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, TH; Zhao, Z; DongyanLiu; Xing, C; Shen, XD; Liu, WQ; LiminWang Author Full Names: Zhai, Xiaojie; Wang, Qingshuang; Luo, Tianhao; Zhao, Zhen; DongyanLiu; Xing, Cheng; Shen, Xiande; Liu, Wanqiang; LiminWang
Source:
MATERIALS RESEARCH BULLETIN, 85 196-201; 10.1016/j.materresbull.2016.09.021 JAN 2017
Abstract:
We report the effect of LiH on the discharge performance of electrodes which are consist of Ti41.5Zr41.5Ni17 quasicrystal in this paper. The Ti41.5Zr41.5Ni17 alloy ribbons are prepared by arc-melting and melt spinning technique subsequently. The final product of Ti41.5Zr41.5Ni17 and LiH composite materials is produced by mechanical alloying (MA) for 20 min, and it is investigated by a three-electrode cell at room temperature. The maximum discharge capacity can achieve 146.6 mAh/g around for Ti41.5Zr41.5Ni17 and LiH composite materials electrode at the first discharge process, which is higher than 96.5 mAh/g of Ti41.5Zr41.5Ni17 quasicrystal at the third discharge process. High-rate dischargeability and cycling stability are improved by adding LiH, which may attribute to the reversible reaction of LiH that enhances the electrochemical reaction activity in the process of electrochemical reaction. The discharge process is also characterized by electrochemical impedance spectroscopy. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
Polarization curling and flux closures in multiferroic tunnel junctions
Authors:
Peters, JJP; Apachitei, G; Beanland, R; Alexe, M; Sanchez, AM Author Full Names: Peters, Jonathan J. P.; Apachitei, Geanina; Beanland, Richard; Alexe, Marin; Sanchez, Ana M.
Source:
NATURE COMMUNICATIONS, 7 10.1038/ncomms13484 NOV 16 2016
Abstract:
Formation of domain walls in ferroelectrics is not energetically favourable in low-dimensional systems. Instead, vortex-type structures are formed that are driven by depolarization fields occurring in such systems. Consequently, polarization vortices have only been experimentally found in systems in which these fields are deliberately maximized, that is, in films between insulating layers. As such configurations are devoid of screening charges provided by metal electrodes, commonly used in electronic devices, it is wise to investigate if curling polarization structures are innate to ferroelectricity or induced by the absence of electrodes. Here we show that in unpoled Co/PbTiO3/(La, Sr)MnO3 ferroelectric tunnel junctions, the polarization in active PbTiO3 layers 9 unit cells thick forms Kittel-like domains, while at 6 unit cells there is a complex flux-closure curling behaviour resembling an incommensurate phase. Reducing the thickness to 3 unit cells, there is an almost complete loss of switchable polarization associated with an internal gradient.

Title:
Semiclassical ground-state phase diagram and multi-Q phase of a spin-orbit-coupled model on triangular lattice
Authors:
Liu, CL; Yu, R; Wang, XQ Author Full Names: Liu, Changle; Yu, Rong; Wang, Xiaoqun
Source:
PHYSICAL REVIEW B, 94 (17):10.1103/PhysRevB.94.174424 NOV 15 2016
Abstract:
Motivated by recent experiments on the frustrated quantum magnetic compound YbMgGaO4, we study an effective spin model on triangular lattice taking into account the effects of the spin-orbit coupling. We determine the classical ground-state phase diagram of this model, which includes a 120 degrees Neel and two collinear antiferromagnetic phases. In the vicinity of the phase boundary between the Neel and collinear phases, we identify three intermediate noncollinear antiferromagnetic phases. In each of them the magnetic moments are ordered at multiple incommensurate wave vector Q values. We further study the effects of quantum fluctuations in this model via a linear spin-wave theory. We find that the spin excitation gap of the noncollinear multi-Q antiferromagnetic states is vanishingly small. We also find that multi-Q states are most fragile against quantum fluctuations, and hence most unstable toward spin liquid phases.

Title:
Effect of cooling rate and Mg addition on the structural evaluation of rapidly solidified Al-20wt%Cu-12wt%Fe alloy
Authors:
Karakose, E; Colak, H Author Full Names: Karakose, Ercan; Colak, Hakan
Source:
MATERIALS CHARACTERIZATION, 121 68-75; 10.1016/j.matchar.2016.09.030 NOV 2016
Abstract:
The present work examines the effect of Mg contents and cooling rate on the morphology and mechanical properties of Al20Cu12Fe quasicrystalline alloy. The microstructure of the alloys was analyzed by scanning electron microscopy and the phase composition was identified by X-ray diffractometry. The melting characteristics were studied by differential thermal analysis under an Ar atmosphere. The mechanical features of the melt-spun and conventionally solidified alloys were tested by tensile-strength test and Vickers micro-hardness test. It was found that the final microstructure of the Al20Cu12Fe samples mainly depends on the cooling rate and Mg contents, which suggests that different cooling rates and Mg contents produce different microstructures and properties. The average grain sizes of the melt spun samples were about 100-300 nm at 35 m/s. The nanosize, dispersed, different shaped quasicrystal particles possessed a remarkable effect to the mechanical characteristics of the rapidly solidified ribbons. The microhardness values of the melt spun samples were approximately 18% higher than those of the conventionally counterparts. (C) 2016 Elsevier Inc. All rights reserved.

Title:
Magnetic structure and effect of magnetic field on its domain structure in magnetoelectric Ba1.3Sr0.7CoZnFe11AlO22
Authors:
Ueda, H; Tanaka, Y; Nakajima, H; Mori, S; Ohta, K; Haruki, K; Hirose, S; Wakabayashi, Y; Kimura, T Author Full Names: Ueda, H.; Tanaka, Y.; Nakajima, H.; Mori, S.; Ohta, K.; Haruki, K.; Hirose, S.; Wakabayashi, Y.; Kimura, T.
Source:
APPLIED PHYSICS LETTERS, 109 (18):10.1063/1.4966623 OCT 31 2016
Abstract:
The magnetic structure and the effect of a magnetic field on its domain structure were investigated in a magnetoelectric Y-type hexaferrite, Ba1.3Sr0.7CoZnFe11AlO22, by means of mapping with a micro-focused and circularly polarized X-ray beam in the resonant X-ray diffraction. It was revealed that this hexaferrite exhibits a magnetic order characterized by two distinct antiferromagnetic components: incommensurate helical and commensurate collinear ones, which can be explained as the development of the so-called alternating longitudinal conical structure. A multidomain state due to the handedness of the helical component, i.e., spin-chirality, is transformed into nearly a mono-domain one by using only a magnetic field. Furthermore, the sign of the spin-chirality in the mono-domain state is reversed by reversing the sign of a magnetic field. These results demonstrate that the spin-chirality in this hexaferrite can be manipulated by a magnetic field alone at room temperature. Published by AIP Publishing.

Title:
Structure and Electrical Conductivity of Ag-Doped TiZrNi Quasicrystals
Authors:
Lee, SH; Park, T; Yi, W; Kim, J Author Full Names: Lee, Sang-Hwa; Park, Taehee; Yi, Whikun; Kim, Jaeyong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 16 (10):10532-10534; 10.1166/jnn.2016.13189 OCT 2016
Abstract:
To investigate the structure and electrical conductivity of Ag-doped TiZrNi quasicrystals, alloys of (Ti53Zr27Ni20)(100) Ag-x(x) (where, x = 0, 4 and 8) were arc-melted and rapidly quenched in an Ar atmosphere. After optimum quenching, the results of the X-ray diffraction (XRD) measurements revealed that the samples have a pure quasicrystal structure. The quasicrystal structure remained to the maximum 8 at.% of Ag without a significant change in the quasi-lattice constant value, 5.12 angstrom. The specific electrical resistance values of the quasicrystals increased from 4.21 to 5.47x10(-4) Omega. cm with increasing Ag contents from 0 to 8 at.% whereas the coherence lengths decreased from 119 to 93 angstrom accordingly. It is interesting to note that the reduction in the electrical conductivity with the increase in Ag contents is mainly due to the structural incoherence factor, not the atomic conductivity of Ag.

Title:
Direct observation of incommensurate structure in Mo3Si
Authors:
Gulec, A; Yu, XX; Taylor, M; Perepezko, JH; Marks, L Author Full Names: Gulec, Ahmet; Yu, Xiaoxiang; Taylor, Matthew; Perepezko, John H.; Marks, Laurence
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 72 660-666; 10.1107/S2053273316012286 6 OCT 2016
Abstract:
Z-contrast imaging, electron diffraction, atom-probe tomography (APT) and density functional theory calculations were used to study the crystal structure of the Mo3Si phase which was previously reported to have an A15 crystal structure. The results showed that Mo3Si has an incommensurate crystal structure with a non-cubic unit cell. The small off-stoichiometry in composition of the sample which was revealed by APT and atomic resolution Z-contrast imaging suggested that site substitution caused the development of split atomic positions, disorder and vacancies.

Title:
Structure determination of modulated structures by powder X-ray diffraction and electron diffraction
Authors:
Zhou, ZY; Palatinus, L; Sun, JL Author Full Names: Zhou, Zhengyang; Palatinus, Lukas; Sun, Junliang
Source:
INORGANIC CHEMISTRY FRONTIERS, 3 (11):1351-1362; 10.1039/c6qi00219f 2016
Abstract:
Since the first discovery and description of materials, whose structures are not periodic, enormous efforts have been made in studying these aperiodic structures. With these efforts including the development of superspace group theory and structure solution algorithms, numerous incommensurately modulated structures which represent the vast majority of known aperiodic structures have been determined with single crystal X-ray diffraction data. However, the determination of modulated structures remains very difficult for polycrystalline materials. Powder X-ray diffraction and electron microscopy techniques yield remarkable information for polycrystalline materials. By combining these two methods, modulated structures of polycrystalline materials that impede solution by conventional methods can be determined. The power of these methods is illustrated with the examples of the determination of modulated structures of polycrystalline materials.

Update: 23-Nov-2016


Title:
Crystallographic Features and State Stability of the Decagonal Quasicrystal in the Al-Co-Cu Alloy System
Authors:
Nakayama, K; Mizutani, A; Koyama, Y Author Full Names: Nakayama, Kei; Mizutani, Akito; Koyama, Yasumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (11):10.7566/JPSJ.85.114602 NOV 15 2016
Abstract:
In the Al-Co-Cu alloy system, both the decagonal quasicrystal with the space group of P (10) over bar m2 and its approximant Al13Co4 phase with monoclinic Cm symmetry are present around 20 at. % Co-10 at. % Cu. In this study, we examined the crystallographic features of prepared Al-(30 - x) at. % Co-x at. % Cu samples mainly by transmission electron microscopy in order to make clear the crystallographic relation between the decagonal quasicrystal and the monoclinic Al13Co4 structure. The results revealed a coexistence state consisting of decagonal quasicrystal and approximant Al13Co4 regions in Al-20 at. % Co-10 at. % Cu alloy samples. With the help of the coexistence state, the orientation relationship was established between the monoclinic Al13Co4 structure and the decagonal quasicrystal. In the determined relationship, the crystallographic axis in the quasicrystal was found to be parallel to the normal direction of the (010) m plane in the Al13Co4 structure, where the subscript m denotes the monoclinic system. Based on data obtained experimentally, the state stability of the decagonal quasicrystal was also examined in terms of the Hume-Rothery (HR) mechanism on the basis of the nearly-free-electron approximation. It was found that a model based on the HR mechanism could explain the crystallographic features such as electron diffraction patterns and atomic arrangements found in the decagonal quasicrystal. In other words, the HR mechanism is most likely appropriate for the stability of the decagonal quasicrystal in the Al-Co-Cu alloy system.

Title:
Prediction of entropy stabilized incommensurate phases in the system MoS2-MoTe2
Authors:
Burton, BP; Singh, AK Author Full Names: Burton, B. P.; Singh, A. K.
Source:
JOURNAL OF APPLIED PHYSICS, 120 (15):10.1063/1.4964868 OCT 21 2016
Abstract:
A first principles phase diagram calculation, that included van der Waals interactions, was performed for the 3D bulk system (1 X).MoS2 (X) . MoTe2. Surprisingly, the predicted phase diagram has at least two ordered phases, at X approximate to 0: 46, even though all calculated formation energies are positive; in a ground-state analysis that examined all configurations with 16 or fewer anion sites. The lower-temperature I-phase is predicted to transform to a higher-temperature I'-phase at T approximate to 500 K, and I0 disorders at T approximate to 730 K. Both these transitions are predicted to be first-order, and there are broad two-phase fields on both sides of the ordered regions. Both the I-and I'-phases are predicted to be incommensurate, i. e., aperiodic: I-phase in three dimensions; and I'-phase in two dimensions.

Title:
Structural transformations in highly oriented seven modulated martensite Ni-Mn-Ga thin films on an Al2O3 (11(2)over-bar0) substrate
Authors:
Sharma, A; Mohan, S; Suwas, S Author Full Names: Sharma, Amit; Mohan, Sangeneni; Suwas, Satyam
Source:
JOURNAL OF MATERIALS RESEARCH, 31 (19):3016-3026; 10.1557/jmr.2016.317 OCT 2016
Abstract:
Highly oriented Ni-Mn-Ga thin film with multiple variants and room temperature orthorhombic martensite structure were prepared on a single crystalline Al2O3 (11 (2) over bar0) substrate by DC magnetron sputtering. X-ray diffraction and rocking curve measurements reveal the film as (202)(7M) oriented with an excellent crystal quality ( = 1.8 degrees). Spot-like pole figures indicate that the Ni-Mn-Ga film grows with a strong in-plane preferred orientation. An in-depth analysis of the measured pole figure reveals the presence of a retained austenite phase in the film. Two phase transformations, M-S approximate to 345 K and T-C approximate to 385 K, are observed and are attributed to first order structural transformation from cubic to orthorhombic, and second order phase transformation from ferromagnetic to paramagnetic, respectively. In situ high temperature x-ray diffraction measurements provide a clear indication of a thermally-induced martensite austenite reversible structural phase transformation in the film. The presence of martensite plates with seven modulated orthorhombic structure and adaptive nano-twins are some of the important microscopic features observed in the film with transmission electron microscopy investigations.

Update: 16-Nov-2016


Title:
A guide to lifting aperiodic structures
Authors:
Baake, M; Ecija, D; Grimm, U Author Full Names: Baake, Michael; Ecija, David; Grimm, Uwe
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (9):507-515; 10.1515/zkri-2016-1982 SEP 2016
Abstract:
The embedding of a given point set with non-crystallographic symmetry into higher-dimensional space is reviewed, with special emphasis on the Minkowski embedding known from number theory. This is a natural choice that does not require an a priori construction of a lattice in relation to a given symmetry group. Instead, some elementary properties of the point set in physical space are used, and explicit methods are described. This approach works particularly well for the standard symmetries encountered in the practical study of quasicrystalline phases. We also demonstrate this with a recent experimental example, taken from a sample with square-triangle tiling structure and (approximate) 12-fold symmetry.

Title:
Effect of Pt addition to Ag-Au bimetallic nanoclusters: A molecular dynamics study of Ag-Au-Pt ternary system
Authors:
Akbarzadeh, H; Shamkhali, AN; Abbaspour, M; Salemi, S; Hajizadeh, Z Author Full Names: Akbarzadeh, Hamed; Shamkhali, Amir Nasser; Abbaspour, Mohsen; Salemi, Sirous; Hajizadeh, Zohreh
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 692 647-657; 10.1016/j.jallcom.2016.09.066 JAN 25 2017
Abstract:
In this work addition of Pt atoms to Ag0.5Au0.5 nanoclusters and formation of Ag0.5-chi Au0.5-chi Pt2 chi (with chi - 0.1, 0.17, 0.2, 0.25, 0.3, and 0.4) and total number of atoms equal to 1415 and 2057 ternary nanoclusters is studied by molecular dynamics simulation. The results indicated that at low concentrations of Pt, nanoclusters exhibit a local-ordered structure in such a way that (Pt-Ag-n-Au-2n) cores are surrounded by extra Ag atoms. By increase of Pt concentration total order of the nanocluster also increases. For nanoclusters with 0.0 < chi(Pt) < 0.4 total order of the system is decreased due to lower concentration of Ag-Pt and Au-Pt interactions. For chi(Pt) - 0.4 system, total order of the nanocluster again increases considerably which represents a Pt-rich nanocluster with some Ag and Au impurity. Also, all nanoclusters with chi(Pt) > 0.0 exhibit an icosahedral-fcc phase transition before melting and temperature of this phase transition is decreased by increase of Pt concentration. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Controlling Magnetic Ordering in Ca1-xEuxCo2As2 by Chemical Compression
Authors:
Tan, XY; Yaroslavtsev, AA; Cao, HB; Geondzhian, AY; Menushenkov, AP; Chernikov, RV; Nataf, L; Garlea, VO; Shatruk, M Author Full Names: Tan, Xiaoyan; Yaroslavtsev, Alexander A.; Cao, Huibo; Geondzhian, Andrey Y.; Menushenkov, Alexey P.; Chernikov, Roman V.; Nataf, Lucie; Garlea, V. Ovidiu; Shatruk, Michael
Source:
CHEMISTRY OF MATERIALS, 28 (20):7459-7469; 10.1021/acs.chemmater.6b03184 OCT 25 2016
Abstract:
To investigate the interplay between electronic structure and itinerant magnetism, Ca1-xEuxCo2As2 solid solutions (x = 0, 0.1, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7, 0.9, 1.0) were prepared by reactions between constituent elements in molten Bi. All of the samples crystallize in the ThCr2Si2 structure type. The crystal structure refinement revealed the formation of Co vacancies, the concentration of which decreases as the Eu content increases. The Eu site exhibits mixed valence in all samples. X-ray absorption near-edge structure spectroscopy revealed that the average Eu oxidation state decreases from +2.17 at 0 < x <= 0.6 to +2.14 at x >= 0.65. The same borderline behavior is observed in magnetic properties. The substitution of Eu for Ca causes the transition from the antiferromagnetic (AFM) ordering of Co moments in CaCo2As2 to ferromagnetic (FM) ordering of Co moments in Ca1-xEuxCo2As2 with 0.1 <= x <= 0.6. At higher Eu content, AFM ordering of Eu moments is observed, whereas the Co sublattice exhibits only paramagnetic behavior. Single-crystal neutron diffraction studies revealed that both Co and Eu sublattices order FM in Ca0.5Eu0.5Co2As2 with the magnetic moments aligned along the tetragonal c axis. In the AFM phases with x >= 0.65, only Eu moments are ordered in a helical spin structure defined by an incommensurate propagation vector k = [00q], with the moment lying in the ab plane. The changes in magnetic behavior are well-justified by the analysis of the electronic density of states and crystal orbital Hamilton population.

Title:
Role of Structure- and Defect Chemistry in High-Performance Thermoelectric Bismuth Strontium Cobalt Oxides
Authors:
Baran, JD; Kepaptsoglou, D; Molinari, M; Kulwongwit, N; Azough, F; Freer, R; Ramasse, QM; Parker, SC Author Full Names: Baran, Jakub D.; Kepaptsoglou, Demie; Molinari, Marco; Kulwongwit, Nuth; Azough, Feridoon; Freer, Robert; Ramasse, Quentin M.; Parker, Stephen C.
Source:
CHEMISTRY OF MATERIALS, 28 (20):7470-7478; 10.1021/acs.chemmater.6b03200 OCT 25 2016
Abstract:
[Bi0.87SrO2](2)[CoO2](1.82) (BSCO) is one of the best p-type thermoelectric oxides but its structural and electronic properties are still poorly understood. BSCO is a misfit-layered compound consisting of an incommensurate stacking of hexagonal CoO2 and double rock-salt BiSrO2 layers. Here we combine experimental and computational approaches to investigate its crystallographic and electronic structure as well as thermoelectric transport properties. Considering different approximations for the subsystems stacking, we present a structural model that agrees well with both bulk and atomic-scale experimental data. This model, which suggests a level of Bi deficiency in the rock-salt layers, is then used to discuss the material's electronic, magnetic, and transport properties. We show that Bi deficiency leads to a band gap opening and increases p-type electronic conductivity due to the formation of Co4+ species that serve as itinerant holes within the predominantly Co3+ framework of the CoO2 layer. We validate these predictions using electron energy loss spectroscopy in the scanning transmission electron microscope. The relationship between the hole-doping mechanism and the changes of the local structure (in particular the level of Bi deficiency) is evaluated. The reliability of the simulations is supported by the calculated temperature dependence of the Seebeck coefficient, in good agreement with experimental measurements.

Title:
Weak coupling of pseudoacoustic phonons and magnon dynamics in the incommensurate spin-ladder compound Sr14Cu24O41
Authors:
Chen, X; Bansal, D; Sullivan, S; Abernathy, DL; Aczel, AA; Zhou, JS; Delaire, O; Shi, L Author Full Names: Chen, Xi; Bansal, Dipanshu; Sullivan, Sean; Abernathy, Douglas L.; Aczel, Adam A.; Zhou, Jianshi; Delaire, Olivier; Shi, Li
Source:
PHYSICAL REVIEW B, 94 (13):10.1103/PhysRevB.94.134309 OCT 21 2016
Abstract:
Intriguing lattice dynamics have been predicted for aperiodic crystals that contain incommensurate substructures. Here we report inelastic neutron scattering measurements of phonon and magnon dispersions in Sr14Cu24O41, which contains incommensurate one-dimensional (1D) chain and two-dimensional (2D) ladder substructures. Two distinct pseudoacoustic phonon modes, corresponding to the sliding motion of one sublattice against the other, are observed for atomic motions polarized along the incommensurate axis. In the long wavelength limit, it is found that the sliding mode shows a remarkably small energy gap of 1.7-1.9 meV, indicating very weak interactions between the two incommensurate sublattices. The measurements also reveal a gapped and steep linear magnon dispersion of the ladder sublattice. The high group velocity of this magnon branch and weak coupling with acoustic and pseudoacoustic phonons can explain the large magnon thermal conductivity in Sr14Cu24O41 crystals. In addition, the magnon specific heat is determined from the measured total specific heat and phonon density of states and exhibits a Schottky anomaly due to gapped magnon modes of the spin chains. These findings offer new insights into the phonon and magnon dynamics and thermal transport properties of incommensurate magnetic crystals that contain low-dimensional substructures.

Title:
Helicity-dependent photocurrent in a Bi2Se3 thin film probed by terahertz emission spectroscopy
Authors:
Hamh, SY; Park, SH; Jerng, SK; Jeon, JH; Chun, SH; Lee, JS Author Full Names: Hamh, Sun Young; Park, Soon-Hee; Jerng, Sahng-Kyoon; Jeon, Jae Ho; Chun, Seung-Hyun; Lee, Jong Seok
Source:
PHYSICAL REVIEW B, 94 (16):10.1103/PhysRevB.94.161405 OCT 20 2016
Abstract:
We investigate photocarrier dynamics in a Bi2Se3 thin film via terahertz (THz) emission spectroscopy. We report amplitude and phase modulations of the emitted THz wave under the variations in a polarization of an input laser beam and sample azimuth. Photon-helicity-dependent responses are manifested in both time and frequency domains, and azimuth dependence of such circular anisotropy exhibits a clear threefold periodicity. We analyze these results based on the symmetry of the bulk and the surface of Bi2Se3 and demonstrate that the observed helicity-dependent photocurrent originates from the circular photon drag effect, namely, linear and angular momentum transfers from photons to photocarriers.

Title:
Crystallographic computing system Jana2006: solution and refinement of twinned structures
Authors:
Petricek, V; Dusek, M; Plasil, J Author Full Names: Petricek, Vaclav; Dusek, Michal; Plasil, Jakub
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (10):583-599; SI 10.1515/zkri-2016-1956 OCT 2016
Abstract:
Twinning is a phenomenon complicating structure analysis of single crystals of standard as well as modulated structures. Jana2006 as a software for advanced structure analysis contains tools for recognition and refinement of twins including most complicated cases of modulated and magnetic structures. In order to efficiently use the tools of Jana2006 related to twinning, we explain the basic terminology and the underlying theory, especially the symmetry of the diffraction patterns affected by twinning. We present typical diffraction patterns of twins and show how twinning can be recognized or detected by various tools and described with twinning matrices. Data processing of twins and ways of how they can be imported to Jana2006 are also discussed. Two examples demonstrate the solution of typical twins: twinning by metric merohedry and twinning by reticular merohedry, followed by the third example demonstrating twinning in a commensurately *modulated structure*. The relationship between the dimensionality of the structure and twinning is discussed, too.

Update: 10-Nov-2016


Title:
Competing magnetic ground states and their coupling to the crystal lattice in CuFe2Ge2
Authors:
May, AF; Calder, S; Parker, DS; Sales, BC; McGuire, MA Author Full Names: May, Andrew F.; Calder, Stuart; Parker, David S.; Sales, Brian C.; McGuire, Michael A.
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep35325 OCT 14 2016
Abstract:
Identifying and characterizing systems with coupled and competing interactions is central to the development of physical models that can accurately describe and predict emergent behavior in condensed matter systems. This work demonstrates that the metallic compound CuFe2Ge2 has competing magnetic ground states, which are shown to be strongly coupled to the lattice and easily manipulated using temperature and applied magnetic fields. Temperature-dependent magnetization M measurements reveal a ferromagnetic-like onset at 228 (1) K and a broad maximum in M near 180 K. Powder neutron diffraction confirms antiferromagnetic ordering below T-N approximate to 175 K, and an incommensurate spin density wave is observed below approximate to 125 K. Coupled with the small refined moments (0.5-1 mu B/Fe), this provides a picture of itinerant magnetism in CuFe2Ge2. The neutron diffraction data also reveal a coexistence of two magnetic phases that further highlights the near-degeneracy of various magnetic states. These results demonstrate that the ground state in CuFe2Ge2 can be easily manipulated by external forces, making it of particular interest for doping, pressure, and further theoretical studies.

Title:
Charge density wave modulation and gap measurements in CeTe3
Authors:
Ralevic, U; Lazarevic, N; Baum, A; Eiter, HM; Hackl, R; Giraldo-Gallo, P; Fisher, IR; Petrovic, C; Gajic, R; Popovic, ZV Author Full Names: Ralevic, U.; Lazarevic, N.; Baum, A.; Eiter, H. -M.; Hackl, R.; Giraldo-Gallo, P.; Fisher, I. R.; Petrovic, C.; Gajic, R.; Popovic, Z. V.
Source:
PHYSICAL REVIEW B, 94 (16):10.1103/PhysRevB.94.165132 OCT 14 2016
Abstract:
We present a study of charge density wave (CDW) ordering in CeTe3 at room temperature using a scanning tunneling microscope and Raman spectroscopy. Two characteristic CDW ordering wave vectors obtained from the Fourier analysis are assessed to be |c* - q| = 4.19 nm(-1) and |q| = 10.26 nm(-1) where |c*| = 2 Pi/c is the reciprocal lattice vector. The scanning tunneling spectroscopy measurements, along with inelastic light ( Raman) scattering measurements, show a CDWgap Delta(max) of approximately 0.37 eV. In addition to the CDW modulation, we observe an organization of the Te sheet atoms in an array of alternating V- and N-shaped groups along the CDW modulation, as predicted in the literature.

Title:
Remarkable Stability of Charge Density Wave Order in La1.875Ba0.125CuO4
Authors:
Chen, XM; Thampy, V; Mazzoli, C; Barbour, AM; Miao, H; Gu, GD; Cao, Y; Tranquada, JM; Dean, MPM; Wilkins, SB Author Full Names: Chen, X. M.; Thampy, V.; Mazzoli, C.; Barbour, A. M.; Miao, H.; Gu, G. D.; Cao, Y.; Tranquada, J. M.; Dean, M. P. M.; Wilkins, S. B.
Source:
PHYSICAL REVIEW LETTERS, 117 (16):10.1103/PhysRevLett.117.167001 OCT 11 2016
Abstract:
The occurrence of charge-density-wave (CDW) order in underdoped cuprates is now well established, although the precise nature of the CDW and its relationship with superconductivity is not. Theoretical proposals include contrasting ideas such as that pairing may be driven by CDW fluctuations or that static CDWs may intertwine with a spatially modulated superconducting wave function. We test the dynamics of CDW order in La1.825Ba0.125CuO4 by using x-ray photon correlation spectroscopy at the CDW wave vector, detected resonantly at the Cu L-3 edge. We find that the CDW domains are strikingly static, with no evidence of significant fluctuations up to 2 (3)/(4) h. We discuss the implications of these results for some of the competing theories.

Title:
Structure of the Al13Co4(100) surface: Combination of surface x-ray diffraction and ab initio calculations
Authors:
Gaudry, E; Chatelier, C; McGuirk, GM; Loli, LNS; de Weerd, MC; Ledieu, J; Fournee, V; Felici, R; Drnec, J; Beutier, G; de Boissieu, M Author Full Names: Gaudry, E.; Chatelier, C.; McGuirk, G. M.; Serkovic Loli, L. N.; de Weerd, M. -C.; Ledieu, J.; Fournee, V.; Felici, R.; Drnec, J.; Beutier, G.; de Boissieu, M.
Source:
PHYSICAL REVIEW B, 94 (16):10.1103/PhysRevB.94.165406 OCT 10 2016
Abstract:
The structure of the quasicrystalline approximant Al13Co4(100) has been determined by surface x-ray diffraction (SXRD) and complementary density-functional-theory (DFT) calculations. Thanks to the use of a two-dimensional pixel detector, which speeds up the data acquisition enormously, an exceptionally large set of experimental data, consisting of 124 crystal truncation rods, has been collected and used to refine this complex structure of large unit cell and low symmetry. Various models were considered for the SXRD analysis. The best fit is consistent with a surface termination at the puckered type of planes but with a depletion of the protruding Co atoms. The surface energy of the determined surface model was calculated using DFT, and it takes a rather low value of 1.09 J/m(2). The results for the atomic relaxation of surface planes found by SXRD or DFT were in excellent agreement. This work opens up additional perspectives for the comprehension of related quasicrystalline surfaces.

Title:
Communication between cation environments in aluminosilicate frameworks: incommensurately modulated crystal structure of an e-plagioclase
Authors:
Fredrickson, RT; Fredrickson, DC Author Full Names: Fredrickson, Rie T.; Fredrickson, Daniel C.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 787-801; 10.1107/S2052520616010350 5 OCT 2016
Abstract:
Despite being one of the most common minerals in the earth's crust the crystal structure of intermediate e-plagioclase remains only partially understood, due in a large part to its complex diffraction patterns including satellite reflections. In this article we present a detailed analysis of the structure of e-plagioclase (An44) using single-crystal X-ray diffraction measured at ambient and low temperature (T = 100 K), in which the full modulated structure is successfully refined. As in earlier studies, the diffraction pattern exhibits strong main a-reflections and weak e-satellite reflections. The average structure could be solved in terms of an albite-like basic cell with the triclinic centrosymmetric and non-centrosymmetric space groups P (1) over bar and P1 (treated in its C (1) over bar and C1 setting, respectively, to follow conventions in the literature), while the incommensurately modulated structure was modeled in (3 + 1) D superspace, employing both the centro-and noncentrosymmetric superspace groups X (1) over bar(alpha beta gamma)0 and X1(alpha beta gamma) 0, where X refers to a special (3 + 1) D lattice centering with centering vectors (0 0 1/2 1/2), (1/2 1/2 0 1/2), and (1/2 1/2 1/2 0). Individual positional and occupational modulations for Ca/Na were refined with deeper insights being revealed in the non-centrosymmetric structure model. Through the structural details emerging from this model, the origin of the modulation can be traced to the communication between Ca/Na site positions through their bridging aluminosilicate (Si/Al) O-4 tetrahedra.

Title:
Charge and spin coupling in magnetoresistive oxygen-vacancy strontium ferrate SrFeO3-delta
Authors:
Lee, SH; Frawley, TW; Yao, CH; Lai, YC; Du, CH; Hatton, PD; Wang, MJ; Chou, FC; Huang, DJ Author Full Names: Lee, S. H.; Frawley, T. W.; Yao, C. H.; Lai, Y. C.; Du, Chao-Hung; Hatton, P. D.; Wang, M. J.; Chou, F. C.; Huang, D. J.
Source:
NEW JOURNAL OF PHYSICS, 18 10.1088/1367-2630/18/9/093033 SEP 20 2016
Abstract:
Using magnetization, conductivity and x-ray scattering measurements, we demonstrate that the giant magnetoresistance of the oxygen-deficient ferrite SrFeO2.875+0.02 is a consequence of the coupling between the charge and spin order parameters and the tetragonal to monoclinic structural distortion. Upon cooling the sample at T similar or equal to 120 K we find a shoulder in both field-cool and zero field cool magnetization data and the simultaneous appearance of incommensurate structural satellites observed using x-ray diffraction. These satellites are shown to be due to incommensurate charge ordering with the high temperature delocalized Fe3.5+ ions becoming localized with a charge disproportion forming an incommensurate charge-ordered phase. Strong resonant enhancement of these satellites at the Fe L-III absorption edge confirms that this charge ordering is occurring at the Fe(2) sites. Further cooling increases the charge order correlation until T similar or equal to 62Kwhere there is a full structural transition from the tetragonal phase to a mononclinic phase. This causes a jump in the charge order wavevector from an incommensurate value of 0.610 to a commensurate ground state position of 5/8. This first-order structural transition displays considerable hysteresis as well as dramatic reductions in the magnetization, resistivity and magnetoresistance. The transition also causes an antiferromagnetic spin-ordering with a doubled unit cell along the c-axis. Well as observing new commensurate magnetic reflections at the Fe-III edge we also observed resonant enhancement at the oxygen K-edge showing considerable hybridization between the Fe 3d and oxygen 2p states at low temperatures. Our results show that the formation of a magnetic long-rage ordered ground state drives the charge ordering from an incommensurate ordering to a commensurate ground state. This is evidence of a strong coupling between the magnetic and charge order parameters which is the basis for the unusual magnetoresistive effects observed at the transition.

Update: 3-Nov-2016


Title:
Ab-initio, Mossbauer spectroscopy, and magnetic study of the approximant Al72Ni9Fe19 to a decagonal Al-Ni-Fe quasicrystal
Authors:
Nejadsattari, F; Stadnik, ZM; Przewoznik, J; Grushko, B Author Full Names: Nejadsattari, Farshad; Stadnik, Zbigniew M.; Przewoznik, Janusz; Grushko, Benjamin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 689 726-732; 10.1016/j.jallcom.2016.08.021 DEC 25 2016
Abstract:
We report the results of ab-initio electronic structure and electric field gradient calculations and of X-ray diffraction, Fe-57 Mossbauer spectroscopy, and magnetic studies of the approximant Al72Ni9Fe19 to a decagonal Al-Ni-Fe quasicrystal. The approximant crystallizes in the hexagonal space group P63/mmc with the lattice parameters a = 7.6989(2) A ($) over circle and c = 7.6724(2) A ($) over circle. A pseudogap in the density of states, centered at similar to 0.30 eV above the Fermi level and with a width of similar to 0.35 eV, is found. Evidence for the covalent nature of the chemical bonding and good metallicity of Al72Ni9Fe19 is provided. The Mossbauer spectra and a 1/T-like dependence of the magnetic susceptibility indicate that Al72Ni9Fe19 is a paramagnet down to 2.0 K. The shape of the Mossbauer spectra is accounted for by a superposition of two quadrupole doublets corresponding to Fe atoms located at two inequivalent crystallographic sites. A sudden change of the quadrupole splittings of the two doublets at similar to 200 K indicates a possible structural phase transition. Excellent agreement between the calculated and measured quadrupole splittings is observed. The Debye temperature of Al72Ni9Fe19 is found to be 431 (3) K. (C) 2016 Elsevier B. V. All rights reserved.

Title:
High temperature phases with wurtzite-derived structure in Zn2LiGaO4-ZnO alloy system
Authors:
Kita, M; Fukada, T; Yamaguchi, S; Omata, T Author Full Names: Kita, Masao; Fukada, Tomoaki; Yamaguchi, Shu; Omata, Takahisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 69-76; 10.1016/j.jallcom.2016.06.249 A DEC 15 2016
Abstract:
We investigated the structural phase transformations of Zn2LiGaO4, which is a quaternary oxide semiconductor with a wide band gap of 4.0 eV, and its alloys with ZnO by using in-situ high-temperature X-ray diffraction (XRD), room-temperature XRD and selected-area electron diffraction of samples quenched from high temperatures of >873 K. Three types of phases with the wurtzite-derived structure were found in the y(Zn2LiGaO4)(1/4)-(1-y)ZnO alloy system. First is the low-temperature phase, phase I, in which constituent cations are ordered similarly to those in a Cd2AgGaS4-type structure. Phase I has an incommensurate modulation vector of 1.04b* and is stable at <1070 K and compositions of 0.96 <= y <= 1 and is stable at room temperature for y = 0.92. The second phase, phase II, appears at intermediate temperatures of 773-1373 K at 0.96 <= y <= 1, and its incommensurate modulation vector is 1.08b*. *Phase* III, which has no long-range cation ordering but still has short-range cation ordering, is stable for 0.92 <= y < 1 at high temperatures and for 0.2 < y < 0.92 from room temperature to high temperatures. We discuss the driving force of the transformations among the three phases in terms of their crystal structure and the mismatch in thermal expansion between -Zn-O-Zn-O- and -Li-O-Ga-O- linkages. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Anisotropy of the electric transport properties of decagonal Al-Cu-Co(Fe) quasicrystals
Authors:
Shulyatev, DA; Klyueva, MV; Devaradjan, U Author Full Names: Shulyatev, D. A.; Klyueva, M. V.; Devaradjan, U.
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 117 (9):883-888; 10.1134/S0031918X16070152 SEP 2016
Abstract:
The method of growth from a melt solution was used to obtain iron-alloyed (0.08 at %) Al-Cu-Co single crystals with a decagonal symmetry. The temperature dependences of the electrical resistivity in magnetic fields of 0-18 T were measured using samples oriented in the periodic direction (rho (p) (T)) and in the quasi-periodic plane (rho (q) (T)). A strong anisotropy of the resistivity was observed; the rho (p) (T) curve is linear, whereas the rho (q) (T) curve is approximated well by a second-order polynomial. A strong anisotropy of the magnetoresistance was also observed; a positive magnetoresistance Delta rho/rho similar to 10(-3) for the current flowing in the quasiperiodic plane; and a weak (close to zero) negative magnetoresistance for the current flowing along the periodic direction.

Update: 27-Oct-2016


Title:
Application of electron backscatter diffraction (EBSD) to quasicrystal-containing microstructures in the Mg-Cd-Yb system
Authors:
Tanaka, R; Ohhashi, S; Fujita, N; Demura, M; Yamamoto, A; Kato, A; Tsai, AP Author Full Names: Tanaka, R.; Ohhashi, S.; Fujita, N.; Demura, M.; Yamamoto, A.; Kato, A.; Tsai, A. P.
Source:
ACTA MATERIALIA, 119 193-202; 10.1016/j.actamat.2016.08.011 OCT 15 2016
Abstract:
We develop a new analysis system for identifying orientation of an icosahedral quasicrystal (iQc) in a SEM installed with an electron backscatter diffraction (EBSD) instrument. The system is successfully applied to determine the orientation of any given iQc grain by reading and assigning the Kikuchi bands obtained with the EBSD. This enables us to analyze relative orientations of iQc and alpha Mg grains in a eutectic structure obtained through a unidirectional solidification process for the Mg-Cd-Yb system. According to EBSD analysis, growth direction of the eutectic structure is shown to be clearly parallel to a two-fold axis of the iQc and {10-10} of alpha Mg, and a unique orientation relationship in iQc and alpha Mg grains is verified in all iQc-alpha Mg coexisting regions. The similarity between primary inter-planar spacings of the iQc and alpha Mg phases is a key factor for stabilizing the interface of two phases and favoring the formation of eutectic structure. This stabilization mechanism is supported by a simple argument on the energetics of a quasiperiodic/periodic lattice interface. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Two-Level Electron Excitations and Distinctive Physical Properties of Al-Cu-Fe Quasicrystals
Authors:
Prekul, A; Shchegolikhina, N Author Full Names: Prekul, Alexandre; Shchegolikhina, Natalya
Source:
CRYSTALS, 6 (9):10.3390/cryst6090119 SEP 2016
Abstract:
This article is not a review in the conventional sense. Rather, it is a monographic study of the implications of detection in Al-Cu-Fe quasicrystals of the electronic heat capacity contributions associated with the two-level electron excitations. Our aim was to reveal correlations between these contributions, on the one hand, and specific features of electron transport, magnetic susceptibility, Hall-effect, tunnelling and optical spectra, on the other hand. It is shown that the full range of these features can be understood in the framework of the unified conceptual scheme based on two-level electron excitations.

Title:
Statistical Approach to Diffraction of Periodic and Non-Periodic Crystals-Review
Authors:
Strzalka, R; Buganski, I; Wolny, J Author Full Names: Strzalka, Radoslaw; Buganski, Ireneusz; Wolny, Janusz
Source:
CRYSTALS, 6 (9):10.3390/cryst6090104 SEP 2016
Abstract:
In this paper, we show the fundamentals of statistical method of structure analysis. Basic concept of a method is the average unit cell, which is a probability distribution of atomic positions with respect to some reference lattices. The distribution carries complete structural information required for structure determination via diffraction experiment regardless of the inner symmetry of diffracting medium. The shape of envelope function that connects all diffraction maxima can be derived as the Fourier transform of a distribution function. Moreover, distributions are sensitive to any disorder introduced to ideal structure-phonons and phasons. The latter are particularly important in case of quasicrystals. The statistical method deals very well with phason flips and may be used to redefine phasonic Debye-Waller correction factor. The statistical approach can be also successfully applied to the peak's profile interpretation. It will be shown that the average unit cell can be equally well applied to a description of Bragg peaks as well as other components of diffraction pattern, namely continuous and singular continuous components. Calculations performed within statistical method are equivalent to the ones from multidimensional analysis. The atomic surface, also called occupation domain, which is the basic concept behind multidimensional models, acquires physical interpretation if compared to average unit cell. The statistical method applied to diffraction analysis is now a complete theory, which deals equally well with periodic and non-periodic crystals, including quasicrystals. The method easily meets also any structural disorder.

Title:
A Review of Transmission Electron Microscopy of Quasicrystals-How Are Atoms Arranged?
Authors:
Li, RT; Li, Z; Dong, ZL; Khor, KA Author Full Names: Li, Ruitao; Li, Zhong; Dong, Zhili; Khor, Khiam Aik
Source:
CRYSTALS, 6 (9):10.3390/cryst6090105 SEP 2016
Abstract:
Quasicrystals (QCs) possess rotational symmetries forbidden in the conventional crystallography and lack translational symmetries. Their atoms are arranged in an ordered but non-periodic way. Transmission electron microscopy (TEM) was the right tool to discover such exotic materials and has always been a main technique in their studies since then. It provides the morphological and crystallographic information and images of real atomic arrangements of QCs. In this review, we summarized the achievements of the study of QCs using TEM, providing intriguing structural details of QCs unveiled by TEM analyses. The main findings on the symmetry, local atomic arrangement and chemical order of QCs are illustrated.

Title:
Elastodynamic Analysis of a Hollow Cylinder with Decagonal Quasicrystal Properties: Meshless Implementation of Local Integral Equations
Authors:
Hosseini, SM; Sladek, J; Sladek, V Author Full Names: Hosseini, Seyed Mahmoud; Sladek, Jan; Sladek, Vladimir
Source:
CRYSTALS, 6 (8):10.3390/cryst6080094 AUG 2016
Abstract:
A meshless approximation and local integral equation (LIE) formulation are proposed for elastodynamic analysis of a hollow cylinder made of quasicrystal materials with decagonal quasicrystal properties. The cylinder is assumed to be under shock loading. Therefore, the general transient elastodynamic problem is considered for coupled phonon and phason displacements and stresses. The equations of motion in the theory of compatible elastodynamics of wave type for phonons and wave-telegraph type for phasons are employed and can be easily modified to the elasto-hydro dynamic equations for quasicrystals (QCs). The angular dependence of the tensor of phonon-phason coupling coefficients handicaps utilization of polar coordinates, when the governing equations would be given by partial differential equations with variable coefficients. Despite the symmetry of the geometrical shape, the local weak formulation and meshless approximation are developed in the Cartesian coordinate system. The response of the cylinder in terms of both phonon and phason stress fields is obtained and studied in detail.

Title:
A ZrNiAl related high-pressure modification of CeRuSn
Authors:
Niehaus, O; Heymann, G; Huppertz, H; Rodewald, UC; Chevalier, B; Matar, SF; Hoffmann, RD; Pottgen, R Author Full Names: Niehaus, Oliver; Heymann, Gunter; Huppertz, Hubert; Rodewald, Ute Ch.; Chevalier, Bernard; Matar, Samir F.; Hoffmann, Rolf-Dieter; Poettgen, Rainer
Source:
DALTON TRANSACTIONS, 45 (36):14216-14229; 10.1039/c6dt02294d 2016
Abstract:
Monoclinic CeRuSn with its own structure type transforms to a high-pressure modification at 11.5 GPa and 1470 K (1000 t press, Walker type module). The structure of the high-pressure phase was refined from X-ray single crystal diffractometer data at room temperature. The HP-CeRuSn subcell structure adopts the ZrNiAl type: P (6) over bar 2m, a = 751.4(3) and c = 394.6(2) pm, wR2 = 0.0787, 310 F-2 values and 15 variables. The Ru2 atoms within the Sn-6 trigonal prisms show a strongly enhanced U-33 parameter. Weak satellite reflections indicate a commensurate modulation: (3 + 1)D superspace group P31m(1/3,1/3,gamma)000, a = 751.4(3) and c = 394.6(2) pm, gamma = -1/3, wR2 = 0.0786, 1584 F-2 values, 32 variables for the main reflections and wR2 = 0.3757 for the satellites of 1st order. A description of this new superstructure variant of the ZrNiAl type is possible in a transformed 3D supercell with the space group R3m and Z = 9. The driving force for formation of the modulation is strengthening of Ru-Sn bonding within the comparatively large Ru@Sn-6 trigonal prisms. Electronic structure calculations point to an almost depleted Ce 4f shell. This is substantiated by temperature-dependent magnetic susceptibility data. Fitting of the data within the inter-configuration fluctuation model (ICF) resulted in cerium valences of 3.41 at 10 K and 3.31 at 350 K. Temperature dependent specific heat data underline the absence of magnetic ordering.

Update: 20-Oct-2016


Title:
Complex magnetic ordering in Tm3Cu4Si4
Authors:
Baran, S; Szytula, A; Kaczorowski, D; Damay, F Author Full Names: Baran, S.; Szytula, A.; Kaczorowski, D.; Damay, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 577-584; 10.1016/j.jallcom.2016.07.241 B DEC 15 2016
Abstract:
Tm3Cu4Si4 crystalizes in the orthorhombic Gd3Cu4Ge4-type crystal structure with trivalent Tm atoms occupying 2(d) and 4(e) Wyckoff sites. Neutron diffraction data shows that at 1.7 K the Tm magnetic moments form a commensurate magnetic structure defined by the propagation vectors (k) over right arrow (2d) = [0,1/2,0] and (k) over right arrow (4e) = [1/4,0,1/2] for the 2(d) and 4(e) sites, respectively. With increasing temperature, the magnetic order in the 4(e) sublattice undergoes near 2.5 K an order-order transition into an incommensurate magnetic structure and then disappears at 2.9 K. Similar changes in the magnetic structure occur in the 2(d) sublattice at 3.3 and 3.8 K, respectively. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Al-rich region of Al-Cu-Mn
Authors:
Grushko, B; Mi, SB Author Full Names: Grushko, B.; Mi, S. B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 957-963; 10.1016/j.jallcom.2016.07.075 B DEC 15 2016
Abstract:
The Al-Cu-Mn alloy system was studied above 45 at.% Al between 550 and 910 degrees C by scanning electron microscopy, powder X-ray diffraction and differential thermal analysis. A wide ternary region of the so-called beta-phase extending along similar to 50 at.% Al was confirmed. It has a CsCl-type structure with a approximate to 0.292-0.298 nm. The total gamma(1)/gamma(2)-region extends from Al-Mn up to similar to 17 at.% Cu and the high-temperature T-Al3Mn phase (Pnma, a approximate to 1.48, b approximate to 1.24, c approximate to 1.25 nm) extends up to similar to 15 at.% Cu. The so-called R-phase (Bbmm, a approximate to 2.41, b approximate to 1.25, c approximate to 0.76 nm) was found to exist in a compositional region of Al74-80Cu5-12.5Mn12.5-18. The ternary phase earlier reported at Al57.9Cu26.3Mn15.8 was confirmed. It exists below 697 degrees C in a compositional region of Al55-58Cu29-Mn-37(7.5-14). The decagonal D-3-phase was concluded to be stable in a compositional region of Al61.5-68.5Cu19-29.5Mn9-16. Below 631 degrees C an fcc phase (a = 0.5814 nm) was revealed around similar to Al60Cu36.5Mn3.5. Partial isothermal sections at 550, 600, 650, 750, 850 and 910 degrees C were constructed. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Microstructural characteristics and mechanical properties of Mg-Zn-Y alloy containing icosahedral quasicrystals phase treated by pulsed magnetic field
Authors:
Zhang, L; Zhou, W; Hu, PH; Zhou, Q Author Full Names: Zhang, L.; Zhou, W.; Hu, P. H.; Zhou, Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 868-874; 10.1016/j.jallcom.2016.07.280 B DEC 15 2016
Abstract:
Pulsed magnetic field (PMF) has been imposed during solidification of Mg-Zn-Y alloy containing icosahedral quasicrystals phase (I-phase) in this work. The effects of vibration power on the solidification microstructure and mechanical properties of Mg93Zn6Y alloy were studied. The results show that the solidification microstructure of the Mg93Zn6Y alloy was further refined with increasing vibration power. The primary alpha-Mg in the alloy treated by PMF was changed from dendrites with the average grain size more than 1 mm untreated by PMF to rosette-like and polyhedral morphology with the average grain size of 122 mm. Moreover, the I-phase was changed from continuous thick skeletal to discontinuous fine reticular and particle-like morphology. The fraction of I-phase in the alloy treated by PMF was also reduced due to the increase of concentrations of Zn and Y elements inside grains. The mechanical properties of Mg93Zn6Y alloy treated by PMF were also improved significantly. The yield strength, ultimate tensile strength and elongation of the alloy treated by PMF at a vibration power of 350 Wat room temperature were 162 MPa, 221 MPa and 1.99%, which were increased by 65%, 66% and 124% respectively, compared to those of the alloy untreated by PMF. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Laser-Induced Charge-Density-Wave Transient Depinning in Chromium
Authors:
Jacques, VLR; Laulhe, C; Moisan, N; Ravy, S; Le Bolloc'h, D Author Full Names: Jacques, V. L. R.; Laulhe, C.; Moisan, N.; Ravy, S.; Le Bolloc'h, D.
Source:
PHYSICAL REVIEW LETTERS, 117 (15):10.1103/PhysRevLett.117.156401 OCT 3 2016
Abstract:
We report on time-resolved x-ray diffraction measurements following femtosecond laser excitation in pure bulk chromium. Comparing the evolution of incommensurate charge-density-wave (CDW) and atomic lattice reflections, we show that, a few nanoseconds after laser excitation, the CDW undergoes different structural changes than the atomic lattice. We give evidence for a transient CDW shear strain that breaks the lattice point symmetry. This strain is characteristic of sliding CDWs, as observed in other incommensurate CDW systems, suggesting the laser-induced CDW sliding capability in 3D systems. This first evidence opens perspectives for unconventional laser-assisted transport of correlated charges.

Title:
Phase transition of solid bismuth under high pressure
Authors:
Chen, HY; Xiang, SK; Yan, XZ; Zheng, LR; Zhang, Y; Liu, SG; Bi, Y Author Full Names: Chen, Hai-Yan; Xiang, Shi-Kai; Yan, Xiao-Zhen; Zheng, Li-Rong; Zhang, Yi; Liu, Sheng-Gang; Bi, Yan
Source:
CHINESE PHYSICS B, 25 (10):10.1088/1674-1056/25/10/108103 OCT 2016
Abstract:
As a widely used pressure calibrator, the structural phase transitions of bismuth from phase I, to phase II, to phase III, and then to phase V with increasing pressure at 300 K have been widely confirmed. However, there are different structural versions for phase III, most of which are determined by x-ray diffraction (XRD) technology. Using x-ray absorption fine structure (XAFS) measurements combined with ab initio calculations, we show that the proposed incommensurate composite structure of bismuth of the three configurations is the best option. An abnormal continuous increase of the nearest-neighbor distance of phase III with elevated pressure is also observed. The electronic structure transformation from semimetal to metal is responsible for the complex behavior of structure transformation.

Title:
Collapse and reappearance of magnetic orderings in spin frustrated TbMnO3 induced by Fe substitution
Authors:
Hong, F; Yue, BB; Wang, JL; Studer, A; Fang, CS; Wang, XL; Dou, SX; Cheng, ZX Author Full Names: Hong, Fang; Yue, Binbin; Wang, Jianli; Studer, Andrew; Fang, Chunsheng; Wang, Xiaolin; Dou, Shixue; Cheng, Zhenxiang
Source:
APPLIED PHYSICS LETTERS, 109 (10):113-117; 10.1063/1.4962465 SEP 5 2016
Abstract:
We studied the temperature dependent magnetic phase evolution in spin frustrated TbMnO3 affected by Fe doping via powder neutron diffraction. With the introduction of Fe (10% and 20%), the long range incommensurate magnetic orderings collapse. When the Fe content is increased to 30%, a long-range antiferromagnetic ordering develops, while a spin reorientation transition is found near 35K from a canted G-type antiferromagnetic ordering to a collinear G-type antiferromagnetic ordering. This work demonstrates the complex magnetic interactions existing in transition metal oxides, which helps to understand the frustrated spin states in other similar systems and design magnetic materials as well. Published by AIP Publishing.

Update: 13-Oct-2016


Title:
Crystallization behavior and mechanical properties of (Al90Fe5Ce5)(100-x)Ti-x amorphous alloys
Authors:
Singh, D; Singh, D; Mandal, RK; Srivastava, ON; Tiwari, RS Author Full Names: Singh, Dharmendra; Singh, Devinder; Mandal, R. K.; Srivastava, O. N.; Tiwari, R. S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 687 990-998; 10.1016/j.jallcom.2016.06.272 DEC 5 2016
Abstract:
The crystallization behavior and mechanical properties of melt-spun (Al90Fe5Ge5)(100-x)Ti-x (x = 0, 4, 8 and 12 at.%) alloys have been investigated. The amorphous phase seems to be stable up to x = 8. The crystallization products for the amorphous alloys with x = 0-8 mainly composed of fcc-Al and icosahedral phases in the glassy matrix. The load dependent hardness behavior of amorphous alloys with and without Ti addition has been studied. The hardness value of the amorphous alloys has been found to be 3.72 and 3.07 GPa for x = 0 and 8 at 100 g load respectively. The annealed ribbons have higher hardness and strength as compared to that of as-synthesized ribbons. The enhanced values of hardness of the (Al90Fe5Ce5)(100-x)Ti-x (x = 0, 4 and 8) alloys are attributed to the combined effects of icosahedral nano particles and Al nanoparticles in amorphous matrix. The absence of cracks around the indentation area up to 500 g of load for amorphous alloys suggests better capability to resist crack propagation in comparison to the annealed alloys. The formation of shear bands around the indentation periphery has been observed. The number of visible shear bands for the as-synthesized ribbons is higher in comparison to those of annealed ribbons. The values of yield strength and Meyer exponent of these alloys are also compared. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Spatially modulated spin structure (SMSS) in BiFeO3-30 years later
Authors:
Sosnowska, IM Author Full Names: Sosnowska, I. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (42):10.1088/0953-8984/28/42/421002 OCT 26 2016

Title:
Martensitic transition, structure and magnetic anisotropy of martensite in Ni-Mn-Sn single crystal
Authors:
Czaja, P; Szczerba, MJ; Chulist, R; Balanda, M; Przewoznik, J; Chumlyakov, YI; Schell, N; Kapusta, C; Maziarz, W Author Full Names: Czaja, P.; Szczerba, M. J.; Chulist, R.; Balanda, M.; Przewoznik, J.; Chumlyakov, Y. I.; Schell, N.; Kapusta, Cz.; Maziarz, W.
Source:
ACTA MATERIALIA, 118 213-220; 10.1016/j.actamat.2016.07.059 OCT 1 2016
Abstract:
The structural and magnetic properties of Ni50Mn37.5Sn12.5 single crystal were investigated. The alloy undergoes martensitic transformation at 308 K from the austenite phase to the structurally modulated tetragonal 4M martensite phase with lattice parameters a(4M) = 6.177 angstrom, c(4M) = 5.669 angstrom. The alloy shows 7.9% pre-strain upon uniaxial compression along the (001) direction, which is near the theoretical 8.2% maximum twinning strain. Magnetization measurements reveal that the magnetic anisotropy of the martensite phase is uniaxial with the easy magnetization axis corresponding to the shortest c axis of the tetragonally distorted unit cell, while its a axis is the hard magnetization direction. The magnetic anisotropy constant K-u saturates at low temperature around 7 x 10(4) j/m(3) and then gradually decreases with increasing temperature as the system approaches the Curie temperature of martensite at 215 K. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Er1.33Pt3Ga8: A modulated variant of the Er4Pt9Al24-structure type
Authors:
Oswald, IWH; Gourdon, O; Bekins, A; Evans, J; Treadwell, LJ; Chan, JY; Macaluso, RT Author Full Names: Oswald, Iain W. H.; Gourdon, Olivier; Bekins, Amy; Evans, Jess; Treadwell, LaRico J.; Chan, Julia Y.; Macaluso, Robin T.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 242 161-167; SI 10.1016/j.jssc.2016.04.009 2 OCT 2016
Abstract:
Single crystals of Er1.33Pt3Ga8 were synthesized in a molten Ga flux. Er1.33Pt3Ga8 can be considered to be a modulated variant of the Er4Pt9Al24-structure type, where the partial occupancies are ordered. Indeed, the presence of weak satellite reflections indicates a complex organization and distribution of the Er and Ga atoms within the [ErGa] slabs. The structure has been solved based on single crystal X-ray diffraction data in the monoclinic superspace group X2/m(0 beta 0)00 with a commensurate modulated vector q=1/3b*. Precession images also indicate diffusion in the perpendicular direction indicating a partial disorder of this arrangement from layer to layer. In addition, Er1.33Pt3Ga8 shows antiferromagnetic ordering at T-N similar to 5 K. (C) 2016 Elsevier Inc. All rights reserved.

Title:
Strong magnetoelastic coupling at the transition from harmonic to anharmonic order in NaFe(WO4)(2) with 3d(5) configuration
Authors:
Holbein, S; Ackermann, M; Chapon, L; Steffens, P; Gukasov, A; Sazonov, A; Breunig, O; Sanders, Y; Becker, P; Bohaty, L; Lorenz, T; Braden, M Author Full Names: Holbein, S.; Ackermann, M.; Chapon, L.; Steffens, P.; Gukasov, A.; Sazonov, A.; Breunig, O.; Sanders, Y.; Becker, P.; Bohaty, L.; Lorenz, T.; Braden, M.
Source:
PHYSICAL REVIEW B, 94 (10):10.1103/PhysRevB.94.104423 SEP 21 2016
Abstract:
The crystal structure of the double tungstate NaFe(WO4)(2) arises from that of the spin-driven multiferroic MnWO4 by inserting nonmagnetic Na layers. NaFe(WO4)(2) exhibits a three-dimensional incommensurate spin-spiral structure at low temperature and zero magnetic field, which, however, competes with commensurate order induced by magnetic field. The incommensurate zero-field phase corresponds to the condensation of a single irreducible representation but it does not imply ferroelectric polarization because spirals with opposite chirality coexist. Sizable anharmonic modulations emerge in this incommensurate structure, which are accompanied by large magnetoelastic anomalies, while the onset of the harmonic order is invisible in the thermal-expansion coefficient. In magnetic fields applied along the monoclinic axis, we observe a first-order transition to a commensurate structure that again is accompanied by large magnetoelastic effects. The large magnetoelastic coupling, a reduction of the b lattice parameter, is thus associated only with the commensurate order. Upon releasing the field at low temperature, the magnetic order transforms to another commensurate structure that considerably differs from the incommensurate low-temperature phase emerging upon zero-field cooling. The latter phase, which exhibits a reduced ordered moment, seems to be metastable.

Title:
Unusual Relaxor Ferroelectric Behavior in Stairlike Aurivillius Phases
Authors:
Steciuk, G; Boullay, P; Pautrat, A; Barrier, N; Caignaert, V; Palatinus, L Author Full Names: Steciuk, Gwladys; Boullay, Philippe; Pautrat, Alain; Barrier, Nicolas; Caignaert, Vincent; Palatinus, Lukas
Source:
INORGANIC CHEMISTRY, 55 (17):8881-8891; 10.1021/acs.inorgchem.6b01373 SEP 5 2016
Abstract:
New ferroelectric layered materials were found in the pseudobinary system Bi5Nb3O15-ABi(2)Nb(2)O(9) (A= Ba, Sr and Pb). Preliminary observations made by transmission electron microscopy indicate that these compounds exhibit a complex incommensurately modulated structure. A (3 + 1)D structural model is obtained using ab initio phasing by charge flipping based on the analysis of precession electron diffraction tomography data. The (3 + 1)D structure is further validated by a refinement against neutron powder diffraction. These materials possess a layered structure with discontinuous [Bi2O2] slabs and perovskite blocks. While these structural units are characteristics of Aurivillius phases, the existence of periodic crystallographic shear planes offers strong similarities with collapsed or stairlike structures known in high-Tc superconductors and related compounds. Using dielectric spectroscopy, we study the phase transitions of these new layered materials. For A = Ba and Sr, a Vogel-Fulcher-like behavior characteristic of the so-called relaxor ferroelectrics is observed and compared to "canonical" relaxors. For A = Sr, the absence of a Bums temperature separated from the freezing temperature appears as a rather unusual behavior.

Title:
An exceptional series of phase transitions in hydrophobic amino acids with linear side chains
Authors:
Gorbitz, CH; Karen, P; Dusek, M; Petricek, V Author Full Names: Gorbitz, Carl Henrik; Karen, Pavel; Dusek, Michal; Petricek, Vaclav
Source:
IUCRJ, 3 341-353; 10.1107/S2052252516010472 5 SEP 2016
Abstract:
The solid-state phase transitions and intermediate structures of S-2-aminobutanoic acid (L-2-aminobutyric acid), S-2-aminopentanoic acid (L-norvaline), S-2-aminohexanoic acid (L-norleucine) and L-methionine between 100 and 470 K, identified by differential scanning calorimetry, have been characterized in a comprehensive single-crystal X-ray diffraction investigation. Unlike other enantiomeric amino acids investigated until now, this group featuring linear side chains displays up to five distinct phases. The multiple transitions between them involve a number of different processes: alteration of the hydrogen-bond pattern, to our knowledge the first example of this observed for an amino acid, sliding of molecular bilayers, seen previously only for racemates and quasiracemates, concerted side-chain rearrangements and abrupt as well as gradual modifications of the side-chain disorder. Ordering of L-norleucine upon cooling even proceeds via an incommensurately modulated structure. L-Methionine has previously been described as being fully ordered at room temperature. An accurate refinement now reveals extensive disorder for both molecules in the asymmetric unit, while two previously unknown phases occur above room temperature.

Title:
Heuristic Description of Magnetoelectricity of Cu2OSeO3
Authors:
Milde, P; Neuber, E; Bauer, A; Pfleiderer, C; Berger, H; Eng, LM Author Full Names: Milde, Peter; Neuber, Erik; Bauer, Andreas; Pfleiderer, Christian; Berger, Helmuth; Eng, Lukas M.
Source:
NANO LETTERS, 16 (9):5612-5618; 10.1021/acs.nanolett.6b02167 SEP 2016
Abstract:
CuO2SeO3 is an insulating material that hosts topologically nontrivial spin whirls, so-called skyrmions, and exhibits magnetoelectric coupling allowing to manipulate these skyrmions by means of electric fields. We report magnetic force microscopy imaging of the real-space spin structure on the surface of a.. bulk single crystal of CuO2SeO3. Based on measurements of the electric polarization using Kelvin-probe force microscopy, we develop a heuristic description of the magnetoelectric properties in CuO2SeO3. The model successfully describes the dependency of the electric polarization on the magnetization in all magnetically modulated phases.

Update: 6-Oct-2016


Title:
Multi-phase quasicrystalline alloys for superior wear resistance
Authors:
Lee, K; Hsu, JL; Naugle, D; Liang, H Author Full Names: Lee, Kyungjun; Hsu, Jialin; Naugle, Donald; Liang, Hong
Source:
MATERIALS & DESIGN, 108 440-447; 10.1016/j.matdes.2016.06.113 OCT 15 2016
Abstract:
Highly wear-resistant alloys are important in many engineering and biomedical applications. In this research, a multi-phase quasicrystal-based alloy was developed using a rapid arc-melting technique. The alloy contains three characteristic phases, hard lambda-Al13Fe4, quasicrystal icosahedral (i-phase), and ductile tau-AlCu. The Vickers micro hardness of each was 828, 795, and 552, respectively, with an overall hardness of 334 (HR15T). Due to the co-existence of these three phases, this alloy exhibits both hardness and ductility. As such, the new material has favorable wear and crack resistance. The approaches used in this study are beneficial for the future design and development of this class of quasicrystalline alloys. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
Quantization of states and strain-induced transformation of charge-density waves in the quasi-one-dimensional conductor TaS3
Authors:
Zybtsev, SG; Pokrovskii, VY Author Full Names: Zybtsev, S. G.; Pokrovskii, V. Ya.
Source:
PHYSICAL REVIEW B, 94 (11):10.1103/PhysRevB.94.115140 SEP 16 2016
Abstract:
We report studies of low-field conductivity, sigma, of nanosized samples of orthorhombic TaS3 as a function of strain, epsilon. The sigma(epsilon) curves show steplike changes associated with the "quantization" of the wave vector, q, of the charge-density wave. Based on the effect we have revealed the change of the q-vector with strain: its in-chain component (normalized by the reciprocal lattice constant) is found to increase with sample stretch. A similar q(epsilon) dependence results from the analysis of the sigma(epsilon) hysteresis for macroscopic samples. This means that the strain-induced anomalies cannot be explained by the transition of the CDW to fourfold commensurability with the pristine lattice (lock-in transition), as it was supposed earlier. We also discuss the metastable length states and the elastic anomalies in TaS3 in light of the observed q(epsilon) dependence.

Title:
Thermoelastic analysis of a two-dimensional decagonal quasicrystal with a conductive elliptic hole
Authors:
Guo, JH; Yu, J; Xing, YM; Pan, EN; Li, LH Author Full Names: Guo, Junhong; Yu, Jing; Xing, Yongming; Pan, Ernian; Li, Lianhe
Source:
ACTA MECHANICA, 227 (9):2595-2607; 10.1007/s00707-016-1657-7 SEP 2016
Abstract:
A general solution in terms of the Stroh-type formalism for quasicrystals is developed for two-dimensional thermoelastic deformation. The solution is then applied to analyze the deformation of a conductive elliptic hole embedded in the decagonal quasicrystal plane which is under a remotely uniform heat flow. The hoop stresses around the elliptic hole are derived in an exact closed form. When the thermal conductivity inside the hole is neglected, the present results are reduced to the existing solutions in the literature. Some numerical examples are provided to show the effects of the geometrical shape of the hole and the thermal conductivity inside the hole on the hoop stresses. The results show that along the hole the variations of the hoop stress of the phonon field are completely different from those of the phason field. Compared to the corresponding insulated case, consideration of a conductive elliptic hole would lead to very different and interesting thermoelastic behaviors.

Title:
Microstructural changes in an extruded Mg-Zn-Y alloy reinforced by quasicrystalline I-phase by small additions of calcium, manganese and cerium-rich mischmetal
Authors:
Medina, J; Perez, P; Garces, G; Tolnai, D; Stark, A; Schell, N; Adeva, P Author Full Names: Medina, J.; Perez, P.; Garces, G.; Tolnai, D.; Stark, A.; Schell, N.; Adeva, P.
Source:
MATERIALS CHARACTERIZATION, 118 186-198; 10.1016/j.matchar.2016.05.019 AUG 2016
Abstract:
The effects of calcium, manganese and cerium-rich mischmetal additions on the microstructure and texture of the extruded Mg-6Zn-1Y (wt.%) alloy have been investigated. The microstructure of the alloys consisted of a magnesium matrix embedding second phase particles aligned along the extrusion direction. The nature and volume fraction of the second phases depended on the alloying element. Thus, Ce-rich mischmetal promoted the formation of T-phase while calcium additions resulted in the formation of a ternary Mg-Zn-Ca compound. Only, manganese additions did not affect the existence of the I-phase present in the ternary alloy. The texture was measured and it was found that calcium addition has a significant effect weakening the extrusion texture. (C) 2016 Elsevier Inc. All rights reserved.

Title:
First Step Towards a Devil's Staircase in Spin-Crossover Materials
Authors:
Trzop, E; Zhang, DP; Pineiro-Lopez, L; Valverde-Munoz, FJ; Munoz, MC; Palatinus, L; Guerin, L; Cailleau, H; Real, JA; Collet, E Author Full Names: Trzop, Elzbieta; Zhang, Daopeng; Pineiro-Lopez, Lucia; Valverde-Munoz, Francisco J.; Carmen Munoz, M.; Palatinus, Lukas; Guerin, Laurent; Cailleau, Herve; Antonio Real, Jose; Collet, Eric
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 55 (30):8675-8679; 10.1002/anie.201602441 JUL 18 2016
Abstract:
The unprecedented bimetallic 2D coordination polymer {Fe[(Hg(SCN)(3))(2)](4,4'-bipy)(2)}(n) exhibits a thermal high-spin (HS)<-> low-spin (LS) staircase-like conversion characterized by a multi-step dependence of the HS molar fraction gamma(HS). Between the fully HS (gamma(HS)= 1) and LS (gamma(HS)= 0) phases, two steps associated with different ordering appear in terms of spin-state concentration waves (SSCW). On the gamma(HS). 0.5 step, a periodic SSCW forms with a HS-LS-HS-LS sequence. On the gamma(HS) approximate to 0.34 step, the 4D superspace crystallography structural refinement reveals an aperiodic SSCW, with a HS-LS sequence incommensurate with the molecular lattice. The formation of these different long-range spatially ordered structures of LS and HS states during the multi-step spin-crossover is discussed within the framework of "Devil's staircase"-type transitions. Spatially modulated phases are known in various types of materials but are uniquely related to molecular HS/LS bistability in this case.

Title:
Atomic-scale mapping of twins and relevant defective structures in Al20Cu2Mn3 decagonal approximant
Authors:
Wang, J; Zhang, B; He, ZB; Wu, B; Ma, XL Author Full Names: Wang, J.; Zhang, B.; He, Z. B.; Wu, B.; Ma, X. L.
Source:
PHILOSOPHICAL MAGAZINE, 96 (23):2457-2467; 10.1080/14786435.2016.1205229 2016
Abstract:
Twins or multiple twins occur frequently in the orthorhombic Al20Cu2Mn3 approximant of decagonal quasi crystal (DQC). Due to the specific structural units, the twins in the Al20Cu2Mn3 approximant usually exhibit the glide-reflection characteristics. Using aberration-corrected transmission electron microscope at the atomic scale, we have observed not only glide-reflection twins but also simple mirror-reflection twins in the Al20Cu2Mn3 approximant. The two twinning modes are found to coexist in the present sample. These twins exhibit variant configurations at the twin boundaries where the tessellations of local subunits are imaged at an atomic scale. At the twin boundaries, diversified tiles such as star-like (S), bowtie-shaped and boat-shaped (B) are observed. The diversified tiles stacking with various manners allow the coexistence of the DQC and the approximant. Furthermore, the variants of B and S tiles are also found.

