Improvement in critical current density under magnetic field in heavily Pb-doped Bi₂Sr₂CaCu₂O_x superconducting tape

A heavily Pb-doped Bi₂Sr₂CaCu₂O_x (Bi-2212) tape has been prepared using an isothermal partial melting method. Width of magnetic hysteresis (ΔM) normalized by ΔM under 0 Oe decreases with increasing magnetic field (H||c axis) at 20–60 K; this occurs more rapidly in pure Bi-2212 tape (Pb-free tape) than in Pb-doped tape. Irreversibility field under the H||c axis is elevated by Pb doping at 20–60 K. Moreover, a decrease in transport critical current density (J_c) with increasing H||c axis is reduced by Pb doping at 20–60 K. In particular, a peak is observed at 2.0 kOe in J_c–H curves at 20 and 30 K. Hole concentration in the Pb-doped tape seems to be close to the optimum, as magnetic superconducting transition starts at 91 K. Therefore, the above results are due to production of new pinning centers induced by applying the magnetic field. It is clear that heavy Pb doping is effective for Bi-2212 polycrystalline tape in producing efficient pinning centers for the H||c axis as reported in Bi-2212 single crystals. © 1997 American Institute of Physics.