Electrical Conduction Process Research Articles

Electrocoagulation efficiency probed using electrochemical impedance spectroscopy

Electrocoagulation efficiency probed using electrochemical impedance spectroscopy

Contribution of strong electron-phonon interaction in the transport properties of La0.8Ca0.2Mn0.5Ni0.5O3 system

La0.8Ca0.2Mn0.5Ni0.5O3 NTC (negative thermal coefficient) thermo-sensitive material was prepared using a conventional solid-state reaction method. From the structural results, we found that the material is pure and crystallizes in the orthorhombic structure with a Pnma space group. It is found that the La0.8Ca0.2Mn0.5Ni0.5O3 ceramic can be used as an NTC thermistor compound in specific temperature sensors and attenuators. Based on Holsten's theory, detailed electrical investigations concerning the nature of the activated small polaron hopping mechanism were reported. The temperature dependence of the DC conductance was used to determine the electrical conduction processes that govern the transport properties of La0.8Ca0.2Mn0.5Ni0.5O3. Hence, the DC mechanisms exhibit changes from the variable range hopping at very low temperatures to the non-adiabatic small polaronic hopping at T = 210 K. In the intermediate temperature range, the semiconductor behavior of La0.8Ca0.2Mn0.5Ni0.5O3 was attributed to the contribution of the tunneling transport process. At various temperatures, the conductance spectra were discussed based on Jonscher and Bruce's laws. Contributions of the overlapping-large-polaron-tunneling, the correlated barrier hopping, the quantum mechanical tunneling, and the non-overlapping small polaron tunneling mechanisms to the transport properties were observed in the dispersive region of the conductance spectra. In addition, Summerfield scaling and corrected Summerfield scaling approaches prove that the charge mobility is temperature-dependent. The positive value of the correction parameter α = 1.2 confirms the presence of interactions in the studied sample.

The Effect of Magnetically Induced Local Structure and Volume Fraction on the Electromagnetic Properties of Elastomer Samples with Ferrofluid Droplet Inserts

The magnetic permeability (μ), dielectric permittivity (ε) and electrical conductivity (σ) of six elastomer samples obtained by mixing silicone rubber (RTV-530) with a kerosene-based ferrofluid in different volume fractions (φ), 1.31%, 2.59% and 3.84%, were determined using complex impedance measurements over a frequency range of 500 Hz–2 MHz. Three samples (A0, B0 and C0) were manufactured in the absence of a magnetic field, and the other three samples (Ah, Bh and Ch) were manufactured in the presence of a magnetic field, H = 43 kA/m. The component μ″ of the complex effective magnetic permeability of all samples presents a maximum at a frequency, fmax, that moves to higher values by increasing φ, with this maximum being attributed to Brownian relaxation processes. The conductivity spectrum, σ (f), of all samples follows the Jonscher universal law, which allows for both the determination of the static conductivity, σDC, and the barrier energy of the electrical conduction process, Wm. For the same φ, Wm is lower, and σDC is higher in the samples Ah, Bh and Ch than in the samples A0, B0 and C0. The performed study is useful in manufacturing elastomers with predetermined properties and for possible applications such as magneto-dielectric flexible electronic devices, which can be controlled by the volume fraction of particles or by an external magnetic field.

Structural, microstructure, dielectric relaxation, and AC conduction studies of perovskite SrSnO3 and Ruddlesden-Popper oxide Sr2SnO4.

Here, we report a comparison study on the synthesis and characterization of perovskite SrSnO3 (SSO) and Sr2SnO4 (S2SO). Rietveld refinement studies were performed on both prepared samples and suggest that they crystallized in cubic (SSO) and tetragonal (S2SO) structures. Fourier-transform infrared (FTIR) and Raman spectroscopy studies supported the XRD observations. Improved dielectric parameters were observed for S2SO over SSO due to differences in dislocation density, larger crystallite size, and denser microstructure. The electrical conduction and relaxation processes followed the Arrhenius type in both samples through the migration of oxygen vacancies via the Sn-site and the transfer of electrons between the Sn sites in two different temperature regions. These processes in the samples occurred via correlated barrier hopping (CBH) in SSO and the non-overlapping of small-polaron tunnelling (NSPT) in S2SO. The conduction and relaxation processes had similar sources of charge carriers but differed in the concentration and mobility of charge carriers. The presented materials can be utilized for dielectric capacitors, sensors, and mixed ionic and electronic conductor-based electrodes in IT-SOFC applications.

