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 mu m thick planar oriented sample of the antiferroelectric liquid cryst al tolane C8, which has a polymorphism similar to that of MHPOBC. Compariso n of these measurements for different frequencies and geometries (in the ca se of the electro-optical experiment) allows one to determine all the trans ition temperatures. The high frequency dielectric permittivity exhibits its maximum (depending on the frequency) inside the SmA phase, whereas the ele ctro-optical coefficient is a maximum at the transition SmA-SmCalpha* indep endent of the frequency. A new method for obtaining the temperature depende nce of the relaxation frequency in the SmA phase is proposed.