研究者詳細 - 徳永　智春

論文 - 徳永　智春

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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

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

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

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

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

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

Topographical and morphological changes of the single-crystal (La<sub>0.3</sub>Sr<sub>0.7</sub>)(Al<sub>0.65</sub>Ta<sub>0.35</sub>)O<sub>3</sub> (001) surface treated with high-purity deionized water

Tokuda, Y; Nishikawa, N; Irimoto, T; Katsuyama, Y; Kobayashi, S; Tokunaga, T; Yamamoto, T

SURFACE AND INTERFACE ANALYSIS 56 巻 ( 8 ) 頁： 564 - 572 2024年8月

掲載種別：研究論文（学術雑誌）出版者・発行元：Surface and Interface Analysis

The topological and morphological changes of the (001) surface of single-crystal (La0.3Sr0.7)(Al0.65Ta0.35)O3 during treatment with high-purity deionized water (DI) have been investigated by atomic force microscopy and scanning transmission electron microscopy (STEM). Etching by DI treatment at room temperature proceeded mainly in anisotropic etching mode, resulting in rectangular etch pits with {001} inner surfaces forming in the surface. The dominant etching mode changed from anisotropic to isotropic with increasing DI-treatment temperature, and the lowest surface roughness occurred for DI treatment at 50°C for 60 min. Direct observation of the atomic structure of the surface by STEM showed that the etched surface was the B-site-terminated (001) surface after anisotropic etching at 50°C for 60 min, in which the B-site-terminated atomic layer was found to maintain the B-site ordered structure existing in the crystal. This is because DI treatment, which does not require high-temperature heat treatment of the substrate, suppresses element diffusion, sublimation, and formation of point defects on and in the vicinity of the surface.

DOI： 10.1002/sia.7313

Optical and mechanical properties of rutile TiO2 subjected to AC flash processing

Masuda, H; Tokunaga, T; Yamamoto, T; Yoshida, H

SCRIPTA MATERIALIA 246 巻頁： 116088 - 116088 2024年6月

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

Unusual physical properties associated with lattice defects induced by flash sintering and processing of oxide ceramics have attracted attentions. In this study, optical and mechanical properties of undoped and polycrystalline rutile TiO2 subjected to alternating current (AC) flash processing were characterized through diffuse reflectance spectroscopy and nanoindentation experiments at room temperature. The flashed sample exhibited substantial optical blackening and elastic softening but negligible changes in the hardness and crystal structure. The elastic softening demonstrated a significant rate dependence (i.e., elastic moduli decreased with testing rate), which was possibly caused by stress-induced reordering of point defects induced by AC flash processing. This elastic softening suggests that pronounced ionic mobility is obtained by flash processing even in undoped systems, which can potentially be extended to a general understanding of mass transport phenomena in transient metal oxides in strong electric fields.

DOI： 10.1016/j.scriptamat.2024.116088

Photoinduced dynamics during electronic transfer from narrow to wide bandgap layers in one-dimensional heterostructured materials 査読有り Open Access

Saida, Y; Gauthier, T; Suzuki, H; Ohmura, S; Shikata, R; Iwasaki, Y; Noyama, G; Kishibuchi, M; Tanaka, Y; Yajima, W; Godin, N; Privault, G; Tokunaga, T; Ono, S; Koshihara, SY; Tsuruta, K; Hayashi, Y; Bertoni, R; Hada, M

NATURE COMMUNICATIONS 15 巻 ( 1 ) 頁： 4600 2024年5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：Nature Communications

Electron transfer is a fundamental energy conversion process widely present in synthetic, industrial, and natural systems. Understanding the electron transfer process is important to exploit the uniqueness of the low-dimensional van der Waals (vdW) heterostructures because interlayer electron transfer produces the function of this class of material. Here, we show the occurrence of an electron transfer process in one-dimensional layer-stacking of carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs). This observation makes use of femtosecond broadband optical spectroscopy, ultrafast time-resolved electron diffraction, and first-principles theoretical calculations. These results reveal that near-ultraviolet photoexcitation induces an electron transfer from the conduction bands of CNT to BNNT layers via electronic decay channels. This physical process subsequently generates radial phonons in the one-dimensional vdW heterostructure material. The gathered insights unveil the fundamentals physics of interfacial interactions in low dimensional vdW heterostructures and their photoinduced dynamics, pushing their limits for photoactive multifunctional applications.

