Increase In Electronic Conductivity Research Articles

Structural and electrical properties of La2–xSrxMo2O9–δ

Sr-doped La2Mo2O9 were prepared by solid state reaction and characterized by XRD, impedance spectroscopy and Hebb- Wagner polarization method. XRD patterns of the samples indicated that the solubility limit of Sr2+ in La2–xSrxMo2O9–δ was in the range of 7 mol.% to 7.5 mol.%, i.e., the maximum stoichiometric coefficient x in La2–xSrxMo2O9–δ was larger than 0.14 and less than 0.15. The cubic lattice parameter of La2–xSrxMo2O9–δ (0<x≤0.14) increased linearly with the content of dopant Sr2+ increasing and the relationship could be expressed as: a=0.7154+0.00451x (mm). The total conductivities of Sr-doped La2Mo2O9 were measured by impedance spectroscopy method in argon and air atmosphere, respectively. The results indicated that substituting Sr2+ for La3+ could suppress the first order phase transform of La2Mo2O9 and stabilize the cubic structure to room temperature, and the conductivities of Sr-doped La2Mo2O9 were more sensitive to the change of atmosphere than that of undoped La2Mo2O9. The conductivity variation of Sr-doped La2Mo2O9 with the dopant content exhibited similar trend in air and argon atmosphere, firstly decreased and then increased with the dopant content increasing, and a minimum value appeared at x=0.1. The electronic conductivities of Sr-doped La2Mo2O9 were measured using Hebb-Wagner polarization method in argon atmosphere. It could be found that Sr-doping caused the increase in electronic conductivity and decrease in oxide-ion transport numbers, but the conducting species were predominantly oxide ions. And the oxide-ion transport numbers of some Sr-doped La2Mo2O9 samples could also reach 0.99.

Effect of Lanthanum Additive on Electrical and Thermal Properties of Bismuth Sodium Titanate Ceramics

This work investigated the preparation and properties of (Bi0.5Na0.5)1–1.5xLaxTiO3 ceramics where x = 0, 0.05, 0.10, 0.15 and 0.20 mol fraction. The powders were fabricated by mixed oxide method and calcined at 800°C for 2 h. The ceramic pellets were prepared by uniaxial pressing method and being sintered at various temperatures ranging from 1150–1200°C for 2 h. Bulk densities, phase, electrical and thermal properties were also measured using various techniques. The result showed that all ceramic samples possessed high density and XRD patterns indicated that all ceramics had a main phase of BNT-based composition with rhombohedral (or pseudocubic) structure. The formation of secondary phase was found for sample containing La greater than 0.10 mol fraction. Electrical resistivity measurements at low frequencies indicated a decreasing trend with increasing La addition indicating an increase in electronic conduction. The dielectric constant and thermal conductivity measurements also showed the effects of charged defects induced by La addition and macro defects present by the formed second phase in this material system.

Engineering nano-composite Li4Ti5O12 anodes via scanning electron-probe fabrication

Spinel lithium tianate Li4Ti5O12 (s-LTO) is attractive for its usage as the anode material in lithium-ion batteries due to its excellent cycling stability, but such an application is very often limited by its low electronic conductivity. This work demonstrates a new electron-probe nanofabrication approach to improving the electronic conductivity of spinel s-LTO. The conducting nano-channels through the s-LTO nanoparticles with the lateral dimension of ∼2nm are fabricated using a sub-nm electron probe in a scanning transmission electron microscope (STEM). These nano-channels consist of a single phase of Li4Ti5O12−x with a rocksalt structure (r-LTO). Using in-situ I–V measurements, we show a gradual increase of electronic conductivity of a single r-LTO nanoparticle up to 5 orders of magnitude of the original s-LTO phase under e-beam irradiation. The local structural analysis, through electron diffraction and high-resolution STEM imaging, reveals the lattice coherence between the induced r-LTO phase and s-LTO, with an orientation relationship of <110>r-LTO//<110>s-LTO and {111}r-LTO//{111}s-LTO. Moreover, under the electron irradiation, the O lattice retains, while all the tetrahedral-coordinated Li ions in the s-LTO migrate to the octahedral sites during the phase transformation. Our results suggest that the s-LTO/r-LTO nano-composite particles with enhanced electronic conductivity are an excellent candidate for the anode materials for lithium-ion batteries.

