Dynamics of defects in superionic fluorites

Abstract

Materials having the fluorite structure are among the simplest superionic conductors, and have been intensively studied both experimentally and by molecular-dynamics simulation. It is described how simulations of superionic CaF₂ have helped to elucidate the results obtained by Hutchings et al. using coherent quasielastic neutron scattering. The experiments reveal strong quasielastic scattering, which is associated with decaying density fluctuations. The simulations show that these fluctuations arise from the motion of anion vacancies and interstitials. New simulation work is presented, which sheds light on the decay rate of the flucturations, i.e. the quasielastic width. It is shown that this rate is intimately related to the electrical conductivity of the system.