Ion irradiation induced order-to-disorder transformation in δ-phase Lu4Hf3O12

In this study, polycrystalline δ-phase Lu4Hf3O12 was irradiated with 6 MeV Xe26+ ions to fluences ranging from 2 × 1013 to 1 × 1015 ions/cm2. Ion irradiation-induced microstructural evolution was examined by using grazing incidence X-ray diffraction (GIXRD). A complete phase transformation from ordered rhombohedral to disordered fluorite (O–D) was observed by a fluence of 1 × 1015 ions/cm2, equivalent to a peak ballistic damage dose of ∼3.49 displacements per atom (dpa). To research the different irradiation effect between light ion and heavy ion on δ-Lu4Hf3O12, 400 keV Ne2+ ions were implanted to ion fluences ranging from 1×1014 to 1×1015 ions/cm2. A complete O–D crystal structure transformation was observed by a fluence of 5×1014 ions/cm2 (∼0.22 dpa). This threshold dose was found to be observably lower than the threshold dose to produce order-to-disorder transformation using Xe26+ ions on δ-Lu4Hf3O12. This suggests that heavy ions are less efficient than light ions in producing the retained defects that are responsible for the O–D transformation. The theoretical calculations show that the O–D transformation of δ-phase was attributed to the anion oxygen Frenkel pair defect. The ion irradiation-induced transformation of δ-phase Lu4Hf3O12 into disordered fluorite structure observed here is also discussed in relation to the temperature–composition (T–C) phase diagrams for the compound.