Alkoxide Solutions Research Articles

Sol–gel synthesis and characterization of Ba (1− x) Sr xTiO 3 ceramics

Ba (1− x) Sr x TiO 3 ( x = 0, 0.1, 0.2, 0.3) nanopowders were synthesized from alkoxide solution precursor by sol–gel process. The Ba (1− x) Sr x TiO 3 powders calcined at 800 °C for 2 h were maintained in cubic phase and the cell parameters were in the range of 4.0282–3.9786. The effects of Sr doping and sintering temperature on structure and dielectric characteristics of the Ba (1− x) Sr x TiO 3 ceramics were investigated. The increase of Sr content in the Ba (1− x) Sr x TiO 3 ceramics causes the inhibition of grain growth and downward shift of Curie temperature ( T c). The T c shift rate is 2.5 °C/mol% with increasing Sr content. At T c, the dielectric constants of Ba (1− x) Sr x TiO 3 ceramics increase with the increasing of sintering temperature, and the highest permittivity (7032) is obtained for x = 0.1 sample sintered at 1400 °C.

Solution derived 12CaO·7Al2O3 thin films on MgO(100) substrate

Abstract 12CaO·7Al 2 O 3 (C12A7) is known as a component of alumina cement and shows various remarkable properties: generation of high oxidizing power using oxygen radical O − , high electric conductivity (∼1500 S cm −1 ) for the electron clathrated one, etc. Most of the C12A7 thin film fabrication processes reported have been based on PLD method so far, which require high vacuum level and high energy consumption. In order to fabricate the C12A7 films with low energy consumption process, we prepared C12A7 films on MgO(1 0 0) substrate by chemical solution deposition (CSD) method from alkoxide solution. Aluminum sec.-butoxide and calcium metal were used as raw materials, and 2-methoxy ethanol was used as a solvent. Crystallization behavior, crystal structure, and morphology of the prepared film, were investigated by XRD, SEM, and TG-DTA. The C12A7 film prepared by the CSD method was mostly polycrystalline, but it showed high peak intensity at (2 1 1) and (4 2 2) reflection compared to the powder C12A7 peaks. This implied the C12A7 film includes slightly (2 1 1) oriented grains among the polycrystalline on the MgO(1 0 0) substrate.

Microstructure and wear resistance of double-layer TiN/PSZ coatings from alkoxide solutions by H 2O-containing thermal plasma CVD

Double-layer TiN/PSZ coatings approximately 2 µm thick were deposited on Si wafers and WC–Co cutting tools from Ti-, Zr-, and Y-alkoxide solutions by Ar/H 2/N 2 thermal plasma chemical vapor deposition with water functioning as an oxidant. A PSZ layer was deposited on TiN films upon oxidation of Zr- and Y-alkoxides by H 2O using five-step-wise and pulse-type supply methods. The double-layer coatings were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), in-depth glow discharge optical emission spectrometry, and cutting tests. Two H 2O supply methods, two-stage pulse and five-step-wise supply methods, were shown to be suitable for the formation of the double-layer coatings by SEM and TEM observation of surface and cross-sectional microstructures. Cutting tests for the double-layer coatings deposited on WC–Co cutting tools prepared by the above two H 2O supply methods were carried out to evaluate their wear resistance.

Coating and Wear Resistance of Ceramic Films from Alkoxide Solutions by Atmosphere Controlled Thermal Plasma CVD

Coating and Wear Resistance of Ceramic Films from Alkoxide Solutions by Atmosphere Controlled Thermal Plasma CVD

Fabrication of BaTiO3 Micropatterns by a Combination of Laser-Induced Pyrolysis Method and Nano-Crystalline Seeding Technique and Their Dielectric Properties

