bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic Structure of a Polar Ceramic/Metal Interface: {222}MgO/Cu
Authors: Benedek R. , Shashkov D. A. , Seidman D. N. , Muller D. A. , Silcox J. , Chisholm M. F. , Yang L. H.
Published: April 2011

{222}MgO/Cu is one of the most extensively characterized ceramic/metal interfaces, in view of the atom-probe field-ion-microscopy, Z-contrast scanning-transmission-electron-microscopy (STEM), and spatially-resolved electron-energy-loss-spectroscopy (EELS) measurements performed by the present authors, as well as the high-resolution electron microscopy (HREM) of this system by others. Atomistic simulations with local density functional theory (LDFT) and molecular dynamics (MD) have been performed to gain additional insight into the structure of this interface. This presentation describes an interface interatomic potential for {222}MgO/Cu derived from LDFT total energy calculations, and its application to structural properties, including the terminating species, the absence of dislocation standoff, and the symmetry of the interfacial dislocation network.
Equilibrium Structure and Schottky Barriers at Eras/Gaas Interfaces
Authors: Petukhov A. G. , Hemmelman B. T. , Lambrecht W. R. L.
Published: April 2011

The equilibrium structures as well as the electronic Schottky barriers for (100) Erbium-Arsenide/Gallium-Arsenide (ErAs/GaAs) arsenic and gallium terminated interfaces have been determined by ab-initio calculations using the local-density approximation and a full-potential linear-muffin-tin-orbital method. In both cases the arsenic sublattice was chosen to be continuous across the interface in accordance with experiments on Rutherford backscattering channeling. Band structures, densities of states, and charge density distributions were also determined for the interfaces. The comparison of the total supercell energies reveals that the gallium terminated (chain) interface is more energetically stable than the arsenic terminated (shadow) interface. It also shows that the equilibrium interface separation for the arsenic terminated interface corresponds to an ideal structure when arsenic forms undistorted face-centered cubic lattice. The separation in the gallium terminated interface is quite substantial and is 60% larger than that of the ideal situation. The model also predicts that no buckling of the ErAs interface monolayer will occur for either structure. The computed Schottky barriers for holes (after a semi-empirical quasiparticle self-energy correction) are 0.6 eV for the chain interface and 0.4 eV for the shadow interface.
Ab-Initio Determination of the Atomic Structure of Symmetrical Tilt Grain Boundaries in BCC Transition Metals
Authors: Elsässer C. , Beck O. , Ochs T. , Meyer B.
Published: April 2011

Atomistic simulations of grain-boundary structures in body-centered cubic transition metals have revealed that angle-dependent contributions to interatomic interactions are essential. Unfortunately, the results of presently available empirical many-body potentials are not yet always sufficiently reliable for quantitative theoretical predictions of grain-boundary structures, which are consistent with experimental observations, e.g. by high-resolution transmission electron microscopy.

Ab-initio electronic-structure calculations based on the local-density-functional theory offer the possibility to determine accurately the microscopic structures of special, high-symmetry grain boundaries, which can be used as data bases for the improvement of empirical many-body potentials. Such ab-initio calculations, with a mixed-basis pseudopotential method and grain-boundary supercells, are presented for Σ5 (310) [001] 36.87° symmetrical tilt grain boundaries in Niobium and Molybdenum.
Monte Carlo and Molecular Dynamics Simulations of Liquid Semiconductor Surfaces
Authors: Wang Zhiqiang , Yu Wenbin , Stroud David
Published: April 2011

We have numerically studied the surface tension and surface profiles of several liquid semiconductors, including Si, Ge, GaAs, CdTe, and their alloys, as a function of temperature and concentration. Two kinds of simulations have been carried out: direct free-energy calculations using Monte Carlo methods, and force summations using molecular dynamics. We use empirical two- and three-body interatomic interactions based on the form originally proposed by Stillinger and Weber for Si, in conjunction with simulation cell sizes ranging from 216 to as large as 8000 atoms and several novel numerical techniques including a direct calculation of the surface entropy. In the case of alloys, we find a striking segregation of the low-surface-tension component to the surface even when the alloy components are miscible at all concentrations.
Thickness Dependencies in the Calculated Properties of Metallic Ultra-Thin Films
Authors: Boettger J. C.
Published: April 2011

Ultra-thin film (UTF) electronic structure calculations are a common tool for investigating surface properties. In this work, electronic structure calculations for A1(111) films ranging from one to twelve atoms thick are used to illustrate some of the difficulties that can arise when one attempts to determine surface properties of metals with UTF calculations.
Ab-Initio Theory of Initial Oxidation of Silicon (001) Surfaces
Authors: Modine N. A. , Zumbach G. , Kaxiras E.
Published: April 2011

The oxidation of the Si(001) surface is an important process on both technological and theoretical grounds. Experimental studies have not provided a clear picture of even the relevant atomic structures during the initial stages of oxidation, while previous theoretical studies of these processes have yielded contradictory results. Using careful first principles total-energy calculations based on density functional theory, we study several mechanisms of incorporating a sub-monolayer coverage of oxygen into the characteristic p(2 × 1) dimer reconstruction of the Si(001) surface. Our recently developed Adaptive Coordinate Real-space Electronic Structure (ACRES) method allows us to obtain results that are adequately converged with respect to the numerous computational parameters associated with this difficult system. We compare our results with previous theoretical work and propose a physically motivated two step pathway for the initial incorporation of an oxygen atom into the dimerized surface. Based on our results, we can explain what formerly appeared to be puzzling Ultraviolet Photoelectron Spectroscopy measurements which indicated that each initial oxygen atom saturates two surface dangling bonds.
Mechanism for Breakage of Si-O Networks of SiO2 Films in HF Solutions
Authors: Oku Tomoki , Hattori Ryo , Sato Kazuhiko
Published: April 2011

