Showing papers on "Conductivity published in 2009"
TL;DR: In this article, the status of zinc oxide as a semiconductor is discussed and the role of impurities and defects in the electrical conductivity of ZnO is discussed, as well as the possible causes of unintentional n-type conductivity.
Abstract: In the past ten years we have witnessed a revival of, and subsequent rapid expansion in, the research on zinc oxide (ZnO) as a semiconductor. Being initially considered as a substrate for GaN and related alloys, the availability of high-quality large bulk single crystals, the strong luminescence demonstrated in optically pumped lasers and the prospects of gaining control over its electrical conductivity have led a large number of groups to turn their research for electronic and photonic devices to ZnO in its own right. The high electron mobility, high thermal conductivity, wide and direct band gap and large exciton binding energy make ZnO suitable for a wide range of devices, including transparent thin-film transistors, photodetectors, light-emitting diodes and laser diodes that operate in the blue and ultraviolet region of the spectrum. In spite of the recent rapid developments, controlling the electrical conductivity of ZnO has remained a major challenge. While a number of research groups have reported achieving p-type ZnO, there are still problems concerning the reproducibility of the results and the stability of the p-type conductivity. Even the cause of the commonly observed unintentional n-type conductivity in as-grown ZnO is still under debate. One approach to address these issues consists of growing high-quality single crystalline bulk and thin films in which the concentrations of impurities and intrinsic defects are controlled. In this review we discuss the status of ZnO as a semiconductor. We first discuss the growth of bulk and epitaxial films, growth conditions and their influence on the incorporation of native defects and impurities. We then present the theory of doping and native defects in ZnO based on density-functional calculations, discussing the stability and electronic structure of native point defects and impurities and their influence on the electrical conductivity and optical properties of ZnO. We pay special attention to the possible causes of the unintentional n-type conductivity, emphasize the role of impurities, critically review the current status of p-type doping and address possible routes to controlling the electrical conductivity in ZnO. Finally, we discuss band-gap engineering using MgZnO and CdZnO alloys.
3,291 citations
TL;DR: In this article, room temperature ionic liquids (RTILs) are used as electrolytes for lithium and lithium-ion batteries. But the authors focus on the formation of the solid electrolyte interface on the anode surface.
1,052 citations
TL;DR: This work suggests that the combination of guest molecules and a variety of microporous frameworks would afford highly mobile proton carriers in solids and gives an idea for designing a new type of proton conductor, particularly for high-temperature and anhydrous conditions.
Abstract: The development of anhydrous proton-conductive materials operating at temperatures above 80 degrees C is a challenge that needs to be met for practical applications. Herein, we propose the new idea of encapsulation of a proton-carrier molecule--imidazole in this work--in aluminium porous coordination polymers for the creation of a hybridized proton conductor under anhydrous conditions. Tuning of the host-guest interaction can generate a good proton-conducting path at temperatures above 100 degrees C. The dynamics of the adsorbed imidazole strongly affect the conductivity determined by (2)H solid-state NMR. Isotope measurements of conductivity using imidazole-d4 showed that the proton-hopping mechanism was dominant for the conducting path. This work suggests that the combination of guest molecules and a variety of microporous frameworks would afford highly mobile proton carriers in solids and gives an idea for designing a new type of proton conductor, particularly for high-temperature and anhydrous conditions.
666 citations
TL;DR: In this paper, a fabrication protocol based on the sol−gel synthesis of nanocrystalline precursor materials and reactive sintering that results in large-grained, polycrystalline BaZr/(0.8)Y_(0.2O3−δ) of total high conductivity, 1 × 10−2) Scm^(−1) at 450 °C.
