Question

Explain Schottky defect with the help of a diagram.

Hint:

Remember: Schottky defect reduces density, whereas Frenkel defect does not.

Answer 1

Step 1: Understanding the Schottky defect.
A Schottky defect occurs when equal numbers of cations and anions are missing from their lattice sites in an ionic crystal.
Step 2: Properties of Schottky defect.
\begin{enumerate} \item It decreases the density of the crystal because some ions are missing. \item It usually occurs in highly ionic compounds with high coordination numbers, such as NaCl, KCl, and CsCl. \item Electrical neutrality is maintained because the number of missing cations equals the number of missing anions. \end{enumerate} Step 3: Diagram representation.
\[ \begin{array}{|c|c|c|c|} \hline + & - & + & -
\hline - & \square & - & +
\hline + & - & \square & -
\hline - & + & - & +
\hline \end{array} \] Here, $\square$ indicates missing ions representing Schottky defects.
Conclusion:
A Schottky defect is a type of vacancy defect in ionic crystals where equal numbers of cations and anions are missing, leading to a decrease in density.