Silica (SiO₂) is the major glass-forming material, and the structures of silica glass and melt have been extensively studied using X-ray and neutron diffraction techniques. The diffraction data of silica glass and melt show the first sharp diffraction peak (FSDP) at Q ∼ 1.5 Å⁻¹, which is a signature of intermediate-range order. In this study, we performed classical molecular dynamics (MD) simulations at 2000 K and 5 GPa to understand the behaviour of the diffraction peak associated with the modification of intermediate-range order. The high-pressure melt data obtained show the decrease in the height of FSDP with a shift of the peak position to the high-Q side in X-ray diffraction data, although the average coordination number of four was maintained. In addition, we observed the formation of OSi₃ triclusters, which share an oxygen atom with a SiO₄ tetrahedron. This unusually dense packed atomic arrangement is the result of high pressure and is associated with the very sharp principal peak observed at Q ∼ 3 Å⁻¹ in the O–O partial structure factor derived by MD simulation.

Tin-doped indium oxide (ITO) thin films are used extensively, particularly in flat-panel displays and photovoltaic cells, because of their exceptional electrical conductivity and high visible-light transmittance. However, ITO is expensive because one of its components is In, which is a rare metal, making a stable supply of ITO difficult to attain. The objective of the present study was to reduce the use of In in ITO by combining it with Al₂O₃, which is relatively inexpensive and highly transparent, and exhibits high mechanical strength. The resulting ITO–Al₂O₃ composite thin films were fabricated by aerosol deposition. The resultant films exhibited a resistivity of 4 × 10⁻³ Ω cm and a visible-light transmittance of 87 % at a wavelength of 600 nm, which are similar to the values for ITO films deposited by the same AD method. The resistivity remained almost constant with increasing volume fraction of Al₂O₃ in the composite thin film until the volume fraction reached 66 %, beyond which a notable increase in resistivity was observed. An increase in the gas flow rate resulted in a reduction in resistivity, with a strong correlation observed between the resistivity and the crystallite size determined by the Williamson–Hall method. Elemental analysis of the cross-section of a composite thin film indicated the presence of In and Al. The distribution of In was found to become more widespread and denser with increasing gas flow rate, indicating densification of the film. The visible-light transmittance exhibited a minimal dependence on the Al₂O₃ volume fraction.

This study presents the first direct measurement of the dielectric breakdown strength (DBS) of oxynitride glass, providing new insights into its electrical insulation properties. Oxynitride glass was prepared using a blend of Si₃N₄, SiO₂, Y₂O₃, and MgO powders and formed into thin glass substrates of varying thicknesses. The DBS measurement was conducted by using circular column shape and McKewon electrodes. DBS measurements revealed that the oxynitride glass exhibited consistently slightly lower DBS values than Si₃N₄ sintered bodies across all tested thicknesses. This finding suggests that DB in Si₃N₄ predominantly occurs within the grain boundary glass phase. These results, aligning with previous studies on the dielectric breakdown mechanisms of silicon nitride ceramics, confirmed the critical role of the grain boundary glass phase in determining their electrical insulation performance.

We fabricated 0.1, 0.3, 1.0, and 3.0 % Tb-doped SrTa₂O₆ single crystal samples using the floating zone method to evaluate their photoluminescence and scintillation properties. The XRD measurement results showed no impurity phases and retained a single-phase structure for all samples. In addition, no clear peak shift was observed, which was thought to be due to a small amount of Tb³⁺ substituted on the Sr²⁺ site or the substitution of Tb⁴⁺ with a close ionic radius on the Ta⁵⁺ site. The photoluminescence measurements of all the samples confirmed luminescence due to the 4f–4f transitions of Tb³⁺ ions at an excitation wavelength of 280 nm, and the maximum internal quantum yield of 25.5 % was observed in the 0.1 % sample. The scintillation spectra were obtained under X-ray irradiation, and several emission peaks were observed in all the samples, originating from 4f–4f transitions of Tb³⁺ ions. The maximum scintillation integral intensity was obtained in the 0.3 % sample, which was about 47 % of the values of BGO set to 100 %.

