Nonlinear Electrical Conductivity Research Articles

Chiral orbital texture in nonlinear electrical conduction

Chiral orbital texture in nonlinear electrical conduction

DC assisted electric field on the improvement of the nonlinear electrical conductivity of SiC/LDPE field grading composites

Nonlinear resistive field grading material presents nonlinear electrical conductivity, and self-homogenizes the electric field distribution. The nonlinear conductivity is closely associated to the filler distribution, which can be modulated by the electric field assist during the material preparation. In this paper, the effects of the direct current (DC) electric field assist on the filler distribution and nonlinear conductivity of the nonlinear resistive field grading materials were studied for the first time. The silicon carbide (SiC)/low-density polyethylene (LDPE) composites were prepared under different DC assisted electric field. The composites’ microstructure, dielectric spectra and DC conductivity were characterized, respectively. Results illustrate that the DC electric field assist leads to the gradient distribution of SiC filler in the matrix, and also contributes to the SiC particles’ chains. Compared with the untreated SiC/LDPE composite, the electric-field assisted composites show more distinct nonlinear conductivity characteristics when the DC assisted electric field exceeds 0.3 kV mm−1, which is attributed to the percolation phenomenon of SiC particles. This work is helpful to design the dielectric functionally graded materials, and to self-homogenize the electric field distribution in power apparatus and electronic devices.

Nonlinear phenomena in charge transport properties of a hole-doped organic spin-liquid compound

The nonlinear electric conductivity of κ-(BEDT-TTF)4Hg2.89Br8, which is known as a hole-doped spin liquid, has been observed by single crystal transport measurements using dc and ac excitations. This compound is known as a charge transfer complex with strong magnetic fluctuations accompanied by electron mass enhancement at ambient pressure. We discuss the nonlinear dc conductivity drastically emerging below 100 K. We also performed ac impedance measurements of this compound and compared the results with those of a typical dimer-Mott compound of deuterated κ-(d8-BEDT-TTF)2Cu[N(CN)2]Br, located just near the Mott boundary. The analyses of the Nyquist plots of κ-(d8-BEDT-TTF)2Cu[N(CN)2]Br and κ-(BEDT-TTF)4Hg2.89Br8 reveal qualitatively different features. The former shows a behavior pertinent to the inhomogeneous distribution of domains due to a mixing of metal and insulating phases, taking into account the influence of the proximity effect, while the doped spin liquid has a distinct semicircle-type frequency dependence in its Nyquist plot in the whole temperature range studied. We conclude that the nonlinear conductivity is intrinsically peculiar to the doped dimer Mott system, where the charge degrees of freedom dominate the itinerancy. We attribute the anomalous features, such as non-Fermi liquid behavior, heat capacity enhancement, and strong antiferromagnetic fluctuations in κ-(BEDT-TTF)4Hg2.89Br8, to a kind of charge confinement effect retained in the hole-doped spin-liquid state.

Nonlinear electrical conductivity characteristics under high impulse current and applications to lightning strike damage simulation for CFRP laminates

This experimental investigation assessed conductive properties of quasi-isotropic CFRP laminates in the thickness direction under high impulse current and clarified the properties’ effects on lightning damage behaviours. For CFRP laminates with interleaf resin layers (T800/3900-2B), experiments confirmed that conductivity in the thickness direction increases irreversibly with applied impulse current (approx. 5.3 kA, approx. 3.2 kV). However, the conductivity of CFRP laminates without interleaf resin layers (T800/2592) changed little during testing. Nonlinear conductive behaviour was applied to lightning strike damage numerical simulations using a coupled thermal–electrical analysis and heat transfer analysis. For numerical analyses, shape and dimensional changes of the applied current on the specimen surface were considered based on high-speed observations made during simulated lightning strike testing. The pyrolysis region calculated using damage analysis agrees well with experimentally obtained results when considering the potential gradient dependence of conductivity: better agreement was obtained than when calculated under a constant value.

