Question

Schottky defect is observed in crystals when ______.

• A. some cations move their lattice site to interstitial site
• B. equal number of cations and anions are missing from the lattice
• C. some lattice site are occupied by electrons
• D. some impurity is peresent in the lattice

Answer 1

Answer: (B)

equal number of cations and anions are missing from the lattice

In ionic crystals, the defect forms when oppositely charged ions leave their lattice sites, creating vacancies. These vacancies are formed in stoichiometric units, to maintain an overall neutral charge in the ionic solid. The surrounding atoms then move to fill these vacancies, causing new vacancies to form. Normally these defects will lead to a decrease in the density of the crystal.

So, correct answer is option $B$.