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Single and multilayer sol-gel thin films of Ti02-PbO, Ti02-Bi203 and Ti02-CeO2 composition were deposited on glasses using the dip coating technique. The precursors included Ti(OPri)4 chemically modified by acetyl acetone and diluted in PriOH and sols of Pb(OAc)2, Bi(NO3)3 5H20 diluted in acetic acid. The Ti02-Ce02 sol was prepared by mixing Ce NH2 (NO3 )6 in ethanol and then adding Ti (O-iso-C3H7 )4. Structure texture and homogeneity of their main constituants was established by XRD, XPS,SIMS and SEM-EDX techniques as a function of heat treatments.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A three dimensional (3D) Electron Paramagnetic Resonance Imaging (EPRI) method has been developed to probe the structure and size of pores in ceramic materials. A computer control current source and magnetic field gradient coil assembly were added on the conventional EPR instrument as imaging devices. This added-on facility was tested using a phantom sample having cavities filled with DPPH (2,2-diphenyl-1-picrylhydrazyl) particles. Pumice was then used to demonstrate the feasibility of the technique. Porous pumice stone was immersed in a 0.5mM 15N-PDT-water solution to introduce the spin labels into the open volume of the sample. A two-dimensional image was reconstructed from a set of 1-D projections using a filtered back-projection technique. A three-dimensional image was derived from 22 2-D images each constructed by 22 1-D projections. At present, the facility allows a resolution of 69 and 46 μm for 2-D and 3-D imaging.

Yttrium methoxyethoxide, barium methoxyethoxide and various copper(II) alkoxide groups were used as precursors for the formation of YBa2Cu3O7-δ stable sols in a 2- methoxyethanol / methyl ethyl ketone / toluene / diisopropyl ketone solvent system. Sol fractal dimensions were varied with the sol concentration and with the addition of pyridine. Strong correlation was found between the wettability and the fractal dimensions of the various precursors as determined by contact angle measurements. YBa2Cu3O7-δ thin films were deposited on sapphire substrates using a dip-coating technique. The films were fired at 850°C under flowing oxygen or an ozone/oxygen mixture. Although the ozonetreatments helped in the formation of single YBa2Cu3O7-δ phase, they contributed to extensive cracking in the films. The different copper(II) alkoxide precursors had little effect on final film microstructure.

Alkoxide sol-gel processing of Y1Ba2Cu3O7-x was performed using copper(II) ethoxide, barium methoxyethoxide, and yttrium methoxyethoxide precursors in a methoxyethanol/methy ethyl ketone/toluene solvent system. In situ neutron diffraction experiments were performed on individual precursors and mixed component gels during heat treatment. Phase development and consumption was observed for both the calcination and annealing segments of the heat treatment. Formation of Y1Ba2Cu3O7-x was observed as early as 700°C. CuO, Cu2O, BaCuO, YCu2O5, BaCO3, BaCO4, and YlBa2Cu3O7-x were observed during the conversion/ consolidation reactions to 850°C.

An alkoxide Sol-Gel system was developed to produce bulk powders of the TI2Ca1Ba2Cu2O8+x high Tc superconducting phase. Methoxyethoxide and Cu(II) ethoxide precursors were used for the formation of homogeneous sols. Solubility of the Cu(II) ethoxide was aided by using a 2-methoxyethanol/methyl ethyl ketone/toluene solvent system. The sols were characterized by small angle x-ray scattering (SAXS) and TEM. Powders were produced by rotary evaporation followed by thermal treatment in a closed container with thallium metal present at 900°C for various calcination times. Powders were characterized by x-ray diffraction, resistivity and magnetic susceptibility measurements, and chemical analysis. Samples exhibited transition onsets between 100 and 110K depending upon the processing conditions.

Texturing in 123 superconductors prepared by citrate-gel method is studied against pressure and MgO whiskers seedingg. A plateau of texturing has been observed at about 340 MPa, while improvement through MgO whiskers incorporation was not significant.

Effects of the fusion temperature and cooling rate on the concentration of the E1 centers in GeO2 glass are studied using EPR and optical methods.

