Step 1: Understanding the Concept:
Schottky defect is a stoichiometric defect found in highly ionic compounds where the size of cations and anions is similar.
Step 3: Detailed Explanation:
In an ionic crystal, if an equal number of cations and anions are missing from their regular lattice sites, it creates vacancies.
This maintains the electrical neutrality of the crystal.
Since mass decreases but volume remains the same, the density of the crystal decreases.
Example: \(NaCl, KCl, CsCl\).
Step 4: Final Answer:
Schottky defect is a vacancy defect that reduces the density of ionic solids.