bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Behavior of Ternary and Quaternary Rual Alloys
Authors: Nandy T. K. , Feng Q. , Banerjee D. , Gigliotti M. F. X. , Pollock T. M.
Published: April 2011

The mechanical behavior of RuAl-base intermetallic alloys with alloying additions of boron, niobium and platinum has been investigated. Compression tests have been performed at room temperature and 973 K. While the addition of alloying elements results in solid solution strengthening, the strain-rate sensitivity and the activation volumes do not show a significant variation, thereby suggesting that the macroscopic flow mechanisms are not strongly affected. Deformation substructure analysis of the niobium-containing alloy shows the presence of <100> and <110> dislocations, while the platinum-containing alloy additionally contains a significant density of <111> dislocations.
Microstructural Evaluation of LENS™ Deposited Nb-Ti-Si-Cr Alloys
Authors: Dehoff Ryan R. , Sarosi Peter M. , Collins Peter C. , Fraser Hamish L. , Mills Michael J.
Published: April 2011

Nb-Ti-Si “in-situ” metal ceramic composites consist of Nb3Si and Nb5Si3 intermetallic phases in a body centered cubic Nb solid solution, and show promising potential for elevated temperature structural applications. The addition of Cr has also been shown to increase the oxidation resistance at high temperatures. In this study, the LENS™ (Laser Engineered Net Shaping) process is being implemented to construct the Nb-Ti-Cr alloy system from elemental powder blends. Advantages of the LENS™ process include the ability to produce near net shaped components with graded compositions as well as a more uniform microstructure resulting from the negative enthalpy of mixing associated with the silicide phases. This study focuses on characterization of the microstructure of the Nb-27Ti-5Si-10Cr (at%) system using SEM and TEM analysis.
Dislocation/Twin/Interface Interactions during Deformation of PST TiAl Single Crystals, an AFM Study
Authors: Chen Yali , Pope David P. , Vitek Vaclav
Published: April 2011

PST TiAl crystals oriented such that the deformation axis lies in the (111) interfacial planes have been deformed in compression. This deformation produces so-called “channeled flow” in which the strain perpendicular to the (111) interfaces is zero, while the other two strains are equal and opposite in sign. Thus the sample simply shortens axially and spreads laterally in the channels defined by the (111) interfacial planes. We have examined the fine structure of deformation bands on the free surface of these deformed samples using AFM to see how the deformation processes interact with the boundaries. By measuring the offset angle at the surface we have been able to show that not only is the macroscopic displacement vector parallel to the lamellar boundaries, but the total shear vector in each layer is also parallel to the lamellar boundaries. However these deformation bands have very different characters, requiring complex deformation processes at the boundaries in order to satisfy this requirement. Some consist of either just super dislocations or just ordinary dislocations with Burgers vectors lying in the interface. But others consist of a special combination of twinning and ordinary dislocations in fixed ratio, such that the net shear vector also lies in the boundary, even though the individual twinning and dislocation shear directions are inclined to it. This results in deformation that is homogeneous and completely ‘channeled’ inside each lamella with no shear vector perpendicular to the lamellar boundaries. We have also shown that the cooperative twinning and slip is homogeneous on the nano-scale, i.e., the twinning and slip occurs in the same volume of material.
Formation of β-Ti Phase in Multi-component Gamma Alloys
Authors: Kobayashi Satoru , Takeyama Masao , Motegi Takahiro , Hirota Noriaki , Matsuo Takashi
Published: April 2011

Effect of combined addition of elements on the formation of high-temperature β-Ti (bcc) phase in Ti-45Al-M1-M2 quaternary alloys has been examined by converting the quaternary system to quasi-ternary system using M1-equivalency of M2: [M1] eq = k [M2]. The k value is evaluated from the ratio of critical concentration, XcM, to form the β phase in the isothermal section of each ternary system at 1473 K: kM1/M2= XcM1/XcM2. In case that M1 and M2 are in the same group element, Mo-equivalency of Cr, kMo/Cr = 0.46 and Nb-equivalency of V, kNb/V = 0.57. The critical concentrations to form the β phase in the quaternary systems become lower than those estimated from these values, and the experimentally determined equivalencies become 0.8 and 1.0, respectively. These results suggest an existence of negative interaction between M1 and M2 to stabilize the β phase even if they were in the same group element. Experimentally determined quaternary phase diagram revealed that the combined addition makes the β+α two-phase region expand to lower temperatures, thereby effective in improving hot workability for development of wrought gamma alloys.
Micromechanisms of deformation in γ-TiAl
Authors: Veyssière Patrick , Chiu Yu-Lung , Grégori Fabienne
Published: April 2011

Investigations conducted in our group on plastic properties of a variety of strained TiAl based alloys and resulting microstructures are reviewed. These include oriented single crystals of Al-rich γ-TiAl and semi-oriented polycrystals with γ + α2 lamellar structure. The wealth of micro-mechanisms encountered in this family of alloys is, to large extent, due to the decomposition of <011] dislocations: <011] ↔ 1/2<112] + 1/2<110]. This transformation sometimes introduces serious uncertainties as to which slip systems were actually operating during deformation. Another transformation involving decomposition is the formation of intralamellar networks during deformation. Mechanisms not involving decomposition include the trailing of faulted dipoles by <011] dislocations and the generation of arrays of prismatic loops of ordinary dislocations. The latter maneuver is at the origin of fundamental processes such as self-organisation in single slip in a variety of crystals.
Effect of Interphase Boundary Character on Mechanical Properties in NiAl(β) Bicrystals with Ni 3Al(γ') Precipitates along Grain Boundary
Authors: Sakata Toshiya , Yasuda Hiroyuki Y. , Umakoshi Yukichi
Published: April 2011

