In this work, a potentially novel ceramic-based composite was developed for photocatalytic activity. Hot-press sintered Al₂O₃/Ti composites containing 20 vol.% of metallic Ti were treated with NaOH and heated to generate a nanometer-scale structure to induce an active surface layer for photocatalytic activity. Because NaOH treatment does not affect Al₂O₃ ceramics, to form a nano-structured titania layer over the entire surface of a composite whose surface contains both Al₂O₃ and Ti, strict control was exerted over the NaOH concentration, treatment temperature, and time. The results showed that Al₂O₃/Ti composites were fully covered by nano-structured sodium containing titanate layers after being treated with 5-M NaOH at room temperature for 3 h and at 60°C for 1 h. After HCl treatment at 25°C or water treatment at 80°C for 24 h, Na⁺ ions were sufficiently removed and a nano-porous structure of titanate remained despite a widened network. HCl treatment and heat treatment at temperatures of 400–600°C changed the surface structure from a nano-porous network to nano-plates or nanorods of titania. The photocatalytic activity of Al₂O₃/Ti composites treated with NaOH, HCl, and heat was also investigated. Samples heated at 600°C exhibited the highest Rhodamine B degradation efficiency of 35% after exposure to ultraviolet light for 12 h, implying the multifunctionality of the surface-modified ceramic/metal composites.

Equipment that can generate a linear drive type of modulated rotating magnetic field (MRF) was developed for three-dimensional magnetic alignment applicable to a continuous production process. This equipment consists of an arrayed magnet unit assembled using permanent magnets and a linear drive system, and it can generate a static magnetic field region with 0.9 T and a rotating magnetic field region with 0.5–0.9 T and 520 rpm. The equipment has been used to successfully biaxially align powders of an orthorhombic cuprate superconductor DyBa₂Cu₃O_y (y∼7) with twin microstructures in epoxy resin at room temperature without rotating the sample.

New technological demand has been opened rapidly to develop a fabrication of coating thin film on various substrates via relatively sustainable methods with consuming least resources and conserving energy. To satisfy the new demand, we propose an original process to fabricate functional ceramic films at ambient temperature by an ultraviolet light reaction after coating of metal–organic compound and nanoparticles on substrates. Based on our research, oxide thin films containing of epitaxially grown grains as well as polycrystals can be individually fabricated by changing the process parameter. In this review, I introduce about highly functional thin films developed with my collaborators. The novel thin films include a flexible transparent conductive film, a high-brightness phosphor film, and bolometer film with a high temperature coefficient of resistivity. I introduce an effectiveness of our laser irradiation process to control a texture such as polycrystals and epitaxially grown grains in novel and/or flexible ceramic thin films. In addition, I explain the mechanism and influencing factors of the generation of these thin films and discuss the applications of the films to electronic and optical components and devices.

TiB₂/Ti₂AlN composites with different proportions were successfully fabricated through solid state reaction of Ti/Al/AlN/BN powders and subsequent hot pressing sintering. The reaction mechanism, microstructures and mechanical properties of the composites were investigated. The Vickers hardness of the samples ascended with increases in the TiB₂ content and reached the highest value of 11.32 ± 0.12 GPa at a TiB₂/Ti₂AlN mole ratio of 1:2 (M2T1). TiB₂/Ti₂AlN composites with a mole ratio of 1:3 (M3T1) and 1:4 (M4T1) exhibited the maximum flexural strength of 497 ± 15 MPa and the highest fracture toughness of 9.52 ± 0.14 MPa·m^1/2, respectively, which are 1.3 times and 1.8 times that of pure Ti₂AlN (MT0) ceramic.

Manganese dioxide having nanorod and nanoflake morphologies have been successfully prepared by electrolysis of KMnO₄ at a temperature of 60°C. The acidity of the solution substantially influenced the particle morphology. The particles had nanorod morphology at a very acid solution (pH 0.2) whereas they had nanoflake shape at the base condition (pH 9). X-ray diffraction analysis revealed that the particles generated at very acid condition were α-MnO₂. On the other hand, the particles synthesized at base condition were amorphous MnO₂. The electrocatalytic activity towards oxygen reduction reaction (ORR) of the materials was studied in oxygen-saturated 0.6 M KOH solution. The electrons transferred per oxygen molecules of ORR for nanorod and nanoflake MnO₂ particles were 2.23 and 1.75, respectively. The results suggest that nanorod MnO₂ particles exhibit better ORR activity corresponding to 2-electron transferred ORR mechanism.

