Solid state electrochemical study of the phase diagram and thermodynamics of the ternary system CuGeO

Coulometric titrations using solid zirconia ionic conductors have been employed to determine the phase diagram of the ternary system CuGeO in the temperature range from 750 to 950°C. CuGeO₃ was found to be the only existing ternary compound in the system. It is in equilibrium with Cu₂O, CuO, GeO₂, and oxygen of atmospheric pressure. Cu and Cu₂O may coexist with GeO₂. The standard Gibbs energy of formation of CuGeO₃ was found to be ΔG°_f (CuGeO₃) = ?424.5 kJ/mole at 900°C. The standard enthalpy and entropy of formation are ΔH⁰_f = ?756.8 kJ/mole and ΔS°_f = ?283 J/mole·K, respectively.