IMPROVEMENT IN CRITICAL-CURRENT DENSITY UNDER MAGNETIC-FIELD IN HEAVILY PB-DOPED BI2SR2CACU2OX SUPERCONDUCTING TAPE

A heavily Pb-doped Bi2Sr2CaCu2Ox (Bi-2212) tape has been prepared usin g an isothermal partial melting method. Width of magnetic hysteresis ( Delta M) normalized by Delta M under 0 Oe decreases with increasing ma gnetic field (H parallel to c axis) at 20-60 K; this occurs more rapid ly in pure Bi-2212 tape (Pb-free tape) than in Pb-doped tape. Irrevers ibility field under the H parallel to c axis is elevated by Pb doping at 20-60 K. Moreover, a decrease in transport critical current density (J(c)) with increasing H parallel to c axis is reduced by Pb doping a t 20-60 K. In particular, a peak is observed at 2.0 kOe in J(c)-H curv es at 20 and 30 K. Hole concentration in the Pb-doped tape seems to be close to the optimum, as magnetic superconducting transition starts a t 91 K. Therefore, the above results are due to production of new pinn ing centers induced by applying the magnetic field. It is clear that h eavy Pb doping is effective for Bi-2212 polycrystalline tape in produc ing efficient pinning centers for the H parallel to c axis as reported in Bi-2212 single crystals. (C) 1997 American Institute of Physics.