Hydrogenated TiO2 Nanotube Arrays as High‐Rate Anodes for Lithium‐Ion Microbatteries

AbstractA simple method has been developed to substantially improve the high‐rate capability of electrochemically anodized TiO2 nanotube arrays targeted for use as anode material in lithium‐ion microbatteries by annealing in a reducing atmosphere (5 % H2 and 95 % Ar). A series of complementary techniques including X‐ray diffraction (XRD) with Rietveld refining, scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HRTEM), X‐ray photoelectron spectroscopy (XPS), Raman spectrometry (Raman), Fourier‐transform infrared spectroscopy (FTIR), galvanostatic measurements, and electrochemical impedance spectroscopy (EIS) have been employed to investigate the structural and morphological changes as well as the electrochemical performance enhancement resulting from hydrogenation treatment of the TiO2 nanotube arrays. The results reveal that improvement of the rate capability is mainly attributed to the electronic conductivity increase of the bulk TiO2 nanotubes rather than conductive characteristics of the surface coating because hydrogenation treatment produces a high number of oxygen vacancies inside the crystal lattices that makes the TiO2 nanotube arrays favor a bulk n‐type conductor. Furthermore, the high‐rate capability of other kinds of TiO2 nanomaterials, including rutile TiO2 nanowire arrays and anatase TiO2 nanoparticles, can also be considerably improved by similar H2 treatment. Therefore, the current H2 treatment method is proved to be a general and facile technique to improve the power density of TiO2 anode materials for next‐generation, high‐power lithium‐ion batteries.

Simultaneous enhancement of electronic and Li+ ion conductivity in LiFePO4

Enhancing the electronic and ionic conductivity in Li compounds can significantly impact the design of batteries. Here, we explore the influence of biaxial strain on the electronic and Li+ ion conductivities of LiFePO4 by performing first-principles calculations. We find that 4% biaxial tensile strain (BTS) leads to 15 times increase in electronic conductivity and 50 times increase in Li+ ion conductivity at 300 K, respectively. Electronic conductivity is enhanced because BTS softens lattice distortions around a polaron, resulting in a reduction of the activation barrier. The extra volume introduced by tensile strain also reduces the barrier of Li+ ion migration.

Codoping effect of Li1.1V0.9O2 anodes for lithium-ion batteries with Mo and W (Li1.1V0.9−2xMoxWxO2): Based on electronic structure calculations using full-potential KKR-Green's function method

Pure crystalline doped Li1.1V0.9O2 powder was prepared. The specific charge/discharge capacities of the doped Li1.1V0.9O2 anodes were more than double of those of the bare Li1.1V0.9O2 anodes, especially at high C-rates. The main origin of such capacities was revealed to be the increase in electronic conductivity upon doping due to the extra free electron.

High temperature properties of Ce 1- xPr xO 2-δ as an active layer material for SOFC cathodes

We prepared Ce 1-xPr xO 2-δ and investigated its high temperature properties as a material for the composite active layer of a solid oxide fuel cell (SOFC) cathode. We found that increasing the Pr concentration increases the total conductivity and oxygen vacancy concentration at high temperature, and this may lead to improvement of the cathodic reaction. When Ce 1-xPr xO 2-δ is heated, it expands significantly at a certain temperature (T inf), and this expansion depends on the Ce 1-xPr xO 2-δ composition. The expansion is associated with an abrupt increase in the unit cell volume of the cubic structure. Abrupt increases in the total conductivity and oxygen vacancy concentration were also observed at T inf. These results can be explained by oxygen vacancy and electron formation (n-type electronic conductivity increase) at T inf and above T inf. A sample with a Ce 1-xPr xO 2-δ composition where x = 1.0 has no such T inf. A composition near x = 1.0 for Ce 1-xPr xO 2-δ is favorable for the active layer material of an SOFC cathode, because of the high conductivity and high concentration of oxygen vacancies.

Improved capacity and rate capability of Ru-doped and carbon-coated Li 4Ti 5O 12 anode material

Pure Li 4Ti 5O 12, modified Li 4Ti 5O 12/C, Li 4Ru 0.01Ti 4.99O 12 and Li 4Ru 0.01Ti 4.99O 12/C were successfully prepared by a modified solid-state method and its electrochemical properties were investigated. From the XRD patterns, the added sugar or doped Ru did not affect the spinel structure. The results of electrochemical properties revealed that Li 4Ru 0.01Ti 4.99O 12/C showed 120 and 110 mAh/g at 5 and 10 C rate after 100 charge/discharge cycles. Li 4Ru 0.01Ti 4.99O 12/C exhibited the best rate capability and the highest capacity at 5 and 10 C charge/discharge rate owing to the increase of electronic conductivity and the reduction of interface resistance between particles of Li 4Ti 5O 12.It is expected that the Li 4Ru 0.01Ti 4.99O 12/C will be a promising anode material to be used in high-rate lithium ion battery.

ChemInform Abstract: Electrical Properties of Ceria-Doped Yttria.

