Showing papers on "Conductivity published in 2011"

A lithium superionic conductor

Abstract: Batteries are a key technology in modern society. They are used to power electric and hybrid electric vehicles and to store wind and solar energy in smart grids. Electrochemical devices with high energy and power densities can currently be powered only by batteries with organic liquid electrolytes. However, such batteries require relatively stringent safety precautions, making large-scale systems very complicated and expensive. The application of solid electrolytes is currently limited because they attain practically useful conductivities (10(-2) S cm(-1)) only at 50-80 °C, which is one order of magnitude lower than those of organic liquid electrolytes. Here, we report a lithium superionic conductor, Li(10)GeP(2)S(12) that has a new three-dimensional framework structure. It exhibits an extremely high lithium ionic conductivity of 12 mS cm(-1) at room temperature. This represents the highest conductivity achieved in a solid electrolyte, exceeding even those of liquid organic electrolytes. This new solid-state battery electrolyte has many advantages in terms of device fabrication (facile shaping, patterning and integration), stability (non-volatile), safety (non-explosive) and excellent electrochemical properties (high conductivity and wide potential window).

Tunable metallic-like conductivity in microbial nanowire networks

Abstract: Networks of nanofilaments derived from natural amino acids can have metallic-like conductivity.

A review of dielectric polymer composites with high thermal conductivity

Abstract: The continuing miniaturization of electronic devices and the increasing power output of electrical equipment have created new challenges in packaging and insulating materials. The key goals are to develop materials with high thermal conductivity, low coefficient of thermal expansion (CTE), low dielectric con stant, high electrical resistivity, high breakdown strength, and most importantly, low cost. Polymeric materials have attracted increasing interest because of their excellent processability and low cost; however, most polymers are thermally insulating and have a thermal conductivity between 0.1 and 0.5 W-m-ι-K"1. One approach to increase the thermal conductivity of a polymer is to introduce high-thermal-conductivity fillers, such as aluminum oxide, aluminum nitride, boron nitride, silicon nitride, beryllium oxide, or diamond. In this review paper, we explore how dielectric polymer composites with high thermal conductivity have been developed.

Wide control of proton conductivity in porous coordination polymers.

Abstract: The proton conductivities of the porous coordination polymers M(OH)(bdc−R) [H2bdc = 1,4-benzenedicarboxylic acid; M = Al, Fe; R = H, NH2, OH, (COOH)2] were investigated under humid conditions. Good correlations among pKa, proton conductivity, and activation energy were observed. Fe(OH)(bdc−(COOH)2), having carboxy group and the lowest pKa, showed the highest proton conductivity and the lowest activation energy in this system. This is the first example in which proton conductivity has been widely controlled by substitution of ligand functional groups in an isostructural series.

Structure and dynamics of the fast lithium ion conductor “Li7La3Zr2O12”

Abstract: The solid lithium-ion electrolyte “Li7La3Zr2O12” (LLZO) with a garnet-type structure has been prepared in the cubic and tetragonal modification following conventional ceramic syntheses routes. Without aluminium doping tetragonal LLZO was obtained, which shows a two orders of magnitude lower room temperature conductivity than the cubic modification. Small concentrations of Al in the order of 1 wt% were sufficient to stabilize the cubic phase, which is known as a fast lithium-ion conductor. The structure and ion dynamics of Al-doped cubic LLZO were studied by impedance spectroscopy, dc conductivity measurements, 6Li and 7Li NMR, XRD, neutron powder diffraction, and TEM precession electron diffraction. From the results we conclude that aluminium is incorporated in the garnet lattice on the tetrahedral 24dLi site, thus stabilizing the cubic LLZO modification. Simulations based on diffraction data show that even at the low temperature of 4 K the Li ions are blurred over various crystallographic sites. This strong Li ion disorder in cubic Al-stabilized LLZO contributes to the high conductivity observed. The Li jump rates and the activation energy probed by NMR are in very good agreement with the transport parameters obtained from electrical conductivity measurements. The activation energy Ea characterizing long-range ion transport in the Al-stabilized cubic LLZO amounts to 0.34 eV. Total electric conductivities determined by ac impedance and a four point dc technique also agree very well and range from 1 × 10−4 Scm−1 to 4 × 10−4 Scm−1 depending on the Al content of the samples. The room temperature conductivity of Al-free tetragonal LLZO is about two orders of magnitude lower (2 × 10−6 Scm−1, Ea = 0.49 eV activation energy). The electronic partial conductivity of cubic LLZO was measured using the Hebb–Wagner polarization technique. The electronic transference number te− is of the order of 10−7. Thus, cubic LLZO is an almost exclusive lithium ion conductor at ambient temperature.

