Zinc oxide nanorods (ZnO-NRs) were prepared on a Si wafer by hydrothermal processing (single-roughness ZnO-NRs). Subsequently, some samples were treated using hydrothermal processing again under an alkaline condition to produce nanoscale roughness on the topmost surface ({0001}) of the rod (double-roughness ZnO-NRs). The obtained samples possessed the expected structure and were coated with a hydrophobic fluoroalkyl silane. These samples consequently became highly hydrophobic. The double-roughness ZnO-NRs exhibited higher sliding angles than the single-roughness ZnO-NRs. The double-roughness ZnO-NRs fog-harvesting performance was better than that of the smooth FAS9 coating or the single-roughness ZnO-NRs. The time dependence of the entire harvested water amount corresponds to the theoretical calculation. The droplet overlapping is expected to affect the results obtained for the double-roughness ZnO-NRs.

The vapor-phase growth of zirconium carbonitride (ZrCN) on carbon substrates was demonstrated by laser chemical vapor deposition using an alkyl-amide precursor as a single source. The effects of deposition temperatures on the phase formation, microstructure, chemical bonding states, and deposition rates of ZrCN layers were investigated. An amorphous layer with a large amount of oxygen impurity was deposited at a temperature of 1373 K, whereas a crystalline ZrCN phase with a face-centered cubic structure (fcc-ZrCN) was formed with an excess amount of free carbon at a deposition temperatures of 1453 K. The fcc-ZrCN layer had cone-like nodular morphology with a dense cross section, where the dendritic microstructure comprising nano-sized ZrCN grains with finely dispersed carbon was formed in the fcc-ZrCN layer at 1453 K. The deposition rate of the fcc-ZrCN layer was 40 µm h⁻¹.

Novel F⁻ ion conducting solid electrolytes of La_1−xMg_xO_1−δF were developed by doping Mg²⁺ cation into the La³⁺ site of lanthanum oxyfluoride (LaOF) solid. By doping the smaller size and lower valent Mg²⁺ cation into the La³⁺ site, both the suppression of the phase transition from α- to β-form and the improvement of conductivity were simultaneously realized. Among the samples holding the single phase of α-LaOF type structure, the La_0.8Mg_0.2O_1−δF solid showed the highest F⁻ ion conductivity, which was ca. 46 times higher than that of non-doped LaOF solid.

Niobates, CaNb₂O₆ with columbite-type structure doped with Er³⁺ (CaNb₂O₆:Er³⁺) and co-doped with Er³⁺ and Yb³⁺ (CaNb₂O₆:Er³⁺/Yb³⁺) were synthesized from precursor solutions using inorganic salts under mild hydrothermal conditions at 240 °C. The as-prepared niobates appeared to be a sheaf of aligned acicular particles. At 3 mol % Er³⁺, the as-prepared CaNb₂O₆:Er³⁺ showed the strongest photoluminescence (PL) in the characteristic green spectral region corresponding to the ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺. The green PL intensity of the sample doped with 5 mol % Er³⁺ after heating at 1300 °C in air was more than 10 times stronger than that before heating when exciting directly at 377 nm. The effect of the concentration of the sensitizer Yb³⁺ on the up-conversion emission of CaNb₂O₆:Er³⁺/Yb³⁺ was investigated using samples after heating in air. The up-conversion emission intensity of CaNb₂O₆:Er³⁺/Yb³⁺ became the maximum at 5 mol % Er³⁺ and 20 mol % Yb³⁺ under excitation at 980 nm.

Luminescent columbite-type CaNb₂O₆ crystals undoped and doped with Eu³⁺ (CaNb₂O₆:Eu³⁺) and Tb³⁺ (CaNb₂O₆:Tb³⁺) have been synthesized at 240 °C using hydrothermal method from precursor solutions of inorganic salts. Microscopic examinations reveal that the morphology of the columbite crystals is like thin rods or needles (width: 0.1–0.3 µm, length 5–10 µm). The red, green, and blue light-emitting CaNb₂O₆-based materials have been prepared. Under the UV light excitation, the as-prepared CaNb₂O₆ presents a broad and blue photoluminescence (PL) peaked at 452 nm, originated from the niobate octahedral group [NbO₆]⁷⁻. The columbite-type CaNb₂O₆ with 12 mol % Eu³⁺ synthesized hydrothermally at 240 °C shows the strongest PL: weak orange and strong red light, attributed to the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions of Eu³⁺, respectively. The intensities of blue–green and green PL bands originated from the ⁵D₄→⁷F₆ and ⁵D₄→⁷F₅ transitions of Tb³⁺, respectively for the as-prepared CaNb₂O₆:Tb³⁺ reach the maximum at 10 mol % Tb³⁺, and their PL intensities have been improved by heating at 1000 °C in air.

