Solid-state properties of materials of the type Cs4MX6(where M = Sn or Pb and X = Cl or Br)

Two new compounds Cs4SnBr6 and Cs4SnCl6 have been prepared and the CsBr–SnBr2 phase diagram is described. Phases of the type Cs4Sn1 –nPbnBr6 –xClx(where n= 0–1, x= 0–6) have been examined by X-ray diffraction, electrical conductivity, Mössbauer spectral, and optical reflectance techniques. The electrical conductivity and optical properties of the phases are explained in terms of the population of solid-state bands by the non-bonding electron pairs of the Group 4 atoms. The structures of all the phases are related to that of Cs4PbCl6 which has been redetermined.