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.


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