  Relaxation of the intergranular critical state has been observed at a very
low applied magnetic field (10-50 Oe) over a temperature regime of 20-77 K in
bulk polycrystalline YBa(2)Cu(3)O(7-x) (YBCO) and
Bi(1.75)Pb(0.35)Sr(2)Ca(2)Cu(3)O(10+x) (BPSCCO) samples. In such a disordered
Josephson junction network, the relaxation is slower than the intragranular
relaxation and, hence, it yields higher flux pinning energy U0 than the
corresponding intragranular values. Silver addition seems to have given rise to
much uniformity in the grain boundary characteristics which results in sharp
drop in the flux pinning energy since it depends on the variation of the
junction coupling energy EJ across the network. While U0 ~ 0.5 and 0.55 eV for
the parent BPSCCO and YBCO samples, respectively, in silver added (10-15 wt%)
samples the corresponding values are ~0.15 and 0.27 eV. The distribution
functions m(U) for the flux pinning energy and n(theta) for the grain boundary
mis-alignment angle(theta) have been evaluated from the experimentally observed
patterns of magnetic relaxation and variation of the grain boundary critical
fields with temperature. The distribution functions become narrower in the case
of silver added samples reflecing a reduction in the degree of disorder. The
variation of the effective vortex mass m* with the variation in the degree of
disorder is observed. Considering the width of the superconducting transition
delTc as the measure of the degree of disorder (inhomogeneity), it has been
shown that the transport critical current density Jc follows a relationship Jc
\~exp(-delTc) while the flux pinning energy U ~ delTc. These relations may help
in devising a suitable strategy for achieving the desired effect : high Jc yet
slower decay rate, i.e., large U.