Nano Granular Metallic Thin Films: Unravelling Non-Linear Electrical Conduction and Resistive Switching for Neuromorphic Applications

Nano Granular Metallic Thin Films: Unravelling Non-Linear Electrical Conduction and Resistive Switching for Neuromorphic Applications

Nonlinear electric conduction of CCTO/EPDM composites used for reinforced insulation in cable accessory

Nonlinear electric conductance of reinforced insulation can homogenize electric field distribution and suppress local electric field distortion inside high-voltage direct current cable accessories. To achieve a significant nonlinear electric conductance in ethylene–propylene–diene misch–polymere (EPDM) used for reinforced insulation of cable accessories, the inorganic micron crystal powder of calcium copper titanate (CCTO) is synthesized by the sol–gel method, which is filled into EPDM to prepare 5∼15 wt% CCTO/EPDM composites by melting blend and hot-press molding methods. Microscopic structure, electric conductivity, direct current (DC) dielectric breakdown strength, and charge trap characteristics of CCTO/EPDM composites are tested to reveal the underlying derivation of electric conduction nonlinearity. Scanning electron microscopy and X-ray diffraction (XRD) demonstrate that CCTO micron fillers are uniformly dispersed in the EPDM matrix. Dielectric breakdown strength of CCTO/EPDM composites gradually decreases with the increase in CCTO content while persisting qualified for electrical insulation of DC cable accessories. CCTO crystal macron fillers introduce shallower charge traps than the intrinsic charge traps derived from the structural defect EPDM matrix, which initiates the percolating conductive channels between charge traps under high electric fields, accounting for the significant nonlinearity in the profile of electric current density versus electric field strength. Finite-element simulations and analyses on the electrostatic field in DC cable terminals prove that employing 15 wt% CCTO/EPDM composite as reinforced insulation can efficiently homogenize the electric field at the interface between the main insulation and accessory insulation of power cables, which is of great interest to develop insulation materials used for DC cable accessories in severe environments.

Enhanced nonlinear conductivity of silicone rubber composites with hybrid graphene and alumina for cable accessory

The electric field distortion and charge accumulation in cable accessories are still challenges for high voltage direct current transmission (HVDC). Using silicone rubber (SR) based materials with nonlinear conductivity properties can ameliorate these problems in cable accessories. Herein, SR composites with hybrid filler network were prepared by adding graphene (G; 0.25 phr) and alumina particles (Al2O3; 5–40 phr) to SR to obtain good nonlinear conductivity and relative high breakdown strength, along with thermal conductivity. The SEM results showed that graphene was well dispersed between Al2O3 particles and a hybrid filler network was constructed in the SR matrix. The G/Al2O3/SR composites exhibited favorable nonlinear electrical conductivity properties and thermal conductivity properties while sustaining high breakdown strength under different electrical and temperature field. The non-linear conductivity α of the 0.25G/40Al2O3/SR composite reached 6.68 at 23 °C, whereas the breakdown field strength E0 of 49.1 kV/mm could comparable to that of pure SR. Moreover, the thermal conductivity of 0.25G/30Al2O3/SR was 0.28 Wm−1K−1 at 23 °C, which increased by 114.98% compared to pure SR. This work suggests the promising application of G/Al2O3/SR composites as cable accessory.

Global sensitivity study for irreversible electroporation: Towards treatment planning under uncertainty.

