bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and Characterization of Microporous Sol-Gel Derived Ceramic Membranes for GAS Separation Applications
Authors: De Lange R. S. A. , Hekkink J. H. A. , Keizer K. , Burggraaf A. J.
Published: March 2011

Mesoporous alumina membranes were modified with microporous silica. The polymeric silica sols consist of very weakly branched polymeric molecules with a fractal dimension of 1.3 and Guinier radius of ≈ 2.0 nm. The resulting top layer material is microporous with a porosity of 40% and a layer thickness of 60 nm. Gas transport is activated with an activation energy of 11 kJ/mol for hydrogen and molecular sieve like separation factors have been obtained. From the mechanism of gas transport the conclusion can be drawn that the pores are of molecular dimensions (0.7 – 1 nm diameter).
Imogolite as a Material for Fabrication of Inorganic Membranes
Authors: Huling Jeffrey C. , Bailey Joseph K. , Smith Douglas M. , Jeffrey Brinker C.
Published: March 2011

Imogolite is a structurally microporous tubular clay comprising one-dimensional pore channels that are 0.8 – 1.2 nm in diameter, depending on composition. The microporous structure of natural and synthetic imogolite has been investigated by nitrogen adsorption as a function of outgassing temperature. A significant increase in adsorption at low relative pressure (P/P0 ∼ 10-6) after 275°C outgassing reflects a high concentration and narrow distribution of 0.8 – 0.9 nm diameter pores (i.e., the imogolite tubes) and supports the potential use of imogolite in inorganic membrane applications.
Metal Complexes in Oxidic Matrices
Authors: Schubert Ulrich , Breitscheidel Boris , Buhler Hermann , Egger Christian , Urbaniak Wlodzimierz
Published: March 2011

Alkoxides of the type (RO)nE-X-A in which a functional organic group A is connected to the alkoxide moiety via an inert and hydrolytically stable spacer X, are used to bind metal complex moieties. Sol-gel processing of the resulting metal complexes [(RO)nE-X-A]yMIm under standard conditions results in the formation of metal complex containing gels. If the metal complex moiety MLm is catalytically active, this method results in the heterogenization of homogeneous catalysts. Another application of the metal complex substituted gels is the preparation of composites containing uniform, nanometer-sized metal particles homogeneously dispersed in a ceramic matrix.
Structure-Related Mechanical Properties of Ormosils by SOL-GEL Process
Authors: Hu Yi , Mackenzie John D.
Published: March 2011

The mechanical properties corresponding to the different structures of organically modified silicates (Ormosils) prepared by the sol-gel process were studied. Tetraethoxysilane (TEOS) and polydimethyl siloxane (PDMS) were used as the inorganic and polymeric components, respectively. Large variations in the microstructure of the Ormosils were found by changing the reaction temperature, and the content of PDMS, acid catalyst (HCI),and water. The structure of the Ormosils and the mechanical properties were correlated by the edge connectivity. Modulus of elasticity and fracture strength were used to study their relations Ormosils structures.
Hydrolysis of Zirconium Propoxide by an Esterification Reaction
Authors: Laaziz I. , Larbot A. , Guizard C. , Julbe A. , Cot L.
Published: March 2011

Zirconium propoxide hydrolysis was performed with the help of an esterification reaction using acetic acid. Products, obtained according to the value of hydrolysis ratio, are successively crystals, sols and gels or precipitates. The similarity of FUR and NMR spectra for crystals and gels allows to think that the arrangements of ligands around the zirconium atoms are close. The crystalline structure determination permits to precise the environment : acetate groups are always bridging and propoxy groups can be bridging or terminal. Clusters containing 9 zirconium atoms, bridged by oxygen atoms, exist in the structure. The colloid size growth was performed by light scattering. A discussion of the role of acetic acid and the competition between the possible reactions is given.
NMR Characterization of Silicon Carbides and Carbonitrides. A Method for Quantifying the Silicon Sites and the Free Carbon Phase.
Authors: Gerardin C. , Henry M. , Taulelle F.
Published: March 2011

