Write note on impurity defect ?

Explanation

(i) The defects in ionic solids in by adding impurity ions.
(ii) If the impurity ions are in different valence state from that of host, vacancies are created in the crystal lattice of the host.
(iii) For example, addition of `CdCl_(2)` to sillver chloride yields solid solutions where the divalent cation `Cd^(2+)` occupies the position of `Ag^(+)`
(iv) This will disturb the electrical neutrality of the crystal.
(v) In order to maintain the same, proportional number of `Ag^(+)` ions leaves the lattices.
(vi ) This produces a cation vacancy in the lattice, such kind of crystal defects are called impurity defects.