bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Catalytic Synthesis of Inorganic Polymers for High Temperature Applications and as Ceramic Precursors
Authors: Rahn Jeffrey A. , Laine Richard M. , Zhang Zhi-Fan 
Published: March 2011

AbsractPolysilsesquioxanes,-[RSi(O)1.5 ]x-, exhibit many properties that are potentially quite useful for industrial applications. These properties include high temperature stability (−600°C in O2); good adhesion and, liquid crystal-like behavior for some derivatives. Moreover, [MeSi(O)l.5]x, polymethylsilsesquioxane has been used successfully as a precursor for the fabrication of carbon fiber/“black glass” (SiO2/SiC/C) composites and “black glass” fibers.Current methods of preparation depend on hydrolysis of RSiCl3 or RSi(OR)3. Unfortunately, this approach leads to several products that are difficult to purify because polysilsesquioxanes exhibit a great propensity for forming gels. We describe here a simple catalytic approach to the synthesis of polymethylsilsesquioxane copolymers of the type -[MeRSiO].3[MeSi(O)1.5].7- where R - H, OMe, OEt, OnPr and OnBu. The R - H copolymer is produced by catalytic redistribution of -[MeHSiO]xoligomers using dimethyltitanocene, Cp2TiMe2 as the catalyst precursor.Following catalytic redistribution, the resulting copolymer, -[MeHSiO].3[MeSi(O)1.5].7−, is reacted in situ with alcohols to produce -[Me(R'O)SiO].3[MeSi(0)1.5].7− (where R' - Me, Et, nPr and nBu) which serve as masked forms of the polymethylsilsesquioxane. These new copolymers have been characterized by 1H, 13C and 29Si NMR TGA and DTA. The NMR studies allow us to assign structures for the copolymer.These new copolymers exhibit improved tractability. Their high temperature properties are all quite similar; although, the MeO-, EtO- and especially the nPrO- derivatives give much higher ceramic yields than expected.
Conducting Molecular Multilayers: Intercalation of Conjugated Polymers in Layered Media
Authors: Mehrotra V. , Giannelis E.P. 
Published: March 2011

ABSTRACTPolyaniline has been synthesized in the galleries of fluorohectorite, a two-dimensional mica-type layered silicate. Intercalation of aniline in the intracrystalline region of Cu-exchanged fluorohectorite results in oxidative polymerization to polyaniline (emeraldine base form) as demonstrated by electronic, infrared and Raman spectroscopy and x-ray diffraction data. The intercalated insulating form of polyaniline becomes conducting on exposure to HCl. In-plane electrical conductivity data measured in the temperature range 274 to 573 K show a complex thermally activated behavior with room temperature conductivity 0.05 Ohm−1cm−1. The polyaniline/layered silicate hybrids represent a new class of nanocomposites consisting of synthetic conductors with molecular dimensions contained in a quasi twodimensional environment of a crystalline host.
Materials Effects on the Radiation Sensitivity of Single Mode Optical Fibers
Authors: Friebele E. J. , Askins C. G. , Gingerich M. E. , Shaw C. M. , Schmidt W. H. 
Published: March 2011

AbstractStatistically significant correlations have been established between certain fabrication parameters of matched clad single mode fiber waveguides and the induced attenuation and recovery kinetics following exposure to an ionizing radiation dose.
Process Analysis in the Preparation of Fluorozirconate Glasses
Authors: Braglia M. , Cocito G. , Ferraris M. , Grego G. , Parisi G. , Chiappetta R. 
Published: March 2011

AbstractDifferent preparation processes for fluorozirconate glasses (ZBLAN) have been investigated by infrared spectroscopy (IR) and x-ray diffraction (XRD). Glasses have been prepared with different NH4 F.HF amount (20–10–5–0% weight) or with NF30 as fluorinating agent. The presence of NF3 in the fluorination step of the preparation is useful to improve the glass quality in terms of oxide and hydroxil content: electron spin resonance (ESR) on these glasses (γ-irradiated, 20 Mrad) does not detect any signal.
Tellurium Halide Glass Fiber for Transmission in the 8–12 μm Region
Authors: Zhang X. H. , Fonteneau G. , Ma H. L. , Lucas J. 
Published: March 2011