With ceramics prepared from organic precursors, polymers are often formed by thermolysis, and the ceramics are obtained by pyrolysis of the polymer. This paper will cover the NMR methods used to characterize the polymerization as well as the pyrolysis of such polymers. The reticulation rate of such materials is measured on the silicon atoms and on the carbon atoms, leading to a silicon reticulation state and a carbon reticulation state. For the ceramics, the quantification of the SiCxH4−x or SiCxN4−x sites is performed using a priori chemical shift calculation. A measure of the H/C of the free carbon phase at the different temperatures of pyrolysis is presented. This measure uses a absolute determination of hydrogen content in ceramics, more accurate than a classical chemical analysis of hydrogen. The evolution of the reticulation, of the free carbon amount and of the H/C ratio in the free carbon phase will be followed with the temperature.
Isocyanate-Modified Polysilazanes: Conversion to Ceramic Materials
Authors: Schwark Joanne M. , Sullivan Mark J.
Published: March 2011

A tailorable viscosity, liquid polysilazane has been developed which thermosets to a solid ceramic precursor for both silicon nitride (Si3N4)andsilicon carbide (SiC). Conversion of the thermoset, crosslinked polysilazane to a ceramic material has been examined. Preferential formation of silicon carbide or silicon nitride is controlled by the pyrolysis conditions employed.
Organometallic Precursors to Vanadium and Titanium Carbonitride
Authors: Laurent Francois , Daures Christophe , Valade Lydie , Choukroun Robert , Legros Jean-Pierre , Cassoux Patrick
Published: March 2011

We repon on the syntheses, structural and thermoanalytical studies of two titanium complexes CpTiCl2N(SiMe3)2 and FTi[N(Sime3)2]3 and one vanadium complex V(NEt2)4. CpTiCl2N(SiMe3)2 has been used in a hot wall CVD reactor as a precursor to titanium nitride. Thin films of typically 1 XPS in thickness have been deposited at 600°C on glass, silicon and tool steel. XPS analyses of the deposits show titanium carbonitride to be formed. The new FTi[N(Sime3)2]3 complex can also be used as a precursor to titanium nitride. V(NEt2>4 led at 500°C to the deposition of vanadium carbonitride characterized by XPS analysis. Films tended to contain excess free carbon.
Titanium Carbide from Carboxylic Acid Modified Alkoxides
Authors: Gallo Tom , Greco Carl , Peterson Claude , Cambria Frank , Burk Johst
Published: March 2011

Transition 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

Second 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

The 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

We 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

Ultrasmall 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

Absorption 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

Small 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

23Na 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

The 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

The 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.
Probing the Nature of Divided Metals
Authors: Edwards Peter P.
Published: March 2011

A review is given on the properties of metals which are neither quite macroscopic, nor microscopic in Nature. Both the geometric and electronic structure of such Divided Metals is discussed, with a special emphasis on recent studies of colloidal metal particles of the transition elements, Pd, Pt, Cu, Ag and Au.
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

High 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

As 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

Selected 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

Ductile 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

The 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

A 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

Microlanminates 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

New 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

Ion 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

A 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

X-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

Magnetization 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

Various 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.
Highly Oriented Very Low Surface Resistance Tl2Ba2Cu2O8 Films on NdGaO3 and LaAlO3
Authors: Holstein William L. , Parisi Louis A.
Published: March 2011

Low surface resistance epitaxial Tl2CaCu2O8 thin films were prepared on orthorhombic (001) NdGaO3 and pseudocubic (100) LaAlO3. The films were c-axis oriented on both substrates, with [100] Yl2Ba2CaCu2O8 parallel to [110] NdGaO3 or pseudocubic [100] LaAlO3. The orientation was particularly good on NdGaO3, where the rocking curve full width at half maximum was 0.19°. Films on LaAlO3 exhibit high Tc and exceptional microwave properties: inductive superconducting Tc of 106 ± 2 K, onset of flux exclusion at 107.6 ± 0.5 K, and 10 GHz surface resistance of 130 ± 20 μΩ at 77 K. These results represent the highest reported Tc of any Tl2Ba2CaCu2O8 films and the lowest surface resistance at 77 K of any films of any phase on any substrate reported to date. On NdGaO3, in spite of a substrate-film reaction, films with high Tc and good microwave properties were also produced: inductive Tc of 105 ± 2 K, onset of flux exclusion at 104.0 ± 0.5 K, and 10 GHz surface resistance at 77 K of 600 ± 100 μΩ.
Phase Relationships in ISO- and Aliovalent Analogues of La2CuO4: Implications for Superconductivity
Authors: Mccarron E. M. , Crawford M. K. , Harlow R. L. , Fameth W. E.
Published: March 2011

