The mobility of F was studied in monocrystals of an anion-deficient solid solution of the form, La1-xSrxF3-x, where x was equal to 0, 0.001, 0.003, 0.01, 0.03, 0.05 or 0.16. The material had the tysonite structure and was studied, by means of 19F nuclear magnetic resonance techniques, at temperatures ranging from 130 to 520K. It was found that, in all of the crystals, F diffusion began on the F1 sub-lattice. Upon increasing the temperature, ionic exchange between the F1 and F2,3 sub-lattices became observable. The addition of small amounts of Sr (x less than 0.003) significantly increased the ionic mobility between the sub-lattices. When x was between 0.003 and 0.03, a further increase in x had no significant effect upon the ionic exchange. When x was equal to about 0.01, the onset of cluster formation was noticeable. At higher concentrations (x between 0.03 and 0.16), it was found that the ionic mobility decreased again and that guest-induced vacancies were preferentially located on the F1 sub-lattice. At these dopant concentrations, the presence of large clusters seemed to play a significant role.

A.F.Privalov, H.M.Vieth, I.V.Murin: Journal of Physics - Condensed Matter, 1994, 6[40], 8237-43