Bilayer Janus Cr2I3Cl3: Sliding ferroelectricity with ultra-low switching barrier and enhanced out-of-plane piezoelectricity

Abstract

Recent experimental and theoretical studies have highlighted interlayer sliding can be an effective pathway to identify 2D ferroelectric materials with strong out-of-plane polarization and low ferroelectric flip-flop barriers. In this work, the electronic properties, ferroelectric switching mechanisms, and piezoelectric characteristics of Janus Cr₂I₃Cl₃ bilayers are researched by the first principles. Electrical property analysis reveals that the interlayer sliding modifies the coupling between adjacent layers, leading to the redistribution of vertical charge and resulting in the reversal of out-of-plane polarization, enabling ferroelectric switching. The vertical polarization direction in the AB stacking of the I-I and Cl-Cl configurations can be switched to the opposite direction in the BA stacking by overcoming energy barriers as low as 8.8 meV and 12.07 meV, respectively. Furthermore, the Janus Cr₂I₃Cl₃ bilayer maintains its indirect bandgap semiconductor nature, making it suitable for piezoelectric applications. The double-layer Janus Cr₂I₃Cl₃ exhibits substantial in-plane piezoelectric stain coefficients d₁₁ (10.65–18.97 pm/V), especially the I-Cl configuration displays significant out-of-plane piezoelectric coefficients d₃₁ (2.47–2.65 pm/V). These remarkable ferroelectric and piezoelectric properties position the Janus Cr₂I₃Cl₃ bilayer as a promising candidate for applications in multifunctional nanoelectronic devices.