Density functional characterization of the electronic structure and optical properties of Cr-doped SrTiO3

First-principles density functional theory electronic structure calculations were carried out for Cr-doped SrTiO3 to evaluate the effect of Cr-doping on the band gap states and the photocatalytic activity of SrTiO3. The defect formation energy is also investigated to determine the energy required for Cr-doping. Our results indicate that substituting Cr for Sr requires smaller formation energy than substituting Cr for Ti in the Cr-doped SrTiO3 structures and the Cr atoms energetically prefer to partially take up some Sr sites, simultaneously partially some Ti sites. Some Cr 3d gap states appear near the bottom of the conduction band in the Cr-doped SrTiO3 structures, which results in the decreased electron transition energy and thus the visible light absorption observed in the experiment. The correlations between the doped Cr atoms at different sites and the environmental O atoms may be responsible for the differences in the visible light photocatalytic activities for the doped SrTiO3. Further research demonstrates that different dopant concentrations in Cr-doped SrTiO3 do not bring significant changes in the electronic characteristics but may change a little the electron transition energy and weaken photocatalytic activity under visible light.