This paper describes a method for fabricating dielectric BaTiO3 (BT) micropatterns. The method used in the present work is a combination of a laser-induced pyrolysis method and a nano-crystalline seeding technique. BT nano-crystalline particles used for the seeding are prepared by hydrolysis of a BT complex alkoxide. A precursor solution of a BT complex alkoxide containing the BT nano-crystalline particles and polyvinylpyrollidone (PVP) is spin-coated on a Pt substrate. Micropatterns with a line width of ca. 1–2 μm are fabricated by irradiating an Ar+ laser beam with a beam waist diameter of 0.74 μm at a laser energy density of 27 MW/cm2 and a scanning speed of 25 μm/s on the spin-coated BT films, and then stripping laser-unirradiated regions on the films with an HCl aqueous solution. The use of BT particles prepared in the presence of PVP with a small molecular weight provides clear micropatterns and high dielectric constant. The dielectric constant and dissipation factor of the micropattern fabricated at 20 vol% BT particles with an average size of 12.9 nm prepared in the presence of PVP with a molecular weight of 10000 attain 78.7 and 0.089, respectively, for a measurement frequency of 100 kHz.

Characterization of barium titanate nanoparticles and dense nanograin free-standing films via sol-gel method using highly concentrated alkoxide solution

This paper reports on two topics regarding nanosized barium titanate (BaTiO3) prepared by the sol–gel method using a highly concentrated alkoxides precursor solution. One topic concerns the crystallographic features of the BaTiO3 nanoparticles. In the case of using a highly concentrated precursor solution, non-core–shell BaTiO3 nanocrystals with a small amount of intraparticle voids, lattice hydroxyl groups and remaining alkoxy groups were efficiently generated by the addition of less excess water during aging at room temperature. The generation of the high-quality BaTiO3 nanocrystals is considered to be due to the hydrolysis and polycondensation reaction of the alkoxides being well promoted in such a concentrated solution. The lattice volume of the BaTiO3 nanocrystals with a crystallite size of 15 nm fired at 600°C was approximately 1 vol % larger than that of bulk crystal. This lattice expansion is more likely to be caused by an intrinsic size effect than an extrinsic effect due to the lattice defects, such as lattice hydroxyl groups. The other topic concerns the dielectric properties of dense nanograin free-standing films with a grain size of 57 nm after applying the same sol–gel method. Significant frequency dispersion behavior of dissipation factor was observed at temperatures less than the Curie temperature. This finding may indicate that the dielectric properties reflect an intrinsic grain size effect without any influence being attributed to the film/substrate interface or lattice defects.

粘土鉱物アロフェン‐酸化チタン複合体光触媒によるトリクロロエチレンの分解特性

Allophane-TiO2 composites as highly adsorptive photocatalysts were prepared by dispersing nanoparticles of the natural clay mineral, allophone, into a titanium alkoxide solution by the sol-gel method. During the photocatalytic degradation of trichloroethylene using the allophane-TiO2 composites, emission of the intermediate product, phosgene, was significantly inhibited. Trichloroethylene was transformed into the intermediate product, phosgene, on the TiO2 during the UV irradiation. This compound was rapidly adsorbed by the allophane. The compounds were gradually degraded after diffusing to the TiO2. Although the degradation rate of the trichloroethylene using the allophane-TiO2 composites was slower than that using TiO2, their activity was improved by heating at 400-500 °C.

Gold nanoparticles supported on ceria-modified mesoporous–macroporous binary metal oxides as highly active catalysts for low-temperature water–gas shift reaction

New gold catalytic system prepared on ceria-modified meso-/macroporous binary metal oxide support (CeO2/TiO2–ZrO2) and used as water–gas shift reaction (WGSR) catalyst is reported. The support was prepared through the surfactant templating technique combining with the use of mixed alkoxide solutions. Ceria-modifying additive and gold were deposited consecutively on the meso-/macroporous TiO2–ZrO2 by deposition-precipitation method. The samples were characterized by powder X-ray diffraction, scanning and transmission electron microscopy, N2 adsorption analysis, and temperature-programmed reduction. The catalytic activity of the new gold-based catalysts was evaluated in WGSR and it was compared with that of gold catalysts supported on simple and binary mesoporous oxides (TiO2, ZrO2, and TiO2–ZrO2) and ceria-modified mesoporous titania support (CeO2/mTiO2). A high degree of synergistic interaction between ceria and support and a positive modification of structural and catalytic properties have been achieved. The new gold catalytic system is found to be a promising catalyst for practical WGSR application.

