Effect of four-phonon interaction on phonon thermal conductivity and mean-free-path spectrum of high-temperature phase SnSe

The phonon thermal conductivity and mean-free-path (MFP) spectrum of high-temperature phase SnSe (β-SnSe) are studied using the Boltzmann transport equation and ab initio approaches. The particle picture for phonon transport in β-SnSe is revisited, and the imaginary phonon frequencies caused by the ground-state within conventional density-functional theory are resolved. We show that between 800 and 950 K, the in-plane and cross-plane thermal conductivity has an average decrease of 38% and 19%, respectively, when four-phonon scatterings are considered. This large suppression of phonon transport stems mainly from the strong redistribution scattering process. With both the phonon and electron MFP spectra revealed, a characteristic length of 10 nm is suggested to reduce the in-plane and cross-plane thermal conductivity by 18% and 52%, respectively, via nanostructure engineering without sacrificing the power factor.