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Journal Articles

Formation of NaCl-type monodeuteride LaD by the disproportionation reaction of LaD$$_{2}$$

Machida, Akihiko; Honda, Mitsunori*; Hattori, Takanori; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Aoki, Katsutoshi; Komatsu, Kazuki*; Arima, Hiroshi*; Oshita, Hidetoshi*; et al.

Physical Review Letters, 108(20), p.205501_1 - 205501_5, 2012/05

 Times Cited Count:10 Percentile:58.4(Physics, Multidisciplinary)

Hydrogen atoms absorbed in a metal occupy the interstitial sites of the metal lattice. In an fcc metal lattice, each metal atom has two tetrahedral (T) and one octahedral (O) sites that can accommodate hydrogen. Rare-earth metal La forms T-site occupied LaH$$_2$$ and fully occupied LaH$$_3$$. O-site occupied or NaCl-type monohydride has yet to be reported for rare-earth metals. Previous X-ray diffraction measurements revealed the pressure-induced decomposition of an fcc-LaH$$_{2.3}$$ into H-rich and H-poor phases around 11 GPa. The present neutron diffraction measurements on LaD$$_{2}$$ confirm the formation of NaCl-type LaD as a counterpart of the D-rich LaD$$_{2+delta}$$ by disproportionation. First-principle calculations demonstrate that the NaCl-type LaH is stabilized at high pressures. Finding the NaCl-type LaH will pave the way for investigations on the site-dependent nature of hydrogen-metal interactions.

Journal Articles

Electronic structure of lithium amide

Kamakura, Nozomu; Takeda, Yukiharu; Saito, Yuji; Yamagami, Hiroshi; Tsubota, Masami*; Paik, B.*; Ichikawa, Takayuki*; Kojima, Yoshitsugu*; Muro, Takayuki*; Kato, Yukako*; et al.

Physical Review B, 83(3), p.033103_1 - 033103_4, 2011/01

 Times Cited Count:5 Percentile:27.56(Materials Science, Multidisciplinary)

The electronic structure of lithium amide, which is lightweight complex hydride expected as a high-capacity hydrogen storage material, is investigated by N 1$$s$$ soft X-ray emission spectroscopy (XES) and absorption spectroscopy (XAS). The overall feature of the electronic structure of lithium amide by the XES and XAS is consistent with the band calculation, while the strongly hybridized state with H 1$$s$$ is located at higher binding energy than the band calculation.

Journal Articles

Effect of hydrogenation on the electronic state of metallic La hydrides probed by X-ray absorption sectroscopy at the La $$L$$-edges

Ishimatsu, Naoki*; Sasada, Ryohei*; Maruyama, Hiroshi*; Ichikawa, Takayuki*; Miyaoka, Hiroki*; Kimura, Toru*; Tsubota, Masami*; Kojima, Yoshitsugu*; Tsumuraya, Takao*; Oguchi, Tamio*; et al.

Journal of Physics; Conference Series, 190, p.012070_1 - 012070_4, 2009/11

 Times Cited Count:4 Percentile:77.5

We have investigated the effect of hydrogenation on La $$5d$$ and $$6p$$ electronic states in metallic LaH$$_x$$ by X-ray absorption near edge structure at the La $$L$$-edges. As the hydrogen content $$x$$ increases from 0 to 2.6, white-line intensity at the La $$L_{2,3}$$-edges shows a remarkable increase in the range of $$x$$ $$>$$ 2.0. This is interpreted as the increase in La $$5d$$ hole induced by interstitial H atoms on the octahedral sites. On the other hand, the shoulder structure at the La $$L_1$$-edge disappears in the process of $$x$$ = 0.0 $$rightarrow$$ 2.0, indicating that the $$p$$-$$ d$$ hybridization is weakened by H atoms on the tetrahedral sites. This study demonstrates that H atoms on the two interstitial H sites provide different contribution to the modification of the electronic states.

Journal Articles

Momentum-resolved charge excitations in high-$$T$$$$_{rm c}$$ cuprates studied by resonant inelastic X-ray scattering

Ishii, Kenji; Hoesch, M.*; Inami, Toshiya; Kuzushita, Kaori*; Owada, Kenji; Tsubota, Masami; Murakami, Yoichi; Mizuki, Junichiro; Endo, Yasuo; Tsutsui, Kenji*; et al.

