Microstructures and Superconducting Properties of Ag Alloy Sheathed Bi-2223 Tapes

Abstract

Bi-2223 superconducting tapes were prepared by the powder-in-tube technique using Ag-10 at%Cu-x at%M (M=Ti, Zr or Hf, X=0 - 1.0) alloy sheaths. The alloy sheathed tapes with a very small amount doping of Ti, Zr or Hf, the doped tapes, exhibited considerably higher Jc values than those of pure Ag or Ag-10 at%Cu sheathed tapes, the non-doped tapes. The highest Jc values at 4.2 K/14 T and 77 K/0.4 T reached around 9.0x and 1.0×104 A/cm2, respectively, for the doped tapes, especially for the 0.1 – 0.03 at%Ti or 0.1 at% Hf doping. Compared with the non-doped tapes, the doped tapes show in most case larger magnetic moment. SEM microstructures observed on the core surfaces of these tapes revealed large flat-shaped Bi-2223 grains containing neither subgrains nor small stick-shaped grains. Furthermore, high resolution transmission electron microscope revealed that amorphous disc-like regions with less than 5 nm in thickness parallel to (001) plane were introduced into Bi-2223 lattice in parallel to CuC2 layer. These changes in grain morphology and existence of amorphous disc-like regions may strongly be related to the high Jc properties of the doped tapes, especially the amorphous regions may play the important role as one of pinning centers.