An extended Hiickel calculation was employed to calculate the total electronic energy and the electron density during the breakage of the Si-O networks of a (F3SiO)2FSiOSiF(OSiF3)2 cluster modelled on the a-cristobalite structure. The Si-O networks are opened by the attack of F- ions on the silicon atoms, and the reaction is exthothermic by 2.7 eV through the attack of H+ ions on the oxygen atoms. Although the hydrogen termination of the oxygen atoms is an early reaction, the fluorine termination of the silicon atoms is a late reaction. The atomic bond population on the Si-O bonds decreases to zero by opening the Si-O networks. We conclude that the a-cristobalite and a-quartz SiO2 are dissolved in HF solutions since the Si-O networks are easily opened by the attack of F- ions. Our conclusion indicates that both cosite and stishovite SiO2, which are not dissolved in the HF solutions, are composed of Si-O networks that can be hardly opened by the attack of F- ions. Moreover, we propose the continual breakage of Si-O networks without the desorption of H2O molecules as an etching mechanism of SiO2 films.
The Effect of the Interface on the Overall Thermal Conductivity of Multi-Phase Composites
Authors: Lipton Robert
Published: April 2011

Multi-phase particle reinforced heat conducting composites are considered. We treat the case when there is an interfacial thermal barrier between phases. We indicate how the particle size distribution and particle geometry influences the overall properties of the suspension. These results apply immediately to the mathematically analogous case of DC electrical conductivity in the presence of electrical contact resistance between phases.
Magnetic Effects at Surfaces and Interfaces (Including Grain Boundaries)
Authors: Freeman A. J. , Wu Ruqian , Chen Lujun , Zhong Lieping
Published: April 2011

First-principles electronic structure studies based on local spin density functional theory and performed on extremely complex simulations of ever increasingly realistic systems, play a very important role in explaining and predicting surface and interface magnetism. This has led to solving even more challenging problems like the embrittlement of the Fe grain boundary, discussed here. Now, a major issue for first-principles theory is the treatment of the weak spin-orbit coupling (SOC) in magnetic transition metals and their alloys and its subsequent effects: (i) A major breakthrough in eliminating the numerical randomness for the determination of the magneto-crystalline anisotropy was made with the state-tracking and torque approaches. This now enables us to treat magnetostriction and its inverse effect, strain-induced magnetic anisotropy in transition metal bulk, thin films and alloys, (ii) The magneto-optical Kerr effects and x-ray magnetic circular dichroism are now directly calculated and compared with experiment. In all this work, and more recently, on the first-principles calculations of giant magneto-resistance in multilayers, extensive first-principles calculations and model analyses provide simple physical insights and guidelines to search for new magnetic recording and sensor materials.
Atomistic Study on Nano Stress-Strain Curves of α-Fe
Authors: Hu Shenyang , Ludwig Matthias , Farrissey Liam , Schmauder Siegfried
Published: April 2011

The atomistic processes and stress-strain-curves during uniaxial tensile deformation of a single α-Fe nanocrystal have been studied with the molecular static method. Periodic boundary conditions are imposed along one direction perpendicular to the tensile axis to model plane strain conditions. The effects of the model sizes in plane, boundary conditions and crystal orientations on the stress-strain curves are systematically analyzed. Various deformation evidences such as dislocation movement, dislocation piling up and twinning are clearly observed. The deformation and fracture characteristics of a-Fe and their dependencies on the boundary conditions are investigated.
Micromorphology, Microstructure and Magnetic Properties of Sputtered Garnet Multilayers
Authors: Marcelli R. , Padeletti G. , Gambacorti N. , Simeone M. G. , Fiorani D.
Published: April 2011

The growth technique, the micromorphological and microstructural characterization by means of atomic force microscopy (AFM) and secondary ions mass spectrometry (SIMS) as well as the magnetic properties of a novel class of magnetic multilayers, based on radio frequency (RF) sputtered thin amorphous garnet films, are presented. One, three and five thin film multilayers composed by amorphous pure yttrium iron garnet (a:YIG) and amorphous gadolinium gallium garnet (a:GGG) have been grown on GGG single crystal substrates. The multilayer interfaces have been found to be comparable in both, the three and five-layers structure. Low field susceptibility measurements, showed a paramagnetic behaviour for the single layer YIG film. For the three and five layers samples, irreversibility effects were observed, giving evidence of magnetic clusters at the interface YIG/GGG.
Improvement of Thermal Stability of Metal/Oxide Interface for Electronic Devices
Authors: Ichikawa Yo , Hiramoto Masayoshi , Matsukawa Nozomu , Iijima Kenji , Kitagawa Masatoshi
Published: April 2011

The nano-meter controlled iron/iron-oxide multilayer materials have been successfully obtained by the pulse reactive sputtering method with high deposition rate. These multilayer demonstrated a good thermal stability of its structure and magnetic properties up to 500°C when a small amount of Si was doped in the structure, whereas the non-doped multilayer degraded at above 300°C. The difference of the oxidation energy between Fe and Si increases the thermal stability of the interface between Fe and Fe-O layer.
Crystallinity and Magnetoresistance in Calcium Doped Lanthanum Manganites
Authors: Gillman E. S. , Dahmen K. H.
Published: April 2011

