bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Dynamics Simulations of Porous Silica
Authors: Beckers J.V.L. , De Leeuw S. W.
Published: April 2011

We describe a new simulation method for the preparation of porous silica and present results from molecular dynamics simulations of the structures obtained. We start from a homogeneous liquid phase with reduced atomic charges. The charges are then slowly rescaled and the atoms start clustering to finally form a porous network. We observe that local ordering precedes formation of long range correlations. We investigate physical properties of porous silica such as porosity, internal surface and fractality. They are in reasonable agreement with experimental data, although internal surface and porosity seem to be systematically larger than those found in adsorption experiments. The vibrational and dielectric power spectra show an enhanced intensity in the low frequency region. These modes can be associated with slow dynamics of clusters.
An Atomistic Study of Ti Segregation to Lamellar Interfaces in Ti-RICH TiAl
Authors: Ito K. , Vitek V.
Published: April 2011

In this paper we analyze the effect of the surplus of titanium in the bulk on γ/γ interfaces. Monte Carlo calculations using a central force many-body potential suggest that in Ti rich alloys titanium segregates to the 120° rotational fault and the pseudotwin. This leads to the formation of a thin region of the DO19 Ti3Al at these interfaces. While titanium does not segregate to the ordered twin, it does to the ordered twin with the APB. But in this case the interface dissociates into the 120° rotational fault and the pseudotwin. The calculations further show that there are two types of atomic sites at the interfaces. One is the same as in the ideal L10 the other, to which the segregation takes place, is specific for interfaces parallel to {111} planes. The specific distribution of the sites favored for segregation is the reason why segregation leads to the formation of a narrow region of the DO19 Ti3Al in the 120° rotational fault and the pseudotwin.
Evolution of Microstructure in the BCC-HCP Martensitic Phase Transition in Zirconium
Authors: Ackland G. J. , Pinsook U.
Published: April 2011

We report molecular dynamics simulations of the martensitic phase transition from bcc to hep in zirconium. We show the evolution of a laminated twinned microstructure, in which some plastic deformation has occurred to rotate the twins manifested as basal stacking faults. This rotation is such as to alter the twinning angle from the 60° between the hep variants to the 61.5° angle of the low energy (1011) twins. These are thus identified as a cause of microscopic irreversibility in the transition.
Structural and Mechanical Properties of Nanophase Ni: A Molecular-Dynamics Study of the Influence of Grain-Boundary Structure on Elastic and Plastic Behavior
Authors: Van Swygenhoven H. , Spaczér M. , Caro A.
Published: April 2011

Molecular dynamics computer simulations of high load plastic deformation at temperatures up to 500K of Ni nanophase samples with mean grain size of 5 nm are reported. Two types of samples are considered: a polycrystal nucleated from different seeds, each having random location and random orientation, representing a sample with mainly high angle grain boundaries, and polycrystals with seeds located at the same places as before, but with a limited missorientation representing samples with mainly low angle grain boundaries. The structure of the grain boundaries is studied by means of pair distribution functions, coordination number, atom energetics, and common neighbour analysis. Plastic behaviour is interpreted in terms of grain-boundary viscosity, controlled by a self diffusion mechanism at the disordered interface activated by thermal energy and stress.
The Role of Preparation Conditions on the SIC(001) Surface Reconstructions: A First Principles Study
Authors: Galli Giulia , Catellani Alessandra , Gygi Francois
Published: April 2011

Using first principles molecular dynamics, we have studied the reconstructions and thermal properties of the (001) surfaces of cubic SiC. Our calculations show that C-terminated surfaces can have different reconstructions, depending on preparation conditions and thermal treatment, and that the Si-terminated surface geometry can be substantially affected by the presence of stress. Our findings allow us to interpret recent experiments about (001) SiC surfaces, in particular STM images.
Stoichiometry and Structure of Polar Group-III Nitride Semiconductor Surfaces
Authors: Fritsch J. , Sankey O. F. , Schmidt K. E. , Page J. B.
Published: April 2011

We use a local-orbital formalism based on density-functional theory to investigate the stoichiometry and structure of the cation- and anion-terminated (0001) surfaces of wurtzite-phase GaN and A1N. We compare the total energies computed for various p(2×2) reconstructions. First-layer atom deficient structures such as vacancies are found to be the most stable configurations for the anion- and cation-terminated surfaces. For metal rich growth conditions our calculations favor the adsorption of metal atoms. Surface chemical reactions relevant for the growth of thin nitride films, such as the adsorption of hydrogen and nitrogen from decomposed ammonia, are discussed. We determine the total energy differences for the co-adsorption of NH2 and H on different surface structures.
Ab Initio Study of Electronic and Geometric Structures of Metal/Ceramic Heterophase Boundaries
Authors: Köstlmeier S. , Elsässer C. , Meyer B. , Finnis M. W.
Published: April 2011

The adhesion geometries of coherent cube-on-cube interfaces between spinel (MgAl2O4) and the two metals Al and Ag were determined by density functional band structure calculations in the local density approximation (LDA). For Al/MgAl2O4, for which experimental data are available, the calculated optimum interface geometry is in excellent agreement with HRTEM measurements (distance dint: 1.90 Å calc., 1.90±0.04 Å exp.).

