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  • 1
    Electronic Resource
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    Springer
    Journal of thermal analysis and calorimetry 60 (2000), S. 699-705 
    ISSN: 1572-8943
    Keywords: crystallization kinetics ; sol-gel ; solid solutions ; ruthenia ; titania
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The preparation of rutile type solid solutions in (TiO2)x -(RuO2)1−x system in the 0≤x ≤0.7 concentration range is described. The single phase solid solutions are formed by controlled nanocrystallization of amorphous gels prepared by the sol-gel method. The kinetics of this crystallization process has been analyzed. It was found that the crystallization does not correspond to the Johnson-Mehl-Avrami model and it can be described by the two-parameter Šesták-Berggren kinetic model.
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  • 2
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    Journal of sol gel science and technology 17 (2000), S. 37-45 
    ISSN: 1573-4846
    Keywords: sol-gel ; ormocers ; films ; quantum dots ; PbS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new method for the preparation of semiconductor PbS quantum dot-doped Ormocer (Organically Modified Ceramic) has been developed. The Ormocer matrix was prepared through the hydrolysis and condensation of alkoxysilane precursors (sol-gel process). Formation of PbS particles took place in the porous Ormocer through H2S gas reaction with a lead precursor incorporated at the solution stage. Control of the PbS dot size was achieved through the use of organically substituted trifunctional silanes. Particle formation and growth was studied under different experimental conditions (e.g. temperature and lead precursor concentrations) where nucleation and aggregation processes occurred. Determination of the average particle size was done by XRD. Transmission electron microscopy was also used to determine particle diameter as well as particle size distribution. Optical absorption spectra were measured at the UV-VIS wavelength range. Absorption edge blue shifts showed the quantum confinement effect in these materials. The non-hydrolyzed groups bonded to the silane prevented uncontrolled nucleation and aggregation during the particle formation and growth, i.e. at the solution stage by the homogeneous distribution of the Pb salts or at the xerogel state by the capping of the growing particles.
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  • 3
    ISSN: 1573-4846
    Keywords: barium titanate ; barium zirconate ; sol-gel ; metal alkoxide ; single-source precursor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sol-gel synthesis of nano-sized BaTiO3, BaZrO3 and BaTi0.5Zr0.5O3 ceramics using alkoxide and semi-alkoxide routes has been investigated and the pervoskites obtained have been compared with respect to crystallisation temperature, crystallite size and compositional purity. Heterometal alkoxides containing two (for BaTiO3 and BaZrO3) and three (for BaTi0.5Zr0.5O3) different metals were used as single-source precursors in the alkoxide route while semi-alkoxide synthesis was performed by reacting barium hydroxide or acetate with Ti and/or Zr alkoxides. Semi-alkoxide synthesis also produces stoichiometric and phase-pure oxides, however, at temperatures higher than 1000°C. At temperatures below 1000°C, BaCO3 and small amounts of other undesired phases (e.g., BaTi2O4) were present in the oxides derived from semi-alkoxide synthesis. Thermal behaviour, studied by TGA/DTA measurements, shows that thermal decomposition occurs in three major steps and depends on the educt composition and the synthesis route. Among alkoxide derived powders, crystalline BaTi0.5Zr0.5O3 phase is formed at 400°C while complete crystallisation of BaMO3 ceramics occurs around 600°C. The cubic to tetragonal phase transition for BaTiO3 is clearly observed at relatively low-temperature of 800°C. The stoichiometry and phase homogeneity of the obtained powders were demonstrated by energy dispersive X-ray analysis and powder diffractometry. The averaged crystallite size of the obtained nano-ceramics was evaluated using the FormFit programme. SEM and TEM observations revealed a high microstructural uniformity.
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  • 4
    ISSN: 1573-4846
    Keywords: sol-gel ; optical fiber ; chemical sensor ; high acidity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nuclear fuel reprocessing requires high acidity levels that should be accurately and rapidly controlled in order to optimize extraction yields and process efficiency. A new optical fiber sensor based on a sol-gel film doped with an acid-sensitive indicator has been developed to improve remote and on-line monitoring. The organic molecule was physically incorporated in an acid-catalyzed sol-gel matrix and coated onto the core of a denuded optical fiber. The sensor response was evaluated in synthetic solutions of nitric acid, concentrations ranging from 1 to 10 mol · l−1. Changes in absorption properties and response characteristics of the sensor, when compared to the indicator in solution, have been discussed. Analytical performances of the sensor, i.e. sensitivity, response time, reversibility and repeatability are very encouraging for the on-line analysis. Viability of the sensor for process measurements depends on the stability which might be improved by a strict control of the sensitive film porosity.
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  • 5
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    Journal of sol gel science and technology 17 (2000), S. 247-254 
    ISSN: 1573-4846
    Keywords: sol-gel ; ceramic thin film ; FTIR ; humidity sensor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The sol-gel synthesis of silicophosphate gels using phosphoryl chloride and tetraethoxysilane as molecular precursors is reported and discussed. Gel-derived glasses and films having the molar compositions 10P2O5 · 90SiO2 and 30P2O5 · 70SiO2 have been obtained. The structure of the dried gels as well as the structural modifications that occurs during the transformations in gel-derived glasses are analyzed by Fourier transform infrared spectroscopy (FTIR). It has been found that the evidence of the P—O—Si linkages begins to appear only on the FTIR spectra of the bulk gels heat treated up to 400°C while they are well resolved on the FTIR spectra of the bulk gel samples heated up to 1000°C indicating that at this temperature the transformation in the corresponding gel-derived glasses occurs. The humidity sensitive properties of the gel-films have been evaluated by electrochemical impedance spectroscopy (EIS). The phosphorous content as well as the temperature of the heat treatments strongly affect the sensitivity to RH of the gel-derived films.
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  • 6
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    Journal of sol gel science and technology 18 (2000), S. 85-90 
    ISSN: 1573-4846
    Keywords: sol-gel ; silica sorbent ; metal removal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Chemically doped sol-gel silica has been developed by entrapping organic dye cibacron blue as a complexing reagent in porous silica prepared by the sol-gel method for removal of metal ions from water samples. In the doped sol-gel silica, the large reagent molecules are entrapped inside the pores while small metal ions can diffuse into the pores where they are complexed by the reagent and retained inside the pores. This new solid sorbent was tested for removal of Zn(II) from aqueous solutions. The kinetics, isotherm, and pH effect of the removal were investigated. With a loading of 0.10 mmol cibacron blue/g, the sol-gel silica sorbent had a capacity of 0.09 mmol Zn/g. It was demonstrated that the sol-gel silica sorbent could be regenerated and reused repeatedly.
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  • 7
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    Journal of sol gel science and technology 18 (2000), S. 119-125 
    ISSN: 1573-4846
    Keywords: sol-gel ; zincborosilicate ; borosilicate ; cesium ; barium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Borosilicate and zincborosilicate glass powders containing up to 20 wt.% of cesium and barium oxide were prepared by the sol-gel method and characterized by XRD and SEM. Monolithic samples of borosilicate and zinc borosilicate glasses were prepared by pressing and annealing the above powders. Leach rates of barium and cesium from the samples in water were measured as a function of time. Leach rates of cesium and barium from zincborosilicate were significantly lower than borosilicate glass, and barium showed higher leachability than cesium in all the prepared glasses.
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  • 8
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    Journal of sol gel science and technology 18 (2000), S. 127-136 
    ISSN: 1573-4846
    Keywords: sol-gel ; SiO2-M x O y ; thin film ; silicic acid ; metal chloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The preparation of SiO2-M x O y (M = V, Sn, Sb) binary oxide thin films by sol-gel method was investigated. The reaction of silicic acid with metal chloride (M = Sn and Sb) or oxychloride (M = V) formed homogeneous solutions. The dip-coating of slide glass and silicon wafer followed by heat treatment gave oxide films having Si—O—M bond. The changes of FT-IR spectra as a function of heat treatment temperature and molar composition confirmed the Si—O—M bonds. The sheet resistance of films increased with an increase on heat treatment temperature and decrease in the content of metal oxide M x O y . X-ray diffraction peaks were observed for the SiO2-V2O5 films with high V2O5 contents and heat-treated above 250°C, while the others were amorphous. Oxide films heat treated at 500°C had a thickness between 340–470 nm.
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  • 9
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    Journal of sol gel science and technology 19 (2000), S. 145-148 
    ISSN: 1573-4846
    Keywords: sol-gel ; aerogels ; ferroelectrics ; lead zirconate titanate ; PZT
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ultrasonic transducers with low acoustic impedances are required for applications in gaseous media. In porous piezoelectrics the pore volume acts as a second medium of a solid-gas composite and thus lowers the overall acoustic impedance. Lead zirconate titanate (PbZr.53Ti.47O3, PZT) aerogels were prepared by sol-gel processing and supercritical drying in isopropanol. Prefiring at 400°C in air and subsequent thermal treatment in saturated PbO-atmosphere results in phase transformation to PZT (perovskite phase), grain growth and aerogel densification. In this paper the densification of this new class of piezoelectric material at temperatures above 600°C is described. Porosities were measured as a function of sintering time and temperature. Changes in the microstructure were characterized by scanning electron microscopy. Dielectric measurements are presented.
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  • 10
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    Journal of sol gel science and technology 17 (2000), S. 137-144 
    ISSN: 1573-4846
    Keywords: sol-gel ; amorphous Si-Al ; FTIR ; UV-Vis ; zeolite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two different sol-gel methods for silica-aluminates have been used for catalyst preparation, one based on inorganic precursors, aluminum nitrate and sodium silicate, and a second based on alkoxides, aluminum tri-sec-butoxide (ATB) and tetra-ethoxy-silane (TEOS). A third element, Y-zeolite was incorporated in both of the gel matrices during the process, in order to alter the acid properties of the catalyst. Although the final compound has approximately the same chemical composition, the crystalline structures of the two catalysts are substantially different. The support made from inorganic precursor yielded a more hydroxylated surface, whereas the support based on organic precursors readily incorporated the metals into the network. The support from organic precursors showed almost total dehydroxylation. The Co-Cu complexes formed at the catalyst surface differ greatly, depending on the preparation method.
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  • 11
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    Journal of sol gel science and technology 18 (2000), S. 199-206 
    ISSN: 1573-4846
    Keywords: tungsten oxide ; sol-gel ; Raman spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In the course of the preparation of WO3 by sol-gel technique we have studied kinetics of its synthesis and the structural changes during gelation. In-situ Raman scattering spectra were obtained for a series of samples during the transition from aqueous solution to gel. The changes in the Raman features were monitored as a function of time during gelation. The removal of water molecules affects the symmetric W=O stretching mode. The Raman spectrum of a gelified sample shows peaks attributed to the O–W–O bending mode and the disappearance of the high-frequency mode attributed to polyanionic species. After two days the gelified sample became a precipitated material, which exhibited the Raman spectrum of a crystalline tungsten oxide hydrate.
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  • 12
    ISSN: 1573-4846
    Keywords: DO3 ; sol-gel ; corona-poling ; second harmonic generation ; relaxation time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An Azo-dye doped organic-inorganic hybrid film was prepared by the sol-gel technique, and optical second-harmonic (SH) nonlinearities were measured as a function of the poling conditions. Azo-dye molecules dispersed in poly-vinylpyrrolidone were complexed with the hydrolyzed silicon-alkoxide. The Maker-fringe pattern composed of a fine oscillating pattern on a broad component, and the highest second-order nonlinear coefficient, d 33, was 0.83 pm/V when poled at 175°C and 4 kV. The analysis of the decay curves of the SH intensities at 150–190°C predicted the relaxation time of about 3 years at room temperature.
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  • 13
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    Journal of sol gel science and technology 19 (2000), S. 413-416 
    ISSN: 1573-4846
    Keywords: sol-gel ; superacid ; sulfated zirconia ; n-hexane isomerization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sulfated zirconia catalysts were prepared by sol-gel method using CH3COOH as in situ water source to control hydrolysis of alkoxide, and following two sulfation procedures. The samples were characterized by N2 adsorption, XRD, chemical analysis, and the activity for isomerization of n-hexane was assessed. It was found that sulfation procedure and the amount of acetic acid added exert a great influence on the catalysts properties. Mixture of sulfuric acid with zirconium propoxide before addition of acetic acid allows the retention of a larger amount of sulfur after calcination and enhances catalytic performances of sulfated zirconia. The use of CH3COOH reduces the rate of hydrolysis, and improves considerably acidic and catalytic properties.
