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

Coatings of Bi4Ti3O12 have been deposited on silicon wafers by using the gels derived from Ti and Bi 2-methoxyethoxides solutions.

Ferroelectric (FE) films, especially PZT films, have received increasing attention for microelectronics applications such as FE memory and in high density DRAM's. While rare earth doped PbTiO3 ceramics has been studied for SAW and piezoelectric applications, rare earth-doped films seldom 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 acetates and alkoxides as precursors. The solutions were spin coated onto platinized Si wafers. The effects of the type and amount of rare incorporation on the phase assembly and microstructure have been quantified. The results of dielectric characterization (e.g., dielectric constant, dissipation factor and leakage currents) and FE behaviors (viz remanent polarization, and coercive 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) thin films were monitored as a function of chemical variations in the precursor sol and of processing variations of the thin films. 6000À Sr0.5Ba0.5Nb2O6 thin films were deposited from different alkoxide based precursors under various hydrolysis conditions. The tetragonal tungsten bronze structure was achieved in films at temperatures on the order of 700°C. Preferential (001) orientation of the tetragonal lattice was found to be very dependent upon the substrate orientation as well as thermal treatment schedule. Transmission electron microscopy (TEM) was used to examine the film microstructure. Orientational effects were verified by TEM as well as a tendency for a porous structure in the alkoxide derived films. Substrate and processing dependent grain size and size distributions were also noted.

The present work deals with the effect of the rare earth nature and the content of the oxide dopants on the stabilization process of zirconia based ceramics. There are two main interests in our work. The first is to verify the possibility of stabilizing a cubic structure of zirconia using a natural mixture of rare earth elements as dopant, and second, to study and to characterize 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. The dielectric investigations of these materials revealed the existence of diffuse ferroelectric transitions. By using a phenomenological model, we could demonstrate the existence of a simple relationship between the diffuse character of the transition and the sample grain-size. This effect has been attributed to interactions between charged defects on the grain surfaces and the spontaneous polarization of the material.

The synthesis of transparent hybrid organic-inorganic coatings obtained from condensation between alkoxysilane containing grafted dyes (azo dyes or phthalocyanines) and metal alkoxides precursors has been performed. The Red 17 azo dye, known for its high second order polarisability, was bonded to the silicon oxide network following two procedures: a silylation reaction between Red 17 and triethoxysilane; a coupling reaction between Red 17 and 3-isocyanatopropyltriethoxysilane. Silicon phthalocyanines (known for their third order polarisability and inverse saturable absorption properties) were incorporated into the silicon oxide network by a silylation reaction. Phthalocyanine doped transparent hybrid organic-inorganic coatings were obtained from condensation between diethoxymethylsilane and zirconium propoxide precursors.

Ethylene diamine tetra-acetic acid (EDTA) doped silica gels were made by the sol-gel process for the potential application as a filter for heavy metal ions in wastewater. The behavior of the organic molecule in the matrix was studied by investigating the percentage of EDTA leached out with a variation in the timing of addition of the EDTA molecule into the starting silica gel solution. Leach tests using water as the medium were performed for 2, 12 and 24 hours in order to determine the amount of EDTA trapped in the pores or in the matrix. A minimum amount of EDTA leached from the gels was detected in the samples to which EDTA was added 4 hours after initial hydrolysis of TEOS. This result was correlated to having a greater percentage of pore volume in the range of 15–20 Å, which was further substantiated with density measurements. The physical changes in the silica matrix altering the pore volume distribution were attributed to the addition of the water into which the EDTA molecule was initially dissolved.

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

The oxygen-ion conductor 0.88ZrO2-0.12Sc2O3 has a discontinuous change in ion conductivity at about 660°C. This change accompanies the structural transition from rhombohedral to cubic phase. Since the high temperature cubic phase shows large ion conductivity, it is of interest to examine whether or not the cubic phase stabilizes in the low temperature region by another dopant . By adding only 0.005 mole % La2O3, the cubic phase is stabilized below about 500 °C without any loss of conductivity compared with 0.88ZrO2-0.12Sc2O3. The ion conductivity of cubic stabilized ZrO2-Sc2O3-La2O3 system is around 1×10-1 S/cm at 800°C. Cubic phase stabilization using second dopant in a ZrO2-Sc2O3 system led to the finding of a fast oxygen-ion conductor in the ZrO2-Sc2O3-La2O3 system.

Etherolysis of metal chlorides offers a versatile, simple nonhydrolytic sol-gel route to transition metal oxides. The main limitation of the process results from the insolubility of some metal chlorides in non aqueous solvents. The general tendency of this nonhydrolytic process is to delay crystallization of metal oxides.

