Preparation of complex oxides in the form of powders and thin films frommetal alkoxides is discussed. Most attention is paid to ferroelectric andrelated materials ‐ complex titanates and zirconates. Techniques forpreparation of high‐purity morphologically homogeneous powders Ti2, ZrO2 barium titanate andBaTiO3‐based solid solutions, MgTiO3, Bi2WO6, Bi2MoO6 are proposedand discussed wilh respect to their application in ceramics technology. Thesolutions prepared electrochemically in methoxyethanol were widely used forformation of thin films, e.g. Y2O3‐stabilized ZrO2 and ρζγ solid solutions on Pt‐coated siliconsubstrates.

The reactions between alkoxides and/or alkoxides and anhydrous acetates havebeen investigated for access to advanced multicomponent niobates ortitanates and with the aim to get insight into relationships between thenature of the initial precursors ‐ single or mixed‐metal derivatives,ligands (OAc or OR, R = Et, iPr),…‐ and the properties of the finalmaterial. 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 thesolution phase to the final product using transmission electron microscopy(TEM), x‐ray diffraction (XRD), and Energy Dispersive X‐ray (EDX) lateralmapping techniques. The starting solutions contain stoichiometric amounts ofthe metal 2‐(2‐methoxyethoxy)ethoxide components in2‐(2‐methoxyethoxy)ethanol and appear to be homogeneous by TEM with auniform distribution of particles having an average size of less than 40 â.Through elemental mapping we see elemental segregation in the hightemperature (950 °C) products, which are orthorhombic by XRD. In elementalmaps of gel samples fired to 700 °C, which are tetragonal by XRD, we alsosee elemental inhomogeneity within particles and phase zoning in maps ofproducts from finely ground gels. A comparison of elemental maps and x‐raydiffraction patterns of the products from gel processing and conventionalsolid state processing is made.

In attempt to ultimately control the characteristics of the PZT films, wehave decided to investigate some of the basic chemistry associated withthese solutions. Frequently, these solutions have been generated from GroupIV metal alkoxides in acetic acid (HOAc). Therefore, studies of the simple reactivity between M(OCHMe2)4 (M = Ti, Zr) and HOAc have beenundertaken. 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 (fromthe titanium reaction) in toluene and aged solutions as well.

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

The dyes oxazine 725, 7-acetoxy-4-methyl coumarin,O-4-methylcoumarinyl-N-[3-(triethoxysilyl)-propyl] carbamate and2′,7′-dichlorofluorescein were introduced during the acid-catalyzedcohydrolysis of various molar ratios of tetraethoxysilane (TEOS) and the gelmodifers, diethoxydimethylsilane (DEDMS) or diethoxymethylvinylsilane(DEMVS). The morphological features and optical absorption spectra of theresulting dye doped gels were followed during subsequent drying and heating.For DEDMS-TEOS molar ratios less than 1.375, gel cracking during drying wasa problem. DEDMS-TEOS molar ratios greater than 2.750 yielded opticallytransparent monoliths, but did not allow for sufficient incorporation of dyeto be useful. However, the functionalized dye,0-4-methylcoumarinyl-N-[3-(triethoxysilyl)-propyl] carbamate, appeared to besignificantly more soluble in such a highly modified matrix. Compared tomatrices derived from pure TEOS the DEDMS or DEMVS modified matricesprovided oxazine 725 doped with improved thermal stabilities. Finally, the2′,7′-dichlorofluorescein doped dimethylsiloxane-oxide matrix showed goodthermal stability in its optical properties, having significant opticalabsorption and little change in the wavelength of the absorption maximumafter heating to 300°C.

The synteses and structure of the three-dimensional perovskite LajCuTiOg aredescribed. In this oxide Cu and Ti atoms are disordered among octahedralsites. The introduction of oxygen vacancies by an adequate cationsubstitution leads to the induction of bidimensionality as well as anordered arrangement of cations and oxygen vacancies as found in the layeredoxides Ln2Ba2Cu2Ti2O11(Ln=La,Nd,Eu).

Hydrothermally derived films of BaTiCO3 were fabricated byreacting thin layers of titanium organometallic liquid precursors in aqueoussolutions containing Ba(OH)2 and having a high pH. Cubicsubmicron polycrystalline films of BaTiCO3 (thickness = 1 μm)were formed at 70°C. Low concentrations of block copolymers of polybutadieneand polystyrene were incorporated into the liquid precursor to preventprecursor film cracking. Higher polymer concentrations allowed fabricationof polymer/ceramic composite films by virtue of the low temperature used inhydrothermal processing.

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

The low temperature interdiffusion of superlattice reactants of the binarysystems niobium‐selenium and copper‐selenium and the ternarycopper‐niobium‐selenium were explored to synthesize amorphous reactionintermediates. Controlled crystallization of this intermediate, whichdepends upon nucleation energetics rather than the thermodynamic stabilityof the final product, was used as we attempted to prepare ternary niobiumcluster compounds. We present data demonstrating the ability to prepareamorphous ternary intermediates without the formation of crystalline binarycompounds as reaction intermediates. Crystallization of the amorphousintermediate 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 theself-polymerization of diglycidyl ether of bisphenol A in the galleries ofacidic alkylammonium ion exchanged forms of montmorillonite. The acidcatalyzed intragallery polymerization process leads to the spontaneousexfoliation to the 10Å-thick clay layers. Intra- and extragallerypolymerization processes are distinguishable by DSC.

Clay-polyimide hybrid composites have also been prepared by theintercalation of polyamic acid in montmorillonites and subsequent thermalconversion to polyimide. In contrast to the completely exfoliatedclay-polyether system, the polyimide system contain regularly intercalatedclay aggregates in the polymer matrix. Although regular face-face clay layeraggregation is extensive, the clay-polyimide hybrid composite films exhibitgreatly improved CO2 barrier properties.

