Electronic Properties of Vanadium-Doped TiO2

The electronic properties of vanadium-doped rutile TiO2 are investigated theoretically with a HartreeFock/DFT hybrid approach. The most common oxidation states (V2+, V3+, V4+, and V5+) in different spin states are investigated and their relative stability is calculated. The most stable spin states are quartet, quintet, doublet, and singlet for V2+, V3+, V4+, and V5+ doping, respectively. By comparing the formation energy with respect to the parent oxides and gas-phase oxygen (?E), we conclude that V4+ (?E=145.3 kJ?mol-1) is the most likely oxidation state for vanadium doping with the possibility of V5+ doping (?E=283.5 kJ?mol-1). The energetic and electronic properties are converged with dopant concentrations in the range of 0.9 to 3.2?%, which is within the experimentally accessible range. The investigation of electronic properties shows that V4+ doping creates both occupied and unoccupied vanadium states in the band gap and V5+ doping creates unoccupied states at the bottom of the conduction band. In both cases there is a significant reduction of the band gap by 0.65 to 0.75 eV compared to that of undoped rutile TiO2.