研究者詳細 - 徳永　智春

論文 - 徳永　智春

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Fractography of vanadium carbide-doped cemented carbide via scanning electron microscopy Open Access

Higuchi K., Tokunaga T., Kodaira A., Yamamoto T.

Materialia 46 巻 2026年5月

出版者・発行元：Materialia

Fractography, performed using scanning electron microscopy (SEM), evaluates fracture mechanisms through detailed observation of fracture-surface morphology, providing key insights into the fracture mechanisms of materials. For this purpose, it is necessary to set the image acquisition conditions appropriately as required to reflect the fracture-surface morphology and compositional information accurately. This study included fractographic analysis of vanadium carbide-doped cemented carbides using low-voltage SEM under appropriate settings, including a selection of secondary and backscattered electron detectors at an accelerating voltage of 3 kV. As a result, the morphology of fractured surfaces was found to be classified into seven forms depending on the crack propagation path, including carbide grain interior, carbide/carbide grain boundary, carbide/binder phase boundary, and binder phase interior. Approximately 42% of the fractured surface showed the presence of the binder phase. The fracture morphology included a stair-like structure fractured along the carbide/binder phase micro-facetted interface composed of (0001) and (101¯0) habit planes, where the microfaceted interface is typically formed in vanadium carbide-doped cemented carbides. The binder phase was revealed to exist only on the (101¯0) habit planes. These findings suggest that the nucleation site of microvoids generated in the process zone at the crack tip depends on whether voids nucleate at the carbide/binder phase interface or within the binder phase near the carbide/binder phase interface.

DOI： 10.1016/j.mtla.2026.102711

Rapid consolidation of cemented tungsten carbide via ultrafast high-temperature sintering 査読有り Open Access

Akutagawa, D; Ihara, K; Sato, T; Tokunaga, T; Yamamoto, T

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS 136 巻 2026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：International Journal of Refractory Metals and Hard Materials

Ultrafast high-temperature sintering (UHS) has garnered attention for facilitating rapid sintering by employing carbon felt as a heat source. In particular, the low oxygen partial pressure achieved by the carbon heater is effective for sintering carbides in a short duration. In this study, WC-11mass%Co was used as a model cemented carbide material to investigate the densification conditions and the resulting alloy microstructure obtained during UHS. A dense alloy composed of only WC and γ-phases was obtained using a dwell time of only 60 s by setting the sintering temperature (carbon felt current) above the eutectic temperature between WC and the γ-phase. Scanning transmission electron microscopy revealed a characteristic microstructure at the WC/γ-phase interface, resulting from the rapid cooling rate achieved by turning off the carbon felt current at the end of UHS. The presence of steps was observed on the WC (0001) surface, but not on the {101¯0} surfaces. Additionally, the WC<inf>1-X</inf> phase, a structurally relaxed phase, was not observed on the WC (0001) surface. However, extending the dwell time to 90 s led to the formation of numerous voids, substantially decreasing the density. The formation of these voids is attributed to localized current concentration within the alloy during UHS. To prevent current inflow during UHS, a thin alumina single-crystal plate was inserted between the carbon felt and the green compact. This effectively suppressed the current inflow, resulting in a dense alloy without voids. To ensure electrical insulation from the carbon felt is essentially necessary for UHS of cemented carbides.

DOI： 10.1016/j.ijrmhm.2025.107582

Enhanced Hydrogen Release from Hydrogen Boride Nanosheets via Carbon Doping 査読有り Open Access

Kawamura, R; Kawamura, R; Varadwaj, A; Kisu, K; Tanaka, R; Yamamoto, A; Ishibiki, R; Ito, S; Fujita, T; Tokunaga, T; Oki, O; Fujimoto, Y; Toyoda, M; Saito, S; Sato, T; Orimo, S; Hosono, H; Matsuda, I; Kotsugi, M; Miyauchi, M; Kondo, T

