We introduce new approaches to break the trade-off relationship between thermopower (S) and electronic conductivity (σ) in thermoelectric oxide materials by using artificially designed thin-film heterostructures. The output electric power generated by thermoelectric conversion is characterized by power factor (PF = S² × σ) but PF takes a maximum at a certain carrier concentration, which is restricted by the electron-diffusion model of transport theory. Here, we employ transition metal oxides of LaTiO₃ and LaNiO₃ to demonstrate two approaches to break the trade-off relationship. One is to introduce compressive strain in LaTiO₃ film to control a Mott insulator state to a massive electron metallic state, allowing improved S and σ, giving rise to a 10²-times enhancement of PF. Second one is to confine massive electrons and enhance phonon-drag effect in ultra-thin LaNiO₃ film sandwiched between wider bandgap LaAlO₃ capping layer and substrate with assistance of phonon-leaking effect, leading to a 10-fold increase of S. The present approaches open up new avenues for developing high-performance thermoelectric oxide materials beyond the conventional electron-diffusion theory.

A crystallized SrTiO₃ (STO) nanocoating on a primary SiO₂ nanoparticle was produced by metal alkoxide processing with chemical modification. The coated layer surface morphology and the coating amount were controlled by molecular design of the STO precursor solution. When using a partially hydrolyzed precursor solution (a partially polymerized precursor solution), an approximately 10-nm-thick homogeneous STO coating layer was obtained on a SiO₂ core particle. From these findings, we concluded that the alkoxide process is an effective method to obtain a homogeneous nanocoating with a complex metal oxide.

This research deals with the synthesis and various characterizations of a couple of substituted columbite of MgNb₂O₆ and CaNb₂O₆ as well as making the solid solution of Mg_1−xCa_xNb₂O₆ (x = 0.00–1.00). Solid solutions are formed in the range of less than 4 % for Ca²⁺ substitution of MgNb₂O₆ (x < 0.04) and 8 % for Mg²⁺ substitution of CaNb₂O₆ (x ≥ 0.92). The preparation of Mg_1−xCa_xNb₂O₆ (x = 0.0–1.0) with atomic ratio Mg/Ca/Nb = 1.00 − x/x/2.00 was carried out by solid-state reaction. The synthesized compounds were well-characterized by X-ray diffraction (XRD) for revealing the structure, scanning electron microscopy (SEM) for analyzing surface morphology as well as chemical composition, and UV–Vis DRS (diffused reflectance spectroscopy) to estimate band gaps. XRD analysis shows that the structure of the crystals corresponds to an orthorhombic system of space group Pbcn(60). Electronics properties (band structure and density of state) were also calculated. Moreover, photoluminescence properties and photocatalytic activity were also measured under visible and ultraviolet light irradiation (showed photocatalytic activity).

Magnetic metal–insulator nanogranular films that can host multiple outstanding functionalities have been widely studied, among which the tunneling magneto-dielectric (TMD) effect is a novel magneto-electric phenomenon discovered by our group. Enhancing their TMD response in a low magnetic field is necessary to practically apply magnetic metal–insulator nanogranular films. Herein, we focused on the effect of film annealing on TMD effect. The nanostructures, magnetic and dielectric properties, and the relationship between annealing temperature were investigated. The film nanostructure (i.e., Co granule size and intergranular distance), which is the key factor in realizing the TMD effect, was discussed. After optimizing the annealing temperature and Co content, a TMD ratio of 3.0 %, which is 75 times higher than that of the reported value, was obtained under a magnetic field of 200 kA/m in annealed Co_0.37–(Al₂O₃)_0.63 nanogranular films. We have revealed that post-annealing is an effective route toward enhancing the low-field sensitivity of the TMD response of nanogranular films.

Oyster is a very important cultured shellfish in Taiwan. About 10 % of oyster shells are discarded as waste every year without proper utilization. Therefore, the waste oyster shells were converted into bone materials included β-tricalcium phosphate [β-Ca₃(PO₄)₂, β-TCP] and 4 kinds of β-tricalcium magnesium phosphate [(Ca,Mg)₃(PO₄)₂, β-TCMP], which were supplemented with 1–4 folds of original amount of magnesium ion (Mg²⁺) in the oyster shell. The crystal structures of these five converted materials were analyzed by X-ray diffraction. The peak of Mg²⁺ was elevated with increasing level of Mg²⁺ in β-TCP. The particle size and surface pore were smaller and more by using scanning electron microscopy observations. The bioactivity of these materials was studied by using osteoblasts (MG-63 cells). All five materials were non-toxic. It had the best cell viability when Mg²⁺ was added with 3 folds of original amount. It was also found that supplement of Mg²⁺ has the effect on promoting the differentiation of osteoblasts. Among them, adding 3 folds of Mg²⁺ in β-TCMP has the best effect on cell differentiation. In addition, Mg²⁺ has the effect on promoting the mineralization of cells. Among them, adding 3 folds of Mg²⁺ in β-TCMP has the best effect. Hence, β-TCP and/or β-TCMP prepared from oyster shells have the effect on increasing bioactivity of osteoblasts. Among of them, β-TCP with 3 folds of original amount of Mg²⁺ in TCP shows the best effect.

