Nonlinear Electrical Properties Research Articles

Nonlinear electrical properties and dielectric properties of ZnO ceramics doped with K2CO3

ZnO ceramics with different amounts of K2CO3 from 0.0 to 1.0 mol% are prepared by traditional solid-state sintering technique. The K2CO3-doping effects on the microstructure, nonlinear electrical properties and dielectric properties of ZnO ceramics are investigated. The grain size of ZnO ceramics increases from 0.9 to 1.5 μm with increasing K2CO3 content. The leakage current density versus electric field characteristics indicate that ZnO ceramic samples exhibit similar nonlinear electrical properties. The switching field and nonlinear coefficient decrease in the range of 246.2 to 1.3 V/mm and 5.3 to 2.4 with the increase of K2CO3 content. The varistor voltage decreases from 344.9 to 2.0 V/mm, while the leakage current increases from 323.0 to 646.1 μA. Meanwhile, as K2CO3 content increases, the dielectric constant and dielectric loss of ZnO ceramics are improved in the frequency range from 102 to 106 Hz at room temperature.

Chemical Control of Electronic Coupling between a Ruthenium Complex and Gold Electrode for Resonant Tunneling Conduction.

Current-voltage (I-V) nonlinearity is essential for information processing in molecular electronics. We used a nanoparticle bridge junction to investigate the effect of electronic coupling between a Ru complex and electrodes on nonlinear electrical properties. Two types of molecular layers, in which the Ru complex forms different chemical bondings to the electrode, were used for electrical measurements. The chemical bond and the surface potential of the Ru complex on Au electrodes were examined by X-ray photoelectron spectroscopy,infrared ray reflection absorbance spectroscopyand Kelvin probe force microscopy, respectively. The device, in which the Ru complex is directly bound to the Au electrode, indicated the nonlinearI-V characteristics with zero-bias conductance because of the direct tunneling conduction. Another device fabricated by inserting a spacer molecule between the Ru complex and the Au electrode realized nonlinear I-V characteristics with a clear threshold voltage and little zero-bias conductance. The I-V curves were well fitted by the resonant tunneling conduction model. The present results show the significance of controlling the electronic coupling for nonlinear I-V characteristics.

Conductivity inversion of ZnO nanoparticles in ZnO-carbon nanofiber hybrid thin film devices by surfactant-assisted C-doping and non-rectifying, non-linear electrical properties via interfacial trap-induced tunneling for stress-grading applications

A special nonrectifying, nonlinear current–voltage characteristic is observed in ZnO nanoparticle-anchored carbon nanofiber (ZnO-CNF) hybrid thin film devices, which has interesting applications in nonlinear stress-grading materials for high-voltage devices and overvoltage protectors in multifunctional electronic circuits. A simple chemical precipitation method is used to fabricate the hybrid films, followed by vacuum annealing at elevated temperatures. Interestingly, the organic surfactant (Triton X-114), used as a binder during the film deposition, manifests unintentional carbon doping into a ZnO lattice, which leads to a conductivity inversion of ZnO from n-type in the lower temperature (300 °C) annealed hybrid into p-type in the higher temperature (600 °C) annealed film. Electrical characterizations reveal that the CNF-ZnO interfaces act as a metal-semiconductor junction with low barrier height, leading to nonrectifying junction properties. Also, the surfactant-induced C-atoms create trap states at the interface which “emit” the trapped charges via interfacial field-assisted tunneling, thus imposing nonlinearity (in both forward and reverse directions) on the I–V curves.

Nonlinear current-voltage and giant dielectric properties of Al3+ and Ta5+ co-doped TiO2 ceramics

The nonlinear current-voltage and dielectric properties of (Al3++Ta5+) co-doped TiO2 (ATTO) ceramics are represented. Microstructural analysis reveals that sintered ceramics are highly dense and nonporous. ATTO ceramics exhibit low loss tangent (tanδ<0.1) and large dielectric permittivity (ε′˜103-104). Furthermore, ATTO ceramics exhibited nonlinear current-voltage characteristics. The best dielectric properties are achieved in the (Al1/2Ta1/2)0.05Ti0.95O2 ceramic with a very low tanδ (˜0.012) and high ε′ (˜104) with excellent dielectric-temperature stability with a temperature coefficient at 150 °C as low as 2.69%. The resistivity of insulating phases decreases with increasing Al3+ and Ta5+ concentrations, which is correlated to decreased breakdown voltage. The nonlinear electrical properties and dielectric response are explained based on the electrical response of internal interfaces.

