Several routes to mixed-metal Bi-Ti species have been investigated. Theinertness of bismuth alkoxides Bi(OR)3 (R = Et, iPr) toward theirtitanium analogs could be overcome by controlled microhydrolysis of Bialkoxides. The first mixed-metal species based on bismuth, BiTi2O(OiPr)9, has thus been isolated andstructurally characterized.

Coatings of Bi4Ti3O12 have been depositedon silicon wafers by using the gels derived from Ti and Bi2-methoxyethoxides solutions.

Ferroelectric (FE) films, especially PZT films, have received increasingattention for microelectronics applications such as FE memory and in highdensity DRAM's. While rare earth doped PbTiO3 ceramics has beenstudied for SAW and piezoelectric applications, rare earth-doped filmsseldom have been systematically explored. A series of sol-gel derived PbTiO3 films with varying amounts (5-15 mole %) of rare earths(such as, Nd, Sm, Tb, Dy, Er ,Yb and La ) have been prepared using acetatesand alkoxides as precursors. The solutions were spin coated onto platinizedSi wafers. The effects of the type and amount of rare incorporation on thephase assembly and microstructure have been quantified. The results ofdielectric characterization (e.g., dielectric constant, dissipation factorand leakage currents) and FE behaviors (viz remanent polarization, andcoercive field) are presented; these films exhibited low leakage currents(3E-10 A/cm2) and much higher dielectric constant (up to 525)compared to undoped PbTiO3 films.

Microstructural changes in sol-gel derived SrxBa1-xNb2O6 (SBN) thinfilms were monitored as a function of chemical variations in the precursorsol and of processing variations of the thin films. 6000À Sr0.5Ba0.5Nb2O6 thin filmswere deposited from different alkoxide based precursors under varioushydrolysis conditions. The tetragonal tungsten bronze structure was achievedin films at temperatures on the order of 700°C. Preferential (001)orientation of the tetragonal lattice was found to be very dependent uponthe substrate orientation as well as thermal treatment schedule.Transmission electron microscopy (TEM) was used to examine the filmmicrostructure. Orientational effects were verified by TEM as well as atendency for a porous structure in the alkoxide derived films. Substrate andprocessing dependent grain size and size distributions were also noted.

The present work deals with the effect of the rare earth nature and thecontent of the oxide dopants on the stabilization process of zirconia basedceramics. There are two main interests in our work. The first is to verifythe possibility of stabilizing a cubic structure of zirconia using a naturalmixture of rare earth elements as dopant, and second, to study and tocharacterize its basic physical-chemical properties such as phase diagrams,zirconia stabilization models and dopant distribution.

Barium titanate ceramics have been obtained by sol-gel methods. Thedielectric investigations of these materials revealed the existence ofdiffuse ferroelectric transitions. By using a phenomenological model, wecould demonstrate the existence of a simple relationship between the diffusecharacter of the transition and the sample grain-size. This effect has beenattributed to interactions between charged defects on the grain surfaces andthe spontaneous polarization of the material.

The synthesis of transparent hybrid organic-inorganic coatings obtained fromcondensation between alkoxysilane containing grafted dyes (azo dyes orphthalocyanines) and metal alkoxides precursors has been performed. The Red17 azo dye, known for its high second order polarisability, was bonded tothe silicon oxide network following two procedures: a silylation reactionbetween Red 17 and triethoxysilane; a coupling reaction between Red 17 and3-isocyanatopropyltriethoxysilane. Silicon phthalocyanines (known for theirthird order polarisability and inverse saturable absorption properties) wereincorporated into the silicon oxide network by a silylation reaction.Phthalocyanine doped transparent hybrid organic-inorganic coatings wereobtained from condensation between diethoxymethylsilane and zirconiumpropoxide precursors.

Ethylene diamine tetra-acetic acid (EDTA) doped silica gels were made by thesol-gel process for the potential application as a filter for heavy metalions in wastewater. The behavior of the organic molecule in the matrix wasstudied by investigating the percentage of EDTA leached out with a variationin the timing of addition of the EDTA molecule into the starting silica gelsolution. Leach tests using water as the medium were performed for 2, 12 and24 hours in order to determine the amount of EDTA trapped in the pores or inthe matrix. A minimum amount of EDTA leached from the gels was detected inthe samples to which EDTA was added 4 hours after initial hydrolysis ofTEOS. This result was correlated to having a greater percentage of porevolume in the range of 15–20 Å, which was further substantiated with densitymeasurements. The physical changes in the silica matrix altering the porevolume distribution were attributed to the addition of the water into whichthe EDTA molecule was initially dissolved.

