Influence of polymorphism on the lattice thermal conductivity of Ga2O3

In this paper, the lattice thermal conductivity of Ga2O3 in its β, α, ɛ(κ), and γ phase is systematically investigated based on the first principles calculation and iterative approaches to solve the phonon Boltzmann equation. The results indicate that the crystal microstructure of Ga2O3 has a significant effect on the lattice thermal conductivity. In addition, the results also find that γ-Ga2O3 has an ultralow lattice thermal conductivity within the temperature range from 50 to 700 K. As for γ-Ga2O3, the obtained lattice thermal conductivity at room temperature (300 K) is 0.1189 W/(m K) along the [100] and [010] directions, and 0.1159 W/(m K) along the [001] direction. The lattice thermal conductivity exhibits the following order: γ-Ga2O3 ≪ ɛ(κ)-Ga2O3 < α-Ga2O3 < β-Ga2O3. The disruptive effect of Ga3+ cation vacancies on the spinel structure's symmetry is responsible for the ultralow lattice thermal conductivity observed in γ-Ga2O3. This disruption increases the complexity of the lattice and hampers the propagation and scattering of phonons. Another contributing factor is the presence of weak chemical bonding, which intensifies the oscillation of Ga atoms. The results of this study have significant implications for further investigating the factors influencing the thermal conductivity of Ga2O3 and developing thermoelectric materials.