Fluorine self-diffusion in CaF2 and BaF2

The self-diffusion of F-18 in single crystals of BaF₂ and CaF₂ was measured between 350 and 940°C. The results were in agreement with diffusion coefficients deduced from ionic conductivity studies, and yieldedH's of 1,6 eV for BaF₂ and of 2.0 eV for CaF₂ for intrinsic diffusion. Below 700°C, extrinsic diffusion behaviour was observed in CaF₂ withH=0.9 eV. The formation energy for anion Frenkel defects was estimated to be in the range 2.2 to 3.1 eV. Both anion and cation diffusion rates were increased in CaF₂ doped with SmF₃ as compared with pure CaF₂, indicating an interrelation between anion and cation defects, as observed previously in the related substances, UO₂ and UO_2+x , The migration energy of cations was estimated to be roughly in the range 1.5±0.6 eV. The implications of the results in terms of diffusion mechanisms are discussed and the remaining uncertainties are indicated.Experiments performed in 1968 at CCR Euratom, Ispra, Italy. The present study constitutes part II of a study of fluorine self-diffusion. Part I is concerned with LiF and NaF (see ref. 6]).