Showing papers on "Conductivity published in 1979"
TL;DR: In this paper, an examination of the conduction processes in semiconducting oxide glasses confirms the applicability of the polaronic hopping model of electrical transport, and some deviation from Mott's theory are observed in phase-separated glasses.
Abstract: Studies of the electrical conductivity of semiconducting oxide glasses are reviewed in the framework of Mott's theory for such materials. An examination of the conduction processes in semiconducting oxide glasses confirms the applicability of the polaronic hopping model of electrical transport. Some deviation from Mott's theory are observed in phase-separated glasses. The thermal activation energy for conduction appears to be the dominating factor which controls conductivity, although in many cases the pre-exponential factor also has a great influence on conductivity. The diffusion-like conduction mechanism in a system of randomly distributed ions is probably not applicable to glasses that exhibit some kind of order in the structure, such as clustering.
422 citations
TL;DR: In this article, the electrical conductivity of cuprous chloride containing a dispersion of fine alumina particles was studied as a function of volume fraction (0.212) and particle size ( 0.3 and 0.06 μm initial particle size).
Abstract: The electrical conductivity of cuprous chloride containing a dispersion of fine alumina particles was studied as a function of volume fraction (0–0.212) and particle size (0.3 and 0.06 μm initial particle size). At low temperatures the ionic conductivity may be increased by as much as two orders of magnitude. The enhanced conductivity, Δσ, was proportional to the surface area of the added alumina. Both these data and the earlier data of Liang (1) were fitted to a relation, where is the radius of the alumina dispersoids and the volume fraction.
247 citations
Journal Article•
236 citations
TL;DR: Empirical equations are given to summarise the dielectric properties of 'average' brain tissue at 37 degrees C for future theoretical studies of microwave absorption in the head.
Abstract: Dielectric permittivity and conductivity are reported for grey and white matter from dog brain tissue between 0.01 and 10 GHz. Between 0.01 and approximately 1 GHz, the permittivity decreases and conductivity increases as a power law of frequency. Above 1 GHz, the conductivity increases quadratically with frequency due to dipolar reorientation of free water molecules in tissue; the apparent rotational relaxation frequency at 37 degrees C is 21--25 GHz, slightly below the 25 GHz characteristic frequency of pure water at that temperature. The microwave data are analysed using the Maxwell mixture theory applicable for a suspension of nonconducting, low permittivity spheres in bulk water. From the increase in conductivity above 1 GHz, and the tissue permittivity at 2--4 GHz, the apparent volume fraction of water is approximately 0.70 and 0.55 for grey and white matter, respectively, about 10--15% lower than respective values from the literature. This discrepancy is apparently due to a small fraction of water which does not contribute to the tissue permittivity above 1 GHz. Empirical equations are given to summarise the dielectric properties of 'average' brain tissue at 37 degrees C for future theoretical studies of microwave absorption in the head.
155 citations
141 citations
TL;DR: In this article, the dielectric constant epsilon e or the conductivity sigma e of a two-phase composite is calculated for a simple cubic array of identical spherical inclusions embedded in a homogeneous host.
Abstract: New methods are described for calculating the dielectric constant epsilon e or the conductivity sigma e of a two-phase composite and these are applied to a simple cubic array of identical spherical inclusions embedded in a homogeneous host. A spectral representation is derived for epsilon e, and numerical results are presented for the poles and the residues. Analytical and numerical methods are used to discuss the conductivity threshold of the cubic array, which occurs when the host is an insulator and the conducting spheres begin to touch each other. It is argued that sigma e as a function of sigma 1/ sigma 2 has an essential singularity at the conductivity threshold.
137 citations
TL;DR: In this paper, a Grotthus-type mechanism of conduction is proposed which involves intermolecular transfer steps (hopping) and inter-parallel transfer steps in comparable numbers, the former facilitated by the high concentration of H 3 O + ions in the structure, and the latter most likely facilitated by high H-bond vacancies.
132 citations
TL;DR: In this paper, a class of partial melt distributions is considered where melt forms is one place and accumulates elsewhere; a case modelled by a simple modification of Archie's Law for porous media.
Abstract: The presence of partial melt can profoundly affect the bulk electrical properties of composite materials. A class of melt distributions is considered where melt distributions is considered where melt forms is one place and accumulates elsewhere; a case modelled by a simple modification of Archie's Law for porous media. This relation provides values for the bulk conductivity intermediate to those for a thoroughly connected melt distribution and those for isolated melt pockets. Thus, if melt is tortously distributed, larger amounts are required to produce a given increase of the bulk conductivity, than if it is thoroughly interconnected along grain boundaries.
