Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Watanuki, Tetsu; Kawana, Daichi*; Machida, Akihiko; Tsai, A. P.*
Hoshako, 25(3), p.176 - 183, 2012/05
Quasiperiodic intermediate-valence systems were prepared by applying pressure to Yb-based quasicrystals. In these systems, each quasiperiodic lattice point has a charge degree of freedom. Synchrotron radiation X-ray absorption spectroscopy experiments near the Yb 
-edge demonstrate that the Yb valence in a Cd-Yb icosahedral quasicrystal increases continuously upon compression from a divalent state at ambient pressure and reaches 2.33 at 31.7 GPa, where the quasiperiodically arranged Yb ions take a valence fluctuation state. For the case of a Cd-Mg-Yb icosahedral quasicrystal, the Yb valence reaches a value of 2.71 at 57.6 GPa. By following the trend of Yb-based intermediate-valence crystalline compounds, this large valence increase suggests that the 4f electron system in this quasicrystal varies from a valence fluctuation regime to a strong correlated electron regime.
Watanuki, Tetsu; Kawana, Daichi*; Machida, Akihiko; Tsai, A. P.*
Physical Review B, 84(5), p.054207_1 - 054207_6, 2011/08
Times Cited Count：14 Percentile：50.26(Materials Science, Multidisciplinary)A quasiperiodic intermediate-valence system was prepared by applying pressure to an icosahedral Cd-Mg-Yb quasicrystal. X-ray absorption spectroscopy near the Yb 
-edge demonstrates that the Yb valence increases continuously upon compression from the divalent state (4
) at ambient pressure and reaches a value of 2.71 at 57.6 GPa, which is close to the trivalent state (4
). By following the trend of Yb-based intermediate-valence crystalline compounds, this large valence increase suggests the change of 4 character in the Cd-Mg-Yb quasicrystal from an itinerant state with weak electron correlations to an intermediate region between an itinerant and a localized state with strong correlations.
Watanuki, Tetsu; Kawana, Daichi*; Machida, Akihiko; Tsai, A. P.*
Journal of the Physical Society of Japan, 80(Suppl.A), p.SA087_1 - SA087_3, 2011/07
Times Cited Count：6 Percentile：42.48(Physics, Multidisciplinary)A quasiperiodic intermediate-valence system is demonstrated by applying pressure to an icosahedral Cd-Mg-Yb quasicrystal as well as our previous report on a Cd-Yb quasicrystal. Yb 
-edge X-ray absorption spectroscopy experiments demonstrate that the Yb valence increases continuously upon compression from the divalent state at ambient pressure, and reaches a valence of 2.37 at 16.3 GPa. Unlike other known quasicrystals, these Yb-based quasiperiodic intermediate-valence systems have the following two characteristics. (1) Each quasiperiodic lattice point has a charge degree of freedom, and (2) pressure can control the strength of the electron correlations.
Kawana, Daichi*; Watanuki, Tetsu; Machida, Akihiko; Shobu, Takahisa; Aoki, Katsutoshi; Tsai, A. P.*
Physical Review B, 81(22), p.220202_1 - 220202_4, 2010/06
Times Cited Count：17 Percentile：57.37(Materials Science, Multidisciplinary)A quasiperiodic intermediate-valence system was prepared by applying pressure to an icosahedral Cd-Yb quasicrystal. In this system, each quasiperiodic lattice point has a charge degree of freedom. Yb X-ray absorption spectroscopy experiments demonstrate that the Yb valence increases continuously upon compression from a divalent state at ambient pressure and reaches 2.33 at 31.7 GPa. A comparison study to the crystalline approximant suggests that the quasiperiodically arranged Yb ions have a homogeneous intermediate valence that takes a valence fluctuation state under pressure.
