Electrocaloric materials for future solid-state refrigeration technologies

The electrocaloric (EC) effect is an adiabatic and reversible temperature change that occurs in a polar material upon application of an electric field. The current intensive research in EC materials has been driven by the quest for new energy efficient and environmentally friendly cooling technologies. The bottle neck for development of EC cooling technologies is in the yet still too small EC temperature changes that can be induced in the materials. To overcome this research has focused on several areas with an emphasis on the development of theoretical understanding, high performance EC materials and smart material engineering. Smart material engineering has produced cooling lines, multilayer EC cooling media, carbon thermal switches and has showed great potential in designing efficient technical solutions to drive the solid-state EC cooling cycle. All this can reduce the critical EC temperature change required for the construction of an efficient EC cooling device. Current theoretical understanding of the EC processes and the influence of material parameters is thorough but experimental development of high-performance EC materials with a high cooling capacity is still in progress. Recently, some very interesting new research directions have been undertaken such as EC relaxors, multilayered EC elements, and oxide and polymer films. This paper insightfully reviews the progress in these research fields and critically discusses the major advances in order to present a compact picture of the state-of-the-art, extract new knowledge and propose promising future research directions.