Electro-caloric behaviors of lead-free Bi_0.5Na_0.5TiO₃-BaTiO₃ ceramics

Electro-caloric (EC) properties of lead-free Ba_0.5Na_0.5TiO₃-xBaTiO₃ (BNT-xBT) ceramics prepared by citrate method are investigated at temperatures of 30–250°C. Based on thermodynamics calculations, BNT-xBT (x = 0, 0.05, 0.06, 0.1, 0.25, 0.3) are found to show EC effects different with other lead-based or lead-free ferroelectric ceramics, i.e., they absorb heats (refrigeration effect) during the processes of field application while other ferroelectric ceramics show refrigeration effect during the processes of field removal. The EC temperature change of BNT-xBT can be as large as 2.1°C under an electric field of 60 kV/cm, which is larger than most of the lead-free ferroelectric bulk ceramics. When x is close to the morphotropic phase boundary (x ~ 0.06–0.1), the EC temperature change of BNT-xBT shows a maximum near the ferroelectric to anti-ferroelectric transition temperature, which is characterized by dynamic mechanical analysis. This study suggests that these lead-free ferroelectric materials are promising in the practical application as EC coolers.