Showing papers on "Conductivity published in 2010"
TL;DR: It is suggested that substrate-induced doping can potentially increase the 2-dimensional DC conductivity enough to make graphene a viable transparent conductor.
Abstract: From published transmittance and sheet resistance data, we have calculated a figure of merit for transparent, conducting graphene films; the DC to optical conductivity ratio, σDC/σOp. For most reported results, this conductivity ratio clusters around the values σDC/σOp = 0.7, 4.5, and 11. We show that these represent fundamental limiting values for networks of graphene flakes, undoped graphene stacks, and graphite films, respectively. The limiting value for graphene flake networks is much too low for transparent-electrode applications. For graphite, a conductivity ratio of 11 gives Rs = 377Ω/◻ for T = 90%, far short of the 10 Ω/◻ minimum requirement for transparent conductors in current driven applications. However, we suggest that substrate-induced doping can potentially increase the 2-dimensional DC conductivity enough to make graphene a viable transparent conductor. We show that four randomly stacked graphene layers can display T ≈ 90% and 10 Ω/◻ if the product of carrier density and mobility reaches n...
526 citations
TL;DR: The fabrication of BaZr(0.8)Y (BZY) proton-conducting electrolyte thin films by pulsed laser deposition on different single-crystalline substrates shows the largest proton conductivity ever reported for BZY samples, and opens new potential for the development of miniaturized SOFCs for portable power supply.
Abstract: R educing the operating temperature in the 500‐750 C range is needed for widespread use of solid oxide fuel cells (SOFCs). Proton-conducting oxides are gaining wide interest as electrolyte materials for this aim. We report the fabrication of BaZr0:8Y0:2O3 (BZY) proton-conducting electrolyte thin films by pulsed laser deposition on different single-crystalline substrates. Highly textured, epitaxially oriented BZY films were obtained on (100)-oriented MgO substrates, showing the largest proton conductivity ever reported for BZY samples, being 0:11 S cm 1 at 500 C. The excellent crystalline quality of BZY films allowed for the first time the experimental measurement of the large BZY bulk conductivity above 300 C, expected in the absence of blocking grain boundaries. The measured proton conductivity is also significantly larger than the conductivity values of oxygen-ion conductors in the same temperature range, opening new potential for the development of miniaturized SOFCs for portable power supply.
451 citations
TL;DR: In this article, a microporous metal−organic framework with pyrazine-2,3-dithiolate was proposed and demonstrated to have an optical bandgap, p-type semiconductivity, and redox activity.
Abstract: The new microporous metal−organic framework Cu[Ni(pdt)2] (pdt2− = pyrazine-2,3-dithiolate) is demonstrated to have an optical bandgap, p-type semiconductivity, and redox activity. The compound can be doped by using I2 as an oxidant, leading to an increase in conductivity by 4 orders of magnitude with retention of porosity.
435 citations
TL;DR: Nanoscale current measurements are investigated as a function of bias and temperature and are shown to be consistent with distinct electronic properties at the domain walls leading to changes in the observed local conductivity.
Abstract: The transport physics of domain wall conductivity in La-doped bismuth ferrite (BiFeO3) has been probed using variable temperature conducting atomic force microscopy and piezoresponse force microscopy in samples with arrays of domain walls in the as-grown state. Nanoscale current measurements are investigated as a function of bias and temperature and are shown to be consistent with distinct electronic properties at the domain walls leading to changes in the observed local conductivity. Our observation is well described within a band picture of the observed electronic conduction. Finally, we demonstrate an additional degree of control of the wall conductivity through chemical doping with oxygen vacancies, thus influencing the local conductive state.
362 citations
TL;DR: LiFePO4/graphene composites in a co-precipitation method, in which graphene nanosheets are used as additives, were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM).
341 citations
TL;DR: In this article, the authors use equilibrium molecular dynamic simulations to compute thermal conductivity of graphene nanoribbons with smooth and rough edges and find that conductivity is the highest for smooth edges and is essentially the same for zigzag and armchair edges.
