Effect of Metal Doping on Electronic Structure and Visible Light Absorption of SrTiO₃ and NaTaO₃ (Metal = Mn, Fe, and Co)

First-principles density functional theory calculations have been performed on the electronic structure of M-doped SrTiO3 (M = Mn, Fe, and Co) to evaluate the effect of metal dopants on the geometric structure and electronic structure of SrTiO3. On the basis of the optimized structures of M-doped SrTiO3, our calculations show that substitutional M at the Ti site requires smaller formation energy than substituting M for the Sr site. Some Mn and Co 3d states appear below the bottom of the conduction band, and some Fe 3d states are located above the top of the valence band, which result in the decreased band gap with respect to the perfect SrTiO3, and thus, the visible light absorption is observed. Further research indicates that different dopant concentrations in M-doped SrTiO3 simulated by changing the size of the supercell do not bring significant effects in the electronic characteristics. On the basis of the calculated results on M-doped SrTiO3, we theoretically predicted that Mn-NaTaO3 is suitable for photo-oxidation of water and theoretically and experimentally found that the absorption edge of Fe-doped NaTaO3 was red-shifted to the visible region, which potentially could be active for overall water splitting under visible light irradiation.