The 9.5 and 35 GHz spectra of GeSx-glasses with x = 1.25−2.01 synthesized in evacuated Vycor ampules between 683°C and 895°C exhibit a symmetric narrow line (A-component: geff = 2.003, ΔHpp (9.5 GHz) = 3 G, ΔHeff (35 GHz) = 4.8 G) and an asymmetric broader resonance (B-component: X-Band, geff = 2.0112, ΔHpp = 16.25 G, Q-band: geff = 2.0045, ΔHpp = 11 G). The line width of the A- and B-components was measured between 10 K and 300 K. For the A component the ΔHpp versus temperature of measurements, TM, and ln(ΔHpp) versus T M − 1 4 plots were best fitted assuming two straight lines in the ranges from 34 K to 160 K and from 160 K to 300 K. The line width of the B-component is invariant with temperature of measurements from 10 K to 300 K. On the basis of the frequency and temperature behavior of these lines we suggest that the A-component is due to a paramagnetic electron hopping between different sites and attribute the B-component to conduction electrons in Ge rich regions in the glass.

Electron-spin-resonance(ESR)-spectra of unirradiated and 60Co γ-ray irradiated GeO2SiO2-fiber optic preform materials, densified (sintered) at 1550°C and 1625°C in air and in vacuum (10−6 Torr) for 75 min., were measured at 9.5 and 35 GHz and room temperature. The spectra of unirradiated preforms, densified in vacuum exhibit an asymmetric line due to the GeO2-E1′-center, [Ge(3)]. After irradiation the Ge(0)- and Ge(2)-germanium E1′ centers were observed with concentrations which depend upon the densification conditions. The Ge(0) center was observed in air as well as in vacuum sintered preform material. The Ge(2) center was observed only in vacuum densified preform material. Saturation of the defect center concentration is obtained at about 6 × 105 R. The total defect center concentration at constant irradiation dose increases with increasing temperature of densification [c(1625°C,air) = 724 × 1015 spins/g, c(1550 °C, air) = 330 × 1015 spins/g]. The defect center concentrations obtained in materials densified at 1550°C in air and in vacuum are equal within experimental errors.

Gamma-ray induced paramagnetic centers were detected at 9.5 GHz and 300 K in supercritically dried 94 SiO26 GeO2 gels after heat treatment at 462°C. The ESR-spectrum of the gel consisted of a narrow (Hpp = 1.6 G, geff = 2.003) and an asymmetric (g1 = 2.001, g2 = 1.995, and g3 = 1.994) line. The asymmetric line was attributed to the Ge-E1′-center. The defect center generating the narrow line has not been identified yet. The supercritically dried gels after heat treatment (TH) at 1000, 1150, and 1280°C were also exposed to γ-ray irradiation. In the gel with TH = 1000°C, the Ge-E1′-center and the Ge(1)-center were detected. An increase in the densification temperature of 150°C (from 1000°C to 1150°C) causes the disappearance of the Ge-E1′-center. At TH = 1150 and 1280°C the signal of the Ge(1)-defect center dominated the ESR-spectra of these samples. The Ge(1)-defect center was described by an electron trapped by a germanium atom co-ordinated through bridging oxygens to two silicon and one germanium atoms.

An alkoxide sol-gel chemistry has been developed to form superconducting Y 1 Ba 2 Cu 3 O 7− x thin films and bulk powders. The Cu(II) ethoxide synthesis and processing steps used to obtain a homogeneous Y-Ba-Cu sol are specifically outlined. Sols were produced using two different solvent systems: toluene and methoxyethanol/methylethylketone. Both systems promote complexation of insoluble Cu(II) ethoxide with the barium and yttrium precursors allowing the formation of nanometer-sized sols. Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were used to characterize the gel decomposition and oxide formation processes. The toluene system produced gels having a crystallization temperature of 425°C while the methoxyethanol/methylethylketone processed gel crystallized at 500°C. The methoxyethanol/methylethylketone gel had essentially complete organic by-product oxidation by 475°C. Films produced on single-crystal SrTiO 3 (for both systems) showed a high degree of orientation and crystal growth.

