Thermal Properties of β-Ga₂O₃ from First Principles

Abstract

The thermal conductivity, bulk modulus, thermal expansion and heat capacity for bulk β-Ga₂O₃ are calculated from lattice dynamics using both a quasi-harmonic approximation and an anharmonic force-constant approach involving a solution of the linearized Boltzmann transport equation. The role of anharmonicity in β-Ga₂O₃ is determined to be small, which leads to the weak volume dependence of the calculated thermal conductivity. The negligible anharmonic contribution to the overall thermal conductivity is consistent with both thermal expansion measurements and also with comparisons between the quasi-harmonic and anharmonic methods. Phonon-mode-dependent Grüneisen parameters are found to be weakly dependent on temperature. Negative values of the mode Grüneisen parameters are found for certain low energy optical modes, but their net effect on the overall thermal expansion is insignificant. Bulk modulus as well as heat capacity are also given and found to be in agreement with experimental results.