Oxygen Vacancies Generated Out-of-Plane and In-Plane Ferroelectricity in Layered Bi2WO6 Nanoflake

Ferroelectricity in ultrathin 2D materials has garnered significant attention owing to its potential applications in nonvolatile memory, nanoelectronics, and optoelectronics. However, the exploration of ferroelectricity in materials possessing inherent centrosymmetric or mirror symmetry, particularly in the 2D domain, remains limited. In this study, the chemical vapor deposition (CVD) technique is utilized to synthesize ultrathin Bi 2 WO 6 (BWO) nanoflakes, revealing robustly intercorrelated out-of-plane (OOP) and in-plane (IP) ferroelectric polarization. The measured ferroelectric phase transition temperature of ultrathin BWO nanoflake is ≈800 K. The emergence of OOP ferroelectricity in BWO nanoflake is ascribed to the displacement of oxygen vacancies between neighboring asymmetric sites, leading to the disruption of local structural mirror symmetry and the alignment of dipole moments. Moreover, the IP and OOP ferroelectric responses are modulated by distinct maximum bias voltages. This investigation offers novel insights into the advancement of 2D ferroelectrics with elevated Curie temperatures.