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Journal Articles

Effect of strong gravitational field on oriented crystalline perovskite-type manganese oxide La$$_{1-x}$$Sr$$_x$$MnO$$_3$$

Tokuda, Makoto*; Mashimo, Tsutomu*; Khandaker, J. I.*; Ogata, Yudai; Mine, Yoji*; Hayami, Shinya*; Yoshiasa, Akira*

Journal of Materials Science, 51(17), p.7899 - 7906, 2016/09

 Times Cited Count:2 Percentile:10.2(Materials Science, Multidisciplinary)

Journal Articles

Precise structural analyses of advanced materials under high-pressure and high-temperature

Yoshiasa, Akira*; Murai, Keiichiro*; Arima, Hiroshi*; Katayama, Yoshinori

International Journal of Modern Physics B, 25(31), p.4159 - 4162, 2011/12

 Times Cited Count:0 Percentile:0.01(Physics, Applied)

Precise structure analyses of advanced materials under pressure were performed using each advantage of X-ray absorption fine structure (XAFS) and diffraction methods. Measurements were performed in-situ under pressure and temperature using a large-volume multi-anvil pressure apparatus and synchrotron radiation. XAFS spectra are useful for phase study under high temperature and high pressure. The XAFS Debye-Waller factor provides anharmonic effective pair potential with a pressure-dependent and temperature-independent shape. The phonon energies and anharmonicity are affected largely by the change in local structure and bonding character.

Journal Articles

High pressure and high temperature EXAFS and diffraction study of AgI (MS35)

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.

Journal Articles

${it In-situ}$ XAFS and XRD studies of pressure-induced local structural change in liquid AgI

Arima, 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:15 Percentile:57.81(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Pressure-induced sharp coordination change in liquid germanate

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:48 Percentile:84.6(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$$_{6}$$ octahedron in the high-density liquid is more compressible than that in solids.

Journal Articles

Anharmonicity of platinum under HP and HT

Okube, Maki*; Yoshiasa, Akira*; Otaka, Osamu*; Katayama, Yoshinori

High Pressure Research, 23(3), p.247 - 251, 2003/09

 Times Cited Count:4 Percentile:35.06(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$$_{3}$$-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, $$sigma$$2 and $$sigma$$3, become smaller with increase of pressure. The anharmonic effective pair potential $$V(u) = (1/2!)au^{2} + (1/3!)bu^{3}$$ was evaluated and the potential coefficient a at 0.1MPa and 6GPa are 4.8 and 5.0eV/$AA $^{2}$$, respectively. The anharmonic potential parameter $$b$$ decreases with increasing pressure.

Journal Articles

Anharmonic effective pair potentials of gold under high pressure and high temperature

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:3 Percentile:21.27(Physics, Condensed Matter)

no abstracts in English

Journal Articles

XAFS study of GeO$$_{2}$$ glass under pressure

Otaka, 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:17 Percentile:63.92(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Phase relations of AgI under high pressure and high temperature

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:65.5(Physics, Condensed Matter)

Using a multi-anvil high-pressure device and synchrotron radiation, X-ray ${it in situ}$$$ observations of AgI high pressure and high temperature up to 6.0 GPa and 1000 K have been  performed to investigate the phase relations between $$$alpha$-AgI, rocksalt-type, disordered rocksalt-type, and liquid phases. The three phases of $$alpha$-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.

Journal Articles

Anharmonicity of gold under high-pressure and high-temperature

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:51.99(Physics, Condensed Matter)

In order to examine the pressure effect on the anharmonicity of Au, EXAFS spectra near Au $$L_{3}$$-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, $$sigma2$$ and $$sigma3$$, become smaller with increase of pressure, which indicates that the potential width become narrower with pressure. The anharmonic effective pair potentials of Au, $$V(u)=au^{2}/2!+bu^{3}/3!$$, at 0.1MPa, 6 and 14GPa have been calculated. The pressure dependence of the coefficient of thermal expansion has also been evaluated.

Journal Articles

Pressure dependence of effective pair potentials in AgBr determined by extended X-ray absorption fine structure

Yoshiasa, Akira*; Murai, Keiichiro*; Nagai, Takaya*; Katayama, Yoshinori

Japanese Journal of Applied Physics, Part 1, 40(4A), p.2395 - 2398, 2001/04

 Times Cited Count:5 Percentile:27.09(Physics, Applied)

The pressure dependence of extended X-ray absorption fine structure (EXAFS) Debye-Waller factors in AgBr has been investigated using the cumulant expansion method. The Br K-edge EXAFS spectra were measured in the transmission mode under high pressure ($$leq$$9.1GPa) at room temperature using a cubic anvil type apparatus (MAX90) and synchrotron radiation from the Photon Factory, Tsukuba. The effective pair potentials $$V(u)=au^{2}/2+bu^{3}/3!$$, were evaluated and the potential coefficient $$a$$ at 2.1, 4.2 and 6.1GPa are 1.59(4), 1.75(4) and 1.91(4) eV/$$AA^{-2}$$, respectively. The energies of the third-order anharmonic potential coefficient $$b$$ maintain nearly constant values with pressure though the third-order cumulant $$sigma_{3}$$ decreases with increasing in pressure.

Journal Articles

Structual changes of quartz-type crystalline and vitreous GeO$$_{2}$$ under pressure

Otaka, 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

Journal Articles

Anharmonic effective pair potentials of $$gamma-$$ and $$alpha-$$CuBr at high pressure

Yoshiasa, 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:45.23(Physics, Applied)

The anharmonic effective pair potentials $$V(u)=au^{2}/2+bu^{3}/3!+cu^{4}/4!$$ for Br-Cu bond in $$gamma-$$ and $$alpha-$$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 $$a$$ for $$gamma$$-phase at 0.1MPa increases by about 20% at the pressure of 4.8GPa. The stastical distribution of Cu in $$alpha$$-CuBr and superionic conduction mechanism have been discussed based on the effective pair potential and distribution of Br-Cu distances.

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