Anisotropic thermoelectric properties of crystal-axis oriented polycrystals of layer-structured oxide in the Ca-Co-O system was discussed. Plate-like particles of (Ca_2.7Bi_0.3) (Co_3.7Cu_0.3)O_9+δ were synthesized. To improve the thermoelectric properties, a c-axis oriented polycrystal of (Ca_2.7Bi_0.3) (Co_3.7Cu_0.3) O_9+δ was successfully fabricated by uniaxial-pressing and sintering. The electrical conductivity along the ab-plane was about four times larger than that along the c-axis, while the Seebeck coefficients were similar. The thermal conductivity along the ab-plane was more than two times larger than that along the c-axis. The resulting figure-of-merit along the ab-plane was enhanced due to the enhanced electrical conductivity.

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BaTi_0.91(Hf_0.5, Zr_0.5)_0.09O₃ thin films were formed on Pt(111)/Ti/SiO₂/Si(100) substrates by pulsed laser deposition using fourth-harmonic-generated light (λ=266nm) of a Nd³⁺: YAG laser beam. Crystallinity and stoichiometry of the thin films were determined by X-ray diffraction, X-ray fluorescence analysis and electron probe microanalysis. Their ferroelectric properties were investigated from electrical measurements. The leakage current density increased from 10^-11 to 10^-3 A·cm^-2 with increasing electric field up to 200kV·cm^-1. The dielectric constant, remanent polarization and coercive field of the BaTi_0.91(Hf_0.5, Zr_0.5)_0.09O₃ thin films were estimated to be 120 at 1kHz, 8.7μC·cm^-2 and 127kV·cm^-1, respectively.

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Diffraction-line broadening was observed in the X-ray diffraction (XRD) profiles for samples sintered in a relatively short period in the perovskite-type solid-solution systems, Ba(Zn_1/3Ta_2/3)_1-xM_xO_3-δ(M=Y, In, Ga), and it decreased with prolonged sintering period. The line broadening was ascribed to a fluctuation of lattice spacing (Δd/d) that originated from structural imperfections due to ionic displacement, based on a β cosθ vs sinθ plot. Furthermore, as a characteristic tendency, when a larger dopant ion substituted for the (Zn_1/3Ta_2/3) site in the solid-solution systems, a larger initial value of Δd/d was observed which also decreased upon prolonged sintering. Electrical conductivity was strongly dependent upon Δd/d. The relationship between electrical conductivity and Δd/d was discussed from the viewpoint of disordering of the oxide ion.

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We evaluated the characteristics of Ni powder used in the fabrication of internal electrodes of multilayer ceramic chip capacitors (MLCs). The effects of particle diameter on the sintering characteristics of Ni powder for use as electrode films were studied. A high tapping density was obtained for all pulverized Ni powders with on average particle diameter of 0.1, 0.2 and 0.4μm. The experimental results revealed that pulverized Ni powders were homogeneously dispersed in the paste. From shrinkage measurements in Ni electrode films with thickness of approximately 200μm, which were formed by an applicator and sintered at temperatures from 400 to 1000°C, it was observed that films composed of 0.1μm and 0.2μm Ni powders showed a larger shrinkage than that from 0.4μm Ni powder. A similar result has been observed for the microstructure of sintered electrode films.

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The origin of the photoresponse in the visible region observed for the sol-gel derived Ti_1-xV_xO₂ thin films has been studied in relation to the doping level, x, which is ranging from 0.03 to 0.12. Effects of the postheating atmosphere and the substrate nature on the crystallization behavior and photoelectrochemical properties of the films were examined. X-ray diffraction analysis revealed that thin films with x≤0.06 consisted only of anatase type TiO₂ phase regardless of the post-heating atmosphere and substrate nature, whereas for the samples with x≥0.07, VO₂ or V₂O₃ phases have been detected in addition to anatase phase depending on the post-heating atmosphere. Differences in photoelectrochemical characteristics between the thin film electrodes with x≤0.06 and x≥0.07 and the origin of the visible photoresponse are discussed on the basis of the difference in crystallization behavior of the Ti_1-xV_xO₂ electrodes.

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Anatase titanium dioxide was annealed under hydrogen atmosphere up to 800°C for several hours. The diffuse reflection spectra and X-ray diffraction were measured for the annealed powders. The changes in reflectance and conversion ratio to rutile depending on annealing conditions indicate that the contact of the powder with hydrogen in the temperature range of 400-700°C results in the formation of oxygen vacancies on the surface of the anatase powder. On the basis of the insignificant decrease in lattice volume depending on annealing temperature, there is a probability that other lattice defects could be formed. The transformation to the rutile phase was observed at temperatures higher than 650°C.

