Ion irradiation-driven unit-cell expansion and strain accumulation behavior in magnesium oxide

Ceramic oxides offer a range of advantageous characteristics for withstanding intense mixed radiation fields, and consequently, interest has grown in exploring their behavior for nuclear applications such as fuel matrices and waste forms. In this study, magnesium oxide (MgO) was irradiated with ions of varying species, energies, and fluences, and the resulting structural modifications were characterized using synchrotron-based x-ray diffraction (XRD) combined with grazing-incidence XRD. Across all irradiation conditions, unit-cell expansion was observed, increasing with fluence. The magnitude of expansion was most significant for ions that primarily lose energy through nuclear interactions and lowest for those dominated by electronic excitations, spanning nearly two orders of magnitude. Under highly ionizing conditions, lattice swelling was reduced, but microstrain accumulation was enhanced, suggesting that defects are more localized and contribute less to long-range structural changes. These findings reveal the distinct roles of nuclear and electronic energy loss in defect formation and provide mechanistic insight into radiation-induced modifications in MgO, with implications for the design of radiation-tolerant materials for advanced nuclear technologies. Finally, the framework we present—incorporating an irradiation matrix that spans both nuclear and electronic energy loss dominated regions, strengthened by advanced quantitative XRD characterization—is widely applicable to the study of defect physics in polycrystalline materials.