bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of Cation Valences and Oxygen Vacancies in Magnetoresistive Oxides by Electron Energy-Loss Spectroscopy
Authors: Wang Z. L. , Yin J. S. , Berta Y. , Zhang J. 
Published: April 2011

ABSTRACTMagnetic oxides of (La,A)MnO3and (La,A)CoO3have two typical structural characteristics: cations with mixed valences and oxygen vacancies, which are required to balance the charge introduced by cation doping. The consequences introduced by each can be different, resulting in different properties. It is important to quantitatively determine the percentage of charges balanced by each, but this analysis is rather difficult particularly for thin films. This paper has demonstrated that electron energy-loss spectroscopy (EELS) can be an effective technique for analyzing Mn and Co magnetic oxides with the use of intensity ratio of white lines, leading to a new technique for quantifying oxygen vacancies in functional and smart materials.
Thin Film Growth and Magnetotransport Study of (La, Sr)MnO3
Authors: Manako Takashi , Obata Takeshi , Shimakawa Yuichi , Kubo Yoshimi 
Published: April 2011

ABSTRACTThin-film samples of La1-xSrxMnO3 (x = 0.20 – 0.30) were grown by pulsed-laser deposition using various target compositions, substrate materials, growth temperatures, oxygen partial pressures, and laser-pulse repetition rates. The crystal structure and the transport and magnetic properties of these films were then examined. Of the growth conditions, the oxygen partial pressure (Po2) had the greatest influence on the electrical and magnetic properties. Films grown under a low Po2 had a low ferromagnetic transition temperature (Tc) and a wide resistive transition width. None of the heat treatments done after growth improved these films’ quality. The film morphology was significantly affected by the substrate material. Our x-ray diffraction analysis and AFM measurements revealed that the films deposited on both MgO (100) and LaAlO3 (100) were epitaxially grown but contained defect structures. In contrast, grain-free thin films were epitaxially grown on the SrTiO3 (100) substrates. The surface roughness of films grown on SrTiO3 was less than 0.3 nm, even for films up to 150 nm thick. Under optimized growth conditions, as-deposited films for x ≥ 0.2 showed a sharp transition in resistivity at Tc. Magnetoresistance at far below Tc was as low as that reported for single-crystal sample. Since large magnetoresistance was often observed in polycrystalline samples and believed to be a grain boundary effect, these results indicate the high quality of the films grown on the SrTiO3 substrates.
Calculated Transport and Magnetic Properties of some Perovskite Metallic Oxides AMO3
Authors: Santi G. , Jarlborg T. 
Published: April 2011

ABSTRACTWe study some compounds of the perovskite (or pseudo-cubic perovskite) series AMO3, where M is a transition metal and A is Ca, Sr, or Nd, by LSDA self-consistent electronic structure calculations with the LMTO method. Transport and magnetic properties, as well as Fermi surfaces are calculated. These materials exhibit sharp density of states features in the vicinity of the Fermi level that strongly affect their transport and magnetic properties and make them very sensitive to structural deformation and stoichiometry. Calculated total energies are very close for anti-ferromagnetic and ferromagnetic solutions. This explains qualitatively the magnetoresistive anomalies shown by this family of compounds.
Experimental Determination of the key Energy Scales in the Colossal Magnetoresistive Manganites
Authors: Dessau D. S. , Saitoh T. , Park C.-H. , Shen Z.-X. , Moritomo Y. , Tokura Y. 
Published: April 2011

ABSTRACTWe have performed X-ray absorption (XAS) and angle-resolved photoemission (ARPES) on single crystals of both the layered and cubic colossal magnetoresistive manganites to determine the electronic structure and the relevant energy scales in the problem: the intra-atomic exchange energy J (∼ 2.7 eV), the Jahn-Teller energy gain EJ-T (<.25 eV), the one-electron bandwidth W (>3 eV for layered compounds) and the lattice relaxation or polaron binding energy EB (.65 eV ferromagnetic phase and.8 eV paramagnetic phase). Lattice polarons are deemed important especially in the paramagnetic but also to a degree in the ferromagnetic phase. Due to the energy scale mismatch, the Jahn-Teller effect is unlikely to be the cause for these lattice polarons, at least for the layered samples.
Dry and Wet Etch Processes for NiMnSb, LaCaMnO3 and Related Materials
Authors: Hong J. , Wang J. J. , Lambers E. S. , Caballero J. A. , Childress J. R. , Pearton S. J. , Dahmen K. H. , Von Molnar S. , Cadieu F. J. , Sharifi F. 
Published: April 2011