Journal of Physics and Chemistry of Solids, 69(12), p.3118 - 3124, 2008/12

 Times Cited Count:3 Percentile:19.29(Chemistry, Multidisciplinary)

Journal Articles

Direct observation of field-induced variant transformation in Fe$$_3$$Pt using pulsed magnetic field X-ray diffraction

Ouyang, Z. W.*; Matsuda, Yasuhiro*; Nojiri, Hiroyuki*; Inami, Toshiya; Owada, Kenji; Tsubota, Masami*; Sakon, Takuo*; Fukuda, Takashi*; Kakeshita, Tomoyuki*

Journal of Applied Physics, 102(11), p.113917_1 - 113917_6, 2007/12

 Times Cited Count:1 Percentile:5.72(Physics, Applied)

Journal Articles

Resonant X-ray scattering of PrRu$$_4$$P$$_{12}$$

Ishii, Kenji; Tsutsui, Satoshi*; Hao, L.*; Hasegawa, Tomoo*; Iwasa, Kazuaki*; Tsubota, Masami; Inami, Toshiya; Murakami, Yoichi*; Saha, S. R.*; Sugawara, Hitoshi*; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.e178 - e180, 2007/03

PrRu$$_4$$P$$_{12}$$ shows a metal-insulator (MI) transition at $$T_{mathrm MI} simeq$$ 62 K accompanied by a structural phase transition. Because LaRu$$_4$$P$$_{12}$$ without $$4f$$ electrons does not shows the MI transition, $$4f$$ electrons in the Pr atom plays an important role in the transition. In order to elucidate a modulation of electronic states of Pr, we have carried out a resonant X-ray scattering study of PrRu$$_4$$P$$_{12}$$ at Pr $$L_2$$- and $$L_3$$-edges. Below $$T_{mathrm MI}$$, resonant signal at the absorption main-edge was successfully observed at the superlattice reflections of the modulation vector $$vec{q}=(1,0,0)$$ in addition to the energy-independent component from the lattice distortion. Because the reflection contains the difference of anomalous scattering factors between two Pr atoms in the unit cell, two different electronic states are actually ordered below $$T_{MI}$$. Furthermore we found that the polarization of X-ray is mostly unrotated even at the resonance, which indicates that the resonant scattering in PrRu$$_4$$P$$_{12}$$ is almost isotropic.

Journal Articles

Doping Momentum dependence of charge dynamics in Nd$$_{2-x}$$Ce$$_{x}$$CuO$$_4$$ (x=0, 0.075, and 0.15) studied by Resonant inelastic X-ray scattering

Ishii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Maekawa, Sadamichi*; Hoesch, M.; Kuzushita, Kaori; Inami, Toshiya; Tsubota, Masami; Yamada, Kazuyoshi*; et al.

AIP Conference Proceedings 850, p.403 - 404, 2006/09

We report a resonant inelastic X-ray scattering (RIXS) study of charge excitations in the electron-doped high-$$T_{c}$$ superconductor Nd$$_{1.85}$$Ce$$_{0.15}$$CuO$$_4$$. The intraband and interband excitations across the Fermi energy are separated for the first time by tuning the experimental conditions properly to measure charge excitations at low energy. A dispersion relation with $${mathbf q}$$-dependent width emerges clearly in the intraband excitation, while the intensity of the interband excitation is concentrated around 2 eV near the zone center. The experimental results are consistent with theoretical calculation of the RIXS spectra based on the Hubbard model.

Journal Articles

Induced orbital polarization of Ga ligand atoms in U$$T$$Ga$$_5$$ ($$T$$=Ni, Pd, and Pt)

Kuzushita, Kaori*; Ishii, Kenji; Wilkins, S. B.*; Janousova, B.*; Inami, Toshiya; Owada, Kenji; Tsubota, Masami; Murakami, Yoichi; Kaneko, Koji; Metoki, Naoto; et al.