In addition to the well known I4/mmm and Bmab phases, recent low temperature structural studies of certain T-type (K2NiF4-related) La2CuO4 analogues have revealed two additional structural modifications, one with Pccn and the other with P42/ncm symmetry. Via appropriate iso- and aliovalent substitution chemistry, regions of T-type phase field have been mapped out and the influence of these phase transitions on superconductivity studied.
Magnetic Alignment of Amorphous Coatings of GD:123
Authors: McKittrick Joanna , Contreras Ramiro
Published: March 2011

High Tc superconducting Gd-Ba-Cu-O materials were synthesized via the acetate precursor process. Aqueous solutions of < 0.6 M of metal cations were applied to substrates of yttria stabilized zirconia. Homogeneous films were applied to the substrates by use of the spin coating technique. The substrates were fired in air at 500°C in between each applied coat. After coating the substrates with 10–30 coats, they were crystallized by heating to 900°C in Ar or O2 with or without a 1 T magnetic field. The applied magnetic field was found to produce c-axis alignment for the thinner coats. Annealing in argon produced alignment but the effect was less pronounced than annealing in oxygen. Substrates with 30 coats were not aligned for either environment.
Transport Study on Overdoped TlBa2CUO6+δ Single Crystal
Authors: Manako Takashi , Shimakawa Yuichi , Kubo Yoshimi
Published: March 2011

Tl2Ba2Cuo6+δ(T1-2201) single crystals are prepared by a KCI flux method. In-plane and out-of plane resistivities (ρabρc as well as the in-plane Hall coefficient are measured for the single crystal samples with various 7c's. The ρc values are as large as ∼10−1 Ω cm, which is larger than that of YBa2Cu3O7, but smaller than that of Bi2Sr2CaCu2O8. Temperature dependences of ρc show metallic behaviors for both normal metallic and 75-K superconducting samples. Temperature dependence of in-plane resistivity par changes from ∼T2 to ∼T1 with increasing Tc In-plane Hall coefficient RH shows a characteristic maximum at about 100 K for all samples. Although both ρab and RH have rather a complicated temperature dependence, inverse Hall mobility μH(=ρab/RH always exhibits clear T2 dependence for all samples. These results suggest that the intrinsic scattering rate of this material varies as ∼T2, just like in an ordinary Fermi liquid, and that the carrier concentration actually changes with temperature like that observed in nH(=1/RHe).
Off-Axis Growth of Y1Ba2Cu3O7-y on Different Substrates
Authors: Broussard P. R. , Cestone V. C. , Allen Laura H. , Reeves M. E.
Published: March 2011

Films of Y1Ba2Cu3O7-y have been grown by off-axis DC sputtering onto substrates of (100) SrTiO3. LaAlO, LaGaO3, Yttria-stabilized Zirconia, and MgO. Our best films, grown on SrTiO3 substrates at a temperature of 650°C and a sputtering pressure of 100 mTorr (consisting of 80 mTorr Ar and 20 mTorr O2) have room temperature resistivities of 280 μΩ-cm, an inductive Tcof 88 K and an inductive Jc 'Sof∼ 2.6 × 106 A/cm2 at 77 K and 3.9 × 107 A/cm2at 4.2 K. Films grown on YSZ tend to have higher resistivities (∼ 600 μΩ-cm) but still have Tc's of 86 K and Jc's of - 106 A/cm2 at 77 K. Films down to 550 Å still have Tc's of 86 K and Jc's at 77 K > 106 A/cm2. Films grown at lower temperatures (600°C) on S1TiO3 begin to show a-axis growth, but the superconducting properties deteriorate.
Mechanical Behaviors of Flux Pinning in GdxY1−x-Ba2Cu3Oy
Authors: Zhu J. S. , Li J. , Lu X. M. , Jin X. , Gu M. , Wang Y. N.
Published: March 2011

