Crystallite size effect on the tetragonal-monoclinic transition of undopednanocrystalline zirconia studied by XRD and Raman spectrometry

Two powdered batches of undoped zirconia, prepared by spray pyrolysis and c haracterized by 6.9 and 13.2 nm average crystallite size were annealed for different temperatures and for different times. The tetragonal-monoclinic p hase transformation was monitored by Raman spectroscopy and X-ray diffracti on. The evolution of parameters such as crystallite size, cia unit cell par ameter ratio, content of monoclinic and tetragonal zirconia, and Raman wave numbers was found to differ from one batch to the other. The destabilizatio n of the tetragonal phase appears for the 10 to 40 nm crystallite size rang e and as a sudden phenomenon, The critical size range varies with preparati on. The wavenumber shifts were also discussed on the basis of internal stre sses associated with mechanical balance between the surface and volume stat es. (C) 2000 Academic Press.