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Showing papers on "Conductivity published in 1992"


Journal ArticleDOI
TL;DR: In this paper, a brief account of phase assemblage expected in commonly used binary and some ternary zirconia (with CaO, MgO, Y 2O3, Sc2O3 and rare-earth oxides) systems is given.

488 citations


Journal ArticleDOI
TL;DR: In this article, the impedance of Li3.3PO3.9N0.17 was analyzed using two models in which the frequency dependence of the bulk response was represented by a Cole-Cole dielectric function and a constant phase angle element.

482 citations


Journal ArticleDOI
TL;DR: The high electron affinity and the existence of radiating [pi]-orbitals when combined with simple ideas for the design of molecular metals and superconductors led the authors to pursue conductivity and super-conductivity in the alkali metal doped fullerenes.
Abstract: The high electron affinity and the existence of radiating [pi]-orbitals when combined with simple ideas for the design of molecular metals and superconductors led the authors to pursue conductivity and superconductivity in the alkali metal doped fullerenes. Further, the authors discuss the preparation and characterization of conducting and superconducting solids and films based on these materials and the current state of understanding within this field.

471 citations


Journal ArticleDOI
21 Feb 1992-Science
TL;DR: Caloric measurements under variation of gas pressure as well as spectral infrared transmission measurements allowed the determination of solid Conductivity, gaseous conductivity, and radiative conductivity as a function of density.
Abstract: The total thermal conductivity lambda of resorcinol-formaldehyde aerogel monoliths has been measured as a function of density rho in the range from rho = 80 to 300 kilograms per cubic meter. A record-low conductivity value in air at 300 K of lambda approximately 0.012 watt per meter per kelvin was found for rho approximately 157 kilograms per cubic meter. Caloric measurements under variation of gas pressure as well as spectral infrared transmission measurements allowed the determination of solid conductivity, gaseous conductivity, and radiative conductivity as a function of density. The development of such low conductivity materials is of great interest with respect to the substitution of environmentally harmful insulating foams made from chlorofluorocarbons.

413 citations


Journal ArticleDOI
TL;DR: In this article, the authors analyzed the thermal conductivity of the ZnS-diamond interface with different values of α, defined to be equal to the Kapitza radius divided by the particle radius.
Abstract: We have observed that the thernal conductivity of zincsulphide is increased by adding large particles of highly conducting diamond, but lowered by the addition of sub-micron size particles of diamond. This effect is explained in terms of the interfacial thermal resistance which becomes increasingly dominant as the particles becomes smaller (because that increases their surface to volume ratio). A phenomonological model in which the interface resistance is expressed as an effective Kapitza radius, ak, is presented. The conductivity of the composite is analyzed for different values of α, which is defined to be equal to the Kapitza radius divided by the particle radius. If α = 1, that is, the actual particle radius is equal to ak then the effective thermal conductivity of the particles is equal to that of the matrix. If α > 1, that is the particles are very small, then the contribution of the particles to the thermal conductivity of the composite is dominated by interfaces; if α < 1 then the bulk property of the particles is important. Our measurements yield ak ≈ 1.5 μm for the ZnS-diamond interface.

355 citations


Journal ArticleDOI
TL;DR: In this article, the electrical conductivity of carbon black (CB) filled polymer blends which are incompatible with each other was studied as a function of the polymer's blend ratio Transmission electron microscope (TEM) analysis shows that CB distributes unevenly in each component of a polymer blend.
Abstract: Electrical conductivity of carbon black (CB) filled polymer blends which are incompatible with each other was studied as a function of the polymer's blend ratio Transmission electron microscope (TEM) analysis shows that CB distributes unevenly in each component of a polymer blend TEM photographs of phase structure of solvent extracted HDPE/PMMA blend and solvent extraction experiments of PMMA/PP blend detect the blend ratio at which the structural continuity of filler rich phase is formed The electrical conductivity of polymer blends is found to be determined by two factors One is the concentration of CB in the filler rich phase and the other is the structural continuity of this phase This double percolation affects the conductivity of conductive particle filled polymer blends

318 citations


Journal ArticleDOI
TL;DR: The phase transitions in mixtures of poly(ethylene oxide) (PEO) (Mn = 4 × 103) with LiN(CF3SO2)2, a lithium salt of low lattice energy recently discovered by Armand and coworkers, are compared with those of the PEOLiCF 3SO3 and PEO-LiClO4 systems as mentioned in this paper.

