Permittivity Spectra Research Articles

Dielectric relaxation study of pyridine-n-propyl alcohol mixture using time domain reflectometry technique

ABSTRACT The Time Domain Reflectometry (TDR) technique was used to analyse the complex permittivity spectra of the Pyridine-n-propyl alcohol mixture across the concentration and temperature range of 10–25°C. The Cole-Davidson model was used to match the Pyridine- n-propyl alcohol complex permittivity spectra. The nonlinear least squares fit approach has been used to obtain the Static dielectric constant (ε0), Relaxation time (τ), Effective Kirkwood correlation factor (geff) Excess permittivity ε 0 E , Thermodynamic parameters (activation enthalpy and activation entropy), and Bruggeman factor (fB). Furthermore, the analysis of excess characteristics and the Bruggeman factor points towards the presence of hydrogen bonding between the pyridine and n-propyl alcohol molecules.

Extrinsic dielectric response due to domain wall motion in ferroelectric BaTiO[formula omitted]

BaTiO3 (BTO) is a prototypical perovskite ferroelectric, whose dielectric permittivity and loss spectra – which are strongly temperature and frequency dependent – include contributions from inhomogeneous polarization patterns, with domain walls (DWs) being the most common types. In order to elucidate how DWs influence dielectric response, we utilized a continuum approach based on the Landau–Ginzburg theory to model field-dependent properties of polydomain tetragonal phase of BTO near room temperature and above. A system with 180∘ DWs was evaluated as a case study, with both position-resolved and volume-averaged dielectric susceptibility and loss computed at different temperatures for a range of applied field frequencies and amplitudes. Our results demonstrate that cooperative dipole fluctuations in the vicinity of the DW provide a large (extrinsic) contribution to the system dielectric response relative to the intrinsic contribution stemming from within the domain. Dynamics of the DW profile fluctuations under applied field can be represented by a combination of breathing and sliding vibrational motions, with each exhibiting distinct dependence on the field frequency and amplitude. The implications of this behavior are important for understanding and improving control of coupled functional properties in ferroelectric materials, including their dielectric, electromechanical, and electrooptical responses. Furthermore, this investigation provides a computational benchmark for future studies and can be readily extended to other topological polarization patterns in ferroelectrics.

Complex Permittivity Spectra of Granular Polymer Composites with Dispersed Ag-Coated Cu Flakes

AbstractConductive particle-containing granular composites with tuneable negative permittivity are being studied to improve the performance of electromagnetic devices, such as shielding materials. In this study, we investigated the relative complex permittivity and electrical conductivity of granular composites of polyphenylene sulfide (PPS) resin and Ag-coated Cu flakes in the radio- to microwave-frequency range and compared them with those of PPS/bare Cu flake composites. Electrical conductivity measurements revealed that the PPS/Ag-coated Cu flake composites have a lower percolation threshold (φc) than the PPS/bare Cu flake composites, whereas the electrical conductivity of the PPS/Ag-coated Cu flake composites in the percolated particle state was higher at the same particle volume fraction. At particle contents above φc, a low-frequency plasmonic state of conduction electrons was achieved in the percolated particle chains in both composites, and negative permittivity spectra were obtained. The percolated PPS/Ag-coated Cu flake composites had a negative permittivity up to a higher frequency than the percolated PPS/bare Cu flake composites. Furthermore, the Drude model was used to analyze the negative permittivity spectra of the composites in the percolated particle state. The plasma frequency of the composites with percolated Ag-coated Cu flakes was higher than that of the composites with percolated bare Cu flakes. Thus, coating Ag on Cu particles improved the conductivity of the composite, leading to negative permittivity up to higher frequencies. This study contributes to the enhancement of the negative permittivity achieved by granular composites, which is useful for microwave technology applications. Graphical Abstract

THz optical response of Ba(Fe[formula omitted]Ni[formula omitted])[formula omitted]As[formula omitted] films analyzed within the three-band Eliashberg s[formula omitted]-wave model