Paramagnetic resonance spectra of virgin glasses and γ‐ray irradiated GeO2 glasses were studied with the electron spin resonance (ESR) method as a function of fusion temperatures. Fusions were made in air at temperatures between 1200 and 1650 °C and cooled at constant rate. In virgin glasses, only the E′ center was detected at concentrations of about 1015/g. After a γ‐ray irradiation, a new resonance at the low‐field side (lfs) of the E′1 center and a symmetric line with g=1.91 were observed. Measurements at various temperatures, power levels, and frequencies provide a basis for resolving the overlapping resonances. We labeled the paramagnetic center causing the lfs signal the H0 center. The g values of the H0 center are the basis for attributing this center to a hole located on a nonbridging oxygen. The g=1.91 resonance is attributed to Cr5+ or M5+0 impurities in the GeO2 glasses. At constant γ‐ray dose, the H0 center concentration decreased and the E1 ‐center concentrations increased with increase of fu...

SiO2 gels produced by 4 and 16 mol water/mol Si(OC2H5)4 [TEOS] were densified at 1000°C and then exposed to γ-ray irradiation in order to produce paramagnetic defect centers. The paramagnetic defect centers detected in the sol-gel (n = 4,16) glasses depend on the mol H2O/mol TEOS ratio (n = 4,16) of the gels from which they wer derived. In the n = 16 sol-gel glass three different O2− ions were detected while in the n = 4 sol-gel glass the E′ center and the CO2− radical were observed. Some of these paramagnetic states were not found in the SiO2 glasses produced by the oxide melting techniques. These differences may suggest structural differences between the structures of the SiO2 glasses produced by the sol-gel and oxide melting techniques.

The 9.5 GHz ESR-spectra of gamma-ray irradiated SiO 2 vacuum dried gels, produced with 2, 4, 8 and 16 mol. of water per mol. tetraethylorthosilicate (TEOS) and gels heat treated at temperatures between 400°C and 1000°C were recorded at 77 K and 300 K. A broad asymmetric line ( ΔH pp = 20.5 G, g eff = 2.006) dominated the room temperature spectra of the dried gels. The ESR-spectra of these gels recorded at 77 K consist of a well resolved characterized by g 1 = 2.004, g 2 = 2.01 and g 3 = 2.04. We tentatively attribute this resonance to O 2 − -ions. The resonance of this O 2 − -specie dominates the spectra of the gels treated up to 500°C. The spectrum of the vacuum dried gel heat treated at 900°C exhibits the resonance of the E 1 ′ -center and non-bridging oxygens. The spectrum of the gel heat treated at 1000°C is composed of several lines attributed to O 2 − radicals having different ligand fields.

The fusion temperature (Tφ), the oxygen partial pressure (PO2) during melting and the quenching rate from Tφ all influence the optical absorption in the 5.06‐eV (245‐nm) region. These observations are consistent with the assumption that the defect responsible for the optical absorption is an oxygen vacancy or complex of vacancies. The activation energy for the formation of the defect in GeO2 glasses which is repsonsible for the optical absorption is 2.3 eV which is larger than the activation energy for oxygen diffusion (∼1 eV).

ESR-studies were conducted at 9.5 GHz on GeS 2±x glasses (x=0,0.1). Glasses were melted at 683°C, 789°C and 895°C in Vycor tubes which were evacuated and sealed before fusion. The ESR-spectra of the virgin glasses are characterized by a narrow symmetric (g=2.0037, Δ H pp =3G, A-component) and a broad asymmetric line (g=2.0113, Δ H pp =17G, B-component). The narrow line was not detected in the GeS 2±x glasses fused at 895°C and in the GeS 2.1 glass fused at 796°C. The narrow line intensity of the sulfur deficit glass is approximately two times the corresponding intensity of the stoichiometric and sulfur excess glass. The intensity of the asymmetric line is negligibly small in the GeS glasses fused at 638°C. It dominates in the spectra of the GeS glasses fused at 789°C, and triples in the GeS glasses fused at 895°C. Structural models for the defect centers which cause the detected lines have not yet been developed by us.

Radiation-induced defects in silicate glasses were studied by the ESR-method. Two types of paramagnetic centers, whose ESR signals show a strong overlap, have been observed. A separation of the spectra was necessary for an exact characterization of these centers. Here, we took advantage of the effect that different centers disappear at different temperatures. By studying the behavior of the single spectra, both as a function of the temperature and of the composition, two types of paramagnetic centers could be isolated, which were called HI- and HII-centers. We developed new models for these centers on the basis of the data obtained from the experiments, computer-simulations and the literature.

