Electronic structure of M-doped ZnGa₂O₄ (M = Mn, Fe, Co, Ni) spinel using DV-Xα method

Molecular orbital (MO) calculations were carried out by the DV-Xα method to clarify the effect of an impurity on the electronic structures of ZnGa₂O₄ crystal. In the calculation for M-doped ZnGa₂O₄ (M being one of the following metals: Mn, Fe, Co, Ni), the new energy states originating from M 3d orbitals appear in the band gap. The gap states split into two energies; the lower state is doubly degenerate e states, the higher one being triply degenerate t₂ states, as predicted by the ligand field theory. These levels tend to decrease in energy as the atomic number of the transition metal ion increases. Furthermore, M-O bonding becomes more covalent with increasing the atomic number of the transition metal ion.