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 material with large polarization usually possesses significant adiabatic temperature change (ATC) near its first-order phase transition point, but the narrow range of ATC existed around the high transition temperature unfortunately hinders its application as ECE cooler. As domain transition is demonstrated to be a powerful tool for tailoring the location and value of ATC, the versatile polar topologies discovered in the PbTiO3/SrTiO3 (PTO/STO) ferroelectric superlattice offers a fruitful playground for creating domain transition induced ECE. Herein, phase field simulation is employed to investigate the topological domain transitions and accompanied ECE response in PTO/STO superlattice. Benefiting from the precise design of the gradient layer thickness of STO, large ECEs with a peak value of ∼6 K and a wide temperature span near room temperature are achieved under a moderate electric field of ∼39 MV/m. With the increase of temperature, continuous topological domain transitions from vertical c domain to a/c domain, to vortex-antivortex pairs, and finally to horizontal a domain are observed in the superlattice system, 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. We anticipate our study thus sheds considerable insight into the topological domain transitions and offers guidance in engineering ferroelectric superlattice to achieve large ECE near room temperature.