Fluorine Substitution Induced High <i>T</i>_c of Enantiomeric Perovskite Ferroelectrics: (<i>R</i>)<i>-</i> and (<i>S</i>)<i>-</i>3-(Fluoropyrrolidinium)MnCl₃

Abstract

The past decade has witnessed much progress in designing molecular ferroelectrics, whose intrinsic mechanical flexibility, structural tunability, and easy processability are desirable for next-generation flexible and wearable electronic devices. However, an obstacle in expanding their promising applications in nonvolatile memory elements, capacitors, and sensors is effectively modulating the Curie temperature ( T_c). Here, taking advantage of fluorine substitution on the reported molecular ferroelectric, (pyrrolidinium)MnCl₃, we present enantiomeric perovskite ferroelectrics, namely, ( R) - and ( S) -3-(fluoropyrrolidinium)MnCl₃. The close van der Waal's radii and the similar steric parameters between H and F atoms ensure the minimum disruption of the crystal structure, while their different electronegativity and polarizability can trigger significant changes in the physical and chemical properties. As expected, the T_c gets successfully increased from 295 K in (pyrrolidinium)MnCl₃ to 333 K in these two homochiral compounds. Such a dramatic enhancement of 38 K signifies an important step toward designing high- T_c molecular ferroelectrics. In the light of the conceptually new idea of fluorine substitution, one could look forward to a continuous succession of new molecular ferroelectric materials and technology developments.