Ferroelectric and Piezoelectric Properties of Fine‐Grained Na 0.5 K 0.5 NbO 3 Lead‐Free Piezoelectric Ceramics Prepared by Spark Plasma Sintering

Lead‐free piezoelectric ceramics have received attention because of increasing interest in environmental protection. Niobate ceramics such as NaNbO 3 and KNbO 3 have been studied as promising Pb‐free piezoelectric ceramics, but their sintering densification is fairly difficult. In the present study, highly dense Na 0.5 K 0.5 NbO 3 ceramics were prepared using spark plasma sintering (SPS). Although the SPS temperature was as low as 920°C, the density of the Na 0.5 K 0.5 NbO 3 solid solution ceramics was raised to 4.47 g/cm 3 (>99% of the theoretical density). After post‐annealing in air, reasonably good ferroelectric and piezoelectric properties were obtained in the Na 0.5 K 0.5 NbO 3 ceramics with submicron grains. The crystal phase of the Na 0.5 K 0.5 NbO 3 has an orthorhombic structure. The Curie temperature is 395°C and the piezoelectric parameter ( d 33 ) of the Na 0.5 K 0.5 NbO 3 ceramics reached 148 pC/N.