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 delta-gamma-beta phases in Sc2O3-ZrO2 phase diagram. Different composition polycrystalline delta-Sc4Zr3O12, gamma-Sc2Zr5O13 and beta-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 200 key Ne+ ions at a dose rate of similar to 1 x 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 degrees. The O-D transformation threshold dose for delta-Sc4Zr3O12 (similar to 0.2 dpa) was found to be noticeably higher than that for gamma-Sc2Zr5O13 and beta-Sc2Zr7O17 (similar to 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 gamma-Sc2Zr5O13 is in fact slightly higher than that for beta-Sc2Zr7O17 as expected from the phase diagram of Sc2O3-ZrO2 system. (C) 2011 Elsevier B.V. All rights reserved.