Physical Review B, 73(10), p.104431_1 - 104431_5, 2006/03

 Times Cited Count:7 Percentile:36.62(Materials Science, Multidisciplinary)

We report a resonant X-ray scattering study of antiferromagnetic uranium compounds U$$T$$Ga$$_5$$ ($$T$$=Ni, Pd, and Pt) at the Ga $$K$$-edge. A large resonant signal is observed below the N$'e$el temperatures. The azimuth dependence in both $$pi$$-$$pi'$$ and $$pi$$-$$sigma'$$ polarization channels establishes that the resonant signal has the symmetry of the magnetic dipole. This resonance with the band electrons is interpreted within a semi-localized model as an orbital polarization of the Ga $$4p$$ states induced through strong hybridization with U $$5f$$ valence level. These results demonstrate that resonant magnetic X-ray scattering at the anions, taken in combination with symmetry arguments, can be used to determine the configuration of the U $$5f$$ moments and provide information about the hybridization.

Journal Articles

Quest for the high-filed phase of CdCr$$_2$$O$$_4$$ using an X-ray diffraction technique

Inami, Toshiya; Owada, Kenji; Tsubota, Masami; Murata, Yuto*; Matsuda, Yasuhiro*; Nojiri, Hiroyuki*; Ueda, Hiroaki*; Murakami, Yoichi*

Journal of Physics; Conference Series, 51, p.502 - 505, 2006/00

 Times Cited Count:15 Percentile:97.63

no abstracts in English

Journal Articles

Magnetic-field-induced transition in the lattice modulation of colossal magnetoelectric GdMnO$$_3$$ and TbMnO$$_3$$ compounds

Arima, Takahisa*; Goto, Tsuyoshi*; Yamazaki, Yuichi*; Miyasaka, Shigeki*; Ishii, Kenji; Tsubota, Masami; Inami, Toshiya; Murakami, Yoichi*; Tokura, Yoshinori*

Physical Review B, 72(10), p.100102_1 - 100102_4, 2005/09

 Times Cited Count:118 Percentile:95.3(Materials Science, Multidisciplinary)

Single-crystal synchrotron X-ray diffraction measurements in strong magnetic fields have been performed for magnetoelectric compounds GdMnO$$_3$$ and TbMnO$$_3$$. It has been found that the ${bf P}$//a ferroelectric phase induced by the application of a magnetic field at low temperatures is characterized by commensurate lattice modulation along the orthorhombic ${it b}$ axis with q=1/2 and q=1/4. The lattice modulation is ascribed to antiferromagnetic spin alignment with a modulation vector of (0 1/4 1). The change of the spin structure is directly correlated with the magnetic-field-induced electric phase transition, because any commensurate spin modulation with (0 1/4 1) should break glide planes normal to the ${it a}$ axis of the distorted perovskite with the space group.

Journal Articles

Momentum dependence of charge excitations in the electron-doped superconductor Nd$$_{1.85}$$Ce$$_{0.15}$$CuO$$_4$$; A Resonant inelastic X-ray scattering study

Ishii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Maekawa, Sadamichi*; Hoesch, M.; Kuzushita, Kaori; Tsubota, Masami; Inami, Toshiya; Mizuki, Junichiro; et al.

Physical Review Letters, 94(20), p.207003_1 - 207003_4, 2005/05

 Times Cited Count:69 Percentile:89.31(Physics, Multidisciplinary)

We report a resonant inelastic X-ray scattering (RIXS) study of charge excitations in the electron-doped high-$$T_{c}$$ superconductor Nd$$_{1.85}$$Ce$$_{0.15}$$CuO$$_4$$. The intraband and interband excitations across the Fermi energy are separated for the first time by tuning the experimental conditions properly to measure charge excitations at low energy. A dispersion relation with $${mathbf q}$$-dependent width emerges clearly in the intraband excitation, while the intensity of the interband excitation is concentrated around 2 eV near the zone center. The experimental results are consistent with theoretical calculation of the RIXS spectra based on the Hubbard model.

Journal Articles

Search for orbital excitation in YTiO$$_3$$ by neutron scattering

Shamoto, Shinichi; Tsubota, Masami*; Iga, Fumitoshi*; F${aa}$k, B.*; Kajitani, Tsuyoshi*

Journal of Neutron Research, 13(1-3), p.175 - 178, 2005/03

YTiO$$_3$$ with T$$_c$$~30 K has been studied by the MARI spectrometer with E$$_i$$=130 meV and 500 meV at T=5 K, 40K, and 200 K. We have not found any clear orbital excitation in a wide Q-E range (0.5$$<$$Q$$<$$25$AA $^{-1}$$, 6$$<$$E$$<$$350 meV). The intensity of orbital excitation would be significantly weak in comparison with the phonon.

