X-ray and neutron diffraction study of the layered compound CoGaInS4

The crystal of the title compound, trigonal (P3m1) with hexagonal parameters a = 3.744(1) and c = 12.149(3)Å, is isostructural with polytype I of ZnIn2S4, being formed by the stacking of hexagonal layers of S anions, with the cations occupying, in intermediate planes, voids of approximate Oh and Td symmetry. Single-crystal X-ray and powder neutron diffraction intensities were used as the basis for the refinement of various models of cation distribution among three different crystallographic sites. Eventually the "best" model was found to be represented by the formula (Co0.38In0.62)o (Co0.29In0.38Ga0.33)t1(Co0.33Ga0.67)t2S4, where the subscript o refers to a pseudooctahedral site and subscripts t1 and t2 refer to two different sites of approximate Td symmetry. Evidence is found for the fact that the center of gravity of the pseudooctahedral site, as determined by the neutron experiment, is different from that "observed" by X-ray diffraction and a possible explanation is presented for this fact. ©