Most of gas sensors are "surface type" gas sensors that utilize only changes in physical properties near the surface of grains. In this paper, the concept of "non-surface type" gas sensors that utilize changes in physical properties throughout the entire grain is proposed. In particular, we focused on a resistive oxygen sensor as one type of "non-surface type" gas sensor, and achieved notable performance with high-speed response to the order of milliseconds in addition to elucidating details of the response mechanism and investigating the stability of the sensor, which is a substantial advantage of "non-surface type" gas sensors. Next, we demonstrated the extension to flammable gas sensors by incorporating a flammable gas-reactive layer into the resistive oxygen sensor. Furthermore, in order to achieve highly sensitive and highly selective "non-surface type" gas sensors, a new sensor material was developed consisting of alternating layers at the molecular level of an inorganic layer to perform the signal conversion function and an organic layer to perform the molecular recognition function. Aldehyde gases were detected selectively by appropriate nanostructural design of the new material.

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Restrictions regarding waste disposal and strict environmental regulations require eco-friendly technologies. Organics such as binders are used extensively in green body fabrication but they must be eliminated and/or decreased due to global problems because during heat treatment carbon dioxide and other hydrocarbon emissions take place after organic decomposition. If it is possible to remove these polymers fully or partially before heat treatment, then harmful gas evolution to the atmosphere can be eliminated and/or controlled. In the cases where the organic usage is imperative, they must be replaced with the low-toxic or non-toxic ones because toxic substances pose the greatest threat to human beings and the environment. It is also important to recycle the wastes from various sources in order to save energy. This paper reviews the efforts to find or explore new eco-friendly processes, modifications and chemical methods in order to replace currently used ones from the viewpoint of sustainable development.

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Three kinds of sintering aids, LiBiO₂, CuBi₂O₄ and LiBO₂, were selected as sintering aids for the low temperature sintering of (Li_0.04K_0.52Na_0.44)(Nb_0.84Ta_0.1Sb_0.06)O₃ (LF4) ceramics and the effects of these compounds on the sintering behavior of the LF4 ceramics was investigated. The addition of LiBiO₂ decreased the sintering temperature of LF4 about 100°C but the effect was limited and the broadening of XRD peaks due to the degradation of crystallinity was observed. The CuBi₂O₄ was also effective to decrease the sintering temperature of LF4 ceramics but a secondary phase was formed when a large amount of CuBi₂O₄ was added. The addition of a small amount of LiBO₂ was very effective to decrease the sintering temperature of LF4 ceramics. By optimizing the sintering conditions, ceramics with the relative density of 95% were obtained at 950°C which was lower than the melting point of Ag. Li ions in LiBO₂ were incorporated into the LF4 lattices, giving rise to the degradation of piezoelectric properties through the change of crystalline phase. The addition of excess Na with LiBO₂ restricted the incorporation of Li ions into the lattice. Ceramics sintered at 950°C showed the relative permittivity of 738 and the d₃₃ constant of 138 pC/N at room temperature.

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The influence of the pulsed DC current and the electric field on the growth of TiC and ZrC layers using Spark Plasma Sintering was investigated at temperature ranging from 1373 to 1823 K. From the results of XRD and EDS analyses, the product layer formed between Ti and C was only TiC, and the layer between Zr and C was only ZrC. In all systems, the thickness and the growth rate constant of the product layers were enhanced in the system with the current compared to that in the system with the negligible current. The activation energy for the TiC layer growth was calculated to be 269 ± 3 kJ/mol in the system with the current, which is smaller than the activation energy of 273 ± 2 kJ/mol in the system with the negligible current. In the Zr-C system, these values were 205 ± 7 kJ/mol and 224 ± 1 kJ/mol, respectively. The increase in the growth of the TiC and ZrC layers was unaffected by the current direction and suggested that the increased point defect mobility by passing the current was a dominant cause of the enhanced growth.

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Sub-micron-size bismuth (Bi) balls with diameters between 100 and 2000 nm were formed on an anodic aluminum oxide (AAO) template using thermal expansion and thermal oil reflow processes. After centrifugal force separation, 100 nm size Bi balls were obtained. In addition, the ball density was approximately 6 × 10⁷/cm² on an AAO surface. Because of their round shape, the contact angle of the Bi nanoballs on the AAO surface was large after hot oil reflow, making it easy to remove them using ultrasound and to separate different sizes of balls using centrifugal force.

