Recent research activities of the author's group concerning second-order optical nonlinearity induced in amorphous oxides and magnetic order in a disordered crystalline lattice are described. For the second-order optical nonlinearity, an attention is paid to second-harmonic generation (SHG) in thermally or optically poled tellurite glasses. Some tellurite glasses which exhibit interesting properties such as very stable second-order nonlinearity and large second-order nonlinear susceptibility are presented. The former is realized in ZnO-TeO₂ glass, and the latter is attained for Na⁺-doped WO₃-TeO₂ glass. Also, the mechanism for SHG in optically poled Nb₂O₅-TeO₂ glasses doped with vanadium ions is argued. A model including two-step absorption at a wavelength of 532 nm and the presence of photo-induced electrons and positive holes trapped at localized states is proposed. On the other hand, magnetic and magnetooptical properties of disordered ZnFe₂O₄ thin film prepared by a sputtering method are reported as an interesting example of magnetic order in a disordered lattice. The resultant disordered thin film shows high magnetization even at room temperature and a spin-freezing temperature higher than room temperature. The temperature dependence of magnetization under the conditions of field cooling and zero-field cooling, the dependence of spin-freezing temperature on frequency of ac magnetic field, and temperature variation of ac nonlinear susceptibility suggest that the spin-freezing or magnetic transition of the disordered ZnFe₂O₄ thin film is explainable in terms of the superparamagnetism with strong intercluster interactions. It is also demonstrated that large Faraday effect is observed in a short wavelength range for the disordered ZnFe₂O₄ thin film.

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Novel AgCl/Al₂O₃-ZSM-5 catalyst was prepared by mechanical mixing of AgCl impregnated Al₂O₃ with ZSM-5 powder and annealing at 873 K. The rate of NO conversion under UV illumination was evaluated in the presence of O₂ in a flow-type reaction over the prepared material and compared against AgCl (Ag: 5.0 mass%)/Al₂O₃ catalyst and previously studied AgCl/Al₂O₃ and Ag/Al₂O₃ catalysts. It was found that generally AgCl containing samples exhibit higher NO conversion rates. The major products of NO conversion over AgCl/Al₂O₃-ZSM-5 were N₂ and O₂, while NO was primarily converted to N₂O on AgCl/Al₂O₃ sample. Characterizations of the prepared materials were carried out using XRD and UV-Vis diffuse reflectance spectroscopy. The peculiarities of the observed behavior were discussed.

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Electrophoretic deposition (EPD) is an attractive powder forming method in which charged particles in a liquid are forced to migrate to an electrode by applied DC electric field and deposit to form a thick film. As an application of the EPD method, a free standing α-alumina thick film was prepared by the EPD using formed carbon powder as an electrode and following firing. The formed carbon electrode was prepared by uniaxial pressing of graphite or graphite/carbon black mixed powder, added with some binder. A commercial α-alumina powder with the median diameter of 0.6 μm was dispersed into ethanol, which contained HCl to enhance its dispersibility, and used for the EPD. After the deposition, the electrode was fired in the furnace with flowing air. For the successful preparation of the alumina thick film, the selection of the binder added to the electrode is important. When paraffin was used as a binder, the alumina deposit was broken into small pieces during heating because the electrode largely expands during heating. On the other hand, when polyvinyl alcohol (PVA) or polyvinyl butyral (PVB) was used, the deposit was sintered into a continuous thick film. The surface of the thick film has a characteristic micrometer-scale uneven texture, which is transferred from the surface of the carbon electrode. This microtexture can be easily controlled by altering the surface texture of the electrode, for example by changing the starting carbon material. As the shape of the formed carbon electrode is easily changed, alumina thick film components with various shapes can be prepared by this method. In this study, an alumina thick film on which some letters were patterned, and a wavy shaped alumina thick film were successively prepared.

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UV light irradiation induced structural changes of the cleavage of silicon-carbon bonds and elimination of organic groups in organosilsesquioxane-titania (RSiO_3/2-TiO₂, R=methyl, ethyl, phenyl and benzyl) hybrid films due to the photocatalytic effect of TiO₂ component. Phenyl and benzyl groups tended to remain in the films after the cleavage of Si-C bonds presumably due to their higher stability of aromatic rings and lager steric effect. The refractive index and dynamic hardness of all the hybrid films increased, and the thickness and contact angle for water decreased by the structural changes induced by the UV light irradiation. On the basis of these changes in film properties, micropatterning was successfully performed on the RSiO_3/2-TiO₂ hybrid films by UV light irradiation through a photomask. The micropatterns thus obtained should be applicable to a printing plate using the surface energy differences as well as a micro-optical component using the surface profiles and refractive index changes.

