bluuebunny/crossref_metadata_2025 huggingface dataset:
Bi1-xSbx Alloy Thin Film and Superlattice Thermoelectrics
Authors: Cho S. , Vurgaftman I. , Shick A. B. , DiVenere A. , Kim Y. , Youn S. J. , Hoffman C. A. , Wong G. K. L. , Freeman A. J. , Meyer J. R. , Ketterson J. B.
Published: April 2011

We have grown Bi1-xSbx alloy thin films on CdTe(111)B over a wide range of Sb concentrations (0≤x≤0.183) using MBE. We have observed several differences with the bulk system. The 3.5 and 5.1% Sb alloys show semiconducting behavior, and the Sb concentration with the maximum bandgap is shifted to a lower Sb concentration, from 15% in bulk to 9%. The power factor S2/ρ (where S is thermoelectric power(TEP) and ρ electrical resistivity) peaks at a significantly higher temperature (250K) than previously reported for the bulk alloy (80K). The magnetotransport properties of Bi1-x,Sbx thin films (x = 0, 0.09, and 0.16) and Bi/CdTe superlattices have been determined by applying the Quantitative Mobility Spectrum Analysis (QMSA) and multicarrier fitting to the magneticfield- dependent resistivities and Hall coefficients, using algorithms which account for the strong anisotropy of the mobilities. The calculated S values are in good agreement with experimental results. The structural stability of bulk Bi is studied using the local density linear muffin-tin orbital method. It is shown that the internal displacement changes the Bi electronic structure from a metal to a semimetal, in qualitative agreement with a Jones-Peierls-type transition. The total energy is calculated to have a double well dependence on the internal displacement, and to provide a stabilization of the trigonal phase. We show that an increase of the trigonal shear angle leads to a semimetal-semiconductor transition in Bi.
Electronic Structure and Transport Properties of CoSb3: A Narrow Band-Gap Semiconductor
Authors: Sofo J. O. , Mahan G. D.
Published: April 2011

We report calculations which show that the band structure of CoSb3 is typical of a narrow band-gap semiconductor. The gap is strongly dependent on the relative position of the Sb atoms inside the unit cell. We obtain a band gap of 0.22 eV after minimization of these position. This value is more than four times larger than the result of a previous calculation which reported that the energy bands near the Fermi surface are unusual. The electronic states close to the Fermi level are properly described by a two-band Kane Model. The calculated effective masses and band gap are in excellent agreement with Shubnikov de Haas and Hall effect measurements. Recent measurements of the transport coefficients of this compound can be understood assuming it is a narrow band gap semiconductor, in agreement with our results.
Fabrication, Characterization and Electronic Properties of Bismuth Nanowire Systems
Authors: Zhang Zhibo B. , Dresselhaus M. S. , Ying Jackie Y.
Published: April 2011

We have fabricated ultra-fine Bi nanowire (10–120 nm) arrays with packing densities as high as 7.1 × 1010/cm2 by pressure injecting its liquid melt into the evacuated nano-channels of an anodic alumina template. Using this fabrication technique, we have also prepared Te-doped n-type Bi nanowires. Free-standing Bi nanowires with an aspect ratio (length/diameter) higher than 500 are obtained by etching away the anodic alumina matrix without attacking the Bi. The resulting Bi nanowires are shown to be single crystals (with the same crystal structure as bulk Bi) and all the wires of a nanowire array are similarly oriented along the wire axis. The small electron effective mass of Bi, the high anisotropy of its Fermi surface, and the large aspect ratio of the Bi nanowires make this a very promising material for low-dimensional thermoelectric applications and an excellent system for studying quantum confinement effects in a quasi-one-dimensional (1D) electron gas. A theoretical model based on the basic band structure of bulk Bi, suitably modified for the 1D situation, is constructed to explore the electrical transport properties of Bi nanowires, which are expected to be very different from those of bulk Bi.
Thermionic Refrigeration
Authors: Mahan G. D.
Published: April 2011

The principles of thermionic refrigeration are explained. The simplest device is composed of two metal plates separated by a vacuum gap. This device is efficient at room temperature only for plates with small work functions (eø <0.3 eV). Small barriers are available in semiconductor-semiconductor interfaces (band off-sets) and in metal-semiconductor interfaces(Schottky barriers). An efficient refrigerator is modeled for these systems. Possible realizations are discussed.
Thermoelectric Transport in Superlattices
Authors: Broido D. A. , Reinecke T. L.
Published: April 2011

A quantitative description of the power factor for thermoelectric transport in quantum well and quantum wire superlattices has been developed. The size dependence of the carrier scattering rates as well as carrier tunneling between layers are included, and results are obtained for full three-dimensional superlattice systems. In addition, model calculations of the lattice thermal conductivity of free standing wells and wires have been obtained, and their implications for the thermoelectric figure of merit are discussed. Illustrative results are given for GaAs and PbTe systems.
Performance of Ultra Hard Carbon Wear Coatings on Microgears Fabricated by Liga
Authors: Ager Joel W. , Monteiro Othon R. , Brown Ian G , Follstaedt David M. , Knapp James A. , Dugger Michael T. , Christenson Todd R.
Published: April 2011

