Gibbs energy of formation of CuCrO₄ and phase relations in the system Cu-Cr-O below 735 K

Abstract

A solid state galvanic cell incorporating yttria-stabilized zirconia electrolyte and ruthenium(IV) oxide electrodes has been used to measure the equilibrium chemical potential of oxygen corresponding to the decomposition of CuCrO₄ in the range 590-760 K. For the reaction CuO(tenorite) + CuCr₂O₄(spinel) + 1.5O₂(g)→2CuCrO₄(orth), ΔG^XXX = -183540 + 249.6T((±900) J mol^-1. The decomposition temperature of CuCrO₄ in pure oxygen at a pressure of 1.01 × 10⁵ Pa is 735(±1) K. By combining the results obtained in this study with data on the Gibbs energy of formation of CuCr₂O₄ and CuCrO₂ reported earlier, the standard Gibbs energy of formation of CuCrO₄ and the phase relations in the system Cu-Cr-O at temperatures below 735 K have been deduced. Electron microscopic studies have indicated that the decomposition of CuCrO₄ to CuCr₂O₄ is topotactic.