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Journal Articles

New precise measurement of muonium hyperfine structure interval at J-PARC

Ueno, Yasuhiro*; Aoki, Masaharu*; Fukao, Yoshinori*; Higashi, Yoshitaka*; Higuchi, Takashi*; Iinuma, Hiromi*; Ikedo, Yutaka*; Ishida, Keiichi*; Ito, Takashi; Iwasaki, Masahiko*; et al.

Hyperfine Interactions, 238(1), p.14_1 - 14_6, 2017/11

 Times Cited Count:3 Percentile:90.77

Journal Articles

New muonium HFS measurements at J-PARC/MUSE

Strasser, P.*; Aoki, Masaharu*; Fukao, Yoshinori*; Higashi, Yoshitaka*; Higuchi, Takashi*; Iinuma, Hiromi*; Ikedo, Yutaka*; Ishida, Keiichi*; Ito, Takashi; Iwasaki, Masahiko*; et al.

Hyperfine Interactions, 237(1), p.124_1 - 124_9, 2016/12

 Times Cited Count:6 Percentile:92.96

Journal Articles

Macroscopic Separation of Dense Fluid Phase and Liquid Phase of Phosphorus

Katayama, Yoshinori; Inamura, Yasuhiro*; Mizutani, Takeshi*; Yamakata, Masaaki*; Utsumi, Wataru; Shimomura, Osamu*

Science, 306(5697), p.848 - 851, 2004/10

 Times Cited Count:123 Percentile:96.05(Multidisciplinary Sciences)

Structural transformation between two liquid structures of phosphorus that occurred at about 1 GPa and 1000$$^{circ}$$C was investigated by in-situ X-ray radiography. When the low-pressure liquid was compressed, dark and round objects appeared in the radiograph. X-ray diffraction measurements confirmed that these objects were the high-pressure liquid. The drops grew and eventually filled the sample space. Decompressing caused the reverse process. The macroscopic phase separation supported the view that it was a first-order liquid-liquid phase transition. X-ray absorption measurements revealed that the change in density at the transition is about 40 % of the density of the high-pressure liquid.

Journal Articles

Kinetics of the graphite-diamond transformation in aqueous fluid determined by in-situ X-ray diffractions at high pressures and temperatures

Okada, Taku; Utsumi, Wataru; Kaneko, Hiroshi*; Turkevich, V.*; Hamaya, Nozomu; Shimomura, Osamu*

Physics and Chemistry of Minerals, 31(4), p.261 - 268, 2004/05

 Times Cited Count:11 Percentile:42.99(Materials Science, Multidisciplinary)

The graphite-diamond transformation was investigated by in situ time-resolved X-ray diffraction experiments using aqueous fluid containing dissolved MgO as the diamond forming catalyst under conditions of 6.6-8.9 GPa and 1400-1835 $$^{circ}$$C. The transformed volume fractions of diamond as a function of time under various pressure-temperature conditions were obtained and analyzed using the JMAK rate equation. Variations in the nucleation and growth processes during diamond formation as a function of pressure and temperature were clarified.

Journal Articles

${it In situ}$ X-ray diffraction of graphite-diamond transformation using various catalysts under high pressures and high temperatures

Utsumi, Wataru; Okada, Taku; Taniguchi, Takashi*; Funakoshi, Kenichi*; Kikegawa, Takumi*; Hamaya, Nozomu; Shimomura, Osamu

Journal of Physics; Condensed Matter, 16(14), p.S1017 - S1026, 2004/04

 Times Cited Count:13 Percentile:55.4(Physics, Condensed Matter)

The graphite-diamond transformation was investigated using in-situ time-resolved X-ray diffraction experiments with a MgO dissolved aqueous fluid as the diamond forming catalyst under conditions of 6.6-8.8 GPa and 1400-1835$$^{circ}$$C. Experiments were conducted using a 180-ton DIA-type cubic-anvil apparatus installed on the beamline BL14B1 at SPring-8, a third-generation synchrotron radiation facility in Japan. By analyzing the kinetic data using the JMAK rate equation, it was clarified that altering the pressure-temperature conditions drastically changes the nucleation and growth process of diamond.

