In situ total scattering studies: Formation mechanisms of ternary multiferroic bismuth ferrates

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Advanced nanoscale materials are frequently synthesized by hydrothermal/solvothermal or sol-gel methods since their particle/crystallite dimensionality, crystallinity and morphology can precisely be controlled. The detailed understanding of these synthesis routes is crucial since it will take the material science community a major step towards the goal of 'materials by design'. A prerequisite to reach this target is the understanding of the complete formation mechanisms all the way from the precursors in solution over the formation of nano-building blocks to the fully crystallized structures. The monitoring of crystal formation in situ is possible via X-ray diffraction techniques using subsequent model calculations. Detailed atomistic information on the structural changes taking place during the progression of the synthesis with a time resolution on the seconds scale or less can be obtained if scattering data at a high-brilliance synchrotron source are collected. By the combination of the Rietveld method and the Pair distribution function (PDF)-technique detailed information can be gained about the long-range order of the atoms from the Bragg reflections and short-range order from the broad, less distinct features in the X-ray diffractogram, respectively. Within the scope of this project, the formation mechanisms of the ternary bismuth ferrate Bi2Fe4O9 will be studied in detail. In this regard, it should be clarified what causes the change of crystallization paths and kinetics from the very beginning of the nucleation, if different synthesis parameters are used (e.g. pH and type of complexing agent) and how the structure builds up from nano-building blocks in general. Furthermore, the formation mechanisms of isostructural Bi2Ga4O9 and Bi2Al4O9 as well as closely related Bi2Mn4O10 will be investigated and compared to that of Bi2Fe4O9. This will help to answer the question, if the formation mechanisms are fundamentally different for different chemical species in the synthesis of advanced nanostructured materials.