New Chiral Molecular Ferroelectrics

2022-6-14

JPS Hot Topics 2, 020

https://doi.org/10.7566/JPSHT.2.020

This article is on

Ferroelectric Transition of a Chiral Molecular Crystal BINOL∙2DMSO
(JPSJ Editors' Choice)

Toshihiro Nomura, Takeshi Yajima, Zhuo Yang, Ryosuke Kurihara, Yuto Ishii, Masashi Tokunaga, Yasuhiro H. Matsuda, Yoshimitsu Kohama, Kenta Kimura, and Tsuyoshi Kimura
J. Phys. Soc. Jpn. 91, 064702 (2022) .

A new chiral ferroelectric material is discovered in a purely organic system, 1,1’-bi-2-naphthol・2 dimethyl sulfoxide (BINOL・2DMSO).

Left- and right-handed crystalline structures of BINOL∙2DMSO. Inside the chiral framework of BINOL, polar molecules DMSO produce the electric polarization.

(view larger image)

Ferroelectrics are widely used for applications including capacitors, memory, and speakers. Despite the extensive research in this field, it remains challenging to theoretically predict new ferroelectric material groups, and in most cases, the discovery of new ferroelectric families is coincidental.

In this research, the authors report a new molecular ferroelectric material with a chiral crystal structure, 1,1’-bi-2-naphthol・2 dimethyl sulfoxide (BINOL・2DMSO). In this crystal, chiral molecules (BINOL) form the structural framework, and DMSO molecules are present at the gap as a guest. At room temperature, the orientation of the DMSO molecule is fluctuating. However, when the crystal is cooled down, the fluctuation is suppressed and the ordering of DMSO occurs at 190 K. At this point, the electric dipole moment of DMSO also orders, resulting in a ferroelectric transition along with the crystal-symmetry breaking. At 125 K, another structural transition occurs. The space group of the crystal subsequently changes as P4₁2₁2 → P4₁ → P112₁. Because of the chiral framework of BINOL, all of these crystal structures are also chiral.

This results of this study demonstrate that when chiral molecules such as BINOL incorporate polar molecules and form a composite molecular crystal, they generally become a chiral (anti-)ferroelectric crystal. This will be useful to guide future research into new chiral ferroelectric materials.

(Witten by T. Nomura on behalf of all authors)

Ferroelectric Transition of a Chiral Molecular Crystal BINOL∙2DMSO
(JPSJ Editors' Choice)