Past exam of the materials science course of the University of Cambridge / 2017 / Paper 1 / 3 / b / i

The even indices give an allowed reflection. Its spacing is $d_{200}=0.280\mathrm{nm}$, andThe $(200)$ planes are parallel to the cut $(100)$ face, so the ordinary coupled reflection scan reaches them directly. This is an easy, strong peak, with the two ionic amplitudes adding rather than subtracting.