Low-frequency Dielectric Dispersion Research Articles

Synthesis of sodium silicate and its application of dielectric relaxation spectroscopy — A report

This study aims to explain the dielectric relaxation in sodium silicate (Na2SiO3) and its direct dependence on temperature across various frequencies. The study examines and elucidates the involvement of various types of polarization in the thermo-active dielectric relaxation process. Both low-frequency dielectric dispersion and complex impedance play pivotal roles in controlling the thermo-active dielectric relaxation process. Utilizing complex data plots, the study actively, and prominently illustrates the relaxation process.

Low frequency dielectric dispersion in the AgNbO3 ferroelectric ceramic system

Lead-free AgNbO3 ceramic system has been synthesized via solid-state reaction sintering method. High-density material has been obtained, revealing the formation of the pure perovskite structure, without secondary phases. Dielectric response showed three typical anomalies in the temperature dependence of the dielectric permittivity, with evident frequency-dependent dielectric dispersion for temperatures close to both the room temperature and the Curie temperature regions. Results have been analyzed and discussed within the framework of the theoretical models reported in the literature.

Correlation of oxygen defects, oxide-ion conductivity and dielectric relaxation to electronic structure and room temperature ferromagnetic properties of Yb3+ doped CeO2 nanoparticles

Ce1-xYbxO2 nanoparticles synthesized using co-precipitation route were studied for properties like structural, optical, impedance and X-ray Photoelectron Spectroscopy. Existence of cubic fluorite structure found intact with heterogeneous aggregation and spherical surface morphology. Red-shifted energy gap along with formation of defects and oxygen vacancies was confirmed with UV–Vis and Photoluminescence analyses. XPS analyses were undertaken to observe the chemical states 2+ and 3+ of Yb and 3+ and 4+ of Ce cations. The magnetization results demonstrated improved ferromagnetic ordering for varying Yb doping, explained with Bound Magnetic Polarons model and F-Centre Mechanism for creation of distinct complexes, Ce4+-Vo-Ce3+ or Yb3+-Vo-Ce3+ in the CeO2 lattice. All samples' dielectric permittivity and modulus were measured in the 120 Hz–100 kHz frequency range. The ∈′ (f) and ∈″(f) plots show two distinct regions: a plateau zone at high frequency and low frequency dielectric dispersion region. These nanoparticles could be employed for photolytic, optoelectronics and energy storage applications.

Effects of crystallization kinetics on the dielectric and electrical properties of BiFeO3films

BiFeO3 thin films were prepared using the chemical solution route on Pt/TiO2/SiO2/Si(100) substrates under different crystallization kinetics. The crystallization kinetic effects on the dielectric and electrical properties have been investigated. These properties included dielectric permittivity, electric modulus, electrical conductivity measurements as a function of the temperature (300–525 K) and frequency (102–106 Hz), and leakage current measurements electric field range ± 30 kV/cm at room temperature. The differences observed in conductivity and current density of the BiFeO3 films were discussed in terms of possible defects induced by the crystallization kinetic. An anomalous relaxor-like dielectric behavior characterized by a broad maximum in the real dielectric permittivity as a function of temperature and the low-frequency dielectric dispersion has been observed. The nonexpected peaks in the real permittivity were accompanied by increasing at least four orders in the conductivity’s magnitude at high temperatures. The origin of the relaxor-like dielectric anomalies is discussed, suggesting that the dielectric permittivity peaks are artifacts due to carrier migration correlated to the onset of the Maxwell–Wagner effect.

A Study of Electrical Characteristics of Crystals of Homogeneously Doped LiNbO3:Zn,Mg in the Temperature Range of 450–900 K

In a series of initially polydomain crystals of LiNbO3:Zn,Mg obtained by the homogeneous doping of the crystals in the concentration ranges of around 1 ± 0.02 mol % MgO and 3.0–4.6 mol % ZnO, abrupt increases in temperature dependences of electrical conductivity σ(T) and dielectric constant e(T) with the manifestation of low-frequency dielectric dispersion are observed near T* ≈ 800 K. At T > T*, these crystals exhibit the activation enthalpy (Ha ≈ 1.76–2.07 eV) and transport enthalpy (Hm ≈ 1.55–2.01 eV) values that are unusually high for cationic conductors, while both values at T T*).

