bluuebunny/crossref_metadata_2025_split huggingface dataset:
The System Li3SbO4 - CuO
Authors: Castellanos R. M. A. , Trujillo T. S. , Skakle J. M. S. , West A. R. 
Published: April 2011

AbstractPhase formation in the system Li3SbO4-CuO has been studied by solid state chemistry reaction, at temperatures between 650° and 1150°C. Two new complex oxides were found and characterized by X-ray powder diffraction (XRD), Li3CuSbO5 (O) and Li3Cu2SbO6 (S). The latter exhibits a new partially ordered rock salt structure and shows a low level of electronic conductivity [1]. The crystal structure of Li3SbO4was determined [2].
Long-Range Order Effects in Ferroelectric Pb(Zr1/2Ti1/2)O3
Authors: Sághi-Szabó G. , Cohen Ronald E. 
Published: April 2011

AbstractThe local orbital extension of the Linearized Augmented Planewave (LAPW+LO) method within the local density and general gradient approximations was used to optimize internal coordinates and calculate total energies of Pb(Zri1/2Ti1/2)O3 (PZT) superlattices with B site cations ordered along the [001] and [111] directions. Ferroelectric structures and bond-length distributions similar to those obtained from experimental data were found for all three investigated chemically ordered phases. The Ti atom sits in an off-center position of a slightly distorted TiO6 octahedron, the structure of which is mostly independent of the chemical ordering pattern. Coupling between the Ti and Zr containing octahedra results in highly distorted ZrO6 units. This relatively high energy part of the structure could decrease the stability of these perovskite compounds against zone-boundary rotations of the BO6 octahedra. Polar, zone-center only distortions result in lower energy [111] ordered superstructures when compared to the [001] ordered structure. The lowest energy chemically ordered PZT is the one with B-site cations ordered along the [111] direction and has 14mm symmetry. Our total energy results and a simple statistical model predict a wide miscibility gap PZT at the morphotropic composition is therefore likely a multiphase or metastable material which may be responsible for its sensitivity to synthesis and annealing conditions.
First Principles Computer Simulation of the Defect Chemistry of Rutile TiO2
Authors: Dawson I. , Bristowe P. D. , White J. A. , Payne M. C. 
Published: April 2011

AbstractThere exists a long-standing controversy concerning the nature of the dominant point defect mechanism in rutile TiO2. Previous classical shell model calculations by Catlow el al [1] find a strong preference for Schottky as opposed to Frenkel-type defects, lending support for oxygen vacancy rather than titanium interstitial compensation in reduced rutile. However, reviews of experimental studies [2], show that many conflicting conclusions have been reached. Ab initio total-energy calculations have been performed on a parallel computer to help resolve this controversy. First results indicate a Schottky formation energy (of the bound Schottky trio) consistent with the Mott-Littleton values of Catlow et al [1]. A first attempt is made at calculating the heat of reduction through determination of the formation energy of a neutral oxygen atom vacancy. As a. result some interesting insight is gained into the redox chemistry of reduced rutile.
Hydrogen Vibration in Cubic Dihydrides MH2 (M=Ti, Zr), and Localization in Cubic Laves Phases ZrM2H1/2 (M=V, Cr, Fe, Co)
Authors: Elsässer C. , Schweizer S. , Fähnle M. 
Published: April 2011

AbstractA study of cubic dihydrides TiH2 and ZrH2 and of H in cubic Laves-phase compounds by means of ab-initio total-energy calculations in the local density-functional approximation is presented. First, for optic vibrational modes in the two dihydrides the calculated local potentials and excitation energies are compared to experimental results obtained by inelastic neutron scattering. Second, the relative stabilities of H on three types of interstitial sites in the cubic Laves-phase compounds, denoted by b, e and g, are investigated. Theoretically, a preference of g sites is found for M=V, Cr, and of e sites for M=Fe, Co. These results are discussed with respect to experimental observations and to empirical criteria for H accomodation in transition-metal compounds.
The Effects of Domain Structure on the Electro-Optic Response of Potassium Niobate Thin Films
Authors: Nystrom M. J. , Wessels B. W. 
Published: April 2011

AbstractEpitaxial potassium niobate films have been deposited by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction of the films deposited on (100) spinel substrates shows (110) and (001) reflections, indicating a multidomain structure. The electro-optic properties of the thin films were measured using a transmission technique. Effective electro-optic coefficients as large as 470 pm/V were observed. The observed electro-optic response was dominated by domain reorientation effects.
About Chemical Bonds in Misfit Layer Chalcogenides
Authors: Rouxel J. , Meerschaut A. 
Published: April 2011

