Phase relations and stability in the Y2O3-BaOCuOx system

Phase relations in the Y2O3-BaO-CuOx system have been studied by X-ray diffraction and thermogravimetry. At 9500C in air there are four oxygen deficient ternary cuprates, and stoichiometric Y2BaCuO5. When these nonstoichiometric cuprates are cooled slowly to room temperature in air they oxidize. The oxygen potential for same chosen four-phase combinations have been measured at 750-10000C using solid ZrO2 + CaO electrolyte. The Gibbs energies for many possible reactions in the system were obtained. The positive entropy for several reactions indicates that ternary cuprates, are entropy - stabilized compounds. These cuprates become increasingly less stable with decreasing temperature and there is a real possibility that they are metastable at ambient temperature