Retention at room temperature of the tetragonal t″-form in Sc2O3-doped ZrO2 nanopowders

Synchrotron X-ray powder diffraction was applied to the study of the effect of crystallite size on the crystal structure of ZrO2–10 mol% Sc2O3 nanopowders synthesized by a nitrate-lysine gel-combustion route. Nanopowders with different average crystallite sizes were obtained by calcination at several temperatures, ranging from 650 to 1200 °C. The metastable t″-form of the tetragonal phase, exhibiting a cubic unit cell and tetragonal P42/nmc spatial symmetry, was retained at room temperature in fine nanocrystalline powders, completely avoiding the presence of the stable rhombohedral β phase. Differently, this phase was identified in samples calcined at high temperatures and its content increased with increasing crystallite size. The critical maximum crystallite size for the retention of the mestastable t″-form resulted of about 35 nm.