Utilization of waste heat is essential for energy conservation and CO₂ reduction, driving demand for the development of efficient thermal storage materials. Although various types of thermal storage materials have been proposed, few meet the requirements of reversibility, high energy density, long life, and ease of handling. This study reports that α-Zr(HPO₄)₂·H₂O and γ-Zr(PO₄)(H₂PO₄)·2H₂O, which possesses a layered structure with one and two interlayer water molecules, exhibits water intercalation at temperatures below 160 and 80 °C and is an excellent candidate for heat storage applications. The apparent activation energy for interlayer water desorption was 91 kJ·mol⁻¹ for both samples. TG and DSC measurements revealed an endothermic reaction during heating, corresponding to the weight loss from desorption of water molecules, and an exothermic reaction during cooling, corresponding to the weight gain from insertion of water molecules. α-Zr(HPO₄)₂·H₂O and γ-Zr(PO₄)(H₂PO₄)·2H₂O also demonstrated excellent cycling performance, with calorific values obtained from the endothermic and exothermic peak areas in the third cycle of −147 and 203 J·g⁻¹, and −82 and 121 J·g⁻¹, respectively. These findings highlight the potential of α-Zr(HPO₄)₂·H₂O and γ-Zr(PO₄)(H₂PO₄)·2H₂O as sustainable heat storage materials for energy conservation and thermal management applications.

The purpose of this work is to clarify the transformation mechanism from hexacelsian to celsian and the thermal expansion properties of celsian solid solutions (Ba_1−xSr_xAl₂Si₂O₈, x = 0–1.0) using high-temperature powder X-ray diffraction and dilatometry of sintered polycrystals. Hexacelsian polycrystals were prepared from BaCO₃, SrCO₃ and finely purified kaolin powder (Al₂O₃·2SiO₂·2H₂O) by heat-treatment at 950–1400 °C. Sr-hexacelsian polycrystals transformed to celsian via nucleation and growth from inner to surface to develop cracks at surface at 1100–1200 °C. Single phase of celsian polycrystals in composition of Ba_1−xSr_xAl₂Si₂O₈ (x = 0–0.8) were prepared by heat-treatment at 1400 °C for 1 h and their dilatometric thermal expansion coefficient (TEC) were almost 4.0–4.2 × 10⁻⁶/°C from 25 to 900 °C. On the other hand, average TEC of unit cell of celsian measured by high temperature X-ray diffraction were lower than the values of dilatometry and increased from 3.0 × 10⁻⁶/°C to 3.8 × 10⁻⁶/°C with the Sr content.

Diamond-reinforced silicon carbide (Diamond/SiC) composites, with their exceptional thermal conductivity and mechanical properties, are considered ideal packaging materials for high-power-density and highly integrated electronic devices. However, their fabrication challenges and insufficient interfacial performance, particularly interfacial defects caused by acoustic and lattice mismatches, significantly limit further performance improvements. To address these issues, this study utilized stereolithography-based 3D printing technology to achieve rapid and precise material shaping, combined with magnetron sputtering to introduce a Ti layer, followed by reactive infiltration to fabricate Diamond/TiC/SiC composites. Advanced characterization techniques, including scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectroscopy, were employed to systematically analyze the effect of TiC interlayer thickness on the interfacial structure and composite performance. The results revealed that the introduction of the TiC interlayer formed a quasi-coherent interface with good lattice matching between diamond and SiC, effectively reducing acoustic mismatch and interfacial dislocation density, thereby significantly enhancing interfacial performance. The thermal conductivity and flexural strength of the composites exhibited a trend of initial increase and subsequent decrease with increasing TiC interlayer thickness. When the TiC layer thickness reached 154 nm, the thermal conductivity and flexural strength achieved maximum values of 478 W/(m·K) and 342 MPa, respectively, representing improvements of 14.6 and 11.4 % compared to composites without the TiC interlayer. This study proposes a strategy to enhance the overall performance of composites by constructing quasi-coherent interfaces, optimizing interfacial bonding, and mitigating acoustic mismatch, providing valuable theoretical and technical guidance for the interfacial design of Diamond/SiC composites and the development of high-performance thermal management materials.