The work of adhesion Wad is calculated for three different high-symmetry translation states between an Al-0 terminated (001) surface of the spinel and the (001) surface of each of the metals. The binding energy curves display a distinct optimum for the adhesion of aluminum atoms on top of the spinel oxygen ions at a Wad value of 2.4 J/m2. For silver several adsorption sites are isoenergetic at 1.1 J/m2 and the intersections of the Wad (dint) curves indicate a low-energy dissociation path. A further analysis of the electronic structure in the Al/MgAl2O4 system reveals the charge redistribution in the metal towards the oxygen ions as the main contribution to bonding. On the contrary, polarization of the metal film is the major effect observed on the adhesion of Ag to the spinel substrate.
The Local Atomic Structure of Lal-xSrxCoO3: Effects Induced by The Spin-State and Non-Metal to Metal Transitions
Authors: Louca Despina , Sarrao J. L. , Kwei G. H.
Published: April 2011

The pair density function (PDF) used in the analysis of pulsed neutron diffraction data of La1-xSrxCoO3 revealed new structural effects which are correlated to the susceptibility and transport transitions. The transition in the spin configuration of the Co ions from the low-spin (LS) to the high-spin (HS) state in the Co perovskite oxides can potentially induce structural distortions due to the coupling of the spin to the lattice and charge. The ground state of the pure compound, LaCoO3, is in the LS state and is non-magnetic. A transition occurs to the HS state at ∼ 50 K as indicated from the susceptibility measurements due to the thermal excitation of electrons to the eg level. The CoLSO6 octahedra associated with the Co ions in the LS configuration are distinguished from the CoHSO6 octahedra with the Co in the HS configuration because the CoLS-O bond length is shorter than the CoHS-O distance due to the different size of the corresponding Co ions. Such bond lengths are clearly identified in the local structure between 15 – 300 K. This finding is in contrast to the average structure which shows only one type of bond length in this temperature range but two types of bond lengths are suggested at considerably higher temperatures. This suggests that whereas the LS and HS CoO6-octahedra coexist, they are randomly distributed in the crystal lattice at lower temperatures and become ordered at higher temperatures. The introduction of charge carriers in the structure does not eliminate the coexistence of both the LS and HS states, indicating that with the transition to the ferromagnetic metallic state, the spin configuration is not entirely of the HS character and structural inhomogeneities are present.
Observation of Large Low Field Magnetoresistance in Ramp-Edge Tunneling Junctions Based on Doped Manganite Ferromagnetic Electrodes and A SrTiO3 Insulator
Authors: Kwon C. , Jia Q. X. , Fan Y. , Hundley M. F. , Reagor D. W. , Hawley M. E. , Peterson D. E.
Published: April 2011

We report the fabrication of ferromagnet-insulator-ferromagnet junction devices using a ramp-edge geometry based on (La0.7Sr0.3)MnO3 ferromagnetic electrodes and a SrTiO3 insulator. The multilayer thin films were deposited using pulsed laser deposition and the devices were patterned using photolithography and ion milling. As expected from the spin-dependent tunneling, the junction magnetoresistance depends on the relative orientation of the magnetization in the electrodes. The maximum junction magnetoresistance (JMR) of 30 % is observed below 300 Oe at low temperatures (T < 100 K).
Microstructural Aspects of Nanocrystalline LiZn Ferrites Densified with Chemically Derived Additives
Authors: Cho Yong S. , Burdick Vemon L. , Amarakoon Vasantha R. W. , Underhill Elijah , Brissette Leo
Published: April 2011

Densification behavior and microstructural characteristics of nanocrystalline LiZn ferrites with chemically derived additives were investigated. Nanocrystalline Li0.3Zn0.4Fe2.3O4 powders having a ≈ 15 nm size were prepared at a low temperature of 450°C by a chemical synthesis using a combustible polyacrylic acid (PAA). Small amounts of Si, Ca and Mn were incorporated into the nanocrystalline ferrites via sol-gel reactions utilizing tetraethyl orthosilicate, calcium isopropoxide and manganese acetate. This process was believed to give a homogeneous distribution of the additives over the nanocrystalline ferrites. A uniform microstructure was obtained without any evidence of exaggerated grain growth after sintering at 1100°C. Saturation magnetization and coercive force were found to increase with the chemical additives. The results were compared with those of the same composition, but processed by the conventional batch-mixing of corresponding oxide additives.
Pressure and Isotope Effects in the Manganese-Oxide Perovskites
Authors: Goodenough J. B. , Zhou J.-S.
Published: April 2011

Measurements of the temperature dependence of the resistivity ρ(T) and thermoelectric power α(T) under several hydrostatic pressures on l8O/l6O isotope-exchanged (La1-xNdxCa0.3MnO3 polycrystalline samples spanning the structural O'-O orthorhombic transition have demonstrated that the perovskite tolerance factor t increases with pressure, signaling an unusually compressible Mn-0 bond. They have also indicated a change at the O'-O transition from static to dynamic cooperative Jahn-Teller deformations, from a second-order to a first-order magnetic transition, from Mn(IV) to two-Mn polarons in the paramagnetic region, from Mn(IV) polarons to a vibronic state below Tc, and a phase segregation in the O phase above Tc that traps out mobile polarons into ferromagnetic Mn(IV)-rich clusters within a Mn(IV)-poor matrix. Specific heat data show a transfer of spin entropy to configurational entropy on cooling through Tcin the O phase, and a single-crystal study of La1-xSrxMnO3, x = 0.12 and 0.15, has demonstrated a transition from polaronic to itinerant e electrons below Tc within the O phase. Magnetic-susceptibility measurements in low fields confirm the phase segregation above Tc and the existence of a ferromagnetic glass below Tc in the O phase. The intrinsic “colossal” magnetoresistance (CMR) is attributed to the growth to their percolation threshold of the ferromagnetic clusters existing above Tc, and the dramatic rise in Tc with increasing tolerance factor t in the O-orthorhombic phase to an increase in the density, and also the mobility, of the untrapped polarons above Tc.
Magnetic Anisotropy and Lattice Distortions in The Doped Perovskite Manganites
Authors: Suzuki Y. , Hwang H. Y. , Cheong S-W. , Van Dover R. B. , Asamitsu A. , Tokura Y.
Published: April 2011

