Enabling Record‐Low Coercive Field and Large Polarization in Hybrid Germanium Iodide Ferroelectric Through Chemical Bonding Engineering

ABSTRACT Ferroelectrics, featuring a natural switchable polarization, have motivated immense interest due to their transformative potential in electronics, micromechatronics and electro‐optics. Despite the remarkable advances achieved, the high coercive field required to reconfigure robust chemical bonds in traditional ferroelectrics fundamentally precludes their applications in next‐generation energy‐efficient devices. Herein, we present an innovative chemical bonding engineering approach to develop a hybrid metal halide ferroelectric, (iso‐amylammonium) 2 CsGe 2 I 7 ( ICGI ), which demonstrates ultra‐low barrier ferroelectricity. Through enhancing the chemical bonding anisotropy via n s 2 lone pairs stereochemical expression, the Ge‐I bonding in ICGI adopts an asymmetrical pyramidal coordination geometry, which breaks structural inversion symmetry and results in a large spontaneous polarization up to 19.09 µC/cm 2 . Particularly, the smooth switching pathway refrained from abrupt breaking and reformation of weakened short‐range bonding interactions results in a record‐low coercive field < 0.35 kV/cm (corresponding to switching energy < 0.0575 J/cm 3 ), much lower than traditional ferroelectrics such as BaTiO 3 (> 1.0 kV/cm) and HfO 2 (> 1000 kV/cm). Furthermore, benefiting from the low barrier ferroelectricity, ICGI demonstrates a low electric field driven pronounced electrocaloric effect with an adiabatic Δ T /Δ E of 800 mK·cm/kV. This work encourages the targeted design of low barrier ferroelectrics, which sheds light on their applications in next‐generation ultralow‐power devices.