Effect of atmosphere and rare earth on liquidus relations in RE–Ba–Cu Oxides

In the processing of the high temperature superconductors RE₁Ba₂Cu₃O_7−x a knowledge of the liquidus temperatures is required in order to avoid liquid formation during the initial reactions of the starting materials. We have investigated the invariant points on the liquidus surface of the RE–Ba–Cu–O systems for RE = Y, Er, Gd, and Nd in oxygen, air, and argon, While the temperatures of the low melting reactions are almost independent of the rare earth species, they are heavily dependent on oxygen partial pressure. In addition, the peritectic decomposition temperature of the REBa₂Cu₃O₇ phase was found to be a function of rare earth with a significantly higher value for the Nd compound than for the other rare earths.