The innovation engine for new materials

Anionic control of functions in transition-metal oxides

Seminar Group: 


Hiroshi Kageyama


Kyoto University


Friday, November 30, 2012 - 4:00pm


ESB 1001


Prof. Ram Seshadri

 Transition-metal oxides show a diverse range of magnetic, transport, catalytic, or optical properties. In most cases, these compounds are easily prepared by high-temperature solid state reactions. However, such a thermodynamic approach allows little room for controlling coordination geometry around a transition metal that is a basis for physical properties. In my talk, I would like to demonstrate our recent attempts to develop new extended solid oxides with an unusual anionic coordination, by using various reactions at low temperatures or in controlled atmosphere.

    (1) Low-temperature hydride reduction can yield novel iron oxides such as SrFeO2, Sr3Fe2O5, BaFeO2 with FeO4/FeO3 planar coordination, featured by strong covalent interactions. The absence of apical oxide ions allows the formation of Fe-Fe bonding and results in interesting transitions like spin crossover under high pressure. (2) Using a similar method, a well-known ferroelectric material BaTiO3 can be converted to an oxyhydride BaTi(O,H)3, with hydride concentrations up to 20% of the anion sites. The oxyhydride is metallic, and the hydride species is exchangeable with hydrogen gas at elevated temperatures, implying diffusion of hydride. (3) A2+Ti3+2Pn2O (Pn = Sb, As) is a layered material with a mixed anionic coordination of TiO2Pn4. This coordination results in the stabilization of one of the T2g orbitals and gives a unique half-filled d1 configuration based on the square lattice (Ti2O), being analogous to d9 high-Tc cuprates. We found that a new compound BaTi2Sb2O shows a superconductivity at Tc = 1.2 K.

[1] Y. Tsujimoto et al., Nature 450, 1062 (2007); T. Kawakami et al., Nat. Chem. 1, 371 (2009); T. Yamamoto et al., J. Am. Chem. Soc. 134, 11444 (2012); C. Tassel and H. Kageyama,Chem. Soc. Rev. 41, 2025 (2012).
[2] Y. Kobayashi et al., Nat. Mater. 11, 507 (2012); T. Yajima et al., J. Am. Chem. Soc. 134, 8782 (2012); T. Sakaguchi et al., Inorg. Chem., in press.
[3] T. Yajima et al., J. Phys. Soc. Jpn. 81, 103706 (2012).