Abstract
Texture observations, second harmonic generation (SHG) and X-ray diffraction measurements have been carried out in the B4 phase of two classical bent-core liquid crystals. Several sample geometries have been used for the different techniques, including a well-aligned cell for the optical studies. An indexation of the whole diffraction diagram was performed on the basis of a three-dimensional lattice. A quantitative analysis of the X-ray data is also reported. The results are compatible with the well-known twist grain boundary (TGB) structure for the B4 phase. However, within the smectic blocks the structure is monoclinic P2, implying an antiferroelectric in-layer arrangement of the molecules instead of the usually accepted ferroelectric. This antiferroelectric packing also explains the low efficiency of the B4 phase for SHG.
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