What type of crystal defect is indicated in the diagram below? $\mathrm{Na}^{+} \mathrm{Cl}^{-} \mathrm{Na}^{+} \mathrm{Cl}^{-} \mathrm{Na}^{+} \mathrm{Cl}^{-}$ Cl □ $\mathrm{Cl}^{-}$ □ $\mathrm{Na}^{+}$ □ $\mathrm{Na}^{+}$ $\mathrm{Na}^{+} \mathrm{Cl}^{-} \square \mathrm{Cl}^{-} \mathrm{Na}^{+} \mathrm{Cl}^{-}$ $\mathrm{Cl}^{-} \mathrm{Na}^{+} \mathrm{Cl}^{-} \mathrm{Na}^{+}$ □ $\mathrm{Na}^{+}$

(B) Frenkel and Schottky defects

JEE Main · 2004 · 24 Apr 2004 · Offline · Solid State

What type of crystal defect is indicated in the diagram below?

Na^{+} Cl^{-} Na^{+} Cl^{-} Na^{+} Cl^{-}

Cl □

Cl^{-}

□

Na^{+}

□

Na^{+}

Na^{+} Cl^{-} □ Cl^{-} Na^{+} Cl^{-}

Cl^{-} Na^{+} Cl^{-} Na^{+}

□

Na^{+}

(A)Frenkel defect
(B)Frenkel and Schottky defects
(C)Interstitial defect
(D)Schottky defect✓ Correct

Answer: (D)

Solution

The sketch shows empty lattice sites, drawn as the blank squares, where both

Na X^{+}

cations and

Cl X^{-}

anions are missing, with no ion pushed into an interstitial gap. Losing equal numbers of cations and anions, so the crystal stays electrically neutral, is the hallmark of a Schottky defect. A Frenkel defect would instead show an ion displaced into an interstitial position, which does not appear here, so this is a Schottky defect.

JEE Main · 2004 · 24 Apr 2004 · Offline · Single correct option

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JEE Main · 2004 · 24 Apr 2004 · Offline · Solid State

Solution

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