Dielectric Permittivity Spectra Research Articles

Determination of Soil Pore Water Salinity Using an FDR Sensor Working at Various Frequencies up to 500 MHz

This paper presents the application of a frequency-domain reflectometry (FDR) sensor designed for soil salinity assessment of sandy mineral soils in a wide range of soil moisture and bulk electrical conductivity, through the determination of soil complex dielectric permittivity spectra in the frequency range 10–500 MHz. The real part of dielectric permittivity was assessed from the 380–440 MHz, while the bulk electrical conductivity was calculated from the 165–325 MHz range. The FDR technique allows determination of bulk electrical conductivity from the imaginary part of the complex dielectric permittivity, without disregarding the dielectric losses. The soil salinity status was determined using the salinity index, defined as a partial derivative of the soil bulk electrical conductivity with respect to the real part of the soil complex dielectric permittivity. The salinity index method enables determining the soil water electrical conductivity value. For the five sandy mineral soils that have been tested, the relationship between bulk electrical conductivity and the real part of dielectric permittivity is essentially linear. As a result, the salinity index method applied for FDR measurements may be adapted to field use after examination of loam and clayey soils.

The study of dielectric relaxation in aqueous carbohydrates solutions using time domain reflectometry technique

Complex permittivity spectra of aqueous solutions of monosaccharide (d-glucose) and disaccharides (d-sucrose) in the frequency range from 10 MHz to 30 GHz at various concentrations and temperatures have been determined using time domain reflectometry technique. The complex dielectric permittivity spectrum of d-glucose and d-sucrose in water shows Cole–Davidson type behaviour. Dielectric constant (e0) and relaxation time (τ), Kirkwood correlation factor, activation enthalpy and entropy parameters have been determined.

Polaronic Mobility in Boron Doped Iron Phosphate Glasses: Influence of Structural Disorder on Summerfield Scaling

The electrical conductivity and dielectric properties of xB2O3–(40−x)Fe2O3–60P2O5 (x = 0–20, mol%) glasses have been investigated by impedance spectroscopy in the frequency range from 0.01 Hz to 1 MHz and over the temperature range from 303 to 523 K. The dc conductivity is strongly controlled by polaron concentration, which depends upon the Fe2O3 content and the average distance between iron ions. The evolution of the complex dielectric permittivity as a function of frequency and temperature was studied. The thermal‐activated relaxation mechanism dominated the observed relaxation behavior. The relationship between relaxation parameters and electrical conductivity indicates the electronic conductivity controlled by polaron migration between iron ions with the distribution of hopping distances. The deviations from the Summerfield scaling in the ac conductivity and dielectric permittivity spectra have been observed for selected polaronic glasses. These deviations are caused by the local structural disorder and/or relaxation generated in the early stage of B2O3 addition as well as at the initial incorporation of BO4 tetrahedra into phosphate chains.

Tuning of dielectric properties of SrTiO3in the terahertz range

Tuning of the dielectric permittivity spectra of strontium titanate (SrTiO${}_{3}$) single crystals in an external electric field is investigated between 90 and 300 K by means of terahertz time-domain spectroscopy. Application of the electric bias leads to an appreciable tuning of the permittivity observed up to room temperature both in the parallel and perpendicular directions to the bias field. The observed behavior is interpreted in terms of soft-mode hardening due to the anharmonic character of its potential. No additional low-frequency relaxation mode was observed. A weak temperature dependence of the anharmonic coefficients was found in agreement with previously published low-temperature data.