We have investigated the magnetic anisotropies of doped manganite materials in epitaxial thin film and single crystal form. Structural characterization, including x-ray diffraction, Rudierford backscattering spectroscopy and atomic force misocroscopy, indicate that our epitaxial films arc single crystalline and have excellent crystallinity. Since lattice distortions greatly affect the magnetic and transport properties of this family of materials, it is not surprising to find the profound effect of strain in films due to the lattice mismatch between the substrate and film. Magnetic anisotropy results of single crystals, subject to no external stress, is compared to those of epitaxial films.
Evidence for a Jahn-Teller Distortion in the CMR Layered Manganite La1.4Sr1.6Mn2O7
Authors: Louca Despina , Kwei G. H. , Mitchell J. F.
Published: April 2011

The changes with temperature in the crystallographic structure of the two-layered La1.4Sr1.6Mn2O7, are on average quite small but the atomic pair density function analysis of pulsed neutron diffraction data shows that the lattice is locally distorted in accordance with the change in the transport properties. In particular, while no Jahn-Teller (JT) distortion is expected in the layered compounds because the octahedral bilayers are almost cubic, lattice distortions attributed to a large JT effect are present and are of comparable magnitude as in the cubic perovskite system. This could in turn explain the similarity in their properties. The number of the JT distorted sites is reduced with temperature concomitantly with the decrease in resistivity of the ab-plane.
Mixed Ionic-Electronic Conduction in N1 Doped Lanthanum Gallate Perovskites
Authors: Long N. J. , Tuller H. L. , Hurt Lower , Zealand New
Published: April 2011

Lanthanum gallate is a promising material for “monolithic” fuel cells or oxygen pumps, i.e. one in which the electrolyte and electrodes are formed from a common phase. We have investigated La1−xSrxGa1–yNiyO3 (LSGNx-y) with x=0.1 and y=0.2 and 0.5 as a potential cathode material for such an electrochemical device. The σ(PO2,T) for LSGN10–20 points to a p-type electronic conductivity at high PO2 and predominantly ionic conductivity at low PO2. LSGN10–50 has an electronic conductivity suitable for SOFC applications of approximately 50 S/cm in air at high temperature. AC impedance spectroscopy on an electron blocking cell of the form M/LSG/LSGN/LSG/M was used to isolate the ionic conductivity in the LSGN10–20 material. The ionic conductivity was found to have a similar magnitude and activation energy to that of undoped LSG material with σi= 0.12 S/cm at 800°C and EA= 1.0 ± 0.1 eV. Thermal expansion measurements on the LSGN materials were characterized as a function of temperature and dopant level and were found to match that of the electrolyte under opeating conditions.
Carbon and Fluorinated Carbon Materials for Fuel Cells
Authors: Wheeler D. , Luczak F. , Fredley R. , Cipollini N.
Published: April 2011

Carbon and fluorinated carbon materials are major constituents of phosphoric acid fuel cells and PEM fuel cells and the stability of these materials is critical for long life operation. Laboratory corrosion studies of separator plate materials were correlated with separator plate changes in commercial PAFC fuel cells. The addition of thin films of Teflon™ to the separator plates extends the life of the separator plates to 60,000+ hours through the formation of a temporary hydrophobic barrier. ESCA studies show the loss of hydrophobicity with time of PAFC electrodes to be a result of delamination of the Teflon from the carbon and not corrosion of the Teflon by phosphoric acid. The projected life of PAFC power plants has been confirmed by commercial operation of power plants for over 40,000 hours.
Accelerated Corrosion of Stainless Steels in the Presence of Molten Carbonate below 923 K
Authors: Ota Ken-ichiro , Toda Katsuya , Motohira Naobumi , Kamiya Nobuyuki
Published: April 2011

The high temperature corrosion of stainless steels (SUS316L and SUS310S) in the presence of molten carbonate [(Li0.62K0.8)2CO3 and (Li0.52Na0.48)2CO3] has been studied in a CO2-O2 atmosphere by measuring the weight gain of the specimens.

