Showing papers on "Conductivity published in 1990"

Ionic Conductivity of Solid Electrolytes Based on Lithium Titanium Phosphate

Abstract: Solid electrolytes based on lithium titanium phosphate were prepared, and their phase, porosity of the sintered pellets, and electrical conductivity were studied. The conductivity was increased and the porosity decreased greatly by partially replacing Ti4+ and P5+ in with M3+ and Si4+ions, respectively. The maximum conductivity at 298 K is for . The conductivity was considerably increased by the mixing of binders such as or with . The main reason for the conductivity enhancement of these electrolytes seems to be attributable to the increase of the sintered pellet density with the enhancement of the lithium concentration at the grain boundaries.

The role of hydrogen in the electrical conductivity of the upper mantle

Abstract: INTERPRETATIONS of the observed electrical conductivity of the upper mantle have relied on laboratory studies of dry olivine and basaltic melts1,2. These studies indicate that the conductivity of the asthenosphere is higher than that of olivine, suggesting that partial melting or other high-conductivity mechanisms such as grain-boundary phases are required2,3. Recent experimental studies4–6, however, have demonstrated that various kinetic processes in silicate minerals are greatly enhanced by the dissolution of hydrogen. As hydrogen is probably present in the upper mantle, studies on dry olivine may not therefore be relevant to the real Earth. Here I use experimental data on the solubility and diff usivity of hydrogen in olivine5,7 to estimate its effect on the electrical conductivity. I conclude that the observed high conductivity in the asthenosphere can be attributed to solid-state conductivity in olivine if a small amount of hydrogen is present. Partial melting of the asthenosphere on a global scale is therefore not required.

Dilute lamellar and L3 phases in the binary water–C12E5 system

Abstract: The binary phase diagram of water–C12E5 has been studied with emphasis on the L3 and dilute lamellar phases, which were found to swell to approximately 99.5 and 98.8 wt % of water, respectively, much further than has been reported previously. Focusing on these two phases, we have carried out static light and small-angle neutron scattering and electrical conductivity measurements. The repeat distance in the lamellar phase was found to exceed 3000 A. A small, but significant deviation from ideal one-dimensional swelling was observed. This deviation may be explained in terms of flexibility of the bilayers that are flat only on average. Electrical conductivity and small-angle neutron scattering data from the isotropic L3 phase are, over most of the stability range, consistent with a three-dimensional continuous bilayer structure. However, at large water contents an increase in the conductivity indicates a breakup of the structure into smaller fragments. Our results show that the simpler binary system exhibits the same characteristic features as the more complex multicomponent systems, involving brine, ionic surfactant and cosurfactant.

Frequency-dependent conductivity in bismuth-vanadate glassy semiconductors.

Abstract: The first measurements are reported for the frequency-dependent (ac) conductivity (real as well as imaginary parts) for various compositions of the bismuth-vanadate glassy semiconductors in the frequency range 10 2 -10 5 Hz and in the temperature range 77-420 K. The behavior of the ac conductivity is broadly similar to what has been observed previously in many other types of amorphous semiconductors, namely, nearly linear frequency dependence and weak temperature dependence. The experimental results are analyzed with reference to various theoretical models based on quantum-mechanical tunneling and classical hopping over barriers. The analysis shows that the temperature dependence of the ac conductivity is consistent with the simple quantum-mechanical tunneling model at low temperatures; however, this model completely fails to predict the observed temperature dependence of the frequency exponent. The overlapping-large-polaron tunneling model can explain the temperature dependence of the frequency exponent at low temperatures. Fitting of this model to the low-temperature data yields a reasonable value of the wave-function decay constant. However, this model predicts the temperature dependence of the ac conductivity much higher than what actual data showed. The correlated barrier hopping model is consistent with the temperature dependence of both the ac conductivity and its frequency exponent. This model provides reasonable values of the maximum barrier heights but higher values of characteristic relaxation times.

Potential dependence of the conductivity of highly oxidized polythiophenes, polypyrroles, and polyaniline: Finite windows of high conductivity

Abstract: In situ measurements of the relative conductivity of polythiophenes, polyaniline, and polypyrroles as a function of electrochemical potential reveal that they have finite potential dependent windows of high conductivity. Further, the high conductivity is found where charge is injected or withdrawn from the polymer. The polymers studied, polyaniline and I-VI, are prepared by anodic polymerization onto microelectrode arrays of the appropriate monomer: thiophene (I), 3-methylthiophene (II), 3-phenylthiophene (III), 1-methyl-1{prime}-(3-(thiophene-3-yl)propyl)-4,4{prime}-bipyridinium (IV), 3,4-dimethylpyrrole (V), and N-methylpyrrole (VI). The use of a liquid SO{sub 2}/electrolyte medium as the electrochemical solvent makes it possible to define the window of high conductivity, because it allows the polymers to be reversibly oxidized to a greater extent than has previously been achieved. The conductivities of I-IV increase by at least 10{sup 6}-10{sup 9} when they are oxidized from neutral to the potential of maximum conductivity and then decrease by 10{sup 1}-10{sup 4} when they are further oxidized to the greatest extent possible without irreversible degradation in liquid SO{sub 2}/electrolyte.

