ANOMALOUS BEHAVIOR IN THE CRITICAL-CURRENT DENSITY OF A (BI-2-X,PB-X)SR2CA2CU3O10-DELTA TAPE BELOW 10 K

The critical current density of a (Bi-2-x,Pb-x)Sr2Ca2Cu3O10-delta silv er-sheathed tape has been measured in fields up to 15 T and at tempera tures from 2 K up to T-c. Measurements were made for three different f ield-current orientations of the tape. Below 10 K there is a dramatic anomalous rise in the critical current as the magnetic field is decrea sed below a value B-A. The value of B-A is temperature dependent but o rientation independent. At 4.2 K and 2 K, B-A is 1.5 T and 2 T respect ively. At 10 K and above this anomalous behaviour disappears. The effe ct is attributed to the existence of a low-T-c (similar to 10 K) super conducting phase at the grain boundaries in the tape and clearly demon strates the importance of intergrain connectivity in obtaining high cr itical current densities in (Bi-2-x, Pb-x)Sr2Ca2Cu3O10-delta tapes.