Nonlinear Electrical Properties Research Articles

Electrical properties of the SnO2-based varistor

The non-linear electrical properties of CoO-doped and Nb2O5-doped SnO2 ceramics were characterized. X-ray diffraction and scanning electron microscopy indicated that the system is single phase. The electrical conduction mechanism for low applied electrical field was associated with thermionic emission of the Schottky type. An atomic defect model based on the Schottky double-barrier formation was proposed to explain the origin of the potential barrier at the ceramic grain boundaries. These defects create depletion layers at grain boundaries, favouring electron tunnelling at high values of applied electrical field. © 1998 Chapman & Hall

TiO2 based varistors derived from powders prepared by a sol-gel process

Abstract Nb and Ba doped TiO 2 oxide powders were prepared by a sol-gel process. XRD was used to identify the phase composition of the gels calcined at different temperatures. Green disks of Ti-Nb-Ba were made from the starting powders and sintered at 1250–1300 °C for 2 h. The microstructures of the sintered compacts were examined by SEM. The dielectric and nonlinear electric properties of the samples were investigated and the results show the Ti-Nb-Ba system is suitable for preparation of varistors.

Non-linear electric and magnetic properties obtained from cubic response functions in the random phase approximation

We derive cubic response functions in the Random Phase Approximation for calculations of non-linear frequency-dependent properties of molecules, and demonstrate an implementation of these functions ...

Microstructure and Nonohmic Properties of ZnO-V2O5 Ceramics

The microstructure and nonohmic characteristics of polycrystalline ZnO-V2O5 ceramics with V2O5 as the only additive ranging from 0 to 2 mol% were investigated. An abnormal grain growth was observed for ZnO doped with V2O5 and sintered at 900° C. However, the non-uniformity of the grain structure alleviated with increasing the V2O5 content or sintering temperature. The ZnO-V2O5 ceramics have shown characteristics of nonohmic V-I behavior and large apparent dielectric constant with a relaxation peak of 0.36 eV at 300 kHz. The electrical properties of these ZnO-V2O5 ceramics depended strongly on the processing conditions and V2O5 content, and there seems a close relation between the nonlinear electric properties and the concentration of the deeply-trapped defects at 0.36 eV in ZnO.

The linear and non-linear electrical properties of the electrode-electrolyte interface

A review of various aspects of electrode-electrolyte interface impedance is presented. The effect of electrode topography on the form and magnitude of the interface impedance is discussed. The work of Schwan and his colleagues on the non-linearity of the interface impedance is presented and interpreted. The electrical properties of silver-silver chloride electrodes (much used in a wide range of biomedical applications) are also briefly reviewed.

Physics of composite media with a periodic microstructure

A composite medium with a periodic microstructure can have some amazing physical properties. We will discuss some of those, including two which have only recently been discovered. We review the phenomenon of sharp resonances which are predicted to occur when a periodic array of identical, small (compared to the wavelength and skin depth) metallic inclusions is imbedded in a dielectric host. We show that if either the dielectric host or the metallic inclusions have nonlinear electrical properties, then by exciting the system near to one of those resonances it should be possible to achieve bistable optical behavior even when the nonlinearity is weak everywhere. Under the influence of a strong magnetic field H , the magnetoresistance of a composite conductor with a periodic microstructure is shown, by calculations, to exhibit a strong dependence on the direction of H . This is surprisingly similar, both qualitatively and quantitatively, to the behavior of the magnetoresistance of a uniform metallic crystal, where it is thought to be due to the open structure of the Fermi surface. In the case of a composite medium there is of course no Fermi surface in the theory, and this behavior can be understood, at least qualitatively, from simple geometric considerations on the microstructure and the local current distribution.

Solitary-wave dynamics in extrinsic semiconductors under dc voltage bias.

Numerical-simulation results are presented for a simple drift-diffusion model which describes time-dependent and nonlinear electrical transport properties of extrinsic semiconductors under time-independent (dc) voltage bias. Simulations for finite-length samples with Ohmic boundary conditions yield dynamically stable solitary space-charge waves that travel periodically across the sample. Numerical estimates of wave speed, the wave size, and onset phenomena are in excellent agreement with recent experiments in p-type germanium.

A dendritic gain control mechanism in axonless neurons of the locust, Schistocerca americana.