AbstractOn the basis of crystal structures and electronic properties, a critical discussion of the nature of chemical bonds in misfit layered chalcogenides is given. It concerns also the various mechanisms of non-stoichiometry that are present in these incommensurate structures. Misfit chalcogenides with a LnY slab opposed to TY2ones (T = Ti, V, Cr, Nb, Ta) appear as infinite two-dimensional intercalation compounds with an electron donation from LnY to TY2. In case of PbY or SnY slabs a more complex mechanism involving coupled substitutions in both slabs seems to prevail.
Phase Equilibria and Dielectric Properties of Rare Earth Containing BaTiO3 Ceramics
Authors: Kolar D. 
Published: April 2011

AbstractAddition of rare earth oxides affects several properties of barium titanate ceramics such as dielectric constant, Curie temperature and electrical conductivity. Electrical properties depend on the composition, firing conditions and mode of incorporation of rare earth ions into perovskite or perovskite-like lattice.Incorporation of rare earth ions into the BaTiO3 lattice was studied by quantitative wavelength dispersive spectroscopy in combination with scanning electron microscopy and X-ray powder diffraction. Broad solubility regions between rare earth titanates and barium titanate were detected, influencing the properties.In present review, phase equilibria and properties of rare earth (La,Nd,Ce) containing BaTiO3 ceramics are compared with particular emphasis on preparation conditions.
Formation and Characterization of “1:1” Ordered Phases in Am4+O3- A(B2+1/3Ta2/3)O3(A= Ba, Sr; B2+= Mg, Zn; M4+= Ti, Sn, Zr, Ce) Perovskites
Authors: Chai L. , Akbas M. A. , Davies P. K. 
Published: April 2011

AbstractPrevious research has demonstrated that the formation of nano-sized “1:1” cation ordered domains in Zr4+substituted Ba(Zn1/3Ta2/3)O3may be responsible for the anomalies in the dielectric loss properties of these perovskite ceramics. To explore the structure and crystal chemistry of these phases, the effect of a series of M4+substitutions (Zr4+, Ce4+, Sn4+, and Ti4+) on the B-site cation ordering in Ba(Zn1/3Ta2/3)O3, Ba(Mg1/3Ta2/3)O3, and Sr(Mg1/3Ta2/3)O3has been examined. In all cases the substitution of low levels (∼ 5 mole %) of “over-sized” tetravalent cations (e.g. Zr4+, Ce4+) promotes a transformation to a 1:1 ordered phase, while the introduction of “under-sized” cations (e.g. Ti4+) stabilizes a disordered perovskite. Using Rietveld methods the structures of the 1:1 ordered A(βI1/2βII1/2)O3phases were found to conform to a “random layer” model in which the βIIpositions are occupied by Ta, and the βIsites by a random distribution of the Mg(Zn), M4+and residual Ta cations.
Investigation of Polarization Mechanism of Relaxor Ferroelectrics
Authors: Cheng Z. -Y. , Katiyar R. S. , Xi Yao 
Published: April 2011

AbstractAddition to thermally activated flips of polar regions in relaxor ferroelectrics, a new polarization mechanism, which originates from the vibrations (breathing) of surface of polar regions, is introduced to explain the dielectric behavior of relaxor ferroelectrics. This new mechanism plays an important role in the dielectric behavior of such materials at low temperature. Based on the above assumption and general dielectric theory, a formula is given to characterize the temperature dependence of the dielectric constant. The correctness of the formula is verified by using it to fit the experimental results of the two typical relaxors. The fitted results show that the method is of high precision and that the temperature of the dielectric constant maximum is decided by the two polarization behavior. It also indicates that the new polarization is a resonance polarization.
Non-Stoichiometry and Structure of SrCe1-xYbxO3 Perovskite-Type Oxides
Authors: Kosacki Igor , Shumsky Mark , Anderson Harlan U. 
Published: April 2011

AbstractThe structural and electrical properties of SrCe1-xYbxO3 ceramics have been studied as a function of temperature and Yb-concentration using x-ray diffraction and impedance techniques. The influence of Yb-dopants on electrical transport and structural disorder has been studied. A correlation between the structural properties, electrical conductivity is observed and discussed. These measurements allow us to determine the mechanism of charge carrier compensation and also the concentration and mobility of the electrical species.
Electrical Conductivity and Nonstoichiometry in Pr0.545Ce0.455O2-x
Authors: Porat O. , Tuller H. L. , Shelef M. , Logothetis E. M. 
Published: April 2011