Stiction and friction are of concern for the reliable, long-term application of Ni-alloy micromachines. We have found that the application of a 30 - 70 nm hard carbon coating produces a significant reduction in the friction coefficient and wear rate of electroformed Ni substrates in reciprocating sliding contact under simulated MEMS operating conditions. To evaluate the performance of coated components, a series of 70-μm-thick microgears ranging in diameter from 0.2 to 2.2 mm were fabricated from electroformed Ni via standard LIGA processes and fixtured on posts in preparation for the coating procedure. A pulsed vacuumarc deposition process was used to deposit a carbon coating on the gears with the plasma incident at a shallow angle to the gears' top surface. A sample bias of −2 keV was used in order to produce a coating with relatively low stress and good adhesion while maintaining high hardness. This coating process is known to be somewhat comformal to the component surfaces. The coating uniformity, particularly in the high-aspect-ratio areas between the gear teeth, was evaluated with micro-Raman spectroscopy. It is shown that the coating can be applied uniformly on the top gear surface. Between the gear teeth the coating was the same thickness as on top of the gear down to a point 50 μm below the top surface. Below that point (i.e. between 50 and 70 μm), the coating thickness is somewhat thinner, but is still present. These results demonstrate that it is possible to a deposit hard carbon coating on microgears to reduce friction and wear in micromachines.
Torsion Testing Of Diffusion Bonded Liga Formed Nickel
Authors: Christenson T. R. , Buchheit T. E. , Schmale D. T.
Published: April 2011

A test technique has been devised which is suitable for the testing of the bond strength of batch diffusion bonded LIGA or DXRL defined structures. The method uses a torsion tester constructed with the aid of LIGA fabrication and distributed torsion specimens which also make use of the high aspect ratio nature of DXRL based processing. Measurements reveal achieved bond stengths of 130 MPa between electroplated nickel with a bond temperature of 450°C at 7 ksi pressure which is a sufficiently low temperature to avoid mechanical strength degradation.
Influence of Specimen Size and Sub-Micron Notch on The Fracture Behavior of Single Crystal Silicon Microelements and Nanoscopic Afm Damage Evaluation
Authors: Minoshima Kohji , Inoue Shigemichi , Terada Tomota , Komai Kenjiro
Published: April 2011

Simple bending tests of single-crystal silicon microelements fabricated by photoetching were performed. Silicon microelements deform elastically until final catastrophic failure, showing a brittle nature. The fracture strength increases with a decrease in specimen size, and the maximum strength reaches about 8 GPa. A Focused ion beam was used to machine a sub-µm deep notch. Such a small notch decreases the fracture strength of a microelement. Some fatigue tests were conducted in laboratory air and in distilled water: water reduces the strength of microelement under fatigue loading. Fracture surface and sample surface were closely examined with a scanning electron microscope and an atomic force microscope, and the fracture mechanisms are discussed from the nanoscopic points of view.
Dry Etching of Sol-Gel Pzt
Authors: Zeto R. , Rod B. , Dubey M. , Ervin M. , Conrad J. , Piekarz R. , Troliermckinstry S. , Su T. , Shepard J.
Published: April 2011

Two techniques for dry etching of sol-gel lead zirconate titanate (PZT 52/48) thin films were investigated: reactive ion etching and argon ion milling. Etched profiles were characterized by scanning electron microscopy. For reactive ion etching, a parallel plate etcher was used with HC2ClF4, an environmentally safe etch gas, in a process described by other researchers. Etch rates were measured and compared as a function of electrode shield material (ardel, graphite, alumina) and RF input power (100 to 500 W). These etch rates varied from 10 to 100 nm/min. Reactive ion etched sidewall angles 12° off normal were consistently produced over a wide range of RF powers and etch times, but overetching was required to produce a clean sidewall. For argon ion milling, a 300 mA/500 V beam 40° off normal to the substrate operating in a 72 mPa argon pressure was used. These ion milling conditions produced an etch rate of 250 nm/min with a sidewall slope angle of about 70°. The ion milling etch rate for sol-gel PZT was significantly faster than rates reported for bulk PZT. The 500 nm thick PZT films used in this study were prepared by the sol-gel process that used methoxyethanol solvent, spin coating on t/Ti/SiO2 silicon substrates, and rapid thermal annealing for 30 s at 650 °C for crystallization of the perovskite phase.
Sol-Gel Casting of Ceramic Microcomponents
Authors: Chan C. M. , Cao G. Z.
Published: April 2011

Development of ceramic microcomponents can open up the current silicon-based MEMS technology to new applications, especially for use in high temperature, chemically reactive environments. We report a study of sol-gel technologies applied to the fabrication of microcomponents. Organic/inorganic hybrid materials, particularly silica-based hybrids, were developed by sol-gel processing. A weak silica network was made possible by using acid catalyst, low functionality organic precursor in the sol preparation. Since the weak network has a high tendency to collapse, the result is a denser material. Incorporation of organic ligands modifies the surface chemistry of gel network so that a greater drying stress was developed and a denser hybrid structure was achieved without high temperature treatment. In addition, the incorporation of organic ligands prevented formation of cracks. Nanoscale oxide particles were dispersed and incorporated into the gel network by surface condensation. The incorporation of solid nanoparticles into sols greatly reduced the shrinkage of gels and enhanced the mechanical strength of the components. In addition, silica sol was applied to coat metallic microcomponents and a thin uniform was formed.
Microstructural Evolution of Co-fired Ceramic Tapes for MEMS Applications
Authors: Charoenmechaikul Suebpong , Luzzi David E.
Published: April 2011

