Showing papers on "Conductivity published in 1985"

Fast ion conducting glasses

Abstract: General aspects of fast ion conducting glasses are first presented. Conduction processes in such glasses are discussed in terms of the “random site model”, the “weak electrolyte model” and the “conduction path model”; the applicability of the conduction path model to some systems is tested. Four problems are then treated as the “future development” of fast ion conducting glasses; (a) the promising conducting species, (b) the mixed anion effect, (c) the highest conductivity expected to be achieved, and (d) the possible technological applications.

The calculation of transport properties and density of states of disordered solids

Abstract: A computational method is presented for the calculation of the conductivity tensor and the density of states of disordered solids. This is a more general and detailed discussion of an algorithm which has been applied to d.c. and a.c. conductivity, Hall effect and density of states of various systems.

Geometrical model of conductive and dielectric properties of partially saturated rocks

Abstract: Dielectric constant and conductivity of three‐component porous media are calculated using a geometrical model Applications are made to experiments on clay‐free sedimentary rocks partially saturated with hydrocarbon and water, and air and water A good agreement with experimental data at high frequency (GHz) is obtained using only a spherical grain shape The low‐frequency (MHz) data cannot be explained by the spherical grain alone, but a bimodal distribution of spherical and platey grains gives a fair agreement The low‐frequency dielectric constant is very sensitive to the grain‐shape distribution, but at high frequency is not

Physicochemical properties of rare earth perovskite oxides used as gas sensor material

Abstract: The change of the conductivity in the rare earth perovskite oxide took place after the chemisorption of flammable gases. The sensitivity for methanol was highest. From the conductivity change of these perovskite oxides after the injection of methanol, the energy needed to promote an electron from a conducting to a nonconducting state, ΔE=E c-E t, could be derived from the equationσ=A σ 0 exp (−ΔE/kT). LnCoO3 had the smallest ΔE and ΔH (metal-O), which is the binding energy of oxygen coordinating to the metal ions, but exhibited the highest activity for gas sensing. The gas sensing mechanism was also considered.

Percolation in an oil-continuous microemulsion.

Abstract: Static and dynamic scaling behaviors of electrical conductivity and dielectric constant are obtained near the percolation transition in an oil-continuous microemulsion. Conductivity data are in agreement with a dynamic percolation picture and inconsistent with the static percolation expected from a bicontinuous structure. The dielectric constant, on the other hand, is found to be insensitive to the dynamical process.

Raman, transmission electron microscopy, and conductivity measurements in molecular beam deposited microcrystalline Si and Ge: A comparative study

Abstract: The structure of molecular beam deposited microcrystalline silicon and germanium films prepared under different growth conditions has been analyzed by conventional transmission electron microscope (TEM) and Raman scattering (RS) and compared to electrical conductivity experiments. The TEM measurements yield an average grain size L0 ranging from 200 A to 1.5 μm. On the other hand, the line shape of the RS is determined by a mean free path related to the average separation l between defects (or impurities), where l≤150 A. We find in a number of cases that the electrical conductivity is determined by l rather than L0. This experiment demonstrates the significance of RS as a structural characterization method when used in conjunction with other techniques such as TEM.

Solubility of BaO in BaTiO3

Abstract: The solubility and mode of incorporation for BaO in BaTiO3 were studied by X-ray powder diffraction, scanning and transmission electron microscopy, electron probe microanalysis, and equilibrium electrical conductivity measurements. The presence of barium orthotitanate, Ba2TiO4, as a second phase for samples containing >0.1 mol% excess BaO was confirmed by direct microscopic examination. There was no evidence to support the incorporation of excess BaO into BaTiO3 by a Ruddlesden-Popper type of superlattice ordering mechanism. Measurement of the equilibrium electrical conductivity showed no detectable shift in the conductivity profile resulting from excess BaO, thus setting an upper limit of 100 ppm for the solubility of BaO in BaTiO3.

High Molecular Weight Polyphenylene Vinylene

Abstract: High molecular weight films, fibers and foams of poly(p-phenylene vinylene), (PPV), have been prepared via a water soluble polyelectrolyte precursor. p-Type chemical doping of these materials with ASF5 and H2SO4 leads to high conductivity and to high electrical anisotropy in oriented films and fibers. n-Doping with sodium naphthalide is also possible giving a semiconducting material. PPV synthesis, processing, and conductivity results are reported.

Instrument for measurement of the organic carbon content of water

Abstract: Apparatus and methods for measurement of total organic carbon content of water, particularly of low relative organic content, are described, featuring a single sample cell for exposure of a static sample to ultraviolet radiation and comprising electrodes for measuring the conductivity of the water. The conductivity is monitored as a function of time and the second time derivative of the conductivity signal is monitored to indicate when the oxidation reaction has been completed. Compensation for the contribution to conductivity of the water sample made by the instrument is achieved by subtracting a quantity proportional to the first time derivative of the conductivity at a time when the second time derivative reaches zero, indicating that the oxidation reaction is complete, from the change in the total conductivity measurement, the remainder being equal to the contribution to conductivity made by oxidation of the organic content of the water. The electrodes may have surfaces of a material which when irradiated by the ultraviolet radiation catalyzes the oxidation reaction. Electrophoresis may also be employed to speed the reaction.

On Structure and Properties of Polypyrrole Alkyl-Sulf(on)Ates

Abstract: Tenside anion “doped”, highly conducting polypyrroles (PPY) have been grown electrochemical-ly from aqueous electrolytes The influence of the electrolysis parameters on the conductivity have been investigated The X-ray diffraction patterns allow to derive a structural model

High-Field Conduction in Dielectric Liquids Revisited

Abstract: The various mechanisms proposed to explain the conductivity of organic dielectric liquids at high fields (50 to 2000 kV/cm) are considered and their range of validity assessed. Avalanche ionization and field-increased mobility are negligible, while Onsager enhanced dissociation of electrolytes can be very effective, but only in hydrocarbons. An ubiquitous phenomenon is oxidoreduction of neutrals followed by ion injection; the quantitative law depends on the shape of the barrier the ions must surmount. At very high fields, however, field emission of electrons at the cathode must be dominant. Abatement of highfield conduction is possible and shows promise of new applications.

