Showing papers on "Conductivity published in 1976"
TL;DR: In this article, the metal-non-metal transition takes place when the volume fraction of the metallic phase approaches the percolation threshold, and it is shown that the static dielectric constant diverges near the threshold.
Abstract: A system consisting of randomly distributed metallic and dielectric regions is considered. The metal-non-metal transition takes place when the volume fraction of the metallic phase approaches the percolation threshold. It is shown that the static dielectric constant diverges near the threshold. Critical indexes are introduced which describe the behaviour of the conductivity and the dielectric constant near the threshold as functions of the volume fraction and frequency. The case of non-zero dc conductivity of dielectric regions is considered also. It is shown that all indexes describing the critical behaviour of complex conductivity can be expressed by two indexes which are known from computer and model experiments. The results of computer calculations of Webman et al. are analysed.
719 citations
TL;DR: In this paper, the authors used a simple capillary model, which assumes that liquid phase and surface conductivities (via exchangeable cations) behave as resistors in parallel, and calculated the values of ECa for each ECw equilibration from measured four-electrode resistances and an appropriate cell constant.
Abstract: Recent research has demonstrated that field soil salinity can be inferred from four-electrode soil electrical conductivity (ECa), if the soil profile is near "field capacity" and calibration curves, based on saturation extract salinity (ECe), are available. To extend the use of this field method to arbitrary water contents, we studied EC in the laboratory as a function of water content and in situ soil water conductivity (ECw). We collected undisturbed cores of four soil types (fsl, vfsl, 1, cl) using Lucite column inserts, which were tapped for later insertion of electrodes. The cells were equilibrated with waters of a desired EC,r and, using a pressure membrane apparatus, adjusted to a desired Values of ECa were calculated for each ECW equilibration from measured four-electrode resistances and an appropriate cell constant. Our results indicated that over the -range of practical concern, ECa = (transmission coefficient) x x ECw + surface conductivity. This relationship is derived using a simple capillary model, which assumes that liquid phase and surface conductivities (via exchangeable cations) behave as resistors in parallel. Additional Index Words: soil electrical conductivity, soil salinity, surface conductance. View complete article To view this complete article, insert Disc 3 then click button8
649 citations
198 citations
TL;DR: In this article, an energy band model of amorphous GexSe1-x films has been proposed for consistent explanations of experimental data, and measurements of the photoconductivity and the absorption spectra have been made at room temperature.
Abstract: Measurements of electrical and optical properties have been made on GexSe1-x amorphous thin films of about 1 µm thickness. From the experiment of electrical conductivity at various temperatures, two processes of the d.c. conductivity in GexSe1-x films are observed in plots of ln σ against 1/T. The thermoelectric power exhibits a maximum value of p-type conduction at pure Se and a change of the sign from positive to negative at 0.4
165 citations
TL;DR: For a homogeneous membrane system, absolute reaction rate theory was used to develop a surface-limited permeation model that includes the resistance to the flow of water not only through the interior region of the membrane but also across possible rate-limiting barriers at the solution-membrane interfaces.
158 citations
TL;DR: In this paper, the b-axis conductivity of polymeric sulfur nitride (SN) x from 4.2-300K was measured for samples having different polymerization times and a general increase in the conductivity was found with longer polymerisation times leading to room temperature conductivities 1200 −3700 (Ω-cm) −1 and resistance ratios 50 −205.
139 citations
TL;DR: In this paper, a displaced Maxwellian approximation for the electron distribution function was used to calculate the hot electron microwave conductivity of the wide bandgap semiconductors GaN, SiC and Diamond.
Abstract: Hot electron microwave conductivity of the wide bandgap semiconductors GaN, SiC and Diamond has been calculated using displaced Maxwellian approximation for the electron distribution function. The effects of both the energy and momentum relaxation times due to scattering by acoustical, optical intervalley phonons and by ionized impurities are included in the derivations. Numerical results for the microwave conductivity and the change in dielectric constant as a function of frequency and bias electric field are presented. It is found that significant change in the conductivity and dielectric constant contribution for a fixed bias field occurs at very high frequencies on the order of 10 12 Hz, which is well beyond the range of current microwave device interest.
