Frequency Dependence Of Electrical Conductivity Research Articles

Frequency and dc bias voltage dependent dielectric properties and electrical conductivity of BaTiO3SrTiO3/(SiO2)x nanocomposites

BaTiO3SrTiO3/(SiO2)x nanocomposites (x = 0, 0.5, 1, 2 and 5%) were produced through solid state reaction. The morphological, structural, spectral, and optical properties were investigated by scanning electron microscope, X-ray powder diffraction (XRD), Fourier transform-infrared spectroscopy and ultraviolet–visible diffuse reflectance spectrophotometry, respectively. All XRD patterns illustrate two distinct phases of BaTiO3 and SrTiO3 with cubic structure. No impurity was noticed for x ≤ 0.5% nanocomposite. However, Ba2TiSi2O8 secondary phase starts to appear for x ≥ 1%. Electrical and dielectric properties were used to analyze the dielectric constant and loss, the conductivity as well as dissipation factors as functions of both frequencies and dc bias voltage for BaTiO3SrTiO3/(SiO2)x nanocomposites. In general, conductivity and dielectric loss obey power law tendencies against frequencies. However, the dc bias was found to be less effective to conduction mechanism having a slight change for a variety of SiO2 percentages.

Investigation of temperature and frequency dependence of electrical conductivity and dielectric behavior in CuS and rGO capped CuS nanocomposites

In this work, we develop a simple and low-cost strategy toward the one-pot synthesis of reduced graphene oxide (rGO) capped copper sulfide (CuS) nanocomposite through an obvious redox transformation reaction between Cu and graphene oxide (GO) without any additive. The prepared CuS and rGO capped CuS nanocomposite have been characterized by various physicochemical techniques for the observation of shape, morphology, and structure. It reveals the average size of the synthesized samples in the range of 10–30 nm with the hexagonal structure. The UV–vis absorption spectra exposed the strong absorption peak of CuS and rGO capped CuS composites in the range of NIR region was observed. The synthesized samples displayed high dielectric constant and electrical conductivity in a wide range of frequency (102–106 Hz). The effect of temperature on the electrical conductivity of the synthesized rGO capped CuS nanocomposite was also investigated. The excellent electrical conductivity performance is ascribed to the synergistic effect between CuS and rGO. As the temperature increases, the maximum electrical conductivity of rGO capped CuS composite was exponentially increased at high temperature. The synthesized composite with a high dielectric constant and electrical conductivity is a promising material in high capacitance, and further, it is used as electrode materials for supercapacitors and energy storage applications.

Frequency Difference EIT With Localization: A Potential Medical Imaging Tool During Cancer Treatment

Electrical impedance tomography (EIT) has attracted great interest in a number of medical applications. It offers several unique advantages, such as being safe, low cost, and having high temporal resolution over other tomographic imaging protocols. The frequency dependence of electrical conductivity in biological samples gives EIT imaging a renewed chance to be a monitoring technique for new and very important medical applications, such as tumor tracking during radiation therapy. Therefore, frequency difference EIT (fdEIT), which reconstructs images using difference data at two injecting frequencies, is a good candidate for high-speed tissue characterization in dynamical settings. However, a low spatial resolution of EIT is a major drawback that limits its uses. In some cases, such as the treatment of tumors, prior knowledge about the location of a tumor is provided by early diagnostic images. This prior knowledge coupled with the spectroscopic knowledge of the frequency response of a tumor against normal tissue gives a possibility for localized fdEIT imaging, which can significantly enhance the spatial resolution. The experimental results in this paper demonstrate this for the purpose of such monitoring of an inclusion exhibiting frequency-dependent impedance and are quantitatively compared with traditional methods. The new method's performances and robustness are demonstrated numerically using several image quality measures. This could give the EIT new roles to play, for motion compensation in conjunction with the traditional low-speed but high-resolution medical imaging systems and dynamic tumor tracking.

Crystal growth, structural and electrical properties of (Cu1-хAgx)7GeS5I superionic solid solutions

Single crystals of (Cu1-хAgx)7GeS5I solid solutions were grown by vertical zone crystallization method. XRD studies have shown that they crystallize in face-centered cubic lattice of the argyrodite structure (space group F4¯3m, Z = 4). Structural studies were performed on the basis of original structure model by means of Rietveld refinement method. Electrical measurements were carried out in the temperature interval 300–360 K and in the range of frequencies 10 Hz–10 GHz. Temperature and frequency dependences of electrical conductivity were analyzed. Influence of cation substitution on the electrical conductivity as well as relationship between structural and electrical properties of (Cu1-хAgx)7GeS5I solid solutions were studied.

