Date of Award
Doctor of Philosophy
Maik K. Lang
William J. Weber, Brian D. Wirth, Steven J. Zinkle
Lanthanide and actinide oxides, such as CeO2 [cerium dioxide], ThO2 [thorium dioxide], and UO2 [uranium dioxide], are attractive candidates for various energy-related applications such as nuclear fuel and electrolytes for solid oxide fuel cells owing in part to the resiliency of their bulk structures at room temperature up to near-melting temperatures. These materials exhibit broad regimes of phase stability under various extreme conditions including high temperature, pressure, and/or energetic ion irradiation. Upon modification from external perturbation (e.g., ion irradiation) or chemical changes (e.g., doping or oxidation), these fluorite-structured oxides incorporate large concentrations of point defects, which can agglomerate and result in complex microstructures that can severely impact component performance. The final state of defect arrangements is governed by unique interactions among the various vacancies, lanthanides, actinides, oxygens, and dopant atoms. This work investigates short-range atomic disorder in swift heavy ion-irradiated CeO2 [cerium dioxide] and ThO2 [thorium dioxide], oxidized UO2 [uranium dioxide], and lanthanide-doped UO2 [uranium dioxide] systems in order to understand how changes in local atomic arrangements correlate to bulk structural modifications and degradation of key material properties. Detailed structural analyses revealed that defect complexes, mostly small oxygen clusters, form in all fluorite-structured oxides after high energy ion irradiation, oxidation, and chemical doping. A number of computational studies have shown that these types of defect agglomerates can exhibit diffusion pathways much faster than isolated point defects. Accurate characterization and understanding of defect cluster stability and migration mechanisms will therefore enable better bulk property predictions that are critical to engineering improved fluorite-structured materials for energy applications.
Palomares, Raul Irvin, "Probing Point Defects in Fluorite-Structured Actinide and Analogue Oxides. " PhD diss., University of Tennessee, 2018.
Available for download on Wednesday, May 15, 2019