Jonscher's Model Research Articles

Ionic conducting characteristics of the solid electrolyte LiMgPO4

Li+ ion-conducting properties in Lithium magnesium orthophosphate compound were investigated in the present study. Our compound was prepared with the standard ceramic method.Vibrational study and impedance spectroscopy were explored to understand the ion dynamics and dielectric properties. The surface morphology of the sample was examined by SEM analysis. Rietveld's refinement of the X-ray diagram shows that the synthesized material was well crystallized in the orthorhombic olivine structure with the Pnma space group.The complex impedance spectra analysis reveals that the electrical properties of the material are heavily dependent on frequency and temperature, indicating a relaxation phenomenon and semiconductor-type behavior.A typical universal dielectric response in the frequency-dependent conductivity at different temperatures was found. The alternative current conductivity is discussed in the framework of Jonscher's model. The Correlated Barrier Hopping "CBH" conduction process is proposed to investigate the transport properties in the dynamic region of the studied compound.Cationic disorder plays a major role in the charge carriers transport. Fitting parameters obtained from the theoretical aspect have been discussed.

Features of immittance spectra as performance indicators for cement-based concretes

Design for durability and performance-based standards and specifications for reinforced concrete infrastructure is limited by the lack of rapid, science-based test methods for characterising the deterioration resistance of concrete. In this paper, this issue is addressed though the application of two-point electrical impedance measurements taken within the frequency range 100 Hz–10 MHz. Data are presented for a range of industry-standard cement-based concrete mixes with and without supplementary cementitious materials. Nyquist plots (−iZ″(ω) against Z′(ω)) and Bode plots (Z*(ω) and θ against frequency) clearly highlight the frequency dependence of the electrical response. However, when presented in the form of permittivity and conductivity, a region of dispersion was evident over the entire frequency range for all concretes. The features of this response, which could be gainfully exploited as durability indices for assessing the long-term performance of concrete, are identified and discussed. A range of formalisms is presented and it is shown that, within this frequency range, conductivity was found to obey Jonscher's universal power law. Two novel durability parameters are presented based on features of Jonscher's model; from a practical viewpoint, the power-law model can be evaluated using conductivity measurements obtained at three, easily measured, spot frequencies (10 kHz, 1 MHz and 10 MHz).

Tuning of the microstructural and electrical properties of undoped BaTiO3 by spark plasma sintering

The distribution of oxygen vacancies in BaTiO3 specimens can greatly affect material electrical properties. Spark plasma sintering followed by annealing in controlled pO2 atmospheres offers the potential to control the oxygen vacancy distribution. Impedance spectroscopy has been used to study the electrical characteristics of undoped BaTiO3 specimens prepared at 1200 °C under a pressing pressure of 5 MPa and 50 MPa using spark plasma sintering (SPS). For both samples, at temperatures greater than 750 °C, the total conductivity is determined by the bulk conductivity (σb), while at temperatures between 550 °C–750 °C the total conductivity is determined by the grain boundary conductivity (σgb). Below 550 °C, the total conductivity is determined by the BaTiO3–Pt interface conductivity (σel). The bulk, grain boundary and electrode interface resistances and activation energies are lower for samples sintered and pressed at 50 MPa, compared to specimens sintered and pressed at 5 MPa. Plots of grain boundary conductivity (σgb) vs. oxygen partial pressure (pO2) (log(σgb) vs. log(pO2)), over the temperature range 517 °C–683 °C, have slopes of approximately 4.0 indicating that doubly charged oxygen vacancies (VO••) are located at the grain boundaries. The grain boundary region and BaTiO3–Pt interface conductivities are highly sensitive to the oxygen partial pressure. Therefore, SPS sintered BaTiO3 specimens that have been subjected to controlled annealing could be used to tailor BaTiO3 dielectric properties, as well as have potential applications in high temperature O2 sensing. Furthermore, analysis of a.c. conductivity using the Jonscher model reveals that the governing charge transport mechanism is via quantum mechanical tunneling (QMT), which operates at temperatures when grain boundaries control the total conductivity. The mechanism switches to the correlated barrier hopping (CBH) model at temperatures when the bulk controls the total conductivity.

