Three-Dimensional Lead Bromide Hybrid Ferroelectric Realized by Lattice Expansion

Three-dimensional (3D) organic-inorganic lead halide hybrids have become a hot academic topic because of their various functional properties. However, 3D lead halide hybrid ferroelectrics are still very rare until now. Here, we report a new 3D lead halide perovskite-related ferroelectric, (EATMP)Pb₂Br₆ [EATMP = (2-aminoethyl)trimethylphosphanium]. Based on nonferroelectric CH₃NH₃PbBr₃, by replacing PbBr₆ octahedra with a Pb₂Br₁₀ dimer of edge-sharing octahedra as the basic building unit, the expanded 3D lead bromide perovskite analog was formed with the large [EATMP]²⁺ cations occupying the voids of framework. Notably, (EATMP)Pb₂Br₆ displays a direct bandgap of 2.81 eV, four polarization directions, and a high Curie temperature (T_c) of 518 K (much beyond that of BaTiO₃, 393 K), which is the highest among all reported 3D organic-inorganic hybrid ferroelectrics. Such a high T_c may result from the high rotational energy barrier of cations induced by a larger molecular volume and relatively low crystal symmetry. Our work provides an efficient avenue to construct new 3D organic-inorganic lead halide hybrids and would inspire the further exploration of 3D lead halide ferroelectrics.