Highly reversible extrinsic electrocaloric effects over a wide temperature range in epitaxially strained SrTiO₃ films

Electrocaloric effects have been experimentally studied in ferroelectrics and incipient ferroelectrics, but not incipient ferroelectrics driven ferroelectric using strain. Here we use optimally oriented interdigitated surface electrodes to investigate extrinsic electrocaloric effects in low-loss epitaxial SrTiO₃ films near the broad second-order 243 K ferroelectric phase transition created by biaxial in-plane coherent tensile strain from DyScO₃ substrates. Our extrinsic electrocaloric effects are an order of magnitude larger than the corresponding effects in bulk SrTiO₃ over a wide range of temperatures including room temperature, and unlike electrocaloric effects associated with first-order transitions they are highly reversible in unipolar applied fields. Additionally, the canonical Landau description for strained SrTiO₃ films works well if we set the low-temperature zero-field polarization along one of the in-plane pseudocubic <100> directions. In future, similar strain engineering could be exploited for other films, multilayers and bulk samples to increase the range of electrocaloric materials for energy efficient cooling.