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

Electrocaloric refrigeration utilizing ferroelectrics has recently 6 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 4 lead-free ferroelectrics in high-efficiency cooling applications. In this work, chemical engineering and thick-film architecture design strategies were integrated into a BaTiO3-based system to resolve this challenge. Novel environmental-friendly Ba(Zr0.20Ti0.80)O-3-Ba(Sn0.11Ti0.89)O-3 (BZT-BST) bilayer films of similar to 13 mu m in single-layer thickness were prepared by the tape casting process. A giant adiabatic temperature change, Delta T similar to 5.2 K, and a large isothermal entropy change, Delta S similar to 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 degrees 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.