We describe a novel precipitation route to silica grain that lies in the interface between sol-gel and Stöber-type silica. The use of acetic acid as a catalyst for TEOS hydrolysis provides access to a precipitation window in which partially hydrolyzed TEOS and TEOS monomer, when reacted with aqueous ammonia, combine to form pumice-like silica particles in up to 90% yield as SlO2. Precipitated particles exhibit narrow particle size distributions that may be controlled for average particle sizes from 50µ to 400 µ. SEM micrographs show that the particles are agglomerates of small particles, which is consistent with the high degree of observed macroporosity.

Silica and titania particles are readily synthesized by the hydrolysis of alkoxides in various alcohols. The present research studies experimentally and models the chemistry and growth kinetics of silica and titania particles in low molecular weight alcohols (methanol, ethanol, 1-propanol, 1-butanol). The theoretical model is based on solving the hydrolysis and condensation kinetic expressions and applying the method of moments to expedite the solution of the governing population balance equation.

The fast sol-gel synthetic route to glass films is facilitated by a solvent-free reaction of trialkoxysilane monomers at 60–80°C and near-stoichiometric water-to-siloxane ratios. The viscous polymer formed within several minutes is spin-cast onto a support (typical thickness 10–25µm), cured within a few hours at 60–70°C or 10–40 min. under an intense electric field at room temperature, and can be characterized on the same day. Multi-layered glass-film assemblies of varying indices of refraction and a total thickness up to 80µm are prepared by the same fast process with slight modifications.

Guest molecules such as laser dyes for 2D lasers and chromophores for second-harmonic-generation are incorporated into these glass films at high concentrations by direct addition to the reaction mixture. Their absorbance and fluorescence spectra are typical of monomeric chromophores up to concentrations of ∼10-2M. Crystallites that may appear at higher concentrations exhibit unusual polymorphism. The smoothness of such films enables surface anchoring of iso-environment photoactive molecules and investigation of their photophysics.

29Si-NMR studies of the hydrolysis pattern in our acid-catalyzed fast sol-gel reaction prove that uniform hydrolysis of the monomer, necessary for a single-phase polymerization, is attained only when the hydrolysis is fast enough to become kinetically controlled, e.g. at elevated temperature or at high acid-concentration. Our reaction pattern and the data of others can be interpreted in terms of a single mechanism of hydrolysis in which two different rate-determining-steps can prevail, depending predominantly on the reactivity of the alkoxysilane and the ratio of the acid-catalyst to the (apparently-inert) proton-binding solvent.

In this paper results of efforts to prepare stable aqueous suspensions of high surface area (> 100 m2 /gr) yttria stabilized tetragonal zirconia powders are presented using a low molecular weight ammonium polyacrylic acid deflocculant. Zetapotentials, viscosities, agglomerate sizes and sedimentation volumes have been measured to find the optimum pH and deflocculant concentration. It has been found that the optimum pH-value coincides with the pH at which the polyacrylic acid is fully dissociated. Using deflocculant concentrations below the optimum value leads to a highly unstable system, while concentrations above the optimum value influence the stability in a much weaker way.

Titania and titania/zirconia sols, with solids loadings exceeding 1000 g dm3, have been prepared on a 10 kg scale by chemical methods involving the hydrolysis of an appropriate mixture of alkoxides, followed by peptisation with dilute nitric acid. The rate of peptisation of the hydrolysates was determined by static light-scattering and photon-correlation spectroscopy, enabling the hydrodynamic radius, the radius of gyration and the fractal dimension of colloidal species to be monitored as a function of peptisation time.

The peptisation kinetics were influenced by a range of factors including the initial solids loading, the acid concentration, the reaction temperature and the age of the alkoxide hydrolysate. Hydrolysate peptisation is first order with respect to concentration of acid and exhibited a non-integer reaction rate order (complex mechanism) with respect to solids concentration. Sols produced from freshly-precipitated hydrolysate peptised at a faster rate than aged precipitates but slowly re-aggregated after peptising, yielding “equilibrium” aggregate sizes often exceeding 100 nm. This effect was not observed in sols produced from aged hydrolysate. These differences are interpreted using DLVO theory.