Microwave dielectric properties of MgTi_1−x(Zn_1/3B_2/3)_xO₃ (B = Nb⁵⁺, Ta⁵⁺, 0.025 ≤ x ≤ 0.125) were investigated based on their structural characteristics and the electronegativity difference of the constituent ions. For the specimens of MgTi_1−x(Zn_1/3Nb_2/3)_xO₃, a single phase of the rhombohedral ilmenite structure appeared for the entire range of compositions (0.025 ≤ x ≤ 0.125), while MgTi_1−x(Zn_1/3Ta_2/3)_xO₃ showed a single phase of ilmenite structure up to x = 0.075, and then MgTi₂O₅ was detected as a secondary phase on further substitution of (Zn_1/3Ta_2/3)⁴⁺ at Ti⁴⁺-site of MgTiO₃. Quality factor value increased with the electronegativity difference up to an electronegativity difference of 2.015 and was dependent on the degree of covalent character of the bond. Temperature coefficient of resonant frequency decreased with an increase in oxygen octahedral distortion. Dielectric constant of the specimens did not exhibit any remarkable change with the substitution of (Zn_1/3B_2/3)⁴⁺ at Ti⁴⁺-site of MgTiO₃.

Ternary rare earth rhenium oxides Ln₃ReO₇ (Ln = Y, Er–Lu) have been prepared. Their X-ray diffraction measurements and the Rietveld analysis show that these compounds have an orthorhombic superstructure of fluorite-type with space group C222₁ (for Ln = Y, Er, Tm) or a defect-fluorite structure Fm3m (for Ln = Yb, Lu). The zero-field-cooling and field-cooling magnetic susceptibility for Y₃ReO₇ diverse when the temperature is decreased through 10 K. At the same temperature, specific heat anomaly is also observed. The results of the specific heat measurements for Tm₃ReO₇ and Yb₃ReO₇ indicate the existence of magnetic anomaly below 7 and 2.2 K, respectively. On the other hand, Er₃ReO₇ and Lu₃ReO₇ are paramagnetic down to 1.8 K.

Single-crystal thin films of gallium oxide (Ga₂O₃), an ultra-wide bandgap semiconductor, were fabricated on c-plane sapphire by mist chemical vapor deposition (mist CVD). The grown α-Ga₂O₃ thin films had low surface roughness, and we characterized their initial crystal growth phase by using atomic force microscopy and X-ray diffraction. By varying the precursor concentration, we changed the surface roughness and crystallinity of the thin films. The lattice constants of the α-Ga₂O₃ thin films almost matched those of the single crystal in the initial growth phase. We also found that these thin films grew hetero-epitaxially. Finally, mist CVD might have a very short incubation time in this system.

One of the methods to improve the lifetime of a multilayer ceramic capacitor with Ni electrode (Ni-MLCC) is vanadium addition. With the addition of vanadium, insulation resistance deteriorates and reliability improves. The resistance elements of the three resistor-capacitor electrical equivalent circuit: dielectric-electrode interface, grain boundary, and grain, all deteriorated. In particular, the interface resistance significantly deteriorated with the increase in vanadium. The experimental results suggest that the high interface resistance is not always necessary to improve reliability of Ni-MLCCs. It is deduced that oxygen vacancy formation is suppressed with vanadium addition from the first principles calculation and the thermally stimulated depolarization current analysis. Therefore, the decrease in oxygen concentration is the main factor for improving reliability with vanadium addition.

We proposed a novel method to evaluate strain components in PbTiO₃ thin films using Raman spectroscopy. In this method, the strain components are calculated from peak shifts of three E(TO)-modes. The coefficients to calculate the strain components were decided via least square technique using experimental values for two-dimensional stress and hydrostatic pressure. The strain components that were estimated using the obtained coefficients were in good agreement with those measured by X-ray diffraction measurement (XRD). The average error between the strain components evaluated by XRD and Raman spectroscopy was about 0.05%.

