A nonhydrolytic sol-gel process that uses acetone as the condensation reagent is described. In the new process, the hydrocarbon soluble Zn(OCEt3)2 is converted to a rigid, transparent gel and then to ZnO by an aldol-condensation-elimination sequence. The chemical pathway for the transformation has been established, and differs completely from the pathway for the conventional hydrolytic sol-gel processing of alkoxide precursors. The new, nonhydrolytic strategy may prove applicable to a variety of metal-alkoxide systems.

Metal alkoxides are often associated with more accessible precursors such as carboxylates, nitrates, B-diketonates, in chemical routes to multicomponent oxides. The molecular constitution of such solutions has been examined for systems based on niobium or zirconium. The heterometallic aggregates MNb2(μOAc)2(μ-0R)4(OR)6 (M = Cd, Mg), PbZr3, (μ4-0)(μ-0Ac)2(μ-0R)5(0R)5 and Gd2Zr6(μ4-O)2(μOAc)6(μOR)10(0R)10 R = iPr have been characterized by X-ray diffraction. Preliminary results on the hydrolysis experiments of these aggregates are given.

Evidence for a tetranuclear aluminum oxoalkoxide cluster Al4(μ4-0) (μ2OBμi)5(OBui)6 is presented, drawing on data from X-ray, NMR, MS and other spectroscopie and experimental investigations. In principle, these compounds are derived from the well-authenticated aluminum alkoxide tetramers by hydrolytic loss of only one alkoxy group. They contain a single central oxo ligand and only 5-coordinate aluminum atoms. They are the simplest discrete oxoalkoxide structures so far reported for aluminum and may be helpful in understanding the hydrolysis and condensation steps leading to hydrated aluminum oxide sols and gels.

Solutions of Sn(OR)4 and R'Sn(OR)3 with different amounts of alkali and alkaline earth metal alkoxides, MI(OR) and MII(OR)2 respectively, have been prepared. Slow evaporation of the solvent resulted in the crystallization of mixed metal alkoxide compounds. Solid state structures have been determined for two examples: K3H[Sn(O/Pr)6]2 and Na2[iPrSn(OiPr)5]·5iPrOH. Solutions as well as solids have been hydrolyzed by moisture. The thermal behaviour of the resulting amorphous powders was investigated by TG, DTA and XRD up to 1000°C in argon atmosphere. The structural evolution during the solid state step mainly depends on the nature and amount of the mono- and bivalent cations. The different influence of both parameters is described.

BuSn(OPri)3 and BuSn(OAmt)3 have been synthesized according to a literature procedure. Their hydrolysis have been studied by 119Sn and 1H NMR spectroscopy. The former precursor yields only a closo-type oxo-hydroxo cation of formula [(BuSn)12O14(OH)6]2+. Investigation of the hydrolysis-condensation products of BuSn(OAmt)3 reveals expanded coordinenceabout the tin atoms from 4 to 5 and 6 when H2O/Sn>l. For butyltin tri-tert-amyloxide, condensation also promotes the formation of a cluster whose structure is as yet unknown.

Sol-gel type hydrolysis and condensation has been studied extensively as a method for the control of evolution of microstructure in the formation of inorganic silicates. However, in non silicate systems, the same level of control of microstructural evolution has yet to be demonstrated. In this work, we report the synthesis of mixed ligand tin (IV) alkoxide complexes specifically designed to undergo sequential hydrolysis reactions, where, as a result, control over porosity of the final metal oxide network is expected. A series of tin (IV) alkoxide compounds modified with difunctional carboxylate ligands as templates has been prepared with internuclear tin separations that are determined by the length of the bridging carboxylate group. The first hydrolysis step consists of the removal of the alkoxide ligands to create a three-dimensional network of oxo-bridged tin carboxylate species. In the second step, the bridging groups are removed by acid hydrolysis to leave pores without creating new Sn-O-Sn bonds. The synthesis and characterization of these species and the connection between pore structure (i.e. micro- vs. meso- porosity) as a function of the dimensions of the bridging ligands will be reported.

