Several new compounds with a pyrochlore-type crystal structure have been synthesized by a low-temperature hydrothermal process under N₂ atmosphere using a mixture of nitrate salts. The chemical compositions of the new pyrochlores are represented as (a) Y₂Sn_1.8Cr_0.2O₇, (b) Y_1.8Sm_0.2Sn_1.8Cr_0.2O₇, (c) Y_1.8Ce_0.2Sn_1.8Cr_0.2O₇, (d) Y_1.8Eu_0.2Sn_1.8Cr_0.2O₇, (e) Y₂Zr_1.8Co_0.2O₇, (f) Ba_0.8Y_1.2Sn_1.8Cr_0.2O₇, (g) Ba_0.6Y_1.2Sm_0.2Sn_1.8Cr_0.2O₇ and (h) Ca_0.8Sm_1.2Sn_1.8Ni_0.2O₇. The Ba- and Ca-containing pyrochlores exhibited excellent spherical morphology with a pure pyrochlore phase structure and were composed of nanometer-sized particles. A- and B-sitedoped pyrochlores maintained a fully ordered crystal structure over a wide temperature range. The pyrochlore oxide powders were tested as catalysts for NO_x absorption and reduction by CH₄. NO could be almost completely converted into N₂ using hydrothermally derived pyrochlore oxide catalysts in the absence of oxygen at high temperatures. Rapid absorption of NO into alkali-substituted pyrochlores was effective for NO removal from the gas phase, absorption being significantly accelerated by the presence of oxygen.

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Dynamical Faraday rotation measurement with the high magnetic fields of-16 T has revealed the presence of microscopic magnetic coupling among trivalent terbium (Tb³⁺) ions at low temperature in Tb₂O₃-riched borate glasses, caused by the superexchange interaction via oxygen ion. Doping by the divalent manganese (Mn²⁺) ions into Tb₂O₃-B₂O₃ glass made the magnetic correlation temperature (T_MC) rising from 120 to 250 K, due to the formation of stronger antiferromagnetic couplings between Tb³⁺ and Mn²⁺ ions. The repetitional application of the 16T-pulsed magnetic fields at lower temperature than 30 K destroyed the magnetic couplings so that the Faraday rotation could be enhanced. After the operations, the Faraday rotation curves at 300 K were drastically changed upon the incorporation of Mn²⁺ ions.

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CaO clinker was sintered from CaCO₃ powder (with purity of more than 98%) at 1300-1600°C by the addition of ZrO₂ to 1% (molar ratio). ZrO₂ reacted with CaO to form CaZrO₃ at all temperatures. The formed CaZrO₃ was mainly located between CaO grains when the sample was sintered at a lower temperature (1300°C), whereas it was mainly located within CaO grains when the sample was sintered at higher temperatures (above 1400°C). The growth of CaO grains was inhibited by the addition of ZrO₂, resulting in poor densification when the sample was sintered at a lower temperature (1300°C). When the sintering temperature was raised, grain growth and densification were promoted and the relative density of the clinker reached a maximum at 1500°C. The slaking test showed a better slaking resistance when the clinker was sintered at 1400-1600°C by the addition of ZrO₂.

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The stress distribution characteristics at the edge of pores of sintered ceramics with fluoric resin coating were investigated by paying attention to the effect of Young's modulus and the thermal expansion coefficient on the stress concentration factor. The residual stress characteristics of ceramic composite, induced by the infiltration of fluoric resin into sintered ceramic pores, were clarified by using the finite element analysis. As a result, it was confirmed that a high compressive residual stress could be induced around the ceramic pores by the mismatch of the thermal expansion coefficients between the ceramics and the fluoric resin. It was also confirmed that the bending strength of sintered 20 mass% alumina and sintered 95 mass% alumina with tetra fluoro ethylene-perfluoro alkylvinyl ether copolymer (PFA) coating was markedly improved in comparison with each as-sintered alumina samples.

