= Solution
\b[The <solid> trace is wurtzite; the dashed trace is <zinc> blende.] The isolated strong dashed peak is the cubic $111$ reflection. The <solid> trace has hexagonal $100$, $002$ and $101$ reflections in this angular interval; its central $002$ peak is the one at $28.65^\circ$, while cubic $111$ occurs at $28.53^\circ$. These assignments are consistent with the absence of lower-angle reflections.
In the ideal close-packed model, the cubic $111$ and hexagonal $002$ reflections probe the same local alternating layer geometry. Their scattering strength per suitably normalized amount of material and their angular factors are therefore very similar, but <powder diffraction multiplicity> differs: the cubic family has eight directed normals, while hexagonal $002$ has two. This explains the approximately \b[fourfold greater intensity] of the dashed peak. Comparing unnormalized conventional-cell <structure factors> alone would be misleading because the cells contain different numbers of formula units. Peak heights additionally depend on line widths; the multiplicity argument applies most directly to integrated intensities.
Back to article page
