Room Temperature Cmcm Phase of Ca_xSn_1–xSe for Thermoelectric Energy Conversion

Abstract

While SnSe has been known as a high figure of merit (ZT) thermoelectric material at high temperatures, it has a low ZT at room temperature. SnSe has the β (Cmcm) phase at high temperature but the α (Pnma) phase at room temperature. In the present work, we first investigate the phase-transition temperature T c between the α and β phases of SnSe based on density functional theory calculations and obtain 740 K, which is close to the experimental value of about 800 K. We then consider Ca alloying in SnSe and calculate T c between the α and β phases of Ca x Sn 1−x Se. It is found that the Ca alloying lowers T c down to 220 K as the Ca content x increases up to x = 0.1875. For x > 0.14, Ca x Sn 1−x Se is obtained to have the β phase at room temperature, allowing it to be suggested as a room-temperature high figure of merit thermoelectric material.