Journal Articles

Congruent melting of gallium nitride at 6 GPa and its application to single-crystal growth

Utsumi, Wataru; Saito, Hiroyuki; Kaneko, Hiroshi*; Watanuki, Tetsu; Aoki, Katsutoshi; Shimomura, Osamu

Nature Materials, 2(11), p.735 - 738, 2003/11

 Times Cited Count:127 Percentile:96.2(Chemistry, Physical)

Synthesis of large single crystal GaN (gallium nitride) is a matter of great importance in optoelectronic devices for blue light-emitting diodes and lasers. Although high quality bulk single crystals of GaN suitable for substrates are desired, the standard method of cooling its stoichiometric melt has been unsuccessful for GaN because it decomposes into Ga and N$$_{2}$$ at high temperatures before its melting point. Here we report that applying high pressure completely prevents the decomposition and allows the stoichiometric melt of GaN. At pressures above 6.0 GPa, congruent melting of GaN occurred around 2220$$^{circ}$$C, and decreasing the temperature allowed the GaN melt to reversibly back-transform into the original crystal structure, which was confirmed by in situ X-ray diffraction. Single crystals of GaN were formed by cooling the melt slowly under high pressures and were recovered at ambient conditions.

Journal Articles

${it In situ}$ X-ray observations of the diamond formation process in the C-H$$_{2}$$O-MgO system

Okada, Taku; Utsumi, Wataru; Shimomura, Osamu

Journal of Physics; Condensed Matter, 14(44), p.11331 - 11335, 2002/11

 Times Cited Count:3 Percentile:21.27(Physics, Condensed Matter)

In order to clarify the mechanism of diamond formation in the Earth's mantle, we studied the diamond formation in the H$$_{2}$$O-fluid by in situ X-ray observation with the simple C-H$$_{2}$$O-MgO system. The results suggest that the solubility of MgO component increases greatly as a function of pressure. However, the generation of fluid is not a sufficient condition for diamond formation, because the carbon quantity in fluid is not increased drastically until just before the diamond formation temperature. This is the first report of the kinetics study in fluid using synchrotron radiation.

Journal Articles

In situ X-ray observations of the decomposition of brucite and the graphite-diamond conversion in aqueous fluid at high pressure and temperature

Okada, Taku; Utsumi, Wataru; Kaneko, Hiroshi*; Yamakata, Masaaki*; Shimomura, Osamu

Physics and Chemistry of Minerals, 29(7), p.439 - 445, 2002/08

 Times Cited Count:14 Percentile:49.96(Materials Science, Multidisciplinary)

An experimental technique to make real-time observations at high pressure and temperature of the diamond forming process in candidate material of mantle fluids as a catalyst has been established for the first time. In situ X-ray diffraction experiments using synchrotron radiation have been performed upon a mixture of brucite (Mg(OH)$$_{2}$$) and graphite as starting material. Brucite decomposes into periclase (MgO) and H$$_{2}$$O at 3.6 GPa and 1050$$^{circ}$$C while no periclase is formed after the decomposition of brucite at 6.2 GPa and 1150$$^{circ}$$C, indicating that the solubility of the MgO component in H$$_{2}$$O greatly increases with increasing pressure. The conversion of graphite to diamond in aqueous fluid has been observed at 7.7 GPa and 1835$$^{circ}$$C. Time-dependent X-ray diffraction profiles for this transformation have been successfully obtained.

Journal Articles

High-pressure X-ray diffraction of icosahedral Zr-Al-Ni-Cu-Ag quasicrystals

Jiang, J.*; Saksl, K.*; Rasmussen, H.*; Watanuki, Tetsu; Ishimatsu, Naoki; Shimomura, Osamu

Applied Physics Letters, 79(8), p.1112 - 1114, 2001/08

 Times Cited Count:15 Percentile:56.12(Physics, Applied)

no abstracts in English

Journal Articles

${it In situ}$ X-ray observation of cubic BC$$_{2}$$N formation under high pressures and temperatures

Utsumi, Wataru; Okada, Taku; Funakoshi, Kenichi*; Shimomura, Osamu

Proceeding of the 8th NIRIM International Symposium on Advanced Materials (ISAM 2001), p.39 - 40, 2001/03

no abstracts in English

Journal Articles

Construction of laser-heated diamond anvil cell system for ${it in situ}$ X-ray diffraction study at SPring-8

Watanuki, Tetsu; Shimomura, Osamu; Yagi, Takehiko*; Kondo, Tadashi*; Isshiki, Maiko*

Review of Scientific Instruments, 72(2), p.1289 - 1292, 2001/02

 Times Cited Count:73 Percentile:93.67(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Laser heated diamond anvil apparatus at the Photon Factory and SPring-8; Problems and improvements