307 citations


Journal ArticleDOI
TL;DR: This issue is investigated by studying a model polymer, the HCl-doped emeraldine salt from of oriented polyaniline (PAN-ES), through the temperature dependence of the dc conductivity, thermoelectric power, complex microwave dielectric constant, EPR, and electric-field dependence of conductivity.
Abstract: It is an open question if ``metallic'' polymers have one-dimensional or three-dimensional conduction states. We investigate this issue by studying a model polymer, the HCl-doped emeraldine salt form of oriented polyaniline (PAN-ES) through the temperature dependence of the dc conductivity, thermoelectric power, complex microwave dielectric constant, electron paramagnetic resonance (EPR), and electric-field dependence of conductivity. The thermopower, microwave dielectric constant, and EPR data suggest that the electrons are three dimensionally delocalized. We propose that oriented PAN-ES consists of coupled parallel chains that form ``metallic'' bundles. These bundles are the ``crystalline'' regions of the polymer in which the electron wave functions are three dimensionally extended. This is in contrast to conventional quasi-one-dimensional conductors (many ``metallic'' charge-transfer salts) in which conducting chains are essentially isolated. However, between bundles are the amorphous (less-ordered) regions in which charge hopping dominates the macroscopic conductivity. The formation of the ``metallic'' bundles is proposed to be the result of a significant charge-interchain-transfer rate inside the crystalline regions. The implications of the results for the improvement of conductivity are addressed.

303 citations


Journal ArticleDOI
TL;DR: In this paper, an attempt was made to improve LaMnO3 high temperature air cathodes by using an electrode structure which resembles that of porous electrodes of liquid electrolyte fuel cells, and the addition of YSZ prevented the formation of highly resistive La2Zr2O7 which has otherwise been formed at the electrode-electrolyte interface.

243 citations


Journal ArticleDOI
TL;DR: In this article, the cmc (critical micelle concentration), counterion binding parameter (β), and aggregation number (n) of aqueous sodium dodecyl sulfate (SDS) are estimated from conductivity data at various temperatures and salinities.
Abstract: The cmc (critical micelle concentration), counterion binding parameter (β), and aggregation number (n) of aqueous sodium dodecyl sulfate (SDS) are estimated from conductivity data at various temperatures and salinities. The conductivity models used are based on mass action micellization thermodynamics and the Debye-Huckel-Onsager conductivity theory. With rigorous parameter estimation methods, the models are optimally fit to previous literature data. Moreover, new data were taken with an experimental design which is based on the precise solution of the inverse problem

215 citations


Journal ArticleDOI
TL;DR: In this paper, the relationship between nonstoichiometry, electrical properties and diffusion of perovskite-type oxides, ABO3 (B = Al, Zr, Bi, Cr, Mn, Fe, Co), was reviewed to elucidate the characteristics of pervskite type electrode materials, La1-xSrxBO3.

Journal ArticleDOI
TL;DR: It was found that the mobility of ions in solutions depends only on the percentage of concentration of added non-electrolytes and practically not on their chemical nature (sugars or polyglycols) and molecular size.
Abstract: A new method of pore size determination is presented. The results of applying this simple method to ion channels formed by staphylococcal α-toxin and its N-terminal fragment as well as to cholera toxin channels are shown. The advantages and the difficulties of this method are discussed. It was found that (i) the mobility of ions in solutions depends only on the percentage of concentration of added non-electrolytes and practically not on their chemical nature (sugars or polyglycols) and molecular size; (ii) the proportional change of both ion channel conductance and bulk solution conductivity by low M. non-electrolytes may be used as an indication of a diffusion mechanism of ion transport through channels; (iii) the slope of the dependence of the ion channel conductance on the bulk conductivity of solutions containing different concentrations of non-electrolyte is a good measure of channel permeability for non-electrolytes.

