Real Conductivity Component Research Articles

Study on charge transfer mechanism and dielectric relaxation of cesium lead bromide (CsPbBr3)

In this work, CsPbBr3 has been successfully synthesized via sol-gel technique. The orthorhombic phase of the material has been verified by X-ray diffraction measurement followed by Rietveld refinement analysis. Morphological study has revealed the cubic shape of particles with dimension ∼3 μm. Electrical properties are characterized by Complex impedance (Z*), dielectric permittivity (ɛ*), and ac conductivity within the frequency range 10 Hz–5 MHz for different temperatures between 313K and 673 K. The dielectric behavior of CsPbBr3 is found to be thermally activated and frequency dependent. The ascensive nature of ɛ′(ω) at lower frequency is assigned to the Maxwell-Wagner type interfacial polarization. ɛ′(ω) has been fitted using Kramers-Kronig relation by including the dielectric constant at infinite frequency. Variation of ɛ″(ω) with frequency has been explained by the hopping of charge carrier over a potential barrier between charge defects. AC conductivity has also been fitted by Jonscher's power law to find the real component of conductivity and it has been described by using the Jump relaxation model. Activation energy has been calculated by fitting the dc conductivity using Arrhenius relation and found to have a value of 0.517 eV. Grain resistance (rg), grain capacitance (cg), grain boundary resistance (rgb), and grain boundary capacitance (cgb) have been accounted by fitting Z′ vs log(f) plot with equivalent circuit and existing theoretical model.

Quasi-Solid Semi-Interpenetrating Polymer Networks as Electrolytes: Part III. Probing the Mechanism of Ionic Charge Transport Employing Temperature-Step Electrochemical Impedance Spectroscopy

The correlated ion-transport mechanism and its dependence on microscopic phase separation for a new class of quasi-solid semi-IPN electrolytes is probed in considerable detail using temperature-step electrochemical impedance spectroscopy. The response of electrolyte matrices under alternating current perturbation is comprehensively analyzed using a simulated model fit to extract pertinent information relevant to the phase composition and homogeneity, contribution of each phase, interfacial charge-transfer resistance, phase entanglement zones, bulk relaxation time for ionic hopping mechanisms, coupled segmental motions, rate of site reorganization that dictates successful hopping events, and estimates of ionic transport numbers. The normalized complex plane Nyquist plots (ρ′ versus ρ″) show two well-defined regions for bulk (in mid- and high-frequency regions) and electrode–electrolyte interfacial impedance (in low-frequency regions). Rigorous analysis indicates the presence of three microscopic phases in the matrix bulk (pure poly(ethylene oxide)–polyurethane (PEO-PU), pure poly(ethylene glycol) dimethyl ether (PEGDME), and PEO-PU/PEGDME mixed phase) along with the charge-transfer resistance (Rct) which contribute to the bulk resistance. Spectroscopic plots of complex impedance against frequency (Z″ versus log f) depict Debye peaks, providing an estimate of the bulk relaxation time (τpeak). Profiles depicting the real component of conductivity (σ′(ω)) as a function of frequency (log f) follow a modified universal power law where the simulated fit results reveal vital information on the site relaxation rates, cumulative favorability for successful hopping events, and predominant charge carrier type. The behavior of the dielectric contributions provides insights into the various ion polarization processes dominant in the high-, mid-, and low-frequency windows of the sweep. These trends were further correlated with our prior evaluation of the physico-chemical properties of the semi-IPN matrices to propose a rational physical model for these complex systems.

INFLUENCE OF CHARACTERISTICS OF THE SYSTEM THIN FILM TRANSDUCER – BUFFER SOLUTION ON CONDUCTOMETRIC BIOSENSOR FUNCTIONALITY

Characteristics of thin film conductometric transducers (sensitivity, equivalence of work and reference channels, frequency dependence and linearity of sensor response) based on gold, platinum, nickel, stainless steel and titan-nickel have been researched in this work. Measurements were conducted in 5 mM potassium phosphate buffer pH 6.5 and different KCl solutions in concentration range 0.1-10 mM. The bases of equivalent circuits for different frequencies and conductance’s of solution have been found. It was shown that enzyme immobilization did not change considerably the real component of conductivity. It was demonstrated that operational conditions of transducer could considerable influence on its biosensory characteristics.

