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Ga
N and InN crystals under high pressuresSaito, Hiroyuki; Utsumi, Wataru; Kaneko, Hiroshi*; Aoki, Katsutoshi
Proceedings of Joint 20th AIRAPT - 43rd EHPRG International Conference on High Pressure Science and Technology (CD-ROM), 4 Pages, 2005/06
We have performed synthesis studies of various III-V nitrides crystals, key materials for optoelectronic and high-power/frequency devices, using a cubic-anvil-type large volume high-pressure apparatus combined with in situ X-ray diffraction. Polly-crystallines of AlGaN alloys covering a composition range of 0 
x 1 were synthesized by a solid-phase reaction under high pressure. In situ X-ray diffraction profiles were measured to observe the alloying process, which started at around 800
C under 6.0 GPa. Single crystal of Al
Ga
N was also successfully obtained by slow cooling of its melt from 2400C at 6.5 GPa. For InN, its phase diagram was determined under high P-T conditions up to 20GPa and 2000C based on the in situ observations, which demonstrates that 19GPa and 1900C are needed for its congruent melting.
Omura, Ayako; Machida, Akihiko; Watanuki, Tetsu; Aoki, Katsutoshi; Nakano, Satoshi*; Takemura, Kenichi*
Proceedings of Joint 20th AIRAPT - 43rd EHPRG International Conference on High Pressure Science and Technology (CD-ROM), 3 Pages, 2005/06
Yttrium hydride shows a structural change from a cubic dihydride to a hexagonal trihydride by hydrogenation. This is accompanied by the metal-insulator transition. The theoretical calculation of yttrium hydride speculates that the hybridization between 4d-Y and 1s-H leads to the opening of a large energy gap. They also predict that a transition from insulator to metal occurs when the volume is reduced to about 85% of the equilibrium volume in yttrium trihydride. Recently, we performed an infrared spectroscopy of yttrium trihydride to investigate pressure-induced metallization under high pressure. The insulator-metal transition occurred with an abrupt disappearance of the optical gap of 
1 eV at 23 GPa. There is a possibility of the electronic transition because no structural changes occur above 20 GPa. The electronic transition can be attributed to the delocalization of the 1s electrons bound to the H+ core ions or the rearrangement of hydrogen atoms.
Utsumi, Wataru; Saito, Hiroyuki; Kaneko, Hiroshi*; Kiriyama, Koji*; Aoki, Katsutoshi
Proceedings of Joint 20th AIRAPT - 43rd EHPRG International Conference on High Pressure Science and Technology (CD-ROM), 5 Pages, 2005/06
We were successful in synthesizing single crystals of GaN (Gallium Nitride) by slow cooling of its congruent melt under high pressure. It was confiremed by in situ X-ray diffraction that applying high pressures above 6.0 GPa completely prevented the decomposition and allowed the congruent melt of GaN at 2220C. Using a cubic-anvil-type large volume high-pressure apparatus and GaN powder as a starting material, single crystal growth was performed by decreasing temperature from 2400C at 6.5 GPa. The X-ray rocking curve of the recovered sample showed very narrow line-width smaller than 30 arcsec, suggesting its low dislocation density.
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
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
Eto, Tetsujiro*; Endo, Shoichi*; Imai, Motoharu*; Katayama, Yoshinori; Kikegawa, Takumi*
Science and Technology of High Pressure (Proceedings of AIRAPT-17), p.487 - 490, 2000/00
The pressure effect on the lattice constant of NiO with the rhombohedral distorted B1 structure was studied up to 141 GPa by 
angle-dispersive x-ray diffraction using synchrotron radiation and an imaging plate, with reference to a recent theoretical calculation within the density-functional formalism with the local-spin density approcximation. The lattice constant 
and 
, expressed in the hexagonal lattice, decrease monotonously with increasing pressure. The axial rage 
decreases monotonously with increasing pressure, indicating the enhancement of the rhombohedral distortion. The signiifcant change of above 60 GPa suggested by the calculation was not observed.
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
Mori, Yuki*; Kato, Sayuri*; Mori, Hiroko*; Katayama, Yoshinori; Tsuji, Kazuhiko*
Review of High Pressure Science and Technology, 7, p.353 - 355, 1998/03
The temperature dependence of phase transitions in GaSb, AlSb, GaAs, GaP, InAs, ZnSe, and CdTe are studied by X-ray diffraction measurements under pressure upto 30 GPa at temperatures of 90-300K. The phase transitions depend on paths in a pressure-temperature phase diagram. The structure of the recovered phase after decompression depends on the ionicity in bonding: amorphous for small ionicity, the stable zincblende structure for large ionicity, and microcrystalline or moderate ionicity. These results are discussed by using a configuration-coordinate model.
Toda, Naohiro*; Katayama, Yoshinori; Tsuji, Kazuhiko*
Review of High Pressure Science and Technology, 7, p.647 - 649, 1998/03
The electrical conductivity 
has been measured at pressures 
to 8 GPa and temperatures 
of 77-300K in evaporated amorphous Ge (a-Ge), a-Ge-Cu alloys and a-Ge-Al alloys. The dependence of is well described by a power lw at low temperatures below 150 K, which is expemcted from a multi-phonon tunneling transition process model with weak electron-lattice coupling, rather than the Mott's variable range hopping conduction model. The exponent 
in the power law changes with increasing pressure. For both a-GeCu and a-GeAl alloys, d(ln )/d show positive values in the low pressure region and negative values in the high pressure region. Results are discussed from several hopping conduction models.
Morimoto, Yoshiki*; Kato, Sayuri*; Toda, Naohiro*; Katayama, Yoshinori; Tsuji, Kazuhiko*; Yaoita, Kenichi*; Shimomura, Osamu
Review of High Pressure Science and Technology, 7, p.245 - 247, 1998/03
X-ray diffraction for liquid Rb and liquid Na has been measured under pressure up to 6 GPa using synchrotron radiation. Volume dependences of static structure factor 
and pair distribution function 
were obtained to the volume range 
of 0.52 for liquid Rb and 
of 0.73 for liquid Na to investigate the effect of the electronic change on the structure of liquid metals. With increasing pressure, the peaks of of both liquid Rb and liquid Na shift towards higher 
, and the heights of the first peak increase. Theses volume dependences of the structural data are compared with those for other metals under pressure and expanded fluids.
Katayama, Yoshinori; *; *; *; *; *; Tsuji, Kazuhiko*
Review of High Pressure Science and Technology, 7, p.251 - 253, 1998/00
no abstracts in English
Utsumi, Wataru; Funakoshi, Kenichi*; Urakawa, Satoru*; Yamakata, Masaaki*; Tsuji, Kazuhiko*; Konishi, Hiroyuki; Shimomura, Osamu
Review of High Pressure Science and Technology, 7, p.1484 - 1486, 1998/00
no abstracts in English
formed under Quasi-hydrostatic compression of cristobaliteYamakata, Masaaki*; Yagi, Takehiko*
Review of High Pressure Science and Technology, 7, p.107 - 109, 1998/00
no abstracts in English
