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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. 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)|
|#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;Under construction&br;&br;今までの酸化物の化学は、複数のカチオンの組合せの化学といっても過言でありません。これに対し私たちは、低温合成法を使うことで複数のアニオンを含む新 物質の開拓に挑みます。例えば，低温イオン交換反応によって，磁性のない酸化物 (O) から２次元磁性をもつ酸塩化物 (O, Cl) への変換に成功しました。 &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)|
|#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;Under construction&br;&br;室温超伝導体が現在の電力ケーブルに置き換われば、温室効果ガス排出量が数十パーセント削減するといわれています。現在の転移温度の世界記録はまだマイナ ス140℃です。２００９年度に採択された超伝導関連の大型プロジェクトで、私たちは新物質開発を担当しており、この究極の夢に挑戦しています。|
|#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;Under construction&br;&br;酸化物ナノシートとは、厚さ方向のみがナノの大きさの究極の２次元酸化物のことです．この次元性の効果によって新しい機能物性が期待されています。酸化物 ナノシートの合成には従来は複雑な過程や時間、コストを必要としましたが、私たちはマンガン酸化物ナノシートを室温，数時間で合成する方法を開発しまし た。この新手法では、１枚の層のみからなる“モノ”シートが高い收率で得られます。現在は，有機無機ナノシートなどへの展開を図っています。 &br; &br;J. Am. Chem. Soc. (2008)|
|#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]

***■　Frustration in a Quantum Magnet [#q9895a9a]
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|#ref(研究内容/SrCu2(BO3)2.gif,center,nowrap,nolink,50%)|Under construction&br;&br;フラストレーション（競合）系は、磁性体でもあっても磁気秩序を示さないなどの不思議な現象を示すことが知られています。１９９８年に発見したSrCu*Sub*2*Sub*(BO*Sub*3*Sub*)*Sub*2*Sub*の銅（丸）の格子は、理論家シャストリー、サザーランドが１９８１年に考察した厳密模型と等価であることがわかり、また、磁化プラトーなどの巨視的量子現象が発見されたことから大きな注目を集めました。 &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)|
|#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)|