The mechanical behaviors of flux pinning in GdxY1−xBa2Cu3Oy with various concentration of Gd were studied comparatively by means of a vibrating reed technique. Both the internal friction and the modulus increased with enhanced flux pinning due to the increasing of Gd content in GdxY1−xBa2Cu3Oy. It was in accordance with the results of the magnetic hysteresis measurements using a vibrating sample magnetometer. These results indicated that the substitution of magnetic rare-earth ions is a practicable method for improving the flux pinning in high Tc superconductor and the mechanical measurement of flux pinning as a judgement for the superconductivity of sample was proved.
Grain Boundary Weak Links in High-TC Superconductors
Authors: Shi Donglu , Sengupta S. , Goretta K. C. , Salem-Sugui S. , Smith M. , Lwin Y. N.
Published: March 2011

The transport critical current density (Jc) for high-Tc thin films, bicrystals, and bulk ceramics is shown to be determined by magnetic field penetration into the grain boundaries. The gross grain orientations may not in all cases be an important factor in determining this penetration. The parameter (λG/λj)2can characterize the strength of the grain boundary coupling, which depends mainly on the crystal coherence and connectivity at the boundary area.
The Single Phase Regions and the Phase Stability of the High-Tc Superconducting Compounds Bi2+x(Sr,Ca)3Cu2O8+d (2212) and Bi2−x(Sr,Ca)4Cu3O10+d (2223)
Authors: Majewski Peter , Hettich Bernhard
Published: March 2011

The 2212 phase exhibits an extended single phase region having a variable Sr/Ca ratio and Bi-content of 2.1 < Bi < 2.3. At T = 820°C the single phase region extends between 2.05/0.95 > Sr/Ca > 1.2/1.8, whereas, at T = 870° C the single phase region extends between 2.2/0.8 > Sr/Ca > 1.6/1.4. The 2223 phase exhibits a significant higher Bi-content of Bi ∼ 2.5 compared to the formal composition Bi2Sr2Ca2Cu3O10. The Sr/Ca ratio varies between 2/2 > Sr/Ca > 1.9/2.1 reffering to Cu-content of Cu = 3. Samples with the nominal composition Bi2.5Sr2Ca2Cu3Ox and Bi2.5Sr1.9Ca2.1Cu3Ox have been sintered at 880 – 885°C for 90 h in air and consist of 90 – 95 volume percent 2223 phase. Tc depends on the chemical composition of the phases. With decreasing Ca- and Bi-content of the phases Tc increases. Both phases are metastable at roomtemperature. 2212 and 2223 rapidly decompose at 600 °C and 800 °C in air, respectively. At 300°c two new Bi-Sr-Cuprates have been found.
Post Sintering Oxygen Pressure Effects on the Jc of BPSCCO- Silver Clad Tapes
Authors: Lay K W
Published: March 2011

Many processing parameters affect the critical current of silver-clad tapes of Bi2−xPbxSr2Ca2Cu3O10+y (2223) made by the powder in tube process. In this paper the effect of oxygen pressure during cooling from the final sintering step will be considered. It is shown that high oxygen pressures will destabilize the 2223 phase with formation of calcium plumbate and the lower Tc Bi2Sr2Ca1Cu2O8+y (2212) phase. This decomposition can drastically lower the critical current. It is shown that cooling in atmospheres containing about 5 % oxygen will avoid the calcium plumbate formation region.
New Layered Perovskite Vanadium Oxide with Negative Magnetization
Authors: Fukushima Noburu , Takeno Shiro , Tanaka Shigenori , Ando Ken
Published: March 2011

A new layered perovskite vanadium oxide Sr4V3O8-d was synthesized and its crystal structure and magnetic properties were studied. Sr4V3O8-d has a novel crystal structure, containing a V-0 octahedron and a two-fold V-0 fence in a unit cell. It exhibits negative magnetization below 30 K. when cooled in a magnetic field. This peculiar magnetism is attributed to N-type parasitic ferrimagnetism.
Electrical Characteristics of All-Oxide S-N-S Junctions in the Normal State
Authors: Tarutani Y. , Hiratani M. , Fukazawa T. , Kabasawa U. , Tsukamoto A. , Suga M. , Takagi K.
Published: March 2011

