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High-Entropy Alloys (HEAs) are a new class of metallic materials based on the combination of multiple principal elements, often with the intention to form a concentrated solid solution. It has been suggested that these solid solution phases could offer enhanced mechanical properties, due to fluctuations in their local atomic environments. However, at present, the thermodynamic stability of the solid solution phases which form in HEAs is poorly understood. This study aims to improve our understanding of phase stability in HEAs and investigate possible differences in the mechanical behaviour of dilute and concentrated solid solutions. Firstly, a systematic series of experiments is presented, which establish the effect of Co and Fe on the phase equilibria of the widely studied CrMnFeCoNi system. Both Co and Fe were found to stabilise the A1 matrix relative to the A2 and D8b phases at elevated temperatures but did not prevent the formation of ordered phases at 500°C. Alongside literature data, the results show that stable single-phase alloys are rare in the CrMnFeCoNi system. Secondly, a systematic assessment of the AlxCrFeCoNi alloy system showed that Al promotes the formation of B2, D8b and A2 phases, and improved our understanding of phase stability in this system, which has strong potential for developing alloys with desirable mechanical properties. In each study, experimental observations were used to test the fidelity of thermodynamic predictions from the latest CALPHAD databases. Whilst the predictions generally provided a close approximation of the observed phase equilibria, inaccuracies were common, especially at lower temperatures. Phase stability investigations also served to identify thermodynamically stable alloys, suitable for the investigation of the Portevin-Le Chatelier (PLC) effect - a discontinuous yielding phenomenon widely attributed to the repeated pinning of dislocations by mobile solute atoms over certain regimes of temperature and strain-rate. Under mechanical testing, the effect is generally associated with serrations in the materials flow curve and the localisation of strain into discrete bands. Serrated flow has been observed in several HEAs but the associated strain localisation behaviour has not yet been reported, so it is uncertain whether this behaviour is similar to the PLC effect in other alloy systems. Thus, a series of alloys based on the stable equiatomic quaternary alloy, CrFeCoNi, were selected to investigate the effect of compositional complexity on the PLC effect. Tensile testing, combined with digital image correlation, enabled simultaneous recording of the materials stress and local strain response across a range of temperatures. The results showed close similarities between the alloys at each temperature, indicating that compositional complexity did not have a dominant influence on the PLC effect. This suggested that the dislocation-solute interactions in the complex, concentrated solid solutions were not substantially different from those of more dilute solutions. Calorimetric investigations also revealed evidence of a varying degree of short-range order among the alloys, the influence of which warrants further investigation.

A great research effort is being employed in the development of Multi-Principal Element Alloys (MPEAs). The major interest on these alloys lies in the vast compositional field in which they exist, which provides a challenging opportunity for designing alloys with improved combinations of properties. Among the MPEAs produced to date, compositions containing large contents of Cr, Co and Ni, including the recently developed and well-studied Cr33Co33Ni33 alloy (in atomic %), are among the most promising for structural application due to their outstanding combination of strength and ductility. The present work is a critical review of some of the important publications on the topic. First, we give a brief history of the MPEA development in recent years highlighting the importance of CrCoNi alloys. Next, a brief explanation of the phase equilibria in this system is given. The third and major part of this work consists in a compilation followed by critical discussion of the main studies explaining the good mechanical properties of these alloys. This compilation includes what is known about grain refinement, solid solution strengthening, twinning and transformation induced plasticity and short-range ordering. The major controversies on the area are pinpointed as well as directions for future research. Several other CrCoNi alloy properties are also reviewed, including what has been published on wear, fatigue, corrosion, oxidation and hot deformation. High Cr-containing alloys have excellent combinations of strength, ductility, corrosion (in saline environments) and oxidation resistance, surpassing some of the best performing Ni-superalloys.

In this paper, we are proposing a novel method to estimate static displacements of atoms caused by size effects in fcc substitutional binary polycrystalline solid solutions. Fourier transforms of static displacements of the atoms on every considered shell were calculated using the equations that include dynamical matrix and Fourier transform of interatomic forces. Short-range order parameters on the first seven shells of Ni-14 at. % Ir alloy have been identified from X-ray diffuse scattering intensity by accounting microscopic static displacements of atoms on a particular shell. Pairwise interatomic potentials on the considered shells and critical temperature of disorder-order phase transition were calculated using values of short-range order parameters.

