Dielectric Relaxation Mechanism Research Articles

Structural, electrical and dielectric characteristics of strontium-modified CaCu3Ti4O12

In order to produce an ultra-high dielectric constant and low loss factor in a polycrystalline material of Sr+2-modified (concentration 15%) CaCu3Ti4O12 (i.e., Ca0.85Sr0.15Cu3Ti4O12, abbreviated as CSCTO-15) was prepared using a cost-effective solid-state reaction technique. Structural analysis using Rietveld refinement of the X-ray diffraction data has confirmed that the sample crystallizes in a cubic system with space group symmetry of Im3. Morphological/microstructural analysis of the natural surface of a pellet shows dense grain growth, with clearly visible grain boundaries. The dielectric relaxation mechanism of CSCTO-15 has been revealed by the detailed study of frequency- and temperature-dependent dielectric parameters (er and tan δ). Analysis of the frequency and temperature dependence of impedance and related parameters, collected by a complex impedance spectroscopic technique, has provided and estimated the contributions of grain, grain boundaries and electrode in the electrical process in the material. The activation energy at high temperatures has been calculated from the temperature-dependent ac conductivity plots at selected frequencies.

Crystal structure, dielectric, magnetic and improved magnetoelectric properties of xNiFe2O4-(1-x)Na0.5Bi0.5TiO3 composites

Magnetoelectric (ME) composites of NiFe2O4 (NFO) and Na0.5Bi0.5TiO3 (NBT) with composition xNiFe2O4-(1-x)Na0.5Bi0.5TiO3 (x = 0.20, 0.40, 0.60) were prepared successfully by solid state reaction method. The crystal structure analysis was carried by using x-ray diffractometer, field emission scanning electron microscope—energy dispersive analysis of x-rays (FESEM-EDX) and Fourier transform infrared spectroscopy (FTIR). The presence of two individual phases corresponding to ferrite and ferroelectric was confirmed by XRD analysis of composites. Rietveld refinement of XRD data further confirms the existence of both cubic (Fd3m) and rhombohedral (R3c) symmetries. FESEM micrographs and EDX spectra revealed the reduction in grain sizes with increase in ferrite content. FTIR spectra depict two prominent absorption bands around 413 cm−1 and 618 cm−1. Dielectric response of these samples was recorded at frequency range 100 Hz–7 MHz for different temperature. Dielectric constant (ε′) and dielectric loss (tanδ) values found higher at low frequencies, decrease with increase in frequencies and become independent at higher frequencies. ε′ and tanδ both enhance with rising temperature and become more stable at higher frequencies. Complex impedance spectroscopy (CIS) investigation was used to understand dielectric relaxation and conduction mechanism in composites. Cole-Cole plots for all samples depict two semicircles and the centre of semicircles is depressed below real axis with temperature. Activation energy rises with increase in ferrite content in composites. Magnetic evaluation of the samples discloses the soft magnetic nature of these composites. The maximum value of saturation magnetization (MS = 22.82 emu g−1) and magnetic moment per formula unit (η = 0.92 μB) is observed for composition having higher NFO content. The highest ME response, α ∼ 1122 μV/cmOe is observed for the composite 0.60NiFe2O4-0.40Na0.5Bi0.5TiO3.

Dielectric relaxation and relevant mechanism in giant dielectric constant Sm2/3Cu3Ti4O12 ceramics

Sm2/3Cu3Ti4O12 ceramics with giant dielectric constant were successfully prepared by the traditional solid-state sintering process. The dielectric characteristics and relevant mechanism were systematically investigated. The dielectric constants of Sm2/3Cu3Ti4O12 ceramics can reach to 104 at 298 K and 1 kHz, and also exhibited two distinct thermal-activated dielectric relaxations in different temperature ranges. The dielectric relaxation at low temperatures was regarded as the effect of the polyvalence structures (Cu2+/Cu3+ and Ti3+/Ti4+) in grains due to the oxygen compensation during the sintering process, while the dielectric relaxation at high temperatures was induced by the grain boundary effects. The giant dielectric response in Sm2/3Cu3Ti4O12 ceramics can be associated with the heterogeneous structure and combined effect of the grain and grain boundary.