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  • 14
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    Journal of sol gel science and technology 19 (2000), S. 243-248 
    ISSN: 1573-4846
    Keywords: germanium sulfide ; sol-gel ; planar waveguides ; non-oxide glass
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Germanium sulfide based glass films have been deposited by spin-coating onto single crystal silicon wafers and silica glass disks, using the reaction between GeCl4, either pure or doped with of 5 mol% of SbCl3, dissolved in toluene, with H2S. The films, heat-treated under different conditions, were characterized by X-ray diffraction, infrared spectroscopy, X-ray photoemission spectroscopy, mechanical profilometry and ellipsometry. Oxide contamination was found in these films, but this was reduced or even eliminated by a heat-treatment in H2S gas, at ∼270°C. A maximum film thickness of ∼1.3 μm was achieved and the refractive indices of the films were in the range of ∼1.9–2.8 at 633 nm. Propagated light was observed by butt-coupling, for waveguides deposited on silica glass disks, at λ = 633 nm. Optical losses in the range of 1.1–1.9 dB/cm were measured at this wavelength, for different regions of different planar waveguides. The present method has achieved reasonably low loss and low levels of oxide contamination, which are promising for active applications.
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  • 15
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    Journal of sol gel science and technology 19 (2000), S. 289-292 
    ISSN: 1573-4846
    Keywords: sol-gel ; sol-gel matrix (SGM) ; E. coli ; K. oxytoca ; biofilm ; fluorescein diacetate ; detection ; surface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sol-gel process is a rapid growing field in material chemistry. The sol-gel matrices (SGM) are basically porous wet-gels or xerogels obtained by the hydrolysis and condensation-polymerisation of metal and semimetal alkoxides, mainly SiO2 materials. The current study presents the uses of sol-gel glass matrix (SGM) that allow direct entrapment of biomolecules within and at surface, which can be utilized by microorganisms. This glass type is solid, transparent, porous and can be modulated to form a hydrophobic or hydrophilic surface. In view of all these beneficial characteristics of SGM, preliminary data is presented on biofilm formed on thin films of SGM doped with a fluorochrome (fluorescein diacetate). The esterase/lipase activity of E. coli CN 13 and K. oxytoca spp. biofilm grown on top of SGM thin film, doped with fluorescein diacetate, was detected at the level of a single cell by epifluorescence microscopy. In view of these preliminary results, sol-gel glass has a considerable potential as a variable matrix for single bacteria and biofilm investigation.
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  • 16
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    Journal of sol gel science and technology 19 (2000), S. 333-336 
    ISSN: 1573-4846
    Keywords: sol-gel ; crystallization ; ultraviolet laser ; transition metal oxide ; perovskite oxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Structural changes stimulated by ultraviolet (UV) laser irradiations of sol-gel derived inorganic oxide films were investigated. Dried gel films of TiO2, Nb2O5, Ta2O5, SrTiO3 and Pb(Zr x Ti1−x )O3 (PZT) were found to be crystallized by the laser irradiation. On the other hand, the photo-induced change in gel films of BaTiO3, LiNbO3 and LiTaO3 was not observed although the laser beams were absorbed in the films. These sol-gel films were thermally crystallized at almost the same temperature around 600–700°C except TiO2. Thus, the UV-laser-induced crystallization is not directly ascribed to a simple thermal effect with the irradiation. Photochemical properties of the cations are assumed to be important for the change in sol-gel films.
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  • 17
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    Journal of sol gel science and technology 19 (2000), S. 611-614 
    ISSN: 1573-4846
    Keywords: sol-gel ; strontium barium niobate ; thin film ; ferroelectric material ; optical waveguide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Strontium barium niobate thin films were prepared by sol-gel method on various substrates using an improved process, two-step heating process. The two-step heating process applies an additive heat-treatment before crystallization for enhancement of the densification and the nucleation of films. Also, highly c-axis oriented SBN thin films with various compositions were obtained on MgO(100) and Pt(100)/MgO(100) substrates. Their optical and electrical properties such as optical propagation loss, refractive index, P-E hysteresis, and dielectric constant, were characterized as a function of the film composition.
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  • 18
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    Journal of sol gel science and technology 19 (2000), S. 661-664 
    ISSN: 1573-4846
    Keywords: heat of reaction ; tetraethyl orthosilicate ; heat of hydrolysis ; heat of polymerization ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Heat of reaction of the hydrolysis-polymerization process of tetraethyl orthosilicate with water in acidic condition was investigated to clarify the thermodynamic driving force of sol-gel reactions. Heat of reaction was measured using an isoperibol calorimeter by mixing a dilute tetraethyl orthosilicate (TEOS) ethanolic solution with another solution of water, ethanol, and hydrochloric acid. The temperature change of the reaction cell had been measured more than 24 hours after mixing under the quasi-isothermal condition. Large exothermic reaction (12.9 kJ·mol−1 for 1 mole of TEOS) due to the hydrolysis of TEOS was observed. A slow exothermic reaction followed it, and after that, the sol-gel reaction was changed to a small endothermic one.
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  • 19
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    Journal of sol gel science and technology 19 (2000), S. 715-718 
    ISSN: 1573-4846
    Keywords: catalyst ; Cu/SiO2 ; Ni/SiO2 ; nanocomposite ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Structural formation process of Ni/SiO2 and Cu/SiO2 catalysts prepared by solution exchange of wet silica gel was investigated. Microstructures of Cu/SiO2 and Ni/SiO2 were quite different from each other. In the case of Cu/SiO2, Cu particles with diameter of ca. 3–5 nm dispersed homogeneously at less Cu content, and the particle size of Cu as well as pore size of silica gel support increased with increasing Cu content. In the Ni/SiO2, the Ni particles with diameter of ca. 6–10 nm gathered densely to form aggregates in silica matrix resulting in sea-island structure, whereas the size of Ni particle slightly increased with increasing Ni content. The difference in the structure of the metal-silica composites is probably caused by the difference in interaction between silica gel network and metal ions during drying and heating processes.
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  • 20
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    Journal of sol gel science and technology 19 (2000), S. 737-740 
    ISSN: 1573-4846
    Keywords: SiO2 ; sol-gel ; thermoluminescence ; ESR ; Eu3+
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract SiO2 crystals have been used in electroluminescence devices and thermoluminescence (TL) dosimeters. However, their emission mechanisms have not yet been clearly explained. Recently, it has become possible to obtain amorphous, highly pure, SiO2 prepared by the sol-gel method. The emission mechanism of TL was investigated using Al3+ and/or Eu3+-doped SiO2 crystalline samples prepared by heat-treating under much lower temperature than the melting point of SiO2. The TL spectrum of Eu3+-doped sample had main peaks due to the electron transitions from 5D2 to 7F5 (ca. 570 nm, yellow peak) and from 5D0 to 7F2 (ca. 610 nm, red peak). The yellow peak intensity has a maximum value in the SiO2 doped with near 1 mmol% of Eu2O3, while the red peak intensity was almost constant. These facts suggest that bright yellow emission of SiO2TL phosphor is synthesized by the diffusion of Eu3+ ion in SiO2 matrix prepared by sol-gel method.
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  • 21
    ISSN: 1573-4846
    Keywords: sol-gel ; precursor chemistry ; fluorescence properties ; optical solids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two fluorescent dyes were incorporated into sol-gel derived SiO2 matrices. The dye was added to SiO2 precursors of different degrees of pre-condensation and the spectroscopic properties of the immobilized dye were measured at various aging and drying stages of the resulting gels. The significant influence of the processing parameters on the spectroscopic properties is manifested in the relative intensity of a second red shifted emission band (550–560 nm), which was observed besides the typical coumarin emission band (495 nm). The appearance of this long wavelength emission might be attributed to dye aggregation or to other reactions with the ambient matrix forced by micro porosity phenomena.
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  • 22
    ISSN: 1573-4846
    Keywords: interpenetrating networks ; sol-gel ; vinylacetate ; tetraethoxysilane ; vinyl-triethoxysilane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In the present work the sol-gel process in the ternary system VAc-VTES-TEOS was approached. The monomer that ensures the crosslinking of the obtained networks is VTES, which could react with VAc by free-radical polymerisation and with TEOS by hydrolysis-polycondensation. The early stage evolution of the process was monitored by gas chromatography coupled with mass spectrometry (GC-MS). The gels obtained were characterised by IR spectroscopy, DTA/TG analysis and DSC measurements. Important differences in the gelling process and in the properties of the obtained gels could be noticed, related to the presence of VAc and VTES in the reaction mixtures. The investigation allowed to establish the compositions and the experimental conditions in which gels with high degree of crosslinking could be obtained.
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  • 23
    ISSN: 1573-4846
    Keywords: WO3 ; electrochromic ; sol-gel ; peroxotungstic acid ; ECD's
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The WO3 electrode is ubiquitous in an electrochromic device (ECD) and is a common choice as the electrochromic (EC) layer. EC films were deposited on different substrates by spin coating using peroxotungstic acid based precursor solutions followed by appropriate thermal treatment. Many properties of the films, including some of the EC properties dependant on microstructure of the films, were found to be modified by the addition of small amounts of organic acid to the precursor solution. A study of structural, electrical and electrochromic properties of films cast by using precursor solution comprising 0 to 10 wt% of oxalic acid dihydrate (OAD) was carried out in terms of surface morphology, electrical resistance, structure and EC response. The important findings are that the addition of oxalic acid to the precursor solution results in films with excellent EC properties, devoid of cracks and decreases their dc electrical resistance.
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  • 24
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    Journal of sol gel science and technology 18 (2000), S. 249-258 
    ISSN: 1573-4846
    Keywords: magneto-optical effect ; magnetite ; silica gel ; sol-gel ; Faraday rotation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The magnetic composite materials that consist of transparent matrix and magnetic fine particles are expected to have large residual magnetization and coercive force because of their fine magnetic domain structure, and also to show magneto-optical effects. Silica gels containing magnetite (Fe3O4) fine particles were prepared by sol-gel method. The magnetic, optical and magneto-optical properties of the composites were investigated by measurements of magnetization curves, UV-visible spectra and Faraday rotation in visible range. The saturation magnetization of the composite was almost as same as that expected from the amount of magnetite fine particles in it. Although the composites had large and broad absorption at around 400 nm, they still maintained their transparency. The origins of decrement of transparency attributed to the optical absorption of magnetite and scattering due to magnetite fine particles. The whole composites showed positive Faraday rotation under external static magnetic field due to the large contribution of diamagnetic silica gel matrix. Magnetite contributed negative Faraday rotation with maximum at around 470–480 nm to the magneto-optical spectra of the composites.
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  • 25
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    Journal of sol gel science and technology 19 (2000), S. 215-218 
    ISSN: 1573-4846
    Keywords: art conservation ; sol-gel ; corrosion protection ; anti-corrosion coatings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A sol-gel coating was used in the long-term protection of the 14th Century mosaic situated above the gates of St. Vitus cathedral, in the center of Prague Castle. The choice of a sol-gel coating is the result of a research effort involving both on-site testing in Prague and accelerated ageing of various polymers and sol-gel materials in the laboratory. The coating selected for treatment of the entire 13 m × 10 m mosaic is a multi-layer system in which an organic-inorganic sol-gel layer is placed between the glass substrate and a fluoropolymer coating. This coating combination performed very well in an accelerated weathering chamber as well as during onsite testing. Since the top layer is scheduled to be removed and re-applied periodically, it is hoped that this concept will allow long term protection to the largest outdoors mosaic north of the Alps. On-site application of the coatings on the entire mosaic started in 1998 and will be completed in 2000.
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  • 26
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    Journal of sol gel science and technology 19 (2000), S. 231-236 
    ISSN: 1573-4846
    Keywords: photonics ; optical amplifiers ; sol-gel ; erbium ; crystallisation ; waveguides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The use of sol-gel to fabricate silica-on-silicon waveguides, and particularly erbium-doped waveguide amplifiers, is reviewed. In particular, efforts to use sol-gel to improve molecular homogeneity in heavily Er-doped silica-based films is discussed. A variety of material studies carried out to investigate the gain limitations found in these materials is then presented. These include x-ray diffraction, ellipsometry and Rutherford backscattering. Excess heat treatment is used to force crystallisation of the films, and analysis of the resulting structure is used to infer properties of the glass before the additional heating. The use of erbium alkoxide precursors is shown to alter the erbium environment in the final glass, in comparison to the use of inorganic erbium salts.
