Pressure-driven phase transformations and phase segregation in ferrielectric <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>CuIn</mml:mi><mml:msub><mml:mi mathvariant="normal">P</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">S</mml:mi><mml:mn>6</mml:mn></mml:msub><mml:mtext>−</mml:mtext><mml:msub><mml:mi>In</mml:mi><mml:mrow><mml:mn>4</mml:mn><mml:mo>/</mml:mo><mml:mn>3</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">…

Layered multiferroic materials exhibit a variety of functional properties that can be tuned by varying the temperature and pressure. As-synthesized $\mathrm{CuIn}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$ is layered material displays ferrielectric behavior at room temperature. When synthesized with Cu deficiencies, spontaneously phase segregates to form paraelectric ${\mathrm{In}}_{4/3}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$ (IPS) domains in two-dimensional self-assembled heterostructure. Here, we study effect hydrostatic pressure on structure Cu-deficient Raman spectroscopy measurements up 20 GPa. Detailed analysis frequencies, intensities, linewidths peaks reveals four discontinuities spectra around 2, 10, 14, 17 At \ensuremath{\sim}2 GPa, observe structural transition initiated diffusion IPS domains, which culminates drastic reduction number 10 We attribute this possible monoclinic-trigonal higher pressures (\ensuremath{\sim}14 GPa), significant increases peak intensities sharpening suggest band gap lowering an isostructural electronic transition, onset metallization above released, again separates into two distinct chemical within same single crystalline framework---however, these are much smaller size than as-synthesized resulting suppression ferroelectricity through nanoconfinement. Hydrostatic thus used tune $\mathrm{CuIn}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$.