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The aim of this study were to fabricate a short-fiber-reinforced SiC composites by hot-pressing using an Al₂O₃-Y₂O₃-CaO mixture as sintering additive, and, to investigate the effect of processing parameters on the mechanical and thermal properties of SiC/SiC composites containing BN-coated Hi-Nicalon short fibers. Fibers were mostly aligned within planes perpendicular to the hot-pressing direction. The composite fabricated by this process achieved nearly full density after hot-pressing at 1700°C. The bending strength increased with increasing sintering temperature and decreased with increasing testing temperature. The fracture behavior of the SiC/SiC composites showed a completely brittle fracture. Results of scanning electron microscopy (SEM) investigation showed that there were pulled-out fibers in the tensile stress zone of the fracture surface, but the degree of pull-out was low. On the basis of these results, the influence of fiber volume fraction on the mechanical and thermal properties of the SiC/SiC composites is discussed.

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Single crystal silicon was soaked in a solution with ion concentrations 1.5 times those of human blood plasma (1.5 SBF) and a bone-like apatite layer formed on it. From analyzing the surface structural change of single crystal silicon and the composition change of solution during soaking, the mechanism of apatite formation was interpreted as follows. The single crystal silicon reacts with 1.5SBF to form a silica gel layer on its surface. The gel layer induces apatite nucleation on its surface and the apatite nuclei grow by consuming calcium and phosphate ions from 1.5SBF. By continuously supplying the ions, a dense and uniform layer of apatite with desired thickness can be formed. This method is promising for developing advanced functional medical devices such as biosensors.

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A new hydrogen sensor based on the thermoelectric oxide of Li- and Na-doped NiO has been fabricated using the screen printing method. The thermoelectric hydrogen sensor, Pt/NiO/alumina, showed voltage signal and built-up temperature difference for 1% H₂/ air mixture gas. At 25°C, the voltage signal and temperature difference were 0.079mV and 0.15°C, respectively, and the signal-to-noise ratio was 16. The increase in operating temperature up to the range of 85-150°C made the catalytic activity more stable, and the response characteristics were also improved. A very clear voltage signal of 1mV for 1% hydrogen gas was observed, and the sensor showed extremely small temperature dependence. The sensor possesses a good linear relationship between the voltage signal and the gas concentration at this operating temperature range.
The lower detection limit of the sensor was found to be below 250ppm, and the sensor provides an output level of 0.1 to 10mV, which corresponds to practical gas concentrations of hundred ppm order to several percent with a high signal-to-noise ratio. From these results, we conclude that this sensor is the most promising candidate for fast and affordable hydrogen leakage detectors for fuel cell driving systems.

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The Rietveld analysis of powder X-ray and neutron diffraction for SBT and Pb_xSr_1-xBi₂Ta₂O₉ revealed that Pb ions were substituted at the perovskite A-site, and the disordering of Pb and Bi ions in Bi₂O₂ layers was not confirmed. The pure solid solutions with the SBT structure were obtained for the samples with x≤0.6, and the unit cell volume slightly increased by Pb substitution. With increasing Pb content (x), parameter c grew while a-b plane was reduced in spite of larger ionic radius of Pb²⁺ than Sr²⁺. These structure changes resulted in a higher T_c for Pb-SBT. Polarization hysteresis measurements using dense ceramics revealed that E_c increased with x while 2P_r at 250kV/cm practically remained constant at around 14μC/cm². The incorporation of Pb into SBT resulted in a higher tilt angle of TaO₆ octahedra along the a-axis (α_x), which is partly responsible for the higher E_c observed for Pb-SBT.

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Electrophoretically deposited polyphenylsilsesquioxane (PhSiO_3/2) particles were thermally softened to form continuous films, via heat treatment. The onset temperature for thermal sintering of the PhSiO_3/2 particles was successfully controlled from 110 to 270°C by changing the time for their condensation, catalyzed by ammonia, from 0.5 to 120 h. The increased onset temperature mainly resulted from an increase in the molecular weight of the particles as the condensation time increased. The PhSiO_3/2 particles with controlled onset temperatures for thermal sintering were used to obtain highly transparent films, -10μm thick, by electronhoretic deposition and consecutive heat treatment at 200°C.

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The oxidation mechanism of a dense Al₄SiC₄ body in the temperature range of 1250-1500°C was investigated using thermo-gravimetry (TG) measurements. Pure Al₄SiC₄ powder was synthesized from Al, Si and C powder, and a dense body was prepared by pulse electronic current sintering (PECS). The oxidation behavior of the body was indicated passive oxidation, and a superior oxidation resistance. Mullite and corundum formed on the surface of the oxidized body, the thickness of the oxidized layer formed by oxidizing at 1500°C for 10 h being about 100μm. The protective layer inhibited oxidation inward the Al₄SiC₄ body. Activation energy and frequency factor for oxidation of Al₄SiC₄ were 483kJ·mol^-1 and 1.86×10⁸kg²·m^-4·s^-1 at temperatures 1300-1500°C, respectively.

