Microstructures in high- Jc Tl-1223/Ag tapes

Abstract

High- T c Tl-1223/Ag tapes with a nominal composition of (Tl 0.93Bi 0.22)(Sr 1.6Ba 0.4)Ca 2Cu 3O x were prepared using the powder-in-tube method combined with the two step reaction method. Their microstructures were examined using scanning and transmission electron microscopy. Tape A ( J c = 5 500 A/cm 2 at 77 K under 0 T) prepared using rolling only has a lower J c than tape B ( J c = 14 000 A/cm 2) prepared using pressing. In both tapes Tl-1223 forms plate-like grains. Although the size of the plates in tape A is larger than those in tape B, their mutual connection is poorer. Many subgrains are formed in each grain with small angle boundaries, which are composed of tilt-type as well as twist-type components in most cases. The boundaries might be considered as effective pinning sites for magnetic flux as far as the tilt component predominates. Additionally, small holes were found at the subgrain boundaries.