Powder X-ray diffraction of van der Waals compound CuInP2S6 under pressures from 2.0−10.8 GPa

Abstract

A synchrotron powder X-ray diffraction experiment observed a monoclinic Cc → a trigonal P31c structural transition of 2D van der Waals ferroic compound CuInP₂S₆ near 5.8 GPa and room temperature. The lattice constants a, b, and c in the Cc phase decrease with pressure, while the monoclinic angle β increases. Near the transition pressure, a, c and β saturate. These parameters collapse upon crossing the transition, but the van der Waals gap is almost constant crossing the phase boundary. This observation suggests that the P31c phase maintains the van der Waals nature, and the inter-layer sliding drives the structural transition.