Phase transitions in the antiferroelectric liquid crystal C8 tolane determined by dielectric and electro-optical measurements

Simultaneous dielectric permittivity measurements and analysis of the first and the second harmonic electro-optical responses have been performed on a 26 mum thick planar oriented sample of the antiferroelectric liquid crystal tolane C8, which has a polymorphism similar to that of MHPOBC. Comparison of these measurements for different frequencies and geometries (in the case of the electro-optical experiment) allows one to determine all the transition temperatures. The high frequency dielectric permittivity exhibits its maximum (depending on the frequency) inside the SmA phase, whereas the electro-optical coefficient is a maximum at the transition SmA-SmC_alpha* independent of the frequency. A new method for obtaining the temperature dependence of the relaxation frequency in the SmA phase is proposed.