Enhancement of critical current density for Bi-2212/Ag tape conductors through microstructure control

Abstract

We investigated the microstructures of Bi 2Sr 2CaCu 2O y (Bi-2212) at the free-surface and at the interface with silver substrate. The alignment of Bi-2212 grains near the silver substrate was better than that near the free-surface. Based on this result, we fabricated tape conductors having various cross-sectional configurations. J c increased with increasing oxide/Ag interface area and with decreasing oxide layer thickness. However, J c was almost independent of the area of the free-surface. These results suggest that most of the superconducting current flows locally near the silver substrate. Furthermore, we found that the alignment of Bi-2212 grains, and hence, J c can be improved by decreasing cooling speed during the heat treatment. The application of cold-rolling to the tape before the heat treatment is also effective in improving the microstructure and J c of Bi-2212/Ag tape. About 2 times larger I c and J c were obtained by ∼50% reduction of the oxide layer. The highest I c and J c obtained in this experiment were I c=450 A and J c=3.5×10 5 A/cm 2 (in 10 T, at 4.2 K), respectively.