AbstractGlasses in the Te-Br-Se and Te-I-Se systems show potential low losses in the 8–12 μm region. They are very stable against crystallization and against moisture. The lowest losses of a fiber at 10.6 μm, measured using a CO2 laser, is about 3 dB/m. The essential diffusion centers in these fibers have been proved to be bubbles. A power delivery experiment was made using a fiber having an attenuation of 5 dB/m. The power density of about 40 kw/cm2 can be injected into the fiber without damaging this fiber.
Structural Stability of Tellurium Halide Glasses
Authors: Yi Jay J. L. , Strutt Peter R. 
Published: March 2011

AbstractIn quantitative studies of the structural stability of Te-Cl and Te-Br glasses, specific attention has been devoted to determining the kinetics of their overall crystallization process and the glass composition range in which chemical decomposition occurs at elevated temperatures. The calorimetric studies reveal that the tendency of crystallization or thermal decomposition of these glasses is related to phase-diagram characteristics. It seems that the structure of these glasses is not an idealized random arrangement as described by the classic model. Underlaying causes for this deviation from a perfect random arrangement to one involving a degree of ordering ( structural group ) is discussed.
Potential Application of Bi(Pb)-Ca-Sr-Cu-O Glasses for Preparation of Integrated Optical Fibers
Authors: Zheng Haixing , Mackenzie J. D. 
Published: March 2011

AbstractThe infrared transmission, and possible high nonlinear optical susceptibility of Bi(Pb)-Ca- Sr-Cu-O glasses as well as their being the precursors for high temperature superconductors make them potential materials for integrated optical fibers. In this work, the glass formation and the fabrication of glass fibers have been investigated. The properties of the glasses have been studied. The infrared cutoff of the glasses is above 7 μm, and a high refractive index (˜ 2.9) and a high density (˜ 6 g/cm3) indicate the possible high nonlinear optical susceptibility. After being heat treated at high temperatures, the glasses become superconductors which show the response to the optical radiation due to the bolometric effect. Fabrication of an integrated optical fiber system incorporating the transmitting medium, optical modulator and detectors is possible.
Growth of Optical Quality Sapphire Single Crystal Fibers
Authors: Jundt Dieter H. , Fejer Martin. M. , Byer Robert. L. 
Published: March 2011

AbstractVoid-free sapphire single crystal fibers with diameters of 110 μm and 60 μm and lengths of over 2 m have been grown by the laser-heated pedestal growth method. The growth dynamics of the floating zone was studied and shows the features expected from a simple theoretical model. Optical losses have a minimum of 0.5 dB/m in the near infrared at 1064 nm. An absorption band centered at 400 nm results in losses of up to 20 dB/m in the visible. The fibers have potential applications in high temperature thermometry and in delivery systems for laser surgery. Absorption losses of 0.88 dB/m with a damage threshold higher than 1.2 kJ/cm2 at 2936 nm made tissue ablation feasible with fibers several meters in length.
Extended X-Ray Absorption Fine Structure study of Potassium Niobate
Authors: Kim K. H. , Elam W. T. , Skelton E. F. 
Published: March 2011

AbstractExtended x-ray absorption fine structure (EXAFS) of potassium niobate (KnbO3 ) was measured at the K edge of Nb, at various temperatures to include all phases of the material. The first shell data were analyzed to determine the distances between the niobium atom and its oxygen neighbors. The single shell amplitude almost vanishes around k-7.5 A−1 at all temperatures, suggesting two distances with a separation of about 0.21 A. Nonlinear fitting was used to determine the structure more carefully and the data at all temperatures can be fit reasonably well with two Nb-O ditances. This is in disagreement with the displacive model which implies only one Nb-O distance in the cubic phase. This result suggests that the niobium atom is displaced along the (111) direction relative to the oxygen atom in all phases. Thus, the transitions are not displacive, but have a strong order-disorder character.
Application-Specific Optical Fibres Manufactured from Multicomponent Glasses.
Authors: Taylor E. R. , Taylor D. J. , Li L. , Tachibana M. , Townsend J. E. , Wang J. , Wells P. J. , Reekie L. , Morkel P. R. , Payne D. N. 
Published: March 2011

AbstractSpecial fibres have been fabricated to demonstrate the potential of using multicomponent glass materials for sensors, devices and fibre lasers. High nonlinearity and large Verdet constants are confirmed for lead-silicate glass fibres. Nonlinear effects such as second harmonic generation (SHG), third harmonic generation (THG), electro-optic (EO) Kerr effect and optical switching are observed for F7 core glass fibres. Compound glasses are investigated as host glasses for fibre lasers and amplifiers. An all glass cladding pumped Nd-doped fibre laser from compound glassses is characterized.
Glasses for Er3+ -Doped Fiber Lasers and Optical Amplifiers
Authors: Miniscalco W. J. , Andrews L. J. , Zemon S. , Hall B. T. , Wei T. , Folweiler R. C. 
Published: March 2011

