Electric field direction dependence of the electrocaloric effect in BaTiO3

Abstract

Single-crystalline ferroelectric (FE) perovskites show a large electrocaloric effect at electric field-induced phase transitions, promising for solid-state cooling technologies. However, paraelectric-FE transition temperatures are often too high for practical applications, and lower transitions are underrepresented in literature. Particularly, the role of thermal hysteresis and electric field direction on the caloric response is critical, especially for polycrystalline materials, but not yet fully understood. Using ab initio-based coarse-grained molecular dynamics simulations, we show how transition temperatures depend on the direction of the applied field. Also, we reveal that the choice of electric field direction can reduce thermal hysteresis and can adjust the temperature ranges where large and reversible caloric responses occur. Furthermore, we propose a phenomenological descriptor for the qualitative changes in transition temperature with field direction. This descriptor is valid for both BaTiO3 and PbTiO3, even though both materials show different microscopic electric field coupling. Finally, we identify favorable temperature and texturing conditions for large and reversible caloric responses in polycrystals.