ANIONIC CONDUCTIVITY AND THERMAL-STABILITY OF SINGLE-CRYSTALS OF SOLID-SOLUTIONS BASED ON BARIUM FLUORIDE

The anionic transport in single crystals with a fluorite-type structur e of the nominally pure BaF2, the dilute doped BaF2 with 0.01 and 0.1 mole % LaF3 and the anion-excess binary Ba1-xLaxF2+x (0 less than or e qual to x less than or equal to 0.5), Ba0.85R0.15F2.15 (R = La, Sm, an d Lu), and Ba0.8R0.2F2.2 (R = La, Ce, Nd, Gd, Tb, and Ho) solid soluti ons were studied by impedance spectroscopy in the temperature range fr om ambient to 1073 K. At high temperatures the conductivity plots for the concentrated solid solutions display a considerable deviation from Arrhenius behaviour. This is caused by the diffuse Faraday phase tran sition in these materials. The microscopic origin of the anionic condu ctivity depends mainly on the nature of the defect structure in the so lid solutions. By controlling the composition of Ba1-xRxF2+x crystals the fluoride ionic conductivity can reach a value of about 1 S cm(-1) at 1073 K.