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This study investigated the amorphous structure of a soda-lime-silicate glass sample (Na 2 O·2CaO·3SiO 2) utilizing in situ X-ray diffraction and Raman spectroscopy at pressures up to 30.3 GPa. These techniques provided insights into the structure of the glass under high pressure. Analysis of the short-range order of the glass in function of pressure was obtained from the pair distribution function, obtained from the diffractograms, and uncovered the emergence of a new amorphous phase at ∼10 GPa, identifiable through the appearance of new peaks in the data beyond this pressure value. Simultaneous measurements from Raman spectroscopy identified the elastic limit of the material at ∼6 GPa and were used to measure the inter-tetrahedral ∠Si–O–Si angle, which also displayed a ∂θ/∂P discontinuity within the 10 GPa range, due to the new amorphous phase. The study emphasized the potential of utilizing a monolithic glass sample within a diamond anvil cell, highlighting its ability to produce a sufficiently intense diffraction signal for structural analysis of glassy samples, provided that the angular aperture and energy employed are sufficiently high. [ABSTRACT FROM AUTHOR]

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Electronic interactions of the Group 2A elements with magnesium have been studied through the dilute solid solutions in binary Mg-Ca, Mg-Sr and Mg-Ba systems. This investigation incorporated the difference in the ‘Work Function’ (ΔWF) measured via Kelvin Probe Force Microscopy (KPFM), as a property directly affected by interatomic bond types, i.e. the electronic structure, nanoindentation measurements, and Stacking Fault Energy values reported in the literature. It was shown that the nano-hardness of the solid-solution α-Mg phase changed in the order of Mg-Ca>Mg-Sr>Mg-Ba. Thus, it was shown, by also considering the nano-hardness levels, that SFE of a solid-solution is closely correlated with its ‘Work Function’ level. Nano-hardness measurements on the eutectics and ΔWF difference between eutectic phases enabled an assessment of the relative bond strength and the pertinent electronic structures of the eutectics in the three alloys. Correlation with ΔWF and at least qualitative verification of those computed SFE values with some experimental measurement techniques were considered important as those computational methods are based on zero Kelvin degree, relatively simple atomic models and a number of assumptions. As asserted by this investigation, if the results of measurement techniques can be qualitatively correlated with those of the computational methods, it can be possible to evaluate the electronic structures in alloys, starting from binary systems, going to ternary and then multi-elemental systems. Our investigation has shown that such a qualitative correlation is possible. After all, the SFE values are not treated as absolute values but rather become essential in comparative investigations when assessing the influences of alloying elements at a fundamental level, that is, free electron density distributions. Our study indicated that the principles of ‘electronic metallurgy’ in developing multi-elemental alloy systems can be followed via practical experimental methods, i.e. ΔWF measurements using KPFM and nanoindentation.

• SFE of a solid-solution is closely correlated with its 'Work Function' level. • KPFM measurements give reliable results for correlating SFE and ΔWF levels. • KPFM measurements can show how alloying elements change ΔWF between eutectic phases. • WF difference between eutectic phases indicate the bond strength between them. • Electronic changes due to SRO can be revealed via ΔWF and nanoindentation readings. Electronic interactions of the Group 2A elements with magnesium have been studied through the dilute solid solutions in binary Mg-Ca, Mg-Sr and Mg-Ba systems. This investigation incorporated the difference in the 'Work Function' (ΔWF) measured via Kelvin Probe Force Microscopy (KPFM), as a property directly affected by interatomic bond types, i.e. the electronic structure, nanoindentation measurements, and Stacking Fault Energy values reported in the literature. It was shown that the nano-hardness of the solid-solution α-Mg phase changed in the order of Mg-Ca>Mg-Sr>Mg-Ba. Thus, it was shown, by also considering the nano-hardness levels, that SFE of a solid-solution is closely correlated with its 'Work Function' level. Nano-hardness measurements on the eutectics and ΔWF difference between eutectic phases enabled an assessment of the relative bond strength and the pertinent electronic structures of the eutectics in the three alloys. Correlation with ΔWF and at least qualitative verification of those computed SFE values with some experimental measurement techniques were considered important as those computational methods are based on zero Kelvin degree, relatively simple atomic models and a number of assumptions. As asserted by this investigation, if the results of measurement techniques can be qualitatively correlated with those of the computational methods, it can be possible to evaluate the electronic structures in alloys, starting from binary systems, going to ternary and then multi-elemental systems. Our investigation has shown that such a qualitative correlation is possible. After all, the SFE values are not treated as absolute values but rather become essential in comparative investigations when assessing the influences of alloying elements at a fundamental level, that is, free electron density distributions. Our study indicated that the principles of 'electronic metallurgy' in developing multi-elemental alloy systems can be followed via practical experimental methods, i.e. ΔWF measurements using KPFM and nanoindentation. [ABSTRACT FROM AUTHOR]

