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.© 2012 Versita Warsaw and Springer-Verlag Wien.