Steurer, Walter
Source:
PHYSICAL REVIEW B 84 (5): 10.1103/PhysRevB.84.054116 AUG 15 2011
Abstract:
Quantum-mechanical molecular dynamics have been used to investigate structural and physical properties of the 1/1 approximant of the icosahedral Al-Cu-Fe quasicrystal. Particular local structural arrangements of atoms, referred to here as clusters, have been analyzed with respect to their properties within the crystal structure. Artificial strain and cracks have been introduced to probe their mechanical properties, and artificial surfaces have been created to investigate their role for surface termination. From the energetics of the ab initio calculations results that flat surfaces cutting clusters are favored over puckered surfaces keeping clusters intact. The Vienna Ab-initio Simulation Package (VASP) was used for all calculations.
Title:
Pressure-induced formation of intermediate-valence quasicrystalline system in a Cd-Mg-Yb alloy
Authors:
Watanuki, T; Kawana, D; Machida, A; Tsai, A Author Full Names: Watanuki, Tetsu; Kawana, Daichi; Machida, Akihiko; Tsai, AnPang
Source:
PHYSICAL REVIEW B 84 (5): 10.1103/PhysRevB.84.054207 AUG 15 2011
Abstract:
A quasiperiodic intermediate-valence system was prepared by applying pressure to an icosahedral Cd-Mg-Yb quasicrystal. X-ray absorption spectroscopy near the Yb L(3) edge demonstrates that the Yb valence increases continuously upon compression from the divalent state (4f(14)) at ambient pressure and reaches a value of 2.71 at 57.6 GPa, which is close to the trivalent state (4f(13)). By following the trend of Yb-based intermediate-valence crystalline compounds, this large valence increase suggests the change of 4f character in the Cd-Mg-Yb quasicrystal from an itinerant state with weak electron correlations to an intermediate region between an itinerant and a localized state with strong correlations. The valence increases sensitively with pressure below similar to 30 GPa; however, the increase is significantly suppressed above similar to 30 GPa. The rate of valence increase with respect to pressure in the lower-pressure region is twice larger than that of a Cd-Yb quasicrystal in our previous study [Phys. Rev. B 81, 220202(R) (2010)]. This is mainly explained by the smaller bulk modulus of the Cd-Mg-Yb quasicrystal compared to the Cd-Yb system. The suppression of valence increase with respect to pressure in the higher-pressure region is most likely due to an increase of conduction-4f electron hybridization that counteracts 4f localization and reduces the Yb valence increase.
Title:
Effect of relaxation state on nucleation and grain growth of nanoscale quasicrystal in Zr-based bulk metallic glasses prepared under various cooling rates
Authors:
Saida, J; Setyawan, AD; Matsubara, E Author Full Names: Saida, Junji; Setyawan, Albertus Deny; Matsubara, Eiichiro
Source:
APPLIED PHYSICS LETTERS 99 (6): 10.1063/1.3622117 AUG 8 2011
Abstract:
Zr(65)Al(7.5)Ni(10)Cu(12.5)Pd(5) bulk metallic glasses (BMGs) in various relaxation states were prepared under different cooling rates. The grain growth rate of the primary quasicrystal was examined near the crystallization temperature. It was approximately 1 x 10(-9) m/s in less relaxed BMGs and approximately twice as large in relaxed BMGs. In contrast, the calculated homogeneous nucleation rate of the less relaxed samples was five to ten times higher (5 x 10(19)-1 x 10(20)/m(3)s) than those in the relaxed BMGs. The results indicate that the relaxation state of glassy alloys has a marked effect on nucleation and grain growth behaviors. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622117]
Title:
Structural behavior and thermoelectric properties of the brownmillerite system Ca(2)(Zn(x)Fe(2-x))O(5)
Authors:
Asenath-Smith, E; Misture, ST; Edwards, DD Author Full Names: Asenath-Smith, Emily; Misture, Scott T.; Edwards, Doreen D.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 184 (8): 2167-2177 10.1016/j.jssc.2011.06.009 AUG 2011
Abstract:
The Ca(2)(Zn(x)Fe(2-x))O(5) series was synthesized and characterized to determine the influence of zinc dopant on the brownmillerite structure for thermoelectric applications. All single-phase compounds exhibited Pnma symmetry at room temperature up to the solubility limit at x=0.10. High-temperature X-ray powder diffraction was used to show that the nature of the Pnma-Imma(0 0 gamma)s00 transition in Ca(2)Fe(2)O(5) is modified by the presence of zinc. While the Zn-free composition transitions to an incommensurate phase, the Zn-containing phases transition instead to a commensurate phase, Imma(0 0 gamma)s00 with gamma=1/2. Both the Neel temperature and the onset temperature of the Pnma-Imma(0 0 gamma)s00 phase transition decreased with increasing zinc concentration. Rietveld analysis of the in situ diffraction pattern for the x=0 sample at 1300 degrees C demonstrates that the structure contains statistically disordered chain orientations as described by space group Imma. Thermoelectric properties were analyzed in air from 100 to 800 degrees C. The positive Seebeck coefficient revealed hole-type conduction for all compositions. Doped samples exhibited electrical conductivities up to 3.4 S/cm and thermal conductivity of 1.5 W/mK Transport analysis revealed thermally activated mobility consistent with polaron conduction behavior for all compositions. (C) 2011 Elsevier Inc. All rights reserved.
Title:
OPTICAL TRANSMISSION COEFFICIENT OF CRYSTALLINE [N(CH(3))(4)](2)MeCl(4) IN THE INCOMMENSURATE PHASE
Authors:
Sveleba, SA; Karpa, IV; Katerynchuk, IM; Semotyuk, OV; Shymkiv, RM; Kunyo, IM; Fitsych, OI Author Full Names: Sveleba, S. A.; Karpa, I. V.; Katerynchuk, I. M.; Semotyuk, O. V.; Shymkiv, R. M.; Kunyo, I. M.; Fitsych, O. I.
Source:
JOURNAL OF APPLIED SPECTROSCOPY 78 (2): 228-233 MAY 2011
Abstract:
This a study of the optical transmission of [N(CH(3))(4)](2)ZnCl(4) and [N(CH(3))(4)](2)CuCl(4) crystals in the incommensurate phase when a defect density wave is present. It is found that an anomalous reduction in the transmission coefficient is caused by scattering of light owing to a realignment of the superstructure during transitions between metastable states. When a defect density wave is present, the anomalous optical transmission of the crystal is related to the scattering of light on superstructure inhomogeneities produced by a superposition of existing modulation waves.

Update: 25-Aug-2011

Title: Magnetic phase diagrams of the CrB- and FeB-type HoSi compounds

Author(s): Schobinger-Papamantellos, P (Schobinger-Papamantellos, P.); Buschow, KHJ (Buschow, K. H. J.); Rodriguez-Carvajal, J (Rodriguez-Carvajal, J.)

Source: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Volume: 323 Issue: 21 Pages: 2592-2607 DOI: 10.1016/j.jmmm.2011.05.044 Published: NOV 2011

Abstract: The temperature magnetic phase diagrams of the dimorphic HoSi compound were studied by neutron diffraction. The sample comprises 35.5% CrB- (Cmcm) and 64.5% FeB-type (Pnma) of structure. Both phases order antiferromagnetically below T(N)=25 K and undergo first-order magnetic transitions at T(ic) = 16.5 K. Their T-phase diagrams comprise a low temperature (LT) 2.7 K - T(ic) and a high temperature (HT) range T(ic) - T(N) with distinct wave vectors. The LT magnetic ordering of the CrB-type HoSi with the wave vector q(1)=(1/2, 0, 1/2) corresponds to a uniaxial magnetic structure, with the Ho moments along the shortest axis c. At 2.7 K the ordered moment value is 8.6(2) mu(B)/Ho atom. The HT ordering, described by the wave vector q(2)=(q(2x), 0, q(2z)) with a T-variable length, corresponds to an amplitude modulated structure. The magnetic ordering of the FeB-type HoSi requires two symmetry independent vectors q(3)=(0, q(3y), q(3z)) for the LT- and q(4)=(q(4x), q(4y), 0) for the HT range. Both vectors correspond to sine wave modulated structures with the Ho magnetic moments confined along the shortest axis b. The q(3) vector has an almost invariable length vs. T close to approximate to (0, 9/17, 1/11). At 2.7 K the amplitude of the wave is 10.9(1) mu(B)/Ho atom. At T(ic) q(3) jumps to the wave vector q(4)=(q(4x), q(4y), 0) with a T-variable length. At 17 K q(4)=(0.092(1), 0.538(3), 0). Around T(ic) there is a narrow coexistence range of the q(3) and q(4) competing phases. Various models are discussed and compared with the isomorphic RSi (R=rare earth) compounds counterparts of HoSi, a comparison that has led us to briefly review the magnetic structures available in the literature for this interesting class of compounds. (C) 2011 Elsevier B.V. All rights reserved.

Title: Antiferromagnetic resonance in ferroborate NdFe(3)(BO(3))(4)

Author(s): Kobets, MI (Kobets, M. I.); Dergachev, KG (Dergachev, K. G.); Khatsko, EN (Khatsko, E. N.); Gnatchenko, SL (Gnatchenko, S. L.); Bezmaternykh, LN (Bezmaternykh, L. N.); Temerov, VL (Temerov, V. L.)

Source: PHYSICA B-CONDENSED MATTER Volume: 406 Issue: 18 Pages: 3430-3435 DOI: 10.1016/j.physb.2011.06.014 Published: SEP 15 2011

Abstract: The AFMR spectra of the NdFe(3)(BO(3))(4) crystal are measured in a wide range of frequencies and temperatures. It is found that by the type of its magnetic anisotropy the compound is an "easy-plane" antiferromagnet with a weak anisotropy in the basal plane. The effective magnetic parameters are determined: anisotropy fields H(a1) = 1.14 kOe and H(a2) = 60 kOe and magnetic excitation gaps Delta v(1) = 101.9 GHz and Delta v(2) = 23.8 GHz. It is shown that commensurate-incommensurate phase transition causes a shift in resonance field and a considerable change in absorption line width. At temperatures below 4.2 K nonlinear regimes of AFMR excitation at low microwave power levels are observed. (C) 2009 Elsevier B.V. All rights reserved.

Title: Incommensurate spin-density wave and a multiband superconducting phase in Na(x)FeAs revealed by nuclear magnetic resonance

Author(s): Klanjsek, M (Klanjsek, M.); Jeglic, P (Jeglic, P.); Lv, B (Lv, B.); Guloy, AM (Guloy, A. M.); Chu, CW (Chu, C. W.); Arcon, D (Arcon, D.)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 5 Article Number: 054528 DOI: 10.1103/PhysRevB.84.054528 Published: AUG 11 2011

Abstract: We report a (23)Na and (75)As nuclear magnetic resonance (NMR) investigation of Na(x)FeAs series (x = 1, 0.9, 0.8) exhibiting a spin-density-wave (SDW) order below T(SDW) = 45, 50, and 43 K for x = 1, 0.9, 0.8, respectively, and a bulk superconductivity below T(c) approximate to 12 K for x = 0.9. Below T(SDW), a spin-lattice relaxation reveals the presence of gapless particle-hole excitations in the whole x range, meaning that a portion of the Fermi surface remains gapless. The superconducting fraction as deduced from the bulk susceptibility scales with this portion, while the SDW order parameter as deduced from the NMR linewidth scales inversely with it. The NMR line shape can only be reproduced assuming an incommensurate (IC) SDW. These findings qualitatively correspond to the mean-field models of competing interband magnetism and intraband superconductivity, which lead to an IC SDW order coexisting with superconductivity in part of the phase diagram.

Title: Effect of selective substitution of Co for Ni or Mn on the superstructure and microstructural properties of Ni(50)Mn(29)Ga(21)

Author(s): Kumar, AS (Kumar, A. Satish); Ramudu, M (Ramudu, M.); Seshubai, V (Seshubai, V.)

Source: JOURNAL OF ALLOYS AND COMPOUNDS Volume: 509 Issue: 32 Pages: 8215-8222 DOI: 10.1016/j.jallcom.2011.05.064 Published: AUG 11 2011

Abstract: Results from a systematic study of the effect of cobalt, selectively substituted for Ni and Mn, in the modulated orthorhombic (7 M) Ni(50)Mn(29)Ga(21) alloy are contrasted. Substitution of Co for Mn resulted in the stabilization of a non-modulated tetragonal (NM) phase at higher Co content. At lower Co contents, a mixture of 7 M and NM phases were found to co-exist. Increasing in Co content caused suppression of long-range twin deformation leading to sporadic islands within which twin variants were confined. These effects are attributed to the considerable stresses generated by an atomic volume change of 9.5% caused locally when Co is substituted for Mn. On the other hand, substitution of Co for Ni, which causes only 1.7% atomic volume change locally, was observed not to alter either the superstructural ordering or the long-range twin deformation. Our results show that the microstructures resultant on Co doping have a strong correlation to the structural ordering, which in turn depends on whether Co is substituted for Mn or for Ni, and also on the concentration of Co. (C) 2011 Elsevier B. V. All rights reserved.

Title: Thermal and electrical transport in the spin density wave antiferromagnet CaFe(4)As(3)

Author(s): Kim, MS (Kim, M. S.); Yin, ZP (Yin, Z. P.); Zhao, LL (Zhao, L. L.); Morosan, E (Morosan, E.); Kotliar, G (Kotliar, G.); Aronson, MC (Aronson, M. C.)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 7 Article Number: 075112 DOI: 10.1103/PhysRevB.84.075112 Published: AUG 5 2011

Abstract: We present here measurements of the thermopower, thermal conductivity, and electrical resistivity of the newly reported compound CaFe(4)As(3). Evidence is presented from specific heat and electrical resistivity measurements that a substantial fraction of the Fermi surface survives the onset of spin density wave (SDW) order at the Neel temperature T(N) = 88 K and its subsequent commensurate lock-in transition at T(2) = 26.4 K. The specific heat below T(2) consists of a normal metallic component from the ungapped parts of the Fermi surface and a Bardeen-Cooper-Schrieffer (BCS) component that represents the SDW gapping of the Fermi surface. A large Kadowaki-Woods ratio is found at low temperatures, showing that the ground state of CaFe(4)As(3) is a strongly interacting Fermi liquid. The thermal conductivity kappa of CaFe(4)As(3) is an order of magnitude smaller than those of conventional metals at all temperatures, due to a strong phonon scattering. The thermoelectric power S displays a sign change from positive to negative indicating that a partial gap forms at the Fermi level with the onset of commensurate spin density wave order at T(2) = 26.4 K. The small value of the thermopower S and the enhancements of the resistivity due to gap formation and strong quasiparticle interactions offset the low value of the thermal conductivity kappa, yielding only a modest value for the thermoelectric figure of merit Z <= 5 x 10(-6) K(-1) in CaFe(4)As(3). The results of ab initio electronic structure calculations are reported, confirming that the sign change in the thermopower at T(2) is reflected by a sign change in the slope of the density of states at the Fermi level. Values for the quasiparticle renormalization Z are derived from measurements of the specific heat and thermopower, indicating that as T -> 0, CaFe(4)As(3) is among the most strongly correlated of the known Fe-based pnictide and chalcogenide systems.

Title: Switching behaviour of modulated ferroelectrics: the kinetics of the field induced lock-in transition in K(2)SeO(4)

Author(s): Leist, J (Leist, J.); Gibhardt, H (Gibhardt, H.); Hradil, K (Hradil, K.); Eckold, G (Eckold, G.)

Source: JOURNAL OF PHYSICS-CONDENSED MATTER Volume: 23 Issue: 30 Article Number: 305901 DOI: 10.1088/0953-8984/23/30/305901 Published: AUG 3 2011

Abstract: The field induced switching process across the ferroelectric lock-in transition in K(2)SeO(4) has been studied on a millisecond timescale using stroboscopic neutron diffraction. The time evolution of both the first and the third order satellites was examined. The time constants are found to vary with temperature between 0.2 and 1.2 ms. This is an order of magnitude faster than in the isostructural Rb(2)ZnCl(4). Moreover, the time dependence of the satellite's linewidth provides information about the evolution of the coherence of the modulated structure.

Title: Pressure-induced change in the magnetic ordering of TbMnO(3)

Author(s): Makarova, OL (Makarova, O. L.); Mirebeau, I (Mirebeau, I.); Kichanov, SE (Kichanov, S. E.); Rodriguez-Carvajal, J (Rodriguez-Carvajal, J.); Forget, A (Forget, A.)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 2 Article Number: 020408 DOI: 10.1103/PhysRevB.84.020408 Published: JUL 20 2011

Abstract: We have studied TbMnO(3) by high-pressure neutron diffraction up to 3.6 GPa and down to 1.5 K. The incommensurate spin structures of the Mn and Tb moments are strongly suppressed under pressure, and an E-type commensurate spin structure with (0,1/2,0) propagation vector is stabilized for the Mn moments. The Mn and Tb incommensurate orders which persist at low pressures or low temperatures are also affected, with a change of phase of the modulation between neighboring Mn chains and a reorientation of the Mn moments along the a axis. The results suggest both a change of the balance of the different Mn-Mn interactions and a strengthening of the Tb-Tb (or Tb-Mn) interactions under pressure.

Title: Transverse and longitudinal lattice modulations in the charge-orbital-ordered manganite Sr(2-x)La(x)MnO(4) around x=0.5

Author(s): Arao, M (Arao, Masazumi); Inoue, Y (Inoue, Yasuhide); Toyoda, K (Toyoda, Kensei); Koyama, Y (Koyama, Yasumasa)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 1 Article Number: 014102 DOI: 10.1103/PhysRevB.84.014102 Published: JUL 15 2011

Abstract: For Sr(2-x)La(x)MnO(4), having a nearly two-dimensional electronic system of e(g) electrons, we have examined the crystallographic features of the charge-orbital-ordered (COO) and charge-exchange (CE)-type magnetic states for 0.40 <= x <= 0.55 by transmission electron microscopy. Incommensurate and commensurate longitudinal lattice modulations were found below similar to 150 K for 0.47 <= x <= 0.51, while the cooling from the disordered tetragonal state resulted in the appearance of transverse modulations below T(COO) for 0.40 <= x <= 0.52. For 0.47 <= x <= 0.51, thus, the longitudinal and transverse modulations were present in both the lower-temperature region of the COO state and the CE-type magnetic state. In addition to these two states, the COO state for 0.40 <= x < 0.47 and 0.51 < x <= 0.52 accompanies only the transverse modulation and should be referred to as the orbital modulated state without a charge modulation.

Title: Neutron diffraction studies of RSn(1+x)Ge(1-x) (R=Tb-Er) compounds

Author(s): Gil, A (Gil, A.); Penc, B (Penc, B.); Baran, S (Baran, S.); Hoser, A (Hoser, A.); Szytula, A (Szytula, A.)

Source: JOURNAL OF SOLID STATE CHEMISTRY Volume: 184 Issue: 7 Pages: 1631-1637 DOI: 10.1016/j.jssc.2011.04.040 Published: JUL 2011

Abstract: The magnetic structures of RSn(1+x)Ge(1-x) (R=Tb, Dy, Ho and Er, x approximate to 0.1) compounds have been determined by neutron diffraction studies on polycrystalline samples. The data recorded in a paramagnetic state confirmed the orthorhombic crystal structure described by the space group Cmcm. These compounds are antiferromagnets at low temperatures. The magnetic ordering in TbSn(1.12)Ge(0.88) is sine-modulated described by the propagation vector k=(0.4257(2), 0, 0.5880(3)). Tb magnetic moment equals 9.0(1)mu(B) at 1.62 K. It lies in the b-c plane and form an angle theta=17.4(2)degrees with the c-axis. This structure is stable up to the Neel temperature equal to 31 K. The magnetic structures of RSn(1+x)Ge(1-x), where R are Dy, Ho and Er at low temperatures are described by the propagation vector k=(1/2, 1/2,0) with the sequence (++- +) of magnetic moments in the crystal unit cell. In DySn(1.09)Ge(0.91) and HoSn(1.1)Ge(0.9) magnetic moments equal 7.25(15) and 8.60(6)mu(B) at 1.55 K, respectively. The moments are parallel to the c-axis. For Ho-compound this ordering is stable up to T(N)=10.7 K. For ErSn(1.08)Ge(0.92), the Er magnetic moment equals 7.76(7)mu(B) at T=1.5 K and it is parallel to the b-axis. At T(t)=3.5 K it tunes into the modulated structure described by the k=(0.496(1), 0.446(4), 0). With the increase of temperature there is a slow decrease of k(x) component and a quick decrease of k(y) component. The Er magnetic moment is parallel to the b-axis up to 3.9 K while at 4 K and above it lies in the b-c plane and form an angle 48(3)degrees with the c-axis. In compounds with R=Tb, Ho and Er the magnetostriction effect at the Neel temperature is observed. (C) 2011 Elsevier Inc. All rights reserved.

Title: Microstructural features and domain formation in (Ba,Sr)(2)TiSi(2)O(8) fresnoites

Author(s): Wong, CL (Wong, Chui Ling); Ferraris, C (Ferraris, Cristiano); White, TJ (White, T. J.)

Source: JOURNAL OF SOLID STATE CHEMISTRY Volume: 184 Issue: 7 Pages: 1768-1776 DOI: 10.1016/j.jssc.2011.05.009 Published: JUL 2011

Abstract: The formation and co-existence of crystallographically modulated and non-modulated regions in (Ba,Sr)(2)TiSi(2)O(8) fresnoites is reviewed, particularly the dependence on local composition. It is shown that perturbations of the average fresnoite structure, determined from appreciable single crystals, are in some cases better described as nanometric domain intergrowths where departures from ideal stoichiometry are characteristics of incommensuration, while modulation is absent from volumes that are less perturbed chemically. Evidence for this differentiation is obtained from selected area electron diffraction (SAED) patterns and high-resolution transmission electron microscopy (HRTEM) images. The domains are readily distinguished by their unique contrast in bright field electron micrographs. Fourier reconstructions of HRTEM images collected from areas with darker contrast show that modulation can change within relatively small volumes. Nearby areas with lighter contrast were found by SAED to be free of structural disorder and incommensurate reflections. (C) 2011 Elsevier Inc. All rights reserved.

Title: Phase diagram studies of Ti-Zr-Ni alloys containing less than 40 at.% Ni and estimated critical cooling rate for icosahedral quasicrystal formation from the liquid

Author(s): Lee, GW (Lee, G. W.); Gangopadhyay, AK (Gangopadhyay, A. K.); Kelton, KF (Kelton, K. F.)

Source: ACTA MATERIALIA Volume: 59 Issue: 12 Pages: 4964-4973 DOI: 10.1016/j.actamat.2011.04.045 Published: JUL 2011

Abstract: A detailed phase diagram study of Ti-Zr-Ni alloys has been conducted using conventional X-ray scattering, microstructural and thermal annealing, and levitation techniques, to improve on the existing phase diagram. Various phases, such as simple crystalline, approximant, icosahedral quasicrystalline, and complex polytetrahedral phases, have been identified. A eutectic composition has been found near 21 at.% Ni for nearly equal Ti and Zr concentrations. From containerless processing studies, using electrostatic levitation, the phase boundary of the icosahedral quasicrystal (i-phase) is placed between 29 and 45 at.% Ti with 21 at.% Ni. A first-time estimate of the critical cooling rate for the formation of the i-phase directly from the liquid in alloys with 21 at.% Ni is less than 100 degrees C s(-1), which is much smaller than for most of the known metastable quasicrystals. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title: Mechanism of exchange striction of ferroelectricity in multiferroic orthorhombic oMnO(3) single crystals

Author(s): Lee, N (Lee, N.); Choi, YJ (Choi, Y. J.); Ramazanoglu, M (Ramazanoglu, M.); atcliff, W (Ratcliff, W., II); Kiryukhin, V (Kiryukhin, V.); Cheong, SW (Cheong, S. -W.)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 2 Article Number: 020101 DOI: .1103/PhysRevB.84.020101 Published: JUL 1 2011

Abstract: E-type perovskite magnet HoMnO(3) is considered to be a prototype Mn-Mn change-striction driven multiferroic. We have grown orthorhombic HoMnO(3) single cryd studied the directional dependence of their electric polarization P. The direction of P is not ong the crystallographic a axis, as predicted, but along the c axis. The magnetic state is commensurate. The direction P along the c axis is primarily induced by Ho-Mn exchange riction, and Mn-Mn striction in the incommensurate spin state leads to an antiferroelecder along the a axis. We predict the rotation of P with temperature in commensurate E-tyMnO(3) (R denotes magnetic rare earth).

Title: Incommensurate Spin-Density Wave Order in Electron-Doped BaFe(2)As(2) uperconductors

Author(s): Pratt, DK (Pratt, D. K.); Kim, MG (Kim, M. G.); Kreyssig, A (Kreyssig, A.); Lee, B (Lee, Y. B.); Tucker, GS (Tucker, G. S.); Thaler, A (Thaler, A.); Tian, W (Tian, W.); arestky, JL (Zarestky, J. L.); Bud'ko, SL (Bud'ko, S. L.); Canfield, PC (Canfield, P. C.); armon, BN (Harmon, B. N.); Goldman, AI (Goldman, A. I.); McQueeney, RJ (McQueeney, R.)

Source: PHYSICAL REVIEW LETTERS Volume: 106 Issue: 25 Article Number: 57001 DOI: 10.1103/PhysRevLett.106.257001 Published: JUN 20 2011

Abstract: Neutron diffraction studies of Ba(Fe(1-x)Co(x-2))As(2) reveal that commensurate ntiferromagnetic order gives way to incommensurate magnetic order for Co compositions etween 0.056 < x < 0.06. The incommensurability has the form of a small transverse splitting , +/-epsilon, 0) from the commensurate antiferromagnetic propagation vector Q(AFM) = (1, 0, ) (in orthorhombic notation) where epsilon approximate to 0.02 - 0.03 and is composition ependent. The results are consistent with the formation of a spin-density wave driven by Ferface nesting of electron and hole pockets and confirm the itinerant nature of magnetise iron arsenide superconductors.

SN: 0031-9007

Title: Stability of the Sr(2)B(3)O(6.5-delta) Phases (B = Fe, Co, Ga): Existence Range, tructural and Physical Properties

Author(s): Desmoulins, H (Desmoulins, H.); Malo, S (Malo, S.); Perez, O (Perez, O.); elloquin, D (Pelloquin, D.); Maignan, A (Maignan, A.); Hervieu, M (Hervieu, M.)

Source: CHEMISTRY OF MATERIALS Volume: 23 Issue: 11 Pages: 2786-2794 DOI: 0.1021/cm103635g Published: JUN 14 2011

Abstract: A large solid solution Sr(2)(Fe(3-x)Co(x-y)Ga(y))O(6.5-delta)), isostructural with thodulated Fe-2201 and Co-2201-type structures, has been characterized using X-ray powdiffraction (XRPD), transmission electron microscopy (TEM), and energy dispersive pectroscopy (EDS) analyses. The disorder phenomena have been studied using High Rransmission Electron Microscopy (HREM). The evolution of the cell parameters, wavelength f the modulated structures, and transport properties are analyzed versus the three B (Fe, Co, o) cation contents, showing a violation of the Vegard law for a ratio Fe/(Fe + Co + Go) close o x approximate to 0.6. By decreasing the Fe content from that x value, an abrupt variation of esistivity of about 2 orders of magnitude is observed. This spectacular behavior is associated ith the creation of percolative - (Co-O-Co)- pathways. A double effect of the (Co/Ga) ubstitution for Fe is observed on the magnetic properties. First, the B-O-B magnetic nteractions (B = Fe, Co, Ga) are diluted because Ga(3+) is a d(10)s(0) cation and, second, the o(3+)-O-Co(3+) magnetic exchange in that structure is smaller than the Fe(3+)-O-Fe(3) ones. his explained why both the magnitude of the ferromagneto-like component and the T(N) vare reduced as compared to the Fe-2201's.

Title: Effect of Quasicrystal Phase Particle Dispersion on Mechanical Properties in Mg-Zn-Al lloys

Author(s): Somekawa, H (Somekawa, Hidetoshi); Osawa, Y (Osawa, Yoshiaki); Singh, A Singh, Alok); Mukai, T (Mukai, Toshiji)

Source: MATERIALS TRANSACTIONS Volume: 52 Issue: 6 Pages: 1111-1115 DOI: 0.2320/matertrans.MC201014 Published: JUN 11 2011

Abstract: Four kinds of Mg-x mass%Zn-y mass%Al (x = 6, 8, 10, 12 and y = 3, 4, 5, 6) alloys, ach with a grain size of 2 similar to 3 gm and containing quasicrystal phase particles, were uccessfully produced by casting and extrusion. These rare-earth free wrought processed agnesium alloys showed a reduction in mechanical asymmetry and a weak basal texture. lthough the yield strength improved, the elongation decreased with increasing volume fraction f quasicrystal phase particle. The decrease in ductility was related to the existence of coarse uasicrystal phase particles. The strength was affected by the interface strength mechanism; owever, the coherency strain in the quasicrystal phase was smaller than that in the cohase, due to the strong matching between the matrix and the quasicrystal phase. [doi: 0.2320/matertrans.MC201014]

Title: Medium-range icosahedral order in quasicrystal-forming Zr(2)Pd binary metallic glass

Author(s): Huang, L (Huang, Li); Fang, XW (Fang, X. W.); Wang, CZ (Wang, C. Z.); Kramer, MJ (Kramer, M. J.); Ding, ZJ (Ding, Z. J.); Ho, KM (Ho, K. M.)

Source: APPLIED PHYSICS LETTERS Volume: 98 Issue: 23 Article Number: 231906 DOI: 10.1063/1.3597302 Published: JUN 6 2011

Abstract: Medium-range order in Zr(2)Pd metallic glass was studied using a combination of x-ray diffraction experiment and atomistic simulations. We show that, in contrast to earlier experimental interpretations, the icosahedral-like polyhedron is centered around Pd, rather than Zr. Furthermore, we find that the ordered icosahedral packing around Pd extends to the third shell in the way similar to that in the Bergman-type clusters. The existence of Bergman-type clusters sheds interesting light into the formation of nanoquasicrystal phase during cprocess of Zr(2)Pd metallic glass. (C) 2011 American Institute of Physics. [doi:10.1063/1.3597302]

Title: Atomic structure of nanoscale quasicrystal-forming Zr-noble metal binary metallic glasses

Author(s): Saida, J (Saida, J.); Itoh, K (Itoh, K.); Sanada, T (Sanada, T.); Sato, S (Sato, S.); Imafuku, M (Imafuku, M.); Ohnuma, M (Ohnuma, M.); Inoue, A (Inoue, A.)

Source: JOURNAL OF ALLOYS AND COMPOUNDS Volume: 509 Pages: S27-S33 DOI: 10.1016/j.jallcom.2010.12.076 Supplement: 1 Published: JUN 2011

Abstract: We report the results of the local structural evaluation and mechanism of QC formation in the Zr(70)Pd(30) and Zr(80)Pt(20) glassy alloys. Voronoi analysis indicates the difference of local environment between two alloys. The perfect icosahedron frequently exists around Zr atom and major polyhedra have prism-like structure around Pd in Zr(70)Pd(30). In contrast, icosahedral-like distorted polyhedra formation is favorable around Pt as well as Zr in Zr(80)Pt(20). It is therefore, concluded that the quasicrystallization originates from the medium-range order based on the Zr-centered perfect icosahedron and the Pd-centered prism-like ones remain during the QC phase formation in Zr(70)Pd(30). Icosahedral-like local structure around Zr and Pt might contribute together to the nucleation of QC phase in Zr(80)Pt(20). This feature with a different mechanism of QC formation in the two alloys may correlate to the difference of solute concentration and the structure of stable crystalline phase after the decomposition of QC phase. (C) 2010 Elsevier B.V. All rights reserved.

Update: 15-Jul-2011

Title:
THE Al-Cr-Fe PHASE DIAGRAM. I. PHASE EQUILIBRIA AT SUBSOLIDUS TEMPERATURES OVER COMPOSITION RANGE 58-100 AT.% Al
Authors:
Khoruzha, VG; Kornienko, KE; Pavlyuchkov, DV; Grushko, B; Velikanova, TY Author Full Names: Khoruzha, V. G.; Kornienko, K. E.; Pavlyuchkov, D. V.; Grushko, B.; Velikanova, T. Ya
Source:
POWDER METALLURGY AND METAL CERAMICS 50 (1-2): 83-97 MAY 2011
Abstract:
Based on transmission and scanning electron microscopy, x-ray diffraction, electron microprobe and differential thermal analyses, the solidus surface of the ternary Al-Cr-Fe system is constructed for the first time on the concentration triangle over composition range 58-100 at.% Al. Four ternary compounds, D-3, O-1, H, and epsilon, with decagonal, orthorhombic base-centered, hexagonal, and orthorhombic primitive lattices participate in phase equilibria on the solidus surface. Solid solutions based on aluminum and binary compounds as well as ternary phases form 12 single-phase surfaces, 25 ruled surfaces of two-phase equilibria bounding two-phase regions, and 14 three-phase isothermal planes corresponding to invariant four-phase equilibria on the solidus surface.
Title:
Magnetic structure of azurite above the magnetization plateau at 1/3 of saturation
Authors:
Aimo, F; Kramer, S; Klanjsek, M; Horvatic, M; Berthier, C Author Full Names: Aimo, F.; Kraemer, S.; Klanjsek, M.; Horvatic, M.; Berthier, C.
Source:
PHYSICAL REVIEW B 84 (1): Art. No. 012401 JUL 1 2011
Abstract:
The transition from the 1/3 magnetization plateau toward saturation magnetization in azurite has been studied by low-temperature, high-magnetic-field, high-frequency proton nuclear magnetic resonance (NMR). The observed symmetrical splitting of the NMR spectra is incompatible with the longitudinal incommensurate order appearing when the longitudinal correlation function becomes dominant over the transverse one, which is the expected framework for the existence of the 2/3 magnetization plateau. The spectra are instead interpreted in terms of a more standard transverse antiferromagnetic (canted) order.
Title:
Mechanism of exchange striction of ferroelectricity in multiferroic orthorhombic HoMnO3 single crystals
Authors:
Lee, N; Choi, YJ; Ramazanoglu, M; Ratcliff, W; Kiryukhin, V; Cheong, SW Author Full Names: Lee, N.; Choi, Y. J.; Ramazanoglu, M.; Ratcliff, W., II; Kiryukhin, V.; Cheong, S. -W.
Source:
PHYSICAL REVIEW B 84 (2): Art. No. 020101 JUL 1 2011
Abstract:
E-type perovskite magnet HoMnO3 is considered to be a prototype Mn-Mn exchange-striction driven multiferroic. We have grown orthorhombic HoMnO3 single crystals and studied the directional dependence of their electric polarization P. The direction of P is not along the crystallographic a axis, as predicted, but along the c axis. The magnetic state is incommensurate. The direction P along the c axis is primarily induced by Ho-Mn exchange striction, and Mn-Mn striction in the incommensurate spin state leads to an antiferroelectric order along the a axis. We predict the rotation of P with temperature in commensurate E-type RMnO3 (R denotes magnetic rare earth).
Title:
First-order nature of the ferromagnetism in CeIn2 investigated using muon spin rotation and by systematic substitution of La for Ce
Authors:
Rojas, DP; Espeso, JI; Fernandez, JR; Sal, JCG; Rusu, C; Andreica, D; Dudric, R; Amato, A Author Full Names: Rojas, D. P.; Espeso, J. I.; Rodriguez Fernandez, J.; Gomez Sal, J. C.; Rusu, C.; Andreica, D.; Dudric, R.; Amato, A.
Source:
PHYSICAL REVIEW B 84 (2): Art. No. 024403 JUL 5 2011
Abstract:
The nature of the first-order ferromagnetic transition in binary CeIn2 alloy is investigated by muon spin rotation (mu SR) measurements and chemical substitution of Ce by La in the La1-xCexIn2 (0.9 <= x <= 1.0) series of alloys. Below 22 K, the analysis of mu SR spectra shows two spin precession frequencies associated with the local field at the muon site created by the surrounding ferromagnetic ordered magnetic moments. These frequencies abruptly disappear above T-C, indicating the first-order character of this transition, as previously reported. For temperatures between 22 and 24 K, the shape of the mu SR spectra indicates the existence of an additional magnetic phase with features of an incommensurate magnetic structure. The presence of this magnetic phase is supported by dc(ac)- magnetic susceptibility and specific-heat results obtained on chemical diluted samples, which also show a magnetic contribution above the ferromagnetic transition. The combined analysis of these results clarifies the first-order character of the ferromagnetic transition in CeIn2, based on the existence of an intermediate magnetic phase between the paramagnetic and ferromagnetic states.
Title:
Commensurate-incommensurate phase transition in bilayer graphene
Authors:
Popov, AM; Lebedeva, IV; Knizhnik, AA; Lozovik, YE; Potapkin, BV Author Full Names: Popov, Andrey M.; Lebedeva, Irina V.; Knizhnik, Andrey A.; Lozovik, Yurii E.; Potapkin, Boris V.
Source:
PHYSICAL REVIEW B 84 (4): Art. No. 045404 JUL 5 2011
Abstract:
A commensurate-incommensurate phase transition in bilayer graphene is investigated in the framework of the Frenkel-Kontorova model extended to the case of two interacting chains of particles. Analytic expressions are derived to estimate the critical unit elongation of one of the graphene layers at which the transition to the incommensurate phase takes place, the length and formation energy of incommensurability defects (IDs), and the threshold force required to start relative motion of the layers on the basis of dispersion-corrected density functional theory (DFT-D) calculations of the interlayer interaction energy as a function of the relative position of the layers. These estimates are confirmed by atomistic calculations using the DFT-D based classical potential. The possibility to measure the barrier for relative motion of graphene layers by the study of formation of IDs in bilayer graphene is discussed.
Title:
Enhanced piezoelectric and magnetic properties of Bi1-xCaxFe1-x/2Nbx/2O3 solid solutions
Authors:
Troyanchuk, IO; Tereshko, NV; Karpinsky, DV; Kholkin, AL; Kopcewicz, M; Barner, K Author Full Names: Troyanchuk, I. O.; Tereshko, N. V.; Karpinsky, D. V.; Kholkin, A. L.; Kopcewicz, M.; Baerner, K.
Source:
JOURNAL OF APPLIED PHYSICS 109 (11): Art. No. 114102 JUN 1 2011
Abstract:
An investigation of the crystal structure, the magnetic and the piezoelectric properties of polycrystalline Bi1-xCaxFe1-x/2Nbx/2O3 (I) and Bi1-xPbxFe1-x/2Nbx/2O3 (II) systems was performed by x-ray diffraction, Mossbauer spectroscopy, vibrating sample magnetometry, and piezoresponse force microscopy. It is shown that an increasing niobium content induces a polar-to-nonpolar morphotropic boundary near x = 0.19 (I) and x = 0.3 (II). Within the polar region of the system (I), (0.15 <= x <= 0.18), the solid solutions are homogeneous weak ferromagnets whereas compounds of the system (II) do not exhibit an appreciable spontaneous magnetization. It is assumed that chemical substitutions leading to a decrease of the initial volume of the unit cell favor the stabilization of the weak ferromagnetic state within the rhombohedral ferroelectric phase. The piezoresponse is significantly enhanced near the morphotropic boundary. The piezoelectric properties of the parent antiferromagnet BiFeO3, harboring a cycloidal spatially modulated spin structure, are compared with those of the polar weak ferromagnet Bi0.82Ca0.18Fe0.91Nb0.09O3. (C) 2011 American Institute of Physics. [doi:10.1063/1.3594251]

Update: 8-Jul-2011

Title:
Phase Transition and Mechanical Properties of Al-Based Composites Reinforced by Al72Ni12Co16 Decagonal Quasicrystalline Particles
Authors:
Zhu, M; Yang, GC; Cheng, SL; Yao, LJ; Zhou, YH Author Full Names: Zhu Man; Yang Gencang; Cheng Suling; Yao Lijuan; Zhou Yaohe
Source:
RARE METAL MATERIALS AND ENGINEERING 39 (9): 1604-1608 SEP 2010
Abstract:
Aluminum-based composites, using Al72Ni12Co16 decagonal quasicrystalline as reinforcing particles and pure Al and Al-5.5%Zn alloys (mass fraction) as base alloy, were fabricated. The microstructure and the particle distribution of the composite were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrum (EDS). Results show that the phase transition occurs because the decagonal quaicrystalline particles are unstable in the melt. Regular polygon-like theta-phase distributes in the Al matrix, with particle sizes mainly ranging from 3.45-40 mu m. At the same time, fine strip-like gamma-phase with the size of 1.15-8.57 mu m are formed along the grain boundaries. Mechanical property testing results reveal that, due to the existence of the final crystallized phases, yield strength, ultimate tensile strength and Young's modulus of the composites are improved, but the elongation is decreased rapidly.
Title:
Lattice modulation induced by magnetic order in the magnetoelectric helimagnet Ba0.5Sr1.5Zn2Fe12O22
Authors:
Asaka, T; Yu, XZ; Hiraoka, Y; Kimoto, K; Hirayama, T; Kimura, T; Matsui, Y Author Full Names: Asaka, T.; Yu, X. Z.; Hiraoka, Y.; Kimoto, K.; Hirayama, T.; Kimura, T.; Matsui, Y.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 130401 APR 26 2011
Abstract:
By means of an electron diffraction technique, crystal-lattice modulations were investigated for a hexaferrite, Ba0.5Sr1.5Zn2Fe12O22, showing a helimagnetic order below T-N = 320 K. We observed a lattice modulation with a wave vector Q = (0,0,3 delta) below T-N. The value of delta varies between similar to 0.23 and 0.5 as a function of temperature and corresponds well to that of the magnetic modulation vector. By applying magnetic fields, Ba0.5Sr1.5Zn2Fe12O22 was found to exhibit successive changes in the lattice modulation, accompanied by the modifications of the helical magnetic order. We concluded that the observed lattice modulation is induced by the helical magnetic order via exchange magnetostriction.
Title:
Effects of pressure and temperature on the thermal conductivity of Sn2P2S6
Authors:
Andersson, O; Chobal, O; Rizak, I; Rizak, V; Sabadosh, V Author Full Names: Andersson, O.; Chobal, O.; Rizak, I.; Rizak, V.; Sabadosh, V.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134121 APR 26 2011
Abstract:
The thermal conductivity kappa of the ferroelectric, paraelectric, and incommensurate phases of polycrystalline Sn2P2S6 has been measured in the 0.1-0.7 GPa range. The thermal conductivity kappa of the ferroelectric phase decreases with increasing pressure p. This unusual behavior, which is found in only a few other phases, is attributed to a negative Gruneisen parameter. The temperature T dependence of kappa for the ferroelectric phase (kappa similar to T-1) is well described by the Debye model for kappa, with three-phonon Umklapp scattering serving as the dominant scattering mechanism near and above the Debye temperature (similar to 100 K) up to a few tenths of degrees below the ferro- to paraelectric phase transition, where kappa(T) gradually changes and becomes temperature independent upon further heating. The thermal conductivity of the paraelectric and incommensurate phases was temperature independent and indistinguishable. Possible causes for the unu! sually weak T dependence at high temperatures and implications of the p dependence of kappa are discussed.
Title:
Noncollinear spin-density-wave antiferromagnetism in FeAs
Authors:
Rodriguez, EE; Stock, C; Krycka, KL; Majkrzak, CF; Zajdel, P; Kirshenbaum, K; Butch, NP; Saha, SR; Paglione, J; Green, MA Author Full Names: Rodriguez, E. E.; Stock, C.; Krycka, K. L.; Majkrzak, C. F.; Zajdel, P.; Kirshenbaum, K.; Butch, N. P.; Saha, S. R.; Paglione, J.; Green, M. A.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134438 APR 28 2011
Abstract:
The nature of the magnetism in the simplest iron arsenide is of fundamental importance in understanding the interplay between localized and itinerant magnetism and superconductivity. We present the magnetic structure of the itinerant monoarsenide FeAs with the B31 structure. Powder neutron diffraction confirms incommensurate modulated magnetism with wave vector q = (0.395 +/- 0.001)c* at 4 K, but can not distinguish between a simple spiral and a collinear spin-density-wave structure. Polarized single-crystal diffraction confirms that the structure is best described as a noncollinear spin-density wave arising from a combination of itinerant and localized behavior with spin amplitude along the b-axis direction being (15 +/- 5)% larger than in the a direction. Furthermore, the propagation vector is temperature dependent, and the magnetization near the critical point indicates a two-dimensional Heisenberg system. The magnetic structures of closely related systems are discussed and compared to that of FeAs.
Title:
Stabilization of commensurate antiferromagnetism in CePt2In7 by pressure up to 2.4 GPa: In-115 NMR and NQR under zero field
Authors:
Sakai, H; Tokunaga, Y; Kambe, S; Lee, HO; Sidorov, VA; Tobash, PH; Ronning, F; Bauer, ED; Thompson, JD Author Full Names: Sakai, H.; Tokunaga, Y.; Kambe, S.; Lee, H. -O.; Sidorov, V. A.; Tobash, P. H.; Ronning, F.; Bauer, E. D.; Thompson, J. D.
Source:
PHYSICAL REVIEW B 83 (14): Art. No. 140408 APR 19 2011
Abstract:
Zero-field In-115-nuclear magnetic resonance (NMR) has been used to study single crystals of CePt2In7, a heavy-fermion antiferromagnet with a Neel temperature (T-N) of 5.2 K at ambient pressure. Narrow linewidths of In-115-nuclear quadrupolar resonance spectra are observed from each of three crystallographically inequivalent In(1), In(2), and In(3) sites. The NMR spectra under zero field near the 3 nu(Q) line of the orthorhombic In(3) sites are tracked by temperatures down to 1.6 K and by hydrostatic pressures up to 2.4 GPa. These data reveal the coexistence of commensurate and incommensurate antiferromagneic orders at ambient pressure and that the commensurate ordering is stabilized by increasing pressures where bulk superconductivity emerges.
Title:
Field-induced incommensurate-to-commensurate phase transition in the magnetoelectric hexaferrite Ba0.5Sr1.5Zn2(Fe1-xAlx)(12)O-22
Authors:
Lee, HB; Song, YS; Chung, JH; Chun, SH; Chai, YS; Kim, KH; Reehuis, M; Prokes, K; Mat'as, S Author Full Names: Lee, Hak Bong; Song, Young-Sang; Chung, Jae-Ho; Chun, Sae Hwan; Chai, Yi Sheng; Kim, Kee Hoon; Reehuis, M.; Prokes, K.; Mat'as, S.
Source:
PHYSICAL REVIEW B 83 (14): Art. No. 144425 APR 26 2011
Abstract:
Using neutron diffraction, we investigated the spin structures of magnetoelectric hexaferrite, Ba0.5Sr1.5Zn2(Fe1-xAlx)(12)O-22 (x = 0.08) under a magnetic field (H perpendicular to c). When the crystal was cooled in a zero field, longitudinal spin cones were observed at low temperatures. These incommensurate phases, however, were replaced by the commensurate phase [ k(1) = (0,0,3/2)] when the ferroelectricity was induced by an external field perpendicular to the c axis. Magnetic structure refinement confirms that this commensurate order is compatible with the spin-current polarization. We argue that planar magnetic anisotropy plays an important role in determining the magnetic structure that is responsible for its magnetoelectricity.
Title:
Electronically phase-separated charge-density waves in Lu2Ir3Si5
Authors:
Lee, MH; Chen, CH; Chu, MW; Lue, CS; Kuo, YK Author Full Names: Lee, M. H.; Chen, C. H.; Chu, M. -W.; Lue, C. S.; Kuo, Y. K.
Source:
PHYSICAL REVIEW B 83 (15): Art. No. 155121 APR 26 2011
Abstract:
We report the investigation of charge density waves (CDW's) in Lu2Ir3Si5 by electron diffraction and dark-field imaging in transmission electron microscopy using superlattice diffraction spots. The CDW state is confirmed by the presence of superlattice reflections. Most interestingly, the CDW state at low temperatures is found to be electronically phase separated, with the coexistence of CDW domains and low-temperature normal phase domains. With a change in temperature, unlike other typical incommensurate CDW systems in which commensurability varies with temperature, we find that commensurability remains unchanged in the present case and that the predominant change is in the redistribution of the area ratio of the two coexisting phases, which is clearly revealed in the dark-field images obtained from the CDW superlattice reflections. The electronic phase separation in the CDW state of Lu2Ir3Si5 is unprecedented in CDW systems, and its temperature dependence is also anomalous.
Title:
Emergent antiferromagnetism in a d-wave superconductor with strong paramagnetic pair-breaking
Authors:
Hatakeyama, Y; Ikeda, R Author Full Names: Hatakeyama, Yuhki; Ikeda, Ryusuke
Source:
PHYSICAL REVIEW B 83 (22): Art. No. 224518 JUN 28 2011
Abstract:
It is theoretically shown that, in the fourfold symmetric d-wave superconducting phase, a paramagnetic pair-breaking (PPB) enhanced sufficiently by increasing the applied magnetic field induces not only the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state but also an incommensurate antiferromagnetic (AFM) order with the Q vector parallel to a gap node. This AFM ordering tends to occur only below H-c2 at low temperatures, i.e., in the presence of a nonvanishing superconducting energy gap Delta rather than in the normal phase. Through a detailed study on the resulting AFM order and its interplay with the FFLO spatial modulation of Delta, it is argued that the strange high-field, low-temperature (HFLT) superconducting phase of CeCoIn5 is a coexisting phase of the FFLO and incommensurate AFM orders, and that this PPB mechanism of an AFM ordering is also the origin of the AFM quantum critical fluctuation which has occurred close to H-c2(0) in several unconventional superconductors including CeCoIn5.
Title:
Magnetic fluctuations and self-energy effects in two-dimensional itinerant systems with a van Hove singularity in the electronic spectrum
Authors:
Igoshev, PA; Irkhin, VY; Katanin, AA Author Full Names: Igoshev, P. A.; Irkhin, V. Yu.; Katanin, A. A.
Source:
PHYSICAL REVIEW B 83 (24): Art. No. 245118 JUN 22 2011
Abstract:
We investigate a competition of tendencies toward ferromagnetic and incommensurate order in two-dimensional fermionic systems within functional renormalization-group technique, accounting for the self-energy corrections and using temperature as a scale parameter. We assume that the Fermi surface (FS) is substantially curved and lies in the vicinity of van Hove singularity points. It is shown that the character of magnetic fluctuations is strongly asymmetric with respect to the Fermi level position relative to van Hove singularity (VHS). For the Fermi level above VHS, we find at low temperatures dominant incommensurate magnetic fluctuations, while below the VHS level, we find indications for the ferromagnetic ground state. In agreement with the Mermin-Wagner theorem, at finite temperatures and in small magnetic fields, we obtain small magnetization, which appears to be a power-law function of magnetic field. It is found that the FS curvature is slightly increased by correlation effects, and the renormalized bandwidth decreases at sufficiently low temperatures.
Title:
Modulated martensite: why it forms and why it deforms easily
Authors:
Kaufmann, S; Niemann, R; Thersleff, T; Rossler, UK; Heczko, O; Buschbeck, J; Holzapfel, B; Schultz, L; Fahler, S Author Full Names: Kaufmann, S.; Niemann, R.; Thersleff, T.; Roessler, U. K.; Heczko, O.; Buschbeck, J.; Holzapfel, B.; Schultz, L.; Faehler, S.
Source:
NEW JOURNAL OF PHYSICS 13: Art. No. 053029 MAY 16 2011
Abstract:
Diffusionless phase transitions are at the core of the multifunctionality of (magnetic) shape memory alloys, ferroelectrics and multiferroics. Giant strain effects under external fields are obtained in low symmetric modulated martensitic phases. We outline the origin of modulated phases, their connection with tetragonal martensite and consequences owing to their functional properties by analysing the martensitic microstructure of epitaxial Ni-Mn-Ga films from the atomic to the macroscale. Geometrical constraints at an austenite-martensite phase boundary act down to the atomic scale. Hence, a martensitic microstructure of nanotwinned tetragonal martensite can form. Coarsening of twin variants can reduce twin boundary energy, a process we could observe from the atomic to the millimetre scale. Coarsening is a fractal process, proceeding in discrete steps by doubling twin periodicity. The collective defect energy results in a substantial hysteresis, which allows the retention of modulated martensite as a metastable phase at room temperature. In this metastable state, elastic energy is released by the formation of a 'twins within twins' microstructure that can be observed from the nanometre to the millimetre scale. This hierarchical twinning results in mesoscopic twin boundaries. Our analysis indicates that mesoscopic boundaries are broad and diffuse, in contrast to the common atomically sharp twin boundaries of tetragonal martensite. We suggest that the observed extraordinarily high mobility of such mesoscopic twin boundaries originates from their diffuse nature that renders pinning by atomistic point defects ineffective.
Title:
Textures and mechanical properties in rare-earth free quasicrystal reinforced Mg-Zn-Zr alloys prepared by extrusion
Authors:
Ohhashi, S; Kato, A; Demura, M; Tsai, AP Author Full Names: Ohhashi, S.; Kato, A.; Demura, M.; Tsai, A. P.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 528 (18): 5871-5874 JUL 15 2011
Abstract:
Microstructure and mechanical properties of quasicrystals dispersed Mg alloys prepared by warm extrusion of the mixtures of Mg and Zn-Mg-Zr quasicrystalline (Qc) powders have been studied. Strong texture oriented along a [10 (1) over bar 0] direction observed in pure Mg was reduced in Qc-dispersed samples, as verified by pole figure method and electron back scattering diffraction. The ultimate tensile strengths at 150 degrees C for Qc-dispersed extrusions were much higher than 110 MPa for pure Mg, which drastically reached 156 MPa for 15 wt.% Qc by preventing the motion of dislocations. Elongation was improved by the randomization of grain orientation: from 5.7% for pure Mg to 12.9% for 10 wt.% Qc at room temperature; from 15% for pure Mg to 37.1% for 5 wt.% Qc at 150 degrees C. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Does the modulated magnetic structure of BiFeO3 change at low temperatures?, (vol 18, pg 2069, 2006)
Authors:
Przenioslo, R; Palewicz, A; Regulski, M; Sosnowska, I; Ibberson, RM; Knight, KS Author Full Names: Przenioslo, R.; Palewicz, A.; Regulski, M.; Sosnowska, I.; Ibberson, R. M.; Knight, K. S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (27): Art. No. 279501 JUL 11 2011
Title:
Kaleidoscopic morphologies from ABC star-shaped terpolymers
Authors:
Matsushita, Y; Hayashida, K; Dotera, T; Takano, A Author Full Names: Matsushita, Yushu; Hayashida, Kenichi; Dotera, Tomonari; Takano, Atsushi
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (28): Art. No. 284111 JUL 20 2011
Abstract:
Star-shaped terpolymers of the ABC type composed of incompatible polymer components give a variety of ordered structures with mesoscopic length scales depending on their composition ratio. Their peculiar features are summarized in this report. Polymer components adopted are polyisoprene (I), polystyrene (S) and poly(2-vinylpyridine) (P), and many monodisperse samples of the IXSY P-Z type were anionically prepared. Firstly our focus is on molecules of the I1.0S1.0Px1 type, where x(1) is only a variable. The complex but systematic morphology change was displayed within the range 0.2 <= x(1) <= 10, that is, their structures change from spherical plus lamellae structure for I1.0S1.0P0.2 to periodic tilings (0.4 <= x(1) <= 1.9), then to lamellae-in-lamella (3.0 <= x(1) <= 4.9) and lamellae-in-cylinder (7.9 <= x(1) <= 10) structures with increasing x(1). Here if we pay attention to the structural variation of the P domain inclusively, it transforms from sphere to cylinder, lamel! la and then to matrix, which is the same as that for linear polymers. Among them, several periodic Archimedean tiling patterns can be naturally formed when the relative lengths of the three chains are close to one another. Moreover, it has been found that the tiling zone is spread out widely. For example, the series I1.0S1.8Px2 (with 0.8 <= x(2) <= 2.9) and the other series I1.0SyP2.0 (with 1.1 <= y <= 2.7) show mostly Archimedean tilings. Additionally, block copolymer/homopolymer blends with a composition of I1.0S2.7P2.5 reveal a quasicrystalline tiling with dodecagonal symmetry. Furthermore, a zinc-blende-type four-branched network structure was created just a little outside of the tiling region for a block copolymer/homopolymer blend of I1.0S2.3P0.8. When some more asymmetry in chain length is introduced, hyperbolic tiling on a gyroid membrane has successfully been constructed for the sample I1.0S1.8P3.2 and it transforms into a hierarchical cylinders-in-lamella structure with further increase in P content to I1.0S1.8P6.4. Thus, kaleidoscopic morphologies have been generated from ABC star-shaped terpolymers and their structural change has turned out to be very sensitive to relative compositions.
Title:
Ductile quasicrystalline alloys (vol 76, pg 967, 2000)
Authors:
Inoue, A; Chen, MW; Sakurai, T; Zhang, T; Saida, J; Matsushita, M Author Full Names: Inoue, A.; Chen, M. W.; Sakurai, T.; Zhang, T.; Saida, J.; Matsushita, M.
Source:
APPLIED PHYSICS LETTERS 98 (25): Art. No. 259902 JUN 20 2011

Update: 1-Jul-2011

Title:
Organic molecular compounds with modulated crystal structures
Authors:
Schonleber, A Author Full Names: Schoenleber, Andreas
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 226 (6): 499-517 2011
Abstract:
Even though the higher-dimensional superspace approach is an established method to describe aperiodic crystal structures, it is not yet fully considered and applied by a larger community of scientists. In this contribution the structural description of incommensurately and commensurately modulated molecular compounds is discussed and it is shown, that the higher-dimensional superspace approach is an elegant way for an exact structural description and an exact crystal-chemical analysis of such structures. While discussing several modulated molecular compounds, the idea behind the higher-dimensional superspace approach is shown. On the examples treated in the discussion it is explained, how to understand and how to interprete modulated molecular compounds. Also a short introduction is given to the higher-dimensional superspace approach itself, to the basic principles and to the applied nomenclature.
Title:
Medium-range icosahedral order in quasicrystal-forming Zr2Pd binary metallic glass
Authors:
Huang, L; Fang, XW; Wang, CZ; Kramer, MJ; Ding, ZJ; Ho, KM Author Full Names: Huang, Li; Fang, X. W.; Wang, C. Z.; Kramer, M. J.; Ding, Z. J.; Ho, K. M.
Source:
APPLIED PHYSICS LETTERS 98 (23): Art. No. 231906 JUN 6 2011
Abstract:
Medium-range order in Zr2Pd metallic glass was studied using a combination of x-ray diffraction experiment and atomistic simulations. We show that, in contrast to earlier experimental interpretations, the icosahedral-like polyhedron is centered around Pd, rather than Zr. Furthermore, we find that the ordered icosahedral packing around Pd extends to the third shell in the way similar to that in the Bergman-type clusters. The existence of Bergman-type clusters sheds interesting light into the formation of nanoquasicrystal phase during crystallization process of Zr2Pd metallic glass. (C) 2011 American Institute of Physics. [doi:10.1063/1.3597302]

Update: 24-Jun-2011

Title:
THE FIBONACCI-PENROSE SEMIGROUP FORMALISM AND MORPHOGENETIC SYNTHESIS OF QUASICRYSTAL MOSAICS
Authors:
Yudin, VV; Startzev, ES; Permyakova, IG Author Full Names: Yudin, V. V.; Startzev, E. S.; Permyakova, I. G.
Source:
THEORETICAL AND MATHEMATICAL PHYSICS 167 (1): 517-537 APR 2011
Abstract:
We construct the group bundle for the inverse Fibonacci semigroups in the axiomatic approach framework. The proper Fibonacci semigroup is the corresponding group bundle for the Penrose semigroups, which can be interpreted as the generating grammar of the morphogenetic synthesis of the pentasymmetric Penrose parquet in the numbers of tiling by golden rhombuses. This morphogenetic synthesis of the Penrose parquet satisfies the scaling principle. Parquet plates are not absolutely rigid, and the relations between their metric characteristics are governed by the golden section and other magic numbers. The characteristic form factors of three-level dual alphabets are the corresponding invariants. We realize the morphogenetic synthesis in the examples of square-octagonal and bihexagonal lattices. We consider cumulative properties of magic series and the evolutionary aspects of semigroup orbits in the entropy representation.
Title:
Improvement of microstructure and mechanical properties of Mg-8Gd-3Y by adding Mg3Zn6Y icosahedral phase alloy
Authors:
Kang, HJ; Wu, SP; Li, XZ; Guo, JJ; Wang, Y Author Full Names: Kang, Huijun; Wu, Shiping; Li, Xinzhong; Guo, Jingjie; Wang, Ye
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 528 (16-17): 5585-5591 JUN 25 2011
Abstract:
Mg-Zn-Y quasicrystal alloy (QA) particles reinforced composite was prepared using an adscititious method, and characterized using scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and tensile testing technique at room temperature. Experimental results indicate that alpha-Mg columnar dendrite gradually becomes fine equiaxed dendrite and ellipsoidal cellular dendrite as more Mg-Zn-Y QA particles are added into the matrix alloy. Thread-like Mg-24(Gd,Y)(5) phases and rod-like Mg-5(Gd,Y) phases are replaced by lamellar Mg-24(Zn,Gd,Y)(5) compounds and granule Mg3Zn6(Y,Gd) quasicrystal l-phases. The ultimate tensile strength and yield strength of the composite increase by about 45 MPa and 20 MPa respectively when the amount of QA particles added increases from 3% to 15%. It can therefore be concluded that the microstructure and mechanical properties of Mg-8Gd-3Y alloy can be improved by adding QA particles. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Inelastic neutron and x-ray scattering from incommensurate magnetic systems
Authors:
Boni, P; Roessli, B; Hradil, K Author Full Names: Boeni, Peter; Roessli, Bertrand; Hradil, Klaudia
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (25): Art. No. 254209 JUN 29 2011
Abstract:
Neutrons and x-rays are powerful probes for studying magnetic and lattice excitations in strongly correlated materials over very wide ranges of momentum and energy transfers. In the focus of the present work are the incommensurate magnetic systems MnSi and Cr. Under application of a magnetic field, helically ordered MnSi transforms into a weak itinerant ferromagnet. Using polarized neutrons we demonstrate that the Stoner excitations are spin-flip excitations. The amplitude (longitudinal) fluctuations associated with the magnon modes are already strong far away from T-c. Interestingly, even the non-spin-flip excitations associated with the Stoner modes are observable. In Cr, we have observed Kohn anomalies in the phonon spectrum at those incommensurate positions in reciprocal space, where the spin density wave is observed. The corresponding phonon and magnon modes are not coupled. In addition, an anomalous softening of a transverse phonon branch along the N-H zone boundary line is observed that is caused by strong electron-phonon coupling. High resolution neutron scattering indicates that the low energy Fincher-Burke excitations may rather correspond to localized modes in momentum and energy and not to propagating collective modes. Finally, we demonstrate that in the near future it may become feasible to investigate excitations in very small samples, thus allowing us to measure the dynamics of strongly correlated materials under extreme conditions and in the vicinity of quantum phase transitions.
Title:
Fano line shape and anti-crossing of Raman active E-2g peaks in the charge density wave state of NbSe2
Authors:
Mialitsin, A Author Full Names: Mialitsin, Aleksej
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 72 (5): 568-571 Sp. Iss. SI MAY 2011
Abstract:
Low energy Raman scattering from the ab-plane of the 2H polytype single crystal NbSe2 has been investigated in the normal (N), incommensurate charge density wave (ICDW) and superconducting (SC) phases. The temperature dependence of the polarization resolved Raman response has been obtained for the excitation wavelength of 647 nm and fitted to phenomenological models for the E-2g and A(1g) symmetry channels. The A(1g) response can be fitted by a simple damped oscillator peak superimposed on continuous background. The E-2g response displays an anti-resonance interference pattern between the inter-layer phonon and the CDW-induced mode such that a hybridized configuration (Fano line shape [1]) is required for modelling. The polarization specific peak maxima positions and line widths as a function of temperature, deduced in this manner, are presented. Partial suppression of the electronic continuum scattering in the Raman shift range up to 110 cm(-1) in the A(1g) symmetry channel and beyond 300 cm(-1) in the E-2g symmetry channel is indicative of high energy electronic states far away from the Fermi surface participating in the ICDW formation. Published by Elsevier Ltd.
Title:
Atomic structure of nanoscale quasicrystal-forming Zr-noble metal binary metallic glasses
Authors:
Saida, J; Itoh, K; Sanada, T; Sato, S; Imafuku, M; Ohnuma, M; Inoue, A Author Full Names: Saida, J.; Itoh, K.; Sanada, T.; Sato, S.; Imafuku, M.; Ohnuma, M.; Inoue, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509: S27-S33 Suppl. 1 JUN 2011
Abstract:
We report the results of the local structural evaluation and mechanism of QC formation in the Zr70Pd30 and Zr80Pt20 glassy alloys. Voronoi analysis indicates the difference of local environment between two alloys. The perfect icosahedron frequently exists around Zr atom and major polyhedra have prism-like structure around Pd in Zr70Pd30. In contrast, icosahedral-like distorted polyhedra formation is favorable around Pt as well as Zr in Zr80Pt20. It is therefore, concluded that the quasicrystallization originates from the medium-range order based on the Zr-centered perfect icosahedron and the Pd-centered prism-like ones remain during the QC phase formation in Zr70Pd30. Icosahedral-like local structure around Zr and Pt might contribute together to the nucleation of QC phase in Zr80Pt20. This feature with a different mechanism of QC formation in the two alloys may correlate to the difference of solute concentration and the structure of stable crystalline phase after the decomposition of QC phase. (C) 2010 Elsevier B.V. All rights reserved.
Title:
The quasicrystalline phase formation in Al-Cu-Cr alloys produced by mechanical alloying
Authors:
Sviridova, TA; Shevchukov, AP; Shelekhov, EV; Diakonov, DL; Tcherdyntsev, VV; Kaloshkin, SD Author Full Names: Sviridova, T. A.; Shevchukov, A. P.; Shelekhov, E. V.; Diakonov, D. L.; Tcherdyntsev, V. V.; Kaloshkin, S. D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509: S299-S303 Suppl. 1 JUN 2011
Abstract:
Almost single-phase decagonal quasicrystal with periodicity of 1.26 nm along 10-fold axis was produced in Al69Cu21Cr10 and Al72.5Cu16.5Cr11 alloys using combination of mechanical alloying (MA) and subsequent annealing. Phase transformations of as-milled powders depending on annealing temperature in the range of 200-800 degrees C are examined. Since the transformations can be explained based on kinetic and thermodynamic reasons it seems that applied technique (short preliminary MA followed by the annealing) permits to produce the equilibrium phases rather than metastable ones. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Microstructures and mechanical properties of conventionally solidified Al63Cu25Fe12 alloy
Authors:
Gogebakan, M; Avar, B; Tarakci, M Author Full Names: Gogebakan, M.; Avar, B.; Tarakci, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509: S316-S319 Suppl. 1 JUN 2011
Abstract:
In this study, the microstructures and mechanical properties of conventionally solidified Al63Cu25Fe12 alloy after different heat-treatments were investigated. The microstructures of the as-cast and subsequently heat-treated samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA). The XRD results showed the presence of quasicrystalline icosahedral phase (i-phase) together with crystalline phases corresponding to beta-AlFe(Cu) solid solution phase (beta-phase) and tau-AlCu(Fe) solid solution phase (tau-phase). The SEM investigations clearly showed the formation of i-phase with pentagonal dodecahedra structure. However, the i-phase together with beta-phase was also observed in the heat-treated samples and the peak intensity of the beta-phase decreased with increasing heat-treatment temperature. From the DTA curves, the melting point of i-phase was determined as 890 degrees C for this alloy composition. Mechanical properties of the as-cast and subsequently heat-treated samples were measured by a Vickers indenter. Results showed that the microhardness (HV) and the elastic modulus (E) of the as-cast sample were around 598 kg fmm(-2) (5.86 GPa) and 104 GPa, respectively. In addition, the characteristic of material plasticity (delta(H)) value was calculated to be 0.54. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Stability of the Sr2B3O6.5-delta Phases (B = Fe, Co, Ga): Existence Range, Structural and Physical Properties
Authors:
Desmoulins, H; Malo, S; Perez, O; Pelloquin, D; Maignan, A; Hervieu, M Author Full Names: Desmoulins, H.; Malo, S.; Perez, O.; Pelloquin, D.; Maignan, A.; Hervieu, M.
Source:
CHEMISTRY OF MATERIALS 23 (11): 2786-2794 JUN 14 2011
Abstract:
A large solid solution Sr-2(Fe3-xCox-yGay)O6.5-delta), isostructural with the modulated Fe-2201 and Co-2201-type structures, has been characterized using X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) analyses. The disorder phenomena have been studied using High Resolution Transmission Electron Microscopy (HREM). The evolution of the cell parameters, wavelength of the modulated structures, and transport properties are analyzed versus the three B (Fe, Co, Go) cation contents, showing a violation of the Vegard law for a ratio Fe/(Fe + Co + Go) close to x approximate to 0.6. By decreasing the Fe content from that x value, an abrupt variation of resistivity of about 2 orders of magnitude is observed. This spectacular behavior is associated with the creation of percolative - (Co-O-Co)- pathways. A double effect of the (Co/Ga) substitution for Fe is observed on the magnetic properties. First, the B-O-B magnetic interactions (B = Fe, Co, Ga) are diluted because Ga3+ is a d(10)s(0) cation and, second, the Co3+-O-Co3+ magnetic exchange in that structure is smaller than the Fe3+-O-Fe-3 ones. This explained why both the magnitude of the ferromagneto-like component and the T-N values are reduced as compared to the Fe-2201's.

Update: 17-Jun-2011

Title:
Symmetry mode analysis of the phase transitions in Rb2ZnBr4
Authors:
Zuniga, FJ; Perez-Mato, JM; Orobengoa, D; Petricek, V; Breczewski, T Author Full Names: Javier Zuniga, Fco; Manuel Perez-Mato, J.; Orobengoa, Danel; Petricek, Vaclav; Breczewski, Tomasz
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 226 (5): 454-466 2011
Abstract:
Crystal structures of low temperature phases HI, IV and V of rubidium zinc bromide have been determined by single crystal X-ray diffraction at 90 K, 85 K, and 30 K, respectively. The analysis of the structures in terms of symmetry-adapted modes of the high temperature prototype phase permits the identification of the modes responsible for each phase and to assess its thermal evolution. The primary mode responsible for the incommensurate and lock-in phases remains dominant throughout the whole transition sequence, maintaining its structure and slightly increasing its amplitude as temperature decreases. The two monoclinic phases IV and V are presumably due to the instability of a second mode associated with a single active irreducible representation. However, the presence with similar weights of several symmetry-adapted distortions of different symmetry indicates a strong hybridization in phase permits the identification of the softer normal modes. A symmetry-mode description of the structures of phase IV and V fully consistent with a simple Landau model, can then only be obtained if phase III is taken as effective parent phase. Besides the insight on the microscopic origin of the different phases, the symmetry modes were used as crystallographic coordinates in the refinement of the structure of phase V. The result shows the advantages of using these non-conventional collective structural parameters instead of individual atomic coordinates. The refinable parameters can be reduced to the amplitudes of those symmetry modes with significant weight in the distortions.
Title:
Spiral ground state against ferroelectricity in the frustrated magnet BiMnFe2O6
Authors:
Abakumov, AM; Tsirlin, AA; Perez-Mato, JM; Petricek, V; Rosner, H; Yang, T; Greenblatt, M Author Full Names: Abakumov, Artem M.; Tsirlin, Alexander A.; Perez-Mato, Juan Manuel; Petricek, Vaclav; Rosner, Helge; Yang, Tao; Greenblatt, Martha
Source:
PHYSICAL REVIEW B 83 (21): Art. No. 214402 JUN 2 2011
Abstract:
The spiral magnetic structure and underlying spin lattice of BiMnFe2O6 are investigated by low-temperature neutron powder diffraction and density functional theory band structure calculations. In spite of the random distribution of the Mn3+ and Fe3+ cations, this centrosymmetric compound undergoes a transition into an incommensurate antiferromagnetically ordered state below T-N similar or equal to 220 K. The magnetic structure is characterized by the propagation vector k = [0, beta, 0] with beta similar or equal to 0.14 and the P22(1)2(1)1'(0 beta 0)0s0s magnetic superspace symmetry. It comprises antiferromagnetic helixes propagating along the b axis. The magnetic moments lie in the ac plane and rotate about pi(1 + beta) similar or equal to 204.8-deg angle between the adjacent magnetic atoms along b. The spiral magnetic structure arises from the peculiar frustrated arrangement of exchange couplings in the ab plane. The antiferromagnetic coupling along the c axis cancels the possible electric polarization and prevents ferroelectricity in BiMnFe2O6.
Title:
Vacancy and substitutional impurities in the spin-density wave state of Cr from first principles
Authors:
Soulairol, R; Fu, CC; Barreteau, C Author Full Names: Soulairol, R.; Fu, Chu-Chun; Barreteau, C.
Source:
PHYSICAL REVIEW B 83 (21): Art. No. 214103 JUN 3 2011
Abstract:
Density functional theory (DFT) calculations are carried out to study magnetic and energetic properties of vacancy, and magnetic and nonmagnetic substitutional impurities (respectively Fe and Cu) in the ground state of bcc Cr, i.e., spin-density wave (SDW). We find the lowest energy site for all the defects to be around a magnetic node, as compared with the high-spin SDW sites and (100)- layered antiferromagnetic (AF) and nonmagnetic (NM) phases. The corresponding differences for vacancy formation energy are 0.29, 0.32, and 0.23 eV, respectively. The migration of a vacancy is revealed to be highly anisotropic in the SDW state, mainly confined in the nodal and adjacent planes. The energy barrier for such a quasi-bidimensional motion is indeed 0.52 eV lower than that for migration in perpendicular directions. Regarding magnetic modifications of the SDW introduced by point defects, they are confirmed to be weak and rather local at low defect concentrations (0.27% and 0.55%). Cu behaves similarly to a vacancy-inducing magnetic moment enhancement on neighboring Cr atoms. On the other side, the presence of Fe atoms leads to multiple energy minima with different local magnetic arrangements, particularly around a node, due to competition between neighboring Fe-Cr, Cr-Cr, and Fe-Fe magnetic coupling tendencies. The present results strongly suggest that simple AF and NM phases may not allow an accurate description of defect properties in the ground state of Cr. Instead, an explicit SDW representation is required. In addition, we point out that the presence of vacancy and both Cu and Fe may promote a migration of SDW nodes, which may activate the SDW-to-AF phase transition through a node-annihilation mechanism as proposed in previous works.
Title:
Competing charge density waves and temperature-dependent nesting in 2H-TaSe2
Authors:
Leininger, P; Chernyshov, D; Bosak, A; Berger, H; Inosov, DS Author Full Names: Leininger, Ph; Chernyshov, D.; Bosak, A.; Berger, H.; Inosov, D. S.
Source:
PHYSICAL REVIEW B 83 (23): Art. No. 233101 JUN 2 2011
Abstract:
Multiple charge density wave (CDW) phases in 2H-TaSe2 are investigated by high-resolution synchrotron x-ray diffraction. In a narrow temperature range immediately above the commensurate CDW transition, we observe a multi-q superstructure with coexisting commensurate and incommensurate order parameters, clearly distinct from the fully incommensurate state at higher temperatures. This multi-q ordered phase, characterized by a temperature hysteresis, is found both during warming and cooling, in contrast to previous reports. In the normal state, the incommensurate superstructure reflection gives way to a broad diffuse peak that persists nearly up to room temperature. Its position provides a direct and accurate estimate of the Fermi surface nesting vector, which evolves nonmonotonically and starts approaching the commensurate position as the temperature is increased. This behavior agrees with our recent observations of the temperature-dependent Fermi surface in the same compound [D. S. Inosov, D. V. Evtushinsky, V. B. Zabolotnyy, A. A. Kordyuk, B. Buchner, R. Follath, H. Berger, and S. V. Borisenko, Phys. Rev. B 79, 125112 (2009).].
Title:
Elastic and antiferromagnetic anomalies in Pr0.48Ca0.52MnO3 as determined by resonant ultrasonic spectroscopy
Authors:
Salje, EKH; Carpenter, MA Author Full Names: Salje, E. K. H.; Carpenter, M. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (24): Art. No. 245401 JUN 22 2011
Abstract:
The Pnma incommensurate phase transition in the perovskite Pr0.48Ca0.52MnO3 at similar to 235 K is accompanied by shear strains of up to similar to 2.5% (from neutron diffraction) and changes in the shear modulus of up to similar to 40% (from resonant ultrasound spectroscopy, RUS), indicating strong coupling between the structural order parameter and strain. In contrast, the antiferromagnetic (AFM) ordering transition at similar to 180 K displays no detectable static strain, implying that there is either no coupling or only very weak coupling between the magnetic order parameter and strain. Conventional analysis of RUS data, based on measurements of resonance peak frequencies and peak widths, also failed to detect any anomaly in elastic or anelastic properties due to the AFM ordering. A new approach to the analysis the RUS data, based on autocorrelation and convolution of the entire spectra, however, has revealed that the AFM order does indeed affect the elastic behaviour in an unexpected manner. The new analysis shows, firstly, that dynamical fluctuations of the charge density ordering at T > T-c = 237 K lead to an increase of the RUS amplitude and of the spectral convolution function. Secondly, fluctuations and convolution effects peak at the transition point and decrease with decreasing temperatures. Below 180 K the stripe structure is essentially static. Finally, AFM ordering leads to an increase in the damping of the elastic resonances.
Title:
Helical magnetism and structural anomalies in triangular lattice alpha-SrCr2O4
Authors:
Dutton, SE; Climent-Pascual, E; Stephens, PW; Hodges, JP; Huq, A; Broholm, CL; Cava, RJ Author Full Names: Dutton, S. E.; Climent-Pascual, E.; Stephens, P. W.; Hodges, J. P.; Huq, A.; Broholm, C. L.; Cava, R. J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (24): Art. No. 246005 JUN 22 2011
Abstract:
alpha-SrCr2O4 has a triangular planar lattice of d(3) Cr3+ made from edge sharing CrO6 octahedra; the plane shows a very small orthorhombic distortion from hexagonal symmetry. With a Weiss temperature of -596 K and a three-dimensional magnetic ordering temperature of 43 K, the magnetic system is quasi-two-dimensional and frustrated. Neutron powder diffraction shows that the ordered state is an incommensurate helical magnet, with an in-plane propagation vector of k = (0, 0.3217(8), 0). Temperature dependent synchrotron powder diffraction characterization of the structure shows an increase in the inter-plane spacing on cooling below 100 K and an inflection in the cell parameters at the magnetic ordering temperature. These anomalies indicate the presence of a moderate degree of magnetostructural coupling.
Title:
Magnetic structure of the Mn5Si3-type Er5Si3 compound
Authors:
Morozkin, AV; Isnard, O; Granovsky, SA Author Full Names: Morozkin, A. V.; Isnard, O.; Granovsky, S. A.
Source:
INTERMETALLICS 19 (7): 871-875 JUL 2011
Abstract:
Neutron diffraction study has been performed on the Er5Si3 compound (hexagonal Mn5Si3-type, hP16, P6(3)/mcm) to understand its magnetic structure. The temperature dependent neutron diffraction results prove that this compound shows a complex antiferromagnetic ordering with sine modulated magnetic moments collinear to the c axis, presenting three subsequent changes in magnetization at similar to 29 K, 13 K and 10 K on cooling. The high-temperature magnetic component of Er5Si3 (C-3v, magnetic point group, P31m magnetic space group, K-1 = [0, 0, +/- 0.277(2)]) exists from 29 K to 10 K, whereas low-temperature magnetic component (symmetry C-1v, magnetic point group, Pm magnetic space group, K-2 = [0, +/- 1/4, 0]) exists from 13 K down to 1.5 K. The low-temperature and high-temperature magnetic components coexist between 13 K and 10 K. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Magnetocaloric properties of as-quenched Ni50.4Mn34.9In14.7 ferromagnetic shape memory alloy ribbons
Authors:
Llamazares, JL; Garcia, C; Hernando, B; Prida, VM; Baldomir, D; Serantes, D; Gonzalez, J Author Full Names: Sanchez Llamazares, J. L.; Garcia, C.; Hernando, B.; Prida, V. M.; Baldomir, D.; Serantes, D.; Gonzalez, J.
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 103 (4): 1125-1130 JUN 2011
Abstract:
The temperature dependences of magnetic entropy change and refrigerant capacity have been calculated for a maximum field change of Delta H = 30 kOe in as-quenched ribbons of the ferromagnetic shape memory alloy Ni50.4Mn34.9In14.7 around the structural reverse martensitic transformation and magnetic transition of austenite. The ribbons crystallize into a single-phase austenite with the L2(1)-type crystal structure and Curie point of 284 K. At 262 K austenite starts its transformation into a 10-layered structurally modulated monoclinic martensite. The first- and second-order character of the structural and magnetic transitions was confirmed by the Arrott plot method. Despite the superior absolute value of the maximum magnetic entropy change obtained in the temperature interval where the reverse martensitic transformation occurs (vertical bar Delta S-M(max)vertical bar = 7.2 J kg(-1) K-1) with respect to that obtained around the ferromagnetic transition of austenite (vertical bar Delta S-M(max)vertical bar = 2.6 J kg(-1) K-1), the large average hysteretic losses due to the effect of the magnetic field on the phase transformation as well as the narrow thermal dependence of the magnetic entropy change make the temperature interval around the ferromagnetic transition of austenite of a higher effective refrigerant capacity (RCeffmagn = 95 J kg(-1) versus RCeffstruct = 60 J kg(-1)).
Title:
Regenerating deuterium absorption of Ti36Zr40Ni20Pd4 icosahedral quasicrystal
Authors:
Huang, HG; Li, R; Liu, TW; Chen, L; Luo, DL Author Full Names: Huang, Huogen; Li, Rong; Liu, Tianwei; Chen, Liang; Luo, Deli
Source:
ACTA METALLURGICA SINICA-ENGLISH LETTERS 23 (6): 446-450 DEC 2010
Abstract:
Ti/Zr-based icosahedral quasicrystals are a kind of promising hydrogen storage materials, however their absorption regeneration after oxidation-poisoning has been scarcely studied. This work is intended to investigate the deuterium-storage regeneration of a suction-cast Ti36Zr40Ni20Pd4 quasicrystal. It was found that only through hot vacuuming the quasicrystal could be refreshed from air-flow poisoning to absorb deuterium in two cycles. During the first absorption course, a pregnancy period was observed before the real deuterium uptake while deuterium was loaded rapidly during the second one. The deuterium concentration in the alloy can reach 0.011 mol.D-2/(g.M) (corresponding to a hydrogen mass percent of 2.2%. D-2 and M denote molecular deuterium and the metallic alloy). But the loaded deuterium was very difficult to release completely even by eight-stage desorption at different temperatures. After the second desorption, the quasicrystal phase remained in a small! volume, as though the desorption temperature was beyond the crystallization temperature of the quasicrystal. This probably is attributed to the solution function of residual deuterium in the alloy.

Update: 10-Jun-2011

Title:
CHANGES OF STRUCTURE CHARACTERISTICS IN Ti41,5Zr41,5Ni17 AND Ti41,5Hf41,5Ni17 RAPIDLY QUENCHED RIBBONS UNDER RADIATION INFLUENCE
Authors:
Azhazha, VM; Lavrinenko, SD; Lonin, YF; Pylypenko, MM; Sereda, BV; Kryachko, SV; Malykhin, SV; Pugachov, AT; Reshetnyak, MV Author Full Names: Azhazha, V. M.; Lavrinenko, S. D.; Lonin, Yu. F.; Pylypenko, M. M.; Sereda, B. V.; Kryachko, S. V.; Malykhin, S. V.; Pugachov, A. T.; Reshetnyak, M. V.
Source:
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY (2): 33-38 2011
Abstract:
Influence of irradiation by X-ray fluxes with energies <= 1 MeV and doses up to 10(4) rad on phase and structural stability of the icosahedral quasicrystal phase (i-phase) and related crystals-approximant phases in Ti41,5Zr41,5Ni17 and Ti(41,5)Hf(41,5)Ni(17)ribbons prepared by rapid quenching was studied by the X-ray diffraction method.
Title:
Short-range and long-range incommensurate magnetic ordering in the frustrated antiferromagnets Ca3Co2-xFexO6: A neutron diffraction study
Authors:
Jain, A; Yusuf, SM Author Full Names: Jain, Anil; Yusuf, S. M.
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 184425 MAY 25 2011
Abstract:
We present the results of a detailed neutron powder diffraction study on the spin-chain compounds Ca3Co2-xFexO6 (x = 0.2 and 0.4), crystallizing in the rhombohedral structure (space group R (3) over barc), in the temperature range of 1.5-20 K. At low temperature, these compounds show a long-range magnetic ordering (LRO) with an incommensurate structure having an amplitude modulation of the moments along the crystallographic c axis. Our analysis also shows that a short-ranged spin-spin correlation along the c axis (incommensurate type such as that of the LRO), however, with a long-range spin-spin correlation in the ab plane, coexists with the LRO below the LRO temperature of 20 and 17 K for x = 0.2 and 0.4 samples, respectively. The observed long-range as well as the short-range magnetic ordering can be described by a model of platelet-like-shaped magnetic crystallites, disorderly stacked along the crystallographic c direction. At 1.5 K, the LRO and short-range ordering (SRO) contribute in the magnetic phase in volume ratios of 13: 7 and 3: 2 for x = 0.2 and x = 0.4, respectively. The magnetic correlation lengths at 1.5 K for the LRO (xi(c)(I)) and SRO (xi(c)(II)) along the c axis are similar to 1027 and 60 angstrom for x = 0.2, and 1021 and 47 angstrom for x = 0.4, respectively. The relative contribution of the LRO and SRO in the magnetic phase remains constant down to 1.5 K (below transition temperature).
Title:
Homogeneous coexistence of superconducting and spin-density-wave states in CaFe1-xCoxAsF as seen via nuclear magnetic resonance
Authors:
Nakano, T; Tsutsumi, S; Fujiwara, N; Matsuishi, S; Hosono, H Author Full Names: Nakano, T.; Tsutsumi, S.; Fujiwara, N.; Matsuishi, S.; Hosono, H.
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 180508 MAY 26 2011
Abstract:
We investigated the homogeneous coexistence of spin-density-wave (SDW) and superconducting (SC) states via As-75-nuclear magnetic resonance (NMR) in CaFe1-xCoxAsF and found that the electronic and magnetic properties of this compound are intermediate between those of LaFeAsO1-xFx and Ba(Fe1-xCox)(2)As-2. For 6% Co-doped samples, the paramagnetic spectral weight completely disappears in the crossover regime between the SDW and SC phases followed by anomalous behavior of relaxation rate (1/T-1), implying that the two phases are not segregated. Co-59-NMR spectra show that spin moments are not commensurate but spatially modulated. These experimental results suggest that incommensurate SDW (IC-SDW) and SC states are compatible in this compound.
Title:
Layered Perovskite-Like Pb2Fe2O5 Structure as a Parent Matrix for the Nucleation and Growth of Crystallographic Shear Planes
Authors:
Batuk, D; Hadermann, J; Abakumov, A; Vranken, T; Hardy, A; Van Bael, M; Van Tendeloo, G Author Full Names: Batuk, Dmitry; Hadermann, Joke; Abakumov, Artem; Vranken, Thomas; Hardy, An; Van Bael, Marlies; Van Tendeloo, Gustaaf
Source:
INORGANIC CHEMISTRY 50 (11): 4978-4986 JUN 6 2011
Abstract:
The Pb2Fe2O5 compound with a layered intergrowth structure has been prepared by a solid-state reaction at 700 degrees C. The incommensurate compound crystallizes in a tetragonal system with alpha = 3.9037(2) angstrom, c = 3.9996(4) angstrom, and q = 0.1186(4)c star, or when treated as a commensurate approximant, alpha = 3.9047(2) angstrom, c = 36.000(3) angstrom, space group I4/mmm. The crystal structure of Pb2Fe2O5 was resolved from transmission electron microscopy data. Atomic coordinates and occupancies of the cation positions were estimated from high-angle annular dark-field scanning transmission electron microscopy data. Direct visualization of the positions of the oxygen atoms was possible using annular bright-field scanning transmission electron microscopy. The structure can be represented as an intergrowth of perovskite blocks and partially disordered blocks with a structure similar to that of the Bi2O2 blocks in Aurivillius-type phases. The A-cation positions at the border of the perovskite block and the cation positions in the Aurivillius-type blocks are jointly occupied by Pb2+ and Fe3+ cations, resulting in a layer sequence along the c axis: -PbO-FeO2-PbO-FeO2-Phys(7/8)Fe(1/8)-O1-x-Fe-5/8/Pb-3/8-O-2-Fe5/8Pb3/8-. Upon heating, the layered Pb2Fe2O5 structure transforms into an anion-deficient perovskite modulated by periodically spaced crystallographic shear (CS) planes. Considering the layered Pb2Fe2O5 structure as a parent matrix for the nucleation and growth of CS planes allows an explanation of the specific microstructure observed for the CS structures in the Pb-Fe-O system.
Title:
Investigation of the thermal diffusion during the formation of a quasicrystalline phase in thin Al-Pd-Re films
Authors:
Seregin, AY; Makhotkin, IA; Yakunin, SN; Erko, AI; Tereshchenko, EY; Shaitura, DS; Chikina, EA; Tsetlin, MB; Mikheeva, MN; Ol'shanskii, ED Author Full Names: Seregin, A. Yu.; Makhotkin, I. A.; Yakunin, S. N.; Erko, A. I.; Tereshchenko, E. Yu.; Shaitura, D. S.; Chikina, E. A.; Tsetlin, M. B.; Mikheeva, M. N.; Ol'shanskii, E. D.
Source:
CRYSTALLOGRAPHY REPORTS 56 (3): 497-501 MAY 2011
Abstract:
The layer mixing during the formation of the Al70Pd20Re10 icosahedral quasicrystalline phase in thin (55 nm) Al-Pd-Re layered film systems subjected to vacuum annealing has been studied. It is shown that a combined layer of Pd and Al atoms (with the Al3Pd2 phase dominating) is formed in the first stage (at 350A degrees C), while the rhenium layer remains invariable. In the second annealing stage (at 450A degrees C), the beta'-AlPd phase is formed and the Re layer is diffused. In the third stage (700A degrees C), Pd and Re atoms are uniformly distributed throughout the film with the formation of a quasicrystalline phase.

Update: 3-Jun-2011

Title:
Stability of quasicrystals composed of soft isotropic particles
Authors:
Barkan, K; Diamant, H; Lifshitz, R Author Full Names: Barkan, Kobi; Diamant, Haim; Lifshitz, Ron
Source:
PHYSICAL REVIEW B 83 (17): Art. No. 172201 MAY 19 2011
Abstract:
Quasicrystals whose building blocks are of mesoscopic rather than atomic scale have recently been discovered in several soft-matter systems. Contrary to metallurgic quasicrystals whose source of stability remains a question of great debate to this day, we argue that the stability of certain soft-matter quasicrystals can be directly explained by examining a coarse-grained free energy for a system of soft isotropic particles. We show, both theoretically and numerically, that the stability can be attributed to the existence of two natural length scales in the pair potential, combined with effective three-body interactions arising from entropy. Our newly gained understanding of the stability of soft quasicrystals allows us to point at their region of stability in the phase diagram, and thereby may help control the self-assembly of quasicrystals and a variety of other desired structures in future experimental realizations.
Title:
Spin-Peierls transition in the S=1/2 compound TiPO4 featuring large intrachain coupling
Authors:
Law, JM; Hoch, C; Glaum, R; Heinmaa, I; Stern, R; Kang, J; Lee, C; Whangbo, MH; Kremer, RK Author Full Names: Law, J. M.; Hoch, C.; Glaum, R.; Heinmaa, I.; Stern, R.; Kang, J.; Lee, C.; Whangbo, M. -H.; Kremer, R. K.
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 180414 MAY 23 2011
Abstract:
We investigated the magnetic and structural properties of the quasi-one-dimensional 3d(1) quantum chain system TiPO4 (J similar to 965 K) by magnetic susceptibility, heat capacity, electron spin resonance, x-ray diffraction, and nuclear magnetic resonance (NMR) measurements, and by density functional theory (DFT) calculations. TiPO4 undergoes two magnetostructural phase transitions, one at 111 K and the other at 74 K. Below 74 K, NMR detects two different P-31 signals and the magnetic susceptibility vanishes, while DFT calculations evidence a bond alternation of the Ti-Ti distances within each chain. Thus, the 74 K phase transition is a spin-Peierls transition which evolves from an incommensurate phase existing between 111 and 74 K.
Title:
Characteristic chemical shift of quasicrystalline alloy Al53Si27Mn20 studied by EELS and SXES
Authors:
Koshiya, S; Terauchi, M; Tsai, AP Author Full Names: Koshiya, S.; Terauchi, M.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 91 (18): 2309-2316 2011
Abstract:
Chemical shifts of all constituent atoms for amorphous (Am), quasicrystalline (QC) and crystalline (Cryst) alloys of Al53Si27Mn20 were investigated for the first time by high energy-resolution electron energy-loss spectroscopy (EELS) and soft-X-ray emission spectroscopy (SXES). Among Al L-shell excitation EELS spectra of Am, QC and Cryst alloys, only QC alloy showed an apparent chemical shift to the larger binding energy side by 0.4 eV. In Al-K-alpha and Si-K-alpha emission SXES spectra of these alloys, only QC alloy showed a chemical shift to the larger binding energy side by 4 eV for Al-K-alpha and 6 eV for Si-K-alpha. These chemical shift values are comparable to those of corresponding metal oxides. This indicates a smaller amount of valence charge at Al and Si atomic sites in QC alloy. On the other hand, Mn-L SXES spectra did not show any chemical shift. Therefore, the decreased charge from Al and Si sites should be distributed between atomic sites, indicating the pres! ence of covalent bonding nature for QC ordered alloy.
Title:
The Eleventh International Conference on Quasicrystals
Authors:
Ishimasa, T; Ishii, Y Author Full Names: Ishimasa, Tsutomu; Ishii, Yasushi
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2419-2420 Sp. Iss. SI 2011
Title:
Once upon a time in Kamchatka: the search for natural quasicrystals
Authors:
Steinhardt, PJ; Bindi, L Author Full Names: Steinhardt, Paul J.; Bindi, Luca
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2421-2426 Sp. Iss. SI 2011
Abstract:
We present evidence for a naturally occurring quasicrystal consisting of micron-sized grains of Al63Cu24Fe13 with icosahedral symmetry embedded in a sample of khatyrkite (nominally, (Cu,Zn)Al2) obtained from the Khatyrka ultramafic zone of the Koryak Mountains in the northern half of the Kamchatka Peninsula.
Title:
High-energy X-ray diffraction studies of i-Sc12Zn88
Authors:
Goldman, AI; Kreyssig, A; Nandi, S; Kim, MG; Caudle, ML; Canfield, PC Author Full Names: Goldman, A. I.; Kreyssig, A.; Nandi, S.; Kim, M. G.; Caudle, M. L.; Canfield, P. C.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2427-2433 Sp. Iss. SI 2011
Abstract:
Although quasicrystals form in a wide variety of ternary and quaternary metallic alloys, examples of stable binary icosahedral quasicrystals are quite rare. Indeed, it has been a decade since the discovery of icosahedral phases in Yb-Cd and Ca-Cd. We have discovered millimeter-sized facetted grains of i-Sc12Zn88 with icosahedral (pentagonal dodecahedral and rhombic triacontahedral) morphologies in solution-grown samples. Structural characterization of the bulk icosahedral phase was accomplished through single-grain high-energy X-ray diffraction. For both growth morphologies, all diffraction peaks could be indexed by a primitive (P-type) icosahedral phase. The two types of morphology do, however, present interesting differences in their respective degrees of quasicrystalline order.
Title:
Solution growth of a decagonal quasicrystal and its related periodic crystals in the Al-Ni-Ru system
Authors:
Dasai, S; Takakura, H Author Full Names: Dasai, Shogo; Takakura, Hiroyuki
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2434-2442 Sp. Iss. SI 2011
Abstract:
Single crystals, with a typical size of several millimetres, of a decagonal phase with 1.6 nm periodicity in the Al-Ni-Ru system were grown successfully by the solution-growth method. The conditions for crystal growth were that the initial composition was Al80Ni16Ru4, the taking-out temperature 900-930 degrees C and the cooling rate 2 degrees C h-1. The lattice parameters were a = 0.2764(2) and c = 1.6523(5) nm, and the composition was in a small range around Al75.2Ni14.6Ru10.2. Single crystals of the orthorhombic Al13(Ni, Ru)4 phase and the monoclinic Al13(Ni, Ru)4 phase located at the high-Ni end also formed under slightly different conditions.
Title:
Synthesis of large single-grain 1/1 approximant crystals in the Ag-In-Eu system by the self-flux method
Authors:
Cui, C; Tsai, AP Author Full Names: Cui, Can; Tsai, An Pang
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2443-2449 Sp. Iss. SI 2011
Abstract:
In this work, we investigate single-grain 1/1 quasicrystal approximant crystals, grown via the self-flux method, in the Ag-In-Eu system, the structure of which is similar to the 1/1 approximant in the Cd-Eu system. Due to the similarities between the Cd-RE (RE = rare earth) and Ag-In-RE systems, Ag-In-RE can be regarded as a pseudo-binary phase, in which Ag and In replace Cd. Thus, based on the binary phase diagram of Cd-Eu, the growth conditions, including the nominal composition and decanting temperatures, for single-grain Ag-In-Eu 1/1 approximant crystal growth from indium-rich melt-solution were studied. A faceted, centimeter-sized single-grain 1/1 approximant crystal was obtained and characterized using powder X-ray diffraction, scanning electron microscopy and back-reflection Laue X-ray diffraction methods. The results are promising for the synthesis of single-grain approximant crystals in other Ag-In-RE systems.
Title:
Rapid synthesis and densification of single-phase Al-Cu-Fe quasicrystals by spark plasma sintering or microwave heating
Authors:
Nicula, R; Ishizaki, K; Stir, M; Shen, Z; Vaucher, S Author Full Names: Nicula, R.; Ishizaki, K.; Stir, M.; Shen, Z.; Vaucher, S.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2450-2457 Sp. Iss. SI 2011
Abstract:
Quasicrystalline (QC) phases are often stable only within narrow composition domains. For this reason, the synthesis of larger amounts of single-phase quasicrystalline powders is difficult. Powder metallurgical approaches, based on mechanical milling followed by conventional heating, have been explored in the recent past. The manufacturing process for single-phase quasicrystals - either in the form of powders or as bulk parts - can be accelerated by orders of magnitude using rapid heating methods that involve pulsed electric currents and/or high-frequency electromagnetic fields. Prior knowledge of the phase transformation sequence and transformation kinetics, as revealed by in situ time-resolved synchrotron radiation experiments, is crucial in obtaining single-phase quasicrystals. We report on the simultaneous synthesis and densification of bulk single-phase Al-Cu-Fe QCs by spark plasma sintering (SPS) within minutes and on the ultrafast synthesis of single-phase Al-Cu-Fe quasicrystalline powders by microwave heating within seconds. The effect of electric current application in the rapid processing of pre-alloyed powders is discussed in relation to the faster diffusion and enhanced phase transformation kinetics.
Title:
Growth morphology of single-crystal grains obtained by directional crystallisation of an Al-Cu-Fe alloy
Authors:
Surowiec, M; Bogdanowicz, W; Krawczyk, J; Formanek, B; Sozanska, M Author Full Names: Surowiec, Marian; Bogdanowicz, Wlodzimierz; Krawczyk, Jacek; Formanek, Boleslaw; Sozanska, Maria
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2458-2465 Sp. Iss. SI 2011
Abstract:
Quasicrystalline as well as crystalline faceted single grains of four phases were obtained during directional crystallisation of an Al-Cu-Fe alloy by the Bridgman technique. The monoclinic phase, Al13(Cu, Fe)4, dominating at high temperatures formed single-crystal lamellae 0.5 mm to 1 mm thick. A second type of attractive morphological form exhibiting flux dissolution terraces was observed on spherical single crystals of phase Al(Fe, Cu). Rectangular, hexagonal and octagonal shaped dissolution terraces were revealed at the positions of two-, three- and four-fold symmetry axes, respectively. A single quasicrystalline phase, Al6Cu2Fe, exhibited icosahedral symmetry with growth forms of a dodecahedron with pentagonal facets. The flux dissolution of the phase apparently plays an essential role in a peritectic reaction leading to quasicrystalline phase formation. Polygonal single grains of phase Al7Cu2Fe exhibiting tetragonal symmetry formed the fourth type of thermodynam ically stable growth forms. Single grains of the phase crystallised in the form of pellets with an octagonal cross-section. The growth morphology of the stable phases was investigated by scanning electron microscopy. The chemical composition of the growth forms described was confirmed by X-ray microanalysis using a scanning electron microscope, whereas the phase composition was determined using electron selected area diffraction and X-ray powder diffraction.
Title:
Synthesis of decagonal Zn-Mg-RE compounds
Authors:
Ors, T; Steurer, W Author Full Names: Oers, Taylan; Steurer, Walter
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2466-2473 Sp. Iss. SI 2011
Abstract:
In this study, the formation of decagonal (d-) quasicrystals in some Zn-Mg-RE systems (with RE = Dy, Er, Ho and Tm) was investigated. For samples with composition Zn58Mg40RE2 reported in literature, decagonal quasicrystals can be obtained as single phase after annealing the prealloys for 100 h at 350 degrees C. However, prolonged annealing at this temperature causes transformation of the d-phase into a hexagonal phase. The d-phase could also be obtained in systems with Er and Ho under different annealing conditions. For Dy- and Er-containing samples, slow cooling (instead of quenching) from higher temperatures also yields predominantly the d-phase.
Title:
Formation of quasicrystalline phase in Al70-xGaxPd17Mn13 alloys
Authors:
Yadav, TP; Singh, D; Shahi, RR; Shaz, MA; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Singh, Devinder; Shahi, Rohit R.; Shaz, M. A.; Tiwari, R. S.; Srivastava, O. N.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2474-2481 Sp. Iss. SI 2011
Abstract:
In the present investigation, the formation and stability of icosahedral phase in Al70-xGaxPd17Mn13 alloys has been explored using X-ray diffraction, scanning, transmission electron microscopy and energy dispersive X-ray analysis. Cast alloys and melt-spun ribbons with x = 2.5, 5, 7.5, 10, 12.5, 15 and 20 have been investigated. In both cases, the alloys up to 5 at% Ga exhibit the formation of pure icosahedral phase. However, for x epsilon 5 at% Ga content, the cast alloy exhibits the formation of multiphase material, consisting of an icosahedral phase along with AlPd-type B2 and ' crystalline (orthorhombic structure with unit cell a = 23.5 angstrom, b = 16.6 angstrom and c = 12.4 angstrom) phases. In the case of the melt spun ribbon for x = 5 at% Ga, only an icosahedral phase has been found, but for 15 x 5 at% Ga, an icosahedral phase is the majority phase with AlPd-type B2 phase being the minority component. For x = 15 at% Ga, a Al3Pd2-type hexagonal phase together with a small amount of quasicrystalline phase is formed. However, for x = 20, only a hexagonal Al3Pd2 phase results.
Title:
Strain-induced structural transformation of single-phase Al-Cu-Fe icosahedral quasicrystal during mechanical milling
Authors:
Mukhopadhyay, NK; Ali, F; Srivastava, VC; Yadav, TP; Sakaliyska, M; Surreddi, KB; Scudino, S; Uhlenwinkel, V; Eckert, J Author Full Names: Mukhopadhyay, N. K.; Ali, F.; Srivastava, V. C.; Yadav, T. P.; Sakaliyska, M.; Surreddi, K. B.; Scudino, S.; Uhlenwinkel, V.; Eckert, J.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2482-2490 Sp. Iss. SI 2011
Abstract:
A single-phase stable icosahedral quasicrystalline sample of high quality with the composition Al62.5Cu25Fe12.5 was produced by the spray forming technique. The material was further investigated by mechanical milling under an argon atmosphere to avoid oxidation during milling. At the initial stages of milling (within 5 h) a significant broadening of the diffraction peaks was observed, indicating a reduction of crystallite size and the introduction of lattice strain, which can be linked to phason strain of the quasilattice. Line broadening was noticed to increase with increasing milling time and in the material milled for longer time only a few broad diffraction peaks, which can be identified as a nanoscale bcc phase (i.e. disordered B2 phase, a 2.9 angstrom), were visible. At this stage the diffraction signals belonging to the quasicrystals were no longer observable, indicating a complete transformation of the quasicrystals into the bcc phase. Finally, the bcc phase formed during milling transformed back to the quasicrystalline phase during subsequent annealing treatment. The microhardness measured on the milled powders was found to decrease with increasing milling time, most likely as a consequence of the increased volume fraction of the ductile bcc phase. Attempts are made to rationalize the structural transformation.
Title:
Anisotropic local structure of decagonal quasicrystals by DAFS
Authors:
Abe, H; Saitoh, H; Nakao, H; Yamamoto, K Author Full Names: Abe, H.; Saitoh, H.; Nakao, H.; Yamamoto, K.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2491-2499 Sp. Iss. SI 2011
Abstract:
Diffraction anomalous fine structure (DAFS) analyses were performed on Al-Ni-Co (ANC) and Al-Ni-Fe (ANF) decagonal quasicrystals at the K-edges of Ni, Co and Fe. In ANC, an order-disorder phase transition with anisotropic atomic short-range order (SRO) is clearly recognizable at high temperature. During in situ observation, a zigzag correlation along the periodic direction developed during the early stage of ordering. Far above the phase transition temperature, this weak correlation along the periodic direction is independent of other correlations along the quasiperiodic one. In ANF, SRO of Fe developed along the quasiperiodic direction, although the local environment of Ni was almost random.
Title:
Structure refinement of decagonal Al-Ni-Co, superstructure type I
Authors:
Kuczera, P; Wolny, J; Fleischer, F; Steurer, W Author Full Names: Kuczera, P.; Wolny, J.; Fleischer, F.; Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2500-2509 Sp. Iss. SI 2011
Abstract:
The structure of decagonal Al-Ni-Co, superstructure type I (the so-called Edagawa phase), was refined in physical space. A statistical approach was used to calculate the structure factors based on a rhombic Penrose tiling, with tile edge length 12.1 angstrom, as reference frame. A total number of 691 parameters was refined against 6843 structure amplitudes, merged in Laue group 10/m.
Title:
Spectroscopic study of Ni-rich Al-Co-Ni quasicrystal
Authors:
Soda, K; Inukai, M; Kato, M; Yagi, S; So, YG; Edagawa, K Author Full Names: Soda, K.; Inukai, M.; Kato, M.; Yagi, S.; So, Y. -G.; Edagawa, K.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2510-2518 Sp. Iss. SI 2011
Abstract:
The valence-band electronic structure of a decagonal Ni-rich Al-Co-Ni quasicrystal, Al72Co8Ni20, was investigated using soft X-ray photoelectron spectroscopy. In particular, the energy distributions of the transition metal 3d bands were determined from the Co and Ni 2p-3d resonance photoemission and compared with those calculated by the discrete variational X method for a model cluster based on a proposed Ni-rich Al-Co-Ni approximant, as well as the 3d band observed in the Co-rich Al-Co-Ni quasicrystal, Al72Co16Ni12. In the Ni-rich Al-Co-Ni, the transition metal 3d band exhibits a peak at a binding energy, EB, of 2.3 eV, which is higher than that of the Co-rich Al-Co-Ni. The observed Ni 3d band has a single-peaked distribution around EB 2.4 eV, in contrast to the calculated bimodal and wide-spread distribution for the proposed Ni-rich Al-Co-Ni model cluster, whereas the Co 3d band is located at EB 1.7 eV, consistent with the model calculation.
Title:
Three-dimensional reconstruction of the atomic arrangement of icosahedral quasicrystals by binary discrete tomography
Authors:
Ishibashi, Y; Sugiura, H; Saitoh, K; Tanaka, N Author Full Names: Ishibashi, Y.; Sugiura, H.; Saitoh, K.; Tanaka, N.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2519-2527 Sp. Iss. SI 2011
Abstract:
A three-dimensional reconstruction of the structure of icosahedral quasicrystals from high-resolution transmission electron microscope images observed along high-symmetry zone-axis projections is studied. As in discrete tomography, the quasicrystalline structure is treated as a discrete set of atoms arranged on the icosahedral lattice, including atom flip sites, which is a structural disorder originating from the degrees of freedom in the internal space. The occupancy of the atoms on each site of the lattice is determined using only the zone-axis projection images without any knowledge of the image intensity. Simulation studies using icosahedral model lattices composed of several thousands of atoms were carried out to test the present reconstruction method. In the case of the ideal icosahedral lattice, a reconstruction rate of 90% is achieved from 10 projection images and a reconstruction rate of 99% is achieved from 18 projections. The reconstruction rate degrad es when the projection images are misaligned. Reconstruction of the three-dimensional distribution of the atom flips is discussed.
Title:
Multiple diffraction in an icosahedral Al-Cu-Fe quasicrystal
Authors:
Fan, CZ; Weber, T; Deloudi, S; Steurer, W Author Full Names: Fan, C. Z.; Weber, Th.; Deloudi, S.; Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2528-2535 Sp. Iss. SI 2011
Abstract:
In order to reveal its influence on quasicrystal structure analysis, multiple diffraction (MD) effects in an icosahedral Al-Cu-Fe quasicrystal have been investigated in-house on an Oxford Diffraction four-circle diffractometer equipped with an Onyx CCD area detector and MoK radiation. For that purpose, an automated approach for Renninger scans (-scans) has been developed. Two weak reflections were chosen as the main reflections (called P) in the present measurements. As is well known for periodic crystals, it is also observed for this quasicrystal that the intensity of the main reflection may significantly increase if the simultaneous (H) and the coupling (P-H) reflections are both strong, while there is no obvious MD effect if one of them is weak. The occurrence of MD events during -scans has been studied based on an ideal structure model and the kinematical MD theory. The reliability of the approach is revealed by the good agreement between simulation and experimen! t. It shows that the multiple diffraction effect is quite significant.
Title:
Hume-Rothery stabilisation mechanism and d-states-mediated Fermi surface-Brillouin zone interactions in structurally complex metallic alloys
Authors:
Mizutani, U; Inukai, M; Sato, H Author Full Names: Mizutani, U.; Inukai, M.; Sato, H.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2536-2542 Sp. Iss. SI 2011
Abstract:
The stability of Co2Zn11 and Al8V5 gamma-brasses, both of which are composed of a transition metal element and polyvalent elements Zn or Al, can be discussed in terms of d-states-mediated Fermi surface-Brillouin zone (FsBz) interactions in the context of first-principles full-potential linearised augmented plane wave (FLAPW) band calculations. A FsBz-induced pseudogap is revealed in the FLAPW-Fourier spectrum, though it is hidden behind a much larger d-band in the total density of states. The stability range of three families of complex metallic alloys (CMAs) that include gamma-brasses, RT-, MI- and Tsai-type 1/1-1/1-1/1 approximants and 2/1-2/1-2/1 approximant, each of which is characterised by [image omitted] = 18, 50 and 125, respectively, can be well scaled in terms of the number of electrons per unit cell (e/uc) given by the product of the number of atoms per unit cell and the e/a value determined by the Hume-Rothery plot on the basis of the FLAPW-Fourier method. This! is taken as the evidence for the justification of the Hume-Rothery stabilisation mechanism for all these CMAs having a pseudogap at the Fermi level.
Title:
Energetics and dynamics of caged Zn4 in i-ScZn
Authors:
Mihalkovic, M; Henley, CL Author Full Names: Mihalkovic, M.; Henley, C. L.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2548-2556 Sp. Iss. SI 2011
Abstract:
In i-ScZn, like other quasicrystals of the i-CaCd class, the innermost shell of the icosahedral cluster is a Zn4 tetrahedron, which thus breaks the symmetry of the outer cluster shells. We investigate theoretically the dynamics of individual tetrahedra, using interatomic pair potentials, fitted from an ab initio database, and molecular dynamics (MD). This includes the formulation of an effective Hamiltonian written in terms of a rigid-body rotation representing the state of each tetrahedron. We characterize the minimum-energy orientations of a tetrahedron, as well as the paths of the transitions between minima (reorientations). The velocity autocorrelations were evaluated for the tetrahedral atoms in the MD dynamics; the corresponding spectral density S() is fairly well fitted by a simplified model in which each atom hops in a double well.
Title:
Cell-constrained melt-quench simulation of d-AlCoNi: Ni-rich versus Co-rich structures
Authors:
Mihalkovic, M; Widom, M; Henley, CL Author Full Names: Mihalkovic, M.; Widom, M.; Henley, C. L.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2557-2566 Sp. Iss. SI 2011
Abstract:
Complex crystalline ground state structures may be obtained by direct (simulated) quenches from the melt for systems of up to a few hundred atoms, given the constraint of a fixed unit cell, coupled with use of (i) replica-exchange Monte Carlo, and (ii) realistic empirical interaction pair potentials. We applied this procedure to decagonal approximants of Al72Co8Ni20 and Al73Co27, obtaining the best energies seen to date for d-AlCoNi models (respectively +20 meV/atom and +9 meV/atom above the tie-plane of competing phases). We elucidated the reasons why different decagonal structures are associated with the Ni-rich and Co-rich compositions. We found a cell doubling to c = 8 angstrom due to layer puckering not only in the Co-rich structure, but (locally) in the nominally c = 4 angstrom Ni-rich structure.
Title:
Ab initio investigations on the stability of seven-fold approximants
Authors:
Orsini-Rosenberg, H; Steurer, W Author Full Names: Orsini-Rosenberg, Heinrich; Steurer, Walter
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2567-2578 Sp. Iss. SI 2011
Abstract:
The stability of theoretical heptagonal approximants was investigated. No approximant phase has yet been confirmed consisting of all three heptagonal rhomb prototiles. To solve this problem, two new approximant structures were constructed from supertiles taken from the ThB4 and YCrB4 structure types. In order to compare structural stability, the total energy convex hulls were calculated for the ternary systems B-Cr-RE (RE = Dy, Er, Ho, Y), as well as B-Mn-Dy and B-Mn-Y, by means of ab initio calculations, using density functional theory. This included all known stable monary, binary and ternary phases. Additionally, several layered boride structure types, which are not stable in the respective ternary systems but show four-, five-, six- or seven-fold local environments, were included by chemical substitution. In all ternary systems, the theoretical approximants were found to be mechanically stable, but chemically unstable by an amount of energy larger than the margin of error. A tendency towards the stabilization of structures showing five- or 10-fold local environments was observed. This is consistent with the findings of decagonal approximants in the systems B-Ti-Ru and B-Mg-Ru.
Title:
Eight different decagonal tilings derived from rhombic Penrose tiling
Authors:
Kato, K; Yamamoto, A Author Full Names: Kato, Kazuyuki; Yamamoto, Akiji
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2579-2586 Sp. Iss. SI 2011
Abstract:
We found 32 variations of dot tiling (DT) reported previously [J. Alloy. Comp. 342 (2002) p.206], which is similar to a tiling consisting of pentagon, hexagons, nonagon and decagons (PHND) [Phil. Mag. A l76 (1997) p.85] employed in the structure analysis of decagonal quasicrystals. They are its superstructures, with a five times larger unit cell in four-dimensional space. These tilings are built up by adding one dot in each fat rhombus in the rhombic Penrose tiling. Eight tilings among 32 DTs do not break the local symmetries of the eight types of vertices in the rhombic Penrose tiling. The eight tilings and their occupation domains are shown.
Title:
Low-temperature structural stability of Cd6M (M = Ho, Er, Tm and Lu) cubic crystalline approximants
Authors:
Nishimoto, K; Sato, T; Muraki, M; Tamura, R Author Full Names: Nishimoto, Kazue; Sato, Takeru; Muraki, Miki; Tamura, Ryuji
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2587-2593 Sp. Iss. SI 2011
Abstract:
TEM observations and electrical resistivity measurements have been performed to investigate the low temperature stability, e.g. the occurrence of a phase transition, in Cd6M (M = Ho, Er, Tm and Lu) approximants, which have the smallest M atomic radii among a series of Cd6M compounds. Unlike other Cd6M compounds, no changes or anomalies were observed in selected-area electron diffraction patterns or in electrical resistivity down to 20 and 15 K, respectively. Therefore, we conclude that a phase transition does not occur in Cd6M (M = Ho, Er, Tm and Lu) and orientational ordering of the Cd4 tetrahedron is kinetically suppressed when the space inside the icosahedral cluster is reduced to a certain level.
Title:
Crystal structure of 1/0-2/1-1/0 Cu-Al-Sc approximant
Authors:
Ishimasa, T; Hirao, A; Honma, T; Mihalkovic, M Author Full Names: Ishimasa, Tsutomu; Hirao, Arina; Honma, Takahiro; Mihalkovic, Marek
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2594-2602 Sp. Iss. SI 2011
Abstract:
The new crystal structure of an orthorhombic phase formed at the alloy composition Cu48.1Al36.4Sc15.5 was analyzed by means of the Rietveld method using synchrotron radiation diffraction data. The starting model for this analysis was constructed theoretically using the so-called 'cell constrained melt-quenching technique'. The space group of the final model is Cmmm, and the unit cell includes 49.0 Cu, 39.0 Al and 16.0 Sc atoms. The lattice parameters are a = 8.337(4) angstrom, b = 22.02(1) angstrom and c = 8.305(4) angstrom, which are related to the six-dimensional lattice parameter, a6D = 6.959 angstrom, of the corresponding Cu-Al-Sc icosahedral quasicrystal as 1/0, 2/1 and 1/0 approximations, respectively. The characteristics of the structure can be understood as a framework consisting of Sc atoms, which is regarded as a tiling of five local structural units; the largest is an icosahedron similar to that included in the Tsai-type quasicrystal. The second exhibits structural similarity to a Mg2Zn11-type crystal and the third is an octahedron.
Title:
Crystal structure of a new orthorhombic Al72Pd18Mn5Si5 approximant phase
Authors:
Simura, R; Kaji, N; Sugiyama, K; Hiraga, K Author Full Names: Simura, Rayko; Kaji, Nobutaka; Sugiyama, Kazumasa; Hiraga, Kenji
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2603-2609 Sp. Iss. SI 2011
Abstract:
The structure of an orthorhmbic Al72Pd18Mn5Si5 phase was determined by single crystal X-ray diffraction: space group Pnma (No.148), a = 1.4396(3) nm, b = 2.4003(2) nm, c = 0.7603(2) nm, V = 2.6272(9) nm3, atoms/cell = 168, F(000) = 3341, = 7.355 mm-1, Dcalc = 4.613 Mgm-3, R(F) = 0.0312 for observed 3919 reflections measured by Mo-K radiation ( = 0.071073 nm). The orthorhombic AlPdMnSi structure is well described by the stacking of a decagonal (0.72 nm) and pentagonal column (0.48 nm) along the b-axis. A new type of decagonal column structures with a periodicity of 1.2 nm (=0.48 + 0.72 nm) is proposed for the decagonal quasicrystals.
Title:
Structure of an approximant crystal in Ni-rich Al71Ni22Co7
Authors:
Abe, E; Yamamoto, A Author Full Names: Abe, E.; Yamamoto, A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2617-2623 Sp. Iss. SI 2011
Abstract:
A novel approximant crystalline structure formed in an Al71Ni22Co7 alloy annealed at 973 K is reported, for which the S1-type superlattice decagonal quasicrystal forms as a major phase. Electron diffraction and atomic-resolution Z-contrast scanning transmission electron microscope investigations successfully identified the approximant as having a monoclinic unit cell with a = c = 3.2 nm (b = 0.4 nm), = 108 degrees; the structure is constructed by the five-fold symmetric decagonal clusters 2 nm across, which are arrayed by inverting their pentagonal directions between the neighbours (antiferro order of the cluster sense). A plausible atomic model of the approximant is proposed by referring to a model structure of the S1-type decagonal quasicrystal, which is composed of the similar local linkages of the five-fold symmetry clusters. The present approximant is shown to share some structural characteristics with the PD3c-approximant reported for a Co-rich Al71.5Ni12.5Co16 alloy.
Title:
Approximant of dodecagonal quasicrystal formed in Mn-Si-V alloy
Authors:
Iga, H; Mihalkovic, M; Ishimasa, T Author Full Names: Iga, Hayato; Mihalkovic, Marek; Ishimasa, Tsutomu
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2624-2633 Sp. Iss. SI 2011
Abstract:
The crystal structure of a hexagonal phase formed in Mn70Si20V10 has been analyzed by the Rietveld method using synchrotron radiation diffraction data. Analysis was carried out by assuming an average metallic element Mn0.875V0.125 via high resolution electron microscopy. The space group of the refined model is P6/mmm (No. 191) and the unit cell includes 18.9 Si and 78.1 metallic atoms. The lattice parameters are a = 17.058(6) angstrom, c = 4.640(1) angstrom. This hexagonal phase is regarded as an approximant of a dodecagonal quasicrystal. The electron diffraction pattern along the c-axis exhibits pseudo 12-fold diffraction symmetry. In the c-projection, the structure is interpreted as the tiling of two types of local structural units, namely an equilateral triangle and square with the same edge length of 4.57 angstrom, which correspond to A15-type and Zr4Al3-type structures in the three dimensions, respectively. Both bond orientational order and scaling property, cha racteristic of a dodecagonal quasicrystal, are imitated in this periodic tiling.
Title:
Diffraction of limit periodic point sets
Authors:
Baake, M; Grimm, U Author Full Names: Baake, Michael; Grimm, Uwe
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2661-2670 Sp. Iss. SI 2011
Abstract:
Limit periodic point sets are aperiodic structures with pure point diffraction supported on a countably, but not finitely generated Fourier module that is based on a lattice and certain integer multiples of it. Examples are cut and project sets with p-adic internal spaces. We illustrate this by explicit results for the diffraction measures of two examples with 2-adic internal spaces. The first and well-known example is the period doubling sequence in one dimension, which is based on the period doubling substitution rule. The second example is a weighted planar point set that is derived from the classic chair tiling in the plane. It can be described as a fixed point of a block substitution rule.
Title:
Colourings of lattices and coincidence site lattices
Authors:
Loquias, MJC; Zeiner, P Author Full Names: Loquias, Manuel Joseph C.; Zeiner, Peter
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2680-2689 Sp. Iss. SI 2011
Abstract:
The relationship between the coincidence indices of a lattice 1 and a sublattice 2 of 1 is examined via the colouring of 1 that is obtained by assigning a unique colour to each coset of 2. In addition, the idea of colour symmetry, originally defined for symmetries of lattices, is extended to coincidence isometries of lattices. An example involving the Ammann-Beenker tiling is provided to illustrate the results in the quasicrystal setting.
Title:
Semi-perfect colourings of hyperbolic tilings
Authors:
de Las Penas, MLAN; Felix, RP; Gozo, BR; Laigo, GR Author Full Names: de Las Penas, Ma Louise Antonette N.; Felix, Rene P.; Gozo, Beaunonie R., Jr.; Laigo, Glenn R.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2700-2708 Sp. Iss. SI 2011
Abstract:
If G is the symmetry group of an uncoloured tiling, then a colouring of the tiling is semi-perfect if the associated colour group is a subgroup of G of index 2. Results are presented that show how to identify and construct semi-perfect colourings of symmetrical tilings. Semi-perfectly coloured tilings that emerge from the hyperbolic semi-regular tiling 8 center dot 10 center dot 16 are reported.
Title:
Determining quasicrystal structures on substitution tilings
Authors:
Akiyama, S; Lee, JY Author Full Names: Akiyama, Shigeki; Lee, Jeong-Yup
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2709-2717 Sp. Iss. SI 2011
Abstract:
Quasicrystals are characterized by the diffraction patterns which consist of pure bright peaks. Substitution tilings are commonly used to obtain geometrical models for quasicrystals. We consider certain substitution tilings and show how to determine a quasicrystalline structure for the substitution tilings computationally. In order to do this, it is important to have the Meyer property on the substitution tilings. We use the recent result of Lee and Solomyak, which determines the Meyer property on the substitution tilings from the expansion maps.
Title:
Aperiodic structures and notions of order and disorder
Authors:
Ben-Abraham, SI; Quandt, A Author Full Names: Ben-Abraham, S. I.; Quandt, A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2718-2727 Sp. Iss. SI 2011
Abstract:
The fabrication of artificial heterostructures is mainly based on substitution systems. We present simple ways to construct double-sided versions of the Fibonacci, Prouhet-Thue-Morse, paperfolding, period doubling and Golay-Rudin-Shapiro sequences. We also construct a generic instance of the two-dimensional Prouhet-Thue-Morse structure and explore its symbolic complexity. The complexity turns out to be polynomial and hence, the entropy goes to zero.
Title:
A long-range hierarchical clustering model for constructing perfect quasicrystalline formations
Authors:
Al Ajlouni, RA Author Full Names: Al Ajlouni, Rima A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2728-2738 Sp. Iss. SI 2011
Abstract:
Since their discovery, the unique structural signature of quasicrystals has posed a perplexing puzzle. Whereas significant progress has been made in determining their physical properties, a deeper understanding of the structure of quasicrystals remains an open question. Although available structural models provide important insights into understanding the quasiperiodic structural order, there is still significant information lacking concerning the determination of the long-range order of quasicrystals. A global multi-level hierarchical framework is presented that is able to describe the long-range translational and orientational order of the global empire pertaining to perfect Penrose tiling (PPT) models. In this order, the global empire is constructed of infinite levels of hierarchical clusters. Any cluster level, in this hierarchy, is composed of four smaller building clusters; two highly symmetrical clusters and their two fragments. Cluster configurations and the geometric arrangements of the multi-level clusters are determined entirely by a geometric progression of framework of nested decagrams. The proposed model suggests that the position of building units, locally and globally, is defined by one global framework, and not tiled based on local rules (matching or overlapping, etc). In this way, quasicrystal formations can grow rapidly ad infinitum without the need for any defects or mismatches.
Title:
Anisotropic Hall effect in Al13TM4 approximants
Authors:
Ivkov, J; Popcevic, P; Stanic, D; Bauer, B; Gille, P; Dolinsek, J; Smontara, A Author Full Names: Ivkov, J.; Popcevic, P.; Stanic, D.; Bauer, B.; Gille, P.; Dolinsek, J.; Smontara, A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2739-2745 Sp. Iss. SI 2011
Abstract:
The Hall coefficient, RH, in monoclinic Y-Al-Ni-Co, orthorhombic Al13Co4 and monoclinic Al13Fe4 and Al13(Fe,Ni)4 single crystals was investigated for all combinations of the electrical current and magnetic field directions and in the temperature interval from 90 to 370 K. In all three intermetallics, which belong to the Al13TM4 (TM = transition metal) class of approximants to the decagonal quasicrystals, the Hall coefficient exhibits well-defined anisotropy. RH is positive hole-like or zero for the magnetic field parallel to the plane that corresponds to the quasiperiodic plane in decagonal (d-) quasicrystals, and is negative electron-like or zero for the magnetic field perpendicular to this plane. The only exception is RH in Al13Fe4 for the field parallel to the stacking direction, which changes its sign from positive to negative value with an increase of temperature. The results for the anisotropy of RH are correlated to the anisotropy of RH in d-Al-Ni-Co and d-Al-Cu-Co quasicrystals and a brief overview of the theoretical results is presented.
Title:
Anisotropic transport properties of the Al13TM4 and T-Al-Mn-Fe complex metallic alloys
Authors:
Smontara, A; Popcevic, P; Stanic, D; Velebit, K; Dolinsek, J Author Full Names: Smontara, A.; Popcevic, P.; Stanic, D.; Velebit, K.; Dolinsek, J.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2746-2755 Sp. Iss. SI 2011
Abstract:
Anisotropy of the transport properties (electrical resistivity, (T), thermoelectric power, S(T), and thermal conductivity, (T)) of the Al76Co22Ni2 (Y-Al-Ni-Co), o-Al13Co4 and T-Al72.5Mn21.5Fe6.0 complex metallic alloys was investigated experimentally. These compounds belong to the class of approximants in decagonal quasicrystals phases with stacked-layer crystallographic structure and enabled us to study the evolution of transport properties with increasing structural complexity and the unit cell size. For Y-Al-Ni-Co and o-Al13Co4, the anisotropic electronic transport coefficients were analyzed theoretically by Boltzmann transport theory and ab initio calculated anisotropic Fermi surface. The non-metallic anisotropic electrical resistivity of the T-Al72.5Mn21.5Fe6.0 may be analyzed in a semi-quantitative way by the theory of quantum transport of slow charge carriers.
Title:
Novel properties of frustrated low-dimensional magnets with pentagonal symmetry
Authors:
Jagannathan, A; Motz, B; Vedmedenko, E Author Full Names: Jagannathan, A.; Motz, Benjamin; Vedmedenko, E.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2765-2772 Sp. Iss. SI 2011
Abstract:
We consider a new type of frustrated spin network with pentagonal loops and long-range quasiperiodic structural order. Five-fold loops can be expected to occur naturally in quasicrystals, and experimental studies of icosahedral alloys show manifestations of local five-fold symmetry in a variety of different physical contexts. Our model considers classical spins placed on the vertices of a subtiling of the two-dimensional Penrose tiling, and interacting with nearest neighbours via antiferromagnetic bonds. The ground state of this fractal system has a complex magnetic structure, and is studied analytically as well by Monte Carlo simulation on finite clusters.
Title:
Fermi surface effects in icosahedral quasicrystals
Authors:
Chernikov, MA; Vekilov, YK Author Full Names: Chernikov, M. A.; Vekilov, Yu. Kh.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2773-2777 Sp. Iss. SI 2011
Abstract:
In icosahedral quasicrystals, due to an interaction of the Fermi sphere with the boundaries of the pseudo-Brillouin zone associated with the strongest Fourier components of the pseudopotential, the Fermi surface consists of many small electron and hole pockets. Such a scenario can be described by the fractional multicomponent model of the Fermi surface. A discussion is provided of the electronic and thermal properties that follow from this model, in particular at high temperatures.
Title:
Breakdown of semi-classical conduction theory in approximants of the octagonal tiling
Authors:
de Laissardiere, GT; Oguey, C; Mayou, D Author Full Names: de Laissardiere, G. Trambly; Oguey, C.; Mayou, D.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2778-2786 Sp. Iss. SI 2011
Abstract:
We present numerical calculations of quantum transport in perfect octagonal approximants. These calculations include a Boltzmann (intra-band) contribution and a non-Boltzmann (inter-band) contribution. When the unit cell size of the approximant increases, the magnitude of the Boltzmann terms decreases, whereas the magnitude of the non-Boltzmann terms increases. This shows that, in large approximants, the non-Boltzmann contributions should dominate the transport properties of electrons. This confirms the breakdown of the Bloch-Boltzmann theory for understanding the transport properties in approximants with very large unit cells, and then in quasicrystals, as found in actual Al-based approximants.
Title:
Variable-range-hopping conductivity in polygrain samples of icosahedral Al-Re-Pd
Authors:
Vekilov, YK; Chernikov, MA Author Full Names: Vekilov, Yu. Kh.; Chernikov, M. A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2787-2791 Sp. Iss. SI 2011
Abstract:
We further develop a model, based on an analogy with granular electronic conductors, which explains the nature of the variable-range-hopping conductivity in polygrain samples of icosahedral Al-Re-Pd with resistivity ratios of [image omitted] in an excess of 13. The electrical conductivity of the model is determined by intergranular tunnelling and electrostatic energy. In polygrain icosahedral Al-Re-Pd, pores and precipitates of secondary phases create the barriers. Depending on the barrier height and electrostatic disorder, either an insulating variable-range-hopping regime of an Efros-Shklovskii or Mott type with elastic co-tunnelling or a metallic regime typical of homogeneously disordered conductors is possible.
Title:
Observation of log-periodic oscillations in the quantum dynamics of electrons on the one-dimensional Fibonacci quasicrystal
Authors:
Lifshitz, R; Mandel, SED Author Full Names: Lifshitz, Ron; Mandel, Shahar Even-Dar
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2792-2800 Sp. Iss. SI 2011
Abstract:
We revisit the question of quantum dynamics of electrons on the off-diagonal Fibonacci tight-binding model. We find that typical dynamical quantities, such as the probability of an electron to remain in its original position as a function of time, display log-periodic oscillations on top of the leading-order power-law decay. These periodic oscillations with the logarithm of time are similar to the oscillations that are known to exist with the logarithm of temperature in the specific heat of Fibonacci electrons, yet they offer new possibilities for the experimental observation of this unique phenomenon.
Title:
Negative refraction and localized states of a classical wave in high-symmetry quasicrystals
Authors:
Zhang, XD; Zhong, W; Feng, ZF; Wang, YQ; Li, ZY; Zhang, DZ Author Full Names: Zhang, Xiangdong; Zhong, Wei; Feng, Zhifang; Wang, Yiquan; Li, Zhi-Yuan; Zhang, Dao-Zhong
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2811-2819 Sp. Iss. SI 2011
Abstract:
Recently, negative refraction of electromagnetic waves in periodic photonic crystals has been demonstrated experimentally and sub-wavelength images observed. A theoretical and experimental investigation is reported of the electromagnetic wave transport in high-symmetry photonic quasicrystals (QCs). It is shown that negative refraction can appear in these transparent quasicrystalline photonic structures. It is interesting that highly symmetric two-dimensional photonic QCs possess a universal feature for non-near-field focus of two kinds of polarized waves (S wave and P wave). That is, the non-near-field focus for two kinds of polarized waves can be realized by using flat lenses, which consist of some high-symmetric two-dimensional photonic QCs with the same structures and parameters. In addition, some two-dimensional and three-dimensional localized states in defect-free photonic QCs have been found. It is evident that these unusual localized states can be explored by means of electron energy loss spectroscopy.
Title:
Internal friction of an Al-Cu-Fe icosahedral quasicrystal and its crystal approximant
Authors:
So, YG; Sato, S; Edagawa, K; Tamura, R Author Full Names: So, Yeong-Gi; Sato, Shun; Edagawa, Keiichi; Tamura, Ryuji
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2820-2827 Sp. Iss. SI 2011
Abstract:
The internal friction was measured for an Al-Cu-Fe icosahedral phase (i-phase) and an Al-Cu-Fe-Si 1/1 approximant phase (1/1-phase) by using a dynamical mechanical analyzer (DMA) in the frequency range 0.05-10 Hz and the temperature range 300-873 K. For the i-phase, four absorption peaks were observed at around 420, 580, 620 and 800 K, respectively. These were of the thermally activated relaxation type, and their activation parameters were evaluated. The parameters evaluated for the peak at 800 K indicate a relaxation process involving a collective atomic motion, which can be attributed to correlated phason jumps. This peak was absent for the 1/1-phase. These results are similar to the results of the internal friction measurements previously reported for an Al-Pd-Mn i-phase and its 1/1 approximant phase. Based on the phonon-phason dynamics model, the magnitudes of phason elastic constants were estimated for the Al-Cu-Fe i-phase.
Title:
On nature of the excess heat capacity in icosahedral quasicrystals
Authors:
Prekul, AF; Shchegolikhina, NI; Edagawa, K Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.; Edagawa, K.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2828-2836 Sp. Iss. SI 2011
Abstract:
Experimental evidence is presented which indicates that the total heat capacity in the Al63Cu25Fe12 icosahedral phase contains a contribution associated with inconstancy of the charge carrier concentration. The contribution has an oscillating temperature dependence and is supposedly traceable to two Schottky-like heat anomalies.
Title:
Effect of Ti addition on the quasicrystalline phase formation and indentation characteristics of Zr69.5Al7.5Cu12Ni11 alloy
Authors:
Singh, D; Yadav, TP; Mandal, RK; Tiwari, RS; Srivastava, ON Author Full Names: Singh, Devinder; Yadav, T. P.; Mandal, R. K.; Tiwari, R. S.; Srivastava, O. N.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2837-2845 Sp. Iss. SI 2011
Abstract:
The crystallisation behaviour and indentation characteristics of melt-spun (Zr69.5Al7.5Cu12Ni11)100-xTix (x = 0-16 at. %) metallic glasses was investigated. Differential scanning calorimetry traces revealed changes in crystallisation behaviour with addition of Ti. Formation of a nanoquasicrystalline phase by annealing the glass was found up to x = 12. Further increase of Ti content gives rise to formation of a Zr2Ni-type crystalline phase. In addition to this, the size of nanoquasicrystals decreases with increasing addition of Ti. The load-dependent hardness behaviour of the metallic glasses and nanoquasicrystal-glass composites is reported in detail. The value of the yield strength of the materials was estimated with the help of hardness values based on the empirical correlations available in literature. The formation of shear bands around the indentation periphery was observed. It was found that microstructural and morphological changes alter the indentation characteristic! s of glasses as well as composites formed after controlled crystallisation.
Title:
Multi-cluster model of Al-Co-Ni Co-rich quasicrystal
Authors:
Yuhara, J; Sato, M; Matsui, T; Tsai, AP Author Full Names: Yuhara, J.; Sato, M.; Matsui, T.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2846-2853 Sp. Iss. SI 2011
Abstract:
We studied the surface modification of Al-Co-Ni Co-rich quasicrystals by Co or Ni deposition, using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). After depositing 0.2 monolayers (ML) of Co or Ni with post-annealing, no clear changes were observed in the spot intensity or pattern of LEED. Only the uppermost surface was successfully modified. Based on the STM images of the modified surface, we found that excess Co atoms modified the 2-nm Co clusters to form 0.47-nm clusters and that excess Ni atoms only formed 0.29-nm Ni clusters on the Al-Co-Ni Co-rich quasicrystal surface. Finally, based on the STM images of a clean Co-rich surface, the Al positions proposed by transmission electron microscopy has been modified to match the STM image. To account for the data, we propose a multi-cluster model - based in part on the Hiraga model - composed of three main clusters for both A and B stacking layers.
Title:
Asymmetric pentagonal cluster on an Al-Cu-Co quasicrystal surface
Authors:
Zenkyu, R; Matsui, T; Tsai, AP; Yuhara, J Author Full Names: Zenkyu, R.; Matsui, T.; Tsai, A. P.; Yuhara, J.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2854-2861 Sp. Iss. SI 2011
Abstract:
The 10-fold surface of a decagonal Al66Cu17Co17 quasicrystal has been studied by scanning tunneling microscopy (STM). Three kinds of characteristic pentagonal clusters are observed in the STM images. Clusters within a given terrace have the same orientation, while those in adjacent terraces have opposite orientations. We show that two of the pentagonal cluster types are part of the 2-nm cluster, which is considered to be the basic structural unit of the Al-Cu-Co quasicrystal. The local atomic arrangement in the 2-nm clusters is found to be asymmetric.
Title:
Step-terrace morphology and reactivity to C60 of the five-fold icosahedral Ag-In-Yb quasicrystal
Authors:
Nugent, PJ; Smerdon, JA; McGrath, R; Shimoda, M; Cui, C; Tsai, AP; Sharma, HR Author Full Names: Nugent, P. J.; Smerdon, J. A.; McGrath, R.; Shimoda, M.; Cui, C.; Tsai, A. P.; Sharma, H. R.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2862-2869 Sp. Iss. SI 2011
Abstract:
The surface of the icosahedral i-Ag-In-Yb quasicrystal provides one of the first non-Al-based aperiodic surfaces that is suitable for study under ultra-high vacuum conditions. We present a scanning tunnelling microscopy (STM) study of the five-fold surface of this new quasicrystal demonstrating detailed structure of the terraces and steps. The analysis of the autocorrelation functions of STM images at opposite bias polarities and of the in-plane structure of the bulk model of i-Cd-Yb, which is isostructural to i-Ag-In-Yb, reveals that the surface terminations occur at the centres of the rhombic triacontrahedral (RTH) clusters, which are the basic building blocks of this material. The study further confirms that the unoccupied electronic states are located on Yb sites. Step edges display a Fibonacci sequence of truncated clusters, which can also be explained in terms of the model structure. Occasionally, a single terrace is found to display different structures at negative bias, whereas the same terrace shows a uniform structure at positive bias. Depositing C60 creates a disordered overlayer on the surface with no resulting FFT or LEED patterns.
Title:
Influence of the substrate temperature and deposition flux in the growth of a Bi thin film on the ten-fold decagonal Al-Ni-Co surface
Authors:
Sharma, HR; Ledieu, J; Fournee, V; Gille, P Author Full Names: Sharma, H. R.; Ledieu, J.; Fournee, V.; Gille, P.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2870-2878 Sp. Iss. SI 2011
Abstract:
We compare the growth of a Bi thin film on the ten-fold surface of the decagonal Al-Ni-Co quasicrystal at different substrate temperatures and fluxes using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The growth at 29 K leads to the formation of a quasicrystalline monolayer, consistent with the results obtained at 300 K. Further deposition at low temperature produces pseudocubic islands with {100} surface orientation. The islands have two or four atomic layer heights. Both STM and LEED measurements reveal that there is a transition from the pseudocubic {100} film to the hexagonal {0001} surface orientation at coverage () 4 6 ML. The hexagonal domains are oriented along the high symmetry directions of the substrate. Growth at room temperature with different fluxes results in different island-height distributions. High flux predominantly produces islands of uniform four-layer high islands, whereas low flux yields islands of varying heig! hts, yielding a rough film morphology. The two-layer high islands are found to be more stable at low temperature than at room temperature.
Title:
Weak bonding of Zn in an Al-based approximant based on surface measurements
Authors:
Yuen, CD; Unal, B; Jing, DP; Thiel, PA Author Full Names: Yuen, Chad D.; Unal, Baris; Jing, Dapeng; Thiel, Patricia A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2879-2888 Sp. Iss. SI 2011
Abstract:
We have studied two surfaces of a new Al-Pd-Zn approximant using mass spectrometry, X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). Zn is bonded weakly in this approximant, perhaps as weakly as in elemental Zn. This is based upon three observations: (1) the low vapor pressure of Zn above the approximant (detectable in the gas phase at 600 K), (2) preferential sputtering of Zn (contrary to the usual preferential sputtering of Al in Al-rich quasicrystals), and (3) preferential surface segregation of Zn. We further show that preferential segregation - and perhaps incipient evaporation - causes the surface to roughen, preventing it from forming a terrace-step morphology. Finally, our data show that at low O2 pressures, Al oxidizes. In air, Zn oxidizes as well. All results and conclusions are similar for the two-fold and pseudo-10-fold surfaces.
Title:
XPS study of adsorption and desorption of a Bi thin film on the five-fold icosahedral Al-Pd-Mn surface
Authors:
Young, KM; Cross, N; Smerdon, JA; Dhanak, VR; Sharma, HR; Lograsso, TA; Ross, AR; McGrath, R Author Full Names: Young, K. M.; Cross, N.; Smerdon, J. A.; Dhanak, V. R.; Sharma, H. R.; Lograsso, T. A.; Ross, A. R.; McGrath, R.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2889-2893 Sp. Iss. SI 2011
Abstract:
We have employed X-ray photoelectron spectroscopy to characterise the growth and thermal stability of a Bi thin film on the five-fold icosahedral Al-Pd-Mn surface. The growth can be characterised as Stranski-Krastanov, in agreement with previous STM studies. As a function of annealing temperature, the multilayer desorbs first and thereafter coverages of 1 ML and 0.5 ML are stable for significant temperature ranges.
Title:
Catalytic properties of Al13Co4 studied by ab initio methods
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, M.; Hafner, J.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2904-2912 Sp. Iss. SI 2011
Abstract:
While the surfaces of ordinary crystals provide only a few inequivalent adsorption sites, the complex landscape of the surfaces of quasicrystals and their approximants provides a rich variety of different adsorption sites. Recently, Armbruster et al. reported that Al13Co4, whose structure is closely related to decagonal Al-Ni-Co quasicrystals, is an efficient and selective hydrogenation catalyst for alkynes. In the present work, the hydrogenation of acetylene to ethylene on the (100) surface of Al13Co4 has been studied using ab initio density-functional simulations. Surprisingly, the stable cleavage surface of Al13Co4 is strongly corrugated. The surface is covered by zig-zag chains of edge-sharing Al pentagons, each centered on a Co atom and separated from neighboring chains by wide troughs. The binding energies for adsorption and co-adsorption of H2 and C2H2 molecules at various surface sites have been calculated. Surprisingly, in the energetically most favorable conf! iguration, acetylene is bound in a di-sigma configuration to two Al atoms, not to the Co atom. We have searched for the optimal reaction pathway for the dissociatible adsorption of hydrogen and for the hydrogenation of acetylene to vinyl, ethylene by a Langmuir-Hinshelwood mechanism. The energetic barriers for all reaction steps were calculated by the nudged-elastic-band method. It was found that the energetic barrier of any reaction step does not exceed 0.65 eV (63 kJ/mol). This value is lower than the activation energies for acetylene to ethylene hydrogenation over a Pd catalyst where barriers of 78 kJ/mol and 85 kJ/mol were reported for the rate-determining steps.
Title:
Theoretical studies on clean and adsorbed surfaces of Ag-In-Yb
Authors:
Nozawa, K; Ishii, Y Author Full Names: Nozawa, Kazuki; Ishii, Yasushi
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2913-2919 Sp. Iss. SI 2011
Abstract:
The adsorption structure of Pb atoms on the five-fold surface of a AgInYb quasicrystal is studied using a first-principles calculation. The aperiodic five-fold surface is replaced by a cluster model, following the quasicrystal model by Takakura et al. The potential energy surface (PES) for a single Pb adsorption reflects the five-fold symmetry of the substrate. The most preferred adsorbed site is a five-fold hollow site surrounded by three In and two Yb atoms, and the most preferred sites form a pentagon with edge length 9.9 angstrom. The PES for the second adsorbed atom is calculated to examine the effects of interadsorbate interaction. It turns out that the interadsorbate interaction is limited, and it does not change the PES essentially. Thus, at low coverage, the Pb atoms presumably adsorb onto the five-fold hollow sites, forming a Pb pentagon with edge length 9.9 angstrom around the cluster center. Possible adsorption structures at higher coverage are also discussed.
Title:
Synthesis of porous Cu from Al-Cu-Co decagonal quasicrystalline alloys
Authors:
Vani, VK; Kwon, OJ; Hong, SM; Fleury, E Author Full Names: Vani, V. Kalai; Kwon, O. J.; Hong, S. M.; Fleury, E.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2920-2928 Sp. Iss. SI 2011
Abstract:
The formation of a porous Cu structure from cast Al-Cu-Co decagonal quasicrystalline alloys has been studied using a selective corrosion technique. Two alkaline solutions were selected based on the electrochemical properties of the constituent elements. Selective corrosion of Al and Co was achieved by chemical immersion of the cast Al-Cu-Co alloy in both 5 M NaOH and 0.5 M Na2CO3 solutions; values for BET surface-to-weight ratio of up to 30 m2/g could be reached. Microstructural analyses indicated that the architecture of the resulting porous structures was composed of a needle-type phase, remaining from the decagonal phase, in addition to Cu and Cu-Co phases.
Title:
Preparation and wear resistance of Ti-Zr-Ni quasicrystal and polyamide composite materials
Authors:
Wang, XL; Li, XS; Zhang, ZJ; Zhang, SS; Liu, WQ; Wang, LM Author Full Names: Wang, Xinlu; Li, Xuesong; Zhang, Zhenjiang; Zhang, Shanshan; Liu, Wanqiang; Wang, Limin
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2929-2936 Sp. Iss. SI 2011
Abstract:
Ti-Zr-Ni icosahedral quasicrystal powders (Ti-QC), prepared by mechanical alloying and then annealing in a vacuum furnace, were used as a novel filler material in polyamide 12 (PA12). The melt processability of the composite was studied using a Haake torque rheometer. This indicates that PA12/Ti-QC composites can be melt-processed into a wear-resistant material. Further, these composites, fabricated by compression molding, were tested in sliding wear against a polished bearing steel counterface. The results from wear testing show that the addition of Ti-QC filler to PA12 enhances wear resistance and reduces volume loss by half compared with neat PA12. Furthermore, it is found that the hardness of the composite increases with increasing content of Ti-QC filler. In addition, PA12/Ti-QC composites exhibit a slightly higher crystallization temperature and better thermal stability than PA12. These combined results demonstrate that Ti-QC filler may be a desirable alternative when attempting to increase the wear resistance of PA12.
Title:
Pressure-composition-temperature curves and structure stability induced by hydrogen in TiZrNi quasicrystals
Authors:
Choi, SB; Lee, SH; Kim, JY Author Full Names: Choi, Soo-bin; Lee, Sang-hwa; Kim, Jae Yong
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2937-2943 Sp. Iss. SI 2011
Abstract:
To evaluate the potential applications of Ti-based quasicrystals as hydrogen storage materials, metastable Ti53-xZr27Ni20Pdx (x = 0, 2, 4, 6) quasicrystals were prepared by a rapid quenching method and equilibrium vapor pressures for hydrogen were measured. Pressure-composition-temperature curves measured in Pd-added TiZrNi quasicrystals revealed a significantly increased equilibrium vapor pressure for hydrogen with increasing Pd concentration, while hydrogen loading capacity decreased. After hydrogen absorption, no hydride phase was found for samples made with less than x = 4. The main peaks shifted to the lower angle of 2 in X-ray diffraction patterns, demonstrating that the quasi-lattice constants increased from 5.13 to 5.38 angstrom after hydrogenation. The quasi-lattice constants linearly expanded with increasing absorption amount of hydrogen. Interestingly, analyzing the full width at half maximum values of the main peaks in the X-ray diffraction patterns showed that the coherence lengths of the quasicrystals significantly increased from 120 to 240 angstrom after hydrogenation, presumably due to kinetic rather than thermal factors.
Title:
Novel HDPE-quasicrystal composite fabricated for wear resistance
Authors:
Kothalkar, A; Sharma, AS; Biswas, K; Basu, B Author Full Names: Kothalkar, Ankush; Sharma, Amit S.; Biswas, Krishanu; Basu, Bikramjit
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2944-2953 Sp. Iss. SI 2011
Abstract:
The present paper reports, for the first time, the processing, characterization and wear property of a novel HDPE-decagonal quasicrystal (QC) composite prepared by compression molding. The composites were prepared at 130 degrees C and an applied pressure of 0.735 MPa with different holding time to obtain a fully dense product. It was found that a holding time of 60 min is the optimum at the specified melting temperature and pressure. The second phase (QC) content was varied from 5 to 20 wt% to obtain optimum mechanical properties. SEM observations indicate well-dispersed QC particles within the HDPE matrix, with fine scale distribution for 20 wt% QC. Ball-on-disc wear tests revealed that the composites showed better wear resistance than pure HDPE samples. The results are discussed using the currently available literature.
Title:
Atomic pair distribution function (PDF) analysis of Raney Pd and Rh fine particles
Authors:
Murao, R; Sugiyama, K; Kashiwagi, Y; Kameoka, S; Tsai, AP Author Full Names: Murao, R.; Sugiyama, K.; Kashiwagi, Y.; Kameoka, S.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2954-2961 Sp. Iss. SI 2011
Abstract:
Raney Pd and Rh fine particles were prepared from decagonal Al75Pd25 and Al9Rh2 with an Al9Co2-type structure, respectively, by leaching with NaOH aqueous solution. The atomic pair distribution functions (PDFs) for the Raney Pd and Rh fine particles indicate structural features similar to an fcc structure, suggesting atomic rearrangement toward the closest packing of constituents during the leaching process. Transmission electron micrographs indicate that Raney Pd and Rh are aggregates of fcc-structured nano-crystallites with a diameter of 5-6 nm.
Title:
Quasicrystals: diversity and complexity
Authors:
Dubois, JM; Lifshitz, R Author Full Names: Dubois, Jean-Marie; Lifshitz, Ron
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2971-2982 Sp. Iss. SI 2011
Abstract:
Scientific presentations at ICQ11 the 11th International Conference on Quasicrystals, which took place in Sapporo, Japan, in June 2010 offered a variety of stimulating new experimental data and novel theoretical results. New aperiodic crystals were presented; new theoretical ideas were described; exciting experimental results were revealed; and potential applications of quasicrystals were reviewed, showing an unprecedented level of development. ICQ11 was a great success thanks to the high standard of its scientific content and to the efficiency of its organization. ICQ11 proved that quasicrystal research is sure to continue offering diverse challenges and profound insights into the complexity of matter.
Title:
Hydrothermal synthesis of compounds in the fresnoite mineral family (Ba2TiSi2O8)
Authors:
Abbott, EE; Mann, M; Kolis, JW Author Full Names: Abbott, Edward E.; Mann, Matthew; Kolis, Joseph W.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 184 (5): 1257-1262 MAY 2011
Abstract:
Crystals of Ba2TiSi2O8, Sr2TiSi2O8, and Ba2VSi2O8, all belonging to the fresnoite family were prepared by the hydrothermal method. Attempts to synthesize other members by substitution at the alkaline earth site, transition metal site, and tetrahedral site were not successful, but did lead to the formation of a variety of other mineral phases as well as the incommensurate structure, Ba2TiGe2O8. Structural studies on this compound and analysis of the other known fresnoite phases were performed to elucidate the nature of the incommensurate structure. (C) 2011 Elsevier Inc. All rights reserved.
Title:
Critical behaviour of optical birefringence near the normal-incommensurate phase transition in [N(CH3)(4)](2)ZnCl4 crystals under the influence of hydrostatic pressure
Authors:
Kushnir, OS; Kityk, AV; Dzyubanski, VS; Shopa, RY Author Full Names: Kushnir, O. S.; Kityk, A. V.; Dzyubanski, V. S.; Shopa, R. Y.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (22): Art. No. 225403 JUN 8 2011
Abstract:
We have estimated the Ginzburg number G governing crossover from the asymptotic to the classical critical behaviour near the normal-incommensurate phase transition in [N(CH3)(4)](2)ZnCl4 (TMAZC) crystals and the dependence of G on the hydrostatic pressure (0.1-330 MPa), following from the experimental data for the optical birefringence and the quantitative analysis of temperature derivatives of the birefringence in the framework of the approximation of weak Gaussian fluctuations. The Ginzburg number found experimentally for TMAZC is G similar to 8 x 10(-3) at the atmospheric pressure and a considerable part of it is assumed to refer to structural defects. It is shown that the G value for TMAZC decreases with increasing hydrostatic pressure and, based on analysis of the literature birefringence data for Cs2CdBr4 and Cs2HgBr4 crystals, this behaviour might be expected to be generally typical for all the A(2)BX(4) family. The results obtained are discussed using a phenomenological theory of second-order structural phase transitions. In particular, they provide a basis for estimating the limits of the asymptotic critical region in TMAZC and demonstrate that the major part of the incommensurate phase should belong to the crossover region.
Title:
The first find of dodecagonal quasiperiodic tiling in historical Islamic architecture
Authors:
Makovicky, E; Makovicky, NM Author Full Names: Makovicky, Emil; Makovicky, Nicolette M.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 44: 569-573 Part 3 JUN 2011
Abstract:
The tympanum of the entrance of the Zaouia Moulay Idriss II in Fez contains the only known example of a dodecagonal cartwheel quasiperiodic pattern in Islamic art, dating possibly from the Merinid epoch. This pattern, carved in a marble plate, is based on a type of Ammann quasilattice known also from modern mathematical literature. The central portions of this pattern were used as elements in a periodic pattern on the walls of the Saadian mausoleum in Marrakech.
Title:
Three-Dimensional Atomic Images of TlInSe2 Thermoelectric Material Obtained by X-ray Fluorescence Holography
Authors:
Hosokawa, S; Happo, N; Hayashi, K; Mimura, K; Wakita, K; Hu, W; Ishii, H; Yoshimura, M; Jeyakanthany, J; Mamedov, N Author Full Names: Hosokawa, Shinya; Happo, Naohisa; Hayashi, Kouichi; Mimura, Kojiro; Wakita, Kazuki; Hu, Wen; Ishii, Hirofumi; Yoshimura, Masato; Jeyakanthany, Jeyaraman; Mamedov, Nazim
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS 50 (5): Art. No. 05FC06 Part 3 Sp. Iss. SI MAY 2011
Abstract:
Three-dimensional (3D) atomic images around the Tl atoms in single-crystal TlInSe2 thermoelectric material in the incommensurate phase were reconstructed by Tl L-III X-ray fluorescence holography measured at room temperature. In the obtained 3D image, the In atoms are clearly visible at the proper positions in the normal phase. The Tl atomic images are also observed but very weakly. By comparing the experimental image with a theoretically calculated one, it is concluded that only the Tl atoms have large spatial fluctuations, which are related to the incommensurate phase of this material. (C) 2011 The Japan Society of Applied Physics
Title:
Charged Defects as an Origin of the Memory Effect in Incommensurate Phase of TlInS2 Ferroelectric-Semiconductors
Authors:
Seyidov, MY; Suleymanov, RA; Mammadov, TG; Fedotov, AK; Babayev, SS; Sharifov, GM Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Mammadov, Tofig G.; Fedotov, Aleksandr K.; Babayev, Sardar S.; Sharifov, Galib M.
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS 50 (5): Art. No. 05FD07 Part 3 Sp. Iss. SI MAY 2011
Abstract:
The effects of annealing within the incommensurate phase and doping with the lanthanum impurity on the dielectric function epsilon of the TlInS2 single crystals have been investigated. It is shown that illumination and application of external electric field transform the epsilon(T) dependences for both the annealed and doped samples in the same manner. The inference is made that the correlation between observed effects is conditioned by the internal electric fields induced either by activation (polarization) of native defects during the annealing procedure or after the doping the crystals with active La centers. (C) 2011 The Japan Society of Applied Physics
Title:
An Incommensurately Modulated Structure of eta '-Phase of Cu3+xSi Determined by Quantitative Electron Diffraction Tomography
Authors:
Palatinus, L; Kementova, M; Drinek, V; Jarosova, M; Petricek, V Author Full Names: Palatinus, Lukas; Kementova, Mariana; Drinek, Vladislav; Jarosova, Marketa; Petricek, Vaclav
Source:
INORGANIC CHEMISTRY 50 (8): 3743-3751 APR 18 2011
Abstract:
The diffraction data of eta'-Cu3+x(Si,Ge) were collected by 3D quantitative electron diffraction tomography on a submicrometer-sized sample, and the structure was solved by the charge-flipping algorithm in superspace. It is shown that the structure is trigonal, and it is incommensurately modulated with two modulation vectors q(1) = (alpha, alpha, 1/3) and q(2) = (-2 alpha, alpha, 1/3), superspace group P (3) over bar 1m (alpha, alpha, 1/3)000(-2 alpha, alpha, 1/3)000. The modulation functions of some atoms are very complicated and reach amplitudes comparable with the unit cell dimensions. The modulated structure can be described as sheets of Cu clusters separated by honeycomb layers of mixed Si/Ge positions. The shape of the Cu clusters in the sheets strongly varies with the modulation phase, and the predominant form is an icosahedron. The striving of the Cu layers to form icosahedral clusters is deemed to be the main driving force of the modulation. The combination of methods used in this work can be applied to other structures that are difficult to crystallize in large crystals and opens new perspectives, especially for investigations of aperiodic or otherwise complex metallic alloys.
Title:
Icosahedrite, Al63Cu24Fe13, the first natural quasicrystal
Authors:
Bindi, L; Steinhardt, PJ; Yao, N; Lu, PJ Author Full Names: Bindi, Luca; Steinhardt, Paul J.; Yao, Nan; Lu, Peter J.
Source:
AMERICAN MINERALOGIST 96 (5-6): 928-931 MAY-JUN 2011
Abstract:
Icosahedrite, ideally Al63Cu24Fe13, is a new mineral from the Khatyrka River, southeastern Chukhotka, Russia. It occurs as dark gray-black anhedral to subhedral grains up to 100 mu m across, closely associated with spine!, diopside, forsterite, nepheline, sodalite, corundum, stishovite, khatyrkite, cupalite, and an unnamed phase of composition AlCuFe. Icosahedrite is opaque with a metallic luster, possesses a gray streak, and is brittle with an uneven fracture. The density could not be determined. For quasicrystals, by definition, the structure is not reducible to a single three-dimensional unit cell, so neither cell parameters nor Z can be given. In plane-polarized incident light, icosahedrite exhibits neither bireflectance nor pleochroism. Between crossed polars, it is isotropic. Reflectance percentages (R-min = R-max) for the four standard COM wavelengths are 62.3 (471.1 nm), 60.6 (548.3 nm), 58.1 (586.6 nm), and 56.0 (652.3 nm), respectively. The X-ray powder pattern was indexed on the basis of six integer indices, as conventionally used with quasicrystals, where the lattice parameter (in six-dimensional notation) is measured to be a(6D) = 12.64 angstrom, with probable space group Fm (3) over bar (5) over bar. The four strongest X-ray powder-diffraction lines [d in angstrom (I/I-0)(n(1),n(2),n(3),n(4),n(5),n(6))] are: 2.006 (100) (4 (2) over bar0 042), 2.108 (90) (42 (2) over bar (2) over bar 22), 1.238 (30) (60 (4) over bar 064), and 3.41 (25) (31 (1) over bar (1) over bar 11). Average results of 34 electron-microprobe analyses gave, on the basis of total atoms = 100, the formula Al63.11Cu24.02Fe12.78Si0.03Co0.01Ca0.01Zn0.01Cr0.02Cl0.01. The simplified formula is Al63Cu24Fe13, which requires the mass fractions Al 43.02, Cu 38.60, Fe 18.38, total 100.00 wt%. The new mineral is named for the icosahedral symmetry of its internal atomic structure, as observed in its diffraction pattern. Both the new mineral and mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification, IMA (2010-042).
Title:
Twin relationships of 5M modulated martensite in Ni-Mn-Ga alloy
Authors:
Li, ZB; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Zongbin; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
ACTA MATERIALIA 59 (9): 3390-3397 MAY 2011
Abstract:
For Ni-Mn-Ga ferromagnetic shape memory alloys, the characteristic features of modulated martensite (including the number/shape of constituent variants, the inter-variant orientation relationship and the geometrical distribution of variant interfaces) determine the attainability of the shape memory effect. In the present work, a comprehensive microstructural and crystallographic investigation has been conducted on a bulk polycrystalline Ni50Mn28Ga22 alloy. As a first attempt, the orientation measurements by electron backscatter diffraction (EBSD) - using the precise information on the commensurate 5M modulated monoclinic superstructure (instead of the conventionally simplified non-modulated tetragonal structure) - were successfully performed to identify the crystallographic orientations on an individual basis. Consequently, the morphology of modulated martensite, the orientation relationships between adjacent variants and the characters of twin interfaces were unambiguously determined. With the thus-obtained full-featured image on the configuration of martensitic variants, the possibility of microstructural modification by proper mechanical "training" was further discussed. This new effort makes it feasible to explore the crystallographic/microstructural correlations in modulated martensite with high statistical reliability, which in turn provides useful guidance for optimizing the microstructure and shape memory performance. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Modulated anharmonic ADPs are intrinsic to aperiodic crystals: a case study on incommensurate Rb2ZnCl4
Authors:
Li, L; Wolfel, A; Schonleber, A; Mondal, S; Schreurs, AMM; Kroon-Batenburg, LMJ; van Smaalen, S Author Full Names: Li, Liang; Woelfel, Alexander; Schoenleber, Andreas; Mondal, Swastik; Schreurs, Antoine M. M.; Kroon-Batenburg, Loes M. J.; van Smaalen, Sander
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 67: 205-217 Part 3 JUN 2011
Abstract:
A combination of structure refinements, analysis of the superspace MEM density and interpretation of difference-Fourier maps has been used to characterize the incommensurate modulation of rubidium tetrachlorozincate, Rb2ZnCl4, at a temperature of T = 196 K, close to the lock-in transition at T (lock-in) = 192 K. The modulation is found to consist of a combination of displacement modulation functions, modulated atomic displacement parameters (ADPs) and modulated third-order anharmonic ADPs. Up to fifth-order Fourier coefficients could be refined against diffraction data containing up to fifth-order satellite reflections. The center-of-charge of the atomic basins of the MEM density and the displacive modulation functions of the structure model provide equivalent descriptions of the displacive modulation. Modulations of the ADPs and anharmonic ADPs are visible in the MEM density, but extracting quantitative information about these modulations appears to be difficult. In the structure refinements the modulation parameters of the ADPs form a dependent set, and ad hoc restrictions had to be introduced in the refinements. It is suggested that modulated harmonic ADPs and modulated third-order anharmonic ADPs form an intrinsic part, however small, of incommensurately modulated structures in general. Refinements of alternate models with and without parameters for modulated ADPs lead to significant differences between the parameters of the displacement modulation in these two types of models, thus showing the modulation of ADPs to be important for a correct description of the displacive modulation. The resulting functions do not provide evidence for an interpretation of the modulation by a soliton model.

Update: 27-May-2011

Title:
Spatially modulated antiferromagnetic structures in an easy-plane multiferroic
Authors:
Kulagin, NE; Popkov, AF; Zvezdin, AK Author Full Names: Kulagin, N. E.; Popkov, A. F.; Zvezdin, A. K.
Source:
PHYSICS OF THE SOLID STATE 53 (5): 970-977 MAY 2011
Abstract:
Possible types of spatially modulated periodic antiferromagnetic structures in a uniaxial rhombohedral multiferroic with BiFeO3 crystal symmetry have been studied depending on the ratio of the uniaxial anisotropy and magnetoelectric interaction parameters. It has been shown that, along with symmetric cycloid antiferromagnetic structures with zero transverse component of the antiferromagnetism vector, there are changes in the antiferromagnetism vector direction with both right and left nonzero components of the antiferromagnetic moment, which are branched from the high-symmetry spatially modulated distribution. These solutions degenerate into a homogeneous state at a critical value of the normalized easy-plane anisotropy parameter. The existence of the found spatially inhomogeneous antiferromagnetic states with an incommensurate period can lead to additional features in magnetoelectric properties in multiferroics of the type under consideration near magnetic phase transitions in electric and magnetic fields.
Title:
Short-range-order diffuse scattering in decagonal Ni-rich Al-Ni-Co quasicrystals
Authors:
Yamamoto, A Author Full Names: Yamamoto, Akiji
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 184203 MAY 12 2011
Abstract:
An analytical expression of the diffuse scattering (DS) intensity due to short-range order derived in a recent paper [A. Yamamoto, Acta Crystallogr. Sect. A 66, 372 (2010)] is applied to analyze DS intensities of the S1 phase at 1120 K and the quenched basic Ni rich (b-Ni) phase in decagonal Al70Ni22Co8 (d-Al70Ni22Co8) quasicrystals. The analysis is based on a microdomain model consisting of 20 angstrom clusters. The S1 and b-Ni phases are low-and high-temperature phases of d-Al70Ni22Co8 so that microdomains with the S1 phase structure are assumed to be formed in the b-Ni phase and vice versa. The intercluster correlation of the 20 angstrom clusters within the microdomains is assumed to be the same as that in a corresponding completely ordered structure up to the third intercluster distance similar or equal to 32 angstrom. It is demonstrated that simulated DS intensity distributions reproduce characteristic features in the observed DS intensity in these phases. This sugg! ests that the analysis of DS intensity is efficient for understanding phase transition mechanisms of quasicrystals. It also shows the effectiveness of the theory and applicability of cluster-based DS intensity calculations to real quasicrystals, which reduce the number of short-range-order parameters drastically.
Title:
Microstructure of Rapidly Solidified Al-12Zn-3Mg-1.5Cu Alloy with Zr and Sc Additions
Authors:
Litynska-Dobrzynska, L; Dutkiewicz, J; Maziarz, W; Goral, A Author Full Names: Litynska-Dobrzynska, Lidia; Dutkiewicz, Jan; Maziarz, Wojciech; Goral, Anna
Source:
MATERIALS TRANSACTIONS 52 (3): 309-314 Sp. Iss. SI MAR 2011
Abstract:
The rapid solidification of Al-12 Mg-1.5 Cu (in mass%) alloy was investigated in order to determine structure changes and the effect of Zr or Sc+Zr additions. Rapidly solidified ribbons with the thickness of 30-50 pm were obtained by a melt spinning technique. The alloys cast into a copper mould were used as a reference material. The mould cast alloys as well as the melt spun ribbons revealed the dendritic microstructure of alpha(Al) solid solution and eta(MgZn2) phase in the interdendritic areas. Additionally the T-Mg-32(Zn. Al)(49) phase with icosahedral quasicrystalline symmetry was found in the form of small particles located mainly at the wheel side in the Zr or Zr+Sc containing ribbons. The refinement of the microstructure and the reduction of volume fraction of the eta phase was observed in the ribbons. Large Al3Zr primary precipitates were observed in the mould cast alloy containing zirconium, while almost whole Zr in the ribbons dissolved in the aluminium solid ! solution. Annealing of ribbons at 400 degrees C led to the precipitation of spherical L1(2)-Al3Zr or Al-3(Sc, Zr) particles, coherent with the matrix. They could be responsible for the improvement of properties of the aluminium alloys by the retardation of recrystallization and grain growth. Plate like precipitates of metastable eta' phase appeared after ageing at 120 degrees C and led to the increase of microhardness up to about 230 HV. [doi:10.2320/matertrans.MB201009]
Title:
Neutron Diffraction Investigations of Magnetism in BiFeO3 Epitaxial Films
Authors:
Ratcliff, W; Kan, D; Chen, WC; Watson, S; Chi, SX; Erwin, R; McIntyre, GJ; Capelli, SC; Takeuchi, I Author Full Names: Ratcliff, William, II; Kan, Daisuke; Chen, Wangchun; Watson, Shannon; Chi, Songxue; Erwin, Ross; McIntyre, Garry J.; Capelli, Sylvia C.; Takeuchi, Ichiro
Source:
ADVANCED FUNCTIONAL MATERIALS 21 (9): 1567-1574 MAY 10 2011
Abstract:
The recovery of a modulated magnetic structure in epitaxial BiFeO3 thin films as revealed by neutron diffraction is reported. The magnetic structure in thin films is found to strongly depend on substrate orientation. The substrate orientation causes different strain-relaxation processes resulting in different thin-film crystal structures. The (110) oriented film with a monoclinic structural phase has a single-domain modulated magnetic structure where the magnetic moment lies in the HHL plane. For the (111) oriented film that has a rhombohedral structure, a modulated structure superimposed on the G-type antiferromagnetic order is found. These results indicate that slight structural modifications in the BiFeO3 thin film cause drastic changes in the magnetic structure.

