Ferroelectric-relaxor crossover induce large electrocaloric effect with ultrawide temperature span in NaNbO3-based lead-free ceramics

In this study, a large electrocaloric effect (ECE) of 0.49 K with an ultrawide temperature span of 80 °C ranging from −15 to 65 °C (0.49 K ± 10%) was reported in the 0.94(0.80NaNbO3–0.20BaTiO3)–0.06Bi0.5Na0.5TiO3 composition. The incorporation of Bi0.5Na0.5TiO3 (BNT) into the NaNbO3–BaTiO3 matrix induced a ferroelectric-to-relaxor (FR) phase transition, accompanied by polar P4 mm evolving to the nonpolar Pm3¯m phase and an increase in the relaxor degree. The inflexions in the peak current density value and Raman spectra indicated a successive downward-shift of FR temperature with the increasing BNT content, which established a continuous modulation of temperature corresponding to the peak ECE in this system. The obtained high ECE performance was believed to originate from an enhanced diffuse phase transition character and coexistence of P4 mm and Pm3¯m phases. This work may provide a guideline to designing high-efficiency solid-state cooling devices that are applied at mutable ambient temperature.