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Showing papers on "Conductivity published in 1989"


Journal ArticleDOI
TL;DR: In this article, a generalized relationship between dopant size and ionic conductivity in binary systems of MO2 oxides was shown, illustrating that the smaller the difference between the dopant ionic radius and the critical dopant radius, the higher the conductivity.
Abstract: Changes in the lattice parameters of fluorite type MO2 oxides (M = Hf4+, Zr4+, Ce4+, Th4+, U4+) due to the formation of solid solutions can be predicted by proposed empirical equations. The equations show the generalized relationship between dopant size and ionic conductivity in the binary systems of these oxides, illustrating that the smaller the difference between the dopant ionic radius and the critical dopant radius, the higher the conductivity. The solubility limit of the same periodic group elements in fluorite-structure MO2 oxides decreaes linearly with the square of Vegard's slope for each solute as determined from the proposed equations.

587 citations


Journal ArticleDOI
TL;DR: The electrical conductivities of rare earth oxides were investigated in fluorite lattice of ceria at low additive concentrations in this article, where the ionic radii of the added cation were investigated.

405 citations


Journal ArticleDOI
TL;DR: In this paper, a polypyrrole has been preparede by chemical polymerization in FeCl 3 solution with various solvents, using methanol as a solvent, along with suitable polymerization conditions.

335 citations



Journal ArticleDOI
TL;DR: In this article, the conductivity and Seebeck coefficient of perovskite-type oxides La 1−x Sr x CoO 3− δ (x=0-0.7) were measured in 10 −5 -1 atm O 2 gas at temperatures 25 o -1000 o C.
Abstract: The conductivity and Seebeck coefficient of the perovskite-type oxides La 1−x Sr x CoO 3− δ (x=0-0.7) were measured in 10 −5 -1 atm O 2 gas at temperatures 25 o -1000 o C. The results are discussed in relation to the lattice-parameter and oxygen nonstoichiometry

207 citations


Journal ArticleDOI
01 Nov 1989-Nature
TL;DR: In this article, the results of measurements of the d.c. electrical conductivity of a mixture of perovskite and magnesiowiistite resulting from disproportionation of olivine, and of pure perovsite were made in an externally heated diamond-anvil cell at pressures of ∼40 GPa.
Abstract: ELECTRICAL conductivity is an important physical property of the Earth's mantle because it controls the transmission of geomagnetic signals from the core to the surface. The lower mantle, from a depth of 670 km down to the core–mantle boundary (2,990 km), is probably composed of (Mg,Fe)SiO3 perovskite and magnesiowustite, (Mg,Fe)O. Analysis of the transient and secular variations of the geomagnetic field yields values of the lower-mantle conductivity of the order of 1 S m−1 at a depth of 1,000 km, increasing to ∼100 S m−1 at the core–mantle boundary1,2. Information about the physical mechanism of the conductivity and its dependence on temperature and pressure would help to constrain the temperature profile in the Earth. In the only study published so far, Li and Jeanloz3,4 reported values of the conductivity of the silicate perovskite and of a mixture of perovskite and magnesio-wiistite lower than 10−3 S m−1 and concluded that the lower mantle is an insulator, thus casting doubt on the geomagnetic results. We report here the results of measurements of the d.c. electrical conductivity of a mixture of perovskite and magnesiowiistite resulting from disproportionation of olivine, and of pure perovskite. The measurements were made in an externally heated diamond-anvil cell at pressures of ∼40 GPa and temperatures from 25 °C to ∼400 °C. Conductivity increases with increasing iron content, increasing temperature and increasing pressure. The activation energy (0.35 eV for 11% Fe) decreases with increasing iron content. The results are compatible with an electron-hopping conduction mechanism. Extrapolation to the temperature appropriate for a depth of 1,100 km, which corresponds to the pressure of our experiments, yields a conductivity of the lower mantle of the order of 1 S m−1; extrapolation to the temperature and pressure of the core-mantle boundary yields values between 50 and 100 S m−1, in agreement with geomagnetic determinations.