Role of the crystallography of Ni 3Al(γ') precipitates along grain boundaries of NiAl(β) in the mechanical properties was systematically investigated using β bicrystals with controlled orientations. γ' phase preferentially precipitated along βgrain boundaries showing a film-like shape. The selected variant of γ'-film satisfied the Kurdjumov-Sachs (K-S) relation with a neighboring βcrystal but it deviated from the relation with another adjacent βcrystal. In the course of tensile deformation at room temperature, fracture occurred preferentially at incoherent (β/γ') interphase boundary deviating from the K-S relation and the fracture stress decreased with increasing deviation angle. In contrast, the interphase boundary sliding occurred preferentially at irrational (β/γ') interface at 1073K. The sliding displacement increased with increasing deviation angle. Thus, the mechanical properties of β bicrystals with γ'-film were found to depend strongly on the interphase boundary character.
A1→D022Transformation and Multi-Variant Structure of Ni3V
Authors: Suzuki Akane , Takeyama Masao , Matsuo Takashi
Published: April 2011

The formation mechanism and morphology of the tetragonal compound Ni3V (D022) quenched from the disordered fcc (A1) state have been examined by TEM using a Ni-25at%V. The alloy is fully transformed to D022in the quenched state. The resulting microstructure exhibits a fine brick-like “multi-variant structure (MVS)” consisting of one major and two minor variants withcaxes perpendicular each other, having coherent interfaces of {102)D022and {100)D022. The major variant particles with a quadrangular-prism shape are alternately arrayed with two minor variants, one parallel to {102)D022and the other {100)D022, respectively. The thermal APDs are formed in the all variants, but the average size within the major is larger than that in the minors. The c/a ratio of the D022in the MVS is 2.006, much smaller than the value (2.04) in equilibrium state. From all these facts, the transformation of A1→D022is assumed to proceed through a selective nucleation and growth of tetragonal A6 phase, followed by ordering to D022. The formation of the tetragonal phase produces an anisotropic strain field due to the contraction and expansion of theaandcaxes against the cubic matrix. The strain field makes {102)D022and {100)D022with the invariant lines become habit, and also drives the selective nucleation and growth of minor variants to minimize the elastic strain energy, thereby leading to the multi-variant structure.
Phase Constitution and Oxidation Resistance of B2 (Ir, Co)Al
Authors: Hosoda Hideki , Noma Hiroshi , Wakashima Kenji
Published: April 2011

B2 iridium aluminide (IrAl) is hopeful for use as an ultrahigh temperature oxidation resistant coating above 1600K. In this study, the effect of Co substitution for Ir on phase constitution, hardness and oxidation behavior was studied for IrAl alloys. Alloys of (Ir, Co)-50mol%Al with various Co contents were fabricated by Ar-arc melting followed by hot-forging at 1773K. Oxidation behavior was evaluated using thermogravimetry (TG) in Ar-67%O2 up to 1823K. XRD and SEM were also carried out for alloy characterization. It was found that a continuous B2 solid solution (Ir,Co)Al is formed between IrAl and CoAl. Depending on the Co concentration, the oxidation products identified after heating to 1873K in Ar-67%O2 were Ir, IrO2 and A2O3 and/or Co2AlO4. Thin and continuous Al2O3 layers were observed after isothermal oxidation at 1673K when Co content is more than 20mol%Co. In this case, the weight change by isothermal oxidation at 1673K becomes higher with decreasing Co content. The (Ir,Co)Al alloys containing 20–40mol%Co exhibit higher oxidation resistance than CoAl and IrAl, and thus oxidation resistance of CoAl is improved by Ir addition.
Processing and Characterizing RuAl Eutectics
Authors: Reynolds Todd , Johnson David
Published: April 2011

Eutectic alloys in the Ru-Al-Mo system were directionally solidified by a cold crucible Czochralski technique. The solidification microstructures and composition of the phases were examined and used to estimate a partial liquidus projection. Preliminary results from compression and hardness testing indicate that the hardness of RuAl varies significantly with composition. The Ru-rich alloys in which RuAl is in equilibrium with the hcp (Ru,Mo) solid solution were found to have the lowest hardness values.
IC Component Level Failure Induced By Intermetallic Layer Structural Defects of Solder Joint
Authors: Sun Ming , Loo Mike , Zhao Lily
Published: April 2011

Solder joint has been widely used in microelectronics industry as an interconnect of Integrated Circuit (IC) chip and Printed Circuit Board (PCB). Frequently, a functional failure of the component on the system is a result of solder joint damage. Eutectic 63Sn/37Pb solder joint mechanical behaviors on Ni/Au plated copper pad and bare copper pad were experimentally investigated to address the effect of pad surface cleanness on the formation of intermetallic compound. The joints with thinner intermetallic compound layer resulted in a poor solder ball shear strength. Microstructural analysis revealed that the oxidations of Ni and Cu during substrate manufacturing contributed to the improper growth of intermetallic compound during assembly and reliability tests. In additions, the experimental results showed that the growth of the intermetallic compound layer were dependent not only on the time and temperature of solder reflow and testing, but also on the cleanness of the pad surfaces and available area for the diffusion of Ni in the case of Ni/Au plated copper pad, Cu in the case of bare copper pad and Sn in the joint area.
Defects Generated by Hydrogen Absorption/Desorption in Lani5 and Derivatives
Authors: Décamps B. , Joubert J.-M. , Cerny R. , Percheron-Guégan A.
Published: April 2011

The combination of bright-field and weak-beam transmission electron microscopy (TEM) techniques has been used to analyse the dislocation systems activated in LaNi5 and derivatives after absorption/desorption hydrogen cycling.

