Positron annihilation investigation and nuclear reaction analysis of helium and oxygen-implanted zirconia

Since irradiation affects in-service properties of zirconia, we investigated the fluence dependence on production and thermal stability of defects induced by helium and oxygen-ion implantation in single crystals of yttria-fully-stabilized zirconia. In either case, depth profiling by slow positron implantation spectroscopy (SPIS) detects a distribution of vacancy-type defects peaking at 60% of the projected ion range Rp. Owing to the saturation of positron-trapping occurring for low fluences, which depends on the ion mass, we could estimate a critical size of clusters ranging from 0.4 to 1.6 nm. The lack of SPIS-evidence of an open-volume excess at Rp is explained by the presence of over-pressurized gas bubbles. This assumption is confirmed by Nuclear Reaction Analysis of 3He concentration profiles, which shows that helium remains partly trapped at Rp, even after annealing above 400 °C.