Dielectric measurements of new antiferroelectric liquid crystals

Abstract

Three new pure antiferroelectric materials, synthesized at the Military University of Technology (MUT), were investigated by dielectric means. Clear relaxation modes were detected, i.e., Soft, Goldstone, low frequency in-phase (PL) as well high frequency anti-phase (PH) modes for paraelectric Sm A*phase, ferroelectric Sm C* phase and antiferroelectric Sm CA* phase, respectively. Additionally, a high relaxation mode in Sm CA* was found. The relaxation frequencies fR of the observed modes were calculated from Cole-Cole diagrams.

Dielectric relaxation spectroscopy and electro-optical studies of a new, partially fluorinated orthoconic antiferroelectric liquid crystal material exhibiting V-shaped switching

“…The increase in GM strength in the SmC * phase in comparison to that in the SmC* phase was previously reported by Uehara et al [30] and Lagerwall et al [31]. Therefore, from the above considerations, we can identify the range from 92.0 to 78.6 C as a new phase and that can be identified as the SmC * phase which is extremely sensitive with respect to the cell conditions, aligning material, etc., and which did not appear in earlier studies [9] in a 5-mm cell due to the suppression of this phase in thin cells. Three dielectric modes are observed in this phase, two in the low frequency region and another one in the high frequency region (Figure 4(b)).…”

“…This should be the Goldstone-like mode in the SmC A * phase and reveals the coexistence of ferroelectric and antiferroelectric orders [19] in the low-temperature phase. In an earlier study of this material, Perkowski et al [9] identified this mode as P L . They denoted the highest frequency (,106 Hz) mode as the X mode and the mode around 105 Hz as the P H mode in the SmCA* phase.…”

“…Moreover, the cell thickness has a dominant role to play in such phases. An earlier study by Perkowski et al [9] investigated the dielectric properties of OAFLC in a 5-mm cell, but in thin cells, where the surface effect has the dominating influence, the whole phase behaviour is affected and, on occasions, a certain thermodynamic phase is suppressed completely. Therefore, we have used a 10-mm cell for dielectric studies and observed another phase appearing in the temperature range between 78.6 and 92 C during heating which did not appear in the differential scanning calorimetry (DSC) curve.…”

Dielectric Behavior of Antiferroelectric Phase Induced in a Binary Mixture

“…From Fig. 9 one can conclude that P H mode is stronger under DC field (when of course SmC A * exists) [7,8]. Below 60 • C the BIAS field does not affect the SmC A * phase at all.…”

The temperature and concentration dependence of helical pitch in the mixtures of antiferroelectric compounds with the opposite helical twist sense

“…The orthoconic antiferroelectric compounds of the homologous series 4'-(1-methylheptyloxycarbonyl) biphenyl-4-yl 4-[(4,4,4,3,3,2,2-heptafluorobutoxy)alk-1-oxy 2-fluorobenzoate (3FmHPhF) were used for investigations (Scheme 1): The phase transitions were confirmed by dielectric measurements [23].…”