Pairwise effective potentials in first seventeen shells of the Ni-22.5at.%Fe alloy are calculated using model potential method with account of the linear size effect. Using obtained values of pairwise effective potentials, the short range order parameters on the first seventeen shells of alloy are calculated by Krivoglaz-Clapp-Moss method. The calculated values ​​of the short-range order parameters were fitted to the experimental values ​​by varying the parameters of static atomic displacements. Reliable value of critical temperature of order-disorder phase transition in Ni-22.5at.%Fe alloy was calculated using obtained meanings of pairwise effective potentials.

The crystalline structure and Fe local environment in a Co-doped Ni–Fe–Ga Heusler alloy, prepared by the melt-spinning technique, were investigated by X-ray diffraction (XRD) and EXAFS at room and low temperatures. The characteristic temperatures of the austenite–martensite phase transitions were determined by differential scanning calorimetry via cooling and heating cycles of the alloy ribbons. As shown by room-temperature XRD, the austenitic phase of the alloy has the chemically ordered L21 Heusler structure. This was confirmed by EXAFS, although this technique was not able to conclusively distinguish between the L21 and B2 structures of the austenite for the analyzed alloy. The low-temperature martensitic phase and its structural evolution towards austenite with increasing temperature were studied by high-energy X-ray diffraction, which evinced the martensite modulation. However, the Fe environment could be fitted by EXAFS with the tetragonal L10 structure of the non-modulated martensite. This proves that the martensite modulation has structural effects on a long-range scale, without significant changes in the short-range order around the atoms. The changes in the local structure around iron on martensitic transformation were correlated with changes in the electronic structure, described by XANES spectroscopy at the Fe K edge.

In this work, we calculated efficient pairwise potentials using the prototype potential method and taking the chemical fraction and the fraction caused by the size effect into account. Unknown efficiency values of individual pair displacements were found using the fitting of values of short-range order parameters calculated by the Krivoglaz–Clapp–Moss method to their known experimental values. The values of the effective pairwise potentials determined by this method were used to calculate the short-range order parameters.

The analysis of the structural phase state of Fe-Cr low concentration solid solutions and steel 1X13, associated with the formation of short-range order (SRO) of various types in them has been performed at the mesoscopic level. A comparison of the SRO and swelling of alloys under irradiation was carried out. It was shown that there is a fairly good qualitative correlation between them.

Summary We synthesized single-crystal (Ga1–xZnx)(N1–xOx) nanowires with fully tunable compositions (0

The comparative analysis of structure in ternary Al-Ge-Fe and Al-Ge-Ni melts has been performed in a wide concentration range using results of X-ray diffraction experiment and RMC simulations. The ...

NbCoSb, nominally a 19-electron half-Heusler (19-HH) compound, is one of the emerging novel thermoelectric (TE) materials and has attracted much attention in recent years. By introducing a large am...

As the numbers of medium- to high-entropy alloys being studied and impressive structural properties they exhibit increase rapidly, questions regarding the role played by their complex chemical fluctuations rise concomitantly. Here, using a combination of large-scale molecular dynamics (MD), a hybrid MD and Monte-Carlo simulation method, and crystal defect analysis, we investigate the role lattice distortion (LD) and chemical short-range order (CSRO) play in the nucleation and evolution of dislocations and nanotwins with straining in single crystal and nanocrystalline CoCrNi, a medium entropy alloy (MEA). LD and CSRO effects are elucidated by comparisons with responses from a hypothetical pure A-atom alloy, which bears the same bulk properties of the nominal MEA but no LD and no CSRO. The analysis reveals that yield strengths are determined by the strain to nucleate Shockley partial dislocations, and LD lowers this strain, while higher degrees of CSRO increase it. We show that while these partials prefer to nucleate in the CoCr clusters, regardless of their size, they find it increasingly difficult to propagate away from these sites as the level of CSRO increases. After yield, nanotwin nucleation occurs via reactions of mobile Shockley partials and is promoted in MEAs, due to the enhanced glide resistance resulting from LD and CSRO.

