scispace - formally typeset
Search or ask a question

Showing papers on "Sol-gel published in 1991"


Journal ArticleDOI
TL;DR: In this article, the porosity and refractive index of thin films from polymeric precursors are varied as follows: volume percent porosity (0% -56%), pore radius (0-3.1 nm); surface area (1.2-263 m 2 g -1 ); refractive indices (118-1.45).

608 citations


Journal ArticleDOI
TL;DR: In this article, a considerable increase in the refractive index can be systematically induced by using titanium tetraisopropoxide, which has an optical dispersion behavior between that of organic polymers and inorganic glasses.
Abstract: New hybrid materials (ceramers) can be prepared by reacting titanium alkoxides with triethoxysilane-capped poly(arylene ether ketone) or poly(arylene ether sulfone). By using titanium tetraisopropoxide, a considerable increase in the refractive index can be systematically induced. Also, these new materials have an optical dispersion behavior between that of organic polymers and inorganic glasses

178 citations



Journal ArticleDOI
TL;DR: In this paper, thin polycrystalline films of VO2 and V2O3 were deposited on a variety of substrates using a sol-gel process and the orientation, microstructure, optical constants, and optical and electrical switching behavior were presented.
Abstract: Thin polycrystalline films of VO2 and V2O3 were deposited on a variety of substrates using a sol‐gel process. The orientation, microstructure, optical constants, and optical and electrical switching behavior are presented. These films exhibited sharp optical switching behavior even on an amorphous substrate such as fused silica. The method yields reproducible results and is amenable to the coating of large substrates and curved surfaces such as mirrors and lenses.

176 citations


Journal ArticleDOI
Abstract: A crack- and pinhole-free composite membrane consisting of an α-alumina support and a modified γ-alumina top layer which is thermally stable up to 1100°C was prepared by the sol–gel method. The supported thermally stable top layer was made by dipcoating the support with a boehmite sol doped with lanthanum nitrate. The temperature effects on the microstructure of the (supported and unsupported) La-doped top layers were compared with those of a common γ-alumina membrane (without doping with lanthanum), using the gas permeability and nitrogen adsorption porosimetry data. After sintering at 1100°C for 30 h, the average pore diameter of the La-doped alumina top layer was 17 nm, compared to 109 nm for the common alumina top layer. Addition of poly(vinyl alcohol) to the colloid boehmite precursor solution prevented formation of defects in the γ-alumina top layer. After sintering at temperatures higher than 900°C, the common alumina top layer with addition of poly(vinyl alcohol) exhibits a bimodal pore distribution. The La-doped alumina top layer (also with addition of poly(vinyl alcohol)) retains a monopore distribution after sintering at 1200°C.

169 citations


Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: In this article, a compatible blend of an inorganic polymer, silica glass, and a π-conjugated non-linear optical polymer, poly(p -phenylene vinylene), homogeneously miscible over wide composition ranges, was reported.

137 citations


Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: In this paper, the authors demonstrate the successful use of a polymeric acid catalyst to prepare these previously described optically clear hybrid materials, and compare their thermogravimetric behavior with those of the same composition catalysed with HCl.

85 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that the reaction mechanism depends on the catalyst's pH (HCl > CH3COOH > H2C2O4> H2O > NH4OH).

82 citations


Journal ArticleDOI
TL;DR: LiNbO3 thin films were prepared on sapphire substrates by a sol-gel process using lithium ethoxide and niobium pentaethoxide as discussed by the authors, which showed a higher preferred orientation in the same crystal plane as the orientation of the substrate.

82 citations


Journal ArticleDOI
TL;DR: In this article, thin films of lead zirconate titanate (PZT) have been prepared by the sol-gel processing method using metal alkoxides and the crystallographic and morphological properties of the films have been analyzed by x-ray diffraction and scanning electron microscopy.
Abstract: Thin films of lead zirconate titanate (PZT) have been prepared by the sol‐gel processing method using metal alkoxides. The crystallographic and morphological properties of the films have been analyzed by x‐ray diffraction and scanning electron microscopy. The elemental composition of the films was determined by Rutherford backscattering, electron microprobe, and Auger electron spectroscopy, and was compared to that of the precursor solution characterized by inductively coupled plasma spectrophotometry. Results are presented which illustrate the relationships between the properties and the observed structure of the thin films, with the processing conditions. The electrical properties, dielectric constant, and ferroelectric hysterisis response were tested to determine the quality of the films. The experimental observations suggest two competing mechanisms during the PZT formation: lead loss out of the film, and nucleation of the PZT phase with its subsequent crystallization.

