High J/sub c/´s in just-rolled Tl-1223/Ag tapes prepared using (Tl,Pb,Bi)-(Sr,Ba)-Ca-Cu-O compositions

The grain morphology, the changes in microstructure and J/sub c/ during the thermo-mechanical treatment, and the field dependence of J/sub c/ in Tl-1223/Ag tapes of Tl/sub 0.8/Pb/sub 0.2/Bi/sub 0.2/Sr/sub 1.6/Ba/sub 0.4/Ca/sub 2/Cu/sub 3/O/sub z/ and Tl/sub 0.8/Pb/sub 0.2/Bi/sub 0.2/Sr/sub 1.8/Ba/sub 0.2/Ca/sub 2.2/Cu/sub 3/O/sub z/ compositions were investigated, and then compared with each other. As a result, high J/sub c/´s near 25000 A/cm/sup 2/ at 77 K and 0 T were obtained in the latter composition, in which plate-like Tl-1223 grains are directionally aligned, at least in local regions. The high J/sub c/´s are attributed to enhanced grain-contact areas resulting from enhanced densification by a repetition of the TMT and the retarded decomposition of Tl-1223 phase in the latter composition. The strong field dependence of J/sub c/ indicates, however, that there still exist significant weak-links.