Batuk Dmitry, Batuk Maria, Abakumov Artem M, Hadermann Joke
EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
Acta Crystallogr B Struct Sci Cryst Eng Mater. 2015 Apr;71(Pt 2):127-43. doi: 10.1107/S2052520615005466. Epub 2015 Mar 31.
The crystal structure solution of modulated compounds is often very challenging, even using the well established methodology of single-crystal X-ray crystallography. This task becomes even more difficult for materials that cannot be prepared in a single-crystal form, so that only polycrystalline powders are available. This paper illustrates that the combined application of transmission electron microscopy (TEM) and powder diffraction is a possible solution to the problem. Using examples of anion-deficient perovskites modulated by periodic crystallographic shear planes, it is demonstrated what kind of local structural information can be obtained using various TEM techniques and how this information can be implemented in the crystal structure refinement against the powder diffraction data. The following TEM methods are discussed: electron diffraction (selected area electron diffraction, precession electron diffraction), imaging (conventional high-resolution TEM imaging, high-angle annular dark-field and annular bright-field scanning transmission electron microscopy) and state-of-the-art spectroscopic techniques (atomic resolution mapping using energy-dispersive X-ray analysis and electron energy loss spectroscopy).
即使使用成熟的单晶X射线晶体学方法，调制化合物的晶体结构解析也常常极具挑战性。对于无法制备成单晶形式、只能获得多晶粉末的材料来说，这项任务变得更加困难。本文表明，透射电子显微镜（TEM）和粉末衍射的联合应用是解决该问题的一种可行方案。以由周期性晶体学剪切面调制的阴离子缺陷钙钛矿为例，展示了使用各种TEM技术可以获得何种局部结构信息，以及如何将这些信息应用于基于粉末衍射数据的晶体结构精修中。讨论了以下TEM方法：电子衍射（选区电子衍射、进动电子衍射）、成像（传统高分辨率TEM成像、高角度环形暗场和环形亮场扫描透射电子显微镜）以及最新的光谱技术（使用能量色散X射线分析和电子能量损失谱进行原子分辨率映射）。