AbstractEr3+-doped silica fibers have demonstrated excellent performance as active optical devices at 1.5 μm. In an effort to identify promising new hosts, we have measureed absorption and emission cross sections for a variety of Er3+-doped glass. Compositions have been identified which have advantages over silica, particularly for pumping with AIGaAs diode lasers at 800 nm.
An Investigation of Optical Fiber Coating Performance in Embedded Sensing Applications
Authors: Haaksma Rebecca A. , Cehelnik Marilyn J. , Kerkhoff M. Jonell 
Published: March 2011

AbstractThe use of composite materials for aerospace applications has created an increased need for developing nondestructive methods for assessment of composite performance. Embedded optical fiber sensor technology provides the potential for monitoring parameters of interest during processing and testing of composite materials as well as the opportunity for tracking properties over the lifetime of composite parts in service. The successful development of this technology depends on designing optical fiber sensor systems suitable for embedding in composite structures.This paper focuses on the role played by optical fiber coatings in the design of embedded sensor systems. The performance of different optical fiber coatings under typical composite processing conditions will be discussed. Photomicrographs of test specimens containing embedded sensors will be presented which show delamination occurring at the coating/optical fiber interface in preference to the coating/epoxy resin interface. Coating performance criteria will be outlined for use in the selection of fiber optic sensors for composite applications.
Fabrication of Oxide Glass Coated Fluoride Glass Optical Fibers for Durability and Strength Improvement
Authors: Ohishi Yasutake , Fujiura Kazuo , Takahashi Shiro 
Published: March 2011

AbstractThe crystallization of fluoride glass being in contact with oxide glass is investigated using thermal analyses to perform oxide glass coating for durability and strength improvement. The chemical reaction does not occur in the fiber drawing temperature range and begin at the melting temperature of fluoride glasses. The crystallization of fluoride glass is suppressed by contact with oxide glass. Smooth contact between fluoride and oxide glasses is confirmed.
Specific Heat Measurements on κ-(Bedt-Ttf)2Cu(Ncs)2
Authors: Goodrich R. G. , Xu Jing-Chun 
Published: March 2011

ABSTRACTWe have measured the specific heat of κ-(BEDT-TTF)2Cu(NCS)2 from 4 to 14 K. The superconducting transition at 9.4 K is observed in zero applied magnetic field and in a field of 0.3 T. Both the magnitude of the change in Cp at Tc and the temperature dependence of Cp below Tc indicate a strong coupling superconductor. If the lattice specific heat is assumed to contain contributions due to the eighteen vibrational degrees of freedom, the phonon contribution to the specific heat in our temperature range can be represented by a Debye integral expression with a Debye temperature of 95 K. A model of collective modes suggesting the origin of the eighteen degrees of freedom is presented.
A New Synthetic Metal Precursor: Dimethyltetrathiotetracene and Related Compounds
Authors: Maruo Toshio , Singh Megh , Jones Thomas M. , Rath Nigam P , Min Dong 
Published: March 2011

ABSTRACTThe successful synthesis of dimethyltetrathiotetracene (DMTTT) has been achieved in our laboratory and an account of the details of the synthesis has been reported. Reported herein are studies of the physical properties of DMTTT and some of its chemistry. Both 1:1 and 2:1 DMTTTX charge transfer salts have been prepared and are in the process of being characterized in our laboratory. Comparisons of physical properties and the results of studies such as single crystal x-ray diffraction, solid state ESR spectra, cyclic voltammetry and electrical conductivity are reported. To date, these comparisons reveal considerable similarity between the properties of any given DMTTT charge transfer salt and its corresponding tetrathiotetracene (TTT) charge transfer salt.
Studies on the Formation of Switching and Memory Storage Materials Constructed from Metallo-Organic Charge-Transfer Complexes
Authors: Duan Hailing , Cowan Dwaine O. , Kruger Jerome 
Published: March 2011

ABSTRACTElectrochemical measurements have been employed to study the formation process of the charge-transfer complexes Cu+TCNQ−,a switching and memory material, in a saturated TCNQ/CH3CN solution. These studies show that the Cu/Cu+TCNQ−(s), TCNQo(CH3CN) system is an active-passive system corroding under diffusion control. A possible mechanism of localized corrosion-crystallization is proposed for the formation of a Cu+TCNQ− film in an acetonitrile solution
Physical Characterization of Organic Radicals by Low-Field Epr Spectrometry
Authors: Moussavi Mehdi , Beranger Marc , Duret Denis , Kernevez Nelly , Secourgeon Liliane 
Published: March 2011

