bluuebunny/crossref_metadata_2025 huggingface dataset:
Can We Exploit Imprint in Ferroelectric Thin Film Capacitors for Memory Applications?
Authors: Yoo In Kyeong , Desu Seshu B.
Published: April 2011

Imprint was observed for fatigued PZT (Zr/Ti = 53/47) capacitors which were subjected to a thermal cycle (at 80°C for a period of time). It was also observed for capacitors whose top electrode was defined by ion milling. In addition, capacitors with an asymmetric multilayered structure showed severe imprint problems. Based on the above observations, imprinting was categorized as:

1) Intrinsic imprint which is caused by inherent conditions such as device structure, configuration, and material composition.

2) Extrinsic imprint which is generated by external sources such as electrical stress, thermal stress, time, and processing.

Imprint mechanisms were discussed for each imprinting category. Most importantly, based on partial switching, a new memory logic was suggested. It is shown that stable imprinting may be useful for low density FRAM applications when the proposed new memory logic is applied. Reliability of the new logic was also shown to be significantly better than conventional operation.
Effects of Electron Beam Irradiation on PZT/PLZT Thin Film Capacitors
Authors: Jiang Bo , Kim Jiyoung , Khamankar Rajesh , Lee Insup , Lee Jack C.
Published: April 2011

The effects of electron beam irradiation on the electrical characteristics of Pt-PZT-Pt and Pt-PLZT-Pt (with La concentration of 5% and 10%) thin film capacitors were studied. The top electrode of each capacitor was bombarded by localized energetic electrons with incident energies varying from 5 keV to 25 ke.V. Large distortions in the hysteresis loops were observed when the incident electrons had enough energy to penetrate the 1000Å Pt top electrode. The damage effects are strongly dependent on the original domain orientation when the film is irradiated, and an applied a.c. field after the irradiation seems to induce some recovery effects. The damage mechanism is explained by a simple model which considers the effect of space charge fields generated by the charge carriers trapped at the domain boundaries.
The Effect of Low-Angle and High-Angle Grain Boundaries on Elevated Temperature Strength
Authors: Kassner M. E.
Published: April 2011

The influence of small (subgrain) misorientation interfaces on the mechanical behavior of metals and alloys deforming within the creep regime has been intensively studied over the past several decades. Controversies have existed, but some new experiments suggest, contrary to the general opinion, that low-angle boundaries are not associated with the rate controlling process for plasticity and do not affect strength. The new evidence will be discussed in terms of other established experimental trends. Large-angle boundaries may have a smaller effect on elevated temperature strength than at ambient temperatures and do not appear to dramatically affect elevated temperature strength. Superplastic effects are not addressed.
Microstructural Effects on the Cyclic Deformation of Polycrystalline FCC Materials
Authors: Peralta P. , Llanes L. , Czapka A. , Laird C.
Published: April 2011

The effect of crystallographic texture and grain size on the cyclic hardening of FCC polycrystals was studied using copper as a model material. Samples with textures approximately random and two grain sizes were tested under cyclic loading. The cyclic response for high values of the plastic strain amplitude of the random-textured material was softer than that of polycrystals with strong <111>-<100> texture reported in [1], and almost the same at low plastic strains, when similar testing conditions were used. The cyclic behavior of specimens with different grain sizes and similar texture was almost the same as well. This result shows that texture had a much more important effect on the cyclic behavior of polycrystalline copper than the grain size. The effect of ramp loading as a pretreatment was also studied. The results show that large grained samples had a softer cyclic response after the ramp than small grained ones, but the effect was still smaller than that of texture.
The Structure and Properties of Centrifugally Spray Formed Ti6AI4V
Authors: Duggan M. A. , Loreito M. H. , Smallman R. E.
Published: April 2011

Ti6AI4V rings have been centrifugally spray deposited with the long term aim of producing sheet which can be superplastically formed. Spray deposition has been carried out under vacuum and under an argon atmosphere in order to assess the significance of gas entrapment during spray forming. Some samples have been HIPped and others have been used for hot rolling trials after spray deposition and the microstructures of these differently treated samples compared. Some preliminary measurements of the room temperature tensile properties have also been made.

The results are briefly discussed in terms of the advantages of using a vacuum spray forming route and in terms of the properties of the spray-formed and HIPped samples.
Mechanical Hardness as a Probe of Nanocrystalline Materials
Authors: Koch C. C. , Shen T. D. , Malow T. , Spaldon O.
Published: April 2011

The use of mechanical hardness as a probe of nanocrystalline materials is reviewed. The fact that the grain size dependence of hardness is very different for nanocrystalline materials compared to conventional (≥1 μm diameter) polycrystals suggests a different deformation mechanism may be operative in nanocrystalline materials. Hardness is useful for following the sintering, densification reactions of nanoparticles. Solid solution hardening in nanocrystalline alloys is found to be overwhelmed by the grain boundary hardening. If alloying decreases the grain boundary hardening, i.e. increases grain size, an apparent solid solution softening effect is observed.
Simulation of Grain Growth During Directional Annealing
Authors: Zacharopoulos N. , Holm E. A. , Srolovitz D. J.
Published: April 2011

