A combination of in situ and ex situ transmission electron microscopy (TEM) experiments was used to study the evolution of defect clusters during implantation of Xe at the energy of 700keV. Xenon has been implanted into CeO 2 and Ce/LaO 2 single crystal thin films up to doses of 1×10 17 ions/cm 2 at room temperature and 600°C. The evolution of microstructure, especially the formation of solid-state precipitates, during irradiation is found to be a function of material composition, irradiation dose and irradiation temperature. The precipitates are either aggregated Xe in the solid state or metallic Ce due to the active redox reaction in CeO 2 and Ce/LaO 2 . Further investigations with the help of X-ray techniques will be carried out in the future.