Question

What type of crystal defects is indicated in the diagram given below?
    $$\begin{array}{rl}& \\ & \begin{array}{cccc}N{a}^{+}& C{l}^{-}& N{a}^{+}& C{l}^{-}\\ C{l}^{-}& & C{l}^{-}& N{a}^{+}\\ N{a}^{+}& Cl& & N{a}^{+}\\ C{l}^{-}& N{a}^{+}& C{l}^{-}& N{a}^{+}\end{array}\begin{array}{c}N{a}^{+}\\ \\ C{l}^{-}\\ \end{array}\begin{array}{c}C{l}^{-}\\ N{a}^{+}\\ C{l}^{-}\\ N{a}^{+}\end{array}\\ & \end{array}$$

(A) Frenkel and schottky defect
(B) Schottky defect
(C) Interstitial defect
(D) Frenkel defect

Answer 1

Hint: In frenkel defect density of the solid remain same, while in schottky defect metal density is decreases. $$\text{AgBr}$$ is the ionic solid that shows both schottky and frenkel defects.

Complete step by step solution:
Any deviation from a perfectly ordered arrangement gives rise to defect or imperfection in the ionic crystal. Defects in crystals are produced either in addition to certain impurities in the pure crystal or by thermal effect.
There are two types of defects in the ionic crystal are stoichiometry defect and non-stoichiometry. Stoichiometry compounds are those compounding which the number of cation and anion are exactly in the ratio as shown by their chemical formula. Two types of defects are observed in these compounds (i) Schottky defect (ii) frenkel defect.

(i) Schottky defect – this type of defect is found when one cation and one anion are missing from there and leaving behind a pair of holes. The solid crystal remains neutral because equal amounts of cation and anion are missing.

(ii) frenkel defect –this is another type of stoichiometric defect, in which an ion leaves its appropriate site in lattice and occupies the interstitial site.
(A) In the given ionic compound there is no atom in the interstitial, so it will not show a frenkel defect.
(B) In this ionic compound equal numbers of cation and anion are missing from the ionic crystal and the crystal leaving and missing ion leaves behind hole.
(C) In an ionic crystal when some extra ion occupies the intestinal space of the lattice, this type defect is called interstitial defect.
(D) In the frenkel defect some ion leaves its appropriate site and occupies the interstitial space.
So, the correct answer is “Option B”.

Note: Frenkel defect is shown by those ionic compound which have much difference in the size of cation or anion, like $$\text{AgBr}$$ while those ionic solid showing schottky defect they do not show much difference in the size of cation or anion like $$\text{NaCl}$$.