Frequency Dependence Of Dielectric Permittivity Research Articles

Effect of sintering temperature on phase structure, microstructure, and electrical properties of (K0.5Na0.5)NbO3–(Ba0.6Sr0.4)0.7Bi0.2TiO3 lead-free ceramics

Lead-free 0.98(K0.5Na0.5)NbO3–0.02(Ba0.6Sr0.4)0.7Bi0.2TiO3 (abbreviated as 0.98KNN–0.02BSBT) ceramics were prepared by the conventional solid-state sintering method. Effect of sintering temperature on 0.98KNN–0.02BSBT ceramics was systematically investigated. The frequency dependent dielectric permittivities show that the ceramics sintered at different temperatures are indeed “relaxor-like” ferroelectric ceramics, which possess a diffuse phase transition without a strong frequency dispersion of dielectric permittivity. The diffuseness parameter γ, the comparison of the relaxor behavior based on empirical parameters (ΔT diffuse) and the slimmer P–E hysteresis loops confirm that the “relaxor-like” characteristics of the ceramics are strengthened with increasing sintering temperature. At the optimum sintering temperature, the dielectric permittivity maximum (ɛ max) has a value of approximately 2795 (at 1 KHz), $$ \tan \delta $$ is lower than 2.5 % and the diffuseness parameter γ = 1.68 at a broad usage temperature range (150–350 °C), which indicate its potential application in high temperature multilayer ceramics capacitor field.

The static dielectric permittivity of ionic liquids

The static dielectric permittivity εS (“static dielectric constant”) is an important quantity for characterizing the solvation capability of a solvent. The past two decades have seen the advent of ionic liquids — low-melting organic salts — as intriguing alternatives to volatile organic solvents. While for non-conducting media εS is readily measured by electrical capacitance methods, such methods fail for electrical conductors because the samples are short-circuited by their intrinsic electrical conductivity. In dielectric theory εS is defined as the zero-frequency limit of the real part of the frequency-dependent complex dielectric permittivity. This definition provides a recipe to determine εS by dielectric relaxation spectroscopy. The paper reviews the achievements in characterizing and understanding the static dielectric constant of Ionic Liquids with particular focus on work in the author's laboratory.

Dielectric response of transformer oil based ferrofluid in low frequency range

In this article, our experimental study of the dynamic dielectric behaviour of transformer oil-based ferrofluid with magnetite nanoparticles is presented. Frequency-dependent dielectric permittivity and dissipation factor were measured within the frequency range from 20 Hz to 2 MHz by a capacitance method. The ferrofluid samples were placed in a liquid crystal cell, and experiments were carried out in an electromagnetically anechoic chamber. Two polarization processes and corresponding relaxations were revealed within the applied frequency range. Schwarz theory of electric double layer polarization is used to explain the low frequency relaxation maximum. Moreover, the shift of the maximum position towards higher frequencies is observed as the magnetic volume fraction in the ferrofluid increases. The related decrease in relaxation time due to higher counterion mobility is analysed. Reduced electric field intensity due to depolarization field, which is dependent on the particle concentration, is proposed as the reason for the maxima shift. This assumption is wholly supported by a complementary experiment.

Electrical properties of lead-free KNN films on SRO/STO by RF magnetron sputtering

Abstract Highly (001) oriented (K,Na)NbO 3 lead-free piezoelectric films were fabricated on SrRuO 3 buffered SrTiO 3 (001) single crystal substrates by RF magnetron sputtering. The films showed a stable frequency dependence of dielectric permittivity and loss tangent in the range of 1 kHz–1 MHz. A fairly high tunability of 69.7% (@400 kV/cm) was obtained in the films. Well saturated P – E hysteresis loops were obtained at E =250 kV/cm, the remnant polarization P r was 8 μC/cm 2 , and coercive field E c was only 40 kV/cm. These films showed a fatigue-free behavior up to 10 10 switching cycles. The decreased coercive field, improved dielectric and fatigue properties may be related to SRO bottom electrodes, which can efficiently suppress the “dead layer” near the ferroelectric-electrode interface. The leakage current density of the films was only 3.48×10 −6 A/cm 2 at the electric field of 250 kV/cm, which is even lower than that of Mn-doped KNN films. In addition, the piezoelectric constant d 33 was estimated to be 36 pm/V.