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 effect of S-content on the medium-and short-range order structure of Ge20Se80−xSx x = 0 , 15 , 30 at % , has been investigated by using high-energy X-ray diffraction. Medium-range order changes, as illustrated by the parameters of the first sharp diffraction peak, were discussed in the light of the microcrystalline model. The short-range order parameters have been obtained by the analysis of the first two peaks in the curve of the total radial distribution function. The current results indicate that S-atoms enter the host network of the stiffness composition (Ge20Se80) as compensation of Se-atoms. [ABSTRACT FROM AUTHOR]

Owing to the unique elemental character, Vanadium (V) has recently gained growing interest in the field of high entropy alloys. It is known that V benefits in the mechanical strength in alloys, accompanying by the unique elemental distribution behaviors. In this work, we concentrate on the mechanism of V's distribution characters in VFeCoNi, which is similar to that of Cr in CrFeCoNi, by evaluating element inherent electronegativity, charge transfer, atomic volume, Voronoi volume and the atomic stress resulting from the combined effects of these factors. Another unique character of electronic interaction in the t 2g and e g orbitals has been observed, which contributed to the fluctuation of atomic volume, thus enhancing solid solution strengthening. The tensile stress-strain tests show that the chemical ordering of V enhanced mechanical strength, especially for the grain boundary. Our work will provide new insights into the nanoscale distribution of V elements and the related macroscopic mechanical effects. [Display omitted] • V atoms exhibit a preference for sublattice sites. • Negative atomic stress of V atoms leads them tooccupy second-nearest neighboring sites. • V features the d electron flexibility. • Chemical ordering of V enhances mechanical properties. [ABSTRACT FROM AUTHOR]

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.

Face-centered cubic (fcc) high and medium entropy alloys (H/MEAs) have been shown to display superior mechanical properties at low temperatures, but significant improvement of their strength at high temperatures is required for industrial applications at extreme conditions. Recently, it has been shown that the breakthrough of the MEAs from equiatomic/near-equiatomic to non-equiatomic ratios leads to strong MEAs with good ductility. To design new H/MEAs, we consider two important factors that may influence strength: the chemical composition and chemical short range order (CSRO). In this study, we investigate the depinning stress (σc) as a criterion of strength of several compositions of VCoNi concentrated solid solution alloys (CSSAs) including V0.33Co0.33Ni0.33, V0.35Co0.2Ni0.45, V0.33Co0.17Ni0.5, and V0.17Co0.33Ni0.5 at 5 K and 300 K, using atomistic simulations. The chosen interatomic potential is shown to be reliable by comparing experimental/ab initio values and calculated parameters such as lattice constant, shear modulus, depinning stress, and temperature variation of stacking fault width for equimolar VCoNi. We find a good agreement between experimental friction stress and the depinning stress extracted from our results for equimolar VCoNi. Also, we find that Vclusters are the main pinning points of dislocations, and With a random distribution of atoms, we find that the alloy composition V0.33Co0.17Ni0.5 displays the largest depinning stress at both 5 and 300 K. Furthermore, to investigate how CSRO affects the strength of these alloys, we design CSRO into the microstructure using two different methods: In the first method, hybrid Molecular-dynamics/Monte-Carlo simulations were employed to simulate annealing at various temperatures. We observe that such simulations create CSRO so that it increases with decreasing annealing temperature. Recently, the CSRO motif and its concentration in an equimolar VCoNi have been determined by experiment. By modeling this experiment, we also implemented the CSRO into microstructure as the second method. By using both methods, the effect of CSRO on the magnitude of the depinning stress is discussed. It was shown that in both methods, CSRO significantly influences the strength of non-equimolar VCoNi alloys.