A solid lithium electrolyte via addition of lithium isopropoxide to a metal-organic framework with open metal sites.

Abstract: The uptake of LiOiPr in Mg2(dobdc) (dobdc4– = 1,4-dioxido-2,5-benzenedicarboxylate) followed by soaking in a typical electrolyte solution leads to the new solid lithium electrolyte Mg2(dobdc)·0.35LiOiPr·0.25LiBF4·EC·DEC (EC = ethylene carbonate; DEC = diethyl carbonate). Two-point ac impedance data show a pressed pellet of this material to have a conductivity of 3.1 × 10–4 S/cm at 300 K. In addition, the results from variable-temperature measurements reveal an activation energy of just 0.15 eV, while single-particle data suggest that intraparticle transport dominates conduction.

Charge-transport in tin-iodide perovskite CH3NH3SnI3: origin of high conductivity

Abstract: The structural and electrical properties of a metal-halide cubic perovskite, CH3NH3SnI3, have been examined. The band structure, obtained using first-principles calculation, reveals a well-defined band gap at the Fermi level. However, the temperature dependence of the single-crystal electrical conductivity shows metallic behavior down to low temperatures. The temperature dependence of the thermoelectric power is also metallic over the whole temperature range, and the large positive value indicates that charge transport occurs with a low concentration of hole carriers. The metallic properties of this as-grown crystal are thus suggested to result from spontaneous hole-doping in the crystallization process, rather than the semi-metal electronic structure. The present study shows that artificial hole doping indeed enhances the conductivity.

Iodine doped carbon nanotube cables exceeding specific electrical conductivity of metals

Abstract: Creating highly electrically conducting cables from macroscopic aggregates of carbon nanotubes, to replace metallic wires, is still a dream. Here we report the fabrication of iodine-doped, double-walled nanotube cables having electrical resistivity reaching ∼10−7 Ω.m. Due to the low density, their specific conductivity (conductivity/weight) is higher than copper and aluminum and is only just below that of the highest specific conductivity metal, sodium. The cables exhibit high current-carrying capacity of 104∼105 A/cm2 and can be joined together into arbitrary length and diameter, without degradation of their electrical properties. The application of such nanotube cables is demonstrated by partly replacing metal wires in a household light bulb circuit. The conductivity variation as a function of temperature for the cables is five times smaller than that for copper. The high conductivity nanotube cables could find a range of applications, from low dimensional interconnects to transmission lines.

Cu2Se Nanoparticles with Tunable Electronic Properties Due to a Controlled Solid-State Phase Transition Driven by Copper Oxidation and Cationic Conduction

Abstract: Stoichiometric copper(I) selenide nanoparticles have been synthesized using the hot injection method. The effects of air exposure on the surface composition, crystal structure, and electronic properties were monitored using X-ray photoelectron spectroscopy, X-ray diffraction, and conductivity measurements. The current−voltage response changes from semiconducting to ohmic, and within a week a 3000-fold increase in conductivity is observed under ambient conditions. The enhanced electronic properties can be explained by the oxidation of Cu+ and Se2− on the nanoparticle surface, ultimately leading to a solid-state conversion of the core from monoclinic Cu2Se to cubic Cu1.8Se. This behavior is a result of the facile solid-state ionic conductivity of cationic Cu within the crystal and the high susceptibility of the nanoparticle surface to oxidation. This regulated transformation is appealing as one could envision using layers of Cu2Se nanoparticles as both semiconducting and conducting domains in optoelectronic...