The uncertainty of the nature of the normal state and superconducting condensate of unconventional superconductors continues to stimulate considerable speculation about the mechanism of superconductivity in these materials. Of particular interest are the type of symmetry of the order parameter and the basic electronic characteristics of the superconducting and normal states. We report the derivation of temperature dependences of the superconducting condensate plasma frequency, superfluid density, and London penetration depth by measuring terahertz spectra of conductivity and dielectric permittivity of the Ba(Fe1−xNix)2As2 thin films with different Ni concentrations. A comprehensive analysis of the experimental data was performed in the framework of the simple three-band Eliashberg model under the assumption that the superconducting coupling mechanism is mediated by antiferromagnetic spin fluctuations. The results of independent experiments support the choice of model parameters. Based on calculations of the temperature dependences of superconducting gaps, we may conclude that the obtained results are compatible with the scenario, in which Ba(Fe1−xNix)2As2 is a multiband superconductor with s±-wave pairing symmetry.

Drug-amino acid interaction: Molecular dynamics in aqueous medium using time domain reflectometry

Present work reports dielectric response of the non-steroidal anti-inflammatory drug (NSAID) aceclofenac in aqueous valine solutions at various concentrations and temperatures (278.15 K–298.15 K) in the frequency range of 0.01 GHz to 30 GHz using Time-domain reflectometry (TDR) technique. The frequency dependent complex dielectric permittivity has been analyzed by Harviliak-Negami equation. Debye model is used for the description of complex dielectric permittivity spectra ε*(ν). The structural and dynamical properties of water has been investigated at different concentrations of valine and aceclofenac using dielectric as well as thermodynamic parameters that includes static dielectric constant (ε0), relaxation time (τ0), Kirkwood correlation factor (g), free energy of activation (ΔF), entropy of activation (ΔS), and enthalpy of activation (ΔH). Towards the measured low temperature and high concentrations of Valine and Aceclofenac (ACF), static dielectric constant (ε0) was found to be increasing. This could be due to increased effective dipole-dipole parallel alignment and can be confirmed by the increasing values of correlation factor (g > 1). The dipole-dipole interaction between Drug-Amino acid resulted in increased dielectric relaxation time (τ0) of system due to increased steric hindrance for the rotation of dipoles. The free energy of activation was found to be in the range of 2.22 and 2.58 Kcal mol-1. The entropy is more negative at high concentration suggesting more ordered structure. The slope of log (Tτ0) vs. 1000/T gives the value of enthalpy (ΔH).

Dielectric characterisation and intermolecular interactions in propionitrile-dimethyl sulphoxide mixtures using a time domain reflectometry

ABSTRACT Complex permittivity spectra of propionitrile (PN) – dimethyl sulphoxide (DMSO) mixtures in the 10 MHz–30 GHz frequency range were investigated using time-domain reflectometry (TDR). The Debye model was employed to fit the measured dielectric spectra, allowing for the calculation of dielectric parameters like the static dielectric constant (ε 0 ) and relaxation time (τ). Excess dielectric constant (ε 0 E ) and excess inverse relaxation time (1/τ) E were subsequently calculated from the measured ε 0 and τ. The observed variations in these excess parameters provide evidence for intermolecular interactions within the PN-DMSO mixtures. Theoretical estimates of the ε 0 were obtained using Luzar’s hydrogen-bonded model.

Improvement of energy storage properties of NN-based ceramics by high-entropy strategy and A-site cation vacancies

High-entropy dielectric capacitors have recently drawn increasing attention in the field of energy storage. In this study, NiO has been incorporated into [(Na0.7Bi0.1)0.8Sm0.02Ca0.02Sr0.02Ba0.02]Nb0.8Sb0.1Ta0.1O3-based ceramics. We applied the concept of high-entropy design to introduce cation vacancies at the A-site, enhancing conformational entropy. This approach led to the successful preparation of a novel type of energy-storage ceramics with an ABO3 perovskite structure, denoted as (1-x)NBSCSBNST-xNiO (x = 0, 0.02, 0.04, & 0.06). We conducted a systematic study of the microstructural, dielectric, and ferroelectric characteristics, along with an exploration of the influence of the high-entropy strategy on their performance. The ΔSconfig increases with NiO doping, and the Eb of the NBSCSBNST-0.02Ni sample exhibits a significant increase to 730 kV/cm from 550 kV/cm of NBSCSBNSTN. This enhancement is accompanied by a recoverable energy density (Wrec) of 4.43 J/cm3 and an efficiency (η) of 75.9 %. As the content of NiO increases from x = 0 to x = 0.06, the phase transition diffusion behavior strengthens. Additionally, the permittivity (εr) spectrum becomes more uniform, and the activation energy of the prepared ceramic samples increases from 1.03 eV to 1.76 eV. This effect suppresses the emergence of localized electric branching, eventually improving the breakdown strength of NBSCSBNST-xNi ceramic materials. The obtained results indicate that the concept of high-entropy design to introduce cation vacancies at the A-site is an efficient approach to improve the energy storage characteristics of lead-free dielectric capacitors.

