Recently, it has been reported that phosphate glasses with high proton conductivity in the intermediate temperature range have been successfully developed using a proton carrier injection technique with a high concentration for electrochemical ion substitution. In this review, we summarize the characteristics of the bonding states between protons and oxygen in phosphates and the concepts of material design for achieving high proton conductivity in phosphate materials. This paper introduces a carrier proton injection technique called the alkali-proton substitution (APS) method, which was developed as a process for increasing the concentration of proton carriers and required a breakthrough in the conventional approach to the development of phosphate-glass-based proton conductors. Additionally, the knowledge obtained regarding the correlations between glass components, glass structure, and proton mobility is summarized. This paper also describes the characteristics of proton-conductive phosphate glasses prepared using the APS method, demonstrating that they have the unique property of being able to carry only protons as charge carriers in any atmosphere. In conclusion, future strategies for improving proton conductivity and the potential for developing new applications are discussed.

We studied the effects of crystallization conditions on the conduction properties of the Na₅YSi₄O₁₂-type sodium ion conducting glass-ceramics. Crystallization process was controlled by varying annealing parameters of nucleation time (0–200 h) and crystal growth temperature (900–1100 °C). The present results showed that a shorter nucleation time with annealing at 900 °C for crystal growth gave rise to higher conductivities of 5 × 10⁻² S cm⁻¹ at representative temperatures of 300 °C and 3 × 10⁻³ S cm⁻¹ at 150 °C, respectively. Those results were attributed to the microstructures of glass-ceramics and the conductivities of a whole glass-ceramic were considered to be dominated by those of grains at 300 °C and, on the other hand, strongly influenced by those of grain boundaries at 150 °C. It was found that the dependence of a whole conductivity on the apparent number of grain boundaries calculated as the ratio of a whole thickness to an average grain diameter was stronger in the measurements at 150 °C than at 300 °C. Considering the result, we propose the use of largely grained glass-ceramics for both higher and lower temperature uses.

The effects of strontium substitution on the electrical properties of La₃Ta_0.5Ga_5.5O₁₄ (LTG) are reported. Strontium substituted LTG (Sr-LTG) with a nominal chemical composition La_2.9Sr_0.1Ta_0.55Ga_5.45O₁₄ crystals were grown using the conventional Czochralski method under high and low oxygen partial pressures. The electrical properties and thermal behaviors of the Sr-LTG crystals were also compared with those of pure crystals. Sr substitution was found to affect the electroacoustic constants and thermal expansion coefficient clearly. These characteristics are discussed from crystallographic perspectives. The Sr-LTG crystals grown at low oxygen partial pressures exhibited higher electrical resistivity ρ for pressure sensors used at high temperatures.

In this paper, the properties of the barium titanate (BT)/polyvinylidene fluoride (PVDF) composites were controlled by the self-assembly of the BT secondary particle groups. The self-assembled BT/PVDF composites of 5–20 vol.% BT were prepared with the difference in the viscosity of polyethylene glycol (PEG) of dispersants involved in the self-assembly process. The multifractal properties and dielectric properties of the self-assembled BT/PVDF composites were investigated with controlling by the formation of the self-assembled BT secondary particle groups. The dielectric constant (ε′) increased with an increase in the average secondary particle area (S) of the BT particles. The S increased with an increase in the viscosity of PEG; whereas, the ε′ decreased with the increase in viscosity. The multifractal analysis indicated that the distribution of self-assembled BT secondary particle groups was affected by PEG viscosity. The sample with PEG1000 had aggregates with a BT/PVDF/BT heterointerface, the sample with PEG20000 had agglomerates with a BT/BT interface, and the sample with PEG2000 had both, aggregates and agglomerates. The BT/PVDF/BT heterointerface in the BT aggregates played an important role in improving the dielectric properties of the BT/PVDF composites. Overall, the viscosity of the dispersant affected the self-assembly process as well as the ε′. It was suggested that the multifractal properties and dielectric properties were controlled by the self-assembly of the BT secondary particle groups.