SMALL STRUCTURES 6 巻 ( 12 ) 2025年12月

記述言語：英語出版者・発行元：Small Structures

Hydrogen boride (HB) nanosheets, which exhibit unique B.H.B bonding and intrinsic hydrogen release properties, show improved performance upon carbon doping. Herein, the synthesis of carbon-doped HB via ion exchange is demonstrated by using carbon-doped MgB<inf>2</inf> as a precursor. Comprehensive spectroscopic analyses inferred carbon substitution at boron sites, leading to structural distortions and electronic modifications. These changes weaken B.H.B bonds, thereby facilitating improved hydrogen release under both thermal and ultraviolet (UV) stimuli. Temperature-programed desorption measurements reveal a reduction in the activation energy for intralayer hydrogen desorption with increasing carbon content, while UV-induced hydrogen evolution shows a markedly lower onset threshold. Density functional theory calculations support these experimental findings, further demonstrating elongation of B.B distances and shifts in vibrational modes. Overall, these results establish carbon doping as an effective strategy for modulating the chemical and electronic environment of HB, offering a promising pathway toward high-efficiency, tunable hydrogen storage, and release materials.

DOI： 10.1002/sstr.202500578

The variation of oxygen and cation vacancies in strontium titanate polycrystals flash-sintered under direct and alternating electric fields 査読有り

Inagaki, S; Tokunaga, T; Kobayashi, K; Yamamoto, T

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 45 巻 ( 15 ) 2025年12月

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

Point defect formation was investigated based on the electron energy-loss near-edge structure observed within the grains and 10 nm from the grain boundaries of strontium titanate flash-sintered under direct (DC) and alternating (AC) electric fields with strengths of 100 and 200 V/cm. More oxygen vacancies were generated in both regions under the DC field than under no field, but the same behavior was only observed under the AC field of 200 V/cm. Similarly, strontium vacancies were generated in both regions under the DC field but only within the grains under the AC field. The discrepancies in vacancy formation may be related to their generation and annihilation rates at grain boundaries under AC electric fields. The intricacies of the electric field-induced vacancy formation mechanism require further elucidation, but this work underscores the importance of considering the roles of both oxygen and cation vacancies in the accelerated mass diffusion during flash sintering.

DOI： 10.1016/j.jeurceramsoc.2025.117611

Rapid titanium carbide synthesis from titanium and graphite powders via ultrafast high-temperature sintering 査読有り Open Access

Akutagawa, D; Sato, T; Tokunaga, T; Kobayashi, K; Yamamoto, T

MATERIALS LETTERS 398 巻 2025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：Materials Letters

Self-propagating high-temperature synthesis (SHS) is a combustion-based method that involves a self-heating chain reaction, which is effective for rapidly producing materials with high melting points. Herein, ultrafast high-temperature sintering (UHS) was leveraged to ignite the SHS of titanium carbide (TiC) from titanium and graphite powders, and the heat generation and microstructural evolution during the process were investigated. The exothermic heat generated during TiC synthesis was confirmed, demonstrating that SHS was initiated in the initial stage of UHS. The incubation time before SHS ignition decreased with an increase in the UHS temperature above the melting point of titanium. Scanning electron microscopy revealed that fine TiC grains formed during SHS, which became denser under continued UHS. Additionally, molten Ti spread over the graphite particles during SHS, which transformed into plate-like TiC grains with elongated voids between them under subsequent heating by UHS. This structural feature was found to hinder further densification.

DOI： 10.1016/j.matlet.2025.138890

Surface step motion on the (001) surface of strontium titanate single crystals during DC electric field-assisted flash treatment 査読有り Open Access

Komori, S; Katsuyama, Y; Tokunaga, T; Yamamoto, T

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 133 巻 ( 11 ) 頁： 635 - 641 2025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 DC electric field-assisted flash treatment was performed on the (001) surface of a SrTiO<inf>3</inf> single crystal on which a step-terrace structure had been formed in advance (by solution etching). The DC electric field was applied along the direction that the surface height increases (up-step) or decreases (down-step) for a very short treatment duration of 1 min. The step-terrace morphology on the (001) surface was observed by atomic force microscopy, and the results were primarily discussed in terms of step stabilization or destabilization. Applying the DC electric field in the up-step direction appeared to stabilize the steps overall, although slight wandering was observed. Conversely, the steps were destabilized when the DC electric field was applied in the down-step direction, and the steps wandered significantly, with terraces protruding in the direction that the surface height decreases. The dependence of the step-terrace morphology on the direction of the DC electric field was consistent with previous studies that employed static electric fields (without a flash event). However, the step-terrace morphology may eventually become destabilized when the DC flash treatment time is extended, regardless of the applied field direction, considering the treatment duration of 10 min used in a previous study. This is inferred to be attributed to the amount of material diffusion relative to that of surface diffusion, which is increased by athermal effects during flash treatment.

