Ionic contribution to the dielectric properties of a nematic liquid crystal in thin cells

We report measurements on dielectric properties of a nematic liquid crystal in planar aligned cells with two different thicknesses (1.2 and 6.7 μm). The nematic has a wide thermal range and the temperature variation of the effective dielectric constant (ε⊥) of the thick cell reflects that of the orientational order parameter. On the other hand, the thin cell exhibits a higher value of ε⊥ which is essentially temperature independent. We have conducted detailed dielectric measurements in the frequency range of 10 Hz–1.1 kHz on both the cells and analyzed the data using a simplified model which takes into account the ionic contribution. It leads to an estimation of the temperature dependencies of the number density and diffusion coefficient of the impurity ions.