Fluoridation Achieved Antiperovskite Molecular Ferroelectric in [(CH₃)₂(F-CH₂CH₂)NH]₃(CdCl₃)(CdCl₄)

Antiperovskites have developed to be one kind of important functional material over the past few decades, showing abundant physical properties such as negative thermal expansion and superconductivity, etc. However, antiperovskite ferroelectrics have scarcely been discovered in inorganic ceramics. In this article, we report a new organic-inorganic hybrid antiperovskite ferroelectric [(CH₃)₂(F-CH₂CH₂)NH]₃(CdCl₃)(CdCl₄) based on the strategy of molecular design. The replacement of one methyl in [(CH₃)₃NH]CdCl₃ with ethyl produces the lower symmetric [(CH₃)₂(CH₂CH₃)NH]CdCl₃ with nonpolar perovskite structure, while the polar hexagonal antiperovskite structure with the formula of X₃BA (where X = [(CH₃)₂(F-CH₂CH₂)NH]⁺, B = [CdCl₃]^-, and A = [CdCl₄]^2-) was received after further fluoridation of the ethyl group. Therefore, fluoridation successfully achieves the structural transformation from perovskite to antiperovskite, as well as the significant changes in physical properties from nonferroelectric to ferroelectric. The antiperovskite [(CH₃)₂(F-CH₂CH₂)NH]₃(CdCl₃)(CdCl₄) exhibits typical ferroelectric phase transition above room temperature ( T_c = 333 K) including thermal anomalies, dielectric transitions, and second harmonic generation (SHG) responses. Moreover, lower coercive fields and easy polarization switching are observed by the measurements of hysteresis loops and ferroelectric domains. The saturated polarization ( P_s) of 4.0 μC/cm² is almost 10 times as large as those recently discovered antiperovskite molecular ferroelectrics. This finding provides a novel strategy to design and explore more antiperovskite organic-inorganic hybrid ferroelectric materials.