bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Ferroelectric Perovskites Through Aqueous Solutions Techniques
Authors: Guzmàn-Martel G. , Aegerter M. A. , Barboux P. 
Published: March 2011

ABSTRACTThe hydrolysis of niobates in aqueous solutions has been studied as a function of pH and concentration. The process has been applied to the coprecipitation of PbNb2/3Mg1/3O3 leading to a low temperature synthesis of this ferroelectric relaxor ceramic. The effect of hydrolysis conditions such as the concentration of bases and acids used, their rate of addition, temperature and the nature of the precursor salts is described. The homogeneity of the precipitates has been characterized through infrared spectroscopy and X-ray diffraction techniques. The perovskite phase appears after heating at 350°C and is obtained as a pure phase above 750°C after one hour heat-treatment. Relaxor ceramics with high dielectric constant can be obtained by sintering above 1000°C. The process also has been successfully applied to the synthesis of other relaxor ceramic compositions such as PZN (PbNb2/3Zn1/3O3), PFN (PbNb1/2Fe1/2O3) as well as CdNb2O6 and MgNb2O6 compounds.
Stabilization of Metal Alkoxides (M = BA, CU) by Alkamolamines
Authors: Hubert-Pfalzgraf L. G. , Massiani M. C. , Daran J. C. , Vaissermann J. 
Published: March 2011

ABSTRACTAlcohol interchange reactions between barium and copper(II) methoxides and triethanolamine give Ba(teaH-l)2,2EtOH and [Cu(teaH-2)]4,3tea, respectively. Triethanolamine appears as a tetradentate ligand -chelating in the case of barium, bridging-chelating for copper - and thus ensures high coordination numbers for the metals - eight for Ba and five for Cu - thus decreasing their susceptibility to hydrolysis. The remaining hydroxyl functionality on the coordinated triethanolamine moities favors the formation of solvates with alcohols via H-bonding.
Solid State Structures, Decomposition Pathways, and Vapor Phase Byproducts of Y(acac)3 Type OMVPE Precursors for thin films of Yttrium -Containing Ceramic Materials
Authors: Ree William S. , Luten Henry A. , Carris Michael W. , Doskocil Eric J. , Goedken Virgil L. 
Published: March 2011

ABSTRACTSeveral useful ceramic materials target compositions contain yttrium, Y2O3and YBa2Cu3O7-δbeing the two most widely employed. One known CVD precursor for yttrium-containing thin films is Y(tmhd)3H2O (tmhd = 2,2,6,6-tetramethylheptane-3,5-dionato). We have determined the structure and examined the vapor phase decomposition of this species. A related compound, [Y(tmod)3]2(tmod = 2,2,7-trimethyloctane-3,5-dionato), has been prepared, structurally characterized, and studied as an organometallic vapor phase epitaxy (OMVPE) precursor for Y and Y2O3films. Mechanisms of vapor phase decomposition are discussed in terms of solid film deposits and vapor phase by-products. The two precursors are compared to each other with respect to their stability windows, defined as being bound by source volatility on the low side and source stability on the high side.
Heterometallic Aggregates as Intermediates on the Molecular Routes to Multicomponent Oxides
Authors: Hubert-Pfalzgraf Liliane G. 
Published: March 2011

ABSTRACTMetal alkoxides are often associated with more accessible precursors such as carboxylates, nitrates, B-diketonates, in chemical routes to multicomponent oxides. The molecular constitution of such solutions has been examined for systems based on niobium or zirconium. The heterometallic aggregates MNb2(μOAc)2(μ-0R)4(OR)6 (M = Cd, Mg), PbZr3, (μ4-0)(μ-0Ac)2(μ-0R)5(0R)5 and Gd2Zr6(μ4-O)2(μOAc)6(μOR)10(0R)10 R = iPr have been characterized by X-ray diffraction. Preliminary results on the hydrolysis experiments of these aggregates are given.
Sol-Gel Process from Heterobimetallic Alkoxides to Incorporate Lanthanides in an Alumina Matrix
Authors: Narula Chaitanya K. 
Published: March 2011