Lithium zinc silicate (Li₃Zn_0.5SiO₄) is a structural analog of the lithium superionic conductor (LISICON) family. In this study, we synthesized a LISICON-type lithium zinc silicate, namely Li₃Zn_0.5SiO₄, from an aqueous solution and found that the electrical conductivity was improved after loading the silicate with 0 to 0.10 mol % Cr, Co, or Ni. X-ray diffraction (XRD) analysis revealed that single-phase Li₃Zn_0.5SiO₄ was obtained at 900 °C for 5 h. The Li₃Zn_0.5SiO₄ exhibited a similar phase to that of basic Li₃Zn_0.5SiO₄ when loaded with less than 0.05 mol % of Cr, Co, or Ni. The electrical conductivity of the synthesized Li₃Zn_0.5SiO₄ was found to be 3.12 × 10⁻⁷ and 2.13 × 10⁻² S·cm⁻¹ at 50 and 300 °C, respectively. The addition of Cr, Co, or Ni to the Li₃Zn_0.5SiO₄ further enhanced the electrical conductivity. Li₃Zn_0.45Ni_0.05SiO₄ exhibited an electrical conductivity of 7.54 × 10⁻⁶ and 4.35 × 10⁻² S·cm⁻¹ at 50 and 300 °C, respectively.

The crystallographic parameters of fluoro-apatite A₅(VO₄)₃F (A = Pb, Sr, and Ba) were refined by the Rietveld method. The refined parameters indicate that the F⁻ anions in Pb₅(VO₄)₃F occupy sites different from those in Sr₅(VO₄)₃F and Ba₅(VO₄)₃F. The F⁻ anions in Pb₅(VO₄)₃F are located around center of the Pb₆ octahedra, while those for Sr₅(VO₄)₃F and Ba₅(VO₄)₃F are located around the center of Sr₃ or Ba₃ triangle. Our structural analysis suggested that this difference is attributed to the over-bonding state of F⁻ anion in Pb₅(VO₄)₃F. The electron density distribution for F⁻ anions suggests the potential ionic conductivity along the c axis in Pb₅(VO₄)₃F.

Bi_1−xLa_xFeWO₆ (0 ≤ x ≤ 0.30) samples were synthesized by a co-precipitation method. Their crystal structure, optical properties, and color of the pigments were characterized as novel inorganic orange pigments. In the case of the La³⁺-doped samples, the target phase was obtained almost in a single-phase form. Strong optical absorption was observed below 550 nm in all samples. As a result, the Bi_1−xLa_xFeWO₆ (0 ≤ x ≤ 0.30) samples exhibited orange colors, and the most vibrant orange hue was obtained at Bi_0.90La_0.10FeWO₆. Although the yellowness value of the Bi_0.90La_0.10FeWO₆ (b* = +37.7) pigment was a little smaller than those of the commercially available orange pigments, the redness value of this pigment (a* = +28.5) was larger. Therefore, this pigment exhibited a reddish orange color as compared with the conventional orange ones. In addition, this pigment was chemically stable. Since the Bi_0.90La_0.10FeWO₆ pigment is composed of non-toxic elements, it could be a new environmentally friendly inorganic orange pigment.

Green-emitting phosphors of Rb₃La_1−xTb_xSi₂O₇ with a K₃NdSi₂O₇-type structure were synthesized via a solid-state reaction technique. Their crystal structures and photoluminescence properties were investigated. Crystal structural analyses of Rb₃LaSi₂O₇ and Rb₃TbSi₂O₇ were carried out for the first time and revealed that the rare-earth sites (La or Tb) were separated by the RbO₆ and SiO₄ units. According to photoluminescence spectroscopy of Rb₃La_1−xTb_xSi₂O₇ monitored at 249 and 481 nm, the highest emission intensity was obtained for the Rb₃TbSi₂O₇ phosphor under the 481-nm excitation, which indicates that the satisfactory separation of the Tb³⁺ ions suppressed the concentration quenching. The intensity of Rb₃TbSi₂O₇ was 32 % in comparison to that of the commercial green-emitting (La_0.52Ce_0.31Tb_0.17)PO₄ phosphor.

