Heavy and light ion irradiation damage effects in δ-phase Sc4Hf3O12

Polycrystalline δ-phase Sc4Hf3O12 was irradiated with light and heavy ions to study the radiation stability of this compound. In order to explore the ion species spectrum effect, the irradiations were performed with 400 keV Ne2+ ions to fluences ranging from 1 × 1014 to 1 × 1015 ions/cm2, 600 keV Kr3+ ions to fluences ranging from 5 × 1014 to 5 × 1015 ions/cm2, and 6 MeV Xe26+ ions to fluences ranging from 2 × 1013 to 1 × 1015 ions/cm2. Irradiated samples were characterized by various techniques including grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). A complete phase transformation from ordered rhombohedral to disordered fluorite was observed by a fluence of 1 × 1015 ions/cm2 with 400 keV Ne2+ ions, equivalent to a peak ballistic damage dose of ∼0.33 displacements per atom (dpa). Meanwhile, the same transformation was also observed by 600 keV Kr3+ ions at the same fluence of 1 × 1015 ions/cm2, which however corresponds to a peak ballistic damage dose of ∼2.2 dpa. Only a partial O-D transformation was observed for 6 MeV Xe26+ ions in the fluence range used. Experimental results indicated that the O-D transformation is observed under both electronic and nuclear stopping dominant irradiation regimes. It was also observed that light ions are more efficient than heavy ions in producing the retained defects that are presumably responsible for the O-D phase transformation. The O-D transformation mechanism is discussed in the context of anion oxygen Frenkel defects and cation antisite defects. We concluded that the irradiation induced O-D transformation is easier to occur in δ-phase compounds with partial order of cations than in that with fully disordered cation structures.