137 citations
TL;DR: In this article, it is suggested that in chalcogenide glasses, elements such as Cu or Mn can have coordination number 4 and be negatively charged, and that the compensating positive charge is provided by D+ centres.
Abstract: It is suggested that in chalcogenide glasses, elements such as Cu or Mn can have coordination number 4 and be negatively charged, and that the compensating positive charge is provided by D+ centres. The law of mass action ensures that the concentration of D-centres is then small. Under these conditions the Fermi energy is no longer pinned and the activation energy for conduction is shown to be decreased by 1/3. Similar considerations are applied to the effect of O, Cl and K on the conductivity of amorphous Se.
133 citations
TL;DR: Dielectric measurements were made on suspensions of intact yeast cells over a frequency range of 10 kHz to 100 MHz and the relatively low dielectric constant of about 50 obtained for the cell interior, in comparison with values of aqueous solutions, may be attributed also to the presence of intracellular organelles and proteins.
Abstract: Dielectric measurements were made on suspensions of intact yeast cells over a frequency range of 10 kHz to 100 MHz. The suspensions showed typical dielectric dispersions, which are considered to be caused by the presence of cytoplasmic membranes with sufficiently low conductivity. Since the conductivity of the cell wall was found to be of nearly the same value as that of the suspending medium, composed of KCl solutions in a range from 10 to 80mm, the cell wall may be ignored in establishing an electrical model of the cells suspended in such media. An analysis of the dielectric data was carried out by use of Pauly and Schwan's theory. The membrane capacitance was estimated to be 1.1±0.1 μF/cm2, which is compared with values reported so far for most biological membranes. The conductivity of the cell interior was almost unchanged with varying KCl concentrations and showed low values owing to the presence of less conducting particles, presumably intracellular organelles. The relatively low dielectric constant of about 50 obtained for the cell interior, in comparison with values of aqueous solutions, may be attributed also to the presence of intracellular organelles and proteins.
128 citations
TL;DR: In this article, the phase of the charge density wave in the Peierls-Frohlich state in the presence of impurity scattering has been analyzed and the frequency dependence of the electrical conductivity, σ(ω), is calculated at T = 0 K for weak pinning forces.
Abstract: The equation is derived which describes the dynamics of the phase of the charge density wave in the Peierls-Frohlich state in the presence of the impurity scattering. By use of the correlation function of the phase, the frequency dependence of the electrical conductivity, σ(ω), is calculated at T =0 K for the case of weak pinning forces. It is found that σ(ω) has a pronounced peak at a finite ω and that the theoretical results. If ω is replaced by ( T - T p ) where T p is the transition temperature the results are reminiscent of the conductivity in the region of fluctuations.
124 citations
TL;DR: In this article, the gallium ion vacancies are the mobile point defects in β -Ga 2 O 3 single crystals in the temperature range 300-1250 K and up to about 900 K.
TL;DR: In this paper, the electrical conductivity of fluidized beds has been extended to cover the full range of conductivity ratio of the two phases, α and a wide range of dispersed phase volume fraction, f.
TL;DR: In this article, the ionic conductivity of polycrystalline lithium nitride has been determined using ac techniques and complex plane analysis, showing that this material may be an interesting lithium-conducting solid electrolyte.
TL;DR: In this article, the authors modeled the interface between two miscible fluids which have identical mechanical properties but disparate electrical conductivities and are stressed by an equilibrium tangential electric field, and derived over-stable (propagating) modes in terms of the complex growth rate and fastest growing wavenumber.
