Showing papers on "Electrical resistivity and conductivity published in 2006"

Iron-Based Layered Superconductor: LaOFeP

Abstract: We report superconductivity in an iron-based layered oxy-pnictide LaOFeP. LaOFeP is composed of an alternate stack of lanthanum oxide (La3+O2-) and iron pnictide (Fe2+P3-) layers. Magnetic and electrical resistivity measurements verify the occurrence of the superconducting transition at ∼4 K.

Dynamical electric and magnetic metamaterial response at terahertz frequencies.

Abstract: Utilizing terahertz time domain spectroscopy, we have characterized the electromagnetic response of a planar array of split ring resonators (SRRs) fabricated upon a high resistivity GaAs substrate. The measured frequency dependent magnetic and electric resonances are in excellent agreement with theory and simulation. For two polarizations, the SRRs yield a negative electric response ($ϵl0$). We demonstrate, for the first time, dynamical control of the electrical response of the SRRs through photoexcitation of free carriers in the substrate. An excited carrier density of $\ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}{10}^{16}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ is sufficient to short the gap of the SRRs, thereby turning off the electric resonance, demonstrating the potential of such structures as terahertz switches. Because of the universality of metamaterial response over many decades of frequency, these results have implications for other regions of the electromagnetic spectrum.

Metallic transport in polyaniline

Abstract: Most plastics are good insulators. But conducting polymers also form the basis of a new field of ‘plastic electronics’. Some of these materials show exceptionally high conductivities, almost as high as metals. But their properties deviate from true metallic behaviour in several important ways. Now a conducting plastic with resistivity properties much more like those of true metals has been synthesized. The properties of this polyaniline compound may bring practical plastic electronics a little closer. True metallic conductivity in a much-studied conducting polymer (polyaniline) is demonstrated, but synthesized by a route that minimizes the density of structural defects believed responsible for the earlier deviations from classical metallic behaviour. Despite nearly three decades of materials development, the transport properties in the ‘metallic state’ of the so-called conducting polymers are still not typical of conventional metals1,2,3,4,5,6,7. The hallmark of metallic resistivity—a monotonic decrease in resistivity with temperature—has not been obtained at temperatures over the full range below room temperature; and a frequency dependent conductivity, σ(ω), typical of metals has also not been observed. In contrast, the low-temperature behaviour of ‘metallic’ polymers has, in all previous cases, exhibited an increase in resistivity as temperature is further decreased, as a result of disorder-induced localization of the charge carriers1,2,3,4. This disorder-induced localization also changes the infrared response such that σ(ω) deviates from the prediction of Drude theory5,6,7. Here we report classic metallic transport data obtained from truly metallic polymers. With polyaniline samples prepared using self-stabilized dispersion polymerization8, we find that for samples having room-temperature conductivities in excess of 1,000 S cm-1, the resistivity decreases monotonically as the temperature is lowered down to 5 K, and that the infrared spectra are characteristic of the conventional Drude model even at the lowest frequencies measured.

Bolometric infrared photoresponse of suspended single-walled carbon nanotube films.

Abstract: The photoresponse in the electrical conductivity of a single-walled carbon nanotube (SWNT) film is dramatically enhanced when the nanotube film is suspended in vacuum. We show here that the change in conductivity is bolometric (caused by heating of the SWNT network). Electron-phonon interactions lead to ultrafast relaxation of the photoexcited carriers, and the energy of the incident infrared (IR) radiation is efficiently transferred to the crystal lattice. It is not the presence of photoexcited holes and electrons, but a rise in temperature, that results in a change in resistance; thus, photoconductivity experiments cannot be used to support the band picture over the exciton model of excited states in carbon nanotubes. The photoresponse of suspended SWNT films is sufficiently high that they may function as the sensitive element of an IR bolometric detector.

Catalytically Induced Electrokinetics for Motors and Micropumps.

