Phase transformation and elastic behavior of MgX (X=S, Se, Te) alkaline earth chalcogenides

Pressure induced structural aspects of NaCl-type (B1) to CsCl-type (B2) structure in alkaline earth chalcogenides (AECs) magnesium chalcogenides (MgX; X=S, Se, and Te) are presented. An effective interionic interaction potential (EIoIP) with long-range Coulomb interactions and the Hafemeister and Flygare type short-range overlap repulsion extending up to the second neighbor ions and the van der Waals (vdW) interaction is developed. The vdW coefficients are evaluated following the Slater-Kirkwood variational method, as both the ions are polarizable. The present calculations have revealed reasonably good agreement with the available experimental data on structural transition (B1-B2 structure), the phase transition pressures P_t of 167 (MgS), 170 (MgSe), and 176 (MgTe) GPa as well the elastic properties. The calculated values of the volume collapses [ΔV(P)/V(0)] are also closer to their observed data. Further, the variations of the second and third 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 rocksalt (B1) type crystal structure. The Born and relative stability criteria is valid in Mg monochalcogenides.