Eu²⁺-activated Ca₃MgSi₂O₈ (Ca₃MgSi₂O₈:Eu²⁺) phosphors were successfully synthesized by an amorphous metal complex method using propylene glycol-modified silane (PGMS) and heat-treatment under a reduced atmosphere at 1400 °C. The photoluminescence (PL) of Ca₃MgSi₂O₈:Eu²⁺ was studied as a function of total Eu concentration. Furthermore, Ca₃MgSi₂O₈ with Eu²⁺ concentrations at 1.0–30 % for Ca exhibited a blue-green emission peaking at approximately 480 nm. In contrast, with increasing Eu²⁺ concentration up to 50 % for Ca, the emission peak of Ca₃MgSi₂O₈:Eu²⁺ phosphors exhibited a redshift to 521 nm with green emissions. The redshift of emissions in Ca₃MgSi₂O₈:Eu²⁺ phosphors could be attributed to the strong electrostatic interactions related to the Eu²⁺ ions occupying the peculiar Ca sites.

Copper-doped hydronium alunite [(H₃O)Al₃(SO₄)₂(OH)₆:Cu], a novel luminescent sulfate material, exhibiting blue luminescence was successfully synthesized under hydrothermal conditions. The originality of this luminescent material is such that the host crystal structure consists of crystal water (hydronium ions and hydroxyl radicals). Herein, we reported the results of a detailed investigation of changes in luminescence characteristics of the material with heat treatments. It was found that the material’s emission intensity was significantly reduced by heat treatment at temperatures ≥318 °C. The effect of varying amounts of copper and the extent of dehydration on the emission intensity was also investigated. As a result, a clear tendency was obtained that the luminescence intensity decreased as the weight loss increased due to dehydration. Thus, the presence of copper and crystal water are important factors affecting the luminescence of the material.

Gd₂O₃–B₂O₃ binary glasses with a wide composition range were fabricated using a levitation technique, which allowed the Gd₂O₃ content of the glasses to be increased to 60 mol %, which is much greater than possible using conventional melt-quenching techniques. The composition dependence of the thermal, optical, and vibrational properties of the Gd₂O₃–B₂O₃ binary glasses was investigated. The glass transition and crystallization temperatures decreased slightly in the B-rich region with increasing Gd₂O₃ content in the glasses, whereas they increased in the Gd-rich region. Both B- and Gd-rich glasses were found to be colorless and transparent over a wide range of visible to near-infrared radiation. With an increase in the Gd₂O₃ content, the optical absorption edge in the ultraviolet region shifted toward a longer wavelength. Additional infrared (IR) transmittance windows were observed in the Gd-rich region. Raman scattering and IR spectra revealed that in the Gd-rich glasses, all of the B atoms formed isolated BO₃ units and the signals for the BO₄ units disappeared. It was concluded that the characteristic local structure around the B atoms is the origin of the additional IR transparency. These results show that by adjusting the Gd₂O₃ content, the resultant borate glasses are expected to be applied as optical components for use over various wavelengths.

We synthesized apatite fibers (AFs) and fabricated a porous hydroxyapatite scaffold (apatite-fiber scaffold; AFS). A tissue-engineered bone involving a three-dimensional structure was constructed by placing AFS in a radial-flow bioreactor (RFB) to culture rat bone marrow mesenchymal stem cells (RBMCs). In this study, we examined whether the tissue-engineered bone derived from the AFS has osteogenic differentiation potential leading to bone-forming ability in vivo in the subcutaneous tissue where bone formation does not occur naturally due to the absence of osteoblasts. The reconstructed tissue-engineered bone was implanted subcutaneously in rat tissue for 4 weeks. The AFS alone was implanted as a control. After implantation, some histological evaluations, i.e., hematoxylin and eosin (HE), alkaline phosphatase (ALP) staining, and immunofluorescence staining for osteocalcin (OC), were performed for the harvested samples. In addition, quantitative evaluation was also performed to determine the ALP activity normalized for the DNA content of the harvested samples. The HE staining revealed that both AFSs (control) and implanted tissue-engineered bone (RFB-bone) were biocompatible, and did not induce inflammation or immunological rejection in vivo. The ALP activity in the RFB-bone was significantly higher than that in the control. Immunofluorescent staining showed the expression of OC in RFB-bone. Therefore, we conclude that the tissue-engineered bone derived from AFS may have the bone-forming ability in vivo in the absence of osteoblasts. These results may provide valuable insights into the design of tissue-engineered bone for clinical applications.