Journal ArticleDOI
J. E. Graebner1, Sungho Jin1, G. W. Kammlott1, J. A. Herb, C. F. Gardinier 
01 Oct 1992-Nature
TL;DR: In this paper, the authors measured thermal conductivity in the experimentally difficult direction perpendicular to the plane of the diamond film and showed that the local conductivity near the top growth surface of a synthetic diamond film is, surprisingly, at least as high as that of gem-quality diamond single crystals.
Abstract: AS high-power electronic devices are packed to progressively higher densities, synthetic diamond films are being considered as heat spreaders for the prevention of thermal damage (see ref. 1 for example). Although diamond single crystals are known to have the highest thermal conductivity for any material at room tem-perature (22 W cm−1 K−1 for diamond with natural isotopic abundance, compared with 4 W cm-1 K-1 for copper), the dependence of conductivity on the microstructure of polycrystalline diamond films is not understood. Using a newly developed laser technique2, we have measured thermal conductivity in the experimentally difficult direction perpendicular to the plane of the diamond film. Taken together with earlier in-plane measurements3, this gives a complete description of the local thermal conductivity, showing a significant gradient and anisotropy correlated with the inhomogeneous grain structure. Despite phonon scattering at lattice defects and grain boundaries, we find that the local conductivity near the top growth surface of a synthetic diamond film is, surprisingly, at least as high as that of gem-quality diamond single crystals.

Journal ArticleDOI
TL;DR: In this paper, a robust method that uses eddy current measurements to determine the conductivity and thickness of uniform conductive layers is described, and the method is tested by estimating the conductivities of aluminum and copper layers on various substrate metals and the thickness and conductivity of free standing foils of aluminum.
Abstract: A robust method that uses eddy current measurements to determine the conductivity and thickness of uniform conductive layers is described. The method was tested by estimating the conductivity and thickness of aluminum and copper layers on various substrate metals, and the thickness and conductivity of free‐standing foils of aluminum. The electrical impedance was measured for air‐core and ferrite‐core coils in the presence and absence of the layer for frequencies ranging from 1 kHz to 1 MHz. The thickness and conductivity of the metal layers were inferred by comparing the data taken with air‐core coils to the exact theoretical solution of Dodd and Deeds [J. Appl. Phys. 39, 2829 (1968)] using a least‐squares norm. The inferences were absolute in the sense that no calibration was used. We report experimental tests for eight different thicknesses of aluminum (20–500 μm) in free space and on four different substrates: Ti‐6Al‐4V, 304 stainless steel, copper, and 7075 aluminum, and for five different thicknesses...

Journal ArticleDOI
TL;DR: In this article, the temperature dependence of the counter-ions due to clays and the electrical conductivity of pore-filling brine is investigated. But the results show that the resistivity index is less sensitive to temperature.
Abstract: In boreholes, temperatures vary and to extract hydrocarbon saturation from conductivity measurements, the influence of temperature on water and rock conductivities must be accounted for. The mobility (μDL) of the counter‐ions due to clays and the electrical conductivity of pore‐filling brine show large changes with variation in temperature, whereas the microgeometry of the pore space exhibits negligible change. Using this idea, the temperature dependence of μDL is extracted using data on dc electrical conductivity of shaly sands (σ) containing varying amounts of clay. The mobility of Na+ counter‐ions is found to vary approximately linearly with temperature. This explicit relationship is tested by comparing the predicted temperature dependence against the measured temperature dependence of conductivity of a set of rocks with high and low clay content. While the rock conductivity shows a large temperature dependence, the resistivity index is less sensitive to temperature. An approximate formula, which is su...

Journal ArticleDOI
TL;DR: In this article, a doubly doped ceria electrolyte is proposed for high power density operation on hydrocarbon fuels, which offers the advantage of high oxide ion conductivity without the restrictive materials problems of a high operating temperature.