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Bi-perovskites, such as BiFeO₃ (BF), BiInO₃ (BI) and BiScO₃ (BS), were added to (Li_0.04K_0.52Na_0.44)(Nb_0.84Ta_0.1Sb_0.06)O₃ (LF4) to improve the piezoelectric properties of lead-free piezoelectric ceramics. The addition of Bi-perovskites up to 0.6 mol% did not depress the sinterbility of ceramics and the relative densities above 96% could be achieved by a powders-solid state reaction process. The c/a ratio of the tetragonal lattice of the LF4 ceramics was monotonously reduced with the amount of the BF added. The electrical insulation of the LF4 was improved with the addition BF, making the poling procedure under high electric fields become easy. The addition of BF was also effective to enhance the remnant polarization of the LF4 and the piezoelectric d₃₃ constant of 358 pm/V was obtained by the addition of 0.4 mol% BiFeO₃. However, the enhancement of the remnant polarization was not observed when the BI and BS were added to the LF4.

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We investigated the magnetic and dielectric properties of a metal (Pt)/insulator (Cr₂O₃)/magnetic floating gate (Fe)/tunnel layer (CeO₂)/semiconductor (Si) capacitor. This capacitor shows capacitance-voltage (C-V) properties typical of a Si Metal-Insulator-Semiconductor (MIS) capacitor with hysteresis, which indicates that electrons have been injected into the Fe layer. The capacitor also shows ferromagnetic properties. The C-V curve has a hysteresis window with a clockwise trace. This hysteresis behavior was changed by the application of an external magnetic field. These results indicate that this MIS capacitor contains a ferromagnetic floating gate and a magneto-electric insulating layer in a single system.

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Adsorption of a low molecular carboxylic acid (adipic acid) on alumina was studied at molecular chemistry standpoint to estimate adsorption behavior of an acrylic polymer containing carboxylic acid group in water-base system. By the zeta potential measurement, adipic acid adsorbs on alumina chemically. The maximum amount of adsorption of adipic acid was observed at pH 5, which is close to pKa₁ (4.41) and pKa₂ (5.28) of adipic acid. In the region over pH 5, the adsorbed amount decreased monotonously with increase of pH. Adsorption behavior of adipic acid is considered by investigating both surface species distribution on alumina (AlOH₂⁺, AlOH, AlO^-), and species distribution diagram of adipic acid (H₂X, HX^-, X^2-; X: -OCOC₄H₈COO-) at various pH. It is supposed that amount of adsorbed adipic acid on alumina is maximum, because the electrostatic attraction between a positive charge of alumina surface and a negative charge of adipic acid is large. By FT-IR analysis of adsorbate, alumina surface reaction with adipic acid produces outer-sphere complex at pH higher than pKa1 of adipic acid. The occupation area of one adipic acid molecule that was calculated from the amount of adsorption agreed with the molecule area estimated by chem-3D simulator. Adipic acid is supposed to be adsorbed on alumina surface perpendicularly in a single molecule layer. Adsorption of acrylic resin on alumina in alkali side was predicted from the knowledge of adsorption behavior of adipic acid. Furthermore, properties of polymer solution, suspension behavior and green sheet were estimated and confirmed. It is found that a molecular chemistry study of adsorption of a low molecular weight carboxylic acid can be adapted to polymer system.

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The nonlinear piezoelectric phenomena were investigated in PbTiO₃-Pb(Sc_1/2Nb_1/2)O₃ (PT-PSN) system ceramics, which is reported to be the ferroelectric relaxer material having a large d₃₁ constant. The calculated values for current-jumping and resonance-frequency change obtained using our old simulation, in which only ξ_D31 is used as a nonlinear piezoelectric coefficient of third-higher term for the electrical field, agreed well with the measured values in the region of tetragonal phase. On the other hand, in the rhombohedral region, the calculated values did not agree with the measured values. This disagreement was resolved by reflecting the contribution of a new nonlinear piezoelectric coefficient of third-higher term for mechanical stress, ζ_D31, in the calculation. Furthermore, a nonlinear loss term was incorporated into the calculation by handing ξ_D31 as a complex number. The use of complex ξ_D31 enabled the exact prediction of the drop point of the current, which has never been possible.

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Manganese oxide electrodeposited films were grown from the solutions containing manganese oxide nanosheet colloid. The nanosheet solutions were prepared by exfoliation of protonated layered manganese oxide by acid treatment of Na- or K-birnessite. The amount of deposit depends on the size of nanosheet, the concentration of added tetrabutylammonium salt and the current between electrodes. The thick film was deposited at low concentration of the salt; however, it was prone to peel off during deposition in the solution. The smooth and flat film can be prepared from the solution with tetrabutylammonium chloride concentration of 1.66 mmol/dm³. The grown films were examined for electrochemical properties by galvanostatic charge-discharge curves and cyclic voltammograms in the NaClO₄ acetonitrile solution. The maximum capacitance estimated by the charge-discharge curves was around 224 F/g; however, the capacitance decrease logarithmically depending on the mass of deposit. The obtained cyclic voltammograms with ideal rectangle shape seemed to result from the electric double layer rather than redox reaction. Therefore, these voltammograms confirm that such capacitive behaviors are possibly controlled by ion-diffusion through the films.