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  • 27
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    Journal of sol gel science and technology 19 (2000), S. 253-256 
    ISSN: 1573-4846
    Keywords: spectral hole burning ; rare earth ion ; Eu3+ ion ; glass ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Persistent spectral hole burning was studied in Eu3+ ions-doped Al2O3-SiO2 glass prepared by a sol-gel method. The gel synthesized by the hydrolysis of Si- and Al-alkoxides and EuCl3·6H2O was heated in air and hydrogen gas atmospheres. For the glass heated in air to contain OH bonds, the hole was formed by the photoinduced rearrangement of the OH bonds surrounding the Eu3+ ions, and was thermally refilled and erased above ∼200 K. On the other hand, the glass heated in hydrogen gas showed the hole spectrum above ∼200 K. It was found that the hole depth was independent of the temperature and was ∼7% of the total intensity at room temperature. The proposed mechanism was the electron transfer between the Eu3+ ions and the defect centers formed in glass matrix.
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    Journal of sol gel science and technology 19 (2000), S. 473-477 
    ISSN: 1573-4846
    Keywords: sol-gel ; precursor chemistry ; thin films ; soluble powders
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sol-gel processing has proved to be a useful method for the preparation of a wide range of inorganic thin films. However, gelation or precipitation of coating solutions and thus limited shelf-life have been drawbacks for the industrial application of this technology. Soluble powders of various compositions can be prepared from modified metal alkoxides commonly employed in sol-gel processing. Even though these powders contain a considerable amount of organic moieties they can be stored indefinitely under ambient conditions, thus diminishing shelf life problems. Redissolution in polar organic solvents, solvent mixtures or even water yields ready-to-use coating solutions. Coating solutions for the preparation of titania (TiO2), zirconia (ZrO2) and lead zirconate titanate (PbTi x Zr1−x O3, PZT) films have been synthesized by this method. Thickness, microstructure and properties of the resulting films can be varied by modification of the solvent, the coating procedure and thermal treatment. Inorganic thin films for various applications have been prepared.
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  • 29
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    Journal of sol gel science and technology 19 (2000), S. 495-499 
    ISSN: 1573-4846
    Keywords: sol-gel ; silicas ; biology ; X-ray diffraction ; IR ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The medium-range-network structure of silicas from different sources was comparatively examined by X-ray diffraction, IR and NMR analyses. Silica gels made through the conventional sol-gel route were found to have a different structure from silica glass, and considered to be composed of 4-fold siloxane ring units, irrespective of preparation conditions. Amorphous silicas in rice-hulls and bamboo leaves showed structure data close to silica glass, being suggested to consist mainly of 6-fold siloxane ring units. The modified sol-gel method, in which siloxane oligomers containing cyclic siloxane tetramers may have been ring-opened and polymerized under the catalytic reaction of NaOH or NH4F in the water-free solution, provided the silica gel of which structure was very similar to silica glass.
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  • 30
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    Journal of sol gel science and technology 19 (2000), S. 599-601 
    ISSN: 1573-4846
    Keywords: SBT ; chemical modification ; metal alkoxides ; crystallization ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract SrBi2Ta2O9 (SBT) has potential application in FERAM. Some problems in the sol-gel processing of SBT, such as the solubility of metal alkoxides, chemical modification with a chelating reagent and crystallization behavior of the gels, are investigated. The starting solutions were prepared with Sr(OC4H9)2, Bi(OC3H7)3, and Ta(OC2H5)5. Ethoxyethanol and acetylacetone (ACAC) were used as solvent and chelating reagent, respectively. Ta- and Bi-alkoxide are chemically modified with ACAC, but Sr-alkoxide was not. The SBT solution was stabilized with ACAC for ca. 3 months. After hydrolysis of the SBT solution with the addition of ACAC, a monolithic and transparent gel was obtained at room temperature in 100 days. The X-ray diffraction peaks of SBT and very weak peaks of SrTa2O6 (ST) and SrBi2O4 (SB) were found after calcination at 700°C for both of the gels obtained with and without addition of ACAC. In contrast, the stronger peaks of ST and SB were observed for the powder mixture of SrCO3, Bi2O3, and Ta2O5 after calcination at 800°C. These results show the better homogeneity of the gels.
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    Journal of sol gel science and technology 19 (2000), S. 677-680 
    ISSN: 1573-4846
    Keywords: silica aerogel ; sol-gel ; polyethoxydisiloxanes ; supercritical drying
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Silica aerogels were made by sol-gel techniques using industrial silicon derivatives (polyethoxydisiloxanes, E-40), followed by supercritical drying with ethanol. The morphology and microstructure of the silica aerogels were investigated by using specific surface area, SBET, SEM, TEM and the pore size distribution techniques. The thermal conductivity was also measured as a function of air pressure. The results show that the diameter of the silica particles is about 13 nm and the pore size of the silica aerogels is 20–80 nm. The specific surface area of the silica aerogel is about 470 m2/g and the thermal conductivity of the silica aerogel prepared with E-40 is 0.014 w m−1 K−1 at room temperature and 1 atm.
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    Journal of sol gel science and technology 19 (2000), S. 701-704 
    ISSN: 1573-4846
    Keywords: Co2+ complex ; sol-gel ; 1-naphthol ; contact ion pair ; separate ion pair
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Changes in coordination number of Co2+ and fluorescence spectra of 1-naphthol during the sol-gel transitions of TEOS have been investigated as a function of time. The change in the coordination number of Co2+ has been observed as follows. Six-coordinated Co2+ decreased quickly within several hours in the first stage of the reaction corresponding to water consumption by initial hydrolysis reaction. Then six-coordinated Co2+ increased around gelation due to polycondensation. After the gelation four-coordinated Co2+ increased, where isomorphous-replacement of Co2+ into the –O–Si–O– networks occurred. In the Co2+/1-naphthol mixed system, separate ion pair of 1-naphthol is preferentially coordinated on the six-coordinated Co2+ where water molecule(s) plays an important role to geometrical relaxation of excited-state 1-naphthol.
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  • 33
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    Journal of sol gel science and technology 19 (2000), S. 343-347 
    ISSN: 1573-4846
    Keywords: self-seeding ; PZT ; low temperature crystallization ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract We propose the novel preparation method, “Self-seeding Process”, based on the following concept for low temperature crystallization of oxide films. Introduction of desirable inhomogeneity should give lowering of a crystallization temperature through heterogeneous nucleation accompanied with reduced activation energy. We carried out inspection of the above concept through use of PZT films. PZT gel films with the desirable inhomogeneity of microstructure were prepared, and their crystallization behaviors was examined. The PZT film was successfully crystallized at 500°C by the self-seeding process. The single phase (001) oriented PZT film with 0.55 μm in thickness was obtained at 550°C for 5 min. The self-seeding process by microstructure control is efficient for the low temperature process of the oxide thin film.
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    Journal of sol gel science and technology 19 (2000), S. 421-424 
    ISSN: 1573-4846
    Keywords: hybrid ; sol-gel ; diol ; mixed oxide Al-Zr
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Monolithic and transparent hybrid Al-Zr gels were obtained by the reaction of homogeneous mixtures of metal alkoxides: (Al(OBus)3 + Zr(OPr)4) with Butan-1,3-diol at room temperature, without solvent, catalyst, or water. The products have been characterized by IR spectroscopy, DTA and TGA. The results show that the diol has reacted with the mixture of alkoxides leading to the monolithic transparent gels in which both organic-inorganic (–Al–O–R–O–Zr–) and inorganic (–Al–O–Zr–O–) bridges are formed. Xerogels obtained after the drying of gels were pyrolysed at different temperatures in air. The structure and morphology of the obtained materials were studied by X-ray powder diffraction (XRD) and the Brunauer-Emmett-Teller (BET) method. At 1200°C, the materials were composed of αAl2O3, t-ZrO2 and m-ZrO2.
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    Journal of sol gel science and technology 19 (2000), S. 453-457 
    ISSN: 1573-4846
    Keywords: hydrotalcite ; layered compounds ; sol-gel ; mixed oxides ; temperature programmed reduction
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Hydrotalcite is an anionic clay mineral (layered double hydroxide) whose general formula is [M(II)1−x M(III) x (OH)2] x+X x/n n− ·mH2O. Anionic clays with a hydrotalcite-type are widely used as useful precursors of multicomponent catalysts. Hydrotalcites with Ni/Al molar ratio 2.5 have been synthesised both by the coprecipitation method, starting with nickel and aluminium nitrates and by the sol-gel method, using nickel acetylacetonate and aluminium isopropylate as precursors. The NiO-Al2O3 oxidic forms have been obtained by the thermal treatment of the precursors at 450°C and 900°C, respectively, and were characterised by DTA, XRD, IR spectroscopy and temperature programmed reduction (TPR). TPR clearly demonstrated a higher reducibility of the oxidic forms derived from the sol-gel synthesised precursors.
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  • 36
    ISSN: 1573-4846
    Keywords: proton conductor ; phosphate glass ; sol-gel ; hydrogen concentration cell
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    Topics: Chemistry and Pharmacology
    Notes: Abstract High proton-conducting P2O5-SiO2 glass was applied to the electrolyte of the hydrogen concentration cell for hydrogen gas sensing. 5P2O5·95SiO2 glass was prepared using the sol-gel method and its electrical conductivity and electromotive force were measured at 50°C as a function of both the ambient humidity and hydrogen gas concentration. The electrical conductivities increased with increasing humidity and reached ∼ 10−2 S/cm at 90% relative humidity. The electromotive force of the hydrogen concentration cell, where the glass was used as a membrane, showed good Nernstian response to hydrogen pressure in the high relative humidity region.
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    Journal of sol gel science and technology 19 (2000), S. 779-783 
    ISSN: 1573-4846
    Keywords: energy transfer ; rare-earth spectroscopy ; cadmium sulfide ; quantum dots ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract We have investigated the energetic correlation between rare-earth ions and semiconductor nanocrystals, using europium ion (Eu3+) doped silica (SiO2) gel with adsorbed cadmium sulfide (CdS) particles. Samples were prepared by a sol-gel technique, in which several methods for the precipitation of CdS colloids were attempted. The fluorescence intensities were compared for different gels, with and without CdS particles. The intrinsic emission lines due to 5D0 → 7FJ(J = 0–4) transitions of Eu3+ were observed, which were enhanced for 24 h-immersed gel (dried at 50°C). From the results on the decay dynamics of fluorescence, we proposed the model that surface-trapped electrons on CdS particles nonradiatively excited 4f electrons in Eu3+ ions due to an energy transfer process.
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  • 38
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    Journal of sol gel science and technology 19 (2000), S. 425-428 
    ISSN: 1573-4846
    Keywords: sol-gel ; inorganic-organic hybrid membrane ; permeation characterization
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Silica-based inorganic-organic hybrid membranes have been prepared on porous α-Al2O3 substrate (pore size, 2 μm) using tetraethoxysilane (TEOS) and phenyltrimethoxysilane (PTMOS) as precursors. The effects of sol synthesis conditions on the processing and performance of deposited hybrid layers were observed. The thickness of the hybrid layers after three deposition cycles is about 2 μm, estimated from their cross-section SEM micrographs. The gas permselectivity of the hybrid membrane was characterized by O2/N2, CO2/N2, and CO2/O2 mixing gases, which was mainly governed by the surface diffusion at lower pressures and Knudson diffusion at higher pressures. The introduction of phenyl groups can not only improve the selectivity of O2/N2 and CO2/N2, but also densify the membrane network.