ABSTRACTA variety of plasma etching chemistries were examined for patterning NiMnSb Heusler thin films and associated A12O3 barrier layers. Chemistries based on SF6 and Cl2 were all found to provide faster etch rates than pure Ar sputtering. In all cases the etch rates were strongly dependent on both the ion flux and ion energy. Selectivities of ≥20 for NiMnSb over A12O3 were obtained in SF6-based discharges, while selectivities ≤5 were typical in Cl2 and CH4/H2 plasma chemistries. Wet etch solutions of HF/H2O and HNO3/H2SO4/H2O were found to provide reaction-limited etching of NiMnSb that was either non-selective or selective, respectively, to A12O3. In addition we have developed dry etch processes based on Cl2/Ar at high ion densities for patterning of LaCaMnO3 (and SmCo permanent magnet biasing films) for magnetic sensor devices. Highly anisotropie features are produced in both materials, with smooth surface morphologies. In all cases, SiO2 or other dielectric materials must be used for masking since photoresist does not retain its geometrical integrity upon exposure to the high ion density plasma.
High Frequency Magneto-Electrodynamics of La1-xSrxMnO3 Single Crystals
Authors: Srikanth H. , Revcolevschi B. , Sridhar S. , Pinsard L. , Revcolevschi A. 
Published: April 2011

ABSTRACTThe radio frequency (RF) response of La1-xSrxMnO3 single crystals reveal a variety of features associated with the structural, electronic and magnetic properties of the system. The resonance technique operating at ∼ 4 MHz employed in this study is sensitive to small changes in both the magnetic susceptibility and resistivity of the samples. Very sharp changes in frequency are observed at the ferromagnetic (FM) and structural phase transitions in both the metallic (x = 0.175) and insulating (0.125) crystals studied.In addition to the known transitions identified as FM and orthorhombic distortions, our experiments show rich structures which are not observed in conventional DC magnetization and transport experiments. Our results demonstrate that RF experiments are ideally suited to investigate the complex phase diagram in the manganites.The colossal frequency change that we observe at the FM transition in the La1-xSrxMnO3 crystals is indicative of the enormous potential for using these materials in high frequency switching applications.
Magnetic and Electronic Transport Properties of Single Crystal La0.64Pb0.36MnO3
Authors: Yang Jihui , Hu Siqing , Uher Ctirad , Han P. D. , Payne D. A. 
Published: April 2011

ABSTRACTWe studied the magnetic and electronic transport properties of a single crystal sample of La0.64Pb0.36MnO3 in the temperature range 5 K to 350 K and magnetic field up to 5.5 T. A magnetic transition is found at 210 K. The single crystal sample is ferromagnetic below the transition temperature (Tc) and becomes paramagnetic at temperatures T > Tc. Magnetization measurements along three different orthorhombic crystal axes show no significant difference. The magnetoresistance approaches a maximum value of about -60% at Tc in 5 T magnetic field strength and has qualitatively different field dependence below and above Tc. The scaling behavior between resistivity and magnetic moment is examined for temperatures both below and above the transition. A low temperature (T<15 K) dp / dT < 0 effect is attributed to possible quantum tunneling of carriers between neighbouring distortions.
Epitaxial Growth Mechanism and Physical Properties of Ultra thin Films of La0.6Sr0.4MnO3
Authors: Konishi Yoshinori , Kasai Masahiro , Kawasaki Masashi , Tokura Yoshinori 
Published: April 2011

ABSTRACTThin films of La1-xSrxMnO3 (x=0.4) were fabricated using pulsed laser deposition (PLD) methods. The surface morphology of the films was sensitively affected by oxygen pressure during deposition. At high oxygen pressure (∑150 mTorr), randomly aligned grains were nucleated on the epitaxial film. When the pressure was reduced to 100 mTorr, the epitaxial film had very smooth surface. Under this condition, the thickness dependence of resistivity and magnetization were analyzed. Even 6 nm thick film showed ferromagnetic metallic behavior. The AFM images of ulta thin films deposited on wet-etched SrTiO3 showed atomically flat terraces and 0.4 nm steps. The film growth mode can be tuned to either layer by layer or step flow by the deposition temperature.
Analysis of Mixtures of Gamma Lithium Aluminate, Lithium Aluminum Carbonate Hydroxide Hydrate, and Lithium Carbonate
Authors: Nemeth M. T. , Ford R. B. , Taylor T. A. 
Published: April 2011

