ヴァレンスの不安定性,相変化,およびYbGaGeシステムの5Kでの急激な格子膨張
Serena Margadonna1, Kosmas Prassides, Andrew N Fitch
1Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK. sm413@cam.ac.uk
Journal of the American Chemical Society
|April 9, 2004
まとめ
混合バレンスのYbGa1.05Ge0.95は,5Kでの突然のYbバレンスの移行により負の熱膨張を示します. 高温は構造的障害と最終的な崩壊につながります.
科学分野:
- マテリアルサイエンス 材料科学
- 凝縮物質物理学 凝縮物質物理学
- 固体化学 固体化学
背景:
- 混合バレンスの化合物は,複雑な電子的および構造的性質を示します.
- 層状の材料は,ユニークな熱膨張特性を提供します.
- イテルビウム (Yb) ベースの化合物は,バレンスの変動があることが知られている.
研究 の 目的:
- 3-1123 K. から YbGa1.05Ge0.95 の熱膨張を調査する.
- 温度による相変化や構造変化を特徴付ける.
- 物質の振る舞いにおけるYbバレンスの状態の役割を理解する.
主な方法:
- 粉末シンクロトロンX線微分法を用いた.
- 温度に依存する測定は,広い範囲 (3-1123 K) で行われました.
主要な成果:
- 5Kで,負の熱膨張を持つ突然の同対称相移行が観察されました.
- この移行は,Ybのバレンスのシフトによって (+(2 + epsilon) から +2.2 に向かって動いている.
- 1123 Kで,構造は,同対のYbと乱雑なGa/Ge平面を持つAlB2型に変形します.
結論:
- Ybのバレンスの状態は,YbGa1.05Ge0.95.5の熱膨張に大きく影響する.
- この材料は,低温で独特の負の熱膨張行動を示しています.
- 高温構造の不安定性と崩壊が観察される.
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