Electric Field Behavior of Nonferroelectric Smectics

In the smectic A phase the director is always perpendicular to the plane of the smectic layers. Thus, only the splay distortion leaves the interlayer distance unchanged [7], and only the elastic modulus K i is finite while K22 and Kzz diverge when approaching the smectic A phase from the nematic phase. On the other hand, the compressibility of the layered structure and the corresponding elastic modulus B is taken into account when discussing the elastic properties of smectic phases. The free energy density for the smectic A phase, subjected to the action of an external electric field, is 

However, the amplitude of the distortion for fields exceeding the threshold, E Eo, is very small, of the order of 

even in this favorable case of the allowed splay-distortion, the Prederiks transition is, in fact, unobservable (ghost-transition). Instead, we observe a texture transition accompanied by the appearance of a number of defects. 

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