Using electron microscopy to complement X-ray powder diffraction data to solve complex crystal structures

摘要

High-resolution X-ray powder diffraction and electron microscopy techniques yield remarkably complementary information for crystal structure determination. By combining the two types of data, structures of polycrystalline materials that resist solution by more conventional methods can be tackled. In particular, crystallographic phase information extracted either from high-resolution transmission electron microscopy (HRTEM) images or from precession electron diffraction (PED) data has proven to be extremely useful in such cases. PED data can also be used to identify weak reflections in the diffraction pattern, and this information, in turn, can be exploited to improve the partitioning of the intensities of reflections that overlap in the powder diffraction pattern. The dual-space (diffraction and real space) structure determination programs Focus and _pCF have been shown to be especially well-suited for combining the two different types of data. The power of this approach is illustrated with the details of the solutions of the structures of TNU-9, IM-5 and SSZ-74, the three most complex zeolite framework structures known.