Abstract: Barium zirconate has attracted particular attention among candidate proton conducting electrolyte materials for fuel cells and other electrochemical applications because of its chemical stability, mechanical robustness, and high bulk proton conductivity. Development of electrochemical devices based on this material, however, has been hampered by the high resistance of grain boundaries, and, due to limited grain growth during sintering, the high number density of such boundaries. Here, we demonstrate a fabrication protocol based on the sol−gel synthesis of nanocrystalline precursor materials and reactive sintering that results in large-grained, polycrystalline BaZr_(0.8)Y_(0.2O3−δ) of total high conductivity, 1 × 10^(−2) Scm^(−1) at 450 °C. The detrimental role of grain boundaries in these materials is confirmed via a comparison of the conductivities of polycrystalline samples with different grain sizes. Specifically, two samples with grain sizes differing by a factor of 2.3 display essentially identical grain interior conductivities, whereas the total grain boundary conductivities differ by a factor of 2.5−3.2, depending on the temperature (with the larger-grained material displaying higher conductivity).
411 citations
TL;DR: The proton conductivity of a one-dimensional coordination polymer, ferrous oxalate dihydrate, was evaluated and found to show 1.3 mS cm(-1) at ambient temperature, suggestive of new proton Conductive materials consisting of coordination polymers.
Abstract: Proton conductive materials become important for their utility to electrolytes of fuel cells or sensors. The proton conductivity of a one-dimensional coordination polymer, ferrous oxalate dihydrate, was evaluated and found to show 1.3 mS cm−1 at ambient temperature. The proton conductivity of this compound is extremely high at ambient temperature without any strong acidic group, and this result is suggestive of new proton conductive materials consisting of coordination polymers.
303 citations
TL;DR: In this paper, the authors report the results of physical experiments that demonstrate the strong influence of the thermal conductivity of the substrate on the evaporation of a pinned droplet and show that this behaviour can be captured by a mathematical model including the variation of the saturation concentration with temperature, and hence coupling the problems for the vapour concentration in the atmosphere and the temperature in the liquid and the substrate.
Abstract: We report the results of physical experiments that demonstrate the strong influence of the thermal conductivity of the substrate on the evaporation of a pinned droplet. We show that this behaviour can be captured by a mathematical model including the variation of the saturation concentration with temperature, and hence coupling the problems for the vapour concentration in the atmosphere and the temperature in the liquid and the substrate. Furthermore, we show that including two ad hoc improvements to the model, namely a Newton's law of cooling on the unwetted surface of the substrate and the buoyancy of water vapour in the atmosphere, give excellent quantitative agreement for all of the combinations of liquid and substrate considered.
281 citations
TL;DR: In this article, a highly conductive poly(3,4-ethylenedioxythiophene):polypoly(styrene sulfonate) (PEDOT:PSS) film, obtained by addition of a polar solvent, dimethylsulfoxide (DMSO), to an aqueous solution of PEDOT-PSS, was thoroughly investigated to gain a deeper understanding of the fundamental characteristics of the solvent-modified PSS film.
Abstract: A highly conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film, obtained by addition of a polar solvent, dimethylsulfoxide (DMSO), to an aqueous solution of PEDOT:PSS, was thoroughly investigated to gain a deeper understanding of the fundamental characteristics of the solvent-modified PEDOT:PSS film Use of the DMSO-modified PEDOT:PSS film as a transparent anode to achieve low-cost and high-efficiency ITO-free organic solar cells (OSCs) based on poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) was also examined Changes in the conductivity, morphology, surface composition, work-function, and anisotropic conductivity in both the parallel and perpendicular directions of solvent-treated PEDOT:PSS films that resulted from the addition of various amounts of DMSO were investigated to better understand the nature of the solvent-modified PEDOT:PSS film and the origin of its dramatically enhanced conductivity Furthermore, the effects of using the modified PEDOT:PSS films as polymer anodes on solar cell performance were investigated by addition of various amounts of DMSO and by the use of PEDOT:PSS films with different thicknesses The ITO-free OSCs with optimized PEDOT:PSS anodes had a high power conversion efficiency that was comparable to that of conventional ITO-based devices
279 citations
TL;DR: The electrical conductivity, structural and optical properties of ZnO nanostructured semiconductor thin film prepared by sol-gel spin coating method have been investigated in this paper, where the X-ray diffraction result indicates that the ZNO film has the polycrystalline nature with average grain size of 28nm.
275 citations
TL;DR: Expanded graphite is a promising heat transfer promoter due to its high conductivity, which improves the thermal conductivity of organic phase change materials as discussed by the authors, and it can also serve as suppo...
