Structure–Property Relations in Metal-Substituted Polar Chalcogenides under Pressure

Layered chalcogenides like CuInP 2 S 6 are attracting attention as room-temperature ferroelectrics with enhanced polarization under compression and the ability to undergo pressure-assisted aging. Less has been done to reveal the impact of combined physical and chemical pressure. In this work, we integrate diamond anvil cell techniques with synchrotron-based infrared absorbance and Raman scattering spectroscopies, lattice dynamics calculations, and an analysis of the energy landscape to explore symmetry and space group progressions in the AB P 2 S 6 family of materials ( A = Cu, Ag; B = Cr, Sc, V, In). All four of the B-site substituted systems host a common set of pressure-driven structural phase transitions near 4 and 12 GPa that follow trends in metal ion size. Within the Cc space group, smaller cations stabilize new states at significantly lower pressures. For instance, while CuInP 2 S 6 displays a monoclinic Cc → trigonal P 31 c symmetry restoration across P C,1 = 4.6 GPa, the Sc analog hosts the same progression at 2.6 GPa. We extend these structure–property relations to quaternary systems (many involving magnetic and/or ferroelectric functionality), further supporting the development of pressure-tunable electronic devices for environmental sensing, robotics, health monitoring, and biomachine interfaces.