THERMODYNAMICS AND PHASE-EQUILIBRIA IN THE CA-CU-O SYSTEM

Phase equilibria in the CaO-CuO-Cu system were determined at 1173 K fr om the results of X-ray diffraction measurements using specimens annea led in the oxygen partial pressure range from p(O2) = 1 to 10(-8) atm. Electromotive force (emf) measurements using ZrO2 solid electrolyte c ells were carried out in the ternary phase equilibria. Gibbs free ener gies for the chemical reactions were summarized by equations with line ar temperature dependence, and the standard free energy of formation f or Ca2CuO3 was derived. The stability conditions of the oxides are dis played in the p-T-x diagram, and the possible phase equilibria with th e liquid are evaluated.