Complex Dielectric Permittivity Spectra Research Articles

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.

Magnetic and Terahertz–Infrared Properties of Nanodispersed Hexaferrite SrxBa(1−x)Fe12O19 Solid Solutions

Hexagonal ferrites with the formula SrxBa(1−x)Fe12O19 (x = 0; 0.3; 0.5; 0.7; and 1) were prepared using the citrate method. The main feature of this synthesis is a relatively low calcination temperature of 700 °C. An X-ray diffraction study revealed a single-phase material. According to SEM, the particles were 50−70 nm in diameter. The Curie temperature of the samples that were determined using the DSC method varied in a very narrow range of 455−459 °C. Analysis of the magnetic hysteresis loops obtained at 300 K and 50 K indicated all samples as magnetically hard materials in a single-domain state. The maximal magnetic characteristics encompass strontium hexaferrite. The terahertz spectra of complex dielectric permittivity and the spectra of infrared reflectivity were measured at room temperature in the range of 6–7000 cm−1. The obtained broad-band spectra of the real and imaginary parts of permittivity reveal significant changes associated with structural distortions of the (Sr,Ba)O12 anti-cuboctahedron caused by the substitution of Ba2+ with Sr2+ in the same crystallographic positions.

Study of molecular interactions in aqueous polymer in presence of NSAID using spectroscopic technique

The dielectric study of aqueous Polyvinylpyrrolidone (PVP) (K-30) has been carried out in the presence of Ibuprofen (IBP) in the frequency range of 0.01 GHz – 30 GHz at the temperature 298.15 K using time domain reflectometry (TDR). Harviliak-Negami equation is used for the description of complex dielectric permittivity. The complex dielectric permittivity spectra ε*(ν) is described by using Cole-Cole model. The various dielectric properties i.e., dielectric constantεi, dielectric relaxation timeτi, correlation factor g, effective dipole moment μeff were calculated. Two relaxation processes has been observed namely low frequency relaxation (secondary) and high frequency relaxation (primary) for aqueous PVP-IBP mixture.

High entropy BaFe12-x(Ti/Mn/Ga/In)xO19 (x = 1–7) oxides: Correlation of the composition, entropy state, magnetic characteristics, and terahertz properties

The BaFe12-x (Ti/Mn/Ga/In)xO19 (x = 1–7) high-entropy oxides (HEOs) were obtained by solid-phase synthesis. The correlation of the chemical composition (the level of the Fe replacement), structural parameters, magnetic characteristics, and terahertz (THz) properties was investigated. All studied samples were single-phase (SG: P63/mmc). Lattice parameters showed a monotonic increasing trend with an increase of (x). The key role in increasing the lattice parameters of HEOs may belong to the influence of In3+ ions, which are much larger in size than Fe3+ ions. As one of the possible reason for explanation of the lattice parameters behavior we hypothesized that partial charge transformation of the Mn3+ state to the Mn2+ state takes place in order to maintain electrical neutrality. Other cations (Ti/Ga/In) have stable oxidation state. The anisotropic nature of the increase in lattice parameters was demonstrated. No strong correlation between chemical composition and microstructural parameters of the investigated HEOs was observed. The magnetic characteristics of the BaFe12-x (Ti/Mn/Ga/In)xO19 (x = 1–7) HEOs were investigated at broad intervals of magnetic fields and temperatures. The behavior of the magnetic characteristics was shown to be the result of the magnetic structure frustration. In addition, terahertz electrodynamic properties were studied by measuring spectra of complex dielectric permittivity at frequencies 0.2–1.2 THz in the temperature interval 20–300 K. The spectra indicate the presence of a higher-frequency infrared phonon resonance, whose damping decreases with cooling, as well as an excitation below 0.2 THz that freezes out at low temperatures, the origin of which is associated with the polycrystalline nature of the materials.

Complex Dielectric Permittivity Spectra of Rapeseed in the 20 MHz-3 GHz Frequency Range.

