The formation of superconducting YBa 2Cu 3O 7−x through solid state reaction

Abstract

DTA, TGA and X-ray diffractometry (XRD) were utilized to study the formation of the high T c superconducting YBa 2Cu 3O 7- x (Y123) phase through solid state reaction of a mixture of Y 2O 3:BaCO 3:CuO, in the molar ratio of 0.5:2:3. For continuous heating at 10°C/min, it was found that the Y123 phase exists at 820–996°C and gradually disappears at higher temperatures. The insulating Y 2BaCuO 5 (Y211) phase exists over the temperature range 987 through 1190°C, while the semiconducting YBa 3Cu 2O 7− y (Y132) phase coexists with the Y123 phase. For isothermal heating, it was found that the most appropriate conditions for the formation of the Y123 phase is isothermal heating at 907°C for more than 16 h. The pure Y123 phase is obtainable since the Y132 and the Y211 phases disappear after prolonged soaking at 907°C. Semiquantitative analyses on the amount of existing phases during continuous heating, including the intermediate binary phases, are also given. The high temperature superconductor can be synthesized reproducibly with a T c of around 93 K by the calcining process based on this study.