Swift heavy ion‐induced defect formation and electronic structure evolution in Zr‐doped CeO ₂ (Ce _0.8 Zr _0.2 O ₂ )

Abstract This study investigates the effects of 100 MeV iodine ion irradiation on zirconia‐doped ceria (Ce 0.8 Zr 0.2 O 2 ) to simulate fission fragment damage in nuclear fuel at fluences up to 5 × 10 13 ions/cm 2 . X‐ray photoelectron spectroscopy confirms the partial reduction of Ce 4+ to Ce 3+ and Zr 4+ to Zr 3+ /Zr 2+ , driven by irradiation‐induced charge trapping and stabilized by oxygen vacancies. These localized electrons distort the lattice, forming small polarons that govern the redox equilibrium and contribute to defect tolerance. UV–Vis diffuse reflectance spectroscopy confirms narrowing of the band gap (3.42–2.85 eV) and increase in Urbach energy from 0.93 to 1.85 eV confirmed enhancement of electronic disorder and band tailing. Photoluminescence measurements reveal a progressive quenching of emission intensity with increasing fluence, associated with nonradiative recombination via polaron‐stabilized defect states. The combined spectroscopic results suggest that both electronic excitation and nuclear energy loss induce a synergistic mechanism involving polaron formation and oxygen Frenkel pair creation. This dual pathway enables defect accommodation without structural collapse. These results demonstrate that Ce 0.8 Zr 0.2 O 2 resists amorphization through a balance of irradiation‐induced redox activity and native nonstoichiometry, making it a strong candidate for radiation‐resistant ceramics in nuclear and aerospace applications, and a mechanistic model for defect‐tolerant oxides.