J(c) property and microstructure of Bi2223 tapes made using AgCu alloy sheaths doped with Ti, Zr or Hf

Bi-2223 superconducting tapes were prepared by the powder-in-tube technique using Ag-10 at%Cu alloy sheaths with and without a small amount of doping elements of Ti, Zr or Hf, and repetition of sintering and cold pressing. The doped samples showed a high critical current density, J(c), of 5-9 x 10(4) A/cm(2), at 4.2 K and 14 T, Micrograph examinations on these samples revealed a modified Bi-2223 grain structure at the sheath/core interface and also a more dense and aligned microstructure. Furthermore, amorphous, small disc-like regions, less than 5 nm in thickness parallel to the (001) plane, were found to be incorporated in the Bi-2223 lattice only for the doped samples. Critical current properties measured by magnetization and resistive methods were described correlating with the microstructures and the magnetic plux pinning. These amorphous regions are likely to provide the effective flux pinning centers in the Bi-2223 superconductors.