bluuebunny/crossref_metadata_2025_split huggingface dataset:
Highly Emissive Lanthanide Compounds in Sol-Gel Derived Materials
Authors: Lessard Ronald B. , Berglundl Kris A. , Nocera Daniel G. 
Published: March 2011

ABSTRACTMolecular composites that possess unique emission properties have been prepared by introducing luminescent molecules into sol-gel based silica glasses. The lumophores chosen for study are terbium(III) and europium(III) ions whose emissions are quenched in aqueous and sol-gel environments owing to coordination of water molecules to the lanthanide ion. To overcome the quenching process the ions have been encapsulated within cryptands. The resulting terbium(IU) and europium(III) cryptates possess long-lived excited states in both aqueous solution and solgel glassy matrices. Measurements of the excited state dynamics of these molecularly engineered composites demonstrate the feasibility of tailoring molecules to retain their excited state properties in sol-gel derived glasses.
Single Crystal Zirconia Thin Films from Liquid Precursors
Authors: Miller K. T. , Lange F. F. 
Published: March 2011

ABSTRACTEpitaxial, single-crystal films of ZrO2 (Y2O3) were formed on (100) oriented single crystal substrates of ZrO2 (9.5 mol% Y2O3) using water-based solutions of zirconium acetate and yttrium nitrate as a precursor. Film compostions of ZrO2 (0 - 40 mol% Y2O3) were examined; since the lattice parameter of ZrO2 (Y2O3) increases with yttria content, the lattice mismatch was systematically varied to a maximum of 1.5%. Precursor films were deposited by spin coating, pyrolyzed, and held for 1 hour at 900°C, 1000°C, and 1100°C. X-ray diffraction showed that a strongly oriented film had developed after pyrolysis of the precursor. In addition, all samples, except those treated at 1100°C containing 6 – 15 mol% Y2O3, gave (111) peaks, indicating film polycrystallinity. Electron back-scattering patterns showed that epitaxial single crystals were formed at 1100°C for films containing 3 – 20 mol% Y2O3. Scanning electron microscopy showed that the epitaxial films had a porous structure. These results indicate that the epitaxy is a two-stage process: oriented nucleation upon pyrolysis, followed, for low mismatches, by subsequent consolidation into a single-crystal film above 1000°C.
Plasma Spraying of Zirconia Coatings
Authors: Varacalle D. J. , Smolik G. R. , Wilson G. C. , Irons G. , Walter J. A. 
Published: March 2011

ABSTRACTAs part of an investigation of the dynamics that occur in the plume of a thermal spray torch, an experimental and analytical study of the deposition of yttria-stabilized zirconia has been accomplished. Experiments were conducted using a Taguchi fractional factorial design. Nominal spray parameters were: 900 A, 36 kW, 100 scfh argon primary gas flow, 47 scfh helium secondary gas flow, 11.5 scfh argon powder carrier gas flow, 3.5 lb/h powder feed rate, 3 in. spray distance, and an automated traverse rate of 20 in./s. The coatings were characterized for thickness, hardness, and microstructural features with optical microscopy, scanning electron microscopy, and x-ray diffraction. Attempts are made to correlate the features of the coatings with the changes in operating parameters. Numerical models of the physical processes in the torch column and plume were used to determine the temperature and flow fields. Computer simulations of particle injection (10 to 75 μm zirconia particles) are presented.
Processing and Properties of Nanophase Oxides
Authors: Eastman J. A. , Liao Y. X. , Narayanasamy A. , Siegel R. W. 
Published: March 2011

ABSTRACTNanophase oxides (Al2O3, MgO, ZnO and TiO2), with typical grain sizes in the range 2–20 nm, have been synthesized by the condensation of ultrafine particles in a convective inert gas followed by their collection and in-situ consolidation in vacuum at ambient temperature. These new materials, owing to the reduced scale of their grains along with the enhanced cleanliness of their grain boundaries, are found to have significantly improved properties relative to those of their coarser-grained, conventionally-prepared counterparts. Nanophase rutile (TiO2) with an initial mean grain diameter of 12 nm, for example, has been found to sinter at 400 to 600°C lower temperatures than conventional rutile powders, without the need for compacting or sintering aids, while retaining a small grain size. Additionally, the importance of the extremely clean surfaces obtained with the gas condensation method has been demonstrated by comparing the sintering behavior of powders with and without air exposure prior to consolidation. The research completed on the processing and properties of nanophase ceramics is reviewed, and the potential for engineering advanced ceramics using the nanophase processing method is discussed.
The Effect of Processing Parameters on the Growth Rate and Microstructure of Al2O3/Metal Matrix Composites
Authors: Nagelberg Alan S. 
Published: March 2011

