Showing papers on "Conductivity published in 1975"
TL;DR: In this paper, the Coulomb interaction between localized electrons is shown to create a soft gap in the density of states near the Fermi level, and the form of the density within the gap is discussed.
Abstract: The Coulomb interaction between localized electrons is shown to create a 'soft' gap in the density of states near the Fermi level. The new temperature dependence of the hopping DC conductivity is the most important manifestation of the gap. The form of the density of states within the gap is discussed.
1,763 citations
TL;DR: In this article, an effective medium approximation for the conductivity tensor of a randomly inhomogeneous medium is generalized to treat, in principle, materials consisting of crystallites of arbitrary shape and conductivities tensors of arbitrary symmetry.
Abstract: An old effective-medium approximation for the conductivity tensor of a randomly inhomogeneous medium is generalized to treat, in principle, materials consisting of crystallites of arbitrary shape and conductivity tensors of arbitrary symmetry. The effective-medium approximation is roughly analogous to the coherent-potential approximation (CPA) of alloy theory. The analog of the average-$t$-matrix approximation (ATA) is also formulated in a general way. The method is fully tractable analytically for ellipsoidal crystallites. Several applications are discussed. The effective conductivity of a polycrystal consisting of randomly oriented uniaxial crystallites is calculated as a function of the anisotropy of the grains. For a model polycrystal in an intense magnetic field, the CPA and ATA are compared, the former giving more accurate results.
473 citations
TL;DR: In this paper, the conductivity of doped ceria with divalent or trivalent cations is investigated and compared to calcia-stabilized zirconia (CSZ), showing a higher conductivity, lower activation energy (0.76 eV), and absence of polarization effects to lower temperatures.
Abstract: Ceria doped with divalent or trivalent cations is a mixed conductor; conduction occurs predominantly by the motion of oxygen vacancies or by electrons, depending on the departure from stoichiometry. In order to establish the electrolytic domain at which behaves primarily as an ionic conductor with transference number , a careful study was made of the conductivity, σ, as a function of temperature and oxygen partial pressure, covering the range of 100;–10−22 atm in small steps. From these data the electrolytic domain was determined; it extends to about 10−13 atm at 600°C. When compared to calcia‐stabilized zirconia (CSZ), doped ceria shows a higher conductivity, lower activation energy (0.76 eV) for anion vacancy migration, and absence of polarization effects to lower temperatures. These results indicate that doped ceria may be an attractive candidate for fuel cells and other applications at temperatures below those at which CSZ is useful.
438 citations
TL;DR: In this paper, an extensive calculation of the optical-phonon-assisted transition rates for non-adiabatic electronic hopping motion in a solid is presented, which involves no restrictions on either the magnitude of the electron-lattice coupling strength, the temperature or the difference between the electronic energies of the initial and final sites.
Abstract: An extensive calculation of the optical-phonon-assisted transition rates for non-adiabatic electronic hopping motion in a solid is presented. Holstein's Molecular Crystal Model is used as a basis for study and the computation involves no restrictions on either the magnitude of the electron-lattice coupling strength, the temperature, or the difference between the electronic energies of the initial and final sites. In the strong-coupling small-polaron regime, the jump rates, associated d.c. conductivity, a.c. conductivity, and electric-field dependence of the d.c. conductivity, for a crystal are all calculated. These transport properties manifest qualitatively distinct behaviours corresponding to whether the temperature is above or well below the optical-phonon temperature. In the low-temperature regime the energy-conserving processes which involve the absorption of the minimum amount of vibrational energy provide the dominant contribution to the thermally activated jump rates. At sufficiently high...
287 citations
TL;DR: Kirchhoff's transformation is summarised in a form appropriate for semiconductor-device heat sinks and then illustrated with a brief application to the thermal resistance of a GaAs laser.
Abstract: Kirchhoff's transformation is summarised in a form appropriate for semiconductor-device heat sinks and then illustrated with a brief application to the thermal resistance of a GaAs laser. Under the most common semiconductor boundary conditions his transformation immediately converts the steady-state linear temperature rise (based on a temperature-independent conductivity σ 0 ) of a uniform heat sink of any shape into the nonlinear rise [based on a temperature-dependent conductivity σ ( T ) of any functional form].
