2022/07/02 更新

写真a

ヒラタ アキヒコ
平田 秋彦
所属
理工学術院 大学院基幹理工学研究科
職名
教授(任期付)

学内研究所等

  • 2020年
    -
    2022年

    理工学術院総合研究所   兼任研究員

学位

  • 早稲田大学   博士(工学)

所属学協会

  •  
     
     

    日本顕微鏡学会

  •  
     
     

    日本金属学会

  •  
     
     

    The Japan Institute of Metals

 

研究キーワード

  • 電子顕微鏡

  • 材料科学

Misc

  • Structural analysis of polycrystalline BiFeO3 films by transmission electron microscopy

    Hiroshi Naganuma, Andras Kovacs, Akihiko Hirata, Yoshihiko Hirotsu, Soichiro Okamura

    MATERIALS TRANSACTIONS   48 ( 9 ) 2370 - 2373  2007年09月

     概要を見る

    A multiferroic polycrystalline BiFeO3 film has been fabricated by a chemical solution deposition followed by the post deposition annealing at 823 K in air. The nanostructure of the BiFeO3 film was characterized by transmission electron microscopy (TEM). The nano-beam electron diffraction and the fast Fourier transform pattern image from the high resolution TEM image were compared with the electron diffraction patterns of the multislice simulation, and it was revealed that the BiFeO3 has R3c rhombohedral structure. Formation of any additional phase or phases was not found in the sample. The BiFeO3 film shows the small saturation magnetization of 5.2emu/cm(3) without spontaneous magnetization at room temperature, which behavior is typical for the weak ferromagnetic materials. The ferroelectric hysteresis loop of the BiFeO3 film was measured at low temperature in order to reduce the leakage current. The remanent polarization and the electric coercive field at 90 K were 52 mu C/cm(2) and 0.51 MV/cm at an applied electric field of 1.4 MV/cm, respectively. The structure-magnetic properties relationship is also discussed.

    DOI

  • Structural analysis of polycrystalline BiFeO3 films by transmission electron microscopy

    Hiroshi Naganuma, Andras Kovacs, Akihiko Hirata, Yoshihiko Hirotsu, Soichiro Okamura

    MATERIALS TRANSACTIONS   48 ( 9 ) 2370 - 2373  2007年09月

     概要を見る

    A multiferroic polycrystalline BiFeO3 film has been fabricated by a chemical solution deposition followed by the post deposition annealing at 823 K in air. The nanostructure of the BiFeO3 film was characterized by transmission electron microscopy (TEM). The nano-beam electron diffraction and the fast Fourier transform pattern image from the high resolution TEM image were compared with the electron diffraction patterns of the multislice simulation, and it was revealed that the BiFeO3 has R3c rhombohedral structure. Formation of any additional phase or phases was not found in the sample. The BiFeO3 film shows the small saturation magnetization of 5.2emu/cm(3) without spontaneous magnetization at room temperature, which behavior is typical for the weak ferromagnetic materials. The ferroelectric hysteresis loop of the BiFeO3 film was measured at low temperature in order to reduce the leakage current. The remanent polarization and the electric coercive field at 90 K were 52 mu C/cm(2) and 0.51 MV/cm at an applied electric field of 1.4 MV/cm, respectively. The structure-magnetic properties relationship is also discussed.

    DOI

  • Structural analysis of polycrystalline BiFeO3 films by transmission electron microscopy

    Hiroshi Naganuma, Andras Kovacs, Akihiko Hirata, Yoshihiko Hirotsu, Soichiro Okamura

    MATERIALS TRANSACTIONS   48 ( 9 ) 2370 - 2373  2007年09月

     概要を見る

    A multiferroic polycrystalline BiFeO3 film has been fabricated by a chemical solution deposition followed by the post deposition annealing at 823 K in air. The nanostructure of the BiFeO3 film was characterized by transmission electron microscopy (TEM). The nano-beam electron diffraction and the fast Fourier transform pattern image from the high resolution TEM image were compared with the electron diffraction patterns of the multislice simulation, and it was revealed that the BiFeO3 has R3c rhombohedral structure. Formation of any additional phase or phases was not found in the sample. The BiFeO3 film shows the small saturation magnetization of 5.2emu/cm(3) without spontaneous magnetization at room temperature, which behavior is typical for the weak ferromagnetic materials. The ferroelectric hysteresis loop of the BiFeO3 film was measured at low temperature in order to reduce the leakage current. The remanent polarization and the electric coercive field at 90 K were 52 mu C/cm(2) and 0.51 MV/cm at an applied electric field of 1.4 MV/cm, respectively. The structure-magnetic properties relationship is also discussed.