A Monte Carlo simulation procedure is applied to simulate non-uniform grain growth during directional annealing. The assumed temperature profile consists of a small, finite size hot zone which blends smoothly into cold zones ahead and behind the hot zone. The hot zone is assumed to move with a constant velocity. The influence of the ratio of hot zone to cold zone temperatures and the velocity of the temperature field are investigated. The grain size is analyzed as a function of these variables. We find that very high aspect ratio grains (long axis parallel to the thermal field velocity vector) are possible within a restricted velocity window. These results are analyzed in terms of an analytic model based upon conventional grain growth laws.
Deformation and Comminution of Shock Loaded α-Al2O3 in the Mescall Zone of Ceramic Armor
Authors: Mcginn J. T. , Klopp R. W. , Shockey D. A.
Published: April 2011

Incursion of high density penetrators into ceramic armor is preceded by the formation of a finely comminuted rubble bed at the penetrator tip, the Mescall zone. The deformation and failure processes that result in the Mescall zone are critical to understanding penetration resistance and to modeling penetration behavior. Transmission electron microscopy (TEM) was used to examine shock loaded material in the vicinity of an explosive detonation in α-Al2O3 and to infer the phenomenology of plasticity and fracture occurring at the tip of an advancing penetrator in ceramic armor. Comminution proceeds by intergranular fracture until the fragment size approaches the grain size. Further fragmentation proceeds by transgranular cracks, which nucleate at preexisting microvoids and at intersections of basal twins and primary and secondary slip bands.
Interfacial Strengthening in Semi-Coherent Metallic Multilayers
Authors: Rao S. I. , Hazzledine P. M. , Dimiduk D. M.
Published: April 2011

Experimental results show that a nanolayered composite structure made of two kinds of metals strengthens dramatically as the layer thickness is reduced. In epitaxial systems, this strengthening has been attributed classically, to the modulus and lattice parameter mismatches between adjacent layers. The modulus mismatch introduces a force between a dislocation and its image in the interface. The lattice parameter mismatch generates stresses and mismatch dislocations which interact with mobile dislocations. In addition to these two interactions, there is the difficulty of operating a Frank-Read source in any very thin layer. However, the calculations suffer from the drawback that elasticity theory is being used at such short range from the dislocations that it is not strictly valid. In this paper the issues in strengthening of multilayer systems are defined within a simple analytical model. Additionally, a parametric approach using the atomistic embedded atom method (EAM), is developed to study, dislocation-interface interactions in metallic multilayers. Preliminary results of the atomistic calculations verify that Koehler strengthening is significant especially when the lamellae are very thin. For thicker lamellae the lattice parameter mismatch effects, which have been modelled within continuum theory, contribute increasingly to the strength. In Cu-Ni, the peak in the yield stress occurs when single dislocations must overcome both barriers. The yield stress drops in thicker lamellae as pile ups of increasing length form in the lamellae, finally conforming to the Hall-Petch equation.
Crack Dynamics and Grain Size
Authors: Gilman John J.
Published: April 2011

Two aspects of fast cracks are considered: 1. the terminal velocity, and corresponding relative kinetic energy; 2. the grain size dependence of the fracture. It is argued that this is determined by the kinetic energies of cracks when they have expanded enough to reach the boundaries of the grains in which they lie. This is more consistent with the observed facts than the more usual quasi-static models.

By considering the limiting conditions at the very tip of a moving crack, many complications are avoided in calculating the terminal velocity. The maximum transverse acceleration of material is limited by the maximum stress (cohesive) that can be applied. The resulting terminal velocity is: 0.4 vs, where vs is the longitudinal sound speed; compared with measured values which average about: 0.31 vs.

In polycrystals, microcracks are found when the applied stress exceeds the yield stress. However, the microcracks do not propagate in fine-grained specimens because they do not have enough kinetic energy to cross a typical grain boundary. This leads to the observed dependence of the fracture stress on the grain size.
Nucleation and Growth Processes During the Chemical Vapor Deposition of Diamond
Authors: Wang Yaxin , Evans Edward A. , Kovach Christopher S. , Landau Uziel , Angus John C.
Published: April 2011

In situmicrobalance measurements of diamond growth rates are described. These results can be used to test proposed mechanisms for diamond growth and suggest mechanisms for sp2impurity incorporation. The Thiele modulus is a simple criterion for growth uniformity and is used to compare hot-filament and combustion-assisted growth.
Molecular Beam Epitaxy of Boron Nitride Thin Films and Their Analytical Characterization
Authors: Davis Robert F. , Kester Daniel J. , Ailey K. Shawn
Published: April 2011

Boron nitride (BN) thin films have been grown on the (100) surfaces of Si, diamond, Ni and Cu via ion beam assisted deposition (IBAD) using electron beam evaporation of B in tandem with N and Ar ion bombardment within the ranges of substrate temperature and ion flux of 200–700°C and 0.20–0.30 mA/Cm2, respectively, Fourier-transform infrared spectroscopy (FTIR) and high resolution transmission electron microscopy (HRTEM) revealed a growth sequence of amorphous (a-BN), hexagonal (h-BN) and cubic (c-BN) layers on Si and diamond under most conditions. This sequence is attributed primarily to increasing biaxial compressive stress with film thickness due to interstitial Ar incorporation observed via Rutherford backscattering spectroscopy (RBS). The effect of deposition conditions, specifically substrate temperature and bombardment intensity, on the film growth was studied. Increasing the substrate temperature above 400°C led to the onset of the cubic phase at a greater film thickness, while increased ion flux led to earlier growth of this phase. These results may be explained by the relaxation of intrinsic stress in the films at higher temperatures due to increased adatom mobility and to increased intrinsic stress in the films resulting from increased ion bombardment, respectively. Lower temperatures led to mixed phase growth. A minimum substrate temperature (200–300°C) is required for nucleation and growth of single phase c-BN by this technique. A combination of h-BN and c-BN was deposited on Ni; only h-BN was obtained on Cu substrates.
Improvement of Adhesion of Diamond Coatings to WC(CO) Tool Substrates
Authors: Fan W. D. , Jagannadham K. , Narayan J.
Published: April 2011