143 citations
TL;DR: In this paper, the energy levels of an electron in a disordered two-dimensional lattice are evaluated numerically for the honeycomb, square and triangular lattices with between 36 and 196 sites.
Abstract: The energy levels of an electron in a disordered two-dimensional lattice are evaluated numerically for the honeycomb, square and triangular lattices with between 36 and 196 sites. The density of states and their localization properties are deduced from the results and the dependence of the positions of the mobility edges on disorder is studied. An analysis of the conductivity confirms the claim that the minimum metallic conductivity should have a universal value in two dimensions and that value was found to be (0.12+or-0.03)e2/h. A comparison of the predictions for the conductivity with the weak scattering limit is given.
139 citations
TL;DR: In this article, optical absorption measurements indicate two Jahn-Teller-split Fe2+ crystalline-field peaks and an absorption edge near 2.4 eV, independent of stoichiometry.
131 citations
TL;DR: In this article, it was concluded from these experiments that the high dark conductivity observed is an interface phenomenon that is due to localized field enhancement near the injecting contact, not being due to positive oxide charge.
Abstract: Several dark‐current and photocurrent techniques have been used to determine the nature of high dark conductivity observed in oxides grown from polycrystalline silicon. Photocurrent measurements on polycrystalline Si‐SiO2‐Al MOS structures give idential interface energy barrier heights to those on single‐crystal Si‐SiO2‐Al MOS structures, and do not show the presence of any measurable oxide charge. Dark‐current measurements on polycrystalline Si MOS structures oxidized to varying degrees show an abrupt conductivity decrease when the polycrystalline Si is completely oxidized to the underlying single‐crystal Si substrate. It is concluded from these experiments that the high dark conductivity observed is an interface phenomenon that is due to localized field enhancement near the injecting contact. This field enhancement, not being due to positive oxide charge, is speculated to be caused by surface asperities.
125 citations
TL;DR: In this article, the electrical conductivity of In2O3 has been measured up to 1400°C in air and the temperature dependence of the conductivity at high temperatures yields an activation energy of 1.5 ± 0.1 eV.
123 citations
TL;DR: In this article, the effects of temperature, f O2 and composition on the electrical conductivity of silicate liquids have been experimentally determined from 1200 to 1550°C under a range of f O 2 conditions sufficient to change the oxidation state of Fe from predominantly Fe 2+ to Fe 3+.
112 citations
TL;DR: In this article, a two-phase material with cylindrical phase boundaries is considered and the generators of the phase boundaries are parallel to the z axis and the x and y axes are the principal axes of the effective conductivity tensor.
Abstract: A two−phase material in which the phase boundaries are cylindrical surfaces is considered. The generators of the phase boundaries are parallel to the z axis and the x and y axes are the principal axes of the effective conductivity tensor. If the two phases have conductivities σ1 and σ2, then the effective conductivity σx* (σ1,σ2) (in the x direction) of the material and the effective conductivity σy* (σ2,σ1) (in the y direction) of the material obtained by interchanging the two phases are related by σx* (σ1,σ2) σy* (σ2,σ1) =σ1,σ2. For a statistically isotropic material σx* (σ1,σ2) =σy* (σ1,σ2) =σ* (σ1,σ2). If, in addition, the material is statistically symmetric so that interchange of the two phases yields again the same material, then σ* (σ1,σ2) =σ* (σ2,σ1) = (σ1σ2)1/2.
TL;DR: The ionic conductivity above and below the melting temperature has been measured for the fluorides, chlorides, and bromides of calcium, strontium, and barium and for magnesium chloride as mentioned in this paper.
TL;DR: In this article, the role of ion-ion repulsion and ion-phonon coupling in superionic conduction is explored and it is argued that the order-disorder phase transition is not associated with the conductivity discontinuity, but with a higher temperature second order phase transition which has been seen in some superionic conductors and which is predicted for others.