Structural, dielectric and electrical properties of pyrochlore-type Gd2Zr2O7 ceramic

This work reports on the dielectric and electrical properties of a single-phase polycrystalline pyrochlore structured Gd2Zr2O7 ceramics with a highly dense and compact microstructure. X-ray diffraction along with Raman spectroscopic studies confirmed the formation of the pyrochlore phase; while the electron microscopy investigations showed the uniformly distributed and densely packed micrometer-sized grains. The relaxation phenomena and conduction processes in Gd2Zr2O7 analyzed using complex impedance spectroscopy which showed the appearance of low-frequency dielectric dispersion suggesting the dominance of conduction by oxygen ions. Observation of double semi-circular arcs in the Nyquist plots confirms that both grains and grain boundaries contribute to the electrical impedance of Gd2Zr2O7. The temperature-dependent ac conductivity studies on Gd2Zr2O7 followed the Jonscher’s power law exhibited a strong dispersive behavior at the low temperature (< 300 °C) over the whole frequency region; whereas a weak dispersive nature observed at the higher temperature in the higher frequency region. An enhanced conductivity with relaxation phenomenon at elevated temperature is attributed to the transition from prolonged hopping to short-range ionic transportation. The increase in the ac conductivity with temperature reveals that Gd2Zr2O7 pyrochlore has a negative coefficient of resistance. Because of the good control of the electrical transport properties of Gd2Zr2O7 ceramic on its structure, it could be further exploited for the development of advanced solid-electrolytes for solid oxide fuel cells.

Structural, magnetic and dielectric properties of CoCr0.4Fe1.6O4

Abstract The bulk magnetostrictive Co Cr 0.4 Fe 1.6 O 4 was synthesized using solid state reaction technique. The correlation of structural properties with magnetic and dielectric properties is studied using powder X-ray diffraction, Scanning Electron Microscope, Vibrating sample magnetometer and Broadband dielectric spectroscopy. The obtained value of magnetization and soft magnetic nature is attributed to the mix cubic spinel crystal structure. The low frequency dielectric dispersion has been observed, which is associated with the presence of large vacant sites and its polycrystalline nature.

Frequency-dependent electrical behaviour of Na2SiO3: a brief report

The present study reports the frequency-dependent electrical properties of sodium silicate (Na2SiO3) (SS) at different temperatures to understand the contribution of grain and grain boundary polarization to its electrical response at a lower frequency region. The low-frequency dielectric dispersion and non-Debye-type dielectric relaxation are attributed to polaron hopping that controls the complex impedance of SS. A single semi-circular arc in Nyquist plot indicates a dominance of grain boundary polarization in the relaxation mechanism. The analysis of frequency-dependent ac conductivity in the studied temperature regime can be used to define the correlated barrier hopping model.

Low‐frequency dielectric dispersion in polymer‐derived amorphous silicon carbonitride ceramics

AbstractThe dielectric response of polymer‐derived amorphous silicon carbonitride (PDC‐SiCN) material was studied over a wide frequency range from 1 mHz to 10 MHz. Aside from presenting a relaxation process over 105 to 0.03 Hz frequency range, the material showed a strong low‐frequency dielectric dispersion (LFDD), which resulted in extremely high permittivities (up to 105) at frequencies lower than 0.03 Hz. It is identified that this LFDD resulted from relaxation process was not induced by conductivity. Therefore, PDC‐SiCN material showed two relaxation processes. Based on its microstructure, two polarization mechanisms were proposed for PDC‐SiCN: a mechanism based on polarons generated by unpaired electrons present in the material and an interfacial polarization mechanism as a result of different properties of SiCxN4−x matrix and free‐carbon clusters. Interfacial polarization process was simulated based on a parallel plate model involving two different materials. The result indicated that the relaxation time of an interfacial polarization can be distributed over a broad time range in the material.

Low frequency complex dielectric (conductivity) response of dilute clay suspensions: Modeling and experiments

In this work, we establish an effective medium model to describe the low-frequency complex dielectric (conductivity) dispersion of dilute clay suspensions. We use previously obtained low-frequency polarization coefficients for a charged oblate spheroidal particle immersed in an electrolyte as the building block for the Maxwell Garnett mixing formula to model the dilute clay suspension. The complex conductivity phase dispersion exhibits a near-resonance peak when the clay grains have a narrow size distribution. The peak frequency is associated with the size distribution as well as the shape of clay grains and is often referred to as the characteristic frequency. In contrast, if the size of the clay grains has a broad distribution, the phase peak is broadened and can disappear into the background of the canonical phase response of the brine. To benchmark our model, the low-frequency dispersion of the complex conductivity of dilute clay suspensions is measured using a four-point impedance measurement, which can be reliably calibrated in the frequency range between 0.1 Hz and 10 kHz. By using a minimal number of fitting parameters when reliable information is available as input for the model and carefully examining the issue of potential over-fitting, we found that our model can be used to fit the measured dispersion of the complex conductivity with reasonable parameters. The good match between the modeled and experimental complex conductivity dispersion allows us to argue that our simplified model captures the essential physics for describing the low-frequency dispersion of the complex conductivity of dilute clay suspensions.