202 citations


Journal ArticleDOI
TL;DR: In this paper, a theoretical model for the prediction of the thermal conductivity of fluid-saturated rocks is presented for predicting the overall conductivity in terms of the conductivities of the solid and fluid phases, the porosity, and an average aspect ratio of the spheroidal pores.

199 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reported detailed measurements of electrical conductivity σ and thermoelectric effect S in the mineral olivine and in synthetic forsterite as functions of temperature in the range from 1000° to 1500°C and oxygen partial pressure, and they interpreted the results to show that both materials have mixed ionic and extrinsic electronic conduction under these conditions.
Abstract: This paper reports detailed measurements of electrical conductivity σ and thermoelectric effect S in the mineral olivine and in synthetic forsterite as functions of temperature in the range from 1000° to 1500°C and oxygen partial pressure in the range from 10−10 to 104 Pa. The two most striking observations are strong conductivity anisotropy in forsterite and a sign change in S in olivine at 1390°C. These results are interpreted to show that both materials have mixed ionic and extrinsic electronic conduction under these conditions. On the basis of these interpretations, we infer that forsterite conductivity is dominated by electronic conduction in the a and b directions and probably by movement involving magnesium vacancies in the c direction, where far higher, PO2-independent conductivity is observed. Olivine appears to show mixed conduction under all the circumstances observed; at low temperatures, electron holes dominate but are superseded by magnesium vacancies at high temperatures.

191 citations


Journal ArticleDOI
TL;DR: In this paper, a simple and renewable two-band electrode for in situ determination of electronic conductivity in polyconjugated polymers is described, and the electrode was tested with electrodeposited polypyrrole, poly- N -methylpyrdrug, polyaniline and poly-3-methylthiophene.

189 citations


Journal ArticleDOI
TL;DR: On discute de l'interpretation de la puissance thermoelectrique dans un milieu heterogene, and a l'aide d'une compilation d'un ensemble of donnees, on analyse la thermo-puissance de polymeres conducteurs comme fonction of the conductivite et of the temperature.
Abstract: We discuss the interpretation of thermoelectric power in heterogeneous media, and using a compilation of many sets of data, we analyze the thermopower of conducting polymers as a function of conductivity and of temperature. For samples of very high conductivity, the thermopower (but not the conductivity) shows typical metallic temperature dependence, which is consistent with a heterogeneous model of metallic fibrils separated by thin electrical barriers. Metallic thermopower is expected rather generally to show significant nonlinearities as a function of temperature, and we demonstrate that the observed thermopower in some highly conducting polymers is very similar to the diffusion thermopower of metals in which a knee is produced at low temperatures by the electron-phonon interaction. The thermopower of moderately doped conducting polymers, like their conductivity, is generally consistent with a significant contribution from variable-range hopping.

176 citations


Journal ArticleDOI
TL;DR: Evolution de la morphologie et de la conductivite a differentes etapes de la polymerisation electrolytique as mentioned in this paper, i.e., evolution of morphologies and conductivites.
Abstract: Evolution de la morphologie et de la conductivite a differentes etapes de la polymerisation electrolytique

Journal ArticleDOI
TL;DR: In this paper, the HCl-doped polyaniline showed three major weight losses at around 100, 200, and 500°C which are assigned to removal of H2O and HCl, and decomposition of the polymer, respectively.
Abstract: Thermal characteristics of chemically synthesized polyaniline with various dopants have been studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), infrared spectroscopy, gel-permeation chromatography (GPC), and chemical titration. The HCl-doped polyaniline shows three major weight losses at around 100, 200, and 500°C which are assigned to removal of H2O and HCl, and decomposition of the polymer, respectively. Thermal aging of the HCl-doped polyaniline performed at 100, 150, and 200°C for various periods of time results in a decrease in conductivity. After the thermal treatments, the polymer can be re-doped with HCl to partially recover the conductivity. However, both the conductivity and the doping level cannot be restored to the level of the original materials owing probably to changes in morphology, crosslinking, or other chemical reactions.

