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論文

Multiple-wavelength neutron holography with pulsed neutrons

林 好一*; 大山 研司*; 八方 直久*; 松下 智裕*; 細川 伸也*; 原田 正英; 稲村 泰弘; 仁谷 浩明*; 宍戸 統悦*; 湯葢 邦夫*

Science Advances (Internet), 3(8), p.e1700294_1 - e1700294_7, 2017/08

Local structures around impurities in solids provide important information for understanding the mechanisms of material functions, because most of them are controlled by dopants. For this purpose, the X-ray absorption fine structure method, which provides radial distribution functions around specific elements, is most widely used. However, a similar method using neutron techniques has not yet been developed. If one can establish a method of local structural analysis with neutrons, then a new frontier of materials science can be explored owing to the specific nature of neutron scattering-that is, its high sensitivity to light elements and magnetic moments. Multiple-wavelength neutron holography using the time-of-flight technique with pulsed neutrons has great potential to realize this. We demonstrated multiple-wavelength neutron holography using a Eu-doped CaF$$_{2}$$ single crystal and obtained a clear three-dimensional atomic image around trivalent Eu substituted for divalent Ca, revealing an interesting feature of the local structure that allows it to maintain charge neutrality. The new holography technique is expected to provide new information on local structures using the neutron technique.

論文

Impurity effects in the microscopic elastic properties of polycrystalline Mg-Zn-Y alloys with a synchronised long-period stacking ordered phase

細川 伸也*; 木村 耕治*; 山崎 倫昭*; 河村 能人*; 吉田 亨次*; 乾 雅祝*; 筒井 智嗣*; Baron, A. Q. R.*; 川北 至信; 伊藤 晋一*

Journal of Alloys and Compounds, 695, p.426 - 432, 2017/02

 被引用回数:3 パーセンタイル:67.8(Chemistry, Physical)

Inelastic X-ray scattering (IXS) was performed on polycrystalline Mg$$_{97}$$Zn$$_1$$Y$$_2$$ and Mg$$_{85}$$Zn$$_6$$Y$$_9$$ alloys with synchronized long-period stacking ordered (LPSO) phase for investigating the impurity effects in the microscopic elastic properties. Inelastic neutron scattering (INS) was also carried out on the former alloy. LA modes were clearly observed in the IXS spectra of both the LPSO alloys, while TA modes can mainly be detected in the second Brillouin zone. Broader inelastic signals and larger quasielastic peaks are characteristic due to the phonon scattering by the Zn/Y impurities. Only the TA excitation energies increase by adding the impurities, which indicates a harder stiffness of the bond angles relating to the L1$$_2$$-type clusters in the LPSO alloys. New dispersion-less excitation modes are observed at about 10 meV by adding the Zn/Y impurities. By comparing with the INS data, the contributions of the impurities to these excitations are discussed using differences in the scattering cross-sections between neutrons and X-rays.

論文

Structural aspects of the superionic conduction mechanism in Ag-GeSe$$_{3}$$ glasses

Stellhorn, J. R.*; 細川 伸也*; Pilgrim, W.-C.*; 川北 至信; 上村 健二*; 木村 耕治*; Blanc, N.*; Boudet, N.*

Zeitschrift f$"u$r Physikalische Chemie, 230(3), p.369 - 386, 2016/03

 被引用回数:4 パーセンタイル:83.8(Chemistry, Physical)

The local and intemediate-range atomic structure in the Ag ion conduction glasses Ag$$_x$$(GeSe$$_3$$)$$_{1-x}$$ with $$x>$$ 0.15 and 0.50 has been investigated by Anormalous X-Ray Scattering experiments at the K absorption edges of each constituent element. This method can provide insight into the structural properties enableing the effect of superionic conductivity for compositions with $$x>$$ 0.33 in the amorphous phase. The experimental results were analyzed with Reverse Monte Carlo modeling, providing the partial structure factors and the corresponding partial pair-distribution functions. Evidence is found for a high level of intermediate range order for low silver concentrations, whereas the superionic conducting phase formed at high silver concentrations is characterized by cluster-like configurations of Ag atoms on a nanometer scale.