Diffraction patterns for liquid Ni2In alloy in assumption of chemical ordering in clusters have been calculated and compared with experimental ones. It is shown that Ni2in kind clusters show the high thermodynamic stability of such structural units in liquid state. Addition of 10 at.% Bi to Ni2In alloy showed no significant solubility of Bi-atoms in such clusters and promotes the formation of inhomogeneities in short range order structure. References Massalski, T. B. (1990). Binary alloy phase diagram. Metals Park, OH: ASM. Wu, R.-R. (2015). Scientific Reports, 5.DOI: https://doi.org/10.1038/srep10772 Gerardo, D.-P. (2014). Journal of Applied Physics, 115. Schmid, J. (1995). Zeitschrift fur Metallkunde, 86(12), 877-881. Rhazi, A., Auchet, J., Gasser, J. G. (1997). j.Phys: Condens. Matter, 9, 10115-10120.DOI: https://doi.org/10.1088/0953-8984/9/46/009 Ruhl, R. C., Giessen, B. C., Cohen, M., Grant, N. J. (1968). Mat.Sci. Eng., 2(6).DOI: https://doi.org/10.1016/0025-5416(68)90050-5 Olyinyk, Z., Korolyshyn, A., Mudry, S. (2018). Phys. Chem. Solid St., 19(4), 336-340.DOI: https://doi.org/10.15330/pcss.19.4.336-339

The aim of the study is to construct a mathematical model to describe the effect of a magnetic field on the melt crystallization, in particular cast iron. The authors’ research is based on the hypothesis of the certain energy function existence in the short-range order region, which describes the equilibrium state of the "fluid - short-range order" thermodynamic system. Using the hypothesis, we simulated the effect of a magnetic field on the melt crystallization process, which is based on the fundamental laws of statistical physics and thermodynamics and includes four components: a model of the stationary state of the short-range order region, a model for determining the energy function of the short-range order region, a model of the effect of a proportional magnetic field, a model the effects of a commensurate magnetic field on the crystallization of molten iron. Being based on the simulation results, test calculations were performed, the results of which are confirmed by previously known studies. The simulation results showed that the influence of a magnetic field on the crystallization of melts is insignificant in comparison with thermal motion. The authors of the work believe that the magnetic field acts on the region of short-range order at the formation time at a fluctuation temperature that is much lower than the equilibrium one.

For simple substances, in which short range order conserves during melting, we suggest phenomenological statistical model based on the statistics of local orientations, which are desscribed in terms of the field of rotational group elements. It is shown that the model provides a universal melting theory with single phenological parameter, which is valid both in two and three dimensional sysytems.

Using Mossbauer spectroscopy on 57Fe nuclei and X-ray diffraction, the mechanism of mechanical alloying in a planetary ball mill of the Fe–Cr nanocrystalline system in a concentration range from 20 to 48 at % Cr has been studied in detail. It has been established that mechanical alloying occurs in one stage at a concentration of up to 30 at % Cr and in three stages at higher concentrations. The change in the mechanism of mechanical alloying occurs as iron is saturated with chromium and is caused by the inversion of the sign of the mixing energy from negative to positive.

Short-range order in Fe–Cr alloys is investigated by Monte Carlo method. The modelling was performed by Metropolis algorithm using the LAMMPS software package. Modelling results were analyzed by the visualization and data analysis package Ovito. The model of the alloys supposed that the lattice structure was fixed and interaction exists between the first and the second neighbours. The Fe–Cr interaction was established with the use of interatomic interaction potential Abell–Brenner–Tersoff (ABOP). Different concentrations of substitutional impurity of chromium in iron were investigated, viz. 5–50 at. %. The energy of mixing in the Fe–Cr system was calculated for various concentrations of substitutional impurity. Calculation showed that the chosen interaction potential reproduces correctly the changes of the sign of the energy of mixing as a function of Cr concentration. When applied in Monte Carlo kinetic modelling the potential predicts correctly the immiscibility of initially chaotic Fe–Cr alloys as a function of Cr content. The Cowley short-range order parameter is determined that is used for quantitative estimation of the degree of ordering. A strong tendency towards ordering in Cr distribution is observed at low concentrations which is exhibited by negative values of short-range order parameters, in accordance with the experiment.