Abstract: The interface between two miscible fluids which have identical mechanical properties but disparate electrical conductivities and are stressed by an equilibrium tangential electric field is studied experimentally and theoretically. A bulk-coupled electrohydrodynamic instability associated with the diffusive distribution of fluid conductivity at the interface is experimentally observed.The configuration is modelled using a layer of exponentially varying conductivity spliced on each surface to a constant-conductivity fluid half-space. Over-stable (propagating) modes are discovered and characterized in terms of the complex growth rate and fastest growing wavenumber, with the conductivity ratio and an inertia-viscosity time-constant ratio as parameters. In the low inertia limit, growth rates are governed by the electric-viscous time τ = η/eE2. Instability is found also with the layer of varying conductivity bounded by rigid equipotential walls. A physical mechanism leading to theoretically determined fluid streamlines in the form of propagating cells is described.At relatively high electric fields, large-scale mixing of the fluid components is observed. Photocell measurements of distributions of average fluid properties demonstrate evolution in time on a scale determined by τ.
TL;DR: In the absence of suitable material on which to make thermal conductivity measurements, it is still possible to compute a value on the basis of an idealized model by the use of appropriate correction factors obtainable from data already in the literature.
Abstract: In the absence of suitable material on which to make thermal conductivity measurements, it is still possible to compute a value on the basis of an idealized model. The Maxwell model for the thermal conductivity of a two-component material, a model which has frequently been successfully used for relatively small values of porosity (<0.1) and moderate conductivity ratios (<10), may be extended to much wider ranges of these parameters (0.3 and 300, respectively) by the use of appropriate correction factors obtainable from data already in the literature. Significant errors due to overlooking a thermal contact resistance have been detected in some experimental work. The errors can be as high as 50 percent in the measured value for an air-filled sandstone of 0.2 porosity. Unless corrected, such errors can contribute a great deal to the lack of agreement between computed and experimental values. Correction for these errors also leads to much better consistency among published experimental values measured with various techniques. Conductivity values accurate to better than 15 percent may therefore be predicted for specimens saturated with low conductivity fluids such as air, steam, or oil.
Alcatel-Lucent1, University of Chicago2, Clemson University3, Rochester Institute of Technology4, Cleveland State University5, DuPont6, University of Illinois at Urbana–Champaign7, IBM8, Johns Hopkins University9, American Cyanamid10, Monsanto11, National Institute of Standards and Technology12, University of Texas at Dallas13, Oak Ridge National Laboratory14, Université Paris-Saclay15
TL;DR: In this article, TTF-TCNQ was measured along the $b$ axis of tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TTE) to provide a comprehensive summary including approximately 600 samples studied at 18 different laboratories.
Abstract: New measurements of electrical conductivity along the $b$ axis of tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ) are combined with published results to provide a comprehensive summary including approximately 600 samples studied at 18 different laboratories The magnitudes of these measured conductivities do not necessitate the assumption of superconducting fluctuations or any other collective state in which the conductivity exceeds the limitations of single-particle scattering Since an adequate theory of the limitations of single-particle scattering for TTF-TCNQ does not exist at present, experiment alone does not rule out the possibility that collective effects may somewhat enhance or suppress the conductivity
TL;DR: In this article, a more detailed examination of two specimens of manganese dioxide showed a semilogarithmic relation between thermoelectric voltage and d.c. conductivity.
Abstract: Measurements of the d.c. conductivity of different types ofγ-manganese dioxide formed under various conditions and of different thermal history indicate a correlation with the combined water content. The specific conductivity increases exponentially as the water content decreases. The values obtained with anhydrous products which then are transformed to aβ-manganese dioxide are similar to those obtained withβ-manganese dioxide prepared by pyrolysis of manganous nitrate. Any effect which might be attributed to the lattice transformation ofγ- intoβ-manganese dioxide could not be observed. A more detailed examination of two specimens of manganese dioxide shows a semilogarithmic relation between thermoelectric voltage and d.c. conductivity. This relationship allows an estimate to be made of the electron concentration at which the electron gas would begin to degenerate. Hence it follows that both forγ- andβ- manganese dioxide the concentration of the conducting electrons is far below the degeneration limit. This result is in agreement with the measured activation energies of the conductivity. It is suggested that the water content influences the electronic band structure by successively deforming the rutile structure ofβ-manganese dioxide and hence the manganese-manganese distances within the lattice.
