Dielectric modes in antiferroelectric liquid crystal observed at low temperatures

Abstract

A broad temperature antiferroelectric binary mixture has been investigated by means of dielectric spectroscopy. The sample was cooled down to –70°C. It was found that the sample was still in antiferroelectric phase. This is the widest antiferroelectric mixture ever seen (∼170°) in which three well-separated modes have been detected at room temperature. In addition, the bias field influence on existing modes has been observed. All modes change their strengths with bias field. Results show that the fastest mode, called X mode previously, gradually disappears around –30°C. When the temperature decreases below –40°C, one can indisputably observe additional mode, faster than X mode. This mode (named as Y mode) observed for extra low temperatures is bias independent. It can be the molecular mode, connected with rotation around long molecular axis. The rotation around short molecular axis seems to be blocked in antiferroelectric packing. To calculate parameters of observed modes, Cole–Cole model was used. The parameters of Y mode are discussed in this article.

Keywords:

• dielectric spectroscopy
• antiferroelectric
• collective mode
• molecular mode
• Cole–Cole model

Acknowledgements

This work was carried out in the year 2012 under the financial support of the Polish Ministry of Sciences and Higher Education, Key Project POIG.01.03.01-14-016/08 ‘New photonic materials and their advanced applications’.