Phase transition of 2D van der Waals ferroelectrics

Abstract

Two-dimensional (2D) van der Waals ferroelectrics with switchable electric polarization offer exciting possibilities in the fields of physics, materials science, and device engineering. Beyond the conventional polarization-state regulation through electric-field, 2D ferroelectrics can offer important additional functionalities through isomeric phases, including paraelectric and antiferroelectric phases. In recent years, a variety of novel ferroelectric orders have been discovered in 2D materials, resulting from intra- or inter-layer symmetry-breaking. These hidden phases, exhibit attractive properties, and understanding their phase transition mechanisms and controlling the transitions has become a central topic in the field of 2D ferroelectrics. Furthermore, phase control is a primary step towards scalable synthesis of 2D ferroelectrics and device applications. Here, we highlight the diverse mechanisms of the phase transitions in 2D ferroelectrics, particularly intrinsic and extrinsic ferroelectrics. We also summarize different approaches and respective conditions for phase control. Moreover, the in situ experimental techniques for studying phase transitions, and the rationalized scalable synthetic methods of 2D ferroelectrics are discussed. Finally, rich functionalities, opportunities and emerging applications combining phase control and ferroelectricity in phase-change ferroelectric devices are envisioned, with the remaining challenges briefly discussed.