We aimed to establish enzyme immobilization technology using the maghemite/hydroxyapatite (Fe₂O₃/HA) composite particles as enzyme immobilization carriers and to clarify the enzyme adsorption characteristics of the composite particles. Seven kinds of enzymes with various isoelectric points (pI) were immobilized on the Fe₂O₃/HA composite particles in buffered solution adjusted at pH = 7.40 or pH = 10.0, 36.5 °C. Effects of the enzyme pI and the solution pH on the immobilization were investigated. In both of the two kinds of buffered solutions, there was an increase or decrease distribution with a maximum local value for |pH-pI|, which indicated the charge state of the enzymes. The interaction between HA on the composite particles and adsorbed enzymes was expected to be the largest when |pH-pI| = 1–2. It was suggested that α-chymotrypsin, whose adsorbed amount was the most among the seven kinds of the enzymes, in addition, formed a monolayer on the surface of the composite particles in the buffered solution at pH = 7.40, 36.5 °C.

Octacalcium phosphate (OCP) coating was formed on the surface of Mg–Al–Zn–Ca alloy (AZX612) by anodically oxidized and subsequently immersed in a supersaturated aqueous solution containing phosphate and calcium ion under ordinary temperature and pressure. The formed OCP layer consisted of both the inner layer of the fine crystallites and the outer layer of the large crystallites, and the inner layer remained on the alloy even after the ultrasonication process. In simulated body fluid, AZX612 treated with both anodic oxidization and subsequent OCP coating process showed higher corrosion resistance than those treated with only anodic oxidization.

The crystal structure of β-tricalcium phosphate (β-TCP), which is used as a bone replacement material, is known to have five crystallographically distinct positions for the Ca atom and three distinct positions for the P atom. In this paper, we have successfully synthesized a new β-type tricalcium phosphate (Na-β-TCP/S) with phosphorus/sulfur-complex cations by solid state reaction method. This was achieved by using Ca₂₀Na₂(PO₄)₁₄ (Na-β-TCP) as a starting material, adjusting the Ca(4) site occupied by Na atoms to become vacancies, and simultaneously adjusting the same moles of S atoms to the P(1) site. The obtained sintered bodies became dense with increasing the sintering temperature. The grain growth of the sintered bodies was inhibited with increasing sulfur content. Although the solubility of Na-β-TCP was about half of that of β-TCP, the solubility of Na-β-TCP/S powder samples slightly increased with increasing sulfur content. These results indicate that Na-β-TCP/S can be prepared by controlling not only the amounts of vacancies in the structure but also the sinterability and solubility of Na-β-TCP/S due to the substitution of phosphorus and sulfur, and that Na-β-TCP/S has potential as a new β-TCP material for bioceramics.

The synthesis of calcium carbonate (CaCO₃) was conducted under the presence of food dye. A food dye was added into Ca(OH)₂ suspension with citric acid aqueous solution, and CaCO₃ was synthesized by reacting prepared Ca(OH)₂ suspension with CO₂ gas. Sunset yellow FCF and brilliant blue FCF were selected for food coloring. All products were calcite which is a stable phase. When the amount of citric acid aqueous solution added was 0–8 cm³, the crystallinity of calcite decreased with increasing the amount added by X-ray diffraction (XRD) patterns. Also, the crystal shapes using scanning electron microscope were observed. At the amount of citric acid aqueous solution 0, 5, and 8 cm³, the shapes of obtained calcite were fine calcite particles, elliptical particles, dumbbell-shaped, and rod-shaped particles. Various forms of calcite were synthesized by changing the amount of citric acid aqueous solution. In addition, the obtained samples were colored bright orange and blue. These products were called colored CaCO₃ and colored by adsorption of dye on CaCO₃ particles and incorporating dyes into CaCO₃ crystals. It was possible to obtain various shapes CaCO₃ colored by synthesizing under the presence of dye in the Ca(OH)₂–CO₂–H₂O reaction system.

