Temperature Dependence of Low Frequency Dielectric Constants in Surface-Stabilized Ferroelectric Liquid Crystal

Abstract

We have studied the temperature dependence of two low-frequency dielectric relaxation modes in a surface-stabilized ferroelectric liquid crystal (SSFLC): space charge accumulation and X modes. From investigation of Cole-Cole plots the temperature dependence of dielectric strength and relaxation frequency ω r for the two low-frequency modes was obtained. The relaxation frequency follows the Arrhenius relation in the respective asymptotic regions far from the phase transition temperatures. From the Arrhenius plots the activation energies for the space charge accumulation mode and the X-mode were obtained as 0.42 eV and 0.13 eV, respectively. Temperature dependence of rotational viscosity in the smectic C * (SmC * ) phase conformed with the temperature dependence of the X-mode parameters in the effective Debye relaxation regime, which implicates a common origin of azimuthal molecular rotation for both the Goldstone mode and the X-mode. However, the X-mode is irrelevant to the symmetry breaking phase transition and continues to be observed at all temperatures far from the phase transition.

Switching and electrical properties of ferro‐ and antiferroelectric phases of MOPB(H)PBC

“…Beresnev et al (14) have also reported two modes in the SmC* phase that were connected to the domain modes (D B and D S modes), but these modes could only be observed after suppression of Goldstone mode with biased electric field. The L F mode may belong to an X-mode caused by distortion of pretilt angle because an X-mode may appear even in absence of bias electric field (15)(16)(17). Furthermore, temperature dependent variations of dielectric strength and relaxation frequency of L F mode are the same as those reported by Wang et al (16).…”

“…In the ferroelectric SmC* phase, the e ' \ , besides the soft mode, reveals another collective mode due to phase fluctuations (Goldstone mode) (11)(12)(13). In addition to Goldstone and soft modes, dielectric measurements have shown the existence of other relaxation modes in surface-stabilised FLC cells or under a biased electric field (14)(15)(16)(17). The dielectric spectrum of an antiferroelectric (SmC A *) phase contains two characteristic relaxation modes (P L , P H ) observed in the kHz and MHz regions, respectively (18)(19)(20)(21)(22)(23)(24)(25)(26)(27).…”