Trapping of Interstitials in Metals

The term trapping is used extensively to refer to the fact that interstitial atoms often find interstices associated with lattice imperfections to be energetically preferable to normal sites. This preference results in a delay of diffusion of interstitial atoms near these sites. As understanding of the details of lattice imperfections has improved, understanding of the effect of traps on the diffusion process has increased. Trapping is often illustrated by the use of a potential energy diagram. This simple model is characterized by a potential energy well deeper than those of surrounding interstitial sites. The energy required for the interstitial to jump into the trap is the same as that required for jumping into other adjacent interstitial sites, but that required for jumping out is greater. The additional energy required to leave the site is often designated as the trap binding energy, E/sub B/. Potential energy diagrams appropriate for most traps in metals are likely to be more complicated, but this simple model is a starting point for more sophisticated models of trapping. Imperfections may occasionally produce interstitial sites less favorable than normal sites and thus be less preferred. Little experimental exploration of this anti-trapping phenomenon has been carried out, however.more » Developments in understanding at various levels of trapping of interstitial impurities by lattice imperfections are examined.« less