Optimisation of SrBi2(Nb,Ta)2O9 Aurivillius phase for lead-free electrocaloric cooling

Abstract The influence of different substitutional mechanisms on the electrocaloric effect of a lead-free SrBi 2 (Nb 0.2 Ta 0.8 ) 2 O 9 Aurivillius phase was studied for application in electrocaloric cooling systems. The A-site substitution with barium efficiently reduced the temperature of maximum permittivity from about 300 °C to 100 °C. The A-site substitution induced phenomena that are typical of strong relaxor ferroelectrics such as significant broadening of the permittivity peak and an increase in its frequency dispersion and with a depolarization temperature below room temperature. These features directly influenced the electrocaloric effect. A direct measurement system, based on a modified-differential scanning calorimeter, was used to analyze the EC effect of the dense (Sr 0.5 Ba 0.5 )Bi 2 (Nb 0.2 Ta 0.8 ) 2 O 9 ceramics. In accordance with the relaxor characteristics, the EC effect was found to increase continuously over a broad temperature range above the room temperature. This was attributed to the alignment of field induced polar nanodomains. Directions for optimization towards a high-performing EC ceramic were identified.