Synthesis and characterization of two lead-containing metal chalcogenides: Ba5Pb2Sn3S13 and Ba6PbSn3Se13.

Two new metal chalcogenides, Ba 5 Pb 2 Sn 3 S 13 (BPSS) and Ba 6 PbSn 3 Se 13 (BPSSe), were successfully synthesized in vacuum–sealed silica tubes for the first time. Both of them are isostructural and crystallize in the Pnma space group of orthorhombic system. Their three-dimensional (3D) framework structures are composed of 2D layers formed by the interconnection of [(Pb/Ba)Q n ] ( n = 6 and 7) polyhedra and isolated SnQ 4 tetrahedra and charge–balanced Ba atoms filled into the interlayers. Note that the Q8 atoms are only surrounded by two Pb/Ba and four Ba atoms to form the distorted octahedra without the covalent Sn-Q bonds in their structures. Measured results of diffuse reflection and Raman spectra show that title compounds possess the wide transmission ranges from 0.5 to 20 µm. Electronic structures and linear optical properties were also systematically investigated by the first–principle calculation, and calculated results indicate that title compounds possess the large birefringences about 0.123 and 0.135 for BPSS and BPSSe at 1 µm, respectively, which indicate that they may be expected as potential IR birefringent materials. [ABSTRACT FROM AUTHOR]