Abstract
The current rates of recycling of precious and rare earth metals from electronic components are
unsatisfactory, only 22% of the materials are recovered[1]. This situation represents a waste of
natural resources, hence more sustainable materials are needed. Molecular ferroelectrics, in par-
ticular plastic crystals, have the unique advantage of being easy to recycle due to their solubility
in organic and aqueous solutions. Furthermore, plastic crystals are flexible and can be produced
and shaped into devices using low temperature processes. Despite these advantages, they have not
yet achieved the electronic properties required to make them attractive for many applications.
The origin of the polarization in molecular ferroelectrics is complex, resulting from many different
factors. To improve understanding of molecular ferroelectrics, we have combined a systematic
search of the literature to find high remanent polarization materials, with density functional theory
(DFT) calculations of several of these materials to gain deeper understanding of the relationship
between the spontaneous polarization, composition and structural properties of the materials.
The search revealed several material systems, (benzylammonium)2PbCl4, HdabcoClO4 and diiso-
propylammonium iodide. In the (benzylammonium)2PbCl4 system the substitution of a Cl-ion for
a H-atom in the benzylammonium molecule increased the polarization by 79%[2]. In HdabcoClO4
the small cation size allowed for grater displacement, thus the material displayed strong spontan-
eous polarization[3]. Finally, the spontaneous polarization found in diisopropylammonium iodide
was 33 μC cm−2 the highest polarization for organic ferroelectrics recorded[4].
Using these materials as prototypical systems, we aimed to develop and easy computational method
for calculating polarization in molecular ferroelectrics, regardless of the polarization mechanism,
in order to better understand the structure-polarization relationships. This will be the basis for a
deeper insight into plastic crystals and enable the possibility to design and engineer materials with
tailored properties and hopefully lead to their replacing non-sustainable components with a more
sustainable technology.