High Frequency Relaxation Process Research Articles

Investigation of alumina- and scandia-doped zirconia electrolyte for solid oxide fuel cell applications: Insights from broadband impedance spectroscopy and distribution of relaxation times analysis

Zirconia based oxygen conductors are state of the art solid electrolytes used for solid oxide fuel cell applications. In this study, we investigated zirconia double-doped with aluminium and scandium oxide. The Al0.04Sc0.06Zr0.9O1.95 electrolyte was prepared using Pechini method. In the 300–800 K temperature range, this material's structure is cubic with a fraction of monoclinic modification, while above 800 K it becomes completely cubic. The ceramic form of Al0.04Sc0.06Zr0.9O1.95 electrolyte was investigated using broadband impedance spectroscopy, utilizing equivalent circuit analysis and distribution of relaxation times (DRT) technique. The high-frequency relaxation process's complexity observed in the spectra's DRT representation at temperatures up to 500 K was associated with the two zirconia phases. The Al0.04Sc0.06Zr0.9O1.95 electrolyte was tested in a hydrogen-oxygen laboratory solid fuel cell in the temperature range 973–1123K. Understanding the fundamentals of the relaxation processes is necessary to increase the durability of the ceramic electrolyte in the fuel cell.

Temperature-dependent hydration behavior of aqueous lysine: an approach towards protein binding through dielectric spectroscopy

Present work reports interaction between water and amino acid lysine for understanding the physicochemical properties that will be useful in the structure formation of protein. The dielectric relaxation of aqueous lysine was systematically investigated over a temperature range spanning from 298.15 K to 278.15 K, encompassing frequencies ranging from 10 MHz to 30 GHz, and across a concentration range of 0.152 M to 0.610 M. Within this study, aqueous lysine revealed the presence of two distinct relaxation modes. The low-frequency relaxation process (l-process) is primarily associated with the relaxation of lysine molecules, whereas the high-frequency relaxation process (h-process) is attributed to water molecules interacting with lysine. Several key dielectric parameters, including static dielectric constant (εj), relaxation time (τj), dipole moment (μj), correlation factor (gj), and the number of water molecules rotationally bonded by solute molecules (Zib), were meticulously determined. These parameters were interpreted in terms of molecular interactions, hydrogen bonding, hydrophobicity, and Lys-Lys binding. Additionally, various thermodynamic parameters such as molar enthalpy (ΔHj), molar entropy (ΔSj), and molar free energy (ΔFj) were calculated to provide further insights into the system’s characteristics and behavior. Communicated by Ramaswamy H. Sarma

Thermodynamic hydration behaviour of glycine below room conditions using time domain reflectometry

The present work reports the concentration-dependent hydrophobicity of glycine below room temperature. The dynamics of aqueous glycine have been studied by means of dielectric relaxation spectroscopy using Time Domain Reflectometry (TDR) technique in the frequency region of 10 MHz–30 GHz. Complex permittivity spectra are obtained using TDR that allowed evaluation of the static dielectric constant (ε0) and average relaxation time (τ). As dielectric relaxation spectroscopy provides information on the average relaxation time (τ) related to the mechanism of hydrogen bond (HB) formation and breaking, therefore the concentration-temperature dependence of τ was used to evaluate and study hydration behaviour through dielectric parameters such as dipole moment (μ), correlation factor (g), and the dynamics of irrationally bound water molecules (Zib). Aqueous glycine relaxes in two different relaxation modes in the broad microwave frequency region from MHz to GHz. The low-frequency relaxation process (l-process) observed is associated with glycine relaxation, while the detected peak in the high-frequency relaxation process (h-process) is attributed to water associated with glycine. We have attempted a concentration-temperature-dependent hydrogen bonding mechanism in both relaxation processes, and the results were corroborated with thermodynamical parameters such as molar entropy of activation (∆Sj), molar enthalpy of activation (∆Hj), and molar free energy of activation (∆Fj).