Update: 20-May-2011

Title:
Ground State of the Quasi-1D Compound BaVS3 Resolved by Resonant Magnetic X-Ray Scattering
Authors:
Leininger, P; Ilakovac, V; Joly, Y; Schierle, E; Weschke, E; Bunau, O; Berger, H; Pouget, JP; Foury-Leylekian, P Author Full Names: Leininger, Ph.; Ilakovac, V.; Joly, Y.; Schierle, E.; Weschke, E.; Bunau, O.; Berger, H.; Pouget, J. -P.; Foury-Leylekian, P.
Source:
PHYSICAL REVIEW LETTERS 106 (16): Art. No. 167203 APR 21 2011
Abstract:
Resonant magnetic x-ray scattering near the vanadium L-2,L-3-absorption edges has been used to investigate the low temperature magnetic structure of high quality BaVS3 single crystals. Below T-N = 31 K, the strong resonance revealed a triple-incommensurate magnetic ordering at the wave vector (0.226 0.226 xi) in hexagonal notation, with xi = 0.033. The azimuthal-angle dependence of the scattering signal and time-dependent density functional theory simulations indicate an antiferromagnetic order within the ab plane with the spins polarized along a in the monoclinic structure.
Title:
Non-nesting spin-density-wave antiferromagnetism in FeAs from first principles
Authors:
Parker, D; Mazin, II Author Full Names: Parker, David; Mazin, I. I.
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 180403 MAY 2 2011
Abstract:
The antiferromagnetic (AFM) state of FeAs is very different from that of the FeAs-based superconductor parent compounds, and it is rather complicated, with the Fe spins forming an incommensurate magnetic spiral pattern with a wavelength of about 15 A. To model this, we perform first-principles calculations and find the nearest-neighbor AFM ordering to be energetically favorable, with the lowest-energy pattern reproducing the experimentally found nearest-neighbor correlations. Other AFM orderings are also very stable, although higher in energy. Unlike in the superconductor parent compounds, the Fermi-surface geometry thus plays a small role. We calculate the bare Lindhard susceptibility in the AFM state and find that the observed spin-density-wave ordering vector Q similar or equal to (0,0,0.4) is not that given by this calculation. This is again unlike the superconductor parent compounds, which generally show a magnetic pattern matching the Lindhard susceptibility maximum. Thus in FeAs, the observed pattern must be due to a subtler mechanism.
Title:
Fermionic Representation of Two-Dimensional Dimer Models
Authors:
Grande, HLC; Salinas, SR; da Costa, FA Author Full Names: Casa Grande, Helder L.; Salinas, S. R.; da Costa, F. A.
Source:
BRAZILIAN JOURNAL OF PHYSICS 41 (1): 86-93 MAY 2011
Abstract:
Dimer models in two dimensions give rise to well-known statistical lattice problems, which can be exactly solved by the same combinatorial techniques associated with the Ising model and which have been used to account for the phase transitions in a number of physically interesting systems. More recently, dimer models have been regarded as classical limits of the quantum ground state of some antiferromagnetic systems. We then revisit an early transfer-matrix calculation for the dimer model on the simple square lattice. We write a spin representation for the transfer matrix associated with the canonical partition function of two paradigmatic dimers models, on the 4-8 lattice, with an Ising-type transition, and on the brick lattice, with a peculiar commensurate-incommensurate transition. Using standard techniques, the problem is reduced to the calculation of the eigenvalues of a system of free fermions.

Update: 13-May-2011

Title:
Effects of Reciprocating Extrusion on Microstructures and Mechanical Properties of as-Cast Mg-0.85Zn-0.15Y-0.6Zr Alloys
Authors:
Li, AT; Wang, JC; Si, L; Lai, YT; Yang, GC Author Full Names: Li Antao; Wang Jincheng; Si Lin; Lai Yunting; Yang Gencang
Source:
RARE METAL MATERIALS AND ENGINEERING 40 (3): 515-518 MAR 2011
Abstract:
Effects of reciprocating extrusion on the microstructures and mechanical properties of as-cast Mg-0.85Zn-0.15Y-0.6Zr alloys enforced by quasicrystal particles were investigated by OM, SEM and XRD. The results show that the reciprocating extrusion can greatly refine the microstructure of as-cast Mg-0.85Zn-0.15Y-0.6Zr alloy, and make I phase relatively uniformly distribute in the alpha-Mg matrix. Compared with that of the as-cast alloy, the yield strength, tensile strength and elongation of the Mg-0.85Zn-0.15Y-0.6Zr magnesium alloys after reciprocating extrusion are increased by 75.8%, 43.2% and 35%, respectively.
Title:
Precipitation hardening through sacrificial phase in aluminum-quasicrystal metal matrix composites
Authors:
Kim, SD; Ko, DS; Jang, WK; Shin, KS; Kim, YW Author Full Names: Kim, Sung-Dae; Ko, Dong-Su; Jang, Woo Kil; Shin, Kwang Seon; Kim, Young-Woon
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 528 (13-14): 4845-4848 MAY 24 2011
Abstract:
Al65Cu20Fe15 quasi-crystalline phase worked as a donor of copper by phase dissociation to form Al-Cu-Mg precipitates in mechanically alloyed, Al-Mg-based composite. Fine precipitates played a major role in the improvement of the strength up to 1 GPa of compressive yield strength. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Temperature effects in ion-electron emission of graphite quasicrystal
Authors:
Avilkina, VS; Andrianova, NN; Borisov, AM; Virgiliev, YS; Kulikauskas, VS; Mashkova, ES; Pitirimova, EA Author Full Names: Avilkina, V. S.; Andrianova, N. N.; Borisov, A. M.; Virgiliev, Yu. S.; Kulikauskas, V. S.; Mashkova, E. S.; Pitirimova, E. A.
Source:
JOURNAL OF SURFACE INVESTIGATION-X-RAY SYNCHROTRON AND NEUTRON TECHNIQUES 5 (2): 221-224 APR 2011
Abstract:
Analysis of the comparative influence of complete amorphization of a polycrystalline graphite surface layer and radiation-induced disordering of highly oriented pyrolytic graphite UPV-1T on the character of temperature dependences of the ion-electron emission yield under high-dose (10(18)-10(19) ion/cm(2)) 30 keV Ar+ ion irradiation has been carried out.
Title:
Plastic analysis of the crack problem in two-dimensional decagonal Al-Ni-Co quasicrystalline materials of point group 10, (10)over-bar
Authors:
Li, W; Fan, TY Author Full Names: Li Wu; Fan Tian You
Source:
CHINESE PHYSICS B 20 (3): Art. No. 036101 MAR 2011
Abstract:
The fundamental plastic nature of the quasicrystalline materials remains an open problem due to its essential complicacy. By developing the proposed generalized cohesive force model, the plastic deformation of crack in point group 10, (10) over bar decagonal quasicrystals is analysed strictly and systematically. The crack tip opening displacement (CTOD) and the size of the plastic zone around the crack tip are determined exactly. The quantity of the crack tip opening displacement can be used as a parameter of nonlinear fracture mechanics of quasicrystalline material. In addition, the present work may provide a way for the plastic analysis of quasicrystals.
Title:
The relation between the generalised Eshelby integral and the generalised BCS and DB models
Authors:
Fan, TY; Fan, L Author Full Names: Fan Tian-You; Fan Lei
Source:
CHINESE PHYSICS B 20 (3): Art. No. 036102 MAR 2011
Abstract:
The generalised BCS dislocation group model and the generalised DB atomic cohesive force zone model have obtained the same results on nonlinear fracture study of some one-, two- and three-dimensional quasicrystals. This work reveals some inherent connection between the two models, and finds that their common basis is the generalised Eshelby integral based on the generalised Eshelby energy momentum tensor for quasicrystals. Further applications of the theory in solving nonlinear fracture problems of the materials are also discussed.

Update: 6-May-2011

Title:
Single crystal growth of Al-based intermetallic phases being approximants to quasicrystals
Authors:
Gille, P; Bauer, B; Hahne, M; Smontara, A; Dolinsek, J Author Full Names: Gille, Peter; Bauer, Birgitta; Hahne, Michael; Smontara, Ana; Dolinsek, Janez
Source:
JOURNAL OF CRYSTAL GROWTH 318 (1): 1016-1020 MAR 1 2011
Abstract:
Decagonal (d) quasicrystals are formed in a number of Al-based ternary systems with d-AlCoNi being the best studied decagonal phase. They are highly anisotropic showing unusual properties of e.g. electric and thermal transport when measured along the periodic or quasiperiodic directions. For a long time, this has been attributed to the lack of periodicity in certain crystallographic orientations. Some neighbouring phases in the Al-Co-Ni system as well as in related ternaries consist of the same type of large icosahedral clusters, but are periodic in all three directions, sometimes with very large unit cells. Therefore, they are called approximants to the decagonal quasicrystals. They allow comparative studies of these phases as to judge whether some unusual properties of quasicrystals arise from the lack of periodicity or from the common atomic arrangements. Additional to decagonal AlCoNi quasicrystals, various approximants (monoclinic Al-13(Co,Ni)(4), orthorhombic Al13CO4, orthorhombic Al-4(Cr,Fe), monoclinic Al13Fe4 and its ternary extensions Al-13(Fe,Cr)(4) and Al-13(Fe,Ni)(4)) were grown by the Czochralski method as large single crystals as to carry out transport orientation-dependent measurements. It could be found that transport properties show remarkably similar anisotropic features when comparing corresponding crystallographic directions in these phases that can be related to the periodic stacking of layers. (C) 2010 Elsevier B.V. All rights reserved.

Update: 29-Apr-2011

Title:
Evidence for Charge Orbital and Spin Stripe Order in an Overdoped Manganite
Authors:
Ulbrich, H; Senff, D; Steffens, P; Schumann, OJ; Sidis, Y; Reutler, P; Revcolevschi, A; Braden, M Author Full Names: Ulbrich, H.; Senff, D.; Steffens, P.; Schumann, O. J.; Sidis, Y.; Reutler, P.; Revcolevschi, A.; Braden, M.
Source:
PHYSICAL REVIEW LETTERS 106 (15): Art. No. 157201 APR 12 2011
Abstract:
Overdoped La0.42Sr1.58MnO4 exhibits a complex ordering of charges, orbitals, and spins. Neutron diffraction experiments reveal three incommensurate and one commensurate order parameters to be tightly coupled. The position and the shape of the distinct superstructure scattering as well as higher-order signals are inconsistent with a harmonic charge and spin-density-wave picture but point to a stripe arrangement in which ferromagnetic zigzag chains are disrupted by excess Mn4+.
Title:
Shape of spin density wave versus temperature in AFe(2)As(2) (A = Ca, Ba, Eu): A Mossbauer study
Authors:
Blachowski, A; Ruebenbauer, K; Zukrowski, J; Rogacki, K; Bukowski, Z; Karpinski, J Author Full Names: Blachowski, A.; Ruebenbauer, K.; Zukrowski, J.; Rogacki, K.; Bukowski, Z.; Karpinski, J.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134410 APR 11 2011
Abstract:
Parent compounds AFe(2)As(2) (A = Ca, Ba, Eu) of the 122 family of the iron-based superconductors have been studied by 57Fe Mossbauer spectroscopy in the temperature range 4.2-similar to 300 K. Spin density waves (SDW) have been found with some confidence. They are either incommensurate with the lattice period or the ratio of the respective periods is far away from the ratio of small integers. SDW shape is very unconventional (i.e., differs from the sinusoidal shape). Magnetic order starts with lowered temperature as narrow sheets of the significant electron spin density separated by areas with very small spin density. Magnetic sheets are likely to be ordered in the alternate antiferromagnetic fashion as the material as a whole behaves similarly to the collinear antiferromagnet. A further lowering of temperature simply expands sheet thickness leading to the near triangular SDW. Finally, sheets fill the whole available space and the almost rectangular shape of the SDW is reached. The substantial maximum amplitude of SDW appears at the temperature just below the magnetic onset temperature, and this maximum amplitude increases slightly with lowering temperature. The square root from the mean squared hyperfine field behaves versus temperature according to the universality class (1,2) (i.e., with the electronic spin space having dimensionality equal to unity and the real space having dimensionality equal to 2). The more or less pronounced tail above transition temperature due to the development of incoherent SDW is seen.
Title:
Magnetic phase diagram of alpha-NdIr2Si2
Authors:
Mihalik, M; Pospisil, J; Hoser, A; Sechovsky, V Author Full Names: Mihalik, M.; Pospisil, J.; Hoser, A.; Sechovsky, V.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134414 APR 12 2011
Abstract:
Magnetism in alpha-NdIr2Si2 single crystals has been probed through specific-heat, magnetization, magnetic susceptibility, and electrical resistivity measurements as a function of temperature, under an applied magnetic field, and for the magnetization curves under high hydrostatic pressures. Neutron diffraction experiments performed with powder and single-crystal samples were focused on microscopic aspects. Two collinear (Nd moments along the c axis) antiferromagnetic phases are found at low temperatures: a longitudinal sine-modulated structure with the magnetic propagation vector k = (0 0 5/6) at temperatures 18.2(2) K < T < 32.3(3) K (+T-N) and a simple AF1-type structure; k = (0 0 1/2) for T < 18.2(2) K (+T-t). Both of the magnetically ordered phases can be destabilized by applying a strong magnetic field along the c axis. The character of the unusual magnetic-field-induced phases is discussed, and the complex magnetic phase diagram is constructed. Applied hydrostatic pressure yields an increase of both TN and Tt. The determined physical properties of a-NdIr2Si2 are discussed in the context of behavior of alpha-PrIr2Si2.
Title:
Long-range magnetic interactions in the multiferroic antiferromagnet MnWO4
Authors:
Ye, F; Fishman, RS; Fernandez-Baca, JA; Podlesnyak, AA; Ehlers, G; Mook, HA; Wang, YQ; Lorenz, B; Chu, CW Author Full Names: Ye, Feng; Fishman, Randy S.; Fernandez-Baca, Jaime A.; Podlesnyak, Andrey A.; Ehlers, Georg; Mook, Herbert A.; Wang, Yaqi; Lorenz, Bernd; Chu, C. W.
Source:
PHYSICAL REVIEW B 83 (14): Art. No. 140401 APR 12 2011
Abstract:
The spin-wave excitations of the multiferroic MnWO4 have been measured in its low-temperature collinear commensurate phase using high-resolution inelastic neutron scattering. These excitations can be well described by a Heisenberg model with competing long-range exchange interactions and a single-ion anisotropy term. The magnetic interactions are strongly frustrated within the zigzag spin chain along the c axis and between chains along the a axis, while the coupling between spin along the b axis is much weaker. The balance of these interactions results in the noncollinear incommensurate spin structure associated with the magnetoelectric effect, and the perturbation of the magnetic interactions leads to the observed rich phase diagrams of the chemically doped materials. This delicate balance can also be tuned by the application of external electric or magnetic fields to achieve magnetoelectric control of this type of materials.
Title:
Dynamic microstructural changes during hot extrusion and mechanical properties of a Mg-5.0 Zn-0.9 Y-0.16 Zr (wt.%) alloy
Authors:
Xu, SW; Zheng, MY; Kamado, S; Wu, K; Wang, GJ; Lv, XY Author Full Names: Xu, S. W.; Zheng, M. Y.; Kamado, S.; Wu, K.; Wang, G. J.; Lv, X. Y.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 528 (12): 4055-4067 MAY 15 2011
Abstract:
In this study, firstly, dynamic microstructural changes of an as-cast Mg-5.0 Zn-0.9 Y-0.16 Zr (wt.%) alloy (designated ZWK510) during hot extrusion at 350 degrees C and a ram speed of 3.33 mm s(-1) was systematically investigated by electron backscattering diffraction (EBSD) analysis. The dynamic recrystallization (DRX) mechanism during hot extrusion was discussed. Then, the effect of microstructure and texture on the mechanical properties of the as-extruded alloy specimens at room temperature was discussed. The as-cast ZWK510 alloy consists of a-Mg and quasicrystalline I-phase. During hot extrusion at 350 degrees C, the main DRX mechanism is the continuous DRX near the original grain boundaries. The I-phase can accelerate the DRX behavior near these areas by obstructing the slip of dislocations. The deformation twins and massive blocky substructures formed in original grains can coordinate the DRX process near the original grain boundaries, however the DRX seldom occurs inside of these area. After further deformation, these deformation twins and massive blocky substructures are elongate I along the material flow and become so-called unDRXed area, then a bimodal "necklace structure" composed of fine DRXed grains of about 2.1 mu m and unrecrystallized coarse area is formed. The extruded ZWK510 alloy shows a DRX ratio of about 58% and a typical basal fiber texture of (0 0 0 1) < 1 0 (1) over bar 0 >(matrix)// extrusion direction (ED). In the DRXed area around the crushed eutectic I-phase a large number or fine I-phase precipitates are observed pinning at the newly formed DRXed grain boundaries. The 0.2% proof strength and the ultimate tensile strength of the extruded ZWK510 alloy specimen are 317 and 363 MPa, respectively, with an elongation to failure of 12%, which have been attributed to strong basal fiber texture, refined grain size as well as the existence of fine precipitates formed during the hot extrusion. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Change in local environment upon quasicrystallization of Zr-Cu glassy alloys by addition of Pd and Pt
Authors:
Saida, J; Sanada, T; Sato, S; Imafuku, M; Ohnuma, M; Ohkubo, T; Hono, K; Matsubara, E Author Full Names: Saida, Junji; Sanada, Takashi; Sato, Shigeo; Imafuku, Muneyuki; Ohnuma, Masato; Ohkubo, Tadakatsu; Hono, Kazuhiro; Matsubara, Eiichiro
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (17): Art. No. 175303 MAY 4 2011
Abstract:
The effects of Pd and Pt, which are known quasicrystal (QC)-forming elements, on the local atomic structure in Zr70Cu30 glassy alloys are investigated. A QC phase precipitates from a glassy phase above a certain temperature by a cooperative-like motion of icosahedral clusters. Quasicrystallization is accompanied by a significant change in the local environment around the Zr atoms and a slight change around the noble metal. However, the local environment around the Cu atoms remains almost the same during QC formation. It is suggested that two types of icosahedral polyhedra exist in the glassy state: one has a relatively perfect icosahedral structure formed around the Zr atoms. The other is in a distorted state around the Cu atoms. We speculate that the medium-range order (i.e. QC nucleus) has a Zr-centered icosahedral cluster as its core, and the QC grows via aggregation of possible clusters in the initial stage. Pd or Pt atoms stabilize and/or connect individual Zr-centered icosahedral clusters, facilitating the formation of the nucleus and growth of the QC phase.
Title:
Microstructure and properties of Ni-Mn-Ga alloys produced by rapid solidification and pulsed electric current sintering
Authors:
Soderberg, O; Brown, D; Aaltio, I; Oksanen, J; Syren, J; Pulkkinen, H; Hannula, SP Author Full Names: Soderberg, Outi; Brown, David; Aaltio, Ilkka; Oksanen, Jussi; Syren, Jesse; Pulkkinen, Heikki; Hannula, Simo-Pekka
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (20): 5981-5987 MAY 19 2011
Abstract:
Ni-Mn-Ga alloys were compacted using pulsed electric current sintering (PECS) at 850-875 degrees C (50 MPa, 8 min) of flake-like powders made from the rapidly quenched melt-spun ribbons. Two kinds of ribbons were used: one made with a relatively slow wheel speed (6 m/s; average grain size similar to 14 mu m), and another with a faster wheel speed (23 m/s; average grain size similar to 5 mu m). Both sets of flake-like powders consisted of a mixture of non-modulated martensite (NM) and seven-layered modulated martensite (7M) structure. The amount of NM was greater in the slower speed material, while the other one exhibited mostly the 7M structure. These crystal structures were inherited by the sintered samples. In the compacts having the NM structure the multi-step martensitic reaction overlapped with the magnetic transition, and the Curie temperatures during heating and cooling differed from each other. In the compacts having mainly 7M structure the Curie point was about 100 degrees C and the martensitic transition took place in the paramagnetic state, while the intermartensitic one occurred in the region of 60-85 degrees C. This material demonstrated good magnetic properties and saturation magnetization, at best similar to 50 emu/g. Mechanical properties of the compacts were good, and comparable to those of the polycrystalline Ni-Mn-Ga samples in compression. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Phase Transitions in Incommensurate Composites
Authors:
Janssen, T Author Full Names: Janssen, T.
Source:
FERROELECTRICS 412: 4-7 2011
Abstract:
Incommensurate phases show a rich variety of phase transitions. We discuss here two types of phase transitions in a class of aperiodic crystals, the incommensurate composites. A model is presented to understand a recently observed phase transition in nona-decane-urea.
Title:
Incommensurate Phases Induced by a Weak Electric Field
Authors:
Sannikov, DG Author Full Names: Sannikov, D. G.
Source:
FERROELECTRICS 412: 8-11 2011
Abstract:
It is shown that an external electric field E-3 (even if it is arbitrary weak) can induce an incommensurate phase in the crystal. The components M-1 and M-2 of the magnetic moment M-i are chosen as the order parameter components.
Title:
Growth temperature dependent graphene alignment on Ir(111)
Authors:
Hattab, H; N'Diaye, AT; Wall, D; Jnawali, G; Coraux, J; Busse, C; van Gastel, R; Poelsema, B; Michely, T; Heringdorf, FJMZ; Horn-von Hoegen, M Author Full Names: Hattab, H.; N'Diaye, A. T.; Wall, D.; Jnawali, G.; Coraux, J.; Busse, C.; van Gastel, R.; Poelsema, B.; Michely, T.; Heringdorf, F. -J. Meyer Zu; Horn-von Hoegen, M.
Source:
APPLIED PHYSICS LETTERS 98 (14): Art. No. 141903 APR 4 2011
Abstract:
The morphology of graphene monolayers on Ir(111) prepared by thermal decomposition of ethylene between 1000 and 1530 K was studied with high resolution low energy electron diffraction. In addition to a well-oriented epitaxial phase, randomly oriented domains are observed for growth temperatures between 1255 and 1460 K. For rotational angles of +/- 3 degrees around 30 degrees these domains lock-in in a 30 degrees oriented epitaxial phase. Below 1200 K the graphene layer exhibits high disorder and structural disintegrity. Above 1500 K the clear moire spots reflect graphene in a single orientation epitaxial incommensurate phase. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3548546]

Update: 22-Apr-2011

Title:
Lattice study of the incommensurate omega phase transition in Zr-Nb alloys
Authors:
Kubo, H; Farjami, S Author Full Names: Kubo, H.; Farjami, S.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134302 APR 7 2011
Abstract:
The stability of the incommensurate omega phase has been studied in the scheme of the Landau-Lifshitz (L-L) free-energy model reformed for the weak first-order phase transition. It is revealed that the negative third-order term of the L-L expansion drives the transition and works, in competition with the second-harmonic term, to form the modulated omega phase; moreover, it functions to maintain soliton walls with constant width against temperature changes. The modulated omega phase is elucidated to have a microstructure with the sequence of subvariants-omega 1-omega 3-omega 2-separated by soliton walls of anti-omega structure. A series of primitive activation units of the modulated omega phase, which can be depicted in a phase diagram, is obtained in the Zr-20 wt% Nb-alloy system by analyzing the L-L free-energy function with the appropriate numerical calculations.
Title:
Anomalous vibrational dynamics in the Mg2Zn11 phase
Authors:
Euchner, H; Mihalkovic, M; Gahler, F; Johnson, MR; Schober, H; Rols, S; Suard, E; Bosak, A; Ohhashi, S; Tsai, AP; Lidin, S; Gomez, CP; Custers, J; Paschen, S; de Boissieu, M Author Full Names: Euchner, H.; Mihalkovic, M.; Gaehler, F.; Johnson, M. R.; Schober, H.; Rols, S.; Suard, E.; Bosak, A.; Ohhashi, S.; Tsai, A. -P.; Lidin, S.; Gomez, C. Pay; Custers, J.; Paschen, S.; de Boissieu, M.
Source:
PHYSICAL REVIEW B 83 (14): Art. No. 144202 APR 7 2011
Abstract:
We present a combined experimental and theoretical study of the structure and the lattice dynamics in the complex metallic alloy Mg2Zn11, by means of neutron and x-ray scattering, as well as ab initio and empirical potential calculations. Mg2Zn11 can be seen as an intermediate step in structural complexity between the simple Laves-phase MgZn2 on one side, and the complex 1/1 approximants and quasicrystals ZnMgAl and Zn(Mg)Sc on the other. The structure can be described as a cubic packing of a triacontahedron whose center is partially occupied by a Zn atom. This partially occupied site turned out to play a major role in understanding the lattice dynamics. Data from inelastic neutron scattering evidence a Van Hove singularity in the vibrational spectrum of Mg2Zn11 for an energy as low as 4.5 meV, which is a unique feature for a nearly-close-packed metallic alloy. This corresponds to a gap opening at the Brillouin zone boundary and an interaction between a low-lying optical branch and an acoustic one, as could be deduced from the dispersion relation measured by inelastic x-ray scattering. Second, the measured phonon density of states exhibits many maxima, indicating strong mode interactions across the whole energy range. The origin of the low-energy modes in Mg2Zn11 and other features of the vibrational spectra are studied, using both ab initio and empirical potential calculations. A detailed analysis of vibrational eigenmodes is presented, linking features in the vibrational spectrum to atomic motions within structural building blocks.
Title:
Effect of particle size and annealing on spin and phonon behavior in TbMnO3
Authors:
Das, R; Jaiswal, A; Adyanthaya, S; Poddar, P Author Full Names: Das, Raja; Jaiswal, Adhish; Adyanthaya, Suguna; Poddar, Pankaj
Source:
JOURNAL OF APPLIED PHYSICS 109 (6): Art. No. 064309 MAR 15 2011
Abstract:
Interest has grown to study TbMnO3 as it was recently reported to show a gigantic magnetoelectric effect. Here, we report the synthesis and detailed magnetic and Raman spectroscopy study on TbMnO3 particles of size similar to 25 nm and 2-3 mu m, respectively. The incommensurate-commensurate (lock-in) transition, usually observed at 27 K for bulk phase of TbMnO3 was not observed in susceptibility versus T curve but was seen at 30 K in the coercivity versus T curve in similar to 25 nm particles. This transition, which is due to the spin modulation length scale, gets weakened in nanosize due to the increased intrinsic lattice strain observed in 2-3 mu m particles, due to the effect of increased particle size. The increased value of magnetization in the 2-3 mu m sample was attributed to double exchange interactions between Mn+3 and Mn+4 spins. The role of annealing related effects on the fate of the Neel temperature for TbMnO3 was investigated. Raman spectroscopy indicated a decrease in the lattice distortion for similar to 25 nm particles. (c) 2011 American Institute of Physics. [doi:10.1063/1.3563571]
Title:
Crystallographic relationship of orthorhombic phi-Al5Mg11Zn4 phase to icosahedral quasicrystalline phase
Authors:
Singh, A; Rosalie, JM; Somekawa, H; Mukai, T Author Full Names: Singh, Alok; Rosalie, J. M.; Somekawa, H.; Mukai, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (14): 4676-4681 APR 7 2011
Abstract:
The orthorhombic phi-Al5Mg11Zn4 phase is known to be related to quasicrystalline phases, but the exact relationship has not been shown yet. In this study, the relationship of this phase to the icosahedral quasicrystalline phase is explored through analysis of the electron diffraction patterns. It is shown that icosahedral coordinations in three orientations occur in the unit cell - one with three mutually perpendicular twofold axes along (100) of the unit cell, and two with a twofold axis along [100] and a fivefold along [001]. In this, this phase is similar to aluminum and zinc based hexagonal phases which are related to quasicrystals. (C) 2011 Elsevier B.V. All rights reserved.

Update: 15-Apr-2011

Title:
Evolution of Paramagnetic Quasiparticle Excitations Emerged in the High-Field Superconducting Phase of CeCoIn5
Authors:
Kumagai, K; Shishido, H; Shibauchi, T; Matsuda, Y Author Full Names: Kumagai, K.; Shishido, H.; Shibauchi, T.; Matsuda, Y.
Source:
PHYSICAL REVIEW LETTERS 106 (13): Art. No. 137004 MAR 30 2011
Abstract:
We present In-115 NMR measurements in a novel thermodynamic phase of CeCoIn5 in a high magnetic field, where exotic superconductivity exists with the incommensurate spin-density wave order. We show that the NMR spectra in this phase provide direct evidence for the emergence of the spatially distributed normal quasiparticle regions. The quantitative analysis for the field evolution of the paramagnetic magnetization and newly emerged low-energy quasiparticle density of states is consistent with the nodal plane formation, which is characterized by an order parameter in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The NMR spectra also suggest that the spatially uniform spin-density wave is induced in the FFLO phase.
Title:
Magnetic structure of epitaxial multiferroic BiFeO3 films with engineered ferroelectric domains
Authors:
Ke, X; Zhang, PP; Baek, SH; Zarestky, J; Tian, W; Eom, CB Author Full Names: Ke, X.; Zhang, P. P.; Baek, S. H.; Zarestky, J.; Tian, W.; Eom, C. B.
Source:
PHYSICAL REVIEW B 82 (13): Art. No. 134448 OCT 29 2010
Abstract:
We report on neutron scattering and piezoresponse force microscopy studies of multiferroic BiFeO3 films epitaxially grown on vicinal SrTiO3 substrates. We find that these BiFeO3 films exhibit a G-type antiferromagnetic structure modulated with cycloidal spiral magnetic ordering with the features of magnetic domains depending upon the ferroelectric domain states: a single antiferromagnetic domain for the films with a ferroelectric monodomain while two- or multiantiferromagnetic domains existing in the films displaying two- or four-ferroelectric variants, respectively. These results imply the correlation between ferroelectric and magnetic order parameters in the BiFeO3 films and the expected strong magnetoelectric coupling makes these multiferroic films promising candidates for device applications with the capability to tune the magnetism using an electric field.
Title:
Magnetic structure of epitaxial multiferroic BiFeO3 films with engineered ferroelectric domains
Authors:
Ke, X; Zhang, PP; Baek, SH; Zarestky, J; Tian, W; Eom, CB Author Full Names: Ke, X.; Zhang, P. P.; Baek, S. H.; Zarestky, J.; Tian, W.; Eom, C. B.
Source:
PHYSICAL REVIEW B 82 (13): Art. No. 134448 OCT 29 2010
Abstract:
We report on neutron scattering and piezoresponse force microscopy studies of multiferroic BiFeO3 films epitaxially grown on vicinal SrTiO3 substrates. We find that these BiFeO3 films exhibit a G-type antiferromagnetic structure modulated with cycloidal spiral magnetic ordering with the features of magnetic domains depending upon the ferroelectric domain states: a single antiferromagnetic domain for the films with a ferroelectric monodomain while two- or multiantiferromagnetic domains existing in the films displaying two- or four-ferroelectric variants, respectively. These results imply the correlation between ferroelectric and magnetic order parameters in the BiFeO3 films and the expected strong magnetoelectric coupling makes these multiferroic films promising candidates for device applications with the capability to tune the magnetism using an electric field.
Title:
Analysis and modelling of structural disorder by the use of the three-dimensional pair distribution function method exemplified by the disordered twofold superstructure of decagonal Al-Cu-Co
Authors:
Schaub, P; Weber, T; Steurer, W Author Full Names: Schaub, Philippe; Weber, Thomas; Steurer, Walter
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 44: 134-149 Part 1 FEB 2011
Abstract:
Theoretical concepts and the practical application of the three-dimensional pair distribution function (3D-PDF) method and its variant, the three-dimensional delta-pair distribution function (3D-delta PDF) method, are presented. In analogy to traditional Patterson function analysis, advantage is taken of the Fourier transformation either of the full three-dimensional diffraction pattern of a disordered crystal or just of the isolated diffuse scattering, respectively. By the use of three-dimensional information, analysis of disorder becomes straightforward, and it becomes possible to investigate far more complicated structures than is feasible with well established powder diffraction-based PDF analysis. Compared to more traditional modelling techniques, such as Monte Carlo simulation, the 3D-delta PDF provides direct access to disorder models and allows selective modelling of distinct structural features, which are, in contrast to reciprocal space, well localized in PDF space. The principles of the 3D-delta PDF approach are exemplified using an analysis of the twofold (similar to 8 A) periodic superstructure of a decagonal Al65Cu20Co15 quasicrystal. Although analysis of disorder in quasicrystals is far more demanding than in the case of periodic structures, details of the disordered structure could be elucidated. The superstructure is found to be built from columnar units, having a maximum diameter of similar to 14.5 A. The lateral correlation between these columns is weak. Internally, the columns consist of a long-range-ordered alternation of flat and puckered layers. The development of the model and the atomic structure of the columns are described in detail.
Title:
Zn2LiGaO4, Wurtzite- Derived Wide Band Gap Oxide
Authors:
Omata, T; Kita, M; Nose, K; Tachibana, K; Otsuka-Yao-Matsuo, S Author Full Names: Omata, Takahisa; Kita, Masao; Nose, Katsuhiro; Tachibana, Kosuke; Otsuka-Yao-Matsuo, Shinya
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS 50 (3): Art. No. 031102 MAR 2011
Abstract:
The phase that appeared in the pseudo-binary LiGaO2-ZnO system was investigated by powder X-ray diffraction (XRD), selected area electron diffraction by transmission electron microscopy (TEM-SAD) and Raman spectroscopy, especially focusing on the 0.5(LiGaO2)(1/2) - 0.5ZnO composition. A new quaternary wurtzite-derived Zn2LiGaO4 phase was found in this system. The TEM-SAD indicated that the phase possesses an incommensurately modulated ordering. The optical energy band gap of Zn2LiGaO4 was determined to be similar to 4: 0 eV from its diffuse reflectance and photoluminescence spectra; and it was suggested that the Zn2LiGaO4 was a direct semiconductor. (C) 2011 The Japan Society of Applied Physics
Title:
Three dimensional elastodynamics of 2D quasicrystals: The derivation of the time-dependent fundamental solution
Authors:
Yakhno, VG; Yaslan, HC Author Full Names: Yakhno, V. G.; Yaslan, H. Cerdik
Source:
APPLIED MATHEMATICAL MODELLING 35 (6): 3092-3110 JUN 2011
Abstract:
The time-dependent differential equations of elasticity for 20 quasicrystals with general structure of anisotropy (dodecagonal, octagonal, decagonal, pentagonal, hexagonal, triclinic) are considered in the paper. These equations are written in the form of a vector partial differential equation of the second order with symmetric matrix coefficients. The fundamental solution (matrix) is defined for this vector partial differential equation. A new method of the numerical computation of values of the fundamental solution is suggested. This method consists of the following: the Fourier transform with respect to space variables is applied to vector equation for the fundamental solution. The obtained vector ordinary differential equation has matrix coefficients depending on Fourier parameters. Using the matrix computations a solution of the vector ordinary differential equation is numerically computed. Finally, applying the inverse Fourier transform numerically we find the values of the fundamental solution. Computational examples confirm the robustness of the suggested method for 2D quasicrystals with arbitrary type of anisotropy. (C) 2010 Elsevier Inc. All rights reserved.
Title:
Determination of the orientation relationship between austenite and incommensurate 7M modulated martensite in Ni-Mn-Ga alloys
Authors:
Li, ZB; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Z. B.; Zhang, Y. D.; Esling, C.; Zhao, X.; Zuo, L.
Source:
ACTA MATERIALIA 59 (7): 2762-2772 APR 2011
Abstract:
For Ni-Mn-Ga ferromagnetic shape memory alloys, a large magnetic-field-induced strain could be reached through the reorientation of martensitic variants in the martensite state. Owing to the collective and displacive nature of the austenite to martensite transformation, a certain orientation relationship (OR) between the parent and the product phase is required to minimize the transformation strain and the strain energy generated, which brings about self-accommodating groups of martensitic variants with specific orientation correlations. In this work, the microstructural and crystallographic characteristics of martensitic variants in a polycrystalline Ni50Mn30Ga20 alloy were investigated by electron backscatter diffraction analysis. With accurate orientation measurement on inherited martensitic variants, the local orientations of parent austenite grains were predicted using four classical OR for the martensitic transformation. Furthermore, a specific OR, namely the Pitsch relation with (1 0 1)(A)//(1 (2) over bar (10) over bar)(7M) and [1 0 (1) over bar](A)//[(10) over bar (10) over bar 1](7M), was unambiguously determined by considering the magnitude of discontinuity between the lattices of the product and parent phases and the structural modulation of the incommensurate 7M modulated martensite. The present procedure to determine the OR, without recourse to the presence of retained austenite, is in general applicable to a variety of materials with modulated superstructure for insight into their martensitic transformation processes. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Elastic and viscoelastic properties of glassy, quasicrystalline and crystalline phases in Zr65Cu5Ni10Al7.5Pd12.5 alloys
Authors:
Pelletier, JM; Louzguine-Luzgin, DV; Li, S; Inoue, A Author Full Names: Pelletier, Jean-Marc; Louzguine-Luzgin, Dmitri V.; Li, Song; Inoue, Akihisa
Source:
ACTA MATERIALIA 59 (7): 2797-2806 APR 2011
Abstract:
The elastic and viscoelastic properties of Zr65Ni10Cu5Al7.5Pd12.5 bulk metallic glass have been studied over a wide temperature and frequency range. In the amorphous state the mechanical response of the alloy is simple, similar to that observed in other bulk metallic glasses. In contrast, the phase-transformation process which occurs during annealing at elevated temperature induces a complex evolution. This alloy transforms to a supercooled liquid and then primarily forms an icosahedral phase followed by the formation of a mixture of crystalline phases. The mechanical properties in the amorphous state are well described using a physical model based on the concept of defects in amorphous materials. Atomic mobility is then governed by two parameters: activation energy U-el (0.92 eV) and correlation factor chi (0.39). The influence of the phase composition on the properties is discussed. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Relation between icosahedral short-range ordering and plastic deformation in Zr-Nb-Cu-Ni-Al bulk metallic glasses
Authors:
Zhu, ZW; Gu, L; Xie, GQ; Zhang, W; Inoue, A; Zhang, HF; Hu, ZQ Author Full Names: Zhu, Z. W.; Gu, L.; Xie, G. Q.; Zhang, W.; Inoue, A.; Zhang, H. F.; Hu, Z. Q.
Source:
ACTA MATERIALIA 59 (7): 2814-2822 APR 2011
Abstract:
The relation between icosahedral short-range ordering (ISRO) and plastic deformation was investigated in Zr70-xNbxCu13.5Ni8.5Al8 (at.%, x = 0, 2, 4, 6, 7, 8, 10) bulk metallic glasses (BMG). The formation of icosahedral quasicrystal (I-phase) during the annealing process implies that ISRO widely exists in these materials. The degree of ISRO is thermodynamically evaluated to show that ISRO increases with increasing Nb content. Compression tests indicate that BMG with 0-7 at.% Nb possess similar unusual plastic deformability, which is attributed to ISRO-mediated local distribution of free volume (FV) and ISRO prompted deformation-induced crystallization. A proposed core shell model coupled with transmission electron microscopy analysis demonstrates that the FV is distributed more heterogeneously with increasing ISRO, which is beneficial for multiplying the shear bands. Deformation-induced crystallization is facilitated, owing to the low interfacial energy of the nucleation and growth of the crystals attributed to ISRO in the amorphous matrix, which improves plasticity by consuming energy and the product altering the stress field in the amorphous matrix. Design of new ductile BMG is discussed in these strategies. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 8-Apr-2011

Title:
Quantitative atom column position analysis at the incommensurate interfaces of a (PbS)(1.14)NbS2 misfit layered compound with aberration-corrected HRTEM
Authors:
Garbrecht, M; Spiecker, E; Tillmann, K; Jager, W Author Full Names: Garbrecht, M.; Spiecker, E.; Tillmann, K.; Jaeger, W.
Source:
ULTRAMICROSCOPY 111 (3): 245-250 FEB 2011
Abstract:
Aberration-corrected HRTEM is applied to explore the potential of NCSI contrast imaging to quantitatively analyse the complex atomic structure of misfit layered compounds and their incommensurate interfaces. Using the (PbS)(1.14)NbS2 misfit layered compound as a model system it is shown that atom column position analyses at the incommensurate interfaces can be performed with precisions reaching a statistical accuracy of +/- 6 pm. The procedure adopted for these studies compares experimental images taken from compound regions free of defects and interface modulations with a structure model derived from XRD experiments and with multi-slice image simulations for the corresponding NCSI contrast conditions used. The high precision achievable in such experiments is confirmed by a detailed quantitative analysis of the atom column positions at the incommensurate interfaces, proving a tetragonal distortion of the monochalcogenide sublattice. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Magnetic transitions in Mn3O4 and an anomaly at 38 K in magnetization and specific heat
Authors:
Guillou, F; Thota, S; Prellier, W; Kumar, J; Hardy, V Author Full Names: Guillou, F.; Thota, S.; Prellier, W.; Kumar, J.; Hardy, V.
Source:
PHYSICAL REVIEW B 83 (9): Art. No. 094423 MAR 23 2011
Abstract:
Mn3O4 is one of the archetypal examples of tetragonally distorted spinels. In this paper we reinvestigate its complex magnetic ordering process by using high-resolution magnetic and calorimetric measurements. The first-order transition to the ground state is found to exhibit a latent heat of similar or equal to 4 J mol(-1) and a thermal hysteresis of similar or equal to 0.6 K. Moreover, the peculiar field-induced broadening observed at this transition is shown to be consistent with general predictions about incommensurate-to-commensurate transition. In addition to the known sequence of transitions at T-N similar or equal to 43 K, T-1 similar or equal to 40 K, and T-2 similar or equal to 34 K, a new anomaly close to T* similar or equal to 38 K is observed in both *magnetization* and heat capacity data. A possible origin of this feature is discussed in terms of magnetic instability within the incommensurate spiral spin configuration.
Title:
Structural and magnetic properties of Sc1.1Fe3.9Al8 alloy
Authors:
Recko, K; Dobrzynski, L; Senyshyn, A; Fuess, H; Szymanski, K; Kotur, BY; Suski, W Author Full Names: Recko, K.; Dobrzynski, L.; Senyshyn, A.; Fuess, H.; Szymanski, K.; Kotur, B. Yu; Suski, W.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 323 (14): 1860-1867 JUL 2011
Abstract:
The crystallochemical and magnetic nature of ternary Sc1+delta Fe4-delta Al8 intermetallic with a small Sc excess delta = 0.1 was investigated by scanning electron microscope, X-ray powder diffraction, neutron diffraction, Mossbauer effect and superconducting quantum interference device techniques. The sample crystallizes in a tetragonal ThMn12 type structure. The excess of Sc atoms substitute Fe at the (8f) positions and have a pronounced effect on the magnetic properties. The experiments carried out in temperature range 4-320 K show that below 120 K the magnetic structure of the alloy forms a double cycloid with magnetic moments rotating according to the incommensurate in-plane wave vector, which is temperature independent upto 160 K. The value of Fe magnetic moment is close to 0.9 mu(B) atom(-1) at 4K. Temperature dependence of unit cell dimensions can be explained within the Debye-Gruneisen approximation. (c) 2011 Elsevier B.V. All rights reserved.
Title:
New high magnetic field phase of the frustrated S=1/2 chain compound LiCuVO4
Authors:
Svistov, LE; Fujita, T; Yamaguchi, H; Kimura, S; Omura, K; Prokofiev, A; Smirnov, AI; Honda, Z; Hagiwara, M Author Full Names: Svistov, L. E.; Fujita, T.; Yamaguchi, H.; Kimura, S.; Omura, K.; Prokofiev, A.; Smirnov, A. I.; Honda, Z.; Hagiwara, M.
Source:
JETP LETTERS 93 (1): 21-25 MAR 2011
Abstract:
Magnetization of the frustrated S = 1/2 chain compound LiCuVO4, focusing on high magnetic field phases, is reported. Besides a spin-flop transition and the transition from a planar spiral to a spin modulated structure observed recently, an additional transition was observed just below the saturation field. This newly observed magnetic phase is considered as a spin nematic phase, which was predicted theoretically but was not observed experimentally. The critical fields of this phase and its dM/dH curve are in good agreement with calculations performed in a microscopic model (M.E. Zhitomirsky and H. Tsunetsugu, Europhys. Lett. 92, 37001 (2010)).
Title:
TEMPERATURE AND SPECTRAL CHANGES IN THE REFRACTIVE INDICES OF LiKSO4 CRYSTALS UNDER UNIAXIAL PRESSURES
Authors:
Stadnyk, VI; Romanyuk, MO; Kushnir, OS; Brezvin, RS; Franiv, AV; Gaba, VM Author Full Names: Stadnyk, V. I.; Romanyuk, M. O.; Kushnir, O. S.; Brezvin, R. S.; Franiv, A. V.; Gaba, V. M.
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B 24 (32): 6219-6233 DEC 30 2010
Abstract:
We have studied spectral and temperature variations of the principal refractive indices of lithium potassium sulfate crystals, LiKSO4, subjected to uniaxial mechanical pressures. Notable baric increases in the refractive indices are found, which have been interpreted using classical single-oscillator dispersion Sellmeier equation and Lorentz-Lorenz formula. Significant pressure-induced shifts of low-temperature phase transitions in LiKSO4 are revealed and qualitatively explained in terms of modifications of crystalline structure imposed by the pressures. It is established that high enough pressures applied along the crystallographic axis c can generate a "triple point" on the phase diagram "temperature-uniaxial pressure". It is inferred that the temperature behavior of the refractive indices below the room temperature cannot be interpreted as a pure result of spontaneous strains and should possibly involve some other mechanisms, e.g., a hypothesis of incommensurately modulated phase existing about below 255 K.
Title:
Selective hydrogenation of Ti-Zr-Ni alloys
Authors:
Kocjan, A; Kovacic, S; Gradisek, A; Kovac, J; McGuiness, PJ; Apih, T; Dolinsek, J; Kobe, S Author Full Names: Kocjan, A.; Kovacic, S.; Gradisek, A.; Kovac, J.; McGuiness, P. J.; Apih, T.; Dolinsek, J.; Kobe, S.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (4): 3056-3061 FEB 2011
Abstract:
We prepared series of Ti-Zr-Ni samples by melt-spinning and subsequent thermal treatment at 700 degrees C for 2 h in dynamic 10(-5) mbar vacuum in order to obtain mixture of crystalline C14 Laves and alpha,beta-(Tr,Zr) phases. These samples were exposed to hydrogen gas at 300 degrees C and 50 bar for 1000 min. The mass% of H was obtained gravimetrically and volumetrically. When approximately 1% of air was present in the Sievert device we found relatively narrow area in Ti-Zr-Ni phase diagram, so-called zero-zone, where hydrogen amounts in crystalline samples varied between 0 and 0.8 mass%. Surprisingly, icosahedral quasicrystalline (i-QC) samples showed no selective hydrogenation and absorbed more than 1.5 mass% H in the interval of compositions, where the i-phase is formed. XPS analysis revealed that the oxide layer thickness is similar after melt-spinning and thermal treatment for both type of samples, i.e. from inside and outside of the zero-zone. However, after hydrogenation the zero-zone samples had 5-times thicker surface oxide layer. In order to find, whether this is correlated to different electronic structure, DOS near E-F was examined by H-1 NMR. In parallel, thermal desorption of hydrogen was performed in order to reveal, if H-bonding sites are correlated to different hydrogenation behaviour of various samples. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Title:
Polarization reversal by intramolecular disordering in organic ferroelectrics: trichloroacetamide
Authors:
Saito, K; Yamamura, Y; Kikuchi, N; Nakao, A; Yasuzuka, S; Akishige, Y; Murakami, Y Author Full Names: Saito, Kazuya; Yamamura, Yasuhisa; Kikuchi, Naoya; Nakao, Akiko; Yasuzuka, Syuma; Akishige, Yukikuni; Murakami, Youichi
Source:
CRYSTENGCOMM 13 (7): 2693-2698 2011
Abstract:
Mechanism of successive ferroelectric-paraelectric phase transitions exhibited by an organic ferroelectric, trichloroacetamide, is clarified through structural and calorimetric experiments. The transition mechanism, intramolecular disordering, reasonably explains the polarization reversal. This mechanism is only possible in molecular solids and is applicable to other compounds as a possible strategy to design new molecular ferroelectrics. Also revealed is the incommensurate nature of the intermediate phase, the origin of which is briefly discussed at phenomenological and molecular levels.

Update: 1-Apr-2011

Title:
Electronic structure of Mg-Zn-based compounds
Authors:
Ishii, Y; Dankhazi, Z; Belin-Ferre, E Author Full Names: Ishii, Yasushi; Dankhazi, Zoltan; Belin-Ferre, Esther
Source:
PHILOSOPHICAL MAGAZINE 91 (11): 1643-1652 2011
Abstract:
We present a comparison between calculated densities of states of the Laves phase MgZn2 and hexagonal Mg28Zn65Y7 and experimental results obtained using both X-ray emission and photoabsorption spectroscopy techniques. We show that there is general agreement between both sets of data for both alloys. We also point out that the two samples retain a metallic character, yet the hexagonal approximant of the Mg-Zn-Y quasicrystal family is less metallic than the Laves phase.
Title:
Structure of liquid Al-Cu-Co alloys near the quasicrystal-forming range
Authors:
Roik, OS; Galushko, SM; Samsonnikov, OV; Kazimirov, VP; Sokolskii, VE Author Full Names: Roik, O. S.; Galushko, S. M.; Samsonnikov, O. V.; Kazimirov, V. P.; Sokolskii, V. E.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 357 (3): 1147-1152 FEB 1 2011
Abstract:
A local short-to-intermediate range order in liquid Al63.9Cu19.4Co16.7. Al71Cu5Co23, and Al60Cu29Co11 alloys was investigated by X-ray diffraction technique and the reverse Monte Carlo modeling. A prepeak at Q similar to 17 nm(-1) originating from the unique bonding between the TM-TM pair (TM = Co, Cu) is observed in the structure factors of all investigated melts. The Voronoi-Delaunay analysis of RMC models indicates that a medium-range ordering of TM atoms in dense non-crystalline polytetrahedral clusters is associated with a chemical short-range order. The icosahedral short-range order is also closely related to the dense packing polytetrahedral clusters. A decrease of temperature leads to an enhancement of both chemical short-range order and icosahedral short-range order. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Raman study of lattice dynamics in quasicrystals
Authors:
Ponosov, YS; Shchegolikhina, NI; Prekul, AF Author Full Names: Ponosov, Yu. S.; Shchegolikhina, N. I.; Prekul, A. F.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 357 (3): 1235-1238 FEB 1 2011
Abstract:
We present the first Raman investigation of icosahedral quasicrystals. Broad structured bands in the energy range up to similar to 500 cm(-1) have been observed in a series of AlCuFe, AlPdMn and AlPdRe systems. Original information on the vibrational density of states g(omega) was obtained for AlPdRe; for AlCuFe and AlPdMn estimated g(omega) shows a good agreement with the previous neutron results, but demonstrates finer structure. Strong increase in the parameter of electron-vibrational coupling for the low-energy vibrations and its correlation with changes in electronic conductivity has been observed in the series from AlCuFe to AlPdRe. This suggests the increase of the degree of localization for these vibrational excitations and involved electronic states. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Magnetic properties of the 1/1 approximant Ag42In42Gd16 to the icosahedral quasicrystal Ag-In-Gd
Authors:
Wang, P; Stadnik, ZM; Przewoznik, J Author Full Names: Wang, P.; Stadnik, Z. M.; Przewoznik, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (8): 3435-3440 FEB 24 2011
Abstract:
The structural, magnetic, and Gd-155 Mossbauer spectral properties of the 1/1 approximant Ag42In42Gd16 to an icosahedral quasicrystal Ag-In-Gd are reported. Based on dc magnetic susceptibility measurements, it is shown that the studied compound develops no long-range magnetic order in the temperature range 1.8-300K. The dc zero-field-cooled and field-cooled susceptibility data indicate that the 1/1 approximant Ag42In42Gd16 is a spin glasss with freezing temperature T-f = 3.6(1)K. This is further confirmed by the analysis of the frequency dependence of T-f using the Vogel-Fulcher law and the dynamic scaling behavior near T-f. It is argued that the spin freezing process is a true equilibrium phase transition rather than a nonequilibrium phenomenon. The large frustration parameter of the studied compound indicates that it belongs to a category of strongly geometrically frustrated magnets. The Gd-155 Mossbauer spectra of the 1/1 approximant Ag42In42Gd16 confirm that the Gd spins are frozen at 1.5K and are fluctuating at 4.6 K. The Debye temperature of the 1/1 approximant Ag42In42Gd16 is 200(1) K. (c) 2010 Elsevier B.V. All rights reserved.
Title:
Planar Symmetry Incompatibility in Ru-Sn-Zn Pseudo-Decagonal Approximants Composed of Novel Pentagonal Antiprisms
Authors:
Xiong, DB; Okamoto, NL; Inui, H Author Full Names: Xiong, Ding-Bang; Okamoto, Norihiko L.; Inui, Haruyuki
Source:
INORGANIC CHEMISTRY 50 (3): 827-835 FEB 7 2011
Abstract:
Two new ternary compounds in the Ru-Sn-Zn system were synthesized by conventional high-temperature reactions, and their crystal structures were analyzed by means of the single crystal X-ray diffraction: Ru2Sn2Zn3 (orthorhombic, Pnma, Pearson symbol oP28, a = 8.2219(16), b = 4.1925(8), c = 13.625(3) angstrom, V=469.66(16) angstrom(3), Z = 4) and Ru4.15Sn4.96Zn5.85 (orthorhombic, Pnma, Pearson symbol oP60-delta, a = 8.3394(17), b = 4.2914(9), c = 28.864(6) angstrom, V = 1032.98(40) angstrom(3), Z = 4). With the increase in the Sn content, the half-decagon structure unit with a triangle center in Ru2Sn2Zn3 grows up to a symmetry incompatible decagonal unit with a central triangle in the common plane in Ru4.15Sn4.96Zn5.85. Both structures can be described by hexagonal arrays of Sn-centered novel pentagonal antiprisms. In light of their pseudodecagonal diffraction in the h0l section and point group mmm, both phases are considered as new quasicrystal approximants in the Ru-Zn Sn ternary system. The temperature dependences of the electrical resistivity for both compounds exhibit metallic behavior, but their Seebeck coefficients are of opposite sign.

Update: 25-Mar-2011

Title:
NdRhSn: A ferromagnet with an antiferromagnetic precursor
Authors:
Mihalik, M; Prokleska, J; Kamarad, J; Prokes, K; Isnard, O; McIntyre, GJ; Donni, A; Yoshii, S; Kitazawa, H; Sechovsky, V; de Boer, FR Author Full Names: Mihalik, M.; Prokleska, J.; Kamarad, J.; Prokes, K.; Isnard, O.; McIntyre, G. J.; Doenni, A.; Yoshii, S.; Kitazawa, H.; Sechovsky, V.; de Boer, F. R.
Source:
PHYSICAL REVIEW B 83 (10): Art. No. 104403 MAR 9 2011
Abstract:
NdRhSn has a ferromagnetic ground state [T-t = 7.6(1) K] with a magnetic moment equal to 2/3 of the free Nd3+-ion moment. Upon cooling from the paramagnetic state, the ferromagnetism is preceded by an incommensurate antiferromagnetic state between T-N = 9.8(1) K and T-t. In both magnetic phases the magnetic moments are locked along the c axis, which is the easy-magnetization axis of the system. We have investigated this unusual situation by measuring anomalies of several bulk physical properties characteristic for the magnetic phase transitions at T-N and T-t and the response of these properties to an applied magnetic field. Neutron-diffraction experiments have been also performed at low temperatures. Furthermore, in order to understand better the physical properties of NdRhSn, single crystals have been studied under external hydrostatic and uniaxial pressure and in high magnetic fields. An antiferromagnetic phase with a propagation vector (0 0 1/11) has been found between T-N and T-t. The magnetic-ordering temperatures T-N and T-t are sensitive to both hydrostatic and uniaxial pressures, but in a different manner. Application of hydrostatic pressure leads to a reduction of the ordering temperatures at rates Delta T-N/Delta p = -0.76(5) K/GPa and Delta T-t/Delta p = -0.9(2) K/GPa while uniaxial pressure applied along the c axis leads to an increase of the ordering temperatures at rates Delta T-N/Delta p = +1.2(5) K/GPa and Delta T-t/Delta p = +2.7(4) K/GPa. No considerable influence of pressure on the antiferromagnetic propagation vector has been found. The peculiar evolution of magnetism in NdRhSn with temperature indicates a complex hierarchy of exchange interactions.
Title:
Electronic structure of EuPtSi3 studied from the first principles calculation
Authors:
Pan, D; Wan, XG Author Full Names: Pan, D.; Wan, X. G.
Source:
PHYSICA B-CONDENSED MATTER 406 (5): 1129-1131 MAR 1 2011
Abstract:
We investigate the electronic structure of EuPtSi3 using full potential linearized augmented plane wave method within the generalized gradient approximation. We reproduce the observed easy axis of magnetization as well as magnetic moment and propose that the magnetic configuration for this compound is incommensurate or noncollinear. We find that the spin configuration has only negligible effect on the band around Fermi energy. EuPtSi3 and its isostructural superconductor BaPtSi3 have similar band structures. Despite the shorter Pt-Si bond, EuPtSi3 possesses larger density of state near the Fermi energy compared with BaPtSi3, thus the structural difference and the associated difference in band structure cannot explain the non-superconductivity of EuPtSi3. (C) 2010 Elsevier B.V. All rights reserved.
Title:
A general solution of elasto-hydrodynamics of two-dimensional quasicrystals
Authors:
Li, XF Author Full Names: Li, X-F
Source:
PHILOSOPHICAL MAGAZINE LETTERS 91 (4): 313-320 2011
Abstract:
Dynamic problems of quasicrystals are analysed within the framework of continuum mechanics. Phonon excitations yield wave propagation while phason excitations yield atomic diffusion. Phonon fields obey the equations of motion and phason fields obey the diffusion equations. Governing equations of elasto-hydrodynamics of decagonal quasicrystals combine characteristics of the equations of motion and diffusion. A general solution is derived in terms of two introduced auxiliary functions. It provides an easy-to-use approach to solve initial-boundary value problems encountered in elasticity problems for quasicrystals. Explicit expressions for displacements and stresses in the phonon and phason fields can be directly obtained. A derived general solution is also applicable to some planar quasicrystals such as pentagonal quasicrystals with fivefold symmetry.
Title:
Mechanical Property and Corrosion Resistance of Mg-Zn-Y Alloys Containing Icosahedral Phase
Authors:
Kim, DH; Kim, YK; Kim, WT; Kim, DH Author Full Names: Kim, Do Hyung; Kim, Young Kyun; Kim, Won Tae; Kim, Do Hyang
Source:
KOREAN JOURNAL OF METALS AND MATERIALS 49 (2): 145-152 FEB 2011
Abstract:
Mechanical and property corrosion resistance of Mg-Zn-Y alloys with an atomic ratio of Zn/Y of 6.8 are investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy, uniaxial tensile test and corrosion test with immersion and dynamic potentiometric tests. The alloys showed an in-situ composite microstructure consisting of alpha-Mg and icosahedral phase (I-phase) as a strengthening phase. As the volume fraction of the I-phase increases, the yield and tensile strengths of the alloys increase while maintaining large elongation (26 similar to 30%), indicating that I-phase is effective for strengthening and forms a stable interface with surrounding alpha-Mg matrix. The presence of I-phase having higher corrosion potential than alpha-Mg, decreased the corrosion rate of the cast alloy up to I-phase volume fraction of 3.7%. However further increase in the volume fraction of the I-phase deteriorates the corrosion resistance due to enhanced internal galvanic corrosion cell between alpha-Mg and I-phase.
Title:
Hydrogen and Zr-based metallic glasses: Gas/solid absorption process and structure evolution
Authors:
Paillier, J; Rongeat, C; Gutfleisch, O; Gebert, A Author Full Names: Paillier, Jerome; Rongeat, Carine; Gutfleisch, Oliver; Gebert, Annett
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (5): 1636-1643 FEB 3 2011
Abstract:
The absorption of hydrogen by means of gas-solid reaction and its consequence on the structure have been studied for fully amorphous alloys as well as quasicrystals/glassy composite alloys based on the composition Zr59Ti3Cu20Al10Ni8. The process of hydrogen absorption has been performed and monitored under 20 bar of H-2 using high pressure-differential scanning calorimetry (HP-DSC). The structure evolution of the samples has been followed by X-ray diffractometry (XRD). Results show that the nature of the surface oxide layer strongly affects the process of hydrogen absorption, especially its starting temperature. The structure evolves nevertheless along the same basic sequence, regardless of the sample: (i) the alloys keep a global amorphous structure up to roughly H/M =0.8 and T= 350 degrees C; (ii) then ZrH2 and at higher temperature Cu2AlZr are formed. The stability of the glass is weakened and the formation of quasicrystals is inhibited under 20 bar of H-2. An heterogeneous distribution of hydrogen atoms inside the amorphous matrix has been inferred from the results. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Formation of nano quasicrystalline and crystalline phases by mechanical alloying
Authors:
Shamah, AM; Ibrahim, S; Hanna, FF Author Full Names: Shamah, A. M.; Ibrahim, S.; Hanna, F. F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (5): 2198-2202 FEB 3 2011
Abstract:
In the present work, the formation of nano quasicrystalline icosahedral phase in Al86Cr14, Al84Fe16 and Al62.5Cu25Fe12.5 alloys has been investigated by mechanical alloying. Mixtures of quasicrystalline and related crystalline phases have been observed under various milling conditions. The X-ray diffraction, differential thermal analysis and electrical resistivity techniques have been used for characterization and physical property measurements. The particle size was calculated by X-ray profile using Williamson-Hall plot method and it was found to be 25-50 nm size. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Effect of processing parameter on hydrogen storage characteristics of as quenched Ti45Zr38Ni17 quasicrystalline alloys
Authors:
Shahi, RR; Yadav, TP; Shaz, MA; Srivastava, ON; van Smaalen, S Author Full Names: Shahi, Rohit R.; Yadav, T. P.; Shaz, M. A.; Srivastava, O. N.; van Smaalen, S.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (1): 592-599 JAN 2011
Abstract:
The present study deals with the microstructural changes with respect to the processing parameter (quenching rate) and their correlation with hydrogen storage characteristics of Ti45Zr38Ni17 quasicrystalline alloys. The ribbons of the alloy have been synthesized at different quenching rates obtained through different wheel speeds (35, 40, 45 and 50 m/s) and investigated for their hydrogen storage characteristics. The lower cooling rate obtained through low wheel speed (35 m/s) produces, i-phase grains whose size ranges from 300-350 nm, whereas higher cooling rates obtained through high wheel speed (45 and 50 m/s) promote the formation of grains with size ranges from 100-150 nm in Ti45Zr38Ni17 ribbons. It has been found that the ribbons synthesized at 35 m/s absorbed similar to 2.0 wt%, whereas ribbons synthesized at 50 m/s absorbed similar to 2.84 wt. % of hydrogen. Thus the hydrogen storage capacity of ribbon increases for the ribbons produced at higher quenching rate. One of the salient features of the present study is that the improvement of hydrogen storage capacity obtained through higher quenching rates (similar to 45 to 50 m/s wheel speed) leading to the formation of lower grain size. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Title:
Electrochemical performance of TiVNi-Quasicrystal and AB(3)-Type hydrogen storage alloy composite materials
Authors:
Liu, WQ; Wang, XL; Hu, W; Kawabe, Y; Watada, M; Wang, LM Author Full Names: Liu, Wanqiang; Wang, Xinlu; Hu, Wen; Kawabe, Yoshiteru; Watada, Masaharu; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (1): 616-620 JAN 2011
Abstract:
The Ti1.4V0.6Ni ribbon alloy and AB(3)-type (La0.65Nd0.12Mg0.23Ni2.9Al0.1) alloy ingot are prepared by melt-spinning technique and induction levitation melting technique, respectively. The Ti1.4V0.6Ni + 20 wt.% AB(3) mixture powders are synthesized by ball-milling the above prepared alloy ingots, and their structures and the electrochemical hydrogen storage properties are investigated. It is found that the icosahedral quasicrystal, Ti2Ni, BCC structural solid solution and AB3-type phases are all presented in the composite material. The maximum electrochemical discharge capacity of the composite electrode is 294.7 mAh/g at the discharge current density of 30 mA/g and 303 K. In addition, the electrode made of Ti1.4V0.6Ni and AB(3) composite holds better high-rate discharge ability than that of Ti1.4V0.6Ni. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Title:
The formation of quasicrystals and their hydrides in Ti-Zr-Ni system
Authors:
Shekhtman, VS; Hakobyan, HG; Aleksanyan, AG; Dolukhanyan, SK; Ter-Galstyan, OP; Sakharov, MK Author Full Names: Shekhtman, V. Sh.; Hakobyan, H. G.; Aleksanyan, A. G.; Dolukhanyan, S. K.; Ter-Galstyan, O. P.; Sakharov, M. K.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (1): 1206-1208 JAN 2011
Abstract:
In the present work, an essentially new approach to production of quasicrystals in Ti-Zr-Ni system is described. It consists in co-compaction and dehydrogenation-sintering of mixture of powders of Ni with two and more hydrides of transition metals of IV group (Ti, Zr). The interaction of some of received quasicrystals with hydrogen in combustion mode is studied, the hydrides of these quasicrystals are synthesized and investigated. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Update: 18-Mar-2011

Title:
Birefringence Properties of Mechanically Clamped K2ZnCl4 Crystals
Authors:
Stadnyk, VI; Gaba, VM; Andrievskii, BV; Kogut, ZO Author Full Names: Stadnyk, V. I.; Gaba, V. M.; Andrievskii, B. V.; Kogut, Z. O.
Source:
PHYSICS OF THE SOLID STATE 53 (1): 131-137 JAN 2011
Abstract:
The effect of uniaxial pressure applied along the principal crystallographic directions on the dispersion and temperature dependences of the birefringence Delta n(i) of K2ZnCl4 crystals has been studied. It has been established that the birefringence Delta n(i) is sensitive to uniaxial pressures and that the uniaxial stresses do not change the character of the dispersion and temperature dependences of Delta n(i). A new "pseudoisotropic" state of this crystal has been revealed. It has been found that the points of the paraphase-incommensurate phase-commensurate phase transitions can be significantly shifted under pressure toward different temperature ranges depending on the direction of the applied pressure due to the effect of uniaxial stresses on the structure of the K2ZnCl4 crystal.
Title:
Universal Hysteresis Scaling for Incommensurate Magnetic Order in Dysprosium
Authors:
Kobayashi, S Author Full Names: Kobayashi, Satoru
Source:
PHYSICAL REVIEW LETTERS 106 (5): Art. No. 057207 FEB 3 2011
Abstract:
We study the scaling properties of magnetic minor hysteresis loops in a polycrystalline dysprosium metal, varying temperature and magnetic-field amplitudes. We observe irreversibility-related hysteresis loss in the helical antiferromagnetic phase, which is related with remanent flux density as a power law with the same scaling exponent of 1.25 +/- 0.05 as that in ferromagnetic materials. In contrast to hysteresis scalings in ferromagnets associated with 180 degrees Bloch walls, the observed law is governed by spiral walls which separate helical domains with oppositely rotating spins.
Title:
Magnetic excitations in the metallic single-layer ruthenates Ca2-xSrxRuO4 studied by inelastic neutron scattering
Authors:
Steffens, P; Friedt, O; Sidis, Y; Link, P; Kulda, J; Schmalzl, K; Nakatsuji, S; Braden, M Author Full Names: Steffens, P.; Friedt, O.; Sidis, Y.; Link, P.; Kulda, J.; Schmalzl, K.; Nakatsuji, S.; Braden, M.
Source:
PHYSICAL REVIEW B 83 (5): Art. No. 054429 FEB 24 2011
Abstract:
By inelastic neutron scattering, we have analyzed the magnetic correlations in the paramagnetic metallic region of the series Ca2-xSrxRuO4, 0.2 <= x <= 0.62. We find different contributions that correspond to two-dimensional ferromagnetic fluctuations and to fluctuations at incommensurate wave vectors Q(1)(IC) = (0.11,0,0), Q(2)(IC) = (0.26,0,0), and Q(alpha beta)(IC) = (0.3,0.3,0). These components constitute the measured response as a function of the Sr concentration x, of the magnetic field, and of the temperature. A generic model is applicable to metallic Ca2-xSrxRuO4 close to the Mott transition, in spite of their strongly varying physical properties. The amplitude, characteristic energy, and width of the incommensurate components vary only slightly as functions of x, but the ferromagnetic component depends sensitively on concentration, temperature, and magnetic field. While ferromagnetic fluctuations are very strong in Ca1.38Sr0.62RuO4 with a low characteristic energy of 0.2 meV at T = 1.5 K, they are strongly suppressed in Ca1.8Sr0.2RuO4, but reappear upon the application of a magnetic field, and form a magnon mode above the metamagnetic transition. The inelastic neutron scattering results document how the competition between ferromagnetic and incommensurate antiferromagnetic instabilities governs the physics of this system.
Title:
Crossover from Commensurate to Incommensurate Antiferromagnetism in Stoichiometric NaFeAs Revealed by Single-Crystal Na-23,As-75-NMR Experiments
Authors:
Kitagawa, K; Mezaki, Y; Matsubayashi, K; Uwatoko, Y; Takigawa, M Author Full Names: Kitagawa, Kentaro; Mezaki, Yuji; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Takigawa, Masashi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (3): Art. No. 033705 MAR 2011
Abstract:
We report the results of Na-23 and As-75 nuclear magnetic resonance (NMR) experiments on a self-flux grown high-quality single crystal of stoichiometric NaFeAs. The NMR spectra reveal a tetragonal to twinned-orthorhombic structural phase transition at T-O = 57K and an antiferromagnetic (AF) transition at T-AF = 45 K. The divergent behavior of nuclear relaxation rate near T-AF shows significant anisotropy, indicating that the critical slowing down of stripe-type AF fluctuations are strongly anisotropic in spin space. The NMR spectra at sufficiently low temperatures consist of sharp peaks showing a commensurate stripe AF order with a small moment of similar to 0.3 mu(B). However, the spectra just below T-AF exhibit a highly asymmetric broadening pointing to an incommensurate modulation. The commensurate-incommensurate crossover in NaFeAs shows a certain similarity to the behavior of SrFe2As2 under high pressure.
Title:
Incommensurate-to-Commensurate Magnetic Phase Transition in SmIn3 Observed by Muon Spin Relaxation
Authors:
Ito, TU; Higemoto, W; Ninomiya, K; Luetkens, H; Sugai, T; Haga, Y; Suzuki, HS Author Full Names: Ito, Takashi U.; Higemoto, Wataru; Ninomiya, Kazuhiko; Luetkens, Hubertus; Sugai, Takashi; Haga, Yoshinori; Suzuki, Hiroyuki S.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (3): Art. No. 033710 MAR 2011
Abstract:
Magnetic susceptibility and muon spin relaxation (mu SR) measurements in the intermetallic cubic compound SmIn3 with a Gamma(8) crystalline-electric-field ground state are reported. Anomalies corresponding to successive phase transitions were observed in the magnetic susceptibility at T-I similar to 16.5 K, T-II similar to 15.1 K, and T-III similar to 14.7 K. A spontaneous local magnetic field was detected below T-I using the mu SR technique in zero applied field in contrast to the pure quadrupolar ordering scenario proposed in the phase between T-I and T-II. This result clearly indicates that the primary order parameters in all the ordered phases are magnetic. The local field distribution changes at around TII from a continuous broad one to a sharp one with decreasing temperature, suggesting that an incommensurate-to-commensurate magnetic phase transition takes place at this temperature. A possible magnetic structure in the ground state and the importance of multipolar interactions in the Gamma(8) subspace are discussed.
Title:
Incommensurate Magnetic Structure and Its Long-Time Variation in a Geometrically Frustrated Magnet Ca3Co2O6
Authors:
Moyoshi, T; Motoya, K Author Full Names: Moyoshi, Taketo; Motoya, Kiyoichiro
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (3): Art. No. 034701 MAR 2011
Abstract:
Magnetization and neutron scattering measurements have been performed on a single crystal of the magnetically frustrated compound Ca3Co2O6. This compound has no random magnetic interactions, but has frustrating magnetic interactions arising from its crystal structure. In this material, a long-time variation in magnetic structure has been observed. After cooling the sample below the transition temperature T-c2 = 13 K, the magnetic Bragg peaks at (1, 0, +/-delta) corresponding to an incommensurate antiferromagnetic structure move toward (1,0,0) with time. The characteristic time for this variation follows the Arrhenius law with an activation energy E-a/k(B) similar to 53 K. A new magnetic structure model of this material is also presented.
Title:
The Al-rich region of the Al-Mn-Ni alloy system. Part II. Phase equilibria at 620-1000 degrees C
Authors:
Balanetskyy, S; Meisterernst, G; Grushko, B; Feuerbacher, M Author Full Names: Balanetskyy, S.; Meisterernst, G.; Grushko, B.; Feuerbacher, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (9): 3795-3805 MAR 3 2011
Abstract:
Phase equilibria in the Al-rich region of the Al-Mn-Ni alloy system were studied at 1000, 950, 850, 750, 700, 645 and 620 degrees C. Three ternary thermodynamically stable intermetallics, the phi-phase (Al5Co2-type, hP26, P6(3)/mmc; a = 0.76632(16), c = 0.78296(15) nm), the kappa-phase (kappa-Al14.4Cr3.4Ni1.1-type, hP227, P6(3)/m; a = 1.7625(10), c = 1.2516(10) nm), and the O-phase (O-Al77Cr14Pd9-type, Pmmn, oP650,: a = 2.3316(16), b = 1.2424(15), c = 3.2648(14) nm), as well as three ternary metastable phases, the decagonal D-3-phase with periodicity about 1.25 nm, the Al-9(Mn,Ni)(2)-phase (Al9Co2-type, P112(1)/a, mP22; a = 0.8585(16), b = 0.6269(9), c = 0.6205(11) nm, beta = 95.34(10)degrees) and the O-1-phase (base-centered orthorhombic, a approximate to 23.8, b approximate to 12.4, c approximate to 32.2 nm) were revealed. Their physicochemical behaviour in the Al-Mn-Ni alloy system was studied. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Structural and hyperfine properties of Ti48Zr7Fe18 nano-compounds and its hydrides
Authors:
Zywczak, A; Gondek, L; Figiel, H; Zukrowski, J; Czub, J; Takasaki, A Author Full Names: Zywczak, A.; Gondek, L.; Figiel, H.; Zukrowski, J.; Czub, J.; Takasaki, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (9): 3952-3957 MAR 3 2011
Abstract:
It is well established that Ti-based nano-alloys are able to absorb hydrogen with relatively high hydrogen to metal ratio of 4/3. In this study the Ti48Zr7Fe18 nano-compound, prepared by mechanical alloying (MA), has been investigated. In its initial state the compound is amorphous, however upon thermal treatment it transforms to the quasicrystalline icosahedral structure (i-phase), which is based on the Mackay cluster type. Structural characterization of the sample was made by means of XRD measurements. Thermodynamic properties were studied by differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS). To find the influence of hydrogen and structure type on hyperfine interactions the Mossbauer spectroscopy (MS) experiment was performed, as well. The amorphous sample after MA was hydrogenated in order to unveil hydrogen influence on crystal properties of the sample. Upon hydrogenation of the amorphous sample a decomposition into simple hydrides took place. (C) 2011 Elsevier B. V. All rights reserved.
Title:
Piezo-optic properties of incommensurately modulated K2ZnCl4 crystals
Authors:
Stadnyk, VI; Kogut, ZO; Brezvin, RS Author Full Names: Stadnyk, V. I.; Kogut, Z. O.; Brezvin, R. S.
Source:
CRYSTALLOGRAPHY REPORTS 56 (1): 84-88 JAN 2011
Abstract:
The effect that uniaxial pressures along the principal crystallophysical directions have on the dispersion and temperature dependences of the birefringence in incommensurate K2ZnCl4 crystals has been investigated in a wide temperature range. This parameter has been established to be fairly sensitive to uniaxial pressures. The spectral and temperature dependences of combined piezo-optic coefficients are analyzed. Significant anomalies of these coefficients are found at the incommensurate-commensurate phase transition. They are due to the change in the induced birefringence that results from spontaneous polarization and to the significant effect of uniaxial stress on the soliton structure of the crystal. The contributions that the electrooptic effect, the elasto-optic effect, and the order parameter make to the spontaneous changes in the piezooptic coefficients are separated.
Title:
Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by H-1 NMR
Authors:
Owczarek, M; Jakubas, R; Bator, G; Pawlukojc, A; Baran, J; Przeslawski, J; Medycki, W Author Full Names: Owczarek, M.; Jakubas, R.; Bator, G.; Pawlukojc, A.; Baran, J.; Przeslawski, J.; Medycki, W.
Source:
CHEMICAL PHYSICS 381 (1-3): 11-20 MAR 18 2011
Abstract:
Dynamics of molecules in morpholinium tetrafluoroborate, [NH2(C2H4)(2)O][BF4], has been studied in a wide temperature range by means of AC calorimetry, H-1 NMR and infrared spectroscopy. Simultaneously, DFT (density functional theory) calculations of the molecular structure and normal vibration frequencies have been performed by using various functionals for initial structural data of the low temperature phase. Infrared spectra of polycrystalline [NH2(C2H4)(2)O][BF4] have been analyzed in a frequency range 4000-400 cm (1). Substantial changes in a temperature evolution of internal modes of both morpholinium cations and [BF4] anions are due to the freezing of these moieties motions below 117 K. A dynamic non-equivalence of protons involved in N-H center dot center dot center dot F and N-H center dot center dot center dot O hydrogen bonds has been detected. Heat capacity anomalies around structural phase transitions detected by AC calorimetry (117 and 153 K) have been evaluated and described. A molecular mechanism of the phase transitions is discussed on the basis of presented results. (C) 2011 Elsevier B. V. All rights reserved.
Title:
Unifying cluster-based structure models of decagonal Al-Co-Ni, Al-Co-Cu and Al-Fe-Ni
Authors:
Deloudi, S; Fleischer, F; Steurer, W Author Full Names: Deloudi, Sofia; Fleischer, Frank; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 67: 1-17 Part 1 FEB 2011
Abstract:
The geometrical building principles of Al-based decagonal quasicrystals and their approximants are discussed from a cluster-based approach. Our investigations cover 11 modifications with two-or four-layer periodicity in the systems Al-Co-Ni, Al-Co-Cu and Al-Fe-Ni. We identified a cluster that leads to a unifying view of all these phases. This unit cluster has similar to 20 angstrom diameter, four-layer periodicity along its tenfold axis and rod symmetry group p (10) over bar 2m. The models obtained are in agreement with all the electron-density maps and electron-microscopy images available.
Title:
Modulated structure of nepheline
Authors:
Friese, K; Grzechnik, A; Petricek, V; Schonleber, A; van Smaalen, S; Morgenroth, W Author Full Names: Friese, Karen; Grzechnik, Andrzej; Petricek, Vaclav; Schoenleber, Andreas; van Smaalen, Sander; Morgenroth, Wolfgang
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 67: 18-29 Part 1 FEB 2011
Abstract:
The incommensurately modulated structure of a natural nepheline of composition K0.54Na3.24Ca0.03Al3.84Si4.16O16 has been determined in superspace. The compound crystallizes in the trigonal centered superspace group X3(00 gamma)0 with gamma = 0.2048 (10), X = (0, 0, 0, 0), (1/3, 2/3, 0, 2/3), (2/3, 1/3, 0, 1/3), a = 17.2889 (8) and c = 8.3622 (10) angstrom. The structure is characterized by a framework of corner-connected (Al,Si)O-4 tetrahedra. The additional cations are incorporated in two different types of channels of the framework. All atoms in the structure are displacively modulated with amplitudes below 0.1 angstrom. The modulation can be well described taking into account harmonics of first order only. Atomic positions in the smaller channels of the framework are fully occupied by Na+. Cationic positions in the larger channel are occupationally modulated, yet the variation of electron density as a function of the internal coordinate t is very small and indicates that the incorporation of different types of cations (K+, Na+, Ca2+) and vacancies is realised in a highly disordered way. Average T-O distances indicate a nearly complete Al/Si ordering in the tetrahedral framework. A large part of the O atoms are approximated by split-atom positions, which are additionally affected by occupational modulation resulting in a high degree of disorder in the modulated structure. Occupational probabilities for the split-atom positions are complementary. Occupational modulations of the cations in the larger channels and the O atoms of the tetrahedral framework are coupled and correlations between occupational and displacive modulations exist.

Update: 11-Mar-2011

Title:
Defect structure and electrical conductivity in the Bi3+xNb0.8W0.2O7.1+3x/2 system
Authors:
Borowska-Centkowska, A; Kario, A; Krok, F; Abrahams, I; Chan, SCM; Liu, X; Wrobel, W; Malys, M; Hull, S; Dygas, JR; Suard, E Author Full Names: Borowska-Centkowska, A.; Kario, A.; Krok, F.; Abrahams, I.; Chan, S. C. M.; Liu, X.; Wrobel, W.; Malys, M.; Hull, S.; Dygas, J. R.; Suard, E.
Source:
SOLID STATE IONICS 181 (39-40): 1750-1756 DEC 20 2010
Abstract:
An investigation of electrical conductivity and defect structure in the fluorite related system Bi3+xNb0.8W0.2O7.1+3x2 (0.0 <= x <= 2.0) using a.c. impedance spectroscopy and powder neutron diffraction is presented. All compositions exhibit incommensurate ordering of the cubic fluorite sublattice, with only the x = 2.0 composition showing evidence for an order-disorder transition above 650 degrees C. Non-linear behaviour in the thermal expansion of the cubic lattice parameter and the Arrhenius plot of total conductivity are discussed in terms of the defect structure. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Colloidal hard dumbbells under gravity: structure and crystallization
Authors:
Marechal, M; Dijkstra, M Author Full Names: Marechal, Matthieu; Dijkstra, Marjolein
Source:
SOFT MATTER 7 (4): 1397-1408 2011
Abstract:
We study the structure and phase behavior of hard dumbbells under gravity. The fluid shows layering near the wall, where subsequent layers of dumbbells align alternatingly parallel or perpendicular to the wall. We observe coexistence of a fluid with a plastic crystal (PC) and an aligned crystal (CP1) in a single sediment for short dumbbells. For longer dumbbells, we observe a direct fluid-CP1 coexistence, while for dumbbells of almost tangent spheres, the aperiodic crystal phase appears in between the fluid and CP1 phase. The locations of the coexistences between these phases are well described by a simple expression based on an approximation similar to the local density approximation, which has been successfully applied to hard spheres under gravity [M. Marechal and M. Dijkstra, Phys. Rev. E, 2007, 75, 061404]. The fluid-PC-CP1 coexistence could not be explained using this expression. We attribute this discrepancy to a lattice constant mismatch between the PC and CP1 phases. Finally, we show using direct simulations that the plastic crystal stacks preferably as the hexagonal close packed crystal for short dumbbells, as is the case for a bulk plastic crystal [M. Marechal and M. Dijkstra, Phys. Rev. E, 2008, 77, 061405].
Title:
Ultra-fine grain size and isotropic very high strength by direct extrusion of chill-cast Mg-Zn-Y alloys containing quasicrystal phase
Authors:
Singh, A; Osawa, Y; Somekawa, H; Mukai, T Author Full Names: Singh, Alok; Osawa, Yoshiaki; Somekawa, H.; Mukai, T.
Source:
SCRIPTA MATERIALIA 64 (7): 661-664 APR 2011
Abstract:
Very fine grain sizes up to similar to 1 mu m with yield strengths up to about 400 MPa in tension and compression, with elongations ranging from 12% to 18%, have been achieved by chill casting and direct extrusion of Mg93Zn6Y alloy containing a quasicrystalline phase. These alloys respond to ageing at 150 degrees C, showing two peaks. The hardness stabilizes at the level of the second peak. The effect of precipitation on the yield strength, ductility and yield asymmetry has been studied. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Structural studies of a mixed-valence state in the incommensurate composite crystal Sr1.261CoO3
Authors:
Isobe, M; Yoshida, H; Muromachi, ET; Ohoyama, K Author Full Names: Isobe, Masaaki; Yoshida, Hiroyuki; Muromachi, Eiji Takayama; Ohoyama, Kenji
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 11 (6): Art. No. 065004 DEC 2010
Abstract:
The incommensurate modulated crystal structure of the hexagonal cobalt oxide Sr1.261CoO3 has been studied using a four-dimensional (4D) superspace profile analysis of neutron powder diffraction data. Sr1.261CoO3 is a composite crystal that consists of the [CoO3] and [2Sr] subsystems. The [CoO3] subsystem forms 1D chains that run parallel to the c-axis and consist of face-sharing CoO6 polyhedra with octahedral (Oh) and trigonal prismatic (TP) coordinations. The structure analysis reveals that the [CoO3] chains contain 73.9% Oh and 26.1% TP sites, and that the TP sites have longer Co-O bonds than the Oh sites: d(av). = 2.039(4) angstrom (TP) and 1.895(3) angstrom (Oh). The averaged Co bond valences are Co3.56(3)+ in the Oh sites and Co2.45(3)+ in the TP sites, suggesting that a considerable amount of Co3+ ions are mixed with Co4+ ions in the Oh sites and with Co2+ ions in the TP sites. The observed magnetic susceptibility can be well explained assuming that the compound has the Co mixed-valence state with the spin configurations of S = 0 low-spin state for Co3+(d epsilon(6)), S = 1/2 low-spin state for Co4+(d epsilon(5)) and S = 3/2 high-spin state for Co2+(d epsilon(5)d gamma(2)). The Weiss temperature, approximately 0.8 K, implies that Sr1.261CoO3 naturally assumes a Curie paramagnetic state, probably owing to the obstruction of the intrachain magnetic interaction by the nonmagnetic Co3+ ions. These results suggest that the nonmagnetic Co3+ ions play an essential role in the magnetism of Sr2 gamma CoO3 systems.
Title:
MECHANICAL PROPERTIES OF Al-Cu-Fe ALLOYS SINTERED AT HIGH PRESSURE
Authors:
Mil'man, YV; Efimov, NA; Ul'shin, SV; Bykov, AI; Neikov, OD; Samelyuk, AV Author Full Names: Mil'man, Yu. V.; Efimov, N. A.; Ul'shin, S. V.; Bykov, A. I.; Neikov, O. D.; Samelyuk, A. V.
Source:
POWDER METALLURGY AND METAL CERAMICS 49 (5-6): 280-288 NOV 2010
Abstract:
The structure and mechanical behavior of bulk Al-Cu-Fe materials sintered at high hydrostatic pressure are studied at room temperature. Quasicrystalline Al63Cu25Fe12 and Al62.7Cu25Fe12Sc0.3 powders and Al66Cu18Fe8Cr8, powder, which is the quasicrystal approximant, are sintered at high pressure. The powders are obtained by high-pressure water atomization. At an optimal hot compaction pressure of 4.5 GPa, the porosity of the compact materials is lower than 2%. Sintering is conducted at 700 degrees C. The stress-strain curves of quasicrystals and their approximants that are brittle in standard test conditions are obtained using indentation method. It is shown that the crystalline approximants of quasicrystals are much closer in their mechanical behavior to quasicrystals than to crystalline solids.
Title:
Nuclear and incommensurate magnetic structure of NaFeGe2O6 between 5 K and 298 K and new data on multiferroic NaFeSi2O6
Authors:
Redhammer, GJ; Senyshyn, A; Meven, M; Roth, G; Prinz, S; Pachler, A; Tippelt, G; Pietzonka, C; Treutmann, W; Hoelzel, M; Pedersen, B; Amthauer, G Author Full Names: Redhammer, Guenther J.; Senyshyn, Anatoliy; Meven, Martin; Roth, Georg; Prinz, Sebastian; Pachler, Astrid; Tippelt, Gerold; Pietzonka, Clemens; Treutmann, Werner; Hoelzel, Markus; Pedersen, Bjoern; Amthauer, Georg
Source:
PHYSICS AND CHEMISTRY OF MINERALS 38 (2): 139-157 FEB 2011
Abstract:
The compound NaFeGe2O6 was grown synthetically as polycrystalline powder and as large single crystals suitable for X-ray and neutron-diffraction experiments to clarify the low temperature evolution of secondary structural parameters and to determine the low temperature magnetic spins structure. NaFeGe2O6 is isotypic to the clinopyroxene-type compound aegirine and adopts the typical HT-C2/c clinopyroxene structure down to 2.5 K. The Na-bearing M2 polyhedra were identified to show the largest volume expansion between 2.5 K and room temperature, while the GeO4 tetrahedra behave as stiff units. Magnetic susceptibility measurements show a broad maximum around 33 K, which marks the onset of low-dimensional magnetic ordering. Below 12 K NaFeGe2O6 transforms to an incommensurately modulated magnetic spin state, with k = [0.323, 1.0, 0.080] and a helical order of spins within the M1-chains of FeO6 octahedra. This is determined by neutron-diffraction experiments on a single crystal. Comparison of NaFeGe2O6 with NaFeSi2O6 is given and it is shown that the magnetic ordering in the latter compound, aegirine, also is complex and is best described by two different spin states, a commensurate one with C2'/c' symmetry and an incommensurate one, best being described by a spin density wave, oriented within the (1 0 1) plane.
Title:
Incommensurate Magnetism in FeAs Strips: Neutron Scattering from CaFe4As3
Authors:
Nambu, Y; Zhao, LL; Morosan, E; Kim, K; Kotliar, G; Zajdel, P; Green, MA; Ratcliff, W; Rodriguez-Rivera, JA; Broholm, C Author Full Names: Nambu, Yusuke; Zhao, Liang L.; Morosan, Emilia; Kim, Kyoo; Kotliar, Gabriel; Zajdel, Pawel; Green, Mark A.; Ratcliff, William; Rodriguez-Rivera, Jose A.; Broholm, Collin
Source:
PHYSICAL REVIEW LETTERS 106 (3): Art. No. 037201 JAN 18 2011
Abstract:
Magnetism in the orthorhombic metal CaFe4As3 was examined through neutron diffraction for powder and single crystalline samples. Incommensurate [q(m) approximate to (0.37-0.39) x b*] and predominantly longitudinally (parallel to b) modulated order develops through a 2nd order phase transition at T-N = 89.63(6) K with a 3D Heisenberg-like critical exponent beta = 0.365(6). A 1st order transition at T-2 = 25.6(9) K is associated with the development of a transverse component, locking q(m) to 0.375(2)b*, and increasing the moments from 2.1(1) to 2.2(3) mu(B) for Fe2+ and from 1.3(3) to 2.4(4) mu(B) for Fe+. The ab initio Fermi surface is consistent with a nesting instability in cross-linked FeAs strips.
Title:
Incommensurate Spin Fluctuations in Hole-Overdoped Superconductor KFe2As2
Authors:
Lee, CH; Kihou, K; Kawano-Furukawa, H; Saito, T; Iyo, A; Eisaki, H; Fukazawa, H; Kohori, Y; Suzuki, K; Usui, H; Kuroki, K; Yamada, K Author Full Names: Lee, C. H.; Kihou, K.; Kawano-Furukawa, H.; Saito, T.; Iyo, A.; Eisaki, H.; Fukazawa, H.; Kohori, Y.; Suzuki, K.; Usui, H.; Kuroki, K.; Yamada, K.
Source:
PHYSICAL REVIEW LETTERS 106 (6): Art. No. 067003 FEB 11 2011
Abstract:
A neutron scattering study of heavily hole-overdoped superconducting KFe2As2 revealed a well-defined low-energy incommensurate spin fluctuation at [pi(1 +/- 2 delta), 0] with delta = 0.16. The incommensurate structure differs from the previously observed commensurate peaks in electron-doped AFe(2)As(2) (A = Ba, Ca, or Sr) at low energies. The direction of the peak splitting is perpendicular to that observed in Fe(Te, Se) or in Ba(Fe, Co)(2)As-2 at high energies. A band structure calculation suggests interband scattering between bands around the Gamma and X points as an origin of this incommensurate peak. The perpendicular direction of the peak splitting can be understood within the framework of multiorbital band structure. The results suggest that spin fluctuation is more robust in hole-doped than in electron-doped samples, which can be responsible for the appearance of superconductivity in the heavily hole-doped samples.
Title:
Nanodomains due to Phason Defects at a Quasicrystal Surface
Authors:
Duguet, T; Unal, B; Ledieu, J; Dubois, JM; Fournee, V; Thiel, PA Author Full Names: Duguet, T.; Uenal, B.; Ledieu, J.; Dubois, J. -M.; Fournee, V.; Thiel, P. A.
Source:
PHYSICAL REVIEW LETTERS 106 (7): Art. No. 076101 FEB 16 2011
Abstract:
Among the three coexisting types of terraces found on the twofold surface of the d-Al-Cu-Co quasicrystal, nanodomains are essentially observed on the transition-metal rich ones, with a coherent interface boundary. Both clean surface and Ag growth analyses, demonstrate that nanodomain surfaces are structurally identical to one of the two other terraces, which contains 85 at.% Al. We provide evidence that the nanodomains are a manifestation of phason defects that extend downward toward the bulk, and state that nanodomains develop because the energetic cost of creating the phason is outweighed by the change in surface energy. Consequently, the formation of nanodomains involves more than just the surface layer, but is driven by surface energetics.
Title:
Variation of growth morphology with chemical composition of terraces: Ag on a twofold surface of a decagonal Al-Cu-Co quasicrystal
Authors:
Duguet, T; Unal, B; Han, Y; Evans, JW; Ledieu, J; Jenks, CJ; Dubois, JM; Fournee, V; Thiel, PA Author Full Names: Duguet, T.; Uenal, B.; Han, Y.; Evans, J. W.; Ledieu, J.; Jenks, C. J.; Dubois, J. M.; Fournee, V.; Thiel, P. A.
Source:
PHYSICAL REVIEW B 82 (22): Art. No. 224204 DEC 9 2010
Abstract:
Growth of Ag thin films on the twofold surface of a decagonal Al-Cu-Co quasicrystal is characterized by scanning tunneling microscopy, at different temperatures, and for coverages ranging from submonolayer to 11 monolayers. From prior work, three types of clean surface terraces are known to exist. By correlation with a bulk structural model, the major difference between them lies in their transition-metal (TM) content, two being aluminum-rich (0 and 15 at. % TM) and one being TM-rich (40-50 at. % TM). The present article focuses on understanding the difference between Ag film morphologies on these terminations, in terms of their chemical content. Growth is found to be smoother on the TM-rich terraces and rougher on the Al-rich ones. The first Ag atomic layer is even pseudomorphic on the TM-rich terraces. Roughness variation with temperature shows that the equilibrium morphology is two dimensional for TM-rich terraces and three dimensional for Al-rich terraces. The explanation of different growth modes in terms of different terrace compositions is supported by calculations of the adhesion energy of a Ag slab with Ag, Al, Cu, and Co slabs, using density-functional theory. For the Al-rich terraces, the roughness variation with temperature also indicates reentrant growth, i.e., anomalously smooth growth at low temperature due to kinetic effects.
Title:
High-pressure suppression of long-range magnetic order in the triangular-lattice antiferromagnet CuFeO2
Authors:
Terada, N; Osakabe, T; Kitazawa, H Author Full Names: Terada, N.; Osakabe, T.; Kitazawa, H.
Source:
PHYSICAL REVIEW B 83 (2): Art. No. 020403 JAN 10 2011
Abstract:
We succeeded in observing pressure-suppressed magnetic long-range ordering (LRO) in the triangular-lattice antiferromagnet CuFeO2, using neutron-diffraction experiments under an isotropic pressure. The magnetic LRO of the four-sublattice ground state under ambient pressure in CuFeO2 almost disappears at the high pressure of 7.9 GPa, and is replaced by an incommensurate order with temperature-independent wave number of (0.192 0.192 1.5). The incommensurate wave number observed at 7.9 GPa corresponds to that observed just above the temperature at which lattice distortion and magnetic LRO simultaneously occur under ambient pressure. Therefore, the long-range magnetic ordering disappears because the high pressure suppressed the lattice distortion that otherwise relieves spin frustration and leads the spin system to LRO.
Title:
Monte Carlo and Molecular Dynamics Simulation of Disorder in the Ag+ Fast Ion Conductors Pearceite and Polybasite
Authors:
Welberry, TR; Pasciak, M Author Full Names: Welberry, T. R.; Pasciak, M.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE 42A (1): 6-13 JAN 2011
Abstract:
The pearceite-polybasite group of minerals (i.e., pearceite, antimonpearceite, arsenpolybasite, and polybasite) of general stoichiometry [(M6T2S7)-T-I-S-III][(Ag9CuS4)-Cu-I-S-I], with M = Ag+, Cu+ and T = As3+, Sb3+, occur relatively commonly in nature. All have recently been shown to exhibit Ag+ fast ion conduction at rather low temperatures (only slightly above or below room temperature([1])). The average crystal structure determination of these materials shows the positions of the Ag+ ions to be smeared out or delocalized within sheets in an ordered framework structure comprised of the other ions. At the same time, strong and highly structured diffuse scattering has been observed, which contains diffuse peaks that are incommensurate with the diffraction peaks of the framework structure. In order to try to understand the origins of the fast ion conduction properties of these materials, we have used computer simulation of a model system (Monte Carlo and molecular dynamics (MD)) to analyze this observed diffuse scattering.
Title:
Short range magnetic correlations induced by La substitution in Ho1-xLaxMn2O5
Authors:
Wang, CW; Wu, CM; Li, CY; Karna, SK; Hsu, CK; Li, CHC; Li, WH; Yu, CC; Wu, CP; Chou, H; Lynn, JW Author Full Names: Wang, Chin-Wei; Wu, Chun-Ming; Li, Chi-Yen; Karna, Sunil K.; Hsu, Chien-Kang; Li, Carissa H. C.; Li, Wen-Hsien; Yu, Chun-Chen; Wu, Chun-Pin; Chou, Hsiung; Lynn, Jeffrey W.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (24): Art. No. 246002 JUN 23 2010
Abstract:
Magnetic susceptibility, x-ray diffraction, neutron diffraction and Raman scattering measurements are employed to study the effects of La substitution on the magnetic properties of multiferroic HoMn2O5. 9% and 18% La-substituted compounds crystallize into the same orthorhombic Pbam symmetry as the parent compound. The magnetic responses to an ac driving magnetic field between 40 and 140 K are greatly enhanced by 18% La substitution. The neutron magnetic diffraction patterns reveal the development of short range magnetic correlations below 140 K. In addition, two Raman peaks and a series of new x-ray diffraction peaks suddenly develop below this temperature. Incommensurate long range antiferromagnetic order appears below 38 K. Magnetic frustration could be the main mechanism governing the present observations.
Title:
Evolution of microstructure induced by calcination in leached Al-Cu-Fe quasicrystal and its effects on catalytic activity
Authors:
Tanabe, T; Kameoka, S; Tsai, AP Author Full Names: Tanabe, Toyokazu; Kameoka, Satoshi; Tsai, An Pang
Source:
JOURNAL OF MATERIALS SCIENCE 46 (7): 2242-2250 APR 2011
Abstract:
Effects of calcination on catalytic activity for steam reforming of methanol (SRM) over an Al-Cu-Fe quasicrystal (QC) leached with NaOH aq. have been investigated in terms of microstructure with X-ray diffraction and transmission electron microscope (TEM). Calcination at 600 A degrees C in air drastically improved the catalytic activity of the leached QC. TEM observations on cross-section of the samples revealed that cubic Cu (x) Fe3-x-y Al (y) O-4 spinel was formed at the outermost layer of the leached QC after calcinations. Prior to the catalytic reaction, the Cu (x) Fe3-x-y Al (y) O-4 spinel decomposed to a composite where fine Cu nanoparticles dispersed in (Fe,Al)(3)O-4 matrix under H-2 treatment at 300 A degrees C. Drastic increase in catalytic activity is responsible for the fine Cu nanoparticles in the composite. The Cu nanoparticles sit along the same orientation with (Fe,Al)(3)O-4, e.g., Cu [013]//(Fe,Al)(3)O-4 [013] and Cu [200]//(Fe,Al)(3)O-4 [400]. This orientation relationship may stabilize the Cu nanoparticles through a bonding of Cu-O-Fe.
Title:
Modulated magnetic structure in quasi-one-dimensional clinopyroxene NaFeGe2O6
Authors:
Drokina, TV; Petrakovskii, GA; Keller, L; Schefer, J; Balaev, AD; Kartashev, AV; Ivanov, DA Author Full Names: Drokina, T. V.; Petrakovskii, G. A.; Keller, L.; Schefer, J.; Balaev, A. D.; Kartashev, A. V.; Ivanov, D. A.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 112 (1): 121-126 JAN 2011
Abstract:
The magnetic structure of the NaFeGe2O6 monoclinic compound has been experimentally investigated using the elastic scattering of neutrons. At a temperature of 1.6 K, an incommensurate magnetic structure has been observed in the form of an antiferromagnetic helix formed by a pairs of the spins of the Fe3+ ions with helical modulation in the ac plane of the crystal lattice. The wave vector of the magnetic structure has been determined and its temperature behavior has been studied. The analysis of the temperature dependences of the specific heat and susceptibility, as well as the isotherms of the field dependence of the magnetization, has revealed the existence of not only the order-disorder magnetic phase transition at the point T (N) = 13 K, but also an additional magnetic phase transition at the point T (c) = 11.5 K, which is assumingly an orientation phase transition.
Title:
Highly repulsive interaction in novel inclusion D-2-N-2 compound at high pressure: Raman and x-ray evidence
Authors:
Kim, M; Yoo, CS Author Full Names: Kim, Minseob; Yoo, Choong-Shik
Source:
JOURNAL OF CHEMICAL PHYSICS 134 (4): Art. No. 044519 JAN 28 2011
Abstract:
We present spectral and structural evidences for the formation of a homogeneous cubic delta-N-2-like, noncrystalline solid and an incommensuratelike hexagonal (P6(3)22) inclusion compound (N-2)(12)D-2, formed by compressing a nitrogen-rich mixture to 5.5 and 10 GPa, respectively. A strong repulsive coupling in (N-2)(12)D-2 is evident from a blue shift, discontinuous changes, and the absence of turnover of the D-2 vibron to 70 GPa-all in sharp contrast to both pure D-2 and other inclusion compounds. This repulsive interaction is responsible to the observed incommensuratelike structure and large internal pressure. (C) 2011 American Institute of Physics. [doi:10.1063/1.3533957]
Title:
Ca14Au46Sn5: a "Colored" Gd14Ag51-Type Structure Containing Columns of Well-Differentiated Hexagonal Gold Stars
Authors:
Lin, QS; Corbett, JD Author Full Names: Lin, Qisheng; Corbett, John D.
Source:
INORGANIC CHEMISTRY 50 (5): 1808-1815 MAR 7 2011
Abstract:
A novel hexagonal phase discovered near the Ca15Au60Sn25 quasicrystal and its cubic approximants (ACs) was synthesized by means of high-temperature solid-state reactions. Single-crystal structural analyses show that this is a Gd14Ag51 isotype with composition within the range Ca14Au45.56(4)-46.67(4)Sn5.14(3)-4.14(3), space group P6/m (No. 175), and lattice parameters a =12.763(3)-12.879(3) angstrom and c = 9.326(3)-9.3815(4) angstrom. In this phase, Sn mixes with Au in two of seven anionic sites to give a strong coloring that generates a narrow honeycomb-like Au/Sn template, in which sizable columns of hexagonal Au stars are confined. This phase transforms into the cubic 211 AC phase through a peritectic reaction at similar to 678 degrees C. The valence electron count per atom (eta) of the present phase is in the range 1.41-1.45. However, it does not appear to follow a Hume-Rothery mechanism.

Update: 4-Mar-2011

Title:
Polar Nanodomains and Giant Converse Magnetoelectric Effect in Charge-Ordered Fe2OBO3
Authors:
Yang, HX; Tian, HF; Song, YJ; Qin, YB; Zhao, YG; Ma, C; Li, JQ Author Full Names: Yang, H. X.; Tian, H. F.; Song, Y. J.; Qin, Y. B.; Zhao, Y. G.; Ma, C.; Li, J. Q.
Source:
PHYSICAL REVIEW LETTERS 106 (1): Art. No. 016406 JAN 7 2011
Abstract:
The magnetoelectric coupling and polar nanodomains in the charge-ordered Fe2OBO3 have been extensively studied from room temperature down to 100 K. In situ TEM investigations demonstrate that the charge-ordering transition characterized by an incommensurate modulation could evidently result in remarkable polar nanodomains at low temperatures. This kind of nanodomain could play a critical role in triggering a high dielectric constant and notable dielectric dispersion as observed in Fe2OBO3. Moreover, measurements of the magnetoelectric coupling under electrical field demonstrate the existence of giant electrically induced changes in magnetization around the magnetic transition.
Title:
Fast diffusion of a graphene flake on a graphene layer
Authors:
Lebedeva, IV; Knizhnik, AA; Popov, AM; Ershova, OV; Lozovik, YE; Potapkin, BV Author Full Names: Lebedeva, Irina V.; Knizhnik, Andrey A.; Popov, Andrey M.; Ershova, Olga V.; Lozovik, Yurii E.; Potapkin, Boris V.
Source:
PHYSICAL REVIEW B 82 (15): Art. No. 155460 OCT 29 2010
Abstract:
Diffusion of a graphene flake on a graphene layer is analyzed and a diffusion mechanism is proposed for the system under consideration. According to this mechanism, rotational transition of the flake from commensurate to incommensurate states takes place with subsequent simultaneous rotation and translational motion until the commensurate state is reached again, and so on. The molecular dynamics simulations and analytic estimates based on ab initio and semiempirical calculations demonstrate that the proposed diffusion mechanism is dominant at temperatures T similar to(1-3)T-com, where T-com corresponds to the barrier for transitions of the flake between adjacent energy minima in the commensurate states. For example, for the flake consisting of similar to 40, 200, and 700 atoms the contribution of the proposed diffusion mechanism through rotation of the flake to the incommensurate states exceeds that for diffusion of the flake in the commensurate states by one to two orders of magnitude at temperatures 50-150 K, 200-600 K, and 800-2400 K, respectively. The possibility to experimentally measure the barriers to relative motion of graphene layers based on the study of diffusion of a graphene flake is considered. The results obtained are also relevant for understanding of dynamic behavior of polycyclic aromatic molecules on graphene and should be qualitatively valid for a set of commensurate adsorbate-adsorbent systems.
Title:
Chemical doping-induced flop of ferroelectric polarization in multiferroic Mn0.9Co0.1WO4
Authors:
Song, YS; Yan, LQ; Lee, B; Chun, SH; Kim, KH; Kim, SB; Nogami, A; Katsufuji, T; Schefer, J; Chung, JH Author Full Names: Song, Y. -S.; Yan, Li Qin; Lee, Bumsung; Chun, Sae Hwan; Kim, Kee Hoon; Kim, Sung Baek; Nogami, A.; Katsufuji, T.; Schefer, J.; Chung, J. -H.
Source:
PHYSICAL REVIEW B 82 (21): Art. No. 214418 DEC 15 2010
Abstract:
We studied the multiferroic properties of the incommensurate spiral phase of Mn1-xCoxWO4 using single-crystal neutron-diffraction and ferroelectric measurements. Whereas the rotational plane of the spin spiral is parallel to the b axis for x <= 0.05, it flops by 90 degrees for x=0.10. As a result, the direction of the ferroelectric polarization also flops from the b to the a axis. These results show that the orientation of the ferroelectric polarization in MnWO4 can be controlled via chemical doping.
Title:
Tuning the superconducting and magnetic properties of FeySe0.25Te0.75 by varying the iron content
Authors:
Bendele, M; Babkevich, P; Katrych, S; Gvasaliya, SN; Pomjakushina, E; Conder, K; Roessli, B; Boothroyd, AT; Khasanov, R; Keller, H Author Full Names: Bendele, M.; Babkevich, P.; Katrych, S.; Gvasaliya, S. N.; Pomjakushina, E.; Conder, K.; Roessli, B.; Boothroyd, A. T.; Khasanov, R.; Keller, H.
Source:
PHYSICAL REVIEW B 82 (21): Art. No. 212504 DEC 7 2010
Abstract:
The superconducting and magnetic properties of FeySe0.25Te0.75 single crystals (0.9 <= y <= 1.1) were studied by means of x-ray diffraction, superconducting quantum interference device magnetometry, muon-spin rotation, and elastic neutron diffraction. The samples with y < 1 exhibit coexistence of bulk superconductivity and incommensurate magnetism. The magnetic order remains incommensurate for y >= 1 but with increasing Fe content superconductivity is suppressed and the magnetic correlation length increases. The results show that the superconducting and the magnetic properties of the FeySe1-xTex can be tuned not only by varying the Se/Te ratio but also by changing the Fe content.
Title:
Selective adsorption and electronic interaction of F16CuPc on epitaxial graphene
Authors:
Wang, YL; Ren, J; Song, CL; Jiang, YP; Wang, LL; He, K; Chen, X; Jia, JF; Meng, S; Kaxiras, E; Xue, QK; Ma, XC Author Full Names: Wang, Yi-Lin; Ren, Jun; Song, Can-Li; Jiang, Ye-Ping; Wang, Li-Li; He, Ke; Chen, Xi; Jia, Jin-Feng; Meng, Sheng; Kaxiras, Efthimios; Xue, Qi-Kun; Ma, Xu-Cun
Source:
PHYSICAL REVIEW B 82 (24): Art. No. 245420 DEC 14 2010
Abstract:
We investigate the electronic coupling between copper hexadecafluoro-phthalocyanine (F16CuPc) and epitaxial graphene (EG) on 6H-SiC (0001) using a combined approach of low-temperature scanning tunneling spectroscopy and electronic structure calculations. The molecules are preferentially adsorbed on monolayer EG than bilayer EG. Competing molecule-surface and intermolecular van der Waals interactions result in two well-ordered incommensurate phases. We show that the amount of charge transfer from EG to F16CuPc can be tuned by applied voltage or the thickness of graphene layers. A characteristic feature at similar to 0.4 eV above the Dirac point is identified in bilayer EG, which indicates its electronic structure is modified via introducing extra unoccupied states upon adsorption.
Title:
Helical magnetic state in the distorted triangular lattice of alpha-CaCr2O4
Authors:
Chapon, LC; Manuel, P; Damay, F; Toledano, P; Hardy, V; Martin, C Author Full Names: Chapon, L. C.; Manuel, P.; Damay, F.; Toledano, P.; Hardy, V.; Martin, C.
Source:
PHYSICAL REVIEW B 83 (2): Art. No. 024409 JAN 24 2011
Abstract:
The magnetic properties of the high temperature a form of the CaCr2O4 compound have been investigated for the first time by magnetic susceptibility, specific heat, and powder neutron diffraction. The system undergoes a unique magnetic phase transition at 43 K to a long-range ordered incommensurate helical phase with magnetic propagation vector k = (0,0.3317(2),0). The magnetic model proposed from neutron diffraction data shows that the plane of rotation of the spins is perpendicular to the wave vector and that the magnetic modulation is consistent with two modes belonging to distinct irreducible representations of the group. The magnetic point group 2221 ' is not compatible with ferroelectricity unlike the CuCrO2 delafossite [Kimura et al., Phys. Rev. B, 78 140401 (2008)], but predicts the existence of quadratic magnetoelectric effects, discussed based on a Landau analysis.
Title:
Hysteretic behavior and magnetic ordering in CeRuSn
Authors:
Mydosh, JA; Strydom, AM; Baenitz, M; Chevalier, B; Hermes, W; Pottgen, R Author Full Names: Mydosh, J. A.; Strydom, A. M.; Baenitz, M.; Chevalier, B.; Hermes, W.; Poettgen, R.
Source:
PHYSICAL REVIEW B 83 (5): Art. No. 054411 FEB 9 2011
Abstract:
We report the thermodynamic and transport properties of the newly synthesized Ce-intermetallic compound CeRuSn. This ternary stannide possesses an unconventional structure with two Ce sites at room temperature which exhibit different valencies. Just below room temperature there are large thermal hysteretic effects in the magnetic susceptibility, in the specific heat, as well as in electronic and heat transport properties suggesting the formation of an incommensurate charge density wave modulation whose q vector changes as a function of temperature. Our measurements indicate that one site displays magnetic Ce3+ behavior while the other is a valence fluctuator. At 2.7 K antiferromagnetic long-range order occurs within one-half of the Ce sites, e.g., the magnetic entropy of the transition is 1/2R ln 2. Below T-N a series of metamagnetic transitions takes place in rather small fields (similar to 1-2 T), leaving a magnetically fluctuating background. Such behavior is unique among the many Ce-transition-metal compounds.
Title:
Misfit strain accommodation in epitaxial ABO(3) perovskites: Lattice rotations and lattice modulations
Authors:
Vailionis, A; Boschker, H; Siemons, W; Houwman, EP; Blank, DHA; Rijnders, G; Koster, G Author Full Names: Vailionis, A.; Boschker, H.; Siemons, W.; Houwman, E. P.; Blank, D. H. A.; Rijnders, G.; Koster, G.
Source:
PHYSICAL REVIEW B 83 (6): Art. No. 064101 FEB 11 2011
Abstract:
We present a study of the lattice response to the compressive and tensile biaxial stress in La0.67Sr0.33MnO3 (LSMO) and SrRuO3 (SRO) thin films grown on a variety of single-crystal substrates: SrTiO3, DyScO3, NdGaO3, and (La,Sr)(Al,Ta)O-3. The results show that, in thin films under misfit strain, both SRO and LSMO lattices, which in bulk form have orthorhombic (SRO) and rhombohedral (LSMO) structures, assume unit cells that are monoclinic under compressive stress and tetragonal under tensile stress. The applied stress effectively modifies the BO6 octahedra rotations, whose degree and direction can be controlled by the magnitude and sign of the misfit strain. Such lattice distortions change the B-O-B bond angles and therefore are expected to affect magnetic and electronic properties of the ABO(3) perovskites.
Title:
Strong magnetoelastic effect on the magnetoelectric phenomena of TbMn2O5
Authors:
Oh, YS; Jeon, BG; Haam, SY; Park, S; Correa, VF; Lacerda, AH; Cheong, SW; Jeon, GS; Kim, KH Author Full Names: Oh, Yoon Seok; Jeon, Byung-Gu; Haam, S. Y.; Park, S.; Correa, V. F.; Lacerda, A. H.; Cheong, S. -W.; Jeon, Gun Sang; Kim, Kee Hoon
Source:
PHYSICAL REVIEW B 83 (6): Art. No. 060405 FEB 17 2011
Abstract:
Comparative studies of magnetoelectric susceptibility (alpha), magnetization (M), and magnetostriction (u) in TbMn2O5 reveal that the increment of M owing to the field-induced Tb3+ spin alignment produces a field-asymmetric line shape in the alpha(H) curve, which is conspicuous in a low-temperature incommensurate phase but persistently subsists in the entire ferroelectric phase. Correlations among electric polarization, u, and M-2 variation represent linear relationships, unambiguously showing the significant role of Tb magnetoelastic effects on the low-field magnetoelectric phenomena of TbMn2O5. An effective free energy capturing the observed experimental features is also suggested.
Title:
Wood anomalies in resonant photonic quasicrystals
Authors:
Poddubny, AN Author Full Names: Poddubny, A. N.
Source:
PHYSICAL REVIEW B 83 (7): Art. No. 075106 FEB 8 2011
Abstract:
A theory of light diffraction from a planar quasicrystalline lattice with resonant scatterers is presented. Rich structure, absent in the periodic case, is found in specular reflection spectra, and interpreted as a specific kind of Wood anomaly, characteristic of quasicrystals. The theory is applied to semiconductor quantum dots arranged in Penrose tiling.
Title:
Resonant x-ray scattering investigation of magnetic ordering in NpAs1-xSex (x=0.05, 0.10)
Authors:
Rodrigues, VH; Paixao, JA; Costa, MMR; Mannix, D; Bombardi, A; Rebizant, J; Lander, GH Author Full Names: Rodrigues, V. H.; Paixao, J. A.; Costa, M. M. R.; Mannix, D.; Bombardi, A.; Rebizant, J.; Lander, G. H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (2): Art. No. 026002 JAN 19 2011
Abstract:
A resonant x-ray scattering investigation of the NpAs1-xSex system with single crystals of 5 and 10% Se content is reported. The main features of the magnetic phase diagram previously studied by neutron scattering were confirmed. The coexistence within a single domain of ferro- and antiferro-components in the low-T ferrimagnetic phase was established, as well as the single-k character of the incommensurate phase and of the antiferromagnetic component of the ferrimagnetic phase. A tetragonal lattice distortion was found in the ferro-and ferrimagnetic phases which is not compatible with the proposed model for the ferromagnetic phase. The study of ferromagnetism was carried out using polarization analysis of the diffracted beam to separate the scattering intensities originating from magnetism and charge, which are superimposed in reciprocal space. The magnetic character of the ferromagnetic signal calculated from the measured intensities in the polarization analysis sigma pi and sigma sigma channels was confirmed by analysis of the corresponding temperature dependence.
Title:
A charge density wave in the hidden order state of URu2Si2
Authors:
Su, JJ; Dubi, Y; Wolfle, P; Balatsky, AV Author Full Names: Su, Jung-Jung; Dubi, Yonatan; Woelfle, Peter; Balatsky, Alexander V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (9): Art. No. 094214 Sp. Iss. SI MAR 9 2011
Abstract:
We argue that the hidden order (HO) state in URu2Si2 will induce a charge density wave. The modulation vector of the charge density wave will be twice that of the hidden order state, Q(CDW) = 2Q(HO). To illustrate how the charge density wave arises we use a Ginzburg-Landau theory that contains a coupling of the charge density wave amplitude to the square of the HO order parameter Delta(HO). This simple analysis allows us to predict the intensity and temperature dependence of the charge density wave order parameter in terms of the susceptibilities and coupling constants used in the Ginzburg-Landau analysis.
Title:
Temperature-pressure phase diagram of an aperiodic host guest compound
Authors:
Toudic, B; Rabiller, P; Bourgeois, L; Huard, M; Ecolivet, C; McIntyre, GJ; Bourges, P; Breczewski, T; Janssen, T Author Full Names: Toudic, B.; Rabiller, P.; Bourgeois, L.; Huard, M.; Ecolivet, C.; McIntyre, G. J.; Bourges, P.; Breczewski, T.; Janssen, T.
Source:
EPL 93 (1): Art. No. 16003 JAN 2011
Abstract:
This letter reports on the structural instabilities of an aperiodic composite crystal under pressure. The (P, T) phase diagram up to 0.55GPa of nonadecane-urea is reported showing various symmetry breakings in crystallographic superspaces, towards three different orthorhombic phases. These structural phase transitions are characterized by a change in the intermodulation and are described by increasing the rank of the crystallographic superspaces. Copyright (C) EPLA, 2011
Title:
Fabrication of quaternary Mg-Zn-Y-Ce quasicrystal alloys and their strengthening effects on AZ91 magnesium alloys
Authors:
Wang, ZF; Zhao, WM; Li, HP; Liang, CY Author Full Names: Wang Zhifeng; Zhao Weimin; Li Haipeng; Liang Chunyong
Source:
CHINA FOUNDRY 7 (4): 342-348 NOV 2010
Abstract:
Quaternary Mg-Zn-Y-Ce quasi-crystal-containing alloys were fabricated using a metal mold casting route. The microstructures of Mg-Zn-Y-Ce alloys and the distribution of the major elements were analyzed. The differences in morphology and micro-hardness between quaternary Mg-Zn-Y-Ce quasi-crystals and ternary M Zn-Y quasi-crystals were discussed. The result showed that the micro-hardness of Mg-Zn-Y-Ce quasi-crystals reached peak value when the content of Ce was 0.8at.%. Subsequently, various contents of Mg-Zn-Y-0.8Ce alloys were used to strengthen AZ91 magnesium alloys. The microstructural modification and mechanical properties of reinforced AZ91 alloys with and without solution as well as their aging treatments were also studied Further research showed that aging-treated AZ91-10wt.%(Mg-Zn-Y-0.8at.%Ce) alloys exhibited excellent mechanical properties: their Brinell hardness, tensile strength, and elongation were HV91, 252 MPa, and 4.1%, respectively. Through this study, the range of application of AZ91 alloys can further be extended.
Title:
Transmission electron microscopy investigation of Ag-free lillianite and heyrovskyite from Vulcano, Aeolian Islands, Italy
Authors:
Mitolo, D; Capitani, GC; Garavelli, A; Pinto, D Author Full Names: Mitolo, Donatella; Capitani, Gian Carlo; Garavelli, Anna; Pinto, Daniela
Source:
AMERICAN MINERALOGIST 96 (2-3): 288-300 FEB-MAR 2011
Abstract:
We present a transmission electron microscopy (TEM) investigation of lillianite (Pb3Bi2S6) and heyrovskyite (Pb6Bi2S9), from Vulcano, Aeolian Islands, Italy. The minerals investigated represent the only naturally occurring Ag- and Cu-free sulfosalts in the lillianite homologous series (LHS). Three methods (crushing, ion-milling, and ultramicrotomy) were used to prepare TEM specimens. Selected area electron diffraction (SAED) patterns and high-resolution TEM (HRTEM) images indicate well-ordered crystals with only minor stacking faults and, more rarely, nanoscale intergrowths of lillianite and heyrovskyite. The latter were sometimes found to form an incommensurate structural modulation with an angle of similar to 29 degrees relative to b* in the (hk0) plane and a wavelength of similar to 75 angstrom. This represents the first observation of such incommensurate modulations in heyrovskyite. Although considerable evidence points toward an artifact induced by the sample preparation technique (i.e., ion-milling), the possibility that the incommensurate modulation could be a primary feature of heyrovskyite itself cannot be completely ruled out. The modulation could derive from an ordering process of Pb and Bi cations over Me4 and Me5 sites within the PbS-like layer or from ordering of vacancies, naturally present or induced by Bi2S3 sublimation during ion-milling.
Title:
Infrared Reflectance Kramers--Kronig Analysis by Anchor-Window Technique
Authors:
Tumenas, S; Kasalynas, I; Karpus, V; Arwin, H Author Full Names: Tumenas, S.; Kasalynas, I.; Karpus, V.; Arwin, H.
Source:
ACTA PHYSICA POLONICA A 119 (2): 140-142 FEB 2011
Abstract:
An algorithm for the Kramers-Kronig analysis of the reflectivity spectra, based on an anchor-window technique is presented. The high-frequency asymptote, required for the Kramers-Kronig analysis, is determined by minimizing differences between the Kramers Kronig-deduced optical constants of a system under investigation and known optical constants measured in a small anchor-window. The algorithm is illustrated by applying it for a reconstruction of the optical conductivity sigma(omega) of the fci-ZnMgRE quasicrystals in the spectral range of 0.01-6.5 eV from the experimental IR Fourier-transform reflectivity data and the experimental spectral ellipsometry VIS-UV data. The reliability of the suggested Kramers-Kronig analysis technique is confirmed by independent infrared spectral ellipsometry sigma(omega) measurements for fci-ZnMgRE.
Title:
ON THE MECHANICAL MILLING OF AlCuCo QUASICRYSTALLINE PHASE.
Authors:
Tellez-Vazquez, JO; Patino-Carachure, C; Garcia-De Leon, E; Rosas, G Author Full Names: Tellez-Vazquez, J. O.; Patino-Carachure, C.; Garcia-De Leon, E.; Rosas, G.
Source:
ACTA MICROSCOPICA 19 (3): 322-327 2010
Abstract:
In the present work, the Al65Cu15Co20 alloy composition was processed by high-energy ball milled to systematically evaluate the phase transitions of the quasicrystalline prealloyed ingot. The quasicrystalline alloy was previously fabricated by conventional casting techniques. Subsequently, this alloy was milled for different times using an SPEX mixer mill. The microstructures were examined by high-resolution electron microscopy and the structural changes were also analyzed by X-ray diffraction patterns. The results indicate that the quasicrystalline alloy is stable after 5 h of milling, containing nano-quasicrystalline domains. However, the sample milled by 10 h shows a quasicrystal-to-amorphous phase transition. Subsequently, after 20 h of milling, the amorphous phase re-crystallizes to the B2 structure type.

Update: 26-Feb-2011

Title:
Structure of BiFeO3 ceramics treated with hot-pressing
Authors:
Su, WN; Wu, XL; Wu, XS; Wang, DH; Du, YW; Chu, PK Author Full Names: Su, W. N.; Wu, X. L.; Wu, X. S.; Wang, D. H.; Du, Y. W.; Chu, Paul K.
Source:
SOLID STATE COMMUNICATIONS 151 (1): 5-8 JAN 2011
Abstract:
BiFeO3 ceramics synthesized at high temperature and pressure is observed to possess large spontaneous polarization and magnetism The selected-area electron diffraction patterns indicate the coexistence of polycrystalline and nanocrystalline grains in the hot-pressed samples Raman spectroscopic studies reveal that the Bi-O bond strain and cations (Fe3+) away from the oxygen octahedral center Induce the polarization The Fe-O bond strain oxygen octahedral rotation around the [111] axis and electromagnons build a long-range interaction between electrical polarization and magnetic moment reorientation to form an Incommensurate spiral magnetic structure This work clearly shows that the hot-pressed treatment can modify the structure and properties of BiFeO3 ceramics (C) 2010 Elsevier Ltd All rights reserved
Title:
Effects of Calcium Addition on High Temperature Creep Resistance of Magnesium Alloys with High Zinc
Authors:
Wan, XF; Sun, YS; Xue, F; Bai, J; Tao, WJ Author Full Names: Wan Xiaofeng; Sun Yangshan; Xue Feng; Bai Jing; Tao Weijian
Source:
RARE METAL MATERIALS AND ENGINEERING 39 (12): 2112-2116 DEC 2010
Abstract:
The effects of trace Ca addition on microstructure and high-temperature creep resistance of as-cast Mg-12Zn-4Al-0.3Mn alloy were investigated. Results show that the as-cast microstructure of the base alloy consists of alpha-Mg matrix and block quasicrystalline phase at gain boundaries. The composition of this quasicrystalline phase is closed to that of the equilibrium tau phase (Mg-32(Al,Zn)(49)) in the Mg-Zn-Al ternary system. A small amount of Ca addition to the base alloy results in the formation of a lamellar eutectic phi(Al2Mg5Zn2) and the transformation of the quasicrystalline phase to the equilibrium tau phase in the as-cast microstructure of the alloy. The volume fraction of the phi phase increases with the increase of Ca addition. The creep resistance of the alloys is significantly improved by Ca addition. The optimum creep resistance of the alloy is obtained by 0.6% Ca addition under the creep condition of 175 degrees C, 70 MPa, whose steady state creep rate is approximately one order of magnitude lower than that of its base alloy.
Title:
Long-range magnetic order in the quasicrystalline approximant Cd6Tb
Authors:
Tamura, R; Muro, Y; Hiroto, T; Nishimoto, K; Takabatake, T Author Full Names: Tamura, R.; Muro, Y.; Hiroto, T.; Nishimoto, K.; Takabatake, T.
Source:
PHYSICAL REVIEW B 82 (22): Art. No. 220201 DEC 8 2010
Abstract:
We report the observation of a long-range magnetic order in a quasicrystalline approximant, i.e., Cd6Tb, demonstrating that a spin glass is not the ground state for the binary approximant but localized spins on the vertices of an icosahedron become antiferromagnetically ordered below 24 K. The result is in contrast to the spin-glasslike behaviors reported for Cd-Mg-R quasicrystals composed of same icosahedral clusters.
Title:
Single composite crystal structure analysis of incommensurate spin-ladder compound Sr2.5Ca11.5Cu24O41
Authors:
Gotoh, Y; Fujihisa, H; Takeya, S; Yamawaki, H; Akimitsu, J Author Full Names: Gotoh, Y.; Fujihisa, H.; Takeya, S.; Yamawaki, H.; Akimitsu, J.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S219-S220 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
Single-crystal X-ray structure analysis of mutually incommensurate (Sr0.36Ca1.64Cu2O3)(0.706)CuO2, "Sr2.5Ca11.5Cu24O41" has been performed on the basis of superspace group approach. The lattice constants of (Sr0.36Ca1.64Cu2O3)(0.706)CuO2 are a = 1.1298(1), b = 1.2582(1), c(1) = 0.2750(1) nm for the CuO2 part and a = 1.1298(1), b = 1.2582(1), c(2) = 0.3897(1) nm for the (Sr0.36Ca1.64Cu2O3) one. From the average structure analysis, it has been expected that the formation of CuO5 with pyramidal coordination by O atoms occurs in the Cu2O3 ladder. The minimum distance between Cu atom in the Cu2O3 ladder and O atom in the CuO2 chain has clearly shown that O in the CuO2 acts as apical oxygen to form the CuO5 coordination. It has been concluded that (Sr0.36Ca1.54Cu2O3)(0.706)CuO2 bears a marked structural resemblance to the cuprate High T-c superconductors. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Phase diagram of the two-dimensional 16-band d-p model for iron-based superconductors
Authors:
Yanagi, Y; Yamakawa, Y; Ono, Y Author Full Names: Yanagi, Y.; Yamakawa, Y.; Ono, Y.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S349-S350 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
The electronic state of the Fe2As2 plane in iron-based superconductors is investigated on the basis of the two-dimensional 16-band d-p model. Using the random phase approximation for the on-site Coulomb interaction between Fe d electrons, we obtain the phase diagram including the magnetic ordered states and the superconductivity. It is found that the s(+/-)-wave superconductivity, where the gap functions have different signs between the electron pockets and the hole pockets, is realized near the incommensurate magnetic ordered phase with q similar to (pi, pi). The absolute values of the gap functions on the Fermi surfaces are almost isotropic but largely depend on the energy bands. (C) 2009 Elsevier B.V. All rights reserved.
Title:
NMR studies of field induced magnetism in CeCoIn5
Authors:
Curro, NJ; Young, BL; Urbano, RR; Graf, MJ Author Full Names: Curro, Nicholas J.; Young, Ben-Li; Urbano, Ricardo R.; Graf, Matthias J.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S521-S524 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
Recent Nuclear Magnetic Resonance and elastic neutron scattering experiments have revealed conclusively the presence of static incommensurate magnetism in the field-induced B phase of CeCoIn5. We analyze the NMR data assuming the hyperfine coupling to the In(2) nuclei is anisotropic and simulate the spectra for several different magnetic structures. The NMR data are consistent with ordered Ce moments along the [001] direction, but are relatively insensitive to the direction of the incommensurate wavevector. (C) 2009 Published by Elsevier B.V.
Title:
NMR study of magnetically-ordered state in a novel superconducting phase in CeCoIn5
Authors:
Kumagai, K; Kondoh, N; Shishido, H; Matsuda, Y Author Full Names: Kumagai, K.; Kondoh, N.; Shishido, H.; Matsuda, Y.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S533-S535 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
The present NMR study indicates an appearance of finite hyperfine fields coupled to incommensurate antiferromagnetic order of the Ce moments in CeCoIn5. The magnetic order is never observed in the normal state and also in the BCS state, but appears only inside the novel superconducting phase. Strong field dependence of the ordered magnetic moments indicates the coexistence of the incommensurate SDW order and an modulated SC (FFLO) state. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Pairing symmetry reflected in vortex lattice structure of noncentrosymmetric superconductors
Authors:
Saiki, T; Hiasa, N; Ikeda, R Author Full Names: Saiki, Taro; Hiasa, Norihito; Ikeda, Ryusuke
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S581-S583 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
A novel type of modulated vortex states to be realized in Rashba noncentrosymmetric superconductors (NCSs) in parallel fields are studied by examining spatial distributions of the gauge-invariant phase of the order parameter Delta. It is found that a modulated structure reflecting a relative shift of the Fermi surfaces is not due to a single type of nodal lines but rather to rows of vortex-antivortex pairs, and that coalescence of these vortex pairs results in a square vortex lattice separated from the familiar triangular lattice via a first order structural transition. Such a structure supported by rows of vortex pairs is also the origin of striped structures in higher odd LL vortex lattices realizable in centrosymmetric systems with a strong paramagnetic depairing. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Se-77 NMR study of nonmagnetic-magnetic transition in (TMTSF)(2)X
Authors:
Mito, T; Nishiyama, K; Koyama, T; Ueda, K; Kohara, T; Takeuchi, K; Akutsu, H; Yamada, J; Kornilov, A; Pudalov, VM; Qualls, JS Author Full Names: Mito, T.; Nishiyama, K.; Koyama, T.; Ueda, K.; Kohara, T.; Takeuchi, K.; Akutsu, H.; Yamada, J.; Kornilov, A.; Pudalov, V. M.; Qualls, J. S.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S592-S593 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
Se-77 NMR measurements have been carried out on (TMTSF)(2)X (X = PF6 and AsF6) single crystals. For both compounds, NMR lines split into double-peaked spectra in the SDW state, which is explained with sinusoidal internal field at Se nucleus positions having the same incommensurate wave number with that of the SDW order. No change in the lineshape was observed at T-x at which the spin-relaxation rate shows a kink, suggesting that this anomaly does not cause significant static changes in internal field at the Se-site. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Ca-for-Sr substitution in the thermoelectric [(Sr,Ca)(2)(O,OH)(2)](q)[CoO2] misfit-layered cobalt-oxide system
Authors:
Yamauchi, H; Karvonen, L; Egashira, T; Tanaka, Y; Karppinen, M Author Full Names: Yamauchi, Hisao; Karvonen, Lassi; Egashira, Takayuki; Tanaka, Yoshiaki; Karppinen, Maarit
Source:
JOURNAL OF SOLID STATE CHEMISTRY 184 (1): 64-69 JAN 2011
Abstract:
Calcium-for-strontium substituted samples of the misfit-layered cobalt-oxide system, [(Sr1-xCax)(2) (O,OH)(2)](q)[CoO2], were successfully synthesized up to x=0.2 with a sample-encapsulation technique originally developed for the x=0 end phase. While the x=0 sample has a commensurate match between the two layer blocks (i.e. q=0.5), isovalent Ca-for-Sr substitution induces lattice misfit (i.e. q > 0.5). At the same time the Seebeck coefficient gets increased, but the increase in resistivity results in suppressing the thermoelectric power factor. The magnetic anomaly in the x=0 sample gets released upon the Ca substitution for the x=0.2 sample to exhibit an almost Curie-Weiss behavior. It is concluded that with increasing x in [(Sr1-xCax)(2)(O,OH)(2)](q)[CoO2] the properties smoothly evolve towards those previously reported for the x=1.0 end member, [Ca1.7O2.1H2.4](0.58)[CoO2]. (C) 2010 Elsevier Inc. All rights reserved.
Title:
Crystal nucleation of colloidal hard dumbbells
Authors:
Ni, R; Dijkstra, M Author Full Names: Ni, Ran; Dijkstra, Marjolein
Source:
JOURNAL OF CHEMICAL PHYSICS 134 (3): Art. No. 034501 JAN 21 2011
Abstract:
Using computer simulations, we investigate the homogeneous crystal nucleation in suspensions of colloidal hard dumbbells. The free energy barriers are determined by Monte Carlo simulations using the umbrella sampling technique. We calculate the nucleation rates for the plastic crystal and the aperiodic crystal phase using the kinetic prefactor as determined from event driven molecular dynamics simulations. We find good agreement with the nucleation rates determined from spontaneous nucleation events observed in event driven molecular dynamics simulations within error bars of one order of magnitude. We study the effect of aspect ratio of the dumbbells on the nucleation of plastic and aperiodic crystal phases, and we also determine the structure of the critical nuclei. Moreover, we find that the nucleation of the aligned close-packed crystal structure is strongly suppressed by a high free energy barrier at low supersaturations and slow dynamics at high supersaturations. (C) 2011 American Institute of Physics. [doi:10.1063/1.3528222]
Title:
Correlation between primary phases and atomic clusters in a Zr-based metallic glass
Authors:
Liu, XJ; Chen, GL; Liu, CT Author Full Names: Liu, X. J.; Chen, G. L.; Liu, C. T.
Source:
JOURNAL OF APPLIED PHYSICS 108 (12): Art. No. 123516 DEC 15 2010
Abstract:
Atomic clusters exiting in the Zr65Ti10Ni25 metallic glass and primary phases generated during crystallization were studied by x-ray scattering and high-resolution transmission microscopy. An intrinsic correlation between the atomic clusters and the primary phases has been revealed. It is found that there are topological icosahedral short-range orders (ISROs) in the as-cast sample in addition to fcc-Zr2Ni-type chemical SROs. These topological ISRO and fcc-Zr2Ni-type chemical SRO can simultaneously quasicrystallize/crystallize into the corresponding nanoscaled icosahedral quasicrystalline phase (I-phase) and fcc-Zr2Ni crystal as primary products during crystallization. The synchronic precipitation of these two metastable phases can be understood in terms of their structural similarity between the fcc-Zr2Ni and I-phase in local atomic configuration. In comparison with fcc-Zr2Ni crystal, the I-phase has a smaller size and lower volume fraction due to its lower growth rate attributed to its more complex composition and higher structural symmetry. The competitive growth between these two phases results in the development of nanostructured materials in this alloy after annealing. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3525985]
Title:
Cold-sprayed Coatings based on High Strength Aluminium alloys Reinforced by Quasicrystalline Particles: Microstructure and Key Properties
Authors:
Byakova, AV; Kiz, MM; Sirko, AI; Yakovleva, MS; Milman, YV Author Full Names: Byakova, A. V.; Kiz, M. M.; Sirko, A. I.; Yakovleva, M. S.; Milman, Yu. V.
Source:
HIGH TEMPERATURE MATERIALS AND PROCESSES 29 (5-6): 325-337 Sp. Iss. SI 2010
Abstract:
This study presents significant advantages of cold-spraying in performance of coatings based on Al matrix reinforced by metastable nano- and submicrosized quasicrystalline particles as compared to those processed by thermal spraying and, in particular, by high velocity oxy-fuel (HVOF) spraying technique. Two kinds of feedstock powders with nominal compositions. Al94Fe3Cr3 and Al94Fe2.5Cr2.5Ti1 were employed in spraying the coatings on cold rolled steel substrate. Microstructure and key mechanical characteristics of feedstock powders and coatings performed by cold-spraying and HVOF process were studied and discussed. The main benefit of cold-spraying as opposed to HVOF spraying was that the composite quasicrystalline structure of initial feedstock powders is retained in the interior of flattened particles heavily deformed under impact in solid state. Strain hardening of coating and substrate is resulted from impact during cold-spraying. The results showed that unlike to HVOF sprayed coatings important advantage of cold-sprayed quasicrystalline coatings is referred to combination of increased hardness with ductility indicated by plasticity characteristic just about critical value delta(H) approximate to 0.9, which is quite enough for preventing brittle failure of material during particle impact onto substrate or previously deposited particles.
Title:
Interfaces between Lead and Amorphous Matrices in Immiscible Alloy Systems
Authors:
Singh, A; Tsai, AP Author Full Names: Singh, Alok; Tsai, A. P.
Source:
HIGH TEMPERATURE MATERIALS AND PROCESSES 29 (5-6): 523-530 Sp. Iss. SI 2010
Abstract:
Interfaces between solid lead and amorphous matrix are described, with experimental data from system of lead particles embedded into Al-Cu-V amorphous matrix. Since the structure of the amorphous matrix cannot be described with surety, it has been approached by taking known factors in account, such as the relative stability of various facets of lead and its interfaces with quasicrystals. Lead particles take a round shape in accordance with the amorphous matrix, and are often twinned to form more uniform facets (with uniform energy) on the surface/interface. Interface stability of the lead particle; is indicated by their melting and solidification behavior. Therefore melting and solidification behavior of the embedded particles in amorphous matrix has been compared with those in crystalline and quasicrystalline matrices.
Title:
Crystal structure of simple metals at high pressures
Authors:
Degtyareva, O Author Full Names: Degtyareva, Olga
Source:
HIGH PRESSURE RESEARCH 30 (3): 343-371 2010
Abstract:
The effects of pressure on the crystal structure of simple (or sp-) elements are analysed in terms of changes in coordination number, packing density, and interatomic distances, and general rules are established. In the polyvalent elements from groups 14-17, the covalently bonded structures tend to transform to metallic phases with a gradual increase in coordination number and packing density, a behaviour normally expected under pressure. Group 1 and 2 metallic elements, however, show a reverse trend towards structures with low packing density due to intricate changes in their electronic structure. Complex crystal structures such as host-guest and incommensurately modulated structures found in these elements are given special attention in this review in an attempt to determine their role in the observed phase-transition sequences.
Title:
Antiferroelectric (Pb,Bi)(1-x)Fe1+xO3-y Perovskites Modulated by Crystallographic Shear Planes
Authors:
Abakumov, AM; Batuk, D; Hadermann, J; Rozova, MG; Sheptyakov, DV; Tsirlin, AA; Niermann, D; Waschkowski, F; Hemberger, J; Van Tendeloo, G; Antipov, EV Author Full Names: Abakumov, Artem M.; Batuk, Dmitry; Hadermann, Joke; Rozova, Marina G.; Sheptyakov, Denis V.; Tsirlin, Alexander A.; Niermann, Daniel; Waschkowski, Florian; Hemberger, Joachim; Van Tendeloo, Gustaaf; Antipov, Evgeny V.
Source:
CHEMISTRY OF MATERIALS 23 (2): 255-265 JAN 25 2011
Abstract:
We demonstrate for the first time a possibility to vary the anion content in perovskites over a wide range through a long-range-ordered arrangement of crystallographic shear (CS) planes. Anion-deficient perovskites (Pb,Bi)(1-x)Fe1+xO3-y with incommensurately modulated structures were prepared as single phases in the compositional range from Pb0.857Bi0.094Fe1.049O2.572 to Pb0.409Bi0.567Fe1.025O2.796. Using a combination of electron diffraction and high-resolution scanning transmission electron microscopy, we constructed a superspace model describing a periodic arrangement of the CS planes. The model was verified by refinement of the Pb0.64Bi0.32Fe1.04O2.675 crystal structure from neutron powder diffraction data ((3 + 1)D S.G. X2/m(alpha 0 gamma), X = [1/2,1/2,1/2,1/2], a = 3.9082(1) angstrom, b = 3.90333(8) angstrom, c = 4.0900(1) angstrom, beta = 91.936(2)degrees, q = 0.05013(4)a* + 0.09170(3)c* at T = 700 K, R-P = 0.036, R-wP = 0.048). The (Pb,Bi)(1-x)Fe1+xO3-y structures consist of perovskite blocks separated by CS planes confined to nearly the (509)(p) perovskite plane. Along the CS planes, the perovskite blocks are shifted with respect to each other over the 1/2[110](p) vector that transforms the corner-sharing connectivity of the FeO6 octahedra in the perovskite framework to an edge-sharing connectivity of the FeO5 pyramids at the CS plane, thus reducing the oxygen content. Variation of the chemical composition in the (Pb,Bi)(1-x)Fe1+xO3-y series occurs mainly because of a changing thickness of the perovskite block between the interfaces, that can be expressed through the components of the q vector as Pb6 gamma+2 alpha Bi1-7 gamma-alpha Fe1+gamma-alpha O3-3 gamma-alpha. The Pb, Bi, and Fe atoms are subjected to strong displacements occurring in antiparallel directions on both sides of the perovskite blocks, resulting in an antiferroelectric-type structure. This is corroborated by the temperature-, frequency-, and field-dependent complex permittivity measurements . Pb0.64Bi0.32Fe1.04O2.675 demonstrates a remarkably high resistivity > 0.1 T Omega cm at room temperature and orders antiferromagnetically below T-N = 608(10) K.
Title:
Structural Evolution of the BiFeO3-LaFeO3 System
Authors:
Rusakov, DA; Abakumov, AM; Yamaura, K; Belik, AA; Van Tendeloo, G; Takayama-Muromachi, E Author Full Names: Rusakov, Dmitriy A.; Abakumov, Artem M.; Yamaura, Kazunari; Belik, Alexei A.; Van Tendeloo, Gustaaf; Takayama-Muromachi, Eiji
Source:
CHEMISTRY OF MATERIALS 23 (2): 285-292 JAN 25 2011
Abstract:
The (1 - x)BiFeO3-xLaFeO(3) system has been investigated and characterized by room-temperature and high-temperature laboratory and synchrotron powder X-ray diffraction, electron diffraction, high-resolution transmission electron microscopy, differential scanning calorimetry, and magnetization measurements. At room temperature, the ferroelectric R3c phase is observed for 0.0 <= x <= 0.10. The PbZrO3-related root 2a(p) x 2 root 2a(p) x 4a(p) superstructure (where a(p) is the parameter of the cubic perovskite subcell) is observed for Bi0.82La0.18FeO3, while an incommensurately modulated phase is formed for 0.19 <= x <= 0.30 with the root 2a(p) x 2a(p) x root 2a(p) basic unit cell. The GdFeO3-type phase with space group Pnma (root 2a(p) x 2a(p) x root 2a(p)) is stable at 0.50 <= x <= 1. Bi0.82La0.18FeO3 has no detectable homogeneity range (space group Pnma, a = 5.6004(1) angstrom, b = 11.2493(3) angstrom, c = 15.6179(3) angstrom). The incommensurately modulated Bi0.75La0.25FeO3 structure was solved from synchrotron X-ray powder diffraction data (Imma(00 gamma)s00 superspace group, a = 5.5956(1) angstrom, h = 7.8171(1) angstrom, c = 5.62055(8) angstrom; q = 0.4855(4)c*, R-P = 0.023, R-wP = 0.033). In this structure, cooperative displacements of the Bi and O atoms occur, which order within the (AO) (where A = Bi, La) layers, resulting in an antipolar structure. Local fluctuations of the intralayer antipolar ordering are compensated by an interaction with the neighboring (AO) layers. A coupling of the an tipolar displacements with the cooperative tilting distortion of the perovskite octahedral framework is proposed as the origin of the incommensurability. All the phases transform to the GdFeO3-type structure at high temperatures. Bi0.82La0.18FeO3 shows an intermediate PbZrO3-type phase with root 2a(p) x 2 root 2a(p) x 2a(p) (space group Pbam; a = 5.6154(2) angstrom, b = 11.2710(4) angstrom, and c = 7.8248(2) angstrom at 570 K). The compounds in the compositional range of 0.18 <= x <= 0.95 are canted antiferromagnets.
Title:
Observation of anomalous phonons in orthorhombic rare-earth manganites
Authors:
Gao, P; Chen, HY; Tyson, TA; Liu, ZX; Bai, JM; Wang, LP; Choi, YJ; Cheong, SW Author Full Names: Gao, P.; Chen, H. Y.; Tyson, T. A.; Liu, Z. X.; Bai, J. M.; Wang, L. P.; Choi, Y. J.; Cheong, S. -W.
Source:
APPLIED PHYSICS LETTERS 97 (26): Art. No. 262905 DEC 27 2010
Abstract:
We observe the appearance of a phonon near the lock-in temperature in orthorhombic REMnO3 (RE denotes rare earth) (RE: Lu and Ho) and anomalous phonon hardening in orthorhombic LuMnO3. The anomalous phonon occurs at the onset of spontaneous polarization. No such changes were found in incommensurate orthorhombic DyMnO3. These observations directly reveal different electric polarization mechanisms in the E-type and incommensurate-type orthorhombic REMnO3. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3533022]

Update: 18-Feb-2011

Title:
Direct methods beyond small-molecule crystallography
Authors:
Fan, HF Author Full Names: Fan, Hai-fu
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 207 (12): 2621-2638 DEC 2010
Abstract:
The development of direct methods outside their traditional field began since the middle 1960s. New applications were explored gradually in four directions. They are the transition of: (i) from single crystals to powder samples, (ii) from X-ray crystallography to electronmicroscopy (EM), (iii) from periodic structures to incommensurate structures and (iv) from small molecules to macromolecular structures. The research on methods of solving crystal structures at the Institute of Physics in Beijing has been focused on the last three directions. The transition of direct methods from X-ray crystallography to EM led to a two-step image processing technique in high-resolution electron microscopy (HREM). This technique combines information of EM and that of electron diffraction (ED) revealing the structure of minute crystals that are unsuitable for X-ray diffraction analysis. The transition of direct methods from periodic crystal structures to incommensurate structures led to the multi-dimensional direct methods enabling ab initio solution of incommensurate modulated structures and composite structures without relying on an assumed modulation model or even the known basic structure. Finally the combination of direct methods with traditional protein crystallographic methods has greatly enhanced the ability of solving protein structures. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Electronic properties of stable decagonal quasicrystals
Authors:
Zhang, DL Author Full Names: Zhang, Dianlin
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 207 (12): 2666-2673 DEC 2010
Abstract:
Selected topics of electronic properties of stable decagonal quasicrystals are reviewed. Phonon localization and enhanced electron-phonon interaction may play important roles in the transport properties of these materials. The electronic specific heat measurements support the picture that the Hume-Rothery instability is responsible for the formation of the phase. On the other hand, careful examination of the magnetoresistance on highly oriented quasicrystalline films does not support the applicability of the quantum interference effect to the phenomenon. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Magnetic Phase Transitions and Magnetic-Field-Induced Polarization Flops in Multiferroic YbMn2O5
Authors:
Fukunaga, M; Sakamoto, Y; Kimura, H; Noda, Y Author Full Names: Fukunaga, Mamoru; Sakamoto, Yuma; Kimura, Hiroyuki; Noda, Yukio
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (1): Art. No. 014705 JAN 2011
Abstract:
We have measured the electric polarization along the b- and a-axes of multiferroic YbMn2O5 under a magnetic field along the c-axis up to 14.5 T. We found that the polarization along the b-axis disappears, while that along the a-axis appears below 5.5 K in 0 T, though the direction of the polarization switches again above 1.5 T at 4.3 K. Ferroelectric hysteresis loops along the both axes of YbMn2O5 were clearly observed by the double-wave method. This polarization-flop phenomenon is very similar to that previously found in TmMn2O5. We have also studied the magnetic phase transitions of YbMn2O5 by neutron diffraction, and compared the data with those of TmMn2O5. The low-temperature incommensurate magnetic phases relating to the polarization flop of YbMn2O5 and TmMn2O5 are similar, though YbMn2O5 lacks a commensurate magnetic and ferroelectric phase which exists in TmMn2O5 and typical similar compounds.
Title:
Magnetic properties of the Ag-In-rare-earth 1/1 approximants
Authors:
Ibuka, S; Iida, K; Sato, TJ Author Full Names: Ibuka, Soshi; Iida, Kazuki; Sato, Taku J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (5): Art. No. 056001 FEB 9 2011
Abstract:
We have performed magnetic susceptibility and neutron scattering measurements on polycrystalline Ag-In-RE (RE, rare-earth) 1/1 approximants. In the magnetic susceptibility measurements, for most of the RE elements, inverse susceptibility shows linear behaviour in a wide temperature range, confirming well localized isotropic moments for the RE3+ ions. Exceptionally for the light RE elements, such as Ce and Pr, nonlinear behaviour was observed, possibly due to significant crystalline field splitting or valence fluctuation. For RE = Tb, the susceptibility measurement clearly shows a bifurcation of the field-cooled and zero-field-cooled susceptibility at T-f = 3.7 K, suggesting a spin-glass-like freezing. On the other hand, neutron scattering measurements detect significant development of short-range antiferromagnetic spin correlations in the elastic channel, which is accompanied by a broad peak at (sic)omega = 4 meV in the inelastic scattering spectrum. These features have striking similarity to those in the Zn-Mg-Tb quasicrystals, suggesting that the short-range spin freezing behaviour is due to local high-symmetry clusters commonly seen in both systems.
Title:
Temperature and magnetic field induced multiple magnetic transitions in DyAg2
Authors:
Arora, P; Chattopadhyay, MK; Chandra, LSS; Sharma, VK; Roy, SB Author Full Names: Arora, Parul; Chattopadhyay, M. K.; Chandra, L. S. Sharath; Sharma, V. K.; Roy, S. B.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (5): Art. No. 056002 FEB 9 2011
Abstract:
The magnetic properties of the rare-earth intermetallic compound DyAg2 are studied in detail with the help of magnetization and heat capacity measurements. It is shown that the multiple magnetic phase transitions can be induced in DyAg2 both by temperature and magnetic field. The detailed magnetic phase diagram of DyAg2 is determined experimentally. It was already known that DyAg2 undergoes an incommensurate to commensurate antiferromagnetic phase transition close to 10 K. The present experimental results highlight the first order nature of this phase transition, and show that this transition can be induced by magnetic field as well. It is further shown that another isothermal magnetic field induced transition or metamagnetic transition exhibited by DyAg2 at still lower temperatures is also of first order nature. The multiple magnetic phase transitions in DyAg2 give rise to large peaks in the temperature dependence of the heat capacity below 17 K, which indicates its potential as a magnetic regenerator material for cryocooler related applications. In addition it is found that because of the presence of the temperature and field induced magnetic phase transitions, and because of short range magnetic correlations deep inside the paramagnetic regime, DyAg2 exhibits a fairly large magnetocaloric effect over a wide temperature window, e.g., between 10 and 60 K.
Title:
Effect of composition on the i-phase cell parameter of Ti-(Zr,Cu)-Ni alloys
Authors:
Kocjan, A; McGuiness, PJ; Recnik, A; Kovac, J; Kobe, S Author Full Names: Kocjan, A.; McGuiness, P. J.; Recnik, A.; Kovac, J.; Kobe, S.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 356 (50-51): 2769-2773 NOV 2010
Abstract:
Quasicrystalline (i-phase) Ti-Zr-Ni samples were obtained using the melt-spinning technique where the Ti/Zr ratio ranged from 1 to 3 while the Ni content remained nearly constant varying between 17 and 20 at % We replaced the Zr with 3 and 5 at % of Cu in order to test the i-phase-forming ability of the samples which were all subsequently hydrided from the gas phase at 45 bar and 300 C for 1000 min We then made XRD analyses of the as spun and loaded samples in order to determine the influence of the composition and the absorbed hydrogen content on the cell parameter of the i phase An almost linear decrease of this parameter with the ([Ti] + [Cu])/[Zr] ratio was found for the as-prepared and hydrided samples where the slope of the lineal fit is preserved after hydrogenation but with about 6% higher values due to the expansion of the quasi lattice XPS analyses of the melt-spun i-Ti45Zr35Ni17Cu3 revealed an oxide-layer thickness of 4 nm A TEM investigation revealed that the size of the i-phase grains on the wheel side of the ribbon was approximately five times smaller than on the bright side as a result of the higher cooling rate and the resulting faster nucleation rate (C) 2010 Elsevier BV All rights reserved
Title:
Magneto structural transition in the DySi CrB- and micro-structural changes in the FeB-type compounds by XRPD and neutron diffraction
Authors:
Schobinger-Papamantellos, P; Brunelli, M; Rodriguez-Carvajal, J; Buschow, KHJ; Ritter, C; Gramm, F Author Full Names: Schobinger-Papamantellos, P.; Brunelli, M.; Rodriguez-Carvajal, J.; Buschow, K. H. J.; Ritter, C.; Gramm, F.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 323 (7): 903-914 APR 2011
Abstract:
We present the magnetic temperature phase diagrams of the CrB- and FeB-type orthorhombic phases of the DySi compound, determined from high-quality powder XRPD and neutron diffraction, as well as the sample microstructure as determined by HRTEM. Both phase diagrams comprise a HT (T-c1, T-c2 - T-N) and a LT range (5K-T-c1, T-c2) separated by a monoclinic phase transition at T-c1 = T-c2 = 23.5 K well below the second-order Neel transition (T-N = 40 K). The transition paths are for CrB-type Cmcm (HT) T-c1 -> C-2/m11 (LT), and for FeB Pnma (HT) T-c2 -> P2(1)/n11 (LT). The transitions are related to non-monotonous changes of the lattice and structural parameters displaying anomalies at T-c1, T-c2 and slight volume changes. For the CrB-type the monoclinic angle decreases smoothly from T-c1 down to 5 K and the maximum strain experienced by the crystal lattice in the (0 2 1) direction was found at T-c1. In the FeB-type, in addition to the magneto-elastic transition at T-c2 = 23.5 K, minor anomalies are found at 13.5 K in the temperature dependence of the monoclinic angle and the maximum strain along (0 1 1). Both temperatures mark the sequence of changes in the magnetic domain microstructure observed in FeB: below T-2 = 23.5 K the incommensurate HT magnetic phase with q(3) approximate to (01/2 1/7) disproportionates into two LT phases q(3) approximate to (01/2 1/11) T-2 and q(2) approximate to (01/2 1/6) coexisting in the form of domains with portions varying with T going from T-2 down to 13.5 K(q(2) increasing at the cost of q(3)). This behaviour could be related to structural inhomogeneities below the first-order magneto-elastic transition T-c2, if one assumes a broad two phase range, where the HT (Pnma) phase coexists with(P2(1)/n) as a metastable phase at LT in the form of domains with different magnetic behaviour. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Helical Magnetic Structure in a Quasi-One-Dimensional LiCu2O2 Multiferroic Crystal According to Cu-63,Cu-65 NMR Studies
Authors:
Sadykov, AF; Gerashchenko, AP; Piskunov, YV; Ogloblichev, VV; Buzlukov, AL; Verkhovskii, SV; Yakubovskii, AY; Kumagai, K Author Full Names: Sadykov, A. F.; Gerashchenko, A. P.; Piskunov, Yu. V.; Ogloblichev, V. V.; Buzlukov, A. L.; Verkhovskii, S. V.; Yakubovskii, A. Yu.; Kumagai, K.
Source:
JETP LETTERS 92 (8): 527-531 OCT 2010
Abstract:
The NMR spectra of Cu-63 and Cu-65 natural copper isotopes in a LiCu2O2 multiferroic single crystal compound have been measured above and below the temperature of magnetic phase transition (T-c = 23 K) in zero magnetic field and in applied magnetic field H-0 = 94 kOe parallel to the c axis of the crystal. In LiCu(2O)2 below T-c, a complicated helical magnetic structure with the magnetic moment of copper ions Cu2+ varying along the chain according to the harmonic law with the wave vector being incommensurate to the crystal lattice constants has been revealed. The experimental results have been successfully interpreted using the model based on the planar helical magnetic structure. It has been found that the plane of rotation for Cu2+ magnetic moments in LiCu2O2 does not coincide at H-0 = 0 with the ab plane. The high magnetic field (H-0 = 94 kOe) applied along the c axis of the single crystal does not affect the spatial orientation of the plane of rotation.
Title:
Ab initio reconstruction of difference densities by charge flipping
Authors:
Palatinus, L; Fleischer, F; Pattison, P; Weber, T; Steurer, W Author Full Names: Palatinus, Lukas; Fleischer, Frank; Pattison, Phillip; Weber, Thomas; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 67: 9-20 Part 1 JAN 2011
Abstract:
The charge-flipping algorithm in its band-flipping variant is capable of ab initio reconstructions of scattering densities with positive and negative values. It is shown that the method can be applied to reconstructions of difference electron densities of superstructures, i.e. densities obtained as a difference between the true scattering density and the average density over two or more subcells of the true structure. The amplitudes of reflections lying on the reciprocal lattice of the subcell are not required for the procedure. A series of examples shows applications of the method to the solution of superstructures in periodic crystals or quasicrystals as well as the application to ab initio solution of modulation of an incommensurately modulated structure from satellite reflections only and solution of a structure from a crystal twinned by reticular pseudomerohedry. The method is especially suited for solving pseudosymmetry problems occurring frequently in superstructures.
Title:
Generation of (3+d)-dimensional superspace groups for describing the symmetry of modulated crystalline structures
Authors:
Stokes, HT; Campbell, BJ; van Smaalen, S Author Full Names: Stokes, Harold T.; Campbell, Branton J.; van Smaalen, Sander
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 67: 45-55 Part 1 JAN 2011
Abstract:
A complete table of (3 + 1)D, (3 + 2)D and (3 + 3)D superspace groups (SSGs) has been enumerated that corrects omissions and duplicate entries in previous tables of superspace groups and Bravais classes. The theoretical methods employed are not new, though the implementation is both novel and robust. The paper also describes conventions for assigning a unique one-line symbol for each group in the table. Finally, a new online data repository is introduced that delivers more complete information about each SSG than has been presented previously.

Update: 4-Feb-2011

Title:
Investigation of thermodynamic properties and magnetic ordering in TmNiIn
Authors:
Baran, S; Kaczorowski, D; Arulraj, A; Penc, B; Szytula, A Author Full Names: Baran, S.; Kaczorowski, D.; Arulraj, A.; Penc, B.; Szytula, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 323 (6): 833-837 MAR 2011
Abstract:
The magnetic, electrical resistivity, specific heat and powder neutron diffraction measurements were performed on a polycrystalline sample of TmNiIn. The compound crystallizes in a hexagonal structure of the ZrNiAl-type. It orders antiferromagnetically below T-N = 2.5 K. The magnetic structure is an incommensurate one and may be described by the propagation vector (k) over right arrow = [k(x),k(x),1/2], where k(x)=0.281(2). The magnetic moments are confined within the basal hexagonal plane. The results are compared with those reported for isostructural thulium compounds like TmAgSi, TmAgGe and TmPtIn. (C) 2010 Elsevier B.V. All rights reserved.

Update: 28-Jan-2011

Title:
Bond orientational ordering in a metastable supercooled liquid: a shadow of crystallization and liquid-liquid transition
Authors:
Tanaka, H Author Full Names: Tanaka, Hajime
Source:
JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT : Art. No. P12001 DEC 2010
Abstract:
It is widely believed that a liquid state can be characterized by a single order parameter, density, and that a transition from a liquid to solid can be described by density ordering (translational ordering). For example, this type of theory has had great success in describing the phase behaviour of hard spheres. However, there are some features that cannot be captured by such theories. For example, hard spheres crystallize into either hcp or fcc structures, without a tendency of bcc ordering which is expected by the Alexander-McTague theory based on the Landau-type free energy of the density order parameter. We also found hcp-like bond orientational ordering in a metastable supercooled liquid, which promotes nucleation of hcp crystals. Furthermore, theories based on the single order parameter cannot explain water-like thermodynamic and kinetic anomalies of a liquid and liquid-liquid transition in a single-component liquid. Based on these facts, we argue that we need an additional order parameter to describe a liquid state. It is bond orientational order, which is induced by dense packing in hard spheres or by directional bonding in molecular and atomic liquids. Bond orientational order is intrinsically of local nature, unlike translational order which is of global nature. This feature plays a unique role in crystallization and quasicrystal formation. We also reveal that bond orientational ordering is a cause of dynamic heterogeneity near a glass transition and is linked to slow dynamics. In relation to this, we note that, for describing the structuring of a highly disordered liquid, we need a structural signature of low configurational entropy, which is more general than bond orientational order. Finally, the water-like anomaly and liquid-liquid transition can be explained by bond orientational ordering due to hydrogen or covalent bonding and its cooperativity, respectively. So we argue that bond orientational ordering is a key to the physical understanding of crystallization, quasicrystallization, glass transition, water-like anomaly and liquid-liquid transition. A unified description of these phenomena may be possible along this line.

Update: 21-Jan-2011

Title:
Effect of infrared illumination on the modulated magnetic structure of the weak ferromagnet FeBO3: Mg
Authors:
Sokolov, BY Author Full Names: Sokolov, B. Yu.
Source:
PHYSICS OF THE SOLID STATE 52 (12): 2527-2534 DEC 2010
Abstract:
The effect of unpolarized white light on the period and conditions of the existence of the modulated magnetic structure of the FeBO3: Mg single crystal, which is formed in this easy-plane weak ferromagnet in the low-temperature range during technical magnetization, has been investigated experimentally. It has been revealed that the degree of light action on the magnetic state of the crystal depends on both the irradiation duration and the orientation of the ferromagnetic vector during illumination. It has been established that light with wavelengths in the range 0.8 mu m < lambda < 0.9 mu m has a maximum effect on the parameters of the modulated magnetic structure formed in the FeBO3: Mg single crystal. The results obtained have been interpreted in the framework of the "magnetic ripple" theory using the model of photosensitivity of anisotropic magnetic centers associated with the presence of Mg impurity ions in the composition of the crystal.
Title:
Quasicrystal-like structure and its crystalline approximant in an Fe48Cr15Mo14C15B6Tm2 bulk metallic glass
Authors:
Hirata, A; Hirotsu, Y; Amiya, K; Inoue, A Author Full Names: Hirata, Akihiko; Hirotsu, Yoshihiko; Amiya, Kenji; Inoue, Akihisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 504: S186-S189 Suppl. 1 AUG 2010
Abstract:
Nanoscale quasicrystal-like structural states have been found in the course of crystallization in an Fe-based Fe48Cr15Mo14C15B6Tm2 bulk metallic glass. The quasicrystal-like structure is similar with the chi-FeCrMo structure exhibiting a deformed tenfold diffraction pattern due to projected pentagonal arrangements regarded as a Mo framework. We show the preliminary structural model for the quasicrystal-like structure and discuss the three-dimensional features based on the chi-FeCrMo crystalline approximant. (C) 2010 Elsevier B.V. All rights reserved.
Title:
TEM study of the cooling rate dependent crystallization behavior of (Zr65Al10Ni10Cu15)(98)Nb-2 metallic glass
Authors:
Wang, YM; Shek, CH; Wang, Q; Qiang, JB; Dong, CA Author Full Names: Wang, Yingmin; Shek, Chan Hung; Wang, Qing; Qiang, Jianbing; Dong, Chuang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 504: S234-S238 Suppl. 1 AUG 2010
Abstract:
The crystallization of (Zr65Al10Ni10Cu15)(98)Nb-2 metallic glasses has been studied using transmission electron microscopy (TEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The ribbon glass and bulk metallic glass (BMG) of this alloy exhibit different crystallization behaviors. For ribbon glass in the first stage crystallization, icosahedral quasicrystal (I-phase) precipitated together with the eta-Zr2Ni (a = 1.226 nm) phase. The BMG alloy transforms into the I-phase and two coherently coexisted phases, namely, the Al2Zr3 phase and an unknown primitive cubic phase (a = 0.76 nm) in this stage. The experimental evidence indicates that the liquid cooling rate for sample preparation has a significant effect on its crystallization behavior of this alloy glass. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Decomposition of icosahedral phase in Ti52Zr28Ni20 powder during electro-discharge sintering
Authors:
Song, GA; Shin, JS; Kang, TJ; Choi, HS; Lee, JK; Lee, MH; Kim, TS; Fleury, E; Prima, F; Lee, WH; Kim, KB Author Full Names: Song, G. A.; Shin, J. S.; Kang, T. J.; Choi, H. S.; Lee, J. K.; Lee, M. H.; Kim, T. S.; Fleury, E.; Prima, F.; Lee, W. H.; Kim, K. B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 504: S302-S305 Suppl. 1 AUG 2010
Abstract:
A single pulse of 0.57-1.1 kJ/0.45 g-atomized spherical Ti52Zr28Ni20 powders in size range of 10-30 and 30-50 mu m consisting of a mixture of beta-(Ti, Zr) and icosahedral phases was applied to understand the structural evolution of icosahedral phase during electro-discharge sintering (EDS). The structural analysis revealed that high electrical input energies leaded to complete decomposition of icosahedral phase into C14 Laves and beta-(Ti, Zr) phases. Furthermore, the critical input energy inducing decomposition of icosahedral phase during EDS is dependent on the size of the powder. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Characterisation of an Al93Fe3Cr2Ti2 alloy obtained by spray forming
Authors:
Garcia-Escorial, A; Echevarria, M; Lieblich, M; Stone, I Author Full Names: Garcia-Escorial, A.; Echevarria, M.; Lieblich, M.; Stone, I.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 504: S519-S521 Suppl. 1 AUG 2010
Abstract:
Al93Fe3Cr2Ti2 is a highly promising alloy due to its capacity to form quasicrystals. In the present work bulk Al93Fe3Cr2Ti2 obtained by spray forming is microstructurally characterised. A microstructure gradient is observed, in which the external layer consists of an alpha-Al matrix with Al3Ti precipitates and fine quasicrystals while the internal core presents intermetallics of the equilibrium phases Al13Cr2 + Al13Fe4, with intermediate stages between both areas. The hardness ranges from the 140Hv of the external layer to the 90Hv of the core. Spray forming can therefore produce nanoquasicrystalline Al93Fe3Cr2Ti2 which evolves towards equilibrium as the process proceeds, due to the heating produced by the deposition of successive layers. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Composites reinforced by Al-Cu-Fe quasicrystalline particles with a copper matrix and their tribological properties
Authors:
Shaitura, DS; Teplov, AA; Chikina, EA; Klevachev, AM; Efimochkin, IY; Fedotov, SV; Petrzhik, MI; Levashov, EA; Abuzin, YA Author Full Names: Shaitura, D. S.; Teplov, A. A.; Chikina, E. A.; Klevachev, A. M.; Efimochkin, I. Yu.; Fedotov, S. V.; Petrzhik, M. I.; Levashov, E. A.; Abuzin, Yu. A.
Source:
JOURNAL OF SURFACE INVESTIGATION-X-RAY SYNCHROTRON AND NEUTRON TECHNIQUES 4 (6): 951-955 NOV 2010
Abstract:
Copper-based composite coatings with addition of 34 wt % of Al-Cu-Fe quasicrystalline powder of dispersity less than 20 fum, as well as 70 wt % of quasicrystalline powder of dispersity less than 40fum and less than 3 fum, were produced by the cold spray process. The phase composition during annealing of samples at various temperatures was studied by X-ray phase analysis. Tribological properties of each composite coating and pure copper were investigated. The experimental results showed a considerable improvement of the tribological properties of the material at the addition of quasicrystals. The least wear was observed in the composite sample containing quasicrystalline inclusions of less than 3 fum subjected to thermal treatment. In this case the counterbody wear was practically absent.

