Relaxation Process Of Ionic Conduction Research Articles

Dielectric relaxation dynamics of Al/epoxy micro-composites

The dynamic dielectric properties of the Al/epoxy composites were investigated by means of broadband dielectric spectroscopy spectrometer with the frequency range 1–107 Hz at the temperature of −20–200 °C. Three relaxation processes are detected in the dielectric spectra as a function of temperature and frequency: (1) Maxwell interfacial polarization (IP) at low frequencies and high temperatures; (2) a primary α-relaxation process near Tg at the middle frequencies; and (3) Intermediate dipolar effect (IDE) relaxation at high frequencies above −20 °C. The dynamics of all the recorded processes include contributions from both polymer and the inorganic reinforcing phases. The analyses of loss tangent and electric modulus spectrum of the composites indicate that the chain segmental dynamics of the polymer are accompanied by the absorption of energy given to the system. Finally, the alternating current (AC) conductivity spectra support the hopping type of conduction in the composites and the ionic conduction relaxation processes are observed also.

Dielectric relaxation and ionic conduction in 66%Silica/CW229-3/HW229-1 microcomposite polymer

Composites of epoxy resin with high percentage of silica fillers (66%) are designed to improve mechanical and electrical properties of transformers used in railway application. FTIR, (DRX and FE-SEM) and absorption/desorption phenomena are used to investigate the structure, the morphology and the diffusion of water in the microcomposites, respectively. Good dispersion of silica filler with size less than 10 μm was assessed by SEM, although some clustering (agglomerates) of greater than 1 μm was observed. The absorption water in the microcomposite obeys to the first Fickian law and shows saturation water of 0.6%. The calculation of the diffusion coefficient of water leads to a value of 2.9*10−12 m2 s−1 in the studied system. Relaxation times of α-relaxation and ionic conduction relaxation processes are determined. A correlation is observed between the ionic conductivity and dielectric relaxation processes. The dc-current behavior shows a change in the conduction mechanism from electronic conduction below the Tg to ionic conduction above the Tg. Shallow traps of 0.54 eV and deep traps of 2.21 eV are determined below and above the Tg, respectively. The TSC analysis confirms the VFT behavior of the α-relaxation of the microcomposite as obtained by the dielectric spectroscopy.

Dielectric Relaxations and Structures of Nanoclay in Solution Cast Poly(Ethylene Oxide)– Montmorillonite Clay Nanocomposites

The relative complex dielectric function, electric modulus and alternating current electrical conductivity spectra and complex impedance plane plots of aqueous solution cast poly(ethylene oxide)–montmorillonite clay (PEO–MMT) nanocomposite films were investigated over the frequency range 20 Hz to 1 MHz at ambient temperature. The intercalated and exfoliated structures of nanoclay dispersed in PEO matrix were recognized by the significant change in real part of dielectric function with clay concentration in the range 0%–20 wt%. The relaxation times corresponding to PEO chain segmental motion and ionic conduction relaxation processes were used to explore the interactions compatibility between PEO molecules and the dispersed MMT clay nanoplatelets and their effect on PEO chain dynamics. Real part of conductivity spectra of these nanocomposites over five decades of frequency has nonlinear behavior, which is influenced by the MMT clay concentration. The complex impedance plane plots confirm the bulk properties of these nanocomposites over the experimental frequency range.

Effect of melt compounding temperature on dielectric relaxation and ionic conduction in PEO–NaClO4–MMT nanocomposite electrolytes

Polymer nanocomposite electrolytes (PNCEs) of poly(ethylene oxide) and sodium perchlorate monohydrate complexes with montmorillonite (MMT) clay up to 20 wt.% MMT concentration of poly(ethylene oxide) (PEO) are synthesized by melt compounding technique at melting temperature of PEO (∼70 °C) and NaClO4 monohydrate (∼140 °C). Complex dielectric function, electric modulus, alternating current (ac) electrical conductivity, and impedance properties of these PNCEs films are investigated in the frequency range 20 Hz to 1 MHz at ambient temperature. The direct current conductivity of these materials was determined by fitting the frequency-dependent ac conductivity spectra to the Jonscher power law. The PNCEs films synthesized at melting temperature of NaClO4 monohydrate have conductivity values lower than that of synthesized at PEO melting temperature. The complex impedance plane plots of these PNCEs films have a semicircular arc in upper frequency region corresponding to the bulk material properties and are followed by a spike in the lower frequency range owing to the electrode polarization phenomena. Relaxation times of electrode polarization and ionic conduction relaxation processes are determined from the frequency values corresponding to peaks in loss tangent and electric modulus loss spectra, respectively. A correlation is observed between the ionic conductivity and dielectric relaxation processes in the investigated PNCEs materials of varying MMT clay concentration. The scaled ac conductivity spectra of these PNCEs materials also obey the ac universality law.

Frequency dependence of ionic conductivity in interacting lattice gas systems

This paper aims at a better understanding of the mechanism of the relaxation generally observed in structurally disordered solid electrolytes. The process is often termed “universal dynamic response”. It is called “universal dielectric response” if the frequency dependence of conductivity and permitivity is considered. The problem is examined critically by the pair approximation of the path probability method (PPM) corrected for the time averaging for binary interacting lattice gases and the results are compared with the cage-effect jump-relaxation model proposed by Funke et al. in a way that the meaning of this specific model can be examined. The binary system treated by the PPM is essentially equivalent to the dilute ionic system with repulsive interaction considered in the jump-relaxation model. Major statistical mechanical features of either treatment are found to be equivalent. In addition, it is possible to demonstrate, by means of the PPM, the relaxation process of ionic conduction in solids (hopping conduction) is intrinsically non-Debye type. This is due to a memory effect provided by a feedback effect of the motion of the particle and by an effect that it takes time for the propagation of information over a distance by a hopping process. The effect is enhanced when there are mutual interactions among conduction ions, in disordered solids, and in systems with conduction paths of low connectivity.