Lattice dynamics and phase transition in CrI$_3$ single crystals

TL;DR

This study investigates the vibrational properties and phase transition of CrI₃ single crystals using Raman spectroscopy, revealing a clear transition at 180 K and confirming theoretical predictions about their structure.

Contribution

The paper provides new experimental evidence for the phase transition in CrI₃ at 180 K and clarifies the vibrational modes and symmetry changes with detailed Raman analysis.

Findings

Observed phase transition at 180 K from R-3 to C2/m

No coexistence of phases over a wide temperature range

Good agreement between experimental data and DFT calculations

Abstract

The vibrational properties of $\mathrm{CrI_3}$ 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 $R\bar{3}$ 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 $p\bar{3}1/m$. In contrast to previous studies we observe the transition from the $R\bar{3}$ to the $\mathrm{C2}/m$ phase at 180\,K and find no evidence for coexistence of both phases over a wide temperature range.