Organic enantiomeric high- <i>T</i> _c ferroelectrics

Abstract

For nearly 100 y, homochiral ferroelectrics were basically multicomponent simple organic amine salts and metal coordination compounds. Single-component homochiral organic ferroelectric crystals with high-Curie temperature ( T c ) phase transition were very rarely reported, although the first ferroelectric Rochelle salt discovered in 1920 is a homochiral metal coordination compound. Here, we report a pair of single-component organic enantiomorphic ferroelectrics, ( R )-3-quinuclidinol and ( S )-3-quinuclidinol, as well as the racemic mixture ( Rac )-3-quinuclidinol. The homochiral ( R )- and ( S )-3-quinuclidinol crystallize in the enantiomorphic-polar point group 6 ( C 6 ) at room temperature, showing mirror-image relationships in vibrational circular dichroism spectra and crystal structure. Both enantiomers exhibit 622 F 6-type ferroelectric phase transition with as high as 400 K [above that of BaTiO 3 ( T c = 381 K)], showing very similar ferroelectricity and related properties, including sharp step-like dielectric anomaly from 5 to 17, high saturation polarization (7 μC/cm 2 ), low coercive field (15 kV/cm), and identical ferroelectric domains. Their racemic mixture ( Rac )-3-quinuclidinol, however, adopts a centrosymmetric point group 2/ m ( C 2h ), undergoing a nonferroelectric high-temperature phase transition. This finding reveals the enormous benefits of homochirality in designing high- T c ferroelectrics, and sheds light on exploring homochiral ferroelectrics with great application.