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Aluminum-silicon carbide composite heat spreaders having high thermal conductivity were successfully fabricated by a hot-forging technique, and the effect of an interfacial reaction between Al and SiC on the thermal conductivity of the composites was quantified by X-ray diffraction and theoretical calculations. Al-SiC composites with SiC dispersions were fabricated by forging pure Al-SiC powder compacts at a variety of temperatures, under a high pressure of 900MPa. At forging temperatures below the melting point of Al, porous specimens were obtained, resulting in low thermal conductivity. In contrast, fully-densified specimens having high thermal conductivity were obtained at forging temperatures above the melting point. The interfacial reaction between the Al matrix and the SiC particles produced an interfacial reaction layer of Al₄C₃, the thickness of which increased with increasing forging temperature. Calculation of the theoretical thermal conductivities of the composites using the Hasselman's model suggests that the increased forging temperature decreases the thermal barrier conductance of the Al-SiC interface, decreasing the overall thermal conductivity of the Al-SiC composites.

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It is known that Sm-doped ceria shows the highest electrical conductivity among the ceria solid-solution systems with various rare-earth cation dopants. In order to clarify the ionic size effect on the oxide-ion conductivity, in the rare-earth co-doped ceria system, Ce_0.8(Ln″_1-xLn′_x)_0.2O_1.8 (Ln′=Y, Gd and Ln″=Nd, La), the compositional fraction (x) of the co-doped cations was determined so that the average ionic size agreed with that of Sm³⁺. The lattice constants of the four ceria-based compounds, which were prepared with various combinations of rare-earth dopants, agreed well with the lattice constant of the Sm-doped sample. However, the electrical conductivity decreased abruptly with increasing difference of the two cationic radii. The electrical conductivity of these co-doped materials was discussed on the basis of the local ionic arrangement in the fluorite-type structure.

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Alumina gels were prepared from aluminum-sec-butoxide by sol-gel method at 0°C using HNO₃ as a catalyst. The crystallization behavior of the gel was compared with that of HCl-catalyzed alumina gels. α-Al₂O₃ did not form until 950°C in HNO₃-catalyzed gels, while HCl-catalyzed one partially transformed to α-Al₂O₃ around 500°C. Corundum-seeding affected crystallization in a different way as compared to the HCl-catalyzed one, i.e., the α-transformation in the temperature range of 800 to 1000°C was better enhanced by seeding and was completed at 800°C when seeded to a level of 5 mass%. It was considered that NO₃- ions assisted the building of a gel structure in which aluminum or oxide ions are readily diffused at temperatures higher than -800°C.

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We have investigated the deformation luminescence (DL) phenomena in sintered Sr₃Al₂O₆: Eu. The DL from sintered Sr₃Al₂O₆: Eu was clearly visible to the naked eye in the atmosphere, and was produced owing to the physical processes induced during deformation. The DL was sensitive to stress and was observed below the pressure of 10MPa. There is no report on the DL of sintered ceramic, the DL phenomenon of sintered ceramic is first reported first to our knowledge. The DL intensity of sintered Sr₃Al₂O₆: Eu decreased on repetitive application of stress, but it was completely recovered by irradiation with ultraviolet light. The DL intensity was recovered by not only ultraviolet light but also visible light. It is suggested that Sr₃Al₂O₆: Eu is a suitable DL material, which shows repeated DL with undiminished intensity. We think that the DL mechanism arises from the movement of dislocations or heat and recombination between electrons and holes released from these traps associated with doped Eu²⁺ centers.

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The piezoelectric characteristics of (Sr_0.2Ca_0.8)_1-xNd_2x/3Bi₂Ta₂O₉+y mass%MnCO₃ ceramics were examined. The samples were prepared by conventional sintering technique at 1190°C to 1250°C for 2h. The Curie temperature of samples gradually decreased from 631°C to 550°C when x increased. In the sample with (x, y)=(0.2, 0.2), the maximum value of mechanical quality factor Q_m was obtained, approximately 27000, and phase curve showed no spurious in thickness extensional vibration mode (t-mode).

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