Renewing Halogen Substitution Strategy for the Rational Design of High-Curie Temperature Metal-Free Molecular Antiferroelectrics.

Metal-free molecular antiferroelectric (AFE) holds a promise for energy storage on account of its unique physical attributes. However, it is challenging to explore high-curie temperature (T c ) molecular AFEs, due to the lack of design strategies regarding the rise of phase transition energy barriers. By renewing the halogen substitution strategy, we have obtained a series of high-T c molecular AFEs of the halogen-substituted phenethylammonium bromides (x-PEAB, x=H/F/Cl/Br), resembling the binary stator-rotator system. Strikingly, the p-site halogen substitution of PEA + cationic rotators raises their phase transition energy barrier and greatly enhances T c up to ~473 K for Br-PEAB, on par with the record-high T c values for molecular AFEs. As a typical case, the member 4-fluorophenethylammonium bromide (F-PEAB) shows notable AFE properties, including high T c (~374 K) and large electric polarization (~3.2 μC/cm 2 ). Further, F-PEAB also exhibits a high energy storage efficiency (η) of 83.6 % even around T c , catching up with other AFE oxides. This renewing halogen substitution strategy in the molecular AFE system provides an effective way to design high-T c AFEs for energy storage devices.