Large electrocaloric response and high energy-storage properties over a broad temperature range in lead-free NBT-ST ceramics

The improvement of the electrocaloric effect (ECE) in (1-x)(Na_0.5Bi_0.5)TiO_3-xSrTiO3 (NBT-ST) lead-free relaxor ferroelectric ceramics was determined by indirect measurements method and is reported here. The phase transition temperature can be reduced to room temperature by tuning the compositions of the (1-x)NBT-xST material. A large ECE (δT_max = 1.64 K, δS_max = 2.52 K and δT/δE = 0.33 K mm kV^-1 at 50 kVcm^-1) was obtained at 60°C when x = 0.25. A suitable response over a broad temperature range from 30°C to 70°C can be obtained with x=0.26 with very high cooling values (δT>1K). In addition, the 0.7NBT-0.3ST AFE-like bulk ceramic exhibited excellent temperature stability in its energy-storage properties from room temperature to 120°C. The maximum value of the recoverable energy density was 0.65 J/cm³ obtained at 65kV/cm. Taken together, these properties signified that (1-x)NBT-xST is a promising material for applications in cooling systems and energy-storage in the room temperature range.