Molecular piezoelectrics
are attracting tremendous interest because
of their easy processing, light weight, low acoustical impedance,
and mechanical flexibility. However, reports of molecular piezoelectrics
with a piezoelectric coefficient <i>d</i><sub>33</sub> comparable
to piezoceramics such as barium titanate (BTO, 90–190 pC/N)
have been scarce. Here, we present a uniaxial molecular ferroelectric,
trimethylchloromethylammonium tribromocadmium(II) (TMCM-CdBr<sub>3</sub>), in which the halogen bonding might be a possible critical point
for the stabilization of one-dimensional (1D) {CdBr<sub>3</sub>}<sup>−</sup> chain and further reservation of its ferroelectricity
in such organic–inorganic hybrid crystalline systems. It has
a large <i>d</i><sub>33</sub> of 139 pC/N, 1 order of magnitude
higher than those of most classically uniaxial ferroelectrics such
as LiNbO<sub>3</sub> (6–16 pC/N) and Rochelle salt (∼7
pC/N), and comparable with those of multiaxial ferroelectrics such
as BTO and trimethylbromomethylammonium tribromomanganese(II) (112
pC/N). Moreover, the simple single-crystal growth and easy-to-find
polar axis enable it to hold a great potential for applying in the
single-crystal form. In light of the strong, specific, and directional
halogen-bonding interactions, this work provides possibilities to
explore new classes of molecular piezoelectrics and contribute to
further developments