Sensitivity of geoelectrical measurements to the presence of bacteria in porous media

We investigated the sensitivity of low‐frequency electrical measurements (0.1–1000 Hz) to (1) microbial cell density, (2) live and dead cells, and (3) microbial attachment onto mineral surfaces of clean quartz sands and iron oxide–coated sands. Three strains of Pseudomonas aeruginosa PAO1 (wild type and rhlA and pilA mutant) with different motility and attachment properties were used. Varying concentrations of both live and dead cells of P. aeruginosa wild type in sand columns showed no effect on the real conductivity component (σ′). However, the imaginary conductivity component (σ″) increased linearly with increasing concentrations of live cells in sand columns, whereas minimal changes were observed with different concentrations of dead cells. A strong power law relationship was observed between σ″ and the number of cells adsorbed onto sand grain surfaces with the rhlA mutant of P. aeruginosa displaying a higher power law exponent compared to the wild type and pilA mutant. In addition, power law exponents were greater in columns with iron oxide–coated sands compared to clean quartz sands. Minimal changes were observed on the σ′ due to the attachment of P. aeruginosa cells onto sands. We relate the measured low‐frequency electrical responses to (1) the distinct electrical properties of live cells and (2) the density of cells attached to mineral surfaces enhancing the surface roughness of sand grains and hence the polarization response. The information obtained from this study enhances our interpretation of microbially induced geoelectrical responses in biostimulated geologic media and may have implications for microbial transport studies.

Effect of bacterial adsorption on low frequency electrical properties of clean quartz sands and iron‐oxide coated sands

Low frequency electrical measurements (0.1–1000 Hz) were conducted to investigate the adsorption effect of Pseudomonas aeruginosa cells onto clean quartz sands and iron‐oxide coated sands. The clean quartz sands showed a gradual increase in the microbial adsorption to mineral grains, concurrent with an increase of 13% in the imaginary conductivity component (σ″). However, iron‐oxide coated sands (20–100% by weight) showed a rapid increase in microbial adsorption with σ″ reaching a maximum of 37 % for the 80–100% iron coated sands. No significant changes were observed in the real conductivity component (σ′) due to microbial adsorption. A power law dependency was observed between the adsorbed cells and σ″. We suggest that the polarization results from the increase in the surface roughness and surface area of the grain due to bacteria sorption. These results suggest that low frequency electrical measurements can play an important role in assessing microbial transport in subsurface environments.

A Critical Review of the Low-Frequency Electrical Properties of Ice Sheets and Glaciers

I review current understanding of the low-frequency electrical properties of glaciers and ice sheets, and identify future research directions that challenge near-surface geophysicists and glaciologists. In cold ice electrical conduction occurs principally via [a] movement of protonic point defects in the lattice in low-impurity ice; [b] networks of impurities at grain boundaries in ice of moderate impurity content; and [c] triple junctions and grain boundaries in ice of high impurity content. I infer that in temperate ice Archie-type conduction is likely dominant. Arrhenius and Looyenga type models, respectively, describe well the increase in bulk resistivity with decreasing ice temperature and density. The activation energy in cold ice and firn is constant at [Formula: see text] but poorly constrained in temperate ice and snow. The bulk resistivity of cold ice ranges from [Formula: see text] at [Formula: see text] at [Formula: see text], and is much higher in temperate ice (up to [Formula: see text]). The effects of impurity characteristics, temperature, and density on complex conductivity are poorly understood, although selected real conductivity components apparently increase with frequency, impurity concentration, or temperature. Future research should exploit more rigorously low-frequency electrical techniques in the field and laboratory, and develop or adapt from other areas of electrical geophysics novel mathematical and statistical concepts for joint data inversion and integration, for glaciological purposes such as ice core logging and investigations of glacier dynamics, ice fracturing, and glacier hydrology. I conclude that low-frequency electrical techniques have unduly been neglected in glaciology as compared with higher-frequency radar techniques over the past few decades, suggesting opportunities for concerted research efforts into these techniques.