TL;DR: In this article, the channel conductance and the Hall voltage in a wide and a long rectangular samples of n-type MOS inversion layers on Si(100) surfaces were measured in a strong magnetic field of 100 kOe at 1.6 K. Good agreement was obtained only in the wide sample by the use of a modified Hall-effect field correction.
Abstract: The channel conductance and the Hall voltage in a wide and a long rectangular samples of n -type MOS inversion layers on Si(100) surfaces are measured in a strong magnetic field of 100 kOe at 1.6 K. A method of transformation from the conductance and the Hall voltage data to the transverse conductivity σ x x and the Hall conductivity σ x y in arbitrary magnetic field strength based on the Hall-effect field correction are described. The conductivity σ x x and σ x y are compared with σ x x measured directly in a Corbino disk sample and σ x y predicted by the quantum transport theory and the electron mobility data. Good agreement is obtained only in the wide sample by the use of a modified Hall-effect field correction. Effects of the electrode resistance, the side edges and the sample geometry are discussed in connection to the modification of the Hall-effect field correction.
TL;DR: The Onsager theory of dissociation, based upon the solution of Brownian equations of motion of charge carriers interacting through a Coulomb potential in an applied electric field, is shown to account for the electric fieldenhanced conductivity in solids as discussed by the authors.
Abstract: The Onsager theory of dissociation, based upon the solution of Brownian equations of motion of charge carriers interacting through a Coulomb potential in an applied electric field, is shown to account for the electric‐field‐enhanced conductivity in solids. In contradistinction to often quoted one‐dimensional macroscopic Poole‐Frenkel theory and its varied three‐dimensional modifications, the Onsager theory is microscopic in nature and thus provides a quantitative description of the observed field enhancement of the conductivity.
TL;DR: In this paper, the electrical conductivity induced by pulse irradiation of liquid cyclohexane has been studied by means of microwave absorption, and it is shown that the conductivity in pure cyclomethane, due principally to the excess electron, is reduced to less than 10% of the initial value on addition of 5 × 10 −4 M of the electron scavenger SF 6.
Patent•
21 Aug 1975TL;DR: In this article, the electrical conductivity of a lamella of conducting material (e.g., semiconductor wafers or metal films) is measured by introducing the lamella into the oscillatory magnetic field of the inductive element of an L-C tank circuit.
Abstract: METHOD FOR THE NONCONTACTING MEASUREMENT OF THE ELECTRICAL CONDUCTIVITY OF A LAMELLA Abstract of the Disclosure The electrical conductivity of a lamella of conducting material (e.g., semiconductor wafers or metal films) is measured by introducing the lamella into the oscillatory magnetic field of the inductive element of an L-C tank circuit. The tank circuit is the frequency determining portion of an oscillator which is adjusted, upon sample introduction, to restore the magnitude of oscillation. With suitable choice of circuit parameters, the incremental current in the tank circuit is linearly proportional to the sheet conductivity of the lamella. An exemplary apparatus, operating at approximately 10 MHz with a 1 cm2 measurement area exhibited approximately 1% linearity over a 100 to 1 range of conductivity with a resolution of approximately one part in 104 with a limiting sensitivity of 1011 carriers per square cm.
TL;DR: In this paper, the conduction mechanisms of ultrathin (10−100 A) metal films are investigated and the electrical conductivity and activation energy of discontinuous Au films are correlated with island size and separation and average film thickness.
Abstract: The conduction mechanisms of ultrathin (10−100 A) metal films are investigated. The electrical conductivity and activation energy of discontinuous Au films grown in UHV are correlated with island size and separation and average film thickness. The relationship between film conductivity and deposition rate and substrate temperature is presented. Film temperature data indicate the validity of the proposed model. Some anomalous conductivity effects are reported for films deposited below the UHV range. The results are explained in terms of substrate and film surface contamination. Data are presented indicating the sensitivity of the conductivity of discontinuous films to ambient gas concentration. Reversible and irreversible situations are discussed.
