Fluoride solid electrolytes containing rare earth elements

来源期刊：Journal of Rare Earths2008年第2期

论文作者：Viera Trnovcová Pavel P. Fedorov Ivan Furár

文章页码：225 - 232

摘    要：Relations between the structure, ionic conductivity and dielectric properties of fluoride systems of different structures containing rare earth elements were presented. Superionic conductivities, by fluoride ions, of fluorite-structured （MF2-REF3, M=Ba, Pb, RE=La-Lu, Sc, Y）, orthorhombic （REF3, RE=Tb-Er,Y）, tysonite-structured （REF3-MF2, RE=La-Nd, M=Sr）, monoclinic （BaRE2F8, RE=Ho-Yb, Y） fluoride single crystals and eutectic composites （LiF-REF3, RE=La-Gd,Y） were compared. Anisotropy of electrical properties of crystals with a lower symmetry was explained by modeling optimum ionic paths. For explanation of concentration dependences of fast ionic conductivity, models of aggregation of defects into clusters were proposed. In fluorite-structured crystals, the highest ionic conductivity was found for PbF2: 7 mol% ScF3 （at 500 K, σ500=0.13 S/cm）. In tysonite-structured crystals, the highest ionic conductivity was found for LaF3: 3 mol% SrF2 （σ500=2.4×10-2 S/cm）. Different types of coordination polyhedrons and their different linking in orthorhombic and tysonite structure ex- plained large differences between conductivities in both structures. Eutectic systems, prepared as directionally solidified composites, enabled to study some orthorhombic fluoride phases （GdF3, SmF3）, which cannot be prepared as single crystals. An influence of the orthorhom- bic-tysonite phase transition on the ionic conductivity was shown.