Question

Explain Schottky defect.

Hint:

Schottky defect reduces density, whereas Frenkel defect does not.

Answer 1

Step 1: Definition.
A Schottky defect is a type of point defect in ionic crystals where equal numbers of cations and anions are missing from their lattice sites.
Step 2: Characteristics.
\begin{enumerate} \item It reduces the density of the crystal. \item It maintains electrical neutrality because both cations and anions are missing in equal numbers. \item It is common in highly ionic compounds with high coordination numbers such as NaCl, KCl, CsCl. \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 the defect.
Conclusion:
A Schottky defect is a vacancy defect where cations and anions are absent from lattice sites, leading to decreased density of the solid.