Electronic structure of (Cu+N) co-doped anatase TiO₂ at the surfaces of (001) and (101): A first-principle study

Abstract

Electronic structures of 3d transition element Cu-doped anatase TiO₂ and (Cu+N) co-doped anatase TiO₂ are studied by using the first-principle method based on density functional theory. The calculations are performed by using the projector augmented wave method within the generalized gradient approximation as implemented in the VASP package. Different doping possibilities, for example, Cu doped in anatase TiO₂ supercell, Cu adsorbed on the surfaces of (001) and (101), Cu replacement on Ti sites at the surfaces and subsurfaces, Cu doped in the vacancy of horizontal and longitudinal directions, as well as six kinds of (Cu+N) co-doping methods, are studied in detail. The formation energies, band structures and electronic density of states are investigated and the most stable structure is obtained theoretically. The results suggest that Cu prefers to be doped at the vacancy of the TiO₂ (001) surface, while N atom prefers to substitute O sites at the horizontal direction. The calculated results also show that 3d<italic> </italic>orbital of Cu interacts with O-2p and N-2p orbitals, which leads to the fission of the O-2p and N-2p orbitals and produces new electronic states in the band gap, and also the band gap of TiO₂ becomes narrow. By analyzing the band structure and the densities of states, it is found that the band edges of system have been modified by (Cu+N) codopants. The valence band edge moves up and close to the Fermi level, while the conduction band edge moves down slightly, which make the band gap narrow. Charge transfer properties are also discussed to show the bond effects after doping. The appearance of the compensated donor (Cu) and acceptor (N) pairs after (Cu+N) co-doping could prevent the recombination of photo-generated electron-hole pairs, which can improve the photoelectrochemical performance of TiO₂.

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