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.     

Strong and weak polarization relaxation processes in solid dielectrics

It is established that an increase in the reach-through electrical conductivity of a dielectric can affect the frequency characteristics of the quantity tanδ in different ways when relaxation polarization processes occur: the extrema of the frequency characteristics can be either suppressed or intensified. In the former case, relaxation processes are referred to as weak; in the latter case, they are referred to as strong. Strong processes lead to the emergence of extrema in the frequency dependence of the imaginary part of complex conductivity. The causes underlying the two polarization relaxation processes are identified.     

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.     

Dielectric properties of modified As<Subscript>2</Subscript>Se<Subscript>3</Subscript>〈Bi〉<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> layers

The dielectric parameters (permittivity ? and dielectric loss tangent tanδ) for As₂Se₃〈Bi〉 _x layers are calculated using the polarization current relaxation curves measured at different strengths of the applied electric field. It is revealed that the bismuth dopant has a considerable effect on the frequency dependences of ? and tanδ, which is probably associated with the existence of microinhomogeneous regions with an increased dopant concentration.     

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.     

Effect of the Chemical Composition of TlIn1 – xErxS2 (0 ≤ x ≤ 0.01) Crystals on Their Dielectric Characteristics and the Parameters of Localized States

Physics of the Solid State - The frequency dependences of the real (ε') and imaginary (ε'') parts of the complex dielectric permittivity, the dielectric loss tangent...     

Mathematical modeling of the multimodal distributions of elastomer relaxation spectra using the family of Pearson curves

An approach to the mathematical modeling of elastomer relaxation spectra obtained via acoustic spectroscopy is presented. The solving of Pearson differential equations is the basis for the calculated dependences. The solutions to the equations describe the frequency and temperature distribution of the mechanical loss tangent. The form of the distribution is estimated from selected statistical moments of the experimental relaxation spectra and the mechanical loss tangent.     

Dielectric response of doped Bi<Subscript>12</Subscript>TiO<Subscript>20</Subscript>: Ru crystals in an alternating electric field

The results of examination of AC dependences of capacitance and dielectric loss tangent of sillenite Bi₁₂TiO₂₀ crystals doped with ruthenium on frequency are presented. Non-Debye dispersion of dielectric coefficients is found in the frequency interval of 5 × 10²–10⁵ Hz, and a resonance phenomenon is observed. Polarization processes in the studied samples are attributed to relaxators associated with metal–oxygen vacancies and structural elements incorporating 6s² lone-pair electrons.     

Semiconductor–Superionic Phase Transition in Silver Sulfide Films

Physics of the Solid State - The frequency dependences of the dielectric loss tangent tan δ(&nbsp;f&nbsp;) and the Cole–Cole diagrams of silver sulfide thin films are...     

AC conductivity and dielectric relaxation in Ba(Sm1/2Nb1/2)O3 ceramic

The complex perovskite oxide a barium samarium niobate (BSN) synthesized by solid-state reaction technique has single phase with cubic structure. The scanning electron micrograph of the sample shows the average grain size of BSN∼1.22 μm. The field dependence of dielectric response and loss tangent were measured in the temperature range from 323 to 463 K and in the frequency range from 50 Hz to 1 MHz. The complex plane impedance plots show the grain boundary contribution for higher value of dielectric constant in the low frequency region. An analysis of the dielectric constant (ε′) and loss tangent (tan δ) with frequency was performed assuming a distribution of relaxation times as confirmed by the scaling behaviour of electric modulus spectra. The low frequency dielectric dispersion corresponds to DC conductivity. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with an activation energy of 0.71 eV. The frequency dependence of electrical data is also analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behaviour of imaginary part of electric modulus M″ and dielectric loss spectra suggest that the relaxation describes the same mechanism at various temperatures in BSN. All the observations indicate the polydispersive relaxation in BSN.     