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The effect of microstructure on dielectric and piezoelectric properties of PbNb₂O₆ was studied to examine the possibility of using powder with the low-temperature rhombohedral form for the preparation of piezoelectric PbNb₂O₆ ceramics. Dense, fine-grained PbNb₂O₆ ceramics with good piezoelectric property with the maximum k_t value of 0.315 were obtained by rapid heating and isothermal soaking at 1250°C of powders with particle size between 0.7 and 1.0 μm. The use of coarse powder resulted in the development of large grains and pores caused by exaggerated grain growth induced by phase transformation from the low- to high-temperature forms. Isothermal soaking at 1300°C resulted in the formation of a duplex structure. These structural defects reduced the piezoelectric property.

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Phase separation and hydrothermal degradation in 3 mol% Y₂O₃-stabilized tetragonal ZrO₂ polycrystal (3Y-TZP) were studied by X-ray diffractometry. The Rietveld analysis showed that crystal structure of sintered body remarkably changes at high temperature. The sintered body is phase separated into high and low yttrium region with increasing sintering temperature. Both regions are assigned to the tetragonal phase. The high yttrium region can be analyzed using tetragonal phase model with c/a≒1. The amount of monoclinic phase induced by hydrothermal degradation increased with increasing degradation time. Aging kinetics of tetragonal to monoclinic phase transition was analyzed with Johnson-Mehl-Avrami equation. Fraction of transformable phase evaluated with the equation is in good agreement with the fraction of low yttrium region determined with the Rietveld analysis. The quantitative analyses clearly show that the low yttrium region selectively transforms into monoclinic phase under the hydrothermal condition, while the high yttrium region does not transform. Transformable fraction during the hydrothermal condition in 3Y-TZP ceramics is governed by the amount of low yttrium region. The formation of low yttrium region due to phase separation is responsible for hydrothermal degradation in sintered body.

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Particle connection in two-component powder compact was quantitatively evaluated by electrical conductivity measurement. As a model system, an Al₂O₃ powder (median size 0.33 μm or 0.51 μm, insulator) was mixed with an indium tin oxide powder (ITO, 90 mass% In₂O₃-10 mass% SnO₂, median size 0.20 μm, electronic conductor) in aqueous solutions with and without polyacrylic acid (dispersant) at pH 3.3-10.0. The packing density of the powder compacts consolidated by filtration depended on the pH of the suspension, the size of Al₂O₃ particles and the volume fraction of ITO. The above green density was well simulated using the fractional collision frequency and packing density of Al₂O₃-Al₂O₃, Al₂O₃-ITO and ITO-ITO clusters in the powder compact. A continuous connection of ITO particles in the consolidated green compact formed at 25 vol% ITO fraction in both the powder compacts with 0.33 μm- and 0.51 μm-Al₂O₃ median size, respectively. On the other hand, particle connection of ITO-ITO formed at 95% relative density for 20 vol% ITO fraction after the sintering at 1400°C. At 10 vol% ITO fraction, no ITO-ITO connection was formed in the dense compact with a relative density above 95%. The conduction path in the green and sintered compacts was formed at Df=0.15 (D: relative density of the compact, f: ITO volume fraction), which corresponded to 0.66 cm of the critical length of connecting ITO particles in a 1 cm-cube of the compact. It is possible to interpret that one string of connecting ITO particles is in contact three-dimensionally with another string to make the conduction path.

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Chemical bonding states of Cu/graphite interfaces were investigated by using the first-principles molecular orbital method with model clusters. It was found that Cu atoms in the interface layer undergo electronic overlap with C atoms at the first and second neighboring sites. Chemical bonding strength across the interface is strongly affected by the presence of Ti or Zr in the interface layer. The interfacial attractive interaction increases by doping the larger-sized Ti or Zr atom, although the interlayer distances between Cu and graphite become larger. Therefore, the interface strength of Cu/graphite can be improved by the additional elements at the interface.

