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

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 group P2(1)/c. It contains (2)(infinity)[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 P (4) over bar2(1)c 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.