2.2.3. X-ray Diffraction and Pawley fit

The crystallinity was investigated by X-ray diffraction (XRD) using a Bruker D8 Advance in reflection mode. It was operated at 20 °C, 40 kV, and 40 mA using Cu-K_α radiation. Each measurement was done 30 min after the low-pressure treatment in a 2θ range from 5° to 70° with a step size of 0.006571365° and 4 s per step, resulting in a total measurement time of 7.25 h. The powder of each sample was transferred into an X-ray amorphous PVC powder carrier and smoothed to ensure no sample displacement. To guarantee that the shift of the reflections in the XRD was not caused by a sample displacement error in the preparation, 2.2 wt% (11 mg) silicon was added as an internal standard. The diffraction patterns were evaluated by the database of the Powder Diffraction File (PDF-2) 2020 of the International Centre for Diffraction Data (ICDD).

Furthermore, the cell parameters were analysed with a Pawley fit [19] using the data provided by Hartman et al. [23], the measured XRD data of this work, and the software TOPASv6 by Bruker.