bluuebunny/crossref_metadata_2025_split huggingface dataset:
Titanium Carbide from Carboxylic Acid Modified Alkoxides
Authors: Gallo Tom , Greco Carl , Peterson Claude , Cambria Frank , Burk Johst 
Published: March 2011

ABSTRACTTransition metal carbide precursors have been made in the past by the reaction of alkoxides with polymeric materials to form gels and resins. A new route to transition metal carbide precursors has been developed using alkoxides polymerized with dicarboxylic acids. (Dicarboxylic acid precursors have the advantage of precipitating as powders that can be removed from solvents by filtration and that are not very air sensitive.) Precursors were pyrolyzed under inert or reducing conditions to form metal carbides.The choice of ligand(s) determined the carbon content after pyrolysis. Unsaturated ligands tended to increase carbon content. Materials from oils to fine powders were produced by varying the stereochemistry of the ligands. The morphology of the pyrolyzed product mimicked that of the precipitated powder. Pyrolysis was typically carried out under Ar/H2 at 1200–1600°C. X-ray diffraction (XRD) was used to follow the incorporation of carbon into the lattice.
Reaction of Barium bis(β-Diketonate) Complexes with the Surface of Magnesium Oxide
Authors: Gardiner R. A. , Kirlin P. S. , Hussein G. A. M. , Gates B. C. 
Published: March 2011

ABSTRACTSecond generation barium MOCVD precursors have been investigated for the growth of high quality superconducting and ferroelectric thin films. Novel barium β-diketonate polyether adducts have been synthesized and characterized by X-ray crystallography, 1H and 13c nmr spectroscopies, elemental analysis, melting and sublimation points. Metalorganic chemical vapor deposition experiments have been performed using this new class of barium β-diketonate polyether adducts. The as-deposited barium films were characterized by scanning electron microscopy and energy dispersive x-ray spectroscopy. These results were correlated with reaction intermediates observed by FT-IR in temperature programmed oxidation of barium bis(2,2,6,6-tetramethyl-3,5-heptanedionate) on magnesium oxide. Conditions under which the barium source reagents proceed to BaO, BaCo3 or BaF2 were elucidated.
Silver Clusters Stabilized by Fe(Co)4 Ligands
Authors: Albano Vincenzo G. , Azzaroni Fabrizio , Iapalucci Maria Carmela , Longoni Giuliano , Monari Magda , Mulley Suzanne 
Published: March 2011

ABSTRACTThe reaction of [Fe(CO)4]2− with Ag+ in tetrahydrofuran or acetonitrile solution affords a series of silver clusters stabilized by Fe(CO)4 pseudo-ligands, formally arising from oligomerization of [AgFe(CO)4]− and their subsequent condensation with Ag+/O/−. The [Ag4Fe4(CO)16]4−, [Ag5Fe4(CO)16]3−, and [Ag13Fe8(CO)32]4− anions have been structurally characterized by X ray studies, while the formulation of all the remaining species is presently based on analytical and spectroscopic characterization, as well as their chemical behavior. Attempts to isolate the [Ag6Fe4(CO)16]2− salts in a crystalline state were unsuccessful due to their ready oligomerization to completely insoluble material of [(Ag+)n{[Ag6Fe4(CO)16]2−}n+1](n+2)− composition. This material is depolymerized by dimethylsulfoxide or by addition of stoichiometric amounts of amines and, upon dissolution, gives the [Ag6Fe4(CO)16]2− dianion.
Preparation of Monodisperse CdS Clusters and Photoconductivity of CdS-Doped Polymers
Authors: Wang Y. , Herron N. , Harmer M. , Suna A. 
Published: March 2011

ABSTRACTWe discuss the preparation of monodisperse ˜10-Å and ˜13-Å CdS clusters by the cluster fusion technique and the development of capillary zone electrophoresis for cluster separation. We also report the observation of photoconductivity in a polymer film doped with CdS nanoclusters.
Preparation of Quantum-Sized Semiconductor Sulfide-Doped Gels
Authors: Gacoin T. , Boilot J.P. , Chaput F. , Lecomte A. 
Published: March 2011

