Which defect leads to decrease in the density of crystal?

In a normal spinel type structure, the oxide ions are arranged in ccp, whereas $$1 / 8$$ tetrahedral holes are occupied by $$\mathrm{Zn}^{2+}$$ ions and $$50 \%$$ of octahedral holes are occupied by $$\mathrm{Fe}^{3+}$$ ions. The formula of compound is

$$\mathrm{NaCl}$$ has face centred structure with edge length equal to $$361 \mathrm{~pm}$$. The radius is

Doping of silicon (Si) with indium (In) leads to the formation of