Temperature-dependent microwave dielectric relaxation studies of hydrogen bonded polar binary mixtures of propan-1-ol and propionaldehyde

The molecular interaction between the polar systems of propan-1-ol and propionaldehyde for various mole fractions at different temperatures were studied by determining the frequency dependent complex dielectric permittivity by using the open-ended coaxial probe technique method in the microwave frequency range from 20MHz to 20GHz. The geometries are optimized at HF, B3LYP and MP2 with 6-311G and 6-311G+ basis sets. Dipole moments of the binary mixtures are calculated from the dielectric data using Higasi’s method and compared with the theoretical results. Conformational analysis of the formation of hydrogen bond between the propan-1-ol and propionaldehyde is supported by the FT-IR and molecular polarizability calculations. The average relaxation times are calculated from their respective Cole–Cole plots. The activation entropy, activation enthalpy and Kirkwood correlation ‘g’ factor, excess permittivity (εE), excess inverse relaxation time (1/τ)E, Bruggeman parameter (fB) have also been determined for propan-1-ol and propionaldehyde and the results were correlated.

Growth and Characterization of Centimeter‐Sized Ba 2 LaFeNb 4 O 15 Crystals from High‐Temperature Solution under a Controlled Atmosphere

Centimeter-sized single crystals of Ba2LaFeNb4O15 were grown from a high-temperature solution by using LiBO2 flux and a sealed platinum assembly. The obtained single crystals display the same physical properties as their ceramic counterparts. A frequency-dependent dielectric permittivity maximum was found (Tm = 100 K at 5 kHz), which indicates relaxor behavior. Magnetic susceptibility measurements revealed purely paramagnetic behavior between 10 and 350 K. X-ray diffraction measurements of Ba2LaFeNb4O15 single crystals revealed an incommensurate structure at room temperature with a bidimensional modulation characterized by vectors q1 = (α, α, 1/2) and q2 = (α, –α, 1/2) with α = 0.295(1). This crystal growth method offers a promising elaboration route to centimeter-sized crystals of niobate-based compounds, which may not be grown from the pure liquid phase, especially those with a tetragonal tungsten bronze (TTB) structure.

Relaxation process in PbI2–Ag2O–V2O5–B2O3 system: Dielectric, AC conductivity and modulus studies

Abstract Silver ion conducting super-ionic glass system xPbI2–(100 − x) [Ag2O–2(V2O5–B2O3)], where, 5 ≤ x ≤ 25, were prepared via melt quenching route and -characterized by XRD and DSC. Their electrical properties were measured by impedance spectroscopy in the frequency range of 2 MHz to 20 Hz from 30 to 120 °C. The electrical relaxation mechanism has been studied using AC conductivity, dielectric modulus function and frequency dependent dielectric permittivity over a wide range of frequency and temperature. Two different scaling approaches for AC conductivity as well as dielectric permittivity spectra were used to understand the nature of relaxation processes.

Electrostrictive and relaxor ferroelectric behavior in BiAlO3-modified BaTiO3 lead-free ceramics

The crystal structure of (1−x)BaTiO3-xBiAlO3 (x = 0, 0.02, 0.05, 0.08, and 0.1) ceramics was determined using X-ray diffraction and Raman spectroscopy at room temperature, which revealed a phase transition from tetragonal to rhombohedral with increasing x. The dielectric properties were studied as a function of temperature at different frequencies, which indicated that the phase transition temperature (Tm) decreased with increasing x. The relaxor behavior was observed by frequency and temperature dependent dielectric permittivity. The Lorenz-type quadratic law was used to characterize the dielectric permittivity peaks near Tm of high-temperature slopes at 1 MHz. The temperatures Tm of dielectric permittivity peaks fit very well with the Vogel-Fulcher law in x = 0.05 and x = 0.1. The polarization hysteresis loops and electrostrictive were displayed at room temperature. The sample for x = 0.1 exhibits a slim loop with negligible hysteresis and a subtle linear feature, which is a promising transducer material for use as an active element.

Large Piezoelectric Response and Polarization in Relaxor Ferroelectric PbTiO3–Bi(Ni1/2Zr1/2)O3

New binary system (1−x) PbTiO3−xBi(Ni1/2Zr1/2)O3 (PT–100x BNZ) with x ≤ 0.45 were synthesized via solid‐state reaction route. A morphotropic phase boundary (MPB) was identified around x = 0.40 by X‐ray diffraction (XRD) method. The ceramics with MPB composition exhibit enhanced ferroelectric properties. A large piezoelectric coefficient (d33) up to 400 pC/N was obtained for the PT–40BNZ, which is comparable with the PbTiO3–BiScO3 (PT–BS, 450 pC/N).The frequency dependence of dielectric permittivity of PT–40BNZ shows characteristic of a strong relaxor feature and a transition temperature around 290°C (1 MHz). Temperature effect on the unipolar strain was also investigated. The present system with high d33 is a competitive piezoelectric material, as no expensive oxide is used here compared with the PT–BS.

