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Various thermodynamic properties of MgO were studied using both ab initio phonon theory and the mean-field potential (MFP) approach. They include thermal pressure, thermal expansion, the 300 K equation of state, and the shock Hugoniot. It is found that the results of ab initio phonon theory and the MFP approach agree with each other, except that ab initio phonon theory gave a poor description of the thermal pressure when temperature became relatively high. [ABSTRACT FROM AUTHOR]

The level of electronic correlation has been one of the key questions in understanding the nature of superconductivity. Among the iron-based superconductors, the iron chalcogenide family exhibits the strongest electron correlations. To gauge the correlation strength, we performed a systematic angle-resolved photoemission spectroscopy study on the iron chalcogenide series Fe1+ySexTe1-x (0

Three-dimensional (3D) topological Weyl semimetals (TWSs) represent a state of quantum matter with unusual electronic structures that resemble both a '3D graphene' and a topological insulator. Their electronic structure displays pairs of Weyl points (through which the electronic bands disperse linearly along all three momentum directions) connected by topological surface states, forming a unique ark-like Fermi surface (FS). Each Weyl point is chiral and contains half the degrees of freedom of a Dirac point, and can be viewed as a magnetic monopole in momentum space. By performing angle-resolved photoemission spectroscopy on the non-centrosymmetric compound TaAs, here we report its complete band structure, including the unique Fermi-arc FS and linear bulk band dispersion across the Weyl points, in agreement with the theoretical calculations. This discovery not only confirms TaAs as a 3D TWS, but also provides an ideal platform for realizing exotic physical phenomena (for example, negative magnetoresistance, chiral magnetic effects and the quantum anomalous Hall effect) which may also lead to novel future applications. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) topological Dirac semimetals (TDSs) are a recently proposed state of quantum matter that have attracted increasing attention in physics and materials science. A 3D TDS is not only a bulk analogue of graphene; it also exhibits non-trivial topology in its electronic structure that shares similarities with topological insulators. Moreover, a TDS can potentially be driven into other exotic phases (such as Weyl semimetals, axion insulators and topological superconductors), making it a unique parent compound for the study of these states and the phase transitions between them. Here, by performing angle-resolved photoemission spectroscopy, we directly observe a pair of 3D Dirac fermions in Cd3As2, proving that it is a model 3D TDS. Compared with other 3D TDSs, for example, β-cristobalite BiO2 (ref. ) and Na3Bi (refs , ), Cd3As2 is stable and has much higher Fermi velocities. Furthermore, by in situ doping we have been able to tune its Fermi energy, making it a flexible platform for exploring exotic physical phenomena. [ABSTRACT FROM AUTHOR]

The nature of metallicity and the level of electronic correlations in the antiferromagnetically ordered parent compounds are two important open issues for the iron-based superconductivity. We perform a temperature-dependent angle-resolved photoemission spectroscopy study of Fe1.02Te, the parent compound for iron chalcogenide superconductors. Deep in the antiferromagnetic state, the spectra exhibit a "peak-dip-hump" line shape associated with two clearly separate branches of dispersion, characteristics of polarons seen in manganites and lightly doped cuprates. As temperature increases towards the Néel temperature (TN), we observe a decreasing renormalization of the peak dispersion and a counterintuitive sharpening of the hump linewidth, suggestive of an intimate connection between the weakening electron-phonon (e-ph) coupling and antiferromagnetism. Our finding points to the highly correlated nature of the Fe1.02Te ground state featured by strong interactions among the charge, spin, and lattice and a good metallicity plausibly contributed by the coherent polaron motion. [ABSTRACT FROM AUTHOR]

Ferroelectric materials directly convert electrical energy to mechanical or thermal work and are critical to applications such as sensors, transducers, actuators, and cooling devices. Numerous efforts have been undertaken to develop materials with high electrocaloric (EC) and electromechanical (EM) responses. Here, we present a theoretical analysis, based on thermodynamic fundamentals, for developing ferroelectric materials with high EC and EM responses, i.e., searching for and operating the material near an invariant critical point (ICP). We show that by tailoring the constraints to maximize the number of coexisting phases near ICPs, large EC and EM responses may be realized. [ABSTRACT FROM AUTHOR]

It is well-known that a ring R is right Noetherian if and only if every direct sum of injective right R-modules is injective. In this paper, we characterize Nonnil-Noetherian rings by nonniMnjective modules. If R is a commutative ring, then we prove that R is a Nonnil-Noetherian ring if and only if the ring R[x]/(xn+1) is Nonnil-Noetherian, where (xn+1) is the ideal generated by xn+1 and n is a non-negative integer. [ABSTRACT FROM AUTHOR]

