Showing papers on "Conductivity published in 2004"
TL;DR: Pure copper samples with a high density of nanoscale growth twins are synthesized and show a tensile strength about 10 times higher than that of conventional coarse-grained copper, while retaining an electrical conductivity comparable to that of pure copper.
Abstract: Methods used to strengthen metals generally also cause a pronounced decrease in electrical conductivity, so that a tradeoff must be made between conductivity and mechanical strength. We synthesized pure copper samples with a high density of nanoscale growth twins. They showed a tensile strength about 10 times higher than that of conventional coarse-grained copper, while retaining an electrical conductivity comparable to that of pure copper. The ultrahigh strength originates from the effective blockage of dislocation motion by numerous coherent twin boundaries that possess an extremely low electrical resistivity, which is not the case for other types of grain boundaries.
2,584 citations
TL;DR: In this paper, the Brownian motion of nanoparticles at the molecular and nanoscale level is a key mechanism governing the thermal behavior of nanoparticle-fluid suspensions (nanofluids).
Abstract: We have found that the Brownian motion of nanoparticles at the molecular and nanoscale level is a key mechanism governing the thermal behavior of nanoparticle–fluid suspensions (“nanofluids”). We have devised a theoretical model that accounts for the fundamental role of dynamic nanoparticles in nanofluids. The model not only captures the concentration and temperature-dependent conductivity, but also predicts strongly size-dependent conductivity. Furthermore, we have discovered a fundamental difference between solid/solid composites and solid/liquid suspensions in size-dependent conductivity. This understanding could lead to design of nanoengineered next-generation coolants with industrial and biomedical applications in high-heat-flux cooling.
1,459 citations
TL;DR: In this article, activation barriers to Li ion motion are calculated and an estimate for Li diffusion constants, in the absence of electrical conductivity constraints, is made using first-principles methods.
Abstract: Materials with the olivine structure form an important class of rechargeable battery cathodes. Using first-principles methods, activation barriers to Li ion motion are calculated and an estimate for Li diffusion constants, in the absence of electrical conductivity constraints, is made. Materials with Fe, Co, Ni are considered. Li diffuses through one-dimensional channels with high energy barriers to cross between the channels. Without electrical conductivity limitations the intrinsic Li diffusivity is high. © 2003 The Electrochemical Society. All rights reserved.
1,005 citations
TL;DR: In this article, the electrical conductivity of polyamide-6 and carbon nanotubes (NT) composites was analyzed and compared to carbon black filled polyamide 6 composites.
695 citations
TL;DR: In this article, the authors proposed a mechanism of conductivity for the proton migration in polybenzimidazole (PB1) film, a candidate polymer electrolyte membrane (PEM) for high-temperature (120-200°C) fuel cells, was cast from PBI/trifluoacetyl/H 3 PO 4 solution with constant molecular weight PBI powder and various acid doping levels.
Abstract: Polybenzimidazole (PB1) film, a candidate polymer electrolyte membrane (PEM) for high-temperature (120-200°C) fuel cells, was cast from PBI/trifluoacetyl/H 3 PO 4 solution with constant molecular weight PBI powder and various acid doping levels. Conductivity measurements on these membranes were performed using an ac method under controlled temperature and relative humidity (RH). A complete set of conductivity data for H 3 PO 4 acid-doped PBI is presented as a function of temperature (60-200°C), RH (5-30%), and acid doping level (300-600 mol %). A mechanism of conductivity is proposed for the proton migration in this PBI/acid system based on this and previous work. Proton transfer in this system appears to occur along different paths for different doping levels, RHs, and temperatures. Hydrogen bonds immobilize the anions and form a network for proton transfer by a Grotthuss mechanism. The rate of proton transfer involving H 2 O is faster, leading to higher conductivity at higher RH. The order of the rate of proton transfer between various species is H 3 PO 4 (H 2 PO 4 -)...H-O-H> H 3 PO 4 ...H 2 PO - 4 > N-H + ...H 2 PO 4 - + N-H + ...H-O-H > N-H + ...N-H. The upper limit of proton conductivity is given by the conductivity of the liquid state H 3 PO 4 .
