Origin of the structural diversity of M2O3 (M = Al, Ga, In)

• The structural stabilities of Al2O3, Ga2O3, and In2O3 have been studied.
• The Coulomb interaction and orbital interaction have been discussed.
• A subtle balance between the Coulomb and orbital interactions is revealed.
• The atom sizes and the valence electron energies play important roles.

Oxide materials have many unique physical properties, including structural diversity. For example, isovalent Al2O3, Ga2O3, and In2O3 are all important materials for technological applications. Although they have the same chemical composition, their crystal structures are all different. Using first-principles calculations, we investigate the structural stability of these oxides. We show that the structural diversity in oxides is due to a subtle balance between the Coulomb energy and the covalent binding energy in these materials. We find that the observed structural stability trends can be explained by the size of the cation atom and the energies of the cation valence electrons.