The contributions which were made, to anion transport, by vacancies and vacancy pairs were deduced from an analysis of anion diffusivities and of the temperature dependence of the Frenkel-defect formation energy, as deduced from Na tracer diffusion. At high temperatures, the 2 contributions were comparable. For the single-vacancy process, the activation energy and pre-exponential factor were anomalously large. For Br diffusion in undoped material, via single vacancies, the results could be described by:

D (cm2/s) = 1.1 x 1016 exp[-3.47(eV)/kT]

In the case of vacancy pairs, the results could be described by:

D (cm2/s) = 447 exp[-1.70(eV)/kT]

A.P.Batra, L.M.Slifkin: Journal of Physics - C, 1978, 11[8], L317-20