Thermally stable mesoporous SnO₂ powders was prepared from sodium stannate by utilizing the self-assembly of n-cetylpyridinium chloride (C₁₆PyCl), followed by treatment with phosphoric acid (PA, 0.1mol·dm^-3). Under the most suitable preparation conditions (C₁₆PyCl conc.=2.0 mass%, [C₁₆PyCl]/[Na₂SnO₃⋅3H₂O]=2.0, [Mesitylene]/[Na₂SnO₃⋅3H₂O]=2.5, pH=10, and aging temperature=20°C), an ordered mesoporous structure (d₁₀₀=ca. 3.1nm) with a large specific surface area (305m²·g^-1) was obtained after calcination of the resultant solid product (having ordered mesopores of d₁₀₀=ca. 4.1nm) at 600°C for 5h. It was confirmed that the PA treatment was useful for reducing the growth of SnO₂ crystallites and then improving the thermal stability of the mesoporous structure.

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We report on photochemical hole burning of Sm²⁺ in sodium borate glasses irradiated with femtosecond-laser pulses of 800nm wavelength. The irradiation of Sm³⁺-doped sodium borate glasses with femtosecond-laser pulses causes electron-trapped Sm³⁺, i.e., Sm²⁺ and point defects such as an oxygen hole center and an electron trapped near Na⁺. The measurements of spectral hole burning were carried out for the ⁵D₀-⁷F₀ transition of Sm²⁺ using a DCM dye laser. Photoionization hole burning is observed at 77K to room temperature for the glasses exposed to femtosecond-laser pulses, and also for the glasses prepared by melting under reducing conditions. The hole-burning efficiency of Sm²⁺ produced by the photoinduced process is about twice higher than that by the thermal process. It is thought that the metastable Sm²⁺ ions and oxygen hole centers induced by femtosecond-laser irradiation are responsible for the observed phenomenon. We propose that the efficient photoionization hole burning is caused by the photostimulated recombination of the electron trapped by Sm³⁺ with the oxygen hole center.

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A silicon single crystal forms a silica gel layer on its surface, when it is soaked in aqueous solutions with pH ranged from 7 to 8. Thus formed silica gel induces apatite formation in aqueous solutions with a higher ionic activity product of the apatite as compared to a simulated body fluid with ion concentrations nearly equal to those of human blood plasma.

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The performance of photostrictive materials can be enhanced by controlling the materials and microstructural characteristics through processing methods, ceramic composition and dopant type/content. In this paper the influence of ceramic processing methods on microstructure and photostrictive responses of Lanthanum modified Lead Zirconate Titanate (PLZT) ceramics have been investigated. Here we have investigated the recent technique of nanocomposite processing which showed good potential for the fabrication of photostrictive materials with enhanced properties. A significant enhancement of photovoltage and photocurrent which led to higher energy conversion ratio has been observed with decreasing grain size of PLZT ceramics with various processing techniques.

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A non-conventional route for controlling both the particle size distribution and the morphology of yttriastabilized tetragonal zirconia has been studied. Non-isothermal decomposition from hydroxide was chosen as a process suitable for preparing the uniformly aggregated nano-crystalline 3Y-TZP powder. The obtained powder had a particle size of 9-18nm, and a narrow aggregate size distribution of 20-70nm. The characteristics of zirconia non-isothermal calcination were investigated in order to choose the best heating regime. Changes in the heating schedule caused changes in the powder morphology. Calcination includes several processes: complete decomposition of hydroxides, crystallization of zirconia, close packing into aggregates, and agglomeration at elevated temperatures because of particle bridging. These processes are superimposed with elevating the calcination temperature. There are two schedules differing both in fineness of the final powder and degree of aggregation-agglomeration. A non-linear heating schedule, produced the finest powder, uniformly aggregated, and non-agglomerated. Keeping lowest possible temperature allowed preventing high-temperature bonding and bridging of particles, which results in hard agglomerates. A high packing density of 56% was achieved after slip casting and cold isostatic pressing, which allowed low-temperature sintering, resulting in a fine-grained dense ceramic body.

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Two types of LiMn₂O₄ particles were synthesized from metallic nitrates and acetates by ultrasonic spray pyrolysis. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis revealed that the starting precursor solution influenced the particle morphology, i.e., the nitrate precursor solution led to the formation of porous particles, and the acetate led to the formation of hollow particles. No differences in crystal phase or crystallinity between the two types of LiMn₂O₄s were detected by X-ray diffraction (XRD) analysis. It was found that the morphology and microstructure of the particles were important factors in determining their electrochemical properties.