Journal ArticleDOI
TL;DR: In this article, the conductivity of prepared flexible films was improved at least one order of magnitude in comparison to pristine PEONaI electrolytes by adding alumina powders, which was compared with those obtained previously by us for PEO based composite solid electrolytes containing NASICON.

Journal ArticleDOI
TL;DR: In this paper, the behavior of polyimide is discussed in view of infrared spectroscopy and ESCA, which shows the formation of graphite-like phases in polyimides and explains the high level of conductivity reached in this type of polymers.
Abstract: Ion beam irradiation of saturated polymers leads to the formation of new carbonaceous materials exhibiting enhanced electrical conductivity and increase of the optical absorption, which shifts gradually from the near UV to the visible. Different techniques, such as the analysis of the gas evolved from the polymer during irradiation, RBS and ERDA show the loss of the more volatile elements which results from the dissociation of the molecular structure. The consideration of different types of polymers indicates that some specific structural elements are preserved and that unsaturated bonds appear at high fluences, which are responsible for the loss of the insulating properties of polymers. The chemical bond modifications are discussed in view of infrared spectroscopy and ESCA, which shows the formation of graphite-like phases in polyimide and explains the high level of conductivity reached in this type of polymers. The appearance of conducting properties cannot be described by a simple model of carbonization and are governed both by the molecular structure of the parent polymer and the beam conditions. The behaviour of polyimide will be considered more in details because of the remarkable level of conductivity ( σ = 10 3 S/cm) and heat stability reached upon irradiation with heavy ions, which render this type of surface processing very efficient in order to produce conductive polymers.

Journal ArticleDOI
TL;DR: The properties of graphite intercalation compounds (GICs) are discussed with respect to possible applications as mentioned in this paper and some problems connected with the production and use of these sheets are discussed.
Abstract: The properties of graphite intercalation compounds (GIC’s) are discussed with respect to possible applications. Five families of intercalates give high electrical conductivity to GIC’s: pentafluorides leading to high conductivity, 108 S/m (higher than metallic copper); metal chlorides; fluorine and alkali metals with bismuth giving relatively high conductivity of the order of 107 S/m plus stability in air; and residual halogens showing extremely high stability under severe conditions, though the conductivity is only of the order of 106 S/m. Electrodes of different GIC’s have been tried in primary and secondary batteries, where their characteristics are high electrical conductivity and easy diffusion of electrochemically active species between the graphite layers. Primary lithium batteries of a covalent graphite fluoride are now widely used commercially. Secondary batteries using different host graphites and intercalates give interesting results. Large amounts of hydrogen can be stored in the functional space in alkali metal-GIC’s. The same GIC’s show high coefficients of isotope separation of hydrogen at liquid nitrogen temperature. The structure and texture of the host graphite play a decisive role in the absorption and separation behaviors of GIC’s. Exfoliated graphite prepared by rapid heating of GIC’s or their residue compounds leads to flexible graphite sheets which have great industrial applications. Some problems connected with the production and use of these sheets are discussed.

Journal ArticleDOI
TL;DR: In this paper, the perovskite structured ceramic SrCeO3, doped with Yb3+ and treated in water vapor, was investigated in the temperature range 25-250°C using complex impedance analysis to allow determination of the true bulk conductivity.

