Past exam of the materials science course of the University of Cambridge / 2022 / Paper 1 / 3 / b / ii / Solution

Keep the matrix spots and add precipitate reflections at all integer $(h,k,0)$ with $0<h^2+k^2\le 8$. Even-even spots are fundamental; every other allowed position in this zone is a superlattice reflection. The added positions are $100,010,110,210,120$ and their symmetry-related signs. Each position actually denotes the corresponding signed index pair, not one radial ring. The precipitate grid spacing is $1/a_p$; the nearest fundamental separation is $2/a_p=0.4878{\mathring{\mathrm{A}}}^{-1}$. If matrix and precipitates are coherent and similarly oriented, their fundamental spots approximately coincide, with finite mismatch potentially giving splitting or broadening. The sketch assumes common orientation, small strain, appreciable sampled precipitate volume and predominantly single scattering; electron diffraction can have dynamical intensity effects.