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Scratch resistance of sodium borosilicate glasses (20Na₂O⋅80(1-x)SiO₂⋅40xB₂O₃ x=0, 0.2, 0.4, 0.6, 0.8, 1) was investigated by using a Knoop indenter. In addition, Vickers hardness, Young's modulus, and fracture toughness were measured and their compositional variations were compared. It was found that the scratch hardness test was a simple and useful method for evaluating the mechanical failure in glass. The maximum Vickers hardness, 4.2GPa, and Young's modulus, 84GPa, were obtained at the composition of x=0.4. It is considered that this compositional dependence is related with the fractions of four- and three- coordinated boron atoms. On the other hand, scratch hardness and fracture toughness decreased monotonically with the increase of x. This result indicates that both scratch resistance and fracture toughness are associated not only with the energy of the fracturing bonds, but also with energy dissipating processes, such as plastic deformation. Under the present testing condition, scratch hardness rather reflects the fracture mechanism than the elastic behavior.

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The mechanism of anionic polymer dispersant acting on dense alumina suspension behavior was analyzed under different solid-volume fractions (ranging from 40 to 55vol%) and counter-ion densities by comparing microscopic solid/liquid interface interaction to suspension viscosity. The solid/liquid interface interaction and adsorbed structure of polymer dispersant on particles were determined by an atomic force microscope (AFM). The dependency of counter-ion density on the suspension viscosity appeared at a relatively low solidvolume fraction (40vol%). However, at a high solid-volume fraction (50vol%), the suspension viscosity was independent of the counter-ion density. To analyze these phenomena, the force curves between a polished surface of alumina and the tip of AFM were measured in solution with polymer dispersant and different counter-ion densities. The increase of counter-ion density reduced the long-range overlapping repulsive force of an electrical double layer ranging over 10nm in surface distance. A short-range steric repulsion force ranging below about 5nm in surface distance slightly depended on counter-ion density. The estimated mean surface distance between particles in dense suspension decreased from about 8 to 4nm with increasing the solid fraction from 40 to 50vol%. Based on both results, it is concluded that the main mechanism for the aggregation/dispersion of alumina powder in dense suspension changed from electrostatic repulsive force to steric force with increasing the solid-volume fraction in suspension.

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Spinel-type lithium manganese oxides with lithium-deficient compositions in the atomic ratio range of Li/Mn=y=0.475-0.485 were obtained in a single phase by sintering a mixture of Li₂CO₃ and MnCO₃ at 750°C in air, followed by quenching into liquid nitrogen. Initially, they were a cubic (Fd3m) compound like the stoichiometric LiMn₂O₄ spinel. However, it was found that the structure turned from cubic to orthorhombic (Fddd) just in storage at room temperature. The change was slow and it took several days or more depending on the sample's composition. The changes in the density, the manganese valence and the weight of the samples accompanied with their structural change were monitored. Those measurements revealed that, though Li-deficient spinels immediately after preparation took a Li (8a)-defective arrangement (Li_xMn₂O₄, x<1), they were gradually changed to a Mn-excess compound (Li_yMn_2+δO_4-δ; y/(2+δ)=x/2, y≤1). It is likely that Jahn-Teller Mn³⁺ ion increased by reduction of the compound generates the structural distortion.

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The chemical stability of calcium doped lanthanum chromites as SOFC interconnect was investigated by annealing in air and durability test under the simulated SOFC operating conditions. The effects of calcium content, A-site excess, water vapor pressure and silicon as impurity were checked. Stable electrical conductivity was obtained in SOFC operating test up to 300h for the samples with lower calcium content and no A-site excess under the silicon-free conditions. The powders calcined at higher temperatures resulted in better durability. After the tests, Ca₅(CrO₄)₃O_0.5 was detected in XRD on the surface exposed in oxidizing atmosphere. Silicon component reacts with Ca-rich secondary phase in the samples and form Ca₂SiO₄, which degrades the electrical conductivity.

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Continuous fiber-reinforced composite with an amorphous Si-N-C matrix was prepared by a polymer impregnation pyrolysis method by using C-B-Si coated silicon nitride fiber as reinforcement. This composite had a fairly high oxidation resistance due to the self-formed seal of B₂O₃-SiO₂ upon oxidation of the C-B-Si fiber-coating. Chemical vapor deposited (CVD) SiC was coated on the composite to further enhance its oxidation resistance. The composite using mono-layered C-B-Si fiber-coating without surface-coating showed a strength decrease from 1136 to 635MPa upon oxidation at 1473K for 720ks. SiC surface coating of 10μm thickness on the composite improved its strength after oxidation to 814MPa. The composite using three-layered C-B-Si fiber-coating showed negligible strength decrease from 979 to 846MPa even without surface-coating. On this better composite, the SiC surface-coating did not improve the oxidation resistance, but decreased the mass gain by oxidation to half.