ABSTRACTCeramic matrix composites can be formed by the directed oxidation of a doped molten aluminum alloy into an inert reinforcement or filler. The resultant ceramic matrix consists of interconnected Al2O3 and partially interconnected metal. The growth kinetics of this Al2O3 /metal ceramic matrix can be altered by numerous parameters. The effect of the growth atmosphere composition and temperature on the composite growth rate is dependent on the alloy dopant utilized. The ceramic matrix formation rate is also dependent on the alloy composition. Likewise, alloy composition has a profound effect on the mechanical properties and microstructure of the composites produced.
Photolithography: a New Tool for Ceramic Science
Authors: Rödel Jürgen , Glaeser Andreas M. 
Published: March 2011

ABSTRACTA recently developed technique combining photolithography, ion beam milling, and hot pressing allows the production of submicron-scale controlled-geometry, controlled-crystallography pore structures in controlled misorientation bicrystals, single crystal-polycrystal ensembles, and polycrystal-polycrystal ensembles. Such microdesigned interfacial structures provide a new tool for studying fundamental aspects of microstructural evolution. Current applications of the technique, opportunities for future research, and future extensions and refinements of the technique are described.
Packing and Structure in Systems Containing Rod-Like Particles
Authors: Chick Larry A. , Viney Christopher , Aksay Ilhan A. 
Published: March 2011

ABSTRACTA non-discrete Monte Carlo algorithm is used to model the packing of static rods. The results establish that inter-rod contact results solely from rod motion, not from space-filling effects. As the concentration of static rods is increased, clusters of aligned rods form and grow. The effects of rod motion are inferred through thermodynamic analysis. At sufficiently high rod concentrations, rod motion is expected to cause structural coarsening wherein the rods rearrange into larger but fewer clusters. These results should be considered when modeling the structure and mechanical behavior of whisker- and chopped-fiber-reinforced composites.
Dispersion and Consolidation of the Colloidal Suspension in the Al2O3Powder – Si3N4Whisker System
Authors: Hirata Yoshihiro , Matsushita Shinichi , Nakagan Susumu , Haraguchi Ichiro , Hanada Noriaki , Ishihara Yoshimi , Hori Saburo 
Published: March 2011

ABSTRACTWhisker-reinforced ceramics have high potential for structural materials application due to their high fracture toughness and high mechanical strength. In this paper, rheological property and consolidation of the colloidal suspension in the alumina powder-silicon nitride whisker system were studied to control the microstructure and density of the green and hot-pressed composite. A12O3particles of average diameter 0.15 μm and Si3N4whisker of average size 0.4 μm × 3.7 μm were electrostatically dispersed in water in pH range 1–11 and consolidated by filtration. A welldispersed state of the composite suspension was achieved at low pH. Decreasing the viscosity while increasing the solid content of the suspension at the same time is the key step in making green compact with higher density and a narrower pore size distribution. These compacts were densified to relative density 98.4–99.4% by hot-pressing at 1500°C at a pressure of 39 MPa in N2atmosphere.
Some Chemical and Structural Aspects of the Bi, Pb-Sr-Ca-Cu-O System
Authors: Takano Mikio 
Published: March 2011

ABSTRACTPhases and their relations in the Bi, Pb–Sr–Ca–Cu–O system have been studied to afford a sound material scientific base. Of particular interest is the chemically most representative system, Bi–Sr–Cu–O, in which a series of solid solutions expressed as Bi2+xSr2−xCu1+yOz are formed. The superconductor (Tc≃10K) corresponds to an extremely narrow range of 0.1<x<0.13. From the composition dependence of the one-dimensional modulation mode a new important factor controlling the modulation mode has been deduced. Substitution of Pb for Bi in the high-Tc phase has been found to induce a stepwise change of the modulation mode, thus suggesting an ordering of Pb in the BiO layer. [CuO2]∞ planes exist both in the holeand electron-carrier superconductors, but their role in the former type of superconductors has not been known. As one possible contribution to attacking this problem, ACuO2 (A: Ba1/3Sr2/3˜Sr˜Ca2/3Sr1/3 ) crystallizing in /A/CuO2/A/CuO2/A/ structure have been prepared using high pressures of 60kb.
Superconducting Properties of Substituted Oxides Bi2Sr2−xLaxCuO6+y and Bi2Sr2Ca1−xYxCu2O8+y Neutron Diffraction of Bi2Sr1.6La0.4CuO6+y and Bi2CaLaCuO6+y
Authors: Darriet J. , Alonso J. A. , Burlet P. , Chevalier B. , Lepine B. , Rossat-Mignod J. , Soethout C. J. P. , Soubeyroux J. L. , Etourneau J. 
Published: March 2011