Journal ArticleDOI
TL;DR: In this paper, Dykaar et al. used the numerical spectral method described in the companion paper (Dykaar and Kitanidis, this issue) to compute the effective conductivity of a three-dimensional Isotropic, stationary, lognormally distributed hydraulic conductivity.
Abstract: Using the numerical spectral method described in the companion paper (Dykaar and Kitanidis, this issue) the effective conductivity of a three-dimensional, Isotropic, stationary, lognormally distributed hydraulic conductivity is computed. Six cases were investigated for variances in log conductivity ranging between 1 and 6. The results show that averaging volumes of at least 30 integral scales are required before the effective conductivity reaches its asymptotic value. The results support Matheron's (1967) hypothesis that Ke = KG exp (σY2/6), where Ke is the effective hydraulic conductivity, and KG and σY2 are the geometric mean and variance, respectively, of the hydraulic conductivity field. We also find that for a Gaussian covariance function, heterogeneities smaller than about 1.3 integral scales do not significantly contribute to the effective conductivity. In two dimensions, averaging volumes of more than 80 integral scales are required before the effective conductivity reaches the analytic infinite-domain result of the geometric mean, while the effective conductivity is insensitive to heterogeneities less than 2 integral scales in size. The method is also applied to data from a shale and sandstone formation, and the results are compared with those from other methods.

Journal ArticleDOI
TL;DR: In this article, structural features in mixed Mn3+, Mn4+ perovskites, Pr1−xAxMnO3 (A = Ca, Sr, Ba) are given.

Journal ArticleDOI
TL;DR: In this article, a series of CVD polycrystalline diamond films with a thermal conductivity that is only 25% less than that of high quality single-crystal natural diamond was studied and the observed gradient is attributed mainly to phonon scattering by the roughly cone-shaped columnar microstructure.
Abstract: Chemical‐vapor‐deposited (CVD) polycrystalline diamond films have recently been reported with a thermal conductivity that is only 25% less than that of high quality single‐crystal natural diamond. By studying a series of such films of various thicknesses grown under virtually identical conditions, we have discovered a significant (factor of four) through the thickness gradient in thermal conductivity. The observed gradient is attributed mainly to phonon scattering by the roughly cone‐shaped columnar microstructure. For 350 μm films, the material near the top (growth) surface has a conductivity of at least 21 W/cm °C, i.e., comparable to the best single crystals. This remarkable dependence of thermal conductivity on microstructure has important implications for thermal management of microelectronic devices using CVD diamond.

Journal ArticleDOI
TL;DR: In this article, a phase transition from α- to β-Na3PS4 has been established via differential thermal analysis and temperature-dependent X-ray powder diffraction, and the space group is P4¯21c with a = 695.20(4)pm and c = 707.57(5)pm.

Journal ArticleDOI
TL;DR: Li et al. as discussed by the authors synthesized a new lithium ion conductive solid electrolyte based on Li 2 S-SiS 2 glass with the composition: 0.03Li 3 PO 4 -0.59Li 2 S 0.38 SiS 2 at ambient pressure by quenching in liquid nitrogen.

Journal ArticleDOI
TL;DR: In this paper, the effects of charged clay platelets on the frequency dependent electrical properties of shaly materials are analyzed using simplified models for the membrane polarization around charged spheres immersed in electrolytic solutions, under a thin double layer approximation.
Abstract: The effects of charged clay platelets on the frequency dependent electrical properties of shaly materials are analyzed using simplified models for the membrane polarization around charged spheres immersed in electrolytic solutions, under a thin double layer approximation. The polarization is defined through two possible mechanisms: (1) a surface conductivity related with a modified Stern double layer model (S-model) according to Schurr-Schwarz theory; (2) a coupled electro-diffusional mechanism occurring in a Guoy-Chapman double layer using Fixman's approach (D-model). By comparing the electric potential in such microscopic models with the external potentials derived for the equivalent homogeneous sphere using a Maxwell-Wagner approach, we obtain the total current conductivity functions for these two models. The theory, therefore, provides explicit expressions relating the total conductivity functions to the model parameters.The behavior of the S-model is described by a complex conductivity exhibiting a simple Debye characteristic. In the D-model, both the conductivity and the dielectric permittivity are given as complex properties, showing similar but much wider dispersion than that of a Debye substance. Our representation of the grains and their associated ionic double layers by an equivalent sphere with effective properties allows us to extend our results to simulate rocks containing clays. This is accomplished using generalized mixture equations written in terms of the total conductivity functions. The frequency behavior of both models are compared and their fit to experimental data on clay-water systems and shaly materials suggest that the D-model is more appropriate for representing the dielectric behavior of clay bearing rocks. The theory can be adapted to estimate the clay parameters of a shaly sandstone using electromagnetic borehole measurements.

