Ionic conductivity of potassium iodide crystals

Ionic conductivity of pure and doped KI is measured in the temperature range 200 to 700°c. A large contribution to the conductivity by the anion vacancies is observed in pure KI at high temperatures. The solubility of Ba 2+ in KI is much higher than that of Cd 2+ , Pb 2+ and Ca 2+ . The behaviour of KI doped with Ba 2+ is similar to the behaviour of KCl and NaCl doped with divalent cation impurities. The solubility of CO 3 2- in KI is also good. Crystals doped with CO 3 2- show an increase in conductivity at high temperatures owing to the increase in anion vacancy concentration. At lower temperatures the conductivity of KI is suppressed by the CO 3 2- impurity. The values obtained for various energies of activation in KI crystals are E c = (0·72±0·02) ev for the migration of a cation vacancy, E A = (1·50±0·05) ev for the migration of an anion vacancy, W s = (1·6±0·1) ev for the formation of a separated pair of Schottky vacancies and W c similar 0·26 ev for the association of a cation vacancy with Ba 2+ impurity.