Multiscale Electrical Response Assessment of Metal Nanowire Transparent Electrodes: A Computational Strategy

Transparent electrodes made of random distributions of metal nanowires (NWs) are appealing for optoelectronic devices, solar cells, light emitting diodes, and transparent heaters. While these electrodes are comparable to thin films in terms of electrical conductivity and transparency, their network structure allows limiting the amount of conductive material and makes them suitable for low-cost solution-based deposition methods, contributing to an overall costs reduction. Despite these advantages, an even material utilization at different length scales is difficult to achieve. The homogeneous distribution of electric current (electrical homogeneity) is indeed not guaranteed in nanowire electrodes but is crucial for the stability of the electrode and actually desirable in most applications. Despite the relevance of this feature, it is common practice to perform qualitative assessments at the electrode scale, overlooking local effects. To address this issue, we have developed a computational strategy to aid in the design of nanowire electrodes with improved electrical homogeneity.We present a computational approach that allows an objective, quantitative, and systematic assessment of the electrical homogeneity. The approach enables a multiscale comparison of electrodes with different NW content and material properties. Nanowire electrodes are modeled as two-dimensional networks of stick and junction resistors (with resistance Rw and Rj, respectively) to simulate the electric conduction process. Electrodes are discretized into regular grids of squares and the electrical power of the network contained in each square is computed. The mismatch between the areal power density of the entire electrode and that of the squares provides a quantitative electrical homogeneity evaluation. Repeating the analysis with squares of different size yields an evaluation that spans across length scales. A scalar indicator, coined the homogeneity index, summarizes the results of the multiscale evaluation.Parametric studies are performed by varying nanowire content and nanowire-to-junction resistance ratio Rw/Rj. We show that electrical homogeneity improves as i) NW density increases, and ii) junction resistance reduces. The ideal condition of negligible junction resistance (Rw >> Rj) leads to the best-case scenario and guarantees the highest rate of improvement of electrical homogeneity with NW content. Nevertheless, we observe that under condition Rw ≈ Rj the response of the system approaches the response of a system meeting the ideal condition Rw >> Rj (15% difference at most in terms of homogeneity index). We therefore conclude that reducing the junction resistance excessively (with the aim of achieving Rw/Rj > 1) may not always be a worthwhile strategy, as it results in only a marginal improvement in terms of electrical homogeneity.The proposed strategy is employed to assess the electrical homogeneity of silver nanowire electrodes through the analysis of scanning electron microscopy images. Our results agree with the outcomes of the experimental assessment performed on the same electrodes.

Structural transition and magnetization reversal in rare earth doped R0.5Sr0.5Fe0.5Cr0.5O3 (R[dbnd]La, Nd and Sm) perovskite oxides containing mixed valent cations at B site: Magnetic, optical and transport properties

In the current paper, the effect of lanthanide metal cation substitution on structural, magnetic, optical and transport properties of R0.5Sr0.5Fe0.5Cr0.5O3 (RLa, Nd and Sm) perovskite oxides have been investigated. Structural investigations reveal that there is a phase transition from cubic to orthorhombic symmetry with the doping of heavier rare earth ion. The findings of XPS studies point to the existence of mixed valence states of Cr and Fe ions. The change in magnetization in response to an external magnetic field reveals that the phases have a mostly antiferromagnetic character with some trace amounts of ferromagnetic components. In temperature dependent magnetization studies, magnetic reversal has been observed in Nd doped sample, while La and Sm doped samples only show positive magnetization. The band gap energies of the synthesized materials determined from the UV–vis reflectance spectroscopy lie in the range of 1.60–1.78 eV indicating the semi-conducting nature of the samples. The temperature-dependent resistivity measurements show semi-conducting behaviour of the samples with decreasing temperature which finally become insulating at low temperature. It has been shown that the VRH model provides the best fit for the resistivity data when compared to the other transport mechanism models that were used to describe the electrical conduction process of synthesized phases.

