Influence of the final heat treatment on properties of Bi-2223 multifilamentary tapes

A set of Ag-sheathed Bi-2223 (Bi1.72Pb0.34Sr1.85Ca1.99Cu3Ox) tapes was produced using the powder-in-tube technique under various final heat treatment conditions. These tapes were comparatively studied by “local” (magneto-optical imaging) and “global” (X-ray diffraction, magnetization and transport measurements) techniques. The combination of the complementary “local” and “global” results was used for establishing links between microstructure formation mechanisms and superconducting properties. Different measurements indicate that the amount of cracks and the grain connectivity, as well as the critical current density, are very sensitive to the second-step sintering conditions. The best results with respect to microstructural and superconducting properties are obtained when the sample is slowly cooled down after the first step sintering at 825 °C.