Electroporation-based cancer treatments are minimally invasive, nonthermal interventional techniques that leverage cell permeabilization to ablate the target tumor. However, the amount of permeabilization is susceptible to the numerous uncertainties during treatment, such as patient-specific variations in the tissue, type of the tumor, and the resolution of imaging equipment. These uncertainties can reduce the extent of ablation in the tissue, thereby affecting the effectiveness of thetreatment. The aim of this work is to understand the effect of these treatment uncertainties on the treatment outcome for irreversible electroporation (IRE) in the case of colorectal liver metastasis (CRLM). Understanding the nature and extent of these effects can help us identify the influential treatment parameters and build better models for predicting the treatmentoutcome. This is an in silico study using a static computational model with a custom applicator design, spherical tissue, and tumor geometry. A nonlinear electrical conductivity, dependent on the local electric field, is considered. Morris analysis is used to identify the influential treatment parameters on the treatment outcome. Seven treatment parameters pertaining to the relative tumor location with respect to the applicator, the tumor growth pattern, and the electrical conductivity of tissue are analyzed. The treatment outcome is measured in terms of the relative tumor ablation with respect to the target ablation volume and total ablationvolume. The Morris analysis was performed with 800 model evaluations, sampled from the seven dimensional input parameter space. Electrical properties of the tissue, especially the electrical conductivity of the tumor before ablation, were found to be the most influential parameter for relative tumor ablation and total ablation volume. This parameter was found to be about 4-15 times more influential than the least influential parameter, depending on the tumor size. The tumor border configuration was identified as the least important parameter for treatment effectiveness. The most desired treatment outcome is obtained by a combination of high healthy liver conductivity and low tumor conductivity. This information can be used to tackle worst-case scenarios in treatment planning. Finally, when the safety margins used in the clinical applications are accounted for, the effects of uncertainties in the treatment parameters reducedrastically. The results of this work can be used to create an efficient surrogate estimator for uncertainty quantification in the treatment outcome, that can be utilized in optimal real-time treatment planning solutions.

Monotonicity Principle for Tomography in Nonlinear Conducting Materials

In this paper, we deal with an inverse electrical conductivity problem which considers the reconstruction of nonlinear electrical conductivity in steady currents operations using boundary measurements. In the current set up, we establish a monotonic relation between the unknown material property to the (measured) Dirichlet-to-Neumann operator (DtN). It is in fact the Monotonicity Principle which is the base of a class of non-iterative and real-time imaging methods and algorithms. To be more precise, we indicate the issues appear in our nonlinear case to transfer this Monotonicity result from the Dirichlet Energy to the DtN operator which is the fundamental huddle in comparison to linear and p-Laplacian cases. Finally, we introduce a new Average DtN operator which is different from the existing ones and resolves complications produced by non-linearity in our problem.

Effect ofSiO2particle size scale on the electrical performance of epoxy‐based nonlinear conductive composite

AbstractIn this paper, SiO2particles with three particle sizes of 60 nm, 2 μm, and 25 μm were added as fillers into the composites prepared by epoxy resin and micron silicon carbide to investigate the mechanism of SiO2particle size on the nonlinear electrical conductivity and breakdown characteristics of the composites. Compared with SiC/EP composites, the smaller the added SiO2particle size, the lower the current density at high fields and the higher the breakdown field strength of SiO2/SiC/EP composites. The nonlinear coefficients of SiO2/SiC/EP composites increased slightly with the addition of 1phr 25 μm SiO2and 4phr 2 μm SiO2, and the breakdown field strengths were increased by 55.36% and 66.77%, respectively. The SiO2/SiC/EP composites with the addition of 4phr 60 nm SiO2particles showed the most significant attenuation of the conductivity current and the most prominent enhancement of the breakdown field strength, but the nonlinear coefficient was reduced by 24.6%. With the increase of SiO2doping amount, compared with the composites with the same particle size and low doping amount, the larger the SiO2particle size, the decrease of the current density of the composites under high field intensity is more obvious, and the dielectric constant drops even more.

Surface treated ZnO whisker optimizing the comprehensive performance of the self-adaptive dielectrics

The application of self-adaptive dielectrics (SADs) is a promising approach to enhancing the insulation performance as well as downsizing of most high voltage apparatus. Beside nonlinear electrical property, good thermal and mechanical performances of SADs are also expected. However, heavy load of functional fillers often leads to poor elasticity of traditional SADs and it is a challenge to decrease filler concentration while ensuring satisfied thermal and nonlinear electrical conductivity. In this paper, tetrapod-shaped ZnO whisker coated with oxides shell and its silicone rubber composites have been manufactured. The core-shell interface equips the ZnO whisker with nonlinear conducting behavior and the composites also exhibit similar self-adaptive electrical property like traditional SADs. Due to the relative large respect ratio, the coated whisker can reduce the filler concentration to about 10 vol% which guarantees good mechanical property of the material. The thermal conductivity of the composites and traditional SADs are compared and an optimized filler concentration range considering comprehensive property of the composite is obtained. This work is helpful to design smart composites to self-adaptively control high electrical field of electrical and electronic devices and increase their stability and durability.