The reverse Monte Carlo (RMC) method has been widely used to gain 3D structural ordering information from experimental scattering data. Recently, we have introduced a novel application of RMC, viz., calculating thermodynamic properties of crystalline materials, construction of phase diagram and rapid estimation of the local structural order [Agrahari and Chatterjee, Physical Review E, 104, 044129 (2021).]. The method has been shown to be accurate and orders-of-magnitude faster than standard Monte Carlo simulations – this makes the approach quite promising. However, the error in RMC has never been systematically quantified. The goal here is to perform a thorough investigation into the types of error in RMC-based thermodynamic calculations, assess the relative magnitude of these errors, and develop strategies to improve the accuracy. Some of the conclusions presented are also relevant to previous experiment-based RMC implementations. [ABSTRACT FROM AUTHOR]

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 analysis of total S(Q) and partial SGe-Ge(Q) structure factors has shown that germanium atoms are present in two structural states: in the local environment of Fe(Ni) atoms and as part of clusters with structure of liquid germanium. Formation of these clusters is a result of displacement of Ge atoms outside the nearest environment of Fe(Ni) atoms due to competition effect between Al and Ge atoms. It has been established that ratio between partial nearest neighbour distances R1(Al-Ni)

The recent development of high-entropy alloys (HEAs) has opened a new avenue for alloy design by incorporating multiple principal elements into a simple crystal lattice. In HEAs, short-range chemical ordering may arise due to the different mixing properties of various constituent elements. In this work, we explore the trend of elemental arrangement in five typical body-centered cubic (BCC) multi-principal element alloys (MPEAs), including CrFeV, HfNbZr, TaVW, NbTaV, and TaTiV. Combining the Monte Carlo method and density-functional theory calculations, we calculated the evolution of short-range order (SRO) parameters in these alloys at 500 K. Our results demonstrated that all these MPEAs might develop a certain degree of SRO, depending on the mixing properties of different element pairs. Using a modified quasi-chemical model, we show that the SRO values in these MPEAs can be accurately predicted as long as the mixing enthalpy values between different atomic pairs are known. The presence of SRO has a profound impact on the local structure of MPEAs, which further alters the electronic and elastic properties of MPEAs. Our results provide a theoretical understanding of the basic alloy structure of novel MPEAs, which is an essential step toward tailoring their properties. [ABSTRACT FROM AUTHOR]

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.

[Display omitted] • Magnetic and electronic properties of RCo 3 B 2 compounds (R = heavy rare earth or yttrium) are investigated. • Small cobalt magnetizations, antiparallel coupled with those of the heavy rare earth elements, are evidenced. • Exchange interactions between R and Co moments are mediated by the rare earth R5d band polarization. • Effective cobalt moments are in the range 1.34 ÷ 1.84 μ B /Co atom, being rather little dependent on the rare earth partner. • Reminiscent R5d-Co3d interactions are present above the Curie points in compounds with R=Tb, Dy and Ho. The magnetic properties of RCo 3 B 2 compounds, with heavy rare earth elements were investigated using magnetic measurements and electronic structure calculations. The cobalt sublattice magnetizations are very small and antiparallel oriented to heavy rare earth moments. The contributions of cobalt moments to the Curie constants are also shown. The magnetic behavior of cobalt has been analyzed in the spin fluctuations model. The presence of short-range order above the Curie temperatures in RCo 3 B 2 compounds with R = Tb, Dy, and Ho has been attributed to reminiscent R5d-Co3d interactions. [ABSTRACT FROM AUTHOR]

