Broadening the operating temperature span of the electrocaloric effect in lead-free ceramics via creating multi-stage phase transitions

Achieving a large adiabatic temperature change (Delta T) and broadening the operating temperature span (T-span) are two main challenges in modulating the electrocaloric (EC) effect of relaxor ferroelectrics. Here, synergistic optimization has been achieved through creating multi-stage phase transitions in layered sodium bismuth titanate (BNT)-based ceramics. A direct measurement indicates that the strategy achieves a large EC response (Delta T >1 K within a T-span of 66 degrees C). The cooling performance exceeds 90% and 80% of the maximum for temperature spans of 44 degrees C and 67 degrees C, respectively, demonstrating excellent temperature stability. Additionally, the difference in dielectric permittivity (epsilon) among ceramic layers creates an uneven distribution of the electric field (E), with their EC effects adaptively compensating for each other with temperature, thereby further enhancing the stability. The novel design strategy and optimization mechanism proposed in this work will guide the development of high-performance EC materials with a wide operating temperature span.