Updated on 2024/02/29

写真a

 
YOKOI Tatsuya
 
Organization
Graduate School of Engineering Materials Physics 2 Lecturer
Graduate School
Graduate School of Engineering
Undergraduate School
School of Engineering Physical Science and Engineering
Title
Lecturer

Degree 1

  1. 博士(工学) ( 2015.3   大阪大学 ) 

Research Interests 3

  1. 理論計算

  2. 格子欠陥

  3. 粒界

Research Areas 1

  1. Nanotechnology/Materials / Inorganic materials and properties  / 計算材料科学

Research History 3

  1. Nagoya University   Lecturer

    2021.9

  2. Nagoya University   Assistant Professor

    2016.9 - 2021.8

      More details

    Country:Japan

  3. Osaka University

    2015.4 - 2016.8

      More details

    Country:Japan

Awards 1

  1. 永井科学技術財団 奨励賞

    2023.2   公益財団法人永井科学技術財団   機械学習と第一原理計算の融合による半導体格子欠陥の原子構造・特性の解明

 

Papers 45

  1. Multicrystalline Informatics Applied to Multicrystalline Silicon for Unraveling the Microscopic Root Cause of Dislocation Generation

    Kenta Yamakoshi, Yutaka Ohno, Kentaro Kutsukake, Takuto Kojima, Tatsuya Yokoi, Hideto Yoshida, Hiroyuki Tanaka, Xin Liu, Hiroaki Kudo, Noritaka Usami

    Advanced Materials   Vol. 36 ( 8 ) page: e2308599   2023.12

     More details

    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Wiley  

    Abstract

    A comprehensive analysis of optical and photoluminescence images obtained from practical multicrystalline silicon wafers is conducted, utilizing various machine learning models for dislocation cluster region extraction, grain segmentation, and crystal orientation prediction. As a result, a realistic 3D model that includes the generation point of dislocation clusters is built. Finite element stress analysis on the 3D model coupled with crystal growth simulation reveals inhomogeneous and complex stress distribution and that dislocation clusters are frequently formed along the slip plane with the highest shear stress among twelve equivalents, concentrated along bending grain boundaries (GBs). Multiscale analysis of the extracted GBs near the generation point of dislocation clusters combined with ab initio calculations has shown that the dislocation generation due to the concentration of shear stress is caused by the nanofacet formation associated with GB bending. This mechanism cannot be captured by the Haasen‐Alexander‐Sumino model. Thus, this research method reveals the existence of a dislocation generation mechanism unique to the multicrystalline structure. Multicrystalline informatics linking experimental, theoretical, computational, and data science on multicrystalline materials at multiple scales is expected to contribute to the advancement of materials science by unraveling complex phenomena in various multicrystalline materials.

    DOI: 10.1002/adma.202308599

    Web of Science

    Scopus

    PubMed

  2. Anharmonicity in grain boundary energy for Al: thermodynamic integration with artificial-neural-network potential Reviewed International journal

    Scripta Materialia   Vol. 236   page: 115685   2023.11

     More details

    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: https://doi.org/10.1016/j.scriptamat.2023.115685

  3. Photoplastic effect in MgO single crystals

    Ogura Yu, Tsuchiya Yuki, Hoshino Sena, Yokoi Tatsuya, Matsunaga Katsuyuki

    Journal of the Ceramic Society of Japan   Vol. 131 ( 10 ) page: 628 - 631   2023.10

     More details

    Language:English   Publisher:The Ceramic Society of Japan  

    <p>The photoplastic effect, phenomena that flow stress and/or hardness change by light illuminations, has been known mainly in II–VI compound semiconductors. In this study, it was revealed for the first time that magnesium oxide (MgO) single crystals exhibit increase in flow stress by light illumination, namely, the positive photoplastic effect. Scanning transmission electron microscope (STEM) observations demonstrated that the plastic deformation of MgO is realized by generation of glide dislocations on the slip system of {110}〈110〉. Therefore, the observed positive photoplastic effect of MgO is likely due to interactions of the glide dislocations and photo-excited carriers. According to the theoretical calculations, individual dislocations in MgO had a specific band structure that differs from the bulk. This also indicates possible interactions between dislocations and carriers. It is expected that light illumination can reduce dislocation mobility in MgO, leading to the increase in flow stress under light illuminations.</p>

    DOI: 10.2109/jcersj2.23060

    CiNii Research

  4. Grain boundary segregation of Y and Hf dopants in α-Al<sub>2</sub>O<sub>3</sub>: A Monte Carlo simulation with artificial-neural-network potential and density-functional-theory calculation

    Yokoi Tatsuya, Hamajima Akihiro, Ogura Yu, Matsunaga Katsuyuki

    Journal of the Ceramic Society of Japan   Vol. 131 ( 10 ) page: 751 - 761   2023.10