The TEM results are discussed and compared with those obtained from the modelling of the anisotropic diffraction peak broadening using only two dislocation slip systems of the hexagonal structure (1).
Enhanced Thermoelectric Properties of [Ca2CoO3-δ]0.62CoO2 Polycrystalline Bulk by Control of Microstructure and Oxygen Content
Authors: Sano M. , Horii S. , Matsubara I. , Funahashi R. , Shikano M. , Otzschi K. , Shimoyama J. , Kishio K.
Published: April 2011

We report preparation of highly grain-aligned and densified [Ca2CoO3-δ]0.62CoO2 bulks and a change of thermoelectric performance for their bulks with different oxygen deficiencies (dgrl). The highly c-axis aligned and highly densified samples which showed low electronic resistivities at room temperature, were obtained by combination of magnetic alignment and spark plasma sintering methods. Electronic resistivity p and Seebeck coefficient S along the ab plane were systematically changed with oxygen contents and a power factor was consequently enhanced up to 3.5×10--6 Wcm-1K-2 at 300K for the sample annealed at 500°C in air. Moreover, the magnetic properties also showed a systematic change with oxygen contents.
A Variable-Emittance Radiator Based on a Metal-Insulator Transition of (La,Sr)MnO3
Authors: Shimakawa Yuichi , Yoshitake Tsutomu , Kubo Yoshimi , Machida Takahiko , Shinagawa Kiminari , Okamoto Akira , Nakamura Yasuyuki , Ochi Atsushi , Tachikawa Sumitaka , Ohnishi Akira
Published: April 2011

Variable-emittance radiators based on the metal-insulator transition of (La,Sr)MnO3 have been developed. The emittance property of the material was evaluated from infrared reflectance spectra; that is, (La,Sr)MnO3 shows low emittance at low temperature but high emittance at high temperature. Moreover, the emittance property significantly changes at the metal-insulator transition temperature, where the material changes from a highly reflective (i.e., low emissivity) metal to a less reflective (i.e., high emissivity) insulator. The (La,Sr)MnO3 thin-films fitted on a spacecraft surface can, therefore, be used to automatically control the emmisive heat transfer from the spacecraft without the need for electrical power. The developed (La,Sr)MnO3 thin-film radiator also greatly reduces the weight and production cost of the thermal control devices.
Open Framework and Microporous Transition Metal Silicates
Authors: Jacobson Allan J. , Wang Xiqu , Liu Lumei , Huang Jin
Published: April 2011

A family of microporous and open-framework microporous transition metal silicates have been prepared by hydrothermal synthesis at T ≤ 240 °C. The structures of the compound are based on a common principle in which anionic silicate components (layers, chains, or cluster anions) are connected by isolated transition metal polyhedra by sharing four corners in a square arrangement. Known examples of this class of compounds are reviewed and some recent progress on extending the syntheses to include organic templates are discussed.
A Novel Nanoparticle/Lamellar Oxide Hybrid: TiO2-pillared MoO3
Authors: Paek Seung-Min , Jung Hyun , Choy Jin-Ho
Published: April 2011

The intercalation into MoO3 with TiO2 nanoparticles has been accomplished via the exfoliating-restacking route. The molybdenum oxide lithiated by LiBH4 is exfoliated in degassed and deionized water. And subsequent restacking of exfoliated MoO3 in the TiO2 nanoparticle solution results in TiO2-pillared MoO3. X-ray diffraction pattern indicates that the TiO2 nanoparticles are successfully intercalated in the interlayer of MoO3. The interlayer expansion of MoO3 with the Ad value of 11.2 Å is consistent with the size of TiO2 nanoparticle. Well-defined (00l) reflections reveal highly ordered lamellar character of TiO2-pillared MoO3. The pre-edge feature in the X-ray absorption spectrum of the TiO2-pillared MoO3 confirms that guest TiO2 in the interlayer of MoO3 is pillared in the form of anatase.
Synthesis and Characterization of Structure Controlled Nano-cobalt Particles
Authors: Hui Shiqiang , Wu Mingzhong , Ge Shihui , Yan Dajing , Zhang Y.D. , Xiao T.D. , Yacaman M. J. , Miki-Yoshida M. , Hines W. A. , Budnick J. I.
Published: April 2011

Nanostructured cobalt particles with and without a ceramic coating have been synthesized using a wet chemical method. The structure and magnetic properties of synthesized powder were characterized using x-ray diffraction (“XRD”), high-resolution transmission electron microscopy (“HRTEM”), and a Quantum Design (SQUID) magnetometer. The cobalt nanoparticles are of either face-centered cubic (“fcc”) and/or hexagonally close-packed (“hcp”) crystalline structures. The average grain size is ∼14 nm for cobalt (either fcc or hcp) with an amorphous silica coating, and the average grain size is ∼9 nm for hcp cobalt and 26 nm for fcc cobalt without a silica coating. The effect of annealing temperature on grain size and magnetic properties are addressed.
Microscale Titania Shapes Grown Within Swollen PDMS
Authors: Brennan Daniel P. , Dobley Arthur D. , Oliver Scott R. J.
Published: April 2011

