In a Bi-based superconductor. the critical current J(c) increases in accord
ance with the length of the sintering time and further increase is attained
by cold isostatic pressing (CIP). The temperature dependence of the resist
ivity in polycrystalline Bi-2223 superconductors with different sintering t
ime (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 irrespectiv
e of t(s), and that the amplitude of fluctuation increases with t(s). The a
nalysis indicates that the correlation length, which is inversely proportio
nal 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 un
iformly aligned with increased t(s) resulting in a shorter correlation leng
th as confirmed by the SEM study. A similar result has been obtained for th
e samples with the CIP process. (C) 2001 Elsevier Science B.V. All rights r
eserved.