Novel precursor reaction pathways to Bi-2212 bulk superconductors

Precursors of defined phases composition were produced by separate calcination of compounds that complete each other to the Bi:2, Sr:2, Ca:1, Cu:2 stoichiometry. The critical current densities (jc) of thick film material processed from these precursors range from 6000 to 8000 A/cm2 (10 μV/cm). It was found that precursors with phase compositions that form rapidly Bi-2212 platelet grains yield lower jc than phase compositions that react sluggishly. The different reactivities can be associated to different reaction pathways to the Bi-2212 phase. Rapid Bi-2212 phase formation is a consequence of melt assistance, which favours a high aspect ratio of the grains. The different jc achieved by the precursors can therefore be attributed to the different particle aspect ratios and the different nuclei densities for the peritectic decomposition that have an influence on the homogeneity of the partial melt state.