Structural comparison between β-Ga 2 O 3 and γ-Ga 2 O 3 : implications for radiation effects

This report analyzes the crystal structures of two polymorphs of gallium sesquioxide, β-Ga2O3 and γ-Ga2O3, to identify structural similarities that may help to rationalize a β→γ polymorphic phase transformation that is observed under displacive radiation damage conditions. A layered atom structure model is used to reveal strong similarities between anion and cation arrangements in the β versus γ crystal structures. Additionally, this report compares arrangements of nearest neighbor Ga cations and structural vacancies surrounding a central O anion in β versus γ. This comparison reveals that, in the β phase, nearest neighbor cations and vacancies to a central O anion are completely ordered. Conversely, in the γ phase, cations and vacancies are highly (but not fully) disordered. This difference in the β versus γ crystal structures is consistent with a concept that β-Ga2O3 undergoes an order-to-disorder transition when the βγ polymorphic transformation occurs under irradiation damage conditions.