At low temperatures, bulk strontium titanate SrTiO₃ is nearly ferroelectric, and voltage-driven changes of local electrical polarisation yield thermal changes (electrocaloric effects) that have been proposed for cryogenic cooling. However, near room temperature, the much smaller electrocaloric effects in bulk strontium titanate are considered useless. We followed the well known procedure of using epitaxial strain to create a ferroelectric phase transition in a film of strontium titanate, and by studying electrocaloric effects near this transition, we performed the first experimental study of electrocaloric effects near any phase transition created by strain. Using our maximum applied field, the strain enhances electrocaloric effects by an order of magnitude over a wide range of temperatures below and around room temperature, consistent with the canonical Landau description for strained strontium titanate after making modifications to match our experimental conditions.

Figure caption: By using epitaxial strain to transform a bad electrocaloric material into a good electrocaloric material, our work bears some parallel with alchemy. (Image credit: Sen Zhang and Xavier Moya)