    DOI

  • Voronoi analysis of the structure of Ni-Zr-Al ternary metallic glass

    T. Fukunaga, K. Itoh, T. Otomo, K. Mori, A. Sugiyama, H. Kato, A. Hasegawa, A. Hirata, Y. Hirotsu, A. C. Hannon

    MATERIALS TRANSACTIONS   48 ( 7 ) 1698 - 1702  2007年07月

     概要を見る

    Ni-Zr metallic glasses have been recognized to be unstable in comparison with Cu-Zr metallic glasses. An analysis of Voronoi polyhedra in the RMC simulations based on the diffraction data could characterize the atomic configurations around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prisni-like, Archimedian antiprism-like, and similar polyhedra. In contrast. icosahedron-like polyhedra are preferred for Cu. The Ni-Zr glasses have been reported to stabilize by adding Al. Therefore, in this work, the analysis of Voronoi polyhedra around Ni, Zr and Al atoms for Ni25Zr60Al15 ternary metallic glass was carried out in order to clarify the difference between the atomic structures for the binary and ternary metallic glasses. Trigonal prism-like, Archimedian antiprism-like and similar polyhedra, which are dominated in the Ni-Zr metallic glasses, decreased in number by adding Al to the Ni-Zr system. On the contrary, the number of icosaliedron-like polyhedra was found to increase. The results apparently indicate that the addition of Al into Ni-Zr binary system promote the formation of icosahedron-like polyhedra in the structure. Therefore, from these results. we can easily recognize that icosahedron-like polyhedra play an important role to stabilize the structure of metallic glasses.

    DOI

  • Voronoi analysis of the structure of Ni-Zr-Al ternary metallic glass

    T. Fukunaga, K. Itoh, T. Otomo, K. Mori, A. Sugiyama, H. Kato, A. Hasegawa, A. Hirata, Y. Hirotsu, A. C. Hannon

    MATERIALS TRANSACTIONS   48 ( 7 ) 1698 - 1702  2007年07月

     概要を見る

    Ni-Zr metallic glasses have been recognized to be unstable in comparison with Cu-Zr metallic glasses. An analysis of Voronoi polyhedra in the RMC simulations based on the diffraction data could characterize the atomic configurations around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prisni-like, Archimedian antiprism-like, and similar polyhedra. In contrast. icosahedron-like polyhedra are preferred for Cu. The Ni-Zr glasses have been reported to stabilize by adding Al. Therefore, in this work, the analysis of Voronoi polyhedra around Ni, Zr and Al atoms for Ni25Zr60Al15 ternary metallic glass was carried out in order to clarify the difference between the atomic structures for the binary and ternary metallic glasses. Trigonal prism-like, Archimedian antiprism-like and similar polyhedra, which are dominated in the Ni-Zr metallic glasses, decreased in number by adding Al to the Ni-Zr system. On the contrary, the number of icosaliedron-like polyhedra was found to increase. The results apparently indicate that the addition of Al into Ni-Zr binary system promote the formation of icosahedron-like polyhedra in the structure. Therefore, from these results. we can easily recognize that icosahedron-like polyhedra play an important role to stabilize the structure of metallic glasses.