CeO₂ coatings were fabricated on conductive polyethylene foams below 100 °C by a gas-assisted liquid phase deposition process. It is possible to coat the foams more deeply with CeO₂ by utilizing a mixture of deionized water and ethanol as a solvent of a starting material solution instead of deionized water. The samples showed a change in resistance with increasing and decreasing humidity. An amount of the change increased with the addition of ethanol in the starting material solution. Decrease in response and recovery times were observed with an increase in the coating temperature due to a larger crystallite size of CeO₂ coatings. The humidity response was evaluated using the formula ΔR/R₀ (%) = (R₀ − R)/R₀ × 100, where R and R₀ are resistance at 80 % relative humidity and minimum one, respectively. The largest value among the samples was 46.16 %. The response and recovery times for this sample were 125 and 132 s, respectively. This research has made it easy to add functionality to porous materials.

In this study, heteroepitaxial ZnO(0001) thin films were grown directly on α-Al₂O₃(0001) substrates at room temperature by laser-molecular beam epitaxy without buffer layers. The epitaxial films were grown on substrates pretreated with strongly alkaline tetramethylammonium hydroxide solution, while the substrates cleaned by hydrochloric acid resulted in uniaxially oriented growth with poor in-plane structural anisotropy. The surfaces of the thin films were ultraflat and composed of ultrafine nanocrystallites based on low-growth temperatures, which well reflected the atomically stepped morphology of the substrates. In addition, the ZnO thin films exhibited high transparency with a transmittance of >80 % in the visible region and optical bandgaps of ∼3.4 eV. The epitaxial and uniaxially oriented ZnO(0001) films were both n-type degenerate semiconductors and demonstrated relatively low resistivities of ∼3.1 × 10⁻³ and ∼2.1 × 10⁻³ Ω cm, respectively, at room temperature. The epitaxial thin film indicated a relatively higher carrier concentration of ∼3.4 × 10²⁰ cm⁻³ and lower mobility of ∼6.1 cm²/V s as compared with the uniaxially oriented film. This suggested a greater number of crystal defects were introduced, including oxygen vacancies based on relaxed epitaxial strain.

Massive H₂ fuel production by water electrolysis is an essential technology for a future sustainable society. In this study, we report a simple electrochemical deposition (ED) method to produce highly active Fe-doped Ni hydroxide electrocatalysts for oxygen evolution reactions (OER). The established key parameters, Fe/Ni ratio of precursor solutions and ED duration, are beneficial to develop a cost-effective route to large-scale production of an optimized Fe/Ni-based catalyst.

Recent development in first-principles modeling and computer performance has made it feasible to predict various properties of inorganic materials at the level of accuracy required for their detailed understanding, design, and prediction. In this article, our computational design and exploration of nitride and oxide semiconductors and related materials are reviewed, along with relevant methodologies. The results presented and discussed here include (i) the modeling of local atomic and electronic structures of native point defects, dopants, and their complexes; (ii) the prediction of reconstructed structures and band positions of surfaces; and (iii) materials screening using high-throughput calculations, identifying promising ternary zinc nitride semiconductors.

Three decades of research in the last century developed silicon nitride (Si₃N₄) as one of the strongest and toughest ceramic material for structural applications; but in this century, we newly discovered its gifted surface biochemistry. In an aqueous environment, Si₃N₄ undergoes surface hydrolysis with the slow but continuous elution of both silicon and nitrogen. A unique environment is created, which greatly enhances healing of soft and osseous tissues, inhibits bacterial biofilm formation, and eradicates viruses. The discovery of Si₃N₄’s biochemistry opens new paths in a wide array of different disciplines inside and outside of the physical body, including orthopedics, dentistry, virology, agronomy, and environmental remediation. In the biomedical field, it paves the way for a new generation of monolithic, composite, or coated implants for bone healing, including spinal arthrodesis, joint arthroplasty, craniomaxillofacial and dental devices. This review describes Si₃N₄’s surface chemistry in an aqueous environment in comparison with oxide ceramics. It discusses the pH-dependent elution kinetics of ammonia and ammonium as the main phenomenon behind its unparalleled behavior and demonstrates its friendly nature to mammalian cells while concurrently lysing invasive pathogens. Finally, a wider perspective is offered for future applications of Si₃N₄ in disease diagnosis and therapies, personal healthcare, agriculture, food and water safety, and environmental protection.