In this study, spodumene tailings (STs) were investigated as a primary raw material for preparing of foamed ceramics (ST-FCs). The effects of Al₂O₃ content on the physical properties and pore structure of the foamed ceramics were systematically investigated. Comprehensive analyses of phase composition, crystalline structure, and high-temperature foaming behavior were conducted to elucidate the influence mechanisms of Al₂O₃ content on the performance of ST-FCs. The results indicate that STs, composed mainly of albite, quartz, and minor muscovite, had a low sintering temperature of 1160 °C, making it an ideal candidate for foamed ceramic production. The Al₂O₃ content significantly influenced the physical properties and pore structure of ST-FCs, which effect was associated with the appearance of the crystals generated in samples during foaming process. Optimal results were achieved at 24.04 wt % Al₂O₃, where the ST-FCs prepared at 1140 °C demonstrated a bulk density of 0.405 g/cm³, compressive strength of 7.84 MPa, and favorable pore structure (average pore diameter of 0.173 mm and apparent porosity as low as 0.96 %). These findings strongly indicated that FCs with high performance could be successfully prepared from STs by optimizing the Al₂O₃ content, which not only mitigated the environmental impact of STs but also effectively reduced the production cost of FCs.

This study reports on the dielectric, piezoelectric, and microstructural properties of Pb(Mg_1/3Nb_2/3)O₃–0.305PbTiO₃ (PMN-PT) single crystals (SCs) prepared by the one-charge Bridgman method, focusing on the effects of varying AC cycles, 1 to 1600, of alternating current poling (ACP) on the piezoelectric properties. Optimal properties were obtained at a low electric field of 3 kVrms/cm with 80 ACP cycles of a 1.0 Hz bipolar sine wave, resulting in a dielectric constant (ε^T₃₃/ε₀) of 14700, a piezoelectric constant d₃₃ of 4200 pC/N and a low dielectric loss of 0.24 %. These superior properties are among the best reported to date for piezoelectric SCs whose phase change temperatures exceed 75 °C. Scanning electron microscopy analysis revealed significant microstructural changes, including the formation of finely striped 1 to 4 µm 109° domain wall patterns (with an average width of 1.5 µm), which developed with increasing ACP cycles. A significant decrease in piezoelectric properties—low ε^T₃₃/ε₀ of 9500 and d₃₃ of 2500 pC/N—were observed after 800 cycles, correlating with the microstructural change. The study demonstrates that precise control of ACP conditions is essential to achieve the desired piezoelectric properties in PMN-PT SC materials. These findings provide critical insights for optimizing the properties of PMN-PT SCs and their potential for high-performance piezoelectric applications.

Metal oxides are one of the promising thermoelectric (TE) materials due to their high-temperature stability, low cost, and non-toxicity. Sodium tungsten bronze (STB), Na_xWO₃, is known to possess high electrical conductivity but the TE performance has not been thoroughly examined. In this study, STB was synthesized via a reduction reaction (RR) and a solid-state reaction (SSR) followed by hot pressing (HP) and spark plasma sintering (SPS). The obtained STB bulk samples have a cubic structure and the composition x of 0.41–0.47. A nanostructure was observed in the sintered RR samples. The RR-SPS sample was composed of several hundred nanometer-sized cubic particles with high porosity. Such morphology resulted in the low thermal conductivity of 6.6 W m⁻¹ K⁻¹ at 800 °C. As a result, the dimensionless figure of merit, ZT, of the RR-SPS sample was higher than those of the dense samples sintered by HP with the maximum ZT of 0.019 at 800 °C.

Magnetoplumbite-type ferrites AFe₁₂O₁₉ (A = Sr, Ba, La, Pb) are widely utilized as practical magnetic materials. Site-selective chemical substitutions for five distinct crystallographic Fe sites in AFe₁₂O₁₉ are desired for precise adjustment of magnetic properties but only a few examples have been reported. In this study, we attempt to synthesize BaFe_12−xRh_xO₁₉ (x = 1–6), where the Fe³⁺ ions at octahedral sites are partially replaced by non-magnetic Rh³⁺ ions with octahedral site preference, in high-pressure and high-temperature conditions of 8 GPa and 1373–1523 K. BaFe_12−xRh_xO₁₉ samples are successfully obtained as the primary phase for all the compositions. The lattice constants a and c of BaFe_12−xRh_xO₁₉ increase and decrease, respectively, with x up to the Rh solubility limit of x = 5. Rietveld refinement reveals that the octahedrally coordinated Fe³⁺ ions are preferentially replaced by the Rh³⁺ ions. Saturation magnetization decreases monotonically with increasing x, and its x dependence is reasonably explained by considering the octahedral site preference of the Rh³⁺ ions. These results show that the high-pressure synthesis is effective for site-selective substitution of the magnetoplumbite-type ferrites over a wide composition range, which may allow precise control of their magnetic properties.

