The influence of Ag on univariant reactions and the oxygen content of the eutectic melt in the Y-Ba-Cu-(Ag)-O system

The influence of Ag admixtures on the phase equilibria of YBa2Cu3O7-delta near the liquidus surface was investigated at 0.21 X 10(5) Pa oxygen partial pressure using thermoanalytic methods (DTA/TG). The temperatures at which the liquid phase occurs are decreased by about 30 K in comparison with pure Y-Ba-Cu-O compositions. The peritectic decomposition of YBa2Cu3O7-delta is replaced by two sequential univariant reactions in the presence of silver: a eutectic reaction with a silver rich liquid at 944 degrees C and a monotectic-like reaction at 980 degrees C resulting in the Y-Ba-Cu-O rich melt besides Y2BaCuO5. Depending on the content of Ag, an enhanced oxygen concentration was detected in the melts which is available as an internal oxygen source during the crystallization of the superconducting phase by melt processing. The solubility of Ag in the melt was found to be 2.5 mol.% in the monotectic-like equilibrium al 980 degrees C. (C) 1998 Elsevier Science B.V.