Ferroelectric materials exhibit a unique photovoltaic (PV) response that conventional pn junctions of semiconductors do not show. Above bandgap photovoltages, light-polarization-dependent photocurrents, photocurrent generation by terahertz light, etc. in ferroelectric PV effect are attractive features for novel optoelectronic devices. Recent studies on the ferroelectric PV effects have revealed that ferroelastic domain walls (DWs) are an active center for the generation of photocarriers. In this review paper, firstly, the history and status of studies on the DW-PV effect are briefly surveyed. Then, an analysis method that we have developed to experimentally quantify the magnitude of the PV response in the DW regions is introduced for BiFeO₃-based ferroelectric epitaxial thin films. Moreover, materials design strategies for further enhancement of the photoresponse based on the engineering of impurity levels, domain structures, and their combinations are presented.

Laminated CuO/Al₂CuO₄/CuO layers were developed to serve as an interlayer between the conducting oxide CaCu₃Ru₄O₁₂ + 30 vol.% CuO and nitride substrate Si₃N₄. Screen-printing was used to fabricate these films. The Al₂CuO₄ layer impeded the chemical reaction between CaCu₃Ru₄O₁₂ and Si₃N₄ and hence suppressed the decomposition of CaCu₃Ru₄O₁₂. The CuO interlayers improved the adhesion between the Si₃N₄ substrate, Al₂CuO₄ layer, and CaCu₃Ru₄O₁₂ + 30 vol.% CuO film. The main difference between the CaCu₃Ru₄O₁₂ + 30 vol.% CuO film on the Si₃N₄ and Al₂O₃ substrates having the same interlayers was the presence of a small amount of RuO₂ (formed from decomposition of CaCu₃Ru₄O₁₂) and cracks in the film on the Si₃N₄ substrate. The difference in the coefficients of thermal expansion between the Si₃N₄ substrate, interlayers, and film caused cracks to appear when the temperature of the film decreased after sintering. The resistivities of the films on the Si₃N₄ and Al₂O₃ substrates were 7 and 3 mΩ·cm at 100 °C, respectively. The film on the Si₃N₄ substrate exhibited higher resistivity than the film on the Al₂O₃ substrate from room temperature to 600 °C. This is because the cracks on the film on the Si₃N₄ substrate scattered the charge carriers. A decrease in crack width with increasing temperature was also observed, which in turn decreased the resistivity of the film with temperature. The conducting properties of the film developed in this work are adequate for practical applications. However, the interlayer can be further improved to obtain films with better performance. The major achievement of the present study is the development of an interlayer that suppresses the chemical reactions between the functional oxide and nitride substrate during high-temperature sintering.

Organic–inorganic hybrid particles have unique properties derived from the combination of their constituents and morphology, thereby enabling them to perform crucial functions in applications across the biomedicine, pharmaceutical, cosmetic, materials science, and engineering industries. This paper reports a method for preparing monodispersed hybrid particles comprising silica and thermosensitive poly(N-isopropylacrylamide) (PNIPAM) hydrogel particles with core–shell or snowman morphologies using a microfluidic device. Here, monodispersed droplets of sodium silicate solution are generated using a flow-focusing microfluidic device. When sodium hydrogen carbonate (NaHCO₃) and N-isopropylacrylamide (NIPAM) are simultaneously transferred to the droplets, sodium silicate reacts with NaHCO₃ to form core–shell structures, wherein silica-rich droplets are generated inside the NIPAM-rich droplets. The droplets are subsequently irradiated with ultraviolet (UV) light to yield monodispersed silica-PNIPAM hydrogel core–shell particles. However, when only NaHCO₃ is transferred to the sodium-silicate solution droplets, a snowman-like structure comprising silica-rich and water-rich droplets is formed. Therefore, NIPAM can be transferred to water-rich droplets and photopolymerized via UV light irradiation to obtain monodispersed snowman-like silica-PNIPAM hydrogel hybrid particles. Furthermore, the PNIPAM hydrogel hybrid-particle size can be easily altered by changing the temperature to approximately the human body temperature.

