In Situ Optical Characterization of Twinning in Liquid Crystalline Blue Phases

Crystal twinning is an intergrowth of two or more single crystals of the same species with specific crystallographic relations in their orientations. Here, we perform microscopic optical characterization of (211) twins in the three-dimensional liquid crystalline phase known as the blue phase (BP), with I4(1)32 space group symmetry. We describe the effect of twinning on the optical diffraction pattern-Kossel pattern-of blue phases and analyze the patterns to deduce structural information such as the twin elements and the previously unnoticed deviations from the perfect cubic structure at zero electric field. Further, we obtain in situ observations as a field is applied along the [110] direction of the twinning crystals and find that the twin boundary shows a pinning effect that defines the orientation of the twinned pair through the cubic-to-orthogonal structure transformation. Our findings not only provide important insights for the application of BPs as electro-optic crystals but also present a step in understanding the hierarchical structures that are crystallographic.

Automated summary

In this study, the microscopic optical characterization of (211) crystal twinning in blue phases was conducted, revealing the effect of twinning on optical diffraction patterns and the pinning effect of twin boundaries during the cubic-to-orthogonal structure transformation. These findings not only provide insights for the application of blue phases as electro-optic crystals but also contribute to understanding hierarchical crystallographic structures.