79 citations


Journal ArticleDOI
TL;DR: In this paper, the precursors for the sol-gel synthesis of tungsten oxide thin films can be obtained via the reaction of Tungsten oxychloride WOCl4 with alcohols.
Abstract: Versatile molecular precursors for the sol–gel synthesis of tungsten oxide thin films can be obtained via the reaction of tungsten oxychloride WOCl4 with alcohols. Oligomeric species [WOCl4 –x(OR)x]n are formed. Their molecular structure is analysed by infrared spectroscopy, nuclear magnetic resonance (NMR) spectroscopy (1H, 13C, 183W), X-ray absorption spectroscopy (EXAFS) and small-angle X-ray scattering (SAXS). Hydrolysis of these precursors leads to the formation of tungsten oxide colloidal solutions. They can be easily deposited by dipcoating. Thin films ca. 3000 A thick are obtained. Their morphology depends on the nature of the alcohol. Homogeneous films are obtained with bulky alkyl groups such as PriOH. These amorphous tungsten oxide layers exhibit electrochromic properties and could be used for display devices or smart windows. They can also be easily transformed, at room temperature, into crystalline hydrates WO3·nH2O (n= 1 or 2) when left in a humid atmosphere.

Journal ArticleDOI
TL;DR: The FT-IR liquid attenuated total reflection (ATR) method was successively used to analyze binary TiO2SiO2 sol-gel reactions between various titanium alkoxide chelates and three silicon alkoxides of different reactivities at various pH as discussed by the authors.
Abstract: The FT-IR liquid attenuated total reflection (ATR) method was successively used to analyze binary TiO2SiO2 sol-gel reactions between various titanium alkoxide chelates and three silicon alkoxides of different reactivities at various pH. The homogeneity of the gels was evaluated by the peak intensity of TiOSi band. The stability of hydrolyzed titanium alkoxide chelates against condensation and the reactivity of silicon alkoxide affected the homogeneity, but the stability of titanium alkoxide chelates against hydrolysis did not. Acidic conditions are favorable to form TiOSi bonds, while the hydrolyzed forms of titanium and silicon alkoxides are both stable against homo-condensation.

Journal ArticleDOI
TL;DR: Tungsten oxide gels were prepared by a sol-gel process from a tungsten ethoxide/ethanol/water solution (sol) by Raman spectroscopy as mentioned in this paper.
Abstract: Tungsten oxide gels were prepared by a sol-gel process from a tungsten ethoxide/ethanol/water solution (sol). Tungstic hydrates were observed in high-viscosity sol by Raman spectroscopy. As the sol is reduced to the gel, Raman bands ascribed to amorphous tungsten oxide appeared. The result of the Raman measurement shows that the structure of the gel changes progressively during heat treatment and that the amorphous tungsten oxide becomes a crystalline solid at 410?C.

Journal ArticleDOI
TL;DR: A solution sol-gel method has been developed to prepare 0.9Pb(Mg1/3Nb2/3)O3-0.1PT) ceramics as discussed by the authors.
Abstract: A solution sol-gel method has been developed to prepare 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (0.9PMN-0.1PT) ceramics. During the processing the gel first converted to cubic pyrochlore phase at a calcination temperature of 600°C followed by the formation of pure perovskite phase at 775°C. The ceramics sintered at 1250°C for 4 h showed ≈98% of the theoretical density. The room-temperature dielectric constant of the pellets sintered at 1250°C showed a maximum value of 25035 at 1 kHz. Sintering studies at different temperatures revealed that the dielectric constant increased with increasing grain size in these ceramics.