The [Ti7O4](OEt)20 molecule, Et = C2H5, is very reactive toward ethanol, and its [Ti7O4] metal oxide core structure is largely decomposed in <10 minutes. The [Ti16O16](OEt232 molecule, however, has a [Ti16O16] core structure which is relatively stable toward alcoholysis, and solid state 17O MAS NMR experiments using selective 17O labeling techniques show that this core structure is preserved in good yield during sol-gel polymerization.

Porous stable metal-organic films can be processed under mild conditions by the hydrolysis of carboxylic acid and titanium isopropoxide mixtures. It is of importance to establish the structure of such materials. Raman spectroscopy is a useful technique in determining structural changes in titanium isopropoxide carboxylate solutions, but weak scattering does not allow for study of thin films unless surface enhancement is used. In an attempt to elucidate the relationship between coating solutions and the final structure of a cast film, we discuss Raman spectra of precursor solutions in a variety of conditions.

Zirconium propoxide hydrolysis was performed with the help of an esterification reaction using acetic acid. Products, obtained according to the value of hydrolysis ratio, are successively crystals, sols and gels or precipitates. The similarity of FUR and NMR spectra for crystals and gels allows to think that the arrangements of ligands around the zirconium atoms are close. The crystalline structure determination permits to precise the environment : acetate groups are always bridging and propoxy groups can be bridging or terminal. Clusters containing 9 zirconium atoms, bridged by oxygen atoms, exist in the structure. The colloid size growth was performed by light scattering. A discussion of the role of acetic acid and the competition between the possible reactions is given.

Several carboxylic acid derivatives of zirconium were investigated for their potential utility as precursors for zirconia fibers and thin films. The reactions of ZrOCl2· 8H2O and ZrCl4 with succinic acid, oxalic acid, maleic acid, benzene tetracarboxylic acid, 2-hydroxyiminopropionic acid, 3-hydroxybutyric acid, and β-alanine were performed and the thermal behavior of the products was investigated by thermal gravimetric analysis. The objective was to find preceramic compounds with low pyrolysis temperatures and physical properties suitable for materials processing.

Polymeric ZrO2 gels were prepared by the controlled chemical modification method (CCM method) of zirconium-n-propoxide. In this method, the steric hindrance by alkoxide-acetic acid chelation could be used to control the hydrolysis and condensation reaction of the zirconium alkoxide if the amount of hydrolysis water was limited. As a result, polycondensaticn occurred uniformly in the solution, forming a linear zirconoxane polymer. When the solvent evaporated, the zirconoxane polymer crosslinked with each other and formed polymeric ZrO2, gels, which were monolithic and transparent. These polymeric gels could be re-dissolved into n-butyl alcohol with acetic acid and mechanical stirring. Heating would enhance the dissolution of the gels. Using the re-dissolved gel solution, dense thin films of ZrO2, could be obtained by dip-coating procedures without many coating operations.

Crystalline perovskite phase mixed metal oxides have been prepared at low temperatures from single-component mixed metal-organic precursors specifically designed for this purpose. Pyridine solutions of divalent metal α-hydroxycarboxylates of general empirical formula A(O2CMe2OH)2 where A = Pb, Ca, Sr, Ba; Me = methyl, react with metal alkoxide compounds such as B(OR')4, where B = Ti, Zr, Sn with the elimination of two equivalents of alcohol to form species with a fixed A:B stoichiometry of 1:1 according to the equation below.

Barium titanate powders and thin films have been processed by the conventional acid pH Pechini process and a modified basic pH Pechini process. Higher pH of the starting solution resulted in significantly finer grains in the sintered thin films. It is proposed that the microstructure refinement is due to the precipitates, formed only in the basic pH solution and resin.

The effects of substituting poly(acrylic acid), PAA, and mucic acid for citric acid in the standard Pechini powder synthesis process was studied. Strontium titanate was chosen as the model system for this study. Powders were prepared from precursor solutions in which PAA (average molecular weight = 2,000 and 5000) was substituted for citric acid (up to 70% by weight), and with reduced weight of total organic reagents (50% reduction). The powders prepared with a 30% substitution of PAA for citric acid produced weakly agglomerated submicron particles after calcining. These powders contained a larger fraction of weak agglomerates than the powders prepared by the original Pechini process. As such, the PAA derived powder could be easily fractionated and dispersed with greater than 70% of the calcined powder having particle sizes less than 0.5 μm

The compounds La1−xBaxTiO3 (0 ≤ × ≤ 1) have been prepared by arc melting stoichiometric amounts of LaTiO3 and BaTiO3. Single phase samples can be made for the entire stoichiometry range. The polycrystalline samples have been characterized by thermal gravimetric analysis, X-ray powder diffraction, and temperature dependent magnetic susceptibility. This series of compounds has been studied as a possible candidate for an early transition metal superconductor.

