Effect of lanthanide doping on structural, microstructural and functional properties of K0.5Na0.5NbO3 lead-free piezoceramics

Lanthanides-doped K0.5Na0.5NbO3(KNN) lead-free piezoelectric ceramics are prepared by conventional solid-state reaction. The effects of lanthanum concentration and the lanthanide type on the structure, microstructure and ferro-piezoelectric properties are evaluated. Ln3+ doping has a slight effect on the structure, but greatly inhibits the grain growth. Moreover, a decrease in the Curie temperature and an increase in the dielectric constant values are observed when doping. Large amounts of lanthanum induce a diffuse phase transition and an increase of the dielectric losses. The piezoelectric properties are greatly improved when doping with small amounts of dopants. As the ionic radii of the lanthanide is reduced, the piezoelectric properties of the ceramics are increased, the Eu3+-doped ceramics show an increase of 29% of the piezoelectric coefficient d33 with respect to pure KNN. The results show that low concentrations of lanthanides improve significantly the functional properties of KNN lead-free piezoceramics. Doping with lanthanides should be taken into consideration in some other compositions based on KNN.