Adhesion of diamond coatings to cutting tool substrates is an important property that is needed to replace the polycrystalline diamond tools (PCD) in machine tool applications. The improvement in adhesion of diamond on WC(Co) tool substrates is brought about by formation of a composite layer. Composite layers made up of TiC or TiN and diamond were formed by laser physical vapor deposition of ceramic coatings and hot filament chemical vapor deposition of diamond films. A first layer of discontinuous diamond film on WC is embedded in the ceramic coatings followed by growth of a continuous diamond film that maintains continuity with the first diamond layer. The composite coatings were characterized by SEM and Raman spectroscopy. Adhesion and wear resistance of the diamond coatings were measured using a polishing wear test. The mechanisms of improvement in adhesion were analyzed by finite element modeling. Results show that TiC composite layers improve the adhesion of diamond coatings significantly. This improvement is considered to arise from the modification of the thermal stress at the interface between the diamond film and the WC(Co) tool substrate.
CVD Precursors Containing Hydropyridine Ligands
Authors: Gordon Roy G. , Thornton John , Chen Feng
Published: April 2011

Hydropyridine is introduced as a new ligand for use in constructing precursors for chemical vapor deposition. Detachment of hydropyridine occurs by a low-temperature reaction leaving hydrogen in place of the hydropyridine, and a very stable byproduct, pyridine vapor. Hydropyridine ligands can be attached to a variety of elements, including main group metals, such as aluminum and antimony, transition metals, such as titanium and tantalum, semiconductors such as silicon, and nonmetals such as phosphorus and arsenic.
AlN Grown by Metalorganic Molecular Beam Epitaxy
Authors: Mackenzie J. D. , Abernathy C. R. , Pearton S. J. , Wilson R. G.
Published: April 2011

Thin film AlN has been grown on Al2O3 and GaAs substrates by metalorganic molecular beam epitaxy (MOMBE) using amine bonded alane precursors, tertiarybutylamine, and nitrogen from a compact electron cyclotron resonance (ECR) plasma source operating at 2.45 GHz. Typical growth pressures were in the 0.5 − 1 × 10−4 Torr range. The growth rates, impurity backgrounds and surface morphologies were examined for both nitrogen sources and both the solid and liquid alanes. In general, growth efficiencies were good for both alane precursors, allowing for deposition of the low temperature, ∼ 400°C, AlN buffers needed for subsequent growth of GaN and InGaAlN alloys. Low growth temperatures could not be obtained using tertiarybutylamine, presumably due to poor decomposition efficiency of the source at low temperatures. The structural quality of material grown at high temperatures from the ECR plasma was measured by atomic force microscopy (AFM) and high resolution x-ray diffraction (HRXRD), indicating a surface roughness of ∼ 8 Å and an x-ray width half maximum (FWHM) of 430 arcsec.
Synthesis and Selected Micro-Mechanical Properties of Titanium Nitride Thin Films by the Pyrolysis of Tetrakis Titanium in Ammonia.
Authors: Bae Y. W. , Lee W. Y. , Besmann T. M. , Blau P. J. , Riester L.
Published: April 2011

Thin films of titanium nitride were chemical vapor deposited on (100)-oriented single-crystal silicon substrates from tetrakis (dimethylamino) titanium, Ti((CH3)2N)4, and ammonia gas mixtures in a cold-wall reactor at 623 K and 655 Pa. The films were characterized by Auger electron spectroscopy, X-ray diffraction, and transmission electron spectroscopy. The nano-scale hardness of the film, measured by nanoindentation, was 12.7±0.6 GPa. The average kinetic friction coefficient against unlubricated, type- 440C stainless steel was determined using a computer-controlled friction microprobe to be ∼0.43.
Ellipsometric Investigation of Metal-Organic Chemical Vapor Deposition of Niobium Oxide Films
Authors: Gerfin Tobias , Graetzel Michael
Published: April 2011

Niobium oxide films have been prepared by metal-organic chemical vapor deposition (MOCVD) in two different systems via thermal decomposition of Nb(OEt)5.A detailed study by exsitu variable-angle spectroscopic ellipsometry indicates a wavelength dependence of the refractive index that could be described by a Cauchy type dispersion formula and typical values of 1.9 to 2.1 at 632.8nm. The band gap of these films were at about 3.5 and 4eV for the indirect and direct transition. Preliminary results of in-situ ellipsometry at four different wavelengths in the visible and UV will be discusssed. The films were amorphous, extremely smooth and pinhole free and therefore they are useful candidates for interdiffusion barrier layers.
Molecular Dynamics of Monomer, Oligomer, and Polymer Liquids in Porous Media: A Field-Cycling Nmr Relaxometry and NMR Field-Gradient Diffusometry Study
Authors: Kimmich R. , Stapf S. , Seitter R.-O. , Callaghan P. , Khozina E.
Published: April 2011

