Cation diffusion along boundaries in sodium chloride

The investigation of 22Na tracer diffusion in NaCl for different annealing times t at 633 K has revealed an inhomogeneous component of fast diffusion at small t, identified as substructure diffusion in single crystals and as grain boundary diffusion in bicrystals. In the latter case the product of boundary diffusion coefficient times boundary width was determined. Substructure and boundary diffusion are associated with a thickness dimension of several μm, which suggests the enhanced transport is most probably due to segregated and/or precipitated residual impurities. The effect of a constant applied electric field is to magnify the inhomogeneous component of transport by a factor that depends on the ratio of the mobility in the substructure to the mobility in the lattice.