Apatite nuclei (ApN) were precipitated by raising the pH of simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. The maghemite (γ-Fe₂O₃) particles were attached to the ApN, and the particles were subsequently soaked in SBF adjusted at pH = 7.60, 36.5 °C for one day. By this treatment, the ApN induced hydroxyapatite (HA) formation and the γ-Fe₂O₃ particles were encapsulated with HA particles with approximately 1–2 µm in diameter. The specific surface area of thus-obtained HA/Fe₂O₃ particles was almost 27 times as large as that of the commercially obtained HA particles. Urease or superoxide dismutase (SOD) was immobilized on the surface of the HA/Fe₂O₃ particles in ultrapure water, and the particles were collected by using a neodymium magnet. It was indicated that more than 90 % of urease or SOD was collected by using the HA/Fe₂O₃ particles. By using the urease immobilized on the HA/Fe₂O₃ particles, furthermore, urea dispersed in buffered solution almost completely decomposed. As the immobilization efficiency of urease increased, the urea decomposition was promoted.

The application of titanate nanosheets chemically modified by organic ligands to a photocatalyst was examined. Titanate nanosheets have very wide band gap, because of quantum size effect. Ultraviolet light with very short wavelength is required for photocatalysis of titanate nanosheets. In order to circumvent this problem, titanate nanosheets were modified by organic ligands, and the charge transfer from the organic ligands to titanate nanosheets was utilized for photocatalysis. Titanate nanosheets were synthesized by bottom-up process in aqueous solution. Catechol, hydrogen peroxide (H₂O₂), and 2,5-dihydroxyterephthalic acid (DHTP) were used as an organic ligand. Upon adding organic ligands to titanate nanosheet sols, the ligands were adsorbed preferentially on the edge of nanosheets. The adsorption of ligands enabled the absorption of light with a long wavelength. In the case using catechol and H₂O₂, the charge transfer from the Highest Occupied Molecular Orbital (HOMO) level of ligands to the conduction band of nanosheets occurred by photo-irradiation. On the other hand, the adsorbed DHTP caused photo-sensitization, that is, the charge transfer from HOMO through Lowest Unoccupied Molecular Orbital of ligands to the conduction band of nanosheets. Furthermore, the photocatalysis of the titanate nanosheets modified by H₂O₂ or DHTP was investigated by utilizing the reduction of [Ag(NH₃)₂]⁺ to metallic Ag nanoparticles. The titanate nanosheets modified by H₂O₂ did not exhibit photocatalytic reactions, while in the case using DHTP, the formation of Ag nanoparticles by photocatalysis was observed. Probably, this difference was attributed to the rate of the recombination of electrons and holes formed by photo-irradiation, which was likely dependent on the mechanism of the charge transfer caused by photo-irradiation.

Various types of samples with nominal compositions of Ba_1−xLn_xFeO_3−δ and BaFe_1−xLn_xO_3−δ (Ln: lanthanoid or Y) were prepared and their phases were analyzed. The types of Ln and their substitutional amounts were clarified to obtain the cubic perovskite phase with a random arrangement of oxide ion vacancies, which have attracted interest as new hole- and oxide-ion-mixed conductors. Ln was classified into three groups based on its ionic radius: Large La was substituted for only the Ba site, whereas small Ln such as Y, Ho, Er, Tm, and Yb were substituted for only the Fe site. Ln with intermediate ionic radii, such as Nd, Sm, Eu, Gd, and Dy, could be substituted for both Ba and Fe sites. Results indicated that the differences in ionic radius between 12-coordinated Ln and Ba as well as between 6-coordinated Ln and Fe were responsible for the determination of substitutional sites. The ratio of the ionic radius of Ln³⁺ to that of O²⁻ was also proposed to be a factor in the determination of substitutional sites, which is in agreement with the rigid sphere model. A cubic perovskite phase with a random arrangement of oxide ion vacancies was obtained for Ba_1−xLn_xFeO_3−δ and BaFe_1−xLn_xO_3−δ with a tolerance factor between 0.996 and 1.035 and between 1.008 and 1.035, respectively.