論文

Local structure of room-temperature superionic Ag-GeSe$$_3$$ glasses

Stellhorn, J. R.*; 細川 伸也*; 川北 至信; Gies, D.*; Pilgrim, W.-C.*; 林 好一*; 大山 研二*; Blanc, N.*; Boudet, N.*

Journal of Non-Crystalline Solids, 431, p.68 - 71, 2016/01

 被引用回数:6 パーセンタイル:54.52(Materials Science, Ceramics)

Anomalous X-ray scattering experiments on amorphous Ag$$_{0.5}$$(GeSe$$_{3}$$)$$_{0.5}$$ at the K absorption edges of each constituent element has been performed to investigate the local- and intermediate-range structure in this material. This method can provide insight into the structural properties enabling the effect of superionic conductivity in the amorphous phase. The experimental results were analyzed with reverse Monte Carlo modeling, providing the partial structure factors and the corresponding partial pair-distribution functions. A nanometer range phase separation tendency of the Ag atoms over a background of a GeSe$$_4$$ tetrahedral network is observed, which may confirm the view of Ag conduction pathways forming in this phase.

論文

Spontaneous formation of suboxidic coordination around Co in ferromagnetic rutile Ti$$_{0.95}$$Co$$_{0.05}$$O$$_2$$ film

Hu, W.*; 林 好一*; 福村 知昭*; 赤木 和人*; 塚田 捷*; 八方 直久*; 細川 伸也*; 大和田 謙二; 高橋 正光; 鈴木 基寛*; et al.

Applied Physics Letters, 106(22), p.222403_1 - 222403_5, 2015/06

 被引用回数:28 パーセンタイル:16.63(Physics, Applied)

The local atomic structures around Co in high temperature diluted ferromagnetic semiconductor Co-doped TiO$$_2$$ has been investigated using X-ray fluorescence holography and X-ray absorption fine structure experiments. While the Co atoms in the Ti$$_{0.99}$$Co$$_{0.01}$$O$$_2$$ simply substituted for Ti sites in the rutile structure, a suboxidic arrangement of CoO$$_2$$Ti$$_4$$ was found to form around Co in the Ti$$_{0.95}$$Co$$_{0.05}$$O$$_2$$ films. First-principles calculations supported the stability of the aggregated suboxidic clusters in the rutile TiO$$_2$$. The suboxidic coordination may be the source of strong exchange interaction, resulting in the high Curie temperature in Co-dopedTiO$$_2$$.

論文

Acute and obtuse rhombohedrons in the local structures of relaxor ferroelectric Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_3$$

Hu, W.*; 林 好一*; 大和田 謙二; Chen, J.*; 八方 直久*; 細川 伸也*; 高橋 正光; Bokov, A.*; Ye, Z.-G*

Physical Review B, 89(14), p.140103_1 - 140103_5, 2014/04

 被引用回数:33 パーセンタイル:14.55(Materials Science, Multidisciplinary)

The local structures around Nb and Pb in the relaxor ferroelectric Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_3$$ were investigated by X-ray fluorescence holography. The Pb atomic images around Nb showed a rhombohedral distortion of the crystal unit cells. The Pb-Pb correlated images showed a local structure of body-center-like $$2a_0times 2a_0 times 2a_0$$ superlattice, proving a rigid three-dimensional network structural model combining the two kinds of rhombohedrons. This superstructure and the fluctuating Pb and Nb atoms play an important role in the relaxor behavior of this material.

論文

X-ray fluorescence holography

林 好一*; 八方 直久*; 細川 伸也*; Hu, W.; 松下 智裕*

Journal of Physics; Condensed Matter, 24(9), p.093201_1 - 093201_15, 2012/03

 被引用回数:60 パーセンタイル:40.56(Physics, Condensed Matter)

X-ray fluorescence holography (XFH) is a method of atomic resolution holography which utilizes fluorescing atoms as a wave source or a monitor of the interference field within a crystal sample. It provides three-dimensional atomic images around a specified element and has a range of up to a few nm in real space. In this article, we explain the theory of XFH including solutions to the twin-image problem, an advanced measuring system, and data processing for the reconstruction of atomic images. Then, we briefly introduce our recent applications of this technique to the analysis of local lattice distortions in mixed crystals and nanometer-size clusters appearing in the low-temperature phase of a shape-memory alloy.

