Construction of a quasi-ternary phase diagram in the NdO1.5-BaO-CuO system in the air atmosphere .2. Phase equilibria of the neodymium-rich Nd1+xBa2-xCu3Oz solid solution

In the present work phase relations in a copper-rich corner of the NdO1.5-BaO-CuO system were studied at 970-1060 degrees C in air by DTA, quenching experiments, EPMA, XRD, ICP AES and finally confirmed by growth of several test single crystals. It was found that in the analyzed region the Nd1+xBa2-xCu3O2 solid solution (Nd123ss) with maximum x values co-exists at 970-1060 degrees C with Cu-rich melt and different solid phases: CuO (970-990 degrees C), Nd2CuO4 (990...995-1045 degrees C) or Nd4Ba2Cu2O10 (1060 degrees C). The decomposition temperature of Nd123ss decreases with increasing the neodymium content, and the limit composition of Nd123ss extends up to Nd2BaCu3Oz at 990-995 degrees C. The Nd123ss unit cell volume deviations from the ideal solution of the Nd123 and Nd213 phases were found positive by XRD, as well as their excess Gibbs energy of mixing, estimated thermodynamically using the experimental phase diagram. This provides a probability of a spinodal decomposition phenomena of such a solution. (C) 1997 Elsevier Science B.V.