Structure, dielectric and piezoelectric properties of NaNbO3–Ba0.6(Bi0.5K0.5)0.4TiO3 lead-free ceramics

Lead-free ceramics (1−x)NaNbO3–xBa0.6(Bi0.5K0.5)0.4TiO3 + 1 mol% MnO2 were prepared by an ordinary sintering method and their structure, dielectric and piezoelectric properties were studied. All the ceramics possess a pure perovskite structure. The ceramics have an orthorhombic symmetry at x ≤ 0.05 and transform gradually to a tetragonal structure with x increasing. A morphotropic phase boundary is formed at 0.05 < x < 0.125. A small amount of Ba0.6(Bi0.5K0.5)0.4TiO3 (x ≥ 0.025) transforms NaNbO3 from antiferroelectric to ferroelectric and strong ferroelectricity is observed in the ceramics with x = 0.05–0.175. The ferroelectric–paraelectric phase transition becomes diffusive with x increasing. High mechanical quality factor Qm values of 1211–1862 are obtained at x = 0.05–0.075. Due to the MPB and the weakened stability of ferroelectric domain induced by the decrease in the TC, the ceramics with x = 0.10–0.175 exhibit the optimum piezoelectric properties, giving d33 = 105–131pC/N and kp = 20.8–26.5%.