Giant electrocaloric response in thiourea under low electric field in the cryogenic region

Abstract

In this work, almost 70 years after thiourea ferroelectricity was discovered, we report hitherto undiscovered electrocaloric properties in this compound. Remarkably, we report a giant electrocaloric strength (ΔS/ΔE = 1.13 J cm kg-1 kV-1) and a large electrocaloric tunability (dTt/dE = 0.7 K cm kV-1) that range within the values obtained for the best bulk electrocaloric materials reported up to date and, moreover, requiring an outstanding low electric field. Furthermore, we identify that the electrocaloric effects can be further enhanced through the application of external pressure, turning this material into a new example of the emerging family of multicaloric materials. We relate such giant electrocaloric parameters to the large dielectric dipole, low molecular weight and weak chemical interactions, especially H-bonds, between the molecules that conform thiourea. Interestingly, these electrocaloric effects take place near 170 K, which could be useful for electrocaloric cooling supporting liquid nitrogen cryogenic systems.