Journal ArticleDOI
Rainer Waser1, Mareike Klee1
TL;DR: The mechanism of dc electrical conduction and breakdown of perovskite-type titanates was investigated by impedance analysis in this article, based on an acceptor doped SrTiO3 model material, samples of different microstructures-ceramics, single crystals, and thin films-were employed.
Abstract: The mechanism of the dc electrical conduction and breakdown of perovskite-type titanates was investigated by impedance analysis. Based on an acceptor doped SrTiO3 model material, samples of different microstructures-ceramics, single crystals, and thin films-were employed. This approach allows us to distinguish conduction contributions of the bulk lattice, grain boundaries, and electrode interfaces. Based on defect chemistry studies, a predominant ionic contribution due to mobile oxygen vacancies and an additional p-type conduction were revealed for the bulk. At interfaces, space charge depletion layers of 100-500 nm width are formed in which the local conductivity is reduced by approx. four orders of magnitude compared to the bulk. Thin films show a similar depression of the conductivity. The combination of these facts may be indicative for considering thin films as distributed Schottky barriers. The field enhancement of the conductivity of thin films and of the interface depletion layers is compared and ...

Journal ArticleDOI
TL;DR: In this paper, the performance of Gd-doped BaCeO 3 ceramics was investigated by electrochemical methods (hydrogen permeation test and hydrogen-oxygen fuel cell test) in the temperature range of 600°C to 1000°C.

Journal ArticleDOI
TL;DR: In this article, the preparation, electrical and rheological properties as well as the electrochemical behavior of gel electrolytes made of (PC) electrolyte mixed with poly(methylmethacrylate) polymer (PMMA) as a stiffener are described.
Abstract: The preparation, the electrical and rheological properties as well as the electrochemical behavior of gel electrolytes made of (PC) electrolyte mixed with poly(methylmethacrylate) polymer (PMMA) as a stiffener are described. The addition of PMMA in various proportions to (M)‐PC electrolyte considerably increases the viscosity to reach for large amounts of PMMA, a solid rubber‐like material. On the other hand the conductivities at room temperature of these gels decrease very slightly and remain very close to the conductivity of the liquid electrolyte. Moreover, the electrochemical study of these materials shows a stability domain on Pt electrode between −3.55 V and +1 V (vs.Ag/Ag+). They behave like a liquid electrolyte. Differential scanning calorimetric data establish the thermal stability of these gels between −110 and +240°C after heat‐treatment and between −90 and +160°C before heat‐treatment. These results indicate that this type of electrolyte which is transparent in thin films is very promising for the realization of solid‐state electrochromic windows.