     More details

    Language:English   Publisher:The Ceramic Society of Japan  

    <p>Artificial-neural-network (ANN) interatomic potentials for Al–Y–O and Al–Hf–O systems are constructed using density-function-theory (DFT) data and combined with Monte Carlo (MC) simulations in order to predict Y and Hf segregation behavior at the ∑7(4<span style="text-decoration: overline;">5</span>10)/[0001] grain boundary (GB) in α-Al<sub>2</sub>O<sub>3</sub>. The ANN potentials are demonstrated to accurately predict preferential substitutional sites of not only an isolated but also multiple dopant ions. This enables us to circumvent DFT calculations for MC trial moves, thereby greatly reducing computational cost. There is a tendency that both Y and Hf ions substitute for 6-fold Al ions with elongated Al–O bonds at the GB and have coordination numbers greater than 6 after structural relaxation. This may suggest that even at the GB, Y and Hf ions prefer atomic environments in Y- and Hf-containing oxides with 7- and 8-fold coordination. Furthermore, effects of dopant species and concentrations on band-gap reduction at the GB are elucidated by analyzing partial density of states for the dopant-segregated GBs. The ANN-MC method with DFT analysis will pave the way for systematically determining atomic and electronic structures of GBs involving dopants, as demonstrated in this work.</p>

    DOI: 10.2109/jcersj2.23044

    CiNii Research

  5. Electronic and atomic structures of Shockley-partial dislocations in CdX (X = S, Se and Te)

    Hoshino Sena, Yokoi Tatsuya, Ogura Yu, Matsunaga Katsuyuki

    Journal of the Ceramic Society of Japan   Vol. 131 ( 10 ) page: 613 - 620   2023.10

     More details

    Language:English   Publisher:The Ceramic Society of Japan  

    <p>II–VI semiconductors, including Cd compounds, become brittle under light illumination. This phenomenon is known as the photoplastic effect (PPE) and is thought to arise from interactions between glide dislocations and photoexcited carriers. The present study investigated atomic structures of 30° Shockley-partial dislocations with and without excess carriers in CdX (X = S, Se and Te), by density-functional-theory (DFT) calculations. It was found that both Cd and anion cores favor unreconstructed atomic structures when excess carriers are absent. In the presence of excess carriers, on the other hand, reconstructed atomic structures were more stable at the anion cores while the unreconstructed ones were still energetically more favorable at the Cd cores. It is thus expected that only the anion cores change their atomic structures by light illumination, which can retard glide-dislocation motion by forming like-atom bonds. Analyses of local densities of states (LDOSs) revealed that the reconstructed Cd and anion cores form shallow and deep defect states within the band gaps, respectively. This determines the possible atomic reconstructions at the dislocation cores in the presence of excess carriers excited by external light.</p>

    DOI: 10.2109/jcersj2.23055

    CiNii Research

  6. Grain-boundary thermodynamics with artificial-neural-network potential: Its ability to predict the atomic structures, energetics, and lattice vibrational properties for Al

    Yokoi Tatsuya, Matsuura Maya, Oshima Yu, Matsunaga Katsuyuki

    PHYSICAL REVIEW MATERIALS   Vol. 7 ( 5 )   2023.5

     More details

    Publisher:Physical Review Materials  

    An artificial neural network (ANN) potential for Al, trained with density-functional-theory (DFT) data, is constructed to accurately predict lattice vibrational properties and thermodynamics of grain boundaries (GBs) in Al. The ANN potential is demonstrated to accurately predict not only atomic structures and energetics of the GBs at 0 K but also partial phonon densities of states and vibrational entropies, even for GBs absent in the training data sets. In addition, their total potential energies and atomic forces by DFT at elevated temperatures up to 800 K can also be well reproduced by molecular dynamics with the ANN potential. In contrast, a modified embedded atom method (MEAM) potential shows larger errors in phonon frequencies and atomic forces for atoms at GBs, as well as in the bulk, than the ANN potential. The MEAM potential is thus likely to be inadequate to quantitatively predict thermodynamic properties of GBs, particularly at high temperature. The present ANN potential is also applied to systematically examine thermodynamic stability of asymmetric tilt GBs. It is predicted that for the ς9 system, the GB free-energy profile as a function of inclination angle exhibits a cusp at elevated temperatures, due to its larger vibrational entropies of asymmetric tilt GBs than those of ς9 symmetric tilt GBs.

    DOI: 10.1103/PhysRevMaterials.7.053803

    Web of Science

    Scopus

  7. Atomic and electronic structure of grain boundaries in a-Al2O3: A combination of machine learning, first-principles calculation and electron microscopy

    Yokoi T., Hamajima A., Wei J., Feng B., Oshima Y., Matsunaga K., Shibata N., Ikuhara Y.