Nanostructure development in photodeposited, titania-based thin films

Ultraviolet irradiation (λ = 248 nm) was used to photocatalyze a solution of the heteroleptic titanium alkoxide (OPy)2Ti(TAP)2 [where OPy = pyridine carbinoxide and TAP = 2,4,6 tris(dimethylamino)phenoxide], leading to the deposition of a titania-based thin film only in the exposed region. The effect of water addition to the (OPy)2Ti(TAP)2 pyridine solution on the properties of the final photodeposited film structure was examined by using vibrational spectroscopy and electron microscopy. Under consistent optical exposure conditions, the amount of water added altered the nanoscale porosity of the final material produced. Films deposited from a solution with a 1:1 H2O/Ti content exhibited surface pores ∼100 nm in diameter, whereas a 4:1 ratio yielded 10-nm pores, and material produced from a 8:1 solution appeared fully condensed. In addition, the effect of postdeposition thermal treatments on the nanostructure and chemistry of the photodeposited films was examined.

Effects of the catalysts on the evolution of in-plane stress in alkoxide-derived silica gel coatings during heating

The effects of the catalysts on the evolution of in-plane stress during heating were studied for silica gel coatings prepared from alkoxide solutions. Tetramethylorthosilicate was hydrolyzed in the presence of nitric acid, acetic acid, and ammonia as catalysts. Gel films were deposited on Si(100) wafers by spin coating, and heated at a constant rate of 5 °C/min up to 500 °C. During heating, in situ measurement of the in-plane stress was conducted by measuring the radius of curvature of the substrate. In-plane, tensile stress increased up to 560 and 370 MPa in the films prepared with HNO3 and CH3COOH, respectively. However, the stress was much smaller at 30–40 MPa, which remained almost constant during heating, for the films prepared with NH3. The much smaller stress resulted from the much lower degrees of the progress of densification during heating, which was revealed in the changes in thickness and infrared absorption spectra during heating. The low degrees of the progress of densification were caused by the colloidal nature of the gel films.

Photo-electric conversion in dye-doped nanocrystalline titania films

Influences of the titania nanostructure and dye dispersion in a dye-doped titania electrode on its photo-electric conversion property were investigated by simple spectroscopic and electric measurements. The dye-doped nanocrystalline titania electrodes were prepared on the glass plates coated with ITO and normal crystalline titania films by the following two procedures: (1) the dye-doped titania gel films were prepared from a titanium alkoxide solution containing the dye and then steam-treated, and (2) the titanium alkoxide sol containing the dye was refluxed and then spread onto the plates. The photocurrent quantum efficiency remarkably increased by the steam treatment and the reflux compared to that of the untreated dye-doped electrode consisting of amorphous titania gel. The efficiency in the former was higher than that in the latter. The growth and crystallization of the titania particles and the decrease in the defect density by these treatments improved the electric conductivity. The steam treatment was the more prominent method because it enhanced the electric conductivity of the titania depending on its nanostructure and the dye–titania interaction depending on the dye dispersion. These factors appear to play important roles in transport in the electron through the electrode.

Coatings and Oxidation of (Ti1-x, A1x)N Films from Alkoxide Solutions by Thermal Plasma CVD

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Water and oil wettability of hybrid organic–inorganic titanate–silicate thin films deposited via a sol–gel route

Hybrid organic–inorganic titanate–silicate thin films were deposited on silicium wafer via a sol–gel route. Hybrid sols were formulated by mixing an inorganic titanium alkoxide solution with solutions of hybrid organic–inorganic silicon alkoxides partially substituted with non-hydrolysable alkyl chains. Three organo-silicate precursors were used to introduce methyl, octyl, or hexadecyl chains in the oxide network. Physico-chemical and morphological properties of derived hybrid films have been studied by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, ellipsometry, and atomic force microscopy. Contact angle measurements have also been performed to assess the water and mineral oil wettability of hybrid films. Wettability properties of these films are discussed with respect to physico-chemical and morphological features. It is shown that increasing the fraction and length of alkyl chains in the oxide network conjointly increases water and oil contact angles measured on such hybrid films.