642 citations
TL;DR: A template-free chemical synthesis is described that produces uniform polyaniline nanofibers with diameters below 100 nm, and the interfacial polymerization can be readily scaled to make gram quantities.
Abstract: The conjugated polymer polyaniline is a promising material for sensors, since its conductivity is highly sensitive to chemical vapors. Nanofibers of polyaniline are found to have superior performance relative to conventional materials due to their much greater exposed surface area. A template-free chemical synthesis is described that produces uniform polyaniline nanofibers with diameters below 100 nm. The interfacial polymerization can be readily scaled to make gram quantities. Resistive-type sensors made from undoped or doped polyaniline nanofibers outperform conventional polyaniline on exposure to acid or base vapors, respectively. The nanofibers show essentially no thickness dependence to their sensitivity.
531 citations
TL;DR: A moving particle model developed from the Stokes-Einstein formula explains the temperature effect and predictions from the combined model agree with the experimentally observed values of conductivity enhancement of nanofluids.
Abstract: A comprehensive model has been proposed to account for the large enhancement of thermal conductivity in nanofluids and its strong temperature dependence, which the classical Maxwellian theory has been unable to explain. The dependence of thermal conductivity on particle size, concentration, and temperature has been taken care of simultaneously in our treatment. While the geometrical effect of an increase in surface area with a decrease in particle size, rationalized using a stationary particle model, accounts for the conductivity enhancement, a moving particle model developed from the Stokes-Einstein formula explains the temperature effect. Predictions from the combined model agree with the experimentally observed values of conductivity enhancement of nanofluids.
528 citations
TL;DR: In this paper, the impedance of cubic perovskite BaZr0.9Y0.1O3-δ has been systematically investigated in dry and wet atmospheres at high and low oxygen partial pressures.
Abstract: The impedance of the cubic perovskite BaZr0.9Y0.1O3-δ has been systematically investigated in dry and wet atmospheres at high and low oxygen partial pressures. In the grain interior, conductivity contributions from oxygen ions, electron holes, and protons can be identified. Below 300°C, proton conduction dominates and increases linearly with the frozen-in proton concentration. The proton mobility, with an activation energy of 0.44 ± 0.01 eV is among the highest ever reported for a perovskite-type oxide proton conductor. For dry oxygen atmos-pheres, electron hole conduction dominates with an activation energy of ∼0.9 eV. At temperatures <500°C, the grain-boundary conductivity can be separated and increases upon incorporation of protons. The high electrical conductivity and chemical stability make acceptor-doped barium zirconate a good choice for application as a high-temperature proton conductor.
451 citations
TL;DR: In this paper, an incoherent particle model was developed to calculate the phonon thermal conductivity of superlattice nanowires, which is an extension of the photon net-radiation method and Schuster-Schwarzschild approximation.
Abstract: An incoherent particle model has been developed to calculate the phonon thermal conductivity of superlattice nanowires. This is an extension of the photon net-radiation method and Schuster–Schwarzschild approximation to dispersive acoustic phonons in a gray medium. By comparing the roughness and geometric variations of typical nanowires to the characteristic phonon wavelength (∼1 nm at 300 K), diffuse scattering and incoherent three-dimensional dispersion are justified. An isotropic sine-type (Born–von Karman) dispersion is used, which requires only the sound velocity, atomic number density, and bulk conductivity to fully describe a material. A simple picture is also given in terms of Matthiessen’s rule and three effective mean free paths. Agreement with available experimental data is poor at the smallest diameters, but good above 30 nm diameter. Compared to a conventional superlattice, calculations show that the additional sidewall scattering in a superlattice nanowire can reduce the thermal conductivity...
372 citations
TL;DR: The temperature and electrical field dependent conductivity of n-type CdSe nanocrystal thin films is investigated and the complete behavior is very well described by variable range hopping with a Coulomb gap.
