In situ studies of ion irradiated zirconolite, pyrochlore and perovskite

The relative radiation resistance of the structures of zirconolite, pyrochlore and perovksite were investigated by in situ transmission electron microscopy using 1.5 MeV Kr+ ions in the HVEM-Tandem User Facility, at Argonne National Laboratory. A suite of six fabricated zirconolites, one fabricated pyrochlore and one natural perovskite was used. Damage accumulation essentially occurs in the same way in all three phases and is revealed by the following changes in SAD patterns: weakening of superlattice Bragg diffraction maxima, appearance of diffuse rings which increase in intensity with dose, disappearance of superlattice or other specific classes of maxima, and disappearance of remaining sublattice maxima leaving only diffuse rings. The average critical doses for amorphisation (Dc) for all the zirconolites (undoped, Nd-doped, U-doped and Th-doped) and the pyrochlore in this study varied by a factor of ∝2 (from 3.5 to 6.1 x 1018 ionsm-2). No correlations were observed between Dc and the atomic weight of dopants in zirconolite or the mean atomic weight of the sample. The Dc value at room temperature of perovskite was found to be 1.8 x 1019 ions m-2, 3-5 times the Dc values for zirconolite. This observation is in line with what one expects from the topologic and chemical complexity of the two phases and is compared with the results of previous authors. Preliminary assessment was made of EELS as a tool for monitoring radiation damage. (orig.)