s Fictive associates are widely used to describe and model liquid phases with strong ordering trends. However, little evidence is known about the assumed associates in most cases. In the present work, an ab initio molecular dynamics (AIMD) study is employed to investigate the characters of the Ba-Bi liquid, in which associates have been assumed in existing thermodynamic modeling. It is found that in the Ba rich melt, the Bi atoms are almost completely surrounded by Ba atoms. The Bi-centered coordination polyhedrons are strongly associated to crystalline structures of Ba5Bi3 and Ba4Bi3 with a longer lifetime than other polyhedrons during the AIMD simulations. In addition, these Bi-centered polyhedrons in Ba rich melt connect with each other through vertex, edge, face, and/or bipyramid sharing to form medium range orders (MRO). In the Bi rich melt, the Ba-centered polyhedrons also form MROs, but they are both structurally and compositionally diverse with a shorter lifetime. These findings from AIMD study provide evidences that there exist a strongly ordering Ba4Bi3 associate and a weakly ordering BaBi3 associate in the Ba-Bi liquid. The predicted enthalpy of mixing in the liquid agrees well with the results by the CALPHAD modeling in the literature.

The structure of liquid bismuth was studied by X-ray diffraction and computer simulation methods. The contraction of the atomic structure within the first coordination sphere in the temperature int...

The element interactions and local structure in molten NiRe and NiAlRe alloys have been investigated via ab initio molecular dynamics (AIMD) simulations. It has been found that the self-interaction of Re evolves from repulsion to attraction with increased Re content, i.e., Re experiences a transition from ordering to clustering, and the trend is further enhanced by Al alloying to NiRe alloys. The finding implies that the aggregation of Re, which is believed to be the main mechanism of Re in improving the mechanical properties of Ni-based single crystal superalloys, may be a kind of positive-feedback process. Our simulation plus experimental results also reveal that the addition of Al enlarges the partition coefficient of Re, which obviously will promote the formation of freckle defect. Both chemical short-range order (CSRO) and relative compactness of solute-centered coordination shell compared with solvent-centered one, obtained in AIMD simulations, are successful in judging the variation of the partition coefficient of Re with added Al. The two quantities may be also useful in revealing the partitioning behavior of elements in complex multi-component alloys whose experimental interaction parameters are lacking.

A new method for calculating the pairwise effective potential on arbitrary shells of the binary disordered solid solutions is proposed with account for the linear size effect. The method is based on the fitting of the order–disorder temperature calculated by the model potential method to its known experimental value. In disordered Cu $${}_{3}$$ Au alloy, the pairwise effective potential is calculated and the short-range order parameters on the first fourteen shells are estimated using the Krivoglaz–Clapp–Moss method. A satisfactory coincidence with the experimental data is obtained.

We observed an order–disorder transition confined to the interface of Pd@Co core–shell nanoparticles with a Pd core and Co shell. A local ordered region with the L10- and L12-type ordered structure...

P2-type Fe- and Mn-based layered sodium transition metal oxides are promising positive electrode materials for sodium batteries due to their high energy density and low costs of the constituting transition metals. However, poor structural reversibility and fast capacity decay have prevented their breakthrough so far. Herein, the real-time dynamic phase transitions and capacity fading mechanism of the P2 Na

Summary Mn-based Li-excess cation-disordered rocksalt (DRX) oxyfluorides are promising candidates for next-generation rechargeable battery cathodes owing to their large energy densities, the earth abundance, and low cost of Mn. In this work, we synthesized and electrochemically tested four representative compositions in the Li-Mn-O-F DRX chemical space with various Li and F content. While all compositions achieve higher than 200 mAh g−1 initial capacity and good cyclability, we show that the Li-site distribution plays a more important role than the metal-redox capacity in determining the initial capacity, whereas the metal-redox capacity is more closely related to the cyclability of the materials. We apply these insights and generate a capacity map of the Li-Mn-O-F chemical space, LixMn2-xO2-yFy (1.167 ≤ x ≤ 1.333, 0 ≤ y ≤ 0.667), which predicts both accessible Li capacity and Mn-redox capacity. This map allows the design of compounds that balance high capacity with good cyclability.

The structure of amorphous silicodiphosphonates made from diphosphonic acids and tetraethoxysilane was investigated by 1H, 13C, 29Si, and 31P single pulse and cross polarization (CP) MAS NMR spectroscopy as well as 1H–31P{29Si} REDOR, 1H–31P–29Si and 1H–29Si–13C double CP MAS experiments. The combination of these solid-state NMR techniques leads to a structural understanding of the short range order. The structure is dominated by [Si(OP)6] units. Besides a few [SiO4] groups, we noticed that HEDP based silicodiphosphonate possesses further five- and sixfold coordinated silicon moieties. Another synthesis route to obtain Si–O–P compounds with higher coordinated silicon species is the reaction of trimethylsilyl-substituted diphosphates and diphosphonates with tetramethoxysilane. The 29Si CP NMR spectra also demonstrate polymeric structures with different [SiO4] units in the solids. Both silyl-substituted phosphorus precursors show a surprising triplet signal in the 29Si INEPT NMR spectra that we interpret using higher order coupling patterns.

