Effect of oxygen partial pressure on quasi-ternary phase diagram of NdO1.5-BaO-CuO system

Quasi-ternary phase diagrams of the NdO1.5-BaO-CuO system under low and high oxygen partial pressure atmospheres (P-O2 = 0.01, 1.00 atm) were constructed. Liquidus curves, solidus Lines, and the equilibrium tie-lines in the two-phase field of liquid and Nd1 + xBa2 - xCu3O6 + delta were determined experimentally. As the oxygen partial pressure of atmosphere increased, liquidus curves were shifted to the Nd-rich region and the Nd solubility in the solvent with lower BaO/CuO ratio was further increased. The stable region of Nd1 + xBa2 - xCu3O6 + delta, which was under the influence of temperature and P-O2, was widened at lower temperature and/or higher P-O2. Especially, its sensitivity to P-O2 was high. BY investigating equilibrium tie-lines, the x value of Nd1 + xBa2 - xCu3O6 + delta was reduced and became insensitive to the BaO/CuO ratio of liquid phase equilibrated with Nd1 + xBa2 - xCu3O6 + delta as the BaO/CuO ratio increased and slightly reduced as temperature decreased, Those tendencies were maintained at different P-O2. It was discussed thermodynamically why NdBa2Cu3O6 + delta (Nd123) superconductors, fabricated in a reduced oxygen atmosphere, show high superconductive critical temperature. One of the reasons for this phenomenon was the decrease of the solubility of Nd1 + xBa2 - xCu3O6 + delta with the oxygen partial pressure of atmosphere. (C) 2000 Elsevier Science B.V. All rights reserved.