研究者詳細 - 徳永　智春

論文 - 徳永　智春

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Shell-like structure to limit further densification formed during flash sintering under alternative current electric field for 8 mol %Y2O3-doped ZrO2 査読有り Open Access

Seko, M; Hattori, K; Ishino, Y; Kodaira, A; Tokunaga, T; Yamamoto, T

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 130 巻 ( 11 ) 頁： 895 - 898 2022年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Ceramic Society of Japan

A phenomenon often appears that the final achieved density is limited during conventional flash sintering even under alternative current electric field. By observing the cross-sectional microstructure of the flash sintered 8 mol %Y2O3-doped ZrO2 at this state, we found that a thin surface portion with near full density surrounds a porous inside with lower density. The densified thin surface portion is shell-like structure covering a whole of the sintered compact. The formation of this characteristic shell-like structure in the early stage of flash sintering greatly restricts subsequent densification of porous inside. In order to suppress the formation of the shell that inhibit densification, a technique of controlling a steep power spike at a flash event must be necessary to be appropriately transitioned.

DOI： 10.2109/jcersj2.22109

A first attempt of automated shrinkage-rate control flash sintering using a current profile without feedback of shrinkage behavior for 8 mol % Y<sub>2</sub>O<sub>3</sub> -doped ZrO<sub>2</sub> 査読有り Open Access

Koike, M; Ishino, Y; Tokunaga, T; Yamamoto, T

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 130 巻 ( 4 ) 頁： 327 - 330 2022年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Ceramic Society of Japan

Shrinkage-rate control flash (SCF) sintering is an attractive flash sintering that is modified to densify ceramic green compacts up to high density, which controls electric current to keep shrinkage-rate constant by feedback from shrinkage behavior during a flash state. To build up easier sintering protocol and to realize faster shrinkage-rate, we attempted automated SCF-sintering using the predicted current profile without feedback of the shrinkage behavior. As results, 8YSZ polycrystal with a density of 5.83 g/cm3 and a grain size of 1.84.5 μm could be produced within 10 min during SCF and soaking regimes at the furnace temperature of 870 °C, although the linearity of shrinkage-rate during automated SCF-sintering is degraded from the assumed shrinkage-rate. In order to improve automated SCF-sintering further, a more accurate method of approximating the current profile would be necessary to realize the higher linearity of shrinkage-rate.

DOI： 10.2109/jcersj2.22009

Crystalline boron monosulfide nanosheets with tunable bandgaps 査読有り Open Access

Kusaka, H; Ishibiki, R; Toyoda, M; Fujita, T; Tokunaga, T; Yamamoto, A; Miyakawa, M; Matsushita, K; Miyazaki, K; Li, LH; Shinde, SL; Lima, MSL; Sakurai, T; Nishibori, E; Masuda, T; Horiba, K; Watanabe, K; Saito, S; Miyauchi, M; Taniguchi, T; Hosono, H; Kondo, T

JOURNAL OF MATERIALS CHEMISTRY A 9 巻 ( 43 ) 頁： 24631 - 24640 2021年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Materials Chemistry A

Two-dimensional (2D) boron monosulfide (BS) nanosheets are predicted to have several stable phases and unique electronic structures, endowing them with interesting attributes, including superconducting, thermoelectric, and hydrogen storage properties. In this paper, we report the experimental realization of 2D BS nanosheets by the physical exfoliation of rhombohedral boron monosulfide (r-BS). Moreover, we demonstrate the facile separation of a mixture of 2D BS nanosheets and the r-BS powder in acetonitrile; the former were selectively separated as a dispersion in the supernatant, whereas the latter remained in the precipitate. In addition, density functional theory calculations reveal a clear dependence of the bandgap energy (Eg) on the number of layers of stacked BS nanosheets, whereEgfor BS nanosheets is approximately 1.0 eV higher than that for r-BS. Atomic force microscopy, cathode luminescence, ultraviolet-visible absorption spectroscopy, and excitation emission matrix experiments revealed a consistent bandgap difference of approximately 1.0 eV between the BS nanosheets and r-BS. We also demonstrate the applications based on the properties that originated from the difference in the bandgap between r-BS and BS nanosheets using photoelectrochemical current switching. These results indicate that the nanosheet bandgap can be tuned to a desired value by controlling the number of stacked 2D BS nanosheets. Therefore, BS nanosheets are promising non-metal 2D materials for applications requiring bandgap control, such as electronics and photocatalysis.