Let R be a ring, G an ordered group and a a map from G into the group of automorphisms of R. If R is reduced, then the Malcev-Nemnann ring R * ((G)) has the same triangulating dimension as R. Furthermore, if R is a PWP ring, then so is R * ((G)). [ABSTRACT FROM AUTHOR]

Abstract: The metastable β″-Mg5Si6 phase is often the most effective hardening precipitate in Al-rich Al–Mg–Si alloys. Two important factors that control the precipitate morphology are the strain energy and the interfacial energy between the precipitate and the matrix. By means of a first-principles supercell approach and density functional theory calculations, we have studied the interfacial properties between β″-Mg5Si6 and α-Al. We carefully construct a large number of interfacial cells in order to elucidate preferred interfacial terminations and orientations, as well as atom alignment and intermixing across the interface. Each of the low-energy interfaces we found possesses two key attributes: a high number of Al–Si bonds across the interface, and a face-centered cubic topological alignment of atoms across those interfaces. Our first-principles results yield quantitative values for the interfacial energies, lattice mismatches and strain energies that can be used in future predictions of precipitate morphologies as a function of size. [Copyright &y& Elsevier]

The thermodynamic properties of Al, Ni, NiAl, and Ni3Al were studied using the first-principles approach. The 0-K total energies are calculated using the ab initio plane wave pseudopotential method within the generalized gradient approximation. The contribution to the free energy from the lattice vibration was calculated using the phonon densities of states derived by means of the ab initio linear-response theory. The thermal electronic contribution to the free energy was obtained from the one-dimensional numerical integration over the electronic density of states. With the deduced Helmholtz free-energy, the thermal expansion and enthalpy as a function of temperature were calculated and compared with the experimental data. Our calculations show that the enthalpies of formation are slightly temperature dependent with a slope of −1.6 J/mol/K for NiAl and −1.2 J/mol/K for Ni3Al. For Ni, the inclusion of thermal electronic excitation results in a 10% increase in thermal expansion and 15% increase in enthalpy at 1600 K. [Copyright &y& Elsevier]

The phase relations in the BaO–TiO2−δ system within the concentration range of 14–65 mol% BaO under reducing conditions were investigated using high temperature DTA and X-ray powder diffraction. The stable compounds under these conditions were determined, together with the temperatures of the invariant reactions and the liquidus boundaries. The phase relations in this BaO–TiO2–Ti2O3 system under elevated temperatures and reducing atmospheres are represented in the form of quasi-binary phase diagrams. [Copyright &y& Elsevier]

A series of barium titanium oxides with various Ba/Ti ratios having a hollandite structure were obtained by firing chemical synthesized oxide precursors under reducing atmosphere conditions (H2/N2 gas mixture flow) at temperatures of 1100°C and above. An oxygen nonstoichiometry was determined by a thermogravimetric analysis through oxidizing in air. It was shown that barium titanium hollandites may adopt both oxygen excess and oxygen-deficient stoichiometries within the structure. As a limiting case the barium titanium hollandites with only tetravalent titanium ions were obtained. The influence of oxygen nonstoichiometry on the hollandite monoclinic–tetragonal phase transition and a barium superstructure ordering was investigated and discussed. Distortion scaling rules are considered to compare this work with earlier investigations on hollandites. [Copyright &y& Elsevier]

A new barium polytitanate Ba1.054Ti0.946O2.946 was synthesized by a citrate chemical route. The X-ray powder pattern of this compound was indexed to a hexagonal system, with space group P63/mmc and lattice parameters a=5.722(4) and c=13.996(8) A˚. Prolonged annealing of the Ba1.054Ti0.946O2.946 in air at temperatures above 1150°C leads to a peritectoid decomposition reaction yielding Ba2TiO4 and cubic-BaTiO3, consistent with the known phase diagram. A thermal stability study of this compound demonstrates it to be a stable phase under ambient conditions and metastable under low oxygen partial pressures. [ABSTRACT FROM AUTHOR]

This paper considers the guaranteed cost control problem of the jump linear system with uncertain parameters and constant time delay. The sufficient and necessary condition for the system to be mean square quadratically stable (MSQS) is obtained. Using the LMI technique, an algorithm to design an output-feedback guaranteed controller which stabilizes the system in the MSQS sense is developed. [ABSTRACT FROM AUTHOR]

This paper considers the class of continuous-time jump linear systems with time-delay and polytopic uncertain parameters. When the time-delay is a known constant, by using the linear matrix inequality (LMI) technique, we first establish delay dependent sufficient conditions for robust stability and robust H∞ control of the class of systems under study. The problem of determining the maximum time-delay under which the system will remain stable is cast into a generalized eigenvalue problem and thus solved by LMI techniques. When the control input contains a time-delay, an algorithm to design a state feedback controller with constant gain matrix is developed. Two examples are given to show the validness of the theoretical results. [ABSTRACT FROM AUTHOR]

