Question

why does AgCl doped with CdCl2 exhibits conductivity?

Answer 1

When AgCl is doped with CdCl2, two Ag+ ions are replaced by 1 Cd2+ ion. So where one Cd2+ ion occupies the site of one Ag+ ion, there is a cationic vacancy at the site of the other Ag+ ion. The released 2Ag+ ions combine with the 2Cl- ions of CdCl2 and become 2AgCl. There is an impurity defect as well as a vacancy defect in the crystal which is responsible for the movement of electrons and finally conduct electricity.