EXPERIMENTAL VERIFICATION OF CORRELATION FACTOR FOR VACANCY DIFFUSION IN SILVER CHLORIDE

Diffusion coefficients for Ag tracers and ionic conductivity have been measured in AgCl containing 100 to 250 mole ppm Cd at temperatures of 125-225°C. Under these circumstances cation vacancies should be dominant, thereby allowing an unambiguous comparison of the measured correlation factor to the theoretical value for vacancies on a f.c.c. lattice. In practice it is found necessary to correct for a finite concentration gradient of Cd along the length of the samples and for a small contribution of residual interstitial Ag ions at the higher temperatures. The possible contribution to diffusion of Ag by cation vacancies associated with divalent Cd ions to form complexes is shown to be negligible at all temperatures because of the very small jump frequency of the Cd ion in the complex. With these corrections complete agreement is found between experimental and theoretical correlation factors within the experimental error of 1.0 to 1.5 per cent, thus demonstrating the absence of any systematic error in either diffusion or conductivity measurements. © 1969.