Lattice dynamics and lattice thermal conductivity of CrSi 2 calculated from first principles and the phonon Boltzmann transport equation

Abstract

Efficiently decreasing the lattice thermal conductivity, κ L, is one of the main concerns in the field of thermoelectrics (TE). Herein, we theoretically investigate κ L for single-crystal and polycrystalline CrSi 2 using first-principles and the phonon Boltzmann transport equation. Though CrSi 2 is known as a potential TE material because of its reasonable power factor, controlling its κ L remains as a challenge to be solved. In this study, we discuss how to decrease κ L efficiently on the basis of the calculation. The phonon band structure and density of states are computed via harmonic calculation. In addition, the achievable lowest lattice thermal conductivity, κ L 0, and cumulative lattice thermal conductivity, κ cum, are estimated using the Cahill model and anharmonic calculation, respectively. We predict κ L 0 for CrSi 2 to be around 2.2 W m - 1 K - 1 at 650 K, which suggests that CrSi 2 is a potential TE material with high z T over 0.39 at 650 K. The phonon mean-free path dependence of κ cum indicates that the critical crystallite size for decreasing κ L for polycrystalline CrSi 2 is 70 nm at 600 K. In addition, it is revealed that the crystallite size should be as small as 7 nm to decrease κ L to half. These calculational findings offer useful insights into how to control κ L for CrSi 2.