DOI： 10.1039/d1ta03307g

Shrinkage rate control during a flash state by current-ramping for 3 mol% Y<sub>2</sub>O<sub>3</sub>-doped ZrO<sub>2</sub> polycrystals 査読有り

Ishino, Y; Taguchi, K; Koike, M; Tokunaga, T; Yamamoto, T

JOURNAL OF THE AMERICAN CERAMIC SOCIETY 104 巻 ( 10 ) 頁： 4960 - 4967 2021年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the American Ceramic Society

3 mol% Y2O3-doped ZrO2 green compacts with rectangular shapes were sintered by maintaining the shrinkage rates at constant values under alternating electric fields by ramping the electric current during flash states. Green compacts were furnace-heated under 40-100 Vrms/cm until current hits an initial current limit of 100 mArms. After then, current-ramping was started to keep the shrinkage rates constant by increasing the limit current value using a programmable power supply operating in a current control mode. Highly densified 3 mol% Y2O3-doped ZrO2 polycrystals with a density of 6.05 g/cm3 as a bulk density and a grain size of about 0.4 μm were obtained at a furnace temperature of about 930℃, 50 Vrms/cm with 1000 Hz and shrinkage rate of about 120 μm/min (0.8%/min against initial lengths of green compacts). The Vickers hardness and indentation fracture toughness of the compact exhibit similar values to those obtained from thermally sintered compacts.

DOI： 10.1111/jace.17912

Rapid sintering of 3 mol % Y<sub>2</sub>O<sub>3</sub>-doped ZrO<sub>2</sub> by a combined rapid furnace heating and shrinkage-controlled flash sintering protocol 査読有り Open Access

Ishino, Y; Taguchi, K; Kodaira, A; Tokunaga, T; Yamamoto, T

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 129 巻 ( 8 ) 頁： 551 - 554 2021年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Ceramic Society of Japan

Flash sintering has attracted much attention as a useful sintering technique that is able to lower the sintering furnace temperature and shorten the sintering time. To further improve this original flash sintering technique, we have developed a technique to facilitate shrinkage at a constant shrinkage rate by controlling the power dissipation during a flash state, which is termed as shrinkage-controlled flash (SCF) sintering. Here, we combine this SCF sintering method with a rapid furnace heating process to shorten the entire sintering process time. Accordingly, we succeed in sintering 3 mol % Y2O3-doped ZrO2 (3YSZ) polycrystals with a high density of 6.05 g/cm3 and a uniform grain size of approximately 0.47 μm with a short sintering time of approximately 40 min. The obtained 3YSZ polycrystals are confirmed to exhibit a Vickers hardness and fracture toughness [by an indentation fracture method] of approximately 1295 HV and 5.3 MPa m1/2, respectively.

DOI： 10.2109/jcersj2.21066

Near complete densification of flash sintered 8YSZ: controlled shrinkage rate effects 査読有り Open Access

Taguchi, K; Ishino, Y; Tokunaga, T; Yamamoto, T

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 41 巻 ( 8 ) 頁： 4567 - 4571 2021年7月

記述言語：英語出版者・発行元：Journal of the European Ceramic Society

Rate-controlled sintering of 8 mol%Y2O3-doped ZrO2 (8YSZ) polycrystals was performed by rating the current limit of alternating current (AC) electric field during a flash event; this method promotes constant linear shrinkage of the green compact with respect to the sintering time. A power dissipation peak associated with the flash event was suppressed by setting the initial current limit at 100 mA; after AC current hits 100 mA, the current limit was rated to a maximum value of 1100−2000 mA to keep shrinkage rate constant. The power dissipation behavior during the current-rating process exhibited a characteristic inverted S-shaped curve as a function of time. 8YSZ polycrystal with a near-theoretical density of 5.97 g/cm3 and a grain size of approximately 3.4 μm was produced in AC electric field (150 V/cm at 1000 Hz) with a final maximum current limit of 1150 mA as a rectangular bulk style.

