Investigation of doping effect on the local structure and photocatalytic activity of SrTiO3

In the present study, we investigated the relation between photocatalytic properties and local structures of SrTiO3 perovskite oxides doped with 0.1–10 at.% indium. From the measurement of photocatalytic degradation of methylene blue (MB), it was found that the In3+ doping improved the photocatalytic activity of SrTiO3. To understand the defect structure arising from In doping, local structures in SrTiO3 were investigated by the time-differential perturbed angular correlation (TDPAC) method with the 111Cd(← 111In) probe. Part of the thermally diffused In ions occupy defect-free substitutional Ti sites in cubic SrTiO3 structure; however, most of the doped In ions occupy the substitutional Ti4+ sites where oxygen vacancy exists in the vicinity of the probes. It was also suggested that the concentration of In3+ reached the solubility limit in SrTiO3 and formed a secondary phase at 1 at.% In doping, resulting in the suppression of photocatalytic activity of SrTiO3. For the photocatalysis of In-doped SrTiO3 synthesized by the conventional solid-state reaction, we found that optimal indium doping is in the concentration range of 0.1–1 at.%.