EuroMinScI_Ordnungsphänomene von Ionen in Mineralen

The project aims at the elucidation of cationic or anionic order in minerals and the relation of the degree of ordering to the formation conditions and thermodynamic history. The main computational aid for the realisation of these studies will be ab-initio calculations within the framework of density functional theory. This approach gives information about the energies and electronic structures of distinct structural configurations from first principles. As a special tool, the superspace formalism (originally derived for aperiodic structures) will be used to deduce possible ordering schemes for the different types of ions. Furthermore, we will explore the potential of the superspace approach for the general description of modular structures. We will focus on three relevant mineralogical questions: F/OH and Mg/Al ordering in phlogopites, the elucidation of structural stabilities and polymorphism in nepheline, and the ordering of cations in the modular structures of sulphosalts. These three families of compounds will serve as model systems to test our newly developed theoretical approaches. The theoretical studies will be combined with detailed experimental investigations concerning natural and synthetic samples of phlogopites, nephelines, and sulphosalts. The main experimental technique will be powder and single crystal X-ray diffraction (including synchrotron radiation) both under ambient and extreme conditions. Special importance will be given to the study of modulated structures, polytypic compounds, and intergrown phases. The necessary computational tools and software for the treatment of these problems will be developed. Solid state NMR spectroscopy will be employed to obtain complementary information on local environment of ions and the formation of ionic clusters. The results from the coordinated experimental and theoretical studies in this project will serve a solid basis for the development of novel approaches to investigate other types of mineral systems in the future.