Microbial growth and biofilm formation in geologic media is detected with complex conductivity measurements

Complex conductivity measurements (0.1–1000 Hz) were obtained from biostimulated sand‐packed columns to investigate the effect of microbial growth and biofilm formation on the electrical properties of porous media. Microbial growth was verified by direct microbial counts, pH measurements, and environmental scanning electron microscope imaging. Peaks in imaginary (interfacial) conductivity in the biostimulated columns were coincident with peaks in the microbial cell concentrations extracted from sands. However, the real conductivity component showed no discernible relationship to microbial cell concentration. We suggest that the observed dynamic changes in the imaginary conductivity (σ″) arise from the growth and attachment of microbial cells and biofilms to sand surfaces. We conclude that complex conductivity techniques, specifically imaginary conductivity measurements are a proxy indicator for microbial growth and biofilm formation in porous media. Our results have implications for microbial enhanced oil recovery, CO2 sequestration, bioremediation, and astrobiology studies.

Investigations on the Mechanisms of Ionic Conductivity in PEO−PU/PAN Semi-interpenetrating Polymer Network−Salt Complex Polymer Electrolytes: An Impedance Spectroscopy Study

This paper is a first comprehensive study on the correlated ion transport mechanisms contributing to the overall conductivity behavior in a new class of poly(ethylene oxide)-polyurethane/polyacrylonitrile (PEO-PU/PAN) semi-interpenetrating polymer networks (semi-IPNs)-salt complex polymer electrolytes. A simultaneous investigation of the electrical response on PEO-PU/PAN/LiClO(4) and PEO-PU/PAN/LiCF(3)SO(3) semi-IPNs with varying EO/Li mole ratios (100, 60, 30, 20, 15, 10) has been carried out by impedance spectroscopy. Analysis of the complex plane and spectroscopic plots indicated the presence of two microscopic phases corresponding to the PEO-PU and PAN domains, which leads to space charge polarization in these systems. A suitably modified approach based on the universal power law (UPL) considering the independent contribution from the individual microphases of semi-IPNs facilitates a complete interpretation of the spectroscopic profiles for the real component of conductivity (sigma'(omega)). The sigma'(omega) spectroscopic profiles were fitted with two power law equations, where the frequency region up to approximately 300 kHz is the conductivity profile associated with the PAN phase and beyond this is the superimposed contribution of the PEO-PU phase. Simulated fits using the UPL equation revealed two relaxation times (tau(PEO)(-)(PU), tau(PAN)) related to ionic hopping in the PEO-PU and PAN phases in addition to the conductivity relaxation time (tau(peak)) determined from the Debye peaks. The respective power law exponents (n(PEO)(-)(PU) approximately 0.5-0.8, n(PAN) approximately 1.0-1.6) indicate that though cationic hopping in the softer PEO-PU phase is favored, anionic hopping in the PAN phase contributes significantly to the charge transport processes in these semi-IPNs. Correlation of the experimental results with the simulated fits enable us to distinguish the effects of semi-IPN composition, temperature, morphology, ion-ion, and ion-polymer interactions, which influence the microscopic molecular events, involved in the charge transport in these complex semi-IPN polymer electrolytes.

AC conductance and impedance spectroscopy of polycrystalline diamond films

Impedance measurements were performed in the frequency and temperature domain to infer the bulk and grain boundary transport of freestanding polycrystalline diamond films. Analyzed samples appear like insulators up to a threshold temperature where leaking becomes evident. Depending on deposition conditions and thickness, frequency independent conduction channels add to AC ones. The real component of conductivity, measured at different temperatures, can be reduced to a master curve according to a single hopping transport process. Therefore, also the real and imaginary component of impedance, measured at different temperatures in the 2–10 7 Hz frequency range, can be reduced to a master curve and plotted vs. a reduced angular frequency showing a circuit structure more complex than a simple Voigt element. The Nyquist plot is formed by two different lobes that have been interpreted as related to grain and grain boundary dielectric contributions. However, only a single dielectric loss peak is achieved by data elaboration. Dissimilarities among materials deposited by using different techniques are also evidenced and discussed.