Update: 14-Jan-2011

Title:
DELONE MEASURES OF FINITE LOCAL COMPLEXITY AND APPLICATIONS TO SPECTRAL THEORY OF ONE-DIMENSIONAL CONTINUUM MODELS OF QUASICRYSTALS
Authors:
Klassert, S; Lenz, D; Stollmann, P Author Full Names: Klassert, Steffen; Lenz, Daniel; Stollmann, Peter
Source:
DISCRETE AND CONTINUOUS DYNAMICAL SYSTEMS 29 (4): 1553-1571 Sp. Iss. SI APR 2011
Abstract:
We study measures on the real line and present various versions of what it means for such a measure to take only finitely many values. We then study perturbations of the Laplacian by such measures. Using Kotani-Remling theory, we show that the resulting operators have empty absolutely continuous spectrum if the measures are not periodic. When combined with Gordon type arguments this allows us to prove purely singular continuous spectrum for some continuum models of quasicrystals.
Title:
X-ray topography study of deformed composites obtained by directional solidification of Al-Cu-Co alloy
Authors:
Krawczyk, J; Bogdanowicz, W; Goryczka, T Author Full Names: Krawczyk, J.; Bogdanowicz, W.; Goryczka, T.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY 45 (12): 1321-1325 Sp. Iss. SI DEC 2010
Abstract:
Fibre-reinforced composites were produced by the modification of the static horizontal Bridgman method. The single-crystalline composite matrix consisted of the tetragonal T phase (Al72Cu27Co1). Decagonal quasi-crystal D phase (Al64Cu20Co16) was the reinforcement in the form of fibres parallel to the solidification direction. These fibres were surrounded by the tetragonal Theta phase (Al66Cu31Co3). The composite specimens in the shape of plates were studied by tensile tests and X-ray topography. The specimens deformed up to rupture and, from the X-ray topographs, the dependence of the composite structure defects on deformation was examined. It was found that the rupture of specimens is related to low-angle boundaries created during deformation. The influence of defects on the strength of the composites is discussed. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Update: 6-Jan-2011

Title:
QUINARY AXIS: AN ELEMENT OF SYMMETRY THAT OCCURS IN MOLECULES AND QUASICRYSTALS - A DIDACTIC EXPERIMENT OF CRYSTALLOGRAPHY.
Authors:
das Neves, PCP; de Freitas, DV; Baptista, LA Author Full Names: Pereira das Neves, Paulo Cesar; de Freitas, Dareson Vieira; Baptista, Luis Andre
Source:
QUIMICA NOVA 33 (9): 1977-1979 2010
Abstract:
QUINARY AXIS: AN ELEMENT OF SYMMETRY THAT OCCURS IN MOLECULES AND QUASICRYSTALS - A DIDACTIC EXPERIMENT OF CRYSTALLOGRAPHY. Axis of quinary symmetry occur in molecular symmetry, as in the case of fullerenes, and in crystalline symmetry, in the quasicrystals. Minerals with pentagonal faces do not have this element of symmetry, as the pyrite (FeS2) which shows a ridge that is different from the other ones, in any face of the crystal. The purpose of this paper is to demonstrate conceptual differences between pyritohedron and regular pentagonal dodecahedron symmetries, discussing students' difficulties to identify them. Also is proposed a didactic experiment with spatial models of the above-mentioned forms and the demonstration of its symmetries in clinographic projections.
Title:
Structural modulation and magnetic properties of hexagonal Ba(Ti1-xFex)O3-delta ceramics
Authors:
Wei, XK; Yao, LD; Shen, X; Yang, Y; You, SJ; Li, FY; Jin, CQ; Yu, RC Author Full Names: Wei, X. K.; Yao, L. D.; Shen, X.; Yang, Y.; You, S. J.; Li, F. Y.; Jin, C. Q.; Yu, R. C.
Source:
PHYSICA B-CONDENSED MATTER 405 (23): 4851-4854 DEC 1 2010
Abstract:
This paper investigates the structural and magnetic properties of hexagonal Ba(Ti1-xFex)O3-delta (x=0.3 and 0.7) ceramics, synthesized with solid-state reaction method. Transmission electron microscope investigations reveal that structural phase separation featured by non-modulated and modulated phases is identified by the electron diffraction patterns taken along [0 0 1] zone axis in x=0.3 sample (BTF30). While for x=0.7 sample (BTF70), a pure phase with commensurate and incommensurate modulations at different directions is identified. The superstructure peaks observed in their X-ray diffraction patterns are verified by their individual commensurate modulation, q(s)=1/2 (31-2) in the modulated phase of BTF30 and q(4,-1)=4/9(3 0 4)-(0 0 1) in BTF70. In addition to the room-temperature weak ferromagnetism of BTF30 and paramagnetism of BTF70, spin glass transitions with T-f=3.4 K for the former and T-f=33.6 K for the latter are observed. On the basis of the structural characteristics, the influence of O1 and O2 vacancies on magnetic and dielectric properties of the doped system is discussed. (C) 2010 Elsevier B.V. All rights reserved.
Title:
The Role of Strain Tensor in Formation of Incommensurate Phases in Quartz
Authors:
Sannikov, DG Author Full Names: Sannikov, D. G.
Source:
FERROELECTRICS 400: 8-11 2010
Abstract:
It is shown that the strain tensor components play a decisive role in the theory of formation of incommensurate phases in quartz.
Title:
Improper Ferroelectric Antiferromagnetics
Authors:
Sakhnenko, VP; Ter-Oganessian, NV Author Full Names: Sakhnenko, V. P.; Ter-Oganessian, N. V.
Source:
FERROELECTRICS 400: 12-18 2010
Abstract:
Experiments reveal that magnetoelectric crystals usually experience incommensurate magnetic ordering. In this work we present symmetry arguments for the intimate coupling between ferroelectric magnetically ordered phases and modulated magnetic order. The obtained results are applied to crystals belonging to the D-2h (mmm) crystallographic class and illustrated by two examples of rare-earth manganites RMn2O5 and MnWO4.
Title:
The modulated structure of the calcium aluminate Ca6AlO212 center dot Bi2O3
Authors:
Perez, O; Malo, S; Hervieu, M Author Full Names: Perez, O.; Malo, S.; Hervieu, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 585-593 Part 6 DEC 2010
Abstract:
Bismuth calcium aluminate, Bi2Ca6Al12O27, has been prepared as a ceramic and a single crystal. Analysis of reciprocal space using both electron and X-ray diffraction show an R-centred hexagonal unit cell: a = b = 17.3892 (4), c = 6.986 (1) A. Additional weak reflections are observed; they require the introduction of a modulation wavevector q = 0.0453 (2)c* for indexing. The modulated structure has been solved using the superspace formalism [superspace group X (3) over bar (00 gamma)0]. A frame-work of corner-sharing AlO4 tetrahedra forms corrugated sixfold rings and uncommon triple rings. The Ca2+ cations exhibit an eightfold coordination sphere; edge-sharing CaO8 polyhedra form intertwinned zigzagging rows along c creating a three-dimensional net. Bi atoms are located in large hexagonal tunnels parallel to c and form Bi2O3 pairs, which adopt a trigonal bipyramidal configuration. The 6s(2) loneelectron pairs (Lp) point along c, in the opposite direction to the three Bi-O strong bonds to form two BiO(3)Lp tetrahedra with a common base. Different orientations of the Bi(2)O(3)Lp(2) pairs, rotated by 60 degrees around c, are observed. Their stacking modes in each of the hexagonal tunnels are described. The sequence of the stacking varies along c in each of the tunnels.
Title:
Crystal chemistry of transition metal diarsenates M2As2O7 (M = Mn, Co, Ni, Zn): variants of the thortveitite structure
Authors:
Weil, M; Stoger, B Author Full Names: Weil, Matthias; Stoeger, Berthold
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 603-614 Part 6 DEC 2010
Abstract:
The structures of the 3d divalent transition-metal diarsenates M2As2O7 (M = Mn, Co, Ni, Zn) can be considered as variants of the monoclinic (C2/m) thortveitite [Sc2Si2O7] structure type with a similar or equal to 6.7, b similar or equal to 8.5, c similar or equal to 4.7 angstrom, alpha similar or equal to 90, beta similar or equal to 102, gamma similar or equal to 90 degrees and Z = 2. Co2As2O7 and Ni2As2O7 are dimorphic. Their high-temperature (beta) polymorphs adopt the thortveitite aristotype structure in C2/m, whereas their low-temperature (alpha) polymorphs are hettotypes and crystallize with larger unit cells in the triclinic crystal system in space groups P (1) over bar and P1, respectively. Mn2As2O7 undergoes no phase transition and likewise adopts the thortveitite structure type in C2/m. Zn2As2O7 has an incommensurately modulated crystal structure [C2/m(alpha,0,gamma) 0s] with q = [0.3190 (1), 0, 0.3717 (1)] at ambient conditions and transforms reversibly to a commensurately modulated structure with Z = 12 (I2/c) below 273 K. The Zn phase resembles the structures and phase transitions of Cr2P2O7. Besides descriptions of the low-temperature Co2As2O7, Ni2As2O7 and Zn2As2O7 structures as five-, three-and sixfold superstructures of the thortveitite-type basic structure, the superspace approach can also be applied to descriptions of all the commensurate structures. In addition to the ternary M2As2O7 phases, the quaternary phase (Ni,Co) 2As2O7 was prepared and structurally characterized. In contrast to the previously published crystal structure of the mineral petewilliamsite, which has the same idealized formula and has been described as a 15-fold superstructure of the thortveitite-type basic structure in space group C2, synthetic (Ni,Co)(2)As2O7 can be considered as a solid solution adopting the alpha-Ni2As2O7 structure type. Differences of the two structure models for (Ni,Co)(2)As2O7 are discussed.

Update: 31-Dec-2010

Title:
Modulation in Tl2SeO4 in the temperature range 298-90 K
Authors:
Fabry, J; Kopecky, M; Kub, J Author Full Names: Fabry, Jan; Kopecky, Milos; Kub, Jiri
Source:
PHASE TRANSITIONS 83 (10-11): 980-984 Sp. Iss. SI 2010
Abstract:
Synchrotron experiments have revealed a structural modulation in Thallium selenate, Tl2SeO4, in the temperature range 298-90 K. The modulation is manifested by the presence of the first-order satellites. In difference to the majority of -K2SO4 compounds where the modulation takes place along the axis a (Pnma setting), the incommensurate modulation in Tl2SeO4 takes place along the b setting emphasizing exceptionality of Tl2SeO4 in this structural family. The modulation vector q = (0.0, 0.397(9), 0.0); the space group Pnma(0b0)000.
Title:
Three-dimensional static vortex solitons in incommensurate magnetic crystals
Authors:
Borisov, AB; Rybakov, FN Author Full Names: Borisov, A. B.; Rybakov, F. N.
Source:
LOW TEMPERATURE PHYSICS 36 (8-9): 766-771 AUG 2010
Abstract:
A new type of three-dimensional magnetic soliton in easy-axis ferromagnets is predicted by taking simultaneous account of the Dzyaloshinsky-Moriya interaction and an external magnetic field. The numerically obtained static three-dimensional solitons with a finite energy are characterized by a Hopf topological index H=0 and have a vortex structure. The structure of these solitons and the dependence of their energy on the external field are determined. The asymptotic behavior of these solitons is investigated and a necessary condition for their existence is found. (c) 2010 American Institute of Physics. [doi:10.1063/1.3493376]
Title:
Atomic and magnetic order in the shape memory alloy Mn2NiGa
Authors:
Brown, PJ; Kanomata, T; Neumann, K; Neumann, KU; Ouladdiaf, B; Sheikh, A; Ziebeck, KRA Author Full Names: Brown, P. J.; Kanomata, T.; Neumann, K.; Neumann, K. U.; Ouladdiaf, B.; Sheikh, A.; Ziebeck, K. R. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (50): Art. No. 506001 DEC 22 2010
Abstract:
Magnetization and high resolution neutron powder diffraction measurements on the magnetic shape memory alloy Mn2NiGa have confirmed that it is ferromagnetic with a Curie temperature above 500 K. The compound undergoes a broad structural phase transformation Delta T similar to 90 K with a mean transition temperature T-M similar to 270 K. The high temperature parent phase is cubic (a = 5.937 angstrom) and has a modified L2(1) structure. At 500 K the ordered magnetic moment essentially all on the 4a site is 1.35 mu B/Mn. The low temperature martensite has space group I4/mmm and is related to the cubic phase through a Bain transformation a(tet) = (a(cub) + b(cub))/2, b(tet) = (a(cub) - b(cub)) and c(tet) = c(cub) in which the change in cell volume is <2.6%. In this structure at 5 K the ordered moment of approximate to 2.3 mu(B) is again found to be confined to the sites with full Mn occupation and is aligned parallel to c. Neutron diffraction patterns obtained at 5 K suggested the presence of a weak incommensurate antiferromagnetic phase characterized by either a (1/3 0 1/3) or (00 1/3) propagation vector.
Title:
REFRACTIVE INDICES OF K2ZnCl4 CRYSTALS IN AN INCOMMENSURATE PHASE UNDER UNIAXIAL STRESSES
Authors:
Gaba, VM; Stadnyk, VI; Kogut, ZO; Brezvin, RS Author Full Names: Gaba, V. M.; Stadnyk, V. I.; Kogut, Z. O.; Brezvin, R. S.
Source:
JOURNAL OF APPLIED SPECTROSCOPY 77 (5): 648-653 NOV 2010
Abstract:
The influence of uniaxial mechanical stresses directed along the principal crystallophysical axes on refractive-index temperature dependences in K2ZnCl4 crystals was studied. It is established that the refractive indices ni are quite sensitive to uniaxial stresses. Significant baric shifts of the paraphase-incommensurate-commensu-rate phase transition points to different temperature regions were observed, which is due to the effect of the uniaxial stress on the K2ZnCl4 crystal structure. It is found that applying uniaxial pressure increases the value of the temperature hysteresis of the commensurate-incommensurate phase transition.
Title:
Specific Heat and Linear Birefringence in Incommensurate Phase of NH4HSeO4 Crystal
Authors:
Przeslawski, J; Kosturek, B; Czapla, Z Author Full Names: Przeslawski, J.; Kosturek, B.; Czapla, Z.
Source:
FERROELECTRICS 401: 79-85 2010
Abstract:
Precise measurements of the specific heat and linear birefringence changes were performed for the NH4HSeO4 crystal. Phase transitions at about 100 K, 252 K and 260 K were confirmed. The continuous second order phase transition at 260 K to the incommensurate phase has been described by the 3D XY model. Thermal parameters (as the excess enthalpy H, and the excess entropy S) of the N-IC transition were estimated. The critical index [image omitted] approximate to 0.832 was determined below Ti from the linear birefringence increment. Hysteretic behaviour of the linear birefringence in the incommensurate phase was observed at various temperature rates.
Title:
Influence of the Chemical Composition of Alloys on the Ideal Local Order in Approximants of the Icosahedral Quasicrystals
Authors:
Chizhikov, VA; Dmitrienko, VE Author Full Names: Chizhikov, V. A.; Dmitrienko, V. E.
Source:
CRYSTALLOGRAPHY REPORTS 55 (6): 953-963 NOV 2010
Abstract:
Correlations between atomic displacements from ideal structural positions in the physical space and the atomic coordinates in the perpendicular space are revealed for approximants of icosahedral quasicrystals. On average, the displacement magnitude increases with an increase in the distance from the center of projection on the perpendicular space; this indicates that disordering in quasicrystals is concentrated at the periphery of atomic surfaces. It is found that the chemical composition of an alloy significantly affects the specific features of distortion of the ideal structure of quasicrystals and their approximants.
Title:
Scaling in the Optical Characteristics of Aperiodic Structures with Self-Similarity Symmetry
Authors:
Zotov, AM; Korolenko, PV; Mishin, AY Author Full Names: Zotov, A. M.; Korolenko, P. V.; Mishin, A. Yu
Source:
CRYSTALLOGRAPHY REPORTS 55 (6): 964-970 NOV 2010
Abstract:
The properties of diffraction gratings and multilayered systems constructed using 1D models of quasicrystals are considered based on numerical simulation. It is shown that there is a direct relationship between the self-similarity symmetry of quasicrystals and scaling in the characteristics of the above-mentioned optical devices. The degree of structural correspondence between the graphical representations of the geometric properties of crystals, light diffraction patterns of gratings, and the transmission spectra of multilayered systems is estimated. It is shown that certain types of self-similarity symmetry make the characteristics of aperiodic diffraction gratings highly stable to a change in the size ratio of forming elements.
Title:
Cluster self-organization of intermetallic systems: Quasi-spherical nanocluster precursors with internal Friauf polyhedra (A-172) and icosahedra (B-137) in the Li19Na8Ba15 (hP842) crystal structure
Authors:
Ilyushin, GD; Blatov, VA Author Full Names: Ilyushin, G. D.; Blatov, V. A.
Source:
CRYSTALLOGRAPHY REPORTS 55 (7): 1093-1099 DEC 2010
Abstract:
A combinatorial and topological analysis of Li19Na8Ba15 (hP842, a = 20 angstrom, c = 93 angstrom, V = 33552 angstrom(3), P (3) over bar) has been performed using computer methods ( the TOPOS program package). Two types of crystal-forming quasi-spherical nanoclusters about 20 angstrom in diameter with internal Friauf polyhedra (A-172) and icosahedra (B-137) have been established by the complete decomposition of the 3D factor graph of the structure into cluster substructures. Each type of nanoclusters forms close-packed 2D layers 3(6), which alternate along the c axis. The B-137 and A-172 nanoclusters are composed of three layers and have shell compositions (1 + 12 + 32 + 92) and (1 + 16 + 59 + 103) with local symmetries 3 and (3) over bar, respectively; they were revealed for the first time in crystal structures as cluster precursors. The icosahedral B-137 nanocluster contains a 104-atom quasicrystal approximant (Samson cluster).
Title:
A low temperature anomaly observed in off-stoichiometric Ni-Mn-Ga system studied by higher harmonic ac-susceptibility measurements
Authors:
Srivastava, SK; Srivastava, VK; Joshi, A; Kamasa, P; Varga, LK; Khovaylo, VV; Chatterjee, R Author Full Names: Srivastava, Saurabh Kumar; Srivastava, Vijay Kumar; Joshi, Anupam; Kamasa, Pawel; Varga, Lajos Karoly; Khovaylo, V. V.; Chatterjee, Ratnamala
Source:
APPLIED PHYSICS LETTERS 97 (12): Art. No. 122505 SEP 20 2010
Abstract:
Results of fundamental and third order ac susceptibility measurements in a Ni49Mn29Ga22 single crystal demonstrate that higher harmonics of ac-susceptibility measurement is an excellent tool to identify transitions/anomalies originating from different magnetic substructures that remain undetected by usual dc susceptibility measurements. Anomaly observed at low temperature (similar to 150 K) has also been explored by differential scanning calorimetry, temperature dependent x-ray diffraction, and transmission electron microscopy measurements. The results demonstrate that the magnetic subsystem in Ni-Mn-Ga is unstable at low temperatures not only for metastable modulated crystal structure but also for very stable nonmodulated tetragonal structure. (C) 2010 American Institute of Physics. [doi:10.1063/1.3486155]

Update: 24-Dec-2010

Title:
Ultrabroadband dielectric spectroscopy and phonons in (Pb1-x/2Lax)(Zr0.9Ti0.1)O-3
Authors:
Buixaderas, E; Bovtun, V; Veljko, S; Savinov, M; Kuzel, P; Gregora, I; Kamba, S; Reaney, I Author Full Names: Buixaderas, E.; Bovtun, V.; Veljko, S.; Savinov, M.; Kuzel, P.; Gregora, I.; Kamba, S.; Reaney, I.
Source:
JOURNAL OF APPLIED PHYSICS 108 (10): Art. No. 104101 NOV 15 2010
Abstract:
The dielectric behavior of (Pb1-x/2Lax) (Zr0.9Ti0.1)O-3 PLZT 100x/90/10 (0 <= 100x <= 1) was studied in the frequency range 10(2)-10(14) Hz using dielectric, time-domain terahertz (THz), far-infrared, and Raman spectroscopy in the temperature interval 10-900 K. PZT 90/10 and PLZT 2/90/10 undergo two phase transitions, from a cubic paraelectric to a rhombohedral untilted ferroelectric (FE) phase and on further cooling to a tilted FE phase. PLZT 4/90/10 and PLZT 10/90/10 are incommensurately modulated and composed of an intergrowth of polar and antipolar cation displacements. These samples consequently demonstrate a FE soft mode which exhibits minimal frequency several tens of degrees above the nominal antiferroelectric phase transition temperature. The dielectric response of PLZT 100x/90/10 is mainly governed by a gigahertz relaxation and a soft phonon component in the THz range. As in other PbO-based perovskites, the soft mode is split into a higher-frequency component (omega similar to 80 cm(-1)) and a highly damped THz component (omega similar to 30 cm(-1)), with larger dielectric strength already in the paraelectric phase. (C) 2010 American Institute of Physics. [doi:10.1063/1.3501105]

Update: 17-Dec-2010

Title:
Growth and superconductivity of 2H-Ni-0 02TaSe2 single crystals
Authors:
Li, LJ; Sun, YP; Zhu, XD; Wang, BS; Zhu, XB; Yang, ZR; Song, WH Author Full Names: Li, L. J.; Sun, Y. P.; Zhu, X. D.; Wang, B. S.; Zhu, X. B.; Yang, Z. R.; Song, W. H.
Source:
SOLID STATE COMMUNICATIONS 150 (45-46): 2248-2252 DEC 2010
Abstract:
2H-Ni-0 02TaSe2 single crystals were successfully grown via the iodine vapor transport technique The typical dimension of the crystal is about 3 x 2 x 0 5 mm(3) Compared with the parent compound 2H-TaSe2 with a superconducting transition temperature T-C = 0 14 K the electronic transport specific heat and magnetization results indicate that the superconductivity of the Ni-0 02TaSe2 single crystal is obviously enhanced (T-C = 2 79 K) In addition It is found that the incommensurate charge-density-wave (ICDW) disappears while the commensurate charge-density-wave (CCDW) shifts to about 96 2 K with the intercalation of a little of Ni It clearly indicates that there is a competition between superconductivity (SC) and charge-density-wave (CDW) order for 2H-TaSe2 system and that between SC and ICDW is more drastic (C) 2010 Elsevier Ltd All rights reserved
Title:
Charge-density waves arising from two electron bands
Authors:
Buker, DW Author Full Names: Buker, Donald W.
Source:
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 467 (2125): 166-173 JAN 8 2011
Abstract:
A theory for a quasi-one-dimensional incommensurate charge-density wave state arising from electron-phonon (el-phon) interaction connecting electron states in two different bands is presented. An expression for the fundamental component of the energy gap as a function of the effective el-phon coupling, valid for all coupling strengths, has been found. For a single band, the expression simplifies to a reciprocal hyperbolic-sine dependence on the reciprocal effective coupling. The effective coupling, although simply related to the n assumed phonon-band frequencies, is not generally expressible as a sum of independent functions of these frequencies. The theory is applied to tetrathiofulvalinium-tetracyanoquinodimethane and to potassium blue bronze.
Title:
Generalized dynamics of moving dislocations in quasicrystals
Authors:
Agiasofitou, E; Lazar, M; Kirchner, H Author Full Names: Agiasofitou, Eleni; Lazar, Markus; Kirchner, Helmut
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (49): Art. No. 495401 DEC 15 2010
Abstract:
A theoretical framework for dislocation dynamics in quasicrystals is provided according to the continuum theory of dislocations. Firstly, we present the fundamental theory for moving dislocations in quasicrystals giving the dislocation density tensors and introducing the dislocation current tensors for the phonon and phason fields, including the Bianchi identities. Next, we give the equations of motion for the incompatible elastodynamics as well as for the incompatible elasto-hydrodynamics of quasicrystals. We continue with the derivation of the balance law of pseudomomentum thereby obtaining the generalized forms of the Eshelby stress tensor, the pseudomomentum vector, the dynamical Peach-Koehler force density and the Cherepanov force density for quasicrystals. The form of the dynamical Peach-Koehler force for a straight dislocation is obtained as well. Moreover, we deduce the balance law of energy that gives rise to the generalized forms of the field intensity vector and the elastic power density of quasicrystals. The above balance laws are produced for both models. The differences between the two models and their consequences are revealed. The influences of the phason fields as well as of the dynamical terms are also discussed.
Title:
Indentation characteristics of metallic glass and nanoquasicrystal-glass composite in Zr-Al (Ga)-Cu-Ni alloys
Authors:
Singh, D; Yadav, TP; Mandal, RK; Tiwari, RS; Srivastava, ON Author Full Names: Singh, Devinder; Yadav, T. P.; Mandal, R. K.; Tiwari, R. S.; Srivastava, O. N.
Source:
INTERMETALLICS 18 (12): 2445-2452 DEC 2010
Abstract:
Indentation characteristics of melt-spun Zr69.5Al7.5-xGaxCu12Ni11 (x = 0-2.5; in at %) metallic glasses have been investigated. Formation of a nano-quasicrystalline phase by annealing the glass has been found only upto x = 1.5. The substitution of Ga changes the size and shape of this phase. The load dependent hardness behaviour of metallic glasses and nanoquasicrystal-glass composites are reported in detail. It has been observed that substitution of 1.5 at % Ga improved microhardness property of Zr-Al-Cu-Ni alloy. The value of yield strength of the materials was estimated with the help of hardness values based on the empirical correlations available in literature. It has been found that microstructural and morphological changes alter the Meyer exponent. Pile up parameters seems to be sensitive to structural and microstructural details. (C) 2010 Elsevier Ltd. All rights reserved.
Title:
Development of an Icosahedral Quasicrystal and Two Approximants in the Ca-Au-Sn System: Syntheses and Structural Analyses
Authors:
Lin, QL; Corbett, JD Author Full Names: Lin, Qisheng; Corbett, John D.
Source:
INORGANIC CHEMISTRY 49 (22): 10436-10444 NOV 15 2010
Abstract:
The realm of Tsai-type (YCd6-type) quasicrystals (QCs) and their approximants (ACs) continues to expand to the east in the Periodic table. The heavy tetrel Sn is now one of the major components in the new Ca15.0(5)Au60.0(4)Sn25.0(2) (atom %) icosahedral QC and in the corresponding 1/1 and 2/1 ACs. (The 2/1 AC with Yb is also established.) Single-crystal X-ray diffraction on a 1/1 AC gives the refined formula of Ca3Au14.36(3)Sn4.38(5) in space group Im (3) over bar, a = 15.131(1) angstrom, whereas a representative 2/1 AC gives Ca13Au47.2(1)Sn28.1(1), Pa (3) over bar and a = 24.444(1) angstrom. Both ACs contain five-shell multiply endohedral triacontahedral clusters as the common building blocks, as in the parent structure of YCd6. The 2/1 AC also contains four Ca-2-dimer-centered prolate rhombohedra (PRs) in the unit cell. The long-range order between triacontahedra and PRs in the 2/1 AC is the same as those in Bergman-type 2/1 ACs. A TB-LMTO-ASA calculation on an ideal 1/1 AC model reveals a shallow pseudogap in the total densities-of-states data around the Fermi energy, as expected. The depth of the pseudogap is considerably enhanced through interactions between the Ca 3d states and s and p states of Au and Sn.
Title:
Tuning macro-twinned domain sizes and the b-variants content of the adaptive 14-modulated martensite in epitaxial Ni-Mn-Ga films by co-sputtering
Authors:
Tillier, J; Bourgault, D; Odier, P; Ortega, L; Pairis, S; Fruchart, O; Caillault, N; Carbone, L Author Full Names: Tillier, Jeremy; Bourgault, Daniel; Odier, Philippe; Ortega, Luc; Pairis, Sebastien; Fruchart, Olivier; Caillault, Nathalie; Carbone, Laurent
Source:
ACTA MATERIALIA 59 (1): 75-81 JAN 2011
Abstract:
In order to obtain modulated martensite in our epitaxial Ni-Mn-Ga films, we tuned the composition by using a co-sputtering process Here we present how the composition affects the variant distribution of the 14-modulated martensite at room temperature The nature of such modulated martensites is still strongly debated for magnetic shape memory alloys It has been very recently demonstrated that the modulated martensites in Ni-Mn-Ga are adaptive phases The results presented here corroborate this theory for the first time, for three different compositions Moreover, we demonstrate with the help of the adaptive modulations theory that b variants of the 14-modulated martensite form close to the free surface of the film to release the stress induced by branching of macro-twinned domains during the martensitic transformation on a rigid substrate At room temperature, the content of such b-variants is found to strongly decrease when the macro-twinned domain sizes increase (C) 2010 Acta Materialia Inc Published by Elsevier Ltd All rights reserved

Update: 10-Dec-2010

Title:
Interplay between spin density wave and pi-phase-shifted superconductivity in the iron pnictide superconductors
Authors:
Lee, N; Choi, HY Author Full Names: Lee, Nayoung; Choi, Han-Yong
Source:
PHYSICAL REVIEW B 82 (17): Art. No. 174508 NOV 10 2010
Abstract:
We explore if the phase separation or coexistence of the spin density wave (SDW) and superconductivity (SC) states has any relation to the incommensurability of the SDW in the Fe pnictide superconductors. A systematic method of determining the phase separation or coexistence was employed by computing the anisotropy coefficient beta from the the fourth-order terms of the Ginzburg-Landau expansion of the free energy close to the tricritical/tetracritical point. It was complemented by the self-consistent numerical iterations of the gap equations to map out the boundaries between the phase separation and coexistence of the SDW and SC phases, and between commensurate (C) and incommensurate (IC) SDW in the temperature-doping plane. Our principal results for the sign reversed s-wave pairing SC, in terms of the multicritical temperature, T-c, the phase separation/coexistence boundary between the SDW and SC,T*, and the boundary between C/IC SDW, T*(M), are: (a) IC-SDW and SC coexist for T-c < T* and phase separate otherwise, (b) SDW takes the C form for T-c > T-M* and IC form for T-c < T-M*, and (c) the thermodynamic first-order phase transition intervenes in between the C-SDW and IC-SDW boundary for large TM 0, where T-M(0) is the SDW transition temperature at zero doping, T* = 0.35T(M)(0) and T-M* = 0.56T(M)(0). The intervention makes the phase diagram more complicated than previously reported. By contrast no coexistence was found for the equal sign pairing SC. These results will be compared with the experimental reports in the Fe pnictide superconductors.
Title:
Magnetic and multiferroic phases of single-crystalline Mn0.85Co0.15WO4
Authors:
Chaudhury, RP; Ye, F; Fernandez-Baca, JA; Wang, YQ; Sun, YY; Lorenz, B; Mook, HA; Chu, CW Author Full Names: Chaudhury, R. P.; Ye, F.; Fernandez-Baca, J. A.; Wang, Y. -Q.; Sun, Y. Y.; Lorenz, B.; Mook, H. A.; Chu, C. W.
Source:
PHYSICAL REVIEW B 82 (18): Art. No. 184422 NOV 17 2010
Abstract:
The magnetic and multiferroic phase diagram of Mn0.85Co0.15WO4 single crystals is investigated by means of magnetic, heat-capacity, dielectric, polarization, and neutron-scattering experiments. Three magnetic phase transitions are detected through distinct anomalies in all physical quantities. The ferroelectric polarization is observed only along the b axis below 10 K but not along the a axis as recently suggested. The magnetic phases studied by neutron scattering are very complex. Up to four different magnetic structures, partially coexisting at certain temperature ranges, have been identified. Upon decreasing temperature two commensurate phases (AF4, AF1) are followed by an incommensurate phase (AF5) and a second incommensurate phase (AF2) is detected as a minor phase. The ferroelectric polarization is possibly associated with both (AF2 and AF5) phases.
Title:
Two- and three-dimensional growth of Bi on i-Al-Pd-Mn studied using medium-energy ion scattering
Authors:
Noakes, TCQ; Bailey, P; McConville, CF; Draxler, M; Walker, M; Brown, MG; Hentz, A; Woodruff, DP; Lograsso, TA; Ross, AR; Smerdon, JA; Leung, L; McGrath, R Author Full Names: Noakes, T. C. Q.; Bailey, P.; McConville, C. F.; Draxler, M.; Walker, M.; Brown, M. G.; Hentz, A.; Woodruff, D. P.; Lograsso, T. A.; Ross, A. R.; Smerdon, J. A.; Leung, L.; McGrath, R.
Source:
PHYSICAL REVIEW B 82 (19): Art. No. 195418 NOV 9 2010
Abstract:
Recent work on the growth of thin metal films on quasicrystalline substrates has indicated the formation of so-called "magic height" islands with multiples of 4 atomic layers (AL) arising as a result of quantum size effects, which lead to enhanced stability. Here the results of a study are reported of Bi deposition on i-Al-Pd-Mn using medium-energy ion scattering to characterize the island thickness and the structural arrangement of Bi atoms within the islands. In addition, data were taken from annealed surfaces after Bi cluster desorption to leave a single aperiodic monolayer of Bi at the surface. Scattered-ion energy spectra from the Bi islands are consistent with a single Bi monolayer covered with mainly 4 AL islands for both 1.8 and 3.2 monolayer equivalent coverages but with some occupation of 2 and 8 Al islands as well. The angular dependence of the scattered-ion intensity ("blocking curve") from Bi has been compared with simulations for various models of both rhombohedral Bi and a distorted "black-phosphorus"-like structure. The data demonstrate bilayer formation within the Bi islands. In the case of the aperiodic Bi monolayer, the blocking curves from substrate scattering are found to be inconsistent with two high-symmetry sites on the quasicrystalline surface that theory indicates are energetically favorable but do not exclude the formation of pentagonal arrangements of Bi atoms as seen in other recent experimental work.
Title:
Martensitic transformation from incommensurate state with nano-scale domain structure in a Ti-42Ni-8Fe (at.%) alloy under a compressive stress
Authors:
Todai, M; Higaki, A; Fukuda, T; Kakeshita, T Author Full Names: Todai, Mitsuharu; Higaki, Akio; Fukuda, Takashi; Kakeshita, Tomoyuki
Source:
PHILOSOPHICAL MAGAZINE LETTERS 91 (1): 31-36 2010
Abstract:
This article reports a martensitic transformation from an incommensurate state with a nano-scale domain-like structure in a Ti-42Ni-8Fe alloy. The martensitic transformation is suppressed at a temperature above 4.2 K under zero stress, but occurs under a compressive stress. The product phase is most likely to be the R-phase, but there is a large temperature hysteresis of about 87 K.
Title:
Strain-induced dimensionality crossover and associated pseudoelasticity in the premartensitic phase of Ni2MnGa
Authors:
Nie, ZH; Ren, Y; Wang, YD; Liu, DM; Brown, DE; Wang, G; Zuo, L Author Full Names: Nie, Z. H.; Ren, Y.; Wang, Y. D.; Liu, D. M.; Brown, D. E.; Wang, G.; Zuo, L.
Source:
APPLIED PHYSICS LETTERS 97 (17): Art. No. 171905 OCT 25 2010
Abstract:
The in situ high-energy x-ray diffraction was used for revealing an atomic mechanism on the two-step pseudoelastic behavior found in the premartensitic phase of Ni2MnGa magnetic shape memory alloy. The applied stress first suppresses the three-dimensional modulated structure of the premartensitic phase to a two-dimensional modulated one, which is accompanied by a change in the modulation wave vector and accommodates a large lattice strain reaching similar to 1%. With further increasing stress, the two-dimensional modulated premartensite transforms to the five-layered modulated martensite. The observation of the stress-induced dimensionality crossover of atomic modulation has broad impacts in understanding not only the mechanical properties of advanced shape memory alloys but also the physical properties of condensed matter with heterogeneous structures. (C) 2010 American Institute of Physics. [doi:10.1063/1.3506508]

Update: 3-Dec-2010

Title:
Charge density waves in NbSe3: The models and the experimental evidence
Authors:
Prodan, A; van Midden, HJP; Zitko, R; Zupanic, E; Bennett, JC; Bohm, H Author Full Names: Prodan, A.; van Midden, H. J. P.; Zitko, R.; Zupanic, E.; Bennett, J. C.; Boehm, H.
Source:
SOLID STATE COMMUNICATIONS 150 (43-44): 2134-2137 NOV 2010
Abstract:
Charge density wave (CDW) ordering in the prototypical low-dimensional compound NbSe3 is reconsidered. It is shown that the model with two incommensurate modulations, q(1) = (0, 0.241, 0) and q(2) = (0.5, 0.260, 0.5), localized on type-III and type-I bi-capped trigonal prismatic columns, does not explain details, revealed by various microscopic methods. An alternative explanation, based on the existence of modulated layered nano-domains below both COW onset temperatures, is suggested. It accounts for the presence of the q(2) modulation in the STM images recorded above the T-2 CDW transition and for the absence of q(2) satellites in the corresponding diffraction patterns. The long periodic modulation, detected by LT STM, is attributed to a beating between the two CDWs, centered on adjacent columns of the same type. Such pairs of alternatively modulated columns represent the basic modulation units, ordered into nano-domains. (C) 2010 Elsevier Ltd. All rights reserved.
Title:
Effect of the pseudogap on suppressing high energy inelastic neutron scattering in superconducting YBa2Cu3O6.5
Authors:
Stock, C; Cowley, RA; Buyers, WJL; Frost, CD; Taylor, JW; Peets, D; Liang, R; Bonn, D; Hardy, WN Author Full Names: Stock, C.; Cowley, R. A.; Buyers, W. J. L.; Frost, C. D.; Taylor, J. W.; Peets, D.; Liang, R.; Bonn, D.; Hardy, W. N.
Source:
PHYSICAL REVIEW B 82 (17): Art. No. 174505 NOV 8 2010
Abstract:
We have measured the spin fluctuations in the YBa2Cu3O6.5 (YBCO6.5, T-c=59 K) superconductor at high-energy transfers above similar to 100 meV. Within experimental error, the momentum dependence is isotropic at high energies, similar to that measured in the insulator for two-dimensional spin waves, and the dispersion extrapolates back to the incommensurate wave vector at the elastic position. This result contrasts with previous expectations based on measurements around 50 meV which were suggestive of a softening of the spin-wave velocity with increased hole doping. Unlike the insulator, we observe a significant reduction in the intensity of the spin excitations for energy transfers above similar to 100 meV similar to that observed above similar to 200 meV in the YBCO6.35 (T-c=18 K) superconductor as the spin waves approach the zone boundary. We attribute this high-energy scale with a second gap and find agreement with measurements of the pseudogap in the cuprates associated with electronic anomalies along the antinodal positions. In addition, we observe a sharp peak at around 400 meV whose energy softens with increased hole doping. We discuss possible origins of this excitation including a hydrogen-related molecular excitation and a transition of electronic states between d levels.
Title:
Bose condensation in flat bands
Authors:
Huber, SD; Altman, E Author Full Names: Huber, Sebastian D.; Altman, Ehud
Source:
PHYSICAL REVIEW B 82 (18): Art. No. 184502 NOV 2 2010
Abstract:
We derive effective Hamiltonians for lattice bosons with strong geometrical frustration of the kinetic energy by projecting the interactions on the flat lowest Bloch band. Specifically, we consider the Bose Hubbard model on the one-dimensional sawtooth lattice and the two-dimensional kagome lattice. Starting from a strictly local interaction the projection gives rise to effective long-range terms stabilizing a supersolid phase at densities above nu(c) = 1/9 of the kagome lattice. In the sawtooth lattice on the other hand we show that the solid order, which exists at the magic filling nu(c) = 1/4, is unstable to further doping. The universal low-energy properties at filling 1/4 + delta nu are described by the well-known commensurate-incommensurate transition. We support the analytic results by detailed numerical calculations using the density-matrix renormalization group and exact diagonalization. Finally, we discuss possible realizations of the models using ultracold atoms as well as frustrated quantum magnets in high magnetic fields. We compute the momentum distribution and the noise correlations, that can be extracted from time of flight experiments or neutron scattering, and point to signatures of the unique supersolid phase of the kagome lattice.
Title:
Phase transformation above T-m in PbSc0.5Ta0.5O3 relaxor as seen via acoustic emission
Authors:
Dul'kin, E; Mihailova, B; Catalan, G; Gospodinov, M; Roth, M Author Full Names: Dul'kin, E.; Mihailova, B.; Catalan, G.; Gospodinov, M.; Roth, M.
Source:
PHYSICAL REVIEW B 82 (18): Art. No. 180101 NOV 3 2010
Abstract:
Chemically B-site disordered PbSc1/2Ta1/2O3 relaxor crystals have been studied by means of dielectric and acoustic emission methods in the vicinity of T-m approximate to 280 K. Along with the intrinsic cubic-to-rhombohedral phase transformation at T-c = 261 K, a phase transformation at T-n = 293 K is evidently detected by acoustic emission. Under an external dc electric field T-c gradually increases with increasing the field, whereas T-n exhibits nontrivial behavior, namely, initially decreases and then starts increasing, similarly to T-c. The characteristic temperature T-n is attributed to the occurrence of incommensurate modulated antiferroelectric regions, which have previously been suggested to coexist with both the cubic paraelectric and rhombohedral ferroelectric phases in the vicinity of T-m. The nontrivial behavior of T-n under an external dc electric field is also discussed.
Title:
Dielectric constant in the incommensurate SDW phase of (TMTTF)(2)Br
Authors:
Matsunaga, N; Akita, T; Ichimura, K; Nomura, K; Kawamoto, A Author Full Names: Matsunaga, Noriaki; Akita, Tomonori; Ichimura, Koichi; Nomura, Kazushige; Kawamoto, Atsushi
Source:
PHYSICA B-CONDENSED MATTER 405 (11): S108-S110 Suppl. S JUN 1 2010
Abstract:
The low-frequency dielectric constant was measured in the pressure induced incommensurate SDW phase of (TMTTF)(2)Br in order to investigate the dynamics of the SDW Under the pressure above 0 5 GPa the huge dielectric constant attributed to the motion of the SDW were observed The temperature dependence of the real part of the dielectric constant epsilon whose amplitudes grow with decreasing frequency shows the peak behavior in the Incommensurate SDW phase In contrast of the case of (TMTSF)(2)PF6 the peak temperature of epsilon ' is constant irrespective of the frequency These peak temperature T-P are scaled as T-P/T-SWD similar to 0 3 irrespective of pressure for the pressure larger than 08 GPa and is associated with the sub-phase transition in the incommensurate SOW proposed by the NMR measurement The dielectric properties are probably connected with the co-existence of the CDW component proposed for high temperature sub-phase (C) 2010 Elsevier B V All rights reserved
Title:
SDW phase of (EDT-TTF)(2)AuBr2
Authors:
Nomura, K; Shimohara, N; Denda, D; Matsunaga, N; Kawamoto, A Author Full Names: Nomura, K.; Shimohara, N.; Denda, D.; Matsunaga, N.; Kawamoto, A.
Source:
PHYSICA B-CONDENSED MATTER 405 (11): S116-S119 Suppl. S JUN 1 2010
Abstract:
The low temperature phase in (EDT-TTF)(2)AuBr2 was investigated by H-1 NMR and magnetic susceptibility measurements for protonated and partially deuterated single crystals Two sharp peaks were observed in the temperature dependence of T-1(-1) for both salts associated with the SOW transition T-SDW and the sub-phase transition T* common in the Incommensurate SDW phase The values of T-SDW determined as 15 and 19K for h- and d-salts respectively indicate the negative chemical pressure effect The obtained ratios T/T-SDW 0 37 and 0 43 for h- and d-salts respectively are slightly larger than the common value T*/T-SDW congruent to 0 3 observed in (TMTCF)(2)X The ratio T*/T-SDW increases for larger T-SDW and the low temperature sub-phase becomes more stable (C) 2009 Elsevier B V All rights reserved
Title:
First observation of superconductivity by uniaxial strain in (TMTTF)(2)X-salt
Authors:
Yokogawa, K; Yoshino, H; Nakamura, T; Brooks, JS; Murata, K Author Full Names: Yokogawa, Keiichi; Yoshino, Harukazu; Nakamura, Toshikazu; Brooks, James S.; Murata, Keizo
Source:
PHYSICA B-CONDENSED MATTER 405 (11): S291-S294 Suppl. S JUN 1 2010
Abstract:
We studied superconductivity and spin density wave by measuring temperature dependence of resistivity of (TMTTF)(2)Br under uniaxial strain up to 3 7 GPa (room temperature) The superconducting phase of (TMTTF)(2)Br under uniaxial strain was observed below 0 8 K at 37 GPa for the first time which was realized by the compression along the a-axis but not along other directions Superconductivity was found below a slight SDW-hump in resistance with the a-axis strain however with the b'- and c*-axis strain both superconductivity and SDW was suppressed The anomaly in d In rho(c)/d(1/T) was observed at T similar to 0 22T(SDW) under uniaxial strain along the a-axis This behavior suggests the existence of the sub-phase structure in incommensurate SDW phase under the a-axis compression This behavior reminds us of the same tendency in (TMTSF)(2)PF6 in the previous reports of Kondo et al where only the a-axis uniaxial strain favors superconductivity even though the SDW transition is not suppressed sufficiently in both samples (C) 2010 Elsevier B V All rights reserved
Title:
Structural evolution induced by acceptor doping into BaTiO3 ceramics
Authors:
Wei, XK; Zhang, QH; Li, FY; Jin, CQ; Yu, RC Author Full Names: Wei, X. K.; Zhang, Q. H.; Li, F. Y.; Jin, C. Q.; Yu, R. C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 508 (2): 486-493 OCT 22 2010
Abstract:
Solid state reaction method is used to synthesize Ba(Tii-xTMx)O3-delta (TM = Fe, Mn and Co) and (Ba1-ySry)(Ti1/3Fe2/3)O3-delta ceramics. The X-ray diffraction, scanning electron microscopy and transmission electron microscopy investigations reveal that structural evolutions from an orthorhombic BaTiO3 to a hexagonal Ba(Ti1-xTMx)O3-delta, a hexagonal to a rhombohedral in Ba(Ti1-xMnx)O3-delta, and a hexagonal to a pseudo-cubic transition in (Ba1-ySry)(Ti1/3Fe2/3)O3-delta are induced by increasing the doping concentration. Due to the oxygen vacancies derived from acceptor doping, nanoscale domains of incommensurate modulation (ICM) resultant are commonly observed in the hexagonal Ba(Ti1-xTMx)O3-delta compounds. The newly discovered rhombohedral Ba(Ti1/3Mn2/3)O3-delta having characteristic of face-sharing prism corner-connected by oxygen atoms is a typical example in searching for novel multiferroics. Discrepancies between the ionic radii of the B- and A-site dopants and that of Ti and Ba as a function of the doping concentrations, i.e., the effects of oxygen vacancies and the electronic configurations of the dopants, are concluded to be the driving forces for the structural transitions. (c) 2010 Elsevier B.V. All rights reserved.

Update: 19-Nov-2010

Title:
Structural Stability and Kinetics of Hydrogen in TiZrNi Quasicrystals
Authors:
Lee, SH; Choi, SB; Ito, E; Kim, JY Author Full Names: Lee, Sang-hwa; Choi, Soo-bin; Ito, Eisuke; Kim, Jae-yong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 10 (11): 7680-7683 Sp. Iss. SI NOV 2010
Abstract:
When hydrogen atoms slowly diffuse into a metastable structure, a coherence length of thin TiZrNi quasicrystal metallic ribbons is increased. Improved atomic order with addition of hydrogen is an uncommon phenomenon in metals, and may reflect the unordinary structural property of quasicrystals. Metastable TiZrNi quasicrystals prepared by rapid quenching of molten ingots were hydrogenated in a low pressure of hydrogen (lower than 1000 Torr) at high temperature. After completion of the pressure-composition-temperature measurements between 200 to 300 degrees C, X-ray diffraction data revealed that the full width at half maximum values of the diffraction peaks were decreased suggesting that the quasicrystal phase may stabilized by hydrogen inclusion. Annealing of the same sample at 200 degrees C without hydrogen yields no change of the relative intensity of diffraction peaks.
Title:
Structural and Magnetic Properties of TiZrNi Thin Films Prepared by Magnetron Sputtering and Thermal Annealing
Authors:
Shin, H; Choi, SB; Lee, IJ; Yu, CJ; Kim, JY Author Full Names: Shin, Hyemin; Choi, Soo-bin; Lee, Ik-jae; Yu, Chung-jong; Kim, Jae-yong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 10 (11): 7804-7807 Sp. Iss. SI NOV 2010
Abstract:
Distinctive thin layers of TiZr and Ni were deposited by using a magnetron sputtering method and a thermal annealing was applied to discover metallic films of quasicrystals. After a heat treatment in vacuum, 70 nm thick deposited layers were well mixed with nominal compositions of 49.7, 29.3 and 21.0 for Ti, Zr and Ni, respectively, which is very close with the one forming a quasicrystalline phase. The magnetization values were significantly decreased from 0.286 to 0.142 emu/mm(3) at 2000 Oe, after annealing, while a shape of magnetic hysteresis was maintained. It is believed that a different magnetic behavior after thermal annealing is due to the homogeneous mixing of atomic elements and possible existence of a metastable phase.
Title:
Simple tilings by polyhedra with five- and six-sided faces
Authors:
Delgado-Friedrichs, O; O'Keeffe, M Author Full Names: Delgado-Friedrichs, Olaf; O'Keeffe, Michael
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 66: 637-639 Part 6 NOV 2010
Abstract:
Thirteen tilings of space by simple polyhedra with five- and six-sided faces (`fullerenes') are reported in which there are up to 11 kinds of vertex (vertex 11-transitive). All tilings contain dodecahedra and one or more of nine other kinds of tile. The duals are tilings by tetrahedra and include the four simplest of the known Frank-Kasper intermetallic structure phases. A fifth structure involving just the Frank-Kasper coordination polyhedra has a higher average coordination number than any known or postulated Frank-Kasper phase.
Title:
Magnetic space and superspace groups, representation analysis: competing or friendly concepts?
Authors:
Petricek, V; Fuksa, J; Dusek, M Author Full Names: Petricek, Vaclav; Fuksa, Jiri; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 66: 649-655 Part 6 NOV 2010
Abstract:
Although encoded in theoretical works, relationships between the diffraction symmetry of magnetic structures and magnetic space/superspace groups are often ignored in practical applications. It is shown that magnetic symmetry operations have a direct impact through the rotation parts in the diffraction symmetry of the crystal and can be used to simplify calculations of magnetic structure factors. Besides, the translation parts can introduce specific systematic extinctions of magnetic reflections. Another point is that the efficiency and stability of refinement of magnetic crystal structures, in analogy with the refinement of nuclear structures, depend on direct application of the magnetic symmetry in the structure-factor formula. Magnetic symmetry also allows diffractionally independent magnetic domains and their mutual spatial orientations to be recognized. The selection of one irreducible representation can provide extra relationships between magnetic moments which do not directly affect diffraction symmetry. Thus the combination of both methods seems to be the most effective way to analyze and refine magnetic structures.

Update: 12-Nov-2010

Title:
Elastic and anelastic relaxations associated with the incommensurate structure of Pr0.48Ca0.52MnO3
Authors:
Carpenter, MA; Howard, CJ; McKnight, REA; Migliori, A; Betts, JB; Fanelli, VR Author Full Names: Carpenter, Michael A.; Howard, Christopher J.; McKnight, Ruth E. A.; Migliori, Albert; Betts, Jon B.; Fanelli, Victor R.
Source:
PHYSICAL REVIEW B 82 (13): Art. No. 134123 OCT 27 2010
Abstract:
The elastic and anelastic properties of a polycrystalline sample of Pr0.48Ca0.52MnO3 have been investigated by resonant ultrasound spectroscopy, as a function of temperature (10-1130 K) and magnetic field strength (0-15 T). Marked softening of the shear modulus as the Pnma <-> incommensurate phase transition at similar to 235 K in zero field is approached from either side is consistent with pseudoproper ferroelastic character, driven by an order parameter with Gamma(+)(3) symmetry associated with Jahn-Teller ordering. This is accompanied by an increase in attenuation just below the transition point. The attenuation remains relatively high down to similar to 80 K, where there is a distinct Debye peak. It is attributed to coupling of shear strain with the Gamma(+)(3) order parameter which, in turn, controls the repeat distance of the incommensurate structure. Kinetic data extracted from the Debye peak suggest that the rate-controlling process could be related to migration of polarons. Elastic softening and stiffening as a function of magnetic field at constant temperatures between 177 and similar to 225 K closely resembles the behavior as a function of temperature at 0, 5, and 10 T and is consistent with thermodynamically continuous behavior for the phase transition in both cases. This overall pattern can be rationalized in terms of linear/quadratic coupling between the Gamma(+)(3) order parameter and an order parameter with Sigma(1) or Sigma(2) symmetry. It is also consistent with a dominant role for spontaneous strains in determining the strength of coupling, evolution of the incommensurate microstructure, and equilibrium evolution of the Jahn-Teller ordered structure through multicomponent order-parameter space.
Title:
Magnetic phase diagram of the multiferroic FeTe2O5Br
Authors:
Pregelj, M; Zorko, A; Zaharko, O; Kutnjak, Z; Jagodic, M; Jaglicic, Z; Berger, H; de Souza, M; Balz, C; Lang, M; Arcon, D Author Full Names: Pregelj, M.; Zorko, A.; Zaharko, O.; Kutnjak, Z.; Jagodic, M.; Jaglicic, Z.; Berger, H.; de Souza, M.; Balz, C.; Lang, M.; Arcon, D.
Source:
PHYSICAL REVIEW B 82 (14): Art. No. 144438 OCT 27 2010
Abstract:
The low-temperature magnetic phase diagram of the multiferroic system FeTe2O5Br down to 300 mK and up to 9 T is presented. Short-range magnetic correlations within the crystal layers start to develop already at similar to 50 K, i.e., far above T-N1 similar to 11.0 K, where the system undergoes a magnetic phase transition into the high-temperature incommensurate (HT-ICM) phase. Only 0.5 K lower, at T-N2, the system undergoes a second phase transition into the low-temperature incommensurately modulated (LT-ICM) phase accompanied by a spontaneous electric polarization. When the magnetic field is applied, the transition temperatures shift depending on the field orientation. In the case of B parallel to b and B > 4.5 T, the HT-ICM phase disappears along with the electric polarization in the LT-ICM phase. The field dependence of the magnetic transition temperatures is explained in the context of the magnetic susceptibility behavior. Similarities and differences between the novel well-established magnetoelectrics are discussed.
Title:
Spray Forming of Bulk Ultrafine-Grained Al-Fe-Cr-Ti
Authors:
Banjongprasert, C; Hogg, SC; Liotti, E; Kirk, CA; Thompson, SP; Mi, J; Grant, PS Author Full Names: Banjongprasert, C.; Hogg, S. C.; Liotti, E.; Kirk, C. A.; Thompson, S. P.; Mi, J.; Grant, P. S.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE 41A (12): 3208-3215 DEC 2010
Abstract:
An Al-2.7Fe-1.9Cr-1.8Ti alloy has been spray formed in bulk and the microstructure and properties compared with those of similar alloys produced by casting, powder aomization (PA), and mechanical alloying (MA) routes. In PA and MA routes, a nanoscale metastable icosahedral phase is usually formed and is known to confer high tensile strength. Unlike previous studies of the spray forming of similar Al-based metastable phase containing alloys that were restricted to small billets with high porosity, standard spray forming conditions were used here to produce a similar to 98 pct dense 19-kg billet that was hot isostatically pressed ("HIPed"), forged, and/or extruded. The microstructure has been investigated at all stages of processing using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and synchrotron X-ray diffraction (XRD) at the Diamond Light Source. Consistent with the relatively low cooling rate in spray forming under standard conditions, the microstructure showed no compelling evidence for the formation of metastable icosahedral phases. Nonetheless, after downstream processing, the spray-formed mechanical properties as a function of temperature were very similar to both PA rapid solidification (RS) materials and those made by MA. These aspects have been rationalized in terms of the typical phases, defects, and residual strains produced in each process route.
Title:
Investigation of the Spin-Glass Regime between the Antiferromagnetic and Superconducting Phases in Fe1+ySexTe1-x
Authors:
Katayama, N; Ji, SD; Louca, D; Lee, S; Fujita, M; Sato, TJ; Wen, JS; Xu, ZJ; Gu, GD; Xu, GY; Lin, ZW; Enoki, M; Chang, S; Yamada, K; Tranquada, JM Author Full Names: Katayama, Naoyuki; Ji, Sungdae; Louca, Despina; Lee, Seunghun; Fujita, Masaki; Sato, Taku J.; Wen, Jinsheng; Xu, Zhijun; Gu, Genda; Xu, Guangyong; Lin, Ziwei; Enoki, Masanori; Chang, Sung; Yamada, Kazuyoshi; Tranquada, John M.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (11): Art. No. 113702 NOV 2010
Abstract:
Using bulk magnetization along with elastic and inelastic neutron scattering techniques, we have investigated the phase diagram of Fe1+ySexTe1-x and the nature of magnetic correlations in three nonsuperconducting samples of Fe1.01Se0.1Te0.9, Fe1.01Se0.15Te0.85, and Fe1.02Se0.3Te0.7. A cusp and hysteresis in the temperature dependence of the magnetization for the x = 0.15 and 0.3 samples indicates spin-glass (SG) ordering below T-sg = 23 K. Neutron scattering measurements indicate that the spin-glass behavior is associated with short-range spin density wave (SDW) ordering characterized by a static component and a low-energy dynamic component with a characteristic incommensurate wave vector of Q(m) = (0.46, 0, 0.50) and an anisotropy gap of similar to 2.5 meV. Our high Q-resolution data also show that the systems undergo a glassy structural distortion that coincides with the short-range SDW order.
Title:
Liquid to quasicrystal transition in bilayer water
Authors:
Johnston, JC; Kastelowitz, N; Molinero, V Author Full Names: Johnston, Jessica C.; Kastelowitz, Noah; Molinero, Valeria
Source:
JOURNAL OF CHEMICAL PHYSICS 133 (15): Art. No. 154516 OCT 21 2010
Abstract:
The phase behavior of con. fined water is a topic of intense and current interest due to its relevance in biology, geology, and materials science. Nevertheless, little is known about the phases that water forms even when confined in the simplest geometries, such as water confined between parallel surfaces. Here we use molecular dynamics simulations to compute the phase diagram of two layers of water confined between parallel non hydrogen bonding walls. This study shows that the water bilayer forms a dodecagonal quasicrystal, as well as two previously unreported bilayer crystals, one tiled exclusively by pentagonal rings. Quasicrystals, structures with long-range order but without periodicity, have never before been reported for water. The dodecagonal quasicrystal is obtained from the bilayer liquid through a reversible first-order phase transition and has diffusivity intermediate between that of the bilayer liquid and ice phases. The water quasicrystal and the ice polymorphs based on pentagons are stabilized by compression of the bilayer and are not templated by the confining surfaces, which are smooth. This demonstrates that these novel phases are intrinsically favored in bilayer water and suggests that these structures could be relevant not only for confined water but also for the wetting and properties of water at interfaces. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3499323]
Title:
Tendencies toward nematic order in YBa2Cu3O6+delta: Uniform distortion vs. incipient charge stripes
Authors:
Vojta, M Author Full Names: Vojta, M.
Source:
EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS 188 (1): 49-59 OCT 2010
Abstract:
Recent neutron scattering and transport data obtained on underdoped YBa2Cu3O6+delta, with strong signatures of rotation symmetry breaking at low temperatures, point toward electron-nematic order in the charge sector. Such order may originate from a uniform distortion with d-wave symmetry or as a precursor of a uni-directional stripe phase. Here, we discuss whether the neutron scattering data can be linked to incipient charge stripes. We employ and extend a phenomenological model for collective spin and charge fluctuations and analyze the resulting spin excitation spectrum under the influence of lattice anisotropies. Our results show that the experimentally observed temperature-dependent magnetic incommensurability is compatible with a scenario of incipient stripes, the temperature dependence being due to the temperature variation of both strength and correlation length of the charge stripes. Finally, we propose further experiments to distinguish the possible theoretical scenarios.
Title:
An ARPES view on the high-T-c problem: Phonons vs. spin-fluctuations
Authors:
Kordyuk, AA; Zabolotnyy, VB; Evtushinsky, DV; Inosov, DS; Kim, TK; Buchner, B; Borisenko, SV Author Full Names: Kordyuk, A. A.; Zabolotnyy, V. B.; Evtushinsky, D. V.; Inosov, D. S.; Kim, T. K.; Buechner, B.; Borisenko, S. V.
Source:
EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS 188 (1): 153-162 OCT 2010
Abstract:
We review the search for a mediator of high-T (c) superconductivity focusing on ARPES experiment. In case of HTSC cuprates, we summarize and discuss a consistent view of electronic interactions that provides natural explanation of both the origin of the pseudogap state and the mechanism for high temperature superconductivity. Within this scenario, the spin-fluctuations play a decisive role in formation of the fermionic excitation spectrum in the normal state and are sufficient to explain the high transition temperatures to the superconducting state while the pseudogap phenomenon is a consequence of a Peierls-type intrinsic instability of electronic system to formation of an incommensurate density wave. On the other hand, a similar analysis being applied to the iron pnictides reveals especially strong electron-phonon coupling that suggests important role of phonons for high-T (c) superconductivity in pnictides.

Update: 5-Nov-2010

Title:
Chiral Charge-Density Waves
Authors:
Ishioka, J; Liu, YH; Shimatake, K; Kurosawa, T; Ichimura, K; Toda, Y; Oda, M; Tanda, S Author Full Names: Ishioka, J.; Liu, Y. H.; Shimatake, K.; Kurosawa, T.; Ichimura, K.; Toda, Y.; Oda, M.; Tanda, S.
Source:
PHYSICAL REVIEW LETTERS 105 (17): - OCT 18 2010
Abstract:
We discovered the chirality of charge-density waves (CDW) in 1T-TiSe2 by using STM and time-domain optical polarimetry. We found that the CDW intensity becomes Ia(1):Ia(2):Ia(3) 1:0.7 +/- 0.1:0.5 +/- 0.1, where Ia(i) (i = 1, 2, 3) is the amplitude of the tunneling current contributed by the CDWs. There were two states, in which the three intensity peaks of the CDW decrease clockwise and anticlockwise. The chirality in CDW results in the threefold symmetry breaking. Macroscopically, twofold symmetry was indeed observed in optical measurement. We propose the new generalized CDW chirality H-CDW equivalent to q(1) . (q(2) x q(3)), where q(i) are the CDW q vectors, which is independent of the symmetry of components. The nonzero H-CDW-the triple-q vectors do not exist in an identical plane in the reciprocal space-should induce a real-space chirality in CDW system.
Title:
Density-wave instability in alpha-(BEDT-TTF)(2)KHg(SCN)(4) studied by x-ray diffuse scattering and by first-principles calculations
Authors:
Foury-Leylekian, P; Pouget, JP; Lee, YJ; Nieminen, RM; Ordejon, P; Canadell, E Author Full Names: Foury-Leylekian, Pascale; Pouget, Jean-Paul; Lee, Young-Joo; Nieminen, Risto M.; Ordejon, Pablo; Canadell, Enric
Source:
PHYSICAL REVIEW B 82 (13): Art. No. 134116 OCT 18 2010
Abstract:
alpha-(BEDT-TTF)(2)KHg(SCN)(4) develops a density wave ground state below 8 K whose origin is still debated. Here we report a combined x-ray diffuse scattering and first-principles density functional theory study supporting the charge density wave (CDW) scenario. In particular, we observe a triply incommensurate anharmonic lattice modulation with intralayer wave vector components which coincide within experimental errors to the maximum of the calculated Lindhard response function. A detailed study of the structural aspects of the modulation shows that the CDW instability in alpha-(BEDT-TTF)(2)KHg(SCN)(4) is considerably more involved than those following a standard Peierls mechanism. We thus propose a microscopic mechanism where the CDW instability of the BEDT- TTF layer is triggered by the anion sublattice. Our mechanism also emphasizes the key role of the coupling of the BEDT- TTF and anion layers via the hydrogen bond network to set the global modulation.
Title:
Possible magnetic order and suppression of superconductivity by V doping in Sr2VO3FeAs
Authors:
Tegel, M; Schmid, T; Sturzer, T; Egawa, M; Su, YX; Senyshyn, A; Johrendt, D Author Full Names: Tegel, Marcus; Schmid, Tanja; Stuerzer, Tobias; Egawa, Masamitsu; Su, Yixi; Senyshyn, Anatoliy; Johrendt, Dirk
Source:
PHYSICAL REVIEW B 82 (14): Art. No. 140507 OCT 21 2010
Abstract:
Superconductivity at 33 K in Sr2VO3FeAs is completely suppressed by small amounts of V doping in Sr2VO3(Fe0.93(+/- 0.01)V0.07(+/- 0.01))As. The crystal structures and exact stoichiometries are determined by combined neutron powder diffraction and x-ray powder diffraction. Sr2VO3FeAs is shown to be very sensitive to Fe/V mixing, which interferes with or even suppresses superconductivity. This inhomogeneity may be intrinsic and explains scattered reports regarding T-c and reduced superconducting phase fractions in Sr2VO3FeAs. Neutron-diffraction data collected at 4 K indicate incommensurate magnetic ordering of the V sublattice with a propagation vector q approximate to(0,0,0.306). This suggests strongly correlated vanadium, which does not contribute significantly to the Fermi surface of Sr2VO3FeAs.
Title:
Induction of charge density waves by spin density waves in iron-based superconductors
Authors:
Balatsky, AV; Basov, DN; Zhu, JX Author Full Names: Balatsky, A. V.; Basov, D. N.; Zhu, Jian-Xin
Source:
PHYSICAL REVIEW B 82 (14): Art. No. 144522 OCT 22 2010
Abstract:
We argue that spin density wave (SDW) phase in ferrous superconductors contains charge density wave (CDW) with the modulation momentum that is a double of characteristic momenta of SDW. We discuss symmetry constraints on allowed momenta of CDW generated by coupling to spin modulations. To be specific, we considered the CDW that could be realized in Fe-11 (e.g., FeTe) and Fe-122 (e.g., BaFe2As2) compounds. In case of commensurate SDW, the CDW modulation vector is at the Bragg-peak positions and could be revealed by local scanned probes. In case of incommensurate SDW, the CDW is incommensurate and can be seen also by x-ray and elastic neutron scattering. We also discuss observable charge modulation due to CDW formation near defects and twin boundaries.
Title:
Temperature-pressure phase diagram and electronic properties of the organic metal kappa-(BETS)(2)Mn[N(CN)(2)](3)
Authors:
Zverev, VN; Kartsovnik, MV; Biberacher, W; Khasanov, SS; Shibaeva, RP; Ouahab, L; Toupet, L; Kushch, ND; Yagubskii, EB; Canadell, E Author Full Names: Zverev, V. N.; Kartsovnik, M. V.; Biberacher, W.; Khasanov, S. S.; Shibaeva, R. P.; Ouahab, L.; Toupet, L.; Kushch, N. D.; Yagubskii, E. B.; Canadell, E.
Source:
PHYSICAL REVIEW B 82 (15): Art. No. 155123 OCT 18 2010
Abstract:
The crystal and electronic band structures as well as the transport properties of the recently synthesized layered radical cation salt kappa-(BETS)(2)Mn[N(CN)(2)](3) are investigated. It is shown that this salt is more anisotropic in the plane of conducting layers than other kappa phases, a feature which noticeably influences its physical behavior. A phase transition resulting in the formation of an incommensurate superstructure below 102 K has been found. At temperature below 30 K a metal-insulator transition is observed. We argue that the transition is associated with electronic interactions rather than with structural changes. The T-P phase diagram has been studied under He-4 gas pressure up to 2.5 kbar. At moderately high pressure P approximate to 0.5 kbar the metal-insulating transition is suppressed and the crystal becomes superconducting with T-c approximate to 5.7 K. In the pressurized metallic state, Shubnikov-de Haas oscillations have been found, revealing a very small closed Fermi surface with a high-effective cyclotron mass influenced by many-body interactions.
Title:
Green's functions for infinite planes and half-planes consisting of quasicrystal bi-materials
Authors:
Gao, Y Author Full Names: Gao, Yang
Source:
JOURNAL OF ZHEJIANG UNIVERSITY-SCIENCE A 11 (10): 835-840 Sp. Iss. SI OCT 2010
Abstract:
This paper deals with the combination of point phonon and phason forces applied in the interior of infinite planes and half-planes of 1D quasicrystal bi-materials. Based on the general solution of quasicrystals, a series of displacement functions are adopted to obtain Green's functions for infinite planes and bi-material planes composed of two half-planes in the closed form, when the two half-planes are supposed to be ideally bonded or to be in smooth contact. Since the physical quantities can be readily calculated without the need of performing any transform operations, Green's functions are very convenient to be used in the study of point defects and inhomogeneities in the quasicrystal materials.
Title:
Molecular dynamics simulations of laser induced surface melting in orthorhombic Al13Co4
Authors:
Sonntag, S; Roth, J; Trebin, HR Author Full Names: Sonntag, S.; Roth, J.; Trebin, H. -R.
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 101 (1): 77-80 OCT 2010
Abstract:
Laser induced surface melting of the aluminum-cobalt alloy Al13Co4 is investigated. For the simulations of the lattice ions we use molecular dynamics, while for the time evolution of the electron temperature a generalized heat-conduction equation is solved. Energy transfer between the sub-systems is allowed by an electron-phonon coupling term. This combined treatment of the electronic and atomic systems is an extension of the well-known two-temperature model [Anisimov et al. in JETP Lett. 39(2), 1974]. The alloy shows large structural affinity to decagonal quasicrystals, which have an in-plane five-fold symmetry,while in perpendicular direction the planes are stacked periodically. As a consequence we observe slight anisotropic melting behavior.

Update: 29-Oct-2010

Title:
Modulated monoclinic crystal structure and large shape memory effect in nickel-rich Ni53.5Mn26.0Ga20.5
Authors:
Ramudu, M; Kumar, AS; Seshubai, V; Muraleedharan, K; Prasad, KS; Rajasekharan, T Author Full Names: Ramudu, M.; Kumar, A. Satish; Seshubai, V.; Muraleedharan, K.; Prasad, K. S.; Rajasekharan, T.
Source:
SCRIPTA MATERIALIA 63 (11): 1073-1076 NOV 2010
Abstract:
We report a seven-layered modulated monoclinic crystal structure in the Ni-rich, Ga-poor Ni53.5Mn26.0Ga20.5 alloy. The present composition exhibits coupled magneto-structural transformation around 350 K. Multi-mode twinning with a predominance of crossing twins, indicative of low residual stresses, is observed. A significant shape memory effect of 1.6% and a high strain recovery ratio of 89% are achieved in the polycrystalline specimen at low stresses, owing to lower twinning energies arising from lattice modulation. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Second harmonic generation on incommensurate structures: The case of multiferroic MnWO4
Authors:
Meier, D; Leo, N; Yuan, G; Lottermoser, T; Fiebig, M; Becker, P; Bohaty, L Author Full Names: Meier, D.; Leo, N.; Yuan, G.; Lottermoser, Th.; Fiebig, M.; Becker, P.; Bohaty, L.
Source:
PHYSICAL REVIEW B 82 (15): Art. No. 155112 OCT 7 2010
Abstract:
A comprehensive analysis of optical second harmonic generation on an incommensurate (IC) magnetically ordered state is presented using multiferroic MnWO4 as model compound. Two fundamentally different SHG contributions coupling to the primary IC magnetic order or to secondary commensurate projections of the IC state, respectively, are distinguished. Whereas the latter can be described within the formalism of the 122 commensurate magnetic point groups the former involves a breakdown of the conventional macroscopic symmetry analysis because of its sensitivity to the lower symmetry of the local environment in a crystal lattice. Our analysis thus foreshadows the fusion of the hitherto disjunct fields of nonlinear optics and IC order in condensed-matter systems.
Title:
Phase Separation and Suppression of the Structural and Magnetic Transitions in Superconducting Doped Iron Tellurides, Fe1+xTe1-ySy
Authors:
Zajdel, P; Hsieh, PY; Rodriguez, EE; Butch, NP; Magill, JD; Paglione, J; Zavalij, P; Suchomel, MR; Green, MA Author Full Names: Zajdel, Pawel; Hsieh, Ping-Yen; Rodriguez, Efrain E.; Butch, Nicholas P.; Magill, Jeff D.; Paglione, Johnpierre; Zavalij, Peter; Suchomel, Matthew R.; Green, Mark A.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 132 (37): 13000-13007 SEP 22 2010
Abstract:
Single crystal and powder samples of the series of iron chalcogenide superconductors with nominal composition, Fe1.15Te1-ySy, are found to form for 0 <= y <= 0.15. They crystallize in the tetragonal anti-PbO structure, which is composed of layers of edge-shared Fe(Te, S)(4) tetrahedra. For y = 0, Fe1+xTe (x approximate to 0.12(1)) is nonsuperconducting and undergoes a tetragonal (P4/nmm) to monoclinic (P2(1)/m) structural transition at similar to 65 K, associated with the onset of commensurate antiferromagnetic order at q = (0.5 0 0.5). We show that on sulfur substitution, Fe1+xTe1-ySy becomes orthorhombic (Pmmn) at low temperature for 0 <= y <= 0.15, where the greatly suppressed magnetic scattering is now incommensurate at q = (0.5-delta 0 0.5) and possesses short ranged magnetic correlations that are well fitted with a two-dimensional Warren peak shape. At much higher concentrations of S (y >= 0.075), there is suppression of both the structural and magnetic transitions and a superconducting transition at 9 K is observed. Between these two composition regimes, there exists a region of phase separation (0.025 <= y <= 0.05), where the low temperature neutron diffraction data is best refined with a model containing both the tetragonal and orthorhombic phases. The increase in the amount of sulfur is found to be associated with a reduction in interstitial iron, x. Microprobe analysis of a single crystal of composition Fe1.123(5)Te0.948(4)S0.052(4) confirms the presence of compositional variation within the crystals, rationalizing the observed phase separation.
Title:
The various modes of growth of metals on quasicrystals
Authors:
Smerdon, JA Author Full Names: Smerdon, J. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (43): Art. No. 433002 NOV 3 2010
Abstract:
Quasicrystals are fascinating intermetallic compounds composed of two or more elements. They differ from conventional crystals in that they possess long-range order, but no translational symmetry-that is, they are aperiodic. Much effort has been expended on identifying routes towards exploiting and exploring the properties of such systems due to their aperiodic nature. One such route is concerned with the deposition of thin films, particularly of metals, to investigate how their growth progresses in this inherently frustrated scenario. This topical review will examine the various epitaxial relationships observed in quasicrystal research with particular emphasis on single-element metallic films deposited under ultrahigh-vacuum conditions.
Title:
Transport properties of electrons in fractal magnetic-barrier structures
Authors:
Sun, LF; Fang, C; Guo, Y Author Full Names: Sun, Lifeng; Fang, Chao; Guo, Yong
Source:
JOURNAL OF APPLIED PHYSICS 108 (6): Art. No. 063715 SEP 15 2010
Abstract:
Quantum transport properties in fractal magnetically modulated structures are studied by the transfer-matrix method. It is found that the transmission spectra depend sensitively not only on the incident energy and the direction of the wave vector but also on the stage of the fractal structures. Resonance splitting, enhancement, and position shift of the resonance peaks under different magnetic modulation are observed at four different fractal stages, and the relationship between the conductance in the fractal structure and magnetic modulation is also revealed. The results indicate the spectra of the transmission can be considered as fingerprints for the fractal structures, which show the subtle correspondence between magnetic structures and transport behaviors. (C) 2010 American Institute of Physics. [doi:10.1063/1.3488647]

Update: 22-Oct-2010

Title:
Dynamics of particle flips in two-dimensional quasicrystals
Authors:
Engel, M; Umezaki, M; Trebin, HR; Odagaki, T Author Full Names: Engel, Michael; Umezaki, Masahiro; Trebin, Hans-Rainer; Odagaki, Takashi
Source:
PHYSICAL REVIEW B 82 (13): Art. No. 134206 OCT 8 2010
Abstract:
The dynamics of quasicrystals is more complicated than the dynamics of periodic solids and difficult to study in experiments. Here, we investigate a decagonal and a dodecagonal quasicrystal using molecular dynamics simulations of the Lennard-Jones-Gauss interaction system. We observe that the short-time dynamics is dominated by stochastic particle motion, so-called phason flips, which can be either single-particle jumps or correlated ringlike multi-particle moves. Over long times, the flip mechanism is efficient in reordering the quasicrystals and can generate diffusion. The temperature dependence of diffusion is described by an Arrhenius law. We also study the spatial distribution and correlation of mobile particles by analyzing the dynamic propensity.
Title:
Electrical transport in charge-ordered Fe2OBO3: Resistive switching and pressure effects
Authors:
Akrap, A; Angst, M; Khalifah, P; Mandrus, D; Sales, BC; Forro, L Author Full Names: Akrap, Ana; Angst, Manuel; Khalifah, Peter; Mandrus, David; Sales, Brian C.; Forro, Laszlo
Source:
PHYSICAL REVIEW B 82 (16): Art. No. 165106 OCT 5 2010
Abstract:
The pressure-temperature-electric field phase diagram of Fe2OBO3 is studied under ambient and high pressure using resistivity and thermoelectric power measurements. The onset of the incommensurate charge order at T-CO=340 K does not depend on pressure up to at least 2 GPa. The temperature of the transition to the commensurate charge order is increased by similar to 10 K/GPa. High pressure stabilizes the commensurate phase. We find evidence for resistive switching in the incommensurate phase, which may be linked to the dynamics of the charge-order domain boundaries.
Title:
The magneto-dielectric properties of compounds and alloys in the systems of TlInS2-TlFeS2, TlInS2-TlFeSe2
Authors:
Veliyev, RG; Seyidov, MY; Gasanov, NZ; Seyidov, FM Author Full Names: Veliyev, R. G.; Seyidov, M. Yu.; Gasanov, N. Z.; Seyidov, F. M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 506 (2): 800-803 SEP 17 2010
Abstract:
The research of dielectric properties of TlInS2-layered compound shows that TlInS2 is extrinsic ferroelectric (T-c approximate to 202.4 K) with intermediate incommensurable phase (T-i approximate to 206.3 K). Analysis of publications was carried out by us on magnetic properties of TlFeS2 and TlFeSe2 compounds, having chained crystalline structure, allows to draw a conclusion that these compounds are highly anisotropic (quasione-dimensional) antiferromagnets with Neel temperatures equal to similar to 12 K and similar to 14 K respectively (long-range magnetic order). Moreover, on the temperature dependence of reverse magnetic susceptibility TlFeS2 and TlFeSe2 in paramagnetic area at 196 K and 290 K respectively, wide minimums exist, which characterize short-range magnetic order in these quasi-one-dimensional antiferromagnets. Using method of differential-thermal analysis were founded regions of homogenous and heterogeneous co-existence of ferroelectric and antiferromagnetic orderings in the systems of TlInS2-TlFeS2 and TlInS2-TlFeSe2. (C) 2010 Elsevier B.V. All rights reserved.

Update: 15-Oct-2010

Title:
Neutron diffraction investigation of the crystal and magnetic structures in KCrF3 perovskite
Authors:
Xiao, Y; Su, Y; Li, HF; Kumar, CMN; Mittal, R; Persson, J; Senyshyn, A; Gross, K; Brueckel, T Author Full Names: Xiao, Y.; Su, Y.; Li, H. -F.; Kumar, C. M. N.; Mittal, R.; Persson, J.; Senyshyn, A.; Gross, K.; Brueckel, Th.
Source:
PHYSICAL REVIEW B 82 (9): Art. No. 094437 SEP 23 2010
Abstract:
KCrF3 represents another prototypical orbital-ordered perovskite, where Cr2+ possesses the same electronic configuration of 3d(4) as that of strongly Jahn-Teller distorted Mn3+ in many colossal magnetoresistance manganites. The crystal and magnetic structures of KCrF3 compound are investigated by using polarized and unpolarized neutron powder-diffraction methods. The results show that the KCrF3 compound crystallizes in tetragonal structure at room temperature and undergoes a monoclinic distortion with the decrease in temperature. The distortion of the crystal structure indicates the presence of cooperative Jahn-Teller distortion which is driven by orbital ordering. With decreasing temperature, four magnetic phase transitions are observed at 79.5, 45.8, 9.5, and 3.2 K, which suggests a rich magnetic phase diagram. Below T-N = 79.5 K, the Cr2+ moment orders in an incommensurate antiferromagnetic arrangement, which can be defined by the magnetic propagation vector (1/2 + delta, 1/2 + delta, 0). The incommensurate-commensurate magnetic transition occurs at 45.8 K and the magnetic propagation vector locks into (1/2, 1/2, 0) with the Cr moment of 3.34(5) mu(B), aligned ferromagnetically in (220) plane, but antiferromagnetically along [110] direction. Below 9.5 K, the canted antiferromagnetic ordering and weak ferromagnetism arise from the collinear antiferromagnetic structure while the Dzyaloshinskii-Moriya interaction and tilted character of the single-ion anisotropy might give rise to the complex magnetic behaviors below 9.5 K.
Title:
The Behavior of Thermal Conductivity in the Chaotic Phase of [N(CH3)(4)](2)ZnCl4 Crystal
Authors:
Sveleba, SA; Karpa, IV; Kunyo, IM; Semotyuk, OV; Katerynchuk, IM; Phitsych, EI; Pankivskyi, YI Author Full Names: Sveleba, S. A.; Karpa, I. V.; Kunyo, I. M.; Semotyuk, O. V.; Katerynchuk, I. M.; Phitsych, E. I.; Pankivskyi, Yu. I.
Source:
CRYSTALLOGRAPHY REPORTS 55 (4): 652-656 JUL 2010
Abstract:
A thermal investigation of the modulated structure dynamics at the transition between metastable states in the incommensurate phase of [N(CH3)(4)](2)ZnCl4 crystal have been performed. It is established that the anomalous behavior of the thermal conductivity in the absence of a defect-density wave is due to the inelastic scattering of thermal phonons from critical phonons of the soft optical branch. In the presence of a defect-density wave, the anomalous increase in thermal conductivity is caused by the existence of a chaotic phase and is related to the contribution that soft optical phonons make to the heat transfer due to the increase in their group velocity.
Title:
2D quasi-periodic Rauzy tiling as a section of 3D periodic tiling
Authors:
Maleev, AV; Shutov, AV; Zhuravlev, VG Author Full Names: Maleev, A. V.; Shutov, A. V.; Zhuravlev, V. G.
Source:
CRYSTALLOGRAPHY REPORTS 55 (5): 723-733 SEP 2010
Abstract:
A method for constructing a 2D quasi-periodic Rauzy tiling Til as a section of some 3D periodic tiling Til (3D) is considered. The translation lattice of the tiling Til (3D) and its connectivity graph are constructed using the discrete modeling of packings. The calculation of the layer-by-layer growth polyhedron for the tiling Til (3D) made it possible to estimate from upper the shape of a growth polygon for the tiling Til. As a result, the growth shape in six out of eight growth sectors has been rigorously proven. A set of quasi-periodic tilings (locally indistinguishable from the Rauzy tiling Til), including seven centrosymmetric tilings, has been obtained.
Title:
Effect of the number of defect density waves on the dynamics of the soliton system in [N(CH3)(4)](2)CuCl4 and [N(CH3)(4)](2)Zn0.98Ni0.02Cl4 crystals
Authors:
Karpa, IV; Sveleba, SA; Kunyo, IM; Katerynchuk, IM; Semotyuk, OV; Blashko, OI Author Full Names: Karpa, I. V.; Sveleba, S. A.; Kunyo, I. M.; Katerynchuk, I. M.; Semotyuk, O. V.; Blashko, O. I.
Source:
CRYSTALLOGRAPHY REPORTS 55 (5): 815-820 SEP 2010
Abstract:
The time dependences of the birefringence and thermal conductivity of [N(CH3)(4)](2)CuCl4 and [N(CH3)(4)](2)Zn0.98Ni0.02Cl4 crystals in the incommensurate phase at a constant temperature have been studied. A multiwave state of modulated superstructure is found to be formed in the presence of defect density waves in the crystal. It is shown that, depending on the number of defect density waves in the crystal, either a superposition of existing modulation waves or a domainlike structure arise in it.
Title:
Magnetic properties of quasicrystalline Al65Cu22Fe13 powders synthesized by solid-phase diffusion
Authors:
Semenovskii, PV; Nikonov, AA; Teplov, AA; Ol'shanskii, ED; Bryazkalo, AM Author Full Names: Semenovskii, P. V.; Nikonov, A. A.; Teplov, A. A.; Ol'shanskii, E. D.; Bryazkalo, A. M.
Source:
CRYSTALLOGRAPHY REPORTS 55 (5): 833-836 SEP 2010
Abstract:
The magnetic properties of quasicrystalline Al65Cu22Fe13 powders synthesized by solid-phase diffusion as a result of thermal treatment in vacuum and in a hydrogen atmosphere have been studied. The magnetic properties of the samples synthesized in hydrogen were found to be much better than those of the samples synthesized in vacuum. It is shown that an increase in the treatment time in vacuum decreases the number of magnetic nanoclusters and elimninates the time instability of their magnetic properties (magnetic susceptibility and magnetization).
Title:
Incommensurately modulated lanthanide coinage-metal diarsenides. I. CeAu1-delta As2 [delta=0.015 (2)] - a new distortion variant of the HfCuSi2 type with irregularly stacked cis-trans chains of arsenic atoms
Authors:
Rutzinger, D; Doert, T; Ruck, M Author Full Names: Rutzinger, D.; Doert, Th.; Ruck, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 519-526 Part 5 OCT 2009
Abstract:
Rare-earth metal coinage-metal diarsenides LnTAs(2) (Ln = Y, La, Ce-Lu; T = Cu, Ag, Au) are known to crystallize in structures closely related to the HfCuSi2 type, which comprises a stacking sequence of puckered TAs layers and planar square As nets, separated by the Ln atoms. CeAu1-delta As2, with delta = 0.015 (2), shows an incommensurate positional modulation of the arsenic atoms in the planar As nets. Based on X-ray diffraction data on a twinned crystal, a structure model in the monoclinic superspace group P12(1)/m1(alpha 0 gamma)00 (No. 11.1) with basic unit-cell parameters of a = 5.804 (1), b = 5.814 (1), c = 10.179 (1) A and beta = 90.09 (8)degrees is presented. The components of the modulation wavevector q = alpha a* + 0b* + gamma c* are alpha = 0.08 (1) and gamma = 0.39 (1). The structure comprises cis-trans chains and rectangles of As atoms and displays an intricate stacking sequence of the modulated arsenic nets. Rod groups and layer groups of the respective arrangements are identified and the arrangement of different motifs of the modulated As net is discussed.
Title:
Incommensurately modulated lanthanide coinage-metal diarsenides. II. GdCuAs2, GdAu1-delta As2 and TbAu1-delta As2 - new distortion variants of the HfCuSi2 type with irregularly stacked zigzag chains of arsenic atoms
Authors:
Rutzinger, D; Bartsch, C; Doert, T; Ruck, M Author Full Names: Rutzinger, D.; Bartsch, C.; Doert, Th.; Ruck, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 527-534 Part 5 OCT 2009
Abstract:
GdCuAs2, GdAu1-delta As2 and TbAu1-delta As2 crystallize as incommensurately modulated variants of the HfCuSi2 type. Structure models have been developed in the monoclinic superspace group P12(1)/m1(alpha 0 gamma)00 (No. 11.1). The components of the modulation wavevectors q = alpha a* + 0b* + gamma c* are alpha = 0.04 (1) and gamma = 0.48 (1) for GdCuAs2, alpha = 0.03 (1) and gamma = 0.48 (1) for GdAu1-delta As2 and alpha = 0.02 (1) and gamma = 0.46 (1) for TbAu1-delta As2. The predominant effect of the positional modulation is the distortion of a square net of arsenic atoms, which results in planar zigzag chains. Rod groups and layer groups of the respective structure motifs are identified and discussed.
Title:
Modulation of atomic positions in CaCuxMn7-xO12 (x <= 0.1)
Authors:
Slawinski, W; Przenioslo, R; Sosnowska, I; Bieringer, M; Margiolaki, I; Suard, E Author Full Names: Slawinski, W.; Przenioslo, R.; Sosnowska, I.; Bieringer, M.; Margiolaki, I.; Suard, E.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 535-542 Part 5 OCT 2009
Abstract:
The modulation of atomic positions in CaCu (x) Mn7-x O-12 (x = 0 and 0.1) was studied using synchrotron radiation powder diffraction below 250 and 220 K, respectively. The copper-rich member CaCu (x) Mn7-x O-12 (x = 0.23) does not show any modulation of the atomic positions at temperatures as low as 10 K. Using low-temperature neutron powder diffraction the modulation of the magnetic moments of Mn ions in CaCu (x) Mn7-x O-12 (x = 0, 0.1 and 0.23) has been investigated. Long-range modulated magnetic ordering in CaCu (x) Mn7-x O-12 (x = 0, 0.1 and 0.23) is observed below 90.4, 89.2 and 78.1 K. (0,0,q (p)) and (0,0,q (m)) are the propagation vectors describing the modulations of the atomic positions and the magnetic moments. For CaCu (x) Mn7-x O-12 (x = 0 and 0.1) the magnetic modulation and atomic modulation lengths are related by a factor of 2 satisfying the relation (1 - q (p)) = 2(1 - q (m)).
Title:
Modulated crystal structure of incommensurate low tridymite
Authors:
Graetsch, HA Author Full Names: Graetsch, Heribert A.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 543-550 Part 5 OCT 2009
Abstract:
The incommensurately modulated crystal structure of low SiO2 tridymite was refined based on single-crystal X-ray diffraction data in the superspace group Cc(alpha 0 gamma)0. The data set consists of 885 main reflections, 1751 first-order, 924 second-order and 119 third-order satellite reflections with I > 3 Sigma(I). The modulation is mainly made up from cooperative twistings of the rigid SiO4 tetrahedra. Two orders of displacement waves are used to describe the modulation of the Si atoms and three orders for the O atoms. The maximal amplitudes are ca 0.6 A. O atoms bridging pairs of tetrahedra in cis and trans configurations show different positional modulation patterns. The anisotropic displacement parameters (ADPs) are also modulated. A correlation between ADP modulations and positional modulations was found.
Title:
Eu3Si15-xAl1+xOxN23-x(x similar or equal to 5/3) as a commensurate composite crystal
Authors:
Michiue, Y; Shioi, K; Hirosaki, N; Takeda, T; Xie, RJ; Sato, A; Onoda, M; Matsushita, Y Author Full Names: Michiue, Yuichi; Shioi, Kousuke; Hirosaki, Naoto; Takeda, Takashi; Xie, Rong-Jun; Sato, Akira; Onoda, Mitsuko; Matsushita, Yoshitaka
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 567-575 Part 5 OCT 2009
Abstract:
A new Eu-SiAlON crystal, Eu3Si15 - x Al1 + x O (x) N23 - x (x similar or equal to 5/3), was found and the structure was determined by an X-ray diffraction technique using a twinned sample. The structure consists of a host framework, which is constructed by the connection of MX (4) tetrahedra (M: Si or Al; X: O or N), and Eu ions as the guest ions. The structure is considered to be a commensurate composite crystal. The basic vectors are a (1) = a/3, b and c for the first substructure, and a (2) = a/5, b and c for the second substructure. The first substructure consists of part of the host framework and the Eu ions, while the remainder of the host structure is taken as the second substructure. Possible phases belonging to the series are proposed using the composite crystal model in (3 + 1)-dimensional superspace. Chemical composition, possible space groups, cell parameters, and the basic model for those phases are presented.
Title:
Ternary fluorides BaMF4 (M = Zn, Mg and Mn) at low temperatures
Authors:
Posse, JM; Grzechnik, A; Friese, K Author Full Names: Maria Posse, Jose; Grzechnik, Andrzej; Friese, Karen
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 576-586 Part 5 OCT 2009
Abstract:
Ternary fluorides BaMF4 (M = Zn, Mg, Mn) have been studied in the temperature range from 300 to 10 K using synchrotron and laboratory powder and single-crystal diffraction. The first two compounds are stable down to 10 K, while the third one undergoes a phase transition to an incommensurately modulated structure at approximately 250 K. The modulated phase is stable down to 10 K. The magnetic anomalies at 45 and 27 K observed previously in BaMnF4 are exclusively reflected in the behavior of the gamma component of the q vector, which assumes an irrational value of approximately 0.395 A-1 at the temperature corresponding to the onset of the magnetic ordering and then stays constant down to 10 K. Mn-Mn distances do not indicate any structural response to the magnetic ordering. The formation of the modulated phase can be explained on the basis of simple geometrical criteria. The incorporation of the large Mn cation in the octahedral sheets implies an increase of the cavity in which the Ba ion is incorporated. This leads to the formation of the modulated structure to adapt the coordination sphere around Ba in such a way that the bond-valence sums can be kept close to the ideal value of two. With further lowering of the temperature, the charge balance around the Ba ion requires an increasingly anharmonic character of the modulation function of Ba, until finally at 10 K a crenel-like shape is assumed for the modulation of this atom.
Title:
Modulated structure and phase transitions of Sr10Ga6O19
Authors:
Kruger, H; Lazic, B; Arroyabe, E; Kahlenberg, V Author Full Names: Krueger, Hannes; Lazic, Biljana; Arroyabe, Erik; Kahlenberg, Volker
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 587-592 Part 5 OCT 2009
Abstract:
The crystal structure of Sr10Ga6O19 was investigated by in situ single-crystal X-ray diffraction in the temperature range 298-673 K. At ambient conditions the compound shows a (3 + 1)-dimensional modulated structure in the superspace group C2/c(0 beta 0)s0 [a = 34.9145 (13), b = 7.9369 (2), c = 15.9150 (7) A and beta = 103.551 (3)degrees] with a modulation wavevector of q = 0.4288 (2)b*. Whereas the presented structural model uses first-order harmonic modulation functions only, some features of the modulations are discussed utilizing an electron density derived by the maximum entropy method. Furthermore, two phase transitions were identified: between 453 and 503 K the incommensurate superstructure is replaced by a doubling of the a and b lattice constants, and between 503 and 673 K a phase with the basic cell is formed, identical to alpha-Sr10Ga6O19. Under some cooling conditions crystals showing a combined diffraction pattern of bot! h superstructures can be obtained. The relation of these results to alpha-Sr10Ga6O19 [Kahlenberg (2001). J. Solid State Chem. 160, 421-429] is discussed.
Title:
Superspace description of the modulated structure of the metal-salt-hybrid Bi7-delta Ni2Br5-2 delta (delta = 1/9)
Authors:
Wahl, B; Ruck, M Author Full Names: Wahl, B.; Ruck, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 593-599 Part 5 OCT 2009
Abstract:
The compound Bi7 - delta Ni2Br5 - 2 delta = (Bi3Ni)(2)[Bi1 - delta Br4]Br1 -2 delta (delta = 1/9) is a sub-bromide of the intermetallic phase Bi3Ni. Its crystal structure contains metallic rods, (1)(infinity)[Bi3Ni], which are embedded in a salt-like matrix of bromido-bismuthate(III) and bromide anions. The non-stoichiometry originates from the variation of the number n of trans edge-sharing octahedra in the [Bi (n) Br4n + 2](n + 2)- oligomers (3 < n < 5), as well as from vacancies on the sites of the isolated Br atoms. The simplified structure is described in the orthorhombic space group Cmcm with a = 4.0660 (4), b = 23.305 (3), c = 17.130 (2) A. It shows a statistical distribution of vacancies and orientational disorder of the concatenated octahedra. By choosing the modulation vector q = a*/9 + b*/2, the additional weak reflections of the diffraction pattern can be indexed. In the [3 + 1]-dimensional superspace group Pmnm(alpha 1/20)000, an ordered structure model is achieved. The modulated crystal structure bears a strong resemblance to the somewhat higher oxidized sub-bromide Bi7 - delta Ni2Br5 (delta = 1/9).

Update: 8-Oct-2010

Title:
Second order incommensurate phase transition in 25L-Ta2O5
Authors:
Audier, M; Chenevier, B; Roussel, H; Salaun, AL Author Full Names: Audier, M.; Chenevier, B.; Roussel, H.; Salauen, A. Lintanf
Source:
JOURNAL OF SOLID STATE CHEMISTRY 183 (9): 2068-2076 SEP 2010
Abstract:
A new structural state 25L-Ta2O5, obtained from sintering and annealing treatments of a Ta2O5 powder, is identified both by electron diffraction and high resolution imaging on a transmission electron microscope (TEM). According to general rules for the different L-Ta2O5 structures proposed by Grey et al. (J. Solid State Chem. 178 (2005) 3308), a structural model is derived from their crystallographic data on 19L-Ta2O5. This model yields simulated images in agreement with high resolution TEM observations of the structure oriented along its [001] zone axis, but only for a very thin crystal thickness of less than 1.2 nm. Such a limitation is shown to be due to a modulation of the structure along its [001] axis. Actually, from an analysis of a diffuse scattering and of its evolution into satellites reflections as a function of the cooling rate, a second order incommensurate phase transition can be assumed to occur in this compound. The property of single phase samples observed by TEM is also verified by X-ray powder diffraction. In a discussion about studies performed by different authors on incommensurate structures in the system Ta2O5-WO3, it is noticed that TEM results, similar to ours, indicate that phase transitions could be expected in these structures. (C) 2010 Elsevier Inc. All rights reserved.
Title:
Magnetic structures of orthorhombic rare earth stannides LSn2 (L = Tb-Tm)
Authors:
Venturini, G; Lemoine, P; Malaman, B; Ouladdiaf, B Author Full Names: Venturini, G.; Lemoine, P.; Malaman, B.; Ouladdiaf, B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 505 (2): 404-415 SEP 3 2010
Abstract:
The magnetic structures of the orthorhombic compounds LSn2 (S.G.: Cmcm; L = Tb-Tm) have been determined from neutron diffraction studies. The compounds LSn2 (L = Tb, Dy, Ho Er) order below 26.7, 17.2, 7.8 and 4.5 K, respectively, in a sine-modulated structure characterized by the propagation vector k = approximate to 0.39, 0, approximate to 0.41). Below 12.7, 5, 4.8 and 2 K, respectively, these compounds undergo a transition towards a collinear antiferromagnetic structure characterized by the propagation vector k = (0, 0, 1/2) for Tb and Er, k = (1/2, 1/2, 0) for Ho and k = (1/2, 1/2, 1/2) for Dy. The compound TmSn2 orders below 4.0 K in a sine-modulated structure characterized by the propagation vector k = (0, 0.667, 0.380). The moment direction is close to [0 0 1] for L = Tb, Dy, Ho and aligned along [1 0 0] for L = Er, Tm. The results are discussed and a relative scale of the stability of the moment configuration in the (0 1 0) plane is proposed. (C) 2010 Elsevier BM. All rights reserved.
Title:
Microindentation of dispersed phases in an Al94Mn2Be2Cu2 alloy
Authors:
Boncina, T; Cekada, M; Markoli, B; Zupanic, F Author Full Names: Boncina, Tonica; Cekada, Miha; Markoli, Bostjan; Zupanic, Franc
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 505 (2): 486-491 SEP 3 2010
Abstract:
This paper investigated properties of dispersed phases in an Al94Mn2Be2Cu2 alloy using a microindentation hardness test. The focus was directed to the possible strengthening phases for aluminium alloys: an icosahedral quasicrystalline phase (i-phase), a hexagonal quasicrystalline approximant with a large unit cell (H-phase) and a ternary cubic Be4AlMn. A single grain mu-Al4Mn was also examined as a reference. The application of scanning electron microscopy and a focussed ion beam, significantly increased the reliability and reproducibility of the microindentation results. The i-phase was distinguished by the highest Vickers hardness and the highest fraction of elastic energy, while the elastic modulus was the highest for Be4AlMn, being close to that of pure Be. The striking resemblances of the indentation curves for the phases with cluster substructures: i-phase, H-phase and mu-Al4Mn, especially the presence of pop-ins, suggested related deformation mechanisms. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Stationary straight cracks in quasicrystals
Authors:
Radi, E; Mariano, PM Author Full Names: Radi, Enrico; Mariano, Paolo Maria
Source:
INTERNATIONAL JOURNAL OF FRACTURE 166 (1-2): 105-120 Sp. Iss. SI NOV 2010
Abstract:
Stationary straight cracks in quasicrystals in linear elastic setting are under scrutiny. The analysis is developed by using Stroh formalism which is modified to account for a totally degenerate eigenvalue problem: in fact, the fundamental matrix of the governing equations of motion admits a repeated eigenvalue corresponding to a single eigenvector. Cases of a semi-infinite rectilinear crack loaded along its margins and a crack of finite length under remote loading conditions are considered. Standard and phason stresses display square-root singularities at crack tip. The latter stresses represent peculiar microstructural inner actions occurring in quasicrystals and are determined by rearrangements assuring quasi-periodicity of the atomic tiling-modes described by a vector field, called phason field, collecting the local degrees of freedom exploited by the atoms within the material elements. Energy release rate increases with the coupling parameter between displacement ! and phason fields.

Update: 1-Oct-2010

Title:
Quasicrystals
Authors:
Vekilov, YK; Chernikov, MA Author Full Names: Vekilov, Yu Kh; Chernikov, M. A.
Source:
PHYSICS-USPEKHI 53 (6): 537-560 2010
Abstract:
We review the structure of quasicrystals and their electronic spectra, lattice excitation spectra, physical properties, and applications. The aperiodic filling of space according to certain rules with several structural units or overlapping atomic clusters is discussed. Perfect tiling, random tiling, and icosahedral glass models, as well as phason strain are considered. The effect that the aperiodic long-range order and local atomic structure have on electron and thermal transport and on the optical, magnetic, and other properties is examined.
Title:
Calorimetric investigation of electronic and lattice excitations of the icosahedral quasicrystal in the range of moderate temperatures
Authors:
Prekul, AF; Shalaeva, EV; Shchegolikhina, NI Author Full Names: Prekul, A. F.; Shalaeva, E. V.; Shchegolikhina, N. I.
Source:
PHYSICS OF THE SOLID STATE 52 (9): 1797-1802 SEP 2010
Abstract:
The precise measurements of the specific heat and the linear expansion coefficient of polygrain samples of the ordered icosahedral phase Al63Cu25Fe12 have been performed in the temperature range 1.8-400.0 K. The deviations from the Gruneisen law, according to which the temperature dependences of the lattice specific heat at constant volume and the linear expansion coefficient are identical to each other, have been analyzed. The proofs that the specific heat of the quasicrystals contains latent electronic and lattice contributions of the Schottky type have been obtained. The revealed contributions can be thermodynamic consequences of the fractal energy spectra.
Title:
Formation Kinetics of a Bi3Nb1-xTaxO7 Fluorite-Type Solid Solution and Thermodynamic Stability of the Bi3TaO7 End Member
Authors:
Pirnat, U; Valant, M; Radmilovic, V Author Full Names: Pirnat, Ursa; Valant, Matjaz; Radmilovic, Velimir
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY 93 (9): 2909-2914 SEP 2010
Abstract:
Analysis of kinetic characteristics of the incommensurate-commensurate transformation in the Bi3Nb1-xTaxO7 system with a fluorite-like crystal structure enabled us to define the compositional and thermal stability ranges of the commensurate tetragonal polymorph. We showed that the tetragonal polymorph across the entire homogeneity range is isostructural to the Bi3NbO7 end member. The kinetics of the transformation from the cubic incommensurate to the tetragonal commensurate phase decreases with an increase in Ta concentration within the Bi3Nb1-xTaxO7 system. The formation studies indicate that the tetragonal Bi3TaO7 is thermodynamically stable; however, its formation via the metastable incommensurate-cubic phase is suppressed.

Update: 24-Sep-2010

Title:
Kagome staircase compound Co3V2O8 in an applied magnetic field: Single-crystal neutron diffraction study
Authors:
Petrenko, OA; Wilson, NR; Balakrishnan, G; Paul, DM; McIntyre, GJ Author Full Names: Petrenko, O. A.; Wilson, N. R.; Balakrishnan, G.; Paul, D. Mck; McIntyre, G. J.
Source:
PHYSICAL REVIEW B 82 (10): Art. No. 104409 SEP 8 2010
Abstract:
The magnetic properties of Co3V2O8 have been studied by single-crystal neutron diffraction. In zero magnetic field, the observed broadening of the magnetic Bragg peaks suggests the presence of disorder both in the low-temperature ferromagnetic and in the higher temperature antiferromagnetic state. The field dependence of the intensity and position of the magnetic reflections in Co3V2O8 reveals a complex sequence of phase transitions in this Kagome staircase compound. For H parallel to a, a commensurate-incommensurate-commensurate transition is found in a field of 0.072 T in the antiferromagnetic phase at 7.5 K. For H parallel to c at low temperature, an applied field induces an unusual transformation from a ferromagnetic to an antiferromagnetic state at about 1 T accompanied by a sharp increase in magnetization.
Title:
Ab initio study of stabilization of the misfit layer compound (PbS)(1.14)TaS2
Authors:
Kabliman, E; Blaha, P; Schwarz, K Author Full Names: Kabliman, Evgeniya; Blaha, Peter; Schwarz, Karlheinz
Source:
PHYSICAL REVIEW B 82 (12): Art. No. 125308 SEP 8 2010
Abstract:
In the present work we perform ab initio electronic-structure calculations of the (PbS)(1.14)TaS2 misfit layer compound in order to understand the basic mechanism of its stabilization. Density-functional based calculations were carried out in commensurate unit cells containing 74 or 296 atoms using the WIEN2K code. The two experimentally predicted mechanisms of stabilization, namely, metal cross substitution (interchange of Pb and Ta atoms in the PbS and TaS2 layers) and nonstoichiometry (substitution of Pb by Ta), were investigated. The results show clearly that the nonstoichiometry mechanism plays the significant role. When Pb inside the PbS layer is substituted by Ta with concentrations around 0.13-0.19, a stabilization is found with respect to the parent PbS and TaS2 compounds. These results are explained by an analysis of partial densities of states. The calculated x-ray photoemission spectroscopy core-level shifts are in reasonable agreement with experiments.
Title:
Symmetry and strain analysis of structural phase transitions in Pr0.48Ca0.52MnO3
Authors:
Carpenter, MA; McKnight, REA; Howard, CJ; Knight, KS Author Full Names: Carpenter, Michael A.; McKnight, Ruth E. A.; Howard, Christopher J.; Knight, Kevin S.
Source:
PHYSICAL REVIEW B 82 (9): Art. No. 094101 SEP 7 2010
Abstract:
Structural evolution as a function of temperature through the Pnma <-> incommensurate (IC) phase transition in Pr0.48Ca0.52MnO3 perovskite has been analyzed from the perspectives of symmetry and strain. The structure and stability of both phases are shown to depend on combinations of order parameters which have symmetries associated with irreducible representations M-3(+), R-4(+), M-2(+), Gamma(+)(3) and Sigma(2) of space group Pm (3) over barm. The physical origin of these can be understood in terms of octahedral tilting, cooperative Jahn-Teller distortions and charge order/Zener polaron ordering. The M-2(+) order parameter describes the Jahn- Teller ordering scheme which develops in LaMnO3 while the Gamma(+)(3) order parameter relates to an ordering scheme in which the unique axes of the distorted octahedra are all aligned in the same direction. Irrep Sigma(2) contains two components with gradient coupling and provides the symmetry-breaking mechanism by which the IC transition can occur. Each order parameter couples with macroscopic spontaneous strains in a manner that depends strictly on symmetry and this leads to specific interactions between the order parameters through their coupling with common strains. In order to establish the extent and importance of this coupling, symmetry- adapted strains have been extracted from a new set of lattice parameters obtained by high-resolution powder neutron diffraction in the temperature interval 10-1373 K. It is found that the predominant strain of the incommensurate structure (up to similar to 2.5%) is a tetragonal shear strain which arises by bilinear coupling with the Gamma(+)(3) order parameter. This combination is probably responsible for most of the energy reduction accompanying the Pnma. IC transition and also gives it some characteristics typical of a pseudoproper ferroelastic transition. Strain coupling promotes mean-field behavior and the evolution of the symmetry-breaking order parameter can be described by a standard Landau tricritical solution, q(4)proportional to(T-c-T) with T-c = 237 +/- 2 K. Octahedral tilting at high temperatures is closely similar to tilting in the Pnma structure of other perovskites, such as SrZrO3. This is accompanied by a degree of Jahn- Teller ordering on the basis of the M-2(+) scheme below similar to 775 K but is replaced by the Gamma(+)(3) scheme below T-c. In contrast with the tilting and Jahn-Teller effects, magnetic ordering at the Neel temperature (similar to 180 K) is accompanied by only the slightest volume strain and is not likely to influence the evolution of the other order parameters to any significant extent, therefore. An additional change in the volume strain below similar to 85 K is perhaps related to changes in magnetic structure at lower temperatures. Line broadening in powder diffraction patterns collected in the temperature interval similar to 150-260 K appears to be related to the presence of ferroelastic twins arising from octahedral tilting and draws attention to the fact that the Pnma <-> IC transition takes place in a material which already contains heterogeneities. Finally, correlation of the repeat distance of the IC structure with Gamma(+)(3) distortions of MnO6 octahedra shows that the nature of the IC structure itself is also deermined essentially by geometrical factors and strain.
Title:
Magnetic structure of the zigzag chain family NaxCa1-xV2O4 determined by muon- spin rotation
Authors:
Ofer, O; Ikedo, Y; Goko, T; Mansson, M; Sugiyama, J; Ansaldo, EJ; Brewer, JH; Chow, KH; Sakurai, H Author Full Names: Ofer, Oren; Ikedo, Yutaka; Goko, Tatsuo; Mansson, Martin; Sugiyama, Jun; Ansaldo, Eduardo J.; Brewer, Jess H.; Chow, Kim H.; Sakurai, Hiroya
Source:
PHYSICAL REVIEW B 82 (9): Art. No. 094410 SEP 7 2010
Abstract:
We present muon-spin-rotation measurements on polycrystalline samples of the complete family of the antiferromagnetic (AF) zigzag chain compounds, NaxCa1-xV2O4. In this family, we explore the magnetic properties from the metallic NaV2O4 to the insulating CaV2O4. We find a critical x(c)(similar to 0.833) which separates the low and high Na-concentration-dependent transition temperature and its magnetic ground state. In the x < x(c) compounds, the magnetic ordered phase is characterized by a single homogenous phase and the formation of incommensurate spin-density-wave order. Whereas in the x > x(c) compounds, multiple subphases appear with temperature and x. Based on the muon data obtained in zero external magnetic field, a careful dipolar field simulation was able to reproduce the muon behavior and indicates a modulated helical incommensurate spin structure of the metallic AF phase. The incommensurate modulation period obtained by the simulation agrees with that determined by neutron diffraction.
Title:
Composition rule for Al-transition metal binary quasicrystals
Authors:
Chen, H; Wang, Q; Wang, YM; Qiang, JB; Dong, C Author Full Names: Chen, Hua; Wang, Qing; Wang, Yingmin; Qiang, Jianbing; Dong, Chuang
Source:
PHILOSOPHICAL MAGAZINE 90 (30): 3935-3946 2010
Abstract:
Compositions of Al-transition metal (TM) binary quasicrystals are revisited using the cluster-plus-glue-atom model. These compositions all conform to a unified cluster formula [icosahedron](glue)1, where the icosahedron is taken from a crystalline approximant. In a given binary system, icosahedral and decagonal quasicrystals are expressed by the same icosahedron but glued, respectively, by one Al and one TM, and their e/a ratios fall close to 1.86 and 1.71-1.79, respectively. Their relative stabilities are discussed by referring to compositions satisfying the fully filled TM-3d states according to Haussler's resonance model.
Title:
Microstructure of a composite with a quasicrystalline phase fraction obtained by directional solidification of Al61Cu27Fe12 alloy
Authors:
Krawczyk, J; Bogdanowicz, W; Goryczka, T Author Full Names: Krawczyk, Jacek; Bogdanowicz, Wodzimierz; Goryczka, Tomasz
Source:
PHILOSOPHICAL MAGAZINE 90 (30): 3987-3998 2010
Abstract:
The microstructure of a composite containing a quasicrystal phase, i.e. so-called crystal-quasicrystal (CQ) composite, was studied. The CQ composite was obtained by the Bridgman method via solidification of Al61Cu27Fe12 alloy (numbers indicate at%). The process was conducted at a pull out rate of v = 0.07 mm/min. The average temperature gradient in the heating zone was 43 K/cm. The composite matrix consisted of cubic phase Al(Fe, Cu), with reinforcement of -phase rod-shaped fibres surrounded by a quasicrystal icosahedral phase, which also existed in the fibre core. The fibres were rhomboidal in cross-section. The composite was studied using X-ray and electron diffraction, light-optical and scanning electron microscopy (SEM), X-ray topography and Laue diffraction.
Title:
Interplay of quantum criticality and geometric frustration in columbite
Authors:
Lee, S; Kaul, RK; Balents, L Author Full Names: Lee, SungBin; Kaul, Ribhu K.; Balents, Leon
Source:
NATURE PHYSICS 6 (9): 702-706 SEP 2010
Abstract:
CoNb2O6 is a material with remarkable properties that are determined by an exciting interplay of quantum mechanics and geometric frustration. On the one hand, weakly coupled ferromagnetic Ising chains of Co2+ ions can be tuned by an applied magnetic field through a quantum critical point to be paramagnetic; on the other hand, the Ising chains must contend with residual interactions on a frustrated triangular lattice in their choice of how to order. Motivated by the material, we theoretically study the phase diagram of quantum ferromagnetic Ising chains coupled antiferromagnetically on a triangular lattice in the plane perpendicular to the chain direction. We combine exact solutions of the quantum criticality in the isolated chains with perturbative approximations for the frustrated interchain couplings. When the triangular lattice has an isosceles distortion, which occurs in the real material, the phase diagram at absolute zero temperature is rich with five different states of matter: ferrimagnetic, Neel, antiferromagnetic, paramagnetic and incommensurate phases, separated by quantum phase transitions. Implications of our results on experiments in CoNb2O6 are discussed.
Title:
Quasicrystalline phase formation during heat treatment in mechanically alloyed Al65Cu20Fe15 alloy
Authors:
Gogebakan, M; Avar, B Author Full Names: Gogebakan, M.; Avar, B.
Source:
MATERIALS SCIENCE AND TECHNOLOGY 26 (8): 920-924 AUG 2010
Abstract:
Quasicrystalline phase formation during heat treatment in the mechanically alloyed Al65Cu20Fe15 powders was studied by X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The mechanical alloying was performed at speed of 300 rev min(-1) for times up to 70 h. It was found that mechanical alloying of the Al65Cu20Fe15 powders did not result in the quasicrystalline (QC) icosahedral phase (i-phase) formation. The long time milling resulted in the formation of a cubic Al (Cu,Fe) solid solution phase (beta-phase). The cubic Al (Cu,Fe) solid solution identified as beta-phase was observed to be present as one of the major phases in the Al65Cu20Fe15 alloy. The formation of the quasicrystalline icosahedral phase (i-phase) was only observed for short time milled powders after additional annealing at temperature above 500 degrees C. The present investigation also showed that a tetragonal Al2Cu phase (theta-phase) forms with short time milling. The tetragonal Al7Cu2Fe1 phase (w-phase) was observed after heat treatment of the short time milled and unmilled powders. The present investigation indicated that an effective process to prepare the quasicrystalline materials was using a combination of short time milling and subsequent annealing.
Title:
Ab initio density-functional calculations in materials science: from quasicrystals over microporous catalysts to spintronics
Authors:
Hafner, J Author Full Names: Hafner, Juergen
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (38): Art. No. 384205 SEP 29 2010
Abstract:
During the last 20 years computer simulations based on a quantum-mechanical description of the interactions between electrons and atomic nuclei have developed an increasingly important impact on materials science, not only in promoting a deeper understanding of the fundamental physical phenomena, but also enabling the computer-assisted design of materials for future technologies. The backbone of atomic-scale computational materials science is density-functional theory (DFT) which allows us to cast the intractable complexity of electron-electron interactions into the form of an effective single-particle equation determined by the exchange-correlation functional. Progress in DFT-based calculations of the properties of materials and of simulations of processes in materials depends on: (1) the development of improved exchange-correlation functionals and advanced post-DFT methods and their implementation in highly efficient computer codes, (2) the development of methods allowing us to bridge the gaps in the temperature, pressure, time and length scales between the ab initio calculations and real-world experiments and (3) the extension of the functionality of these codes, permitting us to treat additional properties and new processes. In this paper we discuss the current status of techniques for performing quantum-based simulations on materials and present some illustrative examples of applications to complex quasiperiodic alloys, cluster-support interactions in microporous acid catalysts and magnetic nanostructures.
Title:
Dichalcogenide Bonding in Seven Alkali-Metal Actinide Chalcogenides of the KTh2Se6 Structure Type
Authors:
Bugaris, DE; Wells, DM; Yao, JY; Skanthakumar, S; Haire, RG; Soderholm, L; Ibers, JA Author Full Names: Bugaris, Daniel E.; Wells, Daniel M.; Yao, Jiyong; Skanthakumar, S.; Haire, Richard G.; Soderholm, L.; Ibers, James A.
Source:
INORGANIC CHEMISTRY 49 (18): 8381-8388 SEP 20 2010
Abstract:
The solid-state compounds CsTh2Se6, Rb0.85U1.74S6, RbU2Se6, TIU2Se6, Cs-0.88(La0.68U1.32)Se-6, KNP2Se6, and CsNp2Se6 of the AAn(2)Q(6) family (A = alkali metal or TI; An = Th, U, Np; Q = S, Se, Te) have been synthesized by high-temperature techniques. All seven crystallize in space group lmmm of the orthorhombic system in the KTh2Se6 structure type. Evidence of long-range order and modulation were found in the X-ray diffraction patterns of TIU2Se6 and CsNp2Se6. A 4a X 4b supercell was found for TIU2Se6 whereas a 5a x 5b x 5c supercell was found for CsNp2Se6. All seven compounds exhibit Q-Q interactions and, depending on the radius ratio R-An/R-A1 disorder of the A cation over two sites. The electrical conductivity of RbU2Se6, measured along [100], is 6 x 10(-5) S cm(-1) at 298 K. The interatomic distances, including those in the modulated structure of TIU2Se6, and physical properties suggest the compounds may be formulated as containing tetravalent Th or U, but the formal oxidation state of Np in the modulated structure of CsNp2Se6 is less certain. The actinide contraction from Th to U to Np is apparent in the interatomic distances.

Update: 17-Sep-2010

Title:
M-Al-M groups trapped in cages of Al13M4 (M=Co, Fe, Ni, Ru) complex intermetallic phases as seen via NMR
Authors:
Jeglic, P; Vrtnik, S; Bobnar, M; Klanjsek, M; Bauer, B; Gille, P; Grin, Y; Haarmann, F; Dolinsek, J Author Full Names: Jeglic, P.; Vrtnik, S.; Bobnar, M.; Klanjsek, M.; Bauer, B.; Gille, P.; Grin, Yu.; Haarmann, F.; Dolinsek, J.
Source:
PHYSICAL REVIEW B 82 (10): Art. No. 104201 SEP 3 2010
Abstract:
The crystallographic structures of decagonal quasicrystals and their periodic approximants are traditionally described as a periodic stacking of atomic planes. By performing a Al-27 NMR spectroscopic study of the Al13M4 (M=transition metal) family of four-layer decagonal approximants, including the orthorhombic o-Al13Co4, the monoclinic Al13Fe4, its ternary derivative Al-13 (Fe,Ni)(4), and the monoclinic Al13Ru4, we show that all these phases contain structural detail of a nearly linear M-Al-M atomic group trapped inside an elongated cage, resembling the three-dimensional (3D) "cage-compound" structure of the intermetallic clath-rates. We determined the electric-field-gradient- (EFG) and the magnetic-shielding tensors at the Al site of the M-Al-M groups. The asymmetry parameter of the EFG tensor was estimated theoretically by a point-charge model, taking into account the charges of both the M-Al-M atoms and the surrounding cage atoms. The calculations support ionic bonding of the M-Al-M group to the cage atoms and the existence of a 3D chemical bonding network in the Al13M4 phases. The above results show that the traditional description of the Al13M4 decagonal approximant phases in terms of two-dimensional (2D) atomic layers stacked along the pseudotenfold crystallographic direction is a convenient geometrical approach to describe their complex structures but is not appropriate for the description of their physical properties, which should be analyzed by taking into account the full 3D nature of the chemical bonding framework. This favors the 3D cage-compound structural description of the Al13M4 phases over the pseudo-2D stacked-layer description.
Title:
Evolution of the magnetic field-temperature phase diagram in UAs1-xSex
Authors:
Plackowski, T; Matusiak, M; Sznajd, J Author Full Names: Plackowski, Tomasz; Matusiak, Marcin; Sznajd, Jozef
Source:
PHYSICAL REVIEW B 82 (9): Art. No. 094408 SEP 3 2010
Abstract:
The evolution of the magnetic field-temperature phase diagram of UAs1-xSex with x in the range of 0-0.1 is studied by means of magnetocaloric and specific-heat measurements. Our interest is focused on the high-temperature phase transitions and especially on the point, where the paramagnetic (P) and two ordered phases meet. For undoped UAs these two ordered states are the ferrimagnetic (Fi) and the type-I antiferromagnetic phases. According to Sinha et al. [Phys. Rev. Lett. 45, 1028 (1980)] the antiferromagnetic phase transition is in the vicinity of a Lifshitz point. Furthermore, Kuznietz et al. [J. Magn. Magn. Mater. 61, 246 (1986)] showed that an incommensurate phase (IC) emerges between the type-I (or type-IA) antiferromagnetic and paramagnetic phases in the case of UAs1-xSex with 0 < x < 0.15 in zero magnetic field. The results reported in this paper show the existence of a T-Fi/IC(B) line that separates the ferrimagnetic region from a phase, which cannot be identified on the basis of our thermodynamic measurements. However, one may assume it is the IC phase, consistent with the above mentioned zero field results. The T-Fi/IC(B) line merges with the order-disorder line at point (B-p, T-p), where the critical line (IC/P) meets with two first order transitions lines: Fi/P and Fi/IC. This point can be considered as an analog of a Lifshitz point. A simple phenomenological description of the phase transitions near this special point is provided.
Title:
Plasticity of quasicrystals and of bulk metallic glasses: An analogy
Authors:
Guyot, P Author Full Names: Guyot, P.
Source:
INTERMETALLICS 18 (10): 1925-1929 Sp. Iss. SI OCT 2010
Abstract:
Despite their antinomic atomic structures, long range ordered but non-periodically for quasicrystals (QC), or disordered for met-glasses (MG), both materials share surprisingly a similar mechanical behaviour: brittleness at low temperature, plasticity at high temperature. Such a-priori surprising results are considered and analysed, focussing on the high temperature ductility. Due to the aperiodic order of the QC atomic structure, the dislocation motion creates a topological and chemical disorder from which a friction stress results. Combining the friction stress strain reduction with classical dynamic properties of dislocations allows to establish a constitutive equation of the deformation, which reproduces the essential characteristics of the experimental stress strain and creep curves [7]. In MG, the diffusion of the free volume flow defects [9] is at the origin of the high temperature plastic strain. Their flow equation, where time and strain variations of the flow carriers density are introduced, leads to a satisfactory description of experimental observations: scaling of the glass viscosity with strain-rate and temperature, transient regimes occurring during specimen loading/unloading or strain-rate changes. Common features underlying the constitutive equation of the high temperature deformation of both materials are emphasized and discussed. (C) 2010 Elsevier Ltd. All rights reserved.

Update: 10-Sep-2010

Title:
Commensurate charge-density wave with frustrated interchain coupling in SmNiC2
Authors:
Wolfel, A; Li, L; Shimomura, S; Onodera, H; van Smaalen, S Author Full Names: Woelfel, Alexander; Li, Liang; Shimomura, Susumu; Onodera, Hideya; van Smaalen, Sander
Source:
PHYSICAL REVIEW B 82 (5): Art. No. 054120 AUG 30 2010
Abstract:
Temperature-dependent x-ray diffraction on SmNiC2 has shown that the orthorhombic lattice symmetry of this compound persist down to a temperature of at least 9 K, i.e., into the charge-density-wave (CDW) state below T-CDW = 148 K and in the ferromagnetically ordered state below T-C = 17.7 K. The modulated crystal structure has been determined for the incommensurate CDW state with q(CDW) = (0.5,0.516,0) at T=60 K. The observed atomic modulation displacements indicate that the CDW should be considered as a commensurate CDW centered on chains of Ni atoms along a. Frustrated interchain coupling is responsible for the incommensurability of the three-dimensionally ordered CDW state.
Title:
Quasicrystals as alloys with short-range order
Authors:
Sulston, KW; Burrows, BL Author Full Names: Sulston, K. W.; Burrows, B. L.
Source:
PHYSICA B-CONDENSED MATTER 405 (18): 3885-3889 SEP 15 2010
Abstract:
The electronic structure of quasiperiodic lattices is studied. An alloy theory, including short-range order effects, is used to approximate Fibonacci and Thue-Morse lattices. Short-range order is treated by embedding small clusters in an alloy that itself incorporates a two-site approximation, and the probabilities of these clusters are used to construct an efficient procedure for the calculation of electronic properties. This approach allows easy identification of the contributions of particular clusters to the electronic density of states. As the short-range order is increased via the number of clusters, the density of states can be clearly seen to transition from that of an alloy to that of a quasicrystal. It is shown that the techniques may be applied to other lattices defined by substitution rules. (C) 2010 Elsevier B.V. All rights reserved.
Title:
A comparative scanning tunneling spectroscopy investigation of the (12110)-surface of decagonal Al-Ni-Co and the (100)-surface of its approximant Y-Al-Ni-Co
Authors:
Mader, R; Widmer, R; Groning, P; Ruffieux, P; Steurer, W; Groning, O Author Full Names: Maeder, Ruben; Widmer, Roland; Groening, Pierangelo; Ruffieux, Pascal; Steurer, Walter; Groening, Oliver
Source:
NEW JOURNAL OF PHYSICS 12: Art. No. 073043 JUL 30 2010
Abstract:
We present a low-temperature scanning tunneling spectroscopy study of the local density of states (LDOS) on the (12110)-surface of the decagonal quasicrystal d-Al-Ni-Co and the (100)-surface of its structurally closely related approximant Y-Al-Ni-Co in the range of +/- 1 eV around the Fermi energy. The LDOS of both surfaces are dominated by a large parabolic pseudogap centered at the Fermi energy, which can be attributed to the Hume-Rothery stabilization mechanism or to an orbital hybridization. Superimposed on this large pseudogap, a spatially varying fine structure is revealed, whose spatial distribution correlates with the structures of both of the surfaces. This fine structure shows narrow peaks and pseudogaps exhibiting typical energy widths between 50 and 150 meV. The spatial extent of these localized states is of the order of the width of the topographic features, which is about 0.45 nm. Our findings show that specific electronic states are localized on equivalent topographic features regardless of the presence of periodic or quasiperiodic long-range order. We interpret this result as an indication that the fine structure in the LDOS is dominated much more by the complex short-range order than by the presence of the quasiperiodic long-range order.
Title:
Mode crystallography of distorted structures
Authors:
Perez-Mato, JM; Orobengoa, D; Aroyo, MI Author Full Names: Perez-Mato, J. M.; Orobengoa, D.; Aroyo, M. I.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 66: 558-590 Part 5 SEP 2010
Abstract:
The description of displacive distorted structures in terms of symmetry-adapted modes is reviewed. A specific parameterization of the symmetry-mode decomposition of these pseudosymmetric structures defined on the setting of the experimental space group is proposed. This approach closely follows crystallographic conventions and permits a straightforward transformation between symmetry-mode and conventional descriptions of the structures. Multiple examples are presented showing the insight provided by the symmetry-mode approach. The methodology is shown at work, illustrating its various possibilities for improving the characterization of distorted structures, for example: detection of hidden structural correlations, identification of fundamental and marginal degrees of freedom, reduction of the effective number of atomic positional parameters, quantitative comparison of structures with the same or different space group, detection of false refinement minima, syste! matic characterization of thermal behavior, rationalization of phase diagrams and various symmetries in families of compounds etc. The close relation of the symmetry-mode description with the superspace formalism applied to commensurate superstructures is also discussed. Finally, the application of this methodology in the field of ab initio or first-principles calculations is outlined. At present, there are several freely available user-friendly computer tools for performing automatic symmetry-mode analyses. The use of these programs does not require a deep knowledge of group theory and can be applied either a posteriori to analyze a given distorted structure or a priori to parameterize the structure to be determined. It is hoped that this article will encourage the use of these tools. All the examples presented here have been worked out using the program AMPLIMODES [Orobengoa et al. (2009). J. Appl. Cryst. 42, 820-833].

Update: 27-Aug-2010

Title:
Effect of Mg-based spherical quasicrystal on microstructures and mechanical properties of ZA54 alloy
Authors:
Zhang, JS; Zhang, YQ; Zhang, Y; Xu, CX; Wang, XM; Yan, J Author Full Names: Zhang Jin-shan; Zhang Yong-qing; Zhang Yan; Xu Chun-xiang; Wang Xiao-ming; Yan Jie
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA 20 (7): 1199-1204 JUL 2010
Abstract:
To improve the strength, toughness and heat-resistance of magnesium alloy, the microstructure and mechanical properties of ZA54 alloy reinforced by icosahedral quasicrystal phase (I-phase) particles were studied. Except alpha-Mg, phi-phase and tau-phase, MgZnYMn I-phase particles can be obtained in ZA54-based composites by the addition of icosahedral quasicrystal-contained Mg-Zn-Y-Mn master alloy. The introduction of MgZnYMn I-phase into ZA54 alloy has great contribution to the refinement of matrix microstructures and the improvement of mechanical properties. When the addition of Mg-based spherical quasicrystal master alloy is up to 3.5% (mass fraction), the macro-hardness of ZA54-based composites is increased to HB 68. The impact toughness of composites reaches the peak value of 18.3 J/cm(2), which is about 29% higher than that of ZA54 mother alloy. The highest tensile properties at ambient and elevated temperatures with master alloy addition of 2.5% (473 K) are also obtained in ZA54-based composites with 3.5% (mass fraction) Mg-Zn-Y-Mn master alloy addition. The ultimate tensile strength of composites at ambient and elevated temperatures are 192.5 MPa and 174 MPa, which are 23.4% and 33.8% higher than that of ZA54 mother alloy, respectively. The improved mechanical properties are mainly attributed to the pinning effect of I-phase on grain boundaries.
Title:
Magnetic field and temperature dependence of the amplitude-modulated magnetic structure of PrNi2Si2 determined by single-crystal neutron diffraction
Authors:
Blanco, JA; Fak, B; Ressouche, E; Grenier, B; Rotter, M; Schmitt, D; Rodriguez-Velamazan, JA; Campo, J; Lejay, P Author Full Names: Blanco, J. A.; Fak, B.; Ressouche, E.; Grenier, B.; Rotter, M.; Schmitt, D.; Rodriguez-Velamazan, J. A.; Campo, J.; Lejay, P.
Source:
PHYSICAL REVIEW B 82 (5): Art. No. 054414 AUG 11 2010
Abstract:
The temperature and magnetic field dependence of the magnetic structure in the singlet crystal-field ground-state system PrNi2Si2 have been determined using single-crystal neutron diffraction. At the magnetic ordering temperature in zero field, T-N=20.0 +/- 0.5 K, an amplitude-modulated magnetic structure sets in with a propagation vector k=(0, 0, 0.87) and the magnetic moments of the Pr3+ ions parallel to the c axis of the body-centered tetragonal structure. The magnetic structure remains amplitude modulated down to low temperatures (T=1.6 K) with only a small tendency to squaring up, as signaled by the weak intensity of the third harmonic that develops below 16 K. With applied field along the easy axis, the modulated structure goes smoothly over into a ferromagnetic state. At the critical field of H-c=58 kOe, the first harmonic disappears and the field-induced ferromagnetic moment shows a kink, in agreement with magnetization measurements. Both the temperature and magnetic field dependence are well described by a periodic field Hamiltonian including magnetic exchange and the crystalline electric field.
Title:
Quasiperiodic Pb monolayer on the fivefold i-Al-Pd-Mn surface: Structure and electronic properties
Authors:
Krajci, M; Hafner, J; Ledieu, J; Fournee, V; McGrath, R Author Full Names: Krajci, M.; Hafner, J.; Ledieu, J.; Fournee, V.; McGrath, R.
Source:
PHYSICAL REVIEW B 82 (8): Art. No. 085417 AUG 11 2010
Abstract:
Lead is one of few elements that adopts a pseudomorphic structure when deposited on quasicrystalline substrates. We present a structural model of quasiperiodic Pb overlayers formed on the fivefold surface of an icosahedral A1-Pd-Mn quasicrystal at two different coverages close to saturation. The skeleton of the Pb monolayer is formed by a network of "starfish" (SF) clusters formed at the initial stages of Pb deposition, as studied in detail in our previous work [Ledieu et al., Phys. Rev. B 79, 165430 (2009)]. The atomic structure of the Pb monolayers can be represented as a decorated pentagonal Penrose P1 tiling. The structural models reproduce also the quasiperiodic superstructure of the layers observed in experimental scanning tunneling microscopy (STM) images which is described by the tau-scaled tau P1 tiling (tau is the golden mean). The atomic structure underlying the observed tau-scaled "white flower" motifs and the origin of irregular bright spots in STM! images are discussed. The bright spots appear in the centers of the SF clusters centered at substrate sites occupied by A1 atoms. The calculated electronic structure shows that the minimum in the density of states (pseudogap) at the Fermi level which is characteristic for the A1-Pd-Mn quasicrystals appears also in the local density of states of the adsorbed Pb monolayer. However, our analysis demonstrates that the formation of this pseudogap is not due to the quasiperiodic arrangement of the Pb atoms but to the strong hybridization of their orbitals with the substrate.
Title:
Structure and reactivity of Bi allotropes on the fivefold icosahedral Al-Pd-Mn quasicrystal surface
Authors:
Smerdon, JA; Cross, N; Dhanak, VR; Sharma, HR; Young, KM; Lograsso, TA; Ross, AR; McGrath, R Author Full Names: Smerdon, J. A.; Cross, N.; Dhanak, V. R.; Sharma, H. R.; Young, K. M.; Lograsso, T. A.; Ross, A. R.; McGrath, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (34): Art. No. 345002 SEP 1 2010
Abstract:
The growth of Bi on a pseudomorphic Bi monolayer on the fivefold surface of the icosahedral Al-Pd-Mn quasicrystal has been investigated using low energy electron diffraction and scanning tunnelling microscopy. Initially randomly oriented pseudocubic islands are formed with a preference for an even number of layers. Subsequently a morphological transformation takes place to hexagonal Bi islands, which align along high symmetry directions of the substrate. The Bi flux is found to have a strong effect on which island structure is preferred. When C-60 is adsorbed on the three different allotropes of Bi present in this system, hexagonal C-60 islands are formed in each case. On the pseudocubic and hexagonal islands, the C-60 islands are aligned with the substrate. We discuss the energetic, kinetic and geometrical factors which influence the morphological transformation referred to above.
Title:
Activated impurity states in the incommensurate phase of ferroelectric semiconductor TlInS2
Authors:
Seyidov, MY; Suleymanov, RA; Salehli, F Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Salehli, Ferid
Source:
JOURNAL OF APPLIED PHYSICS 108 (2): Art. No. 024111 JUL 15 2010
Abstract:
The effect of annealing within the incommensurate phase on the dielectric function epsilon of the TlInS2 single crystals has been investigated. It is shown that the effect of annealing is very close to the effect of doping by electrically active impurity La. The inference is made that the correlation between observed effects in annealed and doped crystals is conditioned by the internal electric fields induced by the activation (polarization) of native defects during the annealing procedure. The investigations of the Second harmonic generation in undoped TlInS2 crystal and the pyrocurrent in TlInS2 : La confirms the proposed model. (C) 2010 American Institute of Physics. [doi:10.1063/1.3466764]
Title:
Magnetic ordering in PrT2Ge2 (T = Ni, Ru and Rh) compounds
Authors:
Szytula, A; Kaczorowski, D; Gondek, L; Pikul, A; Arulraj, A; Balanda, M; Baran, S; Penc, B Author Full Names: Szytula, A.; Kaczorowski, D.; Gondek, L.; Pikul, A.; Arulraj, A.; Balanda, M.; Baran, S.; Penc, B.
Source:
INTERMETALLICS 18 (9): 1766-1771 SEP 2010
Abstract:
X-ray and neutron diffraction, magnetization, magnetic susceptibility and electrical resistivity measurements were performed on polycrystalline samples of PrNi2Ge2, PrRu2Ge2 and PrRh2Ge2. All the investigated compounds crystallize with a tetragonal structure of the ThCr2Si2-type. All of them exhibit metallic-like electrical conductivity and order magnetically at low temperatures, namely PrNi2Ge2 and PrRh2Ge2 are antiferromagnetic below T-N = 23.5 and 45 K, respectively, while PrRu2Ge2 is a ferromagnet with T-C = 14.8 K. The neutron diffraction data indicated a modulated antiferromagnetic structure in PrNi2Ge2 in the entire ordered region. For PrRh2Ge2 a collinear antiferromagnetic ordering was derived below T-t = 30 K and a sine-modulated ordering above that temperature. The neutron diffraction corroborated a simple ferromagnetic structure in PrRu2Ge2. (C) 2010 Elsevier Ltd. All rights reserved.

Update: 20-Aug-2010

Title:
Sound behavior near the Lifshitz point in proper ferroelectrics
Authors:
Kohutych, A; Yevych, R; Perechinskii, S; Samulionis, V; Banys, J; Vysochanskii, Y Author Full Names: Kohutych, A.; Yevych, R.; Perechinskii, S.; Samulionis, V.; Banys, J.; Vysochanskii, Yu.
Source:
PHYSICAL REVIEW B 82 (5): Art. No. 054101 AUG 4 2010
Abstract:
The interaction between soft optic and acoustic phonons was investigated for Sn2P2(Se0.28S0.72)(6) proper uniaxial ferroelectrics by Brillouin-scattering and ultrasonic pulse-echo techniques. The elastic softening of hypersound velocity of transverse-acoustic phonons and for both longitudinal and transverse ultrasound waves which propagate near direction of the modulation wave vector (in the incommensurate phase at x > x(LP)) was found at cooling to the Lifshitz point in the paraelectric phase. The strong increase in the ultrasound attenuation has also been observed. Such phenomena are related to the linear interaction of the soft optic and acoustic branches in the region of relatively short-range hypersound waves and to the strongly developed long-range order-parameter fluctuations in the ultrasound frequency range. The hypersound velocity temperature dependence was described within the Landau-Khalatnikov approximation for the ferroelectric phase.
Title:
Time relaxation of permittivity in [(CH3)2NH2]3CuCl5 crystal under external electric field
Authors:
Eliyashevskyy, Y; Czapla, Z; Dacko, S Author Full Names: Eliyashevskyy, Yu.; Czapla, Z.; Dacko, S.
Source:
PHASE TRANSITIONS 83 (8): 564-571 2010
Abstract:
Continuation of our previous studies connected with dielectric properties of tris-dimethylammoniumpentachlorocuprate crystal [(CH3)2NH2]3CuCl5 crystal under the influence of electric field are presented in this article. We studied the time dependence of the permittivity under the influence of electric field at constant temperatures above Tc. In experiment, slow but significant decrease of permittivity was observed, which can be described with two main relaxation processes. The observed dielectric behavior can be related to the coexistence of phases and slow transition to ferroelectric one through long-time metastable states connected with the presence of incommensurate phase in the studied crystal. The coexistence of phases and slow transition was confirmed from the appearance of induced polarization under external electric field, measured as depolarization current.
Title:
The local structure and composition of Ba4Nb2O9-based oxycarbonates
Authors:
Bezjak, J; Abakumov, AM; Recnik, A; Krzmanc, MM; Jancar, B; Suvorov, D Author Full Names: Bezjak, Jana; Abakumov, Artem M.; Recnik, Aleksander; Krzmanc, Marjeta Macek; Jancar, Bostjan; Suvorov, Danilo
Source:
JOURNAL OF SOLID STATE CHEMISTRY 183 (8): 1823-1828 AUG 2010
Abstract:
X-ray powder-diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), infrared spectroscopy (IR), thermogravimetry (TG) and mass spectroscopy (MS) were performed to investigate the composition and the crystal structure of tetra-barium di-niobate (V) Ba4Nb2O9. The TG, MS and IR studies revealed that the compound is a hydrated oxycarbonate. Assuming that the carbonate stoichiometrically replaces oxygen, the composition of the low-temperature alpha-modification, obtained by slow cooling from 1100 degrees C, corresponds to Ba4Nb2O8.8(CO3)(0.2)center dot 0.1H(2)O, while the quenched high-temperature gamma-modification has the Ba4Nb2O8.42(CO3)(0.58)center dot 0.38H(2)O composition. The alpha-phase has a composite incommensurately modulated structure consisting of two mutually interacting [Ba](infinity) and the [(Nb, square)O-3](infinity) subsystems. The composite modulated crystal structure of the alpha-phase can be described with the lattice parameters a=10.2688(1) angstrom, c=2.82426(8) angstrom, q=0.66774(2)c* and a superspace group R (3) over barm(00 gamma)0s. The HRTEM analysis demonstrates the nanoscale twinning of the trigonal domains parallel to the {1 0 0} crystallographic planes. The twinning introduces a one-dimensional disorder into the [(Nb, square(3)](infinity) subsystem, which results in an average P (6) over bar 2c crystal structure of the alpha-phase. Possible places for the carbonate group in the structure are discussed using a comparison with other hexagonal perovskite-based oxycarbonates. (C) 2010 Elsevier Inc. All rights reserved.
Title:
Magnetic structure of ErCu2Ge2
Authors:
Penc, B; Baran, S; Kaczorowski, D; Hoser, A; Szytula, A Author Full Names: Penc, B.; Baran, S.; Kaczorowski, D.; Hoser, A.; Szytula, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 503 (1): L18-L20 JUL 30 2010
Abstract:
The compound ErCu2Ge2 which crystallizes in the tetragonal ThCr2Si2-type crystal structure orders antiferromagnetically at low temperatures. At 1.4 K, the Er magnetic moments are arranged in a commensurate structure described by the propagation vector (k) over right arrow = [1/2, 0, 1/2]. The magnetic moment is equal to 6.80(7) mu(B) and forms an angle of 27 degrees with the c-axis. At T-t = 2.6 K an additional incommensurate magnetic structure appears and at higher temperatures both structures coexist and concurrently disappear at T-N = 3.1 K. The magnetic phase transitions at T-t and T-N clearly manifest themselves in the heat capacity and thermal expansion data of the compound. (C) 2010 Elsevier B.V. All rights reserved.

Update: 13-Aug-2010

Title:
Coexistence and Competition of Magnetism and Superconductivity on the Nanometer Scale in Underdoped BaFe1.89Co0.11As2
Authors:
Marsik, P; Kim, KW; Dubroka, A; Roessle, M; Malik, VK; Schulz, L; Wang, CN; Niedermayer, C; Drew, AJ; Willis, M; Wolf, T; Bernhard, C Author Full Names: Marsik, P.; Kim, K. W.; Dubroka, A.; Roessle, M.; Malik, V. K.; Schulz, L.; Wang, C. N.; Niedermayer, Ch.; Drew, A. J.; Willis, M.; Wolf, T.; Bernhard, C.
Source:
PHYSICAL REVIEW LETTERS 105 (5): Art. No. 057001 JUL 27 2010
Abstract:
We report muon spin rotation (mu SR) and infrared spectroscopy experiments on underdoped BaFe1.89Co0.11As2 which show that bulk magnetism and superconductivity (SC) coexist and compete on the nanometer length scale. Our combined data reveal a bulk magnetic order, likely due to an incommensurate spin density wave (SDW), which develops below T-mag approximate to 32 K and becomes reduced in magnitude (but not in volume) below T-c = 21.7 K. A slowly fluctuating precursor of the SDW seems to develop already below the structural transition at T-s approximate to 50 K. The bulk nature of SC is established by the mu SR data which show a bulk SC vortex lattice and the IR data which reveal that the majority of low-energy states is gapped and participates in the condensate at T << T-c.
Title:
Synthesis of Ti-Zr-Ni amorphous and quasicrystal powders by mechanical alloying, and their electrochemical properties
Authors:
Takasaki, A; Okuyama, T; Szmyd, JS Author Full Names: Takasaki, Akito; Okuyama, Tetsuya; Szmyd, Janusz S.
Source:
JOURNAL OF MATERIALS RESEARCH 25 (8): 1575-1582 AUG 2010
Abstract:
Mechanical alloying of Ti45Zr38-xNi17+x and Ti45-xZr38Ni17+x (0 <= x <= 8) elemental powders produced an amorphous phase, but subsequent annealing converted the amorphous phase into an icosahedral quasicrystal phase, along with a Ti2Ni-type phase. The discharge capacities, measured in a three-electrode cell at room temperature for both the amorphous and quasicrystal electrodes, increased with increasing Ni substitution for Zr or Ti. The highest discharge capacities, which were about 60 mAh/g for the amorphous electrode and 100 mAh/g for the quasicrystal electrode, were obtained from (Ti45Zr30Ni25) after substitution of Ni for Zr. For the Ti45Zr30Ni25 composition, the discharge performance of the quasicrystal electrode was stable over charge/discharge cycling, but that of the amorphous electrode gradually decreased with cycling. The structure of the quasicrystal phase in the electrodes was stable, even after 15 charge/discharge cycles, but the amorphous phase converted to a (Ti, Zr)H-2 f.c.c. hydride.
Title:
Relation between glass and quasicrystal formation in the Zr-Nb-Cu-Ni-Al alloys upon solidification
Authors:
Zhu, ZW; Zhang, W; Xie, GQ; Inoue, A Author Full Names: Zhu, Zhengwang; Zhang, Wei; Xie, Guoqiang; Inoue, Akihisa
Source:
APPLIED PHYSICS LETTERS 97 (3): Art. No. 031919 JUL 19 2010
Abstract:
We reported the relationship among the icosahedral short-range order (ISRO), glass formation and quasicrystal formation in the Zr-Nb-Cu-Ni-Al alloys. The alloys with the Nb addition stabilized ISRO, making the alloys form the amorphous, quasicrystal and crystal with decreasing the cooling rate. Not only bulk glass but also bulk quasicrystal were found to form for these alloys. The structural evolution from the amorphous phase, to the quasicrystal and crystals with the variation in the Nb content or the cooling rate is present. These findings were related to the degree of ISRO, which are advantageous for understanding the glass formation phenomenon. (C) 2010 American Institute of Physics. [doi:10.1063/1.3467827]

Update: 6-Aug-2010

Title:
Phase separation and ferroelectric ordering in charge-frustrated LuFe2O4-delta
Authors:
Yang, HX; Tian, HF; Zhang, Y; Qin, YB; Zeng, LJ; Ma, C; Shi, HL; Lu, JB Author Full Names: Yang, H. X.; Tian, H. F.; Zhang, Y.; Qin, Y. B.; Zeng, L. J.; Ma, C.; Shi, H. L.; Lu, J. B.
Source:
SOLID STATE COMMUNICATIONS 150 (31-32): 1467-1472 AUG 2010
Abstract:
The transmission electron microscopy observations of the charge ordering (CO) which governs the electronic polarization in LuFe2O4-delta clearly show the presence of a remarkable phase separation at low temperatures. Two CO ground states are found to adopt the charge modulations of Q(1) = (1/3, 1/3, 0) and Q(2) = (1/3 + epsilon, 1/3 + epsilon, 3/2), respectively. Our structural study demonstrates that the incommensurately Q(2)- modulated state is chiefly stable in samples with relatively lower oxygen contents. Data from theoretical simulations of the diffraction suggest that both Q(1)- and Q(2)- modulated phases have ferroelectric ordering. The effects of oxygen concentration on the phase separation and electric polarization in this layered system are discussed. (C) 2010 Elsevier Ltd. All rights reserved.
Title:
Extreme sensitivity of a frustrated quantum magnet: Cs2CuCl4
Authors:
Starykh, OA; Katsura, H; Balents, L Author Full Names: Starykh, Oleg A.; Katsura, Hosho; Balents, Leon
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 014421 JUL 20 2010
Abstract:
We report a thorough theoretical study of the low temperature phase diagram of Cs2CuCl4, a spatially anisotropic spin S = 1/2 triangular lattice antiferromagnet, in a magnetic field. Our results, obtained in a quasi-one-dimensional limit in which the system is regarded as a set of weakly coupled Heisenberg chains, are in excellent agreement with experiment. The analysis reveals some surprising physics. First, we find that when the magnetic field is oriented within the triangular layer, spins are actually most strongly correlated within planes perpendicular to the triangular layers. This is despite the fact that the interlayer exchange coupling in Cs2CuCl4 is about an order of magnitude smaller than the weakest (diagonal) exchange in the triangular planes themselves. Second, the phase diagram in such orientations is exquisitely sensitive to tiny interactions, heretofore neglected, of order a few percent or less of the largest exchange couplings. These interactions, which we describe in detail, induce entirely new phases, and a novel commensurate-incommensurate transition, the signatures of which are identified in NMR experiments. We discuss the differences between the behavior of Cs2CuCl4 and an ideal two-dimensional triangular model, and in particular, the occurrence of magnetization plateaux in the latter. These and other related results are presented here along with a thorough exposition of the theoretical methods, and a discussion of broader experimental consequences to Cs2CuCl4 and other materials.
Title:
Magnetic excitations in Dy/Y superlattices as seen via inelastic neutron scattering
Authors:
Grunwald, ATD; Wildes, AR; Schmidt, W; Tartakovskaya, EV; Kwo, J; Majkrzak, C; Ward, RCC; Schreyer, A Author Full Names: Gruenwald, A. T. D.; Wildes, A. R.; Schmidt, W.; Tartakovskaya, E. V.; Kwo, J.; Majkrzak, C.; Ward, R. C. C.; Schreyer, A.
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 014426 JUL 23 2010
Abstract:
Measurements of the spin excitations propagating normal to the interfaces in Dy/Y superlattices using neutron inelastic scattering are presented. For a given magnon momentum, a neutron-scattering spectrum shows multiple peaks at different energies, which indicates discrete energy spectra. The results are compared with theoretical calculations developed here to describe magnetic excitations in rare-earth superlattices. The theory accounts for Ruderman-Kittel-Kasuya-Yosida (RKKY) and Dzyaloshinsky-Moriya interactions in incommensurate helicoidal structures and achieves a quantitative agreement with the experimental data. This work demonstrates that neutron inelastic scattering can be used for systematic studies of the exchange interactions and spin dynamics in nanomagnetic systems over wide areas of the Brillouin zone.
Title:
Spatial inhomogeneities in iron pnictide superconductors: The formation of charge stripes
Authors:
Gor'kov, LP; Teitel'baum, GB Author Full Names: Gor'kov, Lev P.; Teitel'baum, Gregory B.
Source:
PHYSICAL REVIEW B 82 (2): Art. No. 020510 JUL 21 2010
Abstract:
The heterogeneous coexistence of antiferromagnetism (spin-density wave (SDW)] and superconductivity on a mesoscopic scale was observed in iron pnictides in many recent experiments. We suggest and discuss the scenario in which the heterogeneity is caused by formation of domain walls inherent to the SDW state of pnictides at a proper doping or under applied pressure. Superconductivity would emerge from the modulated SDW structure. The phenomenon is akin to the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) phase in superconductors.
Title:
Light localization in photonic band gaps of quasiperiodic dielectric structures
Authors:
Wang, K Author Full Names: Wang, Kang
Source:
PHYSICAL REVIEW B 82 (4): Art. No. 045119 JUL 23 2010
Abstract:
Localized light wave states in the photonic band gaps in two-dimensional octagonal and decagonal quasiperiodic dielectric media are investigated by considering the corresponding approximant structures. The structure effects on the local resonances at high-symmetry centers are studied in terms of the interscatterer correlation and the coupling strength between neighbor scatterers is analyzed as a function of the local symmetry order, the structure dielectric contrast, and the scatterer size. It is shown that an interscatterer distance threshold can be defined for the light localization regime. The threshold is determined by the geometrical and dielectric properties of the scatterers and independent of the local symmetry. It is thus likely a universal parameter for light localization in dielectric structures containing high-symmetry centers.
Title:
Symmetry and magnetoelectric interactions in BaMnF4
Authors:
Zvezdin, AK; Pyatakov, AP Author Full Names: Zvezdin, A. K.; Pyatakov, A. P.
Source:
LOW TEMPERATURE PHYSICS 36 (6): 532-537 JUN 2010
Abstract:
Symmetry analysis is used to study magnetic anisotropy and magnetoelectric interactions in the ferroelectric antiferromagnet BaMnF4 theoretically. It is shown that symmetry admits the existence in this material of a nonuniform magnetoelectric interaction (flexomagnetoelectric type) with a specific dependence on the magnitude and orientation of the external magnetic field. With increasing magnetic field this interaction can cause a phase transition into a magnetic incommensurate phase with a characteristic jump of the electric polarization. The linear and quadratic magnetoelectric effects and the question of the relativistic canting of the sublattices, which is due to the magnetoelectric interaction, are examined. The proposed approach is a natural generalization of the method of constructing invariants from the magnetic modes of the crystal to the case of phase transitions with a doubled unit cell of the crystal and can be used for symmetry analysis of other ferroelectric magnetic compounds. (c) 2010 American Institute of Physics. [doi:10.1063/1.3455798]
Title:
Quasicrystalline Tenfold Symmetry Order in Boron Compounds
Authors:
Miyazaki, Y; Okada, J; Abe, E; Yokoyama, Y; Kimura, K Author Full Names: Miyazaki, Yoshinobu; Okada, Junpei; Abe, Eiji; Yokoyama, Yoshihiko; Kimura, Kaoru
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (7): Art. No. 073601 JUL 2010
Abstract:
We report the first quasicrystalline boride formed in a rapidly-solidified B40Ti12Ru48 alloy, whose diffraction pattern clearly reveals a tenfold rotation axis of decagonal symmetry. The local structure appears to be significantly deviated from an ideal quasicrystal, but the long-range bond-orientational-order restricted by linkages between the robust unit-clusters has successfully generated the apparent 10-fold-symmetric Bragg peaks. This may be attributed to an extreme case of random-tiling quasicrystals, which enable the occurrence of local tiling disorders to account for entropy.
Title:
High-Temperature Multiferroic State of RBaCuFeO5 (R = Y, Lu, and Tm)
Authors:
Kawamura, Y; Kai, T; Satomi, E; Yasui, Y; Kobayashi, Y; Sato, M; Kakurai, K Author Full Names: Kawamura, Yuji; Kai, Takahiro; Satomi, Erika; Yasui, Yukio; Kobayashi, Yoshiaki; Sato, Masatoshi; Kakurai, Kazuhisa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (7): Art. No. 073705 JUL 2010
Abstract:
Magnetic and/or dielectric/ferroelectric behaviors have been studied for YBaCuFeO5, LuBaCuFeO5, and TmBaCuFeO5, which are members of oxygen-deficient ordered perovskite systems RBaCuFeO5 (R = lanthanide Ln and other trivalent elements) and have two magnetic transitions. The magnetic structure of the high-temperature (T) ordered phase is basically antiferromagnetic, and in the low-T ordered phase, a modulated magnetic component is superposed on the antiferromagnetic moments. The results of the pyrocurrent measurements indicate that electric polarization is induced in all these systems by the ordering to the modulated magnetic structure. For TmBaCuFeO5, the transition to this low-T phase is found at a temperature as high as the melting point of ice.
Title:
Elastic constants and anisotropic internal frictions of decagonal Al72Ni18Co8 single quasicrystal at low temperatures
Authors:
Tarumi, R; Ledbetter, H; Shiomi, S; Ogi, H; Hirao, M; Tsai, AP Author Full Names: Tarumi, R.; Ledbetter, H.; Shiomi, S.; Ogi, H.; Hirao, M.; Tsai, A. P.
Source:
JOURNAL OF APPLIED PHYSICS 108 (1): Art. No. 013514 JUL 2010
Abstract:
We studied the complete set of elastic constants C-ij and internal frictions tensor Q(ij)(-1) of anisotropic decagonal Al72Ni18Co8 single quasicrystal by electromagnetic acoustic resonance at low temperatures, to 5 K. Most C-ij(T) showed usual stiffening upon cooling and their temperature behaviors are well characterized by an Einstein-lattice-vibration model. The average Gruumlneisen parameter estimated from the bulk modulus is 2.4, almost identical to crystalline Al. Ambient temperature Q(ij)(-1) show a linear relationship to the elastic-constants temperature derivatives vertical bar dC(ij)/dT vertical bar/C-ij with a slope of 1.28 K-1, suggesting that lattice anharmonicity plays a dominant role for Q(ij)(-1). The longitudinal modulus for the decagonal axis C-33 and corresponding internal friction Q(33)(-1), however, showed significant deviation from such ideal behavior, suggesting additional low-frequency phonon-excitation modes along the decagonal axis.
Title:
Layers of order - the past, present and future of superspace crystallography
Authors:
Christensen, J Author Full Names: Christensen, Jeppe
Source:
CRYSTALLOGRAPHY REVIEWS 16 (2): 105-114 2010
Abstract:
The importance of having correct structural descriptions is becoming ever clearer, not only in drug discovery research, but also in the development of new advanced materials. Here the key to optimizing properties lies in understanding the structure-property relationships. Without a correct description theoretical calculations will inevitably fail to describe and explain any experimental observations. With increasing complexity of developed materials, modulated structures are likely to make up an increasing proportion of the structures to be investigated in the future. To take up this challenge, a development is needed in three areas of crystallography: The way we teach and what we teach our students; how we think about, and perform our crystallographic investigations; what tools are available, and how we use them. These areas are strongly coupled and any development in one is dependent on progress in the other two.

Update: 30-Jul-2010

Title:
Atomic dynamics of the alpha-(Al,Si)CuFe alloy: A crystalline approximant of a quasicrystal...
Authors:
Parshin, PP; Zemlyanov, MG; Brand, RA; Pavlyuchkov, D; Ollivier, J Author Full Names: Parshin, P. P.; Zemlyanov, M. G.; Brand, R. A.; Pavlyuchkov, D.; Ollivier, J.
Source:
PHYSICS OF THE SOLID STATE 52 (7): 1492-1498 JUL 2010
Abstract:
The atomic dynamics of the Al0.550Si0.070Cu0.255Fe0.125 alloy with the structure that approximates the structure of an icosahedral quasicrystal with a similar chemical composition has been investigated using inelastic neutron scattering. The partial vibrational spectra of copper, iron, and aluminum atoms and the total spectrum of thermal vibrations of the compound have been directly reconstructed from the experimental data for the first time. A combined analysis of the results obtained and the data on the atomic dynamics of the i-AlCuFe icosahedral quasicrystal has been performed.
Title:
Incommensurate Magnetic Order and Dynamics Induced by Spinless Impurities in YBa2Cu3O6.6
Authors:
Suchaneck, A; Hinkov, V; Haug, D; Schulz, L; Bernhard, C; Ivanov, A; Hradil, K; Lin, CT; Bourges, P; Keimer, B; Sidis, Y Author Full Names: Suchaneck, A.; Hinkov, V.; Haug, D.; Schulz, L.; Bernhard, C.; Ivanov, A.; Hradil, K.; Lin, C. T.; Bourges, P.; Keimer, B.; Sidis, Y.
Source:
PHYSICAL REVIEW LETTERS 105 (3): Art. No. 037207 JUL 16 2010
Abstract:
We report an inelastic-neutron-scattering and muon-spin-relaxation study of the effect of 2% spinless (Zn) impurities on the magnetic order and dynamics of YBa2Cu3O6.6, an underdoped high-temperature superconductor that exhibits a prominent spin pseudogap in its normal state. Zn substitution induces static magnetic order at low temperatures and triggers a large-scale spectral-weight redistribution from the magnetic resonant mode at 38 meV into uniaxial, incommensurate spin excitations with energies well below the spin pseudogap. These observations indicate a competition between incommensurate magnetic order and superconductivity close to a quantum critical point. Comparison to prior data on La2-xSrxCuO4 suggests that this behavior is universal for the layered copper oxides and analogous to impurity-induced magnetic order in one-dimensional quantum magnets.
Title:
Neutron-Scattering Measurement of Incommensurate Short-Range Order in Single Crystals of the S=1 Triangular Antiferromagnet NiGa2S4
Authors:
Stock, C; Jonas, S; Broholm, C; Nakatsuji, S; Nambu, Y; Onuma, K; Maeno, Y; Chung, JH Author Full Names: Stock, C.; Jonas, S.; Broholm, C.; Nakatsuji, S.; Nambu, Y.; Onuma, K.; Maeno, Y.; Chung, J. -H.
Source:
PHYSICAL REVIEW LETTERS 105 (3): Art. No. 037402 JUL 16 2010
Abstract:
Neutron scattering is used to investigate spin correlations in ultrapure single crystals of the S = 1 triangular lattice NiGa2S4. Despite a Curie-Weiss temperature of Theta(CW) = -80(2) K, static (T > 1 ns) short-range (zeta(ab) = 26(3) angstrom) incommensurate order prevails for T > 1.5 K. The incommensurate modulation Q(0) = (0.155(3), 0.155(3), 0), Theta(CW), and the spin-wave velocity (c = 4400 m/s) can be accounted for by antiferromagnetic third-nearest-neighbor interactions J(3) = 2.8(6) meV and ferromagnetic nearest-neighbor coupling J(1) = -0.35(9) J(3). Interplane correlations are limited to nearest neighbors and weakened by an in-plane field. These observations show that the short-range ordered glassy phase that has been observed in a number of highly degenerate systems can persist near the clean limit.
Title:
Single-crystal neutron diffraction study of the magnetic structure of Er3Co
Authors:
Gubkin, AF; Podlesnyak, A; Baranov, NV Author Full Names: Gubkin, A. F.; Podlesnyak, A.; Baranov, N. V.
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 012403 JUL 13 2010
Abstract:
The effect of the magnetic field applied along the main crystallographic directions on the magnetic structure of Er3Co has been studied by means of single-crystal neutron diffraction technique. At zero field the compound exhibits a noncoplanar commensurate magnetic structure with ferromagnetic alignment of the Er magnetic-moment projections along the b axis in an orthorhombic unit cell. The present measurements revealed that the application of the magnetic field along the c direction [c perpendicular to (ab)] leads to the pronounced metamagneticlike transition in the low-field region mu H-0<1.2 T, although, the magnetization curve does not exhibit any anomalies. Combining the present single-crystal diffraction and magnetization data with the results of the previous powder neutron diffraction study [Gignoux et al., Solid State Commun. 8, 391 (1970)], we conclude that the nature of the magnetic ion, whether Kramers or non-Kramers, has a decisive effect on the commensurability of the magnetic structure of R3Co. In particular, the commensurate magnetic structure observed in Er3Co originate from the Kramers character of Er3+ ion in contrast to the incommensurate structures found earlier in R3Co with R= Tb and Ho.
Title:
Transition from a phase-segregated state to single-phase incommensurate sodium ordering in gamma-NaxCoO2(x approximate to 0.53)
Authors:
Feyerherm, R; Dudzik, E; Valencia, S; Wolter, AUB; Milne, CJ; Landsgesell, S; Alber, D; Argyriou, DN Author Full Names: Feyerherm, R.; Dudzik, E.; Valencia, S.; Wolter, A. U. B.; Milne, C. J.; Landsgesell, S.; Alber, D.; Argyriou, D. N.
Source:
PHYSICAL REVIEW B 82 (2): Art. No. 024103 JUL 13 2010
Abstract:
Synchrotron x-ray diffraction investigations of two single crystals of sodium cobaltate NaxCoO2 from different batches with composition x=0.525-0.530 reveal homogeneous incommensurate sodium ordering with propagation vector (0.53 0.53 0) at room temperature. The incommensurate (qq0) superstructure exists between 220 and 430 K. The value of q varies between q=0.514 and 0.529, showing a broad plateau at the latter value between 260 and 360 K. On cooling, an unusual reversible phase segregation into two volume fractions is observed. Below 220 K, one volume fraction shows the well-known commensurate orthorhombic x=0.50 superstructure while a second volume fraction with x=0.55 exhibits another commensurate superstructure, presumably with a 6a x 6a x c hexagonal supercell. We argue that the commensurate-to-incommensurate transition is an intrinsic feature of samples with Na concentrations x=0.5+ delta with delta approximate to 0.03.

Update: 23-Jul-2010

Title:
Magnetic structure of the edge-sharing copper oxide chain compound NaCu2O2
Authors:
Capogna, L; Reehuis, M; Maljuk, A; Kremer, RK; Ouladdiaf, B; Jansen, M; Keimer, B Author Full Names: Capogna, L.; Reehuis, M.; Maljuk, A.; Kremer, R. K.; Ouladdiaf, B.; Jansen, M.; Keimer, B.
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 014407 JUL 12 2010
Abstract:
Single-crystal neutron diffraction has been used to determine the incommensurate magnetic structure of NaCu2O2, a compound built up of chains of edge-sharing CuO4 plaquettes. Magnetic structures compatible with the lattice symmetry were identified by a group-theoretical analysis and their magnetic structure factors were compared to the experimentally observed Bragg intensities. In conjunction with other experimental data, this analysis yields an elliptical helix structure in which both the helicity and the polarization plane alternate among copper-oxide chains. This magnetic ground state is discussed in the context of the recently reported multiferroic properties of other copper-oxide chain compounds.
Title:
Surface oxidation of the icosahedral Ag-In-Yb quasicrystal
Authors:
Nugent, PJ; Simutis, G; Dhanak, VR; McGrath, R; Shimoda, M; Cui, C; Tsai, AP; Sharma, HR Author Full Names: Nugent, P. J.; Simutis, G.; Dhanak, V. R.; McGrath, R.; Shimoda, M.; Cui, C.; Tsai, A. P.; Sharma, H. R.
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 014201 JUL 9 2010
Abstract:
The oxidation of the high-symmetry surfaces of a single grain icosahedral (i) Ag-In-Yb quasicrystal has been studied using x-ray photoemission spectroscopy. The oxidation was carried out in vacuum, air, and water. It is found that air exposure results in the same degree of oxidation as exposure to oxygen in vacuum. The oxidation in water is more effective. Among the three constituent elements, the core levels of Yb are most affected by oxidation, Ag core levels are unchanged, and In shows moderate effects as expected from heats of formation of bulk oxides of the three elements. The comparison of the results with pure elements also reveals that the oxidation of Ag, In, and Yb in the quasicrystal is very similar to that of pure elements in all three environments. Scanning tunneling microscopy and low-energy electron diffraction reveal that oxidation destroys the quasicrystalline order of the clean surface.
Title:
Structural study by X-ray diffraction and transmission electron microscopy of the misfit compound (SbS1-xSex)(1.16)(Nb1.036S2)(2)
Authors:
Kars, M; Fredrickson, DC; Gomez-Herrero, A; Lidin, S; Rebbah, A; Otero-Diaz, LC Author Full Names: Kars, Mohammed; Fredrickson, Daniel C.; Gomez-Herrero, A.; Lidin, Sven; Rebbah, Allaoua; Otero-Diaz, L. C.
Source:
MATERIALS RESEARCH BULLETIN 45 (8): 982-988 AUG 2010
Abstract:
In the Sb-Nb-S-Se system, a new misfit layer compound (MSL) has been synthesized and its structure was determined by combining single crystal X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. It presents a composite crystal structure formed by (SbS1-xSex)slabs stacking alternately with double NbS2 layers and both can be treated as separate monoclinic subsystems. The (SbS1-xSex) slabs comprise a distorted, two-atom-thick layer with NaCl-type structure formed by an array of (SbX5) square pyramids joined by edges (X: S, Se); the NbS2 layers consist of (SbX5) trigonal prisms linked through edge-sharing to form sheets, just as in the 2H-NbS2 structure type. Both sublattices have the same lattice parameters a = 5.7672(19) angstrom, c = 17.618(6) angstrom and beta = 96.18(3)degrees, with incommensurability occurring along the b direction: b(1) = 3.3442(13) angstrom for the NbS2 subsystem and b(2) = 2.8755(13) angstrom for the (SbS1-xSex) subsystem. The occurrence of diffuse scattering intensity streaked along c* indicates that the (SbS1-xSex) subsystem is subjected to extended defects along the stacking direction. Published by Elsevier Ltd.

Update: 16-Jul-2010

Title:
Magnetic ordering and low-temperature thermodynamic properties of ErFe2Ge2
Authors:
Szytula, A; Kaczorowski, D; Baran, S; Penc, B; Gil, A; Hoser, A Author Full Names: Szytula, A.; Kaczorowski, D.; Baran, S.; Penc, B.; Gil, A.; Hoser, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (19): 2973-2977 OCT 2010
Abstract:
Polycrystalline sample of ErFe2Ge2 was investigated by means of magnetic susceptibility, heat capacity and electrical resistivity measurements, as well as by powder neutron diffraction. All these experiments yielded an evidence of magnetic ordering setting at about 3 K. The low-temperature neutron data revealed the formation of a sine-modulated commensurate antiferromagnetic structure characterized by the propagation vector k=(0, 0, 14). The erbium magnetic moment is aligned parallel to the crystallographic a-axis. At T=1.55 K it is equal to 7.06(5) mu(B). (C) 2010 Elsevier B. V. All rights reserved.
Title:
Pattern analysis and interpretation of scattering from short-range order stacking in the layered composite crystal 2H-NaxCoO2 center dot yD(2)O (x similar or equal to 0.35, y similar or equal to 1.3)
Authors:
Onoda, M; Takada, K; Sasaki, T Author Full Names: Onoda, Mitsuko; Takada, Kazunori; Sasaki, Takayoshi
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 677-685 Part 4 AUG 2010
Abstract:
Information about the features of Bragg reflections and/or diffuse streaks was obtained through simulation of a neutron powder diffraction pattern based on the model used in a successful analysis of the superconductor 2H-NaxCoO2 center dot yD(2)O (x similar or equal to 0.35, y similar or equal to 1.3). Intensity distributions were calculated based on a superstructure expression of a commensurate composite crystal model, where the structures of the CoO2 part (a(1) = b(1) = 2.82 angstrom) and the guest (a(2) = b(2) = 3.26 angstrom) with short-range order stacking are described on a cell of A = B = 2a(1) = 3(1/2) a(2) = 5.64 angstrom, and with alternate stacking based on c = 4.9 angstrom. It is shown that the most conspicuous diffuse reflection band corresponds to the main reflection scattering of the guest sheet, with local maxima at half-integer positions of zeta' based on the stacking distance 2c, and that the Bragg diffraction components of the host and gues! t are coherent in terms of the peak height at integer zeta '' based on 4c.
Title:
Influence of quasicrystalline phase on transport processes in Zr70Pd30 amorphous alloy
Authors:
Pekala, K; Antonowicz, J; Jaskiewicz, P; Drobiazg, T; Konupek, J Author Full Names: Pekala, Krystyna; Antonowicz, Jerzy; Jaskiewicz, Piotr; Drobiazg, Tomasz; Konupek, Jan
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 500 (2): 145-148 JUN 25 2010
Abstract:
Electron transport and structural properties of amorphous Zr75Pd30 alloy are investigated by electrical resistivity, thermoelectric power, differential scanning calorimetry and X-ray diffraction methods. It was found that appearance of the icosahedral quasicrystalline phase in the first crystallization stage contributes to an increase of the electrical resistivity and Seebeck coefficient. Temperature variation of transport properties in amorphous phase excludes a variable range hopping model, which supplies unreasonable values of hopping energy and hopping distance. A similar degree of agreement between experimental results and both the Ziman and weak localization models is found for the electrical resistivity. However, a relatively high content of early transition Zr atoms in the alloy points rather that the weak localization may play a role. (C) 2010 Elsevier B.V. All rights reserved.
Title:
o '-Al13Co4, a new quasicrystal approximant
Authors:
Fleischer, F; Weber, T; Jung, DY; Steurer, W Author Full Names: Fleischer, F.; Weber, T.; Jung, D. Y.; Steurer, W.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 500 (2): 153-160 JUN 25 2010
Abstract:
The crystal structure of o '-Al13Co4, a new Al13TM4 (TM = transition metal) modification was determined by single-crystal X-ray diffraction. The phase, with Pearson symbol oP204-x (x=6), crystallizes in the orthorhombic space group Pnma (No. 62) with lattice parameters a = 28.890(4) angstrom, b = 8.138(2) angstrom and c = 12.346(1) angstrom. The structure, which can be seen as a stacking of four flat and puckered atomic layers along the pseudo-tenfold b axis, is closely related to o-Al13Co4 and m-Al13Co4. First-principles total-energy calculations indicate that all these related Al13Co4 modifications, some of them stabilized by vacancies, seem to be slightly unstable at low temperatures. (C) 2010 Elsevier B.V. All rights reserved.
Title:
The magnetoelectric effects in weak ferromagnetic YMn2O5 modulated structure: a Landau theory approach
Authors:
Tehranchi, MM; Phirouznia, A Author Full Names: Tehranchi, M. M.; Phirouznia, A.
Source:
EUROPEAN PHYSICAL JOURNAL B 75 (4): 439-442 JUN 2010
Abstract:
According to the group theory approach, linear magnetoelectric effect (ME) can not be obtained for the spatial group of YMn2O5, which was known to be mmm. Regard to the magnetic structure of these type of materials, we propose a magnetic group structure for the YMn2O5 by considering spin orientation of the Mn3+ and Mn4+ ions. According to the landau theory of phase transition it can be shown, how symmetrical rules result in relationship between quantities such as magnetic order, polarization, and etc. This relation shows a weak ferromagnetic state, associated with spontaneous polarization, arisen by Dzyaloshinskii-Moriya type interaction and a field induced change in magnetoelectrical susceptibility.