TL;DR: In this article, it was shown that the power absorbed by a thin semiconductor slice in an oscillating magnetic field is accurately proportional to the material conductivity, and the magnitude of this power absorption can be used to determine the conductivity by coupling the semiconductor to an amplitude-stabilized marginal oscillator and noting the power needed to maintain the demanded level of oscillation.
Abstract: It is shown that, under suitable conditions, the power absorbed by a thin semiconductor slice in an oscillating magnetic field is accurately proportional to the material conductivity. The magnitude of this power absorption can be used to determine the conductivity by coupling the semiconductor to an amplitude‐stabilized marginal oscillator and noting the power needed to maintain the demanded level of oscillation. Instruments of this type have been constructed exhibiting ∼1% linearity over a 100:1 range of sample conductivity, a resolution of ∼1 in 104 and a limiting sensitivity of ∼10−5 mho/⧠. The method may be applied to the measurement of essentially any conducting material from semiconductors to metals.
TL;DR: The electrical conduction in various phases of the system was investigated by measurement of a-c conductivity and the EMF of oxygen gas concentration cell and observation of X-ray diffraction patterns.
TL;DR: In this article, the authors measured the transverse magnetoconductivity σxx and Hall effect in n-type inversion layers of Si(100) MOSFET for various source-drain fields between 0.08 and 40 V/cm under magnetic fields up to 150 kOe at 1.4 K.
TL;DR: In this article, the ionic conductivity for a solid in which the ions are undergoing an order-disorder phase transition is calculated for a lattice gas with a weak hopping term.
Abstract: The ionic conductivity is calculated for a solid in which the ions are undergoing an order-disorder phase transition. The interacting ion system is described by a lattice gas with a weak hopping term. Exact results are obtained in one and two dimensions by using the exact results known for the Ising model. The calculated theoretical conductivity agrees very well with the temperature dependence found experimentally.
TL;DR: The electrical conductivity of fluid selenium has been measured as a function of temperature and pressure to 1750°C and 1200 bars, respectively, and the conductivity isobars exhibit strong increases to nearly-metallic behaviour in the pressure range investigated in this article.
Abstract: The electrical conductivity of fluid selenium has been measured as a function of temperature and pressure to 1750°C and 1200 bars, respectively. The conductivity isobars exhibit strong increases to nearly-metallic behaviour in selenium above 1300°C at supercritical pressures. As the fluid is heated above 1500-1600°C the conductivity isobars drop sharply toward more insulating behaviour in the pressure range investigated here.
TL;DR: In this article, the authors measured the conductivities of Li4SiO4 and its solid solutions with Li4GeO4 over a wide frequency range to separate clearly the effects of electrode polarization, conductance relaxations, etc., and to obtain true “dc” conductivities.
Abstract: Conductivity was measured for Li4SiO4 and its solid solutions with Li4GeO4 over a wide frequency range to separate clearly the effects of electrode polarization, conductance relaxations, etc., and to obtain true “dc” conductivities. The conductivities of all the electrolytes are markedly temperature-dependent, ranging from 10−8 to 10−10Ω−1 cm−1 at 100°C to 10−2 to 1010Ω−1 cm−1 at 700°C. For solid solutions with the Li4GeO4 structure, conductivities fit the Arrhenius equation over a wide temperature range, but at higher temperatures a change in activation energy occurs, corresponding to a first-order phase transition. In contrast, solid solutions with the Li4SiO4 structure show changes in activation energy which do not correspond to phase transitions, but which appear to indicate changes in the conduction mechanism.
TL;DR: The thermal conductivity of composites made from epoxy-resin Epikote 828 with metal-powder fillers has been measured from 1.7 to 300K as mentioned in this paper.
Abstract: The thermal conductivity of composites made from epoxy-resin Epikote 828 with metal-powder fillers has been measured from 1.7 to 300K. The metals were Cu, Ag, Au, Al, Sn, Pb, stainless steel and bronze, and in almost all cases the particles were spherical or rounded. At 20K and above the thermal conductivity is independent of the particle size and is in good agreement with the relation of Meredith and Tobias (1960) (extension of Rayleigh's theory). Below 20K the thermal conductivity of the composite is lower than predicted by the theory especially for specimens containing smaller particles, and it can even be less than that of the unfilled resin. This is due to an acoustic mismatch of the phonons at the resin-particle interfaces. An effective particle conductivity which takes account of this mismatch can be computed, which when incorporated into the theory leads to reasonable agreement with experiment.