We prepared (001) oriented Cd_0.9Mg_0.1O thin films on soda-lime glass substrates using pulsed laser deposition (PLD). Use of the (001) oriented Cd_0.9Mg_0.1O thin film as a buffer layer was attempted to prepare VO₂(R) (rutile) thin film. Because the lattice mismatch between the a-axis of VO₂(R) (a = 0.4555 nm) and Cd_0.9Mg_0.1O (a = 0.4651) is slight (−2.06 %), we expected a (001) oriented VO₂(R) thin film on Cd_0.9Mg_0.1O buffered glass. The results indicate (110) orientation, which is likely attributable to the influence of the surface energy of VO₂(R). In the rutile structure, the (001) plane is unstable because the coordination number of the cations at the outermost surface is low. In contrast, the (110) plane has the lowest surface energy. Therefore, the surface energy of VO₂(R) is considered to exert a stronger effect than the interaction between the substrate and the thin film. The temperature dependence of resistivity of VO₂ thin films with thickness deposited on Cd_0.9Mg_0.1O buffered glass substrates revealed that no metal–insulator transition was observed for thinner VO₂ thin film (thickness less than 59 nm). For large thickness (greater than 82 nm), then a clear metal–insulator transition was observed. This phenomenon was explained in terms of stress and oxygen vacancy. A similar result was obtained from measurement of the temperature dependence of IR transmittance with thickness. For 94-nm-thick VO₂ thin film, IR transmittance change as high as 53.9 % was obtained.

Murataite is a rare oxide mineral composed of Ti, Zn, alkali metals, alkaline earth metals, and rare earth elements. Murataite belongs to the cubic crystal system and has a crystal structure corresponding to the 3 × 3 × 3 (M3) superstructure of the fluorite structure. Synthetic murataite M3, which has a similar crystal structure of natural murataite-(Y) but with different compositions, and its synthetic polymorphs (strictly speaking, “polysomes”) of M5 and M8 are being applied to Synroc as host materials for long-term storage of radioactive actinoids. They are also expected to be used as electroceramics recalled from their fluorite-related crystal structures. This review provides a detailed explanation of the historical background of murataites researches, the crystal structure including polysomes, the processing and microstructure, and the potential applications as “rediscovered” ceramic materials.

Titanite-type oxides, ABMO₅, have been recently recognized as a novel vein of antiferroelectric (AFE) materials due to their unique crystal structure including an antiparallel arrangement of polar chains. This study presents the results of synthesis, structure analysis, and dielectric measurement of titanite-type solid solutions (Ca,Pb)TiGeO₅. With the Pb composition increasing, structural symmetry at room temperature changes from monoclinic to triclinic. We identified the crystal structure of PbTiGeO₅ by Rietveld refinement similar to that of triclinic titanite-type CaZrGeO₅. In addition, the AFE phase transition temperature is decreased by Pb substitution. These indicate the competition between triclinic and AFE distortions, in other words, lone-pair electrons on Pb²⁺ ions and the second-order Jahn–Teller effect on the Ti⁴⁺ ions.

In crystalline materials composed of multiple elements, such as alloys and solid solutions, degrees of freedom for atomic or ionic arrangements arise, making the determination of reasonable atom/ion configurations an important aspect of simulations. However, even in relatively small simulation cells, the number of possible arrangements is vast, rendering exhaustive evaluation infeasible. Although methodologies such as Monte Carlo and special quasi-random structures method have been proposed, genetic algorithm (GA) optimization is particularly useful for identifying stable arrangements, as it is applicable to bulk systems, surfaces, and interfaces. In this study, we improve the search method by combining GA with machine learning (ML), which we refer to as the GA and ML regression analysis (GAML). Specifically, this approach uses ML to screen and evaluate some of the structures generated by a GA, thereby reducing the computational demand of material simulations. This study provides an overview of the GAML, its computational methods, and optimization examples, demonstrating that the GAML achieves optimized structure more efficiently than the conventional GA. Integrating ML into GA significantly enhances the efficiency of optimizing atomic and ionic arrangements in crystalline solids. By achieving stable structures in fewer generations compared with traditional methods, the GAML offers a powerful tool for addressing complex systems with numerous possible configurations, with broad implications for accelerating materials discovery and design, particularly in fields requiring computationally efficient optimization of large and intricate systems.

