Giant electrocaloric response in thiourea under a 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, it exhibits a giant electrocaloric strength (ΔS/ΔE = 1.13 J cm kg⁻¹ kV⁻¹) and a large electrocaloric tunability (dT_t/dE = 0.7 K cm kV⁻¹), comparable to the best bulk electrocaloric materials reported to date, while requiring an exceptionally low electric field. Furthermore, we identify that electrocaloric effects can be further enhanced through the application of external pressure, making this material a new member 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 thiourea molecules of the crystal structure. Interestingly, these electrocaloric effects occur near 170 K, which could be useful for electrocaloric cooling to support liquid nitrogen cryogenic systems.