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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)&br;J. Am. Chem. Soc. (2012)&br;Chem. Soc. Rev. (2012))|

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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 oxidematerials 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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|#ref(Research/BTOH2.jpg,right,nowrap,no link,60%)|&br;The substitution of oxygen by hydride anions in oxide materials to form oxyhydrides has been difficult to achieve because it requires highly reducing conditions without transferring an electron from the hydride. However, we have obtained an oxyhydride of BaTiO3 that is electronically conducting, stable in air and water at ambient conditions, and exchangeable with hydrogen gas at 400 °C. &br;&br;Nature Materials (2012)&br;J. Am. Chem. Soc. (2012)&br;Nature Chemistry (2015)&br;J. Am. Chem. Soc. (2015)&br;J. Am. Chem. Soc. (2016)|



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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;J. Phys. Soc. Jpn. (2012)&br;J. Phys. Soc. Jpn. (2013)&br;&br;Nature Communications (2014)&br;→ [[FIRST PROGRAM>http://www.supera.titech.ac.jp/english/index.html]] |
|#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;J. Phys. Soc. Jpn. (2012)&br;J. Phys. Soc. Jpn. (2013&br;Nature Communications (2014))&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)&br;J. Mater. Chem. Soc. (2011)&br;J. Mater. Chem. Soc. (2012)|

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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)&br;Phys. Rev. Lett. (2013)&br;Phys. Rev. Lett. (2013)|