Understanding Of Electrical Conductivity Research Articles

Dielectric and Impedance Spectroscopy of Samarium and Lanthanum Doped Barium Titanate at Room Temperature

Abstract—Dielectric ceramic samples in the BaO-Re2O3-TiO2 ternary system were synthesized with structural formula Ba2xRe4+2x/3Ti8O24 where Re= rare earth metal and Re= Sm and La where x varies from 0.0 to 0.6 with step size 0.1. Polycrystalline samples were prepared by the conventional solid state reaction technique. The dielectric, electrical and impedance analysis of all the samples in the frequency range 1KHz1MHz at room temperature (25°C) have been done to get the understanding of electrical conduction and dielectric relaxation and their correlation. Dielectric response of the samples at lower frequencies shows dielectric dispersion while at higher frequencies it shows dielectric relaxation. The ac conductivity is well fitted by the Jonscher law. The spectroscopic data in the impedance plane confirms the existence of grain contribution to the relaxation. All the properties are found out to be function of frequency as well as the amount of substitution.

Study of the dielectric response in mineral oil using frequency-domain measurement

Dielectric spectroscopy is a powerful tool to study dipole relaxation, electrical conduction, and structure of molecules. Electrode polarization, as a parasitic effect due to the blocking of charge carriers in the vicinity of an electrode, can make the frequency response at low frequency difficult to understand. Since charge carriers in mineral oil are not only generated from dissociation but also from injection at electrodes, current induced by motion of injected charge carriers should also be taken into consideration. The polarization caused by the injection current has been studied in this paper. When the electric field is not intense, the injection current is proportional to the field and only contributes to the imaginary part of the complex permittivity. A new model has been proposed with this injection current being involved. The frequency responses of three different kinds of mineral oils have been measured and this new polarization model has been used to fit the experimental data. According to the simulation result, the frequency-dependent curves of complex dielectric permittivity calculated from the polarization model could fit the experimental data well. The amount of the injected charge carriers increases with the aging time. This new model enables one to gain a better understanding of electrical conduction in mineral oil.

Quantitative Contributions to Electrical Propagation in 1D Cable Model

From previous experimental and theoretical studies, it is well-known that gap junctional coupling, Na+ channel density, and Na+ channel localization influence the speed of electrical conduction velocity (CV) in multicellular cardiac tissue. However, two recent findings complicate our understanding of electrical conduction: (1) Na+ channels located at the intercalated disk region have different properties than those in the cell center; (2) in disease states, changes in gap junctional coupling occur in tandem with alterations in Na+ channel density, Na+ channel properties, and subcellular structure, which makes it difficult to determine the effects of each change. To gain a greater quantitative understanding of the factors that influence CV, we implemented a one-dimensional mathematical model of electrically coupled human ventricular myocytes. The model accounts for the possibility that electrical fields in the narrow clefts between adjacent cells can influence conduction. To determine how each model variable affects CV, we performed parameter sensitivity analysis under two conditions: (1) normal gap junctional conductance (400 kΩ resistance between cells), and (2) severely reduced gap junctional conductance (40 MΩ resistance between cells). Our simulation results predict the following: (1) Increasing the width of the cleft between adjacent cells increases CV under normal gap junctional conductance conditions but decreases CV when gap junctional coupling is low; (2) reducing cell coupling decreases CV under normal gap junctional conductance conditions, but further changes to coupling have little effect under low gap junctional conductance conditions, (3) Na+ channel activation kinetics and voltage dependence have a greater quantitative effect on CV with low than with normal gap junctional conductance. The simulations generate predictions that can be tested experimentally, and the results provide insight into changes in CV observed in disease.