A natural zeolite-containing esthetic tile was produced by utilizing a geopolymer reaction between a blast furnace slag and sodium silicate solution. Preparation of smooth, flattened, and rigid tiles with maximum flexural strength being 8.0 MPa was achieved by optimizing particle size of the slag (d₅₀ = 5.4 µm) and concentration of the sodium silicate aqueous solution (55 mass %) when dosed rate of the zeolite was fixed to 40 mass % of the whole paste. An amorphous calcium (alumino)silicate hydrate was assumed formed as the cementitious phase after partially dissolving powdery components in the sodium silicate solution. The tiles obtained showed high ability to adsorb NH₃ and H₂S gases, and expressed good antibacterial activity against Escherichia coli. It was also possible to fabricate esthetic, rigid, and deodorant tiles containing the zeolite modified with Cu(II), however, antibacterial activity within 24 h and flexural strength of the tile with the Cu(II)-modified zeolite was slightly less than that without modification. The tiles obtained in this study are considered promising material applicable to interior building products providing us with comfortable lifestyle.

Molten-state potassium metavanadate (KVO₃) supported on mesoporous SiO₂ materials have emerged as active catalysts for SO₃ decomposition over a moderate temperature range (≤650 °C), which is a potential O₂ evolution reaction useful for solar thermochemical water splitting. The molten phase formed at ≥520 °C contained tetrahedral VO₄²⁻, which plays a vital role in accelerating the SO₃ uptake and conversion to SO₂/O₂. The present study aimed to reveal how the SO₃ decomposition activity is affected by adding other oxoanions such as borate (BO₃³⁻), carbonate (CO₃²⁻), and phosphate (PO₄³⁻) into the melt. Although borate showed a deteriorating effect, phosphate tended to improve the catalytic activity when the P/V molar ratio was equal to or less than 0.5. The addition of phosphate produced a mixed phosphate vanadate with a composition of KV₂PO₈, which consists of infinite tetrahedral PO₄ and pyramidal VO₅ linked by vertex sharing. Because of the congruent melting at temperature as low as ∼530 °C, KV₂PO₈ may be expected as another candidate of active molten phase catalyst for SO₃ decomposition.

Waste gypsum board is one of the severe wastes that requires recycling because its emission annually increases. In this study, we attempted to produce a composite consisting of dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HAp) from gypsum and phosphate ions in an aqueous solution. The DCPD-HAp composite was successfully obtained by modifying the pH in the solution to be more basic after the preparation of DCPD. The composite material appeared to have enhanced reactivity toward fluoride ions. These results highlight a novel use of gypsum, which is helpful for the multiple recycling of phosphate and fluoride ions in wastewater without any virgin resources.

SiC fiber-reinforced SiC matrix composite (SiC_f/SiC_m) is one of the most promising materials for application in hot section components of gas turbine engines. However, due to the insufficient chemical durability of SiC_f/SiC_m under combustion environment, environmental barrier coating (EBC) is required as a protective coating on SiC_f/SiC_m surfaces. To determine the suitable materials for EBC, a synthetic process of ceramic powders with excellent compositional controllability should be established, and its calcination and sintering conditions should be determined to allow the preparation of a dense sintered body. Since ytterbium silicates are promising materials as an EBC, in this study, we investigated the synthesis of a precursor polyester containing Yb and Si components through the polymerizable complex (PC) method, which could achieve compositional homogeneity of the obtained oxide powder, as well as the dependence of the densification behavior of Yb–Si–O powder prepared by the calcination of the precursor polyester on calcination temperatures and periods. We successfully obtained a single-phase Yb₂SiO₅ sintered body using the Yb–Si–O powder prepared by the calcination of the precursor polyester synthesized using the PC method. In terms of calcination conditions, calcination at 800–1100 °C for 24 h and at 1100–1400 °C for 1 h were considered appropriate to obtain dense Yb₂SiO₅ sintered body with a relative density of >95 % at the sintering condition with 1700 °C for 5 h.

