bluuebunny/crossref_metadata_2025 huggingface dataset:
An Atomic-Scale Derived Continuous Approach for the Anisotropic Etching
Authors: Moldovan N. , Nedelcu S. , Amon H. C.
Published: April 2011

Starting from the Ising model for the bond-breaking algorithm associated to the problem of anisotropie etching of crystals, a method is used to write the discrete master equation for etching normally to indefinite large planes. This equation links the values of the absence probabilities for bonds placed in neighbouring lattice planes and can be transformed to describe a continuous spatial field of probabilities. The method allows the calculation of the etching rate angular diagrams. Examples are shown for several orientations and sets of parameters governing the bond-breaking scheme at atomic level. Comparisons with experimental results are provided.
Modeling and 2D Numerical Simulation of Transient Phenomena in Floating Body Soi Mosfets
Authors: Ionescu A. M. , Chaudier F. , Chovet A.
Published: April 2011

This paper presents a numerical-simulation-based investigation of drain current transients in floating body partially and fully depleted n-channel SOI MOSFETs. For both Zerbst-type and overshoot transients, analytical models are developed and validated. An original contribution concerns the detailed study of drain and source junction influences on the transient regime.
Monte Carlo Studies for Strong Correlations in Hubbard-Type Models
Authors: Heeb E. S.
Published: April 2011

The tight-binding model with repulsive Hubbard interactions represents an ideal prototype for the study of strong correlations. While exact numerical methods have been used with some success, they are typically limited by the size of the clusters that can be investigated or by the temperatures that can be reached. Variational methods, on the other hand, often require considerable advance knowledge of ground-state properties. The method presented here alleviates this problem by augmenting the variational approach with a scheme similar to Lanczos iterations thus bridging the gap between exact diagonalization and variational approaches. For the t-J model, the low-energy effective Hamiltonian of the Hubbard model, material properties like broken translational invariance or superconducting correlations are then investigated and a region of stability of a superconducting phase is found.
On-Site Correlation in Narrow Band Materials
Authors: Manghi F. , Bellini V. , Rontani M. , Arcangeli C.
Published: April 2011

We present the results of a recently developed approach where the interplay between the itinerant and localized character of electrons in narrow band materials is described by adding on-site correlation effects to a realistic band calculation: the single particle band states are treated as mean field solutions of a multi-orbital Hubbard Hamiltonian and the many-body term associated with localized e-e interaction is described in a configuration-interaction scheme. Quasi-particle states of nickel and CuGe03 have been calculated and compared with spectroscopical results.
Environment-Dependent Tight-Binding Potential Model
Authors: Wang C. Z. , Pan B. C. , Tang M. S. , Haas H. , Sígalas M. , Lee G. D. , Ho K. M.
Published: April 2011

We have developed a tight-binding model which goes beyond the traditional two-center approximation and allows the tight-binding parameters to scale according to the bonding environment. Our studies show that this environment-dependent tight-binding model improves remarkably the accuracy and transferability of the potential to describe the structures and properties of higher coordinated metallic systems in addition to those of low coordinated covalent systems.
Electronic Structure and Transport in Non Periodic Systems: New O(N) Methods
Authors: Mayou D. , Turchi P. E. A. , Roche S. , Julien J. P.
Published: April 2011

The mathematical theory of orthogonal polynomials and continued fractions provides efficient tools, via the recursion and related methods, for calculating diagonal elements of Green's function of tight-binding Hamiltonians. We present two recent generalizations of this formalism. The first one allows the calculation of conductivity and other linear response coefficients. The second one provides a new approach to the solution of mean-field theories of alloys. In particular it is shown that the self-consistent CPA equations can be easily solved, through a real-space calculation, for multi-component alloys based on periodic or non periodic lattices.
Empirical Tight-Binding Applied to Silicon Nanoclusters
Authors: Allan G. , Delerue C. , Lannoo M.
Published: April 2011

The calculation of the electronic structure of silicon nanostructures is used to discuss the accuracy of results obtained by the tight-binding method. We first show that the level of refinement of the tight-binding approximation must be adapted to the calculated property. For example, an accurate description of both the valence and conduction bands which can be achieved with a 3rd-nearest neighbor approximation is necessary to calculate the variation of the gap energy with the silicon crystallite size. The sp3s* model which gives a bad description of the conduction band underestimates the confinement energy but can give good results when it is used to determine the variation of the crystallite band gap with pressure. To study Si-III (BC-8) nanocrystallites, we show that a good description of the bulk band structure can be obtained with non-orthogonal tight-binding but due to the large number of nearest neighbors one must take analytical variations of the parameter with interatomic distances. The parameters involved in these expressions can be easily fitted to the bulk band structures using the k-point symmetry without requiring the use of group theory. Finally we discuss the effect of increasing the size of the minimal-basis set and we show that it would be possible to get the values of the tight-binding parameters from a first-principles localized states band structure calculation avoiding the fit to the energy dispersion curves.
Third-Generation TB-LMTO
Authors: Andersen O. K. , Arcangeli C. , Tank R. W. , Saha-Dasgupta T. , Krier G. , Jepsen O. , Dasgupta I.
Published: April 2011

