Organic Sol-gel Research Articles

Surface smoothing of thin HTc YBa2Cu3O7−δ superconducting films by high-energy iodine ions

Abstract A variety of techniques were applied to probe for surface modifications and structural changes in thin high T c YBa 2 Cu 3 O 7− δ (YBCO) superconducting films prepared onto MgO substrates after time of flight heavy ion elastic recoil detection analysis (HERDA). Films have been prepared by ex-situ processing of a spin-coated organic sol–gel precursor. Evidence is provided for the smoothening of the surface of the films accompanied with an amorphisation of the YBCO films in the HERDA spot region. The virgin surface roughness of 30–50 nm could be reduced to 1–2 nm after bombarding the film for a short time with pA current. However, large scale surface roughness on the 200 nm scale remained unchanged. Importantly, the integrity of the superconductor films did not change significantly during HERDA allowing simultaneous measurements of high resolution Y, Cu, Mg and C depth profiles. Further research will utilise the HERDA depth profiling capability for carbon and copper since the copper stoichiometry and fraction of carbon as an impurity are crucial for an understanding of the performance of the YBCO films.

On the Problem of Drying of a Monolithic Silica Gel

The possible use and the mechanism of action of different drying control chemical additives, the so-called DCCA agents, in synthesizing monolithic silica gels by the organic sol–gel method are discussed.

Dependence of the Pore Size of Silica Gels on the Acidity of the Medium

The influence of the acidity of the medium of the initial sol–gel system on the pore size of a silica gel prepared by the organic sol–gel synthesis form tetramethoxysilane is investigated.

Formation of epitaxial YBCO thin films by ex-situ processing of a polymerized complex

High T/sub c/ and J/sub c/ YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films have been formed by ex-situ processing of a spin coated organic sol-gel precursor based on a polymerized complex. To form the precursor we have reacted metal cations with a chelating organic acid, then formed polyesterified complexes through reaction with a polyhydroxy alcohol. This method permits a simple, cheap and reliable route to the fabrication of YBCO films. The value of J/sub c/ achieved for the film deposited onto a LaAlO/sub 3/ [100] substrate at 77 K under a zero field is routinely as high as 0.25 MA/cm/sup 2/ with T/sub c,zero/ of 90.6 K.

Trifluoroacetic Acid as a New Effective Catalyst for Preparing Monolithic Silica Gel by the Sol-Gel Process

Trifluoroacetic acid was proposed as a new effective catalyst for organic sol-gel synthesis. The influence of the solvent (polar or nonpolar, protic or aprotic) on the sol-gel process was studied.

Preparation and characterization of all organic NLO sol-gel materials based on amino azobenzene dyes

A series or NLO active chromophores based an amino azobenzene dyes have been synthesized by diazotization reaction. All organic NLO-active materials were obtained by introducing the chromophores into (hydroxymethyl)-benzoguanamine (HMBG) systems by a sol-gel process. All the sol-gel materials exhibit excellent optical transparency. Morphology, thermal and optical preperties of these polymers have been characterized. These NLO-active polymers can be classified into reactive systems and guest-host systems. In the reactive systems, the chromophores were condensed with HMBG in the sol-gel process. In the guest-host systems, the nonreactive chromophores were simply doped into HMBG matrix. A second harmonic coefficient, d 33 , of 23.2 pm/V has been obtained. Moreover, a systematic investigation of variation of chromophore chemical structures on NLO properties, has been investigated. Covalent bonding effect between chromophore and benzoguanamine as well as steric effect are shown to greatly enhance the temporal stability for these NLO-active sol-gel systems.

Electrical properties of sol–gel processed NASICON having new compositions

High-conductivity and high-density samples with new compositions in the NASICON-type electrolyte series, i.e., the Na 3Zr 2−( x/4) Si 2− x P 1+ x O 12 system, with x=0(A), 0.667(B), and 1.333(C) were synthesized using a mixed inorganic–organic sol–gel process. The sinterability was improved with increasing the x value, but the conductivity decreased. Highly dense samples were obtained by sintering at 1100°C. The conductivity decreased with decreasing the c lattice parameter of the hexagonal structure. Nevertheless, the CO 2 gas sensors using the highly dense B and C samples showed good EMF response which is very close to the theoretical value.

