$\mathrm{CsCu}{\mathrm{Cl}}_3$ perovskite compound under extreme conditions

Halide perovskites have attracted intense research interest owing to their multifaceted and versatile applications in optoelectronics. This intrigue is further fueled by their propensity to undergo intricate structural modifications under extreme conditions, thereby instigating property changes. Within this context, in this paper, we delve deep into the intricate interplay of structural and vibrational attributes within the inorganic-metal halide perovskite-like $\mathrm{CsCu}{\mathrm{Cl}}_3$. Our approach employs Raman spectroscopy and synchrotron powder x-ray diffraction (SPXRD) techniques harnessed under the dual conditions of low temperatures and high pressures (HPs). We have observed a distinct spin-phonon coupling mechanism by employing Raman spectroscopy at low temperatures; this coupling has been manifested as a renormalization phonon phenomenon that occurs notably at $T^{*}=15$ K. The correlation between spin and phonon dynamics becomes pronounced through a notable hardening of phonon temperature dependence, a behavior intricately linked to the material antiferromagnetic transition at $T_N=10.7$ K. SPXRD under HP showed a first-order structural phase transition (SPT) at the critical pressure $P_c=3.69$ GPa, leading to the transformation from the hexagonal $P{6}_{5}22$ to a base-centered monoclinic cell. Notably, the coexistence of both phases is discernible within the pressure range from 2.79 to 3.57 GPa, indicating that the SPT involves the reorganization of the internal ${\left[{\mathrm{Cu}}_2{\mathrm{Cl}}_9\right]}^{5-}$ dimer unit, with the Cl-Cu-Cl bending contributing more than stretching modes. Furthermore, we demonstrate that the SPT is reversible, but residual strain pressure influences the modification of the critical pressure $P_c$ value upon pressure decrease.