Microstructure and properties of Tl0.75Bi0.25Sr1.6Ba0.4Ca2Cu3Ox tapes

Ag-clad Tl0.75Bi0.25Sr1.6Ba0.4Ca2Cu3Ox tapes were fabricated by a powder-in-tube technique. The starting powders consisted of Bi2Sr2CaCu2Ox plus simple oxides. The tapes were heated in flowing O2 at 835–865 °C for 7.5–10 h. Room-temperature pressing at 1.0–1.5 GPa produced tapes with denser, more phase-pure cores, and transport critical current density Jc at 77 K in self-field that was increased by a factor of ≈2. The maximum Jc value of 6 × 103 A/cm2 was obtained with heating at 840 − 850 °C for ≈ 10 h, with three intermediate pressing steps. The cores of the best tapes were still rather porous and contained significant concentrations of nonsuperconducting phases.