ABSTRACTThe substituted oxides Bi2Sr2−xLaxCuO6+y and Bi2Sr2Ca1−xYxCu2O8+y isostructural to the n = 1 and n = 2 members of the high Tc superconductors have been prepared. The solid solution Bi2Sr2−xLaxCuO6+y shows a superconducting transition for 0.2–0.25<x<0.5 with an onset Tc near 30K and zero resistance temperatures which depend on x and the heat treatment. For x = 1 the isostructural phases Bi2ALaCuO6.5+y with A = Ca or Ba have also been synthesized and are not superconducting. A modelfor the localization of the oxygen atoms is proposed based on neutron diffraction of Bi2Sr1.6La0.4CuO6+y and Bi2CaLaCuO6+y.The Bi2Sr2Ca1−xYxCu2O8+y solid solution exhibits a superconducting transition for 0<x <0.7. The critical temperature remains almost constant (85–90K) for 0<x <0.3 and then decreases rapidly. The oxygen content value 8.65 for Bi2Sr2YCu2O8+y agrees well with the increase of the positive charge when calcium is replaced by yttrium.
Phase Chemistry and Compositional Variability During Processing in the Bi-Pb-Ca-Sr-Cu-O System
Authors: Schwartz Kenneth B. , Thompson Mark , Leong Derek , McConville Richard 
Published: March 2011

ABSTRACTThe formation of superconducting materials in the Bi-Pb-Ca- Sr-Cu-O system was studied to determine the processing parameters and mechanisms responsible for the achievement of superconductivity above 100 K. Non-stoichiometry in the 3-layer superconducting phase (Tc≃100 K) is apparently necessary for formation and appears to be manifested by large vacancy concentrations on the non-Cu-layers of the structure.
Variation of Superlattice Structure of the Bi2Sr2−xCuO6-y Superconductor with Composition and Thermal History
Authors: Chakoumakos B. C. , Budai J. D. , Sales B. C. , Sonder Edward 
Published: March 2011

ABSTRACTSingle crystals of Bi2Sr2−xCuO6−y, (0.1 < x < 0.5, 0 < y < 0.5), were examined using x-ray diffraction techniques. Ditfractometer scans of θ-2θ taken normal to the cleavage planes displayed the even () reflections from = 2 to 26. Weak satellite peaks were observed on either side of each main () reflection, and their intensities relative to the main peak increased as 2θ was increased. With decreasing Sr content, the satellite peaks systematically moved away from the position of the main reflection. In contrast, the positions of the satellite peaks did not change with oxygen content which was varied by up to 0.5 oxygen atoms per formula unit. Since Tc in these crystals is sensitive to oxygen content while the superstructure modulation is not, it is unlikely that superconductivity and the structure modulation are directly related. As shown by a more detailed study of these peaks using a four-circle diffractometer and x-ray precession methods, the satellites that appear in θ-2θ scans are actually the mosaic tails of relatively intense superstructure peaks, positioned off from c* in the b* direction of reciprocal space. Depending on the Sr content of the crystals, generally incommensurate modulations were found with the superstructure periodicity ranging between ˜1/5b* + 0.29c* and ˜1/5b* + 0.65c*. The modulation in Bi2Sr2−xCuO6−y has two components. The component along the b* direction is similar to the superstructure observed in Bi2Sr2CaCu2O7 crystals and thus is probably due to the mismatch between the Bi2O2 layer and the CuO2 layer. The additional component along c* may be due to the ordering of Sr vacancies.
Electron-Doped Superconductivity in CuO2 Layered Compounds with Nd2CuO4− structure
Authors: Takagi H. , Ito T. , Matsubara H. , Watabe H. , Ido T. , Tokura Y. , Uchida S. 
Published: March 2011

ABSTRACTWe have discovered 24 K-superconductivity in a family of compounds Ln2−xCexCuO4−y (Ln=Pr, Nd, Sm). Novel feature of the superconductivity in these family of compounds is that superconductivity is produced by electron-doping in sharp contrast with high-Tc cuprates discovered so far. The effect of doping on physical properties particularly the elecronic phase diagram and transport coefficients which indicate symmetry in many respects between electron- and hole- doping is described.
Antiferromagnetism and onset of Superconductivity in Lanthanum Nickelates
Authors: Spałek J. , Kakol Z. , Honig J. M. 
Published: March 2011