Thin films of calcium doped lanthanum manganites Lal-xCaxMnO3 (LCMO) with x ∼ 0.41 have been prepared on LaAlO3(001) (LAO) Y-stablized ZrO2(001) (YSZ), and Al2O3(0001) (SAP) substrates by liquid delivery metal-organic chemical vapor deposition (LD-MOCVD). The films on YSZ and SAP substrates have a textured, polycrystalline morphology with a preferred orientation of (110). The films on LAO show a single-crystalline morphology and a (100) orientation. Transport measurements show the polycrystalline films have a resistance peak approximately 60K lower than the films on LAO and, in general, have a much higher overall resistance. The magne-toresistance (MR) ratio ([R(H) - R(0)]/R(H)) is sharply peaked near the maximum in resistance for the films on LAO, while the polycrystalline films show a noticeable absence of this sharply peaked behavior and a flat, rather large (∼ 100%) MR ratio over a large temperature range. These results will be discussed in terms of grain boundary scattering, crystallite size, and magnetization.
Low Energy K-Dependent Electronic Structure of the Layered Magnetoresistive Oxide La1.2Sr1.8Mn2O7
Authors: Saitoh T. , Dessau D. S. , Park C.-H. , Shen Z.-X. , Villella P. , Hamada N. , Moritomo Y. , Tokura Y.
Published: April 2011

We have studied the fc-dependent electronic structure of the layered colossal magnetoresistive manganite La1.2Sr1.8Mn2O7 using high-resolution angle-resolved photoemission spectroscopy. We found dispersive energy bands as a function of the crystal momentum k near the Fermi level (EF). We have also performed local spin density approximation (LSDA)+U band-structure calculations on the current system. The overall experimental dispersion relation is basically in agreement with the band-structure calculations yet close to EF there is a significant deviation from the predicted dispersions. Instead of clear Fermi-surface (FS) crossings, we observe a depression of the features as the FS is approached as if there is a “pseudo” gap in the excitation spectrum. The pseudogap continuously opens with temperature and does not show further significant opening above Tc, corresponding to the metal-insulator transition. Those unusual aspects of the spectra has been discussed from the viewpoint of the strong electron-lattice coupling model.
Observation of Growth-Related Magnetic Structures in La0.67Sr0.33MnO3
Authors: Hawley M. E. , Brown G. W. , Kwon C.
Published: April 2011

Ambient observation of magnetic structures by magnetic force microscopy (MFM) in La0.67Sr0.33MnO3 films has not yet been clearly correlated with stresses induced by the kinetic or thermodynamic growth processes or the compressive (LaAlO3) or tensile (SrTiO3) nature of the substrate lattice-mismatch. Although domain-like magnetic structures have been seen in some as-grown films on LAO and related to substrate-induced stress and film thickness, no magnetic structure has been seen for films on STO and other films grown under different kinetic conditions on LAO. In this study we have identified a set of pulsed-laser deposition conditions with the substrate temperature as a variable to determine the relationship between growth and stress-induced magnetic structures. Results from scanning tunneling, atomic force, and MFM microscopies, magnetization, and coercivity measurements will be presented.
Effects of Localized Holes on Charge Transport, Local Structure and Spin Dynamics in the Metallic State of CMR La1-xCaxMnO3
Authors: Heffner R. H. , Hundley M. F. , Booth C. H.
Published: April 2011

We review resistivity, x-ray-absorption fine-structure (XAFS) and muon spin relaxation (μSR) data which provide clear evidence for localized holes causing polaron distortion and unusual spin dynamics below Tc in “colossal magnetoresistive” (CMR) La1-xCaxMnO3. Resistivity measurements for x=0.33 under an applied field H have shown that ln[ρ(H,T)] α -M, where M is the magnetization. The XAFS data show a similar functional dependence for the polaron distortions on M. The data from these two measurements are interpreted in terms of some fraction of the available holes x remaining localized and some increasing fraction becoming delocalized with increasing M. Finally, this polaron-induced spatial inhomogeneity yields anomalously slow, spatially inhomogeneous spin dynamics below Tc, as shown in the μSR data. These experiments individually probe the charge, lattice and spin degrees of freedom in this CMR system and suggest that the polarons retain some identity even at temperatures significantly below Tc.
The Effect of Radiation Induced Disorder on La0.7Ca0.3MnO3–δ Thin Films
Authors: Stroud R. M. , Browning V. M. , Byers J. M. , Chrisey D. B. , Fuller-Mora W. W. , Grabowski K. S. , Horwitz J. S. , Kim J. , Knies D. L. , Osofsky M. S.
Published: April 2011

The effects of disorder on the transport and magnetic properties of pulsed laser deposited La0.7Ca0.3MnO3 thin films were studied. Ion irradiation with 10 MeV I and 6 MeV Si ions was used to produce controlled levels of defects ranging from 0.006 to 0.024 displacements per atom. The peak resistance temperature of the I-irradiated films decreased from 264K for the undamaged film to OK for the 0.016 dpa film. The magnetic ordering temperature decreased from 270K (undamaged) to 130K (0.011 dpa), and remained nearly constant at 130K for higher damage levels. This demonstrates a decoupling of the magnetic and metal-insulator transitions. A characteristic relationship between the peak resistance temperature and activation energy of resistance with the form Tp = 285(1-Δρ/115)0.13, was observed for all films. This characteristic relationship indicates that the range of resistivity and magnetoresistivity values for observed La0.7Ca0.3MnO3 can be explained in terms of disorder-limited polaron hopping.
Effects of Chromium Ion Implantation on the Magneto-Transport Properties of La0.7Ca0.3MnO3 Thin Films
Authors: De Silva P. S. I. P. N. , Malde N. , Hossain A. K. M. A. , Cohen L. F. , Thomas K. A. , Chater R. , Macmanus-Driscoll J. D. , Tate T. J. , Mathur N. D. , Blamire M. G. , Evetts J. E.
Published: April 2011