A variety of titania microstructures have been synthesized using a swollen polymer matrix of polydimethylsiloxane (PDMS). The shapes and structures grown to date include spheres, ‘bowls’, ‘nets’ and ‘brain coral’ matrices. The PDMS polymer network can be swollen by one of a variety of organic solvents. These solvents create internal voids or spaces within the PDMS, of particular volume. These spaces can then be filled with metal alkoxide liquid. The metal alkoxide is then polymerized to form metal oxides, in a shape templated by the swollen PDMS polymer. The resultant product is a composite of metal oxide within a polymer. Some of the shapes can be removed mechanically or chemically. Methods of characterization include scanning electron microscopy (SEM) and optical microscopy. Potential applications of the shaped titania include catalysts, fillers, capsules, and chemical separators. The synthesis and characterization of these compounds will be discussed.
Electrochemical Deposition of Ba1-xSrxMoO4 Thin Films at Room Temperature
Authors: Gao D.J. , Xiao D.Q. , Bi J. , Yu P. , Zhang W. , Yu G L. , Zhu J.G
Published: April 2011

Aseries of well crystallized Ba1-xSrxMoO4 (0≤×≤1) films were prepared on molybdenum substrates in electrolytes embodied Ba2+ and Sr2+ions by electrochemical deposition at room temperature. The composition x is controlled through the starting concentrations of Ba2+ and Sr2+ ions. The measurements of XRD, SEM and XPS for these materials were carried out. The XRD analyses show that the films are good crystalline with single tetragonal structure of scheelite-type, and the a and c axes of the unit cell parameters of the films decrease with the increasing of Sr2+ concentration in the starting electrolytes; the XPS analyses reveal that the composition of the Ba1-xSrxMoO4 films is in agreement with stoichiometry, and the SEM photographs show that the films are condensed deposited.
Sol-gel Synthesis, Magnetic and Structural Characterization of BaFe11.6–2xMxTixO19 (M=Co, Zn, Sn) Compounds.
Authors: Mendoza-Suárez G. , Fuentes A.F. , Escalante-García J.I. , Ayala-Valenzuela O.E.
Published: April 2011

Substituted barium ferrites powders with Ti4+-M2+ (M = Co, Zn, Sn) cationic mixtures were prepared by a sol-gel route. The materials were heat-treated in the range 925–1000 °C and characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The results showed that the effect of the substitution, x was to lower the coercivity (Hc), owing to the decrease of the magnetocrystalline anisotropy of the magnetoplumbite structure of the BaM. In this regard Sn-Ti substitutions tended to decrease Hc more rapidly than Zn-Ti and Ti-Co substitutions, in that order. Regarding the saturation magnetization (Ms), Zn-Ti mixtures showed slightly better Ms than Ti-Co substitutions; however, the Sn-Ti showed a more marked decrease as x increased. As revealed by SEM, the effect of the heat-treatment temperature was to increase the volume of multi-domain particles, following a Hc decrease due to grain coarsening. Contrarily, as a result of the improved crystallinity of the samples, as observed from the XRD peaks, Ms enhancement was recorded. Crystallite sizes decreased below 100 nm as x increased, although it was also dependent on the cationic mixture. In this respect Sn-Ti substitutions needed higher treatment temperatures to yield materials with adequate crystallinity and phase constitution.
Design and Optical Properties of Rare Earth-Based Mixed-Anions (O, S, F) Compounds
Authors: Pauwels Damien , Demourgues Alain , Tressaud Alain
Published: April 2011

Rare earth-based mixed-anions (O, S, F) compounds have been prepared by solid state route. The structures have been determined on the basis of powder diffraction (X-ray/neutrons) refinement and/or single crystal analysis. They have been described as a stacking of [Sx] 2x- layers and fluorite type blocks. The evaluation of the rare earth environment (bondlength, number of neighbors) can be directly related to the bandgap and to the UV-visible absorption in the La-based compounds.
Impedance/Dielectric Spectroscopy of Electroceramics in the Nanograin Regime
Authors: Kidner N. J. , Ingram B. J. , Homrighaus Z. J. , Mason T. O. , Garboczi E. J.
Published: April 2011

In the microcrystalline regime, the behavior of grain boundary-controlled electroceramics is well described by the “brick layer model” (BLM). In the nanocrystalline regime, however, grain boundary layers can represent a significant volume fraction of the overall microstructure and simple layer models are no longer valid. This work describes the development of a pixel-based finite-difference approach to treat a “nested cube model” (NCM), which more accurately calculates the current distribution in polycrystalline ceramics when grain core and grain boundary dimensions become comparable. Furthermore, the NCM approaches layer model behavior as the volume fraction of grain cores approaches unity (thin boundary layers) and it matches standard effective medium treatments as the volume fraction of grain cores approaches zero. Therefore, the NCM can model electroceramic behavior at all grain sizes, from nanoscale to microscale. It can also be modified to handle multi-layer grain boundaries and property gradient effects (e.g., due to space charge regions).
Surface properties of disordered γ MnO2 at the solid-electrolyte interface.
Authors: Prélot Bénédicte , Poinsignon Christiane , Thomas Fabien , Villiéras Frédéric
Published: April 2011

