Inelastic light scattering and phonon-confinement in nanocrystalline Y2O3

Nanocrystalline powders of Y2O3 with grain sizes in the range between 7 and 40 nm were prepared by the microemulsion technique and by condensation from an inert gas atmosphere. The cubic respectively monoclinic powders were examined by means of Brillouin scattering (consolidated samples) and micro-Raman scattering (powders and consolidated samples). Measurements of the elastic properties of quasi-isotropic pellets yield a longitudinal modulus reduced down to 25% compared with that of the monocrystal and point to optical inhomogeneities in the range of the wavelength of the light. With decreasing dimensions of the crystallites a shift of the characteristic Raman lines to lower frequencies and a distinct broadening of the lines are observed. ii trial is made to interpret these features by the phonon-confinement model of Richter et al. [1]. A possibility to characterize the nanocrystalline powders by means of Raman spectroscopy is discussed.