We describe the screened Korringa-Kohn-Rostoker (KKR) method and the third-generation linear muffin-tin orbital (LMTO) method for solving the single-particle Schrödinger equation for a MT potential. In the screened KKR method, the eigenvectors CRL,i are given as the non-zero solutions, and the energies εi as those for which such solutions can be found, of the linear homogeneous equations: , where Ka (ε) is the screened KKR matrix. The screening is specified by the boundary condition that, when a screened spherical wave is expanded in spherical harmonics YR′L′ (ȓR′) about its neighboring sites R′, then each component either vanishes at a radius, rR′=aR′L′, or is a regular solution at that site. When the corresponding “hard” spheres are chosen to be nearly touching, then the KKR matrix is usually short ranged and its energy dependence smooth over a range of order 1 Ry around the centre of the valence band. The KKR matrix, K (εν), at a fixed, arbitrary energy turns out to be the negative of the Hamiltonian, and its first energy derivative, K (εν), to be the overlap matrix in a basis of kinked partial waves, φRL (εν, rR), each of which is a partial wave inside the MT-sphere, tailed with a screened spherical wave in the interstitial, or taking the other point of view, a screened spherical wave in the interstitial, augmented by a partial wave inside the sphere. When of short range, K (ε) has the two-centre tight-binding (TB) form and can be generated in real space, simply by inversion of a positive definite matrix for a cluster. The LMTOs, χRL (εν), are smooth orbitals constructed from φRL(εν, rR) and φRL(εν, rR), and the Hamiltonian and overlap matrices in the basis of LMTOs are expressed solely in terms of K (εν) and its first three energy derivatives. The errors of the single-particle energies εi obtained from the Hamiltonian and overlap matrices in the φ(εν)- and χ(εν) bases are respectively of second and fourth order in εi – εi. Third-generation LMTO sets give wave functions which are correct to order εi – εν, not only inside the MT spheres, but also in the interstitial region. As a consequence, the simple and popular formalism which previously resulted from the atomic-spheres approximation (ASA) now holds in general, that is, it includes downfolding and the combined correction. Downfolding to few-orbital, possibly short-ranged, low-energy, and possibly orthonormal Hamiltonians now works exceedingly well, as is demonstrated for a high-temperature superconductor. First-principles sp3 and sp3d5 TB Hamiltonians for the valence and lowest conduction bands of silicon are derived. Finally, we prove that the new method treats overlap of the potential wells correctly to leading order and we demonstrate how this can be exploited to get rid of the empty spheres in the diamond structure.
Structure, Bonding and Stability of Transition Metal Silicides: A Real-Space Perspective by Tight Binding Potentials
Authors: Miglio Leo , Tavazza Francesca , Garbelli Antonio , Celino Massimo
Published: April 2011

We point out that the predictive power of tight binding potentials is not limited to obtaining fairly accurate total energy calculations and very satisfactory structural evolutions by molecular dynamics simulations. They also allow for a nice physical picture of the links between bonding and stability in different structures, which is particularly helpful in the case of binary suicides
Coupled Dynamics of Electrons and Nuclei in a Molecule Interacting with Ultrashort, Ultra-Intense Laser Pulses
Authors: Khosravi S. , Allen R. E.
Published: April 2011

We have developed a technique for treating the coupled dynamics of electrons and nuclei in a molecule which is subjected to ultrashort and ultra-intense laser pulses. This technique has been employed in quantitatively accurate simulations for . Many interesting phenomena have been observed, including photodissociation, bond softening, above-threshold dissociation, ion-population trapping, electron-population trapping, sudden electronic transitions, Rabi flopping, and harmonic generation. Some representative results are shown here.
Efficient AB Initio Tight Binding
Authors: Horsfield Andrew , Kenny Steven David
Published: April 2011

Tight binding is often seen as a middle ground method, lying between accurate ab iniiio methods, and fast empirical potential methods. The challenge is to make tight binding both as fast and as accurate as possible. One way to achieve this is to take established ab initio methods, and apply systematic approximations and efficient numerical techniques to obtain the greatest possible speed. A recently developed method, employing this approach, is described results presented for silicon, and recent developments (including fully self-consistent extensions) are reported.
Active Site Structure in Zeolite-Supported Lean NOx Catalysts
Authors: Blint Richard J.
Published: April 2011

Copper ions exchanged into the zeolite, ZSM-5, are known to catalyze the reduction of NO to N2 in the oxidizing environment of lean automotive exhaust, but do require trace hydrocarbons. The interface of this catalyst provides a locally reducing environment even when the surrounding exhaust has molecular oxygen concentrations as high as 10%. The mechanism of this reduction is still unclear; however, structure calculations of the active sites and dynamics simulations of species diffusion within the zeolite pores provide insight into the mechanism of reduction. One active site is proposed to be Cu++ ionically bound to a bridge oxygen in a nonsymmetric site within a zeolitic pore. Another proposed site has the copper ion centrally (symmetrically) bound within a six member zeolitic ring. Evidence suggests that the copper ions cycle between Cu++ and Cu+ during the reduction of NO to N2. The nonsymmetric copper ions are shown here to be hydrated ions attached to the Brønsted acid sites in the zeolite. The calculations here show a four member, first hydration shell for Cu++ and a first shell of 2–3 oxygens for the Cu+ ion. An examination of the pore size in ZSM-5 indicates sufficient room for a first and second hydration shell for most of the possible acid sites. The conclusion that the copper ions are typically hydrated suggests that the catalytic mechanism may have much in common with homogeneous catalysis which is sometimes termed heterogenized homogeneous catalysis.
Diffusion of Si Adatoms on H-Terminated Si(001) Surfaces
Authors: Ohno Takahisa , Nara Jun , Sasaki Taizo
Published: April 2011

