Titanium isopropoxide was modified with acetylacetone in order to get stable photosensitive colloids via an hydrolysis-condensation process. The various steps of this process were followed by infrared, 1H and 13C NMR and X-Ray absorption (XANES and EXAFS). The latter techniques provided some interesting structural data (coordination of titanium, Ti-O and Ti-Ti distances) on the various species, from the precursor to the colloids. A structural model is proposed for each one, with a scheme of the different reactions occuring during the process.

Acid and base catalyzed alkoxide silica gels are studied by simultaneous DSC/DTGA under oxidizing and oxygen-free conditions and by intrared spectroscopy. The results are utilized to determine the composition of the dried gels and to estimate the extent of the net hydrolysis reaction. Our results suggest that, with sufficient water, condensation of partially hydrolyzed TEOS is the dominant reaction at high pH whereas, at low pH hydrolysis is rapid, relatively complete and precedes condensation. Thus the dry gels formed at high pH, with sufficient water, contain more alkoxy groups and fewer hydroxyl groups bound to Si than the dry gels formed at low pH.

The low temperatures involved in sol-gel processing have enabled organic and organometallic molecules to be incorporated in gel matrices. These molecules serve as optical probes to characterize gel chemistry and structure. The present paper describes the use of luminescence spectroscopy to detail matrix rigidity effects and protonation/deprotonation reactions during the sol-gel transition and subsequent aging processes. In separate experiments, the addition of a laser dye, rhodamine 6G, has enabled us to demonstrate lasing and optical gain in a silica gel.

Optical properties and durability of thin films are influenced by strain which can be evaluated from frequency shifts of the lattice phonon lines in measured Raman spectra. The response of titania samples to applied pressure is reported in this work. Anatase and rutile samples of thin films (sol-gel and sputter deposited) and bulk materials have been subjected to hydrostatic pressures approaching 100 kbar in a diamond anvil cell. Results indicate that the rutile samples exhibit similar responses to applied pressure. Anatase sol-gel films exhibit a pressure-dependent response that suggests that the sol-gel film is more compressible than the bulk material, and a pressure-induced phase transformation observed for the bulk material is inhibited in the anatase sol-gel film. The anomalous pressure response of the anatase sol-gel film may result from the film microstructure which has been shown by transmission electron microscopy to consist of spheres of crystalline TiO2 surrounded by microscopic voids.

A novel technique for accurately obtaining nitrogen adsorption isotherms on thin porous films has been developed. These isotherms are useful for characterizing the surface area and pore size distribution of porous samples. The sensitivity to adsorbed nitrogen is increased by several orders of magnitude over conventional techniques by forming the test film on the substrate of a surface acoustic wave (SAW) device. This device functions as a microbalance able to detect less than 100 pg/cm2 of film. Surface areas and pore size distributions calculated from adsorption isotherms obtained with this technique on silicate sol-gel films are compared to those for bulk samples prepared from similar sol-gel solutions.

The polarization mechanism of the low frequency dielectric relaxation (R1) observed in water adsorbed in porous silica gel is investigated using monolithic samples. It is attributed to electrode polarization involving proton hopping conduction. The influence of the thickness of the adsorbed water layer on the relaxation mechanism is discussed.

The hydrolysis of tetraethoxysilane was studied in an ethanol-water system with ammonium hydroxide catalyst. Reactions were carried out with water concentrations of 5M and 10M and ammonia concentrations up to 1.7M, and the products examined by electron optical methods. Variation of reagent concentrations lead to changes in the product morphology from small irregular particles, through roughly spherical and spherical particles to large fused particles. Within the range of particulate material the variations in size can be related to the effect of reagent concentrations by consideration of the reactions occurring. The effect on morphology of replacing ammonia with ethylamine was investigated and resembles that of the use of much higher ammonia concentrations.

The gelation reaction for tetraethoxysilane in both acid and base catalyzed environments was studied using cryogenic transmission electron microscopy. The evolution of the gel structure was observed in wet samples by the technique of fast-freeze vitrification, in which the three dimensional gel structure is preserved in vitreous solvent. The sample is then observed in the electron microscope using a cold stage. Samples were prepared and allowed to react until a specific point of gelation was reached, then were vitrified at that point. Results from this technique show a coarse network structure for base catalyzed gels. This network is composed of silica clusters ≈40Å in size. The acid catalyzed gels show an extremely fine texture (<10Å) at end point of gelation. The structures at intermediate stages of gelation were also determined.

