Impedance as a characteristic of relaxation polarization

The electrical characteristics of a dielectric material that can be used to determine the parameters of relaxation polarization arising in a dielectric and the influence on these characteristics of the steady leakage electrical conductivity are discussed. For weak relaxation processes at high electrical conductivities, the imaginary part of impedance can be used as such a characteristic. Extrema in the impedance frequency dependence are observed at any conductivity. However, the frequency dependence of the imaginary part of impedance contains two maxima whose frequency positions depend not only on the relaxation time but on other characteristics of the dielectric as well. In addition, the temperature shifts of the extrema of these curves depend not only on the activation energy of the relaxation process but on the activation energy of the electrical conductivity as well.     

Determining the relaxation polarization parameters in dielectrics with high electrical conductivity

In dielectrics with high steady leakage of conductivity, the frequency–temperature dependences of the dielectric loss tangent generally allow us to determine the relaxation time and activation energy of relaxation process only when they are strong. With weak relaxation processes, there are no extrema in the frequency dependence of the dielectric loss tangent. In such cases, the parameters of the relaxation processes are initially determined from the frequency behavior of the imaginary parts of the electrical module or impedance. However, the frequency dependences of these quantities when there is electrical conduction can contain three extrema. Identifying the maxima associated with relaxation polarization therefore requires additional research.     

The effect of conductivity on describing the non-debye relaxation processes in dielectrics

The distributions and integrated distribution of Cole-Cole and Dawidson-Cole relaxators are described. Based on the effect of conductance on the frequency dependences tanδ, the processes of relaxation polarization in dielectrics with such relaxators can be divided into two categories: strong and weak. In the development of strong processes, the increase in flow-through conductivity does not lead to the disappearance of extrema in frequency dependences tanδ.     

Relaxation polarizations: Strong and weak processes

It has been shown that the through conductivity can differently affect the frequency dependences of the dielectric loss tangent of dielectrics with relaxation polarization. According to this difference, the relaxations in dielectrics are divided into two types: strong and weak. In the case of strong relaxations, the frequency dependences of the imaginary part of the complex conductivity exhibit extrema. Strong and weak relaxations have been investigated in Debye and in non-Debye dielectrics in order to determine the boundary between these processes and explain the existence of relaxations of two types. It has been established that the relaxations in dielectrics can be separated because of the different ratios of the contributions to the polarization of dielectrics from the fast and relaxation polarizations. The corresponding data in the literature are reviewed and the data on the development of strong relaxations in heterogeneous dielectrics are reported.     

Dielectrics with strong and weak processes of polarization relaxation

The relationships between electrical parameters of layers needed both for the transition from strong to weak relaxations and for when there are no extrema in the relation between frequency and the dielectric loss tangent and imaginary parts of dielectric permeability are determined using a model for a double-layered dielectric with the serial inclusion of strata. The literature data was analyzed, allowing us to discover heterogeneous materials with developing strong and weak relaxation polarization. Materials for which the mean time of relaxation for dielectric permeability and conductivity differ were found.     

Physical meaning of conductivity spectra for ZnO ceramics

With the help of broadband dielectric spectroscopy in a wide temperature and frequency range, the conductivity spectra of ZnO polycrystalline ceramics are measured and the direct-current-like (DC-like) conductivity and relaxation polarization conductivity are observed successively along the frequency axis. According to the classical Debye theory and Cole-Cole equation, the physical meanings of the two conductivities are discussed. It is found that the DC-like conductivity corresponds to electron transportation over the Schottky barrier at the grainboundary. The relaxation polarization conductivity corresponds to electronic trap relaxation of intrinsic point defects (zinc interstitial and oxygen vacancy). When in the high frequency region, the relaxation conductivity obeys the universal law with the index n equal to the index α in the Cole-Cole equation as an indictor of disorder degree.     

Process of polarization and analysis of the water adsorption on a zeolite

We report the study of the dielectric relaxation mechanisms in the zeolite Na-X, “Faujasite”, by means of the method of Thermally Stimulated Depolarization Currents (TSDC), and polarization conductivity versus frequency. We give particular interest to the effect of adsorption on the evolution of dielectric parameters. Two distinct relaxation processes attributed to adsorbed water were found by TSDC measurements. Moreover, the polarization conductivity gives two sets of values of the potential barrier height. The evolution of the polarization conductivity as a function of the rate p/p° is comparable to the curve showing the isothermal water adsorption. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 Sept. 1994     

Effect of melt compounding temperature on dielectric relaxation and ionic conduction in PEO–NaClO<Subscript>4</Subscript>–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.     

Investigation of Relaxation Process of Nylon 1212 Using Dielectric Relaxation Spectroscopy

The relaxation processes of α-form nylon 1212 from 50°C up to 160°C were studied by dielectric relaxation spectroscopy (DRS) in a wide frequency range of 63 Hz to 5 MHz. The α relaxation, the electrode relaxation, and the conductivity relaxation of nylon 1212 were observed and analyzed in detail using permittivity and modulus formalism. Electrode polarization and dc conductivity were the origin of high dielectric permittivity values at low frequencies and high temperatures. The strength of the imaginary part of the electric modulus of conductivity relaxation M″ _max was nearly independent of temperature. The distribution of local conductivity and relaxation time became broader with decreasing temperature.     