Dirac semimetals are classified into different phases based on the types of Dirac fermions. Tuning the transition among different types of Dirac fermions in one system remains a challenge. Recently, KMgBi was predicted to be located at a critical state in which various types of Dirac fermions can be induced owing to the existence of a flatband. Here, we carried out systematic studies on the electronic structure of KMgBi single crystals by combining angle-resolve photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. The flatband was clearly observed near the Fermi level. We also revealed a small bandgap of ∼20 meV between the flatband and the conduction band. These results demonstrate the critical states of KMgBi that transition among various types of Dirac fermions can be tuned in one system. [ABSTRACT FROM AUTHOR]

A phase-field model for investigating the surface morphological evolution of a film is developed, taking into account the surface energies of film and substrate, the interfacial energy between the film and substrate, and the elastic energy associated with the lattice mismatch between the film and substrate. Using the lattice mismatch and the surface energies for the Ge/Si heteroepitaxial system, the morphology of islands and the formation of a wetting layer are investigated using two-dimensional simulations. The results show that the wetting angle increases continuously with the increase in the lattice mismatch, and the surface angle of the island on wetting layer varies with the island size. It is demonstrated that the anisotropy of elastic interactions alone is not sufficient to cause surface angle discontinuity or faceting that is observed in experiments. [ABSTRACT FROM AUTHOR]

Angle-resolved photoemission spectroscopy with sub-micrometer spatial resolution (μ-ARPES), has become a powerful tool for studying quantum materials. To achieve sub-micrometer or even nanometer-scale spatial resolution, it is important to focus the incident light beam (usually from synchrotron radiation) using x-ray optics, such as the zone plate or ellipsoidal capillary mirrors. Recently, we developed a laser-based μ-ARPES with spin-resolution (LMS-ARPES). The 177 nm laser beam is achieved by frequency-doubling a 355 nm beam using a KBBF crystal and subsequently focused using an optical lens with a focal length of about 16 mm. By characterizing the focused spot size using different methods and performing spatial-scanning photoemission measurement, we confirm the sub-micron spatial resolution of the system. Compared with the μ-ARPES facilities based on the synchrotron radiation, our LMS-ARPES system is not only more economical and convenient, but also with higher photon flux (>5 × 1013 photons/s), thus enabling the high-resolution and high-statistics measurements. Moreover, the system is equipped with a two-dimensional spin detector based on exchange scattering at a surface-passivated iron film grown on a W(100) substrate. We investigate the spin structure of the prototype topological insulator Bi2Se3 and reveal a high spin-polarization rate, confirming its spin-momentum locking property. This lab-based LMS-ARPES will be a powerful research tool for studying the local fine electronic structures of different condensed matter systems, including topological quantum materials, mesoscopic materials and structures, and phase-separated materials. [ABSTRACT FROM AUTHOR]

A correction to the article "Weyl Semimetal Phase in the Non-centrosymmetric Compound TaAS" published in the August 17, 2015 online issue of the magazine is presented.

The proton mean kinetic energy, Ke(H), of water confined in nanocavities of beryl (Be3Al2Si6O18) at 5 K was obtained by simulating the partial vibrational density of states from density functional theory based first-principles calculations. The result, Ke(H) = 104.4 meV, is in remarkable agreement with the 5 K deep inelastic neutron scattering (DINS) measured value of 105 meV. This is in fact the first successful calculation that reproduces an anomalous DINS value regarding Ke(H) in nano-confined water. The calculation indicates that the vibrational states of the proton of the nano-confined water molecule distribute much differently than in ordinary H2O phases, most probably due to coupling with lattice modes of the hosting beryl nano-cage. These findings may be viewed as a promising step towards the resolution of the DINS controversial measurements on other H2O nano-confining systems, e.g., H2O confined in single and double walled carbon nanotubes. [ABSTRACT FROM AUTHOR]

Background Lipopolysaccharide (LPS) has pro-inflammatory properties. This study was conducted to determine whether the LPS induced pro-inflammatory response in a model of mastitis and in mouse mammary epithelial cells (MEC). Methods To investigate the effects of LPS in vivo, 50 μL of a solution of LPS (20 ng/μL) were infused into the mammary glands of mice. To study the effects of LPS in vitro, MEC were exposed to LPS (20 μg/mL) for 24 h. Activation of nuclear factor kB (NF-κB) and myeloperoxidase (MPO) were studied. Production of pro-inflammatory cytokines (interleukin-6 [IL-6], tumor necrosis factor-alpha [TNF-alpha], interleukin-1 beta [IL-1beta]) and expression of osteopontin (OPN) were also evaluated. Results After LPS administration, route of NF-κB signaling is activated and the activity of MPO is increased. Furthermore, LPS increases the expression of OPN and production of TNF-alpha, IL-6 and IL-1beta. Conclusions Present results demonstrate that LPS induces a pro-inflammatory response in a murine model of mastitis and suggest the involvement of the NF-κB pathway and OPN. [ABSTRACT FROM AUTHOR]