The corrosion of SUS316L significantly depended on the reaction conditions. With the carbonate coating (both Li/Na and Li/K carbonates), severe corrosion occurred during the initial period of the corrosion test below 923 K, especially around 823 K. The initial severe corrosion was a local corrosion which produced through holes in the metal specimens and occurred more clearly at low Pco2 with the Li/Na coating than with the Li/K coating. The corrosion became more severe at higher CO2 pressures and lower O2 pressures. In a pure CO2 atmosphere (without O2), the corrosion rate significantly increased at 823 K. The steel was corroded uniformly at that time.
LiCoO2 Thin Films Grown by Pulsed Laser Deposition on Low Cost Substrates
Authors: Ginley D. S. , Perkins J. D. , McGraw J. M. , Parilla P. A. , Fu M.L. , Rogers C. T.
Published: April 2011

We report on the use of pulsed laser depositon (PLD) to grow thin films of LiCoO2 on a number of low cost substrates including SnO2 coated Upilex, stainless steel and SnO2 coated glass. Highly textured (001) films grown on CVD deposited SnO2 films on 7059 glass, were obtained at 200 to 500 mTorr O2 and a temperature of 500 C. Similar texture was not obtained on the stainless or Upilex however dense films from crystalline to amorphous were obtained. The films were characterized by x-ray diffraction and Raman spectroscopy.
Advances in Battery Technologies and Markets: Material Science Aspects
Authors: Salkind A. J.
Published: April 2011

Advances in materials innovation, availability, processing, and volumetric and gravimetric utilization, have lead to dramatic changes in the technologies and markets for batteries, and other electrochemical storage devices, in recent years. The increased ability to cycle of the new materials and preparations has also resulted in a more dominant proportion of secondary batteries in the market. The growth of the various technology sectors of the battery and energy storage device industry will be compared to the relevant improvements in materials science. The developments needed in materials, composites, and processing techniques is reviewed, in order to match the ongoing changes in electronic circuits, power devices, transportation, and the growth of portable appliances. An analysis of the technical/market segments of the battery industry is presented.
A New Polymer Cathode-Conducting Polymer Interconnected With Sulfur-Sulfur Bonds: Poly(2,2'-Dithiodianiline)
Authors: Naoi Katsuhiko , Kawase Ken-ichi , Mori Mitsubiro , Komiyama Michiko
Published: April 2011

Poly(2, 2'-Dithiodianiline)(Poly(DTDA)), a conducting polymer having disulfide bond in it, has been proposed as a new class of high energy storage material. DTDA has one S-S bond interconnected between two moieties of anilines. The structure of the poly(DTDA) was similar to that of polyaniline in addition that the S-S bond is preserved after electropolymerization of DTDA. The poly(DTDA) has some advantages because of its high theoretical energy density, faster kinetics and higher electrical conductivity than other organosulfur cathodes
Raman Scattering in LiCoO2 Single Crystals and Thin Films
Authors: Perkins J. D. , Fu M. L. , Trickett D. M. , McGraw J. M. , Ciszek T. F. , Pariila P. A. , Rogers C. T. , Ginley D. S.
Published: April 2011

We report Raman scattering measurements for uniaxially textured and randomly oriented polycrystalline LiCoO2 min films as well as for LiCoO2 and LiCo0.4Al0.6O2 single crystals. For both the crystalline LiCoO2 thin film samples and the single crystal LiCoO2 samples, well defined phonon modes are observed at Raman shifts of 486 cm−1 and 596 cm−1corresponding to the expected Eg and Alg modes of the layered LiCoO2 crystal structure with R3m symmetry. Upon Al substitution for Co in LiCoO2, the two phonon modes appear to shift to higher energy, but further work is needed to clarify this point.
Nr Measurements to Study The Reversible Transfer of Lithium Ion in Lithium Titanium Oxide
Authors: Esaka T. , Takai S. , Kamata M.
Published: April 2011

Using Neutron Radiography (NR), the transfer of lithium ions has been investigated in the high temperature-type lithium ion conductor, Li1.33Ti1.67O4. After supplying direct current to the oxides with different isotope ratios (6Li/7Li), NR images were obtained, which confirmed lithium ion movement in the oxides as changes of bright parts on negative films. Analysis of the NR images clarified that lithium ions in the spinel-type Li1.33Ti1.67O4were transported almost reversibly according to the polarity of electric field applied. The relations between the lithium contents in the samples and the film gray level showed that the cathode region in the charged sample contains about twice more lithium than in the original sample. Furthermore, NR method was applied to check lithium ion insertion into the TiO2(rutile) sample. As a result, an informative Neutron Radiogram showing the lithium ion insertion was obtained.
Vibrational Spectroscopic Studies of the Local Environment in 4-Volt Cathode Materials
Authors: Julien C. , Massot M. , Perez-Vicente C. , Haro-Poniatowski E. , Nazri G. A. , Rougier A.
Published: April 2011

We report the vibrational spectra of numerous 4-volt cathode materials, the transition metal oxides which are potential materials for advanced Li-ion batteries. They provide high specific energy density, high voltage, and remarkable reversibility for lithium intercalation-deintercalation process. Studied were carried out by Raman and FTIR spectroscopies. Oxides such as LiMn2O4, LiNiVO4, LiCoVO4 spinels, LiMeO2 (Me=Co, Ni, Cr) layered compounds and their mixed compounds have been investigated. The local environment of cations against oxygen neighboring atoms has been determined by considering tetrahedral and octahedral units building the lattice. Structural modifications induced by the intercalation-deintercalation process, by the cation substitution, or by the low-temperature preparation route are also examined. The results are compared with those of end members.
Influence of Carbon Structure and Physical Properties on The Corrosion Behavior in Carbon Based Air Electrodes for Zinc Air Batteries
Authors: Golovin M. Neal , Kuznetsov Irena , Atijosan Iyi , Tinker Lawrence A. , Pedicini Christopher S.
Published: April 2011

Rechargeable zinc-air batteries are a long run time solution for portable electronics. Cells with a nominal voltage of 1.05 V have a specific energy of 169 Wh kg−1 and aenergy density of 219 Wh L1. This cell is capable of delivering 16 – 18 Ah of capacity at 2 A (16.7 mA cm−2) discharge rate. However, the cycle life of these cells is artificially shortened because of the generation of carbon dioxide in the alkaline electrolyte during the cycling of the cell. The carbon dioxide has the effect of removing the OH− (equation 1) needed by the anode

half reaction (equations 2 and 3). The need for hydroxide is demonstrated in equation 2.

