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*Research [#ya1d188b]
**Recent Topics [#cdc99bdf]
***■　Iron Oxides with Square Planar Coordination [#i4af38e7]
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|#ref(reduction_eng.jpg,right,nowrap,nolink,70%)|&br;We recently found that a low-temperature topochemical reaction by calcium hydride as a reductant provides unique access to iron oxides with square-planar coordination.&br;&br;　SrFeO*Sub*3*Sub* + CaH*Sub*2*Sub* → SrFeO*Sub*2*Sub* + CaO + H*Sub*2*Sub* &br;　Sr*Sub*3*Sub*Fe*Sub*2*Sub*O*Sub*7*Sub* + 2CaH*Sub*2*Sub* → Sr*Sub*3*Sub*Fe*Sub*2*Sub*O*Sub*5*Sub* + 2CaO + 2H*Sub*2*Sub* &br;&br;Surprisingly, the Fe(II)O*Sub*4*Sub* sqaure-planar geometry is more strongly bonded than any known Fe(II) oxides - thus one expects to obtain novel functionalities that can work at ambient conditions such as a permanent magnet. SrFeO*Sub*2*Sub* exhibits a spin transition for the first time for a four-coordinated metal. &br;&br;Nature (2007)&br;Angew. Chem. Int. Ed. (2008)&br;J. Am. Chem. Soc. (2008)&br;J. Am. Chem. Soc. (2008)&br;Nature Chemistry (2009)&br;Nature Chemistry (2010)&br;J. Am. Chem. Soc. (2011)|

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***■　Complex Anion Chemistry [#l966d76c]
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|#ref(Research/ionexchange_eng.jpg,right,nowrap,nolink,45%)|&br;Most of studies of metal oxide materials have been a chemistry of mixed cations (or metals). Our group, however, aims to develop preparation of novel materials containing mixed anions such as O*Sup*2-*Sup*, S*Sup*2-*Sup*, Cl*Sup*-*Sup*, F*Sup*-*Sup*, N*Sup*3-*Sup*, etc using low temperature reactions. We have shown, for example, that (CuCl)LaNb*Sub*2*Sub*O*Sub*7*Sub* prepared from an ion-exchange reaction of RbLaNb*Sub*2*Sub*O*Sub*7*Sub* with CuCl*Sub*2*Sub* is a two-dimensional quantum  spin magnet having novel quantum phenomena such as spin-liquid state and Bose-Einstein condensation.&br;&br; J. Phys. Soc. Jpn (2005)&br;J. Phys. Soc. Jpn (2006)&br;J. Phys. Soc. Jpn. (2007)&br;J. Phys. Soc. Jpn (2007)&br;J. Phys. Soc. Jpn. (2008)&br;Phys. Rev. B (2009)&br;J. Phys. Soc. Jpn. (2010)&br;Phys. Rev. Lett. (2010)|

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***■　High Temperature Superconductivity [#y8e28fcd]
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|#ref(研究内容/superconductor_eng.jpg,center,nowrap,nolink,90%)| &br;The highest T*Sub*c*Sub* is about 130 K found in a cuprate oxide. This world record has not  been broken for more than 20 years. We hope to discover new high T*Sub*c*Sub* superconductors. &br;&br;→ [[FIRST PROGRAM>http://www.supera.titech.ac.jp/english/index.html]] |

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***■　Oxide Nanosheets [#q9895a9a]
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|#ref(TopPage/nanosheet_eng.jpg,right,nowrap,nolink,60%)|&br;Metal oxide nanosheet is a new class of nanoscale materials characterized by a thickness on the order of nanometers and by lateral dimensions of submicro- to micrometers. However, the synthesis of such metal oxide nanosheets requires multistep processing and thus long reaction time. We have developed a new method, a single-step synthesis of MnO*Sub*2*Sub* at room temperature. The reaction finishes in one night and produces a high yield of nanosheests as much as 90%.  &br; &br;J. Am. Chem. Soc. (2008)|

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***■　Frustration in a Quantum Magnet [#q9895a9a]
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|#ref(研究内容/SrCu2(BO3)2.gif,center,nowrap,nolink,50%)|&br;&br;Geometrical frustration (or competing interactions) in magnetic materials often leads to novel phenomena such as spin-liquid state. We previously showed that SrCu*Sub*2*Sub*(BO*Sub*3*Sub*)*Sub*2*Sub* has the experimental realization of the Shastry-Sutherland model (1981) which has an exactly solvable ground state. Under magnetic fields, this material exhibits quantized magnetization plateaus. Recently, (CuCl)LaNb*Sub*2*Sub*O*Sub*7*Sub* was found to be the ferromagnetic version of the Shastry-Sutherland model.&br;&br;Phys. Rev. Lett. (1999)&br;Phys. Rev. Lett. (2000)&br;Phys. Rev. Lett. (2000)&br;Phys. Rev. Lett. (2001)&br;Phys. Rev. Lett. (2001)&br;Phys. Rev. Lett. (2001)&br;Science (2002)&br;Phys. Rev. Lett. (2008)&br;Phys. Rev. Lett. (2010)|