A study of the structure and thermodynamics of the densification process in a model alumina-based ceramic tape system during thermal processing is presented. DuPont's Green Tape™ 951, which is primarily composed of frit (>50% silica), alumina and an organic binder, is used as the model system. The microstructures of annealed specimens are characterized by scanning electron microscopy as a function of annealing time and temperature. The distribution and shape of pre-existent pores and frit particles are found to be strongly dependent on the processing conditions. With the processing temperatures significantly below conventional sintering temperature of alumina, the behavior of the frit is the critical determinant of the final microstructure and mechanical behavior.
A Direct Molding Technique to Fabricate Silica Micro-Optical Components
Authors: Lee Choon-Keat Terence , Vasile Michael J. , Goettert Jost
Published: April 2011

A technology for the direct molding and release of silica micro-optical components in polymethyl methacrylate (PMMA) molds is developed. The objectives of this work are to bypass some of the usual steps in deep x-ray lithography (DXRL) and to determine the suitability of GR650 resin (methylpolysilsequioxane) for molding thick, high aspect ratio structures. The process is initiated by DXRL exposure of PMMA, followed by spin-on glass application, a cure at 85°C to set the shape of the resin, followed by demolding. The cure is below the glass transition temperature of PMMA and the demolding process allows re-use of the mold. There is no need for electroforming in the replication process. PMMA molds with thickness of 250, 350 and 500 um were fabricated by DXRL and standard resist development. A novel metal sacrificial layer technique is used in the release process with initial yield of about 50%. Microoptical elements that were fabricated include lenses, prisms, grating structures and transmission test structures. These components are cured above 400°C after release, to convert the organosilicon polymer to a silica-like material. Weight loss from the high temperature cure was in the range of 15 to 25%, while linear dimensions of the components decreased by about 1%. Composition of the molded, cured structures was measured by XPS depth profiles.
Rapid Thermal Annealing for Residual-Stress Relaxation in Undoped or Doped Polysilicon Thin Films
Authors: Zhang Xin , Zhang Tong-Yi , Zohar Yitshak
Published: April 2011

The residual stress in doped and undoped polysilicon films, before and after rapid thermal annealing (RTA), is investigated using both wafer-curvature and micro-rotating structures techniques. Microstructure characterization has been conducted as well to understand the mechanism of the stress evolution. The results show that the compressive residual stresses in undoped polysilicon films can be reduced or eliminated within a few seconds RTA. Surface nitridation and grain growth are identified as the mechanisms responsible for the stress evolution.
Deep Reactive Ion Etching of Silicon
Authors: Ayón A. A. , Chen K.-S , Lohner K. A. , Spearing S. M. , Sawin H. H. , Schmidt M. A.
Published: April 2011

The ability to etch deep trenches in silicon while controlling not only the profile of etched features but also the etching rate, uniformity and selectivity enable us to expand the number and scope of MEMS devices. In fact, the increase of MEMS applications in different and varied fields requiring deep silicon etching or high aspect ratio structures (HARS) has even been extended to include microturbomachinery which was recently introduced as a feasible source of power generation. Many projects also place additional demands on surface morphology. Thus, the scalloping observed on vertical walls during time multiplexed deep etching (TMDE), the roughness of horizontal surfaces exposed to the glow discharge and the radius at the bottom of etched features are also relevant. Therefore, it is important to understand not only the plasma processes involved but also the dependence of response variables on operating conditions. For this purpose we have designed, performed and analyzed sets of experiments adequate to fit quadratic models. The data was collected using interferometry, atomic force microscopy (AFM), profilometry and scanning electron microscopy (SEM). The exercise involved eight etching variables and it was conducted in an inductively coupled deep reactive ion etcher (DRIE). The mapping of the dependence of response variables on dry processing conditions produced by this systematic approach provide additional insight in the plasma phenomena involved and supply practical tools to locate and optimize robust operating conditions.
The Benefits of Process Parameter Ramping During The Plasma Etching of High Aspect Ratio Silicon Structures
Authors: Hopkins J. , Ashraf H. , Bhardwaj J. K. , Hynes A. M. , Johnston I. , Shepherd J. N.
Published: April 2011

In the ongoing enhancement of MEMS applications, the STS Advanced Silicon Etch, (ASETM). process satisfies the demanding requirements of the industry. Typically, highly anisotropic. high aspect ratios profiles with fine CD (critical dimension) control are required. Selectivities to photoresist of 150:1 with Si etch rates of up to 10μm/min are demonstrated. Applications range from shallow etched optical devices to through wafer membrane etches. This paper details some of the fundamental trends of the ASETM process and goes on to discuss how the process has been enhanced to meet product specifications. Parameter ramping is a powerful technique used to achieve the often-conflicting requirements of high etch rate with good profile/CD control. The results are presented in this paper.
Negative Thermal Expansion Behaviour in The NZP Phase NbTi(PO4)3
Authors: Woodcock D. A. , Lightfoot P. , Smith R. I.
Published: April 2011

We present new detailed structural data versus temperature on the Nasicon structured material NbTi(PO4)3 obtained from powder neutron diffraction studies. This material shows a significant volume contraction over the range 20°C < T < 700°C. αa varies between –4.34 and -0.11 × 10-6°C-1 and αc between 0.08 and 3.07 × 10-6°C-1 over this range. This behaviour contrasts with the case of NaTi2(PO4)3 (NaTP) which shows a positive volume expansion. The difference in this behaviour can be explained by the presence of filled MI sites in NaTP which are vacant in the case of NbTP.
New Organometallic and Coordination Chemistry Routes Towards Unsupported and Silica-Supported Bismuth-Based Oxide-Type Materials
Authors: Devillers M. , Lebrun S. , Tirions O. , Wullens H.
Published: April 2011

