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Methods for applying first principles (FP) calculations to CALPHAD modeling, are discussed, with emphasis on easily calculated quantities that can be used to estimate input parameters for CALPHAD optimizations. Estimations of vibrational entropies, and melting points, from chemical systematics of measured elastic constants, or via semiempirical methods based on FP calculations are reviewed. Some strategies for including higher-order (clusters larger than pairs) short range order correlations in CALPHAD calculations are considered.

In this work, we study vacancy energetics in the equiatomic Nb-Mo-Ta-W alloy, especially vacancy formation and migration energies, using molecular statics calculations based on a spectral neighbor analysis potential specifically developed for Nb-Mo-Ta-W. We consider vacancy properties in bulk environments as well as near edge dislocation cores, including the effect of short-range order (SRO) by preparing supercells through Metropolis Monte-Carlo relaxations and temperature on the calculation. The nudged elastic band (NEB) method is applied to study vacancy migration energies. Our results show that both vacancy formation energies and vacancy migration energies are statistically distributed with a wide spread, on the order of 1.0 eV in some cases, and display a noticeable dependence on SRO. We find that, in some cases, vacancies can form with very low energies at edge dislocation cores, from which we hypothesize the formation of stable 'superjogs' on edge dislocation lines. Moreover, the large spread in vacancy formation energies results in an asymmetric thermal sampling of the formation energy distribution towards lower values. This gives rise to effective vacancy formation energies that are noticeably lower than the distribution averages. We study the effect that this phenomenon has on the vacancy diffusivity in the alloy and discuss the implications of our findings on the structural features of Nb-Mo-Ta-W.

The work is devoted to the study of the permeability and diffusion of hydrogen atoms in pure vanadium and in vanadium with oxygen and sulfur impurities by the method of first-principle molecular dynamics in the temperature range from 500 to 900 K. The partial functions of the radial distribution of atoms in the presence and absence of hydrogen are calculated and the nature of the motion and the nature of the short-range order are analyzed., Работа посвящена исследованию проницаемости и диффузии атомов водорода в чистом ванадии и в ванадии с примесями кислорода и серы методом первопринципной молекулярной динамики в температурном интервале от 500 до 900 К. Рассчитаны парциальные функции радиального распределения атомов при наличии и отсутствии водорода и проанализирован характер движения и характер ближнего порядка.

Solute effects on high-entropy alloys of equiatomic proportions are scientifically intriguing because there is no such well-defined "solute" and "solvent" atoms compared to those of conventional single principal element alloys. To date, most of the face-centered cubic alloys exhibit solid solution strengthening rather than softening due to the interactions between dislocations and solute atoms. Here, we present the careful experimental measurements and demonstrate solid solution softening, albeit weak, in a single phase CoCrFeMnNi through the minor addition of 2. at.% Al. This softening effect is mostly related to the decreased Peierl's stress by Al addition., QC 20200720

SbVO4 series of compounds could be a promising catalyst for the production of 20% cheaper acrylonitrile by the ammoxidation of propane compared to current method from propylene producing above 8 million ton/year, thus more than 1 Kg per human inhabitant of the planet. Composition, oxidation state and subtle structural features influence the activity and selectivity of the highest performance catalyst. In the non-stoichiometric series described as Sb0.9V0.9+x[]0.2-xO4 (0≤x≤0.2), cation vacancies ([]) in the basic rutile type- structure balance V3+/V4+ charges while antimony remains as Sb5+. A reduced phase (richest in V3+) has been reported to be Sb0.9V1.1O4, which shows by electron diffraction (ED) superlattice reflections characteristic of a 2-fold rutile superstructure along c. The reciprocal lattice study by ED revealed the following unit cell for the rutile superstructure: √2ar×√2br×2cr (subindex r refers to the basic rutile unit cell). Its space group, I41md, was determined by CBED. A structural model based on alternating Sb and V cations ordering along c in the chains of edge-sharing octahedra was proposed. No cation vacancies have been observed for this reduced phase, while for the compounds synthesized in oxidizing conditions the presence of vacancies has been confirmed. Magnetic susceptibility data indicate possible magnetic ordering in reduced phases rich on V3+ which are close to the nuclear superstructure by Sb-V ordering. For the simultaneous crystal and magnetic structure determination we have performed a neutron diffraction study on different samples of the series with composition ~SbVO4. Below TN ≤ 50K, new Bragg reflections of pure magnetic nature appear due to the 3D-AF interaction of the vanadium spins changing gradually from the paramagnetic disorder to the magnetically ordered state as the temperature decreases. The periodicity of the magnetic structure develops being close to doubling again the two-fold commensurate supercell of rutile type des

Short-range structural and magnetic order in rapidly solidified nanostructured AgMn alloys featuring nominal large Mn content (x = 25, 32, 40 at.%), well above the maximum equilibrium concentration (x ~ 14 at.%), are quantified using X-ray, neutron and magnetic probes. These inhomogenous alloys contain coexisting Mn-rich and Mn-deficient nanoscopic face-centered-cubic-type phases. Interaction between these regions provides large exchange bias at low temperature, with the magnitude of the unidirectional anisotropy field increasing gradually with increased Mn concentration. Neutron diffraction data reveal no evidence of long-range antiferromagnetic ordering but instead identifies short-range structural order from the presence of a diffuse scattering peak that evolves with Mn content. Moderate annealing temperatures (T = 350 °C) promote homogenization of the Mn content in the alloys with subsequent suppression of exchange bias, confirming the above model. A strong interfacial exchange density between Mn-deficient and the Mn-rich nanocrystalline phases exists that is determined to be of the same order of magnitude as that found in other exchange-biased ferromagnetic/antiferromagnetic systems. The intriguing behavior of these AgMn alloys as a function of temperature, of Mn content and of annealing condition highlights options to manipulate and tailor their magnetic attributes such as interface exchange and magnetic anisotropy.