Journal ArticleDOI
TL;DR: The specific electric conductivity and viscosity of 7.5-100 wt% aqueous phosphoric acid electrolyte have been measured in the temperature range 25-200°C as discussed by the authors.
Abstract: The specific electric conductivity and viscosity of 7.5–100 wt% aqueous phosphoric acid electrolyte have been measured in the temperature range 25–200°C. The product of conductivity and viscosity was found to decrease exponentially with increasing temperature. This suggests that the electric conduction in phosphoric acid follows the Grotthus proton switching mechanism. The measured conductivity data were correlated by the following empirical equation: $$\begin{array}{*{20}c} {k\mu = {\rm A} exp [BT]}\\ {A = 702.7X^{1.5} - 1734.2X^2 + 1446.5X^{2.5} - 350.7X^3 }\\ {B = - 0.010163 + 0.011634X - 0.08313X^2 }\\ \end{array}$$ wherek is conductivity in mho cm−1; μ is viscosity in centipoise;T is the absolute temperature in K; andX is mole fraction of phosphoric acid in the electrolyte. The standard deviation for the percentage difference between the calculated and experimental values of 188 data points was less than 7.5%.

Journal ArticleDOI
TL;DR: The leading correction to the normal-state conductivity due to superconducting fluctuations is calculated as a function of temperature, externally applied magnetic field, and internal pair breaking for anisotropic high-T/sub c/ superconductors.
Abstract: The leading correction to the normal-state conductivity due to superconducting fluctuations is calculated as a function of temperature, externally applied magnetic field, and internal pair breaking for anisotropic high-${T}_{c}$ superconductors.


Journal ArticleDOI
X. X. Xi1, J. Geerk1, G. Linker1, Qi Li, O. Meyer1 
TL;DR: In this article, the Aslamazov-Larkin theory was applied to ultrathin films of YBa2Cu3O7−x with thicknesses down to 2 nm.
Abstract: Ultrathin films of YBa2Cu3O7−x with thicknesses down to 2 nm were grown on(100)SrTiO3 and (100)MgO by inverted cylindrical magnetron sputtering. Metallic behavior and zero resistance temperatures above 4.2 K were obtained in 3‐nm‐thick films on SrTiO3. Thinner films revealed temperature‐activated conductivity and only partial transitions to superconductivity due to inhomogeneities in the film morphology. On MgO, the critical film thickness leading to deteriorations of the transport properties was 6 nm. An analysis of the fluctuation‐enhanced conductivity near Tc in terms of the Aslamazov–Larkin theory [Phys. Lett. A 26, 238 (1968)] revealed three‐dimensional behavior even in the thinnest fully superconducting films.

Journal ArticleDOI
TL;DR: In this paper, a curve of optimum tensile strength against electrical conductivity was determined for alloys of Cu-Fe with iron contents from 10 to 30 wt %, and it was suggested that further improvements may be possible in Cu-Nb alloys by improved thermal mechanism processing.
Abstract: Alloys of Cu-Fe with iron contents from 10 to 30 wt % have been prepared by casting plus mechanical reduction. A series of heat treatments was done at various stages of the mechanical reduction to promote precipitation of the iron from the copper matrix with the hope of optimizing electrical conductivity at a given strength level. A curve of optimum tensile strength against electrical conductivity was determined. It was found to lie significantly below the available data for Cu-Nb alloys and it is suggested that further improvements may be possible in Cu-Fe alloys by improved thermal mechanism processing.

Journal ArticleDOI
TL;DR: In this paper, conditions for the production of thin pyrite layers by spray pyrolysis have been investigated for potential use as a solar cell material, and a simple hydrolysis reaction mechanism is proposed where thiourea, iron chloride and sulfur react on the hot substrate to form CO 2, NH 3, HCl and FeS 2.

Patent
29 Nov 1989
TL;DR: In this article, a conductivity modulated MOSFET with a gate electrode formed on a gate insulating film which is formed on channel region, the channel region being formed in a surface of the base layer between the semiconductor layer and the source layer.
Abstract: A conductivity modulated MOSFET, having a semiconductor substrate of a first conductivity type, a semiconductor layer of a second conductivity type formed on the semiconductor substrate and having a high resistance, a base layer of the first conductivity type formed in the semiconductor layer, a source layer of the second conductivity type formed in the base layer, a gate electrode formed on a gate insulating film which is formed on a channel region, the channel region being formed in a surface of the base layer between the semiconductor layer and the source layer, a source electrode ohmic-contacting the source layer and the base layer, and a drain electrode formed on the surface of the semiconductor substrate opposite to the semiconductor layer, characterized in that the conductivity modulated MOSFET has a saturation current smaller than a latch-up current when a predetermined gate voltage is applied to the gate electrode.