    SCRIPTA MATERIALIA   Vol. 229   2023.5

     More details

    Publisher:Scripta Materialia  

    To accurately determine the atomic and electronic structures of symmetric tilt grain boundaries (GBs) in α-Al2O3, this work employed an artificial-neural-network (ANN) interatomic potential, density-functional-theory (DFT) calculation and scanning transmission electron microscopy (STEM) observation. An ANN-based simulated annealing method was demonstrated to efficiently screen candidate low-energy structures with reasonably high accuracy. For Σ7 and Σ31GBs with the [0001] tilt axis, which were absent in the training datasets for the ANN potential, their lowest-energy structures predicted from ANN and DFT calculations were in quantitative agreement with STEM images in terms of both Al- and O-column positions. The exact GB structures have enabled us to analyze quantitatively the relationship between their atomic and electronic structure. This work will be an important model case where a combination of machine-learning, theoretical calculation and experiment has successfully solved the problem of determining complicated GB structures and their electronic structures in α-Al2O3.

    DOI: 10.1016/j.scriptamat.2023.115368

    Web of Science

    Scopus

  8. Atomic structures of grain boundaries for Si and Ge: A simulated annealing method with artificial-neural-network interatomic potentials (vol 173, 111114, 2023)

    Yokoi Tatsuya, Kato Hirotaka, Oshima Yu, Matsunaga Katsuyuki

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   Vol. 176   2023.5

     More details

    Publisher:Journal of Physics and Chemistry of Solids  

    The authors regret the inclusion of author Hirotaka Kato. Professor Hirotaka Kato name has been removed from the article. The authors would like to apologise for any inconvenience caused.

    DOI: 10.1016/j.jpcs.2023.111273

    Web of Science

    Scopus

  9. Ca-vacancy effect on the stability of substitutional divalent cations in calcium-deficient hydroxyapatite

    Tatsushi Saito, Yuto Ishikawa, Yusuke Noda, Tatsuya Yokoi, Yu Oshima, Atsutomo Nakamura, Katsuyuki Matsunaga

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY   Vol. 106 ( 2 ) page: 1587 - 1596   2023.2

     More details

    Language:English   Publishing type:Research paper (scientific journal)   Publisher:WILEY  

    First-principles calculations were performed to reveal an effect of Ca vacancies on the stability of substitutional divalent cations M2+ (M = Mg, Zn, Sr) in Ca-deficient hydroxyapatite (dHAp). M2+ concentrations up to 20 mol% in dHAp were considered, and the most stable substitutional sites and their lowest energy configurations in the dHAp lattice were examined with the aid of a generic algorithm method. It was found that defect formation energies of substitutional M2+ are lower in dHAp than in stoichiometric HAp (sHAp) at all M2+ concentrations. This indicates that these M2+ ions are more favorably involved in dHAp than in sHAp, which is in reasonable agreement with experiment. Detailed analyses on atomic structures in dHAp show that the presence of a Ca vacancy varies its surrounding Ca-O bond lengths over a wide area so that Ca-O polyhedrons with various sizes are produced. As a result, M2+ ions can predominantly occupy Ca sites at which M2+ fits better, depending on the ionic radii of M2+. For Zn2+ substitution in dHAp, its defect formation energy decreases more with the increasing concentrations and has the minimum value at 15 mol%. Such a trend can be understood from changes in effective coordination numbers of Zn in dHAp.

    DOI: 10.1111/jace.18853

    Web of Science

    Scopus

  10. Atomic structures of grain boundaries for Si and Ge: A simulated annealing method with artificial-neural-network interatomic potentials

    Tatsuya Yokoi, Hirotaka Kato, Yu Oshima, Katsuyuki Matsunaga

    Journal of Physics and Chemistry of Solids   Vol. 173   2023.2

     More details

    Publishing type:Research paper (scientific journal)  

    To accurately predict low-energy structures for symmetric tilt grain boundaries (GBs) in Si and Ge, artificial-neural-network (ANN) interatomic potentials are constructed and are combined with a simulated annealing (SA) method based on molecular dynamics simulations. The ANN-driven SA method is demonstrated to predict GB structures that are in good agreement with previous electron microscopy observations, without prior knowledge about their atomic configurations. Their GB energies also reasonably agree with density-functional-theory (DFT) calculations. By contrast, a conventional empirical potential fails to predict those GB structures. For misorientation angles 2θ≥93.37°, the lowest-energy structures are found to contain atomic configurations that cannot be reproduced by one repeat unit of the perfect crystal along the tilt axis. Such GB structures cannot be obtained using the γ-surface method, although it is most commonly used for exploring low-energy GB structures. These results highlight the importance of using simulation cells with multiple repeat units along the tilt axis and of performing the SA method with high-accuracy interatomic potentials transferable to GBs.

    DOI: 10.1016/j.jpcs.2022.111114

    Web of Science

    Scopus

  11. DFT calculations of carrier-trapping effects on atomic structures of 30° partial dislocation cores in zincblende II-VI group zinc compounds

    Sena Hoshino, Yu Oshima, Tatsuya Yokoi, Atsutomo Nakamura, Katsuyuki Matsunaga

    Physical Review Materials   Vol. 7 ( 1 )   2023.1

     More details

    Publishing type:Research paper (scientific journal)   Publisher:American Physical Society (APS)  

    DOI: 10.1103/physrevmaterials.7.013603

    Scopus

    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevMaterials.7.013603/fulltext

  12. Atomic structures and stability of finite-size extended interstitial defects in silicon: Large-scale molecular simulations with a neural-network potential

    Ohbitsu M., Yokoi T., Noda Y., Kamiyama E., Ushiro T., Nagakura H., Sueoka K., Matsunaga K.