129 citations
TL;DR: In this paper, the authors measured the electrical conductivity of microemulsions water in oil containing cyclohexan, sodium dodecyl sulphate (SDS), and 1 pentanol.
Abstract: 2014 The electrical conductivity G of water in oil microemulsions may be described by percolation models [1] : below a critical water concentration Oc, G seems to diverge as (Oc O)-S’, while for O > Oc G increases as (O Oc)-T’. This physical situation may be called stirred percolation, referring to the Brownian motion of the medium. The exponents S’ and T’ are a priori different from the corresponding S and T in the classical situation of frozen percolation. A simple model of stirred percolation accounts fairly well for the measured value of S’ = 1.2 ± 0.1 while the accepted value for S is 0.7. The exponent T’ (1.4 to 1.6 in our experimental case) is less significant of the difference between stirred and frozen percolation : the values for S’ should be about 1.8 and the value accepted for S should be about 1.6. LE JOURNAL DE PHYSIQUE LETTRES TOME 40, 15 JUILLET 1979, Classification Physics Abstracts 05.50 61.25 72.80 82.70 1. Electrical conductivity of microemulsions. We measured the electrical conductivity of ’ microemulsions water in oil containing cyclohexan, sodium dodecyl sulphate (SDS) and 1 pentanol. The conductivity is extremely sensitive both to temperature and composition. The following procedure allowed a reproducibility of a few percent : a) all the components, except a small quantity of alcohol, are introduced in the conductivity cell, the temperature of which is fixed at 20 °C ± 0.1 oC, b) the alcohol is added slowly while the conductivity is measured, c) a maximum of conductivity is reached when the mixing clears up to make a microemulsion. This value is the conductivity of the microemulsion containing the minimum of alcohol which provides stability. A suitable dilution procedure allows 0 to be varied while the structure of droplets remains fixed [2]. La version francaise sera publiee dans le n° 20 des C.R.A.S., I serie B, du 28 mai 1979. We studied two different types of microemulsions characterized by a volumic ratio, soap to water, in the droplets : The conductivity increases steeply (five orders of magnitude) around a critical concentration fjJc’ The variation above fjJc allows an independent determination of T and ~~ : G 1~T~ ~ (~ 2013 Pc) is linear in ~ and tends to zero at ~=~. The plot of G l/x for different values of x has opposite concavities when T is greater or smaller than T’ (Fig. 1). The results for the three types of microemulsions are presented in table I. When the water concentration is very low (fjJ 0.01) the conductivity is linear in ~, in agreement with a conduction mechanism involving the migration , of charged droplets [1]. The percolation contribution to G is thus obtained by Gp ~ G’/~. Figure 2 presents Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyslet:019790040014033100 L-332 JOURNAL DE PHYSIQUE LETTRES Fig. 1. Determination of the exponent T’ and of the critical water concentration ~~, for 0 > 0, : G l/x is plotted for various x values as a function of ~. Table I. Exponents T’ and S’ measured for microemulsions of different soap/water ratios. Microemulsion A B
116 citations
TL;DR: In this paper, an alternative to the steady heating of a cylindrical probe, in the needle-probe method of conductivity measurement, is the observation of the thermal decay from a short, calibrated, heat pulse.
Abstract: Summary. An alternative to the steady heating of a cylindrical probe, in the ‘needle-probe’ method of conductivity measurement, is the observation of the thermal decay from a short, calibrated, heat pulse. The theoretical solution is the time-differential of that for the former method, and requires only the measurement of point temperatures rather than the determination of a gradient. A careful analysis of the theoretical decay function shows that it should be possible to make accurate conductivity measurements in as little as three probe ‘time constants’ if external information is available on the heat capacity of the medium. A self-contained method, using two temperature determinations from a record about six time-constants long, can be used where such information is not available. The theory was tested by measurements on the ocean-floor, and the data correspond to the theory when a correction was applied for some internal probe conduction problems.
108 citations
TL;DR: In this article, a detailed study of the effects of temperature and hydrostatic pressure on the ionic conductivity of PbF 2 in both the cubic (Fm3m-O h 5 ) and orthorhombic (Pmnb-V 2 h 16 ) phases was performed with some emphasis on the changes in conductivity accompanying the transition between two phases.
