Fig. 2: Rietveld plot of the Si640d NIST standard at different diffraction geometries.

In each case, the calculated profile is given (red line) against experimental data (black dots) and the difference pattern is shown (grey line). The peak split is compatible with the geometrical constraints typically observed in an in situ mechanochemical experiment. The primary beam \(\vec{p}\) (yellow line) passes through the jar and is diffracted by the sample contained within. The contribution to the overall peak shape of the sample distributed within the jar is highlighted in the insets with different colours: the scattering vectors are produced by the sample located at the jar wall closer to the source (\(\vec{{s}_{1}}\), green line), the wall nearer the detector (\(\vec{{s}_{3}}\), blue line), and by the sample distributed randomly within the jar (\(\vec{{s}_{2}}\), pink line). The difference in 2θ angle between scattering vectors \(\vec{{s}_{1}}\) and \(\vec{{s}_{3}}\) is larger when the jar is in a general position with respect to the primary beam \(\vec{p}\) (a). The difference in 2θ angle is minimised when the jar is accurately aligned (b), with negligible scattering contribution from the sample distributed within the jar (i.e. \(\vec{{s}_{2}}\)).