Much enhanced J(c) by intermediate rolling in just-rolled Tl-1223/Ag tapes

Tl-1223/Ag tapes of Tl0.8Pb0.2Bi0.2Sr1.8Ba0.2Ca2.2Cu3Oz nominal composition were prepared using the powder-in-tube method incorporating an in situ rea ction method. Connectivity and directional alignment of plate-like Tl-1223 grains were much enhanced by incorporating an intermediate rolling during t he final heat-treatment process. As a result, high J(c) values near 2.5 - 1 0(4) A/cm(2) at 77 K and 0 T with an excellent reproducibility were obtaine d in just-rolled tapes. The high J(c)'s seem to result from relatively easy recovery of excellent grain-connectivity during the final heat-treatment a fter intermediate rolling, probably due to retarded Tl evaporation and exce ssive Ca content in the present composition. The strong field dependence of J(c) even in low fields, however, indicated that there still existed signi ficant weak-links and the degree of directional grain-alignment was far fro m the desired one. The high J(c) is ascribed to enhanced contact areas betw een Tl-1223 grains rather than enhanced directional grain-alignment. The in tergranular binding in the tapes seemed to be mainly dominated by an SIS ju nctional type. (C) 1999 Published by Elsevier Science B.V. All rights reser ved.