TL;DR: In this article, a technique for making four probe conductivity measurements on small, fragile single crystals of organic compounds is described, where the physical constraint of the sample is minimal, allowing repeated thermal cycling.
Abstract: A technique is described for making four probe conductivity measurements on small, fragile single crystals of organic compounds. Physical constraint of the sample is minimal, allowing repeated thermal cycling.
TL;DR: In this paper, the thermal conductivity of TTF-TCNQ has been determined through a simultaneous measurement of the specific heat and thermal diffusivity using an ac method, assuming the free-electron Lorentz number to be appropriate for this material, that all of the observed electrical conductivity is the result of normal heatcarrying electrons.
Abstract: The thermal conductivity of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) has been determined through a simultaneous measurement of the specific heat and thermal diffusivity using an ac method. A steplike anomaly has been observed which coincides in temperature with anomalies in the specific heat and electrical conductivity. Interpreting ths step to be due to the loss of the electronic contribution to the thermal conductivity at the metal-insulator transition, we show that the Lorentz number is very close to the free-electron value for conductivity enhancement factors in the range 10-30. A mean-field calculation of the thermal current due to paraconductive fluctuations demonstrates that this contribution is negligible. The conclusion follows, assuming the free-electron Lorentz number to be appropriate for this material, that all of the observed electrical conductivity is the result of normal heat-carrying electrons.
TL;DR: The electrical resistivity of amorphous carbon films getter-sputtered at 95°K is well fitted between 300 and 20°K by the relation ϱ = ϱ0 exp [(T0/T)14] with T 0 ≅ 7 × 107K as discussed by the authors.
TL;DR: In this paper, the d.c. conductivity of NaI has been measured in the intrinsic and extrinsic temperature regions and the formation energy Es for the Schottky defects and the energy Em+ for the cation vacancy migrati...
Abstract: The d.c. conductivity of NaI has been measured in the intrinsic and extrinsic temperature regions. The formation energy Es for the Schottky defects and the energy Em+ for the cation vacancy migrati...
TL;DR: The thermal conductivity of argon is determined in the temperature range 350-2500 K in a carefully designed conductivity column and is given by within an estimated uncertainty of about ± 1·5 per cent as mentioned in this paper.
Abstract: The thermal conductivity of argon is determined in the temperature range 350–2500 K in a carefully designed conductivity column and is given by within an estimated uncertainty of about ±1·5 per cent. These values, which are derived from heat transfer measurements in the continuum range, are compared with conductivity values obtained from similar data taken in the temperature-jump regime. The k values are also compared with other available conductivity and viscosity data, and with the predictions based on kinetic theory in conjunction with intermolecular potentials, and the principle of corresponding states. These comparisons have led to many interesting conclusions concerning the quality of other experimental data and the appropriateness of different intermolecular potentials. The predictions based on corresponding states appear most reliable.
TL;DR: In this paper, a multilament superconductor, treated as an anisotropic state of matter, is considered and the results for the permeability, conductivity, and dielectric constant of the superconductivity of the filaments are given.
Abstract: Results are given for the permeability, conductivity, and dielectric constant of a multifilament superconductor, treated as an anisotropic state of matter The calculations are made for the limiting cases of strong and weak ac magnetic fields compared with the field required for complete penetration of the filaments General expressions are given for the ac power loss
TL;DR: In this article, the electrical conductivity, optical absorption, electron spin resonance, Raman spectrum and electron diffraction of a set of a-Si films vaccum deposited at room temperature are reported.
