Question

Examine the given defective crystal.
$\begin{array}{ccccc}{A}^{+}& B^{-}& A^{+}& B^{-}& A^{+}\\ B^{-}& O& B^{-}& A^{+}& B^{-}\\ A^{+}& B^{-}& A^{+}& O& A^{+}\\ B^{-}& A^{+}& B^{-}& A^{+}& B^{-}\end{array}$
Answer the following questions:
(i) What type of stoichiometric defect is shown by crystal?
(ii) How is the density of the crystal affected by this defect?
(iii) What type of ionic substances show such defect?

Answer 1

(i) Schottky defect is shown by the mentioned crystal, as equal number of cations and anions are missing in the crystal lattice.

(ii) This defect leads to decrease in density, as equal number of the cations and anions are missing from the crystal lattice.

(iii) This kind of defect is shown by those ionic substance in which the cations and anions are of almost similar sizes. Examples are $KCl,NaCl,CsCl$.