Lead-Free Bilayer Thick Films with Giant Electrocaloric Effect near Room Temperature

Electrocaloric refrigeration utilizing ferroelectrics has recently gained tremendous attention because of the urgent demand for solid-state cooling devices. However, the low room-temperature electrocaloric effect and narrow operation temperature window hinder the implementation of lead-free ferroelectrics in high-efficiency cooling applications. In this work, chemical engineering and thick-film architecture design strategies were integrated into a BaTiO 3 -based system to resolve this challenge. Novel environmental-friendly Ba(Zr 0.20 Ti 0.80 )O 3 –Ba(Sn 0.11 Ti 0.89 )O 3 (BZT-BST) bilayer films of ∼13 μm in single-layer thickness were prepared by the tape casting process. A giant adiabatic temperature change, Δ T ∼ 5.2 K, and a large isothermal entropy change, Δ S ∼ 6.9 J kg –1 K –1, were simultaneously achieved at room temperature based on the direct measurements, which are much higher than those reported previously in many lead-free ferroelectrics. Moreover, the BZT-BST thick films exhibited a remarkably widened operation temperature range from about 10 to 60 °C. These outstanding properties were mainly attributed to the multiphase coexistence near room temperature, relaxor ferroelectric characteristics, and improved electric-field endurance of the bilayer thick films. This work provides a guideline for the development of environment-friendly electronic materials with both ultrahigh and stable electrocaloric performance and will broaden the application areas of lead-free ferroelectrics.