Thin films of colossal magnetoresistance material La0.7Ca0.3MnO3 were implanted with different fluence 200keV Cr ions. Resistivity measurements in zero and applied fields of up to 8T were made in order to determine the effects of the implanted magnetic ions on the magnetoresistance (MR). As the Cr fluence was increased, the resistivity increased and the metal-insulator transition (MI) temperature was suppressed to values below the experimentally accessible temperature range as a result of oxygen loss and the creation of defects. However, for the highest fluence of 5×1015 ions/cm2, a re-entrant metal-insulator type transition was observed. Furthermore a significant improvement in the low field MR was observed for fields less than 500mT. These results are interpreted in terms of substitution of Cr ions onto Mn sites and the creation of a magnetically inhomogeneous material and the influence of oxygen deficiency.
Phase Diagram and Anisotropic Transport Properties of Nd1-xSrxMnO3 Crystals
Authors: Kuwahara H. , Okuda T. , Tomioka Y. , Kimura T. , Asamitsu A. , Tokura Y.
Published: April 2011

We have investigated electronic transport and magnetic properties of perovskite-type Nd1-xSrxMnO3 crystals with change of controlled hole-doping level (0.30≤x≤0.80). The electronic phase diagram of Nd1-xSrxMnO3 was obtained by systematic measurements of magnetization (magnetic structure), resistivity, and lattice parameter. We have also studied the anisotropie transport properties of x=0.50 and 0.55 crystals with different magnetic structures: CE-type antiferromagnetic (AF) structure for x=0.50 and A-type layered AF one for x=0.55. In the case of the x=0.55 crystal, the metallic behavior was observed within the ferromagnetic (F) layers, while along the AF-coupling direction the crystal remains insulating over the whole temperature region. The observed large anisotropy is due to the magnetic as well as orbital-ordering induced confinement of the spin-polarized carriers within the F sheets. The nearly isotropie transport behavior has been confirmed for the CE-type AF charge-ordered state in the x=0.50 crystal.
Stoichiometry and Magnetic Properties of Iron Oxide Films
Authors: Dimitrov D. V. , Hadjipanayis G. C. , Papaefthymiou V. , Simopoulos A.
Published: April 2011

The stoichiometry, structural and magnetic properties, and Mössbauer spectra of reactively sputtered Fe-O films were studied as a function of the O2 partial pressure during the deposition. By increasing the amount of O2 films with the following crystallographic structures and stoichiometry were fabricated; amorphous Fe-O, mixture of Fe and FeO, offstoichiometric single-phase FexO, mixture of FeO and Fe3O4, single-phase Fe3O4, mixture of Fe3O4 and γ-Fe2O3, mixture of Fe3O4 and α-Fe2O3, and single-phase α-Fe2O3. The Verwey transition in Fe3O4 films was observed in the coercivity versus temperature curve and in the thermomagnetic data. FeO and α-Fe2O3 films showed anomalous ferromagnetic-like behavior, in contrast to their anti ferromagnetic nature in bulk. The unusual magnetic properties were attributed to the formation of clusters of tetrahedraly coordinated Fe3+ ions in FeO and to uncompensated surface spins, in α - Fe2O3 films.
Simulation Studies of Polymer Electrolytes for Battery Applications
Authors: Halley J. W. , Nielsen B.
Published: April 2011

We report modeling studies of polyethylene oxide which are carried out with the goal of elucidating the mechanism of ion conduction in the temperature range of interest to battery applications. We review our previous work in which the amorphous regions of the polymer between its glass and melting temperatures is modeled by a molecular dynamics algorithm in which the model system is polymerized from a model monomeric liquid. We describe new work in which the hydrogen centers are added to the model in order to permit comparison with recent neutron work. We compare our simulations of frequency dependent conductivity with experiment and end with a brief discussion of possibilities for improved conductivity which our current understanding suggests.
Polyacene (PAS) Bάtteries
Authors: Yata Shjzukuni , Tanaka Kazuyoshi , Yamabe Tokio
Published: April 2011

Two crucial characteristics are expected for batteries. One is large capacity (large energy density) and the other high power. In the last decade, the batteries with large capacity and energy density have been strongly required in the field of portable electronics and communication equipments and, hence, the new batteries such as Ni-MH and Li-ion ones have been developed and commercialized. At present, Ui-ion battery has the largest energy density of all the available batteries and its energy density has come up to 300WM/l, twice as large as that of Ni-Cd one. In general, electric power of batteries signifies the amount of energy put out at unit time. Thus the output power discharged from a battery, storing a certain amount of capacity, in Ihour is ten times as much as that discharged in 10 hours. It is indeed an excellent ability to go on walking all the way with a heavy knapsack on one's back but so is it to output a tremendous power at a moment just as in the weightlifting. It is well known that Ni-Cd battery can output the highest power of all the batteries. It can be discharged at about 10C, namely in about 6 minutes. Large energy density and high output power seem to be similar, but they are essentially different.
A COMPOSITE ELECTROLYTE FOR AN SOFC CONSISTING OF A CERIA SHEET AND A ZIRCONIA FILM DEPOSITED BY THE SOL-GEL METHOD
Authors: Chiba Reiichi , Yoshimura Fumikatsu , Yamaki Junichi
Published: April 2011

We investigated a composite electrolyte for solid oxide fuel cells prepared by coating a ceria sheet (Ce0.8Gd0.2O2-d or GDC ) with a scandia alumina doped zirconia (0.850ZrO2-0.110Sc2O3-0.04Al2O3) film by the sol-gel method. The sol-gel film annealed at 1200°C was examined by X-ray diffraction analysis and found to be in a cubic phase at room temperature. The ionic conductivity of this film is comparable to that of bulk sintered at 1620°C. Scanning electron microscope observations revealed that the film forms a good interface with the electrolyte of the ceria sheet, even though the annealing temperature is as low as 1200°C.

