2003 Volume 123 Issue 3 Pages 294-300
It is known that critical current density Jc in Bi-Based superconductors increases with the length of sintering time, and further increases with cold isostatic pressing (CIP) process. Analysis of excess conductivity due to the thermal fluctuation above Tc provides information about fluctuation amplitude and the dimensionality of conduction, and makes it possible to evaluate the superconducting correlation length. In this study, the mechanism of how Jc of Bi-based copper oxide improves by increasing sintering time is discussed on the basis of fluctuation-conductivity analysis. The temperature dependence of the resistance of Bi-based superconductors with various sintering time was measured. It was found that correlation length and effective cross-sectional area obtained from analysis systematically decrease with the sintering time, and that these parameters correlate well with Jc of the samples. It is widely accepted that the increase in Jc of the samples is due to the improvement in the crystallinity, (i.e., the increase in crystal density and better alignment of the crystal grains) which brings about decrease in correlation length and effective cross-sectional area. Therefore, the effect of the improvement in the density and alignment of the crystals, an important factor for increasing critical current density, was evaluated from the fluctuation conductivity analysis.
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The Journal of the Institute of Electrical Engineers of Japan
