The electrocaloric effect (ECE) in lead free (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) and (Ba1-xSrx)(Zr0.1Ti0.9)O3 (BSZTx) ceramics over a wide composition range (x=0.3-0.7 for BZT-xBCT and x=0-0.35 for BSZTx) were investigated using an indirect method based on the thermodynamics Maxwell relations.In BZT-xBCT ceramics, the maximum adiabatic temperature change Δ was found to shift from the proximity of Curie temperature to higher temperatures, owing to a synergistic effect of field induced change in the phase transition temperature and alignment and growth of polar nano-regions. Coexistence of positive and negative ECEs was confirmed in BCT-rich compositions (x ≥ 0.5). The abnormal negative ECE is presumably attributed to the rhombohedral to tetragonal transition occurred at relatively low temperatures. The most promising ECE was found in BZT-0.4BCT ceramics, which exhibited a uniform ECE in the temperature range of interest, with a promising Δ of 0.58 K at ~ 125 ℃ under a moderate electric field of 28 kV/cm. A weakened ECE was shown in the unique composition at morphotropic phase boundary (x = 0.5) due to the possible electric field induced second order phase transition.In BSZTx ceramics, the maxima ECE occurred at temperatures very close to their Curie points. The maximum adiabatic temperature changes Δ and the Curie temperatures of BSZTx decrease with the increasing Sr content. The electrocaloric coefficient (=ΔΔ) in BSZTx is among the highest reported ECE for lead free materials in the literature up to this date. The most promising EC materials are BSZT0 (Δ = 0.38 K, =0.253 10-6K*m/V) and BSZT0.35 (Δ = 0.31 K, =0.207 10-6K*m/V), which make BSZTx attractive for both room temperature and high temperature (~100 ℃) cooling application.
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