ABSTRACTMagnetic moment and resistivity measurements are summarized for the La2−xSrxNiO4system. They show that the system undergoes a structural phase separation below 70 K. The majority of the sample is antiferromagnetic (AF) below 650 K (for x = 0) or 20 K (for x = 0) or 20 K (for x ≃ 0.2 while the minority phase (≤1% at 4.2 K) is superconducting (SC). An analysis of the results leads to the conclusion that SC and AF coexist in the minority part of the sample; the pairing takes place between 2p holes which propagate through a lattice containing localized 3d moments which, in the ground state, are ordered antiferromagnetically.
Interface Velocity and Noble Metal Segregation During Ion Beam Induced Epitaxial Crystallization
Authors: Custer J. S. , Thompson Michael O. , Jacobson D. C. , Poate J. M. 
Published: March 2011

ABSTRACTThe interface velocity of Au and Ag doped amorphous Si during ion beam induced epitaxy was measured using in situ time resolved reflectivity. Interfacial segregation coefficients were determined as a function of composition from numerical simulations. At 320°C Au impurities enhanced the velocity by up to a factor of 2.5 compared to the intrinsic case. Silver slightly retarded re-growth by 10 %. These effects are qualitatively similar to the case of thermal solid phase epitaxy. Using the measured impurity profiles and interface velocity, computer simulations relate the segregation coefficient to the concentrations of the impurity at the interface. In both cases, the segregation coefficient increases with increasing interfacial impurity concentration.
Corrosion Resistivity of Cermet Coating Made by Ion Beam Treatment
Authors: Wei Tian , Weiping Cai 
Published: March 2011

ABSTRACTA cermet coating was obtained on a silicon-deposited pure iron surface by means of a single treatment integrating ion implantation and ion beam mixing. As conpared with either simple ion implantation or simple ion beam mixing,the integrated treatment provides the cermet coating with an electrochemical performance far better than the simple treatments.
Molecular Dynamics Simulations of Low-Energy Ion/Surface Interactions During Vapor Phase Crystal Growth: 10 eV Si Incident on Si(001)2×1
Authors: Kitabatake M. , Fons P. , Greene J. E. 
Published: March 2011

ABSTRACTMolecular dynamics simulations, utilizing the Tersoff many-body potential, were used to investigate the effects of 10 eV Si atom bombardment of a (001)2×1 terminated Si lattice. The irradiation events were initiated at an array of points in the primitive surface unit cell. Each event was followed to determine kinetic energy redistribution in the lattice as a function of time, projectile and lattice atom trajectories, and the nature, number, and depth of residual defects. Dimer breaking, epitaxial growth, position exchange, and the formation of residual hexagonal and split interstitials were observed. There were no residual vacancies. Impact points leading to each of the above results clustered in distinctly different regions of the surface unit cell. Bulk interstitials were annealed out over time scales corresponding to monolayer deposition during Si MBE.
Molecular-Dynamics Study of the Amorphizatton of CuTi
Authors: Sabochick Michael J. , Lam Nghi Q. 
Published: March 2011

ABSTRACTRadiation-induced amorphization of the crystalline compound CuTi was investigated by molecular-dynamics simulations using new interatomic potentials derived from the embedded-atom method. Two different approaches to amorphization were tried: one in which Cu and Ti atoms were randomly exchanged, and another in which Frenkel pairs were introduced at random. The potential energy, volume expansion and pair-correlation function were calculated as functions of chemical disorder and atomic displacements. The results indicate that, although both chemical disordering and point-defect introduction increase the system energy and volume, the presence of Frenkel pairs is essential to trigger the crystalline-to-amorphous transition.
Low Energy Ion Bombardment and Microstructural Evolution in Thin Films
Authors: Yang Chih M. , Atwater Harry A. 
Published: March 2011

ABSTRACTA new approach to modeling the evolution of islands in thin films by growth and coarsening during ion bombardment is described. Solution of a continuity equation and matter conservation relation, coupled with interface-limited and diffusion-limited rate laws for island growth and coarsening allows the kinetics of island evolution to be modeled. Results from the model indicate distinct kinetic paths for island evolution during ion bombardment as a result of growth, enhanced diffusion, island dissociation and monomer sputtering.
Evaluation of Compositional Change in Masklessly Deposited Lines by Micro-Rbs Analysis
Authors: Kinomura A. , Takai M. , Lu Y. F. , Namba S. , Satou M. , Chayahara A. 
Published: March 2011