270 citations
TL;DR: The electron transport behavior of electrochemically gated graphene transistors in different solutions is studied and the minimum conductivity displays an exponential decrease with the density of charged impurities, attributed to the impurity scattering of the carriers.
Abstract: We have studied the electron transport behavior of electrochemically gated graphene transistors in different solutions. In an ionic liquid, we have determined the electron and hole carrier densities and estimated the concentration of charged impurities to be (1−10) × 1012 cm−2. The minimum conductivity displays an exponential decrease with the density of charged impurities, which is attributed to the impurity scattering of the carriers. In aqueous solutions, the position of minimum conductivity shifts negatively as the ionic concentration increases. The dependence of the transport properties on ionic concentration is important for biosensor applications, and the observation is modeled in terms of screening for impurity charges by the ions in solutions.
253 citations
TL;DR: In this paper, a high conductivity additive for organic phase change materials is proposed, which can enhance the thermal conductivity of organic phases change materials, such as β-Aluminum nitride powder.
TL;DR: In this article, the authors study (3+1)-dimensional holographic superconductors in the Einstein-Gauss-Bonnet gravity both numerically and analytically and show that higher curvature corrections make condensation harder.
Abstract: We study (3+1)-dimensional holographic superconductors in Einstein-Gauss-Bonnet gravity both numerically and analytically. It is found that higher curvature corrections make condensation harder. We give an analytic proof of this result, and directly demonstrate an analytic approximation method that explains the qualitative features of superconductors as well as giving quantitatively good numerical results. We also calculate conductivity and $\omega_g / T_c $, for $\omega_g$ and $T_c$ the gap in the frequency dependent conductivity and the critical temperature respectively. It turns out that the `universal' behaviour of conductivity, $\omega_g / T_c \simeq 8$, is not stable to the higher curvature corrections. In the appendix, for completeness, we show our analytic method can also explain (2+1)-dimensional superconductors.
TL;DR: EFTEM results show that the salt is increasingly localized in the middle of the poly(ethylene oxide) (PEO) lamellae as the molecular weight of the copolymers is increased.
Abstract: Energy-filtered transmission electron microscopy (EFTEM) was used to determine the distribution of lithium ions in solid polymer electrolytes for lithium batteries. The electrolytes of interest are mixtures of bis(trifluoromethane)sulfonimide lithium salt and symmetric poly(styrene-block-ethylene oxide) copolymers (SEO). In contrast to current solid and liquid electrolytes, the conductivity of SEO/salt mixtures increases with increasing molecular weight of the copolymers. EFTEM results show that the salt is increasingly localized in the middle of the poly(ethylene oxide) (PEO) lamellae as the molecular weight of the copolymers is increased. Calculations of the inhomogeneous local stress field in block copolymer microdomains, modeled using self-consistent field theory, provide a quantitative explanation for this observation. These stresses, which increase with increasing molecular weight, interfere with the ability of PEO chains to coordinate with lithium cations near the walls of the PEO channels where ion mobility is expected to be low.
TL;DR: A class of nanoparticle-based materials whose conductivity can either increase or decrease on irradiation with visible light of wavelengths close to the particles’ surface plasmon resonance is described.
