Ion irradiation-induced phase transformations in δ–γ–β phases of Sc2O3–ZrO2 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 Sc2O3–ZrO2 phase diagram. Different composition polycrystalline δ-Sc4Zr3O12, γ-Sc2Zr5O13 and β-Sc2Zr7O17 samples were synthesized by mixing 40% Sc2O3+60% ZrO2, 16.67% Sc2O3+83.33% ZrO2, or 12.5% Sc2O3+87.5% ZrO2, respectively. The pressed and polished pellets of these compounds were then irradiated under liquid nitrogen temperature with 200keV Ne+ ions at a dose rate of ∼1×1012ions/cm2/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-Sc4Zr3O12 (∼0.2dpa) was found to be noticeably higher than that for γ-Sc2Zr5O13 and β-Sc2Zr7O17 (∼0.04dpa) 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-Sc2Zr5O13 is in fact slightly higher than that for β-Sc2Zr7O17 as expected from the phase diagram of Sc2O3–ZrO2 system.