Relationships between lattice parameters of manganese dioxides (γ/ε-MD) and their surface properties at the solid-aqueous solution interface were investigated. The studied series ranged from orthorhombic ramsdellite to tetragonal pyrolusite and encompassed disordered MD samples. The structural model used takes into account two structural defects which affect the orthorhombic network of ramsdellite: Pr (rate of pyrolusite intergrowth) and Tw (rate of microtwinning). Water adsorption isotherms showed that the cross sectional surface area of water molecules is linearly correlated to Pr: from 6.3 Å2 (Pr=0.2) to 13.1 Å2 (Pr=1). Titration of their surface charge evidenced a linear relationship between PZC and Pr starting from ramsdellite (Pr = 0, Tw = 0, PZC = 1) to pyrolusite (Pr = 1, Tw = 0, PZC = 7.3). γ-MD with intermediate values of Pr (0.2 to 0.45) have increasing PZC values. For similar Pr values (0.45), high Tw percentage (0.3 and 1) makes the PZC to increase. The experimental results are compared with data collected in the literature for dioxides of transition elements with tetragonal structure. Surface titration leads to the determination of electrochemically active surface area at alkaline pH.
Development of new ceramic doped ionoconducting membranes for biomedical applications.
Authors: Romagnoli Paola , Vona Maria Luisa Di , Traversa Enrico , Narici Livio , Sannita Walter G. , Carozzo Simone , Trombetta Marcella , Licoccia Silvia
Published: April 2011

New ionoconducting composite membranes to be used as an interface between the skin and the actual electrical instrumentation used to produce an electroencephalogram (EEG) have been developed. The gels are based on lithium salts and PMMA (polymethyl methacrylate) and have been doped with nanometric titanium oxide. The samples have been electrochemically characterized by means of impedance spectroscopy and their structure studied by ATR-FTIR and MAS NMR. Spectroscopic studies indicate interactions between the polymer and oxide dopant. The polymeric electrolytes allowed the registration of good electrophysiological cortical signals either spontaneous or stimulus-related.
Next Generation Positive Electrode Materials Enabled by Nanocomposites: -Metal Fluorides-
Authors: Badway F. , Pereira N. , Cosandey F. , Amatucci G. G.
Published: April 2011

Through the use of nanostructures and nanocomposites, the electrochemical activity of metal fluoride materials was opened as potential candidates as next generation high energy density positive electrodes for Li batteries. This class of materials, utilizing FeF3 as an example, is shown to exhibit good reversible behavior of approximately 200 mAh/g in the 3V region. The specific capacity is extended to 600 mAh/g when the discharge is extended to take into account the additional specific capacity associated with a 2V plateau. Through the use of XRD, SAED and high resolution TEM, the 2V reaction mechanism was associated to a reversible metal fluoride conversion mechanism. It is shown that LiF + Fe nanocomposite can be utilized as initial components in order to make the technology suitable for Li-ion applications. Although exhibiting relatively poor rate capabilities at this initial stage, reversible conversion metal fluorides enable for the first time the utilization of all the redox states of the constituent metal in a reversible manner in the positive electrode. This translates to 4X the specific capacity and double the energy density of today's state of the art LiCoO2.
In SituElectrochemical Scanning Probe Microscopy of Lithium Battery Cathode Materials: Vanadium Pentoxide (V2O5)
Authors: Bullard Joseph W. , Smith Richard L.
Published: April 2011

Atomic force microscopy was used to characterize the structural evolution of the V2O5(001) surface during the electrochemical cycling of lithium. With Li insertion, nanometer-scale pits develop at the V2O5(001) surface. The pits first appear as the composition of the crystal approaches Li0.0006V2O5. Pit nucleation and growth continue through further discharge, resulting in a micro-porous (001) surface morphology. During subsequent Li extraction, cracks develop along the V2O5<010> axis. Surface regions in the vicinity of these cracks “swell” during ensuing lithiation reactions, suggesting that the cracks locally facilitate Li uptake.
Sn and SnBi Foil as Anode Materials for Secondary Lithium Battery
Authors: Yang Shoufeng , Zavalij Peter Y. , Stanley Whittingham M.
Published: April 2011

In order to better understand the cycling mechanism of metal alloy anodes, and to mitigate the capacity fade observed in lithium battery use a study of simple systems was initiated. Tin foil and tin-bismuth mixtures were chosen because there is no need for conductive diluents or binders so that the intrinsic behavior could be observed. A pure tin foil was found to react rapidly with lithium, ≥ 3 mA/cm2, and with no capacity fade for over 10 cycles. This is better than tin powder or electrodeposited tin. After the first cycle, the foil reacts with Li following a stepwise formation of different alloys as dictated by the thermodynamics. Incorporation of bismuth into the foil increased the capacity fade after the first few cycles, with the eutectic composition Sn0.57Bi0.43 having better capacity retention than the Sn0.5Bi0.5 composition. XRD and SEM-EDS shows that bismuth is rejected from the tin rich phase during lithium insertion and is not reincorporated on lithium removal, just as expected from the phase diagram.
Synthesis and sintering of Ce1-xGdxO2-x/2 nanopowders via chemical routes.
Authors: Sin Agusti , Aricò Antonino S. , Seregni Massimo , Gullo Laura , Rosa Daniela La , Siracusano Stefania , Antonucci Vincenzo , Tavares Ana , Dubitsky Yuri , Zaopo Antonio
Published: April 2011

Gd-doped ceria (Ce0.80Gd0.20O1.90) obtained by several nanopowder synthesis processes are compared structurally, morphologically and electrochemically. The powders have been sintered into pellets and investigated by ac-impedance measurements. The electrochemical properties of the electrolytes have been correlated to the structural morphology of the sintered pellets. When the intergrain region exhibits an elevated interdiffusion, the observation of the grain boundaries becomes difficult while the electrochemical properties are improved. Acrylamide polymerization and oxalic co-precipitation techniques showed the best properties.
Preparation and Characterization of Metal Sulfide Electro-catalysts for PEM Fuel Cells
Authors: Zhang Hua , Verde-Gómez Ysmael , Jacobson Allan J. , Ramirez Alejandra , Chianelli Russell R.
Published: April 2011

