Defect accumulation in swift heavy ion-irradiated CeO2 and ThO2

Abstract

Neutron total scattering was used to investigate defect accumulation mechanisms in CeO₂ and ThO₂ irradiated with 2.2 GeV Au ions. Pair distribution function (PDF) analysis was applied to characterize the local structural evolution and irradiation-induced defects as a function of irradiation fluence. CeO₂ exhibits a greater amount of disorder than ThO₂ under the same irradiation conditions. The local structures of the two materials evolve differently as a function of ion fluence, even if similar defects are produced. The PDF analysis indicates that oxygen dimer and/or peroxide defects with 〈O–O〉 distances of ∼1.45 Å are formed in CeO₂, while irradiation-induced defects in ThO₂ result in a change in the mean O–Th–O bond angle and a distortion of local ThO₈ polyhedra. Understanding how bound oxygen defects, such as peroxide, affect bulk oxygen transport in CeO₂ will aid in better predicting and improving properties of fluorite structure materials for fast ion conductor applications.