Improving the functional properties of (K_0.5Na_0.5)NbO₃ piezoceramics by acceptor doping

ZrO₂ and TiO₂ modified lead-free (K_0.5Na_0.5)NbO₃ (KNN) piezoelectric ceramics are prepared by a conventional solid-state reaction. The effect of acceptor doping on structural and functional properties is investigated. A decrease in the Curie temperature and an increase in the dielectric constant values are observed when doping. More interestingly, an increase in the coercive field E_c and remanent polarization P_r is observed. The piezoelectric properties are greatly increased when doping with small concentrations dopants. ZrO₂ doped ceramic exhibits good piezoelectric properties with piezoelectric coefficient d₃₃=134pC/N and electromechanical coupling factor k_p=35%. It is verified that nonlinearity is significantly reduced. Thus, the creation of complex defects capable of pinning the domain wall motion is enhanced with doping, probably due to the formation of oxygen vacancies. These results strongly suggest that compositional engineering using low concentrations of acceptor doping is a good means of improving the functional properties of KNN lead-free piezoceramic system.