Ionic conductivity of pure and doped sodium chloride crystals

New measurements are reported for the ionic conductivity of well-annealed crystals of pure NaCl, NaCl doped with Sr 2+ ions, and NaCl doped with S 2− ions. Analysis of these data leads to the conclusions (i) that the Schottky defect model is entirely adequate for NaCl (in contrast to KCl); and (ii) that the activation energy for the migration of anion vacancies is 0.74 eV. This last result is in agreement with values derived from the analysis of conductivity and diffusion data for pure NaCl and NaCl doped with Sr 2+ , and with theoretically-calculated values, but at variance with results from recent measurements on quenched sulphide-doped crystals.