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 Cd2+, Pb2+ and Ca2+. The behaviour of KI doped with Ba2+ is similar to the behaviour of KCl and NaCl doped with divalent cation impurities. The solubility of CO32- in KI is also good. Crystals doped with CO32- 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 CO3 2- impurity. The values obtained for various energies of activation in KI crystals are Ec = (0·72±0·02) ev for the migration of a cation vacancy, EA = (1·50±0·05) ev for the migration of an anion vacancy, Ws = (1·6± 0·1) ev for the formation of a separated pair of Schottky vacancies and Wc similar 0·26 ev for the association of a cation vacancy with Ba2+ impurity.