Structure determination of modulated structures by powder X-ray diffraction and electron diffraction

Abstract

Since the first discovery and description of materials, whose structures are not periodic, enormous efforts have been made in studying these aperiodic structures. With these efforts including the development of superspace group theory and structure solution algorithms, numerous incommensurately modulated structures which represent the vast majority of known aperiodic structures have been determined with single crystal X-ray diffraction data. However, the determination of modulated structures remains very difficult for polycrystalline materials. Powder X-ray diffraction and electron microscopy techniques yield remarkable information for polycrystalline materials. By combining these two methods, modulated structures of polycrystalline materials that impede solution by conventional methods can be determined. The power of these methods is illustrated with the examples of the determination of modulated structures of polycrystalline materials.

Electron diffraction methods have made enormous progress over the last decade. The determination of some structures using solely electron diffraction (ED) techniques, or in combination with powder X-ray diffraction (PXRD) has now become convenient. However, the analysis of complex structures is far from routine even with high-quality single crystal X-ray diffraction (SXRD) data, and the structure analysis of complex structures from ED and/or PXRD data is more challengeable. The international collaborative researching projects of our group and of Lukáš focus on synthetizing some new compounds which have some interesting functions and developing routine PXRD and ED methods to simplify the determination of complex structures of these new compounds.