Microwave dielectric tangent losses in KDP and DKDP crystals

By adding cubic and quartic phonon anharmonic interactions in the pseudospin lattice coupled mode (PLCM) model for KDP-type crystals and using double-time temperature dependent Green's function method, expressions for soft mode frequency, dielectric constant and dielectric tangent loss are obtained. Using model parameters given by Ganguliet al [9] the dielectric losses are calculated for KDP and DKDP crystals. In the microwave frequency range an increase in frequency (1–35 GHz) is followed by an increase in dielectric tangent loss (1–35) at 98 K and (1–15) × 10⁻² at 333 K for KDP and DKDP crystals respectively. The dielectric tangent loss decreases from 0.052 to 0.042 for KDP crystals with increase in temperature from 130 to 170 K and for DKDP crystals it decreases from 0.0166 to 0.0074 with an increase in temperature from 230–343 K in their paraelectric phases at 10 GHz. This shows Curie-Weiss behavior of the dielectric tangent loss     

Dielectric Properties of Ferroelectric Nanocomposites Based on KD2PO4

Russian Physics Journal - The temperature dependences of the dielectric permittivity ε' and dielectric loss tangent tgδ have been studied for KD2PO4 embedded into the pores of the...     

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.     

Dc-bias-field-induced dielectric relaxation and ac conduction in CaCu3Ti4O12 ceramics

The dielectric relaxation and ac conduction of CaCu₃Ti₄O₁₂ (CCTO) ceramics were investigated at different temperatures under a dc bias. The dc bias gives rise to space charge accumulation, i.e. an electrode response, resulting in the significant increase of dielectric permittivity and dielectric loss tangent. Two Debye-like relaxations, arising from electrode and grain boundary responses, are present at low frequency with an increase of the dc bias. The electrode and grain boundary relaxations are distinguished according to the impedance spectroscopy and the frequency-dependent ac conductivity. The relaxation times of electrode and grain boundary relaxation are 0.955 ms and 0.026 ms, respectively, with a dc bias of 10 V at 328 K.     

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.     

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     

Dielectric relaxation and ac conductivity of double perovskite oxide Ho2ZnZrO6

Double perovskite oxide holmium zinc zirconate Ho₂ZnZrO₆ (HZZ) is synthesized by solid state reaction technique under a calcination temperature of 1100 °C. The crystal structure has been determined by powder X-ray diffraction, which shows monoclinic phase at room temperature. The variation of dielectric constant (ε′) and loss tangent (tan δ) with frequency is carried out assuming a distribution of relaxation times. The frequency corresponding to loss tangent peak is found to obey an Arrhenius law with activation energy of 89.7 meV. The frequency-dependant electrical data are analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behaviour of imaginary electric modulus shows the temperature-independent nature of the distribution of relaxation times. Nyquist plots are drawn to identify an equivalent circuit and to know the bulk and interface contributions.     

Low-frequency dielectric properties of yttrium formate crystallohydrate upon heating after quenching to −60°C

The specific features of the dielectric characteristics of yttrium formate crystallohydrate are studied. Its frequency dependences of dielectric permittivity and conductivity are obtained and analyzed in the 10⁻¹–10⁶ Hz range. Anomalies in the narrow temperature intervals of the dielectric properties of yttrium formate crystallohydrate are noted. The activation energies of relaxation processes are calculated from the experimental data. It is assumed that such anomalies are caused by changes in the dynamics of protons that participate in hydrogen bonds in the crystal structure.     

Dielectric properties of CdS nanoparticles synthesized by soft chemical route

CdS nanoparticles have been synthesized by a chemical reaction route using thiophenol as a capping agent. The frequency-dependent dielectric dispersion of cadmium sulphide (CdS) is investigated in the temperature range of 303-413 K and in a frequency range of 50 Hz-1 MHz by impedance spectroscopy. An analysis of the complex permittivity (ɛ′ and ɛ″) and loss tangent (tan δ) with frequency is performed by assuming a distribution of relaxation times. The scaling behaviour of dielectric loss spectra suggests that the relaxation describes the same mechanism at various temperatures. The frequency-dependent electrical data are analysed in the framework of conductivity and modulus formalisms. The frequency-dependent conductivity spectra obey the power law.