Unusual ferroelectric-dependent birefringence in 2D trilayered perovskite-type ferroelectric exploited by dimensional tailoring

Abstract

<h2>Summary</h2> Ferroelectrics with switchable spontaneous polarization have taken a dominant position as the nonlinear optical candidates, of which birefringence is an essential merit to optical devices. Despite the increasing advance of hybrid perovskite ferroelectrics, it remains a great challenge to control and tune their birefringence, thus hindering their practical optical applications. Here, we present a 2D trilayered hybrid perovskite-type ferroelectric obtained by 3D-to-2D dimensional tailoring, [(CH₃)₂CH(CH₂)₂NH₃]₂(CH₃NH₃)₂Pb₃Cl₁₀, showing biaxial polarizations of ∼5 μC/cm² and a relatively wide optical band gap. The intrinsic 2D architecture results in highly anisotropic principal refractive indices, namely, the optical birefringence. Interestingly, its birefringence can be reversibly switched through ferroelectric-to-paraelectric symmetry breaking. The birefringence tuning is further established by virtue of pretransitional modulation of ferroelectricity, exhibiting unusual polarization-dependent behaviors. In our judgment, this study on the polarization-dependent birefringence of hybrid perovskite ferroelectrics will provide a new pathway toward modulating nonlinear optical properties for smart devices.