IN-SITU STUDIES OF ION-IRRADIATED ZIRCONOLITE, PYROCHLORE AND PEROVSKITE

The relative radiation resistance of the structures of zirconolite, py rochlore and perovksite wore investigated by in situ transmission elec tron microscopy using 1.5 MeV Kr+ ions in the HVEM-Tandem User Facilit y, at Argonne National Laboratory. A suite of six fabricated zirconoli tes, one fabricated pyrochlore and one natural perovskite was used. Da mage accumulation essentially occurs in the same way in all three phas es 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 su blattice maxima leaving only diffuse rings. The average critical doses for amorphisation (D-c) for all the zirconolites (undoped, Nd-doped, U-doped and Th-doped) and the pyrochlore in this study varied by a fac tor of similar to 2 (from 3.5 to 6.1 X 10(18) ions m(-2)). No correlat ions were observed between D-c and the atomic weight of dopants in zir conolite or the mean atomic weight of the sample. The D-c value at roo m temperature of perovskite was found to be 1.8 X 10(19) ions m(-2), 3 -5 times the D-c values for zirconolite. This observation is in line w ith what one expects from the topologic and chemical complexity of the two phases and is compared with the results of previous authors. Prel iminary assessment was made of EELS as a tool for monitoring radiation damage. (C) 1997 Elsevier Science B.V.