B1–B2 structural phase transition and elastic properties of UX(X = S,Se, and Te) compounds at high pressure

Abstract

Pressure induced structural phase transformation and mechanical properties ofNaCl-type (B1) to CsCl-type (B2) structure in uranium monochalcogenides (UX;X = S, Se, and Te) are presented. An effective interionic interaction potential is constructed,consisting of the long-range Coulomb and the Hafemeister and Flygare typeshort-range overlap repulsion extended up to the second-neighbour ions and thevan der Waals (vdW) interaction. Particular attention is devoted to evaluatethe vdW coefficients following the Slater–Kirkwood variational method, as boththe ions are polarizable. Our calculated results have revealed reasonably goodagreement with the available experimental data on the phase transition pressures(Pt = 81, 21, 13 GPa) and the elastic properties of UX(X = S, Se, and Te). The equation of state curves (plotted betweenV (P)/V (0) and pressure) for both the NaCl-type (B1) and CsCl-type (B2) structures obtained by us are infairly good agreement with the experimental results. The calculated values of the volume collapses(ΔV (P)/V (0)) are also closer to their observed data. The variations of the second- and third-order elasticconstants with pressure have followed systematic trends, which are almost identical tothose exhibited by the measured and observed data in other compounds of the NaCl-typestructure family.