Films of iron selenide (FeSe) one unit cell thick grown on strontium titanate (SrTiO3 or STO) substrates have recently shown superconducting energy gaps opening at temperatures close to the boiling point of liquid nitrogen (77 kelvin), which is a record for the iron-based superconductors. The gap opening temperature usually sets the superconducting transition temperature Tc, as the gap signals the formation of Cooper pairs, the bound electron states responsible for superconductivity. To understand why Cooper pairs form at such high temperatures, we examine the role of the SrTiO3 substrate. Here we report high-resolution angle-resolved photoemission spectroscopy results that reveal an unexpected characteristic of the single-unit-cell FeSe/SrTiO3 system: shake-off bands suggesting the presence of bosonic modes, most probably oxygen optical phonons in SrTiO3 (refs 5, 6, 7), which couple to the FeSe electrons with only a small momentum transfer. Such interfacial coupling assists superconductivity in most channels, including those mediated by spin fluctuations. Our calculations suggest that this coupling is responsible for raising the superconducting gap opening temperature in single-unit-cell FeSe/SrTiO3. [ABSTRACT FROM AUTHOR]

The mean atomic kinetic energies of the proton, Ke(H), and of the deuteron, Ke(D), were calculated in moderate and strongly hydrogen bonded (HB) systems, such as the ferro-electric crystals of the KDP type (XH2PO4, X = K, Cs, Rb, Tl), the DKDP (XD2PO4, X = K, Cs, Rb) type, and the X3H(SO4)2 superprotonic conductors (X = K, Rb). All calculations utilized the simulated partial phonon density of states, deduced from density functional theory based first-principle calculations and from empirical lattice dynamics simulations in which the Coulomb, short range, covalent, and van der Waals interactions were accounted for. The presently calculated Ke(H) values for the two systems were found to be in excellent agreement with published values obtained by deep inelastic neutron scattering measurements carried out using the VESUVIO instrument of the Rutherford Laboratory, UK. The Ke(H) values of the M3H(SO4)2 compounds, in which the hydrogen bonds are centro-symmetric, are much lower than those of the KDP type crystals, in direct consistency with the oxygen-oxygen distance ROO, being a measure of the HB strength. [ABSTRACT FROM AUTHOR]

The mean atomic kinetic energies of the proton, Ke(H), and of the deuteron, Ke(D), were calculated in moderate and strongly hydrogen bonded (HB) systems, such as the ferro-electric crystals of the KDP type (XH2PO4, X = K, Cs, Rb, Tl), the DKDP (XD2PO4, X = K, Cs, Rb) type, and the X3H(SO4)2 superprotonic conductors (X = K, Rb). All calculations utilized the simulated partial phonon density of states, deduced from density functional theory based first-principle calculations and from empirical lattice dynamics simulations in which the Coulomb, short range, covalent, and van der Waals interactions were accounted for. The presently calculated Ke(H) values for the two systems were found to be in excellent agreement with published values obtained by deep inelastic neutron scattering measurements carried out using the VESUVIO instrument of the Rutherford Laboratory, UK. The Ke(H) values of the M3H(SO4)2 compounds, in which the hydrogen bonds are centro-symmetric, are much lower than those of the KDP type crystals, in direct consistency with the oxygen-oxygen distance ROO, being a measure of the HB strength. [ABSTRACT FROM AUTHOR]

Abstract: The future development of the CALPHAD method requires establishing file and data repositories and tools to automate the modeling process and to enable efficient implementation of new models and the development of multicomponent descriptions. To advance these new repositories and tools, unique phase and materials identifiers must be defined. These identifiers are crucial for the successful linkage between different data repositories and for efficient searching of the needed data for a given materials system. [Copyright &y& Elsevier]

In the past few years, a new state of quantum matter known as the time-reversal-invariant topological insulator has been predicted theoretically and realized experimentally. All of the topological insulators discovered so far in experiment are inversion symmetric-except for strained HgTe, which has weak inversion asymmetry, a small bulk gap but no bulk charge polarization. Strong inversion asymmetry in topological insulators would not only lead to many interesting phenomena, such as crystalline-surface-dependent topological electronic states, pyroelectricity and intrinsic topological p-n junctions, but would also serve as an ideal platform for the realization of topological magneto-electric effects, which result from the modification of Maxwell equations in topological insulators. Here we report the discovery of a strong inversion asymmetric topological insulator phase in BiTeCl by angle-resolved photoemission spectroscopy, which reveals Dirac surface states and crystalline-surface-dependent electronic structures. Moreover, we observe a tenfold increase of the bulk energy gap in BiTeCl over the weak inversion asymmetric topological insulator HgTe, making it a promising platform for topological phenomena and possible applications at high temperature. [ABSTRACT FROM AUTHOR]

