Stucture property relations in anion ordered phases

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Materials chemistry depends to a large extent on reliable determination of structures. Crystalline materials are best investigated by diffraction methods. Powder diffraction methods have been improved significantly during the last decade and due to high-resolution diffractometers and advanced data analysis tools are now reliable methods, almost approaching the performance of single crystal diffraction experiments. High temperature diffraction experiments using a variety of reducing, inert and oxidizing atmospheres permit us now to follow solid state reactions with excellent time resolution. These experiments will improve our understanding of solid state reactions and thus will permit to optimize solid state synthesis methods. Rare-earth transition metal oxychloride and reduced rare-earth transition metal oxides are targeted as model compounds for low-dimensional magnetic sublattices. Low-dimensional paramagnetic sublattices are being realized by means of anisotropic magnetic exchange paths due to different anions. The systems under investigation combine mixed anions (oxychlorides) having ordered and disordered anion lattices with single anion lattices (oxides). These model systems provide an opportunity to evaluate the impact of anion ordering on magnetic exchange interactions in extended solids. Crystallographic phase transitions are investigated by diffraction and differential thermal analysis methods. The research program has a large synthetic component combined with the investigation of physical properties. Bulk physical properties and structural details will be correlated in an attempt to identify structure - property relations.