Thermodynamic and structural evolution of Dy₂Ti₂O₇ pyrochlore after swift heavy ion irradiation

Utilizing a combined approach of high temperature calorimetry and neutron total scattering, we obtained critical insights into the energetics and annealing of radiation damage in swift heavy ion irradiated Dy₂Ti₂O₇ pyrochlore. Oxide melt solution calorimetry reveals that the radiation amorphized Dy₂Ti₂O₇ is destabilized by 243 kJ/mol compared to fully ordered, crystalline pyrochlore. Differential scanning calorimetry of the amorphized sample shows a rapid exothermic event starting at 1063 K, which, based on neutron structural analysis, is related to recrystallization. The heat release on annealing to 1473 K, –137 kJ/mol, is only about half of the total energetic difference between the ordered crystalline and amorphized samples, despite the apparent recovery of long-range pyrochlore-like ordering. Detailed neutron structural analysis confirms the persistence of residual damage in the 1473 K annealed sample. This metastability is attributed to local disorder in the form of weberite-like short-range domains in the recrystallized material. The annealing of radiation damage appears to be a complex, multistep process with decoupled short- and long-range damage recovery. Heating well above the initial recrystallization temperature does not erase all the damage, which may have important implications for the use of pyrochlores as nuclear waste forms.