Thermoelectric properties of Bi-doped SnS: First-principle study

Abstract

Although tin sulfide (SnS) is a potential thermoelectric material, it has not been applied commercially because of its low intrinsic electrical conductivity. Doping is a possible method to improve the thermoelectric properties by promoting its electron and phonon transport characters. In this work, we constructed calculation models for SnS and Sn1-xBixS to investigate their thermoelectric properties. Calculations of phonon and Grüneisen spectra show that Bi doping can reduce the lattice thermal conductivity by affecting lattice vibration in the temperature range of 300–800 K. After Bi doping, the electrical conductivity is enhanced tremendously by the huge promotion of carrier concentration, leading to a significant increase in the power factor PF. The results and analyses indicate that the influence of electron thermal conductivity on the ZT value is important. Although Bi doping increases PF by promotion of electrical conductivity, it simultaneously raises the electron thermal conductivity. However, Bi doping decreases lattice thermal conductivity, which can partially compensate for the negative effect of the increase in electron thermal conductivity on ZT values. The ZT value along the a axis increases from 0.16 to 0.36 after Bi doping at the Bi concentration of 1.56%. Such high ZT values can be attributed to the lowest thermal conductivity and the highest PF along the a axis. The calculation method and model can be extended to predict the thermoelectric performance of other materials.