Theoretical investigation of the thermal conductivity of Ga2O3 polymorphs

Gallium oxide (Ga₂O₃) is a promising thermal preserving and heat-insulating material; understanding the thermal properties is important to improve its performance in technological applications. The thermal conductivities of Ga₂O₃ polymorphs labeled as α, β, δ, and ε are computed via the Boltzmann phonon transport equation (BTE) employing first-principles techniques. The lattice thermal conductivity tensor k of Ga₂O₃ for temperatures ranging from 50 K to 1000 K is derived using the second and third-order interatomic force constants (IFCs) for the potential based on a generalized gradient approximation (GGA), as well as the phonon dispersion relation, projected density of states (PDOS), and phonon group velocities. The results agree with the observed experimental values of rhombohedral polymorph β-Ga₂O₃ and with the previously calculated results of the other phases. At room temperature, the predicted thermal conductivity of the δ-Ga₂O₃ phase is 15.6 W/(m•K). By breaking down k into mode contributions, it is projected that the optical phonons contribute significantly to the lattice thermal conductivity because of a peculiar phonon dispersion relation.