Lattice dynamics and phase transition in CrI3 single crystals

The vibrational properties of CrI3 single crystals were investigated using Raman spectroscopy and were analyzed with respect to the changes of the crystal structure. All but one mode are observed for both the low-temperature R3¯ and the high-temperature C2/m phase. For all observed modes the energies and symmetries are in good agreement with DFT calculations. The symmetry of a single layer was identified as p3¯1/m. In contrast to previous studies we observe the transition from the R3¯ to the C2/m phase at 180 K and find no evidence for coexistence of both phases over a wide temperature range.