Reinvestigation of the thermal properties of single-crystalline SnSe

The simple binary SnSe has been recently proposed as a prospective candidate for thermoelectric applications due to its exceptionally low lattice thermal conductivity. However, the thermal transport in single crystals was found to be significantly lower than in polycrystalline samples despite the presence of grain boundary scattering in the latter. In order to better understand the origin of this issue, we report here on a detailed characterization of the thermoelectric properties of a vertical-Bridgman-grown single-crystal of SnSe along the a, b, and c crystallographic axes in a wide range of temperatures (5-700 K). We find that the thermal conductivity features a pronounced Umklapp peak near 12K whose magnitude depends on the crystal orientation. Unlike prior reports, our results evidence a significant anisotropy between the a, b, and c directions with lattice thermal conductivity values reaching 1.2, 2.3, and 1.7W m(-1) K-1 at 300 K, respectively. While the fundamental reasons behind these differences remain unclear, our results indicate that the intrinsic lattice thermal conductivity of single-crystalline SnSe is likely significantly higher than previously thought. Published by AIP Publishing.