Structural, electric and magnetic properties of CoFe1.8RE0.2O4 (RE=Dy, Gd, La) bulk materials

We investigated the influence of rare earth (RE) additions on the structural, dielectric, magnetic and magnetostrictive properties of cobalt ferrite bulk materials. Three lanthanide ions with different ionic radii and magnetic properties were used as dopants: Dy, Gd, La. The structural properties of the sintered samples were investigated using X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The room temperature hysteresis loops were obtained using a vibrating sample magnetometer. The frequency dependence of dielectric permittivity and tangent loss was investigated in the 20Hz–20kHz range. The variation of the magnetoelectric response with applied dc magnetic field was analyzed. The insertion of rare earth elements influenced the structural characteristics of the samples (density, cell edge, porosity) and the magnetic and electric properties. An increase in coercive field and a decrease in saturation magnetization and magnetostriction coefficient were observed. These results can be partially explained by the weaker nature of the RE3+–Fe3+ interaction compared to Fe3+–Fe3+ interaction and to the antiferromagnetic alignment of the REFeO3 second phase observed in the diffraction patterns after sintering process.

Triethylene glycol stabilized MnFe2O4 nanoparticle: Synthesis, magnetic and electrical characterization

In this study, triethylene glycol (TEG) stabilized superparamagnetic MnFe2O4 nanoparticle (TEG@MnFe2O4) was synthesized via a simple polyol route. Composition of nanoparticle was confirmed as MnFe2O4 and surface conjugation of TEG was confirmed by Fourier transform infrared spectroscopy to be via oxygens on TEG covalently attached to metal centers on the NPs. Vibrating sample magnetometer measurements confirmed the superparamagnetic character of these nanoparticles without reaching to a saturation, and has no coercivity. The TEG@MnFe2O4 nanocomposite showed thermally activated conductivity, significant interfacial polarization effect also in the dielectric permittivity evaluations. Temperature dependency of conductivity is a strong evidence for thermally activated polarization mechanism. dc conductivity is classified into two regions over a limited temperature range and shows maximum conductivity of about 4×10−7Scm−1 at 120°C. Temperature and frequency dependence of dielectric permittivity indicated interfacial polarization and temperature-assisted-reorganization effects.

Microwave dielectric relaxation studies of hydrogen bonded polar binary mixtures of isobutanol and aniline

The molecular interaction between the polar systems of isobutanol and aniline for various mole fractions at different temperatures were studied by determining the frequency dependent complex dielectric permittivity by using the open-ended coaxial probe technique method in the microwave frequency range from 20MHz to 20GHz. The geometries are optimized at HF and B3LYP with 6-31G and 6-31G+ basis sets. Dipole moments of the binary mixtures are calculated from the dielectric data using Higasi’s method and compared with the theoretical results. Conformational analysis of the formation of hydrogen bond between the isobutanol and aniline is supported by the FT-IR and molecular polarizability calculations. The average relaxation times are calculated from their respective Cole–Cole plots. The activation entropy, activation enthalpy and Kirkwood correlation ‘g’ factor, excess permittivities (εE), Bruggeman parameters (fB) have also been determined for isobutanol and aniline and the results were correlated.

Fluctuation electromagnetic interaction between a small rotating particle and a surface

We study the fluctuation electromagnetic interaction between a small neutral rotating particle and a polarizable surface. The attraction force, friction torque and heating are produced by the particle polarization and the fluctuating near field of the surface. Closed analytical expressions are found for these quantities assuming that the particle and the surface are characterized by frequency-dependent polarizability, dielectric permittivity and different temperatures. It is shown that the stopping time of the rolling particle in the near field of the surface is much lower than the stopping time under uniform motion or rolling in vacuum space. This is of paramount importance in the development of NEMS where the corresponding interactions must be taken into account.

Broadband dielectric dispersion in ferroelectric P(VDF-TrFE) copolymer films

Abstract Ferroelectric polyvinylidenefluoride-trifluoroethylene copolymer films with different thicknesses are prepared by a solvent-cast technique, by spin coating, and by a horizontal Langmuir–Blodgett technique respectively. The frequency dependent dielectric permittivity of these films is investigated with varying sample thickness and varying temperature in the ferroelectric as well as in the paraelectric phase. A dielectric relaxation according to a Vogel–Tamman–Fulcher law of the relaxation times is found in all samples. However, the relaxation times extracted from the dielectric permittivity in the frequency range are not consistent with the relaxation times determined from the temperature range. An explanation for this behavior is given by a temperature dependent distribution of relaxation times. Additionally, in thin samples a second relaxation with a weak anomalous temperature dependence, i.e. an increasing relaxation time with increasing temperature, is observed at high frequencies. Detailed investigations show that this behavior can be attributed to an electrode effect.

