A Multiaxial Layered Halide Double Perovskite Ferroelectric with Multiple Ferroic Orders

Halide double perovskites
have emerged as remarkable semiconductors
owing to their nontoxicity and superior optoelectronic features. Despite
recent exciting progress, halide double perovskites with bulk ferroelectricity
are still sparse. Herein, we report the discovery of a multiaxial
layered halide double perovskite ferroelectric, BA2CsAgBiBr7 (1, BA = n-butylammonium),
which exhibits a fascinating ferroelectric feature with a Curie temperature
of ∼273 K and unique semiconducting nature. Particularly, for 1, the dimensional reduction reduced strong coupling of octahedral
rotations and cation ordering leads to a notable spontaneous polarization
of 5.2 μC/cm2 and an extremely high fatigue resistance
(over 107 switching), which are comparable to those of
oxide perovskites. As far as we are aware, this is the first example
of a multiaxial ferroelectric in the booming family of halide double
perovskites. Another fascinating feature is that 1 also
possesses a biaxial ferroelastic order with a high Curie temperature
of 375 K. Such discovery of a halide double perovskite ferroelectric
with multiple ferroic orders signifies an important step toward designing
multifunctional ferroelectric materials as well as inspires their
further applications in optoelectronic devices.