Thermally activated damage recovery in ion-irradiated Gd2Ti2-yZryO7 pyrochlore

Abstract

Ionizing events having a wide variety of radiation-induced effects can radically affect the kinetics of defect production or structural transformation in the pyrochlore structured oxides (A₂B₂O₇). Therefore, a thorough understanding of the kinetics associated with cation ordering and disordering is required for various technological applications. The structural responses of Gd₂Ti_2-yZr_yO₇ (y = 0.4, 1.2, 1.6) pyrochlore series irradiated by 120 MeV Au⁹⁺ ions were investigated using in situ synchrotron x-ray diffraction (SR-XRD), micro-Raman spectroscopy, and scanning electron microscopy (SEM). Each pyrochlore composition irradiated at the highest fluence, where structural modifications occur, was subsequently isochronally annealed from room temperature to 1000°C. The SR-XRD results indicate that Ti-rich composition (y = 0.4) retains its pre-irradiated pyrochlore structure (Fd$\overline{3}$m) at 1000°C. In contrast, Zr-rich compositions exhibit recrystallization to an intermediate defect-fluorite phase (Fm$\overline{3}$m) above 500°C, and the pre-irradiated pyrochlore superstructure does not recover even on annealing at 1000°C. These results reveal that recrystallization temperature strongly depends on the accumulated radiation damage, generally described with the cationic radius ratio (r_A/r_B). Thus, investigation of the thermal annealing behavior of irradiated pyrochlores helps better understanding the general mechanisms of radiation damage and recovery of pyrochlores, which is important for their use in nuclear applications.