Two new high-temperature molecular ferroelectrics[1,5-3.2.2-Hdabcn]X(X=ClO_(4)^(-),ReO_(4)^(-))

Molecular ferroelectrics have attracted much attention because of their excellent piezoelectricity,mechanical workability,and second harmonic effect.Here,we successfully prepared two molecular ferroelectrics[1,5-3.2.2-Hdabcn]X(X=ClO_(4)^(-),1;ReO_(4)^(-),2)by reactions of a quasi-spherical amine 1,5-diazabicycle[3.2.2]nonane(1.5-3.2.2-dabcn)with HX aqueous solution.Compounds 1 and 2 undergo hightemperature phase transitions at 381 K(1)and 396 K(2).Before and after the phase transition,they crystallize in the polar point group mm2,and the centrosymmetric point groups mmm and 4/mmm,respectively.According to Aizu rules,these two compounds experience mmm Fmm2 and 4/mmm Fmm2 type ferroelectric phase transitions,respectively.The ferroelectricity of both compounds is well expressed in their polycrystalline film at room temperature with low coercive voltages of 13 V for 1 and 25 V for 2.Using piezoelectric force microscopy(PFM),the 180°anti-parallel ferroelectric domains and the reversible polarization switching can be clearly observed in 1 and 2.This high-temperature molecular ferroelectric material has great application potential in flexible materials,biomechanics,intelligent wearables and other fields.