Comprehensive characterization of irradiation induced defects in ceria: Impact of point defects on vibrational and optical properties

Validation of multiscale microstructure evolution models can be improved when standard microstructure characterization tools are coupled with methods sensitive to individual point defects. We demonstrate how electronic and vibrational properties of defects revealed by optical absorption and Raman spectroscopies can be used to compliment transmission electron microscopy (TEM) and x-ray diffraction (XRD) in the characterization of microstructure evolution in ceria under non-equilibrium conditions. Experimental manifestation of non-equilibrium conditions was realized by exposing cerium dioxide (CeO2) to energetic protons at elevated temperature. Two sintered polycrystalline CeO2 samples were bombarded with protons accelerated to a few MeVs. These irradiation conditions produced a microstructure with resolvable extended defects and a significant concentration of point defects. A rate theory (RT) model was parametrized using the results of TEM, XRD, and thermal conductivity measurements to infer point defect concentrations. An abundance of cerium sublattice defects suggested by the RT model is supported by Raman spectroscopy measurements, which show peak shift and broadening of the intrinsic T-2g peak and emergence of new defect peaks. Additionally, spectroscopic ellipsometry measurements performed in lieu of optical absorption reveals the presence of Ce3+ ions associated with oxygen vacancies. This work lays the foundation for a coupled approach that considers a multimodal characterization of microstructures to guide and validate complex defect evolution models. Published under an exclusive license by AIP Publishing.

Automated summary

Validation of multiscale microstructure evolution models can be improved by coupling standard microstructure characterization tools with methods sensitive to individual point defects. In this study, optical absorption and Raman spectroscopies were used to characterize microstructure evolution in ceria under non-equilibrium conditions, in conjunction with transmission electron microscopy and x-ray diffraction. Experimental manifestation of non-equilibrium conditions was achieved by exposing cerium dioxide (CeO2) to energetic protons at elevated temperature. The results demonstrated the presence of extended and point defects in the microstructure, and a rate theory model was employed to infer the concentration of point defects. Raman spectroscopy measurements supported the abundance of cerium sublattice defects suggested by the model. This work lays the foundation for a coupled approach to guide and validate complex defect evolution models.