Interfacial Coupling Boosts Giant Electrocaloric Effects in Relaxor Polymer Nanocomposites: In Situ Characterization and Phase‐Field Simulation

The electrocaloric effect (ECE) refers to reversible thermal changes of a polarizable material upon the application or removal of electric fields. Without a compressor or cooling agents, all‐solid‐state electrocaloric (EC) refrigeration systems are environmentally benign, highly compact, and of very high energy efficiency. Relaxor ferroelectric ceramics and polymers are promising candidates as EC materials. Here, synergistic efforts are made by composing relaxor Ba(Zr 0.21 Ti 0.79 )O 3 nanofibers with P(VDF‐TrFE‐CFE) to make relaxor–relaxor‐type polymer nanocomposites. The ECEs of the nanocomposites are directly measured and these relaxor nanocomposites exhibit, so far, the highest EC temperature change at a modest electric field, along with high thermal stability within a broad temperature range span to room temperature. The superior EC performance is attributed to the interfacial coupling between dipoles across the filler/polymer interfaces. The thermodynamics and kinetics of interfacial coupling are investigated in situ by piezoresponse force microscopy while the real‐time evolution of interfacial coupling is simulated and visualized by phase‐field modeling.