Coordination and organometallic compounds containing bismuth, lanthanum or molybdenum are used as precursors for the preparation of unsupported or silica-supported Bi-based oxides. Bismuth (III) and lanthanum (III) polyaminocarboxylates, and more specifically homo- and heteropolymetallic complexes of triethylenetetraaminehexaacetic acid (H6ttha) are shown to constitute adequate precursors for the formation of mixed Bi2-xLaxO3 oxides at moderate temperatures. Silica-supported bismuth molybdates are obtained from impregnation or combined impregnation-deposition procedures involving Bi ß-diketonates, carboxylates or mixed acetate-Nmethylimidazole Bi complexes, in association with molybdenyl acetylacetonate or heteroleptic carbonyl-pyridine Mo complexes, either dissolved or dispersed in various organic solvents.
Reactivity of SnO2, Ruthenium-Supported SnO2, Ruthenium (Platinum) Ion-Exchanged SnO2 with Inert, Combustible Gases and Air: An Electron Paramagnetic Resonance Study
Authors: Canevali C. , Chiodini N. , Morazzoni F. , Scotti R.
Published: April 2011

SnO2, Ru/SnO2 and Pt/SnO2 were prepared by sol-gel condensation method. Ru/SnO2 was also obtained by supporting the metal on SnO2 xerogel. The reactivity of these materials towards CO and air, studied by Electron Paramagnetic Resonance spectroscopy (EPR), suggests that the electron transfer processes at the oxide surface are favored by the presence of the metal, in the order Pt > Ru ion-exchanged > Ru-supported. A rationale was given for the differences and for the choice of a material suitable to high sensitivity gas sensors.
The Valence Electronic Structure of Co3O4: Is It a Charge-Transfer Insulator?
Authors: Langell M.A. , Carson G.A. , Smith S. , Peng L. , Nassir M.H.
Published: April 2011

Despite the relevance to a variety of materials applications, the electronic and bonding properties of spinel transition metal oxides are not well established. We report here the slow oxidation of CoO(100) to Co3O4, studied by photoemission (UPS and XPS), low energy electron diffraction (LEED) and high resolution electron energy loss spectroscopy (HREELS) with the aim of elucidating the valence band electronic structure of the Co3O4 spinel. The original Mott insulator picture of the parent CoO substrate has been revised in recent times, after careful analyses and extensive debate, to the more detailed charge-transfer insulator model which includes some admixture of oxygen 2p levels in the 3d-derived valence band. No equivalent band structure analysis has been performed on the spinel oxides, perhaps in part because of the greater complexity of the 56-atom unit cell with two different cation lattice sites and oxidation states. In this study, we determine the valence band structure of the spinel oxide and address the question of whether Co3O4 can be modeled as a charge-transfer insulator in analogy with its closely related rocksalt substrate.
Electronic Properties of Bi and In Substituted Layered Ba4Pb3O10 Compounds
Authors: Kasal R. , Ulanday J. B. , Obien J. , Jayaram B.
Published: April 2011

Electronic properties of the layered compounds with the general composition Ban+1(Pb,Bi)nO3n+1 are quite interesting as the crystal structure of these materials is quite similar to that of high-Tc cuprates. We have investigated the effect of Bi and In substitution on the structure, oxygen stoichiometry (carrier concentration) and the electronic properties of Ba4Pb3O10 compounds. The X-ray powder diffraction results indicate that the unit cell symmetry changes from body-centered tetragonal to cubic with the increasing concentration (x) of Bi and In. The oxygen stoichiometry of the materials is found to increase monotonically with the increase in x(Bi). On the other hand it decreased almost linearly with the increasing x(In). Resistivity of the materials is measured as a function of temperature in the temperature region 3-300K. It is found that the room temeprature resistivity increases with increasing x(Bi/In). Since the oxygen stoichiometry values suggest an increase in the carrier concentration with increasing x(Bi/In), it appears that the disorder caused by the substitution at the Pb site has lead to the carrier localization. For x(Bi)<0.2, we found that the resistivity varies as a function of lnT, which is indicative of weak localization. However, at higher concentrations 3D-VRH behavior is observed. On the other hand the resistivity of indium substituted samples show M-I transition, at low concentrations.
Liquid Crystal Behavior of V2O5·nH2O Gels
Authors: Livage J. , Davidson P. , Commeinhes X. , Pelletier O.
Published: April 2011

Most liquid crystals are made of organic molecules, very few of them are based on mineral compounds. Vanadium pentoxide gels and sols have been shown to give mesophases. They are made of ribbon-like polymeric particles of vanadium pentoxide dispersed in water. Ansitropic xerogel layers are formed when these gels are deposited and dried onto flat substrates. Dehydration is reversible and fluid phases are again obtained via a swelling process when water is added to the xerogel.

