Room-Temperature Metal-Like Ferroelectric Molecular Crystal with Malleability and Ductility.

Abstract

Ferroelectric crystals possess essential properties for a wide array of applications, while their inherent brittleness presents significant challenges in smart scenarios that demand high flexibility and customizable shapes. Herein, an aminoborane adduct ferroelectric molecular crystal, trimethylamine chloroborane (TMACB), is synthesized, showing room-temperature metal-like malleability and ductility. TMACB crystallizes in rhombohedral R3m space group at room temperature and undergoes structural phase transition to monoclinic Cc space group at 256 K. The compressive strain of TMACB single crystal can reach ≈94% before fracture, more than 16 times that of traditional inorganic ferroelectrics (less than 6% in general), and large ultimate tensile strain of 15.6% can also be achieved. Both polarization-electric field hysteresis loop and piezoresponse force microscopy characterizations have demonstrated ferroelectricity of TMACB, which is further firmly supported by density functional theory calculation. Moreover, compressed thin sheet of TMACB crystal maintains promising ferroelectric performance with a large polarization value of 23.9 microcoulomb per square centimeter, close to that of inorganic ferroelectric BaTiO₃. The discovery breaks through the research paradigm of brittle ferroelectric materials and offers new insights into the exploration of highly deformable ferroelectric crystals for flexible wearable devices and adaptable sensor arrays in the future.