DOI： 10.1016/j.jeurceramsoc.2021.03.005

Constant shrinkage rate control during a flash event for 8 mol%Y<sub>2</sub>O<sub>3</sub>-doped ZrO<sub>2</sub> polycrystals 査読有り Open Access

Taguchi, K; Ishino, Y; Tokunaga, T; Yamamoto, T

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 129 巻 ( 3 ) 頁： 204 - 207 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Ceramic Society of Japan

The shrinkage rate during a flash event is controlled at a constant value by current ramping for 8 mol %Y2O3ZrO2 green compact with a rectangular shape. The green compact is heated at a constant heating rate of 5 °C/min until the occurrence of a flash event under a constant alternative current (AC) field of 50 Vrms/cm and 1000 Hz at a limit current of 100 mArms. After the flash event, current ramping is started to keep the shrinkage rate at a constant value of 120 ¯m/min. Current ramping is conducted by controlling the limit current using a programmable power supply operating in a current control mode. When the limit current reaches 1200 mArms, the sintering condition is kept as it is for 5 min, and the sintering process is completed. 8 mol %Y2O3ZrO2 sintered polycrystal with a relative density of approximately 99 % and a grain size of about 2.5 ¯m can be obtained at a furnace temperature of 870 °C for a current ramping and soaking regime of approximately 30 min.

DOI： 10.2109/jcersj2.20192

Power Dissipation Behaviors during SCF-sintering for 8 mol% Y<inf>2</inf>O<inf>3</inf>-doped ZrO<inf>2</inf> Open Access

Ishino Y., Taguchi K., Kodaira A., Tokunaga T., Yamamoto T.

Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy 68 巻 ( 11 ) 頁： 482 - 486 2021年

出版者・発行元：Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy

Shrinkage behaviors during shrinkage rate-controlled flash (SCF) sintering were investigated for 8 mol% Y2O3–ZrO2 (8YSZ) when shrinkage rates were varied between 60 and 300 μm/min under alternating current fields of 50 Vrms/cm, 1200 mArms, and 1000 Hz at a furnace temperature of approximately 870°C. Volumetric power dissipation and electrical conductivity were shown to exhibit similar dependencies against linear shrinkages even if the shrinkage rates were changed. The 8YSZ polycrystals, with similar microstructure and density, could be produced under all SCF conditions used in this study, which was confirmed as a characteristic feature of SCF sintering. Finally, the 8YSZ polycrystals with a density of 5.91–5.93 g/cm3 and a grain size of 2.2–2.6 μm could be produced with a shrinkage process period of 15–65 min at a furnace temperature of approximately 870°C.

DOI： 10.2497/jjspm.68.482

Cross-sectional Area Dependency of Shrinkages and Grain Sizes of Flash-sintered 3 mol%Y<inf>2</inf>O<inf>3</inf>–ZrO<inf>2</inf> Polycrystals with a Circular Truncated Cone-shape at High Frequency Alternating Electric Current Fields Open Access

Kurachi T., Kobayashi K., Tokunaga T., Yamamoto T.

Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy 68 巻 ( 11 ) 頁： 487 - 493 2021年

出版者・発行元：Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy

The uniformity of shrinkages and the distribution of grain sizes were investigated for flash-sintered 3 mol%Y2O3-ZrO2 compacts in direct current and alternating current (AC) electric fields using rectangular-shaped and circular truncated cone-shaped green compacts. The use of a high-frequency AC electric field enough to suppress electrode overvoltage was confirmed to be advantageous for uniform shrinkages, regardless of the shapes of the green compacts. However, the grain size distribution became larger in cone-shaped green compacts, the cross-sectional areas of which varied along the compact. The grain sizes in flashed cone-shaped green compacts were found to exhibit a near linear relation to current density, which provides a means for determining the grain size distribution upon the flash sintering of green compacts with different cross-sectional areas along an electric field.