The composition dependence of the lattice constant, a , in A x B 1- x O 2-0.5 x V 0.5 x , fluorite-type solid solutions (B = Zr, A = {Nd-Yb, Y}, V = oxygen vacancy) is characterized by changes in slope at x ~ 1/3, which cannot be described by existing models. Moreover, over the range of 0.15 ≤ x ≤ 1/3 the a vs. x data on all systems can be fitted with a linear equation, a = q + rx , with the same intercept, q , however, over the range of 1/3 ≤ x ≤ 1/2 the data bifurcate requiring different intercepts for A={Nd-Gd] and for A={Dy-Yb,Y} systems, implying steeper slopes for the first group. An adequate description is achieved via close-packing models involving two anion species, O2- and V, and three combinations of cation species, namely 8A, 7B, 8B (0 ≤ x ≤ 1/3), 7A, 8A, 7B (1/3 ≤ x ≤ 1/2) and 8A, 6B, 7B (1/3 ≤ x ≤ 1/2), that take into an account the constraint on the average coordination number, K (x), of K (x) = 8 – 2 x and two additional short-range order (SRO) constrains referring to vacancy-vacancy avoidance and vacancy-to-Zr association. The consistent fit to a vs. x data with these models requires the effective size of the oxygen vacancy to be larger than the radius of the oxygen anion by ~11%. The latter observation seems to play an important role in the understanding of structure-property relationships in A x B 1- x O 2-0.5 x V 0.5 x systems. Average coordination numbers of A and B cations in A x B 1- x O 2-0.5 x solid solutions (B = Zr; A = Ln , Y) deviate from the total average coordination number, K = 8 − 2 x , due to cation-vacancy association effects. Two contrasting solutions to the total average seem to exist within the range of 1/3 < x < 2/3. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In the present communication, the structural, microstructural, dielectric, and electrical (impedance, conductivity, polarization) characteristics of a new member of the Aurivillius family (Bi 2 YSnVO 9), processed through a high-temperature solid-state reaction method, have been reported. The formation and content of the compound at room temperature have been analyzed by using X-ray diffraction, Raman spectra, and energy dispersive X-ray spectrum. Analysis of frequency and temperature dependence of impedance and electrical modulus spectroscopic data and Nyquist plots has shown the contributions of grains and grain boundaries to the electrical properties of the prepared material. Detailed dielectric characterizations carried out in a broad spectrum of temperature and frequency have helped to explain the polarization and relaxation mechanism of the sample. The appearance of a hysteresis loop at room temperature and an increasing trend of dielectric constant with temperature to get expected peak at high temperature suggests the existence of ferroelectricity in the material, as of other members of the family. The activation energy of the sample is estimated as 1.19 eV which implies the activation of doubly ionized oxygen vacancy and the electrons released conduct via correlated barrier hopping mechanism. [ABSTRACT FROM AUTHOR]

In order to facilitate the understanding of the current research efforts and directions, this article first introduces the anomalous/problematic features of magnesium (Mg) and presents the recent approach of stacking fault energy (SFE)–based alloying element selection to lessen or eliminate this problem. Stacking fault energy computations via ab initio techniques necessitate an understanding of the free electron density distribution around atoms in a solid solution. Therefore, the assessment of the role of atoms by also considering the possibility of short range order (SRO) formation rather than a random solid solution has been revisited. Two possible types of SRO have been indicated. The relevant electronic interactions between the host Mg and the alloying element atoms are more clearly incorporated in a generally less known model by Miedema based on atomic-level thermodynamics rather than in Hume–Rothery rules. This more successful approach has also been addressed here. An evaluation founded on these premises, introducing the relatively more recent Mg alloy systems, has been given in terms of their achievements toward healing the problematic features of Mg alloys. The spectrum of alloy systems discussed ranges from doping of Mg to dilute alloy systems and to some rich alloy systems that offer remarkable properties. Among the first category, an unorthodox addition, doping with oxygen, and its implications, has been presented. The dilute alloy systems and their compositional design based on SRO and SFE together with their potentials have been reviewed. Among the rich alloy compositions, the most interesting precipitate systems, that is, the ones involving order and intermetallic formations, long-period stacking order phases, and quasi-crystals, have been discussed. Among all the alloying elements, one that deserves particular attention, calcium, with its implications such as being economical, offering environmentally friendly Mg metallurgy, and remedial effects on the shortcomings of engineering properties, and a closely related issue of calcium oxide (CaO) addition have been scrutinized. This article also makes an attempt to point out the future directions throughout the text, whenever possible.