There is literature evidence [1,2] that the CO2 was the result of corrosion of the carbon matrix of the air electrode. We report here the results of our investigation of this corrosion reaction and what properties of the carbon contribute to the corrosion reaction rate.
Application to Lithium Batteries of Ternary Solvent Electrolytes with Ethylene Carbonate – 1,2-Dimethoxyethane Mixture
Authors: Sasaki Y. , Yamazaki N. , Handa M.
Published: April 2011

The electrolytic conductivity, the lithium cycling efficiency of lithium electrode and the energy density for Li/V2O5(2025) coin-type cell were examined in ternary solvent electrolytes containing LiPF6and LiClO4with ethylene carbonate(EC) – 1,2-dimethoxyethane(DME) equimolar binary mixture at 25°C. The solvents applied to EC – DME mixture are dimethyl carbonate(DMC), ethyl methyl carbonate(EMC), diethyl carbonate(DEC), 1,3-dioxolane(DOL), 2,2-bis(trifluoromethyl)-1,3-dioxolane(TFMDOL), 1,3-dimethy1–2-imidazolidinone(DMI) and 1-methyl-2-pyrrolidinone(NMP). The order of decrease of the molar conductivities in ternary solvents electrolytes except DMI and NMP systems is agreement with that of increase in viscosities of the solvents applied to EC – DME binary mixture. The molar conductivities in ternary solvent electrolytes containing DMI and NMP are mainly affected by the dielectric constants rather than viscosities of mixed solvents. The energy density of Li/V2O5(2025) coin-type cell in LiPF6/EC – DME – DOL electrolyte with the highest molar conductivity was 500 Wh kg−1, which is the highest value in every ternary electrolyte. The lithium cycling efficiency(charge - discharge coulombic cycling efficiency of lithium electrode) in EC – DME – EMC, EC – DME – DMI and EC – DME – TFMDOL electrolytes containing LiPF6is more than 75% at 40 cycle numbers. The lithium electrodeposition on the Ni(working) electrode surface in ternary solvent electrolytes by cyclic voltammetry was observed by atomic force microscopy(AFM) and scanning electron microscope(SEM).
Polymer-Oxide Anode Materials
Authors: Kerr T. A. , Leroux F. , Nazar L. F.
Published: April 2011

The adaptable layer structure of molybdenum trioxide was exploited to insert the amino derivative form of the conductive polymer poly(para-phenylene) (PPPNH2) within the van der Waals gap. Two polymer insertion routes were designed that yield novel PPPNH2-MoO3 materials of different composition. Characterization of these materials using powder XRD, thermal analysis, and FTIR spectroscopy shows insertion of the polymer has occurred. The properties of the nanocomposites for low potential electrochemical lithium insertion were compared to those of the sodium molybdenum bronze using the materials as cathodes in conventional lithium cells. Initial results indicate the specific charge capacity and irreversibility during the first charge are effected by polymer content whereas polarization is not.
Variation of Stresses Ahead of The Internal Cracks in ReNI5 Powders During Hydrogen Charging and Discharging Cycles
Authors: Biner S. B.
Published: April 2011

In this study, the evolution of the stress-states ahead of the penny shaped internal cracks in both spherical and disk shaped ReNi5 particles during hydrogen charging and discharging cycles were investigated using coupled diffusion/deformation FEM analyses. The results indicate that large tensile stresses, on the order of 20–50% of the modulus of elasticity, develop in the particles. The disk shaped particles, in addition to having faster charging/discharging cycles, may offer better resistance to fracture than the spherical particles.
Comparison of Carbon and Metal Oxide Anode Materials for Rechargeable Li-Ion Cells
Authors: Huang C.-K. , Sakamoto J. S. , Smart M. C. , Surampudi S. , Wolfenstine J.
Published: April 2011

The state of the art (SOA) Li-ion cells utilize carbon anodes. However, to improve specific energy, energy density, and safety of cells using carbon anodes, alternative anodes must be developed. Recently, Fuji Film Inc. has suggested the use of tin oxide based anodes in Li-ion cells. It is believed mat cells containing tin oxide based anodes have the potential to meet the need for NASA's future missions. As a result, we conducted an analysis to compare the performance of cells containing carbon anodes and cells containing tin oxide anodes. The comparison between these cells involved the following: 1) reaction mechanisms between Li and carbon and reaction mechanisms between Li and tin oxide, 2) half-cell and full-cell performance characteristics, 3) interactions between the anode materials and electrolyte types and compositions, and 4) the optimization of binder composition.
Electrochemical and Spectroscopie Evaluation of Lithium Intercalation in Tailored Polymethacrylonitrile Carbons
Authors: Zavadil Kevin R. , Guidotti Ronald A. , Even William R.
Published: April 2011

