Intense research and development of microwave and millimeterwave dielectric materials is expected for applications in the wireless communications in the ubiquitous age. There are three important directions for research and development of microwave and millimeterwave dielectric materials. We have been studying on these three directions based on the crystallography. In the first direction for miniaturization of mobile equipments, tungstenbronze-type like Ba_6-3xR_8+2xTi₁₈O₅₄ (R=rare earth) solid solutions with high dielectric constant have been studied to improve quality factor based on the compositional ordering of cations. For the second direction for applications in mobile phone base stations, we have developed homologous ALa₄Ti₄O₁₅ (A=Ba, Sr and Ca) compounds with excellent dielectric properties such as high dielectric constant and high quality factor. For the third direction, dielectric ceramics of silicate compounds such as forsterite Mg₂SiO₄ and willemite Zn₂SiO₄, and alumina are expected for millimeterwave applications. The dielectric ceramics with high quality factor are obtained by using high purity raw materials. Temperature coefficients of resonant frequency τ_f of these materials are improved adding rutile with high positive τ_f.

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Porous alumina sintered bodies were fabricated by a new gelate-freezing method. The fabricated porous alumina sintered bodies possess highly continuous open pores, and a wide range of pore size (20-200 μm) and porosity (30-70%). Inside the alumina only a few micro voids were observed. Pore size and porosity were able to be controlled by the alumina and water content in the slurry, and by the cooling temperature and direction.

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A solid-liquid composite electrolyte was synthesized by impregnating a liquid lithium electrolyte into a silica mesoporous thin film. Silica mesoporous thin films were prepared by a self-assemble method using different surfactants as the template, and a lithium liquid electrolyte was impregnated into the mesopores of the films by vacuum impregnation. The ionic conductivity of the composite electrolyte was mainly influenced by pore diameter and the presence of surfactants in the mesopores of the films. The highest conductivity of 2.0×10^-3 S/cm was obtained in the film prepared using Pluronic F127 as a template, with surfactant-free largest mesopores.

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Eu-doped BaTiO₃ ceramics (EBT) were prepared by the cold-pressing ceramic process on the basis of the formula Ba_1-xEu_xTi_1-x/8O₃ (x=0.01-0.05, 0.10). The effects of Eu doping on the structure, microstructure, dielectric and ferroelectric properties of BaTiO₃ ceramics were studied. EBT ceramics have a high density, a low porosity and a fine grain size of 0.7-1.0 μm. As x≤3%, EBT ceramics have a tetragonal perovskite structure. The Curie point decreases linearly at a rate of -11°C/mol% Eu ions with increasing Eu content up to 0.04. However, at x≥0.04, a secondary phase, Eu₂Ti₂O₇, occurs and increases in concentration with increasing Eu, the Curie point remaining constant. The room-temperature dielectric constant of EBT ceramics (ε′_RT=1600-3100) shows a temperature-independent dielectric region below 50°C at x≥0.04, a frequency stability below 10⁶ Hz and good ageing resistance behavior.

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Second harmonic generation was observed from thermally poled GeS_x (x=3, 4, 5, 6) glass system. The intensity of second harmonic generation depended on the S content. From x=3 to 5, the generation increased with increasing S content, and then decreased at x=6. There was apparent dependence of the second harmonic generation on poling temperature. The maxima appeared by poling at near glass transition temperature. By electron spin resonance and Raman scattering measurements before and after poling, it is evident that defects were formed by poling and the structure was deformed, which could relate to the generation. The relaxation of the generation was interpreted according to a recombination of defects and to a relaxation of structural deformation.

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Large ruby crystals, exhibiting the typical transparent-red color, have been successfully synthesized by the evaporation of molybdenum trioxide flux. The grown crystals were up to 3.1×3.0 mm in size. In the case of 99 mass% of flux evaporation, the crystal sizes were dependent on the mixture (solute+flux) amounts. A sixfold increase in the mixture amount (30 to 180 g) resulted in double or higher increase in the average sizes (1.2×1.0 mm to 2.5×2.2 mm). The basic form of the grown crystals was a hexagonal bipyramid which consists of twelve well-developed {1123} faces. Furthermore, {0001} faces were also observed in large crystals, besides {1123} faces.