ABSTRACTUltrasmall semiconductor particles (CdS, ZnS and PbS) are produced either by direct precipitation, γ-radiolysis or in mimetic membranes. A pure cluster powder is then prepared from a chemical capping reaction. The capping of the cluster surface by thiolate complexes permits the separation of aggregates without fusion. These capped clusters can be dispersed in different solvents such as sol-gel precursors allowing to prepare dense and optically transparent xerogels with semiconductor clusters grafted on oxide polymers. The nanocrystallites are characterized by X-ray diffraction, small-angle X-ray scattering and optical spectroscopy.
Optical Properties of Size-Selected Silicon Clusters: 8 – 12 Å Silicon Clusters Are Amazingly Bulk-Like
Authors: Rinnen K.-D. , Mandich M. L. 
Published: March 2011

ABSTRACTAbsorption spectra from 0.94 – 5.58 eV are obtained for gas phase neutral silicon clusters Si18 – Si41 using resonant one- and two-color photodissociation spectroscopy. The spectra of all clusters are essentially identical and exhibit six sharp features above 3.0 eV. Comparisons of the silicon cluster spectra to those of various forms of silicon show that they have much in common with the spectrum of bulk diamond lattice crystalline silicon.
Solution Synthesis and Photoluminescence Studies of Small Crystallites of Cadmium Telluride
Authors: Jarvis Robert F. , Müllenborn Matthias , Yacobi Ben G. , Haegel Nancy M. , Kaner Richard B. 
Published: March 2011

ABSTRACTSmall crystallites of CdTe have been produced using a new solution synthetic method. In this technique, Cdl2 and Na2Te are each dissolved separately in methanol before rapid mixing. The product of this reaction is pure, stoichiometric CdTe with interesting electronic and optical properties. Photoluminescence studies of this material show a blue shift due to the quantum confinement, indicating the presence of small crystallites. Transmission electron microscopy confirms the presence of nanocrystals. Reaction temperature and processing conditions can be varied to change the crystallite sizes produced. This synthesis can also produce nanocrystalline HgTe.
Multinuclear Solid-State Nmr Study of a Sodalite Semiconductor Supralattice
Authors: Jelinek R. , Chmelka B. F. , Stein A. , Ozin G. A. 
Published: March 2011

ABSTRACT23Na double rotation NMR (DOR) and 81Br magic angle spinning (MAS) are used to investigate the synthesis and assembly of sodium, silver-bromide clusters encapsulated in the porous framework of sodalite. The NMR spectra provide site-specific information on the nano-environments of the charge balancing, extraframework Na+ cations, and the encapsulated Br− anions. The results indicate the possibility of a percolation threshold beyond certain Na+ and Br− loadings.
Nanocrystalline Binary, Ternary and Dilute Magnetic Semiconductors from Polychalcogenide Complexes
Authors: Kim Kang-Woo , Cowen J. A. , Dhingra Sandeep , Kanatzidis Mercouri G. 
Published: March 2011

ABSTRACTThe molecular polychalcogenide complexes [M(Se4)2]2−, (M=Mn, Zn, Cd, Hg), [Sn(Se4)3]2−, and [Cu4Se12]2− can be converted to the corresponding binary semiconducting solids. DMF and DMSO solutions of these complexes react with Se-abstracting reagents such as CN− and (n-Bu)3P to yield the corresponding binary solids at 155 °C or less. Appropriate stoichiometric mixtures of [Cu4Se12]2− and [In3Se15]3− react to give CulnSe2. Appropriate stoichiometric mixtures of [Cd(Se4)2]2− and [Mn(Se4)2]2− give solid solutions Cd1−xMnxSe where O<x<l. The Cd1−xMnxSe solid solutions were characterized by variable temperature magnetic measurements. Depending on the reaction conditions, metal precursor complex and Se-abstracting reagent used, the semiconductor particle size ranges from the quantum-size to the bulk regime. This method of synthesis produces the little known γ-MnSe in pure form.
Determination of Structure, Shape and Sizes of Clusters Using Radial Distribution Functions (RDF) Method
Authors: Kolosov Pavel E. , Bubnov A. V. 
Published: March 2011

ABSTRACTThe theoretical reduced intensity of X-ray scattering i(S) may be calculated for a cluster of any structure using Debye's formula. The comparison of both experimental determination and model calculation of the RDF or i(S) allows, to make a conclusions about structure of materials in a wide region of interatomic distances. This is a very important for direct structure characterization of giant clusters, dispersed molybdenum sulfides etc.. The simple formula for the upper limit of interatomic distances when the data are collected at equidistant step on S – scatterinrg vector, may be used for the optimal experimental conditions selection.
Workability of A Dual Phase Titanium Aluminide-TiB2 XdTM Composite
Authors: Zhao D. , Anand K. G. , Valencia J. J. , Wolff S. J. 
Published: March 2011

