Synergistically optimizing electrocaloric effect over a wider temperature span utilizing structural overlap zone

Abstract

The development of high-performance electrocaloric (EC) materials is of great interest for solid-state refrigeration employed in microelectromechanical systems. However, superior adiabatic temperature and excellent temperature stability are long-term challenges in the development of electrocaloric refrigeration materials. Herein, we propose a strategy for optimizing EC performance in which an overlap zone based on tetragonal, rhombohedral or pseudo-cubic states is designed by adjusting La content around the morphotropic phase boundary. Their structures witness the phase evolution from ferroelectric to relaxor state and domain evolution from the micron and submicron ferroelectric domain to polar nano-regions, which encompasses many advantages of larger polarization and lower phase transition temperature as well as wider temperature window. Based on this design strategy, a (Pb_1−1.5xLa_x)(Zr_0.55Ti_0.45)O₃ system is employed to establish an overlap zone between rhombohedral and pseudo-cubic structures by adjusting the La content, where a large pyroelectric coefficient ∂P/∂T from the coexistence of rhombohedral and pseudo-cubic phases, a sluggish phase transition from the relaxor state, as well as excellent temperature stability are employed to optimize the EC response. Among them, PLZT (x = 0.12) achieved an optimized ΔT_max of 1.58 K around room temperature. In addition, the enhanced relaxor state favors broadening of the temperature span (T_span), where a desirable T_span is up to 100 °C (within 90% variation in maximal temperature). Our research not only provides an avenue for developing high-performance EC materials with better EC performance and wider T_span but also broadens the application prospects for PLZT ferroelectric ceramics in the field of refrigeration, as well as offering a beneficial design strategy for electrocaloric materials in other systems.