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Journal Articles

Improvement of hydrogen storage properties of Mg$$_{1-x}$$Pr$$_{x}$$Ni$$_{4}$$ by Changing Mg/Pr ratio

Sakaki, Koji*; Terashita, Naoyoshi*; Kim, H.*; Majzoub, E. H.*; Proffen, T.*; Machida, Akihiko; Watanuki, Tetsu; Tsunokake, Shigeru*; Nakamura, Yumiko*; Akiba, Etsuo*

Sumato Purosesu Gakkai-Shi, 3(6), p.359 - 366, 2014/11

no abstracts in English

Journal Articles

Origin of degradation in the reversible hydrogen storage capacity of V$$_{1-x}$$Ti$$_{x}$$ alloys from the atomic pair distribution function analysis

Kim, H.*; Sakaki, Koji*; Ogawa, Hiroshi*; Nakamura, Yumiko*; Nakamura, Jin*; Akiba, Etsuo*; Machida, Akihiko; Watanuki, Tetsu; Proffen, T.*

Journal of Physical Chemistry C, 117(50), p.26543 - 26550, 2013/12

 Times Cited Count:30 Percentile:72.62(Chemistry, Physical)

Reduction in reversible hydrogen storage capacity with increasing hydrogenation and dehydrogenation cycle number is observed in numerous hydrogen storage materials, but the mechanism behind this unfavorable change has not been elucidated yet. In this study, we have investigated the development of structural defects or disorders in V$$_{1-x}$$Ti$$_x$$H$$_2$$, $$x$$ = 0, 0.2, and 0.5, during the first 15 hydrogen absorption and desorption cycles using the atomic pair distribution function (PDF) analysis of synchrotron X-ray total scattering data to find out the possible structural origin of the poor cyclic stability of V$$_{1-x}$$Ti$$_x$$ alloys.

Journal Articles

Local crystal structures of Ge$$_{2}$$Sb$$_{2}$$Te$$_{5}$$ revealed by the atomic pair distribution function analysis

Shamoto, Shinichi; Kodama, Katsuaki; Iikubo, Satoshi; Taguchi, Tomitsugu; Yamada, Noboru*; Proffen, T.*

Japanese Journal of Applied Physics, Part 1, 45(11), p.8789 - 8794, 2006/11

 Times Cited Count:14 Percentile:49.12(Physics, Applied)

Two types of optical recording crystalline material Ge$$_{2}$$Sb$$_{2}$$Te$$_{5}$$ have been studied by neutron and X-ray powder diffraction measurements. One is the crystalline cubic-phase Ge$$_{2}$$Sb$$_{2}$$Te$$_{5}$$. The other is nanocrystalline-phase Ge$$_{2}$$Sb$$_{2}$$Te$$_{5}$$. For the nanocrystalline phase, the local crystal structure and the particle size distribution were obtained simultaneously by PDF analysis using a spherical-particle form factor. The lattice parameter is longer than that of the crystalline phase, suggesting an antimony-richer composition than the matrix. This compositional deviation would form the nanoparticle, resulting in nucleation-dominated crystal growth.

Journal Articles

Structural study on optical recording materials Ge$$_{2}$$Sb$$_{2+x}$$Te$$_{5}$$ and GeBi$$_{2}$$Te$$_{4}$$

Shamoto, Shinichi; Yamada, Noboru*; Matsunaga, Toshiyuki*; Proffen, T.*

Physica B; Condensed Matter, 385-386(1), p.574 - 577, 2006/11

 Times Cited Count:4 Percentile:23.8(Physics, Condensed Matter)

Crystal structures of optical recording materials Ge$$_{2}$$Sb$$_{2+x}$$Te$$_{5}$$ and GeBi$$_{2}$$Te$$_{4}$$ have been studied in terms of the fast phase transition mechanism by both of real and reciprocal space Rietveld analyses of pulsed neutron powder diffraction data. These crystalline phases had large local lattice distortions. In addition, the crystallite size of GeBi$$_{2}$$Te$$_{4}$$ was very small (about 150${AA}$). These results suggest that the similarity of entropy between crystalline and amorphous phases plays an important role in terms of the fast phase transition mechanisms.

Journal Articles

Large displacement of germanium atoms in crystalline Ge$$_2$$Sb$$_2$$Te$$_5$$

Shamoto, Shinichi; Yamada, Noboru*; Matsunaga, Toshiyuki*; Proffen, T.*; Richardson, J. W.*; Chung, J.-H.*; Egami, Takeshi*

Applied Physics Letters, 86(8), p.081904_1 - 081904_3, 2005/02

 Times Cited Count:47 Percentile:82.45(Physics, Applied)

Local structure of NaCl-type crystalline Ge$$_2$$Sb$$_2$$Te$$_5$$ has been studied by the atomic pair distribution function analysis of pulsed neutron powder diffraction data. We have found the large displacement of germanium atoms in this crystalline phase. Usually, such a large lattice distortion has disadvantage for the electric conductivity. The electronic band structure, however, implies that this significant distortion in addition to the lattice defect at Na site reduces only thermal conductivity, while the highly ordered tellurium atoms at Cl site keep high electric conductivity.

