bluuebunny/crossref_metadata_2025 huggingface dataset:
Impurity Free Vacancy Disordering Using Phosphorus Doped SiO2 and Pure SiO2 Caps
Authors: Cusumano P. , Saher Helmy A. , Ooi B. S. , De La Rue R. M. , Bryce A. C. , Marsh J. H.
Published: April 2011

A spatially selective quantum well intermixing process, using phosphorus-doped silica (SiO2:P) containing 5 wt% P to inhibit intermixing and pure SiO2 to enhance intermixing, is presented. The SiO2:P cap has been found to suppress bandgap shifts in both p-i-n and n-i-p GaAs/AlGaAs quantum well laser structures, with bandgap shift differences as large as 100 meV observed from samples capped with SiO2 and with SiO2:P after rapid thermal processing at temperatures as high as 950 °C for 60 s. Extended cavity ridge lasers exhibited low threshold currents with TE losses of 3.2 cm−1 measured in the passive waveguide sections at the lasing wavelength using the Fabry-Perot resonance method. This value is among the lowest reported so far using an impurity-free disordering technique.
Xps Study of the PbSe/CaF2(111) Interface Grown on Si by MBE
Authors: Fang X. M. , Liu W. K. , McCann P. J. , Strecker B. N. , Santos M. B.
Published: April 2011

The initial stages of MBE growth of PbSe on CaF2/Si(111) were studied by in situ XPS. The surface reaction between CaF2 and elemental Se is also studied as a comparison. Ca 2p, F 1s, Pb 4f and Se 3d peaks all shift to lower binding energies (1.2 – 1.6 eV) with increasing PbSe coverage. This indicates a strong interaction between the PbSe overlayer and the underlying CaF2 and the formation of Pb-F and Ca-Se interfacial bonds. No chemically graded reaction products are detected at the PbSe/CaF2 interface. A transition layer of about 6 ML is observed which can be partially accounted for by the open 3D structure of CaF2 where three layers of atoms are available for bonding with the deposited material. This structure allows interpenetration of the PbSe and CaF2 layers which necessarily leads to a thin transition layer. Based on our XPS results, we propose a model for the bonding arrangements at the PbSe/CaF2(111) interface.
Mechanisms of Shear-Induced Solid-State Reactions
Authors: Gilman J. J.
Published: April 2011

Both experiments and band-structure calculations indicate that shear strains lead to closure of energy band gaps in periodic solids, and closure of the LUMO-HOMO gaps in molecules (this is also expected for non-metallic glasses). It allows athermal and ultrafast mechano-chemical reactions to occur. Simple models account for the phenomena. For periodic solids, shear shortens one axis and extends another. In contrast, hydrostatic compression causes both axes to contract. Thus the former shifts the band gaps oppositely for the two directions, causing a reduction in the minimum gap. For molecules, shear tends to increase the bonding orbitals while decreasing the antibonding orbitals, thereby reducing the LUMO-HOMO gaps. The models are consistent with band structure models for diamond.

Shear-induced gap reductions account for the athermal chemical reactions observed by Bridgman, Enikolopyan, Boldyrev, and others. They account for the ultra-fast reactions that occur in explosives.
Eu2+ Luminescence Color: a Structure-Property Relationship
Authors: Keszler Douglas A. , Diaz Anthony
Published: April 2011

Structural and spectroscopie characteristics of a series of Eu 2+-doped Sr and Ba borates have been studied to establish simple correlations among emission color, excitation energies, Stokes shifts, and O atom environments.
Crystal Chemistry and Electronic Properties of the N = 2 Ruddlesden-Popper Manganates: Unconventional CMR Materials
Authors: Battle P. D. , Blundell S. J. , Cox D. E. , Green M. A. , Millburn J. E. , Radaelli P. G. , Rosseinsky M. J. , Singleton J. , Spring L. E. , Vente J. F.
Published: April 2011

The crystallography and electronic properties of the Ln2-xSr1+xMn2O7 manganese oxides adopting the n = 2 Ruddlesden-Popper (RP) structure are discussed, focusing on the structural phase diagrams and electronic properties in the vicinity of the Mn +3.5 oxidation state and in particular the ease of synthesis of single phases of these materials.
The Synthesis of Transition Metal Sulfides and Sulfo-Salt Crystals in Hydrothermal Brines
Authors: Kolis J. W. , Korzenski M. B.
Published: April 2011

A new procedure for the synthesis of transition metal sulfosalts in hydrothermal brines is presented. Large, well formed crystals of metal antimony sulfides can be prepared under appropriate conditions in supercritical brines. A new compound prepared by this method, MnSb2S4, is structurally characterized.
Synthesis, Structures and Magnetic Properties of a Family of One-Dimensional Oxides
Authors: Zur Loye H.-C. , Núñez P. , Rzeznik M. A.
Published: April 2011

The one-dimensional compounds Sr3MgPtO6, Sr3MgIrO6, Sr3MgRhO6, Sr3GdRhO6, have been synthesized and structurally characterized by Rietveld refinement of powder X-ray diffraction data. All four compounds are isostructural with the rhombohedral K4CdCl6-type structure. The structure consists of infinite one-dimensional chains of alternating face-shared MO6 octahedra (M = Pt, Ir, Rh) and M′O6 (M′ = Gd, Mg) trigonal prisms. The strontium cations are located in a distorted square antiprismatic environment. Magnetic susceptibility data show that both Sr3MgIrO6 and Sr3MgRhO6 obey the Curie-Weiss law with θ = −6(1) K, and θ= −15(3)K, respectively. Sr3GdRhO6 obeys the Curie law with μeff = 7.80 B.M, consistent with an oxidation state of +3 for both rhodium and gadolinium.
Crystallization of Perovskites from Solutions
Authors: Maurin I. , Barboux P. , Boilot J. P.
Published: April 2011

