Pressure induced phase transition (B1–B2) and elastic properties in alkaline earth BaX (X = S, Se and Te) chalcogenides

Abstract

Pressure induced structural aspects of NaCl-type (B1) to CsCl-type (B2) structure in alkaline-earth-chalcogenides (BaX; X = S, Se and Te) are presented. An effective interionic interaction potential (EIoIP) with long-range Coulomb and three-body interactions and the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbour ions and the van der Waals (vdW) interaction is developed. Emphasis has been given to evaluate the vdW coefficients following the Slater-Kirkwood variational method, as both the ions are polarizable. The lattice model calculations have revealed reasonably good agreement with the available experimental data on the phase-transition pressures (P t = 7.0, 7.0, 6.0 GPa) and the elastic properties of BaX (X = S, Se and Te). The equation of state curves (plotted between V (P)/V(0) and pressure) for both the B1and B2 structures obtained by us are in fairly good agreement with the experimental results. The calculated values of the volume collapses [ΔV(P)/V(0)] are also closer to their observed data. Further, the variations of the second order elastic constants with pressure have followed a systematic trend, which are almost identical to those exhibited by the observed data measured for other semiconducting compounds with B1 → B2 structural phase transitions.