Many ceramics are produced by powder processing. Ceramic technologies have been developed on the basis of scientific understanding of powder preparation, molding and sintering. Particle structure is a key factor to predominate the properties of final sintered materials. Although SiC was hardly sinterable, SiC nanopowder significantly enhanced the densification according to the sintering mechanism. The composite particles consisting of multiple components were useful for production of ceramic composites: Si₃N₄ and SiC-base nanocomposites by vapor phase reaction processes, MoSi₂-SiC by carbothermal reduction, Ni-TiC by chemical plating, and Ni-Al₂O₃ by agglomeration coating, improving the mechanical properties. New sintering technique is another factor to control sintered textures as well as appropriate sintering aids. Spark plasma sintering was effective to produce fine-grained microstructures of SiC and Si₃N₄ sintered materials. It was notable that translucent Si₃N₄ ceramics were fabricated using AlN-MgO additive. The translucent Si₃N₄ ceramics were superior in mechanical and thermal properties to the other oxide translucent materials. Ceramics have various possibilities owing to its diversity in elemental combination and microstructure. The importance is new knowledge and technology to draw their essences and design their functional structures.

I introduced my career from early study of the oxide- and carbide-dispersion-strengthened Cu alloys by the internal oxidation and the mechanical alloying to recent study of porous Cu-Ti alloy with the occasional episodes.

Containerless processing is the way to levitate a melt in air. The levitated melt can be undercooled very deeply because it doesn’t have any contacts with a container wall where inhomogeneous nucleation occurs. Metastable phases often solidify from a deep undercooled melt. Solidification without any crystallization leads to a glass formation of a material with a very low glass forming ability. By annealing the glasses, additional metastable crystalline phases may crystallize. Furthermore, considering that a metastable phase has inevitably a lower melting point than a competing stable phase, the metastable phase will solidify directly from the undercooled melt if the temperature of the melt is lowered than the melting point of the metastable phase. Recently, we have successfully synthesized a variety of functional glasses and metastable crystals by containerless processing using an aerodynamic levitation furnace. In this review, the findings about high refractive index glasses, high elastic moduli glasses, crack resistant glasses, metastable ferroelectrics, and metastable magnetic dielectrics are summarized.

Oxygen coordination environments in transition metal oxides often underpin a variety of structural and physical properties. Engineering the oxygen environments in oxide heterostructures is therefore a key for exploring novel phenomena but also for developing novel oxide-based electronic devices. In this article, we present, by ABF-STEM, direct observations of the oxygen coordination environments in heterostructures consisting of perovskite oxides SrRuO₃ and GdScO₃. We also show that the oxygen coordination environments and magneto-transport properties of the entire SrRuO₃ layer can be engineered through the heterointerface structures. The results demonstrate that the oxygen coordination environments can be used as a parameter controlling additional degrees of freedom in functional oxide heterostructures.

The effects of heat-treatments with various conditions such as temperature, atmosphere and fluxing agents on photoluminescence properties of CaSiSiO₄:Eu²⁺ phosphors were investigated in detail. X-ray absorption fine structure of CaSrSiO₄:Eu²⁺ phosphors heat-treated at various temperatures revealed that the reduction from Eu³⁺ to Eu²⁺ in the precursor powder was effectively promoted at the temperatures higher than melting temperature of fluxing agent. We found that red shift of emission peak was caused by pre-heat-treatment under a reduced atmosphere. The effect of fluxing agents such as BaCl₂, SrCl₂, CaCl₂ on photoluminescence properties of CaSrSiO₄:Eu²⁺ phosphor was also examined. The results indicate that CaSrSiO₄:Eu²⁺ phosphor heat-treated using BaCl₂ flux shows high emission efficiency. We also recognized that the small amounts of Ba²⁺ was incorporated into CaSrSiO₄ lattice due to the ion exchange.

Silver containing hydroxyapatite (AgHA) was fabricated by the heat treatment at various temperatures. AgHA composite powders were prepared by ball-milling with crystalline hydroxyapatite powder and silver oxide. These structural characterizations were carried out by SEM, XRD, FT-IR, and XANES measurements. In the case of AgHA sintered at 800 °C, XRD results showed that the peaks of metallic silver and other silver compounds disappeared, and the a-axis of hydroxyapatite expanded drastically. Furthermore, SEM images shows that silver particles were not observed for AgHA sintered at 800 °C and reappeared for AgHA sintered at 1000 °C. The XANES spectrum of Ag-L₃ edge of AgHA sintered at 800 °C was different from ones of reference materials. According to IR measurements, it seemed that the substitution behavior of silver ion was affected by carbonate ions in hydroxyapatite structure through the heat treatments. Consequently, calcium ions were thought to be substituted by silver ions for AgHA sintered at 800 °C. In addition, antibacterial tests showed that AgHA sintered 800 °C and 1000 °C possessed high antibacterial properties against MRSA.