Magnetic field and temperature dependence of critical current density in Hf-doped Bi-2223/Ag-Cu alloy sheathed tapes

Bi-2223/Ag-Cu alloy sheathed tapes have been fabricated by the powder-in-tube technique using Ag-10 at.% Cu alloy sheath doped with Ti or Hf of less than 0.1 at.%. Critical current density (J(c)) was measured as a function of temperature between 30 and 90 K in the magnetic field up to 3 T. The flux-pinning force density (F-p = J(c) X B) was also calculated, Normalized pinning force (f = F-p/F-pmax) vs. normalized field (b = B/B-s) curves for the Hf-doped samples were compared with those of non-doped Bi-2223/pure Ag and Bi-2223/Ag-Cu tapes. High J(c) values of 9.5 X 10(4) A/cm(2) at 30 K, 0 T and 4.5 X 10(4) A/cm(2) at 30 K, 3 T were obtained for the Hf-doped samples. The Hf-doping caused no substantial change in superconducting critical temperature (T-c). The Hf-doping seems to be effective to enhance Bi-2223 crystallization and to improve grain alignment as well as electrical connection between Bi-2223 grains. The n value of Hf-doped sample reached about 13 at 30 K, 1 T, which is lower than 23 of non-doped Bi-2223/pure Ag. (C) 2000 Elsevier Science B.V. All rights reserved.