Assessment of the permeability and pore size of quartz-based consolidated sedimentary rocks by dielectric spectroscopy in the frequency range of 1 kHz - 500 MHz

The spectral-induced polarization (SIP) response of porous materials at frequencies below 1 kHz can be used to determine the pore size and rock permeability. Although the results of certain studies are encouraging, in recent years it has been argued that there cannot be a universally applicable approach to predict permeability using the SIP response. This article proposes a broadband dielectric spectroscopy method in the frequency range from 100 Hz to 500 MHz for assessing the permeability and average pore size. An original experimental setup has been developed that makes it possible to measure the dielectric spectrum of quartz-based consolidated sedimentary samples of porous rocks in this frequency range. The rock samples with permeability from 0.17 to 206 mD and an average pore size from 6.3 to 21.1 μm have been studied during the experiments. The dielectric spectra of four sandstone samples and two siltstone samples moistened with distilled water and a NaCl solution with a concentration of 1.5 and 4 g/L were measured. The volume fraction of the solution in the samples varied from complete saturation to a moisture of 0.04–0.05 m3/m3. The dielectric spectra were modeled by three relaxation processes, the parameters of which were determined using the Debye and Cole-Cole formulas. The strength of two low-frequency processes with the relaxation times of about 1.2 ms and 0.15 ms are well correlated with the low-frequency conductivity of the samples; however, no stochastic dependence on the pore size and permeability was found. The parameters of the high-frequency relaxation process with the relaxation times of tens and hundreds of nanoseconds depend both on the solution ratio in the sample and its concentration, as well as on the pore size and permeability. The strength of this process is better related to the pore size and permeability when moistened with distilled water, and the relaxation time correlates best with them when using the solution with a concentration of 4 g/L. No significant differences in the process parameters in the samples of sandstone and siltstone were found.

Application of the method of dielectric spectroscopy to study theproperties of blood serum of mice with malignant ascites

The article presents the results of a study by the method ofdielectric spectroscopy of high-frequency relaxation processes in the bloodserum of intact mice and mice vaccinated with an oncological disease --- Ehrlich's ascites carcinoma. Using the formalism of the electrical module,the relaxation parameters were calculated for the serum samples of the twostudied systems. Keywords: electrical module, relaxation parameters, oncological disease.\

A new approach to investigate the ionic conductivity of NaCl and KCl solutions via impedance spectroscopy

Lima et al. [1] employed electrical impedance spectroscopy to analyze the electrical impedance behavior of dilute aqueous potassium chloride (KCl) and sodium chloride solutions in the frequency range of 10−1 Hz to 106 Hz (NaCl). The complex impedance Z* data from the solutions were modeled using an analogous electrical circuit that closely matched the experimental data. The electrical characteristics of the solutions were studied as a function of the cation types. The Debye model accurately describes the bulk effects of K+ and Na+ cations. However, it appeared that the analysis presented just the equivalent circuit components as a function of salt concentration. As a result, the current work used a simulation procedure to generate complex impedance (Z*) data from electrical parameters derived from the analogous circuit. To highlight the high-frequency relaxation processes occurring, extrapolation to a broader frequency range was performed. Furthermore, theoretical considerations were introduced in order to derive complex conductivity (σ*) from complex admittance (Y*). In the complex impedance (Z*) and admittance (Y*), there was a good correlation between all parameters derived from both processes. The key relaxation process characteristics, such as ionic strength, relaxation time, and conductivity values at low and high frequencies, were then retrieved. As a function of salt concentration, all of these parameters were evaluated and discussed.

Применение метода диэлектрической спектроскопии для исследования свойств сыворотки крови мышей со злокачественным асцитом

The article presents the results of a study by the method of dielectric spectroscopy of high-frequency relaxation processes in the blood serum of intact mice and mice vaccinated with an oncological disease - Ehrlich's ascites carcinoma. Using the formalism of the electrical module, the relaxation parameters were calculated for the serum samples of the two studied systems.

A Study of Moisture Sorption and Dielectric Processes of Starch and Sodium Starch Glycolate : Theme: Formulation and Manufacturing of Solid Dosage Forms Guest Editors: Tony Zhou and Tonglei Li.

This study explored the potential of combining the use of moisture sorption isotherms and dielectric relaxation profiles of starch and sodium starch glycolate (SSG) to probe the location of moisture in dried and hydrated samples. Starch and SSG samples, dried and hydrated, were prepared. For hydrated samples, their moisture contents were determined. The samples were probed by dielectric spectroscopy using a frequency band of 0.1 Hz to 1 MHz to investigate their moisture-related relaxation profiles. The moisture sorption and desorption isotherms of starch and SSG were generated using a vapor sorption analyzer, and modeled using the Guggenheim-Anderson-de Boer equation. A clear high frequency relaxation process was detected in both dried and hydrated starches, while for dried starch, an additional slower low frequency process was also detected. The high frequency relaxation processes in hydrated and dried starches were assigned to the coupled starch-hydrated water relaxation. The low frequency relaxation in dried starch was attributed to the local chain motions of the starch backbone. No relaxation process associated with water was detected in both hydrated and dried SSG within the frequency and temperature range used in this study. The moisture sorption isotherms of SSG suggest the presence of high energy free water, which could have masked the relaxation process of the bound water during dielectric measurements. The combined study of moisture sorption isotherms and dielectric spectroscopy was shown to be beneficial and complementary in probing the effects of moisture on the relaxation processes of starch and SSG.

