Inelastic neutron scattering measurements of the diffusion in -Ag2S

Inelastic neutron scattering measurements have been performed on Ag2S in both the cubic superionic phase (T>450 K) and the monoclinic low-ionic conductivity phase (T<450 K). 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 (2-meV) 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 the "microdomain" model of silver diffusion in -Ag2S developed to explain the x-ray scattering results.