Yagi, Takehiko*; Kondo, Tadashi*; Watanuki, Tetsu; Shimomura, Osamu; Kikegawa, Takumi*

Review of Scientific Instruments, 72(2), p.1293 - 1297, 2001/02

 Times Cited Count:27 Percentile:78.69(Instruments & Instrumentation)

no abstracts in English

Journal Articles

X-ray diffraction study on structural change in liquid selenium under high pressure

Katayama, Yoshinori; Mizutani, Takeshi; Utsumi, Wataru; Shimomura, Osamu; Tsuji, Kazuhiko*

Physica Status Solidi (B), 223(2), p.401 - 404, 2001/01

 Times Cited Count:18 Percentile:66.36(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Second-order phase transition of FeS under high pressure and temperature

Kusaba, Keiji*; Utsumi, Wataru; Yamakata, Masaaki*; Shimomura, Osamu; Shono, Yasuhiko*

Journal of Physics and Chemistry of Solids, 61(9), p.1483 - 1487, 2000/09

 Times Cited Count:6 Percentile:37.91(Chemistry, Multidisciplinary)

no abstracts in English

Journal Articles

In situ X-ray diffraction experiments under high pressures and high temperatures at BL14B1 beamline

Utsumi, Wataru; Katayama, Yoshinori; Mizutani, Takeshi; Shimomura, Osamu; Yamakata, Masaaki*; Azuma, Masaki*; Saito, Takashi*

Nihon Kessho Gakkai-Shi, 42(1), p.59 - 67, 2000/02

no abstracts in English

Journal Articles

A First-order liquid-liquid phase transition in phosphorus

Katayama, Yoshinori; Mizutani, Takeshi*; Utsumi, Wataru; Shimomura, Osamu; Yamakata, Masaaki*; Funakoshi, Kenichi*

Nature, 403(6766), p.170 - 173, 2000/01

 Times Cited Count:691 Percentile:98.04(Multidisciplinary Sciences)

no abstracts in English

Journal Articles

A New cubic anvil press with radial slit system at the SPring-8

Yamakata, Masaaki*; Mizutani, Takeshi; Utsumi, Wataru; Katayama, Yoshinori; Shimomura, Osamu

Science and Technology of High Pressure (Proceedings of AIRAPT-17), p.1109 - 1112, 2000/00

no abstracts in English

Journal Articles

Anomaly in the melting curve of black phosphorus associated with a liquid-liquid transition

Mizutani, Takeshi; Katayama, Yoshinori; Utsumi, Wataru; Funakoshi, Kenichi*; Yamakata, Masaaki*; Shimomura, Osamu

Science and Technology of High Pressure (Proceedings of AIRAPT-17), p.525 - 528, 2000/00

no abstracts in English

Journal Articles

Optical ionization of DX center in AlGaAs:Se by inner-shell excitation

Yoshino, Yoko; Takarabe, Kenichi*; Ishii, Masashi*; Katayama, Yoshinori; Shimomura, Osamu

Physica B; Condensed Matter, 273-274, p.781 - 783, 1999/12

 Times Cited Count:1 Percentile:8.99(Physics, Condensed Matter)

DX state is strongly localized. This nature could be investigated by observing relaxation process of localized electrons to emptied inner shells. We have found two different optical ionization process of the DX center in Al$$_{x}$$Ga$$_{1-x}$$As:Se (x=0.33,$$N_{rm Se}=5times10^{17}$$(cm$$^{-3}$$)) by using synchrotron radiation. They are tentatively assigned to be a direct lift of an inner-shell electron to the conduction band (CB) followed by a capture of an electron at the DX center to the emptied inner shell $$({rm DX}^{-}+hnu ({rm L,} $$K-edge$$)rightarrow {rm DX}^{0}+e_{rm CB})$$ and the Auger ionization of one electron of the DX center to the CB followed by a capture of another electron to the emptied inner shell $$({rm DX}^{-}+hnu ({rm L,} $$K-edge$$)rightarrow {rm DX}^{+}+e_{rm CB}+e_{rm vacuum})$$.

Journal Articles

EXAFS study on liquid selenium and liquid tellurium under high pressure

Katayama, Yoshinori; Shimomura, Osamu; Tsuji, Kazuhiko*

Journal of Non-Crystalline Solids, 250-252(Part2), p.537 - 541, 1999/08

no abstracts in English

32 (Records 1-20 displayed on this page)