    DOI

  • Voronoi analysis of the structure of Ni-Zr-Al ternary metallic glass

    T. Fukunaga, K. Itoh, T. Otomo, K. Mori, A. Sugiyama, H. Kato, A. Hasegawa, A. Hirata, Y. Hirotsu, A. C. Hannon

    MATERIALS TRANSACTIONS   48 ( 7 ) 1698 - 1702  2007年07月

     概要を見る

    Ni-Zr metallic glasses have been recognized to be unstable in comparison with Cu-Zr metallic glasses. An analysis of Voronoi polyhedra in the RMC simulations based on the diffraction data could characterize the atomic configurations around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prisni-like, Archimedian antiprism-like, and similar polyhedra. In contrast. icosahedron-like polyhedra are preferred for Cu. The Ni-Zr glasses have been reported to stabilize by adding Al. Therefore, in this work, the analysis of Voronoi polyhedra around Ni, Zr and Al atoms for Ni25Zr60Al15 ternary metallic glass was carried out in order to clarify the difference between the atomic structures for the binary and ternary metallic glasses. Trigonal prism-like, Archimedian antiprism-like and similar polyhedra, which are dominated in the Ni-Zr metallic glasses, decreased in number by adding Al to the Ni-Zr system. On the contrary, the number of icosaliedron-like polyhedra was found to increase. The results apparently indicate that the addition of Al into Ni-Zr binary system promote the formation of icosahedron-like polyhedra in the structure. Therefore, from these results. we can easily recognize that icosahedron-like polyhedra play an important role to stabilize the structure of metallic glasses.

    DOI

  • Voronoi analysis of the structure of Ni-Zr-Al ternary metallic glass

    T. Fukunaga, K. Itoh, T. Otomo, K. Mori, A. Sugiyama, H. Kato, A. Hasegawa, A. Hirata, Y. Hirotsu, A. C. Hannon

    MATERIALS TRANSACTIONS   48 ( 7 ) 1698 - 1702  2007年07月

     概要を見る

    Ni-Zr metallic glasses have been recognized to be unstable in comparison with Cu-Zr metallic glasses. An analysis of Voronoi polyhedra in the RMC simulations based on the diffraction data could characterize the atomic configurations around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prisni-like, Archimedian antiprism-like, and similar polyhedra. In contrast. icosahedron-like polyhedra are preferred for Cu. The Ni-Zr glasses have been reported to stabilize by adding Al. Therefore, in this work, the analysis of Voronoi polyhedra around Ni, Zr and Al atoms for Ni25Zr60Al15 ternary metallic glass was carried out in order to clarify the difference between the atomic structures for the binary and ternary metallic glasses. Trigonal prism-like, Archimedian antiprism-like and similar polyhedra, which are dominated in the Ni-Zr metallic glasses, decreased in number by adding Al to the Ni-Zr system. On the contrary, the number of icosaliedron-like polyhedra was found to increase. The results apparently indicate that the addition of Al into Ni-Zr binary system promote the formation of icosahedron-like polyhedra in the structure. Therefore, from these results. we can easily recognize that icosahedron-like polyhedra play an important role to stabilize the structure of metallic glasses.

    DOI

  • Local atomic structure analysis of Zr-Ni and Zr-Cu metallic glasses using electron diffraction

    Akihiko Hirata, Takuro Morino, Yoshihiko Hirotsu, Keiji Itoh, Toshiharu Fukunaga

    Materials Transactions   48 ( 6 ) 1299 - 1303  2007年06月

     概要を見る

    Local atomic structures in Zr66.7Ni33.3 and Zr 66.7Cu33.3 metallic glasses were examined by using nanobeam electron diffraction (NBED), energy-filtered selected area electron diffraction (SAED) and high-resolution electron microscopy (HREM). Locally ordered regions of atomic medium range order (MRO) were observed in both of the specimens by NBED, although it was difficult to recognize the regions using HREM. Statistical analyses for NBED patterns revealed such a difference in the extended MRO regions between the specimens that the MRO structure in Zr 66.7Ni33.3 is more complex with a large dispersion of interplanar spacings than those in Zr66.7Cu33.3. To understand nearest-neighbor atomic coordination, we performed electron intensity analyses using energy-filtered SAED patterns and constructed structure models including about 5000 atoms with the help of reverse Monte Carlo simulation. The nearest-neighbor atomic environments around Ni atoms in Zr66.7Ni 33.3 are also different from those around Cu atoms in Zr 66.7Cu33.3, consistent with the NBED study. The local structural difference between the two glasses was discussed in relation to their glass-forming abilities. ©2007 The Japan Institute of Metals.