Abstract: We use equilibrium molecular dynamic simulations to compute thermal conductivity of graphene nanoribbons with smooth and rough edges. We also study effects of hydrogen termination. We find that conductivity is the highest for smooth edges and is essentially the same for zigzag and armchair edges. In the case of rough edges, the thermal conductivity is a strong function of the ribbon width indicating the important effect of phonon scattering from the edge. Hydrogen termination also reduces conductivity by a significant amount.
323 citations
TL;DR: In this article, the safety and electrochemical properties of Li-ion battery systems based on LiFePO4 cathodes and graphite anodes with mixture electrolytes were investigated.
317 citations
Journal Article•
TL;DR: Based on advanced first-principles calculations, this paper found that nitrogen is actually a deep acceptor, with an exceedingly high ionization energy of 1.3 eV, and hence cannot lead to hole conductivity in ZnO.
Abstract: Based on electronic structure and atomic size considerations, nitrogen has been regarded as the most suitable impurity for p-type doping in ZnO. However, numerous experimental efforts by many different groups have not resulted in stable and reproducible p-type material, casting doubt on the efficacy of nitrogen as a shallow acceptor. Based on advanced first-principles calculations we find that nitrogen is actually a deep acceptor, with an exceedingly high ionization energy of 1.3 eV, and hence cannot lead to hole conductivity in ZnO. In light of this result, we reexamine prior experiments on nitrogen doping of ZnO.
315 citations
TL;DR: In this paper, a correlation study of microstructure-thermal conductivity correlation was conducted on PbTe-based thermoelectric materials and it was shown that phase boundaries, interfacial dislocations and nanometer-scale precipitates play an important role in enhancing phonon scattering and, therefore, in reducing the lattice thermal conductivity.
Abstract: The reduction of thermal conductivity, and a comprehensive understanding of the microstructural constituents that cause this reduction, represent some of the important challenges for the further development of thermoelectric materials with improved figure of merit. Model PbTe-based thermoelectric materials that exhibit very low lattice thermal conductivity have been chosen for this microstructure-thermal conductivity correlation study. The nominal PbTe{sub 0.7}S{sub 0.3} composition spinodally decomposes into two phases: PbTe and PbS. Orderly misfit dislocations, incomplete relaxed strain, and structure-modulated contrast rather than composition-modulated contrast are observed at the boundaries between the two phases. Furthermore, the samples also contain regularly shaped nanometer-scale precipitates. The theoretical calculations of the lattice thermal conductivity of the PbTe{sub 0.7}S{sub 0.3} material, based on transmission electron microscopy observations, closely aligns with experimental measurements of the thermal conductivity of a very low value, {approx}0.8 W m{sup -1} K{sup -1} at room temperature, approximately 35% and 30% of the value of the lattice thermal conductivity of either PbTe and PbS, respectively. It is shown that phase boundaries, interfacial dislocations, and nanometer-scale precipitates play an important role in enhancing phonon scattering and, therefore, in reducing the lattice thermal conductivity.
298 citations
TL;DR: In this article, an arc-discharge method using a buffer gas containing carbon dioxide has been developed for the efficient and large-scale synthesis of few-layered graphene, well-dispersed in organic solvents such as N,N-dimethylformamide (DMF) and 1,2-dichlorobenzene (o-DCB).
Abstract: An arc-discharge method using a buffer gas containing carbon dioxide has been developed for the efficient and large-scale synthesis of few-layered graphene. The resulting samples of few-layered graphene, well-dispersed in organic solvents such as N,N-dimethylformamide (DMF) and 1,2-dichlorobenzene (o-DCB), were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), and thermal gravimetric analysis (TGA). The electrical conductivity and transparency of flexible films prepared using a direct solution process have also been studied.
268 citations
TL;DR: In this article, the authors focused on the transport studies of PVA-chitosan blended electrolyte system and application in proton batteries and obtained a 2.07 × 10−5 Sc m−1.
TL;DR: In this article, a particle-compositing method was used for the first time to disperse different contents of multi-walled carbon nanotubes (CNTs) in micron sized copper powders, which were subsequently consolidated into CNT/Cu composites by spark plasma sintering (SPS).
