Retention at room temperature of the tetragonal tQUOTATION_MARK-form in Sc sub(2)O sub(3)-doped ZrO sub(2) nanopowders

Synchrotron X-ray powder diffraction was applied to the study of the effect of crystallite size on the crystal structure of ZrO sub(2)-10 mol% Sc sub(2)O sub(3) 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 degree C. The metastable t"-form of the tetragonal phase, exhibiting a cubic unit cell and tetragonal P4 sub(2)/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.