Composition induced nonergodic-ergodic transition and electrocaloric evolution in Pb1-1.5xLaxZr0.8Ti0.2O3 relaxor ferroelectric ceramics

Relaxor ferroelectrics, with polar nanoregions (PNRs), are good candidates for electrocaloric (EC) refrigeration. This study investigates the EC performance of the Pb1−1.5x La x Zr0.8Ti0.2O3 relaxor ferroelectric ceramics by the direct measurement using a modified differential scanning calorimeter. All the ceramics exhibit pure perovskite phase with a dense microstructure. The results indicate that the increasing La substitution strengthens the relaxor behaviour, promotes the transition from non-ergodic to ergodic state, and enhances the thermal stability of EC property (instability η < 16% within 0–140°C for x = 0.09). While the EC peak widens and shifts to lower temperatures, the peak value decreases from ΔT max = 0.98 K (@140°C) for x = 0.06 to ΔT max = 0.25 K (@40°C) for x = 0.09 under an electric field of 40 kV/cm. Moreover, the ceramics with x = 0.07, near the non-ergodic–ergodic state boundary, show the optimised room temperature EC performance, i.e. ΔT = 0.41 K (@20°C) and η < 20% within a wide temperature range of 0–80°C. This work provides an effective material design approach for EC refrigeration in different application conditions.