Giant Bidirectional Electrocaloric Effects in Single Relaxor Ferroelectric Film by Manipulating Symmetry‐Conforming Defect Dipole States

ABSTRACT Electrocaloric effect (EC) holds great potential for acting as an advanced cooling solution in highly integrated chips. One of the key restrictions for the practical implementation of EC is how to maximize and control the bidirectional positive and negative electrocaloric effects (PEC and NEC) within a single low‐power EC film. In this study, the remarkable temperature changes of ΔT = 30.2 K for PEC and ΔT = −10.2 K for NEC are achieved via calculation in (111)‐oriented Pb(Ni 1/3 Nb 2/3 ) 0.5 Zr 0.15 Ti 0.35 O 3 (PNN‐PT‐PZ) relaxor thin films, exceedingly almost all representative EC cooling options. Such giant bidirectional electrocaloric effects are ascribed to the different symmetry conforming behavior of defect dipoles at distinct thermal activation states. At room temperature, the interfacial stress and large driving electric field intensified the symmetry conforming between defect dipoles and intrinsic polarization, which facilitated positive coupling for PEC. In comparison, the high temperature not only enables the tetragonal→rhombohedral transitions with positive pyroelectric constants, but also disrupts the intrinsic polarization and symmetry conforming state of defect dipoles, both leading to a polar disorder state under applying electric fields and the appearance of large NEC amplitude. Our findings provide essential insights for developing high‐efficiency silicon‐compatible EC cooling technologies used in chip‐level thermal management.