Past exam of the materials science course of the University of Cambridge / 2022 / Paper 1 / 3 / b / i / 2

For mixed parity, one of the three pair sums is even and two are odd. Thus their phase factors sum to $-1$, givingThese superlattice reflections reveal chemical ordering. Their kinematic intensity is proportional to $|f_{\mathrm{Sc}}-f_{\mathrm{Al}}{|}^2$, and vanishes in the hypothetical limit of equal species scattering factors.