Sr-substituted perovskite LaCo0.4Fe0.6O3 is known to have excellent mixed ionic and electronic conductivity and increased O2 sorption characteristics. These perovskites are usually prepared by lengthy solid-state reactions of the component oxides at temperatures near 1150°C, and often produce inhomogeneous, multi-phase powders. Presently, it has been prepared by the calcination of combustion-derived fine mixed oxides at 850°C in 6 hrs. Combustion reactions are carried out using precursor solutions containing the corresponding metal nitrates (oxidizers) and glycine (fuel) at 250°C. The metal oxides produced by this process and subsequent calcination were characterized by XRD, TEM and BET surface area analysis.

The hydrolysis of niobates in aqueous solutions has been studied as a function of pH and concentration. The process has been applied to the coprecipitation of PbNb2/3Mg1/3O3 leading to a low temperature synthesis of this ferroelectric relaxor ceramic. The effect of hydrolysis conditions such as the concentration of bases and acids used, their rate of addition, temperature and the nature of the precursor salts is described. The homogeneity of the precipitates has been characterized through infrared spectroscopy and X-ray diffraction techniques. The perovskite phase appears after heating at 350°C and is obtained as a pure phase above 750°C after one hour heat-treatment. Relaxor ceramics with high dielectric constant can be obtained by sintering above 1000°C. The process also has been successfully applied to the synthesis of other relaxor ceramic compositions such as PZN (PbNb2/3Zn1/3O3), PFN (PbNb1/2Fe1/2O3) as well as CdNb2O6 and MgNb2O6 compounds.

We have prepared examples of several new classes of group 2 compounds, including ether- and amine-substituted metallocenes, inter- and intra-molecular Lewis base stabilized bis(β-diketonates), and clam-shell oligioether bis(alkoxides), and investigated their use as potential sources in the preparation of ceramic materials from molecular precursors. Examinations have included vapor pressure measurements, hydrolytic, oxidative, thermal and photolytic stability, vapor phase, solution and solid state structures, and evaluation for potential CVD growth of thin films of electronic ceramics. Results to date indicate that intramolecular stabilization is more advantageous than intermolecular stabilization for achievement of optimal CVD source criteria, and that completion of the coordination sphere around the metal atom requires tuning of both ligand spatial and electronic requirements.

Alcohol interchange reactions between barium and copper(II) methoxides and triethanolamine give Ba(teaH-l)2,2EtOH and [Cu(teaH-2)]4,3tea, respectively. Triethanolamine appears as a tetradentate ligand -chelating in the case of barium, bridging-chelating for copper - and thus ensures high coordination numbers for the metals - eight for Ba and five for Cu - thus decreasing their susceptibility to hydrolysis. The remaining hydroxyl functionality on the coordinated triethanolamine moities favors the formation of solvates with alcohols via H-bonding.

Several useful ceramic materials target compositions contain yttrium, Y2O3 and YBa2Cu3O7-δ being the two most widely employed. One known CVD precursor for yttrium-containing thin films is Y(tmhd)3 H2O (tmhd = 2,2,6,6-tetramethylheptane-3,5-dionato). We have determined the structure and examined the vapor phase decomposition of this species. A related compound, [Y(tmod)3]2(tmod = 2,2,7-trimethyloctane-3,5-dionato), has been prepared, structurally characterized, and studied as an organometallic vapor phase epitaxy (OMVPE) precursor for Y and Y2O3 films. Mechanisms of vapor phase decomposition are discussed in terms of solid film deposits and vapor phase by-products. The two precursors are compared to each other with respect to their stability windows, defined as being bound by source volatility on the low side and source stability on the high side.