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 method. Multifilamentary and monofilamentary tapes were sintered with intermediate uniaxial cold pressing. The critical current (I-c) of the tapes 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 nitrogen 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 odistinguished 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 stages. I-c0(s)/I-c0 increases with sintering time, showing that grain alignment and phase purity are more important for the formation of strong than weak links. Therefore, the preparation of the samples requiring a large I-c0(s) has to involve large sintering times. Mechanical deformation after Bi-2223 was fully formed is detrimental for the formation of strong links. An increase of I-c0(s) by a factor 2.6 was obtained with prolonged sintering if the samples are not pressed in the late sintering stages.