Über einen Beitrag der Quantenmechanik zur modernen Strukturaufklärung intermetallischer Phasen

In this thesis, a method for high-resolution structural analysis of intermetallic phases by quantum chemical calculations in combination with solid-state NMR spectroscopy and X-ray diffraction experiments is described. The results of quantum chemical calculations form the focus of the presented work. The theoretical part in the application of the presented methodology is described particularly. Simply constructed Zintl phases and Zintl-like compounds are studied to validate the methodological interplay. The transfer to disordered intermetallic systems, in which different types of point defects are present form the main part of this thesis. The investigation of local arrangements on atomic scale is based on quantum-chemical calculation of structural parameters like lattice parameters and displacement vectors. In addition, the formation energies of different structural motifs are compared. The quantum-chemical calculation of NMR coupling parameters allows a direct comparison with values determined by NMR spectroscopy and thus links theoretical and experimental results. Several examples demonstrate that the presented method expands the classical structure analysis.For the ternary alkali metal silicides, the local ordering of the cations reported in experiments is confirmed by calculated formation energies for different arrangements. Calculation of the chemical shift resulted in an unambiguous assignment of an experimentally observed 29Si signal contribution to a distinct atom. Studying the solid solution Sr1-xBaxGa2, the influence of substitutional disorder in a layered structure was discussed. For three-dimensionally linked anionic sublattice of the BaAl4 structure type, the calculated formation energies and lattice parameters proved a preferred site occupation for the Al atoms in the solid solutions Sr(Al1-xGax)4 and Sr(Al1-xGax)4. Investigations on super lattice structures of Cu1-xAl2 provided a data basis for the analysis of the orientation-dependent electric field gradient of Al to support the analysis and interpretation of NMR experiments on a Cu1-xAl2 single crystal. Based on the reported results, the investigated types of local atomic arrangements can be interpreted as 3-dimensional extended areas in crystalline materials. In these areas changes in the local environment of the atoms occur for the investigated substances and can be resolved by the presented methodological interplay. The degree of change depends on the structure under investigation and the similarity of the exchanged particles in a chemical sense. With respect to the obtained results, a transfer of the presented methodological interplay to more complex systems is possible