Defect modes around low-lying phonon in Ag β-Alumina by Raman scattering with high resolution

Raman spectra for low-lying phonons of Ag β-alumina were measured in the temperature range of 30 K-280 K. The broad band of the low-lying phonon was found to contain three Lorentz bands by a double monochrometer with high resolution (ΔE = 1 cm^{- 1}). Well resolved three bands correspond to the previous Raman results observed from the isomorphous β-alumina of K, Tl or Rb. The decomposed low-lying phonon of Ag β-alumina shows that the band width broadens with an increase in temperature clearly. The damping energy obtained from the Raman line-width of the low-lying phonon was estimated to be 0.51 meV at 30 K. It is in excellent agreement with the value 0.55 meV at 30 K from the femtosecond time-resolved observation [O. Kamishima, B. Paxton, T. Feurer, K.A. Nelson, Y. Iwai, J. Kawamura and T. Hattori, J. Phys.: Condensed Matter 19 (2007) 456215].