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

Two silicon oxycarbide glasses with different compositions (O/Si ratio 1.2 and 1.8) were prepared by pyrolysis at moderate temperature (900 °C) of polysiloxane 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 phase corresponded to a purely random distribution of Si-O and Si-C bonds depending on the O/Si ratio of the glass only and not on the structure of the precursors. At the light of the NMR results, the Si2p XPS spectra of the glasses may be interpreted using the contribution of the five possible SiOxC4-x tetrahedra. The Cls spectra of these glasses indicated the presence of oxycarbide carbon in CSi4 tetrahedra, similar to carbide carbon, and graphitic-like excess carbon.

The rheology of gelcasting slurries of concentrated (30 - 60 vol%) alumina, zirconia, silicon nitride, and sialon powders with isoelectric points varying between pH 5 and 9, was studied by measuring the viscosity and yield stress as functions of pH. Typically, the rheology is non-Newtonian. The lowest values of viscosity and yield stress that permit the highest solids loading were obtained at high and low pH values, where the powders are colloidally stable, far from the isoelectric points. This relationship applies whether or not a polymer dispersant is present. The acrylamide monomer which is used in gelcasting slurries, lowers these non-Newtonian properties permitting the preparation of more concentrated slurries. Fluid and pourable gelcasting slurries of each powder had apparent viscosities and yield stresses less than 2.0 Pa·s and 50 Pa, respectively.

The hydrolysis and condensation reactions of three trifunctional silicon alkoxides, R-Si(OEt)3, with various R alkyl chains (R = CH3, C2H5, C8H17), was followed by 29Si and 1H Nuclear Magnetic Resonance. The condensation reactions are faster for methyltriethoxysilane and the degree of condensation of the system is higher. The other two systems have similar behaviors during the first hours, with lowest degree of condensation. The condensation reactions slow down for the octyltriethoxysilane, due to the presence of the long alkyl chains which prevent condensation reactions between oligomeric species. The influence of the addition of tetraethoxysilane (TEOS) was studied: for all three systems, the degree of condensation of the network is higher, indicating the role of cross-linking played by TEOS.

Rotational motion of cyclohexane in the liquid and the solid plastic phase is studied using Raman light scattering. The results are compared with molecular dynamics simulations run for model pores of diameters similar to those used in the experiment. The presence of the surface layer and its effect on the relaxation times is discussed. The temperature of the solid-solid phase transition is determined from the analysis of the ν21 band shape. It is shown that the depression of the cubic to monoclinic phase transition depends on the pore diameter and is different for modified and unmodified surfaces. It is suggested that molecules near the pore walls form the amorphous structure and only molecules near the center of the pore form crystallographic structure.

Valuable mechanistic information, about the reaction pathway in the formation of the 2223 phase, has been obtained by the use of a solution synthesis route. The presence of lead in the starting mixture has remarkable effects on the nature and stability of the different intermediates: i) the grain size and morphology of Bi2CuO4 is severely changed, ii) calcium carbonate is partially decomposed to yield the calcium plumbate, iii) the 2201 phase results stabilized against the formation of the collapsed phase Bi17Sr16Cu7O49-δ, iv) the melting point of the intermediate 2212 is lowered by about 10 °C. All these effects, due to lead substitution, contribute to promote the formation of the 2223 phase, controlling also the morphology and properties of the final product.

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

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

Several biphasic VOP04/(VO)2P2O7 redox partners seem to be active in the catalytic cycles involved in the mild oxidation of simple hydrocarbons to maleic anhydride. The present X-ray time resolved thermal-diffractometric study reveals the existence of a new anhydrous variety of the oxidized form, ω-VOPO4, which may appear as an intermediate in the formation of the well known β-VOPO4. This new phase only remains well crystallized at relatively high temperatures, and when it is allowed to cool down in wet air VOPO4·2H2O results. In turn, another well defined phase, VOPO4·1.58H2O, can be recognized in the course of the hydration process.

Organically modified silicates (ormosils) of high hardness were prepared by the reactions of tetraethoxysilane (TEOS) and polydimethylsiloxane (PDMS) aided by ultrasonic irradiation. The mechanisms leading to the hard ormosil formation were investigated by liquid state 29Si NMR spectroscopy. PDMS chains were found to be broken into shorter chains and/or 4-membered siloxane rings during the reaction and finally, all PDMS chains were chemically incorporated as short chains into silica networks. Vickers hardnesses of the hard ormosils were measured and compared with those of the hardest transparent plastics. Whereas the hardest transparent plastics have Vickers hardness values of less than 25 kg/mm2, the hard ormosils have Vickers hardnesses up to higher than 150 kg/mm2. A theoretical model was developed for the calculation of Vickers hardnesses of the hard ormosils and agreed well with experimental results. Predictions based on this theory indicate that even harder ormosils can be made when Al2O3, ZrO2 and TiO2 are substituted for SiO2. Results based on these new ormosils are also presented.

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