Update: 29-Sep-2016


Title:
Structure and mechanical properties in a powder-processed icosahedral-phase-strengthened aluminum alloy
Authors:
Watson, TJ; Gordillo, MA; Cernatescu, I; Aindow, M Author Full Names: Watson, Thomas J.; Gordillo, Mauricio A.; Cernatescu, Iuliana; Aindow, Mark
Source:
SCRIPTA MATERIALIA, 123 51-54; 10.1016/j.scriptamat.2016.05.037 OCT 2016
Abstract:
Nanocomposite powder particles of aluminum with dispersed icosahedral quasicrystals were produced by gas atomization from an Al-Cr-Mn-Co-Zr alloy. Bulk dispersion -strengthened material was obtained from the powder by blind-die compaction and forging. The material exhibited an attractive combination of room temperature mechanical properties with a dynamic elastic modulus of 90.5 GPa, a tensile yield strength of 690 MPa with 6% elongation to failure, and a high cycle fatigue life of 109 cycles at 207 MPa applied stress. The material also exhibited significant potential for elevated temperature applications with a modulus of 75 GPa and yield strength of 400 MPa at 300 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
Strengthening mechanisms in an Al-Fe-Cr-Ti nano-quasicrystalline alloy and composites
Authors:
Pedrazzini, S; Galano, M; Audebert, F; Collins, DM; Hofmann, F; Abbey, B; Korsunsky, AM; Lieblich, M; Escorial, AG; Smith, GDW Author Full Names: Pedrazzini, S.; Galano, M.; Audebert, F.; Collins, D. M.; Hofmann, F.; Abbey, B.; Korsunsky, A. M.; Lieblich, M.; Garcia Escorial, A.; Smith, G. D. W.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 672 175-183; 10.1016/j.msea.2016.07.007 AUG 30 2016
Abstract:
We report a study of the structure-processing-property relationships in a high strength Al93Fe3Cr2Ti2 nano-quasicrystalline alloy and composites containing 10 and 20 vol% ductilising pure Al fibres. The superimposed contributions of several different strengthening mechanisms have been modelled analytically using data obtained from systematic characterisation of the monolithic alloy bar. An observed yield strength of 544 MPa has been substantiated from a combination of solid solution strengthening, work hardening, precipitation hardening and Hall-Petch grain size dependent effects. These materials have been shown by other authors in previous published work to be highly sensitive to the size distribution of particles in the powder from which they are made, and the subsequent thermomechanical processing conditions. The processing condition employed in this study provided micron-sized grains with a strong [111] preferential orientation along the extrusion direction and a bimodal size distribution of the icosahedral nano-quasicrystalline precipitates. Both were deemed to be a significant contributor to the high yield strength observed. The addition of pure Al fibres was found to decrease the yield strength linearly with increasing Al content, and to auginent the ductility of the composites. (C) 2016 The Authors. Published by Elsevier B.V.

Title:
Observation and Structure Determination of an Oxide Quasicrystal Approximant
Authors:
Forster, S; Trautmann, M; Roy, S; Adeagbo, WA; Zollner, EM; Hammer, R; Schumann, FO; Meinel, K; Nayak, SK; Mohseni, K; Hergert, W; Meyerheim, HL; Widdra, W Author Full Names: Foerster, S.; Trautmann, M.; Roy, S.; Adeagbo, W. A.; Zollner, E. M.; Hammer, R.; Schumann, F. O.; Meinel, K.; Nayak, S. K.; Mohseni, K.; Hergert, W.; Meyerheim, H. L.; Widdra, W.
Source:
PHYSICAL REVIEW LETTERS, 117 (9):10.1103/PhysRevLett.117.095501 AUG 24 2016
Abstract:
We report on the first observation of an approximant structure to the recently discovered two-dimensional oxide quasicrystal. Using scanning tunneling microscopy, low-energy electron diffraction, and surface x-ray diffraction in combination with ab initio calculations, the atomic structure and the bonding scheme are determined. The oxide approximant follows a 3(2.)4.3.4 Archimedean tiling. Ti atoms reside at the corners of each tiling element and are threefold coordinated to oxygen atoms. Ba atoms separate the TiO3 clusters, leading to a fundamental edge length of the tiling 6.7 angstrom.

Title:
Polymorphism in Zintl Phases ACd(4)Pn(3): Modulated Structures of NaCd(4)Pn(3) with Pn = P, As
Authors:
Grotz, C; Baumgartner, M; Freitag, KM; Baumer, F; Nilges, T Author Full Names: Grotz, Carolin; Baumgartner, Maximilian; Freitag, Katharina M.; Baumer, Franziska; Nilges, Tom
Source:
INORGANIC CHEMISTRY, 55 (15):7764-7776; 10.1021/acs.inorgchem.6b01233 AUG 1 2016
Abstract:
NaCd4P3 and NaCd4As3 were synthesized via short-way transport using the corresponding elements and CdI2 as mineralizer. At room temperature, the two beta-polymorphs adopt the RbCd4As3 structure type which has been recently reported for alkali metal (A)-d(10) transition metal (T)-pnictides (Pn). The title compounds crystallize rhombohedrally in space group R (3) over barm at room temperature and show reversible phase transitions to incommensurately modulated alpha-polymorphs at lower temperatures. The low-temperature phases are monoclinic and can be described in space group Cm(alpha 0 gamma)s with q vectors of q = (-0.04,0,0.34) for alpha-NaCd4P3 and q(1) = (-0.02,0,0.34) for alpha-NaCd4As3. Thermal properties, Raman spectroscopy, and electronic structures have been determined. Both compounds are Zintl phases with band gaps of 1.05 eV for beta-NaCd4P3 and similar to 0.4 eV for beta-NaCd4As3.

Title:
Crystal structure of modulated martensite and crystallographic correlations between martensite variants of Ni50Mn38Sn12 alloy
Authors:
Lin, CQ; Yan, HL; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Lin, Chunqing; Yan, Haile; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 1276-1283; 10.1107/S1600576716010372 4 AUG 2016
Abstract:
A comprehensive study on the crystal structure, the microstructure and the crystallographic features of the martensite in an Ni50Mn38Sn12 alloy has been conducted in the present work. The results show that the martensite possesses a 4O modulated structure. The martensite is organized into broad plates in the original austenite grain. The plates contain irregularly shaped colonies with two characteristic microstructural patterns: a classical lamellar pattern and a herringbone pattern. Crystallographic analyses by scanning electron microscopy/electron backscatter diffraction demonstrate that in each colony there are four orientation variants (A, B, C and D) and they form three types of twins (type I, type II and compound twin). The interfaces between corresponding variants are coincident with their twinning plane K1. The interface planes of the compound twin pairs A&D and B&C can have one or two different orientations, which leads to the two microstructural patterns. The corresponding variants in neighboring colonies within one broad plate (intra-plate colonies) possess close orientations, but the type I and the type II twin relationships are interchanged. The variants in neighboring colonies situated in adjacent plates (inter-plate colonies) are type I or type II twin related but with some angular deviations. The plate interface is defined by the {221} plane of the variant pair with largest thickness. The results of the present work provide comprehensive microstructural and crystallographic information on modulated martensite in NiMnSn alloys that is useful for the understanding of their specific functionalities and helpful for further investigation on property optimization of these materials.

Title:
Superior room-temperature ductility of typically brittle quasicrystals at small sizes
Authors:
Zou, Y; Kuczera, P; Sologubenko, A; Sumigawa, T; Kitamura, T; Steurer, W; Spolenak, R Author Full Names: Zou, Yu; Kuczera, Pawel; Sologubenko, Alla; Sumigawa, Takashi; Kitamura, Takayuki; Steurer, Walter; Spolenak, Ralph
Source:
NATURE COMMUNICATIONS, 7 10.1038/ncomms12261 AUG 2016
Abstract:
The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformation has been found to only be possible at high temperatures or under hydrostatic pressures, and their deformation mechanism at low temperatures is still unclear. Here, we report that typically brittle quasicrystals can exhibit remarkable ductility of over 50% strains and high strengths of similar to 4.5 GPa at room temperature and sub-micrometer scales. In contrast to the generally accepted dominant deformation mechanism in quasicrystals-dislocation climb, our observation suggests that dislocation glide may govern plasticity under high-stress and low-temperature conditions. The ability to plastically deform quasicrystals at room temperature should lead to an improved understanding of their deformation mechanism and application in small-scale devices.

Title:
Magnetism and superconductivity in a quasi-2D anisotropic system doped with charge carriers
Authors:
Palistrant, ME Author Full Names: Palistrant, M. E.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 123 (1):86-97; 10.1134/S1063776116050198 JUL 2016
Abstract:
The theory of multiband superconducting systems with variable density of charge carriers is analyzed. The possibility of emergence of nonphonon high-temperature superconductivity due to the predominance of electron-electron interband interactions over intraband interactions, as well as due to the fact that the thermodynamic and magnetic properties of multiband systems in the superconducting phase differ qualitatively from those of single-band systems, is indicated. Phase transitions in a quasi-2D anisotropic medium upon a change in the carrier concentration, i.e., a transition from the commensurate to the incommensurate state of the spin density wave, are analyzed. Such a transition is observed when the Umklapp processes in the lattice structure are taken into account. These processes facilitate a deviation of wavevector Q of the spin density wave from 2k (F) , as well as a displacement of the bandgap relative to the Fermi surface. This leads to the generation of free charge carriers and the possibility of superconductivity. It is shown that superconductivity accompanies the magnetism. The conditions for the coexistence of these two phenomena are determined.

Title:
Direct imaging of incommensurate wave pockets in the charge-density-wave state of LaTe2
Authors:
Yang, HX; Cai, Y; Ma, C; Li, J; Long, YJ; Chen, GF; Tian, HF; Wei, LL; Li, JQ Author Full Names: Yang, H. X.; Cai, Y.; Ma, C.; Li, J.; Long, Y. J.; Chen, G. F.; Tian, H. F.; Wei, L. L.; Li, J. Q.
Source:
EPL, 114 (6):10.1209/0295-5075/114/67002 JUN 2016
Abstract:
We herein report the study of the atomic structure for a fully incommensurate CDW in LaTe2 using Cs-corrected scanning transmission electron microscopy (STEM). It is directly revealed for the first time that the atomic displacements adopt an incommensurate wave-pocket structure along each Te chain. This pocket structure has a long periodicity determined by the CDW incommensurability. We can use the sinusoidal waves as the first-order approximation to characterize the atomic motions within the pocket pattern, which can yield atomic displacements in good agreement with the theoretical model commonly used for studying CDW. These facts demonstrate that the incommensurate pocket patterns should be an essential structural nature in the CDW states and play a critical role for developing the mechanism of the CDW transitions. Copyright (C) EPLA, 2016

Update: 22-Sep-2016


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

Update: 15-Sep-2016


Title:
Fatigue properties and microstructure of quasicrystalline AlFeCrTi alloy
Authors:
Chlupova, A; Chlup, Z; Kruml, T Author Full Names: Chlupova, Alice; Chlup, Zdenek; Kruml, Tomas
Source:
INTERNATIONAL JOURNAL OF FATIGUE, 91 251-256; 10.1016/j.ijfatigue.2016.06.007 1 OCT 2016
Abstract:
Aluminium based material having chemical composition of Al93Fe3Ti2Cr2 (at.%) was prepared by hot extrusion of gas atomised powder. Microstructure consisting of aluminium matrix and icosahedral quasicrystalline particles was investigated by scanning and transmission electron microscopy a X-ray spectroscopy. Size, distribution and inner structure of quasicrystalline particles were determined. When quasicrystalline particles having submicron size were present in the microstructure together with fine-grained aluminium matrix, it resulted in enhancement of mechanical properties. Fatigue experiments were performed in load controlled regime with positive mean stress and fatigue life data for this quasicrystalline material were compared with similar results for commercially available aluminium alloys. Longer fatigue life together with higher fatigue strength reaching value of 350 MPa was observed. It is approx. 100 MPa higher than for commercially produced coarse-grained aluminium alloys. Fractographic observations revealed presence of fish eye fracture patterns and validity of weakest link fracture mechanism acting in this type of material under investigation. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
Quasi-ordered C-60 molecular films grown on the pseudo-ten-fold (100) surface of the Al13Co4 quasicrystalline approximant
Authors:
Fournee, V; Gaudry, E; Ledieu, J; de Weerd, MC; Diehl, RD Author Full Names: Fournee, V.; Gaudry, E.; Ledieu, J.; de Weerd, M-C; Diehl, R. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (35):10.1088/0953-8984/28/35/355001 SEP 7 2016
Abstract:
The growth of C-60 films on the pseudo-ten-fold (1 0 0) surface of the orthorhombic Al13Co4 quasicrystalline approximant was studied experimentally by scanning tunneling microscopy, low-energy electron diffraction and photoemission spectroscopy. The (1 0 0) surface terminates at bulk-planes presenting local atomic configurations with five-fold symmetry-similar to quasicrystalline surfaces. While the films deposited at room temperature were found disordered, high-temperature growth (up to 693 K) led to quasi-ordered molecular films templated on the substrate rectangular unit mesh. The most probable adsorption sites and geometries were investigated by density functional theory (DFT) calculations. A large range of adsorption energies was determined, influenced by both symmetry and size matching at the molecule-substrate interface. The quasi-ordered structure of the film can be explained by C-60 adsorption at the strongest adsorption sites which are too far apart compared to the distance minimizing the intermolecular interactions, resulting in some disorder in the film structure at a local scale. Valence band photoemission indicates a broadening of the molecular orbitals resulting from hybridization between the substrate and overlayer electronic states. Dosing the film at temperature above 693 K led to molecular damage and formation of carbide thin films possessing no azimuthal order with respect to the substrate.

Title:
Exchange anisotropy as mechanism for spin-stripe formation in frustrated spin chains
Authors:
Pregelj, M; Zaharko, O; Herak, M; Gomilsek, M; Zorko, A; Chapon, LC; Bourdarot, F; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Zaharko, O.; Herak, M.; Gomilsek, M.; Zorko, A.; Chapon, L. C.; Bourdarot, F.; Berger, H.; Arcon, D.
Source:
PHYSICAL REVIEW B, 94 (8):10.1103/PhysRevB.94.081114 AUG 29 2016
Abstract:
We investigate the spin-stripe mechanism responsible for the peculiar nanometer modulation of the incommensurate magnetic order that emerges between the vector-chiral and the spin-density-wave phase in the frustrated zigzag spin-1/2 chain compound beta-TeVO4. A combination of magnetic-torque, neutron-diffraction, and spherical-neutron-polarimetry measurements is employed to determine the complex magnetic structures of all three ordered phases. Based on these results, we develop a simple phenomenological model, which exposes the exchange anisotropy as the key ingredient for the spin-stripe formation in frustrated spin systems.

Title:
Electronic structure and magneto-optical Kerr effect spectra of ferromagnetic shape-memory Ni-Mn-Ga alloys: Experiment and density functional theory calculations
Authors:
Uba, S; Bonda, A; Uba, L; Bekenov, LV; Antonov, VN Author Full Names: Uba, S.; Bonda, A.; Uba, L.; Bekenov, L. V.; Antonov, V. N.
Source:
PHYSICAL REVIEW B, 94 (5):10.1103/PhysRevB.94.054427 AUG 25 2016
Abstract:
In this joint experimental and ab initio study, we focused on the influence of the chemical composition and martensite phase transition on the electronic, magnetic, optical, and magneto-optical properties of the ferromagnetic shape-memory Ni-Mn-Ga alloys. The polar magneto-optical Kerr effect (MOKE) spectra for the polycrystalline sample of the Ni-Mn-Ga alloy of Ni60Mn13Ga27 composition were measured by means of the polarization modulation method over the photon energy range 0.8 <= hv <= 5.8 eV in magnetic field up to 1.5 T. The optical properties (refractive index n and extinction coefficient k) were measured directly by spectroscopic ellipsometry using the rotating analyzer method. To complement experiments, extensive first-principles calculations were made with two different first-principles approaches combining the advantages of a multiple scattering Green function method and a spin-polarized fully relativistic linear-muffin-tin-orbital method. The electronic, magnetic, and MO properties of Ni-Mn-Ga Heusler alloys were investigated for the cubic austenitic and modulated 7M-like incommensurate martensitic phases in the stoichiometric and off-stoichiometric compositions. The optical and MOKE properties of Ni-Mn-Ga systems are very sensitive to the deviation from the stoichiometry. It was shown that the ab initio calculations reproduce well experimental spectra and allow us to explain the microscopic origin of the Ni2MnGa optical and magneto-optical response in terms of interband transitions. The band-by-band decomposition of the Ni2MnGa MOKE spectra is presented and the interband transitions responsible for the prominent structures in the spectra are identified.

Title:
Reflection quasilattices and the maximal quasilattice
Authors:
Boyle, L; Steinhardt, PJ Author Full Names: Boyle, Latham; Steinhardt, Paul J.
Source:
PHYSICAL REVIEW B, 94 (6):10.1103/PhysRevB.94.064107 AUG 25 2016
Abstract:
We introduce the concept of a reflection quasilattice, the quasiperiodic generalization of a Bravais lattice with irreducible reflection symmetry. Among their applications, reflection quasilattices are the reciprocal (i.e., Bragg diffraction) lattices for quasicrystals and quasicrystal tilings, such as Penrose tilings, with irreducible reflection symmetry and discrete scale invariance. In a follow-up paper, we will show that reflection quasilattices can be used to generate tilings in real space with properties analogous to those in Penrose tilings, but with different symmetries and in various dimensions. Here we explain that reflection quasilattices only exist in dimensions two, three, and four, and we prove that there is a unique reflection quasilattice in dimension four: the "maximal reflection quasilattice" in terms of dimensionality and symmetry. Unlike crystallographic Bravais lattices, all reflection quasilattices are invariant under rescaling by certain discrete scale factors. We tabulate the complete set of scale factors for all reflection quasilattices in dimension d > 2, and for all those with quadratic irrational scale factors in d = 2.

Title:
Atomic structure of the i-R-Cd quasicrystals and consequences for magnetism
Authors:
Yamada, T; Takakura, H; Kong, T; Das, P; Jayasekara, WT; Kreyssig, A; Beutier, G; Canfield, PC; de Boissieu, M; Goldman, AI Author Full Names: Yamada, T.; Takakura, H.; Kong, T.; Das, P.; Jayasekara, W. T.; Kreyssig, A.; Beutier, G.; Canfield, P. C.; de Boissieu, M.; Goldman, A. I.
Source:
PHYSICAL REVIEW B, 94 (6):10.1103/PhysRevB.94.060103 AUG 15 2016
Abstract:
We report on the six-dimensional (6D) structural refinement of three members of the i-R-Cd quasicrystals (R = Gd, Dy, Tm) via synchrotron x-ray diffraction from single-grain samples, and show that this series is isostructural to the i-YbCd5.7 quasicrystal. However, our refinements suggest that the R occupancy on the Yb icosahedron sites within the Tsai-type atomic cluster is approximately 80%, with the balance taken up by Cd. Similarities between the i-R-Cd series and i-ScZn7.33, and their differences with i-YbCd5.7 and i-Ca15Cd85, indicate that there are at least two subclasses of Tsai-type icosahedral quasicrystals. We further show from x-ray resonant magnetic scattering (XRMS) measurements on a set of closely related Tb1-xYxCd6 1/1 approximants that the dilution of themagnetic R ions on the icosahedron within the Tsai-type cluster by nonmagnetic Y disrupts the commensurate magnetic ordering in the approximant phase.

Title:
Three-Dimensional Icosahedral Phase Field Quasicrystal
Authors:
Subramanian, P; Archer, AJ; Knobloch, E; Rucklidge, AM Author Full Names: Subramanian, P.; Archer, A. J.; Knobloch, E.; Rucklidge, A. M.
Source:
PHYSICAL REVIEW LETTERS, 117 (7):10.1103/PhysRevLett.117.075501 AUG 8 2016
Abstract:
We investigate the formation and stability of icosahedral quasicrystalline structures using a dynamic phase field crystal model. Nonlinear interactions between density waves at two length scales stabilize three-dimensional quasicrystals. We determine the phase diagram and parameter values required for the quasicrystal to be the global minimum free energy state. We demonstrate that traits that promote the formation of two-dimensional quasicrystals are extant in three dimensions, and highlight the characteristics required for three-dimensional soft matter quasicrystal formation.

Title:
Modulated crystal structure of InMo4O6
Authors:
Schultz, P; Simon, A; Oeckler, O Author Full Names: Schultz, Peter; Simon, Arndt; Oeckler, Oliver
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 642-649; SI 10.1107/S205252061600874X 4 AUG 2016
Abstract:
The (3 + 1)-dimensional modulated crystal structure of the metal-rich cluster compound InMo4O6 was solved and refined from single-crystal data in the superspace group P4/mbm(00 gamma)00ss [q = 0, 0, 0.1536 (4); a = 9.6664 (9), c = 2.8645 (3) angstrom; R1(all) = 0.046, wR(all) = 0.076]. The crystal structure is closely related to the NaMo4O6 structure type. It is built from rods of Mo-6 clusters condensed via trans edges. These form channels parallel to [001], in which In-6 and In-7 oligomers alternate. Weak diffuse planes parallel to (001)* interconnect the *satellite* *reflections*; they occur due to two-dimensional rod disorder of the In oligomer chains.

Title:
Magnetic anisotropy in the frustrated spin-chain compound beta-TeVO4
Authors:
Weickert, F; Harrison, N; Scott, BL; Jaime, M; Leitmae, A; Heinmaa, I; Stern, R; Janson, O; Berger, H; Rosner, H; Tsirlin, AA Author Full Names: Weickert, F.; Harrison, N.; Scott, B. L.; Jaime, M.; Leitmae, A.; Heinmaa, I.; Stern, R.; Janson, O.; Berger, H.; Rosner, H.; Tsirlin, A. A.
Source:
PHYSICAL REVIEW B, 94 (6):10.1103/PhysRevB.94.064403 AUG 1 2016
Abstract:
Isotropic and anisotropic magnetic behavior of the frustrated spin-chain compound beta-TeVO4 is reported. Three magnetic transitions observed in zero magnetic field are tracked in fields applied along different crystallographic directions using magnetization, heat capacity, and magnetostriction measurements. Qualitatively different temperature-field diagrams are obtained below 10 T for the field applied along a or b and along c, respectively. In contrast, a nearly isotropic high-field phase emerges above 18 T and persists up to the saturation that occurs around 22.5 T. Upon cooling in low fields, the transitions at T-N1 and T-N2 toward the spin-density-wave and stripe phases are of the second order, whereas the transition at T-N3 toward the helical state is of the first order and entails a lattice component. Our microscopic analysis identifies frustrated J(1)-J(2) spin chains with a sizable antiferromagnetic interchain coupling in the bc plane and ferromagnetic couplings along the a direction. The competition between these ferromagnetic interchain couplings and the helical order within the chain underlies the incommensurate order along the a direction, as observed experimentally. While a helical state is triggered by the competition between J(1) and J(2) within the chain, the plane of the helix is not uniquely defined because of competing magnetic anisotropies. Using high-resolution synchrotron diffraction and Te-125 nuclear magnetic resonance, we also demonstrate that the crystal structure of beta-TeVO4 does not change down to 10 K, and the orbital state of V4+ is preserved.

Title:
Internal field emission nature of the fine structure of tunnel spectra in icosahedral quasicrystals
Authors:
Prekul, AF; Schegolikhina, NI Author Full Names: Prekul, A. F.; Schegolikhina, N. I.
Source:
JETP LETTERS, 103 (9):603-606; 10.1134/S0021364016090071 MAY 2016
Abstract:
Calorimetric and tunnel data for the icosahedral phases of the Al-Cu-Fe system have been jointly analyzed. It has been found that the field-dependent part of the tunnel conductance can be represented as the sum of elementary terms similar in nature to thermal Schottky anomalies. As a result, the features of the fine structure of tunnel spectra in the form of zero-bias anomalies, peaks, and humps can be due to the internal field emission and can indicate a wide distribution of two-level electron traps in the electronic structure of quasicrystals. It was previously assumed that these features constitute a direct image of the density of single-electron states of the conduction band.

Update: 9-Sep-2016


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

Update: 1-Sep-2016


Title:
Electron diffraction study of cobalt-rich Hf-Co
Authors:
Li, XZ; Jin, YL; Wang, MY; Shield, JE; Skomski, R; Sellmyer, DJ Author Full Names: Li, X. -Z.; Jin, Y. -L.; Wang, M. -Y.; Shield, J. E.; Skomski, R.; Sellmyer, D. J.
Source:
INTERMETALLICS, 75 54-61; 10.1016/j.intermet.2016.06.002 AUG 2016
Abstract:
Intermetallic compounds having compositions from HfCo4 to HfCo8 were investigated by transmission electron microscopy, selected-area electron diffraction, and energy-dispersive x-ray spectroscopy. A major crystalline phase, closely related to the orthorhombic Zr2Co11 phase in structure, has been observed in the samples with the composition ranges from HfCo6 to HfCo8. The phase, referred to as either Hf2Co11 or HfCo7 phase in the literature, is actually one common phase, having a broad composition range and referred to as mu-phase in the present paper. In addition to the mu-phase, we have found coexisted fcc-Co phase and a minor Hf2Co7 phase. The Hf6Co23 phase has been identified in the HfCo4 and HfCo5 samples. Tilt-series electron diffraction revealed that the mu-phase is a one-dimensional incommensurate structure, which can be described approximately as B-centered orthorhombic with a = 0.47 nm, b = 0.82 nm, and c = 3.86 nm. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
Low temperature heat capacity and electrical resistivity of the Ti40Zr25Cu12Ni3Be20 glass forming alloy
Authors:
Liu, BB; Ye, F Author Full Names: Liu, Binbin; Ye, Feng
Source:
INTERMETALLICS, 75 31-35; 10.1016/j.intermet.2016.05.010 AUG 2016
Abstract:
Gaining knowledge of electronic structure provides useful information for understanding unique properties of metallic glasses. In this study, low temperature heat capacity and electrical resistivity of the glass forming Ti40Zr25Cu12Ni3Be20 alloy with glassy, quasicrystalline, or crystalline states below 300 K were investigated. The precipitation of the I-phase was revealed in the initial crystallization process of the Ti40Zr25Cu12Ni3Be20 BMG. The glassy state has higher state density at Fermi level than its quasi crystalline or crystalline counterparts, which could be interpreted by the electron localization in glassy state as well as a pseudo-Brillouin zone formed nearby Fermi surface in the quasicrystalline state. None of the three states showed superconductivity phenomenon down to 1.9 K. Temperature dependence of resistivity for both the glassy state and the quasicrystalline state exhibited negative temperature coefficient and was less sensitive to temperature than the crystalline state. The electrical resistivity showed a smaller value for the I-phase than that for the glass due to lower structural integrity of I -phase. Electrical resistivity as well as heat capacity measurements indicated that the electronic structure of the quasi crystalline state is quite similar to glassy state but far from crystalline state. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
2D materials and van der Waals heterostructures
Authors:
Novoselov, KS; Mishchenko, A; Carvalho, A; Neto, AHC Author Full Names: Novoselov, K. S.; Mishchenko, A.; Carvalho, A.; Castro Neto, A. H.
Source:
SCIENCE, 353 (6298):461-+; 10.1126/science.aac9439 JUL 29 2016
Abstract:
The physics of two-dimensional ( 2D) materials and heterostructures based on such crystals has been developing extremely fast. With these new materials, truly 2D physics has begun to appear ( for instance, the absence of long-range order, 2D excitons, commensurate-incommensurate transition, etc.). Novel heterostructure devices-such as tunneling transistors, resonant tunneling diodes, and light-emitting diodes-are also starting to emerge. Composed from individual 2D crystals, such devices use the properties of those materials to create functionalities that are not accessible in other heterostructures. Here we review the properties of novel 2D crystals and examine how their properties are used in new heterostructure devices.

Update: 25-Aug-2016


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

Update: 18-Aug-2016


Title:
Influence of icosahedral short range order on diffusion in liquids: A study on Al-Zn-Cr alloys
Authors:
Kurtuldu, G; Jarry, P; Rappaz, M Author Full Names: Kurtuldu, Guven; Jarry, Philippe; Rappaz, Michel
Source:
ACTA MATERIALIA, 115 423-433; 10.1016/j.actamat.2016.05.051 AUG 15 2016
Abstract:
It has been shown recently that minute additions of Cr in Al-Zn alloys refine the solidified grain structure and induce multiply-twinned grains which can only be explained if the icosahedral symmetry is considered (Kurtuldu et al., 2013). It has been suggested that Cr addition to Al-Zn alloys promotes the formation of icosahedral short-range order (ISRO) in the liquid, leading to the formation of icosahedral quasicrystals (iQC) acting then as a template for the nucleation of the fcc Al-phase. If ISRO exists in liquid Al-Zn-Cr alloys, this should influence diffusion of solute elements in the liquid. The present study focuses on the effect of Cr addition on Zn diffusion in liquid Al-Zn-Cr alloys. The solute diffusion coefficients of Zn and Cr in the liquid were deduced from the solute profiles in the quenched liquid ahead of a planar solid liquid interface. By comparison with the same measurement in Al-Zn alloys, it is shown that Cr indeed slows down the diffusion (and mobility) of Zn atoms, an effect which reinforces the hypothesis of ISRO in Al-Zn liquid induced by Cr. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Structure and microstructure of Ni-Mn-Ga single crystal exhibiting magnetic shape memory effect analysed by high resolution X-ray diffraction
Authors:
Heczko, O; Cejpek, P; Drahokoupil, J; Holy, V Author Full Names: Heczko, Oleg; Cejpek, Petr; Drahokoupil, Jan; Holy, Vaclav
Source:
ACTA MATERIALIA, 115 250-258; 10.1016/j.actamat.2016.05.047 AUG 15 2016
Abstract:
Subtle changes of (micro-) structure can have far-reaching consequences for magnetic shape memory (MSM) effect, also called magnetic induced reorientation (MIR). Detailed X-ray structure analysis using reciprocal mapping of Ni-Mn-Ga single crystals exhibiting MIR at room temperature and prepared in single macrotwin orientation revealed 10M modulated structure. It indicated that the modulation was harmonic, i.e. commensurate, but it also showed that the difference when compared to non commensurate mode or even to adaptive model was very small. The distinction between commensurate and non-commensurate modulation could not be reliably resolved due to large broadening of diffraction peaks. The broadening was caused by small size (less than 100 nm) of structurally coherent L2(1) ordered domains. The small size of these coherent domains is a result of large concentration of antiphase boundaries. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
The 7 x 1 Fermi Surface Reconstruction in a Two-dimensional f-electron Charge Density Wave System: PrTe3
Authors:
Lee, E; Kim, DH; Kim, HW; Denlinger, JD; Kim, H; Kim, J; Kim, K; Min, BI; Min, BH; Kwon, YS; Kang, JS Author Full Names: Lee, Eunsook; Kim, D. H.; Kim, Hyun Woo; Denlinger, J. D.; Kim, Heejung; Kim, Junwon; Kim, Kyoo; Min, B. I.; Min, B. H.; Kwon, Y. S.; Kang, J. -S.
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep30318 JUL 25 2016
Abstract:
The electronic structure of a charge density wave (CDW) system PrTe3 and its modulated structure in the CDW phase have been investigated by employing ARPES, XAS, Pr 4 f RPES, and first-principles band structure calculation. Pr ions are found to be nearly trivalent, supporting the CDW instability in the metallic Te sheets through partial filling. Finite Pr 4 f spectral weight is observed near the Fermi level, suggesting the non-negligible Pr 4 f contribution to the CDW formation through the Pr 4 f-Te 5p hybridization. The two-fold symmetric features in the measured Fermi surface (FS) of PrTe3 are explained by the calculated FS for the assumed 7 x 1 CDW supercell formation in Te sheets. The shadow bands and the corresponding very weak FSs are observed, which originate from both the band folding due to the 3D interaction of Te sheets with neighboring Pr-Te layers and that due to the CDW-induced FS reconstruction. The straight vertical FSs are observed along k(z), demonstrating the nearly 2D character for the near-E-F states. The observed linear dichroism reveals the in-plane orbital character of the near-E-F Te 5p states.

Update: 11-Aug-2016


Title:
Structure and multiferroic properties of multi-doped Bi1-xErxFe0.96Mn0.02Co0.02O3 thin films
Authors:
Zheng, YJ; Tan, GQ; Xia, A; Ren, HJ Author Full Names: Zheng, Yujuan; Tan, Guoqiang; Xia, Ao; Ren, Huijun
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 684 438-444; 10.1016/j.jallcom.2016.05.193 NOV 5 2016
Abstract:
Multiferroic Bi1-xErxFe0.96Mn0.02Co0.02O3 (BExFMCO, x = 0.08-0.12) thin films have been successfully prepared on fluorine doped tin oxide (FTO) substrates by the chemical solution deposition method. The structural characteristics of the thin films were investigated by X-ray diffraction (XRD), Rietveld refinement and Raman spectra, indicating a structural transition from typical rhombohedral-R3c:H (BFO) to two-phase coexistence of triclinic-P1 and orthorhombic-Pbmn (BE0.12FMCO). XPS analyses suggest there is the coexistence of Fe2+ and Fe3+ ions in all the thin films. The multi-doping exhibits small effects on oxygen vacancies due to the complex effects of doping ions. Intensive super exchange between Fe2+ and Fe3+ and the decreased leakage current densities are observed in BE0.1FMCO thin films. Multi-doped thin films show the superior ferroelectric properties with a giant remanent polarization (the BE0.1FMCO thin film with P-r similar to 104.43 mu C/cm(2)). The enhanced ferroelectric properties of BExFMCO thin films can be mainly attributed to the structural transition via doping. The highest magnetization values of M-s similar to 9.78 emu/cm(3) and M-r similar to 2.1 emu/cm(3) are obtained in the BE0.1FMCO thin films, which can be attributed to the super exchange between Fe2+ and Fe3+ ions and the altered space modulated spin structure due to structural transition. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Chemical Pressure-Driven Incommensurability in CaPd5: Clues to High-Pressure Chemistry Offered by Complex Intermetallics
Authors:
Kilduff, BJ; Fredrickson, DC Author Full Names: Kilduff, Brandon J.; Fredrickson, Daniel C.
Source:
INORGANIC CHEMISTRY, 55 (13):6781-6793; 10.1021/acs.inorgchem.6b01124 JUL 4 2016
Abstract:
While composition and pressure are generally considered orthogonal parameters in the synthesis and optimization of solid state materials, their distinctness is blurred by the concept of chemical pressure (CP): microscopic pressure arising from lattice constraints rather than an externally applied force. In this article, we describe the first cycle of an iterative theoretical/experimental investigation into this connection. We begin by theoretically probing the ability of physical pressure to promote structural transitions in CaCu5-type phases that are driven by CP in other systems. Our results point to the instability of the reported CaCu5-type CaPd5 phase to such a transition even at ambient pressure, suggesting that new structural chemistry should arise at only modest pressures. We thus attempted to synthesize CaPd5 as a starting material for high-pressure experiments. However, rather than obtaining the expected CaCu5-type phase, we encountered crystals of an incommensurately modulated variant CaCu5+q/2, whose composition is related to its satellite spacing, q = qb(basic)* with q approximate to 0.44. Its structure was solved and refined in the (3 + 1)D superspace group Cmcm(0 beta 0)s00, revealing CaCu5-type slabs separated by distorted Pd hexagonal nets with an incommensurate periodicity. DFT-CP analysis on a commensurate model for CaPd5+q/2 indicates that the new Pd nets serve to relieve intense negative CPs that the Ca atoms would experience in a CaCu5-type CaPd5 phase but suffer from a desire to contract relative to the rest of the structure. In this way, both the Pd layer substitution and incommensurability in CaPd5+q/2 are anticipated by the CP schemes of simpler model systems, with CP quadrupoles tracing the paths of the favorable atomic motions. This picture offers predictions for how elemental substitution and physical pressure should affect these structural motifs, which could be applicable to the magnetic phase Zr2Co11 whose previously proposed structures show close parallels to CaPd5+q/2.

Update: 4-Aug-2016


Title:
Distributed Hybridization Model for Quantum Critical Behavior in Magnetic Quasicrystals
Authors:
Otsuki, J; Kusunose, H Author Full Names: Otsuki, Junya; Kusunose, Hiroaki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (7):10.7566/JPSJ.85.073712 JUL 15 2016
Abstract:
A quantum critical behavior of the magnetic susceptibility was observed in a quasicrystal containing ytterbium. At the same time, a mixed-valence feature of Yb ions was reported, which appears to be incompatible with the magnetic instability. We derive the magnetic susceptibility by expressing the quasiperiodicity as the distributed hybridization strength between Yb 4f and conduction electrons. Assuming a wide distribution of the hybridization strength, the most f electrons behave as renormalized paramagnetic states in the Kondo or mixed-valence regime, but a small number of f moments remain unscreened. As a result, the bulk magnetic susceptibility exhibits a nontrivial power-law-like behavior, while the average f-electron occupation is that of mixed-valence systems. This model thus resolves two contradictory properties of Yb quasicrystals.

Title:
Incommensurate Magnetic Structure in the Cubic Noncentrosymmetric Ternary Compound Pr5Ru3Al2
Authors:
Makino, K; Okuyama, D; Avdeev, M; Sato, TJ Author Full Names: Makino, Koya; Okuyama, Daisuke; Avdeev, Maxim; Sato, Taku J.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (7):10.7566/JPSJ.85.073705 JUL 15 2016
Abstract:
Magnetic susceptibility and neutron powder diffraction experiments have been performed on the noncentrosymmetric ternary compound Pr5Ru3Al2. The previously reported ferromagnetic transition at 24K was not detected in our improved-quality samples. Instead, magnetic ordering was observed in the DC magnetic susceptibility at T-c similar or equal to 3.8 K. The neutron powder diffraction experiment further indicates that an incommensurate magnetic structure is established below T-c with the magnetic modulation vector q similar or equal to (0.066, 0.066, 0.066) (r.l.u.). A candidate for the magnetic structure is proposed using representation analysis.

Title:
Local growth of icosahedral quasicrystalline tilings
Authors:
Hann, CT; Socolar, JES; Steinhardt, PJ Author Full Names: Hann, Connor T.; Socolar, Joshua E. S.; Steinhardt, Paul J.
Source:
PHYSICAL REVIEW B, 94 (1):10.1103/PhysRevB.94.014113 JUL 14 2016
Abstract:
Icosahedral quasicrystals (IQCs) with extremely high degrees of translational order have been produced in the laboratory and found in naturally occurring minerals, yet questions remain about how IQCs form. In particular, the fundamental question of how locally determined additions to a growing cluster can lead to the intricate long-range correlations in IQCs remains open. In answer to this question, we have developed an algorithm that is capable of producing a perfectly ordered IQC yet relies exclusively on local rules for sequential, face-to-face addition of tiles to a cluster. When the algorithm is seeded with a special type of cluster containing a defect, we find that growth is forced to infinity with high probability and that the resultant IQC has a vanishing density of defects. The geometric features underlying this algorithm can inform analyses of experimental systems and numerical models that generate highly ordered quasicrystals.

Title:
Unique magnetic structure of YbCo2Si2
Authors:
Mufti, N; Kaneko, K; Hoser, A; Gutmann, M; Geibel, C; Krellner, C; Stockert, O Author Full Names: Mufti, N.; Kaneko, K.; Hoser, A.; Gutmann, M.; Geibel, C.; Krellner, C.; Stockert, O.
Source:
PHYSICAL REVIEW B, 94 (4):10.1103/PhysRevB.94.045116 JUL 14 2016
Abstract:
We report on the results of powder and single-crystal neutron diffraction to investigate the magnetic order in YbCo2Si2 below the Neel temperature T-N = 1.7 K in detail. Two different magnetically ordered phases can clearly be distinguished. At lowest temperatures a commensurate magnetic structure with a propagation vector k(1) = (0.25 0.25 1) is found, while the intermediate phase (T > 0.9 K) is characterized by an incommensurate magnetic structure with k(2) = (0.25 0.086 1). The magnetic structure in YbCo2Si2 is in marked contrast to all other known RCo2Si2 compounds (R = rare earth element) likely due to some itineracy of the Yb 4f states being responsible for the magnetism.

Title:
Reinterpretation of the zero-temperature conductivity in icosahedral AlPdRe
Authors:
Rapp, O Author Full Names: Rapp, O.
Source:
PHYSICAL REVIEW B, 94 (2):10.1103/PhysRevB.94.024202 JUL 13 2016
Abstract:
The zero-temperature conductivity sigma(0) of icosahedral (i)-AlPdRe has been found to be simply related to the resistance ratio R = rho(4.2 K)/rho(295 K) by a power law, sigma(0) similar to R (1.74), over four orders of magnitude in sigma(0). This relation includes metallic single grain samples, and polygrain samples of different morphologies which are metallic for small R values, and insulatinglike at large R. Electronic transport properties of single grain i-AlPdRe samples are thus found to be on common ground with polygrain i-AlPdRe. The relation between R and sigma(0) can be qualitatively understood from published band-structure calculations on quasicrystalline approximants.

Title:
Commensurate and incommensurate magnetic order in spin-1 chains stacked on the triangular lattice in Li2NiW2O8
Authors:
Ranjith, KM; Nath, R; Majumder, M; Kasinathan, D; Skoulatos, M; Keller, L; Skourski, Y; Baenitz, M; Tsirlin, AA Author Full Names: Ranjith, K. M.; Nath, R.; Majumder, M.; Kasinathan, D.; Skoulatos, M.; Keller, L.; Skourski, Y.; Baenitz, M.; Tsirlin, A. A.
Source:
PHYSICAL REVIEW B, 94 (1):10.1103/PhysRevB.94.014415 JUL 13 2016
Abstract:
We report the thermodynamic properties, magnetic ground state, and microscopic magnetic model of the spin-1 frustrated antiferromagnet Li2NiW2O8, showing successive transitions at T-N1 similar or equal to 18 K and T-N2 similar or equal to 12.5 K in zero field. Nuclear magnetic resonance and neutron diffraction reveal collinear and commensurate magnetic order with the propagation vector k = (1/2,0,1/2) below T-N2. The ordered moment of 1.8 mu(B) at 1.5 K is directed along [0.89(9), - 0.10(5), - 0.49(6)] and matches the magnetic easy axis of spin-1 Ni2+ ions, which is determined by the scissor-like distortion of the NiO6 octahedra. Incommensurate magnetic order, presumably of spin-density-wave type, is observed in the region between T-N2 and T-N1. Density-functional band-structure calculations put forward a three-dimensional spin lattice with spin-1 chains running along the [01 (1) over bar] direction and stacked on a spatially anisotropic triangular lattice in the ab plane. We show that the collinear magnetic order in Li2NiW2O8 is incompatible with the triangular lattice geometry and thus driven by a pronounced easy-axis single-ion anisotropy of Ni2+.

Title:
Static magnetic order on the metallic triangular lattice in CrSe2 detected by mu+SR
Authors:
Sugiyama, J; Nozaki, H; Umegaki, I; Uyama, T; Miwa, K; Brewer, JH; Kobayashi, S; Michioka, C; Ueda, H; Yoshimura, K Author Full Names: Sugiyama, Jun; Nozaki, Hiroshi; Umegaki, Izumi; Uyama, Takeshi; Miwa, Kazutoshi; Brewer, Jess H.; Kobayashi, Shintaro; Michioka, Chishiro; Ueda, Hiroaki; Yoshimura, Kazuyoshi
Source:
PHYSICAL REVIEW B, 94 (1):10.1103/PhysRevB.94.014408 JUL 7 2016
Abstract:
The magnetic nature of a metallic two-dimensional triangular compound, CrSe2, has been investigated by muon spin rotation and relaxation (mu+SR) measurements using both powder and single crystal samples. It is found that CrSe2 enters into a static antiferromagnetic (AF) ordered state below 157 K (=T-N). Furthermore, the AF state is slightly changed below around 20 K (=T-N2). Based on the analysis of the internal magnetic fields at the muon sites predicted with DFT calculations, collinear AF and helical 120 degrees AF are clearly eliminated for the ground state of CrSe2. The most probable one is an incommensurate spin density wave order.

Title:
Atomic structure and phason modes of the Sc-Zn icosahedral quasicrystal
Authors:
Yamada, T; Takakura, H; Euchner, H; Gomez, CP; Bosak, A; Fertey, P; de Boissieu, M Author Full Names: Yamada, Tsunetomo; Takakura, Hiroyuki; Euchner, Holger; Gomez, Cesar Pay; Bosak, Alexei; Fertey, Pierre; de Boissieu, Marc
Source:
IUCRJ, 3 247-258; 10.1107/S2052252516007041 4 JUL 2016
Abstract:
The detailed atomic structure of the binary icosahedral (i) ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants K-2/K-1 = -0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye-Waller factor, which explains the vanishing of 'high-Q(perp)' reflections.

Title:
Mysteries of icosahedral quasicrystals: how are the atoms arranged?
Authors:
Ishimasa, T Author Full Names: Ishimasa, Tsutomu
Source:
IUCRJ, 3 230-231; 10.1107/S2052252516009842 4 JUL 2016

Update: 28-Jul-2016


Title:
Defects forming the optical absorption edge in TlGaSe2 layered crystal
Authors:
Seyidov, MY; Suleymanov, RA; Sale, Y Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Sale, Yasin
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 96-97 17-21; 10.1016/j.jpcs.2016.04.009 SEP-OCT 2016
Abstract:
In this work, we present the results of optical experiments designed to investigate the changes in optical absorption spectra of TlGaSe2 ferroelectric-semiconductor with incommensurate (INC) phase in experimental conditions where crystal is kept several hours within the INC-phase (the regime of so called "memory" effect). The fundamental absorption of TlGaSe2, experimentally investigated by optical transmission measurements performed in the temperature range 15-300 K. An extraordinary modification of the optical absorption edge in the range of Urbach's tail is discovered as a result of the annealing within the INC-phase. The role of native defects forming the band edge in the observed phenomena in TlGaSe2 is discussed. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
Phase transitions and magnetic structures in MnW1-xMoxO4 compounds (x <= 0.2)
Authors:
Hardy, V; Payen, C; Damay, F; Meddar, L; Josse, M; Andre, G Author Full Names: Hardy, Vincent; Payen, Christophe; Damay, Francoise; Meddar, Lynda; Josse, Michael; Andre, Gilles
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (33):10.1088/0953-8984/28/33/336003 AUG 24 2016
Abstract:
Temperature-dependent specific heat, magnetization and neutron diffraction data have been collected in zero magnetic field for polycrystalline samples of MnW1-xMoxO4 (x <= 0.2) solid solution whose end-member MnWO4 exhibits a magnetoelectric multiferroic phase (AF2 phase) between T-1 approximate to 8 K and T-2 = 12.5 K. In MnW1-xMoxO4, diamagnetic W6+ are replaced with diamagnetic Mo6+ cations and magnetic couplings among Mn2+ (3d(5), S = 5/2) ions are modified due the doping-induced tuning of the orbital hybridization between Mn 3d and O 2p states. It was observed that magnetic phase transition temperatures which are associated with the second-order AF3-to-paramagnetic (T-N) and AF2-to-AF3 (T-2) transitions in pure MnWO4 slightly increase with the Mo content x. Magnetic specific heat data also indicate that the first-order AF1-to-AF2 phase transition at T-1 survives a weak doping x <= 0.05. This latter phase transition becomes invisible above the base temperature 2 K for higher level of doping x >= 0.10. Neutron powder diffraction datasets collected above 1.5 K for a sample of MnW0.8Mo0.2O4 were analyzed using the Rietveld method. The magnetic structure below approximate to 14 K is a helical incommensurate spin order with a temperature-independent propagation vector k = (-0.217(6), 0.5, 0.466(4)). This cycloidal magnetic structure is similar to the polar AF2 structure observed in MnWO4. The AF1 up-up-down-down collinear spin arrangement observed in MnWO4 is absent in our MnW0.8Mo0.2O4 sample.

Title:
Shock synthesis of quasicrystals with implications for their origin in asteroid collisions
Authors:
Asimow, PD; Lin, C; Bindi, L; Ma, C; Tschauner, O; Hollister, LS; Steinhardt, PJ Author Full Names: Asimow, Paul D.; Lin, Chaney; Bindi, Luca; Ma, Chi; Tschauner, Oliver; Hollister, Lincoln S.; Steinhardt, Paul J.
Source:
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 113 (26):7077-7081; 10.1073/pnas.1600321113 JUN 28 2016
Abstract:
We designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the Khatyrka meteorite. At the boundaries among CuAl5, (Mg0.75Fe0.252+)(2)SiO4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline phase displaying face-centered icosahedral symmetry and low phason strain. The compositional range of the icosahedral phase is Al68-73Fe11-16Cu10-12Cr1-4Ni1-2 and extends toward higher Al/(Cu+Fe) and Fe/Cu ratios than those reported for natural icosahedrite or for any previously known synthetic quasicrystal in the Al-Cu-Fe system. The shock-induced synthesis demonstrated in this experiment reinforces the evidence that natural quasicrystals formed during a shock event but leaves open the question of whether this synthesis pathway is attributable to the expanded thermodynamic stability range of the quasicrystalline phase at high pressure, to a favorable kinetic pathway that exists under shock conditions, or to both thermodynamic and kinetic factors.

Title:
Dynamic stabilities of icosahedral-like clusters and their ability to form quasicrystals
Authors:
Liang, XG; Hamid, I; Duan, HM Author Full Names: Liang, Xiaogang; Hamid, Ilyar; Duan, Haiming
Source:
AIP ADVANCES, 6 (6):10.1063/1.4954741 JUN 2016
Abstract:
The dynamic stabilities of the icosahedral-like clusters containing up to 2200 atoms are investigated for 15 metal elements. The clusters originate from five different initial structures (icosahedron, truncated decahedron, octahedron, closed-shell fragment of an HCP structure, and non-closed-shell fragment of an HCP structure). The obtained order of the dynamic stabilities of the icosahedral-like clusters can be assigned to three groups, from stronger to weaker, according to the size ranges involved: (Zr, Al, Ti) > (Cu, Fe, Co, Ni, Mg, Ag) > (Pb, Au, Pd, Pt, Rh, Ir), which correspond to the predicted formation ability of the quasicrystals. Thedifferences of the sequences can be explained by analyzing the parameters of the Gupta-type manybody inter-atomic potentials. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Update: 22-Jul-2016


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

Update: 14-Jul-2016


Title:
Microstructural control and hardening response of Mg-6Zn-0.5Er-0.5Ca alloy
Authors:
Zheng, XB; Liu, K; Wang, ZH; Li, SB; Du, WB Author Full Names: Zheng, Xiao-Bing; Liu, Ke; Wang, Zhao-Hui; Li, Shu-Bo; Du, Wen-Bo
Source:
RARE METALS, 35 (7):526-531; 10.1007/s12598-015-0462-0 JUL 2016
Abstract:
The effects of heat treatment on microstructures and hardening response of Mg-6Zn-0.5Er-0.5Ca (wt%) alloy were investigated by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM) in this paper. The results show that the Mg-6Zn-0.5Er-0.5Ca alloy contains Mg3Zn6Er1 quasicrystalline phase (I-phase) and Ca2Mg6Zn3 phase under as-cast condition. Most of the Ca2Mg6Zn3 phases and I-phases dissolve into matrix during heat treatment at 475 degrees C for 5 h. After the as-solution alloy was aged at 175 degrees C for 36 h, a large amount of MgZn2 precipitate with several nanometers precipitate. It is suggested that the trace addition of Ca results in refining the size of the precipitate, and the presence of the nanoscale MgZn2 phase is the main factor to improve the peak-aged hardness greatly to 87 HV, which increases about 40 % compared with that of as-cast alloy.

Title:
Atomistic simulation of frictional anisotropy on quasicrystal approximant surfaces
Authors:
Ye, ZJ; Martini, A; Thiel, P; Lovelady, HH; McLaughlin, K; Rabson, DA Author Full Names: Ye, Zhijiang; Martini, Ashlie; Thiel, Patricia; Lovelady, Heather H.; McLaughlin, Keith; Rabson, David A.
Source:
PHYSICAL REVIEW B, 93 (23):10.1103/PhysRevB.93.235438 JUN 23 2016
Abstract:
J. Y. Park et al. [Science 309, 1354 (2005)] have reported eight times greater atomic-scale friction in the periodic than in the quasiperiodic direction on the twofold face of a decagonal Al-Ni-Co quasicrystal. We present results of molecular-dynamics simulations intended to elucidate mechanisms behind this giant frictional anisotropy. Simulations of a bare atomic-force-microscope tip on several model substrates and under a variety of conditions failed to reproduce experimental results. On the other hand, including the experimental passivation of the tip with chains of hexadecane thiol, we reproduce qualitatively the experimental anisotropy in friction, finding evidence for entrainment of the organic chains in surface furrows parallel to the periodic direction.

Title:
Magnetic correlations in a periodic Anderson model with nonuniform conduction electron coordination
Authors:
Hartman, N; Chiu, WT; Scalettar, RT Author Full Names: Hartman, N.; Chiu, W. -T.; Scalettar, R. T.
Source:
PHYSICAL REVIEW B, 93 (23):10.1103/PhysRevB.93.235143 JUN 21 2016
Abstract:
The periodic Anderson model is widely studied to understand strong correlation physics and especially the competition of antiferromagnetism and singlet formation. In this paper we extend quantum Monte Carlo work on lattices with uniform numbers of neighbors to geometries in which the conduction electron sites can have variable coordination z. This situation is relevant both to recently discovered magnetic quasicrystals and also to magnetism in doped heavy fermion systems. Our key results are the presence of antiferromagnetic order at weak interorbital hybridization Vfd, and a delay in singlet formation to larger values of Vfd on sites with larger z. The staggered magnetization tends to be larger on sites with higher z, providing insight into the behavior to be expected in crown, dice, and CaVO lattices.

Title:
Weak crystallization theory of metallic alloys
Authors:
Martin, I; Gopalakrishnan, S; Demler, EA Author Full Names: Martin, Ivar; Gopalakrishnan, Sarang; Demler, Eugene A.
Source:
PHYSICAL REVIEW B, 93 (23):10.1103/PhysRevB.93.235140 JUN 20 2016
Abstract:
Crystallization is one of the most familiar, but hardest to analyze, phase transitions. The principal reason is that crystallization typically occurs via a strongly first-order phase transition, and thus rigorous treatment would require comparing energies of an infinite number of possible crystalline states with the energy of liquid. A great simplification occurs when crystallization transition happens to be weakly first order. In this case, weak crystallization theory, based on unbiased Ginzburg-Landau expansion, can be applied. Even beyond its strict range of validity, it has been a useful qualitative tool for understanding crystallization. In its standard form, however, weak crystallization theory cannot explain the existence of a majority of observed crystalline and quasicrystalline states. Here we extend the weak crystallization theory to the case of metallic alloys. We identify a singular effect of itinerant electrons on the form of weak crystallization free energy. It is geometric in nature, generating strong dependence of free energy on the angles between ordering wave vectors of ionic density. That leads to stabilization of fcc, rhombohedral, and icosahedral quasicrystalline (iQC) phases, which are absent in the generic theory with only local interactions. As an application, we find the condition for stability of iQC that is consistent with the Hume-Rothery rules known empirically for the majority of stable iQC; namely, the length of the primary Bragg-peak wave vector is approximately equal to the diameter of the Fermi sphere.

Title:
Effect of MWNTs-addition on cathodic performance of Ti-V-Ni composites for Ni-MH batteries
Authors:
Lin, J; Sun, LS; Liang, F; Wu, YM; Cao, ZY; Wang, LM Author Full Names: Lin, Jing; Sun, Lianshan; Liang, Fei; Wu, Yaoming; Cao, Zhanyi; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 41 (22):9471-9475; 10.1016/j.ijhydene.2016.03.211 JUN 15 2016
Abstract:
Composites of Ti1.4V0.6Ni alloy and various amounts of multiwalled carbon nanotubes (MWNTs) have been synthesized by high energy mechanical ball-milling method. The composites mainly contain icosahedral quasicrystal and TiNi-type phases. In contrast to Ti1.4V0.6Ni, all milled composites have excellent activation properties activated at the first charge/discharge cycle, together with excellent rate discharge abilities. The composites are able to deliver outstanding maximum discharge capacities of 295.5 mAh g(-1) enhanced by 68.2 mAh g(-1) in comparison to Ti1.4V0.6Ni alloy, and good cycling stabilities with capacity retention of more than 40% after 100 charge/discharge cycles higher than Ti1.4V0.6Ni alloy. Experimental and theoretical investigations suggest that the unusual electrochemical performance of this composite is depended on the copacetic electrocatalytic activity of MWNTs addition and the enhancement of hydrogen diffusion progress. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Title:
Fundamental solutions and analysis of three-dimensional cracks in one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Fan, CY; Li, Y; Xu, GT; Zhao, MH Author Full Names: Fan, CuiYing; Li, Yuan; Xu, GuangTao; Zhao, MingHao
Source:
MECHANICS RESEARCH COMMUNICATIONS, 74 39-44; 10.1016/j.mechrescom.2016.03.009 JUN 2016
Abstract:
In this study, three-dimensional cracks in one-dimensional hexagonal piezoelectric quasicrystals are investigated. Based on the general solutions and Hankel transform, the fundamental solutions for unit point extended displacement discontinuities (including the phonon and phason displacement discontinuities and the electric potential discontinuity) are derived. The extended displacement discontinuity boundary integral equations for a planar crack of arbitrary shape in the periodic plane of one-dimensional hexagonal piezoelectric quasicrystals are established in terms of the extended displacement discontinuities. Using the boundary integral equation method, the singularities of near-crack border fields are obtained and the stress and electric displacement intensity factors are derived. (C) 2016 Elsevier Ltd. All rights reserved.

Update: 7-Jul-2016


Title:
Characterization of SrBiMn2-xTixO6 perovskites: Local ordering influence on the dielectric and magnetic response
Authors:
Alonso-Dominguez, D; Alvarez-Serrano, I; Lopez, ML; Cuello, GJ; Asensio, E; Garcia-Hernandez, M; Veiga, ML; Pico, C Author Full Names: Alonso-Dominguez, D.; Alvarez-Serrano, I.; Lopez, M. L.; Cuello, Gabriel J.; Asensio, Eloy; Garcia-Hernandez, Mar; Veiga, M. L.; Pico, C.
Source:
CERAMICS INTERNATIONAL, 42 (10):11889-11900; 10.1016/j.ceramint.2016.04.111 AUG 1 2016
Abstract:
Two new phases in the (SrTiO3)-(BiMnO3) perovskite type system were studied. These SrBiMn2-xTixO6 (x=0.5 and 0.75) ceramics were prepared by the liquid-mix method as polycrystalline powders. They were characterized by neutron diffraction (ND), electrical and magnetic measurements and these results were analysed in connection with the x=0.25 phase, previously described by us. Their crystal structures were fitted in the tetragonal 14/mcm space group, with additional superstructure reflections suggesting local ordering. Electron microscopy results revealed these ordering effects are actually present concerning both perovskite sublattices. The electrical response pointed to a mechanism consisting in variable range hopping of polarons. A relaxor ferroelectric behaviour dependent on the pellets thickness was found with T-m in the 140-240 K range. The magnetic structures imply an incommensurable modulation of the magnetic moments along the c or a directions, depending on the substitution degree x. A cluster picture in terms of chemically different nanoregions responsible of the macroscopic response is discussed. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Title:
Quasicrystallinity expressed in two-dimensional coordination networks
Authors:
Urgel, JI; Ecija, D; Lyu, GQ; Zhang, R; Palma, CA; Auwarter, W; Lin, NA; Barth, JV Author Full Names: Urgel, Jose I.; Ecija, David; Lyu, Guoqing; Zhang, Ran; Palma, Carlos-Andres; Auwaerter, Willi; Lin, Nian; Barth, Johannes V.
Source:
NATURE CHEMISTRY, 8 (7):657-662; 10.1038/nchem.2507 JUL 2016
Abstract:
The recognition of quasicrystals, which exhibit long-range order but lack translational symmetry, represented both the introduction of a new class of materials and a transformative breakthrough in crystallography. Concomitant with the exploration of quasicrystallinity, metal-organic architectures emerged as promising and versatile systems with significant application potential. Their building principles have been studied extensively and become manifest in a multitude of intricate amorphous and crystalline phases. To date, however, indications for quasicrystalline order have been elusive in metal-organic coordination networks (MOCNs). Here we employ rare-earth-directed assembly to construct a two-dimensional tiling with quasicrystalline characteristics at a well-defined gold substrate. By careful stoichiometry control over europium centres and functional linkers, we produced a porous network, including the simultaneous expression of four-fold, five-fold and six-fold vertices. The pertaining features were directly inspected by scanning tunnelling microscopy, and the molecule-europium reticulation was recognized as square-triangle tessellation with dodecagonal symmetry. Our findings introduce quasicrystallinity in surface-confined MOCNs with a nanoporous structure and anticipate functionalities that arise from quasicrystalline ordering of the coordinative spheres.

Title:
Microstructure and mechanical properties of aluminium matrix composites reinforced by Al62Cu25.5Fe12.5 melt spun ribbon
Authors:
Litynska-Dobrzynska, L; Mitka, M; Goral, A; Stan-Glowinska, K; Dutkiewicz, J Author Full Names: Litynska-Dobrzynska, Lidia; Mitka, Mikolaj; Goral, Anna; Stan-Glowinska, Katarzyna; Dutkiewicz, Jan
Source:
MATERIALS CHARACTERIZATION, 117 127-133; 10.1016/j.matchar.2016.04.025 JUL 2016
Abstract:
Aluminium matrix composites containing 15, 30 and 50 vol.% of pulverized Al62Cu25.5Fe12.5 (in at.%) melt spun ribbons have been prepared by a vacuum hot pressing (T = 673 K, P = 600 MPa). The microstructure of the initial ribbon and the composites was investigated using X-ray, scanning and transmission electron microscopy. In the as-spun ribbon the quasicrystalline icosahedral phase (i-phase) coexisted with the cubic copper rich beta-Al(Cu, Fe) intermetallic compound. The phase composition of Al-Cu-Fe particles changed after consolidation process and the i-phase transformed partially to the omega-Al70Cu20Fe10 phase. Additionally, the Theta-Al2Cu phase formed at the alpha(Al)/Al-Cu-Fe particle interfaces. With an increase in volume fraction of the reinforcement the hardness of the composites increased up to HV = 180 for the highest amount of added particles. The ultimate compression strength of the same sample reached the value of 545 MPa. (C) 2016 Elsevier Inc. All rights reserved.

Title:
Exploring metamagnetism of single crystalline EuNiGe3 by neutron scattering
Authors:
Fabreges, X; Gukasov, A; Bonville, P; Maurya, A; Thamizhavel, A; Dhar, SK Author Full Names: Fabreges, X.; Gukasov, A.; Bonville, P.; Maurya, A.; Thamizhavel, A.; Dhar, S. K.
Source:
PHYSICAL REVIEW B, 93 (21):10.1103/PhysRevB.93.214414 JUN 15 2016
Abstract:
We present here a neutron diffraction study, both in zero field and as a function of magnetic field, of the magnetic structure of the tetragonal intermetallic EuNiGe3 on a single crystalline sample. This material is known to undergo a cascade of transitions, first at 13.2 K towards an incommensurate modulated magnetic structure, then at 10.5 K to an antiferromagnetic structure. We show here that the low-temperature phase presents a spiral moment arrangement with wave vector k = (1/4, delta, 0). For a magnetic field applied along the tetragonal c axis, the square root of the scattering intensity of the (1 0 1) reflection matches very well the complex metamagnetic behavior of the magnetization along c measured previously. For the magnetic field applied along the b axis, two magnetic transitions are observed below the transition to a fully polarized state.

Title:
Commensurate and incommensurate spin-density waves in heavy electron systems
Authors:
Schlottmann, P Author Full Names: Schlottmann, P.
Source:
AIP ADVANCES, 6 (5):10.1063/1.4942549 MAY 2016
Abstract:
The nesting of the Fermi surfaces of an electron and a hole pocket separated by a nesting vector Q and the interaction between electrons gives rise to itinerant antiferromagnetism. The order can gradually be suppressed by mismatching the nesting and a quantum critical point (QCP) is obtained as the Neel temperature tends to zero. The transfer of pairs of electrons between the pockets can lead to a superconducting dome above the QCP (if Q is commensurate with the lattice, i.e. equal to G/2). If the vector Q is not commensurate with the lattice there are eight possible phases: commensurate and incommensurate spin and charge density waves and four superconductivity phases, two of them with modulated order parameter of the FFLO type. The renormalization group equations are studied and numerically integrated. A re-entrant SDW phase (either commensurate or incommensurate) is obtained as a function of the mismatch of the Fermi surfaces and the magnitude of vertical bar Q - G/2 vertical bar. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Update: 30-Jun-2016


Title:
The Z '=12 superstructure of A-cobalt(III) sepulchrate trinitrate governed by C-H center dot center dot center dot O hydrogen bonds
Authors:
Dey, S; Schonleber, A; Mondal, S; Prathapa, SJ; van Smaalen, S; Larsen, FK Author Full Names: Dey, Somnath; Schoenleber, Andreas; Mondal, Swastik; Prathapa, Siriyara Jagannatha; van Smaalen, Sander; Larsen, Finn Krebs
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 372-380; 10.1107/S2052520616005503 3 JUN 2016
Abstract:
A-Cobalt(III) sepulchrate trinitrate crystallizes in P6(3)22 with Z = 2 (Z' = 1/6) at room temperature. Slabs perpendicular to the hexagonal axis comprise molecules Co(sepulchrate) alternating with nitrate groups A and B. Coordinated by six sepulchrate molecules, highly disordered nitrate groups C are accommodated between the slabs. Here we report the fully ordered, low temperature crystal structure of Co(sep)(NO3)(3). It is found to be a high-Z' structure with Z' = 12 of the 12-fold 6a(h) x root 3b(h) x c(h) superstructure with monoclinic symmetry P2(1) (c unique). Correlations between structural parameters are effectively removed by refinements within the superspace approach. Superstructure formation is governed by a densification of the packing in conjunction with ordering of nitrate group C, the latter assuming different orientations for each of the Z' = 12 independent copies in the superstructure. The Co(sep) moiety exhibits small structural variations over its 12 independent copies, while orientations of nitrate groups A and B vary less than the orientations of the nitrate group C do. Molecular packing in the superstructure is found to be determined by short C-H center dot center dot center dot H-C contacts, with H center dot center dot center dot H distances of 2.2-2.3 angstrom, and by short C H center dot center dot center dot O contacts, with H center dot center dot center dot O distances down to 2.2 angstrom. These contacts presumably represent weak C-H center dot center dot center dot O hydrogen bonds, but in any case they prevent further densification of the structure and strengthening of weak N-H center dot center dot center dot O hydrogen bonds with observed H center dot center dot center dot O distances of 2.4-2.6 angstrom.

Title:
New insight on bismuth cuprates with incommensurate modulated structures
Authors:
Mironov, AV; Petricek, V; Khasanova, NR; Antipov, EV Author Full Names: Mironov, Andrei V.; Petricek, Vaclav; Khasanova, Nellie R.; Antipov, Evgeny V.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 395-403; 10.1107/S2052520616005643 3 JUN 2016
Abstract:
The incommensurate modulated crystal structure of Bi2.27Sr1.73CuO6+delta (2201) phase [a = 5.3874 (5), b = 5.3869 (4), c = 24.579 (3) angstrom; beta = 90.01 (1)degrees, q = 0.2105 (3)a* + 0.538 (4)c*, Z = 4, the (3 + 1) -dimensional monoclinic A2/a(alpha 0 gamma) group] has been refined with R = 0.041, wR = 0.052 from X-ray single-crystal data including up to third-order satellite reflections. The same structure has also been considered as incommensurate composite with a(2) = 2.437, b(2) = 5.387, c(2) = 24.614, beta(2) = 93.06, q(2) = 0.4524a(2)* -0.243c(2)* and the (3 + 1)-dimensional A2/m(alpha 0 gamma)0s group for the second component. Both approaches give quite similar results. The structure possesses oxygen disorder in the oxygen-rich region of the BiO layer. An extra 0 atom is determined in the bridging position shifted similar to 0.6 angstrom from BiO towards the SrO layer. Its presence is the cause of the tremendous increase of the bismuth U-11 atomic displacement parameter in similar to 20% of the unit cells (t = -0.05-0.15). Vacancies are determined in the oxygen site of the SrO layer, which may result in the oxygen content variation with annealing at different oxygen pressures. The total refined oxygen content 6.18 (1) corresponds to the results of chemical analysis.

Update: 23-Jun-2016


Title:
Thermo-mechanical study of bulk glass forming Zr-Cu-Ni-Al alloys
Authors:
Spassov, T; Gyurov, S; Stefanov, G; Rangelov, A; Drenchev, L; Russew, K Author Full Names: Spassov, Tony; Gyurov, Stoyko; Stefanov, Georgi; Rangelov, Antoan; Drenchev, Lyudmil; Russew, Krassimir
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 443 103-107; 10.1016/j.jnoncrysol.2016.04.006 JUL 1 2016
Abstract:
The thermal stability and viscous flow behavior of bulk glass forming Zr(68)Cu(13)Ni(11.5)A(17.5) and Zr69Cu12.5Ni11Al7.5 alloys are studied. The viscosity experimental results are interpreted based on the free volume model (FVM). The values of the obtained model parameters are used to estimate the glass forming ability (GFA) in terms of Angell parameter, and the fracture strength of the alloys based on its correlation with the glass transition temperature (T-g). The viscosity data are compared with DSC measurements. The two glasses, having similar composition, revealed comparable T-g, but one of them (Zr68Cu13Ni11.5Al7.5) showed substantially lower crystallization temperature due to quasicrystals formation. Higher GFA was obtained for Zr69Cu12.5Ni11Al7.5 alloy. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Origin of Quantum Criticality in Yb-Al-Au Approximant Crystal and Quasicrystal
Authors:
Watanabe, S; Miyake, K Author Full Names: Watanabe, Shinji; Miyake, Kazumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (6):10.7566/JPSJ.85.063703 JUN 15 2016
Abstract:
To get insight into the mechanism of emergence of unconventional quantum criticality observed in quasicrystal Yb15Al34Au51, the approximant crystal Yb14Al35Au51 is analyzed theoretically. By constructing a minimal model for the approximant crystal, the heavy quasiparticle band is shown to emerge near the Fermi level because of strong correlation of 4f electrons at Yb. We find that charge-transfer mode between 4f electron at Yb on the 3rd shell and 3p electron at Al on the 4th shell in Tsai-type cluster is considerably enhanced with almost flat momentum dependence. The mode-coupling theory shows that magnetic as well as valence susceptibility exhibits chi similar to T-0.5 for zero-field limit and is expressed as a single scaling function of the ratio of temperature to magnetic field T/B over four decades even in the approximant crystal when some condition is satisfied by varying parameters, e.g., by applying pressure. The key origin is clarified to be due to strong locality of the critical Yb-valence fluctuation and small Brillouin zone reflecting the large unit cell, giving rise to the extremely-small characteristic energy scale. This also gives a natural explanation for the quantum criticality in the quasicrystal corresponding to the infinite limit of the unit-cell size.

Title:
Pressure-Driven Quantum Criticality and T/H Scaling in the Icosahedral Au-Al-Yb Approximant
Authors:
Matsukawa, S; Deguchi, K; Imura, K; Ishimasa, T; Sato, NK Author Full Names: Matsukawa, Shuya; Deguchi, Kazuhiko; Imura, Keiichiro; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (6):10.7566/JPSJ.85.063706 JUN 15 2016
Abstract:
We report on ac magnetic susceptibility measurements under pressure of the Au-Al-Yb alloy, a crystalline approximant to the icosahedral quasicrystal that shows unconventional quantum criticality. In describing the susceptibility as chi(T)(-1) - chi(0)(-1) alpha T-gamma, we find that chi(0)(-1) decreases with increasing pressure and vanishes to zero at the critical pressure P-c similar or equal to 2 GPa, with gamma (similar or equal to 0.5) unchanged. We suggest that this quantum criticality emerges owing to critical valence fluctuations. Above P-c, the approximant undergoes a magnetic transition at T similar or equal to 100 mK. These results are contrasted with the fact that, in the quasicrystal, the quantum criticality is robust against the application of pressure. The applicability of the so-called T/H scaling to the approximant is also discussed.

