Insights into the Effect of Particle Size on the Low Energy Radiation Response of Ceria

Understanding the radiation tolerance of ceramics against low energy heavy ions is important for evaluating their stability against alpha recoils, which are a significant source of damage for their application as nuclear fuels and/or waste immobilization matrices. Radiation response of ceramics is significantly affected by the particle size and microstructure in addition to their crystalline structure. With this motivation, three different particle-sized CeO2 samples were subjected to irradiation by 400 keV Kr ion at various fluences. The smaller particle-sized samples are found to be more radiation tolerant, which is attributed to the higher prevalence of grain boundaries that act as sinks for the (irradiation-induced) defects. The predominant defects generated in these systems are observed to be Ce3+ and vacancy-related isolated clusters as investigated by Raman spectroscopy and corroborated by X-ray photoelectron spectroscopy and photoluminescence studies. However, in the micron-sized sample, a secondary fluorite-type defective phase appears upon irradiation, as seen from X-ray diffraction, which continually expands with an increase in fluence, unlike the smaller-sized samples. Interestingly, the relative content of reduced Ce (Ce3+/Ce4+ ratio) is observed to be much higher in the smaller-sized samples post-irradiation, making it an important manifestation of irradiation effects in nanoceria. More importantly, the radiation tolerance as a function of particle size in the low energy regime is observed to have an opposite trend to that under high energy heavy ion irradiation, and this comparison has been discussed. CeO2 is also widely employed as the surrogate for PuO2, and the present study thus has significance to self-irradiation of PuO2 as well.