Molecular Ferroelectric Pyridin-4-ylmethanaminium Perchlorate Undergoes Paraelectric–Ferroelectric and Ferroelectric–Ferroelectric Phase Transitions

Molecule-based ferroelectrics are a class of highly desirable intelligent materials for their rich switchable physical properties, easy and environmentally friendly processing, especial lightweight and mechanical flexibility. In the current work, a new molecule-based ferroelectrics pyridin-4-ylmethanaminium perchlorate was discovered undergoing paraelectric–ferroelectric phase transition at T c = 258.40(8) K and ferroelectric–ferroelectric phase transition at T 1 = 255.93(2) K. It crystallizes in monoclinic crystal system with a centrosymmetric space group of C 2/ c at 293 K and also crystallizes in monoclinic crystal system but with a polar space group of Cc at 223 K. The spontaneous polarization can reach 1.25 μC/cm 2 and the coercive field is about 2.6 kV/cm below 254 K. The paraelectric–ferroelectric phase transition belongs to displacive phase transition and the nearby ferroelectric–ferroelectric phase transition contains order–disorder features, which consistent with the dynamic process including deformations of each pyridin-4-ylmethanaminium cation and the resulting difference for −NH 2 to be protonated. Because of the high pyroelectric coefficient values and small-amplitude anomalies of the ε′ values in the vicinity of T 1 temperature, pyridin-4-ylmethanaminium perchlorate shows two ultrahigh pyroelectric figures of merit (FOMs) with M 1 ≈ 0.16 cm 2 /μC and M 2 ≈ 0.21 cm 3/2 ·J –1/2 . The ultrahigh FOMs could make pyridin-4-ylmethanaminium perchlorate a potential element of the sensitive small-area pyroelectric detectors or pyroelectric vidicons.