Terahertz and infrared spectroscopic evidence of phonon-paramagnon coupling in hexagonal piezomagnetic YMnO3

Terahertz and far-infrared electric and magnetic responses of hexagonal piezomagnetic YMnO${}_{3}$ single crystals are investigated. Antiferromagnetic resonance is observed in the spectra of magnetic permeability ${\ensuremath{\mu}}_{a}$ [H$\phantom{\rule{0.16em}{0ex}}(\ensuremath{\omega})$ oriented within the hexagonal plane] below the N\'eel temperature ${T}_{N}$. This excitation softens from 41 to 32 $\phantom{\rule{0.16em}{0ex}}{\text{cm}}^{\ensuremath{-}1}$ upon heating and finally disappears above ${T}_{N}$. An additional weak and heavily-damped excitation is seen in the spectra of complex dielectric permittivity ${\ensuremath{\varepsilon}}_{c}$ within the same frequency range. This excitation contributes to the dielectric spectra in both antiferromagnetic and paramagnetic phases. Its oscillator strength significantly increases upon heating toward room temperature, thus providing evidence of piezomagnetic or higher-order couplings to polar phonons. Other heavily-damped dielectric excitations are detected near 100 $\phantom{\rule{0.16em}{0ex}}{\text{cm}}^{\ensuremath{-}1}$ in the paramagnetic phase in both ${\ensuremath{\varepsilon}}_{c}$ and ${\ensuremath{\varepsilon}}_{a}$ spectra, and they exhibit similar temperature behavior. These excitations appearing in the frequency range of magnon branches well below polar phonons could remind electromagnons, however their temperature dependence is quite different. We have used density functional theory for calculating phonon dispersion branches in the whole Brillouin zone. A detailed analysis of these results and of previously published magnon dispersion branches brought us to the conclusion that the observed absorption bands stem from phonon-phonon and phonon-paramagnon differential absorption processes. The latter is enabled by strong short-range in-plane spin correlations in the paramagnetic phase.

Radiofrequency dielectric properties of amorphous semiconducting Y–Ba–Cu–O oxide thin films for bolometric detection

We report the study of dielectric properties of amorphous semiconducting YBCO thin films measured in a broad frequency range, from 40Hz to 2GHz and in the 210 to 430K temperature range, using a coaxial discontinuity technique. At all temperatures, dielectric permittivity and conductivity spectra exhibit typical features of dielectric relaxation processes. A first relaxation at low frequency (300Hz–2kHz), observed only at high temperature, might be attributed to interfacial effects. Polarization in the grains of the YBCO thin films could lead to the second relaxation observed at higher frequency (800Hz–660kHz). The relaxation frequencies increase with temperature and follow a thermally activated behavior of the Arrhenius-type. Optical near-infrared response of YBCO bolometers exhibits a corner frequency around 40kHz. Above this frequency, the thermal diffusion is localized inside the YBCO thin film. This frequency is in good agreement with the relaxation frequency attributed to YBCO grains in the thin film, i.e. around 40kHz at 300K.

Dielectric relaxation study of aqueous 2-ethoxyethanol using time domain reflectometry technique

The complex permittivity spectra of 2-ethoxyethanol in water solutions have been studied at different concentrations and temperatures using a picosecond time domain reflectometry technique. The complex dielectric permittivity spectrum of 2-ethoxyethanol shows Cole-Davidson type behavior. Increase in dielectric relaxation time may be due to increase in hetero molecular interaction strength. Minimum in Excess dielectric constant values provides the information about stable complex adduct. The Kirkwood correlation factor, thermodynamic properties and Bruggeman factor have also been determined and the results are interpreted in terms of hydrogen bonding and interactions among the solute — solvent molecules.

On the phase identity and its thermal evolution of lead free (Bi1/2Na1/2)TiO3-6 mol% BaTiO3

Temperature-dependent dielectric permittivity of 0.94(Bi1/2Na1/2)TiO3-0.06BaTiO3 (BNT-6BT) lead-free piezoceramics was studied to disentangle the existing unclear issues over the crystallographic aspects and phase stability of the system. Application of existing phenomenological relaxor models enabled the relaxor contribution to the entire dielectric permittivity spectra to be deconvoluted. The deconvoluted data in comparison with the temperature-dependent dielectric permittivity of a classical perovskite relaxor, La-modified lead zirconate titanate, clearly suggest that BNT-6BT belongs to the same relaxor category, which was also confirmed by a comparative study on the temperature- dependent polarization hysteresis loops of both materials. Based on these results, we propose that the low-temperature dielectric anomaly does not involve any phase transition such as ferroelectric- to-antiferroelectric. Supported by transmission electron microscopy and X-ray diffraction experiments at ambient temperature, we propose that the commonly observed two dielectric anomalies are attributed to thermal evolution of ferroelectric polar nanoregions of R3c and P4bm symmetry, which coexist nearly throughout the entire temperature range and reversibly transform into each other with temperature.