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. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Directional elastic peak electron spectroscopy (DEPES) was used to reveal a short range order within the near-surface region of Pt(111). Experiments were performed at primary electron beam energies in the range from 0.9 keV to 1.8 keV. DEPES signal was recorded for a wide range of polar θ and azimuthal ø angles and then transformed to two-dimensional DEPES maps using stereographic projection. Theoretical DEPES distributions were obtained with the application of the multiple scattering (MS) theory. In MS calculations, the following parameters were varied: the inelastic mean free path λ, the radius around the emitter Rmax and the cones of smoothing M. The comparison of experimental and theoretical DEPES maps was performed by an R-factor analysis in order to find the best correspondence between the recorded and calculated distributions. The absolute minimum of the R-factor was found at rather small values of the radius around the emitter and large inelastic mean free paths. However, the obtained minimum was very shallow and took the form of a characteristic band in the Rmax(l) plots. Thus, other Rmax and λ values corresponding to the local R-factor minimum can also be to some extent used in computations. The cone of smoothing, which reflects the spread of primary beam directions before it strikes the sample, decreases at larger electron energies which scales with better electron focusing at larger Ep values. The discussion concerns the computation time associated with the mentioned parameters and the convergence of theoretical data. [ABSTRACT FROM AUTHOR]

The configurational entropy of mixing was calculated on the basis of the experimental diffraction data of melts of intermediate phases of Cu-In, Bi-Te, Fe-Ge, Ni-In and Bi-Tl systems. The entropy determined in such a way is the difference between the entropy of the melt and the one of an ideal gas of the same atoms being a measure of the degree of ordering of the melt. This value is in fact the excess entropy and differs from the classical definition of configurational entropy for crystals, defined as the difference between total entropy and its vibrational contribution. This approach was used to calculate such a configurational contribution to entropy in the case of one-component melts, but we tried to use it to study two-component melts too, replacing them by effective one-component liquids. Configuration entropy indicates the deviation of the topology of the real atomic distribution from the distribution in the gas of the same atoms, and in the case of binary melts, we have calculated the degree of deviation of the structural state of the melt from the structure of an ideal atomic solution. For a melt with an average atomic distribution, the excess configuration entropy is close to zero, and in the case of significant changes in the atomic distribution during the formation of the melt, it will be different. The transformation of the structure during the melt formation is accompanied by both a change in the interparticle interaction and the topology of the atomic distribution in comparison with the pure components, and these changes will be displayed in the experimental pair correlation function and hence in the configurational entropy of mixing. The concentration dependence of the excess configurational entropy within the concentration range corresponding to the existence of intermediate phases of the studied systems is characterized by minimal values and increases within concentration intervals in which eutectics and atomic solutions exist, that is the evidence of its correlation with equilibrium diagrams of the studied systems. [ABSTRACT FROM AUTHOR]

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 Ba 5 Bi 3 and Ba 4 Bi 3 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 Ba 4 Bi 3 associate and a weakly ordering BaBi 3 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. Snapshots of AIMD configurations for some connected Bi- and Ba-centered coordination polyhedrons in molten Ba 1- x Bi x with x = 0.025 (a), 0.05 (b), 0.10 (c), 0.90 (d), 0.95 (e), and 0.975 (f). The green and purple spheres represent Ba and Bi atoms, respectively. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• In computed phase diagram of CdSe x Te 1−x , consolute temperature = 325 K. • In CdSe x Te 1−x alloy, zincblende-wurtzite phase transition seen at x = 0.5–0.6. • Band gap lowest at 45% Se concentration to be around 1.41 eV due to bowing. • Significant clustering effects are observed in the Te/Se sublattice of CdSe 0.5 Te 0.5. • Negative bowing in effective hole mass contributing to high photo-current. We employ first principles methods based on density functional theory and beyond to study CdSe x Te 1−x alloys in the zincblende and wurtzite structures. From the cluster expansion formalism, we provide a detailed phase diagram showing a consolute temperature of 325 K, above which miscibility may be achieved. In the random solid solution, a zincblende-to-wurtzite phase boundary is found to range from Se concentrations of x = 0.5–0.6, in agreement with experiment, owing to increasing ionic character of the Cd-anion bonds. Disordered CdSe x Te 1−x configurations are modeled using special quasirandom structures, for which optoelectronic properties are computed with the hybrid HSE06 functional. Alloying is shown to cause strong bowing effects in the band gap and effective electron/hole masses, which we attribute to local structural distortions as illustrated by analysis of bond length distributions. Downward bowing in the band gap and effective hole mass of the zincblende structure is highlighted for its potential benefits in photovoltaics through increased net photocurrent. Absorption coefficients and reflectivity are also reported, showing promising results in zincblende CdSe x Te 1−x as indicated by substantial optical absorption throughout all Se concentrations. Lastly, we identify the presence of short-range order in CdSe x Te 1−x characterized by clustering among like atoms in order to minimize strain. The degree of clustering, which may be tuned by temperature, also controls the magnitude of the band gap. Therefore, we propose both composition and short-range order as effective tools to be utilized in the design and synthesis of improved solar cell absorber layer materials. [ABSTRACT FROM AUTHOR]

