Growth of large size SnSe crystal via directional solidification and evaluation of its properties

Abstract

SnSe crystal is an attractive Ⅳ-Ⅵ thermoelectric (TE) material. In this work, a Ø25 × 50 mm3 SnSe crystal was prepared using a directional solidification method. The as-grown crystal has standard Pnma structure at room temperature. The band gap Eg is determined to be 0.96 eV which agrees well with the theoretical value. Thermal expansion measurements show that SnSe crystal has significant anisotropic expansion behaviors. The linear thermal expansion along <010> and <100> directions are positive but is negative in <001> direction. Pnma-Cmcm phase transition has remarkable influence on thermal expansion performance. The electronic and thermal transport properties of SnSe crystal along (100) plane are investigated. It is found the highest power factor PF = 6.20 μWcm−1K−2 and the lowest total thermal conductivity ktot = 0.46 W/m-K both occur near Pnma-Cmcm phase transition temperature. Finally, the maximum ZT = 1.05 appears around 800 K suggesting SnSe crystal is a candidate for middle-temperature TE material.