Microstructure Control and Critical Current Density of Ag Sheathed Y123 and Bi2223 Tapes(High-T_c Superconducting Materials Research)

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High J_c silver sheathed Y123 (YBa_2Cu_3O_<6+x>) and Bi2223 ((Bi, Pb)_2Sr_2Ca_2Cu_3O_y) superconducting tapes were prepared by the powder-in-tube method. The effect of cold-working and heat treatment as well as addition of third elements have been mainly investigated in order to improve the critical current density(J_c). The J_c of Y123 tapes increased with decreasing oxide layer thickness. When various kinds of working techniques have been examined, pressing was found to be the most effective for improving J_c. The specimen with 3300 A/cm^2 at 77 K consisted of the preferred oriented grain structure with low prosity. In the Bi2223 tapes, the repetition of pressing and heat treatment, so called thermomechanical treatment improved greatly the J_c. The specimens with 250, 000 A/cm^2 at 4.2K and zero magnetic field consisted of the highly laminated grain structure, where the c axis of Bi2223 superconducting grains is at most orthogonal to the tape surface. The addition of silver oxide improved the J_c at high magnetic fields. The microstructural factors for optimizing J_c have been compared for both oxide systems.
東北大学の論文