Past exam of the materials science course of the University of Cambridge / 2019 / Paper 1 / 3 / c / iii / Solution

The first peak is $001$, with $d_{001}=c$; the second is $110$, with $d_{110}=a/\sqrt{2}$. Applying Bragg's law with $\lambda =0.193604\mathrm{nm}$ givesThus $c/a=0.927$, consistent with the approximate ratio used to order the reflections. These are the lengths of the supplied larger basal cell; the primitive basal lattice parameter is $a/\sqrt{2}=0.2798\mathrm{nm}$.