We have investigated adsorption and diffusion processes of a Si atom on hydrogen-terminated Si(001)-(2×1) surfaces using first-principles total-energy calculations. The Si adatom segregates H atoms from surface Si dimer atoms on the monohydride terminated Si(001) surface. The migration of the Si adatom is assisted by the mobility of H atoms, that is, the Si adatom migrates on the surface by repeating release and capture of H atoms. The effects of a single H-terminated Si dimer on the Si migration are also examined. Calculated results are in good agreements with the variation in morphology of Si homoepitaxial films induced by hydrogen termination.
Microstructural Size and Alignment Effects on the Dielectric Response of Inhomogeneous Media
Authors: Ferris Kim F. , Exarhos Gregory J. , Risser Steven M.
Published: April 2011

The dielectric response of inhomogeneous media presents a complex boundary problem dependent upon dielectric susceptibility and volume fraction of its components, as well as the physical size of the heterogeneities. In this paper, we have used the LOCALF method to examine the size dependent problem for cubic and columnar defects for ZrO2 dielectric films of varying microstructure size and volume fraction. Both the alignments of low dielectric components with respect to the applied field and their size can effectively modulate the composite response. Comparison of these results with the conventional effective medium approximation methods reinforces the need to include microstructural detail in the modeling approach.
Interfacial Properties and Mechanical Behavior of Titanium Aluminides
Authors: Yoo M. H. , Fu C. L.
Published: April 2011

The role of various interfaces in deformation and fracture behavior of two-phase TiAl-Ti3Al alloys is analyzed on the basis of the specific interfacial and surface energies determined from ab initio calculations. The propensity of twinning observed in these alloys is consistent with the low true-twin boundary energy. The strong plastic anisotropy reported in TiAl polysynthetically twinned (PST) crystals is attributed partly to the localized slip along lamellar interfaces, thus lowering the yield stress for soft orientations. Interfacial fracture energies are estimated to be the highest for the α2/γ lamellar boundary and the lowest for the 120° rotational γ/γ boundary. The fracture mode mixity plays an important role in the crack-tip plasticity by ordinary slip and true-twinning, leading to translamellar and interfacial fracture.
Simulating Stm Images for the Gaas (110) Surface
Authors: Chelikowsky James R. , Kim Hanchul
Published: April 2011

Scanning tunneling microscopy (STM) is one of the most successful experimental tools for probing the structure of semiconductor surfaces. However, care must be taken in interpreting the images at the atomistic limit. Often a “naive” interpretation of the STM image can yield an incorrect surface structure. We illustrate this situation via ab initio pseudopotential calculations for the STM image of the (110) GaAs surface. We will compare theoretical STM images to experimental images for the relaxed surface and for a surface with an As vacancy.
Low-Field Colossal Magnetoresistance in Manganite Tunnel Junctions
Authors: Nassar J. , Viret M. , Drouet M. , Contour J. P. , Fermon C. , Fert A.
Published: April 2011

Large magnetoresistance values are obtained on tunnel junctions epitaxially deposited by pulsed-laser deposition and consisting of ferromagnetic manganite La0.67Sr0.33MnO3 electrodes separated by various tunnel barriers: SrTiO3, PrBaCu2.8Ga0.2O7 and CeO2. The magnetoresistance can be decomposed into a low-field and a high-field contribution. The latter is attributed to the presence of canted interfacial manganite phases, as confirmed by the temperature behaviour of the resistance. A low-field magnetoresistance ratio of 450% below 100 Oe is obtained on a sample with a SrTiO3 barrier, indicating a spin polarization value in excess of 0.83 for the manganite.
In-Plane Grain Boundary Effects on the Transport Properties of La0.7Sr0.3MnO3-δ Thin Films
Authors: Gu J. Y. , Ogale S. B. , Ghosh K. , Venkatesan T. , Ramesh R. , Radmilovic V. , Dahmen U. , Thomas G. , Noh T. W.
Published: April 2011

C-axis oriented La0.7Sr0.3MnO3.δ (LSMO) films were fabricated on the top of SrTiO3/YBa2Cu3O7 grown on MgO(001) substrates. From x-ray φ-scan and planar transmission electron microscopy measurements, the LSMO layer in the LSMO/SrTiO3/YBa2Cu3O7/MgO heterostructure is found to have coherent in-plane grain boundaries with a predominance of 45° rotations (between [100] and [110] grains) in addition to the cube-on-cube epitaxial relationship. Also, epitaxial LSMO/Bi4Ti3O12/LaAl03 (001) and c-axis textured LSMO/Bi4Ti3O12/SiO2/Si(001) with random in-plane grain boundaries are introduced as the counterparts for comparison. The resistivity and magnetoresistance (MR) of LSMO layer were measured and compared in these three different heterostructures. The low field MR at low temperature shows a dramatic dependence on the nature of the grain boundary. An attempt is made to interpret these results on the basis of correlation between the magnetic properties and grain structures.
The Effect of Elastic Strain on the Electrical and Magnetic Properties of Epitaxial Ferromagnetic SrRuO3 Thin Films
Authors: Gan Q. , Rao R. A. , Garrett J. L. , Lee Mark , Eom C. B.
Published: April 2011