The sol-gel process can be used to produce porous inorganic matrices thatare doped with organic molecules. These doped gels can be used as aquantitative method for the spectrophotometric determination of traceconcentrations of metallic ions. For the detection of hexavalent chromium,malachite green was used as the dopant. Preliminary results indicateconcentrations on the order of 5 ppb are detectable using this method.

The oxygen-ion conductor 0.88ZrO2-0.12Sc2O3has a discontinuous change in ion conductivity at about 660°C. This changeaccompanies the structural transition from rhombohedral to cubic phase.Since the high temperature cubic phase shows large ion conductivity, it isof interest to examine whether or not the cubic phase stabilizes in the lowtemperature region by another dopant . By adding only 0.005 mole % La2O3, the cubic phase is stabilized below about500 °C without any loss of conductivity compared with 0.88ZrO2-0.12Sc2O3. The ion conductivityof cubic stabilized ZrO2-Sc2O3-La2O3system is around 1×10-1 S/cm at 800°C. Cubic phase stabilizationusing second dopant in a ZrO2-Sc2O3 systemled to the finding of a fast oxygen-ion conductor in the ZrO2-Sc2O3-La2O3system.

Etherolysis of metal chlorides offers a versatile, simple nonhydrolyticsol-gel route to transition metal oxides. The main limitation of the processresults from the insolubility of some metal chlorides in non aqueoussolvents. The general tendency of this nonhydrolytic process is to delaycrystallization of metal oxides.

A nonhydrolytic sol-gel route to aluminosilicates is proposed which avoidsthe problems associated with different hydrolysis rates for the precursors.Two pre-mullite gels (Al2O3/SiO2=3/2) wereprepared in two different ways. The conversion to mullite was studied as aprobe for chemical homogeneity. The results indicate that a monophasicprecursor (i.e. homogeneous at the atomic level) may be easily obtained byetherolysis of a mixture of SiCl4 and AlCl3.

Two silicon oxycarbide glasses with different compositions (O/Si ratio 1.2and 1.8) were prepared by pyrolysis at moderate temperature (900 °C) ofpolysiloxane precursors. Their structure was investigated using quantitative 29Si solid-state NMR and X-ray photoelectron spectroscopy(XPS). The environment of the silicon atoms in the oxycarbide phasecorresponded to a purely random distribution of Si-O and Si-C bondsdepending on the O/Si ratio of the glass only and not on the structure ofthe precursors. At the light of the NMR results, the Si2p XPS spectra of theglasses may be interpreted using the contribution of the five possible SiOxC4-x tetrahedra. The Clsspectra of these glasses indicated the presence of oxycarbide carbon in CSi4 tetrahedra, similar to carbidecarbon, and graphitic-like excess carbon.

The rheology of gelcasting slurries of concentrated (30 - 60 vol%) alumina,zirconia, silicon nitride, and sialon powders with isoelectric pointsvarying between pH 5 and 9, was studied by measuring the viscosity and yieldstress as functions of pH. Typically, the rheology is non-Newtonian. Thelowest values of viscosity and yield stress that permit the highest solidsloading were obtained at high and low pH values, where the powders arecolloidally stable, far from the isoelectric points. This relationshipapplies whether or not a polymer dispersant is present. The acrylamidemonomer which is used in gelcasting slurries, lowers these non-Newtonianproperties permitting the preparation of more concentrated slurries. Fluidand pourable gelcasting slurries of each powder had apparent viscosities andyield stresses less than 2.0 Pa·s and 50 Pa, respectively.

The hydrolysis and condensation reactions of three trifunctional siliconalkoxides, R-Si(OEt)3, with various R alkyl chains (R = CH3, C2H5, C8H17),was followed by 29Si and 1H Nuclear MagneticResonance. The condensation reactions are faster for methyltriethoxysilaneand the degree of condensation of the system is higher. The other twosystems have similar behaviors during the first hours, with lowest degree ofcondensation. The condensation reactions slow down for theoctyltriethoxysilane, due to the presence of the long alkyl chains whichprevent condensation reactions between oligomeric species. The influence ofthe addition of tetraethoxysilane (TEOS) was studied: for all three systems,the degree of condensation of the network is higher, indicating the role ofcross-linking played by TEOS.