Resolving old problems with layered polytungstates related to hexagonal tungsten bronze: phase formation, structures, crystal chemistry and some properties.

A 60-year-old problem with the atomic arrangements and exact compositions of alkali polytungstates related to hexagonal tungsten bronze (HTB) was solved. The systems A2WO4-WO3 (A = K, Rb) were restudied and the average monoclinic layered structures of stoichiometric polytungstates A4W11O35 (A = K, Rb, Cs, Tl) and A2W7O22 (A = K, Rb, Cs) were first successfully determined. The structures resemble those of "MoW11O36" and "MoW14O45" (J. Graham and A. D. Wadsley, Acta Crystallogr., 1961, 14, 379-383) and are derived from HTB by breaking into slabs parallel to (100) due to the ordered omission of some [WO]∞ chains along the hexagonal tunnels. The slabs in A4W11O35 (A = Cs, Tl) and A2W7O22 (A = Rb, Cs) are mutually shifted by the a/2 HTB unit cell axis. These data mainly confirmed our preliminary structural models of HTB-like alkali polytungstates (S. F. Solodovnikov, N. V. Ivannikova, Z. A. Solodovnikova and E. S. Zolotova, Inorg. Mater., 1998, 34, 845-853) and revealed a new similar thallium polytungstate. The structures of the HTB-like polytungstates and related compounds form a homologous series of layered complex oxides or fluorides An+2-xM3n+2X9n+8 where n = 2, 3 and 4 are equal to the numbers of HTB hexagonal tunnels across the polytungstate slab width for Tl2W4O13, A4W11O35 and A2W7O22 (A = K, Rb, Cs or Tl), respectively. The structures of the HTB-like polytungstates seem to intergrow with HTB-type AxWO3 to form, in particular, higher homologues of the series. Our group-supergroup analysis, measurements of nonlinear optical activity and electrical conductivity, and calculations of the bond-valence site energy barriers indicate possible ferroelectric/ferroelastic properties and moderate 2D oxide-ion mobility within the HTB-type slabs of the studied polytungstates.

Memory effects and nonlinear electrical conductivity of doped perovskite-like lanthanum-strontium ferrite, La-=SUB=-0.5-=/SUB=-Sr-=SUB=-0.5-=/SUB=-Fe-=SUB=-0.75-=/SUB=-Al-=SUB=-0.2-=/SUB=-Ni-=SUB=-0.05-=/SUB=-O-=SUB=-3-delta-=/SUB=-

Analysis of the existence of memory phenomena in model heterostructures based on doped ferrite La0.5Sr0.5Fe0.75Al0.2Ni0.05O3-delta with a perovskite structure has been carried out. It was demonstrated that one 5-10 μm thick ferrite layer sandwiched between Pt and Ni electrodes exhibits an analog memristor behavior. Under positive polarity, this heterostructure shows a smooth increase in electrical conductivity, with an opposite effect under negative polarity. Such phenomena are presumably associated with changing local concentrations of oxygen vacancies due to their drift in the electric field. Since lanthanum-strontium ferrites are sufficiently tolerant with respect to oxygen non-stoichiometry variations, no dendrite growth due to reductive decomposition is observed. The current vs. voltage dependencies display a strong nonlinearity resulting from the Poole--Frenkel effect, namely, a decrease in the activation energy of electron holes trapped on oxygen vacancies. In addition to the Poole--Frenkel effect, pre-exponential factor of the conductivity vs. temperature dependence also increases under electric field, indicating an increase in the effective electron-hole mobility. Keywords: perovskite, lanthanum-strontium ferrites, memory effects, nonlinear electronic transport, memristors.

Research on Improving the Partial Discharge Initial Voltage of SiC/EP Composites by Utilizing Filler Surface Modification and Nanointerface Interaction.

