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Kaita, Japan

Nogita K.,University of Queensland | McDonald S.D.,University of Queensland | Duguid A.,Hydrexia | Tsubota M.,Physonit Inc. | Gu Q.F.,Australian Synchrotron
Journal of Alloys and Compounds | Year: 2013

The hypo-eutectic Mg-Mg2Ni system can be modified by trace elemental additions of Na which change the microstructure and the functional properties of the alloy. The modified microstructure results in improvements to the hydrogen storage properties. In alloys of optimal composition, it has been shown that the reversible storage of 6.5-7 wt% H2 is possible at a rate of reaction that is realistic for industrial applications. This research investigates the release of H2 in air under atmospheric pressure as well as under 0.2 MPa atmospheres of Ar, CO2, N2, and H2. The release kinetics were characterised using in situ crystallographic phase transformation analysis obtained by synchrotron Powder X-ray diffraction (PXRD) at the Australian Synchrotron. The mole fraction of MgH2, Mg, Mg2Ni, and Mg2NiH4 was determined by Rietveld refinement using RIETAN-FP. It was found that the hydrogen release temperature largely depends on the atmosphere. © 2013 Elsevier B.V. All rights reserved. Source


Kozasa W.,Fukuoka Institute of Technology | Tanaka H.,Fukuoka Institute of Technology | Tsubota M.,Physonit Inc. | Kitagawa J.,Fukuoka Institute of Technology
Materials Research Express | Year: 2014

We have investigated a tunability of transport properties of CeZnSbO by optical light with the photon energy larger than the optical band gap. While CeZnSbO is reported to be a nearly degenerate semiconductor, in the present work, a sample of a non-degenerate type can be prepared. The electrical resistivity has been found to be highly sensitive to sample quality. The examinations of photoexcitation effect have revealed that the results depend on the type of semiconductor: degenerate and non-degenerate types. For a degenerate semiconductor, freezing of carriers at low temperatures can be resolved by increasing the fluence rate. On the other hand, in a non-degenerate type, the activation energy at high temperatures is almost independent of fluence rate. We have additionally found a possible opto-mechanical effect in a composite of CeZnSbO and a small amount of Zn4Sb3. © 2014 IOP Publishing Ltd. Source


Orita K.,Fukuoka Institute of Technology | Uenishi K.,Hiroshima University | Tsubota M.,Physonit Inc. | Shimada Y.,Hiroshima University | And 3 more authors.
Journal of Alloys and Compounds | Year: 2015

We have found that Ce3Pd20As6 crystallizes into a cubic C6Cr23-type structure. Combination of electron probe microanalysis of the chemical composition and Rietveld analysis of the powder X-ray diffraction pattern has revealed an inhomogeneous atomic composition of variable stoichiometry. The physical properties of Ce3Pd20As6 were investigated by measuring the magnetization, electrical resistivity and specific heat. The 4f electrons of Ce3+ ions are well localized but do not show phase transition down to 0.5 K. The metallic electrical resistivity shows a weak Kondo screening. The residual resistivity ratio is rather low probably due to the variable stoichiometry. The magnetization curve and magnetic entropy suggest the Γ8 quartet crystalline-electric-field ground state at least one of two Ce sites. © 2014 Elsevier B.V. All rights reserved. Source


Nakagawa T.,University of Ryukyus | Ichikawa T.,Hiroshima University | Miyaoka H.,Hiroshima University | Tsubota M.,Hiroshima University | And 2 more authors.
Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals | Year: 2013

The milling effect during hydrogenation under various conditions for a CaH2-CaB6 mixture was investigated. Two different starting materials, 1) dehydrogenated Ca(BH4)2 and 2) the mixture of commercial CaH2 and CaB6, were used. TG-MS profiles indicated that the hydrogenation kinetics of dehydrogenated Ca(BH 4)2 was better than the commercial CaH2- CaB6 especially at high temperature. XRD and IR profiles revealed that Ca(BH4)2 and/or its intermediate state were produced after milling. These results indicate that milling technique accelerates hydrogenation of CaH2-CaB6 even at room temperature, and the initial crystalline size of CaB6 is important to improve the kinetics of the first hydrogenation step © 2013 The Japan Institute of Metals and Materials. Source


Abe T.,Fukuoka Institute of Technology | Uenishi K.,Hiroshima University | Orita K.,Fukuoka Institute of Technology | Tsubota M.,Physonit Inc. | And 4 more authors.
Results in Physics | Year: 2014

We have found that a cerium palladium phosphide crystallizes into a C6Cr23-type structure with atomic disorder. Prepared polycrystalline samples show a homogeneity range in the ternary Ce-Pd-P phase diagram. The physical properties of the highest-quality sample of Ce2.4Pd20.7P5.9 were investigated by measuring the magnetization, electrical resistivity and specific heat. No pronounced phase transition was observed down to 0.5K. The Kondo screening of localized 4f electrons in metallic Ce2.4Pd20.7P5.9 appears to be weaker than that in the isostructural compounds of Ce3Pd20Si6 and Ce3Pd20Ge6. By a comparative study of Ce2.4Pd20.7P5.9 and Ce3Pd20X6 (X=Si, Ge), the competition between the Kondo temperature and ordering temperatures including the quadrupolar ordering temperature is briefly discussed. © 2014 The Authors. Source

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