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This research aims to enhance the thermal stability of CdS nano-particles by a hydrothermally-formed glassy encapsulation structure of SiO₂-CeO₂. The crystalline phase, thermal effect and microstructure of the encapsulated CdS nanoparticles were investigated by the XRD, DSC-TG and TEM analysis. The results showed that most of the CdS nanoparticles had been encapsulated in the glassy phase of SiO₂-CeO₂ by a hydrothermal treatment at 200°C. This structure was stable up to more than 900°C, and it was destructed by the crystallization of crystalline CeO₂ and SiO₂ at a higher temperature. Protected by the glassy phase, the encapsulted CdS nanoparticles was thermally stable up to more than 900°C, which was gradually oxidized and sublimated at the temperature range of 1000-1200°C.

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Second harmonic generation (SHG) was observed from external stress-applied silica glass. Since no SHG signal was obtained from stress-free silica glass, the SHG is considered to result from the strain caused by the externally stress. The intensity of SHG is about 0.1% of that of Y-cut quartz single crystal. The lost of centrosymmetry in the microstructure induced by external pressure seems to result in the SHG.

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Though occurrence of the antibacterial activity on some oxides, MgO and ZnO, is well-known, it is not clear what the mixing ratio among solid solutions affects antibacterial activity. In present work, change in antibacterial activity with the mixing ratio of two-type solid solutions, Mg_1-XZn_XO with cubic structure and Zn_1-XMg_XO with hexagonal structure, was studied. After MgO and ZnO powders were mixed with the molar ratio (MgO/ZnO) of 0.44, 1.22 and 1.86, the solid solutions were obtained by heating at 1200°C for 5 h in air. By X-ray diffraction measurement, it was found that two-type solid solutions of cubic and hexagonal structure were formed at the molar ratio of 1.22-0.44. The formation amount of cubic-type solid solution increased with increasing the molar ratio. At the molar ratio of 1.86, cubic-type solid solution was formed without any hexagonal-type. In three powder samples of the obtained solid solutions, antibacterial characteristics were examined by colony count method, using Staphylococcus aureus and Escherichia coli. In the case of the mixture of cubic- and hexagonal-type solid solutions, antibacterial activity enhanced with increasing the formation amount of cubic-type solid solution. The powder sample with a single phase of cubic-type solid solution showed strongest antibacterial activity in three powder samples. As mentioned above, the mixing ratio of two-type solid solutions with cubic and hexagonal structure was found to affect antibacterial activity.

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Perovskite-type Na_0.5Bi_0.5TiO₃ was prepared by hydrothermal reaction using TiO₂ (anatase) and Bi₂O₃ in NaOH solution. A single phase of Na_0.5Bi_0.5TiO₃ was obtained when the molar ratio of NaOH/TiO₂ was above 60 and the reaction temperature was above 180°C. In the temperature range from 220 to 300°C large crystals of Na_0.5Bi_0.5TiO₃ were obtained. The maximum dimension of crystals was ~1.0 × 1.0 × 1.0 mm which were obtained under the condition of NaOH/TiO₂ = 60 at 260°C for 2 d. The TG-curve of large crystals showed a mass loss of 0.25 mass% which was caused by release of OH group. The chemical composition for large crystals of Na_0.5Bi_0.5TiO₃ was found to be Na_0.50Bi_0.45H_0.05TiO₃. The X-ray powder diffraction pattern of large crystals was indexed with the cubic cell of the lattice parameter of a = 3.891(1) Å and the cubic phase decomposed to the compound with the hexagonal cell of a = 5.4889(7) and c = 13.423(2) Å and a small amount of an unknown phase at > 1000°C. The samples heated at 1180°C exhibited the Curie point at approximately 330°C and the P-E and S-E hysteresis loops.

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Porous materials were prepared by stacking needle-like boehmite particles using a vacuum filtration. Uniform size of needle-like boehmite particles was prepared via hydrothermal treatment of a precursor gel. Boehmite aqueous suspensions with various pH values were prepared and vacuum-filtered to form porous bulk. Porous materials with uniform microstructures were obtained when the pH value of the suspension was adjusted to 9. The mechanical property of the porous boehmite was improved by heat treatment at 1000°C-1100°C with a slight change of the pore structure. Porous α-alumina was also prepared by heat treatment at higher temperatures. The porous α-alumina prepared from boehmite porous materials with uniform microstructure had a finer microstructure than that prepared from the as-prepared boehmite powder.

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Mesoporous silica rods were prepared inside the channels of porous anodic alumina membranes (PAAMs) by a solvent evaporation method using a precursor solution containing P123 block copolymers. The orientation of the mesochannels within the PAAM channels could be controlled by applying high magnetic field processing under 30 T. When the magnetic field was applied parallel to the PAAM channels, mesochannels were successfully induced parallel along the magnetic direction. Such magnetically induced mesochannels were directly confirmed by TEM observation.

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