硬い酸化物が大きく膨張する新現象を発見 — 結晶の基本骨格と化学組成を保ったまま、原子の並び方が変わることで「戻らない巨大膨張」を実現 —

2026-06-01 物質・材料研究機構

図: 加熱によりルテニウム原子の配置が変わり、結晶の基本骨格を保ったまま体積が増加する模式図。左から右へ、加熱に伴う変化を示す。赤いほど、ルテニウム原子がその位置を占める割合が高いことを示す。冷却後も体積は元に戻らず、膨張した状態が保たれる。なお、格子サイズの変化は視認性のため実際より強調して示している。

＜関連情報＞

• https://www.nims.go.jp/press/2026/06/202606010.html
• https://pubs.acs.org/doi/10.1021/jacs.6c07579

高密度酸化物における構造的フラストレーションの解放による巨大格子膨張 Giant Lattice Expansion through Structural Frustration Release in a Dense Oxide

Zhijun Li,Hongbo Yuan,Alexei A. Belik,Terumasa Tadano,Yoshihiro Tsujimoto,and Kazunari Yamaura
Journal of the American Chemical Society  Published: May 20, 2026
DOI:https://doi.org/10.1021/jacs.6c07579

Abstract

Large lattice responses in dense inorganic oxides are typically driven by structural phase transitions or redox processes that alter the crystal symmetry or composition. Here, we identify a distinct mechanism for such responses: giant lattice expansion through symmetry-preserving cation redistribution in a metastable, structurally frustrated, dense oxide. High-pressure-quenched Ba₄Ru₃O₁₂ undergoes an irreversible volumetric expansion of 4.4% between 450 and 650 K while retaining R3̅m symmetry and oxygen stoichiometry. High-resolution synchrotron diffraction reveals cooperative redistribution of Ru within face-sharing RuO₆ trimers, directly linking the intratrimer cation configuration to the lattice volume. Thermogravimetric, transport, and magnetic measurements exclude decomposition, redox processes, and electronic or magnetic phase transitions. First-principles calculations show that compression stabilizes a low-volume cation configuration, which is retained after recovery to ambient pressure and relaxes upon heating through intratrimer cation exchange. Together, these results establish symmetry-preserving cation redistribution as a mechanism for giant lattice responses in dense oxides and identify metastable frustrated configurations as a route to large structural responses without symmetry-breaking or compositional change.