Tunable electrocaloric effect in lead scandium tantalate through calcium doping

TL;DR

This study demonstrates how calcium doping in lead scandium tantalate allows precise tuning of its electrocaloric effect, including temperature range and effect type, supported by experimental and first-principles analyses.

Contribution

It introduces calcium doping as a method to control phase transitions and electrocaloric response in PST, enabling extended temperature operation and inverse effects.

Findings

Transition temperature shifts between 258 K and 319 K with Ca doping.

Emergence of an antiferroelectric phase at Ca ≥ 2%.

Observation of inverse electrocaloric effect at higher doping levels.

Abstract

State-of-the-art electrocaloric cooling prototypes rely on the conventional electrocaloric effect of ferroelectric lead scandium tantalate (PbSc0.5Ta0.5O3, PST), which peaks near room temperature. Here, we demonstrate that A-site calcium doping in highly ordered PST modifies its phase transitions and enables precise tuning of the electrocaloric response. The transition temperature shifts down to 258 K and up to 319 K, 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 $\geq$ 2\%. These results are supported by first-principles calculations. We observe a conventional electrocaloric effect for Ca $\leq$ 2\% and an inverse electrocaloric effect at higher doping ($\geq$ 2\%). Under an applied field of 110 kV cm$^{-1}$, Ca-doped PST exhibits an adiabatic temperature change of 2 K over a range from 263 K to 353 K. 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.