Disordered polymethacrylonitrile (PMAN) carbon monoliths have been studied as potential tailored electrodes for lithium ion batteries. A combination of electrochemical and surface spectroscopie probes have been used to investigate irreversible loss mechanisms. Voltammetric measurements show that Li intercalates readily into the carbon at potentials IV positive of the reversible Li potential. The coulometric efficiency rises rapidly from 50% for the first potential cycle to greater than 85% for the third cycle, indicating that solvent decomposition is a self-limiting process. Surface film composition and thickness, as measured by x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS), does not vary substantially when compared to more ordered carbon surfaces. Li+ profiles are particularly useful in discriminating between the bound states of Li at the surface of solution permeable PMAN carbons.
Voltage Hysteresis and Heat Generation Behavior in Lithium-Ion Batteries
Authors: Saito Y. , Takano K. , Kanari K. , Nozaki K.
Published: April 2011

In order to characterize the heat generation behavior of a lithium-ion cell during charge and discharge, calorimetry has been carried out. The influence of past treatments applied to the cell is examined based on heat generation. The test cell shows a voltage hysteresis during charge and discharge, and the heat generation behavior is related to this hysteresis. A hard carbon is used in the cell as the negative electrode material, and the hysteresis mechanism and heat generation are discussed based on the reactions in the hard carbon electrode.
Local Structure of Ball-Milled Carbons for Lithium Ion Batteries: A Pair Distribution Function Analysis
Authors: Claye A. , Zhou P. , Fischer J. E. , Disma F. , Tarascon J-M.
Published: April 2011

The local atomic structure of ball-milled carbons was investigated by radial distribution function (RDF) analysis using pulsed time-of-flight neutron diffraction. The results exhibit a gradual loss of long-range order as a function of milling time. Modeling of the elastic structure factors and of the differential correlation functions identified the structure of ball-milled carbons as finite-size graphene fragments whose size decreases continuously with milling time. The large increase in lithium reversible capacity after 20 hours of milling was correlated with the loss of interlayer correlation between graphite flakes, similar to the structure of hard carbons in the “House of Cards” model.
Characteristics of Boron Doped Mesophase Pitch-Based Carbon Fibers as Anode Materials for Lithium Secondary Cells
Authors: Tamaki Toshio , Kawamura Toshifumi , Yamazaki Yoshinori
Published: April 2011

Mesophase pitch-based Carbon Fibers(MCF) have been investigated as anode materials for lithium secondary cells by examining their physical and electrochemical properties. Discharge capacity and initial charge-discharge efficiency of the materials were studied in relation to the heat treatment temperatures of MCF. MCF heat treated at about 3,000° C gave high discharge capacity over 310mAh/g, good efficiency (93 %) and superior current capability of 600mA/g (6mA/cm2). On the other hand, to improve the battery capacity, Boron was doped to the fiber about several % by adding B4C to the pre-carbonized milled fibers and then heat-treated up to 3000°C in Ar. Then heat treated at 2,500°C under vacuum condition to remove remained B 4 C. The structure of Boron-doped fibers was characterized and compared with that of non-doped standard fibers, and also Li ion battery performances are evaluated. The Boron-doped MCF indicated improvement in graphitization and increased discharge capacity as high as 360mAh/g. The voltammograms of both fibers are different from each other. The cell mechanism is discussed based on the unique structure of Boron-doping to the MCF is very effective for the battery performance.
High Surface Area Metal Carbide and Metal Nitride Electrodes
Authors: Wixom M. R. , Tarnowski D. J. , Parker J. M. , Lee J. Q. , Chen P.-L. , Song I. , Thompson L. T.
Published: April 2011

Processes for fabricating new high surface area ceramic electrode materials have been developed. These electrode materials have been applied in electrochemical capacitors and related energy storage and conversion devices. Several synthetic approaches have been developed for producing high surface area carbide or nitride active materials. The fabrication methods provide the capability to vary the composition and microstructure of the electrode material. A number of new candidate high surface area electrode materials have been synthesized. Compositional and microstructural information is presented. Electrodes have been evaluated by cyclic voltammetry, chronopotentiometry, and impedance spectroscopy in acidic and basic aqueous electrolyte systems. Single electrode and single cell performance data are presented. Intrinsic properties such as open circuit potential, electrochemical stability and specific capacitance are discussed with respect to electrode composition. The influence on performance of extrinsic factors such as electrode thickness, particle size, and pore structure is also discussed. The performance of these new materials is compared to carbon, with emphasis on advantages with respect to volumetric energy and power density.
Electrical Properties of Integrated Ta2O5 Metal-Insulator-Metal Capacitors
Authors: Martin B. C. , Basceri C. , Streiffer S. K. , Kingon A. I.
Published: April 2011

We demonstrate the feasibility of a Ta2O5-based metal-insulator-metal (MIM) capacitor module which is integrated into the backend-of-the-line of a 0.5 μm CMOS process flow. The demonstration utilizes 6-inch wafers, sputtered Ta2O5 films with TaN and TiN electrodes, reactive ion etch (RIE) processes for defining the capacitor stack, and a metallization scheme which uses hot Al(Cu) and W plugs and a standard forming gas anneal (N2-5% H2). Acceptable electrical properties have been achieved within these processing constraints for the integrated MIM capacitor module, including specific capacitance (C/A) and leakage current density (J) of ≥ 5 fF/μm2 and ≤ 1 pA/pF-V, respectively. In addition, we compare the fundamental properties of the Ta2O5 dielectric with literature reports and point out that leakage mechanisms must be analyzed with care due to significant dielectric relaxation in the films under certain processing/measurement conditions. For the baseline integrated films, we confirm that leakage is most consistent with a Poole-Frenkel mechanism.
Giant Magnetoimpedance: A Relevant Application of Impedance Spectroscopy
Authors: Garcia K. L. , Valenzuela R.
Published: April 2011