ABSTRACTCompositional deviation from the standard stoichiometry of tin-oxide and silicon-oxide lines masklessly deposited by laser-induced thermochemical reaction was investigated by micro Rutherford backscattering (RBS). Micro-RBS spectra of the lines deposited with various laser powers indicated that the stoichiometry of the deposited lines for both tin-oxide and silicon-oxide was improved by the increase in laser power. A tomographic image of the tin-oxide line showed a compositional inhomogeneity across the line.
In-Situ Ion Beam Measurements of Deuterium Loading in Thin Foil Electrochemical Cells
Authors: Knapp J.A. , Guilinger T.R. , Kelly M.J. , Walsh D. , Doyle B.L. 
Published: March 2011

ABSTRACTA key element of recent assertions of "cold fusion" has been the claim that electrochemical loading of deuterium into Pd electrodes can produce D:Pd levels exceeding 1:1. Using external beam nuclear reaction analysis of Pd foil electrodes in operating electrochemical cells, we have directly monitored deuterium content in-situ. No conditions were found which resulted in loadings higher than ∼0.9.
Time-Resolved Measurements of Solidification and Undercooling in Metals and Alloys
Authors: Atwater Harry A. , West Jeffrey A. , Smith Patrick M. , Aziz M.J. , Tsao J.Y. , Peercy P.S. , Thompson Michael O. 
Published: March 2011

ABSTRACTWe have performed nanosecond-resolution measurements of the lateral electrical resistivity of thin metal films on insulating substrates. Comparison of transient resistivity measurements with optical reflectivity measurements and heat-flow calculations permits the determination of the position and velocity of a planar crystal/melt interface, and an estimate of undercooling during pulsed laser melting of metals. We report detailed results for rapid solidification of Ni, including the observation of hypercooling of .liquid Ni.
Laser Mixing of Titanium on Silicon Carbide
Authors: Jervis T. R. , Hirvonen J-P. , Nastasi M. , Cohen M. R. 
Published: March 2011

ABSTRACTWe have used excimer laser surface processing to melt and mix single Ti layers into the surface of polycrystalline SiC substrates. The mixing of Ti into the surface is very rapid and efficient. Examination of Rutherford backscattering (RBS) data for different mixing conditions shows the formation of a preferred composition at the Ti-substrate interface which propagates from the interface with further mixing. Reconstruction of the RBS spectrum indicates that the composition of the layer is Ti45C37Si18. X-ray diffraction demonstrates the formation of Ti suicides and carbides in the surface region. Profiling of C in both mixed and uncoated samples by 6 MeV He+ scattering demonstrates that laser processing of the SiC does not cause major changes in the stoichiometry of the substrate material.
Microstructural Characterization of Texture in Tungsten Films made by Ion-Assisted Evaporation
Authors: Rajan K. , Roy R. A. , Petkie R. , Ramanathan K. V. 
Published: March 2011

ABSTRACTThe microstructure of tungsten films deposited by ion-assisted evaporation (IAE) has been examined by transmission electron microscopy. It is proposed that grain shape is strongly associated with stress and texture changes in IAE films. Evidence is also found of stress induced damage in the substrate due to stress transfer from the deposited tungsten films.
Migration of Carbon in Tempered Martensitic Steel During Excimer Laser Melting
Authors: Hirvonen J-P. , Jervis T. R. , Zocco T. G. 
Published: March 2011

ABSTRACTThe migration of ion implanted 13C in tempered martensitic steel (nominal composition 1.05 wt. % C, 0.2 wt. % Si, and 0.3 wt. % Mn) during excimer laser melting was examined utilizing the resonance of the l3C(p,γ)14N reaction at Ep = 1747.6 keV. Depth concentration profiles after five and ten laser pulses of 1 J/cm2 revealed a deviation from random walk diffusion in a homogeneous media. This was modelled by using partitionless solidification and solubility controlled flow of carbon in the iron-carbon melt. A diffusion length of nm during the period to τ the melted phase was deduced. Ion implanted surfaces were initially crystalline but significant crystalline to amorphous transformation occurred following laser treatment.
Laser Pulse Triggering of the Explosive Crystallization in Amorphous Si and Ge Thin Films
Authors: Marine W. , Marfaing J. 
Published: March 2011

ABSTRACTThe structure and morphologies of the thin amorphous a-Si and oc-Ge films crystallized “in situ” in an electronic microscope by pulsed YAG laser have been studied using conventional and high-resolution transmission electronic microscopy observations. It is found that the laser induced nucleation rate (I) is laser pulse length dependent. I is about 1021-1022 cm−3 s−1 (α-Si) and 1023-1025 cm−3 s−1 (α-Ge) near the melting point. Explosive dendritic formation is the result of competition between solid state light induced nucleation and melting mediated explosive growth.