ABSTRACTGels form on addition of seven or more moles of water diluted withi-PrOH to one mole of M[Al(O-i-Pr)4]3, M = La, Ce dissolved in i-PrOH. Thermal treatment of xerogels derived from La[AI(O-i-Pr)4]3gives amorphous powders below 900°C. LaAIO3crystallizes out at 900°C and residual alumina remains amorphous. CeO2starts to separate out above 600°C from the xerogels prepared from Ce[M(O-i-Pr)4]3. Thermally induced structural changes in xerogels prepared from the mixtures of La[AI(O-i-Pr)4]3and Ce[AI(0-i-Pr)4]3in 1:1 or 1:3 ratio are different from those prepared from individual precursors. These xerogels remain amorphous below 700°C. Crystalline CeO2forms on heating at 900°C but alumina remains amorphous. Sols are formed on hydrolysis of M[AI(0-/-Pr)4]3in excess water and acidifying the reaction mixture with acetic acid. Sols can be converted to gels by slow evaporation of volatiles. This method is useful in preparing coatings.
Complexation of Zr(IV) Precursors in Aqueous Solutions
Authors: Livage J. , Chatry M. , Henry M. , Taulelle F. 
Published: March 2011

ABSTRACTThe sol-gel synthesis of metal oxides can be performed via the hydroxylation and condensation of metal cations in aqueous solutions. The complexation of these ionic species by anions leads to the chemical modification of inorganic precursors at a molecular level. The whole process of hydrolysis and condensation can then be modified allowing a chemical control of the morphology, the structure and even the chemical composition of the resulting powder.The role of anions during the formation of condensed phases from inorganic precursors in aqueous solutions has to be taken into account. The complexing ability of these anions is described in the frame of the Partial Charge Model as a function of pH and the mean electronegativity of anionie and cationic chemical species. Experimental evidence for the complexation of zirconyl species in aqueous solutions will be given using multinuclear NMR of anions.
Silicon-29 NMR Study on the Initial Stage of the Co-Hydrolysis of Tetraethoxysilane and Methyltriethoxysilane
Authors: Sugahara Yoshiyuki , Tanaka Yoichi , Sato Shuji , Kuroda Kazuyuki , Kato Chuzo 
Published: March 2011

ABSTRACTThe hydrolysis and initial condensation processes of the mixtures of TEOS and MTES have been studied by GC-MS and 29Si-NMR in the systems with TEOS:MTES:ethyl alcohol:water:HCl=1:1:14:28:6×1O-4 and 0.5:1.5:14:28:6×10-4. Thedimer CH3(HO)2SiOSi(OH)3 possessing both TEOS- and MTES-derived units was identified, indicating that the condensation between a hydrolyzed TEOS-derived monomer and a hydrolyzed MTES-derived monomer was one of dominant dimerization.
Structural Characterization of Gels Prepared from Co-Hydrolysis of Tetraethoxysilane and Dimethyldiethoxysilane.
Authors: Babonneau Florence , Bois Laurence , Livage Jacques 
Published: March 2011

ABSTRACTThis work is part of a more general study on the structural characterization of organically modified silica gels that are usually prepared from tetrafunctional, trifunctional and difunctional alkoxides. The systems that were investigated in this paper are gels prepared from co-hydrolysis of dimethyldiethoxysilane (DEDMS) and tetraethoxysilane (TEOS). The condensation process was followed by 29Si and 17O liquid NMR and shows clearly evidence for co-condensation reactions. Gels with various DEDMS/TEOS ratios were studied by 29Si and 1H MAS-NMR. The results are clearly correlated to the change in physical properties of the materials, from flexible polymeric gels at high DEDMS content to crosslinked brittle networks at low DEDMS content.
Further Studies on Aluminum Oxoalkoxide Clusters
Authors: Sinclair R. A. , Brostrom M. L. , Gleason W. B. , Newmark R. A. 
Published: March 2011

ABSTRACTEvidence for a tetranuclear aluminum oxoalkoxide cluster Al4(μ4-0) (μ2OBμi)5(OBui)6 is presented, drawing on data from X-ray, NMR, MS and other spectroscopie and experimental investigations. In principle, these compounds are derived from the well-authenticated aluminum alkoxide tetramers by hydrolytic loss of only one alkoxy group. They contain a single central oxo ligand and only 5-coordinate aluminum atoms. They are the simplest discrete oxoalkoxide structures so far reported for aluminum and may be helpful in understanding the hydrolysis and condensation steps leading to hydrated aluminum oxide sols and gels.
Stress and Phase Transformation Phenomena in Oxide Films: Real-Time Spectroscopic Measurements
Authors: Exarhos Gregory J. , Hess Nancy J. 
Published: March 2011

