Unwinding of the antiferroelectric helix in an electric field.

Using the discrete phenomenological model with interlayer anticlinic and chiral interaction, the unwinding of the antiferroelectric helix in external electric field was studied. The dependence of the helical pitch on the electric field differs essentially in antiferroelectric and ferroelectric phases. It was found that in antiferroelectric the critical electric field E h of the transition into the unwound structure is proportional to the value of chiral interaction and does not depend on the anticlinic interaction between nearest layers. This behavior differs significantly from the case of ferroelectric in which E h increases as the square of the chiral interaction and is inversely related to the synclinic interaction between layers. Peculiarities of the unwinding process and the dependence of the critical field E h on model parameters are discussed. Based on our calculations, we propose an analytical equation for the critical unwinding field in the antiferroelectric.