TL;DR: Using quantum simulation techniques based on either density functional theory or quantum Monte Carlo, clear evidence of a first-order transition in liquid hydrogen, between a low conductivity molecular state and a high conductivity atomic state is found.
Abstract: Using quantum simulation techniques based on either density functional theory or quantum Monte Carlo, we find clear evidence of a first-order transition in liquid hydrogen, between a low conductivity molecular state and a high conductivity atomic state. Using the temperature dependence of the discontinuity in the electronic conductivity, we estimate the critical point of the transition at temperatures near 2,000 K and pressures near 120 GPa. Furthermore, we have determined the melting curve of molecular hydrogen up to pressures of 200 GPa, finding a reentrant melting line. The melting line crosses the metalization line at 700 K and 220 GPa using density functional energetics and at 550 K and 290 GPa using quantum Monte Carlo energetics.
TL;DR: The finding of a strong influence of junction conductivity on the optical spectrum suggests that plasmonic cavities might serve as probes of molecular conductance at elevated frequencies not accessible through electrical measurements.
Abstract: The optical properties of a nanoparticle dimer bridged by a conductive junction depend strongly on the junction conductivity. As the conductivity increases, the bonding dimer plasmon blueshifts and broadens. For large conductance, a low energy charge transfer plasmon also appears in the spectra with a line width that decreases with increasing conductance. A simple physical model for the understanding of the spectral feature is presented. Our finding of a strong influence of junction conductivity on the optical spectrum suggests that plasmonic cavities might serve as probes of molecular conductance at elevated frequencies not accessible through electrical measurements.
TL;DR: Garnets are capable of accommodating an excess of lithium cations beyond that normally found in this prototypical structure and this excess lithium is found in a mixture of coordination environments with considerable positional and occupational disorder and leads to ionic conductivity of up to 4 × 10−4 S cm−1 at room temperature as discussed by the authors.
Abstract: Garnets are capable of accommodating an excess of lithium cations beyond that normally found in this prototypical structure. This excess lithium is found in a mixture of coordination environments with considerable positional and occupational disorder and leads to ionic conductivity of up to 4 × 10−4 S cm−1 at room temperature. This high value for total conductivity, combined with excellent thermal and (electro)chemical resistance makes these candidate materials for operation in all solid-state batteries. This review looks at garnets with a wide range of stoichiometries and lithium concentrations and the impact of complex lithium distributions and crystallographic order/disorder transitions on the transport properties of these materials.
TL;DR: In this article, the authors identify five regions of electrical conductivity that can be directly correlated to the chemical decomposition and microstructural evolution of cellulose during carbonization, and demonstrate a non-linear frequency dependency due to electron hopping, interfacial polarization, and onset of a percolation threshold.
TL;DR: It is shown here that magnetic fields can be used in a very simple and scalable manner to produce highly aligned hexagonally packed cylindrical microdomains in such membranes over macroscopic areas.
Abstract: The self-assembly of diblock copolymers provides a convenient route to the formation of mechanically robust films with precise and tunable periodic arrangements of two physically demixed but chemically linked polymeric materials. Chemoselective transport membranes may be realized from such films by selective partitioning of an active species into one of the polymer domains. Here, lithium ions were selectively sequestered within the poly(ethylene oxide) block of a liquid crystalline diblock copolymer to form polymer electrolyte membranes. Optimization of the membrane conductivity mandates alignment of self-assembled structures such that conduction occurs via direct as opposed to tortuous transport between exterior surfaces. We show here that magnetic fields can be used in a very simple and scalable manner to produce highly aligned hexagonally packed cylindrical microdomains in such membranes over macroscopic areas. We systematically explore the dependence of the ionic conductivity of the membrane on both temperature and magnetic field strength. A surprising order of magnitude increase in conductivity relative to the nonaligned case is found in films aligned at the highest magnetic field strengths, 6 T. The conductivity of field aligned samples shows a nonmonotonic dependence on temperature, with a marked decrease on heating in the proximity of the order-disorder transition of the system before increasing again at elevated temperatures. The data suggest that domain-confined transport in hexagonally packed cylindrical systems differs markedly in anisotropy by comparison with lamellar systems.