Abstract: The temperature and electrical field dependent conductivity of $n$-type CdSe nanocrystal thin films is investigated. In the low electrical field regime, the conductivity follows $\ensuremath{\sigma}\ensuremath{\sim}\mathrm{exp} [\ensuremath{-}({T}^{*}/T{)}^{1/2}]$ in the temperature range $10lTl120\text{ }\text{ }\mathrm{K}$. At high electrical field, the conductivity is strongly field dependent. At 4 K, the conductance increases by 8 orders of magnitude over one decade of bias. At a very high field, conductivity is temperature independent with $\ensuremath{\sigma}\ensuremath{\sim}\mathrm{exp} [\ensuremath{-}({E}^{*}/E{)}^{1/2}]$. The complete behavior is very well described by variable range hopping with a Coulomb gap.
367 citations
TL;DR: LiFePO4/carbon composite cathode materials were synthesized by a sol-gel process as discussed by the authors, where the citric acid in the developed sol−gel process plays the role not only as a complexing agent but also as a carbon source, which improves the conductivity of the composites and hinders the growth of the particles.
Abstract: LiFePO4/carbon composite cathode materials were synthesized by a sol–gel process. The citric acid in the developed sol–gel process plays the role not only as a complexing agent but also as a carbon source, which improves the conductivity of the composites and hinders the growth of LiFePO4 particles. Nano-sized LiFePO4 particles without the impurity phase were successfully synthesized. The grain size of LiFePO4 particles in the range of 20–30 nm is obtained at calcined temperatures from 450 to 850 °C. Increasing the calcination temperature leads to a decrease in the carbon content but an increase in the conductivity of the composites in the range of 400–850 °C. However, the conductivity slightly decreases if the calcination temperature further increases to 950 °C. The LiFePO4/carbon composite synthesized at 850 °C shows the highest conductivity (10−3 S cm−1), the highest specific capacity, and the best rate capability among the synthesized materials. It is worthy to note that the cell performance of the LiFePO4 depends on the electrochemical cycling procedure employed.
TL;DR: In this article, a technique to measure the electrical conductivity of single molecules has been demonstrated, which is based on trapping molecules between an STM tip and a substrate, using thiol groups present at each end of the molecule.
Abstract: A technique to measure the electrical conductivity of single molecules has been demonstrated. The method is based on trapping molecules between an STM tip and a substrate. The spontaneous attachment and detachment of α,ω-alkanedithiol molecular wires was easily monitored in the time domain. Electrical contact between the target molecule and the gold probes was achieved by the use of thiol groups present at each end of the molecule. Characteristic jumps in the tunnelling current were observed when the tip was positioned at a constant height and the STM feedback loop was disabled. Histograms of the measured current jump values were used to calculate the molecular conductivity as a function of bias and chain length. In addition, it is demonstrated that these measurements can be carried out in a variety of environments, including aqueous electrolytes. The changes in conductivity with chain length obtained are in agreement with previous results obtained using a conducting AFM and the origin of some discrepancies in the literature is analysed.
TL;DR: In this article, the authors presented the conductive behavior of carbon fiber cement-based composites and the relationship between conductivity and volume fraction of carbon fibre indicated that the statistical percolation theory is suitable and applicable for the change rule of conductivity of system with the volume of the carbon fiber.
Abstract: The conductive behavior of carbon fiber cement-based composites is presented. The influence of carbon fiber volume, size, cement-based matrix, relative humidity and curing age on the characteristic of system were studied. The relationship between conductivity and volume fraction of carbon fiber indicated that the statistical percolation theory is suitable and applicable for the change rule of conductivity of system with the volume of carbon fiber. Based on the classic percolation theory, the percolation threshold of carbon fiber cement-based composites was determined as φ=φc2 and the conductive mechanism changes from electron tunneling conduction to ohmic contacting conduction. The studies have offered basic theory for smart cement-based composites.
TL;DR: In this article, the role of chemical bonding between the matrix and the fiber on thermal transport in carbon nanotube organic matrix composites was analyzed using molecular dynamics simulations and it was shown that chemical bonding significantly reduces tube-matrix thermal boundary resistance, but at the same time decreases intrinsic tube conductivity.