DOI： 10.2109/jcersj2.25102

Surface mound formation and growth via step destabilization under a direct current electric field on (001) strontium titanate single crystals 査読有り

Katsuyama, Y; Inagaki, S; Tokunaga, T; Yamamoto, T

JOURNAL OF CRYSTAL GROWTH 667 巻 2025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 Crystal Growth

The specific heat-treatment conditions are crucial for facilitating surface-diffusion processes that lead to the reconstruction of surface structures in oxide single crystals. This reconstruction gives rise to a step-terrace structure, which is characterized by steps with heights equivalent to the unit cell and atomically flat terraces. A method using a power spike (i.e., a flash event) generated under an applied electric field above the threshold value has emerged as a promising approach for promoting such surface reconstruction. In this study, we performed Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) to examine the (001) surface structure of a strontium titanate single crystal treated with a flash event induced by a Direct Current (DC) electric field. We observed the formation of a step-terrace structure on the (001) surface even with a short holding time of 1 min under the flash event (initial voltage of 300 V/cm at a limiting current of 35 mA). However, a surface mound with a height of approximately 5.5 nm also formed on the surface, the height of which increased with holding time. SEM and AFM observations of the same surface location revealed that the formation of the surface mound is due to the formation of anti-bands as well as the bunching of surface steps, which is caused by their destabilization under the DC electric field. To avoid the formation of surface mounds, we suggest using an alternating electric field to trigger the flash event, which does not destabilize the steps.

DOI： 10.1016/j.jcrysgro.2025.128281

Electron-Beam-Induced Crystallization of Amorphous Gallium Oxide Thin Films Using Scanning Transmission Electron Microscopy 査読有り

Higuchi, K; Tokunaga, T; Sato, T; Yamamoto, T

CRYSTAL GROWTH & DESIGN 25 巻 ( 11 ) 頁： 3749 - 3755 2025年5月

記述言語：英語出版者・発行元：Crystal Growth and Design

Crystallization of amorphous materials using an electron beam is a promising technique for crystallizing minute regions. The crystallization behavior of amorphous gallium oxide (Ga<inf>2</inf>O<inf>3</inf>) thin films under electron-beam irradiation was investigated with a scanning transmission electron microscope, and patterned line drawing was performed using its line-scan mode. The Ga<inf>2</inf>O<inf>3</inf> thin films exhibited crystallization at threshold electron-beam doses in the range of 53–144 C/cm<sup>2</sup>. The γ- and β-Ga<inf>2</inf>O<inf>3</inf> forms crystallized as grains with an average size of 7 nm. The crystallization volume increased with doses. Crystallized Ga<inf>2</inf>O<inf>3</inf> polymorphs varied predominantly from γ- to β-Ga<inf>2</inf>O<inf>3</inf> with increased doses. The dose dependence of Ga<inf>2</inf>O<inf>3</inf> polymorphs was attributed to the variation in the coordination number of oxygen ions to gallium ions and the formation of oxygen vacancies caused by the electron-beam irradiation. The letter N predominantly composed of β-Ga<inf>2</inf>O<inf>3</inf> single crystals could be drawn with an approximately 10 nm line width in an amorphous Ga<inf>2</inf>O<inf>3</inf> thin film using the line-scan mode. Crystallized β-Ga<inf>2</inf>O<inf>3</inf> at the onset of the line-scan was inferred to grow epitaxially with subsequent scanning, realizing a letter N predominantly composed of single-crystal β-Ga<inf>2</inf>O<inf>3</inf>.

DOI： 10.1021/acs.cgd.5c00148

Healing behavior of microcracks on the surface of yttria-stabilized polycrystals using an ultrafast high-temperature sintering method 査読有り

Sato, T; Kodaira, A; Tokunaga, T; Morita, K; Yamamoto, T

CERAMICS INTERNATIONAL 51 巻 ( 4 ) 頁： 4178 - 4184 2025年2月

記述言語：英語出版者・発行元：Ceramics International

A technique to heal microcracks on ceramic surfaces in a relatively short time is an attractive proposition for extending the lifetime of ceramics. To this end, we used the ultrafast high-temperature sintering (UHS) method, which permits a rapid temperature increase, to heal Vickers indentation microcracks generated in a 4 mol% Y2O3-doped ZrO2 polycrystal. We examined the microstructure following microcrack healing using transmission electron microscopy and scanning electron microscopy with continuous focused ion beam slicing along the microcrack plane. This revealed that the microcrack healing process involves crack pinching and neck formation, followed by the growth of the neck. The microcracks were fully healed at the surface by UHS treatment at 2000 °C for 20 s. However, residual pores corresponding to the unhealed state were observed inside the material. We hypothesized that these pore residues were caused by significant grain coarsening during UHS. It is essential to optimize the UHS temperature and time to account for grain coarsening and facilitate the application of this method to microcrack healing.

