Sintering behavior and electrical properties of K4CuNb8O23 modified K0.5Na0.5NbO3 ceramics with SnO2, ZnO or Yb2O3 doping

Widespread commercial use of environmentally friendly lead-free K0.5Na0.5NbO3 ceramics is limited due to their poor piezoelectric properties in the sintered form. The main drawback is probably the poor electrical reproducibility associated with the low sinterability. Isothermal sintering studies of SnO2, ZnO-SnO2 or Yb2O3 doped K0.5Na0.5NbO3 ceramics in the presence of a liquid phase provider, like K4CuNb8O23, were carried out for the first time and the findings were reported systematically. The optimum sintering temperatures of the neat and SnO2, ZnO-SnO2 and Yb2O3 doped K0.5Na0.5NbO3-0.5 mol% K4CuNb8O23 ceramics were found to be 1120, 1110, 1080 and 1090 °C, respectively, with relative densities more than 98%. A lower shift in the sintering temperature of ZnO-SnO2 co-doped samples by 40 °C as compared to that of neat one was observed in these studies using dilatometric measurements. Considering the upper bound narrow sintering temperature window of K0.5Na0.5NbO3, this shift was a major achievement. Overall, KNN ceramics with various dopants could be sintered to high densities consistently without degrading electrical properties.