Thermal stability and frequency-dependent electrical conductivity of poly(aniline-co-m-nitroaniline)

Herein, we report the frequency-dependent AC conductivity of poly(aniline-co-m-nitroaniline)s which were synthesized by chemical oxidation of aniline and m-nitroaniline using ammonium persulfate as an oxidizing agent by in situ copolymerization approach. AC conductivity of the copolymers was recorded in the frequency range of 10−3 to 108 Hz. The imaginary and real part of permittivity of as-synthesized copolymers has been measured in the frequency limit of 10−2 to 107 Hz. The copolymer PA-co-m-NA20 has demonstrated very high value of permittivity than polyaniline at low frequency. At high frequency, the permittivity of the other PA-co-m-NA is almost unaltered. The SEM images manifest the unique morphology for each copolymer. The crystallinity of the copolymer samples has been studied XRD and the thermal stability of the polymers sample has been studied by differential scanning calorimetry.

ELECTRORHEOLOGICAL BEHAVIOR OF SUSPENSIONS BASED ON POLYDIMETHYLSILOXANE FILLED WITH HALLOYSITE

The rheological behavior at 20 °С of electrorheological fluids based on silicone oil filled with halloysite nanotubes with different water content was studied. Flow and viscosity curves, storage and loss moduli were measured using a cylinder-cylinder rotary viscometer. The frequency dependences of electrical conductivity and dielectric loss tangent were obtained by dielectric spectroscopy. When an electric field is applied to the samples, their rheological behavior changes - the values of the yield stress increase. In this case, the viscosity curves exhibit an elastic behavior at low shear stresses and exhibit a Newtonian flow when the yield point is overcome. The frequency dependences of the storage and loss moduli confirm the results obtained on the flow curves. The electric field intensity influence on the magnitude of the electrorheological effect was also investigated. The effect of water presence on electrorheological and electrophysical properties was shown. Electrorheological fluid with a small amount of water exhibits a better response to the electric field application, as evidenced by higher values of the yield stresses in comparison with the sample containing drained filler. The small water content does not have a strong effect on the electrical conductivity of the systems under study, but its presence significantly changes the form of the dielectric loss tangent - the contribution of the electrical conductivity to the relaxation processes is significant, and the nature of the relaxation transitions changes due to the different polarizabilities of the wet and dried filler. This work demonstrates the prospects of using nanoscaled fillers with a high aspect ratio as the dispersed phase for electrorheological fluids.Forcitation:Kuznetsov N.M., Belousov S.I., Bessonova N.P., Chvalun S.N. Electrorheological behavior of suspensions based on polydimethylsiloxane filled with halloysite. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 6. P. 41-47

Size effects on electrical properties of chemically grown zinc oxide nanoparticles

In the present article, we study ZnO nanoparticles grown by cost effective sol–gel technique for various electrical properties. Structural studies performed by x-ray diffraction (XRD) revealed hexagonal unit cell phase with no observed impurities. Transmission electron microscopy (TEM) and particle size analyzer showed increased average particle size due to agglomeration effect with higher sintering. Dielectric constant (ε′) decreases with increase in frequency because of the disability of dipoles to follow higher electric field. With higher sintering, dielectric constant reduced owing to the important role of increased formation of oxygen vacancy defects. Universal dielectric response (UDR) was verified by straight line fitting of log (fε′) versus log (f) plots. All samples exhibit UDR behavior and with higher sintering more contribution from crystal cores. Impedance studies suggest an important role of boundary density while Cole–Cole (Z″ versus Z′) plots have been studied for the relaxation behavior of the samples. Average normalized change (ANC) in impedance has been studied for all the samples wherein boundaries play an important role. Frequency dependent electrical conductivity has been understood on the basis of Jonscher’s universal power law. Jonscher’s law fits suggest that conduction of charge carrier is possible in the context of correlated barrier hopping (CBH) mechanism for lower temperature sintered sample while for higher temperature sintered ZnO samples, Maxwell–Wagner (M–W) relaxation process has been determined.

