Phase Transitions and Electrical Properties of (Na 1− x K x )(Nb 1− y Sb y )O 3 Lead‐Free Piezoelectric Ceramics With a MnO 2 Sintering Aid

Lead‐free piezoelectric ceramics (Na 1− x K x )(Nb 1− y Sb y )O 3 + z mol% MnO 2 have been prepared by a conventional solid‐state sintering technique. Our results reveal that Sb 5+ diffuses into the K 0.5 Na 0.5 NbO 3 lattices to form a solid solution with a single‐phase orthorhombic perovskite structure. The partial substitution of Sb 5+ for B‐site ion Nb 5+ decreases the paraelectric cubic‐ferroelectric tetragonal phase transition ( T c ) and the ferroelectric tetragonal‐ferroelectric orthorhombic phase transition ( T O–F ), and retains strong ferroelectricity. A small amount of MnO 2 is enough to improve the densification of the ceramics. The co‐effects of MnO 2 doping and Sb substitution lead to significant improvements in ferroelectric and piezoelectric properties. The ceramics with x =0.45–0.525, y =0.06–0.08, and z =0.5–1 exhibit excellent ferroelectric and piezoelectric properties: d 33 =163–204 pC/N, k P =0.47–0.51, k t =0.46–0.52, ɛ=640–1053, tan δ=1.3–3.0%, P r =18.1–22.6 μC/cm 2 , E c =0.72–0.98 kV/mm, and T C =269°–314°C.