Orateur
Description
Understanding how fluorite oxides accommodate irradiation-induced defects is important for the development of radiation-tolerant materials for advanced nuclear systems. In this work, 25 mol% Gd₂O₃-doped CeO₂ nanopowders were synthesized and sintered at 800°C and 1300°C to obtain fluorite microstructures with different grain sizes and investigate their grain-size-dependent response under swift heavy ion (SHI) irradiation. The pellets were irradiated with 100 MeV iodine ions at room temperature to simulate electronic excitation damage caused by fission fragments in nuclear reactor environments. Structural and local electronic modifications were systematically studied using synchrotron GIXRD, Raman spectroscopy, and XANES/EXAFS analyses. Both samples retained the fluorite cubic structure up to the highest fluence of 1×10¹⁴ ions/cm², although the fine-grained sample exhibited comparatively stronger irradiation-induced disorder than the coarse-grained sample. Synchrotron GIXRD revealed lattice distortion, peak broadening, and microstrain accumulation after irradiation. Raman spectroscopy showed broadening and redshift of the Raman-active modes, indicating enhanced oxygen sublattice disorder and defect-complex formation. XANES analysis suggested partial irradiation-induced Ce⁴⁺ to Ce³⁺ reduction, while EXAFS revealed local coordination changes, including Ce–O bond elongation and perturbation of the Gd–O environment associated with oxygen-vacancy-mediated structural relaxation. First-principles GGA–PBE calculations further supported oxygen vacancy stabilization in Gd-doped ceria. These findings provide important insight into defect evolution and local structural relaxation in irradiated fluorite oxides for advanced nuclear applications.