    Scripta Materialia   Vol. 214   2022.6

     More details

    Language:Japanese   Publisher:Scripta Materialia  

    The energetics of various extended interstitial (I) defects in crystalline Si is examined by constructing an artificial-neural-network (ANN) potential trained with density-functional-theory (DFT) data, enabling us to perform accurate large-scale simulations and to obtain well-converged formation energies (Ef). By varying the number of interstitials n to around 1,000, Ef is calculated for the compact cluster, I12-like, (001)-plane, (311)-rod-like and Frank-loop defects. For n ≤ 36, the compact cluster or (311)-rod-like defect is found to be most stable, depending on n. This trend strongly depends on simulation cell sizes, suggesting the importance of sufficiently large cells. For 36 < n ≲ 860, the (311)-rod-like defect is most stable whereas the Frank-loop defect becomes most stable for larger n. The ANN potential is demonstrated to outperform empirical potentials in prediction of Ef and defect structures. Furthermore, ANN values of Ef are fitted to analytic functions with the aim of refining macroscopic simulations for device manufacturing processes.

    DOI: 10.1016/j.scriptamat.2022.114650

    Scopus

  13. First-Principles Analysis of the Oxide-Ion Conduction Mechanism in Si-Deficient Lanthanum Silicate Apatite

    Yusuke Ogura, Tatsuya Yokoi, Kotaro Fujii, Masatomo Yashima, Katsuyuki Matsunaga

    Journal of Physical Chemistry C   Vol. 126 ( 13 ) page: 5805 - 5812   2022.4

     More details

    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER CHEMICAL SOC  

    Si-deficient lanthanum silicate apatites (La9.33+0.67xSi6-0.5xO26, LSOs) have attracted attention for their high oxide-ion conductivities. However, the carrier species and the conduction pathways responsible for the oxide-ion conduction are still unclear. In this study, the conduction mechanism of oxide ions in Si-deficient LSO was studied by first-principles calculations. It was found that Si-deficient LSO can include a small amount of excess oxide ions, which are located at the interstitial site along the c axis. The excess oxide ions in Si-deficient LSO can rapidly diffuse along the c axis by the push-pull mechanism with a potential barrier of 0.35 eV, which involves cooperative movements of two neighboring oxide ions, O4 ions, and the excess oxide ions. The potential barrier height was in good agreement with the experimentally reported activation energy. It is shown that a small amount of excess oxygen contributes critically to oxide-ion conduction in Si-deficient LSO, as was also discussed in stoichiometric La9.33Si6O26. These findings indicate the existence of a mechanism whereby a small amount of excess carriers in the ion-conduction pathways can significantly change the energy profiles for ionic conduction and enhance ion conductivity.

    DOI: 10.1021/acs.jpcc.1c10486

    Web of Science

    Scopus

  14. Accurate prediction of grain boundary structures and energetics in CdTe: a machine-learning potential approach

    Yokoi Tatsuya, Adachi Kosuke, Iwase Sayuri, Matsunaga Katsuyuki

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   Vol. 24 ( 3 ) page: 1620 - 1629   2022.1

     More details

    Language:Japanese   Publisher:Physical Chemistry Chemical Physics  

    To accurately predict grain boundary (GB) atomic structures and their energetics in CdTe, the present study constructs an artificial-neural-network (ANN) interatomic potential. To cover a wide range of atomic environments, large amounts of density functional theory (DFT) data are used as a training dataset including point defects, surfaces and GBs. Structural relaxation combined with the trained ANN potential is applied to symmetric tilt and twist GBs, many of which are not included in the training dataset. The relative stability of the relaxed structures and their GB energies are then evaluated with the DFT level. The ANN potential is found to accurately predict low-energy structures and their energetics with reasonable accuracy with respect to DFT results, while conventional empirical potentials critically fail to find low-energy structures. The present study also provides a way to further improve the transferability of the ANN potential to more complicated GBs, using only low-Σ GBs as training datasets. Such improvement will offer a way to accurately predict atomic structures of general GBs within practical computational cost. This journal is