Oxide-ion conduction in Ba2In2O5 and Ba3In2MO8 (M=Ce, Hf, or Zr)

Abstract: A series of laboratory experiments were performed in order to systematically explore the dielectric response of soils to a frequency range of 1 to 50 MHz. A network analyzer and a coaxial-transmission-line type of dielectric probe were used to measure the complex (both real and imaginary) dielectric response of moist soils. The dielectric probe was placed in a modified Tempe cell in which the moisture content of the soil under investigation could be varied. Both the real and imaginary components of the dielectric permittivity of the moist soils investigated are greatest at 1 MHz and monotonically decrease with frequency. The variation in the dielectric constant among these soils is also greatest at 1 MHz and decreases with increasing frequency. The soils that have a large imaginary dielectric constant also have the largest real dielectric constant dispersion. The loss tangent for a given soil is relatively independent of moisture content over a wide range of soil moisture conditions. At low water contents, both the real and imaginary dielectric values begin to drop rapidly with decreasing water content. There is a significant temperature dependence present in the dielectric response of moist soils, which changes markedly with frequency. Ionic conductivity is the predominant mechanism causing the imaginary dielectric response and can account for many features of the observed dielectric response. A Looyenga-type mixing model incorporating ionic conductivity can account for the frequency dependence of the dielectric constant of soils

Dielectric properties and influence of conductivity in soils at one to fifty megahertz

Abstract: A series of laboratory experiments were performed in order to systematically explore the dielectric response of soils to a frequency range of 1 to 50 MHz. A network analyzer and a coaxial-transmission-line type of dielectric probe were used to measure the complex (both real and imaginary) dielectric response of moist soils. The dielectric probe was placed in a modified Tempe cell in which the moisture content of the soil under investigation could be varied. Both the real and imaginary components of the dielectric permittivity of the moist soils investigated are greatest at 1 MHz and monotonically decrease with frequency. The variation in the dielectric constant among these soils is also greatest at 1 MHz and decreases with increasing frequency. The soils that have a large imaginary dielectric constant also have the largest real dielectric constant dispersion. The loss tangent for a given soil is relatively independent of moisture content over a wide range of soil moisture conditions. At low water contents, both the real and imaginary dielectric values begin to drop rapidly with decreasing water content. There is a significant temperature dependence present in the dielectric response of moist soils, which changes markedly with frequency. Ionic conductivity is the predominant mechanism causing the imaginary dielectric response and can account for many features of the observed dielectric response. A Looyenga-type mixing model incorporating ionic conductivity can account for the frequency dependence of the dielectric constant of soils

Vanadium redox cell electrolyte optimization studies

Abstract: The stability of the positive electrolyte of the vanadium redox cell has been studied at various temperatures and at different solution compositions and solution state-of-charge (SOC). It has been found that at elevated temperatures for extended periods, V(V) can slowly precipitate from solution, the extent and rate of which being dependent on temperature, vanadium and sulphuric acid concentration as well as the SOC of the electrolyte. A H2SO4 concentration of 3–4m has been found to be more suitable than 2m, not only from the point of view of increased stability, but also because of the higher electrolyte conductivity which leads to increased voltage efficiencies during battery cycling.

Proton-conducting polymer electrolyte. I. The polyethylene oxide+NH4ClO4 system

Abstract: Proton transport in solution-cast films of polyethylene oxide (PEO) complexed with ammonium perchlorate (NH4ClO4) has been established using optical microscopy, XRD, DTA, IR, coulometry, transient ionic current and electrical conductivity studies. The solubility of NH4ClO4 in PEO is found to be limited to a maximum concentration NH4+/EO ratio of 0.167. The highest conductivity ( approximately 1.05*10-5 S cm-1) is for the film with NH4+/EO=0.02-0.1. The H+ ion transference number, tH+, and mobility, mu H+, are 0.85 and 1.7*10-4 cm2 V-1 s-1, respectively. The movement of ClO4- ions also contributes slightly to the overall charge transport.

