Syntheses, structures, and optical properties of Ba4MInSe6 (M=Cu, Ag)

Two new quaternary chalcogenides, namely Ba4MInSe6 (M=Cu, Ag), were synthesized by solid state reactions. These two isostructural compounds adopt the Ba2MnS3 structure type in the orthorhombic space group Pnma. In the structure, the M and In atoms randomly occupy one crystallographic unique metal position with the molar ratio of 1:1 The (M/In)Se4 tetrahedra are connected to each other by corner-sharing to form one-dimensional chains along the b direction, which are separated by mono-capped trigonal prismatically coordinated Ba atoms. Based on the diffuse reflectance spectrum, the optical band gaps were determined to be 2.23(2) and 2.41(2) eV for Ba4CuInSe6 and Ba4AgInSe6, respectively.