High densification and dielectric properties of lead-free (K0.5Na0.5)NbO3 piezoelectric ceramics with optimum excess Na2O and K2O contents

Lead-free piezoelectric ceramics based on the (K0.5Na0.5)NbO3 (KNN) system were prepared by the solid-state reaction method. The effects of firing temperatures and excess Na2O and K2O on KNN ceramics were investigated. The samples were calcined between 750 and 950 °C for 4 h and the sintering range was between 1060 and 1140 °C. Impurities phases of Nb2O5 and K2CO3 appeared in all sintered samples, due to evaporation of some elements during in the sintering process. The average particle size and grain size increased with increased firing temperatures. After addition of excess Na2O and K2O with 0, 1, 2, 3, 4, 5 and 10 wt% in the system, the impurities phase did not appear in all samples. The porous microstructure gradually decreased with increased of excess Na2O and K2O up to 1 wt% and then slightly increased with higher than 1 wt% of excess Na2O and K2O. The density and dielectric constant can be improved by adding 1 wt% of excess Na2O and K2O.