A spinel solid solution expressed by a composition formula of Cu_xNi_1−xAl_1.8Cr_0.2O₄ (0 ≤ x ≤ 0.2) was studied focusing on the role of Cu species in the catalytic activity toward NO reduction under a simulated three-way catalysis condition. X-ray Rietveld analysis revealed that Cu and Cr prefer to occupy the tetrahedral site and the octahedral site, respectively, whereas Ni and Al are distributed across both sites. Although NiAl_1.8Cr_0.2O₄ (x = 0) showed negligible catalytic activity for NO reduction, the partial replacement of Ni by Cu significantly enhanced the activity, achieving the highest activity at x = 0.05 not only for NO reduction but also for CO and C₃H₆ oxidation. Based on the infrared spectra and pulsed reaction experiments, it was concluded that the monovalent Cu site in the tetrahedral site plays a key role in CO chemisorption, oxygen vacancy formation, and subsequent NO reduction via the Mars–van Krevelen mechanism.

Layered calcium niobate perovskite with partial substitution of Nb by Ru was prepared for the catalyst of H₂ generation from NH₃. The X-ray photoelectron spectroscopy confirmed that the substituted Ru exists at the intralayer position. The layered perovskite was exfoliated and re-aggregated with Ru and Na cation to increase the surface area to form a card house-type porous hybrid. The surface area apparently increased to around 12–18 times compared to the sample without exfoliation. The amount of interlayer Ru is much larger than that of the intralayer Ru from the X-ray fluorescence measurement. From the H₂ generation measurements, different roles of the intralayer and interlayer Ru were considered as follows. The interlayer Ru lowers the starting temperature of the H₂ generation, whereas the intralayer Ru increase the H₂ generation rate.

Carbon membranes comprising micropores were successfully synthesized for the first time on ceramic supports using a hydrothermal method, and their liquid and gas separation abilities were evaluated. The activation temperature was observed to affect both the microstructure and chemical composition of the membranes. The membrane activated at the optimum activation temperature of 1173 K exhibited good ethanol/water separation ability, with a separation factor of approximately 8.1 for a 5 mol % ethanol aqueous solution. Finally, the excellent water resistance of this optimal membrane was confirmed.

Alumina granules were fabricated by using the spray freeze granulation drying (SFGD) and spray drying (SD) processes, and the granule properties, such as the granule size distribution, packing density, angle of repose, and compression strength, were examined. In addition, powder compacted bodies were made from the SFGD and SD granules, and the corresponding densities and defects were evaluated. Furthermore, the compacted bodies were sintered, and their densities and strength were evaluated. It was found that the properties of SFGD granules were affected by the solid content of the slurry, because the slurry droplets were frozen with water to fabricate these granules. The sintered body fabricated from SFGD granules exhibited a higher strength compared to that from the SD granules, as weak and homogeneous granules were fabricated using SFGD.

Cr and Mn co-doped Zn_0.95−xCr_0.05Mn_xAl₂O₄ nanoparticles with different contents of Mn were synthesized via simple hydrothermal route and heat treatment technology. The influences of Cr and Mn doping on the microstructure, morphology, binding energy and optical property of the as-synthesized samples were characterized. X-ray diffraction confirm that Zn_0.95−xCr_0.05Mn_xAl₂O₄ nanoparticles exhibit cubic spinel structure, the average crystallite size decrease and the lattice parameter increase with the increase of Mn doping concentration. X-ray energy dispersive spectroscopy and X-ray photoemission spectroscopy demonstrate Cr and Mn ions are successfully substituted for the lattice site of Zn²⁺, enter ZnAl₂O₄ matrix and mainly occupy the tetrahedral sites of the doped samples. Scanning electron microscopy and high-resolution transmission electron microscopy show the morphology of the samples are irregular spherical or ellipsoid particles with small particle size and good dispersion. Ultraviolet–visible spectra indicate co-doped samples possess strong visible light absorption ability, and the band gap decrease as Mn ions concentration increase and occur red shift. Photoluminescence spectra show the intensity decrease and occur luminescence quenching phenomenon for doped samples. The intensity of Fourier transform infrared spectroscopy for doped samples decrease slowly and occur red shift.

