Impedance Spectroscopy and AC Conductivity Studies of Bulk 3-Amino-7-(dimethylamino)-2-methyl-hydrochloride

Impedance spectroscopy and alternating-current (AC) conductivity (rAC)
studies of bulk 3-amino-7-(dimethylamino)-2-methyl-hydrochloride (neutral
red, NR) have been carried out over the temperature (T) range from 303 K to
383 K and frequency (f) range from 0.5 kHz to 5 MHz. Dielectric data were
analyzed using the complex impedance (Z*
) and complex electric modulus (M*
)
for bulk NR at various temperatures. The impedance loss peaks were found to
shift towards high frequencies, indicating an increase in the relaxation time
(s0) and loss in the material, with increasing temperature. For each temper-
ature, a single depressed semicircle was observed at high frequencies, origi-
nating from the bulk transport, and a spike in the low-frequency region,
resulting from the electrode effect. Fitting of these curves yielded an equiva-
lent circuit containing a parallel combination of a resistance R and constant-
phase element (CPE) Q. The carrier transport in bulk NR is governed by the
correlated barrier hopping (CBH) mechanism, some parameters of which, such
as the maximum barrier height (WM), charge density (N), and hopping dis-
tance (r), were determined as functions of both temperature and frequency.
The frequency dependence of rAC at different temperatures indicated that the
conduction in bulk NR is a thermally activated process. The rAC value at
different frequencies increased linearly with temperature.