Dielectric Relaxation Behavior and Electrical Conduction Mechanism of PVA/ZnO Nanocomposites for Flexible Electronic Device Application

Transport properties of polyvinyl alcohol/ZnO nanocomposites (PVA/ZnO) of varying ZnO nanofiller are studied focussing on their potential application in electronic device application. The structural, morphological, and elemental composition studies of the prepared samples are done by X‐ray diffraction (XRD), scanning electron microscope (SEM), and energy‐dispersive X‐ray analysis (EDX). XRD confirms the formation of nanocomposites. SEM image shows the dispersion of ZnO nanoparticles on the surface of PVA matrix. EDX verifies that no external impurities are present in the nanocomposite samples. Frequency‐ and temperature‐dependent dielectric measurement of the samples reveals maximum dielectric constant at PVA/15 wt% ZnO nanocomposite. Dielectric loss results show a lossless behavior at higher frequencies (<0.2), indicating their suitability for high‐frequency applications. The AC conductivity studies reveal that electrical conduction mechanism in the nanocomposites is governed by the correlated barrier hopping mechanism. Activation energy of the samples reveals the presence of two thermally activated transport mechanism above and below 353 K. The imaginary part of electric modulus with frequency shows a single relaxation peak indicating the transition from long‐range to short‐range mobility with increasing frequency and temperature above 353 K. The contribution of grain and grain boundary in the electrical conduction process is confirmed from the Nyquist plot.

Quantitative electrical homogeneity assessment of nanowire transparent electrodes.

The homogeneous distribution of electric current (electrical homogeneity) is not guaranteed in nanowire electrodes but is crucial for the stability of the electrode and actually desirable in most applications. Despite the relevance of this feature, it is common practice to perform qualitative assessments at the electrode scale, thus masking local effects. To address this issue, we have developed a computational strategy to aid in the design of nanowire electrodes with improved electrical homogeneity. Nanowire electrodes are modeled as two-dimensional networks of stick and junction resistors (with resistance Rw and Rj, respectively) to simulate the electric conduction process. Electrodes are discretized into regular grids of squares and the electrical power of the network contained in each square is computed. The mismatch between the areal power density of the entire electrode and that of the squares provides a quantitative electrical homogeneity evaluation. Repeating the analysis with squares of different size yields an evaluation that spans across length scales. A scalar indicator, coined the homogeneity index, summarizes the results of the multiscale evaluation. The proposed strategy is employed to assess the electrical homogeneity of silver nanowire electrodes through the analysis of scanning electron microscopy images. Our results agree with the outcomes of the experimental assessment performed on the same electrodes. Parametric studies are performed by varying nanowire content and nanowire-to-junction resistance ratio Rw/Rj. We observe that a significant reduction of contact resistance is not necessary to ensure a high degree of homogeneity. The ideal condition of negligible junction resistance (Rw ≫ Rj) leads to the best-case scenario, a situation which is closely approached if Rw ≈ Rj (15% difference at the most in terms of homogeneity index).

Magnetic field stimulated dielectric, electronic and thermal properties of magnetite nano-hollow spheres based magnetorheological fluids

We present a combination of dielectric and thermal conduction properties of magnetorheological (MR) fluids with Fe3O4 nano-hollow spheres (NHSs). The formation of microstructures in presence of a magnetic field by the suspended NHSs in the base fluids determines the dielectric relaxation and electrical conduction process, depending on the viscosity of the base fluids. We observe a prominent magneto-dielectric effect and an excellent improvement in the electrical conductivity due to chain formation in presence of a magnetic field in the MR fluids. Our thermal conduction experiments establish that not only the heat flow can be improved with the addition of magnetite NHSs in the base fluids, but the direction of heat flow can also be controlled with the orientation of the external magnetic field.

