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Dielectric spectroscopy of liquid crystals : theoretical model of ITO electrodes influence on dielectric measurements

Perkowski P.

Opto-Electronics Review

2009

Vol. 17, No. 2

180-186

Indium tin oxide (ITO) layers are widely used to make electrodes in measuring cells, because these layers are transparent and electrooptical investigations can be performed using such prepared cells. It was found during the dielectric spectroscopy measurements, performed for smectic liquid crystalline mixture, that it is not possible to detect some important relaxation modes in paraelectric SmA*, ferroelectric SmC*, and antiferroelectric SmCA* phases for the frequencies higher than 300 kHz. The measuring cell does not allow to measure relaxations, because its own dielectric behaviour covers the dielectric response of a liquid crystalline medium. One can observe the spurious contribution for high frequency part of the dielectric spectrum, due to the finite resistance of ITO layers. The theoretical model was introduced, which shows how to calculate relaxations related to liquid crystals from dielectric response of the empty and filled measuring cell. The proof of strong influence of cell properties on effective (measuring) values of dielectric permittivities was shown.

Technical aspects of dielectric spectroscopy measurements of liquid crystals

Perkowski P., Łada D., Ogrodnik K., Rutkowska J., Piecek W., Raszewski Z.

Opto-Electronics Review

2008

Vol. 16, No. 3

271-276

The dielectric spectroscopy measurements were performed for antiferroelectric liquid crystalline mixture. For this purpose, the cells with ITO electrodes were prepared. It was found that it is not possible to detect some important relaxation modes in Sm A*, Sm C*, and Sm CA* phases. The own cell mode (related to cell properties, i.e., capacity and resistivity) covers the dielectric response of liquid crystalline medium. Dielectric measurements in cells with gold electrodes were done to show all possible relaxations in antiferroelectric liquid crystals (Lcs).

Dielectric measurements of new antiferroelectric liquid crystals

Perkowski P., Ogrodnik K., Łada D., Piecek W., Rutkowska J., Raszewski Z., Żurowska M., Dąbrowski R., Sun X.

Opto-Electronics Review

2008

Vol. 16, No. 3

277-280

Three new pure antiferroelectric materials, synthesized at the Military University of Technology (MUT), were investigated by dielectric means. Clear relaxation modes were detected, i.e., Soft, Goldstone, low frequency in-phase (PL) as well high frequency anti-phase (PH) modes for paraelectric Sm A* phase, ferroelectric Sm C* phase and antiferroelectric Sm CA* phase, respectively. Additionally, a high relaxation mode in Sm CA* was found. The relaxation frequencies fR of the observed modes were calculated from Cole-Cole diagrams.