    DOI

  • Direct imaging of local atomic ordering in a Pd-Ni-P bulk metallic glass using C-s-corrected transmission electron microscopy

    Akihiko Hirata, Yoshihiko Hirotsu, T. G. Nieh, Tadakatsu Ohkubo, Nobuo Tanaka

    ULTRAMICROSCOPY   107 ( 2-3 ) 116 - 123  2007年02月

     概要を見る

    In amorphous alloys, crystalline atomic clusters as small as 1-2nm are frequently observed as local lattice fringe images by high-resolution electron microscopy (HREM). These clusters can be understood as local structures of amorphous alloys corresponding to "medium-range-order (MRO)". The MRO structure can be observed only under suitable defocusing conditions of the objective lens in HREM. A clear imaging of the MRO structure is difficult in conventional TEMs, mainly due to the delocalization of the image, caused mainly by the spherical aberration of the objective lens and eventually by the chosen defocus. In the present study, we have examined MRO in a Pd-based bulk metallic glass (Pd40Ni40P20) using a high-resolution TEM (acceleration voltage 200 kV) fitted with a spherical aberration constant corrector (C, corrector) for aberration correction. We found that when C, was close to zero and defocus values were near the Gaussian focus, MRO regions with an FCC-Pd structure could be clearly observed with a low image disturbance. Under these conditions, the phase-contrast transfer function was understood to act as an ideal filter function, which distinctly selects specific lattice periods of the FCC-Pd clusters. The obtained atomic images of the glass structure including the FCC-Pd clusters are in good agreement with those expected from image simulation according to our amorphous structure model. In this study, we have demonstrated that the C-s-corrected HREM is a powerful tool to directly image locally ordered structures in metallic glasses. (c) 2006 Elsevier B.V. All rights reserved.

    DOI

  • Direct imaging of local atomic ordering in a Pd-Ni-P bulk metallic glass using C-s-corrected transmission electron microscopy

    Akihiko Hirata, Yoshihiko Hirotsu, T. G. Nieh, Tadakatsu Ohkubo, Nobuo Tanaka

    ULTRAMICROSCOPY   107 ( 2-3 ) 116 - 123  2007年02月

     概要を見る

    In amorphous alloys, crystalline atomic clusters as small as 1-2nm are frequently observed as local lattice fringe images by high-resolution electron microscopy (HREM). These clusters can be understood as local structures of amorphous alloys corresponding to "medium-range-order (MRO)". The MRO structure can be observed only under suitable defocusing conditions of the objective lens in HREM. A clear imaging of the MRO structure is difficult in conventional TEMs, mainly due to the delocalization of the image, caused mainly by the spherical aberration of the objective lens and eventually by the chosen defocus. In the present study, we have examined MRO in a Pd-based bulk metallic glass (Pd40Ni40P20) using a high-resolution TEM (acceleration voltage 200 kV) fitted with a spherical aberration constant corrector (C, corrector) for aberration correction. We found that when C, was close to zero and defocus values were near the Gaussian focus, MRO regions with an FCC-Pd structure could be clearly observed with a low image disturbance. Under these conditions, the phase-contrast transfer function was understood to act as an ideal filter function, which distinctly selects specific lattice periods of the FCC-Pd clusters. The obtained atomic images of the glass structure including the FCC-Pd clusters are in good agreement with those expected from image simulation according to our amorphous structure model. In this study, we have demonstrated that the C-s-corrected HREM is a powerful tool to directly image locally ordered structures in metallic glasses. (c) 2006 Elsevier B.V. All rights reserved.

