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.