The molecular dynamics of fluids in porous media has been studied using field-cycling NMR relaxometry and NMR field-gradient diffusometry. The frequency dependences of the 1H and 2H spin-lattice relaxation times T1 of various liquids in porous glass reveal weak and strong adsorption behaviour depending on the polarity of the adsorbates. Correlation times eight orders of magnitude longer than in bulk have been observed. The T1 dispersion moreover reflects geometrical details of the matrix in a length scale three orders of magnitude longer than the adsorbate molecules. The mean-square displacements of adsorbate molecules on the surface are only one order of magnitude less than in bulk. The global diffusivity is reduced by tortuosity and porosity effects. The observed phenomena may be explained by bulk-mediated surface diffusion, i.e., Lévy walks. The dynamics of polymer chains much longer than the pore size is characteristicly different from that in bulk melts. There is evidence that the reptation mechanism explains at least a part of the phenomena observed for the porous matrix in contrast to findings with bulk polymer melts.
A Vibrational Investigation of Crystal Nucleation and Growth from a Physically Confined and Supercooled Liquid
Authors: Mu R. , Henderson D. O. , Pan Z. , Xue Y.
Published: April 2011

Temperature dependent Raman measurements were conducted on bulk and the confined 2,4,6-trinitrotoluene (TNT) in 2.5, 5, 10, and 20 nm porous silica. Two bands at 23 and 190 cm−1 were chosen to evaluate the structure and the melting and freezing transitions of the confined TNT in pores. The results show that the solid phase TNT confined in larger pores (dp > 5 nm) forms conventional solid TNT structure, while the TNT restricted in small pores has no freezing and melting transition characteristics. The results also suggest that the freezing transition of the confined TNT starts at the pore center and the confined TNT maintains its interconnectivity during the freezing transition.
Reactant Correlation Effects Study of Hydrogen Isotope Exchange Reaction on Supported Metal Catalysts
Authors: Choi Inchan , Kopelman Raoul
Published: April 2011

Non-classical results due to reactant correlation effects have been observed in the study of Monte Carlo simulations of the A2 + B2 → 2AB reaction. These simulation results, interpreted by the Pair Density Analysis method and the experimental kinetic studies, may provide an explanation of the early time anomalous kinetic behavior of the catalytic hydrogen isotope exchange reaction exhibited for surface-diffusion limited conditions on alumina supported platinum islands.
Scaling of Reaction Fronts in the Presence of Disorder
Authors: Araujo Mariela
Published: April 2011

A study of the dynamics of the reaction front that appears in diffusion-reaction systems of the form A + B → C with initially separated reactants in the presence of quenched disorder is presented. The scaling of the width of the front w is analyzed as a function of the “disorder strength” and the dimensionality of the system. It is shown that disorder strongly affects the width exponent α, ω tα even for d ≥ 2, where the mean field approximation is known to be valid. The scaling of the nearest neighbor distance, midpoint fluctuations and concentration profiles near the center of the front, are also studied.
A Population Balance Analysis of Substrate Distribution Effects on Enzymatic Reaction Rates in Reversed Micelles
Authors: Hatton T. Alan , Bommarius Andreas S.
Published: April 2011

A population balance analysis of the statistical distribution of substrates over reversed micelles indicates the importance of accounting for concentration fluctuations within the micelles in interpreting observed enhancements in enzymatically-catalysed reactions in reversed micellar media. When the reactions are slow relative to the rates of solubilizate exchange via micellar coalescence and redispersion processes, analytical solutions to the detailed population balance equations are obtained, and the connection between Michaelis-Menten kinetics in reversed micellar media and bulk aqueous solution is made. It is shown that the finite occupancy number of the micelles at low water content leads to a statistical distribution of substrates over the micelle population, and that this can give rise to changes in the apparent reaction kinetics, even in the absence of changes in the intrinsic reaction parameters themselves. The model predictions are in good qualitative agreement with reported experimental results.
The Mesoscopic Description of Pressure and Velocity Profiles Near Planar Wall in Water Solutions
Authors: Brodsky Anatol , Reinhardt William P.
Published: April 2011

The stress tensor for polar solutions is constructed starting from a nonlocal and nonlinear Landau free energy functional. Explanations of some puzzling properties of liquids near interfaces are proposed.
Preparation and Pretreatment Effects on Co/SiO2 Catalysts for Fischer-Tropsch Synthesis
Authors: Coulter Kent E. , Sault Allen G.
Published: April 2011

Catalyst drying procedures are often given little attention in the experimental section of papers on supported metal catalysts. In general, drying appears to be regarded as a method to remove water and other volatile components prior to calcining or reduction, but not as a method to affect the surface properties of the catalyst. This study uses x-ray photoelectron spectroscopy (XPS) to examine the surface properties of silica supported cobalt catalysts, prepared using incipient wetness impregnation of cobalt nitrate hexahydrate, and finds a wide range of cobalt distributions, extent of nitrate decomposition, and reducibility for various drying procedures. After UHV annealing and subsequent reduction, the final cobalt surface properties are found to depend on the length of heating and the environment during the drying process. Maximum cobalt metal surface area is obtained for samples exposed to limited amounts of air and dried under conditions where gas phase species generated during the precursor decomposition are rapidly removed from the surface of the sample.
Surface Models of Alumina Supported Copper Oxide Prepared by Laser Ablation: Dispersion and Electron Structure Changes Following Reduction and Oxidation Cycles
Authors: Hirschauer B. , Paul J.
Published: April 2011