TL;DR: In this article, Li 3 N is presented as one of the best solid lithium electrolytes available today and its outstanding advantages are simple preparation of crystalline as well as sintered material, stability in moist atmosphere because of a protecting surface layer, stability with elemental lithium metal up to its melting point of 813°C, high Li-ion conductivity of the order of 10 −3 Ω −1 cm −1 at ambient temperature with negligible partial electronic conductivity, and a high decomposition voltage due to a strong kinetic hindrance of the decomposition reaction.
TL;DR: In this article, a new high copper ion conductivity solid electrolyte has been found in the system and powder x-ray diffraction analysis indicates that the crystal structure of is simple cubic with.
Abstract: A new high copper ion conductivity solid electrolyte has been found in the system. This compound has a copper ion conductivity of 0.34 (Ω‐cm)−1 at 25°C, and activation energies for conduction of 7.0 kJ/mole between 130°C and −25°C, and 19 kJ/mole between −25°C and −140°C, respectively. Powder x‐ray diffraction analysis indicates that the crystal structure of is simple cubic with .
TL;DR: The health hazards of NMR imaging are not likely to become important if the RF power densities are less than 10 mW/cm2, static magnetic fields were less than 0.3 tesla and the temporal variation of fields is less than 3 T/sec.
Abstract: The health hazards of NMR imaging are not likely to become important if the RF power densities are less than 10 mW/cm2, static magnetic fields are less than 0.3 tesla and the temporal variation of fields is less than 3 T/sec.
TL;DR: In this article, a concentration cell based on the Nernst equation was proposed for monitoring SO#SOs pollution in air and in combination with an oxygen probe can be used for the determination of SO=/SOs concentrations in coal combustion reactors, for the evaluation of the partial pressure of $2 in coal gasification systems, and for emission control in nonferrous smelters using sulfide ores.
Abstract: Conductivity measurements as a function of temperature and partial pressures of SOs, SO2, and O2, and transference experiments indicate that the transport number of Na + ions is unity in Na2SO4-I. A concentration cell based
on this electrolyte Pt, O2' + SO2' + SOs'/Na2SO4-I/SOa" + SO~" + O~", Pt produces emf's that are in agreement with those calculated from the Nernst equation when equilibrium is assumed between the gas species at the electrodes.
The cell can be used for monitoring the SO#SOs pollution in air, and in combination with an oxygen probe can be used for the determination of SO=/SOs concentrations in coal combustion reactors, for the evaluation of the partial pressure of $2 in coal gasification systems, and for emission control in nonferrous smelters using sulfide ores. The probe is similar to that developed recently by Gauthier et aL (4, 5) using K=SO4 as the electrolyte, but can operate
at higher pressures of SO3. Because of the greater polarizing power of the Na+ ion compared to the K + ion, Na2S207 is less stable and can be formed only at a considerably higher pressure of S03 than that required for K~20~.
TL;DR: In this article, the authors extend Landauer's effective medium model to see if the observations are consistent with a high conductivity layer forming on each non-conducting particle, provided one assumes the layer a few hundred Angstroms thick.
Patent•
07 May 1979TL;DR: In this article, a fracturing and acidization method for increasing the productivity of relatively hard acid-soluble formations about a perforated well, comprising the steps of producing a formation fracture containing a viscous fluid and propping agent, was proposed.
Abstract: A fracturing and acidization method for increasing the productivity of relatively hard acid-soluble formations about a perforated well, comprising the steps of producing a formation fracture containing a viscous fluid and propping agent; injecting an acid solution having a viscosity value fifty times less than the contained viscous fluid into the fluid filled fracture, thereby forming etched channels in the fracture walls and displacing the propping agent from such channels; and lowering the fluid pressure in the fracture to allow the walls thereof to become displaced towards a closing position until held open by the propping agent. Channels so formed have a greater width than can be formed by conventional techniques and consequently substantially increase the productivity of such formations.
TL;DR: In this article, an approximation for the dynamical conductivity of a non-interacting fermion gas moving at zero temperature in a three-dimensional random potential, which exhibits a nonlinear feedback of the density fluctuation spectrum to the frequency-dependent current relaxation rate, was derived.
