Superlattice reflection
= Superlattice reflection
A <diffraction> reflection enabled by a larger chemical or structural repeat than that of a reference parent structure. In ordered $L1_2$ $A_3B$, 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.