SiC/EP composites are promising insulating materials due to their high thermal conductivity, stable chemical properties, and nonlinear electrical conductivity. However, the compatibility of micron-sized SiC particles with the organic polymer matrix is poor, and defects such as air gaps may be introduced at the interface, which reduces the partial discharge resistance of the composite materials. In order to improve the partial discharge initial voltage (PDIV) of SiC/EP composites, in this paper, SiC/EP composites with different proportions were prepared by surface modification of filler and compound of micro/nano particles. Firstly, a method of secondary modification of SiC particles was proposed, which was first modified by alkali washing and then silane coupling agent KH560, and the effectiveness of the modification was verified. Therefore, the interface bonding ability between the filler and the matrix was improved, the air gap defects at the interface were reduced, and the PDIV of the composite material was improved. When the filling ratio is 10 wt%, the PDIV was enhanced by 13.75%, and when the filling ratio was further increased, the improvement was reduced. In contrast, the introduction of nanoparticles into the composites can effectively improve the PDIV of composite materials. In this study, nanoparticles were used to form a shell-core structure in epoxy resins to exert their huge specific surface area and active surface properties, thereby changing the overall crosslinking properties of the composites. Through experimental research, the optimal micro-nano particle compounding ratio was explored. Under the optimal mixing ratio, the PDIV of the composite material can be increased by more than 90%.

Effect of cycle numbers on the structural, linear and nonlinear optical properties in Fe2O3 thin films deposited by SILAR method

Fe2O3 thin films were deposited by Successive Ionic Layer Adsorption and Reaction (SILAR) method onto glass substrates at different cycle numbers to investigate structural, linear and nonlinear optical properties. X-Ray Diffraction (XRD) analysis revealed that the Fe2O3 thin films have a non-crystalline nature. The morphological properties of the films were investigated by Field Emission-Scanning Electron Microscopy (FE-SEM) and the results show that the films’ surfaces are porous. The linear and nonlinear optical parameters were evaluated and analyzed by using transmittance and absorbance measurements. For these measurements, UV–Vis spectroscopy at room temperature was used. The refractive index values were calculated in the range of 1.45–3.23 for visible region (400–700 nm). Obtained results reveal that direct optical band gap changed between 2.62 and 2.68 eV and indirect optical band gap changed between 1.67 and 1.77 eV. Additionally, optical electronegativity, optical dielectric constants, surface and volume energy loss functions, nonlinear refractive index, linear optical susceptibility, third-order nonlinear optical susceptibility, optical and electrical conductivity, and loss tangent values were calculated and discussed in detail. It was found that each parameter studied is dependent on the cycle numbers. Also, it can be stated that Fe2O3 thin films are promising candidate for solar cells and optoelectronic device technology.

A binary classifier based on a reconfigurable dense network of metallic nanojunctions

Major efforts to reproduce the brain performances in terms of classification and pattern recognition have been focussed on the development of artificial neuromorphic systems based on top-down lithographic technologies typical of highly integrated components of digital computers. Unconventional computing has been proposed as an alternative exploiting the complexity and collective phenomena originating from various classes of physical substrates. Materials composed of a large number of non-linear nanoscale junctions are of particular interest: these systems, obtained by the self-assembling of nano-objects like nanoparticles and nanowires, results in non-linear conduction properties characterized by spatiotemporal correlation in their electrical activity. This appears particularly useful for classification of complex features: nonlinear projection into a high-dimensional space can make data linearly separable, providing classification solutions that are computationally very expensive with digital computers. Recently we reported that nanostructured Au films fabricated from the assembling of gold clusters by supersonic cluster beam deposition show a complex resistive switching behaviour. Their non-linear electric behaviour is remarkably stable and reproducible allowing the facile training of the devices on precise resistive states. Here we report about the fabrication and characterization of a device that allows the binary classification of Boolean functions by exploiting the properties of cluster-assembled Au films interconnecting a generic pattern of electrodes. This device, that constitutes a generalization of the perceptron, can receive inputs from different electrode configurations and generate a complete set of Boolean functions of n variables for classification tasks. We also show that the non-linear and non-local electrical conduction of cluster-assembled gold films, working at room temperature, allows the classification of non-linearly separable functions without previous training of the device.

