Some defect structures of iron sulfide

Defect structures of iron sulfide having compositions of FeS and Fe0.94S were examined by X-ray powder, X-ray single crystal and Mössbauer techniques. The crystal structure of Fe0.94S was found to be in the hexagonal acentric space group P63me if ordered, or in the hexagonal centric space group P63/mmc if disordered with cell dimensions a0 = 3.4559 Å and c0 = 5.7789 ± 0.0005 Å. In both space groups there is only one variable positional parameter, i.e. zS/c = ± 0.263; all ot her positional parameters are fixed by symmetry. The atomic packing of the FeS and Fe0.94S structures corresponds to a framework of closepacked sulfide ions having octahedral interstices either smaller than necessary (FeS) or larger (Fe0.94S) to accommodate the iron ions. This phenomenon also suggests a model from which the existence and crystallography of these structures may be rationalized.