CRYSTAL-STRUCTURE AND ANION DISORDER IN BETA-PBF2

The fluorine distribution in beta -PbF//2 was obtained by analyzing the elastic neutron diffraction data. The fluorine distribution at high temperatures shows that the conduction path connects neighboring regular positions of the fluorite structure. The path is not a straight line but bent towards the octahedral void which however is not a point of the conduction path. Interpreting the fluorine distribution in terms of an effective one practical potential it is shown that the defect concentration of the fluorine ions is less than 5%. A potential barrier of 0. 26(5)ev for ionic motion is obtained, which agrees with the activation energy of conductivity at elevated temperatures.