First principle study of anisotropic thermoelectric material: Sb2Si2Te6

Abstract

Layered thermoelectric (TE) materials have received widespread attention because of their inherent low lattice thermal conductivity and good TE properties. Recently, a new type of layered material ${\mathrm{Sb}}_2{\mathrm{Si}}_2{\mathrm{Te}}_6$ polycrystalline was reported to show high power factor ($\sim 10.6\mu \mathrm{W}{\mathrm{cm}}^{-1}{\mathrm{K}}^{-2}$ at 579 K) and low thermal conductivity (0.69–0.74$\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 823 K), which is a kind of very promising TE material. Considering that layered materials are usually anisotropic, we use first principles combined with Boltzmann’s transport equation to comprehensively predict the TE transport characteristics of single crystal p-type and n-type ${\mathrm{Sb}}_2{\mathrm{Si}}_2{\mathrm{Te}}_6$ in this study. The results show that the TE properties of ${\mathrm{Sb}}_2{\mathrm{Si}}_2{\mathrm{Te}}_6$ have obvious anisotropy. It has extremely low lattice thermal conductivity along the cross-plane direction. After the optimization of carrier concentration, the TE figure of merit of n-type ${\mathrm{Sb}}_2{\mathrm{Si}}_2{\mathrm{Te}}_6$ is much higher than that of the p-type. N-type ${\mathrm{Sb}}_2{\mathrm{Si}}_2{\mathrm{Te}}_6$ has good TE performance in the full temperature range [$ZT=1.38$ at 300 K, 3.54 at 500 K, 5.27 at 700 K (along the cross-plane direction); 1.97 at 300 K, 1.94 at 500 K, 3.08 at 700 K (along the in-plane direction)], and the optimal doping concentration at different temperatures is relatively close, showing its great potential in TE applications.