Large room-temperature electrocaloric effect in lead-free BaHfxTi1−xO3 ceramics under low electric field

Fig. 1(a) displays the direct ECE measurements of the BHT (x = 0.17) ceramic under a low electric field (i.e., 10 kV/cm) at 50 °C. Both the exothermic and endothermic peaks are of the similar magnitude, which verifies the reversibility of the electrocaloric effect. Fig. 1(b) presents both the direct and indirect ECE around the DPT under low electric field (i.e., 10 kV/cm). It is found that although the thermal loss during measurements has been neglected, the direct data in this figure is still higher than the indirect data. Meanwhile, the direct ECE reaches the maximum (ΔT = 0.32 °C) and a giant electrocaloric efficiency ΔT/ΔE = 0.32 K mm kV−1 is obtained at 40 °C, which agrees with the ECE estimated from the indirect ECE measurements. The BHT ceramic near DPT shows composition fluctuations, which provides more polar or nonpolar metastable states and hence the system is more sensitive to electric field. Thus, phase structure and the electric field coupling effect are considered to be the main contributions for the enhancement of ECE near DPT.454