  The AC conductivity response in a broad frequency range of disordered
materials is of great interest not only for technological applications, but
also from a theoretical point of view. The Jonscher power exponent value, and
its temperature dependence, is a very important parameter in dielectric data
analysis as well as the physical interpretation of conduction mechanisms in
disordered materials. In some cases the power exponent of AC conductivity has
been reported to be greater than 1 at the low frequency regime. This fact seems
to contradict the universal dynamic response. The present work focuses on the
analysis of dielectric spectroscopy measurements in polymeric materials, below
100 MHz. The apparent power exponent n gets values in the range (0,1) and is
directly related to the characteristics of mobile charges at shorter time
scales, in the case of the occurrence of DC conduction and the slowest
polarization mechanism that is due to the charge motions within sort length
scales, in log(epsilon'')-log(frequenvy) plot. The emergence of apparent n
values in the range [1,2], for a relatively narrow frequency range, may be
attributed to an additional molecular dipolar relaxation contribution at higher
frequencies, in log(epsilon'')-log(frequency) plot. The appearance of apparent
n values in the range (1,2], can be assigned to the existence of a well defined
minimum between DC conductivity contribution and a molecular dipolar dispersion
or between two well separated dielectric loss mechanisms, in
log(epsilon'')-log(frequency) plots, above the crossover frequency. In these
latter cases, the apparent power exponent n is merely related to the
Havriliak-Negami equation shape parameters of the higher frequencies molecular
dipolar relaxations.
