GRANULARITY AND PINNING IN HIGH-JC BI-2223/AG SHEATHED TAPES

This paper addresses the question to what extent the reduction of granularity and the improvement of pinning is responsible for achieving critical current densities of several 10 000 A cm-2 at 77 K in Ag-clad Bi-2223 tapes. The measurement of current carrying length scale shows that granularity can be completely eliminated at 77 K. The pinning properties are characterized through the measurement of the relaxation of the remanent magnetic moment. Compared with single-sintered samples no improvement in pinning is observed in as-cold worked samples, where the dislocation density is expected to be larger than in sintered samples. Although the relaxation in tapes is reduced through press and sinter steps, this is not due to an improvement of bulk properties, because, when breaking the sample into small particles, the relaxation is increased again. The results of the relaxation measurements are discussed in terms of grain boundary pinning.