Structural, elastic, thermal and electronic properties of M2X (M = Sr, Ba and X = Si, Ge, Sn) compounds in anti-fluorite structure: first principle calculations

Abstract

First principle calculations of structural, elastic, thermal and electronic properties of M2X (M = Sr, Ba and X = Si, Ge, Sn) compounds in the anti-fluorite type structure are performed within the framework of density functional theory. The lattice constant, bulk modulus, derivative of bulk modulus and ground state energy are calculated. The calculated elastic properties reveal that Sr2Si, Sr2Ge, Ba2Si and Ba2Ge are classified as brittle, while Sr2Sn and Ba2Sn show ductile nature. It is noted that these compounds are elastically stable and the Debye temperature value decreases from Sr to Ba and from top to bottom in group IV-A of periodic table. From electronic charge density plot in the (110) crystallographic plane it is observed that in Sr2X, Sr shows ionic bond nature with X, while in Ba2X, Ba forms partially ionic and partially covalent bond with X. The density of states and the electronic band structures are also presented. We have found that these compounds possess narrow and direct band gaps. The values of the energy gaps obtained by using the modified Becke–Johnson approach are better than the values obtained from the generalized gradient approximation.