    DOI: 10.1039/d1cp04329c

    Web of Science

    Scopus

    PubMed

  15. Effect of La vacancies on the oxide-ion conduction in lanthanum silicate apatites

    Ogura Yusuke, Yokoi Tatsuya, Fujii Kotaro, Yashima Masatomo, Matsunaga Katsuyuki

    SOLID STATE IONICS   Vol. 373   2021.12

     More details

    Language:Japanese  

    DOI: 10.1016/j.ssi.2021.115793

    Web of Science

  16. Grain-size dependence and anisotropy of nanoscale thermal transport in MgO

    Fujii Susumu, Funai Kohei, Yokoi Tatsuya, Yoshiya Masato

    APPLIED PHYSICS LETTERS   Vol. 119 ( 23 )   2021.12

     More details

    Language:Japanese   Publisher:Applied Physics Letters  

    Controlling thermal conductivity in nanocrystalline materials is of great interest in various fields such as thermoelectrics. However, its reduction mechanism has not been fully given due to the difficulty to assess local thermal conduction at grain boundaries (GBs) and grain interiors. Here, we calculated spatially decomposed thermal conductivities across and along MgO symmetric GBs using perturbed molecular dynamics, varying the GB separation from 2.1 to 20.0 nm. This reveals the different length scale of GB scattering for two directions: over hundreds of nanometers across GBs while within a few nanometers along GBs. Numerical analyses based on the spatially decomposed thermal conductivities demonstrate that the former is dominant upon suppressing thermal conductivity in polycrystalline materials, whereas the latter has a non-negligible impact in nanocrystalline materials because of a large reduction of intragrain thermal conductivity along GBs. These insights provide the exact mechanisms of heat transport in nanocrystalline materials toward more precise control of thermal conductivity.

    DOI: 10.1063/5.0075854

    Web of Science

    Scopus

  17. Preferential growth mode of large-sized vacancy clusters in silicon: A neural-network potential and first-principles study Invited Reviewed

    T. Ushiro, T. Yokoi, Y. Noda, E. Kamiyama, M. Ohbitsu, H. Nagakura, K. Sueoka, K. Matsunaga

    Journal of Physical Chemistry C   Vol. 125 ( 48 ) page: 26869 - 26882   2021.11

     More details

    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1021/acs.jpcc.1c07973

  18. Differential clustering of self-interstitials during Si crystal growth

    Kamiyama Eiji, Yokoi Tatsuya, Noda Yusuke, Sueoka Koji

    JOURNAL OF CRYSTAL GROWTH   Vol. 574   2021.11

     More details

  19. First-principles based theoretical calculations of atomic structures of hydroxyapatite surfaces and their charge states in contact with aqueous solutions

    Saito T., Yokoi T., Nakamura A., Matsunaga K.

    RSC ADVANCES   Vol. 11 ( 54 ) page: 34004 - 34014   2021.10

     More details

    Language:Japanese  

    DOI: 10.1039/d1ra06311a

    Web of Science

  20. Segregation mechanism of arsenic dopants at grain boundaries in silicon

    Yutaka Ohno, Tatsuya Yokoi, Yasuo Shimizu, Jie Ren, Koji Inoue, Yasuyoshi Nagai, Kentaro Kutsukake, Kozo Fujiwara, Atsutomo Nakamura, Katsuyuki Matsunaga, Hideto Yoshida

    Science and Technology of Advanced Materials: Methods     2021.8

     More details

    Publishing type:Research paper (scientific journal)   Publisher:Informa UK Limited  

    DOI: 10.1080/27660400.2021.1969701

  21. Direct imaging of atomistic grain boundary migration

    Wei Jiake, Feng Bin, Ishikawa Ryo, Yokoi Tatsuya, Matsunaga Katsuyuki, Shibata Naoya, Ikuhara Yuichi

    NATURE MATERIALS   Vol. 20 ( 7 ) page: 951 - +   2021.7

     More details

  22. An origin of excess vibrational entropies at grain boundaries in Al, Si and MgO: a first-principles analysis with lattice dynamics

    Yokoi T., Ikawa K., Nakamura A., Matsunaga K.

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   Vol. 23 ( 16 ) page: 10118 - 10129   2021.4

     More details

    Language:Japanese  

    DOI: 10.1039/d1cp00790d

    Web of Science

  23. Photoindentation: A New Route to Understanding Dislocation Behavior in Light

    Nakamura Atsutomo, Fang Xufei, Matsubara Ayaka, Tochigi Eita, Oshima Yu, Saito Tatsushi, Yokoi Tatsuya, Ikuhara Yuichi, Matsunaga Katsuyuki

    NANO LETTERS   Vol. 21 ( 5 ) page: 1962 - 1967   2021.3

     More details

  24. Crystal and Electronic Structures of MoSi2-Type CrGe2 Synthesized under High Pressure

    Sasaki Takuya, Kanie Kota, Yokoi Tatsuya, Niwa Ken, Gaida Nico Alexander, Matsunaga Katsuyuki, Hasegawa Masashi

    INORGANIC CHEMISTRY   Vol. 60 ( 3 ) page: 1767 - 1772   2021.2

     More details

  25. Stable and metastable structures and their energetics of asymmetric tilt grain boundaries in MgO: a simulated annealing approach

    Yokoi T., Kondo Y., Ikawa K., Nakamura A., Matsunaga K.

