Giant and Broad‐Temperature Electrocaloric Cooling via B‐Site Medium‐Entropy Design in PST‐Based Multilayer Ceramics

The practical deployment of electrocaloric solid‐state cooling is hindered by a critical materials challenge: achieving a large ΔT ad over a broad, stable temperature range without requiring excessive electric fields. Here, we overcome this limitation through B‐site medium‐entropy engineering in a relaxor ferroelectric multilayer ceramic capacitor (MLCC). The designed Pb(Sc 0.25 Ta 0.25 In 0.25 Nb 0.25 )O 3 MLCC exhibits a giant directly‐measured ΔT ad of 9.34 K under a moderate field of 370 kV cm −1 , which remains stable across a 90 K temperature window and withstands over 10 6 field cycles. This performance sets a new benchmark for lead‐based dielectric MLCCs. Through atomic‐scale imaging and phase‐field simulation, we reveal that the equimolar medium‐entropy configuration induces synergistic octahedral distortions and polarization nanoregions (PNRs), flattening the free‐energy landscape and significantly reducing the polarization‐switching barrier. This work establishes a generalizable strategy that B‐site medium‐entropy to decouple high EC strength from thermal instability, paving the way for high‐performance, practical solid‐state cooling devices.