Abstract: We use molecular dynamics simulations to analyze the role of chemical bonding between the matrix and the fiber on thermal transport in carbon nanotube organic matrix composites. We find that chemical bonding significantly reduces tube-matrix thermal boundary resistance, but at the same time decreases intrinsic tube conductivity. Estimates based on the effective medium theory predict increase, by about a factor of two, of the composite conductivity due to functionalization of single-walled nanotubes with aspect ratios within 100–1000 range. Interestingly, at high degree of chemical functionalization, intrinsic tube conductivity becomes independent of the bond density.
TL;DR: In this article, a detailed investigation of the processing parameters influencing the oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) and a methanol-substituted derivative was performed with the goal of maximizing the conductivity of the polymer.
Abstract: A detailed investigation of the processing parameters influencing the oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) and a methanol-substituted derivative (EDOT-CH2OH) was performed with the goal of maximizing the conductivity of the polymer. We show that the conductivity can be significantly enhanced by varying the monomer, oxidant (iron(III) p-toluenesulfonate (Fe(OTs)3)), weak base (imidazole (Im)), solvent (various alcohols), and solution concentrations. The effect of each variable on the final materials properties is investigated, and the parameters have been optimized to achieve conductivities as high as 900 S cm−1. Surface resistance below 150 Ω/□ for 80-90 nm thick films with visible-spectrum transparency exceeding 80 % is achieved. The combination of these properties makes the films highly suitable for numerous device applications.
TL;DR: The high dielectric constant in "SrCu3Ti4O4O12" and the giant Dielectric Constant (GDC) in CaCu3 Ti4O6O12 are based on a barrier layer mechanism as discussed by the authors.
Abstract: The high dielectric constant in “SrCu3Ti4O12” and the giant dielectric constant in CaCu3Ti4O12 are based on a barrier layer mechanism. Conductivity in the conducting regions is related to Ti on Cu sites. The insulating barriers are between crystallites in “SrCu3Ti4O12” but within the crystallites in CaCu3Ti4O12.
TL;DR: In this paper, a field effect transistor (FET) based on poly(3-n-hexylthiophene) was investigated to determine the influence of moisture on device characteristics and gain a deep understanding of the mechanism underlying the susceptibility to air of the operation of FETs of this kind.
Abstract: We investigated a field-effect transistor (FET) based on a poly(3-n-hexylthiophene) (P3HT) to determine the influence of moisture on device characteristics and thus gain a deep understanding of the mechanism underlying the susceptibility to air of the operation of FETs of this kind. The fundamental output characteristics, which include effective field-effect modulation and saturation behavior in the output current, remained almost the same for every current–voltage profile in a vacuum, N2 and O2. By contrast, operation in N2 humidified with water resulted in enlarged off-state conduction and deterioration in the saturation behavior, in the same manner as that experienced with exposure to room air. We concluded that atmospheric water had a greater effect on the susceptibility of the device operation to air than O2, whose p-type doping activity as regards P3HT caused only a small increase in the conductivity of the active layer and a slight decrease in the field-effect mobility with exposure at ambient pres...
17 Aug 2004
TL;DR: In this paper, an analytical formulation of Bergman-Milton conductivity bounds is used in a different way to obtain rigorous bounds on the real thermal conductivity of a fluid-saturated porous material.
Abstract: An analytical formulation of Bergman–Milton conductivity bounds is used in a different way to obtain rigorous bounds on the real thermal conductivity of a fluid-saturated porous material. These bounds do not depend explicitly on the porosity, but rather on two formation factors—one associated with the pore space and the other with the solid frame.
TL;DR: In this paper, the performance of a phase boundary nanoporous carbon |1.0m triethylmethylammonium tetrafluoroborate (TEMA) solution in acetonitrile (AN), γ-butyrolactone (GBL), acetone (DMK) and propylene carbonate (PC) was studied using the cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS) methods.
