Solid State Phenomena Vols. 124-126

Abstract: Fabrication of paste at low temperature has been developed in order to apply for various electronic devices, such as bus electrode and address electrode in PDP, especially for enlargement of a screen size. In this study, nano-sized silver particles with 10 - 30 nm were synthesized from silver nitrate (AgNO3) by a chemical reduction method. To prepare Pb-free silver paste, the silver nanoparticles were mixed with conventional silver powder with an average particle size of 1.6
and conventional Pb-free frit. Thick films were fabricated from silver paste by a screen printing on alumina substrate and the films were fried at temperatures ranging from 550 °C to 600 °C. Microstructures of the fried thick films were analyzed by FE-SEM. Sheet resistivity of fried thick films was measured and also the relationship between sinterability and conductivity of these films were investigated.

Abstract: High surface area and uniform nano-sized TiO2 and ZrO2 were prepared readily by the infiltration of metal alkoxides into the nanoporous SiO2, SBA-15 and the following selective dissolution of SiO2. The obtained particles of TiO2 and ZrO2, 8.1 nm were nanocrystalline of which the structure were anatase and tetragonal, respectively. The surface area and pore volume of the nanocrystalline metal oxides can be increased to above 200 m2g-1 and 0.30 cm3g-1, respectively.

Abstract: To identify the possibility of using GdAlO3 (GAO) as a buffer layer for YBa2Cu3O7-δ (YBCO) coated superconductor wire, we report the result of GAO deposition on SrTiO3 (STO) single crystal substrates by sol-gel processing. Precursor solution was prepared by dissolving stoichiometric quantities of gadolinium hexahydrate and aluminum isoproxide in a mixed binary solvent (2-4 pentanedione:methyl alcohol=1:1). The solutions were spin-coated on STO (100) single crystal substrates and heated at 500
~1100
for 2 h in wet Ar-5% H2 atmosphere. A FESEM observation of the surface morphology of the GAO has shown that it has a very smooth surface with a faceted morphology indicating epitaxy. It was shown in x-ray diffraction characterization that epitaxial GAO films with epitaxial orientation relationship of (001)[112]GAO||(100)[110]STO have been grown on STO (100) substrates.

Abstract: The core-shell structure of dye-silica nanoparticle has been prepared. The dye-silica nanoparticle can be used as a substitute of fluorescent dye for bio analysis. The hybrid organicinorganic nanoparticle was prepared by sol-gel process using organic modified silane as the coupling agent for flourescent dye and silica. The size of the particle was about 50 nm, which was measured by DLS and confirmed by SEM photograph. The fluorescent dye (fluorescein-5-maleimide) was reacted with (3-mercaptopropyl) trimethoxy silane to produce dye-silane compound, followed by the sol-gel reaction with tetraethoxysilane(TEOS) and water to produce core-shell structure. The fluorescent spectrum showed that the fluorescent intensity of dye-silica nanoparticle was higher than that of fluorescent dye.

Abstract: The coatings composed of colloidal silica, methyltrimethoxy silane (MTMS), water, and acid catalysts have been prepared with variation of colloidal silica contents from 0 to 20 %. All the coatings were prepared and coated on the aluminum plate under the same condition except the contents of colloidal silica, and the compensating contents of MTMS and water with fixed molar ratio of MTMS and water to be 3. The physical properties were compared in terms of hardness, adhesion strength, corrosion, wear resistance, and thermo gravimetry analysis, etc. The pencil hardness was drastically increased with the addition of 5% colloidal silica particles and was further increased slightly by increase of additional silica. The corrosion resistance of the coating film against alkali solution was improved by increasing colloidal silica content, however, the acid resistance was less affected by the content of colloidal silica.

Abstract: The BaTiO3/SrTiO3 heterolayered thick films were fabricated by two different methods – thick films of BaTiO3 by screen printing method on alumina substrates electrodes with Pt, thin films of SrTiO3 by the spin-coating method on BaTiO3 thick films and once more thick films of BaTiO3 by the screen printing method on SrTiO3 layer. The leakage current and the dielectric properties were investigated for effect of various stacking sequence of sol-gel-prepared SrTiO3 layer at interface of BaTiO3 thick films. The insertion of SrTiO3 interlayer yielded BaTiO3 thick films with homogeneous and dense grain structure with the number of SrTiO3 layers. The leakage current density of the BaTiO3/SrTiO3-7 film is less that 1.5
10-9 A/cm2 at 5 V.

Abstract: PZT(70/30) powder was prepared by a sol-gel method and PZT thick films were fabricated by the screen-printing method on the alumina substrates. The coating and drying procedure was repeated 4 times. And then the PZT(30/70) precusor solution was spin-coated on the PZT thick films. A concentration of a coating solution was 0.5 mol/L and the number of coating was varied from 0 to 6. The porosity decreased and the grain size increased with increasing the number of coatings. The thickness of the PZT-6(6: number of coatings) films was about 60~65μm. All PZT thick films showed the typical XRD patterns of a typical perovskite polycrystalline structure. The relative dielectric constant of the PZT-6 thick film was 540. The remanent polarization and coercive field of the PZT-6 film were 23.6 μC /cm2, 12.0 kV/cm, respectively.

Abstract: Nano size silica particles were produced by direct oxidation of silicon powder in the water with the base catalysts. The average size of 10~100 nm was successfully prepared from the starting material of silicon powder with variable procession parameters such as silicon solid content, choice of catalyst and amount, the order of mixing, etc. The sodium hydroxide and ammonium hydroxide was chosen for the base catalysts and their amount and addition order were found to control the size of silica particles in the oxidation reaction. The limited amount of NH4OH as the first catalyst seemed to limit the number of nucleus particles, and the limited amount of NaOH further feeded only for particle growing rather than nucleus formation, thereby it was observed to be able to control the average size of particles to be as large as 100 nm. The possible mechanism of particle growth was suggested by solubility of silica and relative affinity of NH4 + and Na+ ions to the surface of SiO2.

Abstract: Hydrophobic thin film silica aerogels were synthesized by ambient pressure drying method from silicic acid which was prepared from sodium silicate (water glass) solution. The pH value of the silica precursor sol was adjusted to make a spinable sol, and gel films were coated on a glass substrate by dip coating technique. Aerogel-like thin films with the thickness of about 1 μm could be successfully fabricated by repeating the dip coating process three times.

Abstract: Silica aerogels using sodium silicates was synthesized by atmospheric-pressure drying. Granulation of silica aerogels was carried out in sequence of hydrogel formation, aging, surface modification, and drying. Rapidly prepared aerogels showed good properties in case aging and surface modification was done within 1 day. Drying is critical to aerogel granulation and the BET area of aerogel dried for a short duration had decreasing with time. It is suggested that sodium silicate-based aerogels granulation could be prepared within less than 5 days, half of initial processing. Aerogel granules had the average diameter of 1 mm and nearly spherical shape. It has very low thermal conductivity of 0.010 W/m⋅K, very light-weight and nanoporous structure with a porosity of upto 95%.