Browsing by Author "Ohoyama, K"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Oxyhydrides of (Ca,Sr,Ba)TiO3 perovskite solid solutions
    (American Chemical Society, 2012-11-05) Sakaguchi, T; Kobayashi, Y; Yajima, T; Ohkura, M; Tassel, C; Takeiri, F; Mitsuoka, S; Ohkubo, H; Yamamoto, T; Kim, JE; Tsuji, N; Fujihara, A; Matsushita, Y; Hester, JR; Avdeev, M; Ohoyama, K; Kageyama, H
    The oxyhydride solid solutions (Ca,Sr)TiO3-xHx and (Sr,Ba)TiO3-xHx have been prepared by reducing the corresponding ATiO(3) oxides with calcium hydride. Under the reaction conditions examined, a hydride content of x = 0.1-0.3 was obtained for all compositions. Compared to our previous result with BaTiO3-xHx, the larger particle size in this study (20-30 mu m vs 170 nm) resulted in a somewhat lower hydride amount despite prolonged reaction times. We examined changes in cell volume, octahedral tilt angle, and site occupancy of different anion sites after conversion to oxyhydrides; it appears that these oxyhydrides fit the geometrical descriptions typical for regular ABO(3) perovskites quite well. The hydrogen release temperature, previously shown to be indicative of the hydride exchange temperature, however, does not scale linearly with the A-site composition, indicating a potential effect of chemical randomness. © 2012, American Chemical Society.
  • Thumbnail Image
    Item
    Quantified zero thermal expansion in magnetic R2Fe17-based intermetallic compounds (R = rare earth)
    (American Chemical Society, 2023-06-13) Cao, YL; Matsukawa, T; Gibbs, A; Avdeev, M; Wang, CW; Wu, H; Huang, QZ; Ohoyama, K; Ishigaki, T; Zhou, H; Li, Q; Miao, J; Lin, K; Xing, XR
    Zero thermal expansion (ZTE) has been a fascinating task for the past few decades due to its great scientific and practical merits. To realize ZTE, negative thermal expansion is typically employed by chemical substitutions on tuning structure features, which often relies on trial and error. Here, we report on exploring quantification of thermal expansion with magnetic ordering in an intermetallic class of R2Fe17 (R = rare earth), which can accurately determine the ZTE composition using a documented database. It demonstrates that the magnetic ordering of the Fe-sublattice contributes to the thermal expansion anomaly through simultaneous examinations of magnetization and neutron powder diffraction. Alternative elements can be manipulated on a Fe-sublattice to control both the total ordered magnetic moments of the Fe-sublattice and Curie temperature, which tailors the temperature variation of the magnetic contributions on thermal expansion. The current work might point to a future for ZTE high throughput searches, anticipated to benefit applications. © 2023 American Chemical Society