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.%.