Ionic motion, during molecular dynamics simulations of the ,  and  phases, was studied in detail. In the case of the cubic  phase, the Cu+ ions exhibited large anharmonic vibrations along <111>-type directions and towards the face centers of the tetrahedral cages which were defined by the 4 neighboring I- ions. However, the diffusion path lay along <100>-type directions and towards the edges of these cages. The diffusion mechanism involved the correlated motion of so-called chains of several Cu+ ions. This explained the experimentally observed breakdown of the jump diffusion model. As the temperature was increased, the number of diffusing chains also increased. Interactions between these chains then led to a rapid increase in the diffusion rate, and a transition to the fast ion-conducting  phase. In the case of the hexagonal  phase, the Cu+ ions exhibited a similar behavior. That is, they vibrated towards the cage faces but diffused in the direction of the cage edges. However, the situation was more complicated here because, in this structure, 2 cages shared a common face. This produced a complex behavior in which the average sites of the Cu+ ions were the cage centers in the short term, but were the shared face centers over longer times.

J.X.M.Zheng-Johansson, R.L.McGreevy: Solid State Ionics, 1996, 83[1-2], 35-48