LaMnO3 and PbZrO3 perovskites have been synthesized through coprecipitation and sol-gel techniques. After the drying and calcination steps, amorphous mixtures of oxides have been obtained. They are unstable towards phase separation. Therefore, their homogeneity and reactivity strongly depend on the parameters of the calcination, such as the temperature and heating rate. In all cases, the perovskite structure crystallizes around 600°C through nucleation- or diffusion-limited kinetics. The reaction rate depends on the history of the material. A mechanistic interpretation of the reaction, based on the similarity between the structures of PbO, ZrO2, Mn2O3 and La2O3 is proposed.
Domainlike Organizations in Ferroelectrics Containing Quenched Randomness
Authors: Viehland Dwight , Kim M. Y. , Xu Z. , Li Jie-Fang
Published: April 2011

Transmission electron microscopy studies of the (1-x)Pb(Mg1/3Nb2/3)O3-(x)PbTiO3 (PMN-PT (1-x)/x) crystalline solution have been performed for x=0.1, 0.2, 0.35, and 0.60. Bright-field imaging has revealed a common sequence of domain-like states with increasing x. Normal micron-sized ferroelectric domains were found for x>0.40. Tweed-like structures were found for x∼0.35. These tweedlike structures are similar to those previously reported in pre-martensitic states. Paraelectric clusters were found for x<0.30. The paraelectric cluster state was characterized by the lack of self-assembly amongst embryos and the presence of relaxor behavior in the macroscopic response characteristics. The composition PMN-PT 65/35 was then modified with La for a detailed study of the transition between the tweed-like precursor and paraelectric cluster states with increasing impurity content.
Synthesis of Terbia Doped Yttria Stabilized Zirconia Thin Films by Using the Electrostatic Spray Deposition (ESD) Technique
Authors: Stelzer N.H.J. , Goossens A. , Schoonman J.
Published: April 2011

Terbia doped yttria stabilized zirconia (Tb-YSZ) thin films have been deposited on various substrates by applying the electrostatic spray deposition (ESD) technique. Yttrium- and zirconium-acetylacetonate as well as terbium-acetate hydrate were used as precursors. Butyl carbitol-ethanol mixed alcohol's with ratios of 50:50 vol% and 80:20 vol% were used as solvents for precursor solutions with total metal concentrations between 0.09 M and 0.009 M. Tb-YSZ thin films were deposited at temperatures between 520 K and 730 K. Surface morphology, chemistry, and crystal structure were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD). The Tb-YSZ layers consist of a fully stabilized cubic phases. The surface morphology of deposited Tb-YSZ layers can be controlled by changing different deposition parameters. The adhesion of Tb-YSZ to the substrate can be improved by a high temperature treatment.
Defects and Ion Transport Properties of Yttrium Doped Zirconia
Authors: Chaba P. J. , Ngoepe P. E.
Published: April 2011

A comparison of calculated and experimental temperature variation of elastic constants were used to predict types of oxygen—vacancy dopant clusters in yttria stabilised cubic zirconia, which serves as an electrolyte in solid oxide fuelcells. Such clusters were incorporated in supercells set up for molecular dynamics studies, where oxygen transport properties were investigated at concentrations of 9.4 and 24 mol % of yttrium oxide and up to 1600K.
Mechanochemical Preparation of Ceramic Metal Oxide Electrolytes with Enhanced Conductivity
Authors: Vitlov-Audino R. , Lincoln F. J.
Published: April 2011

In this study, mechanochemical milling (also known as mechanical alloying), has been used as an alternative means of synthesis of ceramic metal oxide electrolytes at room temperature and compared to the conventional calcination methods. The oxide electrolytes prepared by mechanical milling, were, the lanthanide-doped fcc Bismuth Oxides and Cerium Oxides, both of which are oxygen deficient. Conductivities for some of these milled oxides, measured by the four probe technique, were found to be enhanced when compared to those for conventionally prepared materials.
Chemical Diffusion in Mixed Conductors with Comparable Ionic and Electronic Transport Numbers: Results for Ag1.92Te
Authors: Preis W. , Sitte W.
Published: April 2011

Galvanostatic polarization of a mixed conductor located between an ionically blocking electrode and an electronically blocking electrode in an asymmetric electrochemical cell is treated in detail. Evaluation formulae for the determination of the chemical diffusion coefficient of mixed conductors with comparable ionic and electronic transport numbers are introduced. They allow the determination of the chemical diffusion coefficient of Ag1.92Te as a function of composition at 160°C from galvanostatic polarization and depolarization experiments on the asymmetric cell Ag | AgI | Ag1.92Te | Pt. The chemical diffusion coefficient shows composition dependent values between 0.002 and 0.004 cm2s-1. The electronic transport numbers are obtained independently from four-point van der Pauw measurements with typical values around 0.8–0.9.
Characterization of Proton Conducting Antimonic Acids with Amorphous, Cubic and Monoclinic Structures
Authors: Sakka Y. , Sodeyama K. , Uchikoshi T. , Ozawa K. , Amano M.
Published: April 2011

Powders and films of amorphous, cubic and monoclinic antimonic acids are prepared. Their water sorptioh isotherms and the water desorption spectra are measured. The protonie conductivities are very sensitive to water vapor pressure and are discussed with the amount of water. The amorphous and cubic antimonic acids contain larger amounts of water than the monoclinic acid, which can be attributed to the existence of micropores in the structures.
Capillary Condensation of Light Hydrocarbons in MCM-41 - Type Mesoporous Materials
Authors: Ioneva M. A. , Mallinson R. G. , Harwell J. H.
Published: April 2011

