non-Debye Dielectric Relaxation Research Articles

Dielectric relaxation of 4-cyano-4-n-pentylbiphenyl (5CB) thin layer adsorbed on carbon nanotube – MD simulation

The ultra-thin layer of mesogenous molecules 5CB adsorbed on a single walled carbon nanotube (SWNT) has been studied by molecular dynamics (MD) simulation method. The focus was on the temperature dependence (200K<T<350K) and time evolution of the total dipole moment autocorrelation function. The frequency dependence of the dielectric loss of ultra-thin mesogene layer covering carbon nanotube has been also studied. The layer reveals a non-Debye dielectric relaxation. The shape of dielectric loss spectrum significantly depends on the temperature of the system studied.

Dielectric relaxation in glasses: possible origin of the stretched relaxation behaviour

The origin of non-Debye dielectric relaxation observed widely in network forming glasses is examined. It is attributed to the presence of two polarization centers, which relax in the manner of Debye polarization with a time delay between them. The experimentally observed relaxation therefore appears broadened and is fitted well by the powerful Kohlrausch–Williams–Watts (KWW) stretched relaxation function. It is shown that the relaxation behaviour predicted by the present model is in very good agreement with both the experimental and KWW generated relaxation behaviour.

Relaxor Ferroelectrics—From Random Field Models to Domain State Physics

Substitutional charge disorder in ferroelectrics giving rise to quenched electric random-fields (RFs) is probably at the origin of their relaxor behavior. Fluctuating polar nanoregions in the paraelectric regime are related to the spatial fluctuations of the RFs. While they destroy the ferroelectric phase transition and give rise to a glassy state in cubic relaxors like PbMg⅓Nb2/3O3, uniaxial systems like Sr1-x Ba x Nb2O6 exhibit RF Ising model behavior with non-classical critical exponents, e.g. α ≈ 0. Metastable pinned nanodomains in the ferroelectric regime are at the origin of non-Debye dielectric response, non-exponential relaxation, aging and memory effects.

Non-Debye dielectric relaxation in binary dielectric mixtures (50-50): Randomness and regularity in mixture topology

In this article, the frequency dependent dielectric properties ε(ω) of ordered and disordered two-dimensional binary composite structures were investigated and compared. The ordered structures were composed of hard disk inclusions in a matrix phase, and the inclusions were distributed on lattice sites. The disordered structures were, on the other hand, composed of 16 × 16 square networks (crossword puzzle-like structures), and the phases were assigned randomly to each square. The material parameters of the phases were assumed to be frequency independent (ε and σ being constant). Numerical calculations were performed using the finite element method in the frequency domain. We have found that the dielectric relaxation character of the structures, which were due to the interfacial (or Maxwell–Wagner–Sillars) polarization, changed drastically depending on the conductivity ratio of the phases and topology of the structures. Application of a recently developed dielectric data analysis method have resulted additional information about the dielectric relaxations in the considered structures. The regular lattice structures with a less conductive matrix phase than the inclusions’ (match composite), σ1&amp;lt;σ2, show a symmetric distribution of relaxation times, narrower than those with σ1&amp;gt;σ2 (reciprocal composite) when ε1 in both cases were lower than ε2. The generated random structures have, on the other hand, resulted in symmetrical relaxations (of Cole–Cole type) for match composites and asymmetrical relaxations of Davidson–Cole type for reciprocal composites in two dimensions. Therefore, depending on the ratio of the conductivities and permittivities of the phases, the interfacial polarization can be interpreted differently. The obtained relaxation time distributions have revealed that the relaxations were broad, and unlike the responses of the empirical formulas, there existed one maximum and one minimum, or two cutoff, time constants for the dielectric relaxation in dielectric mixtures. Comparison of the data to the Wiener and Hashin–Shtrikman bounds has indicated that the latter one was not valid for the triangular lattice and random structures. Finally, our simulations have also yielded similar dielectric responses as an analytical formula proposed for brine-saturated rock mixtures when σ1&amp;lt;σ2, when the constituent with the lowest ε is also the least conductive, match composite.

Non-Debye dielectric relaxation in complex materials

Abstract The paper considers several examples of non-Debye dielectric response in complex heterogeneous media. The percolation phenomenon and Cole–Cole relaxation in disordered matter are discussed in detail. The proposed models are illustrated by different sample systems: ionic microemulsions, porous glasses, porous silicon, polymer–water mixtures, and polymer–microcomposite materials. The models enable us to establish the relationship between the parameters of dielectric relaxation broadening, structural properties of the media and transport features of charge carriers in the considered systems. In addition, the origins of “strange kinetic” phenomena were discussed based on statistical physics and fractional time evolution ideas.

Multifractal phase transitions in the non-debye relaxation processes

The multifractal measures of the relaxation-time distributions are analytically obtained for some typical non-Debye dielectric relaxation processes. The characteristics of the corresponding multifractal thermodynamics are discussed. It is shown that the probability of the relaxation times near the poles of their distribution function is fractal scaling. The corresponding Lipschitz-Hold singular exponent is, or can be, determined by the so-called shape parameters in the empirical dielectric relaxation formulas. The relationship to some analytical proofs of the empirical dielectric formulas based upon the fractal models is also analyzed. Some generalized multifractal phase transitions with interesting features are reported in this paper. The recent experiment results on the molten-crystal transition in organic glass systems are also discussed to support our conclusions.