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Zirconia-dispersed alumina ceramics were fabricated by pulse electric current sintering (PECS) using transition alumina/zirconia (ZrO₂=5.7-21.0 mass%) composite powders. The composite powders were prepared through a novel sol-gel route using polyhydroxoaluminum (PHA) and polyhydroxozirconium (PHZ) solutions as starting materials. PHA-PHZ composite gels were calcined at 800-1100°C and then ground by a planetary ball mill. Upon heating, the PHA-PHZ composite gels transformed into mixed phases of γ- and χ-alumina and tetragonal ZrO₂, depending on the temperature and ZrO₂ content. In the case of low calcination temperature and/or low ZrO₂ content, t-ZrO₂ was highly dispersed in transition alumina matrix as nanocrystallites. PECS was effective in transforming the composite powders into fully dense sintered bodies at 1250-1500°C under a uniaxial pressure of 40 MPa. Sinterability depended strongly on calcination temperature: the temperature required for full density decreased as calcination temperature increased. The incorporation of ZrO₂ into the alumina matrix through the sol-gel route was very effective in inhibiting grain growth of alumina, leading to finer microstructures. Using composite powders calcined at 1000°C, bending strengths as high as 1.2 GPa were obtained through PECS at 1350°C by the addition of a small amount of ZrO₂ (5.7 mass%). With increasing ZrO₂ content, the bending strength gradually increased up to 1.4 GPa.

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A new type solid-state electrode was investigated for the monitoring of pH in water at 25°C. The cell consists of two half-cells: working electrode using the glass of Li₂O-Y₂O₃-SiO₂ system (Li_xYSi₄O_9.5+x/2, x=2-6) and an Ag/AgCl electrode coated with Nafion film. For glasses of Li_xYSi₄O_9.5+x/2, the conductivity was the highest when x is equal to 5. A stable Nafion film was obtained by heat treatment at 100°C for 1 h. The electromotive force (EMF) of the cell decreased linearly with pH increase in water in accordance with the Nernst's equation. The sensitivity of the cell against pH in water was the highest when x is equal to 4. The EMF was also scarcely influenced in the presence of inorganic ions such as Na⁺ and Cl^-. It was practically confirmed by the pH titration that the solid-state cell behaved similarly to the pH meter with a conventional glass electrode.

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Second harmonic generation (SHG) was observed in heavy metal oxides glasses of PbO-Bi₂O₃-Ga₂O₃ glass system subjected to thermal poling treatment. There was a relaxation with time for the intensity of SHG for all of the present glasses. The intensity of SHG was very sensitive to poling temperature. A small addition of alkali oxides such as Na₂O, increased SHG intensity, which is attributed to the increase of electric field (E_dc) in the glasses.

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A phosphorus-doped Si_0.8Ge_0.2 thin film of 300 nm thickness was deposited by radio-frequency (RF) sputtering with an induction coil. Thermal annealing was carried out to crystallize as-deposited amorphous-like SiGe thin films. The thermoelectric properties of the thin films, such as electrical conductivity, carrier concentration, mobility and Seebeck coefficient, were investigated. After annealing at 1000°C for 5 h, the Si_0.8Ge_0.2 thin films exhibited fine grains of around 30 nm and a smooth surface with an RMS of 1.91 nm. With increasing annealing time, the crystallization of the films progressed, resulting in a high carrier mobility and a large absolute Seebeck coefficient. The phosphorus-doped Si_0.8Ge_0.2 thin film annealed at 1000°C for 50 h showed a low resistivity of 0.04 Ωcm, a large Seebeck coefficient of -0.29 mV/K, a Hall mobility of 5.41 cm²/Vs, and a carrier concentration of 2.7×10¹⁹ cm^-3 at 100°C. The low resistivity of the Si_0.8Ge_0.2 thin film in this study was achieved by strong doping with RF sputtering using the induction coil and resulted in a relatively large thermoelectric power factor of 1.9×10^-3 W/K²m, which is the same as that obtained by CVD.

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A simple fracture testing method, combined with acoustic-emission (AE) monitoring was developed in order to investigate the mechanical performance of solid oxide fuel cells (SOFCs) under simulated environment. The fracture testing method was applied to ceria electrolyte-supported single cells. The fracture damage process was shown to involve vertical cracking and delamination in the cathode, and vertical cracking in the electrolyte, and the fracture damages were most likely due to chemical expansion induced stresses. It was demonstrated that the AE method may enable one to detect the above-mentioned fracture process and to determine the onset condition for fracture damage in the single cell.

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