負の熱膨張は,電荷の同時移転と極性-非極性移行によって引き起こされる
Takumi Nishikubo1, Yuki Sakai1,2, Kengo Oka3
1Laboratory for Materials and Structures , Tokyo Institute of Technology , 4259 Nagatsuta, Midori-ku , Yokohama , Kanagawa 226-8503 , Japan.
Journal of the American Chemical Society
|November 19, 2019
まとめ
負の熱膨張は,ビスムートニッケル酸化鉄で,電荷の移転と相変化により観察された. この新しいBiNi1-xFexO3の発見は,新しい材料の可能性を提供します.
科学分野:
- 材料科学
- 固体化学
- クリスタルグラフィー
背景:
- 負の熱膨張 (NTE) は,材料が加熱すると収縮する性質です.
- NTEの背後にあるメカニズムの理解は,高度な機能的な材料の開発に不可欠です.
- ビスマウト基酸化物は,その多様な構造的および電子的性質で知られています.
研究 の 目的:
- BiNi1-xFexO3における負の熱膨張の発生とメカニズムを調査する.
- 構成,構造,熱膨張特性との関係を調べる
- この物質システムにおける NTE を誘発する同時メカニズムを特定する.
主な方法:
- 異なる鉄含有量 (0.25 ≤ x ≤ 0.5) のBiNi1-xFexO3化合物の合成
- 結晶構造と相変化を決定するために,X線 difraktion (XRD) と温度依存構造分析を行う.
- 電荷分布と電子状態の分析
主要な成果:
- BiNi1-xFexO3 (0.25 ≤ x ≤ 0.5) のNTEの最初の観測は,同時に電荷の移転と極性-非極性移行によって引き起こされた.
- 特定の電荷分布 (Bi3+/Bi5+/Ni2+/Fe3+) を有する低温極相 (空間群R3c) の識別.
- 加熱時の体積減少は,Ni2+が減少したため,xが増加するにつれて減少し,組成独立の~2%の体積減少は,極性-非極性移行と関連していました.
結論:
- 同時に電荷の移転 (Bi5+-Ni2+) と極性-非極性移行は,BiNi1-xFexO3におけるNTEの重要なメカニズムである.
- 負荷移転によるNTEの範囲は組成に依存し,相変化による貢献は組成に依存しない.
- この研究は 適した負の熱膨張特性を持つ材料を 設計するための新しい道を示しています
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