Unveiling the Racemization in Ferroelectrics with Coupled Ferroelectricity and Optical Activity

The most distinctive features of ferroelectrics are spontaneous polarization and depolarization. Ferroelectricity was first observed in Rochelle salt, a compound with a chiral component in which the molecular chirality is not affected by depolarization. For structurally chiral ferroelectrics (SCFs), such as triglycine sulfate, which lacks chiral components, the depolarization effect on chirality presents an intriguing and unexplored topic. In this study, we focus on a newly proposed chiral optical topic in optically active ferroelectrics with coupled ferroelectricity and optical activity. We examined the depolarization effect on the optical activity in these ferroelectric materials and employed chiral-environment crystallization and solid-state circular dichroism (CD) techniques to elucidate the racemization-depolarization mechanism in an SCF for the first time. For polar and nonchiral optically active ferroelectrics, optical activity is averaged out in the powder state, resulting in no CD signal. Additionally, we experimentally validated the consistency between CD measurements and optical activity theory across the four optically active point groups (m, mm2, 4̅, 4̅2m). These findings could advance the development of chiral spintronic devices by leveraging coupled ferroelectricity and optical activity to tune the spin selectivity.