Abstract: We have explored the role of electrokinetics in the spontaneous motion of platinum-gold nanorods suspended in hydrogen peroxide (H2O2) solutions that may arise from the bimetallic electrochemical decomposition of H2O2. The electrochemical decomposition pathway was confirmed by measuring the steady-state short-circuit current between platinum and gold interdigitated microelectrodes (IMEs) in the presence of H2O2. The resulting ion flux from platinum to gold implies an electric field in the surrounding solution that can be estimated from Ohm's Law. This catalytically generated electric field could in principle bring about electrokinetic effects that scale with the Helmholtz-Smoluchowski equation. Accordingly, we observed a linear relationship between bimetallic rod speed and the resistivity of the bulk solution. Previous observations relating a decrease in speed to an increase in ethanol concentration can be explained in terms of a decrease in current density caused by the presence of ethanol. Furthermore, we found that the catalytically generated electric field in the solution near a Pt/Au IME in the presence of H2O2 is capable of inducing electroosmotic fluid flow that can be switched on and off externally. We demonstrate that the velocity of the fluid flow in the plane of the IME is a function of the electric field, whether catalytically generated or applied from an external current source. Our findings indicate that the motion of PtAu nanorods in H2O2 is primarily due to a catalytically induced electrokinetic phenomenon and that other mechanisms, such as those related to interfacial tension gradients, play at best a minor role.

Demonstration of electron filtering to increase the Seebeck coefficient in In 0.53 Ga 0.47 As ∕ In 0.53 Ga 0.28 Al 0.19 As superlattices

Abstract: In this paper, we explore electron filtering as a technique to increase the Seebeck coefficient and the thermoelectric power factor of heterostructured materials over that of the bulk We present a theoretical model in which the Seebeck coefficient and the power factor can be increased in an ${\mathrm{In}}_{053}{\mathrm{Ga}}_{047}\mathrm{As}$-based composite material Experimental measurements of the cross-plane Seebeck coefficient are presented and confirm the importance of the electron filtering technique to decouple the electrical conductivity and Seebeck coefficient to increase the thermoelectric power factor

The effect of water on the electrical conductivity of olivine

Abstract: It is well known that water (as a source of hydrogen) affects the physical and chemical properties of minerals--for example, plastic deformation and melting temperature--and accordingly plays an important role in the dynamics and geochemical evolution of the Earth. Estimating the water content of the Earth's mantle by direct sampling provides only a limited data set from shallow regions (<200 km depth). Geophysical observations such as electrical conductivity are considered to be sensitive to water content, but there has been no experimental study to determine the effect of water on the electrical conductivity of olivine, the most abundant mineral in the Earth's mantle. Here we report a laboratory study of the dependence of the electrical conductivity of olivine aggregates on water content at high temperature and pressure. The electrical conductivity of synthetic polycrystalline olivine was determined from a.c. impedance measurements at a pressure of 4 GPa for a temperature range of 873-1,273 K for water contents of 0.01-0.08 wt%. The results show that the electrical conductivity is strongly dependent on water content but depends only modestly on temperature. The water content dependence of conductivity is best explained by a model in which electrical conduction is due to the motion of free protons. A comparison of the laboratory data with geophysical observations suggests that the typical oceanic asthenosphere contains approximately 10(-2) wt% water, whereas the water content in the continental upper mantle is less than approximately 10(-3) wt%.

Electrical properties of transparent and conducting Ga doped ZnO

Abstract: In this paper, we report on the metal-semiconductor transition behavior observed in transparent and conducting ZnO:Ga films grown by pulsed-laser deposition. The electrical resistivity measurements were carried out on ZnO films with varying Ga concentration in the temperature range of 14to300K. The electrical properties were correlated with film structure, and detailed structural characterization was performed using x-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy. The room-temperature resistivity of these films was found to decrease with Ga concentration up to 5% Ga, and then increase. The lowest value of resistivity (1.4×10−4Ωcm) was found at 5% Ga. Temperature dependent resistivity measurements showed a metal-semiconductor transition, which is rationalized by localization of degenerate electrons. A linear variation of conductivity with T below the transition temperature suggests that the degenerate electrons are in a weak-localization regime. It was also found t...

Mapping thin resistors and hydrocarbons with marine EM methods: Insights from 1D modeling