ABSTRACTA low-field (0.6 Gauss, 2 MHz) EPR spectrometer providing quantitative parameters is described. It gives informations such as frequency dependence of the linewidth, anisotropy of inhomogeneous line and also the values of T1, T2 and the magnetic susceptibility using simple hypothesis.The behaviour of different typical π-systems, as well metallic as semiconducting is compared to a radical anion salt, quinolinium bis tetracyano-quinodinemethane Qn(TCNQ)2 considered as a reference.The materials physical characteristics will be provided by a new variable field (0.6–60 Gauss, 2–200 MHz) which is under realization, for an extended family of organic radicals.
New Electrically Conducting Solids based on Nickel (II) - Bis(1,3-Dithiole-2-Thione-4,5-Diselenolate)
Authors: Kini A. M. , Beno M. A. , Budz S. , Wang H. H. , Williams J. M. 
Published: March 2011

ABSTRACTElectrochemical oxidation of the metal-organic complex, nickel(II)–bis(1,3-dithiole-2-thione-4,5-diselenolate) or simply [Ni(dsit)2]2−, yields highly conducting salts, in which the stoichiometry and packing arrangement depends critically on the size of the counter-cations incorporated. Smaller counter-cations, e.g., tetramethylammonium and tetramethylphosphonium ions, yield salts with a 1:2 cation:[Ni(dsit)2] stoichiometry, while the larger tetraethylammonium ion yields a salt with 2:2 stoichiometry. In both these salts, the [Ni(dsit)2] units occur as tightly bound dimers, in which the coordination geometry of nickel is a unique, but not unprecedented square-pyramidal type. Moreover, the packing arrangement of [Ni(dsit)2]2 dimer units in both (Me4N)[Ni(dsit)2]2 and (Me4P) [Ni (dsit)2]2 is κ-type, similar to that found in the organic superconductor with the highest-known Tc (10.4 K), κ-(BEDT-TTF)2Cu(NCS)2. Both these salts possess good room temperature conductivities (σrt = 36 and 19 S.cm−1 respectively), but the temperature dependance of their conductivities is characteristic of semiconductors with small bandgaps (Eg = 0.11 and 0.13 eV, respectively). The 2:2 salt (Et4N)2[Ni(dsit)2]2, on the other hand, has a substantially lower room temperature conductivity, about six orders of magnitude smaller than that of the 1:2 salts. Its structure is characterized by [Ni(dsit)2]2 dimer units which are separated from each other by the tetraethylammonium cations, with no effective interaction between [Ni(dsit)2]2 dimers. It is suggested that dimeric metal-dithiolene and metal-diselenolene complexes may be potential building blocks in the structural design of κ-type organic conductors and superconductors.
Discotic Liquid Crystalline Porphyrins: Photophysical and Photoelectrical Properties of Large-Area Crystalline Films
Authors: Gregg Brian A. , Fox Marye Anne , Bard Allen J. 
Published: March 2011

ABSTRACTPorphyrins exhibiting discotic liquid crystalline phases have been developed in order to prepare thin, large-area, crystalline films of molecular conductors. A series of octaalkylporphyrins bearing different side chains have been synthesized including some with electron-withdrawing substituents at the meso positions. The photophysical properties of thin films of these compounds are a strong function of the film order (crystallinity). A substantial and persistent photovoltaic effect was achieved (e.g., Voc = 0.3 V, jsc = 0.4 mA/cm2 under white light, 150 mW/cm2) in capillary-filled symmetrical cells with indium-tin oxide electrodes. A model based on kinetically-controlled asymmetric exciton dissociation leading to photoinjection at the illuminated interface is presented to explain these results. This appears to be the first unambiguous example of a photovoltaic cell controlled entirely by interfacial kinetics. The predominance of the photoinjection process in these cells is attributed to the single-crystal-like character of the porphyrin films.
Sound Velocity Study of Bechgaard Salts (TMTSF)2PF6 and (TMTSF)2ClO4
Authors: Shi X. D. , Chiang L. , Upasani R. , Chaikin P. M. 
Published: March 2011