Ruthenium sulfide samples were prepared by flowing pure hydrogen sulfide into an aqueous solution of ruthenium chloride followed by further sulfidation in hydrogen sulfide. The final products were characterized by X-ray diffraction and crystallite-sizes were estimated from line broadening. The specific surface areas of catalysts were measured using the multipoint BET method and compositions were determined by thermogravimetric analysis. Ruthenium sulfide loaded gas diffusion electrodes were fabricated by a spraying technique and their electrochemical behavior studied. The electrochemical oxidation of hydrogen was investigated in a three -electrode cell using a ruthenium sulfide loaded gas diffusion electrode as the working electrode with humidified hydrogen containing small amounts of carbon monoxide. Results on the activity and the effects of carbon monoxide with reference to a standard platinum electrode measured at the same conditions show that ruthenium sulfide has a lower activity for hydrogen oxidation but is not susceptible to CO poisoning.
Corrosion-Resistant Tantalum Coatings for PEM Fuel Cell Bipolar Plates
Authors: Gladczuk Leszek , Joshi Chirag , Patel Anamika , Guiheen Jim , Iqbal Zafar , Sosnowski Marek
Published: April 2011

Tantalum is a tough, corrosion resistant metal, which would be suitable for use as bipolar plates for proton exchange membrane (PEM) fuel cells, if it was not for its high weight and price. Relatively thin tantalum coatings, however, can be deposited on other inexpensive and lighter weight metals, such as aluminum and steel, providing a passive protection layer on these easily formed substrates. We have successfully deposited, high quality α (body-centered-cubic, bcc) and β (tetragonal) phase tantalum coatings that were a few micrometers thick by dc magnetron sputtering on steel and aluminum. The growth of the thermodynamically preferred body-centered-cubic (bcc) tantalum phase was induced by a choice of deposition conditions and substrate surface treatment. The microstructure and corrosion resistance of the α-phase in an environment approximately simulating the electrochemical conditions used in a PEM fuel cell were investigated under potentiodynamic conditions. Preliminary potentiostatic measurements of a β-phase sample are also presented.
A Numerical Study of Compaction of Dry Granular Material
Authors: Sulsky Deborah
Published: April 2011

The material-point method is used to examine numerically the macroscopic stress-strain response of a granular sample under compression. The simulations reproduce experimental observations of the large stiffening that occurs as the granular bed becomes packed. We also show the network of force chains that forms and how the character of contacts between grains changes for large deformations. Finally, we examine the probability distribution of forces and observe exponential distributions above the mean with a small peak at the mean for small deformations, and a transition to a larger peak at larger deformations.
The NSF NSDL GREEN Digital Library:

G

reen's Functions

R

esearch And

E

ducation

E

nhancement

N

etwork
Authors: Bartolo Laura M. , Powell Adam C. , Shreve Gregory M. , Tewary Vinod K.
Published: April 2011

Green's functions are powerful mathematical tools with strong pedagogical value providing not only solutions to difficult problems but also visualization for understanding phenomena. The majority of upper division engineering and materials science students receive very little exposure to Green's functions and the boundary element method. The Green's Functions Research and Education Enhancement Network (GREEN) Digital Library which the authors are developing will, therefore, play an important role in undergraduate and graduate education. The National Science Foundation has launched the National Science, Mathematics, Engineering, and Technology Education Digital Library (NSDL) program to stimulate and sustain continual improvements in the quality of science, mathematics, engineering, and technology education. The NSDL Program is a major digital library initiative and the GREEN Digital Library is a collaboration of the Center for Theoretical and Computational Materials Science of the Materials Science and Engineering Laboratory at the National Institute of Standards and Technology, Kent State University, and the Massachusetts Institute of Technology. This paper describes the primary components of the GREEN Digital Library, an organized collection of educational materials integrating research, education, and application of Green's functions to serve undergraduate and graduate communities:

1. Problem Bank: A bank of available “real-world” problems, introduced by industrial participants.

2. Code Bank: Working code for solved Green's functions routines.

3. Archive: A list of citations to relevant literature, and published / unpublished works subject to copyright restrictions, with links elsewhere for additional information.

4. Teaching Bank: A collection of lecture / course notes from existing university courses, as well as providing a forum for discussion of approaches to teaching this material.
Web-Based Data Analysis and Feedback for General Chemistry Laboratory: Improving Analysis with Timely, Distance Feedback
Authors: Lomax Joseph F. , Dillner Debra K. , Teichert Melonie A.
Published: April 2011

In a general chemistry course, while the hands-on experience of the laboratory is important, the goals of the laboratory are not fulfilled until the calculations and analysis are complete. Quite often students are capable of following laboratory instructions and generating excellent data, only to fail in the data analysis, which rarely occurs in the confines of the laboratory or the presence of the instructor. All too often, students are unable to learn important information from the interpretation of experimental results and draw correct conclusions because they make calculational errors, which are most often discovered by the instructor in the grading process. There is an opportunity for distance learning to help bridge the gap between collection of data and its correct analysis. At the United States Naval Academy (USNA), we have developed a Web-based system where the students input their data and calculational results into a web form with immediate feedback. The students are then allowed to correct their errors and resubmit. This system has been in successful use for 5 years. A description of a typical experiment will be discussed along with an assessment of student and faculty satisfaction with the program.
High Frequency Loss Mechanism in Polymers Filled with Dielectric Modifiers
Authors: Obrzut J. , Anopchenko A. , Kano K. , Wang H.
Published: April 2011