Abstract: The use of marine controlled-source electromagnetic EM (CSEM) sounding to detect thin resistive layers at depths below the seafloor has been exploited recently to assess the resistivity of potential hydrocarbon reservoirs before drilling. We examine the sensitivity of the CSEM method to such layers with forward and inverse modeling in one and three dimensions. The 3D modeling demonstrates that if both source and receivers are over a tabular 3D target, 1D modeling predicts the observed response to very high accuracy. Experimental design can thus be based on 1D analysis in which hundreds of range and frequency combinations can be computed to find the optimal survey parameters for a given target structure. Modeling in three dimensions shows that the vertical electric-field response is largest over the edges of a 3D target. The 3D modeling also suggests that a target body needs to have a diameter twice the burial depth to be reliably seen by CSEM sounding. A simple air-wave model (energy propagating from source to receiver via the atmosphere) allows the effects of the target layer and atmosphere to be separated and shows where sensitivity to the target is diminished or lost because of finite water depth as a function of range, frequency, and seafloor resistivity. Unlike DC resistivity sounding, the marine CSEM method is not completely T-equivalent and, in principle, can resolve resistivity and thickness separately. Smooth inversion provides an estimate of the method’s resolving power and highlights the fact that although the radial CSEM fields contain most of the sensitivity to the thin resistive target, inverted alone they produce only increasing resistivity with depth. Inclusion of the radial mode CSEM data forces the recovery of the thin resistor, but magnetotelluric data can be used more effectively to achieve the same result.

Hydrous olivine unable to account for conductivity anomaly at the top of the asthenosphere

Abstract: The oceanic asthenosphere is observed to have high electrical conductivity, which is highly anisotropic in some locations. In the directions parallel and normal to the plate motion, the conductivity is of the order of 10(-1) and 10(-2) S m(-1), respectively, which cannot be explained by the conductivity of anhydrous olivine. But because hydrogen can be incorporated in olivine at mantle pressures, this observation has been attributed to olivine hydration, which might cause anisotropically high conductivity by proton migration. To examine this hypothesis, here we report the effect of water on electrical conductivity and its anisotropy for hydrogen-doped and undoped olivine at 500-1,500 K and 3 GPa. The hydrous olivine has much higher conductivity and lower activation energy than anhydrous olivine in the investigated temperature range. Nevertheless, extrapolation of the experimental results suggests that conductivity of hydrous olivine at the top of the asthenosphere should be nearly isotropic and only of the order of 10(-2) S m(-1). Our data indicate that the hydration of olivine cannot account for the geophysical observations, which instead may be explained by the presence of partial melt elongated in the direction of plate motion.

Direct ink-jet printing and low temperature conversion of conductive silver patterns

Abstract: A drop-on-demand ink-jet printer has been used in the production of conductive silver tracks onto glass, polyimide, polytetrafluoroethylene, carbon and glass fibre reinforced epoxy substrates Silver patterns were obtained from an organometallic solution by heat treatment at 150°C in air and were found to have resistivity values of 13 to 2 times the theoretical resisitivity of bulk silver Printed track lateral resolution is a function of the ink/substrate wetting behaviour and a simple model is presented that relates track width to equilibrium contact angle The influence of printing parameters and substrate surface properties on line quality is discussed

Hopping conductivity in polymer matrix–metal particles composites

Abstract: Charge transport properties, such as the temperature dependent dc conductivity and the frequency dependent conductance, of polymer matrix–metal particles composites, are investigated in the present study. Dc and ac conductivity is examined with varying parameters the filler content, temperature and the frequency in the case of ac field. The examined systems, though they are characterized as dielectrics, exhibit considerable conductivity, which alters by several orders of magnitude with temperature and frequency. The temperature and frequency dependence of conductivity gives evidence for the charge carriers transport mechanism via the occurred agreement of experimental results with the employed hopping models (variable range hopping model and random free-energy barrier model).

Friedel oscillations, impurity scattering, and temperature dependence of resistivity in graphene.

Abstract: We show that Friedel oscillations (FO) in grapehene are strongly affected by the chirality of electrons in this material. In particular, the FO of the charge density around an impurity show a faster (~r-3) decay than in conventional 2D electron systems and do not contribute to a linear temperature-dependent correction to the resistivity. In contrast, the FO of the exchange field which surrounds atomically sharp defects breaking the hexagonal symmetry of the honeycomb lattice lead to a negative linear T dependence of the resistivity.

Metallic conductivity and metal-semiconductor transition in Ga-doped ZnO

Abstract: This letter reports the metallic conductivity in Ga:ZnO system at room temperature and a metal-semiconductor transition (MST) behavior at low temperatures. Zn0.95Ga0.05O films, deposited by pulsed laser deposition in the pressure range of ∼10−2Torr of oxygen, were found to be crystalline and exhibited degeneracy at room temperature with the electrical resistivity close to 1.4×10−4Ωcm and transmittance >80% in the visible region. Temperature dependent resistivity measurements of these highly conducting and transparent films also showed, for the first time, a MST at ∼170K. Mechanisms responsible for these observations are discussed in the terms of dopant addition and its effect on ionization efficiency of oxygen vacancies.