Abstract: A photoconductor is a material whose electrical conductivity changes when illuminated — invariably increasing in response to the incident light. Now Nakanishi et al. show how nanoparticle-based materials can be engineered, through careful choice of the molecules used to stabilize the nanoparticles, to exhibit negative (or 'inverse') photoconductance — thin films of these materials become less conducting in the presence of light. Nanoparticle-based photoconductors based on the principles underlying these observations could find use as chemical sensors. A photoconductor is a material in which electrical conductivity changes when it is illuminated — invariably increasing in response to impinging light. However, here it is shown that nanoparticle-based materials can be engineered, through the careful choice of the molecules used to stabilize the nanoparticles, to exhibit negative photoconductance: conductivity in these materials decreases in the presence of light. In traditional photoconductors1,2,3, the impinging light generates mobile charge carriers in the valence and/or conduction bands, causing the material’s conductivity to increase4. Such positive photoconductance is observed in both bulk and nanostructured5,6 photoconductors. Here we describe a class of nanoparticle-based materials whose conductivity can either increase or decrease on irradiation with visible light of wavelengths close to the particles’ surface plasmon resonance. The remarkable feature of these plasmonic materials is that the sign of the conductivity change and the nature of the electron transport between the nanoparticles depend on the molecules comprising the self-assembled monolayers (SAMs)7,8 stabilizing the nanoparticles. For SAMs made of electrically neutral (polar and non-polar) molecules, conductivity increases on irradiation. If, however, the SAMs contain electrically charged (either negatively or positively) groups, conductivity decreases. The optical and electrical characteristics of these previously undescribed inverse photoconductors can be engineered flexibly by adjusting the material properties of the nanoparticles and of the coating SAMs. In particular, in films comprising mixtures of different nanoparticles or nanoparticles coated with mixed SAMs, the overall photoconductance is a weighted average of the changes induced by the individual components. These and other observations can be rationalized in terms of light-induced creation of mobile charge carriers whose transport through the charged SAMs is inhibited by carrier trapping in transient polaron-like states9,10. The nanoparticle-based photoconductors we describe could have uses in chemical sensors and/or in conjunction with flexible substrates.
TL;DR: In this article, the power law exponent for chitosan-NH 4 I system was obtained from dielectric loss variation with frequency, and the conduction mechanism of the plasticized system was represented by the small polaron hopping (SPH) model.
Abstract: Chitosan–NH 4 I and chitosan–NH 4 I–EC films have been prepared by solution cast technique. The sample containing 45 wt% ammonium iodide (NH 4 I) exhibited the highest room temperature conductivity of 3.7×10 −7 S cm −1 . The conductivity of the sample increased to 7.6×10 −6 S cm −1 when 40 wt% ethylene carbonate (EC) was added to the 55 wt% chitosan-45 wt% NH 4 I sample. The conductivity–temperature relationship is Arrhenian. From dielectric loss variation with frequency, the power law exponent was obtained. The temperature dependence of the power law exponent for chitosan–NH 4 I system follows the correlated barrier hopping (CBH) model while conduction mechanism of the plasticized system can be represented by the small polaron hopping (SPH) model.
TL;DR: It is shown that the formation of both O vacancies and Zn interstitials becomes significantly enhanced by a strong attractive interaction between them, making these defects an important source of n-type conductivity in ZnO.
Abstract: As the concentration of intrinsic defects becomes sufficiently high in O-deficient ZnO, interactions between defects lead to a significant reduction in their formation energies. We show that the formation of both O vacancies and Zn interstitials becomes significantly enhanced by a strong attractive interaction between them, making these defects an important source of n-type conductivity in ZnO.
TL;DR: In this article, the electrical conductivity of San Carlos olivine aggregate of various water content was measured at a pressure of 10 GPa in a Kawai-type multi-anvil apparatus.
TL;DR: In this paper, a novel method to significantly enhance the conductivity of conducting poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films through a treatment with aqueous solutions of various salts, such as copper(II) chloride.
Abstract: This article reports a novel method to significantly enhance the conductivity of conducting poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films through a treatment with aqueous solutions of various salts, such as copper(II) chloride. Conductivity enhancement by a factor of about 700 was observed. Many salts were investigated, and the conductivity enhancement depended on the softness parameter of cations and the concentration of the salts in solution. A salt like copper(II) chloride or indium chloride, whose cation has positive softness parameter, could enhance the conductivity of the PEDOT:PSS film by 2 orders in magnitude, while other salt like sodium chloride or magnesium chloride, whose cation has negative softness parameter, gave rise to negligible effect on the conductivity. The mechanism for the conductivity enhancement was studied by various characterizations. It is attributed to PSS loss from the PEDOT:PSS film, and conformational change of PEDOT chains resulted from the salt...
TL;DR: In this paper, the authors measured the length and diameter distribution of bucky papers made of different multiwalled carbon nanotubes (MWCNTs) and found that the composite conductivity increases almost 10 times as the aspect ratio increases 55 times.
