THz-TDS measurements were performed with a commercial spectrometer TeraPulse 4000 (TeraView Ltd., Cambridge, UK), and the measurement chamber was purged with nitrogen to eliminate the effect of water vapour. Variable-temperature measurements were facilitated by a cryostat (Janis, Massachusetts, USA) and the temperature was well-controlled with an attached temperature controller Lakeshore 330 (Ohio, USA). The sample pellets were first cooled down to 80 K and then heated up in steps to 300 K to examine the temperaturedependent behaviour of the spectral features. Measuring commercial samples at room temperatures allows the direct comparison of their spectra with those acquired during crystallisation experiments. However, acquiring spectra for crystalline samples at lower temperatures improves their quality since absorption in the terahertz region is highly affected by the temperature background, reflected in effects such as peak broadening and peak shifting.