The intrinsic low lattice thermal conductivity in the rock salt SnSe

Abstract

The rock-salt IV-VI compounds usually have low thermal conductivity, while the orthorhombic Tin Selenide (SnSe) was reported to show extremely low lattice thermal conductivity (κL) and thus achieves a record high zT value. To understand why SnSe has low thermal conductivity and how important role played by the orthorhombic structure, we studied κL for both forms of SnSe, the rock salt and the orthorhombic, based on first-principles calculations and the Boltzmann transport equation. We found an even smaller value of κL for the rock salt structure, which establishes a possibility for even larger zT materials. Detailed analyses were performed on thermal properties for both structures. We attributed the low κL of the rock salt SnSe to its large Grüneisen parameters, which stem from the strongly anharmonic phonons. Our findings indicate the indecisive role that the orthorhombic structure is playing in achieving low κL for SnSe and provide fresh insight in understanding the thermal properties of SnSe.