Electronic band structure and carrier effective mass in calcium aluminates

First-principles electronic band structure investigations of five compounds of the CaO‐Al₂O₃ family, 3CaO∙Al₂O₃, 12CaO∙7Al₂O₃, CaO∙Al₂O₃, CaO∙2Al₂O₃, and CaO∙6Al₂O₃, as well as CaO and α-, θ-, and κ‐Al₂O₃ are performed. We find that the conduction band in the complex oxides is formed from the oxygen antibonding p states and, although the band gap in Al₂O₃ is almost twice larger than in CaO, the s states of both cations. Such a hybrid nature of the conduction band leads to isotropic electron effective masses which are nearly the same for all compounds investigated. This insensitivity of the effective mass to variations in the composition and structure suggests that upon a proper degenerate doping, both amorphous and crystalline phases of the materials will possess mobile extra electrons.