Electric Field and Temperature Simulations of High-Voltage Direct Current Cables Considering the Soil Environment

For long distance electric power transport, high-voltage direct current (HVDC) cable systems are a commonly used solution. Space charges accumulate in the HVDC cable insulations due to the applied voltage and the nonlinear electric conductivity of the insulation material. The resulting electric field depends on the material parameters of the surrounding soil environment that may differ locally and have an influence on the temperature distribution in the cable and the environment. To use the radial symmetry of the cable geometry, typical electric field simulations neglect the influence of the surrounding soil, due to different dimensions of the cable and the environment and the resulting high computational effort. Here, the environment and its effect on the resulting electric field is considered and the assumption of a possible radial symmetric temperature within the insulation is analyzed. To reduce the computation time, weakly coupled simulations are performed to compute the temperature and the electric field inside the cable insulation, neglecting insulation losses. The results of a weakly coupled simulation are compared against those of a full transient simulation, considering the insulation losses for two common cable insulations with different maximum operation temperatures. Due to the buried depth of HV cables, an approximately radial symmetric temperature distribution within the insulation is obtained for a single cable and cable pairs when, considering a metallic sheath. Furthermore, the simulations show a temperature increase of the earth–air interface above the buried cable that needs to be considered when computing the cable conductor temperature, using the IEC standards.

Introducing a novel approach to linear and nonlinear electrical conductivity of MoS2

In regards to the interaction between 2D materials and laser beams, electrical conductivity is the cornerstone due to the fact that the optical absorption is correlated to electrical and opto-electrical properties. In this paper, the linear electrical conductivity (σ(1)) and nonlinear properties (σ(2) and σ(3)) for MoS2 will be investigated theoretically. So as to study the linear electro-optics effect (Pockels effect) in monolayer and the quadratic electro-optics (Kerr effect) in a bilayer of MoS2, σ(2) and σ(3) are derived, respectively. In this work, in order to achieve the σ(1), σ(2) and σ(3), we calculate the first, second and third order of susceptibility of MoS2 (χ(1), χ(2) and χ(3)) by implication of the first order electrical permeability of MoS2 (ɛ(1)), which has been reported in preceding studies. In the next step, by taking advantage of ɛ(E) = ɛ(1) + χ(2)|E| and σ(E) = σ(1) + σ(2)|E|, which express the linear electro-optics (Pockels) effect, the second order of electrical conductivity (σ(2)) can be acquired. Moreover, by considering ɛ(E) = ɛ(1) + χ(3)|E|2 and σ(E) = σ(1) + σ(3)|E|2 as the embodiment of the quadratic electro-optics (Kerr) effect, the third order of electric conductivity (σ(3)) are being calculated. Having this potential for calculating the optical nonlinear response in TMDs would lay the groundwork for designing and engineering a new generation of nonlinear devices premised upon TMDs.

Nonlinear electric conductivity and THz-induced charge transport in graphene

Based on the quantum master equation approach, the nonlinear electric conductivity of graphene is investigated under static electric fields for various chemical potential shifts. The simulation results show that, as the field strength increases, the effective conductivity is firstly suppressed, reflecting the depletion of effective carriers due to the large displacement in the Brillouin zone caused by the strong field. Then, as the field strength exceeds 1 MV m−1, the effective conductivity increases, overcoming the carrier depletion via the Landau–Zener tunneling process. Based on the nonlinear behavior of the conductivity, the charge transport induced by few-cycle THz pulses is studied to elucidate the ultrafast control of electric current in matter.

A Stochastic FE2 Data-Driven Method for Nonlinear Multiscale Modeling.

A stochastic data-driven multilevel finite-element (FE) method is introduced for random nonlinear multiscale calculations. A hybrid neural-network–interpolation (NN–I) scheme is proposed to construct a surrogate model of the macroscopic nonlinear constitutive law from representative-volume-element calculations, whose results are used as input data. Then, a FE method replacing the nonlinear multiscale calculations by the NN–I is developed. The NN–I scheme improved the accuracy of the neural-network surrogate model when insufficient data were available. Due to the achieved reduction in computational time, which was several orders of magnitude less than that to direct FE, the use of such a machine-learning method is demonstrated for performing Monte Carlo simulations in nonlinear heterogeneous structures and propagating uncertainties in this context, and the identification of probabilistic models at the macroscale on some quantities of interest. Applications to nonlinear electric conduction in graphene–polymer composites are presented.