Wednesday, 4 October 2017: 14:30
Chesapeake 6 (Gaylord National Resort and Convention Center)
The unique chemical properties of cerium dioxide, including the ability to readily alternate between the Ce3+ and Ce4+ oxidation states, creates many potential applications. Electron energy loss spectroscopy (EELS) is frequently used to measure the oxidation state of cerium ions. To that point, acquiring accurate measurements and understanding the context in which they were collected is important for the interpretation and dissemination of results. EELS and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) were used to characterize nanoparticles with different morphologies and sizes. The role of dose rate and the environment in which the sample is measured will be covered, specifically demonstrating how these parameters can greatly influence the outcome of oxidation state measurements recorded by EELS. HAADF-STEM and EELS can be used to observe dynamic microstructural processes. The oxidation and reduction of single cerium dioxide nanoparticles was tracked in situ. Imaging enables high-resolution characterization with temporal resolution on the order of a second. Upon reduction, oxygen vacancies form and order and the particle transitions from the fluorite phase to multiple domains of the sesquioxide (C-Ce2O3) phase. Upon oxidation, spatially-dependent behavior is observed; regions along certain facets oxidize more quickly than others. The physical origin of these observations will be discussed.