Space‐Charge Contribution to Grain‐Boundary Diffusion

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Abstract
The contributions of the space‐charge cloud to impurity and self‐diffusion in the grain‐boundary region of ionic materials are shown by calculations for doped KC1. The magnitude of these effects is modest (< 103Dl) and limited in dimension (10 to 200 Å). Both enhancement and reduction in the charge cloud contribution to boundary diffusivities are predicted. In the charge cloud, appreciable diffusivity enhancement is indicated only for the ion on the sublattice opposite that of the principal impurity. The large boundary‐diffusion enhancements and boundary widths often reported in “pure” and doped samples cannot be explained by the space‐charge contribution.