Indirect characterization of point defects in proton irradiated ceria

Abstract

A rate theory model informed by multimodal characterization is used to evaluate the concentration of point defects in irradiated materials. Cerium dioxide (CeO2) is used as a model ionic compound, whose cation and anion sublattice point defects evolve independent of each other, but extended defects in the form of dislocation loops retain stoichiometry of the compound. To demonstrate this, we performed extensive measurement of defect evolution in CeO2 exposed to energetic protons at elevated temperature. Two sintered polycrystalline CeO2 samples were irradiated with protons having energies up to 2.5 MeV. Both samples were irradiated at 600°C to a dose of 0.14 dpa, but with different dose rates. These irradiation conditions produced a rich microstructure with resolvable extended defects and a significant concentration of point defects. Dislocation loop density revealed by electron microscopy and lattice constant changes measured by X-ray diffraction (XRD), and mesoscale thermal conductivity measurements were used to parameterize the rate theory model. The model, which includes point defect generation, recombination, and clustering into stoichiometric interstitial loops, suggests a large concentration of cerium vacancies and interstitials is present under these irradiation conditions. This work lays the foundation for expanded multimodal characterization of microstructure, including more direct characterization of point defects using optical spectroscopies.