The electrical conductivity and ionic domain of several ceriadoped yttria compositions, with up to 10 cation% dopant, were studied as a function of temperature (800° to 1100°C) and oxygen partial pressure (10−15 to 105 Pa). The ionic conduction in ceria-doped yttria involves the transport of interstitial oxygen ion defects. The increase of electronic conductivity under reducing conditions with increasing dopant concentration suggests hopping of small polarons between cerium ions with different valences as the dominant conduction mechanism.

Transparent, Flexible Conducting Hybrid Multilayer Thin Films of Multiwalled Carbon Nanotubes with Graphene Nanosheets

We developed a simple, versatile method of integrating hybrid thin films of reduced graphene oxide (RGO) nanosheets with multiwalled carbon nanotubes (MWNTs) via LbL assembly. This approach involves the electrostatic interactions of two oppositely charged suspensions of the RGO nanosheet with MWNTs. This method affords a hybrid multilayer of graphenes with excellent control over the optical and electrical properties. Moreover, the hybrid multilayer exhibits a significant increase of electronic conductivity after the thermal treatment, producing transparent and conducting thin films possessing a sheet resistance of 8 kOmega/sq with a transmittance of 81%. By taking advantage of the conducting network structure of MWNTs, which provides an additional flexibility and mechanical stability of RGO nanosheets, we demonstrate the potential application of hybrid graphene multilayer as a highly flexible and transparent electrode. Because of the highly versatile and tunable properties of LbL-assembled thin films, we anticipate that the general concept presented here offers a unique potential platform for integrating active carbon nanomaterials for advanced electronic, energy, and sensor applications.

Electrical conduction in the vitreous and crystallized Li 2O–V 2O 5–P 2O 5 system

The glass-forming region of the Li 2O–V 2O 5–P 2O 5 system was examined. The glass transition temperature and stability of glass were enhanced with increasing P 2O 5 content. Li 2O–V 2O 5–P 2O 5 glasses show electronic or ionic conduction depending on the glass composition. The electronic conductivity increases with increasing V 2O 5 content, while the ionic conductivity is proportional to the Li 2O content. The effect of crystallization on the electrical conduction was also investigated. The ionic conductivity decreased by thermal crystallization. Drastic increase of electronic conduction was observed in the crystallization process in glasses of 50Li 2O–25V 2O 5–25P 2O 5 and its neighboring compositions. It was clarified that high electronic conduction occurs in a metastable crystalline phase prior to the thermal equilibrium crystallization.

Electronic properties of protein-methylglyoxal complexes: Strong evidence for energy-band conduction

Various measurements, including piezoelectric, hydration isotherm, microwave Hall effect, steady-state conduction, and dielectric properties over the effective frequency range 10−5 to 1010 Hz, are reported for several protein samples that have been complexed with methylglyoxal. The extent of the binding of methylglyoxal has been established using C14 labeled methylglyoxal and scintillation counting measurements. Compared with the normal proteins, the brown complexed proteins exhibit a marked increase in electronic conductivity, free-electron spin density, and piezoelectric response. Unlike the untreated proteins, the protein complexes also exhibit a distinct low-frequency dielectric dispersion and at 10 GHz there is a reversal of the usual electric-field saturation of polarizability. Compared with normal casein, the casein complex exhibits an increase in the monolayer hydration capacity. These effects can be taken as evidence that when methylglyoxal is incorporated into the structure of a protein molecule, a charge-transfer interaction occurs resulting in the creation of mobile electron “holes.” This, in turn, satisfies the basic prerequisite for the applicability of Szent-Gyorgyi's electronic theory of the “living state” and of cancer.

Electrochemical properties of LiFePO 4 prepared via ball-milling

LiFePO 4 cathode materials with distinct particle sizes were prepared by a planetary ball-milling method. The effects of particle size on the morphology, thermal stability and electrochemical performance of LiFePO 4 cathode materials were investigated. The ball-milling method decreased particle size, thereby reducing the length of diffusion and improving the reversibility of the lithium ion intercalation/deintercalation. It is worth noting that the small particle sample prepared using malonic acid as a carbon source achieved a high capacity of 161 mAh g −1 at a 0.1 C rate and had a very flat capacity curve during the early 50 cycles. However, the big particle samples (∼400 nm) decayed more dramatically in capacity than the small particle size samples (∼200 nm) at high current densities. The improvement in electrode performance was mainly due to the fine particles, the small size distribution, and the increase in electronic conductivity as a result of carbon coating. The structure and morphology of the ground LiFePO 4 samples were characterized with XRD, FE-SEM, TEM, EDS, and DSC techniques.

