Parabolic Graded Structure Enabling Low‐Field‐Driven Multistage Phase Transitions for Broad‐Temperature‐Range Electrocaloric Response

Electrocaloric (EC) cooling technology, which offers advantages of high efficiency, stability, and miniaturization, faces challenges such as high driving electric fields and narrow operating temperature ranges. A synergistic “grain coarsening‐gradient compositing” strategy is proposed for sodium bismuth titanate (BNT)‐based ceramics with a simple compositional design. Through microstructural optimization, the composite ceramics achieve an average grain size of ≈4 µm, significantly reducing grain boundary density. Geometric phase analysis (GPA) reveals that Sr 2 ⁺ induces lattice distortion, thereby lowering the activation energy barrier of electric‐field‐driven switching. Phase‐field simulations further demonstrate that the parabolic compositional gradient structure effectively suppresses the interfacial energy barriers. These synergies collectively enable continuous multistage phase transitions under low electric fields. The dynamic coupling between long‐range ferroelectric domains and polarized ferroelectric clusters induces a peak EC strength of 0.41 K mm kV −1 , while maintaining EC strength >0.3 K mm kV −1 over a 52 °C operational temperature range. This work establishes a novel paradigm for developing low‐field, high‐efficiency EC materials, advancing their engineering applications.