Ferroelectrics usually exhibit temperature‐triggered structural changes, which play crucial roles in controlling their physical properties. However, although light is very striking as a non‐contact, non‐destructive, and remotely controlled external stimuli, ferroelectric crystals with light‐triggered structural changes are very rare, which holds promise for optical control of ferroelectric properties. Here, an organic molecular ferroelectric, N‐salicylidene‐2,3,4,5,6‐pentafluoroaniline (SA‐PFA), which shows light‐triggered structural change of reversible photoisomerization between cis‐enol and trans‐keto configuration is reported. SA‐PFA presents clear ferroelectricity with the saturate polarization of 0.84 μC cm−2, larger than those of some typical organic ferroelectrics with thermodynamically structural changes. Benefit from the reversible photoisomerization, the dielectric real part of SA‐PFA can be reversibly switched by light. More strikingly, the photoisomerization enables SA‐PFA to show reversible optically induced ferroelectric polarization switching. Such intriguing behaviors make SPFA a potential candidate for application in next‐generation photo‐controlled ferroelectric devices. This work sheds light on further exploration of more excellent molecular ferroelectrics with light‐triggered structural changes for optical control of ferroelectric properties.
Chiral organic–inorganic
perovskites (COIPs) have recently
attracted increasing interest due to their unique inherent chirality
and potential applications in next-generation optoelectronic and spintronic
devices. However, COIP ferroelectrics are very sparse. In this work,
for the first time, we present the nickel-nitrite ABX3 COIP
ferroelectrics, [(R and S)-N-fluoromethyl-3-quinuclidinol]Ni(NO2)3 ([(R and S)-FMQ]Ni(NO2)3), where the X-site is the rarely seen NO2
– bridging ligand. [(R and S)-FMQ]Ni(NO2)3 display mirror-relationship
in the crystal structure and vibrational circular dichroism signal.
It is emphasized that [(R and S)-FMQ]Ni(NO2)3 show splendid ferroelectricity with both an
extremely high phase-transition point of 405 K and a spontaneous polarization
of 12 μC/cm2. To our knowledge, [(R and S)-FMQ]Ni(NO2)3 are the
first examples of nickel-nitrite based COIP ferroelectrics. This finding
expands the COIP family and throws light on exploration of high-performance
COIP ferroelectrics.
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.
A salicylaldehyde Schiff base hybrid lead iodide perovskite [SAPD]PbI3 (SAPD = 1-((2-hydroxybenzylidene)amino)pyridin-1-ium) has been synthesized and shows robust nonlinear optical response and large spontaneous polarization. The first introduction of salicylaldehyde...
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