The MCM-41 family of surfactant templated materials were used as model mesoporous sorbents for storage of light hydrocarbon vapors, by utilizing the phenomenon of capillary condensation. The experimental data show that, because of the fine tunability of MCM-41 type materials (mesopore diameter was controlled between 20 and 40 Å), the onset of capillary condensation can be controlled, and from here the point of achieving liquid-like fluid density in the pores. Such a unique characteristic makes the MCM-41 family of materials a potential media for sorptive fractionation.
Catalysts Supported by Porous Ceramic Layers on Ceramic or Metallic Substrates
Authors: Geus John W. , Van Giezen J.
Published: April 2011

After mentioning the need for integration of the catalyst and the catalytic reactor, it is argued that thin (thickness up to about 50 μm) porous layers applied on ceramic or metallic surfaces are presenting interesting possibilities for the development of new catalytic reactors. The first type of reactions that can benefit from the new reactors are liquid-phase reactions catalyzed by a solid. Especially the selectivity of the reactions can be significantly improved. The second type of reactions are gas-phase reactions with a large thermal effect. It is argued that the rate of transport of thermal energy can be greatly improved by using sintered metal bodies within the reactor coated with highly porous ceramic layers. Finally utilization of thin ceramic porous layers in separations combined with catalytic reactions is shortly dealt with.

A very efficient procedure for application of the porous ceramic layers is presented, viz., pyro-lysis of thin layer of silicone rubber or analogous compounds. Addition of, e.g., aluminum or titanium ions can be used to control the thermostability and the pore-size distribution of the layers resulting after combustion of the organic constituents.
Highly Dispersed Partially Stabilized Zirconias: Synthesis, Bulk and Surface Properties, Performance in the Selective Reduction of Nitrogen Oxides by Propane in the Excess of Oxygen
Authors: Sadykov Vladislav A. , Ivanova A. S. , Alikina G. M. , Ivanov V. P. , Bulgakov N. N. , Kharlanov A. N. , Lunina E. V. , Lunin V. V. , Zubareva N. A. , Matyshak V. A. , Rozovskii A. Ya.
Published: April 2011

Bulk and surface properties of dispersed partially stabilized zirconias (PSZ) prepared via coprecipitation of zirconium and alkaline-earth metal hydroxides have been studied by XPD, SIMS, IR spectroscopy of surface hydroxyls and adsorbed C.O. For Sr- and Ca-PSZ, the number of the Lewis acid centers, surface concentration of the guest cation and Zr-O bonding strength at the surface have been found to deviate substantially from the values predicted by a bulk truncation model, while for Ba-PSZ it seems to be valid. A local reconstruction of the near-surface layer into the perovskite-like structure was proposed for the first two systems, which explained satisfactorily their surface properties including catalytic performance in the selective reduction of nitrogen oxides by propane in the excess of oxygen. Such reconstruction is probably facilitated by segregation of the guest cations in the subsurface layer. The driving force for this process depends upon site preference of the alkaline-earth cations to cubooctahedrons and steric factors.
Synthesis and Characterization of GaPO4 Molecular Sieves Using Metal Complexes as Templates
Authors: Balkus Kenneth J. , Kim Sung J. , Sargeson Alan M.
Published: April 2011

Our work on the preparation of zeolite ship-in-a-bottle complexes, which involves the encapsulation of metal complexes during zeolite synthesis, encouraged us to explore the relatively unknown structure directing properties of metal complexes. In particular, we have shown that bis(pentamethylcyclopentadienyl) cobalt(III) hydroxide, Cp*2CoOH was a template for the novel high silica zeolite UTD-1 which is the first zeolite having greater than a 12 membered ring pore structure. We have extended this strategy to other oxide compositions and metal complexes. In this paper we describe the preparation and characterization (XRD, SEM) of the gallophosphates Cloverite and UTD-10 using the metal complex [Co(NMe3)2sar]5+ (where (NMe3)2sar = 1,8-bis(trimethylammonio)-3,6,10,13,16,19-hexaazabicyclo[6.6.6]-icosane) as the template.
Synthesis of Hydrotalcites Using Microwave Irradiation
Authors: Fetter G. , Bosch P. , Hernandez F. A.
Published: April 2011

Hydrotalcites are mineral anion exchangers whose exchange capacity is determined by the amount of structural magnesium atoms (octahedrally coordinated) substituted by aluminium atoms. In this work we study the synthesis of hydrotalcites using a domestic microwave oven at room pressure. The effect of the oven power on the composition and on the resulting structure of two hydrotalcites differing on their nominal Al/Al+Mg ratio is presented.
A Comparison Between the Structural and Catalytic Properties of Supported W2C, WC and WC1−x
Authors: Choi Saemin , Thompson Levi T.
Published: April 2011

A series of γ-Al2O3 and SiO2 supported tungsten carbides was synthesized by the temperature programmed reaction of supported tungstates with CH4/H2 mixtures. The three known phases, W2C, WC and WC1−x, were evaluated as butane dehydrogenation catalysts. The microstructure and composition of the supported carbides depended on the loading and final synthesis temperature. The low and medium loaded materials were x-ray amorphous suggesting highly dispersed carbide domains on the support. The high loaded materials possessed small crystallites of W2C, WC or WC1-x. The supported carbides were as active as a commercial dehydrogenation catalyst with comparable selectivities in several cases. The butane conversion activity decreased in the following order: W2C > WC > WC1-x. The dehydrogenation selectivity decreased as the activity increased. The results suggest that there were two different types of sites, those catalyzing the selective dehydrogenation of butane and those capable of butane hydrogenolysis. The activity of these latter sites declined significantly with time on stream. We believe the hydrogenolysis activity was due to acid sites on the supported carbides.
Preparation and Characterization of High-Surface-Area Aluminum Nitride Thin Films
Authors: Monie S. A. , Pantano C. G.
Published: April 2011

Free-standing aluminum nitride (AlN) films were prepared by ammonia heat-treatment of pseudoboehmite [AIO(OH)] gels derived from an alumina sol. Supported films on sapphire substrates were also made by spin-coating the alumina sol, followed by ammonia nitridation. The conversion of the specimens to AIN as a function of heat-treatment temperature was studied using various characterization techniques.