Metallic glasses exhibit excellent properties such as ultrahigh strength and excellent wear and corrosion resistance, but there is limited understanding on the relationship between their atomic structure and mechanical properties as a function of their structural state. In this paper, we bridge the processing-structure-property gap by utilizing molecular dynamics simulation for a model binary metallic glass, namely Ni80P20. The structural statistics including the fraction of Voronoi index, the distribution of Voronoi volume, and medium-range ordering are calculated to explain the observed changes in mechanical behavior and strain localization upon relaxation and rejuvenation. Our findings demonstrate that the evolution of mechanical properties can be linked to the atomic structure change in terms of short- and medium-range ordering. With the help of structural statistics, the mechanical properties are determined based on simple Voronoi analysis.

Although often conceived as random solid solutions, alloys may exhibit a local short-range order (SRO) where the distribution of atoms deviates from a perfect randomness, owing to complex interactions among alloying elements. SRO can affect various properties of alloys, but understanding their exact forms, roles, and origins remains challenging from experiment alone. Here we show, through combining statistical sampling and ab initio calculations, that a strong and special SRO dominates the structure of SiSn alloy, which is a key subset of group IV alloys for mid-infrared technology. Remarkably, the SRO in SiSn is found to be reflected primarily by a strong depletion in the second Sn-Sn coordination shell. This is distinguished from the main character of the SRO in the closely related GeSn alloy, which is reflected by the depletion within the first Sn-Sn coordination shell. The unique nature of SRO in SiSn alloy is further attributed to the competition between the two unfavorable local configurations in SiSn: A Sn-Sn first-nearest neighbor through a direct bond and a Sn-Sn second-nearest neighbor through a Sn-Si-Sn motif. The large energy penalty induced by Sn-Si-Sn local structural motif is found to be responsible for the difference between SiSn and GeSn in their forms of SRO. The SRO in SiSn alloy is further demonstrated to substantially raise the direct band gap. Our finding thus constitutes a new knowledge of the origin and form of SRO and lays the foundation for understanding the complex structure of SiGeSn ternary alloy.

Unlike the crystalline solids, the atomic arrangements in amorphous solids lack long-range translational and orientational order. Despite intense research activity on their structures, the details of how the atoms are packed in amorphous solids remain mysterious at present. Here, we propose a structure feature like polymers and estimate the nanoscale of short-range order (SRO) and medium-range order (MRO) in this description according to the boson peak in amorphous solids. The result supports the concepts that (a) the low-frequency local vibrations are defined by the characteristic length of nanoscale clusters and (b) a decisive scale correlation of solvent atoms, SRO and MRO is about 1:3:7 in amorphous solids.

Purpose: of this paper is to study the structure of melts of quasi-binary system Bi2Te3-PbTe by means of X-ray diffraction method. The aim of the research was to investigate the short range order in melts comparing it with the structure in solid state. Design/methodology/approach: Analysis of the structural factors, radial distribution functions of atoms and basic structural parameters showed that the structure of melts at temperatures near the liquidus shows microheterogeneity. Findings: On the basis of the analysis of structural factors, functions of the radial distribution of atoms and basic structural parameters, it is shown that in the given concentration the short range order structure of liquid alloys of pseudo-binary PbTe-Bi2Te3 system is microinhomogeneous and is characterized by the presence of associates, whose atomic arrangement is like to the structure of solid compounds, existing in this concentration range. Research limitations/implications: To complete the understanding of short-range order effect on the formation of the physical properties of Pb-Bi-Te alloys, further studies of the thermoelectric properties of these alloys in the liquid state are needed. Practical implications: The promise of the considered direction requires an experimental and theoretical study of the processes of bulk, thin film and nanostructured material. In this case, it is necessary to develop a technology for the synthesis of compounds of Pb-Bi-Te system, obtaining thin films and nanostructures using the vapour phase methods with studying the mechanisms of thermoelectric properties of the material formation and optimization of technological regimes for obtaining effective thermoelectric materials based on compounds of Pb-Te-Bi system. Originality/value: The processes of structure formation of nanosystems with given characteristics are investigated, because among numerous thermoelectric materials, bismuth telluride (Bi2Te3) and its alloys are the most important thermoelectric materials used in state-of-the-art devices near room temperature, and lead telluride (PbTe)-based alloys are extensively used in power supplies for space exploration and generators for use at medium to high temperatures.