Single polaron hopping in Fe doped glassy semiconductors: Structure–electrical transport relationship

The development of glassy nanocomposites, xFe-(1−x) (0.5 V2O5–0.4 CdO–0.1 ZnO) is particularly important not only for exploring their microstructures using x-ray diffraction, FT-IR, and UV–Vis techniques but also for exploring their electrical conduction mechanism in terms of hopping of small polarons. The presence of various nanophases, such as ZnO, CdO, Cd9.5Zn0.5, ZnV, and Zn3V2O8, have been identified and the size of estimated nanocrystallites is found to decrease with more incorporation of the Fe content in the compositions. As the value of lattice strain increases with the increase of the Fe content in the compositions, the present system becomes more and more unstable, which may be favorable for better electrical transport phenomena via the polaron hopping process. Electrical conductivity of the system has been analyzed using modified correlated barrier hopping model, Almond–West formalism, and the alternating-current conductivity scaling. Experimental data reveal that both optical photon and acoustical phonon transitions are responsible for the entire electrical conduction process. Polaron hopping is expected to be of percolation type, which has been validated from an estimated range of frequency exponents. All experimental data have been used to frame a schematic model to explore the conduction mechanism inside the present glassy system.

Facile vacancies engineering of CoFe-PBA nanocubes for enhanced oxygen evolution

Oxygen evolution reaction (OER) is known as the key for the large-scale production of hydrogen through electrochemical processes. Developing highly efficient OER electrocatalysts with well-defined structure remains a considerable challenge. Herein, a unique and facile Ar plasma treatment was introduced to modify cobalt iron Prussian blue analogs (CoFe-PBA) immobilized nickel foam (NF). The in situ generated carbon-nitrogen vacancies can effectively tune the local coordination environment and electronic structure of metal active sites in CoFe-PBA, thus improving the OER performance. The combination of CoFe-PBA and NF presents a 3D interworking network structure with highly exposed active sites and excellent electrical conductivity, guaranteeing stable and efficient OER process. The as-prepared electrocatalyst exhibited excellent OER performance with an overpotential of 256 mV at the current density of 50 mA cm−2 and a small Tafel slope of 39 mV dec−1. This work presents a facile strategy for the design and fabrication of highly efficient PBA-based OER electrocatalyst, and enriches our understanding of the structure-property relationship of the plasma-engineered electrocatalyst.

Structure, charge carrier conduction, dielectric properties and leakage current density of Dy2CoMnO6 double perovskite

In this study, the structure, charge transport properties, dielectric properties, and leakage current density of Dy2CoMnO6 double perovskite are investigated. The sample is prepared via auto–ignition method. The Rietveld refinement of the X–Ray diffraction pattern of the sintered sample reveals the monoclinic phase with space group P21/n. The crystal structure of the sample is distorted and tilted. The dominant oxidation state of Co and Mn are +3 and +4, which are estimated from the bond valence sum method. The values of activation energy for dc conduction are 0.16 eV (≤ 75 ℃) and 0.37 eV (≥ 100 ℃). The charge carrier conduction follows a correlated barrier hopping mechanism (≤ 75 ℃). Scaling spectra confirms the temperature independence nature of the conduction and relaxation mechanism below 75 ℃. The grain boundary conductivity is higher than the grain interior conductivity due to the low grain boundary blocking factor. The sample exhibits a non–Debye type nature. The value of the tangent of dielectric loss lies from 4.15 to 33.11 in the frequency range from 50 Hz to 500 KHz, and the value of real part of complex dielectric constant lies between 102 and 67608 in the frequency range from 500 Hz to 50 kHz. The analysis of the imaginary part of the complex dielectric constant confirms the predomination of the dc electrical conduction process in the sample. The comparable values of the activation energy for dc conduction, grain interior conductivity, grain boundary conductivity, migration energy, and activation energy confirm the interlinking among these processes. The room temperature leakage current density is 4.36 × 10–4 Acm–2 at 8.05 Vcm–1. The leakage current density follows the Ohmic conduction and has been explained with the Schottky barrier model.

High-performance CeO2:Co nanostructures for the elimination of accidental poisoning caused by CO intoxication

Owing to the global upward trend of accidental carbon monoxide (CO) poisoning in the past 30 years, this work aimed to develop Cobalt-doped CeO2 particles by the microwave-assisted hydrothermal route under distinct conditions. Their structural, morphological, spectroscopic and electrical behaviors were investigated to correlate the influence of Co on their properties with the introduction of oxygen vacancies and their sensing capability to assist in the mitigation of CO poisoning cases. The samples were crystalline and had no secondary phases. Two distinct activation energies for the electrical conduction processes were observed due to dopant influence, corroborating the local cluster-to-cluster charge transfer (CCCT) mechanism, resulting in a response time of only 3s for the 4% Co-doped sample. On the other hand, through positron annihilation studies we showed that the oxygen vacancies are preferentially formed near Co ions, reducing the Co ion charge and leading to the formation of neutral VO-Co+2 complex clusters.