We fabricated a single cell consisting of a composite electrolyte, a La0.8Sr0.2MnO3 cathode and a Ni-YSZ anode. The composite electrolyte consisted of zirconia film about one micron thick deposited by the sol-gel method and a 0.2 mm thick ceria sheet.

A cell operated with moist H2 and O2 gas exhibited an open circuit voltage of 1.00 V at 800°C. This value is much closer to the value of 1.13 V expected from the Nernst equation than the value of 0.76 V for a cell with a ceria sheet but without the sol-gel film.
New Interconnections for Planar Alloy-Separator Sofc Stacks
Authors: Yamazaki Y.-T. , Namikawa T. , Ide T. , Oishi N. , Suzuki O.
Published: April 2011

A new design of interconnections between air electrodes and alloy separators in planar stacks is presented. The edges of the air electrodes supporting the electrolyte films are connected, through thin LaCrO3 layers, with the edges of adjacent alloy separators. The electric current in the cell flows radially in the porous thick air electrodes of LSM. The LaCrO3 layers are connected with the alloy separators through nickel felt in the fuel gas atmosphere. By using these interconnections, we can overcome the corrosion problems caused by contacting air electrodes with alloy separators in conventional planar stacks.
Benefits of Rapid Solidification Processing of Modified LaNi5 Alloys by High Pressure Gas Atomization for Battery Applications
Authors: Anderson I. E. , Pecharsky V. K. , Ting J. , Witham C. , Bowman R. C.
Published: April 2011

A high pressure gas atomization approach to rapid solidification has been employed to investigate simplified processing of Sn modified LaNi5 powders that can be used for advanced Ni/metal hydride (Ni/MH) batteries. The current industrial practice involves casting large ingots followed by annealing and grinding and utilizes a complex and costly alloy design. This investigation is an attempt to produce powders for battery cathode fabrication that can be used in an as-atomized condition without annealing or grinding. Both Ar and He atomization gas were tried to investigate rapid solidification effects. Sn alloy additions were tested to promote subambient pressure absorption/desorption of hydrogen at ambient temperature. The resulting fine, spherical powders were subject to microstructural analysis, hydrogen gas cycling, and annealing experiments to evaluate suitability for Ni/MH battery applications. The results demonstrate that a brief anneal is required to homogenize the as-solidified microstructure of both Ar and He atomized powders and to achieve a suitable hydrogen absorption behavior. The Sn addition also appears to suppress cracking during hydrogen gas phase cycling in particles smaller than about 25μm. These results suggest that direct powder processing of a LaNi5−xSnx alloy has potential application in rechargeable Ni/MH batteries.
High Performance Vanadium Oxide Thin Film Electrodes for Rechargeable Lithium Batteries
Authors: Zhang Ji-Guang , Liu Ping , Tracy C. Edwin , Benson David K. , Turner John A.
Published: April 2011

Plasma Enhanced Chemical Vapor Deposition (PECVD) was used to prepare vanadium oxide thin films as cathodes for rechargeable lithium batteries. The reactants consisted of a high vapor pressure liquid source of vanadium (VOCl3) and hydrogen and oxygen gas. Deposition parameters such as the flow rates of H2, O2 and VOCl3, the substrate temperature and the Rf power were optimized, and high deposition rate of 11 Å/s was obtained. Vanadium oxide films with high discharge capacities of up to 408 mAh/g were prepared. The films also showed a superior cycling stability between 4 and 1.5 V at a C/0.2 rate for more than 4400 cycles. The films were amorphous up to a deposition temperature of 300°C, however, deposition on to substrates with textured surfaces facilitated the formation of crystalline films. We demonstrate that both the vanadium oxide material and the PECVD deposition method are very attractive for constructing thin-film rechargeable lithium batteries with high capacity and long-term cyclic stability.
Magnetic and Transport Properties of Heat-Treated Polyparaphenylene-Based Carbons
Authors: Matthews M. J. , Kobayashi N. , Dresselhaus M. S. , Endo M. , Enoki T. , Karaki T.
Published: April 2011

ABSRACT

Electron spin resonance (ESR), magnetic susceptibility, and transport measurements were recently performed on a set of heat-treated polyparaphenylene (PPP)-based carbon samples, which are of significant interest as novel carbon-based anode electrodes in Li-ion batteries. Attention is focused on the evolution of the carbonaceous structures formed at low heat-treatment temperatures (THT) in the regime of 600° C ≤ THT ≤ 800° C, where percolative transport behavior is observed. At the percolation threshold, the coexistence of two spin centers with peak-to-peak Lorentzian linewidths of ΔHpp(300K) = 0.5 and 5.0 G is observed. The relatively high ratio of hydrogen. carbon (H/C) near is believed to influence the ESR results through an unresolved hyperfine interaction. Curie-Weiss temperaures are found from measurements of [Ipp(ΔHpp)2]–1, where Ipp is the peak-to-peak lineheight, yielding results that are in agreement with static susceptibility, χ(T), measurements. At low THT, PPP-based materials exhibit a large amount of disorder and this is evidenced by the high density of localized spins, Nc, which is obtained from a Curie-Weiss fit to χ(T) assuming a spin quantum number of S = ½. A model explaining the microstructure and high electrochemical doping capacity of PPP samples heat-treated to 700° C can be related to Li-ion battery performance.
A Novel Method for Obtaining a High Performance Carbon Anode for Li-Ion Secondary Batteries
Authors: Takamura T. , Sumiya K. , Nishijima Y. , Suzuki J. , Sekine K.
Published: April 2011

