Position-sensitive measurements of the local critical current density in Ag sheathed high-temperature superconductor (Bi, Pb)2Sr2Ca2Cu3Oy tapes: The importance of local micro- and macro-structure

Abstract Small sections cut from within individual superconducting filaments of Ag sheathed (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O y (BSCCO-2223) tapes have critical current densities ( J c ) which depend very much on the local microstructure and which can be as much as five times higher than the average J c . Tapes having average J c values of 12–15 000 A/cm 2 (77 K, 0 T) had local J c values up A/cm 2 , a value larger than hitherto reported for any bulk sample. Close to the Ag sheath the conversion to the 2223 phase is more complete and the grains are larger and better aligned and the J c is then much higjer and less field sensitive. Large variations are also found in more uniformly reacted tapes, perhaps due to variations of the local crack density. The microstructure of the highest J c regions is still far from ideal, thus showing that the limits of this technologically very important system are far from being achieved.