In this study, the surface of zirconia (ZrO₂) substrates was modified by the combination of plasma treatment and coating with silicon-substituted hydroxyapatite (Si-HA) sols, comprising an expected theoretical Si content of 0 (Si-HA0), 1.70 (Si-HA1), 3.44 (Si-HA2), and 7.01 wt % (Si-HA4) for improving the biological performance of substrate. The Si-HA-coating layers were successfully deposited on the ZrO₂ substrate surface. These coating layers exhibited a three-dimensional interconnected microporous structure and a single-phase crystal owing to HA, implying that the Si content hardly affects the phase composition and microstructure of the coating layers. The dissolution rate of the Si-HA coating layers in deionized water increased with the Si content, which affected the proliferation of mouse calvaria pre-osteoblasts (MC3T3-E1). Cytocompatibility test results revealed that Zr-Si-HA2 substrate, which was coated with Si-HA2, promoted the proliferation and differentiation of MC3T3-E1 more rapidly than the other substrates. These results revealed that Zr-Si-HA substrates are ideal biomaterials for bone tissue engineering.

We have studied the water durability of ZrO₂ containing FeO–Fe₂O₃–P₂O₅ glasses for the immobilization of nuclear waste including Zr isotope. ZrP₂O₇ crystals with 1–2 micrometer in diameter were precipitated in the glass matrix incorporated with ≥1 mol % ZrO₂. The molecular structure of phosphate network including ZrP₂O₇ precipitates was analyzed by micro-Raman spectroscopy. Formations of Q¹ and Q⁰ phosphate units contributing to better water durability are ascribed to preferential precipitation of ZrP₂O₇ crystals with Q¹ units and the compensation of phosphate component in residual glass matrix.

Microwave heating is known to provide extremely rapid synthesis of silicon carbide (SiC) from mixtures of silicon and carbon powders. The formation mechanism has long been considered to be a solid-state reaction among the powders in the mixture. Here, we present a new reaction mechanism via a gas-phase route. We have confirmed successful synthesis of β-SiC powder by microwave-heating of a small amount of Si powder that was entered into a quartz tube and then embedded in graphite powder, although no direct contact between the Si and graphite powders was allowed. Scanning electron microscopy observations revealed that the β-SiC powder was formed by direct carbonization of the Si powder. Since the atmosphere during the reaction comprises a vast majority of carbon monoxide (CO) gas according to the Boudouard equilibrium, the carbonization appears to have taken place via the CO gas. The contribution of such a gas-phase reaction could account in part for the rapidity of the microwave-heating reactions reported so far, which can hardly be explained solely by solid-state reactions among the mixed powders.

We have developed methods to functionalize polystyrene (PS) substrates with hydroxyapatite (HAp) via protein adsorption layers in simulated body fluid (SBF), a solution with similar inorganic ion concentrations to those of human plasma. In this study, three-dimensional (3D) porous HAp cell scaffolds were prepared by using PS substrates as a template. Human serum albumin was adsorbed on the 3D porous PS. Then substrates were pretreated with alternate soaking process using solutions containing calcium ions and phosphate ions followed by incubation with SBF. By optimizing the treatment conditions, 3D porous substrates were completely coated with bone-like HAp maintaining porous structures. Human mesenchymal stem cells proliferated and migrated into inside of the HAp-coated scaffolds and secreted abundant fibrous extracellular matrix. This method can provide porous HAp substrates with the specific functions such as biodegradability or excellent strength to weight ratio by changing polymers used as templates.

A tantalum(V) nitride (Ta₃N₅)-containing powder for non-toxic red pigments was prepared by heat-treatment for the mixed powders of tantalum(V) oxide (Ta₂O₅), aluminum nitride and potassium fluoride in nitrogen atmosphere without flowing ammonia. The foreign ions of K⁺ and Al³⁺ were incorporated into Ta₃N₅ in the synthetic process. The incorporation of the ions had an influence on the hue of Ta₃N₅. It can coordinate a reddish color of Ta₃N₅ pigments.