The impedance response of amorphous ferromagnetic wires is measured in the 5 Hz-13 MHz frequency range by applying a small AC current of 1 mA (RMS). A DC magnetic field (in the 0–6.7 kA/m range) is simultaneously applied. The impedance response is analyzed by means of simple series and parallel equivalent circuits. An association of circuit elements and physical parameters of the sample is proposed.
Study of the Molecular Mobility of Polysaccharide Solid Thin Layers by Dielectric Relaxation Spectroscopy
Authors: Liedermann K. , Lapčík L. , Desmedt S.
Published: April 2011

Temperature dependence of measured dielectric relaxation spectra (DRS) in the frequency range 20 Hz - 1 MHz of hydroxyethylcellulose (HEC) are in the temperature range 100 – 350 K. of Arrhenius character with one relaxation process at 150 – 250 K. This process reflects most probably β-relaxation of the side chain groups. Calculated activation energy of this process was 5730 kJ/mole. Four types of polysaccharides were studied at 293 K temperature: hyaluronic acid (HA), chondroitin sulfate (CHS), HEC and carboxymethylcellulose (CMC), in the low-frequency range 10−5 - 100 Hz. Measured dielectric spectra were interpreted as sum of one A.C. conductivity process and of up to two relaxation processes. The relaxation processes were described by means of the Havriliak-Negami formula and their parameters were related to the molecular structure of the polymers. The low value of a in CHS is related to its strong coupling due to the presence of two polar groups in its monomeric unit, whereas low values of α × β are interpreted as being due to the strong steric hindrances caused by long pendants present in HEC.
Complex Dielectric Spectroscopy Characterization of a Li0.982Ta1.004O3 Ferroelectric Single Crystal
Authors: Dong Ming , Gerhardt Rosario A.
Published: April 2011

The dielectric properties of a c-oriented ferroelectric Li0.982Ta1.004O3 single crystal have been investigated. The frequency and the temperature dependence of the dielectric properties have been measured from 500 to 650°C at frequencies ranging from 5 to 106 Hz. Both blocking and non-blocking electrodes were used for separating the electrode effect from the crystal bulk dielectric response. A low-frequency dispersion was identified to be due to the contribution of Li+ ionic carriers. Based on the electrical measurement data and complex nonlinear least squares fitting, an equivalent circuit is proposed to represent the dielectric properties of the single crystal.
Micromachined SFM Probes for High-Frequency Electric and Magnetic Fields
Authors: Van Der Weide D. W. , Agrawal V. , Neuzil P. , Bork T.
Published: April 2011

We discuss micromachined localized high-frequency electric (coaxial) and magnetic (loop) field probes integrated with scanning force microscopes. Our approach enables simultaneous acquisition of both field and topography in the radio frequency (RF) through millimeter-wave regime, enabling more complete characterization of materials, devices and circuits.
The Use of Computer Simulations to Interpret and Understand Electrical Measurements
Authors: Garboczi Edward J.
Published: April 2011

It is very rare to obtain complete 3-D information in the form of images of the microstructure of a material. Most often this information is incomplete because the resolution is inadequate, or is restricted to 2-D, via some kind of micrograph, or is not available at all. In the case of incomplete microstructural information, electrical measurements are then used to try to check a hypothesized microstructure, to see ifit can account for the measured electrical response. But even when complete microstructural information is available, if the microstructure is random, then it is not possible to analytically calculate the electrical response of the microstructure. The use of computer simulations, both to generate material shape and topology and numerically solve the electrical equations, is then required. Computer simulations allow the use of more complex hypotheses for the microstructure of a material, as the electrical response can be accurately computed for a wide range of microstructural shapes and topologies.
Electrochemical Corrosion of Electrodes in a Simulated Nuclear Waste Glass Melt
Authors: Sundaram S. K.
Published: April 2011

Corrosion of potential candidate electrode materials, molybdenum and tantalum, in a simulated nuclear waste glass melt was investigated using electrochemical (dc-powered) and non-powered tests. Electrochemical corrosion data showed that tantalum was more corrosion-resistant than molybdenum in this melt. Tantalum also showed passivation. The non-powered test data showed that tantalum corroded more than molybdenum. This was attributed to penetration of protective passivation layer at the tantalum-glass interface by the glass melt. Microstructural features and chemistry across selected electrode-glass interfacial regions supported these results.
Composition-Dependent Electrical Conductivity of Ionic-Electronic Composite
Authors: Park M. , Choi G. M.
Published: April 2011

Composition. dependence of electrical conductivity of ionic-electronic composite was camined using yttria(8mol%) stabilized zirconia-NiO composites. The contributions of ectronic and ionic charge carriers to the electrical conductivity were determined by Hebb-Vagner polarization technique and electromotive force measurement of galvanic cell. Up to 6 sol% NiO addition, the conductivity decreased since the electronic NiO acted as an insulator in onic matrix. However the ionic transport was dominant until NiO content reaches 26 vol%. Mixed conduction was observed between 26 and 68 vol% of NiO. The effects of composition on he electrical properties were explained by the microstructure and thus by the distribution of two hases.
Microstructural and Electrical Characterization of Misfit Dislocations at the InAs/GaP Heterointerface
Authors: Gopal V. , Chin T. P. , Vasiliev A. L. , Woodall J. M. , Kvam E. P.
Published: April 2011