    DOI

  • Direct imaging of local atomic ordering in a Pd-Ni-P bulk metallic glass using C-s-corrected transmission electron microscopy

    Akihiko Hirata, Yoshihiko Hirotsu, T. G. Nieh, Tadakatsu Ohkubo, Nobuo Tanaka

    ULTRAMICROSCOPY   107 ( 2-3 ) 116 - 123  2007年02月

     概要を見る

    In amorphous alloys, crystalline atomic clusters as small as 1-2nm are frequently observed as local lattice fringe images by high-resolution electron microscopy (HREM). These clusters can be understood as local structures of amorphous alloys corresponding to "medium-range-order (MRO)". The MRO structure can be observed only under suitable defocusing conditions of the objective lens in HREM. A clear imaging of the MRO structure is difficult in conventional TEMs, mainly due to the delocalization of the image, caused mainly by the spherical aberration of the objective lens and eventually by the chosen defocus. In the present study, we have examined MRO in a Pd-based bulk metallic glass (Pd40Ni40P20) using a high-resolution TEM (acceleration voltage 200 kV) fitted with a spherical aberration constant corrector (C, corrector) for aberration correction. We found that when C, was close to zero and defocus values were near the Gaussian focus, MRO regions with an FCC-Pd structure could be clearly observed with a low image disturbance. Under these conditions, the phase-contrast transfer function was understood to act as an ideal filter function, which distinctly selects specific lattice periods of the FCC-Pd clusters. The obtained atomic images of the glass structure including the FCC-Pd clusters are in good agreement with those expected from image simulation according to our amorphous structure model. In this study, we have demonstrated that the C-s-corrected HREM is a powerful tool to directly image locally ordered structures in metallic glasses. (c) 2006 Elsevier B.V. All rights reserved.

    DOI

  • Direct imaging of local atomic ordering in a Pd-Ni-P bulk metallic glass using C-s-corrected transmission electron microscopy

    Akihiko Hirata, Yoshihiko Hirotsu, T. G. Nieh, Tadakatsu Ohkubo, Nobuo Tanaka

    ULTRAMICROSCOPY   107 ( 2-3 ) 116 - 123  2007年02月

     概要を見る

    In amorphous alloys, crystalline atomic clusters as small as 1-2nm are frequently observed as local lattice fringe images by high-resolution electron microscopy (HREM). These clusters can be understood as local structures of amorphous alloys corresponding to "medium-range-order (MRO)". The MRO structure can be observed only under suitable defocusing conditions of the objective lens in HREM. A clear imaging of the MRO structure is difficult in conventional TEMs, mainly due to the delocalization of the image, caused mainly by the spherical aberration of the objective lens and eventually by the chosen defocus. In the present study, we have examined MRO in a Pd-based bulk metallic glass (Pd40Ni40P20) using a high-resolution TEM (acceleration voltage 200 kV) fitted with a spherical aberration constant corrector (C, corrector) for aberration correction. We found that when C, was close to zero and defocus values were near the Gaussian focus, MRO regions with an FCC-Pd structure could be clearly observed with a low image disturbance. Under these conditions, the phase-contrast transfer function was understood to act as an ideal filter function, which distinctly selects specific lattice periods of the FCC-Pd clusters. The obtained atomic images of the glass structure including the FCC-Pd clusters are in good agreement with those expected from image simulation according to our amorphous structure model. In this study, we have demonstrated that the C-s-corrected HREM is a powerful tool to directly image locally ordered structures in metallic glasses. (c) 2006 Elsevier B.V. All rights reserved.

    DOI

  • Mossbauer study of ultrathin Fe/Al multilayer films

    D. Kaptas, J. Balogh, T. Kemeny, L. F. Kiss, L. Bujdoso, A. Kovacs, A. Hirata, I. Vincze

    PHYSICAL REVIEW B   75 ( 1 )  2007年01月

     概要を見る

    Multilayers of Fe (between 0.3 and 2.0 nm thickness) separated by a 3.0 nm thick A1 spacer were prepared by vacuum evaporation and were then investigated by (57)Fe Mossbauer spectroscopy measurements between 4.2 and 300 K and in various external magnetic fields. Mixing of the components at the interface was studied by transmission electron microscopy. The formation of a nonmagnetic A1-Fe interface alloy is verified by a detailed analysis of the low temperature Mossbauer spectra. The effective thickness of the Fe layers was deduced from the amount of the nonmagnetic component and it was found to be correlated with the shape of the Fe hyperfine field distribution. A marked change of the temperature and of the external magnetic field dependence of the Fe hyperfine fields were observed as a function of the effective layer thickness. The hyperfine field component attributed to two monolayer thick Fe regions decreases linearly with increasing temperature; it disappears at well below room temperature and it is hardly influenced by external fields up to 7 T. The formation of three and more monolayer thick regions with increasing effective thickness results in an approach to the bulk behavior, T(3/2)-temperature dependence, and smaller magnetic anisotropy.

