Effect of annealing period on the resistive transitions and AC losses in aBi1.6Pb0.4Sr2Ca3Cu4O12 superconductor fabricated by a wet technique

We estimated the irreversibility lines from the resistive-superconducting t ransition in DC magnetic fields up to 1 T for the Bi1.6Pb0.4Sr2Ca3Cu4O12 su perconducting samples prepared by liquid ammonium nitrate with the same hea t treatment but 25 h and 200 h of annealing time. Increasing the annealing time from 25 h to 200 h at 840 degrees C shifted the irreversibility temper ature to a higher temperature. A non-linear Arrhenius plot of the resistive tail has been found. The activation energy obtainable from Arrhenius plots seems to be non-linear temperature dependent. The peak temperature T-p, in the imaginary part of the AC susceptibility seems to be shifted to a highe r temperature by nearly the same amount as the shift in irreversibility tem perature with increasing annealing time. Temperature variation of the criti cal current density extracted from the theoretical calculation of matrix su sceptibility and irreversibility line obey the same power law dependence of (1 - T/T-c)(n), where n = 2.7 and 2.5 for the 25-h and 200-h samples, resp ectively. (C) 2000 Elsevier Science S.A. All rights reserved.