Influence of pressure on phase transition, electronic and thermoelectric properties of SnSe

Abstract

Single-crystalline Tin Selenide (SnSe) is a good thermoelectric material with record-breaking figure of merit. Here, we reveal the influence of pressure on structures, electronic and thermoelectric properties of SnSe crystals by combining CALYPSO and first-principle calculation. In our results, the experimental synthetic phase Pnma-SnSe is the most stable structure at ambient pressure. However, a phase transition from Pnma to Cmcm occurs at about 22 GPa. More than 22 GPa, some new crystal structures (Pm3¯m-, C2/m- and Cmmm-SnSe) are revealed. The calculated phonon spectrum indicates their dynamic stabilities. From the energy band structures and density of states, it is found that only Pnma-SnSe phase is a semiconductor with bandgap of 0.79 eV which is benefit to suppress thermal activation of electrons in the conduction band, while the other phases are metallic. Moreover, our calculated Seebeck coefficient, conductivity versus time ratio and thermal conductivity indicate that SnSe in Pnma and Cmcm phases possess good thermoelectric properties with the ZT values of 0.9 and 0.8, respectively.