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

Recent achievements in the chemical processing of ferroelectric niobates epitaxial films are reported. The molecular level designing of the precursor solution was stressed as well as the control of key processing factors. Examples are presented for LiNbO3/Ti, K(Ta,Nb)O3 and (Sr,Ba)Nb2O6 films from metal alkoxide precursors. Crystalline epitaxial films with stoichiometry could be synthesized through control of the intermediate state of starting molecules in solution. Water vapor stream was found to play an important role in crystallizing gel films to desired phases at relatively lower temperatures.

Barium titanate (BaTiO3) thin layers were prepared by sol-gel processing. Details are reported for the synthesis route from methoxyethoxide precursors. Partially hydrolyzed solutions were spin-cast onto metallized silicon substrates, and a multilayering technique was used to develop sub-micron structures. Information is reported on the thermal processing conditions used and the development of structure. Crystallization started at 600°C and was fully developed by 700°C. The room temperature structure was cubic, and the grain size was 25–50 nm. Details are reported for the dielectric properties. Ferroelectricity was not observed. Dielectric constant (200–300) increased with increasing grain size, and was stable with respect to temperature, field and frequency. The properties are attractive for potential integrated capacitor applications.

A series of PZT precursor solutions was prepared which incorporated excess PbO to give the composition Pb1+xZr0.53Ti0.47O3+x, where 0 < × < 0.3. These solutions were spin coated on platinized Si wafers and fired at elevated temperatures up to 750C for 30 mins. After crystallization into single-phase perovskite, the films were studied using XRD, optical microscopy and electrical characterization techniques (hysteresis loops and dielectric properties). It was found that the presence of excess PbO significantly improved the PZT films in terms of phase assemblage, microstructure and electrical properties. Under optimized conditions, films with dielectric constants of around 3000 can be obtained.

Lead-zirconate-titanate, Pb(Zr0.53Ti0.47)O3, films were produced by the sol-gel method from alkoxide and acetate precursors in a 2-methoxyethanol solvent system. The PZT films were deposited on platinized silicon and single-crystal SrTiO3 substrates for electrical and optical characterization, respectively. The processing parameters, especially excess PbO content and annealing conditions, were shown to have a significant effects on the properties of PZT films. Epitaxial PZT films deposited on SrTiO3 waveguided over 10 mm distances with propagation losses as low as 5.9 dB/cm at 783 nm and a linear electro-optic effect was also demonstrated.

Pb(ZrxTi1−x)O3 (PZT) solutions were prepared by reacting lead 2-ethylhexanoate with titanium n-propoxide and zirconium n-propoxide. Films were deposited on several kinds of metal substrate by dip-coating. Crystalline PZT films and amorphous PZT films were heat-treated for 1 hour at 650°C and at 400°C, respectively. Electrical properties including dielectric, pyroelectric and ferroelectric properties of both crystalline and amorphous PZT films were measured and compared. The amorphous PZT thin films exhibited ferroelectric-like behaviors.

Barium titanate, lead titanate and barium-lead titanate thin films were prepared by the sol-gel method using metal alkoxides on metallic conducting BaPbO3 ceramic substrates. Thin films were deposited on the polished surfaces of the substrates by spin coating solutions containing Ba(OC2H4OCH3)2, Pb(OCOCH3)2 and Ti(O-iC3H7)4 and methoxyethanol. The gel films were then fired at appropriate temperatures to yield ceramic thin films. A 0.50 µm-thick BaTio3 film showed a dielectric constant of 280 and tan ° of 3% at 1kHz with no distinguishable peak of dielectric constant at any temperature between 20°C and 200°C. Both PbTiO3 (0.75 µm thick) and Ba0.7Pb0.3 (0.2 µm thick) films, on the other hand, showed a distinguishable peak of dielectric constant at their Curie point with a rather deformed P-E hysteresis loop at room temperature.

Two novel processes have been developed to lower the transformation temperature of ferroelectric lead zirconate titanate (PZT) thin films with high Zr/Ti ratio. One process makes use of high pressure and the other process uses seeding to encourage the transformation.

A previous study has shown that nucleation is the rate-limiting step for the perovskite formation. Therefore, any process that enhances the kinetics of the nucleation will likely decrease the transformation temperature. In this process, a very thin seeding layer, which has a low effective activation energy for perovskite formation, is used to provide nucleation sites needed for the low temperature perovskite formation. In this study, the pyrochlore to perovskite phase transformation temperature of PbZrxTi1−xO33 films of high Zr/Ti ratio (e.g. x = 53/47) can be lowered by as much as 100°C.