Magnetic properties and microstructure of SHS-Produced co-containing hexaferrites of the Me2W system

BaCo2 − xZnxFe16O27 hexaferrite powders were prepared by mechanoactivated SHS. The ferrites were characterized by XRD and phase analyses. The values of specific saturation magnetization, field of magnetocrystalline anisotropy, spin reorientation transition, and Curie’s temperatures were derived from static and dynamic measurements of respective magnetic properties. The spectra of magnetic permeability and dielectric permittivity were measured within the microwave range.

Low-energy excitations and stripes in superconducting cuprate La 1.87Sr 0.13CuO 4

The conductivity and dielectric permittivity spectra of single-crystalline La 1.87Sr 0.13CuO 4 are directly measured with the electric field polarized perpendicular to the CuO planes ( E ∥ c ) covering the frequency range 10–40 cm −1 and temperatures 5–300 K. We observe in the superconducting state a well pronounced excitation with strongly temperature dependent parameters. We suggest that the excitation is caused by the transverse Josephson plasma mode that appears due to the different strengths of Josephson coupling between the superconducting charge stripes in the neighboring and next-nearest neighboring copper–oxygen planes of La 1.87Sr 0.13CuO 4. A strongly enhanced low-frequency (below 15 cm −1) absorption is seen in the superconducting state that is assigned to delocalized quasiparticles of as yet unknown origin.

Inelastic light scattering studies of diffuse phase transition in ferroelectric Sr1.9Ca0.1NaNb5O15 thin films

AbstractThe dynamic behavior of highly oriented ferroelectric Sr1.9Ca0.1NaNb5O15 thin films has been investigated by Brillouin light scattering over a wide temperature range between 25 and 450 °C. The temperature variations of the full‐width at half‐maximum (FWHM) of the central peak (CP) are found to exhibit marked changes around the Curie temperature (Tc = 246 °C). The CP reveals a relaxational mode behavior, which is attributed to thermally activated fast relaxation of polar nanoregions (PNRs). The width of the CP decreases steadily upon cooling from ∼400 °C to Tc and shows little subsequent change within the ferroelectric state, indicating an increase of the number of PNRs and a slowing down of their dynamics. By using a modified superparaelectric model, the activation energy (H0) of the relaxation processes and the Burns temperature (TB) are determined to be 2939 and 385 °C, respectively. The evidence for this diffuse phase transition provided by Brillouin scattering is in agreement with results obtained from the temperature‐dependent dielectric permittivity, refractive index, and Raman spectra. Copyright © 2011 John Wiley & Sons, Ltd.

Estimation of entropy and enthalpy of a nematic liquid crystal using time domain reflectometry studies

Abstract Dielectric relaxation behavior of molecules in their pure form, a non-polar solvent, or mixtures of these substances at different microwave frequencies and over a range of temperatures and concentrations give an idea about inter- and intra-molecular forces. Such studies enable one to calculate thermodynamic parameters like change of activation energy for dipole orientation (ΔG*), enthalpy (ΔH*), and entropy (ΔS*) of activation. Such studies in liquid crystals give additional information about the molecular behavior in different phases of liquid crystal under study. An experimental investigation on verity of systems is necessary to draw quantitative conclusions regarding the system of the molecules which are not studied so as to examine if the results obtained are in favor or against, to the general conclusions already arrived at, in other systems. With this in view, the complex dielectric permittivity spectra of p-pentyl phenyl-p-propylbenzoate (PPPB) a nematic liquid crystal are obtained using T...

