How does the hexatic-B phase differ from the smectic-A phase?

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liquid crystal Figure 1: Arrangements of molecules.

The primary difference between the smectic-A phase and the hexatic-B phase lies in the symmetry of the molecules within their layers.1

In the smectic-A phase, the molecules exhibit continuous in-plane rotational symmetry within the layers. In contrast, the hexatic-B phase breaks this continuous rotational symmetry, resulting in bond orientational order. Despite this loss of rotational symmetry, the hexatic-B phase maintains continuous translational symmetry within its layers due to a proliferation of dislocations.1

In summary, while both phases involve layered structures that break translational symmetry in one direction, the hexatic-B phase is characterized by a higher degree of order regarding the orientation of the bonds between molecules compared to the smectic-A phase.1