「中性子カメラ」方式で原子スケールの活動を一瞬でとらえる(‘Neutron camera’ method captures atomic-scale activity in a flash)

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2023-03-21 オークリッジ国立研究所(ORNL)

中性子をカメラのように使用する新しい方法で、材料の局所構造を詳細かつリアルタイムで研究することができるようになりました。この研究は、エネルギー材料で局所的な構造と全体的な構造を調和させるための標準的な方法になる可能性がある中性子のユニークな使用法を示しています。また、熱電効果の背後にある重要なメカニズムも明らかにしました。

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動的結晶構造解析による立方晶GeTeの自発的異方性の解明 Dynamic crystallography reveals spontaneous anisotropy in cubic GeTe

Simon A. J. Kimber,Jiayong Zhang,Charles H. Liang,Gian G. Guzmán-Verri,Peter B. Littlewood,Yongqiang Cheng,Douglas L. Abernathy,Jessica M. Hudspeth,Zhong-Zhen Luo,Mercouri G. Kanatzidis,Tapan Chatterji,Anibal J. Ramirez-Cuesta & Simon J. L. Billinge
Nature Materials  Published:20 February 2023
DOI:https://doi.org/10.1038/s41563-023-01483-7

「中性子カメラ」方式で原子スケールの活動を一瞬でとらえる(‘Neutron camera’ method captures atomic-scale activity in a flash)

Abstract

Cubic energy materials such as thermoelectrics or hybrid perovskite materials are often understood to be highly disordered1,2. In GeTe and related IV–VI compounds, this is thought to provide the low thermal conductivities needed for thermoelectric applications1. Since conventional crystallography cannot distinguish between static disorder and atomic motions, we develop the energy-resolved variable-shutter pair distribution function technique. This collects structural snapshots with varying exposure times, on timescales relevant for atomic motions. In disagreement with previous interpretations3,4,5, we find the time-averaged structure of GeTe to be crystalline at all temperatures, but with anisotropic anharmonic dynamics at higher temperatures that resemble static disorder at fast shutter speeds, with correlated ferroelectric fluctuations along the <100>c direction. We show that this anisotropy naturally emerges from a Ginzburg–Landau model that couples polarization fluctuations through long-range elastic interactions6. By accessing time-dependent atomic correlations in energy materials, we resolve the long-standing disagreement between local and average structure probes1,7,8,9 and show that spontaneous anisotropy is ubiquitous in cubic IV–VI materials.

1700応用理学一般
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