Update: 9-Jul-2010

Title:
THE Al-Cu-Ir ISOTHERMAL SECTION AT 800 degrees C IN THE ALUMINUM-RICH RANGE
Authors:
Kapush, DO; Grushko, B; Velikanova, TY Author Full Names: Kapush, D. O.; Grushko, B.; Velikanova, T. Ya.
Source:
POWDER METALLURGY AND METAL CERAMICS 49 (1-2): 79-85 MAY 2010
Abstract:
The partial isothermal section at 800 degrees C is represented for the first time. The structure of the Al-Cu-Ir alloys in the Al70Ir30-Al40Cu60-Al range, which are quenched from 800 degrees C, is investigated by SEM/EDX and XRD methods. Three ternary phases (decagonal quasicrystalline D-1, orthorhombic epsilon(6), and cubic (fcc) C-2) are stable at this temperature. The (Al9Ir2), phi, epsilon(6), D-1, gamma(1), and epsilon(2) phases coexist with a liquid phase at 800 degrees C.
Title:
Surface Charge Density Wave Phase Transition in NbSe3
Authors:
Brun, C; Wang, ZZ; Monceau, P; Brazovskii, S Author Full Names: Brun, Christophe; Wang, Zhao-Zhong; Monceau, Pierre; Brazovskii, Serguei
Source:
PHYSICAL REVIEW LETTERS 104 (25): Art. No. 256403 JUN 24 2010
Abstract:
The two charge-density wave (CDW) transitions in NbSe3 were investigated by scanning tunneling microscopy (STM) on an in situ cleaved (b, c) plane. The temperature dependence of first-order CDW satellite spots, obtained from the Fourier transform of the STM images, was measured between 5 and 140 K to extract the surface critical temperatures (T-s). The low-T CDW transition occurs at T-2s = 70-75 K, more than 15 K above the bulk T-2b = 59 K while at exactly the same wave number. A plausible mechanism for such an unusually high surface enhancement is a softening of transverse phonon modes involved in the CDW formation. The regime of 2D fluctuations is analyzed according to a Berezinskii-Kosterlitz-Thouless type of surface transition, expected for this incommensurate 2D CDW, by extracting the temperature dependence of the order parameter correlation functions.
Title:
Domains and Domain Walls in Multiferroic Ferroelectric-Ferromagnet and Control of Its Modulation
Authors:
Lykah, VA Author Full Names: Lykah, V. A.
Source:
FERROELECTRICS 398: 71-76 2010
Abstract:
Ferroelectric-ferromagnet with inhomogeneous exchange-relativistic magneto-electric interaction (Dzyaloshinskii-Moriya) is studied theoretically in external electric field. The domain wall combines properties of usual 180 degrees. one in ferroelectric and unusual magnetic one, consisting of linear topological defects (Bloch lines), situated periodically with large density. It is shown that the external electric field changes both ferroelectric and ferromagnetic subsystems. It is found that the helicoids step is formed in each domain in the magnetic subsystem and Bloch lines period demonstrates incommensurate structure. Final solution for magnetic moment in Bloch lines and modulated helicoids period near domain wall can be expressed in Jacobian elliptic functions.
Title:
Tricritical Behavior of Sn2P2S6 Ferroelectrics at Hydrostatic Pressure
Authors:
Vysochanskii, YM; Kohutych, AA; Kityk, AV; Zadorozhna, AV; Khoma, MM; Grabar, AA Author Full Names: Vysochanskii, Yu. M.; Kohutych, A. A.; Kityk, A. V.; Zadorozhna, A. V.; Khoma, M. M.; Grabar, A. A.
Source:
FERROELECTRICS 399: 83-88 2010
Abstract:
For Sn2P2S6 ferroelectrics with three-well potential under hydrostatic compression the second order phase transition approaches tricritical point as expected according to Blume-Emery-Griffiths (BEG) model. Joint consideration of BEG model and known ANNNI model, describing the incommensurate phase appearing as a result of competitive interactions, allows one to draw conclusion about possibility of tricritical point presence on temperature-pressure diagram of Sn2P2S6 without incommensurate phase appearing. Investigations of temperature dependences of longitudinal ultrasound velocity at different pressures for Sn2P2S6 crystals confirm such conclusion.
Title:
Synthesis, Spectroscopic and Magnetic Properties of the Co-2(OH)(PO4)(1-x)-(AsO4)(x) [0 <= x <= 1] Solid Solution
Authors:
de Pedro, I; Rojo, JM; Fernandez, JR; Lezama, L; Rojo, T Author Full Names: de Pedro, Imanol; Maria Rojo, Jose; Rodriguez Fernandez, Jesus; Lezama, Luis; Rojo, Teofilo
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY (17): 2514-2522 JUN 2010
Abstract:
The Co-2(OH)(PO4)(1-x)(AsO4)(x) [0 <= x <= 1] solid solution was prepared by hydrothermal synthesis and, polycrystalline samples characterized by X-ray powder diffraction and spectroscopic measurements. The cell parameters of the isostructural phosphate-arsenate phases follow Vegard's law in the whole range of composition. The IR spectra are characteristic of three distinct features corresponding principally to the vibrations of both the hydroxide and tetrahedral (XO4)(3-) (X = P, As) groups together with the evolution of the intensity of stretching [vas (X-O)] vibration modes corresponding to the PO4 and AsO4 tetrahedra in the solid solution. Diffuse reflectance data show bands belonging to the octahedral and trigonal bipyramidal geometries of the Co2+ ions with a high degree of covalence in the Co-O bonds of the arsenate phases. Magnetization measurements of Co-2(OH)(PO4)(1-x)(AsO4)(x) [0 <= x <= 1] show the existence of antiferromagnetic interactions with the presence of a ferromagnetic component below the ordering temperature. TN decreases from 71 to 19 K as the arsenate amount is increased. ZFC-FC curves show irreversibility just below T-N for Co-2(OH)(PO4)(1-x)(AsO4)(x) [x = 0.1-0.75]. The magnetic behavior of Co-2(OH)(PO4)(0.1)(AsO4)(0.9) is completely different from the rest of the hydroxyphosphate-arsenate members and similar to that observed in the undoped arsenate compound where an incommensurate magnetic phase is observed.
Title:
Incommensurate spin density wave in Co-doped BaFe2As2
Authors:
Bonville, P; Rullier-Albenque, F; Colson, D; Forget, A Author Full Names: Bonville, P.; Rullier-Albenque, F.; Colson, D.; Forget, A.
Source:
EPL 89 (6): Art. No. 67008 MAR 2010
Abstract:
Fe-57 Mossbauer spectroscopy measurements are presented in the underdoped Ba(Fe1-xCox)(2)As-2 series for x=0.014 (T-c < 1.4K) and x=0.03 and 0.045 (T-c similar or equal to 2 and 12K, respectively). The spectral shapes in the so-called spin density wave (SDW) phase are interpreted in terms of incommensurate modulation of the magnetic structure, and allow the shape of the modulation to be determined. In undoped BaFe(2)A(s)2, the magnetic structure is commensurate, and we. nd that incommensurability is present at the lowest doping level (x= 0.014). As Co doping increases, the low-temperature modulation progressively loses its " squaredness" and tends to a sine-wave. The same trend occurs for a given doping level, as temperature increases. We. nd that a magnetic hyper. ne component persists far above the SDW transition, its intensity being progressively tranferred to a paramagnetic component on heating. Copyright (C) EPLA, 2010 Resistivity
Title:
Mossbauer spectroscopy of spin dynamics in MnxFe1-xSe0.85 superconductors: Evidence for an incommensurate-spin-density-wave state
Authors:
Hamdeh, HH; El-Tabey, MM; Asmatulu, R; Ho, JC; Huang, TW; Yeh, KW; Wu, MK Author Full Names: Hamdeh, H. H.; El-Tabey, M. M.; Asmatulu, R.; Ho, J. C.; Huang, T. W.; Yeh, K. W.; Wu, M. K.
Source:
EPL 89 (6): Art. No. 67009 MAR 2010
Abstract:
In the tetragonal crystalline structure of MnxFe(1-x)Se(0.85), the magnetic state contains low-and high-spin Fe2+, with high-spin numbers equal to that of the combined Mn substitute and Se deficiency atoms. The state is pinned by " spin-hopping" around substitution centers via highspin. low-spin conversions. During the structural distortion from tetragonal to orthorhombic, from 90K to 70K, the rate of spin conversions increases and the iterant character of the magnetic state is enhanced. In the orthorhombic structure, the spin dynamics evolve into an incommensurate spin-density wave (ISDW). Excitations of the ISDW decrease with temperature and level out across the superconducting phase. The ISDW appears to have more than one oscillation mode and contributions from high-order harmonics. Copyright (C) EPLA, 2010
Title:
Large increase in perpendicular giant magnetoresistance of quasiperiodic magnetic multilayers
Authors:
Tao, YC Author Full Names: Tao, Y. C.
Source:
EPL 90 (2): Art. No. 27005 APR 2010
Abstract:
Combining the transfer matrix method with Landauer-Buticker formalism, we study the spin-polarized transport in the current-perpendicular-to-the plane (CPP) geometry of a quasiperiodic magnetic multilayered structure consisting of a ferromagnet (FM) and a nonmagnet (NM) arranged in a Fibonacci sequence. The CPP giant magnetoresistance (GMR) in the quasiperiodic structure is found to be largely enhanced compared with that in the periodic one. It is also shown that there are the same and different properties in the variations of the relative conductivities and of the GMR with the number of bilayers between the quasiperiodic and periodic structures, implying that there exist common and different physical origins in them. Copyright (C) EPLA, 2010

Update: 2-Jul-2010

Title:
Synthesis and brittle-to-ductile transition of the omega-Al0.7Cu0.2Fe0.1 tetragonal phase
Authors:
Laplanche, G; Joulain, A; Bonneville, J; Gauthier-Brunet, V; Dubois, S Author Full Names: Laplanche, G.; Joulain, A.; Bonneville, J.; Gauthier-Brunet, V.; Dubois, S.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 527 (16-17): 4515-4518 JUN 25 2010
Abstract:
Synthesis of omega-Al-Cu-Fe single phase material is reported. Microhardness tests performed over the temperature range 293-898 K indicate a brittle-to-ductile transition between 673 K and 823 K. Fracture toughness was determined from indentation cracks at 293 K. Both the hardness and fracture toughness are comparable to that of the icosahedral Al0.635Cu0.240Fe0.125 material. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Structural themes in approximant and decagonal quasicrystalline phases in Al based alloys
Authors:
Boudard, M Author Full Names: Boudard, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 495 (2): 365-371 APR 16 2010
Abstract:
The structure of two periodic phases in the Al-Pd-Mn system showing the importance of chemical ordering in the formation of decagonal quasicrystalline and approximant crystalline structures is reviewed Different descriptions of the periodic phases in terms of clusters, dense planes and pentagonal chains of transition metals are presented. We also review a structural model for AlPdMn decagonal quasicrystals derived from the general schematic distribution of TM existing in the approximant phases This model is discussed in relation of an unique decagonal overlapping cluster in a Penrose pentagonal tiling. (C) 2009 Elsevier B V All rights reserved.
Title:
Nanoquasicrystalline Al-Fe-Cr-based alloys with high strength at elevated temperature
Authors:
Galano, M; Audebert, F; Escorial, AG; Stone, IC; Cantor, B Author Full Names: Galano, Marina; Audebert, Fernando; Garcia Escorial, Asuncion; Stone, Ian C.; Cantor, Brian
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 495 (2): 372-376 APR 16 2010
Abstract:
Nanoquasicrystalline Al-Fe-Cr-based alloys have a microstructure composed of nanoquasicrystalline particles embedded in an alpha-Al matrix, and have high strength at elevated temperatures. However, the metastability of the quasicrystalline phase can limit the use of these alloys at elevated temperatures The microstructure, stability and mechanical properties at different temperatures on melt-spun nanoquasicrystalline Al-Fe-Cr-based alloys containing Ti, V, Nb or Ta have been studied and summarized in the present work The structural characterisation was carried out by means of X-ray diffraction, hot-stage transmission electron microscopy and scanning-transmission electron microscopy The addition of a fourth element to the Al-93(Fe3Cr2)(7) alloy increases the thermal stability, in particular in the case of the Nb and Ta containing alloys, leading to the delay of the phase transformation towards the melting of the alloys. The mechanical properties at elevated temperatures were studied by tensile tests at different test temperatures with different pre-heat treatments. All the alloys showed a very high strength up to 350 C, more than five times the strength of the commercial Al alloys. These values and the enhanced thermal stability achieved in the quaternary nanoquasicrystalline Al-Fe-Cr-(Ti, V, Nb or Ta) alloys make these alloys very promising for industrial applications. (C) 2009 Elsevier B.V All rights reserved
Title:
Laser remelting of Al91Fe4Cr3Ti2 quasicrystalline phase former alloy
Authors:
Gargarella, P; Vilar, R; Almeida, A; Kiminami, CS; Rios, CT; Bolfarini, C; Botta, WJ Author Full Names: Gargarella, P.; Vilar, R.; Almeida, A.; Kiminami, C. S.; Rios, C. T.; Bolfarini, C.; Botta, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 495 (2): 646-649 APR 16 2010
Abstract:
In the present work, an Al-Fe-Cr-Ti alloy with adequate composition to form quasicrystalline phases has been surface remelted using laser processing techniques The surface of spray formed Al91Fe4Cr3Ti2 bulk samples was remelted using a 2 kW CW Nd:YAG laser. Two different laser beam powers were applied with the goal of studying its influence in the quasicrystalline phase formation in the remelted coating. After laser treatment, the samples were characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (FEG-SEM). The formation of quasicrystalline phases was observed in the X-ray diffractograms and their transformations were verified in DSC analyses. A greater formation of quasicrystalline phase was verified in the coating produced with smaller laser beam power, i.e. higher cooling rate, and its morphology was more close to the sphere. The results indicate the possibility of producing low density coatings conta! ining quasicrystalline phases by laser remelting of spray formed materials Crown Copyright (C) 2009 Published by Elsevier B V All rights reserved.
Title:
Interdependence between glass stability and phase formation sequence during crystallization of Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass
Authors:
Mechler, N; Wanderka, N; Macht, MP Author Full Names: Mechler, S.; Wanderka, N.; Macht, M. -P.
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 101 (5): 601-610 MAY 2010
Abstract:
Knowledge of the crystallization sequence of metallic glasses can yield a deep insight into the origin of their thermal stability. Crystallization of metallic glasses often leads to the simultaneous formation of different metastable crystalline phases that makes their identification difficult. In order to separate formation of crystalline phases from each other, long term isothermal pre-annealing below the glass transition temperature of Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk metallic glass prior to crystallization was performed. It is found that this pre-annealing strongly influences the crystallization sequence and depending on the pre-annealing time leads to preferential formation of different phases. In addition to the well known intermetallic Be2Zr phase and a quasicrystalline phase, three further previously unknown crystalline phases are identified and described in terms of their structure and composition. The formation of the crystalline phases is discussed with respect to the glass forming ability and thermal stability of the glass phase.
Title:
Strong crystalline field at the Fe site and spin rotation in olivine LiNi0.99 Fe-57(0.01) PO4 material by Mossbauer spectroscopy
Authors:
Kim, W; Rhee, CH; Kim, HJ; Moon, SJ; Kim, CS Author Full Names: Kim, Woochul; Rhee, Chan Hyuk; Kim, Hyung Joon; Moon, Seung Je; Kim, Chul Sung
Source:
APPLIED PHYSICS LETTERS 96 (24): Art. No. 242505 JUN 14 2010
Abstract:
The crystal structure of LiNi0.99 Fe-57(0.01) PO4 compound has been determined to be orthorhombic by Rietveld refinement method. Temperature dependence of magnetization M shows an anomalous antiferromagnetic behavior. A sudden change in both the magnitude of magnetic hyperfine field and its slope below 11 K suggests that magnetic phase transition related to the spin ordering takes place abruptly. From the result of Moumlssbauer measurement, it is shown that a strong electric crystalline field of octahedral symmetry including the contribution of spin-orbit coupling and magnetic hyperfine field by space-modulated spin structure is acted to the sites of Fe2+ ions simultaneously at low temperature. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3455312]
Title:
Structure factor for decorated Penrose tiling in physical space
Authors:
Kozakowski, B; Wolny, J Author Full Names: Kozakowski, Bartlomiej; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 66: 489-498 Part 4 JUL 2010
Abstract:
The structure factor for an arbitrarily decorated Penrose tiling has been calculated in the average unit cell description. The obtained formula uses only the physical coordinates of the atoms decorating a structure. The final equation can be easily extended so that it can describe the other physical properties of a structure. Its usefulness is demonstrated by its use in the Al-Ni-Co alloy structure-refinement process. (c) 2010 International Union of Crystallography Printed in Singapore - all rights reserved

Update: 25-Jun-2010

Title:
Polychromatic Photonic Quasicrystal Cavities
Authors:
Thon, SM; Irvine, WTM; Kleckner, D; Bouwmeester, D Author Full Names: Thon, Susanna M.; Irvine, William T. M.; Kleckner, Dustin; Bouwmeester, Dirk
Source:
PHYSICAL REVIEW LETTERS 104 (24): Art. No. 243901 JUN 14 2010
Abstract:
Photonic crystal slabs provide unique opportunities for the manipulation of light on semiconductor chips. The patterns of holes in the slabs are typically designed to maximize the width, depth and symmetry of a single photonic band gap. Quasicrystalline patterns are ideal from this point of view; here, we show that, owing to the presence of multiple Bragg scattering length scales, they also have the desirable property of supporting multiple photonic band gaps in the same slab. This opens up the possibility of creating polychromatic cavities that could be used to extend the possibilities for single photons on optical chips, including on-chip frequency conversion in III-V semiconductors. We study several quasicrystalline structures which support high quality cavity modes at multiple resonant frequencies using 2D and 3D FDTD simulations.
Title:
Symmetry replication and toroidic effects in the multiferroic pyroxene NaFeSi2O6
Authors:
Mettout, B; Toledano, P; Fiebig, M Author Full Names: Mettout, Bruno; Toledano, Pierre; Fiebig, Manfred
Source:
PHYSICAL REVIEW B 81 (21): Art. No. 214417 JUN 11 2010
Abstract:
The magnetoelectric and toroidic effects occurring in NaFeSi2O6 are analyzed theoretically. The symmetry-breaking mechanism giving rise to the incommensurate antiferromagnetic-ferroelectric phase observed below 6 K is shown to be induced by replication of a single transition order parameter. It implies an effective-continuous symmetry of the system identified as the phason rotation of the incommensurate order parameter. The magnetic-field induced toroidal moment is expressed in terms of the macroscopic and spin variables. It shows that the toroidal susceptibility components vary critically as the electric polarization, denoting the inherently magnetoelectric nature of the scaling properties of the ferrotoroidic state. The toroidal moment arising under applied field in antiferromagnetic-ferroelectric structures is induced simultaneously with a spin wave which exhibits the same symmetry properties but spans different degrees of freedom. The difference between microscopic spins degrees of freedom and the electromagnetic macroscopic magnetization and toroidal fields is emphasized.
Title:
Zigzag ladders with staggered magnetic chirality in the S=3/2 compound beta-CaCr2O4
Authors:
Damay, F; Martin, C; Hardy, V; Maignan, A; Andre, G; Knight, K; Giblin, SR; Chapon, LC Author Full Names: Damay, Francoise; Martin, Christine; Hardy, Vincent; Maignan, Antoine; Andre, Gilles; Knight, Kevin; Giblin, Sean R.; Chapon, Laurent C.
Source:
PHYSICAL REVIEW B 81 (21): Art. No. 214405 JUN 7 2010
Abstract:
The crystal and magnetic structures of the S=3/2 antiferromagnet beta-CaCr2O4 have been investigated by means of specific heat, magnetization, muon relaxation, and neutron powder diffraction between 300 and 1.5 K. In this compound, in which the unusual topology of the Cr3+ magnetic lattice can be described as a network of triangular "zigzag" ladders with legs parallel to c, a complex antiferromagnetic ordering with an incommensurate propagation vector k=(0,0,q) (q similar to 0.477 at 1.5 K) is evidenced below T-N=21 K. This complex magnetic ordering can be described as a honeycomblike arrangement of cycloids, running along c, and presenting a unique pattern of staggered chirality. To understand the experimental observation of this staggered chirality, we propose to use antisymmetric Dzyaloshinskii-Moriya terms in the exchange Hamiltonian.
Title:
Transport between twisted graphene layers
Authors:
Bistritzer, R; MacDonald, AH Author Full Names: Bistritzer, R.; MacDonald, A. H.
Source:
PHYSICAL REVIEW B 81 (24): Art. No. 245412 JUN 8 2010
Abstract:
Commensurate- incommensurate transitions are ubiquitous in physics and are often accompanied by intriguing phenomena. In few-layer graphene (FLG) systems, commensurability between honeycomb lattices on adjacent layers is regulated by their relative orientation angle theta, which is in turn dependent on sample preparation procedures. Because incommensurability suppresses interlayer hybridization, it is often claimed that graphene layers can be electrically isolated by a relative twist, even though they are vertically separated by a fraction of a nanometer. We present a theory of interlayer transport in FLG systems which reveals a richer picture in which the specific conductance depends sensitively on theta, single-layer Bloch-state lifetime, in-plane magnetic field, and bias voltage. We find that linear and differential conductances are generally large and negative near commensurate values of theta, and small and positive otherwise. We show that accounting for interlayer coupling may be essential for describing transport in FLG despite its physically insignificant effect on the band structure of the system.
Title:
IDENTIFICATION OF A QUASICRYSTALLINE PHASE IN THE Al-Cu-Fe SYSTEM
Authors:
Kalmykov, KB; Zvereva, NL; Dunaev, SF; Kazennov, NV Author Full Names: Kalmykov, K. B.; Zvereva, N. L.; Dunaev, S. F.; Kazennov, N. V.
Source:
METAL SCIENCE AND HEAT TREATMENT 51 (9-10): 440-443 SEP 2009
Abstract:
The methods of scanning and transmission electron microscopy, x-ray phase analysis, and energy dispersive microanalysis are used to study alloys of the Al - Cu - Fe system in the aluminum-rich domain. The range of existence of a quasicrystalline i-phase with composition Al62.5Cu25Fe12.5 is determined.
Title:
Single-molecule probing of incommensurate biphenyl
Authors:
Pars, M; Palm, V; Kikas, J Author Full Names: Paers, M.; Palm, V.; Kikas, J.
Source:
LOW TEMPERATURE PHYSICS 36 (5): 448-450 MAY 2010
Abstract:
Our data on the distribution of purely electronic linewidths of single molecules of terrylene in incommensurate biphenyl crystals are compared with the data obtained by other groups for different low-temperature organic solid hosts and with results of numerical simulations. The first two moments of the distributions measured within a narrow temperature interval have been used to calculate a single dimensionless parameter characterizing each of the respective hosts-the variation coefficient. It appears that different amorphous hosts have similar values of this coefficient, but the value obtained for the incommensurate crystal of biphenyl is significantly different. One can conclude that the remarkable single-molecule line broadening in biphenyl at 1.8 K cannot be solely explained by the interaction with two-level systems, which is considered to cause the broadening in amorphous hosts. (C) 2010 American Institute of Physics.
Title:
Observation of twin-like composition modulation and phase separation with long-range order induced by oxygen deficiency in single crystal manganites
Authors:
Jia, RR; Feng, ZJ; Wang, SP; Liu, YS; Jing, C; Cao, SX; Zhang, JC Author Full Names: Jia, Rongrong; Feng, Zhenjie; Wang, Shipeng; Liu, Yongsheng; Jing, Chao; Cao, Shixun; Zhang, Jincang
Source:
JOURNAL OF CRYSTAL GROWTH 312 (12-13): 1963-1967 JUN 1 2010
Abstract:
Single crystal La2/3Sr1/3MnO3-delta manganite with an unusual structure was obtained by the optical-floating method with controlled growth in a flowing argon atmosphere. A modulated twin-like structure with phase separation characteristics in the long-range order is found. The energy-dispersive X-ray spectroscopy measurement reveals that there is a strong chemical fluctuation for different stripes, i.e. resulting from the nonstoichiometry due to oxygen deficiency. After annealing, the twin-like stripe phase disappears and the single crystal shows excellent properties. These results may be of great significance for controlled growth of oxide electronics materials with artificial superstructure-like technique. (C) 2010 Elsevier B.V. All rights reserved.

Update: 18-Jun-2010

Title:
Effects of Nd and high-valence Mn co-doping on the electrical and magnetic properties of multiferroic BiFeO3 ceramics
Authors:
Hu, ZQ; Li, MY; Yu, Y; Liu, J; Pei, L; Wang, J; Liu, XL; Yu, BF; Zhao, XZ Author Full Names: Hu, Zhongqiang; Li, Meiya; Yu, Yang; Liu, Jun; Pei, Ling; Wang, Jing; Liu, Xiaolian; Yu, Benfang; Zhao, Xingzhong
Source:
SOLID STATE COMMUNICATIONS 150 (23-24): 1088-1091 JUN 2010
Abstract:
Pure BiFeO3 (BFO), 15% Nd doped BFO (BNF), and 15% Nd and 2% high-valence Mn co-doped BFO (BNFM) multiferroic ceramics were prepared by a rapid liquid phase sintering technique. A structural transition from rhombohedral R3c to orthorhombic P4mm occurred in the BNF and BNFM ceramics. The co-doped BNFM ceramics exhibit the largest dielectric constant, the smallest dielectric loss and leakage current, and an improved rectangular-shaped polarization hysteresis loop with a remnant polarization as high as 31 mu C/cm(2), which could be attributed to the lower concentration of charge defects and the structural transition. Besides, enhanced ferromagnetism is confirmed in BNFM with a remnant magnetization of 0.075 emu/g and a coercive magnetic field of 5.8 kOe, which might be attributed to the effective suppression of the spatially modulated spin structure by the Nd and Mn co-doping. (C) 2010 Elsevier Ltd. All rights reserved.
Title:
Hydrogen in the approximant i-TiZrHf: The energy state, charge, and diffusion
Authors:
Belov, MP; Isaev, EI; Vekilov, YK Author Full Names: Belov, M. P.; Isaev, E. I.; Vekilov, Yu. Kh.
Source:
PHYSICS OF THE SOLID STATE 52 (6): 1111-1114 JUN 2010
Abstract:
The energy of hydrogen dissolution in different tetrahedral pores of a 1/1 approximant of the icosahedral TiZrHf quasicrystal has been determined in terms of the density functional theory and ab initio pseudopotentials. At low and high degrees of loading of TiZrHf with hydrogen, the charges of atoms involved in the system and the Mayer bond order have been calculated for all possible M-M and M-H pairs. The diffusion coefficient of a single hydrogen atom in the system under study has been estimated numerically.
Title:
Frustration of the stable Zr-Ti-Ni quasicrystal as the basis of glass formation
Authors:
Mechler, S; Macht, MP; Schumacher, G; Zizak, I; Wanderka, N Author Full Names: Mechler, S.; Macht, M. -P.; Schumacher, G.; Zizak, I.; Wanderka, N.
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 180101 MAY 1 2010
Abstract:
The origin of glass formation and the systematics of quasicrystal formation in Zr-Ti-Ni-(Cu-Be)-based metallic glasses is unraveled. Both are found to rely on frustration of the stable Zr41.5Ti41.5Ni17 quasicrystal. A systematic change in composition of the stable Zr-Ti-Ni quasicrystal prevents icosahedral order from direct growth in the deeply undercooled liquid and induces the glass transition. Quasicrystals form in the amorphous phase to reduce frustration, i.e., to recover the ideal symmetry and composition of the stable Zr-Ti-Ni quasicrystal. This relation is established especially by the discovery of a new type of sequential phase transformations of icosahedral quasicrystalline phases involving chemical redistribution.
Title:
Anisotropic physical properties of the Al13Fe4 complex intermetallic and its ternary derivative Al-13(Fe, Ni)(4)
Authors:
Popcevic, P; Smontara, A; Ivkov, J; Wencka, M; Komelj, M; Jeglic, P; Vrtnik, S; Bobnar, M; Jaglicic, Z; Bauer, B; Gille, P; Borrmann, H; Burkhardt, U; Grin, Y; Dolinsek, J Author Full Names: Popcevic, P.; Smontara, A.; Ivkov, J.; Wencka, M.; Komelj, M.; Jeglic, P.; Vrtnik, S.; Bobnar, M.; Jaglicic, Z.; Bauer, B.; Gille, P.; Borrmann, H.; Burkhardt, U.; Grin, Yu; Dolinsek, J.
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 184203 MAY 1 2010
Abstract:
We have investigated the magnetic susceptibility, the electrical resistivity, the specific heat, the thermoelectric power, the Hall coefficient, and the thermal conductivity of the Al13Fe4 and Al13(Fe, Ni)(4) monoclinic approximants to the decagonal quasicrystal. While the Al13Fe4 crystals are structurally well ordered, the ternary derivative Al-13(Fe, Ni)(4) contains substitutional disorder and is considered as a disordered version of the Al13Fe4. The crystallographic-direction-dependent measurements were performed along the a*, b, and c directions of the monoclinic unit cell, where the (a*, c) atomic planes are stacked along the b direction. The electronic transport and the magnetic properties exhibit significant anisotropy. The stacking b direction is the most conducting direction for the electricity and heat. The effect of substitutional disorder in Al-13(Fe, Ni)(4) is manifested in the large residual resistivity rho(T -> O) and significantly reduced thermal conductivity of this compound, as compared to the ordered Al13Fe4. Specific-heat measurements reveal that the electronic density of states at the Fermi level of both compounds is high. The anisotropic Hall coefficient R-H reflects complex structure of the anisotropic Fermi surface that contains electronlike and holelike contributions. Depending on the combination of directions of the current and the magnetic field, electronlike (R-H<0) or holelike (R-H>0) contributions may dominate, or the two contributions compensate each other (R-H approximate to 0). Similar complicated anisotropic behavior was observed also in the thermopower. The anisotropic Fermi surface was calculated ab initio using the atomic parameters of the refined Al13Fe4 structural model that is also presented in this work.
Title:
Anisotropic physical properties of the Taylor-phase T-Al72.5Mn21.5Fe6.0 complex intermetallic
Authors:
Heggen, M; Feuerbacher, M; Ivkov, J; Popcevic, P; Batistic, I; Smontara, A; Jagodic, M; Jaglicic, Z; Janovec, J; Wencka, M; Dolinsek, J Author Full Names: Heggen, M.; Feuerbacher, M.; Ivkov, J.; Popcevic, P.; Batistic, I.; Smontara, A.; Jagodic, M.; Jaglicic, Z.; Janovec, J.; Wencka, M.; Dolinsek, J.
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 184204 MAY 1 2010
Abstract:
We have investigated anisotropic physical properties (the magnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient and the thermal conductivity) of the single-crystalline Taylor-phase T-Al72.5Mn21.5Fe6.0 complex intermetallic that is an orthorhombic approximant to the d-Al-Mn-Pd decagonal quasicrystal. The measurements were performed along the a, b, and c directions of the orthorhombic unit cell, where (a, c) atomic planes are stacked along the perpendicular b direction. The T-Al72.5Mn21.5Fe6.0 shows spin-glass behavior below the spin-freezing temperature T-f approximate to 29 K with a small anisotropy in the magnetic susceptibility. The anisotropic electrical resistivities are rather large and show negative temperature coefficient. The resistivity is lowest along the stacking direction, which appears to be a common property of the decagonal-approximant phases with a stacked-layer structure. The temperature-dependent resis! tivity was theoretically reproduced by the quantum transport theory of slow charge carriers. The thermopower is positive for all three crystallographic directions, indicating that holes are the majority charge carriers, and no anisotropy can be claimed within the experimental precision. The same conclusion on the holes being the dominant charge carriers follows from the Hall-coefficient measurements, which is a sum of the (positive) normal Hall coefficient and the anomalous term, originating from the magnetization. The anisotropy of the thermal conductivity is practically negligible. The T-Al72.5Mn21.5Fe6.0 Taylor phase can be considered as a "close-to-isotropic" complex intermetallic. The relation of the anisotropic physical properties of the Taylor phase to other families of decagonal-approximant phases with the stacked-layer structure is discussed.
Title:
Incommensurate spin-density wave and magnetic lock-in transition in CaFe4As3
Authors:
Manuel, P; Chapon, LC; Todorov, IS; Chung, DY; Castellan, JP; Rosenkranz, S; Osborn, R; Toledano, P; Kanatzidis, MG Author Full Names: Manuel, P.; Chapon, L. C.; Todorov, I. S.; Chung, D. Y.; Castellan, J. -P.; Rosenkranz, S.; Osborn, R.; Toledano, P.; Kanatzidis, M. G.
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 184402 MAY 1 2010
Abstract:
The magnetic structure for the recently synthesized iron-arsenide compound CaFe4As3 has been studied by neutron-powder diffraction. Long-range magnetic order is detected below 85 K, with an incommensurate modulation described by the propagation vector k=(0, delta, 0), delta similar to 0.39. Below similar to 25 K, our measurements detect a first-order phase transition where delta locks into the commensurate value 3/8. A model of the magnetic structure is proposed for both temperature regimes, based on Rietveld refinements of the powder data and symmetry considerations. The structures correspond to longitudinal spin-density waves with magnetic moments directed along the b axis. A Landau analysis captures the change in thermodynamic quantities observed at the two magnetic transitions, in particular, the drop in resistivity at the lock-in transition.
Title:
H-T phase diagram of the two-dimensional Ising model with exchange and dipolar interactions
Authors:
Diaz-Mendez, R; Mulet, R Author Full Names: Diaz-Mendez, Rogelio; Mulet, Roberto
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 184420 MAY 1 2010
Abstract:
We explore the equilibrium properties of a two-dimensional Ising spin model with short-range exchange and long-range dipolar interactions as a function of the applied magnetic field H. The model is studied through extensive Monte Carlo simulations that show the existence of many modulated phases with long-range orientational order for a wide range of fields. These phases are characterized by different wave vectors that change discontinuously with the magnetic field. In particular, the emergence of novel anharmonic phases that keep the orientational order but are characterized by several wave vectors is studied in detail. We provide numerical evidence supporting the existence of first-order transitions between modulated phases. At higher fields our results suggest a Kosterliz-Thouless scenario for the transition from a bubble to a ferromagnetic phase.
Title:
Synthesis of natural superlattice structure in the binary ZnO-Fe2O3 system by microwave irradiation
Authors:
Katayose, S; Miyazaki, T; Hayashi, Y; Takizawa, H Author Full Names: Katayose, Satomi; Miyazaki, Takamichi; Hayashi, Yamato; Takizawa, Hirotsugu
Source:
JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 118 (1377): 387-389 MAY 2010
Abstract:
Homologous compounds, Fe2O3(ZnO)(m), with the modulated natural superlattice structure were obtained within a short period by solid state reaction of component oxides under 2.45 GHz microwave irradiation. TEM observation revealed that two types of superlattice structures were observed in different Fe concentration; one is longitudinal superlattice structure in a rod shaped precipitation at high Fe concentration, and the other is modulated structure showing zigzag shape at low Fe concentration. It is conclude that the non-equilibrium nature of microwave selective heating, as well as rapid heating and quenching effects, plays a key role to form the superstructure. The obtained products exhibit ferromagnetic behavior with the Curie temperature above 300 K. (C) 2010 The Ceramic Society of Japan. All rights reserved.
Title:
Deformation-induced structural transformation leading to compressive plasticity in Zr65Al7.5Ni10Cu12.5M5 (M = Nb, Pd) glassy alloys
Authors:
Setyawan, AD; Saida, J; Kato, H; Matsushita, M; Inoue, A Author Full Names: Setyawan, Albertus D.; Saida, Junji; Kato, Hidemi; Matsushita, Mitsuhide; Inoue, Akihisa
Source:
JOURNAL OF MATERIALS RESEARCH 25 (6): 1149-1158 JUN 2010
Abstract:
Zr65Al7.5Ni10Cu12.5Nb5 glass was found to exhibit a large plastic compressive strain of over 10% and the property was suggested to be due to deformation-induced nanocrystallization. A transmission electron microscopic observation, however, only revealed obscure ordered clusters with a size of similar to 2 nm in the fracture surface of a deformed sample, instead of well-identified crystals as previously reported for the Zr-Al-Ni-Cu-Pd system. This phenomenon is suggested to correlate with the higher viscosity of supercooled liquid and the slower grain growth of icosahedral phase during primary crystallization in the Zr65Al7.5Ni10Cu12.5Nb5 compared to those in the Zr65Al7.5Ni10Cu12.5Pd5 alloy. The role of the deformation-induced nanoclusters on the enhanced compressive plasticity was discussed.
Title:
Structural and magnetic properties of magnetron sputtered Ni-Mn-Sn ferromagnetic shape memory alloy thin films
Authors:
Vishnoi, R; Kaur, D Author Full Names: Vishnoi, Ritu; Kaur, Davinder
Source:
JOURNAL OF APPLIED PHYSICS 107 (10): Art. No. 103907 MAY 15 2010
Abstract:
In the present study, structural and magnetic properties of Mn-rich, off-stoichiometric, nanocrystalline Ni-Mn-Sn ferromagnetic shape memory alloy thin films, grown on Si (100) substrates at 550 degrees C by dc magnetron sputtering have been systematically investigated. The crystallization, surface morphology, and structural features were studied using x-ray diffraction, atomic force microscopy, and field emission scanning electron microscopy. The structural transition from austenite to martensite was observed with an increase of Mn content. Austenitic phase with mixed L2(1)/A2+B2 structure has been observed at room temperature in Ni52.6Mn23.7Sn23.6 (S-1) and Ni51.5Mn26.1Sn22.2 (S-2) films, while those with composition of Ni58.9Mn28.0Sn13.0 (S-3) and Ni58.3Mn29.0Sn12.6 (S-4) show martensitic phase with 14M modulated monoclinic structures. Field induced martensite-austenite transformation has been observed in magnetization studies using superconducting quantum interference device magnetometer. Temperature dependent magnetization measurements demonstrate the influence of magnetic field on the structural phase transition temperature. The investigations reveal an increase of martensitic transformation temperature (T-M) with corresponding increase in substitution of Mn. The films exhibit ferromagnetic behavior at low temperatures below Curie temperature (T-C). The decrease in saturation moment with increasing Mn content, indicates the existence of antiferromagnetic correlations within ferromagnetic matrix. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3393961]

Update: 3-Jun-2010

Title:
Muon spin relaxation study of the layered magnetoelectric FeTe2O5Br with spin amplitude modulated magnetic structure
Authors:
Zorko, A; Pregelj, M; Berger, H; Arcon, D Author Full Names: Zorko, A.; Pregelj, M.; Berger, H.; Arcon, D.
Source:
JOURNAL OF APPLIED PHYSICS 107 (9): Art. No. 09D906 MAY 1 2010
Abstract:
Local-probe weak-transverse-field and zero-field mu SR measurements have been employed to investigate magnetic ordering in the new magnetoelectric compound FeTe2O5Br. Below the Neel transition temperature T-N=10.6 K a static local magnetic field starts to develop at the mu(+) sites. Fast mu(+) polarization decay below T-N speaks in favor of a broad distribution of internal magnetic fields, in agreement with the incommensurate magnetic structure suggested by neutron diffraction experiments. Above T-N the presence of short-range order is detected as high as at 2T(N), which suggests only weak interlayer magnetic coupling. On the other hand, strong Fe3+ spin fluctuations likely reflect geometrically frustrated structure of [Fe4O16](20-) spin clusters, which are the main building blocks of the layered FeTe2O5Br structure. (C) 2010 American Institute of Physics. [doi:10.1063/1.3362909]
Title:
Hall Coefficient of the Y-Al-Ni-Co Decagonal Approximant
Authors:
Stanic, D; Ivkov, J; Dolinsek, J; Gille, P Author Full Names: Stanic, Denis; Ivkov, Jovica; Dolinsek, Janez; Gille, Peter
Source:
CROATICA CHEMICA ACTA 83 (1): 7-10 Sp. Iss. SI APR 2010
Abstract:
We have investigated anisotropic Hall coefficient of Y-Al-Ni-Co decagonal approximant of the Al76Co22Ni2 composition. The crystalline-direction-dependent studies were performed along three orthogonal directions a*, b and c of the Y-Al-Ni-Co unit cell, where (a,c) monoclinic atomic planes are stacked along the perpendicular b direction. Hall coefficient R-H exhibits pronounced anisotropy, while at the same time the magnetic field in a given crystalline direction yields the same R-H for the current along the other two crystalline directions in the perpendicular plane. The observed anisotropy is studied in terms of the anisotropic structure of the Y-Al-Ni-Co phase and Fermi surface. The results are compared to the anisotropy of the Hall coefficient of the d-Al-Ni-Co decagonal quasicrystal reported in literature.
Title:
Anisotropic Transport Properties of the Orthorhombic Al13Co4 Approximant to the Decagonal Quasicrystal
Authors:
Lukatela, J; Stanic, D; Popcevic, P; Ivkov, J; Dolinsek, J; Gille, P Author Full Names: Lukatela, Jagoda; Stanic, Denis; Popcevic, Petar; Ivkov, Jovica; Dolinsek, Janez; Gille, Peter
Source:
CROATICA CHEMICA ACTA 83 (1): 27-32 Sp. Iss. SI APR 2010
Abstract:
Anisotropic transport properties (electrical resistivity, thermoelectric power, Hall coefficient and thermal conductivity) of the o-Al13Co4 orthorhombic approximant to the decagonal phase were investigated. The crystalline-direction-dependent measurements were performed along the a, b and c directions of the orthorhombic unit cell, where (b, c) atomic planes are stacked along the perpendicular a direction. Anisotropic electrical and thermal conductivities are the highest along the stacking a direction. The anisotropic thermoelectric power changes sign with the crystalline direction and so does the anisotropic Hall coefficient, which changes from the negative electron-like to the positive hole-like for different combinations of the electric current and magnetic field direction. The transport properties of the o-Al13Co4 phase were compared to the literature data on approximant to the decagonal quasicrystals, the Al76Co22Ni2 and the Al80Cr15Fe5, allowing for the study of evolution of transport properties with increasing structural complexity and unit cell size.
Title:
The Influence of Thermal Treatment on Magnetic Moments in i-Al-Pd-Mn Quasicrystals
Authors:
Jagodic, M; Jaglicic, Z; Grushko, B; Dolinsek, J Author Full Names: Jagodic, Marko; Jaglicic, Zvonko; Grushko, Benjamin; Dolinsek, Janez
Source:
CROATICA CHEMICA ACTA 83 (1): 39-42 Sp. Iss. SI APR 2010
Abstract:
The influence of cooling rate on thermal strains in the quasicrystalline icosahedral Al-Pd-Mn complex metallic alloy was investigated. In general, measurements of the electronic magnetization can be used as an indirect method for determining the short-scale disorder in the crystal structure as the magnetic moments at the Mn sites are highly dependent on their local environment. Excluding the contributions of thermal vacancies and second phase precipitates by proper selection of preannealing temperatures and durations, the changes in magnetization can be ascribed to the appearance or disappearance of thermal strains in the crystal structure. It was found that water-quenching increases thermal strains irrespective of previous thermal history.
Title:
The Solidification Path of the Complex Metallic Al-Mn-Be Alloy
Authors:
Markoli, B; Boncina, T; Zupanic, F Author Full Names: Markoli, Bostjan; Boncina, Tonica; Zupanic, Franc
Source:
CROATICA CHEMICA ACTA 83 (1): 49-54 Sp. Iss. SI APR 2010
Abstract:
The solidification paths of the Al86.1Mn2.5Be11.4 and Al84Mn5.1Be10.9 alloys, melt spun, cast into a copper mould and controlled cooled (during DSC) were investigated by means of light-optical microscopy (LOM), differential scanning calorimetry (DSC) combined with thermogravimetry (TG) or simultaneous thermal analysis (STA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and the X-ray diffraction (XRD) line in Elletra Trieste, Italy. The constitutions of samples from both alloys were examined in all three states, i.e., after melt spinning, after casting into a copper mould and after differential scanning calorimetry. It was established that in the cast and controlled-cooled specimens the alloys consisted of an aluminium-rich alpha(Al)-matrix, and the Al4Mn and Be4AlMn phases. In the case of casting and DSC the primary crystallization began with the precipitation of the Be4AlMn phase, followed by what can most lik! ely be characterized as a uni-variant binary eutectic reaction L -> (Be4AlMn + Al4Mn). The solidification process continued with an invariant ternary eutectic reaction, where the remaining melt (L) formed the heterogeneous structure (alpha(Al) + Al4Mn + Be4AlMn) or a ternary eutectic. When extremely high cooling rates were employed, as is the case with melt-spinning, the constituting phases of both alloys were precipitated in a very small form and the Be4AlMn phase was completely absent in the form of primary polygonal particles and replaced by the icosahedral quasicrystalline phase or the i-phase. There was also no evidence of the Al4Mn phase. The distribution, size and shape of all the constituents in the melt-spun alloys also varied from the contact surface towards the free surface of the ribbons. The smallest constituents were established at the contact surface, measuring less than 0.1 mu m, to 0.5 mu m at the free surface. The grains of the aluminium-rich matrix had mean diameters of less than 20 mu m, close to the free surface, down to 1 mu m at the contact surface.
Title:
Open Theoretical Problems in the Physics of Aperiodic Systems
Authors:
Jagannathan, A Author Full Names: Jagannathan, Anuradha
Source:
CROATICA CHEMICA ACTA 83 (1): 59-63 Sp. Iss. SI APR 2010
Abstract:
Quasicrystals have intrigued and stimulated research in a large number of disciplines. Mathematicians, physicists, chemists, metallurgists and materials scientists have found in them a fertile ground for new insights and discoveries. In the quarter century that has ensued since the publication of the experimental observation of a quasiperiodic Al-Mn alloy,(1) many different kinds of quasiperiodic alloys have been manufactured and studied. The physical properties of quasicrystals are no less interesting than the unusual structural properties that led to their discovery in 1984. In this review, some of the properties that characterize quasicrystals are presented, several types of theories that have been put forward briefly discussed, and some new behaviors that might be investigated by experiment described.
Title:
Anisotropic Transport Properties of Complex Metallic Alloys
Authors:
Smontara, A; Dolinsek, J Author Full Names: Smontara, Ana; Dolinsek, Janez
Source:
CROATICA CHEMICA ACTA 83 (1): 75-80 Sp. Iss. SI APR 2010
Abstract:
Anisotropic transport properties (electrical resistivity, rho, and thermal conductivity, kappa) of the Y-phase Al-Ni-Co, o-Al13Co4 and Al-4(Cr,Fe) complex metallic alloys were investigated. They belong to the class of decagonal approximant phases with stacked-layer crystallographic structure and allowed us to study the evolution of anisotropic transport properties with increasing structural complexity and the unit cell size.
Title:
Anisotropic Transport Properties of the Al13Fe4 Decagonal Approximant
Authors:
Popcevic, P; Smontara, A; Dolinsek, J; Gille, P Author Full Names: Popcevic, Petar; Smontara, Ana; Dolinsek, Janez; Gille, Peter
Source:
CROATICA CHEMICA ACTA 83 (1): 101-105 Sp. Iss. SI APR 2010
Abstract:
We have investigated electrical resistivity, thermoelectric power and thermal conductivity of the Al13Fe4 monoclinic approximant to the decagonal quasicrystal. The crystallographic-direction-dependent measurements were performed along the a*, b and c directions of the monoclinic unit cell, where (a*,c) atomic planes are stacked along the perpendicular b direction. The electronic transport exhibit significant anisotropy. The stacking b direction is the most conducting direction for the electricity and heat. The anisotropic thermopower reflects complicated structure of the anisotropic Fermi surface that contains electron-like and hole-like contributions.
Title:
Hall Effect of the Al13Fe4 Decagonal Approximant and Its Ternary Extension Al-13(Fe,Ni)(4)
Authors:
Ivkov, J; Popcevic, P; Dolinsek, J; Gille, P Author Full Names: Ivkov, Jovica; Popcevic, Petar; Dolinsek, Janez; Gille, Peter
Source:
CROATICA CHEMICA ACTA 83 (1): 107-111 Sp. Iss. SI APR 2010
Abstract:
We have measured Hall coefficient and electrical resistivity of the Al13Fe4 and Al-13(Fe,Ni)(4) monoclinic approximants to the decagonal quasicrystal. While the Al13Fe4 crystals are structurally well ordered, the ternary extension Al-13(Fe,Ni)(4) contains quenched disorder and can be viewed as a disordered version of Al13Fe4. The crystallographic-direction-dependent Hall effect measurements were performed along the a*, b and c directions of the monoclinic unit cell, where (a*,c) atomic planes are stacked along the perpendicular b direction. The stacking b direction is the most conducting direction for the electricity. The effect of quenched disorder in Al-13(Fe,Ni)(4) is manifested in the large residual resistivity rho(T -> 0) as compared to the ordered Al13Fe4. The Hall coefficient, R-H, values for all combinations of directions, are typical metallic. The anisotropic Hall coefficient reflects complicated structure of the anisotropic Fermi surface that contains electron-like and hole-like parts. Depending on the combination of directions of the current and magnetic field electron-like (R-H < 0) or hole-like (R-H > 0) contributions may dominate, or the two contributions compensate each other (R-H approximate to 0).
Title:
Lattice dynamics and structural phase transitions
Authors:
Shapiro, SM Author Full Names: Shapiro, S. M.
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 99 (3): 543-548 Sp. Iss. SI JUN 2010
Abstract:
Results of lattice dynamics, or atomic motions in a solid, explain many of the thermodynamic properties of solids. Inelastic neutron scattering conveniently explores the atomic motions, quantized as phonons. Of particular interest are materials that undergo structural phase transitions. The soft mode theory has been successful in relating anomalous phonon behavior to structural changes in solids. One such example is the ferromagnetic shape memory alloy, Ni2MnGa, which undergoes a sequence of phase transitions leading to a magnetic, incommensurate modulated, tetragonal phase as the ground state. The experiments, coupled with first principles calculations, provide evidence that strong electron-phonon coupling is the driving mechanism of the phase transformation.
Title:
Comparing properties of substrate-constrained and freestanding epitaxial Ni-Mn-Ga films
Authors:
Backen, A; Yeduru, SR; Kohl, M; Baunack, S; Diestel, A; Holzapfel, B; Schultz, L; Fahler, S Author Full Names: Backen, Anja; Yeduru, Srinivasa R.; Kohl, Manfred; Baunack, Stefan; Diestel, Anett; Holzapfel, Bernhard; Schultz, Ludwig; Faehler, Sebastian
Source:
ACTA MATERIALIA 58 (9): 3415-3421 MAY 2010
Abstract:
In order to use the magnetic shape memory alloy Ni-Mn-Ga with its high achievable strain of up to 10% for microactuators, freestanding epitaxial films are required. Here we show that these conditions can be fulfilled when using chromium as a sacrificial layer. The low misfit towards Ni-Mn-Ga enables epitaxial growth. Furthermore, Cr can afterwards be removed selectively by wet-chemical etching and during deposition no significant interdiffusion is observed. The structure, microstructure and magnetic properties of micrometer thick films are not affected by the etching process. Films are ferromagnetic at room temperature and we observe the coexistence of non-modulated (NM) and seven layered modulated (14 M) martensite. Tensile stress-strain measurement of a freestanding bridge reveals a broad strain plateau of 12% at a twinning stress of 25 MPa, indicating reorientation of NM variants. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 27-May-2010

Title:
Phenomenological theory of phase transitions in multiferroic MnWO4: magnetoelectricity and modulated magnetic order
Authors:
Sakhnenko, VP; Ter-Oganessian, NV Author Full Names: Sakhnenko, V. P.; Ter-Oganessian, N. V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (22): Art. No. 226002 JUN 9 2010
Abstract:
The phenomenological theory of phase transitions in multiferroic MnWO4 is suggested. The theoretical model uses the assumption that the magnetic order is driven by the instability in the (1/4; 1/2; 1/2) point of the Brillouin zone, which is justified by the symmetry of the low-temperature magnetic phase. It is shown that the experimentally observed incommensurate magnetic order is due to the Lifshitz invariants allowed for the corresponding order parameters. Invariants responsible for the magnetoelectric interaction are found and a schematic phase diagram is calculated. The influence of the magnetic field on the phase transition sequence is also analyzed. It is suggested that the description of the phase transitions in MnWO4 starting from the orthorhombic praphase significantly simplifies the approach and allows us to draw important conclusions.
Title:
TEM-assisted dynamic scanning force microscope imaging of (001) antigorite: Surfaces and steps on a modulated silicate
Authors:
Palacios-Lidon, E; Grauby, O; Henry, C; Astier, JP; Barth, C; Baronnet, A Author Full Names: Palacios-Lidon, Elisa; Grauby, Olivier; Henry, Claude; Astier, Jean-Pierre; Barth, Clemens; Baronnet, Alain
Source:
AMERICAN MINERALOGIST 95 (5-6): 673-685 MAY-JUN 2010
Abstract:
Ultra-high vacuum dynamic scanning force microscopy (dynamic SFM) has been performed on in situ cleaved and as-grown (001) surfaces of low-T, m = 18 and m = 20, antigorite from the Kovdor Mine, Russia. The internal microstructure of the same crystal before cleavage has been checked by conventional TEM on FIB-cut cross-sections. The structural wave is imaged by dynamic SFM with a similar to 0.25 nm topographic amplitude (outcropping tetrahedral sheet) on cleaved and as-grown surfaces, and with a similar to 0.5 nm topographic amplitude (outcropping tetrahedral + octahedral sheets) mostly found on cleaved surfaces. Atomic resolution imaging was successfully applied on the cleavage surface through imaging individual atomic features on the outer hexagonal net of the emerging (Mg, O, OH) octahedra of the half-wave. The antigorite cleavage crack undulates through a single octahedral sheet, thereby avoiding rupture of strong Si-O bonds. The two tetrahedral reversals, which form the edges of the modulation repeat, are found to be strongly non-equivalent in structure: across < 010 >, one reversal is sharp as expected from the standard models of the antigorite structure, whereas the other reversal is unexpectedly "extended." The latter suggests some scheme of anti-polar positioning of silicate tetrahedra along < 010 > at the 6-membered ring reversal. High-resolution transmission electron microscopy (HRTEM) structure imaging of antigorite viewed down to < 010 > confirms spread out electron densities at this reversal. Numerous step height measurements on (001) surfaces show incremental results as integral multiples of 0.25 nm, the spacing between O,OH surfaces along c. Many of them differ in height from integral multiples of the unit cell repeat along c and could be explained from carving the bulk wave structure. For all surfaces and steps, local stoichiometry and global electro-neutrality of the surface are satisfied.

Update: 13-May-2010

Title:
Low-energy lattice excitations in the decagonal Al-Ni-Fe and icosahedral Al-Cu-Fe quasicrystals and the (Al,Si)-Cu-Fe cubic phase
Authors:
Panova, GK; Zemlyanov, MG; Parshin, PP; Shikov, AA; Brand, RA Author Full Names: Panova, G. Kh.; Zemlyanov, M. G.; Parshin, P. P.; Shikov, A. A.; Brand, R. A.
Source:
PHYSICS OF THE SOLID STATE 52 (4): 771-775 APR 2010
Abstract:
The specific heat of decagonal Al71.3Ni24.0Fe4.7 and icosahedral Al62Cu25.5Fe12.5 quasicrystals and the Al55.0Si7.0Cu25.5Fe12.5 cubic phase approximating the structure of the icosahedral alloy has been studied in the temperature range 4.2-40.0 K. All the three compounds exhibit low coefficients of the electronic heat capacity and pronounced deviations of the low-temperature lattice heat capacity from a cubic temperature law in the range 5-10 K. The results obtained by the thermodynamic method and inelastic neutron scattering have been compared and analyzed. It has been established that, at energies E > < 14 meV, the spectral density of thermal vibrations in the icosahedral quasicrystal is substantially higher than those in the cubic approximant and in decagonal quasicrystal.
Title:
Investigation of the structure of compacts and sheets of an Al-Cu-Li alloy strengthened by Al2CuLi (T-1) particles
Authors:
Shamrai, VF; Timofeev, VN; Grushko, OE Author Full Names: Shamrai, V. F.; Timofeev, V. N.; Grushko, O. E.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 109 (4): 383-391 APR 2010
Abstract:
X-ray diffraction and electron microscopy have been used to investigate structural states of the material of compacts and sheets of an aluminum-copper-lithium alloy with a lithium content corresponding to the field of equilibrium of a solid solution with the phase T (1) (Al2CuLi). In pressed strips, there arises a multicomponent texture (Bs "110"aOE (c) 112 >, Cu "211"aOE (c) 111 >, S "123"aOE (c) hkl >) typical of pressed articles of aluminum-lithium alloys. Their microstructure was characterized by the presence of slip bands oriented in the rolling direction. The formation of lamellar precipitates of the T (1) phase at slip-band boundaries in the process of deformation is supposedly stimulated by Shockley partial dislocations. In hot-rolled sheets, there arose an unusually intense nearly single-component texture of the Ex (1) "011"aEuro111aEuro parts per thousand type, whose appearance is mainly caused by the cross rolling of the sheets. The reduced strength characteristics of the sheets examined are connected with a sharply oriented character of the structure of both the matrix phase and the strengthening T (1) phase. A quasicrystalline phase T (2) present in the material and the precipitates of the delta' phase exert no marked effect on the level of mechanical properties.
Title:
Structural phase transformations in quasicrystal-forming Al-Cu-Fe alloys and defects of the icosahedral phase
Authors:
Shalaeva, EV; Prekul, AF Author Full Names: Shalaeva, E. V.; Prekul, A. F.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 109 (4): 392-401 APR 2010
Abstract:
Transmission electron microscopy was used to investigate structural and phase transformations and defects of the icosahedral (iota) phase that is formed upon isothermal annealings (T (ann) = 550-700A degrees C) of quenched quasicrystal-forming alloys Al61Cu26Fe13 and Al63Cu25Fe12 (beta solid solution + iota phase). It has been established that in the Al63Cu25Fe12 alloy there occurs a reversible iota-R-approximant transformation, whereas in the Al61Cu26Fe13 alloy there is formed a single-phase iota structure with regions with a high density of randomly distributed planar defects (T (ann) = 550A degrees C), which are partially annealed at 650A degrees C. The observed defects are, mainly, ultrathin interlayers ("intergrowths" to 3-5 nm in thickness) on quasicrystal planes with A5(iota) axes with an imperfect decagonal structure. As the basic mechanism, the growth mechanism of the formation of defects during the beta -> i transformation is proposed. The role of the alloy composition and low-temperature beta -> 3C-phase transformation in the realization of this mechanism is discussed.
Title:
Charge and spin ordering in the mixed-valence compound LuFe2O4
Authors:
Harris, AB; Yildirim, T Author Full Names: Harris, A. B.; Yildirim, T.
Source:
PHYSICAL REVIEW B 81 (13): Art. No. 134417 APR 1 2010
Abstract:
Landau theory and symmetry considerations lead us to propose an explanation for several seemingly paradoxical behaviors of charge ordering (CO) and spin ordering (SO) in the mixed valence compound LuFe2O4. Both SO and CO are highly frustrated. We analyze a lattice gas model of CO within mean-field theory and determine the magnitude of several of the phenomenological interactions. We show that the assumption of a continuous phase transitions at which CO or SO develops implies that both CO and SO are incommensurate. To explain how ferroelectric fluctuations in the charge-disordered phase can be consistent with an antiferroelectric-ordered phase, we invoke an electron-phonon interaction in which a low-energy (20 meV) zone-center transverse phonon plays a key role. The energies of all the zone center phonons are calculated from first principles. We give a Landau analysis which explains SO and we discuss a model of interactions which stabilizes the SO state, if it is assumed commensurate. However, we suggest a high-resolution experimental determination to see whether this phase is really commensurate, as believed up to now. The applicability of representation analysis is discussed. A tentative explanation for the sensitivity of the CO state to an applied magnetic field in field-cooled experiments is given.
Title:
Sinusoidal magnetic structure in a three-dimensional antiferromagnetic Co-2(OH)AsO4: Incommensurate-commensurate magnetic phase transition
Authors:
de Pedro, I; Rojo, JM; Fernandez, JR; Fernandez-Diaz, MT; Rojo, T Author Full Names: de Pedro, I.; Rojo, J. M.; Rodriguez Fernandez, J.; Fernandez-Diaz, M. T.; Rojo, T.
Source:
PHYSICAL REVIEW B 81 (13): Art. No. 134431 APR 1 2010
Abstract:
Co-2(OH)AsO4 has been prepared by hydrothermal synthesis and characterized from x-ray and neutron powder diffraction. The structure consists of a three-dimensional framework in which Co(1)O-5-trigonal bi-pyramid dimers and Co(2)O-6-octahedra chains are simultaneously present. The magnetic structure has been determined by neutron (D2B and D1B) powder-diffraction data. Below 22 K, the Co-2(OH)AsO4 phase shows an incommensurate antiferromagnetic structure along the b direction. The propagation vector (0, delta, 0) is temperature dependent with a value of delta=0.430 at the lowest temperature (1.8 K). Magnetization measurements of Co-2(OH)AsO4 show a complex magnetic behavior with the presence of three different signals. Between 6 and 21 K, a strong dependence of the magnetic field is observed with a shift of the inflexion point associated to the three-dimensional antiferromagnetic ordered from 18 K at 1 kOe to 20.1 K at 90 kOe. The small sp! litting observed in the zero-field-cooled-field-cooled curves at low temperatures is characteristic of ferromagnetic interactions but saturation is not reached even up to 90 kOe. Heat-capacity measurements show an unusual dependence on the magnetic field for antiferromagnetic transitions with a jump at the Neel temperature quite small (2 J/Kmol). The magnetic contribution exhibits a lambda-type anomaly associated to the three-dimensional antiferromagnetic ordering. Surprisingly, the lambda anomaly grows with the magnetic field and becomes better defined. Neutron powder diffraction in different fields shows a magnetic phase transition. The incommensurate magnetic structure evolves at low temperatures toward a collinear AF phase for fields higher than 35 kOe.
Title:
Magnetic order of multiferroic ErMn2O5 studied by resonant soft x-ray Bragg diffraction
Authors:
Staub, U; Bodenthin, Y; Garcia-Fernandez, M; de Souza, RA; Garganourakis, M; Golovenchits, EI; Sanina, VA; Lushnikov, SG Author Full Names: Staub, U.; Bodenthin, Y.; Garcia-Fernandez, M.; de Souza, R. A.; Garganourakis, M.; Golovenchits, E. I.; Sanina, V. A.; Lushnikov, S. G.
Source:
PHYSICAL REVIEW B 81 (14): Art. No. 144401 APR 1 2010
Abstract:
Resonant magnetic soft x-ray diffraction is used to study the magnetic order of the Mn sublattices in multiferroic ErMn2O5. Data were collected at the Mn L-2,L-3 edges as a function of temperature, incident polarization, including the analysis of scattered polarizations for selected azimuths. The energy dependence of the magnetic reflections depends on the azimuthal angle in the commensurate magnetic (CM) ferroelectric (FE) phase, indicating different contributions to the scattering. In the incommensurate magnetic [two-dimensional (2D)-ICM] phase, the two observed reflections (1/2 +/- delta(x) 0 1/4+delta(z)) have distinct energy dependences too. Different origins of these differences in spectral shape are discussed. The azimuthal angle dependence at the L-3 edge can only be qualitatively described by a generalized magnetic model. The observed discrepancies may indicate the importance of magnetoelectric multipole scattering to these reflections. Reciprocal mesh scans show diffuse scattering along q and perpendicular to q as well as along the (h 0 0) direction in the CM phase. Diffuse scattering is also observed along (h 0 0) in the one-dimensional-ICM phase. At higher temperatures, in the 2D-ICM phase, the diffuse magnetic scattering is almost isotropic.
Title:
V-51 NMR study of the kagome staircase compound Ni3V2O8
Authors:
Ogloblichev, V; Kumagai, K; Verkhovskii, S; Yakubovsky, A; Mikhalev, K; Furukawa, Y; Gerashenko, A; Smolnikov, A; Barilo, S; Bychkov, G; Shiryaev, S Author Full Names: Ogloblichev, V.; Kumagai, K.; Verkhovskii, S.; Yakubovsky, A.; Mikhalev, K.; Furukawa, Yu.; Gerashenko, A.; Smolnikov, A.; Barilo, S.; Bychkov, G.; Shiryaev, S.
Source:
PHYSICAL REVIEW B 81 (14): Art. No. 144404 APR 1 2010
Abstract:
We used V-51 NMR to study magnetic ordering in the Ni3V2O8 single crystal with a Kagome staircase structure of Ni atoms. The NMR spectra were measured in the temperature range T= (3-300) K and magnetic fields H= (2-9.4) T directed along the main a, b, c axes of the orthorhombic (Cmca) crystal. The local magnetic field at the V-51 NMR probe determines position and the shape of the corresponding NMR line. These parameters yield an unique information, respectively, on the uniform and the staggered spin components of the ordered Ni. The NMR data collected at H >= 2 T are considered in line with predictions of the representation theory [A. Harris, Phys. Rev. B 76, 054447 (2007)] with a result that incommensurate amplitude-modulated structure of the spine Ni-s spins acquires in the high-temperature incommensurate (HTI) phase two prominent nearly equal spin components S-a approximate to S-c >> S-b instead of the longitudinal incommensurate spin-density wave (SDW) order with S-a >> S-c, S-b as it was deduced from neutron-diffraction data [M. Kenzelmann et al., Phys. Rev. B 74, 014429 (2006)]. No noticeable variation of SDW polarization in the ab plane was detected below the HTI-low-temperature incommensurate (LTI) transition. In both the HTI and LTI phases two almost equal spin components of the Ni-s spins S-a approximate to S-c >> S-b exist at H < 4.7 T. Their phasing is still not determined. The bulk magnetization in these phases is explained by contribution of the cross-tie Ni-c spins which antiferromagnetic structure in the LTI phase is canted along H.
Title:
Magnetic properties of EuPtSi3 single crystals
Authors:
Kumar, N; Dhar, SK; Thamizhavel, A; Bonville, P; Manfrinetti, P Author Full Names: Kumar, Neeraj; Dhar, S. K.; Thamizhavel, A.; Bonville, P.; Manfrinetti, P.
Source:
PHYSICAL REVIEW B 81 (14): Art. No. 144414 APR 1 2010
Abstract:
Single crystals of EuPtSi3, which crystallize in the BaNiSn3-type crystal structure, have been grown by high-temperature solution growth method using molten Sn as the solvent. EuPtSi3 which lacks the inversion symmetry and has only one Eu site in the unit cell is found to be an antiferromagnet with two successive magnetic transitions at T-N1=17 K and T-N2=16 K, as inferred from magnetic susceptibility, heat capacity, and Eu-151 Mossbauer measurements. The isothermal magnetization data for H parallel to[001] reveal a metamagnetic transition at a critical field H-c=1 T. The magnetization saturates to a moment value of 6.43 mu(B)/Eu above 5.9 T (9.2 T) for H parallel to[001] ([100]), indicating that these fields are spin-flip fields for the divalent Eu moments along the two axes. The origin of this anisotropic behavior is discussed. A magnetic (H and T) phase diagram has been constructed from the temperature dependence of isothermal magnetization data. The reduced jump in the heat capacity at T-N1 indicates a transition to an incommensurate, amplitude modulated antiferromagnetic structure. The shape of the hyperfine field split Mossbauer spectrum at T-N1 provides additional support for the proposed nature of this magnetic transition.
Title:
Incommensurate spin correlations induced by magnetic Fe ions substituted into overdoped Bi1.75Pb0.35Sr1.90CuO6+z
Authors:
Hiraka, H; Hayashi, Y; Wakimoto, S; Takeda, M; Kakurai, K; Adachi, T; Koike, Y; Yamada, I; Miyazaki, M; Hiraishi, M; Takeshita, S; Kohda, A; Kadono, R; Tranquada, JM; Yamada, K Author Full Names: Hiraka, H.; Hayashi, Y.; Wakimoto, S.; Takeda, M.; Kakurai, K.; Adachi, T.; Koike, Y.; Yamada, I.; Miyazaki, M.; Hiraishi, M.; Takeshita, S.; Kohda, A.; Kadono, R.; Tranquada, J. M.; Yamada, K.
Source:
PHYSICAL REVIEW B 81 (14): Art. No. 144501 APR 1 2010
Abstract:
Spin correlations in the overdoped region of Bi1.75Pb0.35Sr1.90CuO6+z have been explored with Fe-doped single crystals characterized by neutron scattering, muon-spin-rotation spectroscopy, and magnetic-susceptibility measurements. Static incommensurate spin correlations induced by the Fe spins are revealed by elastic neutron scattering. The resultant incommensurability delta is unexpectedly large (similar to 0.2 r.l.u.), as compared with delta similar to 1/8 in overdoped superconductor La2-xSrxCuO4. Intriguingly, the large delta in this overdoped region is close to the hole concentration p. This result is reminiscent of the delta approximate to p trend observed in underdoped La2-xSrxCuO4; however, it is inconsistent with the saturation of delta in the latter compound in the overdoped regime. While our findings in Fe-doped Bi1.75Pb0.35Sr1.90CuO6+z support the commonality of incommensurate spin correlations in high-T-c cuprate superconductors, they also s! uggest that the magnetic response might be dominated by a distinct mechanism in the overdoped region.
Title:
Phase diagram of H-2 adsorbed on graphene
Authors:
Gordillo, MC; Boronat, J Author Full Names: Gordillo, M. C.; Boronat, J.
Source:
PHYSICAL REVIEW B 81 (15): Art. No. 155435 APR 15 2010
Abstract:
The phase diagram of the first layer of H-2 adsorbed on top of a single graphene sheet has been calculated by means of a series of diffusion Monte Carlo simulations. We have found that, as in the case of He-4, the ground state of molecular hydrogen is a root 3 x root 3 commensurate structure, followed, upon a pressure increase, by an incommensurate triangular solid. A striped phase of intermediate density was also considered and found lying on top of the equilibrium curve separating both commensurate and incommensurate solids.
Title:
Periodic step arrays on the aperiodic i-Al-Pd-Mn quasicrystal surface at high temperature
Authors:
Sato, Y; Unal, B; Lograsso, TA; Thiel, PA; Schmid, AK; Duden, T; Bartelt, NC; McCarty, KF Author Full Names: Sato, Y.; Unal, B.; Lograsso, T. A.; Thiel, P. A.; Schmid, A. K.; Duden, T.; Bartelt, N. C.; McCarty, K. F.
Source:
PHYSICAL REVIEW B 81 (16): Art. No. 161406 APR 15 2010
Abstract:
We have observed the configuration and motion of surface steps on the aperiodic icosahedral (i-) Al-Pd-Mn quasicrystal using low-energy electron microscopy and scanning tunneling microscopy. As the quasicrystal is cooled from high temperature, bulk vacancies migrate to the surface causing the surface to be etched. Surprisingly, this etching occurs by two types of steps with different heights moving in different directions with different velocities. The steady-state surface morphology is a uniformly spaced rhomboidal step network. This network requires that the layer stacking near the surface deviates from the bulk quasicrystal stacking.
Title:
Quantum critical behavior of antiferromagnetic itinerant systems with van Hove singularities
Authors:
Katanin, A Author Full Names: Katanin, A.
Source:
PHYSICAL REVIEW B 81 (16): Art. No. 165118 APR 15 2010
Abstract:
The interplay of magnetic and superconducting fluctuations in two-dimensional systems with van Hove singularities in the electronic spectrum is considered within the functional renormalization-group (fRG) approach. While the fRG flow has to be stopped at a certain minimal temperature T-RG(min), we study temperature dependence of magnetic and superconducting susceptibilities below T-RG(min) to obtain the crossover temperatures to the regime with strong magnetic and superconducting fluctuations. Near half filling we obtain the largest crossover temperature, corresponding to a regime with strong commensurate magnetic fluctuations, which is replaced by a regime with strong incommensurate fluctuations further away from half filling. With further decreasing density the system undergoes quantum phase transition from incommensurate to paramagnetic phase. Similarly to results of Hertz-Moriya-Millis approach, the temperature dependence of the inverse (in-commensurate) magnetic susceptibility at the magnetic quantum-critical point is found almost linear in temperature.
Title:
Classification and Interpretation of the Polarization of Multiferroic RMn2O5
Authors:
Fukunaga, M; Noda, Y Author Full Names: Fukunaga, Mamoru; Noda, Yukio
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (5): Art. No. 054705 MAY 2010
Abstract:
We have collected and compared temperature-dependent polarization data of multiferroic RMn2O5 for 11 kinds of rare earths (R) from the literature and our own measurements. Although the reported data are inconsistent, it was found that the maximum polarization values for R = Y, Dy, Ho, Er, and Tm are almost equal above 30 K except for the phase transition temperature where the polarization disappears. The findings suggest a standard polarization value for RMn2O5 of 100-120 nC/cm(2) at 30 K in a commensurate magnetic (CM) phase. We discuss the nature and issues of the measured polarization of RMn2O5 from the data and our detailed measurement results for YMn2O5. Temperature-dependent ferroelectric hysteresis loops of YMn2O5 by the double-wave method reveal that an antiferroelectric-like high-temperature incommensurate magnetic (ICM) phase and a ferroelectric low-temperature ICM phase, while the intermediate CM phase is ferrielectric.
Title:
Microstructural and mechanical study of an Al matrix composite reinforced by Al-Cu-Fe icosahedral particles
Authors:
Laplanche, G; Joulain, A; Bonneville, J; Gauthier-Brunet, V; Dubois, S; El Kabir, T Author Full Names: Laplanche, Guillaume; Joulain, Anne; Bonneville, Joel; Gauthier-Brunet, Veronique; Dubois, Sylvain; El Kabir, Tarik
Source:
JOURNAL OF MATERIALS RESEARCH 25 (5): 957-965 MAY 2010
Abstract:
In this study, we produced an Al matrix composite material reinforced by Al-Cu-Fe particles of the icosahedral phase. The composite material was prepared using a hot isostatic pressure technique at T = 673 K and P = 180 MPa. The mechanical properties were investigated by compression tests performed at constant strain rate over the temperature range 290-823 K. The results show a vigorous strengthening effect resulting from the reinforcement particles. Strengthening is attributed to two main contributions arising from load transfer between the Al matrix and the reinforcement particles and from plastic deformation of the Al grains. The present results are compared with those obtained in a previous work on an Al-based composite reinforced by Al-Cu-Fe particles of the omega-tetragonal phase.

Update: 6-May-2010

Title:
Structural and magnetic modulations in CaCuxMn7-xO12
Authors:
Slawinski, W; Przenioslo, R; Sosnowska, I; Bieringer, M Author Full Names: Slawinski, W.; Przenioslo, R.; Sosnowska, I.; Bieringer, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (18): Art. No. 186001 MAY 12 2010
Abstract:
Low temperature atomic position modulations and magnetic moment modulations are reported for CaCuxMn7-xO12 (x = 0.0, 0.1 and 0.23) using neutron powder diffraction. Both modulations are described with propagation vectors (0, 0, q) parallel to the c-axis in the hexagonal setting. The present neutron diffraction studies confirm the quantitative model describing the atomic position modulations in CaCuxMn(7-x)O(12) (x = 0.0 and 0.1) as derived from synchrotron based powder x-ray diffraction studies (Slawinski et al 2009 Acta Crystallogr. B 65 535). Neutron diffraction studies confirm the relation between the atomic position modulation length L-p and the magnetic modulation length L-m = 2L(p) between 50 K and the Neel temperature T-N. CaCuxMn(7-x)O(12) (x = 0.1 and 0.23) shows a magnetic phase transition near 50 K associated with considerable changes of the magnetic modulation length and the magnetic coherence length, similar to that observed in the parent CaMn7O12.
Title:
Magnetic properties of Bi(Fe1-x M (x) )O-3 (M = Mn, Ti)
Authors:
Troyanchuk, IO; Chobot, AN; Mantytskaya, OS; Tereshko, NV Author Full Names: Troyanchuk, I. O.; Chobot, A. N.; Mantytskaya, O. S.; Tereshko, N. V.
Source:
INORGANIC MATERIALS 46 (4): 424-428 APR 2010
Abstract:
The magnetic properties of Bi(Fe1 - x M (x) )O-3(M = Mn, Ti) solid solutions have been studied in magnetic fields of up to 11.2 x 10(3) kA/m, and the composition stability range of the R3c ferroelectric phase has been determined. The results indicate that partial Ti4+ substitution for Fe3+ leads to a transition from a modulated antiferromagnetic state to a homogeneous weakly ferromagnetic ferroelectric state (x = 0.08), whereas the Bi(Fe (1-x) (3+) Mn (x) (3+) )O-3 solid solutions do not exhibit weak ferromagnetism. Charge compensation in is assumed to be ensured by cation vacancies.
Title:
Short-range magnetic order, irreversibility and giant magnetoresistance near the triple points in the (x, T) magnetic phase diagram of ZrMn6Sn6-xGax
Authors:
Mazet, T; Ihou-Mouko, H; Mareche, JF; Malaman, B Author Full Names: Mazet, T.; Ihou-Mouko, H.; Mareche, J. -F.; Malaman, B.
Source:
EUROPEAN PHYSICAL JOURNAL B 74 (4): 487-497 APR 2010
Abstract:
We have studied pseudo-layered ZrMn6Sn6-xGax intermetallics (0.55 a parts per thousand currency sign x a parts per thousand currency sign 0.81) using magnetic, magnetoresistivity and powder neutron diffraction measurements. All the alloys studied have magnetic ordering temperatures in the 450-490 K temperature range. They present complex temperature-dependent partially disordered magnetic structures whose ferromagnetic component develops upon increasing the Ga content. ZrMn6Sn6-xGax alloys with x a parts per thousand currency sign 0.69 are essentially collinear antiferromagnets at high-temperature and adopt antifan-like arrangements at low temperature. For x a parts per thousand yen 0.75, the alloys order ferromagnetically and evolve to a fan-like structure upon cooling. The intermediate compositions (x = 0.71 and 0.73) present a canted fan-like order at high temperature and another kind of antifan-like arrangement at low temperature. The degree of short-range order tends to increase upon approaching the intermediate compositions. The (x, T) phase diagram contains two triple points (x similar to 0.70; T similar to 460 K and x similar to 0.74; T similar to 455 K), where the paramagnetic, an incommensurate and a commensurate phases meet, which possess some of the features of Lifshitz point. Irreversibilities manifest in the low-temperature magnetization curves at the antifan-fan or fan-ferromagnetic boundaries as well as inside the fan region. Giant magnetoresistance is observed, even above room temperature.
Title:
Elastic analysis of an elliptic notch in quasicrystals of point group 10 subjected to shear loading
Authors:
Li, LH Author Full Names: Li Lian-He
Source:
CHINESE PHYSICS B 19 (4): Art. No. 046101 APR 2010
Abstract:
Based on the stress potential and complex variable function method, this paper makes an elastic analysis of an elliptic notch subjected to uniform shear stress at infinity in quasicrystals with point group 10. With the aid of conformal transformation, an exact solution for the elliptic notch of the quasicrystals is obtained. The solution of the mode II Griffith crack as a special case is constructed. The stress intensity factor and energy release rate have been also obtained as a direct result of the crack solution.
Title:
Magnetization plateau and incommensurate spin modulation in Ca3Co2O6
Authors:
Zhao, Y; Gong, SS; Li, W; Su, G Author Full Names: Zhao, Yang; Gong, Shou-Shu; Li, Wei; Su, Gang
Source:
APPLIED PHYSICS LETTERS 96 (16): Art. No. 162503 APR 19 2010
Abstract:
The magnetic properties of a trigonal prism unit of the spin-2 frustrated compound Ca3Co2O6 are studied by means of the density-matrix renormalization group method. A magnetization plateau at m(s)/3 (m(s) is the saturation magnetization) with ferrimagnetic structure is observed. By fitting the experimental data of magnetic curve, an estimation of the couplings gives J(1)=-26.84 K, J(2)=0.39 K, and J(3)=0.52 K. The local magnetic moments are unveiled to exhibit an incommensurate sinusoidally modulation along the three chains of the trigonal prism, which gives a strong theoretical support to the experimentally observed incommensurate partially disordered antiferromagnetic state for Ca3Co2O6. The present result suggests that the modulation indeed originates from the competition of antiferromagnetic and ferromagnetic couplings. (C) 2010 American Institute of Physics. [doi:10.1063/1.3413931]
Title:
OXIDATION BEHAVIOR OF THE PHASE ICOSAEDRAL QUASICRISTAL Al-62,Al- 2 Cu-25,Cu-3 Fe-12,Fe-5
Authors:
Nascimento, L; Agostinho, LCL; Cavalcanti, BF Author Full Names: Nascimento, L.; Agostinho, L. C. L.; Cavalcanti, B. F.
Source:
ACTA MICROSCOPICA 18 (3): 295-303 2009
Abstract:
Oxidation behavior of the quasicrystalline alloy with nominal composition Al-62,Al- 2 Cu-25,Cu-3 Fe-12,Fe-5 was analyzed under different conditions of duration of thermal treatment. It was used X - Ray Diffratometry to follow the alloy phases evolution and Scanning Electron Microscopy (SEM) to analyze the quasicrystal morphology and oxidation. Below 750 degrees C the alloy shows intermetallic phases with associations of the alloy elements and above 675 degrees C the crystalline phase is stable. In icosahedral phase, aluminum oxidation forms a dense passivating layer at the outmost surface of the quasicrystal which causes depletion in both copper and iron. In the dense layer it was observed not only the presence of alumina, gamma - Al2O3, but also the formation of hematite.

Update: 15-Apr-2010

Title:
Microstructures and Phase Transformation of Al-Rased composite materials Reinforced by Al-Cu-Co Decagonal Quasicrystalline Particles
Authors:
Zhu, M; Yang, GC; Cheng, SL; Wang, BH; Zhou, YH Author Full Names: Zhu Man; Yang Gencang; Cheng Suling; Wang Binghui; Zhou Yaohe
Source:
RARE METAL MATERIALS AND ENGINEERING 38 (9): 1584-1588 SEP 2009
Abstract:
Al65Cu15Co20 decagonal quasicrystalline alloys were prepared by an arc-melting furnace. The aluminium-based composites were fabricated by using the Al65Cu15Co20 decagonal quasicrystalline particles as reinforcing phase and Al-4.5 wt%Cu alloy as matrix with mechanical stirring. The microstructures, the phase composition, and the distribution of Al65Cu15Co20 were characterisied by XRD, SEM, SEM and EDS for the Al65Cu15Co20 quasicrystalline alloys and the reinforced composites. And the morphology, chemical composition and structure changes of the quasicrystalline particles before and after adding to the melt were also analysised. As the interdiffusion occurs between the quasicrystalline particles and the melt, the quasicrystalline particles can not exist stably in the melt. The morphology of the particles turns from inregular polygons to block and lath-like in shape as following: D-Al62.10Cu17.46Co20.44 -> theta-Al79.55Cu1.10Co19.32 after adding the quasicrystalline particles into the melt. During the solidification process, the theta phase distributes uniformly along the grain boundaries because of the "interfacial pushing effect".
Title:
Evidence for a Magnetically Driven Superconducting Q Phase of CeCoIn5
Authors:
Kenzelmann, M; Gerber, S; Egetenmeyer, N; Gavilano, JL; Strassle, T; Bianchi, AD; Ressouche, E; Movshovich, R; Bauer, ED; Sarrao, JL; Thompson, JD Author Full Names: Kenzelmann, M.; Gerber, S.; Egetenmeyer, N.; Gavilano, J. L.; Straessle, Th; Bianchi, A. D.; Ressouche, E.; Movshovich, R.; Bauer, E. D.; Sarrao, J. L.; Thompson, J. D.
Source:
PHYSICAL REVIEW LETTERS 104 (12): Art. No. 127001 MAR 26 2010
Abstract:
We have studied the magnetic order inside the superconducting phase of CeCoIn5 for fields along the [1 0 0] crystallographic direction using neutron diffraction. We find a spin-density wave order with an incommensurate modulation Q = (q, q, 1/2) and q = 0.45(1), which within our experimental uncertainty is indistinguishable from the spin-density wave found for fields applied along [1 - 10]. The magnetic order is thus modulated along the lines of nodes of the d(x2-y2) superconducting order parameter, suggesting that it is driven by the electron nesting along the superconducting line nodes. We postulate that the onset of magnetic order leads to reconstruction of the superconducting gap function and a magnetically induced pair density wave.
Title:
Incommensurate spin-density-wave order in quasi-one-dimensional metallic antiferromagnet NaV2O4
Authors:
Nozaki, H; Sugiyama, J; Mansson, M; Harada, M; Pomjakushin, V; Sikolenko, V; Cervellino, A; Roessli, B; Sakurai, H Author Full Names: Nozaki, Hiroshi; Sugiyama, Jun; Mansson, Martin; Harada, Masashi; Pomjakushin, Vladimir; Sikolenko, Vadim; Cervellino, Antonio; Roessli, Bertrand; Sakurai, Hiroya
Source:
PHYSICAL REVIEW B 81 (10): Art. No. 100410 MAR 2010
Abstract:
To clarify the reason for the coexistence of long-range antiferromagnetic order and metallic conductivity for NaV2O4, in which the V ions form quasi-one-dimensional zigzag chains along the b axis, we have performed a neutron-scattering experiment using a powder sample down to 20 K. The analysis of the magnetic powder diffractogram below T-N=140 K demonstrates the formation of an incommensurate spin-density-wave order with k=(0,0.191,0); the ordered moment was estimated as (0,0,0.77 mu(B)) at 20 K.
Title:
Valence band structure of the icosahedral Ag-In-Yb quasicrystal
Authors:
Sharma, HR; Simutis, G; Dhanak, VR; Nugent, PJ; Cui, C; Shimoda, M; McGrath, R; Tsai, AP; Ishii, Y Author Full Names: Sharma, H. R.; Simutis, G.; Dhanak, V. R.; Nugent, P. J.; Cui, C.; Shimoda, M.; McGrath, R.; Tsai, A. P.; Ishii, Y.
Source:
PHYSICAL REVIEW B 81 (10): Art. No. 104205 MAR 2010
Abstract:
The valence band structure of the icosahedral (i) Ag-In-Yb quasicrystal, which is isostructural to the binary i-Cd-Yb system, is investigated by ultraviolet photoemission spectroscopy (UPS). Experimental results are compared with electronic-structure calculations of a cubic approximant of the same phase. UPS spectra from the fivefold, threefold, and twofold i-Ag-In-Yb surfaces reveal that the valence band near to the Fermi level is dominated by Yb 4f-derived states, in agreement with calculations. The spectra also exhibit peaks which are surface core level shifted, caused by changes in the electronic structure in surface layers. Calculations yield a pseudogap in the density of states due to a hybridization of the Yb 5d band with the Ag 5p and In 5p bands. Both experimental and calculated band features are very similar to those of Cd-Yb. The modification of the band structure after surface treatment by sputtering and by oxidation is also studied. Additionally, the work ! function of i-Ag-In-Yb measured from the width of UPS spectrum is found to be almost unaffected by surface orientation, but increases after sputtering or oxidation.
Title:
Static and dynamical susceptibility of LaO1-xFxFeAs
Authors:
Monni, M; Bernardini, F; Profeta, G; Sanna, A; Sharma, S; Dewhurst, JK; Bersier, C; Continenza, A; Gross, EKU; Massidda, S Author Full Names: Monni, M.; Bernardini, F.; Profeta, G.; Sanna, A.; Sharma, S.; Dewhurst, J. K.; Bersier, C.; Continenza, A.; Gross, E. K. U.; Massidda, S.
Source:
PHYSICAL REVIEW B 81 (10): Art. No. 104503 MAR 2010
Abstract:
The mechanism of superconductivity and magnetism and their possible interplay have recently been under debate in pnictides. A likely pairing mechanism includes an important role of spin fluctuations and can be expressed in terms of the magnetic susceptibility chi. The latter is therefore a key quantity in the determination of both the magnetic properties of the system in the normal state and of the contribution of spin fluctuations to the pairing potential. A basic ingredient to obtain chi is the independent-electron susceptibility chi(0). Using LaO1-xFxFeAs as a prototype material, in this report we present a detailed ab initio study of chi(0)(q, omega) as a function of doping and of the internal atomic positions. The resulting static chi(0)(q, 0) is consistent with both the observed M-point-related magnetic stripe phase in the parent compound and with the existence of incommensurate magnetic structures predicted by ab initio calculations upon doping.
Title:
Structure of the (010) surface of the orthorhombic complex metallic alloy T-Al-3(Mn,Pd)
Authors:
Deniozou, T; Addou, R; Shukla, AK; Heggen, M; Feuerbacher, M; Krajci, M; Hafner, J; Widmer, R; Groning, O; Fournee, V; Dubois, JM; Ledieu, J Author Full Names: Deniozou, Th.; Addou, R.; Shukla, A. K.; Heggen, M.; Feuerbacher, M.; Krajci, M.; Hafner, J.; Widmer, R.; Groening, O.; Fournee, V.; Dubois, J. -M.; Ledieu, J.
Source:
PHYSICAL REVIEW B 81 (12): Art. No. 125418 MAR 2010
Abstract:
The atomic and electronic structures of the (010) surface of the T-Al-3(Mn,Pd) complex metallic alloy is investigated by means of low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), x-ray photoelectron diffraction (XPD), and ab initio calculations. While structural imperfections are observed at the surface and out of the various possible terminations, the puckered P2 layer is identified as the only surface termination, thus pointing out the existence of a well-defined minimum in the surface energy landscape. The measured step heights correspond to distances between identical planes along the [010] direction in the bulk model, i.e., b/2. A bias dependency of the STM topography is found. The XPD and LEED patterns confirm the pseudotenfold symmetry of the sample. XPS and UPS show a more metallic signature of the T phase compared to Al-based quasicrystalline phases.
Title:
Incommensurate magnetic order and phase separation in the two-dimensional Hubbard model with nearest- and next-nearest-neighbor hopping
Authors:
Igoshev, PA; Timirgazin, MA; Katanin, AA; Arzhnikov, AK; Irkhin, VY Author Full Names: Igoshev, P. A.; Timirgazin, M. A.; Katanin, A. A.; Arzhnikov, A. K.; Irkhin, V. Yu.
Source:
PHYSICAL REVIEW B 81 (9): Art. No. 094407 MAR 1 2010
Abstract:
We consider the ground-state magnetic phase diagram of the two-dimensional Hubbard model with nearest- and next-nearest-neighbor hopping in terms of electronic density and interaction strength. We treat commensurate ferromagnetic and antiferromagnetic as well as incommensurate (spiral) magnetic phases. The first-order magnetic transitions with changing chemical potential, resulting in a phase separation (PS) in terms of density, are found between ferromagnetic, antiferromagnetic, and spiral magnetic phases. We argue that PS has a dramatic influence on the phase diagram in the vicinity of half-filling. The results imply possible interpretation of the unusual behavior of magnetic properties of single-layer cuprates in terms of PS between collinear and spiral magnetic phases. The relevance of our results to the magnetic properties of the ruthenates is also discussed.
Title:
Single magnetic chirality in the magnetoelectric NdFe3((BO3)-B-11)(4)
Authors:
Janoschek, M; Fischer, P; Schefer, J; Roessli, B; Pomjakushin, V; Meven, M; Petricek, V; Petrakovskii, G; Bezmaternikh, L Author Full Names: Janoschek, M.; Fischer, P.; Schefer, J.; Roessli, B.; Pomjakushin, V.; Meven, M.; Petricek, V.; Petrakovskii, G.; Bezmaternikh, L.
Source:
PHYSICAL REVIEW B 81 (9): Art. No. 094429 MAR 1 2010
Abstract:
We have performed an extensive study of single crystals of the magnetoelectric NdFe3 ((BO3)-B-11)(4) by means of a combination of single-crystal neutron diffraction and spherical neutron polarimetry. Our investigation did not detect significant deviations at low temperatures from space group R32 concerning the chemical structure. With respect to magnetic ordering our combined results demonstrate that in the commensurate magnetic phase below T-N approximate to 30 K all three magnetic Fe moments and the magnetic Nd moment are aligned ferromagnetically in the basal hexagonal plane but align antiferromagnetically between adjacent planes. The phase transition to the low-temperature incommensurate (IC) magnetic structure observed at T-IC approximate to 13.5 K appears to be continuous. By means of polarized neutron studies it could be shown that in the incommensurate magnetic phase the magnetic structure of NdFe3((BO3)-B-11)(4) is transformed into a long-period antiferromagnetic helix with single chirality. Close to the commensurate-incommensurate phase transition third-order harmonics were observed, which in addition indicate the formation of magnetic solitons.
Title:
Theoretical studies of the incommensurate magnetic structure of a heavy fermion system: CeRhIn5
Authors:
Bjorkman, T; Lizarraga, R; Bultmark, F; Eriksson, O; Wills, JM; Bergman, A; Andersson, PH; Nordstrom, L Author Full Names: Bjorkman, Torbjorn; Lizarraga, Raquel; Bultmark, Fredrik; Eriksson, Olle; Wills, John M.; Bergman, Anders; Andersson, Per H.; Nordstrom, Lars
Source:
PHYSICAL REVIEW B 81 (9): Art. No. 094433 MAR 1 2010
Abstract:
We have investigated the electronic structure and the incommensurate magnetic configuration of the pressure-induced superconductor CeRhIn5. Noncollinear first-principles calculations were performed in the local-density approximation plus U scheme. The observed magnetic configuration is described accurately in our calculations, especially considering the minute energy scale which is relevant (microelectron volt). The band structure and Fermi surfaces were investigated and nesting was found to be responsible for the complex noncollinear magnetic state of CeRhIn5.
Title:
Surface plasmon enhanced transmission through gold planar crystals with various aperture arrangements
Authors:
Xue, J; Dong, BQ; Wang, X; Yang, R; Xu, ZC; Chen, YF; Huq, E; Zeng, W; Qu, XP; Liu, R Author Full Names: Xue, Jing; Dong, Bi-Qin; Wang, Xu; Yang, Rong; Xu, Zhen-Cheng; Chen, Yifang; Huq, Ejaz; Zeng, Wei; Qu, Xin-Ping; Liu, Ran
Source:
MICROELECTRONIC ENGINEERING 87 (5-8): 1340-1343 MAY-AUG 2010
Abstract:
Various planar crystals in gold films are fabricated by focused ion beam (FIB) technique. We theoretically and experimentally show that the enhanced transmission through the planar crystals is dependent on the nanoaperture's arrangement and this extraordinary transmission can be attributed to the excitation of surface plasmon polaritons (SPPs) on the metal-air interface. In contrast to other crystals, the quasicrystal exhibits broadband plasmonic resonances. Near-field optical images provide direct evidence for surface plasmon-mediated enhanced transmission in a wide wavelength range through the gold quasicrystal. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Study of Biological Effect of MC3T3-E1 in vitro by A Novel 2.4GHz Radiofrequency Electromagnetic Field Exposure System
Authors:
Cherng, S; Teng, HC Author Full Names: Cherng, Shen; Teng, Hsien-Chiao
Source:
LIFE SCIENCE JOURNAL-ACTA ZHENGZHOU UNIVERSITY OVERSEAS EDITION 6 (4): 41-49 2009
Abstract:
A 2.4GHz mobile-phone/blue-tooth radiofrequency electromagnetic field (RF-EMF) exposure system for cellular experiment MC3T3-E1 in vitro was designed to study the biological effects and demonstrated in this report. Experimental results have illustrated the observation of signal at 14Hz through algorithm analysis of the measured near field magnetic fluctuation and the modulation of gap junction intercellular communication (GJIC) within mouse osteoblast cells (MC3T3-E1) under RF-EMF power density at 0.3mWatt/cm(2). [Life Science Journal. 2009; 6(4): 41 49] (ISSN: 1097-8135).
Title:
Influence of cooling rate and cerium addition on rapidly solidified Al-TM alloys
Authors:
Michalcova, A; Vojtech, D; Schumacher, G; Novak, P; Klementova, M; Serak, J; Mudrova, M; Valdaufova, J Author Full Names: Michalcova, A.; Vojtech, D.; Schumacher, G.; Novak, P.; Klementova, M.; Serak, J.; Mudrova, M.; Valdaufova, J.
Source:
KOVOVE MATERIALY-METALLIC MATERIALS 48 (1): 1-7 2010
Abstract:
Rapidly solidified alloys, based on an aluminium-transition metal (TM) system, are promising structural materials. They show good mechanical properties and excellent thermal stability, which is caused by the very fine nanostructure of these materials and by the presence of nonequilibrium intermetallic phases. Influence of the cooling rate and Ce addition on properties of Al-5.5Ce-3Fe-1.5Ti alloy that was prepared by the melt spinning method was studied in this work. It was shown that formation of the quasicrystalline phase depends on the cooling rate during melt spinning. The addition of a few weight percents of Ce modifies phase composition of the alloy and stabilizes quasicrystals at elevated temperatures. However, the influence of Ce addition on hardness was not observed.
Title:
Anisotropic Thermal Diffusivity and Conductivity of La-Doped Strontium Niobate Sr2Nb2O7
Authors:
Sparks, TD; Fuierer, PA; Clarke, DR Author Full Names: Sparks, Taylor D.; Fuierer, Paul A.; Clarke, David R.
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY 93 (4): 1136-1141 APR 2010
Abstract:
The thermal diffusivity of the La-doped layered perovskite Sr2Nb2O7 parallel and perpendicular to the perovskite layers is reported from room temperature up to 1000 degrees C. The anisotropy persists through an incommensurate-normal ferroelectric phase transformation at 215 degrees C and up to 1000 degrees C, the maximum temperature of our measurements. The thermal conductivity perpendicular to the perovskite layers, derived from the diffusivity in the same direction, calculated using the density and measured heat capacity, has a constant value of 1.05 +/- 0.05 W/mK up to 1000 degrees C. Possible explanations for the low thermal conductivity and anisotropy are described.
Title:
Structurally complex metallic coatings in the Al-Cu system and their orientation relationships with an icosahedral quasicrystal
Authors:
Duguet, T; Kenzari, S; Demange, V; Belmonte, T; Dubois, JM; Fournee, V Author Full Names: Duguet, Thomas; Kenzari, Samuel; Demange, Valerie; Belmonte, Thierry; Dubois, Jean-Marie; Fournee, Vincent
Source:
JOURNAL OF MATERIALS RESEARCH 25 (4): 764-772 APR 2010
Abstract:
Quasicrystals have been identified as alloys possessing unusually low surface energy. This results in poor adhesion properties of quasicrystalline coatings when deposited on metallic substrates, hindering the development of these new materials for technological applications. Here we investigate the possible use of complex Al-Cu metallic phases as interface layers to accommodate the structural and electronic mismatch between a quasicrystalline coating and a metallic substrate and improve adhesion. First, we show that all stable low-temperature phases of the Al-Cu system can be grown as thin films using DC magnetron sputtering. Among the various possible phases, we select the gamma-brass gamma-Al4Cu9 as a promising candidate for the interface layer. Then the gamma-Al4Cu9 phase is grown on the fivefold surface of an icosahedral (i-) Al-Pd-Mn quasicrystal. The interface is investigated by transmission electron microscopy and shows a clear texturing of the film. The gra! ins exhibit rotational epitaxy with the substrate. We find that the interface is mainly composed of a beta-phase of unknown chemical composition and sometimes exhibits gamma grains in direct contact with the quasicrystalline substrate. Occasionally, we observe a fourth phase at the beta/gamma interface, identified as beta(1), possessing a lattice parameter a(beta 1) equal to 2a(beta) and 2/3a(gamma).
Title:
The effect of thermal treatment on the magnetic state and cluster-related disorder of icosahedral Al-Pd-Mn quasicrystals
Authors:
Jaglicic, Z; Jagodic, M; Grushko, B; Zijlstra, ES; Weber, T; Steurer, W; Dolinsek, J Author Full Names: Jaglicic, Z.; Jagodic, M.; Grushko, B.; Zijlstra, E. S.; Weber, Th.; Steurer, W.; Dolinsek, J.
Source:
INTERMETALLICS 18 (4): 623-632 APR 2010
Abstract:
The evolution of the magnetic state and the cluster-related disorder upon thermal treatment of the icosahedral i-Al-Pd-Mn quasicrystals were studied on single-crystalline samples subjected to different thermal annealing sequences involving short and long annealing times and slow or fast cooling modes. In this way, thermal equilibration of the samples was systematically changed by varying the amount of vacancies and thermal strains. The results show that different thermal treatments can reduce or increase reversibly the paramagnetic magnetization of the i-Al-Pd-Mn samples of nominally the same composition by a factor up to 26. Magnetic susceptibility and magnetization measurements have demonstrated comparable importance of the vacancies and thermal strains on the size of the mean effective magnetic moment per Mn atom. While the reduced vacancy concentration reduces the mean effective moment, thermal strains induced by rapid cooling increase it. Theoretical ab-initio calculations of the effect of vacancies and thermal strains on the magnetic properties of a periodic approximant model to the i-Al-Pd-Mn phase predict that vacancies at specific Al sites introduce magnetic moments at the Mn sites, which are otherwise nonmagnetic in the perfect structure. Removal of thermal strains by relaxation of the structure containing vacancies acts in the opposite way by decreasing the moments. X-ray diffraction experiments with full reciprocal space sampling revealed that the cluster-related disorder cannot be improved noticeably by annealing at either 800 degrees C or 600 degrees C even for annealing times as long as three months, suggesting that this disorder may be intrinsic to the i-Al-Pd-Mn phase, needed for the electronic or entropic stabilization of the structure. (C) 2009 Elsevier Ltd. All rights reserved.
Title:
NEPHELINE: STRUCTURE OF THREE SAMPLES FROM THE BANCROFT AREA, ONTARIO, OBTAINED USING SYNCHROTRON HIGH-RESOLUTION POWDER X-RAY DIFFRACTION
Authors:
Antao, SM; Hassan, I Author Full Names: Antao, Sytle M.; Hassan, Ishmael
Source:
CANADIAN MINERALOGIST 48 (1): 69-80 FEB 2010
Abstract:
The crystal structure of three samples of nepheline (ideally, K2Na6[Al8Si8O32]) from the Bancroft area of Ontario (1a, b: Egan Chute, 2: Nephton, and 3: Davis Hill), each with different types of superstructure reflections, has been studied using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinement. The samples have different origins. The structure was refined in space group P6(3). The R-F(2) index, number of unique observed reflections, pseudohexagonal subcell parameters, and site-occupancy factor (sof) for the K site are as follows: Sample 1b: R-F(2) = 0.0433, N-obs = 1399, a = 9.99567(1), c = 8.37777(1) angstrom, V = 724.907(2) angstrom(3), and K (sof) = 0.716(1). Sample 2: R-F(2) = 0.0669, N-obs = 1589, a = 10.00215(1), c = 8.38742(1) angstrom, V = 726.684(1) angstrom(3), and K (sof) = 0.920(1). Sample 3: R-F(2) = 0.0804, N-obs = 1615, a = 9.99567(1), c = 8.37873(1) angstrom, V = 724.991(1) angstrom(3), and K (sof) = 0.778(2). Sample 2 has the largest sof for K and the largest volume. The satellite reflections in the three nepheline samples were observed in the HRPXRD traces and give rise to different incommensurate superstructures. The Al and Si atoms in the T-3 and T-4 sites are ordered differently in the three samples, which may indicate the presence of a domain structure based on Al-Si order. The positions for the Al and Si atoms were interchanged in two samples because of the resulting < T-O > distances. The slight excess of Si over Al atoms, characteristically encountered in well-analyzed samples of nepheline, is reflected in the < T-O > distances.
Title:
The incommensurately modulated structures of natural natrite at 120 and 293 K from synchrotron X-ray data
Authors:
Arakcheeva, A; Bindi, L; Pattison, P; Meisser, N; Chapuis, G; Pekov, I Author Full Names: Arakcheeva, Alla; Bindi, Luca; Pattison, Philip; Meisser, Nicolas; Chapuis, Gervais; Pekov, Igor
Source:
AMERICAN MINERALOGIST 95 (4): 574-581 APR 2010
Abstract:
The incommensurately modulated structure of the mineral natrite has been refined for the first time. Two single-crystal grains, Lv and Kh, from two different occurrences [Mt. Karnasurt, Lovozero massif (Lv), Kola peninsula, Russia, and the pegmatite of Mt. Koashva, Khibiny massif (Kh)], have been investigated at 293 and 120 K using synchrotron X-ray data. The average structures of both minerals are identical and the basic features of the structural modulations are similar to the synthetic gamma-Na2CO3 phase previously published. The gamma (incommensurate) -> delta (lock-in) phase transition reported at low temperature for the synthetic compound was not observed down to 120 K in natural natrite. Crystal-chemical aspects, especially about the second coordination sphere for the carbon atoms, are examined to explain the different structural behaviors observed at low temperature. The possible role played by the minor isomorphous substitutions in natural na! trite specimens is also discussed.

Update: 8-Apr-2010

Title:
Structural investigation of composite phases Ba1+x[(NaxMn1-x)O-3] with x similar or equal to 2/7, 5/17 and 1/3; exotic Mn4.5+ valence
Authors:
Roussel, P; Perez, O; Quarez, E; Leligny, H; Mentre, O Author Full Names: Roussel, Pascal; Perez, Olivier; Quarez, Eric; Leligny, Henri; Mentre, Olivier
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 225 (1): 1-11 2010
Abstract:
Structural models are proposed for three composite compounds of chemical formula Ba1+x[(NaxMn1-x)O-3] (x similar or equal to 2/7, 5/17 and 1/3) by single crystal X-ray diffraction; superspace formalism is used to obtain an unified description of the three phases. The modulation affecting Ba atoms can be easily designed but the competition "occupational/displacive" modulations relating to the Mn/Na metallic columns were particularly difficult to modelize. However, the large amplitude of the displacive modulation affecting the oxygen atoms (similar or equal to +/- 0.7 angstrom) in comparison with that observed for related compounds (similar or equal to +/- 0.3 angstrom) makes it a direct consequence of the Na+ alkali insertion inside the trigonal prisms. Owing to this insertion, the Mn atoms exhibit, in the three phases, an "exotic" oxidation state of about +4.5. In addition, even if the sequence between face sharing MnO6 octahedra and NaO6 trigonal prisms can be analytically deduced from the x value, it is clear that the Na/Mn contrasts play in favour of its accurate determination through the XRD single crystal refinement.
Title:
Spin and Charge Order in the Doped Hubbard Model: Long-Wavelength Collective Modes
Authors:
Chang, CC; Zhang, SW Author Full Names: Chang, Chia-Chen; Zhang, Shiwei
Source:
PHYSICAL REVIEW LETTERS 104 (11): Art. No. 116402 MAR 19 2010
Abstract:
Determining the properties of the two-dimensional Hubbard model is an outstanding problem in physics. Applying recent advances in constrained path auxiliary-field quantum Monte Carlo techniques and simulating large rectangular supercells, we characterize the magnetic and charge properties in the ground state as a function of doping. At intermediate interaction strengths, an incommensurate spin density wave (SDW) state is found, with antiferromagnetic order and essentially homogeneous charge correlation. The wavelength of the collective mode decreases with doping, as does its magnitude. The SDW order vanishes beyond a critical doping. As the interaction is increased, the holes go from a wavelike (delocalized) to a particlelike (localized) state, and charge ordering develops which eventually evolves into stripelike states.
Title:
Quantum dislocations: the fate of multiple vacancies in two-dimensional solid He-4
Authors:
Rossi, M; Vitali, E; Galli, DE; Reatto, L Author Full Names: Rossi, M.; Vitali, E.; Galli, D. E.; Reatto, L.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (14): Art. No. 145401 APR 14 2010
Abstract:
Defects are believed to play a fundamental role in the supersolid state of He-4. We have studied solid He-4 in two dimensions (2D) as a function of the number of vacancies n(v), up to 30, inserted in the initial configuration at rho = 0.0765 angstrom(-2), close to the melting density, with the exact zero-temperature shadow path integral ground state method. The crystalline order is found to be stable also in the presence of many vacancies and we observe two completely different regimes. For small n(v), up to about 6, vacancies form a bound state and cause a decrease of the crystalline order. At larger n(v), the formation energy of an extra vacancy at fixed density decreases by one order of magnitude to about 0.6 K. It is no longer possible to recognize vacancies in the equilibrated state because they mainly transform into quantum dislocations and crystalline order is found almost independently of how many vacancies have been inserted in the initial configuration. The one-body density matrix in this latter regime shows a non-decaying large distance tail: dislocations, that in 2D are point defects, turn out to be mobile, their number is fluctuating, and they are able to induce exchanges of particles across the system mainly triggered by the dislocation cores. These results indicate that the notion of the incommensurate versus the commensurate state loses meaning for solid He-4 in 2D, because the number of lattice sites becomes ill defined when the system is not commensurate. Crystalline order is found to be stable also in 3D in the presence of up to 100 vacancies.
Title:
Characterization of microstructures obtained in wedge shaped Al-Zn-Mg ingots
Authors:
Suarez, MA; Alvarez, O; Alvarez, MA; Rodriguez, RA; Valdez, S; Juarez, JA Author Full Names: Suarez, M. A.; Alvarez, O.; Alvarez, M. A.; Rodriguez, R. A.; Valdez, S.; Juarez, J. A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 492 (1-2): 373-377 MAR 4 2010
Abstract:
The structure present in chill casting taper section of A1-5.3at.%Zn + Mg additions between 3 and 40at.%Mg have been studied by scanning electron microscopy, microanalysis and X-ray diffractometry in order to relate the impact of intermetallic phases such as the tau-Mg-32(Al,Zn)(49) obtained at low Mg-contents with an approximant phase related to quasicrystals at high Mg-contents on its electrochemical efficiency. After microstructural and electrochemical efficiency characterization, it was found that an alloy composition of A1-5.3at.%Zn-10at.%Mg showed a microstructure which consisted of alpha-Al dendrites with tau-phase precipitates showing an electrochemical efficiency of 90% fulfilling the needs for cathodic protection application of structural steels in sea water. (C) 2009 Elsevier B.V. All rights reserved.

Update: 1-Apr-2010

Title:
Transverse modulation and uniform period in Bi1-xSrxMnO3
Authors:
Nagao, M; Kimoto, K; Matsui, Y Author Full Names: Nagao, M.; Kimoto, K.; Matsui, Y.
Source:
PHYSICA B-CONDENSED MATTER 405 (7): 1686-1689 APR 1 2010
Abstract:
The crystal structures of the superstructure phases of the Bi-based manganite Bi1-xSrxMnO3 have been studied by transmission electron microscopy. On the basis of the selected area electron diffraction patterns, our crystallographic analysis revealed that the modulations of Bi1-xSrxMnO3 consist of only transverse modulation associated with the Pcnn-type symmetry, in contrast to the previously believed Ibmm-type symmetry. Moreover, our high-resolution transmission electron microscopy image indicated that a modulation with a noninteger-multiple period has a uniform period but not the mixed state of adjacent integer-multiple periods according to the lever rule. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Superspace description of the homologous series Ga2O3(ZnO)(m)
Authors:
Michiue, Y; Kimizuka, N Author Full Names: Michiue, Yuichi; Kimizuka, Noboru
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 117-129 Part 2 APR 2010
Abstract:
A unified description for the structures of the homologous series Ga2O3(ZnO)(m), gallium zinc oxide, is presented using the superspace formalism. The structures were treated as a compositely modulated structure consisting of two subsystems. One is constructed with metal ions and the other with O ions. The ideal model is given, in which the displacive modulations of ions are well described by the zigzag function with large amplitudes. Alternative settings are also proposed which are analogous to the so-called modular structures. The validity of the model has been confirmed by refinements for phases with m = 6 and m = 9 in the homologous series. A few complex phenomena in real structures are taken into account by modifying the ideal model.
Title:
Modulation functions of incommensurately modulated Cr2P2O7 studied by the maximum entropy method (MEM)
Authors:
Li, L; Schonleber, A; van Smaalen, S Author Full Names: Li, Liang; Schoenleber, Andreas; van Smaalen, Sander
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 130-140 Part 2 APR 2010
Abstract:
The maximum entropy method (MEM) has been used to determine electron density in superspace of incommensurately modulated chromium pyrophosphate from X-ray diffraction data measured by Palatinus et al. [(2006), Acta Cryst. B62, 556-566]. Chromium pyrophosphate, Cr2P2O7, contains ordered regions (83% of the volume) and regions with disorder. Analysis of the MEM density has allowed the determination of the displacive modulation functions within ordered regions. The disordered regions can be described as the alternate occupation of two conformations of the pyrophosphate group and two positions of the chromium atom, with occupational probabilities that depend continuously on the phase of modulation t. A structure model based on the interpretation of the MEM density provides a fit to the diffraction data of the same quality as the model given by Palatinus et al. (2006). The failure to find a model that better fits the data is attributed to the intrinsic inaccuracy of similar to 0.01 angstrom for positions derived from the MEM and to the difficulties in constructing an appropriate model for the anharmonic ADPs and their modulation functions from electron densities.

Update: 25-Mar-2010

Title:
Roles of Bond Alternation in Magnetic Phase Diagram of RMnO3
Authors:
Furukawa, N; Mochizuki, M Author Full Names: Furukawa, Nobuo; Mochizuki, Masahito
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (3): Art. No. 033708 MAR 2010
Abstract:
In order to investigate the nature of the antiferromagnetic structures in perovskite RMnO3, we study a Heisenberg J(1)-J(2) model with bond alternation using analytical and numerical approaches. The magnetic phase diagram which includes incommensurate spiral states and commensurate collinear states is reproduced. We discuss that the magnetic structure with spin up arrow up arrow down arrow down arrow configuration (E-type structure) and the ferroelectricity emerge cooperatively to stabilize this phase. Magnetoelastic couplings are crucial to understand the magnetic and electric phase diagram of RMnO3.
Title:
Theory of Unusual Superconducting Phase Transitions in Heavy Fermion Metals at High Magnetic Fields
Authors:
Zhuravlev, V; Maniv, T; Wosnitza, J Author Full Names: Zhuravlev, V.; Maniv, T.; Wosnitza, J.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 159 (1-2): 138-142 APR 2010
Abstract:
We present a non-perturbative theory of paramagnetically-driven superconducting (SC) phase transitions in heavy-fermion metals, which reliably determines their stable SC phases, treats properly the corresponding finite jumps of the order parameter, and can account for unusual features reported recently for this type of materials. It is found that for quasi-2D heavy-fermion metals, such as CeCoIn5, at high magnetic fields oriented perpendicular to the highly conducting planes, the effect of the Fulde-Ferrel (FF) modulation is too weak to prevent a direct first-order phase transition from the normal to the uniform SC state. For 3D heavy-fermion metals, such as URu2Si2, the FF modulation stabilizes, under a decreasing magnetic field, a non-uniform SC state via a second-order phase transition from the normal state. However, at a slightly lower field the modulated phase becomes unstable, transforming to a uniform SC state via a first-order transition.
Title:
Simulation of modulated reflections
Authors:
Lovelace, JJ; Winn, MD; Borgstahl, GEO Author Full Names: Lovelace, Jeffrey J.; Winn, Martyn D.; Borgstahl, Gloria E. O.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 285-292 Part 2 APR 2010
Abstract:
In a modulated crystal, the repeating unit is not periodic but contains a disorder of the molecules that can sometimes be described with a mathematical function. In the diffraction pattern from such a modulated crystal the standard periodic main reflections are flanked by satellite reflections. Generally, incommensurately modulated crystal diffraction cannot be simply described using integers along the reciprocal-lattice directions. However, in the special commensurate case where the satellite spacing is rational relative to the main reflections, a supercell can be used to describe the modulation. Using a supercell allows structural processing to proceed in a 'normal' fashion but with the downside of dealing with many more atoms. Not much is known about the relationship between a highly modulated macromolecular crystal and the resulting satellite intensities so in this study a modulated protein crystal was simulated using a supercell approach. The protein superstructure was modulated to varying degrees and the resultant diffraction patterns and electron-density maps were studied to understand better how a modulation may manifest itself in real protein data. In the case that was evaluated, relatively small structural modulation resulted in significant satellite intensities. Interesting cases were observed where extinguished main reflections had strong satellites.
Title:
The 5:7 Member of the Spin-Ladder Series in the Bi-Sr-Ca-Cu-O System
Authors:
Zaremba, O; Shcherban, O; Akselrud, L; Gladyshevskii, R; Banfi, F; Giannini, E Author Full Names: Zaremba, O.; Shcherban, O.; Akselrud, L.; Gladyshevskii, R.; Banfi, F.; Giannini, E.
Source:
ACTA PHYSICA POLONICA A 117 (1): 42-47 JAN 2010
Abstract:
The crystal structure of the (Bi0.02Sr0.39Ca0.59)(10)Cu17O29 spin-ladder compound was determined from single-crystal X-ray diffraction data. The precursor powder was prepared from stoichiometric amounts of SrCO3, CaCO3, CuO, and Bi2O3 by calcination at 820 degrees C for 20 h and pressed to form a rod used for the crystal growth. The travelling-solvent-floating-zone method was applied in an image furnace to grow large single crystals. The composite commensurate structure was solved and refined in space group F222, Pearson symbol oF224, a = 11.340(2), b = 12.829(2), c = 19.441(3) angstrom, Z = 4. The composite incommensurate structure of the (Bi0.02Sr0.39Ca0.59)(10)Cu17O29 compound was solved and refined in the (3 + 1)-space group F222(00 gamma), a = 11.340(2), b = 12.829(2), c(1) = 2.7773(4), c(2) = 3.8882(6) angstrom, q = 0.7143.

Update: 18-Mar-2010

Title:
Incommensurate 6M-modulated structure of Ni-Fe-Ga martensite
Authors:
Righi, L; Lazpita, P; Gutierrez, J; Barandiaran, JM; Chernenko, VA; Calestani, G Author Full Names: Righi, L.; Lazpita, P.; Gutierrez, J.; Barandiaran, J. M.; Chernenko, V. A.; Calestani, G.
Source:
SCRIPTA MATERIALIA 62 (6): 383-386 MAR 2010
Abstract:
The crystal structure of the modulated, low-temperature matensitic phase in Ni-2 41Fe0 59Ga ferromagnetic shape memory alloy (FSMA) has been determined by Rietveld refinement of neutron powder diffraction data The structure Shows an incommensurate modulated crystal lattice with some analogies with the 7 M modulated martensitic structure Found in Ni2Mn1 2Ga0 8 Heusler alloy The observed type of lattice modulation with q = 0 3521c* gives rise to a new type of martensitic crystal structure in the FSMAs (C) 2009 Acta Materialia Inc Published by Elsevier Ltd All rights reserved
Title:
NMR study of the high-field magnetic phase of LiCuVO4
Authors:
Buttgen, N; Kraetschmer, W; Svistov, LE; Prozorova, LA; Prokofiev, A Author Full Names: Buettgen, N.; Kraetschmer, W.; Svistov, L. E.; Prozorova, L. A.; Prokofiev, A.
Source:
PHYSICAL REVIEW B 81 (5): Art. No. 052403 FEB 2010
Abstract:
We report on NMR studies of the quasi-one-dimensional antiferromagnetic S= 1/2 chain cuprate LiCuVO4, focusing on the high-field spin-modulated phase observed recently in applied magnetic fields H > H-c2(mu H-0(c2) approximate to 7.5 T). The NMR spectra of Li-7 and V-51 around the transition from the ordered to the paramagnetic state were measured. It is shown that the spin-modulated magnetic structure forms with ferromagnetic interactions between spins of neighboring chains within the ab plane at low temperatures 0.6 K < T < T-N. The best fit provides evidence that the mutual orientation between spins of neighboring ab planes is random. For higher temperatures T-N < T less than or similar to 15 K, short-range magnetic order occurs at least on the characteristic time scale of the NMR experiment.
Title:
Revealing the atomic surface structure of the (100) Y-Al-Ni-Co approximant by low-energy electron diffraction and scanning tunneling microscopy
Authors:
Mader, R; Widmer, R; Bauer, B; Gille, P; Groning, P; Steurer, W; Groning, O Author Full Names: Maeder, R.; Widmer, R.; Bauer, B.; Gille, P.; Groening, P.; Steurer, W.; Groening, O.
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064201 FEB 2010
Abstract:
In this paper we present an investigation of the (100) Y-Al75.8Ni2.1Co22.1 surface, which is structurally and chemically related to the (10000) twofold symmetric surface of the decagonal Al-Ni-Co quasicrystal. The atomic surface structure was probed by low-energy electron diffraction (LEED) and by scanning tunneling microscopy (STM), revealing three different surface terminations and three different types of surface reconstructions. All three terminations were successfully assigned to the densest bulk layers and the origin of the surface reconstructions revealed by LEED could be identified locally by STM. The (100) Y-Al-Ni-Co surface shares with the related (10000) d-AlNiCo quasicrystal surface the strong tendency of reconstruction, which in the former case is occurring along the b axis and in the later along the periodic [00001] direction. Gaining a theoretical understanding of the reconstructions of the (100)Y-Al-Ni-Co surface might therefore help to understand the stability of bulk and surface atomic structures in decagonal quasicrystals. Furthermore, due to the strong relation to the quasicrystalline (10000) d-AlNiCo surface, the crystalline (100) Y-Al75.8Ni2.1Co22.1 surface is now a very promising candidate to study directional anisotropies in epitaxial thin film growth, friction, or the electronic structure, with the advantage of representing a much simpler structure (32 atoms/unit cell) which can be theoretically addressed with less effort compared to its quasicrystalline counter part.
Title:
Hydrodynamic structure factor of quasicrystals
Authors:
Chatzopoulos, A; Trebin, HR Author Full Names: Chatzopoulos, Andreas; Trebin, Hans-Rainer
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064205 FEB 2010
Abstract:
A theory of the hydrodynamic structure factor for quasicrystals is developed and exploited. Based on the hydrodynamic equations for icosahedral quasicrystals we introduce the terms of dynamic correlation and response. The phononic and phasonic diffuse part of the dynamic structure factor are examined in detail in frequency and time domain. We present a complete set of solutions for the hydrodynamic equations. Out of the diffusive modes we separately study the phasonic diffusion, the anisotropy of the phasonic diffusion constants, and the general solution for phason wall diffusion. All results include phonon-phason coupling.
Title:
Phason dynamics in one-dimensional lattices
Authors:
Lipp, H; Engel, M; Sonntag, S; Trebin, HR Author Full Names: Lipp, Hansjoerg; Engel, Michael; Sonntag, Steffen; Trebin, Hans-Rainer
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064302 FEB 2010
Abstract:
In quasicrystals, the phason degree of freedom and the inherent anharmonic potentials lead to complex dynamics, which cannot be described by the usual phonon modes of motion. We have constructed simple one-dimensional model systems, the dynamic Fibonacci chain, and approximants thereof. They allow us to study the dynamics of periodic and quasiperiodic structures with anharmonic double-well interactions both by analytical calculations and by molecular-dynamics simulations. We found soliton modes such as breathers and kink solitons and we were able to obtain closed analytical solutions for special cases, which are in good agreement with our simulations. Calculation of the specific heat shows an increase above the Dulong-Petit value, which is due to the anharmonicity of the potential and not caused by the phason degree of freedom.
Title:
Magnetic phase stability of monolayers: Fe on a TaxW1-x(001) random alloy as a case study
Authors:
Ondracek, M; Bengone, O; Kudrnovsky, J; Drchal, V; Maca, F; Turek, I Author Full Names: Ondracek, M.; Bengone, O.; Kudrnovsky, J.; Drchal, V.; Maca, F.; Turek, I.
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064410 FEB 2010
Abstract:
We present an approach to study the magnetic phase stability of magnetic overlayers on nonmagnetic substrates. The exchange integrals among magnetic atoms in the overlayer are estimated in the framework of the adiabatic approximation and used to construct the effective classical two-dimensional Heisenberg Hamiltonian. Its stability is then studied with respect to a large number of collinear and noncollinear magnetic arrangements which include, as special cases, not only ferromagnetic and various antiferromagnetic configurations but also possible incommensurate spin-spiral structures. This allows us to investigate a broader class of systems than a conventional total energy search based on few, subjectively chosen configurations. As a case study we consider the Fe monolayer on the random nonmagnetic bcc-TaxW1-x(001) surface which was studied recently by a conventional approach. We have found a crossover of the ground state of the Fe monolayer from the ferromagnet on the Ta surface to the c(2 x 2) antiferromagnet on the W surface and that at the composition with about 20% of Ta an incommensurate magnetic configuration might exist.
Title:
Stable and variable features of the magnetic structure of fcc Fe/Cu(001) films
Authors:
Sandratskii, LM Author Full Names: Sandratskii, L. M.
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064417 FEB 2010
Abstract:
After more than a decade of experimental and theoretical studies of the magnetic structure of the fcc Fe/Cu(001) films, most of the researchers agree that the atomic spins of two surface layers are ferromagnetically ordered whereas the magnetic structure of further layers is not ferromagnetic. The conclusions on the magnetic configuration of the nonferromagnetic part vary broadly from a simple collinear layer-by-layer antiferromagnet to complex incommensurate spin-density wave. We report detailed theoretical study of the fcc Fe/Cu(001) films with 6, 7, and 8 ML coverages. The study is based on the density-functional-theory calculations with the code allowing for the consideration of arbitrary noncollinear magnetic configurations. We suggest a view on the magnetism of the Fe/Cu(001) films that includes the grouping of the layers into blocks with robust collinear magnetic structure whereas the variation in the relative directions of the moments of different blocks is energetically relatively inexpensive. The robust magnetic structure of the three surface layers was found to be double down arrow double up arrow double up arrow. Further layers form the pairs with robust antiferromagnetic structure. We demonstrate that the formation of the robust magnetic blocks corresponds to a certain hierarchy of the interlayer exchange interactions. We suggest that the individual defect pattern of each fabricated film influences before all the relative orientation of the block magnetizations keeping the intrablock structure intact. The calculated inter-atomic exchange parameters are used to study magnetic thermodynamics of the films within mean-field approximation. In particular we focus on possible physical reasons of the appearance of the steplike features in the temperature dependence of the magnetization detected experimentally. We emphasize the important consequences of the inequivalence of the Fe atoms belonging to different layers of the film. This inequivalence makes the properties of the films to be essentially different from the properties of the corresponding bulk system. Using a rigid-band model we investigate the dependence of the exchange parameters on the electron number. We critically discuss the possibility of the formation of the incommensurate SDW in the thin Fe/Cu(001) films. The brief formulation of the idea of robust blocking and its experimental confirmation was recently published as a letter [H. L. Meyerheim, J.-M. Tonnerre, L. M. Sandratskii et al., Phys. Rev. Lett. 103, 267202 (2009)].
Title:
Electronic structure, magnetic, and dielectric properties of the edge-sharing copper oxide chain compound NaCu2O2
Authors:
Leininger, P; Rahlenbeck, M; Raichle, M; Bohnenbuck, B; Maljuk, A; Lin, CT; Keimer, B; Weschke, E; Schierle, E; Seki, S; Tokura, Y; Freeland, JW Author Full Names: Leininger, Ph.; Rahlenbeck, M.; Raichle, M.; Bohnenbuck, B.; Maljuk, A.; Lin, C. T.; Keimer, B.; Weschke, E.; Schierle, E.; Seki, S.; Tokura, Y.; Freeland, J. W.
Source:
PHYSICAL REVIEW B 81 (8): Art. No. 085111 FEB 2010
Abstract:
We report an experimental study of NaCu2O2, a Mott insulator containing chains of edge-sharing CuO4 plaquettes, by polarized x-ray absorption spectroscopy (XAS), resonant magnetic x-ray scattering (RMXS), magnetic susceptibility, and pyroelectric current measurements. The XAS data show that the valence holes reside exclusively on the Cu2+ sites within the copper-oxide spin chains and populate a d orbital polarized within the CuO4 plaquettes. The RMXS measurements confirm the presence of incommensurate magnetic order below a NEel temperature of T-N = 11.5 K, which was previously inferred from neutron powder-diffraction and nuclear-magnetic-resonance data. In conjunction with the magnetic-susceptibility and XAS data, they also demonstrate an "orbital" selection rule for RMXS that is of general relevance for magnetic-structure determinations by this technique. Dielectric property measurements reveal the absence of significant ferroelectric polarization below TN, which is in striking contrast to corresponding observations on the isostructural compound LiCu2O2. The results are discussed in the context of current theories of multiferroicity.
Title:
Ordered oxide layers on the pentagonal surface of AlPdMn quasicrystal
Authors:
Burkardt, S; Erbudak, M Author Full Names: Burkardt, S.; Erbudak, M.
Source:
PHYSICAL REVIEW B 81 (8): Art. No. 085417 FEB 2010
Abstract:
Recently, we reported the structural investigation of the oxide layers grown on the pentagonal surface of icosahedral Al70Pd20Mn10 quasicrystal based on low-energy electron diffraction. The oxide layer was described to consist of five twin domains rotated by 2 pi/5 with respect to each other in accordance with the symmetry of the quasicrystalline substrate each of which having one twofold-symmetry direction of the substrate as a mirror plane. Here, we discuss the oxidation process in more detail and report the growth of different oxide structures depending on the sample temperature and its pretreatment. At room temperature, amorphous oxide layers form. In contrast five distinct and few-nanometer-large domains possessing an internal hexagonal structure with substantial amount of contribution from antiphase domain boundaries grow at 700-800 K for small and large coverage. In an intermediate range, a mixture of antiphase domain-boundary contributions and fractional-order spots characteristic to a 2 root 3(1x1)R +/- 30 degrees S reconstruction of the surface oxide layer is found which additionally stabilized the interface. The previously reported twin-domain model, which was derived after an ion bombardment of the preoxidized surface with subsequent reoxidation, is identified as an oxide layer grown on the (110) surface of a crystalline Al-50(PdMn)(50) alloy as a result of the sputtering.
Title:
THE THERMAL CONDUCTIVITY OF Al73Mn27-xFex TAYLOR PHASES
Authors:
Stanic, D; Popcevic, P; Smiljanic, I; Bihar, Z; Lukatela, J; Leontic, B; Bilusic, A; Batistic, I; Smontara, A Author Full Names: Stanic, Denis; Popcevic, Petar; Smiljanic, Igor; Bihar, Zeljko; Lukatela, Jagoda; Leontic, Boran; Bilusic, Ante; Batistic, Ivo; Smontara, Ana
Source:
MATERIALI IN TEHNOLOGIJE 44 (1): 3-7 JAN-FEB 2010
Abstract:
The thermal conductivity (kappa) of Al73Mn27-xFex (x = 0, 2, 4, 6) complex metallic alloys has been measured in the temperature interval from 2 K to 300 K. All the alloys are Taylor (T) phases, except Al73Mn21Fe6, which is a decagonal (d) quasicrystal. The behaviours of kappa are typical for complex metallic alloys, i.e.. a relatively small magnitude, a Change of slope about 50 K and an increase of the conductivity above 100 K. At room temperature the magnitude of kappa for all the samples is between 2.7 W/mK and 3.3 W/mK. which is comparable to that of thermally insulating amorphous SiO2 and Zr/YO2 ceramics. The reason for such a low thermal conductivity is because both, the electronic and lattice conductivity are low. The electronic contribution to the thermal conductivity is low because of the large electrical resistivity of the samples. The lattice (hernial conductivity is greatly reduced because of the enhanced umklapp process of the phonon scattering (caused by (lie large lattice constant) and by the disorder in the structure.
Title:
HALL EFFECT IN THE CRYSTALLINE ORTHOROMBIC o-Al13Co4 APPROXIMANT TO THE DECAGONAL QUASICRYSTALS
Authors:
Ivkov, J; Stanic, D; Popcevic, P; Smontara, A; Dolinsek, J; Gille, P Author Full Names: Ivkov, Jovica; Stanic, Denis; Popcevic, Petar; Smontara, Ana; Dolinsek, Janez; Gille, Peter
Source:
MATERIALI IN TEHNOLOGIJE 44 (1): 9-12 JAN-FEB 2010
Abstract:
We have investigated the anisotropic Hall effect of the o-Al13Co4 orthorhombic approximant to the decagonal phase. The crystalline-direction-dependent measurements were Performed along the a, b and c direction of the orthorhombic Unit cell. The Hall all effect has been measured for all the combinations of the electrical current and magnetic field directions. The Hall coefficients RI, change with the crystallographic direction from negative electron-like or zero to positive hole-like for different combinations of the current and field directions. The results for the anisotropy of R-n is well correlated with the anisotropy of Rn in the d-Al-Ni-Co and d-Al-Cu-Co quasicrystals. The Hall coefficients of the o-Al13Co4 phase were compared to the literature data on single crystals of the Al76Co22Ni2 and the Al80Cr15Fe5 approximants to the decagonal quasicrystals. allowing I study of the evolution of the Hall coefficient with an increasing structural complexity and unit-cell size.

Update: 4-Mar-2010

Title:
STRUCTURE AND PROPERTIES FEATURES OF Ti-Zr-Ni-QUASICRYSTALS
Authors:
Azhazha, VM; Malykhin, SV; Merisov, BA; Pugachov, AT; Khadzhay, GY Author Full Names: Azhazha, V. M.; Malykhin, S. V.; Merisov, B. A.; Pugachov, A. T.; Khadzhay, G. Ya.
Source:
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY (6): 115-126 2009
Abstract:
For Ti-Zr-Ni ingots prepared by equilibrium crystallization, and 20 to 100 gm ribbons obtained by rapid quenching on the same disc, the dependence of phase composition on the super-pure components charge mixture composition and on the disc velocity has been studied. The technology parameters for synthesis of QC single-phase structures or ones with prevailing portion of icosahedral quasicrystalline structure were determined. The peculiarities of structure,. substructure and stress state of the ribbons were studied. Through the ribbon section, the gradient variations of phase composition, grain size, micro- and nano-hardness, Young modulus, structure and substructure parameters, and residual stress level were established. The gradient distributions depend on the quenching speed. The temperature behaviour of electrical resistivity without external magnetic field and under magnetic field was investigated. The transition to superconductivity state was found. The properties of! hydrogen accumulation and the parameters of its diffusion, as well as mechanical properties and deformation features, and thermo-physical properties of Ti-Zr-Ni quasicrystals were studied. The evolution of structure and stress state in quasicrystals as a result of thermal influence, hydrogen saturation, and irradiation was analyzed.
Title:
Origin of Friction Anisotropy on a Quasicrystal Surface
Authors:
Filippov, AE; Vanossi, A; Urbakh, M Author Full Names: Filippov, Aleksander E.; Vanossi, Andrea; Urbakh, Michael
Source:
PHYSICAL REVIEW LETTERS 104 (7): Art. No. 074302 FEB 19 2010
Abstract:
Wearless friction force experiments [Science 309, 1354 (2005)] have recently demonstrated that tribological response in quasicrystals could be related to the exotic atomic structure of the bulk material. Here, by numerical simulations, we address the origin of the experimentally observed friction anisotropy on a twofold decagonal quasicrystal surface. We predict the distinct stick-slip patterns in the lateral force along the periodic and quasiperiodic directions, specifically exploring the temperature dependence that rules the transitions between single and multiple-slip regimes of motion.
Title:
Geometrical property of the cluster model of the Yb-Cd icosahedral quasicrystal (vol 88, pg 1905, 2008)
Authors:
Takakura, H Author Full Names: Takakura, H.
Source:
PHILOSOPHICAL MAGAZINE 90 (5): 525-525 2010
Title:
The magnetic structure of clinopyroxene-type LiFeGe2O6 and revised data on multiferroic LiFeSi2O6
Authors:
Redhammer, GJ; Roth, G; Treutmann, W; Hoelzel, M; Paulus, W; Andre, G; Pietzonka, C; Amthauer, G Author Full Names: Redhammer, Guether J.; Roth, Georg; Treutmann, Werner; Hoelzel, Markus; Paulus, Werner; Andre, Gilles; Pietzonka, Clemens; Amthauer, Georg
Source:
JOURNAL OF SOLID STATE CHEMISTRY 182 (9): 2374-2384 SEP 2009
Abstract:
The clinopyroxene compounds LiFeSi2O6 and LiFeGe2O6 have been investigated by constant wavelength neutron diffraction at low temperatures and by bulk magnetic measurements. Both compounds are monoclinic, space group P2(1)/c and do not exhibit a change in nuclear symmetry down to 1.4 and 5 K respective. However, they transform to a magnetically ordered state below 20 K. LiFeSi2O6 shows a simple magnetic structure with no indication of an incommensurate modulation. The magnetic space group is P2(1)/c' and the structure is described by a ferromagnetic coupling of spins within the infinite M1 chains of edge-sharing octahedra, while the coupling between these M1 chains is antiferromagnetic. The magnetic phase transition is accompanied by magnetostriction of the lattice when passing through the magnetic phase transition. The magnetic structure of LiFeGe2O6 is different to the silicate: the space group is P2(1)'/c and the magnetic unit cell doubled along the a-direction. Within the M1 chains spins are coupled antiferromagnetically, while the chain to chain coupling is antiferromagnetic when coupling goes via the GeB tetrahedron and ferromagnetic when it goes via the GeA tetrahedron. (C) 2009 Elsevier Inc. All rights reserved.
Title:
Magnetic and structural properties of the magnetic shape memory compound Ni2Mn1.48Sb0.52
Authors:
Brown, PJ; Gandy, AP; Ishida, K; Ito, W; Kainuma, R; Kanomata, T; Neumann, KU; Oikawa, K; Ouladdiaf, B; Sheikh, A; Ziebeck, KRA Author Full Names: Brown, P. J.; Gandy, A. P.; Ishida, K.; Ito, W.; Kainuma, R.; Kanomata, T.; Neumann, K. U.; Oikawa, K.; Ouladdiaf, B.; Sheikh, A.; Ziebeck, K. R. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (9): Art. No. 096002 MAR 10 2010
Abstract:
Magnetization and high resolution neutron powder diffraction measurements on the magnetic shape memory compound Ni2Mn1.48Sb0.52 have confirmed that it is ferromagnetic below 350 K and undergoes a structural phase transition at T-M approximate to 310 K. The high temperature phase has the cubic L2(1) structure with a = 5.958 angstrom, with the excess manganese atoms occupying the 4(b) Sb sites. In the cubic phase above approximate to 310 K the manganese moments are ferromagnetically aligned. The magnetic moment at the 4(a) site is 1.57(12) mu(B) and it is almost zero (0.15(9) mu(B)) at the 4(b) site. The low temperature orthorhombic phase which is only fully established below 50 K has the space group Pmma with a cell related to the cubic one by a Bain transformation a(orth) = (a(cub) + b(cub))/2; b(orth) = c(cub) and c(orth) = (a(cub) - b(cub)). The change in cell volume is approximate to 2.5%. The spontaneous magnetization of samples cooled in fields less than 0.5 T decreases at temperatures below T-M and at 2 K the magnetic moment per formula unit in fields up to 5.5 T is 2.01(5) mu(B). Neutron diffraction patterns obtained below approximate to 132 K gave evidence for a weak incommensurate magnetic modulation with propagation vector (2/3, 1/3, 0).
Title:
Structures and Phase Transitions in (MoO2)(2)P2O7
Authors:
Lister, SE; Soleilhavoup, A; Withers, RL; Hodgkinson, P; Evans, JSO Author Full Names: Lister, Sarah E.; Soleilhavoup, Anne; Withers, Ray L.; Hodgkinson, Paul; Evans, John S. O.
Source:
INORGANIC CHEMISTRY 49 (5): 2290-2301 MAR 1 2010
Abstract:
We report structural investigations into (MoO2)(2)P2O7 using a combination of X-ray, neutron and electron diffraction, and solid-state NMR supported by first principles quantum chemical calculations. These reveal a series of phase transitions on cooling at temperatures of 377 and 325 K. The high temperature gamma-phase has connectivity consistent with that proposed by Kierkegaard at room temperature (but with improved bond length distribution), and contains 13 unique atoms in space group Pnma with lattice parameters a = 12.6577(1) angstrom, b = 6.3095(1) angstrom, c = 10.4161 (1) angstrom, and volume 831.87(1) angstrom(3) from synchrotron data at 423 K. The low temperature alpha-structure was indexed from electron diffraction data and contains 60 unique atoms in space group P2(1)/c with cell parameters a = 17.8161(3) angstrom, b = 10.3672(1) angstrom, c = 17.8089(3) angstrom, beta = 90.2009(2)degrees, and volume 3289.34(7) angstrom(3) at 250 K. First principles calculations of P-31 chemical shift and J couplings were used to establish correlation between local structure and observed NMR parameters, and 1D and 2D P-31 solid-state NMR used to validate the proposed crystal structures. The intermediate beta-phase is believed to adopt an incommensurately modulated structure; P-31 NMR suggests a smooth structural evolution in this region.

Update: 25-Feb-2010

Title:
Modulated Lanthanum Chains in the Crystal Structure of La-3.65[Ru(C-2)(3)]
Authors:
Davaasuren, B; Dashjav, E; Doert, T; Kreiner, G; Schnelle, W; Wagner, FR; Mihalkovic, M; Kniep, R Author Full Names: Davaasuren, Bambar; Dashjav, Enkhtsetseg; Doert, Thomas; Kreiner, Guido; Schnelle, Walter; Wagner, Frank R.; Mihalkovic, Marek; Kniep, Ruediger
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 636 (1): 41-49 2010
Abstract:
Lanthanum ruthenium carbide La-3.65[Ru(C-2)(3)] crystallizes hexagonal (P6(3)/m with a 887.9(2) pm and c = 1606.8(6) pm, V = 1096.8(4).10(6) nm(3), and Z = 6. The crystal structure contains trigonal-planar Ru(C-2)(3) groups and lanthanum atoms, which form a partial structure of the chemical composition La3Ru(C-2)(3). Additional lanthanum atoms Occupy hexagonal channels built by those carbon atoms of the C-2 ligands, which are non-bonded to the central ruthenium atoms. The distribution of these lanthanum atoms along the c axis results ill a threefold superstructure, which was refined as a commensurate modulated structure (P6(3)/m (00g)s0, q = (0, 0, 1/3)). Harmonic occupational and displacive modulation functions Were used for the structure refinement. The structure converged to R-1 = 4.9 % for all data (R-1 = 2.6 % for the main reflections, R-1 = 11.1 % for the 1(st) order satellite reflections). A small homogeneity range for this phase is predicted by total energy calculations using the PAW-GGA method (VASP). Chemical bonding analysis reveals that file C-2 pairs are best described as acetylide C-2(2-) units.
Title:
SimulaTEM: Multislice simulations for general objects
Authors:
Gomez-Rodriguez, A; Beltran-del-Rio, LM; Herrera-Becerra, R Author Full Names: Gomez-Rodriguez, A.; Beltran-del-Rio, L. M.; Herrera-Becerra, R.
Source:
ULTRAMICROSCOPY 110 (2): 95-104 JAN 2010
Abstract:
In this work we present the program SimulaTEM for the simulation of high resolution micrographs and diffraction patterns. This is a program based on the multislice approach that does not assume a periodic object. It can calculate images from finite objects, from amorphous samples, from crystals, quasicrystals, grain boundaries, nanoparticles or arbitrary objects provided the coordinates of all the atoms can be supplied. (C) 2009 Elsevier B.V. All rights reserved.
Title:
A Tm-169-Mossbauer spectroscopy investigation of orthorhombic phase o-TmMnO3
Authors:
Salama, HA; Stewart, GA; Hutchison, WD; Nishimura, K; Scott, DR; O'Neill, HS Author Full Names: Salama, H. A.; Stewart, G. A.; Hutchison, W. D.; Nishimura, K.; Scott, D. R.; O'Neill, H. StC.
Source:
SOLID STATE COMMUNICATIONS 150 (5-6): 289-291 JAN 2010
Abstract:
AC susceptibility and specific heat measurements confirm that the Mn sub-lattice of o-TmMnO3 orders at T-N(Mn) approximate to 41 K with a weaker feature at T-C approximate to 32 K. Tm-169-Mossbauer spectra are interpreted in terms of a single, asymmetric, quadrupole-split doublet whose line width increases sharply at T-C. This suggests the presence of a weak induced Tm-site moment, consistent with claims that the Mn sub-lattice magnetism undergoes a transition from incommensurate to collinear antiferromagnetic order at this temperature. (C) 2009 Elsevier Ltd. All rights reserved.
Title:
Direction of modulation during twin boundary motion
Authors:
Chulist, R; Oertel, CG; Skrotzki, W; Lippmann, T Author Full Names: Chulist, R.; Oertel, C. -G.; Skrotzki, W.; Lippmann, T.
Source:
SCRIPTA MATERIALIA 62 (5): 235-237 MAR 2010
Abstract:
To study the change of modulation direction during deformation, two NiMnGa single crystals, one with a five-layered modulated tetragonal structure (5 M) and the other with a seven-layered modulated orthorhombic structure (7 M), were chosen. Synchrotron diffraction experiments show that the modulation takes place on the {1 1 0) plane along the < 1 1 0] directions. During deformation the c-axis orientation changes by twinning, and with this the direction of modulation obeying the twin relation also changes. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Geometrical property of the cluster model of the Yb-Cd icosahedral quasicrystal (vol 88, pg 1905, 2008)
Authors:
Takakura, H Author Full Names: Takakura, H.
Source:
PHILOSOPHICAL MAGAZINE 90 (1-4): 525-525 2010
Title:
LiZnNb4O11.5: A novel oxygen deficient compound in the Nb-rich part of the Li2O-ZnO-Nb2O5 system
Authors:
Morozov, VA; Arakcheeva, AV; Konovalova, VV; Pattison, P; Chapuis, G; Lebedev, OI; Fomichev, VV; Van Tendeloo, G Author Full Names: Morozov, Vladimir A.; Arakcheeva, Alla V.; Konovalova, Vera V.; Pattison, Philip; Chapuis, Gervais; Lebedev, Oleg I.; Fomichev, Valery V.; Van Tendeloo, Gustaaf
Source:
JOURNAL OF SOLID STATE CHEMISTRY 183 (2): 408-418 FEB 2010
Abstract:
A novel lithium zinc niobium oxide LiZnNb4O11.5 (LZNO) has been found in the Nb-rich part of Li2O-ZnO-Nb2O5 system. LZNO, with an original alpha-PbO2 related structure, has been synthesized by the routine ceramic technique and characterized by X-ray diffraction and transmission electron microscopy (TEM). Reflections belonging to the LZNO phase, observed in X-ray powder diffraction (XRPD) and electron diffraction, have been indexed as monoclinic with unit cell parameters a=17.8358(9)angstrom, b=15.2924(7)angstrom, c=5.0363(3)angstrom and gamma=96.607(5)degrees or as alpha-PbO2-like with lattice constants a=4.72420(3)angstrom, b=5.72780(3)angstrom, c=5.03320(3)angstrom, gamma=90.048(16)degrees and modulation vector q=0.3a*+1.1b* indicating a commensurately modulated alpha-PbO2 related structure. The monoclinic cell is a supercell related to the latter. Using synchrotron powder diffraction data, the structure has been solved and refined as a commensurate modulation (superspace group P112(1)/n(alpha beta 0)00) as well as a supercell (space group P2(1)/b). The superspace description allows us to consider the LZNO structure as a member of the proposed alpha-PbO2-Z (3 + 1)D structure type, which unifies both incommensurately and commensurately modulated structures. HRTEM reveals several types of defects in LZNO and structural models for these defects are proposed. Two new phases in Li2O-ZnO-Nb2O5 system are predicted on the basis of this detailed HRTEM analysis. (C) 2009 Elsevier Inc. All rights reserved.
Title:
Cooperative effect of monoclinic distortion and sinusoidal modulation in the martensitic structure of Ni2FeGa
Authors:
Lu, JB; Yang, HX; Tian, HF; Zeng, LJ; Ma, C; Feng, L; Wu, GH; Li, JQ; Jansen, J Author Full Names: Lu, J. B.; Yang, H. X.; Tian, H. F.; Zeng, L. J.; Ma, C.; Feng, L.; Wu, G. H.; Li, J. Q.; Jansen, J.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 183 (2): 425-430 FEB 2010
Abstract:
The structural features of the "5M" martensitic phase in Ni2FeGa alloys have been determined by electron diffraction using the multi-slice least-squares (MSLS) method. The results demonstrate that the "5M" phase contains an evident cooperative effect of monoclinic distortion and sinusoidal modulation along the [110](c) direction. Theoretical simulations based on Our refined data suggest that the "5M" martensitic phase observed in Ni-Fe-Ga and Ni-Mn-Ga has visible common behaviors in both stacking sequence and local structural distortion. Considering the cooperative effect of monoclinic distortion and sinusoidal modulation, we demonstrate that the "7M" martensitic phase could adopt two equivalent structural phases corresponding with the stacking sequences of (43). and (52)2, respectively. Crown Copyright (C) 2009 Published by Elsevier Inc. All rights reserved.
Title:
Advantages of aberration correction for HRTEM investigation of complex layer compounds
Authors:
Spiecker, E; Garbrecht, M; Jager, W; Tillmann, K Author Full Names: Spiecker, E.; Garbrecht, M.; Jaeger, W.; Tillmann, K.
Source:
JOURNAL OF MICROSCOPY-OXFORD 237 (3): 341-346 MAR 2010
Abstract:
Aberration-corrected high-resolution transmission electron microscopy (HRTEM) has been applied to resolve the atomic structure of a complex layered crystal, (PbS)(1.14)NbS2, which comprises a high density of incommensurate interfaces. The strong suppression of image delocalization and the favourable contrast transfer under negative C-s imaging (NCSI) conditions have been exploited for obtaining HRTEM images which directly reveal the projected crystal structure and allow to study lattice imperfections, like stacking disorder and layer undulations, with atomic scale resolution. The advantages of aberration-corrected HRTEM over conventional HRTEM are demonstrated by direct comparison of experimental images and computer simulations.
Title:
Microstructure of electrodeposited NiFe/Cu multilayers
Authors:
Tokarz, A; Wieczorek, P; Lis, AK; Morgiel, J Author Full Names: Tokarz, A.; Wieczorek, P.; Lis, A. K.; Morgiel, J.
Source:
JOURNAL OF MICROSCOPY-OXFORD 237 (3): 456-460 MAR 2010
Abstract:
NiFe/Cu multilayer films have been electrodeposited potentiostatically on (001)-oriented Si and polycrystalline Cu substrates by a single bath technique. Standard error of mean and energy dispersive X-ray studies of single NiFe(Cu) layers allow us to establish the right deposition parameters for NiFe and Cu sublayer. Standard error of mean results reveal the layered structure of deposits for relatively thick bilayer thickness (ca. similar to 200 nm). The modulated structure of NiFe/Cu multilayers with extremely thin bilayer thickness (nominal period Lambda = 8 nm) was investigated by transmission electron microscope techniques. A columnar structure of the deposit with column diameter in the range from 10 to 30 nm was observed. These results are comparable with X-ray diffraction measurements of crystallites size obtained by Scherer equation. The line scans acquired using EDS confirmed the layered structure of the deposit, but pointed towards possibility of intermixing! of species from alternating sublayers especially in case of those with finer period.
Title:
Effect of Titanium, Antimony, Cerium and Carbon Nanotubes on the Morphology and Microhardness of Mg-based Icosahedral Quasicrystal Phase
Authors:
Wang, ZF; Zhao, WM; Li, HP; Ding, J; Li, YY; Liang, CY Author Full Names: Wang, Zhifeng; Zhao, Weimin; Li, Haipeng; Ding, Jian; Li, Yongyan; Liang, Chunyong
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY 26 (1): 27-32 JAN 2010
Abstract:
For the first time, petal-like and spherical Mg-based icosahedral quasicrystal phase (I-phase) were obtained by introducing Ti, Sb, Ce and C nanotubes into Mg-Zn-Y alloy under normal casting conditions. The formation mechanism and stability criterion of spherical I-phase were discussed. The morphology and microhardness of I-phase and their determinants were studied in this paper. The results show that the different value of microhardness of I-phase could be attributed to the different kinds of the fourth component and its content, and its different innate characters. The final morphology of icosahedral quasicrystalline (IQC) is decided by the size of critical stable radius R-r, the content of the fourth component and degree of undercooling.
Title:
SUPERCONDUCTIVITY, SPIN AND CHARGE DENSITY STRUCTURES IN ONE AND TWO-DIMENSIONAL SELF-CONSISTENT MODELS
Authors:
Matveenko, SI Author Full Names: Matveenko, S. I.
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B 23 (20-21): 4297-4310 Sp. Iss. SI AUG 20 2009
Abstract:
We review some analytical results of our studies of the charge- and spin density modulations (CDW and SDW) in a one- and two-dimensional electron systems. Self-consistent solutions of Bogoliubov-de Gennes equations for spin-charge solitonic superstructure and superconducting state are obtained in the framework of one and two-dimensional extended Hubbard models. Possible correspondence of the theory with experimental data on stripe phase in high T-c cuprates is discussed. We found various solutions for the two-dimensional self-consistent model of superconductors with d(x2-y2) symmetry of the order parameter, taking into account spin and charge distributions. Analytical solutions for spin-charge density wave phases in the absence of the superconductivity("stripe" and "checkerboard" structures) are presented. Analytical solutions for coexisting superconductivity and stripe-phase modulations in the cores of the Abrikosov's vortices are also found.

Update: 18-Feb-2010

Title:
STUDY OF Al-Cu-Fe-Ti-Cr-Si POWDERS FOR THERMAL SPRAYING PRODUCED BY MECHANOCHEMICAL SYNTHESIS AND SUBSEQUENT ANNEALING
Authors:
Borisova, AL; Adeeva, LI; Tunik, AY; Karpets, MV; Rupchev, VL; Burlachenko, AN Author Full Names: Borisova, A. L.; Adeeva, L. I.; Tunik, A. Yu.; Karpets, M. V.; Rupchev, V. L.; Burlachenko, A. N.
Source:
POWDER METALLURGY AND METAL CERAMICS 48 (9-10): 514-521 SEP 2009
Abstract:
The paper examines the phase transformations of composite powders based on Al63Cu25Fe12 that contain alloying elements (Ti, Cr, Si in the ratio AlCuFe : TiCrSi = 75 : 25). The powders are produced by mechanochemical synthesis and subsequent thermal treatment. Amorphous and crystalline powder mixtures form during synthesis; their annealing results in multiphase structures consisting of alpha, beta(1), and beta(2) phases. High-temperature x-ray diffraction has revealed an alpha-phase between 700 and 900 degrees C. The new a-phase should be regarded as a 1/1 approximant of the nonequilibrium quasicrystalline phase. The maximum content of the approximant phase (68 wt.%) is observed after five-hour synthesis and subsequent annealing (T = 700 degrees C, tau = 2 h) of pressed powders, microhardness of the particles reaching 8900 MPa.
Title:
The surface science of quasicrystals
Authors:
McGrath, R; Smerdon, JA; Sharma, HR; Theis, W; Ledieu, J Author Full Names: McGrath, R.; Smerdon, J. A.; Sharma, H. R.; Theis, W.; Ledieu, J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (8): Art. No. 084022 MAR 3 2010
Abstract:
The surfaces of quasicrystals have been extensively studied since about 1990. In this paper we review work on the structure and morphology of clean surfaces, and their electronic and phonon structure. We also describe progress in adsorption and epitaxy studies. The paper is illustrated throughout with examples from the literature. We offer some reflections on the wider impact of this body of work and anticipate areas for future development.
Title:
Phase field simulation of microstructure evolution in Fe-Cr-Co alloy during thermal magnetic treatment and step aging
Authors:
Lv, LX; Zhen, L; Xu, CY; Sun, XY Author Full Names: Lv, L. X.; Zhen, L.; Xu, C. Y.; Sun, X. Y.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (8): 987-995 APR 2010
Abstract:
The evolution of modulated structures in Fe-Cr-Co alloys during isothermal aging under an external magnetic field and multiple step aging was simulated based on a phase field method. In this simulation, the magnetic configuration during the decomposition was calculated by a micromagnetic method, and the chemical Gibbs energy function was calculated by the CALPHAD approach based on the experimental equilibrium phase diagram. The calculation results provide a quantitative microstructure change directly linked to the phase diagram and demonstrate obvious microstructure difference between isothermal aging and multiple aging. The ferromagnetic precipitates elongate along the direction of the external magnetic field. The simulated evolution and microstructure are in good agreement with the experimental results. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Desorption of hydrogen from Ti-Zr-Ni hydrides using a mass spectrometer
Authors:
Kocjan, A; McGuiness, PJ; Kobe, S Author Full Names: Kocjan, A.; McGuiness, P. J.; Kobe, S.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 35 (1): 259-265 JAN 2010
Abstract:
We have performed thermogravimetry (TG) and mass-spectrometry measurements of hydrogen desorbed from fully and partially hydrided ternary Ti-Zr-Ni amorphous, quasi-crystalline and crystalline alloys, with four different initial compositions, where the Ti/Zr ratio ranged from 1 to 2.4. The icosahedral, quasicrystalline Ti-Zr-Ni samples were obtained using the melt-spinning technique, and with subsequent annealing of these ribbons at 700 degrees C for 2 h in vacuum we were able to obtain a mixture of crystalline C14 Laves and alpha/beta solid-solution phases. in addition, using subsequent mechanical alloying we produced amorphous powders of Ti-Zr-Ni from the as-spun ribbons. These various samples were then hydrided and analyzed by TG and mass spectrometry. The TG measurements provided us with the mass% of desorbed hydrogen, whereas the mass-spectrometry revealed information about the hydrogen desorption temperatures in the material. Despite the fact that the amorphous and icosahedral. samples undergo some crystallization during the desorption measurements, the resulting mass spectra were different and were closely related to the alloy's structure. In contrast, the shapes of mass spectra were less affected by the composition, the total amount of desorbed hydrogen and the loading pressure. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Title:
Crystal Structure and Optical and Magnetic Properties of Pr-2(MoO4)(3)
Authors:
Logvinovich, D; Arakcheeva, A; Pattison, P; Eliseeva, S; Tomes, P; Marozau, I; Chapuis, G Author Full Names: Logvinovich, D.; Arakcheeva, A.; Pattison, P.; Eliseeva, S.; Tomes, P.; Marozau, I.; Chapuis, G.
Source:
INORGANIC CHEMISTRY 49 (4): 1587-1594 FEB 15 2010
Abstract:
Praseodymium molybdate Pr-2(MoO4)(3) was synthesized using the standard ceramic route. The crystal structure of the material has been successfully solved in superspace group /2/b(alpha beta 0)00 with lattice constants a = 5.30284(4), b = 5.32699(3), c= 11.7935(1) angstrom, gamma = 90.163(1)degrees, and the modulation vector q = 2/3a* + 0.88810(2)b*. The deviation of the q vector from a rational value allows a description of the structure in terms of nanosize domains with the La-2(MoO4)(3)-like structure separated by stacking faults. Under 450 nm excitation, (P-3(0) level) Pr-2(MoO4)(3) exhibits the characteristic red emission, with the most intense band at 649 nm corresponding to a P-3(0) -> F-3(2) transition. Magnetic susceptibility measurements reveal Curie-Weiss paramagnetism with predominating antiferromagnetic interactions between PI-magnetic moments and no evidence of magnetic transitions down to T = 5 K.
Title:
Rational Synthesis and Characterization of a New Family of Low Thermal Conductivity Misfit Layer Compounds [(PbSe)(0.99)](m)(WSe2)(n)
Authors:
Lin, QY; Smeller, M; Heideman, CL; Zschack, P; Koyano, M; Anderson, MD; Kykyneshi, R; Keszler, DA; Anderson, IM; Johnson, DC Author Full Names: Lin, Qiyin; Smeller, Mary; Heideman, Colby L.; Zschack, Paul; Koyano, Mikio; Anderson, Michael D.; Kykyneshi, Robert; Keszler, Douglas A.; Anderson, Ian M.; Johnson, David C.
Source:
CHEMISTRY OF MATERIALS 22 (3): 1002-1009 FEB 9 2010
Abstract:
We describe here a general synthesis approach for the preparation of new families of misfit layer compounds and demonstrate its effectiveness through the preparation of the first 64 members of the [(PbSe)(0.99)](m) (WSe2)(n) family of compounds, where in and it are integers that were systematically varied from 1 to 8. The new Compounds [(PbSc)(1+y)](m) (WSe2)(n) were synthesized by annealing reactant precursors containing 177 layers of alternating elemental Pb and Se followed by it layers ofalternating elemental W and Se, in which the thickness of each pair of elemental layers was calibrated to yield a structural bilayer of rock salt structured PbSe and a trilayer of hexagonal WSe2. The compounds are kinetically trapped by the similarity of the composition profiles and modulation lengths in the precursor and the targeted compounds. The structural evolution from initial reactant of layer elements to crystalline misfit layer compounds was tracked using X-ray diffraction. The crystal structures of new compounds were probed using both analytical electron microscopy and X-ray diffraction. The c-axis of the misfit layer compound is perpendicular to the Substrate, with a c-axis lattice parameter that changes linearly with a slope of 0.612-0.615 nm as in is changed and n is held constant and with a slope of 0.654-0.656 nm as it is varied and m is held constant. The in-plane lattice parameters did not change as the individual layer thicknesses were increased and a misfit parameter of y = -0.01 was calculated, the first negative misfit parameter among known misfit layer compounds. Analytical electron microscopy images and X-ray diffraction data collected on mixed hkl reflections revealed rotational (turbostratic) disorder of the a-b planes.