Journal Articles

Local structure of LiNiO$$_2$$ studied by neutron diffraction

Chung, J.-H.*; Proffen, T.*; Shamoto, Shinichi; Ghorayeb, A. M.*; Croguennec, L.*; Tian, W.*; Sales, B. C.*; Jin, R.*; Mandrus, D.*; Egami, Takeshi*

Physical Review B, 71(6), p.064410_1 - 064410_11, 2005/02

 Times Cited Count:65 Percentile:88.95(Materials Science, Multidisciplinary)

LiNiO$$_2$$ (S=1/2) forms a triangular lattice with the possible magnetic frustration, but the exact state of spin correlation has not yet been known. While there is no signature of long-range Jahn-Teller distortion, local JT distortion has been suspected. We have performed neutron diffraction and atomic pair-density function analyses up to unprecedented large distances to discover a number of unusual features, such as anomalous peak broadening, local JT distortion, sharp oxygen-oxygen distance correlations, and inverted temperature dependence of medium range correlation. These observations are best explained by local orbital ordering of Ni$$^{3+}$$ ions into three sublattices. This orbital ordering, however, cannot develop into long-range order because of the strain field it generates, and domains of about 10 nm in size are formed. Domains are susceptible to random pinning by impurities ssite disorderd resulting in the loss of structural long-range order. We suggest that this local orbital ordering is the basis for the complex magnetic properties observed in this compound.

Oral presentation

The Whole particle structural analysis on TiO$$_{2}$$ and Ge$$_{2}$$Sb$$_{2}$$Te$$_{5}$$ nanoparticles

Shamoto, Shinichi; Kodama, Katsuaki; Iikubo, Satoshi; Taguchi, Tomitsugu; Proffen, T.*; Yamada, Noboru*

no journal, , 

A nanoparticle has large surface area in the ratio, which would have different crystal structure from the inside. As for a catalyst, the surface plays an important role in the functionality. Structural analysis of the whole particle is an important step toward understanding the property. Recent high intensity quantum beams, such as pulsed neutron and synchrotron X-ray provide us a possibility for the analysis, which needs high Q-resolution and high intensity simultaneously. TiO$$_{2}$$ and Ge$$_{2}$$Sb$$_{2}$$Te$$_{5}$$ nanoparticles are photocatalyst and optical recording materials, respectively. The former particles are isolated individually, while the latter particles are embedded in an amorphous matrix. These two typical nanoparticles have been studied by the atomic pair distribution function (PDF) analysis with the spherical particle form factor using neutron powder diffraction data obtained at NPDF in LANSCE.

Oral presentation

Neutron scattering study of nanoparticles by the atomic pair distribution function

Shamoto, Shinichi; Kodama, Katsuaki; Iikubo, Satoshi; Taguchi, Tomitsugu; Proffen, T.*; Yamada, Noboru*

no journal, , 

It will be possible to study novel nanomaterials by high intensity, high Q-resolution, and wide Q-range pulsed neutron scattering at intense pulsed neutron sources. The atomic pair distribution function analysis for the crystalline nanomaterials, however, has not been developed so far. We will discuss the characteristic finite size effects on the PDF analysis.

Oral presentation

Local crystal structures of Ge$$_{2}$$Sb$$_{2}$$Te$$_{5}$$ revealed by the atomic pair distribution function analysis

Shamoto, Shinichi; Kodama, Katsuaki; Iikubo, Satoshi; Taguchi, Tomitsugu; Yamada, Noboru*; Proffen, T.*

no journal, , 

no abstracts in English

Oral presentation

Nanoparticle study by wide r-range atomic pair distribution function

Shamoto, Shinichi; Iikubo, Satoshi; Kodama, Katsuaki; Taguchi, Tomitsugu; Proffen, T.*

no journal, , 

Wide r-range atomic pair distribution function (PDF) over 200 ${AA}$ is becoming available at a high Q-resolution and high intensity total scattering diffractometer in a recent intense pulsed neutron source facility. By using the PDF, whole nanoparticle crystal structure could be studied in principle. Toward the goal, we have studied nanoparticle form factor effects on PDF. Our recent results obtained at NPDF in LANSCE will be reported.

Oral presentation

Structural analysis of nano-transition-metal-oxides

Shamoto, Shinichi; Iikubo, Satoshi; Kodama, Katsuaki; Taguchi, Tomitsugu; Koyanaka, Hideki*; Takeuchi, Ken*; Kohara, Shinji*; Loong, C.-K.*; Proffen, T.*

no journal, , 

Local crystal structures of nano-transition-metal-oxide powder samples, such as manganese oxide and titanium oxide, have been studied by the atomic pair distribution function (PDF) analysis of X-ray and neutron powder diffraction data. For example, the nano-manganese-oxide (nano-Mn-O) sample with unknown crystal structure shows ultrahigh efficiency as a gold adsorbent even from ppt-level aqueous solutions such as the seawater. For the nanomaterials, there are various difficulties to determine the crystallographic parameters. Instead of fitting broad diffraction peaks, the PDF reveals relatively sharp features at short interatomic distances. For example, by analyzing the peak areas in absolute scale, a valence of a manganese ion or an atomic fraction of manganese ion in the nano-Mn-O sample, MnO$$_{x}$$, can be determined.

Oral presentation

PDF study of spinel fine particle with giant magnetic coercive force

Shamoto, Shinichi; Matsumura, Daiju; Yamamoto, Hiroshi*; Taguchi, Tomitsugu; Yamamoto, Hiroyuki; Nishihata, Yasuo; Proffen, T.*; Horiishi, Nanao*

no journal, , 

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