The determination of special molecular arrangements in disordered phases such as liquids is inherently difficult due to its lack of periodicity, in contrast to the crystalline solids. We have already settled a general method to study molecular liquids capable to unveil the details of the molecular ordering from small molecules to systems as big as a protein. However it would be desirable to extract some general features of a liquid phase without going into such details. In this work we propose a method to achieve this challenge by analyzing the probability distributions describing position and orientational molecular ordering within the framework of information theory. (C) 2014 Elsevier B.V. All rights reserved., Postprint (author’s final draft)

The atomic structures of several Ca-Mg-Cu and Ca-Mg-Zn amorphous alloys have been determined using ab initio molecular dynamics simulation and neutron diffraction. Partial pair distribution functions have been produced and the pair bond distances and partial coordination numbers have been reported for these alloys. Similarities and differences in the amorphous structures of the Ca-Mg-Cu and Ca-Mg-Zn alloys have been discussed.

Zr65Ni10Cu7.5A17.5Ag10 bulk metallic glass with a diameter of 2mm was prepared by copper-mould casting. The microstructures of the bulk alloy were examined by X-ray diffraction, optical microscopy and high-resolution electron microscopy. It was found that the structure of the bulk metallic glass formed by copper-mould casting is actually not homogeneous, but composed of three different regions: a purely amorphous portion which makes up the major part of the bulk sample; a second portion containing a few of very small particles in the amorphous matrix, and a third portion consisting of the quasicrystals in the amorphous matrix. The formation of quasicrystal during casting of the melt involved the inward diffusion of Zr and outward diffusion of Ni and Cu. The icosahedral short-range order is likely to have already existed in the glassy state of Zr65Ni10Cu7.5Al7.5Ag10 alloy after casting.

Zr65Ni10Cu7.5A17.5Ag10 bulk metallic glass with a diameter of 2mm was prepared by copper-mould casting. The microstructures of the bulk alloy were examined by X-ray diffraction, optical microscopy and high-resolution electron microscopy. It was found that the structure of the bulk metallic glass formed by copper-mould casting is actually not homogeneous, but composed of three different regions: a purely amorphous portion which makes up the major part of the bulk sample; a second portion containing a few of very small particles in the amorphous matrix, and a third portion consisting of the quasicrystals in the amorphous matrix. The formation of quasicrystal during casting of the melt involved the inward diffusion of Zr and outward diffusion of Ni and Cu. The icosahedral short-range order is likely to have already existed in the glassy state of Zr65Ni10Cu7.5Al7.5Ag10 alloy after casting.

Zr65Ni10Cu7.5A17.5Ag10 bulk metallic glass with a diameter of 2mm was prepared by copper-mould casting. The microstructures of the bulk alloy were examined by X-ray diffraction, optical microscopy and high-resolution electron microscopy. It was found that the structure of the bulk metallic glass formed by copper-mould casting is actually not homogeneous, but composed of three different regions: a purely amorphous portion which makes up the major part of the bulk sample; a second portion containing a few of very small particles in the amorphous matrix, and a third portion consisting of the quasicrystals in the amorphous matrix. The formation of quasicrystal during casting of the melt involved the inward diffusion of Zr and outward diffusion of Ni and Cu. The icosahedral short-range order is likely to have already existed in the glassy state of Zr65Ni10Cu7.5Al7.5Ag10 alloy after casting.

In this study of the effects of rapid solidification on short-range order and magnetic properties, major progress and significant results were achieved in four specific areas. 1) Short-range order in Co80NbxB20-x amorphous alloys was found to be similar at low x and dissimilar at large x to that of the equilibrium crystal structure. This key observation led to a broader model of magnetic properties in amorphous alloys. 2) Devitrification of two different metallic glasses led to technically and scientifically important discoveries related to the fine microstructures produces. 3) Theoretical cluster calculations of electronic structure significantly advanced our understanding of bonding and magnetism in amorphous alloys. Finally, 4), We found that magnetization reversal could be very well described by the soliton-like solutions to a realistic non-linear wave equation. This approach correctly describes the coupling of the wall motion to its own local strain field, a technically important effect.

© 2019 Elsevier Ltd Magnetic properties of a new single crystal MnMgBO 4 have been studied. It was determined that below 16 K antiferromagnet spin order was observed with the axis of easy magnetization along the c axis crystal. The short antiferromagnetic range order was observed below 100 K. The Curie–Weiss temperature has been determined in single crystal MnMgBO 4 as θ CW = −98 K and the frustration parameter has been estimated as 6.125.