FORMATION OF WEAK AND STRONG LINKS IN AG BI-2223 SUPERCONDUCTING TAPES/

Ag-sheathed Bi-2223 tapes were prepared by the oxide-powder-in-tube me thod. Multifilamentary and monofilamentary tapes were sintered with in termediate uniaxial cold pressing. The critical current (I-c) of the t apes was measured at each step of the sintering, before the pressing. Measurements of I-c were performed with the four-probe de method, with the 1 mu V/cm criterion. The samples were submerged in liquid nitroge n and a magnetic field H applied perpendicular to the tape plane. The critical current through the strong links in zero field (I-c0(s)) was distinguished from the total I-c using the field dependence odistingui shed from the total I-c using the field dependence of I-c. I-c0(s) was used asa measure of the population of strong links in the samples. It was found that strong links are mainly formed in the late sintering s tages. I-c0(s)/I-c0 increases with sintering time, showing that grain alignment and phase purity are more important for the formation of str ong than weak links. Therefore, the preparation of the samples requiri ng a large I-c0(s) has to involve large sintering times. Mechanical de formation after Bi-2223 was fully formed is detrimental for the format ion of strong links. An increase of I-c0(s) by a factor 2.6 was obtain ed with prolonged sintering if the samples are not pressed in the late sintering stages.