DOI： 10.1016/j.ceramint.2024.11.394

Microstructural analysis of flash-healed Vickers-indented microcracks near positive/negative electrodes on the (001) surface of cubic zirconia single crystals under direct current electric fields 査読有り

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

CERAMICS INTERNATIONAL 50 巻 ( 19 ) 頁： 37348 - 37355 2024年10月

記述言語：英語出版者・発行元：Ceramics International

Flash healing is a technique that uses power spikes to rapidly repair microcracks on ceramic surfaces. In this study, the microstructures of flash-healed Vickers-indented microcracks near the positive/negative electrodes under a DC electric field were examined by scanning transmission electron microscopy. The microstructural morphology near the positive electrode was almost identical to that of the microcracks located between both electrodes, as previously reported. However, a decrease in the degree of healing was observed near the negative electrode. This was attributed to the insufficient recovery of dislocations generated at the indentation state, which should have occurred in the initial stage of healing. The delay in dislocation recovery prevented contact between the inner surfaces of the microcracks and is possibly related to the increase in oxygen vacancies near the negative electrode.

DOI： 10.1016/j.ceramint.2024.04.251

Variation of surface morphology of material uplift near flash-healed Vickers indents under direct-current electric field in cubic zirconia single crystals 査読有り

Kayukawa, S; Katsuyama, Y; Tokunaga, T; Yamamoto, T

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 132 巻 ( 8 ) 頁： 528 - 531 2024年8月

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

Flash events can cause rapid mass diffusion through instantaneous power spikes that occur in electric fields and at temperatures above certain thresholds. Recent research suggests that such mass diffusion caused by the flash event may include athermal effects in addition to Joule heating due to the power spikes. However, this perspective has not been applied to surface diffusion, one of the mass diffusion pathways. This study examines the athermal effect on surface diffusion during the flash event by analyzing the surface morphology variation of material uplift formed after the flash-/thermal-healing of Vickers-indentation-induced microcracks. The results show that the formation of surface facet structures, one of the material uplift surface morphologies, varies depending on the direction of the direct current (DC) electric field. The direction dependence of the facet structure formed on the material up-lifted surface due to the DC electric field is a result of the electric field drift effect. The athermal effects associated with flash events can be considered to exist also in mass diffusion involving surface diffusion.

DOI： 10.2109/jcersj2.24036

Pulsed laser deposition and structural analysis of Ba<sub>2</sub>Ti<sub>6</sub>O<sub>13</sub> epitaxial thin film on the (210) surface of SrTiO<sub>3</sub> single crystal 査読有り

Kono, R; Hieda, K; Tokunaga, T; Tamura, R; Masamura, R; Hikita, Y; Kano, K; Yamamoto, T

APPLIED PHYSICS EXPRESS 17 巻 ( 7 ) 2024年7月

記述言語：英語出版者・発行元：Applied Physics Express

A single crystalline thin film of Ba2Ti6O13 was grown on the (210) surface of a SrTiO3 single-crystal substrate by pulsed laser deposition. Scanning transmission electron microscopy shows that the Ba2Ti6O13 thin film grew epitaxially with the a-plane, and the b-/c-axes of Ba2Ti6O13 parallel to the (210) plane and the [00 1 ¯ ]/[ 1 ¯ 20] directions of SrTiO3, respectively. The electrical conductance of the Ba2Ti6O13 film was approximately one order larger than that of the reduced SrTiO3−δ single crystal with oxygen deficiency of roughly δ = 0.05. Electronic structure calculations predict that Ba2Ti6O13 is an n-type degenerate semiconductor with spin-split states primarily of Ti 3d orbital.