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(111) or (100)-oriented diamond films were successfully deposited on (111) or (100)-oriented surfaces of Au foil. The (111), (100) surfaces of Au substrates were prepared from commercially available Au foil, by repeated cold-rolling followed by plasma annealing at 900°C in H₂. The microwave plasma chemical vapor deposition (CVD) method was employed for diamond deposition, using CH₄ diluted with H₂ as the carbon source. Au substrates were pretreated methods with supersonic scratching and bias enhanced methods before diamond growth. The diamond films were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), X-ray micro analyzer (XMA) and Raman spectroscopy. By the results of these analysis, diamond films were found to be referentially oriented to the Au (111), (100) substrates with the (111) or (100) planes parallel to the Au substrate.

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TiB₂-B₄C ceramic composites containing no additives were hot-pressed from a mixture of TiB₂ and B₄C powders containing 0 up to 100mol% B₄C (20mol%). Hot-pressing was conducted at 1950°C for 3.6ks under a pressure of 31.2MPa in an Ar gas atmosphere. The mechanical and electrical properties were examined as a function of compositional change from TiB₂ to B₄C. TiB₂-B₄C composites containing 20-60mol% B₄C had a relative density of 97.4-98.9%, Vickers hardness of 23.8-27.2GPa, flexural strength of 589-705MPa, Young's modulus of 490-568GPa, fracture toughness (K_IC) of 6.46-8.05MPa·M^1/2. The mean surface roughness (R_a) was 25.6-30.5nm and the electrical conductivity 0.30-3.96MS·m^-1. Thus, these composites possessed a high electrical conductivity and a smooth surface. Their mechanical properties were 1.5 times higher than those of pure TiB₂ or B₄C ceramics, and comparable to those of SiAlON or hot-pressed Si₃N₄ ceramics. The present composites are suitable as ceramic mold materials, machinable by electric discharge, corrosion-resistant electrode components, tool materials and high-temperature structural materials.

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The thermoelectric properties of dense Fe_1-xMn_xSi₂ (0.00≤x≤0.10) fabricated by spark plasma sintering have been characterized in the temperature range between 300 and 1150K. Fe_1-xMn_xSi₂ is p-type over the measured temperature range. The electrical resistivity (ρ), Seebeck coefficient (S) are strongly affected by the Mn doping concentration (x). The thermal conductivity, (κ) of Fe_1-xMn_xSi₂ is mainly ascribed to the lattice component (κ_ph). At low temperatures, the κ of Fe_1-xMn_xSi₂ is much higher than that of Fe_1-xCo_xSi₂. At x=0.10, the power factor (P=S²/ρ) and the dimensionless figure of merit (ZT) show maximum values of 9.3×10^-4W/m·K² at 940K and 0.21 at 1040K, respectively.

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High-temperature internal friction of unidirectionally solidified Al₂O₃/YAG eutectics and sintered Al₂O₃/YAG composites were examined up to 1400°C in an ambient atmosphere, in comparison with Al₂O₃ single-crystal. The internal friction for all samples slightly increases with increasing temperature at above 1000°C. The internal friction of the sintered spcimen at 1400°C was about seven times higher than that of the unidirectionally solidified one. The internal friction of unidirectionally solidified composite was slightly higher than that of Al₂O₃ single-crystal. The difference in internal friction values among these samples strongly depends on the Al₂O₃/YAG interfacial area per unit volume and may also be related to the characteristic of the grain boundary. The apparent activation energy calculated from the slope of Arrhenius plots was 180, 110, and 110kJ/mol for the sintered composite, the unidirectionally solidified Al₂O₃/YAG eutectic composite, and the Al₂O₃ single-crystal, respectively. The internal friction values at each temperature and/or the apparent activation energy for unidirectionally solidified Al₂O₃/YAG eutectic composite and Al₂O₃ single-crystal are almost the same, which implies composite behaving as a material having no-interface. The shear modulus for all the tested samples gradually decreased with increasing temperature.

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Al-Si₃N₄ composites were fabricated by infiltration of Al melt with Si contents from 0 to 22vol% into a porous Si₃N₄ ceramic and their thermal conductivity was evaluated. A porous Si₃N₄ ceramic having a porosity of 39.5% and consisting of elongated β-Si₃N₄ grains connected at random in three dimensions was used as a substrate. The Al-Si₃N₄ composites were fabricated by infiltration of Al-Si alloys melt into the porous Si₃N₄ ceramic at 800°C under a pressure of 90MPa using hot isostatic pressing (HIP). Although increasing Si content significantly decreased the thermal conductivity of the Al-Si alloys, the decrease in thermal conductivity of the resulting composites was small due to increased thermal barrier conductances of the interfaces between Al and Si₃N₄.

