Kinetic Monte Carlo simulations of organic ferroelectrics

Abstract

Ferroelectrics find broad applications, e.g. in non-volatile memories, but the switching kinetics in real, disordered, materials is still incompletely understood. Here, we develop an electrostatic model to study ferroelectric switching using 3D Monte Carlo simulations. We apply this model to the prototypical small molecular ferroelectric trialkylbenzene-1,3,5-tricarboxamide (BTA) and find good agreement between the Monte Carlo simulations, experiments, and molecular dynamics studies. Since the model lacks any explicit steric effects, we conclude that these are of minor importance. While the material is shown to have a frustrated antiferroelectric ground state, it behaves as a normal ferroelectric under practical conditions due to the large energy barrier for switching that prevents the material from reaching its ground state after poling. We find that field-driven polarization reversal and spontaneous depolarization have orders of magnitude different switching kinetics. For the former, which determines the coercive field and is relevant for data writing, nucleation occurs at the electrodes, whereas for the latter, which governs data retention, nucleation occurs at disorder-induced defects. As a result, by reducing the disorder in the system, the polarization retention time can be increased dramatically while the coercive field remains unchanged.

Suppressing depolarization by tail substitution in an organic supramolecular ferroelectric

“…S13 (ESI †), that show highly ordered directional stacks for the mixtures with a characteristic length scale that is in between the pure linear and branched compounds. The 1 : 1 mixtures having middling characteristics prove that the improvement is linear and no amplification effects, previously demonstrated in diluted solutions of branched-chiral and linear-achiral BTAs mixtures, 50,51 are present in our random stereochemistry mixtures in the solid-state.…”

“…Cornelissen et al have demonstrated by kinetic Monte-Carlo simulations that structural disorder has a much stronger impact on the depolarization rate than on the coercive field value. 50 Therefore, a lower level of structural and energetic disorder allows for significant improvement in polarization retention with only a slight increase in the concomitant coercive field value. These principles hold for blends of linear and branched BTAs, that are discussed further, as well.…”

Ferroelectrically Switchable Axial Polarization in Columnar Liquid Crystalline Phases

“…For the thermally activated nucleation limited switching mechanism, a greater critical domain size would lead to a higher depolarization E a and, in turn, to a longer retention time. This was also in line with the subsequent simulation results produced by the same authors . In addition to the room temperature operation, and fast switching, this BTA compound could be considered as a practical ferroelectric columnar LC.…”

“…This could suggest that the shorter homologs have the ability to enhance the long‐range intermolecular cooperation, resulting in the cumulative effect of the molecular dipole moments and, in turn, higher P s value. The authors confirmed the above experimental result by using a Monte‐Carlo simulation …”

Defects and defect engineering in Soft Matter

“…More recently Kemerink and coworkers developed an electrostatic model that was used as basis for 3D kinetic Monte Carlo simulations in order to describe switching kinetics in these ferroelectrics. 521 The authors found that in the case of spontaneous polarization reversal, nucleation occurs at defects, which are caused by disorder. In contrast, in the field-driven reversal, nucleation occurs at the electrodes.…”