【Domestic Papers】Xinjiang University —— Influence of Polymorphism on the Lattice Thermal Conductivity of Ga₂O₃

Abstract

      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.

FIG. 1. Gallium oxide structure of various phases, (a) α-corundum structure, (b) β-monoclinic structure, (c) κ-orthorhombic structure (Pna2₁), (d) γ-spinel structure.

FIG. 2. Phonon dispersion curves and projected state density distributions for different crystal phases of Ga₂O_3, (a) α-Ga₂O₃, (b) β-Ga₂O₃, (c) κ-Ga₂O₃, (d) γ-Ga₂O₃.