UNUSUAL FORM OF THE TEMPERATURE AND FIELD-DEPENDENCE OF THE GRAIN-BOUNDARY WEAK-LINK DISSIPATION IN AG SHEATHED BSCCO-(2223) TAPES

The impressive critical current performance of Ag sheathed BSCCO (2223) tapes at low temperatures and high fields implies that in them the grain boundary weak links are much less deleterious than in other bulk HTS materials. However, so far there is little understanding of how the improvement comes about. We have looked at the weak-link behaviour in these tapes by examining the form of the I - V characteristics at currents above critical. In contrast to bulk YBCO, textured or not, and to BSCCO thin films, the weak-link dissipation in Ag sheathed BSCCO tapes drops rapidly as the temperature decreases, consistent with the large increase in critical current. Thus, the microscopic nature of the boundaries in these tapes is fundamentally different from that in the other materials.