Investigation of structural, morphological and electromagnetic properties of Mg0.25Mn0.25Zn0.5−xSrxFe2O4 ferrites

Polycrystalline Mg0.25Mn0.25Zn0.5−xSrxFe2O4 (0 ≤ x ≤ 0.20) ferrites were synthesized using the solid state reaction sintering at 1373 K and 1473 K for 4 h. The XRD patterns revealed the formation of single phase cubic spinel with Sr2FeO4 and SrFe12O19 as impurity phases. The decrement in the lattice parameter for Sr2+ substituted samples is attributed to the difference in ionic radii of cations. The crystallite size decreases with increase in Sr2+ content. Low frequency dielectric dispersion is attributed due to the Maxwell-Wagner interfacial polarization. The appearance of the peak in dielectric loss spectrum for x = 0.15 and 0.20 at 1373 K and x = 0.20 at 1473 K suggests the presence of relaxing dipoles. The loss peak shifts towards lower frequency side with Sr2+ content at 1373 K which is due to the strengthening of dipole–dipole interactions. The complex impedance spectra clearly revealed that the both grain and grain boundary effects on the electrical properties. A complex electric modulus spectrum indicates that a non-Debye type of conductivity relaxation exists. The saturation magnetization and remanence gradually decreases with Sr2+ substitution which may be due to the existence of non-magnetic phase in the space between the magnetic particles and the substitution of Zn2+ cation in Mg0.25Mn0.25Zn0.5Fe2O4 ferrite lattice by Sr2+ content. The permeability decreases significantly while the cut-off frequency increases with the Sr2+ content at 1373 K and decreases at 1473 K, obeying the Snoek's law.The decrease in permeability with Sr2+ content is attributed due to the decrease in magnetization because non-magnetic ions weaken the inter-site exchange interaction.

Dielectric and Conduction Properties of Lu&lt;sub&gt;3&lt;/sub&gt;NbO&lt;sub&gt;7&lt;/sub&gt; Transparent Ceramic

The dielectric response and electrical conduction of Lu3NbO7 transparent ceramic produced by spark plasma sintering were investigated. Lu3NbO7 transparent ceramic exhibited low frequency dielectric dispersion and a peak in dielectric loss, shifting to higher frequency at high temperatures. This indicated space charge polarization and broad relaxation time, confirmed by impedance and modulus spectra. The Nyquist plot shows the dominant grain effect in the electrical conduction. The AC conductivity of Lu3NbO7 transparent ceramic is 4.18×10-2 S m-1 at 1073 K, with an activation energy of 1.30 eV.

Influence of Ca2+ ions substitution on structural, microstructural, electrical and magnetic properties of Mg0.2−xCaxMn0.5Zn0.3Fe2O4 ferrites

Mg–Ca–Mn–Zn ferrites having general formula Mg0.2−xCaxMn0.3Zn0.5Fe2O4 (x = 0, 0.10, 0.15 and 0.20) were synthesized using solid state reaction method and sintered at 1100 and 1200 °C for 4 h. Structural, microstructural and elemental analyses of synthesized ferrites were performed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive analysis of X-ray. A cubical spinel crystal structure with secondary phases is conformed in synthesized samples by XRD analysis. The lattice parameter decreased initially and then increases at x = 0.20 at 1100 °C. On contrary, the lattice parameter increases with Ca2+ ions concentration at 1200 °C which is attributed due to the different ionic radius of Mg2+ and Ca2+ ions. The FTIR spectra show the presence of high frequency and low frequency band at 559.36–460.14 cm−1 at 1100 °C and 549.71–558.35 cm−1 at 1200 °C corresponding to the tetrahedral and the octahedral sites. The SEM images revealed that the average grain size increases with the increase of Ca2+ ions concentration which may be attributed due to the fact that Ca2+ ions influences the microstructure by forming a liquid phase during sintering process and expedites the grain growth by lowering the rate of cation interdiffusion. Low frequency dielectric dispersion is consistent with the Maxwell–Wagner interfacial polarization. Dielectric constant increases with Ca2+ concentration for both sintering temperatures. The samples x = 0.10 and 0.15 exhibits highest conductivity at 1100 and 1200 °C, respectively because the electron hopping between Fe3+ and Fe2+ ions increases. The conduction process is attributed due to the presence of grain and grain boundary effect as revealed by the impedance study. The significant decrement in permeability with Ca2+ concentration is attributed due to the lower saturation magnetization and increased inner stress or crystal magnetic anisotropy.