Effect of Zr doping on dielectric properties and grain boundary response of CdCu3Ti4O12 ceramics

An effective strategy to improve the dielectric properties of CdCu3Ti4O12 ceramics was proposed via doping with Zr4+ substituting in Ti4+ sites using the sol-gel method. SEM images of samples with high densification show a fine-grained and uniform-sized microstructure, and the average grain sizes of the ceramics decrease with increasing content of Zr doping. A proper amount of Zr substitution in the CdCu3ZrxTi4-xO12 ceramics was of great benefit to depress the dielectric loss tangent. A CdCTO-Zr05 ceramic exhibited a relatively low dielectric loss tangent value of 0.048 at 1 kHz. Meanwhile, the improved grain boundary response and dielectric properties were closely linked to the enhanced grain-boundary resistance. Data obtained based on complex impedance spectroscopy assessments demonstrated that the giant dielectric permittivity of the samples should be ascribed to the internal barrier layer capacitor (IBLC) effect. Overlapped spectroscopy of scaling behaviours indicated that the electric conduction and dielectric relaxation mechanisms shown in CdCu3ZrxTi4-xO12 ceramics are the same in this work.

Microstructure and dielectric properties of Ag-BaTiO3 composite ceramics

Di-phase composite ceramics based on BaTiO3 with 5 vol% of Ag filler have been prepared by sintering the mixture of powders at temperatures above the silver melting point (1000 °C–1300 °C/2 h). As predicted by finite element calculations, the addition of metallic particles should produce a field concentration in some regions of the BaTiO3 matrix and therefore, an enhanced dielectric response with respect to pure BaTiO3. The role of oxygen vacancies on the dielectric relaxation mechanisms of Ag-BaTiO3 composites has been investigated. The sintering temperature of 1200 °C provided optimized ceramics with excellent dielectric properties, i.e. with low losses (tanδ < 3%) and room temperature permittivity measured at 50 kHz exceeding 6500 (and above 13,000 at the Curie temperature), as result of a good densification (94% relative density) and a synergy effect of the metallic particles inclusions and ceramic grain size in the range of ≈1 μm, where BaTiO3 has a well-known maximum of its permittivity.

Colossal permittivity and defect-dipoles contribution for Ho0.02Sr0.97TiO3 ceramics

High-performance dielectric materials arouse persistently considerable attention due to their potential in the field of solid state capacitors. Ho-doped SrTiO3 ceramics with the composition of Ho0.02Sr0.97TiO3 were prepared by the solid state reaction technique. Structure, colossal dielectric behavior and relaxation mechanism of Ho0.02Sr0.97TiO3 ceramics were investigated in detail. The results indicated that Ho substitution of 0.02 content into the host materials maintain a single cubic perovskite structure. The Ho0.02Sr0.97TiO3 ceramics sintered at high temperature (1350 °C) show colossal permittivity (up to 4908 at 10 kHz) with low dielectric loss (about 0.03) at room temperature, and good dielectric stability over a broad frequency range of 100 Hz - 100 kHz as well. Four kinds of dielectric relaxations are present in a broad temperature range from −140 to +350 °C. Thermally stimulated depolarization current (TSDC) measurements were performed to explore the defects associated relaxation process. Four polarization relaxation peaks were detected in Ho0.02Sr0.97TiO3 ceramics, and three of them were assigned to defect dipole relaxations. There seems a possibility to form some defect dipoles because of the interactions among the defects available such as Sr vacancies, Ti3+, (HoSr)•, ionized oxygen vacancies and localized electrons. These defect clusters would give rise to relaxation behaviors and thus contribute to the colossal dielectric characteristics.