We report the direct measurement of elastic strain effect on the electrical and magnetic properties of single domain epitaxial SrRuO3 thin films, using a lift-off technique. The as-grown films on vicinal (001) SrTiO3 substrates are subjected to elastic biaxial compressive strain within the plane and tensile strain normal to the plane. In contrast, the lift-off films prepared by chemical etching of SrTiO3 substrates, are completely strain free with bulk like lattice. Our measurements indicate that the elastic strain can significantly affect the electrical and magnetic properties of epitaxial ferromagnetic SrRuO3 thin films. For the strained films, the Curie temperature (Tc) was suppressed to 150K and the saturation magnetic moment (Ms) was decreased to 1.15μB/Ru atom as compared to a Tc of 160K and Ms of 1.45μB/Ru atom for the strain free films. These property changes are attributed to the structural distortion due to the elastic strain in the as-grown epitaxial thin films. Our results provide direct evidence of the crucial role of lattice strain in determining the properties of the perovskite epitaxial thin films.
Magneto-Transport Properties in Layered Manganite Crystals
Authors: Kimura T. , Tomioka Y. , Okudat T. , Kuwahara H. , Asamitsu A. , Tokura Y.
Published: April 2011

Anisotropie charge transport and magnetic properties have been investigated for single crystals of the layered manganite, La2–2xMn2O7 (0.3≤x≤0.5). Remarkable variations in the magnetic structure as well as in the charge-transport properties are observed with changing doping-level x. A crystal with x=0.3 behaves like a 2-dimensional ferromagnetic metal in the temperature region between ∼90 K and ∼270 K, and shows the interplane tunneling magnetoresistance at lower temperatures. These characteristic charge-transport properties are attributed to the interplane magnetic coupling between the adjacent MnO2 bilayers, and are strongly affected by the application of pressure as well as low magnetic fields through the change in magnetic structure. With increase of the carrier concentration toward x=0.5, the charge-ordered phase is stabilized and dominates the charge transport and magnetic properties.
Mn K-Edge X-Ray Absorption Spectroscopy (XAS) Studies of La1-xSrxMnO3
Authors: Mini S. M. , Mitchells J. F. , Hinks D. G. , Alatasi Ahmet , Rosenmann D. , Kimball C. W. , Montano P. A.
Published: April 2011

Systematic Mn K-edge x-ray absorption spectroscopy (XAS) measurements on samples of La1-xSrxMnO3, which are precursors to colossal magnetoresistive (CMR) materials, are reported. Detailed results on the edge or chemical shift as a function of Sr concentration (hole doping) and sample preparation (air vs oxygen annealed), are discussed. For comparison, a systematic XANES study of the Mn K-edge energy shift, denoting valence change in Mn, has been made in standard manganese oxide systems. Contrary to expectations, the variation in near-edge energies for Mn in La0.725Sr0.275MnO3 were small when compared to the difference between that for manganese oxide standards of nominal valence of +3 and +4 (Mn2O3 and MnO2).
Hydrothermal Synthesis and Properties of Ceria Solid Electrolytes
Authors: Greenblatt M. , Huang W. , Shuk P.
Published: April 2011

The structure, thermal expansion coefficients and ionic/electronic conductivity of (Ce1−xSmx)1-y(Tb/Pr)yO2-x/2)+δ (x=0–0.30; y=0–0.10) and Ce1−xCaxO2-x ( x= 0–0.17) solid electrolytes prepared hydrothermally were investigated. The uniformly small particle size (7–68 nm) of the hydrothermally prepared materials allows sintering of the samples into highly dense ceramic pellets at 1400°C, a significantly lower temperature, compared to that at 1600–1650°C required for samples prepared by solid state techniques. The maximum ionic conductivity in Ce1−x(Sm/Ca)xO2-δ was found at x= 0.17 for the Sm (σ600°c = 5.7×10−3 S/cm). In (Ceo0.83Sm0.17)1-y(Tb/Pr)yO1.915+δ the maximum conductivity was found at y= 0.17 for the Pr and Tb substituted ceria (σ600°c=7.6x10−3S/cm, Ea= 0.55 eV and σ600°c = 10−2 S/cm, Ea= 0.72 eV respectively) with electronic contribution to total conductivity around 20–30 %. When the Tb or Pr substitution in Ce0.83Sm0.17OO1.915 is reduced, the conductivity becomes more ionic, and is purely ionic at 2 %. However the conductivity at this lower level doping is not significantly lower.
Development of Electrolyte plate for Molten Carbonate Fuel Cell
Authors: Shoji C. , Matsuo T. , Suzuki A. , Yamamasu Y.
Published: April 2011

It is important for the commercialization of molten carbonate fuel cell (MCFC) to improve the endurance and the reliability of the electrolyte plate. The electrolyte-loss in the electrolyte plate increases the cell resistance and deteriorates the cell voltage. The formation of cracks in the electrolyte plate causes a gas cross leakage between the fuel gas and the oxidizer gas. The pore structure of electrolyte plate must be stable and fine to support liquid electrolyte under MCFC operation. It is necessary to prevent the formation of cracks in electrolyte plate during thermal cycling. We have improved the stability of electrolyte plate using advanced LiAIO2powder and improved the durability of electrolyte plate for thermal cycling by the addition of the ceramic fiber.

