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 Cl0.26Br3.74PA4AgSbBr8 (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.

Direction Dependent Ferroelectricity and Conductivity in a Single Crystal 2D Halide Double Perovskite.

Halide ferroelectric materials have garnered a lot of interest because of their distinctive electrical and structural characteristics. In this study, the design and development of a new non-centrosymmetric 2D layered halide double perovskite material, Cl1.14Br2.86PA4AgInBr8 (CPAIn) is reported. This material shows ferroelectric properties above room temperature, with a Curie temperature of 190 °C. This behavior is achieved through the substitution of the halogenated A-site organic linker, 3-chloropropylammonium. CPAIn exhibits anisotropic ferroelectric behavior with higher spontaneous polarization of 6.25 µC cm-2 along the perpendicular direction to the octahedral layers, whereas the value decreases to 0.174 µC cm-2 between sheets. While using bottom contact to study the nature of polarity within a sheet, the P-E loop displays capacitive loop. The nature and value of polarization is highly direction dependent, and to further understand the mechanism of conduction, a combination of temperature-dependent impedance studies and poling dependent conductivity techniques are employed. These directional dependent properties hold immense potential in memory devices, sensors and photovoltaics, piezoelectric devices and energy storage.

The effect of halogenated spacer cations on structural symmetry-breaking in 2D halide double perovskites.

Herein, we present a strategy to introduce above-room temperature non-centrosymmetry into two-dimensional halide double perovskites (A'4M'M''X8) using a halogenated A'-site organic linker, 3-chloro/bromo propyl amine. These crystals exhibit anisotropic polarization with three orders of magnitude variation between different crystallographic axes. The non-centrosymmetry is further confirmed by piezo-force microscopy studies and its role in the thermal and optical properties was investigated.