Coupled simulation of electromagnetic induction and induced polarization effects using stretched exponential relaxation

We have developed a new algorithm for 3D time-domain electromagnetic (EM) modeling, taking full account of induced polarization (IP) and the coupling between EM and IP effects. The algorithm can be used to model grounded source IP surveys that indicate EM induction effects and airborne time-domain EM surveys that exhibit IP effects. IP effects are most often approximated as static or modeled in the frequency domain, using frequency-dependent electrical conductivity. It is difficult to translate the frequency-dependent conductivity approach directly to the time domain in a computationally efficient manner. We take an alternative approach in which we model IP relaxations in time using the stretched exponential (SE) function. We incorporate this IP model into a direct time-stepping discretization of the quasistatic time-domain Maxwell equations. We found that modeling of IP effects with this SE approach is asymptotically equivalent to the commonly used Cole-Cole model of IP transformed to the time domain. We have implemented our algorithm using efficient numerical methods that allow it to tackle large-scale problems and are amenable to use in inversion. In particular, we have developed a parallel time-stepping technique that allows us to compute transient electric fields at multiple time steps simultaneously. We demonstrate the behavior of the SE model of IP decay and the efficiency of our algorithm by applying it to synthetic numerical examples that simulate a grounded source IP survey with significant EM effects and a concentric-loop airborne EM sounding over a chargeable body.

Structure, temperature and frequency dependent electrical conductivity of oxidized and reduced electrochemically exfoliated graphite

The article presents the influence of reduction by hydrogen in statu nascendi and modification by hydrogen peroxide on the structure and electrical conductivity of electrochemically exfoliated graphite. It was confirmed that the electrochemical exfoliation can be used to produce oxidized nanographite with an average number of 25 graphene layers. The modified electrochemical exfoliated graphite and reduced electrochemical exfoliated graphite were characterized by high thermal stability, what was associated with removing of labile oxygen-containing groups. The presence of oxygen-containing groups was confirmed using Fourier-transform infrared spectroscopy. Influence of chemical modification by hydrogen and hydrogen peroxide on the electrical conductivity was determined in wide frequency (0.1 Hz–10 kHz) and temperature range (−50 °C–100 °C). Material modified by hydrogen peroxide (0.29 mS/cm at 0 °C) had the lowest electrical conductivity. This can be associated with oxidation of unstable functional groups and was also confirmed by analysis of Raman spectra. The removal of oxygen-containing functional groups by hydrogen in statu nascendi resulted in a 1000-fold increase in the electrical conductivity compared to the electrochemical exfoliated graphite.

Tunable dielectric and conductivity properties of two 4-n alkoxy benzoic acid

We have presented dielectric and conductivity studies of two liquid crystal (LC) compounds- p-octyloxybenzoic acid (8OBA) and p-decyloxybenzoic acid (10OBA). Dielectric permittivity study of those compounds gives the evidence of space charge polarization and ionic conductance in the samples. Dielectric permittivity is found to be the highest for 8OBA than 10OBA. Both compounds found to exhibit positive dielectric anisotropy. Splay elastic constant as a function of temperature has also been investigated. Frequency and temperature dependent electrical conductivity of these two LC compounds have been studied in detail. Activation energy has been estimated from both dc and ac conduction process.

Electrical conductivity and domain wall motion in proton-irradiated KH 2 PO 4

Abstract We studied the electrical conductivity associated with the domain wall motion in proton-irradiated KH 2 PO 4 below room temperature. The temperature dependence of the power-law exponent n in the frequency-dependent electrical conductivity of anisotropic systems caused changes in the structural phase transition temperature T c that are most likely of a second and weak first order in the transverse and longitudinal direction, respectively. This exponent reflects the electrical conduction, which is activated through the correlation with the domain wall motion in the low-temperature range.

Development of Ni-Ferrite-Based PVDF Nanomultiferroics

Thin-film polyvinylidene fluoride (PVDF)–spinel ferrite nanocomposites with 0–3 connectivity and varying composition, i.e., (1 − x)PVDF–xNiFe2O4 (x = 0.05, 0.1, 0.15), have been fabricated by a solution-casting route. The basic crystal data and microstructure of the composite samples were obtained by x-ray powder diffraction analysis and scanning electron microscopy, respectively. Preliminary structural analysis showed the presence of polymeric electroactive β-phase of PVDF (matrix) and spinel ferrite (filler) phase in the composites. The composites were found to be flexible with high relative dielectric constant (er) and low loss tangent (tan δ). Detailed studies of their electrical characteristics using complex impedance spectroscopy showed the contributions of bulk (grains) and grain boundaries in the resistive and capacitive properties of the composites. Study of the frequency-dependent electrical conductivity at different temperatures showed that Jonscher’s power law could be used to interpret the transport properties of the composites. Important experimental data and results obtained from magnetic as well ferroelectric hysteresis loops and the first-order magnetoelectric coefficient suggest the suitability of some of these composites for fabrication of multifunctional devices. The low electrical conductivity, high dielectric constant, and low loss tangent suggest that such composites could be used in capacitor devices.