Processing, dielectric and electrical characteristics of strontium-modified Ca1Cu3Ti4O12

In the present paper, the strontium (Sr)-modified Ca1Cu3Ti4O12 ceramic (further termed as CSCTO) has been fabricated by a conventional cost-effective ceramic route. The prepared sample is characterized to obtain the relationship between the structural and electrical properties in a wide frequency (103–106 Hz) and temperature (25–315 °C) ranges. X-ray diffraction spectra depict a single-phase formation of the compound, crystallized in the cubic system. The dielectric relaxation mechanism and electrical properties of CSCTO have been revealed by studying frequency and temperature dependence of dielectric parameters (er and tanδ) by dielectric and impedance spectroscopy. The temperature-dependant dielectric constant plots depict that at frequency 1 kHz, the compound has very high dielectric constant (order of 104) and relatively low tangent loss. The occurrence of ultra high dielectric constant of the compound may be due to the space charge polarization, interface and Maxwell–Wagner dielectric relaxation around low frequencies and high-temperature range. The contributions of grains in resistive and capacitive properties of the material can be obtained from the Nyquist plot. It is interesting to note that at room temperature, polarization loop (P ~ E hysteresis loop) of the sintered CSCTO showed lossy behavior. The use of TiO2 and CuO2 nano-sized powders in the starting stage of sample preparation with micron size of CaCO3 and SrCO3 powder promotes the kinetics of quick conventional solid state reaction at a microscopic level, that favors above possible mechanisms.

Structural, Dielectric and Electrical Characteristics of Lead-Free Ferroelectric Ceramic: Bi2SmTiVO9

Studies of structural and electrical properties of Bi2SmTiVO9, a member of the Aurivillius family, synthesized by a mixed oxide reaction method are discussed here. The compound crystallizes in the orthorhombic crystal system. Detailed analysis of surface morphology (using field emission surface electron microscopy and an energy dispersive x-ray analysis profile) has confirmed the formation of high quality samples (i.e., homogeneous distribution of densely populated grains and elements present in required quantity/ratio). Analysis of impedance and modulus data provide the mechanism of dielectric relaxation and transport properties in the sample. The experimental values of the real component of dielectric constant between 250 and 420 and loss tangent between 0.03 and 0.7 of the studied material (Bi2SmTiVO9), obtained in the frequency range of 300 kHz–1 MHz and temperature range of 300–500°C, suggest its applications for high frequency-high temperature devices. The analyses of AC conductivity of the system obeys the universal Jonscher’s power law, and the conduction mechanism of the Correlated Barrier Hopping model type. The existence of a hysteresis loop at room temperature supports the ferroelectric nature in the material.

Influence of nickel incorporation on structural, optical and electrical characteristics of SILAR synthesized CuO thin films

In this report, we have primarily studied the influence of nickel (Ni) incorporation on ac electrical conductivity, dielectric relaxation mechanism and impedance spectroscopy characteristics of copper oxide (CuO) thin films synthesized by successive ion layer adsorption and reaction (SILAR) technique. The materials has been characterized using X-ray diffraction and UV–VIS spectrophotometric measurements. Reduction in grain size in doped films up to a certain extent of doping (tentatively 6%) were confirmed from XRD analysis, beyond which there is a reverse tendency. Increase in band gap in doped films were observed up to 6% doping level which could be associated with enhanced carrier density in doped films. Impedance spectroscopy analysis confirmed enhancement of ac conductivity and dielectric constant for doped samples. The results are useful for capacitive application of the films. Beyond 6% doping level, AC conductivity and dielectric constant shows a reverse tendency indicating reduced density of charge carriers. Nyquist plot shows contribution of both grain and grain boundary towards total resistance and capacitance. Imaginary part of complex modulus and imaginary part of complex impedance was used to find the migration/activation energy to electrical conduction process. Nearly identical result was obtained from relaxation frequency/relaxation time approach suggesting hopping mechanism of charge carriers.

