Question

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?

Answer 1

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.