Rapeseed is one of the most important sources of vegetable oil worldwide. Knowledge of the dielectric properties of rapeseed may be beneficial for moisture content determination and the optimization of microwave treatment processes. The aim of this research was to examine the complex dielectric permittivity spectra of rapeseed of moisture content from 8.3% to 16.1%. The measurements were performed in the 20 MHz–3 GHz frequency range with the use of a vector network analyzer and a coaxial transmission-line cell. The real part of dielectric permittivity significantly depended on the water content of the seeds. The obtained spectra were modeled with the use of a three-pole Debye model with bulk electrical conductivity. Because the highest-frequency pole was found near the high-frequency measurement band limit, the spectra were additionally modeled with the use of an approximate ABC model with two in-band Debye poles. The determined model parameters were found to be highly dependent on the water content of the seeds. The relations between these parameters and water content were analyzed.

Dielectric Spectroscopy of Slightly Saline Sands

Abstract —We present results of experimental measurements of complex dielectric permittivity (CDP) of sand and powders of quartz granules with mass-averaged particle sizes from 5 to 250 μm, saturated with distilled water and NaCl solutions with a conductivity of up to 0.77 S/m. The CDP spectra are measured in a frequency range from 1 kHz to 8.5 GHz. Spectra at frequencies above 1 GHz are simulated using a refractive three-component mixture model. The CDP spectra in a frequency range from 10 kHz to 1 GHz were simulated by three relaxation processes using the Debye and Cole–Cole equations. It is shown that the conductivity of the sample at a frequency of ~5 kHz is not proportional to the conductivity of the saturating solution. The strengths of the two low-frequency processes are more closely correlated with the sample conductivity than with the solution proportion. The relaxation times of the low- and high-frequency processes are statistically related to an average particle size, and the relaxation time of the low-frequency process is additionally correlated with the specific surface area of the particles. We estimated the conductivity of the saturating solution at which the correlation is the strongest.

Understanding the molecular interaction and relaxation findings in amphiphilics on solution state using TDR

The dielectric behavior of stearic acid in 1,4-dioxane medium at various temperature 303 K–288 K and frequency regime (10 MHz–30 GHz) determined from the complex dielectric permittivity spectra obtained by Time Domain Reflectometry(TDR). In this frequency range, the dielectric study gives the electrostatic interaction as well as orientational polarizability of complex mixtures of long chain molecules significantly. Dielectric parameters were calculated from the complex spectra of the binary mixture by non linear least square fit method. The excess permittivity (εE), correlation factors were calculated for the binary system. Thermal parameters(ΔH-enthalpy, ΔS-entropy and ΔG-Gibbs free energy) were calculated and the direction of reaction is determined. The FTIR spectrum of the binary system recorded and the assignments are discussed. The FTIR spectral assignments confirm the molecular interactions.

Radar absorbing and shielding characteristics in ferrite-polymer composites Mn-Zn ferrite/P (TFE-VDF)

The article discusses the electromagnetic absorbing and shielding properties of ferrite-polymer composites of the composition Mn-Zn ferrite/fluoroplast-42, obtained by pressing a mixture of powders with heating. The measurement of the complex magnetic and dielectric permittivity spectra, as well as the reflection coefficient spectra was carried out in the frequency range 0.1-7 GHz. Using the obtained spectra, a comprehensive analysis of the absorbing characteristics of the composites was carried out, and the factors responsible for the absorption were determined. Fitting of the composites magnetic permeability spectra show that the process of natural ferromagnetic resonance prevails over the resonance of domain walls, and a decrease in the concentration of ferrite inclusions leads to a significant shift in the frequency of natural ferromagnetic resonance to high frequencies. It was found that for composites with a thickness of 5-10 mm, compositions with a mass fraction of ferrite ≤0.4 show radio-absorbing properties, while compositions with a fraction of ≥0.6 show shielding properties. Keywords: polymer composite, magnetic properties, radio absorption, feromagnetic resonance, polyvinylidene fluoride, manganese-zinc ferrite.

