Determination of atomistic deformation of tricalcium silicate paste with high-volume fly ash

Jee, H.*; Im, S.*; Kanematsu, Manabu*; Suzuki, Hiroshi; Morooka, Satoshi; Koyama, Taku*; Machida, Akihiko*; Bae, S.*

Journal of the American Ceramic Society, 103(12), p.7188 - 7201, 2020/12

https://doi.org/10.1111/jace.17404

Crystal and magnetic structures of double hexagonal close-packed iron deuteride

Saito, Hiroyuki*; Machida, Akihiko*; Iizuka, Riko*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; Sato, Toyoto*; Orimo, Shinichi*; Aoki, Katsutoshi*

Scientific Reports (Internet), 10, p.9934_1 - 9934_8, 2020/06

https://doi.org/10.1038/s41598-020-66669-4

Neutron powder diffraction profiles were collected for iron deuteride (FeDx) while the temperature decreased from 1023 to 300 K for a pressure range of 4-6 GPa. The ' deuteride with a double hexagonal close-packed (dhcp) structure, which coexisted with other stable or metastable deutrides at each temperature and pressure condition, formed solid solutions with a composition of FeD at 673 K and 6.1 GPa and FeD at 603 K and 4.8 GPa. Upon stepwise cooling to 300 K, the D-content x increased to a stoichiometric value of 1.0 to form monodeuteride FeD. In the dhcp FeD at 300 K and 4.2 GPa, dissolved D atoms fully occupied the octahedral interstitial sites, slightly displaced from the octahedral centers in the dhcp metal lattice, and the dhcp sequence of close-packed Fe planes contained hcp-stacking faults at 12%. Magnetic moments with 2.11 0.06 B/Fe-atom aligned ferromagnetically in parallel on the Fe planes.

Hexagonal close-packed iron hydride behind the conventional phase diagram

Machida, Akihiko*; Saito, Hiroyuki*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; Sato, Toyoto*; Orimo, Shinichi*; Aoki, Katsutoshi*

Scientific Reports (Internet), 9(1), p.12290_1 - 12290_9, 2019/08

https://doi.org/10.1038/s41598-019-48817-7

Hexagonal close-packed iron hydride, hcp FeHx, is absent from the conventional phase diagram of the Fe-H system, although hcp metallic Fe exists stably over extensive temperature () and pressure () conditions, including those corresponding to the Earth's inner core. X-ray and neutron diffraction measurements at temperatures ranging from 298 to 1073 K and H pressures ranging from 4 to 7 GPa revealed that the hcp hydride was formed for FeH compositions when . Hydrogen atoms occupied the octahedral interstitial sites of the host metal lattice both partially and randomly. The hcp hydride exhibited a H-induced volume expansion of 2.48(5) /H-atom, which was larger than that of the face-centered cubic (fcc) hydride. The hcp hydride showed an increase in with , whereas the fcc hydride showed a corresponding decrease. The present study provides guidance for further investigations of the Fe-H system over an extensive -- region.

Maximizing by tuning nematicity and magnetism in FeSeS superconductors

Matsuura, Kohei*; Mizukami, Yuta*; Arai, Yuki*; Sugimura, Yuichi*; Maejima, Naoyuki*; Machida, Akihiko*; Watanuki, Tetsu*; Fukuda, Tatsuo; Yajima, Takeshi*; Hiroi, Zenji*; et al.

Nature Communications (Internet), 8, p.1143_1 - 1143_6, 2017/10

https://doi.org/10.1038/s41467-017-01277-x

Investigation of elastic deformation mechanism in as-cast and annealed eutectic and hypoeutectic Zr-Cu-Al metallic glasses by multiscale strain analysis

Suzuki, Hiroshi; Yamada, Rui*; Tsubaki, Shinki*; Imafuku, Muneyuki*; Sato, Shigeo*; Watanuki, Tetsu; Machida, Akihiko; Saida, Junji*