Langevin approach to the theory of dielectric relaxation of ice Ih

Within the Langevin approach a new phenomenological model of dielectric relaxation of the ice is developed. This model is based on the concepts of defect migration, which is the main mechanism for dielectric relaxation of the ice. The new model allows to describe the relaxation behavior of the ice over a wide temperature range and to explain its characteristic features: changes in the slope of relaxation time at high and low temperatures (“crossovers”), and the non-monotonic temperature dependence of the broadening of dielectric loss peak parameter. The “crossover” of relaxation time at high temperatures is due to the transition from the predominant motion of the orientational defects of Bjerrum to the preferential motion of ionic defects with decreasing temperature and the weak correlation between them. On the contrary, at low temperatures a strongly correlated motion of ionic and orientational defects arises, which causes the observed low-temperature “crossover”.

Correction to: Influence of Cu incorporation on ionic conductivity and dielectric relaxation mechanism in NiO thin films synthesized by CBD

Correction to: Influence of Cu incorporation on ionic conductivity and dielectric relaxation mechanism in NiO thin films synthesized by CBD

Excellent temperature stability, high relative permittivity, and piezoelectric properties of K0.5Na0.5NbO3–Bi(Li1/3Ti2/3)O3 lead-free ceramics

(1 − x)K0.5Na0.5NbO3–xBi(Li1/3Ti2/3)O3 [(1 − x)KNN–xBLT, x = 0, 0.005, 0.01, 0.015, 0.02] ceramics were prepared via a solid-state reaction method. The sintering behavior, phase structure, dielectric properties, piezoelectric performances and conductive behavior of ceramics were investigated. The BLT additive could effectively improve the performances of KNN ceramics. When x = 0.01, piezoelectric constants d33 of 145 pC/N, relative permittivity er of ~ 1551, temperature stability (Δe/e110 °C) of ± 9% (110–330 °C), dielectric loss tanδ ≤ 0.036 (101.5–388 °C) were obtained. The values of activation energy E rel and electrical conductivity activation energy E con changed from 1.1572 to 1.5918 eV and 0.8959 to 1.1088 eV, respectively. Furthermore, a possible mechanism of high temperature dielectric relaxation and conductivity could be attributed to the oxygen vacancy defect of secondary ionization.

AC – Conductivity Study of CdSe Nanorods

The nanorods of cadmium selenide (CdSe) have been synthesized by soft chemical route using mercapto ethanol as a capping agent. The sample forms a rod like shape, confirmed by transmission electron microscope (TEM) measurement. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample at a various temperature region with varying frequency range. Grain and grain boundary effects both are present in the complex impedance plane plot and is analyzed by an electrical equivalent circuit consisting of a resistance and a constantphase element. Dielectric relaxation mechanism shows peak positions in the imaginary parts of the spectra and that is analyzed by Cole–Cole model. The temperature-dependent relaxation times obeys Arrhenius law having activation energy of 0.391 eV, which indicates that polaron hopping is responsible for conduction or dielectric relaxation in this material. The presence of two plateaus in the frequency-dependent conductivity spectra follows double-power law

Electrical conduction mechanism and dielectric characterization of MnTPPCl thin films

The AC conductivity and dielectric properties of MnTPPCl sandwich structure as Au/MnTPPCl/Au were studied. The conductivity of the MnTPPCl thin films have been interpreted by the correlated barrier hopping (CBH) model. The dominant conduction process have found to be the single polaron hopping conduction. The values of the hopping distance, Rω, barrier height, W, and the localized-state density, N, are estimated at different frequencies. The behavior of dielectric constant and dielectric loss was discussed as a function of temperature and frequency. The dielectric constant was described in terms of polarization mechanism in materials. The spectral behavior of dielectric loss is interpreted on the basis of the Giuntini et al. model [1]. The value of WM is obtained as 0.32 eV. A non-Debye relaxation phenomenon was observed from the dielectric relaxation mechanism.

Electric Modulus Spectroscopic Studies of the Dielectric Properties of Carbon Nanotubes/Epoxy Polymer Composite Materials

ABSTRACTThe electrical properties of epoxy polymer/carbon nanotubes composites were characterized using impedance spectroscopy in the frequency range between 1 Hz and 10 MHz and temperature range between 25°C and 105°C. We report the analysis of the experimental data using the electric modulus formalisms to understand the dielectric relaxation mechanisms. The variation of the real and imaginary parts of the electric modulus versus frequency and temperature were suggestive of two relaxation processes, associated with dipolar relaxation and CNT-polymer interfaces. The Havriliak-Negami model of dielectric relaxation was used for modelling the relaxation processes, extracting the relaxation parameters.

