The affect of transients on secondary phase formation in multifilamentary (Bi, Pb)2223/Agcomposite tape

Abstract

The processing of (Bi, Pb)2223 tapes has been investigated extensively since the firstOPIT tapes were made in 1989. The formation of Bi-2223 is via a Pb-inducedliquid phase, which is known to assist the Bi-2223 formation. However, there aremany unsolved microstructural inhomogeneities and defects in current OPIT tape;consequently research has begun to focus on the role of the liquid phase. In thisstudy differential thermal analysis results on green (Bi, Pb)2223 tape in 7.5% ppO2 give direct evidence for two phase transitions, with onset temperatures of 800 and820 °C. XRD phase analysis on tapes heat treated for prolonged periodsshow two distinct secondary phase formation regions: between 800 and820 °C; andabove 820 °C. A link is drawn between the phase transitions in the initial stages of Bi-2223 formationand the long-term secondary phase formation. The relevance of these results to transportproperties is discussed.