ABSTRACTWe have studied the elastic properties of the Bechgaard salts (TMTSF)2PF6 and (TMTSF)2C104 through their Spin Density Wave (SDW) and anion ordering transitions. Using a vibrating reed technique to measure the sound velocity and attenuation, we observed a large softening of sound velocity immediately above the SDW transition temperature, 12K, of (TMTSF)2PF6 followed by a large hardening below the transition. The softening results from a strong dependence of Tc on stress in the most conducting direction, while the hardening results from the loss of screening from the conduction electrons and yields a value for the long wavelength electron-phonon coupling constant. The anion ordering transition at 24K in (TMTSF)2ClO4 is marked by a hardening of the lattice that is considerably larger than expected from the lattice constant changes. Our most interesting finding, however, is the observation of a series of steps in the sound velocity as the Field Induced Spin Density Wave (FISDW) transitions are crossed by increasing the magnetic field at low temperatures. The fact that the sound velocity steps are small at the beginning of the cascade of transitions and increase with field, even as extrapolated to low temperature, is an unexpected result from present theory and may indicate a more direct coupling of the lattice stiffness to the SDW order parameter.
Quantum Hall Effect and Rapid Oscillations in (Tmtsf)2Pf6 under Pressure
Authors: Hannahs S. T. , Brooks J. S. , Kang W. , Chaikin P. M. , Chiang L. Y. , Upasani R. 
Published: March 2011

ABSTRACTWe present magnetotransport data and the phase diagram derived from them for (TMTSF)2PF6 under sufficient pressure that the zero field Spin Density Wave (SDW) is suppressed and the material is superconducting. Application of a large magnetic field perpendicular to the conducting plane then leads to the cascade of Field Induced Spin Density Wave (FISDW) transitions. The transitions are in good agreement with the Standard model for these transitions and in contrast to the more complicated behavior seen in the ClO4 salt. In addition Hall and longitudinal resistivity indicates a behavior much closer to that observed in conventional Quantum Hall devices than in the ClO4 salt or previous studies of PF6. We do observe the “rapid” Schubnikov de Haas like oscillations in magnetoresistance at high field similar to those seen in ClO4, even though in the present case there is no evidence for anion ordering as some theories would require.
Polyaniline: an Old Polymer with New Physics
Authors: Epstein A. J. , MacDiarmid A. G. 
Published: March 2011

ABSTRACTPolyanilines have been known for over one hundred years. Recent studies of this chemically flexible polymer have demonstrated unusual electronic phenomena in both the insulating forms and the conducting forms. Studies of both forms show that the origins of the electronic phenomena are substantially different than those observed in polyacetylene and related earlier studied conjugated carbon backbone polymers. Unusual aspects include the formation of massive polarons upon photoexcitation in the insulating forms. These polarons have unusual time dynamics associated with the roles of ring-flipping and ring-conformation in the polymer system. A new model for the effects of electron lattice coupling via ring rotation has been introduced. The “metallic” form of the polymer shows that the metallic state is associated with the ordered regions of the doped polymer. The roles of localization are important in leading to the formation of a textured, granular metal. At low temperatures for emeraldine salt, and at higher temperatures for derivatized polyanilines, localization is important. Potential new technologies based on the polyanilines, including optical information storage, controlled microwave absorption, and use of a self-protonating derivative that is soluble in aqueous media are noted.
Chemical and Physical Properties of Soluble Part of Emeraldine: Comparison with Insoluble Emeraldine
Authors: Laversanne R. , Vaca P. 
Published: March 2011

ABSTRACTA preliminary physical study of the soluble part of emeraldine is presented. The electrical and magnetic properties of this low weight material are very similar of those of the pristine emeraldine salt. These results emphazise the possible role of short chain species in the conduction mechanism of polyaniline. In order to clarify this point, previous magnetic investigations on insoluble emeraldine salts are revisited. It appears that the fit of the magnetic susceptibility temperature dependence of polyaniline with a Curie law plus a Pauli term might not be justified at
low temperature. A T−α law with a ≈ 0.75 gives a better fit suggesting a behavior similar to the one found in Random Exchange Heisenberg Antiferromagnetic Chain (REHAC)
Moisture Effects in the Conducting Polymer, Polyaniline
Authors: Travers J. P. , Menardo C. , Nechtschein M. , Manohar S. K. , MacDiarmid A. G. 
Published: March 2011

ABSTRACTWater content as well as conductivity have been measured as a function of water vapour pressure on polyaniline and poly-N-methylaniline samples. It is shown that i) absorption is governed by the acid protons of the polymers and ii) enhancement of conductivity needs the existence of protonated imines. It is concluded that moisture favours conductivity through an increase of the interchain transfers.