A precipitation process has been developed to prepare precursor powders which can be calcined and sintered to form high critical temperature superconductors such as YBa2Cu3O7−x. Precursor powders are prepared using a continuous precipitation system in which a solution containing highly soluble salts of the desired metal cations is rapidly and completely mixed with a solution containing precipitating anions such as hydroxide and carbonate ions. The resulting amorphous powder can be calcined to form sub-micron particles of desired superconducting phases which are useful in preparing inks for the ink-jet printing of superconducting interconnects. The powders can be redissolved in organic solvents to form solutions which can be used in spin or dip coating substrates with thin superconducting films. Finally, the powders have been used to prepare bulk ceramics which exhibit the highest reported critical currents of any chem-prep ceramics. Bulk samples prepared from chloride doped precursors exhibit large, oriented grains and extensive flux pinning.

Conventional and chemical processing of the superconducting YBa2Cu3Ox ceramic powders are reviewed. Conditions for calcination, sintering and microstructural development are shown to be important considerations for the superconducting properties of YBa2Cu3Ox ceramics. We examine different forming techniques, e.g. dry pressing, hot pressing, tape casting and screen printing, to prepare superconducting components with different sizes, shapes and configurations. We also identify and discuss problem areas related to incomplete decomposition of BaCo3 precursor; oxidation of YBa2Cu3Ox ceramics; sensitivity of the YBa2Cu3Ox phase to water; reactivity of the YBa2Cu3Ox phase with substrates and co-firing materials; low critical current density in bulk ceramics of YBa2Cu3Ox and low mechanical strength of YBa2Cu3Ox ceramics.

A comparison of the use of three different coordination compounds of copper as precursors for the sol-gel synthesis of YBa2Cu3O7-δ has been made. For yttrium, the tris(isopropoxide) was used exclusively, while the use of both Ba(O-i-Pr)2 and Ba(OCH2CH2OEt)2 (prepared in situ from Ba metal) as sources for Ba were studied. After dissolving Y(O-i-pr)3, a Ba source, and the copper(I) alkoxide, [Cu(O-i-Bu)]4, hydrolysis led immediately to an orange gelatinous solid which yielded YBa2Cu3O7-δ upon firing in oxygen. Copper(II) acetate was found to give heterogeneous mixtures under our conditions and was not further studied. Copper(II) acac (acac = acetylacetonate) yielded the best results. Partially hydrolyzed solutions of Cu(acac)2, Ba(OCH2CH2OEt)2, and Y(O-i-pr)3 were spin coated on SrTi03 (100) and fired under oxygen to give oriented (b axis normal to the surface) thin films of YBa2Cu3O7-δ. The onset of superconductivity for the films was 92 K, but they did not reach zero resistance until much lower temperatures.

Y-Ba-Cu-o fine powders were prepared by coprecipitating in the oxalate form from metal nitrates solution. The stoichiometry of metals in the precipitate was adjusted by systematic change of copper nitrate (or yttrium nitrate) concentration for a fixed concentration of barium nitrate in the ruactant. Approximately one micron size powders, with a uniform size distribution, were obtained by this new approach. The optimum condition for calcination and sintering was studied by thermal gravimetric analysis(TGA), X-ray powder diffraction(XRD) and scanning electron microscopy(SEM).

The freeze-drying method of synthesizing powders of the superconducting oxide YBa2Cu3O7-δ is described. This process produces homogeneous, submicron powders of high purity. The effects of salt selection, solution concentration and pH on the process are described. Some evaluation of the sintering behavior and the effects on critical current density are included.