Update: 11-Feb-2010

Title:
Phase separation in the CoO2 layer observed in thermoelectric layered cobalt dioxides
Authors:
Takami, T; Nanba, H; Umeshima, Y; Itoh, M; Nozaki, H; Itahara, H; Sugiyama, J Author Full Names: Takami, Tsuyoshi; Nanba, Hiroshi; Umeshima, Yasuhide; Itoh, Masayuki; Nozaki, Hiroshi; Itahara, Hiroshi; Sugiyama, Jun
Source:
PHYSICAL REVIEW B 81 (1): Art. No. 014401 JAN 2010
Abstract:
Co-59 nuclear magnetic resonance (NMR) measurements have been performed to study the local magnetic properties of the misfit layered cobalt dioxides (MLCO's) with the CoO2 and rock-salt layers, (Ca2CoO3)(0.62)CoO2 ( Ca3Co3.92O9.34) and Ca3Co3.92O9.34-delta with oxygen nonstoichiometry. The Co-59 NMR spectrum consists of mainly five lines at 4.2 K at which the samples are in a magnetically ordered state. Among the five NMR lines for Ca3Co3.92O9.34, three lines at higher frequencies (f's) satisfy the resonance condition with two branches indicating the presence of antiferromagnetic internal fields (H-int's). The other two lines exhibit one branch, and one of the two has a nonzero H-int under zero external field (ZF), which signifies the existence of ferromagnetic (FM) H-int's. The other has a zero H-int under ZF. By taking account of both the valence state of the Co ions in each layer and the lattice modulation due to the misfit between the CoO2 layer and the rock-salt layer, the NMR spectra at higher f's are attributed to the Co in the rock-salt layer, whereas those at lower f's to the Co in the CoO2 layer. Furthermore, a spin-density wave order appears to coexist with a FM order in the CoO2 layer for MLCO's. The magnetic and transport properties of these materials are discussed in terms of a separation between two phases.
Title:
Thermodynamics of multiferroic spin chains
Authors:
Sirker, J Author Full Names: Sirker, J.
Source:
PHYSICAL REVIEW B 81 (1): Art. No. 014419 JAN 2010
Abstract:
The minimal model to describe many spin-chain materials with ferroelectric properties is the Heisenberg model with ferromagnetic nearest-neighbor coupling J(1) and antiferromagnetic next-nearest-neighbor coupling J(2). Here we study the thermodynamics of this model using a density-matrix algorithm applied to transfer matrices. We find that the incommensurate spin-spin correlations-crucial for the ferroelectric properties and the analog of the classical spiral pitch angle-depend not only on the ratio J(2)vertical bar J(1)vertical bar but also strongly on temperature. We study small easy-plane anisotropies which can stabilize a vector chiral order as well as the finite-temperature signatures of multipolar phases, stable at finite magnetic field. Furthermore, we fit the susceptibilities of LiCuVO4, LiCu2O2, and Li2ZrCuO4. Contrary to the literature, we find that for LiCuVO4 the best fit is obtained with J(2) similar to 90 K and J(2)vertical bar J(1)vertical bar ! 0.5 and show that these values are consistent with the observed spin incommensurability. Finally, we discuss our findings concerning the incommensurate spin-spin correlations and multipolar orders in relation to future experiments on these compounds.
Title:
Anisotropic magnetic field responses of ferroelectric polarization in the trigonal multiferroic CuFe1-xAlxO2 (x=0.015)
Authors:
Nakajima, T; Mitsuda, S; Kanetsuki, S; Yamano, M; Iwamoto, S; Yoshida, Y; Mitamura, H; Sawai, Y; Tokunaga, M; Kindo, K; Prokes, K; Podlesnyak, A Author Full Names: Nakajima, Taro; Mitsuda, Setsuo; Kanetsuki, Shunsuke; Yamano, Motoyoshi; Iwamoto, Shunsuke; Yoshida, Yukihiko; Mitamura, Hiroyuki; Sawai, Yoshiki; Tokunaga, Masashi; Kindo, Koichi; Prokes, Karel; Podlesnyak, Andrey
Source:
PHYSICAL REVIEW B 81 (1): Art. No. 014422 JAN 2010
Abstract:
We have investigated magnetic field dependences of a ferroelectric incommensurate-helimagnetic order in a trigonal magnetoelectric multiferroic CuFe1-xAlxO2 with x=0.015, which exhibits the ferroelectric phase as a ground state, by means of neutron diffraction, magnetization, and dielectric polarization measurements under magnetic fields applied along various directions. From the present results, we have established the H-T magnetic phase diagrams for the three principal directions of magnetic fields; (i) parallel to the c axis, (ii) parallel to the helical axis, and (iii) perpendicular to the c and the helical axes. While the previous dielectric polarization (P) measurements on CuFe1-xGaxO2 with x=0.035 have demonstrated that the magnetic field dependence of the "magnetic domain structure" results in distinct magnetic field responses of P [S. Seki et al., Phys. Rev. Lett. 103, 237601 (2009)], the present study have revealed that the anisotropic! magnetic field dependence of the ferroelectric helimagnetic order "in each magnetic domain" can be also a source of a variety of magnetic field responses of P in CuFe(1-x)A(x)O(2) systems (A=Al, Ga).
Title:
Gutzwiller magnetic phase diagram of the undoped t-t '-U Hubbard model
Authors:
Markiewicz, RS; Lorenzana, J; Seibold, G Author Full Names: Markiewicz, R. S.; Lorenzana, J.; Seibold, G.
Source:
PHYSICAL REVIEW B 81 (1): Art. No. 014510 JAN 2010
Abstract:
We calculate the magnetic phase diagram of the half-filled t-t'-U Hubbard model as a function of t' and U, within the Gutzwiller approximation plus random-phase approximation. As U increases, the system first crosses over to one of a wide variety of incommensurate phases, whose origin is clarified in terms of double nesting. We evaluate the stability regime of the incommensurate phases by allowing for symmetry breaking with regard to the formation of spin spirals, and find a crossover to commensurate phases as U increases and a full gap opens. The results are compared with a variety of other recent calculations, and in general good agreement is found. For parameters appropriate to the cuprates, double occupancy should be only mildly suppressed in the absence of magnetic order, inconsistent with a strong-coupling scenario.
Title:
Charge-ordering transition and incommensurate antiphase structure of Fe2BO4 as seen via transmission electron microscopy
Authors:
Song, YJ; Yang, HX; Tian, HF; Ma, C; Qin, YB; Zeng, LJ; Shi, HL; Lu, JB; Li, JQ Author Full Names: Song, Y. J.; Yang, H. X.; Tian, H. F.; Ma, C.; Qin, Y. B.; Zeng, L. J.; Shi, H. L.; Lu, J. B.; Li, J. Q.
Source:
PHYSICAL REVIEW B 81 (2): Art. No. 020101 JAN 2010
Abstract:
The nature of the charge ordering (CO) in Fe2BO4 was carefully examined by in situ TEM observations from 360 K down to 20 K. An incommensurate structural modulation with the wave vector q = (1/2, 0, epsilon) becomes plainly visible in association with the CO transition at T-CO approximate to 340 K. Careful structural analysis suggests that this incommensurate structure originates from a well-defined Fe2+/Fe3+ ionic order along the FeO6 octahedral ribbons (in the a-axis direction) and from a discommensurate antiphase stripe order along the c-axis direction. The average periodicity of antiphase stripes changes notably with lowering temperature and, via certain intermediate states, toward a superstructure phase with modulation wave vector of q = (1/2, 0, 0) at similar to 150 K in association with a magnetic phase transition.
Title:
Solution growth of a binary icosahedral quasicrystal of Sc12Zn88
Authors:
Canfield, PC; Caudle, ML; Ho, CS; Kreyssig, A; Nandi, S; Kim, MG; Lin, X; Kracher, A; Dennis, KW; McCallum, RW; Goldman, AI Author Full Names: Canfield, P. C.; Caudle, M. L.; Ho, C-S.; Kreyssig, A.; Nandi, S.; Kim, M. G.; Lin, X.; Kracher, A.; Dennis, K. W.; McCallum, R. W.; Goldman, A. I.
Source:
PHYSICAL REVIEW B 81 (2): Art. No. 020201 JAN 2010
Abstract:
We report the discovery of a binary icosahedral phase in a Sc-Zn alloy obtained through solution-growth, producing millimeter-sized, facetted, single grain quasicrystals that exhibit different growth morphologies, pentagonal dodecahedra, and rhombic triacontahedra, under only marginally different growth conditions. These two morphologies manifest different degrees of quasicrystalline order. The discovery of i-Sc12Zn88 suggests that a re-examination of binary phase diagrams at compositions close to crystalline approximant structures may reveal other binary quasicrystalline phases.
Title:
Composition-dependent spin-phonon coupling in mixed crystals of the multiferroic manganite Eu1-xYxMnO3 (0 <= x <= 0.5) studied by Raman spectroscopy
Authors:
Issing, S; Pimenov, A; Ivanov, VY; Mukhin, AA; Geurts, J Author Full Names: Issing, S.; Pimenov, A.; Ivanov, V. Yu.; Mukhin, A. A.; Geurts, J.
Source:
PHYSICAL REVIEW B 81 (2): Art. No. 024304 JAN 2010
Abstract:
Yttrium substitution in Eu1-xYxMnO3 allows a quasicontinuous tuning of the lattice and magnetic properties of this multiferroic manganite without magnetic interference of rare-earth ions. In order to investigate the composition dependence of the spin-phonon coupling we employ polarized Raman scattering of orthorhombic mixed crystals of Eu1-xYxMnO3 (0 <= x <= 0.5) in the 10-300 K temperature range. Phonon frequency shifts and mode-mixing effects occur, depending on the average rare-earth ion radius determined by the concentration of Eu3+ and Y3+. Moreover, we observe a strong spin-phonon coupling with systematic composition dependence. It manifests itself as a mode-specific softening of the phonon modes in the temperature range of the magnetic ordered phases. The spin-phonon coupling is weakened for increasing Y contents but remains nonzero also in the incommensurate spiral magnetic phase, which occurs for 0.3 <= x <= 0.5. Thus for this class of manganites we report the observation of spin-phonon coupling in an ordered magnetic phase without ferromagnetic ordering within the MnO2 plane. Additionally for known sublattice magnetization quantitative values of the spin-phonon coupling constant are derived. Our results prove the suitability of phonons as a sensitive probe for the spin-spin correlation.
Title:
Critical properties of the unconventional spin-Peierls system TiOBr
Authors:
Clancy, JP; Gaulin, BD; Chou, FC Author Full Names: Clancy, J. P.; Gaulin, B. D.; Chou, F. C.
Source:
PHYSICAL REVIEW B 81 (2): Art. No. 024411 JAN 2010
Abstract:
We have performed detailed x-ray scattering measurements on single crystals of the spin-Peierls compound TiOBr in order to study the critical properties of the transition between the incommensurate spin-Peierls state and the paramagnetic state at T-C2 similar to 48 K. We have determined a value of the critical exponent beta which is consistent with the conventional three-dimensional universality classes, in contrast with earlier results reported for TiOBr and TiOCl. Using a simple power-law-fit function we demonstrate that the asymptotic critical regime in TiOBr is quite narrow, and obtain a value of beta(asy) = 0.32 +/- 0.03 in the asymptotic limit. A power-law-fit function which includes the first-order correction-to-scaling confluent singularity term can be used to account for data outside the asymptotic regime, yielding a more robust value of beta(avg) = 0.39 +/- 0.05. We observe no evidence of commensurate fluctuations above T-C1 in TiOBr, unlike its isostructural sister compound TiOCl. In addition, we find that the incommensurate structure between T-C1 and T-C2 is shifted in Q space relative to the commensurate structure below T-C1.
Title:
Tensile and creep behaviors of Mg-5Zn-2.5Er alloy improved by icosahedral quasicrystal
Authors:
Li, JH; Du, WB; Li, SB; Wang, ZH Author Full Names: Li, Jianhui; Du, Wenbo; Li, Shubo; Wang, Zhaohui
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 527 (4-5): 1255-1259 FEB 15 2010
Abstract:
The tensile and tensile creep properties of the as-cast Mg-5Zn-2.5Er (in wt.%) alloy strengthened by icosahedral quasicrystalline phase (1-phase) were studied. The Mg-5Zn-2.5Er alloy had better tensile properties both at room temperature and 175 degrees C than AE42 and Mg-5Zn alloys. Compared to AE42 alloy, the as-cast Mg-5Zn-2.5Er alloy had smaller steady-state creep rate and total creep strain under the creep conditions of 175 degrees C and 70 MPa for 100 h. The better creep resistance of the Mg-5Zn-2.5Er was mainly due to the formation of I-phase with high-thermal stability distributed along grain boundary. Moreover, microstructure analysis indicated that some fine precipitates in the alpha-Mg matrix can pin the dislocation effectively, improving the creep resistance of the alloy. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Directional magnetoelectric effects in MnWO4: magnetic sources of the electric polarization
Authors:
Toledano, P; Mettout, B; Schranz, W; Krexner, G Author Full Names: Toledano, P.; Mettout, B.; Schranz, W.; Krexner, G.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (6): Art. No. 065901 FEB 17 2010
Abstract:
The ferroelectric order and magnetic field induced effects observed in the spiral phase of MnWO4 are described theoretically. It is demonstrated explicitly that the Dzyaloshinskii-Moriya antisymmetric interactions contribute to the correlation between spins and electric dipoles in the incommensurate and commensurate ferroelectric phases of magnetic multiferroics. However, other single-site symmetric interactions are shown to be involved in the magnetoelectric process, suggesting the possible existence of an electric polarization originating from purely symmetric effects.
Title:
TEM study of a fluorite-type (1-x)Bi2O3 center dot xFe(2)O(3) superstructure in BiFeO3 ceramics synthesized by the rapid liquid-phase sintering method
Authors:
Guo, C; Pu, SZ; Chen, ZL; Li, MY; Cao, JF; Zou, HM Author Full Names: Guo, Chao; Pu, Shizhou; Chen, Zhenlian; Li, Meiya; Cao, Jiefeng; Zou, Huamin
Source:
CERAMICS INTERNATIONAL 36 (2): 507-512 MAR 2010
Abstract:
A commensurate modulated structure of (1 - x)Bi2O3 center dot xFe(2)O(3) is found in the BiFeO3 ceramics synthesized by the rapid liquid-phase sintering method. Transmission electron microscopy studies show that the superstructure is based on fluorite-type delta-Bi2O3 and modulated probably by oxygen vacancy ordering. The existence of such a superstructure may increase the leakage current of BiFeO3 ceramics. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Title:
Thermal hysteresis of ferroelectric transition in Sr4R2Ti4Nb6O30 (R=Sm and Eu) tetragonal tungsten bronzes
Authors:
Zhu, XL; Chen, XM Author Full Names: Zhu, X. L.; Chen, X. M.
Source:
APPLIED PHYSICS LETTERS 96 (3): Art. No. 032901 JAN 18 2010
Abstract:
Sr4R2Ti4Nb6O30 (R=Sm and Eu) tungsten bronze ceramics were prepared, and the dielectric properties and ferroelectric transition were investigated together with the crystal structure. A ferroelectric transition peak and a low temperature dielectric relaxation were observed from the curve of permittivity versus temperature during heating process for both ceramics. The ferroelectric transition indicated large thermal hysteresis during the heating and cooling cycles for both ceramics, where the ferroelectric transition peak disappeared during the cooling process, and the low temperature dielectric relaxation was obviously enhanced. Moreover, extremely large depression of the Curie-Weiss temperature (T-0) was observed in the present ceramics. These abnormal features were associated with the complex tetragonal tungsten bronze structure with two ferroelectrically active cations over two sets of sites and weak superstructure change from incommensurate to commensurate on cooling. The low temperature dielectric relaxation was due to the oxygen octahedron rotation in the ab plane and the possible compositional variations in the microscale.
Title:
A complicated quasicrystal approximant epsilon(16) predicted by the strong-reflections approach
Authors:
Li, MR; Sun, JL; Oleynikov, P; Hovmoller, S; Zou, XD; Grushko, B Author Full Names: Li, Mingrun; Sun, Junliang; Oleynikov, Peter; Hovmoller, Sven; Zou, Xiaodong; Grushko, Benjamin
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 17-26 Part 1 FEB 2010
Abstract:
The structure of a complicated quasicrystal approximant epsilon(16) was predicted from a known and related quasicrystal approximant epsilon(6) by the strong-reflections approach. Electron-diffraction studies show that in reciprocal space, the positions of the strongest reflections and their intensity distributions are similar for both approximants. By applying the strong-reflections approach, the structure factors of epsilon(16) were deduced from those of the known epsilon(6) structure. Owing to the different space groups of the two structures, a shift of the phase origin had to be applied in order to obtain the phases of epsilon(16). An electron-density map of epsilon(16) was calculated by inverse Fourier transformation of the structure factors of the 256 strongest reflections. Similar to that of epsilon(6), the predicted structure of epsilon(16) contains eight layers in each unit cell, stacked along the b axis. Along the b axis, epsilon(16) is built by banana-shaped tiles and pentagonal tiles; this structure is confirmed by high-resolution transmission electron microscopy (HRTEM). The simulated precession electron-diffraction (PED) patterns from the structure model are in good agreement with the experimental ones. epsilon(16) with 153 unique atoms in the unit cell is the most complicated approximant structure ever solved or predicted.
Title:
Structures of incommensurate and commensurate composite crystals Rb-x MnO2 (x=1.3711, 1.3636)
Authors:
Nuss, J; Pfeiffer, S; van Smaalen, S; Jansen, M Author Full Names: Nuss, Juergen; Pfeiffer, Steffen; van Smaalen, Sander; Jansen, Martin
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 27-33 Part 1 FEB 2010
Abstract:
Rb1.3711MnO2 (Rb11Mn8O16) has been synthesized via the azide/nitrate route from a stoichiometric mixture of the precursors Mn2O3, RbNO3 and RbN3. The structure of this extremely air- and moisture-sensitive compound can best be described in terms of an incommensurate composite structure, built up by a honeycomb-like framework of Rb ions, as one subsystem and by a second subsystem of chains, consisting of edge-sharing MnO4/2 tetrahedra. These two composite substructures interpenetrate in such a way that the manganate chain polyanions centre the channels of the Rb-honeycomb framework. Crystals transform by an aging process into Rb1.3636MnO2 (Rb15Mn11O22), which has a similar structure but a different commensurate modulation. Two reasons can be established for the origin of the modulations: the charge ordering of Mn2+/Mn3+ on one hand, and the incompatibility of the Mn-Mn and Rb-Rb separations on the other.

Update: 4-Feb-2010

Title:
Novel Geometrical Frustration Effects in the Two-Dimensional Triangular-Lattice Antiferromagnet NiGa2S4 and Related Compounds
Authors:
Nakatsuji, S; Nambu, Y; Onoda, S Author Full Names: Nakatsuji, Satoru; Nambu, Yusuke; Onoda, Shigeki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (1): Art. No. 011003 JAN 2010
Abstract:
Geometrical frustration may Suppress conventional magnetic long-range order and possibly promote a novel type of ordering associated with a higher order degree of freedom than spin dipolar-moment such as vector spin chirality and spin quadrupole moment. After a brief overview of such phenomena due to vector spin chirality, we focus on the two-dimensional (2D) frustrated magnetism in the layered chalcogenide Mott insulator NiGa2S4 and related compounds. NiGa2S4 provides the unique example of a S = 1 2D antiferromagnet on a regular exact triangular lattice. Extensive studies using high-purity samples of NiGa2S4 have revealed that Ni2+ S = 1 Heisenberg spins exhibit resonant critical slowing down at T* = 8.5 K without forming a magnetic long-range order, Signaling a viscous spin-liquid state. The critical spin-fluctuation regime extends over almost all order of magnitude in temperature both above and below T. Even well below T, the spin-spin correlation remains short-ranged at an incommensurate wave vector close to (1/6, 1/6,0), corresponding to a 120 degrees correlation with 2a period. Interestingly, however, a 2D linearly dispersive magnetic mode and a quasi-static spin component exist in the low temperature limit. Possibly relevant scenarios including topological phase transition associated with Z(2) vortex due to vector spin chirality, Spill quadrupolar nematic correlation, and C-3 bond-ordering are reviewed.
Title:
Sliding Friction of Kr Films Adsorbed on Graphite
Authors:
Kobayashi, H; Taniguchi, J; Suzuki, M; Miura, K; Arakawa, I Author Full Names: Kobayashi, Hajime; Taniguchi, Junko; Suzuki, Masaru; Miura, Kouji; Arakawa, Ichiro
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (1): Art. No. 014602 JAN 2010
Abstract:
We have carried Out quartz crystal microbalance (QCM) experiments for Kr films adsorbed on exfoliated graphite from a single crystal, and have examined the coverage dependence of the sliding friction and the depinning transition up to the bilayer film. For the monolayer film, the coupled mass density appears at the commensurate and fluid (C+F) phase. An increase of this density starts at the commensurate (C) phase and continues at the incommensurate (IC) phase after the C-IC transition. It was found that the monolayer film slides not uniformly but partly on the substrate, and that the slip time is 60 ns at the C phase. On the other hand, the film around the layer completion slides almost uniformly, and its slip time is about 10 ns. For the bilayer film, the experimental data are reasonably explained by a model in which the slip occurs at the boundary between the first and second atomic layers, in addition to the boundary between the film and the substrate. For the oscillation amplitude sweep at a constant coverage, a rapid change in frequency was observed for the monolayer and bilayer films, which is attributed to the depinning transition. This magnitude takes the minimum value around the layer completion.
Title:
Low temperature incommensurately modulated and noncollinear spin structure in FeCr2S4
Authors:
Kalvius, GM; Krimmel, A; Hartmann, O; Wappling, R; Wagner, FE; Litterst, FJ; Tsurkan, V; Loidl, A Author Full Names: Kalvius, G. M.; Krimmel, A.; Hartmann, O.; Wappling, R.; Wagner, F. E.; Litterst, F. J.; Tsurkan, V.; Loidl, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (5): Art. No. 052205 FEB 10 2010
Abstract:
FeCr2S4 orders magnetically at T-N approximate to 170 K. According to neutron diffraction, the ordered state down to 4.2 K is a simple collinear ferrimagnet maintaining the cubic spinel structure. Later studies, however, claimed trigonal distortions below similar to 60 K coupled to the formation of a spin glass type ground state. To obtain further insight, muon spin rotation/relaxation (mu SR) spectroscopy was carried out between 5 and 200 K together with new Fe-57 Mossbauer measurements. Below similar to 50 K, our data point to the formation of an incommensurately modulated noncollinear spin arrangement like a helical spin structure. Above 50 K, the spectra are compatible with collinear ferrimagnetism, albeit with a substantial spin disorder on the scale of a few lattice constants. These spin lattice distortions become very large at 150 K and the magnetic state is now better characterized as consisting of rapidly fluctuating short-range ordered spins. The Neel transition is of second order, but ill defined, extending over a range of similar to 10 K. The Mossbauer data around 10 K confirm the onset of orbital freezing and are also compatible with the noncollinear order of iron. The absence of a major change in the quadrupole interaction around 50 K renders the distortion of crystal symmetry to be small.
Title:
EVAL15: a diffraction data integration method based on ab initio predicted profiles
Authors:
Schreurs, AMM; Xian, XY; Kroon-Batenburg, LMJ Author Full Names: Schreurs, Antoine M. M.; Xian, Xinyi; Kroon-Batenburg, Loes M. J.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 70-82 Part 1 FEB 2010
Abstract:
A novel diffraction data integration method is presented, EVAL15, based upon ab initio calculation of three-dimensional (x, y, omega) reflection profiles from a few physical crystal and instrument parameters. Net intensities are obtained by least-squares fitting the observed profile with the calculated standard using singular value decomposition. This paper shows that profiles can be predicted satisfactorily and that accurate intensities are obtained. The detailed profile analysis has the additional advantage that specific physical properties of the crystal are revealed. The EVAL15 method is particularly useful in circumstances where other programs fail, such as regions of reciprocal space with weak scattering, crystals with anisotropic shape or anisotropic mosaicity, K alpha(1)/K alpha(2) peak splitting, interference from close neighbours, twin lattices, or satellite reflections of modulated structures, all of which may frustrate the customary profile learning and fitting procedures. EVAL15 allows the deconvolution of overlapping reflections.
Title:
Ab initio structure solution by iterative phase-retrieval methods: performance tests on charge flipping and low-density elimination
Authors:
Fleischer, F; Weber, T; Deloudi, S; Palatinus, L; Steurer, W Author Full Names: Fleischer, Frank; Weber, Thomas; Deloudi, Sofia; Palatinus, Lukas; Steurer, Walter
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 89-100 Part 1 FEB 2010
Abstract:
Comprehensive tests on the density-modification methods charge flipping [Oszlanyi & Suto (2004). Acta Cryst. A60, 134-141] and low-density elimination [Shiono & Woolfson (1992). Acta Cryst. A48, 451-456] for solving crystal structures are performed on simulated diffraction data of periodic structures and quasicrystals. A novel model-independent figure of merit, which characterizes the reliability of the retrieved phase of each reflection, is introduced and tested. The results of the performance tests show that the quality of the phase retrieval highly depends on the presence or absence of an inversion center and on the algorithm used for solving the structure. Charge flipping has a higher success rate for solving structures, while low-density elimination leads to a higher accuracy in phase retrieval. The best results can be obtained by combining the two methods, i.e. by solving a structure with charge flipping followed by a few cycles of low-density elimination. It is shown that these additional cycles dramatically improve the phases not only of the weak reflections but also of the strong ones. The results can be improved further by averaging the results of several runs and by applying a correction term that compensates for a reduction of the structure-factor amplitudes by averaging of inconsistently observed reflections. It is further shown that in most cases the retrieved phases converge to the best solution obtainable with a given method.
Title:
An electron diffraction and Monte Carlo simulation study of an incommensurate antiferroelectric state in the relaxor ferroelectric Pb2ScTaO6
Authors:
Baba-Kishi, KZ; Pasciak, M Author Full Names: Baba-Kishi, K. Z.; Pasciak, M.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 140-150 Part 1 FEB 2010
Abstract:
Incommensurate satellite reflections modulating along the < 110 >* directions have been observed in the electron diffraction patterns of single crystals of the relaxor ferroelectric Pb2ScTaO6 (PST) recorded via transmission electron microscopy. The satellites occur characteristically within a specific temperature range and display differing or variable modulation vectors relative to their primary reflections. The satellites represent a weak frustrated antiferroelectric state in PST, termed the incommensurate antiferroelectric (IAFE) state. The observed IAFE state coexists with the ferroelectric and paraelectric states within a specific temperature regime and is dynamic in nature, meaning that the dispositions of the satellites can be altered by varying the temperature applied to the crystal, in-situ in the transmission electron microscope. The observed satellites are associated with thin, needle-shaped, closely packed striated domains of about 5-15 nm in width. The satellites appear exclusively in crystals of PST with an advanced degree of 1:1 chemical long-range order, exceeding 90%. The satellites and their domains are interpreted as originating from a displacive, antiferroelectric coupling of the ions, driven in particular by the Pb ions. The Monte Carlo (MC) method was used exhaustively to evaluate the structural regimes that lead to the occurrence of the IAFE state. In the MC simulations, the displacements were correlated with the ferroelectric and antiferroelectric couplings, resulting in the IAFE domains and their associated satellites of differing dispositions or modulation vectors. The results of the MC simulations agree well with the electron diffraction observations, supporting the model of an antiferroelectric displacement with an incommensurate modulation of the Pb ions in the < 110 >* directions.
Title:
EXTRAX: an ImageJ plug-in for electron diffraction intensity extraction
Authors:
Dorcet, V; Larose, X; Fermin, C; Bissey, M; Poullay, P Author Full Names: Dorcet, V.; Larose, X.; Fermin, C.; Bissey, M.; Poullay, P.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 191-195 Part 1 FEB 2010
Abstract:
A plug-in (EXTRAX) has been developed for ImageJ - a public domain Java-based program widely used for image processing and analysis in microscopy. This plug-in allows the extraction and measurement of intensities from electron diffraction spot patterns with a semi-automatic peak location based on a two-dimensional lattice given by the user. It is also possible to take into account supplementary spots originating from high-order Laue zones and/or the existence of a modulation vector.

Update: 29-Jan-2010

Title:
LaSe1.85, CeSe1.83, NdSe1.83 and SmSe1.84 - four new rare earth metal polyselenides with incommensurate site occupancy and displacive modulation
Authors:
Graf, C; Doert, T Author Full Names: Graf, Christian; Doert, Thomas
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 224 (12): 568-579 2009
Abstract:
Crystals of the four new binary rare earth metal polyselenides LaSe1.85, CeSe1.83, NdSe1.83 and SMSe1.84 were obtained by flux reactions. Their two-dimensionally incommensurately modulated structures were solved from X-ray diffraction data. Structure models were established in super space group X4/n(-alpha beta 0)(beta alpha 0)00 with modulation wave vectors q(1) = -alpha a* + beta b* and q(2) = beta a* + alpha b* and the centering vector (0, 0, 1/2, 1/2, 1/2). The unit cell parameters at T = 293 K are a = 4.216(1) angstrom and c = 17.048(2) angstrom for LaSe1.85, a = 4.178(1) angstrom and c = 16.942(3) angstrom for CeSe1.83, a = 4.123(1) angstrom and c = 16.792(2) angstrom for NdSe1.83 and a = 4.080(1) angstrom and c = 16.672(2) angstrom for SmSe1.84; the components of the modulation wave vectors are alpha = beta = 0.292(1) for LaSe1.85 and CeSe1.83, and alpha = beta = 0.293(1) for NdSe1.83 and SmSe1.84, respectively. The modulation originates from a site occupancy wave caused by defects in planar selenium layers coupled to a displacive modulation.
Title:
Interfacial reaction between Al72Ni12Co16 decagonal quasicrystalline particles and liquid aluminium
Authors:
Cheng, SL; Yang, GC; Wang, JC; Liu, F; Zhu, M; Zhou, YH Author Full Names: Cheng, Suling; Yang, Gencang; Wang, Jincheng; Liu, Feng; Zhu, Man; Zhou, Yaohe
Source:
JOURNAL OF MATERIALS SCIENCE 45 (6): 1438-1442 MAR 2010
Abstract:
The interfacial reaction between Al72Ni12Co16 quasicrystalline particles and pure Al melt at 670 A degrees C was investigated. For all the studied samples, only one interfacial reaction product was detected at the interface by scanning electron microscopy. The product was identified to be the Al-9(Co, Ni)(2) crystalline phase, which show an rod-like morphology. The growth rate of the Al-9(Co, Ni)(2) phase layer is very fast. Based on the microstructure analysis results, it is proposed that the layer growth is initially towards the liquid phase, but changes direction towards the quasicrystalline phase by the solid state reaction of diffusional Al with the quasicrystalline phase at the Al72Ni12Co16/Al-9(Co, Ni)(2) interface. A grain boundary grooving effect is deduced to have been involved during the reaction process.

Update: 22-Jan-2010

Title:
STRUCTURE AND PROPERTIES FEATURES OF Ti-Zr-Ni-QUASICRYSTALS
Authors:
Azhazha, VM; Malykhin, SV; Merisov, BA; Pugachov, AT; Khadzhay, GY Author Full Names: Azhazha, V. M.; Malykhin, S. V.; Merisov, B. A.; Pugachov, A. T.; Khadzhay, G. Ya
Source:
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY (6): 115-126 Part 3 2009
Abstract:
For Ti-Zr-Ni ingots prepared by equilibrium crystallization, and 20 to 100 mu m ribbons obtained by rapid quenching on the same disc, the dependence of phase composition on the super-pure components charge mixture composition and on the disc velocity has been studied. The technology parameters for synthesis of QC single-phase structures or ones with prevailing portion of icosahedral quasicrystalline structure were determined. The peculiarities of structure,. substructure and stress state of the ribbons were studied. Through the ribbon section, the gradient variations of phase composition, grain size, micro-and nano-hardness, Young modulus, structure and substructure parameters, and residual stress level were established. The gradient distributions depend on the quenching speed. The temperature behaviour of electrical resistivity without external magnetic field and under magnetic field was investigated. The transition to superconductivity state was found. The properties o! f hydrogen accumulation and the parameters of its diffusion, as well as mechanical properties and deformation features, and thermo-physical properties of Ti-Zr-Ni quasicrystals were studied. The evolution of structure and stress state in quasicrystals as a result of thermal influence, hydrogen saturation, and irradiation was analyzed.
Title:
A neutron powder diffraction study of the helimagnetic structure of TlCo2Se2-xSx
Authors:
Ronneteg, S; Berger, R; Andre, G Author Full Names: Ronneteg, Sabina; Berger, Rolf; Andre, Gilles
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (6): 681-685 MAR 2010
Abstract:
The magneti clayer structure of TlCo2Se2-xSx has been thoroughly re-investigated with neutron powder diffraction. The cobalt magnetic moments are ferromagnetically arranged with in the layers, but the interlayer coupling differs profoundly with varying composition (x): the spins in TlCo2Se2 form a helix along the c-axis with a turning-angle of similar to 119 degrees at 1.4 K. This kind of helical structure prevails for 0 <= x <= 1.5 with a gradual decrease of the angle with increasing sulphur content, down to 34 degrees, showing an almost linear relationship with the interlayer distance of Co-Co. For x >= 1.75 the interlayer couplingchanges to ferromagnetic. Unexpectedly, two helices were found to coexist at x = 0.5 and x = 1.0. The interaction between adjacent cobalt layers is there characterized by an incommensurate angle (106 degrees, resp., 73 degrees) together with a commensurate angle of 90 degrees. The magnetic structures have been refined as two magnetic phases, each having a characteristic wave vector. A tentative model where the symmetry of the structure and the interlayer distance compete is considered for explaining the simultaneous occurrence of the two kinds of diffraction profile satellites. (C) 2009 Elsevier B. V. All rights reserved.

Update: 14-Jan-2010

Title:
Exploring low-energy landscape of quasi-one-dimensional conductors by heat relaxation and magnetic field
Authors:
Biljakovic, K; Lasjaunias, JC; Melin, R; Monceau, P; Remenyi, G; Sahling, S; Staresinic, D Author Full Names: Biljakovic, K.; Lasjaunias, J. C.; Melin, R.; Monceau, P.; Remenyi, G.; Sahling, S.; Staresinic, D.
Source:
SYNTHETIC METALS 159 (21-22): 2402-2405 Sp. Iss. SI NOV 2009
Abstract:
Modulated charge or spin superstructures of organic quasi-one-dimensional conductors exhibit specific low-energy excitations (LEE) at very low temperatures due to metastable states caused by strong pinning centers. These phase excitations (soliton-like topological defects) demonstrate rich and unexpected properties in a magnetic field, due to their magnetic moments. We discuss mainly on the dynamical aspects related to the non-equilibrium phenomena measured in heat relaxation below 1 K. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Magnetoelectric Response of Multiferroic BiFeO3 and Related Materials from First-Principles Calculations
Authors:
Wojdel, JC; Iniguez, J Author Full Names: Wojdel, Jacek C.; Iniguez, Jorge
Source:
PHYSICAL REVIEW LETTERS 103 (26): Art. No. 267205 DEC 31 2009
Abstract:
We present a first-principles scheme for computing the magnetoelectric response of multiferroics. We apply our method to BiFeO3 (BFO) and related compounds in which Fe is substituted by other magnetic species. We show that under certain relevant conditions-i.e., in the absence of incommensurate spin modulation, as in BFO thin films and some BFO-based solid solutions-these materials display a large linear magnetoelectric response. Our calculations reveal the atomistic origin of the coupling and allow us to identify the most promising strategies to enhance it.
Title:
Elastic behavior associated with phase transitions in incommensurate Ba2NaNb5O15
Authors:
Herrero-Albillos, J; Marchment, P; Salje, EKH; Carpenter, MA; Scott, JF Author Full Names: Herrero-Albillos, J.; Marchment, P.; Salje, E. K. H.; Carpenter, M. A.; Scott, J. F.
Source:
PHYSICAL REVIEW B 80 (21): Art. No. 214112 DEC 2009
Abstract:
The elastic behavior of barium sodium niobate (Ba2NaNb5O15) has been investigated by resonant ultrasound spectroscopy through six different structural phases, with emphasis on the five incommensurate phase transitions near 40, 110, 547, 565, and 582 K. Data near 40 K are at least consistent with the existence of a lock-in transition to P4nm at that temperature [Filipic , J. Phys.: Condens. Matter 19, 236206 (2007)], which has been controversial. A relaxation process occurs around the transition near 110 K and is assigned to a process involving movement of domain walls of the phase. Unusual behavior is observed through the high-temperature incommensurate transitions with large variations in frequency in the ultrasonic resonances, and a broad peak in the dissipation. No clear signature of the 1q-2q incommensurate-incommensurate transition at 565 K is observed. This is compatible with a model in which incommensurate-incommensurate transitions are not expected to manifest elastic anomalies.
Title:
Magnetism at surfaces and defects in icosahedral Al-Pd-Mn quasicrystals
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, M.; Hafner, J.
Source:
PHYSICAL REVIEW B 80 (21): Art. No. 214419 DEC 2009
Abstract:
In our recent work [Krajcciacute and Hafner, Phys. Rev. B 78, 224207 (2008)] we have demonstrated that the ground state of bulk i-Al-Pd-Mn quasicrystals is nonmagnetic. Mn atoms located at specific sites can acquire a large magnetic moment if they have at least two Pd neighbors in the first coordination shell. Such configurations can be created by substitutional Al/Pd defects which can be formed at low energetic cost because at these sites the overlap between the pseudo-Mackay and Bergman clusters building the quasicrystalline structure leads to conflicting assignments of the chemical decoration. Besides the large magnetic moments formed on these special Mn sites, we have found a broad diffuse background of smaller magnetic moments on many different Mn atoms induced by the large Mn moments. In the present work we extend these investigations to magnetism at the five-fold surface of the quasicrystal and at isolated point defects with particular attention to the formati! on of induced moments. For the stable five-fold surface we find that Mn atoms located in the surface layer carry indeed large magnetic moments of up to 3 mu(B) and that smaller magnetic moments (aligned both parallel and antiparallel to the surface moments) are induced at distances of up to 10 A degrees below the surface. We have considered three types of isolated point defects (and substitutional defects) around a Mn atom and investigated the formation of magnetic moments on the Mn atom and of induced moments on the surrounding sites. For both the magnetization induced below a magnetic surface and the magnetization induced around an Al/Pd substitutional defect, the induced moments show an irregular dependence on the distance from the inducing "source" moment, but a marked dependence on the location of the Mn atom in the occupation domain in six-dimensional hyperspace. Mn atoms with a large coordinate in perpendicular space show large induced moments. Based on the analysis of the local paramagnetic density of states we demonstrate that the formation of a large induced moment is caused by a large polarizability of these Mn atoms, which is related in turn to a rather loosely packed local environment. Per Mn atom, the sum of the source moment (created by a special substitutional defect in the bulk quasicrystal or by the reduced coordination of a Mn atom at the surface) and of the induced moments reaches values of 6 to 8 mu(B), i.e., much higher than the limit set by Hund's rule for the spin moment of a free Mn atom.
Title:
Multiferroicity and spiral magnetism in FeVO4 with quenched Fe orbital moments
Authors:
Daoud-Aladine, A; Kundys, B; Martin, C; Radaelli, PG; Brown, PJ; Simon, C; Chapon, LC Author Full Names: Daoud-Aladine, A.; Kundys, B.; Martin, C.; Radaelli, P. G.; Brown, P. J.; Simon, C.; Chapon, L. C.
Source:
PHYSICAL REVIEW B 80 (22): Art. No. 220402 DEC 2009
Abstract:
FeVO4 has been studied by heat capacity, magnetic susceptibility, electric polarization and single-crystal neutron-diffraction experiments. The triclinic crystal structure is made of S-shaped clusters of six Fe3+ ions, linked by VO43- groups. Two long-range magnetic ordering transitions occur at T-N1=22 K and T-N2=15 K. Both magnetic structures are incommensurate and below T-N2, FeVO4 becomes weakly ferroelectric coincidentally with the loss of the collinearity of the magnetic structure in a very similar fashion than in the classical TbMnO3 multiferroic material. However we argue that the symmetry considerations and the mechanisms invoked to explain these properties in TbMnO3 do not straightforwardly apply to FeVO4. First, the magnetic structures, even the collinear structure, are all acentric so that ferroelectricity in FeVO4 is not correlated with the fact magnetic ordering is breaking inversion symmetry. Regarding the mechanism, FeVO4 has quenched orbital moments that questions the exact role of the spin-orbit interactions.
Title:
Comparative study on internal friction in an Al-Pd-Mn icosahedral quasicrystal and its crystal approximants
Authors:
So, YG; Sato, S; Edagawa, K; Mori, T; Tamura, R Author Full Names: So, Yeong-Gi; Sato, Shun; Edagawa, Keiichi; Mori, Takahiro; Tamura, Ryuji
Source:
PHYSICAL REVIEW B 80 (22): Art. No. 224204 DEC 2009
Abstract:
The internal friction was measured for an Al-Pd-Mn icosahedral phase (i-phase) and its 1/1 and 2/1 approximant phases in an Al-Pd-Mn-Si system in a forced flexural-oscillation mode in a frequency range of 0.05-20 Hz and a temperature range of 300-873 K. For the i-phase, large and small absorption peaks were observed with Q(-1)approximate to 1.3x10(-2) and 8x10(-4), respectively. These two peaks were absent for the 1/1-phase, which showed two other peaks instead. The 2/1-phase exhibited the features of both the i and 1/1-phases; it showed two peaks of the i-phase and one of the two peaks of the 1/1-phase. All the observed peaks were of the thermally activated relaxation type, and their activation enthalpies and frequency factors were evaluated. The larger peak of the i-phase, which was absent for the 1/1-phase and present with a much reduced intensity for the 2/1-phase, was shown to result from a relaxation process involving collective atomic motion. Collective and correl! ated phason jumps were discussed as a possible mechanism for it. It was speculated that the other peaks observed only for the approximant phases are due to Zener relaxations by the reorientation of atom pairs involving Si.
Title:
Excitation spectrum and magnetic field effects in a quantum critical spin-orbital system: The case of FeSc2S4
Authors:
Chen, G; Schnyder, AP; Balents, L Author Full Names: Chen, Gang; Schnyder, Andreas P.; Balents, Leon
Source:
PHYSICAL REVIEW B 80 (22): Art. No. 224409 DEC 2009
Abstract:
The orbitally degenerate A-site spinel compound FeSc2S4 has been experimentally identified as a "spin-orbital liquid," with strong fluctuations of both spins and orbitals. Assuming that the second-neighbor spin-exchange J(2) is the dominant one, we argued in a recent theoretical study [G. Chen , Phys. Rev. Lett. 102, 096406 (2009)] that FeSc2S4 is in a local "spin-orbital singlet" state driven by spin-orbit coupling, close to a quantum critical point, which separates the spin-orbital singlet phase from a magnetically and orbitally ordered phase. In this paper, we refine further and develop this theory of FeSc2S4. First, we show that inclusion of a small first-neighbor exchange J(1) induces a narrow region of incommensurate phase near the quantum critical point. Next, we derive the phase diagram in the presence of an external magnetic field B, and show that the latter suppresses the ordered phase. Lastly, we compute the field-dependent dynamical magnetic susceptibility chi(k,omega;B), from which we extract a variety of physical quantities. Comparison with and suggestions for experiment are discussed.
Title:
Kinetic magnetism and orbital order in iron telluride
Authors:
Turner, AM; Wang, F; Vishwanath, A Author Full Names: Turner, Ari M.; Wang, Fa; Vishwanath, Ashvin
Source:
PHYSICAL REVIEW B 80 (22): Art. No. 224504 DEC 2009
Abstract:
Iron telluride (FeTe), a relative of the iron-based high-temperature superconductors, displays unusual magnetic order and structural transitions. Here, we explore the idea that strong correlations may play an important role in these materials. We argue that the unusual orders observed in FeTe can be understood from a picture of correlated local moments with orbital degeneracy, coupled to a small density of itinerant electrons. A component of the structural transition is attributed to orbital, rather than magnetic ordering, introducing a strongly anisotropic character to the system along the diagonal directions of the iron lattice. Double exchange interactions couple the diagonal chains leading to the observed ordering wave vector. The incommensurate order in samples with excess iron arises from electron doping in this scenario. The strong anisotropy of physical properties in the ordered phase should be detectable by transport in single domains. Predictions for ARPES, inelastic neutron scattering and hole/electron doping studies are also made.
Title:
Pokrovsky-Talapov model at finite temperature: A renormalization-group analysis
Authors:
Lazarides, A; Tieleman, O; Smith, CM Author Full Names: Lazarides, A.; Tieleman, O.; Smith, C. Morais
Source:
PHYSICAL REVIEW B 80 (24): Art. No. 245418 DEC 2009
Abstract:
We calculate the finite-temperature shift of the critical wave vector Q(c) of the Pokrovsky-Talapov model using a renormalization-group analysis. Separating the Hamiltonian into a part that is renormalized and one that is not, we obtain the flow equations for the stiffness and an arbitrary potential. We then specialize to the case of a cosine potential, and compare our results to well-known results for the sine-Gordon model, to which our model reduces in the limit of vanishing driving wave vector Q=0. Our results may be applied to describe the commensurate-incommensurate phase transition in several physical systems and allow for a more realistic comparison with experiments, which are always carried out at a finite temperature.
Title:
Hyperfine Fields and Magnetic Structure in the B Phase of CeCoIn5
Authors:
Curro, NJ; Young, BL; Urbano, RR; Graf, MJ Author Full Names: Curro, Nicholas J.; Young, Ben-Li; Urbano, Ricardo R.; Graf, Matthias J.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 158 (3-4): 635-646 FEB 2009
Abstract:
We re-analyze Nuclear Magnetic Resonance (NMR) spectra observed at low temperatures and high magnetic fields in the field-induced B phase of CeCoIn5. The NMR spectra are consistent with incommensurate antiferromagnetic order of the Ce magnetic moments. However, we find that the spectra of the In(2) sites depend critically on the direction of the ordered moments, the ordering wavevector and the symmetry of the hyperfine coupling to the Ce spins. Assuming isotropic hyperfine coupling, the NMR spectra observed for H parallel to [100] are consistent with magnetic order with wavevector Q = pi (1+delta/a, 1/a, 1/c) and Ce moments ordered antiferromagnetically along the [100] direction in real space. If the hyperfine coupling has dipolar symmetry, then the NMR spectra require Ce moments along the [ 001] direction. The dipolar scenario is also consistent with recent neutron scattering measurements that find an ordered moment of 0.15 mu(B) along [001] and Q(n) = pi(1+delta/a, 1+delta/a, 1/c) with in-commensuration delta = 0.12 for field H parallel to [1 (1) over bar0]. Using these parameters, we find that a hyperfine field with dipolar contribution is consistent with findings from both experiments. We speculate that the B phase of CeCoIn5 represents an intrinsic phase of modulated superconductivity and antiferromagnetism that can only emerge in a highly clean system.
Title:
Observation of two separate charge density wave transitions in Gd2Te5 via transmission electron microscopy and high-resolution X-ray diffraction
Authors:
Shin, KY; Ru, N; Fisher, IR; Condron, CL; Toney, MF; Wu, YQ; Kramer, MJ Author Full Names: Shin, K. Y.; Ru, N.; Fisher, I. R.; Condron, C. L.; Toney, M. F.; Wu, Y. Q.; Kramer, M. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 489 (2): 332-335 JAN 21 2010
Abstract:
Gd2Te5 is a layered material consisting of alternating single and double square planar Te sheets. At room temperature the material hosts a complex lattice modulation characterized by multiple in-plane wavevectors. Diffraction measurements performed via transmission electron microscopy and high-resolution X-ray scattering reveal two distinct transitions at T-c1 = 410(3) and T-c2 = 532(3) K, associated with an on-axis incommensurate lattice modulation and an off-axis commensurate lattice modulation respectively. Our results show that the two lattice modulations are separate in origin but that there is some coupling between them. (C) 2009 Elsevier B.V. All rights reserved.

Update: 7-Jan-2010

Title:
First-Principles Modeling of Multiferroic RMn2O5
Authors:
Cao, K; Guo, GC; Vanderbilt, D; He, LX Author Full Names: Cao, Kun; Guo, Guang-Can; Vanderbilt, David; He, Lixin
Source:
PHYSICAL REVIEW LETTERS 103 (25): Art. No. 257201 DEC 18 2009
Abstract:
We investigate the phase diagrams of RMn2O5 via a first-principles effective-Hamiltonian method. We are able to reproduce the most important features of the complicated magnetic and ferroelectric phase transitions. The calculated polarization as a function of temperature agrees very well with experiments. The dielectric-constant step at the commensurate-to-incommensurate magnetic phase transition is well reproduced. The microscopic mechanisms for the phase transitions are discussed.
Title:
Electric Control of Spin Helicity in Multiferroic Triangular Lattice Antiferromagnet CuCrO2 with Proper-Screw Order
Authors:
Soda, M; Kimura, K; Kimura, T; Matsuura, M; Hirota, K Author Full Names: Soda, Minoru; Kimura, Kenta; Kimura, Tsuyoshi; Matsuura, Masato; Hirota, Kazuma
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (12): Art. No. 124703 DEC 2009
Abstract:
We have carried out a spin-polarized-neutron study on multiferroic CuCrO2 to clarify the origin of the ferroelectricity. The neutron results demonstrate that an incommensurate proper-screw magnetic structure of CuCrO2 induces electric polarization. Not only the magnetic structure but also the oxygen location contributes to the ferroelectricity of CuCrO2. The electric polarization of CuCrO2 can be explained not by a conventional spin-current model but by a theoretical prediction proposed by Arima. The spin helicities of CuCrO2 can be reversed by the reversal of the electric field E in the multiferroic phase.
Title:
Coexistence of the antiferromagnetic and superconducting order and its effect on spin dynamics in electron-doped high-T-c cuprates
Authors:
Chen, CP; Jiang, HM; Li, JX Author Full Names: Chen, Cui-Ping; Jiang, Hong-Min; Li, Jian-Xin
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (3): Art. No. 035701 JAN 27 2010
Abstract:
In the framework of the slave-boson approach to the t-t'-t ''-J model, it is found that for electron-doped high-T-c cuprates, the staggered antiferromagnetic (AF) order coexists with the superconducting (SC) order in a wide doping level ranged from underdoped to nearly optimally doped at the mean-field level. In the coexisting phase, it is revealed that the spin response is commensurate in a substantial frequency range below a crossover frequency omega(c) for all dopings considered, and it switches to the incommensurate structure when the frequency is higher than omega(c). This result is in agreement with the experimental measurements. Comparison of the spin response between the coexisting phase and the pure SC phase with a d(x2-y2)-wave pairing plus a higher harmonics term (DP + HH) suggests that the inclusion of the two-band effect is important to consistently account for both the dispersion of the spin response and the non-monotonic gap behavior in the electron-doped cuprates.
Title:
The modulated structure and ferromagnetic insulating state in a nine-layer BaRuO3
Authors:
Du, CH; Yao, CH; Ling, DC; Tang, MT; Hsu, FC; Liu, HL; Hatton, PD; Ikeda, N Author Full Names: Du, Chao-Hung; Yao, Chang-Hung; Ling, Dah-Chin; Tang, Mau-Tsu; Hsu, Fon-Chi; Liu, Hsiang-Lin; Hatton, P. D.; Ikeda, Naoshi
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (3): Art. No. 036003 JAN 27 2010
Abstract:
We report the observation of a modulated structure and a ferromagnetic insulating state in a high quality single crystal of a nine-layer BaRuO3. Using x-ray scattering, the modulated satellites were observed to double the unit cell along the c-axis at low temperature. The ferromagnetic insulating state is confirmed by magnetic and resistivity measurements. Analyzing the peak profiles from the modulation and host structure respectively, showed a lattice distortion at T similar to 55 K. These findings elucidate the intimate relationship between ferromagnetism and lattice distortion in a nine-layer BaRuO3.
Title:
Evidence for a Self-bound Liquid State and the Commensurate-Incommensurate Coexistence in 2D He-3 on Graphite
Authors:
Sato, D; Tsuji, D; Takayoshi, S; Obata, K; Matsui, T; Fukuyama, H Author Full Names: Sato, D.; Tsuji, D.; Takayoshi, S.; Obata, K.; Matsui, T.; Fukuyama, Hiroshi
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 158 (1-2): 201-206 Sp. Iss. SI JAN 2010
Abstract:
We made heat-capacity measurements of two dimensional (2D) He-3 adsorbed on graphite preplated with monolayer He-4 in a wide temperature range (0.1 <= T <= 80 mK) at densities higher than that for the 4/7 phase (= 6.8 nm(-2)). In the density range of 6.8 <= rho <= 8.1 nm(-2), the 4/7 phase is stable against additional 3He atoms up to 20% and they are promoted into the third layer. We found evidence that such promoted atoms form a self-bound 2D Fermi liquid with an approximate density of 1 nm(-2) from the measured density dependence of the gamma-coefficient of heat capacity. We also show evidence for the first-order transition between the commensurate 4/7 phase and the ferromagnetic incommensurate phase in the second layer in the density range of 8.1 <= rho <= 9.5 nm(-2).
Title:
Growth of large single-grain quasicrystals in the Ag-In-Yb system by Bridgman method
Authors:
Cui, C; Tsai, AP Author Full Names: Cui, Can; Tsai, An Pang
Source:
JOURNAL OF CRYSTAL GROWTH 312 (1): 131-135 DEC 15 2009
Abstract:
Well-defined single-grain Ag-In-Yb icosahedral quasicrystals of order of centimeter have been grown by the Bridgman method. The scanning electron microscopy (SEM) observation showed that the compositional distribution in the single-grain quasicrystals is uniform and Laue X-ray diffraction measurements verified the formation of single-grain icosahedral quasicrystals. The natural growth direction of the single-grain quasicrystals; is close to a direction parallel to a 2-fold axis. It turns out that the Yb content in the initial melt limited within 15-16 at.% is a critical factor determining the formation of single-grain quasicrystal. Based on the experimental result, the mechanism of the growth of single-grain quasicrystal and formation of intermediate zone between quasicrystal and approximant phases are discussed. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Dense quasicrystalline tilings by squares and equilateral triangles
Authors:
O'Keeffe, M; Treacy, MMJ Author Full Names: O'Keeffe, Michael; Treacy, Michael M. J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 66: 5-9 Part 1 JAN 2010
Abstract:
Dense square-symmetry tilings of the plane by equilateral triangles and squares are described. Repeated substitution of a vertex of a tiling by groups of vertices leads asymptotically to a limiting density that is independent of the starting pattern and to a family of quasicrystalline patterns with 12-fold symmetry. Diffraction patterns were computed by treating the vertices as point scatterers. As the number of substitutions increases, and as the unit-cell size increases, the diffraction patterns from a single unit cell develop a near-perfect 12-fold symmetry. In addition, the low-intensity background scattering in the diffraction patterns exhibits fractal-like self-similar properties, with motifs of local intensity recursively decorating the more intense features as the number of substitutions progresses.

Update: 31-Dec-2009

Title:
Effect of the "negative chemical" pressure on the temperatures of phase transitions in the TlInS2 layered crystal
Authors:
Seyidov, MHY; Suleymanov, RA; Salehli, F Author Full Names: Seyidov, M. - H. Yu.; Suleymanov, R. A.; Salehli, F.
Source:
PHYSICS OF THE SOLID STATE 51 (12): 2513-2519 DEC 2009
Abstract:
The temperature dependences of the permittivity of TlInS2(1 -x)Se2x solid solutions have been experimentally investigated in the temperature range including the points of structural phase transitions in the solid solutions. It has been established that the isovalent substitution of selenium for sulfur in the anion sublattice of the TlInS2(1 - x)Se2x solid solutions shifts the phase transition temperatures T (i) and T (c) toward the low-temperature range with a simultaneous decrease in the temperature interval of the existence of the incommensurate phase. The T-x phase diagram is constructed for the solid solutions under study and the coordinates are determined for a critical point (of the Lifshitz type) at which the lines T (i) (x) and T (c) (x) converge in the phase diagram. The pattern of the T-x phase diagram for the TlInS2(1 - x)Se2x solid solutions has been analyzed within the phenomenological model of a virtual crystal.

Update: 24-Dec-2009

Title:
Hydriding of Ti45Zr38Ni17-xFex nanocompounds
Authors:
Zywczak, A; Shinya, D; Gondek, L; Takasaki, A; Figiel, H Author Full Names: Zywczak, A.; Shinya, Daigo; Gondek, L.; Takasaki, Akito; Figiel, H.
Source:
SOLID STATE COMMUNICATIONS 150 (1-2): 1-4 JAN 2010
Abstract:
Ti-based quasicrystals belong to the second largest group of the stable quasicrystals, showing attractive properties as hydrogen storage materials. The Ti45Zr38Ni17 intermetallic compound forms an icosahedral (i-phase) structure, in which Ti and Zr atoms possess very good chemical affinity for hydrogen absorption. We modified the Ti45Zr38Ni17 compounds by substituting 3d metals (iron) for Ni to obtain amorphous phase. The samples were produced by mechanical alloying. The 3d metal atoms are located in the same positions as nickel. The structural characterization was made by means of XRD measurements. Thermodynamic properties were studied by differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS). The obtained amorphous phases Ti45Zr38Ni(9,13)Fe(8,4) transform to the i-phase at the similar temperature range as Ti45Zr38Ni17. The final concentration of absorbed hydrogen depends on the amount of Fe. When increasing the amount of iron, the hydrogen release temperature becomes lower. After hydriding, the samples decompose into simple metal hydrides. (C) 2009 Elsevier Ltd. All rights reserved.
Title:
MODULATED MAGNETIC STATE OF A NONUNIFORMLY STRAINED IRON BORATE SINGLE CRYSTAL INDUCED BY A MAGNETIC FIELD
Authors:
Boidedaev, SR; Sokolov, BY Author Full Names: Boidedaev, S. R.; Sokolov, B. Yu.
Source:
RUSSIAN PHYSICS JOURNAL 52 (7): 759-762 JUL 2009
Abstract:
A remarkable feature of technical magnetization of a nonuniformly strained iron borate (FeBO3) crystal is long-period spatial modulation of the magnetic order parameter for this weak ferromagnet observed in external magnetic field H-1 <= H <= H-2 [1]. Investigations performed in [1] have demonstrated that the modulated magnetic structure (MMS) of nonuniformly strained FeBO3 arises when the vector. is oriented near a certain reference crystal direction of the easy magnetization (basal) crystal plane. During magnetization in this direction, rotation of the ferromagnetism vector m (or of the antiferromagnetism vector l perpendicular to m by definition) in the basal plane occurs somewhat specifically: after the termination of displacements of the domain boundaries, the single domain structure is first formed in the crystal, and the local vectors m appear oriented along the easy magnetization direction (the uniform low-field phase); then at H = H-1! , the magnetic structure of the crystal changes from the uniform to spatially modulated structure stable for H-1 <= H <= H-2 (the sinusoidal phase); then at H = H-2, the crystal passes once again to the uniform magnetic state with m parallel to H (the uniform high-field phase). The sinusoidal phase has the form of a static transverse spin wave linearly polarized in the basal plane in which the azimuth of the local vector m oscillates about the average magnetization direction. Since the MMS is not observed in FeBO3 without mechanical stresses, the specific feature of magnetization of the examined crystal established in [1] was attributed to the occurrence in its basal plane of additional spatially nonuniform (random) magnetic anisotropy caused by local deformations of the crystal lattice at mechanical stresses. According to models of crystal transition from the uniform to modulated magnetic state suggested in [1], the spatial orientation of the vector m (l) in the sinusoidal magnetic phase is determined by competition between the orienting action of the exchange forces on the local sublattice magnetic moments and the disorienting action of the nonuniform magnetic anisotropy forces. Experimental investigations performed in [1] demonstrated that the MMS was observed at temperatures. T < T-s approximate to 140 K; in the examined temperature interval (90 <= T <= 140 K), the spatial MMS period D remained virtually independent of., but significantly decreased with increasing.. In this case, the direction along which modulation of the azimuth of the vector m (l) is observed is independent of. and.; the amplitude of deviation of the local vector m from the average crystal magnetization direction decreases with increasing. and/or.; the field strengths at which the MMS is observed Delta H = (H-2 - H-1) -> 0 when T -> T-s; transitions low-field uniform phase <-> sinusoidal phase <-> high-field uniform phase are the first-order magnetic phase transitions. The present work analyzes the above-listed main properties and conditions of existence of the MMS in a nonuniformly strained FeBO3 crystal using the model suggested in [1].

Update: 17-Dec-2009

Title:
Origin of the long-wavelength magnetic modulation in Ca3Co2O6
Authors:
Chapon, LC Author Full Names: Chapon, L. C.
Source:
PHYSICAL REVIEW B 80 (17): Art. No. 172405 NOV 2009
Abstract:
The origin of the long-wavelength incommensurate magnetic structure of Ca3Co2O6 is discussed considering possible interchains super-superexchange paths. The experimental value of the propagation vector k=(0,0,Delta) with Delta>1 can be reproduced only if one considers the next-nearest super-superexchange interaction. A spin-dimer analysis using the extended Huckel tight-binding method confirms that, despite longer interatomic Co-Co distances, the latter interaction is indeed much stronger. The stability of the observed structure with respect to certain commensurate states is discussed.
Title:
Magnetic and electronic properties of Eu1-xSrxMnO3 (0.3 < x < 0.7) single crystals
Authors:
Tomioka, Y; Kumai, R; Ito, T; Tokura, Y Author Full Names: Tomioka, Y.; Kumai, R.; Ito, T.; Tokura, Y.
Source:
PHYSICAL REVIEW B 80 (17): Art. No. 174414 NOV 2009
Abstract:
Among versatile perovskite manganites showing colossal magnetoresistance (CMR), Eu1-xSrxMnO3 around x similar to 0.4 shows the ferromagnetic metal with the lowest transition temperature (similar to 40 K) due to the narrowest one-electron bandwidth and hence is readily subject to the drastic phase changes with variations in temperature, magnetic field, and hole doping (x). We have investigated the variation in the electronic state with x with use of single crystals. As x increases, the ferromagnetic metal at 0.38 < x < 0.47 changes to a spin-glasslike insulator at 0.48 < x < 0.5, the layered antiferromagnetic (A-type) state at 0.51 < x < 0.6, and the chained antiferromagnetic (C-type) state at 0.6 < x, respectively. Due to the increased disorder upon alloying of Eu/Sr, the charge/orbital ordering with the modulation vector (0, q, 0) with q=1/2 in the orthorhombic Pbnm setting (a(0)similar to b(0)similar to c(0)/root 2 similar to root 2a(p), a(p) being the lattice parameter of the pseudocubic lattice) cannot be formed in a long range but remains short ranged. In the vicinity of x=0.5, an application of an external magnetic field removes such short-range charge/orbital ordering (q=1/2) to cause an insulator to metal transition or CMR. In a broad range of x (0.55 < x < 0.59), the critical temperature for the layered antiferromagnetic state is relatively lowered and alternatively the charge/orbital ordering with q similar to 1/3 becomes to be visible. It has also been found that the modulation is temperature dependent; commensurate with q similar to 1/3 upon the transition while incommensurate with q>1/3 at low temperatures.
Title:
Transition from spin-density-wave to layered antiferromagnetic state induced by hydrogen as a test for the origin of spin-density waves in chromium
Authors:
Uzdin, VM; Zabel, H; Remhof, A; Hjorvarsson, B Author Full Names: Uzdin, V. M.; Zabel, H.; Remhof, A.; Hjorvarsson, B.
Source:
PHYSICAL REVIEW B 80 (17): Art. No. 174418 NOV 2009
Abstract:
Neutron scattering experiments of Cr/V(001) superlattices are discussed, which show that the incommensurate spin-density-wave (SDW) in thick Cr layers becomes suppressed when the V spacer layers are loaded with hydrogen. The hydrogen loading triggers a transition from the incommensurate SDW state to a commensurate antiferromagnetic state. Model Hamiltonian calculations are presented, which show that this transition is not connected with the nesting property of the Cr Fermi surface. Instead, the transition is a manifestation of the antiferromagnetic ground state of Cr, which is separated from the incommensurate SDW state by an energy barrier. Hydrogen is identified as an effective trigger for reducing the activation barrier, enabling the system to relax to the ground state.
Title:
Mutual enhancement of magnetism and Fulde-Ferrell-Larkin-Ovchinnikov superconductivity in CeCoIn5
Authors:
Mierzejewski, M; Ptok, A; Maska, MM Author Full Names: Mierzejewski, Marcin; Ptok, Andrzej; Maska, Maciej M.
Source:
PHYSICAL REVIEW B 80 (17): Art. No. 174525 NOV 2009
Abstract:
Recent experiments on CeCoIn5 suggest an unusual interplay between superconducting and magnetic orders that gives rise to a multicomponent (magnetosuperconducting) phase. We demonstrate that characteristics of CeCoIn5 make this system particularly well suited for the onset of such a phase. Based on general considerations, we show that superconductivity with nonzero Cooper-pair momentum may lead to an enhancement of the spin-spin response function and, simultaneously, incommensurate spin-density wave may enhance the Cooper-pair susceptibility.
Title:
Incommensurate spin correlation driven by frustration in BiCu2PO6
Authors:
Mentre, O; Janod, E; Rabu, P; Hennion, M; Leclercq-Hugeux, F; Kang, J; Lee, C; Whangbo, MH; Petit, S Author Full Names: Mentre, O.; Janod, E.; Rabu, P.; Hennion, M.; Leclercq-Hugeux, F.; Kang, J.; Lee, C.; Whangbo, M. -H.; Petit, S.
Source:
PHYSICAL REVIEW B 80 (18): Art. No. 180413 NOV 2009
Abstract:
The magnetic properties of BiCu2PO6 have been analyzed by means of magnetic-susceptibility and inelastic neutron-scattering measurements on powder samples by evaluating the spin-exchange interactions on the basis of density-functional calculations and by simulating the inelastic neutron scattering in terms of spin-exchange parameters. BiCu2PO6 exhibits magnetic properties described by the two-leg spin ladder with strong spin frustration along each leg chain and has a gapped quantum singlet ground state with excited magnetic states, showing an incommensurate dispersion arising from frustration.
Title:
Basic Co-rich decagonal Al-Co-Ni: Average structure
Authors:
Strutz, A; Yamamoto, A; Steurer, W Author Full Names: Strutz, Angelica; Yamamoto, Akiji; Steurer, Walter
Source:
PHYSICAL REVIEW B 80 (18): Art. No. 184102 NOV 2009
Abstract:
The two-layer average structure of the high-temperature phase basic Co-rich decagonal Al72.5Co18.5Ni9 was determined based on single-crystal x-ray diffraction data. The five-dimensional (5D) structure model was refined in the noncentrosymmetric 5D space group P10m2 (112 parameters, wR=0.123 and R=0.156 for 957 reflections). The close relationship of the model structure with that of W-Al-Co-Ni, a << 3/2,2/1 >> approximant, is shown.
Title:
Magnetism in CeFeAsO1-xFx and LaFeAsO1-xFx from first principles
Authors:
Sharma, S; Shallcross, S; Dewhurst, JK; Sanna, A; Bersier, C; Massidda, S; Gross, EKU Author Full Names: Sharma, S.; Shallcross, S.; Dewhurst, J. K.; Sanna, A.; Bersier, C.; Massidda, S.; Gross, E. K. U.
Source:
PHYSICAL REVIEW B 80 (18): Art. No. 184502 NOV 2009
Abstract:
Using state-of-the-art first-principles calculations we study the magnetic behavior of CeOFeAs. We find the Ce layer moments oriented perpendicular to those of the Fe layers. An analysis of incommensurate magnetic structures reveals that the Ce-Ce magnetic coupling is rather weak with, however, a strong Fe-Fe and Fe-Ce coupling. Comparison of the origin of the tetragonal to orthorhombic structural distortion in CeOFeAs and LaOFeAs shows marked differences; in CeOFeAs the distortion is stabilized by a lowering of spectral weight at the Fermi level, while in LaOFeAs by increase in Fe spin moment. Finally, we investigate the impact of electron doping upon CeOFeAs and LaOFeAs and show that (a) while in CeOFeAs the ground-state Fe moment remains largely unchanged by doping, the stability of magnetic order goes to zero at a doping that corresponds well to the vanishing of the Neacuteel temperature and, (b) in contrast the LaOFeAs system remains magnetic wit! h a slowly vanishing moment as a function of doping.
Title:
Optimizing the thermoelectric efficiency of icosahedral quasicrystals and related complex alloys
Authors:
Macia, E Author Full Names: Macia, Enrique
Source:
PHYSICAL REVIEW B 80 (20): Art. No. 205103 NOV 2009
Abstract:
In this work we analyze the potential role of quasicrystals and related alloys in thermoelectric material research. Relatively large figure of merit values are expected for those samples exhibiting two properly located narrow features in the density of states close to the Fermi level. It is expected that optimized quasicrystals will perform better at relatively low temperatures, whereas the ZT curve of complex metallic alloys reaches its maximum at high temperatures. Among state-of-the-art quasicrystals most promising samples for thermoelectric applications are found in the AlPd (Mn,Re) system. Quasicrystalline and related approximants in the ScMgCuGa and CaAuIn systems, synthesized on the basis of pseudogap tuning concepts, appear as promising candidates as well.
Title:
Disordered, quasicrystalline and crystalline phases of densely packed tetrahedra
Authors:
Haji-Akbari, A; Engel, M; Keys, AS; Zheng, XY; Petschek, RG; Palffy-Muhoray, P; Glotzer, SC Author Full Names: Haji-Akbari, Amir; Engel, Michael; Keys, Aaron S.; Zheng, Xiaoyu; Petschek, Rolfe G.; Palffy-Muhoray, Peter; Glotzer, Sharon C.
Source:
NATURE 462 (7274): 773-U91 DEC 10 2009
Abstract:
All hard, convex shapes are conjectured by Ulam to pack more densely than spheres(1), which have a maximum packing fraction of phi = pi/root 18 approximate to 0.7405. Simple lattice packings of many shapes easily surpass this packing fraction(2,3). For regular tetrahedra, this conjecture was shown to be true only very recently; an ordered arrangement was obtained via geometric construction with phi = 0.7786 (ref. 4), which was subsequently compressed numerically to phi = 0.7820 (ref. 5), while compressing with different initial conditions led to phi = 0.8230 ( ref. 6). Here we show that tetrahedra pack even more densely, and in a completely unexpected way. Following a conceptually different approach, using thermodynamic computer simulations that allow the system to evolve naturally towards high-density states, we observe that a fluid of hard tetrahedra undergoes a first-order phase transition to a dodecagonal quasicrystal (7-10), which can be compressed to a packing fraction of phi = 0.8324. By compressing a crystalline approximant of the quasicrystal, the highest packing fraction we obtain is phi = 0.8503. If quasicrystal formation is suppressed, the system remains disordered, jams and compresses to phi = 0.7858. Jamming and crystallization are both preceded by an entropy-driven transition from a simple fluid of independent tetrahedra to a complex fluid characterized by tetrahedra arranged in densely packed local motifs of pentagonal dipyramids that form a percolating network at the transition. The quasicrystal that we report represents the first example of a quasicrystal formed from hard or non-spherical particles. Our results demonstrate that particle shape and entropy can produce highly complex, ordered structures.
Title:
Effects of the fourth component and undercooling on morphology of primary Mg-Zn-Y icosahedral quasicrystal phase under normal casting conditions
Authors:
Wang, ZF; Zhao, WM; Hur, BY; Huang, CY; Yu, CQ Author Full Names: Wang Zhifeng; Zhao Weimin; Hur, Bo-Young; Huang Chunying; Yu Chengquan
Source:
CHINA FOUNDRY 6 (4): 293-299 NOV 2009
Abstract:
The paper presents some results of the investigation on effects of the fourth component (Ti, C, Sb or Cu) and undercooling on the morphology, size and forming process of primary Mg-Zn-Y icosahedral quasicrystal phase (I-phase) under normal casting conditions. The result shows that the addition of certain amount of fourth component can transform I-phase morphology from petal-like to spherical. However, I-phase will grow up to petal-like if superfluous addition of the fourth component applied. It is also found that the solidified morphology of I-phase depends on the stability of spherical I-phase during the subsequent growth, and critical radius of maintaining the spherical I-phase interface relatively stable. Further, mini-sized spherical I-phase can be produced with high content of the fourth component by undercooling. Such findings are benefical for industrializing Mg-based quasicrystals.

Update: 11-Dec-2009

Title:
Influence of Boron Additions on Dissipative Properties of Quasicrystalline Al-Cu-Fe Coatings
Authors:
Ustinov, AI; Polishchuk, SS; Telychko, VA; Melnychenko, TV Author Full Names: Ustinov, A. I.; Polishchuk, S. S.; Telychko, V. A.; Melnychenko, T. V.
Source:
METALLOFIZIKA I NOVEISHIE TEKHNOLOGII 31 (6): 847-854 JUN 2009
Abstract:
Influence of boron on mechanical and dissipative properties of quasicrystalline Al-Cu-Fe coatings is studied. As shown, the hardness of coatings based on quasicrystalline Al-Cu-Fe phase under alloying with boron remains practically unchanged, while their fracture toughness slightly increases. At the same time, damping capacity of nanoquasicrystalline coating Al-Cu-Fe-B is found to be essentially lower as compared with that of similar coating without boron. Possible mechanisms of the change in dissipative properties are discussed.
Title:
The commensurate modulated structure of the metastable state in spin crossover complex [Fe(abpt)(2)(NCS)(2)]
Authors:
Sheu, CF; Chen, SM; Wang, SC; Lee, GH; Liu, YH; Wang, Y Author Full Names: Sheu, Chou-Fu; Chen, Szu-Miao; Wang, Shih-Chi; Lee, Gene-Hsiang; Liu, Yi-Hung; Wang, Yu
Source:
CHEMICAL COMMUNICATIONS (48): 7512-7514 2009
Abstract:
Two new polymorphs (C and D) of [t-Fe(abpt)(2)(NCS)(2)] are characterized, a commensurate modulated structure with the c axis tripled in the thermally quenched metastable high spin state at 25 K is found in polymorph C.
Title:
Superplastic Behavior in Mg-Zn-Y Alloy with Dispersed Quasicrystal Phase Particles
Authors:
Somekawa, H; Singh, A; Mukai, T Author Full Names: Somekawa, Hidetoshi; Singh, Alok; Mukai, Toshiji
Source:
ADVANCED ENGINEERING MATERIALS 11 (10): 782-787 OCT 2009

Update: 4-Dec-2009

Title:
Influence of polytypism on structural phase transformations in TlGaSe2 crystals
Authors:
Borovoi, NA; Gololobov, YP; Isaenko, GL; Stepanishchev, NB Author Full Names: Borovoi, N. A.; Gololobov, Yu. P.; Isaenko, G. L.; Stepanishchev, N. B.
Source:
PHYSICS OF THE SOLID STATE 51 (11): 2367-2370 NOV 2009
Abstract:
The polytypism is found to have a significant influence on the structural transformation of the crystal lattice of the TlGaSe2 ferroelectric with variations in temperature. In the 2C-polytype, unlike the C-polytype, a first-order structural phase transition, which leads to a change in the translational symmetry along the C axis, is not observed in the temperature range T = 90-300 K and a second-order phase transition due to the formation of an incommensurate phase occurs at a higher temperature.
Title:
Crossover Induced by Spin-Density-Wave Interference in the Coherence of Singlet Electron Pairs in Cr
Authors:
Robinson, JWA; Halasz, GB; Blamire, MG Author Full Names: Robinson, J. W. A.; Halasz, Gabor B.; Blamire, M. G.
Source:
PHYSICAL REVIEW LETTERS 103 (20): Art. No. 207002 NOV 13 2009
Abstract:
To study the interaction of s-wave superconductivity with spin-density waves (SDWs), we have measured a series of Nb/Cr/Nb Josephson junctions and determined the coherence length xi describing the decay of the critical current with Cr thickness, L. We observe a crossover in xi from approximately 14 nm to 4 nm as L increases to 10 nm, which is consistent with a transition from commensurate to incommensurate SDWs expected for this thickness range.
Title:
Ferroelastic crystals and their nonlinear elastic properties observed in frequency range from gigahertz to milihertz
Authors:
Wiesner, M Author Full Names: Wiesner, Maciej
Source:
PHASE TRANSITIONS 82 (10): 699-754 2009
Abstract:
The experiments reported in this article have been performed to unify the results of earlier and recent determinations of parameters describing the elastic properties of Rb4LiH3(SO4)4, LiCsSO4 (LCS) and KH2PO4 crystals measured by different experimental methods. The above crystals undergo a second-order phase transition, incommensurate phase transition (PT) and a first-order but close to second-order phase transition, respectively. To investigate the elastic properties of the crystals in the frequency range from 10-1 to 1010 Hz, five experimental methods were applied: dynamic mechanical analysis, piezoelectric resonance, composite oscillator bar, ultrasonic wave propagation and Brillouin light scattering. The results of the experiments allowed identification of the processes contributing to the elastic response of the crystals investigated. Moreover, for the LCS crystal a model of the incommensurate PT was presented.
Title:
Quasicrystalline phase formation in the conventionally solidified Al-Cu-Fe system
Authors:
Gogebakan, M; Avar, B; Uzun, O Author Full Names: Gogebakan, M.; Avar, B.; Uzun, O.
Source:
MATERIALS SCIENCE-POLAND 27 (3): 919-926 2009
Abstract:
Structural characteristics and thermal behaviour of the conventionally solidified Al-Cu-Fe alloys with nominal compositions of Al70Cu20Fe10, Al65Cu20Fe15 and Al63Cu25Fe12 were investigated by X-ray diffraction, scanning electron microscopy, and differential thermal analysis techniques. Results show that a single quasicrystalline phase forms in a conventionally solidified Al65Cu20Fe15 alloy, being thermodynamically stable without phase transition up to the melting point. A cubic AlFe(Cu) solid solution, identified as beta phase, and a cubic AlCu(Fe) solid solution, identified as tau phase, were observed with quasicrystalline phase for Al63Cu25Fe12 alloy. Conventional solidification of Al70Cu20Fe10 alloy does not result in quasicrystalline phase formation. However, the formation of quasicrystalline phase in conventionally solidified Al70Cu20Fe10 alloy was observed after additional annealing at elevated temperature. SEM micrographs for Al70Cu20Fe10 and Al63Cu25Fe12 alloys after annealing at 700 degrees C for 4 h revealed the formation of pentagonal dodecahedrons in the quasicrystalline phase, with an edge size of about 30 mu m.
Title:
Monte-Carlo investigation of an anisotropic Ising model
Authors:
Murtazaev, AK; Ibaev, ZG Author Full Names: Murtazaev, A. K.; Ibaev, Zh. G.
Source:
LOW TEMPERATURE PHYSICS 35 (10): 792-796 OCT 2009
Abstract:
The Monte Carlo method is used to study long-period modulated structures in an anisotropic Ising model with competing interactions (ANNNI model). The character, particularities, and dependence of the modulated structures on the temperature and ratio of the exchange interaction constants between the nearest and next-to-nearest neighbors are determined. The phase diagram is constructed. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3253402]
Title:
Lattice Distortion Coupled with Magnetic Ordering in a Triangular Lattice Antiferromagnet CuCrO2
Authors:
Kimura, K; Otani, T; Nakamura, H; Wakabayashi, Y; Kimura, T Author Full Names: Kimura, Kenta; Otani, Tsuyoshi; Nakamura, Hiroyuki; Wakabayashi, Yusuke; Kimura, Tsuyoshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (11): Art. No. 113710 NOV 2009
Abstract:
We investigated magnetostrictive properties of a triangular lattice antiferromagnet CuCrO2 showing an incommensurate proper-screw spin order by means of x-ray diffraction and strain gauge measurements. A deformation of the triangular lattice plane leading to a lowered crystallographic symmetry was found upon the magnetic ordering, which demonstrates a strong spin-lattice coupling in this system. The resultant multiple structural domains can be successfully arranged by magnetic field cooling procedures. We discuss the relationship between the lattice distortion and incommensurability in CuCrO2.
Title:
Renormalization of Commensurate Magnetic Peak in Ni-Doped La1.85Sr0.15CuO4
Authors:
Matsuura, M; Kofu, M; Kimura, H; Hirota, K Author Full Names: Matsuura, Masato; Kofu, Maiko; Kimura, Hiroyuki; Hirota, Kazuma
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (11): Art. No. 114703 NOV 2009
Abstract:
We have studied magnetic excitations in impurity-doped La(1.85)Sr(0.15)Cu(1-y)A(y)O(4) (A = Ni or Zn) by neutron scattering. The dispersion for Zn:y = 0.017 is similar to that for the impurity-free sample: incommensurate peaks with incommensurability delta = 0.12 +/- 0.01 (rlu) do not change their positions up to 21 meV. On the other hand, for Ni:y = 0.029, two incommensurate peaks observed at low energies suddenly change into a single broad commensurate peak at E-cross = 15 meV. Compared with that for the impurity-free sample with a similar Sr concentration of x = 0.16, E-cross for Ni:y = 0.029 is decreased by nearly the same factor as the reduction in T-c. This is very similar to the shift of resonance energy (E-res) in Ni-doped YBa2Cu3O7. These common impurity effects on the shifts of E-cross and E-res suggest the same magnetic origin of the resonance peak in YBa2Cu3O6+x and that of the crossing point of upward and downward dispersions in La2-xSrxCuO4. We propose that the sudden change in the dispersions is better described by a crossover from incommensurate spin fluctuations to a gapped spin wave rather than an hourglass-like dispersion.
Title:
Antiferromagnetic Order and pi-Triplet Pairing in the Fulde-Ferrell-Larkin-Ovchinnikov State
Authors:
Yanase, Y; Sigrist, M Author Full Names: Yanase, Youichi; Sigrist, Manfred
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (11): Art. No. 114715 NOV 2009
Abstract:
The anti ferromagnetic Fulde-Ferrell-Larkin-Ovchinnikov (AFM-FFLO) state of coexisting d-wave FFLO superconductivity and incommensurate AFM order is studied on the basis of Bogoliubov-de Gennes (BdG) equations. We show that the incommensurate AFM order is stabilized in the FFLO state by the appearance of the Andreev bound state localized around the zeros of the FFLO order parameter. The AFM-FFLO state is further enhanced by the induced pi-triplet superconductivity (pair density wave). The AFM order occurs in the FFLO state even when it is neither stable in the normal state nor in the BCS state. The order parameters of the AFM order, d-wave superconductivity, and pi-triplet pairing are investigated by focusing on their spatial structures. Roles of the spin fluctuations beyond the BdG equations are discussed. Their relevance to the high-field superconducting phase of CeCoIn5 is discussed.
Title:
Atomic dynamics of a d-AlNiFe decagonal quasicrystal
Authors:
Parshin, PP; Zemlyanov, MG; Panova, GK; Shikov, AA; Brand, RA; Grushko, B Author Full Names: Parshin, P. P.; Zemlyanov, M. G.; Panova, G. Kh.; Shikov, A. A.; Brand, R. A.; Grushko, B.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 109 (4): 645-651 OCT 2009
Abstract:
The atomic dynamics of an Al71.3Ni24Fe4.7 decagonal quasicrystal has been investigated using the isotopic contrast method for inelastic neutron scattering. The partial vibrational spectra of the Ni, Fe, and Al atoms and the spectrum of the thermal vibrations of the alloy have been reconstructed directly from the experimental data without any model assumptions. The cutoff energies and the positions of the main features of the spectra have been determined. It has been revealed that the average binding energy of the nickel atoms in the quasicrystal under investigation is lower than that of the iron atoms and the vibrational spectrum of the aluminum atoms is noticeably harder than the spectrum of the pure metal. The results obtained for the d-AlNiFe decagonal quasicrystal have been compared with the previously published data for an i-AlCuFe icosahedral quasicrystal.

Update: 26-Nov-2009

Title:
Long-period states of a crystal finite-size-particle system
Authors:
Dmitriev, SV; Potekaev, AI; Samsonov, AV Author Full Names: Dmitriev, S. V.; Potekaev, A. I.; Samsonov, A. V.
Source:
RUSSIAN PHYSICS JOURNAL 52 (6): 622-639 JUN 2009
Abstract:
A one-dimensional model is proposed, which ensures description of origination and main properties of longperiod and incommensurate phases of crystal having complex structure and consists of comparatively rigid "atomic clusters". In the case where reciprocal rotations of theses clusters are considerably large, not only translational but also rotational degrees of freedom have to be taken into account for the clusters. It is consideration of the rotational degrees of freedom which might provide for formation of long-period states and development of a number of physical effects, such as a variety of soliton solutions (of domain walls) and their non-trivial dynamics.
Title:
High-resolution electron microscopy for incommensurate structure of KxRhO2 crystal
Authors:
Yubuta, K; Shibasaki, S; Terasaki, I; Kajitani, T Author Full Names: Yubuta, Kunio; Shibasaki, Soichiro; Terasaki, Ichiro; Kajitani, Tsuyoshi
Source:
PHILOSOPHICAL MAGAZINE 89 (31): 2813-2822 2009
Abstract:
An incommensurate, (3 + 2)- dimensional structure is locally observed in a K0.49RhO2 crystal synthesized by the flux growth method. The averaged potassium to rhodium ratio of the grown crystals was determined as 0.49 using an electron probe microanalyzer operated in the wave dispersive spectroscopy mode. The potassium content of the incommensurate phase was determined as 0.25 by the transmission electron microscopy-energy dispersive spectroscopy method. Satellite reflections of an incommensurate phase having two modulation vectors, q(1)* = 0.15a(o)* + 0.21b(o)* and q(2)* = -0.21a(o)* + 0.36b(o)* (a(o) is the unit cell for a gamma-NaxCoO2-type structure), are indexed successfully. High-resolution electron microscopy (HREM) images show dark streaks running parallel in the a-b plane. The separations and directions of the dark streaks have a close relationship between the q-vector of satellite spots. A HREM image taken with the electron beam parallel to [100] direction shows planer clusters between CdI2-type RhO2 layers. These clusters correspond to the intercalated potassium ions.
Title:
Plastic analysis of crack problems in three-dimensional icosahedral quasicrystalline material
Authors:
Li, W; Fan, TY; Wu, YL Author Full Names: Li, Wu; Fan, Tian You; Wu, Yun Long
Source:
PHILOSOPHICAL MAGAZINE 89 (31): 2823-2831 2009
Abstract:
Due to their complexity, the basic plastic properties of all quasicrystalline materials are essentially unknown [M. Feuerbacher, C. Thomas, K. Urban, Plastic behaviour of quasicrystalline materials, in Quasicrystals: Structure and Physical Properties, H.R. Trebin, ed., Wiley/VCH, Berlin, 2003]. Plastic deformation of cracks in icosahedral quasicrystals have been analyzed in a strict and systematic form and the crack tip opening displacement (CTOD) and size of the plastic zone around the crack tip was determined exactly. CTOD is suggested as a parameter of plastic fracture for quasicrystalline materials. The present work may also provide a novel methodology for plastic analysis of quasicrystals.
Title:
Octahedral tilt twinning and compositional modulation in NaLaMgWO6
Authors:
King, G; Garcia-Martin, S; Woodward, PM Author Full Names: King, Graham; Garcia-Martin, Susana; Woodward, Patrick M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 676-683 Part 6 DEC 2009
Abstract:
A combination of selected-area electron diffraction (SAED), neutron powder diffraction (NPD) and high-resolution transmission electron microscopy (HRTEM) reveals a complex superstructure in the ordered perovskite NaLaMgWO6. Through indexing of SAED patterns the unit-cell dimensions are found to be 46.8 x 7.8 x 7.9 angstrom, which corresponds to a 12a(p) x 2a(p) x 2a(p) superstructure of the simple Pm (3) over barm perovskite unit cell. HRTEM images reveal the formation of an unmistakable stripe contrast that repeats with the same periodicity. Doubling of the b and c axes is brought about by a combination of layered ordering of Na and La, rock-salt ordering of Mg and W, and octahedral tilting. The a axis repeat distance results from a one-dimensional twinning of the octahedral tilts in combination with a compositional modulation. Modeling of the NPD pattern shows that the underlying tilt system is a(-)a(-)c(0) with tilt angles of similar to 8 degrees about the a and b axes. The octahedral tilt-twin boundaries run perpendicular to the a axis and are separated by 6a(p). Simulated HRTEM images show that octahedral tilt twinning alone cannot explain the stripes seen in the HRTEM images, rather a compositional modulation involving the A-site cations is necessary to explain the experimental images.

Update: 19-Nov-2009

Title:
A One-Dimensional Metal Embedded in Salt Matrices: Synthesis, Modulated Crystal Structures, Electrical Conductivity, and Chemical Bonding of (1)(infinity)[PdBi6][(Bi,Sn)(1-delta)Br5-delta,]
Authors:
Wahl, B; Kloo, L; Ruck, M Author Full Names: Wahl, Bernhard; Kloo, Lars; Ruck, Michael
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 635 (12): 1979-1985 2009
Abstract:
The metal-rich compounds (1)(infinity)[PdBi6][(Bi,Sn)(1-delta)Br5-delta,] with delta(1) = 2/13, delta(1)' = 5/26, or delta(2) = delta(2)' = 2/12 were synthesized from Bi2Pd, BiBr3, and Sn at 300 degrees C. The crystal structures contain intermetallic rods (1)(infinity)[Pd@Bi2/1Bi8/2](2.5+) embedded in salt-like matrices, which consist of groups of bromido-bismuthate(III)-stannate(II) octahedra [(Bi,Sn)(n)Br4n+2](m-) (n = 2, 3) and isolated Br- ions. Metrical incompatibilities of the two subsystems in the crystalline metal-salt hybrid result in non-stoichiometry of the salt pan associated with complex superstructures. The average structure is described in the orthorhombic space group Pmmm with a approximate to 408 pm, b approximate to 2263 pm, c approximate to 849 pm. It feigns statistical distribution of vacancies and orientational disorder of the concatenated octahedra. By choosing the modulation vectors q(i) = 2/ta* + 1/2b* + 1/2c* with t(1) = 13 or t(2) = 12, the additional weak reflections of the diffraction patterns are indexed. Ordered structure models are achieved in the [3+1]-dimensional superspace group Pmmm(alpha 1/21/2)000. Metallic conductivity along [100], i.e. the direction of the (1)(infinity)[Pd@Bi2/1Bi8/2](2.5+) rods, was determined for a single-crystal. One-dimensional band structure calculations reveal Bi p-bands crossing the Fermi level for formula charges higher than 2+. The electron localization indicator (ELI) indicates two-center Bi-Bi bonds as well as multi-center bonds inside the metallic part, whereas the bismuth l one-pairs point towards the non-conducting part of the structure.
Title:
Quasiparticles of Spatially Anisotropic Triangular Antiferromagnets in a Magnetic Field
Authors:
Kohno, M Author Full Names: Kohno, Masanori
Source:
PHYSICAL REVIEW LETTERS 103 (19): Art. No. 197203 NOV 6 2009
Abstract:
The spectral properties of the spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice in a magnetic field are investigated using a weak-interchain-coupling approach combined with exact solutions of a chain. Dominant modes induced by interchain interactions in a magnetic field behave as quasiparticles which show distinctive features such as anomalous incommensurate ordering and high-energy modes. In terms of them, various unusual features observed in the anisotropic triangular antiferromagnet Cs2CuCl4 in a magnetic field are quantitatively explained in a unified manner.
Title:
The uniaxially aperiodic structure of a thin Cu film on fivefold i-Al-Pd-Mn
Authors:
Pussi, K; Gierer, M; Diehl, RD Author Full Names: Pussi, K.; Gierer, M.; Diehl, R. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (47): Art. No. 474213 NOV 25 2009
Abstract:
A thin film of copper on the fivefold surface of Al-Pd-Mn forms a structure that is uniaxially commensurate with the aperiodic structure of the substrate. This structure has been analyzed using low-energy electron diffraction and is found to consist of a vicinal surface of a body-centered tetragonal (bct) (100) structure. This bct(100) structure has lattice parameters of a = 2.88 angstrom, b = 2.55 angstrom and c = 2.88 angstrom, with the vicinal surface making an angle alpha of 13.28 degrees relative to the a-b plane. This structure provides an explanation for the delayed ordering observed during the growth of the film. Simple conditions are derived for which the growth of ordered one-dimensionally quasiperiodic thin films on quasicrystals may be favorable. This finding is relevant to the use of quasicrystals as a means of matching interfaces in thin film systems.
Title:
Synthesis of the quasi-crystalline phase in Al63Cu25Fe12 powders prepared by mechanical alloying
Authors:
Avar, B; Gogebakan, M Author Full Names: Avar, B.; Gogebakan, M.
Source:
JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS 11 (10): 1460-1463 OCT 2009
Abstract:
This work investigated the quasicrystalline phase formation during heat treatment in the Al63Cu25Fe12 alloy prepared via mechanical alloying, starting from pure elemental powders. The mechanical alloying process was performed at a speed of 300 rpm for times up to 70 hours. The structural evolution of the mechanically alloyed Al63Cu25Fe12 powders at different stages of milling was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The present results showed that mechanical alloying of the Al63Cu25Fe12 alloy did not result in the quasicrystalline icosahedral phase (i-phase). The long time milling resulted in the formation of an AlFe(Cu) solid solution identified as the beta-phase. In order to examine the structural changes with annealing temperature, the mechanically alloyed powders were heat treated at 600, 700 and 800 degrees C for 4 hours under vacuum. However, the formation of a quasicrystalline phase in the Al63Cu25Fe12 alloy was observed after additional annealing at elevated temperature. In the present work, quasicrystalline phase formation in both the as-milled and heat-treated powders is discussed in detail.
Title:
Minerals as advanced materials
Authors:
Depmeier, W Author Full Names: Depmeier, W.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY 44 (10): 1122-1130 Sp. Iss. SI OCT 2009
Abstract:
A resume is given on relationships between minerals and materials. It is shown that Nature has many advantages over technology which can be profitably exploited for finding new materials with useful properties. However, Nature has also inherent limitations. Therefore, it seems advisable to use the knowledge of minerals as a treasure which can be tapped for getting inspired on the way to finding new materials. Several examples are given, including those of zorite/ETS-4/ETS-10, boracites, zircon, kesterite, a natural quasicrystal, opals, ultramarine and mayenite.

Update: 13-Nov-2009

Title:
AlCoNi quasicrystal sphere growth experiment from a metallic solution
Authors:
Meisterernst, G; Bauer, B; Gille, P Author Full Names: Meisterernst, Goetz; Bauer, Birgitta; Gille, Peter
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 224 (10): 471-477 2009
Abstract:
Crystal growth studies starting from spherical surfaces of single crystals can reveal morphological features that cannot be obtained in usual growth experiments. Especially, facets of a greater variety of crystallographic forms may occur that are otherwise hidden by the slowest growing faces which dominate the crystal's morphology. We did a sphere growth experiment with a decagonal Al72Co9Ni19 quasicrystal prepared from a large single-grain sample formerly grown using the Czochralski method from an off-stoichiometric melt. By heating the polished crystalline half-sphere to a temperature slightly higher than its own growth temperature a thin liquid layer of self-flux formed. A partial evaporation of Al being the solvent of this system caused re-crystallisation at the surface of the quasicrystalline sphere. After several times repeating this process at further increasing temperatures, tiny faces of four different crystallographic forms developed. By using an optical goniometer and electron scanning microscopy indexing of these facets was possible. With the only exception of the decagonal prism {10000} they had not been observed so far in contact to the melt. The results are discussed with respect to the inclined net plane concept established by Steurer and Cervellino [Acta Cryst. A57 (2001) 333-340]. The experimental approach is not specific to sphere growth studies of quasicrystals but can be applied to other high-temperature solution growth systems as well.
Title:
Atomic coexistence of superconductivity and incommensurate magnetic order in the pnictide Ba(Fe(1-x)Cox)(2)As-2
Authors:
Laplace, Y; Bobroff, J; Rullier-Albenque, F; Colson, D; Forget, A Author Full Names: Laplace, Y.; Bobroff, J.; Rullier-Albenque, F.; Colson, D.; Forget, A.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 140501 OCT 2009
Abstract:
As-75 nuclear magnetic resonance (NMR) and susceptiblity were measured in a Ba(Fe1-xCox)(2)As-2 single crystal for x=6%. NMR spectra and relaxation rates allow to show that all Fe sites experience an incommensurate magnetic ordering below T=31 K. Comparison with undoped compound allows to estimate a typical moment of 0.05 mu(B). Anisotropy of the NMR widths can be interpreted using a model of incommensurability with a wave vector (1/2-epsilon,0, l) with epsilon of the order of 0.04. Below T-C=21.8 K, a full volume superconductivity develops as shown by susceptibility and relaxation rate, and magnetic order remains unaffected, demonstrating coexistence of both states on each Fe site.
Title:
Coexistence of incommensurate magnetism and superconductivity in Fe(1+y)SexTe(1-x)
Authors:
Khasanov, R; Bendele, M; Amato, A; Babkevich, P; Boothroyd, AT; Cervellino, A; Conder, K; Gvasaliya, SN; Keller, H; Klauss, HH; Luetkens, H; Pomjakushin, V; Pomjakushina, E; Roessli, B Author Full Names: Khasanov, R.; Bendele, M.; Amato, A.; Babkevich, P.; Boothroyd, A. T.; Cervellino, A.; Conder, K.; Gvasaliya, S. N.; Keller, H.; Klauss, H. -H.; Luetkens, H.; Pomjakushin, V.; Pomjakushina, E.; Roessli, B.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 140511 OCT 2009
Abstract:
We have studied the superconducting and magnetic properties of Fe1+ySexTe1-x single crystals (0 <= x <= 0.5) by magnetic susceptibility, muon-spin rotation, and neutron diffraction. We find three regimes of behavior: (i) commensurate magnetic order for x less than or similar to 0.1, (ii) bulk superconductivity for x similar to 0.5, and (iii) a range x approximate to 0.25-0.45 in which superconductivity coexists with incommensurate magnetic order. The results are qualitatively consistent with two-band mean-field models in which itinerant magnetism and extended s-wave superconductivity are competing order parameters.
Title:
Transition from turbulent to nearly laminar vortex flow in superconductors with periodic pinning
Authors:
Gutierrez, J; Silhanek, AV; Van de Vondel, J; Gillijns, W; Moshchalkov, VV Author Full Names: Gutierrez, J.; Silhanek, A. V.; Van de Vondel, J.; Gillijns, W.; Moshchalkov, V. V.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 140514 OCT 2009
Abstract:
We revisit the vortex dynamics in Al thin films containing an artificial periodic array of antidots by means of electrical transport measurements. We clearly identify a turbulent to laminarlike vortex flow transition which manifests itself as a negative differential resistivity. This transition is accompanied by a strong irreversibility in the voltage-current characteristics. The dynamical phase diagrams obtained as a function of commensurability, temperature, and driving force are in good agreement with the early predictions by Reichhardt et al. [Phys. Rev. Lett. 78, 2648 (1997)] based on molecular dynamic simulations.
Title:
Lattice dynamics and external magnetic-field effects in Ni-Fe-Ga alloys
Authors:
Perez-Landazabal, JI; Recarte, V; Sanchez-Alarcos, V; Rodriguez-Velamazan, JA; Jimenez-Ruiz, M; Link, P; Cesari, E; Chumlyakov, YI Author Full Names: Perez-Landazabal, J. I.; Recarte, V.; Sanchez-Alarcos, V.; Rodriguez-Velamazan, J. A.; Jimenez-Ruiz, M.; Link, P.; Cesari, E.; Chumlyakov, Y. I.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 144301 OCT 2009
Abstract:
Precursor phenomena were investigated in a Ni-Fe-Ga alloy close to the stoichiometric Heusler composition Ni2FeGa. In particular, the phonon-dispersion curves, the diffuse scattering and the magnetic properties of a single crystalline Ni51.5Fe21.5Ga27 alloy were measured as a function of temperature. The TA(2) branch along the [110] direction of the L2(1) phase shows a significant phonon softening around xi = 0.35 resulting in a marked dip which becomes more pronounced as the temperature decreases. Diffuse neutron-scattering measurements performed along [(xi) over bar xi 0] direction around Bragg reflections also reveal the presence of small satellite peaks at xi = 0.33 whose intensity increases on approaching the martensitic transformation temperature. Both elastic and inelastic-scattering anomalies confirm the occurrence of premartensitic phenomena in Ni-Fe-Ga alloys. The influence of an external magnetic field (6 T) on the anomalous phonon is shown to be negli! gible and just a small shift of the transformation temperature takes place because of the magnetic field.
Title:
Thermal entanglement of spin chains with quantum critical behavior
Authors:
Zvyagin, AA Author Full Names: Zvyagin, A. A.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 144408 OCT 2009
Abstract:
Results for the characteristics of the macroscopic thermal entanglement for integrable spin-1/2 antiferro-magnetic chain models with multispin interactions in the thermodynamic limit are presented. Such interactions cause quantum-phase transitions to incommensurate phases with partial spontaneous magnetization. We have derived exact equations, which determine the thermal and magnetic field behavior of the concurrence of spin chains. The analysis of these equations shows that there exists a critical temperature, below which the thermal entanglement of considered spin chains is nonzero. We have shown that at those quantum-phase transitions, caused by multispin interactions, the thermal entanglement is reduced. Also, we have shown that the thermal entanglement is reduced due to nonzero magnetization of spin chains in the ground state, caused by multispin interactions.
Title:
Observation of strong magnetoelastic coupling in a first-order phase transition of CrOCl
Authors:
Angelkort, J; Wolfel, A; Schonleber, A; van Smaalen, S; Kremer, RK Author Full Names: Angelkort, Joachim; Woelfel, Alexander; Schoenleber, Andreas; van Smaalen, Sander; Kremer, Reinhard K.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 144416 OCT 2009
Abstract:
The phase transition of CrOCl toward a state of antiferromagnetic order below T-N=13.5 K has been identified as a first-order phase transition. The transition is accompanied by a lattice and structural distortion toward a twofold, 2b nuclear superstructure with a-axis unique monoclinic symmetry, as evidenced by temperature-dependent x-ray diffraction experiments. Magnetic-susceptibility and magnetization measurements indicate a transition with strong magnetoelastic coupling to a uniaxial antiferromagnet with ordered moments along c. A second transition is discovered at T-c approximate to 27.2 K that is presumably of purely magnetic origin and might indicate the formation of an incommensurate magnetic superstructure. The different behaviors of TiOCl, VOCl, and CrOCl are the result of the different symmetries of the filled 3d orbitals, which lead to different exchange interactions on the MO double layers of these isostructural compounds.
Title:
Formation of a well ordered ultrathin aluminum oxide film on icosahedral AlPdMn quasicrystal (vol 76, 094203, 2007)
Authors:
Longchamp, JN; Burkardt, S; Erbudak, M; Weisskopf, Y Author Full Names: Longchamp, J. -N.; Burkardt, S.; Erbudak, M.; Weisskopf, Y.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 149901 OCT 2009
Title:
Field suppression of the modulated phase of Ce2Pd2Sn
Authors:
Berisso, MG; Sereni, JG; Braghta, A; Schmerber, G; Chevalier, B; Kappler, JP Author Full Names: Gomez Berisso, M.; Sereni, J. G.; Braghta, A.; Schmerber, G.; Chevalier, B.; Kappler, J. P.
Source:
PHYSICA B-CONDENSED MATTER 404 (19): 2930-2933 OCT 15 2009
Abstract:
Low temperature magnetic (M) and thermal (C-p) properties of the intermetallic compound Ce2Pd2Sn have been investigated at zero and different magnetic fields. Two transitions were recognized at T-C = 2.1 K and T-M = 4.8 K, with latter nearly coinciding with the extrapolated Curie-Weiss temperature theta(p) = 4.5 K. The Curie factor evaluated from T >= T-M, is approximate to 2 mu(B) The positive value of theta(p), the triangular coordination of the magnetic (Ce) atoms and the weak effect of applied magnetic field, reveal that T-M cannot be considered as a canonic antiferromagnetic transition like claimed in the literature. M(T) measurements under moderate magnetic fields (0 <= B <= 2.5 kOe) show T-C(B) increasing while T-M(B) is practically not affected. Both transition merge in a critical point at T-cr = (4.3 +/- 0.3)K for B-cr = (2.1 +/- 0.3)kOe, where the intermediate phase is suppressed. At T-C = 2.2 K, the cusp of a first order transition is observed in C-p(T). According to the proposed ferromagnetic ground state, it is followed by a C-p(T)alpha T(3/2)exp(-E-g/T) dependence, with a gap of anisotropy E-g approximate to 7 K. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Antiferromagnetic structure in UNiAl at dilution temperatures
Authors:
Prokes, K; Bruck, E; Sechovsky, V Author Full Names: Prokes, K.; Bruck, E.; Sechovsky, V.
Source:
PHYSICA B-CONDENSED MATTER 404 (19): 3025-3027 OCT 15 2009
Abstract:
Neutron diffraction experiments in zero field reveals that the originally sine-wave-modulated antiferromagnetic structure in UNiAl starts to square-up at low temperatures. The squaring-up is, however, not completed even at 150 mK, most probably due to competing magnetic interactions. The fact that the magnetic moments are not equal at all the uranium atomic sites is responsible at least partially for the enhanced low-temperature-specific heat coefficient observed in UNiAl at low temperatures. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Resonant X-ray scattering study of Ca3Co2O6 ground state: Preliminary results of magnetic field effects
Authors:
Mazzoli, C; Bombardi, A; Agrestini, S; Lees, MR Author Full Names: Mazzoli, C.; Bombardi, A.; Agrestini, S.; Lees, M. R.
Source:
PHYSICA B-CONDENSED MATTER 404 (19): 3042-3044 OCT 15 2009
Abstract:
We present resonant magnetic X-ray scattering (RMXS) measurements in an applied magnetic field on a single crystal of Ca3Co2O6. We focus our attention on the transition from an incommensurate partially disordered antiferromagnetic state to a ferrimagnetic state: a lock-in and a divergence of the magnetic correlation length at the transition shed light on the nature of the ground state and on the c-axis vs. in-plane exchange couplings in this system. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Magnetic properties of the t-J model at low doping
Authors:
Falb, J; Neto, MBS; Muramatsu, A Author Full Names: Falb, J.; Silva Neto, M. B.; Muramatsu, A.
Source:
PHYSICA B-CONDENSED MATTER 404 (19): 3075-3078 OCT 15 2009
Abstract:
A path-integral for the t-J model in two dimensions is constructed based on Dirac quantization, with an action found originally by Wiegmann [Phys. Rev. Lett. 60 (1988) 821; Nucl. Phys. B 323 (1989) 311]. Concentrating on the low doping limit, we assume short range anti ferromagnetic order of the spin degrees of freedom. Going over to a local spin quantization axis of the dopant fermions that follows the spin degree of freedom, staggered CP1 fields result and the constraint against double occupancy can be resolved. The staggered CP1 fields are split into slow and fast modes, such that after a gradient expansion, and after integrating out the fast modes and the dopant fermions, a CP1 field-theory with a massive gauge field is obtained that describes generically incommensurate coplanar magnetic structures, as discussed previously in the context of frustrated quantum anti ferromagnets. The analysis of Landau damping shows that in this case, even in the presence of doping, the dynamical critical exponent z = 1. as a consequence of coupling of the dopant holes to a spin current, as opposed to a spin density. This result agrees with experimental observations in the underdoped region of high temperature superconductors, and departs from the one obtained by Hertz and Millis (z = 2) in the case of spin density waves in the Hubbard model. (C) 2009 Elsevier B.V. All rights reserved.
Title:
X-ray resonant scattering study of the magnetic phase diagram of multiferroic TbMnO3
Authors:
Walker, HC; Ewings, RA; Fabrizi, F; Mannix, D; Mazzoli, C; Wilkins, SB; Paolasini, L; Prabhakaran, D; Boothroyd, AT; McMorrow, DF Author Full Names: Walker, H. C.; Ewings, R. A.; Fabrizi, F.; Mannix, D.; Mazzoli, C.; Wilkins, S. B.; Paolasini, L.; Prabhakaran, D.; Boothroyd, A. T.; McMorrow, D. F.
Source:
PHYSICA B-CONDENSED MATTER 404 (19): 3264-3266 OCT 15 2009
Abstract:
We present the magnetic phase diagram of multiferroic TbMnO3 for H parallel to b determined using X-ray resonant scattering at the Tb L-3-edge. Investigations of two different magnetic domains, C-type and F-type, demonstrate very similar behaviour in high applied magnetic fields, with a low temperature incommensurate to commensurate transition at H similar or equal to 4.5T, concurrent with the polarisation flop observed in bulk magnetoelectric measurements. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Effect of Nonmagnetic Substituents Mg and Zn on the Phase Competition in the Multiferroic Antiferromagnet MnWO4
Authors:
Meddar, L; Josse, M; Deniard, P; La, C; Andre, G; Damay, F; Petricek, V; Jobic, S; Whangbo, MH; Maglione, M; Payen, C Author Full Names: Meddar, Lynda; Josse, Michael; Deniard, Philippe; La, Carole; Andre, Gilles; Damay, Francoise; Petricek, Vaclav; Jobic, Stephane; Whangbo, Myung-Hwan; Maglione, Mario; Payen, Christophe
Source:
CHEMISTRY OF MATERIALS 21 (21): 5203-5214 NOV 10 2009
Abstract:
The effects of substituting nonmagnetic Ma(2+) and Zn2+ ions for the Mn2+ (S = 5/2) ions oil the structural, magnetic, and dielectric properties of the multiferroic frustrated antiferromagnet MnWO4 were investigated Polycrystalline samples of Mn1-xMgxWO4 and Mn1-xZnxWO4 (0 <= x <= 0.3) solid Solutions were prepared via a solid-state route and characterized via X-ray and neutron diffraction, magnetization, and dielectric permittivity measurements. Mg and Zn substitutions result in very similar effects The Neel temperature (T-N), the AF3-to-AF2 magnetic phase-transition temperature (T-2), and the critical ferroelectric temperature (T-c = T-2) of MnWO4 are reduced upon nonmagnetic doping. At the lowest temperature (T = 1.5 K), the incommensurate magnetic Structure for x(Mg) = 0 15 and v(Zn) = 0.15 corresponds to either a sinusoidal spin arrangement or an elliptical spin-spiral phase similar to the polar AF2 structure observed in MnWO4 These findings were discussed by considering the effects of the Mg and Zn Substitutions oil the crystal lattice and on the spin exchange network of MnWO4.

Update: 5-Nov-2009

Title:
Crossover from incommensurate to commensurate magnetic orderings in CoCr2O4
Authors:
Chang, LJ; Huang, DJ; Li, WH; Cheong, SW; Ratcliff, W; Lynn, JW Author Full Names: Chang, L. J.; Huang, D. J.; Li, W-H; Cheong, S-W; Ratcliff, W.; Lynn, J. W.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (45): Art. No. 456008 NOV 11 2009
Abstract:
The conical spin order of multiferroic CoCr2O4 has been studied by a neutron diffraction to investigate its magnetic phase transitions at temperatures below 40 K. Magnetic order of a spiral spin component with an incommensurate propagation vector of (0.63, 0.63, 0) was observed at 26 K, while at 14.5 K, the incommensurate conical spin order showed a transition into the fixed commensurate propagation vector of (2/3, 2/3, 0). In addition, two satellite peaks with propagation vectors of (0.035, 0, 0) and (0, 0.035, 0) from the commensurate vector were observed. The widths of these peaks indicate a long-range magnetic order. This new magnetic configuration below 14.5 K may lead to a new model of multiferroic behavior differing from the well-known spin-current model for magnetic ferroelectricity.

Update: 29-Oct-2009

Title:
Electronic Self-Organization in the Single-Layer Manganite Pr1-xCa1+xMnO4
Authors:
Ye, F; Chi, SX; Fernandez-Baca, JA; Moreo, A; Dagotto, E; Lynn, JW; Mathieu, R; Kaneko, Y; Tokura, Y; Dai, PC Author Full Names: Ye, F.; Chi, Songxue; Fernandez-Baca, J. A.; Moreo, A.; Dagotto, E.; Lynn, J. W.; Mathieu, R.; Kaneko, Y.; Tokura, Y.; Dai, Pengcheng
Source:
PHYSICAL REVIEW LETTERS 103 (16): Art. No. 167202 OCT 16 2009
Abstract:
We use neutron scattering to investigate the doping evolution of the magnetic correlations in the single-layer manganite Pr1-xCa1-xMnO4, away from the x = 0.5 composition where the CE-type commensurate antiferromagnetic (AF) structure is stable. We find that short-range incommensurate spin correlations develop as the system is electron doped (x < 0.5), which coexist with the CE-type AF order. This suggests that electron doping in this system induces an inhomogeneous electronic self-organization, where commensurate AF patches with x = 0.5 are separated by electron-rich domain walls with short-range magnetic correlations. This behavior is strikingly different than for the perovskite Pr1-xCaxMnO3, where the long-range CE-type commensurate AF structure is stable over a wide range of electron or hole doping around x = 0.5.
Title:
Low temperature thermodynamical properties of ErCu2Si2
Authors:
Baran, S; Gondek, L; Szytula, A; Kaczorowski, D; Pikul, A; Penc, B; Piekarz, P; Hoser, A; Gerischer, S Author Full Names: Baran, S.; Gondek, L.; Szytula, A.; Kaczorowski, D.; Pikul, A.; Penc, B.; Piekarz, P.; Hoser, A.; Gerischer, S.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (1): 12-18 JAN 2010
Abstract:
ErCu2Si2 crystallises in the tetragonal ThCr2Si2-type crystal structure. In this paper results of magnetometric, electrical transport, specific heat as well as neutron diffraction are reported. Results of electrical resistivity and specific heat measurements performed at low temperature yield existence of magnetic ordering roughly at 1.3 K. These results are in concert with neutron diffraction measurements, which reveal simple antiferromagnetic ordering between 0.47 and 1.00 K. At temperatures ranging from 1.00 up to 1.50K an additional incommensurate magnetic structure was observed. The propagation vector kappa = (0;0;0.074) was proposed to describe magnetic reflections within the amplitude modulated magnetic structure. Basing on specific heat studies the crystal field levels splitting scheme and magnetic entropy were calculated. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Competing magnetic structures in the DySi FeB-type phase diagram
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Ritter, C; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Ritter, C.; Buschow, K. H. J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (1): 119-132 JAN 2010
Abstract:
The temperature magnetic phase diagrams, of the dimorphic DySi compound, have been studied in terms of wave vectors in the range 1.5-45 K, by neutron diffraction. The polycrystalline sample consists of 26% of CrB-type (Cmcm no. 63, all atoms at 4c site: (0, y, 1/4)) and of 74% of FeB-type (Pnma no. 62, all atoms at 4c site: (x, 1/4, z)). The CrB-ordering is described by the wave vector: q(1) = (0, 0, 1/2) over the entire magnetically ordered regime with a uniaxial magnetic structure along the shortest axis c. The FeB-type magnetic phase diagram reveals three distinct regions of magnetic ordering below T-N and one first order transition at T-2=23.5K (on heating). The ordering is described by two symmetry independent magnetic vectors q(2)=(0, 1/2,1/6) and q(3)=(0, q(3y), q(3z)) with a temperature variable length. At 1.5 K q(3y) approximate to 1/2 and q(3z) approximate to 1/11. The two phases coexist in the form of domains. They differ in the moment orientation of the q(3) phase that deviates by similar to 22 degrees from the b-axis in the (0, 0, 1) plane. The low temperature range (LT) 1.5 K-T-2 subdivides into two regions: (i) LT-1, between 1.5 K-T-1 where the relative amount of the two phases remains unchanged and in (ii) LT-2: T-1-T-2 where the amount of the incommensurate q3 phase increases at the cost of the commensurate q(2) amplitude modulated structure which remains unchanged but fully disappears at the first order transition at T-2=23.5 K. The q(3) phase undergoes minor changes until 22 K and gets destabilised at T-2 where the q(3z) component jumps from the LT value q(3z) approximate to 1/11 to the HT value approximate to 1/7 and the q(3y) component increases from 0.484(1) to 0.495(1). (iii) The high temperature (HT) range T-2-T-N (T-N=40 +/- 1 K) is described by a single wave vector q(3). The disproportionation of the HT magnetic phase q(3) below T-2 into two coexisting distinct phases q(2), q(3) down to 1.5 K is an unusual phenomenon, to our knowledge observed for the first time. Various mechanisms are discussed. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Self-similar transformation and quasi-unit cell construction of quasi-periodic structure with twelve-fold rotational symmetry
Authors:
Liao, LG; Fu, H; Fu, XJ Author Full Names: Liao Long-Guang; Fu Hong; Fu Xiu-Jun
Source:
ACTA PHYSICA SINICA 58 (10): 7088-7093 OCT 2009
Abstract:
The structural properties of a quasicrystal model with twelve-fold rotational symmetry are studied. We correct the errors in the self-similar transformation of the square-rhombus-hexagon tiling model proposed by Socolar. Based on the Stampfli-Gahler square-rhombus-triangle tiling model, the quasi-unit cell is successfully constructed, which can describe the dodecagonal quasiperiodic structure by the covering theory.
Title:
Measurement of anisotropy thermopower of decagonal AlCuCo quasicrystal
Authors:
Fan, ZJ; Geng, XW; Kong, WJ; Jin, YR Author Full Names: Fan Zhen-Jun; Geng Xue-Wen; Kong Wen-Jie; Jin Yi-Rong
Source:
ACTA PHYSICA SINICA 58 (10): 7119-7123 OCT 2009
Abstract:
The thermopower of decagonal AlCuCo quasicrystal was measured in the periodic and quasiperiodic direction by laser heating alternating current measurement method in the temperature range of from 300 K to 1200 K. We found that the thermopower is negative in the periodic direction and positive in the quasiperiodic direction. The thermopower hopps at 1123 K (850 degrees C) along the periodic direction. The change of the thermopower is not monotonic at high temperature. The measurement method we used is sensitive to the phase transition point.
Title:
Multiresolution of quasicrystal diffraction spectra
Authors:
Elkharrat, A; Gazeau, JP; Denoyer, F Author Full Names: Elkharrat, Avi; Gazeau, Jean-Pierre; Denoyer, Francoise
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 65: 466-489 Part 6 NOV 2009
Abstract:
A method for analyzing and classifying two-dimensional pure point diffraction spectra (i.e. a set of Bragg peaks) of certain self-similar structures with scaling factor beta > 1, such as quasicrystals, is presented. The two-dimensional pure point diffraction spectrum Pi is viewed as a point set in the complex plane in which each point is assigned a positive number, its Bragg intensity. Then, by using a nested sequence of self-similar subsets called beta-lattices, we implement a multiresolution analysis of the spectrum Pi. This analysis yields a partition of Pi simultaneously in geometry, in scale and in intensity (the 'fingerprint' of the spectrum, not of the diffracting structure itself). The method is tested through numerical explorations of pure point diffraction spectra of various mathematical structures and also with the diffraction pattern of a realistic model of a quasicrystal.

Update: 22-Oct-2009

Title:
Magnetic Properties of Multiferroics Bi(1-x)A(x)FeO(3-x/2) (A = Ca, Sr, Pb, Ba)
Authors:
Troyanchuk, IO; Mantytskaya, OS; Chobot, AN; Tereshko, NV Author Full Names: Troyanchuk, I. O.; Mantytskaya, O. S.; Chobot, A. N.; Tereshko, N. V.
Source:
PHYSICS OF THE SOLID STATE 51 (10): 2105-2108 OCT 2009
Abstract:
The magnetic properties of Bi(1-x)A(x)FeO(3-x/2) (A is an alkaline-earth ion) solid solutions have been studied in magnetic fields of up to 140 kOe. The ferroelectric phase (space group R3c) transforms into the nonpolar pseudocubic phase at x approximate to 0.2. It is demonstrated that the substitution of alkaline-earth ions for bismuth ions (x >= 0.1) leads to a complete destruction of the modulated antiferromagnetic structure and the appearance of a weakly ferromagnetic state within the R3c state. In the pseudocubic phase, the spontaneous magnetization is absent; however, the field dependence of the magnetization is nonlinear and depends on the magnetic prehistory.
Title:
MATERIALS SCIENCE Quasicrystals from nanocrystals
Authors:
van Blaaderen, A Author Full Names: van Blaaderen, Alfons
Source:
NATURE 461 (7266): 892-893 OCT 15 2009
Title:
Quasicrystalline order in self-assembled binary nanoparticle superlattices
Authors:
Talapin, DV; Shevchenko, EV; Bodnarchuk, MI; Ye, XC; Chen, J; Murray, CB Author Full Names: Talapin, Dmitri V.; Shevchenko, Elena V.; Bodnarchuk, Maryna I.; Ye, Xingchen; Chen, Jun; Murray, Christopher B.
Source:
NATURE 461 (7266): 964-967 OCT 15 2009
Abstract:
The discovery of quasicrystals in 1984 changed our view of ordered solids as periodic structures (1,2) and introduced new long-range-ordered phases lacking any translational symmetry(3-5). Quasi-crystals permit symmetry operations forbidden in classical crystallography, for example five-, eight-, ten-and 12-fold rotations, yet have sharp diffraction peaks. Intermetallic compounds have been observed to form both metastable and energetically stabilized quasicrystals (1,3,5); quasicrystalline order has also been reported for the tantalum telluride phase with an approximate Ta1.6Te composition(6). Later, quasicrystals were discovered in soft matter, namely supramolecular structures of organic dendrimers(7) and tri-block copolymers(8), and micrometre-sized colloidal spheres have been arranged into quasicrystalline arrays by using intense laser beams that create quasi-periodic optical standing-wave patterns(9). Here we show that colloidal inorganic nanoparticles can self-assemble into binary aperiodic superlattices. We observe formation of assemblies with dodecagonal quasicrystalline order in different binary nanoparticle systems: 13.4-nm Fe2O3 and 5-nm Au nanocrystals, 12.6-nm Fe3O4 and 4.7-nm Au nanocrystals, and 9-nm PbS and 3-nm Pd nanocrystals. Such compositional flexibility indicates that the formation of quasicrystalline nanoparticle assemblies does not require a unique combination of interparticle interactions, but is a general sphere-packing phenomenon governed by the entropy and simple interparticle potentials. We also find that dodecagonal quasicrystalline superlattices can form low-defect interfaces with ordinary crystalline binary superlattices, using fragments of (3(3).4(2)) Archimedean tiling as the 'wetting layer' between the periodic and aperiodic phases.
Title:
Magnetic structures of quaternary intermetallic borocarbides RCo2B2C (R = Dy, Ho, Er)
Authors:
ElMassalami, M; Moreno, R; Takeya, H; Ouladdiaf, B; Lynn, JW; Freitas, RS Author Full Names: ElMassalami, M.; Moreno, R.; Takeya, H.; Ouladdiaf, B.; Lynn, J. W.; Freitas, R. S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (43): Art. No. 436006 OCT 28 2009
Abstract:
The magnetic structures of the title compounds have been studied by neutron diffraction. In contrast to the isomorphous RNi2B2C compounds, wherein a variety of exotic incommensurate modulated structures has been observed, the magnetic structure of ErCo2B2C is found to be a collinear antiferromagnet with k = (12, 0, 12) while those of HoCo2B2C and DyCo2B2C are observed to be simple ferromagnets. For all studied compounds, the moments are found to be confined within the basal plane and their magnitudes are comparable to the values obtained from the low-temperature isothermal magnetization measurements. The absence of modulated magnetic structures in the RCo2B2C series (for ErCo2B2C, verified down to 50 mK) is attributed to the quenching of the Fermi surface nesting features.
Title:
A comparative study of the magnetic properties of the 1/1 approximant Ag50In36Gd14 and the icosahedral quasicrystal Ag50In36Gd14
Authors:
Wang, P; Stadnik, ZM; Al-Qadi, K; Przewoznik, J Author Full Names: Wang, P.; Stadnik, Z. M.; Al-Qadi, K.; Przewoznik, J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (43): Art. No. 436007 OCT 28 2009
Abstract:
We report on measurements of the dc and ac magnetic susceptibility, Gd-155 Mossbauer spectra, and specific heat of the 1/1 approximant Ag50In36Gd14, and of the ac magnetic susceptibility of the icosahedral quasicrystal Ag50In36Gd14. These alloys are shown to be spin glasses. For the icosahedral quasicrystal Ag50In36Gd14, spin freezing occurs at T-f = 4.3 K, and the frequency dependence of T-f is well accounted for by the Vogel-Fulcher and power laws. Spin freezing in the 1/1 approximant Ag50In36Gd14 occurs in two stages: at T-f1 = 3.7 K, Gd spins develop short-range correlations but continue to fluctuate, and then long-range freezing is achieved at T-f2 = 2.4 K. The frequency dependences of T-f1 and T-f2 can be accounted for by means of the Vogel-Fulcher law and the critical slowing down dynamics. It is shown that the spin freezing in both alloys is a nonequilibrium phenomenon rather than a true equilibrium phase transition. The Gd-155 Mossbauer spectra of the 1/1 approximant Ag50In36Gd14 confirm that the Gd spins are frozen at 1.5 K and are fluctuating at 4.6 K. The magnetic specific heat exhibits a maximum at a temperature that is 30% larger than T-f1, but the temperature derivative of the magnetic entropy peaks at T-f1. The Debye temperature of the 1/1 approximant Ag50In36Gd14 is 199(1) K as determined from the Mossbauer data, and 205(2) K as determined from the specific heat data.
Title:
Processing and characterization of rapidly quenched Ti-based alloys: Influence of solidification rate on the as-quenched structures
Authors:
Lefaix, H; Vermaut, P; Janickovic, D; Svec, P; Portier, R; Prima, F Author Full Names: Lefaix, H.; Vermaut, P.; Janickovic, D.; Svec, P.; Portier, R.; Prima, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 483 (1-2): 168-172 AUG 26 2009
Abstract:
>From technological viewpoint. icosahedral Ti-Zr-Ni phase may give challenging opportunities as novel hydrogen storage and hydride battery. Nevertheless. from the structural standpoint, the phase selection criterion as function of solidification route remains unclear. A series of Ti45Zr38Ni17 alloys, known to provide stable and well-ordered quasicrystals, was produced by planar flow casting using different processing parameters. From structural characterization, it appears that, at high cooling rate, i.e. high wheel speeds, or for the highest temperature of the melt, the as-quenched sample exhibits a mixture of nanoscale P and amorphous phases. The icosahedral phase precipitates when decreasing the wheel speed, from lower temperatures of the melt or after annealing a crystallized amorphous matrix. The reproducible formation of quasicrystals, observed in the amorphous matrix containing P particles, corroborates the competition between icosahedral and body-centered cubic (bcc) phases during the solidification process. These results are promising since it could be possible to control volume fractions of these two phases by choosing well-fitted thermal treatments so that quasicrystals mechanical properties should be improved by dispersion of a stable bcc phase. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Multi-scaled polymer-based composite materials synthesized by mechanical alloying
Authors:
Kaloshkin, SD; Vandi, LJ; Tcherdyntsev, VV; Shelekhov, EV; Danilov, VD Author Full Names: Kaloshkin, S. D.; Vandi, L. -J.; Tcherdyntsev, V. V.; Shelekhov, E. V.; Danilov, V. D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 483 (1-2): 195-199 AUG 26 2009
Abstract:
Multi-scaled composite materials are of great importance, because they exhibit higher mechanical properties than those attained using conventional fillers or polymer blends. In this work, multi-scaled composite materials based on ultra-high-molecular weight polyethylene (UHMWPE), quasicrystals, polyimide and bronze are investigated for use in the moving parts of machines, gears, bearings, and sliding elements. The main object is to investigate the process of fabricating such composite materials, and to check if these materials are reproducible and reliable to an industrial extent. The specimens were prepared using a high-energy planetary mill. When milled with bronze, the quasicrystalline phase was dissolved into an intermetallic solid solution: milling with polymers showed to conserve the quasicrystalline phase, whereas the crystallization of UHMWPE was achieved during the milling process. Tribological study of consolidated samples showed an increase in the wear resistance for the bronze-containing composite materials. in comparison with pure UHMWPE, the polyimide-based specimen exhibited higher strength and hardness. This work has demonstrated the possibility of producing composite materials with acceptable and reliable properties using the mechanical alloying technology. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Nanostructure controlling in Zr-based metallic glasses using icosahedral local structure
Authors:
Saida, J; Kato, H; Setyawan, AD; Yoshimi, K; Inoue, A Author Full Names: Saida, J.; Kato, H.; Setyawan, A. D.; Yoshimi, K.; Inoue, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 483 (1-2): 231-234 AUG 26 2009
Abstract:
Glass-nano(quasi)crystal composite materials based on Zr-Al-Ni-Cu metallic glasses have been synthesized by controlling the nucleation and growth rates of the precipitated phase correlated with a unique icosahedral local structure. It is well known that the Zr65Al7.5Ni10Cu17.5 metallic glass has a high glass-forming ability (GFA), which enables us to produce the glassy sample with a bulky shape. Controlling a substitution of QC-forming elements such as noble metals with Cu and annealing condition, the nanoscale icosahedral quasicrystalline phase (I-phase) with various grain sizes and nucleus densities can be formed. Moreover, we have succeeded to control the nano-QC phase nucleation by changing the atmosphere pressure during casting, which results in the formation of new bulk metallic glasses (BMGs). These nanoscale structure and nucleation controlling techniques in BMGs bring a significant improvement of mechanical properties such as high strength and good ductility. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Characterization of phases in complex metallic alloys Al73Mn27-xFex (x=2, 4 and 6)
Authors:
Priputen, P; Kusy, M; Kriska, M; Lipka, R; Illekova, E; Svec, P; Bursik, J; Svoboda, M; Dolinsek, J; Janovec, J Author Full Names: Priputen, P.; Kusy, M.; Kriska, M.; Lipka, R.; Illekova, E.; Svec, P.; Bursik, J.; Svoboda, M.; Dolinsek, J.; Janovec, J.
Source:
INTERMETALLICS 17 (12): 1047-1051 DEC 2009
Abstract:
The characterization of phases in Al73Mn27-xFex (x = 2, 4 and 6) alloys was performed using X-ray diffraction, differential thermal analysis, and scanning electron microscopy enabling energy dispersive X-ray spectroscopy. Both the annealed and the thermally cycled states were studied. In the annealed states the occurrence of T-phase was expected, however it was confirmed for alloys Al73Mn25Fe2 and Al73Mn23Fe4 only. The annealing of the Al73Mn21Fe6 alloy probably led to the formation of decagonal quasicrystal (D). The T- and D-phases were found to be unstable at low temperatures. In the states after DTA the low temperature Al-11(Mn,Fe)(4) and gamma(2) phases were observed in the Al73Mn25Fe2 and Al73Mn21Fe6 alloys, while only the former phase was observed in the Al73Mn23Fe4 alloy. (C) 2009 Elsevier Ltd. All rights reserved.
Title:
Structure Determination of Two Modulated gamma-Brass Structures in the Zn-Pd System through a (3+1)-Dimensional Space Description
Authors:
Gourdon, O; Izaola, Z; Elcoro, L; Petricek, V; Miller, GJ Author Full Names: Gourdon, Olivier; Izaola, Zunbeltz; Elcoro, Luis; Petricek, Vaclav; Miller, Gordon J.
Source:
INORGANIC CHEMISTRY 48 (20): 9715-9722 OCT 19 2009
Abstract:
The structure determination of two composite compounds in the Zn-Pd system with close relationships to the cubic gamma-brass structure Zn11-delta Pd2+delta is reported. Their structures have been solved from single crystal X-ray diffraction data within a (3 + 1)-dimensional [(3 + 1)D] formalism. Zn75.7(7)Pd24.3 and Zn78.8(7)Pd21.2 crystallize with orthorhombic symmetry, superspace group Xmmm(00 gamma)0s0 (X [(1/2,1/2,0,0); (0,1/2,1/2,1/2); (1/2,0,1/2,1/2)]), with the following lattice parameters, respectively: a(s) = 12.929(3) angstrom, b(s) = 9.112(4) angstrom, c(s) = 2.5631(7) angstrom, q = 8/13 c* and V-s = 302.1(3) angstrom(3) and a(s) = 12.909(3) angstrom, b(s) = 9.115(3) angstrom, c(s) = 2.6052(6) angstrom, q = 11/18 c* and V-s = 306.4(2) angstrom(3). Their structures may be considered as commensurate because they can be refined in the conventional 3D space groups (Cmce and Cmcm, respectively) using supercells, but they also refined within the (3 + 1)D formalism to residual factors R = 3.14% for 139 parameters and 1184 independent reflections for Zn75.7(7)Pd24.3 and R = 3.16% for 175 parameters and 1804 independent reflections for Zn78.8(7)Pd21.2. The use of the (3 + 1)D formalism improves the results of the refinement and leads to a better understanding of the complexity of the atomic arrangement through the various modulations (occupation waves and displacive waves). Our refinements emphasize a unique Pd/Zn occupancy modulation at the center of distorted icosahedra, a modulation which correlates with the distortion of these polyhedra.
Title:
Nanoquasicrystalline Al-Fe-Cr-based alloys. Part I: Phase transformations
Authors:
Galano, M; Audebert, F; Stone, IC; Cantor, B Author Full Names: Galano, M.; Audebert, F.; Stone, I. C.; Cantor, B.
Source:
ACTA MATERIALIA 57 (17): 5107-5119 OCT 2009
Abstract:
Nanoquasicrystalline Al-Fe-Cr-based alloys composed of sub-micro-sized icosahedral quasicrystalline particles embedded in alpha-Al matrix have a higher strength at elevated temperature compared with commercial Al alloys. However, further improvement of the microstructural stability is desirable in order to maximize the elevated temperature strength. A detailed study of the effect on the microstructure and the phase transformations by the addition of Ti, V, Nb or Ta to a ternary Al-93(Fe3Cr2)(7) alloy was carried out using heat treatment and microstructural characterization. The addition of the fourth element leads to a refined microstructure and can stabilize the icosahedral topology, delaying the quasicrystalline icosahedral phase decomposition until a higher temperature is reached. The addition of Nb or Ta enabled a greater stabilization effect than the addition of Ti or V, retaining a microstructure similar to the as-spun state after heat treatment between 450 and 550 degrees C and even retaining icosahedral particles up to 550 degrees C. The outstanding microstructural stabilization obtained with addition of Nb or Ta leads to very promising applications in the automotive and aeronautic industries. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 15-Oct-2009

Title:
Nonmetallic Nature of the Interrelation of Thermal, Magnetic, and Electrical Properties in Icosahedral Quasicrystals at High Temperatures
Authors:
Prekul, AF; Shchegolikhina, NI; Nazarova, SZ; Edagawa, K Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.; Nazarova, S. Z.; Edagawa, K.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 108 (2): 120-124 AUG 2009
Abstract:
In the icosahedral phase of Al-Cu-Fe alloys in the temperature range above 300 K there has been found an interrelation between the heat capacity, magnetic susceptibility, and conductivity not characteristic of typical metals. It is supposed that these phases are systems whose properties at finite temperatures are predominantly determined by excited electrons rather than by electrons with a Fermi energy E-F.
Title:
Spin Amplitude Modulation Driven Magnetoelectric Coupling in the New Multiferroic FeTe2O5Br
Authors:
Pregelj, M; Zaharko, O; Zorko, A; Kutnjak, Z; Jeglic, P; Brown, PJ; Jagodic, M; Jaglicic, Z; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Zaharko, O.; Zorko, A.; Kutnjak, Z.; Jeglic, P.; Brown, P. J.; Jagodic, M.; Jaglicic, Z.; Berger, H.; Arcon, D.
Source:
PHYSICAL REVIEW LETTERS 103 (14): Art. No. 147202 OCT 2 2009
Abstract:
The magnetic and ferroelectric properties of the layered geometrically frustrated cluster compound FeTe2O5Br were investigated with single-crystal neutron diffraction and dielectric measurements. An incommensurate transverse amplitude modulated magnetic order with the wave vector q = (1/2, 0.463, 0) develops below T-N = 10.6(2) K. Simultaneously, a ferroelectric order due to exchange striction involving polarizable Te4+ lone-pair electrons develops perpendicular to q and to Fe3+ magnetic moments. The observed magnetoelectric coupling is proposed to originate from the temperature dependent phase difference between neighboring amplitude modulation waves.
Title:
Magnetic structure and ferroelectric polarization of MnWO4 investigated by density functional calculations and classical spin analysis
Authors:
Tian, C; Lee, CH; Xiang, HJ; Zhang, YM; Payen, C; Jobic, S; Whangbo, MH Author Full Names: Tian, Chuan; Lee, Changhoon; Xiang, Hongjun; Zhang, Yuemei; Payen, Christophe; Jobic, Stephane; Whangbo, Myung-Hwan
Source:
PHYSICAL REVIEW B 80 (10): Art. No. 104426 SEP 2009
Abstract:
The ordered magnetic states of MnWO4 at low temperatures were examined by evaluating the spin exchange interactions between the Mn2+ ions of MnWO4 on the basis of first principles density functional calculations and by performing classical spin analysis with the resulting spin exchange parameters. Our work shows that the spin exchange interactions are frustrated within each zigzag chain of Mn2+ ions along the c direction and between such chains of Mn2+ ions along the a direction. This explains the occurrence of a spiral-spin order along the c and a directions in the incommensurate magnetic state AF2, and that of a up arrow up arrow down arrow down arrow spin order along the c and a directions in the commensurate magnetic state AF1. The ferroelectric polarization of MnWO4 in the spiral-spin state AF2 was examined by performing Berry phase calculations for a model superstructure to find that the ferroelectric polarization occurs along the b direction,! in agreement with experiment.
Title:
Magnetic and crystal structure of Ho-5(SixGe(1-x))(4) studied by neutron diffraction
Authors:
Ritter, C; Magen, C; Morellon, L; Algarabel, PA; Ibarra, MR; Pereira, AM; Araujo, JP; Sousa, JB Author Full Names: Ritter, C.; Magen, C.; Morellon, L.; Algarabel, P. A.; Ibarra, M. R.; Pereira, A. M.; Araujo, J. P.; Sousa, J. B.
Source:
PHYSICAL REVIEW B 80 (10): Art. No. 104427 SEP 2009
Abstract:
The magnetic and crystal structures of the magnetocaloric Ho-5(SixGe1-x)(4) (x= 1, 0.75, 0.5 and 0) have been studied by neutron powder diffraction experiments. The room-temperature crystal phases of the compositions x= 1, 0.75, and 0.5 are preserved in the whole temperature range 2-300 K, i.e. the Gd5Si4-type Pnma O(I) structure for Ho5Si4, the Gd5Si2Ge2-type P112(1)/a M state in x= 0.75, and the Sm5Ge4-type Pnma O(II) phase in x= 0.5. Ho5Si4 undergoes a second order ferromagnetic (FM) transition at T-C= 77 K into a noncollinear FM structure with the magnetization oriented mainly along the a axis and weak antiferromagnetic (AFM) coupling along b and c (magnetic space group Pnm'a'). Ho5Si3Ge becomes FM at T-C= 50 K (magnetic space group P112(1)'/a). At T-C'similar to 16 K an incipient second incommensurate magnetic phase appears which becomes commensurate below 8 K with a propagation vector k=(0 0 1/4). The magnetic structure of the main phase at 30 and 2 K shows the dominance of a FM coupling along the a axis with an AFM canting along c. Ho5Si2Ge2 stands out for the complexity of its low-temperature magnetic structure. In addition to the Neel transition of the O(II) phase at T-N similar to 30 K (magnetic space group Pn'm'a'), two additional magnetic phases with propagation vectors k=(0 0 1/4) and k=(1/2 0 0) appear at 15 and 12 K, respectively. In Ho5Ge4 the main O(II) structure orders AFM with k=(0 0 0) at T-N similar to 30 K in the same magnetic space group Pn'm'a'. Below 25 K a complete structural transition from high temperature O(II)Pnma to P2(1)/m takes place within the AFM state. The magnetic structure of this new nuclear phase stays AFM with k=(0 0 0), but sees two out of six independent Ho sites non magnetic. A second magnetic transition takes place at about 18 K characterized by the appearance of a second propagation vector k=(0 0 1/2) which magnetically couples the formerly non magnetic Ho sites. Magnetic- field dependent neutron diffractograms demonstrate that FM sets in in Ho5Ge4. The onset of ferromagnetism is associated with the previously reported nucleation of a new high field O(II) Pnma phase. Contrary to the intensity of the magnetic coupling with the propagation vector k=(0 0 0), which disappears quickly with the onset of FM, a progressive decrease of the intensity associated with the state k=(0 0 1/2) suggests a possible relationship between the extent of the magnetic coupling k=(0 0 1/2) and the percentage of remnant P2(1)/m phase.
Title:
Short-range incommensurate magnetic order near the superconducting phase boundary in Fe(1+delta)Te(1-x)Sex
Authors:
Wen, JS; Xu, GY; Xu, ZJ; Lin, ZW; Li, Q; Ratcliff, W; Gu, G; Tranquada, JM Author Full Names: Wen, Jinsheng; Xu, Guangyong; Xu, Zhijun; Lin, Zhi Wei; Li, Qiang; Ratcliff, W.; Gu, Genda; Tranquada, J. M.
Source:
PHYSICAL REVIEW B 80 (10): Art. No. 104506 SEP 2009
Abstract:
We performed elastic neutron-scattering and magnetization measurements on Fe1.07Te0.75Se0.25 and FeTe0.7Se0.3. Short-range incommensurate magnetic order is observed in both samples. In the former sample with higher Fe content, a broad magnetic peak appears around (0.46,0,0.5) at low temperature, while in FeTe0.7Se0.3, the broad magnetic peak is found to be closer to the antiferromagnetic (AFM) wave vector (0.5,0,0.5). The incommensurate peaks are only observed on one side of the AFM wave vector for both samples, which can be modeled in terms of an imbalance of ferromagnetic/antiferromagnetic correlations between nearest-neighbor spins. We also find that with higher Se (and lower Fe) concentration, the magnetic order becomes weaker while the superconducting temperature and volume increase.
Title:
Stability of nodal quasiparticles in underdoped YBa2Cu3O6+y probed by penetration depth and microwave spectroscopy
Authors:
Huttema, WA; Bobowski, JS; Turner, PJ; Liang, RX; Hardy, WN; Bonn, DA; Broun, DM Author Full Names: Huttema, W. A.; Bobowski, J. S.; Turner, P. J.; Liang, Ruixing; Hardy, W. N.; Bonn, D. A.; Broun, D. M.
Source:
PHYSICAL REVIEW B 80 (10): Art. No. 104509 SEP 2009
Abstract:
High-resolution measurements of superfluid density rho(s)(T) and broadband quasiparticle conductivity sigma(1)(Omega) have been used to probe the low-energy excitation spectrum of nodal quasiparticles in underdoped YBa2Cu3O6+y. Penetration depth lambda(T) is measured to temperatures as low as 0.05 K. sigma 1(Omega) is measured from 0.1 to 20 GHz and is a direct probe of zero-energy quasiparticles. The data are compared with predictions for a number of theoretical scenarios that compete with or otherwise modify pure d(x2-y2) superconductivity, in particular, commensurate and incommensurate spin and charge-density waves; d(x2-y2) + is and d(x2-y2) + id(xy) superconductivity; circulating current phases; and the BCS-BEC crossover. We conclude that the data are consistent with a pure d(x2-y2) state in the presence of a small amount of strong scattering disorder, and are able to rule out most candidate competing states either completely or to a level set by the energy scale of the disorder, T-d similar to 4 K. Commensurate spin and charge-density orders, however, are not expected to alter the nodal spectrum and therefore cannot be excluded.
Title:
Structure of the fivefold surface of the Ag-In-Yb icosahedral quasicrystal
Authors:
Sharma, HR; Shimoda, M; Sagisaka, K; Takakura, H; Smerdon, JA; Nugent, PJ; McGrath, R; Fujita, D; Ohhashi, S; Tsai, AP Author Full Names: Sharma, H. R.; Shimoda, M.; Sagisaka, K.; Takakura, H.; Smerdon, J. A.; Nugent, P. J.; McGrath, R.; Fujita, D.; Ohhashi, S.; Tsai, A. P.
Source:
PHYSICAL REVIEW B 80 (12): Art. No. 121401 SEP 2009
Abstract:
The surface structural study of an icosahedral (i) quasicrystal of the Cd-Yb family is presented. Comparison of bias-dependent scanning tunneling microscopy data from the fivefold surface of i-Ag-In-Yb with the refined bulk model of isostructural i-Cd-Yb indicates that surfaces are formed at bulk planes intersecting the center of the rhombic triacontahedral clusters, the building blocks of the Cd-Yb family quasicrystals. These observations open up the possibility of the use of this material as a template for epitaxial structures.
Title:
Electronic structure of RNiC2 (R = Sm, Gd, and Nd) intermetallic compounds
Authors:
Laverock, J; Haynes, TD; Utfeld, C; Dugdale, SB Author Full Names: Laverock, J.; Haynes, T. D.; Utfeld, C.; Dugdale, S. B.
Source:
PHYSICAL REVIEW B 80 (12): Art. No. 125111 SEP 2009
Abstract:
First-principles calculations of the electronic structure of members of the RNiC2 series are presented and their Fermi surfaces investigated for nesting propensities, which might be linked to the charge-density waves exhibited by certain members of the series (R=Sm, Gd, and Nd). Calculations of the generalized susceptibility, chi(0)(q, omega), show strong peaks at the same q vector in both the real and imaginary parts for these compounds. Moreover, this peak occurs at a wave vector which is very close to that experimentally observed in SmNiC2. In contrast, for LaNiC2 (which is a superconductor below 2.7 K) as well as for ferromagnetic SmNiC2, there is no such sharp peak. This could explain the absence of a charge-density wave transition in the former, and the destruction of the charge-density wave that has been observed to accompany the onset of ferromagnetic order in the latter.
Title:
Theoretical study of the magnetism in the incommensurate phase of TiOCl
Authors:
Mastrogiuseppe, DM; Torio, ME; Gazza, CJ; Dobry, AO Author Full Names: Mastrogiuseppe, D. M.; Torio, M. E.; Gazza, C. J.; Dobry, A. O.
Source:
PHYSICA B-CONDENSED MATTER 404 (18): 2805-2808 OCT 1 2009
Abstract:
Going beyond a recently proposed microscopic model [D. Mastrogiuseppe. A. Dobry, arXiv:0810.3018v] for the incommensurate transition in the spin-Peierls TiOX (X = Cl, Br) compounds, in the present work we start by studying the thermodynamics of the model with XY spins and adiabatic phonons. We find that the system enters an incommensurate phase by a first order transition at a low temperature T-c1. At a higher temperature T-C2 a continuous transition to a uniform phase is found. Furthermore, we study the magnetism in the incommensurate phase by density matrix renormalization group (DMRG) calculations on a one-dimensional Heisenberg model where the exchange is modulated by the incommensurate atomic position pattern. When the wave vector q of the modulation is near pi, we find local magnetized zones (LMZ) in which spins abandon their singlets as a result of the domain walls induced by the modulated distortion. When q moves far away enough from pi, the LMZ disappear and the system develops incommensurate magnetic correlations induced by the structure. We discuss the relevance of this result regarding previous and future experiments in TiOCl (C) 2009 Elsevier B.V. All rights reserved.
Title:
Frustration of Magnetic and Ferroelectric Long-Range Order in Bi2Mn4/3Ni2/3O6
Authors:
Claridge, JB; Hughes, H; Bridges, CA; Allix, M; Suchomel, MR; Niu, H; Kuang, X; Rosseinsky, MJ; Bellido, N; Grebille, D; Perez, O; Simon, C; Pelloquin, D; Blundell, SJ; Lancaster, T; Baker, PJ; Pratt, FL; Halasyamani, PS Author Full Names: Claridge, John B.; Hughes, Helen; Bridges, Craig A.; Allix, Mathieu; Suchomel, Matthew R.; Niu, Hongjun; Kuang, Xiaojun; Rosseinsky, Matthew J.; Bellido, Natalia; Grebille, Dominique; Perez, Olivier; Simon, Charles; Pelloquin, Denis; Blundell, Stephen J.; Lancaster, Tom; Baker, Peter J.; Pratt, Francis L.; Halasyamani, P. Shiv
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 131 (39): 14000-14017 OCT 7 2009
Abstract:
The slight incommensurate modulation of the structure of Bi2Mn4/3Ni2/3O6 is sufficient to suppress the electrical polarization which arises in commensurate treatments of the structure, due to antiferroelectric coupling of local polar units of over 900 angstrom(3). The incommensurate structure is produced by the competition between ferroelectric Bi lone pair-driven A site displacement, chemical order of Mn and Ni on the B site, and both charge and orbital order at these transition metals. The interplay between the frustrated polar Bi displacements and the frustrated spin order at the B site, induced by positional disorder, produces magnetodielectric coupling between the incommensurately modulated lattice and the spin-glass-like ground state with an unusual relationship between the magnetocapacitance and the applied field.
Title:
Molecular dewetting on insulators
Authors:
Burke, SA; Topple, JM; Grutter, P Author Full Names: Burke, S. A.; Topple, J. M.; Gruetter, P.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (42): Art. No. 423101 OCT 21 2009
Abstract:
Recent attention given to the growth and morphology of organic thin films with regard to organic electronics has led to the observation of dewetting (a transition from layer (s) to islands) of molecular deposits in many of these systems. Dewetting is a much studied phenomenon in the formation of polymer and liquid films, but its observation in thin films of the 'small' molecules typical of organic electronics requires additional consideration of the structure of the interface between the molecular film and the substrate. This review covers some key concepts related to dewetting and molecular film growth. In particular, the origins of different growth modes and the thickness dependent interactions which give rise to dewetting are discussed in terms of surface energies and the disjoining pressure. Characteristics of molecular systems which may lead to these conditions, including the formation of metastable interface structures and commensurate-incommensurate phase transitions, are also discussed. Brief descriptions of some experimental techniques which have been used to study molecular dewetting are given as well. Examples of molecule-on-insulator systems which undergo dewetting are described in some detail, specifically perylene derivatives on alkali halides, C-60 on alkali halides, and the technologically important system of pentacene on SiO2. These examples point to some possible predicting factors for the occurrence of dewetting, most importantly the formation of an interface layer which differs from the bulk crystal structure.

Update: 8-Oct-2009

Title:
Spin chirality and electric polarization in multiferroic compounds RMn2O5 (R = Ho, Er)
Authors:
Wakimoto, S; Kimura, H; Fukunaga, M; Nishihata, K; Takeda, M; Kakurai, K; Noda, Y; Tokura, Y Author Full Names: Wakimoto, Shuichi; Kimura, Hiroyuki; Fukunaga, Mamoru; Nishihata, Keisuke; Takeda, Masayasu; Kakurai, Kazuhisa; Noda, Yukio; Tokura, Yoshinori
Source:
PHYSICA B-CONDENSED MATTER 404 (17): 2513-2516 SEP 1 2009
Abstract:
Polarized neutron diffraction experiments have been performed on multiferroic materials RMn2O5 (R = Ho, Er) under electric fields in the ferroelectric commensurate (CM) and the low-temperature incommensurate (LT-ICM) phases, where the former has the highest electric polarization and the latter has reduced polarization. It is found that, after cooling in electric fields down to the CM phase, the magnetic chirality is proportional to the electric polarization. Also we confirmed that the magnetic chirality can be switched by the polarity of the electric polarization in both the CM and LT-ICM phases. These facts suggest an intimate coupling between the magnetic chirality and the electric polarization. However, upon the transition from the CM to LT-ICM phase, the reduction of the electric polarization is not accompanied by any reduction of the magnetic chirality, implying that the CM and LT-ICM phases contain different mechanisms of the magnetoelectric coupling. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Solid State Polyselenides and Polytellurides: A Large Variety of Se-Se and Te-Te Interactions
Authors:
Graf, C; Assoud, A; Mayasree, O; Kleinke, H Author Full Names: Graf, Christian; Assoud, Abdeljalil; Mayasree, Oottil; Kleinke, Holger
Source:
MOLECULES 14 (9): 3115-3131 SEP 2009
Abstract:
A large variety of different interactions between the chalcogen atoms, Q, occur in the solid state structures of polyselenides and polytellurides, including both molecular and infinite units. The simplest motifs are classical Q(2)(2-) dumbbells and nonlinear Qn(2-) chains (n = 3, 4, 5,..), e. g. found in alkali metal polychalcogenides. In addition, nonclassical so-called hypervalent motifs exist in the form of linear Q(3)(4-) units or within larger units such as Q(4)(4-) and Q(5)(4-). Infinitely extended Q units include zigzag, cis/trans and linear chains, as well as planar and slightly puckered layers. Several of those are susceptible to Peierls distortions, leading to the formation of both commensurate and incommensurate superstructures and anomalies in transport properties, including metal-nonmetal transitions.
Title:
Manganese adlayers on i-Al-Pd-Mn quasicrystal: growth and electronic structure
Authors:
Shukla, AK; Dhaka, RS; D'Souza, SW; Maniraj, M; Barman, SR; Horn, K; Ebert, P; Urban, K; Wu, D; Lograsso, TA Author Full Names: Shukla, A. K.; Dhaka, R. S.; D'Souza, S. W.; Maniraj, M.; Barman, S. R.; Horn, K.; Ebert, Ph; Urban, K.; Wu, D.; Lograsso, T. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (40): Art. No. 405005 OCT 7 2009
Abstract:
Pseudomorphic growth of thin elemental metal films is often observed on a variety of crystalline solids. On quasicrystalline surfaces with their complex structure and the absence of translational periodicity, the situation is different since elemental metals do not exhibit quasicrystalline order, and hence the specific interaction between overlayer and substrate is decisive. Here we study the growth of manganese films on an icosahedral i-Al-Pd-Mn alloy with a view to establishing the growth mode and electronic structure. Although we observe an exponential intensity variation of the adlayer and substrate related x-ray photoemission spectroscopy (XPS) peaks, low energy electron diffraction (LEED) shows that Mn adlayers do not exhibit quasicrystallinity. The detailed structure of the Mn 2p core level line reveals considerable electronic structure differences between the quasicrystalline and elemental metal environment. Evidence of a substantial local magnetic moment on the Mn atoms in the overlayer (about 2.8 mu(B)) is obtained from the Mn 3s exchange splitting.
Title:
Pressure-induced disorder in Rb2ZnCl4
Authors:
Machon, D; Grzechnik, A; Friese, K Author Full Names: Machon, Denis; Grzechnik, Andrzej; Friese, Karen
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (40): Art. No. 405405 OCT 7 2009
Abstract:
Rb2ZnCl4 in the normal phase (T = 308-313 K) has been studied under pressure by means of single-crystal x-ray diffraction up to 3.84 GPa and Raman spectroscopy up to 5.9 GPa. No pressure-induced phase transition has been observed but an orientational disorder of the tetrahedra is enhanced with the pressure. At the same time a partial one-dimensional correlation of some chlorine atoms might be favoured at high pressures. Raman spectra in the incommensurate phase (T = 293 K) were collected to higher pressure (24.2 GPa) varying the pressure-transmitting medium. The hydrostaticity during the compression is shown to affect drastically the broadness of the Raman peaks, leading to an amorphous-like spectrum in the least hydrostatic case.
Title:
Crystallographic and electrochemical characteristics of Ti-Zr-Ni-Pd quasicrystalline alloys
Authors:
Liu, BZ; Zhang, YD; Mi, GF; Zhang, Z; Wang, LM Author Full Names: Liu, Baozhong; Zhang, Yude; Mi, Guofa; Zhang, Zhi; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 34 (16): 6925-6929 Sp. Iss. SI AUG 2009
Abstract:
Ti45Zr35Ni20-xPdx (x = 0, 1, 3, 5 and 7, at%) alloys were prepared by melt-spinning. The phase structure and electrochemical hydrogen storage performances of melt-spun alloys were investigated. The melt-spun alloys were icosahedral quasicrystalline phase, and the quasi-lattice constant increased with increasing x value. The maximum discharge capacity of alloy electrodes increased from 79 mAh/g (x = 0) to 148 mAh/g (x = 7). High-rate dis-chargeability and cycling stability were also enhanced with the increase of Pd content. The improvement in the electrochemical hydrogen storage characteristics may be ascribed to better electrochemical activity and oxidation resistance of Pd than that of Ni. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Title:
Investigation of the New P ' 3-Na0.60VO2 Phase: Structural and Physical Properties
Authors:
Szajwaj, O; Gaudin, E; Weill, F; Darriet, J; Delmas, C Author Full Names: Szajwaj, Olivier; Gaudin, Etienne; Weill, Francois; Darriet, Jacques; Delmas, Claude
Source:
INORGANIC CHEMISTRY 48 (19): 9147-9154 OCT 5 2009
Abstract:
A new layered phase Na0.60VO2 was synthesized by chemical deintercalation of sodium from the pristine compound O3-NaVO2. The Na0.60VO2 compound exhibits a distorted P'3-type oxygen stacking (AABBCC) with an average monoclinic unit cell containing a = 4.9862(14) angstrom, b = 2.8708(8) angstrom, c = 5.917(2) angstrom, and beta = 104.36(3)degrees. A modulated structure was observed by transmission electron microscopy and X-ray diffraction (XRD) measurements. Indexation of the XRD pattern was achieved by using the q vector equal to 0.44b(star), and the 4D superspace group C2/m (0 beta 0) s0 was then deduced. The specific heat measurement showed a strong correlated system with a gamma value of around 20 mJ . mol(-1) . K-2. The electrical conductivity shows a semiconductor-like behavior with an activation energy of 0.52 eV. A paramagnetic behavior of the susceptibility is observed below room temperature with a Curie constant equal to C = 0.076 emu . K-1 . mol(-1) . Oe(-1). To explain this small value, a model of pseudotriangular clusters of vanadium with a random distribution of V3+ and V4+ was considered.
Title:
Phase formation and structures of quasicrystals and approximants in the Zn-Mg-(Ti, Zr, Hf) system
Authors:
Ohhashi, S; Abe, E; Tanaka, M; Tsai, AP Author Full Names: Ohhashi, S.; Abe, E.; Tanaka, M.; Tsai, A. P.
Source:
ACTA MATERIALIA 57 (16): 4727-4735 SEP 2009
Abstract:
The compositional regions for primitive (P) and face-centered (F) icosahedral quasicrystals (iQc) have been determined to be around Zn84Mg9Zr7 and Zn75Mg18Zr6, respectively. A 1/1 approximant of the F-type iQc was found to have a composition around Zn77Mg18Zr5. A similar tendency has been verified for the Zn-Mg-Hf system. No stable iQc was observed in the Zn-Mg-Ti system. High-resolution X-ray measurements performed with synchrotron radiation showed that the stable iQcs are highly ordered and contain less phason disorder. High-angle annular dark field (HAADF) scanning transmission electron microscopy observation of the 1/1 Zn-Mg-Hf approximant effectively revealed the Hf positions in the structure, whose local contrasts can be reasonably interpreted by a structural model where icosahedral and dodecahedral Hf clusters are mutually interpenetrated. Similar appearances of local contrasts were frequently observed in HAADF images of the F-type iQc, indicating that the iQc structure is also build up of icosahedral clusters that are almost identical to those in the 1/1 approximant. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 1-Oct-2009

Title:
Tailoring Thermally Induced Nano-Quasicrystallization and Deformation-Assisted Nanocrystallization for Mechanical Property Improvement in Zr-Al-Ni-Cu-Pd Bulk Metallic Glasses
Authors:
Saida, J; Setyawan, AD; Kato, H; Matsushita, M; Inoue, A Author Full Names: Saida, Junji; Setyawan, Albertus D.; Kato, Hidemi; Matsushita, Mitsuhide; Inoue, Akihisa
Source:
MATERIALS TRANSACTIONS 50 (8): 2079-2086 AUG 2009
Abstract:
The material design tailoring of a synergistic effect of an in-situ nano secondary phase formation and defomation-induced nanocrystallization for improving the mechanical strength and ductility, has been investigated in Zr65Al7.5Ni10Cu17.5-xPdx bulk metallic glasses (BMGs). As-cast Zr65Al7.5Ni10Cu17.5-xPdx (x = 5-17.5) BMGs have significant ductility in compressive deformation, which is attributed to deformation-induced dynamic nanocrystallization. The 10at% Pd-containing BMG with a low volume fraction of the quasicrystalline (QC) phase of less than 6% exhibits increases in strength and Young's modulus, in addition to a remaining plasticity of similar to 5%, compared with the monolithic glassy alloy. Such improvements in the mechanical properties originate from the combination of two effects of in-situ homogenous nano-QC formation and deformation-induced inhomogeneous nanocrystallization. The present method should be regarded as a new technique for the production of BMGs with high strength and good ductility. [doi:10.2320/matertrans.M2009135]

Update: 24-Sep-2009

Title:
Microstructure, surface composition and chemical stability of partly ordered LaTiO2N
Authors:
Logvinovich, D; Bocher, L; Sheptyakov, D; Figi, R; Ebbinghaus, SG; Aguiar, R; Aguirre, MH; Reller, A; Weidenkaff, A Author Full Names: Logvinovich, Dmitry; Bocher, Laura; Sheptyakov, Denis; Figi, Renato; Ebbinghaus, Stefan G.; Aguiar, Rosiana; Aguirre, Myriam H.; Reller, Armin; Weidenkaff, Anke
Source:
SOLID STATE SCIENCES 11 (8): 1513-1519 AUG 2009
Abstract:
LaTiO2N was synthesized in a thermal ammonolysis process of crystalline La2Ti2O7 prepared by conventional solid state reaction or by ammonolysis of a homogeneous amorphous precursor obtained from a soft-chemistry approach. At room temperature slowly cooled LaTiO2N prepared from either precursor crystallizes in space group I (1) over bar and shows a partially ordered anionic arrangement in contrast to a quenched reference sample. The material possesses a complex microstructure represented by twin domains of different types and orientations, as well as incommensurately modulated fragments. The presence of minor C- and N-containing phases such as carbonates, cyanides and nitrates as well as a small amount of a reoxidation intermediate was detected by infrared and Raman spectroscopy. These small amounts of secondary phases can generally influence the results of the O/N content determination of oxynitride compounds when using thermal analysis methods. The formation of such unwanted secondary phases can be avoided by quenching the oxynitride sample or by cooling in inert atmosphere. (C) 2009 Elsevier Masson SAS. All rights reserved.
Title:
Detailed Phase Analysis and Crystal Structure Investigation of a Bi1-xCaxFeO3-x/2 Perovskite-Related Solid Solution Phase and Selected Property Measurements Thereof
Authors:
Schiemer, J; Withers, R; Noren, L; Liu, Y; Bourgeois, L; Stewart, G Author Full Names: Schiemer, Jason; Withers, Ray; Noren, Lasse; Liu, Yun; Bourgeois, Laure; Stewart, Glen
Source:
CHEMISTRY OF MATERIALS 21 (18): 4223-4232 SEP 22 2009
Abstract:
A well-ordered, perovskite-related, (Bi1-xCaxFeO3-x/2)-O-III solid solution phase is synthesized via a rapid liquid phase sintering technique and shown to exist over the composition range similar to 0.20 < x < similar to 0.49. Two phase regions are shown to separate this phase from compositionally narrow end-member (Bi1-xCaxFeO3-x/2)-O-III solid solutions based on rhombohedral BiFeO3 and brownmillerite, Ca2Fe2O5, respectively. The wide range, non-stoichiometric phase is characterized by a well ordered, (in general) incommensurately modulated structure that varies systematically with composition. Mossbauer spectroscopy is used to verify the oxidation state of iron as (III), as well as showing the existence of three separate iron environments across the solid solution field. HRTEM imaging is used to develop a structural model for the phase at one particular composition. The magnetic, dielectric, and impedance properties of this solid solution phase are reported. Magnetic measurements show antiferromagnetic behavior. There is no change in either susceptibility or antiferromagnetic behavior with composition. Attempts at obtaining saturated ferroelectric loops failed due to high intrinsic conductivity. The phase is found to exhibit a low frequency impedance relaxation that is likely due to correlated oxygen vacancy hopping.
Title:
Differential geometry: a natural tool for describing symmetry operations
Authors:
Kocian, P; Schenk, K; Chapuis, G Author Full Names: Kocian, Philippe; Schenk, Kurt; Chapuis, Gervais
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 329-341 Part 5 OCT 2009
Abstract:
Differential geometry provides a useful mathematical framework for describing the fundamental concepts in crystallography. The notions of point and associated vector spaces correspond to those of manifold and tangent space at a given point. A space-group operation is a one-to-one map acting on the manifold, whereas a point-group operation is a linear map acting between two tangent spaces of the manifold. Manifold theory proves particularly powerful as a unified formalism describing symmetry operations of conventional as well as modulated crystals without requiring a higher-dimensional space. We show, in particular, that a modulated structure recovers a three-dimensional periodicity in any tangent space and that its point group consists of linear applications. (C) 2009 International Union of Crystallography Printed in Singapore - all rights reserved
Title:
Point substitution processes for decagonal quasi-periodic tilings
Authors:
Fujita, N Author Full Names: Fujita, Nobuhisa
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 342-351 Part 5 OCT 2009
Abstract:
A general construction principle for the inflation rules for decagonal quasiperiodic tilings is proposed. The prototiles are confined to be polygons with unit edges. An inflation rule for a tiling is the combination of expansion and division of the tiles, where the expanded tiles can be divided arbitrarily as long as the set of prototiles is maintained. A certain kind of point decoration process turns out to be useful for the identification of possible division rules. The method is capable of generating a broad range of decagonal tilings, many of which are chiral and have atomic surfaces with fractal boundaries. Two new families of decagonal tilings are presented; one is quaternary and the other ternary. The properties of the ternary tilings with rhombic, pentagonal and hexagonal prototiles are investigated in detail. (C) 2009 International Union of Crystallography Printed in Singapore - all rights reserved

Update: 17-Sep-2009

Title:
Symmetry Breaking in Dense Solid Hydrogen: Mechanisms for the Transitions to Phase II and Phase III
Authors:
Toledano, P; Katzke, H; Goncharov, AF; Hemley, RJ Author Full Names: Toledano, Pierre; Katzke, Hannelore; Goncharov, Alexander F.; Hemley, Russell J.
Source:
PHYSICAL REVIEW LETTERS 103 (10): Art. No. 105301 SEP 4 2009
Abstract:
Spectroscopic data for the high-pressure phases of hydrogen together with the topology of the phase diagram provide new insight on the behavior of the material at megabar pressure. Structural mechanisms are proposed for the transitions to phases II and III. These mechanisms include a partially ordered structure (possibly incommensurate) and an ordered isotranslational structure for the two phases, respectively. The analysis supports the existence of an additional phase, isostructural to phase III, with boundary that meets to form a second triple point with phases I and III.
Title:
Aperiodicity, structure, and dynamics in Ni(CN)(2)
Authors:
Goodwin, AL; Dove, MT; Chippindale, AM; Hibble, SJ; Pohl, AH; Hannon, AC Author Full Names: Goodwin, Andrew L.; Dove, Martin T.; Chippindale, Ann M.; Hibble, Simon J.; Pohl, Alexander H.; Hannon, Alex C.
Source:
PHYSICAL REVIEW B 80 (5): Art. No. 054101 AUG 2009
Abstract:
By combining the results of both x-ray diffraction and neutron total-scattering experiments, we show that Ni(CN)(2) exhibits long-range structural order only in two dimensions, with no true periodicity perpendicular to its gridlike layers. Reverse Monte Carlo analysis gives an experimental distinction between M-C and M-N bond lengths in a homometallic cyanide framework and identifies the vibrational modes responsible for anomalous positive and negative thermal expansion in the title compound.
Title:
Origin of Moireacute structures in C-60 on Pb(111) and their effect on molecular energy levels
Authors:
Li, HI; Franke, KJ; Pascual, JI; Bruch, LW; Diehl, RD Author Full Names: Li, H. I.; Franke, K. J.; Pascual, J. I.; Bruch, L. W.; Diehl, R. D.
Source:
PHYSICAL REVIEW B 80 (8): Art. No. 085415 AUG 2009
Abstract:
Low-energy electron diffraction (LEED) indicates that the monolayer structure of C-60 on Pb(111) comprises two coexisting incommensurate structures with nonsymmetry epitaxial rotations near 20 degrees relative to the Pb(111) lattice. These structures are observed in scanning tunneling microscopy (STM) as Moireacute superstructures having periods of about 46 A degrees and 34 A degrees. The Moireacute images and LEED patterns are consistent with two higher-order commensurate (HOC) structures that were identified using the hexagonal number sequence method. These structures are close to predictions from the Novaco-McTague theory of epitaxial rotation, assuming a weakly corrugated substrate potential. As a consequence of the fullerenes within the Moireacute structures having different local environments, the energetic alignment of the molecular resonances is also modulated, with shifts measured by tunneling spectroscopy of up to 20 meV.
Title:
Commensurate lock-in and incommensurate supersolid phases of hard-core bosons on anisotropic triangular lattices
Authors:
Isakov, SV; Chien, HC; Wu, JJ; Chen, YC; Chung, CH; Sengupta, K; Kim, YB Author Full Names: Isakov, Sergei V.; Chien, Hong-Chi; Wu, Jian-Jheng; Chen, Yung-Chung; Chung, Chung-Hou; Sengupta, Krishnendu; Kim, Yong Baek
Source:
EPL 87 (3): Art. No. 36002 AUG 2009
Abstract:
We investigate the interplay between commensurate lock-in and incommensurate supersolid phases of the hard-core bosons at half-filling with anisotropic nearest-neighbor hopping and repulsive interactions on triangular lattice. We use numerical quantum and variational Monte Carlo as well as analytical Schwinger boson mean-field analysis to establish the ground states and phase diagram. It is shown that, for finite-size systems, there exist a series of jumps between different supersolid phases as the anisotropy parameter is changed. The density ordering wave vectors are locked to commensurate values and jump between adjacent supersolids. In the thermodynamic limit, however, the magnitude of these jumps vanishes leading to a continuous set of novel incommensurate supersolid phases. Copyright (C) EPLA, 2009

Update: 10-Sep-2009

Title:
Coupled Magnetic and Ferroelectric Domains in Multiferroic Ni3V2O8
Authors:
Cabrera, I; Kenzelmann, M; Lawes, G; Chen, Y; Chen, WC; Erwin, R; Gentile, TR; Leao, JB; Lynn, JW; Rogado, N; Cava, RJ; Broholm, C Author Full Names: Cabrera, I.; Kenzelmann, M.; Lawes, G.; Chen, Y.; Chen, W. C.; Erwin, R.; Gentile, T. R.; Leao, J. B.; Lynn, J. W.; Rogado, N.; Cava, R. J.; Broholm, C.
Source:
PHYSICAL REVIEW LETTERS 103 (8): Art. No. 087201 AUG 21 2009
Abstract:
Electric control of multiferroic domains is demonstrated through polarized magnetic neutron diffraction. Cooling to the cycloidal multiferroic phase of Ni3V2O8 in an electric field E causes the incommensurate Bragg reflections to become neutron spin polarizing, the sense of neutron polarization reversing with E. Quantitative analysis indicates the E-treated sample has a handedness that can be reversed by E. We further show a close association between cycloidal and ferroelectric domains through E-driven spin and electric polarization hysteresis. We suggest that a definite cycloidal handedness is achieved through magnetoelastically induced Dzyaloshinskii-Moriya interactions.
Title:
Structural transformations and magnetic properties of Bi(1-x)Ln(x)FeO(3) (Ln = La, Nd, Eu) multiferroics
Authors:
Troyanchuk, IO; Bushinsky, MV; Karpinsky, DV; Mantytskaya, OS; Fedotova, VV; Prochnenko, OI Author Full Names: Troyanchuk, I. O.; Bushinsky, M. V.; Karpinsky, D. V.; Mantytskaya, O. S.; Fedotova, V. V.; Prochnenko, O. I.
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 246 (8): 1901-1907 AUG 2009
Abstract:
Crystal structures of Bi(1-x)Ln(x)FeO(3) systems (Ln = La, Nd, Eu) are studied using X-ray and neutron diffraction, magnetization measurements as well as electron microscopy. It was shown that the unit cell of the Bi1-xLaxFeO3 system is described with the R3c space group in the concentration interval 0 < x < 0.15, with the space group Imma (0.4 < x < 0.5) and with the Puma at x > 0.5. The mixed-phase state was observed in the range 0.15 < x < 0.4 independent of synthesis conditions. A similar sequence of the phase transformations was observed for Bi1-xNdxFeO3 system, In the case of qBi(1-x)Eu(x)FeO(3) series the unit cell is rhombohedral (R3c) at x 0.08 and orthorhombic (Pnma) at x > 0.20, whereas no evidence for Imma phase was found. The magnetization study has revealed the spontaneous magnetization to be associated with Prima and Imma phases that do not allow conventional ferroelectricity, The ferroelectric R3c phase exhibits meta-magnetic behavior due to transition from an incommensurately modulated antiferromagnetic state to a weak ferromagnetic state. Substitution of Bi3+ with Ln(3+) leads to a strong decrease of external magnetic field inducing a metamagnetic transition. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Resonant Magnetic X-ray Diffraction Study on the Triangular Lattice Antiferromagnet GdPd2Al3
Authors:
Inami, T; Terada, N; Kitazawa, H; Sakai, O Author Full Names: Inami, Toshiya; Terada, Noriki; Kitazawa, Hideaki; Sakai, Osamu
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (8): Art. No. 084713 AUG 2009
Abstract:
Resonant magnetic x-ray diffraction experiments were carried out on the stacked triangular lattice antiferromagnet GdPd2Al3. The experiments revealed an expected initial collinear c-axis order at T-N1 followed by an additional in-plane order at T-N2, while at the same time we found that the ground state is a helically ordered state of a very long incommensurate period of approximately 700 angstrom. The distribution of K-domains was highly anisotropic, and the domain with the modulation vector normal to the surface of the crystal was ascendant. Low-field magnetization is discussed on the basis of the observed incommensurate magnetic structure.
Title:
Studies of Multiferroic System of LiCu2O2: II. Magnetic Structures of Two Ordered Phases with Incommensurate Modulations
Authors:
Kobayashi, Y; Sato, K; Yasui, Y; Moyoshi, T; Sato, M; Kakurai, K Author Full Names: Kobayashi, Yoshiaki; Sato, Kenji; Yasui, Yukio; Moyoshi, Taketo; Sato, Masatoshi; Kakurai, Kazuhisa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (8): Art. No. 084721 AUG 2009
Abstract:
Neutron diffraction and Li-7-NMR have been applied to determine the three dimensional magnetic structures of the multiferroic system LiCu2O2, which has four chains (ribbon chains) of edge-sharing CuO4 square planes in a unit cell. First, we have confirmed that there are successive magnetic transitions at T-N1 = 24.5 K and T-N2 = 22.8 K. In the T region between T-N1 and T-N2, the quasi one-dimensional spins (S = 1/2) of Cu2+ ions within a chain have a collinear and sinusoidally modulated structure with Cu-moments parallel to the c-axis and with the modulation vector along the b-axis. At T < T-N2, an ellipsoidal helical spin structure with the incommensurate modulation has been found. We present detailed parameters, describing the modulation amplitudes, helical axis vectors as well as the relative phases of the modulations of four ribbon chains, which can well reproduce both the NMR and neutron results, in the two magnetically ordered phases. This finding of the rather precise magnetic structures enables us to discuss the relationship between the magnetic structure and the multiferroic nature of the present system in zero magnetic field, as presented in our companion paper (paper I), and open a way how to understand the reported electric polarization under the finite magnetic field.
Title:
Evaluation of the local environment for nanoscale quasicrystal formation in Zr80Pt20 glassy alloy using Voronoi analysis
Authors:
Saida, J; Itoh, K; Sato, S; Imafuku, M; Sanada, T; Inoue, A Author Full Names: Saida, Junji; Itoh, Keiji; Sato, Shigeo; Imafuku, Muneyuki; Sanada, Takashi; Inoue, Akihisa
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (37): Art. No. 375104 SEP 16 2009
Abstract:
The local atomic structure of nano-quasicrystal-forming Zr80Pt20 binary glassy alloy was investigated by reverse Monte Carlo modeling based on the results of x-ray diffraction. A prepeak at Q similar to 17 nm(-1) originating from the unique bonding between the Pt-Pt pair is observed in the structure factor. Voronoi analysis indicates that an icosahedral-like polyhedron is formed around Pt. It is also found that icosahedral-like polyhedra exist around Zr; however, the fraction of perfect icosahedra is considerably lower than that in the nano-quasicrystal-forming Zr70Pd30 glassy alloy. A difference in the local environment between the two binary quasicrystal-forming glassy alloys is suggested.
Title:
Direct observation of double-k lattice modulation in double-k magnetic structures. The case of CeAl2
Authors:
Stunault, A; Schweizer, J; Givord, F; Vettier, C; Detlefs, C; Boucherle, JX; Lejay, P Author Full Names: Stunault, A.; Schweizer, J.; Givord, F.; Vettier, C.; Detlefs, C.; Boucherle, J-X; Lejay, P.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (37): Art. No. 376004 SEP 16 2009
Abstract:
Symmetry analysis is combined with x-ray scattering experiments to investigate the lattice modulation associated with the incommensurate magnetic structure in the case of a double-k structure. The expansion of the free energy shows that the components of the magnetic structure with propagation vectors k(1) and k(2) can couple via components of lattice modulations. It is shown that the classical diffraction peaks reflecting a 2k propagation vector, associated with magneto-elastic effects in single-k structures, will coexist with diffraction peaks with propagation vectors k(1) - k(2) or k(1) + k(2). The existence of these latter peaks can be considered as a signature of a double-k magnetic structure. In the case of the double-k modulated structure of CeAl2, group theory is applied directly to the study of the charge modulation. An x-ray scattering study of the 2k satellites shows that the lattice displacements of the two Ce sites of the structure are antiparallel to each other, and perpendicular to the direction of the magnetic modulation. We also confirm experimentally the existence of k(1) + k(2) satellites.
Title:
Formation of Nano-Quasicrystalline Decagonal Phase in the Al70Cu10Co5Ni15 System by High Energy Ball Milling
Authors:
Yadav, TP; Mukhopadhyay, NK; Shaz, MA; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Mukhopadhyay, N. K.; Shaz, M. A.; Tiwari, R. S.; Srivastava, O. N.
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 (9): 5527-5532 SEP 2009
Abstract:
A nano decagonal quasicrystalline phase in the Al70Cu10Co5Ni15 alloy has been synthesized by mechanical alloying of a mixture of elemental powders followed by annealing. A high-energy ball milling of the elemental mixture of Al, Cu, Co and Ni leads to the formation of B2 type quaternary intermetallic alloys. The X-ray diffraction and transmission electron microscopy techniques have been employed for characterization of the samples. It was observed that the dissolution of the individual elements into an alloy led to the formation of a nano B2 phase. This phase was found to be quite stable against milling and no other crystalline or amorphous phases could be detected. Milled powder after annealing at 700 degrees C for 60 h was found to transform to nano-decagonal phase. Attempts have been made to understand the evolution of the complex intermetallic nano phases and their relative stability during milling.
Title:
Two Variants of the 1/2[110](p)(203)(p) Crystallographic Shear Structures: The Phasoid Sr0.61Pb0.18(Fe0.75Mn0.25)O-2.29
Authors:
Lepoittevin, C; Hadermann, J; Malo, S; Perez, O; Van Tendeloo, G; Hervieut, M Author Full Names: Lepoittevin, Christophe; Hadermann, Joke; Malo, Sylvie; Perez, Olivier; Van Tendeloo, Gustaaf; Hervieut, Maryvonne
Source:
INORGANIC CHEMISTRY 48 (17): 8257-8262 SEP 7 2009
Abstract:
For the composition (Sr0.61Pb0.18)(Fe0.75Mn0.25)O-2.29, a new modulated crystallographic shear structure, related to perovskite, has been synthesized and structurally characterized by transmission electron microscopy. The structure can be described using a monoclinic supercell with cell parameters a(m) = 27.595(2) angstrom, b(m) = 3.8786(2) angstrom, c(m) = 13.3453(9) angstrom, and beta(m) = 100.126(5)degrees, refined from powder X-ray diffraction data. The incommensurate crystallographic shear phases require an alternative approach using the superspace formalism. This allows a unified description of the incommensurate phases from a monoclinically distorted perovskite unit cell and a modulation wave vector. The structure deduced from the high-resolution transmission electron microscopy and high-angle annular dark-field-scanning transmission electron microscopy images is that of a 1/2[110](p)(203)(p) crystallographic shear structure. The structure follows the concept of a phasoid, with two coexisting variants with the same unit cell. The difference is situated at the translational interface, with the local formation of double (phase 2) or single (phase 1) tunnels, where the Pb cations are likely located.
Title:
Spin density wave dislocation in chromium probed by coherent X-ray diffraction
Authors:
Jacques, VLR; Le Bolloc'h, D; Ravy, S; Giles, C; Livet, F; Wilkins, SB Author Full Names: Jacques, V. L. R.; Le Bolloc'h, D.; Ravy, S.; Giles, C.; Livet, F.; Wilkins, S. B.
Source:
EUROPEAN PHYSICAL JOURNAL B 70 (3): 317-325 AUG 2009
Abstract:
We report on the study of a magnetic dislocation in pure chromium. Coherent X-ray diffraction profiles obtained on the incommensurate Spin Density Wave (SDW) reflection are consistent with the presence of a dislocation of the magnetic order, embedded at a few micrometers from the surface of the sample. Beyond the specific case of magnetic dislocations in chromium, this work may open up a new method for the study of magnetic defects embedded in the bulk.
Title:
Field-dependent competing magnetic ordering in multiferroic Ni3V2O8
Authors:
Singh, AK; Jain, D; Ganesan, V; Nigam, AK; Patnaik, S Author Full Names: Singh, A. K.; Jain, D.; Ganesan, V.; Nigam, A. K.; Patnaik, S.
Source:
EPL 86 (5): Art. No. 57001 JUN 2009
Abstract:
The geometrically frustrated magnet Ni3V2O8 undergoes a series of competing magnetic ordering at low temperatures. Most importantly, one of the incommensurate phases has been reported to develop a ferroelectric correlation caused by spin frustration. Here we report an extensive thermodynamic, dielectric and magnetic study on clean polycrystalline samples of this novel multiferroic compound. Our low-temperature specific heat data at high fields up to 14 Tesla clearly identify the development of a new magnetic-field-induced phase transition below 2 K that shows signatures of simultaneous electric ordering. We also report temperature-and field-dependent dielectric constant that enables us to quantitatively estimate the strength of magnetoelectric coupling in this improper ferroelectric material. Copyright (C) EPLA, 2009
Title:
Theory of magnetic order in Fe1+yTe1-xSex
Authors:
Fang, C; Bernevig, BA; Hu, JP Author Full Names: Fang, Chen; Bernevig, B. Andrei; Hu, Jiangping
Source:
EPL 86 (6): Art. No. 67005 JUN 2009
Abstract:
We develop a local spin model to explain the rich magnetic structures in the ironbased superconductors Fe1+yTe1-xSex. We show that our model exhibits both commensurate antiferromagnetic and incommensurate magnetic order along the crystal a-axis. The transition from the commensurate to the incommensurate phase is induced when the concentration of excess Fe atoms is larger than a critical value. Experimentally measurable spin-wave features are calculated, and the mean-field phase diagram of the model is obtained. Our model also suggests the existence of a large quantum critical region due to strong spin frustration upon increasing Se concentration. Copyright (C) EPLA, 2009
Title:
A "checkerboard" orbital-stripe phase and charge ordering transitions in Pr(SrxCa2-x)Mn2O7 (0 <= x <= 0.45)
Authors:
Li, ZA; Li, X; Wang, Z; Tian, HF; Ma, C; Zeng, LJ; Yang, HX Author Full Names: Li, Z. A.; Li, X.; Wang, Z.; Tian, H. F.; Ma, C.; Zeng, L. J.; Yang, H. X.
Source:
EPL 86 (6): Art. No. 67010 JUN 2009
Abstract:
The charge/orbital ordering (COO) behaviors in the double-layered Pr(SrxCa2-x)Mn2O7 have been investigated by in situ transmission electron microscopy (TEM) observations. The experimental results reveal that two charge ordering (CO) phase transitions, so-called T-co1 and T-co2, commonly exist in the orthorhombic Pr(SrxCa2-x)Mn2O7 (0 <= x <= 0.45) samples. Moreover, a "checkerboard" orbital-stripe phase characterized by two orthogonal COO modulations, q(a) and q(b), is observed between T-co1 and T-co2 in all samples. Detailed TEM investigations on the x=0.2 sample, in which a visible electric polarization was found (Tokunaga Y. et al., Nat. Mater., 5 (2006) 937) demonstrate that the q(b) modulation only survives between T-co1 and T-co2, and the "checkerboard" phase transforms into the conventional one-dimensional COO stripe phase below T-co2. The reversal of in-plane optical anisotropy across the T-co2 transition (Tokunaga Y. et al., Nat. Mater., 5 (2006) 937) is also explained based on TEM result. Copyright (C) EPLA, 2009
Title:
Polygrain icosahedral Al-Pd-Re quasicrystal as a granular electronic conductor
Authors:
Vekilov, YK; Chernikov, MA Author Full Names: Vekilov, Yu. Kh.; Chernikov, M. A.
Source:
EPL 87 (1): Art. No. 17010 JUL 2009
Abstract:
The mechanism of low-temperature electronic transport in polygrain samples of icosahedral Al-Pd-Re is analyzed by analogy with granular electronic systems. The intergranular tunneling and electrostatic energy (Coulomb blockade) are responsible for a specific behaviour of the electrical conductivity in polygrain samples of icosahedral Al-Pd-Re at low temperatures. Depending on the structural state of the sample, both factors may be important and the variable-range hopping regime, of Efros-Shklovskii's type, takes place. For the strong-coupling state the tunneling prevails, and the low-temperature variation of the electrical conductivity is dominated by the Coulomb-interaction and weak-localization corrections. Copyright (C) EPLA, 2009
Title:
Suppression of the current leakage in charge ordered Lu2Fe2Fe1-xMnxO7 (0 < x < 0.86)
Authors:
Qin, YB; Yang, HX; Zhang, Y; Tian, HF; Ma, C; Zeng, LJ; Li, JQ Author Full Names: Qin, Y. B.; Yang, H. X.; Zhang, Y.; Tian, H. F.; Ma, C.; Zeng, L. J.; Li, J. Q.
Source:
APPLIED PHYSICS LETTERS 95 (7): Art. No. 072901 AUG 17 2009
Abstract:
The ferroelectricity, magnetic properties, and charge-ordering modulations in the layered Lu2Fe2Fe1-xMnxO7 have been investigated for x ranging from 0 to 0.86. Experimental measurements reveal that substitution of Mn for Fe could evidently influence the low temperature magnetic transition. Moreover, ferroelectric analysis suggests that introduction of Mn ions in this layered system can efficiently suppress the conducting leakage and result in clear hysteresis loops in the polarization-electric field switching curves. The charge ordering states in Lu2Fe2Fe1-xMnxO7 characterized by two incommensurate modulations has been observed and discussed in association with the local spontaneous polarizations.

