Shielded high-Tc (Bi, Pb)2Sr2Ca2Cu3Oy (Bi-2223) superconducting tapes

A new composite tape was fabricated in which the primary function of the central Ag-sheathed (Bi, Pb)(2)Sr2Ca2Cu3Oy (Bi-2223) filaments was to conduct transport current. A YBa2Cu3O7-delta (Y-123) thin film was deposited on the top of the Ag-sheathed Bi-2223 tape to shield the applied magnetic field and to protect the central Bi-2223 filaments. The critical current densities of the Y-123-coated, Ag-sheathed Bi-2223 tapes were better than those of an uncoated tape. However, the Y-123 thin film exhibited T-c approximate to 72 K and a broad transition region that shifted the effect to lower temperatures. Furthermore, pole figure measurements showed widely spread a, b planes along the rolling direction, indicating high-angle grain boundaries that diminished the magnitude of the effect. Microstructural observations showed platelike grains of Y-123 with fine growth ledges in the thin film that was heat treated, in contrast with the microstructure of an as-coated thin film that showed large twinned grains. From the processing point of view, the results showed that heat treating Y-123 thin film according to the Bi-2223 tape schedule was compatible with and beneficial for Y-123. These preliminary results may provide a basis for further improvements in processing of long-length Bi-2223 tapes for high-field applications.