Advances in fabrication of Ag-clad Bi-2223 superconductors

Powder-in-tube (PIT) processing was used to fabricate multifilamentary Ag-clad Bi2Sr2Ca2Cu3Oy (Bi-2223) superconductors for various electric power applications. The transport current properties of long lengths of multifilament tapes were enhanced by increasing the packing density of the precursor powder, improving the mechanical deformation, and adjusting the cooling rate. The dependence of the critical current density on magnetic field and temperature for the optimally processed tapes was measured. J(c) was > 10(4) A/cm(2) at 20 K in magnetic fields up to 3 T and parallel to the c axis, which is of interest for use in refrigerator-cooled magnets. An attempt was made to combine the good alignment of Bi-2223 grains in Ag-sheathed superconducting tapes to obtain high Je values at high temperature and low field, with the good intrinsic pinning of YBa2Cu3O7-d (Y-123) thin film, in order to maintain high J(c) values in high fields. A new composite multifilament tape was fabricated such that the central part contained Bi-2223 filaments, with the primary function of conducting the transport current. The central Bi-2223 filaments were surrounded by Y-123 thin film to shield the applied magnetic field and protect the Bi-2223 filaments. The J(c) values of the composite tape were better than those of an uncoated tape. In the case of 77 K applications, an I-c of approximate to 60 A was obtained in a 150-m-long tape and zero applied magnetic field. In-situ strain characteristics of the mono- and multifilament tapes were measured.