A crystal system is hexagonal if its unit cell having $\mathrm{a}=\mathrm{b}\ne \mathrm{c}$ axial ratio and
$\mathrm{\alpha }=\mathrm{\beta }=90°,$ $\mathrm{\gamma }=120°$ axial angles. Crystal of $\mathrm{A}\mathrm{g}\mathrm{B}\mathrm{r}$ has both Schottky defect and Frenkel defect. Frenkel defect is shown by ionic solid having low coordination number.