Tatsuya Hiratoko
Kumamoto University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Tatsuya Hiratoko.
Journal of Synchrotron Radiation | 2013
Tatsuya Hiratoko; Akira Yoshiasa; Tomotaka Nakatani; Maki Okube; Akihiko Nakatsuka; Kazumasa Sugiyama
XANES (X-ray absorption near-edge structure) spectra of the Ti K-edges of ATiO3 (A = Ca and Sr), A2TiO4 (A = Mg and Fe), TiO2 rutile and TiO2 anatase were measured in the temperature range 20-900 K. Ti atoms for all samples were located in TiO6 octahedral sites. The absorption intensity invariant point (AIIP) was found to be between the pre-edge and post-edge. After the AIIP, amplitudes damped due to Debye-Waller factor effects with temperature. Amplitudes in the pre-edge region increased with temperature normally by thermal vibration. Use of the AIIP peak intensity as a standard point enables a quantitative comparison of the intensity of the pre-edge peaks in various titanium compounds over a wide temperature range.
Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry | 2016
Tomotaka Nakatani; Akira Yoshiasa; Akihiko Nakatsuka; Tatsuya Hiratoko; Tsutomu Mashimo; Maki Okube; Satoshi Sasaki
A variable-temperature single-crystal X-ray diffraction study of a synthetic BaTiO3 perovskite has been performed over the temperature range 298-778 K. A transition from a tetragonal (P4mm) to a cubic (Pm3m) phase has been revealed near 413 K. In the non-centrosymmetric P4mm symmetry group, both Ti and O atoms are displaced along the c-axis in opposite directions with regard to the Ba position fixed at the origin, so that Ti(4+) and Ba(2+) cations occupy off-center positions in the TiO6 and BaO12 polyhedra, respectively. Smooth temperature-dependent changes of the atomic coordinates become discontinuous with the phase transition. Our observations imply that the cations remain off-center even in the high-temperature cubic phase. The temperature dependence of the mean-square displacements of Ti in the cubic phase includes a significant static component which means that Ti atoms are statistically distributed in the off-center positions.
Journal of Physics: Conference Series | 2016
Akira Yoshiasa; Tomotaka Nakatani; Tatsuya Hiratoko; Tsubasa Tobase; Akihiko Nakatsuka; Maki Okube; Hiroshi Arima; Kazumasa Sugiyama
Zr and Ti K-edge XANES spectra of PbZrO3, PbTiO3 and BaTiO3 perovskite-type compounds were measured in the temperature range from 10K to 850K. Quantitative comparisons for the near-edge spectra were performed in a wide temperature range using the absorption intensity invariant point (AIIP) standardization. Clear temperature dependence for pre-edge shoulder is identified by the calculating the temperature difference of the XANES spectrum intensity. Decrease of pre-edge shoulder and peak intensity is observed only in the para- and ferro-electric phases and draw curves, not straight lines. The gradients for shoulder and pre-edge peak intensity are rich in a variety. The decrease in absorption of pre-edge peak and shoulder is speculated due to the shift from the off-centre position of the Zr atom with respect to the oxygen octahedron to center position. The Zr ion in the PbZrO3 para-electric phase has same temperature behaviors of Ti ions in the ferroelectric perovskite.
Journal of Physics: Conference Series | 2016
Tsubasa Tobase; Akira Yoshiasa; Tatsuya Hiratoko; Hidetomo Hongu; Hiroshi Isobe; Akihiko Nakatsuka; Hiroshi Arima; Kazumasa Sugiyama
The local structures of meteorite fusion crusts were studied by Ca, Ti and Fe K-edge XANES and EXAFS spectroscopy. The surface of meteorites were melted and volatilized with extreme high temperature and large temperature gradient when meteorites were rushed into atmosphere. This study indicated that meteorite fusion crusts have unique local structures. The local structures of fusion crusts differ from tektites especially in intensity of the shoulder in the rising flank of the edge in Ca XANES spectra. It is consistent with chemical composition change by the volatilization of Si at fusion during atmospheric entry. The high estimated Fe3+/ (Fe2++Fe3+) ratio in meteorite fusion crusts indicates that meteorite fusion crusts are formed into atmospheric oxidation condition. The Ca-O distances in meteorite fusion crusts are 2.612.66 A and are extremely longer than in other natural glasses. The fusion crusts have unique local structure since they experienced extremely high temperature and short quenching time. The XAFS method is effective in distinction of meteorite fusion crusts and classification of natural glass.
Ceramics International | 2014
Tatsuya Hiratoko; Akira Yoneda; Masahiro Osako
Journal of Mineralogical and Petrological Sciences | 2013
Ling Wang; Akira Yoshiasa; Maki Okube; Tatsuya Hiratoko; Yuan Hu; Hiroshi Arima; Kazumasa Sugiyama
Physica Status Solidi B-basic Solid State Physics | 2018
Akira Yoshiasa; Ginga Kitahara; Tsubasa Tobase; Tatsuya Hiratoko; Hidetomo Hongu; Tomotaka Nakatani; Kei-ichiro Murai
Journal of Synchrotron Radiation | 2018
Tsubasa Tobase; Akira Yoshiasa; Tatsuya Hiratoko; Akihiko Nakatsuka
Journal of Mineralogical and Petrological Sciences | 2015
Tsubasa Tobase; Akira Yoshiasa; Ling Wang; Tatsuya Hiratoko; Hidetomo Hongu; Maki Okube; Kazumasa Sugiyama
Japan Geoscience Union | 2014
Tsubasa Tobase; Akira Yoshiasa; Ring Wang; Tatsuya Hiratoko