Радиопоглощающие и радиоэкранирующие характеристики феррит-полимерных композитов Mn-Zn феррит/П (ТФЭ-ВДФ)

The article discusses the electromagnetic absorbing and shielding properties of ferrite-polymer composites of the composition Mn-Zn ferrite/fluoroplast-42, obtained by pressing a mixture of powders with heating. The measurement of the complex magnetic and dielectric permittivity spectra, as well as the reflection coefficient spectra was carried out in the frequency range 0.1 - 7 GHz. Using the obtained spectra, a comprehensive analysis of the absorbing characteristics of the composites was carried out, and the factors responsible for the absorption were determined. Fitting of the composites magnetic permeability spectra show that the process of natural ferromagnetic resonance prevails over the resonance of domain walls, and a decrease in the concentration of ferrite inclusions leads to a significant shift in the frequency of natural ferromagnetic resonance to high frequencies. It was found that for composites with a thickness of 5 - 10 mm, compositions with a mass fraction of ferrite ≤ 0.4 show radio-absorbing properties, while compositions with a fraction of ≥ 0.6 show shielding properties.

Terahertz-infrared dielectric properties of lead-aluminum double-cation substituted single-crystalline barium hexaferrite

Hexaferrite materials are highly demanded to develop and manufacture electronic devices operating at radio- and microwave frequencies. In the light of the prospects for their use in the forthcoming terahertz electronics, here, we present our results on the terahertz and infrared dielectric response of a typical representative of hexaferrites family, lead-substituted M-type barium hexaferrite doped with aluminum, Ba0.2Pb0.8AlxFe12-xO19, x(Al) = 0.0, 3.0, and 3.3. We studied uniquely large and high-quality single crystals of the compounds prepared by spontaneous crystallization growth technique. Our aim was to explore the effect of aluminum substitution on the dielectric response of the compounds. Systematic and detailed investigations of the dependences of terahertz-infrared (frequencies 8–8000 cm−1) spectra of complex dielectric permittivity on the temperature, 4–300 K, and on the chemical composition, x(Al) = 0.0, 1.2, 3.0, and 3.3, were performed for two principal polarizations of the electric field E-vector of the probing radiation relative to the crystallographic c-axis, namely E||c and E⊥c. Furthermore, infrared phonon resonances are recorded and discussed. In contrast to undoped BaFe12O19, no softening of the lowest frequency A2u phonon is observed, indicating suppression of a displacive phase transition in substituted compounds. A number of resonance absorption bands are discovered at terahertz frequencies and assigned to transitions between energy levels of the fine-structured ground state of Fe2+ (5E) ions. The temperature and aluminum-doping dependences of the resonances are analyzed with an account taken of disorder introduced by aluminum. Basing on dielectric data and detailed X-ray experiments, we find that for all concentrations of Al3+ ions, x(Al) = 0.0, 1.2, 3.0, and 3.3, they mainly occupy the 2a and 12k octahedral site positions and that the degree of substitution of iron in tetrahedral positions is not substantial. Along with fundamental findings, the obtained data on broad-band dielectric properties of Ba0.2Pb0.8AlxFe12-xO19 crystals provides the information that can be used for development and manufacture of electronic devices with operating frequencies lying in the terahertz spectral band.

Assessment of proton conductivity, dielectric relaxation and other physicochemical properties of LTA zeolite blended chitosan composites for membrane applications

Novel chitosan biopolymer based solid electrolyte system consisting of surfactant-modified zeolite A are fabricated via simple solvent-casting technique to yield thin film proton exchange membrane. The zeolite LTA (Linde type-A) is synthesized and then it is impregnated with a surfactant, sodium dodecyl sulfate. The interfacial compatibility as well as the strong interaction in the polymer-filler system, modification of zeolite-A as well as its elemental composition is confirmed using FTIR, XRD and SEM-EDAX analysis. The physicochemical characteristics of the prepared membranes such as water uptake, IEC, hydration number and dimensional stability found to increase with increasing concentrations of the doped zeolitic filler. The appreciable mechanical as well as oxidative stability displayed by the membranes is due to the strong H-bond interaction between the polymer and modified zeolite. Overall, CSA-1.0 composite membrane showed the highest proton conductivity of 4.45 mS cm−1 at 80 °C, good thermal stability with Tmax = 217 °C and lesser gas permeability around 5 barrer. By determining the bound water content of the membranes using TGA analysis, the self-humidification characteristics were investigated. Good compatibility and interfacial interaction in the composite membranes has resulted in the creation of non-tortuous pathways for efficient proton transfer predominantly through Grotthus type mechanism. The relevant mechanism for the proton transfer along the membranes is evaluated in terms of complex impedance analysis, dielectric permittivity and electric modulus spectra. On the whole, the results obtained from various analysis suggests that the fabricated composite membranes are good alternatives as proton exchange membranes for fuel cell applications.

