Photoelastic effects which were caused by divalent ions that were diffused into crystals were observed. From these observations, diffusion coefficients were calculated for temperatures ranging from 480 to 700. The data could be described by:

D (cm2/s) = 2.5 x 10-2 exp[-1.1(eV)/kT]

Calculations were also made of the volume changes due to impurity-vacancy complexes. Upon monitoring the thermal dissociation of these complexes, it was concluded that the isolated vacancy caused a lattice expansion which was larger than the contraction which was due to the isolated divalent ion.

Effective Volumes of Vacancies of Divalent Ions and their Diffusion Coefficients in Alkali Halides. M.F.De Souza: Physical Review, 1969, 188[3], 1367-70