Defect-controlled transport properties of non-stoichiometric and ion-irradiated Ceria

The transport properties of cerium dioxide (CeO₂), a surrogate for UO₂ nuclear fuel, were investigated as a function of defect structure induced by controlled reduction and ion irradiation. Non-stoichiometric ceria (CeO₂₋ₓ, x up to 0.22) was synthesized via reducing annealing, and its thermal and electrical properties were measured over a wide temperature range. Thermal conductivity decreases with increasing oxygen vacancy concentration due to enhanced phonon scattering, consistent with a modified Callaway model. In contrast, electrical conductivity increases by several orders of magnitude, governed by small-polaron hopping between Ce3 + /Ce4 + sites. Ion irradiation (600 keV Kr) further modifies electron transport behavior, producing a highly conductive near-surface region. Radiation-induced electrical degradation (RIED) is observed, with conductivity increasing with fluence and irradiation temperature. A model linking oxygen depletion to bandgap narrowing is proposed to describe the irradiation-induced conductivity evolution. These results demonstrate that defect engineering via reduction and irradiation provides a powerful route to tune transport properties in fluorite oxides and offers insight into defect-controlled behavior in nuclear fuel materials.