In situ synchrotron Fe Mssbauer spectroscopy of RFe (R = Y, Gd) hydrides synthesized under ultra-high-pressure hydrogen

Mitsui, Takaya; Masuda, Ryo*; Seto, Makoto; Hirao, Naohisa*; Matsuoka, Takehiro*; Nakamura, Yumiko*; Sakaki, Koji*; Enoki, Hirotoshi*

Journal of Alloys and Compounds, 580(Suppl.1), p.S264 - S267, 2013/12

https://doi.org/10.1016/j.jallcom.2013.03.271

Pressure-induced structural change from hexagonal to fcc metal lattice in scandium trihydride

Omura, Ayako; Machida, Akihiko; Watanuki, Tetsu; Aoki, Katsutoshi; Nakano, Satoshi*; Takemura, Kenichi*

Journal of Alloys and Compounds, 446-447, p.598 - 602, 2007/10

https://doi.org/10.1016/j.jallcom.2007.04.018

Pressure-induced structural change from hcp to fcc-like metal lattice was investigated for scandium hydride, ScHx, by X-ray diffraction measurement up to 60 GPa at room temperature. Hydride was prepared in a diamond anvil cell (DAC) by compressing the metal foil with fluid hydrogen. The metal foil reacted with fluid hydrogen to form ScH with an fcc metal lattice at about 4 GPa. Up to 5 GPa, fcc ScH changed for the most part to ScH with a hexagonal metal lattice, which persisted to about 25 GPa together with unreacted ScH. On further compression, the hcp lattice began to transform towards an fcc-like lattice. The transition completed at about 46 GPa. The successive change in diffraction pattern during the transition was quite similar to that observed for YHx, the transient state was not explained by the coexistence phase of ScH and ScH but able to be interpreted in terms of the gradual change in the sequential stacking of the metal layers.

Thermal relaxation of hydrogen disordering in Pd-H system irradiated with high-energy partides

Chimi, Yasuhiro; Adachi, Koichi*; Iwase, Akihiro; Ishikawa, Norito; Yamakawa, Koji*

Journal of Alloys and Compounds, 330-332(1-2), p.187 - 190, 2002/01

https://doi.org/10.1016/S0925-8388(01)01485-2

no abstracts in English

The Characterization of Ti- and Ca-MH systems in the high temperature chemical heat pump for gas-cooled reactor applications

Ishiyama, Shintaro; ; Eto, Motokuni

Journal of Alloys and Compounds, 231, p.895 - 897, 1995/00

https://doi.org/10.1016/0925-8388(95)01778-X

no abstracts in English

X-ray diffraction investigation on the hexagonal-fcc transition process in yttrium trihydride at pressures of 11-21 GPa

Machida, Akihiko; Omura, Ayako; Watanuki, Tetsu; Aoki, Katsutoshi; Takemura, Kenichi*

no journal, , 

no abstracts in English

Instability of cubic-YH at high pressure

Machida, Akihiko; Watanuki, Tetsu; Aoki, Katsutoshi

no journal, , 

The pressure-induced structural change of yttrium dihydride, YH, has been investigated by synchrotron radiation X-ray diffraction experiment at room temperature. We observed a phase separation into two different hydrogen concentration states at high pressure. In the cubic metal lattice of YH, hydrogen atoms occupy the tetrahedral interstitial sites alone; the octahedral interstitial sites remain empty. A single-crystal-like YH specimen was compressed in helium pressure medium with a diamond anvil cell up to 55 GPa. Besides the original Bragg spots from the cubic-YH, new Bragg spots appeared just outside the original ones above 35 GPa, indicating the formation of a cubic lattice with slightly small lattice constants. The cell volume determined from the spot positions was smaller by 18% than that of the coexisting original cubic lattice. The disproportionate mechanism will be discussed on the basis of the further analysis of the X-ray data.

Effect of surface modifications of Pd by ion irradiation on the characteristics of hydrogen absorption

Abe, Hiroshi; Morimoto, Ryo*; Aone, Shigeo*; Uchida, Hirohisa*; Oshima, Takeshi

no journal, , 

In previous studies, the induction of vacancy in palladium (Pd) was found to be effective for an increase in the initial hydrogen absorption rate. As well known, the initial hydrogen absorption rate depends strongly on the surface conditions of metals. Based on these results, we made surface modifications of Pd using various ions at TIARA, JAEA. In this study, we perform Cr ion irradiation into Pd, and the hydrogen absorption rate of ion irradiation Pd was evaluated. The Pd irradiated at a fluence to 110 cm exhibited the highest rate in all samples, and the hydrogen absorption rate became five times higher than that of un-irradiated Pd. Since vacancy type defects which might act as hydrogen trapping site are introduced by irradiation the enhancement of the hydrogen absorption rate obtained inthi study can be interpreted in terms of an increase of hydrogen trapping saites near the surface region due to irradiation of Cr ion into Pd.

Properties of metal hydrides under high pressure studied using synchrotron radiation X-rays

Machida, Akihiko

no journal, , 

Synchrotron radiation (SR) X-rays enable us to investigate the structural and electronic properties of metals that change often dramatically on hydrogenation and/or dehydrogenation. Metal hydrides have been investigated with a focus on hydrogen-metal bonding and hydrogen-hydrogen interaction for their densified states realized under high pressure. Application of pressure results in contraction of the metal lattice and decrease in the interatomic distances. The nature of hydrogen-metal bonding state would change significantly and becomes to be clearly detectable. Another aspect of high pressure effect is direct hydrogenation of metals. The chemical potential of hydrogen increases steeply with increasing pressure. Consequently, the hydrogen dissociation into metal is enhanced. Novel hydrides would be prepared by direct hydrogenation of metals with hydrogen-fluid chemically actived at high temperature and high pressure.

Thermal degradation analysis of deuterium ion implanted hydrogen storage material (TiFe and VCrTi) using synchrotron radiation photoelectron spectroscopy

Tode, Mayumi; Harries, J.; Teraoka, Yuden; Yoshigoe, Akitaka

no journal, , 

In order to study the relationships between the thermal desorption of hydrogen and the surface properties, we have used high-resolution synchrotron radiation X-ray photoelectron spectroscopy to study the thermal degeneration processes of the surface layers. The experiments were performed at the JAEA soft X-ray beamline BL23SU at SPring-8, using the "SUREAC2000" surface reaction analysis apparatus. XPS spectra were recorded for room temperature TiFe and VCrTi following flash heating to 373-1073 K. Spectra were recorded for two samples covered with native oxide layers, one of which was implanted with deuterium ions. In the deuterium-implanted TiFe, the temperature to which it begins to resolve the oxide component has lowered at about 200-250 C. On the other hand, in VCrTi, the thermal stability of a surface natural oxide layer has increased by the deuterium-implanted.

Hydrogenation of aluminum-based alloys under high pressure

Saito, Hiroyuki; Endo, Naruki; Machida, Akihiko; Katayama, Yoshinori; Aoki, Katsutoshi

no journal, ,