Metastable forms of the tetragonal phase in compositionally homogeneous, nanocrystalline zirconia–ceria powders synthesised by gel-combustion

Abstract

The crystal structure of compositionally homogeneous, nanocrystalline ZrO₂–10, 30, 50, 70 and 90 mol% CeO₂ powders synthesised by a pH-controlled nitrate–glycine gel-combustion process has been studied by X-ray diffraction and Raman spectroscopy. All the powders with a CeO₂ content up to 70 mol% exhibited the tetragonal phase (P4₂/nmc space group), whereas the ZrO₂–90 mol% CeO₂ solid solution presented the cubic phase (Fmm space group). The axial ratio c/a decreased with increasing CeO₂ content and became unity for ZrO₂–70 mol% CeO₂ powders. By analysing X-ray diffraction data using the Rietveld method, it was found that this material exhibited the t″-form of the tetragonal phase (the oxygen atoms were displaced from their ideal sites of the cubic phase along the c axis). Raman spectroscopy study confirmed the results found by X-ray diffraction. The morphology of the nanopowders was also evaluated.