Lattice thermal conductivity of two-dimensional CrB4 and MoB4 monolayers against Slack’s guideline

Abstract

Two-dimensional (2D) CrB4 and MoB4 monolayers are typical graphene-like materials with excellent electrical transport properties and high structural stability. Yet, their thermal transport properties are unknown. By first-principles calculations and solving the Boltzmann transport equation iteratively, we report low lattice thermal conductivity (κl) of CrB4 and MoB4 monolayers. At room temperature, κl of CrB4 and MoB4 monolayers are 31.19 and 96.59 W/mK, respectively. This trend is against the well-known Slack’s guideline that the same type of materials with greater atomic mass generally have lower κl. The cause of this anomaly is analyzed from the first-principles harmonic and anharmonic parameters. It is surprising that no obvious correlation is observed between three-phonon scattering rates and mode Grüneisen parameters, despite their common determination by third-order interatomic force constants and one-to-one mode correspondence. The applicability of Grüneisen parameters to searching for novel materials with low κl is discussed from a theoretical viewpoint.