Effect of soil compaction on the measurements of complex dielectric permittivity spectrum with an open-ended antenna probe and the coaxial cell system

The paper proposes the use of dielectric spectroscopy to measure changes in dielectric permittivity for soil subjected to compression. Density-dependent dielectric permittivity characteristics of soils for the entire range of obtained density, and thus for a significant parameter of soil properties corresponding with ideal conditions for plant growth as well as those inhibiting their growth were presented. Measurements were carried out for three soil types with different moisture content using an open-ended antenna probe (OE-A), operating in the frequency range of 20 MHz–1.2 GHz and a coaxial cell system in frequency range of 20 MHz–3 GHz. Experimental results showed that an increase in bulk density and volumetric water content of soil affects the complex dielectric permittivity spectrum – a model for this relationship was proposed. Soil dielectric permittivity as a parameter reflecting soil moisture and density can be useful in assessing soil quality.

Co3+ Doped CdFe2O4 Nanoparticles: Structural, Optical, Magnetic, and Electrical Properties

Through the citrate-gel auto-combustion technique, we synthesized Co-doped cadmium nano ferrites (NFs) with the formula CoxCd1−xFe2O4 (where 0 ≤ x ≤ 1.0 with increments of 0.2). The synthesized materials underwent comprehensive analysis utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy. Magnetic and electrical properties were evaluated using a vibrating sample magnetometer and LCR meter, respectively. XRD analysis confirmed the spinel phase structure and FD3M space group. SEM analysis revealed agglomerations of nanoparticles and grain boundaries. Elemental analysis of the synthesized nanomaterials was provided by energy dispersive spectroscopy. FTIR spectroscopy identified two main broad bands corresponding to the tetrahedral (A) and octahedral (B) sites, confirming the spinel structure. Magnetic properties such as magnetic saturation, coercivity, and remanent magnetization were characterized using VSM. Additionally, the LCR meter assessed frequency and temperature-dependent dielectric parameters, including AC conductivity (σAC), dielectric permittivity, dielectric loss (tan δ), and impedance spectra. An increase in AC conductivity (σAC) was observed with increasing temperature and frequency.

Correlation of relaxation processes by BDS: Calorimetric, spectral findings and molecular dynamics of active side chain amino acids in hydrated medium

The dielectric dispersion behavior of amino acids (L-arginine and L-glutamic acid) was studied in the aqueous state by Broadband Dielectric Spectroscopy (BDS). The complex permittivity spectra of the solutions were recorded for the frequency regime 10 MHz – 50 GHz at a temperature range of 283 K to 303 K for various mole fractions. The interaction of polarized side chains of the solute (positive in L-arginine and negative in L-glutamic acid) with hydrated polar media is the significance of the work. The hydration effect of the amino acid modifies the dielectric and physicochemical properties of the solution. The study of Differential Scanning Calorimetry (DSC) analysis and thermal parameters specifies that the L-glutamic acid has super strong nature than L-arginine. The formation of hydrogen bond, nature and strength of the interaction through side chain are confirmed by spectral analysis (FT-Raman, FT-IR and NMR). The geometrical properties were computed with DFT/B3LYP −6-31G(d,p) basis set. The obtained spectral signals were compared with experimental data. The experimental and quantum mechanical calculations are used to identify the hydrodynamic coupling of the solution. The present study correlate the dielectric, thermal parameters, spectral inferences with molecular structure, dynamics is a novel approach which confirms the nature and strength of the complex formation.

