**2. Materials and Methods**

The elemental educts for the crystal growth of AgCrP2S6, as listed in Table 1, were obtained from Alfa Aesar and kept in an argon filled glove box for storage and handling.


**Table 1.** Elemental educts used for the CVT growth of AgCrP2S6.

The crystals obtained from the CVT crystal growth experiments were thoroughly characterized by scanning electron microscopy (SEM) regarding their morphology and topography using a secondary electron (SE) detector and regarding chemical homogeneity via the chemical contrast obtained from a back scattered electron (BSE) detector. For this, a ZEISS EVO MA 10 scanning electron microscope was used. The chemical composition of the crystals was investigated by energy dispersive X-ray spectroscopy (EDX), which was measured in the same SEM device with an accelerating voltage of 30 kV for the electron beam and using an energy dispersive X-ray analyzer.

The crystal structure of the obtained crystals was investigated by powder X-ray diffraction (pXRD), which was measured on a STOE STADI laboratory diffractometer in transmission geometry with Cu-K*α*<sup>1</sup> radiation from a curved Ge(111) single crystal monochromator and detected by a MYTHEN 1K 12.5◦ -linear position sensitive detector manufactured by DECTRIS. The pXRD patterns were initially analyzed by pattern matching using the HighScore Plus program suite [25]. After the crystallographic phase was identified, a structural refinement of the crystal structure model was performed based on our experimental patterns using the Rietveld method in Jana2006 [26].