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Zeolitic tuff which was milled to different particle size was reacted with 50 mass% of ordinary portland cement as pozzolanic resource in the condition of 60°C-2h steam cure and 180°C-4h hydrothermal treatment. For comparison, fly ash was also used as pozzolanic resource. The structure and the humidity controlling performance of the hardened bodies were investigated. The product from zeolitic tuff of which mean particle size was 7 μm contained portlandite and amorphous calcium silicate hydrate. After hydrothermal treatment, almost all portlandite changed to C-S-H and tobermorite reacting mainly with mordenite in zeolitic tuff but crystalline foreign substances like feldspar. The main peak of pore diameter in the hardened body after hydrothermal reaction was about 4 nm irrelevant to the particle size of the pozzolanic resource. Water vapor adsorption isotherm of the product which was dried at 150°C showed rapid adsorptive and desorptive variation in the range of 30-50 RH%. Compared with the product from fly ash, the amount of water vapor adsorption in the product using zeolitic tuff showed 2 times as much. This result corresponds to the pore volume that was measured by N₂ gas adsorption isotherms. By using bead mill, the mean particle size of zeolitic tuff could reach to 240 nm. The product made by this pozzolanic resource using steam cure and hydrothermal treatment showed that the pore volume around 4 nm considerably increased (0.62 cm³ g^-1), and so did the amount of water vapor adsorption and desorption.

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The objective of this study was to form a crystalline oxide film on an aluminum substrate using micro-arc oxidation (MAO) processing at half-wave rectification current. A crystalline oxide film was able to be formed on an aluminum substrate using this method. It was found that the electrolytic aqueous solution selectivity, discharge condition, oxide film surface condition and reaction mechanism observed in MAO-processing at half-wave rectification current were different from those observed in MAO-processing using a direct current. The electrolytic aqueous solution selectivity range was small, and in many instances a small discharge appeared during MAO-processing at half-wave rectification current. Furthermore, the surface of the film was generally smooth and contained small pores. Combining both of the MAO-processing was possible, with the result that the condition of the film surface was significantly influenced by the second step MAO-processing.

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Several harmful metal ions (M=Mn(II), Cu(II), Zn(II), Cd(II) and Pb(II)) were completely immobilized in the crystalline zirconium phosphate, HZr₂(PO₄)₃, by thermal-treating the mixture of M(NO₃)₂ and HZr₂(PO₄)₃ under the molar ratios of M(NO₃)₂/HZr₂(PO₄)₃=0.1-0.5 at 700°C for 5 h. The XRD analyses suggested that all the M(II) immobilized products have the same structure as that of the NASICON-type HZr₂(PO₄)₃. Such immobilized products were subjected to the leaching test of M(II) ion in 1 mol•dm^-3 HCl at 160°C for 24 h. For the M(II) immobilized products with the ratio of M(NO₃)₂/HZr₂(PO₄)₃=0.5, the leaching rate was decreased with the increase in ionic radius of M(II).

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A planetary homogenizing was employed as a novel method to prepare Al₂O₃ slurries. The planetary-homogenized slurries showed very low viscosity, compared to the ball-milled slurries. Moreover, the viscosity of the planetary-homogenized slurries was stable for long times, whereas that of the ball-milled slurries increased rapidly with time. Casting rate of planetary-homogenized slurries was more sensitive to the solid content of slurry than that of the ball-milled slurries. The relative density of the green bodies prepared from the planetary-homogenized slurries was about 60% or more and was independent of the slurry solid content. On the other hand, the relative density of the green bodies from the ball-milled slurries changed depending on the solid content and was higher than 60% at the solid content of 50% by volume. Linear shrinkage of the sintered bodies prepared from the planetary-homogenized slurries was very low and independent of the solid content; as compared to that observation the sintered bodies prepared from ball-milled slurries, which increased with decreasing solid content.

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Red and transparent ruby crystals have been successfully grown by a evaporation method of A₂O(A=Na, K)-MoO₃ fluxes. The grown crystals were up to 3.4×2.2 mm in size. The evaporation loss of the fluxes (A₂O+MoO₃) decreased linearly with an increase in the amount of A₂O when the holding time was fixed at 5 h. As a result, relatively large crystals were grown from the A₂O-MoO₃ fluxes as compared with the solo MoO₃ flux (max. 1.8×1.7 mm), because time to grow crystals could be lengthened. The influence of a variety of A₂O on ruby crystal growth was hardly observed in our study. The basic form of the ruby crystals was a hexagonal bipyramid bounded by twelve well-developed {1123} faces, and showed the peculiar shape to the MoO₃ system fluxes.

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