A crystalline solid is composed of the elements 'A' and 'B.' A atoms are present at the corners, while B atoms are present at the face centers. However, one atom of A is missing from one of the corner points. What type of crystal defect is this, and how does it happen? What happens to the density of this solid material?
Atoms adjacent to a vacancy are less restrained than those which are completely surrounded by the atoms and thus, can vibrate more randomly. Each vacancy contributes a small amount of vibrational entropy to the total entropy of the crystal.