Microstructural study of SnO 2 thin layers deposited on sapphire by sol–gel dip-coating

Tin oxide (SnO 2) films have been grown onto (006) sapphire substrates by sol–gel dip-coating using tin alkoxide solutions. It is shown, using grazing-incidence X-ray diffraction, reciprocal space mapping and atomic force microscopy, that thermal annealing at 500 °C induces the crystallization of SnO 2 in the rutile-type phase. Further annealing treatments at temperatures lower than 1100 °C give rise to slow grain growth controlled by surface diffusion, whereas rapid grain growth (controlled by an evaporation–condensation mechanism) takes place at temperatures higher than 1100 °C. Concomitantly, the film splits into isolated islands and a fibre texture occurs at higher temperatures.

Preparation and Electrophoretic Deposition of an Yttrium Silicate Precursor Sol

. In the present work we used the sol-gel process to prepare Y2SiO5 precursor sols suitable for electrophoretic deposition (EPD). The sol synthesis was performed through the controlled hydrolysis of alkoxide solutions of tetraethoxysilane and yttriumoxoisopropoxide. During sol development emphasis was put on characterization of particles size and zeta potential of the formed aggregates. We succeeded in synthesizing a clear sol containing polymeric aggregates with acceptable particle charge. The electrophoretic deposition on glassy carbon or C/C-SiC slabs led to homogenous layers. At low sol concentrations micro cracks in the deposited layers were observed whereas higher concentrations led to thin and dense layers. During constant current EPD a constant voltage was recorded indicating that the deposited layer does not lead to an increase in resistivity in this kind of EPD system.

Tin(II) Doped Anatase (TiO2) Nanoparticles: A Potential Route to “Greener” Yellow Pigments

During our exploration of compounds in the Sn(II)-Ti(IV)-O system, we discovered that hydrolysis of titanium alkoxide solution in the presence of Sn(II) salts resulted in stable deep-yellow colored anatase nanoparticles. The samples were characterized by X-ray powder diffraction, electron microprobe, thermal analysis, transmission electron microscopy, and (119)Sn Mössbauer spectroscopy. Mössbauer data of the yellow colored samples showed the presence of both Sn(II) and Sn(IV) in a distorted environment as expected in the anatase structure. It is suggested that the cationic charge imbalance is compensated by oxygen vacancies and/or hydroxyl groups as evidenced by Mössbauer data which show two types of Sn(II) environments. When heated in air to 300 degrees C the samples changed color to completely white and (119)Sn Mössbauer data of these samples showed only the presence of Sn(IV). These observations indicate that the origin of the yellow color in our Sn doped anatase nanoparticles arises from filled Sn 5s states just above the O 2p band, thus decreasing the band gap. The Sn(II) doped anatase TiO(2) nanoparticles reported here can potentially lead to environmentally benign yellow pigments. The simplistic nature of the synthetic procedure could easily be adapted to large-scale industrial manufacture.

Photophysical and photocatalytic properties of nanosized copper-doped titania sol–gel catalysts

The effect of doping the TiO 2 lattice with copper was studied. TiO 2–Cu semiconductors (0.1, 0.5, 1.0 and 5.0 Cu wt.%) were synthesized by the sol–gel method by incorporating Cu (NO 3) 2 into the titanium alkoxide solution. In the samples thermally treated at 500 °C, mesoporous materials (9.5–12 nm) with specific surface areas of 90–52 m 2/g were obtained. The X-ray diffraction (XRD) patterns of the annealed samples present anatase as the sole nanocrystalline phase (∼28 nm). The UV–vis diffuse reflectance spectra of the Cu-doped samples show a shift in the band gap to lower energy levels. The X-ray photoelectron spectroscopy (XPS) reveals a reduction in the oxidation state of the copper precursor, Cu(II), stabilizing Cu(0) and Cu(I) in the annealed solids. The photocatalytic test for the 2,4-dichlorophenoxyacetic acid degradation showed high efficiency and mineralization up to 92% (total organic carbon, TOC) in the Cu-doped sol–gel materials. The enhancement of the photocatalytic activity was discussed as an effect due to the Cu content as well as to the formation of stable Cu(I) in the Cu-doped TiO 2 semiconductors.