TL;DR: In this article, the A-site non-stoichiometry in Ba1−xZr0.8Y0.2O3−δ, a candidate electrolyte material for fuel cell and other electrochemical applications, was investigated.
Abstract: Recent literature indicates that cation non-stoichiometry in proton-conducting perovskite oxides (ABO3) can strongly influence their transport properties. Here we have investigated A-site non-stoichiometry in Ba1−xZr0.8Y0.2O3−δ, a candidate electrolyte material for fuel cell and other electrochemical applications. Synthesis is performed using a chemical solution approach in which the barium deficiency is precisely controlled. The perovskite phase is tolerant to barium deficiency up to x = 0.06 as revealed by X-ray diffraction analysis, but accommodates the non-stoichiometry by incorporation of yttrium on the A-site. The dopant partitioning can explain the decrease in cell constant with increasing x, the decrease in proton conductivity (the latter as measured by a.c. impedance spectroscopy under humidified atmosphere), and the decrease in grain size in the sintered compacts. Within the single-phase region barium deficiency also has a detrimental impact on grain boundary conductivity, as a result both of the decreased grain size, leading to a higher number density of grain boundaries and of an increased per boundary resistivity. At higher values of x, a two phase system is observed, with yttria appearing as the predominant secondary phase and the barium zirconate reverting to an undoped composition. From the relative concentrations of the observed phases and their lattice constants, the ternary phase behavior at 1600 °C (the sintering temperature) is generated. Both the bulk and grain boundary conductivities are sharply lower in the two-phase system than in the single phase compositions. The control over processing conditions demonstrates that it is possible to reproducibly prepare large-grained, stoichiometric BaZr0.8Y0.2O3−δ with a total conductivity of 1 × 10−2 Scm−1 at 450 °C, while revealing the mechanisms by which barium deficiency degrades properties.
TL;DR: In this paper, a new type of proton-conducting hybrid membranes were prepared by in situ cross-linking of a mixture of polymerizable oils containing protic ionic liquids (PILs) and silica nanoparticles or mesoporous silica nanospheres.
Abstract: A new type of proton-conducting hybrid membranes were prepared by in situ cross-linking of a mixture of polymerizable oils containing protic ionic liquids (PILs) and silica nanoparticles or mesoporous silica nanospheres. The resultant hybrid membranes are semitransparent, flexible, and show good thermal stability, good and tunable mechanical properties. Incorporation of proper amount of silica fillers significantly increased the proton conductivity of the membranes, probably due to the ion transport channel or network structures formed in the membranes. However, further addition of silica fillers might block the formed ion transport channels and decrease the conductivity of hybrid membranes. Compared with silica nanoparticles, mesoporous silica nanospheres is more effective in enhancing the conductivity and in preventing the release of ionic liquid component from the composite membranes. Under anhydrous conditions, the produced hybrid membranes show proton conductivity up to the order of 1 × 10−2 S/cm at ...
TL;DR: In this article, a quasi-three-dimensional variable range hopping (VRH) conduction mechanism is used for electron transportation in polypyrrole (PPy) nanocomposites reinforced with tungsten oxide (WO3) nanoparticles and nanorods (NRs) by a surface-initiated polymerization method.
Abstract: Polypyrrole (PPy) nanocomposites reinforced with tungsten oxide (WO3) nanoparticles (NPs) and nanorods (NRs) are fabricated by a surface-initiated polymerization method. The electrical conductivity is observed to depend strongly on the particle loadings, molar ratio of oxidant to pyrrole monomer, and the filler morphology. The electron transportation in the nanocomposites follows a quasi-three-dimensional variable range hopping (VRH) conduction mechanism as evidenced by the temperature-dependent conductivity function. Unique negative permittivity is observed in both pure PPy and its nanocomposites, and the switching frequency (frequency where the real permittivity switches from negative to positive) can be tuned by changing the particle loading, ratio of oxidant to pyrrole monomer, and the filler morphology. The extent of charge carrier localization calculated from the VRH mechanism is well-correlated to the dielectric properties of the nanocomposites. WO3 NRs are observed to be more efficient in improvin...