Title:
d-Density Wave Scenario Description of the New Hidden Charge Order in Cuprates
Authors:
Makhfudz, I Author Full Names: Makhfudz, Imam
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (6):10.7566/JPSJ.85.064701 JUN 15 2016
Abstract:
In this paper, we show that the theory of high T-c superconductivity based on a microscopic model with d-density wave (DDW) scenario in the pseudogap phase is able to reproduce some of the most important features of the recent experimentally discovered hidden charge order in several families of Cuprates. In particular, by computing and comparing energies of charge orders of different modulation directions derived from a full microscopic theory with d-density wave scenario, the axial charge order phi(X(Y)) with wavevector Q = (Q(0), 0)((0, Q(0))) is shown to be unambiguously energetically more favorable over the diagonal charge order phi(X+Y) with wavevector Q = (Q(0), +/- Q(0)) at least in commensurate limit, to be expected also to hold even to more general incommensurate case, in agreement with experiment. The two types of axial charge order phi(X) and phi(Y) are degenerate by symmetry. We find that within the superconducting background, biaxial (checkerboard) charge order is energetically more favorable than uniaxial (stripe) charge order, and therefore checkerboard axial charge order should be the one observed in experiments, assuming a single domain of charge ordered state on each CuO2 plane.

Title:
Superlubricity in quasicrystalline twisted bilayer graphene
Authors:
Koren, E; Duerig, U Author Full Names: Koren, Elad; Duerig, Urs
Source:
PHYSICAL REVIEW B, 93 (20):10.1103/PhysRevB.93.201404 MAY 31 2016
Abstract:
The unique atomic positions in quasicrystals lead to peculiar self-similarity and fractal-like structural morphology. Accordingly, many of the material properties are supposed to manifest exceptional characteristics. In this Rapid Communication, we explain through numerical simulations the fundamental and peculiar aspects of quasicrystals wearless friction manifested in a 30 degrees twisted bilayer graphene system. In particular, the sliding force exhibits a fractal structure with distinct area correlations due to the natural mixture between both periodic and aperiodic lateral modulations. In addition, zero power scaling of the sliding force with respect to the contact area is demonstrated for a geometric sequence of dodecagonal elements.

Title:
Temperature dependences of the electric polarization and wave number of incommensurate structures in multiferroics
Authors:
Pikin, SA Author Full Names: Pikin, S. A.
Source:
CRYSTALLOGRAPHY REPORTS, 61 (3):449-455; 10.1134/S1063774516030214 MAY 2016
Abstract:
It is shown that the electric polarization and wave number of incommensurate modulations, proportional to each other, increase according to the Landau law in spin multiferroic cycloids near the N,el temperature. In this case, the constant magnetization component (including the one for a conical spiral) is oriented perpendicular to the spin incommensurability wave vector. A similar temperature behavior should manifest itself for spin helicoids, the axes of which are oriented parallel to the polarization vector but their spin rotation planes are oriented perpendicular to the antiferromagnetic order plane. When the directions of axes of the magnetization helicoid and polarization vector coincide, the latter is quadratic with respect to magnetization and linearly depends on temperature, whereas the incommensurate-modulation wave number barely depends on temperature. Structural distortions of unit cells for multiferroics of different types determine their axial behavior.

Update: 20-Jun-2016


Title:
Determination of shapes and preferred growth directions of icosahedral quasicrystals from the 2D-sections
Authors:
Zupanic, F; Boncina, T Author Full Names: Zupanic, Franc; Boncina, Tonica
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 681 532-540; 10.1016/j.allcom.2016.04.255 OCT 5 2016
Abstract:
The icosahedral quasicrystalline phases have been present in many alloys either as nearly regular polyhedra or dendrites. This work provides a systematic approach for the determination of shapes of polyhedra with icosahedral symmetry, and the determination of preferred growth directions of icosahedral dendrites from their 2D-sections; i.e. from the surface of polished samples. The possible shapes of polyhedra and dendrites by differently oriented intersecting planes are presented within the icosahedral stereographic triangle. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Incommensurate counterrotating magnetic order stabilized by Kitaev interactions in the layered honeycomb alpha-Li2IrO3
Authors:
Williams, SC; Johnson, RD; Freund, F; Choi, S; Jesche, A; Kimchi, I; Manni, S; Bombardi, A; Manuel, P; Gegenwart, P; Coldea, R Author Full Names: Williams, S. C.; Johnson, R. D.; Freund, F.; Choi, Sungkyun; Jesche, A.; Kimchi, I.; Manni, S.; Bombardi, A.; Manuel, P.; Gegenwart, P.; Coldea, R.
Source:
PHYSICAL REVIEW B, 93 (19):10.1103/PhysRevB.93.195158 MAY 26 2016
Abstract:
The layered honeycomb magnet alpha-Li2IrO3 has been theoretically proposed as a candidate to display unconventional magnetic behaviour associated with Kitaev interactions between spin-orbit entangled j(eff) = 1/2 magnetic moments on a honeycomb lattice. Here we report single crystal magnetic resonant x-ray diffraction combined with powder magnetic neutron diffraction to reveal an incommensurate magnetic order in the honeycomb layers with Ir magnetic moments counterrotating on nearest-neighbor sites. This unexpected type of magnetic structure for a honeycomb magnet cannot be explained by a spin Hamiltonian with dominant isotropic (Heisenberg) couplings. The magnetic structure shares many key features with the magnetic order in the structural polytypes beta- and gamma-Li2IrO3, understood theoretically to be stabilized by dominant Kitaev interactions between Ir moments located on the vertices of three-dimensional hyperhoneycomb and stripyhoneycomb lattices, respectively. Based on this analogy and a theoretical soft-spin analysis of magnetic ground states for candidate spin Hamiltonians, we propose that Kitaev interactions also dominate in alpha-Li2IrO3, indicative of universal Kitaev physics across all three members of the harmonic honeycomb family of Li2IrO3 polytypes.

Title:
Strong enhancement of superconductivity at high pressures within the charge-density-wave states of 2H-TaS2 and 2H-TaSe2
Authors:
Freitas, DC; Rodiere, P; Osorio, MR; Navarro-Moratalla, E; Nemes, NM; Tissen, VG; Cario, L; Coronado, E; Garcia-Hernandez, M; Vieira, S; Nunez-Regueiro, M; Suderow, H Author Full Names: Freitas, D. C.; Rodiere, P.; Osorio, M. R.; Navarro-Moratalla, E.; Nemes, N. M.; Tissen, V. G.; Cario, L.; Coronado, E.; Garcia-Hernandez, M.; Vieira, S.; Nunez-Regueiro, M.; Suderow, H.
Source:
PHYSICAL REVIEW B, 93 (18):10.1103/PhysRevB.93.184512 MAY 24 2016
Abstract:
We present measurements of the superconducting and charge-density-wave (CDW) critical temperatures (T-c and T-CDW) as a function of pressure in the transition metal dichalchogenides 2H-TaSe2 and 2H-TaS2. Resistance and susceptibility measurements show that T-c increases from temperatures below 1 K up to 8.5 K at 9.5 GPa in 2H-TaS2 and 8.2 K at 23 GPa in 2H-TaSe2. We observe a kink in the pressure dependence of T-CDW at about 4 GPa that we attribute to the lock-in transition from incommensurate CDW to commensurate CDW. Above this pressure, the commensurate TCDW slowly decreases, coexisting with superconductivity within our full pressure range.

Title:
Self-lubricating, low-friction, wear-resistant Al-based quasicrystalline coatings
Authors:
de Lima, BASG; Gomes, RM; de Lima, SJG; Dragoe, D; Barthes-Labrousse, MG; Kouitat-Njiwa, R; Dubois, JM Author Full Names: Silva Guedes de Lima, Bruno Alessandro; Gomes, Rodinei Medeiros; Guedes de Lima, Severino Jackson; Dragoe, Diana; Barthes-Labrousse, Marie-Genevieve; Kouitat-Njiwa, Richard; Dubois, Jean-Marie
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 17 (1):71-79; 10.1080/14686996.2016.1152563 2016
Abstract:
After gas atomization, a quasicrystalline powder based on aluminium was used to prepare a thick coating by high-velocity oxygen-fuel flame torch spraying. This layer was deposited on top of a bond-coat layer on a steel plate. A post-spraying annealing treatment turned the two layers to their stable state, a.-brass crystal and an icosahedral quasicrystal, respectively. The projection parameters were selected in such a way that the coating behaved like a self-lubricating material, which offered very good wear resistance (duration of pin-on-disk tests superior to 5 km with negligible material loss) and low friction (mu <= 6% against sintered tungsten carbide), in contrast to the state of the art. This property was achieved thanks to, on the one hand, excellent bonding to the substrate via the bound coat, and on the other hand, presence at the boundaries between quasicrystalline flakes of a mixture of both threefold and fourfold coordinated carbon originating from spray processing. Application to hard materials used in mechanical devices is appealing, especially because soft, lubricating additives may not be needed, thus considerably increasing the lifetime of the devices and reducing waste of materials.

Update: 8-Jun-2016


Title:
Evolution of the magnetic structure of TbRu2Al10 in applied field
Authors:
White, R; Hutchison, WD; Mizushima, T; Studer, AJ Author Full Names: White, R.; Hutchison, W. D.; Mizushima, T.; Studer, A. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 679 169-176; 10.1016/j.jallcom.2016.04.039 SEP 15 2016
Abstract:
TbRu2Al10 is found to undergo two magnetic phase transitions as a function of temperature and three as a function of applied field at low temperature. The Tb3+ magnetic moments order antiferromagnetically along the c-axis at 15.0(3) K, with an incommensurate sinusoidally modulated structure with a propagation vector of k = (0, 0.759(1), 0). At 6.5(3) K the structure switches to square wave order. Analysis of single crystal TbRu2Al10 has revealed that this square wave structure is altered to a 'pulse wave' on application of a 1.30 T magnetic field along the c-axis, with two in fifty of the magnetic moments across the structure changing direction to be aligned parallel with the direction of the field. At 1.85 T a further three moments flip, leading to a duty cycle of 60% and resulting in a total change of one in ten moments from the starting square wave structure. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Two iridates, two models, and two approaches: A comparative study on magnetism in three-dimensional honeycomb materials
Authors:
Lee, EKH; Rau, JG; Kim, YB Author Full Names: Lee, Eric Kin-Ho; Rau, Jeffrey G.; Kim, Yong Baek
Source:
PHYSICAL REVIEW B, 93 (18):10.1103/PhysRevB.93.184420 MAY 17 2016
Abstract:
Two recent theoretical works studied the role of Kitaev interactions in the newly observed incommensurate magnetic order in the hyper-honeycomb (beta-Li2IrO3) and stripy-honeycomb (gamma-Li2IrO3) iridates. Each of these works analyzed a different model (JK Gamma versus coupled zigzag chain model) using a contrasting method (classical versus soft-spin analysis). The lack of commonality between these works precludes meaningful comparisons and a proper understanding of these unusual orderings. In this study, we complete the unfinished picture initiated by these two works by solving both models with both approaches for both three-dimensional (3D) honeycomb iridates. Through comparisons between all combinations of models, techniques, and materials, we find that the bond-isotropic JK Gamma model consistently predicts the experimental phase of beta-Li2IrO3 regardless of the method used, while the experimental phase of gamma-Li2IrO3 can be generated by the soft-spin approach with eigenmode mixing irrespective of the model used. To gain further insights, we solve a one-dimensional (1D) quantum spin-chain model related to both 3D models using the density matrix renormalization group method to form a benchmark. We discover that in the 1D model, incommensurate correlations in the classical and soft-spin analysis survive in the quantum limit only in the presence of the symmetric-off-diagonal exchange Gamma found in the JK Gamma model. The relevance of these results to the real materials is also discussed.

Update: 1-Jun-2016


Title:
Ternary phases forming adjacent to Al3Mn-Al4Mn in Al-Mn-TM (TM = Fe, Co, Ni, Cu, Zn, Pd)
Authors:
Grushko, B; Pavlyuchkov, D; Mi, SB; Balanetskyy, S Author Full Names: Grushko, B.; Pavlyuchkov, D.; Mi, S. B.; Balanetskyy, S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 677 148-162; 10.1016/j.jallcom.2016.03.220 AUG 25 2016
Abstract:
The Al-Mn alloy system contains complex intermetallics in its Al-rich part, and this was the first system where quasiperiodic structures were recognized. In the present work, the solubility of TMs (TM = Fe, Co, Ni, Cu, Zn and Pd) in the stable binaries, the stabilization effect of these elements on the metastable binaries and the formation of ternary compounds are specified and compared. While the solubility of all these TMs in hexagonal mu-Al4Mn and lambda-Al4Mn is low, the high-temperature orthorhombic T-Al3Mn dissolves up to at least 14.5, 12, 16 and 7.5 at.% Fe, Cu, Zn and Pd, respectively. The metastable hexagonal phi-Al10Mn3 is stabilized by Fe, Co and Ni in wide ternary compositional regions, and in Al-Co-Mn such a region propagates up to Al5Co2. In alloys with Fe, Co and Ni, a ternary hexagonal phase isostructural to the Al-Cr-Ni zeta-phase (P6(3)/m, a approximate to 1.76, c approximate to 1.25 nm) is formed along similar to 80 at.% Al, while in alloys with Cu and Pd the orthorhombic so-called R-phase (Bbmm, a approximate to 2.41, b approximate to 1.25, c approximate to 0.76 nm) was found at similar compositions. This structure is also known in Al-Zn-Mn but at much lower-Al Al68Zn14.5Mn17.5, while in the range of 75-80 at.% Al a monoclinic phase isostructural to eta-Al11Cr2 (C2/c, a approximate to 1.76, b approximate to 3.04, c approximate to 1.76 nm, beta approximate to 90 degrees) is formed. In addition to the stable decagonal D-3-phase in Al-Fe-Mn and Al-Pd-Mn reported earlier, the stabilization of binary Al-Mn D-3-phase was revealed around Al64Cu20Mn16. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Medium-range structure and glass forming ability in Zr-Cu-Al bulk metallic glasses
Authors:
Zhang, P; Maldonis, JJ; Besser, MF; Kramer, MJ; Voyles, PM Author Full Names: Zhang, Pei; Maldonis, Jason J.; Besser, M. F.; Kramer, M. J.; Voyles, Paul M.
Source:
ACTA MATERIALIA, 109 103-114; 10.1016/j.actamat.2016.02.006 MAY 1 2016
Abstract:
Fluctuation electron microscopy experiments combined with hybrid reverse Monte Carlo modeling show a correlation between medium-range structure at the nanometer scale and glass forming ability in two Zr-Cu-Al bulk metallic glass (BMG) alloys. Both Zr50Cu35Al15 and Zr50Cu45Al5 exhibit two nanoscale structure types, one icosahedral and the other more crystal-like. In Zr50Cu35Al15, the poorer glass former, the crystal-like structure is more stable under annealing below the glass transition temperature, T-g, than in Zr50Cu45Al5. Variable resolution fluctuation microscopy of the MRO clusters show that in Zr50Cu35Al15 on sub-T-g annealing, the crystal-like clusters shrink even as they grow more ordered, while icosahedral-like clusters grow. Overall, the results suggest that achieving better glass forming ability in this alloy system may depend more on destabilizing crystal-like structures than enhancing non-crystalline structures. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Influence of pre-strain on the aging hardening effect of the Mg-9.02Zn-1.68Y alloy
Authors:
Ye, J; Lin, XP; Zhao, TB; Liu, NN; Xie, HB; Niu, Y; Teng, F Author Full Names: Ye, Jie; Lin, Xiao-ping; Zhao, Tian-bo; Liu, Ning-ning; Xie, Hong-bin; Niu, Yi; Teng, Fei
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 663 49-55; 10.1016/j.msea.2016.03.115 APR 29 2016
Abstract:
The solid-solution state Mg-7.68Zn-1.68Y alloy was pre-compressed before the isothermal aging treatment at 200 degrees C, then the pre-induced twinning and its influence on the aging microstructure and aging hardening effect were investigated using EBSD, TEM and SEM. Results showed that: about 15% (area fraction) lenticular (1012) tensile twinning were induced into the matrix when the alloy was compressed by 3% pre-strain; and when the amount of pre-strain increased, area fraction of twinning would increase, average size of twinning would decrease, morphology and structure of twinning would change: when the pre-strain reached 15%, about 28% (area fraction) of narrow double twinning (10 (1) over bar1)-(10 (1) over bar2)would be induced, while the anamorphosis of double twinning were mostly inter-crossing. In addition, twinning could become an effective substrate for nucleation. And different from precipitates in the matrix, which is rod-shaped beta'(1)1-MgZn2 growing along a certain direction, precipitates in the twin boundaries were granular icosahedral quasi -crystal phase with 5 -times rotational symmetric diffraction pattern. And when the pre-strain was in the range of 3-15%, aging hardening effect increased with pre-strain; when pre-strain were 10-15%, the peak hardness arrived 110HV, 28% improved compared to that of the not pre-deformed one (86HV); when the pre-strain exceeded 20%, the aging hardening effect would decrease. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Determination of the zero-field magnetic structure of the helimagnet MnSi at low temperature
Authors:
de Reotier, PD; Maisuradze, A; Yaouanc, A; Roessli, B; Amato, A; Andreica, D; Lapertot, G Author Full Names: de Reotier, P. Dalmas; Maisuradze, A.; Yaouanc, A.; Roessli, B.; Amato, A.; Andreica, D.; Lapertot, G.
Source:
PHYSICAL REVIEW B, 93 (14):10.1103/PhysRevB.93.144419 APR 22 2016
Abstract:
Below a temperature of approximately 29 K the manganese magnetic moments of the cubic binary compound MnSi order to a long-range incommensurate helical magnetic structure. Here we quantitatively analyze a high-statistic zero-field muon spin rotation spectrum recorded in the magnetically ordered phase of MnSi by exploiting the result of representation theory as applied to the determination of magnetic structures. Instead of a gradual rotation of the magnetic moments when moving along a (111) axis, we find that the angle of rotation between the moments of certain subsequent planes is essentially quenched. It is the magnetization of pairs of planes which rotates when moving along a (111) axis, thus preserving the overall helical structure.

Title:
Incommensurate-commensurate transitions in the monoaxial chiral helimagnet driven by the magnetic field
Authors:
Laliena, V; Campo, J; Kishine, JI; Ovchinnikov, AS; Togawa, Y; Kousaka, Y; Inoue, K Author Full Names: Laliena, Victor; Campo, Javier; Kishine, Jun-Ichiro; Ovchinnikov, Alexander S.; Togawa, Yoshihiko; Kousaka, Yusuke; Inoue, Katsuya
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134424 APR 20 2016
Abstract:
The zero-temperature phase diagram of the monoaxial chiral helimagnet in the magnetic-field plane formed by the components parallel and perpendicular to the helical axis is thoroughly analyzed. The nature of the transition to the commensurate state depends on the angle between the field and the helical axis. For field directions close to the directions parallel or perpendicular to the helical axis the transition is continuous, while for intermediate angles the transition is discontinuous and the incommensurate and commensurate states coexist on the transition line. The continuous and discontinuous transition lines are separated by two tricritical points with specific singular behavior. The location of the continuous and discontinuous lines and of the tricritical points depend strongly on the easy-plane anisotropy, the effect of which is analyzed. For high anisotropy the conical approximation locates the transition line very accurately, although it does not predict the continuous transitions and the tricritical behavior. It is shown that for high anisotropy, as in CrNb3S6, the form of the transition line is universal, that is, independent of the sample, and obeys a simple equation. The position of the tricritical points, which is not universal, is theoretically estimated for a sample of CrNb3S6.

Title:
Low-Temperature Oxidation of Fine UO2 Powders: A Process of Nanosized Domain Development
Authors:
Leinders, G; Pakarinen, J; Delville, R; Cardinaels, T; Binnemans, K; Verwerft, M Author Full Names: Leinders, Gregory; Pakarinen, Janne; Delville, Remi; Cardinaels, Thomas; Binnemans, Koen; Verwerft, Marc
Source:
INORGANIC CHEMISTRY, 55 (8):3915-3927; 10.1021/acs.inorgchem.6b00127 APR 18 2016
Abstract:
The nanostructure and phase evolution in low-temperature oxidized (40-250 degrees C), fine UO2 powders (<200 nm) have been investigated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). The extent of oxidation was also measured via in situ thermogravimetric analysis. The oxidation of fine powders was found to, proceed differently as compared to oxidation of coarse grained UO2. No discrete surface oxide layer was observed and no U3O8 was formed, despite the high degree of oxidation (up to O/U = 2.45). Instead, nanosized (5-15 nm) amorphous nuclei (interpreted as amorphous UO3), unmodulated and modulated U4O9, and a continuous range of U3O7-z phases with varying tetragonal distortion (c/a > 1) were observed. Oxidation involves formation of higher uranium oxides in nanodomains near the grain surface which, initially, have a disordered defect structure ("disordered U4O9"). As oxidation progresses, domain growth increases and the long period modulated structure of U4O9 develops ("ordered U4O9"). A similar mechanism is understood to happen also in U3O7-z.

Title:
Disorder-promoted C-4-symmetric magnetic order in iron-based superconductors
Authors:
Hoyer, M; Fernandes, RM; Levchenko, A; Schmalian, J Author Full Names: Hoyer, Mareike; Fernandes, Rafael M.; Levchenko, Alex; Schmalian, Joerg
Source:
PHYSICAL REVIEW B, 93 (14):10.1103/PhysRevB.93.144414 APR 18 2016
Abstract:
In most iron-based superconductors, the transition to the magnetically ordered state is closely linked to a lowering of structural symmetry from tetragonal (C-4) to orthorhombic (C-2). However, recently, a regime of C-4-symmetric magnetic order has been reported in certain hole-doped iron-based superconductors. This novel magnetic ground state can be understood as a double-Q spin density wave characterized by two order parameters M-1 and M-2 related to each of the two Q vectors. Depending on the relative orientations of the order parameters, either a noncollinear spin-vortex crystal or a nonuniform charge-spin density wave could form. Experimentally, Mossbauer spectroscopy, neutron scattering, and muon spin rotation established the latter as the magnetic configuration of some of these optimally hole-doped iron-based superconductors. Theoretically, low-energy itinerant models do support a transition from single-Q to double-Q magnetic order, but with nearly degenerate spin-vortex crystal and charge-spin density wave states. In fact, extensions of these low-energy models including additional electronic interactions tip the balance in favor of the spin-vortex crystal, in apparent contradiction with the recent experimental findings. In this paper we revisit the phase diagram of magnetic ground states of low-energy multiband models in the presence of weak disorder. We show that impurity scattering not only promotes the transition from C-2 to C-4-magnetic order, but it also favors the charge-spin density wave over the spin-vortex crystal phase. Additionally, in the single-Q phase, our analysis of the nematic coupling constant in the presence of disorder supports the experimental finding that the splitting between the structural and stripe-magnetic transition is enhanced by disorder.

Title:
Low-temperature magnetic phase transitions in the multiferroic Nd0.9Dy0.1Fe3(BO3)(4). Part 1. Transitions induced by magnetic fields directed along the trigonal symmetry axis. Spontaneous transitions with temperature changes
Authors:
Zvyagina, GA; Zhekov, KR; Bilych, IV; Kolodyazhnaya, MP; Zvyagin, AA; Bludov, AN; Pashchenko, VA; Gudim, IA Author Full Names: Zvyagina, G. A.; Zhekov, K. R.; Bilych, I. V.; Kolodyazhnaya, M. P.; Zvyagin, A. A.; Bludov, A. N.; Pashchenko, V. A.; Gudim, I. A.
Source:
LOW TEMPERATURE PHYSICS, 42 (4):273-279; 10.1063/1.4947480 APR 2016
Abstract:
The elastic and magnetic characteristics of single-crystal Nd0.9Dy0.1Fe3(BO3)(4) are studied at low temperatures in zero magnetic field and in external fields H vertical bar vertical bar C-3. The temperature dependences of the acoustic mode velocities and the magnetic susceptibility manifest a transition of the magnetic subsystem into a magnetically ordered state and two successive, spontaneous spin-reorientation phase transitions. The possibility of a spontaneous transition into an incommensurate (spiral) magnetic phase in the crystal is discussed. It is shown that an external magnetic field directed along the trigonal axis of the crystal induces a sequence of spin-reorientation phase transitions. An H-T phase diagram (H vertical bar vertical bar C-3) is constructed for this compound. Published by AIP Publishing.

Title:
3D Morphology and Formation Process of the Icosahedral Quasicrystalline Phase in Rapidly Solidified Al-Mn Alloy
Authors:
Kang, HJ; Hu, ZL; Gao, XX; Chen, ZN; Lu, YP; Jie, JC; Guo, JJ Author Full Names: Kang, Hui-Jun; Hu, Zhong-Lue; Gao, Xiao-Xia; Chen, Zong-Ning; Lu, Yi-Ping; Jie, Jin-Chuan; Guo, Jing-Jie
Source:
ACTA METALLURGICA SINICA-ENGLISH LETTERS, 29 (1):28-31; 10.1007/s40195-015-0357-y JAN 2016
Abstract:
Three-dimensional morphology and formation process of icosahedral quasicrystal phase have been investigated in a melt-spun Al-18Mn alloy (in wt%). Three distinct layers corresponding to varying temperature gradient have been observed on the cross section of the ribbons. 3D morphologies of cellular and dendritic icosahedral phase have been obtained through electro-etching. A model has been proposed to describe the formation process of the icosahedral phase and alpha-Al during the rapid solidification. The icosahedral phases are primarily precipitated from the melt into fine cellular and dendritic particles, and subsequently engulfed by the alpha-Al which propagates in a planar morphology.

Title:
Diffraction pattern of modulated structures described by Bessel functions
Authors:
Wolny, J; Buganski, I; Strzalka, R Author Full Names: Wolny, Janusz; Buganski, Ireneusz; Strzalka, Radoslaw
Source:
PHILOSOPHICAL MAGAZINE, 96 (13):1344-1359; 10.1080/14786435.2016.1161859 2016
Abstract:
We performed detailed analysis of 1D modulated structure (MS) with harmonic modulation within the statistical approach. By applying two-mode Fourier transform, we were able to derive analytically the structure factor for MS with single harmonic modulation component. We confirmed in a very smooth way that ordinary Bessel functions of the first kind define envelopes tuning the intensities of the diffraction peaks. This applies not only to main reflections of the diffraction pattern but also to all satellites. In the second part, we discussed in details the similarities between harmonically modulated structures with multiple modulations and 1D model quasicrystal. The Fourier expansion of the nodes' positions in the Fibonacci chain gives direct numerical definition of the atomic arrangement in MS. In that sense, we can define 1D quasicrystal as a MS with infinite number of harmonic modulations. We prove that characteristic measures (like v(u) relation typical for statistical approach and diffraction pattern) calculated for MS asymptotically approach their counterparts for 1D quasicrystal as large enough number of modulation terms is taken into account.

Title:
The Effect of the Drop Tube Process for the Quasicrystal Fine Particles Formation
Authors:
Takeda, Y; Kawamura, T; Nagayama, K Author Full Names: Takeda, Yuya; Kawamura, Tadaharu; Nagayama, Katsuhisa
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 80 (4):273-279; 10.2320/jinstmet.JBW201506 2016
Abstract:
In general, quasicrystalline structures are produced by liquid quenching using a single roll, Bridgman and Czochralski method, which is typical for the production of single crystals. However, there are few reports of the quasicrystal formation using a containerless process; therefore, the effect of such a process is unclear. In this study, we have investigated the production of quasicrystalline fine particles and the formation ability of Al63Cu25Fe12, Al65Cu20Fe15, and Al70Ni15Co15 ternary alloys using a drop tube apparatus with a free fall length of 2.5 m. In addition, we have aimed to examine the effectiveness of the drop tube process for quasicrystal formation. The formation of dodecahedron crystals, which are considered a quasicrystalline phase, was observed in Al63Cu25Fe12 ternary fine particle samples prepared using the drop tube process under a He atmosphere (1 atm). Based on the heat flux, the calculated results suggested that the icosahedral phase was formed at high cooling rates of similar to 10(5) K/s. In the Al70Ni15Co15 ternary fine particle sample, aggregation of prismatic crystals was observed in the fine particle samples prepared using the drop tube process under an atmosphere of He (1 atm) and Ar (1 atm). Furthermore, formation of prismatic crystals was observed on the surface of fine particle samples prepared under a low-pressure Ar atmosphere (0.5 atm), under which the formation ability of quasicrystals was observed to be the highest. From these results, the formation ability of the Al-Ni-Co-based decagonal phase is suggested to increase with decreasing cooling rates. This result is different from that of the Al-Cu-Fe-based icosahedral quasicrystals.

Update: 27-May-2016


Title:
Self-consistent theory of nanodomain formation on nonpolar surfaces of ferroelectrics
Authors:
Morozovska, AN; Ievlev, AV; Obukhovskii, VV; Fomichov, Y; Varenyk, OV; Shur, VY; Kalinin, SV; Eliseev, EA Author Full Names: Morozovska, Anna N.; Ievlev, Anton V.; Obukhovskii, Vyacheslav V.; Fomichov, Yevhen; Varenyk, Oleksandr V.; Shur, Vladimir Ya.; Kalinin, Sergei V.; Eliseev, Eugene A.
Source:
PHYSICAL REVIEW B, 93 (16):10.1103/PhysRevB.93.165439 APR 28 2016
Abstract:
We propose a self-consistent theoretical approach capable of describing the features of the anisotropic nanodomain formation induced by a strongly inhomogeneous electric field of a charged scanning probe microscopy tip on nonpolar cuts of ferroelectrics. We obtained that a threshold field, previously regarded as an isotropic parameter, is an anisotropic function that is specified from the polar properties and lattice pinning anisotropy of a given ferroelectric in a self-consistent way. The proposed method for the calculation of the anisotropic threshold field is not material specific, thus the field should be anisotropic in all ferroelectrics with the spontaneous polarization anisotropy along the main crystallographic directions. The most evident examples are uniaxial ferroelectrics, layered ferroelectric perovskites, and low-symmetry incommensurate ferroelectrics. Obtained results quantitatively describe the differences at several times in the nanodomain length experimentally observed on X and Y cuts of LiNbO3 and can give insight into the anisotropic dynamics of nanoscale polarization reversal in strongly inhomogeneous electric fields.

Title:
Incommensurate spin correlations in highly oxidized cobaltates La2-xSrxCoO4
Authors:
Li, ZW; Drees, Y; Kuo, CY; Guo, H; Ricci, A; Lamago, D; Sobolev, O; Rutt, U; Gutowski, O; Pi, TW; Piovano, A; Schmidt, W; Mogare, K; Hu, Z; Tjeng, LH; Komarek, AC Author Full Names: Li, Z. W.; Drees, Y.; Kuo, C. Y.; Guo, H.; Ricci, A.; Lamago, D.; Sobolev, O.; Ruett, U.; Gutowski, O.; Pi, T. W.; Piovano, A.; Schmidt, W.; Mogare, K.; Hu, Z.; Tjeng, L. H.; Komarek, A. C.
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep25117 APR 27 2016
Abstract:
We observe quasi-static incommensurate magnetic peaks in neutron scattering experiments on layered cobalt oxides La2-xSrxCoO4 with high Co oxidation states that have been reported to be paramagnetic. This enables us to measure the magnetic excitations in this highly hole-doped incommensurate regime and compare our results with those found in the low-doped incommensurate regime that exhibit hourglass magnetic spectra. The hourglass shape of magnetic excitations completely disappears given a high Sr doping. Moreover, broad low-energy excitations are found, which are not centered at the incommensurate magnetic peak positions but around the quarter-integer values that are typically exhibited by excitations in the checkerboard charge ordered phase. Our findings suggest that the strong inter-site exchange interactions in the undoped islands are critical for the emergence of hourglass spectra in the incommensurate magnetic phases of La2-xSrxCoO4.

Title:
Electronic nature of the lock-in magnetic transition in CeXAl4Si2
Authors:
Gunasekera, J; Harriger, L; Dahal, A; Maurya, A; Heitmann, T; Disseler, SM; Thamizhavel, A; Dhar, S; Singh, DJ; Singh, DK Author Full Names: Gunasekera, J.; Harriger, L.; Dahal, A.; Maurya, A.; Heitmann, T.; Disseler, S. M.; Thamizhavel, A.; Dhar, S.; Singh, D. J.; Singh, D. K.
Source:
PHYSICAL REVIEW B, 93 (15):10.1103/PhysRevB.93.155151 APR 25 2016
Abstract:
We have investigated the underlying magnetism in newly discovered single crystal Kondo lattices CeXAl4Si2, where X = Rh, Ir. We show that the compound undergoes an incommensurate-to-commensurate magnetic transition at T-c = 9.19 K (10.75 K in Ir). The spin correlation in the incommensurate phase is described by a spin density wave configuration of Ce ions, which locks in to the long-range antiferromagnetic order at T = T-c. The analysis of the experimental data, combined with the calculation of the electronic properties, suggests the role of the Fermi surface nesting as the primary mechanism behind this phenomenon.

Title:
Direct imaging of coexisting ordered and frustrated sublattices in artificial ferromagnetic quasicrystals
Authors:
Farmer, B; Bhat, VS; Balk, A; Teipel, E; Smith, N; Unguris, J; Keavney, DJ; Hastings, JT; De Long, LE Author Full Names: Farmer, B.; Bhat, V. S.; Balk, A.; Teipel, E.; Smith, N.; Unguris, J.; Keavney, D. J.; Hastings, J. T.; De Long, L. E.
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134428 APR 25 2016
Abstract:
We have used scanning electron microscopy with polarization analysis and photoemission electron microscopy to image the two-dimensional magnetization of permalloy films patterned into Penrose P2 tilings (P2T). The interplay of exchange interactions in asymmetrically coordinated vertices and short-range dipole interactions among connected film segments stabilize magnetically ordered, spatially distinct sublattices that coexist with frustrated sublattices at room temperature. Numerical simulations that include long-range dipole interactions between sublattices agree with images of as-grown P2T samples and predict a magnetically ordered ground state for a two-dimensional quasicrystal lattice of classical Ising spins.

Title:
Confinement transition to density wave order in metallic doped spin liquids
Authors:
Patel, AA; Chowdhury, D; Allais, A; Sachdev, S Author Full Names: Patel, Aavishkar A.; Chowdhury, Debanjan; Allais, Andrea; Sachdev, Subir
Source:
PHYSICAL REVIEW B, 93 (16):10.1103/PhysRevB.93.165139 APR 25 2016
Abstract:
Insulating quantum spin liquids can undergo a confinement transition to a valence bond solid via the condensation of topological excitations of the associated gauge theory. We extend the theory of such transitions to fractionalized Fermi liquids (FL*): These are metallic doped spin liquids in which the Fermi surfaces only have gauge neutral quasiparticles. Using insights from a duality transform on a doped quantum dimer model for the U(1)-FL* state, we show that projective symmetry group of the theory of the topological excitations remains unmodified, but the Fermi surfaces can lead to additional frustrating interactions. We propose a theory for the confinement transition of Z2-FL* states via the condensation of visons. A variety of confining, incommensurate density wave states are possible, including some that are similar to the incommensurate d-form factor density wave order observed in several recent experiments on the cuprate superconductors.

Title:
Two Kinds of Contact Problems in Dodecagonal Quasicrystals of Point Group 12 mm
Authors:
Zhao, XF; Li, X; Ding, SH Author Full Names: Zhao, Xuefen; Li, Xing; Ding, Shenghu
Source:
ACTA MECHANICA SOLIDA SINICA, 29 (2):167-177; APR 2016
Abstract:
In this paper, two kinds of contact problems in 2-D dodecagonal quasicrystals were discussed using the complex variable function method: one is the finite frictional contact problem, the other is the adhesive contact problem. The analytic expressions of contact stresses in the phonon and phason fields were obtained for a flat rigid punch, which showed that: (1) for the finite frictional contact problem, the contact stress exhibited power-type singularities at the edge of the contact zone; (2) for the adhesive contact problem, the contact stress exhibited oscillatory singularities at the edge of the contact zone. The distribution regulation of contact stress under punch was illustrated; and the low friction property of quasicrystals was verified graphically.

Title:
Structure modulation, band structure, density of states and luminescent properties of columbite-type ZnNb2O6
Authors:
Zhao, D; Ma, FX; Zhang, RJ; Li, FF; Zhang, L; Yang, J; Fan, YC; Xin, X Author Full Names: Zhao, Dan; Ma, Fa-Xue; Zhang, Rui-Juan; Li, Fei-Fei; Zhang, Lei; Yang, Juan; Fan, Yun-Chang; Xin, Xia
Source:
CRYSTENGCOMM, 18 (16):2929-2936; 10.1039/c5ce01828e 2016
Abstract:
Zinc niobate ZnNb2O6, with a columbite-type structure, is a promising dielectric, photocatalytic and luminescent material, but the crystal structure has not been studied in detail. For the first time, we redetermined the crystal structure using single crystal X-ray diffraction and established the commensurately modulated structure model through high-dimensional formalism. The structure features a (3 + 1)-dimensional superspace group Pbcn(alpha 00)00s with the modulation vector q = 1/3a*. At the same time, calculations of the band structure and the density of states were performed using density functional theory to reveal the electronic origins of the optical transitions. In addition, the photoluminescent properties of ZnNb2O6 were studied, showing that a broad emission band at approximately 470 nm can achieve a high quantum efficiency of up to 64% with an optimal sintered temperature of 950 degrees C.

Update: 18-May-2016


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

Update: 12-May-2016


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

Update: 5-May-2016


Title:
Long-period modulated structure and electric-field-induced structural transformation in Na0.5Bi0.5TiO3-based lead-free piezoelectrics
Authors:
Khatua, DK; Senyshyn, A; Ranjan, R Author Full Names: Khatua, Dipak Kumar; Senyshyn, Anatoliy; Ranjan, Rajeev
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134106 APR 14 2016
Abstract:
Na0.5Bi0.5TiO3- based lead-free piezoelectrics exhibiting giant piezostrain are technologically interesting materials for actuator applications. The lack of clarity with regard to the structure of the nonpolar phase of this system has hindered the understanding of the structural mechanism associated with the giant piezostrain and other related phenomena. In this paper, we have investigated the structure and field-induced phase transformation behavior of a model system (0.94 - x) Na0.5Bi0.5TiO3-0.06BaTiO(3)-xK(0.5)Na(0.5)NbO(3) (0.0 <= x <= 0.025). A detailed structural analysis using neutron powder diffraction revealed that the nonpolar phase is neither cubic nor a mixture of rhombohedral (R3c) and tetragonal (P4bm) phases as commonly reported in literature but exhibits a long-period modulated structure, which is most probably of the type root 2 x root 2 x n with n = 16. Our results suggest that the giant piezoelectric strain is associated with a field-induced phase transformation of the long-period modulated structure to rhombohedral R3c structure above a critical field. We also demonstrate that the giant piezostrain is lost if the system retains a fraction of the field-induced R3c phase. A possible correlation among depolarization temperature, giant piezostrain, and its electrical fatigue behavior has also been indicated.

Title:
Temperature-dependent Fermi surface of the misfit cobaltite [Bi2Sr2O4](0.51)CoO2: A comparison with [Bi2Ba2O4](0.50)CoO2
Authors:
Takakura, S; Yamamoto, I; Koga, E; Ichikawa, F; Azuma, J; Maki, M Author Full Names: Takakura, Sho-ichi; Yamamoto, Isamu; Koga, Emi; Ichikawa, Fusao; Azuma, Junpei; Maki, Makoto
Source:
PHYSICAL REVIEW B, 93 (16):10.1103/PhysRevB.93.165118 APR 14 2016
Abstract:
Angle-resolved photoemission spectroscopy has been performed to investigate the Fermi surface (FS) and the electronic structure of misfit cobaltites, by comparing [Bi2Sr2O4](p)CoO2 with [Bi2Ba2O4](0.50)CoO2. In [Bi2Sr2O4](0.51)CoO2, we observed a suppression of spectral weight near the Fermi energy. Nevertheless, the FS can be mapped out by measuring the photoelectron intensity distribution. The FS size changes with temperature. Additionally, results show that the electronic band structure at a higher binding energy was changed by changing the sample temperature. Our results provide insight into the characteristics of the pseudogap state in the misfit-layered cobaltites. The unusual properties are probably related to the local deformations of the incommensurate structure.

Title:
Structure modulations in nonlinear optical (NLO) materials Cs2TB4O9 (T = Ge, Si)
Authors:
Zhou, ZY; Xu, X; Fei, R; Mao, JG; Sun, JL Author Full Names: Zhou, Zhengyang; Xu, Xiang; Fei, Rao; Mao, Jianggao; Sun, Junliang
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 194-200; 10.1107/S2052520615019733 2 APR 2016
Abstract:
Incommensurately modulated borate structures of a new type were studied in detail in the nonlinear optical (NLO) materials Cs2TB4O9 (T = Ge, Si) using single-crystal X-ray diffraction techniques. The structures were solved by the charge-flipping algorithm in the superspace group I2(alpha beta 0)0. The refinement results strongly suggest that the main structure modulation feature of Cs2TB4O9 is the ordering of the O atoms. With these modulated structure models, the unreasonable B-O distances in the average structures were explained as the ordering of BO4 and BO3.

Title:
Melilite-like modulation and temperature-dependent evolution in the framework structure of K2Sc[Si2O6]F
Authors:
Hejny, C; Kahlenberg, V; Eberhard, T; Kruger, H Author Full Names: Hejny, Clivia; Kahlenberg, Volker; Eberhard, Tim; Krueger, Hannes
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 209-222; 10.1107/S2052520615024865 2 APR 2016
Abstract:
The crystal structure of synthetic K2Sc[Si2O6] F has been solved and refined as an incommensurately modulated structure in (3 + 2)-dimensional superspace. This paper describes the tetragonal structure in the superspace group P4(2)/mnm(alpha, alpha,0) 000s(-alpha, alpha,0) 0000 [a = 8.9878 (1), c = 8.2694 (2) angstrom, V = 668.01 (2) angstrom(3)] with modulation wavevectors q(1) = 0.2982 (4)(a* + b*) and q(2) = 0.2982 (4)(-a* + b*). Structure refinement taking into account the modulation of positional and ADP parameters for all atoms from 3074 observed main hkl00 and satellite reflections hklmn of first order with single, m.n = 0, and mixed, m.n = +/- 1, indices converged to a final R value of 0.0514. The structure is a mixed octahedral-tetrahedral framework composed of [ScO4F2] octahedra, [Si4O12] rings and K in variable coordination. Due to the modulation the O atoms move into and out of the first coordination sphere of K leading to a minimum of five and a maximum of 10 interatomic K-O distances up to 3.1 angstrom Although this feature is comparable to observations in modulated fresnoite and melilite group compounds, these structures differ from K2Sc[Si2O6] F with respect to their topology. On temperature increase the intensity of the satellite reflections decreases until they disappear just above 443 K. The high-temperature normal structure, in space group P4(2)/mnm, is identical to the room-temperature average structure of K2Sc[Si2O6]F.

Update: 29-Apr-2016


Title:
Metastable phase formation in ternary Mg-Gd-Zn alloys
Authors:
Grobner, J; Zhu, SM; Nie, JF; Gibson, MA; Schmid-Fetzer, R Author Full Names: Groebner, Joachim; Zhu, Suming; Nie, Jian-Feng; Gibson, Mark A.; Schmid-Fetzer, Rainer
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 675 149-157; 10.1016/j.jallcom.2016.03.106 AUG 5 2016
Abstract:
Two metastable phases have been identified in as-cast Mg-rich Mg-Gd-Zn alloys by TEM characterization. The I-phase was found to have a composition close to Gd11Mg29Zn60 with an icosahedral structure (a(R) = 0.524 nm). The H2-phase, with a composition close to Gd16Mg14Zn70, was identified to have a hexagonal structure (a = 0.937 nm and c = 0.977 nm). An extension of the thermodynamic description of the ternary Mg-Gd-Zn phase diagram to incorporate the formation of these metastable phases has been modelled. Thermodynamic simulation of metastable phase formation has been conducted by suppressing the formation of more stable phases in a constrained Scheil solidification simulation to form I and H2 phases. The results of these solidification simulations are compared with reported as-cast alloy structures. Limiting values for the Gd/Zn atomic ratio, similar to< 0.55 and similar to> 1.4, are found to be crucial for phase selection. An application to Mg-Zn-Gd-Y alloys is discussed briefly. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Phenomenological Magnetic Model in Tsai-Type Approximants
Authors:
Sugimoto, T; Tohyama, T; Hiroto, T; Tamura, R Author Full Names: Sugimoto, Takanori; Tohyama, Takami; Hiroto, Takanobu; Tamura, Ryuji
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (5):10.7566/JPSJ.85.053701 MAY 15 2016
Abstract:
Motivated by the recent discovery of canted ferromagnetism in the Tsai-type approximants Au-Si-REs (RE = Tb, Dy, and Ho), we propose a phenomenological magnetic model reproducing their magnetic structure and thermodynamic quantities. In the model, the cubic symmetry (m (3) over bar) of the approximately regular icosahedra plays a key role in the peculiar magnetic structure determined by a neutron diffraction experiment. Our magnetic model does not only explain magnetic behaviors in the quasicrystal approximants, but also provides a good starting point for the possibility of the coexistence between the magnetic long-range order and the aperiodicity in quasicrystals.

Title:
Low temperature magneto-structural transitions in Mn3Ni20P6
Authors:
Cedervall, J; Beran, P; Vennstrom, M; Danielsson, T; Ronneteg, S; Hoglin, V; Lindell, D; Eriksson, O; Andre, G; Andersson, Y; Nordblad, P; Sahlberg, M Author Full Names: Cedervall, Johan; Beran, Premysl; Vennstrom, Marie; Danielsson, Therese; Ronneteg, Sabina; Hoglin, Viktor; Lindell, David; Eriksson, Olle; Andre, Gilles; Andersson, Yvonne; Nordblad, Per; Sahlberg, Martin
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 237 343-348; 10.1016/j.jssc.2016.02.028 MAY 2016
Abstract:
X-ray and neutron powder diffraction has been used to determine the crystal and magnetic structure of Mn3Ni20P6. The crystal structure can be described as cubic with space group Fm (3) over barm (225) without any nuclear phase transformation within studied temperature interval from room temperature down to 4 K. The magnetic structure of Mn3Ni20P6 is complex with two independent magnetic positions for the Mn atoms and the compound passes three successive magnetic phase transitions during cooling. At 30 K the spins of the Mn atoms on the Wyckoff 4a site (Mn1) order to form a primitive cubic anti ferromagnetic structure with propagation vector k=(0 0 1). Between 29 and 26 K the Mn atoms on the Wyckoff 8c site (Mn2) order independently on already ordered Mn1 magnetic structure forming a commensurate antiferromagnetic structure with propagation vector k= (0 0 1/2) and below 26 K, both Mn positions order to form an incommensurate helical structure with propagation vector k=(0 0 similar to 0.45). Magnetization vs. temperature curve of Mn3Ni20P6 shows a steep increase indicating some magnetic ordering below 230 K and a sharp field dependent anomaly in a narrow temperature range around 30 K. (C) 2016 Elsevier Inc. All rights reserved.

Title:
Europium and manganese magnetic ordering in EuMn2Ge2
Authors:
Ryan, DH; Rejali, R; Cadogan, JM; Flacau, R; Boyer, CD Author Full Names: Ryan, D. H.; Rejali, Rasa; Cadogan, J. M.; Flacau, R.; Boyer, C. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (16):10.1088/0953-8984/28/16/166003 APR 27 2016
Abstract:
The antiferromagnetic structures of both the manganese and europium sublattices in EuMn2Ge2 have been determined using thermal neutron diffraction. T-N(Mn) = 714(5) K with the 3.35(5) mu(B) (at 285 K) Mn moments ordering according to the I4 '/m ' m ' m space group. The Eu order is incommensurate with the 6.1(2) mu(B) (at 3.6 K) Eu moments oriented parallel to the c-axis with a propagation vector of k = [0.153(2) 0 0]. Both neutron diffraction and Eu-151 Mossbauer spectroscopy reveal evidence of magnetic short-range ordering of the Eu sublattice around and above T-N(Eu) similar to 10 K. The ordering temperature of the Eu sublattice is strongly affected by the sample's thermal history and rapid quenching from the melting point may lead to a complete suppression of that ordering.

Title:
Quantum diffusion of electrons in quasiperiodic and periodic approximant lattices in the rare earth-cadmium system
Authors:
Armstrong, NMR; Mortimer, KD; Kong, T; Bud'ko, SL; Canfield, PC; Basov, DN; Timusk, T Author Full Names: Armstrong, N. M. R.; Mortimer, K. D.; Kong, T.; Bud'ko, S. L.; Canfield, P. C.; Basov, D. N.; Timusk, T.
Source:
PHILOSOPHICAL MAGAZINE, 96 (11):1122-1130; 10.1080/14786435.2016.1150612 APR 12 2016
Abstract:
Icosahedral quasicrystals are characterised by the absence of a distinct Drude peak in their low-frequency optical conductivity and the same is true of their crystalline approximants. We have measured the optical conductivity of i-GdCd [GRAPHICS] , an icosahedral quasicrystal, and two approximants, GdCd [GRAPHICS] and YCd [GRAPHICS] . We find that there is a significant difference in the optical properties of these compounds. The approximants have a zero frequency peak, characteristic of a metal, whereas the quasicrystal has a striking minimum. This is the first example where the transport properties of a quasicrystal and its approximant differ in such a fundamental way. Using a generalised Drude model introduced by Mayou, we find that our data are well described by this model. It implies that the quantum diffusion of electron wave packets through the periodic and quasiperiodic lattices is responsible for these dramatic differences: in the approximants, the transport is superdiffusive, whereas the quasicrystals show subdiffusive motion of the electrons.

Title:
Electromagnons, magnons, and phonons in Eu1-xHoxMnO3
Authors:
Chen, ZY; Schmidt, M; Wang, Z; Mayr, F; Deisenhofer, J; Mukhin, AA; Balbashov, AM; Loidl, A Author Full Names: Chen, Zhenyu; Schmidt, M.; Wang, Zhe; Mayr, F.; Deisenhofer, J.; Mukhin, A. A.; Balbashov, A. M.; Loidl, A.
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134406 APR 6 2016
Abstract:
Here we present a detailed study of the terahertz and far-infrared response of the mixed perovskite manganite system Eu1-xHoxMnO3 for holmium concentrations x = 0.1 and 0.3. We compare the magnetic excitations of the four different magnetically ordered phases (A-type antiferromagnetic, sinusoidally modulated collinear, helical phases with spin planes perpendicular to the crystallographic a and c axes). The transition between the two latter phases goes hand in hand with a switching of the ferroelectric polarization from P parallel to a to P parallel to c. Special emphasis is paid to the temperature dependence of the excitations at this transition. We find a significant change of intensity indicating that the exchange-striction mechanism may not be the only mechanism to induce dipolar weight to spin-wave excitations. We also focus on excitations within the incommensurate collinear antiferromagnetic phase and find an excitation close to 40 cm(-1). A detailed analysis of optical weight gives a further unexpected result: In the multiferroic phase with P parallel to c all the spectral weight of the electromagnons comes from the lowest-phonon mode. However, for the phase with the polarization P parallel to a additional spectral weight must be transferred from higher frequencies.

Title:
Effect of platinum substitution on the structural and magnetic properties of Ni2MnGa ferromagnetic shape memory alloy
Authors:
Singh, S; D'Souza, SW; Nayak, J; Caron, L; Suard, E; Chadov, S; Felser, C Author Full Names: Singh, Sanjay; D'Souza, S. W.; Nayak, J.; Caron, L.; Suard, E.; Chadov, S.; Felser, C.
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134102 APR 6 2016
Abstract:
Ni2MnGa exhibits ideal ferromagnetic shape memory properties, however, brittleness and a low-temperature martensite transition hinder its technological applications motivating the search for novel materials showing better mechanical properties as well as higher transition temperatures. In this work, the crystal structure, phase transitions, and the magnetic properties of quaternary Ni2-x Pt-x MnGa(0 <= x <= 1) shape memory alloys were studied experimentally by x-ray diffraction, magnetization measurements, and neutron diffraction and compared to ab initio calculations. Compositions within 0 <= x <= 0.25 exhibit the cubic austenite phase at room temperature. The x approximate to 0.3 composition exhibits a seven-layer modulated monoclinic martensite structure. Within 0.4 <= x <= 1, the system stabilizes in the nonmodulated tetragonal structure. The martensite transition has very narrow thermal hysteresis 0 <= x <= 0.3, which is a typical characteristic of a shape memory alloy. By increasing x, the temperature of the martensite transition increases, while that of the magnetic transition decreases. The x = 1 composition (NiPtMnGa) in the martensite phase undergoes a para-to-ferrimagnetic transition. The saturation magnetization exhibits a nontrivial behavior with increasing up to x approximate to 0.25, above which, it suddenly decreases. Powder neutron diffraction reveals the presence of antisite disorder, with about 17% of the original Ga sites being occupied by Mn. Computations suggest that the antisite disorder triggers an antiferromagnetic coupling between two Mn atoms in different crystallographic positions, resulting into a sudden drop of the saturation magnetization for higher x.

Title:
Comparative study of the field-induced and spontaneous AF2 ' multiferroic phases in MnWO4 and Mn0.90Co0.10WO4 within the magnetic symmetry framework
Authors:
Urcelay-Olabarria, I; Garcia-Munoz, JL; Ressouche, E; Mukhin, AA; Skumryev, V Author Full Names: Urcelay-Olabarria, Irene; Luis Garcia-Munoz, Jose; Ressouche, Eric; Mukhin, Alexander A.; Skumryev, Vassil
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 520-527; 10.1107/S1600576716000881 2 APR 2016
Abstract:
(Mn,Co)WO4 compounds are regarded as reference spin-induced multiferroics. A comparative study is presented here, within the magnetic symmetry framework, of the incommensurate magnetic orders responsible for the ferroelectric phases of (i) MnWO4 under a magnetic field (H vertical bar vertical bar b) and (ii) Mn0.90Co0.10WO4 in the absence of an external field. On the one hand, although these two ferroelectric phases are stabilized under different external physical conditions, both present the same Xc1'(alpha 0 gamma)ss magnetic symmetry and practically the same modulation vector. The magnetic ordering in both phases is an elliptical helix with the magnetic moments (as the polarization vector, P) perpendicular to the b axis, although in most of the ferroelectric compositions of the (Mn,Co)WO4 family the spins rotate in planes containing b (and have P vertical bar vertical bar b). On the other hand, the anisotropy of the resulting magnetic modulations is extraordinarily different in the two phases. This is described and explained in the light of the different anisotropies of Co and Mn ions.

Title:
Structure determination of a pseudo-decagonal quasicrystal approximant by the strong-reflections approach and rotation electron diffraction
Authors:
Singh, D; Yun, YF; Wan, W; Grushko, B; Zou, XD; Hovmoller, S Author Full Names: Singh, Devinder; Yun, Yifeng; Wan, Wei; Grushko, Benjamin; Zou, Xiaodong; Hovmoller, Sven
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 433-441; 10.1107/S1600576716000042 2 APR 2016
Abstract:
The structure of a complicated pseudo-decagonal (PD) quasicrystal approximant in the Al-Co-Ni alloy system, denoted as PD1, was solved by the strong-reflections approach on three-dimensional rotation electron diffraction (RED) data, using the phases from the known PD2 structure. RED shows that the PD1 crystal is primitive and orthorhombic, with a = 37.3, b = 38.8, c = 8.2 angstrom. However, as with other approximants in the PD series, the superstructure reflections (corresponding to c = 8.2 angstrom) are much weaker than those of the main reflections (corresponding to c = 4.1 angstrom), so it was decided to solve the PD1 structure in the smaller primitive unit cell first, i.e. with unit-cell parameters a = 37.3, b = 38.8, c = 4.1 angstrom and space group Pnam. A density map of PD1 was calculated from only the 15 strongest unique reflections. It contained all 31 Co/Ni atoms and many weaker peaks corresponding to Al atoms. The structure obtained from the strong-reflections approach was confirmed by applying direct methods to the complete RED data set. Successive refinement using the RED data set resulted in 108 unique atoms (31 Co/Ni and 77 Al). This is one of the most complicated approximant structures ever solved by electron diffraction. As with other approximants in the PD series, PD1 is built of characteristic 2 nm wheel clusters with fivefold rotational symmetry, which agrees with results from high-resolution electron microscopy images. The simulated electron diffraction patterns for the structure model are in good agreement with the experimental electron diffraction patterns obtained by RED.

Title:
Jacques Friedel and the physics of metals and alloys
Authors:
Villain, J; Lavagna, M; Bruno, P Author Full Names: Villain, Jacques; Lavagna, Mireille; Bruno, Patrick
Source:
COMPTES RENDUS PHYSIQUE, 17 (3-4):276-290; 10.1016/j.crhy.2015.12.010 MAR-APR 2016
Abstract:
This is an introduction to the theoretical physics of metals for students and physicists from other specialities. Certain simple consequences of the Fermi statistics in pure metals are first addressed, namely the Peierls distortion, Kohn anomalies and the Labbe-Friedel distortion. Then the physics of dilute alloys is discussed. The analogy with nuclear collisions was a fruitful starting point, which suggested one should analyze the effects of impurities in terms of a scattering problem with the introduction of phase shifts. Starting from these concepts, Friedel derived a theory of the resistivity of alloys, and a celebrated sum rule relating the phase shifts at the Fermi level to the number of electrons in the impurity, which turned out to play a prominent role later in the context of correlated impurities, as for instance in the Kondo effect. Friedel oscillations are also an important result, related to incommensurate magnetic structures. It is shown how they can be derived in various ways: from collision theory, perturbation theory, self-consistent approximations and Green's function methods. While collision theory does not permit to take the crystal structure into account, which is responsible for electronic bands, those effects can be included in other descriptions, using for instance the tight binding approximation. (C) 2015 The Authors. Published by Elsevier Masson SAS on behalf of Academie des sciences.

Update: 22-Apr-2016


Title:
X-ray study of the anomalous thermal hystereses of the modulation wavevectors in Cs2HgCl4
Authors:
Bagautdinov, B; Shaw, Z; Orlov, A; Aliev, MA Author Full Names: Bagautdinov, Bagautdin; Shaw, Zachery; Orlov, Andrii; Aliev, Marat A.
Source:
PHASE TRANSITIONS, 89 (5):471-479; 10.1080/01411594.2015.1080258 MAY 3 2016
Abstract:
A rich sequence of structural modulations in Cs2HgCl4 as a function of temperature was studied by means of X-ray diffraction. Accurate satellite-position measurements on the cooling and heating paths of the crystal revealed abnormal thermal hystereses for incommensurate phases and coexistences of neighboring commensurate phases. A well-defined X-ray picture of the a-axis modulated phases in the range of 221-184K were observed on the heating path, while the c-axis modulated phases existing below 184K were definitely detected on the cooling path. The proper conditions for a precise phase diagram of Cs2HgCl4 can be correlated with relatively defect-free transformations of a-axis modulations at heating and of c-axis modulations at cooling. The peculiarity of Cs2HgCl4 to switch modulation direction among the a- and c-axes at 184K allows us deliberately accumulate and thus control a majority of mobile defects on the mutually perpendicular (100) or (001) planes by possessing crystal within temperature domain of a- or c-axes modulations, respectively.

Title:
Phase transformation behavior of Cu-10Ni-3Al-0.8Si alloy
Authors:
Shen, LN; Li, Z; Zhao, YY; Wang, Y; Dong, QY; Wang, MY Author Full Names: Shen, Leinuo; Li, Zhou; Zhao, Yuyuan; Wang, Yang; Dong, Qiyi; Wang, Mengying
Source:
MATERIALS CHEMISTRY AND PHYSICS, 173 421-428; 10.1016/j.matchemphys.2016.02.033 APR 15 2016
Abstract:
Microstructure evolution of solution treated Cu-10Ni-3Al-0.8Si alloy aged at different temperatures was investigated and different transformation products were observed: modulated structure resulting from spinodal decomposition, L1(2) ordering of matrix, continuous Ni3Al precipitates, continuous delta-Ni2Si precipitates and discontinuous precipitates. Modulated structure, L1(2) ordering of matrix and micro-twins formed initially at 450 degrees C, while continuous Ni3Al and delta-Ni2Si particles precipitated soon. Increasing temperature led to the formation of discontinuous precipitates, dissolution of Ni3Al and cellular decomposition. The alloy showed excellent over-aging resistance at 450 degrees C because the Ni3Al and delta-Ni2Si precipitates grew very slowly and the addition of silicon hindered the precipitation of the coarsening NiAl phase. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Interplay of charge density wave and multiband superconductivity in 2H-PdxTaSe2
Authors:
Bhoi, D; Khim, S; Nam, W; Lee, BS; Kim, C; Jeon, BG; Min, BH; Park, S; Kim, KH Author Full Names: Bhoi, D.; Khim, S.; Nam, W.; Lee, B. S.; Kim, Chanhee; Jeon, B. -G.; Min, B. H.; Park, S.; Kim, Kee Hoon
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep24068 APR 5 2016
Abstract:
2H-TaSe2 has been one of unique transition metal dichalcogenides exhibiting several phase transitions due to a delicate balance among competing electronic ground states. An unusual metallic state at high-T is sequentially followed by an incommensurate charge density wave (ICDW) state at approximate to 122 K and a commensurate charge density wave (CCDW) state at approximate to 90 K, and superconductivity at T-C similar to 0.14 K. Upon systematic intercalation of Pd ions into TaSe2, we find that CCDW order is destabilized more rapidly than ICDW to indicate a hidden quantum phase transition point at x similar to 0.09-0.10. Moreover, T-C shows a dramatic enhancement up to 3.3 K at x = 0.08, similar to 24 times of T-C in 2H-TaSe2, in proportional to the density of states N(E-F). Investigations of upper critical fields H-C2 in single crystals reveal evidences of multiband superconductivity as temperature-dependent anisotropy factor gamma(H) = H-C2(ab)/HHC2C, quasi-linear increase of H-C2(C) (T), and an upward, positive-curvature in H-C2(ab) (T) near T-C. Furthermore, analysis of temperature-dependent electronic specific heat corroborates the presence of multiple superconducting gaps. Based on above findings and electronic phase diagram vs x, we propose that the increase of N(E-F) and effective electron-phonon coupling in the vicinity of CDW quantum phase transition should be a key to the large enhancement of T-C in PdxTaSe2.

Title:
Synthesis and anisotropic properties of single crystalline Ln(2)Ru(3)Al(15+x) (Ln=Gd, Tb)
Authors:
Morrison, G; Prestigiacomo, J; Haldolaarachchige, N; Rai, BK; Young, DP; Stadler, S; Morosan, E; Chan, JY Author Full Names: Morrison, Gregory; Prestigiacomo, Joseph; Haldolaarachchige, Neel; Rai, Binod K.; Young, David P.; Stadler, Shane; Morosan, Emilia; Chan, Julia Y.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 236 186-194; SI 10.1016/j.jssc.2015.08.009 APR 2016
Abstract:
Single crystals of Ln(2)Ru(3)Al(15+x)(Ln=Gd, Tb) have been grown using the self-flux method under Ru-poor conditions. The structure of the Gd analog is found to be highly dependent on the synthesis method. Gd2Ru3Al15.08 orders antiferromagnetically at 17.5 K. Tb2Ru3Al15.05 enters an antiferromagnetic state at 16.6 K followed by a likely incommensurate-to-commensurate transition at 14.9 K for crystals oriented with HI lab. For crystals oriented with H//c, a broad maximum is observed in the temperature dependent M/H indicative of a highly anisotropic magnetic system with the hard axis in the c-direction. The magnetization as a function of field and magnetoresistance along the ab-direction of Tb2Ru3Al15.05 display a stepwise behavior and indicate strong crystalline electric field effects. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Crystal growth of incommensurate members of 2H-hexagonal perovskite related oxides: Ba4MzPt3-zO9 (M=Co, Ni, Cu, Zn, Mg, Pt)
Authors:
Ferreira, T; Morrison, G; Yeon, J; zur Loye, HC Author Full Names: Ferreira, Timothy; Morrison, Gregory; Yeon, Jeongho; zur Loye, Hans-Conrad
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 236 2-9; SI 10.1016/j.jssc.2015.10.040 APR 2016
Abstract:
Millimeter sized crystals of six oxides of approximate composition Ba4MzPt3-zO9 (M=Co, Ni, Cu, Zn, Mg, Pt) were grown from molten K2CO3 fluxes and found to crystallize in a 2H hexagonal perovskite-related structure type. The compositions of these incommensurate structures, which belong to the A(3n+3m)A'(n) B3m+nO9m+6n family of 2H hexagonal perovskite related oxides, were characterized by X-ray diffraction, energy dispersive spectroscopy, and magnetic susceptibility measurements. The specific synthetic considerations, crystal growth conditions, and magnetic susceptibility measurements are discussed. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Interplay between multiple charge-density waves and the relationship with superconductivity in PdxHoTe3
Authors:
Lou, R; Cai, YP; Liu, ZH; Qian, T; Zhao, LX; Li, Y; Liu, K; Han, ZQ; Zhang, DD; He, JB; Chen, GF; Ding, H; Wang, SC Author Full Names: Lou, Rui; Cai, Yipeng; Liu, Zhonghao; Qian, Tian; Zhao, Lingxiao; Li, Yu; Liu, Kai; Han, Zhiqing; Zhang, Dandan; He, Junbao; Chen, Genfu; Ding, Hong; Wang, Shancai
Source:
PHYSICAL REVIEW B, 93 (11):10.1103/PhysRevB.93.115133 MAR 21 2016
Abstract:
HoTe3, a member of the rare-earth tritelluride (RTe3) family, and its Pd-intercalated compounds, PdxHoTe3, where superconductivity (SC) sets in as the charge-density wave (CDW) transition is suppressed by the intercalation of a small amount of Pd, are investigated using angle-resolved photoemission spectroscopy (ARPES) and electrical resistivity. Two incommensurate CDWs with perpendicular nesting vectors are observed in HoTe3 at low temperatures. With a slight Pd intercalation (x = 0.01), the large CDW gap decreases and the small one increases. The momentum dependence of the gaps along the inner Fermi surface (FS) evolves from orthorhombicity to near tetragonality, manifesting the competition between two CDW orders. At x = 0.02, both CDW gaps decrease with the emergence of SC. Further increasing the content of Pd for x = 0.04 will completely suppress the CDW instabilities and give rise to the maximal SC order. The evolution of the electronic structures and electron-phonon couplings (EPCs) of the multiple CDWs upon Pd intercalation are carefully scrutinized. We discuss the interplay between multiple CDW orders, and the competition between CDW and SC in detail.

Update: 15-Apr-2016


Title:
Cycloid spirals and cycloid cone transition in the HoMn6-xCrxGe6 (T, x) magnetic phase diagramm by neutron diffraction
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Buschow, K. H. J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 408 233-243; 10.1016/j.jmmm.2016.02.018 JUN 15 2016
Abstract:
The structures and magnetic properties of the antiferromagnetic hexagonal pseudo ternary compounds HoMn6-xCrxGe6 (x=1, 1.5 and 2) are studied by neutron diffraction in the temperature range 1.5-300 K. The substitution of nonmagnetic Cr for Mn greatly affects the magnetic properties of HoMn6Ge6 by reducing the ordering temperature from 466 K to 278 K, 205 K and 130 K for (x=0, 1, 1.5 and 2) respectively, increasing the c/a ratio, suppressing the high temperature (HT) commensurate phase with q(2)=(0, 0, 1/2) and changing the high temperature (LT) q(1)=(0, 0, q(1z)) skew spiral rotation plane. HoMn5CrGe6 and HoMn4Cr2Ge6 display in the entire magnetically ordered regime cycloid spiral structures with the wave vector: q=(0, 0, q(z)), q(z) approximate to 0.18(3) r.l.u. and q(z) approximate to 64.8 degrees turn angle. The Ho and Mn/ Cr (001) layers have ferromagnetic arrangements coupled antiferromagnetically. The Ho moments in the z=0 layer are oriented in a direction opposite to the line bisecting the angle 2 phi(Mn) approximate to 2 x 28 degrees of the Mn layers at z = +/-similar to 0.25. This triple unit changes orientation collectively in the direction of q within the (b, c) plane containing the wave vector. Above 50 K, the wave vector length increases linearly from 0.24 to 0.28 (1) r.l.u. below T-N. The HT HoMn4.5Cr1.5Ge6 cycloid spiral, is stable in the range T-t < T < T-N (q(1)=(0,0,q(1z)), q(1z)=0.1711(3) r. I.u., Phi(s), =61.6 degrees at 40 K). At variance to the other compounds, crossing Try 36 K from above, it undergoes a first order magnetoelastic transition from a cycloid HT q(1) to a LT longitudinal cone structure: q(2)=(0, 0, q2z), q2z=0.149 r.l.u., Phi(s)=53.6 degrees and cone angle Phi(c)=47 degrees. The q(1) and q(2) phases coexist in the LT range down to 1.5 K <= T <= T-t in varying amounts with T. This transition is directly manifested by the splitting of the HT magnetic satellites and the increase of characteristic nuclear intensities. The results are summarised in a (T, x) magnetic phase diagram. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Neutron scattering studies of spin-phonon hybridization and superconducting spin gaps in the high-temperature superconductor La2-x(Sr, Ba)(x)CuO4
Authors:
Wagman, JJ; Carlo, JP; Gaudet, J; Van Gastel, G; Abernathy, DL; Stone, MB; Granroth, GE; Kolesnikov, AI; Savici, AT; Kim, YJ; Zhang, H; Ellis, D; Zhao, Y; Clark, L; Kallin, AB; Mazurek, E; Dabkowska, HA; Gaulin, BD Author Full Names: Wagman, J. J.; Carlo, J. P.; Gaudet, J.; Van Gastel, G.; Abernathy, D. L.; Stone, M. B.; Granroth, G. E.; Kolesnikov, A. I.; Savici, A. T.; Kim, Y. J.; Zhang, H.; Ellis, D.; Zhao, Y.; Clark, L.; Kallin, A. B.; Mazurek, E.; Dabkowska, H. A.; Gaulin, B. D.
Source:
PHYSICAL REVIEW B, 93 (9):10.1103/PhysRevB.93.094416 MAR 14 2016
Abstract:
We present time-of-flight neutron scattering measurements on single crystals of La2-xBaxCuO4 (LBCO) with 0 <= x <= 0.095 and La2-xSrxCuO4 (LSCO) with x = 0.08 and 0.11. This range of dopings spans much of the phase diagram relevant to high-temperature cuprate superconductivity, ranging from insulating, three-dimensional commensurate long-range antiferromagnetic order, for x <= 0.02, to two-dimensional (2D) incommensurate antiferromagnetism coexisting with superconductivity for x >= 0.05. Previous work on lightly doped LBCO with x = 0.035 showed a clear enhancement of the inelastic scattering coincident with the low-energy crossings of the highly dispersive spin excitations and quasi-2D optic phonons. The present work extends these measurements across the phase diagram and shows this enhancement to be a common feature to this family of layered quantum magnets. Furthermore, we show that the low-temperature, low-energy magnetic spectral weight is substantially larger for samples with nonsuperconducting ground states relative to any of the samples with superconducting ground states. Spin gaps, suppression of low-energy magnetic spectral weight as a function of decreasing temperature, are observed in both superconducting LBCO and LSCO samples, consistent with previous observations for superconducting LSCO.

