[Southeast University News Network, March 10] (Correspondent: Xiong Rengen) Recently, the paper published by the International Institute of Molecular Ferroelectric Science and Application affiliated to the School of Chemistry and Chemical Engineering of Southeast University and Jiangsu Provincial Key Laboratory of “Molecular Ferroelectric Science and Application” in Journal of American Chemical Society titled “Observation of vortex domains in a two-dimensional lead iodine perovskite ferroelectric” was selected into the ACS Editors’ Choice as a feature article. This article reported a unique “vortex-antivortex” domain structure that was found in molecular ferroelectric thin film for the first time. This achievement was accomplished by Ph.D. candidates Zhang Hanyue, Song Xianjiang and Chen Xiaogang, etc. jointly with Southeast University as the first corresponding unit. Besides, this achievement was funded by “Top Ten Science and Technology Issues of Southeast University” launch cultivation foundation.
(a) (4,4-difluoropiperidinium) 2PbI4 crystal stacking structure at room temperature; (b) the unit cell; (c) the water vortex phenomenon in nature; (c, d) PFM amplitude (d) and phase(e) of vortex domain in (4,4-difluoropiperidinium) 2PbI4 film; (f) Schematic diagram of “vortex-anti-vortex” distribution in a windmill.
The vortex phenomenon exists widely in nature, ranging from the whirlpools formed by water currents to the whirlpool galaxies in the universe. As a matter of fact, the vortex phenomenon is also prevailing in the microscopic field. In the field of condensed matter physics, the vortex domain structure is mostly studied, including ferromagnetic and ferroelectric domains. As a special topological form, the magnetic moment or the electric dipole moment in the vortex domain structure is localized to a closed flux in space, enabling this region, especially the domain wall, to highlight abundant physical properties. This implies enormous potentials in device application. In this paper, an organic-inorganic hybrid perovskite molecular ferroelectric (4,4-difluoropiperidinium) 2PbI4 was successfully synthesized by using the “fluorination effect” modification strategy. The authors observed the ubiquitous 8-level topological domain structure formed by the merger of 8 secondary domains in their film. The 8 secondary domains are categorized into four polarization states, forming a vortex-antivortex polarization distribution in space. The vortex domain originates from the confinement effect of the material’s symmetry, size and geometrical morphology. It is the result of the system’s minimum total free energy. Different from the traditional inorganic ceramic ferroelectrics, the molecular ferroelectrics are characterized by mechanical flexibility and easy film formation, etc., which make (4,4-difluoropiperidinium) 2PbI4 very suitable for building new-type ferroelectric devices. In addition, the ferroelectricity of inorganic ferroelectric materials mostly comes from the displacement of the positive and negative charge center, while the ferroelectricity of molecular ferroelectric materials comes from the order-disorder transition. The two feature different mechanisms. Therefore, the discovery of the vortex domain structure in molecular ferroelectric materials provides a new platform for studying new physical phenomena and mechanisms.
It is reported that ACS Editors’Choice is an initiative launched by the American Chemical Society (ACS) on January 1, 2014 to increase the influence of publications. This service selects an excellent paper of great scientific significance from 51 peer-reviewed journals run by ACS every day, with the selection rate of lower than 1%; besides, itis a permanently free and open browsing resource to the public, without the need for the paper authors to pay as well.
Paper link: https://pubs.acs.org/doi/10.1021/jacs.0c00371
ACS Editors' Choice: https://pubs.acs.org/editorschoice/
(Editor-in-charge: Sun Yan, reviewed by: Li Xiaonan)