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

Published

July 1, 2003

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-CuO_x 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-CuO_x 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, Ba_2-xNd6d1+x^Cu₃O_z (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' Ba_1+xNd_2-xC_uO_z, 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 (Ba_2-xNd_x)CuO_3-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, Ba₄Nd₂Cu₂O_z. The latter phase is an insulator, with a structure comprised of unusual CuO₅ linear chains. A significant difference in tie line distribution involving the Ba_2-xNd_1+xCu₃O_6+z superconductor was found under carbonate-free conditions relative to literature studies completed in air. Instead of the BaCuO_{2 x} - Ba_2+xNd_4-xCu₂O_z tie line normally encountered in air, a Ba_2-xNd_1+xCu₃O_6+z - (Ba,Nd)₂CuO_{3 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 Ba_2-xNd_1+xCu_3Od6+z^ superconductor into the BaO-rich region of the phase diagram. Implications for the processing of materials based on the Ba_2-xNd_1+xCu₃O_6+z superconductor are discussed.

Citation

Journal of Solid State Chemistry

Volume

173

Issue

No. 2

Pub Type

Journals

Keywords

atmospheric-controlled experiments, BaO-Nd₂O₃-CuO_x, phase equilibria, superconductors

Citation

Wong-Ng, W. , Cook, L. , Suh, J. , Coutts, R. , Stalick, J. , Levin, I. and Huang, Q. (2003), BaO-Nd₂O₃-CuO_x Subsolidus Equilibria Under Carbonate-Free Conditions at pO₂ = 100 Pa and at pO₂ = 21 kPa, Journal of Solid State Chemistry (Accessed January 2, 2025)