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BaO-Nd2O3-CuOx Subsolidus Equilibria Under Carbonate-Free Conditions at pO2 = 100 Pa and at pO2 = 21 kPa

Published

Author(s)

Winnie K. Wong-Ng, Lawrence P. Cook, J Suh, R Coutts, Judith K. Stalick, Igor Levin, Qingzhen Huang

Abstract

Subsolidus phase equilibria of the BaO-Nd2O3-CuOx system at pO2 = 100 Pa (0.1 % O2 by volume) and at pO2 = 21 kPa (21 % O2 by volume) have been investigated by applying controlled atmosphere methods to minimize the presence of carbonate and CO2 and H2O contamination. Under carbonate-free conditions, the BaO-Nd2O3-CuOx phase diagrams at pO2 = 100 Pa and at pO2 = 21 kPa are similar to one another except for differences in the extent of the solid solutions. Apart from the limiting binary phases, the ternary system consists of three solid solutions and one stoichiometric ternary compound. The first solid solution is the high Tc series, Ba2-xNd6d1+x^Cu3Oz (0.3 > x 0 at pO2 = 100 Pa; 0.95 > x 0 at pO2 = 21 kPa). At pO2 = 21 kPa, a compositionally dependent phase change was found to occur, from tetragonal (0.7 > x 0) to orthorhombic (0.95 x 0.7). The second solid solution series, the 'brown-phase' Ba1+xNd2-xCuOz, has a narrow homogeneity region (0.10 > x 0 at pO2 = 100 Pa; 0.15 > x 0 at pO2 = 21 kPa). In the high BaO part of the phase diagram, a third solid solution (Ba2-xNdx)CuO3-z (x= 0 to 0.3 at pO2 = 100 Pa; x = 0 to 0.45 at pO2 = 21 kPa) was confirmed, as well as a nominally stoichiometric phase, Ba4Nd2Cu2Oz. The latter phase is an insulator, with a structure comprised of unusual CuO5 linear chains. A significant difference in tie line distribution involving the Ba2-xNd1+xCu3O6+z superconductor was found under carbonate-free conditions relative to literature studies completed in air. Instead of the BaCuO2 x - Ba2+xNd4-xCu2Oz tie line normally encountered in air, a Ba2-xNd1+xCu3O6+z - (Ba,Nd)2CuO3 x tie line was found to occur. The presence of the latter tie line has the effect of substantially expanding the field of stability of the Ba2-xNd1+xCu3Od6+z^ superconductor into the BaO-rich region of the phase diagram. Implications for the processing of materials based on the Ba2-xNd1+xCu3O6+z superconductor are discussed.
Citation
Journal of Solid State Chemistry
Volume
173
Issue
No. 2

Keywords

atmospheric-controlled experiments, BaO-Nd<sub>2</sub>O<sub>3</sub>-CuO<sub>x</sub>, phase equilibria, superconductors

Citation

Wong-Ng, W. , Cook, L. , Suh, J. , Coutts, R. , Stalick, J. , Levin, I. and Huang, Q. (2003), BaO-Nd<sub>2</sub>O<sub>3</sub>-CuO<sub>x</sub> Subsolidus Equilibria Under Carbonate-Free Conditions at pO<sub>2</sub> = 100 Pa and at pO<sub>2</sub> = 21 kPa, Journal of Solid State Chemistry (Accessed June 20, 2024)

Issues

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Created July 1, 2003, Updated February 19, 2017