In this paper we present a detailed analysis of the Raman spectral shape of $\alpha$-AgI crystals as a function of temperature up to 450°C. With the use of a polarizability model based on the charge-induced dipole mechanism, which was already introduced to explain depolarization ratios and integrated intensities, all the spectral features from 0.8 to 250 ${\mathrm{cm}}^{-1\mathrm{}}$ are assigned to the iodine dynamics (acoustical and optical phonons), in agreement with inelastic-neutron-scattering data. Hence we predict that the central line originating from ${\mathrm{Ag}}^{+}$ diffusive motions must be confined to the frequency region below 0.8 ${\mathrm{cm}}^{-1\mathrm{}}$. Some suggestions on the phonon branches are qualitatively derived from the temperature dependence of the spectral shape.

• Received 17 January 1983

DOI:https://doi.org/10.1103/PhysRevB.28.7269