Selfdiffusion in single crystals of sodium iodide. (Ionic conduction)

The conductivity of pure NaI and NaI+CdI 2 and the 22 Na + diffusion in pure NaI has been measured as a function of temperature. From a comparison of the diffusion results obtained by the two methods it is concluded that the point defects in NaI are of the Schottky type and that the cation selfdiffusion, which is the dominant contribution to the conductivity, occurs via isolated vacancies. The conductivity results for the Cd 2+ doped crystals have been analysed in terms of the simple theory of ionic conductance. This analysis gives values of 2.27 eV, 0.47 eV and 0.51 eV for the enthalpies of Schottky defect formation, cation vacancy migration and Cd 2+ -cation vacancy association respectively.