Reinforcing effect of nanosilica on the properties of natural rubber/reclaimed ground rubber tire vulcanizates

AbstractIn this investigation, incorporation of silica into natural rubber (NR)‐reclaim rubber (RR) blend system was carried out by sol‐gel technique at various sol‐gel reaction temperatures. The effect of RR on silica reinforcement, hitherto unexplored, was studied for different NR/RR blend systems. The degree of reinforcement of sol‐gel vulcanizates by equilibrium swelling method indicates that the reinforcing efficiency of the in situ generated silica by sol‐gel technique increases with increasing reclaim rubber content. The reinforcing efficiency, tensile properties and thermal stability of sol gel vulcanizates (SGV) prepared at 50°C become maxima as compared to SGV prepared at 30°C and 70°C. The amount of silica incorporated by sol‐gel technique was determined by thermogravimetry analysis. It indicates that the thermal stability increases with silica content. Attenuated total reflection study indicates that RR forms bond with silica particles due to the presence of active functional site on RR. Scanning electron microscopy studies further indicate the coherency and homogeneity in the silica filled NR/RR vulcanizates. The microwave diagnosis of different SGVs was also carried out and the frequency dependence of dielectric permittivity (E') and loss (E”) were measured. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Towards magnesium ion conducting poly(vinylidenefluoride-hexafluoropropylene)-based solid polymer electrolytes with great prospects: Ionic conductivity and dielectric behaviours

A simple solid polymer electrolyte (SPE) system based purely on poly(vinylidenefluoride-hexafluoropropylene) [P(VdF-HFP)] and magnesium trifluoromethanesulfonate (MgTf) is synthesised via solution casting technique with acetone as solvent. The SPEs produced exhibit high ionic conductivity of ∼10−3S/cm at ambient temperature when 40wt.% of MgTf is incorporated. The major focus of this work is on ionic conductivity and dielectric behaviours. Three dissimilar types of impedance spectra have been identified and differentiated by magnitude of ionic conductivity. The trend of ionic conductivity increases almost proportionally to the content of magnesium salt and can be related to an increase of amorphous phase at high level of dopant salt. This SPE system has also been found to possess Arrhenius temperature dependence. This study discusses three samples with 10, 25 and 40wt.% of magnesium salt, representing low, intermediate and high concentrations of magnesium salt which are examined in frequency-dependence conductivity, dielectric permittivity and dielectric modulus studies.

Activation energy of polarization due to electrical conductivity and dipole rotation in purified ca-bentonite

We determined the activation energy for dipole rotation and electrical conductivity by analyzing the frequency dependent dielectric permittivity measurements of purified Ca-Bentonite. The measurements were performed at four different temperatures between 296K and 353K and at frequencies between 5Hz to 5MHz. We used the Havriliak–Negami (HN) relation to represent the polarization due to dipole orientations and the Maxwell–Wagner–Sillars (MWS) relation with a power law term to represent the interfacial polarization. We obtained expressions for the real and imaginary parts of electric modulus M*(ω).We determined the relaxation times for HN and MWS contributions from a fit of the experimental data. Subsequently, the activation energies for HN and MWS contributions were obtained from an Arrhenius plot. The activation energy for the HN and MWS processes were found to be 22.3kJ/mol and 18.2kJ/mol, respectively.

Synthesis and characterization of poly(1-vinyltriazole)-grafted superparamagnetic iron oxide nanoparticles

We reported on the synthesis and detailed physicochemical characterization of poly(1-vinyltriazole)-grafted iron oxide nanoparticles. Superparamagnetic iron oxide nanoparticles (SPION) were fabricated by gel-to-crystalline conversion method. Telomerization of poly(1-vinyltriazole) on iron oxide nanoparticles was achieved via silanization process. XRD analysis confirmed the crystalline phase as magnetite, and FT-IR analysis confirmed the presence of PVTri on nanoparticles. Particle morphology was observed to be polygonic, due to the synthesis process, while average size estimated from TEM micrographs is 7nm. Agreement between crystallite size estimated from XRD and particle size from TEM affirms single crystalline character of these nanoparticles. Dependence of conductivity on temperature showed a strong evidence for thermally activated polarization mechanism. Temperature and frequency dependence of dielectric permittivity revealed interfacial polarization and temperature-assisted-reorganization effects. Magnetic evaluation showed non-saturation and superparamagnetic characteristics of nanoparticles as well as magnetic particles being single domains.

Concentration effect of BMIMTf on P(VdF-HFP)/MgTf-based solid polymer electrolyte system

Abstract

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.