BPX: A field-induced Tetragonal Blue Phase.

Hornreich et al. predicted that Blue Phase I, II or III should undergo structural transformations into anisotropic uniaxial Blue Phases in electric or magnetic fields. It is shown here that, besides a hexagonal Blue Phase BPH(3D) discovered previously, a novel Blue Phase, called BPX, can be obtained either from BPI for E(vector) // [110] or from BPII for E(vector) // [100]. Using the method of Kossel diagrams clear-cut evidence is presented that Blue Phase X has tetragonal symmetry. The transformation of BPI into BPX involves a homogeneous strain in the plane perpendicular to E(vector) and a dilation in the field direction.