Entire surfaces of the pitch-based well graphitized and poorly graphitized carbon fibers were covered with an evaporated metallic film of Au, Ag, Sn, or Zn, whose thickness was varied from 100 to 600 Å. Li dope and undope characteristics as the anode of Li-ion secondary battery were compared for the samples with and without evaporated film. Not only high rate charge/discharge characteristics but cycleability have been realized to be improved remarkably for the sample whose surface was covered with a thin metal film.
The Corrosion Phenomena in The Coin Cell Br2325 of The “Superstoichiometric Fluorocarbon - Lithium” System
Authors: Mitlcin Valentin N. , Gallon Peter S. , Denisova Tatjana N. , Koreneva Ol'ga V. , Filatov Sergey V. , Shinelev Eugene A. , Alexandrov Alexander B. , Afanasiev Vladimir L. , Enin Alexander A. , Moukhin Viktor V. , Rozhkov Vladimir V. , Telezhkin Vladlen V.
Published: April 2011

It was noted at the earlier study and at the longer observations of the novel various types of superstoichiometric fluorocarbon materials CF1+x, where x = 0.1–0.33 (FCM) and their behavior, that despite of their known hygroscopity during a storage of samples in laboratory and technological utensils nevertheless occurs an appreciable sorption of atmospheric moisture. The color of samples does not change but sometimes there is appears a smell of hydrogen fluoride and even corrosion of glasswares at a long storage. On the basis of these facts was assumed that at a long storage the slow reactions of HF producing with a sorption moisture can proceed. This phenomena is necessary to take into account for successful manufacturing of long life lithium cells based on superstoichiometric fluorocarbon composite cathodes (FCC).
Recent Studies of Interfacial Phenomena which Determine the Electrochemical Behavior of Lithium and Lithiated Carbon Anodes with the Emphasis on In Situ Techniques
Authors: Aurbach D. , Schechter A. , Markovsky B. , Cohen Y. , Weissman I. , Moshkovich M.
Published: April 2011

This paper reports on some new results on the application of surface sensitive techniques for the study of the correlation of surface chemistry, morphology and electrochemical behavior of lithium and lithiated graphite as anodes for rechargeable batteries. Surface sensitive FTIR spectroscopy, atomic force microscopy (AFM), electrochemical quartz crystal microbalance (EQCM) were applied to Li and Li-graphite electrodes in a variety of electrolyte solutions of interest, in conjunction with standard electrochemical techniques. The similarity in the surface chemistry developed on Li and lithiated graphite in solutions is demonstrated and discussed. We demonstrate the strong impact of the surface chemistry on the morphology of Li deposition-dissolution processes, and the use of in situ EQCM measurements for the choice of optimal electrolyte solutions for rechargeable batteries with Li metal anodes.
Low Potential Li Insertion in Transition Metal Oxides
Authors: Leroux F. , Nazar L. F.
Published: April 2011

Low-potential Li insertion materials comprised of molybdenum oxides (AxMoO3) have been prepared by a “chimie douce” route. Li insertion below 200 mV is associated with dramatic transformation of the structure, leading to a material which displays good cyclability with a high reversible specific capacity of 940 mA/g in the voltage window 3.0–0.005V (volumetric capacity of 4000 mAh/cc), albeit with notable polarization on charge. The structural and compositional changes on discharge to 200 mV have been studied by a combination of XRD, and XAS. The interlayer ions have also been exchanged for Sn, and the electrochemical characteristics of these materials are compared with the alkali derivatives.
Improved Carbon Anode Materials for Lithium-Ion Cells
Authors: Flynn J. , Marsh C.
Published: April 2011

Several carbon materials have been studied for suitability as anode materials in lithium-ion cells. Carbons that have been included in this evaluation are three grades of commercially available mesophase carbon microbeads (MCMB) 6–28, 10–28 and 25–28, two specially prepared mesophase fibers (Amoco), a foreign mesophase fiber and KS-15 graphite (Lonza). Differences in cycling behavior between the three types of MCMB material are shown. Data of full lithium-ion cells demonstrate the effect that the choice of carbon material has on the cell discharge voltage and capacity. Lithium reference electrode experiments in full cells (3.0–4.0Ah capacity), elucidate the dynamics under several charge/discharge regimes and provide a comparison between the performance of carbon fiber and graphite anode materials. These test results indicate that the fibers can be charged at significantly higher rates than graphite without showing polarization at the anode. Full and half cell data also demonstrates the high coulombic efficiencies of the mesophase materials and first cycle efficiencies as compared to graphite. A comparison of two mesophase materials with different textures in full cells under strenuous cycling conditions shows significant differences in capacity retention. SEM photos of fibers showing the different textures are also presented.
The Effects of Near Surface and Bulk Microstructure on Lithium Intercalation of Disordered, “Hard” Carbons
Authors: Even William R. , Peng Lawrence W. , Yang Nancy , Guidotti Ronald , Headley Thomas
Published: April 2011