Electrical transport properties of nanocrystalline and bulk nickel ferrite using complex impedance spectroscopy: a comparative study

In this work, the comparative study on the electrical transport properties of nanocrystalline nickel ferrite (NiFe2O4) and its bulk counterpart has been carried out in detail by using complex impedance spectroscopy in a wide range of frequencies (100 Hz–1 MHz) and temperatures (40 °C–320 °C). The dispersive nature of the dielectric constant and loss factor is explained by the Maxwell-Wagner model and Koop’s phenomenological theory. The value of the dielectric constant for nanocrystalline nickel ferrite is found to be more as compared to its bulk counterpart. The frequency variation dielectric permittivity is well fitted with the modified Debye formula, which suggests the presence of multiple relaxation processes. The temperature dependent ac conductivity follows Jonscher’s universal power law and reveals the presence of multiple transport mechanisms from small polaron hopping (SPH) to correlated barrier hopping (CBH) mechanism near 200 °C. The estimated values of Mott parameters are found to be satisfactory. Thermally activated relaxation phenomena have been confirmed by scaling curves of imaginary impedance () and modulus (). The comparison between the and spectra indicates that both long-range and short-range movement of charge carriers contribute to dielectric relaxation with short-range charge carriers predominating at low temperatures while long-range charge carriers are dominating at high temperatures. Analysis of the semicircular arcs of Nyquist plot indicates the presence of grain boundary contribution to the electrical conduction process for the nanocrystalline sample at high temperatures. The non-Debye type of relaxation has been examined by stretching exponential factor (β) which has been estimated by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary electric modulus curve. The value of β is found to be strongly temperature dependent and its value for the nanocrystalline sample is less than that of the bulk system which is explained on the basis of dipole-dipole interaction.

On the mechanism of performance improvement of electroactive polyvinyl chloride (PVC) gel actuators via conductive fillers

The electromechanical actuation of transparent plasticized polyvinyl chloride (PVC) gels with conductive fillers were studied. The effects of functionalized carbon nanotubes (CNTs) and 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) ionic liquid (IL) on both the electrical conduction and dielectric processes within PVC gels were investigated, and the differences between the two were clarified. Both CNTs and IL were shown to increase the conductivity of the gels and produce larger electromechanical transduction of a contraction actuator, but only CNTs were shown to increase the electrostatic adhesion force of the PVC gels. The addition of charge carriers to the gel via the inclusion of ILs was shown to significantly reduce the conductivity relaxation time, and the transient current upon voltage polarity reversal indicated multiple peaks corresponding to the introduction of carriers with different polarities and mobilities into the gel. This is believed to cause a screening effect, reducing the charge accumulation at the anode that is the foundational basis for PVC gels’ actuation mechanism. A recommendation for preferable conductive fillers for various applications is made.

Electrical conduction processes in aluminum: Defects and phonons

It is well known that disorder (structural or thermal) induces electronic scattering processes which determine the resistivity of crystalline metals. In this paper, we employ a variant of the Kubo-Greenwood formula to compute the space-projected conductivity and study the atomistic details of conduction in models of crystalline aluminum within the framework of density functional theory. We consider point and extended lattice defects and show with spatial detail how the defect locally affects conduction. We simulate thermal disorder and determine how the disorder affects the conductivity in real space and reveal the spatial nature of thermal fluctuations. Furthermore, we show that well below the Debye temperature, a classical thermal molecular dynamics simulation reproduces the form of temperature-dependent conductivity predicted by the Bloch-Gr\"uneisen formula.

Evaluation of the microstructure, optical properties and hopping conduction mechanism of rare earth doped Ba0.85Ca0.12RE0.03Ti0.90Zr0.04Nb0.042O3 ceramics (RE = Ce3+ and Pr3+).

