Isotropic pinning in heavily Pb-doped Bi-2212/Ag tapes

Heavily Pb-doped Bi-2212/Ag tapes have been prepared using an isothermal partial melting (IPM) method. Under heavy Pb doping, irreversibility field (H-irr) for magnetic fields parallel to the e-axis (H parallel to c-axis) is elevated at temperatures higher than 20 K and is comparable to H-irr for H parallel to ab-plane. As a result, the original anisotropic pinning properties disappear in Pb-doped tape, At 30 K, the isotropic pinning force suppresses the anisotropy of transport critical current density (J(c)) under magnetic field which is the most serious problem for power applications of Bi-2212 materials. Transmission electron microscopic (TEM) observation shows a disordered stripe structure and stacking faults along the c-axis in the be-plane of Bi-2212 grains in Pb-doped tape. Such a stripe structure or stacking faults seem to be related to the production of strong pinning centers by heavy ph doping. (C) 1999 Elsevier Science B.V. All rights reserved.