What defines a vacant site defect in crystal lattices?

A vacant site defect in crystal lattices is characterized by the absence of an atom that should normally occupy a specific position within the lattice structure. This absence creates a "vacant" site, which is crucial for understanding how defects influence the material properties, such as conductivity and strength.

When an atom is missing from its expected position in the arrangement, it can disrupt the regular periodic structure of the lattice, leading to changes in how the lattice behaves under various conditions, including stress and temperature changes. This defect can affect the overall stability of the crystal and influence processes such as diffusion.

The other options describe different types of defects or alterations within a crystal lattice. For instance, a misplaced atom refers to interstitial defects, where an atom occupies a space that is not the normal lattice site, while an atom that is larger than typical might create strain in the lattice. Lastly, the formation of bonds with adjacent atoms indicates interactions that may not be consistent with a vacancy defect, as they pertain to the nature of bonding rather than the absence of an atom.