White emission for c-axis oriented Tm3+-Dy3+-Eu3+ tri-codoped Bi2VO5.5 ferroelectric thin films

ABSTRACTc-Axis oriented Tm3+-Dy3+-Eu3+ tri-codoped Bi2VO5.5 ferroelectric thin films were prepared on fused silica and Pt(111)/Ti/SiO2/Si substrates by using chemical solution deposition method, and characterized by X-ray diffraction, scanning electron microscopy, and optical and electrical measurements. Tm3+-Dy3+-Eu3+ tri-codoped Bi2VO5.5 ferroelectric thin films show near-white emissions, and the optimization component was selected as (Bi1.79Tm0.10Dy0.05Eu0.06)VO5.5, for which the CIE color coordinates are x = 0.3369 and y = 0.3423. After the rare earth ions co-doping, the low frequency dielectric dispersion weakened, the dielectric constant increased and dielectric loss deceased, while the remanent polarization (2Pr) values remain basically unchanged. As a new multifunctional material, the Tm3+-Dy3+-Eu3+ tri-codoped Bi2VO5.5 ferroelectric thin films could be used for a wide range of application, such as integrated electro-optical devices.

Structural, electrical, magnetic and magnetoelectric properties of (1−y) [Ba0.6−xCaxSr0.4Zr0.25Ti0.75O3] + (y) [(Li0.5Fe0.5)0.4Ni0.18Cu0.12Zn0.3Fe2O4] composites

Magnetoelectric composites having the nominal composition of (1-y) [Ba0.6-xCaxSr0.4Zr0.25Ti0.75O3] (BCSZTO) + (y) [(Li0.5Fe0.5)0.4Ni0.18Cu0.12Zn0.3Fe2O4] (LNCZFO) (x = 0.0, 0.1, 0.2 and y = 0.2, 0.4, 0.6, and 0.8) were synthesized by the solid state reaction method and sintered at 1200 °C for 3 h. The X-ray diffraction analysis confirms the coexistence of tetragonal perovskite BCSZTO and spinel LNCZFO phases with Ba6T17O46 as impurity phase. Microstructural and quantitative elemental of the samples were carried out by Field Emission Scanning Electron Microscopy equipped with Energy Dispersive X-ray Spectroscopy. Low frequency dielectric dispersion is attributed due to Maxwell-Wagner interfacial polarization arising from the interface of the two phases in agreement with Koop's phenomenological theory. Frequency independent behavior of dielectric constant at higher frequencies is attributed due to the inability of electric dipoles to follow the first variation of the alternating applied electric field. The dielectric constant decreases with the increasing Ca2+ concentration which is attributed due to the increased resistivity. Maxima in dielectric loss (tanδ) are appeared when the hopping frequency of electrons between different ionic sites becomes nearly equal to the frequency of the applied field. AC conductivity of the composites follows Jonscher's universal power law and the conduction mechanism is attributed due to small polaron hopping. AC conductivity increases with the increase of Ca2+ concentration. The composite materials are found to exhibit excellent frequency dependence and increases with the ferrite concentration. The permeability decreases with the increase of Ca2+ concentration which is attributed to the smaller grain size and increased magneto crystalline anisotropy. The quality factor increases with the Ca2+ ions substitution on account of the high resistive boundary segregation. The magnitude of magnetoelectric (ME) voltage coefficient increase linearly with the increase of the applied filed may be attributed to the nominally linear gradient of magnetostriction with respect to magnetic field. The magnetoelectric coefficient of the composites increases gradually as the increase in the ferrite content which is attributed due to the increase of the mechanical deformation in the magnetostrictive phase. An optimal magnetoelectric voltage coefficient of ∼1.16 V cm−1 Oe−1 is obtained for x = 80 wt% (C-series composites) at room temperature.

