Achieving Ultrahigh Electrocaloric Response in (Bi_0.5Na_0.5)TiO₃-Based Ceramics through B-Site Defect Engineering

Lead-free electrocaloric (EC) ferroelectrics are considered ideal for the next generation of environmentally friendly solid-state refrigeration materials. However, their inferior performance compared to lead-based materials significantly restricts their potential application. According to phase-field simulations, it is predicted that the pinning effect of a moderate number of defects can effectively enhance the reversible polarization response associated with the entropy change. Herein, sodium-bismuth titanate (BNT) ceramics with high spontaneous polarization are selected to construct B-site defects by introducing Li⁺ and Nb⁵⁺. Under an electric field of 6 kV mm^-1, ultrahigh EC temperature changes of ΔT_pos = 1.77 and ΔT_neg = 1.49 K are achieved at 65 °C by direct measurement (ΔT_neg > 1 K over 55-120 °C). Furthermore, ΔT_neg remains above 0.70 K in the temperature range from 25 to 130 °C, exhibiting immense potential for practical applications. This study offers a promising direction for optimizing the EC response in defect systems.