To stabilize the quality of insulating bricks made from Noto-diatomaceous earth (Noto-DE), control of the shrinkage during firing by the addition of calcium sources to the raw material was investigated. The shrinkage mechanism was elucidated from investigation of the phase change at 1000 °C and comparison of the component distributions of materials between Noto-DE and other diatomaceous earths (DEs) with different characteristics. In every DE, the effect of firing shrinkage control by the addition of calcium sources and the increase of wollastonite phase in the base materials with an increase of the firing times were confirmed. In addition, it can be concluded that the silica source of wollastonite is derived from amorphized clay minerals, due to the absence of Ca in amorphous diatom shells. It is suggested that the control of the firing shrinkage of insulating bricks made from DE with additional calcium sources is due to the crystallization of wollastonite originating from the silica source of amorphized clay minerals.

The chelate flame spray (CFS) method is an inexpensive flame spray technique with low energy consumption used to deposit metal oxide (M₂O₃) films using M-ethylenediaminetetraacetic acid (EDTA·M·H) complexes. In this study, EDTA·Er·H was used as the raw material to investigate the cross-sectional structures of the Er₂O₃ films, and substrates with different common materials, i.e., quartz glass, stainless steel (304), and aluminum-magnesium alloy (A5052), were selected. We found that in the CFS deposition process, EDTA·Er·H was decomposed, oxidized and melted in the flame to form molten Er₂O₃ particles, and Er₂O₃ films with an average thickness of 9.7–13.5 µm, cross-sectional porosity of 1.6–4.9 %, and crack numbers of 29–51 were deposited on quartz glass. Oxide films with 7.6–14.3 µm thickness were synthesized on an aluminum-magnesium alloy (A5052) substrate. The cross-sectional porosity and microcrack numbers of these films were 5.2–6.9 % and 10–20, respectively. In addition, to observe the Er₂O₃ film stacking structure more clearly, we screened the powder raw materials to make them uniform. The results of this study enable the design of a ceramic film microstructure that reduces cracks in the ceramic film, thereby increasing the application potential.

We have for the first time fabricated the textured ceramics of doped lanthanum silicate oxyapatite (LSO) by templated grain growth method. Tabular template particles of K₂O- and F-doped LSO with well-developed {001} faces were grown by KF flux method, and aligned in BaO-doped LSO matrix by tape casting. The tapes were punched out into disk-shaped pieces, stacked in two layers, and sintered at 1873 K for 50 h. We obtained a disk-shape K₂O- and BaO-doped LSO polycrystal aligned in the c-axis with small amounts of two types of interstitial materials. The texture fraction of apatite {0 0 l} planes was 0.45. The doped LSO was characterized by the heterogeneous distribution of K₂O, the component of which originated from the template particles, within the crystal grains. The chemical formula of the doped LSO was derived from the average composition to be (La_8.43K_0.03Ba_1.43□_0.11)_Σ=10(Si_5.96□_0.04)_Σ=6O₂₆, where □ denotes vacancies in La and/or Si sites. One type of the interstitial materials was composed mainly of BaO and La₂O₃, and the other was rich in SiO₂. As the temperature increased from 773 to 1023 K, the bulk oxide-ion conductivity (σ) steadily increased from 1.89 × 10⁻⁴ to 2.48 × 10⁻³ S cm⁻¹, with the activation energy of conduction (E_a) being 0.78 eV. The σ-values of randomly oriented polycrystal with the same bulk chemical composition steadily increased from 3.89 × 10⁻⁵ to 4.99 × 10⁻⁴ S cm⁻¹ with increasing temperature from 773 to 1023 K (E_a = 0.78 eV). When the σ-values were compared at the same temperatures, they were 6.7 (973 K)–8.2 (923 K) times higher for the former polycrystal than for the latter. The larger σ-values of the c-axis-aligned polycrystal would be principally induced by the substantially higher oxide-ion conductivity along the c-axis than along the other directions in K₂O- and BaO-doped LSO.

