He2+/Xe20+ irradiation damage effects of Sr0.5Zr2(PO4)3–(Ce, Nd)PO4 composite ceramics

Composite ceramics, which integrate the advantages of multiple crystal structures, are considered promising candidates for nuclear waste forms capable of simultaneously immobilizing various radionuclides. In this study, a series of 0.4Sr 0.5 Zr 2 (PO 4 ) 3 –0.6Ce 1- x Nd x PO 4 composite ceramics were designed to co-immobilize the simulated fission product Sr and actinide surrogates Ce and Nd. These composite ceramics exhibited homogeneous phase distribution and high densification. Among them, the irradiation-induced damage in the representative sample, 0.4Sr 0.5 Zr 2 (PO 4 ) 3 –0.6Ce 0.6 Nd 0.4 PO 4 composite ceramic, was systematically evaluated under both He 2+ and Xe 20+ irradiation. After He 2+ irradiation, the crystallinity of the irradiated layer was retained despite the disruption of Raman-active bonding groups by point defects. Notably, the Ce 0.6 Nd 0.4 PO 4 phase exhibited significantly higher resistance to He 2+ irradiation than the Sr 0.5 Zr 2 (PO 4 ) 3 phase, as confirmed by GIXRD patterns and geometric phase analysis (GPA). Furthermore, fragmentation of Ce 0.6 Nd 0.4 PO 4 grains was observed, which was attributed to defect accumulation, the thermal spike effect, and the thermal expansion mismatch. Following Xe 20+ irradiation, the irradiated layer of the composite ceramic exhibited reduced crystallinity without complete amorphization, while the Raman-active bonding groups remained largely intact. Additionally, pore formation at grain boundaries was likely caused by the segregation and accumulation of irradiation-induced defects.