Climate change is one of the main challenges in the world today as addressed in the United Nations Sustainable Development Goals and the European Green Deal. An important contribution to global warming comes from the current cooling technology based on vapour compression of greenhouse gases. Electrocaloric (EC) materials show reversible thermal changes in response to an applied electric field known as the electrocaloric effect (ECE), and are in the spotlight as candidates for future green refrigeration with even a better energy efficiency than vapour compression. Despite the intense research activity in EC materials (mostly focused on lead-containing oxides), ECE effects sufficiently large for applications have only been reported in thin films and the progress in the field is hindered by the reliability of the ECE measurement methods. Besides, the microscopic origin of the ECE remains to be understood in order to enable a rational design of EC materials. The aim of this project is to develop new lead-free Aurivillius oxides with strong ECE by: i) implementing experimental setups for direct (calorimeter) and indirect (polarization analyzer) ECE measurements to allow for a comprehensive analysis; ii) synthesizing Aurivillius oxides with targeted compositions towards EC performance, both in bulk and thin-film forms; and iii) combining the macroscopic characterization of the electric and EC properties with an advanced microscopic characterization using cutting-edge synchrotron-based X-ray spectroscopies. The outcomes of this work will include the determination of the most reliable ECE detection method for bulk and thin films, the finding of novel compounds with enhanced EC properties, and new understanding of the underlying mechanisms by which the materials show the ECE behaviour. All these will contribute to open new directions in the field of EC cooling, ultimately also providing guidance for exploiting the ECE in practical refrigeration devices.
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