Charge attachment induced transport (CAIT) studies of energy landscapes in ion conducting solids (Quantification of populated site energy distribution in amorphous and crystalline materials)

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The potential energy landscape of mobile ions in solid-state materials and the atomic scale structure are intimately interrelated and determine the function, e.g. ion transport. Within this project P1 of the research unit FOR5065 the potential energy landscape of ion conducting solids is investigated by a combination of the charge attachment induced transport (CAIT) and the time-of-flight secondary ion mass spectrometry (ToF-SIMS) techniques. The goal is the determination of site energy distributions in the solid as a function of the structural order, i.e. for amorphous, crystalline and bicrystalline states. As materials with model character the focus will be on lithium borates and strontium titanate and derivatives thereof. Within the CAIT technique alkali ions are attached to the samples leading to a charging up of the surface, the concomitant gradients of the electrochemical potential and the transport of the respective charge carrier within the sample. Foreign ions from the ion beam deplete and replace native ions in the direction of transport inside the sample causing concentration depth profiles. The concentration profiles are frozen and subsequently quantitatively analyzed by ToF-SIMS and modelled by means of the Nernst-Planck-Poisson NPP) transport theory. Initially the analysis is elaborated to yield experimental site energy distributions (SED) and populated parts of the SED (PSED). These are transferred to collaboration partners from theory (P5 Maass and P6 Jacob). Later, projects P5 and P6 will return theoretical SED and PSED as input for the NPP analysis within this project P1 (Weitzel). In parallel, the samples are also transferred to collaboration partner Volkert (P3) for atom probe tomography (APT) and Jooss (P4) for transmission electron microscopy (TEM) for detailed atomistic structure analysis. Furthermore, the samples are transferred to the Vogel (P2) group for NMR studies. The latter leads to a distribution of correlation which will be directly compared to the distribution of spatially dependent diffusion coefficients determined within this project.Ultimately, this work is expected to lead to an improved understanding of the potential energy landscape in ion conducting solids and its interrelation with atomistic structure and macroscopic transport function.