True ferroelectric switching in thin films of trialkylbenzene-1,3,5-tricarboxamide (BTA)

Abstract

We have investigated the ferroelectric polarization switching properties of trialkylbenzene-1,3,5-tricarboxamide (BTA), which is a model system for a large class of novel organic ferroelectric materials. In the solid state BTAs form a liquid crystalline columnar hexagonal phase that provides long range order that was previously shown to give rise to hysteretic dipolar switching. In this work the nature of the polar switching process is investigated by a combination of dielectric relaxation spectroscopy, depth-resolved pyroelectric response measurements, and classical frequency- and time-dependent electrical switching. We show that BTAs, when brought in a homeotropically aligned hexagonal liquid crystalline phase, are truly ferroelectric. Analysis of the transient switching behavior suggests that the ferroelectric switching is limited by a highly dispersive nucleation process, giving rise to a wide distribution of switching times.

Tuning the Ferroelectric Properties of Trialkylbenzene‐1,3,5‐tricarboxamide (BTA)

“…A characteristic diffraction peak spacing ratio of 1:√3:2 in the reciprocal q-space further discloses the hexagonal packing character of the molecules in the LC phase, which is considered to be a prerequisite for ferroelectric activity. [35,36] Phase transition temperatures obtained here match the values measured by the DSC ( Figure S1b, Supporting Information).…”

“…While BTA-C18 and BTA-C10 were successfully functioning as ferroelectrics in a columnar hexagonal liquid crystalline phase (Figure 1b), BTA-C6, however, showed no ferroelectric switching in liquid crystal cell devices. [36] Gorbunov et al further studied thin spin-coated BTA-C10 and BTA-C18 films and proved the true ferroelectric nature of the material, [35] which had been predicted in previous theoretical works on BTAs [37][38][39][40] and on dipolar discotic particles in general. [41][42][43][44] This is further discussed in the Supporting Information.…”

“…[31][32][33][34] The ferroelectric behavior, however, is a relatively new finding. [9,35] Fitié et al were first to probe BTA homologues with 18, 10, and 6 carbons-long alkyl chain (BTA-C18, BTA-C10, and BTA-C6). While BTA-C18 and BTA-C10 were successfully functioning as ferroelectrics in a columnar hexagonal liquid crystalline phase (Figure 1b), BTA-C6, however, showed no ferroelectric switching in liquid crystal cell devices.…”

“…Deep in the low temperature crystalline phase the coercive field becomes unattainably high, possibly above the breakdown limit due to reduced molecular mobility; above the melting temperature the material is paraelectric. [35] Therefore, the phase diagram gives the essential information about the operational temperature window of the devices. The DSC trace peak positions for cooling are summarized in Figure 1c.…”

“…Asterisks are data measured by Shishido et al [47] The shaded liquid crystalline phase is ferroelectric. [35] BTA-C6, C8, C10, and C12 material devices successfully operate at room temperature.…”