Field assisted and flash sintering of alumina and its relationship to conductivity and MgO-doping

Abstract: We show that flash-sintering in MgO-doped alumina is accompanied by a sharp increase in electrical conductivity. Experiments that measure conductivity in fully dense specimens, prepared by conventional sintering, prove that this is not a cause-and-effect relationship, but instead that the concomitant increase in the sintering rate and the conductivity share a common mechanism. The underlying mechanism, however, is mystifying since electrical conductivity is controlled by the transport of the fastest moving charged species, while sintering, which requires molecular transport or chemical diffusion, is limited by the slow moving charged species. Joule heating of the specimen during flash sintering cannot account for the anomalously high sintering rates. The sintering behavior of MgO-doped alumina is compared to that of nominally pure-alumina: the differences provide insight into the underlying mechanism for flash-sintering. We show that the pre-exponential in the Arrhenius equation for conductivity is enhanced in the non-linear regime, while the activation energy remains unchanged. The nucleation of Frenkel pairs is proposed as a mechanism to explain the coupling between flash-sintering and the non-linear increase in the conductivity.

Enhanced electrical conductivity in polystyrene nanocomposites at ultra-low graphene content.

Abstract: We compared the electrical conductivity of multiwalled-carbon-nanotube/polystyrene and graphene/polystyrene composites. The conductivity of polystyrene increases from ∼6.7 × 10–14 to ∼3.49 S/m, with an increase in graphene content from ∼0.11 to ∼1.1 vol %. This is ∼2–4 orders of magnitude higher than for multiwalled-carbon-nanotube/polystyrene composites. Furthermore, we show that the conductivity of the graphene/polystyrene system can be significantly enhanced by incorporation of polylactic acid. The volume-exclusion principle forces graphene into the polystyrene-rich regions (selective localization) and generates ∼4.5-fold decrease in its percolation threshold from ∼0.33 to ∼0.075 vol %.

Tunable Surface Conductivity in Bi2Se3 Revealed in Diffusive Electron Transport

Abstract: We demonstrate that the weak antilocalization effect can serve as a convenient method for detecting decoupled surface transport in topological insulator thin films. In the regime where a bulk Fermi surface coexists with the surface states, the low-field magnetoconductivity is well described by the Hikami-Larkin-Nagaoka equation for single-component transport of noninteracting electrons. When the electron density is lowered, the magnetotransport behavior deviates from the single-component description and strong evidence is found for independent conducting channels at or near the bottom and top surfaces. The magnetic-field-dependent part of corrections to conductivity due to Zeeman energy is shown to be negligible for the fields relevant to the weak antilocalization despite considerable electron-electron interaction effects on the temperature dependence of the conductivity.

Analysis of the Effects of Solution Conductivity on Electrospinning Process and Fiber Morphology

Abstract: The electrospinning process and morphology of electrospun nanofibers depend on many processing parameters. These parameters can be divided into three main groups: 1) solution properties; 2) processing conditions; and 3) ambient conditions. In this paper, we report the results of a comprehensive investigation of the effects of changing the conductivity of polyethylene oxide (PEO)/water solution on the electrospinning process and fiber morphology. The effects of the conductivity of PEO solution on the jet current and jet path are discussed. Furthermore, the fiber diameter and fiber uniformity are investigated by using scanning electron microscopy techniques.

Investigations on the effect of complexation of NaF salt with polymer blend (PEO/PVP) electrolytes on ionic conductivity and optical energy band gaps

Abstract: Sodium ion conducting polymer blend electrolyte films, based on polyethylene oxide (PEO) and polyvinyl pyrrolidone (PVP) complexed with NaF salt, were prepared using solution casting technique. The complexation of the salt with the polymer blend was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and UV–vis spectroscopy. Electrical conductivity of the films was measured with impedance analyzer in the frequency range of 1 Hz to 1 MHz and in the temperature range of 303–348 K. It was observed that the magnitude of conductivity increased with the increase in the salt concentration as well as the temperature. UV–vis absorption spectra in wavelength region of 200–800 nm were used to evaluate the optical properties like direct and indirect optical energy band gaps, optical absorption edge. The optical band gaps decreased with the increase in Na+ ion concentration. This suggests that NaF, as a dopant, is a good choice to improve the electrical properties of PEO/PVP polymer blend electrolytes.