DOI： 10.2497/jjspm.68.487

EBV status has prognostic implication among young patients with angioimmunoblastic T-cell lymphoma Open Access

Eladl Ahmed E., Shimada Kazuyuki, Suzuki Yuka, Takahara Taishi, Kato Seiichi, Kohno Kei, Elsayed Ahmed Ali, Wu Chun-Chieh, Tokunaga Takashi, Kinoshita Tomohiro, Sakata-Yanagimoto Mamiko, Nakamura Shigeo, Satou Akira

CANCER MEDICINE 9 巻 ( 2 ) 頁： 678 - 688 2020年1月

記述言語：日本語出版者・発行元：Cancer Medicine

Epstein-Barr virus (EBV)-positive B cells have been detected in 66%-86% of patients with angioimmunoblastic T-cell lymphoma (AITL). However, it remains controversial whether EBV status has an impact on the survival of patients with AITL. In this study, we aimed to reevaluate the impact of EBV on the clinicopathological characteristics of AITL. In particular, we focused on the impact of EBV in younger patients with AITL. In total, 270 cases of AITL were studied. Epstein-Barr virus-positive B cells were detected in 191 (71%) cases (EBER+ group). Among the patients who received anthracycline-based therapy, the EBER status did not affect the overall survival (OS) or progression-free survival (PFS). In the younger group of AITL (≤60 years), PFS was significantly worse in the EBER− group compared to the EBER+ group (P =.0013). Furthermore, the multivariate analysis identified EBER-negative status, thrombocytopenia, and elevated serum IgA level as significant adverse prognostic factors for PFS (P <.001, P <.001, and P =.002). Based on these findings, we constructed new prognostic model for the younger group, based on three adverse factors. We classified the patients into two risk groups: low risk (no or 1 adverse factor) and high risk (2 or 3 adverse factors). This new model for younger patients with AITL showed that both OS and PFS were significantly related to the level of risk (P <.0001). In summary, this study showed that, among younger patients with AITL, an EBER+ status significantly improved prognosis compared to an EBER− status. Our new prognostic model should be applicable to younger patients with AITL.

DOI： 10.1002/cam4.2742

Characterisation of bovine embryos following prolonged culture in embryonic stem cell medium containing leukaemia inhibitory factor Open Access

Hosoe Misa, Furusawa Tadashi, Hayashi Ken-Go, Takahashi Toru, Hashiyada Yutaka, Kizaki Keiichiro, Hashizume Kazuyoshi, Tokunaga Tomoyuki, Matsuyama Shuichi, Sakumoto Ryosuke

REPRODUCTION FERTILITY AND DEVELOPMENT 31 巻 ( 6 ) 頁： 1157 - 1165 2019年5月

記述言語：日本語出版者・発行元：Reproduction, Fertility and Development

In order to help elucidate the process of epiblast and trophoblast cell differentiation in bovine embryos in vitro, we attempted to develop a suitable culture medium to allow extended embryo culture. Day 7 bovine blastocysts developed in conventional medium were cultured further in embryonic stem cell medium with or without leukaemia inhibitory factor (LIF) until Day 23. At Day 14, the expression of octamer-binding transcription factor 3/4 (OCT3/4) and VIMENTIN was significantly higher in embryos cultured with than without LIF, but embryonic disc formation was not observed. Although expression of SRY (sex determining region Y)-box 17 (SOX17) mRNA was significantly lower in Day 14 embryos cultured with and without LIF than in in vivo embryos, hypoblast cells formed just inside the trophoblast cells of the in vitro-cultured embryos. On Day 23, expression of placental lactogen (PL) and prolactin-related protein 1 (PRP1) was not affected by LIF in in vitro-cultured embryos, levels of both genes were significantly lower in the in vitro than in vivo embryos. Similar to in vivo embryos, binucleate cell clusters seen in Day 23 in vitro-cultured embryos were composed of PL-negative and -positive cells. These results suggest that our culture system partially reproduced the differentiation process of trophoblast cells in vivo.

DOI： 10.1071/RD18343

Removal of carbon contamination in ETEM by introducing Ar during electron beam irradiation Open Access

Tokunaga, T; Saito, K; Kuno, K; Higuchi, K; Yamamoto, Y; Yamamoto, T

JOURNAL OF MICROSCOPY 273 巻 ( 1 ) 頁： 46 - 52 2019年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Microscopy