Dielectric and electrical conductivity characteristics of undoped and samarium doped ferroelectric SrBi2Ta2O9 ceramics derived from molten salt synthesis route

ABSTRACTUndoped and samarium doped SrBi2Ta2O9 ferroelectric ceramics have been fabricated by the molten salt synthesis route. The dielectric and electrical conductivity measurements were carried out in the 100 Hz – 1 MHz frequency range at various temperatures. A decrease in dielectric constant maximum (ϵm) and a downward shift in the Curie transition temperature (Tc) have been observed with the increase in samarium concentration.The frequency dependence real and imaginary parts of dielectric constant of these ceramics exhibited low frequency dielectric dispersion. Interestingly, temperature and frequency dependence dielectric constant plots indicated that the formation of oxygen ion vacancies have inhibited by samarium doping in SBT lattice. The activation energy values obtained from the Arrhenius plot have confirmed the existence of motion of oxygen ion vacancies in these ceramics.

Effects of swift heavy ion irradiation on dielectric relaxation and conduction mechanism in Ba0.90Sr0.10TiO3

The effects of 100MeV O8+ ion beam irradiation on the structural and dielectric behavior of Ba0.90Sr0.10TiO3 ceramics have been analyzed. Ion irradiation does not change the crystalline structure, however the tetragonal distortion increases. The low frequency dielectric dispersion especially at high temperatures increases significantly after ion irradiation. The dielectric relaxation phenomenon has been probed through complex impedance and electric modulus approaches. The observed dielectric relaxation has distributed relaxation times and is a thermally activated process. Ion irradiation enhances the cationic disordering. The contributions of grains and grains boundaries towards impedance have been separated. It is inferred that the grain boundaries become more resistive due to ion irradiation and is associated to oxygen vacancies annihilation. Ion irradiation also decreases the bulk ferroelectric polarization demonstrating that the surface or near surface modifications may tune the bulk properties in polar dielectrics.

Anomalous dielectric and piezoelectric properties and electrical conductivity of heavily doped LiNbO3:Zn crystals

In LiNbO3:Zn crystals with near-threshold doping levels ( 4.5–4.7 mol % Zn), high-temperature measurements and high-temperature annealing under short-circuit conditions lead to considerable changes in spontaneous unipolarity. The considerable changes in spontaneous unipolarity are accompanied by well-defined low-frequency dielectric dispersion and sharp anomalies in temperature dependences of electrical conductivity and dielectric permittivity. As a result, the piezoelectric modulus d333 increases to a level approaching the highest values reported in the literature for single-domain nominally pure LiNbO3 crystals.

An effect of the electrode material on space charge relaxation in ferroelectric copolymers of vinylidene fluoride

Processes of relaxation of space charges formed by impurities carriers in isotropic films of vinylidene fluoride and tetrafluoroethylene copolymers of the composition 71/29 and 94/6 were studied. Al and Au symmetric electrodes deposited by evaporation in vacuum have been used. In the case of Al electrodes at temperatures above 100 °C, giant low frequency dielectric dispersion was observed, while it is absent in films with Au electrodes. Causes of this phenomenon were studied by the X-ray photoelectron spectroscopy. It was shown that at Al deposition, new functional groups, such as Al-C, Al-F, and Al2O3, which are not characteristic of the copolymer film surface, formed. They were supposed to be traps for impurity carriers and because of this the electrode became partially blocked. This led to appearance of the giant electrode polarization on the metal-polymer boundary, which did not take place in the case of Au electrodes. Parameters of the Au4f line for the copolymer with different contents of fluorine atoms in the chain were analyzed. An increase in the number of these atoms was shown to result in the line shift to higher energies. This phenomenon was associated with an increase in the shift of the electron density from Au atoms to the F ones which has a high affinity to electrons.

Spontaneous unipolarity and anomalies of the dielectric and piezoelectric properties and electrical conductivity of initially heavily doped polydomain LiNbO3: Zn crystals

A significant spontaneous unipolarity in initially polydomain LiNbO3: Zn crystals doped in the range of “threshold” impurity concentrations (∼4.5–4.7 mol %) has been revealed from high-temperature measurements and after high-temperature annealing under short circuit conditions. The effect of strong increase in the spontaneous unipolarity is accompanied by a pronounced low-frequency dielectric dispersion and abrupt anomalies in the temperature dependences of the electrical conductivity and dielectric permittivity. The piezoelectric coefficient d333 increases to nearly maximum values available in the reference literature for nominally pure single-domain LiNbO3 crystals.