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  • 39
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    Journal of sol gel science and technology 19 (2000), S. 89-94 
    ISSN: 1573-4846
    Keywords: catalysts ; vanadia-alumina ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Vanadia-alumina xerogels were prepared by sol-gel method using organic precursors of metal and acetic acid as hydrolysis source. The purpose of this work is to study the change in the structure of dispersed vanadia as a function of preparation parameters, mainly the hydrolysis ratio k = [CH3COOH]/[Al(O-s-Bu)3] and the vanadium content V/V + Al (%). The amount of acetic acid affects considerably the solid texture, thus the pore size increases with the k ratio. In the same time, 51V NMR spectroscopy shows a decrease in the vanadium coordination from six-fold to fourfold. The investigation by temperature programmed reduction (TPR) shows that the reducibility of catalysts is determined in the order: K = 3 〉 K = 2 〉 K = 1. Furthermore, the catalytic activity in paraxylen oxidation follows a trend similar to that observed in TPR. The increase of vanadium content from 5 to 10%, favours the association of vanadium monomeric species, resulting in a new surface species. Hence, the coordination of vanadium changes from tetrahedral to octahedral, which induces a fall in partial oxidation selectivity.
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    Journal of sol gel science and technology 19 (2000), S. 237-242 
    ISSN: 1573-4846
    Keywords: magneto-optical effect ; bi-substituted YIG ; sodium borosilicate ; sol-gel ; Faraday rotation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Composite materials which consist of ferro- or ferrimagnetic fine particles in a glass matrix are expected to have a large residual magnetization and coercive force because of their fine magnetic domain structure, and has potential for superior magneto-optical properties compared with single or polycrystalline materials. In this study, the sodium borosilicate (NBS) glass containing Bi-substituted yttrium iron garnet (Bi x Y3−x Fe5O12: BiYIG) fine particles, which show a superior magneto-optical effect, was prepared by the sol-gel method. BiYIG fine particles were stable in NBS gel-glass matrix during densification because the sintering temperature (580°C) of NBS gel was low enough to avoid pyrolysis of BiYIG and the reaction between BiYIG fine particles and the matrix. The Faraday rotation angle spectrum of the composite after deducting the contribution of the NBS glass matrix was intermediate between the reported ones of YIG and Bi0.25YIG polycrystalline thin films. The change of the Faraday rotation angles of the composite with imposing magnetic field showed a hysteresis loop. It was in good agreement with that of the magnetization curve of the composite.
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    Journal of sol gel science and technology 19 (2000), S. 325-328 
    ISSN: 1573-4846
    Keywords: lutecium orthosilicate ; sol-gel ; glass-ceramics ; scintillators ; Lu2SiO5
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Cerium-doped lutecium orthosilicate (LSO) is the most promising scintillator discovered in almost five decades. It exhibits a unique combination of important properties for x and gamma-ray spectroscopy: high density, fast decay, and large light yield. However, the practical use of LSO is hindered by difficulties related to its fabrication as a single crystal by the Czochralski method. We report on the usefulness of the sol-gel process in obtaining lutecium silicate scintillators. Upon appropriate drying and firing, lutetium silicate crystals can be grown in a silica matrix. The bulk, polycrystalline transparent scintillators are characterized by XRD, optical absorption, light decay measurement and gamma-ray spectral response. Their properties are comparable to that of traditional LSO single crystals.
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    Journal of sol gel science and technology 18 (2000), S. 145-158 
    ISSN: 1573-4846
    Keywords: tellurium oxide ; tellurium suboxide ; sol-gel ; thin films ; optical properties ; optical data storage
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A novel sol-gel processing route has been developed for the production of tellurium oxide (TeO2) and tellurium suboxide (TeO x ) thin films. The process has been used to deposit thin films on glass substrates by the dip coating process. These films have been shown to undergo thermally induced, reversible changes in optical properties on heating at appropriate temperatures. Formation of TeO x was found to occur at low temperatures by direct breakdown of the sol-gel derived material even in the absence of reducing agents whilst the principal optical effects corresponded to the formation of TeO x and α-TeO2 at temperatures of 〈200°C and 〈450°C respectively. The relatively low temperatures required to induce significant optical effects are comparable with conventionally prepared TeO x and offer the potential application of these materials in optical data storage systems.
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    Journal of porous materials 7 (2000), S. 435-441 
    ISSN: 1573-4854
    Keywords: porous silica ; sol-gel ; tetraethoxysilane ; carbon matrix
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Porous silica was prepared using the sol-gel synthesis with porous carbon matrices as a pore-forming support. Tetraethoxysilane (TEOS) was hydrolyzed in an acid medium in the presence of a substoichiometric amount of water. Various carbon materials were used, among them Sibunit and catalytic filamentous carbon. Carbon matrices were impregnated with hydrolyzed TEOS and dried, then carbon was removed by burning out in air at 873 K. The obtained porous silica samples were studied by adsorption and electron microscopic methods. The specific surface area as high as 1267 m2g and pore volume as high as 5.7 cm3/g were determined for some silica samples. Thus deposited SiO2 was found to cover the carbon surface copying its surface. With CFC used as carbon matrix, silica nanotubes were obtained. Thermostability of such silica is significantly greater as compared to silica gels reported earlier.
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    Reaction kinetics and catalysis letters 69 (2000), S. 325-329 
    ISSN: 1588-2837
    Keywords: Nickel-based catalyst ; methane partial oxidation to syngas ; sol-gel ; carbon-deposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract NiO/γ-Al2O3 catalysts were prepared by the impregnation and the sol-gel method. The sintering and loss of nickel, carbon deposition and 80 h life-test for POM reaction over the catalyst were investigated by a flow-reactor and by XPS, TG, EXAFS and AAS analysis. The results indicated that the sol-gel method could enhance the ability to suppress carbon deposition and to resist nickel sintering and loss over nickel-based catalysts.
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  • 45
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    Journal of thermal analysis and calorimetry 56 (1999), S. 7-15 
    ISSN: 1572-8943
    Keywords: ALE ; CVD ; DSC ; DTA ; EGA ; EL display ; solar cell ; sol-gel ; spray pyrolysis ; super-conductor ; TG ; thin films
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Processing thin films for advanced applications, for instance in electronics and optoelectronics, involves several steps starting from precursor synthesis and ending up with the devices. Especially when optimizing the first steps of this chain of processes, thermoanalytical techniques play an important role. The review will focus on the main chemical deposition methods (CVD, ALE, spray pyrolysis, sol-gel) giving selected examples of problem-solving by thermal analysis. The techniques discussed are TG, DTA/DSC, EGA and their combinations. High-temperature X-ray diffraction (HTXRD) is also a powerful tool for in situ studies of thin films. The examples are taken from solar cell, superconductor and flat panel electroluminescent display technologies.
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    Journal of thermal analysis and calorimetry 56 (1999), S. 199-204 
    ISSN: 1572-8943
    Keywords: aluminium ions ; aluminosilicate gel ; mullite ; silica solution ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The mechanism of mullite formation depends upon the method of combining the silica and alumina-containing reactants. In this work, the effects of the processing variables (dilution, pH, gelling temperature and water content) on mullite formation were investigated. Monophasic gel was synthesized from aluminium nitrate nanohydrate dissolved in an absolute ethyl alcohol and silica sol mixture. The gelling was performed at room temperature and at 60°C. It was found experimentally that the temperature of mullite formation depends on the microstructure of the gel. The lowest temperature of mullite formation (970°C) was observed when the mullite gel was prepared at low pH (pH=1), low water content and high gelling temperature.
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    Journal of sol gel science and technology 14 (1999), S. 69-74 
    ISSN: 1573-4846
    Keywords: sol-gel ; silicon oxycarbide glass ; high temperature stability
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The high temperature stability of sol-gel-derived SiOC glasses has been investigated in order to understand the role played by the presence of a free-carbon phase in the amorphous oxycarbide network. Therefore, pure and excess free-carbon containing SiOC glasses have been prepared from hybrid gels and used for the high temperature stability experiments. Moreover, the possible effects of the sample size with respect to local kinetics and thermodynamics and of the testing environment have also been investigated. Results show that all these parameters play a crucial role in defining the high temperature behavior of SiOC glasses.
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    Journal of sol gel science and technology 16 (1999), S. 101-107 
    ISSN: 1573-4846
    Keywords: sol-gel ; electrical properties ; barium titanate ; conduction mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract BaTiO3 thin films were prepared on single crystal silicon (1 0 0) and platinum substrates by sol-gel technique. Amorphous films with thickness uniformity were obtained by spinning the solution at 3000 rpm for 30 s and by post-deposition annealing at 400°C. The films exhibited good dielectric and insulating properties. The dielectric constant and dissipation factor at a frequency of 100 kHz were 17 and 0.20, respectively, for 1400 Å thick film on platinum substrate (MIM). The corresponding values were 16 and 0.015 for films on Si (MIS). Dielectric properties were also studied as functions of frequency and voltage. The C-V curve for MIS structure exhibited a hysteresis. The density of interface states recharged during the bias cycle in hysteresis measurement was estimated to be of the order of 2.10 × 1011 cm−2 and total oxide charge density was about 4.28 × 1011 cm−2. I-V measurements were performed on films of different thicknesses. The leakage current densities at 5 V for the films having thicknesses 1400 and 2800 Å were 0.86 and 0.11 μA/cm2 respectively. The conduction mechanism is found to be Poole-Frenkel and Schottky mechanisms at low and high fields, respectively.
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    Journal of sol gel science and technology 15 (1999), S. 147-159 
    ISSN: 1573-4846
    Keywords: computer simulation ; modeling ; sol-gel ; phase transition
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Some of our recent work on computer simulation modeling of the sol-to-gel transition for the polymerization by step reaction are presented. Depending on the variants of the model, a random distribution of bifunctional and tetrafunctional monomers of concentration C2 and C4 respectively, and their chains (bond-fluctuating) are used as primary reacting units on a simple cubic lattice as the initial sol-phase. Effects of solvent, temperature, mobility of monomers, rate of reaction, and reversibility are considered in understanding the evolution of microgels, onset of gelation and the nature of sol-to-gel transition, inhomogeneity, etc. Gel point (pc, gel volume fraction (PG), weight average degree of polymerization (MW), structure factor (S(q, t)) show various interesting variations with the conversion factor (p). For example, sol-to-gel transition seems nonuniversal with respect to quality of the solvent, degree of inhomogeneity depends on the quality of solvent and rate of reaction due to interplay between the phase-separation and cross-linking.
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  • 50
    ISSN: 1573-4846
    Keywords: BST ; sol-gel ; thin films ; tunable dielectric
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We have recently isolated the neo-pentoxide (HOCH2CMe3, ONp) derivatives of Ba, Sr, and Ti as Ba4(ONp)8(HONp)6(py)2, Sr5(O)(ONp)8(Solv)5 (Solv = solvent), and Ti2(ONp)8, respectively. The combination of these precursors were found to be readily soluble in a wide range of solvents and thus were excellent candidates for preparation of barium strontium titanate ((Ba,Sr)TiO3 or BST) thin films using spin-cast deposition techniques. The highest quality BST films for this system were generated from ternary mixtures dissolved in either pyridine or pyridine/toluene. By in situ VT-GIXRD analysis it was determined that the perovskite phase of BST was readily formed at 650°C. The electronic properties of films crystallized at 700°C indicated that the thin films (300 nm) possessed a dielectric constant of 120 (tan δ = 0.03) with a tunability of 29% at ±10 V. 300 nm films (700°C) which had been generated from a standard BST solution modified with a novel tridentate ligand, had a higher dielectric constant of 180 and a tunability of 35% at ±10 V. The collective characteristics of these precursors offer an attractive alternative to the more complex, less stable sol-gel precursors currently in use.
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    Journal of sol gel science and technology 16 (1999), S. 173-182 
    ISSN: 1573-4846
    Keywords: PZT ; aerogels ; sol-gel ; sintering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract For ultrasonic applications in gases porous piezoelectric transducers with low acoustic impedances are required. Highly porous piezoceramics can be prepared by sol-gel processing, supercritical drying and subsequent firing. These PT and PZT aerogels are obtainable as crystalline monoliths with porosities up to 70 vol%. In this paper the influence of sol-gel-synthesis, stoichiometry, drying conditions and heat treatment on the material properties are reviewed. Lowering the coercive field strength by dopants is necessary in order to facilitate the polarization of highly porous PZT-ceramics. New results show that the introduction of 2 mol% neodymium is possible in the sol-gel synthesis of the aerogel precursor. Most structural properties of the resulting PbNd0.02Zr0.53Ti0.47O3 aerogels are similar to those of the undoped material.
