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Yoshiasa, Akira*; Arima, Hiroshi; Fukui, Hiroshi*; Okube, Maki*; Katayama, Yoshinori; Otaka, Osamu*
Nihon Kessho Gakkai-Shi, 51(1), p.66 - 69, 2009/02
We have determined a precise P-T phase diagram of AgI by high-temperature high-pressure synchrotron experiments. X-ray diffraction and X-ray absorption measurements were performed using a multi-anvil high pressure apparatus at SPring-8 synchrotron radiation facility. In a disordered rock-salt phase, Ag ions occupy both octahedral and tetrahedral sites. The occupancy of tetrahedral site has a maximum value, 20%, at 2 GPa. A change from rock-salt structure to disordered rock-salt structure is gradual in the X-ray diffraction measurements while it is clearly observed in the X-ray absorption measurements. Analysis of EXAFS Debye-Waller factor is useful because the force constant can be decided directly even at high pressure and high temperature. Pressure influences greatly the effective potential and anharmonicity decreases with increasing pressure.
XAFS and XRD studies of pressure-induced local structural change in liquid AgIArima, Hiroshi*; Otaka, Osamu*; Hattori, Takanori; Katayama, Yoshinori; Utsumi, Wataru; Yoshiasa, Akira*
Journal of Physics; Condensed Matter, 19(7), p.076104_1 - 076104_7, 2007/02
Times Cited Count：16 Percentile：57.68(Physics, Condensed Matter)no abstracts in English
Otaka, Osamu*; Arima, Hiroshi*; Fukui, Hiroyuki*; Utsumi, Wataru; Katayama, Yoshinori; Yoshiasa, Akira*
Physical Review Letters, 92(15), p.155506_1 - 155506_4, 2004/04
Times Cited Count：51 Percentile：84.44(Physics, Multidisciplinary)Local structures around germanium in liquid germanate have been investigated by means of in situ X-ray absorption measurements up to 9 GPa at 1273 K. Liquid germanate consisting of tetrahedrally coordinated germanium contracts with increasing pressure without significant changes in the local structure up to 2.5 GPa and then shows an abrupt fourfold-to-sixfold coordination change around 3 GPa. The coordination change is completed below 4 GPa where upon a high-density liquid consisting of octahedrally coordinated germanium becomes stable. The GeO
octahedron in the high-density liquid is more compressible than that in solids.
Utsumi, Wataru; Katayama, Yoshinori; Saito, Hiroyuki; Kaneko, Hiroshi*; Okada, Taku*; Otaka, Osamu*
Mirai O Hiraku Koatsuryoku Kagaku Gijutsu Semina Shirizu, 28, p.14 - 20, 2004/01
no abstracts in English
Okube, Maki*; Yoshiasa, Akira*; Otaka, Osamu*; Katayama, Yoshinori
High Pressure Research, 23(3), p.247 - 251, 2003/09
Times Cited Count：5 Percentile：38.80(Physics, Multidisciplinary)In order to examine the pressure effect on anharmonic thermal vibrations of Pt, Extended X-ray Absorption Fine Structure (EXAFS) spectra near Pt K-edge and L
-edge were measured in the temperature range from 300 to 800K under pressures up to 6vGPa, using large volume high-pressure devices and synchrotron radiation. We have investigated the anharmonic interatomic potentials by a cumulant expansion method. The values of EXAFS Debye-Waller factors, 
2 and 3, become smaller with increase of pressure. The anharmonic effective pair potential 
was evaluated and the potential coefficient a at 0.1MPa and 6GPa are 4.8 and 5.0eV/
, respectively. The anharmonic potential parameter 
decreases with increasing pressure.
Otaka, Osamu*; Utsumi, Wataru; Kikegawa, Takumi*
Mirai O Hiraku Koatsuryoku Kagaku Gijutsu Semina Shirizu, 27, p.52 - 62, 2003/07
no abstracts in English
glass under pressureOtaka, Osamu*; Yoshiasa, Akira*; Fukui, Hiroyuki*; Murai, Keiichiro*; Okube, Maki*; Takebe, Hitoshi*; Katayama, Yoshinori; Utsumi, Wataru
Journal of Physics; Condensed Matter, 14(44), p.10521 - 10524, 2002/11
Times Cited Count：18 Percentile：64.13(Physics, Condensed Matter)no abstracts in English
Okube, Maki*; Yoshiasa, Akira*; Otaka, Osamu*; Fukui, Hiroyuki*; Katayama, Yoshinori; Utsumi, Wataru
Journal of Physics; Condensed Matter, 14(44), p.11511 - 11515, 2002/11
Times Cited Count：4 Percentile：26.06(Physics, Condensed Matter)no abstracts in English
Otaka, Osamu*; Takebe, Hitoshi*; Yoshiasa, Akira*; Fukui, Hiroshi*; Katayama, Yoshinori
Solid State Communications, 123(5), p.213 - 216, 2002/08
Times Cited Count：18 Percentile：64.13(Physics, Condensed Matter)Using a multi-anvil high-pressure device and synchrotron radiation, X-ray 
observations of AgI high pressure and high temperature up to 6.0 GPa and 1000 K have been performed to investigate the phase relations between 
-AgI, rocksalt-type, disordered rocksalt-type, and liquid phases. The three phases of -AgI, disordered rocksalt-type, and liquid meet in a triple point in the vicinity of 823 K and 1.3 GPa. The melting curve of the disordered rocksalt phase is linear with a positive slope. The transition between rocksalt and the disordered rocksalt phases is a broad and diffuse disordering type within the same structure. The formation of the disordered rocksalt phase has been hence estimated with the variation of a relative intensity ratio of (111) and (200) diffraction from the rocksalt phase. With increasing pressure the rocksalt phase becomes stabel at high temperature. At 6.0 GPa the rocksalt phase directly melts without the transition to the disordered rocksalt phase.
