Enhanced flux pinning in (Bi, Pb)-2223/Ag tapes by slight Pr substitution

Bi 1.8 Pb 0.4 Sr 2 Ca 2.2- x Pr x Cu 3 O y silver sheathed ((Bi, Pb)-2223/Ag) tapes with x = 0.0 (un-doped), 0.001 and 0.002 (Pr doped) have been investigated. X-ray diffraction analyses and transmission electron microscopy observation show that in the Pr-doped tapes there are many defective regions induced by the partial Pr substitution for Ca with a size of about 10 nm. As compared with the un-doped tape, the magnetic field dependence of critical current densities of the Pr-doped tapes are noticeably improved at 77 K. Their irreversibility lines are also shifted to higher temperatures and magnetic fields, and their activation energies of flux motion are increased drastically. The pinning force densities of the tapes are fitted with a improved law from the Dew-Hughes model; the results of this fitting show that the flux pinning enhanced in Pr-doped tapes mainly originates from the fine normal-like defects.