To Be or Not To Be Polar: The Ferroelectric and Antiferroelectric Nematic Phases

We report two new series of compounds that show the ferroelectric nematic, N-F, phase in which the terminal chain length is varied. The longer the terminal chain, the weaker the dipole-dipole interactions of the molecules are along the director and thus the lower the temperature at which the axially polar N-F phase is formed. For homologues of intermediate chain lengths, between the non-polar and ferroelectric nematic phases, a wide temperature range nematic phase emerges with antiferroelectric character. The size of the antiparallel ferroelectric domains critically increases upon transition to the N-F phase. In dielectric studies, both collective (ferroelectric) and non-collective fluctuations are present, and the ferroelectric mode softens weakly at the N-N-X phase transition because the polar order in this phase is weak. The transition to the N-F phase is characterized by a much stronger lowering of the mode relaxation frequency and an increase in its strength, and a typical critical behavior is observed.

Automated summary

Two new series of compounds showing the ferroelectric nematic phase are reported, with the variation of terminal chain length. The temperature at which the axially polar N-F phase is formed decreases as the terminal chain length increases. For compounds with intermediate chain lengths, a wide temperature range nematic phase with antiferroelectric character emerges. Dielectric studies reveal both collective and non-collective fluctuations, with different behaviors observed in different phase transitions.