LAUSR

Halide double perovskites have emerged as remarkable semicon-ductors owing to their non-toxicity and superior optoelectronic features. Despite recent exciting progress, halide double perovskites with bulk ferroelectricity are still sparse. Herein, we report the dis-covery of a multiaxial ferroelectric of layered halide double perov-skite, 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 dimen-sional 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 switch-ing), which are comparable to those of oxide perovskites. As far as we are aware, this is the first example of multiaxial ferroelectric in the booming family of halide double perovskites. Another fascinat-ing feature is that 1 also possesses biaxial ferroelastic order with a high Curie temperature of 375 K. Such discovery of halide double perovskite ferroelectric with multiple ferroic orders signifies an important step toward designing multifunctional ferroelectric mate-rials as well as inspires their further applications in optoelectronic devices.