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    Journal of sol gel science and technology 16 (1999), S. 221-226 
    ISSN: 1573-4846
    Keywords: organic-inorganic hybrid gels ; hydrolysis ; pyrolysis ; sol-gel ; silicon oxycarbide ; silicon carbide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Transparent monolithic discs of organic-inorganic hybrid gels have been prepared by hydrolysis-condensation reactions of tetraethyl orthosilicate with 1,4 butanediol. The gels and glasses have been characterized by infrared spectroscopy and 29Si MAS NMR. The characterization of the gels by infrared spectroscopy showed the incorporation of carbonaceous groups in the polymeric structure and Si–C bonding in the glasses. Pyrolysis of the gels has been studied using thermal analysis. It showed that the pyrolysis of the gels occurs in two temperature domains. The first is below 400°C due to condensation reactions and second is in the temperature range 450–550°C due to decomposition of carbonaceous groups and crosslinking. Pyrolysis of the gels at 1000°C resulted in X-ray amorphous, hard black glasses similar to oxycarbide glasses obtained by pyrolysis of siloxanes. On further heat treatment to 1400–1600°C, development of cristobalite structure and crystalline silicon carbide is observed in the otherwise amorphous black mass. The pyrolysed materials have been found to exhibit good resistance towards oxidation at 1000°C.
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    Journal of sol gel science and technology 15 (1999), S. 263-270 
    ISSN: 1573-4846
    Keywords: processing ; sol-gel ; barium titanate ; magnesium titanate ; lead titanate ; bismuth titanate ; lanthanum titanate ; lead zirconium titanate ; lead magnesium titanate ; barium magnesium tantalate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This review deals with the solution-sol-gel processing (SSG) of powders such as BaTiO3, MgTiO3, PbTiO3, Bi4Ti3O12, La2Ti2O7, Pb(Zr0.52Ti0.48)O3, Pb(Mg1/3Nb2/3)O3 and Ba(Mg1/3Ta2/3)O3. Fine powders of good sinterability can be easily obtained at low temperatures although the process can be expensive and time consuming. We propose a nanocomposite route which utilizes nanophases of different components as a cost-effective alternative to sol-gel process for powder preparation.
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  • 54
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    Journal of sol gel science and technology 15 (1999), S. 201-209 
    ISSN: 1573-4846
    Keywords: sol-gel ; synthesis ; protoenstatite ; 29Si-NMR ; freeze-drying
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Three different magnesium silicate sols were prepared from Mg(OMe)2 and TEOS for which hydrolysis with H2O2 and H2O was under stoichiometric, stoichiometric, or over stoichiometric. Xerogels were prepared from the sols by simple evaporation, spray-drying, or freeze-drying. The freeze-dried precursor formed mostly protoenstatite, a high-temperature polymorph of enstatite (MgSiO3) that is generally not stable at room temperature; the other precursors formed mixtures of protoenstatite and clinoenstatite. The three xerogels and their calcined products were studied with XRD, HTXRD, BET, carbon analysis, TG/DTA and29 Si-NMR. Residual carbon was found to be an important factor in the crystallization, and 29Si-NMR spectroscopy was found to be a better tool than XRD to assess the phase purity of protoenstatite.
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    Journal of sol gel science and technology 15 (1999), S. 57-62 
    ISSN: 1573-4846
    Keywords: glutamate dehydrogenase ; allosteric regulators ; sol-gel ; enzyme activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Glutamate dehydrogenase is encapsulated in a transparent porous silicate matrix by using sol-gel techniques. The inorganic polymer is formed around the enzyme (MW 〉 300,000 D). The enzyme is active in the material, catalyzes the reaction of L-glutamate to 2-oxoglutarate and follows Michaelis-Menten kinetics. The allosteric regulators ADP and GTP inhibit or activate the reaction; at pH 6, GTP acts as a strong activator and ADP acts as an inhibitor. This system involves a complex series of interactions; the co-enzyme NAD+ is required for catalysis, large-scale conformational changes accompany the binding of the substrate and coenzyme to the enzyme, the activators/inhibitors must bind to the enzyme to regulate the reactions, and the substrates and products must diffuse through the matrix to and from the binding site. The influence of the unique matrix on the complex enzymatic system is discussed.
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  • 56
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    Journal of sol gel science and technology 14 (1999), S. 149-162 
    ISSN: 1573-4846
    Keywords: sol-gel ; PbTiO3 fiber ; triethanolamine ; complexed alkoxide ; stabilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sol-gel processing was used to prepare lead titanate fibers. Titanium isopropoxide and lead acetate trihydrate were used as starting materials and triethanolamine (TEA) was added to form stabilized Pb-Ti complex alkoxide. Effects of catalyst and solvent on the state of precursor solutions, gelation reaction, fiber spinnability, pyrolysis and crystallization were investigated.
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  • 57
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    Journal of sol gel science and technology 14 (1999), S. 87-94 
    ISSN: 1573-4846
    Keywords: oxycarbide glasses ; sol-gel ; mechanical properties ; elasticity ; viscosity
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The high temperature behavior of a sol-gel derived silicon oxycarbide glass containing 12 at.% carbon has been characterized by means of creep and in-situ ultrasonic echography measurements. Temperature induced changes include structural relaxation and densification from 1000 to 1200°C, and crystallization to form a fine and homogeneous β-SiC/glass-matrix nanocomposite with 2.5 nm large crystals above 1200°C. Young's modulus measurements clearly reveal a consolidation of the material upon annealing below 1200°C. Crystallization is almost complete after few hours at 1300°C and results in a significant increase in Young's modulus. The viscosity of the oxycarbide glass is much higher than that of fused silica, with two orders of magnitude difference at 1200°C, and the glass transition temperature ranges from 1320 to 1370°C.
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    Journal of sol gel science and technology 14 (1999), S. 113-123 
    ISSN: 1573-4846
    Keywords: oxycarbide glasses ; sol-gel ; glass sheets ; microstructure ; dielectric properties
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Thin (50—1000 μm) silicon oxycarbide glass sheets were synthesized by the pyrolysis of gel sheets obtained from a methyl-modified silica sol containing colloidal silica under inert atmosphere between 900 and 1450°C. The microstructure of these glass sheets was investigated with the help of high resolution scanning and transmission electron microscopy (HR-SEM and HR-TEM), X-ray diffraction and Raman spectroscopy and their dielectric properties were determined. The surface morphology as observed with HR-SEM did not exhibit a notable temperature dependence. HR-TEM studies showed that the glass sheets sintered up to 1200°C are amorphous, whereas those sintered at 1450°C contain uniformly dispersed crystallites of SiC and graphite. X-ray diffraction studies were found in agreement with the HR-TEM results. Raman spectroscopy showed that free carbon is present as an amorphous phase till a temperature of 1000°C, whereas at temperatures ≥1200°C, the presence of graphitic carbon was observed. Silicon oxycarbide glass sheets heat treated at temperatures up to 1200°C, showed a dielectric constant between 4.1 ± 0.11 and 4.6 ± 0.15 in the frequency range from 75 kHz to 5 MHz, with corresponding losses between 0.0008 and 0.1100. Such silicon oxycarbide glass sheets sintered at ≤1200°C could find an application as substrates for electronic packaging.
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  • 59
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    Journal of sol gel science and technology 14 (1999), S. 209-216 
    ISSN: 1573-4846
    Keywords: sol-gel ; silica-titania films ; planar waveguides ; Er doping ; fluorescence lifetime
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Erbium doped silica-titania planar waveguides, co-doped with ytterbium and aluminum, have been prepared by sol-gel processing, using multilayer spin-coating deposition on silicon or silica glass substrates. The Er3+ doping level varied between 0 and 2 at.%, while Yb3+ varied from 0 to 3 at.%. Aluminum was incorporated up to 15 at.% Al and it was found to have no significant effect on the refractive index of the silica-titania (80 : 20 mol%) matrix. The Er3+ fluorescence emission was flat within ±0.5 dB, between 1520 and 1560 nm. The corresponding 4I13/2 metastable level lifetime was found to decrease from 6.1 to 3.5 ms, as the Er concentration increased from 0.1 to 0.5 at.%, for films co-doped with 0.5 at.% Yb and 10 at.% Al and the fluorescence decay was essentially single exponential below a Er quenching concentration of 0.5 at.% (1.1 × 1020 ions/cm3). The lifetime appears to be limited by Er-Er interactions at higher rare-earth ion concentrations and by residual OH species in the sol-gel derived waveguides. Vacuum heat treatment at a temperature near 570°C was somewhat effective in increasing the Er fluorescence lifetime, whereas reactive atmosphere processing in CCl4 or Cl2 at a similar temperature appeared to be less effective.
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    Journal of sol gel science and technology 15 (1999), S. 73-85 
    ISSN: 1573-4846
    Keywords: sol-gel ; Ormosils ; silica-titania thick films ; silica-zirconia thick films ; optical properties
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Crack-free films with thicknesses of up to 30 μm were prepared by the sol-gel process using the dip-coating technique. Thick films were obtained from various starting solutions based on two, three or four components, with particular emphasis on ternary systems. The ternary systems were composed of two tetraalkoxy precursors (a silicon tetraalkoxide and a zirconium or a titanium tetralkoxide ) and a trialkoxysilane with a non-hydrolyzable group. By using these trialkoxysilanes, the tendency of the films to crack during the drying process is reduced because of the stress absorption by the network structure. The use of zirconia or titania allows for control of the refractive index of the films. Optical parameters of the films including refractive index, thickness, surface roughness and UV-Vis and IR transmission spectra were determined for each composition and the structural characteristics of the films were inferred from the IR spectra. UV cut-off and antireflective properties were also studied for some compositions.
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  • 61
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    Keywords: surface modification ; electrophoretic deposition ; sol-gel ; organoalkoxysilane ; inorganic-organic composite
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Thick films were prepared by the electrophoretic sol-gel deposition of organically modified, sub-micron silica particles. The silica particles were modified with 3-aminopropyltriethoxysilane (APS) and vinyltriethoxysilane (VTES). Smooth and crack-free films ca. 15 μm thick were obtained when APS modified silica particles were used for the cathodic electrophoretic deposition. Thick films with decreased open spaces among particles were obtained when silica particles modified with VTES were co-deposited with an organic polymer, polyethylene maleate.
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    Journal of sol gel science and technology 16 (1999), S. 7-12 
    ISSN: 1573-4846
    Keywords: sol-gel ; (Ba,Ca)(Ti,Zr)O3 ; thin films ; dielectric constant ; dielectric loss
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    Topics: Chemistry and Pharmacology
    Notes: Abstract (Ba0.92,Ca0.08)(Ti0.92,Zr0.08)O3 thin films were prepared from Ba-Ti and Ca-Zr precursors by sol-gel processing. Polymerizable solutions containing Ba-Ti and Ca-Zr, respectively, were newly synthesized. Decomposition of the starting compounds and crystallization behavior of the film were examined by using TG/DTA and XRD. Microstructure of thin films was observed by using SEM. Polycrystalline (Ba0.92,Ca0.08)(Ti0.92, Zr0.08)O3 films obtained by firing at 800°C were dense with fine grains. The thin films showed a dielectric constant of 1200 and dielectric loss of 0.5%.
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    Journal of sol gel science and technology 16 (1999), S. 93-99 
    ISSN: 1573-4846
    Keywords: sol-gel ; zinc oxide ; low temperature preparation ; alkoxide structure
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    Topics: Chemistry and Pharmacology
    Notes: Abstract ZnO thin films were prepared on silicon substrate with Pt electrode by the sol-gel processing using Zn alkoxide solution prepared from Zn(NO3)2·6H2O and 2-methoxyethanol. FT-IR spectroscopy showed the presence of Zn species in the alkoxide, with methoxyethoxide and nitrato groups as coordination ligands, indicating formation of Zn(NO3)(OCH2CH2OCH3). Smooth and homogeneous thin films were obtained by heat treating coating gel films in the temperature range from 250 to 500°C. The ZnO thin films exhibited a preferred growth of crystals with c-axis perpendicular to the Si substrate surface when fired at 250°C. It was discussed that the presence of nitrogen atoms in precursors had affected the phase development of crystals and was the basis of the structural relaxation for crystallization at low temperature.