Abstract: Diffusion in dilute Mg–X alloys, where X denotes Al, Zn, Sn and Ca impurities, was investigated with first-principles density functional theory in the local density approximation. Impurity diffusion coefficients were computed as a function of temperature using the 8-frequency model which provided the relevant impurity and solvent (Mg) jump frequencies and correlation factors. Minimum energy pathways for impurity diffusion and associated saddle point structures were computed with the climbing image nudged elastic band method. Vibrational properties were obtained with the supercell (direct) method for lattice dynamics. Calculated diffusion coefficients were compared with available experimental data. For diffusion between basal planes, we find D Mg–Ca > D Mg–Zn > D Mg–Sn > D Mg–Al, where D is the diffusion coefficient. For diffusion within a basal plane, the same trend holds except that D Mg–Zn overlaps with D Mg–Al at high temperatures and D Mg–Sn at low temperatures. These trends were explored with charge density contours in selected planes of each Mg–X alloy, the variation of the activation energy for diffusion with the atomic radius of each impurity and the electronic density of states. The theoretical methodology developed herein can be applied to impurity diffusion in other hexagonal materials. [Copyright &y& Elsevier]

Abstract: Self-diffusion coefficients for hcp Mg and Zn have been calculated from first-principles as a function of temperature, within the generalized gradient and local density approximations. The climbing image nudged elastic band (CI-NEB) method has been used to provide minimum energy pathways and associated saddle point structures. Vibrational properties have been calculated using the direct method to lattice dynamics. A good agreement between our calculated data and available experimental measurements has been obtained. For both Mg and Zn, LDA and GGA results form lower and upper bounds to the experimental data. Calculated results show that diffusion is faster in the basal plane in Mg and along the normal of the basal plane in Zn, in accordance with the available experimental data. Key differences in the diffusion anisotropy of both the metals have been examined in detail. [ABSTRACT FROM AUTHOR]

The interfacial energies of twin boundaries and stacking faults in metal magnesium have been calculated using first-principles supercell approach. Four types of twin boundaries and two types of stacking faults are investigated, namely, those due to the () mirror reflection, the () mirror glide, the () mirror reflection, the () mirror glide, the I1 stacking fault and the I2 stacking fault. The effects of supercell size on the calculated interfacial energies are examined. [Copyright &y& Elsevier]

Sodium is an undesirable impurity in aluminium–magnesium alloys. In trace amounts it leads to high temperature embrittlement (HTE), due to intergranular fracture, which results in edge cracking during hot rolling. In the present work, the results of a thermodynamic investigation to elucidate the mechanism are presented. Correlations between HTE, phase formation, temperature and composition in Al–Mg alloys were determined. It is suggested that: (i) HTE is related to the formation of an intergranular Na-rich liquid phase, which significantly weakens the strength of grain boundaries; (ii) for a given Mg content, there exists a maximum Na content above which HTE cannot be avoided; and (iii) for a given alloy, a proper hot-rolling temperature should be chosen with respect to Na and Mg contents to suppress HTE. The HTE sensitive zone and a hot-rolling safe zone of Al–Mg–Na alloys are defined as functions of processing temperature and alloy composition. The tendency of HTE formation was evaluated based on thermodynamic simulations of phase fraction of the intergranular Na-rich liquid phase. [ABSTRACT FROM AUTHOR]

Abstract: First-principles calculations of the free energy of the intermetallic phases of the Zn–Zr system have been performed. The likely structures of the two allotropes of Zn3Zr are proposed and the structure of Zn2Zr3 is determined. The 0K phase diagram for this system is calculated using the convex hull construction. Two compounds, ZnZr2 and Zn2Zr3, that previously were not considered to form part of the equilibrium phase diagram have been shown to become stable at high temperatures thanks to calculations of their vibrational free energy via the supercell approach within the harmonic approximation. The results from this work will later be used to develop a fully consistent thermodynamic model for this binary. [Copyright &y& Elsevier]

Abstract: In this work the thermodynamic properties of Al, Ni, NiAl and Ni3Al were obtained through ab initio methods. Through the use of density functional theory within the generalized gradient approximation and projector augmented-wave (PAW) pseudopotentials, the 0K energetics of the structures were calculated. The supercell method was used to calculate the vibrational contributions to the free energy. The contribution of electronic degrees of freedom to the total free energy was also included in the calculations. The resulting free energy was used to calculate the enthalpies and entropies of the structures investigated. The comparison with experimental data is satisfactory, and the calculations compare well with recent results using linear response theory. [Copyright &y& Elsevier]

