Preparation of complex oxides in the form of powders and thin films from metal alkoxides is discussed. Most attention is paid to ferroelectric and related materials ‐ complex titanates and zirconates. Techniques for preparation of high‐purity morphologically homogeneous powders Ti2, ZrO2 barium titanate and BaTiO3‐based solid solutions, MgTiO3, Bi2WO6, Bi2MoO6 are proposed and discussed wilh respect to their application in ceramics technology. The solutions prepared electrochemically in methoxyethanol were widely used for formation of thin films, e.g. Y2O3‐stabilized ZrO2 and ρζγ solid solutions on Pt‐coated silicon substrates.

The reactions between alkoxides and/or alkoxides and anhydrous acetates have been investigated for access to advanced multicomponent niobates or titanates and with the aim to get insight into relationships between the nature of the initial precursors ‐ single or mixed‐metal derivatives, ligands (OAc or OR, R = Et, iPr),…‐ and the properties of the final material. Data are based on a variety of techniques: FT‐IR, multinuclear NMR (1H, 13C, 207Pb, 113Cd), X‐ray investigations on single crystals. Powders have been analyzed by TGA, SEM‐EDX, light scattering and XRD.

We have investigated the homogeneity of sol‐gel derived YBa2Cu307‐s from the solution phase to the final product using transmission electron microscopy (TEM), x‐ray diffraction (XRD), and Energy Dispersive X‐ray (EDX) lateral mapping techniques. The starting solutions contain stoichiometric amounts of the metal 2‐(2‐methoxyethoxy)ethoxide components in 2‐(2‐methoxyethoxy)ethanol and appear to be homogeneous by TEM with a uniform distribution of particles having an average size of less than 40 â. Through elemental mapping we see elemental segregation in the high temperature (950 °C) products, which are orthorhombic by XRD. In elemental maps of gel samples fired to 700 °C, which are tetragonal by XRD, we also see elemental inhomogeneity within particles and phase zoning in maps of products from finely ground gels. A comparison of elemental maps and x‐ray diffraction patterns of the products from gel processing and conventional solid state processing is made.

In attempt to ultimately control the characteristics of the PZT films, we have decided to investigate some of the basic chemistry associated with these solutions. Frequently, these solutions have been generated from Group IV metal alkoxides in acetic acid (HOAc). Therefore, studies of the simple reactivity between M(OCHMe2)4 (M = Ti, Zr) and HOAc have been undertaken. These reactions were monitored by 1H, 13C, 17O NMR, FT-IR, TGA/DTA, and single crystal X‐ray studies. Films were produced from spin‐coat deposition of crystalline material (from the titanium reaction) in toluene and aged solutions as well.

A nonhydrolytic sol‐gel route based on the condensation between chlorides and oxygen donors such as ethers and alkoxides is presented. Four examples, silica, alumina, titania and binary oxides in the Al/Si system show that this is a general route. The mechanism of this condensation is completely different from the one of classical sol‐gel process, since it implies nucleophilic substitution at the carbon center instead of the metal center. As a consequence, the differences in reactivity between different metals are reduced. In addition, the structure of the precursors may be retained in the gel. Thus, the nonhydrolytic sol‐gel process is very efficient for the preparation of homogeneous bicomponent oxides. Futhermore, nonhydrated gels are formed, which allowed us to prepare amorphous aluminas with high surface areas.

The dyes oxazine 725, 7-acetoxy-4-methyl coumarin, O-4-methylcoumarinyl-N-[3-(triethoxysilyl)-propyl] carbamate and 2′,7′-dichlorofluorescein were introduced during the acid-catalyzed cohydrolysis of various molar ratios of tetraethoxysilane (TEOS) and the gel modifers, diethoxydimethylsilane (DEDMS) or diethoxymethylvinylsilane (DEMVS). The morphological features and optical absorption spectra of the resulting dye doped gels were followed during subsequent drying and heating. For DEDMS-TEOS molar ratios less than 1.375, gel cracking during drying was a problem. DEDMS-TEOS molar ratios greater than 2.750 yielded optically transparent monoliths, but did not allow for sufficient incorporation of dye to be useful. However, the functionalized dye, 0-4-methylcoumarinyl-N-[3-(triethoxysilyl)-propyl] carbamate, appeared to be significantly more soluble in such a highly modified matrix. Compared to matrices derived from pure TEOS the DEDMS or DEMVS modified matrices provided oxazine 725 doped with improved thermal stabilities. Finally, the 2′,7′-dichlorofluorescein doped dimethylsiloxane-oxide matrix showed good thermal stability in its optical properties, having significant optical absorption and little change in the wavelength of the absorption maximum after heating to 300°C.