Oral presentation

Resonant inelastic X-ray scattering in strongly correlated electron systems

Ishii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Inami, Toshiya; Owada, Kenji; Kuzushita, Kaori*; Hoesch, M.; Tsubota, Masami; Mizuki, Junichiro; et al.

no journal, , 

Resonant inelastic X-ray scattering studies on high-$$T_c$$ superconductors Nd$$_{2-x}$$Ce$$_x$$CuO$$_4$$ and YBa$$_2$$Cu$$_3$$O$$_{6+x}$$ are presented. In Nd$$_2$$CuO$$_4$$ and YBa$$_2$$Cu$$_3$$O$$_6$$, which are Mott insulators, an excitation across the Mott gap is observed around 2 eV. The spectral weight of this excitation shifts to higher energy with increasing the momentum transfer and the dispersion of the excitation is larger along the $$[pi,pi]$$ direction than the $$[pi,0]$$ direction. An intraband excitation in the upper Hubbard band emerges in the spectra of electron-doped Nd$$_{1.85}$$Ce$$_{0.15}$$CuO$$_4$$. As a function of the momentum transfer in the CuO$$_2$$ plane, the excitation shifts to higher energy up to 2-2.5 eV at the zone boundary, accompanied by an increase of the spectral width. On the other hand, excitations from two inequivalent Cu sites in hole-doped YBa$$_2$$Cu$$_3$$O$$_7$$ are distinguished by the momentum dependence and the Mott gap of the CuO chain site is found to be much smaller than that of the CuO$$_2$$ plane site.

Oral presentation

Resonant X-ray scattering of PrRu$$_4$$P$$_{12}$$

Ishii, Kenji; Tsubota, Masami; Inami, Toshiya; Tsutsui, Satoshi*; Hao, L.*; Hasegawa, Tomoo*; Iwasa, Kazuaki*; Murakami, Yoichi; Sugawara, Hitoshi*; Saha, S. R.*; et al.

no journal, , 

PrRu$$_4$$P$$_{12}$$ shows a metal-insulator (MI) transition at $$T_{mathrm MI} simeq$$ 62 K accompanied by a structural phase transition. Because LaRu$$_4$$P$$_{12}$$ without $$4f$$ electrons does not shows the MI transition, $$4f$$ electrons in the Pr atom plays an important role in the transition. In order to elucidate a modulation of electronic states of Pr, we have carried out a resonant X-ray scattering study of PrRu$$_4$$P$$_{12}$$ at Pr $$L_2$$- and $$L_3$$-edges. Below $$T_{mathrm MI}$$, resonant signal at the absorption main-edge was successfully observed at the superlattice reflections of the modulation vector $$vec{q}=(1,0,0)$$ in addition to the energy-independent component from the lattice distortion. Because the reflection contains the difference of anomalous scattering factors between two Pr atoms in the unit cell, two different electronic states are actually ordered below $$T_{MI}$$. Furthermore we found that the polarization of X-ray is mostly unrotated even at the resonance, which indicates that the resonant scattering in PrRu$$_4$$P$$_{12}$$ is almost isotropic.

Oral presentation

Resonant X-ray scattering near the L-edge for chromium

Tsubota, Masami; Inami, Toshiya; Smadici, S.*; Abbamonte, P.*; Murakami, Yoichi*; Mizuki, Junichiro

no journal, , 

no abstracts in English

Oral presentation

An X-ray diffraction experiment of the magnetization plateau phase of CdCr$$_2$$O$$_4$$

Inami, Toshiya; Owada, Kenji; Tsubota, Masami; Matsuda, Yasuhiro*; Nojiri, Hiroyuki*; Ueda, Hiroaki*

no journal, , 

no abstracts in English

Oral presentation

Electronic states of lithium amide

Kamakura, Nozomu; Takeda, Yukiharu; Saito, Yuji; Yamagami, Hiroshi; Tsubota, Masami*; Paik, B.*; Ichikawa, Takayuki*; Kojima, Yoshitsugu*; Muro, Takayuki*; Kinoshita, Toyohiko*

no journal, , 

Lithium amide (LiNH$$_{2}$$) is lightweight complex hydride expected as a high-capacity hydrogen storage material. The electronic structure of lithium amide (LiNH$$_{2}$$) is investigated by soft X-ray emission spectroscopy (XES) and absorption spectroscopy (XAS). The unoccupied and occupied parts of the N 2$$p$$ partial density of states are studied by N 1$$s$$ XAS in the fluorescence yield mode and XES using soft X-ray (h$$nu$$=425eV) of SPring-8. The XES and XAS spectra show a band gap between the valence and conduction bands. The valence band in the XES spectrum consists of three peaks, which extend up to $$sim$$ -8eV from the valence band top. The overall feature of the electronic structure of lithium amide by the XES and XAS is consistent with the band calculation. The strongly hybridized state with H 1$$s$$ observed on the high binding energy side in the XES is discussed.

