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.

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,