Order-to-disorder transformation in δ-phase Sc₄Zr₃O₁₂ induced by light ion irradiation

Polycrystalline δ-phase Sc₄Zr₃O₁₂ was irradiated with 200 keV Ne⁺ ions at cryogenic temperature to fluences ranging from 2 × 10¹⁸ to 1 × 10²¹ Ne/m². Irradiation-induced structural evolution was examined by using grazing incidence x-ray diffraction and cross-sectional transmission electron microscopy. An order-to-disorder (O-D) crystal structure transformation (from an ordered δ-phase to a disordered, fluorite phase) was observed to initiate by a fluence of 2 × 10¹⁸ Ne/m², corresponding to a peak ballistic damage dose of ∼0.075 displacements per atom. This displacement damage dose is much lower than the O-D transformation dose threshold found in previous heavy ion irradiation experiments on δ-Sc₄Zr₃O₁₂ [J.A. Valdez et al., Nucl. Instrum. Methods B250, 148 (2006); K.E. Sickafus et al., Nat. Mater.6, 217 (2007)]. In this study, we contrast the O-D transformation efficiency of the light Ne ions used in these experiments, to the heavy (Kr) ions used previously, and interpret the differences in terms of enhanced damage efficiency for light ions (greater fraction of surviving defects per defect produced). To better quantify this surviving defect phenomenon, we also present new, additional ion irradiation results on δ-Sc₄Zr₃O₁₂, obtained from 300 keV Kr²⁺ and 100 keV He⁺ ion irradiation experiments.