Spatially Resolved Observation of Ferroelectric‐to‐Paraelectric Phase Transition in a Two‐Dimensional Halide Perovskite

Abstract 2D halide perovskite ferroelectrics have garnered significant attention due to their potential applications and intriguing fundamental properties. However, their temperature‐dependent ferroelectric behaviors, particularly at the nanoscale, remain poorly understood. In this study, the nanoscale ferroelectric domain evolution with temperature and ferroelectric‐to‐paraelectric phase transition in (BA)2(MA)Pb2Br7 films are investigated using piezoresponse force microscopy (PFM). Angle‐resolved lateral PFM (LPFM) reveals a complex in‐plane ferroelectric domain structure. Temperature‐dependent LPFM measurements clearly show that the Curie temperature (TC) is ≈353 K, as confirmed by other macroscopic measurements. Notably, it is observed that the ferroelectric‐to‐paraelectric phase transition initiates locally even below TC. As the temperature increases, large ferroelectric domains fragment into smaller ones and the regions with the novel LPFM phase signal emerge, indicating a local phase transition. Furthermore, temperature‐dependent LPFM spectroscopy demonstrates a progressive weakening of the ferroelectricity. The analysis based on Landau–Ginzburg–Devonshire theory identifies a second‐order phase transition, consistent with the gradual evolution of nanoscale ferroelectric domains observed in LPFM images. This spatially resolved observation of phase transition provides critical insights into the temperature‐dependent ferroelectric properties of 2D halide perovskite ferroelectrics and establishes a foundational framework for their future device applications.