Size-dependent Ultrahigh Electrocaloric Effect near Pseudo-First-Order Phase Transition Temperature in Barium Titanate Nanoparticles

The electrocaloric effect (ECE) of ferroelectric materials, which occurs significantly in a narrow temperature region near the first-order paraelectric/ferroelectric transition (FOPFT) Curie temperature, has great potential in solid-state refrigeration. Most ferroelectric materials, however, bear the second-order paraelectric/ferroelectric transition (SOPFT). In the present study, we demonstrate a size-dependent pseudo-first-order phase transition (PFOPT), associated with ultrahigh ECE and Curie temperature in ferroelectric nanoparticles with degradation layers by employing phase field modeling. The PFOPT behavior of the polarization component P3 along the applied electric field direction x3 versus temperature is similar to the classical FOPFT behavior. The results indicate that the ultrahigh ECE and PFOPT occur at temperatures below the Curie temperature of a given nanoparticle size. The adiabatic temperature change is 3.347 K in the simulated barium titanate nanoparticle of 10 × 10 × 8 normalized size under a 96.502 kV cm−1 applied electric field change. The concept of PFOPT should be general, applicable to all ferroelectric perovskite materials. Therefore, the current results provide a novel physical perspective for experiments and for lower power/higher efficiency solid-state cooling devices.