Advanced electron microscopy study of structural and electronic properties of charged ordered manganites

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Charge ordered manganites represent an extremely interesting material system, where the interplay of four degrees of freedom (lattice, orbital, charge and spin) results in fascinating transport properties such as metal-insulator transitions in external fields. Up to now, neither the mechanisms of the phase transitions nor the detailed structures of the various phases are well understood. Actual experiments and theoretical ideas suggest that electronic phase separation with a coexistence and competition of different electronic ground states could govern the insulator-metal transition in external fields. In this project we will focus on the Pr1-xCaxMnO3 compound (0.25 < x < 0.5) which shows a multitude of switching behavior in external fields (magnetic, electric, photonic and strain) with huge resistance changes of up to seven orders of magnitudes. We will address several unsolved questions, i.e. the type of charge and orbital ordering, their connection to atomic structure, the formation of ordering domains, the presence of electronic phase separation and the influence of grain boundaries. For the investigations, advanced methods of transmission electron microscopy (TEM) and insitu TEM measurements of the insulator-metal transition in external fields will be applied.