Atomic structure, diffusivity and viscosity of Al1-xMgx (x=0, 0.0039, 0.1172, 0.9180, 0.9961, 1)melts at 875, 1000, 1125, and 1250K were investigated by the ab initio molecular dynamics (AIMD) simulations. The simulated results are compared with available experimental and calculated data in the literature with reasonable agreements. Considering the results of pair correlation function g(r), it can be observed that Mg atoms in Al0.8828Mg0.1172 melt aggregate more obviously at 1000 and 1250K. For Al0.0820Mg0.9180, Al atom segregation is more obvious at 875 and 1000K. The tracer diffusion coefficients of Al or Mg in Al1-xMgx (x=0.1172, 0.9180) melts, and interdiffusion coefficients of Al0.8828Mg0.1172 and Al0.0820Mg0.9180 melts are all close to the self-diffusion coefficients of Al or Mg. With the increasing temperature, the diffusivity increases linearly. In dilute melts, the tracer diffusion coefficients of solute atom and the interdiffusion coefficients increase nonlinearly with the increasing temperature. For Al0.8828Mg0.1172 and Al0.0820Mg0.9180 melts, the viscosities η are comparatively higher than pure melts. The viscosities of all melts decrease with the increasing temperature, then increase at 1250K. The results obtained in the present work provide an insight into the design of Al and Mg alloys. [ABSTRACT FROM AUTHOR]

The variation of elastic properties, e.g., elastic constants, bulk modulus, and shear modulus of dilute Ni-base superalloys due to alloying elements (X's) and temperature, has been studied via first-principles calculations. Here, 26 alloying elements are considered: Al, Co, Cr, Cu, Fe, Hf, Ir, Mn, Mo, Nb, Os, Pd, Pt, Re, Rh, Ru, Sc, Si, Ta, Tc, Ti, V, W, Y, Zn, and Zr. It is found that (i) both the bulk and shear moduli of Ni-X decrease approximately linearly with increasing equilibrium volume, especially within each group of 3d, 4d, or 5d transition-metal alloying elements; (ii) all alloying elements considered herein increase the ratio of bulk to shear modulus (i.e., the ductility) and the elastic anisotropy of the Ni-X alloys; and (iii) the largest decrease of elastic properties of Ni is caused by alloying element Y. It is observed that the change of elastic properties of Ni due to various alloying elements is traceable from the distribution of (magnetization) charge density, for instance the spherical distribution of charge density facilitates shear deformation, resulting in a lower shear-related property. Using a proposed quasistatic approach based on the predicted elasticity-volume-temperature relationship, the isothermal and the isentropic elastic properties are predicted for the dilute Ni-X alloys at finite temperatures, displaying a decreasing trend with respect to temperature for each Ni-X system. Computed elastic properties are in favorable accord with available experimental data. [ABSTRACT FROM AUTHOR]

The SnSe crystal is a promising candidate in the field of thermoelectric materials. In order to elucidate basic physics in the SnSe system, here we report the heavily hole doping SnSe single crystals by the flux method (using alkali halide as solvent). Compared to bad-metal behavior of SnSe grown by the Bridgeman method, the flux-grown SnSe crystals show the metallic conductive behavior consistent with the Landau Fermi liquid (resistivity ρ ∼ T2) with temperatures ranging from 2 to 300 K. Combined angle-resolved photoemission spectroscopy and empirical Landau Fermi liquid theory, screening lengths λ of Coulomb electron–electron interaction U of SnSe grown by the flux method are 6.6 Å and 6.1 eV, which are much higher than those of normal metals. Remarkably, the excellent electrical conductivity (870 S/cm) of the SnSe crystal grown by the flux method at room temperature is attributed to the higher hole concentration (∼3.8 × 1019 cm−3) and large mobility (152.2 cm2 V−1 s−1). Meanwhile, these SnSe crystals still have large Seebeck coefficients (∼190 μV/K). Thus, the SnSe crystals grown by the flux method have an ultrahigh power factor [∼31.5 μW/(cm K2)] at room temperature, which is ten times larger than that of SnSe crystals grown by the Bridgeman method and as best as currently reported results. Our work shows a method for growing heavily hole-doped SnSe crystals, which provides a platform for understanding the electrical properties and improving its thermoelectric performance. [ABSTRACT FROM AUTHOR]

Weyl semimetals are crystalline solids that host emergent relativistic Weyl fermions and have characteristic surface Fermi-arcs in their electronic structure. Weyl semimetals with broken time reversal symmetry are difficult to identify unambiguously. In this work, using angle-resolved photoemission spectroscopy, we visualized the electronic structure of the ferromagnetic crystal Co3Sn2S2 and discovered its characteristic surface Fermi-arcs and linear bulk band dispersions across the Weyl points. These results establish Co3Sn2S2 as a magnetic Weyl semimetal that may serve as a platform for realizing phenomena such as chiral magnetic effects, unusually large anomalous Hall effect and quantum anomalous Hall effect. [ABSTRACT FROM AUTHOR]