Organic materials, including carbon, exist inside the transmission electron microscope (TEM) chamber and are adsorbed onto samples under observation during TEM. When these adsorbed organic materials are irradiated by an electron beam, the adsorbed gas is decomposed. Carbon atoms remain on the sample and bond with each other forming a material with an amorphous structure. Due to the carbon deposition on the observation area of the sample, it is contaminated and the TEM image quality is decreased. Ar was introduced into environmental TEM (ETEM) to purge organic material from the sample chamber to reduce contamination growth. After Ar gas was introduced, the contamination was gradually removed. The contamination removal rate was dependent on the Ar pressure. Moreover, it was clear that Ar was ionised by electron beam irradiation and the Ar ions were produced in the ETEM during electron beam irradiation. It is proposed that the Ar ions removed the carbon contamination. Lay Description: Organic materials, including carbon, exist inside the transmission electron microscope (TEM) chamber and are adsorbed onto samples under observation during TEM. When these adsorbed organic materials are irradiated by an electron beam, the adsorbed gas is decomposed. Carbon atoms remain on the sample and bond with each other forming a material with an amorphous structure. Due to the carbon deposition on the observation area of the sample, it is contaminated and the TEM image quality is decreased. Ar was introduced into environmental TEM (ETEM) to purge organic material from the sample chamber to reduce contamination growth. After Ar gas was introduced, the contamination was gradually removed. The contamination removal rate was dependent on the Ar pressure. Moreover, it was clear that Ar was ionised by electron beam irradiation and the Ar ions were produced in the ETEM during electron beam irradiation. It is proposed that the Ar ions removed the carbon contamination.

DOI： 10.1111/jmi.12759

Intentionally encapsulated metal alloys within vertically aligned multi-walled carbon nanotube array via chemical vapor deposition technique

Inoue H., Nishikawa T., Hayashi Y., Hada M., Tokunaga T., Amaratunga G., Amaratunga G.

Conference Program Digest - 7th International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale, IEEE 3M-NANO 2017 2018-January 巻頁： 357 - 361 2018年2月

記述言語：日本語出版者・発行元：Conference Program Digest - 7th International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale, IEEE 3M-NANO 2017

This paper presents a growth and characterization of vertically aligned PdxCoi-x alloy encapsulated inside Multi-Walled Carbon Nanotube (MWCNT) arrays on Pd/Co thin layers coated on Si substrate by a dc bias-enhanced plasma chemical vapor deposition (CVD) method. The Metal Alloy Encapsulated within MWCNTs (MAE-MWCNTs) were characterized by a scanning electron microscope (SEM) and a transmission electron microscopy (TEM). The SEM images show the teardrop-shape particles encapsulated within the tube top of MWCNTs. A vibrating sample magnetometer was used to study the magnetism of a large number of MAE-MWCNTs on Si substrate at room temperature. The hysteresis loop of the ME-MWCNTs shows clear ferromagnetic behavior and the easy axis of magnetization is parallel to the MEA-MWCNT tube axis, as can be elucidated from the large coercive fields and remanence values. Moreover, TEM off-axis electron holograms were used to study the magnetism of the individual MAE-MWCNT or the two pair of MAE-MWCNTs. Based on electron holography, we have successfully obtained the saturation magnetization of 0.7 T and 1.12 T for the individual MAE-MWCNT with diameters of 41 nm and 83 nm, respectively.

DOI： 10.1109/3M-NANO.2017.8286262

Dendritic WS2 Nanoribbon Networks Grown in Interfacial Confinement Space: Edge-Rich Architectures for Enhanced Hydrogen Evolution Open Access

Suzuki, H; Hirata, K; Takahashi, Y; Fujii, S; Misawa, M; Tokunaga, T; Nakaya, I; Senda, Y; Hayashi, Y; Takahashi, Y

SMALL STRUCTURES 7 巻 ( 1 ) 2026年1月

掲載種別：研究論文（学術雑誌）出版者・発行元：Small Structures

Fractally grown dendritic nanostructures exhibit exceptional potential across various applications, particularly in electrochemical catalysis, owing to their high surface area and abundant reactive sites. Such structures can be synthesized via diffusion-limited aggregation (DLA), which requires tightly controlled growth conditions, such as a low precursor supply rate. Two-dimensional materials, especially transition-metal dichalcogenides (TMDCs), provide an ideal platform for realizing atomically precise dendritic architectures. In this study, we present a strategy for synthesizing fractal dendritic networks of monolayer WS<inf>2</inf> nanoribbons by employing an interfacial nanoreactor to create a highly confined growth environment. The dendritic WS<inf>2</inf> nanoribbons were formed at the interface between the monolayer WS<inf>2</inf> and the growth substrate, facilitating a DLA-dominated growth regime. Atomic-scale structural analysis revealed atomically sharp edges of dendritic WS<inf>2</inf> nanoribbon networks. High-resolution scanning electrochemical cell microscopy demonstrated enhanced hydrogen evolution reaction activity, with the catalytic current localized at the dense edges. Furthermore, a combination of experimental analysis and theoretical modeling provided insights into the surface-diffusion-governed growth mechanism. These findings offer a new approach for designing edge-rich TMDC nanostructures and pave the way for their integration into high-performance catalytic and electrochemical devices.

