An in-situ electron microscopy study of dual ion-beam irradiated xenotime-type ErPO$_4$

International audience ; Rare-earth phosphates adopting the xenotime (REPO 4 ; RE = Tb − Lu & Y, Sc) structure are proposed as a potential matrix for the confinement of minor actinides. Minor actinides (e.g., Np, Am, Cm) undergo a radioactive decay process in which high-energy recoil atom (70–100 keV) and energetic alpha particles (4.5–5.8 MeV) are produced. In this study, the impact of these energetic decay products on the structure of xenotime-type ErPO 4 has been investigated via high energy dual ion-beam irradiation of ErPO 4 ceramics. Au 2+ (1.5 MeV) and He + (160 keV) ions were used to simulate the effects of recoil atom and α-particles, respectively. Multiple experiments were carried out in which the Au 2+ and He + ions with varying ion-fluences (ions/cm 2 ) and ion-flux (ions/cm 2 /s) were implanted sequentially (Au 2+ followed by He + irradiation) and simultaneously (Au 2+ + He + irradiation) into ErPO 4 ceramics. Sequential ion-irradiation experiments have shown that the xenotime structure was amorphized by Au 2+ ions at a relatively lower ion-fluence (5 × 10 13 ions/cm 2 ) in comparison to the monazite structure. Upon irradiation of the amorphous ErPO 4 with He + ions, recrystallization of the amorphous xenotime due to α-particles was not observed. However, simultaneous ion-irradiation experiments on ErPO 4 showed that the amorphization of the xenotime structure was prevented upon deposition of higher amounts of electronic energy (E electronic ) in the lamella. Likewise monazite samples, the α-healing mechanism was also experimentally demonstrated in synthetic xenotime samples.