Structural stability and thermoelectric property optimization of Ca2Si

Abstract

By using an ab initio evolutionary algorithm structure search, low enthalpy criterion as well as stability analysis, we have found that cubic Fmm Ca₂Si can be achieved under a negative external pressure, and the cubic phase is dynamically and mechanically stable at ambient conditions and high pressure. From first-principle hybrid functional calculations, we have unraveled the direct bandgap nature and bandgap variation of cubic Fmm Ca₂Si with respective to pressure. Moreover, by combining with Boltzmann transport theory and the phonon Boltzmann transport equation, we have predicted that the figure of merit ZT for the cubic Fmm Ca₂Si reaches the maximum value of 0.52 by p-type doping. Our results provide an interesting insight and feasible guidelines for the potential applications of cubic Fmm Ca₂Si and related alkaline-earth metals silicides as the thermoelectric materials for heat-electricity energy convertors.