InAs is a narrow band gap semiconductor with potential for such applications as IR detectors, low temperature transistors, etc‥ However, the lack of suitable substrates has hampered progress in the development of InAs based devices. In the present study, InAs was grown by Molecular Beam Epitaxy on (001) GaP substrates. Though this system has a high lattice mismatch, (∼11%), certain MBE growth conditions result in 80% relaxed InAs layers on GaP with the mismatch accommodated predominantly by 90° pure edge dislocations. Misfit dislocation microstructures were studied using Transmission Electron Microscopy. Electrical characterization using lateral conductance and Hall effect measurements were also performed. Preliminary results indicate the possibility of misfit dislocation related conductivity. The possible correlation between interface structure and electrical properties is discussed.
Analysis of Teos Silicon Dioxide: The Identification of Carbonatious Contaminants
Authors: Pereira Da Silva M. L. , Romanelli Cardoso A. , Santiago-Aviles J. J.
Published: April 2011

This work presents the analysis performed on a SiO2 film deposited from organometallic precursors with the aim of correlating their physico-chemical properties including electrical characteristics with processing variables. The characterization tools used in this study included SEM for film homogeneity; SIMS for the determination of total carbon content; FT-MS and Raman scattering spectroscopy for surface characterization. GC-MS was used to understand the electrochemical reactions taking place while performing I-V characteristics measurements.

The use of these multiple characterization techniques pointed out to deposited films with reasonable deposition characteristics but poor electrical ones. Phase segregated heterogeneity's rich in carbonatious residues influenced the degradation of the electrical characteristics.
Particle and UV-Imaging with Position Sensitive MCP-Detectors-Three-Dimensional Momentum Space Imaging
Authors: Mergel V. , Jagutzki O. , Spielberger L. , Ullmann-Pfleger K. , Dörner R. , Schmidt-Böcking H.
Published: April 2011

Various position sensitive microchannel-plate (MCP) detector systems for ion, electron and photon detection are presented. We have also developed a complete set of electronics to operate the detectors and software to analyze the incoming data. The detectors provide two-dimensional position as well as excellent timing information, e.g. for time-of-flight measurements. All data can be stored in single event mode. These MCP-detectors were used for electron and ion analyzers, which provide a three-dimensional imaging of the momentum space of all detected particles.
Diode-laser-based Atomic Absorption Monitors for Physical Vapor Deposition Process Control
Authors: Wang Weizhi , Hammond R. H. , Fejer M. M. , Beasley M. R.
Published: April 2011

Atomic absorption spectroscopy with tunable diode lasers has been performed for monitoring and study of the physical vapor deposition process. The combination of the wavelength-modulation spectroscopy with diode lasers and the balanced detection scheme guarantees the high sensitivity and reliability of the system. Direct measurements of atomic flux in e-beam evaporated yttrium and barium, which are components in YBCO superconducting thin films, have been demonstrated. The measured velocities show that the e-beam evaporated atoms are in a non-thermal-equilibrium state, dependent on source conditions, implying that the flux measurement rather than a simple density measurement for rate control is necessary. Comparison with quartz crystal monitors shows that the present scheme, employing two laser beams counterpropagating at an angle to the substrate surface for measuring directly the velocity component normal to the substrate surface, can provide a pressure-independent flux measurement. In yttrium, which has an additional significantly populated metastable level, results show that pressure-independent flux measurement requires measurements at both the ground state and the metastable levels. Efforts have also been made to extend the accessible wavelengths of diode lasers to the UV region by using nonlinear optical frequency doubling techniques for other technologically important elements.
Growth of La2−x SrxCuO4 and La2CuO4+δ thin films by Reactive Coevaporation
Authors: Sato H. , Yamamoto H. , Naito M.
Published: April 2011

Thin films of La2−xSrxCuO4 (LSCO) and La2CuO4+δ (LCO) were grown by reactive coevaporation. We obtained LSCO thin films on (001) LaSrA104 (LSAO) substrates with Tc(R=0) = 44 K, which is higher than that for bulk samples. A structural analysis indicates that the increase in Tc is due to compressive strain generated by the lattice mismatch. A similar strain effect is suggested from the substrate dependence of Tc for superconducting LCO thin films, for which Tc(R=0) reached 50 K on (001) LSAO substrates. We also succeeded in obtaining high-quality LSCO ultrathin films without any buffer or cap layers on (001) LSAO substrates, but not on substrates of other materials with the larger lattice mismatch with LSCO. These results demonstrate that the lattice mismatch with the substrates is important in thin-film growth of LSCO and LCO.
Rheed Studies of a-Axis Oriented DyBa2Cu3O7 Films Grown by All-MBE
Authors: Bozovic Ivan , Eckstein J. N. , Bozovic Natasha , O'Donnell J.
Published: April 2011

Real-time, in-situ surface monitoring by reflection high-energy electron diffraction (RHEED) has been the key enabling component of atomic-layer-by-layer molecular beam epitaxy (ALL-MBE) of complex oxides. RHEED patterns contain information on crystallographic arrangements and long range order on the surface; this can be made quantitative with help of numerical simulations. The dynamics of RHEED patterns and intensities reveal a variety of phenomena such as nucleation and dissolution of secondary-phase precipitates, switching between growth modes (layer-by-layer, step-flow), surface phase transitions (surface reconstruction, roughening, and even phase transitions induced by the electron beam itself), etc. Some of these phenomena are illustrated here, using as a case study our recent growth of atomically smooth a-axis oriented DyBa2Cu3O7 films.