AC dielectric relaxation of lightly hydrochloric-acid(HCl)-doped polyanilines

The AC dielectric response of lightly hydrochloric-acid(HCl)-doped polyaniline (PAN) films is studied. The dielectric constant and the conductivity of PAN samples with different doping levels are measured as functions of the frequency and the temperature. The experiments are carried out in the frequency range from 10 Hz to 2 MHz and the temperature range from 78 K to 300 K. The frequency dependence of the dielectric constant is analyzed in terms of a dipolar - or a conductivity - relaxation mechanism. The relation σ(ω)≈σ₀ω^s is observed for the frequency dependence of the AC conductivity. The AC dielectric relaxation time is estimated from the maximum peak of the dielectric loss. The loss peak appears at lower frequency as the pH level increases, which is explained by pair approximation for the AC transport phenomenon. With normalization of the dielectric loss, all data points fit in a characteristic curve, which implies that the mechanism of dielectric loss does not vary with temperature and pH. The activation energy of the systems is estimated from the temperature dependence of the relaxation time or the dielectric constant. The activation energy increases as the pH level increases, which indicates that the barrier height for AC transport of the systems can be controlled through doping. We present the AC conductivity as a function of doping level for different frequencies.