The initial cell voltage using electrolyte plate with advanced LiAIO2powder was 820mV at current density 150mA/cm2and the decay rate of cell voltage was under 0.5%/1000h for 8,800h. According to the post analyses, the pore structure of the electrolyte plate did not change. The stability of advanced LiAIO2powder was confirmed. It was proved that the electrolyte plate reinforced with ceramic fiber is effective for thermal cycling.
Pulsed Field Gradient NMR Investigation of Molecular Mobility of Trimethoxymethane in Nafion Membranes
Authors: Wu Y. , Za Wodzinski T. A. , Smart M. C. , Greenbaum S. G. , Prakash G.K.S. , Olah G. A.
Published: April 2011

Molecular mobility of water and trimethoxymethane (TMM) in NAFION membranes of two different equivalent weights (EW), 1100 and 1500, were investigated. Self-diffusion coefficients were determined by the NMR pulsed field gradient method, using the water and methyl protons NMR signals, in saturated NAFION samples containing concentrations of TMM in water varying between 0.5 and 14 M, and at temperatures varying from 30°C to 80°C. Diffusion of molecular species containing methyl protons is more than a factor of two slower in the 1500 EW membrane than in the 1100 EW membrane at 30°C and 1 M concentration. The difference rises to about a factor of four at 80°C and 14 M concentration. These differences are attributed to the lower extent of plasticization of the higher EW material as well as the greater effective distance between acid functional groups. NAFION samples containing methanol/water mixtures were also investigated. Comparison with the methanol results and the permeation behavior, as characterized by gas Chromatographie methods, show that more than half of the TMM is hydrolyzed to methanol as it passes through the acidic membrane. The implications of these findings for alternative fuels in direct oxidation fuel cells are discussed.
Preparation Of Pt/WO3 Powders and Thin Coatings on Carbon Black and Metal Supports by The Complex Sol-Gel Process (CSGP)
Authors: Deptula A. , Lada W. , Olczak T. , Sartowska B. , Ciancia A. , Giorgi L. , Di Bartolomeo A.
Published: April 2011

In this work the CSGP was applied for preparation of Pt-WOx and its coatings on carbon black, silver and titan substrates. Saturated tungsten sol (0.15M) was prepared by dissolving (NH4)4W5O17 2.5 H2O in ascorbic acid solution. To this solution H2PtCl6 was added to obtain the molar ratio Pt:W=l. After evaporation and heating at 700°C for 2h homogeneous yellow-green powders were obtained. Another part of this solution was diluted with ethanol and after ultrasonic mixing used for preparation of coatings on Ag and Ti substrates by the immersion technique. Gel layers were dried at 200°C for 20h and then calcined at 700°C for 2h. The resulting white colored layers (thickness 10–65μm) were very adherent. Ascorbate aqueous tungsten-platinum sol diluted to 0.03 or 0.06 M ΣMe was used for preparation of Pt-W (10 and 20 %) catalyst by impregnation of carbon black Vulcan XC-72, followed by thermal treatment in air, argon and hydrogen atmospheres.
Determination of Oxygen Permeation Kinetics in A Ceramic Membrane with The Composition SrFeCo0.5O3.25-δ
Authors: Kim S. , Yang Y. L. , Christoffersen R. , Jacobson A. J.
Published: April 2011

The oxygen permeation through an oxide membrane with bulk composition SrFeCo0.5O3.25-δ has been measured as a function of both oxygen partial pressure and temperature. The results of the pressure dependence of the permeation indicate that the oxygen transport in this membrane is dependent primarily on the bulk diffusion rate. Although the permeation experiments were carried out at temperatures within, or very close to, the range where SrFeCo0.5O3.25-δ is stable as a pure single phase, the membrane was found to consist of SrFe1.5-xO3.25-δ(x = ∼0.42) together with fractions of Sr(Co,Fe)O3-δ perovskite and Co-Fe oxide that formed as stable phases during densification of the membrane at high temperature (1090°C). These additional phases persisted in the membrane during the permeation measurements.
Novel Cathode Materials Based on Organic Couples for Lithium Batteries
Authors: Ravet N. , Michot C. , Armand M.
Published: April 2011

The electrochemical reduction of the oxocarbons: squarate, croconate and especially rhodizonate lithium salts have been studied in all solid state lithium batteries. Lithium rhodizonate cells were tested on cycling in the 1.5 – 3.5 V potential range The reduction of lithium rhodizonate occurs in two waves of two electrons. The number of electrons transferred in reduction on the first cycle was around 3.5 based on a capacity of 515 mA.h.g−1 and a discharge depth of 87 %. This process is quite reversible but we observed a fast decline of the capacity on cycling. This loss of capacity may be attributed to residual water in the salt. The reduction of the lithium croconate occurs at a potential of 1.8 V in a quasi-irreversible process. We could not observe the reduction of lithium squarate which occurs in the potential range where the lithium is inserted in carbon black. We also report an investigation on rhodizonate salts of transition metals. The best results, in term of capacity, on the 1.5 – 3.5 V potential range, were obtained with copper rhodizonate which exhibits a capacity of 579 mA.h.g−1 on the first discharge.
Synthesis and Characterization of LiNiO2 as A Cathode Material for Pulse Power Batteries
Authors: Choe H. S. , Abraham K. M.
Published: April 2011

The optimum conditions for preparing LiNiO2 with good electrochemical performance are presented. Three different methods were investigated:

• LiOH and NiO at700°C in air(Batch A),

• LiOH and NiO between 150 and 750 °C in oxygen (Batch B), and

• LiNO3 and NiCO3 between 600 and 750 °C in oxygen (Batch C).