Temperature dependent Broadband dielectric relaxation study of Aqueous Polyvinylpyrrolidone (PVP K-15, K-30 & K-90) using a TDR

ABSTRACT Temperature-dependent dielectric relaxation studies of different viscosity grade Polyvinylpyrrolidones (PVP), PVP K-15, PVP K-30 and PVP K-90 having molecular weight 10,000 gmol−1, 40,000 gmol−1 and 360,000 gmol−1 respectively has been done in the frequency region 10 MHz to 50 GHz using Time domain reflectometry (TDR) technique. The frequency-dependent complex dielectric permittivity spectra have been explored by the Havriliak-Negami expression and is explained by the single relaxation model. The PVP molar concentration comprises the concentration domain of 0.0017 ≤ c/M ≤ 0.0176 for PVP-water system. The values of static dielectric constant (ε0), relaxation time (τ) and the empirical parameter (β) have been determined using non-linear least squares fit method along with the thermodynamic properties (activation enthalpy, entropy and free energy) of aqueous solutions of polymers.

Influence of nano SrTiO3 and ultrasonic irradiation on the properties of polymer blend electrolytes

ABSTRACT Lithium (Li+) ion conducting nanocomposite polymer blend electrolytes (NCPBEs) based on poly(ethylene oxide) (PEO), poly(vinylidene fluoride hexafluoropropylene) (P(VdF-HFP)) as polymer hosts, lithium perchlorate (LiClO4) as an electrolyte and strontium titanate (SrTiO3) as a nanofiller have been prepared by both the conventional stirring and ultrasonic irradiation methods. Complex formation and hence the structural changes of the prepared samples have been confirmed by X-ray diffraction analysis. Conductivity studies have been carried out by means of AC impedance spectroscopy. In order to highlight the role of ultrasonic irradiation, conductivity values have been compared with the values obtained through conventional mechanical stirring method. It has been found that the system with 15 minutes of ultrasonic irradiation resulted in better homogenous dispersion of SrTiO3 in PEO/P(VDF-HFP)/LiClO4 matrix. Maximum ionic conductivity of 2.519 × 10−4 Scm−1 has been obtained for 6 wt% of SrTiO3 system which is a magnitude higher than the ionic conductivity value, 2.031 × 10−5 Scm−1 obtained for the original NCPBE prepared using conventional mechanical stirring at room temperature. Further, ionic conductivity value increases with the increase of temperature and it exhibit the Arrhenius relation. Higher degree of free ionic motion in the samples has been proven by the increase in intensity of photoluminescence spectra peaks. The dielectric properties of the prepared samples have also been studied using the complex dielectric permittivity spectra and complex electric modulus spectra. The morphology and hence the surface roughness of the samples have been depicted through AFM study.

Terahertz-infrared electrodynamics of single-crystalline Ba0.2Pb0.8Al1.2Fe10.8O19 M-type hexaferrite

Spectral response of single-crystalline Ba0.2Pb0.8Al1.2Fe10.8O19 synthesized by a modified Czochralski method is investigated using terahertz-infrared spectroscopy. Reflectivity, transmissivity, and complex dielectric permittivity spectra of the compound are studied in the temperature range from 6 to 300 K and in the frequency interval 8-8000 cm−1 for two principle polarizations of the radiation electric field relative to the crystallographic c-axis, namely E||c and E⊥c. The resonance absorption lines observed above 80 cm−1 are assigned to polar lattice vibrations basing on a factor group analysis and a comparison with a dielectric response of isostructural compounds. A set of absorption bands is observed in a range of 8–80 cm−1. To clarify their nature, a model is developed that considers electronic transitions within the fine-structured ground state of four-fold coordinated Fe2+. It is shown that the trigonal distortions of the crystal field lead to lowering of the symmetry of 4f1 and 4e tetrahedral site-positions of Fe2+ and, as a result, to further splitting of the ground state spin-orbital sub-levels. Electro-dipole transitions between the corresponding sub-levels are associated with the absorption lines observed in a low-energy response (at 8-80 cm−1) of the Ba0.2Pb0.8Al1.2Fe10.8O19 compound. The study paves the way for the development of low cost materials with high dielectric permittivity (about 30) at terahertz frequencies that are promising for the manufacture of electronic devices with enhanced characteristics.