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    Journal of sol gel science and technology 16 (1999), S. 235-241 
    ISSN: 1573-4846
    Keywords: sol-gel ; silica-poly(ethylene oxide) hybrid material ; epoxide polymerization ; optical properties
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Structural evolution and optical properties of the silica-poly(ethylene oxide) hybrid films prepared from γ-glycidoxypropyltrimethoxysilane (GPTS) and 1-methylimidazol (MI) are studied. Polymerization of the epoxy groups is achieved by using 1-methylimidazol as a thermal curing agent. In liquid state 1H &13 C NMR spectroscopy, it is found that silica condensation mainly occurs without epoxy ring opening. The epoxide polymerization is confirmed by using FT-IR, solid state CP-MAS 13C-NMR, and differential scanning calorimetry (DSC). The hybrid material is densified due to the epoxide polymerization as well as silica condensation with thermal curing. As a result, the thermal curing increases refractive index and extinction coefficient and shifts UV optical absorption edge to longer wavelength.
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    Journal of thermal analysis and calorimetry 56 (1999), S. 345-353 
    ISSN: 1572-8943
    Keywords: acidity ; isotopic exchange ; sol-gel ; sulfated zirconia ; thermal analysis
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Sulfated zirconias were prepared either by impregnation of zirconia with sulfuric acid or by a one step sol gel process by using different solvents. Solids prepared under closely similar conditions in different solvents show different amounts of sulfur and surface areas, thus demonstrating that the crystallization is different. Clear differences occur in the DTA-DTG curves with the appearance of a composite peak for the sol-gel catalysts, whereas the solid obtained by the classical two-step technique shows only one peak. The number of acid sites of these samples is changed by a factor of 3 depending on the preparation. Two types of hydroxyls are observed by infrared spectroscopy: one with bands at 3640 and 3585 cm-1, associated with protons of moderate acidity, and a second at about 3300 cm-1 able to exchange D with C6D6. Moreover, the infrared band of sulfates also contains two components: one at 1405 cm-1 more intense for the most acidic solids and a second one at 1380 cm-1. After activation, these solids are as active as zeolite beta for the acylation of anisole with acetic anhydride.
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  • 66
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    Reaction kinetics and catalysis letters 66 (1999), S. 155-162 
    ISSN: 1588-2837
    Keywords: Hydrogenation ; oleic acid ; Ru−Sn catalysts ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The hydrogenation of oleic acid to oleyl alcohol over Ru-alumina and Ru−Sn-alumina sol-gel catalysts has been studied. It was found that, besides its hydrogenation activity, the Ru−Sn-alumina catalyst promotes thecis-trans isomerization of the unsaturated acid. This effect is used to explain some kinetic features of the system, like the high induction time observed in the formation of alcohols, and to re-examine the role of tin.
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    Journal of inorganic and organometallic polymers and materials 8 (1998), S. 205-214 
    ISSN: 1572-8870
    Keywords: Phosphazenes ; sol-gel ; urethane ; surface functionalization ; heparin
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A sol-gel precursor was prepared by the reaction of poly[bis(2-(2-hydroxyethoxy)ethoxy)phosphazene] (1) with 3-isocyanatopropyltriethoxysilane. It was then sol-gel polymerized to produce a covalently interconnected phosphazene-silicate network with urethane functionalities. Isocyanato groups were introduced on the surface of the network through coupling by allophanate formation between hexamethylene diisocyanate and urethane functionalities on the gel surface. Heparin was immobilized on the surface of the network by reacting hydroxyl or amino groups of heparin with the surface isocyanato groups. The activity of the immobilized heparin was 4.0% that of free heparin.
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    Journal of applied electrochemistry 28 (1998), S. 1051-1059 
    ISSN: 1572-8838
    Keywords: Carbon-Ceramic electrodes ; Li ion batteries ; intercalation ; Li salt solutions ; EIS ; sol-gel ; Ormosil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Graphite electrodes comprising silica binder were tested in ethylene carbonate–dimethyl carbonate (EC–DMC), propylene carbonate and tetrahydrofuran solutions. The electrochemical behavior of these electrodes was analyzed using chronopotentiometry, slow-scan rate cyclic voltammetry (SSCV), impedance spectroscopy and potentiostatic intermittent titration technique (PITT). The electrode morphology and integrity were studied by scanning electron microscopy (SEM). Using silica binder, graphite particles are usually embedded in the current collector in an unoriented form. Thus, the electroanalytical study of these electrodes and the comparison of their response with that of highly oriented PVDF based graphite electrodes, provided insight into the effect of particle orientation on the general electrochemical behavior of lithiated graphite anodes. In general, the higher the particle orientation and compact packing in the electrodes' active mass, the better the performance o f the Li–graphite electrodes, as the surface films developed are better passivating and the interparticle electronic contact is also better. The silica binder may have advantages over other binders such as PVDF in its ability to better retain the electrode integrity upon cycling. However, the practical use of such electrodes requires further optimization, especially in connection with particle orientation and compact packing.
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  • 69
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    Microchimica acta 129 (1998), S. 149-165 
    ISSN: 1436-5073
    Keywords: silicates ; organosilicon ; sol-gel ; ORMOSIL ; solid-state lasers ; gas separation membrane ; nonlinear optics ; optical wave guides ; composite films ; chemical sensors ; gas sensors ; catalysis ; chromatographic applications
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Inorganic-organic hybrid materials prepared by the sol-gel process have become an attractive field of study due to the immense versatility associated with this method of composite material preparation. The blending of inorganic precursors with organosilicon reagents enables unique materials to be fabricated with the desired chemical and physical characteristics. The ability to control the interfacial polarity, the degree of porosity, and the chemical functionality in the matrix has been shown to be a powerful tool in the design of materials for sensor, optical, chromatographic, and catalytic applications. In this review, the preparation of the organically modified silicates (ORMOSILs) where the individual precursors are covalently bound to each other is discussed and selected examples of their potential usefulness in analytical applications is presented.
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    Journal of sol gel science and technology 11 (1998), S. 55-66 
    ISSN: 1573-4846
    Keywords: titania coating ; sol-gel ; coating bonding strength to substrate ; biocompatible ; bioactive
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Bioactive ceramic coatings have had poor adhesion to substrate. In this study, the bond strength (tensile strength) of titania gel coating to titanium substrate was studied. In the experiments three different pretreatments were used, namely sodium hydroxide corroding, plasma cleaning and titanium nitride coating. Also the effects of heating temperature, heating in vacuum and titanium surface roughness were studied. The sol properties were altered with valeric acid addition. Samples were analysed by SEM-EDX, AES, AFM and tested by bond strength gauge. Those samples in which the titanium surface was precorroded one hour in sodium hydroxide, predeposited by titanium nitride or ground improved the bonding strengths of titania coatings to over 24 MPa. In these samples a fracture occurred at the glue-coating interface.
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    Journal of sol gel science and technology 11 (1998), S. 289-298 
    ISSN: 1573-4846
    Keywords: Ag/SiO2 ; Cu/SiO2 and Ag-Cu/SiO2 nanocomposite films ; sol-gel ; annealing atmospheres ; clusters growth by thermal annealing ; optical absorption ; X-ray diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In a program on the development of metal nanoclusters in sol-gel derived thin films, attempts were made to synthesize pure and mixed metal clusters, control the cluster size and increase the volume fract f the clusters. Thus, Ag, Cu and Ag-Cu nanoclusters were prepared in silica films using dip- and spin-coating techniques. The annealing of Ag/SiO2 films in different atmospheres (air, argon and 5% H2-95% N2 gas) caused modifications of Ag nanoclusters resulting in changes in their surface plasmon resonance (SPR) peak positions. The Cu and Ag-Cu codoped films were annealed in reducing atmosphere (5% H2-95% N2 gas). In order to prepare Cu nanoclusters of different sizes, the concentrations of Cu in Cu/SiO2 composite films were varied from 8 to 30 mol% and annealed at 800°C for different times for growth. The size of the Cu nanoclusters was measured from the half band width of Cu SPR peak (appearing within 570–557 nm range) and X-ray diffraction. In this way Cu-nanoclusters of size ranges from about 3.5 to 10 nm (average diameters) were prepared . The Ag-Cu nanocluster-containing silica films show the existence of both Ag and Cu SPR peaks with some blue shifting in comparison with to their pure analogues depending on the Ag:Cu ratio.
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    Journal of sol gel science and technology 13 (1998), S. 289-294 
    ISSN: 1573-4846
    Keywords: sol-gel ; metal biosorption ; polysaccharide encapsulation ; column sorption
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    Topics: Chemistry and Pharmacology
    Notes: Abstract In this work we compared biosorbents obtained by encapsulation of polysaccharides, isolated from waste brewing biomass, in sol-gel derived silicates and an organic polymer. Biosorbents were prepared by mixing cross-linking-agents—organic or siliceous—with dried cells envelopes. Siliceous prepolymers were synthezised via transesterification and hydrolysis from tetraethoxysilane (TEOS) and methanol. Sorption of Cd2+, Cu2+ and Ag+ by biosorbent granules (0.25–0.6 mm) was examined in batch and in a packed column. The biosorbent prepared by interesterification of TEOS showed a 2–3 times higher intensity of sorption than the biosorbent cross-linked with epichlorohydrin (the most effective cross-linking organic agent) while the sorption capacity of both biosorbents was equal. The specific surface area of the silica matrix was 597 m2/g but only traces of metals were sequestered from solution with a concentration of Cd2+ of 50 mg/l. The biosorbent with a silica matrix is a heterogeneous material containing microporous matrix inclusions of thin cell walls. Its high sorption intensity and good mechanical strength will be useful in continuous metal uptake of low concentrations of metals.
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    Journal of sol gel science and technology 13 (1998), S. 341-346 
    ISSN: 1573-4846
    Keywords: titanium dioxide ; nanoparticles ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Titania nanoparticles and gels are synthesized in reverse micelles with either an ionic (AOT) or a non-ionic (Triton X-100) surfactant in alkanes with low water contents. Acids were in some cases dissolved in the aqueous phase. Whereas the size of the sol nanoparticles is independent of the micellar composition, the kinetics of the sol-gel transition are not. The gelation time is shorter for the non-ionic surfactant and becomes longer as the acid content in the water increases, and for smaller anions of equal charge.
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    Journal of sol gel science and technology 13 (1998), S. 427-432 
    ISSN: 1573-4846
    Keywords: hybrid gels ; Eu3+ spectroscopy ; polymer electrolytes ; optical probes ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Good optical quality Eu3+-doped silica-polyethyleneglycol hybrids were prepared by the sol-gel process. Thermomechanical analysis showed an increase of the glass transition temperature, due to the stiffness of the polymeric network, as the amount of Eu3+ increased. Europium luminescent properties were used to study structural evolution during the sol-gel transition. For lower doping concentrations dried gels present statistical distributions of Eu3+, typical of an amorphous environment, while for higher concentrations a crystalline-like environment of Eu3+ was observed. A broad emission band was observed in the visible part of the electromagnetic spectrum and assigned to the intrinsic emission from the hybrid polymeric network.
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    Journal of sol gel science and technology 13 (1998), S. 757-761 
    ISSN: 1573-4846
    Keywords: zirconia ; laser damage ; sol-gel ; depth profiling ; thin films
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sol-gel material based mirrors have been produced by forming alternate layers of high refractive index and low refractive index thin films. These mirrors have proven to have a high laser induced damage threshold [LIDT]. Using nitric acid stabilized zirconia derived from zirconium-n-propoxide and base catalyzed silica, a 16 layer mirror with a reflectivity of better than 94% at 351 nm and 45° angle of incidence was fabricated. This had an LIDT of 7.7 J/cm2 at 351 nm with a 0.7 ns pulse width. Crazing prevented further layers being deposited. Both spin and dip coating were attempted with dip coating yielding the best results. The coating structure has been analyzed using XPS depth profiling and AES. The bulk materials have been investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD) and TGA. High refractive index layers using Hafnia with nitric or acetic acid have also been investigated as prospective high LIDT mirrors. Alternative acidic routes to silica have been studied as a possible low index material and a route to preventing crazing.
