Formation and growth mechanisms of Bi-2212/Ag composite tapes

The microstructure changes during the solidification process of Bi-2212 tapes with several nominal compositions of Sr and Ca were investigated using an oil-quenching technique. The formation mechanism was almost the same in all composition tapes. Non-superconducting phases such as Bi-free and Cu-free solid phases exist in the liquid at T/sub max/. The quantity of the non-superconducting phases of Sr/Ca=1.8/1.2 and 2.2/0.8 tapes was larger than those of the 2.0/1.0 tape. With the solidification of the Bi-2212 phase near the oxide/silver interface, the non-superconducting phases melted into the liquid phase and shrank. Bi-2212 grains grew along the silver interfaces. The high J/sub c/ enhancement of the Bi-2212/Ag tape was explained by the excellent grain alignments at the oxide/silver interfaces. Locally, biaxially aligned Bi-2212 was observed at the oxide/silver interface for tapes fabricated using melt-solidification under a temperature gradient.