For the free-standing films, X-ray diffraction (XRD) showed that upon ammonia treatment, the specimens were first transformed from pseudoboehmite to η-alumina and finally to A1N above 1000°C. 27Al magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy confirmed the appearance of Al[N]4 coordination at 1000°C, indicative of AlN. Complete conversion to AlN was achieved after 5 hour nitridation at 1200°C. The 1200°C heat-treated films consisted of crystallites of AlN in the size range 0.01 − 0.15 μm, with pores between 0.03 − 0.25 μm in diameter, as observed by TEM/electron diffraction analyses. These films had BET surface areas of approximately 25 m2/g. Nitridation of the supported films to AlN occurred at lower temperatures (∼900°C), as shown by secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS).
Active Sites of Iron Catalysts for Oxidation Reactions - H2O Oxidation and H2O2 Decomposition
Authors: Kuznetsov V. L. , Elizarova G. L. , Usoltseva A. N. , Matvienko L. G. , Shchegolikhina O. I.
Published: April 2011

Systems containing metal ions stabilized in Si-O matrix are perspective for the development of new selective oxidation catalysts. The comparative study of the following catalysts were performed to elucidate the influence of structural factors on the catalytic properties of iron systems in the reactions H2O oxidation, H2O2 decomposition, N2O decomposition and 16O2 ⇔ O18O2 exchange. The following catalysts were used: A) carbon-supported polyhedral silsesquioxanes (PhSiO1.5)12(MO)nL ((MO)n = (FeO)6, Fe2Ni4O6, (NiO)6; L=ROH, H2O); B) Fe-containing zeolites ZSM-5 (0.1−3.5 wt.% Fe); C) hydroxocomplexes Fe4(OH)10SO4 and NaFe3(OH)6(SO4)2). Fe silsesquoxanes in contrast to Fe-ZSM5 do not activate N2O decomposition and isotopie oxygen exchange. However, they are active in H2O oxidation and H2O2 decomposition. It was found that both reactions proceed via nonradical mechanism in the presence of Fe heterogeneous catalysts. For H2O oxidation active site contains at least two Fe atoms situated at appropriate distance from each other. H2O2 decomposition can proceed with participation either one and two metal active sites.
Effects of Potassium Chemisorption on the Electronic Structure of VxOy/TiO2 Surfaces
Authors: Parmigiani Fulvio , Depero Laura E. , Sangaletti Luigi
Published: April 2011

X-ray photoelectron spectroscopy of pure and K chemisorbed VxOy/TiO2 powders are reported. Core-line and valence band spectra suggest the presence of vanadium open shell ions on the pure VxOy/TiO2 interface, whereas potassium vanadate seems to form after K chemisorption. That results in the presence of a significant amount of gap states, with vanadium character, just above the O2p band edge, for the pure VxOy/TiO2 powder, while K chemisorption, reducing significantly the open shell vanadium ions, quenches the gap emission in the XPS valence band spectra.
Possible Causes of the Change of Dynamics in Glass-Forming Materials Subjected to Reduced Dimension
Authors: Ngai K. L. , Rizos A. K.
Published: April 2011

There is currently many ongoing investigations of the change in the glass transition temperature when a material is reduced in dimension from the normal bulk state. The reduction in dimension can be accomplished by casting the material as thin films with or without a substrate or putting it in nanometer size pores. In this work, we explore possible causes of the change in dynamics of the bulk material when the glass-former is subjected to such modifications. The existence of a growing cooperative length scale L(T) with decreasing temperature in bulk fragile glass-forming liquids reaching the size of approximately 1.5–2.0 nm at the glass transition temperature is the basis of our consideration. When the reduced dimension is comparable to L(Tg), cooperative dynamics within a lengthscale equal to L(Tg) can no longer be maintained in all three dimensions throughout the sample. The imposed reduction of the cooperative length scale speeds up the dynamics and causes a reduction of the glass transition temperature. For polymeric glass-formers particularly at higher molecular weights, reduction of one dimension in thin films engenders orientation of the polymer chains when their radius of gyration becomes comparable to the film thickness. The latter is known to cause also a reduction of the glass transition temeperature.
Dynamics in a Nonfragile Glass-Forming Liquid
Authors: Rufflé B. , Beaufils S. , Etrillard J. , Gallier J. , Toudic B. , Ecolivet C. , Coddens G. , Ambroise J. P. , Guéguen E. , Marchand R.
Published: April 2011

The dynamics of Na0.5Li0.5PO3 (Tg = 515 K, Tm = 749 K) a non fragile glass forming liquid has been investigated over a large temperature range (300 − 1000 K.) and in a wide energy window using various experimental techniques. The susceptibility spectra obtained by coherent neutron scattering and depolarized light scattering between 1 and 104 GHz show mainly two contributions: a low frequency vibrational peak, the so-called Boson peak and a quasielastic component, referred to the βfast process in the mode coupling theory (MCT).

