= Solution
Ordering reflections by $d_{hkl}^{-2}=(h^2+k^2)/a^2+l^2/c^2$ with $c\simeq0.9a$, the first three nonzero families are \b[$001$, $110$ and $111$]. The $100$ family is extinct. Their <structure factors> are
$$
\boxed{F_{001}=2(f_{\rm Au}-f_{\rm Cu}),\quad F_{110}=2(f_{\rm Au}-f_{\rm Cu}),\quad F_{111}=2(f_{\rm Au}+f_{\rm Cu}).}
$$
The <atomic scattering factors> in each expression are evaluated at that reflection's scattering vector, so equal symbolic forms need not mean equal numerical amplitudes at different angles. In particular, the low-angle superlattice peaks need not be the strongest peaks.
Back to article page
