Diffusion of Silver in Silver Bromide and Evidence for Interstitialcy Migration

Experimental results are presented for the diffusion of silver in silver bromide single crystals for temperatures from 140°C to the melting point. The results are obtained by the sectioning technique, using radioactive tracers. The observed diffusion coefficients fall below the values that would normally be expected from the electrical conductivity by a factor of 0.46 to 0.66. The discrepancy is ascribed to the simultaneous occurrence of two types of interstitialcy jumps, with corrections introduced for differing displacements of interstitials and tracer atoms and for correlation effects according to Bardeen and Herring. The resulting mobilities can be represented as $\mu ={\mu }_0\exp (-\frac{U}{\mathrm{kT}})$ over a wide range of temperatures with ${\mu }_0=6.2\mathrm{}\times {10}^{-3\mathrm{}} \mathrm{and} 1.57\times {10}^{-3\mathrm{}}$ ${\mathrm{cm}}^2$/volt-sec and $U=0.078\mathrm{} \mathrm{and} 0.225$ ev, respectively, for collinear and non-collinear jumps. These values are in reasonable agreement with theoretical calculations for silver chloride. The diffusion coefficient is observed to fall increasingly below expected values as the temperature approaches the melting point, and as a possible explanation it is surmised that the activation energy for collinear jumps drops gradually towards zero. A comparison is made to similar results which have been reported for diffusion of silver in silver chloride.