The data are discussed in relation to the mode coupling theory for the liquid glass transition. In particular, the temperature evolution of the susceptibility height in the βfast region is compatible with a crossover temperature Tc ∼ 620 K which is also deduced from a power law temperature dependence of the structural relaxation timescale. As a secondary βslow process, observed by 31P NMR, decouples from the structural relaxation timescale also below 600 K, a real change in the dynamics seems to occur around Tc ∼ 620 K = 1.2 Tg in this non fragile glass Conning liquid.
A Unified Theory for the Glass Transition Dynamics and its Singularities
Authors: Odagaki T. , Matsui J. , Fujisaki M. , Higuchi M.
Published: April 2011

Vitrification is a gradual freezing process of supercooled liquids, during which a slow process is separated from the fast diffusive and microscopic motions. The slow process is identified as a non-trapped jump motion and can be characterized by the waiting time distribution (WTD) of the elementary relaxation process. We first show that the WTD can be expressed as a power law function in the long time limit in general with modest assumptions. Defining the glass transition temperature by vanishing diffusivity or the divergence of the mean waiting time, we relate the exponent to the Adam-Gibbs parameter Tsc(T) where T is the temperature and sc(T) is the excess entropy. We also show that the divergence of the fluctuation of WTD leads to a cross over in the non-Gaussianity and present a unified view of the dynamics in the vitrification process.
Glass Transition and Ultrasonic Relaxation in Polystyrene
Authors: Sahnoune A. , Piché L.
Published: April 2011

We present measurements of the glass transition and the ultrasonic relaxation modulus in a series of monodisperse polystyrenes. The temperature dependence of the modulus was analyzed using Havriliak-Negami relaxation model (HN) and Vogel-Tammann-Fulcher equation (VTF) for the relaxation time. The results allowed us to determine the fragility index, m, which decreases with increasing molecular weight, Mn. Furthermore, the relaxation time was found to saturate at high molecular weights and varies as Mnp, in the low molecular weight region. The exponent is p≈2 at high temperatures and p ≈ 7 at low temperatures close to Tg.
Time and Ensemble Averaged Dynamic Light Scattering in Orthoterphenyl Above and Below the Glass Transition
Authors: Sidebottom D. L. , Sorensen C. M.
Published: April 2011

While traditional dynamic light scattering is useful for following structural relaxation in the liquid, in the glassy domain the technique is limited by the ultimate patience of the experimentalist; i.e., the structural relaxation can not be measured when the experimental time scale is less than the structural relaxation time. Nevertheless, we show how useful information regarding structural relaxation can be accessed from light scattering in the glass using a novel ensemble-averaged technique. Dynamic light scattering (DLS) measurements performed on glass forming orthoterphenyl show an inequality between time and ensemble average correlation functions near and below the calorimetrie glass transition temperature, Tg, and hence demonstrate ergodicity breaking. Our ensemble averaged measurements provide a measure of the so-called non-ergodicity parameter, fq, below Tg. Our DLS results for orthoterphenyl indicate that the functional form for fq is consistent with Mode Coupling theory predictions, but occurs at the glass transition temperature, Tg≈243K, rather than at TC≈290K as observed in neutron scattering studies.
Molecular Dynamics Simulation of Alkali Borate Glass Using Coordination Dependent Potential
Authors: Park Byeongwon , Cormack Alastair N.
Published: April 2011

The structure of sodium borate glass was investigated by molecular dynamics simulation using coordination dependent potential model. The simulated alkali borate glass consists of basic units, BO3, triangle, BO4 tetrahedra and structural groups such as boroxol ring and triborate units. The coordination of boron is converted from 3 to 4 by adding alkali oxide.
Molecular Dynamics Simulations of Fracture in Amorphous Silica
Authors: Wang Jinghan , Omeltchenko Andrey , Kalia Rajiv K. , Vashishta Priya
Published: April 2011

Fracture in amorphous silica is studied using million-atom molecular dynamics simulations. The dynamics of crack propagation, internal stress fields, and the morphology of fracture surfaces are examined as a function of temperature and strain rate. At 300K and 600K we observe brittle fracture: internal stress increases to a critical value (typically 2 – 3 GPa) and then turns over when the crack reaches a terminal speed on the order of half the Rayleigh wave speed. At 900K crack propagation slows down dramatically due to plastic deformation and the material becomes ductile.
Anomalies of the Fast Relaxation Dynamics at Tg In Strong Glass Formers
Authors: Brodin A. , Torell L. M.
Published: April 2011

Structural dynamics of two network forming glasses, B2O3 and GeO2, has been investigated by Raman scattering over a wide temperature range from ∼10 K to above the respective glass transition temperatures (Tg = 526 K for B2O3 and 800 K for GeO2). The spectra are analyzed in terms of two distinct contributions, related to vibrational and fast relaxational dynamics, respectively, and conventionally referred to as the boson peak (BP) and quasielastic scattering (QS). A quantity proportional to the fast relaxation strength may be deduced from the integral intensity of QS relative to BP of the spectra. It turns out, that for T < Tg the so-obtained QS intensity of the two glasses is similar and smoothly temperature dependent, and can qualitatively be described by e.g. the defect model or the soft potential model. As Tg is passed, there is a pronounced change in behavior and dramatic differences between the two systems are observed. Thus, the fast relaxational dynamics is obviously affected by Tg, a finding which is in contrast to the predictions of the mode coupling theory (MCT) of a single crossover temperature Tc > Tg. Moreover, the experimentally obtained value of the MCT exponent a, describing the shape of the fast dynamics, is by far exceeding the limiting value (a ≈ 0.395) of the theory, the deviation increasing with the strength of the system (a ≈ 0.7 for B2O3 and ≈ 0.9 for GeO2). The observed difference between the two glasses is discussed in terms of the fragility of the system manifested in jumps in the specific heat temperature dependences.
Strong Liquid Behavior of Zr-Ti-Cu-Ni-Be Bulk Metallic Glass Forming Alloys
Authors: Busch Ralf , Masuhr Andreas , Bakke Eric , Johnson William L.
Published: April 2011