ABSTRACTLithium aluminate, LiA1O2is a ceramic powder which is used as the porous solid support for the electrolyte in molten carbonate fuel cells (MCFCs). It has previously been reported that gamma LiAlO2will convert to lithium aluminum carbonate hydroxide hydrate, Li2Al4(CO3)(OH)123H2O and Li2CO3when exposed to water vapor and carbon dioxide. We compare three techniques, weight gain, carbonate content and x-ray diffraction to measure the amount of conversion. The reaction may involve amorphous intermediates and no one technique by itself is satisfactory to study the conversion.
Crystal Structures of Mixed-Conducting Oxides Present in The Sr-Fe-Co-O System
Authors: Hodges J. P. , Jorgensen J. D. , Miller D. J. , Ma B. , Balachandran U. , Richardson J. W. 
Published: April 2011

ABSTRACTThe potential applications of mixed-conducting ceramic oxides include solid-oxide fuel cells, rechargeable batteries, gas sensors and oxygen-permeable membranes. Several perovskite-derived mixed Sr-Fe-Co oxides show not only high electrical-conductivity but also appreciable oxygen-permeability at elevated temperatures. For example, dense ceramic membranes of SrFeCo0.5O3-δ can be used to separate oxygen from air without the need for external electrical circuitry. The separated oxygen can be directly used for the partial oxidation of methane to produce syngas. Quantitative phase analysis of the SrFeCo0.5O3-δ material has revealed that it is predominantly composed of two Sr-Fe-Co-O systems, Sr4Fe6-xCoxO13 and SrFe1−xCoxO3-δ. Here we report preliminary structural findings on the SrFe1−xCoxO3-δ (0 ≤ x ≥ 0.3) system.
Application of Eutectic Ceramic Mixtures for The Functional Components of High Temperature Sofc's
Authors: Gerk Ch. , Willert-Porada M. 
Published: April 2011

ABSTRACTA novel design for a high temperature SOFC, based on lamellar electrode-electrolyte segments obtained by solidification of an oxidic eutectic melt on an electrolyte substrate is presented. Such “composite” electrodes contain NiO or MnO - 8Y-ZrO2 lamellae, which after reduction / oxidation yield electrode-electrolyte lamellae with 1–2 μm width and a vertical dimension of> 100 μm, depending upon the amount of eutectic melt solidified on a polycrystalline substrate. The nucleation of the eutectic on a polycrystalline substrate followed by a semi-directional crystallization of the two phases yields a gradient of 3-phase boundaries over the height of such an electrode, with the number of 3-phase boundaries increasing towards the substrate.
Dynamics of the Perovskite-Based High-Temperature Proton-Conducting Oxides: Theory and Experiment
Authors: Karmonik C. , Yildirim T. , Udovic T. J. , Rush J. J. , Hempelmann R. 
Published: April 2011

ABSTRACTThe dynamics of the doped perovskite-based high-temperature protonie conductors (HTPC) were studied by means of neutron vibrational spectroscopy (NVS) and first-principles pseudopotential supercell calculations. Vibrational spectra from hydrogen-charged samples with different rare-earth dopants revealed three well-defined vibrational bands in the energy ranges 20–60, 60–90, and 100–140 meV. The two lowest-energy bands were insensitive to the dopants. First-principles phonon calculations indicate that they are mainly associated with oxygen modes. In contrast, the high-energy band was very sensitive to the dopant, and in this case, calculations indicate that it is associated with OH bending modes.
Carbon Composite for A Pem Fuel Cell Bipolar Plate
Authors: Besmann T. M. , Klett J. W. , Burchell T. D. 
Published: April 2011

ABSTRACTThe current major cost component for proton exchange membrane fuel cells is the bipolar plate. An option being explored for replacing the current, nominal machined graphite component is a molded carbon fiber material. One face and the volume of the component will be left porous, while the opposite surface and sides are hermetically sealed via chemical vapor infiltration of carbon. This paper will address initial work on the concept.
Novel Synthesis Process and Characterization of Li-Mn-O Spinels for Rechargeable Lithium Batteries
Authors: Takada Toshimi , Enoki Hirotoshi , Akiba Etsuo , Ishizu Takenori , Horiba Tatsuo 
Published: April 2011

ABSTRACTA new process has been developed for the synthesis of well-crystallized Li-Mn-O spinels with a homogeneous composition Li[LixMn2-x]O4(0.0≤x≤0.333) using the stoichiometry mixtures of lithium acetate and manganese nitrate as starting materials. The crystal structure of these compounds was studied with Rietveld refinements of the X-ray diffraction profiles. The lattice parameter of the spinels shows a strong dependence on the composition and manganese oxidation state. SEM micrographs indicate that the crystallites appear as single crystals. The size of the crystallites are in the range of 0.1 – 2μm, depending on the synthesis conditions. Samples with x≤0.125 show good electrode performance for the cell Li/Li1+xMn2-xO4in the 4V region, whereas Li4Mn5O2(x=0.333) spinels show good cyclability with a rechargeable capacity of over 100mAh/g in the 3V region.
LiMn2-xCuxO4 Spineis - 5 V Cathode Materials
Authors: Ein-Eli Yair , Howard W. F. , Lu Sharon H. , Mukerjee Sanjeev , McBreen James , Vaughey John T. , Thackeray Michael M. 
Published: April 2011