DOI： 10.1038/s41467-024-48880-3

The use of He buffer gas for moderating the plume kinetic energy during Nd:YAG-PLD growth of Eu<sub>x</sub>Y<sub>2-x</sub>O<sub>3</sub> phosphor films Open Access

Suzuki, S; Dazai, T; Tokunaga, T; Yamamoto, T; Katoh, R; Lippmaa, M; Takahashi, R

JOURNAL OF APPLIED PHYSICS 135 巻 ( 19 ) 2024年5月

掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Applied Physics

We have investigated the He buffer gas process of moderating the kinetic energy of the pulsed laser deposition (PLD) plume during EuxY2−xO3 phosphor film growth. When using a neodymium yttrium aluminum garnet laser for PLD thin film growth, the kinetic energy of the ablation plumes can be high enough to cause the formation of point defects in the film. The buffer gas pressure is an important process parameter in PLD film growth. We find that the presence of the He buffer gas reduces the kinetic energy of the laser deposition plume through many low-angle collisions in the gas phase by a factor of 7 without reducing the deposition rate. This is because He is much lighter than any of the elements in the plume and it does not affect the composition of the oxide films. Consequently, the resputtering of the Y2O3 film surface by the plume was significantly suppressed in the presence of the He gas moderator, leading to a decrease of the defect density in the Y2O3 films. The improvement of the film quality was verified by a systematic analysis of time-resolved photoluminescence (PL) data for EuxY2−xO3 composition-gradient films. The PL lifetime and intensity of Eu0.2Y1.8O3, which shows the highest PL intensity, increased by 13.3% and 36.4%, respectively, when the He gas moderation process was used. The He buffer gas process is applicable to the PLD growth of the other oxide materials as well, where the reduction of the kinetic energy of the plume would bring the PLD process closer to the molecular beam epitaxy growth condition.

DOI： 10.1063/5.0196987

Applying an alternating current to strontium titanate minimizes the change in oxidation state caused by flash sintering

Seko, M; Inagaki, S; Tokunaga, T; Kobayashi, S; Nakamura, A; Yamamoto, T

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 44 巻 ( 5 ) 頁： 2965 - 2971 2024年5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

This study estimated the amount of oxygen deficiency in SrTiO3 polycrystals that were flash sintered under direct current (DC) and alternating current (AC) electric fields, mainly by using the fine structural change of the Ti L23-edges collected by electron energy-loss spectroscopy. The DC electric field corresponded to formation of the maximum amount of oxygen deficiency at approximately δ = 0.07 as SrTiO3−δ, which corresponds to a lattice expansion of roughly 0.1% as a lattice constant of SrTiO3. Furthermore, the oxygen deficiency was distributed unevenly. The formation of dislocation networks in DC-flash-sintered SrTiO3 polycrystals might be related to the lattice strain field caused by this nonuniform oxygen deficiency. In contrast, an AC electric field did not correspond to the oxygen deficiency of SrTiO3, which is similar to the results in thermally sintered SrTiO3 polycrystals.

DOI： 10.1016/j.jeurceramsoc.2023.12.046

Flash healing of Vickers microcracks formed on the (001) surface of cubic zirconia single crystals

Kayukawa, S; Katsuyama, Y; Kodaira, A; Tokunaga, T; Morita, K; Nakamura, A; Yamamoto, T

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 43 巻 ( 14 ) 頁： 6272 - 6278 2023年11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

Flash healing, a technique for microcrack healing using a flash event, has recently attracted attention for effective microcrack healing of ceramics. To investigate the diffusion-accelerated phenomena that occur during flash healing, the flash-healing behavior of Vickers indentation microcracks on (001) zirconia single crystals was investigated, mainly from the viewpoint of microstructure analysis of the healed microcracks. Scanning electron microscopy and atomic force microscopy showed that the surface microcracks were rapidly healed. However, scanning transmission electron microscopy showed that a row of pores remained along the original microcrack inside the crystal, and the crystallographic orientation relationship on both sides of the microcrack was restored to that of the original single crystal. Compared with the findings for healing without an electric field, the distance from the pore closest to the surface was larger and the total pore volume was smaller for flash healing. These results suggest that flash treatment increases lattice diffusion.

