Showing papers on "Conductivity published in 1977"
TL;DR: In this paper, a new reversible photoelectronic effect was reported for amorphous Si produced by glow discharge of SiH4, where long exposure to light decreases both the photoconductivity and the dark conductivity.
Abstract: A new reversible photoelectronic effect is reported for amorphous Si produced by glow discharge of SiH4. Long exposure to light decreases both the photoconductivity and the dark conductivity, the latter by nearly four orders of magnitude. Annealing above 150 °C reverses the process. A model involving optically induced changes in gap states is proposed. The results have strong implications for both the physical nature of the material and for its applications in thin‐film solar cells, as well as the reproducibility of measurements on discharge‐produced Si.
2,673 citations
TL;DR: In this paper, an electrochemical galvanostatic intermittent titration technique (GITT) is described which combines both transient and steady-state measurements to obtain kinetic properties of solid mixed-conducting electrodes, as well as thermodynamic data.
Abstract: An electrochemical galvanostatic intermittent titration technique (GITT) is described which combines both transient and steady‐state measurements to obtain kinetic properties of solid mixed‐conducting electrodes, as well as thermodynamic data. The derivation of quantities such as the chemical and component diffusion coefficients, the partial conductivity, the mobility, the thermodynamic enhancement factor, and the parabolic rate constant as a function of stoichiometry is presented. A description of the factors governing the equilibration of composition gradients in such phases is included. The technique is applied to the determination of the kinetic parameters of the compound which has a narrow composition range. For the chemical diffusion coefficient is at 360°C. This value is quite high, due to a large thermodynamic enhancement factor of . The lithium component diffusion coefficient is comparatively small at this composition, . The partial conductivity and electrical mobility of lithium are and , respectively, at the same stoichiometry and temperature. Because of the very large values of the chemical diffusion coefficient and the fact that 3 moles of lithium can react per mole of antimony, this system may be of interest for use in new types of secondary batteries.
1,482 citations
TL;DR: In this paper, it was shown that the effective conductivity of the material in terms of the average thermal (or electrical) dipole strength of a particle is approximately equal to a weighted sum of the fluxes across the areas near contact points.
Abstract: The material under investigation consists of particles of relatively large conductivity embedded or immersed in a matrix, the volume fraction of the particles being so high that they are in, or nearly in, contact. The particles are arranged randomly, and the material is statistically homogeneous. A general formula gives the effective conductivity of the material in terms of the average thermal (or electrical) dipole strength of a particle. The thermal flux across the surface of a particle is concentrated in areas near points of contact with another particle, and the dipole strength is approximately equal to a weighted sum of the fluxes across the areas near contact points. It is thus necessary to calculate the flux between two adjoining particles at different temperatures, and we do this by solving numerically an integral equation for the distribution of temperature over the (locally spherical) surface of one of the particles near the contact point. The flux between the two particles is found to be proportional to loge ah when a2 2h/a ≫ 1 and to log e a when a 2h/a ≪ 1, where h is the minimum gap between the particle surfaces, a~ 1 the mean of their local curvatures, and a the ratio of the conductivities of the particles and the matrix. In the case of two particles pressed together to form a circular flat spot of radius p , the flux occurs almost wholly in the particle material, and is proportional to p when ap/a ≫ 1. Explicit approximate results are obtained for the effective conductivity of the granular material in the case of uniform spherical particles. For a close-packed bed of particles making point contact the effective conductivity is found to be 4.0 k log e a where k is the matrix conductivity. This asymptotic relation (applicable when a ≫ 1) is seen to be consistent with the available measurements of the conductivity of packed beds of spheres. Values of the effective conductivity for packed beds of particles of different shape are not expected to be greatly different.
535 citations
TL;DR: In this article, the authors focused on the interpretation of three essential aspects of the thermal conductivity K of polymers: the temperature dependence, the crystallinity dependence and the orientation effect.
375 citations
TL;DR: In this article, the authors use effective medium theory to model the conductivity of peridotite as a basalt melt fraction within a mainly olivine matrix, and estimate both the temperature and the degree of partial melting.
Abstract: For mantle regions of anomalously high electrical conductivity (greater than 0.1 S/m) the bulk conductivity is modeled by effective medium theory as a basalt melt fraction within a mainly olivine matrix. In order for the highly conducting melt to affect the bulk conductivity it must form interconnections, so that the very existence of mantle conductivity anomalies constitutes evidence for such interconnections. The inclusion of petrological data on the partial melting of peridotite strongly constrains the range of temperatures and melt fractions that can be used to yield an observed electrical conductivity. Thus from anomalous conductivities which are observed under rift zones, volcanic belts, geothermal areas, and beneath the oceans, it is possible to estimate both the temperature and the degree of partial melting. While other mechanisms for mantle conductivity enhancement may exist, e.g., contributions from contaminated grain boundaries or high volatile contents, these explanations associate a chemical differentiation in the mantle with thermal manifestations and in most cases create conditions that favor melting.
