Extraordinarily Large Electrocaloric Strength of Metal-Free Perovskites

The availability of materials with high electrocaloric (EC) strengths is critical to enabling EC refrigeration in practical applications. Although large EC entropy changes, Delta S-EC, and temperature changes, Delta T-EC, have been achieved in traditional thin-film ceramics and polymer ferroelectrics, they require the application of very high electric fields and thus their EC strengths Delta S-EC/Delta E and Delta T-EC/Delta E are too low for practical applications. Here, a fundamental thermodynamic description is developed, and extraordinarily large EC strengths of a metal-free perovskite ferroelectric [MDABCO](NH4)I-3 (MDABCO) are predicted. The predicted EC strengths: isothermal Delta S-EC/Delta E and adiabatic Delta T-EC/Delta E for MDABCO are 18 J m kg(-1) K-1 MV-1 and 8.06 K m MV-1, respectively, more than three times the largest reported values in BaTiO3 single crystals. These predictions strongly suggest the metal-free ferroelectric family of materials as the best candidates among existing materials for EC applications. The present work not only presents a general approach to developing thermodynamic potential energy functions for ferroelectric materials but also suggests a family of candidate materials with potentially extremely high EC performance.