    JOURNAL OF MATERIALS SCIENCE   Vol. 56 ( 4 ) page: 3183 - 3196   2021.2

     More details

  26. First-principles analysis of oxide-ion conduction mechanism in neodymium silicate

    Ogura Yusuke, Yokoi Tatsuya, Toyoura Kazuaki, Matsunaga Katsuyuki

    SOLID STATE IONICS   Vol. 355   2020.11

     More details

    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.ssi.2020.115367

    Web of Science

  27. Formation energies and site preference of substitutional divalent cations in carbonated apatite

    Saito Tatsushi, Yokoi Tatsuya, Nakamura Atsutomo, Matsunaga Katsuyuki

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY   Vol. 103 ( 9 ) page: 5354 - 5364   2020.9

     More details

    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1111/jace.17263

    Web of Science

  28. Room-temperature creep deformation of cubic ZnS crystals under controlled light conditions

    Oshima Yu, Nakamura Atsutomo, Lagerlof K. Peter D., Yokoi Tatsuya, Matsunaga Katsuyuki

    ACTA MATERIALIA   Vol. 195   page: 690 - 697   2020.8

     More details

    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.actamat.2020.06.016

    Web of Science

  29. Carrier-trapping induced reconstruction of partial-dislocation cores responsible for light-illumination controlled plasticity in an inorganic semiconductor

    Katsuyuki Matsunaga, Sena Hoshino, Masaya Ukita, Yu Oshima, Tatsuya Yokoi, Atsutomo Nakamura

    Acta Materialia   Vol. 195   page: 645 - 653   2020.8

     More details

    Language:Japanese   Publishing type:Research paper (scientific journal)  

    © 2020 Inorganic semiconductors show interesting mechanical behavior in response to their surrounding lighting environments. In fact, we recently found out that zinc sulfide (ZnS) shows the light-illumination controlled plasticity at room temperature. However, its mechanism is poorly understood. Here we report systematic density functional theory results of electronic and atomic structures of glide partial dislocations in ZnS. We have revealed that partial dislocations in ZnS have excess electrostatic fields localized around their cores and can trap electrons or holes, depending on excess ionic species at the cores. Such carrier-dislocation interactions can induce energetically more stable bond reconstruction at their cores, as compared with the case before carrier trapping. Reconstructed bonds at the dislocation cores should be broken upon dislocation glide, and thus can restrict the dislocation motion significantly. Such reduced dislocation motion due to core reconstruction should give rise to increased plastic deformation stresses, namely, hardening of the materials under light illumination. The present results provide a critical understanding of the experimentally observed light-illumination controlled plasticity in ZnS at the electronic level, which is opposed to previously reported plasticity and dislocation motion in other elemental and III-V semiconductors.

    DOI: 10.1016/j.actamat.2020.06.010

    Web of Science

    Scopus

  30. Quantitative prediction of grain boundary thermal conductivities from local atomic environments

    Fujii Susumu, Yokoi Tatsuya, Fisher Craig A. J., Moriwake Hiroki, Yoshiya Masato

    NATURE COMMUNICATIONS   Vol. 11 ( 1 )   2020.4

     More details

    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1038/s41467-020-15619-9

    Web of Science

  31. Direct Measurement of Electronic Band Structures at Oxide Grain Boundaries

    Wei Jiake, Ogawa Takafumi, Feng Bin, Yokoi Tatsuya, Ishikawa Ryo, Kuwabara Akihide, Matsunaga Katsuyuki, Shibata Naoya, Ikuhara Yuichi

    NANO LETTERS   Vol. 20 ( 4 ) page: 2530 - 2536   2020.4

     More details

    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1021/acs.nanolett.9b05298

    Web of Science

  32. Role of phonons on phase stabilization of RE2Si2O7 over wide temperature range (RE = Yb, Gd)

    Fujii Susumu, Ioki Arata, Yokoi Tatsuya, Yoshiya Masato

    JOURNAL OF THE EUROPEAN CERAMIC SOCIETY   Vol. 40 ( 3 ) page: 780 - 788   2020.3

     More details

    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.jeurceramsoc.2019.10.060

    Web of Science

  33. Dependence of excess vibrational entropies on grain boundary structures in MgO: A first-principles lattice dynamics

    Yokoi T., Arakawa Y., Ikawa K., Nakamura A., Matsunaga K.

    PHYSICAL REVIEW MATERIALS   Vol. 4 ( 2 )   2020.2

     More details

  34. Neural-network interatomic potential for grain boundary structures and their energetics in silicon

    Yokoi T., Noda Y., Nakamura A., Matsunaga K.

    PHYSICAL REVIEW MATERIALS   Vol. 4 ( 1 )   2020.1

     More details

  35. Atomistic mechanisms of thermal transport across symmetric tilt grain boundaries in MgO

    Susumu Fujii, Tatsuya Yokoi, Masato Yoshiya

    Acta Materialia   Vol. 171   page: 154 - 162   2019.6

     More details

    Language:Japanese   Publishing type:Research paper (scientific journal)  

