The properties of charged dislocations were exploited to obtain the formation free energies for positive and negative ion vacancies and the cation-vacancy-divalent-impurity binding energy for calcium-doped NaCl. An internal-friction technique was used to determine the temperatures for which the dislocations were uncharged, for four Ca concentrations. These critical temperatures were then related to the defect parameters. At 400 ro 700C, the cation-vacancy free formation energy was 0.635eV-6.1k(T-823K), while the binding energy of a calcium ion and a nearest-neighbor cation vacancy was 0.49eV.

Formation Free Energies and Vacancy-Divalent-Ion Binding Energy from Internal-Friction Experiments on NaCl. K.L.Kliewer, L.S.Koehler: Physical Review, 1967, 157[3], 685-92