Update: 7-Apr-2016


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

Update: 1-Apr-2016


Title:
Evidence of multiferroicity in NdMn2O5
Authors:
Chattopadhyay, S; Baledent, V; Damay, F; Gukasov, A; Moshopoulou, E; Auban-Senzier, P; Pasquier, C; Andre, G; Porcher, F; Elkaim, E; Doubrovsky, C; Greenblatt, M; Foury-Leylekian, P Author Full Names: Chattopadhyay, S.; Baledent, V.; Damay, F.; Gukasov, A.; Moshopoulou, E.; Auban-Senzier, P.; Pasquier, C.; Andre, G.; Porcher, F.; Elkaim, E.; Doubrovsky, C.; Greenblatt, M.; Foury-Leylekian, P.
Source:
PHYSICAL REVIEW B, 93 (10):10.1103/PhysRevB.93.104406 MAR 8 2016
Abstract:
Recently, RMn2O5 (R = rare earth, Bi, Y) type multiferroics have drawn considerable attention, because of magnetically induced ferroelectricity along with an extremely large magnetoelectric coupling. Here, we present a detailed study on NdMn2O5 which is a crucial composition between the nonferroelectric PrMn2O5 and ferroelectric SmMn2O5. We report the results of heat capacity, magnetization, dielectric permittivity, and electric polarization measurements along with an accurate description of the structural and microscopic magnetic properties obtained from high resolution x-ray and neutron diffraction studies. We show that NdMn2O5 is ferroelectric, although the magnitude of polarization is much weaker than that of the other multiferroic members. The direction of the polarization is along the crystallographic b axis and its magnitude can be tuned with the application of a magnetic field. Moreover, unlike the other multiferroic members of this series, ferroelectricity in NdMn2O5 emerges in an incommensurate magnetic state. The present study also provides evidence in support of the influence of the rare-earth size on the magnetoelectric phase diagram.

Title:
Thermally and Electrochemically Driven Topotactical Transformations in Sodium Layered Oxides NaxVO2
Authors:
Didier, C; Guignard, M; Suchomel, MR; Carlier, D; Darriet, J; Delmas, C Author Full Names: Didier, Christophe; Guignard, Marie; Suchomel, Matthew R.; Carlier, Dany; Darriet, Jacques; Delmas, Claude
Source:
CHEMISTRY OF MATERIALS, 28 (5):1462-1471; 10.1021/acs.chemmater.5b04882 MAR 8 2016
Abstract:
Phase diagrams and structural transformations in the complex NaxVO2 system have been studied using electrochemical (de)intercalation and in situ and operando high resolution synchrotron powder diffraction. Starting from O'3-Na1/2VO2 obtained by sodium electrochemical deintercalation of O'3-NaVO2, the structural details of irreversible and reversible thermally driven transformations to P'3 and P3 type structures are presented. Subsequently, these P'3-NaxVO(2) phases provide a platform for operando studies exploring the NaxVO2 phase diagram as a function of sodium electrochemical (de) intercalation. In this system, three single phase domains have been found: a line phase P'3-Na1/2VO2, one solid solution for 0.53 <= x <= 0.55 characterized by an incommensurate modulated structure, and a second solid solution for 0.63 <= x <= 0.65 with a defective structure resulting from a random stack of O'3 and P'3 layers. With further sodium intercalation (x > 0.65), the structure irreversibly transforms to the starting parent phase O3-NaVO2. This work reveals new details about the diverse structural polymorphs found in sodium layered oxides used as electrode battery materials and the transitional pathways between them as a function of temperature and composition.

Title:
Tailoring Magnetic Behavior in the Tb-Au-Si Quasicrystal Approximant System
Authors:
Gebresenbut, GH; Andersson, MS; Nordblad, P; Sahlberg, M; Gomez, CP Author Full Names: Gebresenbut, Girma H.; Andersson, Mikael S.; Nordblad, Per; Sahlberg, Martin; Gomez, Cesar Pay
Source:
INORGANIC CHEMISTRY, 55 (5):2001-2008; 10.1021/acs.inorgchem.5b02286 MAR 7 2016
Abstract:
A novel synthesis method, "arc-melting-self-flux", has been developed and a series of five Tsai-type 1/1 approximant crystals in the Tb-Au-Si system have been synthesized. The synthesis method, by employing a temperature program which oscillates near the melting and nucleation points of the approximants, has provided high-quality and large single crystals in comparison to those obtained from the standard arc-melting-annealing and self-flux methods. The atomic structures of the approximants have been determined from single-crystal X-ray diffraction data and described using concentric atomic clusters with icosahedral symmetry. The compounds are nearly isostructural with subtle variations; two types of atomic clusters which mainly vary at their cluster centers are observed. One type contains a Tb site at the center, and the other contains a disordered tetrahedron decorated with Au/Si mixed sites. Both cluster types can be found coexisting in the approximants. The compounds have different average weighted ratios of central Tb to disordered tetrahedron in the bulk material. Furthermore, a strategy for chemically tuning magnetic behavior is presented. Magnetic property measurements on the approximants revealed that the magnetic transition temperature (T-c) decreases as the occupancy of the central Tb site increases. T-c decreased from 11.5 K for 0% occupancy of the central Tb to 8 K for 100% occupancy. Enhanced magneto crystalline anisotropy is observed for the approximants with higher central Tb occupancy in comparison to their low central Tb occupancy counterparts. Hence, the previously reported "ferrimagnetic-like" magnetic structure model remains valid.

Title:
Athermal and deformation-induced omega-phase transformations in biomedical beta-type alloy Ti-9Cr-0.20
Authors:
Liu, HH; Niinomi, M; Nakai, M; Cho, K Author Full Names: Liu, Huihong; Niinomi, Mitsuo; Nakai, Masaaki; Cho, Ken
Source:
ACTA MATERIALIA, 106 162-170; 10.1016/j.actamat.2016.01.008 MAR 2016
Abstract:
The alloy Ti-9Cr-0.20 has been developed as a potential material for implant rods used in spinal fixation applications, since it exhibits good mechanical properties and a remarkably "changeable Young's modulus", which is achieved by suppressing the athermal omega-phase formed upon quenching and enhancing the deformation-induced omega-phase transformation. In this study, athermal and deformation induced omega-phase transformations in Ti-9Cr-0.20 were investigated systematically by transmission electron microscopy. This was done in order to understand the nature of these omega-phase transformations, as well as the specific functionality the "changeable Young's modulus" resulting from them. In solution-treated alloy samples, in addition to ideal omega-structures, structures considered as initial omega-structures associated with incommensurate omega-phase were observed. This might be attributed to the composition heterogeneity, heterogeneity of oxygen distribution, and/or the inhomogeneous distribution of defects such as vacancies and locally strained areas. Following cold rolling, some of the selected area electron diffraction patterns of the alloy showed that the reflections of one omega-variant had increased significantly in intensity while those of the other omega-variant had decreased sharply. This vanishing of one type of variant omega-structures is attributable to two possible mechanisms: (i) a reversal mechanism, under which the particular <111> partial dislocations transform the corresponding omega-variants back into beta-phase or (ii) a re-orientation mechanism, according to which the omega-variants unfavorable with regard to the loading direction re-orient and turn into the preferred omega-variants. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
SrPt2Al2 - A(3+2)D-incommensurately modulated variant of the CaBe2Ge2 type structure
Authors:
Hoffmann, RD; Stegemann, F; Janka, O Author Full Names: Hoffmann, Rolf-Dieter; Stegemann, Frank; Janka, Oliver
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (3):127-142; 10.1515/zkri-2015-1891 MAR 2016
Abstract:
The first ternary compound in the Sr-Pt-Al system, SrPt2Al2, was synthesized by melting of the elements in a sealed niobium tube in a high frequency furnace. The structure of SrPt2Al2 was determined by single-crystal X-ray diffraction on the basis of data sets recorded at 90, 150, 210, 270 and 300 K. The compound crystallizes in an incommensurately modulated (3+2)D structure being related to the tetragonal primitive CaBe2Ge2 type structure. The structure was refined in the orthorhombic superspace group Pmmn(alpha, 0,0) 0s0(0,beta,0) s00 (alpha = 0.222(1) a*, beta = 0.224(1) b*, a = b = 436.89(5), c = 1010.16(13) pm at 90 K) with R-M = 0.0403, R-S,R-1 = 0.0597 and R-S,R-2 = 0.2046. The structural relation with CaBe2Ge2 along with a refinement in the tetragonal superspace group P4/nmm(alpha, 0,0)-0000(0,alpha,0)00s0 is discussed with respect to the temperature dependence of the q-vectors and by group-subgroup relations. The modulation, from the standpoint of the crystal chemistry, is mainly caused by the distortion of the Pt arrangements within the pseudo-tetragonal ab plane.

Title:
The modulated structure of intermediate-valent CeCoGa
Authors:
Niehaus, O; Hoffmann, RD; Chevalier, B; Pottgen, R Author Full Names: Niehaus, Oliver; Hoffmann, Rolf-Dieter; Chevalier, Bernard; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (3):143-153; 10.1515/zkri-2015-1882 MAR 2016
Abstract:
CeCoGa was synthesized by melting of the elements in an arc-melting furnace as well as in a sealed niobium tube in an induction furnace. A further annealing step improves the purity and crystallinity of the samples significantly. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Already at room temperature CeCoGa crystallizes in a superstructure of the HT-CeCoAl type. This superstructure can be described in the (3 + 1)D superspace group C2/m(alpha 0 gamma) 00; alpha = 2/3, gamma = 1/3 with a temperature independent q-vector (Z = 4). For the 300 K data (also for 90 K) the commensurate *modulated structure* could be refined with 1336 F-2 values, 56 variables and residuals of wR = 0.0348 for the main and wR = 0.0605 for the satellites of 1st order [a = 1101.7(1), b = 436.0(1) and c = 482.4(1) pm, beta = 103.2(1)degrees]. Furthermore a description in a transformed 3D supercell with the space group C2/m and Z = 12 is possible. For the 90 K data this 3D supercell was refined with 1289 F-2 values, 56 variables and a residual of wR = 0.0409 [a = 1618.8(1), b = 435.3(1) and c = 1094.1(1) pm, beta = 119.3(1)degrees]. The relation of the HT-CeCoAl type structure, the (3 + 1)D modulated and the 3D supercell structure are discussed on the basis of a group-subgroup relation. By thermal analysis and magnetic measurements the phase transition temperature to the HT-CeCoAl type structure is stated slightly above 475 K. Furthermore intermediate cerium valence was identified by the magnetic susceptibility.

Title:
The estimation of phason flips in 1D quasicrystal from the diffraction pattern
Authors:
Buganski, I; Strzalka, R; Wolny, J Author Full Names: Buganski, Ireneusz; Strzalka, Radoslaw; Wolny, Janusz
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 253 (3):450-457; 10.1002/pssb.201552426 MAR 2016
Abstract:
The statistical approach based on the average unit-cell concept and the envelop functions for the diffraction pattern were used to estimate the number of phason flips in the model 1D quasicrystal (Fibonacci chain). The characteristic function of a statistical distribution expanded to a power series with distribution moments as coefficients can be used to retrieve phases of diffraction peaks. In addition, the number of flips in the structure can be designated in two ways: with the value of the second moment's value and directly from the shape of a probability density function retrieved from the diffraction pattern. In this paper, all calculations are performed for a nondecorated Fibonacci chain. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Title:
Schottky effect in the i-Zn-Ag-Sc-Tm icosahedral quasicrystal and its 1/1 Zn-Sc-Tm approximant
Authors:
Jazbec, S; Kashimoto, S; Kozelj, P; Vrtnik, S; Jagodic, M; Jaglicic, Z; Dolinsek, J Author Full Names: Jazbec, S.; Kashimoto, S.; Kozelj, P.; Vrtnik, S.; Jagodic, M.; Jaglicic, Z.; Dolinsek, J.
Source:
PHYSICAL REVIEW B, 93 (5):10.1103/PhysRevB.93.054208 FEB 23 2016
Abstract:
The analysis of low-temperature specific heat of rare-earth (RE)-containing quasicrystals and periodic approximants and consequent interpretation of their electronic properties in the T -> 0 limit is frequently hampered by the Schottky effect, where crystalline electric fields lift the degeneracy of the RE-ion Hund's rule ground state and introduce additional contribution to the specific heat. In this paper we study the low-temperature specific heat of a thulium-containing i-Zn-Ag-Sc-Tm icosahedral quasicrystal and its 1/1 Zn-Sc-Tm approximant, both being classified as "Schottky" systems. We have derived the crystal-field Hamiltonian for pentagonal symmetry of the crystalline electric field, pertinent to the class of Tsai-type icosahedral quasicrystals and their approximants, where the RE ions are located on fivefold axes of the icosahedral atomic cluster. Using the leading term of this Hamiltonian, we have calculated analytically the Schottky specific heat in the presence of an external magnetic field and made comparison to the experimental specific heat of the investigated quasicrystal and approximant. When the low-temperature specific heat C is analyzed in a C/T versus T-2 scale (as it is customarily done for metallic specimens), the Schottky specific heat yields an upturn in the T -> 0 limit that cannot be easily distinguished from a similar upturn produced by the electron-electron interactions in exchange-enhanced systems and strongly correlated systems. Our results show that extraction of the electronic properties of RE-containing quasicrystals from their low-temperature specific heat may be uncertain in the presence of the Schottky effect.

Title:
Mechanical and tribological properties of AlCuFe quasicrystal and Al(Si)CuFe approximant thin films
Authors:
Olsson, S; Broitman, E; Garbrecht, M; Birch, J; Hultman, L; Eriksson, F Author Full Names: Olsson, Simon; Broitman, Esteban; Garbrecht, Magnus; Birch, Jens; Hultman, Lars; Eriksson, Fredrik
Source:
JOURNAL OF MATERIALS RESEARCH, 31 (2):232-240; 10.1557/jmr.2015.384 JAN 28 2016
Abstract:
Multilayered thin films of Al/Cu/Fe have been prepared by magnetron sputtering and annealed into quasicrystalline and approximant phases on Al2O3 and Si substrates, respectively. The nanomechanical and nanotribological properties, such as hardness, elastic modulus, friction, and toughness, have been measured using a triboindenter and analytical methods. The approximant phase was proved to be slightly harder than the quasicrystalline phase with a hardness of about 15.6 GPa, and with a similar elastic modulus of about 258 GPa. These values however decreased rapidly with an increasing amount of Si in the approximant. The indentation toughness of the approximant, <0.1 MPa/m(1/2), was however inferior to that of the quasicrystals with 1.5 MPa/m(1/2). Friction coefficients were measured in a range of 0.10-0.14 for both the quasicrystalline and approximant thin films.

Update: 24-Mar-2016


Title:
Design and Synthesis of a Geopolymer-Enhanced Quasi-Crystalline Composite for Resisting Wear and Corrosion
Authors:
Ozaydin, MF; Liang, H Author Full Names: Ozaydin, M. Fevzi; Liang, Hong
Source:
JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, 138 (2):10.1115/1.4031400 APR 2016
Abstract:
Multiphase composites are attractive for improved mechanical performance and corrosion resistance. In this research, a new composite consisting quasi-crystalline Al75Mn14Si7Fe4 alloy of icosahedral, cubic alpha-AlMnSiFe, monoclinic Al13Fe4 phases, and ferro-silico-aluminate geopolymer was synthesized using rapid solidification and thermal treatment methods. The concentration of icosahedral phase (i-phase) was controlled and the formation of geopolymer was obtained through heat treatment. Characterization showed that the microhardness and wear resistance were increased with the amount of i-phase. The corrosion resistance, on the other hand, was improved with the existence of the geopolymer. This research demonstrates an effective approach in processing a multi-phase composite that has desired properties and performance through multiphase design and composition.

Title:
Coexistence of Incommensurate Magnetism and Superconductivity in the Two-Dimensional Hubbard Model
Authors:
Yamase, H; Eberlein, A; Metzner, W Author Full Names: Yamase, Hiroyuki; Eberlein, Andreas; Metzner, Walter
Source:
PHYSICAL REVIEW LETTERS, 116 (9):10.1103/PhysRevLett.116.096402 MAR 4 2016
Abstract:
We analyze the competition of magnetism and superconductivity in the two-dimensional Hubbard model with a moderate interaction strength, including the possibility of incommensurate spiral magnetic order. Using an unbiased renormalization group approach, we compute magnetic and superconducting order parameters in the ground state. In addition to previously established regions of Neel order coexisting with d-wave superconductivity, the calculations reveal further coexistence regions where superconductivity is accompanied by incommensurate magnetic order.

Title:
Evolution of the charge density wave superstructure in ZrTe3 under pressure
Authors:
Hoesch, M; Garbarino, G; Battaglia, C; Aebi, P; Berger, H Author Full Names: Hoesch, Moritz; Garbarino, Gaston; Battaglia, Corsin; Aebi, Philipp; Berger, Helmuth
Source:
PHYSICAL REVIEW B, 93 (12):10.1103/PhysRevB.93.125102 MAR 1 2016
Abstract:
The material ZrTe3 is a well-known example of an incommensurate periodic lattice distortion (PLD) at low temperatures due to a charge density wave (CDW). Previous studies have found a sharp boundary as a function of pressure between CDW below 5 GPa and bulk superconductivity above this value. We present a study of low-temperature-high-pressure single crystal x-ray diffraction along with ab initio density functional theory calculations. The modulation vector q(CDW) is found to change smoothly with pressure until the PLD is lost. Fermi surface calculations reproduce these changes, but neither these nor the experimental crystal lattice structure show a particular step change at 5 GPa, thus leading to the conclusion that the CDW is lost accidentally by tipping the balance of CDW formation in the Fermi surface nesting that stabilizes it.

Title:
Incommensurate spin-density-wave antiferromagnetism in CeRu2Al2B
Authors:
Bhattacharyya, A; Khalyavin, DD; Kruger, F; Adroja, DT; Strydom, AM; Kockelmann, WA; Hillier, AD Author Full Names: Bhattacharyya, A.; Khalyavin, D. D.; Krueger, F.; Adroja, D. T.; Strydom, A. M.; Kockelmann, W. A.; Hillier, A. D.
Source:
PHYSICAL REVIEW B, 93 (6):10.1103/PhysRevB.93.060410 FEB 29 2016
Abstract:
The newly discovered Ising-type ferromagnet CeRu2Al2B exhibits an additional phase transition at T-N = 14.2 K before entering the ferromagnetic ground state at T-C = 12.8 K. We clarify the nature of this transition through high resolution neutron diffraction measurements. The data reveal the presence of a longitudinal incommensurate spin-density wave (SDW) in the temperature range of T-C < T < T-N. The propagation vector q similar to (0,0,0.148) is nearly temperature independent in this region and discontinuously locks into q = 0 at T-C. Mean-field calculations of an effective Ising model indicate that the modulated SDW phase is stabilized by a strong competition between ferromagnetic and antiferromagnetic exchange interactions. This makes CeRu2Al2B a particularly attractive model system to study the global phase diagram of ferromagnetic heavy-fermion metals under the influence of magnetic frustration.

Update: 17-Mar-2016


Title:
The modulated structures of La2-xPrxO2MnSe2 (0 <= x <= 1) and La2-xNdxO2MnSe2 (0 <= x <= 0.6)
Authors:
Peschke, S; Johrendt, D Author Full Names: Peschke, Simon; Johrendt, Dirk
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (2):89-95; 10.1515/zkri-2015-1883 FEB 2016
Abstract:
The solid solutions La2-xPrxO2MnSe2 (0 <= x <= 1) and La2-xNdxO2MnSe2 (0 <= x <= 0.6) were synthesized in a NaI/KI flux between 800 and 900 degrees C. The selenide oxides adopt a ZrCuSiAs-related structure with modulated [MnSe2](2)(-)- layers which consist of a mixture of edge- and corner-sharing MnSe4/2-tetrahedra. The crystal structures are described with a (3+1)D model in superspace group Cmme(alpha 01/2)0s0. The modulation vector q can be-controlled by partial substitution of La3+ for Pr3+ and Nd3+ via the unit cell volume leading to, amongst others, (La0.55Pr0.45)(2)O2MnSe2 with alpha = 1/6, which allows the projection onto 3D space by using a simple sixfold a axis.

Title:
M2PO3N (M = Ca, Sr): ortho-Oxonitridophosphates with beta-K2SO4 Structure Type
Authors:
Marchuk, A; Schultz, P; Hoch, C; Oeckler, O; Schnick, W Author Full Names: Marchuk, Alexey; Schultz, Peter; Hoch, Constantin; Oeckler, Oliver; Schnick, Wolfgang
Source:
INORGANIC CHEMISTRY, 55 (2):974-982; 10.1021/acs.inorgchem.5b02647 JAN 18 2016
Abstract:
Two novel oxonitridophosphates M2PO3N with M = Ca and Sr were synthesized under high-pressure high-temperature (7 GPa and 1100 degrees C) using the multianvil technique or by solid-state reaction in the silica ampules (1100 degrees C) from amorphous phosphorus oxonitride (PON) and the respective alkaline earth oxides MO (M = Ca, Sr). The products represent the first examples of alkaline earth ortho-oxonitridophosphates containing noncondensed [PO3N](4-) ions. The crystal structures were elucidated by single-crystal X-ray diffraction. Sr2PO3N [space group Pnma (No. 62), Z = 4, a = 7.1519(5) angstrom, b = 5.5778(3) angstrom, c = 9.8132(7) angstrom, R1 = 0.020, wR2 = 0.047] crystallizes in the beta-K2SO4 structure type. The structure of Ca2PO3N was solved and refined in the (3 + 1)D superspace group Pnma(a00)0ss [Z = 4, a = 6.7942(7) angstrom, b = 5.4392(6) angstrom, c = 9.4158(11) angstrom, R1 = 0.041, wR2 = 0.067]. It exhibits an incommensurate modulation along [100] with a modulation vector q = [0.287(5), 0, 0]. Rietveld refinements support the structural models as well as the phase purity of the products. Upon doping with Eu2+, Ca2PO3N exhibits luminescence in the green range (lambda(em) = 525 nm) of the visible spectrum if excited by near-UV light (lambda(exc) = 400 nm).

Update: 11-Mar-2016


Title:
Incommensurate crystal supercell and polarization flop observed in the magnetoelectric ilmenite MnTiO3
Authors:
Silverstein, HJ; Skoropata, E; Sarte, PM; Mauws, C; Aczel, AA; Choi, ES; van Lierop, J; Wiebe, CR; Zhou, HD Author Full Names: Silverstein, Harlyn J.; Skoropata, Elizabeth; Sarte, Paul M.; Mauws, Cole; Aczel, Adam A.; Choi, Eun Sang; van Lierop, Johan; Wiebe, Christopher R.; Zhou, Haidong
Source:
PHYSICAL REVIEW B, 93 (5):10.1103/PhysRevB.93.054416 FEB 19 2016
Abstract:
MnTiO3 has been studied for many decades, but it was only in the last few years that its magnetoelectric behavior had been observed. Here, we use neutron scattering on two separately grown single crystals and two powder samples to show the presence of a supercell that breaks R (3) over bar symmetry. We also present the temperature and field dependence of the dielectric constant and pyroelectric current and show evidence of nonzero off-diagonal magnetoelectric tensor elements (forbidden by R (3) over bar symmetry) followed by a polarization flop accompanying the spin flop transition at mu H-0(SF) = 6.5T. Mossbauer spectroscopy on MnTiO3 gently doped with Fe-57 was used to help shed light on the impact of the supercell on the observed behavior. Although the full supercell structure could not be solved at this time due to a lack of visible reflections, the full scope of the results presented here suggest that the role of local spin-lattice coupling in the magnetoelectric properties of MnTiO3 is likely more important than previously thought.

Title:
Magnetic ordering in pressure-induced phases with giant spin-driven ferroelectricity in multiferroic TbMnO3
Authors:
Terada, N; Khalyavin, DD; Manuel, P; Osakabe, T; Kikkawa, A; Kitazawa, H Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Osakabe, Toyotaka; Kikkawa, Akiko; Kitazawa, Hideaki
Source:
PHYSICAL REVIEW B, 93 (8):10.1103/PhysRevB.93.081104 FEB 16 2016
Abstract:
In order to clarify the mechanism associated with pressure/magnetic-field-induced giant ferroelectric polarization in TbMnO3, this work investigated changes in magnetic ordering brought about by variations in temperature, magnetic field, and pressure. This was accomplished by means of neutron diffraction analyses under high pressures and high magnetic fields, employing a single crystal. The incommensurate magnetic ordering of a cycloid structure was found to be stable below the reported critical pressure of 4.5 GPa. In contrast, a commensurate E-type spin ordering of Mn spins and a noncollinear configuration of Tb spins with k = (0, 1/2,0) appeared above 4.5 GPa. The application of a magnetic field along the a axis (H-parallel to a) under pressure induces a k = (0,0,0) antiferromagnetic structure in the case of Tb spins above H-parallel to a, enhancing the ferroelectric polarization, while the E-type ordering of Mn spins is stable even above the critical field. From the present experimental findings, we conclude that the E-type ordering of Mn spins induces giant ferroelectric polarization through an exchange striction mechanism. The H-parallel to a-induced polarization enhancement can be understood by considering that the polarization, reduced by the polar ordering of Tb moments in a zero field, can be recovered through a field-induced change to nonpolar k = (0,0,0) ordering at H-parallel to a similar to 2 T.

Title:
Alumina nanowire growth by water decomposition and the peritectic reaction of decagonal Al65Cu15Co20 quasicrystals
Authors:
Tellez-Vazquez, JO; Patino-Carachure, C; Rosas, G Author Full Names: Tellez-Vazquez, J. O.; Patino-Carachure, C.; Rosas, G.
Source:
MATERIALS CHARACTERIZATION, 112 155-159; 10.1016/j.matchar.2015.12.023 FEB 2016
Abstract:
In this paper, the results of the Al2O3 nanowires' growth through a chemical reaction between Al and water vapor at 1050 degrees C are presented. Our approach is based on two primary considerations. First, at room temperature, the Al65Cu15Co20 alloy is affected by the following mechanism: 2AI (s) + 3H(2)O (g) -> Al2O3 (s) + H-2 (g). In this reaction, the released hydrogen induces cleavage fracture of the material to form small particles. Second, the Al65Cu15Co20 quasicrystalline phase is transformed on heating to liquid + Al (Cu, Co) cubic phase through a peritectic reaction at 1050 degrees C. The Al-rich liquid then reacts with water vapor, forming Al2O3 nanowires. X-ray diffraction (XRD) analysis shows that the formed nanowires have a hexagonal structure, and infrared analysis further confirms the presence of alpha-Al2O3 phase in the final products. Transmission electron microscopy observations show that nanoparticles are present at the end of nanowires, suggesting the VLS growth mechanism. Elemental analysis by energy dispersive spectroscopy (EDS) indicates that the particles at the tip of the nanowires are mainly formed by Co and Cu alloying elements and small amounts of Al. Electron microscopy observations showed nanowires with diameters ranging from 20 to 70 nm; the average diameter was 37 nm and the nanowire lengths were up to several micrometers. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Structure and reactivity with oxygen of Pr2NiO4+delta: an in situ synchrotron X-ray powder diffraction study
Authors:
Broux, T; Prestipino, C; Bahout, M; Paofai, S; Elkaim, E; Vibhu, V; Grenier, JC; Rougier, A; Bassat, JM; Hernandez, O Author Full Names: Broux, Thibault; Prestipino, Carmelo; Bahout, Mona; Paofai, Serge; Elkaim, Erik; Vibhu, Vaibhav; Grenier, Jean-Claude; Rougier, Aline; Bassat, Jean-Marc; Hernandez, Olivier
Source:
DALTON TRANSACTIONS, 45 (7):3024-3033; 10.1039/c5dt03482e 2016
Abstract:
The promising SOFC cathode material Pr2NiO4.22 has been studied in situ under a pure oxygen atmosphere from 25 to 950 degrees C by high resolution synchrotron X-ray powder diffraction. At room temperature (RT) delta = 0.22(1), the average crystal structure turns out to be monoclinic. The subtle monoclinic distortion (gamma = 90.066(1)degrees at RT), retained up to 460 degrees C, is interpreted in terms of specific tilt schemes of the NiO6 octahedra. It is also shown that Pr2NiO4.22 is incommensurately structurally modulated already at room temperature, in the same manner as the homologous cobaltate La2CoO4.14. The phase transition to the High Temperature Tetragonal (HTT) phase was completed at 480 degrees C without any evidence for the Low Temperature Orthorhombic (LTO) phase allowing clarifying the phase diagram of this K2NiF4-type ternary oxide. Moreover, it turns out that above 800 degrees C, the HTT phase transforms reversibly into two coexisting isomorphous tetragonal phases. The incommensurate modulation subsists up to 950 degrees C, although modified concomitantly with the two abovementioned phase transformations. In addition, the role of kinetics on the decomposition process is highlighted through thermo-gravimetric analyses.

Update: 3-Mar-2016


Title:
Analysis of modulated Ho2PdSi3 crystal structure at Pd K and Ho L absorption edges using resonant elastic X-scattering
Authors:
Nentwich, M; Zschornak, M; Richter, C; Novikov, D; Meyer, DC Author Full Names: Nentwich, Melanie; Zschornak, Matthias; Richter, Carsten; Novikov, Dmitri; Meyer, Dirk C.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (6):10.1088/0953-8984/28/6/066002 FEB 17 2016
Abstract:
Replacing Si atoms with a transition metal in rare earth disilicides results in a family of intermetallic compounds with a variety of complex magnetic phase transitions. In particular, the family R2PdSi3 shows interesting magnetic behavior arising from the electronic interaction of the R element with the transition metal in the Si network, inducing the specific structure of the related phase. Within this series, the highest degree of superstructural order was reported for the investigated representative Ho2PdSi3, although several competing superstructures have been proposed in literature. The diffraction anomalous fine structure (DAFS) method is highly sensitive to the local structure of chosen atoms at specific positions within the unit cell of a crystalline phase. In combination with x-ray absorption fine structure (XAFS), this sophisticated synchrotron method has been applied in the present work to several selected reflections, i.a. a satellite reflection. Extensive electronic modeling was used to test the most relevant structure proposals. The 2 x 2 x 8 superstructure has been strongly confirmed, although a small amount of disorder in the modulation is very probable.

Title:
Effect of LiH on electrochemical hydrogen storage properties of Ti55V10Ni35 quasicrystal
Authors:
Liu, DY; Zhao, Z; Luo, TH; Xing, C; Fei, L; Lin, J; Hou, JH; Jiang, DY; Liu, WQ; Wang, LM Author Full Names: Liu, Dongyan; Zhao, Zhen; Luo, Tianhao; Xing, Cheng; Fei, Liang; Lin, Jing; Hou, Jianhua; Jiang, Dayong; Liu, Wanqiang; Wang, Limin
Source:
SOLID STATE SCIENCES, 52 19-22; 10.1016/j.solidstatesciences.2015.12.002 FEB 2016
Abstract:
The electrochemical hydrogen storage properties and mechanisms of the Ti55V10Ni35 quasicrystal + xLiH(x = 3, 6 and 9 wt.%) system are investigated and discussed in this paper. A composite material in the Ti55V10Ni35 quasicrystal and system has been synthesized moderately by means of mechanical milling under an argon atmosphere, which can avoid reaction of releasing of hydrogen during the process of milling. The results indicate that the addition of LiH significantly improves the electrochemical characteristics of composite material. The maximum discharge capacity increases from 220.1 mAh/g to 292.3 mAh/g on Ti55V10Ni35 + 6 wt.% LiH, and the cycling stability is also enhanced too. In addition, the high rate dischargeability (HRD) is ameliorated remarkably, and the value of HRD value at 240 mA/g rises by 78.1%-87.8% for Ti55V10Ni35 + 6 wt.% LiH alloy electrodes. The improvement of characteristics of the electrochemical hydrogen storage characteristics may be attributed to LiH, which has excellent electrochemical activity. (C) 2015 Elsevier Masson SAS. All rights reserved.

Title:
Synthesis, structure, and magnetic characterization of Cr4US8
Authors:
Ward, MD; Chan, IY; Malliakas, CD; Lee, M; Choi, ES; Ibers, JA Author Full Names: Ward, Matthew D.; Chan, Ian Y.; Malliakas, Christos D.; Lee, Minseong; Choi, Eun Sang; Ibers, James A.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 233 67-74; 10.1016/j.jssc.2015.10.009 JAN 2016
Abstract:
The compound Cr4US8 has been synthesized at 1073 K and its crystal structure has been determined at 100 K. The structure is modulated with a two-fold commensurate supercell. The subcell may be indexed in an orthorhombic cell but weak supercell reflections lead to the monoclinic superspace group P2(1)/c (0 alpha gamma)0s with two Cr sites, one U site, and four S sites. The structure comprises a three-dimensional framework of CrS6 octahedra with channels that are partially occupied by U atoms. Each U atom in these channels is coordinated by eight S atoms in a bicapped trigonal-prismatic arrangement. The magnetic behavior of Cr4US8 is complex. At temperatures above similar to 120 K at all measured fields, there is little difference between field-cooled and zero field-cooled data and chi(T) decreases monotonously with temperature, which is reminiscent of the Curie-Weiss law. At lower temperatures, the temperature dependence of chi(T) is complex and strongly dependent on the magnetic field strength. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Electronic transport in polycrystalline samples of icosahedral phases
Authors:
Vekilov, YK; Chernikov, MA; Dolinichek, Y Author Full Names: Vekilov, Yu. Kh.; Chernikov, M. A.; Dolinichek, Ya.
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 117 (1):16-21; 10.1134/S0031918X15110113 JAN 2016
Abstract:
The low-temperature electronic transport in polycrystals of quasicrystalline phases with an icosahedral structure has been analyzed within the model of the granular electronic system. In this model, the grains (drops) of a metallic icosahedral phase are surrounded by extended defects and grain boundaries, which create an insulating environment. The electron transport in this model is determined by the size quantization of electronic states inside metallic grains, by intergranular tunneling, and by electrostatic barriers. Depending on the temperature and structural state of the system, the hopping conductivity with variable lengths of jumps in the Efros-Shklovskii or Mott regime is observed with predominantly elastic cotunneling. In the case of strong intergranular coupling, the system passes into the metallic regime with the exponential temperature dependence of the electrical conductivity.

Update: 25-Feb-2016


Title:
From an electron micrograph to a postage stamp
Authors:
Hargittai, I Author Full Names: Hargittai, Istvan
Source:
STRUCTURAL CHEMISTRY, 27 (1):5-7; SI 10.1007/s11224-015-0629-1 FEB 2016
Abstract:
Soon following Dan Shechtman's discovery of quasicrystals, Agnes Csanady and her associates started producing beautiful quasicrystals of flowerlike morphology. The image of one of their specimen appeared on the Israeli postage stamp honoring Shechtman's discovery, his Nobel Prize, and the International Year of Crystallography.

Title:
Ultrafast resonant soft x-ray diffraction dynamics of the charge density wave in TbTe3
Authors:
Moore, RG; Lee, WS; Kirchman, PS; Chuang, YD; Kemper, AF; Trigo, M; Patthey, L; Lu, DH; Krupin, O; Yi, M; Reis, DA; Doering, D; Denes, P; Schlotter, WF; Turner, JJ; Hays, G; Hering, P; Benson, T; Chu, JH; Devereaux, TP; Fisher, IR; Hussain, Z; Shen, ZX Author Full Names: Moore, R. G.; Lee, W. S.; Kirchman, P. S.; Chuang, Y. D.; Kemper, A. F.; Trigo, M.; Patthey, L.; Lu, D. H.; Krupin, O.; Yi, M.; Reis, D. A.; Doering, D.; Denes, P.; Schlotter, W. F.; Turner, J. J.; Hays, G.; Hering, P.; Benson, T.; Chu, J. -H.; Devereaux, T. P.; Fisher, I. R.; Hussain, Z.; Shen, Z. -X.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.024304 JAN 25 2016
Abstract:
Understanding the emergence of collective behavior in correlated electron systems remains at the forefront of modern condensed matter physics. Disentangling the degrees of freedom responsible for collective behavior can lead to insights into the microscopic origins of emergent properties and phase transitions. Utilizing an optical pump, resonant soft x-ray diffraction probe we are able to track, in real time, the dynamics of the charge density wave (CDW) in TbTe3, a model system that violates traditional views of a Fermi surface nested CDW. We observe coherent oscillations corresponding to the CDW amplitude mode at 2.4 THz and a coherent optical phonon mode at similar to 1.7 THz. We show how such observations reveal the anisotropic energy optimization between in-plane Te charge density modulations and the three-dimensional lattice coupling.

Title:
Ti-V-Ni with graphene-mixing icosahedral quasicrystalline composites: Preparation, structure and its application in Ni-MH rechargeable batteries
Authors:
Lin, J; Lu, C; Sun, LS; Liang, F; Cao, ZY; Wang, LM Author Full Names: Lin, Jing; Lu, Chong; Sun, Lianshan; Liang, Fei; Cao, Zhanyi; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 41 (2):1098-1103; 10.1016/j.ijhydene.2015.11.067 JAN 12 2016
Abstract:
The Ti-V-Niquasicrystalline was prepared by arc-melting and subsequent melt-spinning technique, and the Ti1.4V0.6Ni + x graphene (x = 3, 5, 7, 10 and 13, wt%) composites were obtained by mechanical ball-milling method. The structures and electrochemical hydrogen storage properties of the composites were investigated. The results showed that, the structures of the composites contained icosahedral quasicrystal, Ti2Ni-type, NiTi and graphene phases. The electrochemical hydrogen storage properties of the composites were improved with graphene addition. The cycling stabilities after 50 charging/discharging cycles of Ti1.4V0.6Ni + x graphene composites were improved obviously, especially the Ti1.4V0.6Ni + 10 graphene composite showed the best cycling stability of 70.3%, increased by 6.5%, compared with the Ti1.4V0.6Ni electrode. The high-rate discharge abilities of the composites were also increased appreciably. The improvement in the hydrogen storage characteristics should own to the proper graphene addition and that could cause copacetic electrocatalytic activity and anti-corrosion ability. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Title:
Orientation Relations and Conversion Matrix Between M3 Supercell and Pseudohexagonal Subcell in Tricalcium Silicate Solid Solution
Authors:
Min, HH; Xu, F; Lu, YN; Yang, J; Ding, LF; Su, F; Zhu, JM Author Full Names: Min Hui-Hua; Xu Feng; Lu Yi-Nong; Yang Jing; Ding Lin-Fei; Su Fan; Zhu Jian-Min
Source:
CHINESE JOURNAL OF INORGANIC CHEMISTRY, 32 (1):145-152; JAN 10 2016
Abstract:
A M3 modification of tricalcium silicate (C3S) solid solution was investigated using transmission electron microscope (TEM). Selected area electron diffraction (SAED) patterns and high resolution transmission electron microscopy (HRTEM) images were analyzed based on a pseudohexagonal subcell (Space group R3m; a=0.705 9 nm, b=0.705 5 nm, c=2.492 4 nm, alpha=89.79 degrees,beta=90.04 degrees, gamma=120.14 degrees). Reflections caused by the superstructure were proven to occur along the modulation wave vector [(1) over bar .17](H)(*) with one-dimensional type and could be expressed as ha+kb+lc*+m/[6(-a+b+7C*)], where m=+/- 1,+/- 2 and +/- 3. SAED patterns and HRTEM images based on the M3 supercell (Space group Cm; a=3.310 8 nm, b=0.703 6 nm, c=1.852 1 nm, beta=94.137 degrees) were simulated and finally the orientation relations between M3 supercell and pseudohexagonal subcell were established as follows: (600)(M3), (020)(M3) and (006)(M3) were equivalent to ((1) over bar1 (2) over bar)(H), ((1) over bar(1) over bar0)(H) and ((1) over bar 17)(H)* respectively, and [100](M3)//[(7) over bar7 (2) over bar](H), [010](M3)// [(1) over bar(1) over bar0](H), and [001](M3)//[(1) over bar 11](H): Furthermore, the conversion matrix between M3 supercell and pseudohexagonal subcell was established.

Title:
Soft spherical nanostructures with a dodecagonal quasicrystal-like order
Authors:
Rochal, SB; Konevtsova, OV; Shevchenko, IA; Lorman, VL Author Full Names: Rochal, S. B.; Konevtsova, O. V.; Shevchenko, I. A.; Lorman, V. L.
Source:
SOFT MATTER, 12 (4):1238-1247; 10.1039/c5sm02265g 2016
Abstract:
We develop a theory which predicts curvature-related structural peculiarities of soft spherical nanostructures with a dodecagonal local arrangement of subunits. Spherical templates coated with a thin film of a soft quasicrystal (QC)-forming material constitute the most promising direction to realize these nanostructures. Disordered and perfect spherical nanostructures are simulated using two approaches. The first of them models a random QC-like spherical nanostructure with extended curvature-induced topological defects similar to scars in colloidal spherical crystals. The second approach is inspired by the physics of viral capsids. It deals with the most regular spherical nanostructures with a local QC-like order derived from three well-known planar dodecagonal tilings. We explain how the additional QC-like degrees of freedom assist the nanostructure stabilization and determine the point defect number and location without extended scar formation. Unusual for nanoassemblies snub cube geometry is shown to be the most energetically favorable global organization of these spherical QC nanostructures.

Title:
Thermal conductivity of solid thiophene in an incommensurate orientational state
Authors:
Korolyuk, OA; Krivchikov, AI; Vdovichenko, GA; Romantsova, OO; Horbatenko, YV Author Full Names: Korolyuk, O. A.; Krivchikov, A. I.; Vdovichenko, G. A.; Romantsova, O. O.; Horbatenko, Yu. V.
Source:
LOW TEMPERATURE PHYSICS, 42 (1):68-73; 10.1063/1.4940993 JAN 2016
Abstract:
The thermal conductivity of solid thiophene at equilibrium vapor pressure between 2K < T < 170K, has been measured in a sequence of incommensurate metastable orientationally disordered phases II, II1, II2, and II2g with different degrees of orientational ordering of the molecules. It is found that in phase states II, II1 and II2 with dynamic orientational disorder of the molecules, the thermal conductivity does not depend on the temperature. It is shown that the temperature dependence of the thermal conductivity kappa(T) of orientational glass V-g and II2g (incommensurate) does not have any of the anomalies that are typical for amorphous materials and glasses. The temperature dependence kappa(T) of the incommensurate state of orientational glass II2g is bell-shaped, which is typical for the thermal conductivity of crystals with long-range orientational order. In the II2g state, as temperature drops from T-g to almost 10K, the thermal conductivity increases according to kappa(T) = A/T + B, where the first term describes the input of the propagating phonons, wherein the average length of their mean free path is greater than half of the phonon wavelength. The B term is associated with the input of localized short-wave, or "diffuse" vibrational modes. At low temperatures T <= 7K, kappa(T) proportional to T-3 is observed with increasing temperatures, which corresponds to the boundary scattering of phonons. (C) 2016 AIP Publishing LLC.

Title:
Synthesis of quasi-crystalline phases in the Al-Cu-Fe-Cr system
Authors:
Chugunov, DB; Meshkov, LL; Kalmykov, KB; Osipov, AK Author Full Names: Chugunov, D. B.; Meshkov, L. L.; Kalmykov, K. B.; Osipov, A. K.
Source:
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY, 61 (1):11-17; 10.1134/S003602361601006X JAN 2016
Abstract:
Phase equilibria in the Al-Cu-Fe system alloyed with 5% Cr were studied. Based on the data of X-ray powder diffraction analysis, electron microscopy, and differential thermal analysis, the effect of temperature on i a double dagger" d phase transitions in alloys Al65Cu25Fe5Cr5 and Al70Cu20Fe5Cr5. In the Al-Cu-Fe-Cr system, multiphase structures were detected; these structures are mixtures of quasi-crystalline and approximant phases, the contents and morphologies of which depend on the composition of the initial mixture and the crystallization rate.

Title:
STRUCTURE AND MECHANICAL PROPERTIES OF QUASICRYSTALLINE AND APPROXIMANT PHASES OBTAINED FROM TITANIUM-BASED QUINARY ALLOY
Authors:
Firstov, SA; Gorban', VF; Karpets, MV; Krapivka, NA; Danilenko, NI; Pechkovskii, EP; Rokitskaya, EA Author Full Names: Firstov, S. A.; Gorban', V. F.; Karpets, M. V.; Krapivka, N. A.; Danilenko, N. I.; Pechkovskii, E. P.; Rokitskaya, E. A.
Source:
STRENGTH OF MATERIALS, 47 (6):781-788; 10.1007/s11223-015-9714-3 NOV 2015
Abstract:
The paper presents the investigation of influence of cooling rate and conditions of melt crystallization on the change in phase composition and physical and mechanical properties of alloy Ti60Cr30Al3Si2(SiO2)(5). The influence of thermal treatment on the stability and properties of quasicrystalline and approximant phases is studied. Using the method of high-temperature indentation it is found that the diffusive mechanism of plastic strain of the alloy is strongly observed at 800 degrees C (0.68T(m)).

Update: 18-Feb-2016


Title:
Structural and electrocaloric properties of multiferroic-BiFeO3 doped 0.94Bi(0.5)Na(0.5)TiO(3)-0.06BaTiO(3) solid solutions
Authors:
Zheng, GP; Uddin, S; Zheng, XC; Yang, JH Author Full Names: Zheng, Guang-Ping; Uddin, Sarir; Zheng, Xiucheng; Yang, Junhe
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 663 249-255; 10.1016/j.jallcom.2015.12.056 APR 5 2016
Abstract:
Single-phase (1-x)(0.94Bi(0.5)Na(0.5)TiO(3)-0.06BaTiO(3))-xBiFeO(3) (BNT-BT-xBF, x = 0.05, 0.1 and 0.15) solid solutions are fabricated using a modified citrate method. The structural, ferroelectric and electrocaloric properties are significantly affected by the multiferroic BiFe03 doping, which is found to favor the antiferroelectric (AFE) state of the solid solutions. The dynamic mechanical analysis suggests that the BiFeO3 induced ordering of oxygen octahedrons plays a dominant role in the formation of AFE incommensurate phases and leads to the enhanced negative electrocaloric effect (ECE). A maximum ECE temperature change of 1.65 degrees C under an applied field of 70 kV/cm is observed. It is suggested that the magnetoelectric coupling is effective in enhancing the negative ECE in BNT-BT-xBF. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Indirect assessment of the surface energy of the Al-Cu-Fe quasicrystal
Authors:
de Lima, DCG; Dos Passos, TA; de Weerd, MC; Kenzari, S; Medeiros, RG; de Lima, SJG; Dubois, JM Author Full Names: Guedes de Lima, Danielle Cavalcante; Dos Passos, Tiberio Andrade; de Weerd, Marie-Cecile; Kenzari, Samuel; Medeiros, Rodinei Gomes; Guedes de Lima, Severino Jackson; Dubois, Jean-Marie
Source:
JOURNAL OF MATERIALS SCIENCE, 51 (8):4070-4078; 10.1007/s10853-016-9728-7 APR 2016
Abstract:
This work summarizes an attempt to estimate the surface energy of the stable, icosahedral Al-Cu-Fe quasicrystal (i-ACF hereafter). To this end, samples of i-ACF were prepared by sintering a powder produced by ball milling and heat treating a master ingot of composition Al59Cu25.5Fe12.5B3 (at.%), icosahedral lattice structure, and containing negligibly small amounts of contaminating crystalline phases. This powder was then sintered in the shape of a cylinder appropriate for pin-on-disk tests in ambient air. Variable amounts of either Sn or Bi were added to the powder prior to sintering. These elements do not dissolve in the quasicrystal and form small pockets of pure Sn or Bi that are either isolated or percolating, depending on the added volume of metal. Analysis of pin-on-disk data deduced from tests performed at room temperature allows us to conclude that the surface energy of the quasicrystal itself falls between the respective surface energies of the pure metals: gamma(Bi) a parts per thousand currency sign gamma(QC) a parts per thousand currency sign gamma(Sn) or 0.5 a parts per thousand currency sign gamma(i-ACF) a parts per thousand currency sign 0.8 J/m(2).

Title:
Flexoelectricity, incommensurate phases and the Lifshitz point
Authors:
Pottker, H; Salje, EKH Author Full Names: Poettker, Henning; Salje, Ekhard K. H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (7):10.1088/0953-8984/28/7/075902 FEB 24 2016
Abstract:
The solutions for the minimizers of the energy density f(q, p) = Aq(2) + Bq(4) + p(2) + g(A,B) + beta(q'p-p'q) + vertical bar q'vertical bar(2) + k vertical bar p'vertical bar(2) describe the flexoelectric effect with a flexoelectric coupling coefficient beta. The order parameters q and p can be visualized as strain and polarisation, respectively. The parameter k denotes the ratio of intrinsic length scales for q and p. We show that the structural ground-states include 3 phases, namely the paraelastic state q = p = 0, the ferroelastic state where polarization exists inside and near twin boundaries, and the incommensurate (modulated) phases with a very rich array of structural modulations ranging from nearly pure sine waves to kink arrays and ripple states. The phases coincide in the multicritical Lifshitz point. Linear flexoelectricity p similar to q' is encountered only approximately inside the ferroelastic phase and near the phase boundary between the paraelastic phase and the incommensurate phase. The relationship between the polarisation and the strain gradient is highly non-linear in all other states. The spatial profiles and energy distributions are discussed in detail.

Title:
Muon-spin relaxation study of the double perovskite insulators Sr2BOsO6 (B = Fe, Y, In)
Authors:
Williams, RC; Xiao, F; Thomas, IO; Clark, SJ; Lancaster, T; Cornish, GA; Blundell, SJ; Hayes, W; Paul, AK; Felser, C; Jansen, M Author Full Names: Williams, R. C.; Xiao, F.; Thomas, I. O.; Clark, S. J.; Lancaster, T.; Cornish, G. A.; Blundell, S. J.; Hayes, W.; Paul, A. K.; Felser, C.; Jansen, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (7):10.1088/0953-8984/28/7/076001 FEB 24 2016
Abstract:
We present the results of zero-field muon-spin relaxation measurements made on the double perovskite insulators Sr2BOsO6 (B = Fe, Y, In). Spontaneous muon-spin precession indicative of quasistatic long range magnetic ordering is observed in Sr2FeOsO6 within the AF1 antiferromagnetic phase for temperatures below T-N = 135 +/- 2 K. Upon cooling below T-2 approximate to 67 K the oscillations cease to be resolvable owing to the coexistence of the AF1 and AF2 phases, which leads to a broader range of internal magnetic fields. Using density functional calculations we identify a candidate muon stopping site within the unit cell, which dipole field simulations show to be consistent with the proposed magnetic structure. The possibility of incommensurate magnetic ordering is discussed for temperatures below T-N = 53 K and 25 K for Sr2YOsO6 and Sr2InOsO6, respectively.

Title:
B-cation effect on relaxor behavior and electric properties in Sr2NaNb5-xSbxO15 tungsten bronze ceramics
Authors:
Fan, JY; Yang, B; Wei, LL; Wang, ZM Author Full Names: Fan, Jianyong; Yang, Bian; Wei, Lingling; Wang, Zhongming
Source:
CERAMICS INTERNATIONAL, 42 (3):4054-4062; 10.1016/j.ceramint.2015.11.077 FEB 15 2016
Abstract:
Sr2NaNb5-xSbxO15 ceramics (SNNS, x=0.0, 0.3, 0.5, 1.0) with 'filled' tungsten bronze structure were prepared by the conventional solid-state reaction method. Effects of introducing Sb concentration in B-sites on the microstructure, dielectric and ferroelectric properties were investigated in detail. With increasing of Sb concentration, the crystal structure of SNNS ceramics distorted slightly from the TB orthorhombic Ccm2 phase to tetragonal P4bm phase, and then to paraelectric P4/mbm phase at room temperature. The smaller ionic radius of Sb5+ (0.60 angstrom) compared with that of Nb5+ (0.64 angstrom) contributed to the shrinkage of crystal structure. It was found that accompanying with the introduction of Sb, some unique dielectric and ferroelectric behavior emerged for SNNS ceramics. Only the samples with x < 0.5 showed additional dielectric anomaly in low temperature range, which was attributed to the incommensurate superstructure ICS-associated dielectric dispersion process caused by local structural fluctuation. With increasing of Sb concentration, T-c shifted to lower temperatures, and the diffuse phase transition and relaxor behavior appeared to be exceptionally induced around T-c at higher Sb concentration. The underlying mechanisms of relaxor behavior induced by different Sb concentration in B-sites for SNNS ceramics were clarified in detail. Moreover, the ferroelectric properties deteriorated and even disappeared at higher Sb concentration, because the ceramics showed P4/mbm phase structure as a result of decreasing of T-c to lower than room temperature. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Title:
Glass-like Lattice Thermal Conductivity and Thermoelectric Properties of Incommensurate Chimney-Ladder Compound FeGe gamma
Authors:
Sato, N; Ouchi, H; Takagiwa, Y; Kimura, K Author Full Names: Sato, Naoki; Ouchi, Hideyasu; Takagiwa, Yoshiki; Kimura, Kaoru
Source:
CHEMISTRY OF MATERIALS, 28 (2):529-533; 10.1021/acs.chemmater.5b03952 JAN 26 2016
Abstract:
We have characterized the thermoelectric properties of FeGe gamma which is one of the promising Nowotny chimney-ladder compounds. A glass-like low lattice thermal conductivity below 1.0 W m(-1) K-1 is observed around 373 K because of its complex structural nature, i.e., incommensurate structure. A first-principles band structure calculation implies that a narrow band gap of similar to 0.2 eV is formed near the Fermi level for a hypothetical composition of Fe2Ge3 with a Ru2Sn3-type structure, leading to a large power factor of 1.90 mW m(-1) K-2 near 600 K. The maximum dimensionless figure-of-merit of 0.57 is attractive as a starting point; calculation using the Boltzmann transport equation under a constant relaxation time approximation predicts that a further enhancement of ZT exceeding unity at 600-700 K can be achieved by optimizing the valence electron count per transition metal and further reduction of the lattice thermal conductivity.

Title:
Modulated structures and associated microstructures in the ferroelectric phase of Ba1-xSrxAl2O4 for 0.7 <= x <= 1.0
Authors:
Tsukasaki, H; Ishii, Y; Tanaka, E; Kurushima, K; Mori, S Author Full Names: Tsukasaki, Hirofumi; Ishii, Yui; Tanaka, Eri; Kurushima, Kosuke; Mori, Shigeo
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS, 55 (1):10.7567/JJAP.55.011502 JAN 2016
Abstract:
In order to understand the ferroelectric and ferroelastic phases in Ba1-xSrxAl2O4 for 0.7 <= x <= 1.0, we have investigated the crystal structures and their associated microstructures of the ferroelectric and ferroelastic phases mainly by transmission electron microscopy (TEM) and scanning transmission electron microscopy-high-angle angular dark-field (STEM-HAADF) experiments, combined with powder X-ray diffraction experiments. Electron diffraction experiments showed that the ferroelectric and ferroelastic phases of Ba1-xSrxAl2O4 for 0.7 <= x <= 1.0 should be characterized as a modulated structure with the modulation vector of q = 0, 1/2, 0, whose space group should be monoclinic P2(1). High-resolution TEM experiments revealed that the microstructures in the monoclinic phase can be characterized as twin structures and nanometer-sized planar defects due to the monoclinic structure with the modulated structures, which are responsible for anomalous elastic behaviors and mechanoelectro-optical properties. In addition, subatomic-resolution STEM-HAADF images clearly indicated that the displacement of Al3+ ions involved in the AlO4 tetrahedra should play a crucial role in the formation of the modulated structures and twin structures. (C) 2016 The Japan Society of Applied Physics

Title:
Influence of high energy milling on the microstructure and magnetic properties of the AlCu-Fe phases: the case of the i-Al64Cu23Fe13 quasicrystalline and the omega-Al70Cu20Fe10 crystalline phases
Authors:
Quispe, MP; Landauro, CV; Vergara, MZP; Quispe-Marcatoma, J; Rojas-Ayala, C; Pena-Rodriguez, VA; Baggio-Saitovitch, E Author Full Names: Pillaca Quispe, Mirtha; Landauro, Carlos V.; Pinto Vergara, Milida Z.; Quispe-Marcatoma, Justiniano; Rojas-Ayala, Chachi; Pena-Rodriguez, Victor A.; Baggio-Saitovitch, Elisa
Source:
RSC ADVANCES, 6 (7):5367-5376; 10.1039/c5ra21093c 2016
Abstract:
The effect of mechanical milling in i-Al64Cu23Fe13 quasicrystalline and omega-Al70Cu20Fe10 crystalline phases is systematically investigated in the present work. The Al-Cu-Fe samples were obtained by arc furnace technique and then nanostructured by means of mechanical milling. The results indicate that the solid samples present a weak ferromagnetic behavior at 300 K, showing a saturation magnetization of 0.124 emu g(-1) for the icosahedral phase (i-phase) and 0.449 emu g(-1) for the tetragonal phase (omega phase). These small values could be an indication that only a few percentage of Fe atoms carry magnetic moment. The magnetic response in the nanostructured u-phase increases up to 3.5 times higher than its corresponding solid counterpart. Whereas for the i-phase this increment is about 16 times higher. Moreover, the speed of the variation of the studied physical parameters after reducing the average grain size has been obtained from the exponent (alpha) of a power law fit of the experimental data. The values of a, corresponding to the magnetic response, are slightly different in each phase, which should be related to the different chemical composition and/or the type of long range order. Additionally, we also search for a critical grain size. However, this critical value has not been observed in the studied samples.

Update: 10-Feb-2016


Title:
Magnetic structures in TmPdIn and TmAgSn
Authors:
Baran, S; Szytula, A; Kaczorowski, D; Damay, F Author Full Names: Baran, S.; Szytula, A.; Kaczorowski, D.; Damay, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 662 11-15; 10.1016/j.jallcom.2015.11.200 MAR 25 2016
Abstract:
Low temperature antiferromagnetic structures of TmPdIn and TmAgSn have been derived from powder neutron diffraction data. The magnetic structure of TmPdIn is a commensurate one and related to a propagation vector (k) over right arrow = [1/3, 1/3, 1/2] while the incommensurate sine-modulated structure of TmAgSn is connected with (k) over right arrow = [k(x), -k(x), 0] where k(x) = 0.1314(2). The thulium magnetic moments are constrained within the basal plane and show 'triangular' arrangement. Validity of obtained magnetic structures is discussed on the basis of symmetry analysis. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Mossbauer spectroscopy, magnetic, and ab-initio study of the approximant Al76Ni9Fe15 to a decagonal Al-Ni-Fe quasicrystal
Authors:
Nejadsattari, F; Stadnik, ZM; Przewoznik, J; Grushko, B Author Full Names: Nejadsattari, Farshad; Stadnik, Zbigniew M.; Przewoznik, Janusz; Grushko, Benjamin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 662 612-620; 10.1016/j.jallcom.2015.12.115 MAR 25 2016
Abstract:
The structural, magnetic, and Mossbauer spectral properties of the approximant Al76Ni9Fe15 to a decagonal Al-Ni-Fe quasicrystal, complemented by ab-initio electronic structure and the hyperfine-interaction parameters calculations, are reported. The approximant studied crystallizes in the monoclinic space group C2/m with the lattice parameters a = 15.3898(3) angstrom, b = 8.0840(2) angstrom, c = 12.4169(2) angstrom, and beta = 107.870(2)degrees. The existence of a pseudogap in the calculated electronic density of states slightly above the Fermi level suggests electronic stabilization according to the Hume-Rothery-type mechanism. High metallicity of Al76Ni9Fe15 is predicted. Both the Mossbauer spectra and magnetic susceptibility data indicate that Al76Ni9Fe15 is a paramagnet down to 2.0 K. The presence of the distribution of the electric quadrupole splitting in the Mossbauer spectra measured in the temperature range 4.5-296.1 K is observed. The increase of the average quadrupole splitting with decreasing temperature is well described by a T-3/2 power-law relation. The Debye temperature of Al76Ni9Fe15 is found to be 431(3) K. (C) 2015 Elsevier B.V. All rights reserved.

Title:
The Use and Abuse of Transcranial Magnetic Stimulation to Modulate Corticospinal Excitability in Humans (vol 10, e0144151, 2015)
Authors:
Heroux, ME; Taylor, JL; Gandevia, SC Author Full Names: Heroux, Martin E.; Taylor, Janet L.; Gandevia, Simon C.
Source:
PLOS ONE, 11 (1):10.1371/journal.pone.0147890 JAN 21 2016

Title:
Composition-driven spin glass to ferromagnetic transition in the quasicrystal approximant Au-Al-Gd
Authors:
Ishikawa, A; Hiroto, T; Tokiwa, K; Fujii, T; Tamura, R Author Full Names: Ishikawa, A.; Hiroto, T.; Tokiwa, K.; Fujii, T.; Tamura, R.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.024416 JAN 21 2016
Abstract:
We investigated the composition dependence of the magnetic susceptibility of the quasicrystal approximant Au-Al-Gd. A composition-driven ferromagnetic transition is observed in a quasicrystal approximant, which is attributed to the Ruderman-Kittel-Kasuya-Yosida (RKKY) oscillation via a variation in the Fermi wave vector. The ferromagnetic transition is most simply understood as a result of the close matching of the nearest and second-nearest spin distances with the maximum positions of the RKKY potential. The present work provides an idea that allows us to tailor the magnetic order via the electron concentration in quasicrystal approximants as well as in quasicrystals.

Title:
Complex phase diagram of Ba1-xNaxFe2As2: A multitude of phases striving for the electronic entropy
Authors:
Wang, L; Hardy, F; Bohmer, AE; Wolf, T; Schweiss, P; Meingast, C Author Full Names: Wang, L.; Hardy, F.; Boehmer, A. E.; Wolf, T.; Schweiss, P.; Meingast, C.
Source:
PHYSICAL REVIEW B, 93 (1):10.1103/PhysRevB.93.014514 JAN 19 2016
Abstract:
The low-temperature electronic phase diagram of Ba1-xNaxFe2As2, obtained using high-resolution thermal-expansion and specific-heat measurements, is shown to be considerably more complex than previously reported, containing nine different phases. Besides the magnetic C-2 and reentrant C-4 phases, we find evidence for an additional, presumably magnetic, phase below the usual spin-density-wave transition, as well as a possible incommensurate magnetic phase. All these phases coexist and compete with superconductivity, which is particularly strongly suppressed by the C-4-magnetic phase due to a strong reduction of the electronic entropy available for pairing in this phase.

Title:
Use of frit-disc crucibles for routine and exploratory solution growth of single crystalline samples
Authors:
Canfield, PC; Kong, T; Kaluarachchi, US; Jo, NH Author Full Names: Canfield, Paul C.; Kong, Tai; Kaluarachchi, Udhara S.; Jo, Na Hyun
Source:
PHILOSOPHICAL MAGAZINE, 96 (1):84-92; 10.1080/14786435.2015.1122248 JAN 2 2016
Abstract:
Solution growth of single crystals from high temperature solutions often involves the separation of residual solution from the grown crystals. For many growths of intermetallic compounds, this separation has historically been achieved with the use of plugs of silica wool. Whereas this is generally efficient in a mechanical sense, it leads to a significant contamination of the decanted liquid with silica fibres. In this paper, we present a simple design for frit-disc alumina crucible sets that has made their use in the growth single crystals from high temperature solutions both simple and affordable. An alumina frit-disc allows for the clean separation of the residual liquid from the solid phase. This allows for the reuse of the decanted liquid, either for further growth of the same phase, or for subsequent growth of other, related phases. In this paper, we provide examples of the growth of isotopically substituted TbCd6 and icosahedral i-RCd quasicrystals, as well as the separation of (i) the closely related Bi2Rh3S2 and Bi2Rh3.5S2 phases and (ii) PrZn11 and Pr2Zn17.

Title:
Mn3TeO6 - a new multiferroic material with two magnetic substructures
Authors:
Zhao, L; Hu, ZW; Kuo, CY; Pi, TW; Wu, MK; Tjeng, LH; Komarek, AC Author Full Names: Zhao, Li; Hu, Zhiwei; Kuo, Chang-Yang; Pi, Tun-Wen; Wu, Maw-Kuen; Tjeng, Liu Hao; Komarek, Alexander C.
Source:
PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, 9 (12):730-734; 10.1002/pssr.201510347 DEC 2015
Abstract:
From magnetic susceptibility, dielectric permittivity, electric polarization and specific heat measurements we discover spin-induced ferroelectricity and magnetoelectric coupling in Mn3TeO6 and observe two successive magnetic transitions at low temperatures. A non-ferroelectric intermediate magnetic state occurs below 23 K and a multiferroic ground state emerges below 21 K. Moreover, Mn3TeO6 is a candidate for a multiferroic material where two types of incommensurate spin structures, cycloidal and helical, coexist. Theoretically, both spin substructures may contribute to the macro electric polarization via different mechanisms. This could open new ways of manipulating the ferroelectric polarization in a multiferroic material. (c) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Update: 4-Feb-2016


Title:
Highly modulated structure and upconversion photoluminescence properties of PbGd2(MoO4)(4):Er3+/Yb3+ phosphors
Authors:
Lim, CS Author Full Names: Lim, Chang Sung
Source:
MATERIALS RESEARCH BULLETIN, 75 211-216; 10.1016/j.materresbull.2015.11.058 MAR 2016
Abstract:
Double molybdate of PbGd2-x(MoO4)(4):Er3+/Yb3+ phosphors with the correct doping concentrations of Er3+ and Yb3+ (x= Er3+ + Yb3+, Er3+ = 0.05, 0.1, 0.2 and Yb3+ = 0.2, 0.45) were successfully synthesized by microwave sol-gel process. The highly modulated structure and the upconversion photoluminescence properties were investigated in detail. The synthesized particles, formed after heat-treatment at 900 degrees C for 16 h, showed a well ctystallized morphology with particle sizes of 2-5 mu m. Under excitation at 980 nm, the PbGd1.7(MoO4)(4):Er(0.1)Ybo(0.2) and PbGd1.5(MoO4)(4):Er0.05Yb0.45 particles exhibited a strong 525-nm emission band, a weak 550-nm emission band in the green region, and a very weak 655-nm emission band in the red region. The Raman spectra of the doped particles indicated the disordered structures of PbGd2-x(MoO4)(4) by the incorporation of the Er3+ and Yb3+ ions into the crystal lattice, which resulted in the highly modulated structure as well as a concentration quenching effect of Er3+ ions. (C) 2015 Published by Elsevier Ltd.

Title:
Gabor frames for quasicrystals, K-theory, and twisted gap labeling
Authors:
Kreisel, M Author Full Names: Kreisel, Michael
Source:
JOURNAL OF FUNCTIONAL ANALYSIS, 270 (3):1001-1030; 10.1016/j.jfa.2015.11.011 FEB 1 2016
Abstract:
We study the connection between Gabor frames for quasicrystals, the topology of the hull of a quasicrystal A, and the K-theory of an associated twisted groupoid algebra. In particular, we construct a finitely generated projective module over this algebra, and any multiwindow Gabor frame for A can be used to construct an idempotent representing this module in K-theory. For lattice subsets in dimension two, this allows us to prove a twisted version of Bellissard's gap labeling theorem. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Observation of nonequilibrium behavior near the Lifshitz point in ferroelectrics with incommensurate phase
Authors:
Rushchanskii, KZ; Molnar, A; Bilanych, R; Yevych, R; Kohutych, A; Vysochanskii, YM; Samulionis, V; Banys, J Author Full Names: Rushchanskii, K. Z.; Molnar, A.; Bilanych, R.; Yevych, R.; Kohutych, A.; Vysochanskii, Yu. M.; Samulionis, V.; Banys, J.
Source:
PHYSICAL REVIEW B, 93 (1):10.1103/PhysRevB.93.014101 JAN 14 2016
Abstract:
We have investigated nonequilibrium properties of proper uniaxial Sn2P2(SexS1-x)(6) ferroelectrics with the type II incommensurate phase above Lifshitz point x(LP) similar to 0.28. We performed measurements of dielectric susceptibility in cooling and heating regimes with the rate ranging 0.002-0.1 K/min, as well as high-resolution ultrasound investigation and hypersound Brillouin scattering experiments. For samples with x >= 0.28 clear anomalies are observed at incommensurate second-order transition (T-i) and at first-order lock-in transition (T-c) in the regime of very slow cooling rate, whereas the intermediate incommensurate phase is not observed when the rate is faster than 0.1 K/min. In general, increasing the cooling rate leads to smearing of the anomaly at T-c. We relate this effect to cooling rate dependence of domain-wall concentration and their size: domain width decreases when cooling rate increases. At certain conditions, the size of domain is comparable to the incommensurate phase modulation period, which is in the micrometer range in the vicinity of Lifshitz point and leads to pinning of the modulation period by domain walls.

Title:
Spatial spin-modulated structure and hyperfine interactions of Fe-57 nuclei in multiferroics BiFe1-x T (x) O-3 (T = Sc, Mn; x=0, 0.05)
Authors:
Rusakov, VS; Pokatilov, VS; Sigov, AS; Matsnev, ME; Gapochka, AM; Kiseleva, TY; Komarov, AE; Shatokhin, MS; Makarova, AO Author Full Names: Rusakov, V. S.; Pokatilov, V. S.; Sigov, A. S.; Matsnev, M. E.; Gapochka, A. M.; Kiseleva, T. Yu.; Komarov, A. E.; Shatokhin, M. S.; Makarova, A. O.
Source:
PHYSICS OF THE SOLID STATE, 58 (1):102-107; 10.1134/S1063783416010261 JAN 2016
Abstract:
The results of the Mossbauer studies on Fe-57 nuclei in multiferroics BiFe1-x T (x) O-3 (T = Sc, Mn; x = 0, 0.05) in the temperature range of 5.2-300 K have been presented. The Mossbauer spectra have been analyzed in terms of the model of an incommensurate spatial spin-*modulated structure* of cycloid type. Information has been obtained about the effect of the substitution of Sc and Mn atoms for Fe atoms on the hyperfine parameters of the spectrum: the shift and the quadrupole shift of the Mossbauer line, the isotropic and anisotropic contributions to the hyperfine magnetic field, and also the parameter of anharmonicity of the spatial spin-modulated structure.

Title:
Multilayered sandwich-like architecture containing large-scale faceted Al-Cu-Fe quasicrystal grains
Authors:
Wei, DX; He, ZB Author Full Names: Wei, Dongxia; He, Zhanbing
Source:
MATERIALS CHARACTERIZATION, 111 154-161; 10.1016/j.matchar.2015.11.027 JAN 2016
Abstract:
Faceted quasicrystals are structurally special compared with traditional crystals. Although the application of faceted quasicrystals has been expected, wide-scale application has not occurred owing to the limited exposure of the facets. Using a facile method of heat treatment, we synthesize a multilayered sandwich-like structure with each layer composed of large-scale pentagonal-dodecahedra of Al-Cu-Fe quasicrystals. Moreover, there are channels between the adjacent Al-Cu-Fe layers that serve to increase the exposure of the facets of quasicrystals. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction are used to characterize the multilayered architecture, and the generation mechanisms of this special structure are also discussed. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Effect of applied pressure on microstructure and mechanical properties of Mg-Zn-Y quasicrystal-reinforced AZ91D magnesium matrix composites prepared by squeeze casting
Authors:
Yang, L; Hou, H; Zhao, YH; Yang, XM Author Full Names: Yang, Ling; Hou, Hua; Zhao, Yu-hong; Yang, Xiao-min
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 25 (12):3936-3943; 10.1016/S1003-6326(15)64041-9 DEC 2015
Abstract:
The Mg-Zn-Y quasicrystal-reinforced AZ91D magnesium matrix composites were prepared by squeeze casting process. The effects of applied pressure on microstructure and mechanical properties of the composites were investigated. The results show that squeeze casting process is an effective method to refine the grain. The composites are mainly composed of alpha-Mg, beta-Mg17Al12 and Mg3Zn6Y icosahedral quasicrystal phase (I-phase). With the increase of applied pressure, the contents of beta-Mg17Al12 phase and Mg3Zn6Y quasicrystal particles increase, further matrix grain refinement occurs and coarse dendritic alpha-Mg transforms into equiaxed grain structure. The composite exhibits the maximum ultimate tensile strength and elongation of 194.3 MPa and 9.2% respectively when the applied pressure is 100 MPa, and a lot of dimples appear on the tensile fractography. Strengthening mechanisms of quasicrystal-reinforced AZ91D magnesium matrix composites are chiefly fine-grain strengthening and quasicrystal particles strengthening.