Effect of Interfacial Space‐Charge Polarization on the Ionic Conductivity of Composite Electrolytes

Abstract: An enhanced carrier concentration within the interfacial space-charge layers has been proposed as one possible mechanism leading to the enhanced ionic conductivity observed for a variety of composite electrolytes containing a dispersed second phase of fine insulating particles such as Al2O3. This study tests this proposal by estimating the maximum space-charge polarization that might reasonably occur at interfaces of nominally pure AgCl, US -AgI, and LiI. The resulting interface conductances are used in effective medium calculations of the total conductivity of a randomly distributed composite of these salts with Al2O3 particles. Comparison of the results with published conductivities for the composites shows that the modest enhancement found for AgCl/Al2O3 can be accounted for by the interfacial space-charge polarization. However, the large (50- to 500-fold) enhancements found for US -AgI/Al2O3 and LiI/Al2O3 must be attributed to another mechanism.

Enhancement of ionic conduction in CaF2 and BaF2 by dispersion of Al2O3

Abstract: Ionic conductivity measurements were performed on polycrystalline CaF2, BaF2 and those dispersed with Al2O3 particles. The ionic conductivity of both CaF2 and BaF2 increased by about 1 to 2 orders of magnitude by dispersion of Al2O3 particles, while X-ray diffraction measurements showed there were no other phases present other than fluoride and Al2O3. The conductivity of the dispersed system strongly depended on the particle size and the concentration of Al2O3, which suggested the high ionic-conductivity layers were formed at the interface between the ionic conductor matrix and the Al2O3 particles. The effective thickness and electrical conductivity of the interface layer at 500° C were calculated, using a simple mixing model, to be 0.3 to ~ 0.6μm and ~ 10−3 S cm−1, respectively.

Measurements of Microwave Conductivity and Dielectric Constant by the Cavity Perturbation Method and Their Errors

Abstract: The theory and technique of the cavity perturbation method for measuring the conductivity and dielectric constant of materials are reviewed. An analytical formula for calculating the errors of the conductivity and dielectric constant caused by the measured error in the resonant frequency and quality factor are derived. This formula can be used for both rectangular and cylindrical cavities. The results of measurements on silicon samples are presented to illustrate this analysis.

Analysis of conductivity prefactors and ion hopping rates in AgIAg2 MoO4 glass

Abstract: Measurements of the a.c. conductivity of AgIAg 2 MoO 4 glass over the temperature range − 84 to − 154°C have enabled d.c. conductivities and ion hopping rates to be obtained. The ion hopping rate values have been confirmed by mechanical relaxation measurements at two frequencies, 1.25 and 10 MHz. The anomalously high conductivity prefactor, 6.3 × 10 5 ohm −1 cm −1 K, is associated with a large entropy, S , of activation. A simple relationship between S and activator energy, E , proposed by Dienes, is shown to hold for a range of glassy Ag + conductors whereas the Wert and Zener expression seriously underestimates S , as shown by shear wave velocity and thermal expansion measurements.

Defect‐property correlations in garnet crystals. III. The electrical conductivity and defect structure of luminescent nickel‐doped yttrium aluminum garnet

Abstract: The conduction mechanisms in nickel‐doped yttrium aluminum garnet (Ni:YAG) have been studied as a function of temperature and partial pressue of oxygen. ac conductivity and ionic transference measurements show that Ni:YAG is a mixed ionic‐electronic conductor with an ionic mobility characterized by an activation energy of 2.0–2.2 eV. The reduction of Ni+3 to Ni+2 causes an increase in the oxygen vacancy concentration and a concurrent rise in the magnitude of the ionic conductivity. Codoping with zirconium, on the other hand, fixes the nickel in the divalent state, increases the n‐type conductivity, and lowers the degree of ionic conductivity. A defect model is presented which is consistent with all of these observations.

Partial melt below Iceland: A combined interpretation of seismic and conductivity data

Abstract: A combined interpretation of published seismic and electric data is carried out to impose constraints on the state of melting below Central Iceland. These data indicate high electrical conductivity and low vp velocity (regionally below 6 km/s) for the crust-mantle transition region, while the mantle below shows lower conductivity but still anomalous low velocity. The velocity data are treated by utilizing gravity data to quantify the elastic modulus decrease due to partial melt. A comprehensive set of theoretical models on elasticity, anelasticity, and electrical conductivity of partially molten rock is applied to this data set. The geometry, the fraction, and the interconnection of the melt phase are varied systematically. The conductivity models are based on published laboratory data on conductivity of solid and melt phases of rocks. Anisotropy and possible unexplored conductivity mechanisms near the melting temperature are not considered here. By means of the melt models the data can be explained most easily as follows: in a depth range roughly between 20 and 50 km only a small percentage of melt (≦2%, at the most 5% if melt pockets are also present) occurs in thin films, possibly with a distribution of aspect ratios and a low degree of interconnection. If, in the crust-mantle transition region, zones of low p wave velocity (≦6 km/s) are correlated with those of high conductivity (≧0.08 S/m), melt fractions between 10 and 20% are likely and the degree of interconnection should be high. Thin films can be excluded as a dominant melt geometry in that region. Apart from improved constraints on melt geometry the results are in good agreement with published models based only on conductivity data. However, they disagree with published models based entirely on seismic data. The discrepancy is now resolved by the combined interpretation.