Study on the Origin of Giant Dielectric Constant of CaCu3Ti4O12 Ceramics

CaCu3Ti4O12 ceramic (CCTO) were prepared by traditional solid phase sintering methods at 1100℃ for 20h. In order to learn the influence of atmosphere on point defects and dielectric properties, the samples sintered were heat treated in oxygen-rich or nitrogen-rich atmosphere at 900℃ for 9h. The phase structure and dielectric properties are measured by X-ray diffraction (XRD) and Novocontrol wide band dielectric spectroscopy. It is found that grain resistance and especially grain-boundary resistance increase after oxygen-rich atmosphere treatment. The increase of grain-boundary resistance directly results in the drop of low frequency loss. The increase of grain resistance significantly restrains high frequency giant dielectric constant and dielectric loss. However, the effect of nitrogen-rich atmosphere treatment is quite contrary. It is believed that heat treatment in oxygen-rich or nitrogen-rich atmosphere changes the concentration of oxygen vacancy in CCTO. Different oxygen vacancy concentrations cause huge change of electric performance of grain and grain-boundary, which in turn influences dielectric properties of CCTO ceramics. In addition, the origin of medium and high frequency relaxation peak was done by testing dielectric temperature spectrum of CCTO ceramic, finding that CCTO high frequency relaxation process stems from relaxation polarization caused by monovalent oxygen vacancy, and medium frequency relaxation process stems from relaxation polarization caused by bivalent oxygen vacancy. And the activation energies of the two relaxation processes do not change at all with atmosphere treatment, implying the intrinsic nature of the two intrinsic defects.

Molecular Relaxation of the Side Groups in Poly(vinyl alcohol) Films in GHz Frequency Range

ABSTRACTPoly(vinyl alcohol) (PVA) is a synthetic polymer which has been used in a wide variety of applications. This polymer has been extensively investigated by a large number of techniques to shed light about its physical and chemical properties. In this work, for fist time, high frequency (1x109-3x109 Hz) relaxation process has been observed in the PVA films in the temperature range of -100C to +1200C. This relaxation exhibits negative activation energy below glass transition temperature Tg and at higher temperature positive activation energy with subsequent saturation. Upon cooling the activation energy was negative again. This high frequency relaxation process and its temperature dependence can be attributed to the interaction of the bounded water and the changes of energy and freedom of movement of OH side molecular chains groups. This conclusion has been supported by in situ FTIR measurements. A possible scenario of this relaxation and dynamics of molecular motion has been proposed.

Investigation of liquid crystal dispersion and dielectric relaxation behavior in polymer dispersed liquid crystal composite films

Dispersion dynamics in composites of PMMA-BA and LC E44 were investigated using dielectric relaxation spectroscopy. Morphological studies have shown the homogeneous distribution of LC droplets in the polymer matrix. The outcome was deduced in terms of shape and size of LC droplet, interfacial charge-layer effect, glass transition temperature of composites and miscibility of LC in polymer. The temperature dependent dielectric relaxation spectra have been studied. It was observed that the intensity of Maxwell–Wagner interfacial polarization peak varies with respect to the applied temperature. The high-frequency relaxation process seems to be the Debye-type behavior due to dipolar rotation around the long molecular axis.

Dynamics of Linear Poly(N-isopropylacrylamide) in Water around the Phase Transition Investigated by Dielectric Relaxation Spectroscopy

The molecular dynamics of linear poly(N-isopropylacrylamide) (pNIPAM) in aqueous media at temperatures below and above the lower critical solution temperature (LCST) are investigated using broadband dielectric relaxation spectroscopy in a frequency range from 10(-1) to 10(11) Hz. Below the LCST, two relaxation processes are observed in the megahertz and gigahertz region assigned to the reorientation of dipoles of the solvated polymer segments (p-process) and water molecules (w-process), respectively. Both relaxation processes are analyzed using the Havriliak-Negami (HN) function, taking special attention to the w-process. Above the LCST, the dielectric spectra of the pNIPAM solutions resemble that of pure water, showing only the high frequency relaxation process of the water molecules with a more or less Debye-type behavior. The non-Debye behavior of the w-process below the LCST is mainly induced by the interactions between water and pNIPAM chains via hydrogen bonding. The relaxation time and strength of the w-process is studied with dependence on the concentration, temperature, and the polymer chain length (molecular weight). The information obtained is useful for a deeper understanding of the dehydration behavior at the phase transition. The suggestion of dehydration of the pNIPAM chains at the LCST is confirmed by calculating a dehydration number.

