Fast ionic conductivity of PbF2 : MF2 (M = Mg, Ba, Cd) and PbF2 : ScF3 single crystals and composites

The fluorite-structured heterovalent PbF2:ScF3 and isovalent PbF2:MF2 (M = Mg, Ba, Cd) concentrated solid solutions were prepared as single crystals i n a broad concentration range. In the eutectic systems, PbF2-MgF2 and PbF2- ScF3, the eutectic and near-eutectic composites were prepared from the melt . Saturated solid solutions of each system form two phases of these composi tes. The fast ionic conductivity, static permittivity and microstructure of both the single crystals and the composites are examined. Fastest ionic co nductivity, with a conduction enthalpy of 0.389 eV, is found in PbF2:7 m/o ScF3 solid electrolyte. In this material, the fluoride ion conductivity at 500 K is equal to 0.13 S/cm. Plausible models of defect structures and cond uction mechanisms are proposed for all examined systems. (C) 1999 Elsevier Science B.V. All rights reserved.