Journal of the Ceramic Society of Japan

Journal of the Ceramic Society of Japan
vol. 133, no.10, 2025

◆Full paper◆

Precise determination and analysis of optical properties of large-sized La₂O₃–TiO₂-based glasses prepared by aerodynamic levitation technique

Kohei Yoshimoto, Shuhei Takasu, Motoi Ueda, Atsunobu Masuno and Hiroyuki Inoue

589

La₂O₃–TiO₂ (LT)-based glasses are promising materials for a wide range of optical applications because of their exceptionally high refractive indices and relatively low optical absorption in the visible wavelength range. In this study, LT-based multicomponent glasses were developed using the aerodynamic levitation technique, and their thermal stability, refractive index dispersion, and optical transmittance spectra were comprehensively analyzed. The addition of ZrO₂ and SiO₂ significantly improved the thermal stability of the glasses against crystallization. This enabled the fabrication of samples having diameters up to 25 mm, which is substantially larger than the typical glass size (approximately 2–3 mm) that is achievable through containerless processing. The LT-based glasses exhibited refractive indices at 2.161–2.315 at 587.562 nm, along with excellent transmittance characteristics relative to those of general optical glasses. An analysis of the refractive index dispersion based on the Lorentz model revealed that the densely packed structures and high electronic polarizabilities of oxygen atoms are critical factors in achieving ultra-high refractive indices and superior transmittance characteristics. Prototype lenses and wafer-shaped optical elements were fabricated using a glass molding press to demonstrate the potential of LT-based glasses for use in practical applications.

◆Express letter◆

3D printed porous nickel-cobalt oxide objects synthesized by interconnection and thermal conversion of metal hydroxide acrylate nanoparticles

https://doi.org/10.2109/jcersj2.25091

Yudai Inada, Naoki Tarutani, Miki Asanome, Sota Shimizu, Yasuaki Tokudome, Hiroki Yamada, Toshiaki Ina, Seiya Shimono, Kiyofumi Katagiri and Kei Inumaru

596

We report a cross-linker-free 3D printing strategy for fabricating hierarchically porous nickel-cobalt oxide objects using highly concentrated dispersions of metal hydroxide acrylate nanoparticles. By employing an optimized photoinitiator, millimetre-scale nanoparticle-based structures were successfully printed without the need for cross-linking agents. Upon thermal treatment under inert atmosphere, the printed objects transformed into Co–Ni alloy/carbon nanocomposites via intermediate carbide phases. Subsequent oxidation removed carbon domains and produced porous metal oxide architectures with tuneable meso- to macroporosity, while preserving the original printed shapes. This solid–solid phase separation process enabled pore formation without sacrificial templates or collapse of structure. Our approach offers a streamlined route to functional ceramic frameworks, with potential applications in catalysis, energy storage, and separations.

◆Full papers◆

Enhancing atomic structure exploration: The scaled-LCB and similarity-based structure sharing

https://doi.org/10.2109/jcersj2.25083

Samuel Eka Putra Payong Masan, Thanh Ngoc Pham, Kurt Irvin Medina Rojas, Beatriz Andrea Choi Tan, Febdian Rusydi, Yuji Hamamoto and Yoshitada Morikawa

602

Efficient global optimization is crucial in resource-intensive computations, such as atomistic structure search using density functional theory (DFT) calculations. This has been accomplished by combining the DFT with Gaussian process regression within a genetic algorithm called GOFEE. In this work, we modified the GOFEE algorithm to increase its efficiency. We introduced the scaled lower confidence bound acquisition function, which balances the surrogate energy and uncertainty to improve the atomic structure exploration. We implemented similarity-based structure sharing between independent GOFEE calculations to avoid redundant calculations in the target potential. We applied our modifications to find the global minimum in two-dimensional Himmelblau’s function, various hydrocarbon molecules, C₆₀, TiO₂ anatase surface reconstructions, and bulk Co-doped TiO₂ anatase (Co@TiO₂). While our modifications successfully increased the success rate in finding the global minimum of the former systems, they failed to find the ferromagnetic structure of Co@TiO₂, as observed in experiments.

Preparation of infrared reflective blue and purple pigments in BaO–CuO–SiO₂ system and application to paints

https://doi.org/10.2109/jcersj2.25086

Yuichi Kobayashi, Masatomo Hattori, Hideaki Okano, Chifuyu Tanaka and Jun’ichi Kawano

610

Five types of three-component crystals have been reported in the BaO–CuO–SiO₂ system. Among them, BaCuSi₂O₇ (Colinowensite, Han Purple), BaCuSi₄O₁₀ (Effenbergerite, Han Blue), and BaCu₂Si₂O₇ (Scottyite, Dark Blue) have been known as blue/purple pigments since ancient times. Although there have been detailed reports on the structure and optical properties of these crystals in the visible region, there are no reports on their optical properties in the near-infrared region. In this study, these crystals were synthesized by heat treatment of BaCO₃, CuO, and SiO₂ mixtures at 900–1050 °C, and their visible and near-infrared reflectance was examined. It was found that three crystals exhibit an inherent blue or violet color and brightness, and all three crystals have extremely high near-infrared reflectance. Painted samples show brightness L* of 34–42, near-infrared reflectance of 62–67 %, and solar reflectance of 36–43 %, indicating its potential application as a blue/purple cool-roof paint. These pigments are extremely promising as infrared selective reflective blue/purple pigments needed for heat island measures.

