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
(Tc) 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 Tc 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.