Update: 3-Sep-2009

Title:
Rare-earth free wrought-processed magnesium alloy with dispersion of quasicrystal phase
Authors:
Somekawa, H; Osawa, Y; Singh, A; Mukai, T Author Full Names: Somekawa, Hidetoshi; Osawa, Yoshiaki; Singh, Alok; Mukai, Toshiji
Source:
SCRIPTA MATERIALIA 61 (7): 705-708 OCT 2009
Abstract:
Quasicrystal and related phase particles were successfully dispersed in wrought-processed Mg-7.6 wt.% Zn-3.9 wt.% Al alloy with homogeneous and fine-grained structures. This rare-earth-free alloy showed high strength and ductility balance, which was superior to that of the well-known quasicrystal phase dispersed in Mg-Zn-RE alloys, with a weak texture and a reduction of mechanical asymmetry in yield strength. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Microstructural characterization of a laser remelted coating of Al91Fe4Cr3Ti2 quasicrystalline alloy
Authors:
Gargarella, P; Almeida, A; Vilar, R; Afonso, CRM; Rios, CT; Bolfarini, C; Botta, WJ; Kiminami, CS Author Full Names: Gargarella, P.; Almeida, A.; Vilar, R.; Afonso, C. R. M.; Rios, C. T.; Bolfarini, C.; Botta, W. J.; Kiminami, C. S.
Source:
SCRIPTA MATERIALIA 61 (7): 709-712 OCT 2009
Abstract:
A bulk sample of Al-Fe-Cr-Ti alloy with adequate composition to form quasicrystalline phases has been surface remelted, using laser processing techniques, to produce a quasicrystalline surface coating. After the laser treatment,

Update: 31-Dec-2008

Title:
Lattice dynamical calculation of negative thermal expansion in ZrV2O7 and HfV2O7
Authors:
Mittal, R; Chaplot, SL Author Full Names: Mittal, R.; Chaplot, S. L.
Source:
PHYSICAL REVIEW B 78 (17): Art. No. 174303 NOV 2008
Abstract:
We report lattice dynamics calculations of negative thermal-expansion (NTE) behavior of ZrV2O7 family, extending our previous work on the ZrW2O8 family. The two families of compounds differ in terms of the oxygen coordination around the V/W atoms leading to differences in the nature of soft phonons under compression that are responsible for the NTE. Our calculations quantitatively reproduce the negative expansion over a range of temperatures. We also discuss the relation of the soft phonons with the phase transitions observed in the ZrV2O7 family. Especially, the calculations show a soft-phonon mode at a wave vector of 0.31 < 1,1,0 >, which is in excellent agreement with the known incommensurate modulation in ZrV2O7 below 375 K.
Title:
Infrared-active excitations related to Ho3+ ligand-field splitting at the commensurate-incommensurate magnetic phase transition in HoMn2O5
Authors:
Sirenko, AA; O'Malley, SM; Ahn, KH; Park, S; Carr, GL; Cheong, SW Author Full Names: Sirenko, A. A.; O'Malley, S. M.; Ahn, K. H.; Park, S.; Carr, G. L.; Cheong, S-W.
Source:
PHYSICAL REVIEW B 78 (17): Art. No. 174405 NOV 2008
Abstract:
Linearly polarized spectra of far-infrared (IR) transmission in HoMn2O5 multiferroic single crystals have been studied in the frequency range between 8.5 and 105 cm(-1) and for temperatures between 5 and 300 K. Polarization of IR-active excitations depends on the crystallographic directions in HoMn2O5 and is sensitive to the magnetic phase transitions. We attribute some of the infrared-active excitations to electric-dipole transitions between ligand-field (LF) split states of Ho3+ ions. For light polarization along crystalline b axis, the oscillator strength of electric dipoles at low frequencies (10.5, 13, and 18 cm(-1)) changes significantly at the commensurate-incommensurate antiferromagnetic phase transition at T-3=19 K. This effect shows a strong correlation with the pronounced steps of the b-directional static dielectric function. We propose that the LF on Ho3+ connects the magnetism and dielectric properties of this compound through coupling with the Mn spin structure. We comment on the possibility for composite excitations of magnons and excited LF states.
Title:
Doping-dependent charge and spin superstructures in layered cobalt perovskites
Authors:
Sakiyama, N; Zaliznyak, A; Lee, SH; Mitsui, Y; Yoshizawa, H Author Full Names: Sakiyama, N.; Zaliznyak, A.; Lee, S. -H.; Mitsui, Y.; Yoshizawa, H.
Source:
PHYSICAL REVIEW B 78 (18): Art. No. 180406 NOV 2008
Abstract:
We have investigated cobaltite relatives of the layered perovskite cuprates and nickelates, Pr2-xCaxCoO4 (0.39 <= x <= 0.73) and La2-xSrxCoO4 (x=0.4, 0.61), using elastic neutron scattering. We have discovered doping-dependent incommensurate short-range ordering of charges and magnetic moments, which in cobaltites occur in the nonitinerant polaron phase, for 0.5 <= x <= 0.75. The charge order exists already at room temperature and shows no change on cooling. The incommensurability of its propagation vector, Q(c)=(epsilon(c), 0, l), roughly scales with the concentration of Co2+ ions, epsilon(c) similar to (1-x). Magnetic order follows at low T less than or similar to 40 K and has twice larger periodicity, indicating a dominant antiferromagnetic correlation between the nearest Co2+ spins.
Title:
Magnetic switching and phase competition in the multiferroic antiferromagnet Mn1-xFexWO4
Authors:
Ye, F; Ren, Y; Fernandez-Baca, JA; Mook, HA; Lynn, JW; Chaudhury, RP; Wang, YQ; Lorenz, B; Chu, CW Author Full Names: Ye, F.; Ren, Y.; Fernandez-Baca, J. A.; Mook, H. A.; Lynn, J. W.; Chaudhury, R. P.; Wang, Y. -Q.; Lorenz, B.; Chu, C. W.
Source:
PHYSICAL REVIEW B 78 (19): Art. No. 193101 NOV 2008
Abstract:
Elastic neutron scattering is used to study the spin correlations in the multiferroic Mn1-xFexWO4 with x=0.035, 0.05, and 0.10. The noncollinear incommensurate (ICM) magnetic structure associated with the ferroelectric (FE) phase in pure MnWO4 is suppressed at x=0.035 and completely absent at x=0.10. The ICM spin order and FE phase can be restored by applying a magnetic field along the spin easy axis. The low-T commensurate magnetic structure extends in both H/T with increasing Fe concentration. The systematic evolution of the magnetic and electric properties indicates that the noncollinear ICM spin order results from competing magnetic interactions and its stabilization can be tuned by the internal (x) or external (magnetic-field) perturbations.
Title:
Microscopic model for transitions from Mott to spin-Peierls insulator in TiOCl
Authors:
Zhang, YZ; Jeschke, HO; Valenti, R Author Full Names: Zhang, Yu-Zhong; Jeschke, Harald O.; Valenti, Roser
Source:
PHYSICAL REVIEW B 78 (20): Art. No. 205104 NOV 2008
Abstract:
On the basis of ab initio density-functional-theory calculations, we derive the underlying microscopic model Hamiltonian for TiOCl, a unique system that shows two consecutive phase transitions from a Mott insulator to a spin-Peierls insulator through a structurally incommensurate phase. We show with our model that the presence of magnetic frustration in TiOCl leads to a competition with the spin-Peierls distortion, which results in the unusual incommensurate phase. In addition, our calculations indicate that the spin-Peierls state is triggered by adiabatic phonons, which is essential for understanding the nature of the phase transition.
Title:
Chimie Douce Route to Sodium Hydroxo Titanate Nanowires with Modulated Structure and Conversion to Highly Photoactive Titanium Dioxides
Authors:
Peng, CW; Richard-Plouet, M; Ke, TY; Lee, CY; Chiu, HT; Marhic, C; Puzenat, E; Lemoigno, F; Brohan, L Author Full Names: Peng, Chih-Wei; Richard-Plouet, Mireille; Ke, Tsung-Yin; Lee, Chi-Young; Chiu, Hsin-Tien; Marhic, Christiane; Puzenat, Eric; Lemoigno, Frederic; Brohan, Luc
Source:
CHEMISTRY OF MATERIALS 20 (23): 7228-7236 DEC 9 2008
Abstract:
Sodium hydroxo titanate nanowires with NaTi2O4(OH) formulation are fabricated by chimie-douce from TiO2 powders in a hot concentrated base solution. In the present work, we investigate, in detail, the structure and morphology of the titanate, acid-exchanged materials, and phases formed during dehydration of these compounds; we then discuss the relationship between the initial titanate structure and TiO2 formation. XRD, ED, HRTEM, EDS, density measurements, and TG/MS results suggest that the titanate and acid-exchanged structures were closely related to the pseudolepidocrocite arrangement ("Cs2Ti6O12" type). The average structure of NaTi2O4(OH) nanowires consists of noncorrugated Ti2O3(OH) and NaO layers stacked along the [0 10] direction and an energy minimization was further conducted by theoretical methods. From TEM study, we demonstrated that NaTi2O4(OH) exhibits a modulated structure (q wave vector equals to 1/7 [001]*), which originates from the misfit between the NaO and Ti2O3(OH) sublattices. NaTi2O4(OH) structure has a monoclinic distortion (I2/m space group) with refined unit cell a = 0.37000(6) nm, b = 1.7816(4) nm, c = 2.2077(3) nm, beta = 92.70(1)degrees. Proton exchange followed by heat treatment convert the sodium hydroxo titanate into highly photoactive TiO2 nanowires. The activity is attributed to the presence of preferentially exposed (001) surface plane which is explained by the topotactic phase transformation of TiO2(B) into anatase.
Title:
Activation of magnetic shape memory effect in Ni-Mn-Ga alloys by mechanical and magnetic treatment
Authors:
Straka, L; Heczko, O; Hanninen, H Author Full Names: Straka, Ladislav; Heczko, Oleg; Haenninen, Hannu
Source:
ACTA MATERIALIA 56 (19): 5492-5499 NOV 2008
Abstract:
Mechanical and magnetic training decreased considerably the twinning stress of five-layered modulated, approximately tetragonal martensite (5M) oh Ni-Mn-Ga and Ni-Mn-Ga doped with Fe, and of seven-layered modulated, approximately orthorhombic Ni-Mn-Ga martensite (7M). Repeated compressions along two perpendicular directions of single crystal specimens of 5M and 7M reduced the twinning stress approximately threefold. Further reduction of twinning stress of 7M was achieved by the rotation of the specimen in I T magnetic field several times. The training resulted in the appearance of the magnetic shape memory effect or giant magnetic-field-induced strain in agreement with a simple energy-based model of the effect. The origin of the decrease in twinning stress is discussed. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 19-Dec-2008

Title:
High-temperature heat capacity of the Al63Cu25Fe12 quasicrystal
Authors:
Prekul, AF; Kazantsev, VA; Shchegolikhina, NI; Gulyaeva, RI; Edagawa, K Author Full Names: Prekul, A. F.; Kazantsev, V. A.; Shchegolikhina, N. I.; Gulyaeva, R. I.; Edagawa, K.
Source:
PHYSICS OF THE SOLID STATE 50 (11): 2013-2015 NOV 2008
Abstract:
The mechanisms of energy absorption by metallic alloys with long-range aperiodic lattice order and electronic properties of marginal metals are studied. The heat capacity and linear expansion coefficient of the Al63Cu25Fe12 icosahedral phase in the temperature range 300-1000 K are measured for the first time. Disagreement between the measured heat capacity and predictions made from the Debye model is found and analyzed. It is shown that the excess heat capacity observed at the temperatures of the experiment is fitted by Einstein's function in the approximation T
Title:
Longitudinal Spin Density Wave Order in a Quasi-1D Ising-like Quantum Antiferromagnet
Authors:
Kimura, S; Matsuda, M; Masuda, T; Hondo, S; Kaneko, K; Metoki, N; Hagiwara, M; Takeuchi, T; Okunishi, K; He, Z; Kindo, K; Taniyama, T; Itoh, M Author Full Names: Kimura, S.; Matsuda, M.; Masuda, T.; Hondo, S.; Kaneko, K.; Metoki, N.; Hagiwara, M.; Takeuchi, T.; Okunishi, K.; He, Z.; Kindo, K.; Taniyama, T.; Itoh, M.
Source:
PHYSICAL REVIEW LETTERS 101 (20): Art. No. 207201 NOV 14 2008
Abstract:
>From neutron diffraction measurements on a quasi-1D Ising-like Co2+ spin compound BaCo2V2O8, we observed an appearance of a novel type of incommensurate ordering in magnetic fields. This ordering is essentially different from the Neel-type ordering, which is expected for the classical system, and the peculiar spin structure is caused by quantum fluctuation inherent in the quantum spin chain. A Tomonaga-Luttinger liquid nature characteristic of the gapless quantum 1D system is responsible for the realization of the incommensurate ordering.
Title:
Charge Order in LuFe2O4: Antiferroelectric Ground State and Coupling to Magnetism
Authors:
Angst, M; Hermann, RP; Christianson, AD; Lumsden, MD; Lee, C; Whangbo, MH; Kim, JW; Ryan, PJ; Nagler, SE; Tian, W; Jin, R; Sales, BC; Mandrus, D Author Full Names: Angst, M.; Hermann, R. P.; Christianson, A. D.; Lumsden, M. D.; Lee, C.; Whangbo, M. -H.; Kim, J. -W.; Ryan, P. J.; Nagler, S. E.; Tian, W.; Jin, R.; Sales, B. C.; Mandrus, D.
Source:
PHYSICAL REVIEW LETTERS 101 (22): Art. No. 227601 NOV 28 2008
Abstract:
X- ray scattering by multiferroic LuFe2O4 is reported. Below 320 K, superstructure reflections indicate an incommensurate charge order with propagation close to (1/3 1/3 3/2). The corresponding charge configuration, also found by electronic structure calculations as most stable, contains polar Fe= O double layers with antiferroelectric stacking. Diffuse scattering at 360 K, with (1/3 1/3 0) propagation, indicates ferroelectric short- range correlations between neighboring double layers. The temperature dependence of the incommensuration indicates that charge order and magnetism are coupled.

Update: 12-Dec-2008

Title:
Influence of Rolling on the Precipitation of Icosahedral Quasicrystalline Phase in Zr-Al-Ni-Cu-Ag Amorphous Alloy
Authors:
Dang, SE; Wang, XH; Lian, PX; Hu, Y; Yan, ZJ; Liang, W; Zhang, GQ Author Full Names: Dang Shu'e; Wang Xianghui; Lian Peixia; Hu Yong; Yan Zhijie; Liang Wei; Zhang Guoqing
Source:
RARE METAL MATERIALS AND ENGINEERING 37 (10): 1800-1803 OCT 2008
Abstract:
Influence of rolling on the precipitation of icosahedral quasicrystalline phase (I-phase) in Zr65Al7.5Ni10Cu12.5Ag5 amorphous alloy is investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results show that more I-phase precipitate in the rolled alloys than that in the as-cast one, and that the amount becomes the maximum when the deformation degree epsilon reaches 70 %. Furthermore, the thermal stability of the I-phase increases with the deformation degree increasing. The thermal stability of I-phase shows the maximum at epsilon=70 %, but subsequently decreases. It is attributed to the change of atomic configuration in the alloy during plastic deformation.
Title:
Magnetic Dispersion of the Diagonal Incommensurate Phase in Lightly Doped La2-xSrxCuO4
Authors:
Matsuda, M; Fujita, M; Wakimoto, S; Fernandez-Baca, JA; Tranquada, JM; Yamada, K Author Full Names: Matsuda, M.; Fujita, M.; Wakimoto, S.; Fernandez-Baca, J. A.; Tranquada, J. M.; Yamada, K.
Source:
PHYSICAL REVIEW LETTERS 101 (19): Art. No. 197001 NOV 7 2008
Abstract:
We present inelastic neutron scattering experiments on a single-domain crystal of lightly doped La1.96Sr0.04CuO4. We find that the magnetic excitation spectrum in this insulating phase with a diagonal incommensurate spin modulation is remarkably similar to that in the superconducting regime, where the spin modulation is bond parallel. In particular, we find that the dispersion slope at low energy is essentially independent of doping and temperature over a significant range. The energy at which the excitations cross the commensurate antiferromagnetic wave vector increases roughly linearly with doping through the underdoped regime.
Title:
Effect of the electric polarization on the modulation wave vector of the antiferromagnetic structure of TbMnO3
Authors:
Chupis, IE; Ushakova, IV Author Full Names: Chupis, I. E.; Ushakova, I. V.
Source:
LOW TEMPERATURE PHYSICS 34 (11): 898-900 NOV 2008
Abstract:
The effect of electric polarization on the temperature and field dependences of the modulation vector k of the antiferromagnetic structure in terbium manganite is analyzed. It is shown that in contrast to anharmonicity the electric polarization increases k, which could be why a nonmonotonic temperature dependence of the modulation vector is observed in TbMnO3.
Title:
Nuclear Magnetism in Two-Dimensional Solid Helium Three on Graphite
Authors:
Fukuyama, H Author Full Names: Fukuyama, Hiroshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (11): Art. No. 111013 NOV 2008
Abstract:
Recent studies of nuclear magnetism of monolayer helium three (He-3) adsorbed on graphite are reviewed. This system provides us a fascinating testing ground for physics of highly frustrated quantum spins of two dimensions (2D) such as spin liquids. Particular emphasis is devoted to the gapless spin liquid state observed in the low-density commensurate phase (4/7 phase) in the second layer. Existing experiments on heat capacity in zero magnetic field and magnetization in low fields of this phase show unambiguously the gapless excitations down to three orders of magnitude lower temperatures than the relevant exchange interactions (approximate to 1 mK). This is a new class of spin liquid, and recently electronic counterparts are found in quasi-1D and -2D conductors. On the other hand, measured magnetic properties of the incommensurate phase at much higher densities can be described as a nearly ideal 2D S = 1/2 ferromagnet on a triangular lattice. We propose the existence of a new ferromagnetic commensurate phase at a density in between the 4/7 and incommensurate phases based on new heat capacity data. None of these phases show signatures of finite temperature phase transitions being consistent with the Mermin-Wagner theorem. The exchange interactions among He-3 nuclear spins originate from atom-atom tunnel exchanges due to the large zero-point motions. Because of the steric hindrance, higher order exchanges like three-, four-, five-, and six-spin ring exchanges are expected to compete each other in similar strengths (MSE model). The applicability of the MSE model to the experimental magnetic properties of this system including its density variation is discussed. It is satisfactory except the fact that the model does not reproduce the gapless nature of the 4/7 phase, which recently Stimulates different theoretical approaches such Lis the Hubbard model.
Title:
Symmetry determination following structure solution in P1
Authors:
Palatinus, L; van der Lee, A Author Full Names: Palatinus, L.; van der Lee, A.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 975-984 Part 6 DEC 2008
Abstract:
A new method for space-group determination is described. It is based on a symmetry analysis of the structure-factor phases resulting from a structure solution in space group P1. The output of the symmetry analysis is a list of all symmetry operations compatible with the lattice. Each symmetry operation is assigned a symmetry agreement factor that is used to select the symmetry operations that are the elements of the space group of the structure. On the basis of the list of the selected operations the complete space group of the structure is constructed. The method is independent of the number of dimensions, and can also be used in solution of aperiodic structures. A number of cases are described where this method is particularly advantageous compared with the traditional symmetry analysis. (C) 2008 International Union of Crystallography Printed in Singapore - all rights reserved
Title:
>From space to superspace and back: Superspace Group Finder
Authors:
Orlov, I; Palatinus, L; Chapuis, G Author Full Names: Orlov, Ivan; Palatinus, Lukas; Chapuis, Gervais
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 1182-1186 Part 6 DEC 2008
Abstract:
The symmetry of a commensurately modulated crystal structure can be described in two different ways: in terms of a conventional three-dimensional space group or using the superspace concept in (3 + d) dimensions. The three-dimensional space group is obtained as a real-space section of the (3 + d) superspace group. A complete network was constructed linking (3 + 1) superspace groups and the corresponding three-dimensional space groups derived from rational sections. A database has been established and is available at http:// superspace.epfl.ch/finder/. It is particularly useful for finding common superspace groups for various series of modular ('composition-flexible') structures and phase transitions. The use of the database is illustrated with examples from various fields of crystal chemistry.
Title:
Tetrahedral Chain Order in the Sr2Fe2O5 Brownmillerite
Authors:
D'Hondt, H; Abakumov, AM; Hadermann, J; Kalyuzhnaya, AS; Rozova, MG; Antipov, EV; Van Tendeloo, G Author Full Names: D'Hondt, Hans; Abakumov, Artem M.; Hadermann, Joke; Kalyuzhnaya, Anna S.; Rozova, Marina G.; Antipov, Evgeny V.; Van Tendeloo, Gustaaf
Source:
CHEMISTRY OF MATERIALS 20 (22): 7188-7194 NOV 25 2008
Abstract:
The crystal structure of the Sr2Fe2O5 browninillerite has been investigated using electron diffraction and high resolution electron microscopy. The Sr2Fe2O5 structure demonstrates two-dimensional order: the tetrahedral chains with two mirror-related configurations (L and k) are arranged within the tetrahedral layers according to the -L-R-L-R- sequence, and the layers themselves are displaced with respect to each other over 1/2[111] or 1/2[11 (1) over bar] vectors of the brownmillerite unit cell, resulting in different ordered stacking variants. A unified superspace model is constructed for ordered stacking sequences in brownmillerites based on the averacge brownmillerite structure with a = 5.5298(4)angstrom, b = 15.5875(12)angstrom, c = 5.6687(4)angstrom, and (3 + 1)-dimensional superspace group 12/m(0 beta gamma)0s, q = beta b* + gamma c*, 0 <= beta <= 1/2, 0 <= gamma <= 1.
Title:
Crystal structure of a synthetic tin-selenium representative of the cylindrite structure type
Authors:
Makovicky, E; Petricek, V; Dusek, M; Topa, D Author Full Names: Makovicky, E.; Petricek, V.; Dusek, M.; Topa, D.
Source:
AMERICAN MINERALOGIST 93 (11-12): 1787-1798 NOV-DEC 2008
Abstract:
The synthetic tin-selenium member of the cylindrite structural family, with the empirical formula Sn31.51Sb6.23Fe3.12S59.(12) based on electron-microprobe data, has a triclinic crystal structure composed of two alternating layer types, both with a pronounced one-dimensional modulation, and with a non-commensurate layer match in two dimensions. The pseudotetragonal (Q) layer is a MeSe layer two-atomic planes thick with lattice parameters a = 5.969(2) angstrom, b = 6.004(1) angstrom, and the layer-stacking vector c = 12.238(1) angstrom, alpha = 87.98(4)degrees, beta = 83.14(3)degrees, and gamma = 90.01(4)degrees. The pseudohexagonal (H) layer is a single-octahedral MeSe2 layer with a = 3.831(1) angstrom, b = 6.580(3) angstrom, c = 12.151(5) angstrom, alpha = 87.79(4)degrees, beta = 90.59(3)degrees, and gamma = 89.99(3)degrees; the a and b vectors of the two subsystems are parallel, the c vectors diverge. The transversal wave-like modulation has the wave-normal parallel to b, so that the modulation vector q is 0.0001(3) a* + 0.1921(4) b* - 0.0119(3) c* in terms of the pseudohexagonal subsystem. Superspace structure refinement in the superspace group X (1) over bar where X stands for non-primitive centering vectors (1/2,1/2,0,0,0), (0,0,0,0,1/2), (1/2,1/2,0,0,1/2) in five-dimensional superspace, and based on 2128 observed reflections, resulted in R-1 = 0.038 for all reflections. Composition of the H layer has been modeled as Sn2404+Fe542+Se588, that of the Q layer as Sn3062+Sb1083+Se414. The cation-anion distances in Q layer vary between 2.63 and 3.30 angstrom, indicating that the cations present are primarily Sn2+ (and Sb3+), whereas distances in the H layer lie between 2.665 and 2.721 angstrom and correspond to Sn4+ with admixture of Fe2+. The shortest cation-anion distance across the interlayer space is 3.24 angstrom. Relations between layer match and the modulation vector, divergence of layer stackings of the two components, and reasons for the modulation and for the pronounced disorder of the Q component, as well as the differences and similarities with levyclaudite, franckeite, and synthetic layer-misfit compounds are discussed in detail. In its structural principles, although not in numerical values, the Sn-Se cylindrite corresponds fully to the natural Pb-Sn-S cylindrite previously described.
Title:
Original disorder-order transition related to electronic and magnetic properties in the thermoelectric misfit phase [Ca2CoO3][CoO2](1.62)
Authors:
Muguerra, H; Grebille, D Author Full Names: Muguerra, Herve; Grebille, Dominique
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 676-683 Part 6 DEC 2008
Abstract:
A structural phase transition is shown around 400 K for the thermoelectric lamellar misfit cobalt oxide [Ca2CoO3][CoO2](1.62). This transition is related to a rearrangement of the central [CoO] layer of the [Ca2CoO3] slab of this structure, characterized by a commensurate intrinsic modulation q(2) = 2/3a* -1/3c*. The partial residual disorder related to split Co and O atomic sites along the misfit b direction disappears and one can describe this layer with its triple chains as a modulated configuration with a regular and not distorted periodicity along b. This phase transition is associated with small changes observed in the transport and magnetic properties as a function of temperature.
Title:
Modular crystals as modulated structures: the case of the lillianite homologous series
Authors:
Elcoro, L; Perez-Mato, JM; Friese, K; Petricek, V; Balic-Zunic, T; Olsen, LA Author Full Names: Elcoro, Luis; Perez-Mato, J. M.; Friese, Karen; Petricek, Vaclav; Balic-Zunic, Tonci; Olsen, Lars Arnskov
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 684-701 Part 6 DEC 2008
Abstract:
The use of the superspace formalism is extended to the description and refinement of the homologous series of modular structures with two symmetry-related modules with different orientations. The lillianite homologous series has been taken as a study case. Starting from a commensurate modulated composite description with two basic subsystems corresponding to the two different modules, it is shown how a more efficient description can be achieved using so-called zigzag modulation functions. These linear zigzag modulations, newly implemented in the program JANA2006, have very large fixed amplitudes and introduce in the starting model the two orientations of the underlying module sublattices. We show that a composite approach with this type of function, which treats the cations and anions as two separate subsystems forming a misfit compound, is the most appropriate and robust method for the refinements.

Update: 5-Dec-2008

Title:
Structural State of Surface Layers of Aluminum after Laser Alloying Using a Mixture of Copper and Iron Powders
Authors:
Girzhon, VV; Smolyakov, AV; Tantsyura, IV Author Full Names: Girzhon, V. V.; Smolyakov, A. V.; Tantsyura, I. V.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 106 (4): 384-388 OCT 2008
Abstract:
X-ray diffraction, metallographic, and electron-microscopic methods were used to study the regularities of the structure formation in the surface layers of aluminum upon pulse laser alloying using copper and iron powders taken in an atomic ratio of two to one. It is shown that, in the zone of laser alloying, a quasicrystalline phase can form, which leads to a considerable increase in microhardness. The effect of the thickness of the alloying layer on the structural and phase state of the laser-affected zone is analyzed.
Title:
Phase and Structural Transformations in the Alloy on the Basis of the Orthorhombic Titanium Aluminide
Authors:
Popov, AA; Illarionov, AG; Grib, SV; Demakov, SL; Karabanalov, MS; Elkina, OA Author Full Names: Popov, A. A.; Illarionov, A. G.; Grib, S. V.; Demakov, S. L.; Karabanalov, M. S.; Elkina, O. A.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 106 (4): 399-410 OCT 2008
Abstract:
Phase and structural transformations in the Ti-24.3 Al-24.8 Nb-1.0 Zr-1.4 V-0.6 Mo-0.3 Si (at %) alloy that take place during heating in the temperature range of 700-1050 degrees C have been investigated. The temperature ranges of existence of the O + beta, O + beta + alpha(2), beta + alpha(2), and beta phase fields have been established. A scheme of the relationships between the volume fractions of the O, beta, and alpha(2) phases depending on the temperature of heating of the alloy have been investigated. The formation of an ordered incommensurate omega (V (omega)) phase has been revealed in the alloy during quenching from 900 degrees C. The existence of a correlation between the hardness properties and changes in the phase composition and morphology of particles precipitating in the alloy has been shown.
Title:
Domain fluctuations near the field-induced incommensurate-commensurate phase transition of TbMnO3
Authors:
Barath, H; Kim, M; Cooper, SL; Abbamonte, P; Fradkin, E; Mahns, I; Rubhausen, M; Aliouane, N; Argyriou, DN Author Full Names: Barath, H.; Kim, M.; Cooper, S. L.; Abbamonte, P.; Fradkin, E.; Mahns, I.; Ruebhausen, M.; Aliouane, N.; Argyriou, D. N.
Source:
PHYSICAL REVIEW B 78 (13): Art. No. 134407 OCT 2008
Abstract:
We present temperature- and field-dependent inelastic light-scattering studies of multiferroic TbMnO3. By carefully examining the evolution of magneto-elastic modes in various phases of TbMnO3, our study reveals several features of the field-induced incommensurate-commensurate (IC-C) transition in TbMnO3. We find that, for fields applied along the b axis, there is a coexistence of distinct structural phases in the intermediate field regime (H=4-7 T) around the IC-C-phase transition. We present evidence for the existence of dynamical fluctuations of the C phase for fields lower than the critical field for H along the b axis, H < H-c(b). Furthermore, we present evidence for strong spin-lattice coupling effects in TbMnO3 in the form of zone-boundary phonon modes that strongly couple to the spins by modulating the exchange interaction in this material.
Title:
Raman scattering from the spin-gap mode in the Ni-doped spin-Peierls compound CuGeO3
Authors:
Sekine, T; Kaneko, T; Kuroe, H; Masuda, T Author Full Names: Sekine, Tomoyuki; Kaneko, Tomomi; Kuroe, Haruhiko; Masuda, Takatsugu
Source:
PHYSICAL REVIEW B 78 (13): Art. No. 134409 OCT 2008
Abstract:
By means of Raman scattering we have studied the spin-Peierls (SP) transition in Ni-doped CuGeO3 crystals. The folded-phonon peak extremely broadens and the two-magnetic-excitation mode disappears when the Ni concentration is above about 2.0%, indicating that the SP phase collapses. The spin-gap mode is activated in lightly Ni-doped samples. This peak neither splits nor shifts under magnetic fields in the SP phase, but its frequency increases in the incommensurate phase. The activation of the spin-gap mode is interpreted in terms of a mixing between the spin-singlet ground state and the S-z=0 triplet excited one by staggered fields around the doped impurities. Meanwhile, the two-magnetic-excitation mode gradually diminishes in intensity with increasing magnetic field in the incommensurate phase.
Title:
Fermi-surface-induced lattice modulation and charge-density wave in optimally doped YBa2Cu3O7-x
Authors:
Liu, X; Islam, Z; Sinha, SK; Moss, SC; McQueeney, RJ; Lang, JC; Welp, U Author Full Names: Liu, X.; Islam, Z.; Sinha, S. K.; Moss, S. C.; McQueeney, R. J.; Lang, J. C.; Welp, U.
Source:
PHYSICAL REVIEW B 78 (13): Art. No. 134526 OCT 2008
Abstract:
We have observed a Fermi-surface (FS) induced lattice modulation in a YBa2Cu3O7-x superconductor with a wave vector along CuO chains; i.e., q(1)=(0,delta,0). The value of delta similar to 0.21 is twice the Fermi wave vector (2k(F)) along b(*) connecting nearly nested FS "ridges." The q(1) modulation exists only within O-vacancy-ordered islands [characterized by q(0)=(1/4,0,0)] and persists well above and below T-c. Our results are consistent with the presence of a FS-induced charge-density wave.
Title:
Competing order, Fermi surface reconstruction, and quantum oscillations in underdoped high-temperature superconductors
Authors:
Dimov, I; Goswami, P; Jia, X; Chakravarty, S Author Full Names: Dimov, Ivailo; Goswami, Pallab; Jia, Xun; Chakravarty, Sudip
Source:
PHYSICAL REVIEW B 78 (13): Art. No. 134529 OCT 2008
Abstract:
We consider incommensurate order parameters for electrons on a square lattice which reduce to d-density wave order when the ordering wave vector Q is close to Q(0)=(pi/a,pi/a), a being the lattice spacing and describe the associated charge and current distributions within a single-harmonic approximation that conserves current to lowest order. Such incommensurate orders can arise at the mean-field level in extended Hubbard models, but the main goal here is to explore thoroughly the consequences within a Hartree-Fock approximation. We find that Fermi surface reconstruction in the underdoped regime can correctly capture the phenomenology of the recent quantum oscillation experiments that suggest incommensurate order, in particular the de Haas-van Alphen oscillations of the magnetization in high fields and very low temperatures in presumably the mixed state of these superconductors. For 10% hole doping in YBa2Cu3O6+delta, we find in addition to the main frequency around 530 T arising from the electron pocket and a hole frequency at around 1650 T, a new low frequency from a smaller hole pocket at 250 T for which there are some indications that require further investigations. The oscillation corresponding to the electron pocket will be further split due to bilayer coupling, but the splitting is sufficiently small to require more refined measurements. The truly incommensurate d-density wave breaks both time reversal and inversion, but the product of these two symmetry operations is preserved. The resulting Fermi surface splits into spin-up and spin-down sectors that are inversion conjugates. Each of the spin sectors results in a band structure that violates reflection symmetry, which can be determined in spin and angle-resolved photoemission spectroscopies. For those experiments such as the current photoemission experiments or the quantum oscillation measurements that cannot resolve the spin components, the bands will appear to be symmetric because of the equal mixture of the two spin sectors. There is some similarity of our results with the spiral spin-density wave order which, as pointed out by Overhauser, also breaks time reversal and inversion. Calculations corresponding to higher order commensuration produce results similar to antiphase spin stripes but appear to us to be an unlikely explanation of the experiments. The analysis of the Gorkov equation in the mixed state shows that the oscillation frequencies are unshifted from the putative normal state and the additional Dingle factor arising from the presence of the mixed state can provide a subtle distinction between the spiral spin-density wave and the d-density wave, although this is very difficult to establish precisely.
Title:
Static magnetic order in the triangular lattice of LixNiO2 (x <= 1): Muon-spin spectroscopy measurements
Authors:
Sugiyama, J; Mukai, K; Ikedo, Y; Russo, PL; Nozaki, H; Andreica, D; Amato, A; Ariyoshi, K; Ohzuku, T Author Full Names: Sugiyama, Jun; Mukai, Kazuhiko; Ikedo, Yutaka; Russo, Peter L.; Nozaki, Hiroshi; Andreica, Daniel; Amato, Alex; Ariyoshi, Kingo; Ohzuku, Tsutomu
Source:
PHYSICAL REVIEW B 78 (14): Art. No. 144412 OCT 2008
Abstract:
In spite of numerous experimental and theoretical reports on LiNiO2, no consistent picture has emerged of the nature of its ground state. We have investigated the LixNiO2 system (0.1 <= x <= 1) by means of muon-spin spectroscopy and susceptibility to gain further insight from the effects of varying the magnetic ion concentration. Static magnetic order, most likely to be incommensurate to the spatial lattice period, was found for x >= 0.6 at low temperatures (T), while disordered magnetism due to localized Ni moments appears for x=1/2-1/4 and, finally, Li0.1NiO2 exhibits almost fully nonmagnetic behavior down to the lowest T measured. The ground state of LiNiO2 is inferred to be a "static but short-range" A-type antiferromagnetic ordered system, in which the Ni3+ moments align ferromagnetically along the c axis in the NiO2 plane with an incommensurate modulation probably due to canting of the Ni3+ moments, but align antiferromagnetically between adjacent NiO2 planes.
Title:
Theory of the ordered phase in A-site antiferromagnetic spinels
Authors:
Lee, SB; Balents, L Author Full Names: Lee, SungBin; Balents, Leon
Source:
PHYSICAL REVIEW B 78 (14): Art. No. 144417 OCT 2008
Abstract:
Insulating spinel materials, with the chemical formula AB(2)X(4), behave as diamond lattice antiferromagnets when only the A-site atom is magnetic. Many exhibit classic signatures of frustration, induced not geometrically but by competing first- and second-neighbor exchange interactions. In this paper, we further develop a theory [D. Bergman , Nat. Phys. 3, 487 (2007)] of the magnetism of these materials, focusing on the physics observable within the ordered state. We derive a phenomenological Landau theory that predicts the orientation of the spins within incommensurate spiral ordered states. It also describes how the spins reorient in a magnetic field and how they may undergo a low-temperature "lock-in" transition to a commensurate state. We discuss microscopic mechanisms for these magnetic-anisotropy effects. The reduction in the ordered moment by quantum fluctuations is shown to be enhanced due to frustration. Our results are compared to experiments on MnSc2S4, the best characterized of such A-site spinels, and more general implications are discussed. One prediction is that magnetically induced ferroelectricity is generic in these materials, and a detailed description of the relation of the electric polarization to the magnetism is given.
Title:
Direct measurement of charge transfer in thermoelectric Ca3Co4O9
Authors:
Yang, G; Ramasse, Q; Klie, RF Author Full Names: Yang, G.; Ramasse, Q.; Klie, R. F.
Source:
PHYSICAL REVIEW B 78 (15): Art. No. 153109 OCT 2008
Abstract:
The misfit-layered cobalt oxide Ca3Co4O9 exhibits outstanding physical properties including high thermoelectric power, low thermal conductivity, low resistivity, and high thermal stability. We utilize atomic-resolution Z-contrast imaging in conjunction with electron energy-loss spectroscopy (EELS) in an aberration-corrected scanning transmission electron microscope (STEM) to characterize the local atomic and electronic structure of Ca3Co4O9. We will show that the position of the O atoms in the CoO2 layers can be directly imaged, and that the CoO columns in the rocksalt layer exhibit a strong modulation in the (010) direction. Further, we measure the local Co valence and find significant hole transfer from the rocksalt CoO to the hexagonal CoO2 layers. Our results are confirmed by self-consistent multiple-scattering calculations and we conclude that this hole transfer increases the mobile hole concentration and breaks the electron-hole symmetry in the CoO2 layers, thereby enabling the high thermoelectric power in the strongly correlated CoO2 subsystem.
Title:
Growth of Bi thin films on quasicrystal surfaces
Authors:
Sharma, HR; Fournee, V; Shimoda, M; Ross, AR; Lograsso, TA; Gille, P; Tsai, AP Author Full Names: Sharma, H. R.; Fournee, V.; Shimoda, M.; Ross, A. R.; Lograsso, T. A.; Gille, P.; Tsai, A. P.
Source:
PHYSICAL REVIEW B 78 (15): Art. No. 155416 OCT 2008
Abstract:
We present a comprehensive study of Bi thin-film growth on quasicrystal surfaces. The substrates used for the growth are the fivefold surface of icosahedral (i)-Al-Cu-Fe and i-Al-Pd-Mn and the tenfold surface of decagonal (d)-Al-Ni-Co quasicrystals. The growth is investigated at 300 and 525 K substrate temperatures and at different coverage (theta) ranging from submonolayer to ten monolayers. The film is characterized by scanning tunneling microscopy, reflection high-energy electron diffraction, and x-ray photoelectron spectroscopy. At 300 K, the deposited Bi yields a quasicrystalline film for theta <= 1. For 1
Title:
Effect of composition on the formability of quasicrystalline phase in mechanically alloyed Al-Cu-Fe powders
Authors:
Yin, SL; Li, CX; Blan, Q; Lu, M Author Full Names: Yin, Shilong; Li, Caixia; Blan, Qing; Lu, Min
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 496 (1-2): 362-365 NOV 25 2008
Abstract:
A systematic study has been carried out to investigate the effect of composition on the ability of mechanically alloyed Al-Cu-Fe powders to form quasicrystalline (QC)-phases. Their microstructures were measured by means of X-ray diffraction and transmission electron microscopy (TEM). The results show that the formation of Al-Cu-Fe QC-phases is sensitive to the starting ratio of the elements Al, Cu and Fe and that Al70Cu20Fe10 is the optimum composition among those studied. No single QC-phase was obtained, but a high volume fraction of the QC-phase can be obtained by a suitable choice of the milling time, annealing temperature and annealing time. The volume fraction of the QC-phase in Al70Cu20Fe10 powders milled for 2 h and annealed for 5 h at 750 degrees C is greater than 90%. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Icosahedral quasicrystal phase in Mg-Zn-Nd ternary system
Authors:
Zhang, JS; Yan, J; Liang, W; Xu, CX; Zhou, CL Author Full Names: Zhang, J. S.; Yan, J.; Liang, W.; Xu, C. X.; Zhou, C. L.
Source:
MATERIALS LETTERS 62 (30): 4489-4491 DEC 15 2008
Abstract:
Mg-Zn-Nd master alloy containing icosahedral quasicrystal phase with an interesting macro-shape has been prepared under conventional casting conditions. The microstructures and phases of Mg-Zn-Nd ternary alloy have been investigated by using SEM, EDS and TEM. The results show that the spherical phase in Mg-Zn-Nd master alloy is a simple icosahedral quasicrystal with stoichiometric composition of Mg40Zn55Nd5 and quasilattice a(R) = 0.525 nm. In this research, when the content of Nd is 1.20 at.% and atom ratio value of Mg/Zn at the range of 2.4-2.7, the as-cast solidification microstructure mainly consists of primary I-phase and Mg7Zn3 single-phase matrix. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Deuterium dynamics in the icosahedral and amorphous phases of the Ti40Zr40Ni20 hydrogen-absorbing alloy studied by H-2 NMR
Authors:
Gradisek, A; Kocjan, A; McGuiness, PJ; Apih, T; Kim, HJ; Dolinsek, J Author Full Names: Gradisek, A.; Kocjan, A.; McGuiness, P. J.; Apih, T.; Kim, Hae Jin; Dolinsek, J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (47): Art. No. 475209 NOV 26 2008
Abstract:
The Ti40Zr40Ni20 hydrogen-absorbing alloy was prepared in the icosahedral and amorphous phases by controlling the rotation speed of the melt-spinning method of sample preparation, and the deuterium dynamics was investigated by H-2 NMR dynamic lineshape and spin-lattice relaxation. The results were analysed by the lineshape and relaxation models that assume deuterium thermally activated hopping within a manifold of different chemical environments. The observed 8% larger activation energy for the deuterium hopping over the interstitial sites and the 10% larger static spectrum width of the amorphous phase, as compared to the icosahedral phase, can be accounted for by the larger deuterium content of the investigated amorphous sample. From the deuterium dynamics point of view, the icosahedral phase is not special with respect to the amorphous modification of the same material.
Title:
Noncentrosymmetric commensurate magnetic ordering of multiferroic ErMn2O5
Authors:
Roessli, B; Fischer, P; Brown, PJ; Janoschek, M; Sheptyakov, D; Gvasaliya, SN; Ouladdiaf, B; Zaharko, O; Golovenchits, E; Sanina, V Author Full Names: Roessli, B.; Fischer, P.; Brown, P. J.; Janoschek, M.; Sheptyakov, D.; Gvasaliya, S. N.; Ouladdiaf, B.; Zaharko, O.; Golovenchits, Eu; Sanina, V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (48): Art. No. 485216 DEC 3 2008
Abstract:
The noncentrosymmetric magnetic structure of ErMn2O5 has been shown to be very similar to that of HoMn2O5 (Vecchini et al 2008 Phys. Rev. B 77 134434). The magnetic modulation at 25 K has propagation vector (k) over right arrow = (1/2, 0, 1/4) and the symmetry imposes very few constraints on the magnetic configurations allowed. Only by combining the results of bulk magnetization measurements, powder and single crystal neutron diffraction and spherical neutron polarization analysis was it possible to distinguish clearly between different models. The susceptibility measurements show that the erbium magnetic moments are aligned parallel to the c-axis indicating strong single ion anisotropy. Spherical neutron polarimetry demonstrates the presence of two unequally populated chirality domains in ErMn2O5 single crystals. X-ray diffraction measurements on an ErMn2O5 powder using synchrotron radiation show that the buckling angles of the Mn-O-Mn bond change below the transition to the ferroelectric phase.
Title:
Possible mechanisms of formation of long-periodic magnetic structure in high-symmetry crystals
Authors:
Zavorotnev, YD; Medvedyeva, LI Author Full Names: Zavorotnev, Yu. D.; Medvedyeva, L. I.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 321 (3): 231-233 FEB 2009
Abstract:
On the example of a crystal with point symmetry group and based on the method of integral rational basis of invariants, linear and nonlinear invariants of first spatial derivatives with respect to the order parameters of the exchange origin have been calculated. It is shown the competition of what kind of parameters can initiate modulated magnetic structures in crystals of this symmetry. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Nanoindentation studies on single crystals of Zn-Mg-Er and Zn-Mg-Ho icosahedral phases
Authors:
Mukhopadhyay, NK; Belger, A; Paufler, P; Uhrig, E; Bruhne, S; Assmus, W Author Full Names: Mukhopadhyay, N. K.; Belger, A.; Paufler, P.; Uhrig, E.; Bruehne, S.; Assmus, W.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 466 (1-2): 160-164 OCT 20 2008
Abstract:
Single crystals of Zn-Mg-Er and Zn-Mg-Ho icosahedral phases were grown from the melt using the liquid encapsulated top seeded solution growth technique. The fivefold planes of these as-grown single crystals were polished and used for the present nanoindentation studies using Hysitron triboscope attached to an atomic force microscope with a maximum load up to 16 mN. The reduced Young's modulus (E-r) and nanohardness (H) were found to be 135 +/- 10 GPa and 8.5 +/- 0.2 GPa for the F-type Zn65Mg25Er10 quasicrystal whereas for the P-type Zn74Mg15Ho11 quasicrystal (QC) these were 135 +/- 10 GPa and 7.8 +/- 0.2 GPa, respectively. Using the appropriate constants, the average E in both the quasicrystalline alloys was estimated as 140 10 GPa. The elastic and plastic deformation characteristics in load-displacement, F-h, curve appears to be identical in both the QC phases. The peculiarity in the load-displacement curves, in terms of pop-ins were observed frequently. AFM images showed the steps in the pile-up material which can be identified as shear bands and correlated with the pop-ins. The first pop-in was observed in the load range of 70 mu N in case Zn-Mg-Ho and 84 mu N in case of Zn-Mg-Er QC. The contact pressure, p, turns out to be 13 GPa for Zn-Mg-Ho and 18 GPa for Zn-Mg-Er QC. The maximum shear stress under the indent, TT,,c, is found to vary from 6 to 8 GPa, which is close to the theoretical shear strength of this material (similar to E/20). The energy required for the indentation was determined from the first pop-ins and it turned out to be 0.88 eV/atom, close to the thermal energy required for deformation of quasicrystals. Thus the 'pop-ins' are attributed to the elastic-plastic transition during indentation. (c) 2007 Elsevier B. V. All rights reserved.
Title:
On the Magnetically Driven Ferroelectric Phase in GdMnO3
Authors:
Ribeiro, JL Author Full Names: Ribeiro, J. L.
Source:
FERROELECTRICS 368: 352-357 2008
Abstract:
At room temperature, GdMnO3 is a paraelectric and paramagnetic with a distorted perovskite structure of orthorhombic symmetry (space group Pnma). On cooling, it undergoes a phase transition sequence to a magnetic incommensurate phase ([image omitted] = (T)[image omitted]*; Tc1 = 42 K) and a A-type antiferromagnetic phase (Tc2 = 27 K). At low temperatures (T 12 K), a magnetic field applied along the a-axis destabilizes the antiferromagnetic phase and induces a first order transition to a magnetic commensurate modulated phase ([image omitted] = 1/4[image omitted]*) that is also ferroelectric ([image omitted]//[image omitted]). This work analyses this field induced phase transition from the point of view of the symmetry and Landau theory.
Title:
Crystal Structures and Phase Transitions in A-Site Deficient Perovskites Ln(1/3)TaO(3)
Authors:
Zhou, QD; Saines, PJ; Sharma, N; Ting, J; Kennedy, BJ; Zhang, ZM; Withers, RL; Wallwork, KS Author Full Names: Zhou, Qingdi; Saines, Paul J.; Sharma, Neeraj; Ting, Jimmy; Kennedy, Brendan J.; Zhang, Zhaoming; Withers, Ray L.; Wallwork, Kia S.
Source:
CHEMISTRY OF MATERIALS 20 (21): 6666-6676 NOV 11 2008
Abstract:
The synthesis and structures of the perovskites Ln(1/3)TaO(3) are described. As the size of the Ln cation is reduced, the compounds display a sequence of structure: P4/mmm/La -> Cmmm/Ce-Gd -> Pmma/Tb, Dy -> Pmc2(1)/Ho. Er. Although apparently tetragonal in P4/mmm, electron diffraction patterns of Tm1/3TaO3 reveal this has a complex incommensurate structure. Likewise Gd1/3TaO3 appears metrically tetragonal. but electron diffraction and synchrotron X-ray powder diffraction demonstrate this is actually orthorhombic. The suppression of the spontaneous orthorhombic strain in Gd1/3TaO3 is thought to be due to the proximity to the first-order Cmmm-Pmma transition. Variable temperature studies show both Tb1/3TaO3 and Dy1/3TaO3 undergo a first-order Cmmm-Pmma transition upon heating.
Title:
Applications of Mossbauer Spectroscopy to Studies of Quasicrystals
Authors:
Stadnik, ZM Author Full Names: Stadnik, Z. M.
Source:
ACTA PHYSICA POLONICA A 114 (6): 1475-1482 DEC 2008
Abstract:
A review is presented of the application of the Mossbauer spectroscopy to the study of quasicrystals. The usefulness of the Mossbauer spectroscopy to solving the atomic structure of a complex icosahedral system is illustrated. The role of the Mossbauer spectroscopy in studies of magnetism of quasicrystals is discussed. The Mossbauer spectroscopy results on phason dynamics in quasicrystals are reviewed.

Update: 27-Nov-2008

Title:
Magnetization of Polycrystalline BiFeO3 in High Magnetic Fields
Authors:
Wardecki, D; Przenioslo, R; Sosnowska, I; Skourski, Y; Loewenhaupt, M Author Full Names: Wardecki, Dariusz; Przenioslo, Radoslaw
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (10): Art. No. 103709 OCT 2008
Abstract:
The magnetization of polycrystalline ceramic BiFeO3 has been studied with pulsed magnetic fields up to 58T. We observe a magnetic transition in both, increasing and decreasing magnetic fields. The critical field of the transition decreases with temperature. It is observed at 18.1 T at 80 K and 16.1 T at 235 K for increasing fields, whereas with decreasing fields the transition is observed at about 1.5 T below these values. The observed transition is the same as that reported in BiFeO3 single crystals at 10K [Kadomtseva et al.: JETP Lett. 79 (2004) 571]. It was attributed to the destruction of the modulated magnetic ordering in BiFeO3.
Title:
Evolution of an Unconventional Superconducting State inside the Antiferromagnetic Phase of CeNiGe3 under Pressure: A Ge-73-Nuclear-Quadrupole-Resonance Study
Authors:
Harada, A; Mukuda, H; Kitaoka, Y; Thamizhavel, A; Okuda, Y; Settai, R; Onuki, Y; Itoh, KM; Haller, EE; Harima, H Author Full Names: Harada, Atsushi; Mukuda, Hidekazu
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (10): Art. No. 103710 OCT 2008
Abstract:
We report a Ge-73 nuclear-quadrupole-resonance (NQR) Study on novel evolution of unconventional superconductivity in antiferromagnetic (AFM) CeNiGe3. The measurements of the Ge-73-NQR spectrum and the nuclear spin-lattice relaxation rate (1/T-1) have revealed that the unconventional superconductivity evolves inside a commensurate AFM phase around the pressure (P) where Neel temperature T-N exhibits its maximum at 8.5 K. The superconducting transition temperature T-SC has been found to be enhanced with increasing T-N, before reaching the quantum critical point at which the AFM order collapses. Above T-SC, the AFM structure transits from an incommensurate spin-density-wave order to a commensurate AFM order at T similar to 2 K. accompanied by a longitudinal spin-density fluctuation. With regard to heavy-fermion compounds, these novel phenomena have hitherto never been reported in the P-T phase diagram.
Title:
The roles of "ammonium" and "hydrogen-bond" protons in single crystals of the superionic conductor NH4HSeO4 by H-1 NMR relaxation
Authors:
Lim, AR; Jang, SW; Chang, JH Author Full Names: Lim, Ae Ran; Jang, Seo Won
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 69 (10): 2360-2365 OCT 2008
Abstract:
The variations with temperature of the line-shape, spin-lattice relaxation time, T-1, and spin-spin relaxation time, T-2, of the H-1 nuclei in NH4HSeO4 single crystals were investigated, and with these H-1 NMR results we were able to distinguish the crystals' "ammonium" and "hydrogen-bond" protons. The line width of the signal due to the ammonium protons abruptly narrows near the temperature of the superionic phase transition, T-si, which indicates that they play an important role in this phase transition. The H-1 T-1 for NH4+ and HSeO4- in NH4HSeO4 do not change significantly near the ferroelectric phase transition of T-c1 (= 250 K) and the incommensurate phase transition of T-i (= 261 K), whereas they change near the temperature of the superionic phase transition T-s1 (= 400 K). Our results indicate that the main contribution to the low-temperature phase transition below T-s1 is that of the molecular motion of ammonium and hydrogen-bond protons, and the main contribution to the conductivity at high temperatures above T-s1 is the breaking of the O-H...O bonds and the formation of new H- bonds in HSeO4-. In addition, we compare these results with those for the NH4HSO4 and (NH4)(3)H(SO4)(2) single crystals, which have similar hydrogen-bonded structure. (C) 2008 Elsevier Ltd. All rights reserved.
Title:
A Theory of General Solutions of Plane Problems in Two-Dimensional Octagonal Quasicrystals
Authors:
Gao, Y; Zhao, BS; Xu, SP Author Full Names: Gao, Yang; Zhao, Bao-Sheng
Source:
JOURNAL OF ELASTICITY 93 (3): 263-277 DEC 2008
Abstract:
A theory of general solutions of plane problems is developed for the coupled equations in plane elasticity of two-dimensional octagonal quasicrystals. In virtue of the operator method, the general solutions of the antiplane and inplane problems are given constructively with two displacement functions. The introduced displacement functions have to satisfy higher order partial differential equations, and therefore it is difficult to obtain rigorous analytic solutions directly and is not applicable in most cases. In this case, a decomposition and superposition procedure is employed to replace the higher order displacement functions with some lower order displacement functions, and accordingly the general solutions are further simplified in terms of these functions. In consideration of different cases of characteristic roots, the general solution of the antiplane problem involves two cases, and the general solution of the inplane problem takes three cases, but all are in simple forms that are convenient to be applied. Furthermore, it is noted that the general solutions obtained here are complete in x(3)-convex domains.
Title:
Thermoelectric properties of polygrained icosahedral Al71-xGaxPd20Mn9 (x=0,2,3,4) quasicrystals
Authors:
Takagiwa, Y; Kamimura, T; Hosoi, S; Okada, JT; Kimura, K Author Full Names: Takagiwa, Y.; Kamimura, T.
Source:
JOURNAL OF APPLIED PHYSICS 104 (7): Art. No. 073721 OCT 1 2008
Abstract:
The electrical and thermal transport properties of quaternary icosahedral Al71-xGaxPd20Mn9 (x=0,2,3,4) quasicrystals, obtained by replacing Al in icosahedral Al-Pd-Mn quasicrystal with Ga, have been measured in accordance with the guiding principle of "weakly bonded rigid heavy clusters" (WBRHCs). While the electrical conductivity and Seebeck coefficient were not dramatically changed, the thermal conductivity effectively decreased with increasing Ga concentration except for the sample with x=4. Although the thermoelectric properties do not obey the WBRHCs, the dimensionless figure of merit increased by a factor of 1.4 from 0.18 for Al71Pd20Mn9 to 0.26 for Al68Ga3Pd20Mn9 quasicrystal. (c) 2008 American Institute of Physics.
Title:
Fe-57 Mossbauer Effect Study of Zn-Sc-Fe Icosahedral Quasicrystal and Its 1/1 Crystal Approximant
Authors:
Edagawa, K; Tamura, R; Yamada, T; Oda, K Author Full Names: Edagawa, Keiichi; Tamura, Ryuji
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS 47 (5): 3581-3583 Part 1 MAY 2008
Abstract:
The Zn-Sc-Fe icosahedral quasicrystal and its 1/1 crystal approximant have been studied with Fe-57 Mossbauer spectroscopy at room temperature. The spectra for the two phases exhibit substantially different features, indicating largely different local atomic environments in the two phases. This is in contrast to the results previously reported for the Al-Cu-Fe(-Si) system, in which the icosahedral phase and its crystal approximants show similar features in Mossbauer spectra, indicating similar local atomic environments. Possible Fe sites in the Zn-Sc-Fe approximant phase are discussed on the basis of the crystal structure determined previously. [DOI: 10.1143/JJAP.47.3581]
Title:
A Layered Iron-Rich 2234-Type with a Mixed Valence of Iron: The Ferrimagnetic Tl-Doped Fe-2(Sr2-epsilon Tl epsilon)Sr(3)Fe(4)O14.65
Authors:
Lepoittevin, C; Malo, S; Nguyen, N; Hebert, S; Van Tendeloo, G; Hervieu, M Author Full Names: Lepoittevin, Christophe; Malo, Sylvie
Source:
CHEMISTRY OF MATERIALS 20 (20): 6468-6476 OCT 28 2008
Abstract:
A new Tl-doped strontium ferrite Fe-2(Sr2-epsilon Tl epsilon)Sr3Fe4O14.65, with an original structure, has been synthesized and structurally characterized by powder X-ray diffraction and transmission electron microscopy. The TGA and Mossbauer studies evidence a mixed valence of iron. The structure exhibits a commensurate modulation, with a F-type subcell a approximate to b approximate to 5.4 angstrom ( approximate to a(p)root/2), c approximate to 42 angstrom with a modulation vector (q) over right arrow = alpha(a) over right arrow* with alpha = 0.4. The supercell parameters have been refined as a= 27.1101(8) angstrom, b= 5.5187(2) angstrom and c= 42.0513(9) angstrom, in the space group Fmmm. The electron diffraction and electron microscopy data of this novel ferrite show that it can be described as a Fe-Tl-2234-type structure corresponding to the intergrowth of a quadruple perovskite slice [(SrFeO2.8)(4)] with a complex rock salt related slice Fe-2(Sr2-epsilon Tl epsilon)O-3.4](infinity), built up of one double iron layer [Fe2O2.4] sandwiched between two [SrO] layers. The HRTEM images show that the oxygen atoms and vacancies are randomly distributed in the perovskite layers while the HAADF STEM images evidence the absence of Tl segregation in the matrix. Fe-2(Sr2-epsilon Tl epsilon)Sr3Fe4O14.65 exhibits a very large value of chi (1 lemu/mol) at 5 K, which remains large at 400 K; the M(H) loop presents a shape characteristic of ferrimagnetism, with a large coercive field of 0.3 T. The value of magnetization saturates at 400 K at 0.68 mu(B)/17e. At 10 K. the value of magnetization reaches a maximum of 2 mu(B)/Fe. The resistivity presents a semiconducting-like behavior, with rho similar to 800 Omega.cm at 300 K.

Update: 14-Nov-2008

Title:
On the Ferroelectric Phase Transition in Polytypes of beta-TlInS2 Crystals
Authors:
Borovoi, NA; Gololobov, YP; Gorb, AN; Isaenko, GL Author Full Names: Borovoi, N. A.; Gololobov, Yu. P.
Source:
PHYSICS OF THE SOLID STATE 50 (10): 1946-1950 OCT 2008
Abstract:
Permittivity measurements and x-ray diffraction study were performed for polytypes c and 2c of beta-TlInS2 crystals in the temperature range T = 160-250 K. Substantial differences are revealed in the temperature, sequence, and character of the structural phase transitions associated with the formation of incommensurate modulated structures and the occurrence of a ferroelectric state in these polytypes.
Title:
Quasicrystals - The Silver Jubilee PREFACE
Authors:
Lifshitz, R Author Full Names: Lifshitz, Ron
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1879-1882 2008
Title:
Structures of quasicrystals: Where are the atoms?
Authors:
Gratias, D; Quiquandon, M Author Full Names: Gratias, D.; Quiquandon, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1887-1903 2008
Abstract:
This paper is an attempt to present a chronological review of the structural concepts that have been developed to characterize quasicrystals, starting from the experimental discovery of D. Shechtman and the concomitant theoretical definition of quasicrystal as proposed by D. Levine and P. Steinhardt, up to the present research in the field. The largest part of the paper is a discussion of the specific points that make the atomic structure determination of quasicrystals an original and difficult scientific challenge. We finally discuss the soundness of our knowledge of the actual atomic structure in quasicrystals: we do have quite a solid idea of where the atoms are but we are not sure about the distribution of the chemical species.
Title:
Geometrical property of the cluster model of the Yb-Cd icosahedral quasicrystal
Authors:
Takakura, H Author Full Names: Takakura, H.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1905-1912 2008
Abstract:
The geometrical property of an atomic structure model of the Yb-Cd icosahedral quasicrystal is discussed from the higher-dimensional viewpoint. An occupation domain for the framework that specifies the arrangement of the three building units of the structure is presented based on a specific archetype occupation domain for the cluster centres. Different cluster configurations are enumerated and the numerical values of their frequencies are given.
Title:
Coordination and cluster packing in quasicrystals
Authors:
Fujita, N; Niizeki, K Author Full Names: Fujita, N.; Niizeki, K.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1913-1919 2008
Abstract:
We discuss some local and global characteristics of quasicrystalline structures. Firstly, we present an analysis of the coordination numbers in the Cd5.7Yb binary quasicrystal. A majority of the Cd and Yb atoms occupy 12- and 16-fold coordinated sites, respectively. It is argued that the coordination properties are closely related to the local stability of the quasicrystals. Secondly, a simple inflation algorithm is presented for generating an icosahedral quasilattice which has a dense packing of a given structural motif or cluster. The atomic surface of a P-type icosahedral quasilattice generated in this way has a fractal boundary.
Title:
Structure of quasicrystals described by statistical methods
Authors:
Kozakowski, B; Wolny, J; Kuczera, P Author Full Names: Kozakowski, B.; Wolny, J.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1921-1927 2008
Abstract:
The structure of quasicrystals can be described by using a statistical approach, which can be either in higher dimensions or in three-dimensional physical space only. In the multidimensional approach, complete statistical information is gathered in a so-called atomic surface. In the case of the physical approach, we use the idea of an average unit cell. These two approaches are linked by an oblique projection. For a full description of a diffraction pattern, two projections are required. Statistical methods have been used for the diffraction analysis of the model structures and the structure of real decagonal quasicrystals.
Title:
Structural vacancies in Al-Pd-Mn quasicrystal and its (1/1,2/1)-AlPdMnSi approximant crystals: Positron lifetime studies
Authors:
Takagiwa, Y; Okada, JT; Kimura, K; Kitahata, H; Matsushita, Y; Kanazawa, I Author Full Names: Takagiwa, Y.; Okada, J. T.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1929-1934 2008
Abstract:
Positron annihilation lifetimes of the stable icosahedral (i) Al-Pd-Mn quasicrystal and its (1/1, 2/1)-AlPdMnSi and 1/0-Al12Re approximant crystals were measured at ambient temperature. The observed single-lifetime of the i-Al-Pd-Mn quasicrystal is very close to that of the (1/1, 2/1)-AlPdMnSi approximant crystals, indicating that the same type of structural vacancies exists in all these specimens. On the other hand, the lifetime of 1/0-Al12Re approximant crystal, which has no structural vacancies, is significantly shorter than the above results. We discuss the relationship between the positron lifetimes and mean valence-electron density.
Title:
HAADF-STEM study of B-Mg-Ru approximant crystals
Authors:
Miyazaki, Y; Okada, JT; Abe, E; Kimura, K Author Full Names: Miyazaki, Y.; Okada, J. T.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1935-1940 2008
Abstract:
Two-dimensional structures of decagonal approximant crystals have been studied in a B-Mg-Ru system where decagonal quasicrystals have been predicted. High-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM) imaging confirms that four approximant phases, which form at high temperatures, can be described as tessellations of hexagon and boat subunits with the same atomic decorations as B11Mg5Ru13. The images also support the existence of bow-tie flip structures in the all four approximant crystals. Long periodicities in one direction up to 8.5 nm are interpreted to be caused by modulation of rows of boat tiles.
Title:
Simulations of high-resolution electron microscopy images of icosahedral quasicrystals
Authors:
Quiquandon, M; Beauchesne, JT; Gratias, D Author Full Names: Quiquandon, M.; Beauchesne, J. -T.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1941-1948 2008
Abstract:
We apply the scattering matrix formulation for calculating the images of high-resolution electron microscopy (HREM) images of quasiperiodic crystals and discuss their basic properties. The main feature in the image formation comes from the truncation effects of the q-basis, especially the perpendicular components which must be numerous enough for properly reproducing quasiperiodicity. A comparison between two types of atomic structural model is presented that illustrates the difficulties of differentiating the models from the HREM observations.
Title:
Highly-perfect decagonal quasicrystalline Al64Cu22Co14 with non-centrosymmetry
Authors:
Taniguchi, S; Abe, E Author Full Names: Taniguchi, S.; Abe, E.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1949-1958 2008
Abstract:
The structure of a decagonal quasicrystal of Al64Cu22Co14, which was a single-grain specimen (a few mm in size) grown by slow-cooling from a melt and subsequently annealed at 1073 K, was investigated using electron diffraction and scanning transmission electron microscopy (STEM). Electron diffraction patterns of the Al64Cu22Co14 revealed a large number of sharp reflections that indicate a good long-range quasiperiodic order, and convergent-beam electron diffraction (CBED) analysis identified the space group of the decagonal Al64Cu22Co14 as being non-centrosymmetric P (10) over bar m2. Atomic-resolution Z-contrast STEM imaging showed that the structure can be described based on a fivefold-symmetric decagonal cluster 2 nm across, most of which is found to be located at ideal positions in the pentagonal Penrose tiling with significantly less phason disorders. Therefore, to our knowledge, the present decagonal Al64Cu22Co14 provides one of the best quasiperiodic ordered structures among those belonging to non-centrosymmetric P (10) over bar m2. Further details of atomic configurations within the fivefold-symmetric cluster were also examined using ultrahigh-resolution Z-contrast STEM with an aberration-corrector for the objective lens. This clearly revealed both the Al and Cu/Co sites at resolution close to 1 . Atomic arrangements within the cluster are found to be fairly well described based on the fivefold-symmetry cluster that exists in the W-(AlCoNi) approximant crystal, except for the atomistic disorders localized around the cluster centres.
Title:
Stability of the decagonal quasicrystal in the Lennard-Jones-Gauss system
Authors:
Engel, M; Trebin, HR Author Full Names: Engel, M.; Trebin, H. -R.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1959-1965 2008
Abstract:
Although quasicrystals have been studied for 25 years, there are many open questions concerning their stability: What is the role of phason fluctuations? Do quasicrystals transform into periodic crystals at low temperature? If yes, by what mechanisms? We address these questions here for a simple two-dimensional model system, a monatomic decagonal quasicrystal, which is stabilized by the Lennard-Jones-Gauss potential in thermodynamic equilibrium. It is known to transform to the approximant Xi, when cooled below a critical temperature. We show that the decagonal phase is an entropically stabilized random tiling. By determining the average particle energy for a series of approximants, it is found that the approximant Xi is the one with lowest potential energy.
Title:
Ground-state configurations of decagonal and dodecagonal binary dipolar quasicrystals
Authors:
Roth, J Author Full Names: Roth, J.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1967-1976 2008
Abstract:
We search for ground states of binary decagonal dipolar quasicrystals increasing the parameter space step by step: first testing tiling types and small-scale approximants, then allowing continuous deformation of the tiles, and finally by simulated annealing through tile flips followed by local optimization. It turns out that the quasicrystals are not a true ground state but can be favoured in finite systems by the lack of costly defects. Similar studies for square-triangle binary dipolar quasicrystals show that there the energy reduces with the number of square pairs. Phase-separated crystals turn out to be more stable then quasicrystals.
Title:
Penrose matching rules from realistic potentials in a model system
Authors:
Lim, S; Mihalkovic, M; Henley, CL Author Full Names: Lim, S.; Mihalkovic, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1977-1984 2008
Abstract:
We exhibit a toy model of a binary decagonal quasicrystal of composition Al80.1Co19.9 - closely related to actual structures - in which realistic pair potentials yield a ground state which appears to perfectly implement Penrose's matching rules, for Hexagon-Boat-Star (HBS) tiles of edge 2.45 angstrom. The second minimum of the potentials is crucial for this result.
Title:
Growth of facetted microvoids in Zn-Fe-Sc quasicrystal
Authors:
Ishimasa, T; Matsunagi, J Author Full Names: Ishimasa, T.; Matsunagi, J.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1985-1993 2008
Abstract:
Microvoids, the size of which ranges from 1 to 50 mu m in diameter, have been observed on the fracture surface of a millimeter-sized single icosahedral quasicrystal of stable Tsai-type Zn-Fe-Sc. The shape of the voids consists of planes related to the icosahedral symmetry, typically a dodecahedron with additional truncations by the planes perpendicular to the 2- and 3-fold axes. During controlled cooling from the melting point, approximately 824 degrees C, and additional annealing at 650 similar to 700 degrees C, the growth of the microvoids was observed. Corresponding to the increase of the size, the number density of voids is decreased so as to conserve the total volume of the voids, i.e. the porosity. This is the first direct evidence indicating that the growth process is essentially Ostwald ripening. The origin of the growth between 600 and 800 degrees C is considered to be not the supersaturated thermal vacancies, but vacancies coming from nearby shrinking voids. The growth is well explained by a thermally activated process with activation energy approximately 3.1 eV.
Title:
Formation and stability of icosahedral phase in Al65Ga5Pd17Mn13 alloy
Authors:
Yadav, TP; Shaz, MA; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Shaz, M. A.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1995-2002 2008
Abstract:
The formation and characterization are described of a quaternary (pseudo-ternary) icosahedral quasicrystal in Al65Ga5Pd17Mn13 alloy. X-ray diffraction and transmission electron microscopy observations confirmed the formation of icosahedral, B2 type and xi' crystalline (orthorhombic structure with unit cell a = 23.5 angstrom, b = 16.6 angstrom and c = 12.4 angstrom) phases in as-cast alloy. The icosahedral phase is formed after annealing at 800 degrees C for 60 h. This is the first report of the formation of an icosahedral phase in an Al-Ga-Pd-Mn quaternary alloy by present technique. The energy dispersive X-ray analysis investigations suggest the presence of Ga (similar to 5 at.%) in the alloy. Icosahedral Al-Ga-Pd-Mn provides a new opportunity to investigate various characteristics, including surface characteristics. Attempts are made to discuss the micromechanisms for the formation of the quasicrystalline phase in Al-Ga-Pd-Mn alloys.
Title:
Mapping the aperiodic landscape, 1982-2007
Authors:
Senechal, M Author Full Names: Senechal, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2003-2016 2008
Abstract:
The discovery of quasicrystals galvanized mathematics research in long-range aperiodic order, accelerating the dissolution of the the ancient periodic/non-periodic dichotomy begun by Penrose, Ammann, de Bruijn, and Mackay. What does the aperiodic landscape look like now, 25 years later, and what frontiers are still to be mapped?
Title:
Symmetry properties of Penrose type tilings
Authors:
Cotfas, N Author Full Names: Cotfas, N.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2017-2023 2008
Abstract:
The Penrose tiling is directly related to the atomic structure of certain decagonal quasicrystals and, despite its aperiodicity, is highly symmetric. It is known that the numbers 1, -tau , (-tau )(2), (-tau )(3),..., where tau = (1 + root 5)/2, are scaling factors of the Penrose tiling. We show that the set of scaling factors is much larger, and for most of them the number of the corresponding inflation centres is infinite.
Title:
Coincidences in four dimensions
Authors:
Baake, M; Zeiner, P Author Full Names: Baake, M.; Zeiner, P.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2025-2032 2008
Abstract:
The coincidence site lattices (CSLs) of prominent four-dimensional lattices are considered. CSLs in three dimensions have been used for decades to describe grain boundaries in crystals. Quasicrystals suggest also looking at CSLs in dimensions d > 3. Here, we discuss the CSLs of the root lattice A(4) and the hypercubic lattices, which are of particular interest both from the mathematical and the crystallographic viewpoints. Quaternion algebras are used to derive their coincidence rotations and the CSLs. We make use of the fact that the CSLs can be linked to certain ideals and compute their indices, their multiplicities and encapsulate all this in generating functions in terms of Dirichlet series. In addition, we sketch how these results can be generalized for four-dimensional Z-modules by discussing the icosian ring.
Title:
Aperiodic order and pure point diffraction
Authors:
Lenz, D Author Full Names: Lenz, D.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2059-2071 2008
Abstract:
The paper gives a leisurely introduction to mathematical diffraction theory with a focus on pure point diffraction. In particular, various characterizations of pure point diffraction and common models arising from cut and project schemes are discussed. It finishes with a list of open problems.
Title:
Ordering of adsorbed species on quasicrystal surfaces
Authors:
Smerdon, JA; Wearing, LH; Parle, JK; Leung, L; Sharma, HR; Ledieu, J; McGrath, R Author Full Names: Smerdon, J. A.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2073-2082 2008
Abstract:
We present an overview of experimental studies of the structure of adsorbed atomic and molecular species on quasicrystal surfaces with a particular focus on those systems where quasiperiodic ordering of the adsorbate structure occurs. Atomic adsorption is illustrated with examples from studies of Fe and Gd adsorption on the five-fold surface of i-Al-Pd-Mn. Overlayer structure is correlated with several physical parameters to identify trends. It is concluded that the chemical properties of the adsorbate (metallic radius, electronegativity, melting temperature) are important indicators of quasiperiodic structuring of the adsorbate system. These correlations allow predictions of those elements likely to yield pseudomorphic overlayers. Structural effects upon molecular adsorption on clean quasicrystal surfaces have been less successful. A new approach to ordered molecular adsorption is described and illustrated for C-60 adsorption on a Pb monolayer film on the ten-fold surface of d-Al-Ni-Co.
Title:
Testing bulk models of icosahedral quasicrystals with STM images of clean surfaces
Authors:
Papadopolos, Z; Widmer, R; Groning, O Author Full Names: Papadopolos, Z.; Widmer, R.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2083-2093 2008
Abstract:
In the case of icosahedral Al-Pd-Mn we compare the STM (scanning tunnelling microscopy) image of the real fivefold surface to the STM simulations on the candidates of the fivefold bulk terminations. We make the choice of which termination fits best to the real image. It leads us to some hints important either for the chemistry of the bulk-model or for the eventual correction of the model of atomic positions itself. We work in the frame of the particular model of atomic positions, based on the diffraction data for Al70Pd21Mn9 and Al62Cu25.5Fe12.5. We also discuss the possibilities beyond this model.
Title:
X-ray photoelectron diffraction on the 6-fold (001) mu-Al4Mn approximant surface
Authors:
Widmer, R; Maeder, R; Heggen, M; Feuerbacher, M; Groning, O Author Full Names: Widmer, R.; Maeder, R.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2095-2102 2008
Abstract:
In theoretical investigations, the study of the properties of quasicrystals via analysis of periodic approximant structures has proven to be very successful. We performed experimental surface structure studies on the mu-Al4Mn approximant, exhibiting a large unit cell of 563 atoms, to get on to the origin of the unusual physical properties of complex quasicrystalline systems. The 6-fold (001) mu-Al4Mn surface was investigated by surface-sensitive low energy electron diffraction and X-ray photoelectron diffraction. Detailed analysis of the experimental data using single scattering cluster calculations revealed a pure bulk truncated surface, which is cut at the z = c/2 and 3c/4 layers of the unit cell, with a slight preference for the z = 3c/4 termination. The possibility of preparing well ordered, bulk terminated surfaces of such a complex, yet periodic, crystal structure in the Al-Mn system allows the application of a wealth of surface analytical tool to obtain a greater understanding of the physical properties of complex metallic alloys in relation to quasicrystals.
Title:
Low-energy electron diffraction (LEED) study of an aperiodic thin film of Cu on 5-fold i-Al-Pd-Mn
Authors:
Pussi, K; Reid, DE; Ferralis, N; McGrath, R; Lograsso, TA; Ross, AR; Diehl, RD Author Full Names: Pussi, K.; Reid, D. E.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2103-2110 2008
Abstract:
Thin films of copper grown on five-fold i-AlPdMn at room temperature consist of domains that are rotationally aligned with the five primary symmetry directions of the substrate and which have one-dimensional aperiodic order. This aperiodic order is evident in scanning tunnelling microscopy images as wide and narrow rows that are spaced according to a Fibonacci sequence. A low-energy electron diffraction (LEED) study of this film indicates that the structure within the domains is periodic along the rows, with a repeat distance equal to the nearest-neighbour separation in bulk Cu. To determine the complete structure, a dynamical LEED experiment was performed for a five-layer Cu film at a sample temperature of 85 K. The analysis was performed using two different computational methods, one based on quasicrystalline slabs and the other on periodic approximants. Of the model structures tested, the film is found to be most consistent with a structure based on the Cu{100} surface structure, but having aperiodic displacements, both in-plane and out-of-plane, along a < 110 > direction.
Title:
Co nanocrystallites on an icosahedral Al-Pd-Mn quasicrystal
Authors:
Burkardt, S; Erbudak, M; Longchamp, JN; Weisskopf, Y Author Full Names: Burkardt, S.; Erbudak, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2111-2116 2008
Abstract:
Recently, we reported that submonolayer deposits of Co onto the pentagonal surface of i-Al-Pd-Mn form a stable intermetallic compound of five CsCl-type AlCo domains rotated by 72 degrees with respect to each other. For multilayer deposition, Co was found to grow epitaxially on the AlCo domains in a body-centred cubic structure. Here we discuss this conclusion in more detail and report the formation of atomic rows at the surface for deposits larger than three monolayers. The details of the growth resulting in ordered nanostructures are extracted from low-energy electron diffraction investigations. Surface magneto-optical Kerr effect measurements confirm the decrease in the domain size for thicker films.
Title:
Alkaline-earth metal monolayers on 5-fold i-Al-Pd-Mn surface: Influence of adatom size on quasiperiodic ordering
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2117-2122 2008
Abstract:
The structure and stability of a quasiperiodic alkaline-earth metal monolayer formed on a five-fold surface of an icosahedral Al-Pd-Mn quasicrystal have been investigated using ab initio density-functional methods. We study the influence of the size of the adatom on the regularity of the quasiperiodic ordering. It was found that Ca adatoms at a coverage 0.066 atoms/angstrom(2) (Theta = 0.5)form a highly regular quasiperiodic monolayer on the i-Al-Pd-Mn surface, with an ordering described by a decagonal DHBS tiling of decagons, hexagons, boats and pentagonal stars.
Title:
Discussion on the surface science of quasicrystals
Authors:
Thiel, PA Author Full Names: Thiel, P. A.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2123-2129 2008
Abstract:
This paper contains a short review of four aspects of the surface science of quasicrystals, together with a list of challenges for the scientific community in the near future. The first issue concerns the ability of surface science to shed light on bulk atomic structure. The second is the use of surfaces as quasiperiodic templates, particularly for films of periodic metals. Here, enforcing quasiperiodicity in the film may lead to unusual magnetic, tribological or adsorption properties. The third aspect concerns the effects of surface phasons and phonons on dynamical interactions with adsorbates, such as sticking coefficient, as well as on diffusion between the surface and near-surface region. The final area is tribology, where studies of quasicrystals have suggested that both adhesion and phononic friction may be important.
Title:
Electronic transport in AlMn(Si) and AlCuFe quasicrystals: Breakdown of the semiclassical model
Authors:
de Laissardiere, GT; Julien, JP; Mayou, D Author Full Names: de Laissardiere, G. Trambly; Julien, J. -P.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2131-2144 2008
Abstract:
The semiclassical Bloch-Boltzmann theory is at the heart of our understanding of conduction in solids, ranging from metals to semiconductors. Physical systems that are beyond the range of applicability of this theory are thus of fundamental interest. It appears that in quasicrystals and related complex metallic alloys, a new type of breakdown of this theory operates. This phenomenon is related to the specific propagation of electrons. We develop a theory of quantum transport that applies to a normal ballistic law, and also to these specific diffusion laws. As we show, phenomenological models based on this theory describe correctly the anomalous conductivity in quasicrystals. Ab initio calculations performed on approximants also confirm the validity of this anomalous quantum diffusion scheme. This provides us with an ab initio model of transport in approximants such as alpha-AlMnSi and AlCuFe 1/1 cubic approximant.
Title:
Anisotropic electrical, magnetic and thermal transport properties of the Al80Cr15Fe5 decagonal approximant
Authors:
Dolinsek, J; Vrtnik, S; Smontara, A; Jagodic, M; Jaglicic, Z; Bauer, B; Gille, P Author Full Names: Dolinsek, J.; Vrtnik, S.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2145-2153 2008
Abstract:
The anisotropic magnetic, electrical and thermal transport properties were studied of a single-crystalline Al80Cr15Fe5 approximant to the decagonal quasicrystal. The temperature-dependent electrical resistivity along the b and c crystalline directions shows non-metallic behaviour with a broad maximum, whereas it exhibits a metallic positive temperature coefficient along the a direction perpendicular to the (b, c) atomic planes. The resistivity can be treated with the model of slow charge carriers, where the increased electron-phonon scattering upon raising the temperature induces a transition from dominant Boltzmann (metallic) to dominant non-Boltzmann (insulating-like) regime. The magnetic susceptibility and thermal conductivity also reveal a small anisotropy.
Title:
Coupled quasicrystals
Authors:
Vekilov, YK; Isaev, EI Author Full Names: Vekilov, Yu. Kh.; Isaev, E. I.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2171-2173 2008
Abstract:
We predict that under certain experimental conditions external radiation with frequency half of that for the alternating Josephson effect can appear when a constant voltage is applied to a quasicrystal-quasicrystal tunnelling junction 1. The background for this possibility is the phase coherence of the wavefunctions across the barrier and the absence of scattering on the dynamical degrees of freedom (phonons).
Title:
Magnetism in quasicrystals
Authors:
Hippert, F; Prejean, JJ Author Full Names: Hippert, F.; Prejean, J. J.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2175-2190 2008
Abstract:
The present understanding of magnetic properties of quasicrystals (QCs) is reviewed. In AlMn and AlPdMn QCs, only a few Mn atoms, with concentrations from a few per cent down to 10(-4) carry a localized magnetic moment. These moments are coupled via RKKY interactions, leading to a canonical spin-glass ordering at low temperature. They also exhibit a Kondo effect and AlPdMn QCs turned out to be a model system for studying experimentally the competition between Kondo and RKKY interactions in the absence of long-range magnetic ordering. Besides, the presence of localized moments has very unusual consequences for the electronic transport in AlPdMn QCs. In RMgZn and RMgCd QCs ( R is a magnetic rare earth), with R concentration around 9%, a spin-glass like freezing is observed. However the short-range antiferromagnetic correlations detected above the freezing temperature are unusual and are certainly influenced by the quasiperiodicity.
Title:
Local environment and magnetism in icosahedral quasicrystals
Authors:
Godonyuk, AV; Isaev, EI; Vekilov, YK Author Full Names: Godonyuk, A. V.; Isaev, E. I.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2191-2196 2008
Abstract:
Based on density functional theory and all-electron projector-augmented wave (PAW) potentials, we studied the onset of local magnetic moments in the model icosahedral quasicrystal, Al46-xPd14Mn5Bx, where x is the number of boron (B) atoms with 0 <= x <= 3. We previously studied the dependence of local magnetic moment in Mn atoms on their atomic concentration [J. Magn. Magn. Mater. 300 567 (2006)]. In the current study, however, we have kept the number of Mn atoms constant. We have shown that the magnitude of local magnetic moment in a Mn atom depends significantly on the presence of Pd atoms inside the first coordination sphere. In qualitative agreement with experimental conclusion of Peng et al. [J. Magn. Magn. Mater. 184 319 (1998)], we also found that the average local magnetic moment in Mn depends on B concentration. The influence of B atoms is more pronounced if they are located inside the second coordination sphere.
Title:
In search of multipolar order on the Penrose tiling
Authors:
Vedmedenko, EY; Mandel, SED; Lifshitz, R Author Full Names: Vedmedenko, E. Y.; Mandel, S. Even-Dar
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2197-2207 2008
Abstract:
We use Monte Carlo calculations to analyse multipolar ordering on the Penrose tiling, relevant for two-dimensional molecular adsorbates on quasicrystalline surfaces and for nanomagnetic arrays. Our initial investigations are restricted to multipolar rotors of rank one through four-described by spherical harmonics Ylm with l = 1,....,4 and restricted to m = 0-positioned on the vertices of the rhombic Penrose tiling. At first sight, the ground states of odd-parity multipoles seem to exhibit long-range order, in agreement with previous investigations of dipolar systems. Yet, careful analysis performed here establishes that, despite earlier claims, long-range order is absent for all types of rotors, and only short-range order exists. Nevertheless, we show here that short-range order suffices to yield a superstructure in the form of the decagonal Hexagon-Boat-Star tiling. Our results should be taken as a warning for any future analysis of order in either real or simulated arrangements of multipoles on quasiperiodic templates.
Title:
Discussion of electronic properties of quasicrystals
Authors:
Mayou, D Author Full Names: Mayou, D.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2209-2215 2008
Abstract:
This article gives a short review of some important achievements in the field of electronic properties of quasicrystals. It focuses essentially on: the nature of quasicrystals as Hume-Rothery alloys, the energetics of quasicrystals and related phases, the magnetic properties, the localization of electronic states, and the transport properties. For each part we emphasize some promising directions of research. We end by listing some problems that are related to that of electrons in a quasiperiodic potential.
Title:
Quasicrystals and complex metallic alloys: Trends for potential applications
Authors:
Barthes-Labrousse, MG; Dubois, JM Author Full Names: Barthes-Labrousse, M. -G.; Dubois, J. -M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2217-2225 2008
Abstract:
Although the industrial development of complex metallic alloys (CMAs) and quasicrystals (QCs) has remained quite limited so far, these materials exhibit interesting and sometimes unexpected properties in terms of technological applications. A few selected examples of the most promising properties and trends for potential applications are presented.
Title:
Low-temperature synthesis of nanocrystalline spinel by mechanical milling and annealing of Al-Ni-Fe decagonal quasicrystals
Authors:
Yadav, TP; Mukhopadhyay, NK; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Mukhopadhyay, N. K.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2227-2236 2008
Abstract:
Attempts were made to synthesize a nanocrystalline spinel phase by mechanical milling and subsequent annealing of Al-Ni-Fe decagonal quasicrystalline alloy. The milling of the decagonal phase was carried out in an attritor ball mill at 400 rpm for 1-40 h with ball to powder ratio of 100:1 in hexane medium. Subsequently annealing was performed in vacuum as well as an air ambience for 10, 20, 40 and 80 h. The quasicrystal powders milled for 40 h showed the formation of B2-type nanocrystalline phase (a=2.91 angstrom). Annealing of 40 h milled powder in air at 500 degrees C resulted in the formation of spinel structure (a=8.15 angstrom). X-ray diffraction and transmission electron microscopy investigations confirmed the formation of spinel phase with an average grain size of similar to 60nm. The formation of nanospinels and the advantages of this synthesis route compared to the existing routes for the formation of spinels are discussed.
Title:
Correlation between charge state and diffusion of hydrogen in Ti-based quasicrystals
Authors:
Morozov, AY; Belov, MP; Barbin, NA; Isaev, EI; Vekilov, YK Author Full Names: Morozov, A. Y.; Belov, M. P.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2237-2243 2008
Abstract:
The dependence of the charge state of hydrogen as a function of H content in the 1/1 approximant to icosahedral Ti-based quasicrystals (QCs) was studied using a first-principles method based on the density functional theory and norm-conserving pseudopotentials. It was found that the dependence is strong and non-monotonic. Hydrogen diffusion is significantly hindered in QCs with a charged hydrogen atom.
Title:
Dodecagonal quasicrystal in a polymeric alloy II: specific heat
Authors:
Dotera, T Author Full Names: Dotera, T.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2245-2251 2008
Abstract:
In a previous paper, we reported the formation of a dodecagonal quasicrystal (DDQC) in a quasi-two-dimensional lattice Monte Carlo simulation of a star-shaped polymer. In this paper, we show a series of Archimedean and quasicrystalline phases (4.8(2)) -> (3(2).4.3.4) -> DDQC -> (4.6.12) with increase of one component of ABC star polymers. The phase behaviour can be regarded as a transition between square tiling and triangle tiling via square-triangle tiling. We compare the specific heat for the phases and find that the DDQC sample possesses higher specific heat at high temperatures, which may be attributed to phason dynamics.
Title:
Electronic energy spectra of square and cubic Fibonacci quasicrystals
Authors:
Mandel, SED; Lifshitz, R Author Full Names: Mandel, S. Even-Dar; Lifshitz, R.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2261-2273 2008
Abstract:
Understanding the electronic properties of quasicrystals, in particular the dependence of these properties on dimension, is among the interesting open problems in the field of quasicrystals. We investigate an off-diagonal tight-binding hamiltonian on the separable square and cubic Fibonacci quasicrystals. We use the well-studied Cantor-like energy spectrum of the one-dimensional Fibonacci quasicrystal to obtain exact results regarding the transitions between different spectral behaviours of the square and cubic quasicrystals. We use analytical results for the addition of one-dimensional spectra to obtain bounds on the range in which the higher-dimensional spectra contain an interval as a component. We also perform a direct numerical study of the spectra, obtaining good results for the square Fibonacci quasicrystal, and rough estimates for the cubic Fibonacci quasicrystal.
Title:
The square Thue-Morse tiling for photonic application
Authors:
Moretti, L; Mocella, V Author Full Names: Moretti, L.; Mocella, V.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2275-2284 2008
Abstract:
The photonic properties of a two-dimensional (2D) photonic aperiodic crystal based on the Thue-Morse (ThMo) substitutional sequence were investigated theoretically. In contrast to traditional photonic quasicrystals based on the Penrose tiling, these structures were obtained by removing the lattice points from a square arrangement, following the inflation rules emerging from the ThMo sequence. The resulting structure does not exhibit the typical translational symmetry of photonic crystals. In particular, it is well known that the ThMo sequence has a singular continuous Fourier transform. This property was transferred directly on the 2D ThMo photonic aperiodic crystal represented by an array of pillars in air. The electromagnetic field distribution can be described as a quasi-localized state, with characteristics lying between the localized states, corresponding to the defect state in a photonic crystal, and the Bloch states, as in the case of the eigenmode in a photonic crystal. The photonic bandgap formation was explored as a function of pillar radius. Furthermore, a preliminary investigation of the defect behaviour in square ThMo tiling was carried out. The electric field in the defect state was revealed to be strictly localized in the defect pillar. These structures provide interesting properties, which could be used to design novel optical devices.
Title:
Nonlinear photonic quasicrystals for novel optical devices
Authors:
Bahabad, A; Lifshitz, R; Voloch, N; Arie, A Author Full Names: Bahabad, A.; Lifshitz, R.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2285-2293 2008
Abstract:
Two well-known methods for the design of quasicrystal models are used to create novel nonlinear optical devices. These devices are useful for efficient three-wave mixing of several different processes, and therefore offer greater flexibility with respect to the more common periodic nonlinear photonic crystals. We demonstrate applications for polarization switching as well as multi-wavelength and multi-directional frequency doubling. The generalized dual grid method is proven to be efficient for designing photonic quasicrystals for one-dimensional collinear devices as well as elaborate two-dimensional multi-directional devices. The cut-and-project method is physically realized by sending finite-width optical beams at an irrational angle through a periodic two-dimensional nonlinear photonic crystal. This enables the creation of two simultaneous collinear optical processes that can be varied by changing the angle of the beams.
Title:
Phason modes in quasicrystals
Authors:
De Boissieu, M Author Full Names: De Boissieu, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2295-2309 2008
Abstract:
Studies on phason modes in quasicrystals, but more generally in aperiodic phases, which encompass incommensurately modulated phases, composites and quasicrystals, are reviewed. After an introduction on phason modes in aperiodic phases, the hydrodynamic theory is presented. The case of incommensurately modulated phases is illustrated by results on ThBr4. Atomic models used to simulate phason modes in quasicrystals are then presented, followed by an overview of results obtained for icosahedral and decagonal phases.
Title:
Atomic dynamics of i-ScZnMg and its 1/1 approximant phase: Experiment and simulation
Authors:
Mihalkovic, M; Francoual, S; Shibata, K; De Boissieu, M; Baron, AQR; Sidis, Y; Ishimasa, T; Wu, D; Lograsso, T; Regnault, LP; Gahler, F; Tsutsui, S; Hennion, B; Bastie, P; Sato, TJ; Takakura, H; Currat, R; Tsai, AP Author Full Names: Mihalkovic, M.; Francoual, S.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2311-2318 2008
Abstract:
Quasicrystals are long-range ordered materials that lack translational invariance so that the study of their physical properties remains a challenging problem. In order to study the respective influence of the local order and of the long-range order (periodic or quasiperiodic) on lattice dynamics, we have carried out inelastic X-ray and neutron scattering experiments on single grain samples of the Zn-Mg-Sc icosahedral quasicrystal and of the Zn-Sc periodic cubic 1/1 approximant. Besides the overall similarities and the existence of a pseudo-gap in the transverse dispersion relation, marked differences are observed, the pseudo-gap being larger and better defined in the approximant than in the quasicrystal. This can be qualitatively explained using the concept of pseudo-Brillouin zone in the quasicrystal. These results are compared to simulations on atomic models and using oscillating pair potentials, which have been fitted against ab-initio data. The simulated response function reproduces both the dispersion relation but also the observed intensity distribution in the measured spectra. The partial vibrational density of states, projected on the cluster shells, is computed from this model.
Title:
High-temperature specific heat of icosahedral Al-Cu-Fe and decagonal Al-Ni-Co
Authors:
Shulyatev, DA; Nigmatulin, AS; Lobanova, AV; Gasparyan, TA Author Full Names: Shulyatev, D. A.; Nigmatulin, A. S.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2319-2323 2008
Abstract:
The high-temperature specific heat, c(p)(T), of icosahedral Al-Cu-Fe and decagonal Al-Ni-Co was measured at various temperature ranges between 420 and 1350 K. For both materials, the specific heat increases with increasing temperature, reaching the values that are substantially higher than the Dulong and Petit value. Comparisons are made with previously reported data for icosahedral and decagonal phases.
Title:
Quasicrystal plasticity in the framework of a constitutive model: Interaction of the microstructural parameters at high strain rates
Authors:
Heggen, M; Feuerbacher, M Author Full Names: Heggen, M.; Feuerbacher, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2325-2331 2008
Abstract:
A unified description of quasicrystal plasticity in terms of a quantitative model using constitutive equations was presented by Feuerbacher and co-workers in 2001 [1]. In a later work, the model was successfully applied to a wide range of experimental parameters where various stress-strain behaviours were observed [2]. At high strain rates, for example, the occurrence of a low-strain work-hardening stage, the formation of a stress maximum at around 5%, and work softening at higher strains was observed. In the present work, the complex stress-strain behaviour of quasicrystals at high strain rates is analyzed in terms of the constitutive model. The evolution of the two microstructural parameters, the dislocation density and the order parameter, their interaction with other microstructural parameters and the influence on the macroscopic plastic deformation behaviour are analyzed and discussed.
Title:
Discussion of phasons in quasicrystals and their dynamics
Authors:
Widom, M Author Full Names: Widom, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2339-2350 2008
Abstract:
Phasons are a type of excitation peculiar to quasicrystals and other incommensurate phases arising as a consequence of their spatial quasiperiodicity. Phason-related excitations are also observed in complex crystal structures known as approximants. This article briefly reviews the concepts of phasons with focus on current issues in their regard. We examine both continuum (hydrodynamic) and discrete (tiling) descriptions of phasons and review the state of experimental validation of the basic theoretical notions.
Title:
Twenty-five years of quasicrystals: Where are we now and what does the future hold? - A personal outlook
Authors:
Dubois, JM Author Full Names: Dubois, J. -M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2351-2356 2008
Abstract:
Twenty-five years after the historic discovery of a real material exhibiting fivefold symmetry, the scientific field opened as a result is still robust and active. On the experimental side, it has been strengthened in recent years by new inputs coming from studies of transport properties, surface physics, coating technology, catalysis, etc. Its future probably relies upon combining these very exotic, but now extremely well documented materials with more conventional materials in composites, or challenging the discovery of new, or more exciting properties in a systematic screening of intermetallics compounds with untried compositions. An effort towards making quasicrystals better understood outside our own community has become mandatory with a view to developing the field.
Title:
Transport properties of Ti-Zr-Ni quasicrystalline and glassy alloys
Authors:
Kuo, YK; Kaurav, N; Syu, WK; Sivakumar, KM; Shan, UT; Lin, ST; Wang, Q; Dong, C Author Full Names: Kuo, Y. K.; Kaurav, N.
Source:
JOURNAL OF APPLIED PHYSICS 104 (6): Art. No. 063705 SEP 15 2008
Abstract:
We report on measurements of the temperature dependence of the electrical resistivity (p), thermopower (S), and thermal conductivity (kappa) of Ti-Zr-Ni alloys between 10 and 300 K. A series of Ti-Zr-Ni quasicrystals (QCs) Ti40Zr40Ni20, Ti45Zr35Ni20, and Ti50Zr30Ni20 and metallic glasses Ti35Zr45Ni20 and Ti40Zr40Ni20 was prepared to systematically study the compositional and structural dependences of their transport properties. The resistivity of all these alloys was found to be very weakly temperature dependent with a negative temperature coefficient of resistance. Further, the observed increase in electrical resistivity with increasing Ti/Zr ratio is most likely due to the increase in disorder. The SIT against temperature curves exhibited a maximum between 20 and 50 K and a noticeable deviation from the expected linear behavior in S(T) at higher temperatures. Such observations in the thermopower of QCs have been attributed to the electron-phonon enhancement and phonon drag effect. The measured thermal conductivities were analyzed by separating the electronic and phonon contributions that provide a reasonable explanation for plateau-type feature in kappa(T) of QCs. Our present results suggest that the transport properties of glassy phase are influenced by the same mechanisms as those of quasicrystalline phase. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2977721]
Title:
Crystal structure of the 2/1 cubic approximant Ag42In42Yb16
Authors:
Li, MR; Hovmoller, S; Sun, JL; Zou, XD; Kuo, KH Author Full Names: Li, M. R.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 465 (1-2): 132-138 OCT 6 2008
Abstract:
The crystal structure of the 2/1 cubic approximant Ag42In42Yb16 was determined by single crystal X-ray diffraction. The structure model has the composition of Ag40.42In44.50Yb15.08 with a=24.8687 angstrom, space group Pa (3) over bar (No. 205). Among the 14 independent Ag, 13 In, and 5 Yb sites, 6 Ag sites and 6 In sites are icosahedrally coordinated, whereas two sites (In13, Yb1) are Frank-Kasper polyhedrally coordinated. Four Yb sites (Yb2-5) are double pentagonal antiprisms. The basic structural unit can be described as a 102-atom pseudo-Bergman cluster with three successive shells, of which the second shell consists of a dodecahedron and an only nine-atom polyhedron that breaks icosahedral symmetry. (C) 2007 Elsevier B.V. All rights reserved.
Title:
The effect of cooling rate on the microstructure and mechanical properties of Mg-Zn-Gd-based alloys
Authors:
Liu, Y; Yuan, GY; Yin, J; Lu, C; Ding, WJ; Jiang, JZ Author Full Names: Liu, Yong
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 99 (9): 973-978 SEP 2008
Abstract:
The microstructure and mechanical properties of Mg3.5Zn0.6Gd and Mg3.5Zn0.6Gd1.5Cu alloys were investigated under different solidification conditions. The microstructure and phase constitutions of alloys were characterized using optical microscopy, scanning electron microscopy, X-ray diffraction and differential thermal analysis. The results indicate that the cooling rate plays an important role in grain refinement and phase constitutions of Mg-Zn-Gd alloys. In the cooling rate range from 4.8 K s(-1) to 18.5 K s(-1) for the Mg-Zn-Gd system, higher content of the icosahedral phase (I-phase) was obtained under the condition of higher cooling rate which accelerated the nucleation and growth of the I-phase. Under the cooling rate of 18.5 K s(-1), the mechanical properties of the Mg3.5Zn0.6Gd alloy were further improved by the high I-phase content due to its unique icosahedral structure, in addition to the contribution of grain refinement.
Title:
Computing with almost periodic functions
Authors:
Moody, RV; Nesterenko, M; Patera, J Author Full Names: Moody, R. V.; Nesterenko, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 654-669 Part 6 NOV 2008
Abstract:
This paper develops a method for discrete computational Fourier analysis of functions defined on quasicrystals and other almost periodic sets. A key point is to build the analysis around the emerging theory of quasicrystals and diffraction in the setting on local hulls and dynamical systems. Numerically computed approximations arising in this way are built out of the Fourier module of the quasicrystal in question and approximate their target functions uniformly on the entire infinite space. The methods are entirely group theoretical, being based on finite groups and their duals, and they are practical and computable. Examples of functions based on the standard Fibonacci quasicrystal serve to illustrate the method (which is applicable to all quasicrystals modeled on the cut-and-project formalism). (C) 2008 International Union of Crystallography Printed in Singapore - all rights reserved

Update: 6-Nov-2008

Title:
Electron microscopy of an icosahedral phase in a rapidly solidified Al18Mg3Mn2 complex metallic alloy
Authors:
Mukhopadhyay, NK; Chang, HJ; Lee, JY; Kim, DH Author Full Names: Mukhopadhyay, N. K.; Chang, H. J.
Source:
SCRIPTA MATERIALIA 59 (10): 1119-1122 NOV 2008
Abstract:
The icosahedral quasicrystal (QC) has been found to form, along with a minor amount of alpha-Al, in the rapidly solidified Al18Mg3Mn2 complex metallic alloy. From the compositional analysis, the QC was found to be close to (AlMg)(82)Mn-18. The quasilattice constant (a(R) = 0.4604 nm) of the QC phase suggests that it is basically an Al-Mn type of Mackay quasicrystal, which conforms to the composition analysis. The rationale behind the formation of the Al-Mg-Mn ternary quasicrystal from the T-Al18Mg3Mn2 alloy is discussed. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Electronic structure of CePdAl experiment and calculations
Authors:
Glogowski, W; Goraus, J; Slebarski, A Author Full Names: Glogowski, W.; Goraus, J.
Source:
MATERIALS SCIENCE-POLAND 26 (3): 729-734 2008
Abstract:
CePdAl exhibits an antiferromagnetic phase below T-N = 2.7 K; its physical properties are typical of heavy fermion compounds (specific heat coefficient gamma = C/T = 270 mJ/(mol.K-2)). The triangular coordination symmetry of the magnetic Ce ions gives rise to geometrical frustration and leads to an incommensurate antiferromagnetic structure below T-N, showing a coexistence of ordered and frustrated Ce moments. The purpose of this work was to discuss electronic structure of CePdAl and its influence on the geometrical frustration in the Kagome-like lattice and the Kondo effect in CePdAl. We present the results of the X-ray diffraction analysis and the XPS Ce 3d core and valence band spectra. We also present the spin-polarized band structure calculations for CePdAl, using the LAPW method.
Title:
Crystallography and morphology of twins in equiatomic TiPt martensite
Authors:
Nishida, M; Matsuda, M; Yasumoto, Y; Yano, S; Yamabe-Mitarai, Y; Hara, T Author Full Names: Nishida, M.; Matsuda, M.
Source:
MATERIALS SCIENCE AND TECHNOLOGY 24 (8): 884-889 AUG 2008
Abstract:
Twins in the B19 (2H) martensite in Ti-Pt shape memory alloy have been investigated by transmission electron microscopy. There are three twinning modes evident, i.e. {111}(2H) Type I, < 121 >(2H) Type II and {101}(2H) compound twins. In addition to the 2H martensite, various long period stacking structures are observed such as 2112 stacking and incommensurate like modulated martensites. It is frequently observed that two martensite structures derived from the identical closed packed plane of the parent phase coexist in the same area, namely, 'two-in-one' morphology. The crystallographic aspects of the 'two-in-one' morphology are also discussed.
Title:
TEM investigation of intermediate phase transformation and micromodulation in Ni-Mn-Ga ferromagnetic shape memory alloys
Authors:
Tsuchiya, K; Todaka, Y; Umemoto, M Author Full Names: Tsuchiya, K.
Source:
MATERIALS SCIENCE AND TECHNOLOGY 24 (8): 920-926 AUG 2008
Abstract:
Intermediate phase transformation, martensitic transformations and modulated structures in Ni-Mn-Ga ferromagnetic shape memory alloys were investigated by TEM. The transformation from high temperature L2(1) phase to intermediate phase was characterised by the appearance of diffuse satellite spots at 0.167q(220) positions in electron diffraction patterns and intense fine striations in bright field images. These results are consistent with the reported results of neutron diffraction measurements related to the phonon anomaly. Also, high resolution TEM observations and fast Fourier transformation analysis on the near intermediate phase state in Ni-Mn-Ga-Gd were conducted. It was revealed that the coarse tweed contrast was associated with a long wavelength strain field while the fine striations are associated with the satellite spots and domains of micromodulation aligned parallel to {110}.
Title:
Some symmetry aspects of ferroics and single phase multiferroics
Authors:
Schmid, H Author Full Names: Schmid, Hans
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (43): Art. No. 434201 OCT 29 2008
Abstract:
The symmetry conditions for the occurrence in a same phase of one or more of the four primary ferroic properties, i.e., ferroelectricity, ferromagnetism, ferrotoroidicity and ferroelasticity, are discussed. Analogous conditions are outlined for the admission of so-called secondary and tertiary ferroic effects, such as magnetoelectric, piezoelectric, piezomagnetic, piezotoroidic, etc. Formerly postulated `magnetotoroidic' and 'electrotoroidic' effects are found to be describable as tertiary ferroic magnetoelectric effects. For understanding ferroic and multiferroic domains and their possibilities of switching, knowledge of the pairs of prototype point group/ferroic phase point group (so-called 'Aizu species') is decisive. A classification into ensembles of species with common properties, recently extended to ferrotoroidic crystals, allows distinguishing between full, partial or no coupling between order parameters and understanding domain patterns and poling procedures. The switching by reorientation with angles other than 180 degrees of ferromagnetic, antiferromagnetic and ferroelectric domains by magnetic fields, electric fields or by stress requires the ferroic phase to be ferroelastic. For ferromagnetic/ ferrotoroidic and antiferromagnetic/ ferrotoroidic phases, the ferrotoroidic domains are found to be identical with the ferromagnetic and antiferromagnetic ones, respectively. As a consequence and depending on symmetry, ferrotoroidic domains can be switched by crossed electric and magnetic fields, by collinear electric and magnetic fields or by a magnetic field alone. Examples of ferrotoroidic domains are discussed for Fe2-xGaxO3, Co3B7O13Br and LiCoPO4. Recent new results on symmetry and domains of the antiferromagnetic incommensurate phase of BiFeO3 are also discussed.
Title:
Magnetically induced ferroelectricity in the buckled Kagome antiferromagnet Ni3V2O8
Authors:
Lawes, G; Kenzelmann, M; Broholm, C Author Full Names: Lawes, G.; Kenzelmann, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (43): Art. No. 434205 OCT 29 2008
Abstract:
Ni3V2O8 is one of several recently identified multiferroic materials in which ferroelectricity is produced by long-range magnetic order. This staircase Kagome compound adopts a sequence of distinct low temperature magnetic phases, which exhibit different optical, dielectric, and transport properties, most notably ferroelectric order arising from a polar incommensurate magnetic structure. We give an overview of the experimental results from the existing literature on Ni3V2O8, and briefly discuss models that describe the coupling between magnetic and ferroelectric properties. We show that the temperature dependence of the dielectric constant provides evidence for spin-charge coupling in Ni3V2O8 away from the ferroelectric phase. An anomaly in the thermal conductivity at the incommensurate-commensurate phase transition suggests that spin scattering may limit thermal transport in the incommensurate phase. We associate each of the two incommensurate phase transitions with one magnetic order parameter, and we show that the temperature dependence of the ferroelectric polarization closely follows the product of these two magnetic order parameters-corroborating the validity of the phenomenological trilinear coupling model. Finally, we present inelastic powder neutron scattering measurements that provide evidence of several weakly dispersive magnetic modes that are typical for strongly frustrated antiferromagnets with large spin anisotropies.
Title:
Magnetic and ferroelectric properties of multiferroic RMn2O5
Authors:
Noda, Y; Kimura, H; Fukunaga, M; Kobayashi, S; Kagomiya, I; Kohn, K Author Full Names: Noda, Y.; Kimura, H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (43): Art. No. 434206 OCT 29 2008
Abstract:
The magnetic and ferroelectric properties of multiferroic RMn2O5 (R = Y, Tb, Ho, Er, Tm) are reviewed based on recent neutron diffraction and dielectric measurements. Successive phase transitions of magnetic and dielectric ordering were found to occur simultaneously in this system. The characteristic magnetic ordering of the system exhibits an incommensurate-commensurate phase transition, and again transitions to an incommensurate phase. Special attention is given to the magnetic structure in order to discuss the mechanism for the introduction of ferroelectric polarization. For all the compounds examined, the spin configuration for Mn4+ and Mn3+ ions in the commensurate magnetic phase, where spontaneous electric polarization occurs, was determined to be a transverse spiral spin structure propagating along the c-axis. By contrast, the alignment of the induced 4f moment of R3+ ions showed variation, depending on the character of each of the elements. Corresponding responses to external fields such as a magnetic field, hydrostatic pressure etc at low temperature are strongly dependent on the rare earth element present in the RMn2O5 system. The so-called colossal magnetoelectric effect in this system can be easily interpreted by the phase transition from the magnetic incommensurate and weak ferroelectric phase to the commensurate and ferroelectric phase.
Title:
Phonons and magnetoelectric interactions in Ni3V2O8
Authors:
Yildirim, T; Vergara, LI; Iniguez, J; Musfeldt, JL; Harris, AB; Rogado, N; Cava, RJ; Yen, F; Chaudhury, RP; Lorenz, B Author Full Names: Yildirim, T.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (43): Art. No. 434214 OCT 29 2008
Abstract:
We present a detailed study of the zone-center phonons and magnetoelectric interactions in Ni3V2O8. Using combined neutron scattering, polarized infrared (IR) measurements and first-principles LDA + U calculations, we successfully assigned all IR-active modes, including eleven B-2u phonons which can induce the observed spontaneous electric polarization. We also calculated the Born-effective charges and the IR intensities which are in surprisingly good agreement with the experimental data. Among the eleven B2u phonons, we find that only a few of them can actually induce a significant dipole moment. The exchange interactions up to a cutoff of 6.5 A are also calculated within the LDA + U approach with different values of U for Ni, V and O atoms. We find that LSDA (i.e. U = 0) gives excellent results concerning the optimized atomic positions, bandgap and phonon energies. However, the magnitudes of the exchange constants are too large compared to the experimental Curie-Weiss constant, Theta. Including U for Ni corrects the magnitude of the superexchange constants but opens a too large electronic bandgap. We observe that including correlation at the O site is very important to get simultaneously the correct phonon energies, bandgap and exchange constants. In particular, the nearest and next-nearest exchange constants along the Ni-spine sites result in incommensurate spin ordering with a wavevector that is consistent with the experimental data. Our results also explain how the antiferromagnetic coupling between sublattices in the b and c directions is consistent with the relatively small observed value of Theta. We also find that, regardless of the values of U used, we always get the same five exchange constants that are significantly larger than the rest. Finally, we discuss how the B2u phonons and the spin structure combine to yield the observed spontaneous polarization. We present a simple phenomenological model which shows how trilinear (and quartic) couplings of one (or two) phonons to two spin operators perturbatively affects the magnon ( i.e. electromagnon) and phonon energies.
Title:
Laser deposition of a Cu-based metallic glass powder on a Zr-based glass substrate
Authors:
Sun, H; Flores, KM Author Full Names: Sun, H.; Flores, K. M.
Source:
JOURNAL OF MATERIALS RESEARCH 23 (10): 2692-2703 OCT 2008
Abstract:
Laser Engineered Net Shaping (LENS (TM)) is a laser-assisted manufacturing process that offers the possibility of producing metallic coatings and components with highly nonequilibrium microstructures. In this work, the microstructure developed by LENS deposition of Cu47Ti33Zr11Ni8Si1 powder on a bulk metallic glass substrate, with nominal composition Zr58.5Nb2.8Cu15.6Ni12.8Al10.3, is investigated. Single-layer deposition results in the formation of an inhomogeneous but partially amorphous layer above a crystalline heat-affected zone. Elemental analysis of the deposited layer indicates incomplete mixing of the powder with the melt pool. The as-deposited alloy exhibits a single glass transition event and its primary crystallization event is consistent with the first crystallization temperature of the Cu-based powder. Subsequent remelting of this layer results in a still partially amorphous deposit with a uniform composition of (Zr + Nb)(51.8)Cu24.7Ti3.4Ni16.4Al3.7. The remelted layer exhibits a structural rearrangement immediately prior to the primary crystallization event, possibly associated with the formation of a quasicrystalline phase.
Title:
The isostructural phase transition and frustrated magnetic ordering in TbPd0.9Ni0.1Al studied by neutron diffraction
Authors:
Donni, A; Keller, L; Kitazawa, H; Prchal, J; Fischer, P Author Full Names: Doenni, A.; Keller, L.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 464 (1-2): 67-74 SEP 22 2008
Abstract:
By using powder neutron diffraction we provide a detailed structural and magnetic investigation of the pseudo-ternary compound TbPd0.9Ni0.1Al with hexagonal ZrNiAl-type crystal structure and disorder of palladium and nickel atoms on two crystallographic sites, We provide experimental evidence for the Occurrence of an isostructural phase transition in TbPd0.9Ni0.1Al at 157 K, which is affected by structural disorder compared to that observed in TbPdAl. In TbPd0.9Ni0.1Al the step of the c/a ratio at the first-order phase transition appears about four times smaller than in TbPdAl. TbPd0.9Ni0.1Al undergoes two successive magnetic phase transitions at T-NI = 41 K and T-N2 approximate to 21.5 K. Two third of non-frustrated ordered Tb moments form commenstrate antiferromaganetic chains (k(1) = [1/2, 0, 1/2]) and coexist with one third of frustrated ordered Tb moments, which change from a commensurate structure (k(1) = [1/2. 0, 1/2]) between T-N2 and T-NI to an incommensurate structure (k(2i) = [0.50(1), 0.12(1). 1/21]) below T-N2. Due to the strong magneto-crystal line anisotropy all ordered Tb moments stay perpendicular to the ab-plane and reach at 1.5 K saturation values of 8.6 (2) mu(B) (non-frustrated) and 7.2 (2) mu(B) (frustrated). The symmetry of the magnetic structure of TbPd0.9Ni0.1Al is lower than that of TbNiAl. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Al-rich region of Al-Pd-Ru at 1000 to 1100 degrees C
Authors:
Pavyuchkov, D; Grushko, B; Velikanova, TY Author Full Names: Pavyuchkov, D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 464 (1-2): 101-106 SEP 22 2008
Abstract:
Partial isothermal sections of the Al-Pd-Ru phase diagram at 1000, 1050 and 1100 degrees C are presented here. The Al-Pd orthorhombic epsilon-phases dissolve up to similar to 15.5 at.% Ru, Al13Ru4 < 2.5 at.% Pd and Al2Ru up to 1 at.% Pd. Between 66 and 75 at.% Al, ternary quasiperiodic icosahedral phase and three cubic phases: C (Pm (3) over bar, a = 0.7757 nm) C-1 (lm (3) over bar, a = 1.5532 nm) and C-2 (Fm (3) over bar, a = 1.5566 nm) were revealed. An additional complex cubic structure with a approximate to 3.96 nm was found to be formed at compositions close to those of the icosahedral phase. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Constitution of the high-Al region of Al-Cu-Rh
Authors:
Grushko, B; Kowalski, W; Przepiorzynski, B; Pavlyuchkov, D Author Full Names: Grushko, B.; Kowalski, W.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 464 (1-2): 227-233 SEP 22 2008
Abstract:
Phase equilibria between 540 and 1010 degrees C were studied in Al-Cu-Rh alloys containing more than 50 at.% Al. Congruent equiatomic AlRh dissolves more than 40 at.% Cu and extends up to 58 at.% Al at the high-Cu part of its compositional range. High-temperature cubic C-Al5Rh2 (C-phase) dissolves up to 13 at.% Cu, "Al3Rh" (epsilon(6)-phase) up to 15 at.% Cu and Al9Rh2 up to 1.5 at.% Cu. The solubility of the third element in other binary Al-Rh and Al-Cu phases is below 0.5 at.%. Close to the high-Cu limit of the C-phase region the fee C-2-phase structurally related to the C-phase is formed. Stable decagonal phase (D1-phase) is formed below 1005 degrees C in a compositional range extending from Al65Cu16Rh19 to Al62Cu23Rh15, which shifts to higher Cu concentrations with decreasing temperature. An additional ternary phase forming around the Al70Cu20Rh10 composition below 660 degrees C was revealed. Partial 1010, 990, 900, 800, 700, 600 and 540 degrees C isothermal sections were determined. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Microstructures and mechanical properties of quasicrystal reinforced Mg matrix composites
Authors:
Zhang, YB; Yu, SR; Song, YL; Zhu, XY Author Full Names: Zhang, Yingbo; Yu, Sirong
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 464 (1-2): 575-579 SEP 22 2008
Abstract:
Mg-based composites reinforced with stable in situ icosahedral quasicrystal phase (I-phase) were fabricated in this Study. The effects of Y content on the microstructures and mechanical properties of the composites were investigated. The results Show that the composites comprised dendrites of alpha-Mg matrix separated by interdendritic I-phase and lamellar (I-phase + alpha-Mg) eutectic. With the increase of Y content, the content of I-phase increases; the content and size of (I-phase + alpha-Mg) eutectic cell increase; the lamellar space between I-phase and alpha-Mg in eutectic cell also increases but the grain size of alpha-Mg matrix decreases. The failure mode of M-Zn-Y alloy matrix composites in tensile tests is quasi-cleavage fracture. With the increase of Y content, the tensile strengths of the composites increase, and (he elongation rates increase firstly and then decrease. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Hydrogenation study of suction-cast Ti40Zr40Ni20 quasicrystal
Authors:
Huang, HG; Li, R; Yin, C; Zheng, ST; Zhang, PC Author Full Names: Huang, Huogen; Li, Rong
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 33 (17): 4607-4611 SEP 2008
Abstract:
Suction casting was predicted to be an usable method for improving the hydriding kinetics of Ti/Zr-based icosahedral quasicrystals (IQCs) in our previous work. To further determine it, a suction-cast Ti40Zr40Ni20 IQC alloy was used for hydrogenation studies by Pressure Composition Isotherm (PCI) and Temperature Programmed Desorption (TPD) techniques. The results showed that, this alloy absorbed hydrogen rapidly with obvious hydrogen pressure plateau and some reversibility, however, displayed very limited hydrogen capacity (about 0.7 wt.%) and low equilibrium pressure. After several hydrogenation/dehydrogenation cycles, the IQC structure transformed into two hydride phases, ZrH2-x and one unknown, both of which decomposed at above 600 degrees C, suggesting high thermo-stability for them. On the whole, indeed the suction-casting method can increase the hydrogen absorption rate of Ti/Zr-based IQCs, however, the hydrogenation properties of the Ti40Zr40Ni20 IQC alloy still need a mighty advancement. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Title:
Crystal structure of 7M modulated Ni-Mn-Ga martensitic phase
Authors:
Righi, L; Albertini, F; Villa, E; Paoluzi, A; Calestani, G; Chernenko, V; Besseghini, S; Ritter, C; Passaretti, F Author Full Names: Righi, L.; Albertini, F.
Source:
ACTA MATERIALIA 56 (16): 4529-4535 SEP 2008
Abstract:
For the first time, the 7M modulated structure, frequently observed in ferromagnetic shape memory Ni-Mn-Ga martensitic phases, is solved by powder diffraction analysis. Two polycrystalline samples with composition Ni2Mn1.2Ga0.8 and Ni2.15Mn0.85Ga, respectively, showing a 7M martensitic state stable at room temperature, were studied. The determination of the modulated crystal structure of Ni2Mn1.2Ga0.8 martensite was achieved by refining the X-ray powder diffraction pattern by the Rietveld method. The basic structure belongs to monoclinic symmetry. The crystal structure, solved within the superspace approach, is found to show an incommensurate 7M modulation with q = 0.308c*. The Rietveld refinement for Ni2.15Mn0.85Ga martensite on the basis of neutron powder data surprisingly provides a very similar incommensurate 7M structure with the same periodicity and analogous modulation function. The incommensurate structure presents typical displacive modulation with several analogies with the Zhdanov (5,(2) over bar)(2) stacking sequence. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 31-Oct-2008

Title:
Tl-4(PO2NH)(4) center dot H2O - A commensurately modulated tetrametaphosphimate
Authors:
Sedlmaier, SJ; Oeckler, O; Schnick, W Author Full Names: Sedlmaier, Stefan J.; Oeckler, Oliver
Source:
SOLID STATE SCIENCES 10 (9): 1150-1158 SEP 2008
Abstract:
Tetrathallium(I) tetra-mu-imidocyclotetraphosphate monohydrate, Tl-4(PO2NH)(4)center dot H2O, was obtained by evaporation of combined aqueous solutions of K-4(PO2NH)(4)center dot 4H(2)O and TlOOCCH3 corresponding to the molar ratio of 1:4. The structure determination of Tl-4(PO2NH)(4)center dot H2O was performed by single-crystal X-ray diffraction methods. In addition to the basic structure (P (1) over bar, no. 2, a = 928.3(2), b = 974.6(2), c = 1018.0(2) pm, alpha = 74.47(3)degrees, beta = 64.68(3)degrees, gamma = 78.81(3)degrees, Z = 2), satellite reflections indicate a fourfold superstructure (AT, a = 928.0(2), b = 3897.1(8), c = 2035.4(4), a = 74.47(3)degrees, beta = 64.68(3)degrees, gamma = 78.81(3)degrees, Z = 16) that is described by an a x 4b x 2c, A-centered supercell which mainly concerns one thallium site of the basic structure. In order to reduce the number of parameters, this superstructure was handled as a commensurate occupancy modulation using the structural description in (3 + 1)-dimensional superspace (P (1) over bar(alpha beta gamma), q = 0.25b* + 0.50c*). The crystal structure of Tl-4(PO2NH)(4) center dot H2O consists of infinite columns of the cyclic [(PO2NH)(4)](4-) anions (saddle conformation) which are interconnected by four N-H center dot center dot center dot O hydrogen bonds. By coordination to the Tl+ ions the [(PO2NH)(4)](4-) columns form a three-dimensional network with channels along [100] wherein the thallium ions that are mainly affected by the modulation are located. The commensurate occupancy modulation of these Tl+ ions has been described with a single harmonic wave function. The modulation is verified by P-31 NMR spectroscopy. The thermal behavior of Tl-4(PO2NH)(4)center dot H2O and the IR data are discussed as well. (C) 2008 Elsevier Masson SAS. All rights reserved.
Title:
Characterization of atomized and extruded Al92Fe3Cr2Mn3 alloy
Authors:
Rios, CT; Fogagnolo, JB; Bolfarini, C; Botta, WJ; Kiminami, CS Author Full Names: Rios, C. Triveno; Fogagnolo, J. B.
Source:
REVIEWS ON ADVANCED MATERIALS SCIENCE 18 (4): 408-414 SEP 2008
Abstract:
Powders of the Al92Fe3Cr2Mn3 quaternary alloy were produced by spray atomization processing;, then they were processed by warm extrusion to obtain extruded ingots. The results revealed that in both the powder particles and the extruded bulk samples, alpha-Al, quasicrystalline and intermetallic phases coexist. The quasicrystalline phase was observed as aggregates and its decomposition to crystalline phase occurs above 500 degrees C. Microstructural changes after extrusion were not observed, indicating that the quasicrystalline phase and the intermetallic compounds are stable against coarsening during the time and temperature of extrusion. The presence of micro-porosities after the extrusion is attributed to the spherical form of the powders and mainly to the high volume of intermetallic faceted-particles.
Title:
Anisotropic magnetic, electrical, and thermal transport properties of the Y-Al-Ni-Co decagonal approximant
Authors:
Smontara, A; Smiljanic, I; Ivkov, J; Stanic, D; Barisic, OS; Jaglicic, Z; Gille, P; Komelj, M; Jeglic, P; Bobnar, M; Dolinsek, J Author Full Names: Smontara, Ana; Smiljanic, I.
Source:
PHYSICAL REVIEW B 78 (10): Art. No. 104204 SEP 2008
Abstract:
We have investigated anisotropic physical properties (magnetic susceptibility, electrical resistivity, thermoelectric power, Hall coefficient, and thermal conductivity) of Y-Al-Ni-Co decagonal approximant with composition Al76Co22Ni2. The crystalline-direction-dependent measurements were performed along three orthogonal directions a*,b, and c of the Y-Al-Ni-Co unit cell, where (a,c) monoclinic atomic planes are stacked along the perpendicular b direction. Anisotropic magnetic susceptibility of conduction electrons is paramagnetic for the field lying within the (a,c) atomic planes and diamagnetic for the field along the b direction. Anisotropic electrical resistivity is low in all crystalline directions, appearing in the order rho(a*)>rho(c)>>rho(b). Thermopower shows electron-phonon enhancement effect. Anisotropic bare thermopower (in the absence of electron-phonon interactions) was extracted, appearing in the same order as the resistivity, vertical bar S-a*(bare)/T vertical bar>S-c(bare)/T vertical bar>vertical bar S-b(bare)/T vertical bar. Anisotropic thermal conductivity appears in the order kappa(b)>kappa(c)>kappa(a*), so that b is the most conducting direction for both electricity and heat. Hall coefficient R-H exhibits pronounced anisotropy, where the magnetic field in a given crystalline direction yields the same R-H for the current along the other two crystalline directions in the perpendicular plane. These anisotropies are analyzed in terms of the anisotropic structure of the Y-Al-Ni-Co phase and the ab initio calculated anisotropic Fermi surface. The results are compared with the literature-reported anisotropy of the physical properties of the d-Al-Ni-Co decagonal quasicrystal.
Title:
Determination of magnetic order of the rare-earth ions in multiferroic TbMn2O5
Authors:
Johnson, RD; Bland, SR; Mazzoli, C; Beale, TAW; Du, CH; Detlefs, C; Wilkins, SB; Hatton, PD Author Full Names: Johnson, R. D.; Bland, S. R.
Source:
PHYSICAL REVIEW B 78 (10): Art. No. 104407 SEP 2008
Abstract:
We have employed resonant x-ray magnetic scattering to specifically probe the magnetic order of the rare-earth ions in multiferroic TbMn2O5. Two energy resonances were observed, one originated from the E1-E1 dipolar transition and the other from the E2-E2 quadrupolar transition. These resonances directly probe the valence 5d band and the partially occupied 4f band, respectively. First, full polarization analysis, which is a measurement of the scattered polarization as a function of incident polarization, confirmed a spin polarization of the terbium valence states (probed by the E1-E1 transition) by the Mn4+ spin density in the commensurate phase. Second, full polarization analysis data were collected in the low-temperature incommensurate and commensurate phases when tuned to the E2-E2 resonance. By employing a least-squares fitting procedure, the spin orientations of the terbium ion sublattice were refined.
Title:
Diagonal and collinear incommensurate spin structures in underdoped La2-xBaxCuO4
Authors:
Dunsiger, SR; Zhao, Y; Gaulin, BD; Qiu, Y; Bourges, P; Sidis, Y; Copley, JRD; Kallin, A; Mazurek, EM; Dabkowska, HA Author Full Names: Dunsiger, S. R.; Zhao, Y.
Source:
PHYSICAL REVIEW B 78 (9): Art. No. 092507 SEP 2008
Abstract:
We have studied incommensurate spin ordering in single-crystal underdoped La2-xBaxCuO4 with x similar to 0.08, 0.05, and 0.025 using neutron-scattering techniques. Static incommensurate magnetic order is observed in the La2-xBaxCuO4 (x = 0.05 and 0.025) compounds with ordering wave vectors which are rotated by 45 about the commensurate (0.5,0.5,0) position, with respect to that in the superconducting x = 0.08 material. These spin modulations are one dimensional in the x = 0.05 and 0.025 samples, with ordering wave vectors lying along the orthorhombic b* direction. Such a rotation in the orientation of the static spin ordering as a function of increasing Ba doping, from diagonal to collinear, is roughly coincident with the transition from an insulating to a superconducting ground state and is similar to that observed in the related La2-xSrxCuO4 system. This phenomenon is therefore a more generic property of underdoped La-214 cuprates.
Title:
Nonlocal Landau theory of the magnetic phase diagram of highly frustrated magnetoelectric CuFeO2
Authors:
Plumer, ML Author Full Names: Plumer, M. L.
Source:
PHYSICAL REVIEW B 78 (9): Art. No. 094402 SEP 2008
Abstract:
A nonlocal Landau-type free-energy functional of the spin density is developed to model the large variety of magnetic states, which occur in the magnetic-field-temperature phase diagram of magnetoelectric CuFeO2. Competition among long-range quadratic exchange, biquadratic antisymmetric exchange, and trigonal anisotropy terms, consistent with the high-temperature rhombohedral R (3) over barm crystal symmetry, are shown to all play important roles in stabilizing the unusual combination of commensurate and incommensurate spin structures in this highly frustrated triangular antiferromagnet. It is argued that strong magnetoelastic coupling is largely responsible for the nonlocal nature of the free energy. A key feature of the analysis is that an electric polarization is induced by a canting of the noncollinear incommensurate spin structure. Application of the model to ordered spin states in the triangular antiferromagnets MnBr2 and NaFeO2 is also discussed.
Title:
Differences between the R-phase and the commensurate phase in iron-doped Ti-Ni shape memory alloys
Authors:
Choi, MS; Yamamoto, T; Fukuda, T; Kakeshita, T; Taguchi, E; Mori, H Author Full Names: Choi, Mi-Seon; Yamamoto, Takuya
Source:
PHILOSOPHICAL MAGAZINE 88 (16): 2449-2460 2008
Abstract:
A Ti-44Ni-6Fe (at. %) alloy was recently reported to exhibit a second order-like incommensurate-commensurate transformation. Whether or not the commensurate (C) phase and the R-phase in Ti-Ni alloys are the same phase has now been investigated. Transformation behaviour was examined in a series of Ti-(50-x)Ni-Fe-x (at. %) alloys with x = 2.0, 4.0, 5.0, 5.5, 5.7, 6.0. Transformation temperature, entropy change and the transformation strain decrease continuously as x increases up to x = 5.7, where the product phase is apparently the R-phase. However, there is an obvious discontinuity in these values between x = 5.7 and x = 6.0. In addition, electron diffraction experiments have revealed that the intensity of satellite reflections of the C-phase is obviously weaker than that of the R-phase. These results strongly suggest that the C-phase is different from the R-phase.
Title:
Electric field induced anomalies in ferroelectric K2SeO4
Authors:
Leist, J; Gibhardt, H; Hradil, K; Eckold, G Author Full Names: Leist, J.; Gibhardt, H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (41): Art. No. 415209 OCT 15 2008
Abstract:
The lock-in transition of K2SeO4 at 93.2 K was studied using high-resolution. gamma-ray diffraction, in situ dielectric measurements and neutron scattering. The phase transition shows a coexistence regime of 1.0 K with clearly resolved incommensurate and commensurate satellite reflections. Within a temperature interval of several K above the lock-in transition, strong third order satellites are observed, indicating a pronounced squaring of the modulation wave. Under the influence of high electric fields an intermediate phase is observed, which is characterized by a diffuse intensity distribution. In addition, the dielectric permittivity exhibits two maxima, indicating the existence of two separate phase transitions. This behaviour is attributed to distortions of the discommensuration lattice and pinning of the discommensurations by accumulated charged defects. It seems to be characteristic for modulated ferroelectrics of the A(2)BX(4) group, since a similar behaviour is also found in isostructural Rb2ZnCl4 and K2ZnCl4. The soft-mode dynamics close to T-c is found to be essentially independent of the electric field and not affected by the discommensuration lattice.
Title:
Increasing the structural complexity of chromium(IV) oxides by high-pressure and high-temperature reactions of CrO2
Authors:
Castillo-Martinez, E; Arevalo-Lopez, AM; Ruiz-Bustos, R; Alario-Franco, MA Author Full Names: Castillo-Martinez, E.; Arevalo-Lopez, A. M.
Source:
INORGANIC CHEMISTRY 47 (19): 8526-8542 OCT 6 2008
Abstract:
This work presents an overview of a series of increasingly complex oxides synthesized from CrO2, under high-pressure and high-temperature conditions, having C l in octahedral coordination. Although the emphasis is on the structure and microstructure of the compounds as obtained from X-ray diffraction and transmission electron microscopy and diffraction, attention is also given to their interesting electronic and magnetic properties. The study is complemented with an electron energy loss spectroscopic analysis of the different phases. These are the cubic perovskite SrCrO3, the orthorhombic perovskite CaCrO3, the solid solution Sr1-xCaxCrO3, the Ruddlesden-Popper-type Sr3Cr2O7, the family CrSr2RECu2O8 (RE = rare earth), a compositionally modulated perovskite "PbCrO3", and the misfit layer oxide SrO2[CrO2](1.85).
Title:
Transition-metal oxides with triangular lattices: Generation of new magnetic and electronic properties
Authors:
Maignan, A; Kobayashi, W; Hebert, S; Martinet, G; Pelloquin, D; Bellido, N; Simon, C Author Full Names: Maignan, A.; Kobayashi, W.
Source:
INORGANIC CHEMISTRY 47 (19): 8553-8561 OCT 6 2008
Abstract:
The search for multifunctional materials as multiferroics to be applied in microelectronic or for new, chemically stable and nontoxic, thermoelectric materials to recover waste heat is showing a common interest in the oxides whose structures contain a triangular network of transition-metal cations. To illustrate this point, two ternary systems, Ba-Co-O and Ca-Co-O, have been chosen. It is shown that new phases with a complex triangular structure can be discovered, for instance, by introduction of Ga3+ into the Ba-Co-O system to stabilize Ba6Ga2Co11O26 and Ba2GaCo8O14, which both belong to a large family of compounds with formula [Ba(Co,Ga)O3-delta](n)[BaCo8O11]. In the latter, both sublattices contain triangular networks derived from the hexagonal perovskite and the spinel structure. Among the hexagonal perovskite, the Ca3Co2O6 Crystals give clear evidence where the coupling of charges and spins is at the origin of a magnetocapacitance effect. In particular, the ferrimagnetic to ferromagnetic transition, with a one-third plateau on the M(M curve characteristic of triangular magnetism, is accompanied by a peak in the dielectric constant. A second class of cobaltites is the focus of much interest. Their 2D structure, containing CoO2 planes isostructural to a Cdl(2) slice that are stacked in an incommensurate way with rock salt type layers, is referred to misfit cobaltite. The 2D triangular network of edge-shared CoO6 octahedra is believed to be responsible for large values of the Seebeck coefficient and low electrical resistivity. A clear relationship between the structures-incommensurability ratios-and the electronic properties is evidenced, showing that the charge carrier concentration can be tuned via the control of the ionic radius of the cations in the separating layers.
Title:
Phase transitions in [N(CH3)(4)](2)ZnCl4 and [N(CH3)(4)](2)CuCl4 crystals related with the incommensurate modulation existence
Authors:
Sveleba, S; Semotyuk, O; Katerynchuk, I; Kunyo, I; Karpa, I; Pankivskyi, Y Author Full Names: Sveleba, S.; Semotyuk, O.
Source:
ACTA PHYSICA POLONICA A 114 (4): 791-806 OCT 2008
Abstract:
The continuous phase transitions are observed in the crystals with incommensurate phase. They are transitions of parent-incommensurate phases (T-i); transitions between metastable states; phases (T-i). It was set that phase transition between parent and incommensurate phase is a continuous second-order phase transition with a critical index beta = 0.5. The transition between metastable states is, a continuous phase transition through the intermediate temperature region - incommensurate phase. The wave vector changes with the temperature here and wave vector q* = q(1) - q(2) appears, where q(1), q(2) denote commensurate values of incommensurabilty wave vector of neighboring metastable states. It, was shown that the phase transition between incommensurate and commensurate phases is a continuous phase transition.

Update: 24-Oct-2008

Title:
Synthesis and crystal structure of commensurate polymorph of Ln(4)AlCu(2)B(9)O(23) (Ln=Lu,Ho) and refinement of Cu2Al6B4O17
Authors:
Plachinda, PA; Belokoneva, EL Author Full Names: Plachinda, P. A.; Belokoneva, E. L.
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 634 (11): 1965-1970 2008
Abstract:
Single crystals of new Cu,Lu(Ho) - alumoborate and known Cu,Al-borate were synthesized through reaction between CuB2O4 and LnBO(3) on the Al2O3 surface by annealing at 1100 degrees C. Structure of commensurate modification of Ln(4)AlCu(2)B(9)O(23), (Ln = Lu,Ho), sp. gr. P (4) over bar2(1)m, was solved at room temperature. It was found that a low-temperature (110 K) modification possesses incommensurate modulations with modulation vector q =(0, 0, 0.132). The nonaborate block - [B9O23](19-)- 9[6T+3 Delta] forms an isolated unique dense closed anionic unit. This block is terminated by Al-tetrahedrons in the chessboard pattern, resulting in formation of complex alumoborate layer [AlB9O23](16-). Apical oxygen of central BO3 triangle of the nonaborate block seems to be the source of modulations observed in low temperature polymorph. Cationic layers with the Ln and Cu atoms are alternating along c axis with anionic layers. The structure Cu2Al6B4O17, previously studied by the Rietveld method, was corroborated by single crystal data and was compared with LiAl7B4O17.
Title:
Field-induced discommensuration in charge density waves in o-TaS3
Authors:
Inagaki, K; Tsubota, M; Higashiyama, K; Ichimura, K; Tanda, S; Yamamoto, K; Hanasaki, N; Ikeda, N; Nogami, Y; Ito, T; Toyokawa, H Author Full Names: Inagaki, Katsuhiko; Tsubota, Masakatsu
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (9): Art. No. 093708 SEP 2008
Abstract:
We report a synchrotron X-ray Study of charge density waves (CDWs) in an o-TaS3 crystal. We found that two independent CDWs coexist ill the temperature range of 130-50K. These waves are incommensurate and commensurate CDWs with longitudinal wave vectors q(c) = 0.252c* and 0.250c*, respectively. The temperature and electric current dependences of the intensity of the two CDW satellites were measured. We found that the commensurate CDW was converted to the incommensurate CDW at 80 K by inducing current flow. Our observation was interpreted in terms of the dynamics of topological defects. We determined the edge dislocation configuration from the electric Current dependence of the intensity of the two CDWs. The result implies Cor the first time that discommensurations are induced ill the commensurate CDW by applying an electric field.
Title:
Effect of quenched disorder on charge ordering structure in RE(1.67)AE(0.33)NiO(4) (RE = La, Pr, Nd, Sm; AE = Ca, Sr)
Authors:
Yu, XZ; Arima, TH; Seki, S; Asaka, T; Kimoto, K; Tokura, Y; Matsui, Y Author Full Names: Yu, Xiuzhen; Arima, Taka-hisa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (9): Art. No. 093709 SEP 2008
Abstract:
The structure feature of charge ordering (CO) has been investigated for the layered nickelates RE(1.67)AE(0.33)NiO(4) by transmission electron microscopy (TEM). A long-range commensurate CO is observed along the b-axis in Pr1.67Ca0.33NiO4 with minimal quenched disorder, while only a short-range incommensurate CO is observed in Sm1.67Sr0.33NiO4 with larger disorder. Increasing the quenched disorder, hence the number of stacking faults, leads, to an abrupt decrease in CO correlation length, indicating that the quenched disorder plays an important role in the CO collapse process.
Title:
Discovery of polarization flop transition and simultaneous measurements of magnetic ordering and dielectric properties of TmMn2O5
Authors:
Fukunaga, M; Nishihata, K; Kimura, H; Noda, Y; Kohn, K Author Full Names: Fukunaga, Mamoru; Nishihata, Keisuke
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (9): Art. No. 094711 SEP 2008
Abstract:
We have performed simultaneous measurements of magnetic neutron diffraction, ferroelectric D-E hysteresis loops and permittivity along the b- and a-axes of multiferroic TmMn(2)O(5)down to 2.5 K. It was confirmed that the permittivity peak coincides with an increase in both the polarization along the b-axis and a magnetic commensurate phase, which agrees with a previous similar experiment on ErMn2O5. We also discovered it polarization flop from the b-axis to the a-axis below 5 K coincident with a magnetic phase transition from one incommensurate phase to another incommensurate phase, which was confirmed by the simultaneous measurements. Although both phases are almost equivalent in the magnetic propagation wave vector, different magnetic structures induce it completely different ferroelectricity. Ferroelectric hysteresis loops along both the b- and a-axes were clearly observed by the double-wave method.
Title:
Full-field strain evolution during intermartensitic transformations in single-crystal NiFeGa
Authors:
Efstathiou, C; Sehitoglu, H; Carroll, J; Lambros, J; Maier, HJ Author Full Names: Efstathiou, C.; Sehitoglu, H.
Source:
ACTA MATERIALIA 56 (15): 3791-3799 SEP 2008
Abstract:
Using in situ digital image correlation to obtain full-field measurements, we study the intermartensitic transformations in single-crystal NiFeGa. Full-field strain measurements identify the coexistence of modulated martensite phases during the first plateau of the multistage stress-strain Curve at room temperature. At a higher temperature, the measurements indicate the bypassing of one of the modulated phases. Strain as high as 13% is measured as a result of the transformation to the intermediate monoclinic modulated and final tetragonal phase. Based on the full-field strain measurements, the phase fractions during the nucleation and the progression of the transformation are obtained. The evolution of the local strain and the phase fractions prove critical in explaining strain softening, hysteresis and other phenomena observed in the stress-strain curves. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Orientational ordering in the low-temperature stable phases of deuterated thiophene
Authors:
Damay, F; Rodriguez-Carvajal, J; Andre, D; Dunstetter, F; Szwarc, H Author Full Names: Damay, F.; Rodriguez-Carvajal, J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 589-595 Part 5 OCT 2008
Abstract:
The stable structures of deuterated thiophene C4D4S were investigated at 155 (phase III), 115 (phase IV), 100 and 1.5 K (phase V) by neutron powder diffraction. At 155 K, thiophene is orthorhombic with space group Pbnm. Although there is some degree of in-plane orientational disorder, molecules begin to order along two symmetrically equivalent main orientations. At 115 K the structure is incommensurate, with a wavevector q similar or equal to 0.55a*. At 100 K and below, there is a doubling of the a cell parameter and the structure space group is P2(1). For the first time, it is shown that, unlike C4H4S, phase V of C4D4S is not an orientational glass: thiophene molecules are perfectly ordered and are oriented within the molecular plane along two alternating directions, corresponding to the two main orientations observed at 155 K. This ordering probably originates in the slowing down of the in-plane reorientational dynamics upon deuteration.

Update: 17-Oct-2008

Title:
Structural and magnetic properties of the ferroelectric magnet BaMn1-xZnxF4, a site diluted square-lattice two-dimensional Heisenberg antiferromagnet with S=5/2
Authors:
Veira, JR; Argyriou, DN; Kiefer, K; Wolter, AUB; Alber, D; Meissner, M; Almairac, R; Reehuis, M; Bordallo, HN Author Full Names: Veira, J. R.; Argyriou, D. N.; Kiefer, K.; Wolter, A. U. B.; Alber, D.; Meissner, M.; Almairac, R.; Reehuis, M.; Bordallo, H. N.
Source:
PHYSICAL REVIEW B 78 (5): Art. No. 054104 AUG 2008
Abstract:
The influence of Zn doping on the structural and magnetic properties of multiferroic BaMnF4 has been investigated using temperature dependent x-ray diffraction and magnetization measurements. With increasing Zn content the transition temperatures of the structural incommensurate phase transition as well as the AF ordering decrease. For x=0.75 no incommensurate phase is found anymore. The suppression of the structural transition can be explained due to the smaller size of Zn compared with Mn. The suppression of the antiferromagnetic ordering can be explained by a site dilution of the magnetic structure with nonmagnetic Zn. The percolation threshold is found to be x(p)=0.393(4). This is in agreement with predictions for a site-diluted square-lattice weak-anisotropy two-dimensional Heisenberg antiferromagnet with S = 5/2.
Title:
Origin of incommensurate modulations in the high-pressure phosphorus IV phase
Authors:
Marques, M; Ackland, GJ; Lundegaard, LF; Falconi, S; Hejny, C; McMahon, MI; Contreras-Garcia, J; Hanfland, M Author Full Names: Marques, M.; Ackland, G. J.; Lundegaard, L. F.; Falconi, S.; Hejny, C.; McMahon, M. I.; Contreras-Garcia, J.; Hanfland, M.
Source:
PHYSICAL REVIEW B 78 (5): Art. No. 054120 AUG 2008
Abstract:
We present results from x-ray diffraction experiments and density functional theory calculations which provide a fully consistent picture of the high-pressure phosphorus-IV phase (P-IV). P-IV has an incommensurately-modulated crystal structure described by the four-dimensional superspace group Cmmm(00 gamma)s00. Electronic structure calculations using a three-dimensional commensurate approximant to this structure give excellent agreement with experiment for the structural parameters and their variation with pressure. Density functional perturbation theory shows a phonon instability at the incommensurate wave vector, related to the opening of a pseudogap at the Fermi surface, showing that the atomic motions comprising the incommensuration occur to eliminate Fermi-surface nesting. Unusually, the pseudogap opens not at the incommensurate wave vector (00 gamma) itself, but at two larger wave vectors corresponding to strong reflections in the diffraction pattern.
Title:
Nucleation and growth of a quasicrystalline monolayer: Bi adsorption on the fivefold surface of i-Al70Pd21Mn9
Authors:
Smerdon, JA; Parle, JK; Wearing, LH; Lograsso, TA; Ross, AR; McGrath, R Author Full Names: Smerdon, J. A.; Parle, J. K.; Wearing, L. H.; Lograsso, T. A.; Ross, A. R.; McGrath, R.
Source:
PHYSICAL REVIEW B 78 (7): Art. No. 075407 AUG 2008
Abstract:
Scanning tunneling microscopy has been used to study the formation of a Bi monolayer deposited on the fivefold surface of i-Al70Pd21Mn9. Upon deposition of low submonolayer coverages, the nucleation of pentagonal clusters of Bi adatoms of edge length 4.9 angstrom is observed. The clusters have a, common orientation leading to a film with fivefold symmetry. By inspection of images where both the underlying surface and the Bi atoms are resolved, the pentagonal clusters are proposed to nucleate on pseudo-Mackay clusters truncated such that a Mn atom lies centrally in the surface plane. The density of these sites is sufficient to form a quasiperiodic framework, and subsequent adsorption of Bi atoms ultimately leads to the formation of a quasicrystalline monolayer. The suggested nucleation site is different from that proposed on the basis of recent density-functional theory calculations.
Title:
Neutron powder diffraction study of the magnetic and crystal structures of SrFe2(PO4)(2)
Authors:
Belik, AA; Huang, QZ; Takayama-Muromacchi, E; Lynn, JW Author Full Names: Belik, Alexei A.; Huang, Qingzhen; Takayama-Muromacchi, Eiji; Lynn, Jeffrey W.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 181 (9): 2292-2297 SEP 2008
Abstract:
The crystal and magnetic structures of SrFe22+(PO4)(2) have been determined by neutron powder diffraction data at low temperatures (space group P2(1)/c (no. 14); Z=4: a=9.35417(13)angstrom, b = 6.83808(10) angstrom, c = 10.51899(15) angstrom, and beta = 109.5147(7)degrees at 15 K). Two magnetic phase transitions were found at T-1 = 7.4 K (first-order phase transition) and T-2 = 11.4 K (second-order phase transition). The transition at T2 was hardly detectable by dc and ac magnetization measurements, and a small anomaly was observed by specific heat measurements. At T1, strong anomalies were found by dc and ac magnetization and specific heat. The structure of SrFe2(PO4)(2) consists of linear four-spin cluster units, Fe2-Fe1-Fe1-Fe2. Below T-1, the propagation vector of the magnetic structure is k [0,0,0]. The magnetic moments of the inner Fe1-Fe1 atoms of the four-spin cluster unit are ferromagnetically coupled. The magnetic moment of the outer Fe2 atom is also ferromagnetically Coupled with that of the Fe1 atom but with spin canting. The four-spin cluster units form ferromagnetic layers parallel to the [-101] plane, while these layers are stacked antiferromagnetically in the [-101] direction. Spill canting of the Outer Fe2 atoms provides a weak ferromagnetic moment of about 1 (mu B) along the b-axis. The refined magnetic moments at 3.5 K are 4.09 (mu B) for Fe1 and 4.07 (mu B) for Fe2. Between T-1 and T-2, a few weak magnetic reflections were observed probably due to incommensurate magnetic order. (C)2008 Elsevier Inc. All rights reserved.

Update: 10-Oct-2008

Title:
Devitrification of mechanically alloyed Zr-Ti-Nb-Cu-Ni-Al glassy powders studied by time-resolved X-ray diffraction
Authors:
Scudino, S; Sordelet, DJ; Eckert, J Author Full Names: Scudino, S.; Sordelet, D. J.; Eckert, J.
Source:
REVIEWS ON ADVANCED MATERIALS SCIENCE 18 (3): 221-224 AUG 2008
Abstract:
The crystallization of mechanically alloyed Zr67Ti6.14Nb1.92Cu10.67Ni8.52Al5.75 glassy powder is investigated by time-resolved X-ray diffraction. The powder displays a multi-step crystallization behavior characterized by the formation of a metastable nanoscale quasicrystalline phase during the first stage of the crystallization process. At higher temperatures, coinciding with the second crystallization event, the amorphous-to-quasicrystalline transformation is followed by the precipitation of the tetragonal Zr2Cu phase (space group 14/mmm) and the tetragonal Zr2Ni phase (space group 14/mcm). The transformations are gradual and the quasicrystals and the subsequent phases coexist over a temperature interval of about 25K.
Title:
Manipulating the magnetic structure of Co Core/CoO shell nanoparticles: Implications for controlling the exchange bias
Authors:
Inderhees, SE; Borchers, JA; Green, KS; Kim, MS; Sun, K; Strycker, GL; Aronson, MC Author Full Names: Inderhees, S. E.; Borchers, J. A.; Green, K. S.; Kim, M. S.; Sun, K.; Strycker, G. L.; Aronson, M. C.
Source:
PHYSICAL REVIEW LETTERS 101 (11): Art. No. 117202 SEP 12 2008
Abstract:
We present an experimental study of the effects of oxidation on the magnetic and crystal structures of exchange biased epsilon-Co/CoO core-shell nanoparticles. Transmission electron microscopy measurements reveal that oxidation creates a Co-CoO interface which is highly directional and epitaxial in quality. Neutron diffraction measurements find that below a Neel temperature T-N of similar to 235 K the magnetization of the CoO shell is modulated by two wave vectors, q(1)= (1/2 1/2 1/2)2 pi/alpha and q(2) = (100)2 pi/alpha. Oxidation affects the q(1) component of the magnetization very little, but hugely enhances the q(2) component, resulting in the magnetic decompensation of the core-shell interface. We propose that the large exchange bias effect results from the highly ordered interface between the Co core and CoO shell, and from enhanced core-shell coupling by the uncompensated interface moment.
Title:
Nature of the magnetic order in Ca3Co2O6
Authors:
Agrestini, S; Chapon, LC; Daoud-Aladine, A; Schefer, J; Gukasov, A; Mazzoli, C; Lees, MR; Petrenko, OA Author Full Names: Agrestini, S.; Chapon, L. C.; Daoud-Aladine, A.; Schefer, J.; Gukasov, A.; Mazzoli, C.; Lees, M. R.; Petrenko, O. A.
Source:
PHYSICAL REVIEW LETTERS 101 (9): Art. No. 097207 AUG 29 2008
Abstract:
We present a detailed powder and single-crystal neutron diffraction study of the spin chain compound Ca3Co2O6. Below 25 K, the system orders magnetically with a modulated partially disordered antiferromagnetic structure. We give a description of the magnetic interactions in the system which is consistent with this magnetic structure. Our study also reveals that the long-range magnetic order coexists with a shorter-range order with a correlation length scale of similar to 180 angstrom in the ab plane. Remarkably, on cooling, the volume of material exhibiting short-range order increases at the expense of the long-range order.
Title:
Frustration-induced quantum phases in mixed spin chain with frustrated side chains
Authors:
Hida, K; Takano, K Author Full Names: Hida, Kazuo; Takano, Ken'ichi
Source:
PHYSICAL REVIEW B 78 (6): Art. No. 064407 AUG 2008
Abstract:
A mixed Heisenberg spin chain with frustrated side chains is investigated by numerical and perturbational calculations. A frustration-induced quantum partially polarized ferrimagnetic phase and a nonmagnetic spin quadrupolar phase are found adjacent to the conventional Lieb-Mattis-type ferrimagnetic phase or the nonmagnetic singlet cluster solid phases. The partially polarized ferrimagnetic phase has an incommensurate spin structure. Similar structures are commonly found in other frustration-induced partially polarized ferrimagnetic phases. Numerical results also suggest a series of almost critical nonmagnetic ground states in a highly frustrated regime if the side chain spins weakly couple to the main chain.
Title:
Noncollinear magnetism in the high-pressure hcp phase of iron
Authors:
Lizarraga, R; Nordstrom, L; Eriksson, O; Wills, J Author Full Names: Lizarraga, Raquel; Nordstroem, Lars; Eriksson, Olle; Wills, John
Source:
PHYSICAL REVIEW B 78 (6): Art. No. 064410 AUG 2008
Abstract:
The magnetic structure of iron in its high-pressure hcp phase has been investigated with the full-potential augmented plane wave with local orbitals method that allows for noncollinear magnetism. In our study we consider different spin spiral structures and, three antiferromagnetic configurations that have been previously discussed in the literature. We found that some of the magnetic structures are only metastable, and that a nonsymmetric incommensurate spin spiral state with wave vector q = (0.56, 0.22, 0)2 pi/a and two different antiferromagnetic structures are the most stable ones being almost degenerate around the equilibrium volume. These magnetic structures ought to exist in the pressure range where hcp iron becomes stable.
Title:
Soft x-ray induced Ag diffusion in amorphous pulse laser deposited As50Se50 thin films: An x-ray photoelectron and secondary ion mass spectroscopy study
Authors:
Kalyva, M; Siokou, A; Yannopoulos, SN; Wagner, T; Krbal; Orava, J; Frumar, M Author Full Names: Kalyva, M.; Siokou, A.; Yannopoulos, S. N.; Wagner, T.; Krbal; Orava, J.; Frumar, M.
Source:
JOURNAL OF APPLIED PHYSICS 104 (4): Art. No. 043704 AUG 15 2008
Abstract:
In the present paper, x-ray photoelectron spectroscopy (XPS) is used to induce and study the Ag diffusion and dissolution in pulsed laser deposited As50Se50 amorphous chalcogenide films. Dynamic secondary ion mass spectroscopy (SIMS) is also employed to investigate the Ag atomic concentration in depth. Dynamic SIMS measurements reveal that even before x-ray irradiation a considerable percentage of the total silver amount diffuses into the matrix forming an similar to 70 nm mixed Ag-Se-As layer. XPS analysis shows that x-ray irradiation induces further diffusion of silver into the chalcogenide matrix. At the end of the procedure silver is found to be homogeneously dissolved into the matrix leaving only a 5-7 nm thick surface layer with excess silver concentration. In this surface layer stable Ag2Se clusters existing probably in quasicrystalline form prohibit further diffusion. The origin of the mechanism of the x-ray induced Ag diffusion and dissolution in amorphous chalcogenides is discussed in light of the present results. (c) 2008 American Institute of Physics.
Title:
Disordered structures of the TM-Mg-Zn 1/1 quasicrystal approximants (TM = Hf, Zr, or Ti) and chemical intergrowth
Authors:
Gomez, CP; Ohhashi, S; Yamamoto, A; Tsai, AP Author Full Names: Gomez, Cesar Pay; Ohhashi, Satoshi; Yamamoto, Akiji; Tsai, An Pang
Source:
INORGANIC CHEMISTRY 47 (18): 8258-8266 SEP 15 2008
Abstract:
The structures of three quasicrystal approximant phases in the TM-Mg-Zn (TM = Hf, Zr, Ti) systems with the analyzed compositions Hf5Mg18Zn77, Zr5Mg18Zn77, and Ti5.5Mg17.5Zn77 have been synthesized, and their structures have been analyzed by single-crystal X-ray diffraction. The structure analyses revealed that these cubic phases with the space group Pm contain two different rhombic-triacontahedral clusters. These clusters are so-called Bergman-type atomic clusters and previously known approximants of face-centered icosahedral (F-type) quasicrystals are composed only of Mackay-type clusters, thus these compounds are seen as new prototype structures. Electron density maps calculated by the maximum entropy method (MEM) show that one of the atomic clusters displays characteristic structural disorder. The disorder in these phases is related to the chemical intergrowth of different Friauf polyhedra, and the prospects of new guide lines for finding quasicrystals composed of such polyhedra are discussed.

Update: 3-Oct-2008

Title:
Structure and microstructure of the high pressure synthesised misfit layer compound [Sr2O2][CrO2](1.85)
Authors:
Castillo-Martinez, E; Schonleber, A; van Smaalen, S; Arevalo-Lopez, AM; Alario-Franco, MA Author Full Names: Castillo-Martinez, E.; Schoenleber, A.; van Smaalen, S.; Arevalo-Lopez, A. M.; Alario-Franco, M. A.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 181 (8): 1840-1847 AUG 2008
Abstract:
The strontium chromium oxide [Sr2O2][CrO2](1.85) misfit layer compound has been synthesised at high-pressure and high-temperature conditions. Electron diffraction patterns and high-resolution transmission electron microscopy images along [001] show the misfit character of the different layers composing the structure with a supercell along the incommensurate parameter b approximate to 7b(1)approximate to 13b(2). The modulated crystal structure has been refined within the superspace formalism against single-crystal X-ray diffraction data, employing the (3+1)-dimensional superspace group C'nrnb(0 sigma(2)0)0 0s. The compound has a composite structure with lattice parameters a(1) =5.182(1)angstrom, b(1) = 5.471(1)angstrom, c(1) = 18.194(3)angstrom for the first, SrO, subsystem and the same a and c, but with 152 = 2.925(1) angstrom for the second, CrO2, subsystem. The layer stacking is similar to that of orthorhombic PbS(TiS2)(1.18), but with a much stronger intersubsytem bonding in the case of the oxide. The intersubsystem lattice mismatch is mainly handled by displacement modulations of the Sr atoms, correlated with modulations of the valence, the coordination and the anisotropic displacement parameters. (C) 2008 Elsevier Inc. All rights reserved.
Title:
Single-crystal NMR for the layered semiconductor TlGaSe2
Authors:
Panich, AM; Kashida, S Author Full Names: Panich, A. M.; Kashida, S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (39): Art. No. 395211 OCT 1 2008
Abstract:
We report on a Ga-69 and Tl-205 NMR study of single-crystal thallium gallium selenide. Our findings show that transformation from the high temperature paraelectric phase to the low temperature ferroelectric phase occurs via an incommensurate phase that exists in the temperature range from T-c = 107.5 to T-i = 118 K. On approaching phase transition at Ti from above, the crystal exhibits soft mode behavior, which is somewhat different for thallium and gallium substructures. Redistribution of Ga-69 line intensities with temperature in the ferroelectric phase indicates a variation of the domain structure of this phase.

Update: 26-Sep-2008

Title:
Microstructure of Al-Mn-Be melt-spun ribbons
Authors:
Zupanic, F; Boncina, T; Sustarsic, B; Anzel, I; Markoli, B Author Full Names: Zupanic, Franc; Boncina, Tonica; Sustarsic, Borivoj; Anzel, Ivan; Markoli, Bostjan
Source:
MATERIALS CHARACTERIZATION 59 (9): 1245-1251 SEP 2008
Abstract:
Microstructures of two alloys with the nominal compositions of Al92Mn3Be5 and Al89Mn6Be5 were characterized in the initial as-cast condition (after vacuum induction melting and casting) and after melt spinning. In the initial conditions, both alloys consisted of an aluminum-rich solid solution and two metastable intermetallic phases: Be4AlMn and Al10Mn3(Be). Both alloys melted over a rather large temperature range (between 230 degrees C and 310 degrees C). This was the main reason for the presence of unmelted particles in the melt-spun ribbons. Nonetheless, with the use of optimized melt-spinning parameters a microstructure composed of the Al-rich solid solution and finely dispersed quasicrystalline particles in ribbons with thicknesses ranging from 30-200 mu m was achieved. The dispersion of quasicrystalline particles was finest on the wheel side of the thinnest ribbons, attaining microhardness values between 250 HV and 300 HV. (C) 2007 Elsevier Inc. All rights reserved.