LiNbO3 thin films were deposited by dip coating Li-Nb alkoxide solutions onto silicate glass substrates and single crystal sapphire substrates. Microstructural characterization using transmission electron microscopy (TEM) showed significant differences in film microstructures dependent on the initial solution chemistry. Fully crystalline films could be obtained after heat treatments at 400°C in air. The grain size and porosity were dependent on the amount of water of hydrolysis in the alkoxide sol. The higher the water content, the larger the grain size and porosity. Crystallization studies of nucleation and growth of LiNbO3 for films heat treated from 300–600°C indicated that higher temperatures or long soak times generated large facetted grain structures. Single crystalline films were obtained on (0001) sapphire substrates.

Transparent and uniform thin films of crystalline KNbO3 were synthesized on different substrates such as SrTiO3, ZrO2, MgO and Pt by the dip-coating method using a double alkoxides solution. The film was epitaxially crystallized at the temperature around 750°C for 3 hours in air on SrTiO3 single crystal substrate. The structure of the films has been studied with X-ray and electron diffraction, and transmission electron microscopy.

Different molar ratios of 2-ethylhexanoic acid (2EHA) to alkoxides were applied to control the hydrolysis rate of the sol-gel solution. Dense films were obtained after modification of the alkoxides solution.

In this paper we describe a novel route for the formation of thin films of potassium titanyl phosphate (KTiOPO4 KTP) via a sol-gel route. The ability to form films of high optical quality depends upon the precursor chemistry developed. Formation of stoichiometric films is especially challenging in three component systems and a number of precursors have been investigated. The basic chemistry, processing and resulting microstructure will be described. Transparent, dense and continuous films have been prepared with grain sizes typically of 0.3μm or less depending upon the processing conditions. Some textured growth patterns are observed although the films are essentially polycrystalline. Using the prism coupling technique the films have been found to exhibit waveguiding.

We report on a novel precursor technique to produce highly pure and homogeneous cuprate based high-Tc superconductors based on the formation of a polymer metal complex in which various metal ions in desired stoichiometric ratio can be uniformly dispersed. Application of the polymerized complex method is demonstrated on the ceramic synthesis of polycrystalline compounds viz. YBa2Cu3Oy, YBa2Cu4Oy, Bi1.6Pb0.4Sr2Ca2Cu3Oy and Bi2Sr2Ca0.8Cu2Oy. The superconducting properties were studied with complex magnetic susceptibility measurements which exhibited sharp superconducting transitions without any indication of two-phase character. The materials fabricated by this method showed improved properties compared to those for ceramic samples of previously reported synthesis procedures.

It is found that ethanolamine method, recently developed by us, is very useful to form stable, concentrated (0.4–0.5M) indium oxide-based sols from which very uniform, transparent In2O3 and ITO films are obtained by dip-coating. Indium isopropoxide and acetate can be used as the starting materials. The optical and electrical properties of these films were examined. A transparent ITO film with the highest conductivity (3030 S/cm, after annealing at 0.05 torr-600°C for 60 min) was obtained from the acetate at 600°C. The films from the alkoxide had lower conductivities probably due to the impurities included in the alkoxide.

Tin oxide films were grown from di-n-butyltin diacetate on a heated glass substrate by a pneumatic spraying system The effects of various film growth parameters. i.e solvent, solution feed rate, film thickness, and film growth rate on the microstructures of the films were studied by X-ray diffraction and scanning electron microscopy The SnO2 films of the (200) plane were grown by the optimum growth parameters

We describe a meniscus coating method to produce high-laser damage threshold, silica/alumina sol-gel multilayer reflectors on 30+ cm substrates for laser-fusion applications. This process involves forcing a small suspension flow through a porous applicator tube, forming a falling film on the tube. A substrate contacts this film to form a meniscus. Motion of the substrate relative to the applicator entrains a thin film on the substrate, which leaves behind a porous, optical quality film upon solvent evaporation. We develop a solution for the entrained film thickness as a function of geometry, flow and fluid properties by an analysis similar to that of the classical dip-coating problem. This solution is compared with experimental measurements. Also, preliminary results of multilayer coating experiments with a prototype coater are presented, which focus on coating uniformity and laser damage threshold (LDT).