The atomic structure of amorphous (FeCoNi) 70 Ti 10 B 20 alloy synthesized by mechanical alloying was investigated using high energy synchrotron X-ray diffraction and inverse Monte Carlo simulations of pair distribution functions. Empirical potential structure refinement indicates a chemical short-range order at the length scales of 2.1–2.5 Å via local atomic arrangements forming deformed bcc-like clusters. The structural model obtained was described by bond lengths, coordination numbers, and bond angle distribution functions determined for the first neighbor atoms by x-ray scattering supplemented with 3D Monte Carlo simulations. • Chemically ordering in the short range is consistent with the experimental data. • Deformed bcc-like clusters form the local atomic arrangements. • A clear tendency for clustering around B and Ti atoms, not observed for Fe, Co, and Ni. • Structural motifs are investigated in detail. [ABSTRACT FROM AUTHOR]

A review of directional Auger (DAES) and directional elastic peak electron spectroscopy (DEPES) for investigations of the short range order within a near-surface region, similar to XPD, is presented. The application of these techniques requires nothing more than a retarding field analyser (RFA), commonly applied for the observation of low energy electron diffraction (LEED) patterns and Auger electron spectroscopy (AES) measurements, for in depth structural investigations associated with the short range order within a near-surface region. The physical principles, experimental set-up, as well as examples of experimental and theoretical results, the latter obtained with the use of single scattering cluster (SSC) and multiple scattering (MS) calculations adopted for primary electron plane wave, are shown. The scattering geometry and details concerning the scattering events of primary electrons in crystalline solids described by SSC and MS approximations are presented. Furthermore, some issues related to computation parameters such as: maximal scattering order, the maximum radius around the emitter, the number of cluster layers, and the averaging range considered in the calculations are also addressed. The presentation of the data obtained for clean and covered substrates in the form of polar profiles and stereographic intensity distributions enables the straightforward identification of the crystalline structure within the first few sample layers. The data presented in the form of anisotropy maps enable the identification of interatomic axes formed between substrate and adsorbate atoms at the interface. The contribution of different sample layers to the final DEPES signal is discussed. The comparison of DAES results with those obtained by means of x-ray photoelectron diffraction (XPD) is also presented. The qualitative and quantitative data analysis, the latter achieved by the comparison of experimental data with theoretical results by means of an R-factor analysis, is shown. The application of DAES and DEPES enables the characterization of the crystalline structure of adsorption systems from one monolayer (1 ML) up to thicknesses of the adsorbate limited by the inelastic mean free path of the registered electrons. Exemplary results are presented for adsorption systems, where the adsorbate and the substrate crystallize in the same (Ag/Cu, Pt/Cu, Cu/Pt) and in different (Cu/Ru) structures. The influence of the large unit cell of graphene formed on Ru(0001) on measured DEPES intensities is also shown. The detailed analysis of these results enables an identification of the short range order of atoms within the near-surface region, of adsorbate domains exhibiting different orientation with respect to the crystalline substrate, the determination of the domain populations, the relaxation and termination of the surface, the specific adsorption sites of adsorbed atoms, as well as the positions of atoms within a unit cell and their bond lengths (e.g. O / R u (10 1 ¯ 0) ). [ABSTRACT FROM AUTHOR]