Molecular relaxation in Chitosan films in GHz frequency range

ABSTRACTThe molecular relaxations behavior of chitosan (CS) films in the wide frequency range of 0.1-3x109 Hz (by using three different impedance analyzers) have been investigated in the temperature range of -100C to 120°C using Dielectric Spectroscopy (DS). Additionally to the low frequency molecular relaxations such as α and β relaxations, for the first time, high frequency (1-3 GHz) relaxation process has been observed in the chitosan films. This relaxation exhibits Arrhenius-type dependence in the temperature range of -100 C to 54°C with negative activation energy -2.7 kJ/mol. At temperatures above 54°C, the activation energy changes from -2.7 kJ/mol to +4.4 kJ/mol. Upon cooling, the activation energy becomes negative again with a value of -1.2 kJ/mol. The bound water between chitosan molecules strongly modifies molecular motion and the relaxation spectrum, giving rise to a new relaxation at the frequency at ca. 1 GHz. In situ FTIR analysis has shown that this relaxation related to the changes in vibration of the –OH, NH and –CO functional groups.

Dielectric modulus response of CaCu3Ti4O12 ceramic

The DC conductivity of the CaCu3Ti4O12 ceramic is considerable at low frequency. The dielectric properties of the CaCu3Ti4O12 ceramics are analyzed by dielectric spectrum, and the two relaxation processes are characterized by the dielectric modulus. The two relaxation processes are considered which are dominated by the electronic relaxation of deep bulk traps at the depletion layer edge. The low-frequency and high-frequency relaxation processes are attributed to oxygen-vacancy-related defect and native defect, respectively. It is proved that the modulus response of the CaCu3Ti4O12 ceramic is equivalent to conductivity response at high temperature (low frequency), and the peak value of the M" is inversely proportional to capacitance. The activation energies calculated by conductivity and modulus are equivalent to each other. The modulus spectrum is more effective to the material which has high DC conductivity at low frequency such as CCTO ceramic.

Influence of technological factors on conductivity and dielectric dispersion in ZnO nanocrystalline thin films

Influence of the technological factors such as annealing of a substrate on the dielectric dispersion of the zinc oxide thin films with nanograins was investigated. In the first stage the dielectric dispersion of such nanostructured zinc oxide films at frequency range of 4Hz–100kHz and temperature range of 120–380K was studied. The two types of films were prepared by the RF-magnetron sputtering in argon atmosphere using ZnO targets. The first sample was obtained by sputtering on the substrate heated to 573K, whereas the second sample was manufactured without substrate heating. We observed the relaxation process in these materials at the temperature range of 220–350K within the above mentioned frequency window. The second relaxation process was recognized in the frequency range of 100kHz–2MHz in vicinity of 350K. The specific dispersion connected with a piezoelectric effect in the first sample was observed in vicinity of 215K. The value of dielectric permittivity reaches 1100 at frequencies of few Hertz and decreases with increase of measuring electric field frequency. The nature of the low-frequency relaxation process is connected with space-charge polarization on the grain boundary. It is realized due to the high defect concentration within the interfaces of the ZnO nanograins in comparison with a bulk material. The high-frequency relaxation process corresponds to the thermal dipole polarization involving electrons localized at oxygen vacancies.

Oxygen deficiency and grain boundary-related giant relaxation in Ba(Zr,Ti)O3 ceramics