Metals, 6(1), p.12_1 - 12_11, 2016/01

https://doi.org/10.3390/met6010012

Elastic deformation behaviors of as-cast and annealed eutectic and hypoeutectic Zr-Cu-Al bulk metallic glasses (BMGs) were investigated on a basis of different strain-scales determined by X-ray scattering and the strain gauge. The microscopic strains determined by Direct-space method (DSM) and Q-space method (QSM) were compared with the macroscopic strain measured by the strain gauge, and the difference in the deformation mechanism between eutectic and hypoeutectic Zr-Cu-Al BMGs was investigated by their correlation. The eutectic ZrCuAl BMG obtains more homogeneous microstructure by free-volume annihilation after annealing, improving a resistance to deformation but degrading ductility because of a decrease in the volume fraction of WBRs (Weakly-Bonded Regions) with relatively high mobility. On the other hand, the as-cast hypoeutectic ZrCuAl BMG originally has homogeneous microstructure, but loses its structural and elastic homogeneities because of nanocluster formation after annealing. Such structural changes after annealing might develop unique mechanical properties showing no degradations of ductility and toughness for the structural-relaxed hypoeutectic BMGs.

Melting of Pb charge glass and simultaneous Pb-Cr charge transfer in PbCrO as the origin of volume collapse

Yu, R.*; Hojo, Hajime*; Watanuki, Tetsu; Mizumaki, Masaichiro*; Mizokawa, Takashi*; Oka, Kengo*; Kim, H.*; Machida, Akihiko; Sakaki, Koji*; Nakamura, Yumiko*; et al.

Journal of the American Chemical Society, 137(39), p.12719 - 12728, 2015/10

https://doi.org/10.1021/jacs.5b08216

no abstracts in English

New PbTiO-type giant tetragonal compound BiZnVO and its stability under pressure

Yu, R.*; Hojo, Hajime*; Oka, Kengo*; Watanuki, Tetsu; Machida, Akihiko; Shimizu, Keisuke*; Nakano, Kiho*; Azuma, Masaki*

Chemistry of Materials, 27(6), p.2012 - 2017, 2015/03

https://doi.org/10.1021/cm504133e

no abstracts in English

Observation of transient structural changes on hydrogen absorption process of LaNiSn by time resolved X-ray diffraction

Machida, Akihiko; Higuchi, Kensuke*; Katayama, Yoshinori; Sakaki, Koji*; Kim, H.*; Nakamura, Yumiko*

Nihon Kinzoku Gakkai-Shi, 79(3), p.124 - 130, 2015/03

https://doi.org/10.2320/jinstmet.JC201407

Structural changes on hydrogen absorption process of hydrogen absorbing alloy LaNiSn have been investigated by time-resolved X-ray diffraction measurements using synchrotron radiation source. We have found the transient intermediate phase between the solid solution and hydride phases of LaNiSn under non-equilibrium hydrogen pressure condition at room temperature. LaNiSn has transformed into the hydride through three phase co-existing state. The hydrogen content of the intermediate phase estimated from the unit cell volume is independent of the induced hydrogen gas pressure. The variation of lattice constants indicate that the hydrogen atoms are located at the LaNi(Ni,Sn) octahedron and La(Ni,Sn) tetrahedron in the intermediate phase.

Effect of a quenching rate on hydrogen storage properties of VTiZr

Kim, H.*; Sakaki, Koji*; Asano, Kota*; Ikeda, Kazutaka*; Otomo, Toshiya*; Machida, Akihiko; Watanuki, Tetsu; Nakamura, Yumiko*

Nihon Kinzoku Gakkai-Shi, 79(3), p.131 - 136, 2015/03

https://doi.org/10.2320/jinstmet.JC201405

no abstracts in English

Site occupation state of deuterium atoms in fcc Fe

Aoki, Katsutoshi*; Machida, Akihiko; Saito, Hiroyuki; Hattori, Takanori; Sano, Asami

Hamon, 25(1), p.26 - 31, 2015/02

http://ci.nii.ac.jp/naid/40020357661

The deuterization process of fcc Fe to form solid-solution fcc FeD was investigated by in situ neutron diffraction measurements at high temperature and high pressure. In a completely deuterized specimen at 988 K and 6.3 GPa, deuterium atoms occupy the octahedral and tetrahedral interstitial sites with an occupancy of 0.532(9) and 0.056(5), respectively, giving a deuterium composition of 0.64(1). During deuterization, the metal-lattice expands approximately linearly with deuterium composition at a rate of 2.21 per deuterium atom. The minor occupation of tetrahedral site is likely driven by the intersite movement of deuterium atoms along the direction in the fcc metal lattice. These results provide implications for the light elements in the Earth's core and the mechanism of hydrogen embrittlement of ferrous metals.