DOI： 10.35848/1882-0786/ad605d

Phase textures of metal-oxide nanocomposites self-orchestrated by atomic diffusions through precursor alloys 査読有り

Shudin, NH; Eguchi, R; Fujita, T; Tokunaga, T; Hashimoto, A; Abe, H

PHYSICAL CHEMISTRY CHEMICAL PHYSICS 26 巻 ( 19 ) 頁： 14103 - 14107 2024年5月

記述言語：英語出版者・発行元：Physical Chemistry Chemical Physics

Metal-oxide nanocomposites (MONs) are of pivotal importance as electrode materials, yet lack a guiding principle to tune their phase texture. Here we report that the phase texture of MONs can be tuned at the nanoscale by controlling the nanophase separation of precursor alloys. In situ transmission electron microscopy (in situ TEM) has demonstrated that a MON material of platinum (Pt) and cerium oxide (CeO2) is obtained through promoted nanophase separation of a Pt5Ce precursor alloy in an atmosphere containing oxygen (O2) and carbon monoxide (CO). The Pt-CeO2 MON material comprised an alternating stack of nanometre-thick layers of Pt and CeO2 in different phase textures ranging from lamellae to mazes, depending on the O2 fraction in the atmosphere. Mathematical simulations have demonstrated that the phase texture of MONs originates from a balance in the atomic diffusions across the alloy precursor, which is controllable by the O2 fraction, temperature, and composition of the precursor alloys.

DOI： 10.1039/d3cp05157a

Non-uniformity of shrinkage rate as a function of current acceleration during flash event under voltage-to-current protocol in 8 mol %Y<sub>2</sub>O<sub>3</sub>-ZrO<sub>2</sub> 査読有り

Seko, M; Inagaki, S; Tokunaga, T; Yamamoto, T

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 132 巻 ( 3 ) 頁： 93 - 98 2024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

This study verified the behavior of sample current, volumetric power dissipation, and shrinkage during flash sintering with the voltage-to-current protocol in the time frame of 90 s before and after the flash event. The volumetric power dissipation exhibited a peak value, followed by a decrease to the minimum value, and then increased asymptotically and approached a steady-state value. The discrepancy between the peak and minimum values, ¦P, increased with the limiting current value pre-set at the power supply during the heat-up stage. As ¦P increased, the degree of shrinkage progress decreased in stage III after the flash event, which is caused by the heterogeneity of shrinkage rate inside a compact. To consider the complete shrinkage amount, including stage III, in the current-to-voltage protocol, it is crucial to ensure that ¦P does not reach an excessive level when setting the maximum current.

DOI： 10.2109/jcersj2.23179

DOI： 10.2109/jcersj2.23179

Variation of grain boundary dihedral angles caused by voltage-to-current-based flash treatment in fully stabilized yttria-doped zirconia polycrystals 査読有り

Seko, M; Kayukawa, S; Inagaki, S; Tokunaga, T; Yamamoto, T

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 132 巻 ( 2 ) 頁： 63 - 67 2024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 the Ceramic Society of Japan

The flash sintering method has garnered attention for its ability to significantly accelerate the densification rate of ceramic green compact through the generation of an electric power spike under an electric field exceeding a defined threshold. In order to amass foundational knowledge about the phenomenon that results from an electric field during flash sintering via a voltage-to-current protocol, the dihedral angles of grain boundaries were surveyed in flash-treated pre-sintered fully stabilized zirconia polycrystal. The flash treatment resulted in a reduction of the grain boundary dihedral angle for grain boundaries that are approximately perpendicular to the direction of the electric field. The reduction in the dihedral angle is possibly attributed to a reduction in surface energy which can be observed through the formation of sinuous pores during flash sintering.

DOI： 10.2109/jcersj2.23170

Effect of Initial Grain Size on Crack Healing Behavior under DC Electric Field of Zirconia (8Y-CSZ) Ceramic 査読有り

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

ADVANCED ENGINEERING MATERIALS 25 巻 ( 18 ) 2023年9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：Advanced Engineering Materials

The effect of initial grain size on the flash event was examined in microcrack healing behavior under DC electric field in fine- and coarse-grained 8 mol% Y2O3-stabilized cubic ZrO2 (8Y-CSZ) polycrystals. The healing behavior depends strongly on the initial grain size and is apparently accelerated in fine-grained 8Y-CSZ than in coarse-grained one. Since the crack healing under the flash event is higher than that of static annealing treatment without the electric field, the enhanced healing phenomena cannot be explained only by the thermal effect caused by Joule heating, but nonthermal effects caused by the flash event. The grain size-dependent healing behavior indicates that the grain boundaries play an important role in the flash event and the flash healing would be accelerated through the field/current-enhanced diffusional processes, especially through the grain boundary diffusivity of the cations.