Low-temperature processing based on microwave-assisted hydrothermal synthesis was proposed for deposition of piezoelectric oxoate KNbO₃ films. The films were deposited on various substrates at reaction temperature below 200 °C using Nb₂O₅ powder and KOH solution. Epitaxial (100)_c KNbO₃ film with ∼1.3 µm-thick was deposited at a reaction temperature of 150 °C on (100)_cSrRuO₃//(100)SrTiO₃ using 12 mol dm⁻³ KOH solution for 80 min, which is significantly faster than conventional hydrothermal process.

Layered rock-salt LiNi_(1−x)/2Co_(1−x)/2Ti_xO₂ (0 ≤ x ≤ 0.1) and LiNi_(1−x)/2Co_{(1−x)/2–0.05}Fe_0.05Ti_xO₂ (0 ≤ x ≤ 0.1) were prepared by the electrostatic spray deposition method, which is one of the solution processes, to investigate the correlation between these crystal structures and electrode properties of the multinary oxides with solid solution of Fe and Ti ions. Even with only 5 % solid solution of Fe, the cycle retention rate after 50 cycles decreased by 5–8 %. Regardless of Fe-substitution/non-substitution, the crystallite size of the powder calcined at 973 K under oxygen atmosphere became finer as the amount of Ti substitution increased. Although Ti ions do not contribute to redox, Ti-substituted materials are improved Li diffusion due to finer crystallite size, and show better discharge capacity and cycle performance as Ti content increased. Not only in the Li–Ni–Co system, but also in the Li–Ni–Co–Fe system, crystallite size refinement and improvement in initial discharge capacity and cycle performance were observed depending on the amount of Ti substitution, indicating that Ti ions contribute to lattice stabilization.

In this study, blue-color emitting phosphors CaMgSi₂O₆:Eu²⁺ (CMS:Eu²⁺) were synthesized by the polymerizable complex method at 1000 °C in a reducing atmosphere. After the synthesis, the desired CMS crystals were obtained, but a small amount of impurity phases, such as Ca₂MgSi₂O₇ and Ca₃MgSi₂O₈, were contained. By adding lithium carbonate Li₂CO₃ as a flux to the polymerizable complex method and washing with 1 mol dm⁻³ HCl solution, the desired CMS:Eu²⁺ was obtained in a single phase. The maximum luminescence intensity was obtained at a flux concentration of 8 mol % for the composition CaMgSi₂O₆ when the amount of added flux was varied.

In this review, a comprehensive overview is given that covers the preparation, characterization, properties, and modification of sol–gel derived SiO₂–TiO₂ systems toward the generation of advanced coatings and powders with desirable properties. First, the fundamentals of the preparation and application of sol–gel derived multicomponent oxide coatings and powders are reviewed. Then, the basic physical and chemical properties of sol–gel derived SiO₂–TiO₂ coatings and powders are described. After that, the morphological and structural modification of sol–gel derived SiO₂–TiO₂ systems using organic polymers and surfactants, via their reaction in water vapor and hot water under external fields, are discussed. Finally, the advanced functionalities, such as superhydrophilicity, photocatalytic activity, micropatterning, and holographic recording, of the sol–gel derived SiO₂–TiO₂ coatings are demonstrated. In this context, the contributions of the author in this research field are also presented.

