The formation mechanism of Bi,Pb(2223) outgrowths in multi-filamentary tapes

We present a micro-structural study of the formation of superconducting out growths in multi-filamentary Bi,Pb(2223)/Ag tapes. Such bridges between the filaments have been shown to be capable of carrying sizeable currents and thus can greatly increase AC losses in these conductors, BS. quenching a se ries of tapes at different reaction times, we were able to study how these outgrowths nucleate and develop, A statistical analysis of their number and length shows that they nucleate at predetermined sites and that their grow th holds equal tread with the Bi,Pb(2223) formation within the filaments, b oth processes being governed by the availability of transient liquid. The o rientation distribution of the outgrowths shows that they usually nucleate at 'dents' in the Ag/ceramic interface caused by the mechanical deformation of the inherently inhomogeneous precursor powder. The influence of precurs or powder coarseness,-composition and annealing atmosphere are also discuss ed, The data suggest that outgrowths formation can be minimized by the use of homogeneous and fine-grained powders without hard particle agglomerates.