The viscosities of the Zr46.75Ti8.25Cu7.5Ni10Be27.5 and the Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass forming liquids was determined from the melting point down to the glass transition in the entire temperature range of the supercooled liquid. The temperature dependence of the viscosity in the supercooled liquid obeys the Vogel-Fulcher-Tammann (VFT) relation. The fragility index D is about 20 for both alloys and the ratio between glass transition temperature and VFT temperature is found to be 1.5. A comparison with other glass forming systems shows that these bulk metallic glass formers are strong liquids comparable to sodium silicate glass. Furthermore, they are the strongest among metallic glass forming liquids. This behavior is a main contributing factor to the glass forming ability since it implicates a higher viscosity from the melting point down to the glass transition compared to other metallic liquids. Thus, the kinetics in the supercooled liquid is sluggish and yields a low critical cooling rate for glass formation. The relaxation behavior in the glass transition region of the alloys is consistent with their strong glassy nature as reflected by a stretching exponent that is close to 0.8. The microscopic origin of the strong liquid behavior of bulk metallic glass formers is discussed.
Structural Studies of Rare-Earth Doped Phosphate Glasses
Authors: Matic A. , Börjesson L. , Wannberg A. , McGreevy R. L.
Published: April 2011

We have performed neutron scattering experiments on rare-earth (La, Pr, Ho) doped phosphate glasses around the metaphosphate composition R(PO3)3. Combining the diffraction experiment with Reverse Monte Carlo simulations we obtain a 3-D model of the structure. Our models propose a rare-earth ion environment primarily consisting of oxygens with the average rare earth-oxygen distances; 2.56, 2.51 and 2.40 Å for the La, Pr and Ho samples respectively. We also observe that the rare earth ions are not uniformly distributed. The first R-R shell is on avergae about 3.3 Å to be compared with a value of 7 Å for a uniform distribution of R ions in the structure. From the models we also conclude that a chain like structure of the phosphate network is in agreement with the experiment.
Atomic Force Probe of Mesoscopic Dielectric and Viscoelastic Fluctuations Near the Glass Transition
Authors: Walther L. E. , Israeloff N. E.
Published: April 2011

We report a new experimental approach to study the glass transition and glassy dynamics on a mesoscopic scale. Non contact atomic force microscopy is employed to measure dielectric fluctuations of glass forming polymers such as PVAc. Force modulation techniques, performed with the same instrument, allow us to study viscoelastic properties. A custom-built variable temperature UHV AFM with exceptional thermal stability utilizing piezoresistive cantilevers was used. First results on PVAc include large fluctuations of the viscoelastic properties as a function of applied stress below the glass transition.
Nitridation of Bioresorbable Phosphate Glass
Authors: Jiang H. , Lacourse W. C.
Published: April 2011

The bioresorbable 10CaO·35Na2O·55P2O5 glass was nitrided by melting the glass under anhydrous ammonia. The nitrided glasses were fiberized at about 720 °C in air. The dynamic and the equilibrium pH value of the glass increases with the increase of nitrogen content. The incorporation of nitrogen not only increases the glass transition temperature, but also improves the chemical durability and makes it easier to fiberize. Further more, the nitrided glass is more resistant to devitrification.
Thermochemistry and Electrical Contact Behavior of Electrode-Thermistor Interfaces
Authors: Cann David P. , Randall Clive A.
Published: April 2011

The electronic structure of electrode-thermistor interfaces will be related to the thermochemical properties of the interface. Sessile drop wetting experiments of metallic electrodes on commercial BaTiO3 PTCR ceramic devices in combination with measurements of the electrical contact properties of the interface through impedance spectroscopy measurements will be used to establish a fundamental perspective of the electrode-ceramic interface. It will be shown that the thermodynamic work of adhesion (Wad), which is the sum of the strengths of chemical interactions present at the interface, can be manipulated by the addition of chemically active elements to the electrode metal which can segregate to the interface and enhance adhesion. This same procedure will be used to modify the important electrical interfacial properties such as the contact resistance and capacitance.
Fiber-Matrix Interfaces in Ceramic Composites
Authors: Besmann T. M. , Stinton D. P. , Kupp E. R. , Shanmugham S. , Liaw P. K.
Published: April 2011

The mechanical properties of ceramic matrix composites (CMCs) are governed by the relationships between the matrix, the interface material, and the fibers. In non-oxide matrix systems the use of compliant pyrolytic carbon or BN have been demonstrated to be effective interface materials, allowing for absorption of mismatch stresses between fiber and matrix and offering a poorly bonded interface for crack deflection. The resulting materials have demonstrated remarkable strain/damage tolerance together with high strength. Carbon or BN, however, suffer from oxidative loss in many service environments, and thus there is a major search for oxidation resistant alternatives. This paper will review the issues related to developing a stable and effective interface material for non-oxide matrix CMCs.
Energetics of Ideal Grain Boundary Fracture in Iron and the Thermodynamic Criterion of Impurity Embrittlement
Authors: Krasko Genrich L.
Published: April 2011