CaCu3Ti4O12 陶瓷介电模量响应特性的研究

由于CaCu₃Ti₄O₁₂巨介电常数陶瓷的低频区直流电导较大, 本文采用模量 M"-f频谱表征与分析了低频和高频的两个松弛极化过程. 研究认为, 这两个特征峰属于晶界区Schottky 势垒耗尽层边缘深陷阱的电子松弛过程, 其中高频松弛峰起源于晶粒本征缺陷的电子松弛过程, 而低频松弛峰则为与氧空位有关的松弛极化过程. 对于CaCu₃Ti₄O₁₂这类低频下具有高直流电导的陶瓷材料, 采用模量频谱能更有效地分析研究其损耗极化机理. 关键词： 3Ti₄O₁₂陶瓷')" href="#">CaCu₃Ti₄O₁₂陶瓷 模量 松弛过程 电导     

Macroscopic polarization and thermal conductivity of GaN

We theoretically investigated the effect of macroscopic polarization (sum of spontaneous and piezoelectric polarization) on the thermal conductivity of wurtzite GaN. Macroscopic polarization contributes to the effective elastic constant of the GaN and thus modifies the phonon group velocity. We used the revised phonon velocity to estimate the Debye frequency and temperature. Different phonon scattering rates were calculated as functions of the phonon frequency. The thermal conductivity of GaN was estimated using revised parameters such as the phonon velocity and phonon relaxation rate. The revised thermal conductivity at room temperature increased from 250 to 279 W m⁻¹ K⁻¹ due to macroscopic polarization. The method we developed can be used for thermal budget calculations for GaN optoelectronic devices.     

Strong and weak relaxation polarization in dielectric statistical mixtures of non-extended particles

The heterogeneous dielectric in the form of a statistical mixture of nonextended particles is considered; the existence of through conductivity in each component is examined, and an expression for the complex dielectric permeability of this system is obtained. The conditions for the development of strong relaxation polarization in such systems are found. The transition from strong to weak relaxation polarization is identified from an increase in the relationship between the contributions of the relaxation polarization and the fast polarization processes to the effective polarizability of a heterogeneous system and a change in the distribution parameter.     

Topological structure in polarization resolved conoscopic patterns for nematic liquid crystal cells

We investigate the polarization structure of coherent light, produced by a convergent light beam transmitted through nematic liquid crystal (NLC) cells with different director configurations. Employing solutions to the transmission problem for the case when plane wave propagates through an anisotropic layer, we analyze the arrangement of the topological elements, such as polarization singularities (C points with circular polarization and L lines with linear polarization), saddle points and extrema of polarization azimuth. We observe transformations of the topological structure under the variation of the incident light ellipticity and represent it by corresponding trajectories of topological elements in three-dimensional space. For the cells with uniform and non-uniform director configuration we describe the processes of creation/annihilation of C point pairs, which can be controlled precisely in the case of the cell with non-uniform director. Our experimental measurements for the homeotropically oriented NLC cells are in good agreement with the theoretical predictions.     

A study of various intraband processes inn-InSb by means of stimulated spin-flip raman scattering

The spin-flip Raman (SFR) laser is shown to be an excellent tool to investigate different processes in the conduction band of the SFR laser crystal itself. For the case ofn-InSb, intracavity spectroscopy of inter-Landau transitions is demonstrated to be much more sensitive than conventional transmission spectroscopy. Data on cyclotron harmonic transitions, both free and LO-phonon assisted, are obtained from the output power characteristics of the SFR laser versus magnetic field. The spin-splitting energy and the effectiveg-factor up to 14 T are derived from the SFR laser frequency. The influence of temperature on SFR laser power, threshold and frequency is investigated. The relaxation following the SFR laser pulse is observed in the electrical conductivity. This yields in a direct way the spin-lattice relaxation time at high magnetic fields, which is of the order of 200 ns.     

Relaxation processes in non-Debye dielectrics

The specific features of the relaxation processes in non-Debye dielectrics have been investigated. The nature of the difference between the relaxation frequencies of the dielectric constant and dielectric loss (conductivity) has been explained. It has been shown that the average relaxation frequency of the conductivity is considerably (in some cases, by several orders of magnitude) higher than the relaxation frequency of the dielectric constant owing to an increase in the conductivity spectra of the statistical weight of the relaxation processes with short relaxation times.     

