Aging-induced negative electrocaloric effect in Mn-doped Ba_0.8Sr_0.2TiO₃ ceramics

In contrast to its positive counterpart, the negative electrocaloric effect (ECE) has received relatively less attention, and its underlying mechanisms remain insufficiently understood. In this study, we report pronounced differences in the dielectric and electrocaloric properties of Ba_0.8Sr_0.2TiO₃ (BST) and 1.0 mol. % Mn-doped Ba_0.8Sr_0.2TiO₃ (BST-Mn) ceramics after aging. The structural analysis reveals that the incorporation of Mn ions enhances the proportion of the cubic phase. The maximum negative electrocaloric temperature change (ΔT_max) reaches approximately −0.28 °C under 7 kV/cm, whereas the maximum positive ΔT_max is about 0.61 °C under 20 kV/cm in aged BST-Mn samples. Phenomenological analysis and the symmetry conformation principle for defects suggest that the stabilization of defect dipoles is a key factor contributing to the negative electrocaloric (EC) response. Furthermore, the behavior of defect dipoles appears to be modulated by the interplay between external fields and temperature. These findings deepen our understanding of the ECE in aged lead-free ferroelectric materials and provide insights into their potential for caloric applications.