Metastable Phase Diagram of Nanocrystalline ZrO2−Sc2O3 Solid Solutions

Abstract

We have investigated the crystal structures and phase transitions of nanocrystalline ZrO2−1 to −13 mol % Sc2O3 by synchrotron X-ray powder diffraction and Raman spectroscopy. ZrO2−Sc2O3 nanopowders were synthesized by using a stoichiometric nitrate−lysine gel−combustion route. Calcination processes at 650 and at 850 °C yielded nanocrystalline materials with average crystallite sizes of (10 ± 1) and (25 ± 2) nm, respectively. Only metastable tetragonal forms and the cubic phase were identified, whereas the stable monoclinic and rhombohedral phases were not detected in the compositional range analyzed in this work. Differently from the results of investigations reported in the literature for ZrO2−Sc2O3 materials with large crystallite sizes, this study demonstrates that, if the crystallite sizes are small enough (in the nanometric range), the metastable t′′-form of the tetragonal phase is retained. We have also determined the t′−t′′ and t′′−cubic compositional boundaries at room temperature and analyzed the...