Influence of domain walls and defects on the electrocaloric effect

The electrocaloric (EC) effect is the adiabatic temperature change of a material in a varying external electric field, which is promising for novel cooling devices. While the fundamental understanding of the caloric response of defect-free materials is well developed, there are important gaps in the knowledge about the reversibility and time-stability of the response. In particular, it is not settled how the time-dependent elements of microstructure that are always present in real materials act on the field-induced temperature changes. Ab initio based molecular dynamics simulations allow us to isolate and understand the effects arising from domain walls (DWs) and defect dipoles and to study their interplay. We show that DWs in cycling fields do not improve the response in either the ferroelectric (FE) phase or at the FE phase transition, but may result in irreversible heat losses. The presence of defect dipoles may be beneficial for the EC response for proper field protocols, and interestingly this benefit is not too sensitive to the defect configuration.