Update: 28-Jan-2016


Title:
Controlling many-body states by the electric-field effect in a two-dimensional material
Authors:
Li, LJ; O'Farrell, ECT; Loh, KP; Eda, G; Ozyilmaz, B; Neto, AHC Author Full Names: Li, L. J.; O'Farrell, E. C. T.; Loh, K. P.; Eda, G.; Ozyilmaz, B.; Neto, A. H. Castro
Source:
NATURE, 529 (7585):185-U129; 10.1038/nature16175 JAN 14 2016
Abstract:
To understand the complex physics of a system with strong electron-electron interactions, the ideal is to control and monitor its properties while tuning an external electric field applied to the system (the electric-field effect). Indeed, complete electric-field control of many-body states in strongly correlated electron systems is fundamental to the next generation of condensed matter research and devices(1-3). However, the material must be thin enough to avoid shielding of the electric field in the bulk material. Two-dimensional materials do not experience electrical screening, and their charge-carrier density can be controlled by gating. Octahedral titanium diselenide (1T-TiSe2) is a prototypical two-dimensional material that reveals a charge-density wave (CDW) and superconductivity in its phase diagram(4), presenting several similarities with other layered systems such as copper oxides(5), iron pnictides(6), and crystals of rare-earth elements and actinide atoms(7). By studying 1T-TiSe2 single crystals with thicknesses of 10 nanometres or less, encapsulated in two-dimensional layers of hexagonal boron nitride, we achieve unprecedented control over the CDW transition temperature (tuned from 170 kelvin to 40 kelvin), and over the superconductivity transition temperature (tuned from a quantum critical point at 0 kelvin up to 3 kelvin). Electrically driving TiSe2 over different ordered electronic phases allows us to study the details of the phase transitions between many-body states. Observations of periodic oscillations of magnetoresistance induced by the Little-Parks effect show that the appearance of superconductivity is directly correlated with the spatial texturing of the amplitude and phase of the superconductivity order parameter, corresponding to a two-dimensional matrix of superconductivity. We infer that this superconductivity matrix is supported by a matrix of incommensurate CDW states embedded in the commensurate CDW states. Our results show that spatially modulated electronic states are fundamental to the appearance of two-dimensional superconductivity.

Title:
Structure of periodic crystals and quasicrystals in ultrathin films of Ba-Ti-O
Authors:
Cockayne, E; Mihalkovic, M; Henley, CL Author Full Names: Cockayne, Eric; Mihalkovic, Marek; Henley, Christopher L.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.020101 JAN 7 2016
Abstract:
We model the remarkable thin-film Ba-Ti-O structures formed by heat treatment of an initial perovskite BaTiO3 thin film on a Pt(111) surface. All structures contain a rumpled Ti-O network with all Ti threefold coordinated with O and with Ba occupying the larger. mainly Ti7O7, pores. The quasicrystal structure is a simple decoration of three types of tiles: square, triangle, and 30 degrees. rhombus, with edge lengths 6.85 angstrom, joined edge-to-edge in a quasicrystalline pattern; observed periodic crystals in ultrathin film Ba-Ti-O are built from these and other tiles. Simulated STM images reproduce the patterns seen experimentally and identify the bright protrusions as Ba atoms. The models are consistent with all experimental observations.

Title:
Ultrafast Metamorphosis of a Complex Charge-Density Wave
Authors:
Haupt, K; Eichberger, M; Erasmus, N; Rohwer, A; Demsar, J; Rossnagel, K; Schwoerer, H Author Full Names: Haupt, Kerstin; Eichberger, Maximilian; Erasmus, Nicolas; Rohwer, Andrea; Demsar, Jure; Rossnagel, Kai; Schwoerer, Heinrich
Source:
PHYSICAL REVIEW LETTERS, 116 (1):10.1103/PhysRevLett.116.016402 JAN 6 2016
Abstract:
Modulated phases, commensurate or incommensurate with the host crystal lattice, are ubiquitous in solids. The transition between such phases involves formation and rearrangement of domain walls and is generally slow. Using ultrafast electron diffraction, we directly record the photoinduced transformation between a nearly commensurate and an incommensurate charge-density-wave phase in 1T-TaS2. The transformation takes place on the picosecond time scale, orders of magnitude faster than previously observed for commensurate-to-incommensurate transitions. The transition speed and mechanism can be linked to the peculiar nanoscale structure of the photoexcited nearly commensurate phase.

Title:
Phase diagram of the Kondo lattice model on the kagome lattice
Authors:
Ghosh, S; Brien, PO; Henley, CL; Lawler, MJ Author Full Names: Ghosh, Shivam; Brien, Patrick O'; Henley, Christopher L.; Lawler, Michael J.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.024401 JAN 4 2016
Abstract:
We consider the potential for novel forms of magnetism arising from the subtle interplay between electrons and spins in the underscreened kagome Kondo lattice model. At weak coupling, we show that incommensurate noncoplanar multiwave vector magnetic orders arise at nearly all fillings and that this results from Fermi surface effects that introduce competing interactions between the spins. At strong coupling, we find that such a complex order survives near half filling despite the presence of ferromagnetism at all other fillings. We show this arises due to state selection among a massive degeneracy of states at infinite coupling. Finally, we show that at intermediate filling only commensurate orders seem to survive, but these orders still include noncoplanar magnetism. So, the mere presence of both local moments and itinerant electrons enables complex orders to form unlike any currently observed in kagome materials.

Title:
Incommensurate to commensurate antiferromagnetism in CeRhAl4Si2: An Al-27 NMR study
Authors:
Sakai, H; Hattori, T; Tokunaga, Y; Kambe, S; Ghimire, NJ; Ronning, F; Bauer, ED; Thompson, JD Author Full Names: Sakai, H.; Hattori, T.; Tokunaga, Y.; Kambe, S.; Ghimire, N. J.; Ronning, F.; Bauer, E. D.; Thompson, J. D.
Source:
PHYSICAL REVIEW B, 93 (1):10.1103/PhysRevB.93.014402 JAN 4 2016
Abstract:
Al-27 nuclear magnetic resonance (NMR) experiments have been performed on a single crystal of CeRhAl4Si2, which is an antiferromagnetic Kondo-lattice compound with successive antiferromagnetic transitions of T-N1 = 14 K and T-N2 = 9 K at zero external field. In the paramagnetic state, the Knight shifts, quadrupolar frequency, and asymmetric parameter of electrical field gradient on the Al sites have been determined, which have local orthorhombic symmetry. The transferred hyperfine coupling constants are also determined. Analysis of the NMR spectra indicates that a commensurate antiferromagnetic structure exists below T-N2, but an incommensurate modulation of antiferromagnetic moments is present in the antiferromagnetic state between T-N1 and T-N2. The spin-lattice relaxation rate suggests that the 4 f electrons behave as local moments at temperatures above T-N1.

Title:
Trapping of Oxygen Vacancies at Crystallographic Shear Planes in Acceptor-Doped Pb-Based Ferroelectrics
Authors:
Batuk, D; Batuk, M; Tsirlin, AA; Hadermann, J; Abakumov, AM Author Full Names: Batuk, Dmitry; Batuk, Maria; Tsirlin, Alexander A.; Hadermann, Joke; Abakumov, Artem M.
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 54 (49):14787-14790; 10.1002/anie.201507729 DEC 1 2015
Abstract:
The defect chemistry of the ferroelectric material PbTiO3 after doping with Fe-III acceptor ions is reported. Using advanced transmission electron microscopy and powder X-ray and neutron diffraction, we demonstrate that even at concentrations as low as circa 1.7% (material composition approximately ABO(2.95)), the oxygen vacancies are trapped into extended planar defects, specifically crystallographic shear planes. We investigate the evolution of these defects upon doping and unravel their detailed atomic structure using the formalism of superspace crystallography, thus unveiling their role in nonstoichiometry in the Pb-based perovskites.

Update: 14-Jan-2016


Title:
Dislocations in icosahedral quasicrystalline phase embedded in hot-deformed Mg alloys
Authors:
Huang, H; Tian, Y; Yuan, GY; Chen, CL; Wang, ZC; Ding, WJ; Inoue, A Author Full Names: Huang, Hua; Tian, Yuan; Yuan, Guangyin; Chen, Chunlin; Wang, Zhongchang; Ding, Wenjiang; Inoue, Akihisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 658 483-487; 10.1016/j.jallcom.2015.10.284 FEB 15 2016
Abstract:
We perform a systematic structural investigation of the I-phase particles embedded in Mg matrix in I-phase-reinforced Mg-3.5Zn-0.6Gd alloy and offer evidence to the presence of dislocations in the I-phase particles. Such dislocations are found to be formed on the (0001) plane of Mg matrix, which is attributed to their slipping into the 5-fold and 2-fold planes of I-phase particles. We also discuss how deformation conditions of wrought Mg alloys affect the deformation behaviors of the I-phase and how deformation behavior of I-phase affect the mechanical properties of wrought Mg alloys. The bonding between the I-phase and Mg matrix was also confirmed to be strong. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Microstructures and phase transformations in as-aged Mn2.04NiGa Heusler alloy
Authors:
Du, ZW; Han, XL; Li, T; Liu, EK; Ma, XD; Xiong, JC; Wu, GH Author Full Names: Du, Z. W.; Han, X. L.; Li, T.; Liu, E. K.; Ma, X. D.; Xiong, J. C.; Wu, G. H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 657 443-449; 10.1016/j.jallcom.2015.10.111 FEB 5 2016
Abstract:
The room-temperature microstructures and phase transformation of Mn2.04NiGa alloy were investigated by transmission electron microscopy (TEM), electron backscattered diffraction (EBSD) and high-angle annular dark field scanning-TEM (HAADF-STEM). The Mn2.04NiGa alloy annealed at 1073 K for 72 h is mainly austenite phase with Hg2CuTi-type structure. After 623 K/72 h ageing, nano-scaled MnNiGa precipitates considered as Ni2In-type hexagonal structure were found by TEM. A crystalline orientation relationship between precipitates and austensite can be described by ((22) over bar4)(A)//(0 (1) over bar 10)(H), [1 (1) over bar0](A)//[2 (11) over bar0](H). These precipitates are accompanying with Mn-rich martensite lamellae. Both non-modulated and nearly 16-layered modulated structures are generally in coexistence in one martensite lath. A crystalline orientation relationship between the ageing-induced martensite and austenite is (111)(A)//(110)(M), [011](A)//[1 (1) over bar2]M. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Origin of modulated phases and magnetic hysteresis in TmB4
Authors:
Wierschem, K; Sunku, SS; Kong, T; Ito, T; Canfield, PC; Panagopoulos, C; Sengupta, P Author Full Names: Wierschem, Keola; Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; Canfield, Paul C.; Panagopoulos, Christos; Sengupta, Pinaki
Source:
PHYSICAL REVIEW B, 92 (21):10.1103/PhysRevB.92.214433 DEC 23 2015
Abstract:
We investigate the low-temperature magnetic phases in TmB4, a metallic quantum magnet on the geometrically frustrated Shastry-Sutherland lattice, using coordinated experimental and theoretical studies. Our results provide an explanation for the appearance of the intriguing fractional plateau in TmB4 and accompanying magnetic hysteresis. Together with observation of the bump in the half plateau, our results support the picture that the magnetization plateau structure in TmB4 is strongly influenced by the zero-field modulated phases. We present a phenomenological model to explain the appearance of the modulated phases and a microscopic Hamiltonian that captures the complete magnetic behavior of TmB4.

Update: 7-Jan-2016


Title:
Magnetic properties and complex magnetic phase diagram in non-centrosymmetric EuRhGe3 and EuIrGe3 single crystals
Authors:
Maurya, A; Bonville, P; Kulkarni, R; Thamizhavel, A; Dhar, SK Author Full Names: Maurya, Arvind; Bonville, P.; Kulkarni, R.; Thamizhavel, A.; Dhar, S. K.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 401 823-831; 10.1016/j.jmmm.2015.10.134 MAR 1 2016
Abstract:
We report the magnetic properties of two Eu based compounds, single crystalline EuIrGe3 and EuRhGe3, inferred from magnetisation, electrical transport, heat capacity and Eu-151 Mossbauer spectroscopy. These previously known compounds crystallise in the non-centrosymmetric, tetragonal, I4 mm, BaNiSn3-type structure. Single crystals of EuIrGe3 and EuRhGe3 were grown using a high temperature solution growth method using In as flux. EuIrGe3 exhibits two magnetic transition temperatures T-N1 = 12.4 K, and T(N)2 = 7.3 K, whereas EuRhGe3 presents a single one at T-N = 12K. Eu-151 Mossbauer spectra show evidence for a cascade of transitions from paramagnetic to incommensurate amplitude modulated followed by an equal moment phase at lower temperature in EuIrGe3. This latter phase alone occurs in EuRhGe3. In both compounds, the magnetisation measured up to 14 T suggests that the equal moment magnetic phase has a spiral spin arrangement. The field induced reorientations are also well documented in the magnetotransport data. A superzone gap is observed for the current density J vertical bar vertical bar [001], which is enhanced by a transverse magnetic field. The magnetic phase diagram constructed from all the data is complex, revealing the presence of many phases in the H - T space. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Structural and magnetic phase transitions in CeCu6-xT(x) (T = Ag, Pd)
Authors:
Poudel, L; de la Cruz, C; Payzant, EA; May, AF; Koehler, M; Garlea, VO; Taylor, AE; Parker, DS; Cao, HB; McGuire, MA; Tian, W; Matsuda, M; Jeen, H; Lee, HN; Hong, T; Calder, S; Zhou, HD; Lumsden, MD; Keppens, V; Mandrus, D; Christianson, AD Author Full Names: Poudel, L.; de la Cruz, C.; Payzant, E. A.; May, A. F.; Koehler, M.; Garlea, V. O.; Taylor, A. E.; Parker, D. S.; Cao, H. B.; McGuire, M. A.; Tian, W.; Matsuda, M.; Jeen, H.; Lee, H. N.; Hong, T.; Calder, S.; Zhou, H. D.; Lumsden, M. D.; Keppens, V.; Mandrus, D.; Christianson, A. D.
Source:
PHYSICAL REVIEW B, 92 (21):10.1103/PhysRevB.92.214421 DEC 15 2015
Abstract:
The structural and the magnetic properties of CeCu6-xAgx(0 <= x <= 0.85) and CeCu6-xPdx (0 <= x <= 0.4) have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of CeCu6-xAgx and CeCu6-xPdx as a function of Ag/Pd composition are reported. The end member, CeCu6, undergoes a structural phase transition from an orthorhombic (Pnma) to a monoclinic (P2(1)/c) phase at 240 K. In CeCu6-xAgx, the structural phase transition temperature (T-s) decreases linearly with Ag concentration and extrapolates to zero at x(S) approximate to 0.1. The structural transition in CeCu6-xPd (x) remains unperturbed with Pd substitution within the range of our study. The lattice constant b slightly decreases with Ag/Pd doping, whereas a and c increase with an overall increase in the unit cell volume. Both systems, CeCu6-xAgx and CeCu6-xPdx, exhibit a magnetic quantum critical point (QCP), at x approximate to 0.2 and x approximate to 0.05, respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector (delta(1) 0 delta(2)), where delta(1) similar to 0.62, delta 2 similar to 0.25, x = 0.125 for CeCu6-xPdx and delta(1) similar to 0.64, delta(2) similar to 0.3, x = 0.3 for CeCu6-xAgx. The magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.

Title:
Overcoming magnetic frustration and promoting half-metallicity in spinel CoCr2O4 by doping with Fe
Authors:
Ganguly, S; Chimata, R; Sanyal, B Author Full Names: Ganguly, Shreemoyee; Chimata, Raghuveer; Sanyal, Biplab
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224417 DEC 14 2015
Abstract:
In this paper, we present a systematic study of the effects of Fe doping on the electronic and magnetic structures of spinel CoCr2O4 by ab initio density functional theory and atomistic spin dynamics calculations. Our calculated magnetic structure for pristine CoCr2O4 correctly reproduces the experimental one with a q-vector of (0.67, 0.67,0.0), establishing the accuracy of the calculated interatomic exchange interactions. We show that the noncollinear spin structure with a nonzero q-vector in the spinel structure is driven towards collinearity by Fe doping by a complex interplay between interatomic exchange interactions. In the inverse spinel structure with 100% Fe doping, a collinear antiferromagnetic order develops along with a half-metallic electronic structure, which evolves due to the chemical disorder between Fe and Co in the B sites described by the coherent potential approximation. This is a comprehensive theoretical study to understand the evolution of magnetic and electronic properties of multiferroic CoCr2O4 doped with Fe.

Update: 31-Dec-2015


Title:
Decoupling of the antiferromagnetic and insulating states in Tb-doped Sr2IrO4
Authors:
Wang, JC; Aswartham, S; Ye, F; Terzic, J; Zheng, H; Haskel, D; Chikara, S; Choi, Y; Schlottmann, P; Custelcean, R; Yuan, SJ; Cao, G Author Full Names: Wang, J. C.; Aswartham, S.; Ye, Feng; Terzic, J.; Zheng, H.; Haskel, Daniel; Chikara, Shalinee; Choi, Yong; Schlottmann, P.; Custelcean, Radu; Yuan, S. J.; Cao, G.
Source:
PHYSICAL REVIEW B, 92 (21):10.1103/PhysRevB.92.214411 DEC 8 2015
Abstract:
Sr2IrO4 is a spin-orbit-coupled insulator with an antiferromagnetic (AFM) transition at T-N = 240 K. We report results of a comprehensive study of single-crystal Sr2Ir1-xTbxO4 (0 <= x <= 0.03). This study found that a mere 3% (x = 0.03) of tetravalent Tb4+ (4f(7)) substituting for Ir4+ (rather than Sr2+) completely suppresses the long-range collinear AFM transition but retains the insulating state, leading to a phase diagram featuring a decoupling of the magnetic interactions and charge gap. The insulating state at x = 0.03 is characterized by an unusually large specific heat at low temperatures and an incommensurate magnetic state having magnetic peaks at (0.95,0,0) and (0,0.95,0) in the neutron diffraction, suggesting a spiral or spin-density-wave order. It is apparent that Tb doping effectively changes the relative strength of the spin-orbit interaction (SOI) and the tetragonal crystal electric field and enhances the Hund's rule coupling that competes with the SOI, and destabilizes the AFM state. However, the disappearance of the AFM is accompanied by no metallic state chiefly because an energy level mismatch for the Ir and Tb sites weakens charge carrier hopping and causes a persistent insulating state. This work highlights an unconventional correlation between the AFM and insulating states in which the magnetic transition plays no critical role in the formation of the charge gap in the iridate.

Title:
Long-range magnetic order in models for rare-earth quasicrystals
Authors:
Thiem, S; Chalker, JT Author Full Names: Thiem, Stefanie; Chalker, J. T.
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224409 DEC 7 2015
Abstract:
We take a two-step theoretical approach to study magnetism of rare-earth quasicrystals by considering Ising spins on quasiperiodic tilings, coupled via Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. First, we compute RKKY interactions from a tight-binding Hamiltonian defined on the two-dimensional quasiperiodic tilings. We find that the magnetic interactions are frustrated and strongly dependent on the local environment. This results in the formation of clusters with strong bonds at certain patterns of the tilings that repeat quasiperiodically. Second, we examine the statistical mechanics of Ising spins with these RKKY interactions, using extensive Monte Carlo simulations. Although models that have frustrated interactions and lack translational invariance might be expected to display spin-glass behavior, we show that the spin system has a phase transition to low-temperature states with long-range quasiperiodic magnetic order. Additionally, we find that in some of the systems spin clusters can fluctuate much below the ordering temperature.

Title:
One-Dimensional Quasicrystals from Incommensurate Charge Order
Authors:
Flicker, F; van Wezel, J Author Full Names: Flicker, Felix; van Wezel, Jasper
Source:
PHYSICAL REVIEW LETTERS, 115 (23):10.1103/PhysRevLett.115.236401 DEC 3 2015
Abstract:
Artificial quasicrystals are nowadays routinely manufactured, yet only two naturally occurring examples are known. We present a class of systems with the potential to be realized both artificially and in nature, in which the lowest energy state is a one-dimensional quasicrystal. These systems are based on incommensurately charge-ordered materials, in which the quasicrystalline phase competes with the formation of a regular array of discommensurations as a way of interpolating between incommensurate charge order at high temperatures and commensurate order at low temperatures. The nonlocal correlations characteristic of the quasicrystalline state emerge from a free-energy contribution localized in reciprocal space. We present a theoretical phase diagram showing that the required material properties for the appearance of such a ground state allow for one-dimensional quasicrystals to form in real materials. The result is a potentially wide class of one-dimensional quasicrystals.

Title:
Disorder in the composite crystal structure of the manganese 'disilicide' MnSi1.73 from powder X-ray diffraction data
Authors:
Akselrud, L; Gil, RC; Wagner-Reetz, M; Grin, Y Author Full Names: Akselrud, L.; Gil, R. Cardoso; Wagner-Reetz, M.; Grin, Yu.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 (6):707-712; SI 10.1107/S2052520615019757 DEC 2015
Abstract:
The crystal structure of the higher manganese silicide MnSi1.7 (known in the literature as HMS) is investigated in samples with different compositions obtained by different techniques at temperatures not higher than 1273 K. Powder X-ray diffraction was applied. The crystal structure is described as incommensurate composite. In addition to the ordered model already known in the literature, the partial disorder in the silicon substructure was detected and described introducing an additional atomic site with a different modulation function.

Title:
Type II Bi-1 (-) xWxO1.5 (+) (1.5x): a (3+3)-dimensional commensurate modulation that stabilizes the fast-ion conducting delta phase of bismuth oxide
Authors:
Wind, J; Auckett, JE; Withers, RL; Piltz, RO; Maljuk, A; Ling, CD Author Full Names: Wind, Julia; Auckett, Josie E.; Withers, Ray L.; Piltz, Ross O.; Maljuk, Andrey; Ling, Chris D.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 (6):679-687; SI 10.1107/S2052520615018351 DEC 2015
Abstract:
The Type II phase in the Bi1 - xWxO1.5 (+) (1.5x) system is shown to have a (3 + 3)-dimensional modulated delta-Bi2O3-related structure, in which the modulation vector epsilon 'locks in' to a commensurate value of 1/3. The structure was refined in a 3 x 3 x 3 supercell against single-crystal Laue neutron diffraction data. Ab initio calculations were used to test and optimize the local structure of the oxygen sublattice around a single mixed Bi/W site. The underlying crystal chemistry was shown to be essentially the same as for the recently refined (3 + 3)-dimensional modulated structure of Type II Bi-1 (-) xNbxO1.5 (+) (x) (Ling et al., 2013), based on a transition from fluorite-type to pyrochlore-type via the appearance of W4O18 'tetrahedra of octahedra' and chains of corner-sharing WO6 octahedra along < 110 >(F) directions. The full range of occupancies on this mixed Bi/W site give a hypothetical solid-solution range bounded by Bi23W4O46.5 (x = 0.148) and Bi22W5O48 (x = 0.185), consistent with previous reports and with our own synthetic and analytical results.

Title:
Determination of the incommensurate modulated structure of Bi2Sr1.6La0.4CuO6+delta by aberration-corrected transmission electron microscopy
Authors:
Ge, BH; Wang, YM; Luo, HQ; Wen, HH; Yu, R; Cheng, ZY; Zhu, J Author Full Names: Ge, Binghui; Wang, Yumei; Luo, Huiqian; Wen, Haihu; Yu, Rong; Cheng, Zhiying; Zhu, Jing
Source:
ULTRAMICROSCOPY, 159 67-72; 10.1016/j.ultramic.2015.08.004 1 DEC 2015
Abstract:
The incommensurate modulated structure (IMS) of Bi2Sr1.6La0.4Cu6+delta (BSLCO) has been studied by aberration-corrected transmission electron microscopy in combination with a high-dimensional (HD) space description. Two images are deconvoluted in the negative Cs imaging (NCSI) and positive Cs imaging (PCSI) modes. Similar results for the IMS have been obtained from two corresponding projected potential maps (PPMs), and the size of the dots representing atoms in the NCSI PPM is found to be smaller than that in the PCSI PPM. Considering that the object size is one of the factors that influence the precision of the structural determination, modulation functions for all unoverlapped atoms in BSLCO were determined on the basis of the NCSI PPM in combination with the HD space description. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Crystal Structure and Thermoelectric Properties of Chimney-Ladder Higher Manganese Silicides
Authors:
Miyazaki, Y Author Full Names: Miyazaki, Yuzuru
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 79 (11):530-537; SI 10.2320/jinstmet.JA201508 2015
Abstract:
Crystal structure, electronic structure and thermoelectric (TE) properties of Nowotny chimney-ladder (NCL) higher manganese silicides (HMSs) are reviewed. According to a (3+1). dimensional superspace approach, HMSs are revealed to belong to incommensurate composite crystals, wherein [Mn] and [Si] subsystems possess an irrational c-axis ratio gamma=c(Mn)/c(Si). The gamma parameter, also represents a stoichiometry of the HMSs as MnSi gamma, dictates the electronic structure, directly relating to a valence electron counting number, VEC. The p-type TE performance can be enhanced by a partial substitution of V, Cr, etc., while n-type HMSs can be obtained by heavily substituting Mn with Fe, etc., to realize VEC > 14. A unique thermal expansion has been discovered at T similar to 800 K, which would deteriorate TE performance and hence to be avoided from a practical application point of view.

Title:
Electronic vs. structural ordering in a manganese(III) spin crossover complex
Authors:
Fitzpatrick, AJ; Trzop, E; Muller-Bunz, H; Dirtu, MM; Garcia, Y; Collet, E; Morgan, GG Author Full Names: Fitzpatrick, Anthony J.; Trzop, Eliza; Mueller-Bunz, Helge; Dirtu, Marinela M.; Garcia, Yann; Collet, Eric; Morgan, Grace G.
Source:
CHEMICAL COMMUNICATIONS, 51 (99):17540-17543; 10.1039/c5cc05129k 2015
Abstract:
A symmetry breaking spin transition in a Mn(III) complex is reported with three structural phases, a high symmetry high temperature S = 2 phase, an intermediate S = 1/S = 2 ordered phase and an aperiodic low temperature phase with S = 1 cations. The aperiodicity is interpreted as resulting from long-range ordering of the NTf2- anions.

Title:
Effects of Initial States on the Spinodal Decomposition of Quenched and Melt-Spun Cu-15Ni-8Sn Alloy
Authors:
Kondo, S; Masusaki, A; Ogawa, K; Morimura, T; Nakashima, H Author Full Names: Kondo, Shin-ichiro; Masusaki, Akinori; Ogawa, Kento; Morimura, Takao; Nakashima, Hiromichi
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 79 (12):664-671; 10.2320/jinstmet.J2015012 2015
Abstract:
We investigate early stages of spinodal decomposition in a melt. spun Cu-15Ni-8Sn alloy (melt-spun samples) by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron diffraction analysis through comparison against a quenched alloy of the same composition (quenched samples). In XRD measurements, no sidebands of (200) planes are found in the melt-spun sample after aging at 350 degrees C for 120 min, whereas they are found in the quenched sample after a heat treatment at 350 degrees C for 60 min. TEM observations of a quenched sample after aging at 350 degrees C for 60 min indicate the presence of a modulated structure (lambda= 5-10 nm) in the matrix, whereas those of a melt-spun sample after the same heat treatment also indicate the presence of a modulated structure (lambda: too small to measure). Electron diffraction patterns reveal satellite structures in both samples, although with superlattice reflections from ordering phases visible in the quenched sample. These differences are presumably due to a difference in the size of clusters present in their respective quenched states; in melt. spun samples, cluster size was much smaller as a result of a high cooling rate (approximate to 8 x 10(5 degrees)C/s).

Update: 24-Dec-2015


Title:
Single-Crystal Neutron Diffraction Study of the Heavy-Electron Superconductor CeNiGe3
Authors:
Ikeda, Y; Ueta, D; Yoshizawa, H; Nakao, A; Munakata, K; Ohhara, T Author Full Names: Ikeda, Yoichi; Ueta, Daichi; Yoshizawa, Hideki; Nakao, Akiko; Munakata, Koji; Ohhara, Takashi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (12):10.7566/JPSJ.84.123701 DEC 15 2015
Abstract:
A single-crystal neutron diffraction study was performed on anomalous antiferromagnetic ordering in the heavyelectron superconductor CeNiGe3. We observed incommensurate magnetic Bragg reflections characterized by the incommensurate propagation vector k(2) = (0, 0.41, 1/2) below the Neel temperature of 5K, but no significant magnetic reflection with the commensurate propagation vector k(1) = (1, 0, 0), at which another magnetic reflection was observed in a previous neutron diffraction study with a polycrystalline sample. From the single-crystal study, we suggest that the magnetic phase of CeNiGe3 at ambient pressure is characterized only by the incommensurate propagation vector k(2).

Title:
Electronic Properties of Incommensurate Atomic Layers
Authors:
Koshino, M; Moon, P Author Full Names: Koshino, Mikito; Moon, Pilkyung
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (12):10.7566/JPSJ.84.121001 DEC 15 2015
Abstract:
We present a brief theoretical overview of electronic properties of incommensurate multilayer systems, i.e., a pair of two-dimensional atomic layers stacked in an arbitrary orientation. We introduce the general theoretical scheme to describe the interlayer interaction between incommensurate crystal structures, and apply the formula to two specific examples, the twisted bilayer graphene and graphene-hBN composite bilayer. In each case, we calculate the electronic band structure and demonstrate that the low-energy electronic properties are significantly modified by the interlayer interaction, particularly when the two lattice structures are close to each other. We also study the energy spectrum and the quantum Hall effect in magnetic fields, where we see that the spectral structure exhibits a fractal nature, as known as the Hofstadter butterfly. We argue about the optical absorption properties of the twisted bilayer graphene and show that the interlayer interaction gives rise to the characteristic spectroscopic features in zero magnetic field and also in strong magnetic field.

Title:
Amorphous hydrides of the Ti45Zr38Ni17-xCox nano-powders
Authors:
Zywczak, A; Rusinek, D; Czub, J; Sikora, M; Stepien, J; Gondek, L; Takasaki, A; Hoser, A Author Full Names: Zywczak, A.; Rusinek, D.; Czub, J.; Sikora, M.; Stepien, J.; Gondek, L.; Takasaki, A.; Hoser, A.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 40 (45):15534-15539; 10.1016/j.ijhydene.2015.09.136 DEC 7 2015
Abstract:
The Ti-Zr-Ni alloys can be synthesized in crystalline, amorphous and quasicrystalline phases. They are produced by mechanical alloying or melt-spinning and they are good candidate materials for hydrogen storage applications. In this communication we modified the Ti45Zr38Ni17 compounds by substituting 3d metals (cobalt) for Ni to obtain amorphous phase. The cobalt atoms are located at the same positions as nickel. We describe a series of phase transitions associated with a hydrogen uptake in the amorphous Ti45Zr38Ni17-xCox alloys that were prepared by mechanical alloying. The investigated alloys exhibited a high capacity for gaseous H-2 reaching 2.2 wt.% at elevated temperatures. It has been found, that the amorphous powders were decomposed into simple hydrides being exposed to H-2 at temperatures above 200 degrees C. In order to overcome that problem, a processing route to obtain the amorphous hydrides was established. The heated amorphous hydrides underwent an unusual and fascinating transformation into the glassy quasicrystal phase with no hydrogen loss. A further temperature increase triggered another structural transformation into the cubic phase, which was associated with hydrogen release from the structure. The crystal structure evolution was characterized by the variety of diffraction techniques. Thermodynamic properties were studied by differential scanning calorimetry and thermal desorption spectroscopy. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Title:
Static and quasielastic properties of the spiral magnet Ba2CuGe2O7 studied by neutron resonance spin echo spectroscopy and neutron Larmor labeling
Authors:
Muhlbauer, S; Kindervater, J; Hassler, W Author Full Names: Muehlbauer, S.; Kindervater, J.; Haessler, W.
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224406 DEC 4 2015
Abstract:
We provide a route to use elastic and quasielastic neutron spin echo spectroscopy (Larmor labeling) for a unified approach to study both the static and dynamic properties of incommensurate magnetic structures with small propagation vectors. The archetypal noncentrosymmetric spiral magnet Ba2CuGe2O7 serves as a model system for our study. We show how Larmor labeling can efficiently decouple instrumental wavelength resolution and effective-(Q) over right arrow resolution and give high-precision access to the structural properties of the incommensurate domains of Ba2CuGe2O7.

Title:
Two types of nematicity in the phase diagram of the cuprate superconductor YBa2Cu3Oy
Authors:
Cyr-Choiniere, O; Grissonnanche, G; Badoux, S; Day, J; Bonn, DA; Hardy, WN; Liang, R; Doiron-Leyraud, N; Taillefer, L Author Full Names: Cyr-Choiniere, O.; Grissonnanche, G.; Badoux, S.; Day, J.; Bonn, D. A.; Hardy, W. N.; Liang, R.; Doiron-Leyraud, N.; Taillefer, Louis
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224502 DEC 2 2015
Abstract:
Nematicity has emerged as a key feature of cuprate superconductors, but its link to other fundamental properties such as superconductivity, charge order, and the pseudogap remains unclear. Here we use measurements of transport anisotropy in YBa2Cu3Oy to distinguish two types of nematicity. The first is associated with short-range charge-density-wave modulations in a doping region near p = 0.12. It is detected in the Nernst coefficient, but not in the resistivity. The second type prevails at lower doping, where there are spin modulations but no charge modulations. In this case, the onset of in-plane anisotropy-detected in both the Nernst coefficient and the resistivity-follows a line in the temperature-doping phase diagram that tracks the pseudogap energy. We discuss two possible scenarios for the latter nematicity.

Title:
Direct observation of an optically induced charge density wave transition in 1T-TaSe2
Authors:
Sun, SS; Wei, LL; Li, ZW; Cao, GL; Liu, Y; Lu, WJ; Sun, YP; Tian, HF; Yang, HX; Li, JQ Author Full Names: Sun, Shuaishuai; Wei, Linlin; Li, Zhongwen; Cao, Gaolong; Liu, Y.; Lu, W. J.; Sun, Y. P.; Tian, Huanfang; Yang, Huaixin; Li, Jianqi
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224303 DEC 2 2015
Abstract:
Four-dimensional ultrafast transmission electron microscopy measurements reveal a rich variety of structural dynamic phenomena at a phase transition in the charge density wave (CDW) of 1T-TaSe2. Under photoexcitation, remarkable changes in both the CDW intensity and orientation are clearly observed, associated with the transformation from a commensurate (C) phase into an incommensurate (IC) phase in a time scale of picoseconds. Moreover, the transient states reveal a notable "structural isosbestic point" at a wave vector of q(iso) where the C and IC phases yield their diffracting efficiencies in equal ratio. This observation reveals that the crystal planes parallel to q(iso) adopt a common dynamic feature in the CDW phases throughout whole nonequilibrium transition. The second-order characteristics observed in this nonequilibrium phase transition have also been analyzed based on time-resolved structural data.

Title:
Ancient Metal Mirror Alloy Revisited: Quasicrystalline Nanoparticles Observed
Authors:
Sekhar, JA; Mantri, AS; Yamjala, S; Saha, S; Balamuralikrishnan, R; Rao, PR Author Full Names: Sekhar, J. A.; Mantri, A. S.; Yamjala, S.; Saha, Sabyasachi; Balamuralikrishnan, R.; Rao, P. Rama
Source:
JOM, 67 (12):2976-2983; 10.1007/s11837-015-1524-3 DEC 2015
Abstract:
This article presents, for the first time, evidence of nanocrystalline structure, through direct transmission electron microscopy (TEM) observations, in a Cu-32 wt.% Sn alloy that has been made by an age-old, uniquely crafted casting process. This alloy has been used as a metal mirror for centuries. The TEM images also reveal five-sided projections of nano-particles. The convergent beam nano-diffraction patterns obtained from the nano-particles point to the nano-phase being quasicrystalline, a feature that has never before been reported for a copper alloy, although there have been reports of the presence of icosahedral 'clusters' within large unit cell intermetallic phases. This observation has been substantiated by x-ray diffraction, wherein the observed peaks could be indexed to an icosahedral quasi-crystalline phase. The mirror alloy casting has been valued for its high hardness and high reflectance properties, both of which result from its unique internal microstructure that include nano-grains as well as quasi-crystallinity. We further postulate that this microstructure is a consequence of the raw materials used and the manufacturing process, including the choice of mold material. While the alloy consists primarily of copper and tin, impurity elements such as zinc, iron, sulfur, aluminum and nickel are also present, in individual amounts not exceeding one wt.%. It is believed that these trace impurities could have influenced the microstructure and, consequently, the properties of the metal mirror alloy.

Title:
Mathematical crystallography in the 21st century
Authors:
Senechal, M Author Full Names: Senechal, Marjorie
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 230 (12):691-698; SI 10.1515/zkri-2015-1870 DEC 2015
Abstract:
As crystallography merges with materials science and engineering, mathematical crystallography is growing in new directions, including: Characterizing new materials with unusual properties; Imaging, including but not limited to diffraction; Exploring and exploiting superspaces; Mapping the aperiodic landscape, from chaos to classical periodicity and beyond; Re-modeling the structures of real crystals, both periodic and aperiodic; Modeling self-assembly and self-reorganization on the nanoscale. In short, it's not (just) about space groups and tilings anymore.

Title:
Incommensurate charge density wave modulated by period of Hubbard superlattices
Authors:
Zhang, LL; Huang, J; Duan, CB; Wang, WZ Author Full Names: Zhang, Liang-Liang; Huang, Jin; Duan, Cheng-Bo; Wang, Wei-Zhong
Source:
MODERN PHYSICS LETTERS B, 29 (32):10.1142/S0217984915502085 NOV 30 2015
Abstract:
The charge structure factor of the half-filled Hubbard superlattices with one on-site repulsive site and L-0 free sites per unit cell is investigated numerically. The behaviors of charge structure reveal a kind of evenodd L-0 disparity. For even L-0, we always observe a commensurate charge density wave (CDW). For odd L-0, we observe a commensurateincommensurate CDW transition at a critical on-site repulsion around the particlehole symmetric point. This transition results from the competition between the local charge correlations with odd distance and even distance.

Title:
Incommensurate-commensurate magnetic phase transition in SmRu2Al10
Authors:
Takai, S; Matsumura, T; Tanida, H; Sera, M Author Full Names: Takai, Shun; Matsumura, Takeshi; Tanida, Hiroshi; Sera, Masafumi
Source:
PHYSICAL REVIEW B, 92 (17):10.1103/PhysRevB.92.174427 NOV 30 2015
Abstract:
Magnetic properties of single crystalline SmRu2Al10 have been investigated by electrical resistivity, magnetic susceptibility, and specific heat. We have confirmed the successive magnetic phase transitions at T-N = 12.3 K and T-M = 5.6 K. Resonant x-ray diffraction has also been performed to study the magnetic structures. Below TN, the Sm3+ moments order in an incommensurate structure with q(1) = (0,0.759,0). The magnetic moments are oriented along the orthorhombic b axis, which coincides with the magnetization easy axis in the paramagnetic phase. A very weak third harmonic peak is also observed at q(3) = (0,0.278,0). The transition at T-M is a lock-in transition to the commensurate structure described by q(1) = (0,0.75,0). A well-developed third harmonic peak is observed at q(3) = (0,0.25,0). From the discussion of the magnetic structure, we propose that the long-range RKKY interaction plays an important role, in addition to the strong nearest-neighbor antiferromagnetic interaction.

Title:
Microstructure and High Damping Properties of Mg-Zn-Y Alloys Containing LPSO Phase and I Phase
Authors:
Wan, DQ; Li, JJ; Yu, T Author Full Names: Wan Diqing; Li Junjie; Yu Tian
Source:
RARE METAL MATERIALS AND ENGINEERING, 44 (11):2651-2655; NOV 2015
Abstract:
A high damping Mg-Zn-Y alloy containing LPSO phase and I phase was investigated. The microstructure of a high damping Mg80Y4Zn16 (at%) alloy was examined by optical microscopy (OM) and SEM. Furthermore, the differential thermal analysis (DTA) was used to analyze its phase transformation. Microstructure evolution and damping properties under the conditions of the different solid solution time (3, 6, 9 h) were studied. The results show that the main phase component of the Mg80Y4Zn16 alloy is alpha-Mg, Mg12ZnY (X phase), Mg3Zn6Y (I phase) and Mg10ZnY2 phase (LPSO phase), in which I phase and LPSO phase coexistence is firstly reported. The average damping value of the alloy is 0.03, indicating that it is a high damping alloy. The damping is strain amplitude dependent. The high damping mechanism was also discussed.

Update: 17-Dec-2015


Title:
On the adaptability of 1/1 cubic approximant structure in the Mg-Al-Zn system with the particular example of Mg32Al12Zn37
Authors:
Montagne, P; Tillard, M Author Full Names: Montagne, Pierre; Tillard, Monique
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 656 159-165; 10.1016/j.jallcom.2015.09.201 JAN 25 2016
Abstract:
Intermetallic Mg alloys are of interest in the development of light materials with specific properties and some of them are crystalline approximants of quasicrystalline materials. Mg32Al12Zn37 single crystal structure, cubic, Im (3) over bar, a = 14.1845(1) angstrom, is disordered and belongs to the well known 1/1 approximant structural type commonly called Mg-32(Al1-xZnx)(49) or T-phase. In this family, Mg32Al12Zn37 is a new member remarkable for its very special composition nearby intersection of the 2/1 and 1/1 lines that mark composition domains of cubic 2/1 and 1/1 approximants. Structural features are discussed comparatively with literature data to emphasize the great adaptability through atom disorder of the 1/1 structure. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Icosahedral hydrides of the Ti45Zr38Ni17-xCox nano-powders
Authors:
Zywczak, A; Rusinek, D; Czub, J; Sikora, M; Stepien, J; Gondek, L; Gajewska, M; Takasaki, A; Hoser, A Author Full Names: Zywczak, A.; Rusinek, D.; Czub, J.; Sikora, M.; Stepien, J.; Gondek, L.; Gajewska, M.; Takasaki, A.; Hoser, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 656 702-706; 10.1016/j.jallcom.2015.09.278 JAN 25 2016
Abstract:
In this communication we report the phase transitions associated with a hydrogen uptake in the quasicrystalline Ti45Zr38Ni17-xCox alloys that were prepared by mechanical alloying. The crystal structure evolution of the alloys was characterized by means of the variety of diffraction techniques (X-ray, neutron, and electron) as well as extended X-ray absorption fine structure spectroscopy (EXAFS). That analysis was supported by the results of the thermodynamic measurements, namely differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS). According to the neutron diffraction results, the transformation of the amorphous Ti45Zr38Ni17-xCox phases into the quasicrystalline state starts at the temperature of 475 degrees C. At 525 degrees C the icosahedral phase (the i-phase) is well-developed. At higher temperatures the i-phase transforms into the approximant w-phase and eventually into the cubic phase (the c-phase). The investigated icosahedral nano-powders exhibit a high capacity for gaseous H-2 reaching 2.2 wt.% at elevated temperatures. After a hydrogen uptake, a complex phase constitution including the simple hydrides is evidenced. Although the i-phases form again after hydrogen desorption, they are accompanied by the additional Zr3Co phase. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Thermal diffusivity and 3D-XY critical behavior of ferroelectric semiconductors (PbxSn1-x)(2)P2Se6
Authors:
Shvalya, V; Oleaga, A; Salazar, A; Kohutych, AA; Vysochanskii, YM Author Full Names: Shvalya, V.; Oleaga, A.; Salazar, A.; Kohutych, A. A.; Vysochanskii, Yu. M.
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 88 78-84; 10.1016/j.jpcs.2015.10.004 JAN 2016
Abstract:
An ac photopyroelectric calorimeter has been used to study the thermal diffusivity of the ferroelectric semiconductors family (PbxSn1 (-) (x))(2)P2Se6 (x=0-1) from 30 K to room temperature. Phase transitions have been found for x=0, 0.05, 0.2, 0.47 but not for x=1 in the full temperature range. A continuous phase transition has been found for x=0, 0.05, 0.2 and 0.47 which corresponds to the paraelectric commensurate to incommensurate phase. It has been possible to study the critical behavior of this transition for x=0, 0.05 and the critical parameters obtained have been alpha=-0.019, A(+)/A(-)=1.00 and alpha=-0.026, A(+)/A(-) A(-)=1.03, respectively, having fitted at the same time both the low and high temperature branches of the transition as rigorous critical theory indicates; these results agree with the theoretical prediction from renormalization group theory that this kind of transition complies with the 3D-XY universality class (alpha(theor)=-0.014, A(+)/A(-)=1.06), which has been experimentally confirmed only in a few materials. A first order incommensurate to ferroelectric phase transition has been characterized in x=0, 0.05 at lower temperature. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Planar lattices with tailorable coefficient of thermal expansion and high stiffness based on dual-material triangle unit
Authors:
Wei, K; Chen, HS; Pei, YM; Fang, DN Author Full Names: Wei, Kai; Chen, Haosen; Pei, Yongmao; Fang, Daining
Source:
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 86 173-191; 10.1016/j.jmps.2015.10.004 JAN 2016
Abstract:
The unexpected thermal distortions and failures in engineering raise the big concern about thermal expansion controlling. Thus, design of tailorable coefficient of thermal expansion (CTE) is urgently needed for the materials used in large temperature variation circumstance. Here, inspired by multi-fold rotational symmetry in crystallography, we have devised six kinds of periodic planar lattices, which incorporate tailorable CTE and high specific biaxial stiffness. Fabrication process, which overcame shortcomings of welding or adhesion connection, was developed for the dual-material planar lattices. The analytical predictions agreed well with the CTE measurements. It is shown that the planar lattices fabricated from positive CTE constituents, can give large positive, near zero and even negative CIEs. Furthermore, a generalized stationary node method was proposed for aperiodic lattices and even arbitrary structures with desirable thermal expansion. As an example, aperiodic quasicrystal lattices were designed and exhibited zero thermal expansion property. The proposed method for the lattices of lightweight, robust stiffness, strength and tailorable thermal expansion is useful in the engineering applications. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Magnetic structures of R5Ni2In4 and R11Ni4In9 (R = Tb and Ho): strong hierarchy in the temperature dependence of the magnetic ordering in the multiple rare-earth sublattices
Authors:
Ritter, C; Provino, A; Manfrinetti, P; Pecharsky, VK; Gschneidner, KA; Dhar, SK Author Full Names: Ritter, C.; Provino, A.; Manfrinetti, P.; Pecharsky, V. K.; Gschneidner, K. A., Jr.; Dhar, S. K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (47):10.1088/0953-8984/27/47/476001 DEC 2 2015
Abstract:
The magnetic properties and magnetic structures of the R5Ni2In4 and the microfibrous R11Ni4In9 compounds with R = Tb and Ho have been examined using magnetization, heat capacity, and neutron diffraction data. Rare earth atoms occupy three and five symmetrically inequivalent rare earth sites in R5Ni2In4 and R11Ni4In9 compounds, respectively. As a result of the intra-and inter-magnetic sublattice interactions, the magnetic exchange interactions are different for various rare earth sites; this leads to a cascade of magnetic transitions with a strong hierarchy in the temperature dependence of the magnetic orderings. A transition at T-C = 125 K in Tb5Ni2In4 [kappa(1) = (0, 0, 0)] leads to a ferro/ferrimagnetic order where the magnetic ordering in one of the three R-sublattices leads to the ordering of another one; the third sublattice stays non-magnetic. New magnetic Bragg peaks appearing below T-N = 20 K can be indexed with the incommensurate magnetic propagation vector kappa(2) = (0, 0.636, 1/2); at T-N = 20 K a cycloidal spin order, which acts mostly upon the third R-sublattice, occurs. Ho5Ni2In4 establishes first antiferromagnetism [kappa = (0, 0, 0)] at T-N = 31 K on two R-sublattices; then the system becomes ferro/ferrimagnetic at T-C = 25 K with the third sublattice ordering as well. Tb11Ni4In9 has three magnetic transitions at T-C = 135 K, T-N1 = 35 K and at T-N2 = 20 K; they are respectively coupled to the appearance of different propagation vectors [kappa(1) = (0, 0, 0), kappa(2) = (0, 0, 1/2), kappa(3) = (0, 1, 1/2)], which themselves are operating differently on the five different R-sublattices. Two sublattices remain mostly ferromagnetic down to lowest temperature while the three others are predominantly coupled antiferromagnetically. In Ho11Ni4In9 a purely antiferromagnetic order, described by four different magnetic propagation vectors [kappa(1) = (0, 0.62, 0), kappa(2) = (0, 1, 0), kappa(3) = (0, 0, 1/2), kappa(4) = (0, 1, 1/2)], succeedingly includes all five different sublattices on cooling through transitions at T-N1 = 22 K, T-N2 = 12 K, T-N3 = 8 K and T-N4 = 7 K. The strength of the magnetic interactions of the different sublattices can be linked to structural details for both R5Ni2In4 and R11Ni4In9 compounds.

Title:
Spiral magnetism in the single-band Hubbard model: the Hartree-Fock and slave-boson approaches
Authors:
Igoshev, PA; Timirgazin, MA; Gilmutdinov, VF; Arzhnikov, AK; Irkhin, VY Author Full Names: Igoshev, P. A.; Timirgazin, M. A.; Gilmutdinov, V. F.; Arzhnikov, A. K.; Irkhin, V. Yu
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (44):10.1088/0953-8984/27/44/446002 NOV 11 2015
Abstract:
The ground-state magnetic phase diagram is investigated within the single-band Hubbard model for square and different cubic lattices. The results of employing the generalized non-correlated mean-field (Hartree-Fock) approximation and generalized slave-boson approach by Kotliar and Ruckenstein with correlation effects included are compared. We take into account commensurate ferromagnetic, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often lacking in previous investigations. It is found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistically large Hubbard U by the correlation effects if nesting is absent and van Hove singularities are well away from the paramagnetic phase Fermi level. The magnetic phase separation plays an important role in the formation of magnetic states, the corresponding phase regions being especially wide in the vicinity of half-filling. The details of non-collinear and collinear magnetic ordering for different cubic lattices are discussed.

Title:
Quasicrystals at extreme conditions: The role of pressure in stabilizing icosahedral A(163)Cu(24)Fe(13) at high temperature
Authors:
Stagno, V; Bindi, L; Park, CY; Tkachev, S; Prakapenka, VB; Mao, HK; Hemley, RJ; Steinhardt, PJ; Fei, YW Author Full Names: Stagno, Vincenzo; Bindi, Luca; Park, Changyong; Tkachev, Sergey; Prakapenka, Vitali B.; Mao, H. -K.; Hemley, Russell J.; Steinhardt, Paul J.; Fei, Yingwei
Source:
AMERICAN MINERALOGIST, 100 (11-12):2412-2418; 10.2138/am-2015-5412 NOV-DEC 2015
Abstract:
Icosahedrite, the first natural quasicrystal with composition Al63Cu24Fe13, was discovered in several grains of the Khatyrka meteorite, a CV3 carbonaceous chondrite. The presence of icosahedrite associated with high-pressure phases like ahrensite and stishovite indicates formation at high pressures and temperatures due to an impact-induced shock. Previous experimental studies on the stability of synthetic icosahedral AlCuFe have either been limited to ambient pressure, for which they indicate incongruent melting at similar to 1123 K, or limited to room-temperature, for which they indicate structural stability up to about 35 GPa. These data are insufficient to experimentally constrain the formation and stability of icosahedrite under the conditions of high pressure and temperature that formed the Khatyrka meteorite. Here we present the results of room-temperature, high-pressure diamond-anvil cells measurements of the compressional behavior of synthetic icosahedrite up to 50 GPa. High P-T experiments were also carried out using both laser-heated diamond-anvil cells combined with in situ synchrotron X-ray diffraction (at 42 GPa) and multi-anvil apparatus (at 21 GPa) to investigate the structural evolution and crystallization of possible coexisting phases. The results demonstrate that the quasiperiodic order of icosahedrite is retained over the P-T range explored. We find that pressure acts to stabilize the icosahedral symmetry at temperatures much higher than previously reported. Direct solidification of AlCuFe quasicrystals from an unusual Al-Cu-rich melt is possible but it is limited to a narrow temperature range. Alternatively, quasicrystals may form after crystallization through solid-solid reactions of Al-rich phases. In either case, our results show that quasicrystals can preserve their structure even after hypervelocity impacts spanning a broad range of pressures and temperatures.

Title:
New horizon in quasicrystals
Authors:
Samavat, F; Kiani, M Author Full Names: Samavat, F.; Kiani, M.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (6):935-938; 10.1134/S1063774515060280 NOV 2015
Abstract:
Quasicrystals (QCs) are aperiodic intermetallic alloys that possess a long range positional order. They often exhibit crystallographically forbidden symmetries, most commonly fivefold and tenfold. The forbidden symmetry is related to the fact that the atoms are arranged quasiperiodically. Quasiperiodic translational order has physical consequences. For example, since electrons and phonons in quasicrystals do not encounter a periodic potential, quasicrystals have unusual resistive and elastic properties, and these have been exploited in several applications. The purpose of this introduction is to present certain properties that are relevant to the surface science of quasicrystals, as a launching point for the other articles in this special issue of progress in surface science.

Title:
Penrose tilings as model sets
Authors:
Shutov, AV; Maleev, AV Author Full Names: Shutov, A. V.; Maleev, A. V.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (6):797-804; 10.1134/S1063774515060322 NOV 2015
Abstract:
The Baake construction, based on generating a set of vertices of Penrose tilings as a model set, is refined. An algorithm and a corresponding computer program for constructing an uncountable set of locally indistinguishable Penrose tilings are developed proceeding from this refined construction. Based on an analysis of the parameters of tiling vertices, 62 versions of rhomb combinations at the tiling center are determined. The combinatorial structure of Penrose tiling worms is established. A concept of flip transformations of tilings is introduced that makes it possible to construct Penrose tilings that cannot be implemented in the Baake construction.

Title:
Birefringence of mechanically stressed Rb2ZnCl4 crystals
Authors:
Kurlyak, VY; Stadnyk, VY; Stakhura, VB; Kohut, ZO Author Full Names: Kurlyak, V. Yu.; Stadnyk, V. Yo.; Stakhura, V. B.; Kohut, Z. O.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (6):929-934; 10.1134/S1063774515060164 NOV 2015
Abstract:
The spectral and temperature dependences of the birefringence of mechanically free and uniaxially stressed Rb2ZnCl4 crystals have been investigated. It is shown that annealing a crystal leads to step changes in the birefringence at the phase transition from the incommensurate to commensurate phase, whereas the birefringence of as-prepared crystals changes continuously. It is established that the birefringence of Rb2ZnCl4 crystal is sensitive to uniaxial pressure; however, uniaxial stress does not change the character of its dispersion and temperature dependences. A new "pseudoisotropic" state of this crystal and a baric shift of the points of paraelectric phase-incommensurate phase-commensurate phase transitions to different temperature regions are found.

Title:
Refinement of Thermodynamic Parameters of the Mg24Y5, W and H Phases in the Mg-Zn-Y System
Authors:
Minamoto, S; Horiuchi, T; Miura, S Author Full Names: Minamoto, Satoshi; Horiuchi, Toshiaki; Miura, Seiji
Source:
MATERIALS TRANSACTIONS, 56 (10):60-64; 10.2320/matertrans.MH201418 OCT 2015
Abstract:
The Mg-Zn-Y alloy shows excellent mechanical properties which can be achieved by combining LPSO phase (known as X phase) and an icosahedral quasicrystal phase (land Z phases) in Mg solid solution (a phase). Thermodynamic data for the binary/ternary compounds Mg24Y5, X, Wand H have to be critically assessed to obtain accurate information of three-phase equilibrium in order to understand equilibria among these phases. In this research, we focused on developing CALPHAD (CALculation of PHAse Diagrams) thermodynamic database to evaluate phase diagrams for the Mg-Zn-Y system. Especially thermodynamic models for the Mg24Y5, W and H phases have been determined based on crystallographic data. Then thermodynamic parameters have been assessed to yield experimental data from EPMA/WDS, SEM, TEM and X-Ray diffraction.

Title:
Dielectric Properties and Phase Diagram of (Sr1-xBax)(2)Nb2O7 Single Crystals
Authors:
Akishige, Y; Kamata, M; Tsukada, S Author Full Names: Akishige, Yukikuni; Kamata, Misako; Tsukada, Shinya
Source:
FERROELECTRICS, 485 (1):73-79; SI 10.1080/00150193.2015.1060832 AUG 26 2015
Abstract:
Dielectric constants, epsilon(b) and epsilon(c) along the crystallographic b and c axes respectively, were measured in a temperature range of 10 - 700K on Ba-substituted Sr2Nb2O7 single crystals with different Ba concentrations up to x = 0.32. When x = 0, two dielectric anomalies were observed at T-I = 489K and at T-L = 100K, owing to the incommensurate phase transition and the low-temperature ferroelectric phase transition, respectively. Both T-I and T-L decrease with Ba-content x at initial slopes of ca. -19 and -37K/mol%, respectively, and become broad at x = 0.04 and almost disappear at x = 0.08. Furthermore, Ba-substitution induces a weak and broad dielectric maximum in epsilon(b)' vs. T curve at approximately T-m = 465K for x > 0.2. Phase diagram of this system was proposed.

Update: 10-Dec-2015


Title:
Smearing-type wear behavior of Al62Cu25.5Fe12.5 quasicrystal abrasive on soft metals
Authors:
Chen, YJ; Qiang, JB; Dong, C Author Full Names: Chen, Yongjun; Qiang, Jianbin; Dong, Chuang
Source:
INTERMETALLICS, 68 23-30; 10.1016/j.intermet.2015.09.001 JAN 2016
Abstract:
The abrasive polishing behavior of Al62Cu25.5Fe12.5 quasicrystal on Cu, Al and austenite stainless steel alloys were investigated, to compare with commonly used hard abrasives such as diamond, alumina and silica. The quasicrystal abrasive showed a dominating smearing-type wear mechanism, in sharp contrast to all the other three abrasives, as reflected by large indent size shrinking with respect to surface removal depth. The quasicrystal abrasive polishing, producing a flattened surface with minor depth removal, may open new application fields where low-wearing and fine surface finishing are demanded. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
X-ray diffraction study of the icosahedral AlCuFe quasicrystal at megabar pressures
Authors:
Takagi, S; Kyono, A; Mitani, S; Sugano, N; Nakamoto, Y; Hirao, N Author Full Names: Takagi, Sota; Kyono, Atsushi; Mitani, Saki; Sugano, Neo; Nakamoto, Yuki; Hirao, Naohisa
Source:
MATERIALS LETTERS, 161 13-16; 10.1016/j.matlet.2015.08.057 DEC 15 2015
Abstract:
We report in-situ synchrotron X-ray diffraction study of icosahedral (i)-AlCuFe quasicrystal (QC) at high pressure up to 104 GPa under ambient temperature using the diamond anvil technique. With compression, there is no obvious change of the diffraction pattern within the measured pressure range. Five characteristic peaks from the i-AlCuFe QC maintain up to 104 GPa. The unit cell volume of the i-AlCuFe QC decreases monotonously until 72 GPa. The experimental P-V compression curve below 72 GPa was fitted to the Birch-Murnaghan equation of state with V-0=2023(19) angstrom(3), K-0=131(7) GPa, K'=4.0 (fixed). The resulting EoS parameters are approximately consistent with those observed in previous study. A discontinuous volume change is observed between 72 and 75 GPa. These observed results indicate a phase transition from i-AlCuFe QC to an approximant crystal (AC) which has a similar local atomic arrangement as the QC. This study suggests that i-AlCuFe QC maintains its structure at least up to 72 GPa and then transforms to AC with small displacement of atoms. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Ni coated Ti1.4V0.6Ni composite as the negative electrode in Ni-MH battery
Authors:
Sun, LS; Lin, J; Liang, F; Cao, ZY; Wang, LM Author Full Names: Sun, Lianshan; Lin, Jing; Liang, Fei; Cao, Zhanyi; Wang, Limin
Source:
MATERIALS LETTERS, 161 686-689; 10.1016/j.matlet.2015.09.081 DEC 15 2015
Abstract:
Ti1.4V0.6Ni composite is synthesized by arc-melting and subsequent melt-spinning techniques. An improved electrochemical stability of Ti14V0.6Ni composite is obtained by chemical plating Ni. The phase structures of the composite contain icosahedral quasicrystal phase (i-phase) and TiNi-type phase. Different amount of Ni is coated on the surface of the composite particles. When Ti14V0.6Ni is plated with 19 wt% Ni, the discharge capacity retention ratio is promoted. Ni coating layer inhibits the dissolution of V from the composite and also promotes the high rate discharge property. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Antiphase Boundaries in the Turbostratically Disordered Misfit Compound (BiSe)(1+delta)NbSe2
Authors:
Mitchson, G; Falmbigl, M; Ditto, J; Johnson, DC Author Full Names: Mitchson, Gavin; Falmbigl, Matthias; Ditto, Jeffrey; Johnson, David C.
Source:
INORGANIC CHEMISTRY, 54 (21):10309-10315; 10.1021/acs.inorgchem.5b01648 NOV 2 2015
Abstract:
(BiSe)(1+delta)NbSe2 ferecrystals were synthesized in order to determine whether structural modulation in BiSe layers, characterized by periodic antiphase boundaries and Bi-Bi bonding, occurs. Specular X-ray diffraction revealed the formation of the desired compound with a c-axis lattice parameter of 1.21 nm from precursors with a range of initial compositions and initial periodicities. In-plane X-ray diffraction scans could be indexed as hk0 reflections of the constituents, with a rectangular basal BiSe lattice and a trigonal basal NbSe2 lattice. Electron micrographs showed extensive turbostratic disorder in the samples and the presence of periodic antiphase boundaries (approximately 1.5 nm periodicity) in BiSe layers oriented with the [110] direction parallel to the zone axis of the microscope. This indicates that the structural modulation in the BiSe layers is not due to coherency strain resulting from commensurate in-plane lattices. Electrical transport measurements indicate that holes are the dominant charge carrying species, that there is a weak decrease in resistivity as temperature decreases, and that minimal charge transfer occurs from the BiSe to NbSe2 layers. This is consistent with the lack of charge transfer from the BiX to the TX2 layers reported in misfit layer compounds where antiphase boundaries were observed. This suggests that electronic considerations, i.e., localization of electrons in the Bi-Bi pairs at the antiphase boundaries, play a dominant role in stabilizing the structural modulation.

Title:
Unravelling structural ambiguities in lithium- and manganese-rich transition metal oxides
Authors:
Shukla, AK; Ramasse, QM; Ophus, C; Duncan, H; Hage, F; Chen, GY Author Full Names: Shukla, Alpesh Khushalchand; Ramasse, Quentin M.; Ophus, Colin; Duncan, Hugues; Hage, Fredrik; Chen, Guoying
Source:
NATURE COMMUNICATIONS, 6 10.1038/ncomms9711 OCT 2015
Abstract:
Although Li- and Mn-rich transition metal oxides have been extensively studied as high-capacity cathode materials for Li-ion batteries, the crystal structure of these materials in their pristine state is not yet fully understood. Here we apply complementary electron microscopy and spectroscopy techniques at multi-length scale on well-formed Li-1.2(Ni0.13Mn0.54Co0.13)O-2 crystals with two different morphologies as well as two commercially available materials with similar compositions, and unambiguously describe the structural make-up of these samples. Systematically observing the entire primary particles along multiple zone axes reveals that they are consistently made up of a single phase, save for rare localized defects and a thin surface layer on certain crystallographic facets. More specifically, we show the bulk of the oxides can be described as an aperiodic crystal consisting of randomly stacked domains that correspond to three variants of monoclinic structure, while the surface is composed of a Co- and/or Ni-rich spinel with antisite defects.

Title:
Fermi states and anisotropy of Brillouin zone scattering in the decagonal Al-Ni-Co quasicrystal
Authors:
Rogalev, VA; Groning, O; Widmer, R; Dil, JH; Bisti, F; Lev, LL; Schmitt, T; Strocov, VN Author Full Names: Rogalev, V. A.; Groening, O.; Widmer, R.; Dil, J. H.; Bisti, F.; Lev, L. L.; Schmitt, T.; Strocov, V. N.
Source:
NATURE COMMUNICATIONS, 6 10.1038/ncomms9607 OCT 2015
Abstract:
Quasicrystals (QCs) are intermetallic alloys that have excellent long-range order but lack translational symmetry in at least one dimension. The valence band electronic structure near the Fermi energy E-F in such materials is of special interest since it has a direct relation to their unusual physical properties. However, the Fermi surface (FS) topology as well as the mechanism of QC structure stabilization are still under debate. Here we report the first observation of the three-dimensional FS and valence band dispersions near E-F in decagonal Al70Ni20Co10 (d-AlNiCo) QCs using soft X-ray angle-resolved photoemission spectroscopy. We show that the FS, formed by dispersive Al sp-states, has a multicomponent character due to a large contribution from high-order bands. Moreover, we discover that the magnitude of the gap at the FS related to the interaction with Brillouin zone boundary (Hume-Rothery gap) critically differs for the periodic and quasiperiodic directions.

Update: 3-Dec-2015


Title:
Microstructure and mechanical properties of laser beam welded Al-Li alloy 2060 with Al-Mg filler wire
Authors:
Zhang, XY; Yang, WX; Xiao, RS Author Full Names: Zhang, Xinyi; Yang, Wuxiong; Xiao, Rongshi
Source:
MATERIALS & DESIGN, 88 446-450; 10.1016/j.matdes.2015.08.144 DEC 25 2015
Abstract:
Alloy 2060-T8 is a newly developed high-strength Al-Li alloy for applications in aircraft industry. Crack-free welds were obtained in laser beam welding with 5087 filler wire under optimized welding conditions. In this paper, fusion zone microstructure and joint mechanical properties were investigated. Microstructure typical for the weld metal consists of alpha-Al matrix with a few nanoscale precipitates inside and a coarse icosahedral quasi-crystalline T-2 phase at the dendritic and grain boundaries. The quasicrystalline occurred normally in Al-Li-Cu alloys with higher Li contents. Our investigations show that the icosahedral quasicrystalline phase T-2 phase forms in the laser-welded Al-Li alloy 2060 with lower Li content as a result of segregation and replacement of Mg element. The joint tensile strength in as-welded condition is around 317 MPa, about 63% of that of the base metal, and fracture occurs within the fusion zone. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Explosively welded multilayer Ni-Al composites
Authors:
Bataev, IA; Ogneva, TS; Bataev, AA; Mali, VI; Esikov, MA; Lazurenko, DV; Guo, Y; Jorge, AM Author Full Names: Bataev, I. A.; Ogneva, T. S.; Bataev, A. A.; Mali, V. I.; Esikov, M. A.; Lazurenko, D. V.; Guo, Y.; Jorge Junior, A. M.
Source:
MATERIALS & DESIGN, 88 1082-1087; 10.1016/j.matdes.2015.09.103 DEC 25 2015
Abstract:
In this study, the structure of explosively welded Ni-Al multilayer composites was investigated. In particular, the interface between Ni and Al plates was studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). Continuous interlayers of mixed Al and Ni were found at the interface. The Al and Ni in these zones were heated above their melting temperatures, non-uniformly mixed, and rapidly solidified. Several intermetallic phases, including the decagonal phase and metastable Al9Ni2, were observed in these zones using electron diffraction. A cellular dislocation structure formed in the Ni plates and a polygonized dislocation structure formed in the Al plates due to the extremely high strain rate deformation and heating. Subsequent heat treatment at 620 degrees C led to the rapid formation of stable intermetallic layers at the interfaces. The growth of the intermetallic layers was considerably faster in the explosively welded composite than in the reference sample. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Effect of icosahedral phase on the crystallographic texture and mechanical anisotropy of duplex structured Mg-Li alloys
Authors:
Xu, DK; Li, CQ; Wang, BJ; Han, EH Author Full Names: Xu, D. K.; Li, C. Q.; Wang, B. J.; Han, E. H.
Source:
MATERIALS & DESIGN, 88 88-97; 10.1016/j.matdes.2015.08.123 DEC 25 2015
Abstract:
Through comparing the microstructure and mechanical properties of Mg-6%Li and Mg-6%Li-6%Zn-1.2%Y alloys, the difference in their mechanical anisotropy have been deeply investigated. Due to the formation of I-phase (Mg3Zn6Y, icosohedral structure), the volume fraction of beta-Li phases formed in Mg-6%Li-6%Zn-1.2%Y alloy was two times higher than that in Mg-6%Li alloy even these two alloys having the same Li content. Texture analysis demonstrated that I-phase particle stimulated nucleation of recrystallization (PSN) and the formation of higher volume fraction of beta-Li phases can remarkably weaken the basal texture of alpha-Mg phases, resulting in a very weak mechanical anisotropy. On the contrary, the basal texture of the alpha-Mg phases in Mg-6%Li alloy was quite strong and obvious mechanical anisotropy between differently oriented samples can be observed. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Phase Formation in the Rapidly Solidified Al70-xGaxPd13Mn17 Alloys
Authors:
Yadav, TP; Shaz, MA; Mukhopadhyay, NK; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Shaz, M. A.; Mukhopadhyay, N. K.; Tiwari, R. S.; Srivastava, O. N.
Source:
TRANSACTIONS OF THE INDIAN INSTITUTE OF METALS, 68 (6):1145-1149; 10.1007/s12666-015-0660-3 DEC 2015
Abstract:
In the present investigation, the effect of Ga substitution at Al site on the phase formation and stabilization of decagonal quasicrystalline phase in the rapidly solidified Al70-xGaxPd13Mn17 alloys have been studied by employing X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive x-ray analysis. The as-cast and rapidly solidified alloys with x = 0, 2.5 and 5 have been investigated. The melt-spinning technique has been used for rapid solidification of the as-cast alloys. The alloys up to 5 at.% Ga exhibit the formation of small amount of icosahedral quasicrystalline phases along with major amount of decagonal phase in the rapidly solidied ribbons. The energy dispersive X-ray analysis investigations suggest the homogeneous presence of Ga in the quasicrystalline alloys.

Title:
Three-dimensional charge density wave order in YBa2Cu3O6.67 at high magnetic fields
Authors:
Gerber, S; Jang, H; Nojiri, H; Matsuzawa, S; Yasumura, H; Bonn, DA; Liang, R; Hardy, WN; Islam, Z; Mehta, A; Song, S; Sikorski, M; Stefanescu, D; Feng, Y; Kivelson, SA; Devereaux, TP; Shen, ZX; Kao, CC; Lee, WS; Zhu, D; Lee, JS Author Full Names: Gerber, S.; Jang, H.; Nojiri, H.; Matsuzawa, S.; Yasumura, H.; Bonn, D. A.; Liang, R.; Hardy, W. N.; Islam, Z.; Mehta, A.; Song, S.; Sikorski, M.; Stefanescu, D.; Feng, Y.; Kivelson, S. A.; Devereaux, T. P.; Shen, Z. -X.; Kao, C. -C.; Lee, W. -S.; Zhu, D.; Lee, J. -S.
Source:
SCIENCE, 350 (6263):949-952; 10.1126/science.aac6257 NOV 20 2015
Abstract:
Charge density wave (CDW) correlations have been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured with x-ray scattering at zero and low fields. We combined a pulsed magnet with an x-ray free-electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields of up to 28 tesla. While the zero-field CDW order, which develops at temperatures below similar to 150 kelvin, is essentially two dimensional, at lower temperature and beyond 15 tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW appears around the zero-field superconducting transition temperature; in contrast, the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.

