Frequency Dependent Conductivity Behavior Research Articles

AC Conduction in Polyaniline Emeraldine Salt-Graphite Pellets

The conduction characteristics of Polyaniline emeraldine salt-Graphite (PAni-ES/Gr) pellets were characterized using an impedance analyzer. The pellets were prepared with varying mass fractions of PAni-ES and Gr. FTIR spectra have the stretching vibrations for PAni-ES and absence of peaks for Gr. PAni-ES showed aggregated particles while Gr appeared as sheets and flaky structures. The composition of the pellets was differentiated in the AC conductivity values. The critical frequency representing the transition from frequency-independent to frequency-dependent conductivity decreases with increasing Gr content. Lastly, the frequency-dependent conductivity behavior follows power-law behavior reflecting possible hopping mechanisms and random resistor-capacitor network.

On the variation in the electrical properties and ac conductivity of through-thickness nano-porous anodic alumina with temperature

The electrical response of self-organized through-thickness anodic alumina with hexagonal arrangement of cylindrical pores has been studied as a function of temperature. Mechanically stable thick porous anodic alumina was prepared, by through-thickness anodic oxidation of aluminum sheet in sulfuric acid, with extremely high aspect ratio pores exhibiting fairly uniform diameter and interpore distance. It was observed that the electrical properties of through-thickness anodic alumina are very sensitive to minute changes in temperature and the role of surface conductivity in governing its electrical response cannot be overlooked. At high frequencies, intrinsic dielectric response of anodic alumina was dominant. The frequency-dependent conductivity behavior at low and intermediate frequencies was explained on the basis of correlated barrier hopping (CBH) and quantum mechanical tunneling (QMT) models, respectively. Experimental data was modeled using an equivalent circuit consisting of Debye circuit, for bulk alumina, parallel to surface conduction path. The surface conduction was primarily based on two circuits in series, each with a parallel arrangement of a resistor and a constant phase element. This suggested heterogeneity in alumina pore surface, possibly related with islands of physisorbed water separated by the regions of chemisorbed water. Temperature dependence of some circuit elements has been analyzed to express different charge migration phenomena occurring in nano-porous anodic alumina.

ELECTRICAL CONDUCTIVITY AND DIELECTRIC RELAXATION STUDY OF POLYVINYL ACETATE/POLY METHYL METHACRYLATE BLENDS

Transparent films of PMMA (poly methyl methacrylate), PVAc (polyvinyl acetate) and their blends, have been prepared by using a solution-casting technique. The dielectric properties and the electrical conductivity are reported. The frequency and temperature dependence of the dielectric constant, ε′ and tan δ, have been investigated for the studied samples in the frequency range from 1 kHz to 5 MHz and over a range of temperature from 303–413 K. In addition, AC conductivity values were calculated from the dielectric data and the conduction mechanism is discussed. The frequency-dependent conductivity behavior at different temperatures provides a qualitative description of the conduction mechanism. Also, differential scanning calorimetry (DSC) scans have been measured for the studied samples.

Dielectric permittivity, ac conductivity and phase transition in hydroxyl ammonium sulfate

The complex dielectric permittivity (ε*=ε′−jε″) and ac conductivity σ (ω, T) as a function of temperature (90–375 K) and frequency (0.4 kHz to ≈100 kHz) were measured in this work for polycrystalline samples of hydroxyl ammonium sulfate, (NH3OH)2SO4. The measured electrical parameters revealed the existence of a structural phase transition at T≈312 K, which was further confirmed by a differential thermal analysis thermogram, where a clear endothermic peak centered at ≈312 K is observed. Regarding the charge transport mechanism, it is likely that the behavior of frequency-dependent conductivity follows the universal dynamic response σ (ω,T)=A(T) ωs(T). Moreover, the temperature dependence of the frequency exponent s (0⩽s⩽1) suggests the quantum mechanical tunneling model to be the most likely one that describes the electrical transport mechanism. The data correlate with the crystal structure and the hydrogen-bonding system.

Hopping rates and concentrations of mobile fluoride ions in Pb1−xSnxF2 solid solutions

In the present paper, the ion dynamics and relaxation of fluoride ions in Pb(1-x)Sn(x)F(2) (with x=0.2-0.6) solid solutions, prepared by mechanochemical milling, are studied in the conductivity formalism over wide ranges of frequencies and temperatures. The conductivity spectra of the investigated materials are analyzed by the Almond-West (AW) power-law model. The estimated values of the hopping rates and the dc conductivity of different compositions are thermally activated with almost the same activation energy. The calculated values of the concentration of mobile ions, n(c), are almost independent of temperature and composition for x=0.2-0.4. The maximum value of n(c) is obtained for the x=0.6 sample, although it does not show the maximum conductivity. Therefore, the composition dependence of the ionic conductivity of these solid solutions could be explained based on the extracted parameters. The results presented in the current work indicate that the AW model represents a reasonable approximation of the overall frequency-dependent conductivity behavior of the investigated materials. The conductivity spectra at different temperatures for each composition are successfully scaled to a single master curve, indicating a temperature-independent relaxation mechanism. For different compositions, however, the conductivity spectra cannot be scaled properly, indicating composition-dependent relaxation dynamics.

Electric modulus and AC conductivity studies in conducting PPy composite films at low temperature

Dielectric properties and electrical conductivity of some conducting polypyrrole (PPy) composite films in the temperature range of 180–300 K and in the frequency range of 20–10 5 Hz have been reported. The experimental dielectric data have been analyzed in the light of electric modulus formalism. The electric modulus representation shows well-defined relaxation peaks. The conductivity relaxation energy as well as the AC conductivity activation energy was found to decrease as the PPy content increased. The frequency-dependent conductivity behavior at different temperatures provides a qualitative description of the conduction mechanism. The relaxation, occurs as a result of the hopping of charge carriers between localized states and the correlated barrier hopping model, describes the dominant mechanism.