First-Principles Study of Magnesium-Induced Phase Stabilization in Gallium Oxide Polymorphs.

In this study, we investigate the effect of Mg incorporation on the relative phase stability of the four primary Ga2O3 polymorphs using density functional theory (DFT) calculations, with the goal of rationalizing experimental observations suggesting that diffusion from MgAl2O4 substrates contributes to the relative stabilization of the γ phase. Mg incorporation is modeled up to 25% of Ga sites within supercells derived from fully relaxed unit cells of each polymorph. Our results show that, while β-Ga2O3 remains the thermodynamically most stable phase, the enthalpy and free energy differences between polymorphs decrease with increasing Mg content. The inherently disordered γ phase, with its high configurational entropy, becomes less energetically unfavorable under Mg substitution, suggesting that entropy-driven stabilization may facilitate its formation under high-temperature and/or nonequilibrium growth conditions, such as those previously reported. These findings provide a thermodynamic rationale for the experimental observation of the γ phase during epitaxial growth on MgAl2O4 spinel substrates.