Impedance spectra of soft ionics

Impedance spectroscopy is widely adopted for probing the charge and charge mobility of soft ion-conducting media, such as synthetic membranes and biological tissue. The spectra exhibit a variety of distinctive signatures, but the physical basis of these is not well understood, e.g. models have not previously accounted for viscoelasticity, hydrodynamics or microstructural heterogeneity. This study explores a physically grounded continuum model that captures how these factors shape conductivity spectra. Nonlinear thermodynamics and linearised dynamics of a viscous electrolyte and compressible, elastic polymer network are coupled under the forcing of an oscillatory electric field. The model is solved in a one-dimensional spatially periodic unit cell, reporting conductivity and dielectric permittivity spectra, including Nyquist representations. Whereas rigid microstructures exhibit ion-diffusion-controlled relaxation, which manifests as a low-frequency dielectric ‘constant’, hydrodynamic and elastic forces contribute to a strongly diverging dielectric permittivity at low frequencies for heterogeneous anionic microstructures. The model also captures distinctive characteristics of experimentally reported impedance spectra for films bearing alternating layers of cationic and anionic charge, again highlighting the role of coupled hydrodynamic, elastic and electrical forces. Sufficiently thin and highly charged bilayers exhibit a notably low high-frequency conductivity. This is explained by strong low-frequency electrostatic polarisation and counter-ion release. The one-dimensional solutions computed herein provide a foundation for much more challenging computations in two and three dimensions.

Dielectric and hydrogen bonding studies of butyronitrile with 1,4-dioxane using a time-domain reflectometry

Using time-domain reflectometry (TDR), the complex permittivity of binary mixture of butyronitrile (BTN) and 1,4-dioxane (1,4-DX) at various temperatures and solvent proportions was determined over the frequency range of 10 MHz to 30 GHz. The complex permittivity spectra (CPS) have been fitted to the Havrilik–Negami equation. The relaxation time (τ) and static dielectric constant (ε0) have been calculated for each concentration using the least squares fit method. The nonlinear behavior of dielectric parameters suggests a change in the molecular size and intermolecular bonding of BTN–1,4-DX mixtures. Theoretical static dielectric constants (ε0) have been determined using hydrogen bonded model suggested by Luzar for all solvent proportions and compared with experimental values obtained from TDR.

Self and hetero-association in Benzaldehyde/Quinoline − Formamide solutions: Time Domain Reflectometry studies

The complex permittivity spectra of binary solutions of Benzaldehyde (PhCHO)/Quinoline (QUI) with Formamide (FMD) have been obtained at different mole fractions of FMD in the frequency range from 10 MHz to 30 GHz using the Time Domain Reflectometry (TDR) technique. The complex permittivity spectra have been fitted with Debye function. Dielectric relaxation time values have been interpreted in terms of the nature and size of the self and hetero associates of the binary solutions. The effective Kirkwood correlation factor (geff) has been correlated with closed and open associates of the solutions. The geff∼0.51 is the characteristic value of closed dimers. It appears that geff∼0.75 signifies the presence of both closed and open dimers. The Excess static dielectric constant (εE) shows negative deviation. The corrective Kirkwood correlation factor (gf) and Bruggeman factor (fB) have been used to investigate the strength of the H-bond interactions. The Geometry optimization has been carried out using Density Functional Theory (DFT) with B3LYP/6–311++G (d, p) basis set. Population analysis on the optimized geometries shows that PhCHO has 53.61 and 46.39 % closed and open geometries, respectively, while FMD has 17.11 % open dimers and remaining are closed dimers.

Effective Permittivity of Compacted Granular Materials: Effects of Interfacial Polarization and Pore-filling Fluids

Interfacial polarization dominates the permittivity spectra of heterogeneous granular materials for the intermediate frequency range (i.e., from kHz to MHz). In this study, we examine the corresponding dielectric responses of compacted glass sphere packings saturated with pore-filling fluids under various compressive stresses. The effective permittivity spectra are observed to exhibit consistently a plateau-to-plateau drop, described by low-frequency permittivity, characteristic frequency, and high-frequency permittivity. The permittivity spectra under different compressive levels are found to be influenced by the packing structure, compressive stress, and electrical property contrasts between solid and fluid (specifically permittivity and conductivity). For considered measurement conditions, the variation of packing structure and its associated porosity is found to be more significant than the stress evolution in controlling the interfacial polarization, thus the permittivity spectra, as supported by analytical and numerical results for unit cells. Furthermore, to gain a general rule for dielectric responses for saturated granular materials, we train multi-layer artificial neural network (ANN) models based on a series of simulations for unit cells with various structures, stresses, and electrical and dielectric properties. The predictions with two-layer ANN agree well with experimental measurements, presenting errors smaller than 5% for both low-frequency and high-frequency permittivity. This study offers an effective predicting approach for the dielectric behaviour of heterogeneous and multiphase materials.

