Doping-induced Polar Defects Improve the Electrocaloric Performance of Ba0.9Sr0.1Hf0.1Ti0.9 O3

In materials science, intentional doping has been widely used to improve the properties of a variety of materials. However, such an approach is not yet exploited in the fast-growing field of electrocaloric materials, which represent a serious alternative for next-generation cooling systems. Here we demonstrate with Ba0.9Sr0.1Hf0.1Ti0.9O3, an ecofriendly ferroelectric material, that doping with 2% of Cu introduces defect dipoles into the ferroelectric matrix and results in (i) enhancement of the adiabatic temperature change ΔT by up to 54% while maintaining performance after a large number (up to 104) of electric field cycles, (ii) suppression of the parasitic irreversibility of ΔT between on-field and off-field states, and (iii) an alternative design of refrigeration cycle with a prepoled sample, allowing a two-field-step process showing both conventional (ΔT > 0) and inverse (ΔT < 0) responses when the field is sequentially varied. We also demonstrate that doping significantly increases the energy storage density (by up to 72%). The defect engineering approach therefore offers a path for designing ferroelectrics with improved electrocaloric performances. Beyond ferroelectrics, this strategy could also be promising in other solid-state caloric materials (magnetocalorics, elastocalorics, etc.).