ABSTRACTA series of electroactive spinel compounds, LiMn2-xCuxO4 (0.1 ≤ x ≤ 0.5) has been studied by crystallographic, spectroscopie and electrochemical methods and by electron-microscopy. These LiMn2-xCuxO4 spinels are nearly identical in structure to cubic LiMn2O4 and successfully undergo reversible Li intercalation. The electrochemical data show slight shifts to higher voltage for the delithiation reaction that normally occurs at 4.1 V in standard Li1−xMn2O4 electrodes (1 ≥ x ≥ 0) corresponding to the oxidation of Mn3+ to Mn4+. The data also show a remarkable reversible electrochemical process at 4.9 V which is attributed to the oxidation of Cu2+ to Cu3+. The inclusion of Cu in the spinel structure enhances the electrochemical stability of these materials upon cycling. The initial capacity of LiMn2-xCuxO4 spinels decreases with increasing x from 130 mAh/g in LiMn2O4 (x=0) to 70 mAh/g in “LiMn1.5Cu0.5O4”(x=0.5). Although the powder X-ray diffraction pattern of “LiMn1.5Cu0.5 O4” shows a single-phase spinel product, neutron diffraction data show a small, but significant quantity of an impurity phase, the composition and structure of which could not be identified. X-ray absorption spectroscopy was used to gather information about the oxidation states of the manganese and copper ions. The composition of the spinel component in the LiMn1.5Cu0.5O4 was determined from X-ray diffraction and XANES data to be Li1.01Mn1.67Cu0.32O4 suggesting, to a best approximation, that the impurity in the sample was a lithium-copper-oxide phase.
Silver-Doped Vanadium Oxides as Host Materials for Lithium Intercalation
Authors: Coustier F. , Passerini S. , Hill J. , Smyrl W. H. 
Published: April 2011

ABSTRACTAn improved cathodic material has been obtained by doping vanadium oxide hydrogel with silver. Silver-doped vanadium pentoxides with a silver molar fraction ranging from 0.01 to 1 were synthesized. With the successful doping, the electronic conductivity of V2O5 was increased by 2 to 3 orders of magnitude. The electrochemical performance of the silver doped materials is very high, up to 4 moles of lithium per mole of silver-doped V2O5 were found to be reversibly intercalated. In addition, the lithium diffusion coefficient is found to be high in the silver-doped material and with a smaller dependence on the lithium intercalation level. These enhancements resulted in high rates of insertion and delivered capacities.
Electric Double- Layer Capacitor using Organic Electrolyte
Authors: Morimoto T. , Tsushima M. , Suhara M. , Hiratsuka K. , Sanada Y. , Kawasato T. 
Published: April 2011

ABSTRACTElectric double-layer capacitors based on charge storage at the interface between a high surface area activated carbon electrode and a propylene carbonate solution are widely used as maintenance-free power sources for IC memories and microcomputers. New applications for electric double-layer capacitors have been proposed in recent years. The popularity of these devices is derived from their high energy density compared with conventional capacitors and their long cycle life and high power density relative to batteries.The performance of the capacitor depends not only on the materials used in the cells but also on the construction of the cells. The performance of power capacitors for large power sources as well as materials and construction of these capacitors are described.
Modification of a Carbon Electrode Surface by Cold Plasma Treatment for Electric Double Layer Capacitors
Authors: Ishikawa Masashi , Sakamoto Atsushi , Morita Masayuki , Matsuda Yoshiharu , Ishida Koichi 
Published: April 2011

ABSTRACTActivated carbon fiber cloth (ACFC) electrodes whose surface was modified by “pulsed cold plasma”, i.e., low-temperature plasma generated by a pulsed electric power in argon-oxygen mixed gas at a reduced pressure, were applied to electric double layer (EDL) capacitors with an organic electrolyte composed of propylene carbonate and tetraethylammonium tetrafluoroborate (TEABF4). The treatment of the ACFC electrodes with the pulsed cold plasma increased total capacitance in the EDL capacitors. The observed increase in the total capacitance was ascribed mainly to an ascertained increase in capacitance of a negative ACFC electrode involving TEA+cation adsorption/desorption with the cold plasma treatment. No obvious increase in capacitance of a positive ACFC electrode involving BF4- anion adsorption/desorption was observed with the plasma treatment. The chemical and electrochemical characteristics of a treated ACFC interface were found to be favorable for TEA+cation adsorption/desorption.
First-Principles Theory of Cation and Intercalation Ordering in LixCoO2
Authors: Wolverton C. , Zunger Alex 
Published: April 2011