X-ray diffraction, four-probe electrical resistance and susceptibility measurements have been performed on class I and II ceramic superconductors produced by the sol-gel process. The onset temperature Tc was 91 and 23 K for YBa2Cu3O6 + x (class II) and La1.9Ba0.1CuO4 (class I) respectively. The diamagnetic transition of each sample was consistent with its resistive transition.

Highly oriented YBa2Cu3O6+x superconducting thin films have been developed via sol‐gel processing. Film deposition involved spin coating a ‘‘partially hydrolyzed’’ metal‐alkoxide stock solution onto single‐crystal [100] SrTiO3 substrates. Although scanning electron microscopy revealed the film consisted of oriented polycrystallites, from the broad statistical x‐ray diffraction data the 1000 A film ‘‘appeared’’ to be single crystal with moderate mosaic spread (i.e., full width at half‐maximum was 0.3° in θ at a 2θ of 55°). No twinning of the crystal was found in any of the three orthogonal directions (2θ, φ, χ). The onset temperature Tc for the film was 55 K while the critical current density Jc was found to be 102 A/cm2.

Ferromagnetic resonance (FMR) spectra of an iron-oxide thin film with a thickness of 70 A were recorded between 100 and 410 K at 9.5 GHz after heat treatment at about 500 °C in hydrogen atmosphere. The FMR-signal of this film consisted of two components (A and B) when the film plane was oriented parallel to the external fieTp The intensity of these components is not proportional toT3/2 in the range from 100 to 410 K. The line width of the A-component is determined by inhomogeneities in the magnetic structure. The line width of the B-component may be influenced by the spin-spin relaxation mechanism and skin effect. The temperature behavior of the resonance field of the A- and B-components was tentatively attributed to variation of the local fields with the temperature of measurements.

Gallium Arsenide thin films have been successfully grown onto (1102) sapphire substrates by Molecular Beam Epitaxy methods using a graded growth procedure. The initial layers of GaAs were grown at lower growth rates and at lower substrate temperatures, followed by a thicker GaAs layer grown at usual growth rate of 1 pm/h. The films grown at temperature of 585 °C show good surface morphology. Silicon doped GaAs films exhibit n type conductivity and show low temperature photoluminescence band with peak energy at 1.502 eV and line width of about 42 meV.

The structural evolution of YBa2Cu3O6+x precursor sol was investigated using 13C NMR and quasielastic light scattering. A polydisperse colloidal suspension of yttrium, barium and copper alkoxides was characterized as hydrolysis and complexation reactions occurred. Light scattering data showed that the average particle size of a copper(II) alkoxide suspension decreased by a factor of 5 (1100 nm to 220nm) with the addition of the yttrium and barium alkoxides over a period of 24 hours. The acquired particle size data correlated well with 13C NMR spectra, which showed initial peak broadening and the copper complexing to the yttrium and barium as a function of hydrolysis time.

High Tc superconducting powders and thin films on silicon have been fabricated by the sol-gel process. Both powder and film preparation involved the synthesis of metal alkoxides, followed by the complexation of yttrium, barium, and copper alkoxides in a common solvent. Bulk gels were then vacuum dried and fired at 700 and 950 °C in flowing oxygen. Thin films on (100) silicon were fired at 700 °C in flowing oxygen. Susceptibility vs temperature measurements showed that the thin films on silicon had a Tc of 40 K while the bulk gels fired under the same conditions had a Tc of 75 K. The sample fired at 950 °C was superconducting at 90 K.

