Effect of oxygen partial pressure on quasi-ternary phase diagram of NdO 1.5–BaO–CuO system

Abstract

Quasi-ternary phase diagrams of the NdO 1.5–BaO–CuO system under low and high oxygen partial pressure atmospheres ( P O 2 =0.01, 1.00 atm) were constructed. Liquidus curves, solidus lines, and the equilibrium tie-lines in the two-phase field of liquid and Nd 1+ x Ba 2− x Cu 3O 6+ δ 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 Nd 1+ x Ba 2− x Cu 3O 6+ δ , which was under the influence of temperature and P O 2 , was widened at lower temperature and/or higher P O 2 . Especially, its sensitivity to P O 2 was high. By investigating equilibrium tie-lines, the x value of Nd 1+ x Ba 2− x Cu 3O 6+ δ was reduced and became insensitive to the BaO/CuO ratio of liquid phase equilibrated with Nd 1+ x Ba 2− x Cu 3O 6+ δ as the BaO/CuO ratio increased and slightly reduced as temperature decreased. Those tendencies were maintained at different P O 2 . It was discussed thermodynamically why NdBa 2Cu 3O 6+ δ (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 Nd 1+ x Ba 2− x Cu 3O 6+ δ with the oxygen partial pressure of atmosphere.