論文

Three dimensional atomic image of TlInSe$$_{2}$$ by X-ray fluorescence holography

三村 功次郎*; 細川 伸也*; 八方 直久*; Hu, W.; 林 好一*; 脇田 和樹*; 石井 啓文*; 吉村 政人*; Jeyakanthan, J.*; Mamedov, N.*

e-Journal of Surface Science and Nanotechnology (Internet), 9, p.273 - 276, 2011/07

Three dimensional (3D) atomic images around the Tl atoms in single crystal TlInSe$$_{2}$$ thermoelectric material in the incommensurate phase were reconstructed by using Tl LIII X-ray fluorescence holography measured at room temperature. Comparison of the experimentally obtained 3D images with the theoretically calculated ones suggests that only the Tl atoms have large spatial fluctuations, which are related to the incommensurate phase of this material.

論文

Local structure around Ge atoms in IV-VI ferromagnetic semiconductor Ge$$_{0.6}$$Mn$$_{0.4}$$Te by X-ray fluorescence holography

八方 直久*; 竹原 祐紀*; 藤原 真*; 田中 公一*; 仙波 伸也*; 細川 伸也*; 林 好一*; Hu, W.; 鈴木 基寛*; 浅田 裕法*

e-Journal of Surface Science and Nanotechnology (Internet), 9, p.247 - 250, 2011/06

Local atomic structure around Ge atoms in Ge$$_{1-x}$$Mn$$_{x}$$Te thin film single crystal has been investigated by X-ray fluorescence holography (XFH) at room temperature. Obtained atomic image suggests that the Ge position is not stable in the exact positions of the anion fcc sublattice of the anion, and reveals the fluctuation of the Ge positions or the existence of cation vacancies.

論文

Three-dimensional atomic images of TlInSe$$_{2}$$ thermoelectric material obtained by X-ray fluorescence holography

細川 伸也*; 八方 直久*; 林 好一*; 三村 功次郎*; 脇田 和樹*; Hu, W.; 石井 啓文*; 吉村 政人*; Jeyakanthan, J.*; Mamedov, N.*

Japanese Journal of Applied Physics, 50(5), p.05FC06_1 - 05FC06_2, 2011/05

 被引用回数:5 パーセンタイル:73.06(Physics, Applied)

Three dimensional (3D) atomic images around the Tl atoms in single crystal TlInSe$$_{2}$$ thermoelectric material in the incommensurate phase were reconstructed by using Tl $$L$$$$_{rm III}$$ X-ray fluorescence holography measured at room temperature. In the obtained 3D image, the In atoms are clearly visible at the proper positions in the normal phase. However, the Tl atomic images are also observed but very weak. By comparing the experimental image with a theoretically calculated one, it is concluded that only the Tl atoms have large spatial fluctuations, which are related to the incommensurate phase of this material.

論文

Local structure around Mn atoms in IV-VI ferromagnetic semiconductor Ge$$_{0.6}$$Mn$$_{0.4}$$Te investigated by X-ray fluorescence holography

八方 直久*; 竹原 祐紀*; 藤原 真*; 田中 公一*; 仙波 伸也*; 細川 伸也*; 林 好一*; Hu, W.; 鈴木 基寛*; 浅田 裕法*

Japanese Journal of Applied Physics, 50(5), p.05FC11_1 - 05FC11_2, 2011/05

 被引用回数:4 パーセンタイル:77.96(Physics, Applied)

The local atomic structure around Mn atoms in Ge$$_{1-x}$$Mn$$_{x}$$Te thin-film single crystal has been investigated by X-ray fluorescence holography (XFH) at room temperature. The obtained atomic image suggests that the Mn atoms replace the Ge atoms in the host GeTe, and the Mn position is stable in the exact positions of the anion fcc sublattice. The XFH result also suggests the fluctuation of the Ge positions or the cation vacancies.

論文

Three dimensional local structure analysis of ZnSnAs$$_{2}$$:Mn by X-ray fluorescence holography

林 好一*; 内富 直隆*; Asubar, J. T.*; 八方 直久*; Hu, W.; 細川 伸也*; 鈴木 基寛*

Japanese Journal of Applied Physics, 50(1), p.01BF05_1 - 01BF05_4, 2011/01

 被引用回数:0 パーセンタイル:100(Physics, Applied)

X-ray fluorescence holographic study on a room-temperature ferromagnetic semiconductor film of ZnSnAs$$_{2}$$:Mn was performed using a strong X-ray beam of third generation synchrotron radiation of SPring-8. The real space reconstructions of the environments around Mn atoms were successfully visualized from the observed holograms despite the very small amount of Mn atoms. The reconstructions revealed that the Mn atomsoccupy the cation (Zn or Sn) site.

