Major Scientific Research Achievements of Our University are Published on Official Website of National Natural Science Foundation of China

  • Author : Nanchang University
  • Source : Nanchang University
  • Date : Mar. 15, 2019
  • Hits : 524

Funded by Natural Science Foundation of China (item no.: 21831004, 21427801, 91422301 and 91856114), Nanchang University has made important progress in the field of chiral molecular ferroelectric materials in cooperation with East China Normal University. Relevant results were published in the journal of Proceedings of the National Academy of Sciences of the United States of America (Proc. Natl. Acad. Sci. U. S. A.) with the title of “Organic enantiomeric high-Tc ferroelectrics” (DOI: 10.1073/pnas.1817866116).

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The first ferroelectric Rochelle salt ([KNaC4H4O6]·4H2O) discovered in 1920 is a homochiral molecule compound, containing L(+)-tartaric acid molecule in its structure. However, most ferroelectrics are inorganic ferroelectric ceramics without chiral centers. In the past 100 years, chiral ferroelectrics are basically multi-component organic amine salts or metal complexes.

The scientific research team of Nanchang University reported a pair of unimolecule organic enantiomeric ferroelectrics, (R)-3-Quinuclidino and (S)-3-Quinuclidino as well as racemate (Rac)-3- Quinuclidino for the first time. Chiral (R)-and (S)-3- Quinuclidino crystallize in the enantiomeric heterogeneous polar point group C6 at room temperature, vibrational circular dichroism spectra and crystal structure show a perfect mirror relationship (as shown in the figure). Both enantiomers exhibit 622F6 type ferroelectric phase transition with Curie temperature (Tc) as high as 400 K, which is much higher than other chiral ferroelectrics and comparable to the classical inorganic ferroelectrics, barium titanate (393 K). This phase transition conforms to the chiral retention law, and the paraelectric phase remains in the chiral point group (i.e. D6), which is one of the most important characteristics of chiral crystals. In addition, the saturated polarization intensity (up to 7μC/cm2) is comparable to that of organic polymer ferroelectrics PVDF, and the low coercive field (15kV/cm) ensures that the ferroelectrification is easily reversed. However, their racemic (Rac) -3-Quinuclidinol crystallizes in the non-polar point group C2h without ferroelectricity. Therefore, the introduction of chirality into molecular crystals is conducive to inducing crystallization at polar point groups, thus constructing high temperature ferroelectrics.

This work reveals the great advantage of homochirality in the precise design of high Curie point ferroelectrics, providing a reasonable way for the development of new molecular ferroelectrics, and an effective way for further exploring high-performance multi-level chiral organic ferroelectrics. It has great application prospects in memory devices and optoelectronic devices.

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