Microstructures and Superconducting Properties of Ag Alloy Sheathed Bi-2223 Tapes
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.
KeywordsHysteresis Loop High Resolution Transmission Electron Microscope Normal Field Parallel Field Tape Surface
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