    © 2019 Acta Materialia Inc. Grain boundaries often have a decisive effect on the macroscopic properties of polycrystalline materials, but the wide variety of their atomic structures, interfacial lengths, and compositions makes them difficult to characterize all-encompassingly. An indispensable example in which an understanding of the relationship between grain boundary structures and properties would greatly facilitate development of superior materials is thermal transport, especially with respect to microstructure evolution, thermoelectrics and thermal barrier coatings. To contribute to a more comprehensive understanding, we performed a systematic study of lattice thermal conduction across a wide range of symmetric tilt grain boundaries in MgO using perturbed molecular dynamics. It was found that thermal conductivities vary significantly with grain boundary structure but are strongly correlated with excess volume, which is a measure of the number density of atoms in the vicinity of the grain boundary planes. Real-space analysis revealed that dislocation densities determine the phonon transport paths and thermal conductivity in low-angle boundaries whereas it is the amount of open volume rather than the shape of structural units in high-angle boundaries that determine thermal conductivity. We also found that low-angle boundaries mainly reduce phonon transports at low frequencies whereas high-angle boundaries also reduce it at intermediate and high frequencies effectively, regardless of the shape of structural units. These insights are expected to be applicable to other close-packed oxide systems, and should aid the design of next-generation thermal materials through tailoring of grain boundaries.

    DOI: 10.1016/j.actamat.2019.04.009

    Web of Science

    Scopus

  36. Theoretical Calculations of Characters and Stability of Glide Dislocations in Zinc Sulfide

    Ukita Masaya, Nagahara Ryota, Oshima Yu, Nakamura Atsutomo, Yokoi Tatsuya, Matsunaga Katsuyuki

    MATERIALS TRANSACTIONS   Vol. 60 ( 1 ) page: 99 - 104   2019

     More details

    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.2320/matertrans.M2018253

    Web of Science

  37. Oxide-ion conduction via interstitials in scheelite-type LaNbO4: a first-principles study

    Toyoura Kazuaki, Sakakibara Yusuke, Yokoi Tatsuya, Nakamura Atsutomo, Matsunaga Katsuyuki

    JOURNAL OF MATERIALS CHEMISTRY A   Vol. 6 ( 25 ) page: 12004-12011   2018.7

     More details

    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1039/c8ta02859a

    Web of Science

  38. Interaction of sodium atoms with stacking faults in silicon with different Fermi levels

    Ohno Yutaka, Morito Haruhiko, Kutsukake Kentaro, Yonenaga Ichiro, Yokoi Tatsuya, Nakamura Atsutomo, Matsunaga Katsuyuki

    APPLIED PHYSICS EXPRESS   Vol. 11 ( 6 )   2018.6

     More details

    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.7567/APEX.11.061303

    Web of Science

  39. Atomistic simulations of grain boundary transformation under high pressures in MgO Reviewed

    T. Yokoi, M. Yoshiya

    Physica B: Condensed Matter   Vol. 532   page: 2 - 8   2018.3

     More details

    Language:Japanese   Publishing type:Research paper (scientific journal)  

    © 2017 Elsevier B.V. This study focuses on transformation of grain boundary (GB) structures under high pressures up to 60 GPa by using a simulated annealing technique with molecular dynamics and lattice statics calculations for various symmetric tilt GBs (STGBs) of MgO. It is found that except for the Σ3(111)/[11¯0] that is a rather stable GB, all the STGBs studied transform into a metastable structure more than once at threshold pressures. In addition, the GBs with an open-core structure and small tilt angle are found to be more “flexible” to transform into different structures than the GBs with a dense structure. For polycrystalline MgO, therefore, GBs may also exhibit GB transformation under high pressures and flexible GBs may govern overall transformation and deformation. These findings also suggest that polycrystals sintered at high pressures consist of more pressure-resistant GBs than those at normal pressures.

    DOI: 10.1016/j.physb.2017.03.014

    Web of Science

    Scopus

  40. Structure of the Basal Edge Dislocation in ZnO

    Nakamura Atsutomo, Tochigi Eita, Nagahara Ryota, Furushima Yuho, Oshima Yu, Ikuhara Yuichi, Yokoi Tatsuya, Matsunaga Katsuyuki

    CRYSTALS   Vol. 8 ( 3 )   2018.3

     More details

    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.3390/cryst8030127

    Web of Science

  41. Electronic and atomic structures of edge and screw dislocations in rock salt structured ionic crystals

    Ukita Masaya, Nakamura Atsutomo, Yokoi Tatsuya, Matsunaga Katsuyuki

    PHILOSOPHICAL MAGAZINE   Vol. 98 ( 24 ) page: 2189-2204   2018

     More details

    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1080/14786435.2018.1478146

    Web of Science

  42. Atomically ordered solute segregation behavior in an oxide grain boundary Reviewed

    B. Feng, T. Yokoi, A. Kumamoto, M. Yoshiya, Y. Ikuhara, N. Shibata

    Nature Communications     2016.3

     More details

    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: doi:10.1038/ncomms11079

  43. Atomistic analyses of Competition between Site-Selective Segregation and Association of Point Defects at Grain Boundary in Y2O3-doped ZrO2 Reviewed

    T. Yokoi, M. Yoshiya, H. Yasuda

    Material Transaction     2015.8

     More details

    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: DOI: 10.2320/matertrans.MA201567

  44. On modeling of grain boundary segregation in aliovalent cation doped ZrO2: Critical factors in site-selective point defect occupancy Reviewed

