Cation distribution in MgxNi1–xGa2O4 oxide spinels

Spinels MgxNi1–xGa2O4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1) are synthesized, in polyerystalline form, by solid-state reaction at 1273 K of the individual metal oxides. X-ray diffraction is used to determine the lattice parameter (a0), cation distribution, and oxygen parameter (u) for each spinel. Complete solid solution formation between MgGa2O4 and NiGa2O4 is found, and a0 increases linearly with the composition parameter, x; the oxygen parameter, however, remains approximately constant at u = 0.382 (±1). The cation distribution is found to be dependent upon chemical composition, the proportion of octahedral Ni2+ increasing as the amount of Mg2+ is raised. These results are interpreted in terms of the interplay of the different factors which determine the crystal chemistry of metal oxides.