Investigation of anion disorder in PbF2at high temperatures by neutron diffraction

Single-crystal neutron diffraction has been used to investigate the nature of the dynamic anion disorder in lead fluoride, PbF 2 , at a number of temperatures ranging to above the onset of fast-ion conduction at 711K. The data have been interpreted in terms of several possible models of the time-averaged structure. In order to account for the high-temperature data a large number of vacancies must be included in the anion sublattice. Two of the possible models for the displaced anion positions, both of which distinguish between true interstitials and relaxed anions, are found to account well for the data. These models are consistent with the presence of simple clusters dominating the fluctuating configurations of anions in the dynamic phase.