Total neutron scattering investigation of the structure of a cobalt gallium oxide spinel prepared by solvothermal oxidation of gallium metal

A new solvothermal synthesis route to mixed-metal gallium oxides with the spinel structure has been developed for ternary oxides of ideal composition Ga_3-xM_xO_4-y (M=Co, Zn, Ni). The structure of the novel cobalt gallate produced in this manner, Ga_1.767(8)Co _0.973(8)O_3.752(8), has been determined from total neutron scattering to be a partially defective spinel with mixed-valent cobalt (approximately 25% Co³⁺ and 75% Co²⁺) and with vacancies on approximately 6% of oxygen sites. Pair distribution function (PDF) analysis reveals significant local deviations from the average cubic structure, which are attributed to the conflicting coordination preferences of the Co²⁺ (potential Jahn-Teller distortion) and Ga³⁺ (Ga off-centring). Reverse Monte Carlo (RMC) modelling supports this conclusion since different metal-oxygen bond-distance distributions are found for the two cations in the refined configuration. An investigation of magnetic properties shows evidence of short-range magnetic order and spin-glass-like behaviour, consistent with the structural disorder of the material.