DEFECT-INDUCED RAMAN-SPECTRA IN DOPED CEO2

Polarized Raman-scattering spectra are obtained from oriented single c rystals of yttria-doped CeO2 The temperature and dopant dependencies o f Raman spectra strongly suggest that many structures in the Raman spe ctra of yttria-doped CeO2 are induced by the defect space including an O2- vacancy. The contribution to the frequency distributions of Raman -active modes from the whole Brillouin zone are estimated from the ima ginary, part of the simple projection of the phonon displacement-displ acement Green's functions of undoped CeO2 crystals onto several defect spaces. The observed spectra are well explained by the linear combina tion of the calculated frequency distributions from the defect space c onsisting of the four metal ions and from that consisting of the six n ext-nearest-neighbor O2- ions surrounding an O2- vacancy. Brillouin-sc attering spectra of CeO2 are also measured in order to calculate the p honon-dispersion curves of CeO2. The dependencies of type and concentr ation of defect space on dopant concentration in doped CeO2 are also d iscussed.