磁場中熱処理したBi₂Sr₂CaCu₂O₈線材の電流輸送特性

抄録

The transport properties for in-field heat-treated monocore and multicore Bi₂Sr₂CaCu₂O₈ (Bi2212) tapes and multicore Bi2212 round wires were measured in detail. We found that the in-field heat-treatment enhances not only the critical current density J_c but also the n-value for all samples used in this study. These enhancements for the monocore tapes were more remarkable, compared in those of the multicore tapes and wires. Therefore the in-field heat-treatment is more effective for the Bi2212 tapes with a large core size. Microstructure observation shows that the grain size of the monocore tapes decreases as the result of in-field heat treatment. The analysis based on the percolation model related to the local J_c distribution suggests that the in-field heat-treatment increases the m-value, which determines the shape of the local J_c distribution and is related to the n-values. The two J_c distribution model can explain that the increases in n- and m-values are due to the decreases in the aspect ratio of the grains during in-field heat treatment.