We have explored and developed laser ablation as a tool to synthesize realistic planar models of high surface area catalysts as well as novel materials, not accessible with wet chemical methods. The process is illustrated by data for dispersion and electron structure modifications following thermal treatments of alumina supported copper oxide. Planar models of different wet and dry carrier/overlayer combinations were prepared and exposed to oxidizing and reducing atmosphere at 500°C. Characterization was made by XPS/ESCA. The data reveal the importance of surface hydroxyl groups in the two initial components to control coalescence and interdiffusion. The ablation route is part of our ongoing DENOX project and comparisons are made with other materials, tested for their materials properties and catalytic behavior in HC/NO reactions.
Gas Phase Synthesis of Molybdenum and/or Iron Nitrides, Carbides and Sulfides
Authors: Close Michael R. , Petersen Jeffrey L.
Published: April 2011

The thermolytic decomposition of Mo(CO)6 with hydrogen sulfide or ammonia vapor (in a He carrier stream) at temperatures ranging from 300 to 1100 °C produces high surface area molybdenum sulfides (MoS2 or Mo2S3) or molybdenum carbides (hexagonal Mo2C) and carbonitrides, (hexagonal MoN(C) or cubic Mo2N(C)), respectively. The MoS2 surface areas range from 16.7 to 82.0 m2/g, while the surface areas of molybdenum carbides and carbonitrides vary from 14.9 to 21.1 m2/g. The maximum surface area for MoS2 is achieved at 500 °C and decreases with increasing or decreasing temperature. The surface area of the carbonitrides formed from 300 to 800 °C increases with increasing temperature up to 950 °C, where lower surface area Mo2C is formed. Crystallographically pure hexagonal MoN is prepared by decomposing Mo(CO) 6 in pure ammonia. Fe(CO) 5 decompositions in ammonia produce FexZ (where 5.8≥x≥1.6 and Z=C and N), and in some cases elemental Fe. Hexagonal Fe3 N(C) forms when Fe(CO) 5 is thermolyzed in ammonia from 300 to 600 °C, with surface areas ranging from 9.5 to 13.7 m2/g, whereas orthorhombic Fe3C and cubic Fe are produced at 700, 800, 900 and 1000 °C with surface areas of 6.7, 7.6, 2.2 and 2.0 m2/g, respectively. Within the same phase, the surface areas of the carbonitrides increase with increasing reaction temperature. These iron and molybdenum carbonitrides catalyze the conversion of CO/H2 to alkanes and methanol. Based on preliminary catalytic studies, the highest rate of methane (2850 g/kg/hr at 374 °C) and methanol (440 g/kg/hr at 284 °C) formation was accomplished with an FeMo carbonitride prepared by decomposing Mo(CO)6 and Fe(CO)5 in ammonia at 800 °C.
Carbon Nanofibers as a Novel Catalyst Support
Authors: Kim Myung-Soo , Rodriguez Nelly M. , Baker R. Terry K.
Published: April 2011

Catalytically grown carbon nanofibers have been prepared by the thermal decomposition of carbon containing gases over copper-nickel and iron surfaces. This material is found to be highly graphitic in nature when prepared from certain catalysts and gaseous reactants. In the as-grown state, carbon nanofibers have surface areas in the range 200 to 300 m2/g, and by following careful activation procedures this value can readily be increased to ˜700 m2/g. Electrical measurements indicate that the material has a conductivity approaching that of single crystal graphite. This material combines the attributes of active carbon and graphite and in addition, the physical form of carbon nanofibers offers some interesting opportunities for the design of unique catalyst systems.
Chemistry of Electrochromic IrOx. Films Deposited Under Variable Redox Conditions
Authors: Klein J. D. , Clauson S. L.
Published: April 2011

A thin film deposition technique is described whereby the oxidation condition of as-deposited iridium oxide thin films can be manipulated by varying deposition conditions. Iridium oxide thin films were deposited by reactive rf magnetron sputtering in a H2/O2/Ar gas blend. Optical emission spectroscopy, an in-situ process monitor, was employed to observe redox interactions in the deposition plasma. The plasma spectra exhibited characteristics normally observed in hydrogen flame spectroscopy. A competitive redox balance was found to exist between atomic O and atomic H emissions. Plasma redox conditions defined by the H-O emissions could be accessed by a variety of gas flow conditions. Electrochemical aspects of the IrOx films were examined by cyclic voltammetry. Electrochromic capabilities were demonstrated through optical transmittance.
Sol Gel Intercalation Materials for Lithium Batteries
Authors: Pereira-Ramos J.P. , Bach S. , Farcy J. , Baffler N.
Published: April 2011

This paper emphasizes the interest of sol-gel synthesis in obtaining high performance cathodic materials. New vanadium oxides, vanadium bronzes (MxV2O5) and manganese oxides (MnO2) are prepared via the sol-gel process using inorganic precursors in aqueous medium. Their electrochemical behaviour (working potential, specific capacity, kinetics of Li transport, rechargeability, cycle life) is investigated and discussed in relation with their specific structural, chemical and physical features. In particular, the results are compared to that achieved for the corresponding classical compounds prepared via a synthesis route involving solid state reactions or precipitationreactions.
The Mechanism and Modeling of Conductivity in Polymer Electrolytes
Authors: Lonergan Mark C. , Shriver Duward F. , Nitzan Abraham , Ratner Mark A.
Published: April 2011

