A time-of-flight powder neutron diffraction study of ternary chromium sulfides, Ni_xCr_3-xS₄ (0<x≤1.0)

Time-of-flight powder neutron diffraction has been used to investigate the distribution of nickel and chromium cations between two crystallographically independent sites in the series of ternary sulfides, Ni_xCr_3-xS₄ (0<=1.0). These materials are isostructural with Cr₃S₄ (space group I2/m: a˜5.9 Å, b˜3.4 Å, c˜11.1 Å, ߘ91.5°) over the entire range of composition. At all values of x, nickel cations preferentially occupy sites in an ordered-vacancy layer with only a small percentage (= 15%) residing at sites in a fully occupied metal layer. This distribution is close to that expected for the normal structure type. The absence of any significant dependence on x of the cation distribution is reflected in the magnetic properties, which show relatively little compositional variation. Electronic properties, however, indicate a change in the nature of the valence electrons with decreasing nickel content.