Room-temperature ABX₃-typed molecular ferroelectric: [C₅H₉–NH₃][CdCl₃]

Reaction of CdCl₂ with cyclopentylamine in the presence of aqueous HCl affords an ABX₃-typed perovskite structure compound [C₅H₉–NH₃][CdCl₃] (1). Above 300 K, it is in a paraelectric phase with a centrosymmetric space group Cmcm, while below 300 K it has a noncentrosymmetric space group Cc, corresponding to a ferroelectric phase. The temperature-dependent dielectric constant shows a peak at about 300 K with a 12-fold enhancement which is confirmed by differential scanning calorimetry. The normalized pyroelectric and second-harmonic generation effect as functions of temperature are almost overlapped, probably indicating that the trends with temperature basically satisfy the Landau phenomenological theory, revealing a symmetry-breaking occurrence. The ferroelectricity, a spontaneous saturation polarization approximately reaching 1.7 μC cm⁻², is further confirmed by piezoresponse force microscopy.