TL;DR: In this article, the effect of concentration of embedded Ag nanoparticles on conductivity and dielectric relaxation behavior of polyvinyl alcohol-silver (PVA-Ag) nanocomposite films has been studied.
TL;DR: In this paper, the authors propose polymer blends in which ground state hole carriers, created by doping a minor additive component, are mainly at an orbital energy set below the hole energy of the major component of the blend, leading to a regime in which hole conductivity and Seebeck coefficient may be increased in parallel.
Abstract: The Seebeck coefficient, a defining parameter for thermoelectric materials, depends on the contributions to conductivity of charge carriers at energies away from the Fermi level. Highly conductive materials tend to exhibit conductivity from carriers close to the Fermi level. In this article, we propose polymer blends in which ground state hole carriers, created by doping a minor additive component, are mainly at an orbital energy set below the hole energy of the major component of the blend. Transport, however, is expected to occur through the major component. This leads to a regime in which hole conductivity and Seebeck coefficient may be increased in parallel. While the absolute conductivity of the composite, and thus ZT, are not particularly high, this work demonstrates a route for designing thermoelectric materials in which increases in Seebeck coefficient and conductivity do not cancel each other.
TL;DR: In this article, the percolation threshold was found at 0.11% and 0.068% w/w for the uniformly dispersed and agglomerated polysulfone films, respectively.
Abstract: Electrical conductivity of 150-200 μm thick polysulfone films loaded with 0.05-0.75% w/w multiwall carbon nanotubes was systematically investigated for two types of dispersion states, uniformly dispersed and agglomerated at the micro-scale. The percolation threshold was found at 0.11% and 0.068% w/w for the uniformly dispersed and agglomerated films, respectively. Overall, the conductivity of the films with agglomerated nanotubes was higher than that of the uni- formly dispersed ones, with marked differences of 2 to 4 orders of magnitude for carbon nanotubes loadings in the upper vicinity of the percolation threshold (0.1-0.3% w/w). The increased conductivity of the agglomerated state is explained by the increased nanotube-to-nanotube contact after the percolating network has formed, which facilitates electron transfer.
TL;DR: In this article, the different composition of PVA-LiCF 3 SO 3 polymer electrolyte has been prepared by solution cast technique using DMSO as solvent and the FTIR study confirms the polymer-salt complex formation.
Abstract: The development of polymeric systems with high ionic conductivity is one of the main objectives in Li rechargeable battery. In the present study, the different composition of PVA–LiCF 3 SO 3 polymer electrolyte has been prepared by solution cast technique using DMSO as solvent. The FTIR study confirms the polymer–salt complex formation. The amorphous nature of the polymer has been confirmed by XRD analysis. DSC measurements show decrease in T g with increasing salt concentration. The temperature dependent conductivity obeys Arrhenius relationship. The maximum conductivity has been observed in the order of 7 × 10 − 4 S cm − 1 for 25 mol% of LiCF 3 SO 3 . The activation energy has been found to be 0.16 eV. The two peaks have been observed in the dielectric loss spectrum which shows two types of relaxation α and β.
TL;DR: In this paper, La0.4Sr 0.4TiO3-based ceramics intended for use as anode materials in solid oxide fuel cells were investigated.
Abstract: In this work, La0.4Sr0.4TiO3-based ceramics intended for use as anode materials in solid oxide fuel cells were investigated. The material was found to preserve its cubic structure throughout testing across a range of conditions, although slight signs of phase segregation were also identified under extreme conditions. The thermal expansion coefficient measured on differently processed samples predicts a good thermomechanical compatibility with yttria-stabilized zirconia (YSZ). Conductivity measurements indicated that the material exhibits a fast surface reduction, unlike the bulk reduction, which progresses very slowly. An increase of the prereduction temperature was found to significantly increase the extent of the reduction and, therefore, the conductivity. Samples sintered under a 5% H2/Ar flow, at 1400 °C, showed high conductivities of up to 96 S cm−1 at 880 °C and oxygen partial pressures of pO2 = 10−20 atm. Correlations between the oxygen deficiency, conductivity, porosity, reduction temperature, and...
