Grain boundary diffusion coefficient

The grain boundary diffusion coefficient is the diffusion coefficient of a diffusant along a grain boundary in a polycrystalline solid. It is a physical constant denoted ${\displaystyle D_{b}}$, and it is important in understanding how grain boundaries affect atomic diffusivity. Grain boundary diffusion is a commonly observed route for solute migration in polycrystalline materials. It dominates the effective diffusion rate at lower temperatures in metals and metal alloys. Take the apparent self-diffusion coefficient for single-crystal and polycrystal silver, for example. At high temperatures, the coefficient ${\displaystyle D_{b}}$ is the same in both types of samples. However, at temperatures below 700 °C, the values of ${\displaystyle D_{b}}$ with polycrystal silver consistently lie above the values of ${\displaystyle D_{b}}$ with a single crystal.