Research

Recent Topics

■ Iron Oxides with Square Planar Coordination

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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.

 SrFeO3 + CaH2 → SrFeO2 + CaO + H2
 Sr3Fe2O7 + 2CaH2 → Sr3Fe2O5 + 2CaO + 2H2

Surprisingly, the Fe(II)O4 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. SrFeO2 exhibits a spin transition for the first time for a four-coordinated metal.

Nature (2007)
Angew. Chem. Int. Ed. (2008)
J. Am. Chem. Soc. (2008)
J. Am. Chem. Soc. (2008)
Nature Chemistry (2009)
Nature Chemistry (2010)
J. Am. Chem. Soc. (2011)
J. Am. Chem. Soc. (2012)
Chem. Soc. Rev. (2012))


■ Complex Anion Chemistry

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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 O2-, S2-, Cl-, F-, N3-, etc using low temperature reactions. We have shown, for example, that (CuCl)LaNb2O7 prepared from an ion-exchange reaction of RbLaNb2O7 with CuCl2 is a two-dimensional quantum spin magnet having novel quantum phenomena such as spin-liquid state and Bose-Einstein condensation.

J. Phys. Soc. Jpn (2005)
J. Phys. Soc. Jpn (2006)
J. Phys. Soc. Jpn. (2007)
J. Phys. Soc. Jpn (2007)
J. Phys. Soc. Jpn. (2008)
Phys. Rev. B (2009)
J. Phys. Soc. Jpn. (2010)
Phys. Rev. Lett. (2010)
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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.

Nature Materials (2012)
J. Am. Chem. Soc. (2012)
Nature Chemistry (2015)
J. Am. Chem. Soc. (2015)
J. Am. Chem. Soc. (2016)


■ High Temperature Superconductivity

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The highest Tc 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 Tc superconductors.

J. Phys. Soc. Jpn. (2012)
J. Phys. Soc. Jpn. (2013
Nature Communications (2014))

FIRST PROGRAM


■ Oxide Nanosheets

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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 MnO2 at room temperature. The reaction finishes in one night and produces a high yield of nanosheests as much as 90%.

J. Am. Chem. Soc. (2008)
J. Mater. Chem. Soc. (2011)
J. Mater. Chem. Soc. (2012)


■ Frustration in a Quantum Magnet

SrCu2(BO3)2.gif


Geometrical frustration (or competing interactions) in magnetic materials often leads to novel phenomena such as spin-liquid state. We previously showed that SrCu2(BO3)2 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)LaNb2O7 was found to be the ferromagnetic version of the Shastry-Sutherland model.

Phys. Rev. Lett. (1999)
Phys. Rev. Lett. (2000)
Phys. Rev. Lett. (2000)
Phys. Rev. Lett. (2001)
Phys. Rev. Lett. (2001)
Phys. Rev. Lett. (2001)
Science (2002)
Phys. Rev. Lett. (2008)
Phys. Rev. Lett. (2010)
Phys. Rev. Lett. (2013)
Phys. Rev. Lett. (2013)