Ferroelectric to Relaxor Crossover in Zr-Doped BaTiO3-Based Ceramics and Its Consequences for the Electrocaloric Effect

Abstract

Na0.5Bi0.5TiO3 (NBT)-substituted BaTiO3 (BT)-rich solid solutions demonstrate significant electrocaloric effects owing to the first-order nature of their ferroelectric phase transition. However, their narrow phase transition range and relatively high transition temperature limit their suitability for electrocaloric cooling applications. To address these issues, we have investigated the impact of Zr-substitution (0-5 mol%) at the B-site on the phase transition behaviour of 0.7BT-0.3NBT solid solution. Our findings indicate that Zr-substitution strongly decreases the tetragonality and the Curie temperature of the samples. All samples exhibit relaxor-like characteristics, following the Vogel-Fulcher approach. However, at low Zr doping (0-3 mol%), a spontaneous transition into the ferroelectric phase is also observed on cooling from high temperatures. At higher Zr doping (4-5 mol%), the transition into the ferroelectric phase disappears and the sample presents canonical relaxor behaviour. The samples with canonical relaxor behaviour (4-5 mol% Zr) feature wider temperature ranges where a significant electrocaloric response is sustained, which yielded a large Tspan of similar to 45 degrees C for the 4% Zr-doped sample where a Delta T value of 0.77 K was maintained.