Inelastic neutron scattering measurements of the diffusion beta-Ag2S.

Inelastic neutron scattering measurements have been performed on Ag2S in both the cubic superionic phase (T>450K) and the monoclinic low ionic conductivity phase (T450K). The diffuse scattering observed in x-ray measurements in the superionic phase near Q-> = (1.6, 1,0) is shown to be entirely due to inelastic scattering resulting from correlations among the delocalized silver ions. A low energy (~2meV) excitation has been observed at Q = (1.6, 1,0) in the room temperature phase which may be related to a local mode of the silver atoms. The energy of this mode decreases as temperature is increased. The results are discussed in terms of a complex highly correlated model of silver diffusion in betaAg2S.