Smectic blue phases $\left({\mathrm{BP}}_{\mathrm{Sm}}\right)$ are mesophases of thermotropic liquid crystals, which exhibit both three-dimensional orientational order, such as classical blue phases, and smectic positional order. The ${\mathrm{BP}}_{\mathrm{Sm}}$ phases appear as the three-dimensional counterpart of the twist grain boundary phases. By growing large faceted monocrystals of ${\mathrm{BP}}_{\mathrm{Sm}}$ phase, we provide, for the first time at the length scale of the lattice parameter, information on the symmetry of the orientational unit cell. This study leads us to suggest an orthorhombic structure, contrary to the previous results obtained by x-ray scattering at the length scale of the smectic order.

• Received 30 October 2001

DOI:https://doi.org/10.1103/PhysRevE.65.050701