53 research outputs found
Transformation of polarons to bipolarons in disordered matter
The polaron to bipolaron transition in disordered media under the influence
of a broadband ac electric field is suggested: ac conductivity vs. frequency
measurements in disordered media with inhomogeneous disorder induce
spatio-temporal fluctuations of the density of polarons yielding polaron to
bipolaron transformation. The external field results in the transition,
alternatively to an increasing doping level. The assertion is confirmed by
performing successive complex impedance measurements in disordered media. A
systematic increase of the real part of the ac conductivity in the frequency
domain, followed by mutual reduction of the magnetic inductivity of conducting
polypyrrole, are explained.Comment: 8 pages plus 3 figures. Accepted for publication in Applied Physics
Letter
Long aging time thermal degradation of the ac conductivity and complex permittivity of conducting polypyrrole
The modification of the ac conductivity and the complex permittivity of
conducting polypyrrole was monitored throughout a two years thermal aging at
343K. Reduction of the cross-over frequency is correlated with the degradation
of dc-conductivity, while the ac conductivity region corresponding to the
so-called 'universal' dielectric relaxation remains practically invariant
during the first year of ageing, which implies a collective co-operativity
among multiple degradation processes that yield a practically time-independent
effective disordered environment. A broad dielectric loss peak recorded in
fresh specimens splits into two distinct relaxations for intermediate stages of
the annealing process. The ageing-time evolution of the dc component and the
relaxations are qualitatively analysed and time constants are determined.Comment: Synth. metals (2011) in prin
Effect of composition on the dielectric relaxation of zeolite-conducting polyaniline blends
The complex permittivity of conducting polyaniline and zeolite - polyaniline
blends was measured in the frequency range 0.01 to 2000000 Hz from room
temperature to liquid nitrogen temperature. A loss peak is detected for 25, 35
and 50 wt % zeolite blends. Its position in the frequency domain, activation
energy and intensity is a function of composition. The experimental results are
interpreted through the competing multiple role of zeolite: as being less
conducting than polyaniline, it impedes the electric charge flow by dividing
large conducting polyaniline regions into smaller pieces, subsequently provides
short-range pathways and, moreover, enriches the blend in interfaces separating
zeolite from polyaniline.Comment: Accepted for publication in J. Appl. Phy
Pressure dependence of the dielectric loss in semi-conducting polypyrrole aged at room temperature
The effect of physical aging of semi-conducting polypyrrole at ambient
temperature for two years duration on the dielectric loss at various pressures
is investigated. Changes of the dielectric loss spectra and the modification of
the values of the activation volume for relaxation are interpreted through the
division of chain clusters into smaller components and the reduction of the
size of the conductive grains.Comment: Synthetic Metals (in print
Dielectric properties of Granodiorite partially saturated with water and its correlation to the detection of seismic electric signals
Transient electric signals emitted prior to earthquake occurrence are
recorded at certain sites in the Earth's crust termed sensitive. These field
observations enforce the laboratory investigation of the dielectric response of
rocks forming these localities. The dielectric relaxation of granodiorite rock
coming from such a sensitive locality (Keratea, Greece) reveals, through
complex impedance spectroscopy, that the activation volume for relaxation of
this rock is negative which so far has been reported only rarely. This result,
however, supports a theoretical model on the pre-seismic electric signals and
is likely to be correlated with the sensitivity of the site and hence with the
selectivity
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