DIFFUSION OF CU+ IN BETA-PHASE CUI

Measurements of ionic diffusion of Cu+ in solid CuI in the beta-phase is carried out with a non-destructive radioactive tracer technique, utilizing coincidence counting of the annihilation gammas from the positron decay of Cu-64. The diffusion coefficient and the activation energy for diffusion are evaluated. The experimental results show distinct diffusion character in the beta-phase which differs from those in the gamma- and alpha-phases. The beta-phase diffusion properties together with the previous results for gamma- and alpha-phases will provide valuable guidance for MD calculations, in which the diffusion coefficients and activation energies have been overestimated and the gamma-beta phase transition does not appear. The ionic conductivity of CuI estimated from tracer diffusion results and the Nernst-Einstein relation are compared with values from electrochemical methods. In all three phases the conductivities obtained from electrochemical methods are much lower than those calculated from the measured tracer diffusion coefficients.