CRYSTAL-CHEMISTRY AND PHASE-EQUILIBRIUM STUDIES OF THE BAO(BACO3)-1 2R(2)O(3)-CUOX SYSTEMS IN AIR - VI, R=NEODYMIUM/

Crystal chemistry and subsolidus phase equilibrium studies of the Ba-N d-Cu-O system near the CuO and Nd2O3 corners have been carried out at 950 degrees C in air. Two solid-solution series have been identified i n the Ba-Nd-Cu-O system, The first series involves the high-T-c superc onductor phase, and has the formula Ba2-xNd1+xCu3O6+z, where x < appro ximate to 0.7. At the ideal compound stoichiometry of Ba2NdCu3O6+z, th e transformation from the high-T-c orthorhombic to tetragonal phase oc curs at 550 degrees-575 degrees C in air. This temperature varies as a function of composition, and at x approximate to 0.2 to 0.3 it occurs at 950 degrees C. The second solid solution is the nonsuperconducting ''brown phase'' represented by Ba-2+2x- Nd4-2xCu2-xO10-2x, 0 less tha n or equal to x less than or equal to 0.1. Preliminary phase diagrams of the BaO-Nd2O3 and Nd2O3-CuOx systems are also presented. Standard X -ray diffraction patterns of BaNd2CuO5 and (Nd1.9Ca0.1)CuO4-z are prov ided.