AbstractThe oxygen nonstoichiometry of Pr0.545Ce0.455O2-x was studied by solid state coulometric titration and was found to be extensive (0 ≤ y ≤ 0.28) at temperatures of 400–600 °C. The Po2 - x curves showed evidence of the existence of a number of single and two phase regions. Electrical conductivity measurements, performed under similar conditions, exhibited a p-n transition for temperature of 500 °C and below. The activated p-type conductivity was modeled in terms of the small polaron hopping mechanism. The p-n transition was correlated with the onset of phase separation.
Grain boundary conductivity and microstructure study of 4% Y2O3 doped CeO2 thin films
Authors: Tian Chunyan , Chan Siu-Wai 
Published: April 2011

AbstractThe thin films of 4% Y2O3 doped CeO2 have been deposited on different substrates of Pd film/(001) LaAlO3, Pd film/r-cut sapphire, and Pd film/Quartz using an e-beam deposition technique. The microstructures and electrical properties of the films were investigated by means of x-ray diffraction, transmission electron microscopy, and ac impedance spectroscopy. Both textured and polycrystalline films were produced on different substrates. A brick layer model was adopted to correlate the micro structure and electrical property of the films. Only the grain boundary arc was observed in the film complex impedance plots. The conductivities of the films were similar to the conductivity of 6% Y2O3 doped CeO2 bulk grain boundary because of lower preexponential factor, although the activation energies were smaller than that of bulk grain boundary. The resistive gram boundaries were found to dominate the conductivities of the films.
Synthesis, Characterization, and Electrochemical Performances of Substituted Layered Transition Metal Oxides. LiM1-yM'yO2. (M=Ni and Co. M'= B and AI)
Authors: Nazri G. A. , Rougier A. , Kia K. F. 
Published: April 2011

AbstractThe synthesis, characterization and electrochemical performances of lithiated nickelate and cobaltate doped with Al and B are reported. The synthesis involves solid state reaction between lithium hydroxide, nickel or cobalt oxides and several sources of aluminum and boron. Careful selection of precursors and heat treatment conditions are required to prepare single phase impurity free samples. X-ray diffraction and Rietveld refinement analysis indicate that the layered structure is preserved upon considerable substitution of aluminum and boron. X-ray diffraction line intensities and positions remained in good agreement with the space group. The IR spectra of the samples indicate formation of compressed CoO6 and NiO6, and elongated LiO6 octahedra. The IR vibrational mode of the LiO6 remains in the 200–300 cm-1 and the vibrational modes of the MO6 expand over 400–650 cm-1. Results of long charge-discharge cycling of the samples as cathode materials in lithium cells showed long cycle life. The capacity of the electrodes upon substitution were reduced almost linearly as the concentration of substitution was increased. The solubility limit for the formation of solid solutions upon substitution of Al and B in LiNiO2 and LiCoO2 was found to be around 25%. Specific capacities of the samples were between 120 to 160 mAh/g depending on the amount of substitution.
Ordering in Lithium and Sodium Inserted W18O49
Authors: Martinez De La Cruz A. , Torres-Martinez Leticia M. , Garcia-Alvarado F. , Moran E. , Alario-Franco M. A. 
Published: April 2011

AbstractThe insertion of alkali metals in W18O49 is governed by size of the cations. In this way, lithium insertion ( rVI = 0.76 Å ) seems to be optimal and a maximum of 23.5 lithium per formula can be reached before the irreversible reduction of W18O49. On the other hand, when sodium is inserted ( rVI = 1.02 Å ) an order of magnitude decrease in the amount inserted is observed and a maximum of only 1.8 sodium per formula can be intercalated. On the basis of the different phases that we have previously detected by electrochemical methods in the Li / W18O49 and Na / W18O49 systems, we have started a structural characterization by electron diffraction techniques. These studies have revealed some lithium and sodium ordering states for certain compositions; this can be explained taking into account the different types of tunnels present in W18O49.
Kinetics of Electrochromic Effect in Amorphous Tungsten Trioxide Films
Authors: Konovalov I. A. , Nechitajlo V. B. , Shushakova E. 
Published: April 2011

