ENHANCED FORMATION OF 1223 PHASE BY PARTIAL REPLACEMENT OF BI FOR TL IN IN-SITU SYNTHESIZED SILVER-SHEATHED SUPERCONDUCTING TAPE OF TL1-XBIXSR2-YBAYCA2CU3O9-DELTA

The in-situ synthesis method has been used in fabricating silver-sheathed superconducting tape of Tl1-xBixSr2-yBaCa2Cu3O9-delta. It was surprisingly found that the partial replacement of Bi for Tl greatly enhanced the formation of superconducting 1223 phase, as compared to the partially Pb replaced superconductor Tl0.5Pb0.5Sr1.6Ba0.4Ca2Cu3O9-delta. The critical current densities of tapes with composition in the range of x=0.0-0.4 and y=0.0-2.0 have been determined by transport measurements. We found that the partial substitutions of both TI by Bi and Sr by Ba can vary over a wide range without drastic reduction of the J(c) values, with the highest J(c) values obtained reproducibly at x=0.22 and v=0.4. A pellet of composition Tl0.78Bi0.22Sr1.6Ba0.4Ca2Cu3O9-delta was found to consist of a single 1223 phase according to the XRD patterns. At 77 K and in the absence of an external magnetic field, the observed J(c) is 1.33 X 10(4) A/cm2 for the rolled tapes and 2.1 x 10(4) A/CM2 for the rolled and pressed tapes. In the presence of the external magnetic field, the transport J(c) was limited by weak links.