When observed by polarized light microscopy, colloidal suspensions of V2O5 ribbons display defects typical of lyotropic nematic phases. Dilute nematic suspensions can even be oriented by applying a magnetic field of about 0.5 Tesla. Such a liquid crystal behavior is mainly due to the highly anisotropic shape of vanadium oxide colloidal particles. Acid dissociation at the oxide/water interface gives rise to surface electrical charges and electrostatic repulsions should also be responsible for the stabilization of the nematic phase.
Phase Formation, Stability and Superconducting Properties of Mechanically Alloyed Yttrium-Nickel-Borocarbides
Authors: Ledig L. , Hough D. , Oertel C.-G. , Eckert J. , Skrotzki W.
Published: April 2011

The solid state reaction of YNi2B2C by mechanical alloying of elemental powders has been investigated by X-ray diffraction, transmission electron microscopy and susceptibility measurements. Depending on the ball milling parameters either nanocrystalline YNi2B2C or an amorphous phase can be produced. Crystallization of the amorphous phase by annealing at 893 K produces YNi2B2C as major and Ni2B as minor intermetallic compound. Superconductivity is only observed in the annealed state. However, the transition temperature is much lower than in arc-melted samples. This is discussed with respect to the nanocrystalline and amorphous state as well as deviations from stoichiometry produced by impurities introduced during milling.
6Li and 7Li MAS NMR and In Situ X-ray Diffraction Studies of Lithium Manganate Cathode Materials
Authors: Lee Young Joo , Wang Francis , Grey Clare P. , Mukerjee Sanjeev , McBreen James
Published: April 2011

6Li MAS NMR spectra of lithium manganese oxides with differing manganese oxidation states (LiMn2O4, Li4Mn5O12, Li2Mn4O9, and Li2Mn2O4) are presented. Improved understanding of the lithium NMR spectra of these model compounds is used to interpret the local structure of the LixMn2O4 cathode materials following electrochemical Li+ deintercalation to various charging levels. In situ x-ray diffraction patterns of the same material during charging are also reported for comparison. Evidence for two-phase behavior for x < 0.4 (LixMn2O4) is seen by both NMR and diffraction.
Carbon Powders Prepared in Rf Thermal Plasma and Their Application to Anode of Lithium Secondary Baltery
Authors: Kurihara M. , Uchida S. , Maruyama S. , Takizawa T. , Moriyoshi Y , Ishigaki T , Sato Y
Published: April 2011

Carbon powders prepared by the RF thermal plasma treatment of phenolic resin were examined for the anode materials of lithium secondary battery. Modification of these carbon powders in chemical composition, crystal structure and surface morphology was characteristics of the thermal plasma treatment The treated powders showed the unique microstructure. TEM observation showed the non-uniform distribution of graphitized and amorphous areas in the particles. The electrochemical measurements as an anode for lithium secondary battery were examined in IM LiClO4in a 50:50 mixture of ethylene carbonate and diethyl carbonate. While the electrochemical extraction of lithium ion from plasma-prepared carbon powders proceeded in three stages, the electrochemical insertion looked to proceed in two stages. These electrochemical features can be associated with the uncommon microstructure characteristics.
Thin Films of Ionic Conductors by Laser Ablation
Authors: Morcrette M. , Barboux P. , Perrière J. , Laurent A. , Boilot J. P. , Brousse T.
Published: April 2011

Films of insertion compounds and solid state electrolytes have been synthesized in order to study their applications in the domain of electrochemical ion and gas sensors. Laser ablation was used to deposit lithium metal oxides (LiMO2 where M is a transition metal Co or Mn).

The chemical composition in the films has been studied by Rutherford Backscattering spectrometry and nuclear reactions analysis in the case of the light elements (O, Li). For lithium transition metal oxides (LiMO2), the oxygen and lithium contents are determined by a thermodynamical equilibrium between the films and the partial pressures in the chamber. In these cases, laser ablation allows the synthesis of crystalline structures with a large range of oxygen non stoichiometry as compared to solid state reactions. They lead to interesting electrical properties. Using the appropriate temperatures and oxygen pressures, films with the correct stoichiometry could be obtained as polycrystalline onto Si or Si/Pt substrates whereas they exhibit high texturing and epitaxial growth onto MgO or MgO/Pt.

The films of LiMn2O4 and LiCoO2 have been used as electrochemical sensors for the measurement of the lithium concentration in solutions. They show a very rapid and selective response.
Understanding of Lithium Insertion into λ-MnO2 Compounds
Authors: Sarciaux S. , Salle A. Le Gal La , Verbaere A. , Piffard Y , Guyomard D.
Published: April 2011

A large variety of EMD and HTMD samples with various oxygen and water contents and various structural parameters Pr and Mt has been prepared. We show that the physico-chemical and structural parameters of the λ-MnO2 compounds are related to the synthesis conditions. New compounds were obtained with unusual amounts of intergrowth and twinning defects.

The Li insertion study focuses on a comprehensive investigation of the relationships between the material characteristics of the samples and their Li insertion behavior, and on the structural characterization of selected compounds after cycling. The oxygen content drastically affects the shape of the discharge curve after the first cycle and the total reversible capacity. The amount of structural water has an influence on the transformation kinetics of the starting phase. For optimized oxygen content (y= 2 in MnOY), the intrinsic reversible Li insertion capacity is maximum when the amount of microtwinning defects is minimum and when the structure is either mostly Ramsdellite or faulted Pyrolusite. Results show that, upon cycling, the λ-MnO2 structure seems to evoluate towards less Pyrolusite defects together with the apparition of new kinds of defects.

