Clarifying moderate and nearly isotropic lattice thermal transport in metastable δ-Ga2O3

The intrinsic lattice thermal transport of metastable δ-Ga 2 O 3 remains insufficiently clarified, although thermal transport in other Ga 2 O 3 polymorphs has been widely investigated. Because of its cubic bixbyite-type structure, δ-Ga 2 O 3 has been suggested to possibly possess relatively high and weakly anisotropic lattice thermal conductivity, but its actual conductivity magnitude and phonon-level transport mechanism remain unclear. Here, we construct a dedicated neuroevolution potential for single-phase δ-Ga 2 O 3 through active learning and validate it using density functional theory (DFT) phonon dispersion and first-principles ShengBTE thermal conductivity calculations. Homogeneous nonequilibrium molecular dynamics simulations show that the 300 K lattice thermal conductivities of δ-Ga 2 O 3 along the [100], [010], and [001] directions are 5.85 ± 0.15, 5.90 ± 0.20, and 5.90 ± 0.20 W m −1 K −1 , respectively, indicating nearly isotropic thermal transport within statistical uncertainty. The first-principles ShengBTE calculation gives a room-temperature lattice thermal conductivity of 5.96 W m −1 K −1 , further confirming that the lattice thermal conductivities of Ga 2 O 3 polymorphs follow the order β > α > δ > γ ≥ κ(ε). Compared with other Ga 2 O 3 polymorphs, δ-Ga 2 O 3 exhibits the weakest thermal anisotropy among the phases considered. Phonon-resolved analyses reveal that its nearly isotropic behavior is associated with similar mean free path and spectral thermal conductivity distributions along the three principal directions, whereas its moderate thermal conductivity mainly originates from shortened low-frequency phonon mean free paths. These results clarify the intrinsic thermal transport characteristics of metastable δ-Ga 2 O 3 and establish its position among Ga 2 O 3 polymorphs through comparative analysis with other phases.