A solid electrolyte-type ammonia (NH₃) gas sensor with high durability for water vapor was devised by combining a trivalent Al³⁺ ion-conducting solid electrolyte and ammonium lanthanum niobate (NH₄LaNb₂O₇). The present sensor, using NH₄LaNb₂O₇ as the auxiliary sensing electrode, detected NH₃ gas concentration by obeying the theoretical Nernst relationship even at 180 °C. The present sensor exhibited a quantitative response to NH₃ gas concentration change without the influence of water vapor even in a highly humid atmosphere containing 4.2 vol % H₂O for over 3 months, indicating that the sensor with the NH₄LaNb₂O₇ auxiliary sensing electrode was revealed to possess an extraordinarily high water vapor durability.

Manufacturing processes using 3D additive manufacturing of ceramics have become a rapidly growing area of research. The development of a laser welding technology for thick ceramics would improve productivity and reduce manufacturing costs. In this work, 3-mm-thick Al₂O₃ plates were laser butt joined with Ni foil at different powers and with or without a carbon nanotube sheet, and the mechanical properties and microstructures of the joints were investigated. Plate edge surfaces were metallized with Mo by friction stirring as a pre-treatment to improve wettability and reduce thermal expansion differences by gradually changing the thermal expansion coefficient of the material. The 3-mm-thick laser butt joints obtained at 65 W and with a carbon nanotube sheet showed a deep reaction from the surface towards the interior under laser keyhole welding conditions, resulting in a tensile strength at 0.64 MPa. Tensile strength was insufficient because the weld bead was concave owing to spatter and there were cracks within the weld and heat-affected zone from the surface towards the interior. Crack initiation mechanisms and improvement methods were discussed by direct observation of the joint interface during laser welding.

Apatite-type lanthanoid silicates (Ln₁₀Si₆O₂₇; Ln = La, Pr, Sm, Eu, Gd) were investigated as promoters for PdO/γ-Al₂O₃ catalysts to enhance the performance of catalytic combustion-type methane sensors. X-ray diffraction and fluorescence analyses confirmed successful synthesis of phase-pure Ln₁₀Si₆O₂₇ and PdO/Ln₁₀Si₆O₂₇/γ-Al₂O₃ catalysts with compositions close to the intended stoichiometry. All sensors exhibited fast responses (T₅₀ ≈ 10 s) and excellent linearity (R² > 0.990) in the range of 0–1000 ppm CH₄. Remarkably, the PdO/Gd₁₀Si₆O₂₇/γ-Al₂O₃ sensor enabled quantitative CH₄ detection at 320 °C, the lowest operating temperature among the tested catalysts. Interestingly, sensor sensitivity increased systematically with increasing lanthanoid atomic number, opposite to the trend expected from the oxide-ion conductivity of Ln₁₀Si₆O₂₇, which decreases from La to Gd. Detailed analyses revealed that this discrepancy originated from catalytic activity and oxygen release properties rather than bulk conductivity. H₂-TPR results demonstrated that PdO/Gd₁₀Si₆O₂₇/γ-Al₂O₃ released active oxygen species more readily at low temperatures than the La-based catalyst. XPS further showed that the Pd²⁺/Pd⁰ ratio decreased from La to Gd, with the Gd-based catalyst achieving a balanced distribution that facilitated continuous redox cycling and sustained oxygen supply. This optimized Pd redox environment enhanced the proportion of complete methane oxidation, resulting in higher combustion heat and improved sensor output. These findings highlight that the performance of catalytic combustion-type methane sensors is governed not by intrinsic oxide-ion conductivity of the promoter, but by promoter–PdO interactions controlling Pd redox states and oxygen release dynamics. The results provide new insights into the design of advanced methane sensors operating at lower temperatures with higher sensitivity.

