SEU proposed "Ferroelectrochemistry" for the first time
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Editor’s note:
Recently, under the funding of "Top 10 Scientific and Technical Issues of Southeast University", the International Research Institute of Molecular Ferroelectric Science and Application, School of Chemistry and Chemical Engineering, SEU, and the Key Laboratory of "Molecular Ferroelectric Science and Application" of Jiangsu Province made significant progress in the field of ferroelectricity. The scientific research team tried to understand ferroelectricity from the chemical perspective. Upon unremitting efforts, they discovered ferroelectrics from blind search to targeted chemical design and proposed the concept of "Ferroelectochemistry" for the first time. Related research results titled "Molecular Design Principles for Ferroelectrics: Ferroelectrochemistry" were published in the form of Perspective in the Journal of the American Chemical Society.
Research background
Ferroelectricity refers to the spontaneous polarization of a crystal within a certain temperature range, and such spontaneous polarization direction can be reversed or reoriented under the action of an external electric field. In 1920, Prof. Valasek discovered ferroelectricity in Rochellet salt (potassium sodium tartrate), which opened an era in the field. After that, the research of ferroelectrics mainly focused on the field of inorganic ceramics. With the discovery of a variety of high-performance ferroelectric ceramics, ferroelectricity has been extensively studied in experiments, theories and practical applications. Nevertheless, researchers still failed to have a truly comprehensive understanding of ferroelectricity upon centennial efforts, and there has been a lack of feasible theoretical guidance for the search and exploration of ferroelectrics. In retrospect, the field of ferroelectrics is still in urgent demand of new and disruptive theories and methods.
Achievements
Coincidentally, upon the centennial birthday of ferroelectrics and thanks to the diligent exploration for over two decades, the team led by Prof. Xiong Rengen from the School of Chemistry and Chemical Engineering of Southeast University has thoroughly understood, and creatively summarized and put forward the molecular design principles of ferroelectrics from the chemistry perspective — "the quasi-spherical theory", "the homochiral principle" and "the H/F substitution strategy" in combination with the principles of Curie symmetry, Neumann's principle and Landau's phenomenological theory respectively.
Specifically, the quasi-spherical theory is a chemical design concept for the reduction of crystal symmetry, that is, changing the crystal’s symmetry and specific interaction at the molecular level through chemical modification or tailoring of high symmetry cations so as to design and regulate the ferroelectricity.
It is also an important step to reveal the connection between ferroelectricity and homochirality in the development of molecular ferroelectricity. The introduction of chiral molecules makes it easier for the material to crystallize in the five chiral polar point groups, which may greatly increase the possibility of inducing ferroelectricity; meanwhile, the circularly polarized optical properties of chiral molecules can also further expand the potential applications of molecular ferroelectric materials.
Regarding the H/F substitution strategy that is similar to the H/D isotope effect, the introduction of F atoms usually causes slight structural damages while the polar groups remain unchanged, thereby significantly increasing the material’s Curie temperature and the spontaneous polarization. The introduction of F atoms will also improve the material’s hydrophobicity and fat solubility, which is conducive to its potential applications in biology and medicine.
Significance
Based on the above-mentioned molecular design principles, Prof. Xiong Rengen’s team systematically designed and synthesized various types of multifunctional ferroelectrics, and transformed the discovery of ferroelectrics from attempts and explorations like gold panning from the sand to a kind of reasonable and targeted design and synthesis. Moreover, the team has preliminarily established an effective theoretical system to design, control and optimize the ferroelectricity and piezoelectricity in the molecular systems, and put forward the concept of "ferroelectrochemistry" for the purpose of understanding ferroelectricity from the chemical point of view and providing methodological guidance in exploration of high-performance molecular ferroelectrics. The birth of "ferroelectrochemistry" is expected to initiate a new discipline system, promote the development of ferroelectrics and related fields into a new stage, and bring a new world to the fields of materials, physics and chemistry.
Dr. Zhang Hanyue from School of Chemistry and Chemical Engineering, SEU, has made outstanding contributions to the research as the first corresponding author. Southeast University is the first corresponding and completion institute.
Paper’s link:
https://pubs.acs.org/doi/10.1021/jacs.0c07055