The effect of minute Cr additions on dendritic growth directions in Al-20 wt pct Zn alloy has been investigated. As first evidenced by Gonzales and Rappaz (Metall Mater Trans A 37:2797–2806, 2006) Al-Zn alloys exhibit a Dendrite Orientation Transition (DOT), from 〈100〉 below 25 wt pct Zn to 〈110〉 above 60 wt pct, regardless of the solidification speed. The DOT has been interpreted as a modification of the solid–liquid interfacial energy anisotropy (Gonzales and Rappaz, 2006; Haxhimali et al. in Nat Mater 5:660–664, 2006). However, 0.02 to 0.1 wt pct addition of Cr in Al-20 wt pct Zn drastically modifies the dendrite trunk direction from 〈100〉 to 〈110〉 at low solidification speed, typically 200 μm/s. Even more surprising, 〈100〉 dendrite trunks are retrieved in Al-20 wt pct Zn-0.1 wt pct Cr when the speed is increased to 1000 μm/s, but with the concurrent formation of twinned dendrites. Minute additions of Cr have been reported recently to promote icosahedral short range order (ISRO) in liquid Al-Zn, thus reducing the atomic mobility (Kurtuldu et al. in Acta Mater 115:423–433, 2016) and modifying the nucleation kinetics (Kurtuldu et al. in Acta Mater 61:7098–7108, 2013). The present results indicate that ISRO also modifies the attachment kinetics of icosahedral clusters rather than individual atoms, and is most likely responsible of growth direction change in Al-Zn-Cr alloy and of twinned dendrites formation.

The crystal structure of polylithionite-1M from Darai-Pioz, (K0.97Na0.03Rb0.01)Σ1.01(Li2.04Al0.84 Ti4+0.09Fe3+0.03)Σ3.00(Si3.98Al0.02)O10[F1.68(OH)0.33]Σ2, a 5.1974(4), b 8.9753(6), c 10.0556(7) Å, β 100.454(1)°, V 461.30(6) Å3, space group C2, Z = 2, was refined to R1 = 1.99% using MoKα X-radiation. In the space group C2, there are three octahedrally coordinated M sites in the 1M mica structure: the M(1) site is occupied by Li+ and minor vacancy that is likely locally associated with Ti4+ at the M(2) site; the M(2) site is occupied dominantly by Al3+, with other minor divalent to tetravalent cations; the M(3) site is completely occupied by Li+. In the space group C2, the structure is completely ordered. Each non-bridging O2– ion is surrounded by an ordered arrangement of 2Li+ + Al3+ + Si4+ with an incident bond-valence sum of 1.95 vu (valence units). The F– ion is coordinated by Li+ + Li+ + Al3+ with an incident bond-valence sum of 0.84 vu (values around F– generally tend to be lower than ideal). Thus, the valence-sum rule is satisfied, both long range and short range. In the space group C2/m, there is long-range order but not short-range order. There are three different short-range arrangements, one of which has bond-valence deficiencies of 0.38 and 0.49 vu around the non-bridging O2– ion and the F– ion, destabilizing the structure relative to the more ordered arrangement of the C2 structure, which conforms more closely to the valence-sum rule. The drive to lower the symmetry in polylithionite-1M from C2/m to C2 comes from the short-range bond-valence requirements of the structure.