The domain stability and domain structures of (001)-oriented PbTiO3 ferroelectric thin films subject to anisotropic in-plane strains were studied using phase-field method. Based on the simulation results, a room temperature domain/phase stability diagram was constructed for PbTiO3 thin films with the in-plane strains ranging from -5% to 5%. The predicted diagram is both quantitatively and qualitatively different from those obtained using thermodynamic calculations based on a single-domain assumption. [ABSTRACT FROM AUTHOR]

A single-domain thermodynamic theory is employed to predict the spontaneous polarizations of (001)c, (101)c, and (111)c oriented epitaxial BiFeO3 thin films grown on dissimilar substrates. The effects of various substrate-induced strains on the spontaneous polarization were studied. The dependences of the spontaneous polarization on film orientations and the types of substrate-induced strains were analyzed. [ABSTRACT FROM AUTHOR]

BiFeO3 thin films have been deposited on (001) SrTiO3 substrates by adsorption-controlled reactive molecular-beam epitaxy. For a given bismuth overpressure and oxygen activity, single-phase BiFeO3 films can be grown over a range of deposition temperatures in accordance with thermodynamic calculations. Four-circle x-ray diffraction reveals phase-pure, epitaxial films with ω rocking curve full width at half maximum values as narrow as 29 arc sec (0.008°). Multiple-angle spectroscopic ellipsometry reveals a direct optical band gap at 2.74 eV for stoichiometric as well as 5% bismuth-deficient single-phase BiFeO3 films. [ABSTRACT FROM AUTHOR]

The domain structures in a ferroelectric thin film are studied using a phase-field model. A cubic-to-tetragonal ferroelectric phase transition in lead titanate thin film is considered. Both elastic interactions and electrostatic interactions are taken into account. The focus is on the effect of electrical boundary conditions on the domain morphologies and volume fractions. It is shown that different electric boundary conditions may have a significant effect on the domain structures. [ABSTRACT FROM AUTHOR]

A phase-field model for predicting the coherent microstructure evolution in constrained thin films is developed. It employs an analytical elastic solution derived for a constrained film with arbitrary eigenstrain distributions. The domain structure evolution during a cubic→tetragonal proper ferroelectric phase transition is studied. It is shown that the model is able to simultaneously predict the effects of substrate constraint and temperature on the volume fractions of domain variants, domain-wall orientations, domain shapes, and their temporal evolution. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Highlights • A thermodynamicmodel of the Hf-Ni system is reassessed using new experiments. • Hf-Ni diffusion couples with low Zr contamination (0.25 wt. %) are used. • The measured Hf solubility is larger compared to previous experiments. • Mixing enthalpies for solution phases are obtained using first-principles. • HEXRD experiments confirmed the B2 structure for NiHf above 1433 K. Abstract Hf-Ni is an important binary system for high temperature alloys and shape memory alloys which has been investigated several times in the literature but often using samples of Hf contaminated by Zr. The thermodynamics of this system are remodeled in this work based on first-principles calculations and additional experiments using Hf with relatively low Zr contamination (0.25 wt. %). Diffusion couples in the Ni-rich portion of the Hf-Ni system heat treated at 1173, 1273 and 1373 K are used to measure phase stability and Hf solubility in the fcc phase. The solubility observed in fcc Ni from Ni/Ni 50 Hf 50 (at.%) diffusion couples is larger than that observed in previous experiments. These results are the only source fit to during modeling of the fcc solubility to mitigate effects from Zr contamination. Data in the literature suggests that the high temperature crystal structure of the B33 NiHf phase is, in fact, the B2 structure. High temperature synchrotron measurements provide confirmation of this crystal structure. Modeling of the B2 phase was aided by first-principles calculations using special quasi-random structures (SQS). The present CALPHAD model will prove useful when designing shape memory alloys containing Hf and when modeling the Hf activity in Ni-base high temperature alloys. [ABSTRACT FROM AUTHOR]

A critical thermodynamic assessment of the metastable c-TiAlZrN coatings, which are reported to spinodally decompose into triple domains, i.e., c-TiN, c-AlN, and c-ZrN, was performed via the CALculation of PHAse Diagram (CALPHAD) technique based on the limited experimental data as well as the first-principles computed free energies. The metastable c-TiAlZrN coatings were modeled as a pseudo-ternary phase consisting of c-TiN, c-AlN and c-ZrN species, and described using the substitutional solution model. The thermodynamic descriptions for the three boundary binaries were directly taken from either the CALPHAD assessment or the first-principles results available in the literature except for a re-adjustment of the pseudo-binary c-AlN/c-ZrN system based on the experimental phase equilibria in the pseudo-ternary system. The good agreement between the calculated phase equilibria and the experimental data over the wide temperature range was obtained, validating the reliability of the presently obtained thermodynamic descriptions for the c-TiAlZrN system. Based on the present thermodynamic description, different phase diagrams and thermodynamic properties can be easily predicted. It is anticipated that the present thermodynamic description of the metastable c-TiAlZrN coatings can serve as the important input for the later quantitative description of the microstructure evolution in c-TiAlZrN coatings during service life. [ABSTRACT FROM AUTHOR]