We analyzed the high frequency dielectric relaxation mechanism in high-k composite materials using film substrates made of low loss organic resin filled with ferroelectric ceramics and with single wall carbon nanotubes (SWNT). We performed broadband permittivity measurements of high-k film substrates at frequencies of 100 Hz to about 10 GHz. In order to analyze the effect of the dielectric thickness, dielectric constant, loss and conductive loss on the impedance characteristics, we used a High Frequency Structure Simulator to perform a full wave numerical analysis of several power planes. Small angle neutron scattering (SANS) was used to probe the dispersion of SWNTs in polymer matrices. It was found that organic-ceramic composites exhibit an intrinsic high frequency relaxation behavior that gives rise to frequency dependent dielectric loss. The highest frequency relaxation process dominates the overall loss characteristic. In the case of polymers modified with SWNTs, we observed that 2% mass fraction of p-doped semi-conducting SWNTs increases the dielectric constant by 3 orders of magnitude, in apparent violation of the mixing-rule. The hybrid material appears to have preferential coupling within the dispersed phase. The experimental data and numerical simulation indicate that these materials can play a significant role as embedded passive devices with functional characteristics superior to that of discrete components.
Tunability of Bi-rich BZN Cubic Pyrochlore Thin Films by Reactive Sputtering
Authors: Back Dong Hyuk , Lee Yoon Seop , Hong Young Pyo , Moon Joong Ho , Ko Kyung Hyun
Published: April 2011

(Bi3xZn2−3x)(ZnxNb2−x)O7 thin films (x=1/2 and 2/3) have potential great for tunable RF and microwave devices due to medium dielectric constant and low dielectric loss. The tunable dielectric properties of Bi-rich, (Bi1.5 Zn0.5)(Zn0.5 Nb1.5)O7 thin films were investigated. To make Bi-rich cubic pyrochlore thin films, Bi2O3–ZnO–Nb2O5 monoclinic pyrochlore ceramic targets were used in reactive RF magnetron sputtering process. Substrate heating was employed to improve surface morphology and tunability. As-deposited films were crystallized or amorphous state depending on substrate temperature. All films were annealed at 600°C ∼ 800°C for 3 hours in the air. There were no zinc niobate secondary phases in the films before and after post-annealing, while quite significant amount BZN thin films were found in sputtered using cubic pyrochlore ceramic targets, especially after post-annealing. It was found that Bi-rich BZN films have much larger tunability when as-deposited phase are amorphous. The maximum tunability 38% was obtained when substrate is heated to 350°C and composition of films is close to exact stoichiometric cubic BZN.
High Frequency, High Density Interconnect Using AC Coupling
Authors: Franzon Paul , Kingon Angus , Mick Stephen , Wilson John , Luo Lei , Chandrasakhar Karthik , Xu Jian , Bonafede Salvatore , Huffman Alan , Statler Chad , LaBennett Richard
Published: April 2011

AC Coupled Interconnection (ACCI), in conjunction with buried solder bump technology, provides a method to achieve signal I/O pitches of less than 75 μm and signaling rates greater than 5 Gbps per I/O on integrated circuits, while preserving excellent signal integrity. This paper presents a summary of approaches, status, and discusses material issues important to performance.
Microstructural Evolution of Cu/Ta/GaAs Multilayers with Thermal Annealing
Authors: Wu Wei-Cheng , Chen Chang-You , Lee Chen-Shih , Chang Edward Yi , Chang Li
Published: April 2011

Copper metallization for GaAs was evaluated by using Cu/Ta/GaAs multilayers for its thermal stability. A thin Ta layer of 30 nm thickness was sputtered on the GaAs substrate as the diffusion barrier before copper film metallization. As judged from the results of sheet resistance, X-ray diffraction, Auger electron spectroscopy and transmission electron microscopy, the Cu/Ta films on GaAs were very stable up to 500 °C without Cu migration into GaAs. After 550 °C annealing, the interfacial mixing of Ta with GaAs substrate occurred, resulting in the formation of TaGa2 and TaAs2, and the diffusion of Ga and As through the Ta layer formed the Cu3Ga and Cu3As phases at the Cu/Ta interface. After 600 °C annealing, the reaction of GaAs with Ta and Cu formed TaAs and Cu3Ga, as a result of Cu migration and interfacial instability.
Ferroelectric memory in La substituted Bi4Ti3O12 thin films
Authors: Melgarejo R. E. , Tomar M. S.
Published: April 2011

The recent demonstration of large ferroelectric memory in rare earth substituted Bi4Ti3O12 attracted a lot of research interest in this material. Bi4-xLaxTi3O12 was synthesized by sol-gel route for different compositions: x = 0.00, 0.46, 0.56, 0.75, 0.95 and thin films were deposited by spin coating on Pt (Pt/TiO2/SiO2/Si) substrate. The post annealed films at 700°C were studied for their structural studies using x-ray diffraction and Raman spectroscopy. The prominent effect of La substitution is observed in low frequency Raman modes. X-ray diffraction and Raman studies show that the film growth was c-axis suppressed. Using improved contacts to Pt substrate, ferroelectric polarization Pr = 51 μC/cm2 has been achieved for 0.63 μm thick film of composition: x = 0.56 (BLT56) without appreciable fatigue.
Sample Geometry Effects on Electric-Field-Induced Displacements in Piezoelectric Thin Films Measured by Atomic Force Microscopy
Authors: Okino Hirotake , Matsuda Hirofumi , Iijima Takashi , Yokoyama Shintaro , Funakubo Hiroshi , Yamamoto Takashi
Published: April 2011