ABSTRACTSeveral types of cation- and vacancy-ordering exist in the LixCoO2 battery material. The ordering patterns are of interest due to the fact that they can control the voltage in rechargeable Li batteries. We present a first-principles total energy theory which can predict both cation-and vacancy-ordering patterns at both zero and finite temperatures. Also, by calculating the energetics of the Li intercalation reaction, this theory can provide first-principles predictions of battery voltages of Lix;CoO2/Li cells. Our calculations allow us to search the entire configurational space to predict the lowest-energy ground state structures, search for large voltage cathodes, explore metastable low-energy states, and extend our calculations to finite temperatures, thereby searching for order-disorder transitions and states of partial disorder.
Quantitative Icts Measurement of Interface States at Grain Boundaries in ZnO Varistors
Authors: Mukae K. , Tanaka A. 
Published: April 2011

ABSTRACTIsothermal capacitance transient spectroscopy(ICTS) measurement is applied to ZnO:Pr varistors. A simple peak corresponding to the interface states at grain boundaries was obtained and the energy level of the interface states revealed to be monoenergetic and located around 0.9eV below the conduction band. The cross section was calculated as around 10−14 cm2. Quantitative treatment of the ICTS intensity in relation to the density of interface states at grain boundaries was established. The density of interface states was obtained from the linear relation between ICTS intensity and reciprocal carrier density(ND). According to experiments on series of rare-earth doped ZnO varistors, the interface states of Pr, Tb or Nd doped ZnO varistors had higher density of states than La or Er doped varistors. Moreover, application of ICTS measurement to single grain boundary using microelectrodes revealed that higher density of interface states gave higher nonlinearity in I-V characteristics.
Current Localization, Non-Uniform Heating, and Failures of ZnO Varistors
Authors: Bartkowiak M. 
Published: April 2011

ABSTRACTNon-uniform heating of ZnO varistors by electrical pulses occurs on three different spatial scales: (1) microscopic (sub-micron), (2) intermediate (sub-millimiter), and (3) macroscopic (of order of millimeters or centimeters). Heating on these scales has different origins and different consequences for device failure in large and small varistors. On the microscopic scale, the heating localizes in strings of tiny hot spots. They occur at the grain boundaries in a conducting path where the potential is dropped across Schottky-type barriers. These observations are interpreted by applying transport theory and using computer simulations. It is shown that the heat transfer on a scale of the grain size is too fast to permit temperature differences that could cause a varistor failure. On an intermediate size scale, the heating is most intense along localized electrical paths. The high electrical conductivity of these paths has microstructural origin, i.e., it derives from the statistical fluctuations of grain sizes and grain boundary properties. Current localization on the intermediate size scale appears to be significant only in small varistors. On the macroscopic scale, current localization in large blocks can be attributed to inhomogeneities in the electrical properties which originate during ceramic processing. The resulting non-uniform heating is shown to cause destructive failures of large varistor blocks.
Current Flow and Structural Inhomogeneities in Nonlinear Materials
Authors: Greuter F. , Christen T. , Glatz-Reichenbach J. 
Published: April 2011

ABSTRACTNonlinear current flow in real 3-d composite materials is far more complex than suggested by usual brickstone models. We present experimental results on controlled seeding of structural inhomogeneities in varistor ceramics. In particular, we discuss the influence of mesoscopic imperfections on the characteristic electrical parameters. A main effect is a change in the statistical distribution of the grain size. As a consequence, the breakdown voltage drops very sensitively due to the disorder, while the shape of the I-V curve is hardly affected. We discuss also the extremely nonuniform filamentary current pattern, being illustrated by electroluminescence studies.
Characterizing the Dispersion of Constituents in Concrete by Electrical Resistivity
Authors: Chen Pu-Woei , Fu Xuli , Chung D.D.L. 
Published: April 2011

ABSTRACTCharacterization of the degree of dispersion of constituents in cement paste or mortar by DC electrical resistivity measurement was demonstrated for the constituent being much more conducting than cement (i.e., short carbon fibers) and much less conducting than cement (i.e., latex particles). The fiber dispersion is described by the ratio of the measured conductivity to the calculated value. The latex particle dispersion is described by a factor in an electrical conduction model.