This paper compares the electrophysical (ionic conductivity and ion transport activation enthalpy) and crystal-chemical (lattice parameters, ionic radii, and cation polarizability) characteristics of M1 − xScxF2 + x scandium-containing solid electrolytes, where M = Ca, Sr, Ba, or Pb. The M1 − xScxF2 + x fluorite (space group Fm 3m) solid solutions were prepared from melt by vertical directional crystallization (in single crystals for M = Ca, Sr, or Pb) or spontaneous crystallization (in alloys for M = Ba). The BaF2- and β-PbF2-base fluorite solid solutions have fluoride ion conductivity five to six orders of magnitude higher, and the ion transport activation enthalpy two to four times lower, than the respective values of CaF2- and SrF2-base solid solutions. The high conductivity of M1 − xScxF2 + x (M = Ba or Pb) solid electrolytes is due to the large Ba2+ and Pb2+ ionic radii (the dimensional factor) and the high Pb2+ polarizability (the polarization factor). The interplay of these factors increases the free space and decreases potential barriers to the movement of mobile fluoride ions.
N. I. Sorokin (Sat,) studied this question.