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

• Autorzy: Perkowski P.
• Języki publikacji: EN

Abstrakty

EN

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 SmC_A* 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.

Słowa kluczowe

EN

liquid crystals; dielectric spectroscopy; relaxation modes; capacity; cut-off frequency

• Wydawca: Stowarzyszenie Elektryków Polskich ; Polska Akademia Nauk ; Wojskowa Akademia Techniczna im. Jarosława Dąbrowskiego
• Czasopismo: Opto-Electronics Review
• Rocznik: 2009
• Tom: Vol. 17, No. 2
• Strony: 180--186
• Opis fizyczny: Bibliogr. 8 poz., wykr.

Twórcy

autor

Perkowski P.

• Institute of Applied Physics, Military University of Technology, 2 Kaliskiego Str., 00-908 Warsaw, Poland,

Bibliografia

• [1] P. Perkowski, D. Łada, K. Ogrodnik, J. Rutkowska, W. Piecek, and Z. Raszewski: Technical aspects of dielectric spectroscopy measurements of liquid crystal. Opto-Electron. Rev. 16, 271-276, 2008.
• [2] M. Wojciechowski, G. W. Bąk, and M. Tykarska: Dielectric properties of LC mixture with induced antiferroelectric phase. Opto-Electron. Rev. 16, 257-261, 2008.
• [3] R. Dhar: An impedance model to improve the higher frequency limit of electrical measurements on the capacitor made from electrodes of finite resistances. Indian J. Pure Ap. Phy. 42, 56-61, 2004.
• [4] M. Buivydas, F. Gouda, G. Andersson, S. T. Lagerwall, B. Stebler, J. Bömelburg, G. Heppke, and B. Gestblom: Collective and non-collective excitations in antiferroelectric and ferroelectric liquid crystals studied by dielectric relaxation spectroscopy and electro-optic measurements. Liq. Cryst. 23, 723-739, 1997.
• [5] C. J. F. Bötcher and P. Bordewijk, Theory of Electric Polarization, Elsevier, 1978.
• [6] K. S. Cole and R. H. Cole: Dispersion and absorption in dielectrics. Alternating current characteristics. J. Chem. Phys. 9, 341-351, 1941.
• [7] D. Łada: Technical aspects of dielectric spectroscopy in cells with ITO electrodes. MSc Thesis, Military University of Technology, Warsaw, Poland, 2008. (in Polish)
• [8] M. Buivydas: Collective and non-collective excitations in ferroelectric and antiferroelectric liquid crystals. PhD Thesis, Chalmers University, Göteborg, Sweden, 1997.