This work shows that λ-MnO2, compounds could be good candidates for the cathode application of Li-metal rechargeable batteries, provided that the physico-chemical and structural parameters of the starting compound are well chosen.
Knowledge Discovery in Conducting Polymeric Composite Devices: AN Essential Research Towards New Computer/Sensing Information Devices
Authors: Talaie A. , Eisazadeh H. , Adachi K. , Taguchi T. , Romagnoli J.A. , Buniran S.
Published: April 2011

A composite of two conducting polymers, polyaniline and polypyrrole, could result in much improved physical properties with respect to their applications in pH electrodes and conducting paints/coatings. However, the composite has time dependant properties that made the use of dynamic computational algorithms necessary to control its behaviour. We used a sandwich-modified electrode as a pH-sensing electrode, which was integrated with a pre-trained computer for data processing and knowledge discovery. Conducting polypyrrole/polyaniline colloidal composites have been also prepared by deposition of the mixture solution of polypyrrole and polyaniline at negative potentials. Different substrates were dipped in the solution containing the mixture together with an acrylic latex and after drying the adhesive strength and electroactivity of the paint were studied. Several colloidal composite based coatings were investigated. At last a computer facilitated with powerful artificial ncural network based algorithms classified the paints.
Ionic Space Charge Relaxation and High Dielectric Permittivity in Polyethylene Oxide
Authors: Wagner A. , Kliem H.
Published: April 2011

Thin films (0.3μm to 11.2 μm) of Polyethylene Oxide (PEO) with molecular weights from 6 × 103 to 4 × 105 were prepared from aqueous solutions by a spin technique as AI-PEO-AI structures, or as AI-PEO-Si structures. Dielectric measurements (capacitance and loss angle) were carried out in a frequency range 3 mHz ≤ f ≤ 1 MHz in atmospheres of different relative humidity (0% r.h. to 75% r.h.) and at different temperatures (293 K to 323 K). The nominal dielectric permittivity exhibits a remarkable dependence on the sample thickness and the relative humidity. We find a true volume polarization in the high frequency range and a thermally activated relaxation process in the low frequency range, whose time constant is shifted towards high frequencies with increasing r.h.. It is considered that due to the absorbed dipolar water molecules chemical bonds within the sample are broken and quasi-free ions are generated. These ions move through the sample to the electrode interfaces and form an ionic space charge. We assume that at the PEO-Al interface an oxide layer is formed, which is impermeable for these ions. The transit times and the drift velocities of the ions are almost independent of the electric field strength in the low-field limit. Therefore we conclude that the movement of the ions can be described by a multiwell potential model, where the transition probability between neighbored wells is thermally activated.
An Improved Composite Polymer Electrolyte for Lithium Metal Batteries
Authors: Mastragostino M. , Soavi F. , Zanelli A.
Published: April 2011

We have demonstrated that PEO-based polymer electrolytes prepared by solvent-free procedures and with the addition of particle-size ceramic powder have very stable lithium interface properties—a very important feature for the development of successful lithium metal polymer batteries (LPBs). The results of cyclability tests at different charge-discharge rates carried out on prototypes of LPBs assembled with the dry prepared PEO20-LiCF3SO3-20%w/w λLiAlO2 composite electrolyte and with a composite cathode based on LiMn204 spinel operating at 3V are reported and discussed.
Synthesis of Ceramics/Polymer Nanocomposites Protonic Conducting Membrane
Authors: Honma I. , Hirakawa S. , Bae J.M.
Published: April 2011

High temperature protonic conducting polymer membrane provides new technological applications in the electrochemical devices including electrochromic displays, chemical sensors, fuel cells and others. Organic/inorganiaianocomposites membrane consists of SiO2/PEO (Polyethylene Oxides) hybrid are remarkable family of isotropic, amorphous polymer materials, which has been synthesized through sol-gel processes. The hybrid membrane doped with acidic surfactant molecules shows good protonic conductivities at high temperatures above 100C. The membrane was found to be thermally stable at high temperatures because of the inorganic SiO2 framework in the composites matrix.
Mixed Alkali Effect as a Retarding Effect of Secondary Diffusion Processes in Glass
Authors: Belostotsky Vladimir
Published: April 2011

Ion mobility in mixed alkali glass is discussed in the context of the recent experimental observation that oxygen diffusion from molten salt into glass accompanies the replacement of smaller alkali ions for larger alkali ions during ion exchange. The assumption is made that simultaneous migration of two unlike monovalent cations induces, among other things, oxygenexchange diffusion between sites. Diffusing oxygen molecules form additional fluctuating sites or traps lying along the ion pathways between regular ionic sites. Instead of jumping directly to the regular ionic site, mobile ions are forced to execute several additional hops between fluctuating sites, and this results in significant reduction in ion mobility.
The Role of Effective Rate Constants in Interfacial Kinetics
Authors: Maier Joachim
Published: April 2011

A brief excerpt of a more comprehensive quantitative theoretical analysis on the role of effective rate constants in interfacial processes is given (in particular [1], see also [2,3]). Chemical incorporation, tracer incorporation and steady state electrical experiments are considered. It is shown that besides experimental differences there are mechanistic and conceptual differences between the three effective rate constants (kδ, k*, Qq). The treatment based on irreversible thermodynamics and chemical kinetics shows similarities and differences with respect to the analogous situation in the bulk. As special cases adsorption and transfer limited kinetics are considered. Having related the k-values to the exchange rates of the rate determining step and to the chemical capacitance outside the boundary zone, the characteristic dependencies on controlling parameters and also the correlation with diffusion coefficients can be derived. This is done for electron-rich materials such as SOFC cathodes. A further point which is briefly mentioned in this context is the fact that flux constriction effects may lead to apparent surface rate constants. The role of space charges is briefly discussed for the case of grain boundary kinetics [4]. In electron-poor materials such as SrTiO3(Fe2O3) or Zr02(Y203) additional mechanistic differences should occur, since in the tracer case mechanisms are possible at the surfaces which do not have to involve electrons directly. Here also discrepancies with respect to electrical experiments are predicted (leading to a surface analogue of a Haven ratio). Some experimental results obtained with SrTiO3 are discussed in this context.
Determination of Diffusion Coefficient of Impurity Ions in a Crystal from their Drift Under Electric Field
Authors: Akopyan A.A. , Kislyuk V.V. , Pekar G.S.
Published: April 2011

