Cation Deficiency in Ordered-Vacancy Ternary Sulfides

Powder X-ray diffraction data suggested that materials V_xCr_3-xS₄ (1.0<x<3.0) adopt the Cr₃S₄-type structure. However, a small number of additional weak peaks indicated the presence of a second phase. This could not be identified from X-ray data owing to the very low intensities of the additional reflections. However, the appreciable intensity of the corresponding reflections in powder neutron diffraction patterns led to these being indexed on the basis of a rhombohedral unit-cell and identification of the second phase as V₂O₃. Two-phase structural refinement, by the Rietveld method, using neutron and X-ray data simultaneously, revealed that the ternary phase, although of the Cr₃S₄-type, is cation deficient. Additional cation vacancies are confined to the ordered-vacancy layer.