Prospects and challenges of the electrocaloric phenomenon in ferroelectric ceramics

The electrocaloric effect (ECE), which refers to changes in the temperature of a material when an electric field is applied to or removed from the material, is one of the key phenomena of future highly efficient solid-state refrigeration devices. This field was not explored extensively owing to the deficiencies in usable and sufficient cooling capacity; however, a boom occurred approximately 15 years ago with the discovery of giant ECE in ferroelectric thin films. Since then, many reports have been published proposing different approaches to achieve giant ECE in different compositions or forms of ceramics, which can be broadly categorized as lead-based or lead-free, bulk or thin/thick, and multilayered or heterostructures. Various ECE-based cooling devices were also developed and their cooling performance was demonstrated. Two important aspects in this field are (1) to achieve giant ECE in materials by changing different parameters such as composition, geometry, and type, and (2) successful use of giant ECE in practical EC-based cooling devices. This review provides a focused view of the above two aspects, which will assist not only in the selection of materials for future cooling applications, but also in the realization of solid-state EC-based refrigeration.