Synthesis and Structure of Three New Oxychalcogenides: A₂O₂Bi₂Se₃ (A = Sr, Ba) and Sr₂O₂Sb₂Se₃

Three new compounds have been added to the alkali chalcogenide and oxychalcogenide families: Sr₂O₂Bi₂Se₃, Ba₂O₂Bi₂Se₃, and Sr₂O₂Sb₂Se₃ were synthesized by direct combination of SrO or BaO with Bi₂Se₃ or Sb₂Se₃. The structure, determined from laboratory X-ray powder diffraction data, consists of double chains of edge-sharing BiSe₄O square pyramids. Temperature-dependent resistance data reveal all three compounds to be insulators, while heat capacity data of Ba₂O₂Bi₂Se₃ and Sr₂O₂Bi₂Se₃, in conjunction with the literature reports, reveal low energy phonon modes due to bismuth lone pair effects. We propose a specific materials design principle connecting electron count to structural dimensionality by comparison to related chalcogenides, including the BiS₂ superconductors