Structures and superconducting properties of Bi-2212 oxide cylinders prepared by the dip-coating and subsequent diffusion reaction

Bi-2212 oxide superconductors have been synthesized by the diffusion reaction between a high melting point Bi-free oxide substrate and a low melting point Bi-based oxide coating layer. The substrate is composed of Sr-Ca-Cu oxides with atom I/sub c/ ratio of 2:1:2-3.5, and sintered into cylindrical rods and tubes. The coating layer is composed of the Bi-Cu eutectic oxide with a small amount of Ag addition, and coated around the substrate by dipping into the molten Bi-Cu oxide at 790/spl deg/C. The heat treatment is performed to produce Bi-2212 diffusion layer at 810-870/spl deg/C in air. The Bi-2212 diffusion layer, 100-150 /spl mu/m in thickness, shows a high density and oriented structure with plate-like grains. The maximum transport I/sub c/ and J/sub c/ of the diffusion layer exceed 300 A and 25000 A/cm/sup 2/ at 4.2 K under self-field, respectively. Post annealing in argon gas atmosphere improves T/sub c/ and J/sub c/ at higher temperature of the specimen. Present Bi-2212 oxide cylinders with large transport I/sub c/ and J/sub c/ seem to be promising as current leads and magnetic shields. The dip-coating process is more convenient for the practical fabrication of Bi-2212 oxide cylinders in comparison with the conventional slurry-coating process.