Impact of crystal structure on the lattice thermal conductivity of the IV-VI chalcogenides

We present a detailed comparative study of the lattice thermal conductivity κ_latt of ten reported phases of the IV-VI chalcogenides GeSe, GeTe, SnSe and SnTe, calculated within the single-mode relaxation-time approximation based on third-order interatomic force constants. Differences in κ_latt are attributed quantitatively to the phonon group velocities and lifetimes, and differences in the lifetimes are further attributed to the averaged three-phonon interaction strengths and the “phase space” of allowed energy- and momentum-conserving scattering pathways. Our analysis reveals a complex dependence of the κlatt on the crystal structure: structures that constrain the tetrel atoms to locally-symmetric environments show strong phonon anharmonicity and short lifetimes, but in simple structures such as the rocksalt phase these are counterbalanced by large group velocities and a smaller phase space. We find that these competing effects are optimised for orthorhombic Cmcm SnSe, resulting in the lowest predicted κlatt across the ten systems examined. Our findings provide new insight into the interplay between crystal structure and lattice thermal conductivity, and allow us to propose some new guidelines for how to optimise the thermal transport of the IV-VI chalcogenides through crystal engineering.