Revealing the mechanisms of electrocaloric effects by simultaneously direct measuring local electrocaloric and electrostrain under ambient conditions

Electrocaloric solid-state refrigeration is a primary candidate for the next-generation cooling method for microelectronic systems. However, the mechanisms of electrocaloric effect remain unclear due to the lack of direct correlation evidence, especially for novel negative electrocaloric (NEC) effect. In this work, we develop a high-accuracy direct measurement method for simultaneously measuring local electrocaloric and electrostrain responses under ambient conditions, providing the accompanying electrostrain evidence during electrocaloric effect. Combined with experiments, thermodynamic analyses and finite element simulations, it is found that the electrostrain is very large when NEC and large positive electrocaloric (PEC) responses occur, and NEC effect is caused by ferroelectric-ferroelectric phase transition, while large PEC response originates from paraelectric-ferroelectric phase transition. Results also indicate that NEC temperature change does not increase with electric field, and shows the maximum temperature change at phase transition critical electric field, different from PEC temperature change increasing with electric field. The developed method provides an alternative and sensitive pathway to investigating electrocaloric effect.