Origin of low thermal conductivity in SnSe

We provide direct evidence to understand the origin of low thermal conductivity of SnSe using elastic measurements. Compared to state-of-the-art lead chalcogenides PbQ(Q = Te, Se, S), SnSe exhibits low values of sound velocity (similar to 1420 m/s), Young's modulus (E similar to 27.7 GPa), and shear modulus (G similar to 9.6 GPa), which are ascribed to the extremely weak Sn-Se atomic interactions (or bonds between layers); meanwhile, the deduced average Gr gamma uneisen parameter. of SnSe is as large as similar to 3.13, originating from the strong anharmonicity of the bonding arrangement. The calculated phonon mean free path (l similar to 0.84 nm) at 300 K is comparable to the lattice parameters of SnSe, indicating little room is left for further reduction of the thermal conductivity through introducing nanoscale microstructures and microscale grain boundaries. The low elastic properties indicate that the weak chemical bonding stiffness of SnSe generally causes phonon modes softening which eventually slows down phonon propagation. This work provides insightful data to understand the low lattice thermal conductivity of SnSe.