Scaling parallels in the non-Debye dielectric relaxation of ionic glasses and dipolar supercooled liquids

We compare the dielectric response of ionic glasses and dipolar liquids near the glass transition. Our work is divided into two parts. In the first section we examine ionic glasses and the two prominent approaches to analyzing the dielectric response. The conductivity of ion-conducting glasses displays a power law dispersion $\ensuremath{\sigma}(\ensuremath{\omega})\ensuremath{\propto}{\ensuremath{\omega}}^{n},$ where $n\ensuremath{\approx}0.67,$ but frequently the dielectric response is analyzed using the electrical modulus ${M}^{*}(\ensuremath{\omega})=1/{\ensuremath{\varepsilon}}^{*}(\ensuremath{\omega}),$ where ${\ensuremath{\varepsilon}}^{*}(\ensuremath{\omega})=\ensuremath{\varepsilon}(\ensuremath{\omega})\ensuremath{-}i\ensuremath{\sigma}(\ensuremath{\omega})/\ensuremath{\omega}$ is the complex permittivity. We reexamine two specific examples where the shape of ${M}^{*}(\ensuremath{\omega})$ changes in response to changes in (a) temperature and (b) ion concentration, to suggest fundamental changes in ion dynamics are occurring. We show, however, that these changes in the shape of ${M}^{*}(\ensuremath{\omega})$ occur in the absence of changes in the scaling properties of $\ensuremath{\sigma}(\ensuremath{\omega}),$ for which $n$ remains constant. In the second part, we examine the dielectric relaxation found in dipolar liquids, for which ${\ensuremath{\varepsilon}}^{*}(\ensuremath{\omega})$ likewise exhibits changes in shape on approach to the glass transition. Guided by similarities of ${M}^{*}(\ensuremath{\omega})$ in ionic glasses and ${\ensuremath{\varepsilon}}^{*}(\ensuremath{\omega})$ in dipolar liquids, we demonstrate that a recent scaling approach proposed by Dixon and co-workers for ${\ensuremath{\varepsilon}}^{*}(\ensuremath{\omega})$ of dipolar relaxation also appears valid for ${M}^{*}(\ensuremath{\omega})$ in the ionic case. While this suggests that the Dixon scaling approach is more universal than previously recognized, we demonstrate how the dielectric response can be scaled in a linear manner using an alternative data representation.

Orientational relaxation in a random dipolar lattice: Role of spatial density fluctuations in supercooled liquids.

We have carried out a computer experiment of orientational relaxation in a spatially random and orientationally disordered dipolar lattice (RDL), generated by quenching only the translational motion of a dense liquid. In the high polarity limit, the orientational relaxation of the RDL is dramatically different from that of the parent liquid, the former exhibits a very slow, nonexponential long time decay of the orientational correlation functions and markedly non-Debye dielectric relaxation. These results clearly demonstrate the importance of spatial density fluctuations in orientational relaxation.

Non-Debye dielectric relaxation around the liquid-glass transition of a glass-forming polymer.

The dynamics of glass-forming liquids shows universal features like non-Debye behavior, scaling, and non-Arrhenius temperature dependence of the characteristic rates. These features have been mainly established in the time range between 10 -9 and 10 s. It is well known that when the temperature of a glass-forming liquid is lowered and the characteristic relaxation time becomes larger than hundreds of seconds, the system falls out of equilibrium and a glass is obtained. However, whether or not the typical features of the glass-forming-liquid dynamics extend to the glass phase through the experimental liquid-glass transition, T g is still unknown

Scalable Non-exponential Dielectric Response in Lecithin-Water Multilayers

Abstract Data on the non-Debye dielectric relaxation of hydrated lecithin is analyzed. The fit to Cole-Cole and stretched exponential functions is poor, while the Cole-Davidson function gives a good fit to the data. This is consistent with the Dissado and Hill IR divergence theory of the dielectric response which implies that relaxation is due to proton hopping on finite connected hydrogen-bonded clusters. Alternatively it is possible that the non-Debye response is due to cooperative rotation of the head-groups and water dipoles.

Solvation Structure in the Time Resolved Stokes Shift and Adiabatic Electron Transfer

Abstract There is an important connection between the time resolved Stokes shift of a chromophore in a polar solvent and the dynamical contribution to electron transfer reactions. We present a microscopic theory of the time resolved Stokes shift of a chromophore in a polar solvent which incorporates both non-Debye dielectric relaxation and solvation shell structure, then apply it to the Sparpaglione-Mukamel theory of electron transfer reactions. We find that molecular effects can dramatically affect the rate of reaction. Moreover, we find that when translational motion is fast compared to rotational motion, dielectric continuum theory gives a good approximation to the reaction rate.

On the generalized continuum model of dipolar solvation dynamics

The continuum model of dipolar solvation dynamics is reviewed. The effects of non-spherical molecular shapes, of non-Debye dielectric relaxation of the polar solvent and of dielectric inhomogeneity of the solvent around the solute dipole are investigated. Several new theoretical results are presented. It is found that our generalized continuum model, which takes into account the dielectric inhomogeneity of the surrounding solvent, provides a description of solvation dynamics consistent with recent experimental results.