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 ...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 （BaRE2Fs, 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 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.展开更多
ZrOCl2·8H2O and ZrO（NO3）2·2H2O were used respectively to synthesize a NASICON solid electrolyte by a sol-gel method. The structure and properties of two samples were characterized by X-ray diffraction （XR...ZrOCl2·8H2O and ZrO（NO3）2·2H2O were used respectively to synthesize a NASICON solid electrolyte by a sol-gel method. The structure and properties of two samples were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and electro-chemical impedance spectroscopy （EIS）. The crystal structure was investigated by the Rietveld refinement. It is found that both the samples contain a monoclinic C2/c phase as the main conductive phase with the lattice parameters ofa=1.56312 nm, b=0.90784 nm and c=0.92203 nm, though a small amount of rhombohedral phase is also detected in the final product. The sample synthesized by ZrO（NO3）2·2H/O contains more monoclinic phase （89.48wt%） than that synthesized by ZrOCl2·SH2O（74.91 wt%）. As expected, the ionic conductivity of the latter is higher than that of the former; however, the activation energy of the latter （0.37 eV） is slightly higher than that of the former （0.35 eV）.展开更多
基金the Scientific Grant Agency VEGA, Slovak Republic (1/2100/05 and 1/0173/08)
文摘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 （BaRE2Fs, 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 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.
基金supported by the National Natural Science Foundation of China (No.50974012)Program Changjiang Scholars and Innovative Research Team in Universities (No.0708)
文摘ZrOCl2·8H2O and ZrO（NO3）2·2H2O were used respectively to synthesize a NASICON solid electrolyte by a sol-gel method. The structure and properties of two samples were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and electro-chemical impedance spectroscopy （EIS）. The crystal structure was investigated by the Rietveld refinement. It is found that both the samples contain a monoclinic C2/c phase as the main conductive phase with the lattice parameters ofa=1.56312 nm, b=0.90784 nm and c=0.92203 nm, though a small amount of rhombohedral phase is also detected in the final product. The sample synthesized by ZrO（NO3）2·2H/O contains more monoclinic phase （89.48wt%） than that synthesized by ZrOCl2·SH2O（74.91 wt%）. As expected, the ionic conductivity of the latter is higher than that of the former; however, the activation energy of the latter （0.37 eV） is slightly higher than that of the former （0.35 eV）.