ABSTRACTIn situ optical methods are reviewed for characterization of phase transformation processes and evaluation of residual stress in solution-deposited metastable oxide films. Such low density films most often are deposited as disordered phases making them prone to crystallization and attendant densification when subjected to increased temperature and/or applied pressure. Inherent stress imparted during film deposition and its evolution during the transformation are evaluated from phonon frequency shifts seen in Raman spectra (TiO2) or from changes in the laser-induced fluorescence emission spectra for films containing rare earth (Sm+3:Y3Al5O12) or transition metal (Cr+3 :Al2O3) dopants. The data in combination with measured increases in line intensities intrinsic to the evolving phase are used to follow crystallization processes in thin films. In general, film deposition parameters are found to influence the crystallite ingrowth kinetics and the magnitude of stress and stress relaxation in the film during the transformation. The utility of these methods to probe crystallization phenomena in oxide films will be addressed.
Low Temperature Formation of Ferroelectric thin Films
Authors: Kong Kwok Chi , Desu Seshu B. 
Published: March 2011

ABSTRACTTwo novel processes have been developed to lower the transformation temperature of ferroelectric lead zirconate titanate (PZT) thin films with high Zr/Ti ratio. One process makes use of high pressure and the other process uses seeding to encourage the transformation.A previous study has shown that nucleation is the rate-limiting step for the perovskite formation. Therefore, any process that enhances the kinetics of the nucleation will likely decrease the transformation temperature. In this process, a very thin seeding layer, which has a low effective activation energy for perovskite formation, is used to provide nucleation sites needed for the low temperature perovskite formation. In this study, the pyrochlore to perovskite phase transformation temperature of PbZrxTi1−xO33 films of high Zr/Ti ratio (e.g. x = 53/47) can be lowered by as much as 100°C.
Preparation and Characterization of Sol-Gel Thin Films of KTIOPO4.
Authors: Harmer Mark A. , Roelofs Mark G. 
Published: March 2011

ABSTRACTIn this paper we describe a novel route for the formation of thin films of potassium titanyl phosphate (KTiOPO4 KTP) via a sol-gel route. The ability to form films of high optical quality depends upon the precursor chemistry developed. Formation of stoichiometric films is especially challenging in three component systems and a number of precursors have been investigated. The basic chemistry, processing and resulting microstructure will be described. Transparent, dense and continuous films have been prepared with grain sizes typically of 0.3μm or less depending upon the processing conditions. Some textured growth patterns are observed although the films are essentially polycrystalline. Using the prism coupling technique the films have been found to exhibit waveguiding.
Molecular Recognition on Acoustic Wave Devices: Modified Zeolite-Silica Thin Films With Tailored Adsorption Properties
Authors: Yan Yongan , Bein Thomas , Brown Kelly D. , Forrister Ray , Jeffrey Brinker C. 
Published: March 2011

ABSTRACTMicroporous thin films composed either of zeolite crystals embedded in sol-gel derived glass or of a molecular coupling layer, zeolite crystals and a porous silica overlayer, were formed on the gold electrodes of Quartz Crystal Microbalances (QCM). The microporosity of the thin films was characterized by in situ nitrogen and vapor sorption isotherms. Both preparation methods result in thin films with substantial microporosity. Selective adsorption based on molecular size exclusion from the microporous films could be achieved.
Structure of Thin Sol-Gel Coatings Near The Surface of Substrates
Authors: Hirashima Hiroshi , Kusaka Takao 
Published: March 2011

ABSTRUCTThe sol-gel method is one of the most appropriate technologies for the preparation of functional thin oxide coatings. However, few studies on the structure near the interface between sol-gel coatings and substrates have been reported. In this study, the structures of thin TiO2 gel coatings were investigated by XPS in order to elucidate the interaction between the coatings and the glass substrates. TiO2 gel coatings were prepared from Ti-alkoxide by hydrolysis and dip-coating on silica glass plates. Thickness and refractive index measurements were made by ellipsometry. Changes in Ols spectra for the coatings were observed at locations near the interface. Dynamic microhardness measurements for the coatings and the coated glasses were made. These results suggest the formation of a Ti-O-Si bond at the interface.
Electrophoretic Deposition of Sol-Gel-Derived Ceramic Coatings
Authors: Zhang Yining , Jeffrey Brinker C. , Crooks Richard M. 
Published: March 2011

ABSTRACTThe physical, optical, and chemical characteristics of electrophoretically- and dip-coated sol-gel ceramic films are compared. The results indicate that electrophoresis may allow a higher level of control over the chemistry and structure of ceramic coatings than dip-coating techniques. For example, controlled-thickness sol-gel coatings can be prepared by adjusting the deposition time or voltage. Additionally, electrophoretic coatings prepared in a four-component alumino-borosilicate sol display interesting optical characteristics. For example, the ellipsometrically-measured refractive indices of electrophoretic coatings are higher than the refractive indices of dip-coated films cast from identical sols, and they are also higher than any of the individual sol components. This result suggests that there are physical and/or chemical differences between films prepared by dip-coating and electrophoresis.
Protective Zirconia Thin Films on Metal Substrates.
Authors: Tomasi Andrea , Scardi Paolo , Marchetti Fabio 
Published: March 2011

