Question

What happens when ${\rm{CaC}}{{\rm{l}}_{\rm{2}}}$ is doped with ${\rm{AgCl}}$?

Answer 1

We can understand doping as introducing some impurity as per our intention so as to alter or enhance the properties of the original matter; in this case properties of calcium chloride will be changed.

Complete answer:
We can have three types of point defects namely stoichiometric defects, impurity defects and non-stoichiometric defects. Here, we are adding or we can say introducing an impurity to a crystal of calcium chloride so we will have an impurity defect. Let’s try to understand what actually happens and how we get this impurity defect upon doping calcium chloride with silver chloride.
We know that in the crystal lattice of calcium chloride, we have calcium cations and chloride anions. Now, if we introduce silver chloride to this, anions are common but a different cation is being introduced by us. The new cation that is silver ion $\left( {{\rm{A}}{{\rm{g}}^{\rm{ + }}}} \right)$ has only one positive charge, whereas the original cation that is calcium $\left( {{\rm{C}}{{\rm{a}}^{{\rm{2 + }}}}} \right)$ has a positive charge of two.
So, in order to maintain the charge neutrality, two silver ions are needed to replace a single calcium ion. So the number of anions remains the same but now we have an increased number of cations or we can say metallic ions that will result in metal excess in the crystal lattice.

**Hence, we can say that when ${\rm{CaC}}{{\rm{l}}_{\rm{2}}}$ is doped with ${\rm{AgCl}}$, it leads to metal excess defect in calcium chloride.

Note: **
If we dope silver chloride with calcium chloride, the effect will be reversed as now two silver ions can be replaced with a single calcium ion creating metal deficiency in the silver chloride lattice.