The synteses and structure of the three-dimensional perovskite LajCuTiOg are described. In this oxide Cu and Ti atoms are disordered among octahedral sites. The introduction of oxygen vacancies by an adequate cation substitution leads to the induction of bidimensionality as well as an ordered arrangement of cations and oxygen vacancies as found in the layered oxides Ln2Ba2Cu2Ti2O11 (Ln=La,Nd,Eu).

Hydrothermally derived films of BaTiCO3 were fabricated by reacting thin layers of titanium organometallic liquid precursors in aqueous solutions containing Ba(OH)2 and having a high pH. Cubic submicron polycrystalline films of BaTiCO3 (thickness = 1 μm) were formed at 70°C. Low concentrations of block copolymers of polybutadiene and polystyrene were incorporated into the liquid precursor to prevent precursor film cracking. Higher polymer concentrations allowed fabrication of polymer/ceramic composite films by virtue of the low temperature used in hydrothermal processing.

Reduction of aqueous solutions of tungstates, molybdates or vanadates by aqueous alkali metal borohydrides at ambient‐temperature results in a formation of dark colored gel. The gel is amorphous to X‐ray diffraction and crystallizes sharply at around 300‐500 °C to yield reduced transition metal oxides such as the oxide bronzes, NaxMyOz, or the binary oxides, MO2 (M = V, Mo or W). The nature and composition of the products formed are strongly influenced by the reaction conditions such as the reaction pH as well as the concentration and amount of the reagents. Experimental procedures to obtain the different phases are presented. This novel low‐temperature approach has a potential to access new metastable phases.

The low temperature interdiffusion of superlattice reactants of the binary systems niobium‐selenium and copper‐selenium and the ternary copper‐niobium‐selenium were explored to synthesize amorphous reaction intermediates. Controlled crystallization of this intermediate, which depends upon nucleation energetics rather than the thermodynamic stability of the final product, was used as we attempted to prepare ternary niobium cluster compounds. We present data demonstrating the ability to prepare amorphous ternary intermediates without the formation of crystalline binary compounds as reaction intermediates. Crystallization of the amorphous intermediate resulted in the formation of known ternary compounds directly, also without the formation of binary compounds.

A new type of clay-polyether nanocomposite has been prepared by the self-polymerization of diglycidyl ether of bisphenol A in the galleries of acidic alkylammonium ion exchanged forms of montmorillonite. The acid catalyzed intragallery polymerization process leads to the spontaneous exfoliation to the 10Å-thick clay layers. Intra- and extragallery polymerization processes are distinguishable by DSC.

Clay-polyimide hybrid composites have also been prepared by the intercalation of polyamic acid in montmorillonites and subsequent thermal conversion to polyimide. In contrast to the completely exfoliated clay-polyether system, the polyimide system contain regularly intercalated clay aggregates in the polymer matrix. Although regular face-face clay layer aggregation is extensive, the clay-polyimide hybrid composite films exhibit greatly improved CO2 barrier properties.

The reaction of a wide variety of cyanometalate complexes of the general form [M(CN)x]n- (where M= a transition metal ion) with square planar [PdCl4]2- in aqueous solution leads to the formation of linear polymers. Polymerization occurs via substitution of chloride ligands on the Pd(II) centers, by the nitrogen end of the cyanide ligand to generate extended bridging cyanide structures. Upon generation at room temperature polymer solutions of this type under go a sol-gel transition to generate robust hydrogels having water content in excess of 95%. In the case of the cyanocobaltate/tetrachloropalladate gel, pyrolysis at 900°C produces ferromagnetic Pd/Co metallic alloys having novel morphological character. Materials formed with a hydrogel having a 2:1 Pd to Co stoichiometry are found to be “sponge-like”. When placed in water, the metallic matrix swells becoming pliable and holding up to seven equivalents of water per metal site. The conductivity and magnetic properties of this material are maintained in the swollen state. Sintering of the Pd/Co hydrogel in air generates the layered oxide, PbCoO2 having a delafossite structure.

Thin films of ZrO2 and lead zirconate-titanate, PZT, about 100 to 1000 nm in thickness, were prepared by electrophoretic deposition from transparent sols obtained by hydrolysis of metal alkoxides. Stainless steel plates and Pt-coated glass plates were used as substrates/electrodes. The applied field was up to 20 V/cm. The refractive indices of as dried films were higher than those of dip-coated films. High temperature oxidation of stainless steel plates was suppressed by the ZrO2 coatings. Uniformity of the chemical composition of the as-dried PZT films, determined by Auger electron spectroscopy, was better than the dip-coated PZT films.

