Room temperature electrocaloric effect in PTO/STO superlattice induced by topological domain transition

Environmentally friendly and highly efficient solid-state refrigeration devices based on electrocaloric effect (ECE) are promising substitutes for traditional vapor compression refrigeration. Ferroelectric materials with large polarization usually possess a significant adiabatic temperature change (ATC) near their first-order phase transition point. However, the narrow range of ATC around the high transition temperature unfortunately hinders their application as ECE coolers. As domain transition has been demonstrated as a powerful tool for tailoring the location and value of ATC, the versatile polar topologies discovered in the PbTiO ₃/SrTiO ₃ (PTO/STO) ferroelectric superlattice offer a fruitful playground for creating domain transition-induced ECE. In this study, phase field simulation is employed to investigate the topological domain transitions and accompaning ECE response in the PTO/STO superlattice. By precisely designing the gradient layer thickness of STO, we acheive large ECEs with a peak value of ∼6 K and a wide temperature span near room temperature under a moderate electric field of ∼39 MV/m. With the increase of temperature, continuous topological domain transitions are observed in the superlattice system, starting from vertical c domain and transiting to a/ c domain, followed by the formation of vortex-antivortex pairs, and finally transforming to horizontal a domain, which results in the above-mentioned room temperature ECE. The value of the ATC and temperature range of the large ECE response can be successfully adjusted by changing the STO occupation ratio in the PTO/STO superlattice. Our study sheds considerable insight into the topological domain transitions and offers guidance in engineering ferroelectric superlattice to achieve large ECE near room temperature.