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

• Published in: Nature materials Vol. 23; no. 5; pp. 639 - 647
• Main Authors: Zhang, S., Deliyore-Ramírez, J., Deng, S., Nair, B., Pesquera, D., Jing, Q., Vickers, M. E., Crossley, S., Ghidini, M., Guzmán-Verri, G. G., Moya, X., Mathur, N. D.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.05.2024; Nature Publishing Group
• Subjects: 639/301/119/2795; 639/301/119/544; 639/301/119/996; Biomaterials; Chemistry and Materials Science; Condensed Matter Physics; Energy efficiency; Epitaxy; Ferroelectric materials; Ferroelectricity; Ferroelectrics; Low temperature; Materials Science; Multilayers; Nanotechnology; Optical and Electronic Materials; Phase transitions; Room temperature; Strontium titanates; Substrates; Temperature; Tensile strain; Thin films
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/s41563-024-01831-1

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 SrTiO 3 films near the broad second-order 243 K ferroelectric phase transition created by biaxial in-plane coherent tensile strain from DyScO 3 substrates. Our extrinsic electrocaloric effects are an order of magnitude larger than the corresponding effects in bulk SrTiO 3 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 SrTiO 3 films works well if we set the low-temperature zero-field polarization along one of the in-plane pseudocubic 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. Electrocaloric effects are large in a limited set of materials that display hysteretic first-order phase transitions. Here epitaxial SrTiO 3 thin films are strain engineered to achieve anhysteretic second-order phase transitions, with electrocaloric effects enhanced by one order of magnitude over bulk.