軽希土類元素 (Ce, Pr) を内包する籠状ホウ化物の超高圧合成と価数揺動

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2022-01-27 物質・材料研究機構

超高圧下 (25〜50万気圧) でのレーザー加熱により、サイズの大きな軽希土類元素 (Pr, Ce) を籠状の24配位籠状ホウ素ケージに取り込むことに初めて成功した。ケージの中でCeは価数揺動を示している。軽希土類元素は、特異な物性を示す強相関電子系物質として注目されている。PrB12,CeB12の新規合成は、こうした重い電子系でみられる物理現象解明への糸口を提供すると考えられる。

論文情報

題目
High-pressure synthesis of  light  lanthanide  dodecaborides (PrB12  and CeB12):  Effects  of valence fluctuation  on  volume and  formation  pressure

掲載誌:Inorganic Chemistry

掲載日時:2022年1月25日

DOI:10.1021/acs.inorgchem.1c03525

High-Pressure Synthesis of Light Lanthanide Dodecaborides (PrB12 and CeB12): Effects of Valence Fluctuation on Volume and Formation Pressure

Hitoshi Yusa*, Fumitoshi Iga, and Hiroshi Fujihisa
Cite this: Inorg. Chem. 2022, XXXX, XXX, XXX-XXX
Publication Date:January 25, 2022
https://doi.org/10.1021/acs.inorgchem.1c03525
© 2022 American Chemical Society

SUBJECTS:Chemical structure,Lanthanides,Boron,Diffraction,Lattices

Abstract

Abstract Image
Light lanthanide dodecaborides, RB12 (R = Pr and Ce), were synthesized from a stoichiometric mixture of hexaborides and boron using a laser-heated diamond anvil cell under high-pressure and high-temperature conditions. Contrary to the expectation that lighter lanthanide elements require higher pressure to crystallize RB12, in situ X-ray diffraction experiments reveal that cerium dodecaboride crystallizes at 26 GPa, which is significantly lower than that required to form the heavier praseodymium dodecaboride (35 GPa). In addition to the lower formation pressure, an anomalous volume reduction is also observed in CeB12, which can be explained by a valence fluctuation between Ce3+ and Ce4+ indicated by X-ray absorption near-edge structure measurements. A polyhedral coordination change from a truncated cube in RB6 to a truncated octahedron in RB12 and associated shortening of the R–B bond length result in an increase in bulk modulus and hardness.

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