Journal ArticleDOI
TL;DR: In this paper, the influence of synthesis parameters on the structural properties of mixed oxides derived from silicon tetraethoxide and titanium tetra-isopropoxide precursors has been studied by 29 Si NMR speectroscopy.
Abstract: The influence of synthesis parameters on the structural properties of mixed oxides derived from silicon tetraethoxide and titanium tetra-isopropoxide precursors has been studied by 29 Si NMR speectroscopy. A first set of gels, prepared by complete hydrolysis of the individual precursors and subsequent mixing of the hydrosols, is characterized by comparatively narrow lines for the Q 2 , Q 3 , and Q 4 silica sites. Both the chemical shift values and the time constants of 1 H 29 Si magnetization transfer are similar to those found in pure silica gels. This indicates that these oxides consist of domains of the individual components. A different appearance of the CP/MAS spectra is noted for the second set of gels, which is prepared by addition of the titanium alkoxide component at a stage where the silicon alkoxide hydrolysis has only proceeded to about 50%, on average. The spectra of these samples are characterized by broad lines for the three types of sites. Larger contributions observed for Q 2 and Q 3 sites in these samples are attributed to the presence of SiOTi bridges. The influence of preparation parameters such as hydrolysis pH, drying temperature, and pore ripening treatment by redispersion in base, is studied by monitoring the spectral and dynamic parameters derived from the CP/MAS spectra.

Journal ArticleDOI
TL;DR: In this article, the microstructural evolution of fast fired, sol-gel derived Pb(Zr, Ti)O3 films (Zr/Ti = 54/46) was performed by analytical transmission electron microscopy (TEM).
Abstract: A systematic investigation of the microstructural evolution of fast fired, sol-gel derived Pb(Zr, Ti)O3 films (Zr/Ti = 54/46) was performed by analytical transmission electron microscopy (TEM). It was found that the nucleation and growth of the sol-gel PZT films were influenced by the precursor chemistry. The precursor solution was composed of Pb 2-ethylhexanoate, Ti isopropoxide, and Zr n-propoxide in n-propanol. Porous and spherulitic perovskite grains nucleated and grew from a pyrochlore matrix for NH4OH-modified films, but no chemical segregation was found. These thin films consisted completely of porous spherulitic PZT grains (∼2 μm) when the firing temperature was increased. Chemical phase separation with regions of Zr-rich pyrochlore particles separated by Zr-deficient perovskite grains was observed in the initial stages of nucleation and growth for CH3COOH-modified PZT films. This phase separation is attributed to the effect of acetate ligands on the modification of molecular structure of the PZT precursor. Firing the acid-modified films at higher temperatures for long times resulted in porous perovskite grain structures. The residual porosity in these films is suggested to be a result of differential evaporation/condensation rates during the deposition process and the gas evolution at high temperatures due to trapped organics in the films. Dielectric and ferroelectric properties were correlated to the microstructure of the films. Lower dielectric constants (∼500) and higher coercive fields (∼65 kV/cm) were found for the acid-modified PZT films with phase separation in comparison to those measured from the sol-gel films with a uniform microstructure (∽ > 600, Ec < 50 kV/cm). All films fired at 650 °C showed relatively good remanent polarization on the order of 20 μC/cm2.

Patent
30 Sep 1991
TL;DR: Low porosity titania forms containing only a small amount of hydroxyl groups and possessing a high refractive index which are property stable regardless of humidity level and which prohibit electrical and gas leakage and optical loss, are obtained in a sol-gel process by rapidly heating to curing temperature, e.g. at a rate of 8000° C/min this paper.
Abstract: Low porosity titania forms containing only a small amount of hydroxyl groups and possessing a high refractive index which are property stable regardless of humidity level and which prohibit electrical and gas leakage and optical loss, are obtained in a sol-gel process by rapidly heating to curing temperature, e.g. at a rate of 8000° C./min. One application provides more stable, longer-lasting sol-gel prepared optical interference filters. Other applications provide capacitors with high capacitance and optical planar waveguides.

Journal ArticleDOI
TL;DR: Barium titanates with Ba/Ti ratio 2:9 and 1:5 were prepared by first hydrolyzing titanium alkoxide and then mixing the resulting titania sol with a barium alkoxide-methanol solution as discussed by the authors.
Abstract: Barium titanate precursors with Ba/Ti ratio 2:9 and 1:5 were prepared by first hydrolyzing titanium alkoxide and then mixing the resulting titania sol with a barium alkoxide-methanol solution. After drying, the xerogels of the precursors of barium titanates were sintered at temperatures from 700°C (4 h) to 1200°C (110 h or longer). Characterization of the product was performed using X-ray diffraction and laser Raman spectroscopy. At 700°C, BaTi5O11 was formed from the 1:5 precursor and a two-phase mixture of BaTi2O5 and BaTi5O11 was formed from the 2:9 precursor. After prolonged heating at 1200°C, the latter mixture converted to a single-phase material, Ba2Ti9O20.

