Composition-driven inverse-to-conventional transformation of electrocaloric effect and large energy storage density in strontium modified Ba(Zr_0.1Ti_0.9)O₃ thin films

In this work, (Ba_1-xSr_x)Zr_0.1Ti_0.9O₃ (BSZTx, x = 0, 0.15, 0.25 and 0.35) thin films were successfully deposited on La_0.7Sr_0.3MnO₃ (LSMO)-coated (001) SrTiO₃ (STO) single crystal substrates using laser molecular beam epitaxy. The BSZTx thin films with compositions of x = 0 and 0.15 display an inverse electrocaloric effect (ECE) with a maximum adiabatic temperature change of ΔT ∼ -10 K under 1500 kV cm^-1, while a large positive ΔT amounting to ∼13 K is discovered in the strontium rich composition, i.e. x = 0.35. For the composition of x = 0.25 where weak ECE (|ΔT| < 2 K) is discovered, an energy storage density of 15.5 J cm^-3 with an efficiency of 69.8% is observed in the temperature range of 303-413 K. The composition-tunable electrocaloric effect and large energy storage density with excellent thermal stability in strontium modified Ba(Zr_0.1Ti_0.9)O₃ thin films are ascribed to the synergistic effects of different dynamics of polar nano-regions (PNRs) and conformed defect dipoles under large electric fields at elevated temperatures. This work will facilitate the development of novel solid-state cooling devices and provide a design route for high energy storage density devices.