Abstract The partial, total and average coordination number of atoms and, their neighbor distributions have been determined by the neutron diffraction method and application of the Reverse Monte Carlo modeling for experimental data in As 40 Se 60 , As 40 Se 30 S 30 and As 40 Se 30 Te 30 chalcogenide glasses. The total coordination number of the arsenic and chalcogen atoms is 3 and 2 for all compounds. The average coordination number is 2.4, i.e. the 8-N rule is performed and main structural element is AsSe 3 type pyramids, where depending on the chemical composition Se atom is replaced by S or Te atoms. The proportion of homopolar bonds is significant in As 40 Se 60 and As 40 Se 30 S 30 compositions, but sharply decreases in As 40 Se 30 Te 30. In all compositions the neighbor distances between arsenic and selenium atoms are the same within error: 2.35 Å (Se Se); 2.45 Å (As As) and 2.40 Å (As Se). The existence of medium range order (MRO) is proved by the analysis of the total and partial pair structural factors and correlation functions in above mentioned compositions. The geometric dimensions of the MRO area, i.e. the quasi-periodicity of density fluctuations in the MRO area and the size of nano-voids have determined within Elliott's void-based model. The change of the optical parameters by variation of the chemical composition has been established from the analysis of the optical transmission spectra. Highlights • Local structure of As-Se-Te and As-Se-S glasses was investigated. • The main role in the formation of the MRO region belongs to the Se Se bonds. • The neutron diffraction and optical studies show correlation between the optical band gap (Eg) and local structure. • The existence of medium range order (MRO) is proved by the analysis of the total and partial pair structural factors and correlation functions. [ABSTRACT FROM AUTHOR]

Abstract The atomic level structures of ternary 0.2Na 2 O + 0.8[xBO 3/2 + (1-x)GeO 2 ] glasses have been carefully examined for the first time using a combination of Raman, infrared (IR) and 11B magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopies. It was found that, like in other mixed glass former (MGF) systems, there is an unequal sharing of the sodium oxide between the two glass formers, B and Ge, across this series 0 < x < 1. It is found that for all x > 0, the Na 2 O preferentially reacts with boron to create a larger number of tetrahedral boron, BO 4/2 −1 ≡ B4, units than would be found for a binary sodium borate glass of the same mole fraction, 0.20, of Na 2 O. In addition to this higher than expected fraction of B4 units as determined by the 11B MAS-NMR measurements, the Raman spectra further suggest the presence of high concentrations of octahedrally coordinated GeO 6/2 −2, Ge6, units in the GeO 2 rich end of this compositional series, x ≤ 0.2. Across this series, it is found that there are at most five short range order (SRO) structural units present in these glasses, BO 3/2 (B3), B4, GeO 6/2 −2 (Ge6), GeO 3/2 O−1 (Ge3), and GeO 4/2 (Ge4), where the superscript gives the number of bridging oxygens (BOs) bonded to the central atom. The composition, x, dependence of all of these SRO structural units were determined by combining the results all of these spectral techniques and requiring that the total sum of all the negatively charged SRO units balance the positive (+0.4) charges from the Na+ ions and that the total amount of B balance to 0.8×, the total amount of Ge balance to 0.8*(1-x), and the total amount of oxygen balance to1.8–0.4× as required by the stoichiometry of this compositional series. [ABSTRACT FROM AUTHOR]

The coordination difference between the unprotonated tertiary structures of a native (Tax) peptide and a number of its variants – all peptides presented by HLA-A201 and bound to the human A6 T cell receptor-was discovered to constitute a metric of pMHC–TCR functional avidity. Moreover, increasing coordination deviations from the index were found to flag correspondingly weakening immunological outcomes of the variant peptides. The prognostic utility of the coordination difference of unprotonated tertiary structure was established to operate strictly on the peptide scale, seizing to be of relevance either to the immediate peptide environment (i.e. within the realm of peptide short range order, within 7 Å of any peptide atom) or over the entirety of the pMHC–TCR complex. Additionally, the imprint of peptide immunological identity was expressed both by the total coordination as well as by its C–C partial.