282 citations
TL;DR: In this article, Li ion conductivity in solid solutions formed between and has been measured as a function of temperature and composition using a • c technique, and the highest conductivities were found at 50 and 60 mole percent (m/o) phosphate.
Abstract: Lithium ion conductivity in solid solutions formed between and has been measured as a function of temperature and composition using a‐c techniques. Highest conductivities were found at 50 and 60 mole percent (m/o) phosphate. Empirical conductivity parameters are presented and qualitatively analyzed in terms of structural and compositional effects. Unit cell parameters have been determined across the entire range of solid solution by x‐ray powder diffraction.
192 citations
168 citations
TL;DR: In this paper, single crystals of CdSnO3, Cd2SnO4, ln2TeO6 and CdIn2O4 were grown by either flux or high pressure methods.
147 citations
TL;DR: A review of the basic theory on thermally stimulated luminescence (TSL) and conductivity (TSC) based on a certain simple model is given in this article, where approximate analytical expressions for the shapes of the TSL and TSC curves are derived.
138 citations
TL;DR: In this article, it was shown that the layered hydrate HUO2PO4 is a rapid proton conductor with a room temperature conductivity of 4 × 10−3ohm−1cm−1.
136 citations
TL;DR: In this article, a method of measuring conductivity changes in pulse irradiated liquids, on a ns timescale, by microwave absorption is described, and quantitative relationships between the measured absorption signal and the change in conductivity are derived for several cell designs.
TL;DR: In this article, conductivity data for several new lithium ion conductors are presented, which indicate that the conductivity can be improved by suitable doping, as well as stoichiometric control.
TL;DR: In this paper, it has been found that thermal conductivity and electrical conductivity can both be increased by the addition of conductive fillers to the polymer, and the two parameters that most significantly affect the increase in conductivity of the resulting composite are volume loading of filler and filler shape.
Abstract: In most low-strength applications, plastics offer cost, maintenance, and density advantages over metals. Major deficiencies of plastics, however, are low thermal and electrical conductivities. Various studies have dealt with these problems, and it has been found that thermal conductivity and electrical conductivity can both be increased by the addition of conductive fillers to the polymer. The two parameters that most significantly affect the increase in conductivity of the resulting composite are volume loading of filler and filler shape. Fibrous conductors improve conductivity much-more significantly than spheres, flakes, or irregular particulates. The effect of fillers on thermal and electrical conductivities is not the same. The maximum increase in thermal conductivity that can reasonably be expected over the base polymer is 100:1. Electrical conductivity, on the other hand, can be increased by a factor of 1015. One particularly attractive technique for increasing the electrical conductivity of polymers is electroless plating of metals onto glass fibers which are then incorporated into the polymer. Such a composite can he made electrically conductive with as little as 6 volume percent metal.
TL;DR: In this paper, a complex plane representation was used to analyze frequency dependent a c conductivity data from samples of single crystal and polycrystalline β-Alumina, and measurements were made from room temperature to around 300°C in vacuum.
Abstract: The now well established technique of complex plane representation is used to analyze frequency dependent a c conductivity data from samples of single crystal and polycrystalline β-Alumina. Measurements were made from room temperature to around 300°C in vacuum. Wayne Kerr Bridges B. 221 and B. 601 with external source (Krohn-Hite 4200 Oscillator) and detector (Marconi TF1100 Valve Voltmeter) gave a frequency range of 500 HZ to 2 MHZ. Electrical contact was made via nickel or platinum foils in pressure contact with evaporated metal electrodes. Prior to measurement every specimen was annealed to 300°C in vacuum, within the conductivity rig, to eliminate moisture from the system.
TL;DR: In this article, a model of soil composed of a multiphase mixture of solid particles, water, and air voids is proposed from which the complex permittivity, or dielectric constant and conductivity, is calculated.
Abstract: A model of soil composed of a multiphase mixture of solid particles, water, and air voids is proposed from which the complex permittivity, or dielectric constant and conductivity, is calculated. It is based on the Hanai/Bruggelman/Wagner theory of mixtures and considers the ionic conducting water as partly dispersed and partly the dispersing medium, an important distinction with this theory. The permittivity as a function of frequency and water content is predicted. The increase in dielectric constant with water volume fraction does not differ greatly with soil type in the high-frequency limit and is approximated by a normal curve specified by the theory. A normal curve and the marked increase in dielectric constant at lower frequencies has been observed experimentally. It is concluded that this semidisperse theory of the dielectric permittivity is successful in describing the behavior of soils containing moisture in the high-frequency range (1 MHz-1 GHz). Approximations to the more detailed theory and a series-parallel RC equivalent circuit are given.