Finite element simulation and frequency optimization for wireless signal transmission through RC structures

The enclosed civil structures pose a challenging environment for wireless communication between sensor nodes. Wireless electromagnetic (EM) signal attenuates significantly when transmitting through reinforced concrete structures. This paper simulates the signal attenuation for plain concrete, pure steel rebar lattice and reinforced concrete using finite element method (FEM) in Ansoft High Frequency Structure Simulator (HFSS). Jonscher model is found to be a better concrete dielectric model than Debye model from the attenuation test results. FEM simulation for signal attenuation of reinforced concrete (RC) slab is validated by finite difference time domain (FDTD) simulation and test results from literature. Optimal frequency to minimize the signal attenuation through RC structure is in the range of 0.35 GHz ~ 0.5 GHz. Resonance occurs at t / (λc/4) = 2n and t / (λc/4) = 2n + 1, n = 1, 2, 3, 4, ... for low concrete volumetric water content (VWC). Signal attenuation is highly linear with slab thickness t for high concrete VWC. 433 MHz is suggested for real application of wireless sensor network considering the antenna size and optimization results. FEM simulation is validated by the experiment using intact wireless sensor nodes.

강섬유의 구조적 파라미터에 따른 콘크리트의 전자파 차폐효과 분석

Steel fiber is a material frequently used when contained in concrete because of its various architectural advantages, and it plays a role in increasing the electromagnetic shielding effectiveness (SE) of the building owing to its high conductivity. Thus, this study analyzed the SE of the steel fiber reinforced concrete (SFRC) according to the structural parameters of the steel fiber. The equivalent permittivity of concrete was extracted using the Jonscher model; The concrete was modeled using the electromagnetic simulation tool, and the electromagnetic properties were analyzed according to the orientation, number, and length of the steel fiber. Thus, depending on the structural parameters of the steel fiber, the causal relationship of the polarization of the incident wave, level of the SE, and resonance frequency was derived.

Structural and magnetodielectric properties of BiFeO3-GdMnO3 multiferroics

We report on structural, microstructural, spectroscopic, dielectric, electrical, ferroelectric, ferromagnetic, and magnetodielectric coupling studies of BiFeO3–GdMnO3[(BFO)1–x –(GMO) x ], where x is the concentration of GdMnO3 (x = 0.0, 0.025, 0.05, 0.075, 0.1, 0.15, and 0.2), nanocrystalline ceramic solid solutions by auto-combustion method. The analysis of structural property by Rietveld refinement shows the existence of morphotropic phase boundary (MPB) at x = 0.10, which is in agreement with the Raman spectroscopy and high resolution transmission electron microscopy (HRTEM) studies. The average crystallite size obtained from the transmission electron microscopy (TEM) and x-ray line profile analysis was found to be 20–30 nm. The scanning electron micrographs show the uniform distribution of grains throughout the surface of the sample. The dielectric dispersion behavior fits very well with the Maxwell-Wagner model. The frequency dependent phase angle (θ) study shows the resistive nature of solid solutions at low frequency, whereas it shows capacitive behavior at higher frequencies. The temperature variation of dielectric permittivity shows dielectric anomaly at the magnetic phase transition temperature and shifting of the phase transition towards the lower temperature with increasing GMO concentration. The Nyquist plot showed the conduction mechanism is mostly dominated by grains and grain boundary resistances. The ac conductivity of all the samples follows the modified Jonscher model. The impedance and modulus spectroscopy show a non-Debye type relaxation mechanism which can be modeled using a constant phase element (CPE) in the equivalent circuit. The solid-solutions of BFO-GMO show enhanced ferromagnetic-like behavior at room temperature. The ferroelectric polarization measurement shows lossy ferroelectric behavior. The frequency dependent magnetocapacitance and magnetoimpedance clearly show the existence of intrinsic magnetodielectric coupling. The (BFO)1–x –(GMO) x solid solutions with x = 0.025–0.075 show significantly higher magnetocapacitance and magnetoimpedance compared to the pure BFO.

Linking Degree of Saturation With the Complex Dielectric Permittivity of Limestone in a GPR Frequency Band Using SVR

This article focuses on the development and validation of an innovative method for estimating the degree of saturation (DOS) in limestone. A protocol is designed to control, homogenize, and validate such an estimation. The complex dielectric permittivity is acquired from the coaxial electromagnetic transition line on a limited frequency bandwidth. Calibration curves connecting the dielectric permittivity and the DOS are obtained. The use of variants of Jonscher’s model makes it possible to overcome the frequency dependence and propose a relationship between Jonscher model parameters and the DOS. A supervised learning method [ $v$ -support vector regression (SVR)] has been successfully introduced to estimate the DOS from these parameters. The results have been experimentally validated on a wide range of limestone samples.