Rotational motion of cyclohexane in the liquid and the solid plastic phaseis studied using Raman light scattering. The results are compared withmolecular dynamics simulations run for model pores of diameters similar tothose used in the experiment. The presence of the surface layer and itseffect on the relaxation times is discussed. The temperature of thesolid-solid phase transition is determined from the analysis of the ν21 band shape. It is shown that the depression of the cubicto monoclinic phase transition depends on the pore diameter and is differentfor modified and unmodified surfaces. It is suggested that molecules nearthe pore walls form the amorphous structure and only molecules near thecenter of the pore form crystallographic structure.

Valuable mechanistic information, about the reaction pathway in theformation of the 2223 phase, has been obtained by the use of a solutionsynthesis route. The presence of lead in the starting mixture has remarkableeffects on the nature and stability of the different intermediates: i) thegrain size and morphology of Bi2CuO4 is severelychanged, ii) calcium carbonate is partially decomposed to yield the calciumplumbate, iii) the 2201 phase results stabilized against the formation ofthe collapsed phase Bi17Sr16Cu7O49-δ, iv) themelting point of the intermediate 2212 is lowered by about 10 °C. All theseeffects, due to lead substitution, contribute to promote the formation ofthe 2223 phase, controlling also the morphology and properties of the finalproduct.

The new metal-ferrite composite [Fe0.2Co0.8]0.8[Fe2.38Co0.62O4]is obtained by precipitation of ferrous and cobalt chloride in KOH. Furtherheating under vacuum above 400°C shows a cationic exchange between metal andspinel leading to a new composite made up of cobalt metal and cobalt dopedmagnetite.

HTERM and EDX observations have been carried out on both composites, i.e.,before and after vacuum annealing, We show that cationic exchange occursmainly in crystals made up of spinel, CoO and amorphous nanoparticles.

Several biphasic VOP04/(VO)2P2O7redox partners seem to be active in the catalytic cycles involved in themild oxidation of simple hydrocarbons to maleic anhydride. The present X-raytime resolved thermal-diffractometric study reveals the existence of a newanhydrous variety of the oxidized form, ω-VOPO4, which may appearas an intermediate in the formation of the well known β-VOPO4.This new phase only remains well crystallized at relatively hightemperatures, and when it is allowed to cool down in wet air VOPO4·2H2O results. In turn, another well definedphase, VOPO4·1.58H2O, can be recognized in the courseof the hydration process.

Organically modified silicates (ormosils) of high hardness were prepared bythe reactions of tetraethoxysilane (TEOS) and polydimethylsiloxane (PDMS)aided by ultrasonic irradiation. The mechanisms leading to the hard ormosilformation were investigated by liquid state 29Si NMRspectroscopy. PDMS chains were found to be broken into shorter chains and/or4-membered siloxane rings during the reaction and finally, all PDMS chainswere chemically incorporated as short chains into silica networks. Vickershardnesses of the hard ormosils were measured and compared with those of thehardest transparent plastics. Whereas the hardest transparent plastics haveVickers hardness values of less than 25 kg/mm2, the hard ormosilshave Vickers hardnesses up to higher than 150 kg/mm2. Atheoretical model was developed for the calculation of Vickers hardnesses ofthe hard ormosils and agreed well with experimental results. Predictionsbased on this theory indicate that even harder ormosils can be made when Al2O3, ZrO2 and TiO2 aresubstituted for SiO2. Results based on these new ormosils arealso presented.

Active-filler-controlled-polymer-pyrolysis has recently been reported as anovel processing route for preparing near-net shape bulk ceramic compositematerials. Active fillers, like Ti or Si powders, may react with solid orgaseous decomposition products of the polymer or with the heating gasatmosphere. In this study, a mixture of silicone resin (GE SR350) and Sipowder was heated at temperatures up to 1430°C in Ar or N2. Afterthe highest temperature firing, the resulting material was primarilycomprised of SiC and SiOC when the heating was performed in Ar, or of SiOC,SiC, Si3N4 and Si2N2O when theheating was performed in N2. The evolution of the microstructureof the ceramic composite was followed by DTA-TGA, FT-IR and XRD.