Structural and pyroelectric investigations of ferroelectric liquid crystals with dislocation domain walls

In FLC with spontaneous pòlarization high enough (P ≥ 50 nC/cm 2 ), the formation of special periodic structure takes place after switching the moderate electric field off. There are dislocation walls which separate the regions of inclined smectic layers with the opposite signs of inclination angle & for neighbour regions (domains). We have found that angle 8 is strongly dependent (almost proportionally) on piezoelectric coefficient μ = P/θ, where & is the director tilt angle, S is also a function of e. The pyroelectric measurements have shown field and temperature dependences of the response which has a saturation above a certain critical value of the field E c , E c being a function of the temperature. We explain this effect by the existence of such domain walls, the saturation field being related to removing of the domains and transition to a book-shelf state, and predict a very strong nonlinear dependence of E c on piezoelectric modulus μ. The experimental data agree with these predictions, E c value being determined firstly from X-ray measurements and secondly from the pyroelectric measurements.