Update: 19-Sep-2008

Title:
Synthesis and characterization of GaP nanochains with a twin-modulated quasi-periodic structure
Authors:
Liu, YK; Shan, YY; Wang, HB; Lee, CS; Lee, ST Author Full Names: Liu, Y. K.; Shan, Y. Y.; Wang, H. B.; Lee, Chun-Shen; Lee, Shu-Tong
Source:
SUPERLATTICES AND MICROSTRUCTURES 44 (2): 208-215 AUG 2008
Abstract:
GaP nanochains have been synthesized by hydrogen-assisted thermal evaporation, and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and Raman spectroscopy. GaP nanochains possess a (111) twin crystal plane-modulated quasi-periodic structure, that gives a strong green photoluminescence at 618 nm. While the Raman spectrum of the nanochains is similar to that of the GaP crystal, the intensity of the longitudinal optical (LO) peak is stronger than that of the transverse optical (TO) peak, which is supposedly related to the nanochain microstructures. (C) 2008 Published by Elsevier Ltd.
Title:
Interaction between the chain and ladder subsystems in (Ca, Sr, La)(14)Cu24O41 compounds
Authors:
Schwingenschlogl, U; Schuster, C Author Full Names: Schwingenschloegl, U.; Schuster, C.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (38): Art. No. 382201 SEP 24 2008
Abstract:
We investigate the influence of structural modulations on the electronic properties of incommensurate (Ca, Sr, La)(14)Cu24O41 compounds by band structure calculations based on density functional theory and the local density approximation (LDA). Using a supercell approach with ten CuO2 chain and seven Cu2O3 ladder segments, we take into account the major effects of the structural incommensurability. We find that the LDA electronic states show very little response to these modulations. The coupling between the electronic and structural degrees of freedom, hence, can be well described in terms of two independent subsystems. The incommensurate charge density waves (CDWs) in the chains and the ladders are formed independently of each other.
Title:
Directional growth and characterizations of orthorhombic HoMnO3 films
Authors:
Lin, JG; Han, TC; Wu, CT; Chu, MW; Chen, CH Author Full Names: Lin, J. G.; Han, T. C.; Wu, C. T.; Chu, M. -W.; Chen, C. H.
Source:
JOURNAL OF CRYSTAL GROWTH 310 (16): 3878-3880 AUG 1 2008
Abstract:
In this work, we synthesize the orthorhombic HoMnO3 films on the SrTiO3(1 0 0) and LaAlO3(1 1 0) substrates by pulsed laser deposition and study their crystalline and magnetic properties. The orthorhombic HoMnO3 film with its b-axis perpendicular to the film surface is grown on the LaAlO3(1 1 0) substrate, and shows clearly three magnetic transitions at 45, 10 and 7K, which are attributed to the magnetization process of incommensurate spin structure of Mn3+ for 10K
Title:
Evolution of a nanocrystalline (Co,Ni)Al2O4 spinel phase from quasicrystalline precursor
Authors:
Yadav, TP; Tiwari, RS; Srivastava, ON; Mukhopadhyay, NK Author Full Names: Yadav, Thakur Prasad; Tiwari, Radhey Shyam; Srivastava, Onkar Nath; Mukhopadhyay, Nilay Krishna
Source:
INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY 5 (5): 449-457 2008
Abstract:
This work reports on the synthesis of a spinel phase from a thermodynamically stable decagonal quasicrystalline Al70Co15Ni15 alloy. The Al70Co15Ni15 alloy, synthesized through slow cooling of the molten alloy, was subjected to milling in an attritor ball mill at 400 rpm for 5, 10, 20, 30, and 40 h with a ball to powder ratio of 20:1 in the hexane medium. The differential thermal analysis, X-ray diffraction, scanning, and transmission electron microscopy techniques have been used for characterization of milled as well as annealed powders. The Voigt function analysis has been used for calculation of the effective crystallite size and relative strain of ball-milled samples. The crystallite size has been found to be similar to 14 nm after 40 h of milling along with a lattice strain of 8.1%. The annealing experiments have been carried out under two different conditions: (i) in vacuum and (ii) in air. The results of the present investigation clearly revealed that the nano-decagonal phase was stable in vacuum while annealing at 600 degrees C for 40 h. However, during annealing under a similar condition in air, the formation of a nanospinel of (Ni,Co)Al2O4 of size similar to 60 nm was identified. The possible structural evolution of the spinel from the quasicrystalline phase has been discussed.

Update: 12-Sep-2008

Title:
Temperature behavior of magnetic susceptibility and paramagnetism of the conduction electrons of an icosahedral quasicrystal Al63Cu25Fe12
Authors:
Prekul, AF; Shchegolikhina, NI; Shalaeva, EV Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.; Shalaeva, E. V.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 106 (2): 157-163 AUG 2008
Abstract:
Problem of the origin of the enhanced paramagnetism of icosahedral phases below room temperature is studied experimentally. Temperature dependences of the magnetic susceptibility (chi(T)), Hall constant (R-H(T)), and conductivity (chi(T)) of the i phase of a nominal composition of Al63Cu25Fe12 are studied at temperatures of 4.2-400 K in magnetic fields of to 5 T. Temperature-dependent components of these quantities, namely, sigma (t) , chi(t) , and R-t were separated. The temperature-dependent component of the magnetic susceptibility chi(t) is approximately proportional to T-2. The number of thermally-induced charge carries n (t) and the ratio chi(t)/n (t) are approximately proportional to T-3 and T-1, respectively. Thus, we found two distinctive criteria indicating that temperature-induced changes in the conduction-electron paramagnetism play a substantial role in the magnetic properties of icosahedral phases at low temperatures. Earlier, these changes were considered to be substantial only at temperatures above the Debye temperature.
Title:
Local density of states of one-dimensional Mott insulators and charge-density wave states with a boundary
Authors:
Schuricht, D; Essler, FHL; Jaefari, A; Fradkin, E Author Full Names: Schuricht, Dirk; Essler, Fabian H. L.; Jaefari, Akbar; Fradkin, Eduardo
Source:
PHYSICAL REVIEW LETTERS 101 (8): Art. No. 086403 AUG 22 2008
Abstract:
We determine the local density of states of one-dimensional incommensurate charge-density wave states in the presence of a strong impurity potential, which is modeled by a boundary. We find that the charge-density wave gets pinned at the impurity, which results in a singularity in the Fourier transform of the local density of states at momentum 2k(F). At energies above the spin gap we observe dispersing features associated with the spin and charge degrees of freedom, respectively. In the presence of an impurity magnetic field we observe the formation of a bound state localized at the impurity. All of our results carry over to the case of 1D Mott insulators by exchanging the roles of spin and charge degrees of freedom. We discuss the implications of our result for scanning tunneling microscopy experiments on spin-gap systems such as two-leg ladder cuprates.
Title:
On the nature and stability of phases present in a rapidly solidified aluminium alloy 7010 containing scandium
Authors:
Prasad, KS; Mukhopadhyay, AK; Majumdar, B; Akhtar, D Author Full Names: Prasad, K. S.; Mukhopadhyay, A. K.; Majumdar, B.; Akhtar, D.
Source:
MATERIALS AND MANUFACTURING PROCESSES 23 (7): 658-664 2008
Abstract:
The influence of Sc on the nature and stability of phases present in rapidly solidified (RS) Al alloy 7010 (hereafter termed base alloy) produced by melt spinning were examined and compared with the phases present in the same alloys when produced by the conventional ingot metallurgical (IM) route. Transmission electron microscopy (TEM) revealed that the second phases present in the IM alloys have an HCP structure but with varying lattice parameters. On the other hand, the second phase particles present in the base alloy when produced by rapid solidification (RS) route always have a quasi-crystalline, icosahedral structure. In the rapidly solidified 7010+Sc alloy, however, the icosahedral phase is located only at the grain boundary triple point junctions, and the grain interfaces are populated by the second phase particles having an HCP structure. An analysis of the chemistry of the second phase particles revealed that the icosahedral phase is stabilized by certain minimum concentrations of Zn+Mg/Zn+Mg+Cu. The reason for the absence of the icosahedral phase at the grain interfaces of the rapidly solidified 7010+Sc alloy is the partitioning of relatively lower concentrations of the major alloying elements into the second phases formed at those sites. Micro-hardness measurements revealed higher hardness values for the RS 7010+Sc alloy in both as-melt spun as well as artificially aged conditions. These results are correlated with the microstructures developed in these materials.
Title:
Approximant phases and an icosahedral quasicrystal in the Ca-Au-Ga system: The influence of size of gallium versus indium
Authors:
Lin, QS; Corbett, JD Author Full Names: Lin, Qisheng; Corbett, John D.
Source:
INORGANIC CHEMISTRY 47 (17): 7651-7659 SEP 1 2008
Abstract:
Two crystalline approximants (ACs) and their corresponding icosahedral quasicrystal (i-QC) are obtained in the Ca-Au-Ga system through conventional solid-state exploratory syntheses. Single crystal structural analyses reveal that the 1/1 AC, Ca3AuxGa19-x (x = similar to 9.3-12.1) [Im3, a = 14.6941(6)-14.7594(6) angstrom], has the empty cubes in the prototypic YCd6 (= Y3Cd18) now fully occupied by Ga, resulting in a 3:19 stoichiometry. In parallel, the distorted cubes in the 2/1 AC, Ca13Au57.1Ga23.4 [Pa3, a = 23.9377(8) angstrom] are fully or fractionally occupied by Ga. The valence electron count per atom (e/a) for the 2/1 AC (1.64) is smaller than that over the 1/1 AC composition range (1.76-2.02), and the e/a of the Ca15.2Au50.3Ga34.5 i-QC, 1.84, is somewhat distant from typical values for Tsai-type i-QCs (similar to 2.0). Comparisons of the gallium results with the corresponding In phases suggest that the structural differences result mainly from size rather than electronic factors. The 1/1 and 2/1 appear to be thermodynamically stable on slow cooling, as usual, whereas the i-QC isolated by quenching decomposes on heating at similar to 660 degrees C, mainly into 2/1 AC and Ca-3(Au,Ga)(11). Calculations of the electronic structure of 1/1 AC suggest that the Fermi sphere-Brillouin zone interactions remain important for the Ca-Au-Ga i-QC.

Update: 5-Sep-2008

Title:
Incommensurate spin-density modulation in a copper oxide chain compound with commensurate charge order
Authors:
Raichle, M; Reehuis, M; Andre, G; Capogna, L; Sofin, M; Jansen, M; Keimer, B Author Full Names: Raichle, M.; Reehuis, M.; Andre, G.; Capogna, L.; Sofin, M.; Jansen, M.; Keimer, B.
Source:
PHYSICAL REVIEW LETTERS 101 (4): Art. No. 047202 JUL 25 2008
Abstract:
Neutron diffraction has been used to determine the magnetic structure of Na8Cu5O10, a stoichiometric compound containing chains based on edge-sharing CuO4 plaquettes. The chains are doped with 2/5 hole per Cu site and exhibit long-range commensurate charge order with an onset well above room temperature. Below T-N = 23 K, the neutron data indicate long-range collinear magnetic order with a spin-density modulation whose propagation vector is commensurate along, and incommensurate perpendicular to, the chains. Competing interchain exchange interactions are discussed as a possible origin of the incommensurate magnetic order.
Title:
Magnetic ground state and transition of a quantum multiferroic LiCu2O2
Authors:
Huang, SW; Huang, DJ; Okamoto, J; Mou, CY; Wu, WB; Yeh, KW; Chen, CL; Wu, MK; Hsu, HC; Chou, FC; Chen, CT Author Full Names: Huang, S. W.; Huang, D. J.; Okamoto, J.; Mou, C. Y.; Wu, W. B.; Yeh, K. W.; Chen, C. L.; Wu, M. K.; Hsu, H. C.; Chou, F. C.; Chen, C. T.
Source:
PHYSICAL REVIEW LETTERS 101 (7): Art. No. 077205 AUG 15 2008
Abstract:
Based on resonant soft x-ray magnetic scattering, we report that LiCu2O2 exhibits a large interchain coupling which suppresses quantum fluctuations along spin chains, and a quasi-2D short-range magnetic order prevails at temperatures above the magnetic transition. These observations unravel the fact that the ground state of LiCu2O2 possesses long-range 2D-like incommensurate magnetic order rather than being a gapped spin liquid as expected from the nature of quantum spin-1/2 chains. In addition, the spin coupling along the c axis is found to be essential for inducing electric polarization.
Title:
The synthesis and characterization of new [(BiSe)(1.10)](m)[NbSe2](n), [(PbSe)(1.10)](m)[NbSe2](n), [(CeSe)(1.14)](m)[NbSe2](n) and [(PbSe)(1.12)](m)[TaSe2](n) misfit layered compounds
Authors:
Heideman, C; Nyugen, N; Hanni, J; Lin, Q; Duncombe, S; Johnson, DC; Zschack, P Author Full Names: Heideman, Colby; Nyugen, Ngoc; Hanni, Jonathan; Lin, Qiyin; Duncombe, Scott; Johnson, David C.; Zschack, Paul
Source:
JOURNAL OF SOLID STATE CHEMISTRY 181 (7): 1701-1706 JUL 2008
Abstract:
Fifty-three new misfit layered compounds within the [(BiSe)(1.10)](m)[NbSe2](n), [(PbSe)(1.10)](m)[NbSe2](n), [(CeSe)(1.14)](m)[NbSe2](n) and [(PbSe)(1.12)](m)[TaSe2](n) families of compounds were successfully synthesized. This is the first report of compounds with n and m larger than 3, as self-assembly from designed precursors allows Compounds with particular n and m values to be selectively prepared. The compounds form as crystallographically aligned films, with the c-axis perpendicular to the Substrate, The Compounds are well ordered along the c-axis and in the ab plane, with shorter coherence lengths between the constituent layers. All 18 compounds that were measured were found to be metallic. (C) 2008 Elsevier Inc. All rights reserved.
Title:
The role of nanoquasicrystals on the ductility enhancement of as-extruded Mg-Zn-Gd alloy at elevated temperature
Authors:
Liu, Y; Yuan, GY; Lu, C; Ding, WJ; Jiang, JZ Author Full Names: Liu, Yong; Yuan, Guangyin; Lu, Chen; Ding, Wenjiang; Jiang, Jiangzhong
Source:
JOURNAL OF MATERIALS SCIENCE 43 (16): 5527-5533 AUG 2008
Abstract:
The microstructure and mechanical properties of Mg3.5Zn0.6Gd alloy containing quasicrystals was investigated after extrusion, the role of nanoquasicrystals on the ductility of alloy was analyzed. The results indicate that nanoquasicrystal was formed and distributed along grain boundary and in the matrix for Mg3.5Zn0.6Gd alloy after extrusion. As-extruded Mg3.5Zn0.6Gd alloy containing I-phase showed one relatively random and homogeneous texture due to the local lattice rotation during deformation. The Mg3.5Zn0.6Gd alloy extruded at 673 K exhibits larger elongation about 94% at 473 K, which could been ascribed to the combination of random texture and higher content of I-phase precipitated during extrusion at higher temperature. The a + c type dislocations can be effectively active due to the existence of nanoquasicrystals. The strengthening mechanism of Mg3.5Zn0.6Gd alloy can be explained as the dislocations annihilation effect. This annihilation of dislocations can play a role in the increase of flow strain during deformation.
Title:
Low thermal conductivity in nanoscale layered materials synthesized by the method of modulated elemental reactants
Authors:
Chiritescu, C; Cahill, DG; Heideman, C; Lin, QY; Mortensen, C; Nguyen, NT; Johnson, D; Rostek, R; Bottner, H Author Full Names: Chiritescu, Catalin; Cahill, David G.; Heideman, Colby; Lin, Qiyin; Mortensen, Clay; Nguyen, Ngoc T.; Johnson, David; Rostek, Raimar; Boettner, Harald
Source:
JOURNAL OF APPLIED PHYSICS 104 (3): Art. No. 033533 AUG 1 2008
Abstract:
We report the room-temperature, cross-plane thermal conductivities, and longitudinal speeds of sound of multilayer films [(TiTe2)(3)(Bi2Te3)(x)(TiTe2)(3)(Sb2Te3)(y)](i) (x=1-5, y=1-5) and misfit-layer dichalcogenide films [(PbSe)(m)(TSe2)(n)](i) (T=W or Mo, m=1-5, and n=1-5) synthesized by the modulated elemental reactants method. The thermal conductivities of these nanoscale layered materials fall below the predicted minimum thermal conductivity of the component compounds: two times lower than the minimum thermal conductivity of Bi2Te3 for multilayer [(TiTe2)(3)(Bi2Te3)(x)(TiTe2)(3)(Sb2Te3)(y)](i) films and five to six times lower than the minimum thermal conductivity of PbSe for misfit-layer dichalcogenides [(PbSe)(m)(TSe2)(n)](i). We attribute the low thermal conductivities to the anisotropic bonding of the layered crystals and orientational disorder in the stacking of layered crystals along the direction perpendicular to the surface. (C) 2008 American Institute of Physics.

Update: 29-Aug-2008

Title:
Reducing the positional modulation of NbO6-octahedra in SrxBa1-xNb2O6 by increasing the barium content: A single crystal neutron diffraction study at ambient temperature for x=0.61 and x=0.34
Authors:
Schefer, J; Schaniel, D; Petricek, V; Woike, T; Cousson, A; Wohlecke, M Author Full Names: Schefer, Juerg; Schaniel, Dominik; Petricek, Vaclav; Woike, Theo; Cousson, Alain; Woehlecke, Manfred
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 223 (6): 399-407 2008
Abstract:
We report on the influence of the barium content on the modulation amplitude in SrxBa1-xNb2O6 compounds by comparing Sr0.61Ba0.39Nb2O6 (SBN61) and Sr0.34Ba0.66Nb2O6 (SBN34). Our single crystal neutron diffraction results demonstrate that the amplitude of the positional modulation of the NbO6 octahedra is reduced with increasing barium content, indicating that the origin of the modulation is the partial occupation of the pentagonal channels by Sr and Ba atoms. By increasing the Sr content the bigger Ba atoms are replaced by the smaller Sr atoms, which leads to a larger deformation of the surrounding lattice and hence to a larger modulation amplitude. The more homogeneous the filling of these channels with one atomic type (Ba) the lower the modulation amplitude. Our results also show that the structure can be described with a two-dimensional incommensurate harmonic modulation. No second order modulation has been observed, both by single crystal diffraction measurements and q-scans. The positional modulation of the Nb atoms is much smaller than that of the oxygen atoms, such that the modulation can be seen as a rotational modulation of almost rigid NbO6-octahedra.
Title:
Icosahedral quasicrystal phase in Al15Mg50Zn35 ternary alloy by rapid quenching
Authors:
Zhu, M; Yang, GC; Liu, F; Wan, DQ; Cheng, SL; Zhou, YH Author Full Names: Zhu Man; Yang Gencang; Liu Feng; Wan Diqing; Cheng Suling; Zhou Yaohe
Source:
RARE METAL MATERIALS AND ENGINEERING 37 (7): 1179-1182 JUL 2008
Abstract:
Almost an icosahedral quasicrstyal phase is obtained in the Mg-riched region off the Bergman line by means of rapid quenching in a cool copper mould. The microstructures, chemical composition and atom cluster of the icosahedral phase are charactered by X-ray diffraction (XRD), scanning electron microscopy (SEM), field-emission scanning electron microscopy and transmission electron microscopy (TEM). It is found that the icosahedral quasicrystal phase is obtained with the composition of 39.76 at% Mg, 18.34 at% Al, and 41.90 at% Zn, which nucleates and grows directly from the melt with icosahedral symmetries. It exhibits a characteristic faceted dendritic growth with the fastest growth direction along a three-fold axes. At the same time, the regular hexagonal-polygon icosahedral quasicrystal grains with a size of 0.2 mu m can also be observed. The atomic cluster of icosahedral phase is pentagonal dodecahedron with icosahedral symmetries and micro-lobes on the each faceted pentagonal face.
Title:
Analytic study on specific heat of icosahedral Al-Mn-Pd quasicrystals
Authors:
Wang, J; Fan, TY Author Full Names: Wang, Jian; Fan, Tianyou
Source:
MODERN PHYSICS LETTERS B 22 (17): 1653-1659 JUL 10 2008
Abstract:
A simple and explicit formula for specific heat of icoschedral Al-Mn-Pd quasicrystals is obtained, theoretical predictions of which are in good agreement with that given by experiment.
Title:
Effect of icosahedral phase particles on the texture evolution in Mg-Zn-Y alloys
Authors:
Lee, JY; Lim, HK; Kim, DH; Kim, WT; Kim, DH Author Full Names: Lee, Ju Youn; Lim, Hyun Kyu; Kim, Do Hyung; Kim, Won Tae; Kim, Do Hyang
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 491 (1-2): 349-355 SEP 15 2008
Abstract:
In order to understand the role of the icosahedral phase (I-phase) particles on the improved mechanical properties of Mg-3Zn-0.6Y and Mg-6Zn-1.2Y alloys, the texture evolution has been investigated by the X-ray diffraction and electron back-scattered diffraction (EBSD) analyses. Mg-6Zn-1.2Y alloy exhibits higher strength than Mg-3Zn-0.6Y alloy due to the presence of larger amount of I-phase particles. However, Mg-6Zn-1.2Y alloy exhibits a larger elongation than Mg-3Zn-0.6Y alloy. With increasing the volume fraction of I-phase particles and rolling speeds, the relatively random texture is developed, which is attributed to local lattice rotations around I-phase particles during shear deformation. The relatively random texture plays an important role in enhancing the ductility when larger amount of I-phase particles are present in Mg-6Zn-1.2Y alloy. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Distortion and charge density wave in the Ga square net coupled to the site occupancy wave in YCo0.88Ga3Ge
Authors:
Gray, DL; Francisco, MC; Kanatzidis, MG Author Full Names: Gray, Danielle L.; Francisco, Melanie C.; Kanatzidis, Mercouri G.
Source:
INORGANIC CHEMISTRY 47 (16): 7243-7248 AUG 18 2008
Abstract:
YCo0.88Ga3Ge has an incommensurately modulated structure that was solved with (3 + 1)D superspace techniques. YCo0.88Ga3Ge crystallizes in the orthorhombic superspace group Immm(alpha 00)00s with unit cell constants of a = 4.1639(4), b = 4.1639(4), c = 23.541(2) angstrom and a modulation vector of q = 0.3200(4)a* at 293 K. The incommensurate modulation, which creates a very large supercell (similar to 25 fold), arises from a charge density wave (CDW) in the square net of Ga atoms that is coupled with a site occupancy wave (SOW) of Co atoms. The distorted Ga net features polygallide ribbons, chains, as well as single atoms. Temperature dependent crystallographic studies of the structure from 100-500 K indicate that the CDW is "locked in". Electrical conductivity and thermopower measurements in the temperature range of 300-500 K show that YCo0.88Ga3Ge is a poor metal.
Title:
Formation and properties of quasicrystals
Authors:
Louzguine-Luzgin, DV; Inoue, A Author Full Names: Louzguine-Luzgin, D. V.; Inoue, A.
Source:
ANNUAL REVIEW OF MATERIALS RESEARCH 38: 403-423 2008
Abstract:
This article summarizes the general structural features and important properties of quasicrystals, a relatively new class of materials belonging to solid-state substances. Quasicrystals, which have a long-range quasiperiodic order but no three-dimensional translational periodicity, are structurally different from both conventional crystals and glassy solids. Although applications are still highly limited, quasicrystals are attracting significant attention as a structural constituent of mixed-phase materials exhibiting high strength together with certain ductility and can be applied as structural materials.

Update: 22-Aug-2008

Title:
Magnetic order of LiCu2O2 studied by resonant soft x-ray magnetic scattering
Authors:
Huang, SW; Huang, DJ; Okamoto, J; Wu, WB; Chen, CT; Yeh, KW; Chen, CL; Wu, MK; Hsu, HC; Chou, FC Author Full Names: Huang, S. W.; Huang, D. J.; Okamoto, J.; Wu, W. B.; Chen, C. T.; Yeh, K. W.; Chen, C. L.; Wu, M. K.; Hsu, H. C.; Chou, F. C.
Source:
SOLID STATE COMMUNICATIONS 147 (5-6): 234-237 AUG 2008
Abstract:
We present results of resonant soft x-ray magnetic scattering measurements on single crystals of LiCu2O2 to address the magnetic order. LiCu2O2 exhibits a long-range magnetic order incommensurate with the lattice, and the modulation vector is (0.5, zeta, 0) in reciprocal lattice units with zeta similar to 0.174, depending upon the temperature. The spin-spin correlation length along the spin chain deduced from the width of momentum scan is larger than 2100 angstrom. The inter-chain correlation length that lies within the ab plane was discovered to be substantial, similar to 690 angstrom. (c) 2008 Elsevier Ltd. All rights reserved.
Title:
Phase transformations induced by nitridation of quasicrystalline AlCuFeB powders
Authors:
Kenzari, S; Bonina, D; Dubois, JM; Fournee, V Author Full Names: Kenzari, S.; Bonina, D.; Dubois, J. M.; Fournee, V.
Source:
SCRIPTA MATERIALIA 59 (6): 583-586 SEP 2008
Abstract:
Nitridation is an important reaction which has never been investigated for Al-based quasicrystals. Here we show that AlCuFeB quasicrystalline particles undergo phase transformations upon annealing at high temperature in pure nitrogen. A thick nitride layer grows on the surface of the particles, and Al depletion in the bulk results in transformation of the quasicrystalline phase first into the cubic P-phase and then into the monoclinic X-phase. The kinetics of this transformation is much faster than that of oxidation. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Large-scale synthesis of Al-Cu-Fe submicron quasicrystals
Authors:
Li, LJ; Bi, QL; Yang, J; Fu, LC; Wang, LP; Wang, SC; Liu, WM Author Full Names: Li, Laijun; Bi, Qinling; Yang, Jun; Fu, Licai; Wang, Liping; Wang, Shuncai; Liu, Weimin
Source:
SCRIPTA MATERIALIA 59 (6): 587-590 SEP 2008
Abstract:
Al-Cu-Fe alloy with a nominal composition of Al62Cu25.5Fe12.5 (at.%) has been fabricated by a combination of pressure-assisted self-propagating high-temperature synthesis and rapid solidification. The as-synthesized Al-Cu-Fe alloy mainly consists of icosahedral quasicrystalline (IQC) Psi-Al65Cu20Fe15 and cubic beta-Al (Cu, Fe) solid solution phases, and exhibits finely equiaxed grains with a size ranging from 50 to 200 nm. The mechanism for the formation of the ultrafine-grained IQC phase has been explained. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Pressure-induced phase transitions in PrB6: Electrical resistivity measurements
Authors:
Iwakubo, H; Ikeda, S; Kishino, Y; Tanida, H; Sera, M; Iga, F Author Full Names: Iwakubo, H.; Ikeda, S.; Kishino, Y.; Tanida, H.; Sera, M.; Iga, F.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 012409 JUL 2008
Abstract:
We have studied the electrical resistivity of PrB6 under pressure up to P=0.8 GPa, with magnetic fields applied along the [001] and [111] directions. The commensurate (C) magnetic ordered phase is significantly stabilized by pressure, and another extra phase (denoted phase A) is observed under a low pressure of similar to 0.3 GPa. This phase appears above the transition temperature T-IC1=7 K at which the incommensurate magnetic order sets in at the ambient pressure. The magnetic phase diagram for H parallel to[111] changes drastically under pressure. Short-range interactions, which are strongly dependent on the Pr-Pr distances, are likely to play a dominant role in the relative stability of the different phases.
Title:
Signature of hidden order in heavy fermion superconductor URu2Si2: Resonance at the wave vector Q(0)=(1,0,0)
Authors:
Villaume, A; Bourdarot, F; Hassinger, E; Raymond, S; Taufour, V; Aoki, D; Flouquet, J Author Full Names: Villaume, A.; Bourdarot, F.; Hassinger, E.; Raymond, S.; Taufour, V.; Aoki, D.; Flouquet, J.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 012504 JUL 2008
Abstract:
Simultaneous neutron scattering and thermal expansion measurements on the heavy-fermion superconductor URu2Si2 under hydrostatic pressure of 0.67 GPa have been performed in order to detect the successive paramagnetic, hidden order, and large moment antiferromagnetic phases on cooling. The temperature dependence of the sharp low energy excitation at the wave vector Q(0)=(1,0,0) shows clearly that this resonance is a signature of the hidden order state. In the antiferromagnetic phase, this resonance disappears. The higher energy excitation at the incommensurate wave vector Q(1)=(1.4,0,0) persists in the antiferromagnetic phase but increases in energy.
Title:
Ga-substitution-induced single ferroelectric phase in multiferroic CuFeO2
Authors:
Terada, N; Nakajima, T; Mitsuda, S; Kitazawa, H; Kaneko, K; Metoki, N Author Full Names: Terada, N.; Nakajima, T.; Mitsuda, S.; Kitazawa, H.; Kaneko, K.; Metoki, N.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 014101 JUL 2008
Abstract:
We have succeeded in realizing a single ferroelectric phase in CuFe0.963Ga0.037O2 by substituting nonmagnetic Ga3+ for Fe3+ sites in CuFeO2. Ferroelectric polarization P in CuFe0.963Ga0.037O2 is observed below 7.5 K, and has the relatively large value of similar to 250 mu C/m(2), which is comparable to P=300 similar to 400 mu C/m(2) in the magnetic-field-induced ferroelectric phase of CuFeO2. In neutron-diffraction measurements, a single magnetic diffraction peak with an incommensurate wave number was observed below 7.5 K in CuFe0.963Ga0.037O2, indicating that the ferroelectric-incommensurate (FEIC) phase is realized as a single phase. Therefore, CuFe0.963Ga0.037O2 with a single FEIC phase is strongly expected to provide the best opportunity to investigate unresolved problems regarding the ferroelectric mechanism in CuFeO2. In this paper, we report measurements of magnetic susceptibility, specific heat, pyroelectric, dielectric constant, and neutron diffraction of a single crystal of CuFe0.963Ga0.037O2.
Title:
Effect of inversion symmetry on the incommensurate order in multiferroic RMn2O5 (R=rare earth)
Authors:
Harris, AB; Kenzelmann, M; Aharony, A; Entin-Wohlman, O Author Full Names: Harris, A. B.; Kenzelmann, M.; Aharony, Amnon; Entin-Wohlman, O.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 014407 JUL 2008
Abstract:
Starting from the irreducible representations of the group of the wave vector, we construct the spin-wave functions consistent with inversion symmetry, neglected in the usual representation analysis. We obtain the relation between the basis functions of different members of the star of the wave vector. We introduce order parameters and determine their transformation properties under the operations of the space group of the paramagnetic crystal. The results are applied to construct terms in the magnetoelectric interaction, which are quadratic and quartic in the magnetic order parameters. The higher-order magnetoelectric interactions can in principle induce components of the spontaneous polarization, which are not allowed by the lowest-order magnetoelectric interaction. We also obtain the relation between the spin-wave functions of the incommensurate phase and those of the commensurate phase, which lead to analogous relations between the order parameters of these two phases.
Title:
Magnetic order and multipole interactions in CexPr1-xB6 solid solutions
Authors:
Mignot, JM; Andre, G; Robert, J; Sera, M; Iga, F Author Full Names: Mignot, J. -M.; Andre, G.; Robert, J.; Sera, M.; Iga, F.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 014415 JUL 2008
Abstract:
Magnetic ordering phenomena in CexPr1-xB6 solid solutions have been studied using both powder and single-crystal neutron diffraction. A variety of magnetic structures are observed depending on temperature and Ce concentration. Over a broad composition range (x <= 0.7), Pr-Pr interactions play a dominant role, giving rise to incommensurate structures with wave vectors of the form k(IC1)=(1/4-delta,1/4,1/2) or k(IC2)=(1/4-delta,1/4-delta,1/2). The crossover to a CeB6-like regime takes place near x=0.7-0.8. For the latter composition, the antiferroquadrupolar phase transition observed in transport measurements precedes the onset, at lower temperature, of a commensurate magnetic order similar to that existing in CeB6. However, unlike in the pure compound, an incommensurate magnetic order is formed at even higher temperature and persists in the antiferroquadrupolar phase down to the lock-in transition. These results are shown to reflect the interplay between various type of dipole exchange and higher multipole interactions in this series of compounds.
Title:
Competing magnetic structures and magnetic transitions in Er2Ni2Pb: Powder neutron diffraction measurements
Authors:
Prokes, K; Munoz-Sandoval, E; Chinchure, AD; Mydosh, JA Author Full Names: Prokes, K.; Munoz-Sandoval, E.; Chinchure, Aravind D.; Mydosh, J. A.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 014425 JUL 2008
Abstract:
We have studied the magnetic structures of Er2Ni2Pb using a powder neutron diffraction technique in zero field. Previous bulk measurements suggested three distinct magnetic phase transitions. Our neutron diffraction experiments, which were made in the range 1.5-5 K, showed that magnetic Bragg reflections in Er2Ni2Pb can be indexed by several propagation vectors that coexist over an extensive temperature range. Rather than a homogeneous magnetic structure that is simultaneously described by all the existing propagation vectors, several spatially separated structures appear to exist in Er2Ni2Pb. The appearance/disappearance of representative reflections at T-N=3.5 K, T-m1=3.0 K, T-m2=2.3 K, and T-m3=1.8 K denote magnetic phase transitions. The only magnetic state that is determined by a single propagation vector exists just below T-N. In all other magnetic states, more than one propagation vectors are stable. Except for the lowest temperature state, which is commensurate, all other propagation vectors are incommensurate with respect to the crystal structure. Although the coexistence of several spatially separated magnetic structures can be explained by the competition of magnetic interactions along particular crystallographic directions, some of the details, e.g., the exact ground-state magnetic structure, are still unclear and need further study.
Title:
Magnetic ordering of weakly coupled frustrated quantum spin chains
Authors:
Zvyagin, AA; Drechsler, SL Author Full Names: Zvyagin, A. A.; Drechsler, S. -L.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 014429 JUL 2008
Abstract:
The ordering temperature of a quasi-one-dimensional system, consisting of weakly interacting quantum spin-1/2 chains with antiferromagnetic spin-frustrating couplings (or zigzag ladder), is calculated. The results show that a quantum critical point between two phases of the one-dimensional subsystem plays a crucial role. If the one-dimensional subsystem is in the antiferromagneticlike phase in the ground state, similar to the phase of a spin chain without frustration, weak couplings yield magnetic ordering of the Neel type. For intrachain spin-frustrating interactions larger than the critical one (at which the quantum phase transition takes place), the quasi-one-dimensional spin system manifests a spiral magnetic incommensurate ordering. The obtained results of our quantum theory are compared with the quasiclassical approximations. The calculated features of magnetic ordering are expected to be generic for weakly-coupled quantum spin chains with gapless excitations and spin-frustrating nearest- and next-nearest-neighbor interactions.
Title:
Identification of microscopic spin-polarization coupling in the ferroelectric phase of magnetoelectric multiferroic CuFe1-xAlxO2
Authors:
Nakajima, T; Mitsuda, S; Inami, T; Terada, N; Ohsumi, H; Prokes, K; Podlesnyak, A Author Full Names: Nakajima, Taro; Mitsuda, Setsuo; Inami, Toshiya; Terada, Noriki; Ohsumi, Hiroyuki; Prokes, Karel; Podlesnyak, Andrei
Source:
PHYSICAL REVIEW B 78 (2): Art. No. 024106 JUL 2008
Abstract:
We have performed synchrotron radiation x-ray and neutron diffraction measurements on magnetoelectric multiferroic CuFe1-xAlxO2 (x=0.0155), which has a proper helical magnetic structure with incommensurate propagation wave vector in the ferroelectric phase. The present measurements revealed that the ferroelectric phase is accompanied by lattice modulation with a wave number 2q, where q is the magnetic modulation wave number. We have calculated the Fourier spectrum of the spatial modulations in the local electric polarization using a microscopic model proposed by T. Arima [J. Phys. Soc. Jpn. 76, 073702 (2007)]. Comparing the experimental results with the calculation results, we found that the origin of the 2q-lattice modulation is not the conventional magnetostriction but the variation in the metal-ligand hybridization between the magnetic Fe3+ ions and ligand O2- ions. Combining the present results with the results of a previous polarized neutron diffraction study [Nakajima , Phys. Rev. B 77, 052401 (2008)], we conclude that the microscopic origin of the ferroelectricity in CuFe1-xAlxO2 is the variation in the metal-ligand hybridization with spin-orbit coupling.
Title:
Relaxor ferroelectric behavior in Ca-doped TbMnO3
Authors:
Mufti, N; Nugroho, AA; Blake, GR; Palstra, TTM Author Full Names: Mufti, N.; Nugroho, A. A.; Blake, G. R.; Palstra, T. T. M.
Source:
PHYSICAL REVIEW B 78 (2): Art. No. 024109 JUL 2008
Abstract:
We have studied the effect of Ca-doping in single-crystal Tb1-xCaxMnO3(x <= 0.1) on the crystal and magnetic structure, magnetocapacitance, and electric polarization. For low doping (x=0.05), the presence of Mn4+ ions gives rise to a state with behavior resembling that of a relaxor ferroelectric. The coherence length of the Mn magnetic spin spiral is reduced, while the Mn-modulation wave vector is unchanged. For doping larger than 5%, the ferroelectric state is suppressed, which we ascribe to breakdown of the spiral magnetic structure.
Title:
Magnetic-field-induced transitions in multiferroic TbMnO3 probed by resonant and nonresonant x-ray diffraction
Authors:
Strempfer, J; Bohnenbuck, B; Zegkinoglou, I; Aliouane, N; Landsgesell, S; Zimmermann, MV; Argyriou, DN Author Full Names: Strempfer, J.; Bohnenbuck, B.; Zegkinoglou, I.; Aliouane, N.; Landsgesell, S.; Zimmermann, M. V.; Argyriou, D. N.
Source:
PHYSICAL REVIEW B 78 (2): Art. No. 024429 JUL 2008
Abstract:
Multiferroic TbMnO3 is investigated using x-ray diffraction in high magnetic fields. Measurements on first- and second-harmonic structural reflections due to modulations induced by the Mn and Tb magnetic order are presented as function of temperature and field oriented along the a and b directions of the crystal. The relation to changes in ordering of the rare earth moments in applied field is discussed. Observations below T-N(Tb) without and with applied magnetic field point to a strong interaction of the rare earth order, the Mn moments, and the lattice. Also, the incommensurate to commensurate transition of the wave vector at the critical fields is discussed with respect to the Tb and Mn magnetic order, and a phase diagram on basis of these observations for magnetic fields H parallel to a and H parallel to b is presented. The observations point to a complicated and delicate magnetoelastic interaction as function of temperature and field.
Title:
Very weak electron-phonon coupling and strong strain coupling in manganites
Authors:
Cox, S; Loudon, JC; Williams, AJ; Attfield, JP; Singleton, J; Midgley, PA; Mathur, ND Author Full Names: Cox, S.; Loudon, J. C.; Williams, A. J.; Attfield, J. P.; Singleton, J.; Midgley, P. A.; Mathur, N. D.
Source:
PHYSICAL REVIEW B 78 (3): Art. No. 035129 JUL 2008
Abstract:
We describe transmission electron microscopy experiments that demonstrate the validity of the charge density wave (CDW) Landau theory in describing the so-called stripe phase of the manganites and that permit quantitative estimates of some of the theoretical parameters that describe this state. In polycrystalline Pr0.48Ca0.52MnO3 a lock-in to q/a(*)=0.5 in a sample with x>0.5 has been observed. Such a lock-in has been predicted as a key part of the Landau CDW theory of the stripe phase. Thus it is possible to constrain the size of the electron-phonon coupling in the CDW Landau theory to between 0.08% and 0.50% of the electron-electron coupling term. In the thin film samples, films of the same thickness grown on two different substrates exhibited different wave vectors. The different strains present in the films on the two substrates can be related to the wave vector observed via Landau theory. It is demonstrated that the elastic term, which favors an incommensurate modulation, has a similar size to the coupling between the strain and the wave vector, meaning that the coupling of strain to the superstructure is unexpectedly strong.
Title:
Incommensurability and atomic structure of c(2x2)N/Cu(100): A scanning tunneling microscopy study
Authors:
Choi, T; Ruggiero, CD; Gupta, JA Author Full Names: Choi, T.; Ruggiero, C. D.; Gupta, J. A.
Source:
PHYSICAL REVIEW B 78 (3): Art. No. 035430 JUL 2008
Abstract:
We use a scanning tunneling microscope operating in a low-temperature ultrahigh vacuum environment to study the atomic structure of single layer films of Cu2N grown on Cu(100). The c(2x2) lattice of Cu2N is incommensurate, with a lattice constant of 0.372 +/- 0.001 nm that is 3% larger than the bare Cu(100) surface. This finding suggests that the strain due to lattice mismatch contributes to self-assembly in this system. We find that the image contrast on Cu2N islands depends on bias voltage, which reconciles several interpretations in the literature. We assign features in these STM images to the Cu, N, and hollow sites in the Cu2N lattice with the aid of coadsorbed CO molecules. This atomic registry allows us to characterize four different defects on Cu2N, which influence the sticking coefficient and electronic coupling of adsorbates.
Title:
Structure of Al-Co-Ni pentagonal quasicrystal studied by HAADF-STEM and ab initio calculations
Authors:
Song, S; Wang, J; Wang, R; Xiong, D; Zhao, D; Gui, J; Liu, H; Yan, Y Author Full Names: Song, S.; Wang, J.; Wang, R.; Xiong, D.; Zhao, D.; Gui, J.; Liu, H.; Yan, Y.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 88 (7): 519-531 2008
Abstract:
Using a combination of atomic-resolution high-angle annular dark-field (HAADF) Z-contrast imaging and ab initio calculations, atomic models of clusters 2 nm in diameter and 0.8 nm in height are proposed for the Al-Co-Ni pentagonal quasicrystal. This quasicrystal has 5-fold symmetry (the so-called 5f state) without superstructures, and is one of numerous modifications of the Al-Co-Ni decagonal quasicrystal. HAADF results reveal that the two-dimensional quasi-periodic lattice contains mainly Penrose pentagonal tiling. The centres within the decorated pentagonal tiles, i.e. the so-called pentagonal super-clusters, show structural characteristics having both a satellite-orbit shape and a pentagon-symmetry shape. The proposed atomic models, based directly on the HAADF images, are subjected to ab initio total energy calculations. After relaxation, the calculations demonstrate that the models with 5-fold symmetry are energetically more favourable than those with 10-fold symmetry.
Title:
Commensurate-incommensurate phase transition in muthmannite, AuAgTe2: first evidence of a modulated structure at low temperature
Authors:
Bindi, L Author Full Names: Bindi, Luca
Source:
PHILOSOPHICAL MAGAZINE LETTERS 88 (7): 533-541 2008
Abstract:
To study the temperature-dependent structural changes and to analyze the crystal chemical behavior of silver as a function of temperature, a crystal of muthmannite, AuAgTe2, has been investigated by X-ray single-crystal diffraction methods at 300 K and 110 K. At room temperature, muthmannite was confirmed as belonging to the space group P2/m, while at low temperature (110 K) it undergoes a reversible commensurate-incommensurate phase transition with a modulation wave vector q = 0.215(1)a* + 0.379(2)c*. Muthmannite reconverts to the commensurate type upon returning to room temperature, thus indicating that the phase transition is completely reversible in character. The average structure of the low-temperature muthmannite remains monoclinic, space group P2/m, and shows only normal thermal compression over the entire temperature range investigated. Crystal-chemical characteristics are compared with published data on the other members of the system Au-Ag-Te. Speculations on the possible origin of the modulated structure at low temperature are also given.
Title:
Dielectric, ferroelectric properties, and grain growth of CaxBa1-xNb2O6 ceramics with tungsten-bronzes structure
Authors:
Ke, SM; Fan, HQ; Huang, HT; Chan, HLW; Yu, SH Author Full Names: Ke, Shanming; Fan, Huiqing; Huang, Haitao; Chan, H. L. W.; Yu, Shuhui
Source:
JOURNAL OF APPLIED PHYSICS 104 (2): Art. No. 024101 JUL 15 2008
Abstract:
Dielectric properties, microstructures, and phase transition behaviors of alpha and beta phases of CaxBa1-xNb2O6 (x= 0.22, 0.30, and 0.38) ceramics were investigated. All the three compositions had partially filled tungsten-bronze structure (TTB) and relatively high Curie temperatures (up to 345 degrees C) compared with Sr1-xBaxNb2O6. The alpha phase exhibits unambiguously a diffused phase transition, while the beta phase is associated with an incommensurate phase and needs to be further studied. The dielectric and ferroelectric properties of CaxBa1-xNb2O6 ceramics were strongly processing-dependent. A mechanism was proposed to explain the grain growth behavior of TTB ceramic niobates. (c) 2008 American Institute of Physics.
Title:
Laves phases, gamma-brass, and 2x2x2 superstructures: A new class of quasicrystal approximants and the suggestion of a new quasicrystal
Authors:
Berger, RF; Lee, S; Johnson, J; Nebgen, B; So, ACY Author Full Names: Berger, Robert F.; Lee, Stephen; Johnson, Jeffreys; Nebgen, Ben; So, Adrian Chi-Yau
Source:
CHEMISTRY-A EUROPEAN JOURNAL 14 (22): 6627-6639 2008
Abstract:
Of the most common cubic intermetallic structure types, several (MgCU2, CU5Zn8, Ti2Ni, and alpha-Mn) have superstructures with unusual symmetry properties. These superstructures (Be5Au, Li21Si5, Sm11Cd45, and Mg44Ir7) have the unusual property of pairs of perpendicular pseudo fivefold axes, most apparent in their X-ray diffraction patterns. The current work shows that an 8D to 3D projection method cleanly describes most (and in one case, all) of the atomic positions in the four superstructures mentioned above. This type of projection, which maps the E-8 lattice (a mathematically simple 8D crystal) into 3D space, combines the desired higher dimensional point group's perpendicular fivefold rotations with 3D translational symmetry-exactly what we see in the experimental crystal structures. The projection method successfully accounts for all heavy atom positions in the four superstructures, and at least 60-70% of the light atom positions. The results suggest that all of these structures, previously known to be connected only by qualitative similarities in their atomic "clusters", are approximants of a single, as-yet unknown, class of quasicrystal.

Update: 15-Aug-2008

Title:
Mossbauer study of antiferromagnetic CuFeO2
Authors:
Choi, DH; Shim, IB; Kim, CS Author Full Names: Choi, Dong Hyeok; Shim, In-Bo; Kim, Chul Sung
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 320 (20): E575-E577 OCT 2008
Abstract:
We have studied the magnetic spin structure of antiferromagnetic CuFeO2 by X-ray diffraction (XRD) and Mossbauer spectroscopy. Its crystal structure determined by XRD analysis was a rhombohedral structure ( space group R-3m) and lattice constants a(0) and c(0) were 3.0333 and 17.1595 angstrom, respectively. In spite of 4-Fe sublattices in a delafossite CuFeO2, its Mossbauer spectra were analyzed with 1-set (6-Lorentzian lines) below 10K due to the collinear-commensurate spin structure, but the spectra were fitted with 4-sextet above 10K due to the incommensurate spin structure. This phenomenon was attributed to the spin-lattice relaxation effect. Magnetic Neel temperature was also determined at 18 K, which corresponded to the high-spin Fe3+ valance state. On the other hand, CuFe0.98Al0.02O2 powder with a noncollinear spin structure was fitted with 4-sextet at 4.2 K. (c) 2008 Elsevier B.V. All rights reserved.
Title:
Mechanical alloying and self-propagating high-temperature synthesis of stable icosahedral quasicrystals
Authors:
Bokhonov, BB Author Full Names: Bokhonov, B. B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 461 (1-2): 150-153 AUG 11 2008
Abstract:
The phase evolution of the mechanically alloyed ternary 63%Al + 25%Cu + 12%Fe and 65%Al + 20%Cu + 15%Fe powder mixtures with milling time has been studied by X-ray diffraction method. It was found that an icosahedral quasicrystalline phase was formed directly during high-energy ball milling of the Al-Cu-Fe mixtures. The X-ray and scanning electron microscopic investigations demonstrated the possibility to use self-propagating high-temperature synthesis (SHS) in combination with preliminary mechanical activation for the synthesis of stable icosahedral quasicrystals. The typical morphology of the Al63Cu25Fe12 icosahedral quasicrystals formed in the SHS process is a pentagonal dodecahedron with a size of 3-5 mm. The phase composition of the SHS products depends on the time of preliminary mechanical activation. The content of cubic intermetallic phase in SHS products increases with the time of preliminary mechanical activation of the 63%Al + 25%Cu + 12%Fe powder mixtures. (c) 2007 Elsevier B. V. All rights reserved.

Update: 8-Aug-2008

Title:
Quasicrystals at interfaces
Authors:
Fournee, V; Ledieu, J; Thiel, P Author Full Names: Fournee, Vincent; Ledieu, Julian; Thiel, Patricia
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 310301 AUG 6 2008
Title:
Microstructural evolution and the role of interfaces in Mg-Zn-Y alloys with high strength and formability
Authors:
Chang, HJ; Lee, JY; Kim, DH Author Full Names: Chang, H. J.; Lee, J. Y.; Kim, D. H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314001 AUG 6 2008
Abstract:
Composites consisting of a quasicrystalline, icosahedral phase (I-phase) and ductile alpha-Mg can be fabricated by controlling the alloy composition in the Mg-Zn-Y alloy system. The I-phase in Mg-Zn-Y alloys shows a variation in structural order from a well-ordered icosahedral phase to a 1/1 rhombohedral approximant phase. The structural change in the icosahedral phase can be explained by microdomain formation due to compositional change during solidification. The characteristic of strong bonding between icosahedral particles and the alpha-Mg matrix indicates that the structural change from I-phase to crystalline phase is not discontinuous, but gradual. The interface layer of alpha-Mg with several nm thickness preserves an orientational relationship with the I-phase, although the remaining alpha-Mg shows a different orientation due to plastic deformation during deformation (rolling process). Such a strong interface can provide an excellent combination of high str ength and formability in Mg-based alloys, enabling application as lightweight structural parts.
Title:
Quasicrystal-crystal interfaces in bulk materials
Authors:
Singh, A; Tsai, AP Author Full Names: Singh, Alok; Tsai, A. P.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314002 AUG 6 2008
Abstract:
The formation of interfaces of simple crystals with icosahedral quasicrystals has been described. Crystals take on various orientation relationships (ORs) with the quasicrystals in order to make low energy interfaces by matching close packed planes across the interfaces. In the icosahedral phase the closest packed planes are fivefold and twofold. Among various possibilities, an OR will get selected by the surface on which nucleation of a phase occurs. Since one of the phases is quasicrystalline and the other is crystalline, even within the same OR there are variations of several degrees. The high symmetry of the icosahedral phase ensures many possible orientations for planar matching with another phase. The quasiperiodicity ensures an epitaxy with periodic planes of many possible spacings at the interface. Epitaxy can be observed as coincidence of spots in the reciprocal space and verified by imaging in high resolution electron microscopy. In this article examples of interfaces of Al-Cu-Fe icosahedral phases with lead, bismuth and tin, and Mg-Zn-Y icosahedral phases with magnesium are shown. The high symmetry of the icosahedral phase ensures that epitaxy is produced on nearly all interfaces in bulk. Slight misorientations across interfaces are accommodated by dislocations.
Title:
Models for quasicrystal-crystal epitaxy
Authors:
Widjaja, EJ; Marks, LD Author Full Names: Widjaja, E. J.; Marks, L. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314003 AUG 6 2008
Abstract:
Not long after the discovery of quasicrystals, a specific orientation relationship between crystalline and quasicrystalline structures was observed. The specific orientational relationships were discovered in many systems, for instance surface alterations of bulk quasicrystals, the growth of atomic overlayers on quasicrystalline substrates and quasicrystalline thin films on crystalline substrates. In this paper, we review various models described in the literature in explaining such quasicrystal-crystal epitaxy.
Title:
Epitaxial interfaces between half-crystals of quasicrystalline and periodic material
Authors:
Theis, W; Franke, KJ Author Full Names: Theis, W.; Franke, K. J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314004 AUG 6 2008
Abstract:
We recently demonstrated that epitaxial interfaces can be formed between periodic and quasiperiodic materials (Franke et al 2007 Phys. Rev. Lett. 99 036103). Such interfaces exhibit the same defining characteristic as epitaxial interfaces between commensurate periodic materials, namely the locking into registry of the two half-crystals' atomic structures. This real space characteristic is equivalent to the requirement of a coincidence of reciprocal lattice points. Here, we explore the characteristics of the potential interfaces within the class of quasicrystals exhibiting a periodic direction, including decagonal quasicrystals. We derive our results geometrically from a higher dimensional description, thus providing visual insight into the underlying concepts. Since the reciprocal lattice of quasicrystalline structures is generated by more basis vectors than their periodic counterparts', suitable quasicrystalline interlayers can be designed to epitaxially link incommensurate half-crystals. We give examples of selected model structures as illustrations.
Title:
Nucleation and growth of pseudomorphic monolayers on quasicrystal surfaces
Authors:
Smerdon, JA; Sharma, HR; Ledieu, J; McGrath, R Author Full Names: Smerdon, J. A.; Sharma, H. R.; Ledieu, J.; McGrath, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314005 AUG 6 2008
Abstract:
We present a review of experimental studies of adsorption systems where pseudomorphic growth on quasicrystal surfaces has been observed. From these studies, we correlate information on the known or suggested adsorption and nucleation sites. For fivefold surfaces of icosahedral quasicrystals, two favoured locations emerge: the centres of equatorially truncated pseudo-Mackay clusters, and the centres of pentagonal hollows. The information on adsorption sites on decagonal quasicrystals is less definitive. Nevertheless the correlation of known information leads to a simple picture of pseudomorphic growth, at least for the first monolayer. We also remark on the possibilities for studies using quantitative surface structural techniques.
Title:
Bulk and surface structure of the clean and adsorbate-covered decagonal Al-Co-Ni quasicrystal
Authors:
Burkardt, S; Deloudi, S; Erbudak, M; Kortan, AR; Mungan, M; Steurer, A Author Full Names: Burkardt, S.; Deloudi, S.; Erbudak, M.; Kortan, A. R.; Mungan, M.; Steurer, Andw
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314006 AUG 6 2008
Abstract:
We review our Al adsorption experiments on the tenfold-symmetry surface of the decagonal Al-Co-Ni quasicrystal and present computational simulations of adsorption on a structural model based on a fundamental Al-Co cluster with 20 angstrom diameter, symmetry (102) over barm, and 8 angstrom periodicity. This cluster is the building unit of tau(2)-Al13Co4, from which, by a sequence of minor changes, the structures of the phases in the stability region of decagonal Al-Co-Ni can be derived. The model used for the decagonal Al70Co15Ni15 is an idealized model with a two-layer periodicity (4 angstrom) and no chemical or structural disorder. We find that the bulk and surface properties of this model are in good agreement with experiments. Our molecular-dynamics simulations of Al adsorption reproduce the experimental results and show that by varying the thermal relaxation rates of the adsorbed layer, a variety of different surface morphologies can be achieved. We also present our recent experiments on dissociative adsorption of oxygen on the decagonal surface.
Title:
Gas adsorption on quasicrystalline surfaces
Authors:
Diehl, RD; Setyawan, W; Curtarolo, S Author Full Names: Diehl, R. D.; Setyawan, W.; Curtarolo, S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314007 AUG 6 2008
Abstract:
The low-friction properties of quasicrystal surfaces suggest their use as coatings on moving machine parts, including those in internal combustion engines. In such applications, additional lubricants are typically used. Since the low-friction properties of quasicrystals are thought to depend on their aperiodic structures, the interactions of lubricants on quasicrystalline surfaces may have an impact on their frictional properties. In this paper, we address the fundamental issues that affect the growth and structural properties of gases on a quasicrystal surface. Studies of the adsorption and growth of rare gases on quasicrystal surfaces are reviewed, and new results are presented for the modeling and simulation of hydrocarbons on quasicrystal surfaces. The calculated interaction parameters are presented for methane adsorption on ten-fold Al-Ni-Co. Methane is found to form aperiodically ordered structures, consistent with the rules established earlier for rare gases on Al-Ni-Co.
Title:
Sputter-induced crystalline layers and epitaxial overlayers on quasicrystal surfaces
Authors:
Shimoda, M; Sharma, HR Author Full Names: Shimoda, M.; Sharma, H. R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314008 AUG 6 2008
Abstract:
We present here an overview of surface and interface studies on various quasicrystals, focusing on areas where reflection high-energy electron diffraction plays an important role. Subjects included here are sputter-induced crystalline layers, surface alloying and epitaxial films. These phenomena are observed on the high symmetry surface of Al-based quasicrystals, such as decagonal Al-Ni-Co, icosahedral (i) Al-Cu-Fe and i-Al-Cu-Ru. For comparison, studies on i-Ag-In-Yb quasicrystal, an isostructure of the binary i-Cd-Yb quasicrystal, and. xi'-Al-Pd-Mn approximant are also included.
Title:
Surface alloys as interfacial layers between quasicrystalline and periodic materials
Authors:
Duguet, T; Ledieu, J; Dubois, JM; Fournee, V Author Full Names: Duguet, T.; Ledieu, J.; Dubois, J. M.; Fournee, V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314009 AUG 6 2008
Abstract:
Low adhesion with normal metals is an intrinsic property of many quasicrystalline surfaces. Although this property could be useful to develop low friction or non-stick coatings, it is also responsible for the poor adhesion of quasicrystalline coatings on metal substrates. Here we investigate the possibility of using complex metallic surface alloys as interface layers to enhance the adhesion between quasicrystals and simple metal substrates. We first review some examples where such complex phases are formed as an overlayer. Then we study the formation of such surface alloys in a controlled way by annealing a thin film deposited on a quasicrystalline substrate. We demonstrate that a coherent buffer layer consisting of the gamma-Al4Cu9 approximant can be grown between pure Al and the i-Al-Cu-Fe quasicrystal. The interfacial relationships between the different layers are defined by [111](A1) parallel to [110](Al4Cu9) parallel to [5f](i-Al-Cu-Fe).
Title:
Contact angles of liquid metals on quasicrystals
Authors:
Bergman, C; Girardeaux, C; Perrin-Pellegrino, C; Gas, P; Dubois, JM; Rivier, N Author Full Names: Bergman, Claire; Girardeaux, Christophe; Perrin-Pellegrino, Carine; Gas, Patrick; Dubois, Jean-Marie; Rivier, Nicolas
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314010 AUG 6 2008
Abstract:
Wetting with mu m-sized Pb droplets on thin polycrystalline films of decagonal Al13Co4 is reported. The films were prepared under high vacuum conditions in order to have Pb droplets lying on a clean surface. The method used is sequential deposition and annealing of specific stackings of Al and Co layers of nanometric thicknesses. A 300 nm thick Pb slab was then deposited on top of the films and dewetting experiments were followed in situ in a scanning Auger microprobe. The contact angle between the Pb droplet and the surface of the film is measured to be 49 degrees +/- 7 degrees. Further investigation performed by cross section transmission electron microscopy allows us to better characterize the interface. Taking into account the rugosity of the film, it is concluded that there is partial wetting of the film, which corresponds to a smaller contact angle. The comparison with other results obtained either with pure metals or with a cubic AlCo compound leads to the conclusion that the wetting behaviour of Pb on the surface of a decagonal compound is close to that of a metal with a high melting point and not significantly different from that of a crystalline compound with a small unit cell.
Title:
Measurements of contact angles of water on Al-based intermetallic surfaces
Authors:
Dubois, JM; Fournee, V; Thiel, PA; Belin-Ferre, E Author Full Names: Dubois, J. M.; Fournee, V.; Thiel, P. A.; Belin-Ferre, E.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314011 AUG 6 2008
Abstract:
A systematic study was performed of the contact angle of minute droplets of water deposited on various aluminium-based intermetallics in ambient conditions. The dataset was complemented by measurements of electronic partial densities of states and oxide layer thicknesses. We studied a broad variety of specimens, ranging from simple cubic, CsCl-type phases to quasicrystals and high-order approximants. The thickness of the oxide layer, that is always present in air, was varied between 2 and more than 10 nm. Within these limits, the contact angle varies considerably and, surprisingly, decreases with increasing thickness of the oxide dielectric. Furthermore, it is clearly the highest on samples that show the largest crystal complexity, i.e. quasicrystals. It follows that the reversible adhesion energy directly deduced from contact angle is essentially controlled by the (squared) density of states at Fermi energy in the bulk of the sample and the inverse of the (squared) thickness of the native oxide film at the surface of the material. We interpret these results in terms of electrostatic image forces developed in the conduction cloud by the dipoles of the water molecules.
Title:
Atomic scale friction and adhesion properties of quasicrystal surfaces
Authors:
Park, JY; Thiel, PA Author Full Names: Park, Jeong Young; Thiel, P. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314012 AUG 6 2008
Abstract:
In this paper, we highlight recent studies of the atomic scale friction and adhesion properties of quasicrystals. We review tribological studies carried out in different mechanical regimes (elastic and inelastic) and at different length scales (macroscale and nanoscale). We address the role of the surface oxide and the nature of mechanical contact in determining friction and adhesion properties. We discuss the relationship between the aperiodic atomic structure of quasicrystals and their low friction, for both elastic and inelastic regimes.
Title:
First-principles studies for structural transitions in ordered phase of cubic approximant Cd6Ca
Authors:
Nozawa, K; Ishii, Y Author Full Names: Nozawa, K.; Ishii, Y.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 315206 AUG 6 2008
Abstract:
Recently a low-temperature structural transition has been reported for complex cubic compounds Cd6M (M = Ca, Yb, Y, rare earth) and it is believed that the transition is due to orientational ordering of an atomic shell in the icosahedral cluster in Cd6M. The first-principles electronic structure calculations and structural relaxations are carried out to investigate structures and orientational ordering of the innermost tetrahedral shell of the icosahedral cluster in Cd6Ca. The very short interatomic distances in the experimental average structures are relaxed and the innermost tetrahedral shell of an almost regular shape is obtained. Three types of orientation for the tetrahedral shell and eight different combinations of them for the clusters at a vertex and body-centre of a cubic cell are obtained. A possible model describing the orientational ordering at low temperatures or high pressures is discussed.
Title:
Reciprocal-space imaging of a real quasicrystal. A feasibility study with PILATUS 6M
Authors:
Weber, T; Deloudi, S; Kobas, M; Yokoyama, Y; Inoue, A; Steurer, W Author Full Names: Weber, Thomas; Deloudi, Sofia; Kobas, Miroslav; Yokoyama, Yoshihiko; Inoue, Akihisa; Steurer, Walter
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 669-674 Part 4 AUG 2008
Abstract:
How many of the theoretically densely distributed Bragg reflections of a quasicrystal can be observed employing an area detector and synchrotron radiation? How does the reflection density of a real quasicrystal change as a function of exposure time, and what is the minimum distance between reflections? What does the distribution of diffuse scattering look like? To answer these questions, the Bragg reflection density of a perfect icosahedral quasicrystal with composition Al64Cu23Fe13 was measured employing a novel type of single-photon-counting X-ray pixel detector, PILATUS 6M, which allows noise-free data collection with the extraordinarily large dynamic range of 20 bit. The reflection density was found to be two orders of magnitude lower than expected for a strictly quasiperiodic structure. Moreover, diffuse scattering reflects significant structural disorder, breaking six-dimensional F-lattice symmetry. These findings have some implications for the interpretation! of physical properties.
Title:
Anomalous small-angle scattering from nanoquasicrystalline precipitates in Zr80Pt20 ribbons
Authors:
Okuda, H; Fukumoto, T; Saida, J; Ochiai, S; Sasaki, S; Masunaga, H Author Full Names: Okuda, Hiroshi; Fukumoto, Takefumi; Saida, Junji; Ochiai, Shojiro; Sasaki, Sono; Masunaga, Hiroyasu
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 675-679 Part 4 AUG 2008
Abstract:
Anomalous small-angle X-ray scattering (ASAXS) profiles of Zr80Pt20 ribbons have been measured at the Zr K absorption edge. By annealing the melt-spun ribbons at 800 K, well defined SAXS patterns from nanoquasicrystals were observed, although the compositions of the quasicrystals (QC) and the amorphous matrix have previously been reported to be the same. The SAXS intensities were found to show a small anomalous effect at the Zr K edge. Contrast analysis suggested that the origin of the small-angle scattering is a small compositional fluctuation coupled with a small density difference, which enhances SAXS intensity but reduces the anomalous effect. A constant ASAXS intensity ratio for QC microstructure suggests that the ratio of the composition difference to the density difference between QC and the amorphous matrix is almost constant for the ZrPt ribbons examined here.
Title:
Incommensurate structure of InAl1-xTixO3+x/2 [x=0.701 (1)]: comparison between modulated and composite models
Authors:
Bereciartua, PJ; Zuniga, FJ; Breczewski, T Author Full Names: Bereciartua, P. J.; Zuniga, F. J.; Breczewski, T.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 405-416 Part 4 AUG 2008
Abstract:
The structure of the monoclinic phase of the compound InAl1-xTixO3+x/2 with x = 0.701 (1) has been analyzed within the (3 + 1)-dimensional superspace formalism. Two different models were refined describing the structure as an incommensurate modulated layer and modulated composite, respectively. Both models include the same composition structure relation. In the composite approach it is derived from the mismatching between the two subsystems. In the incommensurate modulated system, it is derived from a closeness condition between O atomic domains. The distribution and coordination of the cations is discussed and compared with previously proposed models for similar compounds.
Title:
Incommensurate structure of Ca2Al2O5 at high temperatures - structure investigation and Raman spectroscopy
Authors:
Lazic, B; Kruger, H; Kahlenberg, V; Konzett, J; Kaindl, R Author Full Names: Lazic, Biljana; Krueger, Hannes; Kahlenberg, Volker; Konzett, Juergen; Kaindl, Reinhard
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 417-425 Part 4 AUG 2008
Abstract:
A high-temperature X-ray diffraction study revealed that brownmillerite-type Ca2Al2O5 transforms to an incommensurately modulated structure at elevated temperatures. Single crystals of Ca2Al2O5 were synthesized in an end-loaded piston cylinder press at 2.5 GPa and 1273 K. The diffraction pattern observed at 1090 (10) K by in situ single-crystal diffraction experiments can be indexed by an I-centred orthorhombic cell and a modulation wavevector of q = 0.595 (1) c*. A (3 + 1)-dimensional model in superspace group Imma(00 gamma)s00 was used to refine the modulated structure. The structure is assembled from two building units: (i) layers of corner-sharing [AlO6] octahedra, stacked along b alternate with (ii) layers of zweier single chains of [AlO4] tetrahedra running along a. The modulated structure arises from an aperiodic sequence of two different configurations of the chains within the tetrahedral layers. The modulated high-temperature phase of Ca2Al2O5 is isotypic to the modulated high-temperature modification of Ca2Fe2O5. A large hysteresis was found in the phase-transition temperature. On heating, the transition occurs at ca 1075 (10) K; on cooling, satellite reflections can be observed down to 975 (10) K. The characterization of Ca2Al2O5 is completed by Raman spectroscopy, including a partial interpretation of the spectra.
Title:
Order, disorder and structural modulations in Bi-Fe-W-O-Br Sillen-Aurivillius intergrowths
Authors:
Avila-Brande, D; Landa-Canovas, AR; Otero-Diaz, LC Author Full Names: Avila-Brande, David; Landa-Canovas, Angel R.; Otero-Diaz, L. Carlos
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 438-447 Part 4 AUG 2008
Abstract:
Transmission electron microscopy observations on a new complex oxybromide with nominal composition Bi4Fe1/3W2/3O8Br, heated at high temperature, reveal the transformation of its basic structure yielding two types of crystals. The first crystal type shows ordered and disordered extended defects leading to a new family of intergrowths between one Sillen block and n Aurivillius blocks and occasionally between one Aurivillius block and n Sillen blocks. The second type presents a compositionally modulated structure, determined by electron diffraction, with an average composition Bi4Fe1/2W1/2O8-delta Br and unit-cell parameters a = (1/gamma) 3.8, b = 3.8, c = 14.5 angstrom (gamma = 0.10-0.15) in the superspace group Immm[(1-gamma)00] no. 71.1.

Update: 1-Aug-2008

Title:
Ab initio calculations of the vibrational spectra of 1/1 approximant of i-AlCuFe quasicrystal
Authors:
Rudenko, AN; Mazurenko, VG Author Full Names: Rudenko, A. N.; Mazurenko, V. G.
Source:
PHYSICS OF THE SOLID STATE 50 (7): 1326-1332 JUL 2008
Abstract:
The partial and total densities of vibrational states of the 1/1 crystal approximant of the icosahedral i-AlCuFe quasicrystal are calculated using the method of pseudopotentials in the generalized gradient approximation (to describe the electronic states) and the frozen-phonon method (to determine the dynamic matrix). The results obtained agree well with experimental inelastic neutron scattering data, which indicates that the method of calculations is appropriate and could be used to calculate other crystal approximants.
Title:
Materials science - A tale of two tilings
Authors:
Glotzer, SC; Keys, AS Author Full Names: Glotzer, Sharon C.; Keys, Aaron S.
Source:
NATURE 454 (7203): 420-421 JUL 24 2008
Title:
Archimedean-like tiling on decagonal quasicrystalline surfaces
Authors:
Mikhael, J; Roth, J; Helden, L; Bechinger, C Author Full Names: Mikhael, Jules; Roth, Johannes; Helden, Laurent; Bechinger, Clemens
Source:
NATURE 454 (7203): 501-504 JUL 24 2008
Abstract:
Monolayers on crystalline surfaces often form complex structures with physical and chemical properties that differ strongly from those of their bulk phases (1). Such hetero-epitactic overlayers are currently used in nanotechnology and understanding their growth mechanism is important for the development of new materials and devices. In comparison with crystals, quasicrystalline surfaces exhibit much larger structural and chemical complexity leading, for example, to unusual frictional(2), catalytical(3) or optical properties(4,5). Deposition of thin films on such substrates can lead to structures that may have typical quasicrystalline properties. Recent experiments have indeed showed 5-fold symmetries in the diffraction pattern of metallic layers adsorbed on quasicrystals (6,7). Here we report a real-space investigation of the phase behaviour of a colloidal monolayer interacting with a quasicrystalline decagonal substrate created by interfering five laser beams. We find a pseudomorphic phase that shows both crystalline and quasicrystalline structural properties. It can be described by an archimedean-like tiling (8,9) consisting of alternating rows of square and triangular tiles. The calculated diffraction pattern of this phase is in agreement with recent observations of copper adsorbed on icosahedral Al70Pd21Mn9 surfaces(10). In addition to establishing a link between archimedean tilings and quasicrystals, our experiments allow us to investigate in real space how single-element monolayers can form commensurate structures on quasicrystalline surfaces.
Title:
Electronic properties and phase transitions in low-dimensional semiconductors
Authors:
Panich, AM Author Full Names: Panich, A. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (29): Art. No. 293202 JUL 23 2008
Abstract:
We present the first review of the current state of the literature on electronic properties and phase transitions in T1X and T1MX2 (M = Ga, In; X = Se, S, Te) compounds. These chalcogenides belong to a family of the low-dimensional semiconductors possessing chain or layered structure. They are of significant interest because of their highly anisotropic properties, semi-and photoconductivity, nonlinear effects in their I-V characteristics (including a region of negative differential resistance), switching and memory effects, second harmonic optical generation, relaxor behavior and potential applications for optoelectronic devices. We review the crystal structure of T1X and T1MX2 compounds, their transport properties under ambient conditions, experimental and theoretical studies of the electronic structure, transport properties and semiconductor -metal phase transitions under high pressure, and sequences of temperature-induced structural phase transitions with intermediate incommensurate states. The electronic nature of the ferroelectric phase transitions in the above-mentioned compounds, as well as relaxor behavior, nanodomains and possible occurrence of quantum dots in doped and irradiated crystals is discussed.
Title:
Dynamic crack propagation in decagonal Al-Ni-Co quasicrystal
Authors:
Zhu, AY; Fan, TY Author Full Names: Zhu, Ai-Yu; Fan, Tian You
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (29): Art. No. 295217 JUL 23 2008
Abstract:
The appearance of unusual internal variables - phason degrees - in quasicrystals challenges the traditional theory of condensed matter in macro- as well as in microscopy, especially for a dynamic process. The elasto-/hydrodynamic model for quasicrystals is suggested and investigated. With this model and the finite difference method the wave propagation and diffusion and their interaction through a cracked sample are revealed in this study. Even though the phason degrees of freedom present the diffusion nature according to the present model, this influences the dynamic process greatly. The influences are different for dynamic initiation of crack growth and fast crack propagation; for the latter the nonlinear effect - moving boundary effect - is evident as well as the wave propagation effect, diffusion effect and phonon-phason coupling effect.
Title:
Effect of hot forging on the microstructure and mechanical properties of Mg-Zn-Y alloy
Authors:
Garces, G; Muller, A; Onorbe, E; Perez, P; Adeva, P Author Full Names: Garces, G.; Mueller, A.; Onorbe, E.; Perez, P.; Adeva, P.
Source:
JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 206 (1-3): 99-105 SEP 12 2008
Abstract:
The use of hot forging as an alternative thermo-mechanical treatment to refine a quasicrystalline reinforced Mg-Zn-Y cast alloy has been explored. Hot forging refines the grain size of the cast Mg-Zn-Y alloy and induces a strong texture with the basal planes perpendicular. to the forging direction. However, forging is not effective to distribute the I-phase homogeneously through the magnesium matrix. At low temperature, grain refinement is the main strengthening mechanism and contributes to increasing the mechanical strength of the forged-Mg-Zn-Y alloy. Furthermore, the basal texture affords an additional strengthening contribution whose magnitude depends only on the texture intensity. (c) 2008 Published by Elsevier B.V.
Title:
Reaction efficiency of diffusion-controlled processes on finite, aperiodic planar arrays
Authors:
Garza-Lopez, RA; Kaufman, A; Patel, R; Chang, J; Brzezinski, J; Kozak, JJ Author Full Names: Garza-Lopez, Roberto A.; Kaufman, Aaron; Patel, Reena; Chang, Joseph; Brzezinski, Jack; Kozak, John J.
Source:
CHEMICAL PHYSICS LETTERS 459 (1-6): 137-140 JUN 27 2008
Abstract:
Using the theory of finite Markov processes, we show quantitatively that diffusion-limited, reactive events on two finite planar arrays having an aperiodic lattice structure are kinetically advantaged relative to processes on platelets having a regular, hexagonal [6(3)] structure. The possible relevance of the results obtained to catalytic processes on quasicrystals and zeolite 'rafts' is noted. (c) 2008 Elsevier B. V. All rights reserved.

Update: 25-Jul-2008

Title:
Main features and the driving force for the formation of the quasicrystalline phase in Al-Cu-Fe powders after mechanoactivation
Authors:
Cherdyntsev, VV; Kaloshkin, SD; Tomilin, IA; Principi, G Author Full Names: Cherdyntsev, V. V.; Kaloshkin, S. D.; Tomilin, I. A.; Principi, G.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 105 (6): 610-621 JUN 2008
Abstract:
The evolution of the phase and structural states during heating of a powder mixture of composition Al65Cu23Fe12 subjected to mechanoactivation has been investigated. The solid-state transformations have been studied using Mossbauer spectroscopy, X-ray diffraction, and differential scanning calorimetry. The sequence of phase formation during heating was compared with the data on the heat of formation of binary solutions and compounds in the system. The analysis performed showed that the nature of transformations in the process of the formation of the quasicrystalline phase was caused by the thermodynamic parameters of the system.
Title:
Metal-insulator transition and its relation to magnetic structure in (LaMnO3)(2n)/(SrMnO3)(n) superlattices
Authors:
Bhattacharya, A; May, SJ; Velthuis, SGET; Warusawithana, M; Zhai, X; Jiang, B; Zuo, JM; Fitzsimmons, MR; Bader, SD; Eckstein, JN Author Full Names: Bhattacharya, A.; May, S. J.; Velthuis, S. G. E. te; Warusawithana, M.; Zhai, X.; Jiang, Bin; Zuo, J. -M.; Fitzsimmons, M. R.; Bader, S. D.; Eckstein, J. N.
Source:
PHYSICAL REVIEW LETTERS 100 (25): Art. No. 257203 JUN 27 2008
Abstract:
Superlattices of (LaMnO3)(2n)/(SrMnO3)(n) (1 <= n <= 5), composed of the gapped insulators LaMnO3 and SrMnO3, undergo a metal-insulator transition as a function of n, being metallic for n <= 2 and insulating for n >= 3. Measurements of transport, magnetization, and polarized neutron reflectivity reveal that the ferromagnetism is relatively uniform in the metallic state, and is strongly modulated in the insulating state, being high in LaMnO3 and suppressed in SrMnO3. The modulation is consistent with a Mott transition driven by the proximity between the (LaMnO3)/(SrMnO3) interfaces. The insulating state for n >= 3 obeys variable range hopping at low temperatures. We suggest that this is due to states at the Fermi level that emerge at the (LaMnO3)/(SrMnO3) interfaces and are localized by disorder.
Title:
Martensitic transformation of Ni2FeGa ferromagnetic shape-memory alloy studied via transmission electron microscopy and electron energy-loss spectroscopy
Authors:
Zhang, HR; Ma, C; Tian, HF; Wu, GH; Li, JQ Author Full Names: Zhang, H. R.; Ma, C.; Tian, H. F.; Wu, G. H.; Li, J. Q.
Source:
PHYSICAL REVIEW B 77 (21): Art. No. 214106 JUN 2008
Abstract:
The structural properties of Ni2FeGa Heusler alloy synthesized by melt-spinning technique have been systematically studied by means of in situ heating and cooling transmission electron microscopy. It was found that the Ni2FeGa alloy was annealed into a well-defined L2(1) structure at around 980 K, and complex microstructural domains appeared along with lowering temperature. At room temperature (293 K), a rich variety of micromodulated domains were observed. The domain structures were aligned along the < 110 > or < 100 > directions resulting to complex tweed structures. Below martensitic transformation (MT) temperature (M-s,similar to 142 K), the cubic parent phase transformed into unmodulated martensitic variants and modulated martensitic variants. The variants were alternated along the < 100 > direction with various arrangements and steplike incommensurate boundaries. The modulated martensitic variants were composed of lamellar structures that have predominately a 5M modulation structure along the < 110 > directions. The electron energy-loss spectroscopy analysis of the low-loss region and the electron energy-loss near-edge fine structure revealed a visible change of the electronic structure along with MT, which can be well interpreted by means of intra-atomic or intraband charge redistribution due to spd orbital hybridization among the Ni-Fe-Ga atoms.
Title:
Ordered magnetic phases of the frustrated spin-dimer compound Ba3Mn2O8
Authors:
Samulon, EC; Jo, YJ; Sengupta, P; Batista, CD; Jaime, M; Balicas, L; Fisher, IR Author Full Names: Samulon, E. C.; Jo, Y. -J.; Sengupta, P.; Batista, C. D.; Jaime, M.; Balicas, L.; Fisher, I. R.
Source:
PHYSICAL REVIEW B 77 (21): Art. No. 214441 JUN 2008
Abstract:
Ba3Mn2O8 is a spin-dimer compound based on pairs of S=1, 3d(2), Mn5+ ions arranged on a triangular lattice. Antiferromagnetic intradimer exchange leads to a singlet ground state in zero field. Here we present the first results of thermodynamic measurements for single crystals probing the high-field ordered states of this material associated with closing the spin gap to the excited triplet states. Specific heat, magnetocaloric effect, and torque magnetometry measurements were performed in magnetic fields up to 32 T and temperatures down to 20 mK. For fields above H-c1 similar to 8.7 T, these measurements reveal a single magnetic phase for H parallel to c but two distinct phases (approximately symmetric about the center of the phase diagram) for H perpendicular to c. Analysis of the simplest possible spin Hamiltonian describing this system yields candidates for these ordered states corresponding to a simple spiral structure for H parallel to c and to two distinct modulated phases for H perpendicular to c. Both single-ion anisotropy and geometric frustration play crucial roles in defining the phase diagram.
Title:
Pressure-induced polarization reversal in multiferroic YMn2O5
Authors:
Chaudhury, RP; dela Cruz, CR; Lorenz, B; Sun, YY; Chu, CW; Park, S; Cheong, SW Author Full Names: Chaudhury, Rajit P.; dela Cruz, Clarina R.; Lorenz, Bernd; Sun, Yanyi; Chu, Ching-Wu; Park, S.; Cheong, Sang-W.
Source:
PHYSICAL REVIEW B 77 (22): Art. No. 220104 JUN 2008
Abstract:
The low-temperature ferroelectric polarization of multiferroic YMn2O5 is completely reversed at a critical pressure of 10 kbar and the phase transition from the incommensurate to the commensurate magnetic phase is induced by pressures above 14 kbar. The high-pressure data correlate with thermal-expansion measurements, indicating a significant lattice strain at the low-temperature transition into the incommensurate phase. The results support the exchange striction model for the ferroelectricity in multiferroic RMn2O5 compounds and they show the importance of magnetic frustration as well as the spin-lattice coupling.
Title:
Incommensurate spin ordering and fluctuations in underdoped La2-xBaxCuO4
Authors:
Dunsiger, SR; Zhao, Y; Yamani, Z; Buyers, WJL; Dabkowska, HA; Gaulin, BD Author Full Names: Dunsiger, S. R.; Zhao, Y.; Yamani, Z.; Buyers, W. J. L.; Dabkowska, H. A.; Gaulin, B. D.
Source:
PHYSICAL REVIEW B 77 (22): Art. No. 224410 JUN 2008
Abstract:
By using neutron scattering techniques, we have studied the incommensurate spin ordering as well as the low energy spin dynamics in single crystal underdoped La2-xBaxCuO4 with x similar to 0.095 and 0.08, which are high temperature superconductors with T-C similar to 27 and 29 K, respectively. Static two dimensional incommensurate magnetic order appears below T-N=39.5 +/- 0.3 K in La2-xBaxCuO4 (x=0.095) and a similar temperature for x=0.08 within the low temperature tetragonal phase. The spin order is unaffected by either the onset of superconductivity or the application of magnetic fields of up to 7 T applied along the c axis in the x=0.095 sample. Such a magnetic field independent behavior is in marked contrast to the field induced enhancement of the staggered magnetization observed in the related La2-xSrxCuO4 system, which indicates that this phenomenon is not a universal property of cuprate superconductors. Surprisingly, we find that the incommensurability delta is only weakly dependent on doping relative to La2-xSrxCuO4. Dispersive excitations in La2-xBaxCuO4 (x=0.095) at the same incommensurate wave vector persist up to at least 60 K. The dynamical spin susceptibility of the low energy spin excitations saturates below T-C in a similar manner to that seen in the superconducting state of La2CuO4+y.
Title:
Change of antiferromagnetic structure near a quantum critical point in CeRh1-xCoxIn5
Authors:
Yokoyama, M; Oyama, N; Amitsuka, H; Oinuma, S; Kawasaki, I; Tenya, K; Matsuura, M; Hirota, K; Sato, TJ Author Full Names: Yokoyama, M.; Oyama, N.; Amitsuka, H.; Oinuma, S.; Kawasaki, I.; Tenya, K.; Matsuura, M.; Hirota, K.; Sato, T. J.
Source:
PHYSICAL REVIEW B 77 (22): Art. No. 224501 JUN 2008
Abstract:
The elastic neutron-scattering experiments were carried out on the solid solutions CeRh1-xCoxIn5 to clarify the nature of the antiferromagnetic (AF) state in the vicinity of the quantum critical point: x(c)similar to 0.8. The incommensurate AF order with the wave vector of q(h)=(1/2,1/2,similar to 0.3) observed in pure CeRhIn5 is weakly suppressed upon doping with Co, and a commensurate q(c)=(1/2,1/2,1/2) and an incommensurate q(1)=(1/2,1/2,similar to 0.42) AF structures evolve at intermediate Co concentrations. The AF orders with q(c) and q(1) are enhanced at x=0.7, and furthermore, the q(h) AF order vanishes. These results suggest that the AF correlations with the q(c) and q(1) modulations are significantly enhanced in the intermediate x range, and may be connected with the evolution of the superconductivity observed above x similar to 0.3.
Title:
Effect of Al addition on the elevated temperature deformation behavior of Mg-Zn-Y alloy
Authors:
Kim, DH; Lee, JY; Lim, HK; Kim, WT; Kim, DH Author Full Names: Kim, Do Hyung; Lee, Ju Yeon; Lim, Hyun Kyu; Kim, Won Tae; Kim, Do Hyang
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 487 (1-2): 481-487 JUL 25 2008
Abstract:
The effect of the addition of Al on the high temperature deformation behavior of wrought Mg-4Zn-0.8Y alloy has been investigated. The addition of Al significantly improves the high temperature formability, i.e. increases elongation from 260% to 370% under a strain rate of 1 x 10(-4) s(-1) at 300 degrees C. Strain rate sensitivity measured at different strain rates shows that the addition of Al induces the transition of high temperature deformation mechanism from dislocation creep mode to grain boundary sliding mode. Effect of alloying elements and microstructural evolution including the role of icosahedral-phase during deformation are discussed. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Characterization of Ni-Mn-Ga alloy with Gd addition
Authors:
Zhang, ZY; Du, ZW; Shao, BL; Liu, AS; Sun, ZM Author Full Names: Zhang, Z. Y.; Du, Z. W.; Shao, B. L.; Liu, A. S.; Sun, Z. M.
Source:
MATERIALS CHARACTERIZATION 59 (8): 1041-1045 AUG 2008
Abstract:
The effect of rare earth element Gd additions in an Ni-Mn-Ga alloy on magnetocaloric effect has previously been investigated. In this paper, the microstructure of Ni53.4Mn20Ga25.6Gd1 was studied by TEM. The results show that Gd partly dissolves in the matrix and partly occurs as precipitates such as Gd and Ni-rich Ni-Mn-Ga-Gd quaternary phases. At room temperature, the alloy is mainly composed of non-modulated martensite with a small amount of seven-layered and ten-layered modulated martensite. The high-resolution electron microscopy (HREM) images also reveal that some layered structures in certain zones are microtwins in nature with a thickness of a few atomic planes as the stacking sequence is not periodic. (C) 2007 Elsevier Inc. All rights reserved.
Title:
Superspace description, crystal structures, and electric conductivity of the Ba4In6-xMgxO13-x/2 solid solutions
Authors:
Abakumov, AM; Rossell, MD; Gutnikova, OY; Drozhzhin, OA; Leonova, LS; Dobrovolsky, YA; Istomin, SY; Van Tendeloo, G; Antipovt, EV Author Full Names: Abakumov, Artem M.; Rossell, Marta D.; Gutnikova, Olga Yu.; Drozhzhin, Oleg A.; Leonova, Ludmila S.; Dobrovolsky, Yuri A.; Istomin, Sergey Ya.; Van Tendeloo, Gustaaf; Antipovt, Evgeny V.
Source:
CHEMISTRY OF MATERIALS 20 (13): 4457-4467 JUL 8 2008
Abstract:
Ba3In6-xMgxO13-x/2 solid solutions have been prepar for 0 <= x <= 0.4 and their crystal structures have been studied by transmission electron microscopy and X-ray powder diffraction. The compounds adopt a modulated structure with a face-centered orthorhombic average unit cell with a(0)approximate to a(p) root 2, b(0)approximate to 20.5 angstrom, c(0)approximate to a(p) root 2 (a(p) - parameter of the perovskite subcell) and modulation vector.q=alpha a(0)* , which is compositionally dependent according to the Ba4In4+4 alpha Mg2-4 alpha O12+2 alpha formula.The -superspace group Xmms(alpha 00)0s0 Xrnrn2(a00)0s0 with centering vectors (0,1/2,1/2,1/2), (1/2,0,1/2,0.(1/2,1/2,0 1/2) was propose ed from electron diffraction and structural considerations. A unified suoersoace model is" construtted'to describe the atomic arrangements and the variable oxygen content in the modulated (In, Mg)2Q2+a layers with rock-salt type structure. This model was used to refine the crystai structures of two x= 0 (R-I 0.040, R-p = 0.042) and x = 0.4 (R-I = 0.062, R-p = 0.040) limiting points of the solid solu tions. The cations in these layers adopt a five-fold coordination that can be virtually classified as strongly distorted trigonal bipyramids and tetragonal pyramids. The close similarity of the structural organization of the Ba4In6-xMgxO13-x/2 solid solutions, Sr4Fe6O13 and its anion-deficient derivatives is discussed. Electric conductivity of the Ba4In6-xMgxO13-x/2 was studied by impedance spectroscopy indicating mixed ionicelectronic type of conductivity. Electronic conductivity at different P(O-2) was compared for Ba4In6-xMgxO13-x/2 and Ba2In2O5 and discussed taking into account the peculiarities of their crystal structures.

Update: 18-Jul-2008

Title:
Software package for structure analysis of quasicrystals
Authors:
Yamamoto, A Author Full Names: Yamamoto, Akiji
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 9 (1): Art. No. 013001 JAN-MAR 2008
Abstract:
Recently a software package for the structure analysis of quasicrystals has been released, giving a better environment for determining quasicrystal structures. Therefore we can analyze their structures if we know data collection and indexing methods and a theory of structure analysis. For the use of the package, the structure analysis method and several techniques used in the package are shortly reviewed. How to treat key information in the input files of the programs is described in detail.
Title:
Icosahedral clusters, icosaheral order and stability of quasicrystals - a view of metallurgy
Authors:
Tsai, AP Author Full Names: Tsai, An Pang
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 9 (1): Art. No. 013008 JAN-MAR 2008
Abstract:
We review the stability of various icosahedral quasicrystals ( iQc) from a metallurgical viewpoint. The stability of stable iQcs is well interpreted in terms of Hume-Rothery rules, i.e. atomic size factor and valence electron concentration, e/a. For metastable iQcs, we discuss the role of phason disorder introduced by rapid solidification, in structural stability and its interplay with chemical order and composition.
Title:
Finite doping of a one-dimensional charge density wave: Solitons vs Luttinger liquid charge density
Authors:
Weiss, Y; Goldstein, M; Berkovits, R Author Full Names: Weiss, Yuval; Goldstein, Moshe; Berkovits, Richard
Source:
PHYSICAL REVIEW B 77 (20): Art. No. 205128 MAY 2008
Abstract:
The effects of doping on a one-dimensional wire in a charge density wave state are studied using the density-matrix renormalization group method. We show that for a finite number of extra electrons, the ground state becomes conducting but the particle density along the wire corresponds to a charge density wave with an incommensurate+ wave number determined by the filling. We find that the absence of the translational invariance can be discerned even in the thermodynamic limit is long as the number of doping electrons is finite. The Luttinger liquid behavior is reached only for a finite change in the electron filling factor, which for an infinite wire corresponds to the addition of an infinite number of electrons. In addition to the half filled insulating Mott state and the conducting states, we find evidence for subgap states at fillings different from half filling by a single electron or hole. Finally, we show that by coupling our system to a quantum dot, one ca! n have a discontinuous dependence of its population on the applied gate voltage in the thermodynamic limit, similar to the one predicted for a Luttinger liquid without umklapp processes.
Title:
Phase transformation behaviour in continuously cooled Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5) glass-forming alloys and consequences for structure and property control
Authors:
Setyawan, AD; Kato, H; Saida, J; Inoue, A Author Full Names: Setyawan, A. D.; Kato, H.; Saida, J.; Inoue, A.
Source:
PHILOSOPHICAL MAGAZINE 88 (8): 1125-1136 2008
Abstract:
Continuous cooling transformation (CCT) diagrams were successfully constructed for Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5) glass-forming alloys, comparing phase-transformation features in the alloy system to composition. While a low-Pd alloy (x=5) showed a single transformation curve, corresponding to the formation of a crystalline phase on the high-temperature side of the undercooled-liquid region, for a given time-scale, a high-Pd alloy (x=17.5) revealed an additional curve, corresponding to quasicrystalline phase formation on the lower temperature side. The result provides a clue to the structural and property control on the alloy system. Glassy specimens of the same size but with different intrinsic structure, evaluated by structural relaxation during continuous heating, could be fabricated for the low-Pd alloy (x=5). Plasticity was found to increase proportionally with the relaxation enthalpy. On the other hand, the critical size for glass formation could be improved considerably from 5 to 7 mm in diameter for the high-Pd alloy (x=17.5).
Title:
A multi-component Fermi surface in the vortex state of an underdoped high-T-c superconductor
Authors:
Sebastian, SE; Harrison, N; Palm, E; Murphy, TP; Mielke, CH; Liang, RX; Bonn, DA; Hardy, WN; Lonzarich, GG Author Full Names: Sebastian, Suchitra E.; Harrison, N.; Palm, E.; Murphy, T. P.; Mielke, C. H.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Lonzarich, G. G.
Source:
NATURE 454 (7201): 200-203 JUL 10 2008
Abstract:
To understand the origin of superconductivity, it is crucial to ascertain the nature and origin of the primary carriers available to participate in pairing(1-6). Recent quantum oscillation experiments on high- transition- temperature ( high- T-c) copper oxide superconductors(7-10) have revealed the existence of a Fermi surface akin to that in normal metals, comprising fermionic carriers that undergo orbital quantization(11). The unexpectedly small size of the observed carrier pocket, however, leaves open a variety of possibilities for the existence or form of any underlying magnetic order, and its relation to d- wave superconductivity(12-15). Here we report experiments on quantum oscillations in the magnetization ( the de Haas- van Alphen effect) in superconducting YBa2Cu3O6.51 that reveal more than one carrier pocket. In particular, we find evidence for the existence of a much larger pocket of heavier mass carriers playing a thermodynamically dominant role in this hole- doped superconductor. Importantly, characteristics of the multiple pockets within this more complete Fermi surface impose constraints on the wavevector of any underlying order and the location of the carriers in momentum space. These constraints enable us to construct a possible density- wave model with spiral or related modulated magnetic order, consistent with experimental observations.
Title:
Origins of superstructure ordering and incommensurability in stuffed CoSn-Type phases
Authors:
Fredrickson, DC; Lidin, S; Venturini, G; Malaman, B; Christensen, J Author Full Names: Fredrickson, Daniel C.; Lidin, Sven; Venturini, Gerard; Malaman, Bernard; Christensen, Jeppe
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (26): 8195-8214 JUL 2 2008
Abstract:
The CoSn structure type contains large interstitial void spaces that frequently host electropositive guest atoms, such as rare earth elements. In this stuffing process, an intriguing ordering occurs between the neighboring void spaces leading to a family of long-period superstructures comprising intergrowths of the ScFe6Ge6 and ScFe6Ga6 structure types. This superstucture ordering culminates in incommensurability in the REFe6Ge6_delta Ga6 systems with RE = Sc, Tb, and Lu. In this work, we derive a 3 + 1 D superspace model encompassing this series of structures and investigate the origins of the structural trends in this family with electronic structure calculations, at both the LDA-DFT and extended Huckel levels. Using our 3 + 1 D model, we refine the structures of four new ErFe6Ge6-delta Ga delta (0 <= 6 <= 6) phases, two commensurate and two incommensurate, from powder X-ray diffraction data. The refinement results confirm trends observed in the Sc-, Tb -, and Lu-based series: a gradual lengthening and, eventually, turning of the q-vector as Ge is progressively exchanged for Ga. These trends, and the incommensurate ordering as a whole, are traced to a tension between two modes by which the host lattice responds to stuffing atom insertion: (1) an atomic charge modulation enhancing the anionic character of the cavity walls around the guest atoms, and (2) a positional modulation expanding the cavities occupied by guest atoms. These two modes direct the stuffing atom ordering pattern toward opposite ends of the ScFe6Ge6-ScFe6Ga6 intergrowth series. The full series of structures, complex and incommensurate, reflects various degrees of balance between these two factors.
Title:
Incommensurate strain-induced ordering of interstitial oxygen in Nb
Authors:
Kurta, RP; Bugaev, VN; Stierle, A; Dosch, H Author Full Names: Kurta, R. P.; Bugaev, V. N.; Stierle, A.; Dosch, H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (27): Art. No. 275206 JUL 9 2008
Abstract:
We present a semi-phenomenological theory of the strain-induced interaction between interstitial oxygen dissolved in Nb and predict an incommensurate oxygen ordering wave which is mediated by the intrinsic bcc instability at kappa = 2/3(111). We discuss the stability range of this ordering phenomenon, which may play a role in the performance of Nb radio frequency (RF) cavities for high energy particle accelerators.
Title:
Effects of Nb on the formation of icosahedral quasicrystalline phase in Ti-rich Ti-Zr-Ni-Cu-Be glassy forming alloys
Authors:
Mei, JN; Li, JS; Kou, HC; Fu, HZ; Zhou, L Author Full Names: Mei, J. N.; Li, J. S.; Kou, H. C.; Fu, H. Z.; Zhou, L.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 354 (28): 3332-3335 JUN 15 2008
Abstract:
As-cast (Ti40Zr25Ni8Cu9Be18)(100-x)Nb-x (0 <= x <= 5) (Phi 3) glassy forming alloys were investigated in order to clarify the role of Nb on the formation of icosahedral quasicrystalline phase (I-phase) in Ti-rich Ti-Zr-Ni-Cu-Be glassy system. It is found that an I-phase is formed in Ti-Zr-Ni-Cu-Be glassy alloy by addition of Nb element; however, the nucleation rate of I-phase increases, whereas the grain growth rate decreases with increasing Nb content. Moreover, with increasing Nb content, the thermal stability against crystallization increases, while the temperature range of stability of the I-phase decreases. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Thermal stability, microstructure and crystallization kinetics of melt-spun Zr-Ti-Cu-Ni metallic glass
Authors:
Scudino, S; Venkataraman, S; Eckert, J Author Full Names: Scudino, S.; Venkataraman, S.; Eckert, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 460 (1-2): 263-267 JUL 28 2008
Abstract:
Melt-spun Zr63.33Ti8.89Cu15.45Ni2.33 glassy ribbons display a double-step devitrification behavior characterized by the precipitation of a metastable quasicrystalline phase in the first stage of the crystallization process, followed by the formation of crystalline phases in the following crystallization event. Investigation of the crystallization kinetics reveal that the initial part of the glass-to-quasicrystalline transformation (x <= 55 vol.%) occurs by diffusion controlled growth with an increasing nucleation rate (Avrami exponent n >= 2.5), whereas the later stage of the transformation (x > 55 vol.%) is dominated by the growth of the formed nuclei rather than by the generation of new nuclei (2.0 <= n <= 2.5). The activation energy for quasicrystallization is 360 kJ/mol, which is comparable to the values reported for other quasicrystal-forming Zr-based metallic glasses. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Unusual devitrification behaviour in rapidly solidified Ti45Zr38Ni17 alloy
Authors:
Lefaix, H; Vermaut, P; Janickovic, D; Svec, P; Gloriant, T; Portier, R; Prima, F Author Full Names: Lefaix, H.; Vermaut, P.; Janickovic, D.; Svec, P.; Gloriant, T.; Portier, R.; Prima, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 460 (1-2): 392-399 JUL 28 2008
Abstract:
In this study, Ti45Zr38Ni17 ribbons have been elaborated using planar flow casting method (v(quenching) 106 K s(-1)). The rapidly quenched samples, displaying a dispersion of nanoscaled beta phase particles in an amorphous matrix, have been extensively characterised using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Devitrification behaviour, investigated by four-probe resistivity measurements and differential scanning calorimetry as well as high resolution TEM analysis, revealed the formation of nanometric quasicrystals (QC) during the first exothermic phase transformation as well as the precipitation of omega domains inside beta particles. On the basis of these data, it has been noticed that nanoscaled beta metastable particles had adopted the same temperature dependence as beta metastable bulk. Furthermore, particular orientation relationships have been observed for QCs in the vicinity of beta particles which have suggested probable influence of crystalline structure on the QCs growth, although the presence of such peculiar materials after annealing treatment could be mainly explained by an icosahedral short-range order prevailing in Ti-Zr-Ni melt and favouring their nucleation. (C) 2007 Elsevier B.V. All rights reserved.

Update: 11-Jul-2008

Title:
SEM study of quasi-crystallized Zr65Cu12.5Ni10Al7.5Ag5 amorphous alloy at initial stage
Authors:
Wu, HM; Sun, W; Zhang, Z; Liu, L; Zhang, T Author Full Names: Wu Huimin; Sun Wei; Zhang Ze; Liu Li; Zhang Tao
Source:
RARE METAL MATERIALS AND ENGINEERING 37 (5): 823-826 MAY 2008
Abstract:
Microstructure evolvement during crystallization process for the melt-spun Zr65Cu12.5Ni10Al7.5Ag5 amorphous alloy has been studied by DSC analysis and TEM. We monitor the crystallization process by DSC, and stop at given temperatures, following by cooling down from these temperatures in the DSC furnace to examine the corresponding microstructure evolvement by TEM. The results show that the crystallization of Zr65Cu12.5Ni10Al7.5Ag5 alloy can be divided into three stages. At the initial stage, an icosahedral quasi-crystal (I-phase) is formed as primary phase from the amorphous matrix without apparent compositional variation. In comparison with the amorphous matrix, the I-phase is Zr-rich and Cu-poor slightly with high nucleation and growth rates by consuming the amorphous matrix, leading to a microstructure with closed packed grains at the first stage of crystallization. However, the residual amorphous phase still exists at this stage.
Title:
Pressure dependence of the magnetic ordering in CeRhIn5
Authors:
Raymond, S; Knebel, G; Aoki, D; Flouquet, J Author Full Names: Raymond, S.; Knebel, G.; Aoki, D.; Flouquet, J.
Source:
PHYSICAL REVIEW B 77 (17): Art. No. 172502 MAY 2008
Abstract:
We determine by neutron diffraction the propagation vector of the magnetic structure of CeRhIn5 under pressures of 1.5 and 1.7 GPa down to 375 mK. For both pressures, an incommensurate propagation vector k(IC2)=(1/2,1/2,0.4) is found in contrast to the low pressure one k(ICI)=(1/2,1/2,0.298). At 1.7 GPa, no change is found in the propagation vector and the intensity of the magnetic peaks in the superconducting phase below 1 K.
Title:
Magnetically asymmetiric interfaces in a LaMnO3/SrMnG(3) superlattice due to structural asymmetries
Authors:
May, SJ; Shah, AB; Velthuis, SGET; Fitzsimmons, MR; Zuo, JM; Zhai, X; Eckstein, JN; Bader, SD; Bhattacharya, A Author Full Names: May, S. J.; Shah, A. B.; Velthuis, S. G. E. te; Fitzsimmons, M. R.; Zuo, J. M.; Zhai, X.; Eckstein, J. N.; Bader, S. D.; Bhattacharya, A.
Source:
PHYSICAL REVIEW B 77 (17): Art. No. 174409 MAY 2008
Abstract:
Polarized neutron reflectivity measurements of a ferromagnetic [(LaMnO3)(11.8)/(SrMnO3)(4.4)](6) superlattice reveal a modulated magnetic structure with an enhanced magnetization at the interfaces where LaMnO3 was deposited on SrMnO3 (LMO/SMO). However, the opposite interfaces (SMO/LMO) are found to have a reduced ferromagnetic moment. The magnetic asymmetry is accompanied by a corresponding asymmetry in the lateral structural roughness of the two interfaces observed via electron microscopy, with enhanced ferromagnetism present at the interfaces that are atomically smooth over tens of nanometers. This result demonstrates that atomic-scale roughness can destabilize interfacial phases in complex oxide heterostructures.
Title:
Spin polarization of the magnetic spiral in NaCu2O2 as seen by nuclear magnetic resonance spectroscopy
Authors:
Gippius, AA; Moskvin, AS; Drechsler, SL Author Full Names: Gippius, A. A.; Moskvin, A. S.; Drechsler, S. -L.
Source:
PHYSICAL REVIEW B 77 (18): Art. No. 180403 MAY 2008
Abstract:
The incommensurate (IC) spin ordering in quasi-one-dimensional edge-shared cuprate NaCu2O2 has been studied by Na-23 nuclear magnetic resonance spectroscopy in an external magnetic field near 6 T applied along the main crystallographic axes. The NMR line shape evolution above and below TN approximate to 12 K yields a clear signature of an IC static modulation of the local magnetic field consistent with a Cu2+ spin spiral polarized in the bc plane rather than in the ab plane, as reported from earlier neutron diffraction data.
Title:
Comparison between experimental surface data and bulk structure models for quasicrystalline A1PdMn: Average atomic densities and chemical compositions
Authors:
Unal, B; Jenks, CJ; Thiel, RA Author Full Names: Unal, Baris; Jenks, C. J.; Thiel, R. A.
Source:
PHYSICAL REVIEW B 77 (19): Art. No. 195419 MAY 2008
Abstract:
We have examined bulk structure models for icosahedral A1PdMn in terms of the densities, compositions, and interplanar spacings for the fivefold planes that might represent physical surface terminations. We focus on four models that contain no partial or mixed occupancies, but some comparison is made to a fifth model containing such sites. Each of the four models contains paired planes (layers) that can be separated into two main families on the basis of three features: the relative densities of the two planes, the gap separating the layer from the nearest atomic plane, and the Pd content in the topmost plane. The experimental data and other arguments lead to the conclusion that the family with no Pd in the top plane is favored. Finally, all models show that correlations should be expected between the heights of steps that delineate terraces and average compositional and/or structural features of the terraces.
Title:
Mechanical properties and microstructure of twin-roll cast Mg-Zn-Y alloy
Authors:
Kim, KH; Lee, JG; Bae, GT; Bae, JH; Kim, NJ Author Full Names: Kim, Kyung-Hun; Lee, Jung Gu; Bae, Geun Tae; Bae, Jun Ho; Kim, Nack J.
Source:
MATERIALS TRANSACTIONS 49 (5): 980-985 MAY 2008
Abstract:
Mg97.3Zn2.3Y0.4 alloy has been subjected to twin-roll casting (TRC) process. As-cast microstructure consists of alpha-Mg dendrite and icosahedral interdendritic phase. The icosahedral phase present in TRC alloy is found to be thermally unstable and transforms to H-phase and W-phase during subsequent thermo-mechanical treatment (TMT) at 400 degrees C. It shows that the pre-heating condition has a significant effect on the microstructural evolution during TMT. The specimen pre-heated at 400 degrees C for 30 min shows elongated microstructure after TMT, while the specimen pre-heated at 400 degrees C for 12 h shows equiaxed recrystallized structure after TMT. Such homogeneous microstructure of the specimen pre-heated at 400 degrees C for 12 h results in better combinations of strength and ductility than the specimen pre-heated at 400 degrees C for 30 min.
Title:
Pressure-induced commensurate magnetic order in multiferroic HoMn2O5
Authors:
Kimura, H; Nishihata, K; Noda, Y; Aso, N; Matsubayashi, K; Uwatoko, Y; Fujiwara, T Author Full Names: Kimura, Hiroyuki; Nishihata, Keisuke; Noda, Yukio; Aso, Naofumi; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Fujiwara, Tetsuya
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (6): Art. No. 063704 JUN 2008
Abstract:
The pressure-temperature (p-T) phase diagram for microscopic magnetism in the multiferroic compound HoMn2O5 was established using neutron diffraction measurements under a hydrostatic pressure up to 1.25 GPa. At ambient pressure, incommensurate-commensurate-incommensurate magnetic phase transitions occur successively with decreasing temperature. Upon applying pressure, the incommensurate phase at the lowest temperature almost decreases and the commensurate phase appears. The p-T phase diagram established shows excellent agreement with the recently reported p-T dielectric phase diagram, where ferroelectricity is induced by applying pressure. We also found that the p-T magnetic phase diagram is quite similar to the previously obtained magnetic field-temperature phase diagram.
Title:
Discommensurate structure in [(Ca0.90Sr0.10)(2)CoO3](0.61)CoO2
Authors:
Yubuta, K; Huang, XY; Miyazaki, Y; Kajitani, T Author Full Names: Yubuta, Kunio; Huang, Xiangyang; Miyazaki, Yuzuru; Kajitani, Tsuyoshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (6): Art. No. 064604 JUN 2008
Abstract:
The crystal structure of partly Sr-substituted Co-121, i.e., "Ca3Co4Co9", single crystal is studied by means of the electron diffraction measurements and high-resolution transmission electron microscopy (HREM). The crystal structure consists of two interpenetrating subsystems of a CoO2 sheet and a distorted three-layered (Ca,Sr)(2)CoO3 rock-salt (RS)-type block layers, which belong to a triclinic system. Both subsystems have common a-, c-axes and alpha-, beta-, gamma-angle with a = 4.8267(1) angstrom, c = 10.9214(3) angstrom, alpha = 90.916(2)degrees, beta = 98.291(5)degrees, and gamma = 89.957(3)degrees. On the other hand, the crystal structure is modulated parallel to the b-axis, along which the CoO2 sheet has b(1) = 2.8346(1) angstrom and the (Ca,Sr)(2)CoO3 RS-type block layer has b(2) = 4.6391(2) angstrom, respectively. On the basis of the b(1)/b(2) ratio and analyzed chemical compositions, the structure analogue is formulated as [(Ca0.90Sr0.10)(2)CoO3](0.61)CoO2. In electron diffraction patterns, there are many new satellite reflections, namely 0101, 0202, 0204, and 0103, which are not present in the end member Co-121, i.e., (Ca2CoO3)(0.620)CoO2. Because of the new superlattice reflections, the crystal structure of the Sr-doped Compound is different from the end member. HREM images were taken with the incident electron beam parallel to the [0010] and [1000] directions. The basic crystal structure of the present system consists of 5-CoO2 and 3-RS subcells with b = 14 angstrom being connected discommensuratedly parallel to the a- and b-axes. Systematic introduction of stacking faults parallel to the a-b plane is also noticed.
Title:
Twin boundary structure of the modulated variants in a Ni-Mn-Ga alloy
Authors:
Han, M; Kong, FF Author Full Names: Han, M.; Kong, F. F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 458 (1-2): 218-222 JUN 30 2008
Abstract:
The micro structure of a Ni-Mn-Ga ferromagnetic shape memory alloy has been characterized by transmission electron microscopy. Electron diffraction reveals that the microstructure of the alloy predominately consists of seven-layer modulated martensite. There exists reflection-twinned relation between the martensitic variants. It is found that there are parallel and equidistant fringes at the boundary. The nature of these fringes is discussed and the results show that the boundary fringes are caused by the elastic strains associated with the coherent interface. (c) 2007 Elsevier B.V All rights reserved.
Title:
Bond stretching phonon anomalies due to incommensurate charge density wave instabilities in high-T-c cuprates
Authors:
Citro, R; Cojocaru, S; Marinaro, M Author Full Names: Citro, R.; Cojocaru, S.; Marinaro, M.
Source:
EUROPEAN PHYSICAL JOURNAL B 63 (2): 179-185 MAY 2008
Abstract:
Phonon anomalies observed in various high T-c cuprates are analyzed theoretically within the Hubbard-Holstein model in the limit of strong local electron correlations and in presence of long-range Coulomb interaction. The phonon self-energy is evaluated by taking into account the charge collective modes that become critical upon doping approaching an instability towards an incommensurate charge density wave (ICDW) driven by electron correlations. The doping dependence of phonon softening features and the highly distinctive phonon self-energy dependence on the wave vector agree with experiments. We discuss relevance of dynamical corrections to the density correlation function to achieve a sizeable bond-stretching phonon softening with a kink-like profile away from the zone boundary.
Title:
Reaction efficiency of diffusion-controlled processes on finite, aperiodic planar arrays
Authors:
Garza-Lopez, RA; Kaufman, A; Patel, R; Chang, J; Brzezinski, J; Kozak, JJ Author Full Names: Garza-Lopez, Roberto A.; Kaufman, Aaron; Patel, Reena; Chang, Joseph; Brzezinski, Jack; Kozak, John J.
Source:
CHEMICAL PHYSICS LETTERS 458 (1-6): 137-140 JUN 27 2008
Abstract:
Using the theory of finite Markov processes, we show quantitatively that diffusion-limited, reactive events on two finite planar arrays having an aperiodic lattice structure are kinetically advantaged relative to processes on platelets having a regular, hexagonal [ 63] structure. The possible relevance of the results obtained to catalytic processes on quasicrystals and zeolite 'rafts' is noted. (c) 2008 Elsevier B. V. All rights reserved.
Title:
Inter-martensite strain evolution in NiMnGa single crystals
Authors:
Hamilton, RF; Sehitoglu, H; Aslantas, K; Efstathiou, C; Maier, HJ Author Full Names: Hamilton, R. F.; Sehitoglu, H.; Aslantas, K.; Efstathiou, C.; Maier, H. J.
Source:
ACTA MATERIALIA 56 (10): 2231-2236 JUN 2008
Abstract:
Stress-induced martensitic transformations are clarified in classes of NiMnGa alloys which undergo the stress-free, thermal-induced inter-martensite transformation austenite (A) reversible arrow pre-martensite (PM) reversible arrow martensite. This study implements a comprehensive experimental approach, including analysis of the strain-temperature and stress-strain response, which discloses stress-induced inter-martensite transitions. The evolution of the transitions is elucidated using in situ digital image correlation (DIC) measurements of meso-scale strain fields. Under stress, this body of work unequivocally demonstrates that the transformation path becomes A reversible arrow PM reversible arrow I reversible arrow 10M. The I-phase is an intermediate stress-induced martensite with a modulation period between three and five-layers. Owing to the intermediate transition, the thermal hysteresis in the strain-temperature response is tiny (<10 degrees C) compared with the hysteresis (32 degrees C) for A reversible arrow 10M. The differential hysteresis levels are rationalized based on a thereto-mechanical formulation. Meso-scale DIC measurements quantify inter-martensite strain levels, which are indistinguishable from macro-scale stress-strain and strain-temperature responses. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Dislocation-climb plasticity: Modelling and comparison with the mechanical properties of icosahedral AlPdMn
Authors:
Mompiou, F; Caillard, D Author Full Names: Mompiou, F.; Caillard, D.
Source:
ACTA MATERIALIA 56 (10): 2262-2271 JUN 2008
Abstract:
A model of plasticity controlled by the pure climb motion of dislocations is proposed and compared with the mechanical properties of icosahedral AlPdMn. This model takes into account the chemical stress due to an out-of-equilibrium average concentration of vacancies, and the difficult nucleation of jog-pairs on climbing dislocations. It accounts for several unexplained properties of AlPdMn, namely a high strain-hardening at yield, a steady-state flow stress twice higher than the elastic limit, and two-stage relaxation curves. It also explains values of the stress-strain rate sensitivity larger than expected a priori, and activation energies larger than the self-diffusion one. The model may also be applicable to high-temperature deformation of crystals. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Elastic properties of two-dimensional quasicrystals
Authors:
Grimmer, H Author Full Names: Grimmer, Hans
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 459-464 Part 4 JUL 2008
Abstract:
Quasicrystals (QC) with two-dimensional quasiperiodic and one-dimensional periodic structure are considered. Their symmetry can be described by embedding the three-dimensional physical space V-E in a five-dimensional superspace V, which is the direct sum of V-E and a two-dimensional internal space V-I. A displacement v in V can be written as v = u + w, where u is an element of V-E and w is an element of V-I. If the QC has a point group P in V-E that is crystallographic, it is assumed that w and a vector u' is an element of V-E lying in the plane in which the crystal is quasiperiodic transform under equivalent representations of P, inequivalent ones if the point group is 5-, 8-, 10-or 12-gonal. From the Neumann principle follow restrictions on the form of the phonon, phason and phonon-phason coupling contributions to the elastic stiffness matrix that can be determined by combining the restrictions obtained for a set of elements generating the point group of interest. For the phonon part, the restrictions obtained for the generating elements do not depend on the system to which the point group belongs. This remains true for the phason and coupling parts in the case of crystallographic point groups but, in general, breaks down for the non-crystallographic ones. The form of the symmetric 12 x 12 matrix giving the phonon, phason and phonon-phason coupling contributions to the elastic stiffness is presented in graphic notation.

Update: 4-Jul-2008

Title:
Single-crystalline B12As2 on m-plane (1(1)over-bar00) 15R-SiC
Authors:
Chen, H; Wang, G; Dudley, M; Xu, Z; Edgar, JH; Batten, T; Kuball, M; Zhang, LH; Zhu, YM Author Full Names: Chen, Hui; Wang, Guan; Dudley, Michael; Xu, Zhou; Edgar, J. H.; Batten, Tim; Kuball, Martin; Zhang, Lihua; Zhu, Yimei
Source:
APPLIED PHYSICS LETTERS 92 (23): Art. No. 231917 JUN 9 2008
Abstract:
Single crystal, heteroepitaxial growth of icosahedral B12As2 (IBA, a boride semiconductor) on m-plane 15R-SiC is demonstrated. Previous studies of IBA on other substrates, i.e., (111)Si and (0001)6H-SiC, produced polycrystalline and twinned epilayers. In contrast, single-crystalline and untwinned IBA was achieved on m-plane 15R-SiC. Synchrotron white beam x-ray topography, Raman spectroscopy, and high resolution transmission electron microscopy confirm the high quality of the films. High quality growth is shown to be mediated by ordered nucleation of IBA on (474) substrate facets. This work demonstrates that m-plane 15R-SiC is a good substrate choice to grow high-quality untwinned IBA epilayers for future device applications. (C) 2008 American Institute of Physics.

Update: 27-Jun-2008

Title:
Analytical solutions for some defect problems in 1D hexagonal and 2D octagonal quasicrystals
Authors:
Wang, X; Pan, E Author Full Names: Wang, X.; Pan, E.
Source:
PRAMANA-JOURNAL OF PHYSICS 70 (5): 911-933 MAY 2008
Abstract:
We study some typical defect problems in one-dimensional (ID) hexagonal and two-dimensional (2D) octagonal quasicrystals. The first part of this investigation addresses in detail a uniformly moving screw dislocation in a ID hexagonal piezoelectric quasicrystal with point group 6mm. A general solution is derived in terms of two functions phi(1), phi(2), which satisfy wave equations, and another harmonic function phi(3). Elementary expressions for the phonon and phason displacements, strains, stresses, electric potential, electric fields and electric displacements induced by the moving screw dislocation are then arrived at by employing the obtained general solution. The derived solution is verified by comparison with existing solutions. Also obtained in this part of the investigation is the total energy of the moving screw dislocation. The second part of this investigation is devoted to the study of the interaction of a straight dislocation with a semi-infinite crack in an octagonal quasicrystal. Here the crack penetrates through the solid along the period direction and the dislocation line is parallel to the period direction. We first derive a general solution in terms of four analytic functions for plane strain problem in octagonal quasicrystals by means of differential operator theory and the complex variable method. All the phonon and phason displacements and stresses can be expressed in terms of the four analytic functions. Then we derive the exact solution for a straight dislocation near a semi-infinite crack in an octagonal quasicrystal, and also present the phonon and phason stress intensity factors induced by the straight dislocation and remote loads.
Title:
Synthesis and stability of Ti-Zr-Ni quasicrystals
Authors:
Azhazha, VM; Bovda, AM; Lavrinenko, SD; Onischenko, LV; Malykhin, SV; Pugachov, AT; Reshetnyak, MV; Stetsenko, OM; Savitskiy, BA Author Full Names: Azhazha, V. M.; Bovda, A. M.; Lavrinenko, S. D.; Onischenko, L. V.; Malykhin, S. V.; Pugachov, A. T.; Reshetnyak, M. V.; Stetsenko, O. M.; Savitskiy, B. A.
Source:
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY (4): 82-87 2007
Abstract:
For the Ti-Zr-Ni ribbons prepared by melt spinning, phase composition, structure, substructure, state of stress and several physical properties were studied as functions of their element compositions; and optimum parameters for single-phase icosahedral quasicrystal synthesis have been found. The icosahedral structure perfection characteristics, namely quasicrystallinity parameter X-ray coherence length, and average micro-strain values were determined for different synthesis regimes. Transversal gradient-like distributions of grain size, micro-and nano-hardness, Young modulus, residual stress, and substructure parameters have been revealed in the ribbons.
Title:
Modulated magnetic structures of the antiferromagnetic hydride CeRuSiH
Authors:
Tence, S; Andre, G; Gaudin, E; Chevalier, B Author Full Names: Tence, S.; Andre, G.; Gaudin, E.; Chevalier, B.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (25): Art. No. 255239 JUN 25 2008
Abstract:
The hydride CeRuSiH is derived from the non-magnetic heavy-fermion ternary silicide CeRuSi that crystallizes in the tetragonal CeFeSi-type structure (P4/nmm space group). This hydride exhibits two antiferromagnetic transitions at T-N1 = 7.5( 2) K and T-N2 = 3.1(2) K, evidenced by magnetization and specific heat measurements. Crystal and magnetic structures of CeRuSiH have thus been investigated by means of neutron powder diffraction, which has shown firstly that H-atoms are fully inserted in the [Ce-4]- tetrahedra. Moreover, between T-N1 and T-N2, the Ce magnetic moments are ordered in a collinear antiferromagnetic sinusoidal structure associated with the propagation vector k = (k(x), k(x), 1/2) (k(x) < 1/3 and tends to 1/3 with decreasing temperature). At T-N2, the magnetic structure becomes square wave modulated and commensurate with k = (1/3, 1/3, 1/2) as propagation vector. At 1.5 K, the structure is antiphase with a Ce magnetic moment of 1.68(2) mu(B). These magnetic structures are compared with those previously reported on the substituted ternary silicides (Ce1-xLax)Ru2Si2 and CeRu2(Si1-xGex)(2), which also present an antiferromagnetic behaviour.
Title:
Designed synthesis of families of misfit-layered compounds
Authors:
Lin, Q; Heideman, CL; Nguyen, N; Zschack, P; Chiritescu, C; Cahill, DG; Johnson, DC Author Full Names: Lin, Qiyin; Heideman, Colby L.; Nguyen, Ngoc; Zschack, Paul; Chiritescu, Catalin; Cahill, David G.; Johnson, David C.
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY (15): 2382-2385 MAY 2008
Abstract:
The synthesis of several new families of misfit-layered compounds is demonstrated. These compounds are crystalline along the c-axis and in the ab-plane, but show very short coherence lengths between ab-planes. This disorder leads to ultra-low and tunable thermal conductivity. Annealing iso-structural samples under a chalcogen vapour until equilibrium is reached results in reproducible Seebeck and resistivity values. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).
Title:
Quasicrystal mystery unraveled with computer simulation
Authors:
[Anon]
Source:
ADVANCED MATERIALS & PROCESSES 166 (6): 12-12 JUN 2008

Update: 20-Jun-2008

Title:
DFT studies on structure, mechanics and phase behavior of magnetic shape memory alloys: Ni2MnGa
Authors:
Kart, SO; Uludogan, M; Karaman, I; Cagin, T Author Full Names: Kart, S. Oezdemir; Uludogan, M.; Karaman, I.; Cagin, T.
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 205 (5): 1026-1035 MAY 2008
Abstract:
Magnetic shape memory alloys (MSMAs) are the smart materials which can undergo a reversible structural phase transition when a magnetic field is applied. The experimentally most studied MSMA, Ni2MnGa, undergoes a martensitic phase transition from a high temperature cubic phase to a low temperature tetragonal phase. In this work, a detailed study of structure, magnetic and mechanical properties of Ni2MnGa in these phases were performed using density functional theory (DFT). The predicted lattice constant, bulk modulus, magnetic moments and elastic constants of the initial L2(1) structure are in good agreement with experimental results and previous calculations. We report the martensitic phase at cla = 1.26 for non-modulated and cla = 0.93 for 5M modulated structures which are consistent with the experiments. Analysis of electronic density of states showed that the double minority spin peak appeared at the Fermi level is due to the hybridization of Ga 4p and Ni 3d states. The peaks in the minority spin in the cubic structure reverse their order during martensitic transformation. The elastic constants of martensitic phases were also calculated to encourage measurements of these quantities.
Title:
An effective model of magnetoelectricity in multiferroics RMn2O5
Authors:
Fang, C; Hu, JP Author Full Names: Fang, Chen; Hu, Jangping
Source:
EPL 82 (5): Art. No. 57005 JUN 2008
Abstract:
An effective model is developed to explain the phase diagram and the mechanism of magnetoelectric coupling in multiferroics, RMn2O5. We show that the nature of magnetoelectric coupling in RMn2O5 is a coupling between two Ising-type orders, namely, the ferroelectric order in the b-axis, and the. coupled magnetic order between two frustrated antiferromagnetic chains. The frustrated magnetic structure drives the system to a commensurate-incommensurate phase transition, which can be understood as a competition between a collinear order stemming from the "order by disorder" mechanism and a chiral symmetry order. The low-energy excitation is calculated and it quantitatively matches experimental results. Distinct features and the effects of external magnetic field in the electromagnon spectra in the incommensurate phase are predicted. Copyright (c) EPLA, 2008.

Update: 13-Jun-2008

Title:
Local structure of perovskite-based "Pb2Fe2O5"
Authors:
Hadermann, J; Abakumov, AM; Nikolaev, IV; Antipov, EV; Van Tendeloo, G Author Full Names: Hadermann, Joke; Abakumov, Artem M.; Nikolaev, Ivan V.; Antipov, Evgeny V.; Van Tendeloo, Gustaaf
Source:
SOLID STATE SCIENCES 10 (4): 382-389 APR 2008
Abstract:
The reciprocal lattice and defect structure of the crystallographic shear (CS) structures in perovskite-based "Pb2Fe2O5" are investigated using transmission electron microscopy. The reciprocal space for all observed 1/2[110](h0l)p CS structures can be described with the same average pseudocubic unit cell with a approximate to a(p) (a(p) - the parameter of the perovskite subcell), and modulation vector q approximate to alpha a* + gamma c* with alpha/y = h/l and superspace group X2/m(alpha 0 gamma) with a centering vector [1/2,1/2,1/2,1/2]. The defect structure is characterized by numerous mirror twins and coherent intergrowths of 1/2[110](h0l)p CS structures with different (h0l)p. There are no single CS planes in the perovskite matrix and there is no variation of the perovskite block thickness between the successive CS planes. The crystallographic similarity and the structural and chemical differences between the CS structures in "Pb2Fe2O5" and those in ReO3 and/or TiO2-type oxides are discussed. (C) 2007 Elsevier Masson SAS. All rights reserved.
Title:
Indentation creep study on a Zr-based bulk metallic glass containing nano-quasicrystals
Authors:
Lendvai, J; Fatay, D; Gubicza, J Author Full Names: Lendvai, J.; Fatay, D.; Gubicza, J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 483: 607-610 Sp. Iss. SI JUN 15 2008
Abstract:
The effect of crystallization on the creep behavior of a Zr-based bulk metallic glass (BMG) with the composition of Zr44Ti11Cu10Ni10B25 (at.%) was studied by indentation technique. The crystallization process was studied by isothermal annealing in a differential scanning calorimeter at three different temperatures above the glass transition temperature (677, 682 and 687 K). Two exothermic peaks are detected, the first one corresponds to the formation of a quasicrystalline phase. Indentation creep tests were carried out isothermally at the same three temperatures for studying the correlation between the amount of quasicrystalline phase and the creep behavior. A simple relationship between the viscosity and the crystalline phase fraction was found and the activation energy was found to decrease with the progress of crystallization. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Model for the transformation of an icosahedral phase into a B2 crystalline phase
Authors:
Kraposhin, VS; Talis, AL; Lam, HT; Dubois, JM Author Full Names: Kraposhin, V. S.; Talis, A. L.; Lam, Ha Thanh; Dubois, J-M
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (23): Art. No. 235215 JUN 11 2008
Abstract:
A model for the transformation of an Al-Cu-Fe icosahedral quasicrystal into a crystal with a B2-type phase is proposed. The model is based on two assumptions: ( 1) the main building block for the quasicrystal structure is a hierarchical dodecahedron composed of two icosahedral clusters, coinciding with two different sections of the {3, 3, 5} polytope; ( 2) the transformation of the quasicrystal into a B2-type crystal phase can be described as the transition between 3D sections of two polytopes, namely {3, 3, 5} and {3, 4, 3}. In the framework of the proposed model, two experimental facts gain plausible explanations: the transformation of the Al-Cu-Fe quasicrystal into the BCC phase specifically and the orientational relationships observed between this BCC phase and the initial icosahedral quasicrystal.
Title:
Amorphous-to-quasicrystalline transformations in the Ti-Zr-Ni and Ti-Hf-Ni systems
Authors:
Kocjan, A; McGuiness, PJ; Linaric, MR; Kobe, S Author Full Names: Kocjan, A.; McGuiness, P. J.; Linaric, M. Rajic; Kobe, S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 457 (1-2): 144-149 JUN 12 2008
Abstract:
We have synthesized Ti-Zr-Ni- and Ti-Hf-Ni-based quasicrystals by the mechanical alloying of elementary powders with an average particle size of 35 mu m in a high-energy planetary ball mill followed by a vacuum heat treatment. The X-ray diffraction (XRD) spectra indicate that the mixture was to a large extent amorphous after mechanically alloying for more than 40 h. These largely amorphous precursors, after various times of mechanical alloying, were subsequently analysed by means of differential scanning calorimetry (DSC) in order to obtain the kinetic parameters of crystallization, such as the temperature and the activation energy. DSC was used in combination with XRD to identify the structural changes related to the peaks in the DSC scans. The morphologies and compositions were analysed using scanning electron microscopy with an energy-dispersive spectrometer. We observed agglomerates ranging in size from 5 to 50 mu m; these agglomerates consisted of smaller particles with sub-micrometer diameters. The composition of the agglomerates was not homogenous, since small areas (similar to 1 mu m) of Zr-rich secondary phase were observed inside them. Using a vibrating-sample magnetometer (VSM) we found that the saturation magnetization decreases with mechanical treatment, and is additionally decreased with the time and temperature of a subsequent vacuum heat treatment. The saturation magnetization (M-s) decreases fairly linearly, from the initial mixture of crystalline elements, which is ferromagnetic due to nickel, through to a largely amorphous phase, and then to the quasicrystalline phase, where the M-s value is the lowest. As a result, measuring the magnetic properties allows us to probe the structural transformations in the material. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Collinear second harmonic generations in a nonlinear photonic quasicrystal
Authors:
Sheng, Y; Koynov, K; Dou, JH; Ma, BQ; Li, JJ; Zhang, DZ Author Full Names: Sheng, Yan; Koynov, Kaloian; Dou, Junhong; Ma, Boqin; Li, Jingjuan; Zhang, Daozhong
Source:
APPLIED PHYSICS LETTERS 92 (20): Art. No. 201113 MAY 19 2008
Abstract:
LiNbO3 nonlinear photonic quasicrystal with octagonal symmetry was fabricated. The collinear quasiphase matched second harmonic generations at 22 wavelengths were observed. It is shown that not only the standard type quasiphase matching but also the recently proposed projection-based quasiphase matching plays an important role in these harmonic generations. (c) 2008 American Institute of Physics.

Update: 6-Jun-2008

Title:
Pseudogap and charge density waves in two dimensions
Authors:
Borisenko, SV; Kordyuk, AA; Yaresko, AN; Zabolotnyy, VB; Inosov, DS; Schuster, R; Buchner, B; Weber, R; Follath, R; Patthey, L; Berger, H Author Full Names: Borisenko, S. V.; Kordyuk, A. A.; Yaresko, A. N.; Zabolotnyy, V. B.; Inosov, D. S.; Schuster, R.; Buechner, B.; Weber, R.; Follath, R.; Patthey, L.; Berger, H.
Source:
PHYSICAL REVIEW LETTERS 100 (19): Art. No. 196402 MAY 16 2008
Abstract:
Using angle-resolved photoemission spectroscopy we demonstrate that a normal-state pseudogap exists above TN-IC in one of the most studied two-dimensional charge-density wave (CDW) dichalcogenides 2H-TaSe2. The initial formation of the incommensurate CDW is confirmed as being driven by a conventional nesting instability, which is marked by a pseudogap. The magnitude, character, and anisotropy of the 2D-CDW pseudogap bear considerable resemblance to those seen in superconducting cuprates.
Title:
Commensurate to incommensurate transition in the chiral helimagnet CuB2O4
Authors:
Fujta, T; Fujimoto, Y; Mitsudo, S; Idehara, T; Saito, T; Kousaka, Y; Yano, SI; Akimitsu, J; Kishine, JI; Inoue, K; Motokawa, M Author Full Names: Fujta, Toshiyuki; Fujimoto, Yoshikuni; Mitsudo, Seitaro; Idehara, Toshitaka; Saito, Teruo; Kousaka, Yusuke; Yano, Shin-ichiro; Akimitsu, Jun; Kishine, Jun-ichiro; Inoue, Katsuya; Motokawa, Mitsuhiro
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (5): Art. No. 053702 MAY 2008
Abstract:
We have studied a commensurate to incommensurate transition in the novel helimagnet CuB2O4 by means of high-frequency ESR. In the commensurate weak ferromagnetic (CWF) state, two ESR modes have been found at low temperatures, which are explained in terms of an electron paramagnetic resonance of the Cu2+ spins at 8d-sites and an antiferromagnetic resonance of the magnetically ordered Cu2+ spins at 4b-sites with the Dzyaloshinskii-Moriya (DM) interaction. The DM interaction among the Cu2+ spins at 4b-sites that carries the CWF state is evaluated quantitatively. The incommensurate helimagnetic state is discussed in terms of the magnetic frustration.
Title:
Field-induced incommensurate lattice modulations in the delafossite CuFeO2
Authors:
Terada, N; Mitsuda, S; Tanaka, Y; Tabata, Y; Katsumata, K; Kikkawa, A Author Full Names: Terada, Noriki; Mitsuda, Setsuo; Tanaka, Yoshikazu; Tabata, Yoshikazu; Katsumata, Koichi; Kikkawa, Akiko
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (5): Art. No. 054701 MAY 2008
Abstract:
The results of synchrotron X-ray diffraction measurements on a single crystal of the triangular lattice antiferromagnet CuFeO2 under zero and non-zero applied magnetic fields are reported. We find four satellite reflections at (0, 3+q, 1/2), (0,4 -q, 1/2), (0,4 -2q, 0), and (0, 3+2q, 0) with the incommensurate wave number q similar to 0.415 in the ferroelectric incommensurate (FEIC) phase which appears in the magnetic field, H, between 7 and 13 T at low temperatures. In the partially disordered (PD) phase which exists in the temperature, T, range between 11 and 14 K, we find two satellite reflections at (0, 4-q, 1/2) and (0, 4-2q, 0) with the incommensurate wave number q similar to 0.4. The T and H dependence of these satellite reflections are studied. We interpret that the reflections observed in the FEIC phase arise from incommensurate lattice modulations caused by a magnetoelastic coupling with the underlying magnetic structure. The observation of the reflection (0, 4-q, 1/2) in finite fields and the (0, 4-2q, 0) reflection at 0 <= H in the PD phase is also explained by the same model. A calculation of the X-ray diffraction intensity assuming the displacement of oxygen ions only successfully explains the observation. We discuss the relevance of these satellite reflections to the ferroelectricity.
Title:
Optical phonon characteristics of incommensurate and commensurate modulated phases of Bi3NbO7 ceramics
Authors:
Moreira, RL; Matinaga, FM; Pirnat, U; Suvorov, D; Dias, A Author Full Names: Moreira, Roberto L.; Matinaga, Franklin M.; Pirnat, Ursa; Suvorov, Danilo; Dias, Anderson
Source:
JOURNAL OF APPLIED PHYSICS 103 (9): Art. No. 094108 MAY 1 2008
Abstract:
Raman and infrared-reflectivity spectroscopies were used to investigate the optical phonon modes of the cubic-incommensurate and tetragonal-commensurate phases of Bi3NbO7 ceramic samples. For both structures, the observed features could be well described by applying the factor-group method to average oxygen-deficient fluorite subcells; i.e., it was possible to predict the correct number and the activities of the observed phonon modes. The spectra showed rather broad bands, which are mainly for the cubic-incommensurate phase, probably because of the disorder of the oxygen vacancies and the folding of the Brillouin zone due to the modulation of the atomic positions. This can partially explain the higher quality factor and the potential interest in the tetragonal phase of this material for applications in microwave devices. (C) 2008 American Institute of Physics.
Title:
Vacancy-ordering effects in AlB2-type ErGe2-x (0.4 < x <= 0.5)
Authors:
Christensen, J; Lidin, S; Malaman, B; Venturini, G Author Full Names: Christensen, Jeppe; Lidin, Sven; Malaman, Bernard; Venturini, Gerard
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 272-280 Part 3 JUN 2008
Abstract:
In the Er-Ge system, the compostion range ErGe2 to Er2Ge3 has been investigated. Eight samples were produced by arc melting of the elements, and analyzed using X-ray powder diffraction. Nine crystal structures were found to be present in the samples. The structures are described as a homologous series and presented within the superspace formalism using the superspace group X2/m(alpha 0 gamma)0s, X representing the centring vector (1/2, 1/2, 0, 1/2). In this description the modulation vector q = (alpha a+gamma c) is shown to be a direct measure of the Ge content as ErGe2-alpha (alpha falls in the range 1/3 to 1/2). The large composition range is achieved by extended vacancy ordering in the planar 6(3) net of Ge with subsequent relaxation.

Update: 30-May-2008

Title:
On the magnetic phase diagram of copper metaborate
Authors:
Popov, MA; Petrakovskii, GA; Bolsunovskaya, OA Author Full Names: Popov, M. A.; Petrakovskii, G. A.; Bolsunovskaya, O. A.
Source:
PHYSICS OF THE SOLID STATE 50 (5): 909-912 MAY 2008
Abstract:
A stepwise transition from one incommensurate state of the spin system of a copper metaborate crystal to another incommensurate state was previously revealed using neutron scattering in an applied magnetic field. In this paper, the new state is interpreted as a combination of a commensurate state of one spin subsystem and an incommensurate state of another spin subsystem of the crystal.
Title:
Plastic fracture of quasicrystals
Authors:
Fan, TY; Fan, L Author Full Names: Fan, T. Y.; Fan, L.
Source:
PHILOSOPHICAL MAGAZINE 88 (4): 523-535 FEB 1 2008
Abstract:
Elasto-plastic crack solutions for some one- and two-dimensional quasicrystals have been found based on the generalized Dugdale-Barenblatt model. The size of the plastic zone and crack tip opening displacement are determined, from which a plastic fracture criterion for the materials is suggested.
Title:
Crystallographic studies on the iron-containing intermetallic phases in the 319-type aluminium casting alloys
Authors:
Hwang, JY; Doty, HW; Kaufman, MJ Author Full Names: Hwang, J. Y.; Doty, H. W.; Kaufman, M. J.
Source:
PHILOSOPHICAL MAGAZINE 88 (4): 607-619 FEB 1 2008
Abstract:
The iron-containing intermetallic compounds in type 319 aluminium casting alloys were investigated using convergent beam electron diffraction (CBED) and electron backscatter diffraction (EBSD). The Chinese script U-phase was identified as having the cubic Im 3 space group consistent with the Al19Fe4MnSi2 phase reported in the literature. However, the atomic ordering of this phase results in complex Kikuchi lines in the CBED and EBSD patterns, which makes phase and orientation identification difficult. In fact, it is shown that the EBSD patterns in the scanning electron microscope and Kikuchi patterns in the transmission electron microscope from this phase are closely related to the structurally similar m (3) over bar (5) over bar icosahedral quasicrystals that form in numerous aluminium-transition metal alloys by both conventional and rapid solidification. The other iron-containing phase in these alloys was determined to be plate shaped and to have the orthorhombic Cmcm space group consistent with the beta-Al5FeSi phase, which has sometimes been confused with having a tetragonal or monoclinic structure. The nature of this structure is such that it frequently grows with a high density of faults that separate equivalent variants; these will be described and related to the previously incorrect interpretations of this being a tetragonal phase.
Title:
Inelastic neutron scattering of a Ti-44 at.%Ni-6 at.%Fe alloy exhibiting an incommensurate-commensurate transition
Authors:
Fukuda, T; Choi, MS; Kakeshita, T; Ohba, T Author Full Names: Fukuda, Takashi; Choi, Mi-Seon; Kakeshita, Tomoyuki; Ohba, Takuya
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 481: 235-238 Sp. Iss. SI MAY 25 2008
Abstract:
Inelastic neutron scattering has been made for a Ti-44 at.%Ni-6 at.%Fe alloy which exhibits a second-order like incommensurate-commensurate (IC-C) transformation [M.-S. Choi, T. Fukuda, T. Kakeshita, Philos. Mag. 86 (2006) 67] in order to understand the nature of the transformation. The phonon frequencies of the [zeta zeta 0]-TA(2) phonon branch near zeta = 1/3 decrease as temperature decreases, exhibit the lowest value at about 200 K and then increase on further cooling. This temperature (200 K) is near the temperature below which diffuse incommensurate scattering can be noticed, and it is by 20 K higher than the IC-C transition temperature. Presumably, the phonon softening is responsible for the formation of the incommensurate state, but not directly connected to the formation of the commensurate state. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Observation of phonon softening in a Ti-Ni-Fe alloy by inelastic X-ray scattering
Authors:
Ohba, T; Kitanosono, D; Morito, S; Fukuda, T; Kakeshita, T; Baron, AQR; Tsutsui, S Author Full Names: Ohba, T.; Kitanosono, D.; Morito, Shigekazu; Fukuda, T.; Kakeshita, T.; Baron, A. Q. R.; Tsutsui, Santoshi
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 481: 254-257 Sp. Iss. SI MAY 25 2008
Abstract:
Phonon softening of the martensitic transformation, which is a typical first-order transformation, is an interesting concept in connection with the transformation mechanism. Recently, Kakeshita and his group studied a wide range of Fe-substituted Ti-Ni alloys [Ti-(50 - x)Ni-xFe, at.%] and reported anomalies in electrical resistivity, magnetic susceptibility and specific heat. Furthermore, they observed electron diffraction patterns and reported second-order-like features in a Ti-44Ni-6Fe alloy with an incommensurate-commensurate phase transformation prior to the transformation to the R phase. Inelastic X-ray scattering experiments were performed in order to observe the phonon behavior in Ti-44Ni-6Fe. Since the energy of phonons is about six orders of magnitude lower than that of X-rays, precise experiments are necessary to observe phonons by X-ray inelastic scattering experiments. The beam-line BL35XU at the synchrotron radiation facility, SPring-8 was utilized f! or the experiments. [zeta zeta 0]TA(2) phonon modes were measured at various temperatures. The temperature at which the softest phonon is observed is at approximately 180 K, corresponding to the incommensurate-commensurate transformation temperature. Possible differences between results of neutron inelastic scattering and X-ray inelastic scattering experiments will be discussed in the text. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Temperature dependence of the damping properties of Ni-Mn-Ga alloys
Authors:
Aaltio, I; Lahelin, M; Soderberg, O; Heczko, O; Lofgren, B; Ge, Y; Seppala, J; Hannula, SP Author Full Names: Aaltio, I.; Lahelin, M.; Soderberg, O.; Heczko, O.; Lofgren, B.; Ge, Y.; Seppala, J.; Hannula, S. -P.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 481: 314-317 Sp. Iss. SI MAY 25 2008
Abstract:
Single-crystalline 5M (exhibiting magnetic shape memory effect) and non-modulated martensitic Ni-Mn-Ga alloys were studied by dynamic mechanical analysis (DMA) at different temperatures. The chemical compositions of the alloys were determined using energy-dispersive X-ray spectrometry in a scanning electron microscope. The crystal structures were confirmed with X-ray diffraction and the transformation temperatures were measured. DMA measurements showed that the mechanical modulus (stiffness) and damping capacity increased during heating and a clear peak of the loss angle, was detected which is related to the reverse phase transformation of martensite to austenite. During cooling, there is a corresponding peak related to the martensite reaction. Significant decrease of the damping capacity occurs during transformation to austenite. Enhanced damping in the martensitic phase can be attributed to the mobility of twin boundaries. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Competing multiple-q magnetic structures in HoGe3: II. Magnetic structures observed in HoGe3
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Tung, LD; Ritter, C; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Tung, L. D.; Ritter, C.; Buschow, K. H. J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (19): Art. No. 195202 MAY 14 2008
Abstract:
The high temperature (HT) and the low temperature (LT) multiple-q vector magnetic structures of the antiferromagnetic HoGe3 compound (T-N = 11 K) are derived from refinements of high resolution neutron data in terms of Fourier analysis. Various models are discussed. Over the HT range T-2 -> T-N, T-2 = 8.1 K (on heating), the magnetic phase is described with the wavevectors (q(1), q(2)) where q(1) = (q(1x), 0, 0) and q(2) = (q(2x), 0, q(2z)), q(1x) = q(2x) approximate to 1 2 and q(2z) approximate to 1 3, with T dependent length. It corresponds to an amplitude modulated magnetic phase with the moments at an angle of 24 degrees (2) with the c axis within the plane (b, c). Surprisingly this structure does not square up to a constant moment structure with q1 = (1 2, 0, 0) and q2 = (1/2, 0, 1/3) or alternatively (2a, b, 3c). Instead of locking, the q(2) vector jumps at T-2 via a first-order transition to a long period structure with an almost 24-times larger cell approximate to (2a, 4b, 3c), or in terms of wavevectors to q(3) = (1/2, q(3y), 0) and q(4) = (1/2, q(4y), 1/3), which dominates the (LT) range 1.6 K -> T-2. The (LT) range subdivides into the lock-in LT1 range 1.6 K -> T-3 (T-3 = 4.8 K on heating) where the q(3y) = q(4y) = 1/4 components have a constant length and the LT2 range T-3 -> T-2 where q(3y) and q(4y) have a length variable with T. In the intermediate temperature range, around the first-order T-2 transition (on heating or cooling), the two structures described with the wavevectors (q(1), q(2)) and (q(3), q(4)) coexist in varying proportions. The most probable LT magnetic structure corresponds to a complex monoclinic multiaxial canted structure with four independent Ho sites as a result of geometric frustration related to the underlying trigonal prism arrangement of the magnetic atoms with antiferromagnetic interactions.
Title:
Protein crystals can be incommensurately modulated
Authors:
Lovelace, JJ; Murphy, CR; Daniels, L; Narayan, K; Schutt, CE; Lindberg, U; Svensson, C; Borgstahl, GEO Author Full Names: Lovelace, Jeffrey J.; Murphy, Cameron R.; Daniels, Lee; Narayan, Kartik; Schutt, Clarence E.; Lindberg, Uno; Svensson, Christer; Borgstahl, Gloria E. O.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 600-605 Part 3 JUN 2008
Abstract:
For a normal periodic crystal, the X-ray diffraction pattern can be described by an orientation matrix and a set of three integers that indicate the reciprocal lattice points. Those integers determine the spacing along the reciprocal lattice directions. In aperiodic crystals, the diffraction pattern is modulated and the standard periodic main reflections are surrounded by satellite reflections. The successful indexing and refinement of the main unit cell and q vector using TWINSOLVE, developed by Svensson [(2003). Lund University, Sweden], are reported here for an incommensurately modulated, aperiodic crystal of a profilin: actin complex. The indexing showed that the modulation is along the b direction in the crystal, which corresponds to an 'actin ribbon' formed by the crystal lattice. Interestingly, the transition to the aperiodic state was shown to be reversible and the diffraction pattern returned to the periodic state during data collection. It is likely that the protein underwent a conformational change that affected the neighbouring profilin: actin molecules in such a way as to produce the observed modulation in the diffraction pattern. Future work will aim to trap the incommensurately modulated crystal state, for example using cryocooling or chemical crosslinking, thus allowing complete X-ray data to be collected.
Title:
Interpenetrating networks of three-dimensional Penrose tiles in CaAu3Ga, the structurally simplest cubic approximant of an lcosahedral quasicrystal
Authors:
Lin, Q; Corbett, JD Author Full Names: Lin, Qisheng; Corbett, John D.
Source:
INORGANIC CHEMISTRY 47 (9): 3462-3464 MAY 5 2008
Abstract:
Double-Friauf polyhedra (DFPs) which play important roles in quasicrystal (QC) models are the unique building blocks in the novel 1/0 AC, CaAu3+Delta Ga1-Delta (Delta approximate to 0-0.13) [Pa (3) over bar; a = 9.0875(3)-9.1107(5) angstrom]. The packing of DFPs generates interpenetrating networks of condensed three-dimensional Penrose tiles, the geometry of which is close to that assumed for QCs.
Title:
Quasicrystal surfaces
Authors:
Thiel, PA Author Full Names: Thiel, Patricia A.
Source:
ANNUAL REVIEW OF PHYSICAL CHEMISTRY 59: 129-152 2008
Abstract:
Studies of ordered, yet nonperiodic, metallic alloys known as quasicrystals have generated exciting questions and fundamental insights about the relationship between surface atomic structure and surface properties. In this review, I give examples from oxidation, friction, heterogeneous catalysis, and solid film growth, in which the Al-rich quasicrystals exhibit unusual properties, relative to crystalline materials of similar composition.

Update: 23-May-2008

Title:
Effect of nano-quasicrystals on viscosity of a Zr-based bulk metallic glass (vol 58, pg 291, 2008)
Authors:
Gubicza, J; Labar, JL; Agocs, E; Fatay, D; Lendvai, J Author Full Names: Gubicza, J.; Labar, J. L.; Agocs, E.; Fatay, D.; Lendvai, J.
Source:
SCRIPTA MATERIALIA 58 (11): 1038-1038 JUN 2008
Title:
Incommensurate magnetic ground state revealed by resonant x-ray scattering in the frustrated spin system Ca3Co2O6
Authors:
Agrestini, S; Mazzoli, C; Bombardi, A; Lees, MR Author Full Names: Agrestini, S.; Mazzoli, C.; Bombardi, A.; Lees, M. R.
Source:
PHYSICAL REVIEW B 77 (14): Art. No. 140403 APR 2008
Abstract:
We have performed a resonant x-ray scattering study at the Co pre-K edge on a single crystal of Ca3Co2O6. The measurements reveal an abrupt transition to a magnetically ordered state immediately below T-N=25 K, with a magnetic correlation length in excess of 5500 A along the c axis chains. There is no evidence for modifications to the Co3+ spin state. A temperature dependent modulation in the magnetic order along the c axis and an unusual decrease in the magnetic correlation lengths on cooling are observed. The results are compatible with the onset of a partially disordered antiferromagnetic structure in Ca3Co2O6.
Title:
Direct observation of charge-density waves in Ho5Ir4Si10
Authors:
Tseng, CM; Chen, CH; Yang, HD Author Full Names: Tseng, C. M.; Chen, C. H.; Yang, H. D.
Source:
PHYSICAL REVIEW B 77 (15): Art. No. 155131 APR 2008
Abstract:
We report the direct observation of charge-density waves in Ho5Ir4Si10 by dark-field imaging in transmission electron microscopy using superlattice diffraction spots. The incommensurate phase of charge-density wave is found to be discommensurate with small commensurate domains separated by domain walls (discommensurations). Configurations of charge-density wave dislocations convincingly show that the charge-density wave phase transition is accompanied by a concomitant cell-doubling crystallographic structural phase transition, an unprecedented phenomenon in other charge-density wave systems.
Title:
Theory of subgap interchain tunneling in quasi 1D conductors
Authors:
Brazovskii, S; Matveenko, SI Author Full Names: Brazovskii, S.; Matveenko, S. I.
Source:
PHYSICAL REVIEW B 77 (15): Art. No. 155432 APR 2008
Abstract:
We suggest a theory of internal coherent tunneling in the pseudogap region when the applied voltage U is below the free electron gap 2 Delta(0). We address quasi-one-dimensional (quasi 1D) systems, where the gap is originated by spontaneous lattice distortions of the incommensurate charge density wave type. The results can be adjusted also to quasi 1D superconductors. The instanton approach allows one to calculate the interchain tunneling current both in single electron (amplitude solitons, i.e., spinons) and bielectron (phase slips) channels. Transition rates are governed by a dissipative dynamics originated by the emission of gapless phase excitations in the course of the instanton process. We find that the single-electron tunneling is allowed down to the true pair-breaking threshold at U-c1=2W(as)< 2 Delta(0), where W-as=2/pi Delta(0) is the amplitude soliton energy. Most importantly, the bielectronic tunneling stretches down to U-c2=0 (in the 1D regime). In both cases, the threshold behavior is given by power laws J similar to(U-U-c)(beta), where the exponent beta similar to v(F)/u is as large as the ratio of the Fermi velocity v(F) and the phase u. In the two-dimensional or three-dimensional ordered phases, at temperature T < T-c, the one-electron tunneling current does not vanish at the threshold anymore, but saturates above it at U-U-c1 similar to T-c <
Title:
Fermi surface nesting and the origin of charge density waves in metals
Authors:
Johannes, MD; Mazin, II Author Full Names: Johannes, M. D.; Mazin, I. I.
Source:
PHYSICAL REVIEW B 77 (16): Art. No. 165135 APR 2008
Abstract:
The concept of a charge density wave (CDW), which is induced by Fermi-surface nesting, originated from the Peierls idea of electronic instabilities in purely one-dimensional metals and is now often applied to charge ordering in real low-dimensional materials. The idea is that if Fermi surface contours coincide when shifted along the observed CDW wave vector, then the CDW is considered to be nesting derived. We show that, in most cases, this procedure has no predictive power, since Fermi surfaces either do not nest at the right wave vector or nest more strongly at the wrong vector. We argue that only a tiny fraction, if any, of the observed charge ordering phase transitions are true analogs of the Peierls instability because electronic instabilities are easily destroyed by even small deviations from perfect nesting conditions. By using prototypical CDW materials NbSe2, TaSe2, and CeTe3, we show that such conditions are hardly ever fulfilled and that the CDW phases are actually structural phase transitions driven by the concerted action of electronic and ionic subsystems, i.e., a q-dependent electron-phonon coupling plays an indispensable part. We also mathematically show that the original Peierls construction is so fragile that it is unlikely to apply to real materials. We argue that no meaningful distinction between a CDW and an incommensurate lattice transition exists.
Title:
Computer simulation solves quasicrystal mystery
Authors:
[Anon]
Source:
MATERIALS WORLD 16 (5): 14-14 MAY 2008
Title:
Friction anisotropy: A unique and intrinsic property of decagonal quasicrystals
Authors:
Park, JY; Ogletree, DF; Salmeron, M; Jenks, CJ; Thiel, PA; Brenner, J; Dubois, JM Author Full Names: Park, Jeong Young; Ogletree, D. F.; Salmeron, M.; Jenks, C. J.; Thiel, P. A.; Brenner, J.; Dubois, J. M.
Source:
JOURNAL OF MATERIALS RESEARCH 23 (5): 1488-1493 MAY 2008
Abstract:
We show that friction anisotropy is an intrinsic property of the atomic structure of Al-Ni-Co decagonal quasicrystals and not only of clean and well-ordered surfaces that can be prepared in vacuum [J.Y. Park et al., Science 309, 1354 (2005)]. Friction anisotropy is manifested in both nanometer-size contacts obtained with sharp atomic force microscope tips and macroscopic contacts produced in pin-on-disk tribometers. We show that the friction anisotropy, which is not observed when an amorphous oxide film covers the surface, is recovered when the film is removed due to wear. Equally important is the loss of the friction anisotropy when the quasicrystalline order is destroyed due to cumulative wear. These results reveal the intimate connection between the mechanical properties of these materials and their peculiar atomic structure.
Title:
A study of the high-Al part of the Al-Pd-Re phase diagram
Authors:
Balanetskyy, S; Grushko, B Author Full Names: Balanetskyy, S.; Grushko, B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 456 (1-2): 105-112 MAY 29 2008
Abstract:
The Al-Pd-Re phase diagram was studied in the compositional range above 50 at.% Al at temperatures between 700 and 1100 degrees C. Apart from the Al-Pd epsilon-phases exhibiting ternary extension up to similar to 6 at.% Re, the binary phases in both Al-Pd and Al-Re dissolve only a little of the third element. In addition to the stable ternary icosahedral and decagonal phases reported earlier a new ternary hexagonal chi-phase (a approximate to 1.231, c approximate to 2.742 nm) was discovered in a compositional range from Al77.8Pd13.8Re8.4 to Al76.2Pd19.0Re4.8. The overall compositional range of the icosahedral phase was found to be between 8.3 and 10.4 at.% Re and between 68.5 and 71.9 at.% Al. This range shifts to lower Re at lower temperatures. Partial isothermal sections at 1100, 1000, 790 and 700 degrees C are presented. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Crystallization behavior and consolidation of ball milled Zr60Ti5Ag5Cu12.5Ni10Al7.5 glassy powders
Authors:
Scudino, S; Venkataraman, S; Sakahyska, M; Eckert, J Author Full Names: Scudino, S.; Venkataraman, S.; Sakahyska, M.; Eckert, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 456 (1-2): 159-162 MAY 29 2008
Abstract:
Zr60Ti5Ag5Cu12.5Ni10Al7.5 glassy powders produced by ball milling of crystalline compounds were consolidated by uniaxial hot pressing. The consolidation parameters were chosen in order to obtain partially crystallized bulk samples with a composite microstructure consisting of glassy, quasicrystalline and tetragonal CuZr2 phases. Hardness measurements reveal promising mechanical properties: Vickers hardness of 4.61 GPa and estimated yield strength of 1.53 GPa. These values are comparable to those reported for bulk Zr-based glassy alloys prepared by other techniques. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Recent topics in microstructure control by magnetic field in Ni2MnGa and CoPt and new transformation behavior in Ti-Ni-Fe alloys
Authors:
Kakeshita, T; Fukuda, T Author Full Names: Kakeshita, T.; Fukuda, T.
Source:
EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS 158: 73-78 MAY 2008
Abstract:
Three topics related to solid-solid phase transformations are presented. The first topic is related to ferromagnetic shape memory alloys. The general condition for rearrangement of martensite variants by magnetic field is discussed quantitatively. The second topic is related to microstructure control of CoPt (tetragonal L1(0)-type structure) during ordering heat-treatment under a magnetic field. We show that a single variant state is realized by magnetic field, and magnetic field is especially effective at the early stage of ordering. The third topic is related to the so-called precursor phenomena in Ti-Ni-Fe shape memory alloys. In the topic we will show the existence of a commensurate phase, which inherits the microstructure of the incommensurate phase and is probably different from the R-phase.
Title:
Crystal structure of martensite and intermediate phases in Ni2MnGa studied by neutron diffraction
Authors:
Kushida, H; Fukuda, K; Terai, T; Fukuda, T; Kakeshita, T; Ohba, T; Osakabe, T; Kakurai, K; Kato, K Author Full Names: Kushida, H.; Fukuda, K.; Terai, T.; Fukuda, T.; Kakeshita, T.; Ohba, T.; Osakabe, T.; Kakurai, K.; Kato, K.
Source:
EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS 158: 87-92 MAY 2008
Abstract:
We have investigated crystal structures of martensite and intermediate phases in stoichiometric Ni2MnGa. The neutron diffraction profile of the martensite phase measured at T = 4.2 K exhibits four satellites between [2 0 0](P)* and [0 2 0](P)* reflections (P stands for the parent phase) at incommensurate positions of [h 2 - h 0](P)* with h = 0.428, 0.863, 1.136 and 1.572. The pro. le of the intermediate phase measured at T = 210 K exhibits two satellites between [2 0 0](P)* and [0 2 0](P)* reflections at incommensurate positions of [h 2 - h 0](P)* with h = 0.343 and 1.657. Although each satellite of the martensite phase moves toward its nearest fundamental reflection as temperature increases, that of the intermediate phase does not move significantly. On the contrary, the intensity of each satellite decreases significantly in the intermediate phase as temperature increases while not in the martensite phase. A synchrotron X-ray diffraction and a Rietveld analysis of the result reveal that, for both the phases, the displacement of atoms from the parent phase are represented by a sine wave whose propagation vector is parallel to [1 1 0](P).

Update: 16-May-2008

Title:
Fivefold i-Al-Pd-Mn surface as template for growing monatomic quasiperiodic layers: First-principles simulations for adatoms from groups one to three
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, Marian; Hafner, J.
Source:
PHYSICAL REVIEW B 77 (13): Art. No. 134202 APR 2008
Abstract:
By using ab initio density-functional calculations, we have explored the conditions for the formation of quasiperiodic overlayers on top of a fivefold surface of an icosahedral Al-Pd-Mn quasicrystal. We calculate binding energies of single adatoms at special sites of the surface, with the aim to construct the potential-energy landscape of the quasiperiodic surface. We show that the energetically favorable adsorption sites are located at the vertices of a DHBS tiling [consisting of decagons (D), hexagons (H), boats (B), and stars (S)] describing the quasiperiodic ordering of the surface. An idealized structural model for the adlayer is constructed by decorating the interior of these tiles such that atoms are placed again in energetically favorable locations and that the local arrangement does not break the fivefold symmetry of the underlying substrate. The stability of this idealized structure is probed for elements from groups one to three of the Periodic Table by performing a conjugate-gradient relaxation under the action of the ab initio calculated forces. We demonstrate that in addition to a strong binding of the adatoms to the substrate, the size of the adatoms and the achievement of a dense surface coverage are the most important factors influencing the stability of quasiperiodic ordering in the adsorbed monolayer. From the analysis of the geometrical distribution of the adsorption sites, we conclude that a dense quasiperiodic overlayer with a density of 0.066 atoms/angstrom(2) (corresponding to a coverage Theta approximate to 0.50 monolayers) can be formed by adatoms with an atomic size of 3.7 angstrom +/- 0.4 angstrom. Atoms with this size are Na, Ca, Y, and La. We suggest that these elements and presumably also most rare-earth elements are good candidates for the formation of highly regular quasiperiodic adlayers with a structure described by a decagonal DHBS tiling consisting of decagons, hexagons, boats, and pen! tagonal stars.
Title:
Formation and properties of Al composites reinforced by quasicrystalline AlCuFeB particles
Authors:
Kenzari, S; Weisbecker, P; Curulla, M; Geandier, G; Fournee, V; Dubois, JM Author Full Names: Kenzari, S.; Weisbecker, P.; Curulla, M.; Geandier, G.; Fournee, V.; Dubois, J. M.
Source:
PHILOSOPHICAL MAGAZINE 88 (5): 755-766 2008
Abstract:
Al-based composites reinforced by icosahedral (i-) Al59Cu25.5Fe12.5B3 quasicrystalline particles were prepared by solid-state sintering. It was found that Al diffusion from the matrix to the quasicrystalline particles induces phase transformation into the omega-Al7Cu2Fe tetragonal phase. In order to preserve the i phase, we used an oxidation pre-treatment of the particles and studied its influence on the kinetics of the phase transformation (Al + i -> omega) as a function of temperature by high energy X-ray diffraction. The oxide layer acts as a barrier, reducing efficiently the diffusion of Al up to a sintering temperature of 823 K, allowing the control of the phases in the composites. The mechanical properties and the friction behaviour of the composites were investigated and show the negative influence of the oxide on the interface strength.
Title:
The influence of cooling rate on the microstructure of an Al-Mn-Be alloy
Authors:
Rozman, N; Boncina, T; Anzel, I; Zupanic, F Author Full Names: Rozman, Niko; Boncina, Tonica; Anzel, Ivan; Zupanic, Franc
Source:
MATERIALI IN TEHNOLOGIJE 42 (2): 65-68 MAR-APR 2008
Abstract:
In ternary Al-Mn-Be alloys a metastable quasicrystalline phase can form at relatively low cooling rates (approximate to 100 K/s); however, besides the quasicrystalline phase other phases can also be present. We found that the investigated alloy is very prone to the formation of metastable phases, which are also quasicrystalline. Using different investigation methods we determined the type of phases, their shape, morphology, chemical composition and distribution. Special attention was given to the micro- and nano-sized quasicrystalline particles. When using slow cooling, Al10Mn3 and Be4AlMn were present; however, with a faster cooling rate a quasicrystal approximant and a quasicrystalline phase were formed.
Title:
Effect of Ti addition on the crystallization behavior and glass-forming ability of Zr-Al-Cu alloys
Authors:
Qiang, JB; Zhang, W; Xie, GQ; Inoue, A Author Full Names: Qiang, J. B.; Zhang, W.; Xie, G. Q.; Inoue, A.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 354 (18): 2054-2059 APR 15 2008
Abstract:
The crystallization behavior of melt-spun (Zr65Al7.5Cu27.5)(100-x)Ti-x (x = 0- 15; in at.%) metallic glasses has been investigated by X-ray diffraction (XRD), transmission electron microscopy(TEM) and differential scanning calorimetry (DSC). The DSC traces showed an altered crystallization mode in the vicinity of 3 at.% Ti addition. A metastable icosahedral quasicrystal precipitated at the first crystallization stage of the Ti-bearing metallic glasses, which subsequently transformed to the stable Zr2Cu-type phase in the followed exothermic reaction. The glass-forming abilities (GFAs) of these metallic glasses were assessed by the recognized GFA indicators T-rg Delta T-x and gamma. BMGs were easily made in the compositions containing 3-7 at.% Ti by means of copper mold casting. The validity of these parameters was clarified using the critical BMG forming diameter evidence. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Electrical and optical properties of the mixed-valence misfit-layer compound (YbS)(1.25)CrS2
Authors:
Ohno, Y; Yamaguchi, T Author Full Names: Ohno, Y.; Yamaguchi, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 455 (1-2): 10-16 MAY 8 2008
Abstract:
The crystals of the new misfit-layer compound (YbS)(1.25)CrS2 were grown by chemical transport reaction in a closed silica ampoule. This compound is built up of alternately stacking of YbS and CrS2 layers. The dimensions of a unit cell are a(1) = 5.31 angstrom, b(1) = 5.75 angstrom, and c(1) = 10.63 angstrom for the YbS sublattice and a(2) = 3.32 angstrom, b(2) = 5.75 angstrom, and c(2) = 10.63 angstrom for the CrS2 sublattice. Both layers are incommensurate along the a-axis and the incommensurability parameter, which is defined by alpha = a(2)/a(1), is about 0.625. It is found from the comparison of lattice parameters among a series of lanthanide misfit-layer compounds and lanthanide monosulfides that Yb is in an intermediate valence state close to trivalency rather than divalency due to charge transfer to CrS2 layers. Temperature-dependent electrical resistivity shows that the compound is a semiconductor with the activation energy of about 0.31 eV. This activation energy almost agrees with that of the acceptor levels in nonstoichiometric YbS samples. A reflectivity spectrum reveals small peaks at 0.8 and 1.1 eV, whereas an absorption spectrum exhibits a large peak at 1.1 eV The results obtained suggest that valence fluctuation happens for Yb-like Eu in (EuS)(1.173)NbS2. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Formation of AlCuFe icosahedral quasicrystal by mechanical alloying: XAFS and XRD studies
Authors:
Yin, SL; Xie, Z; Bian, Q; He, B; Pan, ZY; Sun, ZH; Wei, Z; Qian, LY; Wei, SQ Author Full Names: Yin, Shilong; Xie, Zhi; Bian, Qing; He, Bo; Pan, Zhiyun; Sun, Zhihu; Wei, Zheng; Qian, Liying; Wei, Shiqiang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 455 (1-2): 314-321 MAY 8 2008
Abstract:
The structural evolutions of the mechanically alloyed ternary Al70Cu20Fe10 powders with the milling times and the annealing treatment were studied by X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). It was found that during the milling process, only Cu can incorporate into the lattice of Al to form an Al2Cu compound or an AlCu solid solution, depending on the milling times. However, Fe remains the original structure of bcc alpha-Fe. Annealing treatment at 700 degrees C for 4 h can drive the alpha-Fe to react with the Al2Cu compounds and AlCu solid solution, and the main products of the annealed Al70Cu20Fe10, 0 (10 h) and the annealed Al70Cu20Fe10 0 (40 h) are the icosahedral Al65Cu20Fe15 quasicrystal and the Al(Cu, Fe) solid solution, respectively. The local structural disorders around Fe and Cu atoms in the icosahedral QC phase is about 50% larger than those of the Al(Cu, Fe) solid solution. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Multiferroicity due to nonstoichiometry in the chain cuprate LiVCuO4
Authors:
Moskvin, AS; Drechsler, SL Author Full Names: Moskvin, A. S.; Drechsler, S. -L.
Source:
EPL 81 (5): Art. No. 57004 MAR 2008
Abstract:
The recently observed multiferroic behavior in the s= 1/2 chain cuprate LiVCuO4 (equivalent to LiCuVO4) with edge-shared CuO4 plaquettes and helical spin ordering does not agree with the existing theories such as a spin-current scenario. We argue that the effect can be consistently explained, if the exchange-induced electric polarization on the out-of-chain Cu2+ centers substituting for Li ions in LiVCuO4 is taken into account. These substituent centers are proved to be an effective probe of the spin incommensurability and the magnetic-field effects. Copyright (c) EPLA, 2008.