Ni2+-doped CaCu3Ti4O12/TiO2 nanocomposite ceramics with high temperature stability dielectric and nonlinear electrical properties for X9R capacitors

The temperature stability of the dielectric constant and nonlinear electrical properties of CaCu3Ti4O12 ceramics were improved by fabricating Ni2+-doped CaCu3Ti4O12/TiO2 nanocomposite ceramics. Interestingly, a large reduction of the dielectric loss to 0.009 with high ε′ of 6314 and good temperature stability of the dielectric constant (Δε′) of less than ±15% variation over the temperature from −60 to 210 °C was obtained in a CaCu2.95Ni0.05Ti4O12/TiO2 ceramic sintered at 1060 °C for 8 h. With these excellent properties, this ceramic is proposed for applications in high temperature X8R and X9R capacitors. Nonlinear behavior of J–E curves was observed in all CaCu3−xNixTi4O12/TiO2 ceramics that could be significantly enhanced by Ni2+ doping. Very large α (~53) and Eb (~15,727 V·cm−1) values were obtained in a CaCu2.95Ni0.05Ti4O12/TiO2 ceramic sintered at 1060 °C for 8 h. X-ray absorption near edge spectroscopy (XANES) was performed for verification of the Ti oxidation state of all ceramics. Microstructural and phase composition were studied using field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD).

Globally reinforced mechanical, electrical, and thermal properties of nonlinear conductivity composites by surface treatment of varistor microspheres

The composite filled with zinc oxide (ZnO) varistor microspheres display promising nonlinear conductivity properties and can be used for grading electric field in electrical equipment. However, the mechanical properties of composites containing ZnO varistor microspheres are seriously degraded, so how to balance the mechanical and electrical performances of electric field grading materials is a key issue for practical applications. In this work, concurrent reinforcement effect of surface-treated ZnO varistor microspheres on the mechanical, electrical, and thermal properties of silicone rubber (SR) composites are studied. 3-Aminopropyltriethoxysilane, a silane coupling agent, is used for surface functionalization of ZnO varistor microspheres, which are then used as a filler in SR to prepare an electric field grading material. Mechanical tensile tests reveal that the tensile strength and initial modulus of the composite incorporated with surface-treated filler are markedly improved and the thermal conductivity of this composite is also increased compared with a composite with untreated filler. Meanwhile, the composites with surface-treated filler displays more stable nonlinear electrical properties under mechanical deformation than those with untreated filler. This method would lead to electric field grading composite materials with excellent comprehensive properties towards practical applications in cable insulation, insulators, terminal accessories, etc.

Temperature stability of the dielectric properties of Zr4+-doped CaCu3Ti4.2O12 ceramics for X9R capacitor applications

In the present work, a giant dielectric constant (ε′) ∼ 11672 was developed in a CaCu3Ti4.15Zr0.05O12 ceramic with a very low loss tangent (tanδ) ∼ 0.011 at 30 °C and 1 kHz over a temperature range of −60 °C to 110 °C. The resulting dielectric variation (Δε') < ±15% over a temperature range of −60 °C to 210 °C, as well as good nonlinear properties (α ∼ 24.23 and Eb ∼ 8.37 kV cm−1) were achieved in a CaCu3Ti4.15Zr0.05O12 ceramic sintered at 1080 °C for 8 h. According to the EIA standard, this ceramic's excellent dielectric and nonlinear properties provide for potential applications in X9R capacitors and varistors. Very high performance dielectric and nonlinear electrical properties are suggested to have originated from the very high grain boundary resistance (RGB ∼ 515.5 kΩ cm). This was a result of a TiO2-rich environment at the grain boundaries and Zr4+ doping. The grain resistance (RG) and grain boundary resistance (RGB) were studied using impedance spectroscopy. Backscatter FESEM images with elemental mapping and XRD results confirmed the presence of mixed phases of TiO2 and CaCu3Ti4O12.

Role of sintering temperature on microstructure and nonlinear electrical properties of 0.1 mol.% Nb2O5 added ZnO–V2O5 varistor ceramics

The effect of sintering temperature on the microstructure, density and nonlinear electrical properties of 0.1 mol% Nb2O5 added ZnO–V2O5 varistor ceramics had been investigated. Density measurement, scanning electron microscopy (SEM), X-ray diffraction (XRD) pattern analysis characterized the sintered samples. The electric current and capacitance measurements of the varistor samples were done in varying voltage over a wide range. Image analysis by SEM shows an increase in the average grain size from 2.8 to 7.2 µm when the sintering temperature increases from 850 to 975 °C. The varistor sample, sintered at 850 °C, exhibits breakdown field of 4258 V/cm with nonlinear exponent value of 24. Degradation in breakdown field (1440 V/cm) and nonlinear exponent (9) have been observed with an increase in sintering temperature up to 975 °C. Barrier height estimated from the electric field–current density (E–J) and the capacitance–voltage (C–V) measurements follow an inverse relationship with sintering temperature.