All-oxide S-N-S (superconductor-normal layer-superconductor) junctions having a planar structure are fabricated and their electrical characteristics in the normal state are investigated. The superconducting electrodes are composed of HoBa2Cu3O7−x, and the normal layer is La1.5Ba1.5Cu3O7-y. Conductance characteristics are measured and their behaviors are explained by the geometrical resonance of quasiparticles. A pair potential distribution in the normal layer is estimated from the resonance structure.
Microstructures of YBCO Thin Films Prepared by Pulsed Organometallic Beam Epitaxy
Authors: Hu J. G. , Miller D. J. , Buchholz D. B. , Duray S. J. , Schulz D. , Marl T. J. , Chang R. P. H.
Published: March 2011

The microstructure of Y1Ba2Cu3Oy films and Y1Ba2Cu3Oy / Pr1Ba2Cu3Oy multilayers prepared by a pulsed organometallic beam epitaxy (POMBE) technique have been characterized by transmission electron microscopy (TEM). The microstructure of the films is observed to vary as a function of substrate temperature. At low temperatures, films are polycrystalline and exhibit some impurity phases. At higher substrate temperatures, films grow epitaxially with smooth surfaces and few impurities. Controlled growth at sufficiently high substrate temperatures allows uniform growth of alternating Y1Ba2Cu3Oy and Pr1Ba2Cu3Oy layers.
Ba1−xKxBiO3 Superconducting Crystals with New Solubility Limit
Authors: Tang H. Y. , Chen W. L. , Wen W. J. , Wu M. K. , Norton M. L.
Published: March 2011

Crystalline bismuthates Ba1−xKxBiO3 with x greater than 0.5 are obtained by a low temperature anodic electrocrystallization method in a potassium hydroxide molten flux. The x = 0.56 bismuthate crystal shows 8K superconductivity determined by AC magnetic susceptibility.
Development of Tailored Films and Surfaces for Use in Advanced Chemical Sensors
Authors: Semancik Steve , Cavicchi Richard
Published: March 2011

The microstructure found at the surfaces and interfaces of active sensing materials can strongly affect the performance of solid state chemical sensors. This paper desribes research efforts aimed at improving oxide semiconductor-based gas sensors which utilize changes in conductance and diode current-voltage measurements as detection schemes. Studies of oxide surface modification and the formation of Pd/SnO2(110) and Pd/TiO2(110) interfaces are discussed as are the electrical changes for these systems induced by H2 or O2 adsorption. The fabrication of heteroepitaxial SnO2 films for use in planar sensing arrays is also reported and the expected advantages of these highly-ordered, uniform films for simplifying the transducing process are described.
Micron Sized Arm Using Reversible TiNi Alloy Thin Film Actuators
Authors: Kuribayashi Katutoshi , Taniguchi Takao , Yositake Masaaki , Ogawa Sooichi
Published: March 2011

Reversible TiNi (= RTiNi) alloy thin film actuator has many advantages for micro sized robot. That is. a micro arm could be fabricated easily on silicon wafer because RTiNi alloy thin film has 3 functions. 1) a frame of the arm, 2) a joint of the arm and 3) an actuator of the arm. and moreover, this film could actuates the arm without friction. A micron sized flexible arm using RTiNi alloy thin film was designed on silicon wafer. IC process for fabricating this arm on silicon wafer was designed. The fabricating process for this arm and its heat treatment process for the RTiNi are presented.
Microheater Made of Heavily Boron Doped Single Crystal Silicon Beam
Authors: Kimura Mitsuteru , Komatsuzaki Kazuhiro
Published: March 2011

Microheater made of heavily Boron doped single crystal Si beam covered with SiO2 film, 1000×300×3 μm, is fabricated on the n type Si substrate by the anisotropic etching technique. As this microheater has an air bridge structure of low resistivity semiconductor material with positive but small temperature coefficient of resistance, a broad heating area up to 800 °C is easily obtained and it has quick response with the thermal time constant t of about 4 ms and has small power consumption. Since this heating area is made of p type layer in the n type substrate,this area can be electrically isolated from the substrate because of the formation of p-n junction.
Organic Polymers with Tunable Charge Carrier Mobilities
Authors: Stolka Milan , Abkowitz Martin A.
Published: March 2011