TL;DR: In this article, the presence of the asperities is strongly correlated with the oxide conductivity, as controlled by the oxidation temperature of polycrystalline silicon, and direct evidence of these asperity is shown in SEM micrographs.
Abstract: High conductivity observed in oxides grown on polycrystalline silicon has been previously speculated as being due to asperities on the silicon surface, which enhance the oxide field. Direct evidence of these asperities is shown here in SEM micrographs. The presence of the asperities is strongly correlated with the oxide conductivity (as controlled by the oxidation temperature).
TL;DR: In this paper, the electrical conductivity of graphite powder with antimony pentafluoride in a copper tube and swaging the sheathed compound into wire was examined.
Abstract: The electrical conductivity in graphite measured normal to the crystallographic c-axis is observed to increase after intercalation with acid molecules which act as acceptors. This behaviour is regarded as the result of ionization of the acid molecule which, in turn, increases the positive current carriers in the host graphite. Since the carrier density depends on the degree of ionization of the acid, it follows that the stronger the acid the greater the increase in carrier concentration, and assuming no adverse mobility effects, the greater the electrical conductivity. The hydrogen fluoride-antimony pentafluoride system produces some of the strongest acid substances known. The experiments described here represent the initial examination of the electrical conductivity resulting from intercalation of this material into graphite. The experiments consisted of intercalating graphite powder with antimony pentafluoride in a copper tube and swaging the sheathed compound into wire. The measured conductivity of the graphite intercalation compound, when the copper conductivity is subtracted out and allowance is made for departure from ideal density, is about 1×106 Ω−1 cm−1. This is approximately 40 times the conductivity of pristine graphite and more than one and a half times the conductivity of pure copper.
TL;DR: In this article, the conductivity of two-dimensional and three-dimensional cubic binary random resistor networks is shown to obey a power-law dependence on the conductivities ratio at the percolation threshold.
Abstract: The conductivity of two-dimensional and of three-dimensional cubic binary random resistor networks is shown to obey a power-law dependence on the conductivity ratio at the percolation threshold. The relation recently derived by Straley between the exponent of this power law and the other two critical exponents of the conductivity above and below the percolation threshold is accurately obeyed. Extension of the scaling laws for a complex dielectric function of a binary network is provided.
TL;DR: In this article, a series of a-Si specimens doped substitutionally with phosphorous were used for glow discharge decomposition of silane containing predetermined concentrations of phosphine, and the thermoelectric power of all the samples investigated was negative as expected.
Abstract: Thermoelectric power and conductivity measurements have been made as a function of temperature on a series of a-Si specimens doped substitutionally with phosphorous. The samples were prepared by the glow discharge decomposition of silane containing predetermined concentrations of phosphine. The thermoelectric power of all the samples investigated was negative as expected. For the lightly doped specimens the thermoelectric and conductivity results support the model developed from previous work. Electron transport is in the extended states, but below room temperature there is an increasing contribution from tail state hopping. At higher doping concentrations the data can be interpreted in terms of transport through the extended states and the localized donor states, as suggested by the analysis of recent Hall effect results. The value of the intercept S 0 on the S axis at 1/T = 0 depends strongly on the position of the Fermi energy ∊F with respect to the mobility edge at ∊c. The movement of ∊F with...
TL;DR: In this article, the effective conductivities of simple, face-centered, and body-centered cubic arrays of isotropic spherical particles embedded in an isotropical medium possessing a different conductivity were investigated.
Abstract: Results are presented for the effective conductivities of simple, face-centered, and body-centered cubic arrays of isotropic spherical particles embedded in an isotropic medium possessing a different conductivity. With the use of a multipole expansion technique, numerical and conceptual errors in the prior work of others are corrected. Agreement with existing experimental data is found to be excellent.
TL;DR: In this paper, the problem of the prediction of the effective electrical conductivity of a polycrystal from the conductivities of a single crystal is considered, and it is shown that the average of the principal conductivities is the best upper bound on effective conductivity that can possibly be found.
Abstract: The problem of the prediction of the effective electrical conductivity of a polycrystal from the conductivity of a single crystal is considered. If the only information known about phase geometry is that the aggregate is statistically homogeneous and isotropic, it is shown that the average of the principal conductivities of the single crystal is the best upper bound on effective conductivity that can possibly be found. A new rigorous lower bound is found for the case of axially symmetric crystals. An exact solution is found for the case of a two-dimensional polycrystal.
TL;DR: In this article, it was shown that the conductivity of a SnO2 gas sensor depends on the concentration of CO and H2O in the atmosphere n which it is placed.