Preparation and Nonlinear Conductivity Characteristics of Silicone Rubber Filled with Silver-Coated Tetrapod-Shaped ZnO Whiskers

Tetrapod-shaped zinc oxide (T-ZnO) whiskers were coated with silver by chemical plating (T-ZnO@Ag). T-ZnO(T-ZnO@Ag)/silicone rubber composites were fabricated at a temperature of 165°C and pressure of 15 MPa. The nonlinear conductivity characteristics of T-ZnO (T-ZnO@Ag)/silicone rubber composites with volume fractions of 1 vol.%, 2.4 vol.%, 3.7 vol.%, and 5 vol.% were investigated. The dielectric properties of the composites at frequencies of 0.1 Hz to 10 MHz were analyzed. The conductivity of the T-ZnO/silicone rubber composite increased with the T-ZnO content, while the switching field decreased. Upon the coating of T-ZnO with Ag, the nonlinear characteristics of the T-ZnO@Ag/silicone rubber composite significantly enhanced. The nonlinear coefficient reached 10.95 at the filler content of 2.4 vol.%. The percolation threshold of T-ZnO fillers is significantly lower than that of spherical ZnO fillers. Percolation threshold and Schottky barrier effect were utilized to explain the nonlinear electrical properties.

Giant dielectric response, electrical properties and nonlinear current-voltage characteristic of Al2O3-CaCu3Ti4O12 nanocomposites

In this work, xAl2O3-(1 − x)CaCu3Ti4O12, where x = 0, 2, and 10 vol%, nanocomposites were prepared by a conventional mixed oxide method using Al2O3 nanopowders with particle sizes of ≈20–40 nm. The giant dielectric properties, electrical responses and nonlinear characteristics of Al2O3-CaCu3Ti4O12 nanocomposites were investigated. Interestingly, the (2 vol%)Al2O3-CaCu3Ti4O12 ceramic exhibited significantly improved dielectric properties with large dielectric constant and low loss tangent values of about of 2.0 × 104 and 0.038, respectively. The nonlinear current-voltage properties of CaCu3Ti4O12 ceramics were also enhanced by the addition of Al2O3. X-ray photoelectron spectroscopy technique was used to confirm the existence of Cu+, Cu3+ and Ti3+ ions in the composite ceramics, indicating the primary cause of the conduction mechanism inside the grains. The first principle calculation was performed to predict the most possibility of site preference of Al ion in CCTO lattice structure. The improved dielectric and nonlinear electrical properties can be well explained based on the internal barrier layer capacitor effect, resulting from the improved electrical properties of internal interfaces.

The Non-linear Electrical Properties of Silver/silver Chloride Electrodes in Sodium Chloride Solution.

An electrical measurement is non-linear when it is affected by the applied stimulus, i.e. when the measured phenomenon changes with amplitude. If pinched hysteresis loops can be observed in the voltage current representation, the underlying tissue can be classified as a memristor. Several biological memristors have been published, like human skin and apples. However, changes in the polarization impedance of electrodes may also cause pinched hysteresis loops. The question whether the reported biological memristors are real or whether the results just reflect changes in the polarization impedance arises. If the impedance of the measured object is close to or smaller than the polarization impedance of the used electrodes, the latter may dominate the measurement.In this study, we investigated the non-linear electrical properties of silver/silver chloride electrodes in a sodium chloride solution that has a similar concentration as human sweat and compared these to results from human skin. First of all, we found that silver/silver chloride electrodes in sodium chloride solution can be classified as memristors. However, the currents obtained from the sodium chloride solution are much higher than the currents recorded from human skin and there is a qualitative difference in the pinched hysteresis loops in both cases. We can conclude that the non-linear electrical measurements with silver/silver chloride on human skin are actually dominated by the skin and we can confirm that the human skin memristor really exists.

Rectifying Memristor Bridge Circuit Realized with Human Skin.

It has been demonstrated before that human skin can be modeled as a memristor (memory resistor). Here we realize a memristor bridge by applying two voltages of opposite signs at two different skin sites. By this setup it is possible to use human skin as a frequency doubler and half-wave rectifier which is an application of the non-linear electrical properties of human skin. The corresponding electrical measurements are non-linear since these are affected by the applied stimulus itself.

