Microscopic description of the evolution of the local structure and an evaluation of the chemical pressure concept in a solid solution (original) (raw)
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Local structural evolution in the anionic solid solution ZnSexS1−x
Physical Review B, 2021
The century-old Vegard's law has been remarkably accurate in describing the evolution of the lattice parameters of almost all solid solutions. Contractions or expansions of lattice parameters of such systems depend on the size of the guest atom being smaller or larger than the host atom it replaces to form the solid solution. This has given rise to the concept of "chemical pressure" in analogy to the physical pressure. We have investigated using EXAFS the evolution of the local structure in terms of atom-pair distances extending up to the third-nearest neighbors in the family of compounds, ZnSe x S 1−x as an example of an anionic solid solution, in contrast to all previous studies focusing on cationic solid solutions. Our results establish several common features between these two types of solid solutions, while strongly suggesting that the concept of a chemical pressure is inaccurate and misleading. Most interestingly, we also find a qualitative difference between the cationic solid solutions, reported earlier, and the anionic solid solution.
Microscopic study of the pressure-induced structural phase transition of ZnTe
Physical Review B, 1996
We have performed ab initio pseudopotential calculations within the local-density approximation to investigate the structural phase transition of ZnTe under pressure. By calculating the total energy, atomic forces, and stress tensors, we theoretically determine the structural phase transition of ZnTe from the zinc-blende to the cinnabar to the orthorhombic structure under increasing pressure, which agrees well with experiment. We demonstrate that rotation of bonds toward lower-symmetry positions occurs at the critical pressure to relieve excessive strain.
Effects of applied pressure in ZnV2 O4 and evidences for a dimerized structure
Journal of Applied Physics, 2011
The series of V spinels ½A 2þ V 2 O 4 (A ¼ Cd, Mn, Zn, Mg) provides an opportunity to tune the V-V distance continuously, in the frustrated pyrochlore lattice of the spinel. This system has been shown to approach the metallic state when V-V distance is reduced. The proximity to the transition leads to a dimerized structure in ZnV 2 O 4 caused by lattice instabilities. A different manner to tune the V À V distance of this structure is to fix the A 2þ cation (in our case, Zn) and apply pressure. We have analyzed the evolution of the electronic structure of the system in the dimerized state. Such structure prevents the system to present a metallic phase at moderate pressures. We have also calculated the transport properties in a semiclassical approach based on Boltzmann transport theory. Our results support the validity of this structural distortion by providing a nice fit with experimental measurements. V
Local structure of condensed zinc oxide
Physical Review B, 2003
The high-pressure local structure of zinc oxide has been studied at room temperature using combined energy-dispersive x-ray-diffraction and x-ray-absorption spectroscopy experiments. The structural parameter u and the lattice-parameter ratio c/a of the wurtzite phase is given as a function of pressure and compared with results from ab initio calculations based on a plane-wave pseudopotential method within the density-functional theory. It is shown that an accurate study of ZnO requires the explicit treatment of the d electrons of Zn as valence electrons. In good agreement with present calculations, our experimental data do not show any variation of u( P) in the low-pressure wurtzite phase between 0 and 9 GPa, pressure at which the phase transition to the rocksalt phase occurs. Moreover, no dramatic modification of the r-phase K-edge position up to ϳ20 GPa is observed, indicating the absence of metallization. In view of all these results, theoretical models identifying the wurtzite-to-rocksalt transition as an homogeneous path are discussed.
Computational Materials Science, 2010
We have performed a systematical investigation on the pressure-induced phase transitions between zinc-blende and cinnabar phase for group IIB-VIA compounds: ZnTe, CdTe, and HgTe by ab initio plane-wave pseudopotential density functional theory (DFT). The calculations are performed within the local density approximation (LDA) in the scheme of Ceperley-Alder parametrized by Perdew and Zunger (CA-PZ). The obtained ground state properties and equation of state agree well with the available experimental data and calculated results. The transition pressures P t are determined through both the analysis of enthalpy variation with pressure and the slope of the common tangent of the energy-volume curves. The linear-response approach is used to calculate the phonon dispersions, which agree well with the experiments. Finally, the thermodynamic properties such as the free energy (F), the enthalpy (H), entropy (S) and heat capacity (C v ) are obtained successfully from the phonon density of state.
