Tunable Electrocaloric Effect in Lead Scandium Tantalate through Calcium Doping

State-of-the-art electrocaloric cooling prototypes rely on the conventional electrocaloric effect of ferroelectric lead scandium tantalate, which peaks near room temperature. Here, we demonstrate that A-site calcium doping in highly ordered lead scandium tantalate modifies its phase transitions and enables precise tuning of the electrocaloric response. The transition temperature shifts down to 258K and up to 319K, depending on Ca concentration. Calorimetry under electric field, electrical polarization loops, and piezoresponse force microscopy reveal the emergence of an intermediate antiferroelectric phase stabilized for Ca >= 2%. These results are supported by first-principles calculations. We observe conventional electrocaloric effect for Ca <= 2% and inverse electrocaloric effect at higher doping (4.6% Ca). Under an applied field of 110kV/cm, Ca-doped PST exhibits an adiabatic temperature change of 2K over a range from 263K to 353K. Such Ca-doped PST compounds could be used to expand the temperature range of PST below the freezing point of water. Our results offer a pathway to cascaded electrocaloric cooling devices with extended operating spans.