Multinary Selenides with Unusual Coordination Environment of Bismuth

Abstract

New multinary selenides Ae(3)SnPn(2)Se(8) (Ae = Sr, Ba; Pn = Sb, Bi), Sr8.01Ge2.04Bi7.95Se24, and Sr8YGe2Bi7Se24 were synthesized by solid-state reaction, and their structures were determined by single-crystal X-ray diffraction. These compounds crystallize in orthorhombic space group Pnma (no. 62) for Ae(3)SnPn(2)Se(8) (Ae = Sr, Ba; Pn = Sb, Bi) and in Pna2(1) (no. 33) for Sr8.01Ge2.04Bi7.95Se24 and Sr8YGe2Bi7Se24. The structures feature one-dimensional corner sharing tetrahedral (1)(infinity)[MSe3] units, and one-dimensional edge sharing octahedral (1)(infinity)[M4Se10], packed with the alkaline earth or rare earth cations. Sr8.01Ge2.04Bi7.95Se24 and Sr8YGe2Bi7Se24 contain a triple cell superlattice structure derived from a special arrangement of Bi and Ge in the tetrahedrally coordinated (1)(infinity)[MSe3] chain. Diffuse reflectance spectra and electronic resistivity measurements indicate semiconducting behaviors; the Sr8YGe2Bi7Se24 Seebeck coefficient is -180 mu V/K at 303 K Electronic structure calculations confirm that the electron count for Sr8YGe2Bi7Se24 is optimal for interatomic bonding in the ionic network.