Question

Which of the following point defects are shown by $AgBr\left(s\right)$ crystals?

A) Schottky defect
B) Frenkel defect
C) Metal excess defect
D) Metal deficiency defect

• A. $\left(A\right)$ and $\left(B\right)$
• B. $\left(C\right)$ and $\left(D\right)$
• C. $\left(A\right)$ and $\left(C\right)$
• D. $\left(B\right)$ and $\left(C\right)$

Answer 1

The correct option is A $\left(A\right)$ and $\left(B\right)$

$\text{Analyzing the options}:$

Option (A) & (B):

• Schottky defect in ionic crystals arises when equal number of cations and anions are missing from the normal site of lattice, resulting in equal number of cation and anion vacancies.
• Frenkel defect in ionic crystals arises when a cation is missing from the normal lattice position and is occupying an interstitial site.

$AgBr\left(s\right)$ has $CCP$ (cubic close-packed) type lattice and shows both Schottky and Frenkel defect.

This is mainly due to the intermediate sizes of the $A{g}^{+}$ and $B{r}^{-}$ ions, they can show defects with cation dislocation in the lattice (Frenkel) and the missing equal number of cations and anions (Schottky) as well

Option (C):

A metal excess defect is caused due to anionic vacancies and by the presence of extra cations in the interstitial site and $AgBr$ does not show metal excess defect.


Option (D):

In metal deficiency defect, the positive ion is missing from its lattice site and the extra negative charge is balanced by some nearby metal ion acquiring two charges instead of one and $AgBr$ does not show metal deficiency defect.