SHIELDED HIGH-T-C (BI, PB)(2)SR2CA2CU3OY (BI-2223) SUPERCONDUCTING TAPES

A new composite tape was fabricated in which the primary function of t he 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 app lied magnetic field and to protect the central Bi-2223 filaments. The critical current densities of the Y-123-coated, Ag-sheathed Bi-2223 ta pes were better than those of an uncoated tape. However, the Y-123 thi n film exhibited T-c approximate to 72 K and a broad transition region that shifted the effect to lower temperatures. Furthermore, pole figu re measurements showed widely spread a, b planes along the rolling dir ection, indicating high-angle grain boundaries that diminished the mag nitude of the effect. Microstructural observations showed platelike gr ains of Y-123 with fine growth ledges in the thin film that was heat t reated, in contrast with the microstructure of an as-coated thin film that showed large twinned grains. From the processing point of view, t he results showed that heat treating Y-123 thin film according to the Bi-2223 tape schedule was compatible with and beneficial for Y-123. Th ese preliminary results may provide a basis for further improvements i n processing of long-length Bi-2223 tapes for high-field applications.