DOI： 10.1016/j.jeurceramsoc.2023.06.001

Near-full compaction within only 30 min of total sintering time by shrinkage-rate-controlled flash sintering in 3 mol % Y2O3-doped ZrO2 polycrystal

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

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 131 巻 ( 10 ) 頁： 600 - 607 2023年10月

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 development of a high-speed sintering method that can shorten the entire sintering time while guaranteeing the mechanical properties is very attractive as a sintering process for structural ceramic polycrystals. For this purpose, a sintering protocol that combines shrinkage-rate-controlled flash sintering, which controls the shrinkage rate to be constant with the use of an alternative current electric field, and a rapid furnace ramp were applied to 3-mol % Y2O3-doped ZrO2 (3YSZ). As a result, a 3YSZ sintered polycrystal with about the relative density of 99.5 % (6.06 g/cm3) could be successfully fabricated within 30 min as the entire sintering time, which includes the furnace-heating regime. The sintered 3YSZ polycrystal is confirmed to exhibit a Vickers hardness of approximately 1290 HV and a fracture toughness (KIC) of approximately 5.2 MPa m1/2, which are similar values to those obtained from a typical thermally sintered 3YSZ polycrystal.

DOI： 10.2109/jcersj2.23041

Structural Defect Effect on the Concentration Quenching of TbXY2-XO3 Phosphor Thin Films

Suzuki, S; Dazai, T; Tokunaga, T; Yamamoto, T; Katoh, R; Takahashi, R

JOURNAL OF PHYSICAL CHEMISTRY C 127 巻 ( 19 ) 頁： 9380 - 9387 2023年5月

掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physical Chemistry C

This study investigates the structural defect effect on the luminescence properties of TbxY2-xO3 (x = 0-0.5) composition-gradient films using combinatorial pulsed laser deposition (PLD). TbxY2-xO3 films were grown on a SrTiO3 (001) substrate in an O2/He mixed atmosphere at PO2 = 1 × 10-4 Torr. A He buffer gas moderated the kinetic energy of the PLD plume and suppressed the resputtering of the film surface, resulting in the fabrication of defect-rich and poor TbxY2-xO3 films. The TbxY2-xO3 composition-gradient films exhibited varying green emissions from the Tb-doped Y2O3 films. The luminescence intensity of the defect-rich film was significantly weaker than that of the defect-poor film. Furthermore, concentration quenching of the luminescence occurred at high Tb concentrations. The analysis of the decay profiles of the luminescence as a function of the Tb concentration suggested two possible reasons for luminescence quenching: dynamic quenching induced by structural defects and static quenching induced by the shorter average distance of adjacent Tb ions. The investigation of the structural defect effect on the luminescence properties provides insights into the primary material parameters of phosphor materials and offers a pathway for enhancing their luminescence properties.

DOI： 10.1021/acs.jpcc.3c01679

Mechanistic consideration of ZnTe microspheres formation in a PVP-contained polyol system via hot injection method

Chau, YTR; Nguyen, MT; Tokunaga, T; Yonezawa, T

ADVANCED POWDER TECHNOLOGY 34 巻 ( 4 ) 頁： 103970 - 103970 2023年4月

掲載種別：研究論文（学術雑誌）出版者・発行元：Advanced Powder Technology

Zinc telluride (ZnTe) microspheres have been synthesized in a polyol system with adding various amount of poly(N-vinyl-2-pyrrolidone) (PVP, K-90) at 200 °C via a hot injection method. The smallest sized ZnTe microspheres obtained in this study had an average size of 634 nm through reaction for 48 h using 518 mg of PVP. A retrospective study was conducted to evaluate the formation process of ZnTe microspheres by conducting experiments from 0.2 h to 48 h. Nucleation and growth of ZnTe at the tips of Te rods in a PVP-contained polyol system were observed in sample reacted less than 1 h. More ZnTe microspheres and less Te rods were observed when the reaction was proceeded for longer time, suggesting that Te rods were the sacrificial template for the growth of ZnTe. Amount of PVP is the key factor of controlling dimensions of Te rods formed at the initial stage as well as the sizes of ZnTe microspheres by influencing the nucleation and growth rate of ZnTe. The obtained ZnTe microspheres at 48 h consisted of voids, which were originated by the detachment of ZnTe microspheres from Te rods after their growth.

