Synthesis and phase width of new quaternary selenides PbxSn6−xBi2Se9 (x=0–4.36)

Quaternary chalcogenides PbxSn6−xBi2Se9 (x=0–4.36) were synthesized with solid-state methods; their structures were determined from the X-ray diffraction of single crystals. PbxSn6−xBi2Se9 crystallizes in an orthorhombic space group Cmcm (No. 63); the structure features a three-dimensional framework containing slabs of NaCl-(3 1 1) type that exhibits identical layers containing seven octahedra units, which expand along the direction [0 1 0]. Each slab contains fused rectangular units that are connected to each other with M–Se contacts in a distorted octahedral environment. Calculations of the band structure, measurements of Seebeck coefficient and electrical conductivity confirm that these compounds are n-type semiconductors with small band gaps and large electrical conductivities.