Mössbauer spectroscopy experiments were carried out on corundum-type structured (Fe₂O₃)_1−x(Al₂O₃)_x solid solutions (x = 0–0.67) synthesized by the mechanical alloying method to clarify the contribution of temperature and aluminum concentration to the magnetic properties. The Mössbauer spectra at room temperature gradually change from a sextet (weak ferromagnetism) to a doublet (paramagnetism) with increasing aluminum contents. As the temperature decreases down to 10 K, the sextet component develops for lower aluminum substitution, while the doublet profile changes to sextet for higher aluminum region. The absolute values of quadrupole splitting for the weak ferromagnetic component slightly increase with the aluminum substitution, primarily due to the reduction of the symmetry of the crystal field. The isomer shift δ decreases with the aluminum concentration due to the shrinkage of the lattice, and it also decreases with increasing temperature for the enhanced lattice vibration. Additionally, the hyperfine magnetic field B_hf weakens with the aluminum substitution presumably due to a diminished interaction between the nuclear magnetic moments, which can be observed in the lower temperatures.

First-principles calculations were performed to clarify the reason for the increase in yellowness upon the addition of Al to V-doped tetragonal ZrO₂ (t-ZrO₂). First-principles energy band calculations were performed using V-doped and (V, Al)-doped t-ZrO₂ supercells with theoretically optimized structures. When t-ZrO₂ was doped with V, the band gap exhibited a strongly localized energy level originating from the V 3d states. The V-doped t-ZrO₂ supercell co-doped with Al modified the number and energy positions of the V 3d levels within the ZrO₂ band gap. In the calculated dielectric function of the V-doped ZrO₂ supercell, broad absorption from the O 2p VB states to the V 3d gap states was observed in the visible region, in addition to the d-d transition in V⁴⁺. When Al was co-doped in the V-doped t-ZrO₂, no increase in the optical absorption in the visible-light region was observed. In contrast, the (V, Al)-doped t-ZrO₂ supercells with oxygen vacancies exhibited stronger absorption in the visible light region than the V-doped t-ZrO₂ supercell.

We investigated the effects of the pulse poling process on macroscopic ferroelastic domain structures in (100)/(001)-oriented Pb(Zr_0.44Ti_0.56)O₃ films. The poling process consisted of an applied electric field square waveform for poling cycles (10⁰–10⁷ cycles) combined with triangular waveforms for polarization–electric field and strain–electric field measurements. The remanent polarization (P_r) and the inverse piezoelectric coefficient (d_33,f) were enhanced at 10³ poling cycles but decreased with further increases in poling cycles. After 10³ poling cycles, the 90° domain switching behavior was directly observed via in situ X-ray diffraction (XRD). The results showed a 4 % change in the volume fraction of the c-domain (V_C) during the application of an electric field of +150 kV/cm. The 90° domain structure was altered by the poling process, contributing to increased electric field-induced strain. However, in situ XRD results after 10⁷ poling cycles indicated only slight changes in V_C under an applied electric field, with degraded P_r and d_33,f. The degradation of d_33,f values by pulse poling is partly due to the reduced contribution of ferroelastic 90° domain switching.

The preparation of particles composed of nanoporous silica (NS) and Mg²⁺-whitlockite (Mg-WH) would provide valuable insights for designing particles for biomedical applications. In this study, NS and Mg-WH composite particles were successfully synthesized. The addition of chitosan during synthesis possibly promoted the crystallization of calcium phosphate phases in the composite particles. Pore size distribution analysis of the particles showed a maximum at 3.2 nm. Investigating the adsorption of methylene blue onto the particles in a phosphate buffer (pH 7.4) showed that the saturated adsorption amount of methylene blue on the particles was significantly higher than that on commercial hydroxyapatite. The composite particles provided important results for potential applications as drug carriers for bone regeneration and repair.

Melilite-type silicate single crystals have emerged as promising materials for high-temperature piezoelectric applications in devices such as accelerometers, gas sensors, gas injectors, and pressure sensors. Sr-substituted Ca₂MgSi₂O₇ (Sr-CMS) single crystals were grown using the Czochralski (Cz) method. The Sr-CMS crystals exhibited no phase transition from room temperature to the melting temperature, with a piezoelectric d′₃₁ constant of 2.1 pC/N and a compressive strength of 830 MPa on a (ZXt)45° rotation-cut crystal substrate. Thus, Sr-CMS single crystals are promising for high-temperature pressure sensors. Ca₂Al₂SiO₇ (CAS) single crystals, which can also be grown using the Cz method, were investigated for high-temperature microbalance (MB) applications. They exhibit stable piezoelectric properties at high temperatures and have a lower density than langasite-type crystals. The thickness-shear vibration (d′₁₅ mode) of the CAS crystals was characterized, with the (XYw)45°-cut substrate showing the highest d′₁₅ constant. Using this crystal substrate, an LiZrO₃/Au/CAS device was configured and characterized as an MB. The device exhibited a resonance frequency shift when exposed to CO₂ gas in an air atmosphere at 500 °C, indicating that CAS single crystals can be used for MB applications at high temperatures.

We characterized protonated SrCoO_2.5 epitaxial films by the photoelectron holography technique. We found that photoelectron holography patterns change due to cation displacements induced by electrochemical protonation. By simulating holography patterns based on structural models of the protonated SrCoO_2.5 using machine-learning enhanced global optimization and comparing them with the experimentally observed patterns, we evaluated hydrogen concentration and cation displacements in protonated SrCoO_2.5 films. Our results show that photoelectron holography is useful in characterizing protonation-induced changes in metal transition oxides.

