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The John B. Goodenough Symposium in Materials Science & Engineering – In Honor of His 90 th Birthday The University of Texas at Austin, Austin, Texas October 26-27, 2012 New Iron Oxides by Soft Chemistry Mikio Takano Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Kyoto 606-8501, Japan takano@icems.kyoto-u.ac.jp http://www.icems.kyoto-u.ac.jp/ Abstract Body in Space Below: (Please use single space, Times New Roman or similar font, size 12, and limit to 250 Words. Please DO NOT exceed the space below.) 1: BaFe 4+ O 3 (BFO) A small class of oxides containing iron in a high valence state of Fe 4+ (d 4 ) have been known. The most representative phase is SrFeO 3 (SFO) which crystallizes in the cubic perovskite structure (a = 3.850 Å). All the Fe 2+ - and Fe 3+ -oxides are antiferromagnetic insulators in their ground states, while SFO and related Fe 4+ -oxides commonly exhibit shift toward metallicity and ferromagnetism. We succeeded in obtaining BaFeO 3 (BFO) crystallizing in the cubic perovskite structure (a = 3.971 Å), not in the known hexagonal perovskite structure, by flowing ozone over BaFeO 2.5 powder at a low temperature of 200°C. It has been found that BFO has a spiral spin structure of the A-type below 111 K but turns ferromagnetic with a large moment of 3.5 μ B /Fe on application of a small external field of ~0.3 T at 5 K (0.2 T at 77 K). BFO is the very first Fe-oxide that shows ferromagnetism at ambient pressure (N. Hayashi et al., Angew. Chem. Int. Ed., 43, 12547, 2011). The ferromagnetic transition temperature exceeds 300K as external pressure is increased up to 40 GPa as examined by in-situ Mössbauer measurements. The P-T phase diagram of BFO will be compared with that of SFO which shows pressureinduced ferromagnetism. 2: Biogenous Iron Oxides (BIOX) Prof. J. Takada’s group (Okayama Univ.) has found that the Fe 3+ - based microtubular deposit produced by a species of water-habitant bacteria, Leptothrix ochracea, shows interesting unexpected functionalities as a catalyst support, as a starting materials for beautiful red pigments, and so on. Results of recent studies in which I have been involved will be presented.
The John B. Goodenough Symposium in Materials Science & Engineering – In Honor of His 90 th Birthday The University of Texas at Austin, Austin, Texas October 26-27, 2012 Transiton Metal Oxides: Superconductors, Multiferroics, and Catalysts for Water Splitting Martha Greenblatt Department of Chemistry and Chemical Biology, Rutgers University martha@rutchem.rutgers.edu: Abstract Body in Space Below: (Please use single space, Times New Roman or similar font, size 12, and limit to 250 Words. Please DO NOT exceed the space below.) Combined experimental and DFT theoretical results on low-dimensional new Ni + /Ni 2+ (d 9 /d 8 ) homologous series, Ln n+1 Ni n O 2n+2 with n =2 and 3 layered oxides with Ruddlesden-Popper (RP)-related structures and isostructural and isoelectronic with the high temperature superconducting cuprates are presented. Temperature variation of magnetization, transport, specific heat and 139 La NMR data in La 4 Ni 3 O 8 evidence the presence of a transition near ~105 K. DFT calculations suggest similarity of the band structure with that of the cuprate superconductors and relate the transition at 105 K to a spin density wave nesting instability of the Fermi surface. More recent experimental and theoretical studies suggest that the transition seen at 105 K could be a high spin-to-low spin transition of Ni 2+ (d8). A quaternary perovskite, PbMn 3 Mn 4 O 12 prepared at high pressure and high temperature, undergoes a structural phase transition at ~380 K from the room temperature rhombohedral-to-a high temperature cubic phase. Temperature dependence of magnetic susceptibility, electronic transport and dielectric constant show a transition at ~68 K, which suggest coupling of a ferroelectric-like and magnetic behavior that is potentially multiferroic. Cheaper efficient catalysts made from earth abundant (not noble metals) and environmentally green materials are indispensible for extracting hydrogen from water, the essential precursor to all globally sustainable fuels. Achieving this goal and the reduction of CO 2 to liquid fuels are necessary to replace fossil fuels. We have synthesized different polymorphs of LiCoO 2 and compared their catalytic activity in water oxidation. Our results show that LiCoO 2 is active exclusively in the low-temperature cubic “spinel-like” structure, while inactive as the high-temperature layered phase, which is thermodynamically more stable. The related spinel LiMn 2 O 4 is transformed from an inactive to a highly efficient water oxidation catalyst (λ-MnO 2 ) upon the topotactic removal Li + . These spinel phases contain cubical metal-oxo (M 4 O 4 ) subunits (absent in the layered LiCoO 2 analog) that appear to be the key to catalytic activity. The biological basis of the mechanism for the high activity of the M 4 O 4 -cubical topology of spinels in water oxidation will be discussed.
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