AC conductivity and dielectric relaxation properties of bulk TlInSe2 prepared from single crystal

The dependence of AC conductivity and dielectric properties on the frequency and temperature for TlInSe2 in pellet form obtained from TlInSe2 single crystal were studied in the frequency range of 42 Hz–5 MHz and temperature range of 294–393 K. The structure of TlInSe2 in powder form was examined using X-ray diffraction. TlInSe2 at room temperature was found to be tetragonal system with lattice parameters of a = 8.063 A and c = 6.827 A. The structural parameters, such as crystallite size D, micro strain e, dislocation density δ, and unit cell parameters were determined from XRD spectra. The AC conductivity of the TlInSe2 was found to obey the power law, i.e. $${\sigma }_{ac}\left(\omega \right)= A{\omega }^{s}$$. AC conductivity of TlInSe2 was dominated by the correlated barrier hopping (CBH) model. The obtained activation energy values of the AC conductivity have confirmed that the hopping conduction is the dominant one. Where, a decrease in these values has noticed with the increase in frequency. The density of localized states $$N\left({E}_{F}\right)$$ close to Fermi level for TlInSe2 was obtained in the range of 1.02–2.8 × 1019 eV−1 cm−3 for various temperatures and frequency. The frequencies corresponding to maxima of the imaginary electric modulus at different temperatures were found to satisfy an Arrhenius law with activation energy ER of 0.32 eV. A decrease in the relaxation time τ was observed with the increase in temperature. The average hopping distance R and the average time of charge carrier hoping between localized states t were found in the range of 6.10–11.95 nm and 2 × 10−7–2.4 × 10−2 s respectively, for the investigated range of frequency and the value of the binding energy Wm was 0.52 eV. The dielectric relaxation mechanism was also explained by the Cole–Cole types.

Fine representation of dielectric properties by impedance spectroscopy

Dielectric spectroscopy is used as a quick, precise and nondestructive examination tool of macroscopical dielectric properties for dielectrics. However, if the information of the microstructure and the location of a certain dielectric relaxation can be learned also by dielectric spectroscopy, it will help to reveal point defect structure and macroscopic and microscopic mechanisms of conduction and dielectric relaxation. Fine representation of dielectric properties by impedance spectroscopy (IS) is analyzed carefully in this paper. It is found that IS is not a good tool to describe a uniform system because a pseudo relaxation peaks exists at low frequency limit corresponding to direct current (DC) conductivity, and two relaxation peaks appears simultaneously corresponding to only one relaxation process for a high loss system with tanδ>1. However it is very convenient to describe a multiple phase system with IS for that only one Cole-Cole arc with some distortion appears for every phase with several relaxations, therefore it is very easy to distinguish different phases from each other. Especially, the location of a true relaxation process can be deduced by IS without any uncertainly according to pseudo relaxation theory which is built in this paper. Furthermore, when dielectric properties are shown with specific impedance spectroscopy (SIS), the information of the microstructure can be obtained conveniently. Based on these theoretical results above, dielectric properties of CaCu3Ti4O12 (CCTO) ceramics with giant dielectric constant (GDC) are investigated. It is found that GDC comes from pseudo relaxation of grain.

Structural, electrical, and multiferroic characteristics of lead-free multiferroic: Bi(Co0.5Ti0.5)O3-BiFeO3 solid solution.

