Collective motion in superionic conductors

A theory of collective motion in superionic conductors is described by the use of a model of a crystalline cage immersed in a viscous liquid. The viscoelastic force and the interionic Coulomb force are considered as the cage—liquid interaction. The density-correlation functions and the frequency-dependent conductivity are calculated. The calculated conductivities for α-AgI are in good agreement with experiments. It is concluded that the structure in a.c. conductivity experimentally observed for α-AgI at frequencies below 10 cm^-1 can be ascribed to acoustic phonons.