Polarization Switching Induced by Slowing the Dynamic Swinglike Motion in a Flexible Organic Dielectric

Molecular
motions with large amplitude in close-packed crystals
accompany large distortions of the molecular configuration, which
generally generate orientational structural transitions between diverse
states and enable the tuning of their bulk physical properties. We
present a flexible organic dielectric, di-n-butylammonium
chlorodifluoroacetate (1), which exhibits a reversible
temperature-induced spontaneous polarization switching at 243 K (Tc). Ferroelectric hysteresis loop measurements
and second harmonic generation experiments reveal its excellent polarization
switching capacity with spontaneous
polarization of 3.9 μC cm–2. Temperature-dependent
solid-state nuclear magnetic resonance measurements clearly elucidate
the dynamical mechanism of polarization switching of 1. Above Tc, an active swinglike motion
in long-chain di-n-butylammonium (DBA) cation is
confirmed, resulting in complete obliteration of the dipole moments.
When the temperature decreases below Tc, the swinglike motions are frozen and the whole DBA cation becomes
considerably more rigid, corresponding to polar order, which greatly
contributes to polarization switching. It is believed that this finding
opens up a potential strategy for the design of new polar materials
as switchable electric devices.