Fluctuation conductivity analysis for Bi-2223 superconductors with different sintering time

In a Bi-based superconductor. the critical current J(c) increases in accordance with the length of the sintering time and further increase is attained by cold isostatic pressing (CIP). The temperature dependence of the resistivity in polycrystalline Bi-2223 superconductors with different sintering time (t(s)) of 10-200 h was measured. In order to investigate the mechanism to improve J(c), the excess conductivity caused by the thermal fluctuation above T-c was analyzed using the Aslamazov-Larkin theory. It was found that the samples show a two-dimensional fluctuation in conductivity irrespective of t(s), and that the amplitude of fluctuation increases with t(s). The analysis indicates that the correlation length, which is inversely proportional to the amplitude, decreases with the length of t(s). Therefore, it can be deduced that J(c) of the samples improves as the crystals become more uniformly aligned with increased t(s) resulting in a shorter correlation length as confirmed by the SEM study. A similar result has been obtained for the samples with the CIP process. (C) 2001 Elsevier Science B.V. All rights reserved.