Dielectric spectroscopy of liquid crystals. Electrodes resistivity and connecting wires inductance influence on dielectric measurements

Abstract

Dielectric spectroscopy is a very useful experimental method for liquid crystal investigation. Electrodes made from indium tin oxide (ITO) or gold are widely used in measuring cells. During the dielectric spectroscopy measurements performed for smectic liquid crystalline mixture it was found that detection of some important relaxation modes in paraelectric SmA*, ferroelectric SmC* and antiferroelectric SmCA* phases for frequencies higher than 0.2–0.5 MHz is not possible. The measuring setup does not allow us to measure such relaxations due to its own dielectric response covering the dielectric response of liquid crystalline medium. One can observe the spurious contribution for high frequency part of the dielectric spectrum, due to non-zero resistivity of electrode material or non-zero inductivity of connecting wires. In this paper, the new model was introduced. Its final equations show how to calculate parameters of relaxations observed in liquid crystals, from dielectric response of the empty and filled measuring cell. The experimental proof of strong influence of measuring setup properties on effective (measured) values of dielectric permittivities was shown.

Electro-optical Effect of Gold Nanoparticle Dispersed in Nematic Liquid Crystals

“…The decreased rotational viscosity accelerates the response time of the LC cell with GNP doping. It is worth mentioning that the accurate relaxation frequencies of LC medium should be higher than those of the measured cells in this experiment, because of the cell relaxation [28,29]. The cell relaxation also causes the measured real part of permittivity to be below the vacuum permittivity at high frequencies.…”

“…Dielectric relaxation is a reflection of the fact that electric displacement requires a finite time to reach equilibrium. To confirm the relaxation mode, the dielectric spectra of the empty cell were measured, indicating that the relaxation frequency of the empty cell appeared at~10 7 Hz, which was the cell relaxation originating from the finite resistance of the ITO electrode and the inductance of connecting wires used in the cell [28,29]. Furthermore, as demonstrated in the literature [30,31], in a homogeneously aligned cell filled with pristine E7, the relaxation frequencies of the cell without and with voltage (40 V) supplied were observed at 1 MHz and~10 5 Hz, respectively.…”

Transparent laser damage resistant nematic liquid crystal cell “LCNP3”

“…For the measure− ments HG (HomoGeneous) and HT (HomeoTropic) mea− suring cells with gold electrodes and a thickness of 5 μm were utilized [11][12][13]. The temperature characteristics of real and imaginary parts perpendicular e^(T) and parallel e || (T) components of the permittivity tensors e of LCM were measured at the nematic phase and the value of e I (T) was measured at the isotropic state.…”

Dielectric properties of a wide-temperature ferroelectric phase in a fluorinated compound

“…We decided to start measurements at 100 Hz due to the low accuracy of measurements at frequencies below 100 Hz and ion's CONTACT P. Perkowski pawel.perkowski@wat.edu.pl contribution into the dielectric response [2]. The measurements were finished at 10 MHz due to the high-frequency distortions caused by the finite conductivity of ITO (indium tin oxide) electrodes [3] or the resonance effect, caused by finite value of connecting wires inductance [4]. The measuring cell was prepared in Laboratory of Crystal Physics and Technology at our university in WAT1 standard [5].…”