Electrical properties of single-wall carbon nanotube-polymer composite films

Abstract: The electrical properties of single-walled carbon nanotubes (SWNTs) embedded in a poly(3-octylthiophene) matrix have been investigated as a function of SWNT concentration. The electrical conductivity and its temperature dependence were measured as a function of the SWNT concentration. As the nanotube concentration increased from 0to20wt%, the conductivity of the resulting films is dramatically increased by six orders of magnitude. The enhancement in conductivity can be explained by means of a three dimension simple percolation path theory, resulting in an estimated threshold of 4wt%. The temperature dependence of the SWNT conductivity mat obeys a three-dimensional variable range hopping. In contrast, the polymer-nanotube composite conductivity follows a fluctuation induced tunneling model. The main divergence is that in the polymer-nanotube composite, the nanotubes are coated with polymer, which acts a barrier in bundle to bundle hopping.

Conductivity studies of a chitosan-based polymer electrolyte

Abstract: Ionic conductivity for the chitosan-NH 4 CF 3 SO 3 system was conducted over a wide range of frequency and at temperatures between 298 and 313 K. Dielectric data were analyzed using complex permittivity e * and complex electrical modulus M * for the sample with the highest ionic conductivity at various temperatures. The temperature-dependent conductivity data obeys Arrhenius relationship. Jonschers universal power law was used to analyze AC conductivity of the sample. Hopping frequency was determined and activation energy of hopping is almost equal to the activation energy of conduction. The AC conductivity master curve was obtained for the highest conducting sample when scaled vertically by σ DC and horizontally by ω P .

Superconductivity in doped cubic silicon.

Abstract: Although the local resistivity of semiconducting silicon in its standard crystalline form can be changed by many orders of magnitude by doping with elements, superconductivity has so far never been achieved. Hybrid devices combining silicon's semiconducting properties and superconductivity have therefore remained largely underdeveloped. Here we report that superconductivity can be induced when boron is locally introduced into silicon at concentrations above its equilibrium solubility. For sufficiently high boron doping (typically 100 p.p.m.) silicon becomes metallic(1). We find that at a higher boron concentration of several per cent, achieved by gas immersion laser doping, silicon becomes superconducting. Electrical resistivity and magnetic susceptibility measurements show that boron-doped silicon (Si:B) made in this way is a superconductor below a transition temperature T-c approximate to 0.35 K, with a critical field of about 0.4 T. Ab initio calculations, corroborated by Raman measurements, strongly suggest that doping is substitutional. The calculated electron-phonon coupling strength is found to be consistent with a conventional phonon-mediated coupling mechanism(2). Our findings will facilitate the fabrication of new silicon-based superconducting nano-structures and mesoscopic devices with high-quality interfaces.

Influence of Mn and Nb dopants on electric properties of chemical-solution-deposited BiFeO3 films

Abstract: Polycrystalline Mn-doped, Nb-doped, and pure BiFeO3 (BFO) films were fabricated via chemical solution deposition (CSD) method. Influence of Mn and Nb dopants on electric properties of BFO films were studied. The current density versus electric field (J-E) characteristics indicated that conduction mechanisms of Mn-doped, Nb-doped, and pure BFO films annealed at 500°C were Ohmic conduction, grain boundary limited conduction, and space charge limited conduction, respectively. The effect of Mn and Nb dopants on electric properties of BFO films was interpreted by defect chemistry and chemical reaction in the CSD process. The Nb dopant is effective in improving electrical properties of CSD-derived BFO films, while Mn is harmful in this respect.

Two-photon-induced reduction of metal ions for fabricating three-dimensional electrically conductive metallic microstructure

Abstract: We developed techniques for fabricating three-dimensional metallic microstructures using two-photon-induced metal-ion reduction. In this process, ions in a metal-ion aqueous solution were directly reduced by a tightly focused femtosecond pulsed laser to fabricate arbitrary three-dimensional structures. A self-standing metallic microstructure with high electrical conductivity was demonstrated.