Abstract: We report measurements on the electrical conductivity, optical absorption, electron spin resonance, Raman spectrum and electron diffraction of a set of a-Si films vaccum deposited at room temperature. As revealed by absorption at about 10 μm some of the films grown at deposition rates of about 0.4 A/sec contain considerable amounts of oxygen. All the properties, except Raman spectra and electron diffraction, are found to vary strongly with the deposition rate and the background pressure during evaporation. Qualitatively, these variations show significant correlations. For instance, if the electrical conductivity is higher so is the spin density, the optical absorption and the low-frequency refractive index. Also, increasing oxygen content leads to lower conductivity. In addition, we have tried to establish a rough quantitative relation between the shift in the optical gap and the change in the spin density by connecting each of these changes to the variation in the low-frequency refractive index. The temperature dependence of the electrical conductivity was also measured and it was found that below about 150 K the data are consistent with recent theoretical predictions, i.e., log σ exhibits a ( 1/T) 1 4 dependence.
TL;DR: In this article, a site percolation model of 50×50×50 sites is examined by computer to treat the generalized conductivity characteristic of a two-phase material with random structure (porous material).
Abstract: A site percolation model of 50×50×50 sites is examined by computer to treat the generalized conductivity characteristic of a two-phase material with random structure (porous material) An enumeration of clusters of one phase (pores) in the model provides cluster-size distribution, percolation probability P ( p ) and an estimate of the critical probability 031< p c <032 for the site percolation problem in a simple cubic lattice A direct calculation of the bulk electrical conductivity of the 3D random resistor network derived from the model reveals a special relation between the conductivity k and the concentration p of the one phase (porosity p of the model): k =Const ( p - p c ) 1725±0005 in which p c =0318±0002 The above power law indicates a critical nature of the phenomenon
TL;DR: In this article, the analysis of dielectric measurements made on montmorillonites saturated by bivalent cations was performed at frequencies ranging from 300 to 10,000 Hz.
Abstract: This study deals with the analysis of dielectric measurements made on montmorillonites saturated by bivalent cations. These measurements are performed between -150~ and +30~ at frequencies ranging from 300 to 10,000 Hz. Their interpretation is based on a numerical analysis allowing determination of the dielectric losses due to free charge carriers conductivity phenomena and losses due to relaxation phenomena. The free charge carriers conductivity is due to the movement of protons. It depends very much on the nature of compensating cations and on the water content and seems to be closely related to the characteristics of the swelling. Two types of relaxation phenomenon are described: a Debye relaxation due to electric dipole rotations and a Maxwell-Wagner relaxation due to heterogeneity effects. The analysis of the first phenomenon leads to the examination of the values of the relaxation time. It appears that the rotations of water molecules are difficult with bivalent cations. This essentially is shown by the high activation energy of the phenomenon. The discussion of these parameters shows that the state of adsorbed water molecules are certainly different as compared to the state of water molecules in ice or in liquid water. The characteristics of the second relaxation phenomenon are closely dependent on the free carriers charge conductivity.
TL;DR: In this article, the temperature dependences of the molar volumes, densities and electric conductivities of molten lead and zinc carboxylates of even numbered chain length from C6 to C18 inclusive are reported at temperatures from the melting points to just below the decomposition points.
Abstract: The temperature dependences of the molar volumes, densities and electric conductivities of molten lead and zinc carboxylates of even numbered chain length from C6 to C18 inclusive are reported at temperatures from the melting points to just below the decomposition points. The molar volumes are linear functions of chain length and nearly so of temperature within the interval of measurement. Semilogarithmic plots of specific conductivity against inverse temperature for the zinc soaps are linear and the slopes decrease slightly with increasing chain length, representing enthalpies of about 40 kJ mol–1. A simple model for the system which proposes that the conduction is due to a small concentration of relatively mobile Zn2+ ions is presented.With the lead salts plots of log specific conductivity against inverse temperature show curvature. Attempts to fit the data to the equation κ=A exp[–C/(T–T0)] showed non-random deviations. Instead, a dissociation equilibrium in the melt is proposed which reaches completion in the high temperature range. It is proposed that the major current carrier is the lead ion and values of about 15 kJ mol–1 are found for its activation energy for mobility. An approximate method is used to estimate ΔH and ΔS for the proposed dissociation reaction from the conductivity data. They are found to be about 85 kJ mol–1 and 190 J mol–1 K–1 respectively for all the compounds studied. The high entropy change may indicate considerable aggregation of the undissociated species in the melts.