Oral presentation

Neutron diffraction study of pressure-induced phase separation of LaD$$_{2}$$

Aoki, Katsutoshi; Machida, Akihiko; Honda, Mitsunori; Hattori, Takanori; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Komatsu, Kazuki*; Arima, Hiroshi; Otomo, Toshiya*; et al.

no journal, , 

Neutron diffraction measurements have revealed that LaD$$_{2}$$ undergoes phase separation at high pressure with the relocation of deuterium atoms in the interstitial sites of La metal lattice. Deuterium atoms, which occupy the tetrahedral sites of the fcc metal lattice in LaD$$_{2}$$, move into the empty octahedral sites at 11 GPa to form LaD and LaD$$_{3}$$ both having fcc metal lattices. Mono-hydride with an NaCl structure, which is common for mono-hydrides of transition metals, is formed in rare-earth metals for the first time. The first-principle calculations showed that LaH$$_{2}$$ is stable at low pressure and it undergoes a phase separation into LaH and LaH$$_{3}$$ at 10 GPa, which is excellent agreement with the experimental results. Enthalpy comparison shows that unusual volume contraction in LaH$$_{3}$$ than LaH$$_{2}$$ explains the phase separation phenomena. Lattice dynamics calculations on these lanthanum hydrides shed light on the detailed mechanism.

Oral presentation

Phase separation with inter-site deuteron transfer in LaD$$_{2}$$

Aoki, Katsutoshi; Machida, Akihiko; Honda, Mitsunori; Hattori, Takanori; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Komatsu, Kazuki*; Arima, Hiroshi; Otomo, Toshiya*; et al.

no journal, , 

Synchrotron X-ray and neutron diffraction measurements have revealed that LaD$$_{2}$$ undergoes phase separation at high pressure with the relocation of deuterium atoms in the interstitial sites of La metal lattice. Synchrotron X-ray and neutron experiments were made at BL22XU, SPring-8 and a total scattering device, NOVA, J-PARC. Deuterium atoms, which occupy the tetrahedral sites of the fcc metal lattice in LaD$$_{2}$$, move into the empty octahedral sites at 11 GPa to form LaD and LaD$$_{3}$$ both having fcc metal lattices. Mono-hydride with an NaCl structure, which is common for mono-hydrides of transition metals, is formed in rare-earth metals for the first time. The first-principle calculations showed that LaH$$_{2}$$ is stable at low pressure and it undergoes a phase separation into LaH and LaH$$_{3}$$ at 10 GPa, which is excellent agreement with the experimental results.

Oral presentation

Ionic conduction path in AgGeSe superionic glass

Kawakita, Yukinobu; Otomo, Toshiya*; Ueno, Hiroki; Tsubota, Masami*; Kumara, L. S. R.*; Oshita, Hidetoshi*; Suzuya, Kentaro

no journal, , 

Ag$$_{x}$$(GeSe$$_{3}$$)$$_{1-x}$$ ternary alloy exhibits an extensive compositional range of bulk glass forming and a rapid enhancement in ionic conductivity from 10$$^{-14}$$ to 10$$^{-4}$$ S/cm of these glasses at Ag concentration of x=0.3 with increasing Ag content. Structural models of this material have already been proposed by reverse Monte Carlo simulation based on experimental structural data of neutron and X-ray diffractions and X-ray absorption fine structure. However, there observed micro-phase separation tendency in these glasses. This tendency might relate to formation of ionic conduction path in supercooled liquid on quenching process. The proposed models will be examined by structure factors over a wide Q range including relatively low momentum-transfer region which have been newly obtained by the total neutron scattering instrument installed at BL21 in MLF, J-PARC. This work was supported by NEDO under "Advanced Fundamental Research Project on Hydrogen Storage Materials".

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