The effect of the Sr/Ca ratio and Bi content on the microstructure and J/sub c/ of Ag-sheathed 2212 tapes was studied. Changing the Sr/Ca ratio changed the melting temperature of 2212 phase, the phase assemblage in the melt, and the nonsuperconducting phases in the fully processed tape. In tapes with Sr/Ca=2.75, the 2201 phase crystallizes from the melt before 2212 during cooling, and this 2201 remains in the microstructure. In tapes with Sr/Ca=1.3, there is more liquid left after cooling, and it converts to 2201 as the tape cools to room temperature. Fully processed tape with overall composition 2.1:2:1:2 had the most homogeneous microstructure and highest J/sub c/.
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Zhang et al. (1997) studied this question.
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