Superionic conductivity of the heterovalent solid solutions R 1−x M x F 3−x (R=REE, M=Ca, Ba) with tysonite-type structure

The fluorine-ion conductivity of anion-deficient solid solutions R 1− x Ca x F 3− x and R 1− x Ba x F 3− x having the tysonite (LaF 3 ) structure was investigated by the impedance spectroscopy method. R 1− x Ca x F 3− x ( R =La, Pr, Nd, Sm, Gd, Tb, Dy, Ho) and R 1− x Ba x F 3− x ( R =La, Pr, Nd) single crystals were grown from the melt by the Bridgman-Stockbarger method. The electrophysical measurements were performed in the frequency range 5−5×10 5 and temperature range 300–700 K. The temperature dependences of the electrical conductivity for the crystals studied is determined by the migration of fluorine anions along various structural positions. It is shown that, from the standpoint of increasing the conductivity of tysonite matrices R F 3 ( R =La, Pr, Nd), doping by CaF 2 and BaF 2 is less promising than SrF 2 .