Ion irradiation induced order-to-disorder transformations in δ-phase Sc_4-xZr_3+xO_{12+ x/2}

The purpose of this study is to investigate the role of stoichiometry on crystal structure transformations in derivative fluorite compounds known as delta (δ) phase. In this study, polycrystalline δ-phase ceramic pellets were prepared with stoichiometries given by Sc_{4- x}Zr_3+xO_12+x/2 (x = 0, 0.77 and 1.20)_. The pressed and polished pellets were then irradiated under cryogenic conditions with 200 keV Ne⁺ ions to fluences ranging from 1-5 × 10¹⁴ Ne/cm². An order-to-disorder (O-D) transformation was observed for all compositions, as determined using grazing incidence X-ray diffraction (GIXRD). However, the transformation threshold dose was found to systematically decrease with increasing ZrO₂ content: ∼0.2, ∼0.16, and ∼0.08 dpa for Sc_4-xZr_3+xO_{12+ x/2} with x = 0, 0.77, and 1.20, respectively. These irradiation-induced phase transformation results are discussed in terms of the crystal structure of the δ-phase.