A solid solution of bismuth cobalt titanate [Bi(Co0.5Ti0.5)O3] and bismuth ferrite (BiFeO3) with a composition Bi(Co0.40Ti0.40Fe0.20)O3 (abbreviated as BCTF80/20) was synthesized via a cost effective solid-state technique. Phase identification and basic structural symmetry of the samples were determined by analyzing powder X-ray diffraction data. Field emission scanning electron micrograph (FE-SEM) and energy dispersive X-ray (EDX) spectra were analyzed to evaluate the micro-structural aspects (shape and size, distribution of grains) as well as a quantitative evaluation of the sample. The average crystallite (particle) and grain size were found to be ∼30 nm and ∼1–2 micron, respectively. The electrical parameters (dielectric constant, tangent loss, impedance, modulus, and conductivity) of as-synthesized material were obtained in a temperature range of 300 to 773 K and frequency range of 1 kHz and 1000 kHz. The strong correlation of microstructure (i.e., grains, grain boundary, etc.) and electrical parameters of this material were observed. The frequency dependence of electrical impedance and modulus exhibited a deviation from an ideal Debye-like relaxation process. The dependence of dielectric relaxation mechanism on frequency and temperature is discussed in detail. The field dependent polarization (P–E hysteresis loop) of BCTF80/20 exhibited an enhanced value of remnant polarization as compared to that of BiFeO3 (referred as BFO). At room temperature (300 K), the magnetic hysteresis loop measurements also showed a significant improvement in the magnetization of BCTF80/20. Thus, based on these enhanced values of remnant polarization and magnetic parameters, we can assume that BCTF80/20 may be considered as a promising candidate for some new generations of electronic devices.

PT/BORAX COMPOSITE AS A HIGH DIELECTRIC CONSTANT MATERIAL WITH LOWER DIELECTRIC LOSS

In recent years, high dielectric constant composites have been considered as the key materials for many cutting-edge applications such as supercapacitors, memory devices, electrical, mechanical, and biochemical engineering. However, the high dielectric loss at low frequencies become a crucial problem which makes the composite unsuitable for these technological applications. In this respect, this work has been devoted to prepare a new high dielectric constant composite material with low dielectric loss. From this point of view, Polythiophene /Na₂B₄O₇ (PT/Borax) composites with different borax contents varying from 10.0 wt.% to 50.0 wt.% have been prepared. The morphology and chemical structure of the composites as well as pure PT have been determined by Scanning Electron Microscopy (SEM) and Fourier Transformed Infrared (FTIR) Spectroscopy, respectively. The dielectric properties of the samples have been measured within 100Hz-16.5MHz frequency region at room temperature. The polymer composite with high dielectric constant and low dielectric loss at low frequency for various technological applications has been achieved for 50.0 wt.% Borax additive. The dielectric relaxation mechanism of the samples have also been identified as non-Debye type. The electrical conductivity properties of the samples have also been discussed in terms of Jonscher’s Universal power law.

Dielectric relaxation and conduction mechanism of complex perovskite Ca0.90Sr0.10Cu3Ti3.95Zn0.05O12 ceramic

In this work, Sr and Zn co-doped calcium copper titanate having nominal formula Ca0.90Sr0.10Cu3Ti3.95Zn0.05O12 has been synthesized and systematically studied for structure, dielectric and electrical properties. The phase purity of the prepared composition has been confirmed by X-ray diffraction (XRD) pattern and various structural parameters are presented here with Rietveld refinement data. The Scanning electron microscopy (SEM) image revealed the presence of homogeneous fine-grained microstructure investigated in the prepared ceramic. The impedance data well fitted with 2 R-CPE model confirmed the non-ideality of the system. Dielectric studies have shown the existence of two relaxation processes in low and high frequency domains. Low frequency dielectric response proposed as a combination of Maxwell-Wagner relaxation and intrinsic defect (Vo++) while high frequency behavior has been interpreted in terms of polaronic relaxation caused by hopping process of an electron between Ti3+ and Ti4+ states. The frequency dependent behavior of conductivity has been well fitted to Dong’s model and interpreted in term of Overlapping Large Polaron Tunneling (OLPT) mechanism. The various parameters; relaxation angular frequency (ω1) of Debye process, ionic hopping frequency (ω2), dc conductivity (σo), cole- cole parameter (α) and frequency exponent (s) have been determined by Dong’s Model fitting.