Okube, Maki*; Yoshiasa, Akira*; Otaka, Osamu*; Fukui, Hiroshi*; Katayama, Yoshinori; Utsumi, Wataru
Solid State Communications, 121(5), p.235 - 239, 2002/02
Times Cited Count：11 Percentile：50.63(Physics, Condensed Matter)In order to examine the pressure effect on the anharmonicity of Au, EXAFS spectra near Au 
-edge were measured at the temperature range from 300 to 1000K under pressure up to 14GPa using large volume high-pressure devices and synchrotron radiation. The values of EXAFS Debye-Waller factors, 
and 
, become smaller with increase of pressure, which indicates that the potential width become narrower with pressure. The anharmonic effective pair potentials of Au, 
, at 0.1MPa, 6 and 14GPa have been calculated. The pressure dependence of the coefficient of thermal expansion has also been evaluated.
and HfO under high-temperature and high-pressureOtaka, Osamu*; Fukui, Hiroyuki*; Funakoshi, Kenichi*; Utsumi, Wataru; Irifune, Tetsuo*; Kikegawa, Takumi*
High Pressure Research, 22(1), p.221 - 226, 2002/01
Times Cited Count：30 Percentile：76.56(Physics, Multidisciplinary)no abstracts in English
under high pressure and high peratureOtaka, Osamu*; Fukui, Hiroyuki*; Kunisada, Taichi*; Fujisawa, Tomoyuki*; Funakoshi, Kenichi*; Utsumi, Wataru; Irifune, Tetsuo*; Kuroda, Koji*; Kikegawa, Takumi*
Physical Review B, 63(17), p.174108_1 - 174108_8, 2001/05
Times Cited Count：129 Percentile：96.78(Materials Science, Multidisciplinary)no abstracts in English
Utsumi, Wataru; Funakoshi, Kenichi*; Yagi, Naoto*; Urakawa, Satoru*; Otaka, Osamu*; Katsura, Tomoo*; Irifune, Tetsuo*; Inoue, Toru*; Uchida, Takeyuki*
Ganseki Kobutsu Kagaku, 30(2), p.100 - 101, 2001/03
no abstracts in English
Funakoshi, Kenichi*; Utsumi, Wataru; Otaka, Osamu*; Irifune, Tetsuo*; Inoue, Toru*; Ito, Eiji*; Katsura, Tomoo*; Kubo, Atsushi*; Hirose, Kei*; Ando, Junichi*; et al.
Ganseki Kobutsu Kagaku, 30(2), p.102 - 103, 2001/03
no abstracts in English
under pressureOtaka, Osamu*; Yoshiasa, Akira*; Fukui, Hiroyuki*; Murai, Keiichiro*; Okube, Maki*; Katayama, Yoshinori; Utsumi, Wataru; Nishihata, Yasuo
Journal of Synchrotron Radiation, 8(Part2), p.791 - 793, 2001/03
no abstracts in English
and 
CuBr at high pressureYoshiasa, Akira*; Okube, Maki*; Otaka, Osamu*; Kamishima, Osamu*; Katayama, Yoshinori
Japanese Journal of Applied Physics, Part 1, 39(12A), p.6747 - 6751, 2000/12
Times Cited Count：10 Percentile：44.14(Physics, Applied)The anharmonic effective pair potentials 
for Br-Cu bond in and CuBr under pressure have been investigated by an extended X-ray absorption fine structure (EXAFS) technique. The EXAFS spectra near the Br K-edge were measured under high temperature and high pressure using a large-volume uniaxial press and synchrotron radiation from SPring-8. The anharmonic effective pair potential for each phase is influenced by pressure and become steeper with increasing pressure. The potential parameter 
for 
-phase at 0.1MPa increases by about 20% at the pressure of 4.8GPa. The stastical distribution of Cu in -CuBr and superionic conduction mechanism have been discussed based on the effective pair potential and distribution of Br-Cu distances.
Fukui, Hiroyuki*; Otaka, Osamu*; Nagai, Takaya*; Katsura, Tomoo*; Funakoshi, Kenichi*; Utsumi, Wataru
Physics and Chemistry of Minerals, 27(6), p.367 - 370, 2000/06
Times Cited Count：4 Percentile：21.48(Materials Science, Multidisciplinary)no abstracts in English
Urakawa, Satoru*; Otaka, Osamu*; Funakoshi, Kenichi*; Utsumi, Wataru
Nihon Kessho Gakkai-Shi, 42(1), p.24 - 32, 2000/02
no abstracts in English
under high-temperature and high-pressure conditionsFukui, Hiroyuki*; Otaka, Osamu*; Katsura, Tomoo*; Nagai, Takaya*; Funakoshi, Kenichi*; Utsumi, Wataru; Kikegawa, Takumi*
Science and Technology of High Pressure, p.554 - 557, 2000/00
no abstracts in English
SiO
Determined by in Situ X-ray DiffractionIrifune, Tetsuo*; Nishiyama, Norimasa*; Kuroda, Koji*; Inoue, Toru*; Isshiki, Maiko*; Utsumi, Wataru; Funakoshi, Kenichi*; Urakawa, Satoru*; Uchida, Takeyuki*; Katsura, Tomoo*; et al.
Science, 279(5357), p.1698 - 1700, 1998/03
Times Cited Count：206 Percentile：93.63(Multidisciplinary Sciences)no abstracts in English
