In materials allowing interstitial diffusion, migrating atoms can be incorporated into the interstitial sites of the host lattice to form a solid solution known as an interstitial solid solution. The interstitial sites are determined by the host lattice's geometry. In lattices such as fcc and bcc, the interstitial solutes typically occupy octahedral and/or tetrahedral interstitial sites. The diffusion of an interstitial solute occurs when it jumps from one interstitial site to an adjacent site. This mechanism is referred to as interstitial diffusion, as illustrated in Figure .