Giant negative electrocaloric effect over a broad temperature range in lead-free based Bi0.5(K0.15Na0.85)0.05TiO3 relaxor ferroelectric films

Lead-free based Bi0.5(K0.15Na0.85)0.5TiO3 (BKNT15) films were deposited on Pt/Ti/SiO2/Si(100) substrates using a sol-gel technique. The microstructure, electric domain, dielectric relaxation, ferroelectric properties, and electrocaloric effect were investigated. The giant negative electrocaloric effect (ECE) was obtained over a broad temperature range with the maximum temperature change (ΔT) values reaching −16.55 K at working temperature of 303 K. So strong ECE is mainly attributed to high breakdown electric field and the large entropy change caused by the structural phase transition. As typical relaxation ferroelectric films, the giant negative electrocaloric effect enriches family of the electrocaloric effect, which is helpful to achieve good cooling effect in solid-state refrigeration at room temperature.