An in-situ electron microscopy study of dual ion-beam irradiated xenotime-type ErPO4

Rare-earth phosphates adopting the xenotime (REPO4; 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 (70e100 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 ErPO4 has been investigated via high energy dual ion-beam irradiation of ErPO4 ceramics. Au2+ (1.5 MeV) and He+ (160 keV) ions were used to simulate the effects of recoil atom and alpha-particles, respectively. Multiple experiments were carried out in which the Au2+ and He+ ions with varying ion-fluences (ions/cm(2)) and ion-flux (ions/cm(2)/s) were implanted sequentially (Au2+ followed by He+ irradiation) and simultaneously (Au2+ + He+ irradiation) into ErPO4 ceramics. Sequential ionirradiation experiments have shown that the xenotime structure was amorphized by Au2+ ions at a relatively lower ion-fluence (5 x 10(13) ions/cm(2)) in comparison to the monazite structure. Upon irradiation of the amorphous ErPO4 with He+ ions, recrystallization of the amorphous xenotime due to aparticles was not observed. However, simultaneous ion-irradiation experiments on ErPO4 showed that the amorphization of the xenotime structure was prevented upon deposition of higher amounts of electronic energy (Eelectronic) in the lamella. Likewise monazite samples, the a-healing mechanism was also experimentally demonstrated in synthetic xenotime samples. (c) 2020 Elsevier B.V. All rights reserved.