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 similar 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 (similar to 374 K) and large electric polarization (similar to 3.2 mu C/cm(2)). Further, F-PEAB also exhibits a high energy storage efficiency (eta) 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.