Molecular ferroelectric pyridin-2-ylmethanaminium perchlorate with phase transition induced by disorder of perchlorate.

Molecular ferroelectrics are a kind of functional materials that have large application prospects. Comparing with the traditional inorganic ferroelectrics, they have some advantages, such as easy design, environment-friendliness, nontoxicity, and flexibility. In this study, a new molecular ferroelectric pyridin-2-ylmethanaminium perchlorate was discovered, which undergoes a ferroelectric phase transition at around 264.8 K. The spontaneous polarization reaches 0.22 μC cm, and the coercive fields are as small as 1.1 kV cm at 202 K. The single-crystal X-ray diffraction analysis reveals that the space group transforms from a polar space group of 2 at 173 K to a centrosymmetric space group of 2/ at 293 K. By analyzing the crystal structure changes below and above the phase transition temperature, it can be concluded that the phase transition is induced by the disorder of perchlorate. Its ferroelectricity was confirmed by the measurements of differential scanning calorimetry, dielectric and hysteresis loop.