Journal ArticleDOI
TL;DR: In this article, the high Tc superconducting oxide YBa2Cu3O7−d has been fabricated by a simple colloidal sol-gel precursor technique based on citrate complexes uniformly dispersed into ethyleneglycol and water.
Abstract: The high Tc superconducting oxide YBa2Cu3O7−d has been fabricated by a simple colloidal sol‐gel precursor technique based on citrate complexes uniformly dispersed into ethyleneglycol and water. The present method permits easier fabrication of highly pure and homogeneous superconducting materials when compared with other more elaborate preparation procedures based on solution techniques as it eliminates many steps such as centrifugation, filtration, and pH control. The purity of the final product was estimated to be >99.5% based on the combined results of x‐ray diffraction and Raman scattering analyses. The composition of the sample was determined to be Y1.00Ba1.98Cu3.05O6.85 by inductively coupled plasma spectroscopy and idiometry. The sol‐gel process produced homogeneous materials with particle sizes smaller than ∼3 μm. The superconducting transition determined with resistivity measurements was shown to be sharp with a transition width narrower than 1 K. The magnetic susceptibility measurements exhibited...

Journal ArticleDOI
TL;DR: In this paper, high-resolution Si NMR with polarization transfer was used to identify the various oligomers which formed during the early stages of the reaction and identify the structure of the resulting siloxane polymers.
Abstract: Silicon tetramethoxide (TMOS) monomers have been dissolved in mixtures of methanol and water, hydrolyzed, and condensed to form siloxane polymers. The various oligomers which form during the early stages of the reaction have been identified through high-resolution {sup 29}Si NMR with polarization transfer. At low water/alkoxide ratios the hydrolysis is incomplete and limits the condensation reaction. Small cyclics are formed in addition to linear polymers. At high water/alkoxide ratios, the hydrolysis is fast and complete and the condensation is rate limiting. The polymers are largely branched as indicated by the high proportion of Q{sup 3} chain branching sites and Q{sup 4} three dimensionally cross-linked groups. So highly condensed species including small rings or cagelike structures can be expected in these mixtures.

Journal ArticleDOI
TL;DR: Transmission spectra and ellipsometric measurements showed that spin-coated films were essentially optically equivalent to those prepared by ion-beam sputter deposition, and refractive index and the extinction coefficient were evaluated from transmittance characteristics in the ultraviolet, visible, and nearinfrared regions.
Abstract: Transparent and optical-grade TiO2 coatings were prepared by sol-gel spinning and ion-beam sputtering techniques. We investigate process parameters for the fabrication of sol-gel spin-coated TiO2 films exhibiting high optical quality comparable with that of ion-beam-sputtered TiO2 films. X-ray diffraction studies showed the sol-gel-deposited films to be amorphous for heat treatments below 350° C, whereas the ion-beam-sputtered films were slightly crystalline and exhibited the anatase structure. The refractive index and the extinction coefficient were evaluated from transmittance characteristics in the ultraviolet, visible, and near-infrared regions. Transmission spectra and ellipsometric measurements showed that spin-coated films were essentially optically equivalent to those prepared by ion-beam sputter deposition.


Patent
12 Apr 1991
TL;DR: In this paper, one or more glass layers are formed on the inner surface of the tube by dip-coating the surface with a sol comprising a metal alkoxide dissolved in an alcoholic or aqueous solvent, polymerizing the sol to form a gel, and drying and sintering the gel.
Abstract: The method includes collapsing a silica-based glass tube to make a preform and drawing fiber from the preform. Prior to collapsing the tube, one or more glass layers are formed on the inner surface of the tube by dip-coating the surface with a sol comprising a metal alkoxide dissolved in an alcoholic or aqueous solvent, polymerizing the sol to form a gel, and drying and sintering the gel. A substantial portion the dopant, present within the sintered gel, diffuses into at least one adjoining glass region. A wide selection of dopant materials, in the form of salts or alkoxides, are readily incorporated by dissolving them in the solvent.

