Boosting the electrocaloric effect with broad working temperature span in lead-free relaxor ferroelectrics through disorder modulation

Achieving both high electrocaloric effect and broad working temperature span in ferroelectric materials is crucial for practical cooling applications, yet it remains a big challenge. In the present work, a large electrocaloric temperature change (ΔT) over a wide temperature range is obtained through disorder modulation of perovskite titanates, specifically by introducing an electric field-sensitive Bi0₀.₅Na0₀.₅TiO₃ (BNT) into Ba0₀.₆Sr0₀.₄TiO₃ (BST). Ceramic samples in the BST-100xBNT (0.2 ≤ x ≤ 0.28) solid solution system show typical characteristics of relaxor ferroelectrics with a high density of polar nano-regions due to short-range ordering of A-site cations. As the concentration of BNT (x) increases, the freezing temperature (Tf) decreases and the Burns temperature (TB) increases, suggesting the extension of the temperature range of the relaxor in the ergodic state. Moreover, the field-induced polarization was found to increase along with x. The observed structurally induced changes in the relaxor behavior are proposed to contribute to the optimal electrocaloric performance of the BST-28BNT ceramic, with a maximum ΔT of 0.91 °C and a maximum working temperature span of 24.4 °C under an applied electric field of 5 kV/mm. The concept of the A-site disorder modulation provides an innovative strategy to develop high-performance electrocaloric materials from lead-free relaxor ceramics.