Topical fluoride is used in clinical dentistry to prevent dental caries. The primary reaction product formed on the tooth surface after topical fluoride application is calcium fluoride (CaF₂). In this study, we investigated the effect of deposited CaF₂ on the acid resistance of fluoride-treated hydroxyapatite (HAp). Commercial HAp particles were treated with two types of fluoride-containing acetic acid-sodium acetate (Ac-AcNa) buffer solutions, with and without the addition of phosphate ions. X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analyses confirmed the formation of fluorine-substituted hydroxyapatite (F-HAp), along with a hydration layer containing calcium phosphate and CaF₂. Phase composition analysis revealed that the presence of phosphate ions in the fluoride treatment solution reduced the amount of CaF₂ deposited. Acid resistance evaluation and phase composition analysis indicated that the initial dissolution rate of the fluoride-treated HAp in Ac-AcNa buffer solutions decreased on surfaces densely covered with CaF₂ particles.

In this study, we prepared a brookite-type titanium dioxide particle layer on the surface of titanium substrates via hydrothermal treatment in aqueous urea solutions containing sodium chloride (NaCl) and examined its in vitro apatite-forming ability. Increasing the urea concentration suppressed the formation of anatase-type titanium dioxide on the titanium substrate, forming a particle layer composed of pure brookite-type titanium dioxide. The size and packing density of brookite-type titanium dioxide particles formed on the titanium substrate increased with the NaCl concentration in a 7.0 mol·dm⁻³ urea solution. When titanium substrates hydrothermally treated in aqueous solutions of 7.0 mol·dm⁻³ urea and 2.0 mol·dm⁻³ NaCl were soaked in a simulated body fluid for various periods up to 7 d, the substrate surface was densely covered with hemispherical apatite particles (5.3 µm in diameter) within 3 d, indicating that the brookite-type titanium dioxide particle layer had an excellent apatite-forming ability comparable to that of the anatase-type titanium dioxide particle layer.

Keatite, a polymorph of silica rare in nature, was synthesized by hydrothermal treatment of silicon and water at 100 MPa and 600 °C. The crystal structure of keatite at 24 °C was refined by the Rietveld method using synchrotron X-ray diffraction data. The obtained structure is consistent with the results of previous studies in which some constraints were imposed during refinements. The ²⁹Si MAS NMR spectrum of keatite shows two peaks at −113.9 and −114.3 ppm, which can be assigned to Si at the Si1 and Si2 sites, respectively. The Raman spectrum of keatite shows a prominent peak at 473 cm⁻¹, which is attributable to the Si–O–Si bending mode of the 5-membered ring. These spectra, reported for the first time, are expected to be valuable for the identification of keatite in synthetic and natural samples.

Cubic Li_6.25Al_0.25La₃Zr₂O₁₂ exhibits high Li ionic conductivity (>3 × 10⁻⁴ S·cm⁻¹) at room temperature: however, its sintered body disintegrates upon prolonged exposure to air. To prevent this collapse phenomenon, this study sintered Li_6.25Al_0.25La_3−0.67xM_xZr₂O₁₂ (M = Mg, Ca, Sr, Ba, x = 0.1 to 0.5), wherein a fraction of the La in Li_6.25Al_0.25La₃Zr₂O₁₂ is substituted with alkaline earth metal elements, in a 100 % O₂ atmosphere and allowed the material to cool naturally. The supply of 100 % O₂ during natural cooling is particularly important. Li_6.25Al_0.25La_2.8Mg_0.3Zr₂O₁₂ exhibits a high Li ionic conductivity of 2.7 × 10⁻⁴ S·cm⁻¹ at 25 °C. The X-ray diffraction pattern and Li ionic conductivity of the Li_6.25Al_0.25La_2.8Mg_0.3Zr₂O₁₂ sintered body remains unchanged even after exposure to air for 1 year.

Li_xLa_(1−x)/3NbO₃ with an A-site-deficient perovskite structure was investigated with a focus on the relationship between its atomic configuration and Li⁺ diffusion properties. To this end, total scattering (diffraction) measurements were performed, and then reverse Monte Carlo modeling using the data was employed to construct the atomic configuration. The results suggest that the partial occupancy of La in the La-poor layer facilitate Li⁺ diffusion across the layer owing to the volume contraction. Furthermore, topological analyses conducted via persistent homology using the constructed atomic configuration indicate that a large fourfold ring formed by Nb and O is one of the reasons for superior Li⁺ diffusion in Li_xLa_(1−x)/3NbO₃.