Nonlinear Electrical Properties and Field Dependency of BST and Nano-ZnO-Doped Silicone Rubber Composites

Recently, composite materials with nonlinear dielectric or resistive properties performed well in electric field homogenization and space charge suppression in a high voltage transmission and distribution system. For the purpose of obtaining insulation materials with desirable dielectric and electrical resistance properties, we investigated several fillers with nonlinear electrical properties doped in silicon rubber composites, and their dependency on the temperature and field. The samples of silicone rubber composites with different components were prepared using barium strontium titanate (BST) and zinc oxide (ZnO) as the filler, and high temperature vulcanized silicone rubber (SiR) as the matrix. The investigations revealed that the BST-doped samples showed different dielectric properties compared to ZnO-doped composites, with an increase in the electric field, which was nonlinear. The resistivity of both doped samples was similar. Results demonstrated that it was possible to achieve higher values of permittivity, and lower values of tanδ and resistivity, with respect to unfilled silicone rubber composites over a wide electrical field and temperature range. Discussion of the results attributes these important functional behaviours to the spontaneous polarization of nonlinear nanoparticles and the interaction between the SiR chains and the nonlinear nanoparticles at the interfacial area.

Electromagnetic field in superconductor samples using a partitioned E-H finite element scheme

Abstract The need for new numerical methods that can reduce the time computation for non-linear instantaneous field problems is increasing as for example applications for HTS materials become more and more important. This work proposes a novel numerical approach suitable for the simulation of non-linear materials with lower computational times in the simulation of instantaneous field problems in the presence of high temperature superconductors (HTS). The proposed method is based on a partitioned finite element method (FEM) using an E-H electromagnetic scheme formulation (FEM-EHS). The novelty of this method resides in the separation of the matrix formulation due to the discretization of Amperes and Faradaýs laws, leaving outside the matrix equations of the non-linear magnetic and electric material properties. Therefore, for a time-dependent simulation, the transformation matrices related to the Amperes and Faradaýs laws remain unchanged for the entire time domain, not dependent on the non-linear local Ohḿs law E(J) of the HTS model. Therefore, those matrices can be computed and inverted a priori leading to a fast computation. The method was validated by comparing results with a commercial FEA tool, for the simulation of an HTS bulk magnetization process. With the proposed method, results were obtained in less than 1/3 of the computational time of the commercial tool.

Effect of Y2O3, Nd2O3 or Sm2O3 on the microstructure and electrical properties of ZnVMnNbO varistor ceramics

This study addresses the different effect of doping 0.05 mol% Y2O3, Nd2O3 or Sm2O3 on the microstructure and nonlinear electrical properties of the ZnO–V2O5–MnCO3–Nb2O5 (ZnVMnNbO) ceramic sintered at 930 °C for 3 h using XRD, FESEM, EDS and I–V measurements. The results show the density and the microstructure homogeneity of the ZnVMnNbO ceramic increase with the addition of Y2O3, Nd2O3 or Sm2O3. Meanwhile, REVO4 (RE=Y, Nd or Sm) forms as the new secondary crystalline phase at ZnO grain nodal areas of the ZnVMnNbO ceramic which originally has Zn3(VO4)2, ZnMn2O4 and ZnV2O4 as the secondary phases. The addition of Y2O3 or Sm2O3 can effectively improve the nonlinearity coefficient of the ZnVMnNbO varistor ceramic from 33.6 of the RE-free sample to near 37 by increasing interface state density. In the contrast, Nd2O3 considerably reduces α to 25.9 by decreasing both barrier height (ΦB) and depletion layer width (ω).

Nonlinear dynamic modeling of ultrathin conducting polymer actuators including inertial effects

Trilayer conducting polymer (CP) actuators are potential alternatives to piezoelectric and electrostatic actuators due to their large strain, and recently demonstrated operation at hundreds of Hertz. However, these actuators exhibit nonlinear electrical and mechanical properties as a function of their oxidation state, when operated over their full strain range, making it more challenging to accurately predict their mechanical behavior. In this paper, an analytical multi-physics model of the CP actuators is proposed to predict their nonlinear dynamic mechanical behavior. To demonstrate the accuracy of the model, a trilayer actuator composed of a solid polymer electrolyte sandwiched between two poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes was fabricated and characterized. This system consists of an electrical subsystem represented by an RC equivalent circuit, an electro-mechanical coupling matrix, and a mechanical subsystem described by using a rigid finite element method. The electrical conductivity and the volumetric capacitance, an empirical strain-to-charge ratio, and Young’s modulus of the actuator as a function of the PEDOT electrode charge state were also implemented into the model, using measured values. The proposed model was represented using a bond graph formalism. The concordance between the simulations and the measurements confirmed the accuracy of the model in predicting the nonlinear dynamic electrical and mechanical response of the actuators. In addition, the information extracted from the model also provided an insight into the critical parameters of the actuators and how they affect the actuator efficiency, as well as the energy distribution including dissipated, stored, and transferred energy. These are the key parameters for designing, optimizing, and controlling the actuation behavior of a trilayer actuator.