Thin films of all-proportional PZT system, i.e., Pb(Zr_yTi_1.00−y)O₃ with y = 0–1.00, were deposited by hydrothermal deposition with a low reaction temperature of 150 °C. The PZT films were grown epitaxially on the surface of (100)SrTiO₃:La substrates via a microwave-assisted hydrothermal reaction using various input ratios of precursor chemicals x = [ZrOCl₂]/([ZrOCl₂] + [TiO₂]), which included more Zr ions (or less Ti ions) with a higher y value than that of the input ratio x. Dielectric and ferroelectric parameters for the resulting films, i.e., the relative dielectric constant (ε_r) and remanent polarization (P_r), exhibited maxima at the certain Zr/Ti ratio y = ∼0.60 though these parameters were relatively lower than those of the conventional films.

A multicomponent complex oxide, (W_0.41Mo_0.32V_0.19Ta_0.08)₅O₁₄, with a Mo₅O₁₄-type crystal structure and needle-like particles has been newly observed by scanning transmission electron microscopy (STEM), which confirmed that the four cations were homogeneously distributed in each particle. Each cation of this complex oxide seems to have a certain solid solution range for each valence. In this study, complex oxides with the same type of crystal structure could not be confirmed in a quaternary system or lower-order systems, namely, W–Mo–O, W–V–O and W–Mo–V–O. It is considered that the complex oxide was stabilized by simultaneously adding vanadium and tantalum. In addition, it was shown for the first time that this material has a Mo₅O₁₄-type structure with stable Li-ion battery characteristics. The initial discharge capacity was 161 mAh g⁻¹ (880 mAh cm⁻³) in the range of 1.55–3 V. The capacity was nearly constant and stable above 80 % even after 100 charge/discharge cycles.

Most of the previous photocatalytic carbon dioxide (CO₂) reduction reactions proceeded in water using protons as a mediator. In contrast to conventional CO₂ reduction reactions in water, dry reforming of methane (DRM) reaction is attractive because it is uphill and can directly convert gaseous CO₂ with methane (two major greenhouse gasses) into valuable syngas (CH₄ + CO₂ → 2CO + 2H₂). Previous researches on DRM were mainly studied in the field of thermal catalysis, and it requires high operating temperature and causes deactivation by carbon precipitation so-called coking. The present paper reports an efficient photocatalytic DRM (Photo-DRM) using metal oxide-based semiconductors, such as rhodium loaded strontium titanate (Rh/SrTiO₃). The developed photocatalysts can drive DRM reaction over 50 % H₂ production yield under light irradiation even at low-temperature conditions for long-term. Generated amounts of CO and H₂ are twice as those of CH₄ and CO₂ consumption, suggesting the stoichiometric DRM reaction without any side reactions like coking. The mechanism of Photo-DRM is comprehensively studied by various analyses, including surface temperature measurement, action spectrum, electron spin resonance, isotope trace experiment, and gas-phase photoelectrochemical studies. Based on these analyses, photogenerated electron–hole pairs are the dominant active species for CO₂ reduction and CH₄ oxidation rather than the photo-thermal effect. Interestingly, the lattice oxygen ions (O²⁻) play an important role in Photo-DRM, where O²⁻ ions act as a mediator to link CH₄ oxidation and CO₂ reduction for producing H₂ and CO equally. By optimizing the conductivity of O²⁻ ions and band structure in semiconductors like CeO₂ and TaON, the Photo-DRM activities are greatly improved. The present mechanism using O²⁻ ions is different from the reported conventional photocatalysts, which use protons as a mediator. The concept of this study is not limited to the DRM reaction but is applicable to various other gas-phase reactions.

First-principles and molecular dynamics simulations are used to understand the stability and defect state of vanadium ions at BaTiO₃ grain boundaries. Qualitative analysis is performed based on two approaches to approximate polycrystalline grain boundaries. First, stable grain boundaries are modeled to evaluate the defect formation energies of grain boundary sites and bulk sites. Second, amorphous BaTiO₃ is used to analyze the relationship between defect structure and stability of vanadium. The electronic states of vanadium atoms in the amorphous state are statistically analyzed to understand the effect of complex structures such as grain boundaries. These results suggest that vanadium acts as a donor at grain boundaries.