Kossel diagrams show electric field induced cubic-tetragonal structural transition in frustrated liquid crystal blue phases.

Convergent beam diffraction patterns from a bcc blue phase (BPI) monocrystal in an electric field applied in the [110] direction, show this 2-fold axis transforming through an orthorhombic distortion to become, at a critical field the 4-fold axis of a tetragonal crystal. The implication on structures of BPI is important. Although the transition is weakly first order because the two order parameters describing it are coupled, the diffraction pattern changes continuously through the transition.