Journal ArticleDOI
TL;DR: In this paper, a sol-gel synthesis of α-Zr(HPO4)2·H2O from both inorganic and metallo-organic precursors has been followed by solid-state 31P MAS NMR and X-ray diffraction.
Abstract: Inorganic ion exchangers such as α-Zr(HPO4)2·H2O are usually synthesized from aqueous solution. Amorphous precipitates are then obtained, which crystallize very slowly upon ageing at ca. 90 °C in their mother liquor. Crystallization could be much faster if alkoxide precursors are used. The sol–gel synthesis of α-Zr(HPO4)2·H2O from both inorganic and metallo-organic precursors has been followed by solid-state 31P MAS NMR and X-ray diffraction. Condensation mechanisms leading to the formation of a solid phase are discussed. Compared to ZrOCl2 in aqueous solution, zirconium n-propoxide allows shorter reaction times and lower crystallization temperatures. This results in a material with smaller grains which should exhibit enhanced exchange properties.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the ≡Si-O-M interaction given in the sol-gel catalyst is different from the one in the catalysts obtained by a traditional impregnation method.
Abstract: In this work, metal (Pt, Pd, Ru)/SiO 2 catalysts obtained by the sol-gel method have been studied. When the catalysts are prepared by this method, the metal is on the support surface and part of it is inserted into the silica network. By UV-vis (diffuse reflectance) spectroscopy it is shown that the ≡Si-O-M interaction given in the sol-gel catalyst is different from the one in the catalysts obtained by a traditional impregnation method. The metal inserted into the support structure and the metal complex attached to the silica surface behave independently

Journal ArticleDOI
TL;DR: In this paper, a sol-gel system using pentane-1,5-diol as solvent has been developed for the production of lead titanate, PbTiO3, films.
Abstract: A new sol–gel system utilising pentane-1,5-diol as solvent has been developed for the production of lead titanate, PbTiO3, films. The thickness of crack-free PbTiO3 layers prepared by a single spin coating and firing operation is ca. 0.7 µm, representing a seven-fold increase over existing sol–gel routes. Repeated coating steps, prior to firing, permit production of films up to ca. 5 µm in thickness.

Journal ArticleDOI
TL;DR: The sol-gel process allows preparation of very homogeneous and reactive monolithic, optically clear gels as mentioned in this paper, and the crystallization has been studied by differential thermal analysis, dilatometry, X-ray and electron diffraction and Raman scattering.
Abstract: The sol-gel process allows preparation of very homogeneous and reactive monolithic, optically clear gels. Low-temperature thermal treatments (700–1000 °C) lead to amorphous optically clear samples (“glass”). Amorphous mullite compositions (0.4Al2O3-0.6SiO2 to 0.8Al2O3-0.2SiO2) retain large amounts of Ti and Zr elements. The crystallization has been studied by differential thermal analysis, dilatometry, X-ray and electron diffraction and Raman scattering. The nucleation begins above 1000 °C with the departure of the last protonic species, the amorphous matrix being completely crystallized only above 1400 °C. The addition of Zr and Ti elements leads to a homogeneous nucleation of phases with a composition close to ZrO2 and Al2Ti3O9 (EDX analysis) above the solubility limit. TEM and SEM analyses show that the precipitate size remains submicrometric over a wide temperature range (1000–1400 °C) and consequently glass-like mechanical properties, as well as toughening effects, caused by the presence of nanoprecipitates, are observed.

Journal ArticleDOI
TL;DR: In this article, the structural and electrical properties of 18 mol% La-doped PbTiO3 thin films were revealed to be dependent on the annealing conditions.
Abstract: Lanthanum-doped lead titanate thin films have been prepared by sol–gel processing. These studies reveal the structural and electrical properties of 18 mol% La-doped PbTiO3 thin films to be dependent on the annealing conditions. With appropriate annealing conditions, a relative dielectric constant of about 900 was obtained, comparable to the bulk composition.


Journal ArticleDOI
TL;DR: In this paper, a single phase ceramic material of the superconducting phase YBa2Cu4O8 has been synthesized at 780-790°C under one atmosphere oxygen pressure with a sol-gel powder precursor technique.
Abstract: Single phase ceramic material of the superconducting phase YBa2Cu4O8 has been synthesized at 780–790°C under one atmosphere oxygen pressure with a sol-gel powder precursor technique. The precursor was derived from citrate metal ion complexes uniformly dispersed in a solvent mixture of ethyleneglycol and water. The main advantages of the present method are, apart from the low oxygen pressure needed, the elimination of centrifugation, ageing and fine control of pH usually required for other solution techniques. X-ray diffraction analysis show that the material is virtually of single-phase character with only minor traces of CuO (∼1%). AC-susceptibility measurements indicate a high-quality sample with an onset of the superconducting transition at Tc=82.6 K. The superconducting transition is much sharper, ΔTc(10–90%)=4.5K, than for ceramic samples of previously reported synthesis procedures.