Preparation and optical studies of Er-doped Al–Si–Ti oxide glasses using the ErAl 3(OPr i) 12 isolated Er-ion precursor

We have investigated the possibility of avoiding formation of Er-rich oxide clusters in ErAl 3O 6–TiO 2–SiO 2 glassy films. Samples containing 0.5, 1 and 3 mol% Er 3+ were prepared using a precursor with a single, isolated Er-ion, ErAl 3(OPr i) 12, in the metal–organic sol–gel route. The thermal decomposition of the gel films to form amorphous oxide films was studied by thermogravimetry, Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction and by means of a transmission electron microscope, equipped with an energy dispersive spectrometer. The microscopy studies of the oxide films obtained after 2 h at 900°C showed that they were amorphous and free of Er-rich clusters. The optical and vibrational properties of the glasses were studied using FT-IR, Raman scattering and luminescence spectroscopy. The samples exhibit luminescence both in the visible and IR under excitation of the 514.5 and 488 nm Ar + laser lines. The emission around 1.5 μm was maximum for the 1 mol% sample. The results show that the preparation technique can produce samples with an unusually large amount of Er doping, before Er-clustering induced quenching of the luminescence appears. Up-converted emission was also detected around 21 000 and 24 500 cm −1.

Organic sol‐gel materials for second‐order nonlinear optics based on melamines

A series of all organic nonlinear optical (NLO) sol-gel materials based on melamines and an azobenzene dye (Disperse Orange 3; DO3) have been investigated. Different contents of DO3 were covalently bonded with the melamine-based organic network via condensation of amino and methylol groups. The optically clear samples exhibited second-order optical nonlinearity (second-harmonic coefficient d33) = 35.4 and 11.5 pm/V at 1064 and 1542 nm, respectively) after poling and curing at 220°C for 1 h. Thermal behavior of these organic NLO sol-gel systems was studied by temperature-dependent dielectric relaxation. The results indicate that the incorporation of rigid NLO-active chromophore into the melamine-based matrix leads to high rigidity and dense packing of the organic network. Subsequently, higher glass transition temperatures were obtained for the organic NLO sol-gel material with higher DO3 content. The influence of composition on the temporal stability at 100°C was also investigated. Temporal stability at 100°C was studied as a function of system composition. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2503–2510, 1999

Organic Dye-Doped Hybrid Sol-Gel Coatings and Pigments – Synthesis, Structural Elucidation and Application

AbstractThe chemistry of sol-gel processing of dye-doped, hybrid coatings for glass surfaces has been studied via FT-Raman-, NIR- and NMR-spectroscopy both in the liquid and solid state. Based on these results further investigations are presented aiming at the development of new hybrid pigments by spray drying of two-component sols. The properties of the resulting powders are discussed with respect to their morphology, migration behaviour and photostability.

Low loss second‐order nonlinear optical polymers based on all organic sol‐gel materials

AbstractA new class of all organic sol‐gel second‐order nonlinear optical (NLO) materials based on hexa(methoxymethyl) melamine (HMM) was developed. Two NLO active chromophores, 4 (4′‐nitrophenylazo) aniline (DO3) and 4‐amino‐4′‐nitrobiphenyl (ANB), were incorporated into the melamine matrices. The samples exhibited second‐order optical nonlinearity after poling and curing at 220°C for 30 min. DO3/HMM and ANB/HMM samples showed a second harmonic coefficient, d33 of 10.7 and 1.8 pm/V at 1064 nm, respectively. The temporal stability of both systems was studied at room temperature as well as at 100°C. Waveguide optical losses of samples at 633 and 830 nm were found. © 1995 John Wiley & Sons, Inc.