Nanocarbon/Co3O4/Epoxy Composites for Microwave Shielding and Absorption

The epoxy composite materials (CMs) with a random distribution of nanosized Co3O4 and carbon nanoparticles (graphite nanoplatelets GNP and carbon nanotubes CNT) are fabricated. Complex permittivity, permeability, and shielding properties of composite materials with 30 wt% of Co3O4 and (2–5) wt% of nanocarbon are measured in the frequency range of 1–67 GHz using the transmission–reflection method. A significant increase of microwave permittivity and presence of several peaks on the dependencies of the imaginary part of permittivity on the frequency are found for three‐phase nanocarbon/Co3O4/epoxy CMs. The observed microwave shielding efficiency of three‐phase epoxy composites is enhanced compared to two‐phase nanocarbon–epoxy composites. Such enhancement of shielding efficiency correlates with the increase of DC conductivity of these three‐phase composites. The measured complex permittivity and permeability spectra for nanocarbon/Co3O4/epoxy CMs are used for modeling the reflection loss for studied composites. It is shown that the most preferable for microwave absorption is the composites containing 2 wt% of nanocarbon filler for a sample thickness of 0.5–0.7 mm. The highest reflection loss = 30 dB with an absorption bandwidth of 15 GHz is found for epoxy composite filled with 2 wt% of GNP and 30 wt% of Co3O4 for a sample thickness of 0.5 mm.

Bi–Er–O pre-synthesized phase (Bi1-xErx)2O3 doped ZnO varistors with high nonlinear coefficient and low leakage current

The content of free oxygen Oad at the ZnO grain boundaries has an important impact on the double Schottky barrier and electrical properties of ZnO varistors. In this work, Bi–Er–O pre-synthesized (BE) phase (Bi1-xErx)2O3 (0.25 < x < 0.455) with high conductivity of Oad was prepared using Bi2O3 and Er2O3 as raw materials, and the effects of the BE phase doping on the phase, grain boundary properties, and electrical properties of ZnO–Bi2O3–Sb2O3–Co2O3–MnO2–Cr2O3–SiO2 varistors were studied. XRD analysis shows that the lattice constant of the BE phase (Bi1-xErx)2O3 is between (Bi0.75Er0.25)2O3 and BiErO3. With increasing doping content of the BE phase from 0 to 0.75 wt%, part of Er3+ still exists in the form of the BE phase (Bi1-xErx)2O3 at the ZnO grain boundaries, and its content increases with increasing doping content of the BE phase. The conductivity of Oad in (Bi1-xErx)2O3 is much higher than that in Bi2O3, resulting in the generation of a large number of negative O′ and O″ at the ZnO grain boundaries, and decreasing concentration of the intrinsic point defect zinc interstice Zni. So the donor concentration Nd decreases, the height of the grain boundary barrier increases, the depletion layer widens, and the electrical properties are improved. By analyzing the low-temperature permittivity spectra, it was calculated that with increasing doping content of the BE phase from 0 to 0.75 wt%, the concentration of oxygen vacancy VO• decreases inappreciably, but the concentration of zinc interstice Zni•• decreases by about 23%. When the doping amount of the BE phase is 0.75 wt%, the nonlinear coefficient α of the obtained ZnO varistors is 73.9 ± 0.6, and the leakage current density JL is only 0.3 ± 0.1 μA/cm2. This study provides an important reference for improving the electrical properties of ZnO varistors by manipulating the Bi-rich phase structure to improve the double Schottky barrier characteristics.

High frequency dielectric study on the hydrogen bonding interaction on 1,5-pentanediol + 1,4-dioxane binary mixtures

The complex dielectric permittivity spectra (CPS) of a binary mixture of 1,5-pentanediol (1,5-PD) with 1,4-dioxane (1,4-DX) were determined using time-domain reflectometry in the frequency range of 10 MHz to 30 GHz. The experimental CPS data were fitted to the Cole–Davidson equation using a nonlinear least squares fit method to determine the dielectric relaxation parameters. The intermolecular interactions in the binary liquids were studied through the Kirkwood correlation factor, excess parameters, thermodynamic parameters, and Bruggeman’s factor.