Watanuki, Tetsu; Sato, Taku*; Tsai, A. P.*
Journal of Physics; Conference Series, 215, p.012019_1 - 012019_4, 2010/03
Times Cited Count：4 Percentile：80.66(Instruments & Instrumentation)Synchrotron X-ray powder diffraction studies on an icosahedral Cd-Yb quasicrystal (iCd-Yb), its crystalline approximant of Cd
Yb (cCd-Yb) and the related Cd
Eu
(cCd-Eu) material were performed under pressures of up to about 40 GPa at room temperature. The icosahedral lattice of the atomic cluster in iCd-Yb and the bcc lattices in cCd-Yb and cCd-Eu were found to be stable under pressure. Although the Tsai-type atomic cluster can possibly be distorted in various ways, low-symmetry distortion modes do not seem to develop even at high pressure. It is considered that the cluster structure of centrosymmetric dense atomic packing prevented low-symmetry distortions and consequently provided the cluster lattice stability.
de Boissieu, M.*; Francoual, S.*; Minalkovi
, M.*; Shibata, Kaoru; Baron, A. Q. R.*; Sidis, Y.*; Ishimasa, Tsutomu*; Wu, D.*; Lograsso, T.*; Regnault, L.-P.*; et al.
Nature Materials, 6(12), p.977 - 984, 2007/12
Times Cited Count：44 Percentile：81.42(Chemistry, Physical)We have carried out inelastic X-ray and neutron scattering experiments on single-grain samples of the Zn-Mg-Sc icosahedral quasicrystal and of the Zn-Sc periodic cubic 1/1 approximant, with the aim of studying the respective influence of the local order and the long-range order (periodic or quasiperiodic) on lattice dynamics. Besides the overall similarities and the existence of a pseudo-gap in the transverse dispersion relation, marked difference are observed, the pseudo-gap being larger and better defined in the approximant than in the quasicrystal. These results are compared with simulations on atomic models and using oscillating pair potentials, and the simulations reproduce in detail the experimental results.
Watanuki, Tetsu; Machida, Akihiko; Ikeda, Tomohiro*; Omura, Ayako*; Kaneko, Hiroshi; Aoki, Katsutoshi; Sato, Taku*; Tsai, A. P.*
Philosophical Magazine, 87(18-21), p.2905 - 2911, 2007/06
Times Cited Count：47 Percentile：86.71(Materials Science, Multidisciplinary)We have constructed a single-crystal synchrotron X-ray diffraction system to precisely study the structure under hydrostatic pressure conditions at low temperatures and applied it to a study on the phase transition phenomena of a Cd-Yb periodic approximant and a Cd-Yb quasicrystal. Four phases were newly observed for the 1/1 approximant crystal in a 
span up to 5.2 GPa and down to 10 K. The innermost part of the atomic clusters of Cd tetrahedra exhibited various orientational ordering sensitively depending on pressure and temperature. High pressure diffraction measurements using a highly parallel synchrotron X-ray beam and a hydrostatically compressed single crystal enabled us to detect the weak diffractions due to the subtle structural changes.
Watanuki, Tetsu; Machida, Akihiko; Ikeda, Tomohiro*; Aoki, Katsutoshi; Kaneko, Hiroshi; Shobu, Takahisa; Sato, Taku*; Tsai, A. P.*
Physical Review Letters, 96(10), p.105702_1 - 105702_4, 2006/03
Times Cited Count：31 Percentile：77.02(Physics, Multidisciplinary)The phase study of a Cd-Yb 1/1 approximant crystal over a wide pressure and temperature range is crucial for the comparison study between periodic and quasi-periodic crystals. The Cd4 tetrahedra, the most inner part of the atomic clusters, exhibited various structural ordering in the orientation sensitive to pressure and temperature. Five ordered phases appeared in a P-T span up to 5.2 GPa and down to 10K. The propagation direction of ordering alternated from [110] to 
111
at about 1.0 GPa and again to [110] at 3.5-4.3 GPa. The primarily ordered phases that appeared by cooling to 210-250K between 1-5.2 GPa further transformed to finely ordered ones at 120-155K. In addition to the original short-range type interaction, a long-range type interaction was likely developed under pressure to lead to the primary ordering of Cd4 tetrahedra. Coexistence of the two different type interactions is responsible for the complicated phase behavior.