Sorption properties, induced by surface reaction such as adsorption, absorption, and ion-exchange reactions, of ceramics are affected by crystallographic properties, including crystallinity, structure, size, and morphology. Through the hydrothermal process, which is a part of the liquid-phase synthesis, crystals with various morphologies can be synthesized in a relatively short time and at low temperatures. Therefore, this process is an effective technique for the enhancement of sorption properties as it facilitates morphology control of ceramics-based purification materials. Herein, morphology-control-based techniques based on the hydrothermal processes for achieving high functionalization of ceramic materials, such as hydroxyapatite (HAp) and sodium titanate (ST) are reviewed, and their applicability for the development of environmental purification materials is verified. An overview of the process design for the morphology control of HAp crystals prepared through the hydrothermal process based on changes in the driving force for crystal growth, i.e., the degree of supersaturation, during the liquid-phase synthesis is presented. Furthermore, the high functionalization (in terms of adsorption and ion-exchange properties) of HAp-based materials prepared through the hydrothermal synthesis is demonstrated. In addition, the effects of unique seaweed-like nanostructures, a higher-order structure composed of ST nanofibers, of ST on its sorption properties are discussed, and the applicability of ST as an inorganic ion exchanger is also investigated.

Since the discovery of various blackening behaviors of yttria-stabilized zirconia (YSZ) between direct current (DC) and alternating current (AC) flash treatment, several efforts have been made to explain these phenomena. In this study, we developed a novel model based on electrode overvoltage to explain the blackening behavior of YSZ. It was found that the difference in the blackening behavior by the DC and AC flash treatment of YSZ could be qualitatively explained on the basis of an electrode overvoltage model. However, the true AC-flash state is difficult to understand owing to the limit of the principal in the model. In addition, high-amplitude voltage impedance spectroscopy revealed the nonlinearity problem between the amplitude voltage and current. As a result, new methodologies and theories that are different from conventional ones are essential to clarify the true nature of the flash state of YSZ.

We report here a novel, sensitive detection method for nitrogen dioxide (NO₂) using thin films of CdSe/ZnS core–shell type quantum dots (QDs) with and without noble metal (NM) nanoparticles (Au, Pt, or Pt-Pd alloy) deposited on a glass substrate. The photoluminescence (PL) intensity of the QD-only film and NM-QD composite films with porous microstructure rapidly decreased on exposure to NO₂ (1–100 ppm) in air, and it reversibly recovered after the atmosphere was changed back to air without NO₂. Interestingly, the Au-QD, Pt-QD, and Pt-Pd-QD films showed higher sensitivity when compared with the QD-only film. The reversible responses of QD-only film, Au-QD film, Pt-QD film, and Pt-Pd-QD film to NO₂ in air suggested that the CdSe/ZnS QD film and NM-QD films could be promising PL-based optical NO₂ sensors. Furthermore, the high NO₂ sensitivity, but low ozone sensitivity, in the Pt-Pd-QD film suggests the possibility of recognizing these two oxidizing gases by using the gas-selective catalytic activity of Pd.

When zeolites are synthesized in fluoride-containing media, large crystals tend to be obtained. In this research, we present a multi-stage synthesis strategy for size reduction of silicalite-1 synthesized in fluoride-containing media. Increase of the number of effective nuclei was crucial for the size reduction since, in dense hydrogel systems, only a limited number of nuclei can grow due to the hindrances in solid–liquid contacts. Small crystals are obtained by enhancing such contacts which aids in effective growth of nuclei. An intermediate low-temperature treatment coupled with stirring enhances the contact between the solid and liquid phases. Subsequent high-temperature heating completes the crystallization. The obtained silicalite-1 exhibits characteristics such as large micropore volumes and low number of defects comparable to the samples obtained from a single-stage synthesis.

Aluminum nitride (AlN) possesses excellent thermal conductivity and electrical resistivity, which makes it an ideal candidate for high-power, high-speed integrated circuit substrates. Its low fracture toughness requires the manufacturing of thicker substrates. However, this leads to degraded heat dissipation performance. Herein, we investigated a new strategy, combining the addition of AlN whiskers and tape-casting, to overcome the low fracture toughness disadvantage. The sintered AlN with AlN whiskers addition induced the formation of a highly anisotropic microstructure with aligned rod-like grains, effectively enhancing the fracture toughness to 6.7 MPa m^1/2, while maintaining thermal conductivity but degrading strength.