    T. Yokoi, M. Yoshiya, H. Yasuda

    Scripta Materialia     2015.3

     More details

    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.scriptamat.2015.02.021

  45. Nonrnadom Point Defect Configurations and Driving Force Transitions for Grain Boundary Segregation in Trivalent Cation Doped ZrO2 Reviewed

    T. Yokoi, M. Yoshiya, H. Yasuda

    Langmuir     2014.11

     More details

    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1021/la503338x

▼display all

Presentations 2

  1. First-principles study of dependence of impurity segregation on grain boundary character in silicon

    T. Yokoi, Y. Ohno, A. Nakamura, K. Matsunaga

    10th International Workshop on Crystalline Silicon for Solar Cells 

     More details

    Event date: 2018

    Language:English   Presentation type:Poster presentation  

    Country:Japan  

  2. Atomistic simulations of energetically stable grain boundary structures and its diffusional properties in MgO International conference

    T. Yokoi, A. Nakamura, K. Matsunaga

    12th Pacific Rim Conference on Ceramic and Glass Technology (PACRIM 12) 

     More details

    Event date: 2017

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

Research Project for Joint Research, Competitive Funding, etc. 7

  1. Si系半導体における点欠陥と不純物の欠陥複合体・クラスターの学理深化

    2023.10 - 2025.3

    三菱財団自然科学研究助成(若手助成) 

      More details

    Authorship:Principal investigator 

    Grant amount:\4000000

  2. 化合物半導体における格子欠陥の電子・熱伝導機構の理論的解明と精密設計

    2023.9 - 2025.3

    公益財団法人立松財団 研究助成(一般研究助成) 

      More details

    Authorship:Principal investigator 

    Grant amount:\1500000

  3. 深層学習分子シミュレーションと高精度電子状態計算による化合物半導体における格子欠陥の学理深化と最適設計

    2023.4 - 2024.12

    公益財団法人池谷科学技術振興財団 単年度研究助成 

      More details

    Grant amount:\2000000

  4. 格子欠陥挙動の微視的理解に向けた高精度な深層学習型記述子および原子間ポテンシャルの開発

    2023.1 - 2023.12

    公益財団法人日東学術振興財団 研究助成 

      More details

    Authorship:Principal investigator 

    Grant amount:\1000000

  5. 酸化物異相界面におけるバンド変調機構の解明と制御に向けた原子・電子レベル解析

    2022.12 - 2023.11

    カシオ科学振興財団 研究助成 

      More details

    Grant amount:\1000000

  6. 酸化物セラミックスにおける不純物偏析・拡散ダイナミクスの微視的機構の解明と粒界拡散の原子レベル制御

    2022.4 - 2023.3

    公益財団法人豊田理化学研究所 豊田理研スカラー 

      More details

    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\1000000

  7. 機械学習と電子状態計算の融合による化合物半導体粒界における電子・熱物性の最適制御指針の獲得

    2022.4 - 2023.3

    一般財団法人伊藤忠兵衛基金 学術研究助成 

      More details

    Authorship:Principal investigator 

    Grant amount:\500000

▼display all

KAKENHI (Grants-in-Aid for Scientific Research) 4

  1. 転位・粒界制御によるバックキャスト的材料設計のための電子・熱伝導支配因子の解明

    2023.4 - 2027.3

    科学研究費助成事業  基盤研究(B)

      More details

    Authorship:Coinvestigator(s) 

  2. 機械学習記述子・原子間ポテンシャルによる一般粒界-格子欠陥相互作用の学理構築

    Grant number:23K04381  2023.4 - 2026.3

    科学研究費助成事業  基盤研究(C)

      More details

    Authorship:Principal investigator 

  3. 半導体における転位コア構造および転位ダイナミクスの理論解析

    Grant number:22H04508  2022.4 - 2024.3

    新学術領域研究(研究領域提案型) 

      More details

    Authorship:Principal investigator 

  4. 第一原理粒界熱力学によるセラミックス粒界の原子構造・特性の精密設計

    Grant number:21K14405  2021.4 - 2023.3

    科学研究費助成事業  若手研究

    横井 達矢

      More details

    Authorship:Principal investigator 

    Grant amount:\4680000 ( Direct Cost: \3600000 、 Indirect Cost:\1080000 )

    高温域におけるセラミックス粒界の熱力学的安定性に関する情報は、多結晶組織とその特性を制御する上で不可欠である。本研究では、第一原理計算と機械学習、情報科学的手法を統合して、高精度・高速で粒界の自由エネルギー計算が可能な「第一原理熱力学計算法」を確立する。この手法をセラミックス粒界に適用することで、全温度域を対象に、原子構造という根本から粒界構造と熱力学的安定性との関係を解明する。その知見をもとに「セラミックス粒界状態図」の構築を試みる。

 

Teaching Experience (On-campus) 3

  1. 材料工学実験第2

    2017

  2. 材料工学実験及び演習1

    2017

  3. 材料工学実験基礎

    2017