Dielectric properties and thermal conductivity of graphene nanoplatelet filled poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend

Poly(methyl methacrylate) (PMMA) and graphene nanoplatelet (GNP) was introduced into poly(vinylidene fluoride) (PVDF) via a solution blending process, and a series of PVDF/PMMA/GNP composites were obtained. Scanning electron microscope (SEM) micrographs of the composite with 4 wt% GNP loading showed that GNP randomly dispersed and partly arranged parallel to each other in the matrix. Fourier transform infrared (FT-IR) spectroscopy results and X-ray diffraction (XRD) analysis revealed the increasing percentage of β- and γ-phase PVDF crystals in the composites with increasing the GNP contents. The frequency dependent electrical conductivity and dielectric properties of composites have been performed in the range of 102 − 107 Hz which obeyed the percolation theory. Dielectric constant and dielectric loss of composites increased with increasing GNP contents in the all frequency region. A dielectric constant of ~148 and dielectric loss of ~0.3 was observed at 102 Hz with 4 wt% of GNP loading, which is near the percolation threshold. Meanwhile, the thermal conductivity reached up to 0.84 W/m K for PVDF/PMMA/GNP composites with 4 wt% of GNP loading. An approch was provided to develop a variety of highly thermally conductive dielectric materials.

Study of dielectric anisotropy and other related parametersof a liquid crystal compound 7OAOB

ABSTRACTTemperature-dependent dielectric anisotropy has been measured for the compound 4,4′-di-n-heptyloxy-azoxy benzene (7OAOB) by using a digital LCR bridge (HIOKI 3532-50 LCR HiTESTER). The compound 7OAOB is found to exhibit negative dielectric anisotropy in the nematic and smectic-C phase. Frequency-dependent electrical conductivity has been measured for this compound. The dc conductivity has also been obtained from frequency-dependent total conductivity studies by using universal power law equation. The activation energy of the dc conduction process and relaxation time has been determined in different mesophases. The behavior of splay elastic constant (K11) with temperature has been examined for this compound. From the studies of UV-visible spectra, the values of energy band gap have been evaluated.

Maxwell–Wagner–Sillars mechanism in the frequency dependence of electrical conductivity and dielectric permittivity of graphene-polymer nanocomposites

The Maxwell–Wagner–Sillars (MWS) effects have been reported in various experiments of graphene-polymer nanocomposites under AC loading. It is considered to be the source of the observed high dielectric constant for this class of nanocomposites. But at present no theory seems to exist to provide a physical description of this mechanism, and to transform this effect into the reported high electrical conductivity and dielectric permittivity. In this work we start out from consideration of high disparity of electrical conductivity between graphene and polymer phases to present such a description, and then integrate it into an effective-medium theory to illustrate how it affects the overall properties of the nanocomposite. We model this mechanism with numerous nanocapacitors at the graphene-polymer interfaces, whose charge accumulation is taken to be directly proportional to the difference of conductivities of graphene fillers and polymer matrix. In the context of complex conductivity, this formulation gives rise to an added frequency-dependent conductivity and permittivity of the interface regions. We highlight this theory with an application to reduced graphene oxide/polypropylene (rGO/PP) nanocomposites, and demonstrate that the calculated conductivity and permittivity are in close agreement with experimental data over the frequency range from 103 to 107Hz. This study clearly demonstrates that the MWS mechanism is principally responsible for the frequency dependence of electrical conductivity and dielectric constant of graphene-polymer nanocomposites.

