A study of the anion mobility in mixed fluorides with the tysonite structure

Summary From the studies which have been carried out it follows that in Berthollide solid solutions with the tysonite structure there is intensive diffusion of fluoride ions in the vacancies, and this is responsible for the electrical conductivity of the crystals. It follows from an analysis of the NMR data obtained that the fluorine vacancies are produced in the positions corresponding to fluorine atoms of low mobility, confirming structural studies which indicate the preferential formation of vacancies in the F_III positions. At low temperatures, the movement of the highly mobile F_I fluorine atoms shows practically no association with the low-mobility F_III positions. Thus in spite of the high concentration of anion vacancies in the specimens studied, the mobility of fluorine at low temperatures does not increase, compared with the ideal tysonite structure. It follows from the temperature dependence of the¹⁹F NMR spectra, however, that the presence of vacancies increases the mobility in the subsystems of fluorine atoms with low mobility and increases the exchange between the fluorine atoms with high and low mobilities.L. V. Kirenskii Institute of Physics, Siberian Branch, Academy of Sciences of the USSR. Institute of Crystallography, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 20, No. 4, pp. 622–626, July–August, 1979.