Analysis of quasi-elastic scattering in AgI-based superionic glasses

Brillouin and Raman scattering measurements have been performed on the superionic conductors (AgI)x(AgPO3)1-x in the full glass-forming region (0 < x < 0-55) from 18 to 330 K. For the first time in this kind of solid-state sample we have been able to investigate the full spectral range (0.2-250 cm-1 frequency shift) by using the same spectrometer. By increasing the AgI content, the behaviour of Brillouin and Raman intensities together with the Raman spectral shape suggests the hypothesis that the dynamics of the two pure component are weakly interacting. Further we have been able to separate a quasi-elastic component from the one-phonon disorder-induced density of states by using their different temperature behaviours. We have compared the data obtained with the most likely mechanisms that could account for quasi-elastic scattering in our system (diffusion of Ag+ ions, and two-level states in glasses) but we found that neither of these kinds of process can describe our experimental findings.