Large Electrostrictive Coefficient in a Two-Dimensional Hybrid Perovskite Ferroelectric

Two-dimensional (2D) hybrid organic–inorganic
perovskites
(HOIPs) are attracting tremendous interest for their great scientific
and technological potential in photovoltaics and optoelectronics.
Although the ferroelectricity in 2D HOIPs has been greatly developed,
however, to date no phosphonium-based 2D HOIP ferroelectrics have
yet been found. Meanwhile, electrostriction plays an important role
in the electromechanical behavior of ferroelectrics, while it has
never been reported for 2D HOIP ferroelectrics. Here, we present the
first phosphonium-based 2D HOIP ferroelectric (EATMP)­PbBr4 (EATMP = (2-aminoethyl)­trimethylphosphanium) with a direct bandgap
of 2.84 eV. Notably, (EATMP)­PbBr4 possesses a high Curie
temperature of 534 K, which is the highest among all reported 2D HOIP
ferroelectrics. Moreover, it exhibits a large electrostrictive coefficient
of about 3.96 m4 C–2 as well, far exceeding
those of PVDF (1.3 m4 C–2) and inorganic
ones (∼0.034–0.096 m4 C–2). With excellent ferroelectric and piezoelectric properties and
the merit of easy fabrication, (EATMP)­PbBr4 shows great
potential in applications for future smart devices of actuators, transducers,
and sensors.