The progress of dynamically disordered hopping (DDH) in modelling charge transport in polymer electrolytes is reviewed. The DDH model successfully describes many of the salient features of polymer electrolytes, most notably, the frequency and temperature dependence of the conductivity. Furthermore, analyses and simulations based on the DDH model provide rich mechanistic information. The general picture of charge transport that emerges from the DDH model is one in which two classes of charge carriers exist in thermal equilibrium:quasi-free and bound. The quasi-free carriers dominate the conductivity response and diffuse freely over short distances (≈1Å) with longer range diffusion requiringlocal segmental motions, renewal in the language of DDH, of the polymer solvent. The bound carriers, which are likely polymer solvated ion clusters, are immobile on the time-scale of renewal and contribute relatively little to the conductivity.
Failure of the Frenkel Defect Model to Explain the Trend in Anionic Conductivity in the MF2 Fluorite Structure and Related MSnF4 Materials
Authors: Denes Georges
Published: April 2011

The high fluoride ion conductivity of fluorite type MF2 has been attributed tothe fact that half of the F8 cubes present in this structure are empty and therefore, are potential vacant sites for interstitial fluoride ions in the formation of Frenkel defects. However, the model of long range ion motion through Frenkel defects by use of empty F8 cubes is in contradiction with: (i) the little difference between the conductivities of CaF2 and BaF2, (ii) the conductivity of β-PbF2 being much larger than that of BaF2, and (iii) the much higher performance of MSnF4 even though there is no empty cube to form Frenkel defects in the MSnF4 structures.
Perovskites as Oxide-Ion Electrolytes
Authors: Feng Man , Goodenough John B.
Published: April 2011

Substitution of Nb, Ti, or Sn for In and of La for Ba was used to obtain cubic, anion-deficient perovskites AB03-δ. Neither the ferroelectric character of Nb5+ and Ti4+, nor the more acidic character of Sn4+ suppressed water absorption into the anion vacancies at temperatures T < 500ºC. However, the smaller La3+ ion in Bal-xLaxO2.5+0.5x did suppress the absorption of water for x = 0.4, and Ba0.6La0.4InO2.7 is competitive with yttria-stabilized zirconia as an oxide-ion electrolyte.
Oxygen Permeation Studies of SrCo0.8Fe0.2O3-δ
Authors: Yang Y. L. , Lee T. H. , Qiu L. , Liu L. , Jacobson A. J.
Published: April 2011

Oxygen permeation fluxes through dense SrCo0.80Fe0.20O3-δ discs have been measured in the temperature range of 620-920 °C under various oxygen partial pressure gradients. The permeation results are compared with the previous measurements. Below 800 °C, the apparent activation energy for the overall permeation is 22±4 kcal/mol. The permeation results are discussed in light of the phase diagram of SrCo0.80Fe0.20O3-δ. Based on experiments in which the membrane thickness is varied, we propose that the surface exchange process is the ratelimiting step in the overall permeation reaction. Preliminary catalytic studies of methane partial oxidation in a membrane reactor are reported.
Diffusion-Reaction in Mixed Ionic Electronic Conductor Solid Oxide Membranes with Porous Electrodes
Authors: Deng Huiming , Zhou Minyau , Abeles Benjamin
Published: April 2011

We solve the transport equations for diffusion-reaction, in the limit of a small O2 pressure gradient, in a mixed oxygen ion-electronic conductor (MIEC) solid oxide membrane consisting of a porous anode and cathode separated by a thin dense layer. The enhancement in ion current due to the porous electrodes calculated for MIEC perovskites is of order 100 for electrode surface area of 106 cm2/cm3.
Structural Chemistry of Alkaline Earth Hexa-Aluminates
Authors: Park Jae-Gwan , Cormack A. N.
Published: April 2011

Computer-based atomistic simulation techniques have been used to investigate the crystal chemistry and phase relationships in alkaline earth hexa-aluminates. The lattice energies for hexa-aluminate-related structural models are calculated and successfully predict that barium prefers the β-alumina-type structures with charge-balancing defects, whilst calcium or strontium prefers the ideal magnetoplumbite structure. In the case of magnesium, it is predicted that it does not prefer a hexa-aluminate structure.
Spectrofluorimetric Characterization of an Ionic Conductor: Sodium Sulfate High-Temperature Phases Doped with Europium(III)
Authors: Matithews Lowell R. , Knobbe Edward T. , Dharmasena Gamini , Cole Renée , Frech Roger
Published: April 2011

The highest-temperature polymorph of sodium sulfate, (I), has significant orientational disorder in its structure which allows it to readily accept substitution by di- and trivalent cations. Although Na2SO4 (I) exhibits reasonable ionic conductivity, it cannot be quenched to room temperature without changing phase. However, aliovalent solid solutions of (I) can be quenched to RT and resultant cation vacancies promote conduction via Na+ migration. The closely related but more ordered phase Na2SO4 (III) can also form aliovalent solid solutions which can be quenched to RT.

The europium(III) ion is an extremely sensitive and useful probe of its immediate local environment. The presence, location, and intensity of its fluorescence transitions (particularly the 5D0→7F0-2 emissions) can provide detailed information about the symmetry, nature, and multiplicity of the individual Eu3+ site which cannot be gained from X-ray or neutron diffraction techniques.

