Mechanical, vibrational and thermodynamic properties of Ba _x Sr _{1– x} O compounds: an ab initio study

In this paper, the effect of the barium molar concentration (x) in BaxSr1−xO compounds has been studied using the pseudopotential method calculations. We find that the structural parameter, elastic constants, phonon frequencies at Γ point, Born effective charge, and optical and static dielectric constants follow a quadratic law in (x). Based on the elastic stability, BaxSr1−xO compounds were found to be mechanically stable. The effect of concentration (x) on mechanical properties, such as hardness, brittleness, ductility, Debye temperature and anisotropy factor, is also examined. Anharmonic thermodynamic properties are investigated as a function of temperature and Ba atom molar composition (x) using the quasi-harmonic approximation. The volume thermal expansion does not exhibit any negative behaviour. The Grüneisen parameter increases with the concentration (x) of Ba atom, indicating that the Ba-rich compounds have relatively higher anharmonicity than the Sr-rich ones. Our results are compared with the existing experimental and theoretical findings.