TL;DR: In this paper, electrical conductivity and gas sensing properties of MoO3 lattice were investigated. And two distinct conduction processes were identified from the conductivity experiments carried out under ambient air, moist oxygen, and moist argon.
Abstract: Electrical conductivity and gas sensing properties of MoO3 are investigated. The electrical conductivity is found to be independent of oxygen partial pressure in the temperature range 510–773 K. Two distinct conduction processes were identified from the conductivity experiments carried out under ambient air, moist oxygen, and moist argon. The conductivity in the low temperature range (510–578 K) are attributed to species arising from the reversibly inserted water molecules into MoO3 lattice. The conduction process in the high temperature region (578–773 K) are attributed to the non-stoichiometry existing in the sample due to the presence of Mo5+ ions which was confirmed by EPR and XPS investigations. Sensing characteristics of MoO3 towards NH3, H2, and LPG were studied. Experiments showed that the ammonia sensing mechanism of MoO3 involved the formation of molybdenum suboxides and nitride.
TL;DR: In this paper, the effects of field strength and multiple thermal treatments on electrical conductivity of strawberry products were investigated, and it was found that electrical conductivities depend on the strawberry-based product.
Abstract: The effects of field strength and multiple thermal treatments on electrical conductivity of strawberry products were investigated. Electrical conductivity increased with temperature for all the products and conditions tested following linear relations. Electrical conductivity was found to depend on the strawberry-based product. An increase of electrical conductivity with field strength was obvious for two strawberry pulps and strawberry filling but not for strawberry topping or strawberry-apple sauce. Thermal treatments caused visible changes (a decrease) in electrical conductivity values of both strawberry pulps tested, but the use of a conventional or ohmic pre-treatment induces a different behavior of the pulps’ conductivity values. Ascorbic acid degradation followed first order kinetics for both conventional and ohmic heating treatments and the kinetic constants obtained were in the range of the values reported in the literature for other food systems. The presence of an electric field does not affect ascorbic acid degradation.
TL;DR: The saturated vessel length is likely the optimal length because: (a) shorter vessels have lower conductivities, (b) longer vessels do not increase conductivity when functional yet decrease it more when cavitated, and (c) observed pit structure most closely optimized vessel conductivity at the saturated length.
Abstract: A model predicted pit and vessel conductivity, the air-seed pressure for cavitation, and the implosion pressure causing vessel collapse. Predictions were based on measurements from 27 angiosperm species with circular bordered pits and air-seed pressures of 0.2-11.3 MPa. Vessel implosion pressure exceeded air-seed pressure by a safety factor of 1.8 achieved by the increase in vessel wall thickness per vessel diameter with air-seed pressure. Intervessel pitting reduced the implosion pressure by 20 to 40%. Pit hydraulic conductivity decreased by 30-fold from low ( 10 MPa) air-seed pressure primarily because of decreasing pit membrane conductivity. Vessel conductivity (per length and wall area) increased with vessel length as higher lumen conductivity overcame low pit conductivity. At the "saturating vessel length," vessel conductivity maximized at the Hagen-Poiseuille value for the lumen per wall area. Saturated vessel conductivity declined by sixfold with increasing air-seed pressure because of increased wall thickness associated with increased implosion resistance. The saturated vessel length is likely the optimal length because: (a) shorter vessels have lower conductivities, (b) longer vessels do not increase conductivity when functional yet decrease it more when cavitated, (c) observed pit structure most closely optimized vessel conductivity at the saturated length, and (d) saturated lengths were similar to measured lengths.
TL;DR: Close Ag..Ag interionic contacts of 3.226(1) A were observed in the one-dimensional anionic chain, and the relatively high melting point among the EMI salts with a monoanion appears to be governed essentially by these direct Ag...Ag interactions.
