Van Der Waals Order-Disorder Type Ferroelectric VOCl2 with Unusual Polarization Switching.

Harnessing atomic ordering through order-disorder transition is a powerful strategy to tailor electric polarization and functionality. However, most reported order-disorder ferroelectrics exhibit low Curie temperatures, narrow thermal hysteresis, and limited tunability, restricting their potential in nonvolatile memory technologies. Here, we identify VOCl2 as a new van der Waals order-disorder ferroelectric with site disorder, exhibiting an exceptionally wide thermal hysteresis (ΔT = 220 K) and a high Curie temperature (Tc = 440 K), associated with lattice expansion across the disorder to order transition. Moreover, the sensitivity of V4+ cations to structure distortions allows efficient polarization tuning under hydrostatic pressure, where pressure irreversibly induces the in-plane polarization at 2.3 GPa, and then drives a reversible polarization switching from in-plane to out-of-plane at 8.0 GPa. Such a giant thermal hysteresis and unusual polarization switching of VOCl2 open new opportunities for programmable phase-change devices with a broad operating window.