 Superlattice reflection

A diffraction reflection enabled by a larger chemical or structural repeat than that of a reference parent structure. In ordered $L{1}_2$ $A_{3}B$, sites $(0,0,0)$ and the three face centres give $F=f_B+f_A[(-1{)}^{h+k}+(-1{)}^{h+l}+(-1{)}^{k+l}]$. Equal-parity indices give $f_B+3f_A$; mixed parity gives $f_B-f_A$. The latter vanish when the two scattering factors are equal.