From the present work, combined with previous data, the jump rate of the isolated positive-ion vacancy in NaCl was found to involve a migration energy of 0.80eV. It was concluded that the energy of formation of a Schottky defect in an NaCl crystal was 2.12eV, while the entropy of formation was 6.28k. Very similar results, although of somewhat lower precision, applied to KCl.

Energy and Entropy of Formation and Motion of Vacancies in NaCl and KCl Crystals. R.W.Dreyfus, A.S.Nowick: Journal of Applied Physics, 1962, 33[1], 473-7