Dependence of microwave absorption properties on ferrite volume fraction in MnZn ferrite/rubber radar absorbing materials

We report the analysis of measurements of the complex magnetic permeability ( μ r ) and dielectric permittivity ( ε r ) spectra of a rubber radar absorbing material (RAM) with various MnZn ferrite volume fractions. The transmission/reflection measurements were carried out in a vector network analyzer. Optimum conditions for the maximum microwave absorption were determined by substituting the complex permeability and permittivity in the impedance matching equation. Both the MnZn ferrite content and the RAM thickness effects on the microwave absorption properties, in the frequency range of 2–18 GHz, were evaluated. The results show that the complex permeability and permittivity spectra of the RAM increase directly with the ferrite volume fraction. Reflection loss calculations by the impedance matching degree (reflection coefficient) show the dependence of this parameter on both thickness and composition of RAM.

Study of heterogeneous interaction in binary mixtures of 2-methoxyethanol-water using dielectric relaxation spectroscopy

The dielectric relaxation measurements on binary mixtures of 2-methoxyethanol with water have been carried out over entire concentrations and at temperature range of 0 °C to 25 °C using a picosecond time domain reflectometry technique. The complex dielectric permittivity spectra of 2-methoxyethanol/water mixtures were fitted using Havriliak–Negami equation. The static dielectric constant and relaxation time for all concentrations were obtained using least square fit method. The principal relaxation time is small if compared to that of corresponding alcohol/water mixtures this may be due to the hydrogen bonding ether oxygen in the 2-ME-water system. Excess dielectric properties, Kirkwood correlation factor, thermodynamic properties and Bruggeman factor are also determined and the results are interpreted in terms of heterogeneous interactions among the unlike molecules due to hydrogen bonding.

Broadband dielectric and conductivity spectroscopy of Li-ion conducting three-dimensional hybrid inorganic–organic networks as polymer electrolytes based on poly(ethylene glycol) 400, Zr and Al nodes

The dielectric and conductivity study of two series of five three-dimensional hybrid inorganic–organic networks as polymer electrolytes (3D-HION-APEs), with formula {Al[O(CH 2CH 2O) 8.7] ρ /(LiClO 4) z } n (1.86 ≤ ρ ≤ 2.24, 0 ≤ z ≤ 1.06) and {Zr[O(CH 2CH 2O) 8.7] ρ /(LiClO 4) z } n (1.81 ≤ ρ ≤ 1.99, 0 ≤ z ≤ 0.91) is presented. The real and imaginary components of the complex dielectric permittivity spectra ɛ * and conductivity spectra σ * are measured between −60 °C and 80 °C. Spectral analysis points out that the conductivity mechanism is determined by two dielectric relaxation events, α and β. The relaxation β occurs at higher frequencies than α, and is attributed to the segmental motion with characteristic frequency f seg. The relaxation α is attributed to the ionic motion with characteristic frequency f ion. The profiles of the direct conductivity σ dc and the frequencies f ion and f seg vs. the reciprocal temperature exhibit a Vögel–Tamman–Fülcher (VTF) behavior. The study of the activation energies of the dielectric relaxations α and β allows to determine their relative contribution to the direct conductivity σ dc at lower and higher temperatures. The dependence of the VTF parameters vs. the mole-to-mole ratios n Li/ n O and n Li/ n M (M = Zr, Al) in combination with previous equivalent conductivity studies, allows to identify the role of the ionic species and the metal nodes present in the polymer structure at various salt concentrations. The correlation between the diffusion coefficient D and the relaxation frequencies f seg and f ion of the 3D-HION-APEs is investigated.

Dielectric behaviour of aqueous CsCl solutions

Complex dielectric permittivity spectra, in the frequency range 10 MHz to 20 GHz are reported for aqueous cesium chloride (CsCl) solutions at 250C using time domain reflectometry technique. The static dielectric constant, relaxation time and conductivity have been determined using nonlinear least squares fit method. From the static dielectric constant, hydration numbers were determined by using measured solutions density at different concentrations.

