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

Abstract

Two new antimony selenides, Ba₂Sb₂Se₅ and Ba₆Sb₇Se_16.11, 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) Å; b = 27.567(5) Å c = 4.6422(8) Å; and Ba₆Sb₇Se₁₆: Pnnm (No. 58) Z = 4, a = 12.469(2) Å; b = 62.421(7) Å; c = 4.6305(5) Å. 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.