Abstract: New 1-ethyl-3-methylimidazolium (EMI) salts [EMI][C(CN)3] and [EMI][Ag(CN)2] were prepared and characterized. The C(CN)3 salt has a melting point at −11 °C and shows a low viscosity (18 cP) and a high ionic conductivity (1.8 × 10-2 S cm-1) at room temperature. This conductivity is less than that of [EMI][N(CN)2] salt (2.7 × 10-2 S cm-1), possibly due to the larger molecular weight of the anion. The first EMI salt containing Ag(I) complexes [EMI][Ag(CN)2] has a higher melting point of 73 °C. In the crystal, the C−H···π interionic interactions between cations construct zigzag chains in the cationic two-dimensional layer. Close Ag··Ag interionic contacts of 3.226(1) A were observed in the one-dimensional anionic chain, and the relatively high melting point among the EMI salts with a monoanion appears to be governed essentially by these direct Ag···Ag interactions.
TL;DR: In this paper, the authors explored the interrelations among several structural and thermodynamic parameters for fluorite and perovskite oxides by considering their sensitivities to the individual ionic radii.
TL;DR: In this paper, platelet-shaped particles of similar size and shape were investigated as fillers for improving the thermal conductivity of polymer-ceramic composite materials, and a mechanism was proposed whereby deformation of the soft filler particles provided improved particle-to-particle connectivity and allowed greater packing density, resulting in the ability to achieve much higher conductivity than is possible for hard and stiff particles.
Abstract: Platelet-shaped particles of similar size and shape were investigated as fillers for improving the thermal conductivity of polymer–ceramic composite materials. The conductivities of composites filled with hard, stiff ceramic particles exceeded 3.5 W·(m·K)−1, or >20 times the conductivity of the polymer matrix, and were shown to be almost independent of the intrinsic filler conductivity range of 33–300 W·(m·K)−1. In contrast, the thermal conductivity of composites filled with soft, platelet-shaped BN fillers reached over 13 W·(m·K)−1. A mechanism is proposed whereby deformation of the soft filler particles provides improved particle-to-particle connectivity and allows greater packing density, resulting in the ability to achieve much higher conductivity than is possible for hard and stiff particles of similar initial morphology. Experimental results are discussed in light of various thermal conductivity prediction models in the literature.
TL;DR: It is shown that the dimensions of carbon nanotubes (CNTs) in suspension can be characterized by depolarized dynamic light scattering, and the influence of CNT dimensions on the electrical properties of C NT fibers is demonstrated.
Abstract: We show that the dimensions of carbon nanotubes (CNTs) in suspension can be characterized by depolarized dynamic light scattering. Taking advantages of this in situ technique, we investigate in detail the influence of sonication procedures on the length and diameter of CNTs in surfactant solutions. Sonication power is shown to be particularly efficient at unbundling nanotubes, whereas a long sonication time at low power can be sufficient to cut the bundles with limited unbundling. We finally demonstrate the influence of CNT dimensions on the electrical properties of CNT fibers. Slightly varying the sonication conditions, and thereby the suspended nanotube dimensions, can affect the fibers conductivity by almost 2 orders of magnitude.
TL;DR: PHBV non-woven structures electrospun with salt exhibited a higher degradation rate than those prepared without salt probably due to the increase of surface area of PHBV fibers.
TL;DR: In this article, a simple model based on Butler-Volmer kinetics for electrodes and transport resistance in the polymer electrolyte is analyzed for water electrolysis by using a simple circuit analogy for the sequential kinetic and transport resistances.
TL;DR: In this article, the results of the electrical conductivity and Raman scattering measurements of CeO2 thin films obtained by a polymeric precursor spin-coating technique are presented.
Abstract: The results of the electrical conductivity and Raman scattering measurements of CeO2 thin films obtained by a polymeric precursor spin-coating technique are presented. The electrical conductivity has been studied as a function of temperature and oxygen activity and correlated with the grain size. When compared with microcrystalline samples, nanocrystalline materials show enhanced electronic conductivity. The transition from extrinsic to intrinsic type of conductivity has been observed as the grain size decreases to <100 nm, which appears to be related to a decrease in the enthalpy of oxygen vacancy formation in CeO2. Raman spectroscopy has been used to analyze the crystalline quality as a function of grain size. A direct comparison has been made between the defect concentration calculated from coherence length and nonstoichiometry determined from electrical measurements.