Ab-initio study of phase stability, thermodynamic and elastic properties of beryllium sulfide under extreme condition

Abstract

Pressure-induced phase transition, thermodynamic and elastic properties of BeS are investigated by ab-initio method and quasi-harmonic Debye model. The phase transition of BeS from ZB to RS occurs at 51.45GPa accompanied by 11.23% volume collapse. Phase transition is due to S atom’s weakened electron attraction. Once the shared charge center of shared electron reaches 0.58, will the phase be unstable. Cv is much larger at high temperature, and reduces with pressure. At intermediate temperature, Cv reduces with P rapidly, but the decreasing is unobvious under too low or too high temperature. At sufficiently low temperature, Cv is proportional to T3; at intermediate temperature, Cv rises sharply; at high temperature, Cv reaches to Dulong–Pettit limit. The maximum expansion coefficient is less than 1.5×10−5K−1. Pressure will suppress expansion caused by high temperature evidently. Elastic constants of BeS rise with pressure. Shear moduli (c and c′) of ZB keeps steady relatively; the c′ of RS increases with pressure clearly.