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

Abstract

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.