Thermoelectrical properties of A-site substituted Ca1- xRexMnO3 system

Abstract: CaMnO3 is an electron-doped compound which belongs to the perovskite family. Despite its high Seebeck coefficient S value, the figure of merit at high temperature remains low due to its large resistivity ρ(ρ300K=2Ωcm). To optimize the performance of this material in terms of thermoelectric properties, several substitutions have been attempted on the Ca site to decrease the ρ. Structure and thermoelectric properties of polycrystalline samples Ca1−xAxMnO3 (A=Yb, Tb, Nd, and Ho) have been investigated. Although ρ strongly depends on the ionic radius ⟨rA⟩ and carrier concentration, we have shown that the thermal conductivity κ is mainly driven by the atomic weight of the A site and decreases with it. Therefore, it seems that the S, ρ, and κ could be controlled separately. For instance, the highest dimensionless ZT (=0.16) has been obtained at 1000K in the air for Ca0.9Yb0.1MnO3.

Thermoelectric Properties of Indium-Filled Skutterudites

Abstract: Structural, electrical, and thermal transport properties of CoSb3 partially filled with indium are reported. Polycrystalline samples of InxCo4Sb12 (0 ≤ x ≤ 0.3) were prepared by solid-state reaction under a gas mixture of 5% H2 and 95% Ar. The solubility limit of the indium filling voids in CoSb3 was found to be close to 0.22. Synchrotron X-ray diffraction refinement of the x = 0.2 sample showed that the indium is located in the classic rattler site and has a substantially larger thermal factor than those of Co and Sb. The electrical resistivity, Seebeck coefficients, and thermal conductivity of the InxCo4Sb12 samples were measured in the temperature range of 300−600 K. All samples showed metal-like behavior, and the large negative Seebeck coefficients indicated n-type conduction. The thermal conductivity decreased with increasing temperature for all samples. A thermoelectric figure-of-merit (ZT) ≥ 1 (n-type) has been achieved when x ≥ 0.2 in InxCo4Sb12 at 575 K.

Crystal structure, thermal expansion and electrical conductivity of perovskite oxides BaxSr1-xCo0.8Fe0.2O3-δ (0.3 ≤ x ≤ 0.7)

Abstract: BaxSr1-xCo0.8Fe0.2O3-delta (0.3 0.5 compositions. Furthermore, conductivity relaxation behaviors were also investigated at temperature 400-550 degrees C. Generally, Ba0.4Sr0.6Co0.8Fe0.2O3-delta and Ba0.5Sr0.5Co0.8Fe0.2O3-delta are potential cathode materials. (c) 2005 Elsevier Ltd. All rights reserved.

Electrical properties and defect chemistry of TiO2 single crystal. I. Electrical conductivity.

Abstract: The present work reports the electrical properties of high-purity single-crystal TiO(2) from measurements of the electrical conductivity in the temperature range 1073-1323 K and in gas phases of controlled oxygen activities in the range 10(-13) to 10(5) Pa. The effect of the oxygen activity on the electrical conductivity indicates that oxygen vacancies are the predominant defects in the studied ranges of temperature and oxygen activities. The electronic and ionic lattice charge compensations were revealed at low and high oxygen activities, respectively. The determined semiconducting quantities include: the activation energy of the electrical conductivity (E(sigma) = 125-205 kJ.mol(-1)), the activation energies of the electrical conductivity components associated with electrons (E(n) = 218 kJ.mol(-1)), electron holes (E(p) = 34 kJ.mol(-1)), and ions (E(i) = 227 kJ.mol(-1)), and the enthalpy of motion for electronic defects (DeltaH(m) = 4 kJ/mol). The electrical conductivity data are considered in terms of the components related to electrons, holes, and ions. The obtained data allow the determination of the n-p demarcation line in terms of temperature and oxygen activities. The band gap determined from the electronic component of the electrical conductivity is 3.1 eV.

Electrical conductivity and dielectric properties of multiwalled carbon nanotube and alumina composites

Abstract: Alumina/multiwalled carbon nanotube (MWNT) composites with different MWNT contents ranging from 0.5to10vol% were prepared by spark plasma sintering technique. The dc electrical conductivity and dielectric properties of the composites were investigated and percolation theory was applied to demonstrate the electrical property transition from insulator to conductor. The experimental results have shown that the electrical conductivity increased sharply as the content of MWNTs was close to percolation threshold of 0.79vol%. In the low frequency range, the dielectric constant reached as high as 5000 when the content of MWNTs was at 1.74vol% and nearly frequency independent.