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

Abstract

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 beta 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.