Disordered carbons were synthesized at 700°C from methacrylonitrile-divinylbenzene precursors. The disorder, even at the free surface, was confirmed with TAM. These powdered carbons were subjected to rapid surface heating by a pulsed infrared laser. While the bulk structure remained essentially unchanged, there was substantial surface reconstruction to a depth of 0.25μm after heating (5.9 W average power at 10Hz, 10 ns pulse width, 1064nm wavelength). The surface ordering appears similar to the bulk microstructure of carbons isothermally annealed at 2,200°C (i.e., turbostratic). Improvements were observed in first cycle irreversible loss, rate capability, and coulombic efficiencies of the reconstructed carbons, relative to the untreated carbon.
Application of Ab Initio Methods to Secondary Lithium Batteries
Authors: Aydinol M K. , Van Der Ven A. , Ceder G.
Published: April 2011

Ab initio methods have started to be widely used in materials science for the prediction of properties of metals, alloys and compounds. These methods basically require only the atomic numbers of the constituent species. Such methods not only provide us with predictions of some of the properties of the material (even before synthesizing it) but also help us in understanding the phenomena that control those properties.

The use of ab initio methods in the field of electrochemistry is, however, quite recent and rare [1–4]. In this study, we demonstrate how ab initio methods can be used to investigate the properties of secondary lithium batteries. Particular examples will be given in predicting average insertion voltages in spinel Li-Mn and Li-Co oxides and in layered LiMO2 (M = Ti, V, Mn, Fe, Co and Al) compounds. Additionally, the stability of these compounds to metal reduction and structural stability of LiCoO2 upon lithium removal is investigated. We find that the oxygen anion plays an active role in the electrochemical intercalation of lithium. The amount of electron transfer to oxygen occurring upon lithium intercalation correlates strongly with the cell voltages. The more electron transfer to oxygen occurs, the higher lithium intercalation potential is obtained.
Universality of Dielectric Response as an Aid to Diagnostics
Authors: Jonscher Andrew K
Published: April 2011

The advent of frequency response analysers and the formulation of the universality of dielectric responses have between them greatly enhanced the usefulness of dielectric measurements as a diagnostic tool. The available frequency range was extended to between eight and twelve decades, making it possible to determine spectra with some precision. In addition, we now have a much more complete understanding than was available previously of the significance of various spectral shapes. For charge carrier systems the universal approach is based on the fractional power law of frequency dependence of the real and imaginary components of the susceptibility , where the exponent falls in the range O < n < 1. Values of n close to unity correspond to low-loss behaviour, values close to zero to very lossy processes dominated by low-frequency dispersion (LFD). Examples will be presented of both extremes and an indication will be given of the theoretical significance of these results. A brief discussion will be given of the physical principles of low-loss dielectrics showing “flat” or frequency-independent χ and of the opposite limit of LFD. It will be shown how the presence of universality simplifies the analysis of data and their interpretation.
Very Low Loss Ceramic Dielectric Resonator Materials
Authors: Alford N McN , Penn S J , Templeton A , Wang X , Filhol P , Klein N , Zuccaro C. , Gallop J C
Published: April 2011

The huge increase in the use of microwave communications places severe constraints on the operating performance of the microwave filters. Dielectric resonators are a very attractive option as they can be prepared with very low dielectric loss, moderately high dielectric constant and a low temperature coefficient of the resonant frequency. In filters they possess very low intermodulation products and are capable of handling high power. Certain dielectric oxide single crystals display very low loss at microwave frequencies and on cooling the loss is generally observed to drop. The Q of sapphire at 10 GHz exceeds 107 at low temperatures of around 10K. However, single crystals are expensive and the purpose of this research is to explore inexpensive, sintered polycrystalline alternatives. By very careful attention to purity, processing and microstructure Q values approaching those of single crystals have been achieved. The loss of polycrystalline ceramics of Al2O3, Ba(Mg1/3Ta2/3)O3 (BMT) and Zr0.875Sn0.25Ti0.875O4 (ZTS) has been studied. Alumina, Al2O3 has been studied as a model material for dielectric loss. Theory predicts that the loss in single crystal sapphire should follow a T5 dependence. However at low temperatures the loss is dominated by extrinsic losses due to crystal imperfection, residual dopant atoms, dislocations and other lattice defects and the T5 dependence does not hold. In polycrystalline alumina the intrinsic loss is immediately masked by these extrinsic losses, even at room temperature, and a simple T dependence is observed. Results on polycrystalline alumina show that a Q of > 5×104 at 10 GHz and at room temperature are possible and Q's well in excess of 105 at 10 GHz and 77 K can be achieved.
Impedance Spectroscopy of Nanocrystalline Y-Stabilized Tetragonal Zirconia
Authors: Mondal P. , Hahn H.
Published: April 2011

Impedance Spectroscopy, X-Ray Diffraction and High Resolution Scanning Electron Microscopy have been used to study the effect of extremely fine grain size on electrical properties such as dc-conductivity and activation energies in nanocrystalline Y-stabilized tetragonal zirconia. The samples were prepared from powders produced by the Inert Gas condensation method. X-Ray Diffraction was used to characterize phase and average grain size of the sample. In addition, grain size and microstructure of the sample was examined using High Resolution Scanning Electron Microscopy. With Impedance Spectroscopy relaxations of O−2-ions in the lattice and in the grain boundaries could be resolved. The dc-conductivities of the lattice and the grain boundaries were deduced from the data. The activation energies for ac- and dc-conductivity of the lattice and grain boundary relaxation are reported.
Stability and Conductivity of Gd2((Mo1/3Mn2/3)xTi1-x)2O7
Authors: Sprague J. J. , Porat O. , Tuller H. L.
Published: April 2011