Abstract: An approximation scheme is derived for the dynamical conductivity of a non-interacting fermion gas moving at zero temperature in a three-dimensional random potential, which exhibits a non-linear feedback of the fermion density fluctuation spectrum to the frequency-dependent current relaxation rate The approximation equations describe an insulator-conductor phase transition caused by strong memory effects and important non-localities in the equations for the current relaxation Close to the transition point the dynamical conductivity obeys a scaling law with a scaling function which is a solution of an algebraic equation The main features of the conductivity in the transition regime are a divergence of the insulator polarisability and a continuous decrease of the conductor DC mobility towards a zero at the transition point, a critical slowing down of the current spectrum, a semiconductor-like excitation threshold of the insulator and a strong non-Drudian frequency of the dynamical conductivity
TL;DR: In this article, a novel conduction mechanism was suggested for such a solid system with both conjugated double bonds and extended hydrogen bonds, which was proved both by spectroscopic detection of the hydrogen molecules evolved from d.c. electrolysis of pressed pellets of the powder specimen and by observation of the anomalous increase (three orders of magnitude) of the electric conductivity as an effect of 103 Pa of H2O or D2O vapor on the dehydrated specimen in an evacuated conductivity cell.
Abstract: In a family of catena-μ-N,N′-disubstituted dithiooxamidocopper(II) complexes which have been assumed as two-dimensional coordination polymers, one complex with HOC2H4- substituents is an electronic conductor as well as others, and also a protonic conductor uniquely. The latter property was proved both by spectroscopic detection of the hydrogen molecules evolved from d.c. electrolysis of pressed pellets of the powder specimen and by observation of the anomalous increase (three orders of magnitude) of the electric conductivity as an effect of 103 Pa of H2O or D2O vapor on the dehydrated specimen in an evacuated conductivity cell. A novel conduction mechanism was suggested for such a solid system with both conjugated double bonds and extended hydrogen bonds.
Patent•
28 Mar 1979
TL;DR: An electrodeless conductivity measuring system of the type employing a spaced pair of toroidal ferromagnetic cores, in which anomalies in the permeance of the cores are alleviated by the use of non-permeable shields of conductive material, is described in this paper.
Abstract: An electrodeless conductivity measuring system of the type employing a spaced pair of toroidal ferromagnetic cores, in which anomalies in the permeance of the cores is alleviated by the use of non-permeable shields of conductive material.
Patent•
15 Jun 1979TL;DR: In this article, a method for obtaining measurements dependent upon the vertical conductivity component of formations surrounding a borehole is presented. But the method is not suitable for the measurement of the formation horizontal conductivity.
Abstract: The invention is directed to induction logging apparatus and method for obtaining measurements dependent upon the vertical conductivity component of formations surrounding a borehole. The disclosed techniques can also be used to determine horizontal as well as vertical conductivity of the formations, and thereby achieve determination of formation anisotropy. A transmitter coil is provided with its axis substantially perpendicular to the borehole axis. A receiver coil is provided in spaced relation to the transmitter coil. The axis of the receiver coil is also substantially perpendicular to the borehole axis, and is preferably parallel to the axis of the transmitter coil. Means are provided for detecting signals induced in the receiver coil, these signals being a measure of the formation vertical conductivity. In a preferred embodiment of the invention, the detecting means is operative to detect both the resistive and reactive components of the signals induced in the receiver coils. Indications of formation vertical conductivity are obtained by combining the detected resistive and reactive components. In a further form of the invention, the formation horizontal conductivity can also be obtained from the detected resistive and reactive components. Alternatively, horizontal conductivity may be determined using a pair of spaced coils having a common axis aligned with the borehole axis.
TL;DR: In the solid state, NaMgF3 transforms smoothly with temperature into a solid electrolyte phase; the conductivity is 130 siemens per meter just below the melting point; the isostructural compound MgSiO3 should behave similarly under conditions obtaining in the earth's lower mantle, and so it is expected that the electrical conductivity in that region is ionic rather than electronic.
Abstract: In the solid state, NaMgF(3) transforms smoothly with temperature into a solid electrolyte phase; the conductivity is 130 siemens per meter just below the melting point. The isostructural compound MgSiO(3) should behave similarly under conditions obtaining in the earth's lower mantle, and so it is expected that the electrical conductivity in that region is ionic rather than electronic.
TL;DR: In this paper, a model of a new type of the Wigner lattice formation was proposed and anomalous properties of SmB6 were explained within this model, and the usual hopping type conductivity changes to a constant value without activation.