Bismuth containing oxide superconductors were first encountered in the BaPb1−xBxO3 perovskites [1]. In the the YBa2Cu3Ox family, bismuth was a possible substitute for yttrium and was attempted by us many months ago (and undoubtedly by many other groups) with the result that, under the necessary oxidizing conditions, BaBiO3 formed as a separate phase. Attempts to substitute bismuth into the La2−xSrxCuO4 family were reported [2], with the intriguing result of a 42K superconductor with T c higher than the previous 38K high for the family. A second paper [3] discussed the new compound “Bi2Sr2Cu7+δ, a = 5.32Å, b = 26.6Å, C = 48.8Å”, with TC of 7K to 22K; this was confirmed, but C = 24.4Å was found [4], and it is now clear that this compound is ideally Bi2Sr2CuO6+δ. A higher Tc than in BaPb1−xBixO3 was next detected in the Ba-K-Bi-O system [5]. Work at the Japanese National Research Institute of Metals [6] then disclosed T_ of as high as ∼ 105K in the Bi-Ca-Sr-Cu-O (BCSCO) system; both Ca and Sr must be present to produce these higher values.

We have been investigating the use of “tailored” organo-metallic precursors for the chemical vapor deposition (CVD) of thin films in an effort to open up new approaches to the low-temperature synthesis of ceramic, electronic, and optical materials that contain transition metals. Following our approach to the successful deposition of high-quality titanium carbide thin films at 150–250°C from tetraneopentyltitanium, we have extended this technique to the preparation of other carbides, such as ZrC, HfC, TaC, and WC, at temperatures some 1000°C lower than previous CVD methods from the metal halides and methane. The details of the thermolysis of the organometálico precursors are most consistent with a mechanism involving homolysis of M-C bonds to give alkyl radicals followed by C-C and C-H bond activation steps. Metal diboride thin films such as TiB2, ZrB2, and HfB2 can be prepared at ca. 250 °C by CVD of suitable tetrahydroborate precursors: Ti(BH4)3-(MeOCH2CH2OMe), Zr(BH4)4, and Hf(BH4)4. In these cases, the principal byproducts are hydrogen and diborane. Mirror-bright, adhesive thin films up to 2 μm thick can be grown on a variety of substrates including glass, steel, aluminum, copper, silicon, and graphite. Despite the amorphous nature of the films, their electrical resistivities are essentially identical with those of the bulk polycrystalline material.

Direct processes that may be used to manufacture high purity silicon nitride or silicon carbide are described. Elemental silicon has been found to react directly with liquid ammonia and amines at low temperature to yield compounds for both the ceramic and chemical industries. Silicon-amine direct reactions, previously thought not to occur, were investigated by using 29Si NMR, IR, UV, Raman, XRD, ICP, EDS and TGA methods to detect and characterize product formation. The [Si,N,H] and [Si,C,N,H] products transform to silicon nitride or silicon carbide respectively when heated above 1300°C.

Polymeric adducts, [B10H12L∼∼L]x, have been prepared by reaction of B10H14 with diphosphines and diamines. These show good promise as precursors whose pyrolysis can give either boron carbide (in the case of the diphosphine polymers) or boron carbonitride and boron nitride (in the case of the diamine polymers).

A series of polymeric materials was prepared through the condensation of t ri ethyl borane or tris(dimethylamino)borane with polyfunctional amines. The amines examined and the ceramic yields of the corresponding condensation products after pyrolysis under vacuum at 800°C were as follows: Methylene dipyrazole – 52%, o-phenylenediamine – 85%, 3,3’ diaminobenzidine – 59% and diethylenetriamine – 12%. Volatile products evolved in the pyrolyses were identified and the solid residues characterized by chemical analyses and spectroscopie means.

Reactions of (Me3Si)3 AI·Et2O with NH3 in different stoichiometric ratios have been studied in search of useful precursors to AIN. Two molecular condensation-elimination compounds and an insoluble oligomer have been obtained from these reactions, and pyrolysis of the compounds leads to the convenient formation of AlN/SiC solid solutions.

Solid solutions of SiC and AIN have been prepared by the co-pyrolysis of polysilanes and organoaluminum amides. In the presence of ammonia. Si3N4 and AIN are formed. These materials are fully characterized by TEM, SAD, SEM, XRPD, and elemental analyses. The influence of reaction conditions, as well as precursor properties and reactivity, on the composition and morphology of these materials is addressed.