High conductivity transparent carbon nanotube films deposited from superacid

Abstract: Carbon nanotubes (CNTs) were deposited from a chlorosulfonic superacid solution onto PET substrates by a filtration/transfer method. The sheet resistance and transmission (at 550 nm) of the films were 60 �/ sq and 90.9% respectively, which corresponds to a DC conductivity of 12 825 S cm −1 and a DC/optical conductivity ratio of 64.1. This is the highest DC conductivity reported for CNT thin films to date, and attributed to both the high quality of the CNT material and the exfoliation/doping by the superacid. This work demonstrates that CNT transparent films have not reached the conductivity limit; continued improvements will enable these films to be used as the transparent electrode for applications in solid state lighting, LCD displays, touch panels, and photovoltaics. (Some figures in this article are in colour only in the electronic version)

Chemically Stable Pr and Y Co‐Doped Barium Zirconate Electrolytes with High Proton Conductivity for Intermediate‐Temperature Solid Oxide Fuel Cells

Abstract: A chemically stable and highly proton-conductive electrolyte is developed by partially substituting the Zr site of Y-doped barium zirconate (BZY) with 10 mol% of Pr. Compared to BZY, BaZr0.7Pr0.1Y 0.2O3-δ (BZPY) shows improved sinterability as revealed by dilatometric measurements and scanning electron microscopy (SEM) analysis. Dense samples are obtained after sintering at 1500°C for 8 h. Moreover, BZPY shows good chemical stability in the wide range of fuel-cell operating conditions. The larger density and the enhanced grain growth, compared to BZY, allow the volume content of grain boundaries, which generally show a high resistance for proton transport, to be reduced and, thus, a high proton conductivity can be achieved in the temperature range of interest for practical applications (above 10-2 Scm-1 at 600°C). The good sinterability, chemical stability, and high conductivity of the BZPY electrolyte enabled the fabrication of single-cell prototypes based on a thin BZPY membrane by a simple and cost-saving co-pressing method. Electrochemical impedance spectroscopy (EIS) analysis performed during fuel-cell tests under open-circuit conditions confirms the good electrical performance of BZPY as electrolyte material. To improve the present fuel-cell performance adapted cathode materials for this BZPY electrolyte need to be developed. Pr and Y co-doped barium zirconate (BZPY) is a chemically stable electrolyte with high proton conductivity. The good sinterability of the BZPY electrolyte allows the development of an anode-supported solid oxide fuel cell (SOFC) based on a thin BZPY proton conducting membrane. The performed fuel-cell tests confirm that BZPY is a promising electrolyte material for intermediate-temperature SOFC applications. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

How is charge transport different in ionic liquids and electrolyte solutions

Abstract: In this article we show that, analyzed in a barycentric reference frame, the deviation in conductivity measured directly from impedance experiments with respect to that estimated indirectly from NMR diffusion experiments has different origins in electrolyte solutions and pure salts. In the case of electrolyte solutions, the momentum conservation law is satisfied by solvent + ions. Instead, in a molten salt or ionic liquid momentum conservation must be satisfied solely by the ions. This has significant implications. While positively correlated motion of ions of opposite charge is a well justified explanation for the reduction in impedance conductivity in the case of electrolyte solutions, it is not so in the case of ionic liquids and molten salts. This work presents a set of equations that in the case of ionic liquids and molten salts can be used to obtain from direct measurements of impedance and NMR the distinct part of the diffusion coefficient matrix in the barycentric reference frame. In other words, ...

Effects of Bi nonstoichiometry in (Bi0.5+xNa)TiO3 ceramics

Abstract: Effects of Bi nonstoichiometry on (Bi0.5+xNa)TiO3 (BNT) ceramics were investigated at x=−1–+2 mol % of Bi0.5 covering Bi deficiency and excess. At all compositions, rhombohedrally symmetric BNT perovskite formed without secondary phases. Increasing x caused smaller grains. Higher piezoelectric coefficient (d33) but lower depolarization temperature (Td) occurred at Bi excess than at Bi deficiency and vice versa. Leakage current at room temperature decreased with decreasing x. Electrical conductivity of the stoichiometric BNT (x=0) from 700 to 900 °C increased with decreasing partial oxygen pressure from 1 to 10−5 atm suggesting n-type conductivity at elevated temperatures.

