Thermal annealing behaviour and defect evolution of helium in fully stabilised zirconia

Helium implantations in fully stabilised zirconia have been performed with 30 keV ions with high doses (5.1 × 1016 and 2.6 × 1016 cm−2) and low doses (6.3 × 1015 and 1.7 × 1015 cm−2). The retained amount of helium and depth profiles have been monitored with neutron depth profiling and the damage distribution with positron beam analysis (PBA) after several annealing steps. The temperature dependent helium release was investigated by thermal helium desorption spectrometry. In the low dose samples, helium is released through diffusion as seen by a broadening of the helium distribution peak. PBA, performed with a two-layer model, shows shrinkage of the damage layer during annealing. For the high dose samples the helium peak does not broaden after annealing. Helium is retained up to high temperatures which is ascribed to bubble formation during thermal annealing. Fitting of the PBA results to a three-layer model shows that the ion implanted layer gets narrower after annealing at 600 K, up to 1000 K the S-parameter is increasing because helium is released from the bubbles, whereby vacancy clusters are left behind.