The effect of the ionic radii of rare-earth elements upon anion transport was studied in simple fluorides. The object was to optimize the ion transport characteristics of solid electrolytes with a tysonite-type structure. The anionic conductivity of monocrystals was studied by using impedance spectroscopic methods at frequencies which ranged from 0.1Hz to 1MHz. It was found that the temperature dependence of the conductivity of each material exhibited a change in slope at a so-called kink temperature of about 420K. The data below 420K could be described by:

oT (SK/m) = 8.0 x 105 exp[-0.408(eV)/kT]

The data above 420K could be described by:

oT (SK/m) = 3.6 x 104 exp[-0.301(eV)/kT]

N.I.Sorokin, B.P.Sobolev: Kristallografiya, 1994, 39[1], 114-8 (Crystallography Reports, 1994, 39[1], 101-4)