Microstructural evolution in irradiated uranium-bearing delta-phase oxides A6U1O12 (A=Y, Gd, Ho, Yb, and Lu)

Abstract Irradiation-induced microstructural evolution in uranium-bearing delta-phase oxides of A 6 U 1 O 12 (A = rare earth cations) were characterized using grazing incidence X-ray diffraction and transmission electron microscopy. Polycrystalline Y 6 U 1 O 12 , Gd 6 U 1 O 12 , Ho 6 U 1 O 12 , Yb 6 U 1 O 12 , and Lu 6 U 1 O 12 samples were irradiated with 300 keV Kr ++ to a fluence of 2 × 10 20 ions/m 2 at cryogenic temperature (∼100 K). The crystal structure of these compounds was determined to be an ordered, fluorite derivative structure, known as the delta-phase, a rhombohedral symmetry belonging to space group R 3 ¯ . Experimental results indicate that all these compounds are resistant to amorphization to a displacement damage dose of ∼60 displacements per atom. In these experiments, we sometimes observed an irradiation-induced order-to-disorder phase transformation, from an ordered rhombohedral to a disordered fluorite structure.