Anionic conductivity and thermal stability of single crystals of solid solutions based on barium fluoride

Abstract

The anionic transport in single crystals with a fluorite-type structure of the nominally pure BaF 2, the dilute doped BaF 2 with 0.01 and 0.1 mole % LaF 3 and the anion-excess binary Ba 1 − x La x F 2 + x (0 ≤ x ≤ 0.5), Ba 0.85R 0.15F 2.15( R = La, Sm, and Lu), and Ba 0.8R 0.2F 2.2 ( R = La, Ce, Nd, Gd, Tb, and Ho) solid solutions were studied by impedance spectroscopy in the temperature range from 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 transition in these materials. The microscopic origin of the anionic conductivity depends mainly on the nature of the defect structure in the solid solutions. By controlling the composition of Ba 1 − x R x F 2 + x crystals the fluoride ionic conductivity can reach a value of about 1 S cm −1 at 1073 K.