Electronic properties of vanadium-doped TiO ₂

The electronic properties of vanadium-doped rutile TiO ₂ are investigated theoretically with a Hartree-Fock/DFT hybrid approach. The most common oxidation states (V ²⁺ , V ³⁺ , V ⁴⁺ , and V ⁵⁺ ) in different spin states are investigated and their relative stability is calculated. The most stable spin states are quartet, quintet, doublet, and singlet for V ²⁺ , V ³⁺ , V ⁴⁺ , and V ⁵⁺ doping, respectively. By comparing the formation energy with respect to the parent oxides and gas-phase oxygen (ΔE), we conclude that V ⁴⁺ (ΔE=145.3 kJ mol ^-1 ) is the most likely oxidation state for vanadium doping with the possibility of V ⁵⁺ doping (ΔE=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 V ⁴⁺ doping creates both occupied and unoccupied vanadium states in the band gap and V ⁵⁺ 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 TiO ₂ .