    DOI

  • Change of Nanostructure in (Fe0.5Co0.5)72B20Si4Nb4 Metallic Glass on Annealing

    Mater. Sci. Forum   539-543 2077-2081  2007年

  • Local Structure Studies of Metallic Glasses using HREM and Electron Diffraction

       2007年

  • Change of Nanostructure in (Fe0.5Co0.5)72B20Si4Nb4 Metallic Glass on Annealing

    Mater. Sci. Forum   539-543 2077-2081  2007年

  • Local Atomic Structure Analysis of Zr-Ni and Zr-Cu Metallic Glasses using Electron Diffraction

    Mater. Trans.   48 1229-1303  2007年

    DOI

  • Local Atomic Structure Analysis of Zr-Ni and Zr-Cu Metallic Glasses using Electron Diffraction

    Mater. Trans.   48 1229-1303  2007年

    DOI

  • Observation of Local Structural Change in the Course of Primary Crystallization of Metallic Glasses

       2007年

  • Observation of Local Structural Change in the Course of Primary Crystallization of Metallic Glasses

       2007年

  • Structural Analysis of BiFeO3 Polycrystalline Films by Transmission Electron Microscopy

    Mater. Trans.   48 2370-2377  2007年

    DOI

  • Local Structure Studies of Metallic Glasses using HREM and Electron Diffraction

       2007年

  • Change of Nanostructure in (Fe0.5Co0.5)72B20Si4Nb4 Metallic Glass on Annealing

    Mater. Sci. Forum   539-543 2077-2081  2007年

  • Local Structure Studies of Metallic Glasses using HREM and Electron Diffraction

       2007年

  • Change of Nanostructure in (Fe0.5Co0.5)72B20Si4Nb4 Metallic Glass on Annealing

    Mater. Sci. Forum   539-543 2077-2081  2007年

  • Mossbauer study of ultrathin Fe/Al multilayer films

    D. Kaptas, J. Balogh, T. Kemeny, L. F. Kiss, L. Bujdoso, A. Kovacs, A. Hirata, I. Vincze

    PHYSICAL REVIEW B   75 ( 1 )  2007年01月

     概要を見る

    Multilayers of Fe (between 0.3 and 2.0 nm thickness) separated by a 3.0 nm thick A1 spacer were prepared by vacuum evaporation and were then investigated by (57)Fe Mossbauer spectroscopy measurements between 4.2 and 300 K and in various external magnetic fields. Mixing of the components at the interface was studied by transmission electron microscopy. The formation of a nonmagnetic A1-Fe interface alloy is verified by a detailed analysis of the low temperature Mossbauer spectra. The effective thickness of the Fe layers was deduced from the amount of the nonmagnetic component and it was found to be correlated with the shape of the Fe hyperfine field distribution. A marked change of the temperature and of the external magnetic field dependence of the Fe hyperfine fields were observed as a function of the effective layer thickness. The hyperfine field component attributed to two monolayer thick Fe regions decreases linearly with increasing temperature; it disappears at well below room temperature and it is hardly influenced by external fields up to 7 T. The formation of three and more monolayer thick regions with increasing effective thickness results in an approach to the bulk behavior, T(3/2)-temperature dependence, and smaller magnetic anisotropy.