Thermodynamics Properties of Amino Acid with Water Mixture using Time Domain Reflectometry Technique

In this paper we have reported the thermodynamics properties of the amino acids (L-alanine) in water solution were carried out using time domain reflectometry at 250C to -50C in the frequency range between 10 MHz to 30 GHz. The dielectric parameters i.e. static dielectric constant and relaxation time, were obtained from the complex permittivity spectra using a nonlinear least square fit method. From the values of the relaxation time, the thermodynamic parameters are determined. The dielectric relaxation parameters increase with an increase in concentration (mM) of amino acid due to the structure of hydrogen bond groups by the amino acid molecules in the aqueous solution. The relaxation peak shifted to lower frequency with an increase in molar concentration of amino acid.

What is behind a gas stream scrubbing liquid? Monoethanolamine/water mixtures as seen by dielectric relaxation spectroscopy.

High-quality dielectric data for monoethanolamine (MEA)/water mixtures covering the entire miscibility range are presented. For MEA concentrations c1 ≥ 1 M the obtained complex permittivity spectra, covering the frequency range from 0.05 to 89 GHz, are best described by a sum of four Debye relaxations. Modes at ∼3 GHz and ∼10 GHz are solute-specific. Whilst the first can be assigned to MEA aggregates, the second is a composite arising from "free" MEA dipoles with dynamically retarded water hydrating them. The relaxations at ∼18 GHz and ∼200 GHz essentially reflect the cooperative H-bond fluctuations of more-or-less unperturbed "bulk" water, albeit with minor solute contributions. Evaluation of the bulk-water amplitude reveals that in water-rich mixtures (c1 ≤ 3.5 M) Zt = 3.5 ± 0.2 H2O molecules hydrate a MEA molecule. Then Zt drops linearly, reaching zero for neat MEA. Supported by the literature, this concentration dependence suggests that only H2O molecules H-bonded to the NH2 and OH groups of MEA contribute to Zt. At concentrations beyond hydration shell overlap (c1 ≥ 3.5 M) these H-bonds are gradually eliminated, while new interactions with neighboring MEA molecules are formed. From the evaluation of the MEA-specific amplitudes we conclude that for c1 ≥ 2 M, including neat MEA, ∼35% of the solute molecules are in aggregates, where breaking the intermolecular NH⋯O hydrogen bond determines the dynamics.

Preparation and microwave absorption properties of CoFe2O4/NiCo2O4 composite powders

The magnetic spinel cobalt ferrite (CoFe2O4) powders had the high microwave absorption performance at the large thicknesses on account of the low permittivity. Combining the CoFe2O4 powders with other dielectric loss materials had been suggested to improve their impedance matching and microwave absorption performance. In this work, the microwave absorption performance of the CoFe2O4 powders was enhanced by adding the various amounts of the NiCo2O4 nanoparticles as dielectric loss material. The CoFe2O4-x NiCo2O4 composite powders (x = 0, 12.5, 25, and 50 wt %) were prepared by a facile two-pot solution combustion synthesis method. Although the X-ray diffraction peaks of NiCo2O4 phase were absent, but the decrease of saturation magnetization from 61 to 30 emu/g was related to the amount of NiCo2O4 material. Furthermore, the NiCo2O4 nanoparticles were nucleated and grown on the surface of spongy CoFe2O4 powders because the synthesized CoFe2O4 powders were added to the precursor solution of NiCo2O4 material containing the nickel and cobalt nitrates as oxidants and glycine as organic fuel. The microwave absorption performance was analyzed by measuring the permittivity and permeability spectra which were applied for evaluating the reflection loss versus frequency and thickness. The CoFe2O4-25 wt % NiCo2O4 composite powders had the higher microwave absorption performance including the high reflection loss of −40 dB and broad effective bandwidth of 5.6 GHz of Ku band (12–18 GHz) at a small matching thickness of 1.9 mm. The high microwave absorption performance of the x = 25 wt % sample was attributed to its better impedance matching via a proper combination of the permittivity and permeability values.