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 (<i>T</i>_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, (<i>R</i>)-3-quinuclidinol and (<i>S</i>)-3-quinuclidinol, as well as the racemic mixture (<i>Rac</i>)-3-quinuclidinol. The homochiral (<i>R</i>)- and (<i>S</i>)-3-quinuclidinol crystallize in the enantiomorphic-polar point group 6 (<i>C</i>₆) at room temperature, showing mirror-image relationships in vibrational circular dichroism spectra and crystal structure. Both enantiomers exhibit 622<i>F</i>6-type ferroelectric phase transition with as high as 400 K [above that of BaTiO₃ (<i>T</i>_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/cm²), low coercive field (15 kV/cm), and identical ferroelectric domains. Their racemic mixture (<i>Rac</i>)-3-quinuclidinol, however, adopts a centrosymmetric point group 2/<i>m</i> (<i>C</i>_2h), undergoing a nonferroelectric high-temperature phase transition. This finding reveals the enormous benefits of homochirality in designing high-<i>T</i>_c ferroelectrics, and sheds light on exploring homochiral ferroelectrics with great application.