Slovenčina
Praktické cvičenia z röntgenovej difraktometrie II
E-book
E-book
Solving crystal structures is the royal discipline of X-ray crystallography. Its primary task, with the exception of defects, is to describe the atomic structure of the motif that, by its repetition, fills the volume of the entire crystal or crystalline phase. This task is nowadays more or less routine for single-crystal X-ray diffraction, which can locate hundreds to thousands of non-hydrogen atoms in large unit cells. However, in real practice, we often have material available only in powder form instead of single crystals. Solving the atomic structure from its X-ray diffraction data is non-trivial, mainly because the three-dimensional diffraction space of a single crystal is reduced to one dimension by measuring a large number of randomly oriented microcrystals (crystallites). Therefore, the solution itself requires, in addition to proper measurement methodology, the selection of suitable tools, procedures, and strategies that, through optimization, will lead to the solution and refinement of the given crystalline phase. The current limit of this method is approximately 100 non-hydrogen atoms in the asymmetric part of the unit cell, which, however, is sufficient for most inorganic materials.
The goal of these educational texts is to provide students in the second and third levels of university studies with specific guidance on solving crystal structures from powder X-ray diffraction data. These scripts build upon my first monograph and require practical knowledge of its content. Similar to my previous monograph, I offer solved examples without a deep theoretical introduction, demonstrating procedures and strategies leading to the correct solution of crystalline phases using the freely available GSAS-II program. The examples are arranged from simpler to more complex, and the reader will find many useful pieces of information in the literature references as well as in the comments below the line. Part of these scripts are data intended for your individual practice of the described procedures.
Karel Sakls