ABSTRACTStabilized Zirconia thin films were deposited by R. F. Magnetron Sputtering onto iron substrates. Deposition parameters such as gas pressure and R. F. voltage were optimized to obtain homogeneous and well adherent protective coatings. The morphology and structure of films before and after thermal treatments were investigated by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Thermogravimetrical Analysis (TGA).Auger Electron Spectroscopy (AES) depth profiling techniques were used to obtain the chemical distribution of the elements in order to study the influence of two important parameters on the adhesion of the ceramic: the presence of a thin layer of native metal oxide and the residual surface roughness after polishing.The effectiveness of coatings to protect the metal substrate against high temperature oxidation in air was evaluated by thermogravimetrical analysis at 773K. The protective action of the ceramic film was well demonstrated.
Plasma Sprayed Alumina-Titania Coatings
Authors: Steeper T. J. , Rotolico A. J. , Nerz J. E. , Riggs W. L. , Varacalle D. J. , Wilson G. C. 
Published: March 2011

ABSTRACTThis paper presents an experimental study of the air plasma spraying (APS) of alumina-titania powder using argon-hydrogen working gases. This powder system is being used in the fabrication of heater tubes that emulate nuclear fuel tubes for use in thermal-hydraulic testing. Experiments were conducted using a Taguchi fractional-factorial design parametric study. Operating parameters were varied around the typical spray parameters in a systematic design of experiments in order to display the range of plasma processing conditions and their effect on the resultant coatings. The coatings were characterized by hardness and electrical tests, surface profilometry, image analysis, optical metallography, and x-ray diffraction. Coating qualities are discussed with respect to dielectric strength, hardness, porosity, surface roughness, deposition efficiency, and microstructure. Attempts are made to correlate the features of the coatings with the changes in operating parameters.
Thermal Stability of Supported Titania Membranes
Authors: Kumar Krishnankutty-Nair P. , Zaspalis V. T. , De Mul F. F. M. , Keizer Klaas , Burggraaf Anthonie J. 
Published: March 2011

ABSTRACTThe beneficial effects of the support constraint on the improved thermal stability of supported titania membranes were studied by following the anatase to rutile phase transformation in supported and unsupported titania membranes. This was studied using Raman spectroscopy and XRD. Supported membranes showed a higher transformation temperature, about 150°C higher, (slower rate of transformation) compared to the unsupported ones. Unsupported membranes showed a slight thickness dependence on the phase transformation temperature, but less significant compared to the difference in phase transformation behaviour between supported and unsupported membranes of similar thicknesses.
Preparation and Characterization of Microporous Sol-Gel Derived Ceramic Membranes for GAS Separation Applications
Authors: De Lange R. S. A. , Hekkink J. H. A. , Keizer K. , Burggraaf A. J. 
Published: March 2011

ABSTRACTMesoporous alumina membranes were modified with microporous silica. The polymeric silica sols consist of very weakly branched polymeric molecules with a fractal dimension of 1.3 and Guinier radius of ≈ 2.0 nm. The resulting top layer material is microporous with a porosity of 40% and a layer thickness of 60 nm. Gas transport is activated with an activation energy of 11 kJ/mol for hydrogen and molecular sieve like separation factors have been obtained. From the mechanism of gas transport the conclusion can be drawn that the pores are of molecular dimensions (0.7 – 1 nm diameter).
Imogolite as a Material for Fabrication of Inorganic Membranes
Authors: Huling Jeffrey C. , Bailey Joseph K. , Smith Douglas M. , Jeffrey Brinker C. 
Published: March 2011

ABSTRACTImogolite is a structurally microporous tubular clay comprising one-dimensional pore channels that are 0.8 – 1.2 nm in diameter, depending on composition. The microporous structure of natural and synthetic imogolite has been investigated by nitrogen adsorption as a function of outgassing temperature. A significant increase in adsorption at low relative pressure (P/P0 ∼ 10-6) after 275°C outgassing reflects a high concentration and narrow distribution of 0.8 – 0.9 nm diameter pores (i.e., the imogolite tubes) and supports the potential use of imogolite in inorganic membrane applications.
Metal Complexes in Oxidic Matrices
Authors: Schubert Ulrich , Breitscheidel Boris , Buhler Hermann , Egger Christian , Urbaniak Wlodzimierz 
Published: March 2011