Interaction between 2, 3, 5 and 7 atomic layers of gold and a (111) silicon surface was investigated with the molecular dynamics simulation method. The simulation of the diffusion interaction between gold and silicon in the temperature range 425–925 K has been carried out. The peculiarities of the concentration changes of the interacting components and the atomic density at the boundary of two phases in the direction perpendicular to the crystalline surface were established. By means the formalism of quasi two dimensional partial pair correlation functions the atomic structure of the diffusion region was analyzed. The formation of the alloy of eutectic composition within the gold-silicon interlayer was established. It was shown that the inter-phase mixing in various temperature intervals occurred according to different diffusion mechanisms.

The atomic environment and stability of an amorphous Cr25Nb75 alloy was studied on the basis of average atomic coordination, average cluster number density as well as cluster radial distribution of these quantities based on Reverse Monte Carlo fitting of multiple total scattering datasets. A number of the most representative clusters of the RMC supercell were isolated and relaxed via Density Functional Theory. Average coordination of both Cr and Nb atoms was similar, possibly due to the similarity of their covalent radii. Also, the histograms of average coordination of both species suggested binomial distributions, possibly reflecting two separate modes of atomic bonding. Cr-centered clusters were found to be more cohesive than Nb-centered ones and overall cluster stability appeared to be correlated to minority Cr valence populations.

A study of molten Ni 1−x M x (M = Ta, W, Re, Os, Nb, Mo, Ru, Ti or Cr) at 1773 K was carried out by ab initio molecular dynamics simulation. Static structure factors, pair correlation functions and bond-angle distribution functions were calculated. Chemical short range order, the structure of coordination short range order (SRO), compactness of coordination shell and electronic density of states were studied. Hetero-coordination is preferred in molten Ni 1−x M x (M = Ta, W, Re, Nb, Mo, Ti or Cr), while, self-coordination is preferred in molten Ni 1−x Os x and Ni 1−x Ru x . The affinity between unlike species in molten Ni 1−x M x is decreasing with solute species shifting to the right in the periodic table. The structure difference between M- and Ni-centered coordination SROs is narrowed when solute species shifts to the right in the periodic table. With an increase of solute concentration, the affinity between bonding Ni-M and Ni-Ni atomic pairs both decrease, the solute and solvent centered coordination shells both become looser, in general. The structures of locally favored coordination SROs in molten Ni 1−x M x are diversified and independent of the structure of crystal state. Few FCC- and HCP-type coordination SROs are found in these melts. No BCC type coordination SRO is detected. For these melts, the compactness difference of solute- and solvent-centered coordination shells is correlated with the equilibrium partition coefficients, k 0 , of solute elements. Namely, when the solute centered coordination shell is averagely denser than the Ni centered one, k 0  < 1, vice versa. Our findings shed light on understanding the nature of segregation from the aspect of molten structure at atomic scale. [ABSTRACT FROM AUTHOR]

The ability of alloy 70Ni-27.5Fe-2.5Cr to form an ordered crystalline structure upon application of elevated temperature and the resulting effects on a variety of physical properties such as magnetism, strength, electrical resistance, and specific heat are well known. This paper demonstrates that strain gages made with 70Ni-27.5Fe-2.5Cr foil with an ordered crystalline structure have both high gage factors and high thermal outputs. The thermal output for strain gages made of 70Ni-27.5Fe-2.5Cr foil is demonstrated to be about 1,374 μΩ/Ω/K. The gage factor is nonlinear ranging in magnitude from about 5.0 to 3.6 for applied strains of 300 and 1,300 μE, respectively. The magnitude of gage factor and thermal output correspond with transformation of the crystalline structure from a state of disorder to a state of order. Comparisons to strain gages made with 36Ni-57Fe-7Cr foil are provided because of its use in the manufacturing of metal foil strain gages and their demonstrated high gage factors and high thermal outputs. Practical application for 70Ni-27.5Fe-2.5Cr strain gages is demonstrated by dead-weight loading of shear-beam load cells at low applied strain levels to minimise the effect of nonlinear gage factor; and Wheatstone bridge cancellation of high thermal output. [ABSTRACT FROM AUTHOR]