Charge carrier (hole) mobility in amorphous organic polymeric materiats can be changed at will over at least nine orders of magnitude without increasing the conductivity of the polymers, and also without affecting the carrier range, i.e., without introducing deep traps. The changes in the drift mobility can be accomplished by several means: (1) by changing the density of hopping sites (the concentration of transport-active molecules or groups), (2) by light doping the host polymer with low-oxidation potential compounds (for hole transport), and, eventually, (3) by the nature of the host medium and its polarity. Since the carrier mobility is typically activated and electric field dependent, significant changes can also be made by varying the temperature and the electric field. An enhancement of mobility by heavy doping has also been described. Hole mobilities in the small molecule - host polymer composites and also in polymers in which the transport states are backbone-derived can thus be varied from values below the measurement threshold (<10−10 cm2 V− s−1) to fairly high values in the neighborhood of 10−1 cm2 V−1 s−1 at an electric field of E = 105 V cm−1 and at 295 K.
Integrated Linear and Nonlinear Optics with Novel Macromolecular Systems
Authors: Aust E. F. , Hickel W. , Meyer W. H. , Ringsdorf H. , Sawodny M. , Urban C. , Wegner G. , Knoll W.
Published: March 2011

This paper deals with the application of some recently developed evanescent waveoptical techniques for the characterization of novel macromolecular host-guest systems. In particular, surface plasmon- and guided optical wave-spectroscopies and -microscopies are used to determine the linear and nonlinear optical properties of these materials in thin film form.
Preparation and Third-Order Nonlinear Optical Properties of Host-Guest Molecular Composites
Authors: Jenekhe Samson A. , Roberts Michael F. , Meth Jeffrey S. , Vanherzeele Herman
Published: March 2011

Host-guest molecular composites of conjugated rigid-rod polymers in the matrix of flexible-chain polymers were prepared from blend solutions of the Lewis acid complexes of the component polymers. Molecular composites of poly(p-phenylene benzobisthiazole) (PBZT) with the polyamides Nylon 66 and PTMHT were prepared and their linear and nonlinear optical properties were investigated by optical absorption and third harmonic generation spectroscopy, respectively. Dispersion of PBZT in a polyamide matrix was found to result in reduced π-electron interactions as evidenced by the narrowing of the main absorption band. The χ(3) spectra of composites were measured in the wavelength range 0.8–2.4μm which spans the resonant and nonresonant regions. Nonresonant χ(3) at 1.9μtm was studied as a function of composite composition and linear and nonlinear dependences of χ(3) with mole fraction of PBZT were observed for nylon 66 and PTMHT composites respectively. Our findings that both χ(3) and χ(3)/α can be enhanced in molecular composites suggest that this is an important approach to optimize materials for nonlinear optics. Preliminary results of our studies of other new molecular composites of rigid-rod and ladder polymers are also discussed.
Simulation and Modeling of Amorphous Silicon Thin-Film Devices
Authors: Shaw John G. , Hack Mike G.
Published: March 2011

We describe a computer program which solves the complete set Of transport equations for device-quality amorphous silicon in two spatial dimensions and time. When modeling amorphous silicon devices, it is extremely important to account for the high concentration of time-dependent trapped charge present due to the continuous distribution of localized states in the semiconductor's bandgap. Our model is based on a realistic density-of-states distribution and includes a detailed description of the trap occupation functions for electrons and holes. These occupation functions are calculated self-consistently with respect to the electrostatic potential and free-carrier concentrations within the semiconductor.
Dislocation Generation and Crack Propagation in Metals Examined in Molecular Dynamics Simulations
Authors: Rifkin J. A. , Becquart C. S. , Kim D. , Clapp P. C.
Published: March 2011

We have carried out a series of atomistic simulations on arrays of about 10,000 atoms containing an atomically sharp crack and subjected to increasing stress levels. The ordered stoichiometric alloys B2 NiAl, B2 RuAl and A15 Nb3AI have been studied at different temperatures and stress levels, as well as the elements Al, Ni, Nb and Ru. The many body interactions used in the simulations were derived semi-empirically, using techniques related to the Embedded Atom Method. Trends in dislocation generation rates and crack propagation modes will be discussed and compared to experimental indications where possible, and some of the simulations will be demonstrated in the form of computer movies.