Heat Capacity and Anisotropic Thermal Conductivity in Cr₂AlC Single Crystals at High Temperature

Abstract

The temperature dependences of both heat capacity and thermal conductivity in nano-lamellar Cr 2 AlC single crystals are measured using modulated photothermal radiometry and compared to first-principles calculations. The electronic contribution to the thermal conductivity of Cr 2 AlC single crystals is computed ab initio by determining the electronic transport coefficients using density functional theory and by solving the Bloch-Boltzmann transport equation with a temperaturedependent relaxation time. The lattice thermal conductivity is predicted going beyond the quasiharmonic approximation and considering renormalized second and third order force constant matrices, with anharmonic three-phonon scattering, isotopic scattering, and scattering by carbon vacancies. Isotopic scattering does not modify the lattice thermal conductivity. In contrast, even a small concentration of carbon vacancies induces a substantial decrease of the in-plane lattice thermal conductivity. The anisotropy measured in the thermal conductivity, with a ratio of ∼ 2 over the whole temperature range, is confirmed theoretically. This anisotropy seems to mainly arise from lattice contributions. A similar anisotropy is expected for other MAX phases with identical layered structures.