Inelastic neutron scattering measurements of the diffusion inβ−Ag2S

Inelastic neutron scattering measurements have been performed on ${\mathrm{Ag}}_2$S in both the cubic superionic phase ($T>\mathrm{}450\mathrm{}$ K) and the monoclinic low-ionic conductivity phase ($T<\mathrm{}450\mathrm{}$ K). The diffuse scattering observed in x-ray measurements in the superionic phase near $\overrightarrow{\mathrm{Q}}=(1.6,1,0)\mathrm{}$ 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 $\overrightarrow{\mathrm{Q}}=(1.6,1,0)\mathrm{}$ 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 $\beta -{\mathrm{Ag}}_2\mathrm{S}$ developed to explain the x-ray scattering results.