Title:
Tuning of magnetic ordering by Y substitution onto Tb site in the nanocrystalline TbMnO3
Authors:
Chakraborty, KR; Shukla, R; Kaushik, SD; Mukadam, MD; Siruguri, V; Tyagi, AK; Yusuf, SM Author Full Names: Chakraborty, Keka R.; Shukla, Rakesh; Kaushik, S. D.; Mukadam, M. D.; Siruguri, V.; Tyagi, A. K.; Yusuf, S. M.
Source:
JOURNAL OF APPLIED PHYSICS, 118 (16):10.1063/1.4934251 OCT 28 2015
Abstract:
We report the magnetic properties, of nano-crystalline powders Tb1-xYxMnO3 (x = 0, 0.1, 0.2, 0.3 and 0.4), as perceived by neutron diffraction, and elucidate the effect of Tb site substitution on the magnetic structure of TbMnO3. All samples crystallized in the orthorhombic structure conforming to space group Pnma, and exhibited an incommensurate collinear antiferromagnetic ordering of the Mn ions below similar to 40 K. Furthermore, at T <= 20 K, all these samples showed a change in magnetic structure (of Mn moments) to a spiral ordering down to 2K, the lowest measured temperature. For the samples with x = 0, 0.1, and 0.2, a short-ranged two dimensional (2D) ordering of Tb moments was also observed at 2K. However, for the other samples (x-0.3 and 0.4), no magnetic ordering of Tb moments was found down to 2K. So with Y substitution, a crossover from 2D ordering to a disordering of Tb moments was observed. The moments at the Mn site were found to be lower than the full Mn3+(4 mu B) moment for all the samples below 40 K. The magnetic properties of all the samples studied by us in nano form are more pronounced than those of the reported single crystals of same compositions [V. Yu. Ivanov et al., JETP Lett. 91, 392-397 (2010)]. (C) 2015 AIP Publishing LLC.

Title:
Exchange integrals of commensurate and incommensurate structures of MFe4Al8 (M = U, Sc)
Authors:
Recko, K Author Full Names: Recko, K.
Source:
JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17 (9-10):1403-1409; SEP-OCT 2015
Abstract:
The appearance of the commensurability of UFe4Al8 alloy considering incommensurability of ScFe4Al8 compound is analysed on the basis of Heisenberg Hamiltonian. The influence of Dzyaloshinskii - Moriya and Ruderman-Kittel-Kasuya-Yoshida as well as the dipolar interactions as the main reasons of the noncollinearity and incommensurability of the alloys belonging to ThMn12 family is investigated. The values and directions of the spin ordering found by magnetic diffraction are compared to that one's deriving from grand state configurations obtained by a simulated annealing algorithm. The lock-in magnetic modulations due to substitution of scandium by uranium atoms is discussed based on an appropriate exchange constants ratios.

Title:
The Incommensurate Phase Transformation in TlInS2 Ferroelectric
Authors:
Salnik, A; Gololobov, YP; Borovoy, NA Author Full Names: Salnik, A.; Gololobov, Yu. P.; Borovoy, N. A.
Source:
FERROELECTRICS, 484 (1):62-68; SI 10.1080/00150193.2015.1059716 AUG 5 2015
Abstract:
The features of the crystal structure of c and 2c TlInS2 polytypes have been studied by single-crystal X-ray diffraction method in the temperature range 180 K-300 K. In the c polytype the appearance of the incommensurate phase with modulation vector q. d; 0; 0: 25/. dD0: 04/was observed at the temperature of 238 K (on cooling). The active phase formation occurred between 213 K and 217 K. The incommensurability parameter d decreases monotonically to the zero as the temperature approaches 195 K. For the 2c polytype the modulation satellites for both incommensurate and commensurate phases were not observed in the temperature range 180 K-300 K.

Update: 26-Nov-2015


Title:
Superconductivity in the orthorhombic phase of thermoelectric CsPbxBi4-xTe6 with 0.3 <= x <= 1.0
Authors:
Zhang, RX; Yang, HX; Tian, HF; Chen, GF; Wu, SL; Wei, LL; Li, JQ Author Full Names: Zhang, R. X.; Yang, H. X.; Tian, H. F.; Chen, G. F.; Wu, S. L.; Wei, L. L.; Li, J. Q.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 232 50-55; 10.1016/j.jssc.2015.08.050 DEC 2015
Abstract:
Experimental measurements clearly reveal the presence of bulk superconductivity in the CsPbxBi4-xTe6 (0.3 <= x <= 1.0) materials, i.e. the first member of the thermoelectric series of Cs[PbmBi3Te5+m], these materials have the layered orthorhombic structure containing infinite anionic [PbBi3Te6]- slabs separated with Cs+ cations. Temperature dependences of electrical resistivity, magnetic susceptibility, and specific heat have consistently demonstrated that the superconducting transition in Cs0.96Pb0.25Bi3.75Te6.04 occurs at T-c=3.1 K, with a superconducting volume fraction close to 100% at 1.8 K. Structural study using aberration-corrected STEM/TEM reveals a rich variety of microstructural phenomena in correlation with the Pb-ordering and chemical inhomogeneity. The superconducting material CS0.96Pb0.25Bi3.75Te6.04 with the highest T-c shows a clear ordered structure with a modulation wave vector of q approximate to a*/2+c*/1.35 on the a-c plane. Our study evidently demonstrates that superconductivity deriving upon doping of narrow-gap semiconductor is a viable approach for exploration of novel superconductors. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Phason space analysis and structure modelling of 100 angstrom-scale dodecagonal quasicrystal in Mn-based alloy
Authors:
Ishimasa, T; Iwami, S; Sakaguchi, N; Oota, R; Mihalkovic, M Author Full Names: Ishimasa, Tsutomu; Iwami, Shuhei; Sakaguchi, Norihito; Oota, Ryo; Mihalkovic, Marek
Source:
PHILOSOPHICAL MAGAZINE, 95 (33):3745-3767; 10.1080/14786435.2015.1095365 NOV 22 2015
Abstract:
The dodecagonal quasicrystal classified into the five-dimensional space group P12(6)/mmc, recently discovered in a Mn-Cr-Ni-Si alloy, has been analysed using atomic-resolution spherical aberration-corrected electron microscopy, i.e. high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and conventional transmission electron microscopy. By observing along the 12-fold axis, non-periodic tiling consisting of an equilateral triangle and a square has been revealed, of which common edge length is a=4.560 angstrom. These tiles tend to form a network of dodecagons of which size is (2+root 3)a approximate to 17 angstrom in diameter. The tiling was interpreted as an aggregate of 100 angstrom-scale oriented domains of high- and low-quality quasicrystals with small crystallites appearing at their boundaries. The quasicrystal domains exhibited a densely filled circular acceptance region in the phason space. This is the first observation of the acceptance region in an actual dodecagonal quasicrystal. Atomic structure model consistent with the electron microscopy images is a standard Frank-Kasper decoration of the triangle and square tiles that can be inferred from the crystal structures of Zr4Al3 and Cr3Si. Four kinds of layers located at z = 0, +/- 1/4 and 1/2 are stacked periodically along the 12-fold axis, and the atoms at z = 0 and 1/2 form hexagonal anti-prisms consistently with the 12(6)-screw axis. The validity of this structure model was examined by means of powder X-ray diffraction.

Title:
Effect of Ca and CaO on the microstructure and hot compressive deformation behavior of Mg-9.5Zn-2.0Y alloy
Authors:
Kwak, TY; Lim, HK; Kim, WJ Author Full Names: Kwak, T. Y.; Lim, H. K.; Kim, W. J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 648 146-156; 10.1016/j.msea.2015.09.014 NOV 11 2015
Abstract:
In this study, the effect of adding 0.3 wt% Ca to a Mg-9.5Zn-2.0Y alloy with icosahedral (I) phase (Mg3Zn6Y) was examined. The Ca alloying was done by two different routes, either through a master alloy produced with Mg and CaO (which is convenient from the points of view of safety and cost) or by direct addition of powdered Ca to the molten alloy. The small addition of Ca (CaO) effectively increased the ignition temperature of the alloys (by about 90 K), which is promising for fire suppression and safe handling with the molten alloys, but it led to the formation of Ca2Mg5Zn13 phase at grain boundaries or interdendritic interfaces, causing partial melting and intergranular cracking during compressive deformation near similar to 615 K. As a result, the upper limit of hot workability temperature decreased to 598 K, which is lower than that of the Mg-9.5Zn-2.0Y alloy by 125 K. The cast Mg-9.5Zn-2.0Y-03Ca alloys prepared using the two different routes exhibited high similarity in ignition temperature, chemical composition, microstructure, hot compressive behaviors and processing maps, indicating that the use of CaO is as effective as the use of Ca in producing the same quality of Ca containing Mg alloys. The flow stresses during hot compressive deformation and the activation energy for plastic flow remained unaffected by the Ca (CaO) alloying, but decreased the strain rate sensitivity at high strain rates over 10(-3) s(-1) due to the initiation of either power-law breakdown or partial melting by adiabatic heating. Because of this, the Ca containing alloy lost hot workability at high strain rates by comparison to the Ca-free alloy. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Incommensurateness in nanotwinning models of modulated martensites
Authors:
Benesova, B; Frost, M; Kampschulte, M; Melcher, C; Sedlak, P; Seiner, H Author Full Names: Benesova, Barbora; Frost, Miroslav; Kampschulte, Malte; Melcher, Christof; Sedlak, Petr; Seiner, Hanus
Source:
PHYSICAL REVIEW B, 92 (18):10.1103/PhysRevB.92.180101 NOV 6 2015
Abstract:
We study the formation of modulated martensites in ferromagnetic shape memory alloys by a mathematical model originating from the nanotwinning concept. The results show that the incommensurateness, systematically observed in experiments for the modulated phases, may be understood as a precursor effect of the intermartensitic transitions, and its appearance does not contradict the nanotwinning concept itself. The model sufficiently explains the different levels of incommensurateness reported from different experimental observations for the 14-layered and 10-layered martensites of the Ni-Mn-Ga alloy and outlines the mechanism of formation of faults in the stacking sequences of these materials.

Title:
Quantum phase transitions and decoupling of magnetic sublattices in the quasi-two-dimensional Ising magnet Co3V2O8 in a transverse magnetic field
Authors:
Fritsch, K; Ehlers, G; Rule, KC; Habicht, K; Ramazanoglu, M; Dabkowska, HA; Gaulin, BD Author Full Names: Fritsch, K.; Ehlers, G.; Rule, K. C.; Habicht, K.; Ramazanoglu, M.; Dabkowska, H. A.; Gaulin, B. D.
Source:
PHYSICAL REVIEW B, 92 (18):10.1103/PhysRevB.92.180404 NOV 5 2015
Abstract:
The application of a magnetic field transverse to the easy axis, Ising direction in the quasi-two-dimensional kagome staircase magnet, Co3V2O8, induces three quantum phase transitions at low temperatures, ultimately producing a novel high field polarized state, with two distinct sublattices. New time-of-flight neutron scattering techniques, accompanied by large angular access, high magnetic field infrastructure allow the mapping of a sequence of ferromagnetic and incommensurate phases and their accompanying spin excitations. At least one of the transitions to incommensurate phases at mu H-0(c1) similar to 6.25 T and mu H-0(c2) similar to 7 T is discontinuous, while the final quantum critical point at mu H-0(c3) similar to 13 T is continuous.

Title:
Fluctuating orders and quenched randomness in the cuprates
Authors:
Nie, LM; Sierens, LEH; Melko, RG; Sachdev, S; Kivelson, SA Author Full Names: Nie, Laimei; Sierens, Lauren E. Hayward; Melko, Roger G.; Sachdev, Subir; Kivelson, Steven A.
Source:
PHYSICAL REVIEW B, 92 (17):10.1103/PhysRevB.92.174505 NOV 4 2015
Abstract:
We study a quasi-two-dimensional classical Landau-Ginzburg-Wilson effective field theory in the presence of quenched disorder in which incommensurate charge-density wave and superconducting orders are intertwined. The disorder precludes long-range charge-density wave order, but not superconducting or nematic order. We select three representative sets of input parameters and compute the corresponding charge-density wave structure factors using both large-N techniques and classical Monte Carlo simulations. Where nematicity and superconductivity coexist at low temperature, the peak height of the charge-density wave structure factor decreases monotonically as a function of increasing temperature, unlike what is seen in x-ray experiments on YBa2Cu3O6+x. Conversely, where the thermal evolution of the charge-density wave structure factor qualitatively agrees with experiments, the nematic correlation length, computed to one-loop order, is shorter than the charge-density wave correlation length.

Title:
Symmetries and color symmetries of a family of tilings with a singular point
Authors:
Evidente, IF; Felix, RP; Loquias, MJC Author Full Names: Evidente, Imogene F.; Felix, Rene P.; Loquias, Manuel Joseph C.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 583-591; 10.1107/S2053273315016137 6 NOV 2015
Abstract:
Tilings with a singular point are obtained by applying conformal maps on regular tilings of the Euclidean plane and their symmetries are determined. The resulting tilings are then symmetrically colored by applying the same conformal maps on colorings of regular tilings arising from sublattice colorings of the centers of the tiles. In addition, conditions are determined in order that the coloring of a tiling with singularity that is obtained in this manner is perfect.

Title:
Unusual Strong Incommensurate Modulation in a Tungsten-Bronze-Type Relaxor PbBiNb5O15
Authors:
Lin, K; Zhou, ZY; Liu, LJ; Ma, HQ; Chen, J; Deng, JX; Sun, JL; You, L; Kasai, H; Kato, K; Takata, M; Xing, XR Author Full Names: Lin, Kun; Zhou, Zhengyang; Liu, Laijun; Ma, Hongqiang; Chen, Jun; Deng, Jinxia; Sun, Junliang; You, Li; Kasai, Hidetaka; Kato, Kenichi; Takata, Masaki; Xing, Xianran
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137 (42):13468-13471; 10.1021/jacs.5b08230 OCT 28 2015
Abstract:
Pb- or Bi-based perovskite oxides have been widely studied and used because of their large ferroelectric polarization features induced by stereochemically active 6s(2) lone pair electrons. It is intriguing whether this effect could exist in other related systems. Herein, we designed and synthesized a mixed Pb and Bi A site polar compound, PbBiNb5O15, with the TTB framework. The as-synthesized material turns out to be a relaxor with weak macroscopic ferroelectricity but adopts strong local polarizations. What's more, unusual five orders of incommensurate satellite reflections with strong intensities were observed under the electron diffraction, suggesting that the modulation is highly developed with large amplitudes. The structural modulation was solved with a (3 + 1)D superspace group using high-resolution synchrotron radiation combined with anomalous dispersion X-ray diffraction technique to distinguish Pb from Bi. We show that the strong modulation mainly originates from lone-pair driven Pb2+-Bi3+ ordering in the large pentagonal caves, which can suppress the local polarization in x-y plane in long ranges. Moreover, the as-synthesized ceramics display strong relaxor ferroelectric feature with transition temperature near room temperature and moderate dielectric properties, which could be functionalized to be electromechanical device materials.

Title:
On the stability of a quasicrystal and its crystalline approximant in a system of hard disks with a soft corona
Authors:
Pattabhiraman, H; Gantapara, AP; Dijkstra, M Author Full Names: Pattabhiraman, Harini; Gantapara, Anjan P.; Dijkstra, Marjolein
Source:
JOURNAL OF CHEMICAL PHYSICS, 143 (16):10.1063/1.4934499 OCT 28 2015
Abstract:
Using computer simulations, we study the phase behavior of a model system of colloidal hard disks with a diameter sigma and a soft corona of width 1.4 sigma. The particles interact with a hard core and a repulsive square-shoulder potential. We calculate the free energy of the random-tiling quasicrystal and its crystalline approximants using the Frenkel-Ladd method. We explicitly account for the configurational entropy associated with the number of distinct configurations of the random-tiling quasicrystal. We map out the phase diagram and find that the random tiling dodecagonal quasicrystal is stabilised by entropy at finite temperatures with respect to the crystalline approximants that we considered, and its stability region seems to extend to zero temperature as the energies of the defect-free quasicrystal and the crystalline approximants are equal within our statistical accuracy. (C) 2015 AIP Publishing LLC.

Title:
Corrosion Behavior of Psi and beta Quasicrystalline Al-Cu-Fe Alloy
Authors:
Torres, A; Serna, S; Patino, C; Rosas, G Author Full Names: Torres, Alvaro; Serna, Sergio; Patino, Cristobal; Rosas, Gerardo
Source:
ACTA METALLURGICA SINICA-ENGLISH LETTERS, 28 (9):1117-1122; 10.1007/s40195-015-0302-0 SEP 2015
Abstract:
Two nanostructured Al-Cu-Fe alloys, Al64Cu24Fe12 and Al62.5Cu25.2Fe12.3, have been studied. Icosahedral quasicrystalline (psi) Al64Cu24Fe12 and crystalline cubic (beta) Al62.5Cu25.2Fe12.3 cylindrical ingots were first produced using normal casting techniques. High-energy mechanical milling was then conducted to obtain psi icosahedral and beta intermetallic nanostructured powders. Electrochemical impedance spectroscopy, linear polarization resistance, and potentiodynamic polarization were used to investigate the electrochemical corrosion characteristics of the powders in solutions with different pH values. Current density (i(corr)), polarization resistance (R-p), and impedance modulus (vertical bar Z vertical bar) were determined. The results showed that regardless of pH value, increasing the solution temperature enhanced the corrosion resistance of the both phases. However, the electrochemical behavior of the psi phase indicated that its stability depends on the submerged exposure time in neutral and alkaline environments. This behavior was related to the type of corrosion products present on the surfaces of the particles along with the diffusion and charge-transfer mechanisms of the corrosion process.

Update: 19-Nov-2015


Title:
Large coincidence lattice on Au/Fe3O4 incommensurate structure for spintronic applications
Authors:
Munoz-Noval, A; Rubio-Zuazo, J; Salas-Colera, E; Serrano, A; Rubio-Marcos, F; Castro, GR Author Full Names: Munoz-Noval, Alvaro; Rubio-Zuazo, Juan; Salas-Colera, Eduardo; Serrano, Aida; Rubio-Marcos, Fernando; Castro, German R.
Source:
APPLIED SURFACE SCIENCE, 355 698-701; 10.1016/j.apsusc.2015.07.158 NOV 15 2015
Abstract:
The design of metallic hybrid systems for spintronics has been widely studied during the past decade, motivated by the promising technological applications of these materials. Nevertheless, the importance of preserving the native structure and properties of the interfaces is often ignored. Here, we present the fabrication of nanocrystalline Au(001) onto a single oriented Fe3O4 (0 0 1) thin film as a promising hybrid system to develop spintronic devices by growing Au over the Fe3O4 by using a simple one-pot Pulsed Laser Deposition (PLD) approach. The structural coupling between Au nanocrystals and Fe3O4 layer results in the development of an incommensurate structure based on a coincidence lattice of order 35, which preserves the intrinsic properties of the Au nanocrystals, the Fe3O4 matrix and the interface between them. The general strategy described in the present work preserves the structure and main intrinsic properties of the constituting materials, being a fundamental issue for the future development of spintronic devices. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Unoccupied electronic structure of Ni2MnGa ferromagnetic shape memory alloy
Authors:
Maniraj, M; D'Souza, SW; Rai, A; Schlagel, DL; Lograsso, TA; Chakrabarti, A; Barman, SR Author Full Names: Maniraj, M.; D'Souza, S. W.; Rai, Abhishek; Schlagel, D. L.; Lograsso, T. A.; Chakrabarti, Aparna; Barman, S. R.
Source:
SOLID STATE COMMUNICATIONS, 222 1-4; 10.1016/j.ssc.2015.08.003 NOV 2015
Abstract:
Momentum resolved inverse photoemission spectroscopy measurements show that the dispersion of the unoccupied bands of Ni(2)MaGa is significant in the austenite phase. In the martensite phase, it is markedly reduced, which is possibly related to the structural transition to an incommensurate modulated state in the martensite phase. Based on the first principle calculations of the electronic structure of Ni-Mn-Ga, we show that the modification of the spectral shape with surface composition is related to change in the hybridization between the Mn 3d and Ni 3d-like states that dominate the unoccupied conduction band. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Local cluster symmetry of a highly ordered quasicrystalline Al58Cu26Ir16 extracted through multivariate analysis of STEM images
Authors:
Seki, T; Abe, E Author Full Names: Seki, Takehito; Abe, Eiji
Source:
MICROSCOPY, 64 (5):341-349; 10.1093/jmicro/dfv035 OCT 2015
Abstract:
The structure of a highly ordered Al58Cu26Ir16 decagonal quasicrystal (d-QC), which is constructed by a periodic stack of quasiperiodic atomic planes, was investigated using aberration-corrected scanning transmission electron microscopy. The entire quasiperiodic structure can be well described based on the pentagonal Penrose lattice decorated with a decagonal columnar cluster 2 nm across, and the individual clusters apparently showed up with localized atomic disorder to various degree that blurs the underlying cluster symmetry. Multivariate analysis of the cluster images with principal component analysis has successfully extracted two fundamental clusters, which are with definite mirror and 10-fold-rotation symmetries; this is the first solid example of the d-QC composed of multiple fundamental clusters with different symmetry. Consequently, it is found that all the observed variations can be reasonably interpreted by a linear combination between these two fundamental clusters of mirror and 10-fold symmetries, indicating that the possible atomic disorder is strongly restricted by these particular symmetries. Characteristic distributions of the mirror/10-fold clusters on the pentagonal Penrose lattice are also described.

Update: 12-Nov-2015


Title:
Magnetic anisotropy in FeSb studied by Fe-57 Mossbauer spectroscopy
Authors:
Komedera, K; Jasek, AK; Blachowski, A; Ruebenbauer, K; Krzton-Maziopa, A Author Full Names: Komedera, K.; Jasek, A. K.; Blachowski, A.; Ruebenbauer, K.; Krzton-Maziopa, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 399 221-227; 10.1016/j.jmmm.2015.09.076 FEB 1 2016
Abstract:
The Fe1+xSb compound has been synthesized close to stoichiometry with x=0.023(8). The compound was investigated by Fe-57 Mossbauer spectroscopy in the temperature range 4.2-300 K. The anti-ferromagnetic ordering temperature was found as 232 K i.e. much higher than for the less stoichiometric material. Regular iron was found to occupy two different positions in proportion 2:1. They differ by the electric quadrupole coupling constants and both of them exhibit extremely anisotropic electric field gradient tensor (EFG) with the asymmetry parameter eta approximate to 1. The negative component of both EFGs is aligned with the c-axis of the hexagonal unit cell, while the positive component is aligned with the (120) direction. Hence, a model describing deviation from the NiAs P6(3)/mmc symmetry group within Fe-planes has been proposed. Spectra in the magnetically ordered state could be explained by introduction of the incommensurate spin spirals propagating through the iron atoms in the direction of the c-axis with a complex pattern of the hyperfine magnetic fields distributed within a-b plane. Hyperfine magnetic field pattern of spirals due to major regular iron is smoothed by the spin polarized itinerant electrons, while the minor regular iron exhibits hyperfine field pattern characteristic of the highly covalent bonds to the adjacent antimony atoms. The excess interstitial iron orders magnetically at the same temperature as the regular iron, and magnetic moments of these atoms are likely to form two-dimensional spin glass with moments lying in the a-b plane. The upturn of the hyperfine field for minor regular iron and interstitial iron is observed below 80 K. Magneto-elastic effects are smaller than for FeAs, however the recoilless fraction increases significantly upon transition to the magnetically ordered state. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Flat and conical incommensurate magnetic structures in the two-subsystem partially frustrated Heisenberg ferrimagnet
Authors:
Martynov, SN Author Full Names: Martynov, S. N.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 398 121-126; 10.1016/j.jmmm.2015.09.046 JAN 15 2016
Abstract:
The phase transitions into flat and conical incommensurate magnetic structures are considered for a ferrimagnet with the dominant nonfrustrated exchange between the spins in one crystallographic position, competing exchanges between the spins in another position and frustrated exchange between the spins in different positions. The appearance conditions and the temperatures of the second order phase transitions are analytically obtained in the mean field approximation. The first order phase transition between these states is studied and the phase diagrams of temperature vs frustrated exchanges are calculated by the numerical minimization of free energy. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Temperature dependence of the propagation vector in Ni3-xCoxV2O8 with x=0.1 and 0.5
Authors:
Lee, S; Lee, H; Choi, YN; Semkin, MA; Teplykh, AE; Skryabin, YN; Li, WH; Pirogov, AN Author Full Names: Lee, Seongsu; Lee, Heeju; Choi, Yong Nam; Semkin, M. A.; Teplykh, A. E.; Skryabin, Yu. N.; Li, Wen-Hsien; Pirogov, A. N.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 397 225-229; 10.1016/j.jmmm.2015.08.106 JAN 1 2016
Abstract:
We present the susceptibility and neutron diffraction data on multiferroic Ni3-xCoxV2O8 with x=0.1 and 0.5. The temperature dependence of the susceptibility indicates that the magnetic order-disorder transition occurs at T-HTI=8.5 K in both samples. Below T-HTI, the high-temperature incommensurate magnetic structure is realized, which undergoes a transition to the low-temperature incommensurate phase when the sample is cooled. The temperature evolution of the propagation vector k for x=0.1 is very weak, which confirms previous studies showing that substitution of 3.5% Ni ions by Co ions suppresses the explicit temperature dependence of k that is observed in the parent compound. On the other hand, we found that the vector k for x=0.5 exhibits a definite temperature dependence, which differs from the case of the undopal sample (x=0)., (C) 2015 Elsevier By. All rights reserved.

Title:
Microstructure of mechanically alloyed and annealed Al62Cu25.5Fe12.5 powder
Authors:
Mitka, M; Goral, A; Rogal, L; Litynska-Dobrzynska, L Author Full Names: Mitka, Mikolaj; Goral, Anna; Rogal, Lukasz; Litynska-Dobrzynska, Lidia
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 653 47-53; 10.1016/j.jallcom.2015.08.250 DEC 25 2015
Abstract:
The influence of mechanical alloying (MA) of Al62Cu25.5Fe12.5 (at.%) powder obtained with different milling speeds and milling time and subsequent annealing on its microstructure and phase composition was investigated by means X-ray diffraction, scanning and transmission electron microscopy (SEM and TEM) methods. The power was milled in a high energy planetary ball mill at the rotation speed 250, 300 and 350 rpm for 3, 6, 10 and 20 h using WC milling media. The annealing of milled powders was performed at 800 degrees C for 4 h. Nano-quasicrystalline icosahedral phase (i-phase) was obtained in the as-milled powder at a speed 350 rpm, while the lower milling speed resulted in the formation of cubic beta-Al(Cu, Fe) phase. In all annealed powders the i-phase coexisting with the ordered lambda-Al(Cu, Fe) phase and small amount of the l-Al13Fe4 phase has been observed. The highest volume fraction of i-phase was found in the annealed powder milled at 250 rpm. After annealing the grain size increases compared to the as-milled powder. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Fabrication and properties of Ti-Zr-Ni quasicrystal and bulk composite materials by high pressure sintering
Authors:
Han, QG; Zhong, JL; Zhang, Q; Liu, B; Wang, LM Author Full Names: Han, Qi-Gang; Zhong, Ji-Lun; Zhang, Qiang; Liu, Biao; Wang, Li-Min
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 428 62-67; 10.1016/j.jnoncrysol.2015.08.008 NOV 15 2015
Abstract:
The overall composition of Ti40.83Zr40.83Ni18.34 quasicrystal powders that consist of the stable icosahedral phase (I-phase) was prepared by mechanical alloying and the subsequent heat treatment in a vacuum furnace. Then, bulk composite materials (BCMs) with the composition of Ti40.83Zr40.83Ni18.34 I-phase quasicrystal powders and carbonyl nickel powders as metal bonding agent (20 wt.%), have been fabricated by high pressure sintering. The Vickers hardness, compressive strength, deformation at fracture, Young's modulus, and wear resistance of the BCMs have been studied in detail, after being sintered at different pressure and temperature. It indicates that high pressure sintering enables us to produce the BCMs (about 10 mm in diameter and 3 mm in height) with a short sintered time of 10 mm and high pressure of 3.0 GPa. In addition, the optimum sintered condition is 3.0 GPa-600 degrees C, which is beneficial of the improvement of the performances of BCM, such as the Vickers hardness of 389, the compressive strength of 430 MPa, the deformation at fracture of 2.20%, the Young's modulus of 19 GPa, the lowest value of friction coefficient at 0.45 +/- 0.13, and wear mass losses of 024 mm(3). This work shows a promise in practical fabrication of BCM that consist of the stable Ti-Zr-Ni icosahedral quasicrystalline phase may be developed. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Nanosized helical magnetic domains in strongly frustrated Fe3PO4O3
Authors:
Ross, KA; Bordelon, MM; Terho, G; Neilson, JR Author Full Names: Ross, K. A.; Bordelon, M. M.; Terho, G.; Neilson, J. R.
Source:
PHYSICAL REVIEW B, 92 (13):10.1103/PhysRevB.92.134419 OCT 26 2015
Abstract:
Fe3PO4O3 forms a noncentrosymmetric lattice structure (space group R3m) comprising triangular motifs of Fe3+ coupled by strong antiferromagnetic interactions (vertical bar circle dot(CW)vertical bar > 900 K). Neutron diffraction from polycrystalline samples shows that strong frustration eventually gives way to an ordered helical incommensurate structure below T-N = 163 K, with the helical axis in the hexagonal ab plane and a modulation length to similar to 86 angstrom. The magnetic structure consists of an unusual needlelike correlation volume that extends past 900 angstrom along the hexagonal c axis but is limited to similar to 70 angstrom in the ab plane, despite the three-dimensional nature of the magnetic sublattice topology. The small in-plane correlation length, which persists to at least T = T-N/40, indicates a robust blocking of long-range order of the helical magnetic structure, and therefore stable domain walls, or other defect spin textures, must be abundant in Fe3PO4O3. Temperature-dependent neutron powder diffraction reveals small negative thermal expansion below T-N. No change in lattice symmetry is observed on cooling through TN, as revealed by high-resolution synchrotron x-ray diffraction. The previously reported reduced moment of the Fe3+ ions (S = 5/2), mu similar to 4.2 mu(B), is confirmed here through magnetization studies of a magnetically diluted solid solution series of compounds, Fe(3-x)GaxPO4O3, and is consistent with the refined magnetic moment from neutron diffraction 4.14(2) mu(B). We attribute the reduced moment to a modified spin density distribution arising from ligand charge transfer in this insulating oxide.

Title:
Solitonic Spin-Liquid State Due to the Violation of the Lifshitz Condition in Fe1+yTe
Authors:
Materne, P; Koz, C; Rossler, UK; Doerr, M; Goltz, T; Klauss, HH; Schwarz, U; Wirth, S; Rossler, S Author Full Names: Materne, Ph.; Koz, C.; Roessler, U. K.; Doerr, M.; Goltz, T.; Klauss, H. H.; Schwarz, U.; Wirth, S.; Roessler, S.
Source:
PHYSICAL REVIEW LETTERS, 115 (17):10.1103/PhysRevLett.115.177203 OCT 21 2015
Abstract:
A combination of phenomenological analysis and Mossbauer spectroscopy experiments on the tetragonal Fe1+yTe system indicates that the magnetic ordering transition in compounds with higher Fe excess, y >= 0.11, is unconventional. Experimentally, a liquidlike magnetic precursor with quasistatic spin order is found from significantly broadened Mossbauer spectra at temperatures above the antiferromagnetic transition. The incommensurate spin-density wave order in Fe1+yTe is described by a magnetic free energy that violates the weak Lifshitz condition in the Landau theory of second-order transitions. The presence of multiple Lifshitz invariants provides the mechanism to create multidimensional, twisted, and modulated solitonic phases.

Title:
Rare earth ferrites LuFe2O4 +/- x polymorphism, polytypism and metastable phases
Authors:
Hervieu, M; Damay, F; Maignan, A; Martin, C Author Full Names: Hervieu, M.; Damay, F.; Maignan, A.; Martin, C.
Source:
SOLID STATE SCIENCES, 48 A1-A16; 10.1016/j.solidstatesciences.2015.07.013 OCT 2015
Abstract:
This work is a compendium of the structural properties of layered LnFe(2)O(4 +/- x) ferrites, focussed on recently discovered polymorphs and their transitions through five complex commensurate and incommensurate modulated structures. These phases are obtained varying the oxygen content (reversibly from O-4.0 to O-4.5) or applying high pressure (up to 15 GPa). The relationships between the different structures are discussed and models are proposed. These ferrites, which contain magnetic cations and exhibit remarkable 3D flexibility, open the road for magnetic, electric, catalytic or energy materials. (C) 2015 Elsevier Masson SAS. All rights reserved.

Title:
Low temperature oxygen diffusion mechanisms in Nd2NiO4+delta and Pr2NiO4+delta via large anharmonic displacements, explored by single crystal neutron diffraction
Authors:
Ceretti, M; Wahyudi, O; Cousson, A; Villesuzanne, A; Meven, M; Pedersen, B; Bassat, JM; Paulus, W Author Full Names: Ceretti, M.; Wahyudi, O.; Cousson, A.; Villesuzanne, A.; Meven, M.; Pedersen, B.; Bassat, J. M.; Paulus, W.
Source:
JOURNAL OF MATERIALS CHEMISTRY A, 3 (42):21140-21148; 10.1039/c5ta05767a 2015
Abstract:
We investigated the structure of Nd2NiO4+delta and Pr2NiO4+delta by single crystal neutron diffraction studies. While the real structure of both compounds is incommensurate, the scattering density of the respective average structures was explored using the Maximum Entropy Method. Unusually high displacement factors were found for the equatorial and apical oxygen atoms showing respectively large displacement amplitudes towards [001] and [110] with respect to the F-symmetry cell. The shifts of the apical oxygen atoms reach up to 1 angstrom from their average position, corresponding to a 25 degrees tilt of the NiO6 octahedra. At 400 degrees C, i.e. slightly above the orthorhombic-tetragonal phase transition, the anharmonic apical oxygen displacements towards [110] in the commensurate tetragonal parent structure are strongly enhanced, showing a double-well potential and pointing towards the interstitial vacancy sites, creating a quasi continuous shallow energy diffusion pathway between apical and interstitial oxygen sites. These large displacement amplitudes are considered to be - at least partially - of dynamical origin, which is consistent with a phonon assisted diffusion mechanism, already activated at very moderate temperatures.

Update: 5-Nov-2015


Title:
Effects of cyclic extrusion and compression parameters on microstructure and mechanical properties of Mg-1.50Zn-0.25Gd alloy
Authors:
Huang, H; Tang, ZB; Tian, Y; Jia, GZ; Niu, JL; Zhang, H; Pei, J; Yuan, GY; Ding, WJ Author Full Names: Huang, Hua; Tang, Zibo; Tian, Yuan; Jia, Gaozhi; Niu, Jialin; Zhang, Hua; Pei, Jia; Yuan, Guangyin; Ding, Wenjiang
Source:
MATERIALS & DESIGN, 86 788-796; 10.1016/j.matdes.2015.07.155 DEC 5 2015
Abstract:
Mg-1.50Zn-0.25Gd (at.%) alloy reinforced by icosahedral quasicrystalline phase (I-phase) was fabricated and then subjected to cyclic extrusion and compression (CEC) at 250, 300, 350 and 400 degrees C, respectively. The effects of CEC parameters including passes and temperatures on microstructure evolution and room temperature tensile mechanical properties were characterized and discussed. The results show that more passes are beneficial for secondary phase precipitation, grain refinement and basal texture weakening; while moderate temperature is beneficial for secondary phase precipitation and basal texture weakening by particle stimulated recrystallization nucleation (PSN), and lower temperature is beneficial for grain refinement. The alloy has the highest yield strength after CEC at 250 degrees C because of grain refinement and basal texture strengthening, while it has the highest elongation after being processed with 8 passes of CEC due to grain refinement and basal texture weakening. The processing passes have more important effects on microstructure evolution and mechanical properties than that of temperature during CEC. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Evolution of the dense packings of spherotetrahedral particles: from ideal tetrahedra to spheres
Authors:
Jin, WW; Lu, P; Li, SX Author Full Names: Jin, Weiwei; Lu, Peng; Li, Shuixiang
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep15640 OCT 22 2015
Abstract:
Particle shape plays a crucial role in determining packing characteristics. Real particles in nature usually have rounded corners. In this work, we systematically investigate the rounded corner effect on the dense packings of spherotetrahedral particles. The evolution of dense packing structure as the particle shape continuously deforms from a regular tetrahedron to a sphere is investigated, starting both from the regular tetrahedron and the sphere packings. The dimer crystal and the quasicrystal approximant are used as initial configurations, as well as the two densest sphere packing structures. We characterize the evolution of spherotetrahedron packings from the ideal tetrahedron (s = 0) to the sphere (s = 1) via a single roundness parameter s. The evolution can be partitioned into seven regions according to the shape variation of the packing unit cell. Interestingly, a peak of the packing density Phi is first observed at s approximate to 0.16 in the Phi-s curves where the tetrahedra have small rounded corners. The maximum density of the deformed quasicrystal approximant family (Phi approximate to 0.8763) is slightly larger than that of the deformed dimer crystal family (Phi approximate to 0.8704), and both of them exceed the densest known packing of ideal tetrahedra (Phi approximate to 0.8563).

Title:
Neutron diffraction investigation of the H - T phase diagram above the longitudinal incommensurate phase of BaCo2V2O8
Authors:
Grenier, B; Simonet, V; Canals, B; Lejay, P; Klanjsek, M; Horvatic, M; Berthier, C Author Full Names: Grenier, B.; Simonet, V.; Canals, B.; Lejay, P.; Klanjsek, M.; Horvatic, M.; Berthier, C.
Source:
PHYSICAL REVIEW B, 92 (13):10.1103/PhysRevB.92.134416 OCT 20 2015
Abstract:
The quasi-one-dimensional antiferromagnetic Ising-like compound BaCo2V2O8 has been shown to be describable by the Tomonaga-Luttinger liquid theory in its gapless phase induced by a magnetic field applied along the Ising axis. Above 3.9 T, this leads to an exotic field-induced low-temperature magnetic order, made of a longitudinal incommensurate spin-density wave, stabilized by weak interchain interactions. By single-crystal neutron diffraction we explore the destabilization of this phase at a higher magnetic field. We evidence a transition at around 8.5 T towards a more conventional magnetic structure with antiferromagnetic components in the plane perpendicular to the magnetic field. The phase diagram boundaries and the nature of this second field-induced phase are discussed with respect to previous results obtained by means of nuclear magnetic resonance and electron spin resonance, and in the framework of the simple model based on the Tomonaga-Luttinger liquid theory, which obviously has to be refined in this complex system.

Title:
Microscopic adjustment of misfit strain and charge segregation in [Bi2Sr2O4](0.51)CoO2
Authors:
Maki, M; Takakura, S; Nishizaki, T; Ichikawa, F Author Full Names: Maki, Makoto; Takakura, Sho-ichi; Nishizaki, Terukazu; Ichikawa, Fusao
Source:
PHYSICAL REVIEW B, 92 (16):10.1103/PhysRevB.92.165117 OCT 16 2015
Abstract:
From scanning tunneling microscopy of the misfit-layered cobaltate [Bi2Sr2O4](0.51)CoO2 single crystals, we observed structural short corrugations oriented in the direction inclined with respect to the incommensurate axis. Results show that the spatial distribution of the electronic charge density is also modified in relation to the atomic displacement. Our data strongly suggest that the rocksalt structure flexibly mounted on the CoO2 layer affects the electronic properties of this system.

Title:
Phase Diagram of Modulated Structures in Ferroelectric Crystals Based on Quantum Ising Model with Third-Neighbor Interactions
Authors:
Mashiyama, H Author Full Names: Mashiyama, Hiroyuki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (10):10.7566/JPSJ.84.104712 OCT 15 2015
Abstract:
Incommensurate commensurate phase transitions are analyzed using a model derived from the normal coordinate Hamiltonian for a crystal lattice. The Hamiltonian consists of a local self-potential and effective third-neighbor interactions. Free energies of various modulated phases are calculated with a mean-field approximation under the condition that two quantum states within the local potential are important at low temperature. It is demonstrated that the quantum effect works to stabilize the incommensurate phase rather than the commensurate phase. Even at zero temperature, the incommensurate phase can occupy a finite region in the phase diagram. This situation is similar to quantum paraelectricity in some ferroelectrics, and can be expected as a general feature of modulated structures of dielectric crystals. The phase diagram for ferroic first- and third-neighbor interactions but antiferroic second-neighbor interactions is constructed theoretically and is discussed in detail to explain qualitatively the low-temperature behavior of some ferroelectric crystals.

Title:
Competing magnetic and structural states in multiferroic YMn2O5 at high pressure
Authors:
Kozlenko, DP; Dang, NT; Kichanov, SE; Lukin, EV; Pashayev, AM; Mammadov, AI; Jabarov, SH; Dubrovinsky, LS; Liermann, HP; Morgenroth, W; Mehdiyeva, RZ; Smotrakov, VG; Savenko, BN Author Full Names: Kozlenko, D. P.; Dang, N. T.; Kichanov, S. E.; Lukin, E. V.; Pashayev, A. M.; Mammadov, A. I.; Jabarov, S. H.; Dubrovinsky, L. S.; Liermann, H. -P.; Morgenroth, W.; Mehdiyeva, R. Z.; Smotrakov, V. G.; Savenko, B. N.
Source:
PHYSICAL REVIEW B, 92 (13):10.1103/PhysRevB.92.134409 OCT 12 2015
Abstract:
The magnetic, structural, and vibrational properties of YMn2O5 multiferroic have been studied by means of neutron, x-ray powder diffraction, and Raman spectroscopy at pressures up to 6 and 30 GPa, respectively. Application of high pressure, P > 1 GPa, leads to a gradual suppression of the commensurate and incommensurate antiferromagnetic (AFM) phases with a propagation vector q = (1/2,0, q(z) similar to 1/4) and appearance of the commensurate AFM phase with q = (1/2,0,1/2). This observation is sharply contrasting to general trend towards stabilization of commensurate AFM phase with q = (1/2,0,1/4) found in other RMn2O5 compounds upon lattice compression. At P similar to 16 GPa a structural phase transformation accompanied by anomalies in lattice compression and pressure behavior of vibrational modes was observed. The comparative analysis of high-pressure and R-cation radius variation effects clarified a role of particular magnetic interactions in the formation of the magnetic states of RMn2O5 compounds.

Update: 29-Oct-2015


Title:
First-order commensurate-incommensurate magnetic phase transition in the coupled FM spin-1/2 two-leg ladders
Authors:
Jahangiri, J; Hadipour, H; Mandavifar, S; Shayesteh, SF Author Full Names: Jahangiri, J.; Hadipour, H.; Mandavifar, S.; Shayesteh, S. Farjami
Source:
PHYSICA B-CONDENSED MATTER, 476 24-28; 10.1016/j.physb.2015.07.012 NOV 1 2015
Abstract:
We consider the spin-1/2 two-leg ladders with ferromagnetic (FM) interactions along legs and rungs. Using the stochastic series expansion QMC method, we study the low-temperature magnetic behavior of the system. An isolated spin-1/2 FM two-leg ladder is in the gapped saturated FM phase at zero temperature. As soon as the spin-1/2 FM two-leg ladders are connected with antiferromagnetic (AFM) inter-ladder interaction, a first-order commensurate-incommensurate quantum phase transition occurs in the ground state magnetic phase diagram. In fact a jump in the magnetization curve is observed. We found that, coupled spin-1/2 FM two-leg ladders are in a nonmagnetic phase at zero temperature. Applying a magnetic field, the ground state of coupled spin-1/2 FM two-leg ladders remains in the nonmagnetic phase up to a quantum saturate critical field. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Predicting complex mineral structures using genetic algorithms
Authors:
Mohn, CE; Kob, W Author Full Names: Mohn, Chris E.; Kob, Walter
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (42):10.1088/0953-8984/27/42/425201 OCT 28 2015
Abstract:
We show that symmetry-adapted genetic algorithms are capable of finding the ground state of a range of complex crystalline phases including layered- and incommensurate superstructures. This opens the way for the atomistic prediction of complex crystal structures of functional materials and mineral phases.

Title:
Incommensurate modulation and thermal expansion of Sr3B2 (+) Si-x(1) (-) O-x(8) (-) (x/2) solid solutions
Authors:
Volkov, S; Bubnova, R; Bolotina, N; Krzhizhanovskaya, M; Belousova, O; Filatov, S Author Full Names: Volkov, Sergey; Bubnova, Rimma; Bolotina, Nadezhda; Krzhizhanovskaya, Maria; Belousova, Olga; Filatov, Stanislav
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 489-497; 10.1107/S2052520615011713 5 OCT 2015
Abstract:
Crystal structures of Sr3B2 (+) Si-x(1) (-) O-x(8) (- x/2) solid solutions with nominal compositions x = 0.28, 0.53, 0.78 in the Sr3B2SiO8-Sr2B2O5 section of the SrO-B2O3-SiO2 system are refined using single-crystal X-ray diffraction data. Incommensurate structure modulations are mainly associated with various orientations of corner-sharing (B,Si)-polyhedra. Preference is given to the (3 + 2)-dimensional symmetry group Pnma(0 beta gamma)000(0 beta gamma)000 for a single crystal compared with an alternate model of a twin formed by monoclinic components, each of them corresponding to the (3 + 1)-dimensional symmetry group P2(1)/n(0 beta gamma). Single-phase polycrystalline samples of solid solutions are investigated by high-temperature X-ray powder diffraction in air. Orientation preferences of the BO3 units lead to a strong anisotropy of thermal expansion. Negative expansion is observed along the a axis over the temperature range 303-753 K. Anisotropy decreases both on heating and decreasing of the boron content.

Title:
Decagonite, Al71Ni24Fe5, a quasicrystal with decagonal symmetry from the Khatyrka CV3 carbonaceous chondrite
Authors:
Bindi, L; Yao, N; Lin, C; Hollister, LS; Andronicos, CL; Distler, VV; Eddy, MP; Kostin, A; Kryachko, V; MacPherson, GJ; Steinhardt, WM; Yudovskaya, M; Steinhardt, PJ Author Full Names: Bindi, Luca; Yao, Nan; Lin, Chaney; Hollister, Lincoln S.; Andronicos, Christopher L.; Distler, Vadim V.; Eddy, Michael P.; Kostin, Alexander; Kryachko, Valery; MacPherson, Glenn J.; Steinhardt, William M.; Yudovskaya, Marina; Steinhardt, Paul J.
Source:
AMERICAN MINERALOGIST, 100 (10):2340-2343; 10.2138/am-2015-5423 OCT 2015
Abstract:
Decagonite is the second natural quasicrystal, after icosahedrite (Al63Cu24Fe13), and the first to exhibit the crystallographically forbidden decagonal symmetry. It was found as rare fragments up to similar to 60 mu m across in one of the grains (labeled number 126) of the Khatyrka meteorite, a CV3 carbonaceous chondrite. The meteoritic grain contains evidence of a heterogeneous distribution of pressures and temperatures that occurred during impact shock, in which some portions of the meteorite reached at least 5 GPa and 1200 degrees C. Decagonite is associated with Al-bearing trevorite, diopside, forsterite, ahrensite, clinoenstatite, nepheline, coesite, pentlandite, Cu-bearing troilite, icosahedrite, khatyrkite, taenite, Al-bearing taenite, and steinhardtite. Given the exceedingly small size of decagonite, it was not possible to determine most of the physical properties for the mineral. A mean of seven electron microprobe analyses (obtained from three different fragments) gave the formula Al70.2(3)Ni24.5(4)Fe5.3(2), on the basis of 100 atoms. A combined TEM and single-crystal X-ray diffraction study revealed the unmistakable signature of a decagonal quasicrystal: a pattern of sharp peaks arranged in straight lines with 10-fold symmetry together with periodic patterns taken perpendicular to the 10-fold direction. For quasicrystals, by definition, the structure is not reducible to a single three-dimensional unit cell, so neither cell parameters nor Z can be given. The likely space group is P10(5)/mine, as is the case for synthetic A(17)Ni(24)Fe(5). The five strongest powder-diffraction lines [d in angstrom (I/I-0)] are: 2.024 (100), 3.765 (50), 2.051 (45), 3.405 (40), 1.9799 (40). The new mineral has been approved by the IMA-NMNC Commission (IMA2015-017) and named decagonite for the 10-fold symmetry of its structure. The finding of a second natural quasicrystal informs the longstanding debate about the stability and robustness of quasicrystals among condensed matter physicists and demonstrates that mineralogy can continue to surprise us and have a strong impact on other disciplines.

Title:
Secondary phases in quasicrystal-reinforced Mg-3.5Zn-0.6Gd Mg alloy
Authors:
Huang, H; Tian, Y; Yuan, GY; Chen, CL; Wang, ZC; Ding, WJ; Inoue, A Author Full Names: Huang, Hua; Tian, Yuan; Yuan, Guangyin; Chen, Chunlin; Wang, Zhongchang; Ding, Wenjiang; Inoue, Akihisa
Source:
MATERIALS CHARACTERIZATION, 108 132-136; 10.1016/j.matchar.2015.09.005 OCT 2015
Abstract:
The secondary phases in quasicrystal-reinforced Mg-Zn-Gd alloys are investigated by transmission electron microscopy. The orientation relationships between the dendritic I-phase and the Mg matrix are identified to be [1 1 (2) over bar 0](Mg)parallel to[2-fold](I-phase) and (0001)(Mg)parallel to(5-fold)(I-phase). We also find that the dendritic I-phase is brittle along 2-fold, 5-fold, and 3-fold atomic planes during hot extrusion. Moreover, new orientation relations [(1) over bar 101](Mg)parallel to[mirror 2-fold](I-phase) and (0 (1) over bar 1 1)(Mg)parallel to(5-fold)(I-phase) are found between nanoscale I-phase and Mg matrix. The findings have implications for our understanding of excellent mechanical properties of the I-phase-strengthened Mg alloys. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Strain induced incommensurate structures in vicinity of reconstructive phase transitions
Authors:
Korzhenevskii, AL; Dmitriev, V Author Full Names: Korzhenevskii, A. L.; Dmitriev, V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (37):10.1088/0953-8984/27/37/375401 SEP 23 2015
Abstract:
General conditions controlling the formation of incommensurate phases in crystals undergoing reconstructive phase transitions are analyzed in the framework of a model-free phenomenological approach. A universal trend to stabilizing such intermediate phases in the vicinity of reconstructive phase transitions stems from the fact that certain high-order improper Lifshitz invariants reduce at such transformations to ones bi-linearly coupling critical displacement gradients and strains or even to the proper Lifshitz invariant. The approach developed here introduces a universal mechanism for the formation both of premartensite incommensurate phases and complex structures with giant unit cells, as found in some elemental crystals at high pressure.

Title:
Characteristics of 5M modulated martensite in Ni-Mn-Ga magnetic shape memory alloys
Authors:
Cakir, A; Acet, M; Righi, L; Albertini, F; Farle, M Author Full Names: Cakir, A.; Acet, M.; Righi, L.; Albertini, F.; Farle, M.
Source:
AIP ADVANCES, 5 (9):10.1063/1.4932233 SEP 2015
Abstract:
The applicability of the magnetic shape memory effect in Ni-Mn-based martensitic Heusler alloys is closely related to the nature of the crystallographically modulated martensite phase in these materials. We study the properties of modulated phases as a function of temperature and composition in three magnetic shape memory alloys Ni49.8Mn25.0Ga25.2, Ni49.8Mn27.1Ga23.1 and Ni49.5Mn28.6Ga21.9. The effect of substituting Ga for Mn leads to an anisotropic expansion of the lattice, where the b-parameter of the 5M modulated structure increases and the a and c-parameters decrease with increasing Ga concentration. The modulation vector is found to be both temperature and composition dependent. The size of the modulation vector corresponds to an incommensurate structure for Ni49.8Mn25.0Ga25.2 at all temperatures. For the other samples the modulation is incommensurate at low temperatures but reaches a commensurate value of q approximate to 0.400 close to room temperature. The results show that commensurateness of the 5M modulated structure is a special case of incommensurate 5M at a particular temperature. (C) 2015 Author(s).

Update: 22-Oct-2015


Title:
Thermoelectric properties of Tsai-type Au-Al-RE (RE: Yb, Tm, Gd) quasicrystals and approximants
Authors:
Takagiwa, Y; Kimura, K; Sawama, K; Hiroto, T; Nishio, K; Tamura, R Author Full Names: Takagiwa, Y.; Kimura, K.; Sawama, K.; Hiroto, T.; Nishio, K.; Tamura, R.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 652 139-144; 10.1016/j.jallcom.2015.08.081 DEC 15 2015
Abstract:
The thermoelectric properties of Tsai-type Au-Al-RE (RE: Yb, Tm, Gd) icosahedral quasicrystals (QCs) and their approximant crystals (ACs) have been investigated from 373 K to 873 K. Comparison of their thermoelectric properties above room temperature is of great interest since resonant states are likely to be present in the electronic density of states near the Fermi level for the Au-Al-Yb QC, which should influence the thermoelectric properties and, hence, the dimensionless figure of merit. The electrical conductivity of Au-Al-Yb ACs varies significantly, i.e. from 3000 Omega(-1) cm(-1) to 5200 Omega(-1) cm(-1), with changing the Au/Al composition whereas the other compounds have conductivities of similar to 3000 Omega(-1) cm(-1). Such an anomalous behavior of the Au-Al-Yb ACs is understood to be due to the existence of a resonant peak originating from hybridization of Yb f-states and Au/Al sp-states. A maximum power factor of 230 mu Wm(-1) K-2 at 873 K is obtained in 1/1-Au48Al37Yb15 AC, which is significantly higher than those of Al-based icosahedral phases at the same temperature. On the other hand, the room-temperature thermal conductivities for Au-Al-RE compounds range from 3 to 4 W m(-1) K-1, reflecting their complex crystal structures with a large unit cell and mixed and/or partially occupied sites. Consequently, both 1/1-Au50Al35Yb15 and Au48Al37Yb15 ACs have similar maximum figures of merit of 0.014 at 873 K. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Deformation mechanism of Ni54Mn25Ga20.9Gd0.1 high-temperature shape memory alloy
Authors:
Zhang, X; Sui, JH; Cai, W; Liu, QS; Liu, AL Author Full Names: Zhang, Xin; Sui, Jiehe; Cai, Wei; Liu, Qingsuo; Liu, Ailian
Source:
INTERMETALLICS, 67 52-55; 10.1016/j.intermet.2015.07.017 DEC 2015
Abstract:
Ni54Mn25Ga20.9Gd0.1 Polycrystalline high-temperature shape memory alloy displayed high compressive fracture strain of 24.6% and large shape memory effect of 7.5%. However, its deformation mechanism was still unknown. In this paper, the structure revolution characterized by XRD and TEM indicated a new deformation mechanism different before was found. The deformation process of Ni54Mn25Ga20.9Gd0.1 alloy could be divided into four stages, including elastic deformation of non-modulated tetragonal martensite (T), stress-induced T to seven-layered modulated martensite (7 M) transformation, variants reorientation of 7 M, and elastic plastic deformation of reoriented 7 M. The 7 M formed by compression deformation disappeared completely after heating to the temperature above A(f). (C) 2015 Elsevier Ltd. All rights reserved.

Title:
From crystal morphology to molecular and scale crystallography
Authors:
Janner, A; Janssen, T Author Full Names: Janner, A.; Janssen, T.
Source:
PHYSICA SCRIPTA, 90 (8):10.1088/0031-8949/90/8/088007 AUG 2015
Abstract:
A number of topics, ranging from morphology of aperiodic crystals to indexed enclosing forms of axial-symmetric proteins, nucleic acids and viruses, have been selected among those investigated by the authors in 50 years of research. The basic symmetries involved in fields like superspace, molecular and scale crystallography, are considered from a personal point of view in their time evolution. A number of specific subjects follow, chosen among a few highlights and presented according to the experience of the authors: snow crystals, calaverite AuTe2, the incommensurately modulated crystals Rb2ZnBr4, [N(CH3)(4)](2)ZnCl4 and the mitochondrial ferritin.

Title:
Atomic structure of icosahedral quasicrystals: stacking multiple quasi-unit cells
Authors:
Madison, AE Author Full Names: Madison, Alexey E.
Source:
RSC ADVANCES, 5 (97):79279-79297; 10.1039/c5ra13874d 2015
Abstract:
An effective tiling approach is proposed for the structural description of icosahedral quasicrystals based on the original substitution algorithm. The atomic structure of icosahedral quasicrystals may by derived by using the iterative and recursive inflation/deflation procedure with subsequent decoration of quasi-unit cells. The quasi-unit cells are stacked in three-dimensional space face-to-face without any gaps between them producing the whole infinite icosahedral structure in the same manner as the usual periodic crystals are generated by multiplication of their unit cells containing one or more atoms in a specific spatial arrangement. A variety of examples illustrating the efficiency of the general algorithm is presented. Stacking of quasi-unit cells along the five-fold axis, as well as the arrangement of cells normal to the five-fold, three-fold, and two-fold axes are presented. The possible atomic structure of an icosahedral single-component quasicrystal is derived. Three types of inequivalent sites with exact icosahedral symmetry may simultaneously exist in the quasicrystalline structure. The structure of characteristic clusters enforced by the compatibility with the quasicrystalline type of ordering is discussed.

Update: 15-Oct-2015


Title:
Solid-state formation of icosahedral quasicrystals at Zn3Mg3Y2/Mg interfaces in a Mg-Zn-Y alloy
Authors:
Liu, JF; Yang, ZQ; Ye, HQ Author Full Names: Liu, J. F.; Yang, Z. Q.; Ye, H. Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 65-69; 10.1016/j.jallcom.2015.07.254 NOV 25 2015
Abstract:
Solid-state formation of Zn6Mg3Y icosahedral quasicrystals was observed at interfaces between Mg and W-Zn3Mg3Y2 crystals in a Mg-Zn-Y alloy by in situ transmission electron microscopy investigations. The quasicrystals were formed at about 593 K which is about 130 K below the peritectic temperature. Thermally driven interdiffusion of atoms across the W/Mg interface firstly produces local regions with Zn:Mg:Y close to 6:3:1 at the surface of W phase particles, where the cuboctahedral packing of atoms in W phase transforms to icosahedral packing through slight rearrangement of atoms, leading to the nucleation and growth of icosahedral clusters. The icosahedral clusters act as nuclei for the growth of icosahedral quasicrystals. Both valence electron concentration and the densest packing of atoms play important roles in the formation of Zn6Mg3Y quasicrystals. Solid-state formation of icosahedral quasicrystals at W/Mg interfaces provide a feasible way to modify the weakly bonded W/Mg interfaces, which is thus believed to be able to improve the magnesium alloy's mechanical properties. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Properties of Ti40.83Zr40.83Ni18.34 quasicrystalline alloys sintered by Spark Plasma Sintering
Authors:
Han, QG; Chen, ML; Zhang, Q; Sun, LS; Lin, J; Wang, LM Author Full Names: Han, Qi-Gang; Chen, Meng-Lu; Zhang, Qiang; Sun, Lian-Shan; Lin, Jing; Wang, Li-Min
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 154-158; 10.1016/j.jallcom.2015.07.297 NOV 25 2015
Abstract:
The quasicrystalline alloy powders with the composition of Ti40.83Zr40.83Ni18.34 are prepared by mechanical alloying (MA) techniques, and the bulk part is obtained by Spark Plasma Sintering (SPS) method. The structure, mechanical properties, friction and wear properties of the bulk part are investigated. The results showed that the structure of the bulk part is pure icosahedral quasicrystalline phase (I-phase). The Vickers Hardness of the bulk part is 7.03 GPa. The maximum compression strength, the elastic deformation and Young modulus is (662 +/- 50) MPa, 2.7 +/- 0.1% and (30 +/- 3) GPa, respectively. The lowest value of friction coefficient is 0.40 at a normal load of 100 N, a sliding velocity of 10 mm/s, a sliding time of 10 min and an ambient temperature of 293.15 K. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Electrochemical hydrogen storage properties of Ti1.4V0.6Ni alloy comprising quasicrystal coating with Cu
Authors:
Sun, LS; Lin, J; Cao, ZY; Liang, F; Wang, LM Author Full Names: Sun, Lianshan; Lin, Jing; Cao, Zhanyi; Liang, Fei; Wang, Limin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 15-21; 10.1016/j.jallcom.2015.07.252 NOV 25 2015
Abstract:
The Ti1.4V0.6Ni alloy ribbons are prepared by arc-melting and subsequently melt spinning technique. Different percentage compositions of x Cu (x = 1, 3, 5 and 10 wt%) are covered on the surface of the alloy particles utilizing electro-less plating method. The phase structures of the Ti1.4V0.6Ni alloy contain icosahedral quasicrystal phase (I-phase), fcc-Ti2Ni-type phase and bcc-V-based solid solution phase. With increasing x value, the maximum electrochemical hydrogen storage capacity reaches 260 mAh g(-1) when x = 10. After 100 cycles, 23% capacity retention rate is promoted by covering 10 wt% Cu on the alloy than the bare Ti1.4V0.6Ni. Cu offers well electrical conductivity and corrosion resistance, especially it also inhibits the dissolution of V from the alloys. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Investigation on incommensurate modulation structure and T-c in Ca-doped Bi-2201 system
Authors:
Sun, BZ; Zhang, M; Wang, RY; Jiang, YL; Wang, H; Qi, Y Author Full Names: Sun, B. Z.; Zhang, M.; Wang, R. Y.; Jiang, Y. L.; Wang, H.; Qi, Y.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 430-435; 10.1016/j.jallcom.2015.08.015 NOV 25 2015
Abstract:
A series of samples with the nominal composition of Bi2Sr2-xCaxCuO6+delta (x = 0.2, 0.4, 0.6, 0.8, 1.0) ceramics are synthesized by sol-gel growth. The microstructure and the incommensurate modulation structure (IMS) were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. The superconductivity and the onset temperature of superconducting transition (T-c,T-onset) were analysed. In the whole Ca-doping range, an IMS in b-c planes can be identified and the values of T-c,T-onset are all exceed 80 K. With an increase of chi, the b-component of modulation vector q*, the basic *structural* parameters b and c of Bi-2201 phase have a trend of fall first then rise, whereas the c-component of modulation vector, the angle theta between q* and b* vectors and the values of T-c,T-onset are reversely varied. It can be verified that Ca concentration x = 0.6 is an extreme value, at which the distortion of the CuO2 layers makes the concentration of mobile carriers and the value of T-c,(onset) optimizing. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Approximants of Al-Cr-Fe-Si decagonal quasicrystals described by single structural block
Authors:
He, ZB; Wei, DX; Shen, X; Chen, Y; Ma, HK; Wang, LL; Du, K; Yao, Y; Yu, RC Author Full Names: He, Zhanbing; Wei, Dongxia; Shen, Xi; Chen, Yuan; Ma, Haikun; Wang, Leilei; Du, Kui; Yao, Yuan; Yu, Richeng
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 647 797-801; 10.1016/j.jallcom.2015.06.165 OCT 25 2015
Abstract:
The orthorhombic (3/2, 2/1) approximant with a = 3.06 nm, b = 1.23 nm, c = 2.24 nm, and the coexisting (2/1, 3/2) approximant of decagonal quasicrystals with a = 1.90 nm, c = 3.64 nm, and beta congruent to 90 degrees are found in Al-Cr-Fe-Si alloys by aberration-corrected transmission electron microscope. The structural relationships of these two approximants are analyzed and discussed based on the high-angle annular dark-field scanning transmission electron microscopy images at atomic resolution. We find that both of their structural tiling along the [010] direction can be described by one shield-like tile, with the superiority over the previous HBS tiling model due to the clarity. Combining the shield-like tile and HBS tiling model, the domains of approximants are clearly demonstrated. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Incommensurate antiferromagnetism induced by a charge density wave in the cubic phase of TbGe2.85
Authors:
Tsvyashchenko, AV; Salamatin, DA; Sidorov, VA; Petrova, AE; Fomicheva, LN; Kichanov, SE; Salamatin, AV; Velichkov, A; Kozlenko, DR; Nikolaev, AV; Ryasny, GK; Makarova, OL; Menzel, D; Budzynski, M Author Full Names: Tsvyashchenko, A. V.; Salamatin, D. A.; Sidorov, V. A.; Petrova, A. E.; Fomicheva, L. N.; Kichanov, S. E.; Salamatin, A. V.; Velichkov, A.; Kozlenko, D. R.; Nikolaev, A. V.; Ryasny, G. K.; Makarova, O. L.; Menzel, D.; Budzynski, M.
Source:
PHYSICAL REVIEW B, 92 (10):10.1103/PhysRevB.92.104426 SEP 23 2015
Abstract:
Temperature dependencies of the electrical resistivity, magnetic susceptibility, and heat capacity have been obtained in the cubic phase of TbGe2.85 (the AuCu3 structure), synthesized at high pressure. The macroscopic measurements indicate that a charge density wave is formed below 145 K and an antiferromagnetic ordering is realized below 19 K. Hyperfine interaction data obtained with the time differential perturbed angular correlation method with Cd-111 probes inserted in the TbGe2.85 lattice suggest that the charge density wave is incommensurate in the temperature region 19-145 K, but becomes commensurate below 19 K. The neutron diffraction reveals a complex antiferromagnetic spiral structure in the magnetically ordered phase. We discuss relations between the charge density wave and helical ordering in TbGe2.85 and TbPd3.

Title:
Direct evidence of an incommensurate phase in NaNbO3 and its implication in NaNbO3-based lead-free antiferroelectrics
Authors:
Guo, HZ; Shimizu, H; Randall, CA Author Full Names: Guo, Hanzheng; Shimizu, Hiroyuki; Randall, Clive A.
Source:
APPLIED PHYSICS LETTERS, 107 (11):10.1063/1.4930067 SEP 14 2015
Abstract:
Hot-stage in situ transmission electron microscopy was employed to investigate the temperature-induced complex sequence of phase transitions in NaNbO3 polycrystalline. In addition to the commonly recognized P (Pbma) -> R (Pmnm) -> S (Pnmm) phase transitions, incommensurate phases were observed to exist in P and R phase regions. The former (in the P -> R transition region) is coincident with a diffused dielectric peak appearing at similar to 170 degrees C, and the latter (in the R -> S transition region) serves as an intermediate structure to bridge the two sub-phases in the R phase region. The incommensurate phase in the P phase region can be inferred from the polarization current density and differential dielectric permittivity anomalies, and it provides the bridge structure during the electric field-induced polarization reversal and antiferroelectric-to-ferroelectric transition in NaNbO3 solid solutions. (C) 2015 AIP Publishing LLC.

Title:
Structure and electrical properties of tetragonal tungsten bronze Ba2CeFeNb4O15
Authors:
Ma, HQ; Lin, K; Liu, LJ; Yang, BL; Rong, YC; Chen, J; Deng, JX; Kawaguchi, S; Kato, K; Xing, XR Author Full Names: Ma, Hongqiang; Lin, Kun; Liu, Laijun; Yang, Baoling; Rong, Yangchun; Chen, Jun; Deng, Jinxia; Kawaguchi, Shogo; Kato, Kenichi; Xing, Xianran
Source:
RSC ADVANCES, 5 (94):76957-76962; 10.1039/c5ra16115k 2015
Abstract:
The crystal structure and electrical microstructure of a tetragonal tungsten bronze (TTB) ceramic, BaCeFeNb4O15 (BCFN), were investigated by high-resolution synchrotron X-ray powder diffraction (SPD), selected area electron diffraction (SAED), and AC impedance spectroscopy. SPD and SAED reveal that the BCFN has a tetragonal structure with space group P4/mbm, and includes an incommensurate modulated behavior. Impedance and AC conductivity tests in the range of 200-360 degrees C suggest thermally activated electrical behavior which originates from both the bulk and the grain boundary elements of the ceramics. The dielectric relaxation in the grain boundaries is due to the trap-controlled ac conduction around doubly ionized oxygen vacancies while the relaxation of the bulk may be associated with the localized electron hopping between the transition-metal ions. These results could be helpful in understanding the electrical conduction and relaxation processes in Fe-containing TTB-type oxides.

Update: 8-Oct-2015


Title:
Oxygen vacancy ordering and its mobility in YMnO3
Authors:
Zhang, QH; Shen, X; Yao, Y; Wang, YG; Jin, CQ; Yu, RC Author Full Names: Zhang, Q. H.; Shen, X.; Yao, Y.; Wang, Y. G.; Jin, C. Q.; Yu, R. C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 648 253-257; 10.1016/j.jallcom.2015.07.032 NOV 5 2015
Abstract:
Oxygen vacancy (V-O) ordering and its mobility in YMnO3 have been studied via electron-beam irradiation. By controlling the beam intensity, three commensurate (A, B and C-type) and one incommensurate V-O-orderings can be formed. The transformation from the A-type to the C-type ordering has also been revealed, which could be attributed to the migration of V-O from the apical V-O site to the planar V-O site. Further, intense irradiation can introduce more V(O)s and make a breakdown of the ferroelectric displacements of Y ions. These results suggest that the V(O)s in YMnO3 system are highly active in several ordered ways and also have a high mobility. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Evolution of atomic distribution during devitrification of bulk metallic glass investigated by atom probe microscopy
Authors:
Mridha, S; Jaeger, DL; Arora, HS; Banerjee, R; Mukherjee, S Author Full Names: Mridha, Sanghita; Jaeger, David L.; Arora, Harpreet Singh; Banerjee, Rajarshi; Mukherjee, Sundeep
Source:
MATERIALS LETTERS, 158 99-103; 10.1016/j.matlet.2015.05.034 NOV 1 2015
Abstract:
Evolution of atomic distribution during devitrification of a zirconium-based bulk metallic glass, Zr41.2Ti13.8Cu12.5Ni10.0Be22.5, was investigated using three-dimensional atom probe microscopy. Atom probe analysis showed uniform distribution of constituent elements for the as-cast alloy, with no phase separation. The metallic glass was annealed at different temperatures to study the crystallization pathways and the length scale, distribution, and morphology of the phases formed. Devitrification was found to proceed via the formation of a metastable icosahedral phase. The devitrification pathway is explained based on "strong-liquid" behavior of this alloy. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Conduction mechanisms and enhanced multiferroic properties of Sr doped Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 thin films
Authors:
Yan, X; Tan, GQ; Ye, W; Ren, HJ; Xia, A Author Full Names: Yan, Xia; Tan, Guoqiang; Ye, Wei; Ren, Huijun; Xia, Ao
Source:
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 26 (10):7407-7414; 10.1007/s10854-015-3371-y OCT 2015
Abstract:
Pure BiFeO3 (BFO) and Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 (BPSxFMO, x = 0.02-0.05) thin films were deposited on fluorine-doped SnO2 (FTO/glass) substrates by a sol-gel method. The systematic studies of crystalline structure, surface morphologies, leakage conduction mechanisms, ferroelectric and magnetic properties of pure BiFeO3 and Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 thin films were investigated. X-ray diffraction patterns, Rietveld analysis and Raman scattering spectra reveal that the (Pr, Sr and Mn) co-doped BiFeO3 thin films give rise to a trigonal (R3m: R) structure transition with respect to the original rhombohedral structure of pure BiFeO3 film. Fowler-Nordheim tunneling conduction mechanism dominates the leakage current of all the films in the relatively high electric field. The significantly enhanced ferroelectric properties of the Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 thin films were observed in comparison with pure BiFeO3 film. In addition, the BPS2FMO film shows the enhanced ferromagnetism with the saturation magnetization (M (s) similar to 1.97 emu cm(-3)), which is almost three times larger than that of pure BFO film (M (s) similar to 0.67 emu cm(-3)), as a result of the small grain size effect and the collapse of space modulated spin structure by the structure transition.

Title:
Crystalline and Spin Chiralities in Multiferroics with Langasite-type Structure and Fe1-xCoxSi Crystals
Authors:
Pikin, SA; Lyubutin, IS; Dudka, AP Author Full Names: Pikin, S. A.; Lyubutin, I. S.; Dudka, A. P.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (5):729-736; 10.1134/S1063774515050077 SEP 2015
Abstract:
It is shown that, when magnetic ordering occurs in layered iron-containing langasites (sp. gr. P321), one of the reasons for spin chiralities of different signs is the presence of structural chirality (the existence of inversion twins), which, in turn, is due to the nonsymmetricity of these crystals. Spin helicoids arise in these multiferroics at split sites of Fe3+ ions below the N,el point. The direction of electric polarization vectors coincides with the direction of the magnetic helicoid axes because of the piezoelectric properties of these materials. Due to the magnetostriction effects, structural chirality wave vector k (z) exceeds the magnetic helicoid wave vector by a factor of 2: k (z) = 2q (z). The temperatures of transitions to the chiral structural and chiral magnetic states may differ. In particular, if the structural transition initial temperature exceeds the magnetic transition temperature (T-U > T-M ), structural displacements may arise in the absence of magnetism at T-M < T < T-U. In noncentrosymmetric Fe1-xCoxSi crystals (sp. gr. P2(1)3), which are not multiferroics, magnetic chirality is due to the Dzyaloshinski-Moriya interaction. The dependence of the moduli of incommensurate wave number of the corresponding helicoid on the atomic composition of the crystals under consideration is nonmonotonic.