Journal of the American Ceramic Society, 2014
A systematic first-principles investigation, by using the density functional formalism with the nonlocal B3LYP approximation including a long-range dispersion correction, has been performed to calculate the structural and electronic properties and phase transitions under pressure of the three phases of ZnS (cubic zinc blende, ZB, hexagonal wurtzite, W, and cubic rock salt, RS). Numerical and analytical fittings have been carried out to determine the equilibrium unit cell geometry and equation of state parameters for the ZnS phases. The band structures, energy gap, density of states, and vibrational frequencies and their pressure dependences are investigated. The present results illustrate that both phases, W and ZB, present very similar enthalpy and the RS phase becomes thermodynamically more stable than ZB and W structures at 15.0 and 15.5 GPa, respectively. These phase transitions are accompanied by an increase of the first shell coordination number of Zn atom and by a cell volume collapse of 13.9% and 14.3% for ZB and W phases, respectively. The atomic contributions of the conduction and valence bands, as well the binding energy for the Zn 3d orbital have been obtained.
ZnTe at high pressure: X-ray-absorption spectroscopy and x-ray-diffraction studies
Physical Review B, 1993
ZnTe has been studied by x-ray-absorption spectroscopy at the Zn K edge and by x-ray diffraction up to 30 GPa. Crystallographic transitions were observed at 9.5 and 12 GPa by both techniques. The cornbination of x-ray-absorption near-edge structure, extended x-ray-absorption fine structure, and diffraction analysis enables us to determine the structure of ZnTe-II which is cinnabar with two pairs of 0 first neighbors at approximately the same distance (-2.558 A at 11. 7 GPa), maintaining the fourfold 0 coordination, the third pair of neighbors being much farther (-3.37 A). At 12 GPa ZnTe-II destabilizes and gives rise to a distorted rocksalt-type coordination, which remains stable at least up to 30 GPa. The succession of transitions is structurally reversible and takes place without amorphization. The hysteresis of the transitions has also been studied. A Murnaghan equation of state fitted to the values of the ZnTe cell parameter in ZnTe-I gives a bulk modulus of 50.5+3 GPa in good agreement with previous work.
On the electronic structure and equation of state in high pressure studies of solids
Bulletin of Materials Science, 2003
We discuss the high pressure behaviour of zinc as an interesting example of controversy, and of extensive interplay between theory and experiment. We present its room temperature electronic structure calculations to study the temperature effect on the occurrence of its controversial axial ratio (c/a) anomaly under pressure, and the related electronic topological transition (ETT). We have employed a dense 63 × × 63 × × 29 kpoint sampling of the Brillouin zone and find that the small (c/a) anomaly near 10 GPa pressure persists at room temperature. A weak signature of the anomaly can be seen in the pressure-volume curve, which gets enhanced in the universal equation of state, along with that of K-point ETTs. We attribute the change of slope in the universal equation of state near 10 GPa pressure, mainly to hybridization effects. The temperature effect in fact enhances the possibility of L-point ETT. We find that the L-point ETT is very sensitive to exchange correlation terms, and hence we suggest that further refinements in the theoretical techniques are needed to resolve the controversies on the ETT in Zn.
Physical Review B, 1985
The total-energy and pressure-volume relations are calculated nonrelativistically for Si, Ge, and a-Sn within the local-density-functional formalism, with use of first-principles nonlocal pseudopotentials. Ground-state static structural properties (total energy, lattice constant, and bulk modulus and its pressure derivative) are obtained and are in good agreement with experimental values. A prediction of these for cz-Sn from pressure determinations has not yet been reported. Its bulk modulus from both total-energy and pressure calculations is much smaller than that determined by experimental measurement. This confirms a recent theoretical prediction from other authors casting doubts on the experimental value. An assessment has been made on the advantages and disadvantages of pressure calculations over total-energy calculations and on the influence on the results of the size of all cutoff parameters and perturbative schemes used.