Journal ArticleDOI
TL;DR: In this paper, an expansion of Archie's law relates the electrical resistivity of the unsaturated zone to pore-water resistivity, porosity, saturation, electrical matrix conductivity, and lithological constants.
Abstract: An expansion of Archie's law relates the electrical resistivity of the unsaturated zone to pore-water resistivity, porosity, saturation, electrical matrix conductivity, and lithological constants. With decreasing saturation the effect of the matrix conductivity increases relative to the electrical conduction of the pore fluid. The bulk electrical resistivity depends on water quality and quantity due to its dependence on pore-water resistivity and porosity. It is also influenced by the hydraulic conductivity due to the surface conductivity of the grain matrix, which is proportional to grain size. Pore-water conductivity and grain-surface conductivity can be distinguished from each other if resistivity measurements at various degrees of saturation are available. Observations in test wells through glacial stream deposits with a neutron moisture probe show, as expected, a decrease in the saturation of the vadose zone during the transition from late spring to the dry summer season. This decrease was correlated with the transverse resistance of the unsaturated zone derived from an interpretation of geo-electrical depth soundings near the test wells. In the fine to medium sand of the glacial outwash material, the surface conduction of the grains was found to be negligibly small.

Journal ArticleDOI
TL;DR: In this paper, the electrical conductivity of diamond thin films produced by the hot-filament technique was found to increase when diborane is incorporated in the precursor gas mixture.
Abstract: The electrical conductivity of diamond thin films produced by the hot‐filament technique is found to increase when diborane is incorporated in the precursor gas mixture. The combination of well‐defined bulk conductivity measurements with quantitative secondary‐ion mass spectrometry and Raman spectroscopy shows that the conductivity increase is associated with atomic boron doping and rules out any significant role for a graphitic‐type component.

Journal ArticleDOI
TL;DR: In this paper, the high frequency resistance of a Nafion® perfluorosulfonic membrane is measured by means of the AC impedance technique using a mercury cell, which is able to follow the variation of the resistance as a function of the water content and of the nature of the cation present in the membrane.

Journal ArticleDOI
TL;DR: In this paper, the effect of high pressure up to 12 kbar on thermal conductivity of silicate rocks was determined by the transient hot wire method on 23 samples, with the exception of one sedimentary rock, one meteorite and manufactured fused and crystalline quartz.

Journal ArticleDOI
TL;DR: In this article, the authors generalize previous work on the relation between the frequency-dependent dielectric constant and conductivity and time correlation functions of electrical current and polarization in electrolyte solutions by allowing the ions and solvent molecules to be polarizable.
Abstract: We generalize previous work [J. Chem. Phys. 85, 6645 (1986)] on the relation between the frequency‐dependent dielectric constant and conductivity and time correlation functions of electrical current and polarization in electrolyte solutions by allowing the ions and solvent molecules to be polarizable. Detailed results are given for the infinite system (no boundary), spherical system embedded in a continuum and periodic boundary conditions. The Stillinger–Lovett (SL) sum rules are derived for these geometries. It is shown, in particular, that they provide a means of calculating the high frequency dielectric constant in a molecular dynamics simulation. A test of the phenomenological coefficient‐susceptibility relations and the SL conditions is presented in part II by performing molecular dynamics simulations on a model electrolyte solution with different boundary conditions.

Journal ArticleDOI
TL;DR: In this paper, the ultra-high-vacuum (UHV) preparation of PbPc thin-film samples (d < 1000 nm) on single-crystal SiO2 and Al2O3 substrates is reported.