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3-Aminopropyltriethoxysilane (APTS) thin membranes with amino groups (positive surface) were successfully fabricated on pure titanium surfaces by the method of liquid phase processing. A two-step soaking procedure was employed to prepare HAp coating on the titanium surface modified with an APTS thin membrane. At the first step the negatively charged microparticles of calcium phosphate (CP) homogeneously formed in the supersaturated solution (1.5SBF, pH=7.6) at 50°C were attracted to attach to the modified titanium substrate (positive) due to the electrostatic interaction (attractive), while no CP microparticles were observed on the unmodified titanium substrate. At the second step, after the growth of microparticles through consumption of Ca²⁺ and PO₄^3- in the solution (1.0SBF, pH=7.25, 37°C) the dense coating of hydroxyapatite was formed on the modified Ti substrate. The results verified our expectation that CP microparticles formed in the solution dominated the formation of hydroxyapatite on the substrate with positive surface potential.

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The hydration enthalpies of allophane and imogolite have been measured by means of the adiabatic vapor absorption calorimeter. The hydration enthalpy (ΔH_h) of allophane and imogolite were -63.2kJ/mol and -59.8kJ/mol, respectively, which were almost the same as those of a zeolite group. The total heat of hydration (Q) of allophane was 409kJ/kg at the dehydration temperature of 80°C, and was 1.5 times larger than that of the Mg-A type zeolite, The Q-value of imogolite was 405kJ/kg at the dehydration temperature of 40°C, and was 2.2 times larger than that of the Mg-A type zeolite. Allophane and imogolite are thus characterized by larger Q-values than that of Mg-A type zeolite when they are dehydrated at low temperature below 100°C. This shows that allophane and imogolite are suitable for heat exchange absorbents of zeolite-water heat pumps for low temperature heat sources.

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LaCo_xMn_1-xO₃ (x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) compounds were prepared by commercial sintering technique in air and O₂ atmospheres at temperatures of 1100 to 1200°C. Magnetic and electric properties of the compounds were measured by means of inductance, vibrating sample magnetometer and four-electrode technique in the temperature range between 298 and 78K, respectively. Saturation magnetization decreased monotonously with increasing the substitutional amount of Co ion for Mn ion. While, coercivity, remanence and Curie temperature increased with increasing Co up to x=0.5, and beyond this region, they decreased reversely with increasing Co substitute. Electric resistivity exponentially increased with lowering temperature, like behavior of semiconductor materials. The logarithmic values of the resistivity obeyed a linear-relation with reciprocal temperature.

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Nd-Ba-Cu-O thick films were fabricated onto (100) YSZ substrates by screen printing method. Two kinds of powders with different nominal compositions were used to form the ink for printing. In order to supress film-substrate interaction, the printed films were fired at relatively low temperature of T_s=990°C in various kinds of gases; Ar, Ar+0.1%O₂, Ar+3%O₂ and N₂. After being fired at T_s for 5min, the films were cooled from Ts to 500°C by two steps. The superconducting properties of the films were found to strongly depend on the preprocessed powder for ink, the kind of flowing gas and the cooling conditions. The film, which was cooled rapidly from T_s to 890°C at a rate of 400°C/h and then cooled to 500°C at a rate of 50°C/h in Ar+0.1%O₂, showed relatively a high J_c value of about 500 A·cm^-2 (77K, 0T).

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Mo₅Si₃ reinforced silicon nitride composite was fabricated by sintering a Mo-solution infiltrated porous silicon nitride at 1850°C in N₂ atmosphere; silicon nitride containing solid lubricant particles of MoO₃ at the surface layer was developed by oxidizing a Mo₅Si₃-Si₃N₄ composite at 700°C in air. The mechanical properties and the tribology behavior of Mo₅Si₃-Si₃N₄ composite were evaluated. It was found that the Mo₅Si₃ dispersed at grain boundary of silicon nitride, the average diameters of Mo₅Si₃ particles being in the range 0.2 to 0.6μm. The flexural strength of the Mo₅Si₃-Si₃N₄ composite was 881MPa, which was higher than that of unreinforced silicon nitride by about 20%, because of the Mo₅Si₃ sub-micron particles reinforced the grain boundaries of silicon nitride. The friction coefficient of silicon nitride depended on the stress conditions and the shape of the pin. When increasing the spherical radius of the pin from 5 to 18mm, the friction coefficient of the Mo₅Si₃-Si₃N₄ composite decreased and the wear mechanism shifted from adhesive-abrasive wear to a complex type of adhesive-abrasive and abrasive wear mechanism. The formation of MoO₃ on the surface layer of Mo₅Si₃-Si₃N₄ after oxidation treatment lowered the friction coefficient, the friction coefficient of oxidized Mo₅Si₃-Si₃N₄ composite being 0.46 in the dry friction condition. Due to the self-lubricant effect of MoO₃, the friction coefficient of oxidized Mo₅Si₃-Si₃N₄ composite was lower than that of conventional silicon nitride by about 25%.