Investigation of Dielectric and Noise Properties of the Multiferoic Composite BaTiO3 with CoFe2O4

Dielectric and noise characteristics of CoFe2O4-BaTiO3 ceramic composites were investigated. The complex dielectric permittivity displays a broad maximum around 300 K, where a phase transition occurs. The dielectric spectra of the complex dielectric permittivity are caused by the conductivity above 300 K. Intensive almost periodic telegraphic noise with relaxation type spectra is observed in the same temperature range (around 300 K). An investigation of the noise characteristic shows that several noise intensity peaks occur during this phase transition.

Dynamic magnetic characteristics of a composite polymeric material based on carbonyl iron

Nowadays microwave radiation is used not only in special means: consumer devices of high-frequency radio electronics move actively ahead, including mobile telephones, computers, and photo- and videocameras. Due to mastering of gigahertz frequencies, miniaturization, small weight, and high speed of modern hardware is provided. Active mastering of the microwave range has aggravated the need for magnetic materials absorbing electromagnetic radiation. Such materials are required to reduce harmful influence on biological objects, to provide electromagnetic compatibility of units and blocks of high-frequency devices, and to construct anechoic chambers. Magnetic elastomers representing composite microwave materials put on metal surfaces whose main components are ferri- and ferromagnetic fillers are used as absorbers [1]. Carbonyl iron is one of the perspective materials for manufacturing absorbing coatings [2]. The frequency band of natural ferromagnetic resonance (NFMR) in the presence of the domain structure lies generally in the limits from 2πf1 = γHa to 2πf2 = γ(Ha + 4πМS) [3]. The anisotropy field of carbonyl iron is Ha ≈ 500 Oe, its saturation magnetization is MS ≈ 1.7⋅10 3 G, and γ/2π = 2.8 GHz/kOe, that is, the NFMR frequency band lies in the limits from f1 ≈ 1.4 GHz to f2 ≈ 61 GHz. Samples of composite materials consisting of P-10 grade carbonyl iron powders in polyethylene matrix were fabricated. Powders of the given iron grade have bulbous structure with average particle sizes of ~3.5 μm. The thickness of the examined plane samples was 1 mm, and the volume iron contents were 50 and 15%. To measure the magnetic permeability (μ = μ′ – iμ″) and the dielectric permittivity (e = e′ – ie″) spectra, a Universal Broadband Radiospectrometer was used based on an E8363В Vector Circuit Analyzer of the Agilent Technologies. Measurements were performed in the frequency range 10 MHz – 20 GHz. A coaxial waveguide, an irregular microstrip resonator [4], and a set of rectangular multimode volume resonators were used as measuring cells [5].

The Role of Probe Attenuation in the Time-Domain Reflectometry Characterization of Dielectrics

The influence of the measurement set-up on the estimation of dielectric permittivity spectra from time-domain reflectometry responses is investigated. The analysis is based on a simplified model of the time-domain reflectometry measurement set-up, where an ideal voltage step is applied to an ideal transmission line that models the probe. The main result of this analysis is that the propagation in the probe has an inherent band limiting effect, and the estimation of the high-frequency permittivity parameters is well conditioned only if the wave attenuation for a round-trip propagation in the dielectric sample is small. This is a general result, holding for most permittivity model and estimation schemes. It has been verified on real estimation problems by estimating the permittivity of liquid dielectrics and soil samples via an high-order model of the time-domain reflectometry set-up and a parametric inversion approach.

Dielectric relaxation studies on [PEO–SiO2]:NH4SCN nanocomposite polymer electrolyte films

Present work deals with findings on dielectric relaxation behaviour and a.c. conduction in a SiO2-doped polymer nanocomposite electrolyte system, namely, [(100 − x)PEO + xSiO2]:yNH4SCN. The formation of nanocomposite has been ascertained by XRD measurements. The effect of salt and filler (SiO2) on conductivity response of PEO-based nanocomposite polymer electrolyte has been investigated by impedance spectroscopy. The variation of dielectric permittivity, dielectric loss and modulus spectra with frequency and temperature was carried out from impedance spectroscopy data. The a.c. conductivity seems to follow the universal power law.