Enabling Record-Low Coercive Field and Large Polarization in Hybrid Germanium Iodide Ferroelectric Through Chemical...

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)₂CsGe₂I₇ (ICGI), which demonstrates ultra-low barrier ferroelectricity. Through enhancing the chemical bonding anisotropy via ns² 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/cm². 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/cm³), much lower than traditional ferroelectrics such as BaTiO₃ (> 1.0 kV/cm) and HfO₂ (> 1000 kV/cm). Furthermore, benefiting from the low barrier ferroelectricity, ICGI demonstrates a low electric field driven pronounced electrocaloric effect with an adiabatic ΔT/ΔE 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.