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As factors which affect the flow resistance of ground coat glass, the type of base metal and the particle size of the silica powder which is used as mill additive were investigated. Carbon steel (SS400), ferritic stainless steel (SUS430) and austenitic stainless steel (SUS304) were used as base metals. Three types of silica powder of various average particle sizes were used as mill additives. The following results were obtained. The glass flow decreased in the order of SS400, SUS430 and SUS304. The glass flow of SUS304 decreased to approximately one-third that of SS400. The glass flow increased with increasing diffusion length of the Fe ion. A high-Cr-concentration layer existed between the ground coat layer and the base metal in the cases of SUS430 and SUS304 base metals. The glass flow decreased with increasing average particle size of the silica powder. The glass flow of the sample with the silica powder of 139μm average particle size decreased to approximately one-third that of the sample with the silica powder of 8μm average particle size.

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Aluminum nitride powder was prepared by calcination of an organic precursor, which was synthesized by adding aluminum chloride powder in an ethylenediamine solvent in a dry N₂ atmosphere. It was confirmed from X-ray diffraction analysis and Fourier transform infrared spectroscopy that amorphous and hexagonal AlN powders formed from the precursor after calcination at 800 and 1200°C for 5h in flowing dry N₂, respectively. Scanning electron microscopic observation revealed that the AlN crystallites obtained at 1200°C were less than 25nm in diameter, though they easily agglomerated to form large grains of 60-100μm. The particle size was comparable to the crystallite size (≈17.5nm) calculated from the half width of the XRD (100) peak.

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A porous titania film was prepared on a glass substrate by a spin-coating technique from the precursor solution containing titanium tetraisopropoxide and stearic acid. Stearic acid formed a 2:2 complex with titanium in the dried film, and the complex melted before decomposition. Before the coating of the precursor solution, methylsilane precoating on the hydrophilic glass surface was effective in preparing a uniform film because of hydrophobicity of the complex melt. The resultant film was transparent and composed of anatase after heating at 500°C. Micrometer-scale rough surface with aggregates of secondary particles composed of primary crystallites was observed in the film, and mesopores seem to be located at the inter-crystallites. It is probable that decomposition of stearic acid and aggregation of anatase crystallites occur simultaneously to provide the porous structure during heating.

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A power-law analysis of conductivity spectra was conducted to elucidate electron transport properties of Mg(Fe, Al)₂O₄ spinel solid solutions. The crossover frequency was extracted from the conductivity spectra which exhibit the universal dynamic response. The mobility and concentration of carries were estimted by using this crossover frequency. The cooling rate of samples after sintering as well as the Fe content in Mg(Fe, Al)₂O₄ was found to greatly affect the mobility and its activation energy.

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For ceramic materials, the statistical distribution of defects is closely connected to the fracture stresses. This relationship has been used to derive the distribution of flaw sizes and their positions from different fracture experiments. Reversely, fracture stresses were predicted from the measurement of flaw populations, which would offer a non-destructive tool to measure mechanical properties. There are two obstacles for precise predictions, on the one hand the small size of the defects and on the other hand their complicated geometry. In the literature, considerable effort was undertaken to find an answer to this question and to develop suited tools for determining the size distribution of defects. For the description of the mechanical behaviour, the most frequently used approach is the Weibull theory. The Weibull statistics naturally arises if the number of the defects shows an inverse power law with respect to their size. Because of the technical importance for the prediction of strength and life-time of ceramic components, the limits and the restrictions by the statistical description were of particular interest. From theoretical considerations by analytical models as well as from computer simulations, the reliability of the Weibull theory is predicted, i.e. the variation coefficient of the Weibull modulus and the scale parameter are calculated for a certain material and a certain number of experimental tests. This allows to calculate the number of specimens required to predict the strength at a certain given accuracy.

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Impurities at grain boundaries have been known to play very important roles in ceramic materials for wide range of applications. In the last decade, high resolution electron microscopy including analytical and high spatial resolution microscopy has revealed the presence and chemistry of the intergranular glassy films (IGF) in Si₃N₄ and other ceramic materials. Equilibrium thickness theory has been developed on the basis of these observations. Theoretical calculations on IGF have then been attempted. On the other hand, “dry” boundaries showing no IGF but impurity segregation have recently been observed in many other ceramic materials. In order to discuss both kinds of boundaries in common, a unified theory should be useful. Adsorption theory has been proposed to describe not only these boundaries but also for impurities in external surfaces. Progress of these scientific researches on impurities at grain boundaries in ceramics is reviewed with some outlooks for the near future.

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