Enhanced electrocaloric effect in NaNbO3-based lead-free ceramics via adjusting the ratio of relaxor ferroelectric phase over normal ferroelectric phase

Solid-state refrigeration based on electrocaloric effect (ECE) is regarded as one of the potential candidates to replace the vapor-compression refrigeration. Nowadays, the challenge for ECE refrigeration devices is mainly due to the lack of high-performance ECE materials. Recently, the lead-free NaNbO3(NN)-based ceramics have attracted great interest in ECE properties due to their multi-phase structures, which may generate large quantities of polar states. In this work, the ([Formula: see text])[0.9NaNbO[Formula: see text]Ba(Zr[Formula: see text] Bi([Formula: see text] (NN-BZT-BMZ, [Formula: see text], 0.02, 0.04 and 0.06) ceramics were designed via adjusting the ratio of relaxor ferroelectric phase (RFE) over normal ferroelectric (NFE) phase. X-ray diffraction (XRD) patterns indicate the phase changes from ferroelectric (FE) tetragonal phase to pseudo-cubic phase with the increasing Bi(Mg[Formula: see text]Zr[Formula: see text]O3 (BMZ) content. Raman spectroscopy and piezoelectric force microscopy verified the polar nanoregions (PNRs) in sample, indicating the coexistence of NFE and RFE phases. Direct ECE measurement indicated that a [Formula: see text] [Formula: see text]K was obtained in [Formula: see text] sample at 5[Formula: see text]MV/m and 80∘C via a modified differential scanning calorimetry (DSC) setup. This work provides a novel strategy to design electrocaloric materials with large ECE.