Structural transformation in nanosized zirconium oxide - art. no. 155404

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.