Experimental evidence for an achiral orthogonal biaxial smectic phase without in-plane order exhibiting antiferroelectric switching behavior

Abstract

We report unambiguous experimental evidence for an achiral orthogonal biaxial smectic-A phase which exhibits antiferroelectric switching behavior. The evidence is based on x-ray-diffraction measurements, texture observation, and the results of dielectric and electro-optical measurements.

Field-induced transformations in the biaxial order of non-tilted phases in a bent-core smectic liquid crystal

“…The orthogonal phases of the bent-core materials consist of SmAP A and SmAP R . SmAP A was first discovered by Eremin et al [11] who also proposed that the polar directors in the neighboring layers were packed antiferroelectrically and ferroelectricity was induced by the application of the electric field above a threshold value. The SmAP R phase with uniaxial structure was discovered by Pociecha et al [13], where they postulated a random arrangement of the polar directors among the neighboring layers.…”

Dark conglomerate phases of bent-core liquid crystals

“…They mainly include SmAPR, SmAPA, SmAPAR, SmAP and SmAPF phases, where random, ferroelectric, antiferroelectric are represented by the subscripts R, A and F, respectively. The first experimental evidence for the existence of a SmAP phase in bent-core liquid crystals was given by Eremin et.al [12] The compound exhibited a biaxial antiferroelectric polar smectic A (SmAPA) phase with the polarization of alternating neighbouring layers being antiparallel [ Fig.1]. A number of novel electro-optic effects in the SmAPA phase were reported by Nagaraj et al [13] where the reorientations in the SmAPA phase exhibit biaxial-uniaxial-biaxial transitions, with switching times of the order of ~500 µsec [13][14].…”

Dual Symmetry in Bent-Core Liquid Crystals and Unconventional Superconductors

“…In fact, we have shown in references [5] that EL and EL' are actually incommensurate. In EL the polarization wave reads: (11) where e X (z)=cos(Qz) e x -sin(Qz) e y and e Y (z)=sin(Qz) e x +cos(Qz) e y are perpendicular unit vectors turning within the x-y plane. The two wavelengths λ mod =1/Q and λ =1/K<<λ mod are incommensurate.…”

“…[7,8] that this model permits to foresee the stabilization of four ordered phases, denoted by C, R, and EL corresponding, respectively, to linear, circular and elliptic polarizations of the order-parameter wave. R describes the smectic C P phase predicted in 1992 [10] and then observed in bent-core systems [10,11], EL describes the commonly observed B2 phase [12,13], and we have proposed that C is an unmodulated approximation of the intriguing B7 phase found in 1999 [2]. In these phases the polarization and tilt waves are "parallel", in a sense explained below.…”