Effect of Mn Doping on Electrocaloric Properties of 0.77NaNbO₃–0.23BaTiO₃ Ferroelectric Ceramics

The electricaloric refrigeration is based on the electricaloric effect due to its high energy conversion efficiency, environment friendly, small size and easy integration as a novel efficient refrigeration technology, which has become one of the emerging research hotspots in the field of ferroelectric. The solid solutions of 0.77NaNbO₃–0.23BaTiO₃+wMn (w=0, 0.2%, 0.4% and 0.6%, in mass fraction) electrocaloric ceramics were prepared by a conventional solid-state reaction method. The phase composition and microstructure of 0.77NaNbO₃–0.23BaTiO₃ ceramics with different Mn doping contents were characterized by X-ray diffraction and scanning electron microscopy. Meanwhile, the dielectric-temperature spectra, polarization electric field hysteresis loops and electrocaloric effect of the samples with different Mn doping contents were determined. The results indicate that Mn doped ceramics can promote the grain compaction, improve the dielectric constant and saturation polarization strength, reduce the dielectric loss, and enhance the electrocaloric effect. For the ceramic with Mn doping content w of 0.4%, ΔT=0.39 K, and ΔS=0.71 J·kg^–1·K^–1, the electrocaloric strength of ΔT/ΔE enhances from 0.05×10^–6 K·m·V^–1 to 0.13×10^–6 K·m·V^–1, and ΔS/ΔE enhances from 0.08×10^–6 K m·V^–1 to 0.24×10^–6 J·m·kg^–1·K^–1·V^–1 under 30 kV·cm^–1 at room temperature. It is indicated that 0.77NaNbO₃–0.23BaTiO₃+0.4%Mn ceramic could be used as an promising electrocaloric refrigeration material.