Conductivity measurements were used to study the migration of cation vacancies in NaCl crystals. The activation energy for migration in undoped crystals, at temperatures ranging from 200 to 400C, was equal to 2.3eV. For crystals which were doped with 4.6 x 10-4 %Sr, it was equal to 0.75eV.

E.Laredo, E.Dartyge: Solid State Communications, 1969, 7[17], 1225-8