Abstract: It is shown that the conductivity of a SnO2 gas sensor depends on the concentration of CO and H2O in the atmosphere n which it is placed The experimental data can be explained in a consistent manner by hypothesizing that 1) adsorbed oxygen depletes the surface electron concentration and therefore decreases the conductivity; 2) adsorbed water causes electrons to accumulate at the surface and therefore increases the conductivity; 3) CO increases the conductivity by removing adsorbed oxygen by reacting with it to form CO2; and 4) adsorbed water catalyzes the CO to CO2 reaction
01 Apr 1977
TL;DR: In this article, a perturbation formulation of the equations of linear piezoelectricity is obtained using a Green's function approach, which is applied in the calculation of the attenuation of surface waves due to the finite electrical conductivity of thin metal films plated on the surface and air loading.
Abstract: A perturbation formulation of the equations of linear piezoelectricity is obtained using a Green’s function approach. Although the resulting equation for the first perturbation of the eigenvalue strictly holds for real perturbations of real eigenvalues only, it is formally extended to the case of purely imaginary perturbations of real eigenvalues. The extended equation is applied in the calculation of the attenuation of surface waves due to the finite electrical conductivity of thin metal films plated on the surface and air loading. The influence of the viscosity of the air is included in the air‐loading analysis, and the calculated attenuation increases accordingly. Since the metal films are thin compared with a wavelength, an approximate thin‐plate conductivity equation is employed in the determination of the attenuation due to the electrical conductivity of the films. The resulting attenuation is obtained over a very large range of values of sheet conductivity. This is accomplished by using the equatio...
TL;DR: In this paper, the free energy of formation has been determined by assuming that the creation of a vacancy is accompanied by a local dilatation, and taking the thermal expansivity into account, the corresponding formation enthalpy and entropy were found to be temperature dependent.
TL;DR: In this paper, the thermal conductivity of semicrystalline polymers, regarded as two-phase materials, is discussed in terms of the Maxwell model generalized to the case where the inclusions are thermally anisotropic.
TL;DR: In this paper, the temperature dependence of conductivity under conditions where equilibrium with the atmosphere is not maintained indicates both the position of the energy level of titanium (TiAlx) in the forbidden gap and the temperature dependent of the mobility of the native ionic defects (Al vacancies, VAlm).
Abstract: Titanium-doped α-Al2O3 exhibits a high-temperature conductivity which is ionic at high oxygen pressures and electronic at low oxygen pressures. Both are isotropic. The temperature dependence of conductivity under conditions where equilibrium with the atmosphere is not maintained indicates both the position of the energy level of titanium (TiAlx) in the forbidden gap and the temperature dependence of the mobility of the native ionic defects (Al vacancies, VAlm). Optical absorption responsible for the pink color of the reduced crystals is measured as a function of po2 and is used to determine concentrations of Ti3+ and Ti4+. Parameters for the equilibrium constants of the reactions involving electrons by which the composition of Al2O3:Ti and undoped Al2O3 is varied are determined. The chemical diffusion data by Jones et al. are described quantitatively.
TL;DR: In this article, a selfconsistent field approach for the calculation of optical properties of a random n-component medium composed of discrete small particles is applied to an insulator-metal mixture for the case of metal formed into small spheres.
Abstract: A self-consistent field approach for the calculation of optical properties of a random n-component medium composed of discrete small particles is applied to an insulator-metal mixture for the case of metal formed into small spheres The real part of the resulting conductivity exhibits broad surface plasmon absorption and a zero-frequency percolation conductivity This result is contrasted with the Maxwell-Gamett theory for the effective composite conductivity The effects of an insulating coat on the metal particles' response are examined and shown to produce profound effects at low frequency Modifications introduced by a distribution of particle sizes are examined, and a completely self-consistent form of the mean field equations for an n-component system, each of whose constituents is distributed in size, is proposed
TL;DR: In this article, a phenomenological introduction to the important physical parameters involved in ionic conduction in solids is followed by order of magnitude estimates of these quantities for materials which can be considered to be fast ion conductors.
Abstract: A brief phenomenological introduction to the important physical parameters involved in ionic conduction in solids is followed by order of magnitude estimates of these quantities for materials which can be considered to be fast ion conductors. Experimental techniques are outlined, and a comprehensive compilation of currently available data on fast ion conductors is presented. The conductivity and diffusion data are coupled with additional criteria to indicate broad classes of materials which may show enhanced ion conductivity.
TL;DR: In this article, the influence of doubly ionized TCNQ in the samples is discussed and D+ impurities compensating the excess charge is discussed, which is correlated with the presence of doubley ionized QN(TCNQ)2 in the sample.
Abstract: Variations in the conductivity of QN(TCNQ)2 depending on sample preparation are correlated with the presence of doubly ionised TCNQ in the samples. Increasing TCNQ2- concentration results in decreasing conductivity and increasing activation energy. The influence of D+ impurities compensating the excess charge is discussed.