Phase formation and critical current density in Bi,Pb(2223) tapes

Abstract

The various fabrication and reaction processes leading to multifilamentary Bi,Pb(2223) tapes with high transport are described. In air, the Bi,Pb(2223) phase in pressed powders is found to be formed by nucleation, following the complete decomposition of the Bi,Pb(2212) intermediate phase. In this work, the precise formation conditions of the Pb-free phase Bi(2223) are described for the first time. It is shown that the presence of Pb leads to a lowering of the melting temperature from 879 to and of that of the `transient liquid' . The latter is formed after decomposition of the 2-layer compound and is necessary to the formation of the 3-layer compound. Thus Pb is found to have no influence on the formation mechanism of the 3-layer compound, which always starts by a nucleation process. Nucleation processes are also found to occur in the first phase of reaction inside Ag sheathed tapes, intercalation being possible at later stages.