Computer simulation of ionic disorder in high-temperature PbF2

The authors present a series of computer simulations of cubic PbF 2 using the molecular dynamics technique. The calculations are based on a rigid-ion model in which the particles bear the full ionic charges, the parameters of the short-range interionic potentials being chosen so as to reproduce the low-temperature bulk and defect properties of the crystal. The simulated system exhibits a diffuse transition from a non-conducting to a fast-ion conducting state at about 700K, in agreement with experiment. The spatial distribution of anions in the high-temperature disordered state is in satisfactory agreement with the results of neutron diffraction measurements. The authors study different methods of analysing the defect concentration, and find that the value obtained for this quantity can vary by an order of magnitude according to the method adopted. They discuss the significance of this result for understanding of fast-ion conduction in fluorite compounds.