Effects of Yb:Ti ratio on transport properties of Yb 2 ± xTi 2 ± xO 7 ± δ

The ionic conductivity of Yb 2Ti 2O 7-based materials can be improved by compositional changes, including deviations from the nominal cation ratio Yb:Ti, combined with optimization of high temperature processing. Structural refinement indicates that a slight spontaneous anti-site occupancy occurs in stoichiometric Yb 2Ti 2O 7, and that major anti-site occupancy occurs in compositions with excess of Yb and excess of Ti. Yb-excess should thus act as an acceptor-type additive, with increase in ionic transport, suppression of the electronic contribution, and an extended electrolytic domain. However, the actual results show that a small Yb-excess actually suppresses the ionic conductivity. On the contrary, the highest conductivity in air was found for samples with slight excess of Ti in spite of its expected donor-type character. The increase in electronic conductivity of Ti-excess compositions is also weaker than expected. These effects can be explained by significant structural differences between off-stoichiometric and stoichiometric compositions. Furthermore, the actual results also suggest that the nominal composition Yb 2Ti 2O 7 is likely to undergo structural changes on cooling from sintering temperatures, and thus dependence of transport properties on thermal history.

Microemulsion synthesis of LiFePO 4/C and its electrochemical properties as cathode materials for lithium-ion cells

The electroactive LiFePO 4/C nano-composite powders have been synthesized by a microemulsion method. The material were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopic, scanning electron microscopy and its electrochemical properties were investigated by cyclic voltammetry, AC impedance and charge–discharge tests. The as-prepared LiFePO 4/C composite had a high capacity of 163 mAh g −1 at the C/10 rate, i.e. 95.9% of the theoretical capacity. The composite also display a good rate capability and stable cycle-life. The improved electrode performance originates mainly from the fine particle of nanometric dimension and the uniform size distribution in the product as well as the increase in electronic conductivity by the carbon coating.

Structural, dielectric, and conducting properties of brownmillerite solid solutions (La0.2Sr1.8)[Ga(Fe1−x M x)]O5.1±y (M = Cu, Ni)

Oxygen-conducting (La0.2Sr1.8)[Ga(Fe1−x M x)]O5.1±y (M = Cu, Ni) ceramics with brownmillerite structure were studied. It is found that the lattice contracts with an increase in the concentration of nickel cations; this observation indicates the possible presence of cations in the Ni4+ oxidation state and an increase in the total conductivity with substitution of iron with nickel and copper cations (i.e., an increase in electronic conductivity).

Effect of carbon on the electronic conductivity and discharge capacity LiCoPO 4

The effect of added carbon (3, 5 and 10 wt.%) on the electronic conductivity and discharge capacity of LiCoPO 4 was investigated. It was found after heat-treatment that the samples consisted of a LiCoPO 4 majority phase and Co 2P second phase. The added carbon was consumed reducing the LiCoPO 4 surface layers to Co 2P. The electronic conductivity increased as the amount of the Co 2P phase increased. It was observed that the discharge capacity increased with increased Co 2P content to ∼4–5 wt.%, after which the capacity rapidly decreased with increasing Co 2P content. The increase in discharge capacity is likely a result of the increase in electronic conductivity. At higher Co 2P volume fractions the presence of the electrochemically inert Co 2P phase causes decreased capacity by: (1) reducing the amount of LiCoPO 4 present and (2) preventing Li +-ions from entering/leaving LiCoPO 4, even though the highest values of electronic conductivity were exhibited.

Novel composite anode materials of Ag and polymeric carbon for lithium ion batteries

AbstractA new composite anode material of Ag and polymeric carbon was prepared by heat‐treating the mixture of polyacrylonitrile and AgNO3. They were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) and electrochemical measurements. It was found that the addition of Ag was favorable for the improvement of electrochemical performance of the composite in comparison with the virginal polymeric carbon. These improvements were due to an increase of electronic conductivity, alloying of lithium with Ag and smaller particle size of the composites. The optimal amount of Ag addition is 5% based on the molar ratio of the monomer unit. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Structure and electrical conductivity of (La0.9Sr0.1)[(Ga1 − x Crx)0.8Mg0.2]O3 − δ (x = 0–0.35) solid solutions

(La0.9Sr0.1)[(Ga1 − x Crx)0.8Mg0.2]O3 − δ (x = 0–0.35) perovskite-like solid solutions have been prepared by ceramic processing route, and their structural parameters, microstructure, and electrical conductivity have been determined. The results indicate that the cation substitutions reduce the unit-cell volume of the solid solutions and raise their total conductivity via an increase in electronic conductivity, while their ionic conductivity seems to decrease with increasing x.

A study on mixed conducting property of LixV2O5 (x = 0.4–1.4)

AbstractThe mixed conducting nature of the lithium vanadate LixV2O5 (x = 0.4 – 1.4) prepared by solid state reaction has been analyzed by Wagner's polarization method. The increase of electronic conductivity with increase in lithium content has been observed. The low diffusion constant has been observed for lithium ionic motion in high lithium content samples. The conductivity spectra analysis shows the high columbic repulsive forces between mobile lithium ions in high lithium content samples. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)