The concept of tailored interfaces has been applied to the synthesis of nano-scaled Y2O3/ZrO2 powders. The microemulsion technique as well as the thermodynamically controlled growth reaction have been utilized for this purpose. Both methods yielded agglomerate free amorphous powders with particles sizes of 8 nm and 15 nm, respectively. Cubic zirconia was obtained by calcination between 300 and 400 °C and crystallite coarsening was not observed. The calcined powders could be redispersed by treating them with tertiary amines in aqueous solutions.

A commercially available water-soluble starch derivative was used as the sole organic precursor in the Liquid-Mix synthesis of mixed-cation oxide powders and thin films. The acidified polymer (by nitric acid) was able to complex metal ions through the carboxylate ligands. Loosely agglomerated fine powders as well as dense thin films of complex oxides have been prepared using the same type of polymer. Oxide powders of Cr-doped lanthanum aluminate and yttrium aluminum garnet both crystallized in a single step, without forming any intermediate or second phases, when the amorphous resin intermediates were calcined at 650°C and 750°C for 2 hours, respectively. It was demonstrated that nitric acid could effectively reduce the viscosity of the polymer-nitrate solution to make it suitable for spin coating process. Dense thin films of Y(8 mol%)-doped ZrO2 were formed on Si and A12O3 substrates by spin coating the polymeric solution and heating at temperatures below 1000°C.

A three-step sol-gel process was developed to prepare organic dye-doped thin films with tailored porosity for applications in chemical sensing and optoelectronics. Varying the acid- and base-catalyzed hydrolysis steps of sols prepared from tetraethoxysilane with identical final H2O/Si ratios, dilution factors and pH resulted in considerably different distributions of the silicate polymers in the sol (determined by 29Si NMR) and considerably different structures for the polymer clusters (determined by SAXS). During film formation these kinetic effects cause differences in the packing and collapse of the silicate network, leading to thin films with different refractive indices and volume fraction porosities. Under conditions where small pore-plugging species were avoided, the porosities of as-deposited films could be varied by aging the sol prior to film deposition. This strategy, which relies on the growth and aggregation of fractal polymeric clusters, is compatible with the low temperature and near neutral pH requirements of organic dyes.

RSn(OAmt)3 with R = n-butyl, n-butenyl or para-styryl, which are monomeric precursors, have been hydrolyzed. The so-obtained products have been characterized mainly by 119Sn NMR. In every cases, tin expands its coordination from 4 to 5 and 6, and hydrolysis yields tin oxo-hydroxo species of small size. For n-butyl and n-butenyl, a cage-like tin oxo-hydroxo cluster, {(RSn)12(μ3–O)14(μ2-OH)6}2+, was evidenced as the major compound formed. Organic polymerization of the unsaturated organic groups linked to tin was initiated on the hydrolysis products and yielded hybrid systems which can be pictured as tin oxo-hydroxo oligomers attached together by polymeric chains.

Poly(phenyleneterephthalamide) chains having carbonyl chloride end groups were prepared by reacting a mixture of m- and p--phenylene diamines with terephthaloyl chloride, and were then end-capped with aminophenyl-trimethoxysilane. The polymer thus prepared was used to synthesize a hybrid material in which it was chemically bonded to a silica network produced in-situ by hydrolyzing tetramethoxysilane. Films prepared from this hybrid material were yellow but transparent, and quite tough. The transparency of the films and their mechanical strength were considerably improved relative to the corresponding systems in which the inorganic network was not bonded to the organic phase. Tensile strength was found to increase initially with addition of silica but then to decrease rapidly with further additions. Elongation at rupture also decreased after an initial small increase. A systematic increase in the tensile modulus and hardness with increase in the silica content and a decrease in water absorption were also observed. SEM analysis showed that the silica particle size depends on the silica content, and was 0.5 μm or less. These transparent ceramers were found to withstand tensile stresses the order of 175 MPa and had thermal decomposition temperatures around 460 - 475 ° C, and could thus be very useful in engineering applications at high temperatures.

Scratch resistant transparent organically modified sol-gel materials typically utilize organics as acrylates, or pre-polymer silicon or carbon backbone material. The use of diepoxide monomers within a sol-gel matrix has yet to be described as a means of obtaining high performance coating materials. This paper describes the preparation and characterization of UV curable inorganic-organic hybrid glass materials based on the incorporation of cycloaliphatic diepoxide monomers into a sol-gel composition of TEOS and the epoxide silane coupling agent glycidoxypropyl-trimethoxysilane. We report aging and humidity studies along with processing conditions that affect the silicate distribution and cationic cure of the diepoxide resin based on solution and solid state NMR experiments. Mechanical analysis of thin films prepared by varying processing conditions and length of the diepoxide backbone are also discussed.