Electric-field-induced displacements of PZT film capacitor Pt/PZT(5μm)/Pt/SiO2/Si(100) were calculated by finite element method with various parameters of sample geometry: the diameter of top electrode φ TE ranging from 0.2 μ m to 1000 μ m and whether PZT film was continuous or side-etched. If φ TE was larger than 40μ m, surface longitudinal displacement (corresponding to AFM-measured strain) was not equal to net longitudinal displacement of PZT film, including a contribution of the bending motion of substrate. In contrast, if φ TE was smaller than 4μ m and PZT film was continuous, effective d33 evaluated from net longitudinal displacement was smaller than intrinsic d33, because the side PZT film clamped the edge of the capacitor disk and prevented the whole disk from elongating longitudinally. It was also revealed that d33 value calculated from net longitudinal displacement of PZT film depended on the Poisson's ratio of PZT and was not equal to intrinsic d33, excluding the case that φ TE was smaller than 4μ m and PZT film was side-etched. In conclusion, it is suggested that smaller φ TE (< 4μ m, in our case) and side-etch treatment permit a precision measurement of d33; however this condition is difficult to be satisfied experimentally.
Simulation of Phonon-Polariton Generation and Propagation in Ferroelectric LiNbO3 Crystals
Authors: Ward David W. , Statz Eric , Stoyanov Nikolay , Nelson Keith A.
Published: April 2011

We simulate propagation of phonon-polaritons (admixtures of polar lattice vibrations and electromagnetic waves) in ferroelectric LiNbO3 with a model that consists of a spatially periodic array of harmonic oscillators coupled to THz electromagnetic waves through an electric dipole moment. We show that when this model is combined with the auxiliary differential equation method of finite difference time domain (FDTD) simulations, the salient features of phonon-polaritons may be illustrated. Further, we introduce second order nonlinear coupling to an optical field to demonstrate phonon-polariton generation by impulsive stimulated Raman scattering (ISRS). The phonon-polariton dispersion relation in bulk ferroelectric LiNbO3 is determined from simulation.
Electrode effect on microwave properties of ferroelectric (BaxSr1-x)TiO3 thin films
Authors: Kim Won-Jeong , Kim Sang-Su , Song Tae-Kwon , Moon Seung Eon , Kim Eun-Kyoung , Kwak Min-Hwan , Han Seok-Kil , Kim Young-Tae , Ryu Han-Cheol , Lee Su-Jae
Published: April 2011

Microwave properties of coplanar waveguide (CPW) transmission lines fabricated on high dielectric materials, such as ferroelectric Ba1−xSrxTiO3 films, are highly sensitive on the dimension and shape of electrodes. A small change in device dimension affects the total electrical length of the CPW, which may mislead the effective dielectric constant of the dielectric layer. Furthermore, extracting dielectric constant of high-k thin films from the measured microwave properties, such as S-parameters, is very difficult. The well known a modified conformal mapping method frequently exhibits an inconsistent dielectric constant for CPW on high-k materials. CPW transmission lines were fabricated on high-k thin films, ferroelectric Ba0.6Sr0.4TiO3, which were deposited by the pulsed laser deposition with partial oxygen backgrounds. A large phase shift angle of 100° at 10 GHz was observed from the CPW (gap = 4 μm, length = 3 mm) with a 40 V of dc bias, which supports that the idea of the tunable microwave device application using ferroelectrics films. The dielectric constant of the thin ferroelectric film was extracted from the dimension of the CPW (gap, width, length) and the measured S-parameters by a modified conformal mapping. However, the dielectric constant of the ferroelectric thin film calculated by a modified conformal mapping exhibits a gap dependency; dielectric constant (990 ∼ 830) decreases with increasing gap size (4 ∼ 19 μm, respectively). For comparison, dielectric properties have been extracted by extensive EM-simulation using a HFSS™ (Ansoft) with observed dimensions of CPW devices. Total phase, which is closely related with the dielectric constant of the film, is strongly affected by gap size, film thickness, and slanted angle of CPW.
Selection of Materials and Sensors for Health Monitoring of Composite Structures
Authors: Kessler Seth S. , Spearing S. Mark
Published: April 2011

Embedded structural health monitoring systems are envisioned to be an important component of future transportation systems. One of the key challenges in designing an SHM system is the choice of sensors, and a sensor layout, which can detect unambiguously relevant structural damage. This paper focuses on the relationship between sensors, the materials of which they are made, and their ability to detect structural damage. Sensor selection maps have been produced which plot the capabilities of the full range of available sensor types vs. the key performance metrics (power consumption, resolution, range, sensor size, coverage). This exercise resulted in the identification of piezoceramic Lamb wave transducers as the sensor of choice. Experimental results are presented for the detailed selection of piezoceramic materials to be used as Lamb wave transducers.
Coupled Magneto-mechanical Modeling of Composites Containing Aligned Ferromagnetic Particles
Authors: Yin Huiming , Sun Lizhi
Published: April 2011

The objective of this paper is to investigate effective magneto-mechanical behavior of composites containing aligned ferromagnetic particles. The effective magneto-elastic properties and the overall magnetostriction of the composites are derived by considering the pair-wise interaction between ferromagnetic particles. For the composites with soft elastomer matrix, the microstructural configuration rapidly changes with the magnetic and mechanical loads so that the local magnetic and elastic fields are fully coupled. This model accounts for the coupled magneto-elastic interaction and pair-wise interaction between particles. The results show that the Young's modulus along the particle-chain direction is reduced and the shear modulus is increased under the applied magnetic field. Predictions from the proposed model are compared with available experimental data and other models.