Dielectric spectroscopy of liquid crystals. Theoretical model of ITO electrodes influence on dielectric measurements |
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Authors: | P Perkowski |
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Institution: | (1) Institute of Applied Physics, Military University of Technology, 2 Kaliskiego Str., 00-908 Warsaw, Poland |
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Abstract: | 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. |
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Keywords: | liquid crystals dielectric spectroscopy relaxation modes capacity cut-off frequency |
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