Electronic structure and defect states of transition metal doped rutile TiO2

The electronic structure and defect states of 6.25% transition metal (TM = Fe and Cc) doped rutile titanium dioxide were investigated by ab initio ultrasoft pseudopotential plane wave method based on density functional theory. When a Fe or Co atom was substituted for a Ti site of TiO2 lattice, additional unoccupied 3d-states of TM appeared as defect states in band-gap and occupied 3d-states represented metallic behavior (half-filled states). It was found that two occupied defect states and one half-filled defect state were the 3d-states of TM from the calculation of band decomposed charge density. The higher unoccupied states were hybridized with unoccupied oxygen 2p-states and located at the middle of band-gap.