TL;DR: In this paper, solid polymer electrolytes based on polyvinyl alcohol (PVA) complexed with sodium fluoride (NaF) at different weight percent ratios were prepared using solution cast technique.
TL;DR: In this paper, transparent conducting zinc oxide thin films were prepared by spray pyrolytic decomposition of zinc acetate onto glass substrates with different thickness, and the crystallographic structure of the films was studied by X-ray diffraction.
TL;DR: In-plane microwave penetration depth lambda_{ab} and quasiparticle conductivity at 28 GHz are measured in underdoped single crystals of the Fe-based superconductor PrFeAsO_{1-y} (T_{c} approximately 35 K) by using a sensitive superconducting cavity resonator.
Abstract: In-plane microwave penetration depthab and quaiparticle conductivity at 28 GHz are measured in underdoped single crystals of the Fe-based superconductor PrFeAsO1 y (Tc � 35 K) by using a sensitive superconducting cavity resonator. �ab(T) shows flat dependence at low temperatures, which is incompatible with the presence of nodes in the superconducting gap �(k). The temperature dependence of the superfluid density demonstrates that the gap is non-zero (�/kBTc & 1.6) all over the Fermi surface. The microwave conductivity below Tc exhibits an enhancement larger than the coherence peak, reminiscent of high-Tc cuprate superconductors.
TL;DR: In this paper, the selection and optimization of nonaqueous electrolytes for ambient operations of lithium/air batteries has been studied and it has been found that PC/EC mixture is the best solvent system and LiTFSI is the most feasible salt for ambient operation of Li/Air batteries.
Abstract: The selection and optimization of non-aqueous electrolytes for ambient operations of lithium/air batteries has been studied. Organic solvents with low volatility and low moisture absorption are necessary to minimize the change of electrolyte compositions and the reaction between lithium anode and water during discharge process. It is critical to make the electrolytes with high polarity so that it can reduce wetting and flooding of carbon based air electrode and lead to improved battery performance. For ambient operations, the viscosity, ionic conductivity, and oxygen solubility of the electrolyte are less important than the polarity of organic solvents once the electrolyte has reasonable viscosity, conductivity, and oxygen solubility. It has been found that PC/EC mixture is the best solvent system and LiTFSI is the most feasible salt for ambient operations of Li/air batteries. Battery performance is not very sensitive to PC/EC ratio or salt concentration.
TL;DR: In this article, the effect of plasticizer on dielectric and electrical properties of an ionically conducting polymer nanocomposites PEO 25 -NaI+5.5 ¼wt.% PEG 200 with different value of x has been investigated.
TL;DR: The segmental and local dynamics as well as the transport of Li(+) cations in a series of model poly(ethylene oxide)-based single-ion conductors with varying ion content are investigated, using dielectric relaxation spectroscopy.
Abstract: We investigate the segmental and local dynamics as well as the transport of Li(+) cations in a series of model poly(ethylene oxide)-based single-ion conductors with varying ion content, using dielectric relaxation spectroscopy. We observe a slowing down of segmental dynamics and an increase in glass transition temperature above a critical ion content, as well as the appearance of an additional relaxation process associated with rotation of ion pairs. Conductivity is strongly coupled to segmental relaxation. For a fixed segmental relaxation frequency, molar conductivity increases with increasing ion content. A physical model of electrode polarization is used to separate ionic conductivity into the contributions of mobile ion concentration and ion mobility, and a model for the conduction mechanism involving transient triple ions is proposed to rationalize the behavior of these quantities as a function of ion content and the measured dielectric constant.
TL;DR: In this article, thin films of arc discharge single walled nanotubes were prepared by vacuum filtration, and the optical transmittance scales with film thickness as expected for a thin conducting film with optical conductivity of 1.7 × 104 S/m (λ = 1.5 µm).
TL;DR: In this article, a consistent set of ionic conductivity data is developed, where the samples are synthesized under similar experimental conditions, and the minimal elastic strain due to the presence of dopant is observed in Dy 0.10 Ce 0.90 O 2-δ.