Physical properties in nano-crystalline Ho2CoMnO6

3d based double perovskite materials have received much attention in recent years due to their exotic magnetic structure and magneto-electric coupling. In this work we have prepared and studied the nano-crystalline sample of Ho2CoMnO6. Structural, magnetic, Raman and dielectric properties have been studied in detail. The structural analysis shows that the sample crystallize in monoclanic crystal structure with P21/n phase group. The X-ray photoelectron spectroscopy have been employed to confirms the charge state of cations presents in the material. Magnetic study shows that the sample undergoes a paramagnetic to ferromagnetic phase transition around Tc ~85 K. The isothermal magnetization measurements shows hysteresis curve hence confirm ferromagnetic behavior at low temperature. Temperature dependent Raman study reveals that there is spin phonon coupling in the sample marked by deviation in phonon mode from anharmonic behavior. Dielectric response of Ho2CoMnO6 shows the large dispersion and large dielectric constant. Impedance spectroscopy and electrical modulus study reveal that system shows deviation from ideal Debye model. AC conductivity have been studied as a function of both temperature and frequency. We found that the conduction mechanism is obeyed by Jonscher's model. The exponent factor n is suggest that the material deviates from ideal Debye model.

Physical characterizations of the sprayed ZrMo2O8 thin films

The objective of this work is to synthesize and evaluate the physical properties of the Zirconium-Molybdate-Oxide thin films via structural, optical and electrical measurements. The films were deposited on glass substrates using a chemical spray technique. The structural properties of obtained samples were analyzed by XRD technique and hexagonal ZrMo2O8 structure was revealed in the films. The surface topography, as observed by scanning electron microscopy (SEM), shows the presence of randomly orientated spherical asperities ~ 2.5 μm in size. In addition, the optical parameters such as band gap energy value, refractive index and extinction coefficient were studied using spectrophotometry UV–VIS–NIR and spectroscopic ellipsometry. Finally, the dependences of electrical properties of ZrMo2O8 thin film on temperature and frequency have been reported. The ac conductivity is investigated through the Jonscher model. The dc conductivity is thermally activated and the semiconductor-type behavior of the ZrMo2O8 thin films is revealed. From the relaxation frequency, the activation energy value is about 1.29 eV.

Full-waveform inversion using a stepped-frequency GPR to characterize the tack coat in hot-mix asphalt (HMA) layers of flexible pavements

The use of tack coats in the construction of road structures is a technique that ensures pavement layer bonding. Unfortunately, existing techniques commonly used in France to estimate tack coat conditions require coring structures for ad hoc characterization in the laboratory. This paper investigates a non-destructive approach to characterize changes in geometric and dielectric properties of the tack coats present inside the hot-mix asphalt (HMA) layers of flexible pavements, with the use of a stepped-frequency radar combined with a mono-static, off-ground, ultra-wideband Vivaldi antenna. The principle of this method is to consider the flexible pavement as a multi-layered medium with changing properties (thicknesses, dielectric susceptibilities and dispersion parameters). Then a full-waveform inversion is applied, which allows for the extraction of the dielectric and geometric parameters of each layer composing the structure. Following numerical validations, the multi-layered forward model, namely, a Green's function model integrating the 2-parameter variant of Jonscher's model, combined with Lambot's et al. radar full-wave method was experimentally validated using calibrating media (up to three layered media). Then, the link between both the dielectric and the geometric parameters of the tack coats and the emulsion quantity (bonding) was analyzed. The results showed good agreement between measured and modeled radar data. Radar data inversions showed in particular that the dielectric susceptibility and thickness of the transition zone increase with the emulsion quantity. Future research will focus on the establishment of a reference database of calibration curves linking dielectric susceptibility and tack coat characteristics.

Near-Field Full-Waveform Inversion of Ground-Penetrating Radar Data to Monitor the Water Front in Limestone

Limestone has been a widely used building material for many years. Its degradation process has been strongly linked to its water content, to which the radar waves are sensitive. In this paper, the closed-form, near-field full-wave radar model of Lambot et al. is utilized for monitoring water ingress in limestone. This model is based on planar layered media Green's functions combined with an intrinsic representation of the antenna through global reflection and transmission functions. The Jonscher model is used to describe the frequency dependence of the limestone electromagnetic properties. Then, an inversion method based on a genetic algorithm is developed and optimized. The method is numerically validated by simulating electromagnetic wave propagation in medias, using a three-dimensional finite element software, namely high-frequency electromagnetic field simulation. Finally, the method is experimentally validated, with a stepped-frequency radar system and an ultrawide band antenna, during an imbibition process of a limestone slab. Results are compared to gammadensimetry measurements, a nuclear and semidestructive approach, performed as the reference. Analyses of the results show that the average relative difference between the estimated and the reference water front is 2.5%, thereby demonstrating the performance of the proposed nondestructive method.

