Ultralow-Barrier Antiferroelectric–Ferroelectric Transition Enabled by Competing Polar Distortion in Two-Dimensional Ruddlesden–Popper Nitride Perovskites

High Resolution Image Download MS PowerPoint Slide Two-dimensional Ruddlesden–Popper (2D RP) nitride perovskites, combining strong covalency with reduced dimensionality and weak interlayer coupling, are promising candidates for low-energy polarization control. Here, we study 2D RP nitride perovskite La 2 WN 4 using first-principles calculations in combination with symmetry analysis and mode decomposition. La 2 WN 4 hosts a competing semiconducting ferroelectric (FE, Aba 2) phase and antiferroelectric (AFE, Pna 2 1 ) phase, where polarization originates from WN 6 octahedral distortions coupled to nitrogen displacements. Both the AFE–FE interconversion and polarization reversal proceed over low barriers, enabling fast, energy-efficient switching. External stimuli provide effective control, given that 1% biaxial compressive strain or an in-plane electric field of 0.025 V/Å can reversibly toggle between AFE and FE states. Moreover, La 2 WN 4 can be exfoliated into a stable semiconducting monolayer that retains sizable in-plane polarization with a low switching barrier, highlighting its potential for low-power-programmable AFE/FE functionalities.