  Halide perovskite has attracted intense research interest owing to its
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, our study delves deep into the intricate interplay of
structural and vibrational attributes within the inorganic-metal halide
perovskite-like CsCuCl3. Our approach employs Raman spectroscopy and
Synchrotron Powder X-Ray Diffraction (SPXRD) techniques harnessed under the
dual conditions of low temperatures and high pressures. 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 TN = 10.7 K. The SPXRD under high pressure
showed a first-order structural phase transition (SPT) at the critical pressure
Pc = 3.69 GPa, leading to the transformation from the hexagonal P6522 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 [Cu2Cl9]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 Pc value upon pressure decrease.
