Ferroelectric Smectic C Liquid Crystal Phase with Spontaneous Polarization in the Direction of the Director

TL;DR

This study identifies a ferroelectric smectic C liquid crystal phase with spontaneous polarization aligned with the director, using 3D reciprocal space analysis from X-ray diffraction data, expanding the understanding of liquid crystal phases.

Contribution

The paper introduces a novel method of 3D reciprocal space analysis to definitively identify a ferroelectric smectic C phase with spontaneous polarization.

Findings

Confirmed the smectic C phase via 3D reciprocal space analysis.

Demonstrated spontaneous polarization aligned with the director.

Provided a new classification for liquid crystalline phases.

Abstract

In our previous study, we demonstrated the existence of an unidentified ferroelectric smectic phase in the low-temperature region of the ferroelectric smectic A phase, where the layer spacing decreases with decreasing temperature. In the present study, we identified the phase by taking 2D X-ray diffraction images of a magnetically oriented sample while allowing it to rotate and constructed a 3D reciprocal space with the sample rotation angle as the third axis for the whole picture of the reciprocal lattice vectors originating from the smectic structure. Consequently, circular diffraction images were obtained when the reciprocal lattice vectors were evenly distributed on the conical surface at a certain inclination angle in the reciprocal space. This result provides clear evidence that the phase in question was smectic C. The polarization properties also showed that the observed smectic C phase had spontaneous polarization in the direction parallel to the director and was identified as ferroelectric smectic C. These results provide a new type of classification for liquid crystalline phases that has been established over many years and is a significant contribution to the basic science of soft matter research.