THE BLISTERING PHENOMENON IN BISCCO-2223 HIGH-T-C SUPERCONDUCTING TAPES

The blistering phenomenon in OPIT-derived Bi(Pb)SCCO/Ag (Bi-2223/Ag) c omposite tapes has been studied for a wide range of tape processing pa rameters. A Pb-free and Bi-deficient phase was observed after prolonge d sintering (for 50-100 h at 830-840 degrees C) at the internal surfac e of an cylindrical cavity formed inside a ceramic core during heating . It depressed the 2212-to-2223 transformation in the blistered sample and led to an extremely low value of J(c) of 500 A cm(-2) at 77 K. At a given sample length a critical heating rate existed below which cyl inders did not grow. This rate decreased with sample length increase. Preliminary rolling of a blistered tape just after cylinder formation as well as the annealing of as-rolled tape at 500-700 degrees C preven ted blistering during the subsequent thermomechanical processing. Thes e measures resulted in the value of J(c) exceeding 1 x 10(4) A cm(-2) at 77 K.