PREPARATION AND CHARACTERIZATION OF SILVER-CLAD (BI,PB)-SR-CA-CU-O 2223 SUPERCONDUCTING TAPES WITH HIGH CRITICAL-CURRENT DENSITY

Silver clad Bi-2223 tapes with consistently high critical current densities of over 30,000 A/cm(2) at 77 K and zero held were prepared by powder-in-tube (PIT) technique. Powder XRD, electron microscopy, a.c. susceptibility and critical current measurements were used to study the phase assemblage, microstructure and transport properties of these tapes at various stages of processing. The precursor powder for PIT process was prepared by a sol-gel route by acrylate method using freshly prepared nitrates of Pi, Pb, Sr, Ca and Cu. The carbon content in the powder was minimized by subjecting it under dynamic vacuum calcination followed by heating in free flow of oxygen for long durations with intermittent grindings. The choice of initial stoichiometry, high reactivity of the precursor, effective removal of carbon, choice of phase assemblage at the filling stage and the multistage thermomechanical processing at optimized conditions were found to be responsible for the high critical current density.