Local atomic-scale structure of ionic conducting oxides from atom probe tomography

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Atomic arrangements, potential energy landscapes and ion conductivities of solid state materials are intimately interconnected. The chemical identity, electronic structure and local arrangement of atoms in a solid prescribes the potential energy landscape, and this in turn controls the energetics and kinetics of the mobile species. Their motion changes the atomic structure and shifts the energy landscape, leading to a coupled and dynamic state. Insights into the energy landscape can be gained from experimental studies of solubilities, segregation coefficients and ion conductivity and diffusion. Combined with theory, these studies provide the basis for developing a complete picture of the dynamic coupling between atomic scale structure and mobility. The goal of the ELSICS Research Unit is to apply this methodology to gain a mechanistic understanding of ion mobility in several model technologically relevant ion conductors.Atom probe tomography (APT) has emerged over the last several decades as a powerful method to obtain local, atomic-scale information of three-dimensional element distributions in materials. Even challenging materials such as electrically insulating, ionic conducting, and brittle oxides have been successfully analysed using laser excitation and by careful optimization of measurement parameters and reconstruction algorithms. In the context of the proposed Research Unit, APT will be combined with SIMS (P1 Weitzel), NMR (P2 Vogel), and TEM (P4 Jooss) to determine concentration gradients and atomic scale structure of several ion conductors, from which site energy distributions and ion conductivity will be predicted by theory (P5 Maass and P6 Jacob) and compared with measurements of ion motion with CAIT (P1 Weitzel) and NMR (P2 Vogel). Very recently, atom probe methods have also been used to gain information about individual ion dynamics using selective field evaporation and subsequent APT. The possibilities and potential of this method to detect local migration paths in ion conductors will also be explored.