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論文

Local- and intermediate-range order in room temperature superionic conducting Ag-GeSe $_{3}$ glasses

細川伸也*; 川北至信; Stellhorn, J. R.*; Pusztai, L.*; Blanc, N.*; Boudet, N.*; 池田一貴*; 大友季哉*

JPS Conference Proceedings (Internet), 33, p.011070_1 - 011070_7, 2021/03

BB2019-1957.pdf:3.47MB

https://doi.org/10.7566/JPSCP.33.011070

銀イオン伝導体Ag $_{x}$ (GeSe $_{3}$ ) $_{1-x}$ のx=0.15, 0.28, 0.33, 0.50の試料について局所・中距離原子秩序がAXS, XRD, ND, RMCモデリングを組合せて調べられた。AXSとXRDで得られた結果にNDを加えることによって、もっともらしい部分構造と部分pdfを得ることができた。AXSとRMCによる以前の結果とは対照的に、多くのAg-Ge, Ge-Ge相関が第一近接殻内に見られるようになり、第一原理MDシミュレーションと一致する結果となった。GeとSeの配位数は、Agを考慮に入れなければ、すべてのAg濃度で8-規則にほぼ乗っている。Ag濃度が増加すると、Ag周りのGeとSeの部分配位数が著しく増加し、一方Ag-Ag配位数はわずかに増加するのみである。このことは、Agの伝導経路がAg-Ag相関の第2近接を経由して形成されていることを示している。

論文

Detailed investigations on short- and intermediate-range structures of Ge-Se glasses near the stiffness transition composition

細川伸也*; 川北至信; Pusztai, L.*; 池田一貴*; 大友季哉*

Journal of the Physical Society of Japan, 90(2), p.024601_1 - 024601_12, 2021/02

https://doi.org/10.7566/JPSJ.90.024601

被引用回数：2 パーセンタイル：30.35(Physics, Multidisciplinary)

In order to improve the reliability of short- and intermediate-range atomic structures of GeSe $_{1-x}$ glasses, high quality neutron diffraction data, in both the real and reciprocal spaces, were added to the existing anomalous X-ray scattering and X-ray diffraction datasets [Hosokawa et al., Phys. Rev. B 84, 014201 (2011)] for reverse Monte Carlo modeling. This addition proved to be highly effective for obtaining well-refined structural data and for revealing a close relationship between the compositional stiffness transition occurring at about = 0.20-0.26 and the partial structures. Although the $S_{ij}(Q)$ and $g_{ij}(r)$ functions gradually change with varying , important indications on the stiffness transition are confirmed on the basis of the intermediate-range element-selective atomic structures () more clearly than it was possible by previous results. An abrupt decrease in terms of the the prepeak intensity of $S_{GeGe}(Q)$ , a rapid disappearance of the Ge-Ge homopolar bonds, anomalies in the ratio of edge- and corner-sharing Ge(Se $_{1/2}$ ) tetrahedra, and characteristic changes in the tetrahedral connections with decreasing X across the so-called intermediate phase have all been observed.

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

http://doi.org/10.1126/sciadv.1700294

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

https://doi.org/10.1016/j.jallcom.2016.10.266

被引用回数：3 パーセンタイル：16.72(Chemistry, Physical)

Inelastic X-ray scattering (IXS) was performed on polycrystalline Mg $_{97}$ ZnY and Mg $_{85}$ ZnY 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-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 fr Physikalische Chemie, 230(3), p.369 - 386, 2016/03

https://doi.org/10.1515/zpch-2015-0667

被引用回数：4 パーセンタイル：9.34(Chemistry, Physical)

The local and intemediate-range atomic structure in the Ag ion conduction glasses Ag(GeSe) $_{1-x}$ with 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 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 glasses

Stellhorn, J. R.*; 細川伸也*; 川北至信; Gies, D.*; Pilgrim, W.-C.*; 林好一*; 大山研司*; Blanc, N.*; Boudet, N.*

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

https://doi.org/10.1016/j.jnoncrysol.2015.02.027

被引用回数：6 パーセンタイル：30.51(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 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 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

https://doi.org/10.1063/1.4921847

被引用回数：39 パーセンタイル：81.57(Physics, Applied)

The local atomic structures around Co in high temperature diluted ferromagnetic semiconductor Co-doped TiO 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 simply substituted for Ti sites in the rutile structure, a suboxidic arrangement of CoOTi was found to form around Co in the Ti $_{0.95}$ Co $_{0.05}$ O films. First-principles calculations supported the stability of the aggregated suboxidic clusters in the rutile TiO. The suboxidic coordination may be the source of strong exchange interaction, resulting in the high Curie temperature in Co-dopedTiO.

論文

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

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

https://doi.org/10.1103/PhysRevB.89.140103

被引用回数：48 パーセンタイル：85.62(Materials Science, Multidisciplinary)

The local structures around Nb and Pb in the relaxor ferroelectric Pb(Mg $_{1/3}$ Nb $_{2/3}$ )O 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 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

https://doi.org/10.1088/0953-8984/24/9/093201

被引用回数：86 パーセンタイル：60.71(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

https://doi.org/10.1380/ejssnt.2011.273

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

https://doi.org/10.1380/ejssnt.2011.247

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

https://doi.org/10.1143/JJAP.50.05FC06

被引用回数：7 パーセンタイル：31.23(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 $_{rm III}$ 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

https://doi.org/10.1143/JJAP.50.05FC11

被引用回数：5 パーセンタイル：23.4(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

https://doi.org/10.1143/JJAP.50.01BF05

被引用回数：1 パーセンタイル：4.79(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 (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 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.