Microscopic origin of the extremely low thermal conductivity and outstanding thermoelectric performance of BiSbX3 (X = S, Se) revealed by first-principles study

Abstract

In this paper, we performed comprehensive investigations of both the thermal and electrical transport properties of BiSbSe₃ and BiSbS₃ by using first-principles calculations and Boltzmann transport theory. Due to the repulsion between the lone-pair electrons of Sb and the p orbital of Se(S), both BiSbSe₃ and BiSbS₃ show strong anharmonicity with Grüneisen parameters of 1.90 and 1.79, respectively. As a result, these two materials possess extremely low lattice thermal conductivities. Meanwhile, both BiSbSe₃ and BiSbS₃ exhibit similar anisotropic thermal transport behaviors, which is due to the smaller phonon group velocities along the a axis. The predicted highest ZT values at 750 K are 2.9 for n-type BiSbSe₃ and 1.2 for p-type BiSbS₃. Our calculations provide insights into the origin of the extremely low thermal conductivity in BiSbSe₃ and BiSbS₃, which is meaningful for exploiting high performance thermoelectric materials with low thermal conductivity.