TL;DR: In this paper, the problem of the prediction of the effective electrical conductivity of a polycrystal from the electrical conductivities of a single crystal is considered and it is shown that the familiar Voigt-Reuss bounds on the behavior of polycrystals are the very best generally valid bounds that have thus far been proposed and that the various methods that are claimed to predict exact effective conductivity (or narrow bounds) all include implicit restrictions on the internal geometry of the poly-crystal.
Abstract: The problem of the prediction of the effective electrical conductivity of a polycrystal from the electrical conductivity of a single crystal is considered. It is shown that the familiar Voigt‐Reuss bounds on the behavior of a polycrystal are the very best generally valid bounds that have thus far been proposed and that the various methods that are claimed to predict exact effective conductivity (or narrow bounds) all include implicit restrictions on the internal geometry of the polycrystal. This is accomplished by constructing a series of statistically homogeneous and isotropic polycrystal models for which the effective conductivity can be exactly calculated. It is hence to be expected that no universal relationship between single‐crystal and polycrystal conductivity exists. Experimental evidence is adduced to support this conclusion. The results are also applicable to the analogous problems of thermal conductivity and electrical permittivity.
TL;DR: In this article, a chalcogenide glass of a weakly frequency-dependent electrical conductivity obeying the usual empirical relation σ' (ω) ∝ωn but with a much lower than normal value of the exponent n, in the range 0.1-0.25 instead of 0.6-1.0.
TL;DR: Experimental results are consistent with the hypothesis that the membrane permeable species are dimers formed by combination of neutral and dissociated pentachlorophenol molecules, and several schemes of membrane conduction, including dimer formation in the aqueous phase as well as at the membrane-water interface have been considered.
TL;DR: Ionic conductivity measurements on LiAlSiO/sub 4/ glass and glass-ceramic showed these materials to be good lithium ion conducting solid electrolytes at high temperatures as discussed by the authors.
Abstract: Ionic conductivity measurements on LiAlSiO/sub 4/ glass and glass-ceramic showed these materials to be good lithium ion conducting solid electrolytes at high temperatures This composition crystallizes in the beta-eucryptite structure which is attractive for solid electrolyte applications because of its low thermal expansion The glasses were prepared by quenching from the melt and were annealed to remove strain The glass-ceramic (beta-eucryptite) samples were crystallized (aided by TiO/sub 2/ and ZrO/sub 2/ nucleating agents) by using a heat treatment determined through differential thermal analysis The conductivity (sigma) was measured (to 650/sup 0/C) with a variety of techniques, including 2-terminal ac, 3-terminal guarded ac, 4-terminal ac, 2-terminal dc, and a pulsed method Vapor-deposited Cr contacts were used Different sample geometries, contact geometries, and measurement circuitries were employed All results are in excellent agreement, and the a-c techniques appear to be the most versatile and accurate of the methods examined In these materials the conductivity is thermally activated (sigma = sigma/sub 0/e/sup -E/kT/) with typical values of sigma/sub 0/ = 19 x 10/sup 2/ (ohm-cm)/sup -1/ and E approximately 068 eV for the glasses, and sigma/sub 0/ = 21 x 10/sup 4/ (ohm-cm)/sup -1/ and E approximately 105 eV for the glass-ceramics Themore » TiO/sub 2/ and ZrO/sub 2/ nucleating agents (concentrations up to 28 mole percent) did not appear to influence the ionic conductivity Data were also taken on a (beta-eucryptite) glass-ceramic with a composition near the beta-eucryptite/beta-spodumene phase boundary The ionic conductivity of this material is lower than that of the LiAlSiO/sub 4/ materials Data are also provided on beta-spodumene material 8 figures, 35 references (auth)« less