DETERMINATION OF THE INTRAGRAIN CRITICAL-CURRENT DENSITY OF THE BI(2223) PHASE INSIDE AG-SHEATHED TAPES

Multifilamentary Ag-sheathed (Bi, Pb)(2)Sr2Ca2Cu3O10 tapes, prepared b y the powder-in-tube method, have been characterized by both transport and magnetic techniques at temperatures T between 4.5 K and 85 K in a magnetic field mu(0)H up to 15 T, with the aim of studying the residu al presence of a granular behaviour over this wide H-T range. From a c omparison between these measurements we have determined a domain of th e H-T plane where the current density is still limited by the quality of the boundaries between adjacent grains and the polycrystalline supe rconductor behaves as a granular one and, on the contrary, the tempera ture region where it behaves like a strongly connected body. Finally, the temperature behaviour of the intrinsic Bi(2223) current density ha s been evaluated. At temperatures below 30 K in zero applied field, th e intragrain current density is at least an order of magnitude higher than the transport current density.