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    Journal of sol gel science and technology 13 (1998), S. 821-825 
    ISSN: 1573-4846
    Keywords: thick film ; sol-gel ; PZT ; interfacial polymerization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The formation of a PZT film of 10–20 μm in thickness via an interfacial polymerization of metal-organic precursors has been studied. A commercially available PZT precursor solution developed for dip- or spin-coating was diluted with hexane containing acetylacetone as chelating agent. The solution was poured on water contained in a teflon reaction container of 88 mm inside diameter. A translucent gel film was formed at the interface of the two immiscible liquids. While floating on water it shrank as the evaporation of solvent proceeded until its diameter decreased to about 45% of its initial value. The dried gel film was almost pore free and its thickness was estimated to be about 10 μm.
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    Journal of sol gel science and technology 11 (1998), S. 229-240 
    ISSN: 1573-4846
    Keywords: sol-gel ; optical waveguides ; quantum dots ; optics: nonlinear
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Thin silica and silica-titania films doped with sulfide nanocrystals of controlled size were fabricated by a method based on the preparation of colloidal particles and their introduction into a glassy matrix through the sol-gel method. Colloidal sols of composition HgxCd1-xS and PbxCd1-xS (with x ranging from 0 to 1) were prepared and used to dope alkoxide solutions for the deposition of thin silica and silica-titania films. Optical absorption spectra were taken on both precursor colloidal sols and derived doped films. X-ray diffraction characterization gave structural information on the nature and size of particles in powders obtained by precipitation from colloidal sols and in doped films. The advantages and limits of the investigated systems are discussed in light of possible applications. The nonlinear properties of the most interesting PbS-doped planar waveguides have been investigated in the near-infrared, at 1.064 μm. A reversible nonlinear effect was measured, with n 2 values ranging from -5 to -20×10-9 cm2/kW.
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  • 78
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    Journal of sol gel science and technology 12 (1998), S. 181-184 
    ISSN: 1573-4846
    Keywords: sol-gel ; Sb2S3 microcrystallite doped glasses ; transmission spectrum ; second harmonic generation
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The sol-gel process has been applied to the preparation of nano-size Sb2S3 crystallite doped silica glasses and thin films. Silica glasses containing 1–1.5 wt% Sb2S3 are prepared by hydrolysis of complex solution of Si(OC2H5)4, SbCl3 and SC(NH2)2, and subsequent heat treatment. The nano-size crystallite in the matrix is observed by means of TEM. The transmission spectra of the films show that the transmission valley shifts toward longer wavelengths with increasing heat treatment time and temperature. Second harmonic generation (SHG) has been observed in the glasses illuminated with intense 1.06 μm and frequency-doubled laser beams from mode-locked Nd:YAG laser.
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  • 79
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    Journal of sol gel science and technology 13 (1998), S. 735-738 
    ISSN: 1573-4846
    Keywords: sol-gel ; organic-inorganic nanocomposite ; protective coating ; nanosized particles
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Organic-inorganic nanocomposite protective coatings are prepared on aluminum substrates by the spinning technique with the concept of incorporating homogeneously nanosized particles (of AlOOH, Al2O3, ZrO2, SiC) into molecular organic-inorganic hybrid matrices. The hybrid matrices are prepared from epoxysilane and bisphenol A with imidazol as catalyst. The AlOOH particles are derived from aluminum isoprooxide and introduced into the hybrid sols directly, and Al2O3, ZrO2, SiC particles are first surface-modified with Si–OH from hydrolyzed TEOS. The coatings are dense, smooth and flexible and inhibit corrosion.
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  • 80
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    Journal of sol gel science and technology 13 (1998), S. 827-831 
    ISSN: 1573-4846
    Keywords: sol-gel ; thin films ; ferroelectricity ; lead zirconate titanate (PZT)
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Precursor powders for Pb(Zr1 − xTix) O3 (PZT) thin films were produced by the reaction of zirconium-and titanium-n-propoxides with acetylacetone and lead acetate trihydrate. The subsequent complete removal of volatile components yielded powders that can be handled in air. The powders are indefinitely stable under ambient conditions. High molarity (〉2m) coating sols were prepared by dissolution of the precursor powders in mixtures of 1,3-propanediol, triethanolamine (TEA) and water. Excess amounts of lead to compensate lead loss during firing were easily introduced into these solutions. The deposition of these sols on steel substrates and firing at 600°C yielded PZT films. Many physical parameters like film thickness, morphology and electrical performance could be influenced by choice of the solvent mixture composition and oxide content of the sols. Depending on the preparation dielectric permittivities, εr of up to 840 were measured at 1 kHz. By hysteresis measurements at 50 Hz and a field amplitude of 50 V/μm a remanent polarization of about 40 μC/cm2 and coercivity of about 8 V/μm was obtained. The films were stable against dielectric breakdown up to 70V/μm.
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  • 81
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    Journal of sol gel science and technology 13 (1998), S. 27-30 
    ISSN: 1573-4846
    Keywords: sol-gel ; structure control ; X-ray scattering ; polyviologen ; lyotropism
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Two polyviologens synthesized by the Menshutkin reaction were incorporated into silica networks using the sol-gel method. The effects of the incorporated polymers on the structure of the resulting organic-inorganic hybrid materials were investigated using X-ray scattering (small and wide angle). This provided evidence that the polyviologens in a lyotropic liquid crystalline state were causing the silica network to become more dense and less branched than sol-gel glasses synthesized without added polyviologen. Additional evidence for the templating effect of these polymers was obtained using FTIR spectroscopy and N2 adsorption-desorption isotherms.
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  • 82
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    Journal of sol gel science and technology 13 (1998), S. 109-112 
    ISSN: 1573-4846
    Keywords: inorganic oxide ; sol-gel ; non-hydrolytic ; catalyst ; calcination
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Inorganic oxides have been synthesized successfully under mild reaction conditions using a solvent-free non-hydrolytic sol-gel process based on the condensation reaction of “metal” chlorides with oxygen donors such as alkoxides, aldehydes and ethers. Iron(III) chloride was found to be an effective catalyst for the reactions. The order of reactivity of the halides was generally titanium 〉 aluminium 〉 silicon, but in some cases reaction was halted by premature gelation of intermediate species. Silica, alumina and titania were all prepared and characterized by various methods. Calcination studies on the silicas showed these materials to be amorphous up to at least 700°C, but devitrification occurred at 1000°C. Crystallization was studied by X-ray powder diffraction.
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  • 83
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    Journal of sol gel science and technology 13 (1998), S. 95-98 
    ISSN: 1573-4846
    Keywords: sol-gel ; composite ; matrices ; fluorescence ; probing
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Transparent composite SiO2/organic matrices have been made by the sol-gel method using tetramethoxysilane and either cetyltrimethylammoniumbromide (CTAB) or a polyethylene glycol oligomer (PEG-200) or a cationic polyelectrolyte. We have investigated conditions under which transparent xerogel matrices are possible and we have characterized them mainly by time-resolved fluorescence probing using stretched exponentials. CTAB creates a hydrophobic and PEG-200 a hydrophilic subphase in the matrix. An important property of these composite matrices is that they allow molecular diffusion contrary to matrices made in the absence of surfactants or polymers.
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  • 84
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    Journal of sol gel science and technology 13 (1998), S. 559-563 
    ISSN: 1573-4846
    Keywords: sol-gel ; hybrid ; nanocomposite ; optical nonlinearity
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    Topics: Chemistry and Pharmacology
    Notes: Abstract In this paper the nonlinear refractive index, optical limiting effect, photoinduced and electroinduced second harmonic generation of dye-doped hybrid and nanoparticle-doped composite materials prepared by the sol-gel process have been reported. The origin of these nonlinear optical effects has been discussed.
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  • 85
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    Keywords: porous layers ; chemical sensing ; sol-gel ; optical fiber
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    Notes: Abstract Polysiloxane porous layers doped with TiO- and phenyl-groups were fabricated by the sol-gel method. Starting sols were prepared from alkoxides using catalysis by HCl or HF. Stable SiO-TiO-sols were obtained by using HF. Porous gel layers with thicknesses of 0.3–1.1 μm were coated on fiber surfaces or silicon wafers. Layers with the refractive index of 1.38–1.48 were prepared. The fractional porosity of the layers was estimated to be 0.1–0.35. The interactions of the layers with vapor or liquid chlorinated hydrocarbons, alcohols or aromatic hydrocarbons have been studied in immersing experiments by measuring the output light intensity from the fibers. The observed changes of the output intensity could be correlated to changes of the refractive index of the layer caused by the penetration of the tested chemicals into the layer pores.
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  • 86
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    Journal of sol gel science and technology 13 (1998), S. 535-539 
    ISSN: 1573-4846
    Keywords: optical waveguide amplifiers ; erbium ; sol-gel ; GeO2-SiO2
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    Topics: Chemistry and Pharmacology
    Notes: Abstract GeO2-SiO2 sol-gel planar waveguides doped with Er were deposited by spinning on silica substrates. P2 O5 or Al2O3 were used as co-dopants to improve erbium dissolution in the GeO2-SiO2 matrix. Multilayer amorphous films were obtained at 600 or 700°C. Er ions in the planar waveguide pumped at 980 nm showed fluorescence features around 1530 nm. Narrow fluorescence spectra (∼20 nm) and long lifetimes (∼6 ms) were found in P2O5 co-doped samples, whereas Al2O3 co-doping gave wider spectra (∼50 nm) with slightly lower lifetimes (∼5 ms). The quenching concentration in the Al2O3 co-doped samples was 0.9 mol% Er. Heat treatments in CCl4 improve the active properties and the addition of Yb enhances the pump absorption efficiency.
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  • 87
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    Journal of sol gel science and technology 13 (1998), S. 439-443 
    ISSN: 1573-4846
    Keywords: photoluminescence ; sol-gel ; polysiloxane gel ; conjugated polymer
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Photoluminescence of a polysiloxane gel film incorporating a partially conjugated copolymer polyether-polyphenylenevinylene (PEPPV) has been studied and compared with results obtained from bulk and vacuum evaporated films of the same starting material. The evaporation clearly affects the distribution of lengths of the conjugated parts, yet the incorporation in the gel matrix induces only slight changes in the spectroscopic properties of the polymer.
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  • 88
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    Journal of sol gel science and technology 13 (1998), S. 529-533 
    ISSN: 1573-4846
    Keywords: sol-gel ; aluminosilicate thin films ; waveguides ; erbium doping
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Er3+ doped-aluminosilicate thin films were prepared on silica and silica/Si substrates by the sol-gel process and dip-coating. The sol-gel aluminosilicate planar waveguides were prepared from silicon and aluminium alkoxides. Their structural characterization has been carried out by Raman spectroscopy, Atomic Force and Scanning Electron Microscopies. The results indicated that these films present an amorphous structure until an annealing temperature of 900°C, while at temperatures higher than 1000°C, crystallization occurs. An estimate of microcrystallite sizes using Raman spectroscopy is given, which agrees with data from scanning electron microscopy. The optical properties have been investigated by Fluorescence spectroscopy in the visible region.
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  • 89
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    Journal of sol gel science and technology 13 (1998), S. 673-678 
    ISSN: 1573-4846
    Keywords: electrochromism ; sol-gel ; tungsten oxide ; peroxotungstic acid ; nanocrystalline
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Stable tungsten oxide coating sols suitable for electrochromic applications were prepared by a modified peroxotungstic acid route. Layers up to 250 nm thickness could be deposited on ITO-coated and/or FTO-coated glass substrates in a single dip-coating process. Optoelectrochemical measurements were employed to determine the variation of the electrochromic properties (change in optical density (ΔOD) and switching times) of WO3-layers, investigated as a function of coating parameters, such as chamber humidity and the temperature of heat treatment. High resolution transmission electron microscopy (HR-TEM) has shown that the optimized layers possess a partially crystalline morphology with nanocrystalline regions 2–3 nm in size.
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  • 90
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    Journal of sol gel science and technology 13 (1998), S. 1023-1026 
    ISSN: 1573-4846
    Keywords: PZT fibers ; piezoelectric fibers ; sol-gel ; fibers
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A fiber forming PZT gel containing 58.5 wt% PZT was synthesized by using zirconium-n-propylate, titanium-iso-propylate, lead acetate and butoxyethanol. Unseeded PZT gels and gels containing 0.5 wt% PZT perovskite seeds (Ø = 200–300 nm) could be extruded through a monofilament nozzle (Ø = 100 μm) at pressures between 50 and 150 bar, whereas PZT gels, containing 1 and 2 wt% PZT particles, were pressed through the nozzle at higher pressures (200–300 bar). The microstructure of unseeded and seeded (0.5, 1, 2 wt% PZT) PZT fibers was characterized by SEM. Unseeded fibers had three different shells at 450°C: an external dense shell (approx. 200 nm thick), a middle shell consisting of a porous structure (1.5μm thick) and the center of the fiber, characterized by a matrix containing globular particles. At 700°C, a 200–250 nm thick and dense external shell and a porous fiber interior were be observed. 2 wt% of PZT seeds was necessary to densify the fiber completely. The seeds were located in the center of each PZT perovskite rosette.