Abstract: In the past, it has been suggested that the maximum ionic conductivity is achieved in ceria, when doped with an acceptor cation that causes minimum distortion in the cubic fluorite crystal lattice. In the present work, this hypothesis is tested by measuring both the ionic conductivity and elastic lattice strain of 10 mol% trivalent cation-doped ceria systems at the same temperatures. A consistent set of ionic conductivity data is developed, where the samples are synthesized under similar experimental conditions. On comparing the grain ionic conductivity, Nd 0.10 Ce 0.90 O 2-δ exhibits the highest ionic conductivity among other doped ceria systems. The grain ionic conductivity is around 17% higher than that of Gd 0.10 Ce 0.90 O 2-δ at 500°C, in air. X-ray diffraction profiles are collected on the sintered powder of all the compositions, from room temperature to 600°C, in air. From the lattice expansion data at high temperatures, the minimal elastic strain due to the presence of dopant is observed in Dy 0.10 Ce 0.90 O 2-δ . Nd 0.10 Ce 0.90 O 2-δ exhibits larger elastic lattice strain than Dy 0.10 Ce 0.90 O 2-δ with better ionic conductivity at intermediate temperatures. Therefore, it is shown that the previously proposed crystal structure-ionic conductivity relationship based on minimum elastic strain is not sufficient to explain the ionic conductivity behavior in ceria-based system.
TL;DR: In this paper, a micromechanics model is developed to assess the impact of the effects of electron hopping and the formation of conductive networks on the electrical conductivity of CNT-polymer nanocomposites.
Abstract: The introduction of carbon nanotubes (CNTs) into nonconducting polymers has been observed to yield orders of magnitude increases in conductivity at very low concentrations of CNTs. These low percolation concentrations have been attributed to both the formation of conductive networks of CNTs within the polymer and to a nanoscale effect associated with the ability of electrons to transfer from one CNT to another known as electron hopping. In the present work, a micromechanics model is developed to assess the impact of the effects of electron hopping and the formation of conductive networks on the electrical conductivity of CNT-polymer nanocomposites. The micromechanics model uses the composite cylinders model as a nanoscale representative volume element where the effects of electron hopping are introduced in the form of a continuum interphase layer, resulting in a distinct percolation concentration associated with electron hopping. Changes in the aspect ratio of the nanoscale representative volume element are used to reflect the changes in nanocomposite conductivity associated with the formation of conductive networks due to the formation of nanotube bundles. The model results are compared with experimental data in the literature for both single- and multi-walled CNT nanocomposites where it is observed that the model developed is able to qualitatively explain the relative impact of electron hopping and nanotube bundling on the nanocomposite conductivity and percolation concentrations.
TL;DR: This paper studies the AC conductivity and permittivity of hydroxyapatite (HA)-based ceramics from 0.1 Hz-1 MHz at temperatures from room temperature to 1000 degrees C to indicate that hydroxyl ions are responsible for conductivity.
TL;DR: In this article, the authors focus on characterizing PVA: NH4X (X = Cl, Br, I) proton conducting polymer electrolyte prepared by solution casting technique using XRD, FTIR and ac impedance spectroscopic studies.
Abstract: The present study focuses on characterizing PVA: NH4X (X = Cl, Br, I) proton conducting polymer electrolyte prepared by solution casting technique using XRD, FTIR and ac impedance spectroscopic studies. The XRD patterns of all the prepared polymer electrolytes reveal the amorphous nature of the films. The FTIR spectroscopic study indicates the detailed interaction of PVA with proton. From ac impedance spectroscopic studies, it has been found that PVA doped with NH4I have high ionic conductivity (2.5 × 10−3S cm−1) than PVA doped with NH4Br (5.7 × 10−4S cm−1) and NH4Cl (1.0 × 10−5S cm−1) polymer electrolytes. This is due to the large anionic size and low lattice energy of NH4I (in comparison with NH4Br and NH4Cl).The temperature dependence of ionic conductivity for all the PVA: NH4X (X = Cl, Br, I) polymer films obey Arrhenius equation. Ionic transference number measured has been found to be in the range of 0.93–0.96 for all the polymer electrolytes proving that the total conductivity is mainly due to ions.