LAUSR

The application of pressure on halide perovskite materials provides key insights into their structural properties and the collective motions of their basic structural units. Here, we use synchrotron X-ray diffraction and Raman spectroscopy measurements combined with density functional theory calculations to perform a comprehensive study on the structural and vibrational properties of the so-called defect halide perovskites Cs2SnX6 (X = Cl, Br, I) under high hydrostatic pressures up to 20 GPa. We find that, while Cs2SnCl6 and Cs2SnBr6 retain a face-centered cubic (FCC) structure for all studied pressures, Cs2SnI6 undergoes successive phase transformations initially to a more disordered structure and secondly to a low-symmetry monoclinic I2/m phase. The first transition is only evidenced by certain features emerging in the Raman spectra at ∼3.3 GPa, whereas the latter happens in a pressure window of around 8–10 GPa and involves tilting and elongation of SnI6 octahedra and hysteretic behavior with pressure r...