Dielectric polarization and relaxation processes of the lithium-ion conducting PEO/PVDF blend matrix-based electrolytes: effect of TiO2 nanofiller

The effect of TiO2 nanofiller concentration on the dielectric polarization and relaxation processes of (75PEO/25PVDF)/25 wt% LiClO4–x wt% TiO2 (x = 0, 2, 5, 10, 15, and 20) compositions based nanocomposite solid polymer electrolyte (NSPE) films has been investigated by employing the dielectric relaxation spectroscopy. The SEM micrographs demonstrate that the dispersion of TiO2 nanoparticles enormously alters the spherulitic morphology with the development of some cracks, pores, and wrinkles of these solution-cast prepared NSPE films. The X-ray diffraction study confirms that the heterostructures of these NSPE materials are semicrystalline and their degree of crystallinity increases irregularly with the increase of TiO2 concentration, however the crystallinity of host polymer blend matrix of these electrolytes decreases. The complex dielectric permittivity spectra of these NSPE materials in the frequency range from 20 Hz to 1 MHz at 27 °C reveal that there is a dominant contribution of electrode polarization and interfacial polarization at lower frequencies, whereas the high frequency permittivity values attribute to dipolar and ionic polarizations. Four types of relaxation processes have been probed by the ‘master curve representation’ of the dielectric and electrical spectra of these solid ion–dipole complexes. It is observed that the addition of TiO2 nanoparticles up to 10 wt% in these electrolytes influences the dielectric properties anomalously, but a huge decrease in the dielectric polarization and increase in the relaxation times are noted resulting in a significant decrease in the ionic conductivity of the film at 20 wt% TiO2 concentration. The dependence of dc ionic conductivity of these lithium-ion conducting NSPE materials on the chain segmental relaxation time and also the degree of crystallinity has been explored. The results of these NSPE materials have also been compared with the TiO2 nanoparticles loaded different polymer matrices and salts based electrolytes and discussed appropriately. These lithium-ion based electrolyte films are accredited for the solid-state ion-conducting energy storing devices from their electrochemical parameters characterized by LSV, CV, and CA techniques.

Magnetic Structured Nickel Core-Shell @ Silica/PMMA Nanocomposites from Synthesis to Applications

Incorporating Ni@SiO2 nanoparticles on poly-methyl methacrylate (PMMA) can alter electrical, optical, and magnetic properties of Ni nanoparticles to be used for energy storage applications, photo electronic devices and spintronic applications. The Ni@SiO2/PMMA nanocomposite samples are prepared by casting method. The morphology of the prepared nanoparticles was examined through high resolution transition electron microscope revealed the formation of SiO2 coating on ni nanoparticles. Furthermore, the topography of nanocomposites was characterized by the field emission scanning electron microscope. We investigated the formation of crystalline phase of Ni nanoparticles through X-ray diffraction. The Complex dielectric permittivity, electrical conductivity, electric modulus and impedance spectra of the PNC films were investigated in the frequency range from 0.1 Hz to 10 MHz. The real and imaginary parts of the permittivity decrease with increasing frequency due to an increase in Ni@SiO2 content. All the nanocomposites showed relatively low conductivity values and high impedance that could be used for nano-dielectrics. UV–Vis spectrophotometer was used to measure optical properties such as transmittance, and absorbance at normal incidence in the wavelength range of 200–1100 nm. The transmittance was found to decrease while the absorbance increases with increasing Ni@SiO2 nanoparticles. The indirect optical band gap of the composite films was calculated, and it was sharply decreased. Magnetic hysteresis plots at room temperature of composites Ni@SiO2/PMMA were studied. All samples demonstrate ferromagnetic behavior with well pronounced magnetic hysteresis.