The nematic state, where a system is translationally invariant but breaks rotational symmetry, has drawn great attention recently due to the experimental observations of such a state in both cuprates and iron-based superconductors. The origin of nematicity and its possible tie to the pairing mechanism of high-Tc, however, still remain controversial. Here, we study the electronic structure of a multilayer FeSe film using angle-resolved photoemission spectroscopy. The band reconstruction in the nematic state is clearly delineated. We find that the energy splitting between dzx and dyz bands shows a nonmonotonic distribution in momentum space. From the Brillouin zone center to the Brillouin zone corner, the magnitude of splitting first decreases, then increases, and finally reaches the maximum value of ~70 meV. Moreover, besides the dzx and dyz bands, band splitting was also observed on the dxy bands with a comparable energy scale around 45 meV. Our results suggest that the electronic anisotropy in the nematic state cannot be explained by a simple on-site ferro-orbital order. Instead, strong anisotropy exists in the hopping of all dzx,dyz, and dxy orbitals, the origin of which holds the key to a microscopic understanding of the nematicity in iron-based superconductors. [ABSTRACT FROM AUTHOR]

This letter reports quaternary Cr-Co-Nb-B bulk metallic glasses (BMGs) with ultrahigh hardness and Young's moduli. Especially, Cr55Co24Nb7B14 BMG exhibits ultrahigh Vickers hardness and Young's modulus of 1605 and 278 GPa, respectively, and the highest specific Young's modulus of 37.0106 Nm/kg among all the developed BMGs so far. It is considered that the high hardness and Young's moduli for this kind of BMGs are intrinsically attributed to the strong interactions between metallic constituent elements and B. [ABSTRACT FROM AUTHOR]

Iron-based composites were reinforced with TiC particulates by in situ synthesis. The microstructure was characterised by transmission electron microscope. The bright field image, dark field image and diffraction pattern of reinforcing particulates and graphite harmful phase were obtained. Meanwhile, the interface between reinforcing particulates and matrix of TiCp/Fe composite material was also observed by scanning electron microscope and transmission electron microscope. The results showed that the calculated lattice constant of reinforcing TiC particulates was 0·41 nm and the calculated lattice constants of graphite were a = 0·282 nm and c = 0·459 nm. The TiC particulates had quadrilateral morphology, and were chemically wetted in Fe matrix without distinct interface product. There was no transition layer at the interface, avoiding pollution of reinforcing particulates. This study provided some details for understanding the bonding interface of in situ metal matrix composites. [ABSTRACT FROM AUTHOR]

We report findings of strong anomalies in both mutual inductance and inelastic Raman spectroscopy measurements of single-unit-cell FeSe film grown on Nb-doped SrTiO3, which occur near the temperature where the superconducting like energy gap opens. Analysis suggests that the anomaly is associated with a broadened ferroelectric transition in a thin layer near the FeSe/SrTiO, interface. The coincidence of the ferroelectric transition and gap-opening temperatures adds credence to the central role played by the film-substrate interaction on the strong Cooper pairing in this system. We discuss scenarios that could explain such a coincidence. [ABSTRACT FROM AUTHOR]

The glass-forming abilities of Fe78B22, Fe70Y6B24, Fe72Y6B22 and Fe72.5Y3.5B24 alloys were characterized comprehensively using ab initio molecular dynamics simulations. The calculated results were correlated with the properties and atomic structures. It was found that the Fe72Y6B22 alloy consists of both the most stable and the least deformed body centered cubic atomic packing structures in the supercooled liquid and glassy states. It was observed that the local compositions in the Fe72Y6B22 alloy significantly deviate from the compositions of stable crystalline phases, indicating that the Fe72Y6B22 alloy has the best glass-forming ability among the alloys studied. However, Fe72Y6B22 alloy has two flaws in terms of glass-forming ability, i.e. relatively large atomic diffusivity and insufficiently close atomic packing. The best performance in these two aspects is observed in the Fe72.5Y3.5B24 alloy. Thus, the theoretical study predicts that the best glass former for the Fe-Y-B system is within the compositional range of 22-24at.% B and 3.5-6at.% Y. [ABSTRACT FROM AUTHOR]