AbstractReversible coloration occurs in tungsten trioxide (WO3) films when double injection of electrons and ions is provided in its volume. Experiments were performed in electrochemical cell with liquid electrolyte, where protons were used for injection in amorphous WO3 films. Kinetics of electrochromic coloration process was studied in spectral range of 300 nm to 1200 nm. Dependence of optical density on injected charge was found to be different in various spectral regions for coloring and bleaching. Infrared vibrational spectra of electro-chemically colored crystalline and amorphous WO3 were obtained. Electronic structure features of amorphous WO3 related to electorchromism are discussed.
Chemistry and Structure of Internal Interfaces in Inorganic Materials
Authors: Rühle M. , Recnik A. , Ceh M. 
Published: April 2011

AbstractPhysical properties of polycrystalline materials are controlled by intergranular as well as intragranular effects. In most cases materials' properties adhere to the bonding character of internal interfaces and plasticity of bulk parts. The nature of interfaces is in general difficult to understand, although they have far reaching consequences to overall properties of processed materials. To properly understand the effects brought by such interfaces one has to correlate particular properties with their local chemistry and structure. The availability of modern instrumentation that can provide a detailed chemical and structural information down to a subnanometer scale has helped greatly in tackling many fundamental problems in materials science. Our systematic studies of several metal/ceramic and ceramic/ceramic interfaces has given us a wealth of information that brings us closer to the answer on the formation mechanisms of the internal interfaces and other structural transformations in materials.
Synthesis of Inorganic Aromatic Hydrocarbon Polymers on Metal Surfaces
Authors: Perry Dale L. , Lewis Crystal , Pugh Mishi 
Published: April 2011

AbstractFilms of copper(II) imidazolate, an aromatic, heterocyclic hydrocarbon polymer, have been synthesized in situ at room temperature on copper surfaces. The films were made using a copper(II) salt formed as a thin film on an metallic copper substrate with subsequent complexation and deprotonation of the imidazole molecule. The in-situ formed copper(II) imidazolate polymer films have been studied by elemental analyses, scanning electron microscopy, and x-ray photoelectron and Auger spectroscopy. The copper Auger parameter has been derived for the films.
Synthesis of New Alkali-Metal-Intercalated Layered-Silicate Compounds and Their Magnetic Properties
Authors: Wada N. , Okui Hideaki , Omura Yasuyuki , Fujiwara Akihiko , Suematsu Hiroyoshi , Murakami Youichi 
Published: April 2011

AbstractSingle crystals and powders of vermiculite are dehydrated and then intercalated with alkali metals (K and Rb) using a two-temperature-zone furnace. The samples, originally transparent, exhibit metallic silver color upon intercalation. Our x-ray diffraction experiments indicate that the c-axis lattice constant becomes smaller after the intercalation process. A SQUID magnetometer is used to measure the magnetization of the samples as functions of temperature and magnetic field. Evidence for Pauli paramagnetism and enhancement of ferromagnetism are found in the Rb- and K-intercalated compounds, in addition to Curie paramagnetism due to iron impurities in the original vermiculite.
Synthesis of Carbon Spheres/Tubes Using a Mixed-Valent Oxide-Catalytic Carbonization Process
Authors: Kang Z. C. , Wang Z. L. 
Published: April 2011

ABSTRACTA mixed-valent oxide-catalytic carbonization (MVOCC) process is described for synthesizing monodispersed carbon spheres (or tubes) in macroscopic quantities at low cost. The technique uses natural gas and reusable catalysts and produces no environmental waste or pollution. The product is controlled to be either all of spheres (∼ 210 nm) or all of tubes with high purity (> 95 %). In spherical form, the product is solid and comprised of layered graphitic flakes containing paired pentagonal-heptagonal carbon-rings. In spiral tube form, the product is composed of twisted graphitic helix layers containing spherical nodes. A growth mechanism has been proposed, in which the pairing of pentagonal and heptagonal carbon-rings plays an important role. It is concluded that a change in fraction and nucleation rates of pentagonal, hexagonal and heptagonal carbon-rings results in the growth of different geometrical shapes. The success of using mixed-valence metal oxides as catalysts has opened a new field in catalysis research and applications.
Reforming with Novel Borosilicate Molecular Sieve Catalysts
Authors: Chen C. Y. , Rainis A. , Zones S.I. 
Published: April 2011