DOI： 10.1002/sstr.202500542

Suppression of carbon contamination in tungsten oxide by oxygen-plasma-assisted electron beam-induced deposition

Kato, S; Tsuji, A; Ogasawara, H; Tokunaga, T; Yamamoto, T; Kobayashi, S

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 43 巻 ( 6 ) 2025年12月

掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Vacuum Science and Technology B

Electron beam-induced deposition (EBID) is a direct-writing technique that utilizes a focused electron beam and a precursor gas to fabricate materials with arbitrary shapes. One of the challenges of EBID is the incorporation of residual carbon, primarily originating from organometallic precursors, which hampers the formation of high-purity deposits. In this study, we present a plasma-assisted EBID method in which externally generated oxygen plasma is introduced into the deposition chamber during growth to mitigate carbon contamination. Using tungsten oxide as a model system, thin films were deposited from tungsten hexacarbonyl in different plasma environments. The tungsten oxide fabricated under oxygen plasma showed a significant reduction in carbon content, as confirmed by scanning transmission electron microscopy and electron energy loss spectroscopy. Furthermore, the tungsten oxide deposited under the oxygen plasma condition was found to have an oxygen-rich composition, and an increase in conductivity was also observed. These findings highlight the critical role of the oxygen plasma in enhancing the chemical and electrical properties of oxide films fabricated by EBID.

DOI： 10.1116/6.0004857

Conversion of the (001) Strontium Titanate Surface to Titanium Monoxide via Ultrafast High-Temperature Sintering

Ihara, K; Sato, T; Tokunaga, T; Kobayashi, S; Kobayashi, K; Yamamoto, T

CRYSTAL GROWTH & DESIGN 25 巻 ( 20 ) 頁： 8393 - 8398 2025年10月

掲載種別：研究論文（学術雑誌）出版者・発行元：Crystal Growth and Design

The reconstruction of crystal surfaces (the alteration of the surface structure from that of the bulk) is imperative for the development of catalysts and energy-related materials. In this study, ultrafast high-temperature sintering (UHS) was employed to rapidly heat and reconstruct a model surface, namely the (001) surface of a SrTiO<inf>3</inf>single crystal. The structural changes were investigated by X-ray diffraction, scanning transmission electron microscopy, and electron energy-loss spectroscopy. Following treatment at 1650 °C for 180 s using UHS, a gold-colored transformation was observed on the surface; however, this was not the case after treatment at 1550 °C. Microscopic and spectroscopic analysis have revealed that the gold-colored surface layer possesses a thickness of approximately 100 nm, predominantly comprising rock salt-type cubic TiO. Furthermore, the electrical conductivity exhibited by the surface layer was very close to that reported for cubic TiO. The reconstruction mechanism of the (001) surface during UHS treatment was inferred to be similar to the incongruent sublimation of the SrTiO<inf>3</inf>surface that has previously been observed under vacuum at extremely low oxygen partial pressures. In conclusion, UHS has been demonstrated to be a highly efficacious technique for expeditious reconstruction of crystal surfaces, encompassing other metal oxides.