1. To understand the possible function of active dendritic currents in local neurons, the non-linear electrical properties of locust axonless non-spiking interneurons were considered in parallel with the properties of graded transmitter release from their dendrites. 2. The dendritic membrane of the non-spiking interneurons was least responsive to an applied or synaptic current at potentials between -55 and -45 mV. This is because, at these potentials, the input resistance of the dendrites is reduced by the activation of voltage-dependent K+ conductances. Conversely, the membrane of the non-spiking interneurons was most responsive to an applied or synaptic current at potentials more negative than -55 mV (where the membrane behaves more or less passively), or more positive than -45 mV (where the activation of a Ca2+ current can boost depolarizing potentials). 3. The threshold for detectable release at the non-spiking synapse was around -65 mV. The dynamic gain of the synape (slope of the synaptic transfer curve) was maximum around -50 mV. Saturation was observed around -40 mV. Synaptic transfer is therefore most efficient at presynaptic potentials where the non-spiking dendritic membrane is least responsive to incoming signals. 4. The possible consequences of this matching of membrane and synaptic non-linearities was studied theoretically, with computer-assisted simulations, and experimentally, by recording simultaneously from the dendrites of synaptically connected non-spiking interneurons and motoneurons. This precise matching of non-linearities was found to have two important consequences: (i) it allowed the effective gain of polysynaptic pathways via non-spiking dendrites to depend little on the state of the interposed interneuron (linearization) and (ii) it optimized coding by preventing undesired over-amplification and synaptic saturation.

Nonlinear electrical properties of lead-lanthanum-titanate thin films deposited by multi-ion-beam reactive sputtering

The high-field electrical properties of ferroelectric lead-lanthanum-titanate (PLT) thin films deposited by multi-ion-beam reactive sputtering are presented. Space-charge-limited (SCL) conduction theory incorporating the effects of electron traps is used to explain the current-density dependence on applied voltage. Three conduction mechanisms, ohmic, SCL, and trap-filled limited (TFL), were observed with increasing applied potential. Increasing excess PbO content in PLT films increases the absolute current density measured in all three conduction regions and decreases the potential required for the transition between ohmic conduction and SCL conduction. Electron trap density is increased with the addition of La, resulting in increased voltages for the transition between SCL and TFL conduction. Permittivity and polarization hysteresis behavior is interpreted by considering the conduction contributions under linear low-field conditions and nonlinear high-field conditions. Hysteresis loop frequency dependence, asymmetry, and off-center shift from the zero-field and zero-polarization origin arise from conduction contributions and nonlinear internal fields, which are explained by applying SCL theory. Pulse switching results, which eliminate conduction contributions, are compared with normal Sawyer–Tower hysteresis loop measurements of the remanent polarization.

Non-linear electric properties of polyaniline doped with organic acceptors

Complexes of polyaniline (PANI) with various organic r -electron acceptors such as TCNQ and others were prepared by the automatic doping method. The relationship between current and applied voltage was linear and ohmic in argon atmosphere at voltages below 5 V, but in air it was non-linear. A field-effect current was observed at PANI-chloranil complex on silicon substrate.

Chemical Vapor Deposition of Epmtaxial BaTiO3 Films for Frequency Doubling Devices

AbstractFerroelectric materials such as BaTiO3 are notable for their nonlinear optical and electrical properties. Optical frequency doubling in thin films integrated with compact semiconductor laser pumped solid state lasers is an attractive candidate for high efficiency generation of blue light. Chemical vapor deposition (CVD) using a single liquid source has been used to grow BaTiO3 films on MgO. X-ray diffraction in the pole figure configuration indicates the films to be epitaxial, and rocking curves had FWHM ≈ 0.7°. An optical scatterometer (λ = 633 nm.) has been used to identify deposition conditions that result in the lowest scatter losses. This paper describes these results as well as waveguide designs to enhance the second harmonic generation efficiency in epitaxial BaTiO3 films on MgO.

Nonlinear Electrical Properties of Evaporated Lead Phthalocyanine Films

Current-voltage characteristics of Au/evaporated lead phthalocyanine film/Au sandwich-type cells showed nonlinear electrical electrical properties with asymmetric barriers. From analyses of crystal structures of PbPc films, these barriers were found to be attributable to nonuniformity of crystal structure and orientation along the film thickness

Remarks on some problems in 1D-physics: nonlinear optics of (A–B) conjugated polymers and the role of electron-electron scattering in conducting Q1D materials with a soft phonon mode

Abstract Nonlinear optical and conducting properties of Q1D materials are considered. The nonlinear optics of (A–B) polymers are discussed on the basis of the Hamiltonian of Rice and Mele. The unified theory of nonlinear susceptibilities on the framework of the nonequilibrium Keldysh technique is presented. It has been shown that the second harmonic generation takes place. The real and imaginary parts of the second hyperpolarizability are calculated and their frequency dependence found. Nonlinear electrical properties of Q1D metals are considered. It is shown that the conductivity mechanism is due to a new phase state, named a charge-density wave. A new transport properties' model of these materials in a high temperature phase has been proposed. It has been shown that the transport should be determined by electron-electron scattering and the interaction with a soft phonon mode in the vicinity of a structural phase transition.

Syntheses, Structures, and Thermal, Transport and Nonlinear Optical Properties of Tyc -Txf Compounds

Abstract The syntheses, electric and structural properties of a series of uncapped C6X4Y4 compounds (tetrakis(n-alkylchalcogeno)- tetrachalcogenafulvalenes; TYC -TXF) and nonlinear electric and optical properties of their CTn complexes are described.

