Journal of the Ceramic Society of Japan
vol. 133, no.5, 2025

◆Full paper◆

Site-selective Rh substitution and magnetic property of magnetoplumbite-structured BaFe12−xRhxO19pdf

https://doi.org/10.2109/jcersj2.25027

Ippo Aoki, Ikuya Yamada and Kenta Kimura

171

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 BaFe12−xRhxO19 (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. BaFe12−xRhxO19 samples are successfully obtained as the primary phase for all the compositions. The lattice constants a and c of BaFe12−xRhxO19 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.

◆Special Article-Academic Achievements◆

The 79th CerSJ Awards for Academic Achievements in Ceramic Science and Technology: Review

Photocatalytic gaseous carbon dioxide reduction for valuable fuel productionpdf

https://doi.org/10.2109/jcersj2.25025

Masahiro Miyauchi

178

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.

◆Review◆

Murataite ceramics – mineral, structure, synthesis and applications: A reviewpdf

https://doi.org/10.2109/jcersj2.25023

Yoshikazu Suzuki and Hiroya Abe

189

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.

◆Full papers◆

Development of tungsten–molybdenum-based multicomponent complex oxidespdf

https://doi.org/10.2109/jcersj2.24121

Daisuke Fukushi, Akito Sasaki, Masaki Toyoshima and Seiichi Suenaga

197

A multicomponent complex oxide, (W0.41Mo0.32V0.19Ta0.08)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.

Morphology and thermoelectric performance of bulk sodium tungsten bronze prepared via low energy-consuming routepdf

https://doi.org/10.2109/jcersj2.24118

Sasikan Maneeyom, Michitaka Ohtaki and Koichiro Suekuni

204

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), NaxWO3, 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.

Investigating the effect of alumina content on physical properties and pore structure of spodumene tailings-derived foamed ceramicspdf

https://doi.org/10.2109/jcersj2.24129

Xuexiang Ge, Weiwei Sun, Lei Huang, Yonggang Dai, Mingkai Zhou, Hui Yang and Ying Zhang

210

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.

Elimination of volatile organic compound by hydroxyapatites derived from waste bone biomasspdf

https://doi.org/10.2109/jcersj2.25032

Yunzi Xin, Yuma Kamisaka and Takashi Shirai

220

In present work, altered natural hydroxyapatite (HAp) was extracted from pig bone wastes of different parts (rib, spine, shoulder, forefoot) via well-controlled calcination. The prepared HAp powders were applied as non-noble metal and green catalyst towards oxidative decomposition of volatile organic compound (VOC) as practical application for the first time. With systemic characterization of the chemical composition, crystal structure, microstructure, surface chemical state, VOC adsorption property of observed HAp powders that extracted under different calcination temperatures, the correlation with resultant catalytic activity was also discussed in detail. The result in present work not only opens new possibility for the efficient removal of VOC by natural HAps but also provide new insights into the recycling of bone waste biomass and development of functional ceramic materials.

Efficient optimization of atom/ion arrangements in crystalline solids using genetic algorithms and machine-learning regressionpdf

https://doi.org/10.2109/jcersj2.25006

Tsubasa Koyama, Yumika Yokoyama, Naoto Tanibata, Hayami Takeda and Masanobu Nakayama

225

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.

◆Announcement◆

Call for a Guest Editor for the Featurepdf

https://doi.org/10.2109/jcersj2.133.A5-1

A5-1


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