Fluoride solid electrolytes containing rare earth elements |
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Authors: | Viera Trnovcov Pavel P Fedorov Ivan Furr |
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Affiliation: | aDepartment of Physics, Faculty of Materials Science and Technology, Slovak University of Technology, SK-91724 Trnava, Slovakia;bInstitute of General Physics, Russian Academy of Sciences, Moscow, Russia |
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Abstract: | 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, σ 500=0.13 S/cm). In tysonite-structured crystals, the highest ionic conductivity was found for LaF3: 3 mol% SrF2 (σ 500=2.4 × 10?2 S/cm). Different types of coordination polyhedrons and their different linking in orthorhombic and tysonite structure explained 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 orthorhombic-tysonite phase transition on the ionic conductivity was shown. |
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Keywords: | rare earth containing fluorides superionic conductivity defects conduction mechanisms clustering single crystals composites rare earth elements containing electrolytes solid influence phase transition enabled study coordination linking large differences models aggregation defects clusters explanation concentration fast ionic conductivity |
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