Gibbs energy of formation of cobalt divanadium tetroxide

The Gibbs energy of formation of V₂O₃-saturated spinel CoV₂O₄ has been measured in the temperature range 900–1700 K using a solid state galvanic cell, which can be represented as $\text{Pt, Co + CoV}{}_2\text{O}{}_4\text{+}\text{V}{}_2\text{O}{}_3\text{(CaO)}\text{ZrO}{}_2\text{Co}\text{+}\text{CoO, Pt}$. The standard free energy of formation of cobalt vanadite from component oxides can be represented as CoO (rs) + V₂O₃ (cor) → CoV₂O₄ (sp), ΔG° = ?30,125 ? 5.06T (± 150) J mole^?1. Cation mixing on crystallographically nonequivalent sites of the spinel is responsible for the decrease in free energy with increasing temperature. A correlation between “second law” entropies of formation of cubic 2–3 spinels from component oxides with rock salt and corundum structures and cation distribution is presented. Based on the information obtained in this study and trends in the stability of aluminate and chromite spinels, it can be deduced that copper vanadite is unstable.