Electrical conductivity of hydrous basaltic melts: implications for partial melting in the upper mantle

Abstract: The Earth’s uppermost asthenosphere is generally associated with low seismic wave velocity and high electrical conductivity. The electrical conductivity anomalies observed from magnetotelluric studies have been attributed to the hydration of mantle minerals, traces of carbonatite melt, or silicate melts. We report the electrical conductivity of both H2O-bearing (0–6 wt% H2O) and CO2-bearing (0.5 wt% CO2) basaltic melts at 2 GPa and 1,473–1,923 K measured using impedance spectroscopy in a piston-cylinder apparatus. CO2 hardly affects conductivity at such a concentration level. The effect of water on the conductivity of basaltic melt is markedly larger than inferred from previous measurements on silicate melts of different composition. The conductivity of basaltic melts with more than 6 wt% of water approaches the values for carbonatites. Our data are reproduced within a factor of 1.1 by the equation log σ = 2.172 − (860.82 − 204.46 w 0.5)/(T − 1146.8), where σ is the electrical conductivity in S/m, T is the temperature in K, and w is the H2O content in wt%. We show that in a mantle with 125 ppm water and for a bulk water partition coefficient of 0.006 between minerals and melt, 2 vol% of melt will account for the observed electrical conductivity in the seismic low-velocity zone. However, for plausible higher water contents, stronger water partitioning into the melt or melt segregation in tube-like structures, even less than 1 vol% of hydrous melt, may be sufficient to produce the observed conductivity. We also show that ~1 vol% of hydrous melts are likely to be stable in the low-velocity zone, if the uncertainties in mantle water contents, in water partition coefficients, and in the effect of water on the melting point of peridotite are properly considered.

Characterization of chitosan/PVA blended electrolyte doped with NH4I

Abstract: The (chitosan–PVA)–NH 4 I electrolytes have been prepared by the solution casting method. The prepared electrolytes are analyzed using Fourier transform infrared (FTIR) spectroscopy in order to determine the interaction between salt and the polymer blend hosts which can be deduced from the band shifting. From infrared spectra, shifts are observed at the amine, carboxamide, carbonyl and hydroxyl bands of chitosan and PVA. These shifts indicate that complexation has occurred. The crystallinity/amorphousness of the blended electrolytes has been examined by X-ray diffraction (XRD). XRD pattern shows that the crystallinity of chitosan–NH 4 I electrolyte increases with PVA concentration. Impedance of the electrolytes has been measured using electrochemical impedance spectroscopy (EIS) over the frequency range from 50 Hz to 1 MHz. The highest conducting sample 55 wt.% (chitosan–PVA)–45 wt.% NH 4 I has conductivity of 1.77 × 10 − 6 S cm − 1 . The chitosan:PVA ratio is 1:1. This is higher than the conductivity for the unblended electrolyte 55 wt.% chitosan–45 wt.% NH 4 I which is 3.73 × 10 − 7 S cm − 1 . From ln τ versus 10 3 / T plot, the activation energy for relaxation process is 0.87 eV. This is different from activation energy for dc conductivity which is 0.38 eV. Ion conduction is by hopping.

High and Highly Anisotropic Proton Conductivity in Organic Molecular Porous Materials