Book•
14 Oct 2010
TL;DR: In this article, the authors present a sensor array and micro total analysis system for sensor arrays and Micro Total Analysis Systems. But they do not discuss the use of sensors as indicators.
Abstract: Fundamentals.- Semiconductor Structures as Chemical Sensors.- Mass-Sensitive Sensors.- Conductivity Sensors and Capacitive Sensors.- Thermometric and Calorimetric Sensors.- Electrochemical Sensors.- Optical Sensors.- Chemical Sensors as Detectors and Indicators.- Sensor Arrays and Micro Total Analysis Systems.
TL;DR: The effects of dissolved H2O on the electrical conductivity and its anisotropy in olivine (Fo90) at 8 GPa were investigated by complex impedance spectroscopy as discussed by the authors.
TL;DR: In this article, the effect of chloride binding on concrete resistance is assessed by thermodynamic modeling and compared with chloride content measured with acid and water extraction, showing that chloride binding is strongly related to the hydration degree of the cement and of the mineral admixtures.
Abstract: The chloride resistance of concrete mixtures produced with different binders and water-to-binder ratios is determined by three different methods (natural chloride diffusion, accelerated chloride migration and conductivity measurement). The influence of mix design and type of binder are evaluated and related to porosity. The effect of chloride binding on chloride resistance is assessed by thermodynamic modeling and compared with chloride content measured with acid and water extraction. Chloride resistance depends on the type of binder and on water-to-binder ratio. Chloride content measurements and thermodynamic modeling both show that chloride binding is strongly related to the hydration degree of the cement and of the mineral admixtures. However, the decisive parameter for chloride resistance in all the tests is the permeability while the influence of chloride binding is less important.
TL;DR: In this article, a proton-conducting polymer electrolyte based on starch and ammonium nitrate (NH4NO3) has been prepared through solution casting method, and the amount of NH4 NO3 was found to influence the proton conduction; the highest obtainable room temperature conductivity was 2.83 × 10−5 S cm−1.
Abstract: A proton-conducting polymer electrolyte based on starch and ammonium nitrate (NH4NO3) has been prepared through solution casting method. Ionic conductivity for the system was conducted over a wide range of frequency between 50 Hz and 1 MHz and at temperatures between 303 K and 373 K. Impedance analysis shows that sample with 25 wt.% NH4NO3 has a smaller bulk resistance (Rb) compared to that of the pure sample. The amount of NH4NO3 was found to influence the proton conduction; the highest obtainable room temperature conductivity was 2.83 × 10−5 S cm−1, while at 100 °C, the conductivity in found to be 2.09 × 10−4 S cm−1. The dielectric analysis demonstrates a non-Debye behavior. Transport parameters of the samples were calculated using the Rice and Roth model and thus shows that the increase in conductivity is due to the increase in the number of mobile ions.
TL;DR: In this paper, the effect of the anion, namely dicyanamide, hexafluorophosphate, trifluoroacetate, or triffluoromethanesulfonate, on the conductivity of 1-N-butyl-3-Nethylimidazolium-based room-temperature ionic liquids (RTILs) was studied over the temperature range (248 to 468) K. The uncertainty in κ was estimated to be less than 0.5 %.
Abstract: The effect of the anion, namely dicyanamide, hexafluorophosphate, trifluoroacetate, or trifluoromethanesulfonate, on the conductivity (κ) of 1-N-butyl-3-N-methylimidazolium-based room-temperature ionic liquids (RTILs) was studied over the temperature range (248 to 468) K. The uncertainty in κ was estimated to be less than 0.5 %. The conductivity values obtained are well-described by the Vogel−Fulcher−Tammann equation. Additionally, densities (ρ) and the corresponding molar conductivities (Λ) are reported for the temperature range (278 to 338) K. The data for Λ and the associated viscosities (η) were found to fit fractional forms of the Walden relationship.