It was recalled that it had been shown, for this Frenkel disordered material as well as for AgI, AgCl and AgBr, that the anomalous conductivity increase at high temperatures could be described by a cube-root term in the chemical potential of the defects. This reflected their mutual interaction, in a mean-field sense. In the case of the present material, it was assumed that only one charge carrier was responsible for the conduction. In the case of materials which underwent a higher-order phase transition, the description also included the conductivity behavior at, and above, the transition. An investigation was made here of the above model by using molecular dynamics and Monte Carlo simulations. The defect concentrations and the defect energies, including excess energies, were calculated as a function of temperature on the basis of a classical semi-empirical potential. The concentrations of fluoride defects were estimated as a function of temperature, and the conduction mechanism was investigated. The mobility of fluoride ions was estimated by comparing defect concentrations with experimental conductivity data. The results showed that the conductivity anomaly was essentially caused by an anomalous increase in defect concentrations. The cube-root approximation was quite well fulfilled. The calculations also indicated that there was a perceptible contribution from interstitial defect conductivity above 600K.

The Conductivity Anomaly in PbF2 - a Numerical Investigation by Classical MD and MC Simulations. F.Zimmer, P.Ballone, M.Parrinello, J.Maier: Solid State Ionics, 2000, 127[3-4], 277-84