    DOI

  • Local Atomic Structure Analysis of Zr-Ni and Zr-Cu Metallic Glasses using Electron Diffraction

    Mater. Trans.   48 1229-1303  2007年

    DOI

  • Observation of Local Structural Change in the Course of Primary Crystallization of Metallic Glasses

       2007年

  • Observation of Local Structural Change in the Course of Primary Crystallization of Metallic Glasses

       2007年

  • Local Structure Studies of Metallic Glasses using HREM and Electron Diffraction

       2007年

  • Local atomic structure of Pd-Ni-P bulk metallic glass examined by high-resolution electron microscopy and electron diffraction

    Akihiko Hirata, Yoshihiko Hirotsu, Tadakatsu Ohkubo, Nobuo Tanaka, T. G. Nieh

    INTERMETALLICS   14 ( 8-9 ) 903 - 907  2006年08月

     概要を見る

    Structural fluctuation in a Pd40Ni40P20 bulk metallic glass is investigated by transmission electron microscopy and electron diffraction. Local atomic ordered regions with a fcc-(Pd,Ni) type structure was sharply imaged by a high-resolution electron microscopy (HREM) attached with a Cs-corrector. Interference function for the glassy state was obtained from electron-diffraction intensity profiles using energy-filter and imaging-plate techniques. We used a reverse Monte Carlo (RMC) simulation method to develop a realistic structure model. The model consists of a dense-random-packing structure, in which an fee ordered region with Pd. Ni, and P atoms was embedded. The structure model is consistent with the diffraction and HREM results. In Voronoi polyhedral analysis of the RMC simulated structure, P-centered (Pd,Ni)-P trigonal prisms are found primarily in the matrix structure embedding the fcc-cluster. Around Pd and Ni atoms deformed-fcc type polyhedra were frequently observed. From these local structural features, nanoscale phase separation was revealed to occur during the glass formation. (c) 2006 Elsevier Ltd. All rights reserved.

    DOI

  • Local atomic structure of Pd-Ni-P bulk metallic glass examined by high-resolution electron microscopy and electron diffraction

    Akihiko Hirata, Yoshihiko Hirotsu, Tadakatsu Ohkubo, Nobuo Tanaka, T. G. Nieh

    INTERMETALLICS   14 ( 8-9 ) 903 - 907  2006年08月

     概要を見る

    Structural fluctuation in a Pd40Ni40P20 bulk metallic glass is investigated by transmission electron microscopy and electron diffraction. Local atomic ordered regions with a fcc-(Pd,Ni) type structure was sharply imaged by a high-resolution electron microscopy (HREM) attached with a Cs-corrector. Interference function for the glassy state was obtained from electron-diffraction intensity profiles using energy-filter and imaging-plate techniques. We used a reverse Monte Carlo (RMC) simulation method to develop a realistic structure model. The model consists of a dense-random-packing structure, in which an fee ordered region with Pd. Ni, and P atoms was embedded. The structure model is consistent with the diffraction and HREM results. In Voronoi polyhedral analysis of the RMC simulated structure, P-centered (Pd,Ni)-P trigonal prisms are found primarily in the matrix structure embedding the fcc-cluster. Around Pd and Ni atoms deformed-fcc type polyhedra were frequently observed. From these local structural features, nanoscale phase separation was revealed to occur during the glass formation. (c) 2006 Elsevier Ltd. All rights reserved.

    DOI

  • Local atomic ordering and nanoscale phase separation in a Pd-Ni-P bulk metallic glass

    Y Hirotsu, TG Nieh, A Hirata, T Ohkubo, N Tanaka

    PHYSICAL REVIEW B   73 ( 1 )  2006年01月

     概要を見る

    The local structure in a Pd40Ni40P20 bulk metallic glass was examined using a spherical-aberration-corrected high resolution TEM. Fcc-Pd(Ni) type nanoclusters and local compound (phosphide)-like nanoclusters with sizes of 1-2 nm embedded in a dense-randomly-packed amorphous matrix were clearly observed under an appropriate imaging condition. However, three-dimensional atom-probe elemental mapping revealed there is virtually no nanoscale compositional difference between the nanoclusters and amorphous matrix beyond the statistical error range. A very small interfacial energy between the nanophase and the matrix is able to form a metastable amorphous phase with a structural fluctuation.