ABSTRACTHigh temperature compression tests have been performed on a Ti-44a/o Al-3a/o V-7.5v/o TiB2XD composite over the temperature range 1000 to 1300°C and the strain rate range 10-3 to 10s-1. The workability of this material for metalforming processes was determined using both dynamic material modeling and workability testing approaches to cover both internal and surface cracking. At higher temperatures and strain rates internal fracture occurred in the material, while at lower temperatures and higher strain rates surface cracks occurred. Use of lower temperatures and strain rates inhibited internal instabilities and surface cracking in the composite. A finite element model (FEM) was developed to describe the stress and strain states during the deformation process. Mechanical flow behavior obtained from the compression tests was used as input to the model. A fracture criterion developed from Kuhn's surface crack equation was coupled with the FEM model to predict bulk formability in a forging process.
Influence of Interfacial Characteristics on the Mechanical Properties of Continuous Fiber Reinforced Nial Composites
Authors: Bowman Randy R. 
Published: March 2011

ABSTRACTAs part of a study to assess NiAl-based composites as potential high-temperature structural materials, the mechanical properties of polycrystalline NiAl reinforced with 30 vol.% continuous single crystal Al2O3 fibers were investigated. Composites were fabricated with either a strong or weak bond between the NiAl matrix and Al2O3 fibers. The effect of interfacial bond strength on bending and tensile properties, thermal cycling response, and cyclic oxidation resistance was examined. Weakly-bonded fibers increased room-temperature toughness of the composite over that of the matrix material but provided no strengthening at high temperatures. With effective load transfer, either by the presence of a strong interfacial bond or by remotely applied clamping loads, Al2O3 fibers increased the high-temperature strength of NiAl but reduced the strain to failure of the composite compared to the monolithic material. Thermal cycling of the weakly-bonded material had no adverse effect on the mechanical properties of the composite. Conversely, because of the thermal expansion mismatch between the matrix and fibers, the presence of a strong interfacial bond generated residual stresses in the composite that lead to matrix cracking. Although undesirable under thermal cycling conditions, a strong interfacial bond was a requirement for achieving good cyclic oxidation resistance in the composite. In addition to the interfacial characterization, compression creep and room temperature fatigue tests were conducted on weakly-bonded NiAl/Al2O3 composites to further evaluate the potential of this system. These results demonstrated that the use of A12O3 fibers was successful in improving both creep and fatigue resistance.
Fracture Mechanisms in NiAlCr Eutectic Composites
Authors: Chang Keh-Minn 
Published: March 2011

ABSTRACTSelected eutectic compositions in Ni-Al-Cr ternary systems were processed by directional solidification (DS) with various growth rates. Fracture toughness tests were performed at room temperature and 400 °C; fracture surfaces of broken specimens were examined using SEM to investigate fracture behavior of each alloy. The alignment of eutectic phases was found to play an important role in composite toughening for the intermetallic matrix. Binary eutectic composites consisting of bcc α-Cr and B2 β-NiAl phases with a directional, well-aligned structure showed improved fracture properties over NiAl single crystals. Ternary eutectics, which contain an fcc γ-Ni phase, offered an excellent fracture resistance at room temperature.
On the Mechanisms of Ductility Enhancement in β+γ′- Ni70Al30 and β+(γ+γ)-Ni50Fe30Al20In Situ Composites
Authors: Misra A. , Noebe R. D. , Gibala R. 
Published: March 2011

ABSTRACTDuctile phase reinforcement is an attractive approach for improving room temperature ductility and toughness of intermetallics. Two alloys of nominal composition (at.%) Ni70Al30 and Ni50Fe30Al20 were directionally solidified to produce quasi-lamellar microstructures. Both alloys exhibit ∼10% tensile ductility at 300 K when the ductile phase is continuous, while the Ni70Al30 alloy has a tensile ductility of ∼4% when the γ′ phase is discontinuous. Observations of slip traces and dislocation substructures indicate that a substantial portion of the ductility enhancement is a result of slip transfer from the ductile phase to the brittle matrix. The details of slip transfer in the two model materials and the effect of the volume fraction and morphology of the ductile phase on the ductility enhancement in the composite are discussed.
Creep Behavior of SiC-Reinforced XDTM MoSi2 Composite
Authors: Suzuki M. , Nutt S. R. , Aikin M. 
Published: March 2011