We studied the drift of Cd interstitials in CdS single crystals at an electric field applied to the crystal. These atoms are totally ionized at moderate temperatures of the investigation (300 - 400 K). Mobile Cd ions drift from the anode to the cathode. A time-dependence was studied experimentally for the voltage dropped on the crystal at the constant value of the current passed through the sample. A non-stationary problem developed for the transient process allowed to derive the ion mobility in such a process from the experimental data. Concentration profiles and their time history were investigated in detail for the ions and free carriers.
Doping of Ionic Compounds: Solubility Limit and Charge Compensation
Authors: Tsur Y. , Riess I.
Published: April 2011

An analysis is presented that allows calculating properties of primary solid solutions in ionic crystals. These properties are expressed in terms of properties of the undoped host material and the impurity.

One can calculate the solubilities of the impurities with a knowledge of the concentration of what is defined as the “corresponding native species”, the standard chemical potential of the materials involved and the local shear modulus of the host material.

The changes in concentrations of ionic point defects as well as electron/hole concentrations due to doping are also calculated. In order to do so one has to know the concentrations of the native point defects in the undoped host material and the concentration of the dopant. It is shown that in a native p-type semiconductor (e.g., Cu20) extrinsic donors are mainly self-compensated by ionic defects, while extrinsic acceptors are compensated significantly by holes.
Electrical Conductivity in Nanocrystalline ZrO2:Y
Authors: Kosacki Igor , Petrovsky Vladimir , Anderson Harlan U.
Published: April 2011

The electrical conductivity of nanocrystalline thin films and bulk microcrystalline ZrO2:16%Y (YSZ) has been studied as a function of oxygen activity and correlated with the microstructure. Nonacrystalline films are characterized by enhanced conductivity and different stoichiometry compared with microcrystalline specimens. The interpretation of the results is based on a defect pair association model with partly ionizated acceptor and donor centers.
The Synthesis and Electrical Conductivity of Novel Mixed Ionic and Electronic Conductors in The Gd2GaSbO7-Gd2Zr2O7 Solid Solution
Authors: Takamura H. , Tuller H. L.
Published: April 2011

The synthesis and electrical conductivity of a novel solid solution pyrochlore Gd2GaSbO7 - Gd2Zr2O7 were studied as a function of x in Gd2(GaSb)1-xZr2xO7 (0 ≤ x ≤ 1). In this study, single phases with the pyrochlore structure were obtained in the range of x ≤ 0.2, while a garnet phase appeared as a minor second phase for x ≥ 0.3. In the x = 0.2 sample, evidence of the displacement of 48f oxygens towards the normally empty 8b site was suggested by Rietveld analysis. The total electrical conductivity of the pyrochlores was 2.6x 10−2 S/m for x = 0.0 and 6.0×10−3S/m for x = 0.2 at 1273 K, respectively. In addition, evidence for n-type semiconductivity was obtained for x = 0.2 under reducing conditions. Further studies are underway to identify the dominant carriers under oxidizing conditions.
Improvement of Fluorite Structures in M203-CeO2 (M=Sm, La) System Based on a Novel Effective Index
Authors: Mori Toshiyuki , Ikegami Takayasu , Yamamura Hiroshi
Published: April 2011

M2O3-CeO2(M=Sm, La) system is one of the most interesting of fluorite oxides since the oxide ionic conductivity of it is higher than that of yttria-stabilized zirconia. In this study, the effective index for the improvement of ionic conductivity in CeO2 systems was defined using information regarding ionic radii and the level of oxygen vacancies from the perspective of crystallography. It is assumed that the M2O3 CeO2 based oxides approach the ideal fluorite structure for fast ionic conduction when the effective index increases toward 1. A small amount of alkali- or alkali-earth doped M2O3-CeO2 (M=Sm, La) solid solutions were prepared based on this effective index. The oxide ionic conductivity increased with an increase of this effective index. (La0.75Sr0.2Ba0.05)0.175 Ce0.825 O1.89 that had high effective index, showed high oxide ionic conductivity over the order of magnitude in comparison with 8mol% yttria-stabilized zirconia. Moreover, the oxygen partial pressure dependence of oxide ionic conductivity of M2O3-CeO2(M=Sm, La) solid solutions was improved by the increasing effective index. The utility of this effective index, for improvement of the electrical properties in fluorite CeO2 based materials, was investigated.
Development and Performance of A Rechargeable Thin Film Solid State Microbattery
Authors: Jones Steven D. , Akridge James R. , Middaugh Richard L.
Published: April 2011

The fabrication of thin-film batteries has been achieved for more than a decade (Energizer1, Oak Ridge2, Seoul National Univ.3). The inventor of the process was K. Kanehori(ndeI u 1) The processes utilized; sputtering, vapor deposition, solvent coating of electrolyte, have succeeded in laboratory trials in making working cells. No large commercial process nor application has developed to date though pilot plant capability exists4. Performance characteristics of microbatteries are sufficient to easily power micro-sensors and CMOS microelectronics. On chip carrier power capability could be realized. The materials of today's microbattery are detrimental to silicon technology which can be a draw back to commercialization. New materials and processes need to be investigated.
Magnesium Primary Batteries
Authors: Koval'Chuk E.P. , Skolozdra O.M.
Published: April 2011