Our research (supported by the National Science Foundation and the State of Oklahoma) involves the structural characterization of two europium-doped sodium sulfate phases via fluorescence spectroscopy.
Electrical Properties of High ion Conductive Polymer Complexes Containing Room Temperature Molten Salt
Authors: Aoshima Norio , Rikukawa Masahiro , Sanui Kohei , Ogata Naoya
Published: April 2011

New ion conductive polymers were obtained by dissolving polycations into room temperature molten salt consisting of methyltriethylammonium chloride (MEAC1) and aluminium chloride (A1C13). These complexes formed viscoelastic solids when the polycation content was increased more than 4 unit mol%. The ionic conductivity of polycation complexes was in the range of 10-4-10-3 Scm-1 at room temperature and were affected by their composition, types of polycations, and counter anion species.
Preparation and Characterization of Polyaniline-Palladium Composite Films
Authors: Li Hongshi , Baer D. R. , Engelhard M. H. , Janata J. , Josowicz M.
Published: April 2011

Electrosynthesized polyaniline (PANi) can be chemically functionalized by incorporation of palladium clusters. The functionalization of electrochemically, freshly prepared and dried PANi film occurs spontaneously during the relaxation process. This process is carried out in sulfuric acid containning palladium salt. The material properties of the new composite PANi-Pd film were investigated by applying electrochemical, UV-visible spectroscopic and surface microscopy techniques. The PANi-Pd composite materials behaved electrochemically different than PANi film alone or Pd film deposited electrochemically. This finding is particularly important for developing layers for chemical sensors, electrocatalysis or supercapacitors applications.
Ionic Current Induced Migration of a Hot Spot in GdBa2Cu3O7-δ, Ceramics
Authors: Okamoto T. , Huybrechts B. , Takata M.
Published: April 2011

An electric field sensitive moving hot spot appeared when a dc voltage over 5 V was applied at room temperature to GdBa2Cu3O7-δceramic thin rods under oxygen partial pressures ranging from 0.05 to 1.00 atm (5 kPa to 100 kPa). The spot moved to the negative electrode, and the direction of movement could be reversed time after time by switching the positive and negative electrode. This is believed to be caused by electric field movement of oxygen ions, thereby generating an ionic current. The total current after the appearance of the hot spot was independent of the applied voltage for every oxygen partial pressure, PO2. However the current and spot velocity increased significantly with increasing PO2. By the best of the authors's knowledge this is the first report on the influence of the PO2 on the moving hot spot. The potential use of this phenomenon as an oxygen sensor will be shown.
Crystal Chemistry and Electrochemical Behavior of New Manganese Substituted Nickel Hydroxides
Authors: Guerlou-Demourgues L. , Delmas C.
Published: April 2011

Ageing of the manganese substituted nickel hydroxides in 5M-KOH electrolytic medium leadsto a structure interstratification which is related to spontaneous oxidation of trivalentmanganese ions to the tetravalent state, As far as the electrochemical behavior is concerned, the trend to interstratification has a positive influence on the stability of the capacity upon cycling. In addition, the chargeability is improved by the presence of manganese.
Electrochemical Activity of Natural and Synthetic Manganese Dioxides
Authors: Amarilla J.M. , MacLean L.A.H , Tedjar F. , Cras F. Le , Strobel P. , Poinsignon C.
Published: April 2011

even manganese dioxide (MD) forms including natural ramsdellite, β-MnO2 and samples with structures intermediate between these two types, have been analyzed interms of chemical and structural disorder. XRD and IR spectra show that natural ramsdellite contains groutellite, MnO1.5(OH)0.5. The OH absorption band in the 3400cm-1 region is sharp for groutellite, less intense on CMD spectrum, andsuperimposed to a broad and diffuse absorption ranging from 3600 to 2000cm-1 in most γ-MnO2's. The OH groups are associated with Mn+3 defects, while the broad and diffuse absorption band can be assigned to protons in empty MnO6 octahedra, and so related to instable manganese oxydation state between Mn3+ and Mn4+.

A potentiostatic study in IM and 7M KOH shows that the stoichiometric oxides, ramsdelliteand β-MnO2, are not reduced, while CMD and EMD are reversibly reduced by H+/-einsertion. In 7M KOH, a reversible reduction occurs for both CMDs and EMDs until -0.2 V, while a heterogeneous mechanism destroys the structure at lower potential (70% capacity loss after 3 redox cycles). Only ramsdellite and β-MnO2 can be cycled reversibly below -0.37 V, but the drained capacity is very low for β-MnO2.

