THE EFFECTS OF VARIABLE OXYGEN PARTIAL PRESSURES DURING BI-2223 TAPE PROCESSING

The effect of changes in the oxygen partial pressure during the heat t reatment of Bi-2223 tapes has been investigated. Distinct differences were observed in the phase assemblages, compositions, and critical cur rent densities, Of particular importance in the correlation of transpo rt properties and microstructure was the redistribution of lead in bot h the secondary phases and the Bi-2223 matrix. The highest J(c) values were associated with tapes that contained Ca2PbO4 as part of the phas e assemblage coupled with lower concentrations of lead in the supercon ducting phase. The high J(c) of 30.4 kA/cm(2) was obtained in tapes pr ocessed at 820 degrees C where the oxygen partial pressure was increas ed from 10% O-2/Ar to 20% O-2/Ar after 25 h of each 50-h sinter cycle. Samples processed only in 10% O-2/Ar at 820 degrees C did not contain Ca2PbO4, had slightly higher concentrations of lead in the supercondu cting phase, and had significantly lower J(c) values.