Synthesis, crystal structure, and thermoelectric properties of two new barium antimony selenides: Ba2Sb2Se5 and Ba6Sb7Se16.11

Two new antimony selenides, Ba2Sb2Se5 and Ba6Sb7Se16.11, were synthesized via high-temperature solid-state reactions and their structures were determined by single crystal X-ray diffraction. Both of the title compounds crystallize in two new structure types in orthorhombic space groups, Ba2Sb2Se5: Pbam (No. 55) Z = 4, a = 8.403(2) angstrom; b = 27.567(5) angstrom c = 4.6422(8) angstrom; and Ba6Sb7Se16: Pnnm (No. 58) Z = 4, a = 12.469(2) angstrom; b = 62.421(7) angstrom; c = 4.6305(5) angstrom. The crystal structures of both phases contain Sb-Se slabs and one-dimensional Ba-Se chains that are not commonly found in alkaline-earth antimony selenides. Ba2Sb2Se5 is an n-type semiconductor with a bandgap close to 1 eV as revealed by resistivity measurements and UV-visible spectroscopy. Due to the complex crystal structure and disorder in the Se sublattice, Ba2Sb2Se5 exhibits extremely low thermal conductivity (0.4 W m(-1) K-1) from room temperature to 800 K.