CuBiP₂Se₆ (Copper Bismuth Phosphorus Selenide)

A layered van der Waals metal phosphochalcogenide related to the CuInP₂S₆ family, in which Cu and Bi cations occupy the octahedral sites of a P₂Se₆ framework. It is a candidate two-dimensional ferroelectric / antiferroelectric semiconductor, where off-centering of the Cu⁺ (and lone-pair-active Bi³⁺) ions produces switchable electric polarization that persists to few-layer thickness. Its combination of van der Waals layering and tunable polar order makes CuBiP₂Se₆ a candidate for two-dimensional ferroelectrics, non-volatile memory, and negative-capacitance devices.