外延X射线吸收精细结构和负热膨胀

EXTENDED X-RAY-ABSORPTION FINE STRUCTURE AND NEGATIVE THERMAL EXPANSION

外延X射线吸收精细结构(extended X-ray-absorption fine structure,EXAFS)技术是研究局部结构和动力学的有力工具。它在探讨引起材料负热膨胀(negative thermal expansion,NTE)机理方面能提供详细信息。本文在简要介绍EXAFS后, 对EXAFS和Bragg衍射进行了比较,介绍和比较了具有不同结构的NTE晶体的最新研究结果。在有关NTE研究中,能从EXAFS获得的物理量包括:邻近键的真实膨胀和相关原子振动的各向异性。对现有的结果和仍待展开的某些问题进行了讨论。

Extended X-ray-absorption fine structure （EXAFS） is a powerful probe of local structure and dynamics, and can give original information on the mechanisms at the origin of negative thermal expansion （NTE）. In this paper, after a short introduction to EXAFS and a comparison between EXAFS and Bragg diffraction, the results of some recent studies on NTE crystals of different structures are presented and compared. The physical quantities obtainable from EXAFS, most relevant for NTE studies, are the true nearest-neighbor bond expansion and the anisotropy of relative atomic vibrations. The results up to now obtained, as well as some still open questions, are critically discussed.