SUPERCONDUCTING WIRES OBTAINED BY BI-2223 COATING, OR BI-2223 SYNTHETIZATION FROM PRECURSORS, ON A METAL CORE - IMPORTANCE OF THE METAL CORE AND OF AN EXCESS OF PBO DURING SINTERING

Superconducting wires have been prepared by Bi1.6Pb0.4Sr2Ca2Cu3O10 (Bi -2223) coating of a great number of different metallic cores. The best electrical results (high T-c0 and small Delta T-c) were obtained with silver and silver coated iron cores for a sintering temperature T-s = 835 degrees C. For short sintering durations (less than 32 h) the res istance-versus-temperature curves R = f(T) presented several drops rev ealing the existence of several phases. In most cases one of these pha ses at least presents a large Delta T-c value that can be estimated by a percolation based parametrization method. For very long sintering d urations, up to six days, and with addition of an excess of PbO (the p ercentage of PbO in excess is related to the sintering duration), thes e curves presented only one drop. In the latter case T-c0 = 108 K, cor responding to 60% Bi-2223, as shown by the percolation based parametri zation method. It has been shown also that it is not necessary to use a good Bi-2223 ceramic to obtain these results, even precursors can be used, the Bi-2223 coating being then synthesized on the silver core. The role of the substrate, sintering temperature and of the excess of PbO will be discussed.