ABSTRACTThe compressive creep behavior of MoSi2 reinforced with 30v/o SiC fabricated by in situ XDTM process was investigated at 1050°C–1300°C in anaerobic and aerobic test ambients. Creep experiments performed with the composite in dry nitrogen and in air showed power-law type constitutive behavior and a stress exponent of ∼3.5. Creep deformation occurred by dislocation glide accompanied by cavitation, and the apparent activation energy for creep at 1100°C–1300°C was bi-vaiued with a threshold temperature of ∼1170°C. Microstrucural observations by TEM indicated that the rate-controlling process changed from dislocation glide to dislocation climb at higher temperature, corresponding to the change in activation energy. Creep damage occurred by cavitation at SiC-matrix interfaces and at grain boundaries within polycrystalline SiC particles. This process was apparently facilitated by the accumulation of glassy phase at these sites during creep. Creep experiments in air showed there was no appreciable atmospheric effect on the response of the composite, while an increased strain rate was observed in the base alloy due to an increase in glass phase resulting from thermal oxidation.
In Situ Synthesis of A MoSi2/SiC Composite Using Solid State Displacement Reactions
Authors: Henager C. H. , Brimhall J. L. , Vetrano J. S. , Hirth J. P. 
Published: March 2011

ABSTRACTA high-strengthin situcomposite of MoSi2/SiC was synthesized using a solid state displacement reaction between Mo2C and Si by blending Mo2C and Si powders and vacuum hotpressing the powders at 1350°C for 2 h followed by 1 h at 1700°C. The resulting microstructure consisted of 1-μm diameter β-SiC particles (30 vol%) uniformly dispersed in a fine grained MoSi2matrix. Transmission electron microscopy was used to study the fine-scale morphology and phase distribution of the composite. Evidence for a small amount of grain boundary glass phase was observed using diffuse dark field imaging. The β-SiC particles were distributed mainly on grain boundaries and triple points within the MoSi2matrix. These findings were used to rationalize the observed mechanical property behavior.
The Synthesis and Evaluation of Nb3Al-Nb Laminated Composites
Authors: rowe R. G. , Skelly D. W. 
Published: March 2011

ABSTRACTMicrolanminates of Nb3Al and Nb were synthesized in-situ by high rate magnetron sputtering. Three composites were fabricated. They had thicknesses ranging from 19 to 146 μm (5.5 mils) with 11 to 91 layers. The volume fraction of the Nb lamellae was approximately 0.4 for two and 0.5 for the third. Room temperature fracture of the composites revealed that some cleavage cracking in the Nb3Al intermetallic layers was arrested by the ductile Nb layer. The Nb layers failed by chisel point fracture and shear.
Microstructures and Properties of Refractory Metal-Silicide Eutectics
Authors: Bewlay B. P. , Chang K-M. , Sutliff J. A. , Jackson M. R. 
Published: March 2011

ABSTRACTNew materials with improved high temperature properties are required for higher efficiency gas turbines. One group of alloys which show promise in this area are the eutectic systems Cr-Cr3Si, Nb-Nb3Si, and V-V3Si. Crystals of these refractory metalsilicide eutectics were directionally solidified using Czochralski crystal growth in conjunction with cold crucible levitation melting. The crystals were examined using scanning electron microscopy and transmission electron microscopy. In the present paper, these systems are examined with respect to the directionally solidified eutectic microstructures, phase equilibria, crystallography and mechanical properties.
Scanning Tunneling Microscopy and Spectroscopy of Y-Ba-Cu-O Thin Films Produced by Ion Beam Sputter-Deposition
Authors: Chapman R. C. , Aucffillo O. , LichtenWalner D. J. , Adu R. P. , SobleII C. N. , Christensen K. N. , Woolcott R. R. , Chen L. M. , Barr T. R. , Kingon A. I. 
Published: March 2011