Batch C exhibited the highest first discharge capacity of about 150 mAh/g between 2.0 and 4.0V with a solid state Li/LiNiO2 cell containing a PAN-based polymer electrolyte. Solid state carbon/LiNiO2 cells and two-cell bipolar batteries demonstrated high rate capabilities at room temperature with an ability to sustain pulsed discharge currents as high as 50 mA/cm2. About 22 500,13 000, and 1000 pulses were obtained at current densities of 10, 20, and 50 mA/cm2, respectively, with a 10 ms pulse width followed by a 50 ms interpulse rest period.
Hydrothermal Synthesis and Characterization of A Series of Novel Zinc Vanadium Oxides as Cathode Materials
Authors: Zhang Fan , Zavalij Peter Y. , Whittingham M. Stanley
Published: April 2011

We report here the hydrothermal synthesis of a series of novel zinc vanadium oxides, using tetramethyl ammonium ion in order to stabilize the layered structure of vanadium oxide during electrochemical redox reactions with lithium. The compounds were synthesized by the reaction of zinc chloride, vanadium (V) oxide, and tetramethyl ammonium hydroxide at 165°C for 60 hours. Four new zinc vanadium oxide compounds were discovered, only one of which contained the organic cation; another was found to have a layered structure with bridging V-O-V groups analogous to that of beta alumina. These compounds were characterized by X-ray powder diffraction, and IR. Three of the compounds reacted readily with lithium, and their electrochemical behavior in lithium cells were determined.
Lithium Insertion Behaviour of Li1+xV3O8 Prepared by Sol-Gel Method in Methanol
Authors: Kawakita J. , Katayama Y. , Miura T. , Kishi T.
Published: April 2011

Li1+xV3O8 (LT-M form) was obtained by sol-gel method in CH3OH. This form, prepared at 350°C, possessed smaller grain size and better electrochemical performance than the HT form prepared by conventional high temperature synthesis. High discharge capacity (372 mAh·g−1: x = 4.0) and reversible discharge and charge cycle were attained. When heated at 200°C, CH3OH molecules remained in the compound and crystallinity became lower by lithium insertion over x = 2.0. The lithium de-intercalation was irreversible.
High Density Active-Site MnO2 Nanofibers for Energy Storage and Conversion Applications
Authors: Xiao T. D. , Reisner D. E. , Strutt P. R.
Published: April 2011

This investigation involves the synthesis of MnO2 nanofibrous materials, via an aqueous chemical synthesis route. A critical step in the synthesis is the extended period of the refluxing of the reactive constituents, which enables the gradual transformation of the initial amorphous nanoparticles into a random-weave nanofibrous structure, in the form of a bird's nest superstructure. The bird's nest has a diameter of approximately 10 μm, which is an assemblage of many individual nanofibers with a diameter of about 15 nm, and a length up to 1 μm. Partial transformation of the nanostructured MnO2 realizes a novel bimodal morphology, which combines a high density of chemically active sites with an enhanced percolation rate. Characterization of these nanofibers include SEM, TEM, surface area, and chemical analysis. High resolution TEM observations reveals that the as-synthesized MnO2 nanofibers contain lattice defects, including molecular pores, meso- and micro-pores.
Amorphous and Nanocrystalline Oxide Electrodes for Rechargeable Lithium Batteries
Authors: Manthiram A. , Kim J. , Tsang C.
Published: April 2011

Oxo ions (MO4)n- (M = V, Cr, Mn and Mo) have been reduced in aqueous solutions with potassium borohydride to obtain the binary oxides MO2+δ. While the vanadium and manganese oxides are nanocrystalline, the chromium and molybdenum oxides are amorphous. The nanocrystalline VO2 having a metastable structure and the amorphous CrO2 and MoO2.3 transform to the thermodynamically more stable phases upon heating above 300–400 °C. These metastable oxides after heating in vacuum at 200–300 °C to remove water show good electrode performance in lithium cells. VO2, CrO2 and MoO2.3 show a reversible capacity of, respectively, 290 mAh/g in the range 4–1.5 V, 180 mAh/g in the range 3.3–2.3 V, and 220 mAh/g in the range 3–1 V. MnO2 obtained by this process does not show good electrode properties.
Thermal Stability of Lithium Ion Battery Electrode Materials in Organic Electrolytes
Authors: Richard M. N. , Dahn J. R.
Published: April 2011

The technology of lithium ion batteries has been developed so that these systems can be used to power portable electronic devices. The next step is to increase the size of the batteries so that they power larger systems such as electric vehicles. However, before such a step can be taken the thermal stability of any materials placed in such a battery must be determined. Although the thermal properties of the materials are important for the small systems, which can reach high temperatures when abused, they become even more important in large systems where heat dissipation is more difficult because of the physical size of the system. This paper will discuss our approach, which uses an Accelerated Rate Calorimeter, to the study of the thermal behaviour of lithium ion battery electrode materials.
Lithium Ion Diffusion Through Glassy Carbon Plate
Authors: Inaba M. , Nohmi S. , Funabiki A. , Abe T. , Ogumi Z.
Published: April 2011

The electrochemical permeation method was applied to the determination of the diffusion coefficient of Li+ion (DLi+) in a glassy carbon (GC) plate. The cell was composed of two compartments, which were separated by the GC plate. Li+ions were inserted electrochemically from one face, and extracted from the other. The flux of the permeated Li+ions was monitored as an oxidation current at the latter face. The diffusion coefficient was determined by fitting the transient current curve with a theoretical one derived from Fick's law. When the potential was stepped between two potentials in the range of 0 to 0.5 V, transient curves were well fitted with the theoretical one, which gaveDLi+ values on the order of 10−8cm2s−1. In contrast, when the potential was stepped between two potentials across 0.5 V, significant deviation was observed. The deviation indicated the presence of trap sites as well as diffusion sites for Li+ions, the former of which is the origin of the irreversible capacity of GC.
Strontium Ruthenate Perovskites with High Specific Capacitance for use in Electrochemical Capacitors
Authors: Wilde P. M. , Guther T. J. , Oesten R. , Garche J.
Published: April 2011

