| 1. |
M. M. Rahman, T. Yamamoto, S. Matsumura, J. M. Costantini, K. Yasuda, Ab Initio molecular dynamics study of threshold displacement energy in Zirconium Nitride, Journal of Nuclear Materials, 10.1016/j.jnucmat.2021.153076, 554, 2021.10, Zirconium nitride (ZrN) is a promising matrix candidate for advanced nuclear fuels and transmutation of minor actinides. This study investigates the displacement process induced by low-energy recoils in ZrN using ab initio molecular dynamics (AIMD) simulations to evaluate the threshold displacement energy (Ed). Observations of the collision processes of primary knock-on atoms (PKAs) for both Zr and N atoms were performed for seven different directions: [100], [110], [111], [210], [211], [221], and [321], which cover most regions of the stereographic triangle. The values of Ed ranged from 15 eV to 50 eV, and the collision processes were dependent on the crystallographic orientations. The weighted average values of Ed evaluated from the PKA directions investigated in this study were 33 eV and 29 eV for the Zr and N atoms, respectively. Anti-site defects were not formed for either Zr or N PKAs. Sequential replacement collisions along the [110] atomic row played an important role in the collision process, providing a lower value of Ed in the crystallographic directions. Furthermore, configurations of interstitials were different between the Zr and N atoms, which also influenced Ed values.. |
| 2. |
Kohei Kusada, Tomokazu Yamamoto, Takaaki Toriyama, Syo Matsumura, Katsutoshi Sato, Katsutoshi Nagaoka, Kenji Terada, Yasuyuki Ikeda, Yoshinari Hirai, Hiroshi Kitagawa, Nonequilibrium Flow-Synthesis of Solid-Solution Alloy Nanoparticles: From Immiscible Binary to High-Entropy Alloys, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/acs.jpcc.0c08871, 125, 1, 458-463, 2021.01, Solid-solution alloy nanoparticles (NPs), where the constituents mix at the atomic level, show a variety of attractive properties due to their tunable electronic structures. However, it is still difficult to stably synthesize them, particularly nonequilibrium alloys that consist of combinations immiscible in the bulk. Here, we first report the successful syntheses of solid-solution alloy NPs including PdRu and PdRuIr, which are immiscible in the bulk, and of IrPdPtRhRu high-entropy alloy NPs through a continuous-flow reactor providing a high productivity with high reproducibility. The designed solvothermal flow reactor enabled us to use a lower alcohol as a reductant that cannot be applied in a batch synthesis for these NPs.. |
| 3. |
Wenhui Yang, Tomokazu Yamamoto, Kohei Aso, Flora Somidin, Kazuhiro Nogita, Syo Matsumura, Atom locations in a Ni doped η-(Cu,Ni)6Sn5 intermetallic compound, Scripta Materialia, 10.1016/j.scriptamat.2018.08.020, 158, 1-5, 2019.01, © 2018 Elsevier Ltd The present study has succeeded in direct determination of the location of dopant Ni atoms in η-(Cu,Ni)6Sn5 by aberration-corrected scanning transmission electron microscopy (STEM) including atomic-resolution imaging as well as elemental mapping by X-ray energy-dispersive spectroscopy (XEDS). The three sublattices of Sn, Cu1 and Cu2 were distinguished in atomic-resolution images observed along the [21¯1¯0] direction. Atomic-resolution XEDS maps have verified for the first time that the dopant Ni atoms located at the Cu2 sites in η-(Cu,Ni)6Sn5, taking advantage of the Poisson non-local principal component analysis (NLPCA) processing and the lattice-averaging procedure.. |
| 4. |
Quan Zhang, Kohei Kusada, Dongshuang Wu, Tomokazu Yamamoto, Takaaki Toriyama, Syo Matsumura, Shogo Kawaguchi, Yoshiki Kubota, Hiroshi Kitagawa, Selective control of fcc and hcp crystal structures in Au-Ru solid-solution alloy nanoparticles, Nature Communications, 10.1038/s41467-018-02933-6, 9, 1, 2018.12, © 2018 The Author(s). Binary solid-solution alloys generally adopt one of three principal crystal lattices - body-centred cubic (bcc), hexagonal close-packed (hcp) or face-centred cubic (fcc) structures - in which the structure is dominated by constituent elements and compositions. Therefore, it is a significant challenge to selectively control the crystal structure in alloys with a certain composition. Here, we propose an approach for the selective control of the crystal structure in solid-solution alloys by using a chemical reduction method. By precisely tuning the reduction speed of the metal precursors, we selectively control the crystal structure of alloy nanoparticles, and are able to selectively synthesize fcc and hcp AuRu3 alloy nanoparticles at ambient conditions. This approach enables us to design alloy nanomaterials with the desired crystal structures to create innovative chemical and physical properties.. |
| 5. |
T. Yamamoto, A. Chartier, K. Yasuda, C. Meis, K. Shiiyama, S. Matsumura, Molecular dynamics simulation of point defect accumulation in MgAl2O4, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, 10.1016/j.nimb.2008.03.231, 266, 12-13, 2676-2682, 2008.06, The kinetics of phase transformation under irradiation of magnesium aluminate spinel MgAl2O4 has been investigated by means of continuous Frenkel pair introduction in the framework of empirical potential molecular dynamics simulations. Phase transformation to defective rock-salt structure was observed with a cation displacement dose rate of 5 × 108 dpc/s (dpc: displacements per cation) at temperatures ranging from 30 to 2200 K. The critical dose for the phase transformation is in the range of 0.5-2.5 dpc, and it is prolonged with increasing temperature. No amorphization was realized in the simulations at 30 K up to a dose of 68 dpc with an accelerated displacement dose rate of 5 × 109 dpc/s. © 2008 Elsevier B.V. All rights reserved.. |
