The system Cu3AsS4–Cu3SbS4and investigations on normal tetrahedral structures

Abstract

AbstractIn order to develop a novel model to predict if a so called normal tetrahedral compound crystallizes in awurtzite- orsphaleritesuperstructure type, the system Cu3AsS4–Cu3SbS4was reinvestigated. A solid solution series was prepared and the mixed crystals were characterized by powder X-ray techniques. The crystal structures of Cu3As0.330Sb0.670S4, Cu3As0.736Sb0.264S4, and Cu3AsS4were refined from single crystal X-ray data. The refinements converged toR= 0.0209,wR2 = 0.0484 (Cu3As0.330Sb0.670S4, 201 unique reflections, 15 parameters),R= 0.0235,wR2 = 0.0596 (Cu3As0.736Sb0.264S4, 218 reflections, 15 parameters), andR= 0.0241,wR2 = 0.0669 (Cu3AsS4, 721 reflections, 45 parameters).Zis 2 for all compounds. The volumes of the tetrahedra [MS4] were calculated for the investigated compounds. In addition, the corresponding data were calculated for further solids from literature data. The volumes of the tetrahedra are used to separate compounds with asphaleritetype anion arrangement from compounds with hexagonal packed anions. A closer inspection of the tetrahedra volumes reveals a greater variation for one given material in the case ofwurtzitetype superstructures than forsphaleritetype superstructures. A critical difference in the tetrahedra volumes is derived from these data.