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The formation of ceria-zirconia solid solution by the solid phase reaction of ceria and zirconia powders near room temperature during wet attrition milling was recently reported. The solid phase reaction occurred as a result of a large plastic deformation, breaking and mutual combining on the ceria particle as well as the solid solution. The size of the particle in which the solid phase reaction can occur was examined in this study. The reaction that forms ceria-zirconia solid solution from large ceria particles (4m²/g) begins when the average particle size reaches 28nm or smaller. The reaction does not occur in CeO₂ powder with particle size larger than 30nm. The critical particle size of ceria powder to begin the reaction with zirconia is thought to be approximately 20nm, which was found asymptotically by two methods, X-ray diffraction and specific surface area measurements.

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The effect of RuO₂ thin films on stabilizing the thermal properties of Au thin films deposited on Al₂O₃ substrates was investigated. Dependencies on temperature of both sheet resistance and adhesion strength were measured. The adhesion strength of the Au/RuO₂ system was constant with temperature, while that of the Au/Pt/Ti system decreased as increasing temperature beyond 400°C. The adhesive properties of the Au/RuO₂ system were not influenced by heating and stable up to 800°C. The sheet resistance of the Au/RuO₂ system remained constant up to 700°C. The RuO₂ thin films can operate as heat-resisting adhesion layers in Au thin films. Au thin films were highly oriented in the Au(111) plane.

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A photocatalyst which has extensively been studied so far is TiO₂ with a 3.0-3.2eV band gap. Well-known photocatalysts with visible-light response are only Pt/CdS and WO₃. Thus, photocatalyst materials mainly employed have been so limited. In such a background, new photocatalysts with high activity have recently been developed. Alkali and alkaline earth tantalates have arisen as a new group of photocatalyst materials for water splitting into H₂ and O₂ under ultra-violet light irradiation. They showed the activities even without co-catalysts such as Pt, being different from titanate photocatalysts. When NiO co-catalysts were loaded on tantalate photocatalysts, except for LiTaO₃, the photocatalytic activities were drastically increased. Among the tantalates, NiO/NaTaO₃ showed the highest activity. Moreover, the activity of NiO/NaTaO₃ was improved by La-doping. On the other hand, highly crystalline BiVO₄ powders with scheelite (monoclinic) and zircon type (tetragonal) structure were selectively synthesized by an aqueous process. The BiVO₄ powder with the scheelite structure showed a high photocatalytic activity for O₂ evolution in the presence of sacrificial reagent (Ag⁺) under visible light irradiation (λ>420nm). The photocatalytic activity of the BiVO₄ powder prepared by the aqueous process was much higher than that of BiVO₄ prepared by a conventional solid state reaction. Zn_0.957Cu_0.043S (band gap: 2.5eV) and Zn_0.999Ni_0.001S (band gap: 2.3eV) photocatalysts showed high activities for H₂ evolution from an aqueous K₂SO₃ and Na₂S solution under visible light irradiation without co-catalysts such as Pt. ZnNb₂O₆, Bi₂W₂O₉, Bi₂WO₆, and Bi₃TiNbO₉ consisting of ions with d¹⁰ and s² configuration were also active for H₂ or O₂ evolution from aqueous solutions containing sacrificial reagents.

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The temperature dependences of Young's modulus (E) and fracture toughness (K_1c), as well as the flow behavior, including stress relaxation, creep and superplasticity of several silicon nitride-based materials, monoliths and composites, are reviewed. A transition range between a low softening rate and a higher one, which coincides with the onset of creep ductility, is observed between 1080 and 1150°C on the E(T) curves and is attributed to the behavior of the secondary glassy phases. The higher the Y/Al ratio or the SiC content, the higher the transition temperature. The K_1c(T) curves exhibit four different stages which were discussed and interpreted through a theoretical analysis, warning against the frequent confusion between the intrinsic and the apparent (experimentally accessible) toughness. Reliable creep resistant- or inversely superplastic-ceramics are now available. However, the high temperature deformation mechanisms are not well understood yet. Non-Newtonian flow regimes and the pronounced tension/compression flow asymmetry are still intriguing. Today, it can be anticipated that with the development of materials containing low amounts of highly refractory grain boundary phases, ceramists are facing a situation that places them closer to metallurgists, and which should allow them to derive more benefit from the exceptional intrinsic properties of covalent crystals such as Si₃N₄. Consequently, grains should play a more and more important role on the high temperature mechanical behavior.

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