The current research work examines the impact of Rare Earth (RE3+) ion substitution on the structural, optical and conduction properties of a Ba0.85Ca0.12RE0.03Ti0.90Zr0.04Nb0.042O3 (BCRETZN) (RE = Ce, Pr) ceramic compound produced via a solid-state route. The Rietveld method of the X-ray data revealed a tetragonal (P4mm) structure at room temperature for our ceramic compound. The morphology of the compound was explored using Scanning Electron Microscopy (SEM) as well as optical response and conduction behavior. The photoluminescence properties revealed that the BCPrTZN sample results in green and red photoemissions under laser excitation at 450 nm at RT. Furthermore, for the BCCeTZN sample, the photoluminescence data demonstrated that strong violet emission bands were acquired, at RT upon an excitation at 350 nm. The electrical conduction process was verified via the correlated barrier Hopping method. The scaling behavior suggests that the electrical conduction mechanism is independent of temperature. The existence of Ce3+ and Pr3+ ions in these materials could have important technological potential in new multifunctional devices.

Measurement of two-dimensional electrical potential fields in CFRP using four-probe resistance scans

The carbon fibers in fiber reinforced plastics could be used sensorially to observe the present stress state of the structural component by measuring its electrical resistance. However, the use of resistivity requires a detailed understanding of the electrical potential distribution in a given specimen. Current experimental techniques measure the electrical potential on a limited amount of relatively large electrodes mounted onto the parts surface. This approach suffers from the limited spacial resolution as well as the retroactivity between attached electrodes and observed specimen. This article discusses an experimental method to scan the electrical potential distribution on the surface of a conductor using a typical 4-probe setup and a gantry style robot to move one of the probes. The method is applied to eletrical conduction processes in carbon fiber reinforced plastics (CFRPs) in an effort to visualize the electrical potential distribution near current contacts. This approach allows us to have a much more detailed understanding of electrical conduction processes in CFRP, which can help to better interpret experimental data in the future. A two-dimensional mathematical model based on Laplace equation is derived with appropriate boundary conditions and compared to the measured results. Experimental and numerical results agree well and show the existance of strong current inhomogeneities within the CFRP part. The developed setup is simple to implement, but nevertheless prooved to be effective in measuring the explicit electrical conduction paths in both isotropic and anisotropic conductors.

Effects of Resin/Filler Adhesion on the Thermal and Electrical Conductivity of Polyimide Nanocomposites

With an aim to develop a good coil winding insulation film, fillers of boehmite alumina in the shape of a roughly rectangular plate were added with ratios of 10 and 20 wt% to polyimide. The filler surface was untreated or treated with a methacrylic or an epoxy silane coupling agent. Such prepared polyimide nanocomposites were subjected to various tests to measure the tensile strength, elastic modulus, complex permittivity, and thermal conductivity. It was found that samples with fillers treated using the methacrylic silane coupling agent have the strongest adhesion at the filler/polyimide interfaces and the lowest dielectric loss factor at high temperatures. A positive relationship between the filler/polyimide adhesion and the thermal conductivity is also indicated. These findings are significant since they indicate that the adhesion status at the filler/polymer interface exerts a strong influence on the thermal and electrical conduction processes in the polymer.

Rational design of Schottky heterojunction with modulating surface electron density for high-performance overall water splitting

The development of non-precious metal electrocatalysts to synergistically expose more active sites and optimize intrinsic activity still remains a huge challenge. Transition metal layered double hydroxide (LDH) has a great potential in electrocatalysis due to its unique sheet-like nanostructure and low cost. However, the poor electrical conductivity and sluggish water dissociation process hinder their development. Herein, the interface effect of Schottky heterostructure between cobalt-iron hydroxide and MXene and surface electron density modification with phosphorus (P) doping provide an efficient method to solve these crucial issues. The novel Schottky heterostructure catalyst (P-CoFe-LDH@MXene/NF) with self-driven charge transfer can enhance electron transport efficiency. In addition, the surface electron density optimized by P-doping will promote the ability of H+/OH- ion adsorption and redox reaction for overall water splitting. The as-prepared P-CoFe-LDH@MXene/NF requires overpotentials of only 85 mV at 10 mA cm−2 for HER and 252 mV at 200 mA cm−2 for OER in 1.0 M KOH, respectively. And under an alkaline electrolyzer, it can be driven 10 mA cm−2 at a low voltage of 1.52 V for overall water splitting with remarkable durability for 100 h. More broadly, this design concept is universal and it can be extended to design other transition metal-based catalysts.