Neutron and Raman scattering studies of surface adsorbed molecular vibrations and bulk phonons in ZrO2 nanoparticles ☆

Inelastic neutron-scattering method (neutron spectroscopy) was applied to the study of the phonon densities of states of zirconia nanoparticles, the OH stretch vibrations of physisorbed water molecules and chemisorbed hydroxyl groups on the surface. Raman scattering was also used to measure the zone-center phonon modes. The observed distinct phonon frequencies and band widths at 10–120 meV reflect the different crystalline symmetries and compositional fluctuations in the small grain and interfacial regions of monoclinic ZrO2, tetragonal or mixed cubic and tetragonal rare-earth-modified zirconia. The observed neutron spectra for pure ZrO2, Ce0.1Zr0.9O2 and Nd0.1Zr0.9O1.95 display a band consisting of peaks at 25, 30, and meV and a broad band extending from 50 to 100 meV. The OH bonds in surface hydroxyl groups and water on these zirconias result in the different frequencies of the OH stretch vibrations at 400–600 meV.