Modeling of grain boundary (GB) relaxation during ideal fracture, and the fracture energetics of a Σ3 (111) GB in Fe was performed using the modified Finnis-Sinclair semi-empirical method, and utilizing the so-called “environment-sensitive embedding energies” of impurity atoms, introduced earlier by the author. The calculations were done for both the clean GB, and GB with the following impurity atoms: H, B, C, N, O, P and S. The ideal fracture was modeled by separating the two halves of crystal normal to the GB, step-wise, minimizing the total crystal energy at every step. The interplanar distances were varied, while the Fe interatomic spacing within the hexagonal planes was held fixed. When the distance between the two crystal halves: one with the impurity and another without, exceeded the interatomic interaction cut-off radius (3.6 Å), two different free surfaces - with and without the impurity - emerged. The GB and surface energies were found both for the pure Fe, and that with impurity atoms at the GB or free surface. Both the (111) GB energy and the (111) surface energy of pure Fe agree well with experimental data and results of previous semi-empirical modeling. In general, the correlation between the embrittling/ cohesion enhancing effect of impurities in GB and the difference between the GB and free surface energies agrees with the thermodynamic criterion of embrittlement.
Compositional Effects on Grain Boundary Dislocation Stability in Pure Aluminum and Aluminum Alloys
Authors: Song S. G. , Vetrano J. S. , Bruemmer S. M.
Published: April 2011

The dissociation of extrinsic grain boundary dislocations in Al, Al-Mg and Al-Mg-Sn alloys was studied at various temperatures to examine the compositional effect on the dissociation process. It was found that both alloying elements (Mg and Sn) hinder the dissociation, however the effect of Sn is more significant even at a very low concentration due in part to grain boundary segregation.
Intergranular Fracture in Neutron Irradiated Vanadium-20 Wt.% Titanium Alloys Undoped and Doped with Phosphorus
Authors: Kameda J. , Bloomer T. E. , Lyu D. Y.
Published: April 2011

This paper presents the effect of neutron irradiation (9.8 × 1024 n/m2 at 438 °C) on the mechanical properties in V-20 wt.% Ti alloys undoped and doped with P using a small punch testing method. The same amount of neutron irradiation-induced hardening, that is almost temperature independent, was observed in undoped and P doped alloys. Neutron irradiation facilitated heterogeneous formation of grain boundary microcracks, not leading to specimen failure, in the undoped alloy. An irradiated undoped alloy showed ductility loss, that is not as much as expected from the easy microcrack formation due to a mixed mode of intergranular and transgranular cracking. Conversely, in the P doped alloy, intergranular microcracking was suppressed and low temperature ductility was improved by the irradiation. The intergranular fracture behavior controlling the ductility change is discussed in terms of the grain boundary composition and yield strength affected by the neutron irradiation.
Formation Process of Ti3Al in Ti/Al2O3 System
Authors: Maruyama M. , Nakamura S. , Suenaga S. , Nakahashi M.
Published: April 2011

It has been reported that Ti reduces Al2O3 forming Ti3Al at the interface. From the viewpoint that the structural change of the Ti3Al phase influences the metal-ceramic joining strength, the Ti3Al formation process was analyzed by XPS, XRD, TEM and RBS. Titanium films were deposited on the (1102) surface of Al2O3 substrates and annealed. XRD analysis shows that Ti3Al formation starts at 1073 K. Initially, the (1120) and (2020) Ti3Al planes are oriented parallel to the surface. After 1173 K-300 s heat treatment, XRD shows only the (2020) Ti3Al peak; After 1173 K-600 s heat treatment, HREM observation shows that the lattices of the Ti3Al (0220) plane match those of the A12O3 (1210) plane at the interface. It is suggested that the (2020) oriented grains grow preferentially on the (1102) Al2O3 plane.

The quantity of formed Al increases with heating time. After 420 s, the rate of Al formation falls off. The rate of the Al2O3 reduction is in good agreement with the slightly modified Johnson-Mehl equation. The Ti2O/Ti3Al(O)/Al2O3 layer sequence and morphology can be explained by the pure Ti decrease.
The Effect of Protective Organic Thin Film Coatings on BaTiO3 Powders With Respect to Aqueous Processing
Authors: Lee Donghun , Condrate Robert A.
Published: April 2011

Surface properties of BaTiO3 which contain different Ba/Ti ratios were examined by FTIR spectroscopy. Most of the carbonates on the surfaces of these powders were removed by heat treatment at 1200°C. However, it was more difficult to remove the carbonates from the powder with a higher ratio of Ba/Ti. Analysis of the heat treated, aged powders in humid air showed that the barium-excess powder recovered carbonates within several hours. In contrast, titanium-excess powders took a longer time, indicating that barium ion concentration is a reaction-control parameter. It was found that oleic and stearic acids were effective in retarding the degradation of the BaTiO3 powders. They also made the dissolution rate of the powders in water considerably slower.
Acoustic Signature of Defects in SiC/Porous SiC Laminated Ceramics
Authors: Esquivel-Sirvent R. , Noguez C.
Published: April 2011

The sensitivity of acoustic techniques to topological and morphological variations in SiC/porous SiC laminated ceramics is studied using a transfer matrix formalism. To implement this transfer matrix technique, the mechanical properties of the SiC porous layers are characterized using the effective medium approximation of Kuster and Toksoz. We show that topological defects have a stronger acoustic signature than morphological defects. Also, we observe that there are particular frequencies at which the defects do not present any acoustic signature.
Analysis of the Interface Between Plasma-Sprayed Calcium Phosphate Coating and Ti-6Al-4V
Authors: Park Eunsung , Hoelzer David T. , Condrate Robert A.
Published: April 2011