    DOI

  • Local atomic ordering and nanoscale phase separation in a Pd-Ni-P bulk metallic glass

    Y Hirotsu, TG Nieh, A Hirata, T Ohkubo, N Tanaka

    PHYSICAL REVIEW B   73 ( 1 )  2006年01月

     概要を見る

    The local structure in a Pd40Ni40P20 bulk metallic glass was examined using a spherical-aberration-corrected high resolution TEM. Fcc-Pd(Ni) type nanoclusters and local compound (phosphide)-like nanoclusters with sizes of 1-2 nm embedded in a dense-randomly-packed amorphous matrix were clearly observed under an appropriate imaging condition. However, three-dimensional atom-probe elemental mapping revealed there is virtually no nanoscale compositional difference between the nanoclusters and amorphous matrix beyond the statistical error range. A very small interfacial energy between the nanophase and the matrix is able to form a metastable amorphous phase with a structural fluctuation.

    DOI

  • Nanostructures of binary and ternary Fe-B based glasses studied by HREM and electron diffraction

    Archives of Materials Science   Vol.26 No.1-2 pp.25-29  2005年

  • Local atomic structures of amorphous Fe80B20 and Fe70Nb10B20 alloys studied by electron diffraction

    Materials Transaction    2005年

    DOI

  • Local atomic structures of amorphous Fe80B20 and Fe70Nb10B20 alloys studied by electron diffraction

    Materials Transaction    2005年

    DOI

  • Crystallographic correspondence between the bcc and C14-type structures in the Fe-Ti alloy system

    A Hirata, Y Koyama

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   374 ( 1-2 ) 72 - 76  2004年06月

     概要を見る

    The orientation relationship between the bcc and C14 structures in the (bcc --> bcc + C14) reaction of Fe-Ti alloys was determined by transmission electron microscopy. A relationship of (1 1 0)(bcc)//(00 (.) 1)(C14) and [1 1 2](bcc)//[10 (.) 0](C14) was found. Based on the relationship, the atomic displacement for the formation of the C14 structure from the bcc structure was proposed. (C) 2004 Published by Elsevier B.V.

    DOI

  • Crystallographic correspondence between the bcc and C14-type structures in the Fe-Ti alloy system

    A Hirata, Y Koyama

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   374 ( 1-2 ) 72 - 76  2004年06月

     概要を見る

    The orientation relationship between the bcc and C14 structures in the (bcc --> bcc + C14) reaction of Fe-Ti alloys was determined by transmission electron microscopy. A relationship of (1 1 0)(bcc)//(00 (.) 1)(C14) and [1 1 2](bcc)//[10 (.) 0](C14) was found. Based on the relationship, the atomic displacement for the formation of the C14 structure from the bcc structure was proposed. (C) 2004 Published by Elsevier B.V.

    DOI

  • Crystallographic feature of Laves phase formation in Fe-Mo alloy

       2004年

  • Fe-Bアモルファス合金におけるナノスケール相分離

    まてりあ    2004年

  • Crystallographic feature of Laves phase formation in Fe-Mo alloy

       2004年

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Works(作品等)

  • 融体・金属ガラスの局所原子構造のその場観察

    2005年
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  • 気相急冷による硬質磁性合金ナノ粒子の形成と電子線構造解析ならびに磁性評価

    2005年
    -
     

  • 急相急冷による硬質磁性合金ナノ粒子の形成と電子線構造解析ならびに磁性評価

    2004年
    -
     

受賞

  • Best Poster Young Researcher Presentation Award in BMGV

    2006年  

共同研究・競争的資金等の研究課題

  • -

特定課題研究

  • アモルファス系電池用材料の局所原子配列と充放電機構

    2020年  

     概要を見る

    次世代のリチウムイオン電池の負極材として期待されているアモルファスシリコンに関して、その充放電機構の理解へ向け、アモルファスの局所構造、特にこれまで不明な点が多かった中距離秩序構造の解明を試みた。本研究では、回折実験を再現するアモルファスシリコンの構造モデルを分子動力学法に作製し、幾何学的手法であるボロノイ多面体解析を用いて特に第2近接配位に関する解析を行った。その結果、中距離秩序構造を特徴づけるボロノイ指数が見いだされ、それらと関連結晶相の構造の比較も行った。今後、シリコンの電池利用において、充放電時における構造変化の理解のために、本研究で提案した解析は有用な手法であると思われる。

 

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