Robust Room-Temperature Ferroelectricity in β-Bi2SeO5 Thin Films

Atomic-scale two-dimensional (2D) ferroelectrics are garnering immense research interest for powering next-generation high-performance nanoelectronics. Herein, we report the discovery of robust room-temperature out-of-plane ferroelectricity in thin 2D β-Bi2SeO5 films, with the ferroelectric response persisting even down to the monolayer limit. The ferroelectricity of a 10 nm thick β-Bi2SeO5 thin film was also unambiguously revealed by ferroelectric analysis using a ferroelectric analyzer, achieving an out-of-plane polarization of 10 μC/cm2. Furthermore, a pronounced in-plane ferroelectricity and photoelectric effect were also observed, along with a strong coupling between them. First-principles density functional theory calculations identify the displacement and distortion of [SeO3] tetrahedra under external electric fields as the primary origin of the observed out-of-plane and in-plane ferroelectric polarization in β-Bi2SeO5 films. These findings open up new possibilities for using β-Bi2SeO5 thin films in future nanoscale electronic and quantum devices.