Crystal structure and properties of K0.5Na0.5NbO3–Bi0.5Na0.5TiO3–LiSbO3 lead-free piezoelectric ceramics

(1 − x)(0.99K0.5Na0.5NbO3–0.01Bi0.5Na0.5TiO3)–xLiSbO3 (KNN–BNT–LS100x, x = 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.1) lead-free piezoelectric ceramics were fabricated by conventional ceramic technique. The crystal structure, dielectric and piezoelectric properties of the ceramics were investigated. The X-ray diffraction (XRD) analysis revealed that the ceramics sintered in air at 1040–1080 °C for 3–4 h possessed a pure perovskite structure when LiSbO3 content was 0–5 mol%. A morphotropic phase boundary (MPB) between the orthorhombic and tetragonal phases was identified in the composition range of 0.01 < x < 0.04. The Curie temperature (Tc) and the orthorhombic–tetragonal transition temperature (TO–T) shifted to lower temperature with increasing LiSbO3 content. The ceramics close to the MPB exhibited enhanced dielectric and piezoelectric properties. The highest piezoelectric constant d33 = 250 pC/N, electromechanical coupling factors, kp = 0.29, kt = 0.35 and k33 = 0.447, mechanical quality factor, Qm = 33, Tc = 339 °C, TO–T = 65 °C, dielectric constant, ε33T/ε0 = 640 and loss tangent, tan δ = 0.031 were obtained for the KNN–BNT–LS4 ceramic which has a tetragonal phase near the MPB.