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In this work, the (100-x)Ba(Hf 0.2 Ti 0.8 )O 3 -x(Ba 0.7 Ca 0.3 )TiO 3 (BHT–xBCT) ferroelectric ceramics were fabricated by a conventional solid-state reaction method. The electrocaloric effect (ECE) of these ceramics was studied by both indirect and direct methods over a wide temperature range with the composition changing from x = 20 to 50. The most excellent direct ECE occurs in the BHT–50BCT with a good direct ΔT EC = 0.27 K (at 92 °C) under the electric field of 10 kV/cm. What's more, the direct EC effect peaks not only locates at near the Curie temperature, but also at the phase-transition temperatures corresponding to the transitions between different ferroelectric phases. In particular, it is found that BHT–50BCT exhibits a direct ECE anomaly ΔT EC = 0.1 K at 30 °C under an electric field of 10 kV/cm, which can be ascribed to the orthorhombic to tetragonal phase transition, proposing that one can achieve a broad temperature window by tuning the temperature gap between ferroelectric (FE) to paraelectric (PE) boundary and FE-FE boundary. In addition, BHT–30BCT shows good stability of indirect ΔT EC,max /ΔE and a broad ECE peak at a higher electric field, indicating that it is possible for electrocaloric temperature ΔT EC to be tuned linearly by electric field. Overall, our results imply that the BHT– xBCT ceramics are promising candidates for lead-free cooling refrigeration applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] Rhombohedral–tetragonal phase coexistence was designed in the ternary system. [•] R–T phase coexistence was identified in the ceramics with 0.03⩽ x <0.05. [•] Enhanced dielectric, ferroelectric, and piezoelectric properties were found in the ceramic with x =0.035. [•] d 33 ∼310pC/N, k p ∼0.45, ɛ r ∼1249, tan δ ∼0.025, and T C ∼338°C were observed in the ceramic with x =0.035. [ABSTRACT FROM AUTHOR]

• Ca2+ and Sr2+ can increase the stability of antiferroelectric phase while Ba2+ decreases it. • An enhanced negative ECE of Δ T around − 10.6 K was obtained in the Pb 0.9 Sr 0.1 ZrO 3 thin film at room temperature. • The modification of antiferroelectric-ferroelectric phase transition is an effective strategy to enhance the negative electrocaloric effect in antiferroelectric thin films. In the Pb 0.9 Sr 0.1 ZrO 3 thin film, an enhanced negative electrocaloric effect (ECE) has been observed based on the Maxwell relation, with Δ T of around − 10.6 K under 450 kV/cm at room temperature, as compared with the pristine PbZrO 3 thin film (with Δ T of around −7.3 K under 300 kV/cm at 361 K), as shown in the figure. Our work demonstrates that modifying antiferroelectric-ferroelectric phase transition is an effective way to enhance the negative ECE in antiferroelectric thin films. [Display omitted] Electrocaloric effect (ECE) in dielectric materials has attracted much attention due to its promising applications in solid-state cooling devices. In this work, alkaline-earth doped PbZrO 3 antiferroelectric thin films (Pb 0.9 A 0.1 ZrO 3 (A=Ca, Sr, and Ba)) were deposited by a sol-gel method and its antiferroelectric-ferroelectric phase competition as well as the negative ECE were studied. It is found that Ca2+ and Sr2+ expand the antiferroelectric phase region while Ba2+ reduces it, due to the different ion radii of these alkaline-earth elements. As a result, the Pb 0.9 Sr 0.1 ZrO 3 thin film exhibits an enhanced negative ECE with Δ T of around − 10.6 K under 450 kV/cm whereas the Pb 0.9 Ba 0.1 ZrO 3 thin film shows a decreased negative ECE with Δ T of around − 2.5 K under 200 kV/cm, as compared with the pristine PbZrO 3 thin films (with Δ T of around −7.3 K under 300 kV/cm). This work provides an effective method to enhance the negative ECE of antiferroelectrics in electrical cooling applications by adjusting their antiferroelectric to ferroelectric phase transition. [ABSTRACT FROM AUTHOR]