Giant room temperature elastocaloric effect in metal-free thin-film perovskites

Abstract Solid-state refrigeration which is environmentally benign has attracted considerable attention. Mechanocaloric (mC) materials, in which the phase transitions can be induced by mechanical stresses, represent one of the most promising types of solid-state caloric materials. Herein, we have developed a thermodynamic phenomenological model and predicted extraordinarily large elastocaloric (eC) strengths for the (111)-oriented metal-free perovskite ferroelectric [MDABCO](NH₄)I₃ thin-films. The predicted room temperature isothermal eC ΔS_eC/Δσ (eC entropy change under unit stress change) and adiabatic eC ΔT_eC/Δσ (eC temperature change under unit stress change) for [MDABCO](NH₄)I₃ are −60.0 J K⁻¹ kg⁻¹ GPa⁻¹ and 17.9 K GPa⁻¹, respectively, which are 20 times higher than the traditional ferroelectric oxides such as BaTiO₃ thin films. We have also demonstrated that the eC performance can be improved by reducing the Young’s modulus or enhancing the thermal expansion coefficient (which could be realized through chemical doping, etc.). We expect these discoveries to spur further interest in the potential applications of metal-free organic ferroelectrics materials towards next-generation eC refrigeration devices.