Silica/polyethyleneimine (PEI) inorganic–organic hybrid oil/water separation membranes were prepared by sol–gel method using tetramethoxysilane (TMOS), 3-glycidoxypropyltrimethoxysilane (GPTMOS) and PEI, and cross-linking reaction between glycidoxy functional group of 3-glycidoxypropyltrimethoxysilane (GPTMOS) and amino functional group of PEI. The effects of TMOS content on the water flux and oil/water separation efficiency of the membranes were also investigated. Oil/water separation efficiency of PEI60TM10 (60 wt % PEI to GPTMOS, 1.0 molar ratio TMOS to GPTMOS) was high (96 %) and water flux was also high (680 L·m⁻²·h⁻¹). The hybrid oil/water separation membranes exhibit higher oil/water separation efficiency and higher water flux.

Highly efficient energy storage devices are essential for a sustainable society. Since the launch of lithium-ion batteries in 1991, optimization efforts over the past 30 years have significantly improved their performance, such as energy density, and they now occupy the largest share of the energy storage device market. However, LiCoO₂-based positive electrode materials face supply risks due to cobalt availability and have reached their performance limits, which inhibits further large-scale deployment. In this review, we summarize the recent progress in advanced positive electrode materials for lithium-ion batteries.

An interparticle photo-crosslinkable Pickering emulsion with a high transparency was prepared to improve the printing resolution of porous silica components when using the digital light processing (DLP) approach. A transparent photocurable Pickering emulsion was obtained by vigorously mixing a mixture of isopropyl myristate (IPM) and turpentine oil into a dimethyl sulfoxide aqueous suspension of silica particles in which small amounts of diacrylate monomers and photo-radical initiator were pre-dissolved. Pickering emulsions with a high linear transmittance were prepared by adjusting the refractive indices of the continuous and dispersed phases to be close to that of silica particles by adjusting the solvent mixing ratio. The effects of the in-line transmittance of the Pickering emulsions on the curing depth and overcuring behavior of the photocured bodies were evaluated. The improved in-line transmittance was found to help suppress light scattering during the photocuring process, resulting in a higher printing resolution compared with the use of opaque Pickering emulsions.

γ-CuI is a p-type semiconductor with high mobility and chemical stability; it has potential applications as a hole-transport layer in organic solar cells and light-emitting diodes. To clarify the mechanism by which Zn doping controls the p-type conduction in γ-CuI, the types of defects formed in Zn-doped γ-CuI were comprehensively investigated through X-ray fluorescence holography (XFH), positron annihilation lifetime spectroscopy (PALS), coincidence Doppler broadening spectroscopy (CDBS), and density functional theory (DFT) calculations. The XFH demonstrated the presence of Zn atoms at the Cu sites (Zn_Cu). Furthermore, PALS and DFT calculations revealed the presence of isolated Cu vacancies (V_Cu). The CDBS suggested the formation of Zn_Cu–V_Cu defect pairs due to Zn doping. These findings supported that Zn doping suppresses p-type conduction via the formation of Zn_Cu–V_Cu defect pairs, as predicted by previous DFT studies. The combination of XFH, PALS and CDBS experiments and DFT calculations is effective for identifying the defect types in semiconductors.

In recent, nano-CeO₂ has attracted attention as a new inorganic antiviral material. For this study, Gd-doped CeO₂ (CGO), known as a solid electrolyte, was prepared using hydrothermal method. Also, Cu was modified on the particle surface. Then the CGO antiviral activity was investigated in the dark and under visible light. With the obtained single-phase CGO, at least a part of the surface-modified Cu formed a solid solution. Antiviral activity tests were performed against bacteriophage Qβ, a non-enveloped virus, in accordance with ISO. Findings indicate that CGO exhibits antiviral activity against Qβ in the dark, and that it possesses high activity in an enzyme protein inactivation test, which is attributed to its peptide affinity, water repellency, and genome destruction ability derived from the element. The Cu modification effect on the antiviral activity in the dark was not clear. However, it was improved by Cu modification under visible light, which suggested a contribution by the photocatalytic reaction. These findings revealed Cu-modified CGO as a material that exhibits antiviral activity both in the dark and under visible light.

Introducing oxygen deficiencies into metallic oxides dramatically improves their functional properties, such as their catalytic activity, ion conductivity, visible-light response, ferroelectric behavior, and ferromagnetism. We successfully produced oxygen-defective Gd₂O_3−x films by an oxidation process using Gd metal foil as the starting material and investigated the films’ optical properties and microstructures. A black oxygen-defective Gd₂O_3−x film nearly 1 µm thick was formed on the surface of Gd metal foil annealed at 773 K for 600 s in air. The Gd₂O_3−x film consisted of a cubic-Gd₂O₃ structure with an equiaxed grain size of a few hundred nanometers. The diffuse reflectance of the Gd₂O_3−x film was less than 30 %, indicating the absorption of both visible and near-infrared light. We also produced several-micrometer-thick oxygen-defective Gd₂O_3−x films on the surface of a Gd metal foil by a two-step heat treatment involving annealing at 773 K for 600 s in air and subsequent heating at 1073 K for 3.6 ks under an O₂ partial pressure of 1.01 × 10⁻⁵ Pa. The Gd₂O_3−x film exhibited less than 20 % reflectance in the visible region. Transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy observations revealed that the Gd₂O_3−x film was composed of a periodic structure with a spacing of several nanometers, which originated from the presence and absence of oxygen deficiencies in the cubic-Gd₂O₃ structure; that is, it was composed of a “hyper-ordered structure.”