DOI： 10.1021/acs.cgd.5c00622

Fracture strength recovery in zirconia (8Y-CSZ) polycrystal through crack healing under strong DC electric field

Morita, K; Takahashi, S; Nambu, K; Terada, D; Tokunaga, T; Yamamoto, T

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 45 巻 ( 12 ) 頁： 117406 - 117406 2025年9月

掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the European Ceramic Society

The effect of the flash event on crack healing and the recovery of mechanical strength was examined under direct electric field/current (DC) in 8 mol% Y<inf>2</inf>O<inf>3</inf> stabilized cubic ZrO<inf>2</inf> (8Y-CSZ) polycrystal. Under the DC flash event, the micro-cracks with a length of 20 μm can be healed at furnace/sample temperatures for 10 min. As compared to the crack healing under heating treatment (HT) without the electric field/current, the crack healing was accelerated by more than 180 times under the DC flash even at the same specimen temperature of T<inf>s</inf> = 1223 °C. The rapid flash healing succeeded to recover the bending strength from ∼180 MPa with microcracks to ∼400 MPa, which is almost the same to that of the as-sintered state. This indicates that the flash treatment is an effective method not only to heal the micro-crack microstructure, but also to recover the mechanical strength through the crack healing.

DOI： 10.1016/j.jeurceramsoc.2025.117406

Microstructure analysis for zirconium oxynitrides formed in 8 mol% yttria-doped zirconia by a flash event under a direct current electric field in an ambient atmosphere 査読有り

45 巻 ( 7 ) 2025年7月

Ultrasonically Activated Liquid Metal Catalysts in Water for Enhanced Hydrogenation Efficiency

Manyuan, N; Tanimoto, N; Ueda, K; Yamamoto, K; Tokunaga, T; Nishio, M; Yonezawa, T; Kawasaki, H

ACS APPLIED MATERIALS & INTERFACES 17 巻 ( 4 ) 頁： 6414 - 6427 2025年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Materials and Interfaces

Hydride (H-) species on oxides have been extensively studied over the past few decades because of their critical role in various catalytic processes. Their syntheses require high temperatures and the presence of hydrogen, which involves complex equipment, high energy costs, and strict safety protocols. Hydride species tend to decompose in the presence of atmospheric oxygen and water, which reduces their catalytic activities. These challenges highlight the need for further research to improve the stability and efficiency of catalytic processes and develop safer and cost-effective synthesis methods. This paper introduces an ultrasonic fabrication method for gallium hydride species on liquid metal (LM) nanoparticles (Ga-H@LM NPs) in water and describes the evaluation of their catalytic properties. The Ga-H@LM NPs were synthesized by dispersing liquid metals of eutectic gallium-indium in water using a two-step ultrasonication process in an ice bath. The presence of Ga-H species was confirmed by Fourier-transform infrared spectroscopy. The Ga-H@LM NPs demonstrated the rapid catalytic hydrogenation of 4-nitrophenol and reductive degradation of azo dyes within minutes without the need for external reducing agents like NaBH4. The proposed mechanism involves high-energy ultrasonic cavitation at the interface between LM NPs and water, which promotes the formation of H2 from water and its activation to form Ga-H on particles surface during ultrasonication. This study has significant implications for advancing the field of catalysis because it provides a novel and efficient catalytic method for the synthesis of stable hydride species on gallium oxides.

DOI： 10.1021/acsami.4c19936

Variation of (001) surface structures of strontium titanate single crystals caused by flash event under direct/alternative current electric fields

Katsuyama, Y; Kayukawa, S; Tokunaga, T; Kobayashi, S; Hidaka, S; Nakamura, A; Yamamoto, T

CERAMICS INTERNATIONAL 50 巻 ( 19 ) 頁： 37366 - 37372 2024年10月

掲載種別：研究論文（学術雑誌）出版者・発行元：Ceramics International

Flash events, which are electric power spikes occurring under an electric field and temperature above the threshold, can significantly accelerate mass diffusion over short periods of time. This study investigated the surface structure of the (001) surface of strontium titanate single-crystal treated by flash events caused by direct current (DC) and alternating current (AC) electric fields from a viewpoint of surface-related mass diffusion. The surface structuring caused by flash events was significantly different among DC and AC electric fields. The DC-flash event destabilized surface steps, causing them to wander and form surface mounds with a height of several tens of nanometers. In addition, numerous two-dimensional (2D) nuclei with a size of several nanometers are formed on the terraces. In contrast, the AC-flash event stabilized surface steps without the formation of surface mounds, causing them nearly straight with uniform terrace width at approximately 500 nm. 2D nuclei with a size of a few 10 nm were formed at the step edges with round shapes. Both methods were confirmed as evidenced by the formation of two-dimensional nuclei on the surface after the flash events, to enhance surface-related mass diffusion.

DOI： 10.1016/j.ceramint.2024.05.055

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