Crystallite Size Effect on the Tetragonal-Monoclinic Transition of Undoped Nanocrystalline Zirconia Studied by XRD and Raman Spectrometry

Two powdered batches of undoped zirconia, prepared by spray pyrolysis and characterized by 6.9 and 13.2 nm average crystallite size were annealed for different temperatures and for different times. The tetragonal–monoclinic phase transformation was monitored by Raman spectroscopy and X-ray diffraction. The evolution of parameters such as crystallite size, c/a unit cell parameter ratio, content of monoclinic and tetragonal zirconia, and Raman wavenumbers was found to differ from one batch to the other. The destabilization of the tetragonal phase appears for the 10 to 40 nm crystallite size range and as a sudden phenomenon. The critical size range varies with preparation. The wavenumber shifts were also discussed on the basis of internal stresses associated with mechanical balance between the surface and volume states.