Direct confirmation of the dopant site in indium-doped SrTiO₃ photocatalyst via atomic-scale analytical transmission electron microscopy imaging

Confirming the dopant site of In³⁺-doped SrTiO₃ (In–STO) is essential to reveal the mechanism of its photocatalytic activity. In a previous study, x-ray absorption spectroscopic analysis and theoretical investigations were performed to discuss the dopant site, and In³⁺–Ti⁴⁺ substitution was proposed. However, direct confirmation of the In³⁺ dopant site has not yet been reported. Here, we performed direct atomic-scale imaging of In–STO crystals via analytical transmission electron microscopy and revealed the dopant site based on real-space elemental mapping. The Ti and Sr sites in the SrTiO₃ crystal lattice were well identified by atomic column elemental mapping using energy dispersive x-ray spectroscopy (EDS). The EDS signal of indium has a stronger intensity at the Ti site than at the Sr site, based on the total analysis of each Ti and Sr atomic column. By applying principal component analysis on the raw EDS spectral imaging data cube, the indium site was clearly imaged; it completely fit into the Ti atomic column positions. These results provide direct evidence of In–Ti substitution in In-STO photocatalysts.