Anisotropy in lattice thermal conductivity tensor of bulk hexagonal-MT2 (M = W, Mo and T = S and Se) by first principles phonon calculations

Abstract

Using the phonon spectra obtained from first principles calculations, and a modified empirical phonon–phonon Umklapp scattering expression at high temperature, the anisotropy in thermal conductivity is investigated for four semiconducting transition metal dichalcogenides. Our calculations confirm that the anisotropic thermal conductivity in H-MT₂ phases is mainly caused by strong directional dependence of phonon dispersions in a layered crystal. The heavy molecular mass can further increase the anisotropic feature of thermal properties. Acoustic phonon bands play dominate role in total thermal conductivity. It is found that longitudinal acoustic phonon band along provides at least 50% of total heat conductance. Contributions from remaining optical phonons are usually less than 1%. Thermal conductivities in [100] and [001] directions are calculated, and they are compared with other experimental and theoretical results. Our current method underestimates the intrinsic thermal conductivity. However, the large anisotropy in thermal conductivity is successfully captured by this simple and efficient approach.