Physical and ethanol sensing properties of sprayed Fe2(MoO4)3 thin films

Monoclinic Fe2(MoO4)3 thin films have been prepared by chemical spray technique deposited on glass substrates and investigated their physical properties. The obtained thin films were characterized by X-rays diffraction (XRD) using Rietveld's method which confirm the appearance of pure monoclinic Fe2(MoO4)3 thin films. Moreover, the surface morphological was investigated using scanning electron microscope (SEM), which showed the formation of porous microstructures with rough surfaces and spherical nanoparticles.The spectrophotometer UV–Vis–NIR reveals that the sample presents an optical gap equal to 2.0 eV. Electrical properties dependence on both temperature and frequency of the Fe2(MoO4)3 thin films have been reported. The ac conductivity plot showed a universal power law according to the Jonscher model. Activation energy values deduced from the relaxation frequency is of the order of 0.71 eV. Finally, Fe2(MoO4)3 thin films have been tested as sensitive films against ethanol vapor at different operating temperatures and gas concentrations. The films showed promising ethanol sensing behavior with good reproducibility and especially an excellent sensing performance at 275 °C.

Enhanced dielectric behavior and ac electrical response in Gd-Mn-ZnO nanoparticles

The investigations of the structural, optical, dielectric and ac electrical properties of Gd0.05MnxZn0.95-xO (weight percentage x = 0.03, 0.05 and 0.07 respectively) nanoparticles have been done in this report. The nanoparticles were synthesized by hydrothermal method. The X-ray diffraction analysis reveals the presence of hexagonal wurtzite crystalline structure for all the undoped and doped samples. Photoluminescence emission spectra for the entire samples confirm the presence of various defect centers inside the doped ZnO wurtzite nanostructure. Dielectric measurements show dispersion behavior for all the samples and it was found to increase with the doping concentration. The dielectric behavior has been explained on the basis of Maxwell-Wagner-Sillars polarization phenomenon. High value of dielectric constant (1.2 × 106) was observed due to the presence of grain boundary defects and oxygen vacancies. Incorporation of Gd and Mn inside the ZnO wurtzite structure can causes more grain boundary defects which can enhance polarization. The ac conductivity of entire samples was temperature and frequency dependent. The ac conductivity was governed by universal ac power law σac = Bωn according to the Jonscher model. Variation of frequency exponent “n” from 0.2841 to 0.0484 suggests that diffusion controlled charge carrier hopping mechanism is also involves in the conduction phenomenon.

Ac conductivity and dielectric behavior of hydrated homoionic alkali-cations-exchanged montmorillonite

ABSTRACTThe dielectric properties of a series of homoionic alkali-exchanged montmorillonites were studied at different treatment temperatures and various water loadings by means of complex impedance spectroscopy. To date, however, this method has been underutilized in clay minerals studies. The main objective of the present work is to understand the relaxation mechanisms of water molecules interacting with different hydration centers in clay minerals, with a view to eventually control their interactions with the alkali extra-framework cations. The other part of our study is to study the dielectric properties such as real and imaginary parts of dielectric permittivity, loss tangent, and ac conductivity in the frequency range 10−2–106 Hz and temperature range 173–333 K of these clay minerals. The obtained results have been discussed in terms of the Jonscher model.

Determination of concrete water content by coupling electromagnetic methods: Coaxial/cylindrical transition line with capacitive probes

This paper deals with the development and the validation of an innovative, easy-to-use and on site technique for determination of concrete water content. The on-site technique is the capacitive probe, able to characterize in situ dielectric media in the 30–35MHz frequency band (around 33MHz). For the evaluation of water content in various civil engineering structures, a calibration methodology has to be developed and is presented herein. It is based on the complex permittivity estimation of various dispersive concretes, which is carried out by a cylindrical coaxial electromagnetic (EM) transition line allowing the characterization in laboratory of material samples in a large GPR frequency bandwidth [50–600MHz]. This methodology consists then on a coupling between the results of both the capacitive probes and the coaxial EM cell extrapolated at low frequency (33MHz). The extrapolation procedure used to link physically the results of the two techniques is provided by the 4parameter-variant of Jonscher's model which is parameterized to obtain dispersion curves of the complex permittivity for very wide frequency bands. The methodology is checked by a parametric study that associates the 4p-variant of Jonscher's model with the physical and hydric characteristics of the six concrete mix designs representing high performance and ordinary concretes at various hydric states. The surface testing results measured by capacitive probes on slabs are successfully compared to the extrapolated results obtained on cores.

