Interplay of Structural and Bonding Characters in Thermal Conductivity and Born-Effective Charge of Transition Metal Dichalcogenides

Thermal transport in a material is governed by anharmonicity of crystal potential, which depends on the type of interatomic interaction. Using first-principles calculations, we report that lattice thermal conductivity (κ_latt) and its anisotropy (κ^x,y - κ^z) of transition metal dichalcogenides (TMDs) increase by orders of magnitude with the change of constituent metal atom from Zr/Hf to Mo/W. This unprecedented difference in κ_latt is substantiated by lower phonon group velocity, and 4 times larger anharmonicity of Zr/Hf based TMDs compared to Mo/W based TMDs. The sign and the absolute value of the Born effective charges, which emerges from the ionicity of the bonds, are found to be different for these two classes of materials. This leads to a significant difference in their interlayer van der Waals (vdW) interaction strengths, which are shown to be inversely related to the anisotropy in κ_latt.