The non-linear electrical properties of human skin make it a generic memristor

An electrical measurement is non-linear when the applied stimulus itself affects the electrical properties of the underlying tissue. Corresponding voltage-current plots may exhibit pinched hysteresis loops which is the fingerprint of a memristor (memory resistor). Even though non-linear electrical properties have been demonstrated for different biological tissues like apples, plants and human skin, non-linear measurements as such have not been defined, yet. We are studying the non-linear properties of human skin systematically and initiate non-linear measurements on biological tissues as a field of research in general by introducing applicable recording techniques and parameterization. We found under which voltage stimulus conditions a measurement on human skin is non-linear and show that very low voltage amplitudes are already sufficient. The non-linear properties of human skin originate from the sweat ducts, as well as, from the surrounding tissue, the stratum corneum and we were able to classify the overall skin memristor as a generic memristor. Pinched hysteresis loops vary largely among subjects; an indication for the potential use in biomedical sensor applications.

Effect of Sintering Temperature on Zinc Oxide Varistor Ceramics

Zinc oxide (ZnO) varistors is a solid state electronic ceramic component whose function to protect electronic devices against over voltage surges due to their highly nonlinear electrical properties and ability in controlling the energy. In this study, ZnO varistor is prepared via solid state reaction method. The ZnO based varistor ceramics undergoes sintering temperature at 900 °C, 1100 °C and 1300 °C for 45 minutes. The used of sintering temperature from 900 to 1300 °C, has increased the grain size of ZnO and improved their crystallinity as shown from the peaks intensity of X-ray diffraction (XRD). Current-Voltage properties exhibit the value of nonlinear coefficient in the range of 1.44 to 1.76. Different sintering temperature is used to adjust the microstructure and improve the varistor ceramic characteristics where it shows a potential difference in various application of electronic devices. Increasing in sintering temperature would lead to improved grain growth for better electrical properties.

Effect of Na2O and B2O3 Addition on Nonlinear Electrical Properties of WO3-Based Capacitor–Varistors

WO3-based varistors with added Na2O and B2O3 were synthesized by the solid-state reaction. The undoped and B2O3-doped WO3 ceramics exhibited weak nonlinear I–V characteristics. The nonlinear I–V characteristics of the ceramics increased slightly after the addition of Na2O and more significantly after the addition of Na2O and B2O3. The nonlinearity coefficients α of the WO3, Na0.005WO3, and Na0.005WO3–5 wt % B2O3 ceramics were 1.86, 2.03, and 5.22, respectively. The breakdown voltages of the WO3, Na0.005WO3, and Na0.005WO3–5 wt % B2O3 ceramics were 1.56, 6.05, and 12.42 V/cm, respectively. The dielectric constant and the dielectric loss of the Na0.005WO3–5 wt % B2O3 ceramic were ~50–150 and less than 0.3, respectively, for frequencies ranging from 1 to 1000 kHz.

Investigation of nonlinear electrical properties of ZnO/PPy nanocomposite and its application as a low-voltage varistor

The present study reports the electrical characteristics of a low voltage ZnO/Polypyrrole nanocomposite varistor which was fabricated as a thin disk based on zinc oxide with different weight percentages of polypyrrole as additive using a cold pressing method. Current-voltage characteristics and nonlinear coefficients of the ZnO/Polypyrrole nanocomposite thin disks were studied in direct current mode. Results showed good varistor behavior of prepared ZnO/Polypyrrole nanocomposite. According to the results, ZnO/Polypyrrole nanocomposite thin disk varistors can be utilized to preserve circuits from 35 V up to 350 V over voltages. I-V characteristics of nanocomposite samples showed that by increasing zinc oxide content from 98.52% to 99.01%, the breakdown voltage of ZnO/Polypyrrole nanocomposite varistor increased whereas its nonlinear coefficient decreased. However, more increase in ZnO content of nanocomposite caused to the reduction of its breakdown voltage and increase of nonlinear coefficient. The results obtained from SEM micrographs indicated that by increasing ZnO content, both the grain numbers and their morphologies are changed which is caused the different effects in the grain boundaries, I-V characteristics, and varistor properties of nanocomposites. As a very important result, in this experimental work, an ideal varistor with sufficient low breakdown voltage and acceptable high nonlinear coefficient was obtained.