Non-linear concentration-dependent electrical properties of some semiconducting vanadate glasses

Characterizations of (50 − x) P2O5-x M-50V2O5 (M = Bi2O3, Sb2O3, and GeO2 and x=0 to 45 mol% M) and P2O5-Bi2O3 semiconducting oxide glasses have been made from studies of electrical conductivities (both a.c. and d.c.) in the temperature range 77 to 400 K. All these glasses showed some interesting non-linear variation of d.c. and a.c. conductivity, together with other properties for particular values of M (between 20 and 30 mol% M). Because the non-vanadate (1−x) P2O5-x Bi2O3 glasses also showed similar conductivity anomaly (minimum) around 25 mol% Bi2O3 with a corresponding maximum in the activation energy (W), it is concluded (in contradiction to earlier suggestions) that not only the ratio β (= V5+/V4+) but also the network-former ions in the vanadate glasses make a substantial contribution to the anomalous concentration variation of the physical properties of these glasses. The electrical conduction in these glasses is found to be mainly due to hopping of polarons in the adiabatic approximation. At low temperature, the d.c. conductivity obeys Mott's T−1/4 behaviour. The a.c. conductivity obeying the general ωs law (exponent s lying between 0.85 and 0.98) supports the theory based on the hopping over the barrier model.

Microstructure and ferroelectrical properties of the copolymers of vinylidene fluoride with tetrafluoroethylene of composition 71:29

From the 19F NMR data the microstructure of the copolymers of vinylidene fluoride with tetrafluoroethylene of composition 71:29 is characterized by the presence of 5 mol.% diads in the tetrafluoroethylene blocks. The share of the “head-to-head” defects in the vinylidene fluoride blocks is 2.5 mol.%. Films of the copolymers display ferroelectric properties both in the isotropic and textured states. In the last case the region of the fields where non-linear electrical properties manifest themselves are shifted to lower values. The idea is proposed that fall in the share of the “head-to-head” defects in the vinylidene fluoride blocks may be responsible for the weakening of the “memory” effects in temperature-field investigations of the ferroelectricity in these compounds.

Analysis of some significant processes for molecular polarization

The polarisability, the first and second hyperpolarisabilities of NH2—C6H4—CnHn—CHC5H4, where n= 2, 4 and 6, as well as of some related compounds are reported. The effects of isomerism, conjugation and charge-transfer on the properties are discussed. In addition the influence of increasing the length of the conjugation path on the linear and non-linear electric properties has been commented upon. The properties have been computed using an extended-basis CNDO wavefunction and the coupled Hartree–Fock perturbation theory of McWeeney et al. The employed basis sets have been shown to give polarisability (α) and second hyperpolarisability (γ) values, for some fragments of the considered molecules, in reasonable agreement with the experimental results.

A mixed numerical-analytical approach to the calculation of non-linear electric properties

Non-linear electric properties of atoms and molecules can be determined by computing the second-order polarizabilities from the analytic perturbation equations, numerically modified by the presence of an additional finite field. The scheme is applied in a test calculation of the He atom hyperpolarizabilities, γ( 0;0,0,0) and γ(-ω;ω,0, 0).

The biophysical properties of spines as a basis for their electrical function: a comment on Kawato & Tsukahara (1983)

In a theoretical study of the passive cable properties of dendritic spines Kawato & Tsukahara (1983) claim to have proved that "the dendritic spine has no significant electrical function" (from their discussion). However, Kawato & Tsukahara restrict their analysis to current inputs to spines. Since the dimensions of spines are very small, their input resistance is expected to be very large and the synaptic input to spines has to be modeled as conductance change. Under this assumption, spines show interesting (non-linear) electrical properties: i) the somatic potential induced by an excitatory synapse on a spine may depend strongly on the shape of the spine and ii) the effect of inhibition might be confined to the spine.

Second phase development in Sr-doped TiO2

In the Ti-rich region of the SrO-TiO2 system, a temperature-composition range is found to exhibit limited solubility of strontium, the maximum limit being 0.5 mol % Sr. It is also found that a two-phase region exists between this solubility limit and SrTiO3, in agreement with existing phase diagrams. When the strontium concentration is small (⩽ 0.5 mol %), strontium segregates to the grain boundaries to form a second phase of SrTiO3 below the solubility limit. Above 1200‡ C, this second phase is continuous; shape instability causes it to break up into discrete particles below 1200‡ C. At higher strontium concentration (about 2 mol % Sr), nucleation of SrTiO3 crystallites occurs both inside the TiO2 grains and at the grain boundaries. The morphology of these crystallites after long time annealing suggests that the {110} plane has the fastest growth rate. The appropriate range of composition and heat treatment to form a continuous SrTiO3 grain boundary layer is discussed in relation to the optimum heat treatment to develop the best nonlinear electrical properties of varistor devices.