Effects of Nb concentration on Nb-doped anatase TiO2: DFT + U calculations

The crystal structure, formation energy, electronic structure, electrical properties and optical properties of anatase TiO2 with various Nb concentrations were studied by first-principles calculations based on density functional theory (DFT) and the Hubbard U correction. Firstly, the crystal structures of TiO2 with various Nb concentrations were optimized successfully. The higher concentrations of Nb facilitate the synthesis of Nb-doped TiO2 systems in an O-rich environment. Furthermore, the band structures and density of states prove that the electronic structure of Nb-doped TiO2 is mainly transformed by the hybridization of Ti 3d, Nb 4d and O 2p states. Next, broadening of the valence band and occupied states at the bottom of the conduction band enhance the conductivity of Nb-doped TiO2, and the conductivity reaches the maximum value at the high Nb-doping concentration of 6.25 at.%. Last but not least, the calculated optical properties show that the absorption edge of Nb-doped TiO2 produces an blue shift. TiO2 with Nb-doping concentration below 14.58 at.% exhibits the high transmittance in the visible region.