We report a large electrocaloric effect with an adiabatic temperature change (ΔT) of 0.47 K under 20 kV cm⁻¹ combined with a broad temperature span (T_span) of 23 K within 90% ΔT (maximum) attenuation in a (Ba_0.87Ca_0.13)(Ti_0.87Hf_0.13)O₃ ceramic by indirect measurement. Here, in this (Ba_0.87Ca_0.13)(Ti_0.87Hf_0.13)O₃ ceramic, Ca²⁺ and Hf⁴⁺ are introduced into BaTiO₃ to obtain a multiphase coexisting region with a diffuse phase transition character. The large electrocaloric effect benefits from a larger number of possible equilibrium orientations of polar states due to multiphase coexistence, and the broad temperature span comes from the diffuse phase transition character. Compared to the control sample, BaTi_0.82Hf_0.18O₃ with only diffuse transition but no multiphase coexistence, (Ba_0.87Ca_0.13)(Ti_0.87Hf_0.13)O₃ displays a ΔT value nearly 1.5 times larger than that of BaTi_0.82Hf_0.18O₃ (ΔT ∼ 0.33 K), although they exhibit similar T_span values. Our work may shed light on developing high performance electrocaloric materials with broad temperature ranges.

We study the electrocaloric effect (ECE) in a typical relaxor ferroelectric ceramic of ${\mathrm{Pb}}_{0.91}{\mathrm{La}}_{0.06}{\mathrm{Zr}}_{0.8}{\mathrm{Ti}}_{0.2}{\mathrm{O}}_3$ by analyzing the respective contributions of long-range-ordered ferroelectric macrodomains and short-range-ordered polar nanoregions (PNRs) by both direct and indirect characterization. The ECE exhibits two peaks in its dependence on temperature, the former responds to the transition from long-range ferroelectric order to short-range-ordered PNRs and the latter likely to the transition between two kinds of PNRs with different phase structures or motion states. The contributions of different mechanisms are clarified by resolving the overlapping peaks in direct heat flow experimental results. The first peak has a $\mathrm{\Delta }{T}_{\max }=0.7\mathrm{K}$ at 80 °C (approximately $T_d$) and the second a $\mathrm{\Delta }{T}_{\max }=0.98\mathrm{K}$ at 140 °C (approximately $T_m$) under 40 kV/cm. We conclude that the thermodynamic method based on the Maxwell relation is not applicable if PNRs are involved as their signatures are only picked up by direct measurements, but is valid for the case of ferroelectric domain rotation or phase transition where it provides a reasonably accurate ECE result. Besides the impact on aspects related to metrology, our work suggests that the region between the peaks in ΔT-T curves may be used to produce a large electrocaloric ΔT over a broad temperature range, which is highly desirable in cooling applications.

The temperature-dependence behaviors of ferroelectric, piezoelectric, k _p and electrical-field-induced strain were carefully evaluated for high-performance BiFeO ₃ –0.3BaTiO ₃ (BF–0.3BT) ceramics.

This paper demonstrated the flexible control of positive and negative electrocaloric effects (ECEs) in ⟨001⟩-Pb(Mg_1/3Nb_2/3)_0.7Ti_0.3O₃ single crystal, and a dual cooling cycle is proposed using their combination to improve cooling capacity. The ECE exhibits a complex evolution of positive-negative-positive within 20–140 °C, where the negative ECE originates from the electric field-induced transition from rhombohedral phase to high-symmetric tetragonal phase. Since the coexistence of different ECEs at some temperatures, the positive and negative ECEs alternately appear in neighboring cycles under proper applied fields, i.e., dual cooling. A significant improvement of ∼150% in cooling capacity is directly characterized by the isothermal heat flow measurement.