The reaction of a wide variety of cyanometalate complexes of the generalform [M(CN)x]n- (where M= a transition metal ion) withsquare planar [PdCl4]2- in aqueous solution leads tothe formation of linear polymers. Polymerization occurs via substitution ofchloride ligands on the Pd(II) centers, by the nitrogen end of the cyanideligand to generate extended bridging cyanide structures. Upon generation atroom temperature polymer solutions of this type under go a sol-geltransition to generate robust hydrogels having water content in excess of95%. In the case of the cyanocobaltate/tetrachloropalladate gel, pyrolysisat 900°C produces ferromagnetic Pd/Co metallic alloys having novelmorphological character. Materials formed with a hydrogel having a 2:1 Pd toCo stoichiometry are found to be “sponge-like”. When placed in water, themetallic matrix swells becoming pliable and holding up to seven equivalentsof water per metal site. The conductivity and magnetic properties of thismaterial are maintained in the swollen state. Sintering of the Pd/Cohydrogel in air generates the layered oxide, PbCoO2 having adelafossite structure.

Thin films of ZrO2 and lead zirconate-titanate, PZT, about 100 to1000 nm in thickness, were prepared by electrophoretic deposition fromtransparent sols obtained by hydrolysis of metal alkoxides. Stainless steelplates and Pt-coated glass plates were used as substrates/electrodes. Theapplied field was up to 20 V/cm. The refractive indices of as dried filmswere higher than those of dip-coated films. High temperature oxidation ofstainless steel plates was suppressed by the ZrO2 coatings.Uniformity of the chemical composition of the as-dried PZT films, determinedby Auger electron spectroscopy, was better than the dip-coated PZTfilms.

The concept of tailored interfaces has been applied to the synthesis ofnano-scaled Y2O3/ZrO2 powders. Themicroemulsion technique as well as the thermodynamically controlled growthreaction have been utilized for this purpose. Both methods yieldedagglomerate 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 couldbe redispersed by treating them with tertiary amines in aqueoussolutions.

A commercially available water-soluble starch derivative was used as thesole organic precursor in the Liquid-Mix synthesis of mixed-cation oxidepowders and thin films. The acidified polymer (by nitric acid) was able tocomplex metal ions through the carboxylate ligands. Loosely agglomeratedfine powders as well as dense thin films of complex oxides have beenprepared using the same type of polymer. Oxide powders of Cr-doped lanthanumaluminate and yttrium aluminum garnet both crystallized in a single step,without forming any intermediate or second phases, when the amorphous resinintermediates were calcined at 650°C and 750°C for 2 hours, respectively. Itwas demonstrated that nitric acid could effectively reduce the viscosity ofthe 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 polymericsolution and heating at temperatures below 1000°C.

A three-step sol-gel process was developed to prepare organic dye-doped thinfilms with tailored porosity for applications in chemical sensing andoptoelectronics. Varying the acid- and base-catalyzed hydrolysis steps ofsols prepared from tetraethoxysilane with identical final H2O/Siratios, dilution factors and pH resulted in considerably differentdistributions of the silicate polymers in the sol (determined by 29Si NMR) and considerably different structures for thepolymer clusters (determined by SAXS). During film formation these kineticeffects cause differences in the packing and collapse of the silicatenetwork, leading to thin films with different refractive indices and volumefraction porosities. Under conditions where small pore-plugging species wereavoided, the porosities of as-deposited films could be varied by aging thesol prior to film deposition. This strategy, which relies on the growth andaggregation of fractal polymeric clusters, is compatible with the lowtemperature and near neutral pH requirements of organic dyes.

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

Poly(phenyleneterephthalamide) chains having carbonyl chloride end groupswere prepared by reacting a mixture of m- and p--phenylene diamines with terephthaloyl chloride, andwere then end-capped with aminophenyl-trimethoxysilane. The polymer thusprepared was used to synthesize a hybrid material in which it was chemicallybonded to a silica network produced in-situ by hydrolyzingtetramethoxysilane. Films prepared from this hybrid material were yellow buttransparent, and quite tough. The transparency of the films and theirmechanical strength were considerably improved relative to the correspondingsystems in which the inorganic network was not bonded to the organic phase.Tensile strength was found to increase initially with addition of silica butthen to decrease rapidly with further additions. Elongation at rupture alsodecreased after an initial small increase. A systematic increase in thetensile modulus and hardness with increase in the silica content and adecrease in water absorption were also observed. SEM analysis showed thatthe silica particle size depends on the silica content, and was 0.5 μm orless. These transparent ceramers were found to withstand tensile stressesthe order of 175 MPa and had thermal decomposition temperatures around 460 -475 ° C, and could thus be very useful in engineering applications at hightemperatures.

Scratch resistant transparent organically modified sol-gel materialstypically utilize organics as acrylates, or pre-polymer silicon or carbonbackbone material. The use of diepoxide monomers within a sol-gel matrix hasyet to be described as a means of obtaining high performance coatingmaterials. This paper describes the preparation and characterization of UVcurable inorganic-organic hybrid glass materials based on the incorporationof cycloaliphatic diepoxide monomers into a sol-gel composition of TEOS andthe epoxide silane coupling agent glycidoxypropyl-trimethoxysilane. Wereport aging and humidity studies along with processing conditions thataffect the silicate distribution and cationic cure of the diepoxide resinbased on solution and solid state NMR experiments. Mechanical analysis ofthin films prepared by varying processing conditions and length of thediepoxide backbone are also discussed.