First-principles study on the thermoelectric properties of Sr2Si and Sr2Ge

The development of environmentally friendly thermoelectric materials composed of earth-abundant, non-toxic elements is highly desirable in thermoelectric technology. In this study, the thermoelectric properties of n-type doped Sr2Si and Sr2Ge were systematically investigated using first-principles density functional theory calculations combined with semi-classical Boltzmann transport theory. The multi-band feature in the conduction band of Sr2Ge leads to a higher Seebeck coefficient than Sr2Si, resulting in a higher power factor. The phonon transport calculations using third-order perturbation theory predict ultra-low lattice thermal conductivity of 0.42 Wm−1K−1 for Sr2Si and 0.33 Wm−1K−1 for Sr2Ge at 900 K. The maximum figure of merit ZT is 1.44 for Sr2Ge, which is approximately 1.25 times higher than that of 1.15 for Sr2Si at 900 K. Our results indicate that the Sr2Ge and Sr2Si are promising candidates for high-performance thermoelectric materials.