Interaction between organic dyes and sol gel matrices

Interaction between organic dyes and sol gel matrices

Chemical processing of (Ba, Sr)(Ti, Zr)O3 perovskite ceramics

Stoichiometric high-purity submicrometre-size perovskite powders have long been of interest for the preparation of dense ferroelectric bodies, thin film electronic components piezoelectrics and electro-optic materials. In recent years, numerous methods of preparing fine perovskite powders have been developed, such as the thermal decomposition of oxalates, citrates and carbonates [1-3], the organic sol-gel technique from metal alkoxides [4-6] and more recently the metallo-organic decomposition [7, 8]. The organic techniques which lead to homogeneity, stoichiometry and high purity in fine particles, offer a great flexibility because of the large variety of organic precursors that are available. However, concerning the very interesting barium or strontium perovskites, the use of the expensive alkaline earth alkoxides is generally very inconvenient because of their high reactivity to moisture and of the high molecular complexity which decreases their solubility in alcohols. We have studied the synthesis of alkaline earth perovskite ceramics from a sol-gel route, previously proposed by Kiss et al. [9] for barium titanate, in which titanium and zirconium alkoxides are hydrolysed by an aqueous solution of barium and/or strontium hydroxides. The method first makes possible the synthesis of a cubic perovskite phase from 100 ° C [10, 11], second, a low sintering temperature (1150°C in the barium titanate) of the powder compact to near theoretical density, and finally the preparation of uniform grain-size bodies. Fig. 1 shows the diagram of preparation of perovskites by the alkoxide-hydroxide method. The organic mixture containing titanium and/or zirconium normal butoxides and 2-butanol in the equimolar proportions is hydrolysed, at about 80 ° C, in a carbon dioxide-free atmosphere, by an aqueous solution containing barium and/or strontium hydroxides with a concentration of about 2.5moll-L For all the compositions, doping elements (Nb, Sb, La, etc.) can be easily introduced by mixing alkoxides in inorganic salts with the organic solution of butoxides. Reactions which take place during this method have been previously described by Flashen for the barium titanate [10]. When a pH of 11 to 14 is maintained, in the presence of hydroxyl ions, four molecules of water and two hydroxyl groups attach through their oxygen atoms to the titanium of Ti(OR)4 in a nucleophilic process and, following an electronic rearrangement, four molecules of alcohol are expelled (Fig. 2). The result of the initial step is an anion of the formula Ti(OH)~ or Zr(OH)~ which is neutralized by the Ba 2+ or Sr 2+ ions in the solution following Equation 1.

Dielectric Properties of Sol - Gel Silica Glasses

AbstractDielectric properties have been measured for a series of porous and fully densified silica glasses, prepared by the sol-gel technique starting from Si-methoxide or Si-fume. The results for the partially densified glasses do not show any preferred orientation for porosity. When fully densified (˜2.25 gms/cc) without any prior treatment of the gels, they have dielectric constants of ≥ 6.5 and loss factors of 0.002 at 1 MHz, compared to values of 3.8 and <0.001 for commercial fused silica. There is no corresponding anomaly in the d.c. resistivity. Elemental carbon present to the extent of 400–500 ppm is likely to be the main cause for this enhanced dielectric constant. Extensive cleaning of the gels prior to densification to remove this carbon were not completely successful pointing to the difficulty in preparing high purity, low dielectric constant glasses via the organic sol-gel route at least in the bulk form.

Dielectric Properties Of Sol - Gel Silica Glasses

ABSTRACTDielectric properties have been measured for a series of porous and fully densified silica glasses, prepared by the sol-gel technique starting from Si-methoxide or Si-fume. The results for the partially densified glasses do not show any preferred orientation for porosity. When fully densified (∼2.25 gms/cc) without any prior treatment of the gels, they have dielectric constants of ≥ 6.5 and loss factors of 0.002 at 1 MHz, compared to values of 3.8 and <0.001 for commercial fused silica. There is no corresponding anomaly in the d.c. resistivity. Elemental carbon present to the extent of 400–500 ppm is likely to be the main cause for this enhanced dielectric constant. Extensive cleaning of the gels prior to densification to remove this carbon were not completely successful pointing to the difficulty in preparing high purity, low dielectric constant glasses via the organic sol-gel route at least in the bulk form.