Investigation into the optoelectrical properties of tungsten oxide thin films annealed in an oxygen air

Tungsten oxide (WOx) thin film have been deposited onto glass substrates using the thermal vacuum evaporation technique, monitored by an annealing process in a variable oxygen atmosphere. Analysis by X-ray diffraction and Raman spectroscopy showed the structural changes from orthorhombic to monoclinic which depend on the annealing temperature and the oxygen content. AFM study shows that the increase of oxygen content leads to a decrease of the root-mean-square from 94.64nm to 2nm. Ellipsometric measurements have been used to evaluate the optical constants. Further, it is found that when the oxygen content increases, the band gap of the annealed layer varies from 3.01eV to 3.52eV by against, the Urbach energy decreases. The AC conductivity plot showed a universal power law according to the Jonscher model. Moreover, at high frequency semiconductor-to-metallic behavior has been observed. Finally, the effect of annealing in oxygen atmosphere on their structural modifications, morphological, optical properties and electrical conductivity are reported.

Dynamics of Mn3+ in off-stoichiometric LiMn1.5Ni0.5O4

LiMn1.5Ni0.5O4 is investigated by anelastic spectroscopy in order to study the manganese dynamics. An intense thermally activated peak, detectable only in off-stoichiometric samples, is attributed to a polaronic conduction due to an electron transfer from Mn3+ to a Mn4+, and the consequent motion of the Jahn–Teller lattice distortion. In order to have a good fit of the experimental data, the Jonscher model for ionic dynamics is adopted for the first time in this spinel structure. A value of about 0.3eV for the energy barrier of the polaronic conduction is obtained.

Electrical conductance through adsorbed water molecules on freshly fractured glass surfaces

Plate glass sheets of low emissivity glass were cut into small rectangles and scratched with a diamond tipped scribe from one edge to another. The scratch was deep enough to locally remove the conducting tin oxide surface and to fracture the glass beneath, leaving behind conducting electrodes on either side. They were connected by gold wires to a standard meter to measure the complex admittance at different relative humidities (14–79%) and frequencies (20Hz to 1MHz). The raw data was converted to the complex susceptibility after subtracting the signal due to the bulk glass substrate and analyzed using the universal dielectric response model developed by Jonscher. The change in the conductance and capacitance, as measured in a parallel mode, gave a measure of the humidity sensing ability of the scratch and roughly followed an exponential dependence. A control plain glass sample showed a very small effect. The Jonscher index “n” for the susceptibility (χ′) in the high frequency range was seen to be about +0.5, which is characteristic of ionic or hopping conductance and which we expect to be the Grotthuss process. The somewhat lower values of the index seen for the dielectric loss (χ″) data are typical of a lossy material. A combined plot of χ′ versus χ″ of all the data for all humidities and frequencies showed that the Jonscher model was well obeyed in the present work, with a log–log slope close to one as required by the model. Although one scratch sample is highlighted in this work, measurements are presented that show reproducibility between a number of samples as well as a minor amount of aging in repeat measurements on the same sample.

USE OF JONSCHER MODEL FOR ESTIMATING THE THICKNESS OF A CONCRETE SLAB BY TECHNICAL GPR

The thickness measurement of concrete is one of the most important commercial applications of ground-penetrating radar (GPR) technique. This paper describes a procedure for estimating the thickness of concrete slab for difierent moisture contents (MCs) in frequency domain, as in Impulse-Response (IR) Method, over the radar frequency band (100MHz{2GHz). The method is based on predicting the re∞ected frequency spectrum through a concrete slab using Jonscher model. The procedure is explained and examples of results are presented.

Modelling dielectric-constant values of concrete: an aid to shielding effectiveness prediction and ground-penetrating radar wave technique interpretation

A number of efficient and diverse mathematical methods have been used to model electromagnetic wave propagation. Each of these methods possesses a set of key elements which eases its understanding. However, the modelling of the propagation in concrete becomes impossible without modelling its electrical properties. In addition to experimental measurements; material theoretical and empirical models can be useful to investigate the behaviour of concrete's electrical properties with respect to frequency, moisture content (MC) or other factors. These models can be used in different fields of civil engineering such as (1) electromagnetic compatibility which predicts the shielding effectiveness (SE) of a concrete structure against external electromagnetic waves and (2) in non-destructive testing to predict the radar wave reflected on a concrete slab. This paper presents a comparison between the Jonscher model and the Debye models which is suitable to represent the dielectric properties of concrete, although dielectric and conduction losses are taken into consideration in these models. The Jonscher model gives values of permittivity, SE and radar wave reflected in a very good agreement with those given by experimental measurements and this for different MCs. Compared with other models, the Jonscher model is very effective and is the most appropriate to represent the electric properties of concrete.