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

The occurrence of metastable tetragonal (t') phase and its transformation into monoclinic (m) in nanocrystalline ZrO2 were systematically studied by using X-ray diffraction with respect to the grain size and processing conditions. The zirconia particles in the average size range 7-20 nm were prepared by hydrolyzis of zirconium oxy-chloride solution for different hydrolyzing periods. Drastic changes in grain size and the phase formation with the hydrolyzing time were observed The amorphous ZrO2 crystallizes in the t' phase around 718 to 753 K on heating. However, if the crystallization occurs curing the hydrolyzis itself, the monoclinic phase is formed even the grain size is less than 10 nm. The microstructural defects seem to dominate the grain size effect causing the reduction in crystal symmetry in the nanocrystalline zirconia obtained after 72 h of hydrolyzis. (C) 1999 Elsevier Science Limited. All rights reserved.