Nature of Disordering in γ-Ga_{2}O_{3}.

Polymorphs commonly exist for various materials, enabling phase engineering for diverse material properties. While the crystal structures of different polymorphs can, in principle, be experimentally characterized, interpreting and understanding complex crystal structures can be very challenging. Using Ga_{2}O_{3} as a prototype, here we show that the crystal structure of γ-Ga_{2}O_{3} has long been misinterpreted from either theory or experiment. By lattice mapping based crystallographic analysis and combinatorial crystal structure search, we reveal the nature of γ-Ga_{2}O_{3} as a disordered form of β-Ga_{2}O_{3}, which is further confirmed by Monte Carlo simulations of the order-disorder transition. Our insights are critical for correct interpretation and characterization of γ-Ga_{2}O_{3}, and the established physics is expected to be widely applicable to a variety of polymorphic systems.