How broad band (from radio frequency to microwaves) dielectric parameters describe synthetic chemical reactions

Large differences in the dielectric responses of isolated molecules and associated reactive mixtures are observed over a wide frequency spectrum ranging from low to microwave frequencies. We present the results obtained for the curing (cross‐linking) of a resin mixed with a hardener. Electrical dipoles contribute to orientation polarization whose responses lie in the 1 kHz to over 1 GHz frequency range, which is predominantly higher than the 0.1 Hz–10 kHz range in which ionic conductivity is observed. It is the relaxation frequency of the reactive mixture that will be considered as the reaction marker. We also describe the results obtained with the saponification of an ester in the presence of a catalyst, with the reactive mixture containing – as in the previous case – electric dipoles and ions, but with responses superimposed in the 1 MHz–10 GHz frequency band. In this case, and for simplification reasons, the low frequency band ionic conductivity is the reaction marker. The aim of this paper is to translate synthetic chemical reactions into electronic terms, in order to allow electronics engineers to understand the interaction between electromagnetic waves and materials. Copyright © 2008 John Wiley & Sons, Ltd.     

Dielectric relaxation spectroscopy of phlogopite mica

An in-depth investigation of the dielectric characteristics of annealed phlogopite mica has been conducted in the frequency range 0.1 Hz–10 MHz and over the temperature range 653–873 K through the framework of dielectric permittivity, electric modulus and conductivity formalisms. These formalisms show qualitative similarities in relaxation processes. The frequency dependence of the M″ and dc conductivity is found to obey an Arrhenius law and the activation energy of the phlogopite mica calculated both from dc conductivity and the modulus spectrum is similar, indicating that same type of charge carriers are involved in the relaxation phenomena. The electric modulus and conductivity data have been fitted with the Havriliak–Negami function. Scaling of M′, M″, ac conductivity has also been performed in order to obtain insight into the relaxation mechanisms. The scaling behaviour indicates that the relaxation describes the same mechanism at different temperatures. The relaxation mechanism was also examined using the Cole–Cole approach. The study elaborates that the investigation regarding the temperature and frequency dependence of dielectric relaxation in the phlogopite mica will be helpful for various cutting edge applications of this material in electrical engineering.     

巨介电常数氧化物CaCu3Ti4O12的介电和阻抗特性

采用固相烧结法合成了单相巨介电常数氧化物CaCu₃Ti₄O₁₂（CCTO）.用阻抗分析仪分析了10—420 K温度范围内的介电频谱和阻抗谱特性,并结合ZVIEW软件进行了模拟.结果表明：温度高于室温时,频谱出现两个明显的弛豫台阶,低频弛豫介电常数随温度升高而显著增大,表现出热离子极化特点;温度低于室温时,频谱表现出类德拜弛豫,且高、低平台介电常数值基本不随温度变化,表现出界面极化特点和较好的温度稳定性.频谱中依次出现的介电弛豫对应于阻抗谱中 关键词： 3Ti₄O₁₂')" href="#">CaCu₃Ti₄O₁₂ 介电频谱 阻抗谱 Cole-Cole半圆弧     

Electrical conduction and polarization in PbWO<Subscript>4</Subscript> crystals

The regularities of ion-electron processes in an undoped PbWO₄ single crystal upon transition to a quasi-equilibrium state in an external dc electric field with a linear variation in the temperature in the range 290–600 K are investigated using different methods. The total conductivity, thermally stimulated polarization current, and thermally stimulated depolarization current are measured. It is assumed that the temperature dependence of the conductivity can be described within the theory of small-radius polarons. The thermally stimulated polarization (depolarization) currents are interpreted in terms of the space-charge (peaks of the current in the range 400–550 K) and dipole (peaks of the current in the range 290–370 K) mechanisms of generation of a polarization charge in the sample. The inference is drawn that the dominant contribution to the dipole polarization is made by dipolons, namely, doubly charged (cation-anion) vacancy pairs coupled through electrostatic interaction. The basic parameters of relaxation phenomena and charge transfer are calculated.     

Dielectric relaxation in PEO-based polymer electrolytes

Dielectric properties of cross-linked poly(ethylene oxide) (PEO) with different mesh sizes, doped with lithium salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), have been studied in frequency region between 0.1 and 10⁷ Hz and in broad temperature range. Results were compared with linear PEO of 1000 g/mol. Dielectric responses of the systems are dependent on frequency and thermally activated. Systems exhibit different responses in semi-crystalline and molten state. Increase of temperature promotes polarization; whereas, increase of frequency lessens it. In other words, polarization is thermally activated and local conductivity reduced. Generally, one observes enhanced dc conductivity in linear PEO as compared to cross-linked PEO at high temperature and the opposite at low temperature. Resonance responses are observed in low-molecular cross-linked PEO and in linear PEO at low temperature. These responses lead to splitting of polarization relaxation at frequencies beyond low-frequency range. Salt-comprising systems display only relaxation-type dielectric response. Imaginary parts of response spectra show distribution of relaxation times. It turns out that this distribution is independent of temperature in the low-frequency range, but depends on concentration of salt in the cross-linked polymer. In both systems, neat cross-linked and linear polymer of low-molecular mass, one observes coexistence of non-local and local motions of charged entities even at very low temperature.