Synthesis, structure, band gap, and electronic structure of CsAgSb4S7

The compound CsAgSb4S7 has been synthesized by the reaction of the elements in a Cs2S3 flux at 773 K. The compound crystallizes in a new structure type with eight formula units in space group C2/c of the monoclinic system in a cell at 153 K of dimensions image, image, image, image, and image. The structure contains two-dimensional image layers separated by Cs atoms. Each image layer is built from edge-sharing one-dimensional image and image chains. Each Ag atom is tetrahedrally coordinated to four S atoms. Each Sb3+ center is pyramidally coordinated to three S atoms to form an SbS3 group. CsAgSb4S7 is insulating with an optical band gap of 2.04 eV. Extended Hückel calculations indicate that the band gap in CsAgSb4S7 is dominated by the Sb 5s and S 3p states above and below the Fermi level.