Construction of a quasi-ternary phase diagram in the NdO 1.5BaOCuO system in the air atmosphere Part II. Phase equilibria of the neodymium-rich Nd 1+ xBa 2− xCu 3O z solid solution

Abstract

In the present work phase relations in a copper-rich corner of the NdO 1.5BaOCuO system were studied at 970–1060°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 Nd 1+ x Ba 2− x Cu 3O z solid solution (Nd123ss) with maximum x values co-exists at 970–1060°C with Cu-rich melt and different solid phases: CuO (970–990°C), Nd 2CuO 4 (990…995–1045°C) or Nd 4Ba 2Cu 2O 10 (1060°C). The decomposition temperature of Nd123ss decreases with increasing the neodymium content, and the limit composition of Nd123ss extends up to Nd 2BaCu 3O z at 990–995°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.