DOI： 10.1002/adem.202201807

DOI： 10.1002/adem.202201807

Layer transfer of ultrathin Ge crystal segregated on Al/Ge(111) structure 査読有り Open Access

Matsushita, K; Ohta, A; Shibayama, S; Tokunaga, T; Taoka, N; Makihara, K; Miyazaki, S

JAPANESE JOURNAL OF APPLIED PHYSICS 62 巻 ( SG ) 2023年6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：Japanese Journal of Applied Physics

Effects of the surface modification by O2 plasma exposure on the Al/Ge(111) structure have been investigated in order to get an insight into a layer transfer technique of the ultrathin Ge layer segregated on the Al/Ge(111) structure toward the device fabrication, and then the wafer bonding of the Al/Ge(111) structure to the thermally-grown SiO2/Si structure has been demonstrated. The O2 plasma treatment and the subsequent pure water rinse were found to be effective to form the hydrophilic surface of the Al/Ge(111) structure with a suppression of the segregated Ge layer oxidation. The Al/Ge(111) structure with the hydrophilic surface was then bonded to the SiO2/Si substrate, and its bonding strength was enough to perform Ge thinning by the chemical mechanical polishing and the wet-chemical etching using H2O2-based solutions. Ohmic contact of the ring-type device pattern with the segregated Ge/Al stack was achieved by using the remaining p-type Ge substrate as the contact pads.

DOI： 10.35848/1347-4065/acb65c

DOI： 10.35848/1347-4065/acb65c

Scanning electron microscopy observation in wide field of view for SrO/TiO2-terminated step-terrace structure formed on SrTiO3(001) single crystal surface 査読有り Open Access

Katsuyama, Y; Kodaira, A; Tokunaga, T; Yamamoto, T

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 131 巻 ( 5 ) 頁： 135 - 139 2023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：Journal of the Ceramic Society of Japan

SrO-terminated terraces were formed along TiO2-terminated step edges by annealing (001) surfaces of SrTiO3 single crystal originally with step-terrace structure fully terminated at TiO2 atomic layer. The prepared step-terrace structure with the two different terminations were visualized in a wide field of view using scanning electron microscopy (SEM) under a low acceleration voltage of 1 kV and a short working distance of 2 mm. The different termination was clearly identified by an in-column secondary electron detector even in the wide-field region with dimensions of 30 © 30 ¯m2. As results, the uniformity of the step-terrace structure was found to be limited only at a localized area. The wide-field observation revealed that there exist many “step-defects” such as pinning of the step lines and wandering so large that it goes around to an opposite side. Step-defects were present in at least several for 30 © 30 ¯m2 sized observation areas with a probability of about 60 %.

DOI： 10.2109/jcersj2.23011

DOI： 10.2109/jcersj2.23011

Local Crystallization of Amorphous Aluminum Oxide Thin Film Using Electron Beam Irradiation by SEM Open Access

Tanahashi, S; Okawara, S; Tokunaga, T; Yamamoto, T

MATERIALS TRANSACTIONS 64 巻 ( 1 ) 頁： 184 - 190 2023年

Shrinkage-rate controlled flash sintering for 3-10 mol %Y<sub>2</sub>O<sub>3</sub>-doped ZrO<sub>2</sub> polycrystals 査読有り Open Access

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

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 130 巻 ( 12 ) 頁： 906 - 912 2022年12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 controlled flash (SCF) sintering using alternative current electric field was systematically performed for 310 mol% Y2O3-doped ZrO2. As results, the uniformly densified compacts with about 99% relative densities could be produced at furnace temperatures of about 754781 °C for about 30 min as SCF-regime irrespective of Y concentration, while the achieved densities were limited by conventional flash sintering. The shrinkage-rates during SCF-sintering were found to be enhanced in lower temperature range comparing those during thermal-sintering. The enhancement of shrinkage-rates in lower temperature range observed in SCFsintering is possibly related to the reduction of apparent activation energy of sintering under electric fields.

DOI： 10.2109/jcersj2.22114

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