Octacalcium phosphate (OCP) blocks are attractive feedstocks for new biomaterials because of their excellent biocompatibility. Attaching an interconnected porous structure (i.e., a foam) is a good way to use OCP as a bone substitute because this structure allows tissue penetration in the materials. However, the foaming structure shows a lower mechanical strength compared to block-formed materials. In this study, we fabricated OCP foams with enough mechanical strength from calcium dihydrogen phosphate granules of different sizes (100–250, 250–500, 500–1000, and 1000–2000 µm) through a setting reaction using an acidic phosphate solution and a phase-conversion process. The fabricated OCP foams were found to have high enough mechanical strength (>0.5 MPa in diametral tensile strength) and porosity (∼70 %). For small granules, a relatively low concentration of acidic phosphate solution was suitable for the setting reaction.

Sodium manganese oxide plays an important role in the cathode application of sodium ion batteries. In this study, sodium manganese oxide Na₂Mn₃O₇ (NMO) with a triclinic structure was successfully synthesized via a low-cost, simple conventional mixing method. NaMnO materials were synthesized by mixing Na₂CO₃ precursors and the two different types of Mn precursors, namely MnO₂ by a solid method (the sample C) and MnCl₂ by a sol–gel method (the Sample D). The calcination of both samples was carried out at 800 °C for 3 h. The results shown that the thermal behavior and crystal characteristics of the Sample D are slightly better than another one. Nevertheless, the Sample C exhibits a better microstructure, showing rod-like particles more dominant than particular particles. In addition, the Sample C reveals a little bit larger surface area than the Sample D.

In this study, we introduce a simple and effective method for producing a ternary solid-solution of diborides, a medium-entropy Zr_1/3Hf_1/3Ta_1/3B₂. Using commercially available diboride powders with equimolar ratio and performing spark plasma consolidation at 1927 °C we demonstrate that single-phase medium-entropy ceramic can be consolidated using an hour-long procedure. The flexural strength and fracture toughness at room temperature were 318 ± 14 MPa and 2.9 MPa m^1/2, respectively.

This study investigated the in-flight melting method using an oxygen-excess gas burner with which glass powder with specific elemental components can be easily produced in one quick energy-saving-process (<1 s). First, granulated raw powder was formed from soda-lime-glass batch components by using a spray-drying machine and dropped directly into an oxygen–excess gas burner with a vertical downward converging flame. Partially or fully melted materials with powder-like shapes were formed in the flame and collected along the flight path through the flame. Granulated raw powder and powder-like sample materials collected at different positions in the flight path were observed by X-ray diffraction (XRD), optical microscopy, and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The granulated raw powder included only crystals. The XRD peaks of these crystals disappeared and the halo identifying them as glass materials became more pronounced in the powder-like materials collected in going from the upstream to downstream positions in the flight path. We calculated the vitrification ratios by using the main peak intensities of SiO₂ in the XRD data; the vitrification ratio for a ∼600-mm-long path was ∼85 %. We observed changes in the morphology and elemental distribution on the surfaces of the samples by using optical microscopy and SEM-EDS and in cross sections of the samples by SEM-EDS. Although the sodium and oxygen, the silicon and oxygen, and the calcium partial distributions differed from each other on the surfaces and in the cross sections of the granulated raw powder and sodium parts were often observed around the silicon part on the surfaces and in the cross sections of the granulated raw powder and samples collected at upstream positions, the elemental distributions of the collected materials became more homogenous as vitrification proceeded from up-to-downstream, and the materials eventually became glass.

We successfully fabricated dense aluminum nitride (AlN) ceramics containing AlN whiskers by low-temperature pressureless sintering and evaluated their microstructures, thermal conductivities, and mechanical strengths. Furthermore, the anisotropy of thermal conductivities caused by the orientation of AlN whiskers was also evaluated. The thermal conductivities of the samples measured in parallel and perpendicular to the longer direction of AlN whiskers were 98 and 67 W m⁻¹ K⁻¹, respectively. The bending strengths of the samples without and with AlN whiskers were 147 and 235 MPa, respectively. From the observation of the fracture surface of the samples, AlN whiskers in the samples probably withstand the fracture originating from weak grain boundaries.