Johnson, W. R.*; Trester, P. W.*; Sengoku, Seio; Ishiyama, Shintaro; Fukaya, Kiyoshi; Eto, Motokuni; Oda, Tomomasa*; Hirohata, Yuko*; Hino, Tomoaki*; Tsai, H.*
Journal of Nuclear Materials, 283-287(Part1), p.622 - 627, 2000/12
Times Cited Count：2 Percentile：19.11(Materials Science, Multidisciplinary)no abstracts in English
Watanuki, Tetsu; Machida, Akihiko; Omura, Ayako; Aoki, Katsutoshi; Owada, Kenji; Sato, Taku*; Tsai, A. P.*
no journal, ,
no abstracts in English
Watanuki, Tetsu; Machida, Akihiko; Omura, Ayako; Aoki, Katsutoshi; Owada, Kenji; Sato, Taku*; Tsai, A. P.*
no journal, ,
no abstracts in English
Kawana, Daichi; Watanuki, Tetsu; Machida, Akihiko; Aoki, Katsutoshi; Tsai, A. P.*
no journal, ,
no abstracts in English
Kawana, Daichi; Watanuki, Tetsu; Machida, Akihiko; Aoki, Katsutoshi; Tsai, A. P.*
no journal, ,
no abstracts in English
Watanuki, Tetsu; Machida, Akihiko; Kawana, Daichi; Tsai, A. P.*
no journal, ,
no abstracts in English
Watanuki, Tetsu; Machida, Akihiko; Aoki, Katsutoshi; Kawana, Daichi; Sato, Taku*; Tsai, A. P.*
no journal, ,
no abstracts in English
Kawana, Daichi; Watanuki, Tetsu; Machida, Akihiko; Shobu, Takahisa; Aoki, Katsutoshi; Tsai, A. P.*
no journal, ,
no abstracts in English
Kawana, Daichi; Watanuki, Tetsu; Machida, Akihiko; Aoki, Katsutoshi; Tsai, A. P.*
no journal, ,
no abstracts in English
Watanuki, Tetsu; Machida, Akihiko; Kawana, Daichi; Aoki, Katsutoshi; Tsai, A. P.*
no journal, ,
The phase study of a Cd-Yb 1/1 approximant crystal over a wide pressure and temperature range is crucial for the comparison study between periodic and quasi-periodic crystals. Our previous X-ray diffraction study revealed that the Cd4 tetrahedra, the most inner part of the atomic clusters, exhibit various structural ordering in the orientation sensitive to pressure and temperature. Five ordered phases appear in a P-T span up to 5.2 GPa and down to 10K. In this study we surveyed higher pressure region up to 30 GPa at room temperature. Single crystal diffraction experiments at SPring-8 (BL22XU) using a helium pressure medium in a diamond anvil cell elucidated that the crystal undergoes successive structural phase transition with an alternation of the period. The bcc phase at ambient pressure transformed to a 3-fold ordered phase at about 12 GPa, and to 4-fold one at about 20 GPa. These phases are different from those found at the previous study.
Watanuki, Tetsu; Kawana, Daichi; Machida, Akihiko; Tsai, A. P.*
no journal, ,
A single crystal X-ray diffraction study of the Cd-Yb crystalline approximant was performed under pressure up to 33 GPa at SPring-8. The bcc phase at ambient pressure transformed to a 3-fold ordered phase at about 12 GPa, and to 4-fold one at about 20 GPa. These phases are different from those found at the previous study. These Sequential transitions would be induced by continuous decrease of the ionic radius of the Yb ion.
Watanuki, Tetsu; Machida, Akihiko; Kawana, Daichi; Tsai, A. P.*
no journal, ,
no abstracts in English