Plasma sprayed calcium phosphate coatings on Ti(alloy) have been considered advantageous over the uncoated Ti as dental implants or orthopedic prostheses due to their abilities to decrease healing time, attach firmer to the bone, and inhibit ion release from the Ti substrate. However, the coating was found not to adhere well to the Ti substrate, presumably because there is no or little chemical bonding between the calcium phosphate coating and the Ti substrate. The interfacial bond strength relies almost entirely on the mechanical locking of calcium phosphate splats onto the roughened Ti surface. In this study, the interfacial area between the calcium phosphate coating and the Ti-6A1–4V substrate was characterized using SEM and TEM. The results revealed the presence of amorphous calcium phosphate layer at the interface, which is believed to be responsible for the low bond strength. Also small particles were observed which were embedded in the amorphous phase near the interface. The presence of the amorphous phases is very important since they are more easily attacked by the physiological solution than crystalline phases are.
Oxide Laminates with High Strength and Work-of-Fracture
Authors: Kuo D. H. , Kriven W. M.
Published: April 2011

Six types of oxide laminates consisting of combinations of xenotime (YPO4) with zirconia (ZrO2), monazite (LaPO4) with ZrO2, and aluminum orthophosphate (AlPO4) with alumina (Al2O3) were studied. They were fabricated by repeatedly stacking two or three kinds of tape-cast layers, lamination, organic burnout and consolidation by hot-pressing. Two of the YPO4-containing ZrO2 laminates were stacked in a YPO4/yttria-stabilized ZrO2 (Y-ZrO2)/30 vol% Y-ZrO2-70 vol% Al2O3(YZ3-A7)/Y-ZrO2 sequence and in a YPO4/Y-ZrO2 sequence. High strength (∼360 MPa) and apparent work-of-fracture (WOF = ∼ 8.2 kJ/m2) were measured in the first laminate. This oxide laminate demonstrates high damage-tolerance without loss of strength. Both properties were comparable with those of non-oxide laminates. There was an approximately 200-fold increase in WOF, as compared with pure Al2O3. A toughening mechanism by means of the residual, interlaminar shear stress-enhanced, interface delamination is proposed for these good results. Two of the LaP04-containing ZrO2 laminates were fabricated in a LaPO4/70 vol% doped ZrO2-30 vol% Al2O3 stacking sequence and in a LaPO4/Y-ZrO2 sequence. Another two of the AlPO4-containing Al2O3 laminates are fabricated in an AlPO4/Al2O3 and in a (50 vol% AlPO4-50 vol% Al2O3)/Al2O3 stacking sequence. The fracture behavior of these multilayered laminates was also studied. The different results among the three kinds of laminates are discussed.
Porous Silicon Organic Vapor and Humidity Sensor
Authors: Poon M. C. , Sin J.K.O. , Wong H. , Han P. G. , Kwok W. H. , Bow Y. C.
Published: April 2011

This paper presents new organic vapor sensitive device using anodized porous silicon (PS). The sensor has aluminum (Al)/PS/p-Si/Al Schottky diode structure and sensitivity at room temperature in 2600 ppm acetone, methanol, 2-propanol and ethanol is about 4, 5, 10 and 40 times respectively. The sensitivity in 800–2600 ppm ethanol vapor is 2 to 40 times. The diode sensor can be converted into an Al/PS/Al resistor sensor by switching the electrical contacts, and the sensitivity is about 500 times for a humidity change of 43–75%. All sensors have response time of about 0.5 min. The sensitivity is stable with time and the PS sensor can be integrated into VLSI Si devices to form novel microelectronic systems.
Optical Fibers with Patterned ZnO/Electrode Coatings for Flexural Actuators
Authors: Trolier-McKinstry S. , Fox G. R. , Kholkin A. , Muller C. A. P. , Setter N.
Published: April 2011

Piezoelectric ZnO coatings were used in this work to develop a flexural actuator for an optical fiber. The basic device geometry was as follows: inner Cr/Au electrodes were evaporated onto a cleaned optical fiber; a thick ZnO coating was then grown by sputtering; finally a set of 2mm ring top electrodes were deposited through a shadow mask. Flexural actuators were made by photolithographically patterning either the inner or outer Cr/Au drive electrodes so that it was split down the length of the fiber. This enables each half of the fiber to be actuated independently. The result is that the optical fiber is forced to flex.

A processing scheme by which 30 μm gaps could be patterned into the electrodes was developed using standard clean room techniques. Such flexural actuators are attractive for scanning near field optical microscopes and in fiber alignment devices.
Surface Relaxation in Ferroelectric Perovskites: An Atomistic Study
Authors: Dorfman Simon , Heifets Eugene , Fuks David , Kotomin Eugene , Felsteiner Joshua
Published: April 2011

The effect of the [001] surface relaxation on the polarization of the paraelectric BaTiO3 is simulated in the framework of the shell model. Our atomistic simulations show a large polarization of ions in the first several layers nearby the surface and confirm the possibility of co-existence of Ti-and Ba-terminated [001] BaTiO3 surfaces which have very close surface energies.
The R-Phase Transformation in the Ti-Ni Shape Memory Alloy and its Application
Authors: Ohkata I. , Tamura H.
Published: April 2011

We discuss a comprehensive design approach of Ti-Ni alloy coil springs and introduce a new application of the R-phase transformation. In order to attain high cyclic performance, one must understand the two relationships between design parameters and material characteristics and between material characteristics and cyclic performance. Metallurgical parameters and coil spring dimensions play an important role as design parameters in the former relationship. High cyclic performance of an actuator is closely related to the suppression of the monoclinic martensite. Transformation temperatures and their stress dependence is of primary importance as material characteristics in the latter relationship. A thermostatic mixing valve, which is the latest application of the R-phase transformation in Japan is then discussed as a new type of a shape memory alloy actuator. The R-phase transformation is employed to achieve not only a long cycle life but a linear operation with the set temperature to continuously control the mixing ratio of hot and cold water. This is achieved by changing the total length of the two-way actuator in a linear manner with the set temperature. The linear characteristic is satisfied between 35–50°C by optimizing thermomechanical treatment and the dimensions of Ti-Ni and biasing coil springs.