Browsing by Author "Yamamoto, T"

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    Field-induced ferromagnetism of Fe4+-perovskite system, Sr(1-x)BaxFeO3 (0 ≤x≤1)
    (The Physical Society of Japan, 2013-09-05) Hayashi, N; Yamamoto, T; Kitada, A; Matsuo, A; Kindo, K; Hester, JR; Kageyama, H; Takano, M
    A series of cubic perovskite-type oxides, Sr1-xBaxFe4+O3 (0≤x≤1 ), have been studied through measurements of neutron diffraction and magnetization. It has been found that their helical spin structure changes from the G-type to the A-type with increasing Ba content at x∼0.85 . The application of an external magnetic field induces ferromagnetism with ∼3.5 µB/Fe, and the strength of the critical field decreases markedly from 39 T for SrFeO3 to 0.3 T for BaFeO3. The transition process can be categorized into three: SrFeO3, Sr0.4Ba0.6FeO3, and BaFeO3 types. © 2013 The Physical Society of Japan
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    Impact of lanthanoid substitution on the structural and physical properties of an infinite-layer iron oxide
    (American Chemical Society, 2016-11-01) Yamamoto, T; Ohkubo, H; Tassel, C; Hayashi, N; Kawasaki, S; Okada, T; Yagi, T; Hester, JR; Avdeev, M; Kobayashi, Y; Kageyama, H
    The effect of lanthanoid (Ln = Nd, Sm, Ho) substitution on the structural and physical properties of the infinite-layer iron oxide SrFeO2 was investigated by X-ray diffraction (XRD) at ambient and high pressure, neutron diffraction, and 57Fe Mössbauer spectroscopy. Ln for Sr substituted samples up to ∼30% were synthesized by topochemical reduction using CaH2. While the introduction of the smaller Ln3+ ion reduces the a axis as expected, we found an unusual expansion of the c axis as well as the volume. Rietveld refinements along with pair distribution function analysis revealed the incorporation of oxygen atoms between FeO2 layers with a charge-compensated composition of (Sr1–xLnx)FeO2+x/2, which accounts for the failed electron doping to the FeO2 layer. The incorporated partial apical oxygen or the pyramidal coordination induces incoherent buckling of the FeO2 sheet, leading to a significant reduction of the Néel temperature. High-pressure XRD experiments for (Sr0.75Ho0.25)FeO2.125 suggest a possible stabilization of an intermediate spin state in comparison with SrFeO2, revealing a certain contribution of the in-plane Fe–O distance to the pressure-induced transition. © 2016 American Chemical Society
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    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.
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    Synthesis and physical properties of the new oxybismuthides BaTi2Bi2O and (SrF)2Ti2Bi2O with a d1 square net
    (Physical Society of Japan, 2012-12-11) Yajima, T; Nakano, K; Takeiri, F; Hester, JR; Yamamoto, T; Kobayashi, Y; Tsuji, N; Kim, J; Fujiwara, A; Kageyama, H
    We have recently reported the d(1) square-lattice compound BaTi(2)Sb(2)O, which shows superconductivity at T(c) = 1.2K coexisting with a charge- or spin-density wave (CDW/SDW) state. Here, we successfully prepared two new oxybismuthides, BaTi(2)Bi(2)O and (SrF)(2)Ti(2)Bi(2)O, as the first Pn = Bi compounds in the ATi(2)Pn(2)O family. The CDW/SDW state disappeared for both compounds, presumably owing to the considerable interaction between the Ti-3d and Bi-6s orbitals. The complete suppression of the CDW/SDW instability resulted in an enhanced T(c) of 4.6 K for BaTi(2)Bi(2)O. However, (SrF)(2)Ti(2)Bi(2)O exhibits no superconductivity, suggesting the importance of the interlayer interaction for superconductivity. © 2012, Physical Society of Japan