The influence of the oxygen vacancies on the dielectric response of BaZr0.10Ti0.90O3 ceramics prepared by solid-state reaction and sintered at 1400 °C for 2 h was investigated. The as-sintered ceramic exhibits a giant relaxation with a shift of the transition temperature from ∼85 °C to above 170 °C in the frequency ranges of 1 Hz–100 kHz, with high losses above unity and two components in the complex impedance plot. A complex dielectric relaxation response, with at least two thermally activated defect mechanisms with activation energies of ∼0.2 eV below the transition temperature and ∼0.7 eV for higher temperatures in the range of 85 °C–170 °C was determined. The observed giant relaxation is an extrinsic effect related to the oxygen deficiency, inhomogeneous distributed in the ceramic grain and not to the relaxor behavior of this system. After a post-annealing treatment at 1000 °C for 50 h, the dielectric response is completely changed: the permittivity vs. temperature dependences present maxima located at around Tm ≈ 90 °C, with almost no frequency dispersion. The conductivity spectra remained almost unchanged after the annealing, showing that the level of oxygen deficiency in this case is related to dielectric relaxations and not to the ac-conductivity dispersion. Two thermally activated dielectric relaxation processes were still identified, but with activation energies of ∼2.7 eV below the transition temperature and of ∼0.87 eV for higher temperatures in the range of 85 °C–170 °C. The high frequency relaxation process is almost suppressed by the reoxidation and its activation energy increased with more than one order in magnitude. One single component in the complex impedance plot found after reoxidation shows that the annealing allowed the homogenization of the oxygen level within the ceramic grains.

Dielectric properties of microvillous cells simulated by the three-dimensional finite-element method

Most of biological cells have microvilli on their surfaces, which significantly influence their dielectric properties. The complex permittivity of a cubical system containing a spherical cell model with cylindrical projections was calculated over a frequency range of 10 kHz to 100 MHz using the three-dimensional finite-element method. The spectra of the complex permittivity consisted of low- and high-frequency relaxation processes which were respectively attributed to the polarization of the membranes covering the projections and the spherical body. Conventional analysis based on the spherical shell model was applied to the simulated spectra to discuss the effects of cell surface morphology on the electric parameters estimated for the plasma membrane and the cytoplasm.

Monomer Exchange and Rotational Isomerization of Alkyl Monoglycosides in Water

Ultrasonic attenuation spectra between 100 kHz and 400 MHz are reported for solutions of hexyl-, heptyl, octyl-, and nonyl-beta-d-glucopyranoside in water. Results for a mixture of an octyl glucopyranoside with an octyl galactopyranoside are also presented. The analytical descriptions of the spectra in terms of relaxation spectral functions feature up to four relaxation regions. The high-frequency relaxation processes, with relaxation times at around 2 and 10 ns, respectively, correspond with molecular processes also existing in saccharide solutions. They are assigned to the exocyclic hydroxymethyl group isomerization as well as to the rotation around glycosidic bond angles. The low frequency terms, with relaxation times in the range from 30 ns to 3 mus, are characteristic of micelle solutions. They are discussed in terms of two modes of monomer exchange. One mode reflects the well-known exchange kinetics of systems with Gaussian size distribution of globular micelles. The other mode is considered to be due to the monomer exchange at micelle sites with closer packing of surfactants, as is characteristic of large micelles with nonglobular shape.

Complex Impedance and Dielectric Dispersion in Carbon Fiber Reinforced Cement Matrices

The electrical response of carbon fiber reinforced cement mortar over the frequency range 1 Hz–10MHz has been presented. The low frequency conductivity is shown to be directly influenced by increasing fiber dosage, with conductivity percolation occurring at dosages in the range 0.35%–1.0% (by volume). When viewed across the entire frequency spectrum, the conductivity and dielectric constant frequency dispersions reveal two regions of relaxation. The definition of these regions becomes more pronounced as the fiber dosage is increased. It is proposed that the low frequency relaxation process (1 Hz–1 kHz) is related to the enhanced charge transfer characteristics at the electrode–material interface produced by the presence of the carbon fibers in the vicinity of the electrodes. The high frequency relaxation process (5 kHz–10 MHz) results from a Maxwell–Wagner effect produced by the presence of highly conducting inclusions (the carbon fibers) in the low conductivity mortar matrix.

Electrical conductivity and translational diffusion in the 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid

Broadband dielectric and terahertz spectroscopy (10(-2)-10(+12) Hz) are combined with pulsed field gradient nuclear magnetic resonance (PFG-NMR) to explore charge transport and translational diffusion in the 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid. The dielectric spectra are interpreted as superposition of high-frequency relaxation processes associated with dipolar librations and a conductivity contribution. The latter originates from hopping of charge carriers on a random spatially varying potential landscape and quantitatively fits the observed frequency and temperature dependence of the spectra. A further analysis delivers the hopping rate and enables one to deduce--using the Einstein-Smoluchowski equation--the translational diffusion coefficient of the charge carriers in quantitative agreement with PFG-NMR measurements. By that, the mobility is determined and separated from the charge carrier density; for the former, a Vogel-Fulcher-Tammann and for the latter, an Arrhenius temperature dependence is obtained. There is no indication of a mode arising from the reorientation of stable ion pairs.