2 Interstitial mechanism to be effective for diffusion in interstitial sol sol 3. Vacancy mechanism Atoms jump directly in to nearby vacant site, AG being small Different kind of atoms has different( chemical) affinity for vacancy Motion of atom Motion of vacancy (a)Vacancy mechanism (b)Interstitial mechanism2. Interstitial mechanism to be effective for diffusion in interstitial sol.sol. 3. Vacancy mechanism. Atoms jump directly in to nearby vacant site, being small. Different kind of atoms has different (chemical) affinity for vacancy.  G