The theory of random walks in random barrier networks has been applied to describe the properties associated with the hopping motion of fluoride ions in single crystals ${\mathrm{Sr}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Ce}}_{\mathrm{x}}$${\mathrm{F}}_{2+\mathrm{x}}$. It appears that theoretically predicted features like anomalous diffusion, leveling off of the mean-square displacement, and normal diffusion in the long-time limit can be observed for these crystals.

• Received 5 June 1989

DOI:https://doi.org/10.1103/PhysRevB.40.5817