Subsolidus phase relationships of the BaO–R 2O 3–CuO z (R = Eu, Dy, and Ho) systems under carbonate-free conditions at T = 810 °C and [formula omitted

Abstract

For applications of phase equilibria to second-generation coated-conductor high- T c superconductor processing, phase diagrams constructed under carbonate-free conditions are needed. Using a procedure for preparing carbonate-free precursors based on BaO, the phase diagrams of three BaO–R 2O 3–CuO z systems (R = Eu, Dy, and Ho) were determined at 810 °C and p O 2 = 100 Pa (0.1% O 2 by volume). The three phase diagrams are substantially different from one another. Among the three systems, Eu 3+ has the largest ionic radius and therefore most closely matches the ionic size of Ba 2+. Two solid solution series, namely, Ba 2− x Eu x CuO 3+ z and Ba 2− x Eu 1+ x Cu 3O 6+ z were found in the BaO–Eu 2O 3–CuO z system. The BaO–Dy 2O 3–CuO z and the BaO–Ho 2O 3–CuO z systems do not contain solid solution phases. In these systems, which contain the smaller R = Dy, and Ho rare earths, the Ba 2− x Eu x CuO 3+ z solid solution and Eu 2CuO 4 phases of the Eu-system are replaced by the Ba 6RCu 3O z (6 1 3) phase and the R 2Cu 2O 5 phase, respectively. Additionally, the Ba 4RCu 3O z (4 1 3) phase appears in systems with smaller R (Dy and Ho) but not in the Eu-system. The Ho-system contains the Ba 3R 4O 9 phase, as well. Consequently, the tie-line relationships are substantially different in these three systems. Among the three diagrams, the diagram for R = Ho is most similar to that of the R = Y system.