The presence of Mn3+ and Mn4+ vacancies associated to structural disorderin synthetic MDs increases their reduction potential and completely modifies the chemicalproperties. This mixed valence state seems to be at the origin of the reduction properties by proton insertion in protonic electrolytes.
Gypsum-Free Portland Cement Pastes of Low Water-to-Cement Rat10
Authors: ŠkvÁra FrantiŠek
Published: April 2011

Gypsum-free portland cement is a low porosity hydraulic binder based on finely groundportland cement clinker with addition of synergetic system containing an anion-active surface active agent (usually a sulphonated polyelectrolyte) and an inorganic salt (usually sodium carbonate) for regulation of the hardening process. The properties of GF cement are different from ordinary portland cement; they display, for example, higher strength, better corrosion resistance and thermal stability. These positive differences arise from the different mineralogy and microstructure of the hydration products, for example the absence of portlandite crystals. The main component of the binder product in hardened GF cement pastes is C-S-H (mean C/S ratio 2.7, based on EDAX analysis) intergrown with very fine Ca(OH)2 and highly dispersed C-A-H phases (hexagonal and cubic). The absence of crystalline formations in the GF hardened pastes is responsible for highermechanical strength. In the Czech Republic, GF cement is produced in the cement works of CEVA Prachovice Inc. ( Holderbank group) and is used for special works in the building industry.
Microstructure-Electrical Propertyrelationships in Cement-Based Materialss
Authors: Olson R.A. , Moss G.M. , Christensen B.J. , Shane J.D. , Coverdale R.T. , Garboczi E.J. , Jennings H.M. , Mason T.O.
Published: April 2011

There has been much recent progress on the application of impedance spectroscopy (IS) to the study of microstructure and transport in cement-based materials. The IS spectrum allows for the precise determination of bulk resistance, which is a measure of the pore phase interconnectivity, and calculation of the relative dielectric constant, which is related to the capillary pore size and distribution. High values of the relative dielectric constant (σ105) observed in cement paste at early hydration times are the direct result of the microstructure inducing dielectric amplification. Solvent exchange and freezing experiments, combined with digital-image-based computer modeling, have confirmed the role of large capillary pores in the dielectric amplification in young pastes.

The conductivities (σ) and relative dielectric constants (εr) of ordinary portland cement (OPC) pastes were monitored during cooling and solvent exchange with isopropanol and methanol. Dramatic decreases in σ and εr, in some cases over two orders of magnitude, occurred at the initial freezing point of the aqueous phase in the macropores and large capillary pores. The same dramatic decreases in a and er were observed at the onset of solvent exchange. Both effects provide experimental support for the dielectric amplification mechanism within the microstructure on the μm-scale. A secondary dielectric amplification was observed in the frozen and solvent exchanged pastes, which produced dielectric constants on the order of 103. This effect is attributed to amplification on the nm-scale within the layered calcium silicate hydrate (C-S-H) gel microstructure. Additional insight into the variable nature of the C-S-H microstructure was obtained by comparing the dielectric behavior of methanol-exchanged OPC pastes to isopropanolexchanged OPC pastes.
The Interfacial Transition Zone and its Influence on the Fracture Behavior of Concrete
Authors: Zampini Davide , Jennings Hamlin M. , Shah Surendra P.
Published: April 2011

Concrete specimens of constant water-to-cement ratio and varying amounts of gravel aggregate were tested under 3-point bend. The fracture toughness of the composite and surface roughness of the paste are determined. Fracture parameters obtained from the Two ParameterFracture Model (TPFM) such as the critical stress intensity factor (KIc) and critical effective crack extension (Δao) are found to be related to the average surface roughness of the paste. The Interfacial Transition Zone (ITZ) and the bulk paste are distinguished by different values of roughness. The surface roughness of the area adjacent to the aggregate particle is evaluated as a function of the distance from the aggregate surface. In particular, the surface roughness of the paste near the aggregate is greater than that of the paste far from the aggregate, and it decreases with distance from the aggregate. The higher roughness of the paste near the aggregate indicates that aggregate particles, and more specifically the ITZ associated with them, act to toughen the paste in concrete.
Crack Stability in the Fracture of Cementitious Materials
Authors: Tandon S. , Faber K.T. , Bazant Z.P.
Published: April 2011

The aim of the present study is to investigate the stability of crack propagation in cementitious materials. Tests were conducted on bend specimens in three-point and four-point loading conditions. Three-point bend specimens showed stable crack growth for mortar, normal strength and high strength concrete specimens. Alternatively, four-point bend specimens showed catastrophic failure for mortar and quasi-catastrophic failure for normal strength and high strength concrete specimens. Results will be discussed in relation to brittleness number model and specific microstructural features including the interfacial transition zone between the cement paste and the aggregate and the attendant toughening mechanisms.
Effect of the ITZ on the Leaching of Calcium Hydroxide from Mortar
Authors: Carde Christophe , François Raoul
Published: April 2011

This paper deals with the effect of the ITZ on the leaching process of cement based materials.

In order to characterize this effect, we have performed experiments on mortar samples and pure cement paste samples. Two aggressive waters were used, the first one with pH=4.5 and the second one with pH=8.5. These two aggressive waters were modelled by a solution of ammonium nitrate. Compression tests were conducted on micro-cylinder samples (10, 12 and 14 mm of diameter) because of the slow kinetics of degradation due to the leaching.

In the case of a sample made with cement paste only, the leaching process leads to a uniform degradation of the samples. The thickness of this degraded zone is the same whatever the size of the sample. The decrease in compression strength is thus completely explained by this degraded zone. In the case of a sample made with mortar, the leaching process leads also to a degradation zone whose thickness is the same whatever the size of the sample. But, the decrease in mechanical properties and the increase in irreversibility couldn't be explained for the different sizes of samples by the same thickness of leaching zone. This is due to the fact that the chemical attack progresses through the interfacial zones because they have a higher porosity than the bulk paste. The relative volume of interfacial zones linked together with the aggressive environment is more important in the case of the smaller sample.