Structure and Electrical Properties of Polyacetylene Yielding a Conductivity of 10 5 S/cm

Abstract: We have prepared polyacetylene (ν-(CH)x) yielding a conductivity of more than 105 S/cm, by making some modifications on Naarmann et al.'s method. Structural analyses of this polymer were carried out by use of various analysis techniques such as SEM, IR and resonance Raman spectroscopy to characterize ν-(CH)x. No distinct differences in structure between conventional polyacetylene and ν-(CH)x were observed except for morphology and specific gravity. Upon iodine doping, conductivity increases stepwisely, which may suggest the formation of a staging structure and/or the transformation to metallic phase. However, in the temperature dependence of conductivity, we could not find any differences which distinguish the metallic ν-(CH)x from conventional polyacetylene.

Estimating thermal conductivity in sedimentary basins using lithologic data and geophysical well logs

Abstract: A method for estimating in-situ thermal conductivity profiles in oil and gas wells is advanced to rectify a major shortcoming in thermal analyses of sedimentary basins. Thermal conductivity estimates are made in a two-stage procedure and are based on a model for the conductivity of mixtures and input data from lithological and geophysical logs. First, rock matrix conductivity for an arbitrary depth interval (i.e., drill cuttings sample interval, which is about 3 m) is determined from the laboratory-calibrated conductivities and volumetric representation of its individual lithologic components using a geometric mean model. In-situ conductivity is then estimated by a second application of the model, correcting for temperature and porosity determined from geophysical logs. > The method is illustrated for three Uinta basin (Utah) wells that penetrate a series of Tertiary sandstones, shales, and muddy carbonates. Detailed lithologic descriptions, together with sonic and neutron logs, were digitized and used for estimating in-situ conductivity. The validity of the method was tested by comparing the prediction against laboratory measurements on 565 samples from the same wells. Rock matrix thermal conductivity ranges from 1.6 to 6.8 W/m/K and is predicted within 20% of the actual measurement for 90% of the samples. Both in-situ conductivity values and variations for a given lithologic unit are reduced at increased porosity and increased temperature. Thermal conductivity nomograms are presented as useful tools to predict directly the in-situ thermal conductivit of a formation from a well log signal.

Electrical properties of natural and synthetic pyrite (FeS2) crystals

Abstract: We have prepared a series of synthetic n-type pyrite (FeS2) crystals by chemical vapor transport and high temperature solution growth. These and natural crystals were characterized with respect to Hall mobility, carrier concentration, and conductivity, and chemically analyzed by mass spectroscopy and atomic emission spectroscopy. The results are compared in detail to previous work on natural crystals. Conductivity and carrier concentration in our measurements varied between 0.05 and 3.5 (Ω cm)−1 and between 6.9·1015 and 5.4·1017 cm−3, respectively. The peak mobilities have values ranging from 100 to 2000 cm2/Vs. We find that sulfur deficiency and a number of impurity elements, such as Si, Cu, and Al, can qualitatively account for the trends in the electronic properties.

Sulfonic acid ring-substituted polyaniline, a self-doped conducting polymer

Abstract: Sulfonic acid ring-substituted polyaniline has been synthesized and characterized by elemental analysis, FTIR, UV-vis and electron spin resonance spectroscopy. Approximately 50% of the total number of phenyl rings in the polymer are mono-substituted by -SO− 3 groups. Without external doping, the ring-sulfonated polyaniline has a conductivity of ∼0.03 S/cm; it is therefore a “self-doped” conducting polymer. The water soluble sodium salt of the ring-sulfonated polyaniline is an insulator and can be reversibly converted back to the self-doped conducting form by treatment with aqueous acid.

Electrical conductivity of olivine, a dunite, and the mantle

Abstract: Laboratory studies of the electrical conductivity of rocks and minerals are vital to the interpretation of electromagnetic soundings of the Earth's mantle. To date, the most reliable data have been collected from single crystals. We have extended these studies with electrical conductivity measurements on a dunite from North Carolina, in the temperature range of 600°–1200°C and under controlled oxygen fugacity. Observations of conductivity as a function of oxygen fugacity and temperature demonstrate that conduction in the dunite is indistinguishable from conduction in single olivine crystals. Thus the common practice of exaggerating the single-crystal conductivities to account for conduction by grain boundary phases in the mantle is unnecessary. Because the dunite conductivity is consistent with that published for single crystals under similar conditions, we have made a combined analysis of these data. Conductivity as a function of temperature between 600° and 1450°C displays three conduction mechanisms whose activation energies may be recovered by nonlinear least squares fitting, yielding activation energies of 0.21±2.56×10−19 J (0.13±1.60 eV) below 720°C, 2.56±0.02×10−19 J (1.60±0.01 eV) between 720°C and 1500°C and 11.46±0.90×10−19 J (7.16±0.56 eV) above 1500°C. The behavior of conductivity as a function of oxygen fugacity is well explained by a model in which an ƒo2-independent population of charge carriers is supplemented at high oxygen fugacities with a population that is proportional to ƒo20.3. This parametrization produces a clear correlation of the ƒo2 dependent term with iron content, which is otherwise obscured by variations in conductivity among olivines.

