An above-room-temperature ferroelectric two-dimensional halide double perovskite with direction dependent properties.

Herein, we introduce a new non-centrosymmetric 2D halide double perovskite Cl 0.26 Br 3.74 PA 4 AgSbBr 8 (CPAS) with A-site linker, 3-chloropropylamine. CPAS exhibits above room-temperature ferroelectricity, with spontaneous polarization of 3.4 μC cm -2 . The polarization is direction dependent, where ferroelectricity is observed perpendicular to octahedral sheets but mere capacitive phenomena between the sheets. The material shows defect- or phonon-mediated charge conduction. The optical properties reveal a bandgap of 2.48 eV with blue emission.