The diffusion of Fe2+ ions was measured, at temperatures ranging from 240 to 420C, by using a tracer and serial-sectioning technique. The temperature dependence of the diffusion (table 8) could be described by:

D (cm2/s) = 4.9 x 103 exp[-1.42(eV)/kT]

It was concluded that the migration of Fe2+ ions proceeded via vacancy association. Upon assuming an activation enthalpy of 0.2eV for Fe-vacancy complexes, the activation enthalpy for the migration of Fe2+ was estimated to be 1.1eV. This was some 3 times the migration enthalpy of the free unassociated vacancy. Diffusion of Ferrous Ion in Silver Bromide and Evidence of Vacancy Migration. W.J.Mealing, A.L.Laskar: Physical Review B, 1978, 17[2], 860-5