Domain Structures and Temperature Induced Phase Transitions in Perovskite Molecular 3‐Ammonioquinuclidinium‐NH 4 Cl 3

Abstract Molecular ferroelectric 3‐ammonioquinuclidinium‐NH 4 Cl 3 (3‐AP‐NH 4 Cl 3 ) crystals were prepared. DSC‐C P ‐TG curves were studied and a small endothermic peak was discovered at 146 °C without obvious mass change. Dielectric properties were measured and a sharp peak was found at 146 °C in the dielectric constant versus temperature curve. Temperature‐dependent domain evolution was observed in situ by polarized light microscopy (PLM). The extinction‐variation temperature range agreed well with the phase transition temperature that takes place in the dielectric measurement. This result further confirmed a phase transition from ferroelectric phase to paraelectric phase. A schematic diagram is also established to clarify the temperature induced phase transition. The shape change of free energy curve caused by temperature may result in the phase transition.