Update: 1-Oct-2015


Title:
Strongly anisotropic and complex magnetic behavior in EuRhGe3
Authors:
Bednarchuk, O; Kaczorowski, D Author Full Names: Bednarchuk, Oleksandr; Kaczorowski, Dariusz
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 646 291-297; 10.1016/j.jallcom.2015.06.125 OCT 15 2015
Abstract:
Single crystals of EuRhGe3 were studied by means of magnetic susceptibility, magnetization, heat capacity, resistivity and magnetoresistance measurements, performed in wide ranges of temperature and magnetic field strength. The compound was characterized as a Curie-Weiss paramagnet, due to divalent Eu ions, that orders antiferromagnetically at T-N = 11.3 K. In the ordered state, EuRhGe3 exhibits strong magnetic anisotropy. The magnetic moments are probably nearly confined within the ab plane of the tetragonal crystallographic unit cell, and the magnetic propagation vector is likely perpendicular to this plane. The bulk thermodynamic and transport data concordantly suggest that in zero magnetic field the magnetic structure of EuRhGe3 is incommensurate with the chemical one and bears an amplitude-modulated character. In external magnetic field applied within the easy magnetization plane, two other magnetic structures were detected, each of them having an antiferromagnetic nature. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Electrochemical synthesis of Co7Ni3 and Co6Ni4 nanorods with controlled crystalline phase. Application to methanol electro-oxidation
Authors:
Vilana, J; Escalera-Lopez, D; Gomez, E; Valles, E Author Full Names: Vilana, Joan; Escalera-Lopez, Daniel; Gomez, Elvira; Valles, Elisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 646 669-674; 10.1016/j.jallcom.2015.06.134 OCT 15 2015
Abstract:
CoNi nanorods with modulated crystalline phase have been synthesised by means of a potentiostatic deposition method, using a single electrolytic bath, by only varying the electrodeposition potential. The growth of the nanorods in the interior on the nanochannels of the membrane is mainly controlled by the limited transport of the Co(II) and Ni(II) ions to the growth front. Two types of CoNi nanorods of several microns long, with similar composition but different crystalline phases depending on the applied potential, have been obtained. The potentials for the electrosynthesis of the nanorods have been selected to induce different deposition rates and, as a consequence, different crystalline phases, hcp for the lower deposition rates and fcc (+hcp) for the highest ones. For each selected potential, the nanorods present the same composition and crystalline phase along the rods. The test of the two types of nanorods for the methanol electro-oxidation demonstrated both the specific electrocatalytic behaviour of each one and the promising behaviour of the nanorods as electrocatalysts in direct methanol fuel cells in basic medium, due to their higher surface/volume ratio than that of thin films and the superior stability than that of nanoparticles. The influence of the crystalline phase in the methanol electro-oxidation has been also corroborated from pure-hcp and pure-fcc CoNi films. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Structural phase transitions in the Ti45Zr38Ni17-xFex nano-alloys and their deuterides
Authors:
Rusinek, D; Czub, J; Niewolski, J; Gondek, L; Gajewska, M; Takasaki, A; Hoser, A; Zywczak, A Author Full Names: Rusinek, D.; Czub, J.; Niewolski, J.; Gondek, L.; Gajewska, M.; Takasaki, A.; Hoser, A.; Zywczak, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 646 90-95; 10.1016/j.jallcom.2015.06.023 OCT 15 2015
Abstract:
The mechanically alloyed Ti-Zr-Ni materials are extensively studied due to their promising properties concerning biomedical, electronic or hydrogen related applications (for example the gaseous hydrogen storage and the MNiH batteries). In this paper we address the very crucial issue of the structural properties and transformations of the amorphous and quasicrystalline Ti45Zr38Ni17-xFex (x = 0, 4, 8) and their hydrides. According to the neutron diffraction results, the transformation of the amorphous Ti45Zr38Ni17 phase into the icosahedral quasicrystalline state (the i-phase) is quasi-continuous and starts at the relatively low temperature of 300 degrees C. At 500 degrees C the i-phase is well-developed. At higher temperatures the i-phase transforms into the approximant w-phase and eventually into the cubic phase (the c-phase). Interestingly, the deuterided i-phase exhibits completely different thermal evolution. Namely, this phase decomposes into the simple intermetallic compounds above 625 degrees C. What is worth-mentioning is that the release of deuterium is strictly related to that structural decomposition. The possibility of hydrogenation of the amorphous Ti45Zr38Ni17-xFe (x) phases with maintaining the amorphous nature of the alloys is the other extremely important field of our interest. We established a processing route to meet our goal. Finally, we show that introducing deuterium triggers an exciting phase transition from the deuterided amorphous phase into the unknown before, partially disordered, quasicrystallinelike phase (the glassy quasicrystal) without releasing of deuterium. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Reassessment of the effects of Ce on quasicrystal formation and microstructural evolution in rapidly solidified Al-Mn alloys
Authors:
Coury, FG; Botta, WJ; Bolfarini, C; Kiminami, CS; Kaufman, MJ Author Full Names: Coury, F. G.; Botta, W. J.; Bolfarini, C.; Kiminami, C. S.; Kaufman, M. J.
Source:
ACTA MATERIALIA, 98 221-228; 10.1016/j.actamat.2015.07.046 OCT 1 2015
Abstract:
Rapidly solidified Al-Mn-Ce alloys have been reported to exhibit desirable properties due to the uniform distribution of quasicrystalline (QC) particles in an Al matrix. In this study, several ternary alloy compositions that encompassed the alloys reported in the previous reports, namely Al-6Mn-2Ce, Al-6Mn-4Ce, AI-8Mn-4Ce, Al-12Mn-2Ce and Al-10Mn-5Ce, were prepared by melt spinning and their microstructures were characterized by electron microscopy and X-ray diffraction. The results are in direct contrast with the previous reports available in the literature in that the formation of QCs was only observed in the Al-12Mn-2Ce alloy; in the others, the dispersed phase was not the QC; rather, the structural and compositional information presented in this paper together with data recently published in the literature enabled a reinterpretation of the effect of Ce on rapidly solidified Al-Mn alloys. The main conclusion is that Ce favors the formation of a ternary metastable phase with approximate stoichiometry Al20Mn2Ce. This phase forms in a wide portion of the Al-rich region of the ternary phase diagram and can even coexist with the QC phase in alloys containing low amounts of Ce; in this case, the QC contains no detectable Ce by TEM/EDS, consistent with the conclusion that Ce does not favor QC formation in contrast to the previous reports. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Discovery of a Sodium-Ordered Form of Na3V2(PO4)(3) below Ambient Temperature
Authors:
Chotard, JN; Rousse, G; David, R; Mentre, O; Courty, M; Masquelier, C Author Full Names: Chotard, Jean-Noel; Rousse, Gwenaelle; David, Renald; Mentre, Olivier; Courty, Matthieu; Masquelier, Christian
Source:
CHEMISTRY OF MATERIALS, 27 (17):5982-5987; 10.1021/acs.chemmater.5b02092 SEP 8 2015
Abstract:
The crystal structure of the NASICON Na3V2(PO4)(3) phase (NVP) has been investigated as a function of temperature. Combining laboratory and synchrotron X-ray powder diffraction with single crystal X-ray diffraction, we demonstrate the presence of four polymorphs of NVP from 30 to 225 degrees C. While the high temperature gamma-NVP crystallizes in the classical rhombohedral cell (S.G. R (3) over barc, a = 8.73382(4) angstrom, c = 21.91438(17) angstrom), the low temperature alpha-NVP undergoes a monoclinic distortion (S.G. C2/c, a = 15.1244(6) angstrom, b = 8.7287(3) angstrom, c = 21.6143(8) angstrom, beta = 90.163(2)degrees) together with an ordering of the Na atoms. In the middle temperature range, two incommensurate modulated structures (beta- and beta '-NVP) are also reported for the first time.

Title:
Intermediate-valent CeCoAl - a commensurate modulated structure with short Ce-Co distances
Authors:
Niehaus, O; Hoffmann, RD; Tence, S; Chevalier, B; Poettgen, R Author Full Names: Niehaus, Oliver; Hoffmann, Rolf-Dieter; Tence, Sophie; Chevalier, Bernard; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 230 (9-10):579-591; 10.1515/zkri-2015-1856 SEP 2015
Abstract:
CeCoAl was synthesized by melting of the elements in a sealed niobium tube in an induction furnace. Annealing of the sample gave access to a single phase sample. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Above 271 K CeCoAl crystallizes in its own structure type in the space group C2/m [a = 1107.4(2), b = 440.6(1) and c = 479.6(1) pm, beta = 104.6(1)degrees]. Data obtained at 300 K lead to 511 F-2 values with 20 variables and a residual of [I >= 3 sigma(I)] wR = 0.0539. Below 271 K satellites give rise to the superspace group C2/m(alpha 0 gamma) 00; alpha = 2/3, gamma = 2/5 with a temperature independent q-vector. For the 90 K data (also for 180 and 220 K) the commensurate modulated structure could be refined with 4817 F-2 values, 129 variables and residuals of wR = 0.0347 (main), wR = 0.1927 (satellites 1st order), wR = 0.1541 (satellites 2nd order) and wR = 0.1768 (satellites 3rd order) [a = 1107.5(1), b = 440.3(1) and c = 479.0(1) pm, beta = 104.7(1)degrees]. For the three temperatures only minor variations of the modulation amplitudes are observed. The relation of the low temperature (3+1)D 3a x 5c approximant and the room temperature 3D structure is discussed on the basis of a group-subgroup relation. By investigation of the heat capacity, the phase transition could be identified as a second order one with a transition temperature of 271 K. Magnetic measurements clearly prove the intermediate cerium valence which is in line with the short Ce-Co distances.

Title:
The birth of time-of-flight (TOF) neutron powder diffraction at pulsed neutron source (invited)
Authors:
Sosnowska, IM Author Full Names: Sosnowska, Izabela M.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 50 (9-10):705-715; 10.1002/crat.201400439 SEP 2015
Abstract:
Behind every improvement there is a story. The early history of the TOF neutron powder diffraction technique is presented. Successes and problems in the application of this technique in material science are reported. Powder diffraction technique is very useful when materials, in a single crystal form, reveal complicated electric and magnetic domain structures. Finding and describing the magnetic structure of multiferroics is the great success of ultra-high resolution TOF neutron diffraction. This unique role of the TOF method in discovery of the modulated magnetic structure of BiFeO3 is presented. To date, the TOF powder neutron diffraction technique gives the richest information on the long period modulated magnetic structure of BiFeO3 and its solid solutions. Determination of magnetic moment direction in a crystal lattice is the unique area of application of the TOF technique. The current status and perspectives of the application of the TOF neutron powder diffraction technique in material science are presented in the review.

Update: 24-Sep-2015


Title:
HREM observation and high-pressure composition isotherm measurement of Ti45Zr38Ni17 quasicrystal powders synthesized by mechanical alloying
Authors:
Tominaga, T; Takasaki, A; Shibato, T; Swierczek, K Author Full Names: Tominaga, Tomoki; Takasaki, Akito; Shibato, Tsuyoshi; Swierczek, Konrad
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 645 S292-S294; 1 10.1016/j.jallcom.2014.12.200 OCT 5 2015
Abstract:
Elemental powders consisted of chemical composition of Ti45Zr38Ni17 were mechanical alloyed and annealed subsequently, and the microstructures were characterized by high-resolution electron microscopy (HREM) and an X-ray diffractometry, and hydrogen absorption and desorption pressure-composition (PC) isotherms were measured at 523 K, 573 K and 623 K by a Sieverts type apparatus. The annealing after mechanical alloying (MA) caused formation of an icosahedral quasicrystal with a Ti2Ni type crystal phases. 5 or 10-fold rotational symmetry, which is prohibited to normal crystals, was observed by HREM in a digital diffractogram and an simulated atomic arrangement derived from the digital diffractogram. The hydrogen storage capacity (hydrogen to metal atom ratio: H/M) at 523 K was about 1.3, which decreased with increasing hydrogenation temperatures. All the PC isotherms were steep, and no plateau pressure was observed. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Hydrogen storage properties for Mg-Zn-Y quasicrystal and ternary alloys
Authors:
Luo, XL; Grant, DM; Walker, GS Author Full Names: Luo, Xuanli; Grant, David M.; Walker, Gavin S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 645 S23-S26; 1 10.1016/j.jallcom.2015.01.266 OCT 5 2015
Abstract:
Three Zn-Mg-Y alloys with nominal compositions of Zn50Mg42Y8 and Zn60Mg30Y10 were prepared by induction melting or gas atomisation. XRD and SEM analysis shows samples ZMY-1 and ZMY-2 consisted of multiple phases including icosahedral quasicrystal (QC) i-phase, hexagonal H-phase and Mg7Zn3, whilst ZMY-3 contained QC only. The hydrogen storage properties of the Zn-Mg-Y quasicrystal and ternary alloys were investigated for the first time. The quasicrystal sample ZMY-3 hydrogenated at 300 degrees C had 0.3 wt.% capacity and the DSC decomposition peak temperature was 503 degrees C. Amongst the three samples, the highest hydrogen storage capacity (0.9 wt.%) and the lowest decomposition peak temperature (445 degrees C) was achieved by sample ZMY-1. The pressure-composition-isotherm (PCI) curve of ZMY-1 sample showed a flat plateau gave a plateau pressure of 3.5 bar at 300 degrees C, which indicates a lower dehydrogenation enthalpy than MgH2. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Electrochemical properties of Ti49Zr26Ni25-xPdx (x=0-6) quasicrystal electrodes produced by mechanical alloying
Authors:
Ariga, Y; Takasaki, A; Kimijima, T; Swierczek, K Author Full Names: Ariga, Youhei; Takasaki, Akito; Kimijima, Tsubasa; Swierczek, Konrad
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 645 S152-S154; 1 10.1016/j.jallcom.2015.01.114 OCT 5 2015
Abstract:
Elemental powders consisted of chemical composition of Ti49Zr26Ni25 Pd-x(x) (x = 0, 1, 3, 6) were mechanically alloyed and annealed subsequently, and the discharge performance of the electrodes was measured by a three-electrode cell at room temperature. The annealing after mechanical alloying caused a formation of the icosahedral quasicrystal phase with a Ti2Ni type crystal, C14 Laves and alpha-Ti/Zr phases. The quasilattice constant increased with increasing amount of Pd substituted for Ni up to 3 at.% due to difference in atomic radius between Pd and Ni. The maximum discharge capacity achieved was about 220 mA h/g from a (Ti49Zr26Ni22Pd3) electrode at the first discharge process. (C) 2015 Elsevier B.V. All rights reserved.

Title:
TEM study of the (SbS)(1+delta)(NbS2)(n), (n=1, 2, 3; delta similar to 1.14, 1.20) misfit layer phases
Authors:
Gomez-Herrero, A; Landa-Canovas, AR; Otero-Diaz, LC Author Full Names: Gomez-Herrero, A.; Landa-Canovas, A. R.; Otero-Diaz, L. C.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 230 357-368; 10.1016/j.jssc.2015.07.029 OCT 2015
Abstract:
In the Sb-Nb-S system four new misfit layer phases have been found and carefully investigated via Transmission Electron Microscopy (TEM). Their structures are of composite modulated structure type with stoichiometries that can be formulated as (SbS)(1+delta)(NbS2)(n); for n=1, delta similar to 1.14 and 1.19; for n=2, delta similar to 1.18 and for n=3, delta similar to 1.19. Selected Area Electron Diffraction (SAED) patterns show an almost commensurate fit between the pseudo-tetragonal (SbS) and the pseudo-orthohexagonal (NbS2)(n) subcells along the misfit direction a, with 3(SbS) approximate to 5(NbS2), being b the same for both sub-lattices and c the stacking direction. For n=1, a commensurate phase with 4a(SbS)=7a(NbS2) has also been observed. In addition to the characteristic misfit and associated modulation of the two sub-structures, a second modulation is also present which appears to be primarily associated with the (SbS) sub-structure of both the n=1 and n=2 phases. High Resolution Transmission Electron Microscopy (HRTEM) images show ordered stacking sequences between the (SbS) and (NbS2)(n) lamellae for each of the four phases, however, disordered intergrowths were also occasionally found. Most of the crystals showed different kinds of twinning defects on quite a fine scale. Many crystals showed curled up edges. In some cases the lamellar crystals were entirely folded giving rise to similar diffraction patterns as found for cylindrical crystals. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Enhancement of superconductivity at the onset of charge-density-wave order in a metal
Authors:
Wang, YX; Chubukov, AV Author Full Names: Wang, Yuxuan; Chubukov, Andrey V.
Source:
PHYSICAL REVIEW B, 92 (12):10.1103/PhysRevB.92.125108 SEP 4 2015
Abstract:
We analyze superconductivity in the cuprates near the onset of an incommensurate charge-density-wave (CDW) order with momentum Q = (Q, 0)/(0, Q), as observed in experiments. We first consider a semiphenomenological charge-fermion model in which hot fermions, separated by Q, attract each other by exchanging soft CDW fluctuations. We find that in a quantum-critical region near the CDW transition, T-c = A (g) over bar (c), where (g) over bar (c) is charge-fermion coupling and Ais the prefactor, which we explicitly compute. We then consider the particular microscopic scenario in which the CDW order parameter emerges as a composite field made of primary spin-density-wave fields. We show that charge-fermion coupling (g) over bar (c) is of the order of spin-fermion coupling (g) over bar (s). As a consequence, superconducting Tc is substantially enhanced near the onset of CDW order. Finally, we analyze the effect of an external magnetic field H. We show that, as H increases, the optimal Tc decreases and the superconducting dome becomes progressively more confined to the CDW quantum-critical point. These results are consistent with experiments.

Title:
Quasiperiodicity and 2D topology in 1D charge-ordered materials
Authors:
Flicker, F; van Wezel, J Author Full Names: Flicker, F.; van Wezel, Jasper
Source:
EPL, 111 (3):10.1209/0295-5075/111/37008 AUG 2015
Abstract:
The mathematical description of 1D quasicrystals has recently been linked to that of 2D quantum Hall states. The topological classification of 1D quasicrystals and the corresponding interpretation of their observed charge transport have been widely discussed. We demonstrate the equivalence of both 1D quasicrystals and 2D quantum Hall states to a mean-field treatment of charge order. Using the fractal nature of the spectrum of charge-ordered states we consider incommensurate order as a limit of commensurate. The topological properties of both are identical, arising from a 2D parameter space of phase and wave vector, and fit into class A of the Tenfold Way. The topological nature of all the systems can be tested by measuring a quantized particle transport upon dragging the charge order. Copyright (C) EPLA, 2015

Update: 17-Sep-2015


Title:
Low temperature superplasticity of ultrafine grained Mg-9.25Zn-1.66Y alloy with an icosahedral quasicrystalline phase
Authors:
Kim, WJ; Yoo, YJ Author Full Names: Kim, W. J.; Yoo, Y. J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 643 47-50; 10.1016/j.msea.2015.07.022 SEP 3 2015
Abstract:
The ultrafine grained Mg-9.25Zn-1.66Y alloy sheet with I-phase prepared by directly applying high-ratio differential speed rolling to the as-cast microstructure exhibited excellent low-temperature super-plasticity (386-888% at 443-473 K) at a moderately high strain rate of 10(-3) s(-1). A criterion for achieving low temperature superplasticity was proposed. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Premartensite to martensite transition and its implications for the origin of modulation in Ni2MnGa ferromagnetic shape-memory alloy
Authors:
Singh, S; Bednarcik, J; Barman, SR; Felser, C; Pandey, D Author Full Names: Singh, Sanjay; Bednarcik, J.; Barman, S. R.; Felser, C.; Pandey, Dhananjai
Source:
PHYSICAL REVIEW B, 92 (5):10.1103/PhysRevB.92.054112 AUG 28 2015
Abstract:
We present results of a temperature-dependent high-resolution synchrotron x-ray powder diffraction study of sequence of phase transitions in Ni2MnGa. Our results show that the incommensurate martensite phase results from the incommensurate premartensite phase and not from the austenite phase assumed in the adaptive phase model. The premartensite phase transforms to the martensite phase through a first order phase transition with coexistence of the two phases in a broad temperature interval (similar to 40 K), discontinuous change in the unit cell volume as also in the modulation wave vector across the transition temperature, and considerable thermal hysteresis in the characteristic transition temperatures. The temperature variation of the modulation wave vector q shows smooth analytic behavior with no evidence for any devilish plateau corresponding to an intermediate or ground state commensurate lock-in phase. The existence of the incommensurate 7M-like modulated structure down to 5 K suggests that the incommensurate 7M-like modulation is the ground state of Ni2MnGa and not the Bain distorted tetragonal L1(0) phase or any other lock-in phase with a commensurate modulation. These findings can be explained within the framework of the soft phonon model.

Title:
KEu(MoO4)(2): Polymorphism, Structures, and Luminescent Properties
Authors:
Morozov, VA; Arakcheeva, AV; Pattison, P; Meert, KW; Smet, PF; Poelman, D; Gauquelin, N; Verbeeck, J; Abakumov, AM; Hadermann, J Author Full Names: Morozov, Vladimir A.; Arakcheeva, Alla V.; Pattison, Philip; Meert, Katrien W.; Smet, Philippe F.; Poelman, Dirk; Gauquelin, Nicolas; Verbeeck, Johan; Abakumov, Artem M.; Hadermann, Joke
Source:
CHEMISTRY OF MATERIALS, 27 (16):5519-5530; 10.1021/acs.chemmater.5b01622 AUG 25 2015
Abstract:
In this paper, with the example of two different polymorphs of KEu(MoO4)(2), the influence of the ordering of the A-cations on the luminescent properties in scheelite related compounds (A',A '') [(B',B '')O-4](m) is investigated. The polymorphs were synthesized using a solid state method. The study confirmed the existence of only two polymorphic forms at annealing temperature range 923-1203 K and ambient pressure: a low temperature anorthic alpha-phase and a monoclinic high temperature beta-phase with an incommensurately *modulated structure*. The *structures* of both polymorphs were solved using transmission electron microscopy and refined from synchrotron powder X-ray diffraction data. The monoclinic beta-KEu(MoO4)(2) has a (3+1)-dimensional incommensurately modulated structure (superspace group I2/b(alpha beta 0)00, a = 5.52645(4) angstrom, b = 5.28277(4) angstrom, c = 11.73797(8) angstrom, gamma = 91.2189(4)degrees, q = 0.56821(2)a*-0.12388(3)b*), whereas the anorthic alpha-phase is (3+1)-dimensional commensurately modulated (superspace group I (1) over bar(alpha beta gamma)0, a = 5.58727(22) angstrom, b = 5.29188(18)angstrom, c = 11.7120(4) angstrom, alpha = 90.485(3)degrees, beta = 88.074(3)degrees, gamma = 91.0270(23)degrees, q = 1/2a* + 1/2c*). In both cases the modulation arises due to Eu/K cation ordering at the A site: the formation of a 2-dimensional Eu3+ network is characteristic for the alpha-phase, while a 3-dimensional Eu3+-framework is observed for the beta-phase structure. The luminescent properties of KEu(MoO4)(2) samples prepared under different annealing conditions were measured, and the relation between their optical properties and their structures is discussed.

Title:
Precipitates in a quasicrystal-strengthened Al-Mn-Be-Cu alloy
Authors:
Zupanic, F; Wang, D; Gspan, C; Boncina, T Author Full Names: Zupanic, Franc; Wang, Di; Gspan, Cristian; Boncina, Tonica
Source:
MATERIALS CHARACTERIZATION, 106 93-99; 10.1016/j.matchar.2015.05.013 AUG 2015
Abstract:
In this work, an Al-Mn-Be-Cu alloy was studied containing a primary and eutectic icosahedral quasicrystalline phase in the as-cast microstructure. Special attention was given to a transmission electron microscopy investigation of precipitates formed within the aluminium solid solution (Al-ss) at different temperatures. At 200 degrees C, only binary Al-Cu precipitates (theta') were formed. At 300 degrees C, icosahedral quasicrystalline (IQC) precipitates prevailed with a crystallographic orientation relationship with the Al-ss. The rods of the T-phase (Al20Mn3Cu2) which were precipitated above 400 degrees C, also had a specific orientation relationship with the Al-ss. The primary and eutectic IQC microstructural constituent started to transform rapidly to the T-phase and Be4Al(Mn,Cu) at 500 degrees C. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Self-assembly of the decagonal quasicrystalline order in simple three-dimensional systems
Authors:
Ryltsev, R; Klumov, B; Chtchelkatchev, N Author Full Names: Ryltsev, Roman; Klumov, Boris; Chtchelkatchev, Nikolay
Source:
SOFT MATTER, 11 (35):6991-6998; 10.1039/c5sm01397f 2015
Abstract:
Using molecular dynamics simulations we show that a one-component system can be driven to a three-dimensional decagonal (10-fold) quasicrystalline state just by purely repulsive, isotropic and monotonic interaction pair potential with two characteristic length scales; no attraction is needed. We found that self-assembly of a decagonal quasicrystal from a fluid can be predicted by two dimensionless effective parameters describing the fluid structure. We demonstrate stability of the results under changes of the potential by obtaining the decagonal order for three particle systems with different interaction potentials, both purely repulsive and attractive, but with the same values of the effective parameters. Our results suggest that soft matter quasicrystals with decagonal symmetry can be experimentally observed for the same systems demonstrating the dodecagonal order for an appropriate tuning of the effective parameters.

Update: 10-Sep-2015


Title:
The Effect of Icosahedral Phase on Dynamic Recrystallization Evolution and Hot Workability of Mg-2.0Zn-0.3Zr-0.2Y Alloy
Authors:
Lv, BJ; Peng, J; Chu, Z Author Full Names: Lv, Bin-Jiang; Peng, Jian; Chu, Zhong
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 24 (9):3502-3512; 10.1007/s11665-015-1604-0 SEP 2015
Abstract:
The effect of Icosahedral phase (I-phase) on hot deformation behavior, dynamic recrystallization (DRX) evolution, and hot workability of Mg-2.0Zn-0.3Zr-0.2Y alloy has been investigated in the temperature range of 300-500 A degrees C and strain rate range of 0.001-1 s(-1) using Gleeble 3500D thermo-mechanical simulator. Based on regression analysis for Arrhenius-type equation of flow behavior, the average activation energy of deformation was determined as Q = 277.8 kJ/mol. The model of DRX evolution is . The DRX model agreed well with the microstructure evolution of the alloy at all deformation conditions. At lower strain rates (0.001-0.01 s(-1)), continuous DRX (CDRX) is the main DRX mechanism that occurred near the original grain boundaries. Twin-dynamic recrystallization (TDRX) began to occur at lower deformation temperatures and higher strain rates (0.1-1 s(-1)). At a deformation temperature range of 250 to 350 A degrees C and a strain rate of 1 s(-1), the main DRX mechanism is TDRX, and the density of twins decreased, and CDRX began to occur near the original grain boundaries. When the deformation temperature increased to 400 A degrees C, TDRX disappeared and CDRX occurred near original grain boundaries and I-phase particles. According to the flow stress behavior and DRX model, the processing maps have exhibited the optimum deformation conditions to be 450 A degrees C and the strain rate range of 0.01-0.001 s(-1).

Title:
Crystal chemistry of layered structures formed by linear rigid silyl-capped molecules
Authors:
Lumpi, D; Kautny, P; Stoger, B; Frohlich, J Author Full Names: Lumpi, Daniel; Kautny, Paul; Stoeger, Berthold; Froehlich, Johannes
Source:
IUCRJ, 2 584-600; 10.1107/S2052252515011665 5 SEP 2015
Abstract:
The crystallization behavior of methylthio-or methylsulfonyl-containing spacer extended Z, Z-bis-ene-yne molecules capped with trimethylsilyl groups obtained by (tandem) thiophene ring fragmentation and of two non-spacer extended analogs were investigated. The rigid and linear molecules generally crystallized in layers whereby the flexibility of the layer interfaces formed by the silyl groups leads to a remarkably rich crystal chemistry. The molecules with benzene and thiophene spacers both crystallized with C2/c symmetry and can be considered as merotypes. Increasing the steric bulk of the core by introduction of ethylenedioxythiophene (EDOT) gave a structure incommensurately modulated in the [010] direction. Further increase of steric demand in the case of a dimethoxythiophene restored periodicity along [010] but resulted in a doubling of the c vector. Two different polytypes were observed, which feature geometrically different layer interfaces (non-OD, order-disorder, polytypes), one with a high stacking fault probability. Oxidation of the methylthio groups of the benzene-based molecule to methylsulfonyl groups led to three polymorphs (two temperature-dependent), which were analyzed by Hirshfeld surface d(e)/d(i) fingerprint plots. The analogously oxidized EDOT-based molecule crystallized as systematic twins owing to its OD polytypism. Shortening of the backbone by removal of the aryl core resulted in an enantiomorphic structure and a further shortening by removal of a methylthio-ene fragment again in a systematically twinned OD polytype.

Title:
Good reproductive preparation method of Li-intercalated hexagonal boron nitride and transmission electron microscopy - Electron energy loss spectroscopy analysis
Authors:
Sumiyoshi, A; Hyodo, H; Sato, Y; Terauchi, M; Kimura, K Author Full Names: Sumiyoshi, A.; Hyodo, H.; Sato, Y.; Terauchi, M.; Kimura, K.
Source:
SOLID STATE SCIENCES, 47 68-72; 10.1016/j.solidstatesciences.2015.04.011 SEP 2015
Abstract:
A Li-intercalated hexagonal boron nitride (Li-h-BNIC) phase was synthesized using a highly reproducible method that involves annealing an Li3N and h-BN mixture at 1220 K. Powder X-ray diffraction, electrical conductivity measurements, transmission electron microscopy (TEM) and electron energy loss spectroscopy were performed. The stacking of BN atomic layers in the Li-h-BNIC phase is not the same as the two-layer stacking periodicity of h-BN. TEM observation suggests the existence of incommensurate periodicity along the intralayer direction. From the low-loss and core-loss spectra, the Li-h-BNIC phase is not metal as predicted by the first-principle calculations. Satellite peaks of 1 s to pi* transition in the B K-edge core-loss spectrum indicate the presence of N atom vacancies modified by O atoms in the h-BN atomic layer. (C) 2015 Elsevier Masson SAS. All rights reserved.

Title:
Cluster-Based Solidification and Growth Algorithm for Decagonal Quasicrystals
Authors:
Kuczera, P; Steurer, W Author Full Names: Kuczera, P.; Steurer, W.
Source:
PHYSICAL REVIEW LETTERS, 115 (8):10.1103/PhysRevLett.115.085502 AUG 21 2015
Abstract:
A novel approach is used for the simulation of decagonal quasicrystal (DQC) solidification and growth. It is based on the observation that in well-ordered DQCs the atoms are largely arranged along quasiperiodically spaced planes parallel to the tenfold axis, running throughout the whole structure in five different directions. The structures themselves can be described as quasiperiodic arrangements of decagonal columnar clusters (cluster covering) that partially overlap in a systematic way. Based on these findings, we define a cluster interaction model within the mean field approximation, with effectively asymmetric interactions ranging beyond the nearest neighbors. In our Monte Carlo simulations, this leads to a long-range ordered quasiperiodic ground state. Indications of two finite-temperature unlocking phase transitions are observed, and are related to the two fundamental length scales that are characteristic for the system.

Title:
Complex variable method for an anti-plane elliptical cavity of one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Yu, J; Guo, JH; Xing, YM Author Full Names: Yu Jing; Guo Junhong; Xing Yongming
Source:
CHINESE JOURNAL OF AERONAUTICS, 28 (4):1287-1295; 10.1016/j.cja.2015.04.013 AUG 2015
Abstract:
Based on the fundamental equations of piezoelasticity of quasicrystal media, using the symmetry operations of point groups, the linear piezoelasticity behavior of one-dimensional (1D) hexagonal quasicrystals is investigated and the piezoelasticity problem of 1D hexagonal quasicrystals is decomposed into two uncoupled problems, i.e., the classical plane elasticity problem of conventional hexagonal crystals and the phonon-phason-electric coupling elasticity problem of 1D hexagonal quasicrystals. The final governing equations are derived for the phonon-phason-electric coupling anti-plane elasticity of 1D hexagonal quasicrystals. The complex variable method for an anti-plane elliptical cavity in 1D hexagonal piezoelectric quasicrystals is proposed and the exact solutions of complex potential functions, the stresses and displacements of the phonon and the phason fields, the electric displacements and the electric potential are obtained explicitly. Reducing the cavity into a crack, the explicit solutions in closed forms of electro-elastic fields, the field intensity factors and the energy release rate near the crack tip are derived. (C) 2015 The Authors.

Update: 27-Aug-2015


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

Update: 20-Aug-2015


Title:
Field-induced spin density wave and spiral phases in a layered antiferromagnet
Authors:
Stone, MB; Lumsden, MD; Garlea, VO; Grenier, B; Ressouche, E; Samulon, EC; Fisher, IR Author Full Names: Stone, M. B.; Lumsden, M. D.; Garlea, V. O.; Grenier, B.; Ressouche, E.; Samulon, E. C.; Fisher, I. R.
Source:
PHYSICAL REVIEW B, 92 (2):10.1103/PhysRevB.92.020415 JUL 28 2015
Abstract:
We determine the low-field ordered magnetic phases of the S = 1 dimerized antiferromagnet Ba3Mn2O8 using single-crystal neutron diffraction. We find that for magnetic fields between mu H-0 = 8.80 T and 10.56 T applied along the [1 (1) over bar0] direction the system exhibits spin density wave order with incommensurate wave vectors of type (eta,eta,epsilon). For mu H-0 > 10.56 T, the magnetic order changes to a spiral phase with incommensurate wave vectors only along the [hh0] direction. For both field-induced ordered phases, the magnetic moments are lying in the plane perpendicular to the field direction. The nature of these two transitions is fundamentally different: the low-field transition is a second-order transition to a spin density wave ground state, while the one at higher field, toward the spiral phase, is of first order.

Title:
Symmetry-Based Computational Tools for Magnetic Crystallography
Authors:
Perez-Mato, JM; Gallego, SV; Tasci, ES; Elcoro, L; de la Flor, G; Aroyo, MI Author Full Names: Perez-Mato, J. M.; Gallego, S. V.; Tasci, E. S.; Elcoro, L.; de la Flor, G.; Aroyo, M. I. Edited by: Clarke DR
Source:
ANNUAL REVIEW OF MATERIALS RESEARCH, VOL 45, 45 217-248; 10.1146/annurev-matsci-070214-021008 2015 Book Series: Annual Review of Materials Research
Abstract:
In recent years, two important advances have opened new doors for the characterization and determination of magnetic structures. Firstly, researchers have produced computer-readable listings of the magnetic or Shubnikov space groups. Secondly, they have extended and applied the superspace formalism, which is presently the standard approach for the description of nonmagnetic incommensurate structures and their symmetry, to magnetic structures. These breakthroughs have been the basis for the subsequent development of a series of computer tools that allow a more efficient and comprehensive application of magnetic symmetry, both commensurate and incommensurate. Here we briefly review the capabilities of these computation instruments and present the fundamental concepts on which they are based, providing various examples. We show how these tools facilitate the use of symmetry arguments expressed as either a magnetic space group or a magnetic superspace group and allow the exploration of the possible magnetic orderings associated with one or more propagation vectors in a form that complements and goes beyond the traditional representation method. Special focus is placed on the programs available online at the Bilbao Crystallographic Server (http://www. cryst.ehu.es).

Update: 13-Aug-2015


Title:
Thermodynamic Aspects of Homogeneous Nucleation Enhanced by Icosahedral Short Range Order in Liquid Fcc-Type Alloys
Authors:
Rappaz, M; Kurtuldu, G Author Full Names: Rappaz, Michel; Kurtuldu, Gueven
Source:
JOM, 67 (8):1812-1820; 10.1007/s11837-015-1328-5 AUG 2015
Abstract:
We have recently shown that minute solute element additions to liquid metallic alloys can strongly influence the nucleation of the fcc phase and act as a grain refinement method. Electron back-scattered diffraction observations revealed a concomitant increase in the percentage of nearest neighbor (nn) grains that are in a twin relationship. Furthermore, multiple-twinned (MT) nn grain configurations with a fivefold symmetry around a common < 110 > direction have been identified, an occurrence that can be explained when the symmetry of the icosahedron is accounted for. It was then conjectured that a new nucleation mechanism occurs in two steps: first, the formation of small icosahedral quasicrystals in the melt, followed by heteroepitaxy of the fcc phase on facets of these quasicrystals. In the present contribution, based on thermodynamics arguments, it is proposed that the first step occurs by spinodal decomposition of the liquid, in a manner similar to Guinier-Preston zones formation in solid state precipitation, while the second step is a transformation of these quasicrystal precursors into MT-fcc nanocrystals once the driving force for this transformation is sufficient to overcome the fcc-liquid interfacial energy and the elastic strains associated with MT-fcc nanoparticles. This explanation sets up guidelines for finding solute elements and composition ranges that favor this grain refinement mechanism.

Title:
Symmetry of icosahedral quasicrystals
Authors:
Madison, AE Author Full Names: Madison, A. E.
Source:
STRUCTURAL CHEMISTRY, 26 (4):923-942; 10.1007/s11224-014-0559-3 AUG 2015
Abstract:
The concept of infinitely fragmented fractal tiling is proposed for the description of the structure and symmetry of quasicrystals. Fractal tilings may serve as unique "parent" structures for the corresponding local isomorphism class. The generating symmetry elements and some special features of the resulting symmetry groups of the fractal tilings are analyzed. Simple inflation/deflation rules for icosahedral quasicrystals are proposed, and natural local matching rules are derived.

Title:
Incommensurate spin density wave at a ferromagnetic quantum critical point in a three-dimensional parabolic semimetal
Authors:
Murray, JM; Vafek, O; Balents, L Author Full Names: Murray, James M.; Vafek, Oskar; Balents, Leon
Source:
PHYSICAL REVIEW B, 92 (3):10.1103/PhysRevB.92.035137 JUL 21 2015
Abstract:
We explore the ferromagnetic quantum critical point in a three-dimensional semimetallic system with upwardand downward-dispersing bands touching at the Fermi level. Evaluating the static spin susceptibility to leading order in the coupling between the fermions and the fluctuating ferromagnetic order parameter, we find that the ferromagnetic quantum critical point is masked by an incommensurate, longitudinal spin density wave phase. We first analyze an idealized model that, despite having strong spin-orbit coupling, still possesses O(3) rotational symmetry generated by the total angular momentum operator. In this case, the direction of the incommensurate spin density wave propagation can point anywhere, while the magnetic moment is aligned along the direction of propagation. Including symmetry-allowed anisotropies in the fermion dispersion and the coupling to the order parameter field, however, we find that the ordering wavevector instead breaks a discrete symmetry and aligns along either the [111] or [100] direction, depending on the signs and magnitudes of these two types of anisotropy.

Title:
Spin- and Pair-Density-Wave Glasses
Authors:
Mross, DF; Senthil, T Author Full Names: Mross, David F.; Senthil, T.
Source:
PHYSICAL REVIEW X, 5 (3):10.1103/PhysRevX.5.031008 JUL 20 2015
Abstract:
Spontaneous breaking of translational symmetry, known as density-wave order, is common in nature. However, such states are strongly sensitive to impurities or other forms of frozen disorder leading to fascinating glassy phenomena. We analyze impurity effects on a particularly ubiquitous form of broken translation symmetry in solids: a spin-density wave (SDW) with spatially modulated magnetic order. Related phenomena occur in pair-density-wave (PDW) superconductors where the superconducting order is spatially modulated. For weak disorder, we find that the SDW or PDW order can generically give way to a SDWor PDW glass-new phases of matter with a number of striking properties, which we introduce and characterize here. In particular, they exhibit an interesting combination of conventional (symmetry-breaking) and spin-glass (Edwards-Anderson) order. This is reflected in the dynamic response of such a system, which-as expected for a glass-is extremely slow in certain variables, but, surprisingly, is fast in others. Our results apply to all uniaxial metallic SDW systems where the ordering vector is incommensurate with the crystalline lattice. In addition, the possibility of a PDW glass has important consequences for some recent theoretical and experimental work on La2-xBaxCu2O4.

Title:
A magnetocaloric effect arising from a ferromagnetic transition in the martensitic state in Heusler alloy of Ni50Mn36Sb8Ga6
Authors:
Tian, FH; Zeng, YY; Xu, MW; Yang, S; Lu, T; Wang, JQ; Chang, TY; Adil, M; Zhang, Y; Zhou, C; Song, XP Author Full Names: Tian, Fanghua; Zeng, Yuyang; Xu, Minwei; Yang, Sen; Lu, Tao; Wang, Jieqiong; Chang, Tieyan; Adil, Murtaza; Zhang, Yin; Zhou, Chao; Song, Xiaoping
Source:
APPLIED PHYSICS LETTERS, 107 (1):10.1063/1.4926411 JUL 6 2015
Abstract:
We report a magnetocaloric effect with nearly zero thermal hysteresis in Heusler alloy of Ni50Mn36Sb8Ga6 around room temperature due to a ferromagnetic transition in martensitic state (FTMS). The refrigerant capacity value of this ferromagnetic transition in the vicinity of onset temperature T-M(C) can arrive at 163.8 J/kg, much higher than that of first-order magnetically martensitic transition in the same alloy. Such a magnetocaloric effect in FTMS is attributed to a second-order (or a weak first-order) transition from an antiferromagnetic phase with modulated 7M orthorhombic structure to a ferromagnetic phase with modulated 4O orthorhombic structure. (C) 2015 AIP Publishing LLC.

Update: 6-Aug-2015


Title:
Microstructural transformation of quasicrystalline AlFeCrTi extruded bars upon long thermal treatments
Authors:
Garcia-Escorial, A; Natale, E; Cremaschi, VJ; Todd, I; Lieblich, M Author Full Names: Garcia-Escorial, A.; Natale, E.; Cremaschi, V. J.; Todd, I.; Lieblich, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 643 S199-S203; 1 10.1016/j.jallcom.2014.12.164 SEP 15 2015
Abstract:
Bulk Al93Fe3Cr2Ti2 bars extruded from gas atomised powder particles present a microstructure of an aluminium matrix reinforced with a spherical nanoquasicrystalline phase. In this work the evolution of the microstructure of Al93Fe3Cr2Ti2 extruded bars upon heating at 400 degrees C for up to 1000 h is investigated by means of X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. According to our observations we propose that the quasicrystalline alloy evolves in two steps: a first step consists in the decomposition of the supersaturated solid solution of the matrix and the quasicrystals, and a second step in the transformation of the quasicrystals into the equilibrium phases. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Characterization of aluminium matrix composites reinforced by Al-Cu-Fe quasicrystalline particles
Authors:
Litynska-Dobrzynska, L; Dutkiewicz, J; Stan-Glowinska, K; Wajda, W; Dembinski, L; Langlade, C; Coddet, C Author Full Names: Litynska-Dobrzynska, L.; Dutkiewicz, J.; Stan-Glowinska, K.; Wajda, W.; Dembinski, L.; Langlade, C.; Coddet, C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 643 S114-S118; 1 10.1016/j.jallcom.2014.11.125 SEP 15 2015
Abstract:
Aluminium matrix composites were consolidated from elemental Al powder and atomised Al65Cu20Fe15 particles by vacuum hot pressing technique. The spherical Al65Cu20Fe15 particles consisted of icosahedral quasicrystalline dendrites or cells and cubic tau-AlCu(Fe) phase located in interdendritic areas. The composites with different content of the reinforcement particles (20, 40 and 60 wt%) were prepared. All composites showed density about 99% and a good bonding between the Al65Cu20Fe15 particles and the matrix. It was shown that the phase composition of the atomised particles did not change after consolidation for the composite containing 20% and 40% added particles while Al2Cu precipitates formed at the Al/Al65Cu20Fe15 interfaces and inside the matrix in the composite with 60% of Al65Cu20Fe15 particles. With the increase of the volume fraction of the reinforcement in the composite the hardness as well as compressive strength increased reaching the value of 173 HV0.5 and 370 MPa, respectively for 60% of Al65Cu20Fe15 particles. The friction coefficient slightly varied in the range 0.5-0.7 depending on the composition. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Formation of Complex Intermetallics in the Al-Rich Part of Al-Pt-Ru
Authors:
Kapush, D; Samuha, S; Meshi, L; Velikanova, TY; Grushko, B Author Full Names: Kapush, D.; Samuha, S.; Meshi, L.; Velikanova, T. Ya.; Grushko, B.
Source:
JOURNAL OF PHASE EQUILIBRIA AND DIFFUSION, 36 (4):327-332; 10.1007/s11669-015-0385-3 AUG 2015
Abstract:
The study confirmed the stability of the previously reported ternary C-phase (, a = 0.77353(3) nm for Al73.5Pt10Ru16.5), whose composition was found to range between Al73Pt6Ru21 and Al73.5Pt14.5Ru12. The thermodynamically stable decagonal phase was revealed for the first time at 700-900 A degrees C in a small compositional region around Al78Pt6Ru16. It belongs to the D-4 structural type (1.65 nm periodicity in the specific direction). The metastable Al-Pt chi-phase (P31c) is stabilized by the addition of only similar to 1.5 at.% Ru and extends up to similar to 12 at.% Ru. The lattice parameters for Al76Pt18.6Ru5.4 are a = 1.2256(4) and c = 2.7331(4) nm.

Title:
Periodic almost-Schrodinger equation for quasicrystals
Authors:
Blinov, IV Author Full Names: Blinov, Igor V.
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep11492 JUL 24 2015
Abstract:
A new method for finding electronic structure and wavefunctions of electrons in quasiperiodic potential is introduced. To obtain results it uses slightly modified Schrodinger equation in spaces of dimensionality higher than physical space. It enables to get exact results for quasicrystals without expensive non-exact calculations.

Title:
Complex antiferromagnetic structure in the intermediate-valence intermetallic Ce-2 RuZn4
Authors:
Hartwig, S; Prokes, K; Hansen, T; Ritter, C; Gerke, B; Pottgen, R; Mydosh, JA; Forster, T Author Full Names: Hartwig, Steffen; Prokes, Karel; Hansen, Thomas; Ritter, Clemens; Gerke, Birgit; Poettgen, Rainer; Mydosh, J. A.; Foerster, Tobias
Source:
PHYSICAL REVIEW B, 92 (2):10.1103/PhysRevB.92.024420 JUL 17 2015
Abstract:
Neutron powder diffraction experiments were performed on the intermediate-valence Ce-2 RuZn4 intermetallic compound and combined with magnetic bulk measurements including high magnetic field experiments up to 58 T. Previous theoretical studies suggest that only one (here Ce1) out of two inequivalent Ce sites is magnetically active. Ce-2 RuZn4 orders antiferromagnetically at T-N = 2.3 K. The magnetic structure is characterized by an incommensurate propagation vector q(m) = (0.384, 0.384, 1/2). Assuming that the Ce2 site does not carry any substantial moment, Ce1 magnetic moments are confined to the (110)-type planes and transversely modulated with an amplitude of 1.77(3) mu(B).

Title:
Commensurate and incommensurate spin-density waves and the superconductivity dome in heavy electron systems
Authors:
Schlottmann, P Author Full Names: Schlottmann, P.
Source:
PHYSICAL REVIEW B, 92 (4):10.1103/PhysRevB.92.045115 JUL 16 2015
Abstract:
The nesting of the Fermi surfaces of an electron and a hole pocket separated by a nesting vector Q and the interaction between electrons gives rise to itinerant antiferromagnetism. The order can gradually be suppressed by mismatching the nesting and a quantum critical point is obtained as the Neel temperature tends to zero. If the vector Q is commensurate with the lattice (umklapp with Q = G/2), pairs of electrons can be transferred between the pockets and a superconducting dome above the quantum critical point may arise. If the vector Q is not commensurate with the lattice, there are eight phases that need to be considered: commensurate and incommensurate spin and charge density waves and four superconductivity phases, two of them with a modulated order parameter of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type. The renormalization group equations are studied and numerically integrated. The phase diagram is obtained as a function of the mismatch of the Fermi surfaces and the magnitude of vertical bar Q - G/2 vertical bar.

Title:
Non-Fermi-Liquid Behavior in Metallic Quasicrystals with Local Magnetic Moments
Authors:
Andrade, EC; Jagannathan, A; Miranda, E; Vojta, M; Dobrosavljevic, V Author Full Names: Andrade, Eric C.; Jagannathan, Anuradha; Miranda, Eduardo; Vojta, Matthias; Dobrosavljevic, Vladimir
Source:
PHYSICAL REVIEW LETTERS, 115 (3):10.1103/PhysRevLett.115.036403 JUL 14 2015
Abstract:
Motivated by the intrinsic non-Fermi-liquid behavior observed in the heavy-fermion quasicrystal Au51Al34Yb15, we study the low-temperature behavior of dilute magnetic impurities placed in metallic quasicrystals. We find that a large fraction of the magnetic moments are not quenched down to very low temperatures T, leading to a power-law distribution of Kondo temperatures P(T-K) similar to T-K(alpha-1), with a nonuniversal exponent alpha, in a remarkable similarity to the Kondo-disorder scenario found in disordered heavy-fermion metals. For alpha < 1, the resulting singular P(T-K) induces non-Fermi-liquid behavior with diverging thermodynamic responses as T -> 0.

Update: 30-Jul-2015


Title:
Effect of Ti addition on the glass forming ability, crystallization, and plasticity of (Zr64.13Cu15.75Ni10.12Al10)(100-x)Ti-x bulk metallic glasses
Authors:
Shi, B; Xu, YL; Ma, WL; Li, C; Estefania, CV; Li, JG Author Full Names: Shi, Bo; Xu, Yuanli; Ma, Wenli; Li, Chao; Estefania, Carmen Verge; Li, Jiangong
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 639 345-349; 10.1016/j.msea.2015.04.100 JUL 15 2015
Abstract:
A series of (Zr(64.13)Cu(15.7)sNi(10.12)Al(10))(100-x)Ti-x (x=0-7) bulk metallic glasses were prepared by water-cooled copper mold casting method. The glass forming ability, crystallization behavior, and plasticity of the (Zr64.13Cu15.75Ni10.12Al10)(100-x)Ti-x alloys with different Ti contents were studied. The reduced glass transition temperature increases with Ti addition and a maximum value of 0.562 is achieved at x=5, indicating that the glass forming ability increases with Ti addition. Compared with that of one crystallization step for the sample without Ti addition, the Ti (x >= 2) containing alloys exhibit a two-step crystallization behavior. In addition, the initial crystallization temperature decreases from 744 to 684 K as x increases from 0 to 7. Icosahedral quasicrystal phase was found to precipitate in the amorphous matrix in the first crystallization step, implying that strong icosahedral short-range order may exist in the Ti (x >= 2) containing alloys. moreover, the (Zr64.13Cu15.75Ni10.12Al10)(100-x)Ti-x bulk metallic glasses exhibit excellent plasticity, i.e., a plastic engineering strain in compression larger than 80% for x <= 6. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Effects of Al-Cr-Fe Quasicrystal Content on Tribological Properties of Cold-Sprayed Titanium Composite Coatings
Authors:
Khun, NW; Li, RT; Loke, K; Khor, KA Author Full Names: Khun, N. W.; Li, R. T.; Loke, K.; Khor, K. A.
Source:
TRIBOLOGY TRANSACTIONS, 58 (4):616-624; 10.1080/10402004.2014.991860 2015
Abstract:
Titanium (Ti) composite coatings were prepared on commercially available Ti substrates via a cold-spray process. Quasicrystalline Al-Cr-Fe particles were incorporated in the cold-sprayed Ti matrices at different contents to form a new type of wear-resistant Ti composite coating. The tribological properties of the Ti composite coatings were systematically investigated using steel ball-on-disc microtribological testing. The incorporation of 10 wt% Al-Cr-Fe particles gave rise to the higher wear resistance of the Ti composite coating than that of the Ti coating due to the higher wear resistance of the Al-Cr-Fe particles than that of the Ti matrix. As a result, an increase in the Al-Cr-Fe particle content to 20 wt% increased the wear resistance of the Ti composite coating. However, the wear resistance of the Ti composite coating decreased with a further increase in the Al-Cr-Fe particle content to 30 wt% due to the significantly increased volume of micropores in the composite coating. It could be concluded that the Ti composite coating with 20 wt% Al-Cr-Fe particles had the highest wear resistance among the cold-sprayed coatings used in this study.

Title:
Complex physical properties of EuMgSi - a complementary study by neutron powder diffraction and Eu-151 Mossbauer spectroscopy
Authors:
Niehaus, O; Ryan, DH; Flacau, R; Lemoine, P; Chernyshov, D; Svitlyk, V; Cuervo-Reyes, E; Slabon, A; Nesper, R; Schellenberg, I; Pottgen, R Author Full Names: Niehaus, O.; Ryan, D. H.; Flacau, R.; Lemoine, P.; Chernyshov, D.; Svitlyk, V.; Cuervo-Reyes, E.; Slabon, A.; Nesper, R.; Schellenberg, I.; Poettgen, R.
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 3 (27):7203-7215; 10.1039/c5tc01017a 2015
Abstract:
X-ray pure samples of EuMgSi were synthesized by reactions of the elements in sealed niobium tubes using a high frequency and subsequently a resistance furnace. The structure was investigated by single crystal X-ray diffraction: TiNiSi-type, Pnma, a = 769.5(2), b = 455.0(1), c = 836.9(2) pm, wR(2) = 0.033 [I > 2 sigma(I)], and 705 F-2 values with 20 variables. Powder synchrotron radiation diffraction experiments did not reveal any structural changes down to 4.3 K. Magnetic susceptibility data and Eu-151 Mossbauer spectra clearly indicate a stable Eu2+ configuration. Two distinct magnetic anomalies around 12 and 14 K can be observed for different samples with dc- and ac-susceptibility, heat capacity and resistivity measurements. Fitting of hyperfine field splitting as a function of temperature (Eu-151 Mossbauer spectroscopy data) with a Brillouin function also leads to a magnetic ordering around 14 K. Electronic structure calculations in coincidence with the resistivity measurement prove narrow (or nearly zero) gap-semiconducting behaviour. The calculated band gap energy of 0.03 eV should be considered with precautions due to the accuracy of this method. An incommensurate magnetic structure with the propagation vector k = [q(x) approximate to 0.37, 0, 0] was determined using neutron diffraction data at 5.5 K. In consensus of dc- and ac-susceptibility and neutron powder diffraction a complex combination of antiferromagnetic and ferromagnetic interactions, most likely by super-exchange, is confirmed. These cause two magnetic ordering temperatures, though only one independent crystallographic Eu site in terms of the crystal structure is present in EuMgSi.

Update: 23-Jul-2015


Title:
Microstructure and mechanical properties of sand mold cast Mg-4.58Zn-2.6Gd-0.18Zr magnesium alloy after different heat treatments
Authors:
Liu, SJ; Yang, GY; Luo, SF; Jie, WQ Author Full Names: Liu, S. J.; Yang, G. Y.; Luo, S. F.; Jie, W. Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 644 846-853; 10.1016/j.jallcom.2015.05.062 SEP 25 2015
Abstract:
Microstructure and mechanical properties of sand mold cast Mg-4.58Zn-2.6Gd-0.18Zr magnesium alloy after different heat treatments were investigated. As-cast alloy was composed of alpha(Mg) matrix, interdendritic alpha(Mg) + W(Mg3Zn3Gd2) eutectic, icosahedral quasicrystalline I(Mg3Zn6Gd) phase and Mg3Gd particles within alpha(Mg) matrix. After solution treatment at 505 degrees C for 16 h, most of alpha(Mg) + W(Mg3Zn3Gd2) eutectic dissolved into alpha(Mg) matrix, but a new phase, Zn2Zr3, precipitated within alpha(Mg) matrix. The appropriate aging treatment was done at 220 degrees C for 16 h, after which some dispersive fine eutectics re-precipitated along the grain boundary. Furthermore, rod-like beta(1)' and plate-like beta(2)' formed within alpha(Mg) matrix. The ultimate tensile strength, yield strength and elongation of the experimental alloy in the T6 state at room temperature were 280 MPa, 175 MPa and 7.5%, respectively. According to strengthening contribution calculation, it is revealed that both the second phase strengthening and the solid solution strengthening played important roles in improving the mechanical properties after T6 treatment. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Hot compression characteristics and processing maps of a cast Mg-9.5Zn-2.0Y alloy with icosahedral quasicrystalline phase
Authors:
Kwak, TY; Lim, HK; Kim, WJ Author Full Names: Kwak, T. Y.; Lim, H. K.; Kim, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 644 645-653; 10.1016/j.jallcom.2015.04.158 SEP 25 2015
Abstract:
Hot compressive characteristics and processing maps of a cast Mg-9.5Zn-2.0Y alloy with I-phase (ZW92) were studied in the temperature range between 523 and 723 K and in the strain rate range between 10(-3) and 10 s(-1). According to the analysis of deformation behavior, the rate-controlling mechanism governing deformation during entire compression process was lattice diffusion controlled dislocation climb creep and power-law breakdown. Comparison of the processing maps of ZW92 with those of the cast Mg-Zn-Y alloys with different types of intermetallic compounds (W- and long period stacking ordered phases) and the cast Mg-Al-Zn alloy (AZ80) alloy with beta-Mg17Al12 phase in terms of eta values and the domain sizes of the unstable regime indicated that ZW92 exhibited a better hot workability at high strain rates above 1 s-1. This result was attributed to the suppression of power law breakdown in ZW92 due to occurrence of extensive dynamic recrystallization at high strain rates, which was facilitated by the effective fragmentation and dispersion of I-phase during deformation at high strain rates. A fully recrystallized microstructure composed of defect-free fine grains (9.34 mu m) with high fraction of high angle grain boundaries (0.81) was obtained at 623 K - 10 s(-1). (C) 2015 Elsevier B.V. All rights reserved.

Update: 16-Jul-2015


Title:
Structural crossover from nonmodulated to long-period modulated tetragonal phase and anomalous change in ferroelectric properties in the lead-free piezoelectric Na1/2Bi1/2TiO3-BaTiO3
Authors:
Rao, BN; Khatua, DK; Garg, R; Senyshyn, A; Ranjan, R Author Full Names: Rao, Badari Narayana; Khatua, Dipak Kumar; Garg, Rohini; Senyshyn, Anatoliy; Ranjan, Rajeev
Source:
PHYSICAL REVIEW B, 91 (21):10.1103/PhysRevB.91.214116 JUN 29 2015
Abstract:
The highly complex structure-property interrelationship in the lead-free piezoelectric (x) Na1/2Bi1/2TiO3 - (1 - x) BaTiO3 is a subject of considerable contemporary debate. Using comprehensive x-ray, neutron diffraction, dielectric, and ferroelectric studies, we have shown the existence of a new criticality in this system at x = 0.80, i.e., well within the conventional tetragonal phase field. This criticality manifests as a nonmonotonic variation of the tetragonality and coercivity and is shown to be associated with a crossover from a nonmodulated tetragonal phase (for x < 0.8) to a long-period modulated tetragonal phase (for x > 0.80). It is shown that the stabilization of long-period modulation introduces a characteristic depolarization temperature in the system. While differing qualitatively from the two-phase model often suggested for the critical compositions of this system, our results support the view with regard to the tendency in perovskites to stabilize long-period modulated structures as a result of complex interplay of antiferrodistortive modes [Bellaiche and Iniguez, Phys. Rev. B 88, 014104 ( 2013); Prosandeev, Wang, Ren, Iniguez, ands Bellaiche, Adv. Funct. Mater. 23, 234 (2013)].

Title:
Crystal structure, incommensurate magnetic order, and ferroelectricity in Mn1-xCuxWO4 (0 <= x <= 0.19)
Authors:
Kumar, CMN; Xiao, Y; Lunkenheimer, P; Loidl, A; Ohl, M Author Full Names: Kumar, C. M. N.; Xiao, Y.; Lunkenheimer, P.; Loidl, A.; Ohl, M.
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235149 JUN 29 2015
Abstract:
We have carried out a systematic study on the effect of Cu doping on nuclear, magnetic, and dielectric properties in Mn1-xCuxWO4 for 0 <= x <= 0.19 by a synergic use of different techniques, viz, heat capacity, magnetization, dielectric, and neutron powder diffraction measurements. Via heat capacity and magnetization measurements we show that with increasing Cu concentration magnetic frustration decreases, which leads to the stabilization of commensurate magnetic ordering. This was further verified by temperature-dependent unit cell volume changes derived from neutron diffraction measurements which was modeled by the Gruneisen approximation. Dielectric measurements show a low temperature phase transition below about 9-10 K. Furthermore, magnetic refinements reveal no changes below this transition indicating a possible spin-flop transition which is unique to the Cu doped system. From these combined studies we have constructed a magnetoelectric phase diagram of this compound.

Title:
Interplay between magnetic order at Mn and Tm sites alongside the structural distortion in multiferroic films of o-TmMnO3
Authors:
Windsor, YW; Ramakrishnan, M; Rettig, L; Alberca, A; Bothschafter, EM; Staub, U; Shimamoto, K; Hu, Y; Lippert, T; Schneider, CW Author Full Names: Windsor, Y. W.; Ramakrishnan, M.; Rettig, L.; Alberca, A.; Bothschafter, E. M.; Staub, U.; Shimamoto, K.; Hu, Y.; Lippert, T.; Schneider, C. W.
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235144 JUN 26 2015
Abstract:
We employ resonant soft x-ray diffraction to individually study the magnetic ordering of the Mn and the Tm sublattices in single-crystalline films of orthorhombic (o-)TmMnO3. The same magnetic ordering wave vector of (0 q 0) with q approximate to 0.46 is found for both ionic species, suggesting that the familiar antiferromagnetic order of the Mn ions induces a magnetic order on the Tm unpaired 4f electrons. Indeed, intensity variations of magnetic reflections with temperature corroborate this scenario. Calculated magnetic fields at the Tm sites are used as a model magnetic structure for the Tm, which correctly predicts intensity variations at the Tm resonance upon azimuthal rotation of the sample. The model allows ruling out a bc-cycloid modulation of the Mn ions as the cause for the incommensurate ordering, as found in TbMnO3. The structural distortion, which occurs in the ferroelectric phase below T-C, was followed through nonresonant diffraction of structural reflections forbidden by the high-temperature crystal symmetry. The (0 q 0) magnetic reflection appears at the Mn resonance well above T-C, indicating that this reflection is sensitive also to the intermediate sinusoidal magnetic phase. The model presented suggests that the Tm 4f electrons are polarized well above the ferroelectric transition and are possibly not affected by the transition at T-C. The successful description of the induced order observed at the Tm resonance is a promising example for future element-selective studies in which "spectator" ions may allow access to previously unobtainable information about other constituent ions.

Title:
Superspace crystallography: a key to the chemistry and properties
Authors:
Pinheiro, CB; Abakumov, AM Author Full Names: Pinheiro, Carlos Basilio; Abakumov, Artem M.
Source:
IUCRJ, 2 137-154; 10.1107/S2052252514023550 1 JAN 2015
Abstract:
An overview is given of the recent advances in the field of modulated molecular and inorganic crystals with an emphasis on the links between incommensurability, intermolecular and interatomic interactions and, wherever possible, the properties of the materials. The importance of detailed knowledge on the modulated structure for understanding the crystal chemistry and the functional properties of modulated phases is shown using selected examples of incommensurate modulations in organic molecular compounds and inorganic complex oxides.

Title:
A CENTURY OF X-RAY CRYSTALLOGRAPHY AND 2014 INTERNATIONAL YEAR OF X-RAY CRYSTALLOGRAPHY
Authors:
Kojic-Prodic, B Author Full Names: Kojic-Prodic, Biserka
Source:
MACEDONIAN JOURNAL OF CHEMISTRY AND CHEMICAL ENGINEERING, 34 (1):19-32; 2015
Abstract:
The 100(th) anniversary of the Nobel prize awarded to Max von Laue in 1914 for his discovery of diffraction of X-rays on a crystal marked the beginning of a new branch of science - X-ray crystallography. The experimental evidence of von Laue's discovery was provided by physicists W. Friedrich and P. Knipping in 1912. In the same year, W. L. Bragg described the analogy between X-rays and visible light and formulated the Bragg's law, a fundamental relation that connected the wave nature of X-rays and fine structure of a crystal at atomic level. In 1913 the first simple diffractometer was constructed and structure determination started by the Braggs, father and son. In 1915 their discoveries were acknowledged by a Nobel Prize in physics. Since then, X-ray diffraction has been the basic method for determination of three-dimensional structures of synthetic and natural compounds. The three-dimensional structure of a substances defines its physical, chemical, and biological properties. Over the past century the significance of X-ray crystallography has been recognized by about forty Nobel prizes. X-ray structure analysis of simple crystals of rock salt, diamond and graphite, and later of complex biomolecules such as B12-vitamin, penicillin, haemoglobin/myoglobin, DNA, and biomolecular complexes such as viruses, chromatin, ribozyme, and other molecular machines have illustrated the development of the method. Among these big discoveries the double helix DNA structure was an epochal achievement of the 20(th) century. These discoveries, together with many others of the X-ray crystallography, have completely changed our views and helped to develop other new fields of science such as molecular genetics, biophysics, structural molecular biology, material science, and many others. During the last decade, the implementation of free electron X-ray lasers, a new experimental tool, has opened up femtosecond dynamic crystallography. This highly advanced methodology enables to solve the structures and dynamics of the most complex biological assemblies involved in a cell metabolism. The advancements of science and technology over the 20th and 21(st) centuries are of great influence on our views in almost all human activities. The importance of Xray crystallography for science and technology advocates for its high impact on a wide area of research and declares it as a highly interdisciplinary science. In short, crystallography has defined the shape of the modern world. Focusing on single crystal diffraction, this essay tackles only one field of crystallography; the comprehensive review on X-ray crystallography can hardly be fitted into a single article. The aim with this review was to highlight the most striking examples illustrating some of the milestones over the past century.

Title:
A modulation wave approach to the order hidden in disorder
Authors:
Withers, R Author Full Names: Withers, Ray
Source:
IUCRJ, 2 74-84; 10.1107/S2052252514022556 1 JAN 2015
Abstract:
The usefulness of a modulation wave approach to understanding and interpreting the highly structured continuous diffuse intensity distributions characteristic of the reciprocal spaces of the very large family of inherently flexible materials which exhibit ordered 'disorder' is pointed out. It is shown that both longer range order and truly short-range order are simultaneously encoded in highly structured diffuse intensity distributions. The long-range ordered crystal chemical rules giving rise to such diffuse distributions are highlighted, along with the existence and usefulness of systematic extinction conditions in these types of structured diffuse distributions.

Update: 9-Jul-2015


Title:
Microwave sol-gel synthesis and upconversion photoluminescence properties of CaGd2(WO4)(4):Er3+/Yb3+ phosphors with incommensurately modulated structure
Authors:
Lim, CS; Aleksandrovsky, A; Molokeev, M; Oreshonkov, A; Atuchin, V Author Full Names: Lim, Chang Sung; Aleksandrovsky, Aleksandr; Molokeev, Maxim; Oreshonkov, Aleksandr; Atuchin, Victor
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 228 160-166; 10.1016/j.jssc.2015.04.032 AUG 2015
Abstract:
CaGd2-x(WO4)(4):Er3+/Yb3+ phosphors with the doping concentrations of Er3+ and Yb3+ (x=Er3++Yb3+, Er3+=0.05, 0.1, 0.2 and Yb3+=0.2, 0.45) have been successfully synthesized by the microwave sol-gel method. The crystal structure of CaGd2-x(WO4)(4):Er3+/Yb3+ tungstates have been refined, and upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after the heat-treatment at 900 degrees C for 16 h, showed a well crystallized morphology. Under the excitation at 980 nm, CaGd2(WO4)(4):Er3+/Yb3+ particles exhibited a strong 525-nm and a weak 550-nm emission bands in the green region and a very weak 655-nm emission band in the red region. The Raman spectrum of undoped CaGd2(WO4)(4) revealed about 12 narrow lines. The strongest band observed at 903 cm(-1) was assigned to the v(1) symmetric stretching vibration of WO4 tetrahedrons. The spectra of the samples doped with Er and Yb obtained under the 514.5 nm excitation were dominated by Er3+ luminescence preventing the recording of these samples Raman spectra. Concentration quenching of the erbium luminescence at H-2(11/2)-> I-4(15/2) transition is weak in the range of erbium doping level x(Er)=0.05-0.2, while, for transition S-4(3/2)-> 4I(15/2), the signs of concentration quenching become pronounced at x(Er)=0.2. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Direct evidence for stress-induced transformation between coexisting multiple martensites in a Ni-Mn-Ga multifunctional alloy
Authors:
Huang, L; Cong, DY; Wang, ZL; Nie, ZH; Dong, YH; Zhang, Y; Ren, Y; Wang, YD Author Full Names: Huang, L.; Cong, D. Y.; Wang, Z. L.; Nie, Z. H.; Dong, Y. H.; Zhang, Y.; Ren, Y.; Wang, Y. D.
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 48 (26):10.1088/0022-3727/48/26/265304 JUL 8 2015
Abstract:
The structural response of coexisting multiple martensites to stress field in a Ni-Mn-Ga multifunctional alloy was investigated by the in situ high-energy x-ray diffraction technique. Stress-induced transformation between coexisting multiple martensites was observed at 110 K, at which five-layered modulated (5M), seven-layered modulated (7M) and non-modulated (NM) martensites coexist. We found that a tiny stress of as low as 0.5 MPa could trigger the transformation from 5M and 7M martensites to NM martensite and this transformation is partly reversible. Besides the transformation between coexisting multiple martensites, rearrangement of martensite variants also occurs during loading, at least at high stress levels. The present study is instructive for designing advanced multifunctional alloys with easy actuation.

Title:
Quasicrystal dissolution and performance of isothermally heat-treated Mg-Zn-Y alloy
Authors:
Wan, DQ; Luo, X; Liu, YJ; Yu, T Author Full Names: Wan, Di-Qing; Luo, Xian; Liu, Ya-Juan; Yu, Tian
Source:
RARE METALS, 34 (7):452-456; 10.1007/s12598-013-0119-9 JUL 2015
Abstract:
Conventional casting method was employed to prepare Mg-Zn-Y alloy only with alpha-Mg+I-phase; however, the grain size of quasicrystal is quite large in the as-cast state. Therefore, isothermal treatment was applied to refine the quasicrystal phase. The result shows that after the Mg-Zn-Y alloy was isothermally treated at 500 degrees C for several hours, the coarse quasicrystal can be gradually dissolved and thus refined. Generally, the dissolving processes of quasicrystal are slow first and then accelerate; after isothermally treated with 8 h at 500 degrees C, the quasicrystal is almost completely dissolved into the matrix only with 1-5 mu m tiny quasicrystals remained. Refinement of quasicrystal can markedly reduce the wear resistance, but increase the corrosion resistance.