Strontium ruthenates with the perovskite type structure ABO3 have been shown to exhibit attractive capacitive properties. Doping on the A site with La lead to typical capacitance values of 21 F/g. These materials were synthesized by coprecipitating metal hydroxides from a stoichiometric salt solution and subsequent firing at 800 °C in air. In this paper we present a new procedure to synthesize the materials which are crystalline and nevertheless show appreciable capacitances in contrast to ruthenium dioxide material, which only works in a hydrated amorphous structure. The process basically consists in a pyrolysis of concentrated metal salt solutions of the respective chlorides and nitrates at 500 °C for several minutes. Excess soluble phases are removed by washing out with water. X-ray diffraction experiments revealed similar phase purity and crystallinity as known from the coprecipitated materials. However the measured capacitances of undoped perovskites reached high values of 200 F/g exceeding twenty times the value of respective coprecipitated materials. First experiments on doping the materials promise further progress. The new synthesis route introduces a higher surface area by leaving cavities from leached soluble phases and bulk defects into the crystal structure. The first effect increases the number of active sites in contact with the electrolyte while the latter enhances the protonie conduction which is necessary to keep the charge balance within the material during cycling.
Experimental Electrochemical Capacitor Test Results
Authors: Wright R. B. , Murphy T. C. , Rogers Susan A. , Sutula Raymond A.
Published: April 2011

Various electrochemical capacitors (ultracapacitors) are being developed for hybrid vehicles as candidate power assist devices for the Partnership for a New Generation of Vehicles (PNGV) fast-response engine. The envisioned primary functions of the ultracapacitor are to level the dynamic power loads on the primary propulsion device and recover available energy from regenerative breaking during off-peak power periods. This paper will present test data from selected U.S. Department of Energy (DOE) supported ultracapacitor projects designed to meet the fast response engine requirements.

This paper will address the temperature dependence of test data obtained from a set of three devices provided from Maxwell Energy Products, Inc. These devices are rated at 2300 F at 2.3 V. Constant-current, constant-power, and self-discharge testing as a function of temperature have been conducted. From these tests were determined the capacitance, equivalent series resistance, specific energy and power, and the self-discharge energy loss factor as a function of the device operating temperature.
Computational, Electrochemical and 7Li NMR Studies of Lithiated Disordered Carbons Electrodes in Lithium Ion Cells
Authors: Sandί G. , Gerald R. E. , Scanlon L. G. , Carrado K. A. , Winans R. E.
Published: April 2011

Disordered carbons that deliver high reversible capacity in electrochemical cells have been synthesized by using inorganic clays as templates to control the pore size and the surface area. The capacities obtained were much higher than those calculated if the resultant carbon had a graphitic-like structure. Computational chemistry was used to investigate the nature of lithium bonding in a carbon lattice unlike graphite. The lithium intercalated fullenere Lin-C60 was used as a model for our (non-graphitic) disordered carbon lattice. A dilithium-C60 system with a charge and multiplicity of (0,1) and a trilithium-C60 system with a charge and multiplicity of (0,4) were investigated. The spatial distribution of lithium ions in an electrochemical cell containing this novel disordered carbon material was investigated in situ by Li-7 NMR using an electrochemical cell that was incorporated into a toroid cavity nuclear magnetic resonance (NMR) imager. The concentration of solvated Li+ ions in the carbon anode appears to be larger than in the bulk electrolyte, is substantially lower near the copper/carbon interface, and does not change with cell charging.
Effects of Sc or Tb Addition on the Microstructures and Resistivities of Al Thin Films
Authors: Takayama Shinji
Published: April 2011

The resistivities of Al thin films with added Sc or Tb largely decrease at over 350 °C. They reach to 5 -7 μΩcm after annealing at 450 °C, together with the segregation of fine Al3RE (RE = Sc or Tb) metallic compounds. However, the temperatures at which resistivity starts to decrease largely are much lower for Al-SC alloy films (150 °C) than for Al-Tb ones (250 °C). Furthermore, thermal defects of hillocks or whiskers start to appear on the film surface after annealing at 200 °C and 450 °C for Al-Sc and Al-Tb alloy films, respectively. It was revealed that the further addition of Zr to these binary alloy films largely retards a large decrease of resistivities on annealing and enhances the formation of hillocks or whiskers. On the contrary, the addition of Cu to Al-Tb or Al-Sc films significantly suppresses the formation of thermal defects and shows relatively low resistivities after annealing at 350 °C.
Application of Broad-Band Dielectric Spectroscopy for Investigations of Liquid Crystal - Porous Media Microcomposites
Authors: Sinha G. P. , Batalla B. , Aliev F. M.
Published: April 2011

