Precise Molecular Design Toward Organic-Inorganic Zinc Chloride ABX₃ Ferroelectrics

Organic-inorganic ABX₃ (A, B = cations, X = anion) hybrids with perovskite structure have recently attracted tremendous interest due to their structural tunability and rich functional properties, such as ferroelectricity. However, ABX₃ hybrid ferroelectrics with other structures have rarely been reported. Here, we successfully designed an ABX₃ hybrid ferroelectric [(CH₃)₃NCH₂F]ZnCl₃ with a spontaneous polarization of 4.8 μC/cm² by the molecular modification of [(CH₃)₄N]ZnCl₃ through hydrogen/halogen substitution. It is the first zinc halide ABX₃ ferroelectric, which contains one-dimensional [ZnCl₃]^- chains of corner-sharing ZnCl₄ tetrahedra, distinct from the anionic framework of corner-sharing or face-sharing BX₆ octahedra in the ABX₃ perovskites. From zero dimension to one dimension, the high symmetry of ZnCl₄ tetrahedra is broken, and all of them align along one direction to form a polar [ZnCl₃]^- chain, beneficial to the generation of ferroelectricity. This finding provides an efficient polar anionic framework for enriching the family of hybrid ferroelectrics by assembling with various cations and should inspire further exploration of new classes of organic-inorganic ABX₃ ferroelectrics.