Anionic transport in single crystals (fluorite-type structure) of nominally pure BaF2, in material doped with 0.01 or 0.1mol%LaF3 and in anion-excess binary Ba1-xLaxF2+x (x = 0 to 0.5), Ba0.85R0.15F2.15 (R = La, Sm, Lu), and Ba0.8R0.2F2.2 (R = La, Ce, Nd, Gd, Tb, Ho) solid solutions was studied, by using impedance spectroscopy, from ambient to 1073K. At high temperatures, the conductivity plots for the concentrated solid solutions exhibited considerable deviations from Arrhenius behavior. This was caused by a diffuse Faraday phase transition in the materials. The microscopic origin of the anionic conductivity depended mainly upon the nature of the defect structure in the solid solutions. By controlling the composition of Ba1-xRxF2+x crystals, the fluoride ionic conductivity could reach a value of about 1S/cm at 1073K.

Anionic Conductivity and Thermal Stability of Single Crystals of Solid Solutions based on Barium Fluoride. N.I.Sorokin, M.W.Breiter: Solid State Ionics, 1997, 99[3-4], 241-50