In x Ga 1−x ) 2 O 3 alloys show promise as transparent conducting oxides. Using hybrid density functional calculations, band gaps, formation enthalpies, and structural parameters are determined for monoclinic and bixbyite crystal structures. In the monoclinic phase the band gap exhibits a linear dependence on alloy concentration, whereas in the bixbyite phase a large band-gap bowing occurs. The calculated formation enthalpies show that the monoclinic structure is favorable for In compositions

more »

... to 50% and bixbyite for larger compositions. This is caused by In strongly preferring sixfold oxygen coordination. The formation enthalpy of the 50:50 monoclinic alloy is much lower than the formation enthalpy of the 50:50 bixbyite alloy and also lower than most monoclinic alloys with lower In concentration; these trends are explained in terms of local strain. Consequences for experiment and applications are discussed.