A systematic change in the partial molar enthalpy of mixing (Δh¯Hmix) and partial molar excess entropy (Δs¯Hex) for dilute hydrogen-metal systems at the solid-liquid transition is reported. Expressions for Δh¯Hmix and Δs¯Hex are derived from the Fowler model of hydrogen solubility, and the change in Δs¯Hex at melting is bounded. The theoretical bound is in agreement with measured data. A connection is made between the change in Δs¯Hex and short range order in the metal-hydrogen system., National Science Foundation (Grant 1562545)

The short-range order in Li–Al–(OH−, F−) tourmalines with Y[Li/Al] ≈ 1 and different Na/Ca ratio was investigated by means of bond valence theory, experimental IR spectroscopic data and the results of X-ray single crystal diffraction. The stability of the arrangements coordinating W- and V-crystallographic sites occupied by OH−, F− and O2− ions was refined. A unified model of assignment of absorption bands in the IR spectra to the local arrangements (clusters) was suggested taking into account the first and the second OH−coordination spheres. The types of local cation arrangements around the W- and V-anion sites, alongside with clusters ratio and their distribution were brought out. The short-range order in Li–Al tourmalines controlled not only by local restrictions of the bond valence theory, but also by the long-range order was described.

In this work results of studies on the short-range order and on the atomic dynamics in different stable and undercooled glass-forming metallic melts are reviewed. In order to undercool the melts deeply below the melting temperature and to avoid chemical reactions of the melts with crucible materials, the samples are containerlessly processed utilizing the electromagnetic or the electrostatic levitation technique. The short-range structure of the melts is studied by neutron diffraction, while the atomic dynamics are investigated by quasielastic neutron scattering. The relationship between short-range structure and atomic dynamics is discussed within the mode coupling theory of the glass transition. We will show that taking the time- and space-averaged structural information provided by measured partial structure factors as an input, mode coupling theory is able to explain the experimental results concerning the activation energies for self-diffusion and the coupling/decoupling behavior of the self-diffusion coefficients of the different alloy components.

The short/long-range order formation in Fe1-x-Co-x (x < 0.3) alloys has been studied by the nuclear magnetic resonance (NMR) technique, as well as ab initio based atomistic simulation. The NMR m ...

We study magnetic short-range order in Fe and Ni above the Curie temperature using the nonlocal dynamic spin-fluctuation theory with self-consistent calculation of the self-energy. We calculate the spatial correlation function of Fe and Ni at nearest neighbours, next-nearest neighbours, etc., in a wide range of temperatures. Our results are in agreement with neutron scattering experiments but give a larger short-range order compared to classical spin models. We show that the spatial spin correlator decreases ten times at distances of about 6 A in Fe and 8 A in Ni at T / T C = 1.1 and short-range order remains well above the Curie point.

An expression for calculating the critical temperature of order-disorder transition in face-centered cubic alloys is developed with accounting of pairwise interatomic potential in the first eleven shells. Obtained expression was applied for the estimation of critical temperatures at Cu3Au, CuAu, and CuAu3alloys in comparison with experimental data from phase diagram of Cu-Au system. Magnitudes of the pairwise interatomic potential in considered alloys was computed using values of the short-range order parameters which were experimentally obtained from X-ray diffuse scattering intensity. In this computation, the Krivoglaz-Clapp-Moss approximation and Cowley equations were applied.

To clarify the critical role of chemical short-range order on the formation of shear bands in metallic glasses, atomistic simulations are performed on Pd82Si18 and Cu50Zr50 with different cooling history. It is found that shear bands are prone to form in samples with higher level of chemical short-range order. The magnitude of stress overshoot in shear stress-strain curve and the spatial fluctuation of short-range chemical composition are proposed to characterize shear banding susceptibility and chemical short-range order, respectively. A quantitative correlation is therefore established between shear banding and chemical short-range order. The microstructural origin of the correlation is discussed.

The diffuse scattering of X-rays is used to study the short-range order in a polycrystalline solid solution of Ni—14 at % Pt. Its parameters are determined on the initial six coordination spheres. We experimentally prove that short-range order of the L12 type occurs. The ordering energies for the considered coordination spheres are estimated. The stabilizing role of short-range order in the formation of the crystal structure of Ni—14 at % Pt alloy is shown. The temperature of the order—disorder phase transition is estimated.

Crystalline solids are characterized by periodic structures, resulting in a diverse assortment of crystal structures that exhibit a wide variety of properties. Here we report short-range order, which results in characteristic diffuse bands in electron diffraction patterns, in a series of defective 19-electron half-Heusler compounds for the first time. The co-existence of the vacancy-related short-range order and the crystalline long-range periodic structure makes these defective half-Heusler compounds promising thermoelectric materials with low thermal conductivity and high electrical conductivity simultaneously. This new finding provides important insights into the intrinsic nature of defective HH compounds, and also proposes a possible strategy for tuning the degree of ordering to offer great potential for further improvement of thermoelectrics.