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  • 91
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    Journal of sol gel science and technology 13 (1998), S. 1027-1031 
    ISSN: 1573-4846
    Keywords: alumina-silica ; methanol conversion ; pore design ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Amorphous alumina-silicas were prepared from a tetra-alkoxysilane and anhydrous aluminum trichloride or an aluminum alkoxide by a sol-gel process using 2-methyl-2,4-pentanediol, pinacol, 1,2-propanediol, 2,3-butanediol or ethylene glycol as the solvent or complexing agent, and the effect of diols and alkoxy groups on the physical and chemical properties of the alumina-silicas was examined. When the diol or the alkoxy group was bulky, the alumina-silicas had relatively larger micropores, a larger pore volume and higher surface areas. In the conversion of methanol catalyzed by the alumina-silicas, the bulkier diols and alkoxides gave catalysts that produced dimethyl ether in higher yield and hydrocarbons in lower yield. Thus, when ethylene glycol was used as the diol, the best catalyst for the production of hydrocarbons, especially the production of olefins such as ethylene, propylene and butene, was obtained. Furthermore, in comparison with alumina-silica prepared by a traditional kneading process, it was found that the sol-gel alumina-silica could efficiently convert methanol to dimethyl ether and hydrocarbons, but the material prepared by kneading had a very low conversion of methanol to other compounds.
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  • 92
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    Journal of sol gel science and technology 13 (1998), S. 961-967 
    ISSN: 1573-4846
    Keywords: sol-gel ; thin film ; SnO2 : Sb ; transparent conducting coatings ; laser densification ; electrical properties ; morphology
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Sb doped sol-gel SnO2 single layers (thickness ≈100 nm) were prepared from alcoholic solution and deposited via a dip coating process on fused silica substrates. The coatings have been sintered at a typical rate of 10–15 cm2/s by CO2 laser irradiation. The laser spot was scanned in one direction at a speed of 15,000 cm/s and the sample was moved in a perpendicular one at a speed up to 250 mm/s. The temperature of the topmost 10 μm layer was monitored by a fast pyrometer (μs resolution). The following properties of the coatings have been determined: the electrical resistivity ρ, the carrier density n, and mobility μ, the structure, the thickness, the mesoscopic and micromorphology and the density. The sintering by CO2 laser radiation is mainly a thermal driven process. At T ≈500°C it allows to obtain coatings with a smaller resistivity (6.8×10−3 Ωcm) than those produced by conventional furnace firing (ρel≈2.9×10−2 Ωcm). The results are discussed in terms of particle size and packing density.
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  • 93
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    Journal of sol gel science and technology 13 (1998), S. 915-921 
    ISSN: 1573-4846
    Keywords: vanadium dioxide ; thermochromism ; sol-gel ; optical switching
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Vanadium dioxide thin films have been deposited from vanadium alkoxides VO(OR)3. An amorphous film is formed that transforms into crystalline VO2 upon heating at 500°C under a reducing atmosphere. Optically transparent VO2 thin films are then obtained that exhibit both electrical and optical switching around 70°C. The switching temperature together with the shape of the hysteresis loop can be modified by doping VO2 films with foreign cations. Doped MxVO2 (M = W6+, Nb5+, Ti4+, Cr3+ or Al3+) thin films have been prepared under the same conditions by mixing the vanadium alkoxide and a metal salt in an alcoholic solution. The switching temperature decreases when the film is doped with high-valent cations (W6+) and increases with low-valent cations (Al3+, Cr3+). The transition temperature first decreases and then increases when TiIV is added to the VO2 film while the width of the hysteresis loop is significantly reduced.
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  • 94
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    Journal of sol gel science and technology 13 (1998), S. 547-551 
    ISSN: 1573-4846
    Keywords: sol-gel ; fast ; micro-optics ; patterning ; replication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The fast sol-gel method enables facile preparation of siloxane-based glassy matrices, in which polymerization is completed within minutes and volume changes 〈5% take place upon curing. Single-face and two-face replication of micro-optical arrays have been obtained, as well as crack-free elements 〉10 mm thick. Minimizing shrinkage and enabling relaxation of the drying sol-gel are key factors in the elimination of cracking. These features and the resulting optical quality of the glass make this method technologically and economically attractive for replication-produced micro-lenses and micro-optical arrays.
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  • 95
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    Journal of sol gel science and technology 13 (1998), S. 1043-1047 
    ISSN: 1573-4846
    Keywords: magnesium oxide ; sol-gel ; magnesia acidity ; pyridine adsorption
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Traditionally, magnesium oxide has been considered a typical basic catalyst, catalyst carrier and/or adsorbent. In this study MgO was prepared using Mg-ethoxide dissolved in ethanol and hydrolyzed with various aqueous inorganic acids and bases. We have found that it is possible to induce Brønsted and Lewis acid sites depending on the method of preparation and, more specifically, on the type of inorganic acids used in the hydrolysis stage. In the FTIR spectra of adsorbed pyridine on MgO obtained using aqueous HCl (pH = 3), the bands corresponding to Lewis (1603, 1496 and 1444 cm−1) and Brønsted (1550 cm−1) acid sites are observed. The fact that upon vacuum and high temperature treatment, i.e., at 773 K, the above mentioned bands are clearly distinguishable indicated that the acid sites are very strong. On the other hand, the MgO materials obtained using aqueous acetic acid as a hydrolysis catalyst (pH = 5), and that without any catalyst (pH = 7) showed only Lewis acid sites which decreased markedly upon higher temperature treatment. When aqueous NH4OH (pH = 9) was used as the hydrolysis catalyst, the MgO obtained showed only Lewis acid sites. In all cases the number of Lewis acid sites was greater than that of Brønsted sites.
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  • 96
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    Journal of sol gel science and technology 13 (1998), S. 213-217 
    ISSN: 1573-4846
    Keywords: bismuth oxide ; bismuth silicate ; thin film ; sol-gel ; surface techniques
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bi2O3 thin films were prepared by dipping silica slides in ethanolic solutions of tris(2,2′-6,6′-tetramethylheptane-3, 5-dionato)bismuth(III) [Bi(dpm)3] [1] and heating in air at temperatures ≤500°C. Bi4(SiO4)3 homogeneous thin films were obtained from the reaction of the bismuth oxide coating with the silica glass substrate at temperatures higher than 700°C. For heat treatments at temperatures between 600°C and 700°C, Bi2SiO5 coatings were obtained. The composition and microstructure evolution of the films were determined by Secondary Ion-Mass Spectrometry (SIMS), X-Ray Photoelectron Spectroscopy (XPS) and Glancing Angle X-Ray Diffraction (GA-XRD). The synthesis procedure was reproducible and allowed the control of the Bi2O3 phase composition. Moreover, the thin film annealing parameters were correlated with the formation of bismuth silicates, among which Bi4(SiO4)3 (BSO) is very appealing for the production of fast light-output scintillators [2].
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  • 97
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    Journal of sol gel science and technology 13 (1998), S. 461-466 
    ISSN: 1573-4846
    Keywords: sol-gel ; ORMOSILs ; X-ray diffraction (XRD)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract ORMOSILs have been prepared in the series TMOSx·MTMS(100 − x) (where TMOS is tetramethoxysilane; MTMS is methyltrimethoxysilane; x is mol% silane with respect to total silane for 0 ≤ x ≤ 100) by means of acid catalyzed, sol-gel processing. After drying at 60°C, small bulk samples were obtained of excellent optical clarity. Powder X-ray diffraction (XRD) patterns, in the range of 5 to 60°2Θ, were compared with that of fused silica. All the prepared samples were amorphous. Fused silica exhibits one broad peak, d2 centered at d-spacing 4.12 Å. For the TMOS100 silica xerogel, the analogous broad peak had shifted slightly, to be centered at 3.88 Å; and remained in about the same position as x was decreased for the series TMOSx·MTMS(100 − x). In addition, a second, broad peak, d1, was observed for the ORMOSIL series centered at the d-spacing 8.7 Å for MTMS100 (i.e., x = 0) and increasing smoothly as x was increased, reaching 11.3 Å for x = 70, and 〉11.3 Å for x 〉 70. The intensity of d1 was found to have trebled, relative to the intensity of d2, on increasing the organic character of the matrix from TMOS70·MTMS30 to MTMS100. The d2 peak appearing at about 4 Å for both fused silica and the ORMOSILs is assumed to be associated with the spacing between silicon atoms connected by means of an oxygen bridge. The Si–O–Si angle for silica xerogels is known to depend upon the nature of the sol-gel processing and is bigger than that of fused silica. The d1 peak may be associated with the spacing between silicons attached to methyl groups and indicative of channels of methyl groups in the structure. Alternatively, the d1 peak may have its origin in a preferred, discrete structural unit in the matrix for instance cubane based on a octameric silicon arrangement.
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    Journal of sol gel science and technology 13 (1998), S. 763-767 
    ISSN: 1573-4846
    Keywords: sol-gel ; coatings ; corrosion ; morphology ; atomic force microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Atomic force microscopy (AFM) was used to study the performance of ≈80 nm thick Al2O3-TiO2-SiO2 sol-gel coatings on glass substrates following corrosion in 1 M NaOH solutions at 60°C. The as-prepared coatings were homogeneous on a nanoscale and displayed the “glass pattern” before corrosion. Layers with different compositions behaved differently during the corrosion process. Thus, TiO2 or TiO2-dominated layers had tetragonal-like crystals on their surfaces after corrosion, possibly of anatase composition. On the other hand, layers with a molar ratio Al2O3 : SiO2 near 1 : 2 displayed a pseudo-hexagonal morphology, possibly with a nepheline (Na2O · Al2O3 · 2SiO2) composition. Layers of 5Al2O3-40TiO2-55SiO 2 were corroded is a stepwise fashion and had no special surface morphology.
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  • 99
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    Journal of sol gel science and technology 13 (1998), S. 523-527 
    ISSN: 1573-4846
    Keywords: nanocomposite ; sol-gel ; photopolymerization ; channel waveguides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The development and characterization of channel waveguides using wet-process, low temperature sol-gel chemistry is described. Two structures have been developed. The first one is a one-layer structure, composed of a sol-gel solution which is a mixture of photopolymerizable organosilicate and organozirconate precursors. The other is a multilayer structure with a buffer under the guide and a protective coating. The layers are deposited by the dipping technique. The devices are obtained by UV light exposure of the coating through a predefined mask (channel waveguides). The refractive index increase is sufficient enough to allow the use of waveguides in the 1.55 μm telecommunication window. These waveguides are thick enough to reduce the coupling losses with an optical fiber below 0.5 dB. Also, because of our sandwich structure, the propagation losses are less than 0.1 dB.
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  • 100
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    Journal of sol gel science and technology 13 (1998), S. 541-545 
    ISSN: 1573-4846
    Keywords: spectral hole burning ; Sm2+-doped glass ; sol-gel ; fluorescence line narrowing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sm2+-doped glasses in the system of Al2O3-SiO2 were prepared by sol-gel processing of metal alkoxides and reacting with H2 gas at 800°C. The hole burning properties of these glasses were investigated. The holes were burned in the 7F0 → 5D0 line of the Sm2+ ions using a DCM dye laser at 77 K. The hole depth increased with increasing the laser irradiation time, reaching up to ∼15% of the total intensity within a few hundred seconds. The hole width was 3 cm−1 full width at half maximum. Fluorescence line narrowing spectra of the 5D0 → 7 F1 transition were analyzed to study the local structure surrounding the Sm2+ ion. It is concluded that the Sm2+ ions are closely coordinated with nine oxygens of the AlO6 group in aluminosilicate glasses and that the addition of Al3+ ions into glass induces an increase in the coordination number of the Sm2+.
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