◆Technical report◆

Evaluation of sodium magnesium silicate-based glasses for alkali waste

https://doi.org/10.2109/jcersj2.25069

Hiromichi Takebe, Nobuyasu Nishioka, Kohei Owaku and Katsuhiko Hatakeyama

618

Na₂O–MgO–SiO₂ glasses were evaluated as a matrix of alkali waste solidification in the plutonium-uranium redox extraction (PUREX) process. Effects of ZnO, Al₂O₃, and B₂O₃ additions in small concentrations (≤4 mol %) on thermal stability against crystallization at high temperatures and water durability were studied. Infrared spectroscopy was used to evaluate the network structures of the Si–O and B–O bonds. Melt viscosity was measured by an inner rotation method in the temperature range between 1100 and 1300 °C. The results revealed that the addition of B₂O₃ and ZnO significantly contributed to respective enhancements of the thermal stability and water durability of silicate glasses with moderate melt viscosities at the operating temperatures of the glass solidification method for nuclear waste.

◆Notes◆

Relation between high thermal conductivity and dissolved-oxygen content in AlN ceramics fabricated by spark plasma sintering

https://doi.org/10.2109/jcersj2.25079

Runa Miyata, Ryota Kobayashi, Satofumi Maruyama and Ai Momozawa

622

AlN ceramics with small grain sizes were fabricated by spark plasma sintering (SPS) using Y₂O₃ as the sintering aid. The thermal conductivity of the ceramics increased with rising sintering temperature; the specimen sintered at 1850 °C exhibited a thermal conductivity of 163 W m⁻¹ K⁻¹, comparable to that of ceramics produced by pressureless sintering at the same temperature. The amount of oxygen dissolved in AlN was estimated from the lattice parameter c, and its relation with thermal resistivity was analyzed by Slack’s plot. A higher sintering temperature enhanced the trapping effect of the sintering aid and reduced the oxygen content in the solid solution. In addition, SPS-prepared samples showed higher bending strength than those obtained by pressureless sintering (PLS). These findings demonstrate that the combined use of SPS and sintering aids suppresses grain growth and lowers the dissolved-oxygen level, resulting in AlN ceramics with both high thermal conductivity and bending strength.

Low-temperature formation of TaB₂ powder from oxides and sodium metal with concurrent generation of water glass

https://doi.org/10.2109/jcersj2.25080

Akira Hosono, Atsuki Sawa, Takashi Endo and Takahiro Yamada

626

Tantalum borides have conventionally been produced via high-temperature solid-state reactions of the corresponding elemental raw materials. In this study, a unique chemical reaction design to add SiO₂ to the starting materials for an assist of TaB₂ formation is demonstrated. Powder mixtures of Ta₂O₅, B₂O₃, and SiO₂ were heated together with Na metal. TaB₂ was formed with concurrent generation of Na₂SiO₃ (otherwise known as water glass) in the reaction. Nearly single phase of TaB₂ powders with 50–200 nm particle sizes were obtained by by heating at a temperature range from 800 to 1000 °C followed by the successive removal of unreacted sodium and washing with ethanol and water. TaB₂ grains having a hexagonal prism morphology and sizes of several micrometers were grown in the sample heated at 1100 °C, possibly because molten Na₂SiO₃ with a melting point of 1088 °C acted as a flux.

Formation of hydroxy-carbonate apatite on the surfaces of strontium-containing aragonite

https://doi.org/10.2109/jcersj2.25093

Kohei Hosoki, Akiko Obata and Toshihiro Kasuga

630

Composite particles consisting of aragonite and hydroxy-carbonate apatite (HCA) were developed using strontium-containing aragonite [(Ca,Sr)CO₃] as the precursor via a phosphate-solution reaction under controlled conditions. An HCA layer with an approximate thickness of 1 µm was uniformly formed on the surfaces of the (Ca,Sr)CO₃ particles. The formation of this HCA layer was achieved using (Ca,Sr)CO₃; the introduction of Sr into aragonite, along with the adjustment of the phosphate solution’s pH and temperature, contributed to the moderate dissolution of aragonite. The gradual release of Ca²⁺ and Sr²⁺ ions from the particles, followed by their rapid reaction with phosphate ions in the solution, resulted in the formation of HCA on the particle surfaces.

◆Announcement◆

Call for a Guest Editor for the Feature

https://doi.org/10.2109/jcersj2.133.A10-1

A10-1