The pressure influence on structural parameters and elastic properties of rock-salt CaX (X=S, Se and Te) materials

Abstract

The structural parameters and elastic properties of rock-salt CaX (X = S, Se and Te) materials are explored employing the CASTEP code established on the density functional theory (DFT). The energy of exchange-correlation is calculated using the generalized gradient approximation (GGA). The convention between our outcomes related to the lattice parameter and experiment is 0.50%, 0% and 1% for CaS, CaSe and CaTe materials, respectively. The lattice constant augments when proceeding from CaS to CaSe to CaTe. This lowers also the modulus of compressibility. The studied materials present a weak elastic constants for C12 and C44. This signalizes that these materials are supplementary reluctant to the unidimensionelle compression than to the perversion of cisaillement. C11 increases very rapidly. However, C12 and C44 increase very slowly. The material stability of the structure for the results of interest is stable at zero pressure. A phase transition will happen at pressures of 25.20 GPa for CaSe and 20.10 GPa for CaTe. No phase transition has been detected for CaS up to 30 GPa. All studied materials have comported as fragile in the pressure range 0 to 4 GPa. The variation of energy under any little deformity is positive. The anisotropy indicates that all materials are anisotropic in the pressure range up to 30 GPa and they are more rigid along the axes 〈100〉.