Fig. 1: Schematic representation of the milling setup used in this study.

The PMMA jars are used with the Fritsch Pulverisette 23 (a). The primary X-ray beam \(\vec{p}\) (yellow line) passes through the jar and is diffracted by the sample contained within (light blue). Two different jars were developed (see Supplementary Note 2 for details), made from PMMA (transparent) and PVC (black) or stainless steel caps. The jar used for Reactions I–III is 12 mm internal diameter and comprises 0.75 mm walls, whereas the jar used for Reaction IV is 10 mm internal diameter with 0.5 mm walls. Diffraction with this setup results in splitting of each Bragg reflection into a convolution of 2θ positions (b–d), as the powder inside the jar is distributed across different locations and hence a range of sample-to-detector distances. Thus, the measured scattering vectors are markedly offset when the jar is investigated in a general position with respect to the primary beam (c, d) and can be minimised with accurate jar alignment (b).