Update: 9-May-2008

Title:
Thermoelectrical properties of a monocrystalline Al64Cu23Fe13 quasicrystal
Authors:
Smiljanic, I; Bilusic, A; Bihar, Z; Lukatela, J; Leontic, B; Dolinsek, J; Smontara, A Author Full Names: Smiljanic, Igor; Bilusic, Ante; Bihar, Zeljko; Lukatela, Jagoda; Leontic, Boran; Dolinsek, Janez; Smontara, Ana
Source:
MATERIALI IN TEHNOLOGIJE 41 (6): 265-270 NOV-DEC 2007
Abstract:
We performed investigations of the electrical resistivity, thermopower and thermal conductivity of a monocrystalline i-Al64Cu23Fe13 as well as a polycrystalline i-Al63Cu25Fe12 icosahedral quasicrystal, for comparison. The electrical resistivity of both samples, the monocrystalline i-Al64Cu23Fe13 and the polycrystalline i-Al63Cu25Fe12, exhibits a negative temperature coefficient with rho(4K) = 3950 mu Omega cm and rho(4K)= 4900 mu Omega cm, and the ratio rho(4K)/rho(300K) = 1-8, rho(4K)/rho(300K) = 1.7, respectively. The thermopowers are large and have a negative sign. In addition, the thermopower of the monocrystalline i-Al64Cu23Fe13 exhibits a sign reversal at T = 278 K. The thermal conductivity is anomalously low, of the order of 1 W/mK at room temperature, with a slightly different temperature variation at low temperatures. On the basis of these results, we concluded that there are no systematic differences between the high-quality monocrystalline and polycrystalline icosahedral i-Al-Cu-Fe quasicrystals. Moreover, the reported transport properties of i-Al-Cu-Fe appear to be intrinsic to this family of icosahedral quasicrystals.
Title:
Phases in a quasicrystalline alloy Al(64,4)Cu(23,5)Fe13,1
Authors:
Boncina, T; Markoli, B; Anzel, I; Zupanic, F Author Full Names: Boncina, Tonica; Markoli, Bogtjan; Anzel, Ivan; Zupanic, Franc
Source:
MATERIALI IN TEHNOLOGIJE 41 (6): 271-277 NOV-DEC 2007
Abstract:
In the ternary system Al-Cu-Fe an i-phase (icosahedral quasicrystal) is present. It is thermodynamically stable and a part of the equilibrium phase diagram. However, according to the chemical composition and conditions during the solidification and heat treatment, a considerable number of intermetallic phases can be in stabile or metastabile equilibrium with the i-phase. Consequently, synthesis of onephase quasicrystalline alloy is possible only in a narrow concentration range and after appropriate heat treatment. In the investigation, alloy Al64,4Cu22,5Fe13,1 was synthesized and heat treated to increase the fraction of the i-phase. The presence of phases and other microstructural characteristics were determined using appropriate metallographic preparation methods, light microscopy (LM), scanning electron microscopy (SEM), microchernical analyses (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and microhardness measurements. The presence of quasicrystalline phase i was clearly confirmed using XRD and TEM.
Title:
Hydrogen absorption by Ti-Zr-Ni-based alloys
Authors:
Skulj, I; Kocjan, A; McGuiness, PJ; Sustarsic, B Author Full Names: Skulj, Irena; Kocjan, Andraz; McGuiness, Paul J.; Sustarsic, Borivoj
Source:
MATERIALI IN TEHNOLOGIJE 41 (6): 279-282 NOV-DEC 2007
Abstract:
Some transition metals and their alloys have the ability to reversibly absorb considerable amounts of hydrogen. The amount of absorbed hydrogen and the absorption kinetics depend on interactions between the hydrogen atoms and the alloy. Titanium and zirconium show a high affinity for hydrogen, and Ti-Zr-Ni alloys with either amorphous or quasicrystalline structures have proved to be excellent absorbers of hydrogen. In this study we have focused on processing Ti-Zr-Ni ribbons with four different compositions and investigating their hydrogenation behaviour. A melt-spinning process was used as the alloy-preparation technique, and samples from each composition were examined before and after the hydrogenation process. The ribbons were analysed by X-ray diffraction (XRD) and examined with a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). Only the sample with the lowest nickel concentration was found to absorb any significant quantity of hydrogen under the applied experimental conditions.
Title:
Structural and magnetic roughness in a Co/Ru multilayer patterned into a large scale hexagonal array
Authors:
Kinane, CJ; Porter, NA; Marrows, CH; Hickey, BJ; Arena, DA; Dvorak, J; Sirotkin, E; Ogrin, FY; Charlton, T; Langridge, S Author Full Names: Kinane, C. J.; Porter, N. A.; Marrows, C. H.; Hickey, B. J.; Arena, D. A.; Dvorak, J.; Sirotkin, E.; Ogrin, F. Y.; Charlton, T.; Langridge, S.
Source:
JOURNAL OF APPLIED PHYSICS 103 (7): Art. No. 07B513 APR 1 2008
Abstract:
Self-assembled arrays of nanospheres have been used to pattern a Co/Pt multilayer into nanopillars. On top of this has been deposited a Co/Ru multilayer, which is antiferromagnetically coupled. The nanopillars introduce a known structural and magnetic lateral modulation into the multilayer. Soft x-ray magnetic scattering was used to observe the interference patterned from the patterned substrate. This has allowed us to show how the magnetic roughness correlates with the structural roughness and obtain selective magnetometry of the various magnetic elements. (C) 2008 American Institute of Physics.
Title:
Formation of periodic magnetic structure by localized amorphization of crystalline Co2MnSi using femtosecond laser
Authors:
Baek, KH; Park, JH; Kim, JH; Kim, CK; Yoon, CS; Lee, GJ; Lee, YP Author Full Names: Baek, Kwang H.; Park, Jun H.; Kim, Jung H.; Kim, Chang K.; Yoon, Chong S.; Lee, Geon Joon; Lee, Young Pak
Source:
JOURNAL OF APPLIED PHYSICS 103 (7): Art. No. 07E701 APR 1 2008
Abstract:
Femtosecond laser-interference induced amorphization (FLIA) was used to form a spatially periodic magnetic structure by selectively amorphizing the surface of bulk Co2MnSi. Regularly spaced alternating lines with a periodicity of 2 mu m were produced by FLIA. Magnetic force microscopy of the samples clearly revealed one-dimensional periodic magnetic domains resulting from the modulated surface structure which was confirmed by transmission electron microscopy. The periodicity of the modulated structure can be further decreased or the process can be modified to write two-dimensional pattern so that the resulting magnetic structure can be potentially utilized for a permanent magnetic identification. (C) 2008 American Institute of Physics.
Title:
A superstructure modulation induced by La doping of the layered manganate LaxSr4-xMn3O10
Authors:
Yang, H; Tang, YK; Yao, LD; Zhang, W; Li, QA; Li, FY; Jin, CQ; Yu, RC Author Full Names: Yang, H.; Tang, Y. K.; Yao, L. D.; Zhang, W.; Li, Q. A.; Li, F. Y.; Jin, C. Q.; Yu, R. C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 454 (1-2): 1-4 APR 24 2008
Abstract:
In this paper, transmission electron microscopy (TEM) has been used for studying the slightly La-doped layered manganate LaxSr4-xMn3O10. Albeit the samples for x <= 0. 15 appear single phased from the powder X-ray diffraction (XRD) analysis, the presence of numerous modulated domains in them has been revealed by electron diffraction and high-resolution electron microscopy. Electron diffraction data indicate that the local superstructure modulation is two-dimensional, and the modulation plane lies in the ac plane. The two primary modulation vectors are q(1) = (1/4)a* and q(2) = (1/2)c*. High-resolution electron microscopy data suggest that the origin of the modulated structure is possibly attributable to an ordering of the La dopants. The locally modulated structure may have a correlation with the magnetic properties, typical of the ferromagnetic (FM) clusters, of the LaxSr4-xMn3O10 manganate. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Phase equilibria of the Al-Fe-Ni system at 850 degrees C and 627 degrees C
Authors:
Zhang, LJ; Du, Y; Xu, HG; Tang, CY; Chen, HL; Zhang, WQ Author Full Names: Zhang, Lijun; Du, Yong; Xu, Honghui; Tang, Chengying; Chen, Hailin; Zhang, Wenqing
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 454 (1-2): 129-135 APR 24 2008
Abstract:
The phase equilibria at 850 degrees C and 627 degrees C in the Al-Fe-Ni system with Al content above 50 at.% are investigated by using 19 alloys. The annealed alloys are examined by means of X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) and election probe microanalysis (EPMA). It is confirmed that tau(2) phase (Al10Fe3Ni) with hexagonal structure and tau(3) phase (Al71Fe5Ni24) with the decagonal quasi-crystalline structure, exist at 850 degrees C. The homogeneity of tau(2) spans in the range of 5.7-13.1 at.% Ni and 14.4-22.2 at.% Fe. At 850 degrees C, the maximum solubilities of Ni in Al5Fe2 and Al2Fe are determined to be 1.3 at.% and 2.1 at.%, respectively, while the maximum solubility of Fe in Al3Ni2 is measured to be 4,9 at.%. At 627 degrees C, tau(1) (Al9FeNi) and tau(2) exist. At this temperature, the hornogeneity range for tau(1) is from 8.7 at.% to 14.3 at.% Ni and 4.5 at.% to 10.0 at.% Fe, and that for tau(2) is within the range of 7.2-12.4 at.% Ni and 15.6-22.5 at.% Fe. The maximum solubilities of Ni in Al13Fe4, Al5Fe2 and Al2Fe are determined to be 8.9, 1.5, and 2 at.%, respectively, while that of Fe in Al3Ni is measured to be 3.6 at.%. At 627 degrees C, the maximum solubilities of both Fe and Ni in (Al) phase are determined to be extremely small, about 0.58 at.% for both elements. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Comment on "Model of rotational tunneling in quasicrystals of the Cd6Yb parent compound"
Authors:
Coddens, G Author Full Names: Coddens, Gerrit
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 454 (1-2): 523-524 APR 24 2008
Abstract:
We show that in a recent model calculation on tunneling of Cd-4 "clusters" in CdYb quasicrystals (QC) and its approximants the assumption that the clusters would be rigid is not justified. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Single-crystal X-ray study of Ba2Cu2Te4O11Br2 and its incommensurately modulated superstructure companion
Authors:
Takagi, RF; Johnsson, M; Lidin, S Author Full Names: Takagi, Rie Fredrickson; Johnsson, Mats; Lidin, Sven
Source:
CHEMISTRY-A EUROPEAN JOURNAL 14 (11): 3434-3441 2008
Abstract:
Compounds containing lone-pair elements such as Te-IV are very interesting from the structural point of view, as the lone-pair nonbonding regions create low-dimensional geometrical arrangements. We have synthesized two new compounds with these features-Ba2Cu2Te4O11Br2 (I) and Ba2Cu2Te4O11-delta(OH)(2 delta)Br-2 (II, delta approximate to 0.57) - as members of the AE-M-Te-O-X (AE=alkaline-earth metal, M = transition metal, X=halide) family of compounds by solid-state reactions. Preliminary single-crystal X-ray analysis indicated that compound I crystallizes in the orthorhombic system, but attempts at refinement proved unsatisfactory. Closer inspection of the reciprocal lattice revealed systematic, non-crystallographic absences that indicate twinning. The structure is in fact triclinic, space group C (1) over bar (equivalent to P (1) over bar), with unit cell parameters (at 120 K) of a = 10.9027(9), b = 15.0864(7), c = 9.379(2) angstrom, beta = 106.8947 degrees. It is layered and built from [TeO3E] tetrahedra, [TeO3+1E] trigonal bipyramids (where E is the lone pair of Te-IV), [CuO4] squares and irregular [BaO10Br] polyhedra. The crystal structure of 11 shows the same basic structure as I but contains additional oxygen, probably in the form of OH groups. The presence of satellites reveals that ordering on this 0 site creates an incommensurate modulation, primarily affecting Br and Te. The modulated structure of II was solved in the triclinic superspace group X (1) over bar(alpha beta gamma)0 with the vector q approximate to 1/16 c*.

Update: 2-May-2008

Title:
On the magnetic structure of quasi one dimensional spin 1/2 system of Li2ZrCuO4
Authors:
Tarui, Y; Kobayashi, Y; Sato, M Author Full Names: Tarui, Yasuko; Kobayashi, Yoshiaki; Sato, Masatoshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (4): Art. No. 043703 APR 2008
Abstract:
Magnetization and Li-7-NMR measurements have been carried out for an a-axis-aligned sample of Li2ZrCuO4, which has quasi one-dimensional Cu2+ spins (s = 1/2) in chains of edge-sharing CuO4 square planes and exhibits the magnetic transition at temperature T-N similar to 7 K. The NMR results at similar to 2 K indicate that the system has an incommensurate helical order of Cu spins within the ac-plane. Although the feroelectricity is predicted in this ordered state by existing theories developed for a single chain, no anomalies have been observed in the dielectric susceptibility E and electric polarization P for polycrystalline samples.
Title:
Competition of magnetic and quadrupolar order parameters in HoB4
Authors:
Okuyama, D; Matsumura, T; Mouri, T; Ishikawa, N; Ohoyama, K; Hiraka, H; Nakao, H; Iwasa, K; Murakami, Y Author Full Names: Okuyama, Daisuke; Matsumura, Takeshi; Mouri, Takuya; Ishikawa, Naoko; Ohoyama, Kenji; Hiraka, Haruhiro; Nakao, Hironori; Iwasa, Kazuaki; Murakami, Youichi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (4): Art. No. 044709 APR 2008
Abstract:
The successive magnetic phase transitions of HoB4 with T-N1 = 7.1 K and T-N2 = 5.7 K have been investigated in detail by neutron and X-ray diffraction. Since Ho ions in the c-plane form a Shastry-Sutherland lattice, geometrical frustration has been expected in this compound. Below T-N1, HoB4 exhibits an incommensurate antiferromagnetic order with q = (delta, delta, delta ') (delta = 0.022, delta ' = 0.43), followed by a first-order transition at T-N2 into a commensurate order with q = (0, 0, 0), where four magnetic moments are antiferromagnetically coupled in a unit cell. After determining the magnetic structures of the two phases by neutron powder diffraction, we pay particular attention to diffuse scatterings responsible for the critical behavior. Very broad diffuse scatterings, extending almost to the zone boundary, are observed already in the paramagnetic phase at around q = (0, 0, 0) and (0, 0, 1/2) with magnetic correlation lengths of xi < 10 angstrom. Below T-N1, a strong diffuse scattering develops in a more concentrated region at around q = (0, 0, with 30 A, followed by the appearance of a Bragg peak at (delta, delta, delta '). Simultaneously, a sharp Bragg peak corresponding to q = (0, 0, 0) also develops at (1, 0, 1) upon diffuse scattering. This complex critical behavior is discussed from the viewpoint of competing order parameters of magnetic and quadrupolar origins. The striking resemblance of the critical behavior to that of HoB2C2 with a square lattice of Ho is interpreted as a manifestation of a universality for a three-dimensional system with competing magnetic and quadrupolar order parameters and a long-ranged RKKY interaction. It is considered that the microscopic difference in interionic interaction due to the difference in crystal structure becomes less prominent in the critical behavior as the correlation length becomes much larger than the lattice constant. On the other hand, the strong diffuse scattering in HoB4, which is hardly d etected in HoB2C2, might be ascribed to geometrical frustration. The softening of the elastic constant in HoB4 and HoB2C2 is also discussed.
Title:
Synthesis and structural properties of n=1 Ruddlesden-Popper manganites Nd1-xCa1+xMnO4
Authors:
Nagai, T; Yamazaki, A; Kimoto, K; Matsui, Y Author Full Names: Nagai, T.; Yamazaki, A.; Kimoto, K.; Matsui, Y.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 453 (1-2): 247-252 APR 3 2008
Abstract:
Polycrystalline samples of n = 1 Ruddlesden-Popper manganites Nd1-xCa1+xMnO4 (0.55 <= x <= 1.00) were synthesized by a solid-state reaction. X-ray diffraction (XRD) and electron diffraction (ED) measurements confirmed that the fundamental crystal structure at room temperature consists of three distorted K2NiF4-types: orthorhombic Bmab (64) phase in 0.55 <= x< 0.73, orthorhombic Acam (64) phase in 0.73 <= x<0.85 and tetragonal I4(1)/acd(142) phase in 0.85 <= x <= 1.00. Furthermore, in a whole range of 0.55 <= x <= 0.75, low-temperature magnetic and ED measurements revealed charge-orbital ordering (COO) states, which are accompanied by suppression of magnetization and structural modulations with q = (1 - x)a*. The COO transition temperatures are high with a maximum of similar to 330 K at x=0.67, and then higher than those in non-distorted n = I Ruddlesden-Popper manganites. The observations suggest that COO states are much stabilized by the distortion in the fundamental structures. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Effect of Mg-based spherical quasicrystals on microstructure and mechanical properties of AZ91 alloys
Authors:
Zhang, JS; Pei, LX; Du, HW; Liang, W; Xu, CX; Lu, BF Author Full Names: Zhang, Jinshan; Pei, Lixia; Du, Hongwei; Liang, Wei; Xu, Chunxiang; Lu, Binfeng
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 453 (1-2): 309-315 APR 3 2008
Abstract:
To lay theoretical foundations for room and elevated temperature application of AZ91 magnesium alloys, microstructure and mechanical properties of AZ91 magnesium alloys strengthened by Mg-based spherical quasicrystalline phase have been investigated using XRD, SEM, TEM, hard-meter and impact testing machine. The experiment results show that macro-hardness and impact toughness of AZ91 magnesium alloys were improved a lot as the addition level of spherical quasicrystal containing Mg-Zn-Y-Mn master alloy increased; while adding 5.1 wt.% spherical quasicrystal containing master alloy, impact toughness of AZ91 matrix composites reached the peak value, 15.3 J cm(-2), which was about 252% as many as that of AZ91 master alloy. Majority of beta-Mg17Al12 phase dissolved when spherical quasicrystal particles remained stable after 28-h T4 solution treating. Small dimples on fracture surface by impact of AZ91 magnesium alloy strengthened by quasicrystal particles exhibited the feature of ductile fracture. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Quasiperiodic plane tilings based on stepped surfaces
Authors:
Shutov, AV; Maleev, AV Author Full Names: Shutov, A. V.; Maleev, A. V.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 376-382 Part 3 MAY 2008
Abstract:
Static and dynamic characteristics of layerwise growth in two-dimensional quasiperiodic Ito-Ohtsuki tilings are studied. These tilings are the projections of three-dimensional stepped surfaces. It is proved that these tilings have hexagonal self-similar growth with bounded radius of neighborhood. A formula is given for the averaged coordination number. Deviations of coordination numbers from its average are quasiperiodic. Ito-Ohtsuki tiling can be decomposed into one-dimensional sector layers. These sector layers are one-dimensional quasiperiodic tilings with properties like Ito-Ohtsuki tilings.
Title:
A new simple tiling, with unusual properties, by a polyhedron with 14 faces
Authors:
Gabbrielli, R; O'Keeffe, M Author Full Names: Gabbrielli, Ruggero; O'Keeffe, Michael
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 430-431 Part 3 MAY 2008
Abstract:
A monotypic simple tiling by a 14-face polyhedron that does not admit an isohedral tiling is described. The tiling is triclinic and contains four distinct, but combinatorially equivalent, kinds of tile.

Update: 25-Apr-2008

Title:
Structural properties of octagonal quasicrystal based on covering theory
Authors:
Liao, LG; Fu, XJ Author Full Names: Liao, Longguang; Fu, Xiujun
Source:
SOLID STATE COMMUNICATIONS 146 (1-2): 35-38 APR 2008
Abstract:
Cluster covering is a new approach to generate quasicrystal models, based on which a two-dimensional quasilattice can be described in terms of a single quasi-unit cell. We investigate the structural properties of a covering model of the octagonal quasicrystal. The pair covering rules, the nearest-neighbor configurations, and the configuration distributions are presented.(c) 2008 Elsevier Ltd. All rights reserved.
Title:
Magnetic properties and neutron diffraction study of two manganese sulfosalts: monoclinic MnSb2S4 and benavidesite (MnPb4Sb6S14)
Authors:
Leone, P; Doussier-Brochard, C; Andre, G; Moelo, Y Author Full Names: Leone, Philippe; Doussier-Brochard, Charlotte; Andre, Gilles; Moelo, Yves
Source:
PHYSICS AND CHEMISTRY OF MINERALS 35 (4): 201-206 MAY 2008
Abstract:
Mn2+Sb2S4, a monoclinic dimorph of clerite, and benavidesite (Mn2+Pb4Sb6S14) show well-individualized ingle chains of manganese atoms in octahedral coordination. Their magnetic structures are presented and compared with those of iron derivatives, berthierite (Fe2+Sb2S4) and jamesonite (Fe2+Pb4Sb6S14). Within chains, interactions are antiferromagnetic. Like berthierite, MnSb2S4 shows a spiral magnetic structure with an incommensurate 1D propagation vector [0, 0.369, 0], unchanged with temperature. In berthierite, the interactions between identical chains are antiferromagnetic, whereas in MnSb2S4 interactions between chains are ferromagnetic along c-axis. Below 6 K, jamesonite and benavidesite have commensurate magnetic structures with the same propagation vector [0.5, 0, 0]: jamesonite is a canted ferromagnet and iron magnetic moments are mainly oriented along the a-axis, whereas for benavidesite, no angle of canting is detected, and manganese magnetic moments are oriented along b-axis. Below 30 K, for both compounds, one-dimensional magnetic ordering or correlations are visible in the neutron diagrams and persist down to 1.4 K.
Title:
Polarized neutron scattering study on antiferromagnetic states in CeRh0.6Co0.4In5
Authors:
Yokoyama, M; Oyama, N; Amitsuka, H; Oinuma, S; Kawasaki, I; Tenya, K; Matsuura, M; Hirota, K Author Full Names: Yokoyama, M.; Oyama, N.; Amitsuka, H.; Oinuma, S.; Kawasaki, I.; Tenya, K.; Matsuura, M.; Hirota, K.
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 812-814 APR 1 2008
Abstract:
Polarized neutron scattering experiments were performed on mixed compound CeRh0.6Co0.4In5 to clarify the nature of the low-temperature ordered states. Three nonequivalent Bragg peaks, characterized by the wave vectors of q(h)similar to(1/2,1/2,0.3), q(1)similar to(1/2,1/2,0.4) and q(c) = (1/2, 1/2, 1/2), were observed at 1.4K. These Bragg peaks are found to occur entirely in spin-flip channel. This indicates that these Bragg peaks originate from the magnetic scattering, i.e., the antiferromagnetic orders with three different modulations appear in this compound. (c) 2007 Elsevier B.V. All rights reserved.
Title:
How do holes get heavy and superconduct?
Authors:
Harrison, N; Sebastian, SE; Batista, CD; Trugman, SA Author Full Names: Harrison, N.; Sebastian, S. E.; Batista, C. D.; Trugman, S. A.
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 977-981 APR 1 2008
Abstract:
We discuss the implications of recent de Haas-van Alphen effect (magnetic quantum oscillation) measurements on cubic CeIn3, which reveal pockets of f-electron holes centered at Q/2 in the Brillouin zone (where Q = [pi, pi, pi] is the antiferromagnetic modulation vector). This system had previously been identified as a local-moment magnet in which the f-electrons are completely localized. We discuss the Lifshitz Fermi surface topological changes in these pockets that takes place in strong magnetic fields and that is likely to take place as a function of pressure. We further discuss the implications for pressure-tuned superconductivity and the relevance of the experimental findings to CeRhIn5 and cuprate superconductors. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Intimate interplay between superconductivity and antiferromagnetism in CeNiGe3 : A(73) Ge-NQR study under pressure
Authors:
Harada, A; Mukuda, H; Kitaoka, Y; Thamizhavel, A; Okuda, Y; Settai, R; Onuki, Y; Itoh, KM; Haller, EE; Harima, H Author Full Names: Harada, A.; Mukuda, H.; Kitaoka, Y.; Thamizhavel, A.; Okuda, Y.; Settai, R.; Onuki, Y.; Itoh, K. M.; Haller, E. E.; Harima, H.
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 1020-1022 APR 1 2008
Abstract:
We report the Ge-73-NQR studies on the antiferromagnetic (AFM) heavy-fermion compound CeNiGe3 which shows two domes like pressure-induced superconducting phases in the pressure (P) ranges of 1.7-3.7GPa and 5.9-7.3GPa denoted as SC1 and SC2, respectively [M. Nakashima, et al., J. Phys. Condens. Matter. 16 (2004) L255, H. Kotegawa, et al., J. Phys. Soc. Jpn. 75 (2006) 044713]. The NQR spectra have revealed a change from an incommensurate AFM structure at P = 0 and 2.0 GPa into a commensurate one at P = 2.8 GPa. The onset of the SCI may be relevant to an intimate evolution from the incommensurate into commensurate AFM-spin structure as P increases. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Occurrence of magnetism in CeMIn5-xHgx (M = Rh, Ir)
Authors:
Bauer, ED; Ronning, F; Maquilon, S; Pham, LD; Thompson, JD; Fisk, Z Author Full Names: Bauer, E. D.; Ronning, F.; Maquilon, S.; Pham, L. D.; Thompson, J. D.; Fisk, Z.
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 1135-1137 APR 1 2008
Abstract:
The physical properties of CeM(In1-xHgx)(5) (M = Rh, Ir) including specific heat and magnetic susceptibility are reported. Two magnetic phases exist in CeRhIn(In1-xHgx)(5) with some evidence of a change from incommensurate magnetic order to a commensurate structure near 10% nominal Hg substitution. In CeIr(In1-xHgx)(5), an antiferromagnetic quantum critical point near x = 3% (followed by robust long-range antiferromagnetism for x > 5%) appears to be separated from superconductivity in CeIrIn5. The multitude of magnetic ground states observed in the CeM(In1-xHgx)(5) Materials is quite sensitive to doping and magnetic fields. (C) 2007 Published by Elsevier B.V.
Title:
The pressure effect on the magnetic commensurability and ferroelectricity in multiferroic HoMn2O5
Authors:
dela Cruz, CR; Lorenz, B; Ratcliff, W; Lynn, J; Gospodinov, MM; Chu, CW Author Full Names: dela Cruz, C. R.; Lorenz, B.; Ratcliff, W.; Lynn, J.; Gospodinov, M. M.; Chu, C. W.
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 1359-1361 APR 1 2008
Abstract:
The multiferroic HoMn2O5 is a frustrated magnetic system with a non-collinear commensurate structure in its ferroelectric state. This work presents polarization measurements under isotropic pressure showing the stabilization of the high ferroelectric polarization state. This is associated with the pressure induced phase transition from an incommensurate magnetic structure to a commensurate one once the critical pressure is passed as shown by elastic powder neutron diffraction measurements. In addition, the small increase in the polarization upon spin reorientation in the commensurate magnetic state of HoMn2O5 is associated with a change in the magnetic structure without change in commensurability. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Specific heat of the Kagome mixed compounds (Co1-xNix)(3)V2O8
Authors:
Zhang, Q; Knafo, W; Grube, K; Lohneysen, HV; Meingast, C; Wolf, T Author Full Names: Zhang, Qin; Knafo, William; Grube, Kai; Loehneysen, Hilbert V.; Meingast, Christoph; Wolf, Thomas
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 1404-1405 APR 1 2008
Abstract:
We present high-resolution specific heat data from 2 to 3 0 K of the mixed Kagome compounds (Co1-xNix)(3)V2O8 for x = 0, 0.12, 0.2, 0.5 and 1.0. We show that the specific heat at the first-order transitions of the end compounds (x = 0 and 1), obtained using relaxation calorimetry, is up to a factor of 10 larger than that previously reported in the literature. The mixed compounds exhibit only the highest temperature transition to an presumably, incommensurate magnetic structure. A slope change of T-N versus x at x = 0.2 indicates the transition from the Ni3V2O8- to Co3V2O8-type magnetic structures. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Influence of chemical substitutions on the charge instability of BaVS3
Authors:
Bernu, S; Foury-Leylekian, P; Pouget, JP; Akrap, A; Berger, H; Forro, L; Popov, G; Greenblatt, M Author Full Names: Bernu, S.; Foury-Leylekian, P.; Pouget, J. P.; Akrap, A.; Berger, H.; Forro, L.; Popov, G.; Greenblatt, M.
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 1625-1627 APR 1 2008
Abstract:
We study the influence of Sr substitutions on the structural counterpart of the MI transition of BaVS3. When Sr content increases, the commensurate CDW modulation of pure BaVS3 is changed into an incommensurate short range modulation that we attribute to a charge ordering of the e(t(2g)) electrons. The same features are observed in S deficient samples. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Equilibrium and non-equilibrium microstructures of Mg-Zn-Y quasicrystal alloy
Authors:
Wan, DQ; Linlin, GYC; Feng, ZG Author Full Names: Wan, Diqing; Linlin, Gencang Yang; Feng, Zhigang
Source:
MATERIALS LETTERS 62 (10-11): 1711-1714 APR 15 2008
Abstract:
Applied SEM and TEM methods, an investigation on the difference between equilibrium and non-equilibrium microstructures of Mg-Zn-Y quasicrystal alloys have been carried out. lcosahedral quasicrystal (1-phase), W-phase, and Mg7Zn3 phase have been obtained in the as-cast alloy, while the non-equilibrium microstructure, which is mainly made up of amorphous composition and stable I-phase, is gained in the as-quenched Mg-Zn-Y alloy. The mechanism of formation of the non-equilibrium microstructure in as-quenched alloy is also discussed. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Theoretical calculations of phase transitions and optical properties of solid iodine under high pressures
Authors:
San, XJ; Wang, LC; Ma, YM; Liu, ZM; Cui, T; Liu, BB; Zou, GT Author Full Names: San, Xiaojiao; Wang, Liancheng; Ma, Yanming; Liu, Zhiming; Cui, Tian; Liu, Bingbing; Zou, Guangtian
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (17): Art. No. 175225 APR 30 2008
Abstract:
The structural stability and optical properties of solid iodine under pressure have been studied using the ab initio pseudopotential plane-wave method. The dependence of lattice parameters on pressure indicates that the first structural phase transition from phase I to phase V occurs at about 20 GPa. From the pressure dependence of our elastic constants for solid iodine in phase I, it is found that the first structural transformation from molecular phase I to the intermediate phase V occurs at about 20 GPa due to the softening of the elastic constant C-44, which is very close to the transition pressure of 20 GPa obtained by geometry optimizations and 23.2 GPa obtained by experimental measurements. The optimized structure for phase V is a face-centered orthorhombic (fco) phase with equal interatomic distances d(1) = d(2) = d(3), but this fco structure is mechanically unstable, with shear elastic stiffness coefficient C-44 < 0. To understand the modulated phase V, we use a periodic crystal structure to mimic the incommensurate phase V and obtain some quantitative information. In our calculation, the modulated phase is thermodynamically and mechanically stable. It is believed that phase V is not a monatomic phase but an intermediate state between a molecular and a monatomic state.

Update: 11-Apr-2008

Title:
X-ray resonant diffraction study of multiferroic DyMn2O5
Authors:
Ewings, RA; Boothroyd, AT; McMorrow, DF; Mannix, D; Walker, HC; Wanklyn, BMR Author Full Names: Ewings, R. A.; Boothroyd, A. T.; McMorrow, D. F.; Mannix, D.; Walker, H. C.; Wanklyn, B. M. R.
Source:
PHYSICAL REVIEW B 77 (10): Art. No. 104415 MAR 2008
Abstract:
X-ray resonant scattering has been used to measure the magnetic order of the Dy ions below 40 K in multiferroic DyMn2O5. The magnetic order has a complex behavior. There are several different ordering wave vectors, both incommensurate and commensurate, as the temperature is varied. In addition a nonmagnetic signal at twice the wave vector of one of the commensurate signals is observed, the maximum intensity of which occurs at the same temperature as a local maximum in the ferroelectric polarization. Some of the results, which bear resemblance to the behavior of other members of the RMn2O5 family of multiferroic materials, may be explained by a theory based on so-called acentric spin-density waves.
Title:
Spin dynamics near the critical doping in weakly superconducting underdoped YBa2Cu3O6.35 (T-c=18 K)
Authors:
Stock, C; Buyers, WJL; Yamani, Z; Tun, Z; Birgeneau, RJ; Liang, R; Bonn, D; Hardy, WN Author Full Names: Stock, C.; Buyers, W. J. L.; Yamani, Z.; Tun, Z.; Birgeneau, R. J.; Liang, R.; Bonn, D.; Hardy, W. N.
Source:
PHYSICAL REVIEW B 77 (10): Art. No. 104513 MAR 2008
Abstract:
>From neutron inelastic and elastic scattering we have determined the magnetic structure and fluctuations in the YBa2Cu3O6.35 (YBCO) superconductor (T-c = 18 K) near the boundary of the superconducting phase. The long-range ordered collinear spins of the insulating antiferromagnet are replaced by a commensurate central mode arising from slow, isotropically polarized, short-range spin correlations extending over four planar unit cells. The inelastic spectrum up to 30 meV is also broad in wave vector and commensurate. In contrast to the resonance peak of higher-T-c superconductors, the spins exhibit a single overdamped spectrum whose rate of relaxation Gamma decreases on cooling and saturates at 2 Gamma= 5 +/- 1 meV below similar to 50 K. As the relaxation rate saturates, the quasistatic spin correlations grow and become resolution limited in energy. The spin susceptibility above similar to 50 K follows the same omega/T scaling relation found for the monolayer La2-xSrxCuO4 system, indicating that the dominant energy scale is set by the temperature. Below 50 K the scale length is geometric and not linked by velocity to dynamic widths. Despite the large differences from an antiferromagnet, we show that integrated intensity conserves the total moment sum rule, and that on cooling the spectral weight transfers from the inelastic spin relaxation to the elastic central peak. There is no observable suppression of the spin fluctuations or central mode upon the onset of superconductivity. The spins respond not to coherent charge pairs but to hole doping, allowing coexistence of glassy short-range spin order with superconductivity. Since the physics of the weakly superconducting system YBCO6.35 must connect continuously with that in more strongly superconducting YBCO6.5, we find that neither incommensurate stripe-like spin modulations nor a well-defined neutron spin resonance are essential for the onset with doping of pairing in a high-temperature cuprate superconductor.
Title:
Investigation of defects in Al-Pd-Mn icosahedral quasicrystals by simulation of x-ray topography images
Authors:
Ma, JY; Wang, JB; Wang, RH Author Full Names: Ma, Jiayan; Wang, Jianbo; Wang, Renhui
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS 41 (8): Art. No. 085413 APR 21 2008
Abstract:
The simulation of the diffraction contrast in x-ray topography has been extended from conventional crystals to quasicrystals (QCs). Case studies are presented for the investigation of two kinds of typical defects, i.e. spherical inclusions and straight dislocations, in an Al-Pd-Mn icosahedral QC using the extended program. The good agreement between the simulated and experimental images for spherical inclusions validates the extension. The systematic simulation for straight dislocations employing both phonon and phason strain fields illustrates not only the contrast dependences on various parameters, i.e. Burgers vector, diffraction vector, wavelength, deviation from exact Bragg diffraction, etc, but also the important contribution from the phason component, which is peculiar for QCs and normally makes the experimental analysis much more complex. The calculation can be applied to any defect in QCs in general and be of help in the defect characterization by matching with the experimental images, as in conventional crystals.
Title:
Band structure and localization of electronic states in a fivefold symmetric quasicrystal model
Authors:
Fu, XJ; Zhang, XW; Hou, ZL Author Full Names: Fu, Xiujun; Zhang, Xiaowei; Hou, Zhilin
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 354 (15-16): 1740-1743 MAR 15 2008
Abstract:
A fivefold symmetric quasilattice is constructed by the self-similar transformation on Gummelt two-color decagon and a single electron tight-binding model is proposed. We reduce the Hamiltonian to five identical subsets and analyze the spectral properties. By numerical calculation, three kinds of wave functions are found, which correspond to extended, localized and intermediate states, respectively. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Remarks on symmetries of 2D-quasicrystals
Authors:
Artamonov, V; Sanchez, S Author Full Names: Artamonov, V.; Sanchez, S.
Source:
INTERNATIONAL JOURNAL OF COMPUTER MATHEMATICS 85 (3-4): 319-328 2008
Abstract:
The paper presents a strict mathematical proof of the classifications of finite groups of symmetries of two-dimensional quasicrystals given by Hermisson, Richard and Baake in 1997.
Title:
Optical response of fci-ZnMgHo quasicrystal
Authors:
Karpus, V; Babonas, GJ; Reza, A; Suchodolskis, A; Tumenas, S; Hunderi, O; Assmus, W; Bruhne, S Author Full Names: Karpus, V.; Babonas, G. -J.; Reza, A.; Suchodolskis, A.; Tumenas, S.; Hunderi, O.; Assmus, W.; Bruehne, S.
Source:
ACTA PHYSICA POLONICA A 113 (3): 1005-1008 MAR 2008
Abstract:
The results of an optical spectroscopy study of the icosahedral fci-ZnMgHo quasicrystal are presented. The dielectric function of the quasicrystal was measured by the spectroscopic ellipsometry technique in the spectral range of 0.1-5.0 eV. The analysis of the dielectric function shows that an optical response of fci-ZnMgHo is a superposition of the free-electron Drude-type contribution and that of the interband transitions across the fci-ZnMgHo pseudogap.
Title:
Diffuse neutron scattering in the Mn0.4Cu0.6 alloy
Authors:
Jankowska-Kisielinska, J; Mikke, K; Fijal-Kirejczyk, I Author Full Names: Jankowska-Kisielinska, J.; Mikke, K.; Fijal-Kirejczyk, I.
Source:
ACTA PHYSICA POLONICA A 113 (4): 1171-1178 APR 2008
Abstract:
The diffuse neutron scattering in the Mn0.4Cu0.6 alloy was measured in the temperature range 15-390 K at the 3-axis neutron spectrometer at MARIA reactor in Swierk. The broad maxima of the neutron intensity were observed in the surrounding of the (0.5,1,0) reciprocal lattice point and other symmetry related points. The effect is similar to that observed in Mn-Cu alloys with lower Mn content at room temperature. Our results are in agreement with the earlier finding that the maxima of the short-range order incommensurate spin density wave scattering are placed at the (0.5 +/- delta,1,0) reciprocal lattice point with a linear dependence of delta on the Mn concentration. In addition, some commensurate antiferromagnetic short-range order was found.

Update: 4-Apr-2008

Title:
Role of smectite quasicrystal dynamics in adsorption of dinitrophenol
Authors:
Pereira, TR; Laird, DA; Thompson, ML; Johnston, CT; Teppen, BJ; Li, H; Boyd, SA Author Full Names: Pereira, Tanya R.; Laird, David A.; Thompson, Michael L.; Johnston, Cliff T.; Teppen, Brian J.; Li, Hui; Boyd, Stephen A.
Source:
SOIL SCIENCE SOCIETY OF AMERICA JOURNAL 72 (2): 347-354 MAR-APR 2008
Abstract:
Understanding sorption mechanisms and processes is critical for predicting the fate of organic pollutants in soils and for development of effective remediation strategies for contaminated soils. A novel suspension x-ray diffraction (XRD) technique was used to elucidate the influence of the size and swelling of K- and Ca-smectite quasicrystals in aqueous suspensions on adsorption of 4,6-dinitro-o-cresol (DNOC). X-ray diffraction patterns of randomly oriented smectite quasicrystals in aqueous suspensions were compared with diffraction patterns for air-dried and oven-dried oriented films of the same smectites. The XRD patterns reveal that the phenolate form of DNOC, which is predominant in solution with pH >= 4.4, is primarily adsorbed on external surfaces of K-smectite quasicrystals in aqueous suspensions and may enter the interlayers as a K-DNOC complex when K-smectite quasicrystals coalesce. In Ca-smectite suspensions with pH > 4.4, the phenolate form of DNOC is adsorbed only on external surfaces; however, DNOC may become entrapped between substacks within Ca-smectite quasicrystals as the smectite suspension dries to form an oriented film. The neutral form of DNOC (pH <= 4.4) was adsorbed in the interlayers of a low-charge-clensity Ca-smectite in aqueous suspension but not in the interlayers of the high-charge-density Ca-smectite, apparently due to steric restrictions. Clearly, XRD analysis is a valuable toot for gaining insight into interactions between smectites and organic molecules, but caution must be used in extrapolating data based on XRD patterns of air-dried and oven-dried smectite films to processes that may occur in aqueous smectite suspensions.
Title:
Theoretical sequence of s- and t-incommensurate phases in quartz
Authors:
Sannikov, DG Author Full Names: Sannikov, D. G.
Source:
PHYSICS OF THE SOLID STATE 50 (3): 507-510 MAR 2008
Abstract:
The sequence of s- and t-incommensurate phases observed with variations of the temperature in quartz is substantiated theoretically.
Title:
Effect of Nb on nanoquasicrystalline Al-based alloys
Authors:
Galano, M; Audebert, F; Stoney, IC; Cantor, B Author Full Names: Galano, M.; Audebert, F.; Stoney, I. C.; Cantor, B.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 88 (4): 269-278 2008
Abstract:
Nanoquasicrystalline Al-based alloys, containing icosahedral particles in alpha-Al matrix, exhibit high strength at elevated temperature. The metastability of the quasicrystals can limit the use of these alloys. In the present work, the microstructural evolution of Al-93(Fe3Cr2)(7) and Al93Fe3Cr2Nb2 (at%) alloys was studied using heat treatments and structural characterization by XRD, TEM and STEM-EDX analysis. It was observed that the Nb is dissolved in the Al-Fe-Cr icosahedral phase. This provides higher thermal stability, retaining the fine nanoquasicrystalline microstructure for longer times at high temperature.
Title:
A new orthorhombic approximant of the icosahedral Al-Cu-Fe quasicrystal
Authors:
Lei, Y; Kenzari, S; Demange, V; Fournee, V; Dubois, JM Author Full Names: Lei, Y.; Kenzari, S.; Demange, V.; Fournee, V.; Dubois, J. M.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 88 (4): 279-286 2008
Abstract:
We report on the formation of a new crystalline approximant phase of the icosahedral (i-)Al-Cu-Fe quasicrystal. This phase is formed during sintering of Al-based composites reinforced with i-AlCuFeB quasicrystalline particles. The structure of this phase has been characterized by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). TEM revealed that it is a B-centred orthorhombic phase with lattice parameters a = 1.166 nm, b = 1.195 nm and c = 3.44 nm. Its chemical composition, as determined by electron energy loss spectroscopy (EELS), is close to Al76.9Cu2.7Fe20.4, with an average number of valence electrons per atom e/a of 1.92, similar to the value in all other approximants of the i-phase discovered thus far. Initial results on local atomic arrangements along one of its pseudo-5-fold axes are also presented.
Title:
Observation of beta phase particles in an isothermally aged Al-10 mass%Mg alloy with and without 0.5 mass%Ag
Authors:
Kubota, M Author Full Names: Kubota, Masahiro
Source:
MATERIALS TRANSACTIONS 49 (2): 235-241 FEB 2008
Abstract:
Characterization of the beta' and beta precipitate phases formed in the aged Al-10mass%Mg alloy with and without 0.5mass%Ag at 200 degrees C and 240 degrees C has been carried out using TEM. The plate-like precipitate particles were formed in binary alloys aged from 2 h at 200 degrees C. The plate-like particles had habit planes of {100}(alpha), and were identified as the beta' phase. Whereas the very fine scale, uniformly distributed precipitate particles with a spherical shape were formed as the dominant precipitate particle in ternary alloy aged at 200 degrees C for periods of 4 h and 6 h. These small spherical particles were identified to be icosahedral phase while no icosahedral phase was observed in the Ag-free alloys when samples were aged at 200 degrees C. Formation of a precipitate cluster consisting of two distinguishable parts has been observed in binary alloys aged 5 h at 240 degrees C, and these precipitate particles were identified as the equilibrium beta and metastable beta' phases. Whereas a higher volume fraction of dispersed precipitate phases which comprised a mixture of a coarse-scale, rod-like particles and blocky particles, was observed in ternary alloy aged 5 h at 240 degrees C. With further increase of ageing time up to 24 h at 240 degrees C, the microstructure contained a high volume fraction of coarse-scale, globular precipitate particles, together with a secondary distribution of fine-scale spheroidal precipitates, these coarse globular particles were identified to be the equilibrium beta phase.
Title:
Crystal and magnetic structures in the Tb(Pd, Ni) Al series
Authors:
Javorsky, P; Prokleska, J; Isnard, O; Prchal, J Author Full Names: Javorsky, P.; Prokleska, J.; Isnard, O.; Prchal, J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (10): Art. No. 104223 MAR 12 2008
Abstract:
We report on the magnetic structures in the TbPd1-xNixAl compounds as determined by powder neutron diffraction. The development of magnetic structures in the Tb(Pd, Ni) Al series is relatively simple. All the compounds show the existence of two magnetic phases with almost unchanged Neel temperature T-N similar or equal to 44 K and an additional magnetic phase transition temperature T-1 similar or equal to 23 K. The arrangement of the Tb moments between T-N and T-1 is identical for all the concentrations and is characterized by a (1/2, 0, 1/2) propagation vector with one-third of Tb moments frustrated to nearly zero. Certain concentration development occurs only below T-1. Magnetic moments that are frustrated between T-N and T-1 change their propagation below T-1 to commensurate (1/2, -1/2, 1/2) or incommensurate (1/2, -tau, 1/2), depending on the Ni concentration. The magnetic moments stay parallel to the hexagonal c axis for all concentrations and temperatures.
Title:
Magnetic phase diagram of Ho-Ag
Authors:
Paul-Boncour, V; Hoser, A; Hense, K; Gratz, E; Rotter, M; Stusser, N Author Full Names: Paul-Boncour, V.; Hoser, A.; Hense, K.; Gratz, E.; Rotter, M.; Stuesser, N.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (10): Art. No. 104225 MAR 12 2008
Abstract:
The magnetic phase diagram of Ho-Ag has been established using magnetoresistance, magnetostriction and neutron diffraction experiments versus applied field and temperature. Three different magnetic phases were observed: an incommensurate antiferromagnetic phase (IC) below T-N = 33 K, a commensurate antiferromagnetic phase (C) above 5 T and below T-1 (5-8 K) and a ferromagnetic component above 3 T. The IC phase undergoes spin reorientations around 5 T (IC') and 13 T (IC'').
Title:
Magnetic excitations in the ordered phases of praseodymium hexaboride
Authors:
Le, MD; McEwen, KA; Park, JG; Lee, S; Iga, F; Rule, KC Author Full Names: Le, M. D.; McEwen, K. A.; Park, J-G; Lee, S.; Iga, F.; Rule, K. C.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (10): Art. No. 104231 MAR 12 2008
Abstract:
We have made the first inelastic neutron scattering measurements on single crystal PrB6, studying the magnetic excitations in the ordered phases. The lowest energy mode has a minimum energy of approximate to 1.0 meV at the magnetic zone centre, with a significant dispersion along the [001] direction, but very little dispersion along [110]. Interactions out to fourth nearest neighbours are required to explain the [001] dispersion. Measurements of the temperature dependence of the excitations show a strong softening and broadening of the lowest energy mode at the magnetic zone centre between 2 K (commensurate phase) and 5 K (incommensurate phase).
Title:
Effects of oxygen deficiency on the magnetic ordering of Mn in (TbNa0.1MnO2.9)-Na-0.9
Authors:
Yang, CC; Wu, CM; Li, WH; Chan, TS; Liu, RS; Chen, YY; Avdeev, M Author Full Names: Yang, C. C.; Wu, C-M; Li, W-H; Chan, T. S.; Liu, R. S.; Chen, Y. Y.; Avdeev, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (10): Art. No. 104234 MAR 12 2008
Abstract:
Monovalent Na+ ions have been incorporated into a multiferroic TbMnO3 compound. Structural studies, using high-resolution neutron diffraction patterns, show that monovalent Na+-doping results in a noticeable oxygen deficiency in the compound. The alternations in crystalline and magnetic structures due to oxygen deficiency are investigated by neutron diffraction and magnetic susceptibility measurements. Na-doping turns the modulated incommensurate Mn spin structure, observed for the parent compound, into a simple commensurate one. The observed magnetic diffraction patterns agree very well with that calculated assuming a D-type arrangement for the Mn spins, with the moments pointing along the c-axis direction. No significant alternation in the ordering temperature of the Mn moments is found.
Title:
Charge ordering in CaCuxMn7-xO12 (x=0.0 and 0.1) compounds
Authors:
Slawinski, W; Przenioslo, R; Sosnowska, I; Bieringer, M; Margiolaki, I; Fitch, AN; Suard, E Author Full Names: Slawinski, W.; Przenioslo, R.; Sosnowska, I.; Bieringer, M.; Margiolaki, I.; Fitch, A. N.; Suard, E.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (10): Art. No. 104239 MAR 12 2008
Abstract:
The crystal structure of CaMn7O12 and CaCu0.1Mn6.9O12 has been studied by synchrotron radiation (SR) based powder x-ray diffraction and neutron powder diffraction in the temperature range from 10 K up to 290 K. The lattice parameter a exhibits a minimum at 45 K in CaMn7O12. The c lattice parameter in CaMn7O12 and CaCu0.1Mn6.9O12 has a maximum at the same temperature. Additional Bragg peaks have been found in the SR diffraction patterns in CaMn7O12 and CaCu0.1Mn6.9O12 below 250 K and 220 K, respectively. All diffraction peaks have been indexed as (h, k, l +/- k), where. was equal to 0.079(15) for CaMn7O12 and 0.093( 15) for CaCu0.1Mn6.9O12. The incommensurate low-temperature diffraction peaks are not observed in neutron diffraction patterns. This leads to the conclusion that the phase transition to the incommensurate structure is due to charge ordering rather than atomic position modulation. The charge ordering temperature coincides with dielectric constant changes of four orders of magnitude for CaMn7O12.
Title:
The structure model of a cubic aperiodic phase ('quasicrystal without forbidden symmetry axes')
Authors:
Kraposhin, VS; Talis, AL; Lam, HT Author Full Names: Kraposhin, V. S.; Talis, A. L.; Lam, Ha Thanh
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (11): Art. No. 114115 MAR 19 2008
Abstract:
A model structure of the aperiodic cubic phase (a cubic quasicrystal) has been constructed as a periodical packing of hierarchical octahedral clusters which were composed of truncated tetrahedra (Friauf-Laves polyhedra) and chains of Frank-Kasper polyhedra with 14 vertices. The construction of the hierarchical model for the cubic aperiodic phase became possible due to the discovery of a new space subdivision with equal edges and with vertices belonging to two orbits of the space group Fm3m. The subdivision is characterized by unique values and unique relations between the coordinates of the starting points of two orbits. Calculated x-ray diffraction patterns for the proposed hierarchical model are in qualitative agreement with published experimental x-ray patterns for aperiodical phases observed in melt-quenched Mg-Al and Fe-Nb-B-Si alloys.
Title:
Electronic and atomic disorder in icosahedral AlPdRe
Authors:
Rapp, O; Karkin, AA; Goshchitskii, BN; Voronin, VI; Srinivas, V; Poon, SJ Author Full Names: Rapp, O.; Karkin, A. A.; Goshchitskii, B. N.; Voronin, V. I.; Srinivas, V.; Poon, S. J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (11): Art. No. 114120 MAR 19 2008
Abstract:
Relations between electronic and atomic disorder of i-AlPdRe have been investigated by studies of neutron irradiated and annealed samples. The advantage with this technique is that a single sample can be monitored over a significant range of varying electronic properties, without concern for any influence of varying impurities. X-ray diffraction, the electrical resistivity and its temperature dependence, and the magnetoresistance are studied. The results show that annealings of an irradiated sample lead to improvement of the atomic order, as reflected in increased intensities of the x-ray diffraction peaks, while electronic properties change in the direction of increasing electronic disorder towards a metal-insulator transition. The observed relation in quasicrystals that improved atomic structure is associated with stronger anomalies in transport properties is thus also seen in i-AlPdRe. In particular, the variation of the diffusion constant in the region of small values of the resistivity is found to be similar for annealed polygrain samples and for single grain samples with varying Pd concentration, as evaluated from literature data, indicating a similar development of electronic disorder in both sets of samples. However, the problem remains as to why the resistivity is small in single grain samples which are atomically well-ordered. The possibility of a strong sensitivity to concentration differences is pointed out.
Title:
Thermodynamic properties of Al-Mn, Al-Cu, and Al-Fe-Cu melts and their relations to liquid and quasicrystal structure
Authors:
Zaitsev, AI; Zaitseva, NE; Shimko, RY; Arutyunyan, NA; Dunaev, SF; Kraposhin, VS; Lam, HT Author Full Names: Zaitsev, A. I.; Zaitseva, N. E.; Shimko, R. Yu; Arutyunyan, N. A.; Dunaev, S. F.; Kraposhin, V. S.; Lam, Ha Thanh
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (11): Art. No. 114121 MAR 19 2008
Abstract:
Thermodynamic properties of molten Al-Mn, Al-Cu and Al-Fe-Cu alloys in a wide temperature range of 1123-1878 K and the whole range of concentrations have been studied using the integral effusion method and Knudsen mass spectrometry. Thermodynamic functions of melts were described by the associated solution model. The possibility of icosahedral quasicrystal (i-QC) precipitation from liquid Al-Mn and Al-Cu-Fe alloys was found to be a consequence of the existence in liquid associates (clusters). A geometric model is suggested for the structure of associates in liquid.
Title:
(Ca0.37Sr0.63)TiO3 perovskite - an example of an unusual class of tilted perovskites
Authors:
Howard, CJ; Withers, RL; Knight, KS; Zhang, Z Author Full Names: Howard, C. J.; Withers, R. L.; Knight, K. S.; Zhang, Z.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (13): Art. No. 135202 APR 2 2008
Abstract:
The structure of Ca0.37Sr0.63TiO3 perovskite has been carefully investigated using electron and neutron diffraction. Electron diffraction supports the supercell and Pbcm space group previously proposed, while high resolution neutron powder diffraction data provide the basis for a new structure refinement. The distortions of the resultant structure relative to the ideal parent perovskite structure type have been decomposed into normal modes. It is found that the primary modes of distortion are octahedral tilting modes associated with the R point (k = [1/2, 1/2, 1/2]*) and the xi = 1/4 point on the T line of symmetry (k = [1/2, 1/2,xi]*). There is a smaller secondary, probably induced, mode of distortion involving antiferroelectric displacements of the Ti cations associated with the xi = 1/4 point on the Delta line of symmetry (k = [0, 0, xi]*). This compound provides one of the very few currently known examples of a tilted perovskite structure that shows tilting modes associated with the ubiquitous k = < 1/2, 1/2, xi > modulation wavevectors for a value of xi different from 0 and 1/2.
Title:
The accurate magnetic structure of CeAl2 at various temperatures in the ordered state
Authors:
Schweizer, J; Givord, F; Boucherle, JX; Bourdarot, F; Ressouche, E Author Full Names: Schweizer, J.; Givord, F.; Boucherle, J-X; Bourdarot, F.; Ressouche, E.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (13): Art. No. 135204 APR 2 2008
Abstract:
The magnetic structure of the cubic compound CeAl2 is incommensurate and double-k. The moments on the two Ce sites describe two elliptical helices of opposed chiralities and lie in the (1 (1) over bar0) plane, with their Fourier components m(k) close to the [111] direction. Recent symmetry considerations, including for the first time the inversion center of the crystal, have reduced the number of parameters of this structure and have underlined the existence of a phase difference between the projections m(x)(k), m(y)(k) and m(z)(k) of m(k). Up to now, although many neutron investigations have been carried out on CeAl2 single crystals, no set of magnetic intensities was available which was large and good enough to check whether this phase difference exists or not. We have measured such a set of data, taking great care of the instrumental resolution in order to avoid unwanted contributions to the intensities from other domains. As the magnetic form factor of the Gamma(7) ground state of CeAl2 depends very much on the direction of the applied field, it was necessary to go through a self-consistent determination of the magnetic form factor in the direction of the Fourier components m(k) to obtain good agreement between the refined magnetic structure and the experimental data. The resulting Fourier components are close but not exactly along the [111] direction and their departure from this direction at low temperature reduces the ellipticity of the helices. The phase difference between the projections m(x)(k), m(y)(k) and m(z)(k) is small but undoubtedly exists and is temperature dependent. It leads to a small distortion of the elliptical helices, with magnetic moments slightly out of the (1 (1) over bar0) plane.
Title:
Glass formation dependence on casting-atmosphere pressure in Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5) alloy system: A resultant effect of quasicrystalline phase transformation and cooling mechanism during mold-casting process
Authors:
Setyawan, AD; Kato, H; Saida, J; Inoue, A Author Full Names: Setyawan, Albertus D.; Kato, Hidemi; Saida, Junji; Inoue, Akihisa
Source:
JOURNAL OF APPLIED PHYSICS 103 (4): Art. No. 044907 FEB 15 2008
Abstract:
A different dependence of apparent glass-forming ability (GFA) on casting-atmosphere pressure is observed in a Zr65Al7.5Ni10Cu17.5-xPdx (x = 0-17.5) alloy system. Low-Pd alloys (x < 12.5) reveal low GFA dependence, while high-Pd ones (x >= 12.5) show high GFA dependence on atmosphere pressure applied during casting. The phenomenon is suggested to originate from the fact that for the high-Pd alloys, the transformation region of supercooled-liquid to quasicrystalline phase is located at the low-temperature side of the undercooled-liquid region where the atmosphere-pressure dependence of cooling characteristic coincidently takes place. The on-cooling phase transformation in the alloy system and the cooling mechanism during mold-casting process are discussed comprehensively. (c) 2008 American Institute of Physics.
Title:
Quasicrystalline phase in melt-spun Al-Mn-Be ribbons
Authors:
Zupanic, F; Boncina, T; Krizman, A; Grogger, W; Gspan, C; Markoli, B; Spaic, S Author Full Names: Zupanic, Franc; Boncina, Tonica; Krizman, Alojz; Grogger, Werner; Gspan, Christian; Markoli, Bostjan; Spaic, Savo
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 452 (2): 343-347 MAR 20 2008
Abstract:
The quasicrystalline phase in melt-spun Al-Mn-Be alloys was investigated. In ribbons 40-60 mu m thick the phase was present in the form of small particles rather uniformly dispersed in an aluminium solid solution matrix. The quasicrystalline phase had a primitive icosahedral structure. It was confirmed that it contained a substantial amount of Be. Nonetheless, it seemed that the electron-to-atom ratio remained close to that of binary Al80Mn20 quasicrystal. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Formation of icosahedral phase in Zr65Al7.5Ni10Cu12.5Ag5 metallic glass
Authors:
Yan, ZJ; Dang, SE; Li, QS; Hao, WX; Hu, Y Author Full Names: Yan, Z. J.; Dang, S. E.; Li, Q. S.; Hao, W. X.; Hu, Y.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 452 (2): 359-366 MAR 20 2008
Abstract:
Two Zr65Al7.5Ni10Cu12.5Ag5 amorphous specimens were prepared from the mother ingots with different solidification microstructures. Observation by high-resolution electron microscopy (HREM) revealed that there existed numerous nano-sized short-range order regions (SRORs) in the as-cast specimens although their amorphous nature had been verified by X-ray diffraction (XRD). The average size of the SRORs decreased significantly as the solidification microstructure of the mother ingot became finer. The transformation from amorphous to icosahedral phase (I-phase) in the Zr65Al7.5Ni10Cu12.5Ag5 metallic glass was systematically investigated by differential scanning calorimetry (DSC) under isochronal and isothermal conditions. The results indicated that the transformation kinetics slightly changed, and that the formation of I-phase was triggered by the growth of those SRORs as the pre-existing embryos. It was strongly suggested that the atomic configuration of the unit structure in the metallic glasses showed an icosahedron-like one. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Quasicrystal derived catalyst for steam reforming of methanol
Authors:
Ngoc, BP; Geantet, C; Aouine, M; Bergeret, G; Raffy, S; Marlin, S Author Full Names: Ngoc, B. Phung; Geantet, C.; Aouine, M.; Bergeret, G.; Raffy, S.; Marlin, S.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 33 (3): 1000-1007 FEB 2008
Abstract:
Two alloys of composition Al(59)Cu(25.5)sFe(12.4)B(3) and Al71Cu9.7Fe8.7Cr10.6 were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The latter forms a mixture of imperfect icosahedral phase and cubic phase upon rapid solidification from the liquid state. After heat treatment, this alloy transforms into a decagonal quasicrystalline phase. Both alloys can be used as catalysts precursors and transformed into active metallic phases after alkali leaching with a NaOH solution. These catalysts were used for hydrogen production by steam reforming of methanol between 473 and 773 K. The catalytic activities of these treated alloys were compared to that of a reference Cu/ZnO/Al2O3 catalyst. Quasicrystal derived catalysts showed a high catalytic activity for the production of hydrogen. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Update: 28-Mar-2008

Title:
Spin resonance in the d-wave superconductor CeCoIn5
Authors:
Stock, C; Broholm, C; Hudis, J; Kang, HJ; Petrovic, C Author Full Names: Stock, C.; Broholm, C.; Hudis, J.; Kang, H. J.; Petrovic, C.
Source:
PHYSICAL REVIEW LETTERS 1 (8): Art. No. 087001 FEB 29 2008
Abstract:
Neutron scattering is used to probe antiferromagnetic spin fluctuations in the d-wave heavy fermion superconductor CeCoIn5 (T-c=2.3 K). Superconductivity develops from a state with slow (h Gamma=0.3 +/- 0.15 meV) commensurate [Q(0)=(1/2,1/2,1/2)] antiferromagnetic spin fluctuations and nearly isotropic spin correlations. The characteristic wave vector in CeCoIn5 is the same as CeIn3 but differs from the incommensurate wave vector measured in antiferromagnetically ordered CeRhIn5. A sharp spin resonance (h Gamma < 0.07 meV) at h omega=0.60 +/- 0.03 meV develops in the superconducting state removing spectral weight from low-energy transfers. The presence of a resonance peak is indicative of strong coupling between f-electron magnetism and superconductivity and consistent with a d-wave gap order parameter satisfying Delta(q+Q(0))=-Delta(q).
Title:
Deposition of atoms on a quasicrystalline substrate: Molecular dynamics study in three dimensions
Authors:
Mungan, M; Weisskopf, Y; Erbudak, M Author Full Names: Mungan, Muhittin; Weisskopf, Yves; Erbudak, Mehmet
Source:
PHYSICAL REVIEW B 76 (19): Art. No. 195443 NOV 2007
Abstract:
We study the three-dimensional structure formation when atoms are deposited onto a substrate with a decagonal quasicrystalline order. Molecular dynamics calculations show that the adsorbate layer consists of ordered nanoscale domains with orientations determined by the underlying substrate symmetry. Depending on the relative strength of the interactions of adsorbate atoms with each other and with the substrate atoms, different morphologies are observed ranging from layer-by-layer growth to cluster formation. We also find that the film thickness likewise affects the overall structure of the growing film: Depending on the relative strength of the interaction between adsorbate atoms, a structural transition of the configuration of the adsorbate layers closest to the substrate can occur as the number of deposited layers increases. This is a simulation of three-dimensional crystal growth on a quasicrystal on a scale large enough to capture the formation of multiple domains.
Title:
Morphotropic phase-boundary-like characteristic in a lead-free and non-ferroelectric (1-x)NaNbO3-xCaTiO(3) system
Authors:
Tripathi, S; Pandey, D; Mishra, SK; Krishna, PSR Author Full Names: Tripathi, Saurabh; Pandey, Dhananjai; Mishra, Sanjay Kumar; Krishna, P. S. R.
Source:
PHYSICAL REVIEW B 77 (5): Art. No. 052104 FEB 2008
Abstract:
We report here an anomalous peak in the composition dependence of the dielectric permittivity of non-ferroelectric (1-x)NaNbO3-xCaTiO(3) ceramics for the composition range 0.10 < x < 0.20. This is reminiscent of a similar phenomenon in the ferroelectric morphotropic phase boundary ceramics. Rietveld analysis of the powder x-ray diffraction data for various compositions reveals that this peak is linked with a change of crystal structure from one orthorhombic phase in the Pbma space group for 0 <= x <= 0.10 to another orthorhombic phase in the Pbnm space group for x >= 0.20 through an intermediate long period modulated orthorhombic phase whose lattice parameter is similar to 14 times the lattice parameter of the Pbnm phase of CaTiO3 in the [010] direction (q similar to[0,1/14,0]).
Title:
Friedel oscillations of density of states in a one-dimensional Mott insulator and incommensurate charge-density wave or superconductor
Authors:
Tsvelik, AM Author Full Names: Tsvelik, A. M.
Source:
PHYSICAL REVIEW B 77 (7): Art. No. 073402 FEB 2008
Abstract:
Oscillations of local density of states generated by a single scalar impurity potential are calculated for one-dimensional systems with dynamically generated charge or spin gap. At zero temperature, the oscillations develop at finite wave vector (pi for the Mott insulator and 2k(F) for incommensurate charge-density wave or superconductor) and at frequencies larger than the soliton spectral gap m. Their amplitude has a broad maximum at omega approximate to 3m, where m is the gap magnitude.
Title:
Self-assembly, structure, and electronic properties of a quasiperiodic lead monolayer
Authors:
Ledieu, J; Leung, L; Wearing, LH; McGrath, R; Lograsso, TA; Wu, D; Fournee, V Author Full Names: Ledieu, J.; Leung, L.; Wearing, L. H.; McGrath, R.; Lograsso, T. A.; Wu, D.; Fournee, V.
Source:
PHYSICAL REVIEW B 77 (7): Art. No. 073409 FEB 2008
Abstract:
A quasiperiodic Pb monolayer has been formed on the fivefold surface of the Al-Pd-Mn quasicrystal. Growth of the monolayer proceeds via self-assembly of an interconnected network of pentagonal Pb stars, which are shown to be tau inflated compared to similar structural elements of the quasiperiodic substrate. Measurements of the electronic structure of the system using scanning tunneling spectroscopy and ultraviolet photoemission spectroscopy reveal that the Pb monolayer displays a pseudogap at the Fermi level which is directly related to its quasiperiodic structure.
Title:
Complex metallic alloys in the Ce-Au-Sn system: a study of the atomic and electronic structures
Authors:
Kenzari, S; Demange, V; Boulet, P; de Weerd, MC; Ledieu, J; Dubois, JM; Fournee, V Author Full Names: Kenzari, S.; Demange, V.; Boulet, P.; de Weerd, M. C.; Ledieu, J.; Dubois, J. M.; Fournee, V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (9): Art. No. 095218 MAR 5 2008
Abstract:
We report the formation of a new stable quasicrystal approximant in the Ce-Au-Sn system. The crystalline structure of the Ce15Au65Sn20 compound is investigated by x-ray diffraction and is found to be of similar structure type to the Zn17Sc3 1/1 approximant. Large clusters with icosahedral symmetry are located at the node of the body-centred cubic (bcc) unit cell (a = 1.5190 nm) containing 161 atoms. We have used transmission electron microscopy to emphasize the relationship of this new compound with the icosahedral space group. The valence band has been investigated by photoemission spectroscopy and shows an indication of Van Hove singularities in the density of states, characteristic of quasicrystalline and related approximant phases. We expect similar 1/1 approximant and possibly icosahedral phases to be discovered in the new RE-Au-Sn systems (where RE is rare earth). We also found a hexagonal phase with a large unit cell possessing local icosahedral order, co-existing as a minority phase.
Title:
The magnetic composition-temperature phase diagram of the kagome mixed system (CoxNi1-x)(3)V2O8
Authors:
Qureshi, N; Fuess, H; Ehrenberg, H; Hansen, TC; Ritter, C; Adelmann, P; Meingast, C; Wolf, T; Zhang, Q; Knafo, W Author Full Names: Qureshi, N.; Fuess, H.; Ehrenberg, H.; Hansen, T. C.; Ritter, C.; Adelmann, P.; Meingast, C.; Wolf, Th; Zhang, Q.; Knafo, W.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (9): Art. No. 095219 MAR 5 2008
Abstract:
The magnetic composition-temperature (x-T) phase diagram of the mixed kagome system (CoxNi1-x)(3)V2O8 (CNVO) deduced from neutron powder diffraction and single-crystal heat capacity experiments is presented. CNVO changes its magnetic structure twice below 5.5 K as a function of the compositional parameter x. A sample with x = 0.98 has been found to be of a critical composition where both ferromagnetic and antiferromagnetic reflections of the Co3V2O8 (CVO) type magnetic structure have been observed in the diffraction pattern. Below this composition the ferromagnetic phase is completely suppressed and antiferromagnetic short-range order is present, which is modulated by a propagation vector k(1) = (0, delta, 0) with delta being temperature and composition dependent. Below 4.2 K delta has a constant value of 0.4 for 0.76 < x < 0.92. In the region 0.71 < x < 0.76 a change of the magnetic structure into the long-range ordered Ni3V2O8 (NVO) type with k(2) = (delta, 0, 0), where delta is only dependent on x, takes place. Finally, for x < 0.035 the positions of the magnetic reflections become temperature dependent again.
Title:
A linked structural and electronic transition in Na0.63CoO2
Authors:
Zhou, T; Wright, AJ; Zhang, D; Button, TW; Greaves, C Author Full Names: Zhou, Tong; Wright, Adrian J.; Zhang, Dou; Button, Tim W.; Greaves, Colin
Source:
JOURNAL OF MATERIALS CHEMISTRY 18 (12): 1342-1346 2008
Abstract:
A structural transition at 158 degrees C in Na0.63CoO2 is associated with a resistivity anomaly. Raman spectroscopy suggests a change in Na ordering at the transition and, for the first time, we have identified the nature of this rearrangement using variable temperature neutron powder diffraction. On heating, some Na ions migrate to the thermodynamically less stable (Na1) site from Na2, consistent with loss of an incommensurate superstructure. It is suggested that the change in Na order is linked to a change in the electronic band structure, which is reflected in the resistivity anomaly.
Title:
Method on holomorphic vector functions and applications in two-dimensional quasicrystals
Authors:
Gao, Y; Xu, BX Author Full Names: Gao, Yang; Xu, Bai-Xiang
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B 22 (6): 635-643 MAR 10 2008
Abstract:
Generalization of the Stroh formalism to two-dimensional quasicrystal materials results in a ten-dimensional formalism for which there are five pairs of complex eigenvalues. By virtue of the generalized Stroh formalism, two-dimensional problems of quasicrystals elasticity are transferred into the boundary value problems of holomorphic vector functions in a given region. If the conformal mapping from an ellipse to a circle is known, a general method can be presented for solving the boundary value problems of holomorphic vector functions. Using the necessary and sufficient condition of boundary value problems of holomorphic vector functions, several basic two-dimensional problems in two-dimensional quasicrystals are solved.
Title:
Characterization and hydrogen absorption at low temperature of suction-cast Ti45Zr38Ni17 quasicrystalline alloy
Authors:
Huang, HG; Dong, P; Yin, C; Zhang, PC; Bai, B; Dong, C Author Full Names: Huang, Huogen; Dong, Ping; Yin, Chen; Zhang, Pencheng; Bai, Bin; Dong, Chuang
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 33 (2): 722-727 JAN 2008
Abstract:
The formation of surface oxide layer often brings an obstacle for the hydrogen absorption of Ti-based icosahedral quasicrystals (IQCs). This work is presented to investigate the hydrogenation properties of the Ti45Zr38Ni17 alloy which was produced by suction casting and then exposed to ambient air for about two months. XRD, SEM, EDS, TEM, XPS techniques were used to the characterization of the alloy. The results show that, a mixture of IQC, beta-Ti/Zr and C14 Laves phases was formed in the alloy which yielded a surface oxide layer, approximately 70 nm thick. By being crushed into particles, however, the alloy can absorb 1.5 wt% H with an induction time of about 500s at 30 degrees C and 2.88wt% H (correspondingly H/M approximate to 1.6) at 60 degrees C more rapidly, giving a preliminary evidence that suction casting may be a feasible approach to promote the hydrogenation properties of Ti-based IQC alloys. After several hydriding cycles, the primary phases were replaced by two hydride phases, tetragonal ZrH2 and hexagonal TiZrH1.68. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Title:
Disordered misfit [Ca2CoO3][CoO2](1.62) structure revisited via a new intrinsic modulation
Authors:
Muguerra, H; Grebille, D; Bouree, F Author Full Names: Muguerra, Herve; Grebille, Dominique; Bouree, Francoise
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 144-153 Part 2 APR 2008
Abstract:
The structure of the thermoelectric lamellar misfit cobalt oxide [Ca2CoO3][CoO2](1.62) was refined again using single-crystal X-ray diffraction data. A new commensurate intrinsic modulation was observed involving a modulation vector orthogonal to the misfit direction (2/3,0, -1/3). The five-dimensional superspace group is C2/m(1 delta 0)(alpha 0 gamma) gm and the structure was solved using a commensurate approximation. A new model is given involving an occupation modulation of the split sites of the [CoO] layer. This [CoO] layer can be described by triple chains running along b. The residual disorder along b can then be explained by the assumption of a local ordering with two types of clusters: CoO2 and Co5O4. A powder neutron diffraction experiment confirmed the ordering evidenced by the single-crystal X-ray diffraction study, but was not sufficient by itself to deal with this double modulated scheme. The new intrinsic modulation is destroyed by partial metal substitutions in the [CoO] layer. The structural modifications of this layer directly influence the physical properties which are related to the electronic structure of the [CoO2] layers.
Title:
KSm(MoO4)(2), an incommensurately modulated and partially disordered scheelite-like structure
Authors:
Arakcheeva, A; Pattison, P; Chapuis, G; Rossell, M; Filaretov, A; Morozov, V; Van Tendeloo, G Author Full Names: Arakcheeva, Alla; Pattison, Philip; Chapuis, Gervais; Rossell, Marta; Filaretov, Andrey; Morozov, Vladimir; Van Tendeloo, Gustaaf
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 160-171 Part 2 APR 2008
Abstract:
The incommensurately modulated scheelite-like KSm( MoO4)(2) structure has been refined in the monoclinic superspace group I2/b(alpha beta 0)00 by the Rietveld method on the basis of synchrotron radiation powder diffraction data. The systematic broadening of satellite reflections has been accounted for by applying anisotropic microstrain line-broadening. The microstructure has been studied by transmission electron microscopy (TEM). The partial disorder of the K and Sm cations in the A position is best approximated by a combination of harmonic and complex crenel functions with (0.952Sm + 0.048K) and (0.952K + 0.048Sm) atomic domains. This combination yields a compositional wave distribution from {KMoO4} to {SmMoO4} observed in the ab structure projection along q. The specific features of KSm(MoO4)(2) and degree of the A-cation ordering are discussed in comparison with the previously reported structure of KNd(MoO4)(2).

Update: 21-Mar-2008

Title:
Observation of correlations up to the micrometer scale in sliding charge-density waves
Authors:
Le Bolloc'h, D; Jacques, VLR; Kirova, N; Dumas, J; Ravy, S; Marcus, J; Livet, F Author Full Names: Le Bolloc'h, D.; Jacques, V. L. R.; Kirova, N.; Dumas, J.; Ravy, S.; Marcus, J.; Livet, F.
Source:
PHYSICAL REVIEW LETTERS 1 (9): Art. No. 096403 MAR 7 2008
Abstract:
A high resolution coherent x-ray diffraction experiment has been performed on the charge-density wave (CDW) system K0.3MoO3. The 2k(F) satellite reflection associated with the CDW has been measured with respect to external dc currents. In the sliding regime, the 2k(F) satellite reflection displays secondary satellites along the chain axis which corresponds to correlations up to the micrometer scale. This super long-range order is 1500 times larger than the CDW period itself. This new type of electronic correlation seems inherent to the collective dynamics of electrons in charge-density wave systems. Several scenarios are discussed.
Title:
Magnetic-field dependence of the ferroelectric polarization and spin-lattice coupling in multiferroic MnWO4
Authors:
Taniguchi, K; Abe, N; Sagayama, H; Ohtani, S; Takenobu, T; Iwasa, Y; Arima, T Author Full Names: Taniguchi, K.; Abe, N.; Sagayama, H.; Ohtani, S.; Takenobu, T.; Iwasa, Y.; Arima, T.
Source:
PHYSICAL REVIEW B 77 (6): Art. No. 064408 FEB 2008
Abstract:
The magnetic-field dependence of the ferroelectric polarization and the spin-lattice coupling in multiferroic MnWO4 have been investigated. The ferroelectric transition from the low temperature paraelectric phase occurs when the magnetic field is applied along the a, c, and the spin easy axes. The ferroelectric polarization in the magnetic field along the a and the c axis shows a contrasting behavior depending on the field direction, possibly reflecting the relative configuration between the crystallographic axis and the magnetic principal axis in the ac plane. Incommensurate lattice modulation observed in the ferroelectric spiral-spin phase confirms the existence of spin-lattice coupling in MnWO4. The lattice modulation indicates that the ferroelectric AF2 phase also takes the incommensurate magnetic structure in a magnetic field. In the high-field phase, which appears in high magnetic fields above 12 T along the easy axis, the magnetic-field-induced ferroelectric polarization disappeared.
Title:
Broken ergodicity, memory effect, and rejuvenation in Taylor-phase and decagonal Al-3(Mn,Pd,Fe) complex intermetallics
Authors:
Dolinsek, J; Slanovec, J; Jaglicic, Z; Heggen, M; Balanetskyy, S; Feuerbacher, M; Urban, K Author Full Names: Dolinsek, J.; Slanovec, J.; Jaglicic, Z.; Heggen, M.; Balanetskyy, S.; Feuerbacher, M.; Urban, K.
Source:
PHYSICAL REVIEW B 77 (6): Art. No. 064430 FEB 2008
Abstract:
The Taylor-phase complex intermetallic compound T-Al3Mn, its solid solutions with Pd and Fe, T-Al-3(Mn,Pd) and T-Al-3(Mn,Fe), and the related decagonal d-Al-Mn-Fe quasicrystal belong to the class of magnetically frustrated spin systems that exhibit rich out-of-equilibrium spin dynamics in the nonergodic phase below the spin-freezing temperature T-f. Performing large variety of magnetic experiments as a function of temperature, magnetic field, aging time t(w), and different thermal histories, we investigated broken-ergodicity phenomena of (i) a difference in the field-cooled and zero-field-cooled susceptibilities, (ii) the frequency-dependent freezing temperature, T-f(nu), (iii) hysteresis and remanence, (iv) ultraslow decay of the thermoremanent magnetization, (v) the memory effect (a state of the spin system reached upon isothermal aging can be retrieved after a negative temperature cycle), and (vi) "rejuvenation" (small positive temperature cycle within the nonergodic phase erases the effect of previous aging). We show that the phenomena involving isothermal aging periods (the memory effect, rejuvenation, and the ultraslow decay of the thermoremanent magnetization) get simple explanation by considering that during aging under steady external conditions, localized spin regions quasiequilibrate into more stable configurations, so that higher thermal energy is needed to destroy these regions by spin flipping, as compared to the thermal energy required to reverse a frustrated spin in a disordered spin-glass configuration that forms in the case of no aging. Common to all the investigated broken-ergodicity phenomena is the slow approach of a magnetically frustrated spin system toward a global equilibrium, which can never be reached on accessible experimental time scales due to macroscopic equilibration times.
Title:
Dynamical magnetic susceptibility in the lamellar cobaltate superconductor NaxCoO2 center dot yH(2)O
Authors:
Korshunov, MM; Eremin, I Author Full Names: Korshunov, M. M.; Eremin, I.
Source:
PHYSICAL REVIEW B 77 (6): Art. No. 064510 FEB 2008
Abstract:
We systematically analyze the influence of the superconducting gap symmetry and the electronic structure on the dynamical spin susceptibility in superconducting NaxCoO2 center dot yH(2)O within three different models: The single a(1g)-band model with nearest-neighbor hoppings, the realistic three-band t(2g) model with, and without e(g)' pockets present at the Fermi surface. We show that the magnetic response in the normal state is dominated by the incommensurate antiferromagnetic spin density wave fluctuations at large momenta in agreement with experimental temperature dependence of the spin-lattice relaxation rate. Also, we demonstrate that the presence or the absence of the e(g)' pockets at the Fermi surface does not significantly affect this conclusion. In the superconducting state our results for d(x)(2)-y(2)- or d(xy)-wave symmetries of the superconducting order parameter are consistent with experimental data and exclude nodeless d(x)(2)-y(2)+id(xy)-wave symmetry. We further point out that the spin-resonance peak proposed earlier is improbable for the realistic band structure of NaxCoO2 center dot yH(2)O. Moreover, even if present the resonance peak is confined to the antiferromagnetic wave vector and disappears away from it.
Title:
X-ray scattering study of charge density waves in La2-xBaxCuO4
Authors:
Kim, YJ; Gu, GD; Gog, T; Casa, D Author Full Names: Kim, Young-June; Gu, G. D.; Gog, T.; Casa, D.
Source:
PHYSICAL REVIEW B 77 (6): Art. No. 064520 FEB 2008
Abstract:
We report a comprehensive x-ray scattering study of charge density wave (stripe) ordering in La2-xBaxCuO4 (x approximate to 1/8), for which the bulk superconducting T-c is greatly suppressed. Strong superlattice reflections corresponding to static ordering of charge stripes were observed in this sample. The structural modulation at the lowest temperature was deduced based on the intensity of over 70 unique superlattice positions surveyed. We found that the charge order in this sample is described with one-dimensional charge density waves, which have incommensurate wave vectors (0.23, 0, 0.5) and (0, 0.23, 0.5), respectively, on neighboring CuO2 planes. The structural modulation due to the charge density wave order is simply sinusoidal, and no higher harmonics were observed. Just below the structural transition temperature, short-range charge density wave correlation appears, which develops into a large scale charge ordering around 40 K, close to the spin density wave ordering temperature. However, this charge ordering fails to grow into a true long range order, and its correlation length saturates at similar to 230 angstrom, and slightly decreases below about 15 K, which may be due to the onset of two-dimensional superconductivity.
Title:
Study on as-cast microstructures and solidification process of Mg-Zn-Y Alloys
Authors:
Zhang, YB; Yu, SR; Zhu, XY; Luo, YR Author Full Names: Zhang, Yingbo; Yu, Sirong; Zhu, Xianyong; Luo, Yanru
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 354 (14): 1564-1568 MAR 1 2008
Abstract:
The microstructures and phases of as-cast Mg-Zn-Y alloys were investigated by means of scanning electron microscopy (SEM), energy-dispersive spectrum (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) in this study. Stable icosahedral Mg30Zn60Y10 quasicrystals were obtained using common casting technique. With increasing Y content, the contents of quasicrystals increased, the distribution of quasicrystals was improved, and the morphologies of quasicrystal and other microstructures of Mg-Zn-Y alloys showed different characteristics. In addition, the solidification process of Mg-Zn-Y alloys was analyzed. Icosahedral Mg30Zn60Y10 quasicrystalline phase is easy to nucleate in slow cooling. (C) 2007 Elsevier B.V. All rights reserved.

Update: 14-Mar-2008

Title:
Solid-state physics - How does your quasicrystal grow?
Authors:
Steinhardt, PJ Author Full Names: Steinhardt, Paul J.
Source:
NATURE 452 (7183): 43-44 MAR 6 2008
Title:
Efficient photocatalytic decomposition of acetaldehyde over a solid-solution perovskite (Ag0.75Sr0.25)(Nb0.75Ti0.25)O-3 under visible-light irradiation
Authors:
Wang, DF; Kako, T; Ye, JH Author Full Names: Wang, Defa; Kako, Tetsuya; Ye, Jinhua
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (9): 2724-+ MAR 5 2008
Abstract:
A green chemistry process for environmental purification is realized on a novel visible-light-active photocatalyst (Ag0.75Sr0.25) (Nb0.75Ti0.25)O-3. This mixed valent solid-solution perovskite with a modulated electronic structure possesses a strong oxidative 4 potential for efficient photocatalytic decomposition of acetaldehyde into CO2 at ambient temperature.
Title:
Anomalous behavior of hardness and crystal structure in CeRh3Bx (x=0-1) phase
Authors:
Yubuta, K; Nomura, A; Yamamura, T; Shishido, T Author Full Names: Yubuta, K.; Nomura, A.; Yamamura, T.; Shishido, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 451 (1-2): 301-304 FEB 28 2008
Abstract:
We have examined the relationship between hardness and crystal structure of a Cu3Au-type compound CeRh3Bx (x = 0-1) by electron diffraction and high-resolution electron microscopy. The electron diffraction revealed 1/2 1/2 1/2-type superlattice reflections and fine satellite ones in B content range of 0.4 < x < 0.5, where anomalous decrease of hardness was observed. The observed high-resolution image taken with a diffraction pattern showing the satellite reflections along the [011] direction shows a domain structure with size of about 3 nm, and a lattice modulation and some edge dislocations have been observed at boundaries between the domains. Conclusively, ordering of B atoms and followed by the appearance of the long-ranged modulated structure could lead to the anomalous behavior of hardness in CeRh3Bx. (c) 2007 Elsevier B.V. All rights reserved.

Update: 7-Mar-2008

Title:
Phase separation and crystallization in a melt-spun Ti45Zr35Ni17Cu3 alloy
Authors:
Wang, LM; Liu, BZ; Ma, LQ; Ma, CL; Inoue, A Author Full Names: Wang, Limin; Liu, Baozhong; Ma, Liqun; Ma, Chaoli; Inoue, Akihisa
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 354 (10-11): 1010-1014 FEB 1 2008
Abstract:
Structure and crystallization behavior of amorphous and quasicrystalline Ti45Zr35Ni17Cu3 alloy have been studied. DSC trace of the amorphous alloy obtained during continuous heating to 1300 K shows distinctly an exothermic peak and two endothermic peaks. The amorphous alloy has different structures depending on annealing temperature. The first exothermic reaction at low temperature region from 400 K to 900 K is due to the precipitation of an icosahedral quasicrystalline phase, and the second endothermic reaction at higher temperature region from 950 K to 990 K results from the transformation of the I-phase to C14 Laves and alpha-(Ti, Zr) phases. (C) 2007 Published by Elsevier B.V.
Title:
On phase transformations in mechanically alloyed and subsequently annealed Al70Cu20Fe10
Authors:
Wang, Y; Tian, Y; Wang, Y; Geng, HR; Zhang, ZH Author Full Names: Wang, Yan; Tian, Ying; Wang, Yi; Geng, Haoran; Zhang, Zhonghua
Source:
INTERMETALLICS 16 (2): 121-129 FEB 2008
Abstract:
In the present work, phase transformations during mechanical alloying (MA) and post-MA annealing of Al70Cu20Fe10 have been investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). No icosahedral quasicrystalline phase (i-phase) is observed during the milling process of Al70Cu20Fe10. A totally disordered beta-Al(Cu,Fe) phase firstly forms in the as-milled powders after 40 h of MA and thus transforms into the stable beta-phase with a B2 structure with increasing milling time up to 70 h. The i-phase appears in the as-annealed products and its amount increases with increasing milling time. In addition, the omega-Al7Cu2Fe phase only forms after heat treatment of the milled Al70Cu20Fe10 powders. Furthermore, the formation of both the i-phase and omega-phase depends upon the milling time and annealing temperature. (C) 2007 Elsevier Ltd. All rights reserved.
Title:
Higher-dimensional point groups in superspace crystallography
Authors:
Janner, A Author Full Names: Janner, A.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 280-283 Part 2 MAR 2008
Abstract:
Crystallographic puzzles not covered by the present crystallography, like integral indexing and crystallographic scaling of axial-symmetric biomacromolecules and icosahedral viral capsids and/or integral lattices, can possibly be explained by extending (n, d)-dimensional superspace crystallography to include finite subgroups of the higher-dimensional orthogonal group O(n) and not only those of O(d), as restricted by the physical dimension d.

Update: 29-Feb-2008

Title:
Sound velocity and absorption measurements under high pressure using picosecond ultrasonics in a diamond anvil cell: Application to the stability study of AlPdMn
Authors:
Decremps, F; Belliard, L; Perrin, B; Gauthier, M Author Full Names: Decremps, F.; Belliard, L.; Perrin, B.; Gauthier, M.
Source:
PHYSICAL REVIEW LETTERS 1 (3): Art. No. 035502 JAN 25 2008
Abstract:
We report an innovative high pressure method combining the diamond anvil cell device with the technique of picosecond ultrasonics. Such an approach allows us to measure sound velocity and attenuation of solids and liquids under pressure of tens of GPa, overcoming all the drawbacks of traditional techniques. The power of this experimental technique is demonstrated in studies of lattice dynamics and relaxation processes in a metallic single grain of AlPdMn quasicrystal, and in rare gas solids neon and argon.
Title:
Strain amplification of the 4k(F) chain instability in Sr14Cu24O41
Authors:
Rusydi, A; Abbamonte, P; Eisaki, H; Fujimaki, Y; Smadici, S; Motoyama, N; Uchida, S; Kim, YJ; Rubhausen, M; Sawatzky, GA Author Full Names: Rusydi, A.; Abbamonte, P.; Eisaki, H.; Fujimaki, Y.; Smadici, S.; Motoyama, N.; Uchida, S.; Kim, Y. -J.; Ruebhausen, M.; Sawatzky, G. A.
Source:
PHYSICAL REVIEW LETTERS 1 (3): Art. No. 036403 JAN 25 2008
Abstract:
We used resonant soft x-ray scattering to study the chain ordering in Sr14Cu24O41 (SCO). We observed, for the first time, both the chain and ladder orders in SCO with the same probe. We found that the chain modulation in SCO is incommensurate with wave vector L-c=0.318, is strongly temperature (T) dependent, and is accompanied by a substantial hole modulation. By contrast, the chain modulation in a hole-depleted control sample La6Ca8Cu24O41 was commensurate (L-c=0.3), T independent, and purely structural. We conclude that the chain charge order in SCO is a 4k(F) charge density wave stabilized by the misfit strain between the ladder and chain substructures.
Title:
Optical coupling to spin waves in the cycloidal multiferroic BiFeO3
Authors:
de Sousa, R; Moore, JE Author Full Names: de Sousa, Rogerio; Moore, Joel E.
Source:
PHYSICAL REVIEW B 77 (1): Art. No. 012406 JAN 2008
Abstract:
The magnon and optical phonon spectrum of an incommensurate multiferroic such as BiFeO3 is considered in the framework of a phenomenological Landau theory. The resulting spin wave spectrum is quite distinct from commensurate substances due to soft mode anisotropy and magnon zone folding. The former allows electrical control of spin wave propagation via reorientation of the spontaneous ferroelectric moment. The latter gives rise to multiple magnetodielectric resonances due to the coupling of optical phonons at zero wave vector to magnons at integer multiples of the cycloid wave vector. These results show that the optical response of a multiferroic reveals much more about its magnetic excitations than previously anticipated on the basis of simpler models.
Title:
Neutron scattering study on spin correlations and fluctuations in the transition-metal-based magnetic quasicrystal Zn-Fe-Sc
Authors:
Sato, TJ; Kashimoto, S; Masuda, C; Onimaru, T; Nakanowatari, I; Iida, K; Morinaga, R; Ishimasa, T Author Full Names: Sato, Taku J.; Kashimoto, Shiro; Masuda, Chihiro; Onimaru, Takahiro; Nakanowatari, Isao; Iida, Kazuki; Morinaga, Rei; Ishimasa, Tsutomu
Source:
PHYSICAL REVIEW B 77 (1): Art. No. 014437 JAN 2008
Abstract:
Spin correlations and fluctuations in the 3d-transition-metal-based icosahedral quasicrystal Zn-Fe-Sc have been investigated by neutron scattering using polycrystalline samples. Magnetic diffuse scattering has been observed in the elastic experiment at low temperatures, indicating development of static short-range-spin correlations. In addition, the inelastic scattering experiment detects a Q-independent quasielastic signal ascribed to single-site relaxational spin fluctuations. Above the macroscopic freezing temperature T-f similar or equal to 7 K, the spin relaxation rate shows Arrhenius-type behavior, indicating thermally activated relaxation process. In contrast, the relaxation rate remains finite even at the lowest temperature, suggesting a certain quantum origin for the spin fluctuations below T-f.
Title:
Structural modulation and electronic structural features in the charge ordered state of La0.5Sr1.5MnO4
Authors:
Zeng, LJ; Ma, C; Yang, HX; Xiao, RJ; Li, JQ; Jansen, J Author Full Names: Zeng, L. J.; Ma, C.; Yang, H. X.; Xiao, R. J.; Li, J. Q.; Jansen, J.
Source:
PHYSICAL REVIEW B 77 (2): Art. No. 024107 JAN 2008
Abstract:
The structural changes associated with the charge ordering (CO) transition in layered La0.5Sr1.5MnO4 have been determined by electron diffraction using the multislice least-squares method. The results demonstrate that the structural deformations of the Mn3+O6 octahedra can be well characterized by a transverse modulation wave along the < 110 > direction. Based on these structural data, we have performed a theoretical calculation of the electronic structure by density functional theory plus the on-site Coulomb interaction U. The resultant density of states exhibits a clear band gap at the Fermi level for this low-temperature CO insulating state. It is also noted that the essential Jahn-Teller effects in this layered system can evidently affect the electronic structures and orbital hybridization appearing with the CO transition. Charge disproportionation and orbital ordering in La0.5Sr1.5MnO4 have been extensively discussed in comparison with the data obtained for the cubic perovskite La0.5Ca0.5MnO3.
Title:
Displacive mechanisms and order-parameter symmetries for the A7-incommensurate-bcc sequences of high-pressure reconstructive phase transitions in Group Va elements
Authors:
Katzke, H; Toledano, P Author Full Names: Katzke, Hannelore; Toledano, Pierre
Source:
PHYSICAL REVIEW B 77 (2): Art. No. 024109 JAN 2008
Abstract:
The high-pressure structural transitions observed in the Group Va elements P, As, Sb, and Bi are described by displacive atomic mechanisms. A theoretical analysis of the proposed mechanisms shows that two different structural paths are followed relating the low-pressure A7 structure to the highest-pressure bcc structure. One structural path gives rise to the host-guest structures found in As, Sb, and Bi, whereas another path yields the incommensurate P IV structure recently disclosed in P. The incommensurate character of the host-guest and P IV structures is shown to be imposed by the energetically most favorable path relating the A7 and bcc structures.
Title:
Weakly anisotropic frustrated zigzag spin chain
Authors:
Dmitriev, DV; Krivnov, VY Author Full Names: Dmitriev, D. V.; Krivnov, V. Ya.
Source:
PHYSICAL REVIEW B 77 (2): Art. No. 024401 JAN 2008
Abstract:
The frustrated spin-1/2 model with weakly anisotropic ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchanges is studied with use of variational mean-field approach, scaling estimates of the infrared divergencies in the perturbation theory and finite-size calculations. The ground-state phase diagram of this model contains three phases: the ferromagnetic phase, the commensurate spin-fluid phase, and the incommensurate phase. The nontrivial behavior of the boundaries between these phases and the character of the phase transitions in case of weak anisotropy are determined.
Title:
A study of an incommensurately modulated structure in Ca0.28Ba0.72Nb2O6 by electron microscopy
Authors:
Ge, BH; Wang, YM; Li, XM; Li, FH; Song, HL; Zhang, HJ Author Full Names: Ge, B. H.; Wang, Y. M.; Li, X. M.; Li, F. H.; Song, H. L.; Zhang, H. J.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 88 (3): 213-217 2008
Abstract:
Two equivalent modulation wavevectors of the incommensurately modulated structure (IMS) observed in the tetragonal tungsten bronze Ca0.28Ba0.72Nb2O6 were determined by electron diffraction to be q(1) = 0.286(a* + b*) + 0.5c*and q(2) = 0.286(a - b) + 0.5c*. The projection of the IMS in the a + b direction has been obtained from a single high-resolution electron microscope image via image deconvolution. According to the high-dimensional space description of the IMS, a (1 + 1)-dimensional hypersection passing through the pentagonal channels has been obtained, showing both occupational and displacive modulations. The origin of the incommensurate modulation is discussed.
Title:
Formation of omega-Al7Cu2Fe phase during laser processing of quasicrystal-forming Al-Cu-Fe alloy
Authors:
Biswas, K; Chattopadhyay, K Author Full Names: Biswas, K.; Chattopadhyay, K.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 88 (3): 219-230 2008
Abstract:
The formation of an omega-Al7Cu2Fe phase during laser cladding of quasicrystal-forming Al65Cu23.3Fe11.7 alloy on a pure aluminium substrate is reported. This phase is found to nucleate at the periphery of primary icosahedral-phase particles. A large number of omega-phase particles form an envelope around the icosahedral phase. On the outer side, they form an interface with an alpha-Al solid solution. Detailed transmission electron microscopic observations show that the omega phase exhibits an orientation relationship with the icosahedral phase. Analysis of experimental results suggests that the omega phase forms by precipitation on an icosahedral phase by heterogeneous nucleation and grows into the aluminium-rich melt until supersaturation is exhausted. The microstructural observations are explained in terms of available models of phase transformations.
Title:
Effects of extrusion on the microstructure and mechanical properties of Mg-Zn-Gd alloy reinforced with quasicrystalline particles
Authors:
Yuan, GY; Liu, Y; Ding, WJ; Lu, C Author Full Names: Yuan, Guangyin; Liu, Yong; Ding, Wenjiang; Lu, Chen
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 474 (1-2): 348-354 FEB 15 2008
Abstract:
The microstructure and mechanical properties of Mg95.9Zn3.5Gd0.6 alloy reinforced with icosahedral quasi-crystalline particles (I-phase) were investigated after extrusion at 573 K and 673 K. The effects of extrusion temperature and heat treatment on the microstructure and mechanical properties of the alloy were analyzed and the strengthening effect of I-phase was discussed. The results show that the I-phase is significantly refined upon extrusion. At room temperature, the alloy extruded at 573 K exhibits better tensile mechanical properties as compared to the alloy extruded at 673 K. At 473 K, the as-extruded alloy exhibits high elongation of about 94% due to the high cohesion of the I-phase with the matrix. As compared to the alloy extruded at 573 K, the alloy extruded at 673 K exhibits higher precipitate strengthening effect due to a higher density of I-phase precipitates, which results in not only a high ultimate tensile strength of 117 MPa, but also a high elongation of 82.5% at 473 K. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Iron deposition on the tenfold surface of the Al72Ni11Co17 decagonal quasicrystal
Authors:
Wearing, LH; Smerdon, JA; Leung, L; Dhesi, SS; Ledieu, J; Bencok, P; Fisher, I; Jenks, CJ; McGrath, R Author Full Names: Wearing, L. H.; Smerdon, J. A.; Leung, L.; Dhesi, S. S.; Ledieu, J.; Bencok, P.; Fisher, I.; Jenks, C. J.; McGrath, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (1): Art. No. 015005 JAN 9 2008
Abstract:
The adsorption behaviour of Fe on the tenfold surface of the decagonal quasicrystal Al72.6Ni10.5Co16.9 has been studied using scanning tunnelling microscopy, low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and x-ray magnetic circular dichroism (XMCD). The results show the growth of a disordered film up to a coverage of 9 MLE (monolayer equivalent) after which polycrystalline island growth is observed. These islands are interconnected, and the LEED pattern indicates that they preferentially align along five directions. The AES results indicate that the film is composed of Fe intermixed with the substrate elements. The XMCD results point to an induced magnetic moment for Co and Ni in the intermixed layer/interface region.
Title:
Effect of Tb doping on electric and magnetic behavior of BiFeO3 thin films
Authors:
Wang, Y; Nan, CW Author Full Names: Wang, Yao; Nan, Ce-Wen
Source:
JOURNAL OF APPLIED PHYSICS 103 (2): Art. No. 024103 JAN 15 2008
Abstract:
The effect of Tb doping on crystal structure and electric and magnetic behavior of BiFeO3 thin films prepared via a solution processing on (111)Pt/Ti/SiO2/Si substrates was studied. The substitution of Bi ions by a small amount of Tb ions could stabilize the valence of Fe3+ in BiFeO3 thin films, and as indicated by transmission electron microscope images and largely reduced leakage current in comparison with pure BiFeO3 thin films, the quality of the films was improved by Tb doping. Electric and magnetic behavior of Tb-doped BiFeO3 films was investigated with employing La-doped BiFeO3 films as comparison. Large enhancement in both remnant and saturation polarization and the polarization switching were observed in Tb-doped BiFeO3 films, while the inhomogeneous spin-modulated magnetic structure of BiFeO3 was not modified through Tb substitution but by La substitution. (C) 2008 American Institute of Physics.

Update: 22-Feb-2008

Title:
New general solutions of plane elasticity of one-dimensional quasicrystals
Authors:
Gao, Y; Xu, BX; Zhao, BS; Chang, TC Author Full Names: Gao, Yang; Xu, Bai-Xiang; Zhao, Bao-Sheng; Chang, Tian-Chun
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 245 (1): 20-27 JAN 2008
Abstract:
A theory of general solutions of plane problems is developed for the coupled equations of plane elasticity of one-dimensional quasicrystals. By introducing a displacement function, very large numbers of complicated equations of the in-plane problem are simplified to a sixth-order partial differential governing equation, and then three general solutions are presented through an operator method. Since the displacement function is required to satisfy the sixth-order governing equation, it is still difficult to obtain rigorous analytic solutions from the higher-order equation directly and is not applicable in most cases. Therefore, a decomposition and superposition procedure is employed to replace the higher-order displacement function with three second-order displacement functions, and accordingly the general solutions are simplified in terms of these functions. In consideration of different cases of three characteristic toots, the general solutions involve three cases, but all are in simple forms that are conveniently applied. Furthermore, it is worth noting that the general solutions obtained here are complete in X-3-convex domains. To illustrate the application of the general solutions obtained, the closed form solutions are obtained for wedge problems subjected to point phonon force and phason force at the apex.
Title:
Wave models of non-crystallographic structures
Authors:
Losev, A Author Full Names: Losev, A.
Source:
PHILOSOPHICAL MAGAZINE 88 (2): 201-208 2008
Abstract:
Combinations of oscillations with incommensurate periods are utilized to generate discrete planar structures with non-crystallographic symmetries. Some previously known tilings and results are reconsidered in this context. A new kind of decagonal tiling, its relations with the Penrose tilings, and some experimental reports are discussed.
Title:
New sequences of phase transition in ni-mn-ga ferromagnetic shape memory nanoparticles
Authors:
Liu, DM; Nie, ZH; Wang, YD; Liu, YD; Wang, G; Ren, Y; Zuo, L Author Full Names: Liu, D. M.; Nie, Z. H.; Wang, Y. D.; Liu, Y. D.; Wang, G.; Ren, Y.; Zuo, L.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE 39A (2): 466-469 FEB 2008
Abstract:
In-situ high-energy X-ray diffraction was used for tracing the structural transitions in Ni2MnGa and Ni47Mn25Ga22Co6 nanoparticles that were prepared by a ball-milling and subsequent annealing process. A decrease in martensitic transformation temperature was evidenced in all annealed nanoparticles. It was found that a three-layered modulated structure, usually observed as a metastable premartensitic phase in coarse-grained alloys, becomes a stable phase in the annealed Ni2MnGa nanoparticles up to 4 K.
Title:
Friction and wear behavior of as-cast Mg-Zn-Y quasicrystal materials
Authors:
Zhang, YB; Yu, SR; Luo, YR; Hu, HX Author Full Names: Zhang, Yingbo; Yu, Sirong; Luo, Yanru; Hu, Haixia
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 472 (1-2): 59-65 JAN 15 2008
Abstract:
Mg-Zn-Y quasicrystal materials were fabricated using casting method. The friction and wear behaviors of the quasicrystal materials were investigated under dry sliding condition. The results show that the friction coefficients decreased with increasing applied loads in all Mg-Zn-Y quasicrystal materials. High applied load brought about high plastic deformation on the worn surface of the Mg-Zn-Y quasicrystal materials. The friction coefficients and the wear mass losses of the Mg-Zn-Y quasicrystal materials decreased firstly and then increased with increasing Y content. When the Y content was 2at.%, the Mg-Zn-Y quasicrystal materials exhibited the lowest friction coefficients and the best wear resistance at all applied loads. There existed noncrystal phase in the wear debris of the Mg-25Zn-1.5Y quasicrystal material at the applied load of 70 N. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Effect of quasicrystal and Laves phases on strength and ductility of as-extruded and heat treated Mg-Zn-Gd-based alloys
Authors:
Yuan, GY; Liu, Y; Lu, C; Ding, WJ Author Full Names: Yuan, Guangyin; Liu, Yong; Lu, Chen; Ding, Wenjiang
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 472 (1-2): 75-82 JAN 15 2008
Abstract:
Microstructure and mechanical properties of Mg95.9Zn3.5Gd0.6 and Mg94.4Zn3.5Gd0.6Cu1.5 alloys reinforced by icosahedral quasicrystalline phase (I-phase) and Laves phase have been studied after extrusion at 573 K and 673 K. Extrusion significantly refined the I-phase and Laves phase, and made them exist as particles along the grain boundary and in the matrix. The strengthening effect of I-phase and Laves phase has been analyzed. The combination of I-phase and Laves phase has higher contribution to the improvement of yield strength, which made the Mg94.4Zn3.5Gd0.6CU1.5 alloy exhibits strong heat resistance. The results show that the two alloys have different heat treatment effect due to different fraction of I-phase and Laves phase. The Mg94.4Zn3.5Gd0.6 alloy after extrusion at 673 K has higher elongation about 94% at 473 K due to higher fraction of I-phase. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Optical transmission through generalized SML superlattices
Authors:
Yin, HL; Yang, XB; Guo, Q; Lan, S Author Full Names: Yin, Hailong; Yang, Xiangbo; Guo, Qi; Lan, Sheng
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (35): Art. No. 356221 SEP 5 2007
Abstract:
The SML model is a kind of one-dimensional (1D) quasiperiodic three-tile structure proposed by Liu et al (1991 Phys. Rev. B 43 13240; 1991 Chin. Phys. Lett. 8 533) based on the experimental results of Al-Si-Mn quasicrystals (Boissieu et al 1990 J. Phys.: Condens. Matter 2 2499). Generalized SML models (GSML(m, n)) are extensions of the SML one. In this paper, we study the transmission properties of light through GSML(m, n) aperiodic superlattices and use the transparent-component-decimation (TCD) method to analyze the relationship between the characteristics of structures and transmission coefficients. It is found that the propagation matrices (PMs) and transmission coefficients (TCs) for GSML(m, n) multilayers exhibit interesting properties: (1) when n is even, they are all constant; (2) when n is odd but m is even, the former exhibit a six-cycle property while the latter possess a three-cycle feature; (3) when n is odd and m = 1, they both possess a pseudo-seven-! cycle characteristic. The analytic results are confirmed by numerical evaluations.
Title:
Synthesis, structure, and bonding of Sc4MgxCu15-Ga-x similar to(7.5) (x=0, 0.5). Two incommensurately modulated scandium substitution derivatives of cubic Mg2Cu6Ga5
Authors:
Lin, QS; Lidin, S; Corbett, JD Author Full Names: Lin, Qisheng; Lidin, Sven; Corbett, John D.
Source:
INORGANIC CHEMISTRY 47 (3): 1020-1029 FEB 4 2008
Abstract:
The substitution of scandium for magnesium in Mg2Cu6Ga5 (Mg2Zn11-type) yields an irrational superstructure phase that includes the refined compositions, Sc4Mg0.50(2)Cu14.50(2)Ga7.61(2) and Sc4Cu14.76(2)Ga7.51(2)- These crystallize in Cmmm, a = similar to 8.31 angstrom, b = similar to 21.72 angstrom, c = -8.30 angstrom. The structures feature Sc-2 dimers, Cu-6 octahedra, a 3D CuGa (Cu12Ga2) framework, and arachno gallium-centered Cu4Ga6 icosahedra that are condensed into zigzag chains. The arrangement of these building blocks exhibits a topologic relationship to Mg2Cu6Ga5. Further studies reveal that the quaternary compound exhibits incommensurate modulations along a, with q = (0.694, 0, 0). Structure refinements with superspace group Xmmm(a00)000 led to saw-tooth modulations for two fractional or mixed sites that avoid short Cu-Ga distances. Band structure analyses reveal that the Fermi surface and bonding are sensitive to the incommensurately modulated atoms.
Title:
All the disorder mechanisms in the 13 : 58 phases come together. out of the modulated confusion rises the remarkable phase Ce12.60Cd58.68(2)
Authors:
Piao, SY; Palatinus, L; Lidin, S Author Full Names: Piao, Shu Ying; Palatinus, Lukas; Lidin, Sven
Source:
INORGANIC CHEMISTRY 47 (3): 1079-1086 FEB 4 2008
Abstract:
The compound Ce12.60Cd58.68(2) is a metrically commensurate representative of the incommensurately modulated phase Ce13Cd57+delta. It is most likely a lock-in phase. The structure, which was solved using seeding of the modulation from those positions most affected as well as direct solution by charge flipping, represents a rare case of ordering in a family of structures where disorder is the rule. The disorder mechanisms, known from other RE13Zn/Cd-58 phases, order in this phase to give rise to a remarkable interplay between interstitials and vacancies. The compound crystallizes in the super space group Ccmm(alpha 00)00s (standard setting Amma(00 gamma)s00) with cell parameters a 27.2789(14) angstrom, b = 15.7592(1) angstrom, and c = 15.5816(4) angstrom and a q vector close to 2/3.

Update: 15-Feb-2008

Title:
Solidification of Mg28Zn2Y and Icosahedral quasicrystal morphology evolution
Authors:
Wan, DQ; Yang, GC; Zhou, YH Author Full Names: Wan Diqing; Yang Gencang; Zhou Yaohe
Source:
RARE METAL MATERIALS AND ENGINEERING 36 (12): 2166-2168 DEC 2007
Abstract:
Applying XRD, OM, SEM and TEM techniques, an investigation on the solidification of Mg28Zn2Y quasicrystal alloy was carried out. It is found that alpha-Mg phase, Mg7Zn3 phase and icosahedral quasicrystal phase coexist in the as-solidified morphology. A perfect five-branch icosahedral quasicrystal morphology was observed. It is attributed to the icosahedral quasicrystal free growth with preferred growth direction of five-fold symmetry axes resulting in five-branch morphology. Furthermore, the effect of cooling rate on the quasi-crystal morphology was also studied. High cooling rate leads to rapid solidification, and in turn, petal-like quasi-crystal morphology is reserved. On the other hand, slow cooling rate favors coarsening and branching of the quasi-crystal, and subsequently, subjected to long curing time, the formation of polygonal quasi-crystals driven by the action of interface energy.
Title:
Pseudospin soliton in the nu=1 bilayer quantum Hall state
Authors:
Fukuda, A; Terasawa, D; Morino, M; Iwata, K; Kozumi, S; Kumada, N; Hirayama, Y; Ezawa, ZF; Sawada, A Author Full Names: Fukuda, A.; Terasawa, D.; Morino, M.; Iwata, K.; Kozumi, S.; Kumada, N.; Hirayama, Y.; Ezawa, Z. F.; Sawada, A.
Source:
PHYSICAL REVIEW LETTERS 1 (1): Art. No. 016801 JAN 11 2008
Abstract:
We investigate a domain structure of pseudospins, a soliton lattice in the bilayer quantum Hall state at total Landau level filling factor nu=1, in a tilted magnetic field, where the pseudospin represents the layer degree of freedom. An anomalous peak in the magnetoresistance R-xx appears at the transition point between the commensurate and incommensurate phases. The R-xx at the peak is highly anisotropic for the angle between the in-plain magnetic field B-parallel to and the current, and indicates a formation of the soliton lattice aligned parallel to B-parallel to. The temperature dependence of the R-xx peak reveals that the dissipation is caused by thermal fluctuations of pseudospin solitons. We also study a phase diagram of the bilayer nu=1 system, and the effects of density imbalance between the two layers.
Title:
Two-dimensional quasicrystals of decagonal order in one-component monolayer films - Comment
Authors:
Schmiedeberg, M; Stark, H Author Full Names: Schmiedeberg, Michael; Stark, Holger
Source:
PHYSICAL REVIEW LETTERS 1 (1): Art. No. 019601 JAN 11 2008
Abstract:
A Comment on the Letter by A. Patrykiejew and S. Sokolowski, Phys. Rev. Lett. 99, 156101 (2007). The authors of the Letter offer a Reply.
Title:
Two-dimensional quasicrystals of decagonal order in one-component monolayer films - Reply
Authors:
Patrykiejew, A; Sokolowski, S Author Full Names: Patrykiejew, A.; Sokolowski, S.
Source:
PHYSICAL REVIEW LETTERS 1 (1): Art. No. 019602 JAN 11 2008
Abstract:
A Reply to the Comment by Michael Schmiedeberg and Holger Stark.
Title:
Long- and short-range order in stuffed titanate pyrochlores
Authors:
Lau, GC; McQueen, TM; Huang, Q; Zandbergen, HW; Cava, RJ Author Full Names: Lau, G. C.; McQueen, T. M.; Huang, Q.; Zandbergen, H. W.; Cava, R. J.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 181 (1): 45-50 JAN 2008
Abstract:
We report a structural study of the stuffed pyrochlore series Ln(2)(Ti(2-x)Ln(x))O7-x/2 (Ln = Ho, Yb; 0 <= x <= 0.67). Electron microscopy and Rietveld refinements of neutron powder diffraction data for the x = 0.67 end members, HO2TiO5 and Yb2TiO5, reveal that small domains (similar to 50 angstrom, or less) exist where the Ln and Ti/Ln sublattices are pyrochlore like, while the average structure is fluorite like. Both the Ho and Yb stuffed pyrochlore series for 0.1 <= x <= 0.5 are shown to be a composite of long- and short-range-ordered pyrochlore phases. The relative fraction of long-range vs. short-range pyrochlore order decreases with increasing Ln doping. An additional complex structural modulation of the pyrochlore structure is observed in electron diffraction and high-resolution electron microscopy images. (c) 2007 Elsevier Inc. All rights reserved.
Title:
In situ synchrotron radiation monitoring of phase transitions during microwave heating of Al-Cu-Fe alloys
Authors:
Vaucher, S; Nicula, R; Catala-Civera, JM; Schmitt, B; Patterson, B Author Full Names: Vaucher, Sebastien; Nicula, Radu; Catala-Civera, Jos-Manuel; Schmitt, Bemd; Patterson, Bruce
Source:
JOURNAL OF MATERIALS RESEARCH 23 (1): 170-175 JAN 2008
Abstract:
The effect of rapid microwave heating has so far been evaluated mainly by comparing the state of materials before and after microwave exposure. Yet, further progress critically depends on the ability to follow the evolution of materials during ultrafast heating in real time. We describe the first in situ time-resolved monitoring of solid-state phase transitions during microwave heating of metallic powders using wide-angle synchrotron radiation diffraction. Single-phase Al-Cu-Fe quasicrystal powders were obtained by microwave heating of nanocrystalline alloy precursors at 650 degrees C in <20 s.
Title:
Martensitic phase transformation in rapidly solidified Mn50Ni40In10 alloy ribbons
Authors:
Llamazares, JLS; Sanchez, T; Santos, JD; Perez, MJ; Sanchez, ML; Hernando, B; Escoda, L; Sunol, JJ; Varga, R Author Full Names: Llamazares, J. L. Sanchez; Sanchez, T.; Santos, J. D.; Perez, M. J.; Sanchez, M. L.; Hernando, B.; Escoda, Ll.; Sunol, J. J.; Varga, R.
Source:
APPLIED PHYSICS LETTERS 92 (1): Art. No. 012513 JAN 7 2008
Abstract:
Heusler alloy Mn50Ni40In10 was produced as preferentially textured ribbon flakes by melt spinning, finding the existence of martensitic-austenic transformation with both phases exhibiting ferromagnetic ordering. A microcrystalline three-layered microstructure of ordered columnar grains grown perpendicularly to ribbon plane was formed between two thin layers of smaller grains. The characteristic temperatures of the martensitic transformation were M-S=213 K, M-f=173 K, A(S)=222 K, and A(f)=243 K. Austenite phase shows a cubic L2(1) structure (a=0.6013(3) nm at 298 K and a Curie point of 311 K), transforming into a modulated fourteen-layer modulation monoclinic martensite. (c) 2008 American Institute of Physics.
Title:
On twinning and microstructures in calcite and dolomite
Authors:
Larsson, AK; Christy, AG Author Full Names: Larsson, Ann-Kristin; Christy, Andrew G.
Source:
AMERICAN MINERALOGIST 93 (1): 103-113 JAN 2008
Abstract:
Apparent superlattice reflections obtained in electron diffraction patterns of modulated calcite and dolomite have been ascribed to local domains of various different metastable Ca-Mg ordering schemes that are not known as macroscopic phases. We show that the type "c" reflections in diffraction patterns of supposed superstructures can in fact be produced by superposition of diffraction from the host crystal and that from domains that are in an orientation related to the host by twinning on (104). From details of the additional reflections present, we deduce that the carbonate anions are orientationally disordered in the twin nanodomains, which have the R (3) over barm space group of high-temperature disordered calcite. This twinning can explain the diffraction ascribed to type "gamma"/"mu"/"v" superstructures, and resolves controversies over the occurrence of these purportedly different superstructures. The relationships between composition, orientational order of the carbonates, molar volume and known macroscopic structures, and the possibility of interfacial strain reduction by static disorder in the twin domain, are discussed. We stress the importance of checking for presence of twinned nanodomains using microdiffraction before attributing an apparent superstructure modulation to local cation ordering. High-resolution imaging may not be diagnostic, since overlap of small domains and host matrix can give Moire patterns that resemble superlattice fringes.
Title:
Synthesis and characterization of low-OH-fluor-chlorapatite: A single-crystal XRD and NMR spectroscopic study
Authors:
Mccubbin, FM; Mason, HE; Park, H; Phillips, BL; Parise, JB; Nekvasil, H; Lindsley, DH Author Full Names: Mccubbin, Francis M.; Mason, Harris E.; Park, Hyunsoo; Phillips, Brian L.; Parise, John B.; Nekvasil, Hanna; Lindsley, Donald H.
Source:
AMERICAN MINERALOGIST 93 (1): 210-216 JAN 2008
Abstract:
Low-OH apatite of the compositional rangeCa(4.99-5.06)(PO4)(2.98-3.00)F0.51-0.48Cl0.38-0.36OH0.14-0.1, was synthesized and characterized structurally by synchrotron-based single-crystal X-ray diffraction (XRD), and multiple nuclear magnetic resonance (NMR) spectroscopic techniques. The average structure is hexagonal with space group P6(3)/m. The presence of scattering in the single-crystal diffraction data set, which is incommensurate within the average hexagonal structure, suggests the presence of localized short-range monoclinic domains. Complex lineshapes in the P-31 and F-19 MAS NMR spectra are also consistent with the presence of an incommensurate phase. No evidence was detected for splitting of the Ca2 site into two distinct sites (as had been previously reported for hexagonal ternary apatites). Structure refinement and F-19 {Cl-35} TRAPDOR NMR experiments verified intercolumnal neighborine of F and Cl atoms (inter-column distance of 2.62 angstrom) within this low-OH- apatite suggesting that long-range neighboring of F and Cl within the apatite anion channels is feasible.
Title:
Capabilities and limitations of a (3+d)-dimensional incommensurately modulated structure as a model for the derivation of an extended family of compounds: example of the scheelite-like structures
Authors:
Arakcheeva, A; Chapuis, G Author Full Names: Arakcheeva, Alla; Chapuis, Gervais
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 12-25 Part 1 FEB 2008
Abstract:
The previously reported incommensurately modulated scheelite-like structure KNd(MoO4)(2) has been exploited as a natural (3 + 1)-dimensional superspace model to generate the scheelite-like three-dimensional structure family. Although each member differs in its space-group symmetry, unit-cell parameters and compositions, in ( 3 + 1)-dimensional space, they share a common superspace group, a common number of building units in the basic unit cell occupying Wyckoff sites with specific coordinates (x, y, z) and specific basic unit-cell axial ratios (c/a, a/b, b/c) and angles. Variations of the modulation vector q, occupation functions and t(0) are exploited for the derivation. Eight topologically and compositionally different known structures are compared with their models derived from the KNd(MoO4)(2) structure in order to evaluate the capabilities and limitations of the incommensurately modulated structure to act as a superspace generating model. Applications of the KNd(MoO4)(2) structure as a starting model for the refinement and prediction of some other modulated members of the family is also illustrated. The (3 + 1)dimensional presentation of the scheelite-like structures reveals new structural relations, which remain hidden if only conventional three-dimensional structure descriptions are applied.

Update: 8-Feb-2008

Title:
Structure and properties of mechanically alloyed composite materials Al/Al-Cu-Fe quasicrystal
Authors:
Cherdyntsev, VV; Kaloshkin, SD; Tomilin, IA; Shelekhov, EV; Laptev, AI; Stepashkin, AA; Danilov, VD Author Full Names: Cherdyntsev, V. V.; Kaloshkin, S. D.; Tomilin, I. A.; Shelekhov, E. V.; Laptev, A. I.; Stepashkin, A. A.; Danilov, V. D.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 104 (5): 497-504 NOV 2007
Abstract:
The structure and properties of metal-matrix Al/Al-Cu-Fe-quasicrystal composites produced by compacting mechanically alloyed powders have been studied. An increase in the time of mechanical alloying was found to lead to an increase in the microhardness. Compression tests showed that the failure of samples occurred via the intense formation of cracks along the direction parallel to the applied stresses; the ultimate strength increases with increasing time of mechanical alloying. As the compacting temperature increases, the ultimate strength remains unchanged to temperatures of 300-400 degrees C; at higher temperatures, a marked increase in the ultimate compression strength is observed. An increase in the compacting temperature leads to an improvement of frictional characteristic of samples.
Title:
Incommensurate charge order phase in Fe2OBO3 due to geometrical frustration
Authors:
Angst, M; Hermann, RP; Schweika, W; Kim, JW; Khalifah, P; Xiang, HJ; Whangbo, MH; Kim, DH; Sales, BC; Mandrus, D Author Full Names: Angst, M.; Hermann, R. P.; Schweika, W.; Kim, J. -W.; Khalifah, P.; Xiang, H. J.; Whangbo, M. -H.; Kim, D. -H.; Sales, B. C.; Mandrus, D.
Source:
PHYSICAL REVIEW LETTERS 99 (25): Art. No. 256402 DEC 21 2007
Abstract:
The temperature dependence of charge order in Fe2OBO3 was investigated by resistivity and differential scanning calorimetry measurements, Mossbauer spectroscopy, and synchrotron x-ray scattering, revealing an intermediate phase between room temperature and 340 K, characterized by coexisting mobile and immobile carriers, and by incommensurate superstructure modulations with temperature-dependent propagation vector (1/2, 0, tau) . The incommensurate modulations arise from specific antiphase boundaries with low energy cost due to geometrical charge frustration.
Title:
X-ray scattering study of the spin-Peierls transition and soft phonon behavior in TiOCl
Authors:
Abel, ET; Matan, K; Chou, FC; Isaacs, ED; Moncton, DE; Sinn, H; Alatas, A; Lee, YS Author Full Names: Abel, E. T.; Matan, K.; Chou, F. C.; Isaacs, E. D.; Moncton, D. E.; Sinn, H.; Alatas, A.; Lee, Y. S.
Source:
PHYSICAL REVIEW B 76 (21): Art. No. 214304 DEC 2007
Abstract:
We have studied the S=1/2 quasi-one-dimensional antiferromagnet TiOCl using single crystal x-ray diffraction and inelastic x-ray scattering techniques. The Ti ions form staggered spin chains which dimerize below T-c1=66 K and have an incommensurate lattice distortion between T-c1 and T-c2=92 K. Based on our measurements of the intensities, wave vectors, and harmonics of the incommensurate superlattice peaks, we construct a model for the incommensurate modulation. The results are in good agreement with a soliton lattice model, though some quantitative discrepancies exist near T-c2. The behavior of the phonons has been studied using inelastic x-ray scattering with similar to 2 meV energy resolution. For the first time, a zone-boundary phonon which softens at the spin-Peierls temperature T-SP has been observed. Our results show reasonably good quantitative agreement with the Cross-Fisher [Phys. Rev. B. 19, 402 (1979)] theory for the phonon dynamics at wave vectors near the zone boundary and temperatures near T-SP. However, not all aspects of the data can be described, such as the strong overdamping of the soft mode above T-SP. Overall, our results show that TiOCl is a good realization of a spin-Peierls system, where the phonon softening allows us to identify the transition temperature as T-SP=T-c2=92 K.
Title:
Comment on "Extrinsic origin of the insulating behavior of polygrain icosahedral Al-Pd-Re quasicrystals"
Authors:
Poon, SJ; Rapp, O Author Full Names: Poon, S. J.; Rapp, O.
Source:
PHYSICAL REVIEW B 76 (21): Art. No. 216201 DEC 2007
Abstract:
In a recent paper, Dolinsek et al. [Phys. Rev. B 74, 134201 (2006)] suggested that the insulating behavior of icosahedral (i) Al-Pd-Re is of extrinsic origin. Large resistivities and insulatinglike properties of high resistivity samples were conjectured to result from the porous structure and the observed enhanced oxygen concentration in between the quasicrystal grains in some i-Al-Pd-Re samples. We point out that these hypotheses are incompatible with published work on the structure and properties of i-Al-Pd-Re.
Title:
Reply to "Comment on 'Extrinsic origin of the insulating behavior of polygrain icosahedral Al-Pd-Re quasicrystals' "
Authors:
Dolinsek, J; McGuiness, PJ; Klanjsek, M; Smiljanic, I; Smontara, A; Zijlstra, ES; Bose, SK; Fisher, IR; Kramer, MJ; Canfield, PC Author Full Names: Dolinsek, J.; McGuiness, P. J.; Klanjsek, M.; Smiljanic, I.; Smontara, A.; Zijlstra, E. S.; Bose, S. K.; Fisher, I. R.; Kramer, M. J.; Canfield, P. C.
Source:
PHYSICAL REVIEW B 76 (21): Art. No. 216202 DEC 2007
Abstract:
We clarify issues raised in the preceding Comment regarding the viewpoint that the highly porous and oxidized arc-melted polygrain i-Al-Pd-Re samples could reveal intrinsic electrical transport properties of this icosahedral family. Flux-grown single-grain i-Al-Pd-Re samples of superior structural quality do not show insulatinglike behavior, and their transport properties are on common ground with all other Al-based icosahedral families.
Title:
Spin-density wave in polycrystalline Cr films from infrared reflectivity
Authors:
Boekelheide, Z; Helgren, E; Hellman, F Author Full Names: Boekelheide, Z.; Helgren, E.; Hellman, F.
Source:
PHYSICAL REVIEW B 76 (22): Art. No. 224429 DEC 2007
Abstract:
The spin-density wave properties of polycrystalline chromium thin films were determined by using infrared reflectivity to determine the gap energies. The incommensurate spin-density wave of bulk chromium is highly sensitive to perturbations from stress, disorder, and finite size effects, such as those found in polycrystalline films. Films prepared under various conditions display three different types of spin-density wave behavior: incommensurate, commensurate, and mixed. Unexpectedly, the mixed phase includes the incommensurate spin-density wave and two different forms of commensurate spin-density wave. A phenomenologically determined low-temperature phase diagram is created to describe the spin-density wave in chromium in the stress-disorder plane. The effects of stress and disorder on the spin-density wave of chromium films are analogous to the effects of dilute alloying in bulk chromium. In this case, tensile stress has a similar effect to Mn impurities, while disorder has a similar effect to Al.
Title:
Random walk analysis of the commensurate-incommensurate transition in the isotropic spin-1 chain
Authors:
Yarotsky, DA Author Full Names: Yarotsky, D. A.
Source:
JOURNAL OF STATISTICAL PHYSICS 130 (5): 957-981 MAR 2008
Abstract:
It has been observed that in the isotropic spin-1 chain a transition in the asymptotic properties of the correlation function (commensurate-incommensurate transition) occurs at the AKLT point. We propose a simple random-walk-type argument, explaining this transition. Also, we consider a modification of the AKLT model, for which this argument can be turned into a rigorous proof.

Update: 1-Feb-2008

Title:
Fascinating quasicrystals
Authors:
Steurer, W; Deloudi, S Author Full Names: Steurer, Walter; Deloudi, Sofia
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 1-11 Part 1 JAN 2008
Abstract:
It took Dan Shechtman more than two years to get his discovery of an Al-Mn phase with icosahedral diffraction symmetry and sharp Bragg reflections published. A paradigm shift had to take place before this novel ordering state of matter - seemingly contradicting crystallographic laws - could be accepted. Today, more than 25 years later, the existence of quasicrystals is beyond doubt. However, not everything is settled yet. All the factors governing formation, growth, stability and structure of quasicrystals are still not fully understood, nor is it resolved whether their structures are strictly or only on average quasiperiodic, and it is still an open question why only quasicrystals with 5-, 8-, 10- and 12-fold rotational symmetry have been experimentally observed so far. These points will be addressed in this review article.
Title:
The charge flipping algorithm
Authors:
Oszlanyi, G; Suto, A Author Full Names: Oszlanyi, Gabor; Suto, Andras
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 123-134 Part 1 JAN 2008
Abstract:
This paper summarizes the current state of charge flipping, a recently developed algorithm of ab initio structure determination. Its operation is based on the perturbation of large plateaus of low electron density but not directly on atomicity. Such a working principle radically differs from that of classical direct methods and offers complementary applications. The list of successful structure-solution cases includes periodic and aperiodic crystals using single-crystal and powder diffraction data measured with X-ray and neutron radiation. Apart from counting applications, the paper mainly deals with algorithmic issues: it describes and compares new variants of the iteration scheme, helps to identify and improve solutions, discusses the required data and the use of known information. Finally, it tries to foretell the future of such an alternative among well established direct methods.

Update: 25-Jan-2008

Title:
Effect of nano-quasicrystals on viscosity of a Zr-based bulk metallic glass
Authors:
Gubicza, J; Labar, JL; Agocs, E; Fatay, D; Lendvai, J Author Full Names: Gubicza, J.; Labar, J. L.; Agocs, E.; Fatay, D.; Lendvai, J.
Source:
SCRIPTA MATERIALIA 58 (4): 291-294 FEB 2008
Abstract:
The effect of formation of nano-quasicrystals on the creep behavior of a Zr44Ti11Cu10Ni10Be25 bulk metallic glass was studied by the indentation technique above the glass transition temperature. The apparent viscosity of the supercooled liquid-quasicrystal composite increases with increasing volume fraction of the quasicrystalline phase following a simple relationship derived previously for dilute suspensions. The formation of quasicrystalline particles is accompanied by the decrease of activation energy of creep. This was related to the increase of the Be/Ti ratio in the supercooled liquid phase. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Chiral magnetic ordering and commensurate-to-incommensurate transition in CuB2O4
Authors:
Kousaka, Y; Yano, SI; Kishine, JI; Yoshida, Y; Inoue, K; Kikuchi, K; Akimitsu, J Author Full Names: Kousaka, Yusuke; Yano, Shin-Ichiro; Kishine, Jun-Ichiro; Yoshida, Yusuke; Inoue, Katsuya; Kikuchi, Koichi; Akimitsu, Jun
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (12): Art. No. 123709 DEC 2007
Abstract:
We measured the anisotropic magnetization processes of copper metaborate CuB2O4 in detail. We propose an interpretation of the magnetization anomaly observed under the magnetic field applied perpendicular to the tetragonal axis, based on the field- and temperature- induced commensurate-to-incommensurate (C-IC) transition (Freedericksz transition) accompanied by the chiral soliton lattice formation.
Title:
Very low temperature electronic transport in Al-Pd-Re quasicrystalline alloys
Authors:
Rosenbaum, R; Balanetskyy, S; Grushko, B; Przepiorzynski, B Author Full Names: Rosenbaum, Ralph; Balanetskyy, Sergiy; Grushko, Benjamin; Przepiorzynski, Bartosz
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 150 (1-2): 82-100 JAN 2008
Abstract:
Electrical resistivities of two icosahedral (I) Al-Pd-Re alloys have been measured between room temperature and mK temperatures. One quasicrystalline (QC) polygrain Al-Pd-Re sample exhibited insulating behavior in its resistivities, increasing by a factor of r=R(4 K)/R(300 K)=7.76; its room temperature resistivity was 9,890 mu Omega cm. A "phenomenological" expression fitted the conductivity data well between 300 K to 0.5 K. Below 0.4 K a crossover to an activated variable-range hopping law was observed. Low temperature magnetoresistance ratio data and fits using the wave function shrinkage theory are presented. A second QC Al-Pd-Re sample had a small resistance temperature ratio r=2.12. The room temperature resistivity was extremely large, rho(300 K)approximate to 40,980 mu Omega cm. Its conductivity could be described well using a simple temperature power law between 300 K to 20 K. Below 20 K there was a crossover to a new behavior. Below 1 K, the conductivity could be fitted using a very weakly insulating power law where sigma(T)approximate to 11.37T(0.032) in (Omega cm)(-1), suggesting that this sample is located just below the metal-insulator transition. The magnetoconductivity data could not be fitted successfully using the 3D weak localization (WL) theory and inserting into it physical and realistic fitting magnitudes for the inelastic magnetic field B-in.
Title:
New potassium bismuth thiophosphates including the modulated K1.5Bi2.5(PS4)(3)
Authors:
Gave, MA; Weliky, DP; Kanatzidis, MG Author Full Names: Gave, Mafthew A.; Weliky, David P.; Kanatzidis, Mercouri G.
Source:
INORGANIC CHEMISTRY 46 (26): 11063-11074 DEC 24 2007
Abstract:
The compounds K3Bi3(PS4)(4) (I), K1.5Bi2.5(PS4)(3) (II), and KgBi(PS4)(4) (III) were synthesized, and their properties are described. Red needles of I crystallize in the tetragonal spacegroup P4/ncc with a = 21.0116(8) angstrom and c = 13.3454(10) angstrom and have a three-dimensional Bi/P/S framework structure with large channels occupied by K+ ions. Deep-red plates of 11 crystallize in the monoclinic super spacegroup P2/c(alpha(1/2 gamma))00 with a = 21.8034(12) angstrom, b = 8.8064(7) angstrom, c = 10.0333(6) angstrom, and beta = 90.004(5)degrees. This compound has an incommensurately modulated superstructure with the modulation vector q = 0.25a* + 0.5b* + 0.16c*. Bright-red irregularly shaped blocks of III crystallize in the orthorhombic space group P2(1)2(1)2 with a = 18.306(4) angstrom, b = 8.926(2) angstrom, and c = 9.710(2) angstrom and have a discrete molecular salt structure with mononuclear [Bi(PS4)(4)](9-) complexes. The structures reveal that as the relative amount of K3PS4 increases, there is a marked decrease in dimensionality of the framework. It was also possible to form a glass with the same stoichiometry as that of compound I. When annealed at 320 degrees C, the glass crystallized into compound II. The (31)p solid-state NMR spectra are reported, and they are consistent with the crystallographic results.
Title:
A water-based synthesis of octahedral, decahedral, and icosahedral Pd nanocrystals
Authors:
Lim, B; Xiong, YJ; Xia, YN Author Full Names: Lim, Byungkwon; Xiong, Yujie; Xia, Younan
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 46 (48): 9279-9282 2007

Update: 18-Jan-2008

Title:
Microstructure and mechanical properties of Mg-Zn-Gd-based alloys strengthened with quasicrystal and Laves phase
Authors:
Liu, Y; Yuan, GY; Lu, C; Ding, WJ Author Full Names: Liu Yong; Yuan Guang-yin; Lu Chen; Ding Wen-jiang
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA 17: S353-S357 Part A Sp. Iss. 1 NOV 2007
Abstract:
One kind of Mg3.5Zn0.6Gd-based alloy strengthened with quasicrystals was designed, and the effect of alloying elements on microstructure and mechanical properties of as-cast Mg-Zn-Gd alloy at room temperature and elevated temperatures were studied. The results indicate that MgZnCu Laves phase, which coexists with quasicrystal at grain boundary, emerges with the addition of copper element in Mg-Zn-Gd alloy. The strength of alloys exhibits the parabola curve with the increase of copper content. The alloy with 1.5% (mole fraction) Cu shows better mechanical properties at room temperature: tensile strength 176 MPa, yield strength 176 MPa and elongation 6.5%. The existence of MgZnCu Laves phase can effectively improve the heat resistance and elevated temperature properties of the alloy. The alloy with 1.5% Cu has better mechanical properties at 200 degrees C: tensile strength 130 MPa and elongation 18.5%. The creep test of the alloys at 200 degrees C and 50 MPa for 102 h indicates that Mg3.5Zn0.6Gd alloy reinforced with quasicrystal has better creep properties than AE42, which can be further improved with the introduction of Laves phase in the alloy.
Title:
Competition between local potentials and attractive particle-particle interactions in superlattices
Authors:
Lima, NA; Malvezzi, AL; Capelle, K Author Full Names: Lima, N. A.; Malvezzi, A. L.; Capelle, K.
Source:
SOLID STATE COMMUNICATIONS 144 (12): 557-560 DEC 2007
Abstract:
Naturally occuring or man-made systems displaying periodic spatial modulations of their properties on a nanoscale constitute superlattices. Such modulated structures are important both as prototypes of simple nanotechnological devices and as particular examples of emerging spatial inhomogeneity in interacting many-electron systems. Here we investigate the effect different types of modulation of the system parameters have on the ground-state energy and the charge-density distribution of the system. The superlattices are described by the inhomogeneous attractive Hubbard model, and the calculations are performed by density-functional and density-matrix renormalization group techniques. We find that modulations in local electric potentials are much more effective in shaping the system's properties than modulations in the attractive on-site interaction. This is the same conclusion we previously [M.F. Silva, N.A. Lima, A.L. Malvezzi, K. Capelle, Phys. Rev. B 71 (2005) 125130.] obtained for repulsive interactions, suggesting that it is not an artifact of a specific state, but a general property of modulated structures. (c) 2007 Elsevier Ltd. All rights reserved.
Title:
Phase diagram of hole doped two-leg Cu-O ladders
Authors:
Chudzinski, P; Gabay, M; Giamarchi, T Author Full Names: Chudzinski, P.; Gabay, M.; Giamarchi, T.
Source:
PHYSICAL REVIEW B 76 (16): Art. No. 161101 OCT 2007
Abstract:
In the weak coupling limit, we establish the phase diagram of a two-leg ladder with a unit cell containing both Cu and O atoms, as a function of doping. We use bosonization and design a specific renormalization group procedure to handle the additional degrees of freedom. Significant differences are found with the single orbital case; for purely repulsive interactions, a completely massless quantum critical region is obtained at intermediate carrier concentrations (well inside the bands) where the ground state consists of an incommensurate pattern of orbital currents plus a spin density wave structure.
Title:
Photonic band gaps in quasiperiodic photonic crystals with negative refractive index
Authors:
Vasconcelos, MS; Mauriz, PW; De Medeiros, FF; Albuquerque, EL Author Full Names: Vasconcelos, M. S.; Mauriz, P. W.; De Medeiros, F. F.; Albuquerque, E. L.
Source:
PHYSICAL REVIEW B 76 (16): Art. No. 165117 OCT 2007
Abstract:
We investigate the photonic band gaps in quasiperiodic photonic crystals made up of both positive (SiO2) and negative refractive index materials using a theoretical model based on a transfer matrix treatment. The quasiperiodic structures are characterized by the nature of their Fourier spectrum, which can be dense pure point (Fibonacci sequences) or singular continuous (Thue-Morse and double-period sequences). These substitutional sequences are described in terms of a series of generations that obey peculiar recursion relations. We discussed the photonic band gap spectra for both the ideal cases, where the negative refractive index material can be approximated as a constant in the frequency range considered, as well as the more realistic case, taking into account the frequency-dependent electric permittivity epsilon and magnetic permeability mu. We also present a quantitative analysis of the results, pointing out the distribution of the allowed photonic bandwidths for high generations, which gives a good insight about their localization and power laws.
Title:
Anomalous properties of the band-edge states in large two-dimensional photonic quasicrystals
Authors:
Lai, Y; Zhang, ZQ; Chan, CH; Tsang, L Author Full Names: Lai, Yun; Zhang, Zhao-Qing; Chan, Chi-Hou; Tsang, Leung
Source:
PHYSICAL REVIEW B 76 (16): Art. No. 165132 OCT 2007
Abstract:
By using the sparse-matrix canonical-grid method, we performed large-scale multiple-scattering calculations to study band-edge states in large-sized two-dimensional photonic quasicrystals. We find that the band-edge states evolve in an abrupt and irregular way when the sample size is increased. New states with reduced symmetries can emerge at the band edge in large samples. Strong multifractal behaviors in the wave functions are also observed. Our findings unveil important differences between quasiperiodic and periodic systems at band edges.
Title:
Scanning tunneling microscopy observation of Pb-induced superstructures on Si(557)
Authors:
Morikawa, H; Kim, KS; Jung, DY; Yeom, HW Author Full Names: Morikawa, Harumo; Kim, Keun Su; Jung, Duk Yong; Yeom, Han Woong
Source:
PHYSICAL REVIEW B 76 (16): Art. No. 165406 OCT 2007
Abstract:
Pb-induced superstructures on Si(557) are investigated by low-energy-electron diffraction (LEED) and scanning tunneling microscopy (STM). Using an indirect heating method, we have succeeded in obtaining almost perfect single-domain LEED patterns of one-dimensional wire (chain) structures, so called alpha x2 and beta x2 phases. Careful LEED analysis and STM investigation reveal that these phases are formed on the (223) and (112) facets, respectively. The alpha x2 phase has regular bundles of triple wires at low annealing temperature but wider bundles through step bunching after a higher temperature annealing. Along the wires of the alpha x2 phase, which was recently reported to exhibit a transition between one-dimensional (1D) metallic and 2D semiconducting conductance, a clear commensurate x2 modulation is observed at 78-120 K in contrast to the incommensurate and disordered structure reported previously. A tentative atomic structure model of the alpha x2 phase is proposed based on the dense Pb overlayers on (111) and (223) facets. The details of the STM images of the beta x2 phase are discussed.
Title:
Ferroelectric polarization and magnetic structure in Eu0.595Y0.405MnO3
Authors:
Kajimoto, R; Yokoo, T; Kofu, M; Noda, K; Kuwahara, H Author Full Names: Kajimoto, R.; Yokoo, T.; Kofu, M.; Noda, K.; Kuwahara, H.
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 68 (11): 2087-2090 Sp. Iss. SI NOV 2007
Abstract:
A neutron diffraction study was performed on a single crystal of 4f-moment-free perovskite manganite Eu0.595Y0.405MnO3 to elucidate the relation between the spontaneous ferroelectric polarization and the magnetic structure. Eu0.595Y0.405MnO3 shows an incommensurate magnetic ordering below T-N = 47 K. The ferroelectric polarization P along the c axis appears below 25 K, and it is replaced by P along the a axis below 23 K. We have observed the change of magnetic structure at temperatures where the ferroelectric polarization appears and changes its polarization direction. (c) 2007 Elsevier Ltd. All rights reserved.
Title:
Neutron and X-ray diffraction studies on the Tb2Ni3Si5 single crystal
Authors:
Hashimoto, Y; Kawano, S; Koyano, N; Takahashi, M Author Full Names: Hashimoto, Yuzo; Kawano, Shinji; Koyano, Nobumitu; Takahashi, Miwako
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 68 (11): 2095-2098 Sp. Iss. SI NOV 2007
Abstract:
Neutron and X-ray diffraction studies on the Tb2Ni3Si5 single crystal have been done to investigate its crystal modulation and magnetic properties. The modulated single crystal is constructed by the TbNiSi2 (CeNiSi2-type Cmcm) and the Tb2Ni3Si5 (U2Co3Si5-type Ibam) lattices. The relationship between the two lattices is described as direction of the b(1) (12)-axis coincides with the a(235)-axis. The crystal modulation gives significant effects on magnetism. Each of the two lattices takes complex antiferromagnetism with multiplex propagation vectors. (c) 2007 Elsevier Ltd. All rights reserved.
Title:
Antiferromagnetic spin structure in BaCoO3 below 15 K determined by neutron and mu+SR
Authors:
Nozaki, H; Janoschek, M; Roessli, B; Sugiyama, J; Keller, L; Brewer, JH; Ansaldo, E; Morris, GD; Takami, T; Ikuta, H Author Full Names: Nozaki, H.; Janoschek, M.; Roessli, B.; Sugiyama, J.; Keller, L.; Brewer, J. H.; Ansaldo, E. J.; Morris, G. D.; Takami, T.; Ikuta, H.
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 68 (11): 2162-2165 Sp. Iss. SI NOV 2007
Abstract:
The magnetic structure of the anti ferromagnetic (AF) hexagonal perovskite BaCoO3 was investigated by means of neutron powder diffraction in the temperature range between 60 and 1.5 K. AF diffraction peaks appear below the Neel temperature (T-N = 15 K). Although several possible spin arrangements fit the neutron diffraction pattern, when combined with the results of a muon spin spectroscopy experiment, the most reasonable description of the AF state in BaCoO3 is a modulated structure along the (110) direction, described as m(1) = m(0) cos(2 pi kl), where m(1) is the moment at the Co4+ site 1, m(0) = (0, 0, 0.53 mu(B)) at 1.5 K and k is the propagation vector(1/3, 1/3, 0). (c) 2007 Elsevier Ltd. All rights reserved.
Title:
Magnetic soliton lattice in CuB2O4 under an applied magnetic field
Authors:
Kousaka, Y; Yano, S; Nishi, M; Hirota, K; Akimitsu, J Author Full Names: Kousaka, Y.; Yano, S.; Nishi, M.; Hirota, K.; Akimitsu, J.
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 68 (11): 2170-2173 Sp. Iss. SI NOV 2007
Abstract:
We report here the formation of soliton lattice in copper metaborate CuB2O4,which is an candidate for a chiral magnetic structure. We performed the neutron diffraction experiments under an applied magnetic field perpendicular to the helical axis. In the temperature between 1.6 and 6K under the magnetic field, we found a new incommensurate magnetic phase, which was supposed to be a commensurate magnetic structure from the magnetization measurements. In the boundary just between the conventional incommensurate and the new incommensurate magnetic phases, we observed higher order magnetic satellite peaks, which can be an evidence of chiral soliton formation. (c) 2007 Elsevier Ltd. All rights reserved.
Title:
Detecting quasiperiodic structures with double diffraction
Authors:
Xu, J; Hubler, AW Author Full Names: Xu, J.; Huebler, A. W.
Source:
EPL 81 (1): Art. No. 16002 2008
Abstract:
We study interference patterns of double-diffraction systems with quasiperiodic structures. A quasiperiodic linear array of scatterers converts single delta pulses into a sequence of quasiperiodic pulses. This pulse train is diffracted from a second set of scatterers. We find that the interference pattern after the second diffraction has a pronounced peak if both sets of scatterers have similar quasiperiodic structures. We show that this method can be used for identifying the Fibonacci chain and related quasiperiodic sequences, if the number of scatterers in the first set is at least twice as large as the number of scatterers in the second set, and if the distances among the two sets of scatterers and the detector are all large compared to the size of the sets. This method may provide a methodology for identifying the structure of quasicrystals and quasiperiodic layered materials with a large signal-to-noise ratio. Copyright (C) EPLA, 2008.
Title:
Synthesis and characterization of new AA'BWO6 perovskites exhibiting simultaneous ordering of A-site and B-site cations
Authors:
King, G; Thimmaiah, S; Dwivedi, A; Woodward, PM Author Full Names: King, Graham; Thimmaiah, Srinivasa; Dwivedi, Akansha; Woodward, Patrick M.
Source:
CHEMISTRY OF MATERIALS 19 (26): 6451-6458 DEC 25 2007
Abstract:
Six new AA'BB'O-6 perovskites KLaMnWO6, NaLaMnWO6, NaNdMnWO6, NaTbMnWO6, NaNdCoWO6, and NaNdMgWO6 have been prepared. Each possesses the unusual combination of layered ordering of the A-site cations and rock-salt ordering of the B-site cations. The structure and properties of these samples have been characterized using monochromatic X-ray and neutron powder diffraction, UV-vis diffuse reflectance spectroscopy, and SQUID magnetometry. NaLaMnWO6, NaNdMnWO6, and NaTbMnWO6 adopt a structure with monoclinic P2(1) symmetry arising from the combination of cation ordering and a(-)a(-)c(+) octahedral tilting. The structures of the other three compounds are similar, but the presence of satellite reflections in the neutron diffraction data suggests a more complicated superstructure. Each of the four AA'MnWO6 samples shows a paramagnetic to antiferromagnetic transition with Neel temperatures ranging from 6 to 15 K. The NaTbMnWO6 compound shows a second magnetic transition at similar to 9 K. The origin of two magnetic phase transitions appears to arise from coupling between the Mn2+ sublattice and the Tb3+ sublattice.

Update: 11-Jan-2008

Title:
Hidden degrees of freedom in aperiodic materials
Authors:
Toudic, B; Garcia, P; Odin, C; Rabiller, P; Ecolivet, C; Collet, E; Bourges, P; McIntyre, GJ; Hollingsworth, MD; Breczewski, T Author Full Names: Toudic, Bertrand; Garcia, Pilar; Odin, Christophe; Rabiller, Philippe; Ecolivet, Claude; Collet, Eric; Bourges, Philippe; McIntyre, Garry J.; Hollingsworth, Mark D.; Breczewski, Tomasz
Source:
SCIENCE 319 (5859): 69-71 JAN 4 2008
Abstract:
Numerous crystalline materials, including those of bioorganic origin, comprise incommensurate sublattices whose mutual arrangement is described in a superspace framework exceeding three dimensions. We report direct observation by neutron diffraction of superspace symmetry breaking in a solid- solid phase transition of an incommensurate host- guest system: the channel inclusion compound of nonadecane/ urea. Strikingly, this phase transition generates a unit cell doubling that concerns only the modulation of one substructure by the other- an internal variable available only in superspace. This unanticipated pathway for degrees of freedom to rearrange leads to a second phase transition, which again is controlled by the higher dimensionality of superspace. These results reveal nature's capacity to explore the increased number of phases allowed in aperiodic crystals.
Title:
How do quasicrystals grow?
Authors:
Keys, AS; Glotzer, SC Author Full Names: Keys, Aaron S.; Glotzer, Sharon C.
Source:
PHYSICAL REVIEW LETTERS 99 (23): Art. No. 235503 DEC 7 2007
Abstract:
Using molecular simulations, we show that the aperiodic growth of quasicrystals is controlled by the ability of the growing quasicrystal nucleus to incorporate kinetically trapped atoms into the solid phase with minimal rearrangement. In the system under investigation, which forms a dodecagonal quasicrystal, we show that this process occurs through the assimilation of stable icosahedral clusters by the growing quasicrystal. Our results demonstrate how local atomic interactions give rise to the long-range aperiodicity of quasicrystals.
Title:
Valence changes and structural distortions in "Charge Ordered" manganites quantified by atomic-scale scanning transmission electron microscopy
Authors:
Loudon, JC; Kourkoutis, LF; Ahn, JS; Zhang, CL; Cheong, SW; Muller, DA Author Full Names: Loudon, J. C.; Kourkoutis, L. Fitting; Ahn, J. S.; Zhang, C. L.; Cheong, S. -W.; Muller, D. A.
Source:
PHYSICAL REVIEW LETTERS 99 (23): Art. No. 237205 DEC 7 2007
Abstract:
We investigate the microscopic nature of the "charge ordering" modulation in mixed-valent manganites in real space using scanning transmission electron microscopy. The modulation in Bi0.5Sr0.4Ca0.1MnO3 has a uniform periodicity appearing as stripes in high angle annular dark field images. Geometric phase analysis shows the modulation to be a displacement wave with transverse amplitude (0.008 +/- 0.001)a and longitudinal amplitude (0.003 +/- 0.001)a. Series of energy loss spectra taken across the stripes show no periodic changes and place an upper bound of +/- 0.04 on any valence changes of the Mn ions.
Title:
Competition between unconventional superconductivity and incommensurate antiferromagnetic order in CeRh1-xCoxIn5
Authors:
Ohira-Kawamura, S; Shishido, H; Yoshida, A; Okazaki, R; Kawano-Furukawa, H; Shibauchi, T; Harima, H; Matsuda, Y Author Full Names: Ohira-Kawamura, S.; Shishido, H.; Yoshida, A.; Okazaki, R.; Kawano-Furukawa, H.; Shibauchi, T.; Harima, H.; Matsuda, Y.
Source:
PHYSICAL REVIEW B 76 (13): Art. No. 132507 OCT 2007
Abstract:
Elastic neutron diffraction measurements were performed on the quasi-two-dimensional heavy-fermion system CeRh1-xCoxIn5, ranging from an incommensurate antiferromagnet for low Co composition x to an unconventional superconductor on the Co-rich end of the phase diagram. We found that the superconductivity competes with the incommensurate antiferromagnetic (AFM) order characterized by q(I)=(1/2,1/2,delta) with delta=0.298, while it coexists with the commensurate AFM order with q(c)=(1/2,1/2,1/2). This is in sharp contrast to the CeRh1-xIrxIn5 system, where both the commensurate and incommensurate magnetic orders coexist with the superconductivity. These results reveal that particular areas on the Fermi surface nested by q(I) play an active role in forming the superconducting state in CeCoIn5.
Title:
Biquadratic antisymmetric exchange and the magnetic phase diagram of magnetoelectric CuFeO2
Authors:
Plumer, ML Author Full Names: Plumer, M. L.
Source:
PHYSICAL REVIEW B 76 (14): Art. No. 144411 OCT 2007
Abstract:
Biquadratic antisymmetric exchange terms of the form -[C(ij)e(ij)(alpha)(s(i)xs(j))(z)](2), where e(ij) is the unit vector connecting sites i and j and alpha=x,y, due partially to magnetoelectric coupling effects, are shown to be responsible for the spin-flop helical phase in CuFeO2 at low magnetic field and temperature. Usual biquadratic symmetric exchange, likely due to magnetoelastic coupling, is found to support the stability of axial magnetic states at higher fields in this nearly-Heisenberg-like stacked triangular antiferromagnet. A model Hamiltonian which also includes substantial interplane and higher-neighbor intraplane exchange interactions reproduces the unique series of observed commensurate and incommensurate periodicity phases with increasing applied magnetic field in this highly frustrated system. The magnetic-field-temperature phase diagram is discussed in terms of a Landau-type free energy.
Title:
Symmetry and magnetically driven ferroelectricity in rare-earth manganites RMnO3 (R=Gd,Tb,Dy)
Authors:
Ribeiro, JL Author Full Names: Ribeiro, J. L.
Source:
PHYSICAL REVIEW B 76 (14): Art. No. 144417 OCT 2007
Abstract:
This work investigates the magnetically driven ferroelectricity in orthorhombic manganites RMnO3 (R=Gd, Dy, or Tb) from the point of view of the symmetry. The method adopted generalizes the one used to characterize the polar properties of displacive modulated structures to the case of an irreducible magnetic order parameter. The symmetry conditions for magnetically induced ferroelectricity are established, and the Landau-Devonshire free energy functionals are derived from general symmetry considerations. The ferroelectric polarization observed in DyMnO3 and TbMnO3 at zero magnetic field is explained in terms of the symmetry of a reducible magnetic order parameter. The polarization rotation induced in these compounds by external magnetic fields and the stabilization of a ferroelectric phase in GdMnO3 are accounted for by a mechanism in which magnetization and polarization are secondary order parameters that are not directly coupled but compete with each other through their coupling to competing primary modulated order parameters.
Title:
Coordination-induced structure of the Mg 2p core level in i-ZnMgR quasicrystals
Authors:
Karpus, V; Suchodolskis, A; Taulavicius, J; Karlsson, UO; Le Lay, G; Assmus, W; Bruhne, S Author Full Names: Karpus, V.; Suchodolskis, A.; Taulavicius, J.; Karlsson, U. O.; Le Lay, G.; Assmus, W.; Bruehne, S.
Source:
PHYSICAL REVIEW B 76 (15): Art. No. 155119 OCT 2007
Abstract:
We present a detailed analysis of Mg 2p photoemission (PE) spectra in icosahedral ZnMgR (R=Y, Ho, Er) quasicrystals and in the crystalline Zn2Mg Laves phase. Synchrotron-radiation PE measurements were performed on in situ cleaved single-grain samples at 10(-10) mbar pressure and low, 90-150 K, temperature. The analysis of Mg 2p PE spectra in Zn2Mg reveals a surface shift of the core level of -0.12 eV. The Mg 2p PE spectra in i-ZnMgR quasicrystals are essentially broadened as compared to spectra in Zn2Mg Laves phase. The effect is due to the coordination-induced structure of the Mg 2p levels. Different local surroundings of Mg atoms in quasicrystals induce both different shifts of the Mg 2p level and splittings of its spin-orbit components. The local coordination potential at different Mg sites in the quasicrystalline lattice is calculated on the basis of the face-centered icosahedral ZnMgY atomic structure data, recently determined from the pair distribution function analysis. The coordination shifts calculated are spread within an interval of about 0.3 eV, while the splittings of the 2p(3/2) component are of the order of 1-10 meV. The simulated theoretical Mg 2p PE spectra of fci-ZnMgR quasicrystals perfectly fit the experimental data.
Title:
Coupled In/Te and Ni/vacancy ordering and the modulated crystal structure of a B8 type, Ni3 +/- xIn1-yTe2+y solid solution phase
Authors:
Larsson, AK; Noren, L; Withers, RL; Rundlof, H Author Full Names: Larsson, A. -K.; Noren, L.; Withers, R. L.; Rundlof, H.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 180 (10): 2723-2733 OCT 2007
Abstract:
The commensurate superstructures of a NiAs/Ni2In type parent structure, Ni3.32InTe2 and Ni3.12In0.86Te2.14 (q = gamma[0 0 1]*, gamma = 2/3) as well as one dimensionally incommensurate structure of Ni31nTe2 (gamma = 0.71) were refined from neutron powder diffraction data (R-wp = 4.77%, 4.53% and 4.91 % for the three structures, respectively, at 298 K). The commensurate structures were refined in the P6(3)/mmc space group (c = 3c(NiAs)). The stacking sequence at the hcp array is -In/Te/Te/- and the trigonal bipyrainidal site within the In layer, Ni(2), is partially occupied while it is empty in the Te layers. The octahedral position in between the In and Te layers, Ni(1a), is fully occupied while the octahedral position in between two adjacent Te layers, Ni(1b), is partially occupied. With decreasing In and Ni content, the modulation wave vector,, was found to increase continuously until gamma = 1. From this, crenel functions to describe the whole homogeneity range of the solid solution were constructed with the length of the atomic domains Delta(Te) = gamma (and hence Delta(In) = Delta(Ni) = 1-gamma) and Delta(Ni(1b)) = gamma/2 (and hence Delta(Ni(1a)) = 1-gamma/2) which were then used for the refinement of the incommensurate structure of Ni3InTe2. The corresponding effect in real space is that the single In layers separating double layers of Te, occur less frequent when y in increasing until at gamma = 1 the CdI2 type structure of Ni1+xTe2 is reached. (C) 2007 Elsevier Inc. All rights reserved.
Title:
The influence of cobalt doping on photocatalytic nano-titania: Crystal chemistry and amorphicity
Authors:
Lim, SH; Ferraris, C; Schreyer, M; Shih, K; Leckie, JO; White, TJ Author Full Names: Lim, Suo Hon; Ferraris, Cristiano; Schreyer, Martin; Shih, Kalmin; Leckie, James O.; White, T. J.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 180 (10): 2905-2915 OCT 2007
Abstract:
Photocatalysts of nominal composition (Ti1-xCox)O2-delta with 0.001 <= x <= 0.05 were prepared via a sol-gel technique followed by air firing (200-1000 degrees C). The incorporation of cobalt inhibited crystal growth and slightly raised the anatase to rutile transformation temperature (similar to 700 degrees C). An amorphous component was invariably significant with the maxmum content (41-53wt%) appearing simultaneously with the removal of anatase, suggesting that rutile crystallizes via an aperiodic structure. While the introduction of cobalt shifted the apparent band gap to visible light energies this did not enhance performance as there was limited miscibility of cobalt in titania, non-catalytic secondary phases were present, and active Ti3+ sites were displaced by cobalt. (C) 2007 Elsevier Inc. All rights reserved.
Title:
Improvement of plasticity by tailoring combination of constituent elements in Ti-rich Ti-Zr-Be-Cu-Ni bulk metallic glasses
Authors:
Park, ES; Chang, HJ; Lee, JY; Kim, DH Author Full Names: Park, E. S.; Chang, H. J.; Lee, J. Y.; Kim, D. H.
Source:
JOURNAL OF MATERIALS RESEARCH 22 (12): 3440-3447 DEC 2007
Abstract:
The effect of replacement of Ti with Y or Nb in Ti-rich Ti-Zr-Be-Cu-Ni bulk metallic glasses (BMGs) has been investigated. The minor addition (MA) of Y (Y-Ti: +58 kJ/mol) induced phase separation into Y-rich crystalline particles and Ti-rich amorphous matrix, while the MA of Nb (Nb-Ti: +10 kJ/mol) led to nanocrystallization in Ti-rich BMGs with icosahedral nuclei. This result indicates that MA of elements having positive enthalpy of mixing can induce a different degree of instability in the single amorphous matrix depending on the amount of repulsive interaction energy. In particular, MA of Nb (up to 4 at.%) significantly increased the compressive fracture strain (is an element of(f)) up to similar to 9.35 +/- 0.2%, which indicates that the plasticity of BMGs can be enhanced by the size-modulated icosahedral phase embedded in the amorphous matrix.
Title:
Synthesis, crystal structure, and magnetic properties of Sr1.31Co0.63Mn0.37O3: A derivative of the incommensurate composite hexagonal perovskite structure
Authors:
Mandal, TK; Abakumov, AM; Hadermann, J; Van Tendeloo, G; Croft, M; Greenblatt, M Author Full Names: Mandal, Tapas Kumar; Abakumov, Artem M.; Hadermann, Joke; Van Tendeloo, Gustaaf; Croft, Mark; Greenblatt, Martha
Source:
CHEMISTRY OF MATERIALS 19 (25): 6158-6167 DEC 11 2007
Abstract:
We report the synthesis, structural investigation, and magnetic property studies of Sr1.31Co0.63Mn0.17O3 that adopts an incommensurate composite hexagonal perovskite-related structure. The crystal structure has been solved using a (3 + 1)-dimensional suRerspace approach from powder X-ray and neutron diffraction data (SSG R (3) over barm(00 gamma)0s, a = 9.5548(1) angstrom, q = 2.5599(l) A, q = 0.65581(4)c*, R-B = 0.041 R-P = 0.059). The structure consists of face-sharing chains of octahedra and trigonal prisms, wherein the trigonal prismatic sites are preferentially occupied by Co with some cation disorder. A combination of electron diffraction and high-resolution electron microscopic analysis has demonstrated that the compound possesses a complicated microstructure related to the formation of domains with slightly different lengths of the modulation vector. X-ray absorption near-edge spectroscopic (XAS) studies clearly indicate the presence of Mn in the 4+ and Co in the 3+ oxidation state. While the magnetic susceptibility data indicates the presence of anti ferro magnetic correlations in the system, the calculation of effective paramagnetic moment (mu(cal) = 3.561 mu(B)), assuming the metal oxidation states as obtained from XAS and the cation distribution as obtained from neutron refinement, is in agreement with the value obtained experimentally (mu(exp) = 3.676 mu(B)).

Update: 4-Jan-2008

Title:
Pressure-induced enhancement of ferroelectricity in multiferroic RMn2O5 (R=Tb,Dy,Ho)
Authors:
dela Cruz, CR; Lorenz, B; Sun, YY; Wang, Y; Park, S; Cheong, SW; Gospodinov, MM; Chu, CW Author Full Names: dela Cruz, C. R.; Lorenz, B.; Sun, Y. Y.; Wang, Y.; Park, S.; Cheong, S-W.; Gospodinov, M. M.; Chu, C. W.
Source:
PHYSICAL REVIEW B 76 (17): Art. No. 174106 NOV 2007
Abstract:
Measurements of ferroelectric polarization and dielectric constant were done on RMn2O5 (R=Tb,Dy,Ho) with applied hydrostatic pressures of up to 18 kbar. At ambient pressure, distinctive anomalies were observed in the temperature profile of both physical properties at critical temperatures marking the onset of long range antiferromegnetic order (T-N1) and ferroelectricity (T-C1), as well as at temperatures when anomalous changes in the polarization, dielectric constant, and spin wave commensurability have been previously reported. In particular, the step in the dielectric constant at low temperatures (T-C2), associated with both a drop in the ferroelectric polarization and an incommensurate magnetic structure, was shown to be suddenly quenched upon passing an R-dependent critical pressure. This was shown to correlate with the stabilization of the high ferroelectric polarization state, which is coincident with the commensurate magnetic structure. The observation is suggested to be due to a pressure-induced phase transition into a commensurate magnetic structure, as exemplified by the pressure-temperature (p-T) phase diagrams constructed in this work. The p-T phase diagrams are determined for all three compounds.
Title:
Origin of anisotropic nonmetallic transport in the Al80Cr15Fe5 decagonal approximant
Authors:
Dolinsek, J; Jeglic, P; Komelj, M; Vrtnik, S; Smontara, A; Smiljanic, I; Bilusic, A; Ivkov, J; Stanic, D; Zijlstra, ES; Bauer, B; Gille, P Author Full Names: Dolinsek, J.; Jeglic, P.; Komelj, M.; Vrtnik, S.; Smontara, Ana; Smiljanic, I.; Bilusic, A.; Ivkov, J.; Stanic, D.; Zijlstra, E. S.; Bauer, Birgitta; Gille, P.
Source:
PHYSICAL REVIEW B 76 (17): Art. No. 174207 NOV 2007
Abstract:
We present a study of the anisotropic transport properties (electrical resistivity, thermoelectric power, Hall coefficient, and thermal conductivity) of a single-crystalline Al80Cr15Fe5 complex metallic alloy that is an excellent approximant to the decagonal quasicrystal with six atomic layers in one periodic unit. Temperature-dependent electrical resistivity along the b and c crystalline directions shows a nonmetallic behavior with a broad maximum, whereas it shows a metallic positive temperature coefficient along the a direction perpendicular to the (b,c) atomic planes. Ab initio calculations of the electronic density of states reveal that the nonmetallic transport occurs in the presence of a high density of charge carriers. The very different temperature-dependent electrical resistivities along the three crystalline directions can all be treated within the same physical model of slow charge carriers due to weak dispersion of the electronic bands, where the increased electron-phonon scattering upon raising the temperature induces transition from dominant Boltzmann (metallic) to dominant non-Boltzmann (insulatinglike) regime. The temperature dependence of the resistivity is governed predominantly by the temperature dependence of the electronic diffusion constant D and the transition has no resemblance to the Anderson-type metal-to-insulator transition based on the gradual electron localization. Structural considerations of the Al80Cr15Fe5 phase show that the anisotropy of the transport properties is a consequence of anisotropic atomic order on the scale of nearest-neighbor atoms, suggesting that the role of quasiperiodicity in the anisotropic transport of decagonal quasicrystals is marginal. We also present a relaxed version of the Al-4(Cr,Fe) structural model by Deng et al.
Title:
Temperature-dependent photoemission spectra, spectral weight transfer, and chemical potential shift in Pr1-xCaxMnO3: Implications for charge-density modulation
Authors:
Ebata, K; Hashimoto, M; Tanaka, K; Fujimori, A; Tomioka, Y; Tokura, Y Author Full Names: Ebata, K.; Hashimoto, M.; Tanaka, K.; Fujimori, A.; Tomioka, Y.; Tokura, Y.
Source:
PHYSICAL REVIEW B 76 (17): Art. No. 174418 NOV 2007
Abstract:
We have studied the temperature dependence of the photoemission spectra of Pr1-xCaxMnO3 (PCMO) with x=0.25, 0.3, and 0.5. For x=0.3 and 0.5, we observed a gap in the low-temperature charge-exchange-type charge-ordered (CO) phase and a pseudogap with a finite intensity at the Fermi level (E-F) in the high-temperature paramagnetic insulating (PI) phase. Within the CO phase, the spectral intensity near E-F gradually increased with temperature. These observations are consistent with the results of Monte Carlo simulations on a model including charge ordering and ferromagnetic fluctuations [H. Aliaga , Phys. Rev. B 68, 104405 (2003)]. For x=0.25, on the other hand, little temperature dependence was observed within the low-temperature ferromagnetic insulating (FI) phase and the intensity at E-F remained low in the high-temperature PI phase. We attribute the difference in the temperature dependence near E-F between the CO and FI phases to the different correlation lengths of orbital order between both phases. Furthermore, we observed a chemical potential shift with temperature due to the opening of the gap in the FI and CO phases. The doping dependent chemical potential shift was recovered at low temperatures, corresponding to the disappearance of the doping dependent change of the modulation wave vector. Spectral weight transfer with hole concentration was clearly observed at high temperatures but was suppressed at low temperatures. We attribute this observation to the fixed periodicity with hole doping in PCMO at low temperatures.
Title:
Fincher-Burke spin excitations and omega/T scaling in insulating La1.95Sr0.05CuO4
Authors:
Bao, W; Chen, Y; Yamada, K; Savici, AT; Russo, PL; Lorenzo, JE; Chung, JH Author Full Names: Bao, Wei; Chen, Y.; Yamada, K.; Savici, A. T.; Russo, P. L.; Lorenzo, J. E.; Chung, J. -H.
Source:
PHYSICAL REVIEW B 76 (18): Art. No. 180406 NOV 2007
Abstract:
Insulating La1.95Sr0.05CuO4 shares with superconducting cuprates the same Fincher-Burke spin excitations, which usually are observed in itinerant antiferromagnets. The local spectral function satisfies omega/T scaling above similar to 16 K for this incommensurate insulating cuprate, together with previous results in commensurate insulating and incommensurate superconducting cuprates, further supporting the general prediction for square-lattice quantum spin S=1/2 systems. The width of incommensurate peaks in La1.95Sr0.05CuO4 scales to a similar finite value as at optimal doping, strongly suggesting that they are similarly distant from a quantum critical point. They might both be limited to a finite correlation length by partial spin-glass freezing.
Title:
Structure, charge ordering and physical properties of LuFe2O4
Authors:
Zhang, Y; Yang, HX; Guo, YQ; Ma, C; Tian, HF; Luo, JL; Li, JQ Author Full Names: Zhang, Y.; Yang, H. X.; Guo, Y. Q.; Ma, C.; Tian, H. F.; Luo, J. L.; Li, J. Q.
Source:
PHYSICAL REVIEW B 76 (18): Art. No. 184105 NOV 2007
Abstract:
Microstructural properties, phase transitions, and charge ordering of LuFe2O4 have been extensively investigated by means of transmission electron microscopy (TEM) in a large temperature range from 20 to 550 K. The experimental results demonstrate that the LuFe2O4 crystal is commonly modulated by charge ordering (CO), which is often recognizable by superstructure reflections. The (001) twinning domains as a common defect often appear in the LuFe2O4 crystals along the c-axis direction, with the crystals across each (001) boundary rotated by 180 degrees with respect to one another. The in situ cooling TEM observations from 300 K down to 20 K reveal remarkable alternations of the superstructures, suggesting a complex CO process in the present system. Careful analysis shows that the CO in the frustrated ground state is characterized by a modulation with a wave vector of q(1)=(1/3 1/3 2). In situ heating TEM observations from 300 to 550 K clearly reveal that the CO modulation in LuFe2O4 becomes invisible above a critical temperature of about T-C=530 K. These facts suggest that the CO should be the essential driving force for the structural transitions and ferroelectricity observed in this kind of layered material. Experimental measurements on the ferroelectricity show that the LuFe2O4 material, in general, has a large dielectric constant of about 10 000 at room temperature. In order to understand the properties of low-temperature phase transitions, the magnetization and specific heat from 300 to 4 K have been briefly discussed.
Title:
Ferroelectric phase transitions of 3d-spin origin in Eu1-xYxMnO3
Authors:
Yamasaki, Y; Miyasaka, S; Goto, T; Sagayama, H; Arima, T; Tokura, Y Author Full Names: Yamasaki, Y.; Miyasaka, S.; Goto, T.; Sagayama, H.; Arima, T.; Tokura, Y.
Source:
PHYSICAL REVIEW B 76 (18): Art. No. 184418 NOV 2007
Abstract:
Perovskite-type rare-earth manganites RMnO3 (R=Tb and Dy) undergo the ferroelectric transitions concomitantly with the collinear to noncollinear magnetic transitions of Mn 3d spins, in which the electric polarization direction can be controlled by an external magnetic field. To clarify how the magnetic transition of Mn 3d spins is correlated with the ferroelectric transition, we have investigated a mixed-crystal system of perovskite-type Eu1-xYxMnO3 (0 <= x <= 0.4) without the 4f magn