Electric double layer capacitor

Abstract: PURPOSE: To obtain an electric double layer capacitor allowing large area and capacitance without liquid leakage and drip by providing an electrolyte thin film constituted by a solid-state electrolyte thin film which has fixed ion conductor in the holes of a porous thin film CONSTITUTION: An electric double layer capacitor possesses an electrolyte thin film between electrodes and its electrolyte thin film is constituted by a solid-state electrolyte thin film 1 which has fixed ion conductor in the holes of a porous thin film Therefore, the electrolyte thin film can be treated as a solid as a whole without liquid leakage and has excellent ion conductivity The porous thin film used has a function as the supporting body of the ion conductor and is made of polymeric material which has excellent mechanical strength Thus, the super thin electric double layer capacitor allowing large area and capacitance is obtained without liquid leakage and drip COPYRIGHT: (C)1991,JPO&Japio

Thermal Inertia of Conductivity Cells: Observations with a Sea-Bird Cell

Abstract: We have examined the magnitude and relaxation time of the thermal anomaly of the fluid flowing through the conductivity cell manufactured by Sea-Bird Electronics (SBE) that is induced by the heat stored in the wall of this cell using oceanic data collected in a thermohaline staircase. The relaxation is 9 to 10 s, about twice the value predicted by Lueck, while the initial magnitude of the conductivity error is 2.8%, about 35% smaller than predicted. The error in the measured conductivity is significant and long-lived and results in density errors detectable for 45 s after the sensor enters an isopycnal layer. An efficient numerical algorithm removes the anomaly from the measured conductivity signal and clears the resulting error from the computed salinity and density.

Conductivity of tetra-alkylammonium salts in polyaromatic solvents

Abstract: It is shown that the conductivity of tetra-alkylammonium salts in low dielectric constant media is not greatly affected by the length of the carbon chain of the cation. The effect upon the conductivity of varying the size of anions and cations has been analysed in several pure and mixed solvents using a modified Fuoss–Kraus theory to take into account the activity coefficient of the undissociated electrolyte. The interionic distance parameter of the ion pairs is calculated and shown to be fairly constant, indicating interpenetration of the ions. Also, following on from the preceding paper, the effect upon the conductivity of the local environment around the solute is found to be negligible. The bulk dielectric constant of the solvent is shown to be the major factor affecting the conductivity of salts.

Measurement of dielectric response of water-saturated rocks

Abstract: We tabulate an extensive set of measurements of the complex permittivity (i.e., dielectric constant and conductivity) of brine saturated rocks in the frequency range 10-1300 MHz. Rather than listing the permittivity at each frequency, we present the parameters of a Cole-Cole function used to fit the data for each rock sample. We choose the Cole-Cole function for the following reason. The data sets from 271 rock samples were fitted to the commonly used functions in the literature, i.e., Cole-Cole, Cole-Davidson, and power law functions. We found that within experimental errors the fits to both the Cole-Cole function and the power law represent the frequency dependence of the data better than the Cole-Davidson function. Further, the Cole-Cole function fits the data better at the high-frequency end of our data. This result implies that five parameters of the Cole-Cole function describe the frequency dependence of the complex permittivity of rock samples in the range 10-1300 MHz within experimental errors.

Application of the Anderson-Stuart model to the AC conduction of ionically conducting materials

Abstract: A new conductivity model for ionically conducting materials is proposed. For the first time, the Anderson-Stuart model, originally developed to account for the dc conductivity activation energy in silicate glasses, is extended to describe the ac conductivity based on a thermally activated hopping charge process. The theoretical results obtained are analysed and compared with previous experimental data. Despite the paucity of and variation in the experimental results, the present model is not inconsistent with these data and, therefore, may be a new and interesting approach to understand the ac conductivity behaviour of ionic conductors.

Electrical Properties of Sintered Lithium Titanium Phosphate Ceramics (Li1+XMXTi2−X(PO4)3, M3+ = Al3+, Sc3+, or Y3+)

Abstract: Activation energies of electrical conduction for bulk and grain boundary in Li1+XMXTi2−X(PO4)3 (M = Al, Sc, or Y) systems were determined. The activation energy for the bulk kept constant in spite of the M3+ substitution, while that for the grain boundary appreciably decreased. The total conductivity enhancement by the M3+ substitution was attributed to the decrease in the activation energy of the grain boundary component.