Influence of structural evolution on electrocaloric effect in Bi0.5Na0.5TiO3-SrTiO3 ferroelectric ceramics

The electrocaloric effect (ECE) in lead-free relaxor ferroelectrics has gained significant interest over the past decades. However, certain aspects of the ECE in relaxor ferroelectrics, such as Bi0.5Na0.5TiO3, remain poorly understood. In this work, we investigate the ECE by considering Bi0.5Na0.5TiO3-SrTiO3 (BNT-ST) as an example. The results show that, for BNT-0.25ST ceramics, the directly-measured ECE is optimal when the freezing temperature is tailored to be about room temperature. For this material, ΔT = 0.51 K under an electric field of 6 kV/mm and the ECE has excellent thermal stability (the instability η ≤ 20% in the range 30–120 °C). The addition of strontium increases the cubic-phase fraction, enhances the local random field, and changes the local structure, as clarified by in situ Raman spectroscopy and piezoelectric force morphology. In addition, we discuss in detail the correlation between the ECE and local structure. This work thus improves our understanding of the ECE in BNT-based materials for EC cooling technologies.