Chemistry - Solid State Question with Solution | TestHub

In an impurity defect, foreign atoms are present in the crystal lattice of the host.

When the impurity atoms replace host atoms at regular lattice sites, it is a substitutional impurity defect. When the impurity atoms occupy the interstitial spaces (voids) of the host lattice, it is an interstitial impurity defect.

Steel is iron with a small amount of carbon. The Fe atoms occupy the regular lattice sites, while the much smaller C atoms occupy the interstitial spaces of the Fe lattice.

Therefore, stainless steel is an example of an interstitial impurity defect.