Publication date: 21st July 2025
The catalytic activity of exsolved particles is strongly linked to their size and population. However, which parameters affect particle size as well as how this size in turn affects other properties of the exsolved particles is often only poorly understood.
In this contribution, we explore the interplay between the size of exsolved particles and their re-dissolution behavior using a novel approach that allows for the control of the sample’s oxygen activity under Ultra-High Vacuum (UHV) conditions. Utilizing a Solid Oxide Cell (SOC) like design, we can precisely control the oxygen activity in the working electrode by applying a bias relative to an oxygen ion buffering counter electrode, while excluding any effects of gas phase adsorbates. Applying this Electrochemical oXygen Activity ConTrol (EXACT), SrTi0.3Fe0.7O3-δ (STF) was repeatedly reduced and oxidized at 600 °C while the exsolution behavior was monitored via X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). Simultaneously, oxygen stoichiometry changes were tracked by coulometry to correlate surface processes with changes of the bulk material.
With this method, we have achieved the in-situ observation of the formation and growth of Fe particles upon reduction and the complex Fe particle re-oxidation behavior. We find that repeated oxidation and reduction (redox-cycling) enhances particle agglomeration and that the resulting change in particle size alters the re-dissolution behavior. While re-dissolution is observable for small particles, larger particles get oxidized without re-incorporation into the perovskite lattice at the investigated temperature. Overall, we can show that the exact voltage program for exsolution formation can strongly influence the properties of the exsolved particles.
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