We applied ultra broad-band dielectric spectroscopy in the frequency range from 10–3 Hz to 109 Hz to investigate the effect of size, shape and volume fraction of the pores in the porous matrices on the dielectric properties of liquid crystals (LC) dispersed in these matrices. Measurements in such a broad frequency range make it possible to obtain detailed information on the important aspects of the electrical behavior of heterogeneous materials such as: conductivity, surface polarization, and influence of confinement on dynamics of molecular motion of polar molecules forming LC. We investigated alkylcyanobiphenyls in the isotropie, nematic and smectic phases dispersed in porous glasses (average pore sizes - 100 Å and 1000 Å) which have randomly oriented, interconnected pores, and anopore membranes (pore diameters - 200 Å and 2000 Å) with parallel cylindrical pores. Dispersion of LC resulted in qualitative changes of their dielectric properties. Analysis of broad-band dielectric spectra shows that in organic (LC) - inorganic (porous matrix) heterogeneous composites conductivity plays an important role at F <1 Hz. We observe the appearance of new dielectric modes: a very slow process with characteristic frequency ≃ (1 – 10) Hz and a second process in frequency range about (103 - 106) Hz. The slow process arises due to the relaxation of interfacial polarization at pore wall - LC interface. The origin of this could be due to absorption of ions at the interface. Another possibility is the preferential orientation of the permanent dipoles at pore surface. The second new mode is due to the hindered rotation of the molecules near the interface. Additionally we observed two bulk like modes due to the rotation of the molecules around their short and long axii which are modified.
The Dielectric Loss of Single Crystal and Polycrystalline TiO2
Authors: Wang Xiaoru , Templeton Alan , Penn Stuart J. , Alford Neil McN.
Published: April 2011

The dielectric loss of single crystal and polycrystalline TiO2 has been studied. In polycrystalline TiO2 the dielectric loss is determined by both the microstructure and by the oxygen stoichiometry. Experiments have been carried out to determine the influence of both the microstructure (particularly porosity) and the oxygen stoichiometry. The TiO2 powder has been doped with partially stabilised zirconia, an oxygen ion conductor, in order to modify the oxygen stoichiometry. Sintered discs have been examined for loss as a function zirconia doping, pore volume and as a function of temperature. The behaviour of the doped and undoped titania powders is significantly different. Since many microwave dielectric materials contain Ti eg Ba-Ti-O, Ba-Nd-Ti-O, (Ba-RE-Ti-O, RE=Rare Earth), Zr-Sn-Ti-O etc it is essential to understand the role of the titanium, particularly as it can exist in mixed valence states, and the role of oxygen and its influence on the dielectric loss.
High Power Switching Behavior in Conductor-Filled Polymer Composites
Authors: Duggal Anil R. , Levinson Lionel M.
Published: April 2011

It has generally been assumed that the switching properties of conductor-filled polymer composites are based on a positive temperature coefficient of resistance (PTCR) effect where, at a certain switch temperature, the material resistivity increases by orders of magnitude. Here we present studies of the electrical switching behavior at high current densities which demonstrate that, in the high power regime, the observed switching is not based on the PTCR effect. Instead, we show that this type of switching appears to be a general feature in conductor-filled polymer composite materials and a qualitative model for the switching phenomenon is proposed. These results suggest that conductor-filled polymer composite materials can provide a new non-mechanical way of rapidly limiting high power short circuit currents. This should have broad applications in the circuit protection industry.
Microstructural Correlation with Electrical Properties for Y2O3 Doped CeO2 Thin Films
Authors: Tian Chunyan , Chan Siu-Wai
Published: April 2011

High quality textured 0.58% Y2O3 doped CeO2 films with (001), (111)/(001) and (110) were prepared using an e-beam deposition technique on substrates of (001) LaAlO3, r-cut sapphire, and fused silica, respectively. The composition and stoichiometry of the films were verified by Rutherford backscattering spectroscopy analysis. Both x-ray diffraction and transmission electron microscopy analyses gave consistent microstructural information. Complex impedance measurements have been performed to study the electrical properties of these films as a function of temperature. The conductivities of the films were dominated by grain boundaries of high conductivities as compared to that of the bulk ceramic of the same dopant concentration. The activation energies for the film conductivities were only slightly higher than that for the bulk lattice conductivities, but much lower than that for the bulk grain boundary conductivity. These results have been discussed in terms of the differences of the grain size and grain boundary microstructures between the films and the bulk ceramics.
Correlation Between Electrical Properties and Composition / Microstructure of Si-C-N Ceramics
Authors: Haluschka C. , Engel C. , Riedel R. , Kleebe H.-J. , Franke R.
Published: April 2011

In this paper we report on the measurement of electrical properties of multielement ceramics in the ternary Si-C-N system using the impedance spectroscopy. The results were correlated to the chemical composition, the hybridization state and the microstructural characteristics investigated by chemical analysis, X-Ray absorption near edge spectroscopy (XANES), Raman Spectroscopy, high resolution transmission electron microscopy (HRTEM) and X-Ray powder diffraction (XRD).
Low-Frequency Scanning Capacitance Microscopy
Authors: Lányi Š. , Hruškovic M.
Published: April 2011

The operation principle and main properties of a Scanning Capacitance Microscope (SCM) are described. It is called low-frequency, because in its design typical low-frequency techniques are utilised. The main attention is focused on its lateral resolution, signal-to-noise ratio and the possibility to detect dielectric losses.

Mapping the electrostatic field of a shielded microscope probe was used to calculate the stray capacitance, flux density, sensitivity and contrast obtained on a flat conducting surface, as well as on a surface covered by a thin dielectric film. The effect of dielectric losses, represented by a parallel conductance, on the detected capacitance and the resulting phase shift has been derived.

Using the results of mapping, the requirements on a SCM input stage and the possible solutions are discussed. From the point of view of frequency range and noise the best is an electrometric input stage, with input impedance represented by its capacitance.

The achieved signal-to-noise ratio of the low frequency Scanning Capacitance Microscope renders the extension of the working frequency range to lower frequencies. The input stage can be optimised for a frequency range from about 1 kHz to a few MHz, with the possibility to extend it to about 10 MHz at the cost of reduced sensitivity at the lowest frequencies.