High-Quality Bi-2223/Ag Multifilament Tapes Fabricated Using a Two-Powder Process

Many studies have shown that the phase assemblage of starting powders influences the phase evolution of the 2223 phase; but it is quite difficult to control the phase balance in precursor powders using a single-powder process. In this study, (Bi, Pb)-2212 and CaCuO₂ are formed as separate intermediate phases, then mixed and processed together within a silver sheath. The phase transformation kinetics, microstructure and transport properties of the resulting tapes are strongly dependence on the phase content of the precursor powders. Nearly pure 2223 can been produced when sintering for as little as 40 h, using (Bi, Pb)-2212 and CaCuO₂ presursors, and the fraction of non-superconducting phases seem to become minimum at the boundary of the oxide core. The effects of mechanical deformation and heat treatment cycles on silver-core interfaces and critical current densities in 37-, 61- and 85- filament tapes have been studied for the tapes fabricated using the two-powder process. A smooth Ag-oxide interface has been obtained through accurate control of the pass reduction ratios. This experiment demonstrates that the existence of large plate-like 2212 grains in the presursors can accelerate the diffusion of Ca, Cu during sintering stage and increase the degree of texture of 2223 grains. Tapes with a thickness of 0. 24 mm can be made using flat rolling without any 'sausaging' effect. J_c values of 3. 0 × 10⁴ A/cm² (I_c = 53 A) and 1. 7 × 10⁴ A/cm² (I_c = 35 A) at 77 K and self field are achieved for rolled short samples and tapes 20 m long, respectively.