Polyaniline, aniline and o-NO2-aniline copolymer were synthesized using (NH4)2S2O8 as oxidant in 1 M HCl water solution. By means of IR, Raman spectroscopy, gravimetric and microanalysis it was confirmed that the obtained product is oxydized emeraldine. We developed Mg|2 M MgCl2(H2O + CH3) (3:1)| co-polymer (polyaniline) prismatic-type cells. The highest specific charge and energy were observed for cell with co-polymer AN:o-NO2-AN (8:2) which were 420.74 Ah kg−- and 424.95 Wh kg−-, respectively.
Catalytic Combustion of Methane Over Metal Oxide Catalysts
Authors: Eguchi Koichi , Takahara Hiroyuki , Inoue Hiroshi , Sekizawa Koshi
Published: April 2011

Cation-substituted hexaaluminate compounds, ABAl11O19-μ (A = La, Pr, Sm, and Nd; B = Cr, Mn, Fe, Co, Ni, and Cu) were investigated for application to high temperature catalytic combustion. Two series of modifications of the compounds was made by cation substitution; substitution of large cations in the mirror plane with lanthanides ions, and of transition metals for Al site in the spinel block. In a series of AMnAlllO19-μ, surface area and catalytic activity increased with an increase in ionic radius of lanthanides. La3+ is superior as the large cation in the mirror plane of the hexaaluminate to other tri-valent cations with small ionic radii. The catalytic activi- ties of LaBAl11O19-μ, were enhanced when Mn and Cu were employed as the B-site substituents. Although Mn and Cu were also effective substituents for enhancing catalytic activity in Ba-based hexaaluminate compounds, their activity was low as compared with the La-based catalysts. These results indicate that the redox cycle of transition metal in hexaaluminate lattice and cata- lytic activity appears to be affected sensitively with the electronic or structural effect of large cation in the mirror plane.
Photocatalytic Reductions of Nitric Oxide in gas Phase and Nitrate ion in Water with Reducing Agents on Hollandite Catalyst
Authors: Mori Toshiyuki , Suzuki Jun , Fujiimoto Kenjim , Watanabe Mamom , Hasegawa Yoshio
Published: April 2011

Photoctalysis of a unique hollandite compound was investigated for the reductions of nitric oxide (NO) in gas phase and nitrate ion (NO3) in water with reducing agents under UV irradiation. Both NO and NO3 are hazardous chemicals to human. Recently, it was reported that titanium oxide (TiO2) photocatalyst perfomaed the oxidative decomposition of NO to NO3. However, an ideal photocatalytic removal of NO would be the reductive decomposition of NO to N2 and O2 without by-products. In this study, the surface activity of the unloaded hollandite, prepared by sol-gel method, was applied to the photocatalytic reaction. The present photocatalysis was quantitatively examined by using on-line mass spectrometry and ion chromatography, and the adsorption species on the hollandite surface was analyzed by in-situ IR spectroscopy. UV-ixradiated hollandite extu'bited high selectivity for the formation of N2 in the reductive decomposition of NO. Moreover, this catalyst also showed the reductive decomposition of NO3 to NO2 and N2 in water. In particular, the photocatalytic decomposition of NO3 would be a new pathway that has not been reported for popular photo-catalysts such as unloaded TiO2. Probably, this type compound is expected to have potentialities as a new type photocatalyst.
Heterogeneous Catalysts and Inorganic Sorbents: Modeling Applications and Opportunities
Authors: Freeman C.M. , Hill J.-R. , Wimmer E.
Published: April 2011

Simulation in catalyst and sorbent research spans a wide range of techniques and applications complementing and enhancing experimental approaches. This includes (i) model construction and visualization, (ii) materials characterization through simulation of experiments such as x-ray diffraction, (iii) atomistic simulations of dynamic processes such as docking and diffusion using empirical potentials, and (iv) quantum mechanical methods predicting chemical bonding and reactivity. Thorough technical validation, algorithmic and accessibility enhancements, and a strong industrial focus continue to drive key developments. The focus on practical catalyst and sorbent problems is illustrated here by (i) a simulation of the energetic diffusion barrier experienced by a toluene molecule in the microporous material boggsite and (ii) the structure, energetics and bond strengths of acidic protons in faujasite using a localized-orbital density functional approach.
Comparing the DBT Conversion by Using Crystalline WS2 and WS2 Electron Irradiated Catalyst
Authors: Rangel R. , Alonso G. , Adem E. , Fuentes S. , Galvan D. H.
Published: April 2011

A catalytic study has been performed in WS2 irradiated with electrons at 1000 kGy. The purpose is to compare irradiated WS2 with WS2 crystalline in terms of DBT conversion, selectivity and surface area analysis. Also, Scanning Electron Microscope (SEM), X-raydiffraction were performed to show microstructural changes induced by irradiation. We found that DBT conversion increased by 55 % if compared with WS2 crystalline. The surface area decreased and the initial rate constants increased by a factor of four times. The selectivity for DCH after irradiation has decreased, while the selectivity for DIF and PCH has increased substantially. The DYH/DHS ratio has decreased in 42 %. The SEM micrographs showed that irradiation, at this level, produced certain damage in the crystallinity. The X-ray analysis showed different distribution in the intensity of the principal peaks after irradiation was achieved. This behavior could be correlated to the surface area decrement and the enhancing of the catalytic activity in WS2.