Structure and Superconducting Properties of Bi-2212 Cylinders Prepared by Diffusion Process
Bi-2212 oxide superconductors have been synthesized by the diffusion reaction between Sr-Ca-Cu oxide substrate and Bi-Cu oxide coating layer. The substrate with Sr:Ca:Cu atomic ratio of 2:1:2 is pressed into a cylindrical rod or tube by CIP, and then sintered. The coating layer with Bi:Cu ratio of 2:1 and Ag20 addition is coated around the surface of the substrate. The Bi-2212 diffusion phase shows high density and oriented structure with plate-like grains. The transport Ic and Je of the diffusion layer, about 150 µm in thickness, exceed 300 A and 2 × 10 4 A/cm2 at 4.2 K, respectively. The transport Jc decreases with temperature, and is about 1 × 10 4 A/cm2 at 30 K under 1 T. Post annealing in inert gas atmosphere such as Ar and N2 improves Tc of the specimen. The overall resistivity of bulk ends of the specimen is in the order of 10−8 Ω.cm2 at 4.2 K, and shows an ohmic relationship up to Ic. Bulk Bi-2212 oxide cylinders prepared by the present process with large transport Ic and Jc as well as low contact resistivity seem to be promising as a current lead for superconducting magnets.
KeywordsContact Resistance Diffusion Reaction Post Annealing Bulk High Temperature Superconductor Etching Reagent
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