口頭

Direct observation of higher order atomistic structure in Ti$$_{50}$$Ni$$_{44}$$Fe$$_{6}$$ at lower temperature phase

Hu, W.; 林 好一*; 八方 直久*; 細川 伸也*; 寺井 智之*; 福田 隆*; 掛下 知行*; 高橋 正光

no journal, , 

The Ti-Ni series shape memory alloys shows novel phase transition behaviours depending on the concentrations of doped third element Fe and only the precursor phenomena are observed when more than 6 at.% of Fe atoms are substituted for Ni. In the present work, we have focused on Ti$$_{50}$$Ni$$_{44}$$Fe$$_{6}$$, which exhibits only a second-order-like parent (P) - incommensurate (IC) - commensurate (C) transition, and investigated the local structure around Fe and Ni by the X-ray fluorescence holography (XFH). We successfully obtained 3D real space local structures at both the P- and C-phases. Cluster-like structure appears around Fe and the direct evidence of the existence of supperlattice structure at C-phase appears around Ni. We discuss structural changes by comparing the microstructures obtained around Fe and Ni at two phases. The results provide hints on the lattice modulation related to precursors of the martensitic transition and direct evidence of superlattice phenomena.

口頭

Direct observation of local structure distortion in Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_{3}$$ by X-ray fluorescence holography

Hu, W.; 林 好一*; 八方 直久*; 大和田 謙二; Chen, J.*; Ye, Z.-G*; 細川 伸也*; 高橋 正光

no journal, , 

The chemical ordering regions (CORs) and polar nanoregions (PNRs) in relaxor ferroelectrics have been long believed to the origin of their high and temperature-independent permittivities. In the present work, we carried out X-ray fluorescence holography (XFH) experiments of Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_{3}$$ (PMN) and La-doped PMN (2 at% La, PLMN) single crystals, which are prototype relaxor ferroelectric material, and investigated the local structure around Nb atoms at BL22XU of SPring-8. The La-doped PMN single crystal shows much bigger CORs than pure PMN. Nb K$$alpha$$ (16.6 keV) fluorescent X-rays were analyzed and focused on an avalanche photodiode detector with a cylindrical graphite-crystal energy analyzer. The results indicate that both Pb-site and Mg/Nb-site atoms have big fluctuations in PMN system and 1st neigher Pb atoms tend to shift toward central Nb atom along [111] direction.

口頭

3D local structure analysis of relaxor ferroelectrics by X-ray fluorescence holography

Hu, W.; 林 好一*; 八方 直久*; 大和田 謙二; Chen, J.*; Ye, Z.-G*; 細川 伸也*; 高橋 正光

no journal, , 

Relaxor ferroelectrics as a class of disordered crystals possessing peculiar structure and properties have attracted significant research attention. However, quantitative analysis of its local structure and lattice distortion is difficult by conventional diffraction methods. In the present work, the authors carried out X-ray fluorescence holography experiments on PMN and La-doped PMN (PLMN) single crystals at BL22XU of SPring-8 and successfully obtained 3D atomic images around Nb and Pb elements up to 20${AA}$ with atomic resolution, respectively. The local distortion of Pb atoms was directly revealed by comparing the atomic images with the reference sample SrTiO$$_{3}$$ (ideal perovskite structure). We will discuss the differences between PMN and PLMN by comparing the obtained middle range local structures around Nb and Pb, and the pure structure of the chemical ordered domains on the atomic scale.

口頭

蛍光X線ホログラフィーによるPb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_{3}$$リラクサー強誘電体の三次元局所構造解析

Hu, W.; 林 好一*; 八方 直久*; 大和田 謙二; Chen, J.*; Ye, Z.-G*; 細川 伸也*; 高橋 正光

no journal, , 

Relaxor ferroelectrics as a class of disordered crystals possessing peculiar structure and properties have attracted significant research attention. However, quantitative analysis of its local structure and lattice distortion is difficult, and there is no report to our knowledge of direct observation of its three-dimensional local structure. In the present work, we carried our X-ray fluorescence holography experiments on Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_{3}$$ (PMN) single crystal at BL22XU of SPring-8 and successfully obtained 3D atomic images around Nb and Pb elements up to 2 nm with atomic resolution. Our result shows the direct evidence of the rhombohedral distortion in PMN. Comparing with theoretical calculation, coexistence of two rhombohedral distortions was confirmed. In this presentation, we will discuss the short-range distortion of Pb atoms by comparing the obtained 3D atomic images around Nb at room temperature and 100 K.

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