In recent years the cost of research is increasingly dear to the sponsoring organizations, whether we speak of the public or private sector. Yet to meet the demand to make advances in product-generating technologies and to do so with slimmer margins, cost savings have to be developed along the chain of process events needed for production. In addition, the public atlarge has voiced their mandate for more environmentally benign operations. One look at the program for the 5th World Congress of Chemical Engineering (San Diego, 1996) would quickly show this trend. Both of the above-mentioned concerns merge together in the world of the chemical producer, generating a call for breakthroughs in the synergy of combining advanced catalytic materials with novel engineering processes. Thus, catalysis remains a focal point for technological progress [1].Zeolites continue to be used as advanced catalytic materials, their contribution of molecular size discrimination, potential stability and high activity highlighting them as candidates for use in developing new process chemistry. Production of alkyl aromatics has seen recent trends in the replacement of existing corrosive catalyst technology by the safer solid acid zeolite catalysts [2]. The lube oil business has experienced the introduction of new Isodewaxing catalysts, capable of producing higher yields of desired product, and thereby reducing waste loss in the overall process scheme [3].
Activation of Oxidation Catalysts by Solvation
Authors: Eddowes Annette D. , Stallings Dana , Hightower Caprice L. , Jansen Susan A. 
Published: April 2011

AbstractThe versatility of heteropolyanions implies many different uses for Keggin type catalysts. However, new roles for these catalysts must first be preceeded by further understanding of the mechanisms by which they operate. It has been observed that the solvation and/or complexation of heteropolyanions promotes or limits activity in homogeneous chemistry. For this reason the solution state and the solvation characteristics of the catalyst were studied in oxidation and photochemical reactions. Simple oxidation reactions provide a system by which the solution state of the catalyst can be studied. The catalyst used for these mechanistic studies is the Keggin ion (PMo10V2O40)−5.
Automotive Applications of Sol-Gel Processed Materials: Novel, Low Power Consumption, Electrically Heatable Catalyst Devices
Authors: Nakouzi S. R. , McBride J. R. , Nietering K. E. , Visser J. H. , Adamczyk A. A. , Narula C. K. 
Published: April 2011

ABSTRACTExhaust gas heat is the primary source of warming in a conventional automotive exhaust catalyst. It typically becomes operational within minutes after the initial start-up of an engine, when it attains temperatures greater than approximately 350°C. However, around 70% of the total hydrocarbon and carbon monoxide (CO) emissions of a modern gasoline powered vehicle, under a normal driving cycle, are released during this period of cold-start. One of the strategies suggested to treat the pollutants during the first minute after initial start-up involves electrically heating the catalyst. However, devices developed for this purpose are power intensive, can require a second battery and can reduce fuel economy. The increased weight, in turn, results in increased pollution. Here we describe a low power consumption prototype which contains a conducting layer beneath the washcoat. The prototype [4 cm2] was tested at a gas flow rate of 100 seem and required less than 5 Watts to attain temperatures greater than 350°C in less than 10 seconds. The prototype was tested in a flow reactor and found to rapidly heat up to light-off temperatures where the conversion of the hydrocarbons and CO takes place. We also summarize progress made in our laboratory in the fabrication of a test device employing sol-gel processed metal oxide films.
Effective Decomposition of Nitric Oxide Using Pd/YSZ/Au Electrochemical Membrane Reactor
Authors: Kanai Y. , Ichimura H. , Kawakami H. 
Published: April 2011

ABSTRACTThe direct decomposition of NO (2NO → N2+02) has been carried out using an electrochemical membrane reactor composed of an yttria-stabilized zirconia (YSZ) disc deposited with Pd and Au metal films at reaction temperature of 773∼1023 K and applying voltage of 0∼1.8 V. N2 and O2 were continuously produced in the cathode and anode chambers, respectively. NO decomposition activity increased by applying electrical potential. It was clearly shown that the enhancement of the catalytic activity was due to electrochemical pumping, by which the surface oxygen species formed by the dissociation of NO were transported from cathode to anode through YSZ. By comparing the catalytic activity between Pd/YSZ/Au and Au/YSZ/Au systems, it is suggested that the NO decomposition occurs mainly on the Pd surface, and YSZ itself did not catalyze the reaction at lower temperature. The rate-determining step for the reaction was the adsorption of NO at 973 K, while at 773 K, the step was either a diffusion of O2- in YSZ or a migration of surface oxygen species on the Pd surface. The surface observation of Pd films by SEM showed that many microvoids were created throughout the Pd surface after the reaction. The creation of the microvoids results in an increase in the number of three-phase boundary sites, which will play an important role for the enhancement of the NO decomposition. Moreover, it was found that Pd/YSZ/Au resisted a serious degradation of the activity in the presence of O2 in the feed stream.