Structural properties of calcined ZrO2 nanopowders having various sizes wer
e investigated by Raman spectroscopy, x-ray diffraction, and high-resolutio
n transmission electron microscopy. For grain sizes of the order of a few n
anometers the Raman spectrum is typical of an amorphous material as is the
corresponding x-ray diffractogram. As the size of the grains increases, the
spectra progressively evolve towards that of a crystallized sample, furthe
rmore, two regimes of growth, vitreous and crystalline, are evidenced. As o
pposed to the acoustical, the optical branches exhibit a strong discontinui
ty near the amorphous-crystalline transition. From the analysis of the Rama
n spectra as a function of size one can infer the phonon dispersion curves
that has so far been inaccessible by neutron diffraction. A simple analysis
using a classic elastic model shows that the Raman frequencies of the acou
stical phonon bands of the nanograins are linearly dependent upon their siz
e.