Microstructural evolution in irradiated uranium-bearing delta-phase oxides A 6U 1O 12 (A = Y, Gd, Ho, Yb, and Lu)

Irradiation-induced microstructural evolution in uranium-bearing delta-phase oxides of A ₆U ₁O ₁₂ (A = rare earth cations) were characterized using grazing incidence X-ray diffraction and transmission electron microscopy. Polycrystalline Y ₆U ₁O ₁₂, Gd ₆U ₁O ₁₂, Ho ₆U ₁O ₁₂, Yb ₆U ₁O ₁₂, and Lu ₆U ₁O 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 R3¯. 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.