Conductivity measurements were used to study the migration of cation vacancies in NaCl crystals. The activation energy for migration in undoped crystals, at 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.

Migration of Cation Vacancies in NaCl Crystals Highly Doped with Sr2+. E.Laredo, E.Dartyge: Solid State Communications, 1969, 7[17], 1225-8