X-ray diffraction study of phase transformation in hydrolyzed zirconia nanoparticles

The occurrence of metastable tetragonal (t') phase and its transformation i nto monoclinic (m) in nanocrystalline ZrO2 were systematically studied by u sing X-ray diffraction with respect to the grain size and processing condit ions. The zirconia particles in the average size range 7-20 nm were prepare d by hydrolyzis of zirconium oxy-chloride solution for different hydrolyzin g periods. Drastic changes in grain size and the phase formation with the h ydrolyzing time were observed The amorphous ZrO2 crystallizes in the t' pha se around 718 to 753 K on heating. However, if the crystallization occurs c uring the hydrolyzis itself, the monoclinic phase is formed even the grain size is less than 10 nm. The microstructural defects seem to dominate the g rain size effect causing the reduction in crystal symmetry in the nanocryst alline zirconia obtained after 72 h of hydrolyzis. (C) 1999 Elsevier Scienc e Limited. All rights reserved.