Ba2AgInS4 and Ba4MGa5Se12 (M = Ag, Li): syntheses, structures, and optical properties

Abstract

The first two members in alkaline-earth/group XI/group XIII/chalcogen system, namely Ba₂AgInS₄ and Ba₄AgGa₅Se₁₂, were synthesized along with a Li analogue Ba₄LiGa₅Se₁₂. Ba₂AgInS₄ crystallizes in space groupP2₁/c. It contains ² _∞[AgInS₄]^{4 −} layers built from AgS₃ triangles and InS₄ tetrahedra with Ba²⁺ cations inserted between the layers. Ba₄AgGa₅Se₁₂ and Ba₄LiGa₅Se₁₂ adopt two closely-related structure types in space group P2₁c with structural difference originating from the different positions of Ag and Li in them. The three-dimensional framework in Ba₄AgGa₅Se₁₂ is composed of GaSe₄ tetrahedra with the Ba and Ag atoms occupying the large and small channels respectively, whereas that in Ba₄LiGa₅Se₁₂ is built from LiSe₄ and GaSe₄ tetrahedra with channels to accommodate the Ba atoms. As deduced from the diffuse reflectance spectra measurement, the optical band gaps were 2.32 (2) eV, 2.52 (2) eV, and 2.65 (2) eV for Ba₂AgInS₄, Ba₄AgGa₅Se₁₂, and Ba₄LiGa₅Se₁₂, respectively.