Terahertz-infrared spectroscopy of Ti4+-doped M-type barium hexaferrite

We report on the first detailed investigations of the terahertz-infrared dielectric response of potential multiferroic single crystalline Ti-doped M-type barium hexagonal ferrite, BaFe12-xTixO19, with concentrations of the dopant above (x = 1.15) and below (x = 0.62) the critical concentration that corresponds to changes of the charge compensation mechanism. Employing terahertz time-domain spectroscopy and Fourier-transform infrared spectroscopy, we performed measurements of the spectra of complex dielectric permittivity ε*(ν) = ε′(ν)+iε"(ν) at frequencies ν = 2-8000 cm−1 (0.06–240 THz) and in the temperature interval T = 10–300 K. The effect of aliovalent cation substitution on the low-energy response of barium hexaferrite is analyzed and discussed. A rich set of polarization- and temperature-dependent excitations is observed and their origin assigned to the electronic transition within the ground state 5E of the four-fold coordinated divalent iron, to relaxational dynamics of domains, and to phonon resonances.

Terahertz shielding properties of aero-GaN

The electrodynamic properties of the first aero-material based on compound semiconductor, namely of Aero-GaN, in the terahertz frequency region are experimentally investigated. Spectra of complex dielectric permittivity, refractive index, surface impedance are measured at frequencies 4–100 cm−1 and in the temperature interval 4–300 K. The shielding properties are found based on experimental data. The aero-material shows excellent shielding effectiveness in the frequency range from 0.1 to 1.3 THz, exceeding 40 dB in a huge frequency bandwidth, which is of high interest for industrial applications. These results place the aero-GaN among the best THz shielding materials known today.

Effect of aluminium substitution on low energy electrodynamics of barium-lead M-type hexagonal ferrites

We present the first detailed study of the terahertz-infrared dielectric response of single crystalline lead-substituted M-type barium hexaferrites doped with Al3+. The broadband spectra of complex dielectric permittivity ε*(v)=ε’(v)+iε"(v) of Ba0.8Pb0.2AlxFe12-xO19 with concentrations of the dopant x(Al)=1.2, 3, 3.3 are obtained for two principle polarizations using Fourier-transform infrared spectroscopy and terahertz time-domain spectroscopy in the temperature range from 4 to 300 K and at frequencies from 10 cm−1 up to 8000 cm−1. We observe a rich set of excitations and assign them to the electronic transitions within the ground state 5E of the 4-fold coordinated divalent iron and to phonon resonances. Effect of Al3+ cation substitution on low energy (terahertz) dielectric response and infrared phonon spectra of barium-lead M-type hexaferrites is analysed and discussed.

Preparation, structural analysis, morphological investigation and electrical properties of gold nanoparticles filled polyvinyl alcohol/carboxymethyl cellulose blend

Polymer nanocomposite samples have been prepared through the solution casting method utilizing a polymer blend of polyvinyl alcohol and carboxymethyl cellulose (70/30wt.%) as organic host matrix and different concentrations of biosynthesized gold nanoparticles (Au NPs) by the leaf extract of green mint (Mentha Spicata L.) as inorganic nanofiller. The structural, optical and morphological properties of these samples have been through FT-IR, XRD, UV/Vis. and SEM techniques. The FT-IR spectra confirm the blend components are miscible by the formation of Hydrogen bond interaction and show the polymer-nanoparticle interactions. The XRD analyses depict the semicrystalline structure of these samples and the crystallinity degree decrease with increase of Au NPs content within the PVA/CMC structure. The TEM micrograph of biosynthesized Au NPs indicates that shapes of these NPs are spherical NPs and triangular/hexagonal nanoplates with average size range 5–29nm. The alternating electrical conductivity, electrical impedance, complex dielectric permittivity and electric modulus spectra of prepared samples have been investigated at 25°C in the frequency range (0.1Hz–20MHz). Thus, the variations in values of conductivity, dielectric permittivity and relaxation times indicate the feasibility of these materials as flexible nanodielectric of frequency tunable permittivity for radio/audio frequency operating microelectronic/conventional devices.