Title:
How important is the {103} plane of stable Ge2Sb2Te5 for phase-change memory?
Authors:
Zhang, W; Zheng, WT; Kim, JG; Cui, XQ; Li, L; Qi, JG; Kim, YJ; Song, SA Author Full Names: Zhang, W.; Zheng, W. T.; Kim, J. -G.; Cui, X. Q.; Li, L.; Qi, J. G.; Kim, Y. -J.; Song, S. A.
Source:
JOURNAL OF MICROSCOPY, 259 (1):10-15; 10.1111/jmi.12242 JUL 2015
Abstract:
Closely correlating with {200} plane of cubic phase, {103} plane of hexagonal phase of Ge2Sb2Te5 plays a crucial role in achieving fast phase change process as well as formation of modulation structures, dislocations and twins in Ge2Sb2Te5. The behaviors of {103} plane of hexagonal phase render the phase-change memory process as a nanoscale shape memory. Lay description Exploring the phase-change mechanism, structures and properties of chalcogenides has been currently one of the hot topics. Ge-Sb-Te chalcogenides are of tremendous technological importance ranging from optical data storage to PRAM. Exhibiting the best performance for DVD-RAM in terms of speed and stability, Ge2Sb2Te5 is currently the most important phase-change alloy. There exist three solid phases in Ge2Sb2Te5: amorphous, metastable rocksalt (FCC) and stable hexagonal (Hex) phases. The whole switching operation in optical data storage and electronic memories is based on the following rapid cycling processes by either laser or electric heating: amorphousFCC (Erase/SET process)Hexliquidamorphous (Write/RESET process). The stable Hex is an indispensable concern to bridge the aforementioned whole cycling framework. In this work, structural correlations between the two crystalline phases were analyzed and the rich structural phenomena were unraveled. Closely correlated with {200} plane of FCC phase, {103} plane of Hex phase of Ge2Sb2Te5 plays a crucial role in achieving fast phase change process as well as formation of modulation structures, dislocations and twins in Ge2Sb2Te5. We propose that from a point view of maintaining the ultra-high transition speed, (103) of Hex phase can effectively facilitate phase-change memory. This leads to a novel concept that phase-change process can be treated as a nanoscale shape-memory, towards essential understanding of the relevant structural features of Ge-Sb-Te chalcogenides.

Title:
Antiferromagnetic Dichroism in a Complex Multisublattice Magnetoelectric CuB2O4
Authors:
Boldyrev, KN; Pisarev, RV; Bezmaternykh, LN; Popova, MN Author Full Names: Boldyrev, K. N.; Pisarev, R. V.; Bezmaternykh, L. N.; Popova, M. N.
Source:
PHYSICAL REVIEW LETTERS, 114 (24):10.1103/PhysRevLett.114.247210 JUN 19 2015
Abstract:
Magnetic control of the crystal chirality was announced by Saito et al. [Phys. Rev. Lett. 101, 117402 (2008)] on the ground of experiments in CuB2O4. This claim has raised a sharp dispute in the literature because it seemed to contradict the fundamental symmetry principles. We settle this dispute on the basis of a high-resolution optical spectroscopy study of excitonic transitions in CuB2O4. We find that a large sublattice-sensitive antiferromagnetic linear dichroism (LD) emerges at the Neel temperature T-N = 21 K and show how it could simulate a "magnetic-field control of the crystal chirality." We prove that the discovered LD is related microscopically to the magnetic Davydov splitting. This LD is highly sensitive to subtle changes in the spin subsystems, which allowed us to observe a splitting of the phase transition into an incommensurate magnetic phase into two transitions (T-1* = 8.5 and T-2* = 7.9 K) and to suggest elliptical spiral structures below T-1*, instead of a simple circular helix proposed earlier.

Title:
Lattice vibrations in the Frenkel-Kontorova model. I. Phonon dispersion, number density, and energy
Authors:
Meng, QP; Wu, LJ; Welch, DO; Zhu, YM Author Full Names: Meng, Qingping; Wu, Lijun; Welch, David O.; Zhu, Yimei
Source:
PHYSICAL REVIEW B, 91 (22):10.1103/PhysRevB.91.224305 JUN 17 2015
Abstract:
We studied the lattice vibrations of two interpenetrating atomic sublattices via the Frenkel-Kontorova (FK) model of a linear chain of harmonically interacting atoms subjected to an on-site potential using the technique of thermodynamic Green's functions based on quantum field-theoretical methods. General expressions were deduced for the phonon frequency-wave-vector dispersion relations, number density, and energy of the FK model system. As the application of the theory, we investigated in detail cases of linear chains with various periods of the on-site potential of the FK model. Some unusual but interesting features for different amplitudes of the on-site potential of the FK model are discussed. In the commensurate structure, the phonon spectrum always starts at a finite frequency, and the gaps of the spectrum are true ones with a zero density of modes. In the incommensurate structure, the phonon spectrum starts from zero frequency, but at a nonzero wave vector; there are some modes inside these gap regions, but their density is very low. In our approximation, the energy of a higher-order commensurate state of the one-dimensional system at a finite temperature may become indefinitely close to the energy of an incommensurate state. This finding implies that the higher-order incommensurate-commensurate transitions are continuous ones and that the phase transition may exhibit a "devil's staircase" behavior at a finite temperature.

Title:
Lattice vibrations in the Frenkel-Kontorova Model. II. Thermal conductivity
Authors:
Meng, QP; Wu, LJ; Welch, DO; Zhu, YM Author Full Names: Meng, Qingping; Wu, Lijun; Welch, David O.; Zhu, Yimei
Source:
PHYSICAL REVIEW B, 91 (22):10.1103/PhysRevB.91.224306 JUN 17 2015
Abstract:
We applied the formulas for the phonon spectral-density function that we presented in the previous paper of this series to analyze the thermal conductivity of the lattice in the framework of the Frenkel-Kontorova (FK) model. We found that two extra mechanisms of phonon scattering (different from the point impurities, three-phonon processes, and boundary scattering typical of all crystals), viz., resonance, and anharmonic scattering, that mainly influences the thermal conductivity of the lattice. The frequencies of resonance scattering are discrete, and their number increases from a finite number to infinity with their transition from the commensurate to the incommensurate state. Changing the amplitude and period of the FK model changes the frequencies and the frequency number of resonance scattering and the intensity of anharmonic scattering. We analyze these changes in detail. Our theory can explain all existing numerical results on this problem and suggest strategies to reduce the thermal conductivity of the lattice of layered materials.

Title:
Characterization of deep level defects and thermally stimulated depolarization phenomena in La-doped TlInS2 layered semiconductor
Authors:
Seyidov, MY; Suleymanov, RA; Mikailzade, FA; Kargin, EO; Odrinsky, AP Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Mikailzade, Faik A.; Kargin, Elif Orhan; Odrinsky, Andrei P.
Source:
JOURNAL OF APPLIED PHYSICS, 117 (22):10.1063/1.4922347 JUN 14 2015
Abstract:
Lanthanum-doped high quality TlInS2 (TlInS2: La) ferroelectric-semiconductor was characterized by photo-induced current transient spectroscopy (PICTS). Different impurity centers are resolved and identified. Analyses of the experimental data were performed in order to determine the characteristic parameters of the extrinsic and intrinsic defects. The energies and capturing cross section of deep traps were obtained by using the heating rate method. The observed changes in the Thermally Stimulated Depolarization Currents (TSDC) near the phase transition points in TlInS2: La ferroelectric-semiconductor are interpreted as a result of self-polarization of the crystal due to the internal electric field caused by charged defects. The TSDC spectra show the depolarization peaks, which are attributed to defects of dipolar origin. These peaks provide important information on the defect structure and localized energy states in TlInS2: La. Thermal treatments of TlInS2: La under an external electric field, which was applied at different temperatures, allowed us to identify a peak in TSDC which was originated from La-dopant. It was established that deep energy level trap BTE43, which are active at low temperature (T <= 156 K) and have activation energy 0.29 eV and the capture cross section 2.2 x 10(-14) cm(2), corresponds to the La dopant. According to the PICTS results, the deep level trap center B5 is activated in the temperature region of incommensurate (IC) phases of TlInS2: La, having the giant static dielectric constant due to the structural disorders. From the PICTS simulation results for B5, native deep level trap having an activation energy of 0.3 eV and the capture cross section of 1.8 x 10(-16) cm(2) were established. A substantial amount of residual space charges is trapped by the deep level localized energy states of B5 in IC-phase. While the external electric field is applied, permanent dipoles, which are originated from the charged B5 deep level defects, are aligned in the direction of the applied electric field and the equilibrium polarization can be reached in a relatively short time. When the polarization field is maintained, while cooling the temperature of sample to a sufficiently low degrees, the relaxation times of the aligned dipoles drastically increases. Practically, frozen internal electric field or electrets states remain inside the TlInS2: La when the applied bias field is switched off. The influence of deep level defects on TSDC spectra of TlInS2: La has been revealed for the first time. (C) 2015 AIP Publishing LLC.

Title:
Coexistence of the spin and electron-hole quantum liquids in frustrated manganites La1-y Sm (y) MnO3+delta
Authors:
Bukhanko, FN; Bukhanko, AF Author Full Names: Bukhanko, F. N.; Bukhanko, A. F.
Source:
PHYSICS OF THE SOLID STATE, 57 (6):1114-1127; 10.1134/S1063783415060062 JUN 2015
Abstract:
The structural, electronic, and magnetic phase transformations induced in the temperature range of 4.2-300 K by the isovalent substitution of the rare-earth Sm3+ ion for the La3+ ion with a larger radius have been investigated in the system of self-doped manganites La1-y Sm (y) MnO3+delta (delta similar to 0.1, 0 a parts per thousand currency sign y a parts per thousand currency sign 1). It has been found using the X-ray diffraction analysis that the substitution La -> Sm is accompanied by a significant increase of the GdFeO3-type and Jahn-Teller-type lattice distortions. At a temperature of 300 K, an increase in the Sm concentration y leads to a concentration phase transition from the pseudocubic O* phase to the orthorhombic O phase, as well as to the appearance of an s-shaped anomaly of the lattice parameter a at concentrations y a parts per thousand yen 0.4 and an anomalous peak in the concentration dependence of the electrical resistance R(y) near y a parts per thousand 0.85. The magnetic T-y-aOE (c) r (A) phase diagrams of the La1-y Sm (y) MnO3+delta system in the temperature range of 4.2-250 K have been constructed according to the results of measurements of the temperature dependences of the direct-current (dc) magnetization M(T). It has been revealed that the samples with y a parts per thousand yen 0.8 exhibit signs of the melting of the A- and CE-type modulated antiferromagnetic (AFM) structures in the form of an anomalous decrease both in the critical temperature of the transition to a frustrated AFM state and in the magnetization of the samples with an increase in the concentration y. The anomalies observed in the temperature dependences of the alternating-current (ac) dielectric permittivity of the La1-y Sm (y) MnO3+delta samples have been explained within the existing concepts of the Bose-Einstein condensation of an electron-hole liquid in the form of metallic droplets in an excitonic insulator.

Update: 2-Jul-2015


Title:
Ni- and Cu-free Ti-based metallic glasses with potential biomedical application
Authors:
Guo, Y; Bataev, I; Georgarakis, K; Jorge, AM; Nogueira, RP; Pons, M; Yavari, AR Author Full Names: Guo, Y.; Bataev, I.; Georgarakis, K.; Jorge, A. M., Jr.; Nogueira, R. P.; Pons, M.; Yavari, A. R.
Source:
INTERMETALLICS, 63 86-96; 10.1016/j.intermet.2015.04.004 AUG 2015
Abstract:
In the present work Ti-Fe-Si and Ti-Fe-Si-X (X = Zr, Pd, Ge) glassy alloys are discussed as potential biomedical materials. Depending on composition and experimental conditions these alloys possess glassy, quasicrystalline or crystalline structure. The glassy state and crystallization behavior of the melt spun ribbons were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and the Hank's solution was used as simulated body fluid for corrosion tests. Ternary Ti-Fe-Si alloys near the Ti65Fe30Si5 eutectic point were prone to form quasicrystals if the cooling rate was not high enough to retain amorphous structure. The compositions on the steeper side of the eutectic point could be vitrified. The results indicate that small additions of Zr can have a positive effect on glass formation, while additions of Ge, Pd may have a detrimental effect by promoting crystallization. Ti Fe Si and Ti Fe Si Zr alloys exhibited high corrosion properties, superior to that of pure Ti and most of Ti-based glassy alloys reported in the literature. Being free of Ni and Cu this group of alloys may be considered for possible biomedical application. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Amorphous-i phase-big cube-amorphous cyclic phase transformation of mechanically alloyed Zr75Ni20Al5 system
Authors:
El-Eskandarany, MS Author Full Names: El-Eskandarany, M. Sherif
Source:
INTERMETALLICS, 63 27-36; 10.1016/j.intermet.2015.01.010 AUG 2015
Abstract:
Cyclic glassy-metastable-glassy phase transformations were investigated during mechanical alloying of Zr75Ni20Al5 powders, using high-energy ball milling technique. After 20 h of continuous milling, a single glassy phase was obtained. The synthesized glassy powder, which is homogeneous in structure and composition, showed a glass transition temperature lied at 510 degrees C and a large supercooled liquid region extended to 86.5 degrees C. This glassy phase, which crystallized through a single sharp exothermic peak at 596.5 degrees C, tended to transformed into icosahedral (i-phase) nano-quasicrystalline grains upon further milling to 30 h. This i-phase showed serious instability against the mechanical deformations generated by the milling tools, and hence transformed into big cube phase with increasing the milling time to 45 h. In a cyclic phase transformation the obtained big cube phase subsequently transformed into the same glassy phase after 60 h of milling. This observed cyclic phase transformation was observed twice upon further milling to 90 h without serious compositional changes. The iron contamination contents in the ball-milled powders had constant values of about 0.16 wt.% and did not change with changing the structure of the powders. The present work shows that this phenomenon does not have any obvious analogues with the periodic redox reactions or with diffusive-reactive phenomena known in chemistry. On the basis of our results, the destabilizing effect of the defects created by the milling media (balls), which leads to the cyclic transformations, depends on the milling time. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Direct observation of solid-state reversed transformation from crystals to quasicrystals in a Mg alloy
Authors:
Liu, JF; Yang, ZQ; Ye, HQ Author Full Names: Liu, Jian-Fang; Yang, Zhi-Qing; Ye, Heng-Qiang
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep09816 JUN 12 2015
Abstract:
Phase transformation of quasicrystals is of interest in various fields of science and technology. Interestingly, we directly observed unexpected solid-state epitaxial nucleation and growth of Zn6Mg3Y icosahedral quasicrystals in a Mg alloy at about 573 K which is about 300 K below the melting point of Zn6Mg3Y, in contrast to formation of quasicrystals through solidification that was usually found in many alloys. Maximizing local packing density of atoms associated with segregation of Y and Zn in Mg adjacent to Mg/Zn3MgY interfaces triggered atomic rearrangement in Mg to form icosahedra coupled epitaxially with surface distorted icosahedra of Zn3MgY, which plays a critical role in the nucleation of icosahedral clusters. A local Zn: Mg: Y ratio close to 6:3:1, corresponding to a valence electron concentration of about 2.15, should have been reached to trigger the formation of quasicrystals at Mg/Zn3MgY interfaces. The solid-state icosahedral ordering in crystals opens a new window for growing quasicrystals and understanding their atomic origin mechanisms. Epitaxial growth of quasicrystals onto crystals can modify the surface/interface structures and properties of crystalline materials.

Title:
Bulk electronic structure of Zn-Mg-Y and Zn-Mg-Dy icosahedral quasicrystals
Authors:
Nayak, J; Maniraj, M; Gloskovskii, A; Krajci, M; Sebastian, S; Fisher, IR; Horn, K; Barman, SR Author Full Names: Nayak, J.; Maniraj, M.; Gloskovskii, A.; Krajci, M.; Sebastian, S.; Fisher, I. R.; Horn, K.; Barman, S. R.
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235116 JUN 11 2015
Abstract:
We use bulk sensitive hard x-ray photoelectron spectroscopy to provide unambiguous evidence for a pseudogap in the density of states around the Fermi level in icosahedral Zn-Mg-Y and Zn-Mg-Dy quasicrystals, in agreement with our density functional theory calculations. The pseudogap in these Zn-based quasicrystals is less pronounced compared to the Al-based ones such as Al-Pd-Mn and Al-Cu-Fe [J. Nayak et al., Phys. Rev. Lett. 109, 216403 ( 2012)]. This observation is in agreement with transport studies that indicate a larger charge carrier concentration in the Zn-based quasicrystals. Compared to Zn-Mg-Dy, the pseudogap is somewhat deeper in Zn-Mg-Y. The larger width of the Mg 1s and Zn 2p core-level spectra in Zn-Mg-Y is explained by different configurations of the local atomic surrounding compared to Zn-Mg-Dy.

Title:
Synthesis, structures and magnetic properties of the dimorphic Mn2CrSbO6 oxide
Authors:
Dos Santos-Garcia, AJ; Solana-Madruga, E; Ritter, C; Avila-Brande, D; Fabelo, O; Saez-Puche, R Author Full Names: Dos Santos-Garcia, Antonio J.; Solana-Madruga, Elena; Ritter, Clemens; Avila-Brande, David; Fabelo, Oscar; Saez-Puche, Regino
Source:
DALTON TRANSACTIONS, 44 (23):10665-10672; 10.1039/c4dt03849e 2015
Abstract:
The perovskite polymorph of Mn2CrSbO6 compound has been synthesized at 8 GPa and 1473 K. It crystallizes in the monoclinic P2(1)/n space group with cell parameters a = 5.2180 (2) angstrom, b = 5.3710(2) angstrom, c = 7.5874(1) angstrom and alpha = 90.36(1)degrees. Magnetic susceptibility and magnetization measurements show the simultaneous antiferromagnetic ordering of Mn2+ and Cr3+ sublattices below T-N = 55 K with a small canting. Low temperature powder neutron diffraction reveals a commensurate magnetic structure with spins confined to the ac-plane and a propagation vector kappa = [1/2 0 1/2]. The thermal treatment of this compound induces an irreversible phase transition to the ilmenite polymorph, which has been isolated at 973 K and crystallizes in R (3) over bar space group with cell parameters a = 5.2084 (4) angstrom and c = 14.4000 (11) angstrom. Magnetic susceptibility, magnetization and powder neutron diffraction data confirm the antiferromagnetic helical ordering of spins in an incommensurate magnetic structure with kappa = [00 0.46] below 60 K, and the temperature dependence of the propagation vector up to kappa = [00 0.54] at about 10 K.

Title:
Ordering effects in the crystal structure and electrochemical properties of the Gd0.5Ba0.5Mn0.5Fe0.5O3-delta perovskite
Authors:
Munoz-Gil, D; Avila-Brande, D; Urones-Garrote, E; Garcia-Martin, S Author Full Names: Munoz-Gil, Daniel; Avila-Brande, David; Urones-Garrote, Esteban; Garcia-Martin, Susana
Source:
DALTON TRANSACTIONS, 44 (23):10867-10874; 10.1039/c4dt03873h 2015
Abstract:
Layered-type ordering and oxygen vacancies ordering are revealed in GdBaMnFeO6-delta perovskite. Selected area electron diffraction and high-resolution transmission electron microscopy results indicate a modulation of the crystal structure. Ba and Gd ordering in (001)(p) layers is confirmed by high angle annular dark field scanning transmission electron microscopy and electron energy-loss spectroscopy. These techniques also revealed formation of layer-stacking defects in the crystals. Direct imaging of the oxygen sublattice is obtained by phase image reconstruction. Location of the oxygen vacancies in the (GdO)(x) layers is achieved by analysis of the intensity of the averaged phase image. Physical properties of the GdBaMnFeO6-delta perovskite, are likely to be strongly affected by its ordering effects and crystal microstructure. In this sense, layered-type GdBaMnFeO6-delta perovskite show better electrochemical properties as cathodes in SOFCs than ion disordered Gd0.5Ba0.5Mn0.5Fe0.5O3-delta perovskite.

Update: 25-Jun-2015


Title:
Symplectic approach for the plane elasticity problem of quasicrystals with point group 10 mm
Authors:
Wang, H; Li, LH; Huang, JJ; Chen, A Author Full Names: Wang, Hua; Li, Lianhe; Huang, Junjie; Chen, Alatancang
Source:
APPLIED MATHEMATICAL MODELLING, 39 (12):3306-3316; 10.1016/j.apm.2014.10.060 JUN 15 2015
Abstract:
The symplectic approach is introduced into the plane elasticity problem of quasicrystals with point group 10 mm. The basic equations of the problem are equivalently written as the Hamiltonian dual equations. It is shown that the generalized eigenvector system of the corresponding Hamiltonian operator matrix is complete in the Cauchy Principal Value (CPV) sense. The analytical solution and related numerical results of the problem are then given. (C) 2014 Elsevier Inc. All rights reserved.

Title:
Magnetic structure and multiferroic coupling in pyroxene NaFeSi2O6
Authors:
Baum, M; Komarek, AC; Holbein, S; Fernandez-Diaz, MT; Andre, G; Hiess, A; Sidis, Y; Steffens, P; Becker, P; Bohaty, L; Braden, M Author Full Names: Baum, M.; Komarek, A. C.; Holbein, S.; Fernandez-Diaz, M. T.; Andre, G.; Hiess, A.; Sidis, Y.; Steffens, P.; Becker, P.; Bohaty, L.; Braden, M.
Source:
PHYSICAL REVIEW B, 91 (21):10.1103/PhysRevB.91.214415 JUN 9 2015
Abstract:
By comprehensive neutron diffraction measurements we have studied the magnetic structure of aegirine (NaFeSi2O6) in and above its multiferroic phase. Natural aegirine exhibits two magnetic transitions into incommensurate magnetic order with a propagation vector of (k) over right arrow (inc) = (0, similar to 0.78,0). Between 9 and 6 K, we find a transverse spin-density wave with moments pointing near the c direction. Below 6 K, magnetic order becomes helical and spins rotate in the ac plane. The same irreducible representation is involved in the two successive transitions. In addition, the ferroelectric polarization (P) over right arrow appearing along the b direction cannot be described by the most common multiferroic mechanism but follows (P) over right arrow proportional to ($) over right arrow (i) x (S) over right arrow (j). Synthetic NaFeSi2O6 does not exhibit the pure incommensurate helical order but shows coexistence of this order with a commensurate magnetic structure. By applying moderate pressure to natural aegirine, we find that the incommensurate magnetic ordering partially transforms to the commensurate one, underlining the nearly degenerate character of the two types of order in NaFeSi2O6.

Title:
Matrix product state approach to a frustrated spin chain with long-range interactions
Authors:
Li, ZH; Wang, AM Author Full Names: Li, Zhi-Hua; Wang, An-Min
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235110 JUN 8 2015
Abstract:
We make extensive simulations over a spin chain model that combines the frustrated J(1) - J(2) spin chain and the long-range nonfrustrated (-1)((r-1))r(-alpha) decay interactions through the variational matrix product state method for both finite and infinite lengths. We study both the ground-state entanglement and phase diagram. We find that it is most entangled in the rotation invariant long-range ordered antiferromagnetic phase, where the entanglement scales approximately logarithmically. We determine the development of the Majudar-Ghosh point to a disorder line from entanglement. And we approximately determine the transition from the dimerized and incommensurate phase of the J(1) - J(2) model to a decoupled phase by studying spin correlation and the dimerization order parameter. Some implications for entanglement in systems with long-range interactions are stated.

Title:
Influence of Ti doping on the incommensurate charge density wave in 1T-TaS2
Authors:
Chen, XM; Miller, AJ; Nugroho, C; de la Pena, GA; Joe, YI; Kogar, A; Brock, JD; Geck, J; MacDougall, GJ; Cooper, SL; Fradkin, E; Van Harlingen, DJ; Abbamonte, P Author Full Names: Chen, X. M.; Miller, A. J.; Nugroho, C.; de la Pena, G. A.; Joe, Y. I.; Kogar, A.; Brock, J. D.; Geck, J.; MacDougall, G. J.; Cooper, S. L.; Fradkin, E.; Van Harlingen, D. J.; Abbamonte, P.
Source:
PHYSICAL REVIEW B, 91 (24):10.1103/PhysRevB.91.245113 JUN 8 2015
Abstract:
We report temperature-dependent transport and x-ray diffraction measurements of the influence of Ti hole doping on the charge density wave (CDW) in 1T-Ta1-xTixS2. Confirming past studies, we find that even trace impurities eliminate the low-temperature commensurate (C) phase in this system. Surprisingly, the magnitude of the in-plane component of the CDW wave vector in the nearly commensurate (NC) phase does not change significantly with Ti concentration, as might be expected from a changing Fermi surface volume. Instead, the angle of the CDWin the basal plane rotates, from 11.9 degrees at x = 0 to 16.4 degrees at x = 0.12. Ti substitution also leads to an extended region of coexistence between incommensurate (IC) and NC phases, indicating heterogeneous nucleation near the transition. Finally, we explain a resistive anomaly originally observed by Di Salvo [F. J. Di Salvo et al., Phys. Rev. B 12, 2220 (1975)] as arising from pinning of the CDW on the crystal lattice. Our study highlights the importance of commensuration effects in the NC phase, particularly at x similar to 0.08.

Title:
Dispersionless Spin Waves and Underlying Field-Induced Magnetic Order in Gadolinium Gallium Garnet
Authors:
d'Ambrumenil, N; Petrenko, OA; Mutka, H; Deen, PP Author Full Names: d'Ambrumenil, N.; Petrenko, O. A.; Mutka, H.; Deen, P. P.
Source:
PHYSICAL REVIEW LETTERS, 114 (22):10.1103/PhysRevLett.114.227203 JUN 2 2015
Abstract:
We report the results of neutron diffraction and inelastic neutron scattering on a powder sample of Gd3Ga5O12 at high magnetic fields. Analysis of the diffraction data shows that in high fields (B greater than or similar to 1.8 T) the spins are not fully aligned, but are canted slightly as a result of the dipolar interaction. The magnetic phase for fields less than or similar to 1.8 T is characterized by antiferromagnetic peaks at (210) and an incommensurate wave vector. The dominant contribution to inelastic scattering at large momentum transfers is from a band of almost dispersionless excitations. We show that these correspond to the spin waves localized on ten site rings, expected on the basis of nearest neighbor exchange interaction, and that the spectrum at high fields B greater than or similar to 1.8 T is well described by a spin wave theory.

Title:
Aperiodic crystals and beyond
Authors:
Grimm, U Author Full Names: Grimm, Uwe
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 258-274; 10.1107/S2052520615008409 3 JUN 2015
Abstract:
Crystals are paradigms of ordered structures. While order was once seen as synonymous with lattice periodic arrangements, the discoveries of incommensurate crystals and quasicrystals led to a more general perception of crystalline order, encompassing both periodic and aperiodic crystals. The current definition of crystals rests on their essentially point-like diffraction. Considering a number of recently investigated toy systems, with particular emphasis on non-crystalline ordered structures, the limits of the current definition are explored.

Title:
Structures beyond superspace
Authors:
Senechal, M Author Full Names: Senechal, Marjorie
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 250-251; 10.1107/S2052520615009907 3 JUN 2015

Title:
The modulated average structure of mullite
Authors:
Birkenstock, J; Petricek, V; Pedersen, B; Schneider, H; Fischer, RX Author Full Names: Birkenstock, Johannes; Petricek, Vaclav; Pedersen, Bjoern; Schneider, Hartmut; Fischer, Reinhard X.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 358-368; 10.1107/S205252061500757X 3 JUN 2015
Abstract:
Homogeneous and inclusion-free single crystals of 2: 1 mullite (Al4.8Si1.2O9.6) grown by the Czochralski technique were examined by X-ray and neutron diffraction methods. The observed diffuse scattering together with the pattern of satellite reflections confirm previously published data and are thus inherent features of the mullite structure. The ideal composition was closely met as confirmed by microprobe analysis (Al-4.82 (3) Si-1.18 (1) O-9.59 (5)) and by average structure refinements. 8 (5) to 20 (13)% of the available Si was found in the T* position of the tetrahedra triclusters. The strong tendencey for disorder in mullite may be understood from considerations of hypothetical superstructures which would have to be n-fivefold with respect to the three-dimensional average unit cell of 2: 1 mullite and n-fourfold in case of 3: 2 mullite. In any of these the possible arrangements of the vacancies and of the tetrahedral units would inevitably be unfavorable. Three directions of incommensurate modulations were determined: q(1) = [0.3137 (2) 0 1/2], q(2) = [0 0.4021 (5) 0.1834 (2)] and q(3) = [0 0.4009 (5) -0.1834 (2)]. The one-dimensional incommensurately modulated crystal structure associated with q1 was refined for the first time using the superspace approach. The modulation is dominated by harmonic occupational modulations of the atoms in the di- and the triclusters of the tetrahedral units in mullite. The modulation amplitudes are small and the harmonic character implies that the modulated structure still represents an average structure in the overall disordered arrangement of the vacancies and of the tetrahedral structural units. In other words, when projecting the local assemblies at the scale of a few tens of average mullite cells into cells determined by either one of the modulation vectors q(1), q(2) or q(3) a weak average modulation results with slightly varying average occupation factors for the tetrahedral units. As a result, the real structure of mullite is locally ordered (as previously known), but on the long-range its average is not completely disordered, the modulated structure of mullite may be denoted the true 'average structure of mullite'.

Title:
Neutron Laue and X-ray diffraction study of a new crystallographic superspace phase in n-nonadecane-urea
Authors:
Zerdane, S; Mariette, C; McIntyre, GJ; Lemee-Cailleau, MH; Rabiller, P; Guerin, L; Ameline, JC; Toudic, B Author Full Names: Zerdane, S.; Mariette, C.; McIntyre, G. J.; Lemee-Cailleau, M. -H.; Rabiller, P.; Guerin, L.; Ameline, J. C.; Toudic, B.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 293-299; 10.1107/S2052520615005442 3 JUN 2015
Abstract:
Aperiodic composite crystals present long-range order without translational symmetry. These materials may be described as the intersection in three dimensions of a crystal which is periodic in a higher-dimensional space. In such materials, symmetry breaking must be described as structural changes within these crystallographic superspaces. The increase in the number of superspace groups with the increase in the dimension of the superspace allows many more structural solutions. This is illustrated in n-nonadecane-urea, revealing a fifth higher-dimensional phase at low temperature.

Title:
One-Third Magnetization Plateau with a Preceding Novel Phase in Volborthite
Authors:
Ishikawa, H; Yoshida, M; Nawa, K; Jeong, M; Kramer, S; Horvatic, M; Berthier, C; Takigawa, M; Akaki, M; Miyake, A; Tokunaga, M; Kindo, K; Yamaura, J; Okamoto, Y; Hiroi, Z Author Full Names: Ishikawa, H.; Yoshida, M.; Nawa, K.; Jeong, M.; Kraemer, S.; Horvatic, M.; Berthier, C.; Takigawa, M.; Akaki, M.; Miyake, A.; Tokunaga, M.; Kindo, K.; Yamaura, J.; Okamoto, Y.; Hiroi, Z.
Source:
PHYSICAL REVIEW LETTERS, 114 (22):10.1103/PhysRevLett.114.227202 JUN 1 2015
Abstract:
We have synthesized high-quality single crystals of volborthite, a seemingly distorted kagome antiferromagnet, and carried out high-field magnetization measurements up to 74 T and V-51 NMR measurements up to 30 T. An extremely wide 1/3 magnetization plateau appears above 28 T and continues over 74 T at 1.4 K, which has not been observed in previous studies using polycrystalline samples. NMR spectra reveal an incommensurate order (most likely a spin-density wave order) below 22 T and a simple spin structure in the plateau phase. Moreover, a novel intermediate phase is found between 23 and 26 T, where the magnetization varies linearly with magnetic field and the NMR spectra indicate an inhomogeneous distribution of the internal magnetic field. This sequence of phases in volborthite bears a striking similarity to those of frustrated spin chains with a ferromagnetic nearest-neighbor coupling J(1) competing with an antiferromagnetic next-nearest-neighbor coupling J(2)

Title:
Pressure-induced normal-incommensurate and incommensurate-commensurate phase transitions in CrOCl
Authors:
Bykov, M; Bykova, E; Dubrovinsky, L; Hanfland, M; Liermann, HP; van Smaalen, S Author Full Names: Bykov, Maxim; Bykova, Elena; Dubrovinsky, Leonid; Hanfland, Michael; Liermann, Hanns-Peter; van Smaalen, Sander
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep09647 MAY 21 2015
Abstract:
The high-pressure behavior of layered CrOCl is shown to be governed by non-bonded interactions between chlorine atoms in relation to a rigid framework composed of Cr and O atoms. The competition between optimizing intra-and interlayer Cl-Cl distances and the general trend towards denser packing defines a novel mechanism for high-pressure phase transitions of inorganic materials. CrOCl possesses an incommensurate phase for 16-51 GPa. Single-crystal x-ray diffraction in a diamond anvil cell provides an accurate description of the evolution of the incommensurate wave with pressure. It thus demonstrates a continuous increase of the amplitude up to 30 GPa, followed by a decrease of the wavelength until a lock-in transition occurs at 51 GPa.

Title:
Magnetism in rare-earth quasicrystals: RKKY interactions and ordering
Authors:
Thiem, S; Chalker, JT Author Full Names: Thiem, Stefanie; Chalker, J. T.
Source:
EPL, 110 (1):10.1209/0295-5075/110/17002 APR 2015
Abstract:
We study magnetism in simple models for rare-earth quasicrystals, by considering Ising spins on a quasiperiodic tiling, coupled via RKKY interactions. Computing these interactions from a tight-binding model on the tiling, we find that they are frustrated and strongly dependent on the local environment. Although such features are often associated with spin glass behaviour, we show using Monte Carlo simulations that the spin system has a phase transition to a low-temperature state with long-range quasiperiodic magnetic order. Copyright (C) EPLA, 2015

Title:
Synthesis and structure of the new pentanary uranium (VI) silicate, K4CaUSi4O14, a member of a structural family related to fresnoite
Authors:
Morrison, G; Smith, MD; Tran, TT; Halasyamani, PS; Loye, HCZ Author Full Names: Morrison, Gregory; Smith, Mark D.; Tran, T. Thao; Halasyamani, P. Shiv; Loye, Hans-Conrad Zur
Source:
CRYSTENGCOMM, 17 (22):4218-4224; 10.1039/c5ce00504c 2015
Abstract:
Single crystals of K4CaUSi4O14 have been grown from a eutectic CaF2-KF flux. K4CaUSi4O14 crystallizes in a new structure which exhibits a 49-fold superstructure believed to be due to a modulation of the uranium and silicon polyhedra. We report the sub-cell of the structure which adopts the tetragonal space group P (4) over bar n2 with lattice parameters a = 9.2862(2) angstrom c = 8.3796(4) angstrom, and V = 722.60(5)angstrom(3). K4CaUSi4O14 is a member of a structural family related to the mineral fresnoite which we describe here. Finally, we report UV-vis absorbance and SHG measurements on the compound, which is non-centrosymmetric.

Title:
The symmetry of the thermoelastic properties of quasicrystals
Authors:
Sokolova, MY; Khristich, DV Author Full Names: Sokolova, M. Yu.; Khristich, D. V.
Source:
PMM JOURNAL OF APPLIED MATHEMATICS AND MECHANICS, 78 (5):524-528; 10.1016/j.jappmathmech.2015.03.012 2014
Abstract:
The thermoelastic properties of quasicrystals, possessing 5-th, 8-th, 10-th and 12-th order rotational axes, not characteristic of crystalline bodies, are considered. Using group analysis, canonical representations of the second and fourth rank tensors, characterizing the properties of quasicrystals, are constructed. The fact that orthogonal, decagonal and dodecagonal quasicrystals belong to the class of transversely isotropic materials and the isotropy of icosahedric quasicrystals and fullerenes are proved. (C) 2015 Elsevier Ltd. All rights reserved.

Update: 18-Jun-2015


Title:
Magnetostructural transitions in Mn-rich Heusler Mn-Ni-In melt-spun ribbons with enhanced magnetocaloric effect
Authors:
Li, HW; Feng, ST; Ren, J; Zhai, QJ; Fu, JX; Luo, ZP; Zheng, HX Author Full Names: Li, Hongwei; Feng, Shutong; Ren, Jian; Zhai, Qijie; Fu, Jianxun; Luo, Zhiping; Zheng, Hongxing
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 391 17-21; 10.1016/j.jmmm.2015.04.098 OCT 1 2015
Abstract:
The magnetostructural transition behavior and magnetocaloric effect of Mn-rich Heusler Mn-Ni-In melt spun ribbons have been investigated in the present study. Experimental results showed that the martensitic transition temperatures decreased by substituting small amounts of Ni with Mn in Mn49+xNi42-xIn9 (x=0,1,2). Within a temperature range from 100 K to 380 K, the Mn(49)Ni(41)ln(9) underwent a martensitic transformation from a paramagnetic L2(1)-type cubic austenite to a ferromagnetic modulated fourteen layered monoclinic (14M) martensite, followed with a ferromagnetic -> weak-magnetic transition in martensite upon cooling. While for both Mn50Ni41In9 and Mn51Ni40In9, the paramagnetic -> ferromagnetic transition in austenite occurred prior to the martensitic transformation upon cooling. Under a magnetic field change of 30 kOe, the maximum magnetic entropy changes of the Mn50Ni41In9 melt spun ribbons were found to be 5.7 J/kg K and -2.3 J/kg K in the vicinity of martensitic transformation and magnetic transition of austenite, respectively. An enhanced total effective refrigeration capacity as high as 184.2 J/kg was obtained in the Mn50Ni41In9 melt spun ribbons. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Microstructure and phase transformation of forged Mg-3.7Zn-0.3Y-0.3Gd quasicrystal alloy
Authors:
Yang, Y; Zhang, K; Ma, ML; Li, XG Author Full Names: Yang, Yang; Zhang, Kui; Ma, Minglong; Li, Xinggang
Source:
JOURNAL OF MATERIALS RESEARCH, 30 (10):1693-1700; 10.1557/jmr.2015.97 MAY 28 2015
Abstract:
An alloy with the composition of Mg-3.7Zn-0.3Y-0.3Gd (in at.%) which contains quasicrystal phase was studied by multiple means. The as-cast alloy has dendritic structure and consists of -Mg, I-phase, W-phase, and Mg-Zn precipitations. The alloy was forged one pass and annealed at 440 degrees C for 4 h, then followed by two passes of compressions. Eutectics were crushed and partially dissolved after deformation and annealing. The tensile strength increased after each forge pass. Submicron scale particles precipitated all around the grains during the deformations, and the amount of precipitations was proportional to the amount of deformations. These precipitated particles were observed by high resolution transmission electron microscopy (TEM). The existence of rhomboid W'-phase with face center cubic (FCC) structure and globular I-phase was confirmed. A quasi-periodicity lamellar phase combined with I-phase was founded, which was considered to be the transient phase between I-phase and I-phase.

Title:
Effect of substrate and orientation on charge ordering behaviors in epitaxial Pr0.5Ca0.35Sr0.15MnO3 films
Authors:
Yang, HW; Wang, C; Cai, RS; Hu, FX; Wang, YQ; Sun, JR Author Full Names: Yang, H. W.; Wang, C.; Cai, R. S.; Hu, F. X.; Wang, Y. Q.; Sun, J. R.
Source:
JOURNAL OF APPLIED PHYSICS, 117 (17):10.1063/1.4913731 MAY 7 2015
Abstract:
The charge ordering (CO) behaviors of Pr0.5Ca0.35Sr0.15MnO3 films grown on STO(100), STO(110) and LAO(100) are systematically investigated by transport measurements and transmission electron microscopy (TEM) examinations. From the transport measurements, the CO transition temperatures of all the three films are much higher than those of the bulk materials, showing that the film strain could enhance the CO transition. From TEM observations, many superlattice spots appear in the electron diffraction patterns taken from the films, indicating the appearance of the CO modulation structures at room temperature. The modulation vectors are determined to be (1/2, 0, 0) for STO (100), (1/2, 1/2, 1/2) for STO (110), and both (0, 1/2, 0) and (1/2, 1/2, 0) for LAO (100). It is shown that both the substrate orientation and the film strain have a great effect on the CO modulation structures. The CO state is much easier to appear in the compressive strain direction which is due to the Mn-O-Mn angle tilting. (C) 2015 AIP Publishing LLC.

Title:
Spin reorientation in multiferroic spinel Co0.5Fe0.5Cr2O4 with Mossbauer spectroscopy
Authors:
Myoung, BR; Kim, CS Author Full Names: Myoung, Bo Ra; Kim, Chul Sung
Source:
JOURNAL OF APPLIED PHYSICS, 117 (17):10.1063/1.4918968 MAY 7 2015
Abstract:
We studied the magnetic properties of multiferroic spinel Co0.5Fe0.5Cr2O4, especially focusing on the spin-ordering, spin-reorientation, and charge re-distribution effects. From the Rietveld refinement analysis, the crystal structure was identified to be a normal cubic spinel of Fd-3m. Based on the temperature-dependent measurements of the magnetization and magnetic hyperfine field (H-hf), Curie temperature (T-C) of Co0.5Fe0.5Cr2O4 was determined to be around 86K where H-hf (sic) 0. From the change of slope in the M-T curve, the conical-spiral magnetic ordering temperature was determined to be 20 K, which coincides with H-hf measurement. Also, we have observed the decrease in the slope of the electric quadrupole splitting (Delta E-Q) curve above 20K, suggesting that the change in Delta E-Q around T-S is originated from charge redistribution due to the spin-relocation associated with the distortion of each tetrahedral site around Fe2+ ion above T-S. This indicates that Co0.5Fe0.5Cr2O4 has the noncollinear conical-spiral spin ordering with incommensurate spin structure below T-S, while above T-S, it has ferrimagnetic spin ordering with commensuration in the collinear state. In addition, the Jahn-teller distortion temperature is measured to be around 155K, since both Delta E-Q and Delta(1) of T-5(2g) band decrease rapidly with increasing temperature and disappear around 155 K. (C) 2015 AIP Publishing LLC.

Title:
Zone-Folded Phonons and the Commensurate-Incommensurate Charge-Density-Wave Transition in 1T-TaSe2 Thin Films
Authors:
Samnakay, R; Wickramaratne, D; Pope, TR; Lake, RK; Salguero, TT; Balandin, AA Author Full Names: Samnakay, R.; Wickramaratne, D.; Pope, T. R.; Lake, R. K.; Salguero, T. T.; Balandin, A. A.
Source:
NANO LETTERS, 15 (5):2965-2973; 10.1021/nl504811s MAY 2015
Abstract:
Bulk 1T-TaSe2 exhibits unusually high charge density wave (CDW) transition temperatures of 600 and 473 K below which the material exists in the incommensurate (I-CDW) and the commensurate (C-CDW) charge-density-wave phases, respectively. The (13)(1/2) x (13)(1/2), C-CDW reconstruction of the lattice coincides with new Raman peaks resulting from zone-folding of phonon modes from middle regions of the original Brillouin zone back to Gamma. The C-CDW transition temperatures as a function of film thickness are determined from the evolution of these new Raman peaks, and they are found to decrease from 473 to 413 K as the film thicknesses decrease from 150 to 35 nm. A comparison of the Raman data with ab initio calculations of both the normal and C-CDW phases gives a consistent picture of the zone-folding of the phonon modes following lattice reconstruction, The Raman peak at similar to 154 cm(-1) originates from the zone-folded phonons in the C-CDW phase. In the I-CDW phase, the loss of translational symmetry coincides with a strong suppression and broadening of the Raman peaks. The observed,change: in the C-CDW transition temperature is consistent with total energy calculations of bulk and monolayer 1T-TaSe2.

Title:
Temperature-Pressure Phase Diagram for Rb2ZnCl4 Crystals
Authors:
Kurlyak, VY; Stadnyk, VY; Stakhura, V Author Full Names: Kurlyak, V. Yu.; Stadnyk, V. Yo.; Stakhura, V.
Source:
JOURNAL OF APPLIED SPECTROSCOPY, 82 (2):228-233; 10.1007/s10812-015-0090-3 MAY 2015
Abstract:
We have studied the effect of uniaxial stress along the principal crystallophysical directions on the temperature variations in the birefringence Delta n (i) and the refractive indices ni for Rb2ZnCl4 crystals in the region of phase transitions from the paraelectric phase to the incommensurate phase and then to the commensurate ferroelectric phase. We have established that Delta n (i) and n (i) are rather sensitive to the action of uniaxial stresses. We have observed a significant pressure-induced shift of the paraelectric - incommensurate - ferroelectric phase transition points in different temperature regions, depending on the direction of the uniaxial compression.

Update: 11-Jun-2015


Title:
Effect of Li on electrochemical properties of Ti1.4V0.6Ni quasicrystal alloy produced by rapid quenching
Authors:
Ouyang, ZT; Liu, K; Shang, JM; Xing, C; Liu, WQ; Wang, LM Author Full Names: Ouyang, Zhongtao; Liu, Kun; Shang, Jinming; Xing, Cheng; Liu, Wanqiang; Wang, Limin
Source:
INTERMETALLICS, 62 50-55; 10.1016/j.intermet.2015.03.010 JUL 2015
Abstract:
The effect of Li on the electrochemical performance of electrodes consisting of Ti1.4V0.6Ni quasicrystal was investigated at room temperature in three-electrode cell set-up. The quasicrystal sample was initially synthesized by arc melting, followed by melt-spinning, and then infiltrated with Li atoms by electroosmosis. According to X-ray diffraction, all ribbon samples were determined to be icosahedral quasicrystal phase (I-phase), V-based solid solution phase with BCC structure and face centered cubic (FCC) phase with Ti2Ni-type structure. After infiltrating some Li atoms into the Ti1.4V0.6Ni quasicrystal lattice under the condition of an electroosmosis current of 0.6 A, we could observe the appearance of Li diffraction peaks. Importantly, the slight shift to the left observed in the diffraction peaks indicated that lattice expansion was caused by the infiltration of Li. The discharge capacity of Ti1.4V0.6Ni-Li material was higher than that of Ti1.4V0.6Ni.The maximum discharge capacity of 307.1 mAh/g was recorded for Ti1.4V0.6Ni Li at a current density of 30 mAh/g. Both high-rate dischargeability and cycling stability were enhanced as a result of infiltrating Li. The lithium could get into the lattice, which resulted in the formation of microspores on surface of alloy, thus improving electrochemical activity of the alloy electrode. At the same time, the electrochemical reaction kinetics of alloy electrodes was also researched. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Synthesis and Characterization of Bulk Al-Cu-Fe Based Quasicrystals and Composites by Spray Forming
Authors:
Mukhopadhyay, NK; Uhlenwinkel, V; Srivastava, VC Author Full Names: Mukhopadhyay, N. K.; Uhlenwinkel, V.; Srivastava, V. C.
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 24 (6):2172-2178; SI 10.1007/s11665-015-1442-0 JUN 2015
Abstract:
The bulk quasicrystalline (QC) materials and their composites have attracted considerable interest due to their promising mechanical properties. In the present investigation, spray forming has been used to synthesize bulk single-phase icosahedral quasicrystals and composites in Al62.5Cu25Fe12.5 system as well as in quaternary system containing 10% Sn. The elemental materials were induction melted under nitrogen cover and a billet of 250 mm in diameter and 350 mm in height was spray formed. The phase constitution of the spray-formed materials showed a bulk single-phase icosahedral quasicrystal as a major phase along with other crystalline phases. A large number of annealing twins were observed in the microstructure in ternary AlCuFe alloys. It is interesting to note that due to addition of Sn, the volume fraction of beta-Al(CuFe) phase was found to increase and annealing twins were almost absent. The hardness of the single-phase AlCuFe alloy and Sn-containing composites was found to be 8.6 and 6.0 GPa, respectively, at a load of 300 g. In general, the hardness decreases with heat treatment at high temperatures. However, in case of Sn-ontaining alloy, hardness increases with low-temperature heat treatment. Long and hair-like cracks (Palmqvist type) are observed to form from the corner of the indentations of the ternary alloys, whereas in Sn-containing composites, the cracks are not sharp and long suggesting the enhancement of fracture toughness in the composites. Attempts have been made to understand the effect of Sn on the evolution of icosahedral phase, other crystalline phases and their composite effects on the mechanical properties.

Title:
Superconductivity and the electronic phase diagram of LaPt2-xGe2+x
Authors:
Maeda, S; Matano, K; Yatagai, R; Oguchi, T; Zheng, GQ Author Full Names: Maeda, S.; Matano, K.; Yatagai, R.; Oguchi, T.; Zheng, Guo-qing
Source:
PHYSICAL REVIEW B, 91 (17):10.1103/PhysRevB.91.174516 MAY 22 2015
Abstract:
In many cases, unconventional superconductivity are realized by suppressing another order parameter, such as charge density wave (CDW) or spin density wave (SDW). This suggests that the fluctuations of these order parameters play an important role in producing superconductivity. LaPt2Ge2 undergoes a tetragonal-to-monoclinic structural phase transition (SPT) at T-s = 394 K, accompanying a double period modulation in the a-axis direction, and superconducts at T-c = 0.41 K. We performed band calculations and found 2D (two dimensional)-like Fermi surfaces with partial nesting. A reduction in the density of states in the monoclinic phase was found in the calculation and confirmed by Pt-195-NMR. We suggest a CDW as a possible cause for the SPT. By changing the stoichiometry between Pt and Ge, we succeeded in suppressing T-s and increasing T-c in LaPt2-xGe2+x. Comparison of La-139- and Pt-195-NMR data reveals moderate fluctuations associated with SPT. From La-139-NQR measurements at zero field, we found that an isotropic superconducting gap is realized in LaPt2-xGe2+x (x = 0.20). We discuss the relationship between superconductivity and the SPT order/fluctuations.

Title:
Oxygen octahedra distortion induced structural and magnetic phase transitions in Bi1-xCaxFe1-xMnxO3 ceramics
Authors:
Kumar, P; Shankhwar, N; Srinivasan, A; Kar, M Author Full Names: Kumar, Pawan; Shankhwar, Nisha; Srinivasan, A.; Kar, Manoranjan
Source:
JOURNAL OF APPLIED PHYSICS, 117 (19):10.1063/1.4921433 MAY 21 2015
Abstract:
The co-doping of Ca and Mn in respective Bi and Fe-sites of BiFeO3 lattice leads to structural transition from rhombohedral (R3c space group) to orthorhombic (Pbnm space group) crystal symmetry. The tilt angle for anti-phase rotation of the oxygen octahedra of BiFeO3 at room temperature is observed to be similar to 13.8 degrees. It decreases with the increase in the co-doping percentage which suggests the composition-driven structural phase transition. The remnant magnetization for sample with 15% of co-doping becomes about 16 times that of BiFeO3. It may be attributed to the suppression of cycloid spin structure and uncompensated spins at the surface of nanocrystallites. Further increase in co-doping percentage results in the sharp reduction of remnant magnetization due to the dominant contribution from the collinear antiferromagnetic ordering in the Pbnm space group. The Arrott plot analysis clearly indicates the composition-driven crossover from the antiferromagnetic to weak ferromagnetic ordering and vice versa. Electron spin resonance results provide the evidence for the composition-driven phase transitions from an incommensurate spin cycloidal modulated state to one with nearly homogeneous spin order. The band gap (2.17 eV) of BiFeO3 measured using UV-Vis spectra was supported by the resonance Raman spectra. (C) 2015 AIP Publishing LLC.

Title:
Coexistence of Charge-Density-Wave and Pair-Density-Wave Orders in Underdoped Cuprates
Authors:
Wang, YX; Agterberg, DF; Chubukov, A Author Full Names: Wang, Yuxuan; Agterberg, Daniel F.; Chubukov, Andrey
Source:
PHYSICAL REVIEW LETTERS, 114 (19):10.1103/PhysRevLett.114.197001 MAY 15 2015
Abstract:
We analyze incommensurate charge-density-wave (CDW) and pair-density-wave (PDW) orders with transferred momenta (+/- Q, 0)/(0, +/- Q) in underdoped cuprates within the spin-fermion model. Both orders appear due to an exchange of spin fluctuations before magnetic order develops. We argue that the ordered state with the lowest energy has nonzero CDW and PDW components with the same momentum. Such a state breaks C-4 lattice rotational symmetry, time-reversal symmetry, and mirror symmetries. We argue that the feedback from CDW/PDW order on fermionic dispersion is consistent with ARPES data. We discuss the interplay between the CDW/PDWorder and d(x2-y2) superconductivity and make specific predictions for experiments.

Title:
Incommensurate Systems as Model Compounds for Disorder Revealing Low-Temperature Glasslike Behavior
Authors:
Remenyi, G; Sahling, S; Biljakovic, K; Staresinic, D; Lasjaunias, JC; Lorenzo, JE; Monceau, P; Cano, A Author Full Names: Remenyi, G.; Sahling, S.; Biljakovic, K.; Staresinic, D.; Lasjaunias, J. -C.; Lorenzo, J. E.; Monceau, P.; Cano, A.
Source:
PHYSICAL REVIEW LETTERS, 114 (19):10.1103/PhysRevLett.114.195502 MAY 14 2015
Abstract:
We show that the specific heat of incommensurately modulated crystals with broken translational periodicity presents similar features at low temperatures to those of amorphous and glass materials. Here we demonstrate that the excess to the constant C-p(T)/T-3 law (or Debye limit) is made up of an upturn below 1 K and of a broad bump at T approximate to 10 K that directly originates from the gapped phase and amplitude modes of the incommensurate structure. We argue that the low-energy dynamics of incommensurate systems constitute a plausible simplification of the landscape of interactions present in glasses, giving rise to their low-temperature anomalies.

Title:
A Crystal-Chemical Framework for Relaxor versus Normal Ferroelectric Behavior in Tetragonal Tungsten Bronzes
Authors:
Zhu, X; Fu, M; Stennett, MC; Vilarinho, PM; Levin, I; Randall, CA; Gardner, J; Morrison, FD; Reaney, IM Author Full Names: Zhu, X.; Fu, M.; Stennett, M. C.; Vilarinho, P. M.; Levin, I.; Randall, C. A.; Gardner, J.; Morrison, F. D.; Reaney, I. M.
Source:
CHEMISTRY OF MATERIALS, 27 (9):3250-3261; 10.1021/acs.chemmater.5b00072 MAY 12 2015
Abstract:
Tetragonal tungsten bronzes (TTBs), an important class of oxides known to exhibit ferroelectricity, undergo complex distortions, including rotations of,oxygen octahedra, which give rise to either incommensurately or commensurately modulated superstructures. Many TTBs display broad, frequency-dependent relaxor dieletric behavior rather than sharper frequency-independent normal ferroelectric anomalies, but the exact reasons that favor a particular type of dielectric response for a given composition remain unclear. In this contribution the influence of incommensurate/commensurate dispiacive modulations on the onset of relaxor/ferroelectric behavior in TTBs is assessed in the context of basic crystal-chemical factors, such as positional disorder, ionic radii and polarizabilities, and point defects. We present a predictive crystal-chemical model that rationalizes composition structure properties relations for a broad range of TTB systems.

Title:
Structural transformation in quasicrystal-forming Al-Cu-Fe alloys
Authors:
Boularas, H; Debili, MY; Alleg, S Author Full Names: Boularas, H.; Debili, M. Y.; Alleg, S.
Source:
METALLURGICAL RESEARCH & TECHNOLOGY, 112 (2):10.1051/metal/2015008 2015
Abstract:
Three Al-Cu-Fe alloys with various iron contents (6 at.%, 12 at.% and 15 at.%), were synthesized by fusion under high-frequency magnetic induction and characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry(DSC). The microstructure evolution was carried out both in the as-quenched state as well after heat treatment at 500 degrees C in relation to iron composition. Particular attention was been paid to the alloy containing 15%, and we were been able to determine by DSC that a massive transformation from crystal (beta) to quasicrystal i-psi (Al6Fe2Cu) occurs for this composition.

Title:
Formation of an Icosahedral Quasicrystal and Its Approximant in Au-Al-Sc System
Authors:
So, YG; Kimoto, K; Edagawa, K Author Full Names: So, Yeong-Gi; Kimoto, Koji; Edagawa, Keiichi
Source:
MATERIALS TRANSACTIONS, 56 (4):495-499; 10.2320/matertrans.M2014421 2015
Abstract:
The formation of the icosahedral (i-) and 1/1-approximant (1/1-) phases in the Au-Al-Sc system has been investigated. A primitive-type i-phase was found to form in an Au45Al40Sc15 alloy. This i-phase was shown to be thermodynamically stable at 973 K. A stable 1/1-phase was found to form at 1173K for compositions of Au44+xAl41-xSc15 (x = 0, 1, 2, 3). High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed that the 1/1-phase consists of Tsai-type icosahedral clusters. Similar local structures were observed in the HAADF-STEM image for the i-phase, indicating that the i-phase consists of Tsai-type clusters identical to the clusters in the 1/1-phase. The composition of the Au-Al-Sc i-phase is consistent with the formation conditions, including those in the valence electrons per atom ratio and in the atomic size factor, which has been shown previously for other Tsai-type i-phases. This fact demonstrates the importance of these conditions for stabilization of Tsai-type i-phases.

Update: 3-Jun-2015


Title:
The study of Al-3(Mn, Pd) crystal and Al-Mn-Pd decagonal quasicrystal by spherical aberration-corrected scanning transmission microscopy and atomic-resolution energy dispersive X-ray spectroscopy
Authors:
Yasuhara, A; Hiraga, K Author Full Names: Yasuhara, Akira; Hiraga, Kenji
Source:
PHILOSOPHICAL MAGAZINE, 95 (14):1511-1523; 10.1080/14786435.2015.1039623 MAY 13 2015
Abstract:
An Al3Mn-type Al-3(Mn, Pd) crystal and an Al-Mn-Pd decagonal quasicrystal (DQC) in an Al70Mn20Pd10 alloy are studied using a spherical aberration (Cs)-corrected scanning transmission electron microscope (STEM) with high-angle annular dark-field (HAADF) and annular bright-field (ABF) techniques, together with atomic-resolution energy dispersive X-ray spectroscopy (EDS). Mn and Pd atomic positions in the Al-3(Mn, Pd) structure projected along the b-axis (pseudo-tenfold rotational axis) are represented by separate bright dots in observed HAADF-STEM images. Besides, Al as well as Mn and Pd atomic positions are represented as dark dots in ABF-STEM images. Most Mn and Pd atomic positions in the Al-3(Mn, Pd) structure can be observed on atomic-resolution EDS maps. On the basis of the good correlation between the STEM images and the EDS maps, and also considering the structure of the Al-3(Mn, Pd) crystal, which was determined by X-ray diffraction using a single crystal, observed HAADF and ABF-STEM images of the Al-Mn-Pd DQC have been interpreted. Pd and Mn atomic positions in the Al-Mn-Pd DQC can be detected on the observed EDS maps. It can be seen that Pd is enriched around the centre of the columnar clusters, having a decagonal section with 2nm in diameter. It can therefore be concluded that Pd plays an important role in the stabilization of the decagonal clusters, which form the Al-Mn-Pd DQC structure.

Title:
The structure of an Al-Rh-Cu decagonal quasicrystal studied by spherical aberration (Cs)-corrected scanning transmission electron microscopy
Authors:
Hiraga, K; Yasuhara, A; Yamamoto, K; Yubuta, K Author Full Names: Hiraga, Kenji; Yasuhara, Akira; Yamamoto, Kazuki; Yubuta, Kunio
Source:
PHILOSOPHICAL MAGAZINE, 95 (14):1524-1535; 10.1080/14786435.2015.1039624 MAY 13 2015
Abstract:
The structure of an Al-Rh-Cu decagonal quasicrystal formed with two quasiperiodic planes along the periodic axis in an Al63Rh18.5Cu18.5 alloy has been studied by spherical aberration (Cs)-corrected high-angle annular detector dark-field (HAADF)- and annular bright-field (ABF)-scanning transmission electron microscopy (STEM). Heavy atoms of Rh and mixed sites (MSs) of Al and Cu atoms projected along the periodic axis can be clearly represented as separate bright dots in observed HAADF-STEM images, and consequently arrangements of Rh atoms and MSs on the two quasiperiodic planes can be directly determined from those of bright dots in the observed HAADF-STEM image. The Rh atoms are arranged in pentagonal tiling formed with pentagonal and star-shaped pentagonal tiles with an edge-length of 0.76nm, and also MSs with a pentagonal arrangement are located in the pentagonal tiles with definite orientations. The star-shaped pentagonal tiles in the pentagonal tiling are arranged in tau(2)(tau: golden ratio)-inflated pentagonal tiling with a bond-length of 2nm. From arrangements of Rh atoms placed in pentagonal tilings with a bond-length of 2nm, which are generated by the projection of a five-dimensional hyper-cubic lattice, occupation domains in the perpendicular space are derived. Al atoms as well as Rh atoms and MSs are represented as dark dots in an observed ABF-STEM image, and arrangements of Al atoms in well-symmetric regions are discussed.

Update: 28-May-2015


Title:
Refinement of the icosahedral quasicrystalline phase and the grain size of Mg-9.25Zn-1.66Y alloy by high-ratio differential speed rolling
Authors:
Kwak, TY; Lim, HK; Han, SH; Kim, WJ Author Full Names: Kwak, T. Y.; Lim, H. K.; Han, S. H.; Kim, W. J.
Source:
SCRIPTA MATERIALIA, 103 49-52; 10.1016/j.scriptamat.2015.03.004 JUL 1 2015
Abstract:
Differential speed rolling was applied to a Mg-9.25Zn-1.66Y alloy with an icosahedral quasicrystalline (I) phase to refine its cast microstructure by severe plastic deformation. The grain size was reduced to gm. A higher speed ratio, which produces a higher shear strain, was more effective in breaking up the eutectic I phase structure and dispersing the broken particles into the matrix. The processed alloy exhibited a high yield stress of 337 MPa and a good elongation of 10.7%. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Evidence for magneto-electric and spin-lattice coupling in PbFe0.5Nb0.5O3 through structural and magneto-electric studies
Authors:
Matteppanavar, S; Rayaprol, S; Singh, K; Reddy, VR; Angadi, B Author Full Names: Matteppanavar, Shidaling; Rayaprol, Sudhindra; Singh, Kiran; Reddy, V. Raghavendra; Angadi, Basavaraj
Source:
JOURNAL OF MATERIALS SCIENCE, 50 (14):4980-4993; 10.1007/s10853-015-9046-5 JUL 2015
Abstract:
Neutron diffraction (ND) studies were carried out on polycrystalline single-phase multiferroic Pb(Fe0.5Nb0.5)O-3 (PFN) in the temperature range of 290-2 K to understand the structural and magnetic properties as a function of temperature. ND data were refined using the Rietveld refinement method for both crystallographic and magnetic structures. The structure at room temperature was found to be monoclinic, in Cm space group. No structural transition was observed till 2 K. At low temperatures (i.e., from T < T (N); T (N) = 155 K), an additional peak appears at scattering vector, Q = 1.35 (-1), indicating the onset of antiferromagnetic ordering. The magnetic structure was found to be commensurate with the crystallographic structure and could be refined using the propagation vector, k = [0.125, 0.5, and 0.5]. Magnetization, ferroelectric P-E loops, and dielectric measurements on PFN reveal a strong anomaly at the antiferromagnetic transition temperature (T (N)) indicating the magneto-electric coupling. The refined temperature-dependent structural parameters such as unit cell volume and monoclinic distortion angle (beta) reveal pronounced anomalies at the magnetic ordering temperature (T (N)), which indicates strong spin-lattice coupling. An anomaly in lattice volume was observed with a small negative thermal expansion below and a large thermal expansion above the T (N), respectively. It shows the occurrence of isostructural phase transition accompanying the magnetic ordering below T (N) 155 K, leading to significant change in ionic polarization, octahedral tilt angle, and lattice strain around T (N). We have used refined atomic positional coordinates from the nuclear and magnetic structures, to obtain ionic polarization. These detailed studies confirm the magneto-electric and spin-lattice coupling in PFN across T-N.

Title:
Pressure-induced successive magnetic and structural phase transitions in Fe1.087Te
Authors:
Jorgensen, JE; Hansen, TC Author Full Names: Jorgensen, Jens-Erik; Hansen, Thomas Christian
Source:
EUROPEAN PHYSICAL JOURNAL B, 88 (5):10.1140/epjb/e2015-50713-6 MAY 11 2015
Abstract:
The crystal and magnetic structures of Fe1.087Te have been studied by neutron powder diffraction in the temperature range from 5 to 170 K at pressures in the range from approximate to 0.8 to approximate to 7 GPa. The p, T-phase diagram contains three phases with monoclinic, orthorhombic and tetragonal symmetry. The monoclinic and orthorhombic phases are both antiferromagnetically ordered and stable at temperatures below approximate to 69 K while the non-magnetic tetragonal phase is stable above this temperature. The monoclinic phase is stable for p less than or similar to 1.2 GPa while the orthorhombic phase is stable for 1.2 less than or similar to p less than or similar to 1.7 GPa and the tetragonal phase becomes stable at higher pressures at the lowest measured temperatures. The magnetic ordering is antiferromagnetic bicollinear and commensurate in the monoclinic phase but incommensurate and pressure dependent in the orthorhombic phase. The pressure-induced collapse of magnetic order at approximate to 1.7 GPa is accompanied by abrupt changes in volume and compressibility, suggestive of a spin state change of the Fe2+ ions in the FeTe layers.

Title:
Amount of valence charge of Al- and Zn-based quasicrystals and related approximant crystals evaluated by chemical shift observations and Bader analysis
Authors:
Koshiya, S; Terauchi, M Author Full Names: Koshiya, S.; Terauchi, M.
Source:
PHILOSOPHICAL MAGAZINE, 95 (13):1462-1470; 10.1080/14786435.2015.1033486 MAY 3 2015
Abstract:
The amounts of decreased charge at Al sites of Al-based (Al-Pd-Cr-Fe, Al-Si-Mn, and Al-Re-Si) and at Zn sites of Zn-based (Zn-Mg-Zr) quasicrystals and approximant crystals were estimated. The evaluation was done by comparisons between chemical shifts experimentally observed by soft-X-ray emission spectroscopy and the amount of valence charge obtained by Bader analysis for first principle calculations of reference materials (Al, alpha-Al2O3, Zn, and ZnO). Decreased charges at Al sites of Al-based quasicrystals and at Zn sites of Zn-based quasicrystals were evaluated to be 1.0-2.5 e(-)/atom and 1.1-1.2 e(-)/atom, respectively. A covalent bonding nature alloy of Al-Re-Si also showed a decrease in valence charge at Al sites.

Title:
Infinitely Adaptive Transition Metal Oxychalcogenides: The Modulated Structures of Ce2O2MnSe2 and (Ce0.78La0.22)(2)O2MnSe2
Authors:
Wang, CH; Ainsworth, CM; Gui, DY; McCabe, EE; Tucker, MG; Evans, IR; Evans, JSO Author Full Names: Wang, Chun-Hai; Ainsworth, Chris M.; Gui, Dong-Yun; McCabe, Emma E.; Tucker, Matthew G.; Evans, Ivana R.; Evans, John S. O.
Source:
CHEMISTRY OF MATERIALS, 27 (8):3121-3134; 10.1021/acs.chemmaer.5b00666 APR 28 2015
Abstract:
This article reports the syntheses, structures, and physical properties of the oxychalcogenides (Ce1-xLax)(2)O2MnSe2 with x = 0-0.7. These materials have a layered structure related to that of the LaOFeAs-derived superconductors but with the transition metal sites 50% occupied. Ce2O2MnSe2 contains alternating layers of composition: [Ce2O2](2+) and [MnSe2](2-). The size mismatch between the layers leads to an incommensurate structure with a modulation vector of q = ae+ Ob*+0.5c* with a = 0.158(1), which can be described with a (3 + 1)D superspace structural model in superspace group Cmme(a,0,(1) / OM [67.12]. There is a strong modulation of Mn site occupancies, leading to a mixture of corner- and edge-sharing MnSe4/2 tetrahedra in the [MnSe2](2-) layers. The modulation vector can be controlled by partial substitution of Ce3+ for larger La3+, and a simple commensurate (Ce0.78La0.22)(2)O2MnSe2 with a = 1/6. The materials respond to the change in relative size of the oxide and chalcogenide blocks by varying the ratio of corner- to edge-sharing tetrahedra. The superspace model lets us unify the structural description of the five different ordering patterns reported to date for different Ln(2)O(2)MSe(2) (Ln = lanthanide) materials. Mn moments in Ce2O2MnSe2 and (Ce0.78La0.22)(2)O2MnSe2 order antiferromagnetically below TN = 150 K, and Ce moments order below similar to 70 K. The magnetic structures of both materials have been determined using neutron diffraction. Both materials are semiconductors; Ce2O2MnSe2 has a = 9 x 10(-6) Omega(-1) cm(-1) at room temperature and an activation energy for charge carrier mobility from RT to 170 degrees C of -,0.4 eV.

Title:
Effect of Pd Substitution on Phase Formation and Stability in Ti-Zr-Ni Quasicrystalline Alloys
Authors:
Huang, HG; Chen, L; Xu, QY Author Full Names: Huang Huogen; Chen Liang; Xu Qinying
Source:
RARE METAL MATERIALS AND ENGINEERING, 44 (4):821-825; APR 2015
Abstract:
Pd can be used as an adding element to improve hydrogenation properties of Ti-Zr-Ni quasicrystalline alloys. However, the action mechanism of Pd addition is unclear yet. The effects of Pd substituting Ti and Zr in Ti45Zr38Ni17 and Ti40Zr40Ni20 alloys were studied by means of XRD, TEM and DSC examination. The results show that icosahedral quasicrystal can be formed purely through 4%similar to 6% Pd substitution for Ti or 4% for Zr in the Ti45Zr38Ni17 alloy, as well as 3%similar to 4% for Ti or possibly below 3% for Zr in the Ti40Zr40Ni20 alloy. This indicates a higher substitution limit for Ti in order for the heritance of the quasicrystal phase. Two derived quasicrystals Ti39Zr38Ni17Pd6 and Ti36Zr40Ni20Pd4 can be transformed into crystalline phases after annealing at 400 degrees C, demonstrating their lower thermo-stabilities in comparison to such Ti-Zr-Ni alloys being stable at about 700 degrees C. Both the replacement tendency and the decrease of the thermostability of quasicrystal phase might be ascribed to appropriate atomic size of Pd.

Title:
X-ray induced lock-in transition of cycloidal magnetic order in a multiferroic perovskite manganite
Authors:
Yamasaki, Y; Nakao, H; Murakami, Y; Nakajima, T; Sampietro, AL; Ohsumi, H; Takata, M; Arima, T; Tokura, Y Author Full Names: Yamasaki, Y.; Nakao, H.; Murakami, Y.; Nakajima, T.; Sampietro, A. Lafuente; Ohsumi, H.; Takata, M.; Arima, T.; Tokura, Y.
Source:
PHYSICAL REVIEW B, 91 (10):10.1103/PhysRevB.91.100403 MAR 24 2015
Abstract:
We report the x-ray photoexcitation effects on cycloidal magnetic order in a multiferroic perovskite-type manganite Gd0.5Tb0.5MnO3. The material exhibits a competition between the P (electric polarization)parallel to a ferroelectric state with the commensurate (C) ab-plane cycloidal and the P parallel to c ferroelectric state with the incommensurate (IC) bc-plane cycloidal spin structure. The phase transition between these two phases can be induced by an application of a magnetic field. We found that the x-ray irradiation can induce the bidirectional and persistent phase transition between IC and C phases. The nonresonant x-ray magnetic diffraction revealed that both the initial and the x-ray induced phases have the bc-plane cycloidal magnetic structure, whereas the magnetic wave number varies between IC and C. The x-ray induced bc-plane cycloidal C phase is thus the hidden multiferroic phase in the Gd1-xTbxMnO3 system, which does not show up with the application of any static field.

Update: 20-May-2015


Title:
High-resolution Brillouin scattering studies of phase transitions in Ca2MgSi2O7 and Ca2ZnSi2O7 silicates
Authors:
Maczka, M; Hanuza, J; Kaminskii, A; Kojima, S Author Full Names: Maczka, Miroslaw; Hanuza, Jerzy; Kaminskii, Alexander; Kojima, Seiji
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 638 34-37; 10.1016/j.jallcom.2015.03.055 JUL 25 2015
Abstract:
Temperature-dependent Micro-Brillouin scattering studies of Ca2MgSi2O7 and Ca2ZnSi2O7 single crystals were performed. Step-like decrease of Brillouin shifts and strong broadening of Brillouin bands corresponding to the c(33) elastic constant were observed at 351 K for Ca2MgSi2O7 and 407 K for Ca2ZnSi2O7. This behavior was attributed to coupling of strain to the square of the order parameter due to structural transitions into incommensurate phases. Analysis of the observed acoustic anomalies showed critical slowing down behavior of the relaxation time