Characterization of Planar Defect in Layered Perovskite Photocatalyst Y2Ti2O5S2 by Electron Microscopy and First-Principles Calculations

Layered perovskite Y2Ti2O5S2 is a promising semiconductor photocatalyst with an electronic structure suitable for overall water splitting under visible light. However, similar to other photocatalysts, structural defects during synthesis should be controlled. Transmission electron microscopy (TEM) revealed extremely large planar defects composed of S-Mg-S layers in Y2Ti2O5S2 synthesized using the flux method. We determined the planar defect structure and electronic structure using first-principles calculations based on the density functional theory. The evaluation of the formation energy suggests that S-and Mg-poor conditions may prevent defect formation. Furthermore, we discuss the impurity levels caused by the planar defects and their effects on the electronic state and catalytic performance.