Optical and dielectric properties of transparent ZrO2–TiO2–Li2B4O7 glass system

Abstract A new series of transparent zirconium titanium lithium diborate glasses of the nominal composition 85 Li 2 B 4 O 7 –(15–x) TiO 2 – x ZrO 2 (x = 0, 5, 10 and 15 mol %) was prepared using melt quenching method. The investigated glasses are characterized in an attempt to determine the effect of different zirconium ion concentrations on their structural, optical and dielectric properties. X-ray diffraction (XRD) patterns confirmed the amorphous nature of the present glass system. The main features concerning the local structure of the present glass system were determined by Fourier transform infrared (FTIR) spectroscopy. The addition of Zr ions to borate glass changed the coordination of borate matrix and consequently converted BO 4 to BO 3 (BO 4 →BO 3 back conversion effect). Optical transmission and reflection measurements were performed as a function of wavelength, showing highly transparent glasses. The optical constants such as refractive index, extinction coefficient, absorption coefficient and optical band gap were calculated. The actual value of the optical band gap energy for these glasses was established by studying the absorption band profile. The frequency and temperature dependent dielectric constant, dielectric loss and AC electrical conductivity measurements were carried out. Excellent structural and physical, optical and dielectric properties of the present glass system indicate prospects for various photonic devices.

Studies of temperature and frequency dependence of dielectric permittivities of two Schiff's base liquid crystal compounds

Abstract Effect of temperature and frequency on the dielectric permittivities of two Schiff's base liquid crystal compounds p-ethoxybenzylidine p-heptylaniline(EBHA) and p-butoxybenzylidine p-heptylaniline(BBHA) have been studied by using a digital LCR bridge (HIOKI 3532-50 LCR HiTESTER). Due to the changes of CH 2 groups at the oxygen containing flexible side chain between these two compounds, some changes occur in the behavior of their temperature dependent physical properties such as dielectric anisotropy, splay elastic constant, relaxation time, which has been studied extensively. The frequency dependent electrical conductivity of these two compounds has also been carried out. At the nematic mesophase the values of activation energy have been estimated from the temperature dependent DC and AC conductivity curves. The optical band gap of EBHA and BBHA has been calculated from UV spectra.

Polyvinyl pyrrolidone/Mg(ClO4)2 solid polymer electrolyte: structural and electrical studies

Polymer electrolytes comprising polyvinyl pyrrolidone (PVP) as host polymer and Mg(ClO4)2 as dopant salt have been prepared by solution casting technique using double-distilled water as solvent. The changes in the structural properties on the incorporation of dopant were investigated by XRD and FTIR analysis. The ionic conductivity and dielectric behavior were explored using AC impedance spectroscopy. The ionic conductivity increases with increasing dopant concentration. The conductivity enhancement with the increasing salt concentration is correlated with the increase in amorphous nature of the electrolytes. The frequency dependence of electrical conductivity obeys the universal Jonscher power law. The electrical modulus representation shows a loss feature in the imaginary component. The distribution of relaxation times was indicated by a deformed arc form of the Argand plot. The relative dielectric constant (er) decreases with increase in frequency in the low frequency region whereas a frequency-independent behavior is observed in the high frequency region. The total ionic transference number studies have confirmed that the mobile charge carriers are ions. Results obtained by cyclic voltammetry on SS/60 mol% PVP/40 mol% Mg(ClO4)2 SPE/SS symmetrical cell show evidence for reversibility.

Ferroelectric domain freezing and charge conduction in proton-irradiated K(H0.36D0.64)2PO4

We have studied the effects of proton irradiation in K(H0.36D0.64)2PO4 single crystals by employing impedance spectroscopy. Frequency-dependent dielectric loss measurements allowed us to investigate changes in the domain wall dynamics of a proton-irradiated crystal with a ferroelectric phase transition temperature raised by 5 K. Thus, the increase caused by proton irradiation in the activation energy of the domain freezing in the direction of the hydrogen bonds was found to be significantly greater than in the case of KH2PO4. Furthermore, the temperature dependence of the power-law exponent n in the frequency-dependent electrical conductivity in the proton-conducting systems manifested changes arising from the proton irradiation in the interactions between the mobile ionic (proton) charges and their environments.

Optical conductivity of warm dense matter within a wide frequency range using quantum statistical and kinetic approaches.

Fundamental properties of warm dense matter are described by the dielectric function, which gives access to the frequency-dependent electrical conductivity; absorption, emission, and scattering of radiation; charged particles stopping; and further macroscopic properties. Different approaches to the dielectric function and the related dynamical collision frequency are compared in a wide frequency range. The high-frequency limit describing inverse bremsstrahlung and the low-frequency limit of the dc conductivity are considered. Sum rules and Kramers-Kronig relation are checked for the generalized linear response theory and the standard approach following kinetic theory. The results are discussed in application to aluminum, xenon, and argon plasmas.