Abstract: Specific heat and transport properties are measured on good single crystals of SmB6. The specific heat experiment indicates that there is a gap of near 100 K in the 4f system leaving a very small T linear term. Conductivity experiment indicates that the usual hopping type conductivity changes to a constant value without activation which is, however, three orders of magnitude smaller than the so far believed minimum metallic conductivity. The usual Anderson localization proposed before by us is clearly not applicable. Here, we propose a model of a new type of the Wigner lattice formation. Various anomalous properties mentioned above are explained within this model.
TL;DR: For a variety of doped amorphous Si films (glow discharge and evaporated films doped p-type and n-type with substitutional and interstitial donors) it was shown that the transport mechanism in all cases is similar as discussed by the authors.
TL;DR: In this paper, tracer diffusion and ionic conductivity were measured on the same single crystals of sodium beta-alumina of composition 1.23 Na20.11 Al2O3.
TL;DR: In this article, an important drop in the longitudinal conductivity of TTF-TCNQ occurring at constant temperature in the metallic phase and in a narrow pressure domain located around 19 kbar was reported.
Abstract: We report an important drop in the longitudinal conductivity of TTF-TCNQ occurring at constant temperature in the metallic phase and in a narrow pressure domain located around 19 kbar. The drop of conductivity has been related to a \ifmmode\times\else\texttimes\fi{} 3 commensurability of the longitudinal distortion with the lattice. This experiment, together with x-ray diffuse scattering of TTF-TCNQ could suggest that a significant fraction of the metallic conductivity below ambient temperature is due to the fluctuating collective mode.
TL;DR: In this paper, the glass phases showing high ionic conductivity at room temperature were prepared through a rapid quenching of the molten mixtures of the system AgIAg2OB2O3 (a fixed Ag2O/B 2O3 = 1 molar ratio was always considered): the obtained specimens were homogeneous and transparent cylindrical blocks.
TL;DR: In this paper, the influence of argon partial pressure pAr on the photoconductivity, four-probe conductivity and photoluminescence of rf−sputtered a−Si-H alloys was reported.
Abstract: We report the influence of argon partial pressure pAr on the photoconductivity, four‐probe conductivity and photoluminescence of rf‐sputtered a‐Si–H alloys. As pAr is increased from 5 to 30 mTorr, for fixed hydrogen partial pressure pH, photoconductivity increases by as much as three orders of magnitude and then saturates. Over this range the dark conductivity activation energy decreases, a plot of log conductivity versus inverse temperature becomes increasingly less linear and the photoluminescence intensity increases slightly and then drops back. We note that high pAr films become slowly contaminated upon exposure to air. These results are interpreted in terms of a reduction in energetic silicon atom bombardment of the growing film with increased pAr. For our sputtering arrangement, we show that silicon atoms ejected from the target become significantly more thermalized at pAr=10 mTorr than at 5 mTorr. Based primarily on the fact that the conductivity activation energy is more strongly dependent on pH f...
TL;DR: In this article, the frequency and temperature dependence of the ac conductivity of anthracene carbons are explained within two theoretical models, where the current flow is due to electron hops over a potential barrier between localized sites.
Abstract: The frequency (10-10 8 Hz) and temperature (100–400 K) dependence of the ac conductivity of anthracene carbons is explained within two theoretical models. The properties of carbon heat treated up to 600°C are correctly explained by means of a model where the current flow is due to electron hops over a potential barrier between localized sites. The conductivity of the carbon heat-treated up to 650°C is interpreted using a theory proposed by Mott and Davis. The spatial densities of states are determined in both cases.
TL;DR: In this paper, an iterative solution of the path-variable formulation of the Boltzmann transport equation is used to calculate the transport of electrons at high electric fields in SiO2.
Abstract: The transport of electrons at high electric fields in SiO2 has been calculated using an iterative solution of the path‐variable formulation of the Boltzmann transport equation. Scattering due to the polar‐optical modes and acoustic modes of the lattice are included. It is found that both the 0.153‐ and 0.063‐eV polar‐optical modes are important for scattering electrons. The electron velocity ’’saturates’’ near 1.9×107 V/cm for fields below 5×106 V/cm. The calculated curves are in excellent agreement with experimental data and indicate a best estimate of the polaron‐corrected conductivity mass of 1.3m0. Above 5×106 V/cm, the electric field induced modifications of the carrier scattering rates cause the velocity to rise sharply. Time‐resolved polar runaway is observed with an absolute threshold in the field range of (7–8) ×106 V/cm, with the runaway field increasing for short times, as may be appropriate for transport through thin oxides. Impact ionization is governed by the polar runaway, and carrier gener...