Indium oxychalcogenides would be attractive semiconductors considering the practical use of indium oxides and sulfides such as indium–tin oxides (ITO) and copper–indium–gallium diselenides (CIGS). In this work, a novel layered indium oxysulfide, LaOInS2, was synthesized by a metathesis reaction between LaOCl and NaInS2. Synchrotron X-ray diffraction showed that LaOInS2 consisted of alternately stacked rocksalt-type In–S and PbO-type La–O layers. The InS6 octahedron had split In sites with abnormally large anisotropic atomic displacement factors. LaOInS2 was found to be a direct semiconductor. Density functional theory calculations exhibited well-dispersed bands composed of In 5s/5p and S 3p/O 2p orbitals with a band gap of ∼2.4 eV, which was close to the experimental value estimated by optical absorption (2.64 eV). Under visible light irradiation this visible-light absorption, LaOInS2 exhibited photocatalytic activity for H2 and O2 evolution from water with the aid of Pt and IrO2 cocatalysts, respectively.