ABSTRACTAlkoxides of the type (RO)nE-X-A in which a functional organic group A is connected to the alkoxide moiety via an inert and hydrolytically stable spacer X, are used to bind metal complex moieties. Sol-gel processing of the resulting metal complexes [(RO)nE-X-A]yMIm under standard conditions results in the formation of metal complex containing gels. If the metal complex moiety MLm is catalytically active, this method results in the heterogenization of homogeneous catalysts. Another application of the metal complex substituted gels is the preparation of composites containing uniform, nanometer-sized metal particles homogeneously dispersed in a ceramic matrix.
Structure-Related Mechanical Properties of Ormosils by SOL-GEL Process
Authors: Hu Yi , Mackenzie John D. 
Published: March 2011

ABSTRACTThe mechanical properties corresponding to the different structures of organically modified silicates (Ormosils) prepared by the sol-gel process were studied. Tetraethoxysilane (TEOS) and polydimethyl siloxane (PDMS) were used as the inorganic and polymeric components, respectively. Large variations in the microstructure of the Ormosils were found by changing the reaction temperature, and the content of PDMS, acid catalyst (HCI),and water. The structure of the Ormosils and the mechanical properties were correlated by the edge connectivity. Modulus of elasticity and fracture strength were used to study their relations Ormosils structures.
Hydrolysis of Zirconium Propoxide by an Esterification Reaction
Authors: Laaziz I. , Larbot A. , Guizard C. , Julbe A. , Cot L. 
Published: March 2011

ABSTRACTZirconium propoxide hydrolysis was performed with the help of an esterification reaction using acetic acid. Products, obtained according to the value of hydrolysis ratio, are successively crystals, sols and gels or precipitates. The similarity of FUR and NMR spectra for crystals and gels allows to think that the arrangements of ligands around the zirconium atoms are close. The crystalline structure determination permits to precise the environment : acetate groups are always bridging and propoxy groups can be bridging or terminal. Clusters containing 9 zirconium atoms, bridged by oxygen atoms, exist in the structure. The colloid size growth was performed by light scattering. A discussion of the role of acetic acid and the competition between the possible reactions is given.
NMR Characterization of Silicon Carbides and Carbonitrides. A Method for Quantifying the Silicon Sites and the Free Carbon Phase.
Authors: Gerardin C. , Henry M. , Taulelle F. 
Published: March 2011

ABSTRACTWith ceramics prepared from organic precursors, polymers are often formed by thermolysis, and the ceramics are obtained by pyrolysis of the polymer. This paper will cover the NMR methods used to characterize the polymerization as well as the pyrolysis of such polymers. The reticulation rate of such materials is measured on the silicon atoms and on the carbon atoms, leading to a silicon reticulation state and a carbon reticulation state. For the ceramics, the quantification of the SiCxH4−x or SiCxN4−x sites is performed using a priori chemical shift calculation. A measure of the H/C of the free carbon phase at the different temperatures of pyrolysis is presented. This measure uses a absolute determination of hydrogen content in ceramics, more accurate than a classical chemical analysis of hydrogen. The evolution of the reticulation, of the free carbon amount and of the H/C ratio in the free carbon phase will be followed with the temperature.
Isocyanate-Modified Polysilazanes: Conversion to Ceramic Materials
Authors: Schwark Joanne M. , Sullivan Mark J. 
Published: March 2011

ABSTRACTA tailorable viscosity, liquid polysilazane has been developed which thermosets to a solid ceramic precursor for both silicon nitride (Si3N4)andsilicon carbide (SiC). Conversion of the thermoset, crosslinked polysilazane to a ceramic material has been examined. Preferential formation of silicon carbide or silicon nitride is controlled by the pyrolysis conditions employed.
Organometallic Precursors to Vanadium and Titanium Carbonitride
Authors: Laurent Francois , Daures Christophe , Valade Lydie , Choukroun Robert , Legros Jean-Pierre , Cassoux Patrick 
Published: March 2011

ABSTRACTWe repon on the syntheses, structural and thermoanalytical studies of two titanium complexes CpTiCl2N(SiMe3)2 and FTi[N(Sime3)2]3 and one vanadium complex V(NEt2)4. CpTiCl2N(SiMe3)2 has been used in a hot wall CVD reactor as a precursor to titanium nitride. Thin films of typically 1 XPS in thickness have been deposited at 600°C on glass, silicon and tool steel. XPS analyses of the deposits show titanium carbonitride to be formed. The new FTi[N(Sime3)2]3 complex can also be used as a precursor to titanium nitride. V(NEt2>4 led at 500°C to the deposition of vanadium carbonitride characterized by XPS analysis. Films tended to contain excess free carbon.