Abstract: The search for new highly proton-conducting materials has been a subject of intense research because of their potential applications in fuel cells, sensors, and other areas. In recent years, metal–organic frameworks (MOFs) with well-defined pores have been investigated for this purpose because guest molecules, such as water and imidazole in the channels, and/or functional groups lining the channels can provide proton conduction pathways. However, to date, most MOFs do not show high proton conductivity, long-term stability, or durability in moisture. Similar to MOFs, in principle, are organic molecular porous materials, which may serve as good proton conductors, but their proton conduction behavior has never been investigated. We recently reported an organic molecular porous material based on cucurbit[6]uril (CB[6]), a member of the hollowed-out pumpkin-shaped macrocycle family cucurbit[n]uril (CB[n], n= 5–8, 10) having a hydrophobic cavity accessible through two polar carbonyl-laced portals. The organic molecular porous material has permanent porosity and high thermal and chemical stability, which makes it useful for gas storage and other applications. While investigating its crystal structure, we noticed that there is an array of water and acid molecules filling in the channels of the porous material, which prompted us to investigate the proton conductivity of this and related materials. Herein, we present the high and highly anisotropic proton conductivity in cucurbituril-based organic molecular porous materials, which can be modulated by the nature and amount of guest acid molecules present in the channels. Their proton conductivity along the channel direction, which was demonstrated by single-crystal conductivity measurements, is comparable or superior to that of most MOFs or organic proton conductors. To the best of our knowledge, this investigation of the proton conductivity in organic molecular porous materials with permanent porosity is unprecedented. Recrystallization of CB[6] from 2.4m HCl and 2.4m H2SO4 solutions produced the isostructural organic molecular porous materials CB[6]·1.1HCl·11.3H2O (1) and CB[6]·1.2H2SO4·6.4H2O (2), respectively. Single-crystal Xray analysis revealed that both 1 and 2 have a honeycomb-like structure with one-dimensional (1D) channels with an average diameter of 7.5 and an aperture of about 6 along the c axis (Figure 1a), which are filled with water and

A new potential barrier model in epoxy resin nanodielectrics

Abstract: The dielectric constant and the conductivity of epoxy resin nanocomposites exhibit a lower value at slight filler loading compared with the host epoxy resin. The electrical strength has an increase and presents an optimal value at filler loading of 1 wt%. The interaction zone between the nanoparticles and the polymeric matrix is considered as an independent region. Accordingly, a new potential barrier model is proposed. Based on the model, carriers are restrained in the interaction zone when nanoparticle is in an isolated dispersion, leading to a decrease in both mobility and density of carriers. As a result, the conductivity decrease and the electrical strength increase. The restriction of dipole movement in the interaction zone and the increase of free volume are collectively contributed to the reduction of the dielectric constant. With increasing filler loading, the thickness of the interaction zone extends due to the overlap of the interaction zone, even a conductive path occurs when filler loading exceeds the percolation threshold, leading to a great increase in both mobility and density of carriers. Consequently, the conductivity increase and the electrical strength decrease. The increase of the dielectric constant is chiefly ascribed to the particles.

Electrical impedance of spin-coatable ion gel films.

Abstract: The electrical properties (capacitance, resistance, and conductivity) of ion gel films were examined as a function of film geometry and temperature by using electrical impedance spectroscopy. Ion gel films, which consist of a triblock copolymer, poly (styrene-b-methyl methacrylate-b-styrene) [SMS], and an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMI][TFSI], were deposited by spin coating from ethyl acetate solution. The thickness (2.2−13.4 μm) and the area (0.01−0.06 cm2) of the film sandwiched between two gold electrodes were varied systematically to investigate the relation between the electrical properties and the geometry of the film. The resistance (R) was directly proportional to the thickness and the reciprocal area, as expected, whereas the specific capacitance (C′) was insensitive to the film geometry. Importantly, the gel polarization time constants (RC, where C = C′ × area) were as small as 2.8 μs for 2.2 μm thick ion gel films. Conductivity and capacitance ...

Permittivity, thermal conductivity and thermal stability of poly(vinylidene fluoride)/graphene nanocomposites

Abstract: Poly(vinylidene fluoride) (PVDF)/graphene nanocomposites were prepared by solution blending. The incorporation of graphene sheets (GSs) increased the permittivity, thermal conductivity and thermal stability of PVDF, resulting in a transition from electrical insulator to semiconductor with a percolation threshold of 4.5 wt%. The composite containing 7.5% GSs had a permittivity higher than 300 at 1000 Hz, which is about 45 times that of pure PVDF. The thermal conductivity of the composite with 0.5% GSs was increased by approximately a factor of 2 when compared with the pure PVDF. The addition of 0.05% GSs produced an increase in the maximum decomposition temperature of PVDF of over 20°C.