Quartz powders having different particle size distributions were mixed with feldspar and kaolin to make traditional porcelain bodies. The effects of quartz particle size on the elastic modulus and thermal expansion characteristics of these porcelains were investigated. Porcelain bodies prepared from quartz particles finer than 20 µm and heat-treated between 1275 and 1300 °C showed Young’s modulus 80 GPa or higher, and showed coefficient of thermal expansion (CTE) above 6 × 10⁻⁶/K. Porcelain bodies prepared from coarser quartz particles in size showed elastic modulus 35 GPa or lower, and the CTE below 5.3 × 10⁻⁶/K. These differences were caused by sufficient sintering and microcracks due to the difference in thermal expansion between quartz and glass-mullite matrix, and the critical quartz grain size for microcracks in porcelain was found to be in the range of 20–32 µm. Wearability and polishing performance of abrasive media with varying Young’s modulus were also studied.

Although silica substitution into apatites is an attractive method for improving biocompatibility and their bone-remodeling stimulation abilities, residual organic matter from organic silica as a silica source is a disadvantage for silica doping. In this study, we fabricated silica-substituted apatite blocks from silica-substituted octacalcium phosphate (OCP-silica) blocks by immersion in (NH₄)₂CO₃ solutions. At below 1-mol/L (NH₄)₂CO₃, the treated blocks retained their original OCP-silica block shapes while being converted to apatites containing both silica and CO₃. As the (NH₄)₂CO₃ concentration in the treated solutions increased, the CO₃ content of the apatite blocks increased, whereas their silica content decreased. The formed carbonate apatite (CO₃Ap) phase was categorized as AB-type CO₃Ap. The mechanical strength of the fabricated silica-substituted CO₃Ap blocks was approximately 150 kPa in diametral tensile strength (DTS) values.

Regression analysis was performed on the data of low-melting phosphate glasses extracted from a glass database. The data were categorized based on duplication, and the most commonly used components for each temperature range were extracted. The relationship between metal-oxide-based compositions and cation-based compositions was examined. Even though various compositions were included in the database, it was found that the average and standard deviation values of divalent or tetravalent cations in cation-based compositions were approximately 2/3 of those in oxide-based compositions. Multiple regression analysis suggested that cation-based analysis is more suitable than oxide-based analysis. Predictions using cations are expected to become more important in future structure-driven data analyses of glasses.

We prepared sintered reaction-bonded silicon nitride (SRBSN) ceramics using yttria and magnesia as sintering additives and evaluated the effects of heating rates of nitridation on their microstructure, bending strength, fracture toughness, and thermal conductivity of the specimens post-sintered at 1850 °C for 6 h. The heating rate strongly affected the microstructure of the nitrided compacts obtained by heating at 1400 °C for 4 h. A too-high heating rate (e.g., 10 °C/min) could result in the formation of Si droplets on the surface due to melting of Si particles at the high local temperature caused by the exothermic nitridation reaction. While the heating rate was sufficiently low, the pores inside the nitrided compacts were small because the solid Si particles fully reacted with nitrogen gas to form tiny Si₃N₄ particles at relatively lower temperatures. The difference in the amount and structures of the pores in the nitrided body affected the densification of the nitrided body and the shape of β-Si₃N₄ grains formed during post-sintering, thereby leading to variations in the mechanical and thermal properties.

Using SnO and MoO₃ as starting materials, a SnO₂–MoO₂ solid solution (SnMO) was prepared using mechanochemical method. Then its antiviral and antifungal activities were evaluated. The obtained sample was a powder with specific surface area of 5.7 m²/g with a rutile-type crystal structure. The amount of ion elution for SnMO into 1/500NB solution was an order of magnitude lower than that of MoO₃. This powder exhibited high antiviral activity against both bacteriophage Qβ and bacteriophage Φ6, suggesting contributions to antiviral activity by both low pH and eluted ions from the powder. Furthermore, a test based on JIS standards revealed that SnMO possesses high antifungal activity. These findings indicate SnMO as an effective material against widely various microorganisms.

We herein report a new method of synthesizing highly crystalline hydrated layered polysilicates (HLSs) using a coarse quartz glass block as a precursor. Magadiite, a type of HLS, is synthesized through hydrothermal reactions at 150 °C with a SiO₂/NaOH/H₂O ratio of ≈4.4/1.0/81.1. The results showed that when the particle size of the precursor was classified as <1000 µm, it was transformed into magadiite. However, if the particle size was larger than that, the precursor remained mostly in an amorphous phase. In addition, the hydrothermal reactions using finer precursors tended to result in the crystallization of by-products such as kenyaite and α-quartz. Hence, the particle size (s) of the quartz glass precursor suitable for synthesizing magadiite is 10 < s < 500 µm. This finding will contribute to a new method of synthesizing HLSs and related materials, e.g., their recycle synthesis with industrial quartz glass waste.