Electrical and Mechanical Properties of Fine‐Grained Li/Ta‐Modified (Na,K)NbO 3 ‐Based Piezoceramics Prepared by Spark Plasma Sintering

Dense and fine‐grained (Na 0.535 K 0.485 ) 1− x Li x (Nb 0.8 Ta 0.2 )O 3 ( x =0.02–0.07) (abbreviated as NKL x NT) lead‐free piezoceramics were fabricated by spark plasma sintering (SPS), followed by postannealing in air. All the NKL x NT ceramics showed single perovskite structures with a phase transition from an orthorhombic symmetry to a tetragonal one across a composition region of 0.04< x <0.05. The sample with a composition of x =0.05 had the maximum values of piezoelectric coefficient ( d 33 =243 pC/N) and planar electromechanical coupling coefficient ( k p =46.1%), and other good properties such as Q m =85, ɛ r =1240, and tg δ=0.023. Because of the enhanced densification and refined microstructure, the SPS‐processed NKL x NT ceramics also had better fracture strength than that prepared by normal sintering.