A composite solid state electrochemical device, with (Gd1-xCax)2Ti2O7 serving as the electrolyte and Gd2(Ti1-xMox)2O7 (GT-Mo) as the anode has recently been proposed. The latter exhibits high levels of mixed conduction under reducing atmospheres, but decomposes at high Po2. We have recently succeeded in extending the stability limits of the GT-Mo to higher Po2 with the addition of Mn. In this study, we report on the conductivity and stability of Gd2((Mo13Mn2/3)xTi1-x)207 (GMMT) as a function of Po2, T, and composition utilizing impedance spectroscopy and x-ray diffraction. The addition of Mn extends the stability region of the material to Po2 = 1 atm with little change in the magnitude of the conductivity. Defect models explaining the dependence of the conductivity on oxygen partial pressure are presented. Preliminary results from the use of an electronic blocking sandwich cell used to isolate the ionic conductivity of GMMT are also presented.
Formation of Dislocations in NiAl Single Crystals Studied by In Situ Electrical Resistivity Measurement
Authors: Sun Y. Q. , Hazzledine P. M. , Dimiduk D. M.
Published: April 2011

This paper reports experiments in which in situ electrical resistivity measurements were used to monitor the formation of dislocations in initially dislocation-free NiAl single crystals. The electrical resistivity is found to exhibit an abrupt jump at the onset of plastic yielding. This is interpreted to result from an abrupt nucleation of a massive density of dislocations at the yield point.
In-situ Characterization of Laser Deposited Fe/Ag Multilayers by a Combination of Time-of-Flight, Rheed and Resistance Measurements
Authors: Fähler Sebastian , Weisheit Martin , Krebs Hans-Ulrich
Published: April 2011

Fe/Ag multilayers, prepared by pulsed laser deposition (PLD) using KrF radiation, were characterized in-situ by RHEED (diffraction of high energetic electrons) and resistance measurements during deposition, and by X-ray diffraction after deposition. While the x-ray diffraction experiments give indications for sharp interfaces, the in-situ investigations clearly show an asymmetry of the structural behaviors at the interfaces and mixing effects on a nm scale, especially as soon as Fe is deposited on Ag. Time-of-flight (TOF) measurements performed with a Faraday cup show that during PLD in ultrahigh vacuum ions are deposited with kinetic energies of more than 100 eV. The results are modeled and discussed with respect to implantation and mixing effects due to the high kinetic energy of the deposited particles during PLD.
In Situ Plasma Characterization of Laser-Ablated BaxSr1-xTiO3
Authors: Venizelos D. T. , Sengupta S. , Sausa R. C.
Published: April 2011

High speed imaging and emission spectroscopy are used to characterize the plumes generated from the ablation of bulk barium strontium titanium oxide material in vacuum and 30–60 mTorr of O2 using a pulsed 248-nm laser with fluences ranging from 5–8 J/cm2. High speed imaging reveals that in vacuum the leading edge of the plume expands normal to the substrate surface with a velocity of 19.7 km/sec. The ratio of distance traveled to the plume's radius is ˜ 2 at the early stages of the expansion and 3.2 at the later stages near the substrate. Similar observations are observed when the plume expands in 30 mTorr of O2 for times less than 2.0 μsec. However, at times greater than 2.0 μsec the plume's expansion is retarded due to collisional momentum transfer and reactions with the background gas. This effect is more pronounced when the plume expands in 60 mTorr of O2. Blast wave theory is used to model these results. Time-resolved emission spectroscopy of Ba(I) lines in the 735–770 nm region reveals that the plume' electron temperatures, Te, in a vacuum expansion range from 18000±2000 K at 0.1 μsec to 15000±1500 K at 2.0 /μsec. In contrast, in 30 mTorr of O2 the values of Te range from 17000±2000 K at 0.1 μsec to 4000±500 K at 8.0 μsec. At 0.1 μsec the plume's electron density is estimated as 1.7±0.4 × 1017 cm−3 in both vacuum and 30 mTorr of O2. We also determine the Stark broadening of the Ba(I) line at 746 nm to be 0.5±0.1 Åat an electron temperature of 1 eV and an electron density of 1017 cm−3.
In situ Monitoring of the Effects of Gas Mixtures on Ion Beam Depositions of Diamond-Like Carbon Films
Authors: Wu R. L. C. , Lanter W. , Monreal R. , Kosel P. B. , Miyoshi K.
Published: April 2011

A quadrupole mass spectrometer and a total ion-current measuring device have been utilized to monitor the ion compositions of gas mixtures of CH4/H2 and CH4/H2/O2 during the deposition for quality control and process optimization. An ultra high vacuum system using a 20 cm diameter RF excited (13.56 MIfz) ion gun and a four-axis substrate scanner has been developed for deposition of diamond-like carbon films for electrical, optical, and tribological applications. At a constant RF power of 179W, the mass spectra of gas mixture CH4/H2 (1:2.5) showed the most abundant ion is CH3+. Addition of O2 to the ion source has been found to affect the adhesion, deposition rate, and physical and chemical properties of the DLC films. By use of a mass spectrometer with and without the electron beam, the degree of ionization of CH4 was calculated to be about 10%. As the concentration of O2 was increased, all hydrocarbon ions decreased and H3O+ increased, resulting in a decrease in the film growth rate and an increase in etching of Si and glass substrates. In general, the optical bandgap, adsorption coefficients and refractive index decreased as oxygen concentration increased. Raman spectra showed the G-peak position shifted toward the graphitic peak with narrow peak width as oxygen concentration increased. At ultra high vacuum, the coefficient of friction increased with increased adhesion on substrates as oxygen was increased.