Journal ArticleDOI
TL;DR: A nonlinear least squares optimization program, RETC as discussed by the authors, was used to analyze 36 unsaturated hydraulic conductivity distributions obtained from the literature for 23 different soils, and compared measured, predicted, and estimated relative conductivity for the group of data, the efficiency and accuracy of this approach for characterizing the soil hydraulic properties was determined.
Abstract: A nonlinear least-squares optimization program, RETC, which uses empirical relationships for describing the water-retention curve and predictive models for characterizing the unsaturated hydraulic conductivity relationship was used to analyze 36 unsaturated hydraulic conductivity distributions obtained from the literature for 23 different soils. By comparing the measured, predicted, and estimated relative conductivity for the group of data, the efficiency and accuracy of this approach for characterizing the soil hydraulic properties was determined. The analysis consisted of comparing measured, predicted, and estimated conductivities using three predictive methods and two simultaneous methods (which include known values of the conductivity). The results indicate that for this group of data, the best method for determining the model parameters that will accurately describe both the water retention and unsaturated hydraulic conductivity relationships is to use a simultaneous approach with either five or six parameters. It was also found that the predictive approach introduces a bias into the estimates of the unsaturated hydraulic conductivity and a predictive approach with scaling did not significantly improve the estimates of the unsaturated hydraulic conductivity. View complete article To view this complete article, insert Disc 5 then click button8

Journal ArticleDOI
TL;DR: In this article, the positive lead dioxide active mass (PAM) is viewed as a gel-crystal system, where the gel is composed of hydrated lead dioxide, PbO(OH) 2 that forms linear polymer chains.
Abstract: Up to now, the positive lead dioxide active mass (PAM) has been treated as a crystal system. Its behavior, however, could not be fully explained by its crystal nature. In the present paper, a new approach is suggested which views PAM as a gel-crystal system. Crystal zones are built of PbO 2 and exhibit electron conductivity. Gel zones are composed of hydrated lead dioxide, PbO(OH) 2 , that forms linear polymer chains. These allow electrons to move in the gel hopping from one Pb 4+ ion to the other along the polymer chain and from one polymer chain to the other between the crystal zones

Journal ArticleDOI
TL;DR: A detailed study of protonic conductivity in Nd-doped BaCeO3 is made using water-uptake and galvanic-cell measurements to supplement the conductivity results as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this article, a geostatistical model for hydraulic conductivity at both the core or point scale and that of grid blocks is presented, where the average of point-scale conductivities is obtained empirically as a spatial power-average of point scale values.
Abstract: Numerical models of groundwater flow require the assignment of hydraulic conductivities to large grid blocks discretizing the flow domain; however, conductivity data is usually available only at the much smaller scale of core samples. This paper describes a geostatistical model for hydraulic conductivity at both the core or point scale and that of grid blocks. Conductivity at the block scale is obtained empirically as a spatial power-average of point scale values. Assuming a multivariate Gaussian model for point log-conductivity, expressions are derived for the ensemble mean and variance of block conductivity. The expression for the ensemble mean of block scale conductivity is found to be similar to an expression for the ensemble effective conductivity of an infinite field derived analytically by earlier authors. Here, block conductivities obtained by power averaging are compared with effective conductivities obtained from a numerical flow model and are found to be in excellent agreement for a suitably chosen averaging exponent. This agreement deteriorates gradually as the log variance of conductivity increases beyond 2. For arbitrary flow field geometry and anisotropic conductivity covariances, the averaging exponent can be calibrated by recourse to numerical flow experiments. For cubic fields and an isotropic spatial covariance, the averaging exponent is found to be 1/3. In this particular case, it was found that flow field discretization at the block scale through local averaging of point conductivities gave similar results to those obtained directly using a point scale discretization of the flow field.

Journal ArticleDOI
TL;DR: In this article, a new proton conducting polymer electrolyte PEO + NH4l system has been investigated and solution-cast films of different stochiometric ratios have been prepared and characterized.
Abstract: A new proton conducting polymer electrolyte PEO + NH4l system has been investigated. The solution-cast films of different stochiometric ratios have been prepared and characterized. Proton transport has been established using various experimental studies, namely optical microscopy, X-ray diffraction, differential thermal analysis, infrared, coulometry transient ionic current and electrical conductivity measurements at different temperatures and humidity. The maximum conductivity of the complexed material has been found to be ∼10−5 S cm−1. Both H+ ion and I− anion movements are involved with respective transference numbers and mobilities ast H+=0.74, ,t l−=0.09, μH+=4.97 × 10−6 cm2 V−1 s−1 and μl−=7.65.