Ion irradiation-induced phase transformations in δ-γ-β phases of Sc ₂O ₃-ZrO ₂ mixtures

The purpose of this study is to investigate the role of stoichiometry in crystalline structure transformations in derivative fluorite compounds known as δ-γ-β phases in Sc ₂O ₃-ZrO ₂ phase diagram. Different composition polycrystalline δ-Sc ₄Zr ₃O ₁₂, γ-Sc ₂Zr ₅O ₁₃ and β-Sc ₂Zr ₇O ₁₇ samples were synthesized by mixing 40% Sc ₂O ₃ + 60% ZrO ₂, 16.67% Sc ₂O ₃ + 83.33% ZrO ₂, or 12.5% Sc ₂O ₃ + 87.5% ZrO ₂, respectively. The pressed and polished pellets of these compounds were then irradiated under liquid nitrogen temperature with 200 keV Ne ⁺ ions at a dose rate of ∼1 × 10 ¹² ions/cm ²/s. An order-to-disorder (O-D) transformation was observed for all compositions, as determined using grazing incidence X-ray diffraction (GIXRD) at an incident angle of 0.25°. The O-D transformation threshold dose for δ-Sc ₄Zr ₃O ₁₂ (∼0.2 dpa) was found to be noticeably higher than that for γ-Sc ₂Zr ₅O ₁₃ and β-Sc ₂Zr ₇O ₁₇ (∼0.04 dpa) based on both GIXRD and cross-sectional transmission electron microscopy (TEM) measurements. However, due to experimental difficulty and uncertainty, our GIXRD and TEM data were unable to conclusively confirm that the O-D transformation threshold dose for γ-Sc ₂Zr ₅O ₁₃ is in fact slightly higher than that for β-Sc ₂Zr ₇O ₁₇ as expected from the phase diagram of Sc ₂O ₃-ZrO ₂ system.