DOI： 10.1016/j.apt.2023.103970

Microcrack healing in single-crystal cubic zirconia by thermal annealing 査読有り

Kayukawa, S; Katsuyama, Y; Kodaira, A; Tokunaga, T; Morita, K; Nakamura, A; Higuchi, K; Yamamoto, T

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 43 巻 ( 3 ) 頁： 1078 - 1086 2023年3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

Thermally healed Vickers microcracks perpendicular to (001) surface of cubic zirconia single crystals were investigated mainly with scanning transmission electron microscopy. The orientational relationship of areas containing healed microcracks was completely restored to that of the original single crystal, but a row of pores corresponding to the unhealed state remained where the original microcrack was located. Isolated pore formation proceeded from dislocation recovery via heat treatment, which brought the inner surfaces of the microcrack into contact, followed by diffusion bonding via surface diffusion. Once isolated pores were formed, the total pore volume did not significantly change by increasing the healing temperature, although pore sizes increased and the number of pores decreased. Ostwald ripening became pronounced in pore microstructure evolution when pore elimination was dominated by lattice diffusion after complete crystallographic restoration to a single crystal.

DOI： 10.1016/j.jeurceramsoc.2022.10.065

Flash self-joining of Y-TZP ceramics assisted with an AC electric field 査読有り

Nambu, K; Kitaoka, T; Morita, K; Soga, K; Tokunaga, T; Yamamoto, T; Masuda, H; Yoshida, H

JOURNAL OF THE AMERICAN CERAMIC SOCIETY 106 巻 ( 3 ) 頁： 2073 - 2082 2023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 American Ceramic Society

In this study, flash joining experiments were conducted using an AC field on 3 mol% Y2O3‐stabilized tetragonal ZrO2 polycrystal (Y‐TZP) bodies. Furthermore, the necessary conditions to obtain an almost complete self‐joining of Y‐TZP bodies were clarified. The specimens were successfully joined by applying an AC field at 60 mA·mm−2 for 80 s at a furnace temperature of 1000°C, thus resulting in a successfully joined specimen with 92% of the flexural strength of the as‐sintered Y‐TZP body. Almost complete self‐joining of Y‐TZP was achieved at current densities above 30 mA·mm−2, and input energy densities of >24 J·mm−3. Both the input energy density and electric current were critical factors for producing the reliable joining of ceramics.

DOI： 10.1111/jace.18889

A technique to modify the photoluminescence intensity of β-Ga<sub>2</sub>O<sub>3</sub> polycrystals using an electric field during sintering 査読有り

Ono, R; Kodaira, A; Tokunaga, T; Yoshida, H; Yamamoto, T

JOURNAL OF LUMINESCENCE 254 巻頁： 119508 - 119508 2023年2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 Luminescence

Beta gallium trioxide (β-Ga2O3) is an attractive wide bandgap oxide that exhibits photoluminescent emission in the ultraviolet and blue/green regions. In the present study, we describe the tuning and enhancement of photoluminescent emission in the blue/green region by applying an instantaneous electric field during the sintering of a β-Ga2O3 green compact. Blue/green emission at around 480 nm increases by a factor of approximately 16 in β-Ga2O3 polycrystal prepared with the sintering protocol that a green compact was heated up to 1300 °C and an alternating current electric field (50 V/cm at 1000 Hz) was isothermally loaded. Considering that the enhancement occurs at the cathode side under a direct current electric field, the enhanced blue/green photoluminescence is likely due to an increase in the number of oxygen vacancies.

DOI： 10.1016/j.jlumin.2022.119508

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