Silica glass platelets have been implanted with Fe(+) ions, 125 KeV and 10⋀-5 A to doses of 10⋀14 cm⋀-2, 10⋀15 cm⋀-2, 10⋀16 cm⋀-2 and 5 x 10⋀16 cm⋀-2. Ion scattering measurements show that the peak of the Fe ion distribution is ~95 nm below the sample surface, approximately Gaussian, with a width at half maximum amplitude of 100 nm. The intensity of a component in the EPR spectra of implanted samples with a width of 300 gauss and an approximately isotropic shape increases with increasing dose. The increase, proportional to dose for doses

The 9.5 GHz ESR-spectra of gamma-ray irradiated 94 SiO2 6 GeO2 (mol%) aero gels heat treated at 462°C were recorded at 300 K. The ESR-spectrum of this gel consisted of an asymmetric line (g1 = 2.001, g2 = 1.995, and g3 = 1.994) attributed to the Ge(3)-center and other components which have not yet been identified. The 94 SiO2 6 GeO2 gel was treated at 1000 and 1280°C and then exposed to gamma-ray radiation. The Ge(1)- and Ge(3)-centers were identified in the 94 SiO2 6 GeO2 gel with TH = 1000°C. At TH = 1280°C the signal of the Ge(1)-center dominated the spectrum of this sample. The spectra of the 58 SiO2 42 GeO2 gels with TH = 1200 and 1400°C can be described by the Ge(3)-center. The Ge(1)-center was of minor importance in these samples.

We have synthesized orthorhombic phase YBa2Cu3O7−x superconductors by using metal alkoxides. Cu (II) ethoxide was first partially dissolved in toluene, followed by the addition of Ba-methoxyethoxide and Y-methoxyethoxide in methoxyethanol to further enhance the solution solubility. A homogeneous gel-like paste was obtained both by adding water to the stock solution and by exposing it to the atmosphere. The gels were then vacuum dried and fired at 800 and 850°C in flowing O2. The superconducting transition temperature was 90 +K.

We present here a study of the effect of Fe doping and hydration on the NMR, EPR spectra and Tc of slowly and rapidly cooled Y-1 Ba2Cu3O6+x Superconductor. The g-values of the EPR signals are related to Cu2+ ions in six-fold coordination. Tc is suppressed 10–20°C due to changes in processing conditions and the addition of Fe. The 89Y MAS-NMR spectra show that Y is more shielded (more ionically bonded) in the slowly cooled sample than in the rapidly cooled sample and the hydrated slowly cooled sample is less shielded. The effect of hydration on 89Y chemical shift is consistent with the presence of protons near the Y.

Tin-oxide/iron-oxide and yttrium-iron-oxide thin-films have been produced with the sol-gel method. Film thicknesses from 50 to 155 nm were deposited by the sol-to-gel transformation onto borosilicate substrates. The dielectric losses of the films were deduced by the complex reflection coefficient of these materials in the range from 2 GHz to 18GHz using an HP network analyzer.Samples of 5 cm × 5 cm were centered on the waveguide flange and a shorting plate (12.2 cm × 15.2 cm) of brass centered over the sample. Measurements were automatically made using the HP software provided.In the X-Band region, three absorption bands at 8.3, 9.4, and 11.5 GHz were detected for the substrate, with losses (absorption peaks) ranging from 13.5, 11.9, and 9.9, respectively. For the tin-oxide/iron-oxide sol-gel coated substrate, three bands at 8.4, 9.5, and 11.6 GHz were observed having losses of 16.2 to 13.4, 12.9 to 11.4. and 11.3 to 9.7, respectively, depending upon thickness and orientation. For the yttrium-iron-oxide sol-gel coated substrate, three bands at 8.4, 9.5, and 11.6, with losses depending upon solgel thickness and orientation.

The molecular structure of sol-gel processed silica can be studied using electron-spin resonance (ESR) spectroscopy. Spectra reveal changes in structure from sol to gel and from gel to glass. Gels prepared under various conditions contain intrinsic and extrinsic defects. Other spectroscopies that have been used to investigate gels are nuclear magnetic resonance (NMR), Raman, and visible.

Iron oxide films on borosilicate glasses were produced with the sol‐gel method. The ESR spectra of the as‐produced films exhibit two signals, one at g about 4.2 and the other at g about 2. A ferromagnetic signal was detected by heat‐treating the samples in hydrogen atmosphere between 500 and 800 °C. Angular variation of the ferromagnetic resonance signals revealed an internal field parallel to the plane of the films. The internal field was about 3500 G in the film heat treated at 620 °C for 120 min. Scanning electron microscopy was also used for detailed surface characterization. Before treatments the film is characterized by a fine texture and a few voids whose dimensions are about 5×15 μ. After treatments the film contains particles about 15 μ in size.