Preparation of MgFe2O4 nanoparticles by microemulsion method and their characterization

This work presents the preparation and characterization of magnesium ferrite which is one of the important magnetic oxides with spinel structure. Magnesium ferrite was prepared via microemulsion method mediated hydrolytic decomposition of mixed alkoxide solutions. This microemulsion was using for preparation magnesium ferrit for the first time. The starting solution, composed from magnesium methoxide and iron ethoxide in dry ethanol, was introduced in to the prepared microemulsion and sequentially hydrolyzed by distilled water addition (Pithan et al. in J Cryst Growth 280:191–200, 2005; Shiratori et al. in J Eur Ceram Soc 25:2075–2079, 2005; Herrig and Hempelmann in Mater Lett 27:287–292, 1996). After raw powder precipitation, the samples were decantanted by ethanol and then calcined at temperatures 800, 900, 1,000 or 1,100 °C for 1 h. The resulting samples were characterized using powder X-ray diffraction, high resolution transmission electron microscopy, Mossbauer spectroscopy and magnetic measurements. X-ray diffraction and Mossbauer spectroscopy confirmed the presence of the spinel phase. The particles size was calculated from the XRD line broadening using Scherrer equation and their size was found about 31–38 nm, with only slight dependence on the heat treatment temperature. TEM revealed the particles size of about 39 nm. Magnetic measurements showed a ferrimagnetic behavior for all samples.

Structure and electrical properties of BaTiO 3 prepared by sol–gel process

BaTiO 3 nanopowders were synthesized from alkoxide solution precursor by sol–gel process. Attempts had been made to understand the synthesis process with the help of thermo gravimetric (TG) and differential scanning calorimetry (DSC). XRD and SEM results showed that the BaTiO 3 powders calcined at 700 °C for 2 h were maintained in cubic phase and the average size was 25 nm. The effects of the initial grain sizes of BaTiO 3 powders on the phase structures, microstructures and dielectric properties of the ceramics were investigated. The results indicated that both the grain size and the relative density of the ceramics increased with the increase in sintered temperature. The permittivity at room temperature was not sensitive to the grain size.

Sol–gel modified TiO 2 powder films for high performance dye-sensitized solar cells

Techniques in TiO 2 film fabrication process are a very important aspect in construction of efficient dye-sensitized solar cells (DSSCs). Among fundamental factors in high efficiency solar cells is the development of a highly porous nanocrystalline film in a relatively thick and mechanical stable TiO 2 network. In present work, two types of commercial titania powders with high loading (74% (wt.%) in the final films), Degussa P25 powders and Ishihara ST-01 powders, have been successfully incorporated into a mesoporous structured TiO 2 crystalline network. The good mechanical stability of both types of films involves the presence of a titanium alkoxide solution mixed with non-ionic surfactant Tween 20 as a suitable binder precursor to immobilize commercial titania nanoparticles on a SnO 2:F conductive glass via a dip coating sol–gel process. The results of photoelectrochemical characterization of the films in a dye-sensitized solar cell showed that both films presented high conversion efficiency (about 6%) with only a slight difference on their photovoltaic behavior, when a quasi-solid state electrolyte was employed. The crystalline structure of the foreign titania particles, the particle size and the existence of any agglomeration, as well as the surface area and the pore structure of these films made of different titania powder sources were examined in detail and are discussed in relation to the relatively high solar to electrical energy conversion efficiency obtained in such quasi-solid state DSSCs.