Molecular wires in future nanoelectronics systems

Physical performance limits of microelectronics devices demand a new form of electronics, in which molecules replace semiconductor-based structures. One of these limits is put up by destructive mass transport due to electromigration in nanoscale metallic wires, and the enormous heat generation caused by the extremely high charge density involved in signal transport. We propose a new approach, by which alloying elements in matrix metals are selected on the basis of their chemical valence, in order to improve these properties. Most probably will silicon-based chip technology and molecular electronics be developed in parallel during the next decade. The understanding of electrical conductivity along chemically designed molecular wires is required to that end. An outstanding feature of molecular charge transfer (CT) materials consists of the possibility to influence their properties by means of the coupled structural and electronic change of the molecular state. In the present work, the effect of ligand size on the degree of CT in Zn-Naphtholimines with TCNQ CT-complexes is studied. Incorporating either of H, CH 3, and CH 2CH 3 as aliphatic radical, we found, that a smaller ligand size brings about a stronger degree of CT. Vibration spectroscopy is applied in order to determine transition band frequencies and related shifts with ligand incorporation. The CT is determined from the band-shift of the C≡N stretch mode.

Conduction in RuO2-based thick films†

The dependence of RuO2-glass thick-film electrical conductivity on the concentration of metallic component reveals a metal-insulator transition. Resistance versus temperature characteristics measured in the range 4-2-400 K are presented for a set of seven composites of varying composition. The results obtained can be divided into two groups: composites incorporating ≥:0.12 (per unit volume) of metallic component yield minima of R( T) curves and possess parabola-like shapes, and composites with a small content of metallic component (<0.12) show a negative temperature coefficient of resistance over the whole range of measured temperatures. In the insulating region, data are analysed in terms of various conduction mechanisms, giving rise to an understanding of electrical conduction in RuO2-glass thick resistive films.

Modelling Geomagnetic Variations in or near an Ocean using a Generalized Image Technique

Summary A generalized image technique is described for modelling electromagnetic induction in two-dimensional systems, consisting of a thin (Price-type) ocean overlying a perfect conductor in the mantle. The method constructs a Green’s function for currents in the ocean by conformally mapping the perfect conductor boundary into a straight line. Examples are given that show the effects to be expected at an ocean-continent boundary with isotherms rising under the ocean, and at a mid-ocean rise where the high temperatures are believed to be quite shallow. The object of most magnetic variation and magnetotelluric surveys is an understanding of electrical conductivity at great depth (anywhere from 5 to 1000 km depending on the frequency band). When such studies are made near or in the ocean, the conductivity of the water is great enough to modify the fields and complicate the interpretation of the observations (Parkinson 1959); it is therefore important that theoretical studies be capable of accounting for the presence of the ocean in a realistic fashion. Price (1949) develops an approach to this problem in which the oceans are represented by an infinitesimally thin conducting sheet, with integrated conductance defined by 3 = @y, where cr is the conductivity of the water and y the vertical co-ordinate. With this approximation, 5 is allowed to vary from place to place; included in such variations are the ocean depth, salinity and temperature, of which the first is the most important. Electric currents with a component normal to the ocean surface are ignored, but we feel this is entirely reasonable. Although the ocean itself appears to be adequately described by this representation at frequencies above 2 cycles per hour, the incorporation of realistic upper mantle conductivity structures has proved more problematic. Earlier work on this topic (Roden 1964; Bullard & Parker 1970) employed the method of images, which meant that the mantle conductivity was modelled by a perfect conductor (conductivity infinite) with a horizontal surface. Schmucker’s (1971) technique enables us to deal with arbitrary horizontally layered media and, although this method was developed neglecting the Earth’s curvature and only in two dimensions, neither restriction is essential.$ The obvious way to remove the requirement of horizontal layering in the

A theory of the permanent magnetic field of the Sun and Earth

In this paper (published in full in Phys. Rev., v. 34, 335–343, 1929) the motions of electrons executing short free‐paths under the influence of thermal agitation in an inhomogeneous magnetic field or in crossed electric and magnetic fields is shown to give rise to electric current‐systems. Gravitational separation of charge produces a symmetrical radial electric field inside the Earth and Sun. This radially symmetrical electric field and a small initial symmetrical inhomogeneous magnetic field give rise to current‐systems which are in such a direction as to increase the original magnetic field and regeneration takes place. The field is limited by some mechanism which is not understood. The permanent fields arise from the thermal energy of the body and would be maintained even if the bodies ceased their rotation. In order to account quantitatively for the observed current‐system it is necessary that the electron mean free‐path inside the Earth approximate 10−7 cm. The theory emphasizes the necessity for a better understanding of electrical conduction in solids; in particular a more satisfactory theory of the Hall effect is desirable.