ABSTRACTIon beam sputter-deposition has been used to produce high temperature superconducting (HTSC) thin films with controlled orientation. Room temperature scanning tunneling microscopy (STM) studies of ion beam sputter-deposited Y-Ba-Cu-O thin films indicate that the growth mode depends on whether the films are a- or c-axis oriented. The c-axis oriented films appear to grow by a screw dislocation mechanism, producing layered spirals similar to those observed in films grown by plasma sputtering and laser ablation-deposition. STM images of the a-axis oriented films show a growth mode which appears to produce layered structures perpendicular to the substrate with no spirals. Scanning tunneling spectroscopy (STS) studies of the a- and c-axis oriented films tend to reflect the anisotropy of the Y-Ba-Cu-O structure. Both the c-axis and the a-axis oriented films have semiconducting characteristics, possibly due to a native oxide, with a band gap estimated to be 1.4 eV. The c-axis oriented film, however, exhibits more fine structure in its density of states. This apparent anisotropie band structure reflects the anisotropie Y-Ba-Cu-O microstructure and superconducting characteristics. Investigations with x-ray photcelectron spectroscopy (XPS) establish a substantial chemical difference between the two surfaces inferring more substantial native oxides and air-induced by-products on the a-axis oriented film.
Defects Near the Y2BaCuO5/YBa2Cu3O7−x Interface and their Effect on Flux-Pinning in Melt-Processed and Quench-Melt-Growth Processed YBa2Cu3O7−x
Authors: Wang Z. L. , Goyal A. , Kroeger D. M. , Armstrong T. 
Published: March 2011

ABSTRACTA detailed examination of the Y2BaCuO5 (211)/ YBa2Cu3O7−x (123) interface in several melt-processed 123 samples prepared using different methods was undertaken using analytical electron microscopy. It is found that there exists a significant increase in the a-b planar stacking fault density in 123, near the 211/123 interface. When viewed along [001], these faults appear as disks with diameter from a few to 30 nm and are bounded by dislocation loops. Most stacking faults are confined to the (001) basal plane. The size and density of defects around the 211 particles suggest that these defects could act as effective flux-pinning sites and may explain the observations of increased Jc with increasing volume fraction of 211 and a maximum in Jc when the applied field parallel to the c-axis.
Pinning Force and Time-Dependent Response in a Grain-Oriented Yttrium 1:2:3 Superconductor
Authors: Foldeaki M. , Ledbetter H. , O'Handley R. C. , Oti J. , Yamamoto T. 
Published: March 2011

ABSTRACTX-ray diffraction shows a preferred orientation of the 1:2:3 crystallites with the (ab) planes parallel to the longitudinal axis of the bar-shaped specimen, and a random orientation of the c axes. The dc magnetic hysteresis and time-dependent response were measured parallel to the (ab) planes or parallel to the random axis. The orientation dependence of the shape of the dc magnetic hysteresis proved the anisotropie nature of the flux-line structure and flux pinning. The experimental points were fitted to theoretical equations, allowing quantitative characterization of the orientation and temperature-dependent pinning. Time-dependent response was found to be logarithmic below a critical temperature in the range of 0.5 Tc. Activation energies determined in this region by assuming thermally assisted flux flow were found to be significantly higher than those in polycrystalline YBCO. Several activation processes or steps could be clearly distinguished. The field-cooled and zero-field-cooled specimens did not show significant differences, neither did the transport and magnetic critical current. This proves the presence of clean grain boundaries in this investigated high-quality sample.
What Can we Learn from Magnetization Experiments on HIGH-TC Superconductors? an Overview
Authors: Thompson J. R. 
Published: March 2011

ABSTRACTMagnetization studies provide a facile and convenient means for investigating high temperature superconductors. This work provides an overview and some specific examples of the types of information attainable through magnetic experiments. Regimes to be discussed include the Meissner region with low applied magnetic fields; the mixed state in higher fields at high temperatures, where equilibrium superconductive properties are accessible; and the magnetically irreversible mixed state at lower temperatures, often with large critical current densities Jc. Generally, the critical currents in the last region are metastable. The associated flux creep phenomenon also provides insight into the materials problem of optimizing the pinning of vortices, in order to maximize Jc.
Synthesis and Investigation of Superconducting Bi-Sr-Ca-Cu-O Thin Films with 2212-Like Structure and Superconducting Transitions at 95 K
Authors: Vengalis B. , Flodström A. , Brazdeikis A. 
Published: March 2011

ABSTRACTVarious compositions Bi-Sr-Ca-Cu-O thin films having 2212–1 ike structure have been synthesized on MgO substrates using Molecular Beam Epitaxy. Four Knudsen metal sources were utilized to prepare alloy films which were subsequently post annealed in air atmosphere. Quenching of the films from the annealing temperature, 800°C-820°C, increased the superconducting transition temperature Tc. The highest Tcs, 90 K - 95 K, were attained for compositions with slightly lower Ca and Sr content if compared to the nominal 2212 and 2223 ones. Plasma frequency of free carriers, ωp, determined from optical reflectivity measurements have been found to increase with the average density of CuO2 units. However, no substantial shift ofωp was displayed by the highest Tc films.